@article { ISI:000281754000029, title = {DFT Study of lewis base interactions with the MgCl2 surface in the ziegler-natta catalytic system: expanding the role of the donors}, journal = {Journal of Physical Chemistry C}, volume = {114}, number = {37}, year = {2010}, month = {SEP}, pages = {15771-15781}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We present a computational study, using density functional theory, of the role of internal and external donors in supported heterogeneous Ziegler-Natta polymerization catalyst systems. The focus of the investigation is the ability of the donors to stabilize the MgCl2 support through the zip mode of coordination. Phthalates and alkoxy benzoates have been considered as representative internal and external donors, respectively. Models for the alpha (ccp) and the beta (hcp) phases of the (110) MgCl2 lateral cut have been considered. Studies were first done with a {\textquoteleft}{\textquoteleft}Fully Fixed Model{\textquoteright}{\textquoteright}, where the atoms in the MgCl2 lateral cuts were kept fixed. The studies indicated that the phthalate donors would preferentially stabilize the alpha phase of MgCl2, while the alkoxy benzoate donors would stabilize the beta phase more, corroborating experimental results. A comparison of the zip coordination mode with other modes of coordination (mono, chelate, and bridge) indicates that it would be preferred over the mono and chelate coordination modes and be competitive with the bridge coordination mode. The validity of the Fully Fixed Model was then tested by doing calculations with the Partially Relaxed (some of the magnesium and chlorine atoms unfixed) and the Fully Relaxed (all atoms free) Models. The results from the latter two models corrected some of the discrepancies that had been observed for the Fully Fixed Model in comparison to previous experimental and computational investigations but were in general agreement with the Fully Fixed Model, indicating that the overall conclusions drawn with the earlier model are correct. Insertion studies done on an octahedrally coordinated titanium site flanked by two zip-coordinated phthalate donor molecules indicated that the zip-coordinating donors can confer exceptional regioselectivity to the titanium center. A list of potential donors that could serve as external donors, with di-iso-butyl phthalate (DIBP) as the internal donor, was investigated, and it was found that 1,3-diethers would serve as the best external donors to DIBP.

}, issn = {1932-7447}, doi = {10.1021/jp106673b}, author = {Vanka, Kumar and Singh, Gurmeet and Iyer, Divya and Gupta, Virendra K.} } @article { ISI:000295696300005, title = {DFT investigation of the potential of porous cages for the catalysis of ammonia borane dehydrogenation}, journal = {Chemical Communications}, volume = {47}, number = {41}, year = {2011}, month = {SEP}, pages = {11417-11419}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Full DFT based quantum mechanical studies reveal that zero dimensional porous structures, especially the newly proposed phosphorus incorporated organic cages, can be excellent catalysts for the dehydrogenation of ammonia borane.

}, issn = {1359-7345}, doi = {10.1039/c1cc13285g}, author = {Pal, Amrita and Vanka, Kumar} } @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 {43030, title = {Decoding the morphological diversity in two dimensional crystalline porous polymers by core planarity modulation}, journal = {Angewandte Chemie - International Edition}, volume = {55}, year = {2016}, month = {JUN}, pages = {7806-7810}, doi = {10.1002/anie.201600087}, author = {Halder, Arjun and Kandambeth, Sharath and Biswal, Bishnu P. and Kaur, Gagandeep and Roy, Neha Chaki and Addicoat, Matthew A. and Salunke, Jagadish K. and Banerjee, Subhrashis and Vanka, Kumar and Heine, Thomas and Verma, Sandeep and Banerjee, Rahul} } @article {43728, title = {DBU-mediated diastereoselective aldol-type cyanomethylation of isatins}, journal = {Journal of Organic Chemistry}, volume = {82}, year = {2017}, month = {APR}, pages = {4489-4496}, type = {Article}, abstract = {An efficient, metal-free approach to 3-substituted 3-hydroxybxindole by DBU-mediated highly diastereoselective addition of aryl acetonitrile to N-protected isatin under mild conditions has been developed. The reaction proceeds smoothly to produce respective cyanomethylated adducts in good yield and excellent diastereoselectivity. Further transformation of the cyanide group allowed the synthesis of an advance intermediate of corresponding (+/-) CPC analogue. The mechanistic insight :toward the aldol-type cyanomethylation, of N-tritylisatin with benzyl cyanide was obtained by DFT calculations.}, doi = {10.1021/acs.joc.7b00512}, author = {Rao, V. U. Bhaskara and Kumar, Krishna and Das, Tamal and Vanka, Kumar} } @article {46322, title = {Diastereoselective multi-component tandem condensation: synthesis of 2-amino-4-(2-furanone)-4H-chromene-3-carbonitriles}, journal = {Organic \& Biomolecular Chemistry}, volume = {17}, year = {2019}, month = {OCT}, pages = {8853-8857}, type = {Article}, abstract = {

