Rhodium and Iridium Complexes with Chelating C–C - ACS Publications

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Rhodium and Iridium Complexes with Chelating C−C′Imidazolylidene−Pyridylidene Ligands: Systematic Approach to Normal, Abnormal, and Remote Coordination Modes Candela Segarra, Elena Mas-Marzá,* José A. Mata, and Eduardo Peris* Departamento de Química Inorgánica y Orgánica, Universitat Jaume I, Avenida Vicente Sos Baynat s/n, Castellón E-12071, Spain S Supporting Information *

ABSTRACT: A series of linked imidazolium−pyridinium salts ([Him-pyH](X)2) have been used as imidazolylidene− pyridylidene ligand precursors for the preparation of rhodium(III) and iridium(III) complexes. The relative configuration of the [Him-pyH](X)2 salts determines whether the coordination of the pyridylidene occurs through the normal, abnormal, or remote form. In order to obtain complexes with the imidazolylidene part of the ligand coordinated through the abnormal form, salts with the C2 position of the imidazolium blocked with a methyl group were used, although the products resulting from the C−H aliphatic activation of the methyl group or the C−C cleavage of the C2−Me bond were obtained instead. The crystallographic study of three molecules allowed us to evaluate the relative trans influence of the normal, abnormal, and remote coordination forms of the pyridylidene and also to compare it to the trans influence provided by the imidazolylidene.

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INTRODUCTION The coordination chemistry of N-heterocylic carbenes (NHCs) has experienced an explosive development in the past few years not only due to the extremely large number of their catalytic applications1,2 but also due to the easy access to a large library of ligands with almost “on-demand” stereoelectronic properties.2,3 Azolium salts are often found to be excellent NHC precursors because they are generally easy to make and they provide a variety of topologies that may facilitate the preparation of metal complexes with different architectures. This versatility comes not only from the different structures available from the NHC precursors but also from the coordination modes that these preligands can afford depending on whether the “expected” (normal) or “unexpected” (abnormal) coordination modes may occur. Since Crabtree and co-workers described for the first time the abnormal (or C4) coordination of imidazolium-based NHCs, the number of such types of “wrong way”, “unusual”, or “nonclassical” imidazolylidenes has enormously increased.4,5 Abnormal carbenes not only are limited to imidazolylidenes or other five-membered ring NHCs but are also easy to find in pyridinebased NHCs, where remote carbenes (without a heteroatom adjacent to the carbene carbon) are also accessible.4,6,7 Because the chemical functionalization of imidazoles and pyridines is very well established, both imidazolylidenes and pyridylidenes can be connected to a variety of functionalities that allow them to be embedded in chelating environments.4,8 With NHC chemistry in continuous growth, and with the increasing interest in finding new coordination modes that can facilitate © 2012 American Chemical Society

ligands with novel stereoelectronic properties, we found it interesting that only a very few examples of linked imidazolylidene (or triazolylidene)−pyridylidenes have been described so far.9−11 Interestingly, the strong σ-donor properties of this type of ligand have been used for the preparation of iridium(III) complexes with excellent activity in catalytic water oxidation,11 thus exemplifying the interesting potential applications of these ligands. In response to the above background we sought to make and investigate the chemistry of transition metal complexes incorporating linked imidazolylidene−pyridylidene (C,C′-impy) ligands, in which the relative configuration of the imidazolium−pyridinium ligand precursors facilitates the systematic coordination of the chelate ligand in all possible combinations of normal, abnormal, and remote modes (Scheme 1). We herein report the systematic preparation and full characterization of a series of Ir and Rh complexes with a full set of chelate C,C′-im-py ligands. All complexes are obtained by a base-free C−H activation route under mild reaction conditions. The molecular structures of three representative complexes are also described.

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RESULTS AND DISCUSSION The [Him-pyH](X)2 salts were prepared by a two-step procedure implying the Ullmann coupling of the imidazole to Received: June 8, 2012 Published: July 5, 2012 5169

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Organometallics

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Scheme 1. Imidazolium−Pyridinium Salts Used in This Worka

a

Arrows indicate the potential coordination sites.

Scheme 2

and not for the iodides. The reason for this may be due to the high trans effect provided by the pyridylidene, which facilitates the rapid exchange between the CH3CN ligand trans to the metalated pyridine and the iodide counterion, an effect that cannot be produced with a noncoordinating anion such as hexafluorophosphate. The signals due to the pyridylidene carbene carbons display a big difference depending on whether the remote pyridylidene is coordinated to rhodium or iridium, as seen by the resonances at δ 183.9 (d, 1JRh−C = 28 Hz) for the rhodium complex 5 and at δ 164.7 and 164.8 for the iridium compounds 6-Me and 6-nBu, respectively. This almost 20 ppm shift is also displayed for the signals attributed to the carbene carbons of the imidazolylidene, which appear at δ 167.4 (d, 1 JRh−C = 43 Hz) for 5 and at δ 149.3 and 149.4 for 6-Me and 6nBu, respectively. These findings should not be considered as surprising, if we take into account similar chemical shift differences for the same type of coordinated imidazolylidene (or triazolylidene)−pyridylidene complexes of iridium10,11 and rhodium.9 When 1 reacts with [RhCl(NBD)]2 in acetonitrile in the presence of an excess of KI, under exactly the same reaction conditions as those used for the preparation of 5, a new Rh(III) complex with the normal coordination of the pyridylidene is obtained as the only isolable product, in 66% yield (compound 7 in Scheme 2). The normal coordination of the pyridylidene is confirmed by the hyperfine structure of the signals due to the pyridine ring in the 1H NMR spectrum. The 13C NMR spectrum shows the signal due to the carbene carbon atom of the pyridylidene as a doublet at 175.7 ppm (1JRh−C = 36 Hz), while the doublet due to the carbene carbon atom of the imidazolylidene appears at 162.7 (d, 1JRh−C = 42 Hz). The preparation of the rhodium and iridium complexes with the chelate C,C′-im-py ligands in which the pyridylidene is bound by the abnormal position could be achieved by using the [Him-pyH]2(I)2 salt 3 (Scheme 3). For the reactions with

the 3- or 4-bromopyridine, followed by addition of an excess of MeI (or nBuI, in the case of 1-nBu). Anion metathesis in methanol with ammonium hexafluorophosphate allowed the precipitation of the [Him-pyH](PF6)2 salt, in the case of [1Me](PF6)2. Because, in general, pyridiniums are considered less acidic than imidazoliums, we reasoned that all salts 1−4 should first coordinate to the metal via the imidazole ring and then facilitate the pyridinium C−H activation at the ortho position by chelation assistance. The reaction of 1 with [MCl(COD)]2 (M = Rh, Ir) in acetonitrile in the presence of an excess of KI affords the corresponding [(C,C′-im-py)MIIII2(CH3CN)2]+ complexes, in which the pyridylidene unequivocally coordinates to the metal center through the para carbon atom, affording the remote coordination mode rather than the coordination through the carbon adjacent to the nitrogen atom. This selectivity is remarkable, especially if we consider that previous studies with N-butyl-3-(2-pyridyl)pyridinium iodide show that the reactions with [IrCl(COD)]2 afford a mixture of two complexes, probably due to the presence of the two possible carbene types.12 Scheme 2 displays the preparation of complexes 5 and 6 as iodide salts. The hexafluorophosphate analogues were also obtained starting from [1-Me](PF6)2. All yields were above 50%. Compounds 5 and 6 were characterized by NMR spectroscopy, elemental analysis, and mass spectrometry. The assignation of the remote coordination of the pyridylidene can be easily determined by the evaluation of the hyperfine structure of the signals attributed to the protons of the pyridine ring in the corresponding 1H NMR spectra. The most representative 13C NMR signals are the ones attributed to the metalated carbons. It is important to point out that for all the rhodium complexes reported in this work the 13C NMR chemical shifts attributed to the carbene carbon of the pyridylidene could be observed only for the PF6− derivatives 5170

