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Unravelling the Role of Al‐alkyl Cocatalyst for the VO x /SiO 2 Ethylene Polymerization Catalyst: Diethylaluminum Chloride Vs. Triethylaluminum
Author(s) -
Deng Shiheng,
Liu Zhen,
Liu Boping,
Jin Yulong
Publication year - 2021
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202001929
Subject(s) - silanol , chemistry , catalysis , alkyl , ethylene , steric effects , polymerization , chloride , medicinal chemistry , vanadium , organic chemistry , polymer chemistry , stereochemistry , polymer
Vanadium‐based catalysts for olefin polymerization are unique in their strong preference for Cl containing Al‐alkyl cocatalysts. In this work, we performed theoretical studies on VO x /SiO 2 /diethylaluminum chloride (DEAC) and VO x /SiO 2 /triethylaluminum (TEA) with V(III) and V(IV) cluster models to provide comprehensive insight into how this catalyst system is affected by cocatalysts and why DEAC is mostly superior to TEA as activators. It is found that DEAC would hemilabily complex with the catalyst and weaken the bonds between V centers and SiO 2 , though the overall steric hindrance is enhanced as well. It ensures the faster C 2 H 4 insertion and even turns the inert V(IV) sites into active ones. Similar situation is seen when TEA is added. However, the ethyl in TEA has larger size than Cl in DEAC, and TEA also complexes with the V center more tightly, generating V‐diethyl‐(like) species, which have to experience energy costly reorganizations into the monoethyl configuration for insertion. Hence, the complexed TEA even slows the insertion kinetics down. Furthermore, the V‐diethyl‐(like) species are readily to undergo α‐H elimination, yielding inert V‐alkylidene for subsequent enchainment via the Green‐Rooney mechanism. We also investigated the effect of Al‐alkyls on V(III) site rigidly constrained by an adjacent silanol, finding the grafted DEAC and TEA, though have bigger size than the silanol, just loosely restrict the V center and liberate the sites poisoned by silanol.