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 π-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)(PPh 3 ), due to the π-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)(PPh 3 ) is unstable and susceptible to the formation of the inactive carbonyl-bridged Rh-dimer.