Reactivity of TpMe2-containing hydride-iridafurans with alkenes, alkynes, and H2

1 Reactivity of TpMe2-Containing Hydride-Iridafurans with Alkenes, Alkynes and H2 Ángela Vivancos,† Cristina M. Posadas,† Yohar A. Hernández,† Nuria Rendón,† Silvia García-Rubín,‡ Eleuterio Álvarez,† Margarita Paneque,*,† and Manuel L. Poveda*,† †Instituto de Investigaciones Químicas (IIQ), Departamento de Química Inorgánica, and Centro de Innovación en Química Avanzada (ORFEO-CINQA), CSIC and Universidad de Sevilla, Avda. Américo Vespucio 49, 41092 Sevilla, Spain ‡Departamento de Química Orgánica, Facultad de Química and Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain *To whom correspondence should be addressed. E-mail: pane[email protected]. RECEIVED DATE ABSTRACT: The TpMe2-containing hydride-iridafurans 2a,b (TpMe2 = hydrotris(3,5- dimethylpyrazolyl)borate) cleanly reacted with ethylene to give the bicyclic derivatives 6a,b. Formation of the latter complexes is a reversible process and it is proposed to occur by an electrocyclic ring closure that takes place between C2H4 and the 16e- unsaturated intermediates A resulting from hydride migration to the -carbon of the metallacycle. Similar reactions were observed with a variety of alkynes RCCR (R = H, Ph, CO2Me) and R´CCH (R´= CO2Me, Ph, CMe3) with the regioselectivity observed for the latter substrates depending on the nature of R´. In the case of Me3SiCCH the structure of an 2 unexpected byproduct indicates that an alkyne-vinylidene rearrangement has taken place on the metal coordination sphere during the reaction and this observation suggests that in the mechanism of all these coupling processes the corresponding -adducts are active intermediates. Finally, complexes 2a,b reacted with H2 to give products derived from the hydrogenation of their alkenyl arms. INTRODUCTION Metallafurans1 are the most common members of the family of 6-aromatic metallacycles, which also include the growing type of metallabenzenes.2 They are known for quite a few transition metals and have been synthetized by a variety of methods. In a recent paper3 we have described the synthesis of hydride-iridafurans of structure 2 by the reaction of the bis(ethylene) Ir(I) species TpMe2Ir(C2H4)2 (1) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) with dimethyl acetylenedicarboxylate (DMAD) in the presence of aromatic aldehydes ArCHO (CH2Cl2, 60 ºC, 14 h, Scheme 1). Both electron-donating and electron-withdrawing substituents in the para position of the phenyl ring of the aldehyde were successfully used for iridafuran formation and DMAD and 1 equiv. of aldehyde formally coupled in the iridium coordination sphere to form the metallacycle. However, a second molecule of the aldehyde is required for the formation of complexes 2. Thus, the reaction of 1 and ArCHO (1:2, 25 ºC), gives rise to the very fast and almost quantitative formation of intermediates 3, and these species eventually convert 3 into the final compounds 2. However, species 3 evolve differently depending of the nature of the aldehyde. At variance with what we have reported for 3a (Scheme 2), where a mixture of the iridafuran 2a and the aldehyde adduct 4a is initially formed, we have noticed that for the case of p-O2N-C6H4- CHO, a new compound, resulting from the formal addition of the released C2H4 to the corresponding hydride-iridafuran 2b, was slowly formed. This unexpected result launched the study reported herein where we describe the reactivity of complexes 2a,b against alkenes, alkynes and finally H2. Scheme 1. Formation of the hydride-iridafurans 2 by the reaction of complex 1 with DMAD and aromatic aldehydes Scheme 2. Formation of the alkoxyde intermediate 3a in route to complex 2a and evolution of the former species in CH2Cl2 4 RESULTS AND DISCUSSION Reactivity of the hydride-iridafurans 2a,b with olefins. Monitorization (1H NMR, CD2Cl2, 25 ºC) of the reaction of 1 with 1 eq. of DMAD and 2 eq. of p-O2N-C6H4-CHO indicated very fast quantitative formation of intermediate 3b, which slowly evolved ([Ir] ≈ 0.07 mM, CH2Cl2, 25 ºC, 14 h) at room temperature to a mixture of the products depicted in Scheme 3. In addition of 2b, two other species, 5b and 6b, were also formed. Scheme 3. Formation and room temperature evolution of complex 3b in CH2Cl2 (spectroscopic yields in parenthesis) 5 Complex 5b, a water adduct,4 was easily isolated in pure form due to its insolubility in CH2Cl2 and probably derived from the reaction of 2b with adventitious water and, in fact, it is formed in ca. 80% yield if the reaction was carried out in the presence of added water. Interestingly, only the iridafuran 2b affords an aquo adduct as neither 2a nor the parent species derived from benzaldehyde3 reacted with water in this way. Species 6b, with a metallabicyclic structure, was easily purified by chromatography, and completely characterized by the usual analytical and spectroscopic methods. Thus, the two adjacent CH2 groups resonate at 3.00 and 2.46 (IrCH2CH2) and at 2.08 (IrCH2CH2) ppm in the 1H NMR spectrum while the corresponding 13C signals appear at 37.8 (IrCH2CH2) and at -15.2 (IrCH2CH2) ppm. The  carbon =C(CO2Me) in 2b was transformed in a  aliphatic quarternary carbon atom in 6b and consequently the corresponding 13C resonance shifts upfield from 137.0 ppm to 75.8 ppm. From the structure of