Ring Opening of (Spiro[2.4]hepta-4,6-diene)tricarbonyliron:  A Revisit

(Spiro[2.4]hepta-4,6-diene)tricarbonyliron (2) self-converts to the tethered acyl complex (CO)₂FeC(O)CH₂CH₂(η⁵-C₅H₄) (3) when refluxed for 1 h in common organic solvents. The reaction of 2 with an external electrophile (CPh₃⁺, H⁺) opens the three-membered ring, resulting in the cation (η⁵-C₅H₄CH₂CH₂R)Fe(CO)₃⁺ whose structure was determined by spectroscopic methods and confirmed by X-ray analysis of the PPh₃ derivative (η⁵-C₅H₄CH₂CH₃)Fe(CO)₂(PPh₃)⁺. The reaction of 3 with a strong electrophile (CPh₃⁺, Me⁺) affords the rotationally restricted Fe−(alkoxy)carbene cation (CO)₂FeC(OR)CH₂CH₂(η⁵-C₅H₄)⁺, which can be converted to the Fe−(anilino)carbene cation (CO)₂FeC(NHPh)CH₂CH₂(η⁵-C₅H₄)⁺.