Functionalization of 3-Iridacyclopentenes

1 Functionalization of 3-iridacyclopentenes Margarita Gómez,[a] Nuria Rendón,[a] Eleuterio Álvarez,[a] Kurt Mereiter,[b] Manuel L. Poveda,*[a] and Margarita Paneque*[a] Abstract: A series of iridacyclopentenes of composition [TpMe2Ir(k2- C,C-CH2CR’=CRCH2)(CO)] (TpMe2 = hydrotris(3,5-dimethyl- pyrazolyl)borate; R = R’ = H, 1; R = Me, R’ = H, 2; R = R’ = Me, 3) have been subjected to common organic chemistry procedures for hydrogenation, cyclopropanation, epoxidation, water addition through hydroboration, cis-dihydroxylation and ozonolysis. The stability of metallacycles 1-3, provided by the presence of the coligands TpMe2 and CO, directs the reactivity towards the C=C double bonds, and further the stereochemistry of the products formed is strongly dictated by the steric demands of the TpMe2 ligand. While the products obtained in some of the above mentioned reactions are the expected ones from an organic chemistry point of view, in other cases the results differ from the outcomes of similar reactions carried out with the all-carbon counterparts. Introduction Some years ago we briefly reported the transformation of the IrIII 18 e-, 3-iridacyclopentene complex [TpMe2Ir(k2-C,C- CH2CH=CHCH2)(CO)] (1) (TpMe2 = hydrotris(3,5- dimethylpyrazolyl)borate) into the methylene-3- iridacyclobutanone shown in Scheme 1a.[1] The overall process involved several synthetic steps that can be described as typical using standard organic chemistry reagents, work-up and purification techniques. It started with the hydration of the double bond of 1 via a hydroboration-oxidation sequence and finished with a Wolff rearrangement of a carbene intermediate. The success of this synthesis heavely relies on the well-known nonlabile nature of the coligands TpMe2 and CO on the IrIII coordination sphere,[2] which prevents thermal substitution reactions, as well as their kinetic chemical stability towards many reagents even under forcing conditions (notice that the C—H of the aromatic pyrazolyls, the B—H, and the B—N bonds of the TpMe2 ligand are sterically protected from chemical attack by the 3,5-Me substituents). Last but not least the Ir—C bonds of the iridacycle of all the complexes reported herein are very highly stable vs. common acids and bases, and this, among other consequences, greatly facilitates the work-up of many reactions. The use of Organic Chemistry procedures on synthetic organometallic chemistry is not new, and has been for long applied to, for instance, the well-studied functionalization of aromatic ligands such as cyclopentadienyls (e.g. ferrocene) and benzenes (e.g. [(  6-C6H6)Cr(CO)3]), and Schemes 1b[3] and 1c[4] show, respectively, an old and a quite recent further examples of these types of reactions. In this contribution we fully report the results obtained in the functionalization, and subsequent chemistry derived thereof, of the 3-metallacyclopentene IrIII complexes 1-3 which are easily obtained by the reaction of the corresponding 4-IrI butadienes with carbon monoxide (Scheme 1d).[5] Among other findings, we have obtained interesting organometallic species which would be very difficult to obtain by alternative methods. As already mentioned part of this work has been communicated.[1] [a] Dr. M. Gómez, Dr. N. Rendón, Dr. E. Álvarez, Prof. Dr. M. L. Poveda, Prof. Dr. M. Paneque Instituto de Investigaciones Químicas Departamento de Química Inorgánica Centro de Innovación en Química Avanzada (ORFEO-CINQA) Consejo Superior de Investigaciones Científicas (CSIC) Universidad de Sevilla Avenida Américo Vespucio 49, 41092 Sevilla (Spain) E-mail: panequ[email protected].es [email protected] [b] Prof. Dr. K. Mereiter Department of Chemistry Vienna University of Technology Gestreidemarkt 9/164SC, 1060 Vienna (Austria) Supporting information for this article is given via a link at the end of the document. 2 Scheme 1. a) Multi-step conversion of the 3-iridacyclopentene 1 into a methylene-3-iridacyclobutanone. b) Catalytic hydrogenation of the free C=C double bond of the cyclopentadiene adduct of a ReI complex. c) An interesting application of C=C metathesis, using a Grubbs catalyst, to a Fe(CO)3(PR3)2 complex. d) Synthesis of the 3-iridacyclopentenes 1-3 studied in this work. In addition, the designation of the exo and endo faces of these metallacycles is depicted. This nomenclature also applied to the faces of all others iridacycles described herein and also to the stereochemistry of the substituents. Results and Discussion Some common reactions of unactivated C=C double bonds carried out with complexes 1-3 Hydrogenation: Compound 1 very slowly added H2, under forcing conditions (4 atm, dioxane, 80 ºC) and in the presence of PtO2 as a catalyst, to give the iridacyclopentane 4. As expected from the known trend that increasing substitution in the C=C double bond of olefins increases the difficulty of this reaction, complexes 2 and 3, which contain 1 and 2, respectively, Me groups on the olefinic moiety, did not afford detectable amounts of the hydrogenated products after a similar treatment. Although no demonstrated, it is proposed that the addition of H2 takes place in cis,[6] and through the less sterically hindered exo face of the olefin, as is the case for all other additions studied in this section (Scheme 2a). Cyclopropanation: The room temperature reaction of complex 1 with an excess of the Simmons-Smith carbenoid,[7] i.e. the result of the interaction between ZnEt2 and CH2I2 in diethyl ether, led to the clean formation (ca. 80% conversion) of the expected metallabicyclic complex 5 (Scheme 2b). This species could not be isolated in pure form from the mixture with compound 1, neither by fractional crystallization nor by column chromatography on silica gel. Its purification was carried out by conversion of the remaining starting material 1 into its epoxide derivative (by reaction with m-chloroperbenzoic acid, see below) and subsequent separation by column chromatography. Complex 5 was completely characterized by NMR spectroscopy, its stereochemistry deduced from the NOESY spectrum and unambiguously corroborated crystallographically (Figure 1). Scheme 2. Some common reactions of unactivated C=C double bonds as applied to complexes 1-3: a) Catalytic hydrogenation. b) Cyclopropanation. c) Epoxidation. d) Hydration by a hydroboration-oxidation sequence. e) Cisdihydroxylation. f) Ozonolysis. 3 Figure 1. X-ray structure of complex 5 (30% displacement ellipsoids; H atoms are omitted for clarity). Selected bond lengths [Å]: Ir—N(1) 2.155(4), Ir—N(3) 2.169(7), Ir—C(11) 2.072(5), C(11)—C(12) 1.506(10), C(12)—C(13) 1.567(13). The two methyl substituents of the C=C double bond of complex 3 should, in principle, sterically inhibit a similar carbenoid attack but, in the other hand, the electron-donating character of these groups makes this functionality more susceptible to the reaction with the electrophilic “:CH2” reagent. In practise, 3 reacted with a ZnEt2:CH2I2 mixture, under the same conditions used for complex 1, giving the cyclopropanated compound 6 (which was characterized by NMR spectroscopy only) although with less than 80% conversion. Epoxidation: The epoxidation of complexes 1-3 was carried out with m-chloroperbenzoic acid[8] (CH2Cl2, 25 ºC) to cleanly afford species 7-9 (Scheme 2c; of them, compound 8 was characterised by NMR spectroscopy only). As expected, the epoxidation takes place in the exo-face of the olefin, as deduced from their NOESY spectra. For complex 7 the structure was also proven crystallographically (Figure S2). Water addition through hydroboration: We have applied the hydroboration-oxidation method (an anti-Markovnikov addition of water) to obtain alcohols.[6,9] Thus, when complexes 1 and 2 were reacted with the adduct BH3·THF in THF, and the corresponding borane derivatives oxidized with H2O2-NaOH, the alcohols 10 and 11 were obtained in high yields (94 and 91% respectively; 11 characterized only by NMR) (Scheme 2d). The exo disposition of the OH group in both derivatives and the transoid stereochemistry of the methyl group, with respect to the OH, in compound 11 were deduced from NOESY studies. In addition, compound 10 has been characterized crystallographically (Figure S3). Surprisingly, complex 3 did not yield the expected tertiary alcohol under the same reaction conditions shown in Scheme 2d. In fact, it was recovered unaltered and this strongly contrasts with the facility with which 1,2-dimethylcyclopentene gives the corresponding alcohol. It may be possible that in this case the hydroboration-oxidation process has taken place, but with the resultant alcohol being much more prone to back-dehydration than its all-carbon organic counterpart. Cis-dihydroxylation: Derivatives 1-3 reacted with stoichiometric amounts of OsO4 with formation of stable osmiate derivatives which, when decomposed with Na2S2O5 yielded the expected cis-diol derivatives 12-14 (Scheme 2e).