GENERATION OF THE IRON METHYLENE COMPLEXES [(ETA(5)-C5ME5)FE(CO)2(=CH2)]- THROUGH INNER-SPHERE VS OUTER-SPHERE ELECTRON-TRANSFER PROCESSES AND REACTIVITY TOWARD SULFUR-COMPOUNDS(X)

The methylene complexes [M(CP)(CO)2(CH2)]+X- (3a, M = Fe; 3b, M = Ru) generated in situ by protonation of M(CP)(CO)2CH2OCH3 (2a, M = Fe; 2 b, M = Ru; Cp = eta5-pentamethylcyclopentadienyl) in the presence of Fe(Cp)(CO)2CH2SR (1a, R = Me; lb, R = Ph) yield the binuclear sulfoni um compounds [(Fe(Cp)(CO)2(CH2)}(SR){M(Cp*)(CO)2(CH2)}]-BF4 (4a, M = Fe, R = Me; 4b, M = Fe, R = Ph; 4c, M = Ru, R = Me). The iron methylen e complex 3a reacts with dimethyl disulfide and diphenyl disulfide to give [Fe(Cp)(CO)2(eta1-RSCH2SR)BF4 (6a, R = Me; 6b, R = Ph) in 60-80% yields. The X-ray crystal structure of 6b shows that it crystallizes in the monoclinic space group P2(1)/c with unit cell parameters a = 24 .564(9) angstrom, b = 11.210(4) angstrom, c = 20.595(6) angstrom, beta = 104.27(4)-degrees, and Z = 8. The structure was solved and refined (4404 reflections) to the final residual values R = 0.46 and R(w) = 0. 43. The methylene complex 3a is also generated from la and lb by ferro cenium oxidation under CO atmosphere. The metallathiacyclopropane comp lexes Fe(Cp)(CO)(eta2-CH2SR) (7a, R = Me; 7b = R = Ph), prepared by i rradiation of la or lb in the near-UV region, are isolated as pure sin gle diastereoisomers. These complexes give the same products as la and lb give upon ferrocenium oxidation. A cyclic voltammetry study indica tes that the 17-electron Fe(III) metallacyclic compounds [Fe(Cp)(CO)( eta2-CH2SR)]+ and the 19-electron [Fe(Cp)(CO)2(eta2-CH2SR)]+ should b e intermediates in the generation of methylene complex 3a and the subs equent formation of complexes 4 and 6 during the one-electron-oxidatio n pathway. Treatment of 1a with [Ph3C][PF6] affords the trityl adduct [Fe(Cp)(CO)2CH2S(CH3)(CPh3)][PF6] (9a). Complex 9a thermally reacts i n situ to form the methylene complex 3a, trapped as phenylcyclopropane in the presence of styrene, or it reacts with 1 b to give 4b isolated in 55% yield. A mechanism is proposed and the dichotomy observed for the ferrocenium and trityl oxidation of the thioalkoxyalkyl complexes la and lb is discussed in terms of inner-sphere versus outer-sphere el ectron transfer.