A general strategy for a one-pot stereoselective synthesis of 2-amino-4-(2-furanone)-4H-chromene-3-carbonitriles by reaction of salicylaldehyde, malononitrile and butenolides via a tandem Knoevenagel/Pinner/vinylogous Michael condensation is presented. The beta,gamma-butenolides gave a syn-selective MCR adduct with a dr up to 11.5 : 1. The mechanistic insight into the MCR was obtained by DFT calculations.

}, issn = {1477-0520}, doi = {10.1039/c9ob01345h}, author = {Gupta, Vijay and Sahu, Debashish and Jain, Shailja and Vanka, Kumar and Singh, Ravi P.} } @article {47644, title = {Deoxygenative hydroboration of primary and secondary amides: a catalyst-free and solvent-free approach}, journal = {Chemical Communications}, volume = {57}, year = {2021}, month = {OCT }, pages = {10596-10599}, type = {Article}, abstract = {In contrast to the recent reports on catalytic hydroboration of amides to amines with pinacolborane (HBpin), a simple catalyst-free and solvent-free method for the hydroboration of a variety of amides has been realized. To get the mechanistic insights, DFT calculations have been performed.}, issn = {1359-7345}, doi = {10.1039/d1cc04148g}, author = {Kumar, Rohit and Bisai, Milan Kumar and Jain, Shailja and Vanka, Kumar and Sen, Sakya S.} } @article {47422, title = {Diverse reactivity of carbenes and silylenes towards fluoropyridines}, journal = {Chemical Communications}, volume = {57}, year = {2021}, month = {MAY }, pages = {4428-4431}, type = {Article}, abstract = {

The reaction of IDipp with C5F5N led to functionalization of all three carbon atoms of the imidazole ring with HF2- as the counter-anion (1). Reactivity with 2,3,5,6-tetrafluoropyridine gives only C-F bond activation leaving C-H bonds intact (5b). The reaction of SIDipp with C5F5N in the presence of BF3 afforded the ring cleavage product (3). Analogous reactions with silylene led to oxidative addition at the Si(II) center.

}, issn = {1359-7345}, doi = {10.1039/d1cc01401c, Early Access Date = MAR 2021}, author = {Kundu, Gargi and Ajithkumar, V. S. and Bisai, Milan Kumar and Tothadi, Srinu and Das, Tamal and Vanka, Kumar and Sen, Sakya S.} } @article {47086, title = {Diverse reactivity of hypersilylsilylene with boranes and threecomponent reactions with aldehyde and HBpin}, journal = {Inorganic Chemistry}, volume = {60}, year = {2021}, month = {FEB }, pages = {1654-1663}, type = {Article}, abstract = {