[6,10,11] These compounds were characterized only by NMR spectroscopy and for complex 12 also by X-ray crystallography (Figure 2). Clearly OsO4 attacks the exo-face of the C=C double bonds. Figure 2. X-ray structure of complex 12 (30% displacement ellipsoids; H atoms are omitted for clarity). Selected bond lengths [Å]: Ir—N(12) 2.168(5), Ir—N(22) 2.183(4), Ir—N(32) 2.165(4), Ir—C(1) 1.827(6), Ir— C(2) 2.086(6), Ir—C(5) 2.081(6). Ozonolysis: Finally in this section, the reactions of complexes 1- 3 with O3 were carried out as usual[6] and the resulting products 15-17 (Scheme 2f; 16 and 17 characterized only by NMR) purified by column chromatography on silica gel. The structure of compound 15 was, in addition, authenticated by X-ray crystallography (Figure S5). Lewis acid promoted ring-opening of the epoxides 7-9 Ring-opening of epoxides is commonly carried out[6] with BF3·Et2O and thus, when epoxide 7 was reacted with an excess of this reagent (diethyl ether, room temperature), quantitative formation of the trans-diol 18 took place (Scheme 3a). It is proposed that intermediate A, resulting from the addition of BF3 to the epoxide, easily hydrates to give the observed product. Scheme 3. Ring-opening of epoxides 7-9 by the action of BF3·Et2O. 4 In contrast, ketone 19 was obtained when compound 8, with only one methyl substituent, was subjected to the action of BF3·Et2O in dichloromethane. Complex 19 has been completely characterized by NMR spectroscopy and crystallographically (Figure S6). To explain the stereoselectivity shown in Scheme 3b, i.e. with the Me of 19 being in the exo position, we propose that in the reaction of 8 with BF3 the intermediate B experiences a suprafacial migration of the methine hydrogen atom. Therefore, we have to conclude that the presence of the methyl substituent in intermediate B, as compared to A, enhances the mobility of the C—H hydrogen and/or makes the former species less susceptible to water addition. The CHMe group adjacent to the keto functionality in 19 must be easily epimerizable and, in fact, when this compound was treated with NaOH in methanol at 60 ºC the thermodynamically more stable isomeric species epi-19 was obtained in 80% spectroscopic yield (Scheme 4). We propose that subtle steric factors, rather than electronic ones, are responsible for the energetic difference between these two ketones. Interestingly, and in comparison to similar organic compounds,[12] this isomerization requires quite drastic conditions and this fact is probably due to the steric protection of the enolizable hydrogen. Scheme 4. Epimerization of ketone 19 in basic medium. Epoxide 8 was also opened by the action of silica gel in dichloromethane but, surprisingly, the allylic alcohol 22 was obtained instead of ketone 19 (Scheme 5). Compound 22 has been completely characterized by NMR spectroscopy and the endo disposition of the OH group was deduced from the NOESY spectrum. Scheme 5. Ring-opening of epoxide 8 by silica gel in CH2Cl2. This kind of isomerization is of great interest in organic synthesis and is usually carried out by indirect methods.[13] It has been reported that the epoxide of 1-methylcyclopentene gives, in the presence of activated alumina, an allylic alcohol related to 22 but in admixture with other products.[14] However, in a control experiment, we have found that this substrate is not altered by silica gel using the conditions of Scheme 5. Another different result was observed in the reaction of complex 9 with BF3·Et2O in Et2O (Scheme 3c). In this case a dehydration process took place giving a mixture, in a ca. 1:2 ratio, of the dienes 20 and 21. In the case of derivative 20 the two lost hydrogen atoms derive from the two Ir—CH2 groups while in the formation of derivative 21 one of the hydrogen atoms comes from a methyl group. The same mixture of products are more satisfactorily obtained by an alternative procedure (see below). Ring-opening of epoxide 8 under oxidative conditions Epoxide 8 also experienced a ring-opening process when reacted with pyridinium chlorochromate (PCC)[15] which, under the conditions specified in Scheme 6 afforded a mixture of ketones 23 and 24. The former compound is an  -hydroxyl ketone with the OH group in an endo disposition (NOESY evidence) while the latter, characterized only by NMR, is an  ,  - enone, which formally derives from 23 by a simple dehydration, although this point has not been tested experimentally. In comparison, when the epoxide of 1-methylcyclopentene was treated similarly a complex mixture of products was obtained. Scheme 6. Reaction of epoxide 8 with PCC. A reasonable mechanism that may explain the formation of compound 23, with ketone 19 acting as an intermediate, is shown in Scheme 7. However, this is clearly no the case as this ketone did not react when treated similarly with PCC and so far we can not offer a mechanistic explanation for its formation. Scheme 7. A plausible, but incorrect, mechanism for the formation of compound 23 in the reaction of 8 with PCC. Interestingly, we have found a simple method for the synthesis, in almost quantitative yield, of ketone 24. This consists on the reaction of complex 2 with SeO2 in ethanol at 90 ºC (Scheme 8). This result is quite surprising since, if present as is the case, this reagent usually reacts with allylic C—H moieties.[16] Scheme 8. Unexpected outcome of the oxidation of complex 2 with SeO2. Oxidation of alcohols 10-11 The reaction of alcohols 10 and 11 with PCC, in CH2Cl2 at 25 ºC, afforded the corresponding ketones 25[17] (characterized by X- ray crystallography, Figure S7) and epi-19 (Scheme 9). However, we have found that if the reaction of complex 11 with PCC was carried out under more forcing conditions (THF-H2O, 60 ºC) an overoxidation took place and the -hydroxylketone epi-23 slowly 5 appeared, in admixture with epi-19, in the reaction mixture. As expected, and with the aid of a control experiment, it was demonstrated that the latter species is an intermediate in the formation of the former (Scheme 10). Clearly PCC attacks the exo face of epi-19. Scheme 9. Oxidation of alcohols 10 and 11 with PCC. Scheme 10. Reaction of complex 11 with PCC under more forcing conditions than those depicted in Scheme 9. Surprisingly, the oxidation of the allylic alcohol 22 with PCC gave the  ,  -unsaturated aldehyde 26 (Scheme 11; 26 characterized only by NMR) instead of the expected  - methylenketone. This reaction may be explained by invoking that an isomerization of 22 to the thermodynamically more stable primary alcohol C, takes place followed by its oxidation to 26. Scheme 11. Oxidation of the allylic alcohol 22 with PCC. The proposed isomerization can not be based on acid catalysis because, first, the reaction took place in the presence of NaOAc and second, and more importantly, complex 22 experienced a fast isomerization to 19 in the presence of ptoluenesulfonic acid at room temperature (Scheme 12). If this last reaction occurs through formation of the carbocation D shown in Scheme 12, i.e. by protonation of the methylene group, this has to be followed by a suprafacial migration of the hydrogen and final deprotonation of the hydroxyl group, and the resulting product would be epi-19, i.e. the thermodynamically more stable of the two epimers. Consequently, for the time being we do not have a satisfactory mechanistic explanation for the formation of complex 19 in this reaction. Scheme 12. Isomerization of complex 22 in the presence of a strong acid. Carbocation D can not be an active intermediate in this transformation. We have also studied the oxidation of alcohol 10 with Dess-Martin periodinane (DMP), in a mixture of DMSO and H2O at 70 ºC, to find out that this reaction gave the conjugated enone 27 (Scheme 13). Clearly, a double oxidation has taken place which consists on the transformation of the alcohol onto a keto functionality and on the dehydrogenation of the Ir-CH2CH2- moiety with formation of a Ir-CH=CH- group. It is well-known that DMP oxidizes alcohol functionalities to keto groups,[18] while use of this reagent, and related species, in the dehydrogenation of suitable ketones with formation of conjugated enones,[19] has been studied in detail.[20] In fact, ketone 25 yielded 27 under the same reaction conditions (Scheme 13b). Scheme 13. Reaction of alcohol 10 (a) and of ketone 25 (b) with DMP. Reactions of ketone 25 and enone 24 with RLi and RMgX Ketone 25 reacted with MeLi and PhLi with formation of the alcohols 28 and 29, respectively (Scheme 14a; 28 characterized only by NMR). Quite surprisingly both the R- nucleophiles added to the C=O carbon through the endo face (NOESY evidence), i.e. the one that “apparently” is the sterically less favoured. Interestingly, this is also the case for its reaction with NaBH4 that gave alcohol 10 (Scheme 14b). 