Synthesis and Structure of (Triphenylsilyl)imido Complexes of Titanium and Zirconium

Titanium and zirconium (triphenylsilyl)imido complexes are available through transimination from the tert-butylimido complexes with H2NSiPh3. The useful starting material
Ti(NSiPh3)Cl2(py)2 (1) is prepared in 88% yield by treatment of Ti(NBut)Cl2(py)3 with
H2NSiPh3. Imido 1 is a dimer in the solid state with bridging chlorides; however, solution
molecular weight studies indicate that 1 is a monomer in CH2Cl2. 1 reacts with 4,4‘-di-tert-butyl-2,2‘-bipyridine (bpy) to generate the pseudo-octahedral Ti(NSiPh3)(bpy)(py)Cl2 (2) in
74% recrystallized yield. Replacement of the chloride ligands of 1 with 2 equiv of Lidap, 1
equiv of Libap, or 1 equiv of Lipap afforded the pyrrolylimido complexes Ti(NSiPh3)(dap)2
(3), Ti(NSiPh3)(bap)Cl (4), and Ti(NSiPh3)(pap)Cl (5), respectively. The reaction of 2 equiv
of neophyl (Nph) magnesium bromide with 1 provided [Ti(μ-NSiPh3)(Nph)2]2 (6) in 59% yield.
The pseudo-octahedral complex Ti(NSiPh3)(dpma)(bpy) (8) was available through addition
of Li2dpma to 1, forming Ti(NSiPh3)(dpma)(py)2 (7) followed by treatment with bpy.
Alternatively, 8 was prepared by addition of bpy and H2NSiPh3 to Ti(NMe2)2(dpma). The
zirconium tert-butylimido complex Zr(NBut)(dpma)(bpy) (9) was available in 43% yield by
treatment of Zr(NMe2)2(py)(dpma) with bpy and H2NBut. Transimination on 9 with H2NSiPh3
provided the (triphenylsilyl)imido complex Zr(NSiPh3)(dpma)(bpy) (10) in 34% yield. In an
unusual transformation, 10 reacts with excess sodium 2,6-dimethylphenoxide in THF to
afford [Na(bpy)][Zr(dpma)(OAr)3] (11), where the Na coordinates to the bpy and both pyrrole
rings of the dpma in an η5 fashion. Compounds 1, 5, 6, 8, and 11 were structurally
characterized.