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).