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Scheme 3

Scheme 4

In order to prepare complexes with the bis-abnormally bound C,C′-im-py ligand, we decided to use the [Him-pyH](I)2 salt 4, which differs from 3 by the presence of a methyl group blocking the C2 position of the imidazolium ring. Surprisingly, when the reaction between 4 and [MCl(COD)]2 (M = Rh, Ir) is carried out under similar reaction conditions to those described for the coordination of 1−3, we obtained compounds 8 and 9, as the only isolable products (Scheme 3), although this time the yields were low (20−24%). This unexpected C−C cleavage in the metalation of C2-substituted imidazoliums was first described by Crabtree for reactions implying silver oxide,14 and we are unaware of any other similar examples of such type of process regarding any other transition metals. Very recently Albrecht and co-workers described that the demethylation of a C2-Me-substituted imidazolium may take place in the presence of CsOH, forming a cyclic urea,17 which actually supports the idea previously reported by Crabtree that this demethylation may take place via an initial four-electron oxidation of the imidazolium 2-methyl to give a 2-formyl ion, followed by the hydrolytic cleavage to give the NHC,14 in our case trapped by the rhodium or iridium centers. Although we have not studied the fate of the leaving methyl group, we believe that these two previous studies may give some important mechanistic clues.14,17 Crabtree suggested that 2-Me can be an unreliable blocking group for imidazolium/Ag2O,14 but our results widen the warning to other transition metals such as Rh and Ir. While this C−C cleavage at the C2-substituted imidazolium is rare, there are many examples in which C2−H or C2−X (X = I, Cl) activations are observed.18 The molecular structures of 6-nBu, 7, 8, and 10 were confirmed by means of X-ray diffraction studies. Unfortunately, the molecular structure of complex 7 presents some disorder due to the presence of two molecules with a different orientation of the C,C′-im-py ligand, so an averaged structure, not suitable for a detailed analysis, was obtained. The crystallographic data of complex 7 can be found in the Supporting Information of this article. The molecular structure of 6-nBu (Figure 1) displays a pseudo-octahedral arrangement about the iridium center. Two iodide ligands in a relative trans configuration occupy the axial

[MCl(COD)]2 (M = Rh, Ir), the expected M(III) complexes with the abnormal coordination of the pyridylidene were obtained in moderate yields (above 50%). Again, the coordination of the chelate ligand and the type of coordination of the pyridylidene can be unambiguously determined by NMR spectroscopy. The 13C NMR spectra display the resonance due to the carbene carbon of the pyridine ring at δ 169.3 (d, 1JRh−C = 47 Hz) for 8 and δ 160.8 for 9. The signals assigned to the carbene carbon of the imidazolylidene are shown at δ 139.6 (d, 1 JRh−C = 34 Hz) and δ 152 for 8 and 9, respectively. In order to facilitate the coordination of the imidazolylidene by an abnormal coordination mode, we decided to use one [Him-pyH]2(I)2 salt with the C2 position of the imidazolium blocked with one methyl group (2, in Scheme 4). This strategy for the preparation of C4-bound imidazolylidenes has been successfully used previously.13−15 While the reaction of 2 with [RhCl(COD)]2 afforded mixtures of compounds that we were unable to indentify, the reaction with [IrCl(COD)]2 allowed the formation in good yield (65%) of an iridium(III) complex, in which the chelate ligand is coordinated through the pyridylidene and a methylene group resulting from the C−H activation of the C2-Me group at the imidazolium ring (10, Scheme 4). Although this was not our expected result, we may rationalize this result as a consequence of the kinetic preference of the aliphatic (methyl) C−H activation over the aromatic (imidazole) one in the formation of methylene-bound versus abnormally bound imidazoliums, as we have previously described.15 In our case this observation can also be supported by the kinetic preference for the formation of a sevenmembered iridacycle versus the themodynamic preference for the formation of a six-membered iridacycle, as previously described for the reactions of [IrCl(COD)]2 with C2substituted imidazoliums.16 Compound 10 was characterized by NMR spectroscopy, elemental analysis, and mass spectrometry. The remote coordination of the pyridylidene can be easily confirmed by looking at the pattern of the resonances coming from the pyridylidene ring. The 13C NMR spectrum shows significant signals at 168.9 (carbene carbon) and −25.5 (metalated methylene) ppm. 5171

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Figure 1. Molecular diagram of complex 6-nBu. Ellipsoids are at the 50% probability level. Hydrogens and counterion (iodide) are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir(1)−I(1) 2.6585(4), Ir(1)−C(1) 1.981(5), Ir(1)−I(2) 2.6610(4), Ir(1)−N(4) 2.086(4), Ir(1)−N(5) 2.122(5), Ir(1)−C(8) 1.989(5), I(1)−Ir(1)− I(2) 177.548(14), C(1)−Ir(1)−C(8) 79.7(2).

Figure 3. Molecular diagram of complex 10. Ellipsoids are at the 50% probability level. Hydrogens, counterion (iodide), and solvent (acetonitrile) are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir(1)−I(2) 2.6608(7), Ir(1)−I(3) 2.6881(6), Ir(1)− N(2) 2.102(6), Ir(1)−N(4) 2.111(8), Ir(1)−C(5) 2.003(7), Ir(1)− C(7) 2.083(8), I(2)−Ir(1)−I(3) 178.00(2), C(5)−Ir(1)−C(7) 89.0(3).

axis of the molecule. A chelate C,C′-im-py ligand and two acetonitriles complete the coordination sphere. The pyridylidene is coordinated to the metal via the remote form. The Ir− Cimz and Ir−Cpyr distances are 1.981 and 1.989 Å, respectively. The structure provides an excellent opportunity to evaluate the relative trans influence of the two different carbene ligands within the same molecule, by comparing the Ir−N distances of the acetonitriles trans to the imidazolylidene (2.086 Å) and to the pyridylidene (2.122 Å), therefore suggesting the stronger trans influence of the latter one. Figure 2 shows the molecular structure of complex 8. The molecule consists of a distorted octahedral structure with two

iodides occupying a transoid disposition (I(2)−Ir(1)−I(3) = 178.00°). The structure confirms that the chelate ligand is coordinated through the remote position of the pyridylidene and the methylene group at the C2 position of the imidazolium, forming a distorted six-membered iridacycle. The chelate bite angle is 89.0°. The Ir−N distance of the acetonitrile trans to the remote pyridylidene is 2.102 Å, similar to that found for the analogous bond in 6-nBu. The evaluation of the NMR spectroscopy and crystallographic data of the complexes described in this work reveal some features that are worth mentioning. With regard to the 13 C NMR spectroscopy, we observed that the resonances due to the carbene carbons of the pyridylidenes decrease in the order Rhodium: remote (δC = 183.9) > normal (δC = 175.7) > abnormal (δC = 169.3) Iridium: remote (δC = 164.7) > abnormal (δC = 160.8)

