Wide bite angle amine, arsine and phosphine ligands in rhodium- and platinum/tin-catalysed hydroformylation

Abstract

New wide bite angle amine, arsine and mixed phosphineamine and phosphinearsine ligands based on xanthene backbones were synthesized. The co-ordination chemistry and the catalytic performance of these ligands were compared to those of the parent phosphine ligands. The amine based xanthene ligands do not form rhodium–hydride complexes and therefore give very poor rhodium hydroformylation catalysts. The catalytic performance of the xantarsine and the mixed xantphosarsine ligands is comparable with that of the xantphos ligands and they form similar (ligand)Rh(CO)₂H and [(ligand)Rh(CO)₂]₂ complexes. In the platinum/tin-catalysed hydroformylation the xantarsine and the mixed xantphosarsine ligands proved to be superior to the xantphos ligands. The remarkably high selectivity and activity that is displayed by the mixed xantphosarsine ligand is explained by its wide natural bite angle and the formation of cis co-ordinated platinum complexes.