Kartik Chandra Mondal

(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.

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

The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)P−Cl (2/2') was isolated from the direct reaction between cAAC and phosphorus trichloride (PCl3). Compound 2/2' has been characterized by NMR spectroscopy and mass spectrometry. 31P NMR investigations [δ≈160 ppm (major) and δ≈130 ppm (minor)] reveal that there are two different P environments of the P−Cl unit. X-ray single-crystal determination suggests a co-crystallization of two conformational isomers of (cAAC)P−Cl (2/2'); the major compound possessing a cAAC−PCl unit with CcAAC−P 1.75 Å. This C−P bond length is very close to that of (NHC)2P2 [NHC=N-heterocyclic carbene]. The residual density can be interpreted as a conformational isomer with a shorter CcAAC−P bond similar to a non-conjugated phosphaalkene [R−P=CR2]. Our study shows an unprecedented example of two conformational isomers with different Ccarbene−element bonds. Additionally, Br (3c/3c'), I (4c/4c'), and H (5c/5c') analogues [(Me2-cAAC)P−X; X=Br (3), I (4), H (5)] of 2c/2c'[(Me2-cAAC)P−Cl] were also synthesized and characterized by NMR spectroscopy suggesting similar equilibrium in solution. The unique property of cAAC and the required electronegativity of the X (X=Cl, Br, I, and H) atom play a crucial role for the existence of the two isomers which were further studied by theoretical calculations.

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

The existence of a metal-metal bond in organometallic and coordination complexes is a very important aspect. Metal-carbonyl, carbene-metal-carbonyl and metal-carbene complexes were studied for having this feature. Herein, an air stable dark green color dicobalt coordination complex [Co(III)2(hep)3(N3)3] (1) [hepH = 2-(2-ethylhydroxy)pyridine] with three μ-alkoxide bridges has been synthesized and characterized by X-ray single crystal diffraction, NMR and UV/vis spectroscopy. Complex 1 has a short Co⋅⋅⋅Co distance (2.595(6) Å) and thus it has been studied by theoretical calculations. QTAIM (quantum theory of atoms in molecules) as well as EDA-NOCV analysis (energy decomposition analysis - natural orbitals for chemical valence) do not indicate any significant metal-metal interaction. The bonding in 1 can be best represented by the interaction of two alkokxy bridged valence electrons fragment Co(III)(hep)2N3 (3d6) with Co(III)(hep)(N3)2 (3d6) where the donation of the lone pair of electrons from three bridging Ohep-atoms stabilizes the dinuclear Co(III) complex. Additionally, thermolysis of 1 at 550 oC led to the formation sponge like Co3O4 oxide.

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.

Cyclic alkyl(amino) carbene (cAAC)-supported, structurally diverse alkali metal-phosphinidenides 2–5 of general formula ((cAAC)P-M)n(THF)x [2: M=K, n=2, x=4; 3: M=K, n=6, x=2; 4: M=K, n=4, x=4; 5: M=Na, n=3, x=1] have been synthesized by the reduction of cAAC-stabilized chloro-phosphinidene cAAC=P-Cl (1) utilizing metallic K or KC8 and Na-naphthalenide as reducing agents. Complexes 2–5 have been structurally characterized in solid state by NMR studies and single crystal X-ray diffraction. The proposed mechanism for the electron transfer process has been well-supported by cyclic voltammetry (CV) studies and Density Functional Theory (DFT) calculations. The solid state oligomerization process has been observed to be largely dependent on the ionic radii of alkali metal ions, steric bulk of cAAC ligands and solvation/de-solvation/recombination of the dimeric unit [(cAAC)P-M(THF)x]2.

Fluoro- and chloro-phosphasilynes [X-SiP (X = F, Cl)] belong to a class of illusive chemical species which are expected to have Si P multiple bonds. Theoretical investigations of the bonding and stability of the corresponding Lewis base-stabilized species (L′)PSi(X)(L) [L′ = cAACMe(cyclic alkyl(amino) carbene); L = cAACMe, NHCMe(N-heterocyclic carbene), PMe3, aAAC (acyclic alkyl(amino) carbene); X = Cl, F] have been studied using the energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) method. The variation of the ligands (L) on the Si-atom leads to different bonding scenarios depending on their σ-donation and π-back acceptance properties. The ligands with higher lying HOMOs prefer profoundly different bonding scenarios than the ligands with lower lying HOMOs. The type of halogen (Cl or F) on the Si-atom was also found to have a significant influence on the overall bonding scenario. The reasonably higher value and endergonic nature of the dissociation energies along with the appreciable HOMO-LUMO energy gap may corroborate to the synthetic viability of the homo and heteroleptic ligand-stabilized elusive PSi(Cl/F) species in the laboratory.

Two novel 3d (Ni)/4 f (Dy and Y) metal ions and polydentate organic ligands (H2L1 and H2L2) based tetranuclear coordination complexes, [(L1)4NiII2DyIII2(DMF)2(NO3)2]⋅DMF (1) and [(L2)4NiII2YIII2(DMF)2(NO3)2]⋅DMF⋅H2O (2), have been synthesized and characterized using IR, elemental analysis and single crystal X-ray diffraction studies. The application of these complexes as C−C bond coupling homogeneous catalysts has been logically shown. The complex 1 acts as an excellent catalyst (with a very low catalyst loading of 0.17 mol%) for the syntheses of a wide range of bis(indolyl)methane derivatives in good yields using various indoles and aromatic/hetero aromatic aldehydes under optimized reaction conditions. A plausible reaction mechanism has been proposed showing the coordinative binding of the aromatic aldehyde at NiII centre along with the associative π-stacking interaction between the ligand (H2L1) and the phenyl ring of the aromatic aldehyde and/or indole leading to the formation of the desired bis(indolyl)methanes under the metal assisted C−C bond forming reaction with subsequent elimination of water molecule in polar protic solvent.

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag12Cl3, Ag29, and Ag8 cores [((cAAC)P)6Ag12Cl3](OTf)3 (1), [((cAAC)P)6Ag29] (2), and [((cAAC)P)4Ag8] (3) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP−) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1, and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P−) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P−B(NiPr2)2 through cleavage of the P−B bond with the help of a triflate anion (OTf−) as a weak nucleophile. Equivalent number of the (cAAC)P− anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)2P2 leading to the generation of Ag0 ions in solution for the formation of the unprecedented mixed-valence Ag NC 2. Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf2. The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1–3, further providing a three- (1, 2)/two- (3) fold stand. The Ag12Cl3 NC (1) with a tricationic core [AgI12Cl3] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag29 (2) and Ag8 (3) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag0 at room temperature.