@article { ISI:000301128300003, title = {Radical mediated deoxygenation of inositol benzylidene acetals: conformational analysis, DFT calculations, and mechanism}, journal = {Carbohydrate Research}, volume = {351}, year = {2012}, month = {APR}, pages = {26-34}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

Xanthates of 1,3-benzylidene acetal derivatives of myo- and neo-inositols undergo dideoxygenation under Barton-McCombie conditions, as a result of intramolecular abstraction of the benzylidene acetal hydrogen and subsequent cleavage of the acetal ring. Scrutiny of structure of these bicyclic inositol derivatives shows that although the conformation of the two rings can vary depending on the configuration of the inositol ring and the phase in which the molecules are present, both the xanthates lead to the formation of the same dideoxyinositol. DFT calculations on these molecular systems suggest that neo-inositol derivatives undergo conformational change prior to radical formation while myo- inositol derivatives undergo conformational change subsequent to radical formation, during the deoxygenation reaction. A low barrier for intramolecular hydrogen transfer supports the extreme facility of this deoxygenation reaction. (C) 2012 Elsevier Ltd. All rights reserved.

}, keywords = {Deoxygenation, DFT, Inositol, Mechanism, Radical, Xanthate}, issn = {0008-6215}, doi = {10.1016/j.carres.2012.01.001}, author = {Gurale, Bharat P. and Vanka, Kumar and Shashidhar, Mysore S.} } @article { ISI:000326674800001, title = {GIAO/DFT studies on 1,2,4-triazole-5-thiones and their propargyl derivatives}, journal = {Magnetic Resonance in Chemistry}, volume = {51}, number = {12}, year = {2013}, month = {DEC}, pages = {767-774}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

Density functional theory (DFT)/Becke-Lee-Yang-Parr (B3LYP) and gauge-including atomic orbital (GIAO) calculations were performed on a number of 1,2,4-triazole derivatives, and the optimized structural parameters were employed to ascertain the nature of their predominant tautomers. C-13 and N-15 NMR chemical shifts of 3-substituted 1,2,4-triazole-5-thiones and their propargylated derivatives were calculated via GIAO/DFT approach at the B3LYP level of theory with geometry optimization using a 6-311++G** basis set. A good agreement between theoretical and experimental C-13 and N-15 NMR chemical shifts could be found for the systems investigated. The data generated were useful in predicting N-15 chemical shifts of all the nitrogen atoms of the triazole ring, some of which could not be obtained in solution state N-15 HMBC/HSQC NMR measurements. The energy profile computed for the dipropargylated derivatives was found to follow the product distribution profile of regioisomers formed during propargylation of 1,2,4-triazole thiones. Copyright (c) 2013 John Wiley \& Sons, Ltd.

}, keywords = {1, 2, 4-triazole-5-thiones, C-13, DFT, GIAO, N-15, NMR, Regioisomers, tautomers}, issn = {0749-1581}, doi = {10.1002/mrc.4012}, author = {Phalgune, Usha D. and Vanka, Kumar and Rajamohanan, P. R.} } @article {46716, title = {Amidinato germylene-zinc complexes: synthesis, bonding, and reactivity}, journal = {Chemistry-An Asian Journal}, volume = {15}, year = {2020}, month = {OCT }, pages = {3116-3121}, type = {Article}, abstract = {

Despite the explosive growth of germylene compounds as ligands in transition metal complexes, there is a modicum of precedence for the germylene zinc complexes. In this work, the synthesis and characterization of new germylene zinc complexes [PhC(NtBu)(2)Ge{N(SiMe3)(2)}-\> ZnX2](2)(X= Br (2) and I (3)) supported by (benz)-amidinato germylene ligands are reported. The solid-state structures of2and3have been validated by single-crystal X-ray diffraction studies, which revealed the dimeric nature of the complexes, with distorted tetrahedral geometries around the Ge and Zn center. DFT calculations reveal that the Ge-Zn bonds in2and3are dative in nature. The reaction of2with elemental sulfur resulted in the first structurally characterized germathione stabilized ZnBr(2)complexes PhC(NtBu)(2)Ge(=S){N(SiMe3)(2)}-\> ZnBr2(5). Therefore, the Ge=S in5is in-between Ge-S single and Ge=S double bond length, owing to the coordination of a sulfur lone pair of electrons to ZnBr2.

