Unusual hafnium-pyridylamido/ERn heterobimetallic adducts (ERn=ZnR2 or AlR3)

NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)–pyridylamido catalytic system for olefin polymerization, [{N⁻,N,C_Nph⁻}HfMe][B(C₆F₅)₄] (1, Nph=naphthyl), interacts with ERn (E=Al or Zn, R=alkyl group) to afford unusual heterobimetallic adducts [{N−,N}HfMe(μ‐C_Nph)(μ‐R)ER_n−1][B(C₆F₅)₄] in which the cyclometalated Nph acts as a bridge between Hf and E. 1H VT (variable‐temperature) EXSY NMR spectroscopy provides direct evidence of reversible alkyl exchanges in heterobimetallic adducts, with ZnR₂ showing a higher tendency to participate in this exchange than AlR₃. 1‐Hexene/ERn competitive reactions with 1 at 240 K reveal that the formation of adducts is strongly favored over 1‐hexene polymerization. Nevertheless, a slight increase in the temperature (to >265 K) initiates 1‐hexene polymerization.