complex 6b it can be concluded that its formation is the formal result of the coupling of a molecule of free ethylene, released from complex 1, with the iridafuran 2b and in fact this species cleanly reacted with C2H4 at 25 ºC to give 6b (Scheme 4). The stereochemistry of the Ir-CHR- carbon, easily deduced from the NOESY spectrum, is in accord with the mechanism proposed for its formation (see below). Scheme 4. Reversible reaction of 2a,b with ethylene Formation of complex 6b is a reversible process and, upon heating (CH2Cl2, 60 ºC), it returned to the starting hydride-iridafuran 2b (Scheme 4). It was also found that the reactivity just commented 6 was independent on the nature of the Ar-substituent of the iridafuran as complex 2a also experienced the processes shown in Scheme 4 but, in contrast, neither propene (CH2=CHMe) nor methyl acrylate (CH2=CHCO2Me) were effective reaction partners and this may reflect, at least partially, the influence of the steric effects on the addition process. The structure of complex 6a has been confirmed by single crystal X-ray diffraction studies (Figure 1). Figure 1. X-ray structure of compound 6a (30% displacement ellipsoids, H atoms except the H atoms on C(19) and B(1) omitted for clarity). Selected bond lengths (Å) and angles (deg): Ir(1)—C(16) = 2.077(2), Ir(1)—C(19) = 2.1004(19), Ir(1)—O(1) = 2.0587(15), Ir(1)—N(1) = 2.1294(17), Ir(1)—N(3) = 2.0530(17), Ir(1)—N(5) = 2.2075(17), C(16)—C(17) = 1.536(3), C(16)—Ir(1)—C(19) = 82.07(8), C(16)—Ir(1)—O(1) = 83.29(7), C(19)—Ir(1)—O(1) = 78.56(7). With respect to the mechanism of formation of the bicyclic derivatives 6 it is proposed that after hydride migration to the -carbon of species 23 the resulting unsaturated species A of Scheme 5 experiences a 1,3-electrocyclic coupling with C2H4 to give the final products.5 The same mechanism is probably responsible for the reaction of complexes 2 with the alkynes described below, and acetylene 7 has been used as the representative reacting species in Scheme 5. In these couplings it is not known if - adduct formation is a necessary step previous to the electrocyclic closure, i.e. if we are dealing with a neat, more or less isochronous, concerted step or with a mechanism consisting of two well defined steps. As will be discussed later, the formation of compound 19a (see below) may suggest a two-steps mechanism. Scheme 5. Proposed mechanism for the reaction of complexes 2 with C2H4 and C2H2. Reactivity of complexes 2 with MeO2CCCCO2Me (DMAD), HCCH and PhCCPh. On the basis of the ethylene reactivity already commented we studied the reaction of complexes 2a,b with DMAD. Thus, complex 2b reacted with an excess (3 equiv.) of this alkyne (CH2Cl2, 80 ºC, 48 h) to form a related bicyclic species 7b isolated in almost quantitative yield (Scheme 6a). Complex 7b was completely characterized by, among other analytical techniques, NMR spectroscopy (see Experimental Section). Interestingly, when the same reaction was carried out with 2a the corresponding species 7a was not selectively formed but the carboxylate-bound6 compound 8a (ca. 3:1 ratio, Scheme 6b) was also generated. These two species were easily separated and purified by chromatography and both have been characterized unambiguously, among other techniques, by single crystal X-ray studies (Figures 2 and 3). Complex 8a seems to proceed from 7a by hydrolysis of the −CO2Me substituent of 7a, coordination of 8 the resulting carboxylate group to the iridium center and transfer of the released proton to the carbon atom of the cyclic structure which was previously bound to the Ir center. However, attemps to induce this hydrolysis reaction in dichloromethane solutions by a variety of methods were fruitless. Scheme 6. Reactions of complexes 2a,b with DMAD (isolated yields in parenthesis) 9 Figure 2. X-ray structure of compound 7a (30% displacement ellipsoids, H atoms except the H atom on C(23) and B(1) omitted for clarity). Selected bond lengths (Å) and angles (deg): Ir(1)—C(16) = 2.001(2), Ir(1)—C(23) = 2.072(2), Ir(1)—O(9) = 2.0599(16), Ir(1)—N(1) = 2.0459(19), Ir(1)—N(3) = 2.1451(19), Ir(1)—N(5) = 2.180(2), C(16)—Ir(1)—C(23) = 78.77(9), C(16)—Ir(1)—O(9) = 84.28(8), C(23)—Ir(1)—O(9) = 84.28(8). Figure 3. X-ray structure of compound 8a (30% displacement ellipsoids, H atoms except the H atoms on C(30) and B(1) omitted for clarity). Selected bond lengths (Å) and angles (deg): Ir(1)—C(30) = 16 solution as an equilibrated mixture of conformational rotamers (i.e. atropoisomers) (NOESY evidence) in a ca. 1:0.2 ratio. We proposed that the presence of the two CO2Me substituents in the -CHRCH2R chain generates two rotameric, energetic local minima. Compound 21a is, in turn, the result of a trans (NOESY evidence) stereospecific hydrogenation of the alkenyl moiety of 2a and it is best characterized by the two doublets (5.29 and 5.13 ppm, 3JHH = 1.6 Hz) in the 1H NMR spectrum which correspond to the Ir-CH(R)-CH(R)- hydrogens respectively. When 2a was reacted with D2 under identical conditions (C6H12, 3 atm, 90 ºC, 24 h) 20a-d1.8 was obtained thus confirming the stoichiometry of the reaction and showing, as deduced from the 1H NMR spectrum, that no further scrambling, with excess of D2, occurred. The label was found to be distributed among the hydride ligand and the three CH positions and a similar distribution