3‐(Pyridin‐2‐yl)imidazo[1,5‐a]pyridine (Pyridylindolizine) as Ligand in Complexes of Transition and Main‐Group Metals

FULL PAPER 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (pyridylindolizine) as ligands in complexes of transition and main-group metals. Celedonio M. Álvarez, Lucía Álvarez-Miguel, Raúl García-Rodríguez, Jose M. Martín-Álvarez and Daniel Miguel *[a] Abstract: The coordination of the easily prepared 3-(pyridin-2-yl)imidazo[1,5- a]pyridine (pyridyl aza indolizine, Py-indz) ligand to several metal moieties has been studied, and its electronic properties, similar to the classical ligands 2,2’-bipyridine (bipy) and 1,10-phenanthroline (o-phen) are reported. New complexes have been prepared and fully characterized by X-ray crystallography and other typical spectroscopic methods when possible. Paramagnetic complexes [Ni(S2X)2(Py-indz)] X = P(OEt)2 (1), COEt (2), [Ni(acac)2(Py-indz)] (3), [Ni(Py-indz)3](PF6)2 (4), [Mn2Cl4(Py-indz)2] (6) and [MnCl2(Py-indz)2] (7) have the magnetic moment expected for a metallic cation with two or five unpaired electrons. Diamagnetic complexes show NMR spectra with a similar pattern with small differences depending on the complex. [M(S2P(OEt)2)2 (Py-indz)] M = Zn (8), Cd (9) have pentacoordinated and hexacoordinated structures respectively. Octahedral tin complexes [SnL4(Py-indz)] L4 = I4 (10), Cl3Ph (11), Cl2nBu2 (12) have different behaviors in solution, while complex 10 is practically insoluble, complex 11 displays the expected pattern in its NMR spectrum, and complex 12 shows dynamic behavior. The Pyindz ligand is also able to stabilize copper (I) and forms [Cu(PPh3)2(Py-indz)]BF4 (13). The synthesis of the carbonyl complexes [MBr(CO)3(Py-indz)] M = Mn (14), Re (15) and [Mo(CO)4(Py-indz)] (16) has been followed by IR spectroscopy in solution. [RuClp-cym(Py-indz)]PF6 (17) has the familiar halfsandwich ‘‘three-legged piano-stool’’ geometry. Introduction We have recently reported a facile method for the preparation of Mn(II) complexes with 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (pyridyl aza indolizine, Py-indz) acting as chelate ligands. The heterocyclic ligand containing a 9-aza-indolizine skeleton is produced by condensation of two molecules of pyridine-2- carboxaldehyde and one mol of ammonium cation within the coordination sphere of a Mn(II) bis dithiophosphate complex.[ 1 ] The Py-indz ligand can be easily removed from the manganese complex and isolated as a high purity crystalline solid. Previous methods based mainly on the cyclization of N-2-pyridylmethyl amines were modestly efficient,[ 2 ] and other new routes were proposed, based on the acid-promoted condensation of dipyridylamines,[ 3 ] the oxidative condensation of aldehydes with 2-pyridyl-amines,[ 4 ],[ 5 ] the aza-Wittig reaction on N-vinyl phosphazenes[ 6 ] or the cyclization of 2-enynylpyridines,[ 7 ] and coupling reactions to provide imidazo[1,5-a]pyridine N- heterocyclic carbene precursors. [ 8 ] There are only a few examples of the use of 3-(pyridin-2-yl)- imidazo[1,5-a]pyridines as ligands in Cu(II),[ 9 ] Ni(II),[ 10 ] V(V),[ 11 ] Ir(III)[ 12 ] and Re(I) complexes,[ 13 ] or analogues in Cd(II),[ 14 ] to prepare boron complexes[ 15 ] or involved in catalytic process of N-heterocyclic synthesis.[ 16 ] Some related derivatives of 3- (pyridin-2-yl)-imidazo[1,2-a]pyridine have been used in situ to regulate metal-induced amyloid-aggregation.[ 17 ] These ligands with a 2-azaindolizine skeleton have received some attention recently due to their interesting properties[ 18 ] and potential pharmacological applications.[ 19 ],[ 20 ] This prompted us to screen the potential of the now easily available Py-indz ligand in the preparation of complexes. While research on the mechanism and the optimization of the reaction leading to Py-indz is currently in progress in our laboratory we have found that Pyindz can act as a versatile ligand towards a wide range of either transition or main group metals, coexisting with a wide range of accompanying ligands, either soft such as iodide, phosphine or dithiolate, or hard such as nitrogen or oxygen donors, with classic and organometallic fragments. Herein we report the preparation of a variety of complexes with transition and main group metals together with their characterization by spectroscopic and crystallographic methods. Results and Discussion In view of the stability and the facile preparation and purification of the derivatives containing the manganese bis-dithiophosphate moiety, we sought to prepare the analogous complexes with nickel using the readily available Ni(II) bis dithiophosphate. The reaction of [Ni{S2P(OEt)2}2] with one mol-equivalent of Py-indz gave compound 1 in good yield. The analogous reaction starting from the xanthate gave 2 and using [Ni(acac)2(MeOH)2] gave 3 (Scheme 1). Compounds 1-3 were readily purified by recrystallization and their structures were determined using X- ray crystallography (see Figures 1, 2 and Table 1). [a] GIR MIOMET-IU CINQUIMA Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47011 Spain. [email protected].es Supporting information for this article is given via a link at the end of the document. FULL PAPER Scheme 1. Synthesis of nickel complexes with Py-indz.. The tris-chelate complex [Ni(Py-indz)3](PF6)2 (4), can be obtained by adding three mol-equivalents of Py-indz to nickel perchlorate hexahydrate and subsequent anion exchange with KPF6. The structure of the cation is shown in Figure 3. The values of the magnetic moment at room temperature for Py-indz nickel (II) compounds 