Rh(i) complexes supported on a biopolymer as recyclable and selective hydroformylation catalysts

Abstract

Chitosan-supported Rh complexes were prepared in a stable form to form new catalysts and have been characterized using elemental analysis, UV-vis, FT-IR, ICP-MS, PXRD, solid state 31P and 13C NMR spectroscopy and TEM. Mononuclear Rh(I) complexes (as models for the heterogenized catalysts) were also prepared via the Schiff-base condensation reaction and the crystal structure of the cyclohexyl iminophosphine Rh(I) complex was elucidated. The chitosan-supported Rh complexes and mononuclear analogues are active catalysts in the hydroformylation of 1-octene with optimal reaction conditions realized at 75 °C and 30 bar syngas pressure. Under these conditions, 1-octene conversion to the desired linear aldehydes was observed and the best selectivity in this regard was shown by the supported iminophosphine-based rhodium catalyst. Overall, the supported catalysts showed similar chemo- and regioselectivities in comparison to their mononuclear counterparts but where more stable, being reused up to four times without loss of activity and selectivity.