Presence Of Hydrosilanes Research Articles

Exploring the reductive CO2 fixation with amines and hydrosilanes using readily available Cu(II) NHC-phenolate catalyst precursors.

N-Methylation of amines is of great interest in the synthesis of pharmaceuticals and valuable compounds, and the possibility to perform this reaction with an inexpensive and non-toxic substrate like CO2 and its derivatives is quite appealing. Herein, the synthesis of four novel homoleptic Cu(II) complexes with hybrid NHC-phenolate (NHC = N-Heterocyclic Carbene) ligands is reported, and their use in the catalytic N-methylation of amines with CO2 in the presence of hydrosilanes is explored. Both bidentate or tetradentate ligands can be used in the preparation of the complexes provided that the structural requirement that the two NHC and the two phenolate donors in the metal coordination sphere are mutually in trans is fulfilled. A new reaction protocol to perform the N-methylation of secondary aromatic amines and dibenzylamine in high yield under mild reaction conditions is developed, using the ionic liquid [BMMIM][NTf2] (1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide) as solvent and the catalyst precursor [Cu(L2)2]. Reactivity studies indicate that the reaction follows two different pathways with different hydrosilanes, and that the starting Cu(II) complexes are reduced under the catalytic conditions.

Palladium-catalyzed alkyne hydrocarbonylation under atmospheric pressure of carbon monoxide in the presence of hydrosilane

An ultramild reaction condition for the hydrocarbonylation of alkynes, which is performed under atmospheric pressure of CO in the absence of acids, has been developed.

PNP-type ligands enabled copper-catalyzed N-formylation of amines with CO2 in the presence of silanes.

The sustainable catalytic transformation of carbon dioxide into valuable fine chemicals with high efficiency is a global challenge as although CO2 is an abundant, nontoxic, and sustainable carbon feedstock it is also the most important factor behind the Greenhouse Effect. We describe herein a PNP-type ligand-enabled copper-catalyzed N-formylation of amines utilizing CO2 as the building block in the presence of hydrosilane as the reductant. Our current protocol featured newly synthesized PNP-type ligands with broad substrate scope under mild reaction conditions.

An efficient Mn-catalyzed reductive carbonylation of aryl iodides to aryl aldehydes and their benzimidazole and benzoxazoles

The present study envisaged the development of an efficient protocol of Mn-catalyzed reductive carbonylation of aryl iodides to aryl aldehydes and their corresponding imidazole and oxazole derivatives, by using CO as a carbonyl source, in the presence of hydrosilanes and base [Na2CO3 and NaHCO3 (1:1)] under mild reaction conditions gave a series of aldehydes in good yields. This approach could be extended for further functionalization of aryl aldehydes and to their corresponding benzimidazole and benzoxazole derivatives with high efficiency.

Recyclable polymerized Lewis acid poly-BPh(C6F5)2 catalyzed selective N-formylation and N-methylation of amines with carbon dioxide and phenylsilanes

A new boron-centered polymer, which is named poly-BPh(C6F5)2 (polymerized-bis(perfluorophenyl)-(phenyl)borane) was designed and synthesized, which is found to be an efficient catalyst for selective N-formylation and N-methylation of amines using CO2 as C1 building block in the presence of hydrosilanes. Milder reaction conditions (even at room temperature and 1 bar of CO2), remarkable recyclability, tolerance against a variety of functional groups and excellent yields reveal the excellent stability and catalytic activity of poly-BPh(C6F5)2. The process herein represents a simple, ecologically friendly and efficient route for CO2 chemical fixation into value-added chemicals.

Sustainable Catalyst-free N-formylation using CO2 as a Carbon Source.

The development of new sustainable catalytic conversion methods of carbon dioxide (CO2) is of great interest in the synthesis of valuable chemicals. N-formylation of CO2 with amine nucleophiles as substrates has been studied in depth. The key to benign formylation is to select a suitable reducing agent to activate CO2. This paper showcases the activation modes of CO2 and the construction strategies of sustainable and catalyst-free N-formylation systems. The research progress of catalyst-free N-formylation of amines and CO2 is reviewed. There are two broad prominent categories, namely reductive amidation of CO2 facilitated by organic solvents and ionic liquids in the presence of hydrosilane. Attention is also paid to discussing the involved reaction mechanism with practical applications and identifying the remaining challenges in this field.

Copper‐Catalyzed Asymmetric Hydroallylation of Vinylsilanes

AbstractA copper‐catalyzed asymmetric hydroallylation of readily available vinylsilanes with allylic phosphates in the presence of hydrosilane was developed. These transformations can be performed under mild reaction conditions and provide the useful chiral organosilanes with good to excellent level of enantiocontrol.

DFT insight into asymmetric alkyl-alkyl bond formation via nickel-catalysed enantioconvergent reductive coupling of racemic electrophiles with olefins.

