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Iridium(I) and Iridium(III) Complexes Supported by a Diphenolate Imidazolyl-Carbene Ligand

Weinberg, David R. and Hazari, Nilay and Labinger, Jay A. and Bercaw, John E. (2010) Iridium(I) and Iridium(III) Complexes Supported by a Diphenolate Imidazolyl-Carbene Ligand. Organometallics, 29 (1). pp. 89-100. ISSN 0276-7333.

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Deprotonation of 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolium chloride (1a) followed by reaction with chloro-1,5-cyclooctadiene Ir(I) dimer affords the anionic Ir(I) complex [K][{OCO}Ir(cod)] (2: OCO = 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolyl; cod = 1,5-cyclooctadiene), the first Ir complex stabilized by a diphenolate imidazolyl-carbene ligand. In the solid state 2 exhibits square-planar geometry, with only one of the phenoxides bound to the metal center. Oxidation of 2 with 2 equiv of [FeCp_2][PF_6] generates the Ir(III) complex [{OCO}Ir(cod)(MeCN)][PF_6] (3). Reaction of 3 with H_2 results in the liberation of cyclooctane and a species capable of catalyzing the hydrogenation of cyclohexene to cyclohexane. Displacement of cyclooctadiene from 3 can be achieved by heating in acetonitrile to form [{OCO}Ir(MeCN)3][PF_6] (4) or by reaction with either PMe_3 or PCy_3 to generate [{OCO}Ir(PMe_3)_3][PF_6] (5) or [{OCO}Ir(PCy_3)_2(MeCN)][PF_6] (6), respectively. 6 reacts with CO in acetonitrile to give an equilibrium mixture of 6 and [{OCO}Ir(PCy_3)_2(CO)][PF_6] (7) and with chloride to generate [{OCO}Ir(PCy_3)_(2)Cl] (8). The solid-state structure of 8 shows that the diphenolate imidazolyl-carbene ligand is distorted from planarity; DFT calculations suggest this is due to an antibonding interaction between the phenolates and the metal center in the highest occupied molecular orbital (HOMO) of the complex. 8 undergoes two successive reversible one-electron oxidations in CH_(2)Cl_2 at −0.22 and at 0.58 V (vs ferrocene/ferrocenium); EPR spectra, mass spectroscopy, and DFT calculations suggest that the product of the first oxidation is [{OCO}Ir(PCy_3)_(2)Cl]+ (8+), with the unpaired electron occupying a molecular orbital that is delocalized over both the metal center and the diphenolate imidazolyl-carbene ligand.

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Labinger, Jay A.0000-0002-1942-9232
Additional Information:© 2009 American Chemical Society. Received September 14, 2009. Publication Date (Web): December 7, 2009. We thank Larry Henling and Mike Day for X-ray crystallographic characterization of complexes, Mona Shahgholi for mass spectroscopic characterization of complexes, and Angel J. Di Bilio for assistance with EPR experiments. We are grateful to BP for financial support through the MC2 program. DFT calculations were carried out using the Molecular Graphics and Computation Facility, College of Chemistry, University of California, Berkeley, California, with equipment support from NSF grant CHE-0233882.
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Official Citation:Iridium(I) and Iridium(III) Complexes Supported by a Diphenolate Imidazolyl-Carbene Ligand David R. Weinberg, Nilay Hazari, Jay A. Labinger, John E. Bercaw Organometallics 2010 29 (1), 89-100
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ID Code:17340
Deposited By: Jason Perez
Deposited On:29 Jan 2010 21:30
Last Modified:03 Oct 2019 01:26

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