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 [Ph4 P][closo,nido-CoH(2,4-C2 B8 H10 )(7,8-C2 B8 H11 )] (1) either by H2 O2 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 [Ph4 P][Co(2,4-isonido-C2 B8 H10 )2 ] (2) with the {CoC2 B8 }-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 [Ph3 PCu][Co(2,4-isonido-C2 B8 H10 )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 CH2 Cl2 in the presence of 2-fold excess of PPh3 readily converts to a new anionic species [(Ph3 P)3 Cu][Co(2,4-isonido-C2 B8 H10 )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.