1-3 are 2.78, 2.40, 2.78 BM respectively, and 2.90 BM for compound 4 at 20 K. These values indicate the presence of two unpaired electrons, as expected for octahedral Ni(II) complexes. Figure 1. Perspective view of compounds 1 and 2 showing the atom numbering. Selected bond lengths (Å) and angles (º) for 1: Ni(1)-S(1) 2.474(2), Ni(1)-S(2) 2.502(2), Ni(1)-S(3) 2.476(2), Ni(1)-S(4) 2.480(2), Ni(1)-N(1) 2.118(4), Ni(1)-N(2) 2.053(4), S(2)-Ni(1)-S(1) 80.90(5), S(4)-Ni(1)-S(3) 81.78(5), N(2)-Ni(1)-N(1) 78.46 (17). Selected bond lengths (Å) and angles (º) for 2: Ni(1)-S(1) 2.409(1), Ni(1)-S(2) 2.468(1), Ni(1)-S(3) 2.430(1), Ni(1)-S(4) 2.451(1), Ni(1)-N(1) 2.118(2), Ni(1)-N(2) 2.036(2), S(2)-Ni(1)-S(1) 73.06(3), S(4)-Ni(1)-S(3) 73.28(3), N(2)-Ni(1)-N(1) 77.49(9). Figure 2. Perspective view of the nickel acetylacetonate derivative 3 showing the atom numbering. Selected bond lengths (Å) and angles (º): Ni(1)-O(1) 2.032(3), Ni(1)-O(2) 2.018(3), Ni(1)-O(3) 2.049(3), Ni(1)-O(4) 2.009(3), Ni(1)- N(1) 2.115(3), Ni(1)-N(2) 2.062(3), O(2)-Ni(1)-O(1) 90.50(12), O(4)-Ni(1)-O(3) 90.49(13), N(2)-Ni(1)-N(1) 77.55(13). The Py-indz ligand structure is reminiscent to the classical 2, 2’- bipyridine and 1,10-phenanthroline ligands, and we expected the same behavior when coordinated to a transition metal. To test this, tris-Py-indz nickel (II) complexes, analogous to the well known tris-bipy or tris-phen complexes, were prepared using standard methods and their UV-Vis spectroscopic properties measured and summarized in Table 1. Table 1. UV-Vis spectroscopic properties of tris-nitrogen donor quelate nickel(II) complexes Absorption bands (cm -1 ) and  (M -1 cm -1 ) Δo f(10-3) h [Ni(phen) 3 ] 2+a 12700(6,80) 19300(11,90) [a] 12700 [a] 1,426 [b] - [Ni(bipy) 3 ] 2+ 12650(7,10) [a] 19200(11,60) [a] 12650 [a] 1,430 [b] - 12674(6,33) 19194(12,16) 12674 1,424 2,630 [Ni(Pyindz) 3 ] 2+ 12555(6,15) 19011(11,95) 12554 1,410 2,690 [a] Values obtained from C K Jorgensen, Acta Chem. Scand. 1955, 9, 1362. [b] Values obtained from (1) Figgis, B. N. Introduction to Ligand Field Theory; Interscience: NewYork, 1966, (2) B.N. Figgis, M.A. Hitchmann, Ligand Field Theory and Its Applications, Wiley, New York, 2000. The calculated values of , f and h for tris-Py-indz nickel (II) are similar to the reported values for the bipy and phen Ni(II) complexes confirming that the Py-indz ligand displays electronic effects close to those known for 2,2’-bipyridine and 1,10- phenanthroline. FULL PAPER Figure 1. Perspective view of the cation in 4 showing the atom numbering. Selected bond lengths (Å) and angles (º): Ni(1)-N(1) 2.089(5), Ni(1)-N(2) 2.053(6), Ni(1)-N(3) 2.111(5), Ni(1)-N(4) 2.054(5), Ni(1)-N(5) 2.113(6), Ni(1)- N6 2.047(5), N(1)-Ni(1)-N(2) 78.9(2), N(3)-Ni(1)-N(4) 78.4(2), N(5)-Ni(1)-N(6) 77.7(2), N(1)-Ni(1)-N(6) 98.2(2), N(2)-Ni(1)-N(6) 173.6(2). A similar procedure as for the above nickel complex gave diamagnetic, low spin d6, [Fe(Py-indz)3](PF6)2 complex (5) as a microcrystalline solid. 1D and 2D NMR spectra showed signals of the expected fac- and merisomers, but they were overlapped and it was not possible to make an assignment for each individual isomer (see Experimental Section and Supplementary Information). Despite repeated attempts it was not possible to grow crystals suitable for X-ray analysis for the tris-chelate iron complex 5 but a HRMS (High Resolution Mass Spectrum) could be carried out confirming the empirical formula. In the case of high-spin d5 Mn(II) complexes in which there is no Crystal Field Stabilization Energy (CFSE), the structure can be induced by the stoichiometry of the reagents used in the preparation (Scheme 2). Scheme 1. Synthesis of Mn(II) complexes with Py-indz Addition of only one mol-equivalent of Py-indz to MnCl2 resulted in the formation of the binuclear complex [Mn2Cl2(-Cl)2(Pyindz)2] (6), in which the structure consists of two manganese centers bridged by two chloride atoms. Mn ion lies in a distorted square-pyramidal coordination involving the two N and Cl atoms in the basal plane and one Cl ion in the apical position. Mn atom is displaced 0.720 Å out of the N(1), N(2), Cl(2) and Cl(2A) least squares plane toward the apical halide. This considerable distortion is found in similar binuclear chloride bridged complexes of Mn (II). [ 21 ] The addition of two mol-equivalents of Py-indz to MnCl2 produces the expected distorted octahedral [MnCl2(Py-indz)2] (7) (Figure 4). The values of magnetic moments at room temperature for Pyindz adducts of 6 and 7 compounds are 5.65 and 5.84 BM respectively, corresponding to 5 unpaired electrons. Figure 2. Compounds 6 (left) and 7 (right). Selected bond lengths (Å) and angles (º) of 6: Mn(1)-N(1) 2.262(2), Mn(1)-N(2) 2.168(2), Mn(1)-Cl(1) 2.336(1), Mn(1)-Cl(2) 2.487(1), Mn(1)-Cl(2A) 2.508(1), N(1)-Mn(1)-N(2) 73.40(8), Cl(1)- Mn(1)-Cl(2) 105.46(3), Cl(1)-Mn(1)-Cl(2A) 108.64(3), Cl(2)-Mn(1)-Cl(2A) 85.89(3). Selected bond lengths (Å) and angles (º) of 7: Mn(1)-N(1) 2.337(2), Mn(1)-N(2) 2.242(2), Mn(1)-N(3) 2.400(2), Mn(1)-N(4) 2.235(2), Mn(1)-Cl(1) 2.445(1), Mn(1)-Cl(2) 2.442(1), N(1)-Mn(1)-N(2) 70.39(6), N(4)-Mn(1)-N(5) 69.95(6), Cl(1)-Mn(1)-Cl(2) 100.62(2) The readily available bis dithiophosphates of Zn (II), [ 22 ] and Cd (II) can be used as starting materials for the preparation of heteroleptic complexes with N-donor ligands, [ 23 ] [M(S2P(OEt)2)2(Py-indz)], M = Zn (8) and Cd (9). As can be seen in Figure 5, the cadmium complex 9 is, as expected, hexacoordinate, while the Zn complex 8 is pentacoordinate with the Py-indz and one dithiophosphate