Zwitterionic d⁰ Metal Complexes [(Cy₂N)₃M]⁺[(μ-Me)B(C₆F₅)₃]⁻ (M = Ti, Zr, Hf) Derived from Tris(dicyclohexylamido)methyl Metal Precursors

The synthesis and characterization of tris­(dicyclohexyl)­amido hafnium complexes ClHf­(NCy₂)₃ (1-Hf) and MeHf­(NCy₂)₃ (2-Hf) are presented. The reactions of the group 4 derivatives of this compound class (MeM­(NCy₂)₃; M = Ti (2-Ti), Zr (2-Zr), Hf (2-Hf)) with B­(C₆F₅)₃ are investigated. Their reactions with strong Lewis acids lead to the first examples of zwitterionic group 4 complexes employing three amido ligands at the electrophilic metal center ([(Cy₂N)₃M]⁺[(μ-Me)­B­(C₆F₅)₃]⁻). The solid-state structures of all of the betaines (3-Ti, 3-Zr, 3-Hf) are presented and compared. In all homologues the methyl group is abstracted by the Lewis acid but remains in interaction with the electron-deficient metal center, resulting in a linearly bridging methyl group. The M···C distances of 3-M are elongated by 0.25 Å (av) in comparison to 2-M.