| Abstract
| - AzametallacyclobuteneCp2ZrN-t-BuCEtCEt (1)underwent an insertion reaction with CO to formthe acyl complex 2(Cp2Zr(N-t-BuCEtCEtCO), 67% yield).The addition of acetone to azametallacyclobutene 3 (Cp2Zr(NArCMeCPh), Ar =2,6-dimethylphenyl) yielded the N-bonded enamine andO-bonded enolate complex of zirconocene 4(Cp2Zr(NArCMeCPhH)(OCMeCH2),76% yield). Theaddition of aldehydes RCOH to metallacycle 3 resulted in theinsertion of the aldehyde into theZr−C bond to form complexesCp2Zr(NArCMeCPhCRHO) (8a) andCp2Zr(NArCMeCPhC(i-Pr)HO(9) in 85% (R = Ph) and 73% yields, respectively.Similarly, treatment of metallacycle 10(Cp2Zr(NArCEtCEt)) with benzaldehyde yielded the insertion product11(Cp2Zr(NArCEtCEtCPhHO))in 56% isolated yield. The structure of complex 11 wasconfirmed by an X-ray crystallographicstudy. Heating the insertion products 8a and9 led to elimination of the α,β-unsaturatedimines13 and 14a (ArNCMeCPhCRH) in 53% and 72%yields, respectively, and the formation ofoxozirconocene oligomer(Cp2ZrO)n. Theoxozirconocene monomer was trapped by dimethylzirconocene, preventing the formation of oligomer and resulting in theisolation of product 15. Akinetic study of this retrocycloaddition produced the followingactivation parameters: ΔH⧧ =26.5kcal/mol, ΔS⧧ = 3.48 eu. A Hammettσ/ρ study showed that electron-donating groups α tothemetallacycle oxygen accelerate the retrocycloaddition (ρ =−0.8).
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