Synthesis and Coordination of a Bisphosphine-[NHC-borane] Compound: A Ligand Framework for Bimetallic Structure Featuring a Boron-Bridging Moiety

A unique bisphosphine-(NHC-borane) compoundwas shown tosupport a bimetallic structure leading to the isolation of a rareAu(4) cluster with a B-H fragment bridging two Aucenters. We report herein the synthesis of a bisphosphine-[NHC-BH3] compound and its coordination toward gold. The ligand isshownto support a bimetallic structure bisphosphine-[NHC-BH3]-(AuCl)(2). The abstraction of one chloride from the goldmetal center triggers the activation of a BH3 fragment,leading to the reductive elimination of H-2 and the formationof a dicationic Au-4 (2+) complex featuring Au centersat the +0.5 oxidation state, via a (mu-H)-Au-2 intermediate,characterized in situ at 183 K. The reactivity ofAu(4) with thiophenol led to the reoxidation of the goldmetal centers to a (mu-S-(Ph))-Au-2 complex. In the differentcomplexes, borane fragment was shown to bridge the Au-2 corevia weak interaction with [BH], [BCl], and [BH2] moieties.