This trend is along the same lines as that found by Albrecht and co-workers for a series of palladium complexes with normal, abnormal, and remote pyridylidenes.7 When these 13C NMR resonances of the coordinated carbenes are compared to the corresponding resonances in the precursor pyridiniums, it is observed that abnormal bonding induces the smallest chemical shift difference. On the basis of bond length analyses of the crystal structures that we have described in this work, we can clearly state that pyridylidenes provide a larger trans influence than imidazolylidenes. By comparing the bond lengths of a series of Pd and Ni complexes with different pyridylidenes and imidazolylidenes, it was previously stated that remote pyridylidenes exhibit larger trans influence than imidazolylidenes.19,20 It was also suggested that carbene ligands with remote heteroatoms display a greater trans influence than those with the N atom adjacent to the carbene carbon.20 However, we did not find any studies in which a clear comparison between remote and abnormal pyridylidenes was made. By evaluating the bond distances of complexes 6-nBu and 8, we can now confirm that both

Figure 2. Molecular structure of compound 8. Ellipsoids are at the 50% probability level. Hydrogens and counterion (iodide) are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Rh(1)−I(2) 2.6666(6), Rh(1)−I(3) 2.6504(6), Rh(1)−N(18) 2.096(5), Rh(1) − C(11) 1.995(6), Rh(1)−C(4) 1.962(6), Rh(1)−N(21) 2.127(5), I(3)−Rh(1)−I(2) 177.99(2), C(4)−Rh(1)−C(11) 79.6(2).

transoid iodides. The chelate C,C′-im-py ligand is coordinated through the abnormal position of the pyridylidene and forms a five-membered rhodacycle, with a chelate bite angle of 79.6°. The Ir−Cimz and Ir−Cpyr distances are 1.962 and 1.995 Å, respectively. Again, the structure offers a good opportunity to evaluate the relative trans influence of the two types of carbenes, by comparing the Rh−N distances of the acetonitriles trans to the imidazolylidene (2.096 Å) and pyridylidene (2.127 Å), therefore confirming the stronger trans influence of the latter one. The molecular structure of 10 is shown in Figure 3. The molecule consists of a distorted octahedral structure with two 5172

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dide precipitated in the reaction media as a pale yellow solid. The compound was isolated by filtration, washed with diethyl ether (3 × 5 mL), and dried under vacuum. Yield: 4.90 g (71%). For 1-(3′pyridyl)imidazole: 1H NMR (500 MHz, DMSO-d6, 303 K): δ 8.95 (s, 1H, CHpyr), 8.57 (d, 3JHH = 4 Hz, 1H, CHpyr), 8.35 (s, 1H, CHimz), 8.11 (d, 3JHH = 8 Hz, 1H, CHpyr), 7.84 (s, 1H, CHimz), 7.57 (dd, 3JHH = 4 Hz, 3JHH = 8 Hz, 1H, CHpyr), 7.16 (s, 1H, CHimz). For [1-(3′-(1′methylpyridiniumyl)-3-methyl]imidazolium diiodide: 1H NMR (500 MHz, DMSO-d6, 303 K): δ 9.94 (s, 1H, CHpyr), 9.72 (s, 1H, CHimz), 9.18 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.97 (d, 3JHH = 8 Hz, 1H, CHpyr), 8.46 (dd, 3JHH = 6 Hz, 3JHH = 8 Hz, 1H, CHpyr), 8.35 (s, 1H, CHimz), 8.06 (s, 1H, CHimz), 4.45 (s, 3H, CH3pyr), 4.03 (s, 3H, CH3imz). 13C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ 145.9, 140.5, 138.0, 137.3, 133.6, 128.2, 124.9, 121.1 (s, CHimz, Cpyr and CHpyr), 48.7 (s, CH3pyr), 36.7 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 174.1 [M − 2I − H]+, m/z 87.8 [M − 2I]2+. Anal. Found (calcd) for C10H13N3I2: C, 28.43 (27.99); H, 2.75 (3.05); N, 9.50 (9.79). Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-3-methyl]imidazolium Di(hexafluorophosphate), [1-Me](PF6)2. NH4PF6 (1.14 g, 7 mmol) was added slowly to a solution of 1-Me (1.00 g, 2.33 mmol) in methanol (25 mL). The mixture was stirred at room temperature for 2 h. During this time [1-Me](PF6)2 precipitated in the reaction media as a colorless solid. The compound was isolated by filtration, washed with cold methanol (3 × 5 mL) and diethyl ether (3 × 5 mL), and dried under vacuum. Yield: 0.83 g (77%). 1H NMR (500 MHz, DMSO-d6, 303 K): δ 9.95 (s, 1H, CHpyr), 9.73 (s, 1H, CHimz), 9.18 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.97 (d, 3JHH = 8 Hz, 1H, CHpyr), 8.45 (dd, 3JHH = 6 Hz, 3JHH = 8 Hz, 1H, CHpyr), 8.35 (s, 1H, CHimz), 8.05 (s, 1H, CHimz), 4.45 (s, 3H, CH3pyr), 4.02 (s, 3H, CH3imz). 13 C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ 146.1, 140.6, 138.2, 137.4, 133.9, 128.3, 125.1, 121.2 (s, CHimz, Cpyr and CHpyr), 48.7 (s, CH3pyr), 36.7 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 174.1 [M − 2(PF)6 − H]+, m/z 87.7 [M − 2(PF6)]2+. Anal. Found (calcd) for C10H13N3P2F12: C, 26.13 (25.82); H, 2.93 (2.82); N, 9.31 (9.03). Synthesis of [1-(3′-(1′-n-Butylpyridiniumyl)-3-n-butyl]imidazolium Diiodide, 1-nBu. The same procedure and quantities as compound 1-Me were used, except with the use of 1-iodobutane (5.5 mL, 48 mmol). Yield: 4.0 g (50%). 1H NMR (500 MHz, DMSOd6, 303 K): δ 10.06 (s, 1H, CHpyr), 9.84 (s, 1H, CHimz), 9.31 (d, 3JHH = 6 Hz, 1H, CHpyr), 9.04 (d, 3JHH = 8 Hz, 1H, CHpyr), 8.50 (dd, 3JHH = 6 Hz, 3JHH = 8 Hz, 1H, CHpyr), 8.45 (s, 1H, CHimz), 8.18 (s, 1H, CHimz), 4.72 (t, 3JHH = 7 Hz, 2H, CH2pyr), 4.35 (t, 3JHH = 7 Hz, 2H, CH2imz), 2.01 (m, 2H, CH2CH2pyrCH2), 1.90 (m, 2H, CH2CH2imzCH2), 1.36 (m, 4H, CH2CH3), 0.94 (t, 3JHH = 7 Hz, 6H, CH3). 13C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ 145.0, 139.6, 138.4, 136.7, 134.4, 128.5, 123.7, 121.5 (s, CHimz, Cpyr and CHpyr), 61.4 (s, CH2pyr), 49.5 (s, CH2imz), 32.2 (s, CH2CH2pyrCH2), 30.9 (s, CH2CH2imzCH2), 18.7 (s, CH2pyrCH3), 18.6 (s, CH2imzCH3), 13.3 (s, CH3pyr), 13.2 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 202.1 [M − 2I − nBu]+, m/z 258.0 [M − 2I − H]+. Anal. Found (calcd) for C16H25N3I2: C, 37.67 (37.45); H, 5.02 (4.91); N, 8.03 (8.19). Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-2,3-dimethyl]imidazolium Diiodide, 2. A 50 mL Schlenk flask was charged with 2-methylimidazole (1.04 g, 12.66 mmol), 3-bromopyridine (0.61 mL, 6.33 mmol), CuSO4 (40 mg, 0.25 mmol), and K2CO3 (1.31 g, 9.49 mmol). The reaction mixture was heated for 48 h to 185 °C under a nitrogen atmosphere. The reaction mixture was then allowed to cool to room temperature, and the resulting brown solid was dissolved in 50 mL of H2O and extracted with ethyl acetate, to obtain 1-(3′-pyridyl)-2-methylimidazole and unreacted 2-methylimidazole. This mixture, without further purification, was refluxed with iodomethane (1.18 mL, 19 mmol) in CH3CN (20 mL) for 24 h. During this time [1-(3′-(1′-methylpyridiniumyl)-2,3-dimethyl]imidazolium diiodide precipitated in the reaction media as a pale yellow solid. The compound was isolated by filtration, washed with ether (3 × 5 mL), and dried under vacuum. Yield: 1.12 g (35%). For 1-(3′-pyridyl)-2-methylimidazole: 1H NMR (300 MHz, CDCl3, 303 K): δ 8.67 (m, 1H, CHpyr), 8.62 (m, 1H, CHpyr), 7.65 (m, 1H, CHpyr), 7.45 (m, 1H, CHpyr), 7.07 (d, 3JHH = 1.5 Hz, 1H, CHimz), 7.02 (d, 3JHH = 1.5 Hz, 1H, CHimz), 2.37 (s, 3H, C−CH3imz). For [1-(3′-(1′-

