Ligand effects in rhodium-catalyzed hydroformylation with bisphosphines:steric or electronic?

\u3cp\u3eTwelve commercially available bisphosphine ligands have been evaluated in rhodium-catalyzed hydroformylation reactions. All ligands exhibited high chemoselectivities for aldehyde formation. The highest enantioselectivity (53% ee) of styrene hydroformylation was achieved with (S)-BTFM-Garphos (L7) substituted with electron withdrawing substituents. High pressure NMR (HP-NMR) spectroscopy and in situ high pressure IR spectroscopy (HP-IR) were used to study the resting states of the catalyst species in the reactions. The ligand effect on the structures of the observable species was examined. Both electronic and steric factors were considered to contribute to the performance of the various ligands. The results showed that decreasing the phosphine basicity increased the enantioselectivity, while in the systems studied here the steric character plays a less important role than the electronic features in achieving good regioselectivities.\u3c/p\u3

Platinum Complexes of Rigid Bidentate Phosphine Ligands in the Hydroformylation of 1-Octene

The synthesis of the two novel diphosphine compounds 1,2-bis(3-(diphenylphosphino)-4-methoxyphenyl)benzene (1; Terphos), and 1,2-bis(2-diphenylphosphino)benzene (2), both derived from a terphenyl backbone structure, are described. Straightforward synthetic routes have been employed to obtain these ligands in good yields from cheap starting materials. The coordination of ligands 1 and 2 with PtCl2(cod) has been studied by NMR spectroscopy, and the X-ray crystal structures of the resulting complexes 4 and 5 were determined. The 31P NMR spectra of the mononuclear products demonstrate solely cis coordination for both bidentate ligands, with corresponding coupling constants JPt-P of 3810 Hz (cis-[PtCl2(1)], complex 4) and 3712 Hz (cis-[PtCl2(2)], 5). The bite angles P1-Pt-P2 were 98.74 and 105.89°, respectively, in the distorted square-planar complexes. The new diphosphines have been applied in the platinum/tin-catalyzed hydroformylation of 1-octene, and both ligands give active and selective platinum catalysts