SYNTHESIS AND CRYSTAL-STRUCTURE OF A NOVEL, TMEDA-STABILIZED CLOSO-COBALT(II) CARBORANE - AN INTERMEDIATE FOR ANIONIC, COMMO-COBALT(III)CARBORANE COMPLEXES

The reaction of H)2Li-(TMEDA)]-1-Li(TMEDA)-2,4-(SiMe3)2-2,4-C2B4H4 (2) with CoCl2 in a molar ratio of 1:1 in a solvent mixture of dry benzen e and n-hexane at 0-degrees-C and then at room temperature produces, i n 92% yield, deep green crystals of a paramagnetic, half-sandwich Co(I I) carborane, closo-1-(TMEDA)-1-Co-2,4-(SiMe3)2-2,4-C2B4H4 (1), which does not undergo disproportionation to give the corresponding Co(III) species and elemental cobalt. Unlike the cases of main-group metallaca rboranes, the coordination of the metal in 1 with the Lewis base TMEDA does not produce a distortion of the metallacarborane. Thus, 1 exhibi ts an almost undistorted ''carbons apart'' pentagonal-bipyramidal geom etry, which was confirmed by a single-crystal X-ray diffraction study.