abnormal and remote pyridylidenes provide a larger trans influence that normal imidazolylidenes. Although the remotely bound complex 6-nBu and the abnormally bound compound 8 contain different metals (iridium and rhodium, respectively), we can estimate the relative trans influence between these two types of pyridylidenes by comparing with the trans influence provided by the imidazolylidene in each complex. In this regard, the Ir−N bond distance of the acetonitrile trans to the remote pyridylidene is larger by 1.7% than the Ir−N distance of the acetonitrile trans to the imidazolylidene in complex 6-nBu. The analogous comparison for the Rh−N distances in complex 7 affords a similar bond length increase (1.5%), which may be interpreted as a consequence of a similar trans influence provided by the remote and abnormal pyridylidenes.

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CONCLUSIONS In this work we have shown the systematic preparation of the series of imidazolylidene−pyridylidene complexes of rhodium(III) and iridium(III) with the three possible types of coordination of the pyridylidene (normal, abnormal, and remote). Attempts to obtain analogous complexes with the abnormal coordination of the imidazolylidene by using a C2Me-substituted imidazolium resulted in the aliphatic C−H activation of the methyl group, affording the methylene-bound imidazolium, or C−C bond cleavage, affording the demethylated products, which are similar to the products obtained when nonsubstituted imidazoliums were used. Although the aliphatic C−H activation of the methyl group in C2-Me-substituted imidazoliums has already been described for iridium and rhodium complexes,15,16 this is the first time that the demethylation is observed for these two metals. In any case, the difficulties in achieving the abnormal coordination of the imidazolylidene when a pyridylidene is bound to the metal are remarkable and may deserve further studies. The evaluation of the crystal structures of complexes 6-nBu, 8, and 10 allows us to evaluate the relative trans influence of the pyridylidene and the imidazolylidene. Both remote and abnormal coordinations of the pyridylidene provide similar trans influence, this being larger than the one provided by the imidazolylidene.

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EXPERIMENTAL SECTION

General Procedures. All manipulations were performed under a nitrogen atmosphere using standard Schlenk techniques. Solvents and reagents are commercially available and were used as received from commercial suppliers. NMR spectra were recorded on Varian Innova 300 and 500 MHz spectrometers, using CDCl3, CD3CN, and DMSOd6 as solvents (Merck and Aldrich). Elemental analyses were carried out in an EA 1108 CHNS-O Carlo Erba analyzer. Electrospray mass spectra (ESI-MS) were recorded on a Micromass Quattro LC instrument, and nitrogen was employed as drying and nebulizing gas. A solution of leucine enkephalin (m/z = 556.2771) was employed as standard. [IrCl(COD)]2,21 [RhCl(COD)]2,22 and [RhCl(NBD)]223 were prepared according to literature procedures. Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-3-methyl]imidazolium Diiodide, 1-Me. Imidazole (2.18 g, 32 mmol), 3bromopyridine (1.54 mL, 16 mmol), CuSO4 (100 mg, 0.60 mmol), and K2CO3 (2.95 g, 21 mmol) were heated in a 50 mL Schlenk flask at 150 °C for 48 h under a nitrogen atmosphere. After this time, the reaction mixture was cooled to room temperature, and the resulting brown solid was dissolved in 50 mL of H2O and extracted with ethyl acetate to obtain 1-(3′-pyridyl)imidazole and unreacted imidazole. This mixture, without further purification, was refluxed with iodomethane (3 mL, 48 mmol) in CH3CN (20 mL) for 24 h. During this time [1-(3′-(1′-methylpyridiniumyl)-3-methyl]imidazolium diio5173