}, keywords = {DFT, Germathione, Germylene, X-ray Structure, zinc}, issn = {1861-4728}, doi = {10.1002/asia.202000807, Early Access Date = SEP 2020}, author = {Yadav, Sandeep and Kumar, Rohit and Raj, K. Vipin and Yadav, Prashant and Vanka, Kumar and Sen, Sakya S.} } @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.} } @article {47654, title = {Unsymmetrical sp(2)-sp(3) disilenes}, journal = {Angewandte Chemie-International Edition}, volume = {60}, year = {2021}, month = {SEP }, pages = {20706-20710}, type = {Article}, abstract = {Disilenes with differently coordinated silicon atoms are not known. Here, we have shown the high yield synthesis of a range of disilenes (2-4 and 6) upon reaction of a hypersilyl silylene PhC(NtBu)(2)SiSi(SiMe3)(3) (1) with aliphatic chlorophosphines. The most striking characteristic of these disilenes is the presence of two differently coordinated Si atoms (one is three-coordinated, the other four-coordinated). The analogous reaction with Ph2PCl did not afford the desired disilene, but, surprisingly, led to the first tetraphosphinosilane (8). DFT calculations were performed to understand the bonding in disilenes and differences in reactivity of the complexes.}, keywords = {chlorophosphine, DFT, disilene, hypersilylsilylene}, issn = {1433-7851}, doi = {10.1002/anie.202107847}, author = {Bisai, Milan Kumar and Das, Tamal and Vanka, Kumar and Gonnade, Rajesh G. and Sen, Sakya S.} } @article {48755, title = {Enhancing diradical character of chichibabin{\textquoteright}s hydrocarbon through fluoride substitution}, journal = {ChemPlusChem}, volume = {88}, year = {2023}, month = {AUG}, pages = {e202300273}, type = {Article}, abstract = {

In this work, 5-SIDipp [SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene] (1) derived Chichibabin{\textquoteright}s hydrocarbon with an octafluorobiphenylene spacer (3) has been reported. The addition of two equivalents of 5-SIDipp with decafluorobiphenyl in presence of BF3 gives the double C-F bond activated imidazolium salt with two tetrafluoroborate anions, 2. Further reduction of 2 gives the fluorine substituted 5-SIDipp based Chichibabin{\textquoteright}s hydrocarbon, 3. Quantum chemical calculations suggested a singlet state of 3 with a singlet-triplet energy gap (?ES-T) of 3.7 kcal mol(-1), which is substantially lower with respect to the hydrogen substituted NHC-based Chichibabin{\textquoteright}s hydrocarbons (10.7 kcal mol(-1), B3LYP). As a result, the diradical character (y) of 3 (y=0.62) is also noticeably higher than the hydrogen substituted CHs (y=0.41-0.43). The ?ES-T was found to be higher in CASSCF (22.24 kcal mol(-1)) and CASPT2 (11.17 kcal mol(-1)) for 3 and the diradical character (d) is 44.6 \%.

}, keywords = {C-F Bond Activation, Chichibabin \& PRIME, DFT, N-Heterocyclic carbene, s Hydrocarbon}, issn = {2192-6506}, doi = {10.1002/cplu.202300273}, author = {Kundu, Gargi and Dash, Soumya Ranjan and Kumar, Ravi and Vanka, Kumar and Ghosh, Aryya and Sen, Sakya S.} } @article {49417, title = {Designing of imine thiophene-ligated metal-complexes and implication in ethylene polymerization}, journal = {Journal of Macromolecular Science Part A-Pure and Applied Chemistry}, year = {2024}, month = {SEP}, type = {Article; Early Access}, abstract = {

Polyethylene is the single largest volume polymer produced globally using Ziegler-type catalysts. Numerous modifications have been reported in search of a better catalyst that can control molecular weight, polydispersity, and branching. In our attempts to identify a suitable imine thiophene-ligated chromium complex, we examined 9 different titanium complexes computationally. The DFT investigations considered barriers for insertion, propagation, and termination by beta-H elimination or chain transfer, and identified N-(4-methoxyphenyl)-2-phenyl-1-(thiophen-2-yl)ethan-1-imine(L9) as the most suitable ligand. Subsequently, L9 was prepared in good yield (70\%) by condensing 2-phenyl-1-(thiophen-2-yl)ethan-1-one with 4-methoxyaniline. Ligand L9 was treated with early transition metal precursors (Ti, Cr, Zr) to generate a homogenous catalyst. The identity of these catalysts was unambiguously ascertained using a combination of NMR, ICP, FT-IR, UV-Vis spectroscopy, and ESI-MS. The performance of L9-ligated titanium complex [Cat.1] was examined in ethylene polymerization using MMAO as a co-catalyst. Insertion of ethylene was tracked using high-pressure NMR experiments and Cat.1 was found to be active in the polymerization. Ethylene polymerization conditions were optimized to obtain high activity and molecular weight polyethylene. The chromium complex [Cat.2] outperformed the Ti and Zr-derived catalysts with the highest TOF of 6294 mol of PE/mol of Cr/h. Cat.2 produced high molecular weight, high-density polyethylene.

}, keywords = {Cr-complexes, DFT, high-density polyethylene, Imine thiophene ligand, Polyethylene}, issn = {1060-1325}, doi = {10.1080/10601325.2024.2409753}, author = {Shaikh, Maulali H. and Ramekar, V. Rohan and Jawoor, Shailaja and Dash, Soumya R. and Birajadar, Rajkumar S. and Pawal, Sandip B. and Thenmani, Nandakumar and Vanka, Kumar and Chikkali, Samir H.} }