of deuteriums was observed for 21a-d1.8. Having in mind the experimental fact that 21a did not afford complex 20a after prolongued heating in C6H12 at 90 ºC and the distribution of deuterium just mentioned, the formation of both species may be explained with the mechanism shown in Scheme 14. First, an iridium(V) trishydride12 intermediate D, having a 2-TpMe2 ligand, is formed with all the three hydrides (D2H in the reaction with D2) behaving as equivalent. From this intermediate different routes can be advanced for the formation of 20a and 21a and two of them, not described textually in any detail, are shown in Scheme 14. In both cases, the keto-enol tautomerization proposed as the final step should be a reversible process and therefore the isomer with a cisoid H,H chain stereochemistry (i.e. epi-21a) should also be accessible kinetically but we believe that its unfavourable thermodynamics is preventing its detection. Scheme 14. Proposed mechanisms for the reaction of complex 2a with hydrogen 17 Hydrogenation of compound 2b under the same reaction conditions (C6H12, 3 atm, 90 ºC, 24 h) gave rise to complex 20b as the main reaction product. In this case the expected hydride 21b was not detected but the carbonyl derivative 22b was formed instead (Scheme 15). Both compounds were easily separated and purified by chromatography and fully characterized by the usual methods. The carbonyl ligand of 22b is responsible for a strong absorption, at 2040 cm-1, in the IR spectrum and a 13C{1H} NMR resonance at 163.0 ppm. In turn, the Ir-CH2 group gives rise to two doublets in the 1H NMR spectrum (4.00 and 3.62 ppm, 2JHH = 13.9 Hz) and to a signal at 3.4 ppm in the 13C{1H} NMR spectrum. With respect to the mechanism of its formation, it can be proposed that the -CO2Me group in 2b has been hydrogenated according to the formal equation: H-Ir-C(CO2Me)= + H2 → OC-Ir-CH2- + MeOH. This is not the first time that a CO2Me substituent in this type of iridacycles is involved in a reaction.6 Scheme 15. Reactivity of complex 2b with hydrogen 18 CONCLUDING REMARKS The TpMe2-containing hydride-iridafurans studied in this report normally react through 16e- unsaturated intermediates that result from the hydride migration to the -carbon of the metallacycle. In contrast to the adduct formation observed previously for hard or soft (NCMe, CO) Lewis bases, with ethylene and alkynes as substrates they experience electrocyclic ring closure to give bicyclic structures. Based in some experimental evidence it is suggested that -adducts species act as active intermediates before the electrocyclic coupling takes place. 19 EXPERIMENTAL SECTION General Considerations. All the manipulations were carried out under an inert atmosphere, following Schlenk techniques. The solvents employed were dried before use. The elemental analyses of the new compounds were carried out using a Perkin-Elmer Series II CHNS/O 2400 analyzer at the Microanalytical Service of the Instituto de Investigaciones Químicas (Sevilla). IR spectra were recorded on a Perkin-Elmer system 2000 FT-IR. NMR instruments were Bruker models DPX-300, DRX-400, and DRX-500. 1H and 13C resonances were referenced with respect to SiMe4 using the residual protio solvent peaks as internal standard (1H NMR) and the characteristic resonances of the solvent 13C nuclei (13C NMR). Most of the 1H and 13C assignments were based in one- and two-dimensional experiments (13C{1H} gated, COSY, NOESY, 1H-13C HSQC, and HMBC). Compounds 2a,b were prepared by the procedures described in the literature.3 One-pot synthesis of compound 2a. To a solution of compound 1 (0.30 g, 0.55 mmol) in dichloromethane (10 mL) at -20 ºC, MeO2CC≡CCO2Me (0.066 mL, 0.55 mmol) and p-anisaldehyde (0.135 g, 1.10 mmol) were added sequentially. The cold bath was then removed and the resulting mixture stirred at 60 ºC 20 h. The volatiles were then removed under reduced pressure and the residue washed with hexane at -30 ºC (8x6 mL). Yield: 0.393 g (93%) of compound 2a with enough purity to be use as starting material. Synthesis of compound 5b. To a solution of compound 1 (0.10 g, 0.18 mmol) in dichloromethane (4 mL) at -20 ºC, MeO2CC≡CCO2Me (0.022 mL, 0.18 mmol) and water (0.2 ml, 11.0 mmol) were added sequentially. After stirring for 10 min at this temperature, p-nitrobenzaldehyde (0.056 g, 0.36 mmol) was added. The cold bath was then removed and the resulting mixture stirred at 20 room temperature for 14 h. After this period of time, a bright yellow precipitate of 5b was formed, which was separated by filtration from a dark brown solution and dried under vacuum. Yield: 0.12 g (80%). 1H NMR (Acetone-d6, 25 ºC;  (ppm)): 8.13, 7.75 (d, 2 H each, 3JHH = 8.6 Hz, 2 HB, 2 HA, resp.), 6.55 (br s, 2 H, H2O), 6.12 (s, 1 H, C1H), 5.84, 5.81, 5.59 (s, 1 H each, 3 CHpz), 3.41, 2.93 (s, 3 H each, 2 CO2Me), 2.65, 2.45, 2.44, 2.37, 2.37, 2.34 (s, 3 H each, 6 Mepz). 