Metal-Free Reduction of CO2 to Methoxyborane under Ambient Conditions through Borondiformate Formation

Four-electron reduction of CO2: from formaldehyde and acetal synthesis to complex transformations

The expansive and dynamic field of the CO2 Reduction Reaction (CO2RR) seeks to harness CO2 as a sustainable carbon source or energy carrier. While significant progress has been made in two, six, and eight-electron reductions of CO2, the four-electron reduction remains understudied. This review fills this gap, comprehensively exploring CO2 reduction into formaldehyde (HCHO) or acetal-type compounds (EOCH2OE, with E = [Si], [B], [Zr], [U], [Y], [Nb], [Ta] or -R) using various CO2RR systems. These encompass (photo)electro-, bio-, and thermal reduction processes with diverse reductants. Formaldehyde, a versatile C1 product, is challenging to synthesize and isolate from the CO2RR. The review also discusses acetal compounds, emphasizing their significance as pathways to formaldehyde with distinct reactivity. Providing an overview of the state of four-electron CO2 reduction, this review highlights achievements, challenges, and the potential of the produced compounds - formaldehyde and acetals - as sustainable sources for valuable product synthesis, including chiral compounds.

Zinc-Catalyzed Hydroboration of Carbon Dioxide Amplified by Borane-Tethered Heteroscorpionate Bis(Pyrazolyl)methane Ligands

The borane-functionalized (BR2) bis(3,5-dimethylpyrazolyl)methane (LH) ligands 1a (BR2: 9-borabicyclo[3.3.1]nonane or 9-BBN), 1b (BR2: BCy2), and 1c (BR2: B(C6F5)2) were synthesized by the allylation-hydroboration of LH. Metalation of 1a,b with ZnCl2 yielded the heteroscorpionate dichloride complexes [(1a,b)ZnCl2] 3a,b. The reaction of 1a with ZnEt2 led to the formation of the zwitterionic complex [Et(1a)ZnEt(THF)] 5. The reaction of complex 3a with two equivalents of KHBEt3 under a carbon dioxide (CO2) atmosphere gave rise to the formation of the dimeric bis(formate) complex [(1a)Zn(OCHO)2]2 8, in which its borane moieties intermolecularly stabilize the formate ligands of opposite metal centers. The allylated precursor Lallyl and its zinc dichloride, diethyl and bis(formate) complexes [(Lallyl)ZnCl2] 2, [(Lallyl)ZnEt2] 4, and [(Lallyl)Zn(OCHO)2] 7 were also isolated. The catalyst systems composed of 1 mol % of 3a or 3b and two equivalents of KHBEt3 hydroborated CO2 at 1 bar with pinacolborane (HBPin) to the methanol-level product H3COBPin (and PinBOBPin) in yields of 42 or 86%, respectively. The catalyst systems using the unfunctionalized complex [(LH)ZnCl2] 6 and KHBEt3 or KHBEt3/nOctBR2 (BR2: 9-BBN or BCy2) hydroborated CO2 to H3COBPin but in 2.5- to 6-fold lower activities than those exhibited by 3a,b/KHBEt3. The hydroboration of CO2 using 8 as a catalyst led to yields of 39-43%, comparable to those obtained with 3a/KHBEt3. The results confirmed that the catalytic intermediates benefit from the incorporated boranes' intra- or intermolecular stabilizations.

Bicyclic (alkyl)(amino)carbene (BICAAC) in a dual role: activation of primary amides and CO2 towards catalytic N-methylation

Herein, we report the first catalytic methylation of primary amides using CO₂ as a C1 source. A bicyclic (alkyl)(amino)carbene (BICAAC) exhibits dual role by activating both primary amide and CO₂ to carry out this catalytic transformation which enables the formation of a new C-N bond in the presence of pinacolborane. This protocol was applicable to a wide range of substrate scopes, including aromatic, heteroaromatic, and aliphatic amides. We successfully used this procedure in the diversification of drug and bioactive molecules. Moreover, this method was explored for isotope labelling using ¹³CO₂ for a few biologically important molecules. A detailed study of the mechanism was carried out with the help of spectroscopic studies and DFT calculations.

