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

Half-peak oxidation potentials, E-p/2(ox) were obtained for two congeneric series of (BDA)Fe(CO)(2)L (BDA = (C6H5)CH= CHC(O)CH3, benzylideneacetone) complexes, one with L = CO, phosphites and the other with L = phosphites. Correlations of the E-p/2(ox) data with ligand parameters such as Giering electronic parameter, chi(d), for the phosphorus ligands, and Mossbauer isomer shifts, -delta, and quadrupole splittings, DeltaE(q), 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 d(pi)-L-pi* back bonding is predominant for L = CO, significant for L = phosphites, and small for L = phosphines. (C) 2002 Elsevier Science B.V. All rights reserved.