ИСТИНА

The first seven-membered zirconacyclocumulene complex was synthesized in 1993 by Buchwald [1] and a year later five-membered zirconacyclocumulene [2] was obtained. Despite the deviation of the butatriene moiety from linearity, these complexes turned out to be extremely stable at room temperature for an indefinite period of time, in contrast to organic cumulenes. Interest in such compounds is also due to their ability to catalyze the formation of pyrimidines in the coupling reactions of diacetylenes with nitriles [3]. During our study we have found that heating five-membered metallacyclocumulenes with two equivalents of acetonitrile leads to the formation of dimeric metallaazacyclopentadienes, bicyclic amidines, and tricyclic complexes [4]. The found transformations are studied in detail, a mechanism is proposed in which metallaazacyclopentadienes can be considered as а kinetic but bicyclic and tricyclic complexes as thermodynamic reaction products.