GENERATION, CHARACTERIZATION, AND CHEMISTRY OF THE METHYLENE COMPLEXES [FE(ETA-5-C5ME5)(CO)(CO)(=CH2)]+, [FE(ETA-5-C5ME5)(CO)(PPH3)(=CH2)]+ AND THE X-RAY CRYSTAL-STRUCTURE OF [FE(ETA-5-C5ME5)(CO)2(CH2PPH3)]+BF-

The unstable methylene complexes [Fe(Cp*)(CO)(L)(═CH2)]+X- (Cp* = η5-C5Me5; L = CO (3), PPh3 (13)) are generated at -80 °C by the reaction of H+BF4--Et2O or Me3SiOSO2CF3 or CF3CO2H in CH2Cl2 with the precursor complexes [Fe(Cp*)(CO)(L)(CH2OCH3)] (L = CO (2), PPh3 (12)). The ancillary PPh3 ligand stabilizes the iron–methylene complex so that 13a is stable up to –10 °C. The methylene unit is aligned with the CO–Fe bond (Scheme III) and is characterized by two distinct broad singlets at δ 16.67 and 15.10 ppm in the1H NMR spectrum at – 80 °C. These coalesce at – 45 °C and give a sharp singlet (δ 15.95 ppm) at – 20 °C (ΔG‡ = 10.9 ± 0.1 kcal mol-1). Methylene transfer has been obtained by reaction of 3 with styrene to give phenylcyclopropane and with Ph3SiH to give Ph3SiMe. Both reactions occur at – 80 °C with 100% chromatographic yield. Thermal decomposition of 3 gives [Fe(Cp*)(CO)3]+BF4- (9) and [Fe(Cp*)(CO)2(CH2═CH2)]+BF4- (10). The unstable methylene complex 2 can be trapped with CF3CO2H give mainly [Fe(Cp*)(CO)2(CH2OCOCF3)] (7) and with PPh3 and H+BF4--Et20, which gives [Fe(Cp*)(CO)2(CH2PPh3)]+BF4- (4). The X-ray crystal structure of 4 was obtained and shows a ∠FeCP angle of 118°, larger than the regular sp3 angle because of the steric repulsion between the Cp* and PPh3 ligands. Crystals of 4, FeC31H32O2PBF4, are orthorhombic, space group P212l2l, and have cell constants a = 13.078 (2) Å, b = 14.511 (5) Å, c = 17.160 (4) Å, V = 3257 Å3, and Z = 4. A total of 3216 reflections (radiation Mo Kα, μ = 7.2 cm-1) were used in the refinement, resulting in a final R value of 0.093 (Rw = 0.102). © 1990, American Chemical Society. All rights reserved.