Reaction of 14-electron RuH(CO)L-2(+) (L = (PBu2Me)-Bu-t, anion = B[C6H3(CF3)(2)](4)(-)) with Me3SiC=CPh gives the silyl-migrated product Ru[CH=C(SiMe3)Ph] (CO)L-2(+), in which the ortho H on phenyl syn to Ru is agostic to the metal, to give a square-pyramidal coordination geometry augmented by an agostic interaction with a Bu-t methyl group. These interactions, from X-ray diffraction, persist in solution. Reaction at lower temperature reveals (NMR studies) one detectable species which, however, is unlikely to be an intermediate. Under 1 atm of CO, this cation adds three CO's to give Ru(CO)(2)[CO-CH=C(SiMe3)Ph]L-2(+), which is shown ((CO)-C-13 labeling) to add an additional CO. In the absence of excess CO, this acyl complex forms RuH(CO)(3)L-2(+) with release of Me3SiC=CPh; Me3Si migration is thus reversed.