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Organometallics

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methylpyridyl)-2,3-dimethyl]imidazolium diiodide: 1H NMR (300 MHz, DMSO-d6, 303 K): δ 9.54 (s, 1H, CHpyr), 9.24 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.86 (d, 3JHH = 8 Hz, 1H, CHpyr), 8.43 (dd, 3JHH = 8 Hz, 3 JHH = 6 Hz, 1H, CHpyr), 8.01 (d, 3JHH = 2.4 Hz, 1H, CHimz), 7.95 (d, 3 JHH = 2.4 Hz, 1H, CHimz), 4.44 (s, 3H, CH3pyr), 3.90 (s, 3H, CH3imz), 2.67 (s, 3H, C−CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K): δ 146.7, 146.5, 144.3, 142.6, 133.6, 128.4, 123.4, 122.0 (s, Cimz, CHimz, Cpyr and CHpyr), 48.6 (s, CH3pyr), 35.5 (s, CH3imz), 11.1 (s, C-CH3imz). ESI-MS (20 V, CH3OH): m/z 94.5 [M − 2I]2+. Anal. Found (calcd) for C11H15N3I2: C, 29.67 (29.82); H, 3.19 (3.41); N, 9.42 (9.48). Synthesis of [1-(4′-(1′-Methylpyridiniumyl)-3-methyl]imidazolium Diiodide, 3. Imidazole (0.70 g, 10.28 mmol), 4bromopyridine hydrochloride (1.00 g, 5.14 mmol), CuSO4 (32.8 mg, 0.21 mmol), and K2CO3 (2.13 g, 15.43 mmol) were heated in a 50 mL Schlenk flask at 185 °C for 72 h under a nitrogen atmosphere. After this time, the reaction mixture was cooled to room temperature, and the resulting brown solid was dissolved in 50 mL of H2O and extracted with ethyl acetate, to obtain 1-(4′-pyridyl)imidazole and unreacted imidazole. This mixture, without further purification, was refluxed with 1-iodomethane (1 mL, 15,42 mmol) in CH3CN (20 mL) for 24 h. During this time [1-(4′-(1′-methylpyridiniumyl)-3-methyl]imidazolium diiodide precipitated in the reaction media as a yellow solid. The compound was isolated by filtration, washed with ether (3 × 5 mL), and dried under vacuum. Yield: 1.17 g (53%). For 1-(4′-pyridyl)imidazole: 1H NMR (300 MHz, CDCl3, 303 K): δ 8.68 (m, 2H, CHpyr), 8.01 (s, 1H, CHimz), 7.38 (s, 1H, CHimz), 7.33 (m, 2H, CHpyr), 7.23 (s, 1H, CHimz). For [1-(4′-(1′-methylpyridyl)-3-methyl]imidazolium diiodide: 1H NMR (300 MHz, DMSO-d6, 303 K): δ 10.28 (s, 1H, CHimz), 9.33 (d, 3JHH = 6.5, 2H, CHpyr), 8.62 (s, 1H, CHimz), 8.57 (d, 3JHH = 6.5 Hz, 2H, CHpyr), 8.09 (s, 1H, CHimz), 4.40 (s, 3H, CH3pyr), 4.01 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K): δ 148.0, 146.1, 138.2, 125.4, 120.0, 118.1 (s, CHimz, Cpyr and CHpyr), 47.9 (s, CH3pyr), 36.9 (s, CH3imz). Anal. Found (calcd) for C10H13N3I2: C, 27.89 (27.99); H, 2.98 (3.05); N, 9.70 (9.79). Synthesis of [1-(4′-(1′-Methylpyridiniumyl)-2,3-dimethyl]imidazolium Diiodide, 4. The same procedure and quantities as compound 3 were used, except with the use of 2-methylimidazole (0.84 g, 10.28 mmol). Yield: 0.757 g (33%). For 1-(4′-pyridyl)-2methylimidazole: 1H NMR (300 MHz, CDCl3, 303 K): δ 8.66 (m, 2H, CHpyr), 7.20 (m, 2H, CHpyr), 7.02 (d, 3JHH = 1.5 Hz, 1H, CHimz), 6.98 (d, 3JHH = 1.5 Hz, 1H, CHimz), 2.39 (s, 1H, C−CH3imz). For [1(4′-(1′-methylpyridyl)-2,3-dimethyl]imidazolium diiodide: 1H NMR (300 MHz, DMSO-d6, 303 K): δ 9.32 (d, 3JHH = 6 Hz, 2H, CHpyr), 8.44 (d, 3JHH = 6 Hz, 2H, CHpyr), 8.13 (s, 1H, CHimz), 7.99 (s, 1H, CHimz), 4.46 (s, 3H, CH3pyr), 3.91 (s, 3H, CH3imz), 2.72 (s, 3H, C− CH3imz). 13C{1H} (75 MHz, DMSO-d6, 303 K): δ 148.0, 146.9, 146.4, 124.1, 123.9, 121.2 (s, Cimz, CHimz, Cpyr and CHpyr), 48.2 (s, CH3pyr), 35.6 (s, CH3imz), 11.8 (s, C-CH3imz). Anal. Found (calcd) for C11H15N3I2: C, 29.73 (29.82); H, 3.06 (3.41); N, 9.24 (9.48). Synthesis of Compound 5. A mixture of [1-(3′-(1′-methylpyridiniumyl)-3-methyl]imidazolium diiodide (1-Me; 87 mg, 0.2 mmol), [RhCl(cod)]2 (50 mg, 0.1 mmol), and KI (34 mg, 0.2 mmol) were dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a yellow band containing [RhCl(COD)]2. Further elution with CH2Cl2/CH3CN (1:1) afforded the separation of a red band that contained compound 5. Compound 5 was obtained as a red solid by precipitation from CH3CN/Et2O. Yield: 72.5 mg (50%). 1H NMR (300 MHz, CD3CN, 303 K): δ 8.86 (s, 1H, CHpyr), 8.45 (d, 3 JHH = 6 Hz, 1H, CHpyr), 8.08 (d, 3JHH = 2 Hz, 1H, CHimz), 7.95 (d, 3 JHH = 6 Hz, 1H, CHpyr), 7.37 (d, 3JHH = 2 Hz, 1H, CHimz), 4.28 (s, 3H, CH3pyr), 3.99 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): the signal corresponding to Rh-Cimz could not be observed, δ 183.6 (d, 1JRh−C = 28 Hz, Rh-Cpyr), 147.5 (s, Cpyr), 137.0 (s, CHpyr), 136.4 (s, CHpyr), 126.9 (s, CHimz), 125.2 (s, CHpyr), 117.8 (s, CHimz), 47.7 (s, CH3pyr), 38.3 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 611.7 [M − I]+, m/z 570.7 [M − I − CH3CN]+. Anal. Found (calcd) for C14H17N5I3Rh: C, 28.43 (28.76); H, 2.75 (2.32); N, 9.50 (9.48).

Synthesis of Compound [5]PF6. The same procedure and quantities as compound 5 were used, except with the use of [1-(3′-(1′methylpyridiniumyl)-3-methyl]imidazolium di(hexafluorophosphate) ([1-Me](PF6)2; 94 mg, 0.2 mmol). The compound was purified by column chromatography. Elution with CH2Cl2 separated a yellow band containing [RhCl(COD)]2. Further elution with CH2Cl2/ CH3CN (9:1) afforded the separation of an orange band that contained compound [5]PF6. Compound [5]PF6 was obtained as an orange solid by precipitation from CH3CN/Et2O. Yield: 85 mg (56%). 1 H NMR (300 MHz, CD3CN, 303 K): δ 8.42 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.34 (s, 1H, CHpyr), 7.87 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.80 (d, 3 JHH = 2 Hz, 1H, CHimz), 7.34 (d, 3JHH = 2 Hz, 1H, CHimz), 4.22 (s, 3H, CH3pyr), 3.99 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): δ 183.9 (d, 1JRh−C = 28 Hz, Rh-Cpyr), 167.4 (d, 1JRh−C = 43 Hz, Rh-Cimz), 147.5 (s, Cpyr), 136.9 (s, CHpyr), 136.4 (s, CHpyr), 127.0 (s, CHimz), 124.8 (s, CHpyr), 117.2 (s, CHimz), 47.8 (s, CH3pyr), 38.3 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 570.9 [M − PF6 − CH3CN]+, m/z 529.9 [M − PF6 − (CH3CN)2]+. Anal. Found (calcd) for C14H17N5I2RhPF6: C, 22.43 (22.21); H 2.25 (2.26); N 9.43 (9.25). Synthesis of Compound 6-Me. A mixture of [1-(3′-(1′methylpyridiniumyl)-3-methyl]imidazolium diiodide (1-Me; 64 mg, 0.15 mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a minor red band containing [IrCl(COD)]2. Further elution with CH2Cl2/CH3CN (1:1) afforded the separation of an orange band that contained compound 6-Me. Compound 6-Me was obtained as an orange solid by precipitation from CH3CN/Et2O. Yield: 74 mg (60%). 1H NMR (300 MHz, CD3CN, 303 K): δ 8.75 (s, 1H, CHpyr), 8.23 (d, 3JHH = 7 Hz, 1H, CHpyr), 7.92 (s, 1H, CHimz), 7.78 (d, 3JHH = 7 Hz, 1H, CHpyr), 7.32 (s, 1H, CHimz), 4.22 (s, 3H, CH3pyr), 4.00 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K): δ 164.7 (s, Ir-Cpyr), 148.1 (s, Ir-Cimz), 146.8 (s, Cpyr), 136.2 (s, CHpyr), 133.8 (s, CHpyr), 126.3 (s, CHimz), 123.6 (s, CHpyr), 115.3 (s, CHimz), 46.0 (s, CH3pyr), 42.6 (s, CH3imz). ESI-MS (15 V, CH3CN): m/z 701.9 [M − I]+, m/z 660.9 [M − I − CH3CN]+. Anal. Found (calcd) for C14H17N5I3Ir: C, 20.46 (20.30); H, 1.99 (2.07); N, 8.50 (8.46). Synthesis of Compound [6-Me]PF6. The same procedure and quantities as compound 6-Me were used, except with the use of [1-(3′(1′-methylpyridiniumyl)-3-methyl]imidazolium di(hexafluorophosphate) ([1-Me](PF6)2; 70 mg, 0.15 mmol). The compound was purified by column chromatography. Elution with CH2Cl2 separated a red band containing [IrCl(COD)]2. Further elution with CH2Cl2/CH3CN (9:1) afforded the separation of a yellow band that contained compound [6-Me]PF6. Compound [6-Me]PF6 was obtained as a yellow solid by precipitation from CH3CN/Et2O. Yield: 70 mg (55%). 1H NMR (300 MHz, CD3CN, 303 K): δ 8.32 (s, 1H, CHpyr), 8.20 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.72 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.68 (s, 1H, CHimz), 7.30 (s, 1H, CHimz), 4.17 (s, 3H, CH3pyr), 4.01 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): δ 164.6 (s, Ir-Cpyr), 149.3 (s, Ir-Cimz), 145.7 (s, Cpyr), 138.0 (s, CHpyr), 134.8 (s, CHpyr), 125.7 (s, CHimz), 124.2 (s, CHpyr), 116.7 (s, CHimz), 47.5 (s, CH3pyr), 37.7 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 701.9 [M − PF6]+, m/z 660.8 [M − PF6 − CH3CN]+. Anal. Found (calcd) for C14H17N5I2IrPF6: C, 19.93 (19.87); H, 2.07 (2.02); N, 8.41 (8.28). Synthesis of Compound 6-nBu. Same procedure and quantities as compound 6-Me, but using [1-(3′-(1′-n-butylpyridiniumyl)-3-nbutyl]imidazolium diiodide (1-nBu; 77 mg, 0.15 mmol). Compound purified by column chromatography. Elution with CH2Cl2 separated a red band containing [IrCl(COD)]2. Further elution with CH2Cl2/ CH3CN (7:3) afforded the separation of an orange band that contained compound 6-nBu. Compound 6-nBu was obtained as an orange solid by precipitation from CH3CN/Et2O. Crystals suitable for X-ray crystallography were obtained from a concentrated solution of compound 6-nBu in CH3CN. Yield: 68 mg (50%). 1H NMR (500 MHz, CD3CN, 303 K): δ 8.59 (s, 1H, CHpyr), 8.24 (d, 3JHH = 6 Hz, 5174

