Kinetics and Mechanisms of Homogeneous Catalytic Reactions. Part 10. Regioselective Hydrogenation of Quinoline Catalyzed by the Systems M2Cl2(COE)4/2 Triphos [M = Rh, Ir; COE = Cyclooctene; Triphos = 1,1,1-Tris(diphenylphosphinomethyl)Ethane]

Autor: Rosales, Merlin, Vallejo, Regina, Soto, Juan José, Bastidas, Luis Jhonatan, Molina, Karely, Baricelli, Pablo J.
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Zdroj: Catalysis Letters; Jan2010, Vol. 134 Issue 1/2, p56-62, 7p, 1 Diagram, 3 Charts, 2 Graphs
Abstrakt: The systems prepared in situ by addition of two equivalents of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to M2Cl2(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 r = { K1 k2/(1 + K1[H2])}[M][H2]2; it 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 H2, 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 systems prepared in situ by addition of two equivalents of 1,1,1-tris(diphenylphosphinomethyl)ethane (triphos) to M2Cl2(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 r = { K1 k2/(1 + K1[H2])}[M][H2]2; it 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 H2, 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.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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