13C{1H} NMR (Acetone-d6, 25 ºC;  (ppm)): 185.0 (C3), 184.3, 168.0 (CO2Me), 154.6, 154.0, 152.0, 145.2, 144.0, 143.8 (Cqpz), 148.6 (C4), 147.7 (C7), 130.9, 122.6 (C5, C6, resp.), 112.0 (C2), 108.8, 108.5, 107.3 (CHpz), 50.0, 49.6 (CO2Me), 17.7 (C1, 1JCH = 132 Hz), 14.8, 13.9, 13.1, 12.6, 12.6, 12.0 (Mepz). Elemental analysis for C28H35BN7O8Ir·0.5CH2Cl2 (sample crystallized from CH2Cl2:Et2O): C, 40.6; H, 4.1; N, 11.6. Found: C, 40.8; H, 4.4; N, 11.2. IR (Nujol): υ(OH) 3361, (CO, CO2Me) 1704, 1681, (NO2) 1550 cm-1. Synthesis of compound 6a. Complex 2a (0.15 g, 0.19 mmol) was dissolved in dichloromethane (7 mL) and the solution placed in a Fisher-Porter vessel which was pressurized with C2H4 (3 atm). The resulting mixture was stirred at 60 ºC for 14 h. The volatiles were removed under vacuum and quantitative conversion into compound 6a was ascertained by 1H NMR. This compound was purified by column chromatography on silica gel using diethylether:hexane (1:3) → diethylether:hexane (1:1) mixtures as eluent. Yield: 0.14 g (90%). An analytically pure sample, as dark red crystals, was obtained by slow diffusion of pentane into a dichloromethane solution at room temperature. 21 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.79, 6.89 (d, 2 H each, 3JHH = 8.0 Hz, 2 CHA, 2 CHB, resp.), 5.81, 5.68, 5.65 (s, 1 H each, 3 CHpz), 5.43 (s, 1 H, C1H), 3.84 (s, 3 H, C7OMe), 3.68, 3.25 (s, 3 H each, 2 CO2Me), 2.95, 2.39 (td, m, 1 H each, 2JHH = 11.3, 3JHH = 3.3 Hz, HE, HF, resp.), 2.62, 2.46, 2.35, 2.31, 2.14, 1.91 (s, 3 H each, 6 Mepz), 2.20, 2.03 (m, 1 H each, HC, HD, resp.). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 222.4 (C3), 184.7, 172.3 (CO2Me), 163.2 (C7), 152.5, 152.1, 149.6, 143.7, 143.2, 142.5 (Cqpz), 131.1, 113.3 (C5, C6, resp.), 129.4 (C4), 109.1, 107.0, 106.9 (CHpz), 75.8 (C2), 55.5 (C7OMe), 51.8, 50.4 (CO2Me), 38.8 (C8, 1JCH = 131 Hz), 24.7 (C1, 1JCH = 138 Hz), 16.0, 13.4, 13.3, 13.2, 12.8, 12.5 (Mepz), - 15.9 (C9, 1JCH = 130 Hz). Elemental analysis for C31H40BN6O6Ir: C, 46.8; H, 5.0; N, 10.5. Found: C, 47.2; H, 5.4; N, 10.0. Rf = 0.29 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1721, 1678 cm-1. Synthesis of compound 6b. To a solution of TpMe2Ir(C2H4)2 (1) (0.50 g, 0.92 mmol) in dichloromethane (7 mL) at -20 ºC, MeO2CC≡CCO2Me (0.11 mL, 0.92 mmol) was added. After stirring for 10 min at this temperature, p-nitrobenzaldehyde (0.28 g, 1.83 mmol) was added. The cold bath was then removed and the resulting mixture stirred at room temperature for 14 h. The volatiles were removed under reduced pressure and 1H NMR monitoring revealed the presence of 2b, 6b and 5b in 35, 40 and 25% spectroscopic yield, respectively. Only the title compound was isolated by column chromatography on silica gel using diethylether:hexane (1:5) → diethylether mixtures as eluent. Yield: 0.23 g (30%) of a violet microcrystalline solid. 22 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.25, 7.90 (d, 2 H each, 3JHH = 8.4 Hz, 2 HB, 2 HA, resp.), 5.83, 5.69, 5.65 (s, 1 H each, 3 CHpz), 5.64 (s, 1 H, C1H), 3.62, 3.31 (s, 3 H each, 2 CO2Me), 3.00, 2.46 (ddd, m, 1 H each, 2JHH = 11.2, 3JHH = 6.0, 2.3 Hz, HE and HF, resp.), 2.61, 2.47, 2.35, 2.31, 2.13, 1.86 (s, 3 H each, 6 Mepz), 2.08 (m, 2 H, HC and HD). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 226.3 (C3), 185.9, 171.2 (CO2Me), 152.5, 152.0, 149.5, 143.8, 143.8, 142.8 (Cqpz), 149.0 (C7), 143.9 (C4), 128.0, 123.1 (C5, C6, resp.), 109.3, 107.1, 107.0 (CHpz), 78.4 (C2), 52.0, 50.8 (CO2Me), 37.9 (C8, 1JCH = 131 Hz), 25.5 (C1, 1JCH = 141 Hz), 16.1, 13.3, 13.3, 13.2, 12.8, 12.4 (Mepz), -15.2 (C9, 1JCH = 133 Hz). Elemental analysis for C30H37BN7O7Ir·CH2Cl2 (sample crystallized from CH2Cl2-Et2O): C, 41.6; H, 4.4; N, 11.0. Found: C, 41.2; H, 4.8; N, 11.2. Rf = 0.20 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1737 (br), (NO2) 1550 cm-1. Synthesis of compounds 7a and 8a. To a solution of compound 2a (0.15 g, 0.19 mmol) in dichloromethane (7 mL), MeO2CC≡CCO2Me (0.07 mL, 0.58 mmol) was added. The resulting mixture was stirred at 80 ºC for 48 h, and then the volatiles were removed under reduced pressure. 1H NMR analysis revealed the formation of 7a and 8a in 80 and 10% spectroscopic yield, respectively. They were isolated by column chromatography on silica gel using diethylether:hexane (1:1) → ethylacetate:diethylether (1:1) mixtures as eluent. Yield: 0.13 g (72%, yellow solid) and 0.025 g (14%, orange solid) of 7a and 8a, respectively. Analytically pure samples of both were obtained by slow diffusion of pentane into dichloromethane solutions at room temperature (bright yellow crystals, 7a; bright orange crystals, 8a). 23 7a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.34, 6.89 (d, 2 H each, 3JHH = 9.0 Hz, 2 HA, 2 HB, resp.), 5.90 (s, 1 H, C1H), 5.80, 5.71, 5.61 (s, 1 H each, 3 CHpz), 3.84 (s, 3 H, C7OMe), 3.73, 3.70, 3.31, 3.22 (s, 3 H each, 4 CO2Me), 2.48, 2.48, 2.36, 2.31, 2.10, 1.58 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 214.8 (C3), 182.5, 175.1, 169.4, 162.3 (CO2Me), 169.3 (C9), 164.4 (C7), 155.1, 152.7, 150.6, 144.3, 143.7, 142.8 (Cqpz), 134.7 (C8), 133.6, 113.2 (C5, C6, resp.), 128.7 (C4), 108.6, 107.5, 106.1 (CHpz), 79.7 (C2), 55.5 (C7OMe), 52.1, 51.8, 50.7, 50.5 (CO2Me), 37.1 (C1, 1JCH = 141 Hz), 17.1, 13.5, 13.3, 12.6, 12.5, 12.3 (Mepz). Elemental analysis for C35H42BN6O10Ir: C, 46.2; H, 4.6; N, 9.2. Found: C, 46.0; H, 4.8; N, 8.7. Rf = 0.50 (silica gel, 6:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1758, 1721, 1691 cm-1. 