Carbon-Carbon Bond Formation at a Dinuclear Iron Center. 4. Synthesis of [Fe₂(CO)₆(μ-C(OR)H)(μ-CR’=CR’H)]- Anions (R = Me, Et; R’ = Ph, H) and the Subsequent Formation by Protonation of the Bridging Vinylcarbene Ligands >CHCR’=CR’H or >CR’CH=CR’H, Depending on the Reaction Conditions

The reaction of Fe2(CO)6(μ-COR)(μ-CR’=CR’H) (1a, R = Me, R’ = Ph; 1b, R = Et, R’ = Ph; 4, R = Et, R’ = H) complexes with [Na][BH4] (R = Me, Et; R’ = Ph) or [PPN][BH4] (R = Et; R’ = H) leads to the formation of the [Fe2(CO)6(μ-C(OR)H)(μ-CR,=CR’=CR’H)- anions 2a, 2b, and 5, in good yield. The X-ray structure has been determined where R = Et, R’ = Ph when associated with the [PPh4]+ cation. Crystals are triclinic, space group PI, with Z = 2 in a unit cell with a = 15.006 (3) Å, b = 13.143 (2) Å, c = 11.868 (2) Å, α = 100.20 (2)°, β = 74.97 (2)°, γ = 113.90 (2)°. When R’ = Ph, protonation leads to the formation of Fe2(CO)6(μ-COEtCPhCPH) (6). In the presence of L = PPh3 or PMe2Ph, protonation gives Fe2-(CO)6L(μ-CPhCHCPhH) complexes 7 and 8. The latter result suggests that the intermediate formation of 1,3-diphenylcyclopropene arises from a [1 + 2] addition of the CH and CPhCPhH fragments. © 1990, American Chemical Society. All rights reserved.