The systems prepared in situ by addition of two equivalents of diphosphine [1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp) and 1,4-bis(diphenylphosphino)butane (dppb)] to M2Cl2(COE)(4) (M = Rh, Ir; COE = cyclooctene) showed to be efficient and regioselective precatalysts for the hydrogenation of quinoline, isoquinoline, 5,6- and 7,8-benzoquinoline and acridine, under mild reaction conditions (130 degrees C and 4 atm H-2). The Rh systems showed to be more active than the corresponding Ir ones, except for the case of acridine, where an inversed tendency was observed (Ir > Rh).