6 Scheme 14. Reaction of ketone 25 with a) MeLi and PhLi and with b) NaBH4. By contrast, and upon reaction with MeMgCl,[21] ketone 25 afforded the 2-iridacyclopentene derivative 30 (Scheme 15).[22] This compound seems to be the result of the addition of Me- to the ketone group to give alcohol 28 followed by a regiospecific dehydration (no isomers of 30 were observed). If this alcohol is an intermediate in this transformation it is quite plausible that the magnesium cation, acting as a Lewis acid, is responsible for the dehydration process, and in fact 28 gave 30 upon interaction with MgCl2 in Et2O (Scheme 15). It is worthy of remark that the formation of the C=C double bond is somehow specially favored in this system since the reaction of cyclopentanone with MeMgCl (Et2O, 25 ºC) yields only the corresponding tertiary alcohol. Scheme 15. Reaction of ketone 25 with MeMgCl to give complex 30 and formation of the latter species by treatment of alcohol 28 with MgCl2. We have also found that compound 30 isomerized to compound 2, in CDCl3 in the presence of p-toluenesulfonic acid, with a thermodynamic equilibrium being stablished with the latter species predominating (K = 10, Scheme 16). Scheme 16. Complex 30 equilibrates with its isomer 2 in the presence of ptoluenesulfonic acid. Dehydration of the phenyl derivative 29 can also be induced easily, but slowly, by stirring its CH2Cl2 solutions, at 25 ºC, in the presence of silica gel. Under these conditions, a mixture of the isomeric olefins 31 (characterized only by NMR) and 32 was formed with the former being the kinetic product which then transformed into the more stable species 32. This isomerization was faster in the presence of p-toluensulfonic acid (CDCl3) and this has allowed for the thermodynamic ratio 5:1 to be easily reached (Scheme 17). Scheme 17. Ketone 31 is the kinetic product of the acid-catalyzed dehydration of alcohol 29 but its isomer 32 is thermodynamically favoured. We have also studied the reaction of ketone 25 with CH2=CHMgBr to find out that it gave exclusively the conjugated diene 33 (Scheme 18). In addition to being characterized by NMR spectroscopy, this compound has also been subjected to X-ray crystallography (Figure S8). It is quite possible that, in accord with the results already presented, this may be the kinetic product while the isomer having the internal C=C double bond in the 3-position being the thermodynamically favored. Scheme 18. Reaction of ketone 25 with CH2=CHMgBr. Finally in this section, it was observed that enone 24 reacted with MeMgCl with formation of a 1:2 mixture of the previously described dienes 20 and 21 (Scheme 19a). It is quite probable that this ratio is under thermodynamic control as it is also the one obtained by the very different synthetic method depicted in Scheme 3c. By contrast, its reaction with PhLi gave diene 34 exclusively (characterized only by NMR) (Scheme 19b).[23] Scheme 19. Reactions of enone 24 with a) MeMgCl and with b) PhLi. -Formylation of the 3-iridacyclopentanone 25 and further functionalization of the resulting product 35 The room temperature reaction of 25 with ethyl formate in a mixture of benzene-methanol, in the presence of NaOMe, gave the  -formylketone 35 (Scheme 20). This Claisen condensation is a commonly used procedure in Organic Chemistry to introduce a formyl group in  to an enolizable ketone.[24] Compound 35 (characterized only by NMR) could, in principle, exists as the four isomeric structures represented in Scheme 20.[25] In this case, and in general in related organic derivatives, the hydroxymethylene species predominates in CDCl3 solutions, as suggested by resonances at 8.58 and 121.2 ppm, in the 1H NMR and the 13C{1H} NMR spectra, respectively, in accord with a =CH(OH) functionality. 7 Scheme 20.  -Formylation of ketone 25 and the four possible equilibrating structures of the resulting product 35. Ozonolysis of compound 35 yielded diketone 36 (Scheme 21).[26] It is worth to mention that, contrary to some cases described in the literature, a Baeyer-Villiger overoxidation process, yielding an acid anhydride by the oxidative rupture of the -C(=O)—C(=O)- bond, did not take place.[6] However, this acid anhydride has been obtained by an alternative procedure (see below). Scheme 21. Ozonolysis of compound 35. Diketone 36 is characterized by an absorption at 1712 cm-1 in the IR spectrum and its symmetric structure is manifested by quite simple 1H and 13C{1H} NMR spectra. Interestingly, its solutions in CDCl3 are stable for long periods of time while  ,  - cyclopentadione appears to exist, in solution, mainly as the enolic form with the diketo-keto/enol equilibrium being quite fast at room temperature in the laboratory time scale. The enhanced stability of the diketo tautomer of 36 seems to be kinetic in nature since it was transformed quantitatively to the keto-enol isomer 37 by reaction with an excess of NaOMe, in a benzene:methanol mixture, followed by acid treatment (Scheme 22). Scheme 22. Isomerization of diketone 36 into the enol 37 by sequential treatment with an excess of NaOMe and of HCl. 1H NMR monitoring of the reaction of derivative 35 with an excess of m-chloroperbenzoic acid, in CDCl3 at 25 ºC, showed the formation of three products, the diketone 36, the acid anhydride 38 (having one carbon atom less than the starting material; only characterized by NMR) and the diacylcarbinol 39 (with an expanded ring) (Scheme 23).[27] Scheme 23. Reaction of complex 35 with an excess of m-ClC6H4CO3H in CDCl3 at 25 ºC. From this monitoring, and supported by other control experiments, it is concluded that acid anhydride 38 appears at the expenses of diketone 36 via a Baeyer-Williger oxidation.[26] Curiously, the competitive paths leading to the diketone and to the diacylcarbinol are kinetically controlled by the acidity of the solution and thus, when the oxidation of 35 was carried out in the presence of the stronger acid p-toluenesulfonic acid, derivative 39 was exclusively obtained (Scheme 24; characterized only by NMR), while in the presence of sodium bicarbonate derivative 38 was mainly formed (Scheme 24). Scheme 24. Influence of the medium acidity in the outcome of the oxidation of complex 35 with m-ClC6H4CO3H. Compounds 38 and 39 were characterized by NMR spectroscopy, and the configuration of the CH(OH) moiety of the latter species based on its NOESY spectrum. Interestingly, the structure of compound 39 contrasts with those found for pure organic derivatives in which the enol form predominates, at least in solution. More specifically, and for unknown reasons, 39 does not adopt the expected enodiolic form, -C(OH)=C(OH)-C(=O)-, which is stabilized by two hydrogen bonding interactions. Compounds with such a structure, called acireductones,[27] are very susceptible to oxidation, even by air, to give  ,  ,  -triketones. Perhaps compound 39 can not be overoxidized because its enolic form is not kinetically available. Scheme 25 shows a plausible mechanism for these oxidations in which intermediate E, responsible for the formation of both 38 and 39, is obtained by hydroxylation[28] of the less 8 stable endo-formyl tautomer of compound 35 previously depicted in Scheme 20. Scheme 25. Proposed mechanism for the formation of compounds 38 and 39. Finally, in this section, we have to mention that the acid anhydride 38 can be hydrolyzed, but with great difficulty, to the diacid 40 (Scheme 26; 40 characterized only by NMR). Scheme 26. Hydrolisis of acid anhydride 38. Five to four iridacycle-ring contraction reactions Complex 30 reacted with m-chloroperbenzoic acid, in CH2Cl2 at 25 ºC, with formation of the corresponding epoxide 41 (Scheme 27a) and, as expected, the peracid has attacked the exo face of the olefin (NOESY evidence). This epoxide further reacted with the stronger acid p-toluenesulfonic acid, in benzene at 25 ºC, to give complex 42, an iridacyclobutane[29] with an exo-acetyl substituent in the -position with respect to the metal center (Scheme 27b). Both compounds 41 and 42 have been fully characterized only by NMR spectroscopy and their stereochemistry deduced from their NOESY spectra. Scheme 27. a) Epoxidation of complex 30 to give 41 and b) ring contraction of the latter compound in the presence of a strong acid. Formation of complex 42 may be explained by an acidcatalyzed isomerization in which the epoxide first opened and the resulting intermediate then contracted. However, this process description is not satisfactory since the protonation of the epoxide oxygen is expected to form carbocation G, in which a suprafacial migration of the hydrogen atom converts it to H, an intermediate that should afford the acyl I by deprotonation (Scheme 28). Scheme 28. Expected, but unobserved, acid-mediated isomerization of epoxide 41. Therefore complex 42 must result from a preferred alternative kinetic route and a reasonable mechanism for its formation is shown in Scheme 29. Here, the protonation of 41 is followed by the formation of the alternative carbocation J in which the positive charge is in  position with respect to the metal. This species then contracts to K by a Wagner-Meerwein exo migration of the  -CH2 group (notice that this process must be preferred to an alternative methyl migration that would give ketone M) which finally deprotonates to give the observed product. In consequence, it has to be proposed that the iridium atom should somehow stabilize a carbocation in  , i.e. J versus G in Scheme 28, and also that the exo migration of a carbon to this cationic center must be specially favoured (the CH2 group may migrate exo or endo while the methyl substituent has to migrate endo). 