A Zintl Cluster for Transition Metal-Free Catalysis: C═O Bond Reductions

The first fully characterized boron-functionalized heptaphosphide Zintl cluster, [(BBN)P7]2- ([1]2-), is synthesized by dehydrocoupling [HP7]2-. Dehydrocoupling is a previously unprecedented reaction pathway to functionalize Zintl clusters. [Na(18-c-6)]2[1] was employed as a transition metal-free catalyst for the hydroboration of aldehydes and ketones. Moreover, the greenhouse gas carbon dioxide (CO2) was efficiently and selectively reduced to methoxyborane. This work represents the first examples of Zintl catalysis where the transformation is transition metal-free and where the cluster is noninnocent.

Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy

The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO2 emissions. Outpacing the natural carbon cycle, atmospheric CO2 levels increased by 50 % since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chemical recycling of CO2 to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO2 , CO and their derivatives as potential low-temperature alternatives to the commercial processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the critical assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.

An Unsymmetrical, Cyclic Diborene Based on a Chelating CAAC Ligand and its Small-Molecule Activation and Rearrangement Chemistry

A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved via consecutive two-electron reduction steps from an adduct of CAAC and B2 Br4 (SMe2 )2 . Theoretical studies revealed that this diborene has a considerably smaller HOMO-LUMO gap than those of reported NHC- and phosphine-supported diborenes. Complexation of the diborene with [AuCl(PCy3 )] afforded two diborene-AuI π complexes, while reaction with DurBH2 , P4 and a terminal acetylene led to the cleavage of B-H, P-P, and C-C π bonds, respectively. Thermal rearrangement of the diborene gave an electron-rich cyclic alkylideneborane, which readily coordinated to AgI via its B=C double bond.

Group 6 transition metal-based molecular complexes for sustainable catalytic CO2 activation

CO2 activation is one of the key steps towards CO2 mitigation. In this context, the group 6 transition metal-based molecular catalysts can lead the way.

Regioselective ring-opening of epoxides towards Markovnikov alcohols: A metal-free catalytic approach using abnormal N-heterocyclic carbene

Herein we report the first metal-free regioselective Markovnikov ring-opening of epoxides (selectivity up to 99%) using an abnormal N-heterocyclic carbene (aNHC) to yield secondary alcohols. DFT calculations and X-ray crystallography...

Selective Catalytic Frustrated Lewis Pair Hydrogenation of CO2 in the Presence of Silylhalides

The frustrated Lewis pair (FLP) derived from 2,6-lutidine and B(C6 F5 )3 is shown to mediate the catalytic hydrogenation of CO2 using H2 as the reductant and a silylhalide as an oxophile. The nature of the products can be controlled with the judicious selection of the silylhalide and the solvent. In this fashion, this metal-free catalysis affords avenues to the selective formation of the disilylacetal (R3 SiOCH2 OSiR3 ), methoxysilane (R3 SiOCH3 ), methyliodide (CH3 I) and methane (CH4 ) under mild conditions. DFT studies illuminate the complexities of the mechanism and account for the observed selectivity.

Carbon-based metal-free electrocatalysts: from oxygen reduction to multifunctional electrocatalysis

Since the discovery of N-doped carbon nanotubes as the first carbon-based metal-free electrocatalyst (C-MFEC) for oxygen reduction reaction (ORR) in 2009, C-MFECs have shown multifunctional electrocatalytic activities for many reactions beyond ORR, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), nitrogen reduction reaction (NRR), and hydrogen peroxide production reaction (H₂O₂PR). Consequently, C-MFECs have attracted a great deal of interest for various applications, including metal-air batteries, water splitting devices, regenerative fuel cells, solar cells, fuel and chemical production, water purification, to mention a few. By altering the electronic configuration and/or modulating their spin angular momentum, both heteroatom(s) doping and structural defects (e.g., atomic vacancy, edge) have been demonstrated to create catalytic active sites in the skeleton of graphitic carbon materials. Although certain C-MFECs have been made to be comparable to or even better than their counterparts based on noble metals, transition metals and/or their hybrids, further research and development are necessary in order to translate C-MFECs for practical applications. In this article, we present a timely and comprehensive, but critical, review on recent advancements in the field of C-MFECs within the past five years or so by discussing various types of electrocatalytic reactions catalyzed by C-MFECs. An emphasis is given to potential applications of C-MFECs for energy conversion and storage. The structure-property relationship for and mechanistic understanding of C-MFECs will also be discussed, along with the current challenges and future perspectives.

