17-ELECTRON ALKYNYL COMPLEXES OF CYCLOPENTADIENYLIRON(III)

The complexes [Fe(C=R)(L-L)(eta-C5R'5)] [R = Bu(t), CO2Me, CO2Et, SiMe 3, Ph or CH2OMe, L-L = Ph2PCH2PPh2 (dppm), R' = H; R = Bu(t) or Ph, L- L = Ph2PCH2CH2PPh2 (dppe), R'= Me] undergo reversible one-electron oxi dation at a platinum electrode in CH2Cl2. Chemical oxidation with [Fe( eta-C5H5)2][PF6] gave the isolable salts [Fe(C=CR)(dppe)(eta-C5Me5)][P F6] (R = Bu(t) or Ph) which Mossbauer spectroscopy suggests to be comp lexes of Fe(III). The ESR spectra of these salts, and of the cations [ Fe(C=CR)(dppm)(eta-C5H5)]+ (R = Bu(t) CO2Me, CO2Et or Ph), generated b y in situ oxidation with [Fe(eta-C5H5)2][PF6], are similar to those of low-spin d5 complexes of Cr(I), Mn(II) and Fe(III).