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

Treatment of M(Me4C5SiMe2NR)Cl-2 [M=Zr, R=CMe3 or CHMe(1-C10H7): M=Ti, R=CMe3] with "butadienemagnesium" gave the respective M(s-cis-eta(4)-C4H6)(Me4C5SiMe2NR) complexes in good yield. In solution, the parent zirconium system Zr(s-cis-eta(4)-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-eta(4)-C4H6)(Me4C5SiMe2NCMe3) case (A:B=5:95). Complex Zr[s-cis-eta(4)-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 sigma(2),pi-type (s-cis-eta(4)-butadiene) metal framework, whereas the titanium structure is more like that expected for a conventional pi-butadiene metal complex.