@article { ISI:000341409900005, title = {Donor decomposition by lewis acids in Ziegler-Natta catalyst systems: a computational investigation}, journal = {Organometallics}, volume = {33}, number = {17}, year = {2014}, month = {SEP}, pages = {4357-4367}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The development of new donors (Lewis bases, usually containing oxygen atoms) is one of the chief areas of research in Ziegler-Natta (ZN) olefin polymerization systems. The addition of such donors has led to improvement in the activity and selectivity of ZN systems. However, in order for the donor to be effective, it has to be chemically stable and resistant to decomposition by Lewis acidic species such as AlEt3. Discussed in the current work is the chemical stability of different ester donors, including aromatic benzoate donors and the silyl ester-a promising new donor class in ZN systems. Full quantum chemical calculations with density functional theory (DFT) indicate that esters can undergo decomposition through different pathways upon interaction with species such as the AlEt3 dimer: Al2Et6. Moreover, the studies show that the active, supported titanium catalyst species can cause donor decomposition and, in fact, is likely to be the greater threat to donor decomposition than Al2Et6. This explains why the addition of excess donors can lead to the poisoning of the active site in ZN systems. We have also computationally investigated means of improving the silyl ester donors in order to make them more robust and resilient to donor decomposition by Al2Et6 and the supported active titanium species.

}, issn = {0276-7333}, doi = {10.1021/om5001259}, author = {Kumawat, Jugal and Gupta, Virendra Kumar and Vanka, Kumar} } @article { ISI:000343819200016, title = {Nature of the active site in ziegler-natta olefin polymerization catalysis systems - a computational investigation}, journal = {European Journal of Inorganic Chemistry}, number = {29}, year = {2014}, month = {OCT}, pages = {5063-5076}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, abstract = {

Pull quantum chemical calculations with density functional theory (DET) show that a principal role of donors in Ziegler-Nana (ZN) oh-din polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight riolymers. If an -OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process.

}, keywords = {Alkene polymerization, Density functional calculations, heterogeneous catalysis, Insertion, Polymers}, issn = {1434-1948}, doi = {10.1002/ejic.201402180}, author = {Kumawat, Jugal and Gupta, Virendra Kumar and Vanka, Kumar} } @article { ISI:000379531300011, title = {Effect of donors on the activation mechanism in ziegler-natta catalysis: a computational study}, journal = {Chemcatchem}, volume = {8}, number = {10}, year = {2016}, month = {MAY}, pages = {1809-1818}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

Full quantum chemical calculations, using density functional theory (DFT), have been conducted to explain the effect of donors on the {\textquoteleft}{\textquoteleft}activation mechanism{\textquoteright}{\textquoteright} in the Ziegler-Natta (Z-N) catalyst system. In the activation mechanism, the inactive (TiCl4)-Cl-IV catalyst converts into the active (TiCl2Et)-Cl-III catalyst with the help of the AlEt3 present in the system. The donors that have been considered in this study are: ethyl benzoate (eb), two representative diether cases, a phthalate donor, and a silyl ester donor. The results indicate that eb and the diether donor cases donor have a negative effect on the barriers for the activation mechanism. However, the eb donor can be displaced from the MgCl2 surface by AlEt3, which matches experimental observations. For the phthalate, silyl ester and TiCl3-OC4H8Cl cases, the results indicate that a significant induction period would be present in Z-N systems employing such donors or having such a catalytic center, before catalysis could commence.