Hydroboration of aldehydes, ketones and CO2 under mild conditions mediated by iron(iii) salen complexes

The hydroboration of aldehydes, ketones and CO₂ is demonstrated using a cheap and air stable [Fe(salen)]₂-μ-oxo pre-catalyst with pinacolborane (HBpin) as the reductant under mild conditions. This catalyst system chemoselectively hydroborates aldehydes over ketones and ketones over alkenes. In addition, the [Fe(salen)₂]-μ-oxo pre-catalyst shows good efficacy at reducing "wet" CO₂ with HBpin at room temperature.

A Bottleable Imidazole-Based Radical as a Single Electron Transfer Reagent

Reduction of 1,3-bis(2,6-diisopropylphenyl)-2,4-diphenyl-1H-imidazol-3-ium chloride (1) resulted in the formation of the first structurally characterized imidazole-based radical 2. 2 was established as a single electron transfer reagent by treating it with an acceptor molecule tetracyanoethylene. Moreover, radical 2 was utilized as an organic electron donor in a number of organic transformations such as in activation of an aryl-halide bond, alkene hydrosilylation, and in catalytic reduction of CO₂ to methoxyborane, all under ambient temperature and pressure.

From CO2 activation to catalytic reduction: a metal-free approach

Over exploitation of natural resources and human activities are relentlessly fueling the emission of CO2 in the atmosphere. Accordingly, continuous efforts are required to find solutions to address the issue of excessive CO2 emission and its potential effects on climate change. It is imperative that the world looks towards a portfolio of carbon mitigation solutions, rather than a single strategy. In this regard, the use of CO2 as a C1 source is an attractive strategy as CO2 has the potential to be a great asset for the industrial sector and consumers across the globe. In particular, the reduction of CO2 offers an alternative to fossil fuels for various organic industrial feedstocks and fuels. Consequently, efficient and scalable approaches for the reduction of CO2 to products such as methane and methanol can generate value from its emissions. Accordingly, in recent years, metal-free catalysis has emerged as a sustainable approach because of the mild reaction conditions by which CO2 can be reduced to various value-added products. The metal-free catalytic reduction of CO2 offers the development of chemical processes with low cost, earth-abundant, non-toxic reagents, and low carbon-footprint. Thus, this perspective aims to present the developments in both the reduction and reductive functionalization chemistry of CO2 during the last decade using various metal-free catalysts.

Ph2PCH2CH2B(C8H14) and Its Formaldehyde Adduct as Catalysts for the Reduction of CO2 with Hydroboranes

We study two metal-free catalysts for the reduction of CO₂ with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane Ph₂P(CH₂)₂BBN (1), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.1]nonane (H-BBN), and its formaldehyde adduct Ph₂P(CH₂)₂BBN(CH₂O) (2), detected in the catalytic reduction of CO₂ with 1 as the catalyst but properly prepared from compound 1 and p-formaldehyde. Reduction of CO₂ with H-BBN gave mixtures of CH₂(OBBN)₂ (A) and CH₃OBBN (B) using both catalysts. Stoichiometric and kinetic studies allowed us to unveil the key role played in this reaction by the formaldehyde adduct 2 and other formaldehyde-formate species, such as the polymeric BBN(CH₂)₂(Ph₂P)(CH₂O)BBN(HCO₂) (3) and the bisformate macrocycle BBN(CH₂)₂(Ph₂P)(CH₂O)BBN(HCO₂)BBN(HCO₂) (4), whose structures were confirmed by diffractometric analysis. Reduction of CO₂ with catecholborane (HBcat) led to MeOBcat (C) exclusively. Another key intermediate was identified in the reaction of 2 with the borane and CO₂, this being the bisformaldehyde-formate macrocycle (HCO₂){BBN(CH₂)₂(Ph₂P)(CH₂O)}₂Bcat (5), which was also structurally characterized by X-ray analysis. In contrast, using pinacolborane (HBpin) as the reductant with catalysts 1 and 2 usually led to mixtures of mono-, di-, and trihydroboration products HCO₂Bpin (D), CH₂(OBpin)₂ (E), and CH₃OBpin (F). Stoichiometric studies allowed us to detect another formaldehyde-formate species, (HCO₂)BBN(CH₂)₂(Ph₂P)(CH₂O)Bpin (6), which may play an important role in the catalytic reaction. Finally, only the formaldehyde adduct 2 turned out to be active in the catalytic hydroboration of CO₂ using BH₃·SMe₂ as the reductant, yielding a mixture of two methanol-level products, [(OMe)BO]₃ (G, major product) and B(OMe)₃ (H, minor product). In this transformation, the Lewis adduct (BH₃)Ph₂P(CH₂)₂BBN was identified as the resting state of the catalyst, whereas an intermediate tentatively formulated as the Lewis adduct of compound 2 and BH₃ was detected in solution in a stoichiometric experiment and is likely to be mechanistically relevant for the catalytic reaction.

