Syntheses and Chemistry of the Diynyl Complexes M(C⋮CC⋮CH)(CO) 3 (η-C 5 H 5 ) (M = Mo, W):  Crystal Structures of W(C⋮CC⋮CSiMe 3 )(CO) 3 (η-C 5 H 5 ), W{C⋮CC[CH=C(CN) 2 ]=C(CN) 2 }(CO) 3 (η-C 5 H 5 ), and cis -W(C⋮CPh)(CO)