}, keywords = {Alkylation, aluminum, Density functional calculations, surface chemistry, titanium}, issn = {1867-3880}, doi = {10.1002/cctc.201600281}, author = {Kumawat, Jugal and Gupta, Virendra Kumar and Vanka, Kumar} } @article {44216, title = {Role of the (104) MgCl2 lateral cut in ziegler-natta catalysis: a computational investigation}, journal = {Journal of Physical Chemistry C}, volume = {122}, year = {2018}, month = {JAN}, pages = {285-296}, type = {Article}, abstract = {

Density functional theory (DFT) has been used for the study of ethylene polymerization in the Ziegler-Natta (ZN) olefin polymerization system for eight different alkoxy group containing titanium catalysts (Cat-A-h), Ti(III)Et(OR)(OR{\textquoteright}) (where R =-CH3,-Et,-tert-butyl, cyclohexane, R{\textquoteright} = CH3,-Et,-tert-butyl, cyclohexane). What is of significance is that the catalysts studied were all considered to be tethered to the (104) MgCl2 surface, which has traditionally been considered a {\textquoteleft}{\textquoteleft}dormant{\textquoteright}{\textquoteright} surface in Z-N catalysis systems, in contrast to the {\textquoteleft}{\textquoteleft}more active{\textquoteright}{\textquoteright} (110) MgCl2 surface. Our calculations indicate that the binding of all the catalysts to the (104) surface is favorable, even after taking entropic effects into account. For purposes of comparison, ethylene polymerization has been investigated for the Cat-C (TiEt(OEt)(2)) and the Cat-H (TiEt(CI)(OC4H8Cl)) (OC4H8Cl = the chlorobutoxy group) cases, for both the (i) (110) and the (ii) (104) MgCl2 surfaces. It has been seen that for both (i) and (ii)-the energy gap between insertion and the termination barriers (Delta X) was nearly the same for both the Cat-C and Cat-H eases, which shows that ethylene polymerization on the (104)MgCl2 surface is likely to be a ptoininent occurrence in Z-N catalysis, when alkoxy groups are bound to the titanium center. Additionally, for the Cat-C and the Cat-H cases, the regio-and stereoselective behavior of the propylene monomer on the titanium species present on the (110) and the (104) MgCl2 surfaces has also been investigated, and the results indicate that the (104) MgCl2 surface is only slightly less effective than the (110. However, the calculations also indicate that for Cat-H the (104) MgCl2 surface significantly improves the molecular weight of polypropylene in comparison to the (110) surface, further showcasing how the (104) surface (ignored until date) might be a major player in ZN catalysis. Given that a major portion of the MgCl2 support is made up of (104) lateral cuts, the current findings are of considerable relevance.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.7b07893}, author = {Kumawat, Jugal and Gupta, Virendra Kumar and Vanka, Kumar} } @article {46630, title = {Insights into the nature of self-extinguishing external donors for ziegler-natta catalysis: a combined experimental and DFT study}, journal = {ChemCatChem}, volume = {13}, year = {2021}, month = {JAN }, pages = {674-681}, type = {Article}, abstract = {

Developing donors for Ziegler-Natta (ZN) catalysis to control the polymerization reaction and produce polymers with desirable properties has always been challenging due to the multi-component nature of the catalytic systems. Here, we have developed a new synthetic protocol for making two external donors, D-1 (2,2,2-trifluoroethyl myristate) and D-2 (2,2,2-trifluoroethyl palmitate) that show self-extinguishing properties, followed by a systematic DFT study to understand this peculiar property of these donors. D-1 and D-2 can undergo parallel reactions with aluminum and titanium species present in the system to produce ketones and aldehydes, which are poisons for ZN catalytic systems, thus explaining their self-extinguishing nature. The non-covalent interaction between the long alkyl chain of the donors with the surface plays a vital role in determining the donors {\textquoteleft} self-extinguishing nature. There is a significant thermodynamic preference for the binding of the donor with the longer alkyl chain at the titanium center. The current work, therefore, provides interesting insights into how self-extinguishing donors function in ZN catalytic systems.

}, keywords = {DFT, donors, non-covalent interactions, self-extinguishing, Ziegler-Natta catalysis}, issn = {1867-3880}, doi = {10.1002/cctc.202001493, Early Access Date = NOV 2020}, author = {Vipin Raj, K. and Kumawat, Jugal and Dhamaniya, Sunil and Subaramanian, Murugan and Balaraman, Ekambaram and Kumar Gupta, Virendra and Vanka, Kumar and Grubbs, Robert H.} }