Hydrocarbamoylation of C2H2 by N,N-dimethylformamide (DMF) to N,N-dimethylacrylamide was effected by a series of cluster-opening reactions with Ru-5(mu(5)-C)(CO)(15) (1). The reaction of 1 with DMF yielded the new complexes Ru-5(mu(5)-C)(CO)(14)(mu-eta(2)-O=CNMe2)(mu-H) (2) and a minor coproduct Ru-5(mu(5)-C)(CO)(13)(HNMe2)(mu-eta(2)-O=CNMe2)(mu-H) (3) by a cluster-opening activation of the formyl C-H bond of DMF. Compound 3 was obtained from 2 by a further reaction with DMF. Compound 3 reacted with C2H2 (1 atm, 70 degrees C) to yield Ru-5(mu(5)-C)(CO)(13)(mu-eta(3)-O= CNMe2CHCH)(mu-H) (4) by the addition and coupling of C2H2 to the bridging dimethylformamido ligand. Compound 4 contains a sigma-pi-coordinated, dimethylformamido-substituted vinyl ligand that bridges a Ru-Ru edge of an open Ru5C cluster. The formamido group is also coordinated to one of the metal atoms. The addition of CO (1 atm, 25 degrees C) to 4 yielded the CO adduct Ru-5(mu(5)-C)(CO)(14)(eta(2)-O=CNMe2CH=CH)(mu-H) (5) containing a chelating dirnethylacrylamido ligand, which released dimethylacrylamide by the reductive elimination of a C-H bond upon a further addition of CO (400 psi, 125 degrees C) with the re-formation of 1. All of the products were characterized by single-crystal X-ray diffraction analyses.