9 Scheme 29. Proposed mechanism for the formation of the iridacyclobutane 42 by the acid-catalyzed isomerization of epoxide 41. A positional isomer of compound 42, ketone 43, was obtained when the cis-diol 13 was treated with p-toluenesulfonic acid (Scheme 30). This reaction may be described as an acidcatalyzed dehydration coupled to a ring contraction of the metallacycle with formation of an exo-acetyl substituent in the  position with respect to the metal center. Again, the exo disposition of the C(=O)Me group was deduced from the analysis of its NOESY spectrum. Scheme 30. Reaction of diol 13 with p-toluenesulfonic acid. Formation of complex 43 (characterized only by NMR) is best explained through the formation of intermediate N (Scheme 31) which then contracts similarly to J in Scheme 29. However, it is difficult to understand why the alternative intermediate O, which should give derivative 19, is not formed at all.[30] Scheme 31. Proposed mechanism for the formation of complex 43 by the reaction of diol 13 with acid. The Wolff rearrangement consists on the transformation/s of a diazoalkane having an adjacent keto group, i.e. the functionality R-C(=N2)-C(=O)-R´, which takes place via thermal (with or without a metal-based catalyst) or photochemical activation. Carbene R-C(:)-C(=O)-R´ seems to be the main, unstable, reaction product which evolves depending on the nature of R, R´ and the reaction media.[31] One of the most interesting cases of this reaction occurs when the -diazoketone functionality belongs to a carbocycle because, in general, it yields derivatives having a contracted ring. This is particularly important for the synthesis of cyclobutanes[32] from fivemembered rings and the simplest example is shown in Scheme 32a. As can be observed, the carbene intermediate gives a ketene functionality by migration of a CH2 moiety, in the  position with respect to the carbene, with concomitant formation of the cyclobutane ring. Generally, the ketene is not isolated but it is trapped by any adequate reagent present in the reaction mixture. Scheme 32. a) Thermal (with or without a metal-based catalyst) or photochemical evolution of  -diazocyclopentanone. b) Transformation of  - formylcyclopentanone (for convenience the enol tautomer is the one depicted herein) to the corresponding  -diazoketone by its reaction with TsN3 in the presence of NEt3. Of the different methods reported to obtain  -diazoketones, one of particular interest to us, is the reaction of -formylketones with tosyl azide in the presence of a base[30] (Scheme 32b). Interestingly, when this reaction was carried out with compound 35, in CH2Cl2 at 25 ºC in the presence of NEt3, the expected diazoalkane was not observed but instead compound 44 formed in ca. 45% isolated yield (Scheme 33)[33] along with an insoluble product, namely compound 45 (see below). was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (10:1) as eluent. Yield: 44 mg, 0.077 mmol (45%). Rf = 0.27 [silica gel; nhexane:Et2O (1:5)]. An analytically pure sample, as white needles, was obtained by crystallization from a mixture of nhexane:CH2Cl2 (1:2) at -20 ºC. 1H NMR (CDCl3, 25 ºC):  = 5.81 (s, 3 H, 3 CHpz), 2.64, 2.16 (m, 2 H each, 2 CHAHB), 2.52, 2.40, 2.36 (s, 1:2:3, 6 Mepz), 1.88, 1.66 (m, 2 H each, 2 CHCHD); 13C{1H} NMR (CDCl3, 25 ºC):  = 169.7 (CO), 151.0, 150.8, 144.0, 143.5 (2:1:1:2, Cqpz), 109.3, 107.2 (1:2, CHpz), 35.3 (C2, 1JCH = 122 Hz), 15.2, 14.6, 13.5, 12.8 (1:2:1:2, Mepz), 2.8 (C1, 1JCH = 125 Hz); IR (Nujol):  1987 cm-1 (Ir— CO); elemental analysis calcd (%) for C20H30BN6OIr: C 41.9, H 5.2, N 14.7; found: C 41.4, H 5.2, N 15.0. Compound 5. To a solution of compound 1 (0.10 g, 0.17 mmol) in diethyl ether (5 mL), an excess of ZnEt2 (2.8 mL, 1 M in hexane, 2.8 mmol) and CH2I2 (0.34 mL, 4.2 mmol) were added sequentially. The resulting mixture was stirred at room temperature for 12 h and, after this period of time a NH4Cl-saturated water solution was added. The organic phase was separated, dried with MgSO4 and taken to dryness. 1H NMR analysis of the resulting product showed that only a partial transformation of 1 into compound 5 has occurred (80% conversion). 5 could not be separated from 1 by column chromatography on silica gel, hence the crude mixture was treated with m-chloroperbenzoic acid to transform 1 into 7 (see below). In this way 5 was separated by column chromatography on silica gel eluting with a mixture of nhexane:Et2O (10:1). Yield: 65 mg, 0.11 mmol (65%). Rf = 0.55 (silica gel; nhexane: Et2O, 5:1). An analytically pure sample, as white crystals, was obtained by crystallization from a mixture of nhexane:CH2Cl2 (1:2) at -20 ºC. 1H NMR (CDCl3, 25 ºC):  = 5.79, 5.75 (s, 1:2, 3 H, 3 CHpz), 2.54 (d, 2 H, 2JAB = 11.1 Hz, 2 HB), 2.52, 2.33, 2.32, 2.29 (s, 1:1:2:2, 18H, 6 Mepz), 2.36 (dd, 2H, 3JCA = 2.8 Hz, 2 HA), 0.77 (m, 2 H, 2 HC), 0.33 (td, 1 H, 3JBD = 8.3 Hz, 2JED = 4.5 Hz, HD), 0.20 (q, 1 H, 3JCE = 4.5 Hz, HE); 13C{1H} NMR (CDCl3, 25 ºC):  = 170.9 (CO), 150.7, 150.6, 143.6, 143.3 (1:2:1:2, Cqpz), 108.7, 106.8 (1:2, CHpz), 27.3 (C2, 1JCH = 157 Hz), 14.4, 13.1, 13.0, 12.5 (2:1:1:2, Mepz), 9.7 (C3, 1JCH = 157 Hz), 4.6 (C1, 1JCH = 129 Hz); IR (Nujol):  1986 cm-1 (Ir—CO); elemental analysis calcd (%) for C21H30BN6OIr: C 43.1, H 5.1, N 14.4; found: C 43.4, H 5.1, N 15.2. Compound 6. Following the same procedure described above for the synthesis of 5, but starting with complex 3, a 1:4 mixture of compounds 3:6 was obtained. Complex 6 was characterized by NMR spectroscopy in admixture with 3. 1H NMR (CDCl3, 25 ºC):  = 5.77 (s, 3 H, 3 CHpz), 2.77 (d, 2 H, 2JAB = 11.2 Hz, 2 HB), 2.36, 2.33, 2.32 (s, 1:1:1, 18 H, 6 Mepz), 2.05 (d, 2 H, 2 HA), 1.16 (s, 6 H, 2 Me), 0.54 (d, 1 H, 2JCD = 4.2 Hz, HD), -0.34 (d, 1 H, HC); 13C{1H} NMR (CDCl3, 25 ºC):  = 170.8 (CO), 150.6-143.1 (Cqpz), 108.1, 106.8 (1:2, CHpz), 34.2 (C2), 22.5 (C3, 1JCH = 164 Hz), 21.6 (Me), 14.5, 12.8, 12.5, 11.9 (2:1:2:1, Mepz), 13.1 (C1, 1JCH = 130 Hz). Compound 7. A solution of m-ClC6H4CO3H (0.13 g, 0.75 mmol) in dichloromethane (5 mL) was added to a solution of compound 1 (0.30 g, 0.52 mmol) in the same solvent (5 mL) at 0 ºC. The resulting solution was stirred at room temperature for 1 h and, after this period of time, a NaHCO3-saturated water solution added. The organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the resulting product revealed quantitative formation of compound 7. An analytically pure sample, as white needles, was obtained by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC. Yield: 180 mg, 0.31 mmol (60%). 1H NMR (CDCl3, 25 ºC):  = 5.82, 5.79 (s, 1:2, 3 H, 3 CHpz), 2.89 (s, 2 H, 2 CHC), 2.66 (d, 2 H, 2JAB = 13.0 Hz, 2 HB), 2.36, 2.34, 2.33, 2.28 (s, 1:2:2:1, 18H, 6 Mepz), 2.17 (d, 2 H, 2 HA); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.9 (CO), 151.0, 150.4, 144.0, 143.7 (2:1:1:2, Cqpz), 109.3, 107.2 (1:2, CHpz), 65.8 (C2, 1JCH = 170 Hz), 14.7, 13.6, 13.2, 12.8 (2:1:1:2, Mepz), 2.1 (C1, 1JCH = 127 Hz); IR (Nujol):  1999 cm-1 (Ir—CO); elemental analysis calcd (%) for C20H28BN6O2Ir: C 40.9, H 4.8, N 14.3; found: C 40.8, H 4.6, N 13.9. Compound 8. Following the same procedure described above for complex 7, but starting with 2 (0.30 g, 0.51 mmol) complex 8 was quantitatively obtained. A spectroscopically pure sample, a microcrystalline pale yellow solid, was obtained by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC. Yield: 235 mg, 0.39 mmol (76%). 1H NMR (CDCl3, 25 ºC):  = 5.82, 5.77 (s, 1:2, 3 H, 3 CHpz), 2.82 (s, 1 H, HC), 2.65 (d, 1 H, 2JDE = 12.8 Hz, HE), 2.61 (d, 1 H, 2JAB = 12.8 Hz, HB), 2.35, 2.34, 2.33, 2.32 (s, 1:1:2:2, 18 H, 6 Mepz), 2.14 (dd, 1 H, 3JCD = 1.7 Hz, HD), 2.05 (d, 1 H; HA), 1.55 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 169.1 (CO), 151.0, 150.5, 144.0, 143.7 (2:1:1:2, Cqpz), 109.1, 107.2 (1:2, CHpz), 72.4 (C3, 1JCH = 168 Hz), 71.4 (C2), 19.5 (Me), 14.8, 14.7, 13.4, 13.3, 12.8 (1:1:1:1:2, Mepz), 6.0 (C1, 1JCH = 127 Hz), 0.9 (C4, 1JCH = 134, 127 Hz); IR (Nujol):  2007 cm-1 (Ir— CO). Compound 9. Following the same procedure described above for complex 7, but starting with 3 (0.30 g, 0.50 mmol), complex 9 was quantitatively obtained. An analytically pure sample, a microcrystalline pale yellow solid, was obtained by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC. Yield: 240 mg, 0.38 mmol (76%). 