A very readily prepared ligand for rhodium catalysed propene hydroformylation

In the search for an easy-to-make ligand that would enable Rh catalysed hydroformylation of propeneto favour the branched aldehyde, iso-butanal, bis-phosphonites and bis-phosphoramidites were designed.Catalysts derived from bis-phosphonites gave the desired low n:iso ratios, but were unstable to hydrolysis. A bis-phosphoramidite ligand (EasyDiPhos) that can be made in just one synthetic step has been discovered thatenables Rh-catalysed hydroformylations to proceed with unusually low n:iso ratios. They were also found to havesignificant stability to moisture, air, and to relatively high temperatures during hydroformylation conditions. The latter was studied using a combination of High-Pressure-Infra-Red spectroscopy and NMR analysis of the catalyst resting state after 1 week under relevant conditions. Propene hydroformylation with n:iso ratios well below 1 was carried out and with turnover numbers around 1000 mol/mol in one hour reaction time. One of the ligands, whilst not being the most iso-selective example, had a partially flexible n:iso ratio depending on temperature and pressure. Two Pt(II) complexes were prepared and their X-ray crystal structures determined.The most iso-selective catalyst was examined at low temperature (prioritising iso-selectivity over rates) inhydroformylation of some other terminal alkenes with significant branched selectivity.