Transition-metal-cyanocarbon chemistry. 2. Cyanoacetylenes insertions into the metal-hydrogen bond of (.eta.5-C5H5)(CO)3MH (M = Mo, W) complexes. Formation of phosphorus ylide complexes and the structure of (.eta.5-C5H5)(CO)2Mo[.eta.2-C(CN)PPh3CHCN]