dx.doi.org/10.1021/om3005096 | Organometallics 2012, 31, 5169−5176

Organometallics

Article

CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite and all volatiles were removed under reduced pressure. The crude solid was purified as explained in method a. Yield: 29 mg (20%). 1H NMR (300 MHz, DMSO-d6, 303 K): δ 9.12 (s, 1H, CHpyr), 8.74 (d, 3JHH = 11 Hz, 1H, CHpyr), 8.44 (d, 1H, 3JHH = 4 Hz, CHimz), 8.12 (d, 3JHH = 11 Hz, 1H, CHpyr), 7.72 (d, 3JHH = 4 Hz, 1H, CHimz), 4.29 (s, 3H, CH3pyr), 4.03 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K): δ 169.3 (d, 1JRh−C = 47 Hz, Rh-Cpyr), 157.9 (s, Cpyr), 153.5 (s, CHpyr), 143.1(s, CHpyr), 139.6 (d, 1JRh−C = 34 Hz, Rh-Cimz), 127.0 (s, CHpyr), 117.5 (CHimz), 109.0 (s, CHimz), 47.3 (s, CH3pyr), 35.9 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 570.7 [M − I − CH3CN]+, m/z 529.7 [M − I − (CH3CN)2]+. Anal. Found (calcd) for C14H17N5I3Rh: C, 22.89 (22.76); H, 2.26 (2.32); N, 9.36 (9.48). Synthesis of Compound 9. Method a. A mixture of [1-(4′-(1′methylpyridiniumyl)-3-methyl]imidazolium diiodide (3; 64 mg, 0.15 mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a red band containing [IrCl(COD)]2. Further elution with CH2Cl2/CH3CN (9:1) afforded the separation of a yellow band that contained compound 9. Compound 9 was obtained as a yellow solid by precipitation from CH3CN/Et2O. Yield: 70 mg (56%). Method b. A mixture of [1-(4′-(1′-methylpyridiniumyl)-2,3dimethyl]imidazolium diiodide (4; 66 mg, 0.15 mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified as explained in method a. Yield: 30 mg (24%). 1H NMR (500 MHz, CD3CN, 303 K): δ 8.42 (s, 1H, CHpyr), 8.04 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.80 (d, 1H, 3JHH = 2 Hz, CHimz), 7.69 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.33 (d, 3JHH = 2 Hz, 1H, CHimz), 4.21 (s, 3H, CH3pyr), 4.04 (s, 3H, CH3imz). 13C{1H} NMR (125 MHz, CD3CN, 303 K): δ 160.8 (s, Ir-Cpyr), 152.0 (s, Ir-Cimz), 148.4 (s, CHpyr), 142.4 (s, CHpyr), 128.5 (s, Cpyr), 125.4 (s, CHpyr), 116.6 (s, CHimz), 107.6 (s, CHimz), 47.1 (s, CH3pyr), 36.9 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 701.9 [M − I]+, m/z 660.8 [M − I − CH3CN]+. Anal. Found (calcd) for C14H17N5I3Ir: C, 20.18 (20.30); H, 2.32 (2.07); N, 8.72 (8.86). Synthesis of Compound 10. A mixture of [1-(3′-(1′-methylpyridiniumyl)-2,3-dimethyl]imidazolium diiodide (2; 67 mg, 0.15 mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was dissolved in CH3CN (20 mL) and refluxed for 18 h. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a red band containing [IrCl(COD)]2. Further elution with CH2Cl2/ CH3CN (1:1) afforded the separation of an orange band that contained compound 10. Compound 10 was obtained as an orange solid by precipitation from CH3CN/Et2O. Slow diffusion of Et2O into a concentrated solution of compound 10 in CH3CN gave crystals suitable for X-ray crystallography. Yield: 78 mg (62%). 1H NMR (300 MHz, CD3CN, 303 K): δ = 8.51 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.21 (s, 1H, CHpyr), 7.63 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.52 (d, 3JHH = 2 Hz, 1H, CHimz), 7.16 (d, 3JHH = 2 Hz, 1H, CHimz), 4.10 (s, 3H, CH3pyr), 3.99 (s, 2H, Ir−CH2imz), 3.72 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): δ 168.9 (s, Ir-Cpyr), 163.5 (s, Cimz), 145.6 (s, CHpyr), 144.8 (s, Cpyr), 135.1 (s, CHpyr), 130.0 (s, CHpyr), 122.2 (s, CHimz), 118.7 (s, CHimz), 46.8 (s, CH3pyr), 35.8 (s, CH3imz), −25.5 (s, Ir-CH2imz). ESI-MS (20 V, CH3CN): m/z 674.0 [M − I − CH3CN]+, m/z 633.9 [M − I − (CH3CN)2]+. Anal. Found (calcd) for C15H19N5I3Ir: C, 21.43 (21.39); H, 2.35 (2.27); N, 8.23 (8.31). X-ray Crystal Structure Determinations. Diffraction data were collected on a Agilent SuperNova diffractometer equipped with an Atlas CCD detector using Mo Kα radiation (λ = 0.71073 Å). Single crystals were mounted on a MicroMount polymer tip (MiteGen) in a random orientation. Absorption corrections based on the multiscan method were applied.24 Structures were solved by direct methods in

