DFT mechanistic study of the H₂-assisted chain transfer copolymerization of propylene andp-methylstyrene catalyzed by zirconocene complex

Abstract

DFT computations have been performed to investigate the mechanism of H 2 -assisted chain transfer strategy to functionalize polypropylene via Zr-catalyzed copolymerization of propylene and p-methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2-insertion over 2,1-insertion both kinetically and thermodynamically, explaining the observed 1,2-insertion regioselectivity for propylene insertion. (ii) The 2,1-inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2-insertion. The observation of 2,1-insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H 2 can react with the deactivated [Zr]2pMS2PP n facilely, which displace functionalized pMS2PP n chain and regenerate [Zr]AH active catalyst to continue copolymerization. The effects of counterions are also discussed.

Computational Studies on the Selective Polymerization of Lactide Catalyzed by Bifunctional Yttrium NHC Catalyst

“…One d-polarization function (exponent of 0.284) was augmented for the basis set of Si atoms [55]. Such a computational strategy has been widely used for the study of transition metal-containing systems [56][57][58][59][60][61]. The transition states were ascertained by a single imaginary frequency for the correct mode.…”

Data on electronic structures for the study of ligand effects on the zirconocene-mediated trimethylene carbonate polymerization

“…The effective core potential double-ζ basis set (LANL2DZ) [6] was used for Zr atom, while a double-ζ basis set (6–31G(d)) for all non-metal atoms (C, H, O, F, Si, and Ge). This DFT/mixed basis set method has been shown to reproduce the X-ray structure [7] and has been widely applied in the field of transition metal complexes [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] . Frequency calculations were performed on all optimized structures to confirm the nature of stationary points as minima or transition states.…”

Extent of structural change during the reaction and its relationship to isoselectivity in polypropylene polymerization with ansa‐zirconocene/borate catalyst: A computational study

“…QC approaches, including QM/MM techniques, were also applied to relevant research on olefin polymerization with metallocenes and properties of metallocenes themselves, including studies on monomer insertion, chain growth, chain termination, polymer rotation barriers, ligand hapticity, bridge effects, monomer oligomerization, counter‐ion effects, and copolymerization . As other examples, Green discussed the bent structure of metallocene species from a molecular orbital (MO) viewpoint .…”

“…Most QC‐based research was performed by assuming short growing chains for several monomer insertion steps, whereas a limited number of studies treat longer growing chains, for example, Ref. in which the computation was performed until the sixth monomer insertion steps without a cocatalyst. Does such a longer growing chain affect the catalytic site and its isoselectivity, especially under including a cocatalyst?…”

“…QC studies explicitly including a cocatalyst in the calculation model have increased. However, QC‐based research on “isoselectivity” that explicitly included a cocatalyst is extremely limited . It is especially worthwhile to understand the effect of the cocatalyst on the electronic states of the catalytic center and its influence on the isoselectivity.…”