A DFT study has been conducted to understand the asymmetric alkyl–alkyl bond formation through nickel-catalysed reductive coupling of racemic alkyl bromide with olefin in the presence of hydrosilane and K3PO4. The key findings of the study include: (i) under the reductive experimental conditions, the Ni(ii) precursor is easily activated/reduced to Ni(0) species which can serve as an active species to start a Ni(0)/Ni(ii) catalytic cycle. (ii) Alternatively, the reaction may proceed via a Ni(i)/Ni(ii)/Ni(iii) catalytic cycle starting with a Ni(i) species such as Ni(i)–Br. The generation of a Ni(i) active species via comproportionation of Ni(ii) and Ni(0) species is highly unlikely, because the necessary Ni(0) species is strongly stabilized by olefin. Alternatively, a cage effect enabled generation of a Ni(i) active catalyst from the Ni(ii) species involved in the Ni(0)/Ni(ii) cycle was proposed to be a viable mechanism. (iii) In both catalytic cycles, K3PO4 greatly facilitates the hydrosilane hydride transfer for reducing olefin to an alkyl coupling partner. The reduction proceeds by converting a Ni–Br bond to a Ni–H bond via hydrosilane hydride transfer to a Ni–alkyl bond via olefin insertion. On the basis of two catalytic cycles, the origins for enantioconvergence and enantioselectivity control were discussed.

A Strategy for Accessing Aldehydes via Palladium‐Catalyzed C−O/C−N Bond Cleavage in the Presence of Hydrosilanes

AbstractWe report the catalytic reduction of both active esters and amides by selective C(acyl)−X (X=O, N) cleavage to access aldehyde functionality via a palladium‐catalyzed strategy. Reactions are promoted by hydrosilanes as reducing reagents with good to excellent yields and with excellent chemoselectivity for C(acyl)−N and C(acyl)−O bond cleavage. Carboxylic acid C(acyl)−O bonds are activated by 2‐chloro‐4,6‐dimethoxy‐1,3,5‐triazine (CDMT) to form triazine ester intermediates, which further react with hydrosilanes to yield aldehydes in one‐pot two‐step procedures. We demonstrate that C(acyl)−O cleavage/formylation offers higher yields and broader substrate scopes compared with C(acyl)−N cleavage under the same reaction conditions.magnified image

Rhodium‐Catalyzed Direct Reductive Amination of Aldehydes and Ketones with Hydrosilanes

AbstractThe commercially available chlorodicarbonylrhodium(I) dimer was shown to be a highly active catalyst in the hydrosilylation of aldimines and ketimines under mild conditions. From these initial results, new procedures for the direct reductive amination of aldehydes and ketones employing this rhodium complex were developed with various primary and secondary amines in the presence of hydrosilanes.

Tetracoordinate borates as catalysts for reductive formylation of amines with carbon dioxide

The first example of borate-catalyzed N-formylation of amines using CO2 as the carbon source in the presence of hydrosilanes is demonstrated using sodium (trihydroxy)phenylborate as a transition metal-free catalyst.

Disrotatory Ring-Opening of Furans Gives Stereocontrol.

The ring-opening of 2-methylfuran and 2,3-dihydro-5-methylfuran catalyzed by the Lewis acid catalyst tris(pentafluorophenyl)borane in the presence of hydrosilanes was studied using quantum chemical methods. In a previous study, it was suggested that the stereoselective formation of the product is due to a nucleophilic vinylic substitution (SNV) during the reaction. Our calculations show that the pathway involving the SNV reaction is energetically not accessible. Instead, the intramolecular C-O bond cleavage is found to be much more favorable in energy for the ring opening reaction. The experimentally observed excellent stereoselectivity toward the Z-isomer product originates from an intrinsic preference of the furan ring to couple the C-O bond cleavage with a disrotatory motion of the oxygen and carbon fragments. This stereoselective feature is naturally programmed into the furan ring manifold and should be generally exploitable for engineering stereoselective ring-opening processes of bioderived furans.

CuH-Catalyzed Synthesis of 3-Hydroxyindolines and 2-Aryl-3H-indol-3-ones from o-Alkynylnitroarenes, Using Nitro as Both the Nitrogen and Oxygen Source.

CuH-catalyzed diasterospecific synthesis of 3-hydroxyindolines and 2-aryl-3H-indol-3-ones have been developed from o-alkynylnitroarenes in the presence of hydrosilane as the reductant. The protocol employs nitro as both nitrogen and oxygen sources for the intramolecular simultaneous construction of C-N and C-O bonds.

Metal-Free Catalytic Formylation of Amides Using CO2 under Ambient Conditions

This study reports the metal-free formylation of amides using carbon dioxide under ambient conditions. An abnormal N-heterocyclic carbene (aNHC) acts as an efficient catalyst for the formylation of amides in the presence of hydrosilane at room temperature. This methodology enables the formation of a C–N bond and can be utilized in building up core moieties of two natural products having strong larvicidal activity such as alatamide and lansiumamide A. A preliminary mechanistic picture for this transformation has been proposed through isolation of reaction byproduct (confirmed by single crystal X-ray study) as well as by characterizing intermediates with spectroscopy.

Efficient Conversion of Carbon Dioxide with Si-Based Reducing Agents Catalyzed by Metal Complexes and Salts.

