Hydroformylation of oct-1-ene catalyzed by dinuclear gem-dithiolato-bridged rhodium(I) complexes and phosphorus donor ligands

The dinuclear gem-dithiolato bridged compounds [Rh2(μ-S2Cptn)(cod)2] (1) (CptnS22− = 1,1-cyclopentanedithiolato), [Rh2(μ-S2Chxn)(cod)2] (2) (ChxnS22− = 1,1-cyclohexanedithiolato), [Rh2(μ-S2CBn2)(cod)2] (3) (Bn2CS22− = 1,3-diphenyl-2,2-dithiolatopropane) and [Rh2(μ-S2CiPr2)(cod)2] (4) (iPr2CS22− = 2,4-dimethyl-2,2-dithiolatopentane) dissolved in toluene in the presence of monodentate phosphine or phosphite P-donor ligands under carbon monoxide/hydrogen (1:1) atmosphere are efficient catalysts for the hydroformylation of oct-1-ene under mild conditions (6.8 atm of CO/H2 and 80 °C). The influence of the gem-dithiolato ligand, the P-donor co-catalyst and the P/Rh ratio on the catalytic activity and selectivity has been explored. Aldehyde selectivities higher than 95% and turnover frequencies up to 245 h−1 have been obtained using P(OMe)3 as modifying ligand. Similar activity figures have been obtained using P(OPh)3 although the selectivities are lower. Regioselectivities toward linear aldehyde are in the range 75–85%. The performance of the catalytic systems [Rh2(μ-S2CR2)(CO)2(PPh3)2]/PPh3 has been found to be comparable to the systems [Rh2(μ-S2CR2)(cod)2] at the same P/Rh ratio. The system [Rh2(μ-S2CBn2)(cod)2] (3)/P(OPh)3 has been tested in the hydroformylation-isomerization of trans-oct-2-ene. Under optimized conditions up to 54% nonanal was obtained. Spectroscopic studies under pressure (HPNMR and HPIR) evidenced the formation of hydrido mononuclear species under catalytic conditions that are most probably responsible for the observed catalytic activity.

A series of dinuclear compounds [Rh2(μ-S2CR1R2)(cod)2] having bridging gem-dithiolato ligands (R1, R2–(CH2)4–, –(CH2)5–; R1R2Bn, iPr) in the presence of monodentate phosphine or phosphite ligands are efficient catalyst precursors for the hydroformylation of oct-1-ene under mild conditions. The catalytic activity is strongly influenced both by the structure of catalyst precursor and the P/Rh ratio being the precursors containing acyclic gem-dithiolato ligands considerably more active. Spectroscopic studies under pressure showed that mononuclear species formed under catalytic conditions are most likely responsible for the observed catalytic activity.Figure optionsDownload as PowerPoint slide