Ruthenium Complexes Containing Bis(diarylamido)/Thioether Ligands: Synthesis and Their Catalysis for the Hydrogenation of Benzonitrile

Abstract

Treatment of the thioethers (RNH-o-C6H4)2S (H2[R2NSN]; R = Xy, Xyf; Xy = 3,5-Me2C6H3, Xyf = 3,5-(CF3)2C6H3) with 2 equiv of n-BuLi followed by addition of 0.5 equiv of [(η6-C6H6)RuCl2]2 in THF gave the bis(diarylamido)/thioether complexes [(η6-C6H6)Ru[R2NSN]] (R = Xy (1a), R = Xyf (1b)) in moderate yields. In the presence of 1a (1 mol %) and PCy3 (2 mol %; Cy = cyclohexyl), benzonitrile was catalytically hydrogenated to give benzylamine (72%) and benzylidenebenzylamine (27%) at 80 °C and 30 atm, while the hydrogenation with 1b as a catalyst precursor resulted in the formation of benzylamine (37%) and benzylidenebenzylamine (51%) under the same reaction conditions. The yield of benzylamine was improved up to 92% by using a catalyst mixture of 1a (1 mol %)/PCy3 (2 mol %)/t-BuONa (10 mol %). On the other hand, the reaction of 1a with excess PMe3 afforded the tris(trimethylphosphine) derivative [(PMe3)3Ru[Xy2NSN]] (2). Treatment of 2 with excess PhCN, MeCN, or N2H4·H2O resulted in the replacement of a PMe3 ligand by these substrates to give [(PMe3)2LRu[Xy2NSN]] (3, L = PhCN; 4, L = MeCN; 5, L = N2H4), while the reaction of 2 with benzoylhydrazine gave the κ2-benzoylhydrazido complex [(PMe3)2Ru(κ2-(O,N)-PhC(O)NNH2)(H[Xy2NSN])] (6). Structures of 1a, 1b, 2, 5, and 6 have been determined by X-ray crystallography.