Chiral modification of trinuclear ruthenium clusters with proline and cysteine derivatives. Synthesis, crystal structure, and catalytic properties of [(μ 2-H)Ru 3(CO) 10- (μ 2,η 2-OC [formula omitted]HCH 2OCH 3)] and [(μ 2-H)Ru 3(CO) 9(μ 3,η 2- [formula omitted]HCH 2OCH 3)

Abstract

Proline and cysteine derivatives have been used for the chiral modification of the trinuclear ruthenium cluster system. Whereas proline derivatives yield carbamoyl Ru 3 clusters by NH activation, the cysteine derivatives react by SH activation to give mercapto Ru 3 clusters. The chiral methoxymethyl pyrrolydine carbamoyl clusters catalyse the enantioselective isomerization of nerol to give citronellal with an enantiomeric excess of 12.4%. The structures of [(μ 2-H)Ru 3(CO) 10(μ 2,η 2- OC NCH 2CH 2CH 2C HCH 2OCH 3)] ( R- 2) and [(μ 2-H)Ru 3(CO) 9(μ 3,η 2- NCCH 2CH 2C HCH 2OCH 3)] ( S- 3) have been determined by X-ray diffraction methods. Crystals of R- 2 are monoclinic, space group P2 1 with Z = 2, in a unit cell of dimensions a = 8.662(4), b = 18.234(4), c = 7.662(2) Å, β = 94.87(2)°. Crystals of S- 3 are monoclinic, space group P2 1 with Z = 2 in a unit cell of dimensions a = 8.881(4), b = 16.720(6), c = 7.567(3) Å, β = 112.15(2)°. Both structures have been solved by direct and Fourier methods and refind by full-matrix least-squares to R = 0.0581 ( R- 2) and R = 0.0239 ( S- 3) for 2366 ( R- 2) and 2454 ( S- 3) observed reflections. The structure of R- 2 consists of a ruthenium triangle of unequal edges with both the hydride and carbamoyl ligands bridging the longest edge; the carbamoyl ligand interacts through the carbon and oxygen atoms. The structure of S- 3 shows a metal triangle of unequal edges in which the dehydrogenated substituted pyrrolidine ligand interacts with all three Ru atoms through the C and N atoms of the imine group to form two σ-bonds with the two metals defining the longest edge (bridged also by the hydride ligand) and a π-bond with the third one.