8a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.97, 6.87 (d, 2 H each, 3JHH = 9.0 Hz, 2 HA, 2 HB, resp.), 6.82 (s, 1 H, C9H), 6.05 (s, 1 H, C1H), 5.76, 5.74, 5.66 (s, 1 H each, 3 CHpz), 3.87 (s, 3 H, C7OMe), 3.76, 3.74, 2.89 (s, 3 H each, 3 CO2Me), 2.49, 2.44, 2.41, 2.33, 2.07, 2.00 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 218.0 (C3), 183.2, 169.5, 168.3 (CO2Me), 166.6 (C10), 165.7 (C7), 152.7, 152.6, 150.7, 145.0, 143.2, 142.9 (Cqpz), 140.0 (C8), 133.8, 114.2 (C5, C6, resp.), 128.5 (C4), 128.0 (C9, 1JCH = 162 Hz), 108.7, 108.6, 106.6 (CHpz), 73.8 (C2), 55.8 (C7OMe), 52.4, 52.4, 50.6 (CO2Me), 26.0 (C1, 1JCH = 138 Hz), 14.6, 14.6, 12.9, 12.7, 12.0, 12.0 (Mepz). Elemental analysis for C34H40BN6O10Ir: C, 45.6; H, 4.5; N, 9.4. Found: C, 45.2; H, 5.0; N, 9.9. Rf = 0.14 (silica gel, diethylether). IR (Nujol): υ(CO, CO2Me, CO2Ir) 1728, 1702 cm-1. 24 Synthesis of compound 7b. To a solution of compound 2b (0.075 g, 0.137 mmol) in dichloromethane (5 mL), MeO2CC≡CCO2Me (0.05 mL, 0.411 mmol) was added. The resulting mixture was stirred at 80 ºC for 48 h, and then the volatiles were removed under reduced pressure. 1H NMR analysis revealed the formation of 7b in 90% spectroscopic yield. Compound 7b was purified by column chromatography on silica gel using diethylether:hexane (1:1) → ethylacetate mixtures as eluent. Yield: 0.05 g (56%) of a dark red microcrystalline solid. 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.39, 8.25 (d, 2 H each, 3JHH = 8.5 Hz, 2 HA, 2 HB, resp.), 6.03 (s, 1 H, C1H), 5.83, 5.76, 5.62 (s, 1 H each, 3 CHpz), 3.74, 3.70, 3.33, 3.27 (s, 3 H each, 4 CO2Me), 2.51, 2.48, 2.38, 2.32, 2.14, 1.50 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)):  219.5 (C3), 183.1, 174.6, 168.7, 162.4 (CO2Me), 170.9 (C9), 155.2, 152.7, 150.5, 144.7, 144.1, 143.1 (Cqpz), 149.9 (C7), 142.2 (C4), 133.7 (C8), 130.3, 122.8 (C5, C6, resp.), 108.9, 107.7, 106.3 (CHpz), 81.3 (C2), 52.3, 52.2, 50.9, 50.9 (CO2Me), 37.6 (C1, 1JCH = 143 Hz), 17.2, 13.6, 13.3, 12.9, 12.4, 12.3 (Mepz). Elemental analysis for C34H39BN7O11Ir: C, 44.2; H, 4.2; N, 10.6. Found: C, 44.0; H, 4.6; N, 10.3. Rf = 0.42 (silica gel, 3:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1757, 1723, 1699, (NO2) 1551 cm- 1. Synthesis of compound 9a. Method a: Compound 2a (0.09 g, 0.12 mmol) was dissolved in dichloromethane (5 mL), placed in a Fisher-Porter vessel, pressurized with C2H2 (2 atm) and then stirred at 60 ºC for 14 h. The volatiles were removed under vacuum and quantitative conversion into compound 9a was ascertained by 1H NMR. This compound, a bright orange microcrystalline solid, was purified by 25 column chromatography on silica gel using a diethylether:hexane (1:1) mixture as eluent. Yield: 0.075 g (81%). Method b: To a solution of compound 1 (0.10 g, 0.18 mmol) in dichloromethane (3 mL) at -20 ºC, MeO2C≡CCO2Me (0.022 mL, 0.18 mmol) and p-anisaldehyde (0.045 mL, 0.36 mmol) were added sequentially. The cold bath was then removed and the resulting mixture stirred at 60 ºC for 20 h. After cooling at 25 ºC, the reaction mixture was placed in a Fisher Porter vessel, pressurized with C2H2 (2 atm) and then stirred at 60 ºC for 14 h. Compound 9a was purified by column chromatography on silica gel using diethylether:pentane (1:1) mixture as eluent. Yield: 0.111 g (76%). 1H NMR (CDCl3, 25 ºC;  (ppm)): 9.18 (d, 3JHH = 5.8 Hz, 1 H, C9H), 7.76, 6.87 (d, 2 H each, 3JHH = 8.9 Hz, 2 HA and 2 HB, resp.), 6.19 (d, 1 H, C8H), 5.73, 5.71, 5.31 (s, 1 H each, 3 CHpz), 5.31 (s, 1 H, C1H), 3.83 (s, 3 H, C7OMe), 3.77, 3.30 (s, 3 H each, 2 CO2Me), 2.47, 2.40, 2.38, 2.34, 1.95, 1.80 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 215.8 (C3), 184.3, 171.9 (CO2Me), 162.7 (C7), 153.7, 153.0, 149.5, 143.8, 143.6, 142.4 (Cqpz), 149.1 (C9), 130.9 (C5), 129.5 (C4), 127.6 (C8), 113.6 (C6), 108.3, 107.4, 105.7 (CHpz), 82.0 (C2), 55.3 (C7OMe), 51.8, 50.4 (CO2Me), 34.5 (C1), 15.7, 13.2, 13.1, 12.7, 12.2, 10.9 (Mepz). Elemental analysis for C31H38BIrN6O6: C, 46.9; H, 4.8; N, 10.6. Found: C, 46.8; H, 4.9; N, 10.3. Rf = 0.24 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1720, 1680, 1600 cm-1. 32 17a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 10.13 (s, 1 H, C9H), 7.73, 6.85 (d, 2 H each, 3JHH = 8.9 Hz, 2 HA and 2 HB, resp.), 5.73, 5.70, 5.69 (s, 1 H each, 3 CHpz), 5.41 (s, 1 H, C1H), 3.83 (s, 3 H, C7OMe), 3.74, 3.31 (s, 3 H each, 2 CO2Me), 2.46, 2.39, 2.34, 2.32, 1.89, 1.77 (s, 3 H each, 6 Mepz), - 0.06 (s, 9 H, SiMe3). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 217.9 (C3), 185.0, 171.5 (CO2Me), 169.4 (C9), 162.0 (C7), 153.5, 152.8, 149.3, 143.7, 143.6, 142.4 (Cqpz), 139.9 (C2), 130.8 (C5), 130.7 (C4), 112.5 (C6), 108.3, 107.2, 105.8 (CHpz), 85.2 (C8), 55.2 (C7OMe), 51.5, 50.4 (CO2Me), 35.6 (C1), 15.3, 13.1, 13.0, 12.7, 12.2, 10.8 (Mepz), 0.0 (SiMe3). Elemental analysis for C34H46BIrN6O6Si: C, 47.2; H, 5.3; N, 9.7. Found: C, 47.0; H, 5.2; N, 9.7. Rf = 0.30 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1720, 1685, 1600 cm-1. 18a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.78, 6.89 (d, 2 H each, 3JHH = 8.9 Hz, 2 HA and 2 HB, resp.), 6.57 (s, 1 H, C8H), 5.77, 5.69, 5.66 (s, 1 H each, 3 CHpz), 5.40 (s, 1 H, C1H), 3.87 (s, 3 H, C7OMe), 3.80, 3.33 (s, 3 H each, 2 CO2Me), 2.52, 2.39, 2.34, 2.18, 1.92, 1.75 (s, 3 H each, 6 Mepz), - 0.41 (s, 9 H, SiMe3). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 214.9 (C3), 184.7, 171.8 (CO2Me), 164.3 (C9), 162.6 (C7), 153.8, 152.9, 149.3, 143.7, 143.7, 142.5 (Cqpz), 138.8 (C2), 130.8 (C5), 129.7 (C4), 113.3 (C6), 108.4, 107.1, 105.8 (CHpz), 84.5 (C8), 55.3 (C7OMe), 51.9, 50.4 (CO2Me), 33.2 (C1), 17.5, 13.2, 13.1, 12.8, 12.6, 12.2 (Mepz), 0.3 (SiMe3). 