Iridium complexes with chiral and achiral β-aminophosphane ligands:: Catalysts for >C=O hydrogenation and H/D exchange involving both homo- and heterolytic H2 activation

Chiral and achiral P,N-chelated Ir-I complexes of the general type [(COD)Ir(Pboolean ANDNR(1)R(2))]BF4, where COD = eta(4)-1,5-C8H12 and Pboolean ANDNR(1)R(2) = (1R,2R)-, (1S,2S)-, or (1R,2S)-(Ph2PCH)-H-1(Ph)(CH)-H-2(Me)(NRR2)-R-1 ((NRR2)-R-1 = NH2, NHMe, NHCH2Ph, NHCHMe2, NMe2), Ph2PCH2CR2NH2 (R = H, Me), or 2-Ph2PC6H4NHMe, have been prepared by treating [Ir(COD)(2)]BF4 with the required beta-aminophosphane in THF. The monolithiated ligands Ph2PCH2CMe2N(Li)H and 2-Ph2PC6H4N(Li)Me interacted with [{(COD)Ir(mu-Cl)}(2)] to give the neutral alkyl- and arylamido compounds [(COD)Ir(Ph2PCH2CMe2NH)] and [(COD)Ir(2-Ph2PC6H4NMe)]. All Ir-I complexes [(COD)Ir(Pboolean ANDNR(1)R(2))]BF4 acted as catalysts for the direct hydrogenation of alkyl aryl ketones to the corresponding 1-phenylalkanols, if combined with an alkaline or amine base in methanol under H-2 (10-50 bar) between 25 and 50 degreesC. The reaction occurred with modest to moderate enantioselectivity (ca. 20-75% ee) if chelate complexes bearing the various optically active beta-aminophosphanes were used as catalysts. The base-free amido complexes [(COD)Ir(Pboolean ANDNR)] displayed similar catalytic activity to the combined systems [(COD)Ir(Pboolean ANDNHR)]BF4-KOH (Pboolean ANDNHR = Ph2PCH2CMe2NH2, 2-Ph2PC6H4NHMe). The ability of both the cationic beta-amino- and the neutral beta-amidophosphane Ir-I complexes to undergo oxidative H-2 addition and the observation of H-2/D+ as well as H-2/D-2 exchange processes during catalysis provided evidence for a mechanism involving reversible "[Ir-III(H)(2)-Pboolean ANDNHR](+) reversible arrow [(eta(2)-H-2)-Ir-III(H)-Pboolean ANDNR](+)" proton-to-hydride transfer and heterolytic H-2 cleavage on amino-dihydride and amido-dihydrogen-monohydride tautomers. The crystal structures of [(COD)Ir{(1S,2S)-Ph2PCH(Ph)CH(Me)NHCH2Ph}]BF(4)(.)2THF, [(COD)Ir{1R,2S-Ph2PCH(Ph)CH(Me)NHMe}](BF4THF)-T-., and the orthometalated 18e Ir-I complex [(COD)Ir{(1R,2S)-Ph2PCH(C6H4-o)CH(Me)NHCHMe2}], which resulted from treatment of [(COD)Ir{(1R,2S)-Ph2PCH(Ph)CH(Me)NHCHMe2}]BF4 with excess KOH, have been determined by single crystal X-ray diffraction studies. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.