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Metal-free disproportionation of formic acid mediated by organoboranes.

ABSTRACT: In the presence of dialkylboranes, formic acid can be converted to formaldehyde and methanol derivatives without the need for an external reductant. This reactivity, in which formates serve as the sole carbon and hydride sources, represents the first example of the disproportionation of formate anions under metal-free conditions. Capitalizing on both experimental and computational (DFT) mechanistic considerations, the role of transient borohydride is highlighted in the reduction of formates and this reactivity was further exemplified in the methylation of TMP (2,2,6,6-tetramethylpiperidine) and in the transfer hydroboration reactions for the reduction of aldehydes.

SUBMITTER: Chauvier C

PROVIDER: S-EPMC6021958 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Dehydrogenation, disproportionation and transfer hydrogenation reactions of formic acid catalyzed by molybdenum hydride compounds.

Project description:The cyclopentadienyl molybdenum hydride compounds, CpRMo(PMe3)3-x (CO) x H (CpR = Cp, Cp*; x = 0, 1, 2 or 3), are catalysts for the dehydrogenation of formic acid, with the most active catalysts having the composition CpRMo(PMe3)2(CO)H. The mechanism of the catalytic cycle is proposed to involve (i) protonation of the molybdenum hydride complex, (ii) elimination of H2 and coordination of formate, and (iii) decarboxylation of the formate ligand to regenerate the hydride species. NMR spectroscopy indicates that the nature of the resting state depends on the composition of the catalyst. For example, (i) the resting states for the CpMo(CO)3H and CpMo(PMe3)(CO)2H systems are the hydride complexes themselves, (ii) the resting state for the CpMo(PMe3)3H system is the protonated species [CpMo(PMe3)3H2]+, and (iii) the resting state for the CpMo(PMe3)2(CO)H system is the formate complex, CpMo(PMe3)2(CO)(?1-O2CH), in the presence of a high concentration of formic acid, but CpMo(PMe3)2(CO)H when the concentration of acid is low. While CO2 and H2 are the principal products of the catalytic reaction induced by CpRMo(PMe3)3-x (CO) x H, methanol and methyl formate are also observed. The generation of methanol is a consequence of disproportionation of formic acid, while methyl formate is a product of subsequent esterification. The disproportionation of formic acid is a manifestation of a transfer hydrogenation reaction, which may also be applied to the reduction of aldehydes and ketones. Thus, CpMo(CO)3H also catalyzes the reduction of a variety of ketones and aldehydes to alcohols by formic acid, via a mechanism that involves ionic hydrogenation.

| S-EPMC5649328 | biostudies-literature

Metal-free dehydrogenation of formic acid to H2 and CO2 using boron-based catalysts.

Project description:Formic acid is at the crossroads of novel sustainable energy strategies because it is an efficient H2 carrier. Yet, to date, its decomposition to H2 relies on metal-based catalysts. Herein, we describe the first metal-free catalysts able to promote the dehydrogenation of formic acid. Using dialkylborane derivatives, HCOOH is decomposed to H2 and CO2 in the presence of a base with high selectivity. Experimental and computational results point to the involvement of bis(formyloxy)borates as key intermediates in the C-H bond activation of a formate ligand.

| S-EPMC5655896 | biostudies-other

Manganese-Mediated C-C Bond Formation: Alkoxycarbonylation of Organoboranes.

Project description:Alkoxycarbonylations are important and versatile reactions that result in the formation of a new C-C bond. Herein, we report on a new and halide-free alkoxycarbonylation reaction that does not require the application of an external carbon monoxide atmosphere. Instead, manganese carbonyl complexes and organo(alkoxy)borate salts react to form an ester product containing the target C-C bond. The required organo(alkoxy)borate salts are conveniently generated from the stoichiometric reaction of an organoborane and an alkoxide salt and can be telescoped without purification. The protocol leads to the formation of both aromatic and aliphatic esters and gives complete control over the ester's substitution (e.g., OMe, O t Bu, OPh). A reaction mechanism was proposed on the basis of stoichiometric reactivity studies, spectroscopy, and DFT calculations. The new chemistry is particularly relevant for the field of Mn(I) catalysis and clearly points to a potential pathway toward irreversible catalyst deactivation.

| S-EPMC7988452 | biostudies-literature

Cytenamide-formic acid (1/1).

Project description:IN THE CRYSTAL STRUCTURE OF THE TITLE COMPOUND [SYSTEMATIC NAME: 5H-dibenzo[a,d]cyclo-hepta-triene-5-carboxamide-meth-anoic acid (1/1)], C(16)H(13)NO·CH(2)O(2), the cytenamide and solvent mol-ecules form a hydrogen-bonded R(2) (2)(8) dimer motif, which is further connected to form a centrosymmetric double-motif arrangement. The asymmetric unit contains two formula units.

| S-EPMC2962013 | biostudies-literature

Cobalt-Catalyzed Aqueous Dehydrogenation of Formic Acid.