19a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.90, 6.92 (d, 2 H each, 3JHH = 8.9 Hz, 2 HA and 2 HB, resp.), 5.79, 5.75, 5.74 (s, 1 H each, 3 CHpz), 5.70 (s, 1 H, C1H), 5.27, 4.61 (s, 1 H each, CH2), 3.87 (s, 3 H, C7OMe), 3.85, 3.51 (s, 3 H each, 2 CO2Me), 2.52, 2.45, 2.42, 2.38, 2.16, 1.91 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 216.5 (C3), 182.8, 171.3 (CO2Me), 164.0 (C7), 154.0, 152.4, 150.9, 144.1, 143.4, 142.6 (Cqpz), 132.8 (C5), 132.5 (C8), 128.0 (C4), 113.8 (2C6), 112.2 (C9), 108.8, 106.7, 106.4 (CHpz), 88.0 (C2), 55.6 (C7OMe), 51.8, 51.3 (CO2Me), 16.5, 13.3, 13.0, 12.7, 12.5, 12.4 (Mepz), 9.8 (C1). Elemental analysis for C31H39BIrN6O6: C, 46.9; H, 4.8; N, 10.6. Found: C, 47.0; H, 4.9; N, 10.8. Rf = 0.37 (silica gel, 2:1 diethylether:hexane). IR (Nujol): υ(CO, CO2Me) 1725, 1690, 1600 cm-1. 33 Synthesis of compounds 20a and 21a: Compound 2a (0.10 g, 0.13 mmol) was suspended in cyclohexane (7 mL), placed in a Fisher-Porter vessel and pressurized with H2 (3 atm). The resulting mixture was stirred at 90 ºC for 24 h and the volatiles removed under vacuum. 1H NMR analysis of the resulting residue revealed the formation of 20a (as a mixture of rotamers in 1:0.2 ratio) and 21a in 80% and 20% spectroscopic yield, respectively. They were separated by column chromatography on silica gel, using diethylether:hexane (1:10) → (1:1) mixtures as eluent. Yield: 0.075 g (75%, orange microcrystalline solid) and 0.012 g (12%, orange microcrystalline solid) of 20a and 21a, respectively. 20a, major rotamer: 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.83, 7.04, 6.55 (d, d, dd, 1 H each, 3JHH = 9.1, 4JHH = 2.2 Hz, HA, HC, HB, resp.), 5.88, 5.80, 5.54 (s, 1 H each, 3 CHpz), 4.88 (dd, 1 H, 3JHH = 9.3, 4.9 Hz, C2H), 3.78 (s, 3 H, C7OMe), 3.71, 3.61 (s, 3 H each, 2 CO2Me), 3.33, 2.94 (dd, 1 H each, 2JHH = 17.6 Hz, C1H2), 2.41, 2.39, 2.37, 2.16, 1.08 (s, 1:2:1:1:1, 6 Mepz), -22.54 (s, 1 H, Ir–H). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 209.7 (C3), 179.8 (C9), 171.7, 169.5 (CO2Me), 164.1 (C7), 151.9, 151.6, 151.5, 143.8, 143.3, 142.8 (Cqpz), 138.7 (C4), 134.1, 119.4, 109.4 (C5, C8, C6, resp.), 106.4, 106.4, 105.8 (CHpz), 55.3 (C7OMe), 52.8, 52.6 (CO2Me), 46.0 (C2, 1JCH = 135 Hz), 33.4 (C1, 1JCH = 134, 131 Hz), 16.6, 14.3, 13.1, 12.4, 12.3, 10.8 (Mepz). 20a, minor rotamer: 1H NMR (CDCl3, 25 ºC;  (ppm)): 7.77, 7.06, 6.55 (d, d, dd, 1 H each, 3JHH = 8.8, 4JHH = 2.2 Hz, HA, HC, HB, resp.), 5.88, 5.80, 5.54 (s, 1 H each, 3 CHpz), 4.88 (dd, 1 H, 3JHH = 9.3, 4.9 Hz, C2H), 3.78 (s, 3 H, C7OMe), 3.74, 3.66 (s, 3 H each, 2 CO2Me), 3.28, 2.72 (dd, 1 H each, 2JHH = 17.6 Hz, C1H2), -22.56 (s, 1 H, Ir–H). Resonances corresponding to the methyl groups of the 34 pyrazolyl rings have not been assigned. 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 210.2 (C3), 180.3 (C9), 171.7, 170.0 (CO2Me), 162.5 (C7), 151.9, 151.6, 151.5, 143.8, 143.3, 142.8 (Cqpz), 138.5 (C4), 134.7, 119.6, 109.5 (C5, C8, C6, resp.), 106.4, 106.4, 105.9 (CHpz), 55.3 (C7OMe), 52.7, 52.6 (CO2Me), 45.9 (C2, 1JCH = 135 Hz), 34.1 (C1, 1JCH = 131 Hz). Resonances corresponding to the methyl groups of the pyrazolyl rings have not been assigned. Elemental analysis for C29H38BN6O6Ir·0.5CH2Cl2 (sample crystallized from CH2Cl2:Et2O): C, 43.6; H, 4.8; N, 10.4. Found: C, 43.9; H, 5.1; N, 10.2. Rf = 0.41 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(Ir–H) 2152 (CO, CO2Me) 1739 (br) cm-1. 21a: 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.01, 6.89 (d, 2 H each, 3JHH = 8.9 Hz, 2 HA and 2 HB, resp.), 5.75, 5.71, 5.62 (s, 1 H each, 3 CHpz), 5.29, 5.13 (d, 1 H each, 3JHH = 1.6 Hz, C1H and C2H, resp.), 3.86 (s, 3 H, C7OMe), 3.75, 2.92 (s, 3 H each, 2 CO2Me), 2.40, 2.37, 2.32, 2.18, 1.75 (s, 2:1:1:1:1, 6 Mepz), -22.52 (s, 1 H, Ir–H). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 217.4 (C3), 186.1, 170.8 (CO2Me), 164.5 (C7), 152.7, 152.7, 150.5, 143.1, 142.7, 142.7 (Cqpz), 132.0, 114.8 (C5 and C6, resp.), 128.1 (C4), 106.9, 105.9, 105.2 (CHpz), 63.1 (C2, 1JCH = 128 Hz), 55.7 (C7OMe), 52.6, 50.4 (CO2Me), 15.9, 14.0, 13.7, 13.0, 12.6, 12.4 (Mepz), 9.4 (C1, 1JCH = 136 Hz). Elemental analysis for C29H38BN6O6Ir·0.5CH2Cl2 (sample crystallized from CH2Cl2:Et2O): C, 43.6; H, 4.8; N, 10.4. Found: C, 44.1; H, 4.9; N, 10.2. Rf = 0.27 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(Ir-H) 2147, (CO, CO2Me) 1743 (br) cm-1. Synthesis of compounds 20b and 22b. Compound 2b (0.135 g, 0.25 mmol) was suspended in cyclohexane (8 mL), placed in a Fisher-Porter vessel and pressurized with H2 (3 atm). The resulting mixture was stirred at 90 ºC for 24 h and the volatiles were removed under vacuum. 1H NMR analysis of the resulting residue revealed the formation of 20b (as a mixture of rotamers in 1:0.8 ratio) and 22b in 53% and 20% spectroscopic yield, respectively. They were separated by column chromatography on 35 silica gel, using diethylether:hexane (1:5) → (1:1) mixtures as eluent. Yield: 0.065 g (48%, dark red microcrystalline solid) and 0.026 g (14%, brown microcrystalline solid) of 20b and 22b, respectively. 20b, major rotamer: 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.30, 8.09, 7.75 (d, d, dd, 1 H each, 3JHH = 8.8, 4JHH = 1.8 Hz, HC, HA, HB, resp.), 5.92, 5.88, 5.53 (s, 1 H each, 3 CHpz), 5.05 (dd, 1 H, 3JHH = 14.7, 8.1 Hz, C2H), 3.76, 3.65 (s, 3 H each, 2 CO2Me), 3.30, 3.12 (dd, 1 H each, 2JHH = 17.6, C1H2), 2.42, 2.40, 2.40, 2.36, 2.10, 0.95 (s, 3 H each, 6 Mepz), -22.33 (s, 1 H, Ir–H). