@article {45469, title = {Facile activation of Si-H bond by an electrophilic carbene}, journal = {Indian Chemical Society}, volume = {95}, year = {2018}, month = {JUL}, pages = {789-793}, type = {Article}, abstract = {Herein, we have explored the chemistry of 1,3-bis(2,6-di-isopropylphenyl)-5,5-dimethy1-4,6-diketopyrimidinyl-2-ylidene (1) with various silanes under mild conditions. The oxidative addition of Si-H bond of phenylsilane with DAC 1 affords the compound 2, which is unambiguously characterized by muitinuclear NMR spectroscopy, elemental analysis, and X-ray single crystal diffraction studies. Interestingly, DAC 1 activates silicon hydride bond of chlorosilanes at room temperature and results in the corresponding silylation products.}, issn = { 0019-4522}, author = {Swamy, V. S. V. S. N. and Kundu, Gargi and Sen, Sakya S.} } @article {46425, title = {Saturated N-heterocyclic carbene based thiele{\textquoteright}s hydrocarbon with a tetrafluorophenylene linker}, journal = {Chemistry-A European Journal}, year = {2019}, month = {NOV}, type = {Article; Early Access}, abstract = {

The synthesis of a SIPr [1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene] derived Kekule diradicaloid with a tetrafluorophenylene spacer (3) has been described. Two synthetic routes have been reported to access 3. The cleavage of C-F bond of C6F6 by SIPr in the presence of BF3 led to double C-F activated compound with two tetrafluoro borate counter anions (2), which upon reduction by lithium metal afforded 3. Alternatively, 3 can be directly accessed in one step by reacting SIPr with C6F6 in presence of Mg metal. Compounds 2 and 3 were well characterized spectroscopically and by single-crystal X-ray diffraction studies. Experimental and computational studies support the cumulenic closed-shell singlet state of 3 with a singlet-triplet energy gap (Delta ES-T) of 23.7 kcal mol(-1).

}, keywords = {C-F activation, Density functional calculations, fluorine, Kekule diradicaloids, saturated NHC}, issn = {0947-6539}, doi = {10.1002/chem.201904421}, author = {Kundu, Gargi and De, Sriman and Tothadi, Srinu and Das, Abhishek and Koley, Debasis and Sen, Sakya S.} } @article {46679, title = {Cyanosilylation by compounds with main-group elements: an odyssey}, journal = {ACS Omega}, volume = {5}, year = {2020}, month = {OCT}, pages = {25477-25484}, type = {Review}, abstract = {

The past few decades have seen remarkable headways in the structural and reaction chemistry of compounds with heavier main-group elements. In recent years, there is an ongoing effort to derive catalytic chemistry involving main-group compounds, driven by their lower costs and higher terrestrial abundances. Here, a survey on the state-of-the-art in the development of cyanosilylation methodology by compounds with heavier main-group elements has been given. Once dominated by transition metals, the field has matured to embrace the majority of the main-group elements including aluminum, silicon, and calcium. Of particular focus will be how the mechanism of cyanosilylation involving compounds with main-group elements differs from those of transition metals.

}, issn = {2470-1343}, doi = {10.1021/acsomega.0c03293}, author = {Pahar, Sanjukta and Kundu, Gargi and Sen, Sakya S.} } @article {46599, title = {Stepwise nucleophilic substitution to access saturated N-heterocyclic carbene haloboranes with boron-methyl bonds}, journal = {Organometallics}, volume = {39}, year = {2020}, month = {DEC}, pages = {4696-4703}, type = {Article}, abstract = {

Compounds of boranes with N-heterocyclic carbenes are known, yet little attention has been paid to NHC compounds of boron bearing methyl and halogen moieties together. The reason can be attributed to the hazardous methyldichloroborane (MeBCl2), which ignites in air. We describe here convenient solution-phase access to SIDipp.MeBCl2 (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) (3) by a salt metathesis reaction of SIDipp.BCl3 (2) with MeLi. Replacement of the chlorine atoms of 3 with stepwise addition of AgOTf led to the formation of SIDipp.MeBCl(OTf) (4) and SIDipp.MeB(OTf)2 (5). In the case of 4, all of the substituents on the boron atom are different. Subsequently, we extended our synthetic approach to the amidinate system and prepared PhC(NtBu)2B(Me)Cl (7) from the reaction of PhC(NtBu)2BCl2 (6) with MeLi.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.0c00691}, author = {Kundu, Gargi and Pahar, Sanjukta and Tothadi, Srinu 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 {48142, title = {Nucleophilic substitution at a coordinatively saturated five-membered NHC center dot haloborane centre}, journal = {Inorganics}, volume = {10}, year = {2022}, month = {JUL}, pages = {97}, type = {Article}, abstract = {

