Catalytic Acceptorless Dehydrogenation of Amines with Ru(P^R₂N^R′₂) and Ru(dppp) Complexes

[Ru­(Cp)­(PPh2NBn2)­(MeCN)]­PF6 (1; PPh2NBn2 = 1,5-benzyl-3,7-phenyl-1,5-diaza-3,7-diphosphacyclooctane) and [Ru­(Cp)­(dppp)­(MeCN)]­PF6 (2; dppp = 1,3-bis­(diphenylphosphino)­propane) are both active toward the acceptorless dehydrogenation of benzylamine (BnNH2) and N-heterocycles. The two catalysts have similar activities but different selectivities for dehydrogenation products. Independent synthesis of a [Ru­(Cp)­(PPh2NBn2)­(NH2Bn)]­PF6 adduct (3) reveals the presence of a hydrogen bond between the bound amine and the pendent base of the PPh2NBn2 ligand. Preliminary mechanistic studies reveal that the benzylamine adduct is not an on-cycle catalyst intermediate.