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 te thered 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 externa l electrophile (CPh3+, H+) opens the three-membered ring, resulting in the cation (eta(5)-C5H4CH2CH2R)Fe(CO)(3)(+) whose structure was deter mined 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 re stricted 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(N HPh)CH2CH2(eta(5)-C5H4)(+).