β‑Hydrogen Abstraction of an Ethyl Group Provides Entry to Titanium and Zirconium Ethylene Complexes

Treatment of trichloride complexes
[(PNP)­MCl3] (M =
Ti or Zr) with 3 equiv of ethyl-Grignard reagent cleanly results in
transmetalation followed by β-hydrogen abstraction to form the
ethylene-ethyl species [(PNP)­M­(η2-H2CCH2)­(CH2CH3)]. In the case of zirconium,
we can replace the ethylene ligand with an imido or 2,2′-bipyridine
(bpy) to form [(PNP)­ZrN­[1-adamantyl]­(CH2CH3)] or [(PNP)­Zr­(bpy)­(CH2CH3)], respectively.
The ethylene-methyl derivative [(PNP)­Zr­(η2-H2CCH2)­(CH3)] can also be prepared
cleanly from the precursor [(PNP)­Zr­(CH3)2(OTf)]
and ethyl-Grignard reagent. Using the isotopologue [(PNP)­Zr­(CD3)2(OTf)] we found that α-abstraction is not
a pathway to ethylene formation.