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

Abstract

The addition of the atropisomeric racemic sulfur compound 4,4′-biphenanthrene-3,3′-dithiol (H 2 biphes) to a dichloromethane solution of [{M( μ-OMe)(cod)} 2] (M = Rh, Ir, cod = cycloocta-1,5-diene) afforded the dithiolate-bridged complexes [{Rh 2( μ-biphes)(cod) 2} n ] ( n = 2 5 or n = 1 6) and [{Ir 2( μ-biphes)(cod) 2} n ]· n CH 2Cl 2 7. When 1,1′-binaphthalene-2,2′-dithiol (H 2 binas) reacted with [{Ir( μ-OMe)(cod)} 2], complex [Ir 2( μ-binas)(cod) 2] 8 was obtained. Complexes 5 and 6 reacted with carbon monoxide to give the dinuclear tetracarbonyl complex [Rh 2( μ-biphes)(CO) 4] 9. The reaction of 9 with PR 3 provided the mixed-ligand complexes [{Rh 2( μ-biphes)(CO) 2(PR 3) 2} 2] · xCH 2Cl 2 (R = Ph, x = 2 10, C 6H 11, x = 1 11) and [{Rh 2( μ-biphes)(CO) 3(PR 3)} 2] · CH 2Cl 2 12 (R = OC 6H 4Bu t- o). The crystal structure of 6 was determined by X-ray diffraction. Reaction of the dithioether ligand Me 2biphes with [Rh(cod) 2]ClO 4 in CH 2Cl 2 solution afforded the cationic complex [Rh(cod)(Me 2biphes)]ClO 4 · CH 2Cl 2 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%.