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Mono- and Bis(iminoxolene)iridium Complexes: Synthesis and Covalency in π Bonding

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journal contribution
posted on 31.03.2022, 15:39 authored by Thomas H. Do, Seth N. Brown
N-(2,6-Diisopropylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone (Diso) reacts with the (cyclooctadiene)iridium chloride dimer to form a monoiminoxolene complex, (Diso)­Ir­(cod)­Cl. Reaction of 2 equiv of the iminoquinone with chlorobis­(cyclooctene)­iridium dimer affords the bis-iminoxolene (Diso)2IrCl. This five-coordinate complex adopts a distorted square pyramidal structure with an apical chloride ligand and undergoes halide exchange to form an air-stable iodide complex. (Diso)2IrCl can be reduced by one electron to form neutral, square planar (Diso)2Ir, while oxidation with PhICl2 gives octahedral trans-(Diso)2IrCl2. The cis isomer can be prepared by air oxidation of (Diso)2IrCl; cis/trans isomerization is not observed even on prolonged heating. Structural and spectroscopic features of the complexes are consistent with the presence of strong, covalent π bonding between the metal and the iminoxolene ligands, with structural data suggesting between 45 and 60% iridium character in the π bonding orbitals, depending on the ancillary ligands. The spectroscopic similarity of (Diso)2Ir and (Diso)2IrCl to their cobalt congeners suggests that the first-row metal complexes likewise have appreciably covalent metal-iminoxolene π bonds.

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