Group 14 and 15 Heteroallenes ECC and ECE

This review describes the synthesis, physical properties, and some aspects of the reactivity of heteroallenes, namely the heavier congeners of allenes containing one or two doubly bonded heavier elements of groups 14 (Si, Ge, Sn) and 15 (P, As, Sb). The key factor for their preparation lies in the use of synthetic methods effective under mild conditions:  i.e., in many cases, the dehalogenation at low temperature of dihaloheteropropenes by lithium derivatives. Their stabilization was successful, owing to very bulky substituents; substituted aromatic groups were often used, particularly the 2,4,6-tri-tert-butylphenyl group (supermesityl). Whereas various types of heteroallenes containing a doubly bonded element of the second or third long row have been isolated, their heavier counterparts of the fourth row have only been postulated as reaction intermediates.