Now showing 1 - 10 of 35
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    Dinitrogen Binding Relevant to FeMoco of Nitrogenase: Clear Visualization of σ-Donation and π-Backdonation from Deformation Electron Densities around Carbon/Silicon-Iron Site
    (29-03-2022)
    Devi, Kavita
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    Gorantla, Sai Manoj N.V.T.
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    Dinitrogen (N2) binding and electron transfer reduction of N2 to ammonia (NH3) by the FeMoco cofactor of the nitrogenase enzyme are captivating. They are a part of the textbook for general chemistry. The nature of N2 bonding by reduced FeMoco is speculated based on the experimental evidence. The inorganic core MoFe7S9C1− possesses a Fe6(μ6-C4−) unit. The mode of N2-binding at one of the Fe-centers of the elusive Fe6(μ6-C4−) unit and the role of light element C4− is intriguing. In the past, the mode of N2-binding and the kinetics of N2 reduction have been studied by spectroscopic and other tools. Herein, we report on the energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) calculations/analyses to shed light on the deeper insight of the N2 binding and especially on the influence of the C-atom of previously reported Fe-complexes with an EP3 donor set (E=C, Si). The role of the C-atom in the iron-carbon site has been studied by elaboration with deformation electron densities. The intrinsic interaction energy of the bond between Fe and N2 and pairwise orbital interactions between them have been quantitatively estimated. The influence of σ-donation of three phosphine ligands and their effects on the Fe−N2 bond have been thoroughly studied.
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    The Labile Nature of Air Stable Ni(II)/Ni(0)-phosphine/Olefin Catalysts/Intermediates: EDA-NOCV Analysis
    (04-10-2022)
    Gorantla, Sai Manoj N.V.T.
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    Metal ions-based inorganic-organic hybrid composites are often reported acting as good to excellent catalysts with various substrate scopes under milder reaction conditions. The active catalyst of a catalytic cycle is sometimes proposed to be a short-lived reactive intermediate species. A three coordinate (L−Me)Ni(II) intermediate species [L−Me=O2N donor dianionic ligand] can bind with short-lived carbene-ester ligands to produce four coordinate Ni(II) species which can act as carbene transfer intermediate under suitable reaction conditions for C−H functionalization and/or cyclopropanation reactions. The dissociation of phosphine (PPh3) from the Ni(II) centre of (L−Me)Ni(II)(PPh3) (1 a) and binding of short lived carbene esters (:CR1−CO2R2; R1=H, Ph; R2=aliphatic group; 2–4 and other carbenes; 5–10) to Ni(II) rationalize the phenomenon in solution. Air stable Ni(0)-olefin complexes/intermediates (12–18) have recently been shown to mediate a variety of organic transformations. This analysis will further help organic/organometallic chemists to rationalize the design and synthesis of future catalysts for organic transformation. EDA-NOCV calculations have been performed to shed light on the stability and bonding of those species. Additionally, our analysis provides a proper reason why the analogous (L−Me)Pd−PPh3 complex (1 b) does not dissociate in solution and hence, a similar catalytic product has not been isolated from identical reaction conditions. The stability and the labile nature of Ni(II/0) complexes have been investigated by state-of-the-art EDA-NOCV analyses.
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    Uncovering the hidden reactivity of benzyne/aryne precursors utilized under milder condition: Bonding and stability studies by EDA-NOCV analyses
    (05-09-2022)
    Gorantla, Sai Manoj N.V.T.
