Effects of the ligands on the electrochemical oxidation of (benzylydeneacetone)Fe(CO)2L, with L=CO, phosphines and phosphites

Half-peak oxidation potentials, Ep/2ox were obtained for two congeneric series of (BDA)Fe(CO)2L (BDA=(C6H5)CHCHC(O)CH3, benzylideneacetone) complexes, one with L=CO, phosphites and the other with L=phosphites. Correlations of the Ep/2ox data with ligand parameters such as Giering electronic parameter, χd, for the phosphorus ligands, and Mössbauer isomer shifts, −δ, and quadrupole splittings, ΔEq, for the iron atom are presented. These correlations helped to describe and quantify the electronic effects of the phosphorous ligands on the Lewis acid iron(0) center. Transmission of these effects to the BDA ligand throughout the metal center was also examined. The results support the idea that dπLπ* back bonding is predominant for L=CO, significant for L=phosphites, and small for L=phosphines.