Carbon-carbon bond formation at diiron centres V. Synthesis of anionic vinyl-bridged diiron complexes and their reactivity toward alkynes

The reaction of acetylenes with [PPh4][HFe(CO)4] in the presence of Fe2(CO)9 in THF solution leads to the formation in high yields of the complexes [PPh4][Fe2(CO)6(μ-CO)(μ-CR1CR2H)] where R1 = Ph and R2 = H; R1 = R2 = Ph; R1 = tBu and R2 = H; R1 = SiMe3 and R2 = H; R1 = CO2Me and R2 = H. The complex [PPh4][Fe2(CO)6(μ-CO)(μ-CHCRH)] with R = H or Ph) reacts with the alkynes R3CCR3 (R3 = Ph, C(O)OMe, CF3) in a different way from that previously observed for the alkyne with R3 = Ph. The reaction involves insertion of the alkyne into the iron-carbon σ bond of the alkenyl bridge, to give [PPh4][Fe2(CO)6(μ-CR3CR3CHCHR)] complexes (R = H). Depending on the R3 group, two modes of bonding of the organic bridge have been observed, μ-η2,η2 (R3 = Ph) and μ-η3,η1 (R3 = CF3). The complexes have been obtained from these reactions [PPh4][Fe2(CO)6(μ-CR3CR3C(O)CHCH(R)] with R3 = Ph; R = H; R3 = CF3 or C(O)OMe; R = Ph. © 1990.