Double and Reversible Alkyl Transfer from ZrBn 4 /HfBn 4 to a Diiminepyridine Ligand

Reaction of MBn 4 (M = Zr, Hf) with diiminepyridine ligands Me DIP, Et DIP and i Pr DIP [ R DIP = 2,6‐(2,6‐R 2 C 6 H 3 N=CMe) 2 ‐C 5 H 3 N] results in the transfer of two benzyl groups to the DIP imine carbon atoms, generating mixtures of rac and meso isomers of [ R DIP + 2Bn]MBn 2 . The diastereomers could in several cases be separated by fractional crystallization, and the X‐ray structures of rac and meso [ Et DIP + 2Bn]ZrBn 2 , meso ‐[ Me DIP + 2Bn]ZrBn 2 and meso ‐[ Et DIP + 2Bn]HfBn 2 are reported. On heating either diastereomer of [ Et DIP + 2Bn]ZrBn 2 in solution, the other isomer grows back in, demonstrating reversibility of the alkyl transfer. Transfer to other positions of the DIP skeleton was not observed. The reaction of [ Et DIP + 2Bn]ZrBn 2 with two equivalents of TEMPO produced structurally characterized [ Et DIP + 2Bn]Zr(Bn)(TEMPO) which shows no tendency to isomerize.