ligand acting as bidentate chelate, and the second dithiophosphate acting as monodentate. The Zn(1)-S(4) distance is 4.074(2) Å too long for a significant interaction (cf with the bonded Zn(1)-S(3) 2.308(1) Å). This square pyramidal distortion is typical in adducts of bis-dialkyl dithiophosphate Zn (II) complexes. [2323b, 23c] Being diamagnetic, these Zn and Cd complexes could also be characterized by NMR spectroscopy. The 31P{1H} NMR spectrum of compound 8 at room temperature display only one signal for the two dithiophosphate ligands, suggesting a fast exchange between the two coordination modes. The dynamic equilibrium is rapid on the NMR time scale and can’t be stopped at -50ºC, as deduced from the absence of splitting of the dithiophosphate signals in a low temperature spectrum (-50ºC). FULL PAPER The 1H NMR spectra of compounds 8 and 9 have a representative pattern, similar to the one shown by the Py-indz free ligand, giving signals in the range  6.70-10.00 ppm for protons of “pyridine” and “imidazole” rings. Only a few chemical shifts show significant changes when the ligand is coordinated (a Scheme with the correspondence between the signals of the free ligand and the coordinated ligand can be seen in the Supporting Information). The larger shift occurs for the proton attached to C17 (H5) since it is H-bonded to the N1 atom in the free ligand and that H-bond has to be broken upon coordination. A 1H-1H NOESY experiment (supporting information) shows a cross peak between H5 and H3’ (proton attached to C14) confirming the assignment of the signals based on 13C{1H} , 31P{1H}, 1H-1H gCOSY, 1H-13C gHSQC, and 1H-13C gHMBC experiments. Figure 3. Compounds 8 and 9. Selected bond lengths (Å) and angles (º) for 8: Zn(1)-S(1) 2.780(1), Zn(1)-S(2) 2.365(1), Zn(1)-S(3) 2.308(1), Zn(1)-S(4) 4.074(2), Zn(1)-N(1) 2.192(2), Zn(1)-N(2) 2.023(2), S(2)-Zn(1)-S(1) 79.26(3), N(2)-Zn(1)-N(1) 77.12(9). Selected bond lengths (Å) and angles (º) for 9: Cd(1)-S(1) 2.734(1), Cd(1)-S(2) 2.649 (1), Cd(1)-S(3) 2.672(1), Cd(1)-S(4) 2.675(2), Cd(1)-N(1) 2.432(3), Cd(1)-N(2) 2.319(3), S(2)-Cd(1)-S(1) 75.77(4), S(3)-Cd(1)-S(4) 76.20(4), N(2)-Cd(1)-N(1) 70.00(10). A new family of complexes can be obtained by using Lewis acids such as SnI4, PhSnCl3 or nBu2SnCl2 as stating materials. The complexes [SnI4(Py-indz)] (10), [SnCl3Ph(Py-indz)] (11), and [SnCl2(nBu)2(Py-indz)] (12), (Scheme 3) were isolated in good yields, and characterized by spectroscopic methods. Their structures are depicted in Figure 6, showing octahedral arrangement around the tin atom. The main distortion from the ideal octahedral geometry comes from the small bite angle, N(1)-Sn(1)-N(2), of the Py-indz ligand (71.6(4), 70.8(2) and 67.53(14) for complexes 10, 11 and 12 respectively). Scheme 3. Synthesis of tin complexes. It is noticeable that the Sn-halogen (I or Cl) distances are consistently longer when the halogen is in the trans position with respect to other halogen, compared to those in which the halogen is trans to nitrogen. This can be ascribed to the existence of some kind of trans influence, which is greater for the halogen and smaller for the nitrogen ligand. To support this argument, theoretical calculations have been carried out on complex 10. Starting from the geometry obtained by X-ray diffraction, an optimization at the B3LYP level using the LANL2DZ basis set for Sn and I, and 6-31G(d,p) for the rest of elements, led to a minimum in which the Sn-I distance is longer when another iodine is situated in the trans position. The same effect is seen in the related compound [SnI4(bipy)] that was reported by Medvedev et al (2.813 and 2.819 Å for the Sn-I distances with another I trans, 2.787 and 2.788 Å for the Sn-I distances with a N atom trans).[ 24 ] Figure 4. Compounds 10, 11 and 12. Selected bond lengths (Å) and angles (º) for 10: Sn(1)-I(1) 2.821(1), Sn(1)-I(2) 2.829(1), Sn(1)-I(3) 2.741(1), Sn(1)-I(4) 2.767(1), Sn(1)-N(1) 2.303(10), Sn(1)-N(2) 2.212(10), I(2)-Sn(1)-I(1) 169.87(4), I(1)-Sn(1)-I(3) 93.14(4), I(3)-Sn(1)-I(4) 100.65(4), N(2)-Sn(1)-N(1) 71.6(4). Selected bond lengths (Å) and angles (º) for 11: Sn(1)-Cl(1) 2.454(2), Sn(1)- Cl(2) 2.462(2), Sn(1)-Cl(3) 2.389(2), Sn(1)-C(31) 2.171(7), Sn(1)-N(1) 2.311(6), Sn(1)-N(2) 2.186(6), Cl(2)-Sn(1)-Cl(1) 165.99(7), Cl(2)-Sn(1)-Cl(3) 91.78(8), Cl(3)-Sn(1)-C(31) 101.97(19), N(2)-Sn(1)-N(1) 70.8(2). Selected bond lengths (Å) and angles (º) for 12: Sn(1)-Cl(1) 2.511(1), Sn(1)-Cl(2) 2.534(2), Sn(1)- C(31) 2.123(5), Sn(1)-C(41) 2.128(5), Sn(1)-N(1) 2.439(4), Sn(1)-N(2) 2.366(4), Cl(2)-Sn(1)-Cl(1) 106.28(5), Cl(1)-Sn(1)-C(31) 94.60(15), C(31)-Sn- C(41) 170.34(19), N(2)-Sn(1)-N(1) 67.53(14) FULL PAPER Tin complexes 10, 11 and 12 are diamagnetic and can be studied by NMR in solution but, unfortunately, compound 10 couldn’t be dissolved in the usual deuterated solvents. Complex 11 gives the representative pattern discussed above, but complex 12 shows a more complicated spectrum. At room temperature most of the signals of aromatic protons of 12 are so broad that they are indistinguishable from the baseline, suggesting some kind of dynamic process in solution. At lower temperature the process rate is reduced and at -50ºC the nine signals corresponding to the Py-indz ligand chelated to metal can be observed although they are still very broad (see Figure 7). The low temperature spectrum is consistent with the structure observed in solid state by X-ray diffraction. At 20ºC the spectrum shows the expected well resolved sharped signals corresponding to the butyl ligands but they are Figure 7. Variable