1H NMR (CDCl3, 25 ºC):  = 5.81, 5.77 (s, 1:2, 3 H, 3 CHpz), 2.79 (d, 2 H, 2JAB = 13.0 Hz, 2 HB), 2.34, 2.23 (s, 5:1, 18 H, 6 Mepz), 2.08 (d, 2 H, 2 HA), 1.40 (s, 6 H, 2 Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.9 (CO), 150.9, 150.5, 144.0, 143.6 (2:1:1:2, Cqpz), 108.9, 107.1 (1:2, CHpz), 73.8 (C2), 19.3 (Me), 14.7, 13.2, 12.8, 12.6 (2:1:2:1, Mepz), 8.5 (C1, 1JCH = 127 Hz); IR (Nujol):  2007 cm-1 (Ir— CO); elemental analysis calcd (%) for C22H32BN6O2Ir·H2O: C 42.9, H 5.2, N 13.6; found: C 41.7, H 5.7, N 13.1. Compound 10. To a cold (0 ºC) solution of 1 (0.20 g, 0.35 mmol) in THF (10 mL) an excess of BH3·THF (2.5 mL, 1 M in THF, 2.5 mmol) was added. The reaction mixture was stirred at 0 ºC for 30 min and then at room temperature for 4 h. After cooling the system at 0 ºC, NaOH (2.5 mL, 3 M in H2O) and H2O2 (2.5 mL, 30% in H2O) were added and the resulting mixture stirred for 2 h at room temperature. Upon addition of 10 mL of Et2O the organic phase was separated, washed with NaCl-saturated water, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed quantitative formation of 10, which was purified by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC as white needles. Yield: 195 mg, 0.33 mmol (94%). 1H NMR (CDCl3, 25 ºC):  = 5.78, 5.77 (s, 1:2, 3 H, 3 CHpz), 4.40 (m, 1 H, HC), 2.59 (dd, 1 H, JHH = 12.4 and 6.6 Hz, HD), 2.50, 2.45 (m, 1 H each, 2 H, HE and HG), 2.41, 2.38, 2.36, 2.32 (s, 1:1:1:3, 18 H, 6 Mepz), 2.26 (m, 1 H, HA), 1.82 (td, 1 H, JHH = 10.2 and 7.2 Hz, HF), 1.50 (m, 1 H, HB); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.7 (CO), 150.8, 150.7, 150.1, 143.9, 143.3 (1:1:1:1:2, Cqpz), 109.0, 107.0, 106.9 (CHpz), 80.7 (C2, 1JCH = 141 Hz), 45.2 (C3, 1JCH = 123 Hz), 15.0, 14.4, 14.2, 13.2, 12.52, 12.5 (Mepz), 10.5 (C1, 1JCH = 127 Hz), -6.1 (C4, 1JCH = 129 Hz); IR (Nujol):  2001 cm-1 (Ir—CO); elemental analysis calcd (%) for C20H30BN6O2Ir: C 40.7, H 5.1, N 14.3; found: C 40.6, H 4.8, N 14.0. Compound 11. Following the same procedure described above for complex 10, but starting with 2 (0.20 g, 0.34 mmol), complex 11 was quantitatively obtained. A spectroscopically pure sample, a pale brown solid, was obtained by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC. Yield: 185 mg, 0.31 mmol (91%). 1H NMR (CDCl3, 25 ºC):  = 5.80, 5.78, 5.75 (s, 1 H each, 3 H, 3 CHpz), 4.04 (q, 1 H, 3JED = 3JFD = 3JCD = 8.2 Hz, HD), 2.63, 2.57 (dd, 1 H each, 2JEF = 12.1 Hz, HE and HF), 2.42, 2.41, 2.33, 2.32, 2.31 (s, 1:1:1:1:2, 18 H, 6 Mepz), 2.35 (dd, 1 H, 2JAB = 11.0, 3JCB = 5.5 Hz, HB), 1.66 (m, 1 H, HC), 1.51 (dd, 1 H, 3JCA = 13.2 Hz, HA), 1.14 (d, 3 H, 3JCMe = 6.0 Hz, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.7 (CO), 151.0, 150.2, 144.3, 143.6 (2:1:1:2, Cqpz), 109.4, 107.4, 107.1 (CHpz), 84.5 (C3, 1JCH = 138 Hz), 53.8 (C2, 1JCH = 131 Hz), 21.7 (Me), 16.0, 14.6, 13.5, 12.7 (1:1:1:1:2, Mepz), 6.2 (C4, 1JCH = 129 Hz), 2.3 (C1, 1JCH = 127 Hz); IR (Nujol):  1994 cm-1 (Ir—CO). Compound 12. TMEDA (0.1 mL) was added to a cold (0 ºC) solution of compound 1 (0.10 g, 0.17 mmol) in CH2Cl2 (15 mL). After cooling the system at -78 ºC an excess of OsO4 (3 mL, 0.1 M in tBuOH, 0.3 mmol) was added. The resulting mixture was stirred for 10 min at -78 ºC and then for 4 h at room temperature. The volatiles were removed under reduced pressure and upon addition of 10 mL of THF and Na2S2O5-saturated water (10 mL), the resulting mixture was refluxed for 3 h. The organic phase was separated and the aqueous phase washed twice with CH2Cl2 (2 x 5 mL). The organic phases were combined, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed the formation of compound 12, which was purified by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC as a pale yellow solid. Yield: 85 mg, 0.14 mmol (82%). Slow evaporation of a solution of compound 12 in C6H12:CH2Cl2 (1:1) provided quality crystals for X-ray crystallography. 1H NMR (CDCl3, 25 ºC):  = 5.77 (s, 3 H, 3 CHpz), 4.22 (m, 2 H, 2 HC), 2.40 (dd, 2 H, 2JAB = 12.7, 3JCB = 4.0 Hz, 2 HB), 2.38, 2.36, 2.32 (s, 1:2:3, 18 H, 6 Mepz), 2.28 (dd, 2 H, 3JCA = 6.1 Hz, 2HA); 13C{1H} NMR (CDCl3, 25 ºC):  = 167.9 (CO), 150.8, 149.8, 144.1, 143.3 (2:1:1:2, Cqpz), 109.1, 107.0 (1:2, CHpz), 80.8 (C2, 1JCH = 142 Hz), 15.4, 14.3, 13.2, 12.5 (1:2:1:2, Mepz), 2.1 (C1, 1JCH = 130 Hz); IR (Nujol):  2009 (Ir—CO). Compound 13. Following the same procedure described above for complex 12, but starting with 2 (0.10 g, 0.17 mmol), complex 13 was quantitatively obtained. A spectroscopically pure sample, a pale yellow solid, was obtained by crystallization from a mixture of hexane:CH2Cl2 (1:2) at -20 ºC. Yield: 83 mg, 0.13 mmol (77%). 1H NMR (CDCl3, 25 ºC):  = 5.81, 5.78, 5.76 (s, 1 H each, 3 H, 3 CHpz), 4.26 (t, 1 H, 3JDC = 3JEC = 8.1 Hz, HC), 2.48, 2.42 (m, 1 H each, HD and HE), 2.46, 2.41, 2.35, 2.34, 2.33, 2.31 (s, 3 H each, 18 H, 6 Mepz), 2.41 (d, 1 H, 2JAB = 12.0 Hz, HB), 2.11 (d, 1 H, HA), 1.38 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 167.7 (CO), 150.9, 150.8, 149.8, 144.1, 143.4, 143.3 (Cqpz), 109.1, 107.1, 106.9 (CHpz), 83.4 (C2), 82.9 (C3, 1JCH = 139 Hz); 27.4 (Me), 15.3, 14.7, 13.9, 13.3, 12.5, 12.4 (Mepz), 9.9 (C1, 1JCH = 129 Hz), 1.6 (C4, 1JCH = 129 Hz); IR (Nujol):  2004 cm-1 (Ir—CO). Compound 14. Following the same procedure described above for complex 12, but starting with 3 (0.10 g, 0.17 mmol), complex 14 was quantitatively obtained, which was crystallized as a pale yellow solid from a mixture of hexane:CH2Cl2 (1:2) at -20 ºC. Yield: 82 mg, 0.13 mmol (76%). 1H NMR (CDCl3, 25 ºC):  = 5.79, 5.76 (s, 2:1, 3 H, 3 CHpz), 2.62 (s, 4 H, 2 HA and 2 HB), 2.48, 2.45, 2.32, 2.31 (s, 1:2:2:1, 18 H, 6 Mepz), 1.38 (s, 6 H, 2Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 166.1 (CO), 150.9, 150.2, 144.1, 143.6 (2:1:1:2, Cqpz), 109.7, 107.1 (1:2, CHpz), 85.2 (C2), 28.8 (Me, 1JCH = 125 Hz), 17.9 (C1, 1JCH = 129 Hz), 15.7, 14.8, 13.5, 12.7 (1:2:1:2, Mepz); IR (Nujol):  1996 cm-1 (Ir—CO). Compound 15. In a two-necks round-bottom flask, a flow of O3 was passed through a cold (-70 ºC) solution of compound 1 (0.10 g, 0.17 mmol) in dichloromethane (20 mL) for 15 min. PPh3 (0.05 g, 0.17 mmol) was then added and the resulting suspension stirred at -70 ºC until the phosphine was dissolved. This solution was stirred at room temperature for 30 min. and the volatiles were removed under reduced pressure. 1H NMR analysis of the crude product revealed the formation of compound 15, which was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (1:5) as eluent. Yield: 40 mg, 0.066 mmol (39%) (white crystals). Rf = 0.16 [silica gel; nhexane:Et2O (1:5)]. 1H NMR (CDCl3, 25 ºC):  = 9.40 (dd, 2 H, 3JHH = 5.3 and 4.2 Hz, 2 CHO), 5.87, 5.83 (s, 1:2, 3 H, 3 CHpz), 3.43, 3.07 (dd, 2 H each, 2JHH = 9.9 Hz, 2C1H2), 2.61, 2.37, 2.36, 2.34 (s, 1:2:1:2, 18 H, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 207.9 (C2, 1JCH = 166 Hz), 165.0 (CO), 152.5, 151.2, 144.7, 144.6 (1:2:1:2, Cqpz), 109.9, 108.0 (1:2, CHpz), 15.6, 14.7, 13.2, 12.8 (1:2:1:2, Mepz), 8.5 (C1, 1JCH = 132 Hz); IR (Nujol):  2036 (Ir—CO), 1668 cm-1 (C=O); elemental analysis calcd (%) for C20H28BN6O3Ir: C 39.8, H 4.6, N 13.9; found: C 40.0, H 4.3, N 14.5. Compound 16. Following the same procedure described above for complex 15, but starting with 2 (0.10 g, 0.17 mmol), complex 16 was obtained. It was purified by column chromatography on silica gel using a mixture ofhexane:Et2O (1:5) as eluent to give a white solid. Yield: 46 mg, 0.075 mmol (44%). Rf = 0.29 [silica gel; nhexane:Et2O (1:5)]. 1H NMR (CDCl3, 25 ºC):  = 9.24 (dd, 1 H, 3JHH = 5.7 and 3.5 Hz, CHO), 5.87, 5.84, 5.80 (s, 1 H each, 3 H, 3 CHpz), 3.52, 3.13 (d, 1 H each, 2JHH = 10.8 Hz, C1H2), 3.41, 2.95 (dd, 1 H each, 2JHH = 10.1 Hz, C3H2), 2.66, 2.38, 2.36, 2.35, 2.34, 2.33 (s, 3 H each, 18 H, 6 Mepz), 2.16 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 215.6 (C2), 208.4 (C4, 1JCH = 167 Hz), 165.5 (CO), 152.1, 151.2, 150.4, 144.3, 144.3, 144.2 (Cqpz), 109.7, 107.8, 107.7 (CHpz), 30.9 (Me), 14.5, 14.3, 14.1, 12.9, 12.6, 12.5 (Mepz), 10.8 (C1, 1JCH = 130 Hz), 6.8 (C3, 1JCH = 130 Hz); IR (Nujol):  2021 (Ir—CO), 1685 cm-1 (C=O). Compound 17. Following the same procedure described above for complex 15, but starting with 3 (0.10 g, 0.17 mmol), complex 17 was obtained in ca. 90% spectroscopic yield. This compound was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (1:5) as eluent. Yield: 70 mg, 0.11 mmol (65%) (white solid). Rf = 0.13 [silica gel; nhexane:Et2O (1:5)]. 