Ionic Rh(I)-complexes containing π-accepting and hemilabile P,N-ligands as efficient catalysts for hydroformylation of 1-octene

The ionic hybrid P,N-ligands of 1 and 2 have been synthesized as one type of unconventional tertiary phosphines with the advantages of both the pi-accepting ligands and the hemilabile ligands. The corresponding ionic Rh(I)-complexes of 1A and 2A proved to be more efficient catalysts for hydroformylation of 1-octene over isomerization than the traditional Rh-I(acac)(CO)(PPh3), due to the pi-backdonation interaction in Rh -> P linkage and the hemilabile ligation of N,P-coordinating sites to Rh-center. The in situ high-pressure FT-IR analysis indicated that: (1) the formation and lifetime of the active Rh-H species (2047 cm(-1)) derived from 1A are facilitated by the presence of ligand 1; (2) the formation of the active Rh-H species is depressed without the aid of the P,N-hemilabile ligation; and (3) the active Rh-H species derived from Rh-I(acac)(CO)(PPh3) is unstable and susceptible to the formation of the inactive carbonyl-bridged Rh-dimer. (C) 2014 Elsevier B.V. All rights reserved.