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)(2)FeC(O)CH2CH2(eta(5)-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 (eta(5)-C5H4CH2CH2R)Fe(CO)(3)(+) whose structure was determined by spectroscopic methods and confirmed by X-ray analysis of the PPh3 derivative (eta(5)-C5H4CH2CH3)Fe(CO)(2)(PPh3)(+). The reaction of 3 with a strong electrophile (CPh3+, Me+) affords the rotationally restricted Fe-(alkoxy)carbene cation (CO)(2)Fe=C(OR)CH2CH2(eta(5)-C5H4)+, which can be converted to the Fe-(anilino)carbene cation (CO)2Fe=C(NHPh)CH2CH2(eta(5)-C5H4)(+).