Kinetic Studies on Reactions of Activated Triruthenium Carbonyl Clusters with Phosphorus Ligands

Reactions of the cluster complexes [PPN][Ru3(μ3-η2-Xpy)(CO)9] (1−3) (Xpy = 2-substituted pyridyl group; 1, X = PhN; 2, X = MeN; 3, X = S) with phosphines in THF solution are described. Complex 1, containing the 2-anilinopyridyl group, reacts with P(n-Bu)3 or PPh3 at room temperature to yield the addition product [PPN](Ru3(μ-η2-PhNpy)(CO)9L] (4a,b) (a, L = P(n-Bu)3; b, L = PPh3). This adduct slowly loses either the phosphine or a CO ligand to give a mixture of the starting antecedent species and its monosubstituted derivative. The corresponding intermediate adducts are not seen with 2-(methylamino)pyridyl and 2-thiopyridyl complexes 2 and 3 which react with P(n-Bu)3 to yield respectively the monosubstituted complex [PPN][Ru3(μ3-η2-MeNpy)(CO)8P(n-Bu)3] (5a) and the disubstituted complex [PPN][Ru3(μ3-η2-Spy)(CO)7(P(n-Bu)3)2] (6a). Kinetic results for these reactions are reported. The reactions are first-order in complex and first-order in ligand concentrations. It is proposed that the initial step for these reactions is an associative nucleophilic attack of phosphine ligands on the metal atom accompanied by opening of the μ-X bridge bond to form the adducts [PPN][Ru3(μ-η2-Xpy)(CO)9L]. The rates of reaction increase in the order 2-MeNpy < 2-Spy < 2-PhNpy. The reactivity order of these complexes toward nucleophiles is discussed in terms of electronic effects of their ancillary ligands.