Search

We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1; phen=1,10‐phenanthroline), formed as an intermediate during the Zn(OAc)2/phen‐catalyzed synthesis of organic carbamates from CO2, amines, and the reusable reactant Si(OMe)4. Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five‐coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five‐coordinated silicon species. This sustainable and effective method can be used to synthesize various N‐aryl and N‐alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure. [ABSTRACT FROM AUTHOR]

We report results of density functional theory (DFT) calculations conducted to investigate the reaction mechanism for the formation of MeSi(OMe)3 from tetramethoxysilane [Si(OMe)4], using metal hydrides. In the present study, the effects of three different metal hydrides on the conversion reaction were investigated. This procedure represents an alternative route for the direct conversion from Si–O to Si–C bonds. Our DFT calculations revealed that the most energetically favorable reaction path that leads to the formation of the final product [MeSi(OMe)3] proceeding through the formation of HSi(OMe)3 as an intermediate. We found that the new Si–C bond originates from the methyl group transfer from another molecule of Si(OMe)4, and that this was the most energetically demanding process. We have also identified the origin of the reactivity difference between three metal hydrides. In agreement with the experiment, our results indicated that NaH was the best choice for this conversion reaction. The reaction mechanism for the formation of MeSi(OMe)3 from tetramethoxysilane, Si(OMe)4, using metal hydrides, is investigated using DFT. The most energetically favorable path to the final product, MeSi(OMe)3, proceeds through intermediate HSi(OMe)3. The new Si–C bond originates from the methyl group transfer from another molecule of Si(OMe)4, and this is the most energetically demanding process. [ABSTRACT FROM AUTHOR]

Amines, carbon dioxide fixation, density functional calculations, sustainable chemistry, zinc Cover Feature: N-Aryl and N-Alkyl Carbamates from 1 Atmosphere of CO2 (Chem. Eur. J. 72/2021) Keywords: amines; carbon dioxide fixation; density functional calculations; sustainable chemistry; zinc EN amines carbon dioxide fixation density functional calculations sustainable chemistry zinc 17974 17974 1 12/27/21 20211223 NES 211223 B We have successfully isolated b the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) ( B 1 b , phen=1,10-phenanthroline), which is an intermediate in the Zn(OAc) SB 2 sb /phen-catalyzed synthesis of organic carbamates from CO SB 2 sb , amines, and Si(OMe) SB 4 sb . [Extracted from the article]

We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1; phen=1,10‐phenanthroline), formed as an intermediate during the Zn(OAc)2/phen‐catalyzed synthesis of organic carbamates from CO2, amines, and the reusable reactant Si(OMe)4. Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five‐coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five‐coordinated silicon species. This sustainable and effective method can be used to synthesize various N‐aryl and N‐alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure. [ABSTRACT FROM AUTHOR]

• R 3 Si-NHC-Pd complexes (1Pd‒7Pd) are feasible for Suzuki-Miyaura reaction. • All complexes 1Pd–7Pd showed higher catalytic activity than the IPr-Pd complex. • The 1Pd complex is tolerable for various products of the cross-coupling reaction. A series of R 3 Si-NHC-Pd complexes 1Pd-7Pd was successfully tested as a pre-catalyst for the Suzuki-Miyaura cross-coupling reaction of aryl chlorides and arylboronic acid derivatives to form a wide range of valuable biphenyl products. Use of the readily available weakly basic potassium carbonate as a base and the highly polar protic ethanol as the reaction solvent gave the target coupling products in good-to-excellent yields. The experimental data pointed to the crucial importance of the preliminary pre-catalyst activation step [i.e., the conversion of Pd(II) to Pd(0)], which is remarkably facilitated by the electron-donating trialkylsilyl groups on the NHC ligands of 1Pd–7Pd , thereby rendering them superior compared to the commercially available IPr-Pd complexes. Computational analysis revealed the mechanism of the Pd(II)→Pd(0) activation step, demonstrating the critical role of the reaction solvent and the base in the preference of our 1Pd–7Pd pre-catalysts, for which this step is both thermodynamically and kinetically more feasible. The graphical abstract synopsis: The [4-R 3 Si-IPr]Pd(allyl)Cl complexes catalyzed the Suzuki-Miyaura cross-coupling of aryl chlorides and arylboronic acids, remarkably outperforming commercially available [IPr]Pd(allyl)Cl complex. Both experimental and computational data provide evidence for the importance of the pre-catalyst activation step [Pd(II)→Pd(0)], facilitated in the presence of EtOH as a reaction solvent and K 2 CO 3 as a base. [Display omitted] [ABSTRACT FROM AUTHOR]