1. Metal–carbon bond strengths under polymerization conditions: 2,1-insertion as a catalyst stress test
- Author
-
Vincenzo Busico, Peter H. M. Budzelaar, Christian Ehm, Ehm, Christian, Budzelaar, Petrus Henricus Maria, and Busico, Vincenzo
- Subjects
Chain propagation ,010405 organic chemistry ,Bond strength ,Chemistry ,TiâC BDE ,Post-metallocene catalyst ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Bond-dissociation energy ,Catalysis ,Catalysi ,0104 chemical sciences ,Homolysis ,Cyclopentadienyl complex ,Polymerization ,2,1 insertion ,TiâC homolysi ,Physical and Theoretical Chemistry ,Catalyst mileage ,Olefin polymerization ,Catalyst decay - Abstract
Quantitative agreement between experimentally determined M–C bond dissociation energies (BDE) and DFT predictions (M06-2X/TZ//TPSSTPSS/DZ) can be reached by choosing the correct anchor for experimentally derived BDE. For the example of the archetypical metallocene catalyst Cp 2 TiCl 2 , it is shown that titanium–carbon bonds are very weak under polymerization conditions and fluctuate; steric strain is introduced after 2,1 insertion and via olefin capture. Thus, homolysis can become competitive with chain propagation. Depending on the catalyst and temperature, 2,1 insertion can be only a temporary inconvenience (dormancy) or a definitive decay event. It is then shown for a set of nine common Ti and Zr polymerization catalysts how ligand variation affects the metal–carbon BDE. Predicted stabilities of the M(IV) oxidation state with respect to homolysis are in nice agreement with the experimentally observed temperature tolerance of the various catalysts: homolysis is easier for Ti than for Zr, and cyclopentadienyl groups in particular facilitate homolysis, especially in bis-cyclopentadienyl systems.
- Published
- 2017
- Full Text
- View/download PDF