Metal complexes with atropisomeric sulfur ligands in asymmetric hydroformylation X-ray structure of [Rh2(μ-biphes)(cod)2] (H2biphes = 4,4′-biphenanthrene-3,3′-dithiol)

The addition of the atropisomeric racemic sulfur compound 4,4'-biphenanthrene-3,3'-dithiol (H(2)biphes) to a dichloromethane solution of [{M(mu-OMe)(cod)}(2)] (M = Rh, Ir, cod = cycloocta-1,5-diene) afforded the dithiolate-bridged complexes [{Rh-2(mu-biphes)(cod)(2)}(n)] (n = 2 5 or n = 1 6) and [{Ir-2(mu-biphes)(cod)(2)}].nCH2Cl2 7. When 1,1'-binaphthalene-2,2'-dithiol (H(2)binas) reacted with [{Ir(mu-OMe)(cod)}(2)], complex [Ir-2(mu-binas)(cod)(2)] 8 was obtained. Complexes 5 and 6 reacted with carbon monoxide to give the dinuclear tetracarbonyl complex [Rh-2(mu-biphes)(CO)(4)] 9. The reaction of 9 with PR3 provided the mixed-ligand complexes [{Rh-2(mu-biphes)(CO)(2)(PR3)}(2)]. xCH(2)Cl(2) (R = Ph, x = 2 10, C6H11, x = 1 11) and [{Rh-2(mu-biphes)(CO)(3)(PR3)}(2)]. CH2Cl2 12 (R = OC6H4But-o). The crystal structure of 6 was determined by X-ray diffraction. Reaction of the dithioether ligand Me(2)biphes with [Rh(cod)(2)]ClO4 in CH2Cl2 solution afforded the cationic complex [Rh(cod)(Me(2)biphes)]ClO4 . CH2Cl2 13. 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%. (C) 1997 Elsevier Science S.A.