Homogeneous hydrogenation of imines catalyzed by rhodium and iridium complexes -: Kinetics and mechanism of the hydrogenation of N-(β-naphthyl methylene) aniline using [Ir(COD)(PPh3)2]PF6 as catalyst precursor

The regioselective hydrogenation of some imines to the corresponding amines is efficiently catalyzed by [Ir(COD)(PPh3)(2)]PF6 (1) and [Rh(COD)(PPh3)(2)]PF6 (2) at 60 degreesC and 200 psi of H-2. The kinetics of the hydrogenation of N-(beta -naphthyl methylene) aniline (N beta NA) with [Ir(COD)(PPh3)(2)]PF6 in tetrahydrofuran (THF) have been studied. The experimentally determined rate law is r(i) = k(cat) [Ir][N beta NA][H-2] where k(cat) = (2.2 +/- 0.3) x 10(3) M-2 s(-1) at 323 K and the corresponding activation parameters are: DeltaH degrees = (4.0 +/-0.4) kcal mol(-1); DeltaS degrees = (-32 +/-2) e.u.; DeltaG degrees = (14 +/-2) kcal mol(-1). A catalytic cycle is proposed on the basis of the kinetic experiments and some NMR data. (C) 2001 Elsevier Science B.V. All rights reserved.