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A palladium-catalyzed four-component carboxylative cyclization comprising propargylic amines, aryl iodides, CO2 and CO was developed. By selecting Et3N and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the base, respectively, both terminal and internal propargylic amines proceeded well facilitated by Pd(PPh3)2Cl2, affording the functionalized 2-oxazolones in moderate yields. This protocol enlarges the product diversity based on CO2 conversion and simultaneously provides a cooperative transformation route for both CO2 and CO. [ABSTRACT FROM AUTHOR]

Photocatalytic CO2 reduction to valuable chemicals, especially fuels, is considered as a promising strategy to mitigate CO2 accumulation and tackle the energy crisis, among which photocatalysis is vital to achieve efficient and selective reduction of CO2. In this work, phosphorus-doped hollow polygonal g-C3N4 rods were prepared through phosphoric acid assisted self-assembly under hydrothermal conditions and subsequent thermal polymerization using phosphoric acid as the phosphorus source and melamine as the nitrogen-rich precursor. The resulting phosphorus-doped hollow polygonal g-C3N4 rods feature increased specific surface area, visible light absorption and photogenerated carrier separation and transfer efficiency according to the structure and photoelectric properties characterization. Coupled with an earth abundant metal-based complex, i.e. [Co(bpy)3]Cl2, as a co-catalyst, the phosphorus-doped hollow polygonal g-C3N4 rods deliver a CO evolution rate of up to 447.5 μmol g−1 h−1 with a selectivity of ca. 96%, being much higher compared to the pristine g-C3N4 (67.01 μmol g−1 h−1 with a selectivity of ca. 94%) resulting from the improved light harvesting and charge transfer to the co-catalyst. Remarkably, the phosphorus-doped hollow polygonal g-C3N4 rods can be reused 6 times while retaining constant catalytic activity in the photoreduction reaction. This work presents new insights into photocatalytic CO2 reduction by developing non-metal doping and hollow structural designs for semiconductor photocatalysts. [ABSTRACT FROM AUTHOR]

The photocatalytic reduction of CO2 into fuels offers the prospect for creating a new CO2 economy. Harnessing visible light‐driven CO2‐to‐CO reduction mediated by the long‐lived triplet excited state of rhenium(I) tricarbonyl complexes is a challenging approach. We here develop a series of new mononuclear rhenium(I) tricarbonyl complexes (Re‐1−Re‐4) based on the imidazole‐pyridine skeleton for photo‐driven CO2 reduction. These catalysts are featured by combining pyridyl‐imidazole with the aromatic ring and different pendant organic groups onto the N1 position of 1,3‐imidazole unit, which display phosphorescence under Ar‐saturated solution even at ambient conditions. By contrast, {Re[9‐(pyren‐1‐yl)‐10‐(pyridin‐2‐yl)‐9H‐pyreno[4,5‐d]imidazole)](CO)3Cl} (Re‐4) by introducing pyrene ring at the N1 position of pyrene‐fused imidazole unit exhibits superior catalytic performance with a higher turnover number for CO (TONCO=124) and >99.9 % selectivity, primarily ascribed to the strong visible light‐harvesting ability, long‐lived triplet lifetimes (164.2 μs) and large reductive quenching constant. Moreover, the rhenium(I) tricarbonyl complexes derived from π‐extended pyrene chromophore exhibit a long lifetime corresponding to its ligand‐localized triplet state (3IL) evidenced from spectroscopic investigations and DFT calculations. [ABSTRACT FROM AUTHOR]

The straightforward synthesis of α-amino phosphine oxides via three-component reactions involving arynes, formamides and diarylphosphine oxides is disclosed. This method employs the aryne to activate formamide, without an external activating reagent, which is operationally simple under mild conditions with high efficiency. Furthermore, mechanistic perception suggests a cascade sequence including formal [2 + 2] cycloaddition of the aryne with a C＝O bond, and a 1,4-addition of the H–P(O) compounds to the enamine intermediates. [ABSTRACT FROM AUTHOR]

Developing effective sunlight-driven systems for CO2 reduction is one of the most promising subjects from the perspective of sustainably producing solar fuels. Herein, we develop a strategy to boost CO2 reduction performance by enhancing intermolecular electron transfer efficiency and visible light-absorption ability by introducing bifunctional pyrene groups on the ligand. This catalyst exhibits high-efficiency performance for natural light-powered CO2 reduction (TONCO up to 350 ± 36, ΦCO up to 46.6 ± 3%). This is the first report on using a single-molecule photocatalyst for CO2 reduction under natural conditions. Through the combination of experimental results and DFT calculations, the appending pyrene groups have been proven to promote the catalyst's ability to harness visible light as well as facilitate electron transfer (ET) through intermolecular π–π interactions. Due to the accelerated intermolecular ET, TONCO can be further boosted up to 1367 ± 32 in the presence of the ruthenium photosensitizer. Moreover, an enhancement in CO2 electroreduction performance can also be observed for the pyrenyl-functionalized rhenium catalyst further highlighting the versatile applications of this methodology. [ABSTRACT FROM AUTHOR]

