Heteroleptic dirhodium(II,II) acetato-bipyridyl complexes: Evaluation as catalyst precursors for hydroformylation reactions

Abstract

The synthesis of cationic bimetallic ‘pseudo-paddlewheel’ dirhodium(II,II) acetato-bipyridyl complexes of the type [Rh2(OAc)2(bis-4,4′-R-bipy)2]2+ containing either acetate (AcO-) or hexafluorophosphate (PF6-) counter ions is described. In both series, the 4 and 4′ positions of each bipyridyl ligand are substituted such that R = H, CF3 or OMe (complexes 1-3 for AcO- and 4-6 for PF6- derivatives). As catalyst precursors for the hydroformylation reaction, the complexes were initially evaluated using 1-octene as a substrate. The complex which displayed the greatest chemoselectivity toward aldehydes was evaluated further as a catalyst precursor for the hydroformylation of styrene, cyclohexene and 7-tetradecene as substrates. A correlation between product distributions in terms of chemo- and regioselectivity in the hydroformylation reaction versus axial site interaction is delineated. Recyclability was achieved through suitable modification of the substituent and counter ion, culminating in a simplistic method of post-catalytic precursor collection with minimal reduction of the catalytic activity over 5 cycles.