1H NMR (CDCl3, 25 ºC):  = 5.86, 5.82 (s, 1:2, 3 H, 3 CHpz), 3.36, 3.15 (AB spin system, 2 H each, 2JHH = 12.1 Hz, 2 IrCH2), 2.75, 2.35, 2.33, 2.32 (s, 1:1:2:2, 18 H, 6 Mepz), 2.13 (s, 6 H, 2 Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 216.1 (C2), 166.8 (CO), 151.9, 150.5, 144.4, 144.3 (1:2:2:1, Cqpz), 109.8, 107.9 (1:2, CHpz), 30.7 (Me), 15.5, 14.6, 13.2, 12.9 (1:2:1:2, Mepz), 11.8 (C1, 1JCH = 127 Hz); IR (Nujol):  2026 (Ir—CO), 1672 cm-1 (C=O). Compound 18. An excess of BF3 in Et2O was added dropwise to a solution of compound 7 (0.12 g, 0.20 mmol) in dichloromethane (5 mL) at -78 ºC. The cooling bath was then removed and the resulting reaction mixture stirred while allowing to reach room temperature. CH2Cl2 (5 mL) was then added and the resulting solution washed sequentially with NaHCO3-saturated water (10 mL), NaOH (10 mL, 1 M) and NaCl-saturated water (10 mL). The organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 18. This compound was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (7:1) as eluent. Yield: 78 mg, 0.13 mmol (65%) (white solid). Rf = 0.61 [silica gel; nhexane:Et2O (1:1)]. 1H NMR (CDCl3, 25 ºC):  = 8.58 (s, 1 H, HC), 5.89, 5.81, 5.67 (s, 1 H each, 3 H, 3 CHpz), 2.99, 2.78 (d, 1 H each, 2JAB = 16.4 Hz, CHAHB), 2.37, 2.35, 2.34, 2.31, 2.30, 2.09 (s, 3 H each, 18 H, 6 Mepz), 1.83 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  218.3 (C2), 164.9 (CO), 152.4, 151.5, 150.1, 148.6, 144.2, 143.9, 143.8 (Cqpz and C3), 145.5 (C4, 1JCH = 149 Hz), 109.5, 107.1, 106.9 (CHpz), 17.6 (Me, 1JCH = 126 Hz), 14.4, 14.1, 13.7, 13.0, 12.5, 12.4 (Mepz), 11.3 (C1, 1JCH = 128 Hz). Compound 25. A solution of complex 10 (0.20 g, 0.34 mmol) in CH2Cl2 (5 mL) was added to a cold (0 ºC) mixture of PCC (0.22 g, 1.02 mmol), sodium acetate (0.05 g, 0.61 mmol), celite (0.6 g) and molecular sieves (0.1 g) in CH2Cl2 (10 mL). After stirring for 30 min at 0 ºC and for 1 h at room temperature, the resulting suspension was filtered through celite, the cake was washed with CH2Cl2 and the volatiles were removed under reduced pressure. 1H NMR analysis of the crude product revealed the formation of 25, which was purified by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC as white needles. Yield: 110 mg, 0.19 mmol (56%). 1H NMR (CDCl3, 25 ºC):  = 5.81, 5.80, 5.79 (s, 1 H each, 3 H, 3 CHpz), 3.19 (d, 1 H, 2JAB = 17.0 Hz, HB), 2.80 (dd, 1 H, 4JHH = 1.5 Hz, HA), 2.73 (dd, 1 H, 2JDC = 17.9, 3JEC = 7.3 Hz, HC), 2.58 (t, 1 H, 2JEF = 3JDF = 10.6 Hz, HF), 2.44 (dt, 1 H, 3JED = 10.0 Hz, HD), 2.40, 2.34, 2.33, 2.27, 2.22 (s, 1:1:2:1:1, 18 H, 6 Mepz), 1.80 (dt, 1 H, HE); 13C{1H} NMR (CDCl3, 25 ºC):  = 231.8 (C2), 167.9 (CO), 150.8, 150.7, 150.7, 143.9, 143.7 (1:2:1:1:1, Cqpz), 109.3, 107.2, 106.9 (CHpz), 46.1 (C3), 14.4, 14.3, 14.1, 13.0, 12.5, 12.4 (Mepz), 11.8 (C1), –15.3 (C4); IR (Nujol):  2000 (Ir—CO), 1696 cm-1 (C=O); elemental analysis calcd (%) for C20H28BN6O2Ir: C 40.9, H 4.8, N 14.3; found: C 40.6, H 4.6, N 14.0. Compound 26. A solution of compound 22 (0.10 g, 0.16 mmol) in dichloromethane (5 mL) was added to a cold (0 ºC) mixture of anhydrous sodium acetate (0.03 g, 0.36 mmol), celite (0.2 g), pyridinium chlorochromate (0.11 g, 0.5 mmol) and molecular sieves (0.04 g) in dichloromethane (10 mL). The resulting mixture was stirred for 30 min at 0 ºC and for 4 h at room temperature before the suspension was filtered through celite, the cake washed with dichloromethane and the filtrate taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 26, which was purified by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC as a white solid. Yield: 51 mg, 0.085 mmol (53%). 1H NMR (CDCl3, 25 ºC):  = 9.83 (s, 1 H, HB), 6.98 (m, 1 H, HA), 5.80, 5.79, 5.73 (s, 1 H each, 3 H, 3 CHpz), 3.27, 2.91 (dm, dq, 1 H each, 2JHH = 18.6, JHH = 2.3 Hz, C1H2 or C3H2), 3.24, 2.66 (d, dq, 1 H each, 2JHH = 15.5, JHH = 2.6 Hz, C3H2 or C1H2), 2.36, 2.35, 2.34, 2.34, 2.32, 2.01 (s, 3 H each, 18 H, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 190.7 (C5, 1JCH = 169 Hz), 169.8 (C4, 1JCH = 150 Hz), 167.8 (CO), 158.4 (C2), 151.5, 151.1, 150.7, 143.8, 143.5 (1:1:1:1:2, Cqpz), 108.8, 107.0 (1:2, CHpz), 14.4, 14.2, 13.0, 12.5, 12.4, 12.4 (Mepz), 2.1 (C1 or C3, 1JCH = 131 Hz), -3.3 (C3 or C1, 1JCH = 136 Hz); IR (Nujol):  2014 (Ir—CO), 1682 cm-1 (C=O). Compound 27. An excess of DMP (0.36 g, 0.85 mmol) was added to a solution of 10 (0.10 g, 0.17 mmol) in DMSO (5 mL), the resulting mixture stirred for 5 min at room temperature, H2O (0.08 mL, 2.5 equiv.) then added and the mixture stirred at 70 ºC for 12 h. Et2O (5 mL) was then added and, after vigorously shaken, the organic phase was separated, washed sequentially with NaHCO3- saturated and NaCl-saturated water, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 27, which was purified by crystallization from a mixture of Et2O:CH2Cl2 (1:2) at -20 ºC. Yield: 75 mg, 0.13 mmol (77%) (white solid). A sample of analytical purity was obtained by crystallization from a mixture of nhexane:CH3OH (1:1). 1H NMR (CDCl3, 25 ºC):  = 9.12 (d, 1 H, 3JCD = 7.6 Hz, HD), 6.73 (d, 1 H, HC), 5.89, 5.82, 5.68 (s, 1 H each, 3 H, 3 CHpz), 2.93, 2.85 (d, 1 H each, 2JAB = 16.4 Hz, CHAHB), 2.37, 2.35, 2.32, 2.32, 2.31, 2.24 (s, 3 H each, 18 H, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 220.4 (C2), 164.7 (CO), 153.4 (C4, 1JCH = 153 Hz), 152.9, 151.6, 150.1, 144.2, 144.0, 143.9 (Cqpz), 144.3 (C3, 1JCH = 161 Hz), 109.5, 107.2, 106.9 (CHpz), 14.4, 14.1, 14.0, 13.0, 12.5, 12.4 (Mepz), 11.5 (C1, 1JCH = 130 Hz); IR (Nujol):  2021 (Ir—CO), 1665 cm-1 (C=O); elemental analysis calcd (%) for C20H26BN6O2Ir·5/2CH3OH: C 40.6, H 5.4, N 12.6; found: C 40.4, H 4.9, N 12.1. Compound 28. An excess of MeLi (0.14 mL, 1.6 M in Et2O, 0.22 mmol) was added to a cooled (0 ºC) solution of compound 25 (0.05 g, 0.085 mmol) in diethyl ether (5 mL), the resulting mixture stirred for 24 h at room temperature, NH4Cl-saturated water (10 mL) was then added and, after vigorously shaken, the organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product (white solid, 20 mg) revealed the formation of compound 28 but also the presence of starting material, which could not be separated. 1H NMR (CDCl3, 25 ºC):  = 5.80, 5.78, 5.75 (s, 1 H each, 3 CHpz), 2.69 (ddd, 1 H, 2JEF = 10.6, 3JCF = 18.4, 3JDF = 7.7 Hz, HF), 2.43, 2.41, 2.34, 2.33, 2.32 (s, 1:1:1:2:1, 6 Mepz), 2.40 (d, 1 H, 2JBA = 12.4 Hz, HA), 2.25 (dd, 1 H, 4JEB = 2.6 Hz, HB), 2.11 (ddd, 1 H, 2JDC = 7.7, 3JEC = 10.9 Hz, HC), 1.95 (td, 1 H, HE), 1.53 (m, 1 H, HD), 1.49 (s, 3 H, Me). Represented NOEs in the figure have been deduced from NOESY spectra in C6D6, CDCl3 and different mixtures of them; 13C{1H} NMR (CDCl3, 25 ºC):  = 169.1 (CO), 150.9, 150.7, 150.2, 143.9, 143.3 (1:1:1:1:2, Cqpz), 109.0, 106.9 (1:2, CHpz), 87.0 (C2), 45.4 (C3, 1JCH = 123 Hz), 28.8 (Me), 19.0 (C1, 1JCH = 123 Hz), 14.8, 14.4, 14.0, 13.2, 12.6, 12.5 (Mepz), -7.5 (C4, 1JCH = 128 Hz). IR (Nujol):  1999 cm-1 (Ir—CO). Compound 29. An excess of PhLi (0.5 mL, 3 M in hexane, 1.5 mmol) was added to a cooled (0 ºC) solution of compound 25 (0.20 g, 0.34 mmol) in diethyl ether (10 mL), the resulting mixture stirred for 24 h at room temperature, NH4Cl- saturated water was then added and, after vigorously shaken, the organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 34 which was purified by column chromatography on silica gel using a mixture of nhexane:AcOEt (10:1) as eluent to give a white solid. Yield: 160 mg, 0.24 mmol (71%). Rf = 0.66 [silica gel; nhexane: Et2O (10:1)]. The sample used for elemental analysis was obtained by crystallization from a mixture of nhexane: CH2Cl2 (1:1). 1H NMR (CDCl3, 25 ºC):  = 7.74, 7.45, 7.33 (d, t, t, 2:1:2, Ph), 5.85, 5.81, 5.80 (s, 1 H each, 3 CHpz), 3.00 (d, 1 H, 2JBA = 11.9 Hz, HA), 2.87 (ddd, 1 H, 2JEF = 11.5, 3JHH = 10.1, 8.2 Hz, HF), 2.49 (dd, 1 H, JEB = 2.1 Hz, HB), 2.46, 2.40, 2.39, 2.37, 2.36 (s, 2:1:1:1:1, 6 Mepz), 2.41 (m, 1 H, HC), 2.07 (td, 1 H, 3JHH = 11.0, 2.1 Hz, HE), 1.87 (m, 1 H, HD). OH resonance has not been located. NOESY experiment was registered in a mixture of CDCl3:C6D6 (4:1); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.8 (CO), 150.9, 150.7, 150.3, 148.9, 144.1, 143.4 (1:1:1:1:1:2, Cqpz + CqPh), 128.1, 126.1, 125.4 (2:1:2, CHPh), 109.0, 107.1, 107.0 (CHpz), 89.9 (C2), 45.6 (C3, 1JCH = 123 Hz), 17.5 (C1, 1JCH = 126 Hz), 14.8, 14.7, 13.9, 13.3, 12.6, 12.5 (Mepz), -8.3 (C4, 1JCH = 131 Hz); IR (Nujol):  2004 cm-1 (Ir—CO); elemental analysis calcd (%) for C26H34BN6O2Ir·1/2CH2Cl2: C 44.9, H 4.9, N 11.9; found: C 45.3, H 5.2, N 11.6. Compound 30. An excess of MeMgCl (0.53 mL, 0.68 M in THF, 0.36 mmol) was added to a cooled (0 ºC) solution of compound 25 (0.10 g, 0.17 mmol) in diethyl ether (10 mL), the resulting mixture stirred for 24 h at room temperature and the volatiles were then removed under reduced pressure. CH2Cl2 (10 mL) and NH4Cl-saturated water (10 mL) were then added and, after vigorously shaken, the organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 30 with ca. 10% of starting material remaining. Complex 30 was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (100:1) as eluent to give a white solid. Yield: 90 mg, 0.15 mmol (88%). 