1H, CHpyr), 7.86 (s, 1H, CHimz), 7.80 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.33 (s, 1H, CHimz), 4.40 (t, 3JHH = 7.5 Hz, 2H, NCH2pyr), 4.35 (t, 3JHH = 7.5 Hz, 2H, NCH2imz), 1.98 (m, 4H, CH2CH2CH2), 1.42 (m, 2H, CH2pyrCH3), 1.37 (m, 2H, CH2imzCH3), 0.98 (m, 6H, CH3). 13C{1H} NMR (125 MHz, CD3CN, 303 K): δ 164.8 (s, Ir-Cpyr), 149.4 (s, IrCimz), 146.8 (s, Cpyr), 137.1 (s, CHpyr), 134.9 (s, CHpyr), 124.7 (s, CHimz), 123.4 (s, CHpyr), 117.3 (s, CHimz), 60.9 (s, CH2pyr), 49.9 (s, CH2imz), 33.5 (s, CH2CH2pyrCH2), 32.4 (s, CH2CH2imzCH2), 20.4 (s, CH2pyrCH3), 20.1 (s, CH2imzCH3), 14.1 (s, CH3pyr), 13.7 (s, CH3imz). ESI-MS (15 V, CH3CN): m/z 786 [M − I]+, m/z 745 [M − I − CH3CN]+. Anal. Found (calcd) for C20H29N5I3Ir: C, 26.45 (26.33); H 3.00 (3.20); N 7.80 (7.68). Synthesis of Compound 7. A mixture of [1-(3′-(1′-methylpyridiniumyl)-3-methyl]imidazolium diiodide (1-Me; 93 mg, 0.22 mmol), [RhCl(NBD)]2 (50 mg, 0.11 mmol), and KI (36 mg, 0.22 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite, and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a yellow band containing [RhCl(NBD)]2. Further elution with CH2Cl2/CH3CN (1:1) afforded the separation of a red band that contained compound 7. Compound 7 was obtained as a red solid by precipitation from CH3CN/Et2O. Slow diffusion of Et2O into a concentrated solution of compound 7 in CH3CN gave crystals suitable for X-ray crystallography. Yield: 107 mg (66%). 1H NMR (500 MHz, DMSO-d6, 303 K): δ 8.60 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.30 (d, 3JHH = 2 Hz, 1H, CHimz), 8.17 (d, 3JHH = 8 Hz, 1H, CHpyr), 7.63 (d, 3JHH = 2 Hz, 1H, CHimz), 7.54 (dd, 3JHH = 6 Hz, 3JHH = 8 Hz, 1H, CHpyr), 4.52 (s, 3H, CH3pyr), 4.04 (s, 3H, CH3imz). 13C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ the signals corresponding to the two Rh-C could not be observed, 147.7 (s, Cpyr), 143.0 (s, CHpyr), 127.2 (s, CHimz), 121.1 (s, CHpyr), 119.1 (s, CHpyr), 117.0 (s, CHimz), 51.6 (s, CH3pyr), 37.1 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 571.0 [M − I − CH3CN]+, m/z 529.9 [M − I − (CH3CN)2]+. Anal. Found (calcd) for C14H17N5I3Rh: C, 28.43 (28.76); H, 2.75 (2.32); N, 9.50 (9.48). Synthesis of Compound [7]PF6. The same procedure and quantities as compound 7 were used, except with the use of [1-(3′-(1′methylpyridiniumyl)-3-methyl]imidazolium di(hexafluorophosphate) ([1-Me](PF6)2; 101 mg, 0.22 mmol). The compound was purified by column chromatography. Elution with CH2Cl2 separated a yellow band containing [RhCl(NBD)]2. Further elution with CH2Cl2/ CH3CN (9:1) afforded the separation of an orange band that contained compound [7]PF6. Compound [7]PF6 was obtained as an orange solid by precipitation from CH3CN/Et2O. Yield: 88 mg (54%). 1 H NMR (300 MHz, CD3CN, 303 K): δ 8.36 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.93 (d, 3JHH = 8 Hz, 1H, CHpyr), 7.85 (s, 1H, CHimz), 7.47 (m, 1H, CHpyr), 7.34 (s, 1H, CHimz), 4.52 (s, 3H, CH3pyr), 4.03 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): δ 175.7 (d, 1JRh−C = 36 Hz, Rh-Cpyr), 162.7 (d, 1JRh−C = 42 Hz, Rh-Cimz), 148.1 (s, Cpyr), 143.7 (s, CHpyr), 127.8 (s, CHimz), 122.7 (s, CHpyr), 121.5 (s, CHpyr), 117.4 (s, CHimz), 54.7 (s, CH3pyr), 39.0 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 529.8 [M − PF6 − (CH3CN)2]+. Anal. Found (calcd) for C14H17N5I2RhPF6: C, 22.38 (22.21); H, 2.33 (2.26); N, 9.20 (9.25). Synthesis of Compound 8. Method a. A mixture of [1-(4′-(1′methylpyridiniumyl)-3-methyl]imidazolium diiodide, (3; 87 mg, 0.2 mmol), [RhCl(COD)]2 (50 mg, 0.1 mmol), and KI (34 mg, 0.2 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room temperature, the reaction mixture was filtered over Celite and all volatiles were removed under reduced pressure. The crude solid was purified by column chromatography. Elution with CH2Cl2 separated a yellow band containing [RhCl(COD)]2. Further elution with CH2Cl2/CH3CN (7:3) afforded the separation of an orange band that contained compound 8. Compound 8 was obtained as an orange solid by precipitation from CH3CN/Et2O. Slow diffusion of Et2O into a concentrated solution of compound 8 in CH3CN gave crystals suitable for X-ray crystallography.Yield: 79 mg (54%). Method b. A mixture of [1-(4′-(1′-methylpyridiniumyl)-2,3dimethyl]imidazolium diiodide (4; 90 mg, 0.2 mmol), [RhCl(COD)]2 (50 mg, 0.01 mmol), and KI (34 mg, 0.2 mmol) was dissolved in 5175

dx.doi.org/10.1021/om3005096 | Organometallics 2012, 31, 5169−5176

Organometallics

Article

SHELXS-97 and refined by the full-matrix method based on F2 with the program SHELXL-97 using the OLEX software package.25 Crystal Data and Structure Refinement for Complex 6-nBu. C20H29N5I3Ir, M = 912.38, triclinic, a = 8.1564(4) Å, b = 13.2101(6) Å, c = 14.2977(7) Å, α = 108.985(4)°, β = 102.089(4)°, γ = 98.667(4) °, V = 1383.96(11) Å3, T = 293(2), space group P1̅ (no. 2), Z = 2, μ(Mo Kα) = 8.185, 17 980 reflections measured, 6199 unique (Rint = 0.0321), which were used in all calculations. The final wR2 was 0.0769 (all data), and R1 was 0.0322 (>2σ(I)). Crystal Data and Structure Refinement for Complex 8. C14H17I3N5Rh, M = 738.94, monoclinic, a = 11.3673(4) Å, b = 24.5851(7) Å, c = 7.6286(3) Å, β = 100.612(3)°, V = 2095.48(12) Å3, T = 199.95(10), space group P21/c (no. 14), Z = 4, μ(Mo Kα) = 5.240, 24 019 reflections measured, 5217 unique (Rint = 0.0414), which were used in all calculations. The final wR2 was 0.1056 (all data), and R1 was 0.0417 (>2σ(I)). Crystal Data and Structure Refinement for Complex 10. C17H22I3IrN6, M = 883.31, triclinic, a = 10.1810(6) Å, b = 11.0855(5) Å, c = 12.6852(7) Å, α = 107.112(4)°, β = 94.167(4)°, γ = 112.461(5)°, V = 1236.42(11) Å3, T = 220(2), space group P1̅ (no. 2), Z = 2, μ(Mo Kα) = 9.158, 27 397 reflections measured, 6297 unique (Rint = 0.0658), which were used in all calculations. The final wR2 was 0.1252 (all data), and R1 was 0.0462 (>2σ(I)).