The recently reported hypersilylsilylene PhC-(NtBu)(2)SiSi(SiMe3)(3) (1) reacts with BH3, 9-BBN, and PhBCl2 to yield the respective Lewis acid base adducts 2-4, respectively. Compound 4 undergoes isomerization to form a ring expansion product 5. The same silylene was found to initially form an adduct with HBpin (6) and subsequently isomerized to 7 via the rupture of the B-H bond of HBpin (7), where the hydride was bound to the carbon atom of the amidinate ligand and the Bpin unit was attached to the silicon center. Surprisingly, the reaction of 1 with HBcat results in PhC(NtBu)(2)Bcat (8). Subsequently, we have shown that HBcat forms the same product when it reacts with related silylene PhC(NtBu)(2)SiN(SiMe3)(3) (1{\textquoteright}). With all of these reactions in hand, we ponder if silylene can activate two small molecules at one time. In this work, we delineate the three-component reactions of silylenes 1 and 1{\textquoteright} with 4-fluorobenzaldehyde and HBpin, which afforded unusual coupling products, 9 and 10, respectively. Note that 9 and 10 were prepared from the cleavage of the B-H and C=O bonds by silylene in a single reaction and are the first structurally attested Si-C-O-B coupled products.

}, issn = {0020-1669}, doi = {10.1021/acs.inorgchem.0c03137}, author = {Bisai, Milan Kumar and Swamy, V. S. V. S. N. and Raj, K. Vipin and Vanka, Kumar and Sen, Sakya S.} } @article {48069, title = {Direct (hetero)arylation (DHAP) polymerization of conjugated polymers - new A-B-A monomer design for P(NDI2OD-T2) \& the challenges of adopting DHAP for continuous flow processes}, journal = {Journal of Materials Chemistry C}, volume = {10}, year = {2022}, month = {SEP}, pages = {13025-13039}, type = {Article}, abstract = {

P(NDI2OD-T2), also known as Polyera ActivInk N2200, was synthesized by the atom-economic direct hetero arylation polymerization (DHAP) route using a newly designed A-B-A monomer. The new monomer design involved flanking naphthalene diimide with bithiophene units in the bay position, which was further polymerized with bay substituted 1,4-dibromo naphthalene diimide, to afford the same polymer structure as P(NDI2OD-T2). The new monomer design resulted in a very high molecular weight (M-n: 99.5 kDa, D-M: 2.8) defect-free polymer in a quantitative yield by the DHAP batch process using 1,2,4-trichlorobenzene (TCB) as the solvent. DFT studies revealed that the abstraction of the alpha-proton from the naphthalene diimide substituted 2,2 {\textquoteleft}-bithiophene was favorable by 2.6 kcal mol(-1) (Delta Delta G) as compared to that from 2,2 {\textquoteleft}-bithiophene. The reason for this improved C-H activation at the alpha position can be attributed to the presence of C-HMIDLINE HORIZONTAL ELLIPSIS pi stabilizing interactions in naphthalene diimide substituted 2,2 {\textquoteleft}-bithiophene, which strengthens upon the extended charge delocalization throughout the ring, thus stabilizing the conjugate base generated after the proton abstraction. Continuous flow polymerization was carried out by pumping the DHAP reaction mixture including the monomers, catalyst, and additive (pivalic acid) solubilized in degassed TCB through a pre-heated glass condenser packed with K2CO3 and Celite under aerobic conditions. Reproducible molecular weights of M-n: 29.5 kDa, D-M: 1.7 were obtained at much lower concentrations of reactant mixture compared to that for batch polymerization. This is the first report of the synthesis of P(NDI2OD-T2) by a Continuous Flow Process adopting the DHAP route to obtain a defect-free polymer with reasonable molecular weights. P(NDI2OD-T2) was also synthesized by Stille polymerization as a reference control sample to compare the thermal and charge carrier transport properties of the DHAP polymers. Organic field-effect (OFET) mobility measurements indicated mobility values in the order of 10(-3) cm(2) V-1 s(-1) for the DHAP batch polymer (using the novel monomer design). The P(NDI2OD-T2) synthesized by DHAP batch using the commonly used starting materials - bisbromo naphthalene diimide and bithiophene, exhibited OFET mobilities which were one order less, similar to 10(-4) cm(2) V-1 s(-1). This observation highlights the importance of structural design in the monomer to enhance reactivity and thereby the bulk properties using the DHAP route.