1H NMR (CDCl3, 25 ºC):  = 5.96 (s, 1 H, HE), 5.81, 5.78, 5.68 (s, 1 H each, 3 CHpz), 2.56, 2.50 (m, 1 H each, CHAHB), 2.49, 2.37 (m, 1 H each, CHCHD), 2.38, 2.34, 2.33, 2.31, 2.30 (s, 1:2:1:1:1, 6 Mepz), 1.87 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 168.4 (CO), 153.3 (C3), 151.7, 150.9, 150.3, 143.5, 143.2 (1:1:1:1:2, Cqpz), 110.6 (C4, 1JCH = 148 Hz), 109.0, 106.7, 106.3 (CHpz), 43.9 (C2, 1JCH = 125 Hz), 21.1 (Me, 1JCH = 130 Hz), 13.8, 13.5, 12.9, 12.5, 12.4, 11.8 (Mepz), -1.3 (C1, 1JCH = 133 Hz); IR (Nujol):  2001 cm-1 (Ir—CO); elemental analysis calcd (%) for C21H30BN6OIr: C 43.1, H 5.1, N 14.5; found: C 43.2, H 5.1, N 14.0. Compounds 31 and 32. Method A: To a solution of compound 29 (0.05 g, 0.075 mmol) in acetic anhydride (2 mL), Na2SO4 (0.1 g) was added and the resulting mixture stirred at 60 ºC for 3 days. The solvent was then removed under reduced pressure and 1H NMR analysis of the crude product showed the formation of a ca. 1:2 mixture of compounds 31 and 32 which could not be separated by column chromatography. Method B: To a solution of compound 29 (0.05 g, 0.075 mmol) in dichloromethane (5 mL), silica gel was added (0.5 g) and the resulting suspension stirred at room temperature for 3 days. It was then filtered and the filtrate taken to dryness. 1H NMR analysis of the crude product showed the formation of a ca. 1:2 mixture of compounds 31 and 32. Selected NMR data for compound 31: 1H NMR (CDCl3, 25 ºC):  = 7.37 (d, 1 H, JHH = 2.3 Hz, HE), 3.06 (m, 2 H, CHCHD), 2.75 (m, 2 H, CHAHB); 13C{1H} NMR (CDCl3, 25 ºC):  = 155.7 (C3), 118.4 (C4, 1JCH = 151 Hz), 41.3 (C2, 1JCH = 123 Hz), -1.8 (C1, 1JCH = 131 Hz). Selected NMR data for compound 32: 1H NMR (CDCl3, 25 ºC):  = 6.22 (m, 1 H, HE), 3.44, 3.07 (d, 1 H each, 2JHH = 15.0 Hz, CHCHD), 3.32, 2.73 (dm, 1 H each, 2JHH = 16.4 Hz, CHAHB); 13C{1H} NMR (CDCl3, 25 ºC):  = 152.1 (C3), 139.7 (C2, 1JCH = 148 Hz), 5.1 (C4, 1JCH = 141, 129 Hz), 2.6 (C1, 1JCH = 130 Hz). Compound 33. An excess of CH2=CHMgBr (0.34 mL, 1 M in THF, 0.34 mmol) was added to a cooled (0 ºC) solution of compound 25 (0.10 g, 0.17 mmol) in diethyl ether (10 mL), the resulting mixture stirred for 24 h at room temperature, NH4Cl-saturated water (10 mL) was then added and, after vigorously shaken, the organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed formation of compound 33 which was purified by column chromatography on silica gel using a mixture of nhexane:AcOEt (10:1) as eluent to give a pale yellow solid. Yield: 45 mg, 0.075 mmol (44%). Rf = 0.63 [silica gel; nhexane: Et2O (10:1)]. 1H NMR (CDCl3, 25 ºC):  = 6.90 (s, 1 H, HA), 6.48 (dd, 2JIF = 17.5, 2JGF = 10.6 Hz, HF), 5.84, 5.81, 5.68 (s, 1 H each, 3 CHpz), 4.93, 4.81 (dd, 1 H each, 2JIG = 1.4 Hz, CHIHG), 2.83, 2.57 (m, 2 H, CHCHB), 2.70, 2.59 (m, 2 H, CHEHD), 2.41, 2.35, 2.31, 2.24 (s, 1:2:2:1, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 167.7 (CO), 158.2 (C2), 151.9, 151.1, 150.4, 143.7, 143.4, 143.3 (Cqpz), 138.0 (C5, 1JCH = 156 Hz), 126.5 (C1, 1JCH = 148 Hz), 109.0, 106.9, 106.4 (CHpz), 108.0 (C6, 1JCH = 156 Hz), 37.4 (C3, 1JCH = 125 Hz), 13.9, 13.8, 13.0, 12.6, 12.4, 14.4 (Mepz), -1.8 (C4, 1JCH = 131 Hz); IR (Nujol):  2011 cm-1 (Ir—CO). Compound 34. An excess of PhLi (0.25 mL, 3 M in hexane, 0.75 mmol) was added to a cooled (0 ºC) solution of compound 24 (0.10 g, 0.17 mmol) in diethyl ether (10 mL), the resulting mixture stirred for 24 h at room temperature, NH4Cl- saturated water was then added and, after vigorously shaken, the organic phase was separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude product revealed the formation of compound 34 (pale brown solid). 1H NMR (CDCl3, 25 ºC):  = 7.44 (s, 1 H, HA), 7.4-7.2 (m, 5 H, Ph), 7.00 (s, 1 H, HB), 5.86, 5.84, 5.62 (s, 1 H each, 3 CHpz), 2.41, 2.38, 2.36, 2.30 (1:1:3:1, 6 Mepz), 2.02 (s, 3 H, Me); 13C{1H} NMR (CDCl3, 25 ºC):  = 163.0 (CO), 160.9 (C2), 154.4, 151.2, 143.9, 143.7, 143.6 (Cqpz + CqPh), 152.6 (C3), 127.7, 127.4, 125.3 (2:2:1, CHPh), 127.8 (C1, 1JCH = 154 Hz), 120.4 (C4, 1JCH = 153 Hz), 108.7, 106.6 (1:2, CHpz), 22.1 (Me), 14.4, 14.3, 13.0, 12.5, 11.6 (1:1:1:2:1, Mepz). Compound 35. To a cold (0 ºC) solution of complex 25 (0.10 g, 0.17 mmol) in C6H6 (5 mL), HCO2Et (0.18 mL, 2.22 mmol) and methanol (0.1 mL) were added. The resulting mixture was then added dropwise over NaH (0.06 g, oil free), stirred a room temperature for 48 h and, in turn, added to cracked ice. The mixture was acidified with HCl (5 mL, 10% in H2O), vigorously shaken, and the organic layer separated. After extraction of the aquous portions with Et2O (3 x 5 mL), the combined organic phases were dried with Na2SO4 and taken to dryness. The resulting crude product was crystallized from Et2O:CH2Cl2 (1:2) at -20 ºC. Isolated yield: 82 mg, 0.13 mmol (77%) (white solid). 1H NMR (CDCl3, 25 ºC):  = 8.58 (s, 1 H, HE), 5.81, 5.80, 5.78 (s, 1 H each, 3 CHpz), 3.25 (d, 1 H, 2JCD = 12.9 Hz, HD), 3.09 (d, 1 H, 2JAB = 18.3 Hz, HB), 2.98 (d, 1 H, HA), 2.53 (d, 1 H, HC), 2.39, 2.34, 2.32, 2.14 (s, 1:3:1:1, 6 Mepz). The OH group has not been located; 13C{1H} NMR (CDCl3, 25 ºC):  = 204.7 (C2), 180.0 (C5, 1JCH = 174 Hz), 167.1 (CO), 151.4, 150.9, 150.8, 143.9, 143.6 (1:1:1:1:2, Cqpz), 121.2 (C3), 109.1, 107.2, 107.0 (CHpz), 14.3, 14.2, 12.9, 12.7, 12.5, 12.4 (Mepz), 4.2 (C1, 1JCH = 129 Hz), -10.9 (C4, 1JCH = 131 Hz); IR (Nujol):  2009 (Ir—CO), 1591 cm-1 (C=O). Compound 36. In a two-necks round bottom flask O3 was passed during 1 minute through a solution of compound 35 (0.10 g, 0.16 mmol) in dichloromethane (10 mL) at -78 ºC. Then, Me2S (0.05 mL) was added, the cooling bath removed, and the resulting mixture stirred at room temperature for 3 h. Water (10 mL) was then added, the mixture shaken vigorously and the organic layer separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude reaction showed almost quantitative formation of the title compound along with a small quantity of starting material remaining. Complex 36 was purified by column chromatography on silica gel to give a yellow solid. 1H NMR (CDCl3, 25 ºC):  = 5.85 (s, 3 H, 3 CHpz), 3.07, 3.05 (AB spin system, 2 H each, 2JAB = 16.9 Hz, 2 CHAHB), 2.36, 2.31, 2.19 (s, 3:2:1, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 210.2 (C2), 164.6 (CO), 150.9, 150.7, 144.3, 144.2 (2:1:1:2, Cqpz), 110.1, 107.5 (1:2, CHpz), 14.8, 14.4, 12.9, 12.5 (1:2:1:2, Mepz), 2.57 (C1, 1JCH = 131 Hz); IR (Nujol):  2015 (Ir—CO), 1712 cm-1 (C=O). Compound 37. A cold (0 ºC) solution of compound 36 (0.10 g, 0.16 mmol) in a C6H6 (5 mL) - methanol (0.10 mL) mixture was added dropwise to NaH (0.06 g) clean of oil. The resulting mixture was stirred at room temperature for 1 h and then added to a water-cracked ice mixture. The mixture was acidified with HCl (5 mL, 10% in H2O) and then vigorously stirred for 10 minutes. After extraction of the aquous layer with Et2O (3 x 5 mL), the combined organic phases were dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude reaction showed quantitative formation of 37 which was purified by column chromatography on silica gel using a mixture of nhexane:Et2O (10:1) as eluent to give a pale yellow solid. Yield: 50 mg, 0.08 mmol (50%). Rf = 0.13 [silica gel; nhexane: Et2O (1:1)]. 1H NMR (CDCl3, 25 ºC):  = 7.39 (s, 1 H, HA), 5.88, 5.82, 5.67 (s, 1 H each, 3 CHpz), 5.78 (brs, 1 H, OH), 2.91, 2.50 (d, 1 H each, 2JCD = 17.1 Hz, CHCHD), 2.37, 2.36, 2.33, 2.32, 2.29, 2.08 (s, 3 H each, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 210.7 (C3), 164.1 (CO), 154.2 (C2), 152.4, 151.4, 150.5, 144.2, 143.9 (1:1:1:1:2, Cqpz), 109.6, 107.2, 106.9 (CHpz), 109.5 (C1, 1JCH = 150 Hz), 14.3, 14.2, 13.6, 12.9, 12.5, 12.4 (Mepz), -4.2 (C4, 1JCH = 130 Hz); IR (Nujol):  2023 (Ir—CO), 1642 cm-1 (C=O); elemental analysis calcd (%) for C20H26BN6O3Ir: C 39.9, H 4.3, N 13.9; found: C 40.1, H 4.4, N 13.3. 1H NMR (CDCl3, 25 ºC):  = 5.85, 5.79, 5.76 (s, 1 H each, 3 CHpz), 3.10 (d, 1 H, 2JBA = 14.6 Hz, HA), 3.05 (d, 1 H, 2JDC = 6.6 Hz, HC), 2.86 (d, 1 H, HD), 2.82 (d, 1 H, HB), 2.37, 2.36, 2.35, 2.30, 2.28, 2.16 (s, 3 H each, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 217.2 (C2), 164.4 (CO), 152.2, 151.2, 144.4, 143.9 (1:2:1:2, Cqpz), 109.7, 106.8, 106.7 (CHpz), 53.3 (C4, 1JCH = 177, 174 Hz), 41.0 (C3), 14.5, 14.0, 13.1, 13.0, 12.4, 12.3 (Mepz), 1.0 (C1, 1JCH = 139 Hz); IR (Nujol):  2023 (Ir—CO), 1714 cm-1 (C=O). Compound 47. In a two-necks round bottom flask O3 was passed during 10 min through a solution of compound 44 (0.10 g, 0.17 mmol) in dichloromethane (20 mL) at -78 ºC. Then, Me2S (0.05 mL) was added, the cooling bath removed, and the resulting mixture stirred at room temperature for 3 h. Water (10 mL) was then added, the mixture shaken vigorously and the organic layer separated, dried with Na2SO4 and taken to dryness. 1H NMR analysis of the crude reaction showed the formation of the title compound which was purified by column chromatography on silica gel using a mixture of hexane:Et2O (10:1) as eluent. Yield: 52 mg, 0.09 mmol (53%). Rf = 0.30 [silica gel, hexane:Et2O (10:1)]. 