6,6′-Diphenyl derivatives of cobalt and nickel bis(dicarbollide) were synthesized starting from nido-carborane by the insertion—deboronation—insertion sequence of reactions. The by-products of the insertion of PhBCl2 into the nido-carborane cage, diethyloxonium derivatives of nido-carborane [9-Et2O-7,8-C2B9H11] and [10-Et2O-7,8-C2B9H11], were isolated and characterized. Treatment of the latter with pyridine resulted in the elimination of one ethyl group to give the corresponding ethoxy derivatives. The structures of nido-carborane 10-diethyloxonium derivative and cobalt bis(dicarbollide) 6,6′-diphenyl derivative were established by X-ray diffraction analysis.