Structural characterization of M(s-cis-η4-C4H6)(Me4C5SiMe2NR) (M = Ti or Zr, R = CMe3 or CHCMe(1-C10H7)

Abstract

Treatment of M(Me₄C₅SiMe₂NR)Cl₂ [M = Zr, R = CMe₃ or CHMe(1-C₁₀H₇): M = Ti, R = CMe₃] with “butadienemagnesium” gave the respective M(s-cis-η⁴-C₄H₆)(Me₄C₅SiMe₂NR) complexes in good yield. In solution, the parent zirconium system Zr(s-cis-η⁴-C₄H₆)(Me₄C₅SiMe₂NCMe₃) forms a 85∶15 equilibrium mixture of the supine (A) and prone (B) isomers, whereas the isomer which has the s-cis-butadiene ligand oriented with its open side toward the amido group (prone) is favored in the Ti(s-cis-η⁴-C₄H₆)(Me₄C₅SiMe₂NCMe₃) case (A∶B = 5∶95). Complex Zr[s-cis-η⁴-C₄H₆){Me₄C₄SiMe₂NCHMe(1-C₁₀H₇)] was obtained as a single isomer (supine orientation A favored). The favored isomers were in each case characterized by single crystal X-ray structure analyses. The zirconium complexes contain a central metallacyclic σ²,π-type (s-cis-η⁴-butadiene) metal framework, whereas the titanium structure is more like that expected for a conventional π-butadiene metal complex.