Formation of Formic Acid Derivatives through Activation and Hydroboration of CO2 by Low-Valent Group 14 (Si, Ge, Sn, Pb) Catalysts

The chemistry of low-valent main group elements has attracted much attention in the past decade. These species are relevant because they have been able to mimic transition metal behavior in catalytic applications, with decreased material costs and diminished toxicity. In this contribution, we study the L¹EH catalysts (E = Si(II), Ge(II), Sn(II), and Pb(II); L¹ = [ArNC(Me)CHC(Me)NAr] with Ar = 2,6-iPr₂C₆H₃) for the formation of formic acid derivatives through hydroboration of CO₂. Detailed characterization of relevant structures on the potential energy surface enabled us to rationalize different paths for the hydroboration of CO₂. Interestingly, it was found that according to the activation energies for the whole catalytic cycle, the process of transformation of CO₂ becomes more favored going down group 14. However, an effective energetic decrease for the process (taking as the reference the uncatalyzed reaction between CO₂ and HBpin) is evidenced just from the germanium analogue. The trend in reactivity found in the present study is a direct consequence of the change in the central main group element, enabling enhanced polar character of the E-H (L¹EH in the CO₂ activation step) and E-O (metal formates in the hydroboration step) bonds as the atomic radius increases. The transient stabilization of reaction intermediates found in the hydroboration step was rationalized through the non-covalent interaction index (NCI) and symmetry-adapted perturbation theory (SAPT). This computational study highlights the reactivity trends in group-14-based hydride catalysts in hydrometalation and posterior hydroboration to form formic acid intermediates. We hope that this study will motivate further experimental work in low-valent lead chemistry.

Stable abnormal N-heterocyclic carbenes and their applications

Although N-heterocyclic carbenes (NHCs) have been known as ligands for organometallic complexes since the 1960s, these carbenes did not attract considerable attention until Arduengo et al. reported the isolation of a metal-free imidazol-2-ylidene in 1991. In 2001 Crabtree et al. reported a few complexes featuring an NHC isomer, namely an imidazol-5-ylidene, also termed abnormal NHC (aNHCs). In 2009, it was shown that providing to protect the C-2 position of an imidazolium salt, the deprotonation occurred at the C-5 position, affording imidazol-5-ylidenes that could be isolated. Over the last ten years, stable aNHCs have been used for designing a range of catalysts employing Pd(ii), Cu(i), Ni(ii), Fe(0), Zn(ii), Ag(i), and Au(i/iii) metal based precursors. These catalysts were utilized for different organic transformations such as the Suzuki-Miyaura cross-coupling reaction, C-H bond activation, dehydrogenative coupling, Huisgen 1,3-dipolar cycloaddition (click reaction), hydroheteroarylation, hydrosilylation reaction and migratory insertion of carbenes. Main-group metal complexes were also synthesized, including K(i), Al(iii), Zn(ii), Sn(ii), Ge(ii), and Si(ii/iv). Among them, K(i), Al(iii), and Zn(ii) complexes were used for the polymerization of caprolactone and rac-lactide at room temperature. In addition, based on the superior nucleophilicity of aNHCs, relative to that of their nNHCs isomers, they were used for small molecules activation, such as carbon dioxide (CO₂), nitrous oxide (N₂O), tetrahydrofuran (THF), tetrahydrothiophene and 9-borabicyclo[3.3.1]nonane (9BBN). aNHCs have also been shown to be efficient metal-free catalysts for ring opening polymerization of different cyclic esters at room temperature; they are among the most active metal-free catalysts for ε-caprolactone polymerization. Recently, aNHCs successfully accomplished the metal-free catalytic formylation of amides using CO₂ and the catalytic reduction of carbon dioxide, including atmospheric CO₂, into methanol, under ambient conditions. Although other transition metal complexes featuring aNHCs as ligand have been prepared and used in catalysis, this review article summarize the results obtained with the isolated aNHCs.

