NET AMINE DEALKYLATION AT A DIRUTHENIUM CENTER - DEHYDROGENATION OF A SECONDARY AMINE AND HYDROLYSIS OF A COORDINATED IMINE

Reaction of excess benzylamine with Ru2Cl4(dppb)(2) (1) or RuCl2(dppb)(PPh(3)) (2) under Ar or with Ru2Cl5(dppb)(2) (3) under H-2 or in air generates RuCl2(dppb)(NH(2)CH(2)Ph)(2) [dppb = 1,4-bis(diphenylphosphino)butane, Ph(2)P(CH2)(4)PPh(2)]. Use of 1 equiv of amine per [Ru(II)](2) gives dinuclear Ru2Cl4(dppb)(2)(NH(2)CH(2)Ph) (4a) as a mixture of isomers. The corresponding reactions with dibenzylamine yield only dinuclear products: either Ru2Cl4(dppb)(2)[NH(CH(2)Ph)(2)] (4b), for reactions under H-2, or a mixture of this species and the dealkylation product 4a. The mechanism proposed for formation of the latter involves dehydrogenation of the secondary amine adduct to Ru2Cl4(dppb)(2)[PhCH(2)N=C(H)Ph], followed by hydrolysis of the coordinated imine. Direct reaction of PhCH(2)N=C(H)Ph with 3 under H-2 permits isolation of solely 4b. The findings are of interest also in context of thermal degradation of tertiary amines and hydrogenation of imines catalyzed by Ru ditertiary phosphine complexes.