Novel gem-dithiolato-bridged rhodium hydroformylation catalysts: Bridging the gap in dinuclear rhodium thiolate chemistry

The direct protonation of the bridging hydroxo ligands in [Rh(μ-OH)(cod)]2 by 1,1-dimercaptocyclohexane [Chxn(SH) 2] yields the gem-dithiolato-bridged compound [Rh2(μ- S2Chxn)-(cod)2] (1). The dinuclear framework in 1 is supported by a 1,1-cyclohexanedithiolato ligand exhibiting a 1:2κ2S,1:2κ2S′ coordination mode. Compound 1 is an active catalyst precursor in the presence of P-donor ligands for the hydroformylation of oct-1-ene under mild conditions of pressure and temperature (100 PSI, 353 K). The best results were obtained with phosphite ligands as modifying ligands. An aldehyde selectivity of 97 %, a regioselectivity towards the linear aldehyde of 81 %, and turnover frequencies of up to 198 h-1 were obtained with the catalytic system 1/P(OMe)3. The dinuclear compound [Rh2(μ-S 2Chxn)(CO)2(PPh3)2] (2) was isolated from the catalytic solutions resulting from the system 1/PPh3 and was characterized by spectroscopic means and by X-ray diffraction to be the frans isomer. The mixed-ligand dinuclear complexes 2 and [Rh2(μ- S2Chxn)(CO)2(PCy3)2] (3) (Cy = cyclohexyl) were independently prepared by reaction of Chxn(SH)2 with the mononuclear complexes [Rh(acac)(CO)-(PR3)] in the appropriate molar ratio.The financial support from Ministerio de Educación y Ciencia (MEC/FEDER) is gratefully acknowledged (Project CTQ2006-03973/BQU and Factoría de Cristalización, CONSOLIDER INGENIO-2010). A. B. R. thanks the Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (CYTED, Project V.9) for a fellowship. A. J. P. thanks to Fonacit-Venezuela (S1-2002000260) for financial support.Peer Reviewe