ONO Dianionic Pincer-Type Ligand Precursors for the Synthesis of σ,π-Cyclooctenyl Iridium(III) Complexes: Formation Mechanism and Coordination Chemistry

Abstract

The σ,π-cyclooctenyl iridium(III) pincer compounds [Ir(κ3-pydc-X)(1-κ-4,5-η-C8H13)] (X = H (1), Cl, Br) have been prepared from [Ir(μ-OMe)(cod)]2 and the corresponding 4-substituted pyridine-2,6-dicarboxylic acids (H2pydc-X) or, alternatively, from their lithium salts (X = H) and [Ir(cod)(CH3CN)2]PF6. Deuterium labeling studies in combination with theoretical calculations have shown that formation of 1 involves a metal-mediated proton transfer in the reactive intermediate [Ir(κ2-Hpydc)(cod)], through the solvent-stabilized hydrido complex [IrH(κ3-pydc)(cod)(CH3OH)], followed by olefin insertion. The formation of this hydrido intermediate results from solvent-assisted proton transfer through a hydrogen-bonding network, forming an eight-membered metallacycle. In contrast, reaction of [Ir(μ-OMe)(cod)]2 with iminodiacetic acid derivatives, RN(CH2COOH)2, gave the stable iridium(I) mononuclear [Ir{κ2-MeN(CH2COOH)(CH2COO)}(cod)] (R = Me) complex having a free carboxymethyl group and the tetranuclear complex [Ir4...