Migratory Insertion of an Isocyanide into 1-Zirconacyclopent-3-ynes

The reactions of the 1-zirconacyclopent-3-ynes Cp‘2Zr(η4-H2C4H2) with Cp‘2 = Cp2 (1), (η5-t-Bu-C5H4)2 (2), and Me2Si(η5-C5H4)2 (3) and of the zirconacyclopropene Me2Si(η5-C5H4)2Zr(THF)(η2-Me3SiC2SiMe3) (8) toward t-Bu-NC are described. In the case of the 1-zirconacyclopent-3-ynes 2 equiv of t-Bu-NC were inserted into the β-Zr−C bonds of the zirconacycle. After subsequent rearrangement the substituted 1-zircona-2,5-diazacyclopent-3-enes 4, 5, and 6, possessing an anellated cyclobutene ring having two exocyclic double bonds, were obtained. In the protolysis of 6 with MeOH the metal-free cyclobutene 7 was formed. The alkyne complex 9 reacted with the isocyanide to give end-on complexation instead of an expected insertion, resulting in the alkyne complex Me2Si(η5-C5H4)2Zr(η1-CN-t-Bu)(η2-Me3SiC2SiMe3) (11).