| Abstract
| - (Cyclooctadiene)iridium(I) chloride dimer reacts with 2,6-disubstituted aryl Grignard reagents to form air-stable diiridium complexes with an unsymmetrical, σ/π-bridging aryl group. Both the σ- and the π-linkages are stabilized by resonance between σ/η6-arene and carbene/η5-cyclohexadienyl canonical forms, rendering the bridging aryl unit inert to a variety of chemical transformations which can be carried out at the square-planar iridium center.
- 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,κ1:η6-Ar)Ir(cod) (Ar = 2,4,6-Me3C6H2 (2), 2,6-Me2C6H3 (3)). The aryl groups in these compounds areσ-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 bestdescribed as a resonance hybrid between a zwitterionic σ-aryl/η6-arene structure and aneutral 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 resultthat the bridging aryl moiety is extremely chemically robust. The complexes react selectivelyat the square-planar iridium, undergoing ligand substitution of the cyclooctadiene or halideand oxidative addition of I2.
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