Synthesis and Structure of Carbonyliron Complexes of Allenecarboxylates and Allenic Lactones

On irradiation in the presence of Fe(CO)5, the allenecarboxylates 1 afforded binuclear carbonyliron complexex 6 (Scheme 3), whereas the allenic lactone 7 under similar conditions gave a mixture of one binuclear and two mononuclear carbonyliron complexes (9,8, and 10; Scheme 4). The structure of the complexes has been elucidated by X‐ray crystallography. The structure of the binuclear complex 9 corresponds to that of 6, while 8 has been shown to be a 1,3‐butadiene(tricabonyl)iron complex. The unique structure of the 10 represents a new type of allenic complex. A stepwise formation of the complexes via intermediate allene(tetracarbonyl) iron complexes type 11 and 13 is suggested. Treatment of the binuclear complex 6b with FeCl3 led to the formation of the free ligand and a mixture of mononuclear complexes 13 and 14 (Scheme 5). On heating, the 1,3‐diene complex 8 yielded the free ligand 15, the prouduct of a (1,3) H shift in the allene 7; the complex 10 on the other hand liberates 7 on treatment with ethylenetracarbonitrile (TCNE) (Scheme 6).