temperature 1H NMR spectra of complex 12. For clarity, only the aromatic proton range (10.0 to 6.3 ppm), and the alkyl proton range (2.0 to 0.0 ppm) are shown. An impurity appears at 8.58 ppm. Addition of Py-indz to [Cu(PPh3)2(NCMe)2]BF4 produces the substitution of the acetonitrile ligands to afford [Cu(PPh3)2(Pyindz)]BF4 (13) as a yellow crystalline solid. The structure (Figure 8) shows a tetrahedral disposition around the copper atom. Again the main distortion corresponds to the small bite angle of the Py-indz ligand N(1)-Cu-N(2), with a value of 79.49(9), very similar to the one found in bipy Cu (II) analogous complexes. [ 25 ] Figure 8. Cation of Compound 13. Selected bond lengths (Å) and angles (º): Cu(1)-N(1) 2.115(2), Cu(1)-N(2) 2.067(2), Cu(1)-P(1) 2.257(1), Cu(1)-P(2) 2.271(1), N(1)-Cu(1)-N(2) 79.49(9), P(1)-Cu(1)-P(2) 125.07(3), N(1)-Cu(1)- P(1) 107.50(7), N(1)-Cu(1)-P(2) 106.80(7), N(2)-Cu(1)-P(1) 119.30(7) Diimine ligands such as bipy or phen, have been used extensively as ancillary ligands in carbonyl complexes of middle transition metals. Py-indz can be used in thermally induced substitution reactions in the same way as bipy or phen. Thus, reaction with bromopentacarbonyl complexes of manganese or rhenium, or with molybdenum hexacarbonyl, produced [M(CO)3(Py-indz)Br], M = Mn (14), Re (15), or [Mo(CO)4(Pyindz)] (16) as depicted in Scheme 5. We have been interested in complexes containing pyridine-2-carboxaldehyde (pyca) as chelating κ2 (N,O) ligands which can serve as precursors for the introduction of metal-ligand fragments in biomolecules.[ 26 ] Scheme 2. Synthesis of carbonyl complexes with Py-indz. The (CO) bands of the coordinated carbonyls can be easily observed by IR spectroscopy in solution. The three band pattern expected for a fac-tricarbonyl arrangement appears at frequencies close to those observed for the bipy and phen analogues [ 27 ] (see Table 2). FULL PAPER Figure 9. Compounds 14, 15 and 16. Selected bond lengths (Å) and angles (º) for 14: Mn(1)-Br(1) 2.548(1), Mn(1)-N(1) 2.066(2), Mn(1)-N(2) 2.016(2), Mn(1)- C(1) 1.787(4), Mn(1)-C(2) 1.795(3), Mn(1)-C(3) 1.794(4), C(2)-Mn(1)-C(1) 89.15(16), C(2)-Mn(1)-C(3) 88.89(16), C(2)-Mn(1)-Br(1) 91.68(11), N(2)- Mn(1)-N(1) 78.63(9). Selected bond lengths (Å) and angles (º) for 15: Re(1)- Br(1) 2.636(1), Re(1)-N(1) 2.190(4), Re(1)-N(2) 2.158(4), Re(1)-C(1) 1.904(7), Re(1)-C(2) 1.897(6), Re(1)-C(3) 1.921(7), C(2)-Re(1)-C(1) 88.0(2), C(2)- Re(1)-C(3) 88.5(2), C(2)-Re(1)-Br(1) 94.95(18), N(2)-Re(1)-N(1) 74.59(16). Selected bond lengths (Å) and angles (º) for 16:, Mo(1)-N(1) 2.271(3), Mo(1)- N(2) 2.200(3), Mo(1)-C(1) 2.010(4), Mo(1)-C(2) 1.944(4), Mo(1)-C(3) 1.952(4), Mo(1)-C(4) 2.027(4) C(2)-Mo(1)-C(1) 84.01(15), C(2)-Mo(1)-C(3) 90.97(16), C(2)-Mo(1)-C(4) 87.67(15), N(2)-Mo(1)-N(1) 71.83(10). Finally, Ru(II) complex 17 was obtained through the reaction of [RuCl(p-cym)(NCMe)2]PF6 and Py-indz ligand. The complex has the familiar half-sandwich ‘‘three-legged piano-stool’’ geometry with the η6- π-bound arene ring forming the seat, and the two nitrogen atoms of the ligand and one terminal chloride ligand as the legs of the piano-stool. The arene is formally covering three facial coordination sites. If the center of the aromatic ring is considered as a single site, the Ru environment may be regarded as tetrahedral with a significant trigonal distortion. The Ru distance to the centroid (called Cent from now on) of the aromatic ring was found to be 1.676(5) Å. The Cl(1)– Ru(1)–N(1), Cl(1)–Ru(1)–N(2) and N(1)–Ru(1)–N(2) angles are 85.85(11)°, 84.66(12)° and 76.23(15)° respectively, while the angles Cl(1)–Ru(1)–Cent 128.27(2)°, N(1)–Ru1–Cent 131.29(2)° and N(2)–Ru(1)–Cent 132.15(2)° are significantly wider than the ideal tetrahedral angle (109.47°) The coordination bond distances and angles agree well with the literature values of Ru complexes. 28 Scheme 5. Synthesis of complex 17 Contrary to the expected behaviour, some of the structures discussed above show twisted indolizine ligands. The twist angles, defined as the dihedral angle between the mean planes of the pyridine and imidazo rings, have been calculated with the Mercury program and are gathered in the Table 3. Examining the packing of the different structures, it is observed that the indolizine ligand is almost planar when is -stacked with another indolizine from a neighboring molecule. To support the idea that the twisting is related to the packing and not to electronic effects, an optimization of the structure for the Ni complex 1 was performed at the B3LYP level, using the LANL2DZ basis set for the Ni, P and S atoms, and 6-31G(d,p) for the rest of elements. The optimization was started at the geometry of the X-ray structure, with a twist angle of approximately 20º, and the minimum was found with a much less twisted indolizine ligand (7º). Table 1. Twist angles between the pyridine and imidazo rings of the Py-indz complexes. Complexes 1 2 3 4 6 7 8 9 Twist angle (°) 19.93 2.67 9.29 9.10[a] 9.44 0.38 7.23 22.39 Complexes 10 11 12 13 14 15 16 17 Twist angle (°) 3.52 4.81 2.69 12.07 3.77 5.00 9.11 9.10 [a] Calculated as an average of the twist angle of the three Py-indz ligands Table 2. Carbonyl stretching frequencies (cm-1, THF solution)[a] ν1(ms) ν2(s) ν3(s) [Mn(CO)3Br(Py-indz)] 2022 1934 1911 [Mn(CO)3Br(bipy)] 2023 1935 1915 [Mn(CO)3Br(phen)] 2024 1936 1915 [Re(CO)3Br(Py-indz)] 2018 1917 1891 [Re(CO)3Br(bipy)] 2020 1920 1896 [Re(CO)3Br(phen)] 2021 1920 1897 ν1(m) ν2(s) ν3(m, sh) ν1(m) [Mo(CO)4(Py-indz)] 2010 1895 1878 1838 [Mo(CO)4(bipy)] 2013 1901 1883 