Structure and Isotope Effects of the β-H Agostic (α-Diimine)Nickel Cation as a Polymerization Intermediate

Hongwei Xu, Paul B. White, Chunhua Hu, Tianning Diao

Research output: Contribution to journalArticlepeer-review

Abstract

Single-crystal X-ray characterization of cationic (α-diimine)Ni-ethyl and isopropyl β-agostic complexes, which are key intermediates in olefin polymerization and oligomerization, are presented. The sharp Ni-Cα-Cβangles (75.0(3)° and 74.57(18)°) and short Cα−Cβdistances (1.468(7) and 1.487(5) Å) provide unambiguous evidence for a β-agostic interaction. An inverse equilibrium isotope effect (EIE) for ligand coordination upon cleavage of the agostic bond highlights the weaker bond strength of Ni−H relative to the C−H bond. An Eyring plot for β-hydride elimination–olefin rotation–reinsertion is constructed from variable-temperature NMR spectra with13C-labeled agostic complexes. The enthalpy of activation (ΔH) for β-H elimination is 13.2 kcal mol−1. These results offer important mechanistic insight into two critical steps in polymerization: ligand association upon cleavage of the β-agostic bonds and chain-migration via β-H elimination.

Original languageEnglish (US)
Pages (from-to)1535-1538
Number of pages4
JournalAngewandte Chemie - International Edition
Volume56
Issue number6
DOIs
StatePublished - 2017

Keywords

  • inverse kinetic isotope effect
  • nickel
  • polymerization intermediates
  • β-agostic interactions

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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