SYNTHESIS, STRUCTURE DETERMINATION AND IMMOBILIZATION OF SOME DIRHODIUM COMPLEXES WITH CHIRAL BINDING THIOLATO LIGANDS - INVESTIGATION OF THEIR CATALYTIC ACTIVITY FOR ENANTIOSELECTIVE HYDROGENATION

(-)-cis-[Dicarbonyl-mu-chloro-[mu-6,6-dimethylbicyclo[3.1.1]heptane-2-methanethiolato-S:S)]]bis[tris(1,1-dimethylethyl)phosphine]dirhodium (5a) and (+)-cis-[dicarbonyl-mu-chloro-[mu-5-beta-methyl-2-alpha-(1-methylethyl)cyclohexanethiolato-S:S]]bis[tris(1,1-dimethylethyl)phosphiine]dirhodium (5b) were prepared from [Rh(CO)2]2(mu-Cl)2, P(t-Bu)3 and the corresponding sulfides (-)-cis-(myrtanethio)trimethylsilane (4a) and (+)-(neomenthanethio)trimethylsilane (4b). The molecular structures of 5a and 5b were determined by single-crystal X-ray diffraction (5a: C222(1), a = 13.749(4), b = 23.509(9), c = 27.271(9) angstrom, Z = 8, R = 0.0443, R(W) = 0.0491. 5b: P1BAR, a = 16.209(6), b = 14.150(5), c = 9.899(3) angstrom, Z = 2, R = 0.058, R(W) = 0.094). Complex 5b was found to exist in the crystal as a pair of 1R,2R,5S- and 1S,2R,5S-epimers. Both chiral complexes have been immobilized by attachment to divinylbenzene-crosslinked polystyrene resins. Application of the chiral dirhodium complexes as catalysts for hydrogenation of methyl alpha-acetamidocinnamate revealed that while 5b leads to optically active N-acetylphenylalanine methyl alpha-acetamidocinnamate revealed that while 5b leads to optically active N-acetylphenylalanine methyl ester (up to 50% ee) 5a gives only the racemic product. The immobilization of the complexes proved to improve the enantioselectivity of 5a but decreases the ability of 5b to induce asymmetric reduction.