Metal Complexes with Atropisomeric Sulfur LIGANDS IN Asymmetric Hydroformilation. X-ray Structure of (Rh2(?-biphes)(cod)2)

The addition of the atropisomeric racemic sulfur compound 4,4?-biphenanthrene-3,3?-dithiol (H2 biphes) to a dichloromethane solution of [{M(?-OMe)(cod)}2] (M = Rh, Ir, cod = cycloocta-1,5-diene) afforded the dithiolate-bridged complexes [{Rh2(?-biphes)(cod)2}n] (n = 2 5 or n = 1 6) and [{Ir2(?-biphes)(cod)2}n]·nCH2Cl27. When 1,1?-binaphthalene-2,2?-dithiol (H2 binas) reacted with [{Ir(?-OMe)(cod)}2], complex [Ir2(?-binas)(cod)2] 8 was obtained. Complexes 5 and 6 reacted with carbon monoxide to give the dinuclear tetracarbonyl complex [Rh2(?-biphes)(CO)4] 9. The reaction of 9 with PR3 provided the mixed-ligand complexes [{Rh2(?-biphes)(CO)2(PR3)2}2] · xCH2Cl2 (R = Ph, x = 2 10, C6H11, x = 1 11) and [{Rh2(?-biphes)(CO)3(PR3)}2] · CH2Cl212 (R = OC6H4But-o). The crystal structure of 6 was determined by X-ray diffraction. Reaction of the dithioether ligand Me2biphes with [Rh(cod)2]ClO4 in CH2Cl2 solution afforded the cationic complex [Rh(cod)(Me2biphes)]ClO4 · CH2Cl213. Asymmetric hydroformylation of styrene was performed using the complexes described. The extent of aldehyde conversion ranges from 53 to 100%, with selectivities towards branched aldehydes in the range 51 to 96%. The enantioselectivities were quite low and did not exceed 20%.