Homogeneous metal complex and salt catalysts were developed for the reductive transformation of CO2 with Si-based reducing agents. Cu-bisphosphine complexes were found to be excellent catalysts for the hydrosilylation of CO2 with polymethylhydrosiloxane (PMHS). The Cu complexes also showed high catalytic activity and a wide substrate scope for formamide synthesis from amines, CO2 , and PMHS. Simple fluoride salts such as tetrabutylammonium fluoride acted as good catalysts for the reductive conversion of CO2 to formic acid in the presence of hydrosilane, disilane, and metallic Si. Based on the kinetics, isotopic experiments, and in-situ NMR measurements, the reaction mechanism for both catalyst systems, the Cu complex and the fluoride salt, have been proposed.

Directly Bridging Indoles to 3,3'-Bisindolylmethanes by Using Carboxylic Acids and Hydrosilanes under Mild Conditions.

A straightforward Lewis acid-promoted protocol for 3,3'-bisindolylmethanes (BIMs) synthesis by reductive alkylation of indoles at the C3 position with carboxylic acids in the presence of hydrosilane was developed for the first time. Instead of aldehydes, more readily available, stable, and easy-to-handle carboxylic acids have been employed as alternative alkylating agents. As an efficient organocatalyst, B(C6 F5 )3 enables the reductive alkylation of various substituted indole derivatives with carboxylic acids with up to 98 % yield at room temperature and under neat conditions. This metal-free strategy offers an alternative approach for the direct functionalization of indoles to BIMs with carboxylic acids and such protocol allows selective reduction of carboxylic acid to aldehyde in combination with C-C bond formation.

Depolymerization of Waste Plastics to Monomers and Chemicals Using a Hydrosilylation Strategy Facilitated by Brookhart’s Iridium(III) Catalyst

Plastic waste management is a major concern. While the societal demand for sustainability is growing, landfilling and incineration of waste plastics remain the norm and methods able to efficiently recycle these materials are desirable. Herein, we report the depolymerization, under mild conditions, of oxygenated plastics in the presence of hydrosilanes with the cationic pincer complex [Ir(POCOP)H(THF)][B(C6F5)4] (POCOP = 1,3-(tBu2PO)2C6H3)) as catalyst. The iridium catalyst, with a low loading (0.3–1 mol %), proves selective toward the formation of silyl ethers or the corresponding alkanes depending only on the reaction temperature. It is noteworthy that the depolymerization of real household waste plastics such as PET (from plastic bottles) and polylactic acid (PLA) from 3D printer filaments is not altered by the presence of dye or other plastic’s additives.

Density Functional Theory Mechanistic Study of Boron-Catalyzed N-Alkylation of Amines with Formic Acid: Formic Acid Activation by Silylation Reaction.

New methodology for the alkylation of amines is an intriguing issue in both academia and industry. Recently, several groups reported the metal-free B(C6 F5 )3 -catalyzed N-alkylation of amines, but the mechanistic details of these important reactions are unclear. Herein, a computational study was performed to elucidate the mechanism of the N-alkylation of amines with formic acid catalyzed by the Lewis acid B(C6 F5 )3 in the presence of hydrosilane. We found that the reaction started with the activation of formic acid through a novel model. Then, the high electrophilicity of the C center of the formic acid unit and the nucleophilic character of the amine resulted in a C-N coupling reaction. Finally, two sequential silyl-group and H- transfer steps occurred to generate the final product. Upon comparing the reaction barrier and the hydrogenation of indole, our mechanism is more favorable than that proposed by the group of Yu and Fu.

Direct and Regioselective Introduction of Acetals into Imidazoles at the 2‐Position by an Iridium‐Catalyzed Reaction with Formates in the Presence of Hydrosilanes

The iridium‐catalyzed reaction of imidazoles with formates in the presence of hydrosilanes as coreactants led to the production of 2‐[(alkoxy)(siloxy)methyl]imidazoles. Dimethyl acetylenedicarboxylate was the additive of choice for the reaction in terms of reaction efficiency. No reaction was observed in the absence of the hydrosilanes. Whereas substituents at the 1‐ and 5‐positions on the imidazole ring did not affect the reaction, substituents at the 4‐position greatly retarded the reaction. The regioselective reaction of 1‐methyl‐1,2,4‐triazole occurred at the carbon atom between the sp3 and sp2 nitrogen atoms of the ring but not between two sp2 nitrogen atoms. The products were converted into imidazole 2‐carbaldehydes by hydrolysis under acidic conditions.

CO2 as a C1 Source: B(C6F5)3-Catalyzed Cyclization of o-Phenylene-diamines To Construct Benzimidazoles in the Presence of Hydrosilane.

The catalytic construction of benzimidazoles using CO2 as a carbon source represents a facile and sustainable approach to obtaining these valuable compounds. Herein, we describe the B(C6F5)3-catalyzed synthesis of benzimidazoles via cyclization of o-phenylenediamines with CO2 and PhSiH3. This metal-free catalytic route achieves the desired products in high yield under convenient reaction conditions and is applicable to a broad substrate scope. A plausible mechanism for the reaction involving a frustrated Lewis pair pathway is proposed based on spectroscopic characterization (e.g., 13C NMR) of the reaction intermediates.