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 FeCl 3 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) .