Formation and Rearrangement of Reduced Diiminepyridine Complexes of Zr and Hf

Reduction of seven‐coordinate [( Et DIP)MCl 4 ] { Et DIP = 2,6‐(2,6‐Et 2 –C 6 H 3 N=CMe) 2 C 5 H 3 N; M = Zr or Hf} produces formally divalent complexes [( Et DIP)MCl 2 ] containing in reality a doubly reduced DIP ligand. The Hf complex is five‐coordinate, but the Zr analog crystallizes as a chloride‐bridged dimer with an unusual coordination geometry; the monomer‐dimer equilibrium is fast at room temperature. Reaction of [( Et DIP)HfCl 2 ] with MeMgBr or LiCH 2 SiMe 3 produced the corresponding dialkyls [( Et DIP)HfR 2 ]. An unexpected ligand isomerization to an amido/enamido form was observed for [( Et DIP)ZrCl 2 ], [( Et DIP)HfMe 2 ] and [( Et DIP)TiMe 2 ], and a mechanism is proposed based on DFT calculations.