1842 [Mo(CO)4(phen)] 2012 1901 1884 1842 [a] For a more accurate comparision, the spectra of the complexes with bipy and phen have been taken in the same solvent and measured with the same instrument. FULL PAPER Figure 10. Cation of compound 17. Selected bond lengths (Å) and angles (º): Ru(1)-N(1) 2.104(4), Ru(1)-N(2) 2.061(4), Ru(1)-Cl(1) 2.394(1), Ru(1)-Cent 1.676(5), N(1)-Ru(1)-N(2) 79.49(9), Cl(1)-Ru(1)-N(I) 85.85(11), Cl(1)-Ru(1)- N(2) 84.66(12), Cl(1)-Ru(1)-Cent 128.27(2), N(1)-Ru(1)-Cent 131.29(2), N(2)- Ru(1)-Cent 132.15(2). Conclusions A variety of new complexes has been prepared using main group and transition metal moieties and the Py-indz ligand, and their structures have been fully characterized by spectroscopic methods and X-ray crystallography. In some cases, the structures can be induced by stoichiometry and complexes can be obtained with one, two or three molecules of the ligand. The twist angle between the imidazo and pyridine rings of the ligand is related to the packing mode of the structures, when two Pyindz ligands from neighbouring molecules are -stacked, these ligands are approximately planar, while when the -stacking is missing the twisting is significant. The ability of Py-indz to act as ligand towards metals in very different environments has been fully demonstrated. The Py-indz ligand behaves as a chelating ligand with similar electronic properties to the classical 2,2’- bipyridine or 1,10-phenanthroline. In this way, a value of 12554 for o was found in tris-chelate complexes of Py-indz with Ni(II), while o ranges from 12650 to 12700 for the corresponding bipy or phen Ni(II) complexes.Main Text Paragraph. Experimental Section Materials and general methods: some operations were performed under an atmosphere of dry nitrogen using Schlenk and vacuum techniques. Solvents, ligands and other reagents were purchased and used without purification unless otherwise stated. 3-(Pyridin-2- yl)imidazo[1,5-a]pyridine (Py-indz) was prepared using the method reported by us.[¡Error! Marcador no definido.] The precursors were prepared following the literature: [Ni(S2P(OEt)2)2], [ 29 a] [Ni(S2COEt)2],[29b] [Ni(acac)2(MeOH)2], [29c] [Zn(S2P(OEt)2)2] , [22a] [Cd(S2P(OEt)2)2], [23a] [Cu(NCMe)2(PPh3)2]BF4,[ 30 ] [MBr(CO)5] M= Mn,[ 31 ] Re,[ 32 ] [RuClpcymene(NCMe)2]PF6 was prepared from [RuCl2(p-cymene)2], [ 33 ] with NH4PF6 and stirring 12 hours in acetonitrile. All others agents were obtained from the usual commercial suppliers, and used as received. Kieselguhr (diatomaceous earth, Merck) was used for filtration. IR spectra in solution were recorded with a Perkin Elmer Spectrum RX I FT- IR instrument, using cells with CaF2 windows. All NMR solvents were stored over molecular sieves and degassed prior to use. NMR experiments were measured on an Agilent MR400 and Agilent DDR2 500 spectrometers. Chemical shift values are given in ppm using the residual solvent signal as an internal reference. The splitting of proton resonances in the reported 1H NMR data is defined as s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet. 2D experiments such as 1H−1H gCOSY, 1H−1H NOESY, 1H−13C gHSQC, and 1H−13C gHMBC were recorded using standard pulse sequences. All NMR data processing was carried out using MestReNova, version 9.1.0. The magnetic moments were calculated from magnetic susceptibilities which were measured in Unidade de Magnetosusceptibilidade of Santiago de Compostela University. HRMS measurement (High Resolution Mass Spectroscopy) was performed in the Laboratorio de Técnicas Instrumentales of Valladolid University. Elemental analyses were performed on a Perkin- Elmer 2400B microanalyzer. Computational details: all computations were carried out using the GAUSSIAN09 package,[ 34 ] in which the hybrid method B3LYP was applied with the Becke three-parameter exchange functional,[ 35 ] and the Lee-Yang-Parr correlation functional.[ 36 ] Effective core potentials (ECP) and their associated double-z LANL2DZ basis set were used for the heavy atoms (Ni, P, S, Sn, I).[ 37 ] The light elements (O, N, C, and H) were described with the 6-31G** basis.[ 38 ] Geometry optimizations were performed under no symmetry restrictions, using initial coordinates derived from X-ray data of the same complexes, and frecuency analyses were performed to ensure that a minimum structure with no imaginary frecuencies was achieved in each case. Scheme 6. Numbering scheme for the protons and carbons of Py-indz ligand. Ni(S2P(OEt)2)2(Py-indz)] (1): to a violet solution of [Ni(S2P(OEt)2)2] (0.429 g, 1 mmol) in dichloromethane was added Py-indz (0.195 g, 1 mmol) and the mixture was stirred overnight. The resulting solution was concentrated in vacuo to afford compound 1 as a green microcrystalline solid. Yield 0.582 g, 93%. Analysis calculated for C20H29N3Ni1O4P2S4: C 38.48, H 4.68, N 6.73. Found: C 39.06, H 4.48, N 6.40. eff (293K): 2.78 BM. Crystals of 1 suitable for X-ray analysis were grown from CH2Cl2– hexane at −20 °C. [Ni(S2COEt)2(Py-indz)] (2): to a black solution of [Ni(S2COEt)2] (0.429 g, 1 mmol) in dichloromethane was added Py-indz (0.195 g, 1 mmol) and the mixture was stirred overnight. The resulting solution was concentrated in vacuo to afford compound 2 as a green microcrystalline solid. Yield 0.472 g, 95%. Analysis calculated for C18H19N3Ni1O2S4: C FULL PAPER 43.56, H 3.86, N 8.47. Found: C 43.16, H 3.72, N 8.23. eff (293K): 2.40 BM. Crystals of 2 suitable for X-ray analysis were grown from CH2Cl2– hexane at −20 °C. [Ni(acac)2(Py-indz)] (3): to a blue pale solution of [Ni(acac)2(MeOH)2] (0.321 g, 