NHC-catalyzed silylative dehydration of primary amides to nitriles at room temperature

Herein we report an abnormal N-heterocyclic carbene catalyzed dehydration of primary amides in the presence of a silane. This process bypasses the energy demanding 1,2-siloxane elimination step usually required for metal/silane catalyzed reactions. A detailed mechanistic cycle of this process has been proposed based on experimental evidence along with computational study.

Acetate-catalyzed hydroboration of CO2 for the selective formation of methanol-equivalent products

The acetate anion is a highly robust and effective catalyst for the selective hydroboration of CO₂ to methanol-equivalent products.

A crystalline C5-protonated 1,3-imidazol-4-ylidene

The first C5-protonated 1,3-imidazole-based mesoionic carbene (iMIC^Bp) has been isolated and characterized by single-crystal X-ray diffraction.

Transition metal-free catalytic reduction of primary amides using an abnormal NHC based potassium complex: integrating nucleophilicity with Lewis acidic activation

An abnormal N-heterocyclic carbene (aNHC) based potassium complex was used as a transition metal-free catalyst for reduction of primary amides to corresponding primary amines under ambient conditions. Only 2 mol% loading of the catalyst exhibits a broad substrate scope including aromatic, aliphatic and heterocyclic primary amides with excellent functional group tolerance. This method was applicable for reduction of chiral amides and utilized for the synthesis of pharmaceutically valuable precursors on a gram scale. During mechanistic investigation, several intermediates were isolated and characterized through spectroscopic techniques and one of the catalytic intermediates was characterized through single-crystal XRD. A well-defined catalyst and isolable intermediate along with several stoichiometric experiments, in situ NMR experiments and the DFT study helped us to sketch the mechanistic pathway for this reduction process unravelling the dual role of the catalyst involving nucleophilic activation by aNHC along with Lewis acidic activation by K ions.

An abnormal N-heterocyclic carbene (aNHC) based potassium complex was used as a transition metal-free catalyst for reduction of primary amides to corresponding primary amines under ambient conditions.

Catalytic CO2 Reduction with Boron- and Aluminum Hydrides

The previously reported dimeric NHI aluminum dihydrides 1 a,b, as well as the bis(NHI) aluminum dihydride salt 9 +[OTs]-, the bis(NHI) boron dihydride salt 10 +[OTs]-, and the "free" bis(NHI) ligand 12 were investigated with regard to their activity as a homogenous (pre)catalyst in the hydroboration (i. e. catalytic reduction) of carbon dioxide (CO2) in chloroform under mild conditions (i. e. room temperature, 1 atm; NHI=N-heterocyclic imine, Ts=tosyl). Borane dimethylsulfide complex and catecholborane were used as a hydride source. Surprisingly, the less sterically hindered 1 a exhibited lower catalytic activity than the bulkier 1 b. A similarly unexpected discrepancy was found with the lower catalytic activity of 10 + in comparison to the one of the bis(NHI) 12. The latter is incorporated as the ligand to the boron center in 10 +. To elucidate possible mechanisms for CO2 reduction the compounds were subjected to stoichiometric reactivity studies with the borane or CO2. Aluminum carboxylates 4, 6, and 7 + with two, four, and one formate group per two aluminum centers were isolated. Also, the boron formate salt 11 +[OTs]- was characterized. Selected metal formates were subjected to stoichiometric reactions with boranes and/or tested as a catalyst. We conclude that each type of catalyst (1 a,b, 9 +, 10 +, 12) follows an individual mechanistic pathway for CO2 reduction.

Green Synthesis of Novel Polyesterurethane Materials from Epoxides and Carbon Dioxide by New Set of One-Dimensional Coordination Polymer Catalyst

