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BPh 3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO 2 and PhSiH 3 ; these reactions proceed at 30-40 °C under solvent-free conditions. In contrast, B(C 6 F 5 ) 3 shows little or no activity. 11 B NMR spectra suggested the generation of [HBPh 3 ] - . The detailed mechanism of the BPh 3 -catalyzed N-methylation of N-methylaniline (1) with CO 2 and PhSiH 3 was studied by using DFT calculations. BPh 3 promotes the conversion of two substrates (N-methylaniline and CO 2 ) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N + CO 2 - ⋅⋅⋅BPh 3 ]. The carbamate and BPh 3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH 3 to generate [HBPh 3 ] - , which is used to produce key CO 2 -derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1. DFT calculations also suggested other mechanisms involving water for the generation of [HBPh 3 ] - species., (© 2022 Wiley-VCH GmbH.)

BPh3 catalyzes the N‐methylation of secondary amines and the C‐methylenation (methylene‐bridge formation between aromatic rings) of N,N‐dimethylanilines or 1‐methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent‐free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3‐catalyzed N‐methylation of N‐methylaniline (1) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N‐methylaniline and CO2) into a zwitterionic carbamate to give three‐component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2‐derived species, such as silyl formate and bis(silyl)acetal, essential for the N‐methylation of 1. DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) was used as a C1 source to prepare silyl formates, formamides, and aldehydes. Tetrabutylammonium acetate (TBAA) catalyzed the solvent-free N-formylation of amines with CO2 and hydrosilane to give formamides including Weinreb formamide, Me(MeO)NCHO, which was successively converted into aldehydes by one-pot reactions with Grignard reagents. [ABSTRACT FROM AUTHOR]

Bifunctional ZnII porphyrin catalysts bearing tributylammonium bromide groups at the meta positions of the meso-phenyl groups showed high catalytic activity for the synthesis of cyclic carbonates from epoxides and CO2. Herein, several substituents with different electronic properties were introduced at the para positions. Introduction of electron-donating groups decreased the catalytic activity, whereas the introduction of electron-withdrawing groups increased the activity. The substituents modulated the Lewis acidity of the zinc center, which was confirmed by binding constant experiments. The bifunctional catalyst bearing cyano groups showed the highest catalytic activity with a turnover frequency of up to 42 000 h−1. [ABSTRACT FROM AUTHOR]

Highly active bifunctional metalloporphyrin catalysts were developed for the coupling reaction of epoxides with CO2 to produce cyclic carbonates. The bifunctional catalysts have both quaternary ammonium halide groups and a metal center. To elucidate the roles of these catalytic groups, DFT calculations were performed. Control reactions using tetrabutylammonium halide as a catalyst were also investigated for comparison. In the present article, the results of our computational studies are overviewed. The computational results are consistent with the experimental data and are useful for elucidating the structure-activity relationship. The key features responsible for the high catalytic activity of the bifunctional catalysts are as follows: 1) the cooperative action of the halide anion (nucleophile) and the metal center (Lewis acid); 2) the near-attack conformation, leading to the efficient opening of the epoxide ring in the rate-determining step; and 3) the conformational change of the quaternary ammonium cation to stabilize various anionic species generated during catalysis, in addition to the robustness (thermostability) of the catalysts. [ABSTRACT FROM AUTHOR]

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso-phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent-free conditions. The meta-substituted catalysts exhibited high catalytic performance, whereas the para- and ortho-substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta-substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h−1 at 170 °C) at an initial CO2 pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO2 pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides. [ABSTRACT FROM AUTHOR]

Highly active bifunctional diporphyrin and triporphyrin catalysts were synthesized through Stille coupling reactions. As compared with a porphyrin monomer, both exhibited improved catalytic activities for the reaction of CO2 with epoxides to form cyclic carbonates, because of the multiple catalytic sites which cooperatively activate the epoxide. Catalytic activities were carefully investigated by controlling temperature, reaction time, and catalyst loading, and very high turnover number and turnover frequency were obtained: 220 000 and 46 000 h−1, respectively, for the magnesium catalyst, and 310 000 and 40 000 h−1, respectively, for the zinc catalyst. Results obtained with a zinc/free-base hybrid diporphyrin catalyst demonstrated that the Br− ions on the adjacent porphyrin moiety also function as nucleophiles. [ABSTRACT FROM AUTHOR]

Metalloporphyrins were immobilized on biogenous iron oxide (BIO) produced by iron-oxidizing bacteria, Leptothrix ochracea. These organic–inorganic hybrid materials were used as immobilized catalysts for the synthesis of cyclic carbonates from epoxides and CO2 under solvent-free conditions. ZnII porphyrin immobilized via four tetraalkylammonium bromide groups showed high catalytic activity and reusability at a catalyst loading of 0.1 mol%. The product was obtained in 99% yield after nine times reuse, and the substrate scope was broad. [ABSTRACT FROM AUTHOR]

Porphyrinoids CO2 is a cheap, abundant, and nontoxic C1 source, and the chemical conversion of CO2 into useful organic compounds has become increasingly important. In their Full Paper on page 6556 ff., C. Maeda, J. Hasegawa, T. Ema et al. describe the synthesis of bifunctional metalloporphyrins with quaternary ammonium bromides at the meta, para, or ortho positions of the meso‐phenyl groups and investigated their catalytic activities in the formation of cyclic carbonates from epoxides and CO2 under solvent‐free conditions. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) was used as a C1 source to prepare silyl formates, formamides, and aldehydes. Tetrabutylammonium acetate (TBAA) catalyzed the solvent-free N-formylation of amines with CO2 and hydrosilane to give formamides including Weinreb formamide, Me(MeO)NCHO, which was successively converted into aldehydes by one-pot reactions with Grignard reagents. [ABSTRACT FROM AUTHOR]

Review: 67 refs. [ABSTRACT FROM AUTHOR]

Review: [12 refs. [ABSTRACT FROM AUTHOR]

Highly active bifunctional diporphyrin and triporphyrin catalysts are synthesized through Stille coupling reactions. [ABSTRACT FROM AUTHOR]