MOSSBAUER-SPECTROSCOPY OF (BENZYLIDENEACETONE)FE(CO)2L COMPLEXES WITH L=CO, PHOSPHITES AND PHOSPHINES - AN ANALYSIS OF LIGAND EFFECTS

Abstract

The (benzylideneacetone)Fe(CO)2L complexes, with L = CO, PPh3, PMePh2, PMe2Ph, PEt3, PCy3, P(OPh)3, P(OMe)3, P(OEt)3 and P(O(i)Pr)3 have been studied by Mossbauer spectroscopy. The spectra are compatible with a distorted octahedral geometry with the iron atom at the center. The isomer shifts delta and quadrupole splittings DELTAE(q) are correlated with the Giering electronic parameter chi(d) of the phosphines and phosphites and with the C-13 NMR complex shifts DELTAC4 of coordinated benzylideneacetone. The results are discussed in terms of the stereoelectronic effects of the ligand L. Correlation between isomer shifts and quadrupole splittings indicates that d(pi)-L(pi)star back bonding is predominant in the complexes with L = CO and phosphites and negligible in the complexes with L = phosphines.