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

The reactions of the 1-zirconacyclopent-3-ynes Cp‘ 2 Zr(η 4 -H 2 C 4 H 2 ) with Cp‘ 2 = Cp 2 ( 1 ), (η 5 - t -Bu-C 5 H 4 ) 2 ( 2 ), and Me 2 Si(η 5 -C 5 H 4 ) 2 ( 3 ) and of the zirconacyclopropene Me 2 Si(η 5 -C 5 H 4 ) 2 Zr(THF)(η 2 -Me 3 SiC 2 SiMe 3 ) ( 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 Me 2 Si(η 5 -C 5 H 4 ) 2 Zr(η 1 -CN- t -Bu)(η 2 -Me 3 SiC 2 SiMe 3 ) ( 11 ).