Synthesis of sandwich metallaboranes [M(B11H11)2]3– (M = Cu, Ag) via polyhedral expansion of the closo-undecaborate anion [B11H11]2–

Reactions of the undecahydro-closo-undecaborate anion [B11H11]2– with copper(I) and silver(I) complexes [(Ph3P)3MX] (M = Cu, X = Cl; M = Ag, X = NO3) were found to result in the polyhedral expansion with the formation of the corresponding metallaboranes (Bu4N)3[commo-M(B11H11)2] rather than the M–H–B complexes typical of borane ligands. The crystal structure of complex (Bu4N)3[Ag(B11H11)2] was determined by single-crystal X-ray diffraction. Hirschfeld surface analysis and DFT calculations for both metallaboranes [M(B11H11)2]3– (M = Cu, Ag) were carried out.