KINETICS AND MECHANISMS OF HOMOGENEOUS CATALYTIC REACTIONS .3. REGIOSELECTIVE, CATALYZED [RUH(CO)(NCME)(2)(PPH(3))(2)]BF4 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)(2)(PPh(3))(2)]BF2 (1) as the precatalyst. The experimentally determined rate law was r={k(2)K(1)/(1+K-1[H-2])}[Ru-0][H-2](2), which becomes r=k(2)K(1)[Ru-0]-[H-2](2) at low hydrogen concentrations (k(2)K(1)=28.5 M(-2) s(-1) at 398 K). The corresponding activation parameters s were found to be Delta H-not equal=42+/-6 kJ mol(-1), Delta S-not equal=-115+/-2 JK(-1) mol(-1) and Delta G(not equal)=92+/-8 kJ mol(-1) Complex (1) was found to react with Q in CHCl3 under reflux to yield [RuH(CO)(NCMe)(N-Q)(PPh(3))(2)]BF4 (2) which was also isolated from the hydrogenation runs, These experimental findings, together with the results of ab initio 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 (2) to yield the corresponding dihydroquinoline (DHQ) species [RuH-(Co)(NCMe)(DHQ)(PPh(3))(2)]BF4 (4), followed by a rate-determining second hydrogenation of DHQ to yield [RuH(Co)(NCMe)(THQ)(PPh(3))(2)]BF4 (3).