SYNTHESIS OF THE NEW CHIRAL AMINODIPHOSPHINE LIGANDS -METHYLBENZYL)BIS(2-(DIPHENYLPHOSPHINO)ETHYL)AMINE AND -METHYLBENZYL)BIS(2-(DIPHENYLPHOSPHINO)ETHYL)AMINE AND THEIR USE IN THE ENANTIOSELECTIVE REDUCTION OFALPHA,BETA-UNSATURATED KETONES TO ALLYLIC ALCOHOLS BY IRIDIUM CATALYSIS

Synthesis of the potentially tridentate, optically pure ligands C6H5C H(Me)N(CH(2)CH(2)PPh(2))(2) (R)-(+)- and (S)-(-)-PNP; 5a,b) from thei r corresponding chiral primary amines was achieved with excellent yiel ds. The catalytic hydrogen-transfer reduction of PhCH=CHCOMe and other alpha,beta-unsaturated or unsymmetrical ketones in the presence of [I r(COD)(OMe)](2) and 5a,b is reported. These catalytic systems show hig h activity and chemoselectivity for the reduction of the carbonyl grou p (up to 94%). Due to the presence of the stereogenic center on the PN P ligands 5a,b, asymmetric induction was also achieved with enantiose lectivities up to 54%. Discussion concerning the catalytic pathway and the intermediates involved is reported in conjunction with independen t reactions of isolated, optically active compounds. Some of these are the iridium(I) cyclooctadiene complexes (R)- and (S)-[IrH(COD){C6H5C H(Me)N(CH(2)CH(2)PPh(2))(2)}] (8a,b) and the iridium(III) ortho-metala ted dihydrides fac-exo-(R)- fac-exo-(S)-, fac-endo-(R)-, and endo-(S)[ IrH2{C6H4C:H(Me)N(CH(2)CH(2)PPh(3))(2)}] 10a,b and 11a,b). X-ray crys tal data are given for exo-(R)-[IrH2-{C6H4CH(Me)N(CH(2)CH(2)PPh(2))(2 )}] (10a), a distorted octahedron. The (R)-PNP ligand facially coordi nates to the iridium metal center, with the two hydride ligands cis to one another. The sixth coordination site is occupied by the ortho car bon atom of the phenyl substituent bound to the stereocenter. Crystal data: monoclinic, P2(1), with a = 12.623(2) Angstrom, b = 18.265(3) An gstrom, c = 14.032(3) Angstrom, beta = 92.55(1)degrees, V = 3232 Angst rom(3), Z = 4, R = 0.037, and R(w) = 0.041.