Two novel polyesterurethane materials, PEU1 and PEU2, were synthesized via nontoxic and isocyanate-free route by simple conversion of two epoxides 1,2-epoxy-3-phenoxy propane (2) and styrene epoxide (3) utilizing CO₂. Epoxides 2 and 3 were converted to the respective cyclic carbonates 4 and 5 by a new set of cobalt-based catalyst 1a in the presence of 10 bar of CO₂ and 80 °C temperature without using cocatalyst tetrabutylammonium bromide (TBAB). The mechanistic pathway of the catalysis reaction for the cycloaddition of epoxides with CO₂ to generate the cyclic carbonates was investigated by several spectroscopic techniques and utilizing analogous zinc-based 1D coordination polymer 1b, which does not act as an efficient catalyst in the absence of TBAB. Cyclic carbonates 4 and 5 were converted to the respective polyesterurethanes PEU1 and PEU2 sequentially by first synthesizing the ring-opened diols 6 and 7 reacting with ethylenediamine and subsequently annealing the respective diols 6 and 7 at 120 °C in the presence of terepthalyl chloride and triethylamine. The polyesterurethanes PEU1 and PEU2 were characterized by multinuclear NMR and FTIR. PEU1 was also characterized by MALDI-TOF mass spectrometry. The thermal studies of PEU1 and PEU2 showed the stability up to 200-270 °C. The number-average and weight-average molecular weights were determined for PEU1 and PEU2 by GPC analysis. The weight-average molecular weight for PEU1 was found to be 5948 with a polydispersity of 1.1, and PEU2 showed the weight-average molecular weight as 4224 with a polydispersity of 1.06.

Transforming atmospheric CO2 into alternative fuels: a metal-free approach under ambient conditions

This work demonstrates the first-ever completely metal-free approach to the capture of CO₂ from air followed by reduction to methoxyborane (which produces methanol on hydrolysis) or sodium formate (which produces formic acid on hydrolysis) under ambient conditions. This was accomplished using an abnormal N-heterocyclic carbene (aNHC)-borane adduct. The intermediate involved in CO₂ capture (aNHC-H, HCOO, B(OH)₃) was structurally characterized by single-crystal X-ray diffraction. Interestingly, the captured CO₂ can be released by heating the intermediate, or by passing this compound through an ion-exchange resin. The capture of CO₂ from air can even proceed in the solid state via the formation of a bicarbonate complex (aNHC-H, HCO₃, B(OH)₃), which was also structurally characterized. A detailed mechanism for this process is proposed based on tandem density functional theory calculations and experiments.

Carbodiimides as catalysts for the reduction of CO2 with boranes

Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25-60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.

Zwitterionic indenylammonium with carbon-centred reactivity towards reversible CO2 binding and catalytic reduction

We report the synthesis and characterization of a zwitterionic indenylammonium compound and its carbon-centred reactivity towards reversible CO₂ binding at ambient temperature through its formal insertion into a C-H bond as well as the catalytic hydroboration of CO₂ to methanol derivatives.

Hydroboration of carbon dioxide with catechol- and pinacolborane using an Ir–CNP* pincer complex. Water influence on the catalytic activity

Lutidine-derived CNP*–Ir complexes catalyze the hydroboration of CO₂ to methoxyborane and formoxyborane in the presence of small amounts of water.

CO2 Complexes with Five-Membered Heterocycles: Structure, Topology, and Spectroscopic Characterization

In a first step toward the rational design of macrocyclic structures optimized for CO₂ capture, we systematically explored the potential of 30 five-membered aromatic heterocycles to establish coordinating complexes with this pollutant. The interactions between the two moieties were studied in several orientations, and the obtained complexes were analyzed in terms of electron density and vibrational fingerprint. The former is an aid to provide an in-depth knowledge of the interaction, whereas the latter should help to select structural motifs that have not only good complexation properties but also diagnostic spectroscopic signals.

External electric field control: driving the reactivity of metal-free azide–alkyne click reactions

An external electric field is demonstrated as an efficient catalyst to accelerate click reactions.

Pyridine-decorated carbon nanotubes as a metal-free heterogeneous catalyst for mild CO2 reduction to methanol with hydroboranes

Pyridine decorated multi-walled carbon nanotubes have been employed as heterogeneous metal-free catalysts for CO₂ hydroboration to methyl borinate under mild conditions. Mechanistic insights have unveiled the non-innocent role of the nanotube carrier in the catalytic performance.

Transition metal free catalytic hydroboration of aldehydes and aldimines by amidinato silane

Benz-amidinato dichlorosilane [PhC(NtBu)₂SiHCl₂] has been reported to catalyze hydroboration of aldehydes at room temperature and aldimines under slightly harsh conditions.

Facile routes to abnormal-NHC-cobalt(ii) complexes

Deprotonation of 1 with Co{N(SiMe₃)₂}₂ affords aNHC-Co(ii) complex 2, whereas carbene transfer from 3 to Co{N(SiMe₃)₂}₂ enables access to complex 4.

Chemical reduction of CO2facilitated by C-nucleophiles

This feature article describes recent advances in chemical reduction of CO₂facilitated by carbon-based molecular nucleophiles.