Zirconium complexes of a cyclopentadienylamido ligand with a pendant amine donor via amine and alkane elimination

Zirconium complexes of the multidentate ligand CpH^NMeSiN(H)R (SiNR = -SiMe₂N-t-butyl; NMe = -CH₂CH₂NMe₂, 1) were prepared and characterized via amine and alkane elimination procedures. Reaction of 1 with Zr(NMe₂)₄ gave a mixture of bis-amido complexes 2 in which the ligand was 1,2 and 1,3 substituted. This mixture was converted to the analogous dichlorides 3 using Me₂NH·HCl and 1,3-3 was purified at this stage; alternatively, 1,3-3 was obtained in one pot from 1 and Zr(NMe₂)₄ in ≈70% yield. Conversion of 1,3-3 to dimethyl compound (Cp^NMeSiNR)Zr(CH₃)₂, 1,3-4, was accomplished via reaction of the dichloride with methyllithium; methide abstraction with the Lewis acids B(C₆F₅)₃ and [Ph₃C]⁺[B(C₆F₅)₄] generated the cationic alkyls [(Cp_NMeSiNR)Zr(CH₃)]⁺[R′B(C ₆F₅)₃]^- (R′ = CH₃, 6a; C₆F₅, 6b), which were characterized by NMR spectroscopy. Zirconium complexes containing 1 ligated as its 1,2 isomer were obtained from alkane elimination reactions between 1 and in situ prepared R_nZrCl_4-n (R = CH₃, n = 3; R = CH₂SiMe₃, n = 2). 1,2-3 and the methyl chloride complex 1,2-(Cp^NMeSiNR)Zr(CH₃)Cl, 5, were obtained in 18 and 30% yield, respectively. Complex 5 was characterized by X-ray crystallography (monoclinic, space group P 2₁/a, a = 9.6951(10) Å, b = 14.3794(16) Å, c = 14.364(3) Å, V = 1990.3(5) ų, Z = 4, R = 0.046, R_w = 0.041.).