Tushar Singh

Bio: Tushar Singh is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Dehydrogenation & Catalysis. The author has co-authored 1 publications.

Well-Defined Bis(NHC)Mn(I) Complex Catalyzed Tandem Transformation of α,β-Unsaturated Ketones to α-Methylated Ketones Using Methanol

Abstract: Tandem transformation of α,β-unsaturated ketones to α-methylated ketones by utilizing methanol as both the hydrogen and C1 sources is reported in the presence of a phosphine-free bis-N-heterocyclic carbene-Mn(I) (bis-NHC-Mn(I)) catalyst. The dehydrogenative coupling between methanol and α,β-unsaturated ketones produces the corresponding α-methylated ketones along with 1 equiv of formaldehyde and water. Among different bis-NHC-Mn(I) complexes, the ethyl wingtip-substituted complex with a triflate counteranion showed the highest catalytic activity. This catalytic system was highly effective for the reductive methylation of a wide variety of substrates including aromatic, heteroaromatic, and aliphatic straight chains containing α,β-unsaturated ketones. Notably, this methodology led to the synthesis of pharmaceutically important drug molecules such as eperisone and lanperisone. Several control experiments, kinetic studies, Hammett studies, and density functional theory (DFT) calculations were carried out to understand this tandem catalytic process.

Tailoring Active Cu2O/Copper Interface Sites for N-Formylation of Aliphatic Primary Amines with CO2/H2.

Abstract: Heterogenous catalyzed N-formylation of amines to formamide with CO2/H2 has been highly attractive on the valorization of the CO2. However, the relationship of the catalytic performance with the catalyst structure is still elusive. Herein, the mixed-valence catalysts containing Cu2O/Cu interface sites were constructed for this transformation. Both aliphatic primary and secondary amines with diverse structures were efficiently converted into the desired formamides with good to excellent yields. Combined ex and in situ catalyst characterizations revealed that the presence of Cu2O/Cu interface sites was vital for the excellent catalytic activity. Density functional theory (DFT) calculations demonstrated that better catalytic activity of Cu2O/Cu(111) than Cu(111) can be attributed to the assistance of oxygen at the Cu2O/Cu interface (Ointer) in formation of Ointer-H moieties, which not only reduce the apparent barrier of HCOOH formation but also benefit the desorption of the desired N-formylated amine, leading to the high activity and selectivity.

(NNC)Ru(II) Complex Catalyzed Selective Functionalization of Ketones with Methanol: Understanding the Role of Ancillary Ligands

Abstract: Employing a single catalyst and substrate, the selective synthesis of all probable products upon varying the reaction conditions is uniquely challenging and exciting to explore. Utilizing methanol, cyclometalated (NNC)Ru(II) complex catalyzed selective transformation of a wide variety of ketones to the corresponding alcohols, β-methylated alcohols, and α-methylated ketones is disclosed. Notably, by changing the reaction parameters, the selective synthesis of all the probable products for the reactions of ketones with methanol was achieved. For these transformations, the role of different ancillary ligands (DMSO, CH3CN and PPh3) coordinated to the Ru(II) center was investigated. This protocol was successfully applied for the functionalization of a few pharmaceutically important molecules and to sterically hindered α, α′-disubstituted and α, α′, α′′-trisubstituted ketones. Several control experiments, kinetic studies, Hammett studies, and DFT calculations were carried out to understand this catalytic process.