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Keywords:

  • Rhodium;
  • Hydroformylation;
  • Density functional calculations;
  • Hemilabile ligands

Abstract

The synthesis and spectroscopic characterization of [Rh{R2P(S)NP(S)R2-S,S′}(cod)] [cod = 1,5-cyclooctadiene; R = Ph (1), iPr (4)], [Rh{Ph2P(S)NP(S)Ph2-S,S′}(CO)2] (2) and [Rh{Ph2P(S)NP(S)Ph2-S,S′}(CO)(PPh3)] (3) is described. The crystal structures of complexes 1 and 3 are also presented. The synthesized RhI complexes are essentially not catalytically active against olefin hydroformylation, in contrast to the previously reported complex [Rh{Ph2P(O)NPPh2-P,O}(CO)(PPh3)] (6). Differences in the catalytic activity were interpreted with the aid of a well-defined DFT-based protocol involving relativistic effects and dispersion correction. The steric and electronic effects of the RhI coordination environment with respect to their activation by H2 are discussed. The results demonstrate that the presence of the more electronegative oxygen atom in the RhI coordination sphere polarizes the H–H bond and promotes its heterolytic cleavage, thereby leading to the formation of a RhI–monohydride complex in which the oxygen atom of the ligand is protonated.