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 215.9 (C3), 177.7 (C9), 171.7, 168.5 (CO2Me), 152.1, 151.5, 151.3, 144.4, 143.8, 143.2 (Cqpz), 150.0 (C7), 149.0 (C4), 132.5, 131.8, 113.9 (C5, C8, C6, resp.), 106.9, 106.7, 106.0 (CHpz), 53.0, 52.3 (CO2Me), 47.0 (C2, 1JCH = 135 Hz), 33.3 (C1, 1JCH = 133 Hz), 16.3, 14.3, 13.0, 12.3, 12.3, 11.1 (Mepz). 20b, minor rotamer: 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.32, 7.99, 7.75 (d, d, dd, 1 H each, 3JHH = 8.8, 4JHH = 1.8 Hz, HC, HA, HB, resp.), 5.92, 5.88, 5.53 (s, 1 H each, CHpz), 5.07 (dd, 1 H, 3JHH = 14.7, 8.1 Hz, C2H), 3.71, 3.63 (s, 3 H each, 2 CO2Me), 3.30, 2.91 (m, dd, 1 H each, 2JHH = 18.0 Hz, C1H2), -22.33 (s, 1 H, Ir–H). Resonances corresponding to the methyl groups of the pyrazolyl rings have not been assigned. 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 216.2 (C3), 178.2 (C9), 171.7, 169.1 (CO2Me), 152.1, 151.6, 151.3, 144.4, 143.8, 143.2 (Cqpz), 150.0 (C7), 148.9 (C4), 132.3, 131.9, 114.0 (C5, C8, C6, resp.), 106.9, 106.9, 106.1 (CHpz), 53.2, 52.3 (CO2Me), 47.0 (C2, 1JCH = 135 Hz), 33.7 (C1, 1JCH = 135 Hz). Resonances corresponding to the methyl groups of the pyrazolyl rings have not been assigned. 36 Rf = 0.34 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(Ir–H) 2149, (CO, CO2Me) 1743, 1738, (NO2) 1548 cm-1. 22b: 1H NMR (CDCl3, 25 ºC;  (ppm)): 8.15, 7.57 (d, 2 H each, 3JHH = 7.3 Hz, 2 HB and 2 HA, resp.), 5.88, 5.83, 5.75 (s, 1 H each, 3 CHpz), 4.00, 3.62 (d, 1 H each, 2JHH = 13.9 Hz, C1H2), 3.57 (s, 3 H, CO2Me), 2.51, 2.43, 2.39, 2.35, 2.31, 2.27 (s, 3 H each, 6 Mepz). 13C{1H} NMR (CDCl3, 25 ºC;  (ppm)): 180.6 (C3), 167.7 (CO2Me), 163.0 (CO), 152.6, 151.6, 150.9, 145.0, 144.0, 143.7 (Cqpz), 147.2 (C7), 145.4 (C4), 129.4, 122.8 (C5 and C6, resp.), 113.5 (C2), 108.9, 108.1, 107.0 (CHpz), 50.6 (CO2Me), 15.0, 13.0, 12.9, 12.7, 12.1, 12.0 (Mepz), 3.4 (C1, 1JCH = 136 Hz). Elemental analysis for C27H31BN7O6Ir: C, 43.1; H, 4.1; N, 13.0. Found: C, 43.9; H, 4.4; N, 13.2. Rf = 0.27 (silica gel, 1:1 diethylether:hexane). IR (Nujol): υ(CO) 2040, (CO, CO2Me) 1745, 1656, (NO2) 1548 cm-1. Structural Analysis of complexes 6a, 7a and 8a. Crystals of suitable size for X-ray diffraction analysis, were coated with dry perfluoropolyether and mounted on glass fibers and fixed in a cold nitrogen stream (T = 213 K) to the goniometer head. Data collections were performed on a Bruker- Nonius X8Apex-II CCD diffractometer, using monochromatic radiation λ(Mo Kα) = 0.71073 Å, by means of ω and φ scans with a width of 0.50 degree. The data were reduced (SAINT)13 and corrected for absorption effects by the multi-scan method (SADABS).14 The structures were solved by direct methods (SIR-2002)15 and refined against all F2 data by full-matrix least-squares techniques (SHELXTL-6.12)16 minimizing w[Fo2-Fc2]2. All the non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were included in calculated positions and allowed to ride on the attached atoms with the isotropic temperature factors (Uiso values) fixed at 1.2 times (1.5 times for methyl groups) those Ueq values of the corresponding attached atoms. Crystal data for 6a: C31H40BIrN6O6, M = 795.70, triclinic, a = 8.2638(4) Å, b = 12.0184(5) Å, c = 18.0299(8) Å, α = 98.159(2)°, β = 90.250(2)°, γ = 105.906(2)°, V = 1702.93(13) Å3, T = 100(2) K, 37 space group P , Z = 2, μ = 3.970 mm-1, 25739 reflections measured, 10343 independent reflections (Rint = 0.0190). The final R1 values were 0.0176 (I > 2σ(I)). The final wR(F2) values were 0.0605 (I > 2σ(I)). The final R1 values were 0.0184 (all data). The final wR(F2) values were 0.0612 (all data). The goodness of fit on F2 was 1.125. CCDC 1015996. Crystal data for 7a: 2(C35H42BIrN6O10)•CH2Cl2, M = 1904.44, triclinic, a = 8.6180(2) Å, b = 12.6109(3) Å, c = 19.4614(4) Å, α = 107.9940(10)°, β = 93.4270(10)°, γ = 105.5080(10)°, V = 1914.86(7) Å3, T = 173(2) K, space group P , Z = 1, μ = 3.620 mm-1, 58223 reflections measured, 11583 independent reflections (Rint = 0.0269). The final R1 values were 0.0234 (I > 2σ(I)). The final wR(F2) values were 0.0673 (I > 2σ(I)). The final R1 values were 0.0262 (all data). The final wR(F2) values were 0.0686 (all data). The goodness of fit on F2 was 0.996. CCDC 1015997. Crystal data for 8a: C34H40BIrN6O10, M = 895.73, monoclinic, a = 17.2496(13) Å, b = 17.2877(14) Å, c = 25.6049(17) Å, α = 90.00°, β = 98.640(3)°, γ = 90.00°, V = 7548.9(10) Å3, T = 100(2) K, space group P21/n, Z = 8, μ = 3.599 mm-1, 68501 reflections measured, 15477 independent reflections (Rint = 0.0885). The final R1 values were 0.0447 (I > 2σ(I)). The final wR(F2) values were 0.1083 (I > 2σ(I)). The final R1 values were 0.0687 (all data). The final wR(F2) values were 0.1180 (all data). The goodness of fit on F2 was 0.997. CCDC 1015998. 38 ASSOCIATED CONTENT Supporting Information. CIF file giving crystallographic data for compounds 6a, 7a and 8a. