Comparative reactivity of triruthenium and triosmium μ₃-η²-Imidoyls.1.Dynamics and reactions with carbon monoxide, phosphine, and isocyanide

The reactivity and ligand dynamics of the μ₃-η²-imidoyl clusters Ru₃(CO)₉(μ₃-η ²-RC=NR′)-(μ-H) (R = CH₃, R′ = Et 2; RR′ = (CH₂)₃, 3; RR′ = (CH₂)₂C(H)CH₂OCH₃ 4, R = R′ = CH₃, 5) are compared with the previously reported osmium analogs. The lowest energy dynamical process in these clusters is the "windshield wiper" motion over the face of the cluster whereas tripodal rotation of the carbonyl groups on the unbridged metal atom is the fastest process in the analogous osmium compounds. Although the structures of the phosphine and isocyanide substitution products reported, Ru₃(CO)₈(μ₃-η ²-RC=NR′)(μ-H)L (R = CH₃, R′ = CH₂CH₃, L = PPh₃ (8a), L = CNMe (12); R = R′ = (CH₂)₃, L = PPh₃ (9), L = CNMe (13); R = R′ = CH₃, L = PPh₃ (10), are identical to their osmium analogs, the pathway to their formation reflects the lower CO dissociation energies for ruthenium clusters and a greater sensitivity to the substituents on the imidoyl group. The solid state structures of 9 and 12 are reported as well as that of Os₃(CO)₈(μ-η²-C=N(CH₂) ₃(μ-H)(PPh₃)(MeNC) (15). The latter illustrates the hemilabile nature of the μ₃-imidoyl ligand even in phosphine-substituted derivatives and the structural preferences of phosphine and isocyanide ligands in this class of clusters.