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Unsymmetrically Bridging Aryls of Iridium

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journal contribution
posted on 27.10.2003, 00:00 by John Muldoon, Seth N. Brown
The iridium(I) complex [(cod)IrCl]2 (1; cod = 1,5-cyclooctadiene) reacts with 2,6-disubstituted aryl Grignard reagents to give air-stable diiridium complexes (cod)IrBr(μ,κ16-Ar)Ir(cod) (Ar = 2,4,6-Me3C6H2 (2), 2,6-Me2C6H3 (3)). The aryl groups in these compounds are σ-bonded to one square-planar iridium(I) center and π-bonded to another (cyclooctadiene)iridium(I) fragment. Spectroscopic and structural data indicate that the bonding is best described as a resonance hybrid between a zwitterionic σ-aryl/η6-arene structure and a neutral carbene/η5-cyclohexadienyl structure, with the former making a greater contribution. The resonance appears to stabilize both the iridium(I)−aryl σ- and π-bonds, with the result that the bridging aryl moiety is extremely chemically robust. The complexes react selectively at the square-planar iridium, undergoing ligand substitution of the cyclooctadiene or halide and oxidative addition of I2.