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    Arenes [C6H3R(TMS)(OTf); also called benzyne/aryne precursors] containing inter-related leaving groups Me3Si (TMS) and CF3-SO3-(OTf) on the adjacent positions (1,2-position) are generally converted to their corresponding aryne-intermediates via the addition of fluoride anion (F−) and subsequent elimination of TMS and OTf groups. This reaction is believed to proceed via the formation of an anionic intermediate [C6H4(TMS-F)(OTf)]−. The EDA-NOCV analysis (EDA-NOCV = energy decomposition analysis-natural orbital for chemical valence) of over 35 such precursors of varied types have been reported to reveal bonding and stability of CAr-Si and C-OTf bonds. EDA-NOCV showed that the nature of the CAr-Si bond of C6H3R(TMS)(OTf) can be expressed as both dative and electron sharing [CAr-Si, CAr→Si]. The CAr-OTf bond, on the other hand, can be described explicitly as dative [CAr←OTf]. The nature of CAr-Si bond of [C6H4(TMS-F)(OTf)]− exclusively changes to covalent dative σ-bond CAr→S(Me)3F on the attachment of F− to the TMS group of C6H4(TMS)(OTf). Introduction of σ-electron withdrawing group (like OMe, NMe2, and NO2) to the ortho-position of the TMS group of functionalized arynes C6H3R(TMS)(OTf) prefer to have a covalent dative σ-bond (CAr→Si) over an electron-sharing covalent σ-bond (CAr-Si). If this σ-electron withdrawing group is shifted from ortho-position to meta- and para-positions, then the preference for a dative bond decreases significantly, implying that the electronic effect on the nature of chemical bonds affects through bond paths. This effect dies with distance, similar to the well-known inductive effect.
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    Dinitrogen Binding and Activation: Bonding Analyses of Stable V(III/I)-N2-V(III/I) Complexes by the EDA-NOCV Method from the Perspective of Vanadium Nitrogenase
    (06-09-2022)
    Chauhan, Akshay
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    Karnamkkott, Harsha S.
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    Gorantla, Sai Manoj N.V.T.
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    The FeVco cofactor of nitrogenase (VFe7S8(CO3)C) is an alternative in the molybdenum (Mo)-deficient free soil living azotobacter vinelandii. The rate of N2 reduction to NH3 by FeVco is a few times higher than that by FeMoco (MoFe7S9C) at low temperature. It provides a N source in the form of ammonium ions to the soil. This biochemical NH3 synthesis is an alternative to the industrial energy-demanding production of NH3 by the Haber-Bosch process. The role of vanadium has not been clearly understood yet, which has led chemists to come up with several stable V-N2 complexes which have been isolated and characterized in the laboratory over the past three decades. Herein, we report the EDA-NOCV analyses of dinitrogen-bonded stable complexes V(III/I)-N2 (1-4) to provide deeper insights into the fundamental bonding aspects of V-N2 bond, showing the interacting orbitals and corresponding pairwise orbital interaction energies (ΔEorb(n)). The computed intrinsic interaction energy (ΔEint) of V-N2-V bonds is significantly higher than those of the previously reported Fe-N2-Fe bonds. Covalent interaction energy (ΔEorb) is more than double the electrostatic interaction energy (ΔEelstat) of V-N2-V bonds. ΔEint values of V-N2-V bonds are in the range of-172 to-204 kcal/mol. The V → N2 ↠V π-backdonation is four times stronger than V ↠N2 → V σ-donation. V-N2 bonds are much more covalent in nature than Fe-N2 bonds.
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    Fluorescent organo-antimony compounds as precursors for syntheses of redox-active trimeric and dimeric alkali metal antimonides: An insight into electron transfer reduction processes
    (07-02-2022)
    Nag, Ekta
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    Kulkarni, Aditya
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    Gorantla, Sai Manoj N.V.T.
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    Graw, Nico
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    Francis, Maria
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    Herbst-Irmer, Regine
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    Stalke, Dietmar
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    Roesky, Herbert W.
