Reactions of Ru(η 4 -1,5-COD)(η 6 -1,3,5-COT) (1) (COD ) cyclooctadiene, C 8 H 12 ; COT ) cyclooctatriene, C 8 H 10 ) with a series of Lewis bases are studied. Treatments of 1 with P(OMe) 3 , P(OEt) 3 , P(OMe) 2 Ph, P(OEt) 2 Ph, P(O i Pr) 3 , P(OMe)Ph 2 , or P(OEt)Ph 2 lead to the formation of Ru(η 4 -1,5-COD)(η 4 -1,3,5-COT)L (2) followed by preferential liberation of the 1,5-COD ligand to give COT complexes formulated as Ru(6-η 1 :1-3-η 3 -COT)L 3 (3) and Ru-(η 4 -1,3,5-COT)L 3 (4). Reaction of 1 with P(OPh) 3 also gives 2, but further treatment of this system leads to the liberation of both 1,5-COD and 1,3,5-COT to give a mixture of Ru(η 4 -1,5-COD)L 3 (5) and Ru(6-η 1 :1-3-η 3 -COT)L 3 (3) and finally gives Ru{P(OC 6 H 4 )(OPh) 2 } 2 -{P(OPh) 3 } 2 (6h). In the reaction of 1 with tert-butylisonitrile, 1,3,5-COT is initially liberated with concomitant formation of Ru(η 4 -1,5-COD)(CN t Bu) 3 (5j), which further reacts with the liberated 1,3,5-COT, giving eventually Ru(6-η 1 :1-3-η 3 -COT)(CN t Bu) 3 (3j). The molecular structure of 5j determined by X-ray structure analysis reveals that one of the isonitrile ligands has a considerable carbene character. In the presence of excess isonitrile, the homoleptic complex Ru(CN t Bu) 5 ( 7) is formed. On the other hand, 1 does not react with poor π-accepting ligands such as NEt 3 , pyridine, and (dimethylamino)pyridine as well as bulky phosphorus ligands such as triphenylphosphine and tricyclohexylphosphine. These results suggest that the initial coordination of electron-donating ligands to Ru essentially encourages the dissociation of the 1,5-COD ligand, but the π-accepting ability of the ligand induces the dissociation of the 1,3,5-COT ligand.
