Unusual hafnium-pyridylamido/ER(n) heterobimetallic adducts (ER(n) = ZnR2 or AlR3).
NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)-pyridylamido catalytic system for olefin polymerization, [{N(-),N,CNph(-)}HfMe][B(C6F5)4] (1, Nph = naphthyl), interacts with ER(n) (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N(-),N}HfMe(μ-CNph)(μ-R)ER(n-1)][B(C6F5)4 in which the cyclometalated Nph acts as a bridge between Hf and E. (1)H 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.
Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Via Elce di sotto, 8, 06123 Perugia (Italy); Dutch Polymer Institute (DPI), PO box 902, 5600 AX Eindhoven (The Netherlands).
Luca
L
Rocchigiani
Vincenzo
V
Busico
Antonello
A
Pastore
Giovanni
G
Talarico
Alceo
A
Macchioni
NMR spectroscopy; bimetallic compounds; metal-alkyl compounds; molecular modeling; polymerization