[(μ-C){Re(CO)2(η-C5H5)}2]: A Surprisingly Simple Bimetallic Carbido Complex

摘要

The bonding in the majority of binuclear μ-carbido complexes may, to a first approximation, be described by one of two extreme canonical forms (A and B; Scheme 1). Symmetrical bimetallic complexes in which similar metal centers are bound to the central carbon atom are generally considered to adhere to a dimetallaallene-like bond localization (class A). Most examples of this type of bonding have so far arisen from the reduction of Group 8 porphyrin complexes in the presence of CI4; this synthetic strategy ensures that both metal termini are identical, though examples do exist which involve disparate metals. The alternative, and more commonly encountered class B "metallacarbyne" carbido complex involves essentially localized triple and single metal-carbon bonds that reflect the electronic requirements of the necessarily different metals. A third class (C) of bridging carbido ligand has been observed, which might be described as polar covalent or dative in nature; however, at present few examples exist.