Square-Planar Carbonylchlororhodium(I) Complexes Containing trans-Spanning Diphosphine Ligands as Catalysts for the Carbonylation of Methanol

摘要

The rhodium(I) complexes -[Rh(diphos)(CO)Cl] (diphos=pbpb), (diphos=nbpb), and (diphos=cbpb) were synthesized () and used as catalysts for the carbonylation of MeOH to AcOH (). The coordination imposed by the rigid C-spacer framework of the diphos ligands pbpb, nbpb, and cbpb, demonstrated by P-NMR and IR spectroscopy of - and unambiguously confirmed by single-crystal X-ray structure analysis of , improved the thermal stability of the rhodium(I) system under carbonylation conditions and, hence, the catalytic performance of the complexes. For the catalytic carbonylation of MeOH, the active catalyst could be prepared from the mixture of [Rh(CO)Cl] and the corresponding diphos ligand pbpb, nbpb, or cbpb, giving the same results as carbonylation in the presence of the isolated complexes , or (see ). The highest activity was observed for complex (or the mixture [Rh(CO)Cl]/pbpb, the catalytic turnover number (TON) being 950 after 15 min (170°, 22 bar).