Sharanappa Nembenna

Aluminum Monohydride Catalyzed Selective Hydroboration of Carbonyl Compounds

The well-defined aluminum monohydride compound [{(2,4,6-Me3-C6H2)NC(Me)}2(Me)(H)]AlH·(NMe2Et) (1) catalyzes hydroboration of a wide range of aldehydes and ketones under mild reaction conditions. Moreover, compound 1 displayed chemoselective hydroboration of aldehydes over ketones at rt.

An efficient and recyclable thiourea-supported copper(I) chloride catalyst for azide–alkyne cycloaddition reactions

A reaction between two equivalents of bulky thiourea, i.e., 1,3-bis(2,6-dimethylphenyl)thiourea (L) [L = (ArNH)2C = S; Ar = 2,6-Me2C6H3], and CuCl2 or CuCl in THF solvent afforded a bulky thiourea-stabilized copper(I) halide complex, LCu(Cl)L (1). Compound 1 was characterized by NMR spectroscopy, mass spectrometry and X-ray structural analysis. Further, we tested the catalytic activity of this well-defined compound 1 for azide–alkyne cycloaddition (AAC) reactions in solvent-free conditions. Compound 1 shows a high catalytic activity for the synthesis of 1,4-di- and 1,4,5-trisubstituted 1,2,3-triazoles in good to excellent yields from azides (aliphatic or aromatic) and alkynes (both terminal and disubstituted). Furthermore, three-component CuAAC reactions were successfully carried out to obtain both 1,4-di- and 1,4,5-trisubstituted 1,2,3-triazoles in good to excellent yields from an organic halide, sodium azide and alkyne (both terminal and disubstituted) in greener solvent water. More importantly, the catalyst can be reused efficiently up to ten consecutive cycles with negligible loss of catalytic activity.

Mixed guanidinato-amido Ge(IV) and Sn(IV) complexes with GeE (E = S, Se) double bond and SnS4, Sn2Se2 rings

The first bulky guanidinate supported germathioamide [{ArNC(NiPr2)NAr}GeN(SiMe3)2(S)]; (Ar = 2,6-Me2–C6H3) (3) and germaselanoamide [{ArNC(NiPr2)NAr}GeN(SiMe3)2(Se)] (4) complexes with GeS (3) and GeSe (4) moieties, have been synthesized and structurally characterized. Both compounds 3 and 4 were prepared by the oxidative addition of elemental sulfur and selenium, respectively, to the heteroleptic germylene complex [{ArNC(NiPr2)NAr}GeN(SiMe3)2] (1) in THF/ether at room temperature. Similarly, reaction of compound [{ArNC(NiPr2)NAr}SnN(SiMe3)2] (2) with an equimolar amount of elemental chalcogen (S and Se) led to the formation of cyclic tetrasulfido tin [{ArNC(NiPr2)NAr}SnN(SiMe3)2(S4)] (5) with an SnS4 ring and dimeric bridged seleno tin [{ArNC(NiPr2)NArN(SiMe3)2Sn(μ-Se)}2] (6) with an Sn2Se2 ring, respectively. All compounds 3–6 were confirmed by multinuclear NMR spectroscopy, elemental analysis and single crystal X-ray structural analysis.

Catalyst free C–N bond formation by the reaction of amines with diimides: bulky guanidines

We have shown an atom economical and catalyst free addition of cyclic secondary amines to various bulky aryl symmetrical and unsymmetrical carbodiimides to afford N,N′N′′N′′-tetra substituted guanidines in quantitative yields at ambient reaction conditions. Furthermore, it was established that the addition of diamine to bulky aryl symmetrical carbodiimides (2 equiv.) led to the formation of bulky aryl biguanidines.

Metal-free access of bulky N,N′-diarylcarbodiimides and their reduction: bulky N,N′-diarylformamidines

A metal-free synthesis of symmetrical and unsymmetrical bulky N,N′-diaryl carbodiimides from the dehydrosulfurisation of their corresponding N,N′-diarylthiourea with 4-dimethylaminopyridine (DMAP) and iodine under mild reaction conditions with moderate to excellent yields has been established. In the literature, the classical method of dehydrosulfurisation of bulky N,N′-diarylthiourea to N,N′-diarylcarbodiimide has been reported using toxic metal oxide (HgO) and magnesium sulphate (MgSO4) under harsh reaction conditions. Furthermore, easy access to 1,3-disubstituted symmetric and unsymmetrical N,N′-diaryl formamidines involving the reaction of symmetrical and unsymmetrical N,N′-diaryl carbodiimides with sodium borohydride is described. The widely used method for the preparation of bulky N,N′-diaryl formamidines is the treatment of primary amines with triethylorthoformate in the presence of acid under high temperature reaction conditions.

Structure, bonding and energetics of N-heterocyclic carbene (NHC) stabilized low oxidation state group 2 (Be, Mg, Ca, Sr and Ba) metal complexes: A theoretical study

AbstractA series of N-heterocyclic carbene stabilized low oxidation state group 2 metal halide and hydrides with metal-metal bonds ([L(X) M-M(X) L]; L = NHC ((CHNH)2C:), M = Be, Mg, Ca, Sr and Ba, and X = Cl or H) has been studied by computational methods. The main objective of this study is to predict whether it is possible to stabilize neutral ligated low oxidation state alkaline-earth metal complexes with metal-metal bonds. The homolytic metal-metal Bond Dissociation Energy (BDE) calculation, Natural Bond Orbital (NBO) and Energy Decomposition Analyses (EDA) on density functional theory (DFT) optimized [L(X)M-M(X)L] complexes revealed that they are as stable as their β-diketiminate, guanidinate and α-diimine counterparts. The optimized structures of the complexes are in trans-linear geometries. The bond order analyses such as Wiberg Bond Indices (WBI) and Fuzzi Bond Order (FBO) confirm the existence of single bond between two metal atoms, and it is covalent in nature. SynopsisN-heterocycle carbene (NHC)-supported low oxidation state of group 2 metal complexes with metal-metal bonds have been studied by computational methods. The complexes were found to be thermodynamically stable. The bond order analyses confirm the presence of single bond between two metal atoms.