Chakraborty, Subrata

We present here acceptorless dehydrogenative coupling of primary amines to form secondary aldimines catalyzed by a complex of Earth-abundant chromium. The reaction is promoted by Cr(DAFO)(CO)4 (DAFO = 4,5-diazafluorene-9-one) without using any additives, base or oxidant generating NH3 and H2 as sole by-products. Dehydrogenative cross-coupling of primary amines with aniline derivatives to unsymmetrical secondary imines was also achieved with good to excellent yields. A probable mechanism is proposed based on the stoichiometric investigation and computational studies. © 2025 The Royal Society of Chemistry.

Catalytic hydrogenation of the potent greenhouse gas carbon dioxide to obtain value-added products represents a much sought after methodology in academia and industry. Hydrogenation of CO2 to formic acid catalyzed by molecular complexes is a highly desirable protocol because of the industrial importance of formic acid and its potential application as a renewable hydrogen storage material. Herein we disclose that the bench-stable, low-valent phosphine-tethered chromium carbonyl complex Cr(DPPP)(CO)4 (C-3) (DPPP = 1,3-bis(diphenylphosphino)propane) catalyzed efficient hydrogenation of CO2 to formate giving a maximum turnover number (TON) of 259,000 at 130 °C in THF/H2O mixture after 24 h at the expense of 40 bar (CO2:H2 = 10:30) pressure. Biologically relevant sodium bicarbonate and inorganic carbonates were also tested for hydrogenation to sodium formate, furnishing decent yields of the desired products. Mechanistic investigation along with theoretical studies revealed that the reaction proceeded via the formation of a metallacarboxylate intermediate, which was further converted to a formato complex via an anionic hydrido carbonyl intermediate.

Herein, we present the first example of earth-abundant 3d metal-catalyzed ambient pressure carbon dioxide transfer hydrogenation to formate using isopropanol as an inexpensive and environmentally benign hydrogen source. The bidentate phosphine bis(diphenylphosphino)propane (DPPP, βn = 91°)-derived low-valent Cr(0) complex Cr(DPPP)(CO)4 C-3 emerged as the most efficient catalyst yielding sodium formate with a TON of up to 1974 under 1 bar CO2 and 2231 under 5 bar CO2 in the presence of NaOH in a THF:H2O mixture after 24 h at 130 °C. The catalyst was also found to be active in the transfer hydrogenation of sodium bicarbonate and carbonate to produce their corresponding formates in low yields. Mechanistic experiments revealed formation of an anionic hydride complex, which is believed to be an active catalyst for CO2 transfer hydrogenation. © The Royal Society of Chemistry 2025.

Herein, we report the hydrogenation of carbon dioxide to sodium formate catalyzed by low-valent molybdenum phosphine complexes. The 1,3-bis(diphenylphosphino)propane (DPPP)-based Mo complex was found to be an efficient catalyst in the presence of NaOH affording formate with a TON of 975 at 130 °C in THF/H2O after 24 h utilizing 40 bar (CO2 : H2 = 10 : 30) pressure. The complex was also active in the hydrogenation of sodium bicarbonate and inorganic carbonates to the corresponding formates. Mechanistic investigation revealed that the reaction proceeded via an intermediate formato complex.

An Earth-abundant Mn-PNP pincer complex-catalyzed terpenylation of cyclic and acyclic ketones and secondary alcohol 1-phenylethanol using isoprenoid derivatives prenol, nerol, phytol, solanesol, and E-farnesol as allyl surrogates is reported. The C-C coupling reactions are green and atom-economic, proceeding via dehydrogenation of alcohols following a hydrogen autotransfer methodology aided by metal-ligand cooperation. © 2024 American Chemical Society.

We present here a phosphine-free, quinoline-based pincer Mn catalyst for α-alkylation of methyl ketones using primary alcohols as alkyl surrogates. The C-C bond formation reaction proceeds via a hydrogen auto-transfer methodology. The sole by-product formed is water, rendering the protocol atom efficient. Electronic structure theory studies corroborated the proposed mechanism.

We report here the catalytic hydrogenation of carbon dioxide to formate using a Cr(ii) pincer complex. The complex CrCl2(PNP) C-1 {PNP = N,N-bis(diphenylphosphinoethyl)amine} in combination with NaHBEt3 in the presence of NaOH in a THF:H2O mixture yielded formate after 48 h with a TON of up to 8700. The complex C-1 was also found to be an active catalyst for the hydrogenation of sodium bicarbonate, furnishing formate with up to 62% yield. Stoichiometric experiments were carried out based on which a probable mechanism involving metal–ligand cooperation is proposed. © 2025 Elsevier B.V., All rights reserved.

We report the bidentate-phosphine-ligand-based molybdenum ?-allyl complex [Mo(CO)2(?3-C3H5)(DPPE)Cl] (Mo-1; DPPE = 1,2-bis(diphenylphosphino)ethane) for the dehydrogenative annulation of 2-aminobenzyl alcohol with a wide variety of methylketones to form N-heterocycle quinoline derivatives. The complex Mo-1 also catalyzed the formation of substituted quinolines through the reaction of 2-aminobenzyl alcohol with 1-phenylethanol derivatives. This methodology demands low loading of the complex (1 mol%) and a catalytic base. The process produces water and hydrogen gas as the only byproducts. Thus, the reactions are atom-efficient and environmentally benign.