Project description:Among the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3. Compared to related ruthenium and manganese complexes 7 and 8, this optimal cobalt complex showed improved performance. DFT computations support an innocent non-classical bifunctional outer-sphere mechanism on the triplet state potential energy surface.

| S-EPMC6618042 | biostudies-literature

Hydrogen Generation from Additive-Free Formic Acid Decomposition Under Mild Conditions by Pd/C: Experimental and DFT Studies.

Project description:Safe and efficient hydrogen generation and storage has received much attention in recent years. Herein, a commercial 5 wt% Pd/C catalyst has been investigated for the catalytic, additive-free decomposition of formic acid at mild conditions, and the experimental parameters affecting the process systematically have been investigated and optimised. The 5 wt% Pd/C catalyst exhibited a remarkable 99.9% H2 selectivity and a high catalytic activity (TOF?=?1136 h-1) at 30 °C toward the selective dehydrogenation of formic acid to H2 and CO2. The present commercial catalyst demonstrates to be a promising candidate for the efficient in-situ hydrogen generation at mild conditions possibiliting practical applications of formic acid systems on fuel cells. Finally DFT studies have been carried out to provide insights into the reactivity and decomposition of formic acid along with the two-reaction pathways on the Pd (111) surface.

| S-EPMC6413809 | biostudies-literature

Uracil in formic acid hydrolysates of deoxyribonucleic acid.

Project description:1. When DNA is hydrolysed with formic acid for 30min. at 175 degrees and the hydrolysate is chromatographed on paper with propan-2-ol-2n-hydrochloric acid, in addition to expected ultraviolet-absorbing spots corresponding to guanine, adenine, cytosine and thymine, an ultraviolet-absorbing region with R(F) similar to that of uracil can be detected. Uracil was separated from this region and identified by its spectra in acid and alkali, and by its R(F) in several solvent systems. 2. Cytosine, deoxyribocytidine and deoxyribocytidylic acid similarly treated with formic acid all yielded uracil, as did a mixture of deoxyribonucleotides. 3. Approx. 4% of deoxyribonucleotide cytosine was converted into uracil by the formic acid treatment.

| S-EPMC1264832 | biostudies-other

Charge disproportionation and the pressure-induced insulator-metal transition in cubic perovskite PbCrO3.

Project description:The perovskite PbCrO3 is an antiferromagnetic insulator. However, the fundamental interactions leading to the insulating state in this single-valent perovskite are unclear. Moreover, the origin of the unprecedented volume drop observed at a modest pressure of P = 1.6 GPa remains an outstanding problem. We report a variety of in situ pressure measurements including electron transport properties, X-ray absorption spectrum, and crystal structure study by X-ray and neutron diffraction. These studies reveal key information leading to the elucidation of the physics behind the insulating state and the pressure-induced transition. We argue that a charge disproportionation 3Cr(4+) ? 2Cr(3+) + Cr(6+) in association with the 6s-p hybridization on the Pb(2+) is responsible for the insulating ground state of PbCrO3 at ambient pressure and the charge disproportionation phase is suppressed under pressure to give rise to a metallic phase at high pressure. The model is well supported by density function theory plus the correlation energy U (DFT+U) calculations.

| S-EPMC4330739 | biostudies-literature

First identification of unstable phosphino formic acid (H2PCOOH).

Project description:The hitherto elusive phosphino formic acid molecule (H2PCOOH) was detected for the first time in the gas phase. Theoretical calculations revealed an unexpected kinetic stability of H2PCOOH compared to the isovalent carbamic acid (H2NCOOH) although the replacement of a single nitrogen atom by phosphorus decreases the bond order from a partial double (-C[double bond, length as m-dash]N-) to a single (-C-P-) bond. This work provides a fundamental framework to explore the synthesis and stability of derivatives of carbonic acid (H2CO3), in which one or both hydroxyl groups (OH) are replaced by hydride moieties involving third row atoms.

| S-EPMC6340708 | biostudies-literature

Visible light mediated metal-free thiol-yne click reaction.

Project description:The carbon-sulfur bond formation reaction is of paramount importance for functionalized materials design, as well as for biochemical applications. The use of expensive metal-based catalysts and the consequent contamination with trace metal impurities are challenging drawbacks of the existing methodologies. Here, we describe the first environmentally friendly metal-free photoredox pathway to the thiol-yne click reaction. Using Eosin Y as a cheap and readily available catalyst, C-S coupling products were obtained in high yields (up to 91%) and excellent selectivity (up to 60?:?1). A 3D-printed photoreactor was developed to create arrays of parallel reactions with temperature stabilization to improve the performance of the catalytic system.

| S-EPMC5355861 | biostudies-other

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