}, issn = {2050-7526}, doi = {10.1039/d2tc02514k}, author = {Kakde, Navnath R. and Bharathkumar, H. J. and Wavhal, Bhaiyyasaheb A. and Nikam, Arun and Patil, Suneha and Dash, Soumya Ranjan and Vanka, Kumar and Krishnamoorthy, K. and Kulkarni, Amol and Asha, S. K.} } @article {48096, title = {Direct oxidation of bromo-derived Fischer-Borsche oxo-ring using molecular iodine with combined experimental and computational study}, journal = {Organic \& Biomolecular Chemistry}, volume = {20}, year = {2022}, month = {JUL}, pages = {5726-5729}, type = {Article}, abstract = {

A direct oxidation of the bromo-derived Fischer-Borsche oxo-ring leading to carbazolequinone has been developed by using molecular iodine. This unprecedented transformation has been used for the modular synthesis of the anti-cardiotonic agent murrayaquinone. Furthermore, the present method has been generalized to a broad range of functional groups, with good to excellent yield.

}, issn = {1477-0520}, doi = {10.1039/d2ob00793b}, author = {Humne, Vivek T. and Ghom, Monica H. and Naykode, Mahavir S. and Dangat, Yuvraj and Vanka, Kumar and Lokhande, Pradeep} } @article {48301, title = {Dual routes toward observation of a trans-H2/hydride complex in an iridium pincer system and hydrogenation catalytic activity}, journal = {Organometallics}, volume = {42}, year = {2023}, month = {MAR}, pages = {441-456}, type = {Article}, abstract = {

The Abstraction of chloride from a six- coordinate complex, trans-[ Ir(H)(Cl)((iPr)4)(POCOP)(PPh3)] (1) [((iPr)4)(POCOP) = 2,6-bis(di-iso-propylphosphinito)benzene,kappa(3)-C6H3-1,3-[OP(Pr-i)(2 )](2)], using NaBAr4f leads to the generation of a dinitrogen complex, trans-[Ir(H)(N-2)((iPr)4)(POCOP)(PPh3)][BAr4f] (6). Addition of H-2 to [Ir(H)(N-2)((iPr)4)(POCOP)(PPh3)](+) (6) under extremely mild conditions (1 bar, 298 K) resulted in the reversible coordination of H-2 to generate the cis-[Ir(H)(eta H-2-(2))((iPr)4)(POCOP)(PPh3)](+) (cis-11) complex. The cis-[Ir(H)(eta(2)-H-2)((iPr)4)(POCOP)(PPh3)](+) complex (cis-11) isomerized to a trans isomer, trans-[Ir(H)(eta(2)-H-2)((iPr)4)(POCOP)(PPh3)](+) (trans-11), at 253 K. The isomerization process has been studied and supported by computations. Employing an alternative route, protonation of the trans-[Ir(H)(2)((iPr)4)(POCOP)(PPh3)] complex (2) at 183 K resulted in the formation of an identical, trans-[Ir(H)(eta(2)-H-2)((iPr)4)(POCOP)(PPh3)](+) complex (trans-11); upon warming the sample, the trans-H-2/hydride complex isomerized to the cis isomer above 253 K. Two independent routes to obtain trans-[Ir(H)(eta(2)-H-2)((iPr)4)(POCOP)(PPh3)](+) (trans-11) species have been established. Reaction of trans-[Ir(H)(N-2)((iPr)4)(POCOP)(PPh3)][BAr4f] (6) with C2H4 gave the cis-[Ir(H)(eta(2)-C2H4)((iPr)4)(POCOP)(PPh3)](+) complex (cis-15), which also undergoes isomerization to yield an equilibrium mixture of cis/trans-[Ir(H)(eta(2)-C2H4)((iPr)4)(POCOP)(PPh3)](+) complexes (cis-15 and trans-15) at 253 K. The trans-[Ir(H)(N-2)((iPr)4)(POCOP)(PPh3)](+) complex (6) is an excellent catalyst for hydrogenation of ethylene to ethane under very mild conditions.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.2c00641}, author = {Agrawal, Nisha K. and Dash, Soumya R. and Vanka, Kumar and Jagirdar, Balaji R.} }