In this paper, we have used a saturated five-membered N-Heterocyclic carbene (5SIDipp = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-ylidine) for the synthesis of SNHC-haloboranes adducts and their further nucleophilic substitutions to put unusual functional groups at the central boron atom. The reaction of 5-SIDipp with RBCl2 yields Lewis-base adducts, 5-SIDipp center dot RBCl2 [R = H (1), Ph (2)]. The hydrolysis of 1 gives the NHC stabilized boric acid, 5-SIDipp center dot B(OH)(3) (3), selectively. Replacement of chlorine atoms from 1 and 2 with one equivalent of AgOTf led to the formation of 5-SIDipp center dot HBCl(OTf) (4) and 5-SIDipp center dot PhBCl(OTf) (5a), where all the substituents on the boron atoms are different. The addition of two equivalents of AgNO3 to 2 leads to the formation of rare di-nitro substituted 5-SIDipp center dot BPh(NO3)(2) (6). Further, the reaction of 5-SIDipp with B(C6F5)(3) in tetrahydrofuran and diethyl ether shows a frustrated Lewis pair type small molecule activated products, 7 and 8.

}, keywords = {NHC-haloboranes, nucleophilic substitution, saturated NHC, tetra-coordinate boron}, doi = {10.3390/inorganics10070097}, author = {Kundu, Gargi and Tothadi, Srinu and Sen, Sakya S.} } @article {48126, title = {Six-membered saturated NHC-stabilized borenium cations: isolation of a cationic analogue of borinic acid}, journal = {Inorganic Chemistry}, volume = {61}, year = {2022}, month = {AUG}, pages = {12991-12997}, type = {Article}, abstract = {

The reaction of six-membered saturated NHC [1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene; henceforth abbreviated as 6-SIDipp] with PhBCl2 yields a Lewis base adduct, 6-SIDipp.PhBCl2 (1), which readily undergoes nucleophilic substitution reaction with AgNO3, leading to the single (2) and double (3) substitution of both chlorides with ONO2 moieties at the boron atom. The reaction of 1 with 1 equiv of AlCl3 resulted in a borenium cation of composition [6-SIDipp.B(Ph)Cl]+ (4) with AlCl4- as the counteranion. Although borenium cations with different substituents on boron have been reported, a structurally characterized phenylchloroborenium cation remains unknown. Similarly, the reaction of 1 with triflic acid provides the first representative of a new class of borenium cations bearing one hydroxyl and one phenyl group on boron (5), a cationic analogue of borinic acid. Ph-BN H Diphenylborinic acid

}, issn = {0020-1669}, doi = {10.1021/acs.inorgchem.2c00611}, author = {Kundu, Gargi and Balayan, Kajal and Tothadi, Srinu and Sen, Sakya S.} } @article {48149, title = {Substitution at sp(3) boron of a six-membered NHC center dot BH3: convenient access to a dihydroxyborenium cation}, journal = {Chemical Communications}, volume = {58}, year = {2022}, month = {MAR }, pages = {3783-3786}, type = {Article}, abstract = {

Herein, we have undertaken the synthesis and investigated the reactivity of a 6-membered saturated NHC borane adduct (1). Direct electrophilic halogenation of 1 with a stoichiometric amount of I-2 led to NHC boryl iodides, 6-SIDipp center dot BH2I (2) and 6-SIDipp center dot BHI2 (3), which were further reacted with various nucleophiles to give novel 6-SIDipp based mono and disubstituted boranes with OTf (4 and 6) or ONO2 (5 and 7) functional groups. The addition of Br-2/H2O to 1 smoothly results in a dihydroxyborenium cation (8).