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    Roy, Sudipta
    (Tip)2SbCl (1, Tip = 2,4,6-triisopropylphenyl) has been utilized as a precursor for the synthesis of the distibane (Tip)4Sb2 (4) via one-electron reduction using KC8. The two-electron reduction of 1 and 4 afforded the novel trinuclear antimonide cluster [K3((Tip)2Sb)3(THF)5] (6). Changing the reducing agent from KC8 to a different alkali metal resulted in the solid-state isolation of corresponding stable dimeric alkali metal antimonides with the general formula [M2((Tip)2Sb)2(THF)p-x(tol)x] (M = Li (14), Na (15), Cs (16)). In this report, different aspects of the various reducing agents [K metal, KC8, and [K2(Naph)2(THF)]] used have been studied, correlating the experimental observations with previous reports. Additional reactivity studies involving 1 and AgNTf2 (Tf = trifluoromethanesulfonyl) afforded the corresponding antimony cation (Tip)2Sb+NTf2- (19). The Lewis acidic character of 19 has been unambiguously proved via treatment with Lewis bases to produce the corresponding adducts 20 and 21. Interestingly, the precursors 1 and 4 have been observed to be highly luminescent, emitting green light under short-wavelength UV radiation. All the reported compounds have been characterized via NMR, UV-vis, mass spectrometry, and single-crystal X-ray diffraction analysis. Cyclic voltammetry (CV) studies of 1 in THF showed possible two electron reduction, suggesting the in situ generation of the corresponding radical-anion intermediate 1- and its subsequent conversion to the monomeric intermediate (Tip)2Sb- (5) upon further reduction. 5 undergoes oligomerization in the solid state to produce 6. The existence of 1- was proved using electron paramagnetic resonance (EPR) spectroscopy in solution. CV studies of 6 suggested its potential application as a reducing agent, which was further proved via the conversion of Tip-PCl2 to trimeric (Tip)3P3 (17), and cAACP-Cl (cAAC = cyclic alkyl(amino)carbene) to (cAAC)2P2 (18) and 4, utilizing 6 as a stoichiometric reducing agent.
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    Synthesis, oligomerization and catalytic studies of a redox-active Ni4-cubane: A detailed mechanistic investigation
    (30-06-2021)
    Kushvaha, Saroj Kumar
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    Francis, Maria
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    Kumar, Jayasree
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    Nag, Ekta
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    Ravichandran, Prathap
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    Roy, Sudipta
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    A robust tetrameric nickel complex [Ni4((Oal-)2L-Me)4(s)4] (3) (s = solvent) with cubane-like Ni4O4 core topology was isolated as a light greenish-orange crystalline solid in excellent yield. The mechanism of formation of 3 involving the two chloride-containing precursors [Ni4((Oal-)2L-Me)4(s)4]·2MeOH (1) and [Ni4((O-)2L-Me)3((Oal-)(OH)L-Me)Cl] (2) was studied by ESI mass spectrometry and confirmed by the solid state isolation and single-crystal X-ray diffraction. The challenging ligand fields containing mono/di-anionic O2N donating atoms and/or chloride ions stabilized the pentacoordinate Ni(ii) ions in 1-2 upon controlling the experimental conditions. Complexes 1-3 have been characterized by NMR, UV-Vis and mass spectrometric analysis. Complex 3 was found to be redox active by cyclic voltammetry (CV) studies. Theoretical calculations were carried out to shed light on the effects of ligand fields on the stability of complexes 1-3. Complex 3 was found to be a potential catalyst for the diastereoselective cyclopropanation of heteroarenes with good to excellent yields. The ESI mass spectrometric analysis revealed the existence of solution dynamics and oligomerization of 3 in solution. Mechanistic investigation of the catalytic cycle revealed that complex 3 and its various oligomers bind to the diazoester employed, followed by dissociative insertion of the respective carbene moieties to the C2-C3 double bond of the involved aromatic heterocycle, leading to the diastereoselective cyclopropanation. This journal is
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    Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes
    (01-04-2022)
    Kumar Kushvaha, Saroj
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    Mishra, Ankush
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    Roesky, Herbert W.