1H NMR (CDCl3, 25 ºC):  = 5.89, 5.83, 5.72 (s, 1 H each, 3 CHpz), 2.73, 2.71 (AB spin system, 2 H, 2JHH = 14.0 Hz, C1H2), 2.41, 2.39, 2.37, 2.33, 2.32, 2.23 (s, 3 H each, 6 Mepz); 13C{1H} NMR (CDCl3, 25 ºC):  = 188.6 (C2), 160.5 (CO), 152.5, 152.1, 151.5, 144.9, 144.3, 144.1 (Cqpz), 109.6, 107.4, 106.5 (CHpz), 14.9, 13.5, 12.9, 12.7, 12.6, 12.0 (Mepz), -6.1 (C1, 1JCH = 140 Hz); IR (Nujol):  2033 (Ir—CO), 1710 cm-1 (C=O); elemental analysis calcd (%) for C20H26BN6O2Ir·C6H14: C 43.6, H 4.7, N 12.7; found: C 43.3, H 4.4, N 12.6. II X-RAY STRUCTURE ANALYSIS Crystals suitable for X-ray diffraction analysis were coated with dry perfluoropolyether, mounted on glass fibers, and fixed in a cold nitrogen stream (except for 7) to the goniometer head. Data collections were performed on a Bruker-Nonius X8 Apex-II CCD diffractometer (5, 10, 19, 25, 33 and 45) or a Bruker Smart Apex CCD diffractometer (7, 12 and 15) using graphite monochromated Mo radiation (λ(Mo Kα) = 0.71073 Å) and fine-sliced ω and φ scans (scan widths 0.30° to 0.50°). The data were reduced (SAINT)[2] and corrected for absorption effects by the multiscan method (SADABS). [2] The structures were solved by direct methods (SIR2002, [3] SHELXS[4]) and refined against all F2 data by full-matrix least-squares techniques (SHELXTL-6.12) minimizing w[Fo2-Fc2]2. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were included in calculated positions and allowed to ride on their carrier atoms with the isotropic temperature factors Uiso fixed at 1.2 times (1.5 times for methyl groups) of the Ueq values of the respective carrier atoms. Some geometric restraints (SADI and DFIX shelxl instructions), the ADP restraint SIMU and the rigid bond restraint (DELU and ISOR) were used to make the geometric and ADP values of the disordered atoms more reasonable. As examples: positional disorder: 10 and 33, structural disorder: 25, and disordered CHCl3 solvent molecules in 45. CCDC 1565331 (5), 1565332 (7), 1565333 (10), 1565334 (12), 1565335 (15), 1565336 (19), 1565337 (25), 1565338 (33) and 1565339 (45) contain the supplementary crystallographic data for this paper. Figure S1: ORTEP drawing of 5 at 30% ellipsoids probability, most of hydrogen atoms are omitted for clarity. Table S1: Crystal data and structure refining for 5: Empirical formula C21H30BIrN6O Formula weight 585.52 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P 21/m Unit cell dimensions a = 7.8986(5) Å = 90°. b = 13.2259(9) Å = 105.185(2)°. c = 11.0710(7) Å  = 90°. Volume 1116.16(13) Å3 Z 2 Density (calculated) 1.742 Mg/m3 Absorption coefficient 6.006 mm-1 F(000) 576 Crystal size 0.27 x 0.26 x 0.18 mm3 Theta range for data collection 1.91 to 25.25°. Index ranges -8<=h<=9, -15<=k<=15, -13<=l<=13 Reflections collected 11339 Independent reflections 2114 [R(int) = 0.0284] Completeness to theta = 25.25° 99.6 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.4111 and 0.2939 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2114 / 299 / 154 Goodness-of-fit on F2 1.275 Final R indices [I>2sigma(I)] R1 = 0.0421, wR2 = 0.1207 R indices (all data) R1 = 0.0433, wR2 = 0.1224 Largest diff. peak and hole 2.740 and -1.184 e.Å-3 Figure S2: ORTEP drawing of 7 at 30% ellipsoids probability, most of hydrogen atoms are omitted for clarity. Table S2: Crystal data and structure refining for 7: Empirical formula C20H28BIrN6O2 Formula weight 587.49 Temperature 299(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P21/m Unit cell dimensions a = 7.983(2) Å = 90°. b = 13.312(3) Å = 108.450(10)°. c = 11.005(2) Å  = 90°. Volume 1109.4(4) Å3 Z 2 Density (calculated) 1.759 Mg/m3 Absorption coefficient 6.046 mm-1 F(000) 576 Crystal size 0.60 x 0.20 x 0.02 mm3 Theta range for data collection 2.48 to 25.05°. Index ranges -9<=h<=9, -15<=k<=15, -13<=l<=13 Reflections collected 10662 Independent reflections 2046 [R(int) = 0.1020] Completeness to theta = 25.05° 98.8 % Absorption correction Analytical Max. and min. transmission 0.92 and 0.36 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2046 / 0 / 154 Goodness-of-fit on F2 1.018 Final R indices [I>2sigma(I)] R1 = 0.0780, wR2 = 0.1778 R indices (all data) R1 = 0.0971, wR2 = 0.1869 Largest diff. peak and hole 5.265 and -2.018 e.Å-3 Figure S3: ORTEP drawing of 10 at 30% ellipsoids probability, most of hydrogen atoms are omitted for clarity. Table S3: Crystal data and structure refining for 10: Empirical formula C20H31BIrN6O2 Formula weight 590.51 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P 21/m Unit cell dimensions a = 7.9367(8) Å = 90°. b = 13.1619(13) Å = 105.384(2)°. c = 10.9680(10) Å  = 90°. Volume 1104.69(19) Å3 Z 2 Density (calculated) 1.775 Mg/m3 Absorption coefficient 6.072 mm-1 F(000) 582 Crystal size 0.39 x 0.09 x 0.09 mm3 Theta range for data collection 3.08 to 25.24°. Index ranges -9<=h<=9, -15<=k<=15, -12<=l<=13 Reflections collected 16605 Independent reflections 2088 [R(int) = 0.0308] Completeness to theta = 25.24° 99.7 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.6110 and 0.2005 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2088 / 56 / 169 Goodness-of-fit on F2 1.280 Final R indices [I>2sigma(I)] R1 = 0.0300, wR2 = 0.0811 R indices (all data) R1 = 0.0302, wR2 = 0.0812 Largest diff. peak and hole 2.085 and -1.380 e.Å-3 Figure S4: ORTEP drawing of 12 at 30% ellipsoids probability, most of hydrogen atoms are omitted for clarity. Table S4: Crystal data and structure refining for 12: Empirical formula C43H66B2Ir2N12O6 [2(C20H30BIrN6O3), 0.5(C6H12)] Formula weight 1253.10 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P21/n Unit cell dimensions a = 16.3066(6) Å = 90°. b = 18.1340(7) Å = 104.459(2)°. c = 17.1839(7) Å  = 90°. Volume 4920.4(3) Å3 Z 4 Density (calculated) 1.692 Mg/m3 Absorption coefficient 5.461 mm-1 F(000) 2480 Crystal size 0.36 x 0.14 x 0.12 mm3 Theta range for data collection 2.28 to 27.00°. Index ranges -20<=h<=20, -23<=k<=23, -21<=l<=21 Reflections collected 59327 Independent reflections 10670 [R(int) = 0.0484] Completeness to theta = 27.00° 99.6 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 1.000 and 0.586 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 10670 / 0 / 598 Goodness-of-fit on F2 1.008 Final R indices [I>2sigma(I)] R1 = 0.0364, wR2 = 0.0814 R indices (all data) R1 = 0.0538, wR2 = 0.0892 Largest diff. peak and hole 1.547 and -1.544 e.Å-3 Figure S8: ORTEP drawing of 33 at 30% ellipsoids probability, most of hydrogen atoms are omitted for clarity. Table S8: Crystal data and structure refining for 33: Empirical formula C22H30BIrN6O Formula weight 597.53 Temperature 100(2) K Wavelength 0.71073 Å Crystal system Triclinic Space group P 1  Unit cell dimensions a = 10.0761(7) Å = 115.898(2)°. b = 11.5751(8) Å = 93.773(2)°. c = 12.2502(9) Å  = 112.071(2)°. Volume 1144.89(14) Å3 Z 2 Density (calculated) 1.733 Mg/m3 Absorption coefficient 5.857 mm-1 F(000) 588 Crystal size 0.17 x 0.14 x 0.09 mm3 Theta range for data collection 3.31 to 25.25°. Index ranges -12<=h<=11, -13<=k<=13, -14<=l<=14 Reflections collected 13246 Independent reflections 4000 [R(int) = 0.0210] Completeness to theta = 25.25° 98.6 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.6207 and 0.4359 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4000 / 0 / 340 Goodness-of-fit on F2 1.056 Final R indices [I>2sigma(I)] R1 = 0.0194, wR2 = 0.0464 R indices (all data) R1 = 0.0227, wR2 = 0.0476 Largest diff. peak and hole 0.854 and -1.384 e.Å-3 Figure S9: ORTEP drawing of 45 at 30% ellipsoids probability, most of hydrogen atoms and CHCl3 solvent molecules are omitted for clarity. Table S9: Crystal data and structure refining for 45: Empirical formula C40H47BCl15IrN8O7S2 [C35H42BIrN8O7S2, 5(CHCl3)] Formula weight 1550.74 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P 21/n Unit cell dimensions a = 12.5792(6) Å = 90°. b = 31.0920(13) Å = 107.1790(10)°. c = 16.4342(6) Å  = 90°. Volume 6140.9(4) Å3 Z 4 Density (calculated) 1.677 Mg/m3 Absorption coefficient 2.945 mm-1 F(000) 3072 Crystal size 0.37 x 0.28 x 0.17 mm3 Theta range for data collection 1.45 to 25.25°. Index ranges -15<=h<=15, -37<=k<=36, -19<=l<=19 Reflections collected 54334 Independent reflections 11090 [R(int) = 0.0308] Completeness to theta = 25.25° 99.8 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.6344 and 0.4087 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 11090 / 182 / 709 Goodness-of-fit on F2 1.122 Final R indices [I>2sigma(I)] R1 = 0.0468, wR2 = 0.1137 R indices (all data) R1 = 0.0510, wR2 = 0.1166 Largest diff. peak and hole 1.999 and -1.411 e.Å-3 III REFERENCES [1] M. Paneque, M. L. Poveda, V. Salazar, E. Gutiérrez-Puebla, A. Monge, Organometallics 2000, 19, 3120-3126. [2] Bruker (2001). Programs SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. [3] M. C. Burla, M. Camalli, B. Carrozzini, G. L. Cascarano, C. Giacovazzo, G. Polidori and R. Spagna, J. Appl. Crystallogr. 2003, 36, 1103. [4] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122.