1 mmol) in tetrahydrofuran was added Py-indz (0.195 g, 1 mmol) and the mixture was stirred overnight. The resulting solution was concentrated in vacuo to afford compound 3 as a green microcrystalline solid. Yield 0.413 g, 91%. Analysis calculated for C22H23N3Ni1O4: C 58.44, H 5.13, N 9.29. Found: C 58.32, H 5.02, N 9.22. eff (293K): 2.78 BM. Crystals of 3 suitable for X-ray analysis were grown from THF–hexane at −20 °C. [Ni(Py-indz)3](PF6)2 (4): to a 10 mL aqueous solution of Ni(ClO4)2·6H2O (0.366 g, 1 mmol) was added 10 mL of Py-indz (0.585 g, 3 mmol) in dichloromethane with stirring and NH4PF6 (0.326 g, 2 mmol). The green solution was stirred 6 hours and then an extraction with dichloromethane was done (3  15 mL), followed by drying over MgSO4. Slow evaporation at reduced pressure gave compound 4 as a microcrystalline solid. Yield 0.700 g, 75%. Analysis calculated for C36H27N9Ni1P2F12: C 46.28, H 2.91, N 13.49. Found: C 46.10, H 2.72, N 13.52. eff (20K): 2.90 BM. Crystals of 4 suitable for X-ray analysis were grown from CH2Cl2-ether at −20 °C. [Fe(Py-indz)3](PF6)2 (5): a similar procedure to that described for 4 was used to obtain 5, using (NH4)2Fe(SO4)·6H2O (0.392 g, 1 mmol), and Pyindz (0.585 g, 3 mmol). The red compound 5 precipitated after NH4PF6 (0.326 g, 2 mmol) was added. Extraction with dichloromethane (3  15 mL), followed by drying over MgSO4, filtering through Kieselghur and slow evaporation at reduced pressure gave compound 5 as a microcrystalline solid. Yield 0.822 g, 88%. Analysis calculated for C36H27FeN9P2F12: C 46.42, H 2.92, N 13.53. Found: C 46.40, H 2.84, N 13.71. HRMS (ESITOF) m/z= 320.612 [M-2PF6]2+, calcd. 320.586 for C36H27N9Fe. 1H NMR (400 MHz, Me2CO-d6): 9.27-9.18 (m, 2H, H5isomerA, H5isomerB), 8.76-8.64 (m, 2H, H6’A, H6’B), 8.24-8.15 (m, 2H, H5’A, H5’B), 7.98-7.82 (m, 2H, H3’A, H3’B), 7.82-7.70 (m, 2H, H8A, H8B), 7.41 – 7.30 (m, 2H, H4’A, H4’B), 7.30- 7.23 (m, 4H, H7A, H7B, H1A, H1B), 7.23 – 7.14 (m, 2H, H6A, H6B) ppm. 13C NMR (101 MHz, Me2CO-d6):  155.77, 155.74 (s, C3’A, C3’B); 151.80, 151.70 (s, C2’A, C2’B); 138.12, 138.04 (s, C5’A, C5’B); 136.17, 136.02 (s, C3A, C3B); 135.85, 135.72 (s, C9A, C9B); 124.86, 124.73 (s, C6A, C6B); 123.70, 123.54 (s, C4’A, C4’B); 123.29, 123.23 (s, C5A, C5B); 122.89, 122.72 (s, C1A, C1B); 120.48, 120.10 (s, C6’A, C6’B); 117.91, 117.86 (s, C8A, C8B); 116.43, 116.43 (s, C7A, C7B) ppm. 31P NMR (162 MHz, Me2CO-d6): -144.31 ppm. [Mn2Cl4(Py-indz)2] (6): to a colorless solution of anhydrous MnCl2 (0.126 g, 1 mmol) in methanol was added Py-indz (0.195 g, 1 mmol). After 2 hours with stirring, the solution changed to yellow and evaporated to dryness. The residue was dissolved in dichloromethane and filtered and the resulting solution was concentrated to give the yellow compound 6 as a microcrystalline solid. Yield 0.610 g, 95%. μeff: 5.65 BM. Analysis calculated for C24H18Cl4Mn2N6: C 44.89, H 2.83, N 13.09. Found: C 44.77, H 2.91, N 13.26. Orange crystals of 6 suitable for X-ray analysis were grown from CH2Cl2–hexane at room temperature. [MnCl2(Py-indz)2] (7): compound 7 was prepared as described above for 6, using anhydrous MnCl2 (0.126 g, 1 mmol) and Py-indz (0.390 g, 2 mmol).Yield 0.502 g, 97%. eff (293K): 5.84 BM. Analysis calculated for C24H18N6Cl2Mn1: C 55.83, H 3.51, N 16.28. Found: C 55.62, H 3.11, N 16.18. Yellow crystals of 7 suitable for X-ray analysis were grown from CH2Cl2–hexane at room temperature. [Zn(S2P(OEt)2)2 (Py-indz)] (8): to a colorless solution of [Zn(S2P(OEt)2)2] (0.436 g, 1 mmol) in dichloromethane was added Pyindz (0.195 g, 1 mmol) and the mixture was stirred overnight. The resulting solution was concentrated in vacuo to afford compound 8 as a yellow microcrystalline solid. Yield 0.612 g, 97%. Analysis calculated for C20H29N3O4P2S4Zn1: C 38.07, H 4.63, N 6.66. Found: C 38.17, H 4.48, N 6.42. Crystals of 8 suitable for X-ray analysis were grown from CH2Cl2– hexane at −20 °C. 1H NMR (400 MHz, Me2CO-d6): 9.19 (d, J = 6.4 Hz, 1H, H5), 8.95 (d, J = 5.03 Hz 1H, H6’), 8.55 (d, J = 8.2 Hz, 1H, H3’), 8.31 (td, J = 7.9, 1.7 Hz, 1H, H4’), 8.11 (s, 1H, H1), 8.08 – 7.99 (d, J = 7.02 Hz, 1H, H8), 7.72 (ddd, J = 7.7, 5.1, 1.0 Hz, 1H, H5’), 7.31 – 7.20 (m, 2H, H6, H7), 3.96 (dq, J = 9.6, 7.1 Hz, 8H, CH2), 1.14 (t, J = 7.1 Hz, 12H, CH3) ppm. 13C NMR (101 MHz, Me2CO-d6):  150.81 (s, C6’), 145.09 (s, C2’), 141.41 (s, C4’), 137.81 (s, C3), 135.13 (s, C9), 125.12 (s, C5’), 124.71 (s, C5), 123.21 (s, C7), 122.02 (s, C1), 120.94 (s, C3’), 120.71 (s, C8), 118.07(s, C6), 110.93, 62.92 (s, CH2), 16.17 (s, CH3) ppm. 31P NMR (162 MHz, Me2CO-d6): 103.21 ppm. [Cd(S2P(OEt)2)2 (Py-indz)] (9): to a colorless solution of [Cd(S2P(OEt)2)2] (0.482 g, 1 mmol) in dichloromethane was added Pyindz (0.195 g, 1 mmol) and the mixture was stirred overnight. The resulting solution was concentrated in vacuo to afford compound 9 as a yellow microcrystalline solid. Yield 0.663 g, 98%. Analysis calculated for C20H29Cd1N3O4P2S4: C 35.43, H 4.31, N 6.20. Found: C 35.52, H 4.28, N 6.32. Crystals of 9 suitable for X-ray analysis were grown from CH2Cl2– hexane at −20 °C. 1H NMR (500 MHz, CDCl3):  9.18 (d, J = 7.0 Hz, 1H, H6’), 8.68 (d, J = 7.1 Hz, 1H, H5’), 8.01-7.97 (m, 2H, H3’ y H4’) 7,99 (s, 1H, H1), 7.67 (d, J = 8.6 Hz, 1H, H8), 7.42 (ddd, J = 7.3, 5.0, 1.3 Hz, 1H, H5’), 7.02 – 6.98 (m, 1H, H7), 6.96 (td, J = 6.9, 1.4 Hz, 1H, H6), 4.20 (dq, J = 9.5, 7.1 Hz, 8H, CH2), 1.33 (t, J = 6.9Hz, 12H, CH3) ppm. 13C NMR (126 MHz, CDCl3):  150.53 (s, C6’), 144.40 (s, C2’), 139.01 (s, C4’), 134.12 (s, C3), 133.94 (s, C9), 123.82 (s, C5’), 122.70 (s, C5), 121.37 (s, C7), 121.34 (s, C3’), 120.00 (s, C8), 119.49 (s, C1), 116.60 (s, C6), 63.74-63.69 (d, CH2), 16.18-16.11 (d, CH3). 