SYNTHESIS OF PT COMPOUNDS CONTAINING CHIRAL S)-PENTANE-2,4-DIYL-BIS(5H-DIBENZO[B]PHOSPHINDOLE) AS LIGAND AND THEIR USE IN ASYMMETRIC HYDROFORMYLATION OF STYRENE DERIVATIVES

Unlike bis(diphenyl)phosphine derivatives in general, )-pentane-2,4-di yl-bis(5H-dibenzo[b]phosphindole), S,S-BDBPP, gives a trans oligomeric compound [PtCl2(S,S-BDBPP)](n), 1, in reaction with dichloro-Pt precu rsors such as PtCl2(PhCN)(2), PtCl2(CH3CN)(2) and PtCl2(COD) at room t emperature. Compound 1, which could be readily isolated, slowly rearra nges in solutions at room temperature to the expected cis-monomer PtCl 2(S,S-BDBPP), 3. Heating or the presence of PtCl2(COD) accelerates the transformation of compound 1 to 3. SnCl2 adducts of both compounds, t rans-[PtCl(SnCl3)(S,S-BDBPP)](n), 2, and cis-PtCl(SnCl3)(S,S-BDBPP), 4 , as well as the known cis-PtCl(SnCl3)(S,S-BDPP), 5, (S,S-BDPP = (2S,4 S)-2,4-bis(diphenylphosphino)pentane have been tested as catalysts in the asymmetric hydroformylation of p-isobutylstyrene. The phenyl analo g 5 provides up to 75% e.e. bur moderate yields to chiral 2-(4-isobuty lphenyl)-2-propanal. Compared to this, the regioselectivity to the bra nched aldehyde is remarkably increased; however, the enantioselectivit y is drastically decreased by the use of both dibenzophosphole derivat ives 2 and 4. The similarities in the selectivities provided by 2 and 4 indicate that the trans oligomer 2 transforms to the cis-monomer 4 d uring the catalytic process, X-ray crystal structure determination of compound 3 shows a half-chair conformation for the chelate ring with a symmetric arrangement of dibenzophosphole groups. Besides a preferenc e for the latter achiral conformation, the planar structure of the dib enzophosphole groups can also be considered as reason for the moderate enantioselectivities provided by 4. (C) 1997 Elsevier Science S.A.