Rhodium(I), palladium(II), and platinum(II) complexes containing new mixed phosphane-phosphite ligands - Effect of the catalytic system stability on the enantioselective hydroformylation of styrene

The new mixed phosphane-phosphite ligands I and 2, derived from 3,3'-di-tert-butyl-2,2'-dihydroxy-5,5'-dimethoxybiphenyl and (S)-binaphthol, respectively, reacted with [Rh(COD)(THF)(2)]CF3SO3 to give the compounds [Rh(COD)(1)]CF3SO3 and [Rh(COD)(2)]CF3SO3 in which the ligands 1 and (S)-2 are chelated to the rhodium centre, The reaction with [Rh(CO)(2)Cl](2) gave two different products, [Rh(CO)(2)(L)Cl and [Rh(CO)(L)Cl [L = 1 and (S)-2], containing L as a chelate. On the basis of the IR and NMR spectroscopic data, the proposed structure of the pentacoordinate species is a trigonal bipyramide in which the phosphane-phosphite ligand assumes an equatorial-axial coordination. The reactions of 1 and 2 with [Pd(C6H5CN)(2)Cl-2] and [Pt(COD)I-2] gave the corresponding compounds [Pd(L)Cl-2] and [Pt(L)I-2] in which the ligands are chelated to the metal centre. The crystal structure of the chloroform solvate of [Pd(L)Cl-2] was fully characterised by an X-ray study, The chiral ligands (S)-2 and (S)-3 [derived from the ortho-bis (trimethylsilyl)-substituted (S)-binaphthol] were tested in the hydroformylation of styrene. The results obtained were discussed in light of the catalytic system stability.