Reactivity of a Seven-Membered Zirconacyclocumulene towards CN Multiple Bonds - Formation of Metallaheterocycles by Insertion of CN and C=N Groups

The reactions of the seven-membered zirconacyclocumulene [Cp2Zr{eta(4)-Me3SiC4(SiMe3)-C(C2SiMe3)=CSiMe3}] (1) with nitriles (RC N, R = Me, Ph) started with an insertion of a cyanide group into the metal-butadiyne bond followed by an alkyne-nitrile coupling and formation of 1-zircona-2-azacyclopenta-2,4-dienes. The reaction product for R = Me is stabilized by dimerization to give a compound containing a four-membered -N-Zr-N-Zr- ring and two identical five-membered 1-metalla-2-aza-cyclopentadiene rings. In case of R = Ph, a metallacycle could not be isolated, and a pyrimidine was formed. The catalytic potential of this reaction was investigated. For PhN=C(H) Ph, again after insertion and coupling, a corresponding 1-zircona-2-azacyclopenta-4-ene was established. The reaction of this compound with carbon dioxide led to ring expansion and formation of a seven-membered product, which released CO2 at higher temperature and to give back the reactant. The above-mentioned products were characterized by NMR spectroscopy and single-crystal X-ray structure analysis.