31P NMR (162 MHz, CDCl3)  108.11 ppm. [SnI4(Py-indz)] (10): to an orange solution of SnI4 (0.626 g, 1 mmol) in dichloromethane was added Py-indz (0.195 g, 1 mmol) with stirring. After two hours a red precipitate appeared. The solution was filtered with a fritted funnel and the crude was washed three times with hexane. Yield 0.790 g, 96%. Analysis calculated for C12H9I4N3Sn1: C 17.54, H 1.10, N 5.12. Found: C 17.62, H 1.19, N 5.07. Suitable crystals of 10 for X-ray analysis appeared at the wall of the vial after two days at room temperature by layering a solution of SnI4 in methanol with another solution of the Py-indz ligand in ether. [PhSnCl3(Py-indz)] (11): to a light yellow solution of PhSnCl3 (0.302 g, 1 mmol) in dichloromethane was added Py-indz (0.195 g, 1 mmol) with stirring. After two hours a yellow precipitate appeared. The solution was filtered with a fritted funnel and the crude was washed three times with dichloromethane. Yield 0.400 g, 80%. Analysis calculated for C18H14Cl3N3Sn1: C 43.47, H 2.84, N 8.45. Found: C 43.10, H 2.75, N 8.33. Crystals of 11 suitable for X-ray analysis were grown from MeOH-ether at −20 °C. 1H NMR (400 MHz, acetone)  9.51 (d, J = 6.4 Hz, 1H, H6’), 9.30 (d, J = 6.5 Hz, 1H, H5), 8.89 (d, J = 8.2 Hz, 1H, H3’), 8.62 (t, J = 7.35 Hz, 1H, H4’), 8.38 (s, 1H, H1), 8.25 – 8.18 (m, 1H, H8), 8.06 (t, J = 6.5 Hz, 1H, H5’), 7.56 – 7.45 (m, 2H, H7,6), 7.27 – 7.08 (m, 5H, (H)Ph). 13C NMR (101 MHz, acetone)  145.65 (s, C6’), 137.32 (s, C4’), 128.83 (s, Ph), 128.0 (s, Ph), 126.52 (s, C5), 126.00 (s, C5’), 124.78 (s, C3’), 121.72 (s, C1), 120.45 (s, C7), 119.11 (s, C8), 117.24 (s, C6) ppm. [nBu2SnCl2(Py-indz)] (12): BunSnCl2 (0.304 g, 1 mmol) and Py-indz (0.195 g, 1 mmol) were stirred overnight in dichloromethane. Slow evaporation at reduced pressure gave compound 12 as a microcrystalline solid. Yield 0.790 g, 94%. Analysis calculated for C20H27Cl2N3Sn1: C 48.16, H 5.45, N 8.42. Found: C 48.23, H 5.19, N 8.07. Yellow crystals of 12 suitable for X-ray analysis were grown from CH2Cl2- ether at room temperature. 1H NMR (500 MHz, -50ºC, Nitromethane-d3)  FULL PAPER 9.17 (s, 1H, H5), 8.97 (s, 1H, H6 ), 8.41 (s, 1H, H3’), 8.32 (s, 1H, H4’), 8.10 (s, 1H, H1), 7.94 (s, 1H, H8), 7.72 (s, 1H, H5’), 7.28 (d, J = 8.5 Hz, 1H, H7), 7.25 (s, 1H, H6), 1.47 (m, 4H, CH2-Sn), 1.21 (m, 4H, -CH2-), 1.04 (m, 4H, CH2-Me), 0.62 (m, 6H, CH3). 13C NMR (101 MHz, -50ºC, Nitromethaned3):  148.65 (s, C5), 140.76 (s, C4’), 124.68 (s, C5’), 123.94 (s, C6’), 123.16 (s, C7), 120.45 (s, C3’), 119.55 (s, C1), 119.55 (s, C8), 117.44 (s, C6), 29.33 (s, CH2-Sn), 28.19 (s, -CH2-), 25.91(s, CH2-Me), 12.82 (s, CH3) ppm. [Cu(PPh3)2(Py-indz)]BF4 (13): compound 13 was prepared with a similar procedure to 8 by using [Cu(NCMe)2(PPh3)2]BF4 (0.757 g, 1 mmol) and Py-indz (0.195 g, 1 mmol) in dichloromethane with stirring. Yield 0.790 g, 94%. Analysis calculated for C48H39Cu1N3P2B1F4: C 66.49, H 4.19, N 4.85. Found: C 66.07, H 4.53, N 4.78. Light yellow crystals of 13 suitable for X-ray analysis were grown from CH2Cl2-ether at room temperature. 1H NMR (400 MHz, Me2CO-d6)  8.99 (d, J = 6.5 Hz, 1H, H5), 8.62 (d, J = 5.0 Hz, 1H, H6’), 8.45 (d, J = 8.2 Hz, 1H, H3’), 8.16 (t, J = 7.9 Hz, 1H, H4’), 7.86 (s, 1H, H1), 7.82 – 7.75 (m, 1H, H8), 7.41 (m, 1H, H5’), 7.41 (d, J = 7.3 Hz, 6H, Ph-Hpara), 7.28 (dd, J = 14.6, 7.4 Hz, 24H, Ph-Hortho,meta), 7.22 – 7.12 (m, 2H, H6,7). 13C NMR (101 MHz, Me2CO-d6) 150.85 (s, C6’), 145.38 (s, C2’), 138.81 (s, C4’), 135.12 (s, C3’), 134.58 (s, C9), 133.15 (s, CHortho), 130.17 (s, CHpara), 128.76 (s, CHmeta), 123.88 (s, C5’), 123.33 (s, C5), 122.13 (s, C7), 121.26 (s, C1), 120.66 (s, C3’), 119.06 (s, C8), 116.42 (s, C6). 31P NMR (202 MHz, Me2CO-d6):  -99.97 ppm. [MnBr(CO)3(Py-indz)] (14): to a solution of Py-indz (0.195 g, 1 mmol) in hexane (20 mL) was added [MnBr(CO)5] (0.275 g, 1 mmol) and the mixture was refluxed for 2 hours under nitrogen atmosphere. After that time a yellow solid was formed, which was filtered off, washed with hexane (3 × 15 mL) and dried in vacuo. Yield 0.213 g, 78%. Analysis calculated for C15H9Br1Mn1N3O3: C 43.51, H 2.19, N 10.15. Found: C 43.62, H 2.11, N 10.72. IR (THF, cm−1), ν(CO): 2022 vs, 1934 s, 1911 s. Yellow crystals of 14 suitable for X-ray analysis were grown from CH2Cl2- ether at room temperature. 1H NMR (500 MHz, Me2CO-d6)  9.28 (d, J = 5.18 Hz, 1H, H6’), 9.06 (d, J = 6.8 Hz, 1H, H5), 8.50 (d, J = 7.9 Hz, 1H, H3’), 8.28 (s, 1H, H1), 8.21 (m, 1H, H4’), 7.98 (d, J = 9.4 Hz, 1H, H8), 7.59 (m, 1H, H5’), 7.29 (s m, 1H, H5’), 7.29 (t, J = 7.7 Hz, 1H, H7), 7.22 (m, 1H, H6) ppm. 13C NMR (126 MHz, Me2CO-d6)  166.10 (s, CO), 154.67 (s, C6’), 147.54 (s, C2’), 138.78 (s, C4’), 135.94 (s, C3), 134.34 (s, C9), 124.18 (s, C1), 123.67 (s, C5’), 123.27 (s, C5), 122.57 (s,C7), 120.20 (s, C3’), 118.55 (s, C8), 116.55 (s, C6) ppm. [ReBr(CO)3(Py-indz)] (15): to a solution of Py-indz (0.195 g, 1 mmol) in hexane (20 mL) was added [ReBr(CO)5] (0.275 g, 1mmol) and the mixture was refluxed for 8 hours under nitrogen atmosphere. After that time a yellow solid was formed, which was filtered off, washed with hexane (3 × 15 mL) and dried in vacuo. Yield 0.463 g, 85%. Analysis calculated for C15H9Br1Re1N3O3: C 33.04, H 1.66, N 7.71. Found: C 33.29, H 1.68, N 7.90. IR (THF, cm−1), ν(CO): 2018 vs, 1917 s, 1891 s. Yellow crystals of 15 suitable for X-ray analysis were grown from CH2Cl2- ether at room temperature. 