Novel gem‐Dithiolato‐Bridged Rhodium Hydroformylation Catalysts: Bridging the Gap in Dinuclear Rhodium Thiolate Chemistry

Abstract

AbstractThe 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‐S2Chxn)(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 trans 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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)