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- Title
Structure and Isotope Effects of the β-H Agostic (α-Diimine)Nickel Cation as a Polymerization Intermediate.
- Authors
Xu, Hongwei; White, Paul B.; Hu, Chunhua; Diao, Tianning
- 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-Cβ angles (75.0(3)° and 74.57(18)°) and short Cα−Cβ distances (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 with 13C-labeled agostic complexes. The enthalpy of activation (Δ H≠) 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.
- Subjects
AGOSTIC interaction; NICKEL isotopes; OLIGOMERIZATION; POLYMERIZATION; LIGANDS (Chemistry)
- Publication
Angewandte Chemie International Edition, 2017, Vol 56, Issue 6, p1535
- ISSN
1433-7851
- Publication type
Article
- DOI
10.1002/anie.201611282