The systems prepared in situ by addition of the corresponding equivalents of the respective phosphine (mono-, di-and tridentated), called M 2 Cl 2 (COE) 4 /n phosphine (M = Rh, Ir; and COE = cyclooctene), are efficient and regioselective precatalysts for the hydrogenation of quinoline, isoquinoline, 5,6-and 7,8-benzoquinoline and acridine. The Rh systems were more active than the corresponding Ir ones, being the systems with 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) more active than those with 1,2-bis(diphenylphosphino)ethane (dppe), except for the case of acridine, where the inversed tendencies were observed (Ir > Rh and dppe > triphos). The systems with triphenylphosphine showed the lowest activities.

The systems prepared in situ by addition of two equivalents of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to M 2 Cl 2 (COE) 4 (M = Rh, Ir; COE = cyclooctene) showed to be efficient and regioselective precatalysts for the hydrogenation of quinoline. For both systems, kinetic studies lead to the rate laws rit was proposed that the catalytically active species are the cationic unsaturated complexes [M(Q)(triphos)] ? . The general mechanism involves a rapid and partial hydrogenation of these species to generate complexes of the type [M(H) 2 (Q)(triphos)] ? (isolated and characterized for M = Ir), which transfer the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H 2 , considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yield THQ, regenerates the active species and restarts the catalytic cycle.

The system prepared in situ by addition of two equivalents of 1,2-bis(diphenylphosphino)ethane (dppe) to Rh 2 Cl 2 (COE) 4 (COE = cyclooctene) showed to be an efficient and regioselective precatalyst for the hydrogenation of quinoline (Q). This reaction showed to be independent of the Q concentration and of fractional order on H 2 and catalyst concentrations (1.5 and 0.6, respectively). The fractional order on catalyst concentration indicates that several catalytic species with different activities are present in the reaction medium; however, the cationic species [Rh (dppe) 2 ] ? was the only phosphorous-containing compound detected by 31 P{ 1 H} NMR. For the acac salt of this cationic bis(dppe) complex, a kinetic study led to the rate law r = {K 1 k 2 /(1 ? K 1 [H 2 ])}[M][H 2 ] 2 ; [M(Q)(j 2 -dppe) (j 1 -dppe)] ? was proposed as the catalytically active species (CAS) of the cycle. The general mechanism involves a reversible oxidative addition of H 2 to generate a dihydrido complex, which transfers the hydride ligands to the coordinated Q to yield species containing a 1,2-dihydroquinoline (DHQ) ligand, followed by a second oxidative addition of H 2 , considered as the rate-determining step of the cycle; hydrogen transfer toward the DHQ ligand yields THQ, regenerates the CAS and restarts the catalytic cycle.

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