Dataset Information

Mechanism Insights into the Iridium(III)- and B(C₆F₅)₃-Catalyzed Reduction of CO₂ to the Formaldehyde Level with Tertiary Silanes.

ABSTRACT: The catalytic system [Ir(CF₃CO₂)(κ²-NSi^Me)₂] [1; NSi^Me = (4-methylpyridin-2-yloxy)dimethylsilyl]/B(C₆F₅)₃ promotes the selective reduction of CO₂ with tertiary silanes to the corresponding bis(silyl)acetal. Stoichiometric and catalytic studies evidenced that species [Ir(CF₃COO-B(C₆F₅)₃)(κ²-NSi^Me)₂] (3), [Ir(κ²-NSi^Me)₂][HB(C₆F₅)₃] (4), and [Ir(HCOO-B(C₆F₅)₃)(κ²-NSi^Me)₂] (5) are intermediates of the catalytic process. The structure of 3 has been determined by X-ray diffraction methods. Theoretical calculations show that the rate-limiting step for the 1/B(C₆F₅)₃-catalyzed hydrosilylation of CO₂ to bis(silyl)acetal is a boron-promoted Si-H bond cleavage via an iridium silylacetal borane adduct.

SUBMITTER: Guzman J

PROVIDER: S-EPMC10468102 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Mechanism Insights into the Iridium(III)- and B(C6F5)3-Catalyzed Reduction of CO2 to the Formaldehyde Level with Tertiary Silanes.

Guzmán Jefferson J Urriolabeitia Asier A Padilla Marina M García-Orduña Pilar P Polo Víctor V Fernández-Alvarez Francisco J FJ

Inorganic chemistry 20221206 50

The catalytic system [Ir(CF3CO2)(κ2-NSiMe)2] [1; NSiMe = (4-methylpyridin-2-yloxy)dimethylsilyl]/B(C6F5)3 promotes the selective reduction of CO2 with tertiary silanes to the corresponding bis(silyl)acetal. Stoichiometric and catalytic studies evidenced that species [Ir(CF3COO-B(C6F5)3)(κ2-NSiMe)2] (3< ...[more]

PMID: 36472385

Similar Datasets

Project description:Using density functional theory computations, we investigated in detail the underlying reaction mechanism and crucial intermediates present during the reduction of carbon dioxide to methane with silanes, catalyzed by the cationic Ir-pincer complex ((POCOP)Ir(H)(acetone)+, POCOP = 2,6-bis(dibutylphosphinito)phenyl). Our study postulates a plausible catalytic cycle, which involves four stages, by sequentially transferring silane hydrogen to the CO2 molecule to give silylformate, bis(silyl)acetal, methoxysilane and the final product, methane. The first stage of reducing carbon dioxide to silylformate is the rate-determining step in the overall conversion, which occurs via the direct dissociation of the silane Si-H bond to the C[double bond, length as m-dash]O bond of a weakly coordinated Ir-CO2 moiety, with a free energy barrier of 29.5 kcal mol-1. The ionic SN2 outer-sphere pathway in which the CO2 molecule nucleophilically attacks at the η1-silane iridium complex to cleave the η1-Si-H bond, followed by the hydride transferring from iridium dihydride [(POCOP)IrH2] to the cation [O[double bond, length as m-dash]C-OSiMe3]+, is a slightly less favorable pathway, with a free energy barrier of 33.0 kcal mol-1 in solvent. The subsequent three reducing steps follow similar pathways: the ionic SN2 outer-sphere process with silylformate, bis(silyl)acetal and methoxysilane substrates nucleophilically attacking the η1-silane iridium complex to give the ion pairs [(POCOP)IrH2] [HC(OSiMe3)2]+, [(POCOP)IrH2] [CH2(OSiMe3)2(SiMe3)]+, and [(POCOP)IrH2] [CH3O(SiMe3)2]+, respectively, followed by the hydride transfer process. The rate-limiting steps of the three reducing stages are calculated to possess free energy barriers of 12.2, 16.4 and 22.9 kcal mol-1, respectively. Furthermore, our study indicates that the natural iridium dihydride [(POCOP)IrH2] generated along the ionic SN2 outer-sphere pathway could greatly facilitate the silylation of CO2, with a potential energy barrier calculated at a low value of 16.7 kcal mol-1.

Project description:A rise in atmospheric CO2 levels, following years of burning fossil fuels, has brought about increase in global temperatures and climate change due to the greenhouse effect. As such, recent efforts in addressing this problem have been directed to the use of CO2 as a non-expensive and non-toxic single carbon, C1, source for making chemical products. Herein, we report on the use of tetrazolyl complexes as catalyst precursors for hydrogenation of CO2. Specifically, tetrazolyl compounds bearing P-S bonds have been synthesized with the view of using these as P∧N bidentate tetrazolyl ligands (1-3) that can coordinate to iridium(III), thereby forming heteroatomic five-member complexes. Interestingly, reacting the P,N'-bidentate tetrazolyl ligands with [Ir(C5 Me 5)Cl 2]2 led to serendipitous isolation of chiral-at-metal iridium(III) half-sandwich complexes (7-9) instead. Complexes 7-9 were obtained via prior formation of non-chiral iridium(III) half-sandwich complexes (4-6). The complexes undergo prior P-S bond heterolysis of the precursor ligands, which then ultimately results in new half-sandwich iridium(III) complexes featuring monodentate phosphine co-ligands with proton-responsive P-OH groups. Conditions necessary to significantly affect the rate of P-S bond heterolysis in the precursor ligand and the subsequent coordination to iridium have been reported. The complexes served as catalyst precursors and exhibited activity in CO2 and bicarbonate hydrogenation in excellent catalytic activity, at low catalyst loadings (1 μmol or 0.07 mol% with respect to base), producing concentrated formate solutions (ca 180 mM) exclusively. Catalyst precursors with proton-responsive P-OH groups were found to influence catalytic activity when present as racemates, while ease of dissociation of the ligand from the iridium center was observed to influence activity in spite of the presence of electron-donating ligands. A test for homogeneity indicated that hydrogenation of CO2 proceeded by homogeneous means. Subsequently, the mechanism of the reaction by the iridium(III) catalyst precursors was studied using 1H NMR techniques. This revealed that a chiral-at-metal iridium hydride species generated in situ served as the active catalyst.

Dataset Information

Mechanism Insights into the Iridium(III)- and B(C₆F₅)₃-Catalyzed Reduction of CO₂ to the Formaldehyde Level with Tertiary Silanes.

Publications

Mechanism Insights into the Iridium(III)- and B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>-Catalyzed Reduction of CO<sub>2</sub> to the Formaldehyde Level with Tertiary Silanes.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets