COMPARATIVE REACTIVITY OF TRIRUTHENIUM AND TRIOSMIUM MU(3)-ETA(2)-IMIDOYLS .1. DYNAMICS AND REACTIONS WITH CARBON-MONOXIDE, PHOSPHINE, AND ISOCYANIDE

The reactivity and ligand dynamics of the mu(3)-eta(2)-imidoyl cluster s Ru-3(CO)(9)(mu(3)-eta(2)-RC=NR')(mu-H) (R = CH3, R' = Et 2; RR' = (C H2)(3), 3; RR' = (CH2)(2)C(H)CH2OCH3 4, R = R' = CH3, 5) are compared with the previously reported osmium analogs. The lowest energy dynamic al process in these clusters is the ''windshield wiper'' motion over t he face of the cluster whereas tripodal rotation of the carbonyl group s on the unbridged metal atom is the fastest process in the analogous osmium compounds. Although the structures of the phosphine and isocyan ide substitution products reported, Ru-3(CO)(8)(mu(3)-eta(2)-RC=NR')(m u-H)L (R = CH3, R' = CH2CH3, L = PPh3 (So), L = CNMe (12); R = R' = (C H2)(3), L = PPh3 (9), L = CNMe (13); R = R' = CH3, L = PPh3 (10), are identical to their osmium analogs, the pathway to their formation refl ects the lower CO dissociation energies for ruthenium clusters and a g reater sensitivity to the substituents on the imidoyl group. The solid state structures of 9 and 12 are reported as well as that of s-3(CO)( 8)(mu-eta(2)-C=N(CH2)(3)(mu-H)(PPh3)(MeNC) (15). The latter illustrate s the hemilabile nature of the mu(3)-imidoyl ligand even in phosphine- substituted derivatives and the structural preferences of phosphine an d isocyanide ligands in this class of clusters.