}, issn = {1359-7345}, doi = {10.1039/d1cc06816d}, author = {Kundu, Gargi and Ajithkumar, V. S. and Raj, K. Vipin and Vanka, Kumar and Tothadi, Srinu and Sen, Sakya S.} } @article {48162, title = {Versatile chemistry of six-membered NHC with boranes: bromination at sp(3) borane, activation of the B-H bond of HBpin, and ring expansion of NHC}, journal = {Dalton Transactions}, volume = {51}, year = {2022}, month = {OCT}, pages = {14452-14457}, type = {Article}, abstract = {

The NHC.borane chemistry has been majorly restricted to imidazol-2-ylidene classes of carbenes. In our previous communication, we reported the synthesis of 6-SIDipp center dot BH3 [6-SIDipp = 1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene] and its electrophilic substitution reaction with iodine. Here, we have shown selective bromination of a 6-SIDipp stabilized sp(3) B-H bond. Treatment of 1.2 equivalents of N-bromosuccinamide with 6-SIDipp center dot BH3 gives a mixture of mono- and disubstituted products 6-SIDipp center dot BH2Br (1) and 6-SIDipp center dot BHBr2 (2). However, the reactions with alkyl bromides or carbon tetrabromide resulted in 6-SIDipp center dot BH2Br (1) selectively. Exploration of the chemistry of 6-SIDipp with BHCl2 and 9-BBN (9-borabicyclo[3.3.1]nonane) led to mono-6-SIDipp adducts 3 and 6a. Furthermore, 6a undergoes ring expansion to afford a seven-membered product, 6b, under mild conditions. Unlike BHCl2 or 9-BBN, the B-H bond of HBpin undergoes oxidative addition upon reaction with 6-SIDipp, epitomizing the first example (7) of a B-H bond insertion at NHCs. The analogous reactivity with HBcat led to a tetra-hydropyrimidinium salt with B(cat)(2) as a counteranion (8).

}, issn = {1477-9226}, doi = {10.1039/d2dt01707e}, author = {Kundu, Gargi and Dixit, Ruchi and Tothadi, Srinu and Vanka, Kumar 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 {48738, title = {Six-membered NHC stabilized monomeric zinc complexes}, journal = {European Journal of Inorganic Chemistry}, volume = {26}, year = {2023}, month = {JUL}, pages = {e202300167}, type = {Article}, abstract = {

This paper describes the rare use of a 6-membered saturated N-heterocyclic carbene (NHC) known as 1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene (abbreviated as 6-SI-Dipp) as a ligand in zinc chemistry. We report on the investigation of the reactions between 6-SI-Dipp and ZnX2, which resulted in a range of new monomeric 6-SIDipp center dot ZnX2 complexes (X=Et (1), Cl (2), Br (3), and I (4)). We also prepared a new NHC zinc complex where the two substituents of the zinc atom are different, 6-SIDipp center dot Zn(Et)Br (7) through the reaction of the proligand [6-SIDippH]Br with ZnEt2. We have observed that the reactions of complex 1 with sulfur and HBpin led to the removal of the ZnEt2 moiety, resulting in the formation of a C=S double bond and a B H activation product, respectively. Lastly, the reaction of 1 with five-membered NHCs led to the exchange of carbene and the formation of either 5-IDipp center dot ZnEt2 (8) or 5-SIDipp center dot ZnEt2 (9).

}, keywords = {Lewis adduct, NHC, X-ray diffraction, zinc}, issn = {1434-1948}, doi = {10.1002/ejic.202300167}, author = {Gour, Kritika and Kundu, Gargi and Dash, Soumya Ranjan and Vanka, Kumar and Tothadi, Srinu and Sen, Sakya S.} } @article {48769, title = {Taming the parent oxoborane}, journal = {Chemical Science}, volume = {14}, year = {2023}, month = {JUN}, pages = {5894-5898}, type = {Article}, abstract = {

Despite recent advancements in the chemistry of multiply bound boron compounds, the laboratory isolation of the parent oxoborane moiety, HBO has long remained an unsolved and well-recognized challenge. The reaction of 6-SIDipp(.)BH3 [6-SIDipp = 1,3-di(2,6-diisopropylphenyl)tetrahydropyrimidine2-ylidene] with GaCl3 afforded an unusual boron-gallium 3c-2e compound (1). The addition of water to 1 resulted in the release of H-2 and the formation of a rare acid stabilized neutral parent oxoborane, LB(H)]O (2). Crystallographic and density functional theory (DFT) analyses support the presence of a terminal B=O double bond. Subsequent addition of another equivalent of water molecule led to hydrolysis of the B-H bond to the B-OH bond, but the {\textquoteleft}B=O{\textquoteright} moiety remained intact, resulting in the formation of the hydroxy oxoborane compound (3), which can be classified as a monomeric form of metaboric acid.

}, issn = {2041-6520}, doi = {10.1039/d3sc01544k}, author = {Kundu, Gargi and Amrutha, P. R. and Raj, K. Vipin and Tothadi, Srinu and Vanka, Kumar and Sen, Sakya S.} }