756411-90-2Relevant academic research and scientific papers
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
Dahlenburg, Lutz,Goetz, Rainer
, p. 888 - 905 (2007/10/03)
Chiral and achiral P,N-chelated IrI complexes of the general type [(COD)Ir(P∩NR1R2)]BF4, where COD = η4-1,5-C8H12 and P∩NR1R 2 = (1R,2R)-, (1S,2S)-, or (1R,2S)-Ph2PC 1H(Ph)C2H(Me)NR1R2 (NR 1R2 = NH2, NHMe, NHCH2Ph, NHCHMe2, NMe2), Ph2PCH2CR 2NH2 (R = H, Me), of 2-Ph2PC6H 4NHMe, have been prepared by treating [Ir(COD)2]BF 4 with the required β-aminophosphane in THF. The monolithiated ligands Ph2PCH2CMe2N(Li)H and 2-Ph 2PC6H4N(Li)Me interacted with [{(COD)Ir(μ-Cl))2] to give the neutral alkyl- and arylamido compounds [(COD)-Ir(Ph2PCH2CMe2NH)] and [(COD)Ir(2-Ph2PC6H4NMe)]. All IrI complexes [(COD)Ir(P∩NR1R2)]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 H2 (10-50 bar) between 25 and 50 °C. The reaction occurred with modest to moderate enantioselectivity (ca. 20-75% ee) if chelate complexes bearing the various optically active β-aminophosphanes were used as catalysts. The base-free amido complexes [(COD)-Ir(P∩NR)] displayed similar catalytic activity to the combined systems [(COD)Ir(P∩NHR)]BF 4-KOH (P∩NHR = Ph2PCH2CMe 2NH2, 2-Ph2PC6H4NHMe). The ability of both the cationic β-amino- and the neutral β-amidophosphane IrI complexes to undergo oxidative H 2 addition and the observation of H2/D+ as well as H2/D2 exchange processes during catalysis provided evidence for a mechanism involving reversible "[IrIII(H) 2-P∩NHR]+ ? [(η2-H2)-Ir III(H)-P∩NR]+" proton-to-hydride transfer and heterolytic H2 cleavage on amino-dihydride and amido-dihydrogen- monohydride tautomers. The crystal structures of [(COD)Ir{(1S,2S)-Ph 2PCH(Ph)CH(Me)NHCH2Ph}]BF4·2THF, [(COD)Ir{1R,2S-Ph2PCH(Ph)CH(Me)NHMe}]BF4·THF, and the orthometalated 18e IrI complex [(COD)Ir{(1R,2S)-Ph 2PCH(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. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
