Nucleophilic reactions of chiral heterobimetallic cobalt-molybdenum propargylium complexes, involving the first example of phosphine migration. X-ray crystal structures of [(.mu.-.eta.2-.eta.3-HC.tplbond.CCH(CH3))CoMoCp(CO)5][BF4] and [(.mu.-.eta.2-.eta.3-HC.tplbond.CCH(CH3))CoMoCp(CO)4(PPh3)][BF4]