Kinetics and mechanisms of homogeneous catalytic reactions. Part 3. Regioselective, catalysed [RuH(CO)(NCMe)(PPh)]BF reduction of quinoline

A kinetic study of the regioselective homogeneous hydrogenation of quinoline (Q) to 1,2,3,4-tetrahydroquinoline (THQ) was carried out using the cationic complex [RuH(CO)(NCMe)(PPh)]BF () as the precatalyst. The experimentally determined rate law was = {/(1+[H])}[Ru][H], which becomes = {[Ru]−[H] at low hydrogen concentrations ( = 28.5 s at 398 K). The corresponding activation parameters were found to be Δ = 42 + 6 kJ mol, Δ = − 115 ± 2JKmol and Δ = 92 ± 8 kJ mol. Complex was found to react with Q in CHCl under reflux to yield [RuH(CO)(NCMe)(N-Q)(PPh)]BF which was also isolated from the hydrogenation runs. These experimental findings, together with the results of self-consistent-field molecular orbital calculations on the free organic molecules involved, are consistent with a mechanism involving a rapid and reversible partial hydrogenation of to yield the corresponding dihydroquinoline (DHQ) species [RuH(CO)(NCMe)(DHQ)(PPh)]BF, followed by a rate-determining second hydrogenation of DHQ to yield [RuH(CO)(NCMe)(THQ)(PPh)]BF.