Carbaboranerhodium complexes with Rh–Rh, Rh–Cu and Rh–Au bonds; crystal structure of [NEt4][Rh2(µ-σ : η5-C2B9H8Me2)(CO)3(η5-C2B9H9Me2)]
摘要:
The compound [NEt4][Rh(CO)(PPh3)(eta-5-C2B9H9Me2)] has been prepared and used to synthesise the dimetal complexes [RhM(CO)(PPh3)2(eta-5-C2B9H9Me2)] (M = Cu or Au) and [RhCu(CO)(PMe3)(PPh3)(eta-5-C2B9H9Me2)]. Protonation of [NEt4][Rh(CO)(PPh3)(eta-5-C2B9H9Me2)] gives an unstable hydride [RhH(CO)(PPh3)(eta-5-C2B9H9Me2)]. In contrast, treatment of [NEt4][Rh(CO)2(eta-5-C2B9H9Me2)] with HBF4.Et2O affords a dirhodium complex [Rh2(CO)3(eta-5-C2B9H9Me2)2] in which one carbaborane fragment bridges the Rh-Rh bond via an exopolyhedral B-H half-arrow-pointing-right Rh bond. This species can be deprotonated to give an anionic complex [Rh2(mu-sigma:eta-5-C2B9H8Me2)(CO)3(eta-5-C2B9H9Me2)]-, the [NEt4]+ salt of which may be obtained directly from [NEt4][Rh(CO)2(eta-5-C2B9H9Me2)] by treatment of the latter with [NHMe3]Cl. An X-ray crystallographic study established the structure of the anion. One rhodium centre is ligated by a CO molecule and by a C2B9H9Me2 cage in the normal eta-5 bonding mode, the other carries two CO groups and an eta-5-C2B9 cage. However, a boron atom beta to the carbons in the pentagonal open activated CCBBB face of this cage forms a sigma bond to the other rhodium atom [B-Rh 2.05(3) angstrom], so that this C2B9H9Me2 group bridges the Rh-Rh bond [2.876(3) angstrom]. The NMR data for the new compounds are reported and discussed.