Hydroformylation of 1-octene using low-generation Rh(i) metallodendritic catalysts based on a tris-2-(2-pyridyliminoethyl)amine scaffold

Abstract

The synthesis and characterization of low-generation pyridylimine Rh(I) metallodendrimers is described. These metallodendrimers were obtained via a Schiff base condensation of tris-2-(aminoethyl)amine with 2-pyridinecarboxaldehyde to afford the tris-2-(2-pyridylimine ethyl) amine ligand (1). Subsequent complexation reactions with [RhCl(CO)₂]₂ and [RhCl(COD)]₂ yielded the corresponding metal-containing dendrimers containing –RhCl(CO) and –Rh(COD) moieties on the periphery. These new rhodium metallodendrimers (2 and 3) and their precursor ligand (1) are thermally stable and have been characterized using ¹H NMR, ¹³C NMR, ³¹P NMR, FT-IR spectroscopy, elemental analysis as well as mass spectrometry. The Rh(I) metallodendrimers are highly active and chemo- and regioselective in the hydroformylation of 1-octene. Aldehydes were favoured at moderate to high temperatures (95 °C and 75 °C) and pressure (30 bars), while more iso-octenes were formed at low temperature (55 °C) and pressures (5 and 10 bars). The mononuclear analogues (5 and 6) also produced more aldehydes (albeit showing catalyst decomposition at 95 °C and 75 °C, 30 bars) and these aldehydes were mostly branched.