Trimethyl phosphite complexes of iron( II ): preparation, characterisation, and Mössbauer spectra

The preparation of a novel series of neutral and cationic low spin iron(II) complexes containing trimethyl phosphite is reported. These complexes are more closely analogous to those of isocyanides than those of other non-chelating tertiary phosphine ligands. Mössbauer spectra show that the unexpected bonding characteristics of P(OMe)3, being both a strong σ-donor and π-acceptor, account for much of this unexpected chemical behaviour. P(OMe)3 preferentially displaces iodide from Fe(CO)2I2{P(OMe)3}2 to give the stable intermediate [Fe(CO)2I{P(OMe)3}]+, from which carbonyl can be displaced subsequently by more phosphite yielding trans-Fe(CO)I{[P(OMe)3}4]+. These species are isoelectronic to known manganese(I) complexes.