Distorted commo-Cobaltacarboranes Based on the 5,6-Dicarba-nido-decaborane(12): The First Bimetal Cobalt–Copper Zwitterion-Containing Cluster with Four (B–H)4···Cu Bonds Not Showing Fluxional Behavior in Solution

Treatment of a recently reported complex [Ph4P]­[closo,nido-CoH­(2,4-C2B8H10)­(7,8-C2B8H11)] (1) either by H2O2 in acetone or NaH in THF leads to the loss of both the bridging and terminal hydrides yielding the diamagnetic salt of an anionic commo-cobaltacarborane [Ph4P]­[Co­(2,4-isonido-C2B8H10)2] (2) with the {CoC2B8}-cluster units adopting a distorted skeletal geometry of the isonido-type. The anionic commo complex 2 reacts with in situ generated cationic [CuPPh3]+ species to give stable copper–cobalt zwitterion [Ph3PCu]­[Co­(2,4-isonido-C2B8H10)2] (3) with four two-electron, three-center (B–H)4···Cu bonds, and exhibits no fluxional behavior in solution. Complex 3, at the same time, in CH2Cl2 in the presence of 2-fold excess of PPh3 readily converts to a new anionic species [(Ph3P)3Cu]­[Co­(2,4-isonido-C2B8H10)2] (4) which retains initial isonido geometry. All newly obtained diamagnetic commo complexes were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of complexes 2 and 3.