Unsymmetrically Bridging Aryls of Iridium

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 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.

一价铱配合物[(cod)IrCl]₂（编号1；cod即1,5-环辛二烯(cyclooctadiene)）可与2,6-二取代芳基格氏试剂反应，生成空气稳定的二铱配合物(cod)IrBr(μ,κ¹:η⁶-Ar)Ir(cod)（其中Ar为2,4,6-三甲基苯基2,4,6-Me₃C₆H₂，编号2；2,6-二甲基苯基2,6-Me₂C₆H₃，编号3）。此类化合物中的芳基，分别与一个平面正方形配位的一价铱中心形成σ配位键，同时与另一个(环辛二烯)合一价铱片段形成π配位键。光谱与结构数据表明，该成键模式最优可描述为两性离子σ-芳基/η⁶-芳烃结构与中性卡宾/η⁵-环己二烯基结构之间的共振杂化，且前者的结构贡献占比更高。该共振效应可同时稳定一价铱-芳基的σ键与π键，使得桥联芳基片段具备极强的化学稳定性。此类配合物可在平面正方形配位的铱位点发生选择性反应：经历环辛二烯或卤离子的配体取代，以及与碘单质(I₂)的氧化加成。