@article {43051, title = {Benz{\textendash}amidinato stabilized a monomeric calcium Iodide and a lithium calciate(II) cluster featuring group 1 and group 2 elements}, journal = {ChemistrySelect}, volume = {1}, year = {2016}, month = {APR}, pages = {1066{\textendash}1071}, abstract = {

Soluble calcium halides reported so far are mostly dimeric in nature. The halides occupy the bridging position and thus provide additional coordination to the metal. We obtained a monomeric calcium iodide [{PhC(NiPr)(2)} CaI(thf)(3)] (1) from the reaction of [PhC(NiPr)(2)] Li with Cal(2) in THF. The compound has been stabilized by electronic donation and steric shielding from the amidinate ligand as well as coordination of three THF molecules. 1 does not show any propensity towards ligand exchange reaction. When the same reaction is carried out in diethyl ether instead of THF, it led to the formation of a Li calciate(II) cluster of composition L2Ca4I8Li4O (L= PhC(NiPr)(2)) (2) with an encapsulated O2+ in the middle of a tetrahedron spanned by four Ca2+ ions. 2 represents a metal-rich halide comprising of both alkali and alkaline earth metals which is quite unprecedented. Another notable aspect is that the amidinate ligand binds to the calcium atom in chelating bidentate mode in 1, whereas in 2 each N atom of the amidinate ligands binds to two Ca atoms leading to bridging bis-chelating coordination mode.

}, doi = {10.1002/slct.201600285}, author = {Yadav, Sandeep and Swamy, V. S. V. S. N. and Gonnade, Rajesh G. and Sen, Sakya S.} } @article { ISI:000370029900002, title = {Compounds with low-valent p-block elements for small molecule activation and catalysis}, journal = {Chemcatchem}, volume = {8}, number = {3}, year = {2016}, month = {FEB}, pages = {486-501}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

The past decade has witnessed staggering progress in the chemistry of compounds with low-valent main-group elements. Although these discoveries are mostly fundamental by nature, these compounds show promising reactivity towards small molecule activation. The reactivity of these compounds stems from the modest HOMO-LUMO energy gap; a characteristic known for the transition metals. The journey began in 2005 with the facile activation of dihydrogen by an alkyne analog of germanium [ArGeGeAr; Ar=2,6-Trip(2)-C6H3 (Trip=2,4,6-iPr(3)-C6H2)]. Subsequently, tremendous progress has been achieved in understanding and elucidating the potential of these compounds to activate small molecules as well as to use them in a variety of stoichiometric and catalytic transformations. In this review, we focus on developments in the activation of H-2, NH3, CO, and CO2 by compounds with multiply bound or open shell main-group elements. Emphasis will be given to their catalytic activity.

}, keywords = {activation, carbenes, main-group elements, silylenes, small molecules}, issn = {1867-3880}, doi = {10.1002/cctc.201501015}, author = {Yadav, Sandeep and Saha, Sumana and Sen, Sakya S.} } @article { ISI:000378295200030, title = {Facile access to a Ge(II) dication stabilized by isocyanides}, journal = {Chemical Communications}, volume = {52}, number = {50}, year = {2016}, month = {MAY}, pages = {7890-7892}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Herein, we introduce isocyanide as a ligand in main group chemistry and describe the facile isolation of a Ge(II) dication. The reaction of 2,6-dimethylphenylisocyanide with GeCl2 leads to the formation of a Ge(II) dication with two [GeCl3](-) molecules as counter anions. The dicationic Ge(II) center is bound to four isocyanide ligands and also holds a lone pair of electrons. DFT calculations reveal that the dication is stabilized only by sigma-donation from the four isocyanide ligands. Natural population analysis gives a charge of +0.74 on the Ge(II) center, indicating that the positive charge is shared by the isocyanide substituents.

}, issn = {1359-7345}, doi = {10.1039/c6cc03789e}, author = {Swamy, V. S. V. S. N. and Yadav, Sandeep and Pal, Shiv and Das, Tamal and Vanka, Kumar and Sen, Sakya S.} } @article {43866, title = {Unprecedented solvent induced inter-conversion between monomeric and dimeric silylene-zinc iodide adducts}, journal = {Dalton Transaction }, volume = {46}, year = {2017}, month = {SEP}, chapter = {11418-11424}, abstract = {

Usually, when a silylene reacts with a transition metal Lewis acid, it forms an adduct which could be either monomeric or dimeric. However, we present here that a silylene, [PhC(NtBu)(2)SiN(SiMe3)(2)] can form both monomeric [PhC(NtBu)(2)Si{N(SiMe3)(2)} -\> ZnI2]center dot THF (1) and dimeric [{PhC(NtBu)(2)}(N(SiMe3)(2))SiZnI,(mu-I)](2) (2) adducts upon reaction with ZnI2. The formation of 1 and 2 relies upon the solvent used for the reaction or crystallization. When the crystallization is carried out in THF complex 1 is formed, however, when the reaction and crystallization are performed in acetonitrile complex 2 is obtained. Both 1 and 2 were structurally authenticated and the nature of the Si-Zn bond in these complexes was determined by quantum chemical calculations. In addition, a spontaneous inter-conversion between 1 and 2 just by changing the solvents has been also observed; a feature presently not known for silylene-transition metal Lewis adducts.

