Tanmay Malakar

The Role of Solvent and of Species Generated in Situ on the Kinetic Acceleration of Aminoborane Oligomerization

The unexpected role of nucleophilic assistance of solvents and intermediates generated in situ in catalyzing NH2BH2 oligomerization is revealed in a computational study. The rate-determining free-energy barrier E(A) that is due to solvent participation for conversion of NH2BH2 to cyclotriborazane (NH2BH2)3 is only 12.7 kcal  mol(-1), whereas without nucleophilic assistance it is as high as 29.0 kcal  mol(-1) in THF (see figure).

Theoretical Investigation on the Chemistry of Entrapment of the Elusive Aminoborane (H2NBH2) Molecule

Aminoborane (H2 N=BH2 ) is an elusive entity and is thought to be produced during dehydropolymerization of ammonia borane, a molecule of prime interest in the field of chemical hydrogen storage. The entrapment of H2 N=BH2 through hydroboration of exogenous cyclohexene has emerged as a routine technique to infer if free H2 N=BH2 is produced or not during metal-catalyzed ammonia borane dehydrogenation reactions. But to date, the underlying mechanism of this trapping reaction remains unexplored. Herein, by using DFT calculations, we have investigated the mechanism of trapping of H2 N=BH2 by cyclohexene. Contrary to conventional wisdom, our study revealed that the trapping of H2 N=BH2 does not occur through direct hydroboration of H2 N=BH2 on the double bond of cyclohexene. We found that autocatalysis by H2 N=BH2 is crucial for the entrapment of another H2 N=BH2 molecule by cyclohexene. Additionally, nucleophilic assistance from the solvent is also implicated for the entrapment reaction carried out in nucleophilic solvents. In THF, the rate-determining barrier for formation of the trapping product was predicted to be 16.7 kcal mol(-1) at M06 L(CPCM) level of theory.

In Pursuit of Sustainable Hydrogen Storage with Boron-Nitride Fullerene as the Storage Medium.

Using well calibrated DFT studies we predict that experimentally synthesized B24 N24 fullerene can serve as a potential reversible chemical hydrogen storage material with hydrogen-gas storage capacity up to 5.13 wt %. Our theoretical studies show that hydrogenation and dehydrogenation of the fullerene framework can be achieved at reasonable rates using existing metal-free hydrogenating agents and base metal-containing dehydrogenation catalysts.

Copper(II) complexes of 3,4,5-trisubstituted pyrazolates: in situ formation of pyrazole rings from different carbon centers.

The synthesis and characterization of two pyrazolate-bridged dicopper(II) complexes, [Cu(2)(L(1))(2)(H(2)O)(2)](ClO(4))(2) (1, HL(1)=3,5-dipyridyl-4-(2-keto-pyridyl)pyrazole) and [Cu(2)(L(2))(2)(H(2)O)(2)](ClO(4))(2) (2, HL(2)=3,5-dipyridyl-4-benzoylpyrazole), are discussed. These copper(II) complexes are formed from the reactions between pyridine-2-aldehyde, 2-acetylpyridine (for compound 1) or acetophenone (for compound 2), and hydrazine hydrate with copper(II) perchlorate hydrate under ambient conditions. The single-crystal X-ray structure of compound 1·2H(2)O establishes the formation of a pyrazole ring from three different carbon centers through C-C bond-forming reactions, mediated by copper(II) ions. The free pyrazoles (HL(1) and HL(2)) are isolated from their corresponding copper(II) complexes and are characterized by using various analytical and spectroscopic techniques. A mechanism for the pyrazole-ring synthesis that proceeds through C-C bond-forming reactions is proposed and supported by theoretical calculations.