Synthesis, Electronic Properties, and Lewis Acidity of Rhodium Complexes Bearing X-Type PBP, PAlP, and PGaP Pincer Ligands

Abstract

Abstract We have synthesized rhodium complexes that bear X-type PBP and PGaP pincer ligands. X-ray diffraction analysis and IR spectroscopy of the PBP– and PGaP–Rh(CO)2 complexes showed that the σ-donicity and trans-influence of the X-type boryl ligand are stronger than those of the X-type gallyl ligand. Moreover, the Lewis acidity of the PEP–Rh complexes (E = B, Al, Ga) was examined. The PBP–Rh complex did not interact with the Lewis base N,N-dimethyl-4-aminopyridine (DMAP), while the PAlP–Rh complex coordinated DMAP more strongly via the Al atom than the PGaP–Rh complex via the Ga atom. DFT calculations of the PEP–Rh complexes revealed the details of the electronic properties and Lewis acidity of the X-type PEP pincer ligands. Their σ-donicity increases in the order Ga < B < Al, and the strength of their trans-influence follows the order Ga < Al < B. The polarity of the Eδ+–Rhδ− bond was found to be the greatest for Al and the smallest for B. The Lewis acidity based on the calculated binding energy increases in the order B ≪ Ga < Al, which is consistent with the experimental results.