}, keywords = {Bis(Silylene ), Carbene Complexes, Crystal -structure Determination, Dative bond, Lewis acid base reaction, Ligands, Main- group compounds, Reactivity, Silicon(II) Bis(Trimethylsilyl)Amide; Carbonyl-Complexes}, issn = {1477-9226}, doi = {10.1039/c7dt01823a}, author = {Yadav, Sandeep and Sangtani, Ekta and Dhawan, Diksha and Gonnade, Rajesh G. and Ghosh, Debashree and Sen, Sakya S.} } @article {44204, title = {Beyond hydrofunctionalisation: a well-defined calcium compound catalysed mild and efficient carbonyl cyanosilylation}, journal = {Chemistry-A European Journal}, volume = {24}, year = {2018}, month = {JAN}, pages = {1269-1273}, type = {Article}, abstract = {

Organocalcium compounds have been reported as efficient catalysts for various transformations, for cases in which one of the substrates contained an E-H (E=B, N, Si, P) bond. Here, we look at the possibility of employing an organocalcium compound for a transformation in which none of the precursors has a polar E-H bond. This study demonstrates the utilization of a well-defined amidinatocalcium iodide, [PhC(NiPr)(2)CaI] (1) for cyanosilylation of a variety of aldehydes and ketones with Me3SiCN under ambient conditions without the need of any co-catalyst. The reaction mechanism involves a weak adduct formation between 1 and Me3SiCN leading to the activation of the Si-C bond, which subsequently undergoes sigma-bond metathesis with a C=O moiety. Such a mechanistic pathway is unprecedented in alkaline earth metal chemistry. Experimental and computational studies support the mechanism.

}, keywords = {Ca catalysis, carbonyls, cyanosilylation, Density functional calculations, transition-metal free}, issn = {0947-6539}, doi = {10.1002/chem.201705795}, author = {Yadav, Sandeep and Dixit, Ruchi and Vanka, Kumar and Sen, Sakya S.} } @article {46289, title = {Lithium compounds as single site catalysts for hydroboration of alkenes and alkynes}, journal = {Chemical Communications}, volume = {55}, year = {2019}, month = {OCT }, pages = {11711-11714}, type = {Article}, abstract = {

The hydroboration of alkenes and alkynes using easily accessible lithium compounds [2,6-di-tert-butyl phenolatelithium (1a) and 1,1 {\textquoteleft} dilithioferrocene (1b)] has been achieved with good yields, high functional group tolerance and excellent chemoselectivity. Deuterium-labeling experiments confirm the cis-addition of pinacolborane. The methodology has been further extended to myrcene, which undergoes selective 4,3-hydroboration. DFT calculations provide insights into the mechanism.

}, issn = {1359-7345}, doi = {10.1039/c9cc05783h}, author = {Bisai, Milan Kumar and Yadav, Sandeep and Das, Tamal and Vanka, Kumar and Sen, Sakya S.} } @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 {46956, title = {Tale of biphenyl and terphenyl substituents for structurally diverse ketiminato magnesium, calcium and germanium complexes}, journal = {Chemistry-An Asian Journal}, volume = {15}, year = {2020}, month = {MAR}, pages = {820-827}, type = {Article}, abstract = {

In this paper, we have used two N,O-ketiminato ligands (L1 and L2) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe3)(2) and subsequent reaction with MgI2 led to a homoleptic dinuclear magnesium complex (1) with a Mg2O2 four-membered ring. Deprotonation with nBuLi and subsequent reaction with MgI2 afforded a unusual dinuclear magnesium complex (2) with a Mg2O2 ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex (3) with six four-membered Ca2O2 rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium (4) and calcium (5) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride (7) with L1. However, with L2, an unusual ligand scrambling, and a C-C coupling take place, leading to the formation of a secondary carbocation with GeCl3- as a counter-anion (8). Besides, a germanium dichloride adduct (9) bound to the oxygen center of the ligand was obtained as the minor product.

}, keywords = {calcium, Germylene, ligand, Magnesium, X-ray Structure}, issn = {1861-4728}, doi = {10.1002/asia.201901801, Early Access Date = FEB 2020}, author = {Kumar, Rohit and Yadav, Sandeep and Gour, Kritika and Sangtani, Ekta and Ranjan Dash, Soumya and Raja, Abhishekram and Vanka, Kumar and Gonnade, Rajesh G. and Sen, Sakya S.} } @article {47382, title = {Substrate, catalyst, and solvent: the triune nature of multitasking reagents in hydroboration and cyanosilylation}, journal = {Organometallics}, volume = {40}, year = {2021}, month = {APR}, pages = {1104-1112}, type = {Article}, abstract = {

A truly green chemical process would avoid the use of an external catalyst, while still achieving high efficiency. This has been realized in the very recent past for hydroboration, cyanosilylation, acetalization, and the aza-Michael addition, among other reactions. The current combined computational and experimental study unlocks the secret to how this highly desirable outcome is accomplished: one of the reactants in the process also acts as the catalyst. Specifically, this is shown (i) for the important hydroboration reaction, with pinacolborane (HBpin) as the hydroborating reagent and benzaldehyde, acetophenone, benzoic acid and p-methoxyphenylacetylene as the hydroborated substrates, and (ii) for cyanosilylation, with trimethylcyanosilane (TMSCN) as the cyanosilylating agent and benzaldehyde as the substrate. The mechanistic understanding thus gained has then been further exploited experimentally to bring hydroboration and cyanosilylation closer to experimental conditions in catalysis. These insights can potentially be expanded to the rapidly growing area of solvent-free and internal catalyst chemistry.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.1c00070}, author = {Dixit, Ruchi and Bisai, Milan Kumar and Yadav, Sandeep and Yadav, Vinita and Sen, Sakya S. and Vanka, Kumar} }