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]s (M. P.) Notes The authors declare no competing financial interest. ACKNOWLEDGMENT Financial support (FEDER contribution and ESF) from the Spanish Ministry of Science (projects CTQ2010-17476 and Consolider Ingenio 2010 CSD 2007-0006) and the Junta de Andalucía (Grant FQM-119 and project P09-FQM-4832) is acknowledged. N. R. thanks the Spanish Ministry of Science and University of Seville for a “Ramón y Cajal” contract. REFERENCES (1) Bleeke, J. R. Acc. Chem. Res. 2007, 40, 1035-1047. For -metallafurans, see: (b) Bierstedt, A.; Clark, G. R.; Roper, W. R.; Wright, L. J. J. Organomet. Chem. 2006, 691, 3846-3852. (c ) Sunley, G. J.; Menanteau, P. del C.; Adams, H.; Bailey, N. A.; Maitlis, P. M. J. Chem. Soc. Dalton Trans. 1989, 2415- 39 2421. (d) Esteruelas, M. A.; Hernández, Y. A.; López, A. M.; Oliván, M.; Oñate, E. Organometallics 2005, 24, 5989-6000. (e) Eguillor, B.; Esteruelas, M. A.; Oliván, M.; Oñate, E. Organometallics 2005, 24, 1428-1438. (f) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; Oñate, E. Organometallics 2001, 20, 2635-2638. (g) Buil, M. L.; Esteruelas, M. A.; Garcés, K.; Oliván, M.; Oñate, E. Organometallics 2008, 27, 4680-4690. (h) Esteruelas, M. A.; Lahoz, F. J.; Oñate, E.; Oro, L. A.; Zeier, B. Organometallics 1994, 13, 1662-1668. (i) Castarlenas, R.; Esteruelas, M. A.; Martín, M.; Oro, L. A. J. Organomet. Chem. 1998, 564, 241-247. (j) Eguillor, B.; Esteruelas, M. A.; Oliván, M.; Oñate, E. Organometallics 2004, 23, 6015-6024. (k) Gong, L.; Lin, Y.; Wen, T. B.; Zhang, H.; Zeng, B.; Xia, H. Organometallics 2008, 27, 2584-2589. (l) Li, X.; Vogel, T.; Incarvito, C. D.; Crabtree, R. H. Organometallics 2005, 24, 62-76. (m) Li, X.; Chen, P.; Faller, J. W.; Crabtree, R. H. Organometallics 2005, 24, 4810-4815. (n) He, X-M.; Liu, Q.; Gong, L.; Lin, Y.; Wen, T. B. Inor. Chem. Comm. 2010, 13, 342-345. (o) Esteruelas, M. A.; Larramona, C.; Oñate, E. Organometallics 2013, 32, 2567-2575. For -metallafurans, see: (p) Shih, K. Y.; Fanwick, P. E.; Walton, R. A. J. Am. Chem. Soc. 1993, 115, 9319-9320. (q) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. Organometallics 1994, 13, 1235-1242. (r) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. J. Chem. Soc. Chem. Commun. 1994, 861-862. (s) Kort, D. A.; Shih, K.-Y.; Wu, W.; Fanwick, P. E.; Walton, R. A. Organometallics 1995, 14, 448-455. (2) (a) Dalebrook, A. F.; Wright, L. J. Adv. Organomet. Chem. 2012, 60, 93-177. (b) Chen, J.; Jia, G. Coord. Chem. Rev. 2013, 257, 2491-2521. (c) Frongley, B. J.; Wright, L. J. Coord. Chem. Rev. 2014, 270-271, 151-166. (3) Posadas, C. M.; Rendón, N.; López-Serrano, J.; Hernández, Y. A.; Álvarez, E.; Paneque, M.; Poveda, M. L. Chem. Eur. J. 2013, 19, 1796-1809. (4) Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendón, N.; Álvarez, E.; Mereiter, K. Chem. Eur. J. 2007, 13, 5160-5172. 40 (5) A referee has correctly suggested that by considering the resonance form of A in which there is a double bond of the type Ir-=O+—, this intermediate may be somewhat resembling a metalheterocyclopentadiene and therefore that the electrocyclation could be of the [4+2] type. (6) For a related Ir(III) carboxylate, see: Cristóbal, C.; García-Rubín, S.; Hernández, Y. A.; López- Serrano, J.; Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendón, N.; Álvarez, E. Organometallics 2010, 29, 5744-5747. (7) No more than 2 equiv. of DMAD can be added as this iridacyclopentadiene easily reacts with any excess of this alkyne giving an iridacycloheptatriene, see: Paneque, M.; Posadas, C. M.; Poveda, M. L.; Rendón, N.; Santos, L. L.; Álvarez, E.; Salazar, V.; Mereiter, K.; Oñate, E. Organometallics 2007, 26, 3403-3415. (8) Roa, A. E.; Salazar, V.; López-Serrano, J.; Oñate, E.; Alvarado-Rodríguez, J. G.; Paneque, M.; Poveda, M. L. Organometallics 2012, 31, 3185-3198. (9) Alías, F. M.; Daff, P. J.; Paneque, M.; Poveda, M. L.; Carmona, E.; Pérez, P. J.; Salazar, V.; Alvarado, Y.; Atencio, R.; Sánchez-Delgado, R. Chem. Eur. J. 2002, 8, 5132-5146. (10) For a related 4-membered iridacycle with a moiety, see: Gómez, M.; Paneque, M.; Poveda, M. L.; Álvarez, E. J. Am. Chem. Soc. 2007, 129, 6092-6093. (11) (a) Bustelo, E.; Carbó, J. J.; Lledós, A.; Mereiter, K.; Puerta, M. C.; Valerga, P. J. Am. Chem. Soc. 2003, 125, 3311-3321. (b) De Angelis, F.; Sgamellotti, A.; Re, N. Dalton Trans. 2004, 3225-3230. (c) Paneque, M.; Poveda, M. L.; Rendón, N.; Mereiter, K. Organometallics 2009, 28, 172-180. (d) Werner, H. J. Organomet. Chem. 1994, 475, 45-55. (e) Werner, H.; Baum, M.; Schneider, D.; Windmueller, B. Organometallics 1994, 13, 1089-1097. (f) Werner, H.; Lass, R. W.; Gevert, O.; Wolf, J. Organometallics 1997, 16, 4077-4088. (g) Jiménez, M. V.; Sola, E.; Lahoz, F. J.; Oro, L. A. Organometallics 2005, 24, 2722-2729. (h) Ilg, K.; Paneque, M.; Poveda, M. L.; Rendón, N.; Santos, L. 41 L.; Carmona, E.; Mereiter, K. Organometallics 2006, 25, 2230-2236. (i) Batuecas, M.; Escalante, L.; Esteruelas, M. A.; García-Yebra, C.; Oñate, E.; Saá, C. Angew. Chem. Int. Ed. 2011, 50, 9712-9715. (12) For a related tetrahydride of Ir(V), see: Gutiérrez-Puebla, E.; Monge, A.; Paneque, M.; Poveda, M. L.; Taboada, S.; Trujillo, M.; Carmona, E. J. Am. Chem. Soc. 1999, 121, 346-354. (13) Bruker (2007). APEX2. Bruker AXS Inc., Madison, Wisconsin, USA. (14) Bruker (2001). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. (15) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; Giacovazzo, C.; Poliori, G.; Spagna, R. SIR2002: the program J. Appl.Cryst. 2003, 36, 1103. (16) Sheldrick, G. M. Acta Cryst. 2008, A64, 112-122. For table of contents use only: