2,3,5-Trimethylenehexanediyl (allene trimer) hexacarbonyldi-iron complexes with no iron–iron bond
Reaction of allene with [Fe3(CO)12] at 85–90° gives a yellow, binuclear complex of formula [Fe2(CO)6(C9H12)](I); this can also be prepared from the allene dimer complex, [Fe2(CO)6(C6H8)]. At 120° the reaction affords a second isomer (II), which is orange-yellow and can be alternatively derived by thermal isomerisation of (I). A third isomer (III), which is lemon-yellow is obtained by thermal isomerisation of (I) or (II). The stepwise transformation (I)→(II)→(III) demonstrates the relative thermal stability. The molecular structures for the three diamagnetic complexes were deduced primarily on the basis of 1H n.m.r. spectra and the structure of (II) was confirmed by X-ray analysis.