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

Treatment of a recently reported complex [PhP][closo,nido-CoH(2,4-CBH)(7,8-CBH)] (1) either by HO 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 [PhP][Co(2,4-isonido-CBH)] (2) with the {CoCB}-cluster units adopting a distorted skeletal geometry of the isonido-type. The anionic commo complex 2 reacts with in situ generated cationic [CuPPh] species to give stable copper-cobalt zwitterion [PhPCu][Co(2,4-isonido-CBH)] (3) with four two-electron, three-center (B-H)···Cu bonds, and exhibits no fluxional behavior in solution. Complex 3, at the same time, in CHCl in the presence of 2-fold excess of PPh readily converts to a new anionic species [(PhP)Cu][Co(2,4-isonido-CBH)] (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.