1H NMR (400 MHz, Me2CO-d6)  9.16 (d, J = 6.8 Hz, 1H, H5), 9.12 (d, J = 5.6 Hz, 1H, H6’), 8.63 (d, J = 8.3 Hz, 1H, H3’), 8.31 (td, J = 8.0, 1.7 Hz, 1H, H4’), 8.17 (s, 1H, H1), 8.01 (d, J = 9.0 Hz, 1H, H8), 7.62 (dd, J = 7.7, 5.6 Hz, 1H, H5’), 7.40 – 7.33 (m, 1H, H7), 7.31 (td, J = 6.9, 1.5 Hz, 1H, H6) ppm. 13C NMR (101 MHz, Me2CO-d6)  166.10 (s, CO), 154.24 (s, C6’), 148.09 (s, C2’), 139.63 (s, C4’), 138.85 (s, C3), 135.02 (s, C9), 124.59 (s, C5’), 123.77 (s, C1), 123.42 (s, C5), 123.26 (s, C7), 121.02 (s, C3’), 118.97 (s, C8), 117.36 (s, C6) ppm. [Mo(CO)4(Py-indz)] (16): to a solution of Py-indz (0.195 g, 1 mmol) in toluene (20 mL) was added [Mo(CO)6] (0.264 g, 1mmol) and the mixture was refluxed for 6 hours under nitrogen atmosphere. After that time the solution changed to yellow-orange. Toluene was evaporated and the crude was dissolved in dichloromethane and filtered off. Hexane was added to precipitate complex 16 as a microcrystalline yellow solid. Yield 0.356 g, 88%. Analysis calculated for C16H9Mo1N3O4: C 47.66, H 2.25, N 10.42. Found: C 47.52, H 2.19, N 10.26. IR (THF, cm−1), ν(CO): 2010 vs, 1895 vs, 1878 s, 1838 s. Yellow crystals of 16 suitable for X-ray analysis were grown from CH2Cl2-ether at -20°C. 1H NMR (400 MHz, Me2CO-d6)  9.13 (ddd, J = 5.5, 1.6, 0.9 Hz, 1H, H6’), 9.08 (dd, J = 7.2, 1.0 Hz, 1H, H5), 8.52 (dt, J = 8.3, 1.0 Hz, 1H, H3’ ), 8.19 (ddd, J = 8.2, 7.5, 1.7 Hz, 1H, H4’), 8.02 (d, J = 0.9 Hz, 1H, H1), 7.94 (dt, J = 9.2, 1.4 Hz, 1H, H8), 7.51 (ddd, J = 7.6, 5.4, 1.1 Hz, 1H, H5’), 7.27 (td, J = 6.7, 1.4 Hz, 1H, H7), 7.19 (td, J = 6.9, 1.4 Hz, 1H, H6). 13C NMR (101 MHz, Me2CO-d6)  165.10 (s, CO), 153.78 (s, C6’), 147.44 (s, C2’), 138.31 (s, C4’), 136.0 (s, C3), 134.40 (s, C9), 124.27 (s, C1), 123.45 (s, C5), 123.01 (s, C5’), 122.45 (s, C7), 120.46 (s, C3’), 118.54 (s, C8), 116.28 (s, C6) ppm. [RuClp-cym(Py-indz)]PF6 (17): Py-indz (0.195 g, 1 mmol) was added to a [RuClp-cym(NCMe)2]PF6 (0.474 g, 1 mmol) solution in dichloromethane under nitrogen atmosphere. After two hours, the colour changed from orange to yellow. The solution was concentrated to give a yellow microcrystalline solid which was recrystallized from CH2Cl2–hexane. Yield 0.472 g, 95%. Analysis calculated for C22H23Cl1F6N3P1Ru1: C 43.25, H 3.80, N 6.88. Found: C 43.16, H 3.92, N 6.52. Orange crystals of 17 suitable for X-ray analysis were grown from CH2Cl2-ether at room temperature. 1H NMR (400 MHz, Me2CO-d6)  9.63 (d, J = 5.6 Hz, 1H, H6’), 9.11 (d, J = 7.0 Hz, 1H, H5), 8.66 (s, 1H, H1), 8.56 (d, J = 8.1 Hz, 1H, H3’), 8.29 (t, J = 7.8 Hz, 1H, H4’), 8.01 (d, J = 8.9 Hz, 1H, H8), 7.64 (t, J = 6.7 Hz, 1H, H5’), 7.44 – 7.35 (m, 1H, H7), 7.30 (t, J = 6.9 Hz, 1H, H6), 6.23 (dd, J = 12.5, 6.1 Hz, 2H, ArH), 6.00 (dd, J = 12.0, 6.0 Hz, 2H, ArH), 2.77 (s, 1H, CHiPr), 2.27 (s, 3H, CH3Ar), 1.13 (dd, J = 10.9, 6.7 Hz, 6H, CH3iPr). 13C NMR (101 MHz, acetone)  157.44 (s, C6’), 140.52 (s, C4’), 135.20 (s, C6’), 126.28 (s, C1), 125.22 (s, C5’), 124.62 (s, C7), 124.47 (s, C5), 121.68 (s, C3’), 119.46 (s, C8), 118.26 (s, C6), 105.78 (s, ArC*), 103.06 (s, ArC*), 86.55 (s, ArCH), 85.84 (s, ArCH), 85.41 (s, ArCH), 84.15 (s, ArCH’), 31.87 (s, CHiPr), 22.47 (s, CH3iPr), 22.09 (s, CH3iPr), 18.80 (s, CH3Ar). X-Ray Diffraction Study of 1 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17: diffraction data were collected using an Oxford Diffraction Supernova diffractometer, equipped with an Atlas CCD area detector and a four-circle kappa goniometer. For the data collection Mo or Cu microfocus sources with multilayer optics were used. Data integration, scaling and empirical absorption correction was carried out using the CrysAlis Pro program package. [ 39 ] The structure was solved using direct methods and refined by Full-Matrix-Least-Squares against F2 with SHELX [ 40 ] under OLEX2. [ 41 ] The non-hydrogen atoms were refined anisotropically and hydrogen atoms were placed at idealised positions and refined using the riding model. Graphics were made with OLEX2 and MERCURY. [ 42 ] Crystal data, particular details and CCDC reference numbers are given in Table 4. [ 1 ] C. M. Alvarez, L. Alvarez-Miguel, R. Garcia-Rodriguez, D. Miguel, Dalton Trans. 2012, 41, 7041-7046. [ 2 ] R. Grigg, P. Kennewell, V. Savic, V. Sridharan, Tetrahedron, 1992, 47, 10423-10430. [ 3 ] a) J. M.Crawford, M. Paoletti, Tetrahedron Lett., 2009, 50, 4916-4918. b) J. Wang, R. Mason, K. VanDerveer, D. Feng, X. R. Bu, J.Org.Chem., 2003, 68, 5415-5418. c) J. Wang, L. Jr Dyers, R. Mason, P. Amoyaw, X. R. Bu, J.Org.Chem., 2005, 70, 2353-2356. d) S. A. Siddiqui, T. M. Potewar, R. J. Lahoti, K. V. Srinivasan, Synthesis, 2006, 17, 2849-2854. e) S. V. Arvapalli, G. Chen, S. Kosarev, E. M. Tan, D. Xie, L. Yet, Tetrahedron Lett., 2010, 51, 284-286. f) M. Ostermeier, C. Limberg, B. Ziemer, V. Karunakaran, Angew. Chem., Int. Ed., 2007, 46, 5329-5331. FULL PAPER Keywords: Chelate complexes / N ligands / Ligand effects / Ligand design / D-block metals Entry for the Table of Contents FULL PAPER A thorough screening confirms the potential of the now easily available 3-(pyridin-2-yl)imidazo[1,5- a]pyridine (Py-indz) ligand in the preparation of complexes with transition and main-group metallic centers in very different environments. Alvarez, Celedonio; Alvarez-Miguel, Lucia; García-Rodríguez, Raúl; Martin- Alvarez, Jose; Miguel, Daniel*. Universidad de Valladolid, IU CINQUIMA/Quimica Inorganica Page No. – Page No. Title 3-(pyridin-2-yl)imidazo[1,5- a]pyridine (pyridylindolizine) as ligands in complexes of transition and main-group metals. *one or two words that highlight the emphasis of the paper or the field of the study