NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)–pyridylamido catalytic system for olefin polymerization, [{N,N,C }HfMe][B(C F ) ] (1, Nph 654 Nph = naphthyl), interacts with ERn (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N ,N}HfMe(m-CNph)(m-R)ERn1][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 heterobimetal- lic adducts, with ZnR2 showing a higher tendency to participate in this exchange than AlR3. 1-Hexene/ERn competitive reac- tions 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.
Unusual Hafnium–Pyridylamido/ERn Heterobimetallic Adducts (ERn = ZnR2 or AlR3)
ROCCHIGIANI, LUCA;MACCHIONI, Alceo
2014
Abstract
NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)–pyridylamido catalytic system for olefin polymerization, [{N,N,C }HfMe][B(C F ) ] (1, Nph 654 Nph = naphthyl), interacts with ERn (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N ,N}HfMe(m-CNph)(m-R)ERn1][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 heterobimetal- lic adducts, with ZnR2 showing a higher tendency to participate in this exchange than AlR3. 1-Hexene/ERn competitive reac- tions 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