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    Isolation of cyclic (alkyl) amino carbenes (cAACs) in 2005 has been a major achievement in the field of stable carbenes due to their better electronic properties. cAACs and bicyclic(alkyl)(amino)carbene (BicAAC) in essence are the most electrophilic as well as nucleophilic carbenes are known till date. Due to their excellent electronic properties in terms of nucleophilic and electrophilic character, cAACs have been utilized in different areas of chemistry, including stabilization of low valent main group and transition metal species, activation of small molecules, and catalysis. The applications of cAACs in catalysis have opened up new avenues of research in the field of cAAC chemistry. This review summarizes the major results of cAAC chemistry published until August 2021.
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    Highly fluorescent aryl-cyclopentadienyl ligands and their tetra-nuclear mixed metallic potassium-dysprosium clusters
    (30-10-2020)
    Arumugam, Selvakumar
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    Reddy, Pulikanti Guruprasad
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    Francis, Maria
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    Kulkarni, Aditya
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    Roy, Sudipta
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    Two alkyl substituted triaryl-cyclopentadienyl ligands [4,4′-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) (1) and 4,4′,4′′-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been synthesized via cross-aldol condensation followed by Zn-dust mediated cyclization and acid catalyzed dehydration reactions. The fluorescence properties of 1 and 2 have been studied in solution and solid state. The ligands exhibited aggregation-induced emission enhancement (AIEE) in THF/water solution. 1 and 2 have been found to be significantly more fluorescent in the solid state than in their respective solutions. This phenomenon can be attributed to the strong intermolecular CH⋯π interactions present in 1 and 2 which leads to the tight packing of molecules in their solid-state. Both 1, 2 and their corresponding anions have been studied by theoretical calculations. Ligands 1 and 2 have been shown to react with anhydrous DyCl3 in the presence of potassium metal at high temperature to afford two fluorescent chloride-bridged tetra-nuclear mixed potassium-dysprosium metallocenes [(Me2Cp)4Dy2IIICl4K2]·3.5(C7H8) (5) and [(Me3Cp)4Dy2IIICl4K2]·3(C7H8) (6), respectively in good yields. This journal is
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    Dipotassiumtetrachloride-bridged dysprosium metallocenes: a single-molecule magnet
    (01-01-2023)
    Arumugam, Selvakumar
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    Schwarz, Björn
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    Ravichandran, Prathap
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    Kumar, Sunil
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    Ungur, Liviu
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    The present work describes the dynamic magnetic properties of the complex [(CpAr3)4DyIII2Cl4K2]·3.5(C7H8) (1), synthesized by employing a tri-aryl-substituted cyclopentadienyl ligand (CpAr3), [4,4′-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) = CpAr3H]. Each Dy(iii)-metallocene weakly couples via K2Cl4, displaying slow relaxation of magnetization below 14.5 K under zero applied dc field via KD3 energy levels with an energy barrier of 136.9/133.7 cm−1 on the Dy sites. The single-ion axial anisotropy energy barrier is reduced by geometrical distortion due to the coordination of two chloride ions at each Dy centre.
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    Tridentate Nickel(II)-Catalyzed Chemodivergent C-H Functionalization and Cyclopropanation: Regioselective and Diastereoselective Access to Substituted Aromatic Heterocycles
    (21-08-2020)
    Nag, Ekta
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    Gorantla, Sai Manoj N.V.T.
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    Arumugam, Selvakumar
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    Kulkarni, Aditya
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    Roy, Sudipta
    A Schiff-base nickel(II)-phosphene-catalyzed chemodivergent C-H functionalization and cyclopropanation of aromatic heterocycles is reported in moderate to excellent yields and very good regioselectivity and diastereoselectivity. The weak, noncovalent interaction between the phosphene ligand and Ni center facilitates the ligand dissociation, generating the electronically and coordinatively unsaturated active catalyst. The proposed mechanisms for the reported reactions are in good accord with the experimental results and theoretical calculations, providing a suitable model of stereocontrol for the cyclopropanation reaction.