Bond Character between Iron and Phosphorus in Fe−P(E)YZ (E = O, S; Y, Z = Alkoxy, Amino, Phenyl) As Inferred from 57Fe Mössbauer Measurements

Abstract

A series of (η5-C5R5)(CO)2Fe{P(E)YZ} complexes (R = H, Me; E = O, S; Y, Z = OMe, OEt, NEt2, MeNCH2CH2NMe, Ph), (η5-C5H5)(CO)2FeX (X = Cl, Br, I), and (η5-C5Me5)(CO)2FeCl were prepared, and the 57Fe Mossbauer spectra together with IR(νCO) and 31P NMR spectra were measured. The Fe−P bond in (η5-C5R5)(CO)2Fe{P(E)YZ} is found to be as covalent as the Fe−Me bond in (η5-C5H5)Fe(CO)2Me. There are linear correlations between isomer shifts (IS) and quadrupole splittings (QS) in the 57Fe Mossbauer spectra, between IS and chemical shifts in the 31P NMR spectra (δ), between IS and the IR stretching frequencies in the CO region (νCO), and between δ and νCO. These correlations indicate that the electron-donating group on the phosphorus atom (Y, Z) increases the electron density on the phosphorus atom, increases π-donation from P(E)YZ to the Fe, and concomitantly increases π-back-donation from iron to the CO ligands. The systematic replacement of the carbonyl group by phosphine or phosphites shows the large shift in IS ...