With the increasing awareness of sustainable chemistry and green chemistry, photochemical CO2 fixation has drawn more and more attention in response to the need for renewable C1 resources and inexhaustible clean energy resources. It is appealing to provide carboxylic acids and derivatives using CO2 as a renewable feedstock, which is widely used in the manufacture of pharmaceuticals, pesticides, dyes and other fine chemicals. Classifying them by the types of reaction sites, this review presents an overview of the recent advances and achievements in the photocarboxylation of C(sp3)–X (X = H, N) bonds, C(sp2)–X (X = H, N, (pseudo)halide) bonds and C(sp)–H bonds with CO2, with an emphasis on the mechanistic aspects of the reactions and a perspective on their future prospects, hopefully stimulating the further research and development of this appealing field. [ABSTRACT FROM AUTHOR]

The electrocatalytic CO2 reduction reaction (ECO2RR) is one promising method for storing intermittent clean energy in chemical bonds and producing fuels. Among various kinds of catalysts for ECO2RR, molecular metal complexes with well‐defined structures are convenient for studies of their rational design, structure–reactivity relationships, and mechanisms. In this Review, we summarize the molecular engineering of several N‐based metal complexes including Re/Mn bipyridine compounds and metal macrocycles, concluding with general modification strategies to devise novel molecular catalysts with high intrinsic activity. Through physical adsorption, covalent linking, and formation of a periodic backbone, these active molecules can be heterogenized into immobilized catalysts with more practical prospects. Finally, significant challenges and opportunities based on molecular catalysts are discussed. [ABSTRACT FROM AUTHOR]

The electrocatalytic CO2 reduction reaction (ECO2RR) is one promising method for storing intermittent clean energy in chemical bonds and producing fuels. Among various kinds of catalysts for ECO2RR, molecular metal complexes with well‐defined structures are convenient for studies of their rational design, structure–reactivity relationships, and mechanisms. In this Review, we summarize the molecular engineering of several N‐based metal complexes including Re/Mn bipyridine compounds and metal macrocycles, concluding with general modification strategies to devise novel molecular catalysts with high intrinsic activity. Through physical adsorption, covalent linking, and formation of a periodic backbone, these active molecules can be heterogenized into immobilized catalysts with more practical prospects. Finally, significant challenges and opportunities based on molecular catalysts are discussed. [ABSTRACT FROM AUTHOR]

A triblock amphiphilic polymer derived from the copolymerization of CO2 and epoxides containing a bipyridine rhenium complex in its backbone is shown to effectively catalyze the visible‐light‐driven reduction of CO2 to CO. This polymer provides uniformly spherical micelles in aqueous solution, where the metal catalyst is sequestered in the hydrophobic portion of the nanostructured micelle. CO2 to CO reduction occurs in an efficient visible‐light‐driven process in aqueous media with turnover numbers up to 110 (>99 % selectivity) in the absence of a photosensitizer, which is a 37‐fold enhancement over the corresponding molecular rhenium catalyst in organic solvent. Notably, the amphiphilic polycarbonate micelle rhenium catalyst suppresses H2 generation, presumably by preventing deactivation of the active catalytic center by water. [ABSTRACT FROM AUTHOR]

A triblock amphiphilic polymer derived from the copolymerization of CO2 and epoxides containing a bipyridine rhenium complex in its backbone is shown to effectively catalyze the visible‐light‐driven reduction of CO2 to CO. This polymer provides uniformly spherical micelles in aqueous solution, where the metal catalyst is sequestered in the hydrophobic portion of the nanostructured micelle. CO2 to CO reduction occurs in an efficient visible‐light‐driven process in aqueous media with turnover numbers up to 110 (>99 % selectivity) in the absence of a photosensitizer, which is a 37‐fold enhancement over the corresponding molecular rhenium catalyst in organic solvent. Notably, the amphiphilic polycarbonate micelle rhenium catalyst suppresses H2 generation, presumably by preventing deactivation of the active catalytic center by water. [ABSTRACT FROM AUTHOR]

An unprecedented strategy has been developed involving the earth-abundant Cu-catalyzed hydrocarboxylation of alkynes with HCOOH to (E)-acrylic derivatives with high regio- and stereoselectivity via synergistic effects with ppm levels of a Pd catalyst. Both symmetrical and unsymmetrical alkynes bearing various functional groups were successfully hydrocarboxylated with HCOOH, and the modification of a pharmaceutical molecule exemplified the practicability of this process. This protocol employs HCOOH as both a CO surrogate and hydrogen donor with 100% atom economy and it can be viewed as an alternative approach for indirect CO2 utilization. Mechanistic investigations indicate a Cu/ppm Pd cooperative catalysis mechanism via alkenylcopper species as potential intermediates formed from Cu-hydride active catalytic species with HCOOH as a hydrogen source. This bimetallic system involving inexpensive Cu and trace Pd provides a reliable and efficient hydrocarboxylation method to access industrially useful acrylic derivatives with HCOOH as a hydrogen source, and it provides novel clues for optimizing other Cu–H-related co-catalytic systems. [ABSTRACT FROM AUTHOR]