N′N′N pincer and N′N bidentate(pyrazolylpyridyl) Rh(I) complexes as catalyst precursors for hydroformylation of olefins

Abstract

The industrial process of hydroformylation or the oxo process has been used for many years in the production of aldehydes from alkenes. Different metals have been used as efficient catalysts for hydroformylation, in which linear and branched aldehydes are the products obtained; therefore, the development of new catalysts for hydroformylation with high selectivity to aldehydes is important. Rhodium complexes 6–9 were synthesized using [RhCl(CO)₂]₂, or [RhCl(COD)]₂, with either pyrazolylpyridyl N′N′N pincer ligands or a pyrazolylpyridyl N′N ligand. These complexes were then evaluated as catalyst precursors in the hydroformylation reaction using a variety of alkenes. The catalysts all showed activity in hydroformylation but the most active catalyst was methyl-substituted pyrazolyl–rhodium complex 7 following optimization of temperature, syngas pressure and amount of catalyst. Other olefinic substrates were used for hydroformylation in the presence of 7 under the optimum hydroformylation conditions. Undecene and dodecene as substrates only showed minimal formation of aldehydes with predominantly isomerization of the alkene being observed.