Silyl migration of Me3SiCCPh coordinated to [RuH(CO)((PBu2Me)-Bu-t)(2)]BAr'(4) can be reversed: Synthesis and structure of [Ru(CH=C(SiMe3)(Ph))(CO)((PBu2Me)-Bu-t)(2)]BAr '(4)

Reaction of 14-electron RuH(CO)L-2(+) (L = (PBu2Me)-Bu-t, anion = B[C6H3(CF 3)(2)](4)(-)) with Me3SiC=CPh gives the silyl-migrated product Ru[CH=C(SiMe 3)Ph] (CO)L-2(+), in which the ortho H on phenyl syn to Ru is agostic to th e metal, to give a square-pyramidal coordination geometry augmented by an a gostic interaction with a Bu-t methyl group. These interactions, from X-ray diffraction, persist in solution. Reaction at lower temperature reveals (N MR studies) one detectable species which, however, is unlikely to be an int ermediate. 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 add itional 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.