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G.; Kruger, G. J.; Otte, R.; Van Zyl, W. E.; Olivier, P. J. Organomet. Chem. 1994, 466, 291. (7) Stander-Grobler, E.; Schuster, O.; Heydenrych, G.; Cronje, S.; Tosh, E.; Albrecht, M.; Frenking, G.; Raubenheimer, H. G. Organometallics 2010, 29, 5821. (8) Corberan, R.; Mas-Marza, E.; Peris, E. Eur. J. Inorg. Chem. 2009, 1700. Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2781. (9) McSkimming, A.; Ball, G. E.; Bhadbhade, M. M.; Colbran, S. B. Inorg. Chem. 2012, 51, 2191. McSkimming, A.; Bhadbhade, M.; Colbran, S. B. Dalton Trans. 2010, 39, 10581. (10) Lalrempuia, R.; Muller-Bunz, H.; Albrecht, M. Angew. Chem., Int. Ed. 2011, 50, 9969. (11) Lalrempuia, R.; McDaniel, N. D.; Muller-Bunz, H.; Bernhard, S.; Albrecht, M. Angew. Chem., Int. Ed. 2010, 49, 9765. (12) Song, G. Y.; Zhang, Y.; Su, Y.; Deng, W. Q.; Han, K. L.; Li, X. W. Organometallics 2008, 27, 6193. (13) Chianese, A. R.; Kovacevic, A.; Zeglis, B. M.; Faller, J. W.; Crabtree, R. H. Organometallics 2004, 23, 2461. Alcarazo, M.; Roseblade, S. J.; Cowley, A. R.; Fernandez, R.; Brown, J. M.; Lassaletta, J. M. J. Am. Chem. Soc. 2005, 127, 3290. Bacciu, D.; Cavell, K. J.; Fallis, I. A.; Ooi, L. L. Angew. Chem., Int. Ed. 2005, 44, 5282. Heckenroth, M.; Kluser, E.; Neels, A.; Albrecht, M. Angew. Chem., Int. Ed. 2007, 46, 6293. Heckenroth, M.; Albrecht, M. Chimia 2008, 62, 253. (14) Chianese, A. R.; Zeglis, B. M.; Crabtree, R. H. Chem. Commun. 2004, 2176. (15) Viciano, M.; Feliz, M.; Corberan, R.; Mata, J. A.; Clot, E.; Peris, E. Organometallics 2007, 26, 5304. (16) Song, G. Y.; Li, X. W.; Song, Z. C.; Zhao, J.; Zhang, H. J. Chem.Eur. J. 2009, 15, 5535. (17) Petronilho, A.; Müller-Bunz, H.; Albrecht, M. Chem. Commun. 2012, DOI: 10.1039/c2cc32843g. (18) Hahn, F. E.; Naziruddin, A. R.; Hepp, A.; Pape, T. Organometallics 2010, 29, 5283. Kösterke, T.; Pape, T.; Hahn, F. E. J. Am. Chem. Soc. 2011, 133, 2112. Viciano, M.; Poyatos, M.; Sanau, M.; Peris, E.; Rossin, A.; Ujaque, G.; Lledos, A. Organometallics 2006, 25, 1120. Viciano, M.; Mas-Marza, E.; Poyatos, M.; Sanau, M.; Crabtree, R. H.; Peris, E. Angew. Chem., Int. Ed. 2005, 44, 444. Fraser, P. J.; Roper, W. R.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1974, 102. Fraser, P. J.; Roper, W. R.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1974, 760. McGuinness, D. S.; Cavell, K. J.; Yates, B. F.; Skelton, B. W.; White, A. H. J. Am. Chem. Soc. 2001, 123, 8317. Furstner, A.; Seidel, G.; Kremzow, D.; Lehmann, C. W. Organometallics 2003, 22, 907. Arduengo, A. J.; Tapu, D.; Marshall, W. J. J. Am. Chem. Soc. 2005, 127, 16400. (19) Schneider, S. K.; Roembke, P.; Julius, G. R.; Loschen, C.; Raubenheimer, H. G.; Frenking, G.; Herrmann, W. A. Eur. J. Inorg. Chem. 2005, 2973. (20) Schneider, S. K.; Julius, G. R.; Loschen, C.; Raubenheimer, H. G.; Frenking, G.; Herrmann, W. A. Dalton Trans. 2006, 1226. (21) Herde, J. L.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974, 14, 18. (22) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88. (23) Abel, E. W.; Bennett, M. A.; Wilkinson, G. J. Chem. Soc. 1959, 3178. (24) Clark, R. C.; Reid, J. S. Acta Crystallogr., Sect. A 1995, 51, 887. (25) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.

ASSOCIATED CONTENT

* Supporting Information S

Crystallographic information files for compound 6-nBu, 7, 8, and 10 are available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the financial support from the Ministerio de Economiá y Competitividad of Spain (CTQ201124055/BQU) and Bancaixa (P1.1B2010-02). C.S. thanks the Ministerio de Economiá y Competitividad for a doctoral fellowship. E.M.-M. thanks the Juan de la Cierva program. We also want to thank the SCIC-UJI for the instrumental facilities.

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REFERENCES

(1) Herrmann, W. A.; Kocher, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2163. Herrmann, W. A.; Elison, M.; Fischer, J.; Kocher, C.; Artus, G. R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2371. de Fremont, P.; Marion, N.; Nolan, S. P. Coord. Chem. Rev. 2009, 253, 862. Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109, 3677. Crabtree, R. H. Coord. Chem. Rev. 2007, 251, 595. (2) Hahn, F. E. Angew. Chem., Int. Ed. 2006, 45, 1348. (3) Diez-Gonzalez, S.; Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874. Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122. (4) Schuster, O.; Yang, L. R.; Raubenheimer, H. G.; Albrecht, M. Chem. Rev. 2009, 109, 3445. (5) Albrecht, M. Chimia 2009, 63, 105. Albrecht, M. Chem. Commun. 2008, 3601. Arnold, P. L.; Pearson, S. Coord. Chem. Rev. 2007, 251, 596. (6) Raubenheimer, H. G.; Cronje, S. Dalton Trans. 2008, 1265. Strasser, C. E.; Stander-Grobler, E.; Schuster, O.; Cronje, S.; Raubenheimer, H. G. Eur. J. Inorg. Chem. 2009, 1905. Heydenrych, G.; von Hopffgarten, M.; Stander, E.; Schuster, O.; Raubenheimer, H. G.; Frenking, G. Eur. J. Inorg. Chem. 2009, 1892. Schneider, S. K.; Roembke, P.; Julius, G. R.; Raubenheimer, H. G.; Herrmann, W. A. Adv. Synth. Catal. 2006, 348, 1862. Raubenheimer, H. G.; Toerien, J. 5176

dx.doi.org/10.1021/om3005096 | Organometallics 2012, 31, 5169−5176