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.

Pd/C-Catalyzed Selective N-Monomethylation by Transfer Hydrogenation of Urea Derivatives using Methanol as H2 and C1 Sources

N-monomethyl amines are useful intermediates in drugs, natural products, paints. Yet their synthesis is a tremendous challenge due to their high reactivity, typically leading to overmethylation. In this contribution, a highly selective catalytic N-methylation methodology is reported, converting urea derivatives to monomethylated amines, using a commercially available heterogeneous Pd/C catalyst and methanol as unique reagent. Methanol provides a sustainable alternative protocol for the selective preparation of mono-methylated derivatives as it acts as both H2 and C1 sources. In addition, several control experiments were performed to provide a proposal for the mechanism, namely dehydrogenation of methanol and subsequent hydrogenation of urea derivatives, followed by reduction of the in situ formed methyl imine. Importantly, the approach is simple, highly productive and enables novel synthetic procedures for the preparation of monomethylamines from urea derivatives.

Homogeneous Catalysis in N-Formylation/N-Methylation Utilizing Carbon Dioxide as the C1 Source

The growing emphasis on sustainable chemistry has driven research into utilizing carbon dioxide (CO2) as a nontoxic, abundant, and cost-effective C1 building block. CO2 offers a promising avenue for direct conversion into valuable chemicals ranging from fuels to pharmaceuticals. This review focuses on the utilization of CO2 for reductive N-formylation/N-methylation reactions of various amines, providing advantages over conventional methods involving toxic CO and other methylating reagents. The approach employs readily available reductants such as silane, borane reagents, and hydrogen (H2). The discussion encompasses recent developments in transition metal and organocatalyst systems for these reactions, highlighting mechanistic interpretations and factors influencing product selectivity.

A Guide for Mono-Selective N-Methylation, N-Ethylation, and N-n-Propylation of Primary Amines, Amides, and Sulfonamides and Their Applicability in Late-Stage Modification

This review provides a comprehensive overview of mono-alkylation methodologies targeting crucial nitrogen moieties - amines, amides, and sulfonamides - found in organic building blocks and pharmaceuticals. Emphasizing the intersection of chemical precision with drug discovery, the central challenge addressed is achieving one-pot mono-selective short-chain N-alkylations (methylations, ethylations, and n-propylations), preventing undesired overalkylation. Additionally, sustainable, safe, and benign alternatives to traditional alkylating agents, including alcohols, carbon dioxide, carboxylic acids, nitriles, alkyl phosphates, quaternary ammonium salts, and alkyl carbonates, are explored. This review, categorized by the nature of the alkylating agent, aids researchers in selecting suitable methods for mono-selective N-alkylation.

Borohydride Ionic Liquids as Reductants of CO2 in the Selective N-formylation of Amines

Borohydride imidazolium ionic liquids, [IL]BH4, used for the first time as reductants in the N-formylation of various amines with CO2, provided an excellent yield of formamides. Under the same conditions, 5 bar CO2 and 80 °C, NaBH4 produced a mixture of N-formylated and N-methylated products in a ratio of 1 : 2. An alternative approach, based on the addition of halide imidazolium salts ([IL]Cl or [IL]Br) to the reactions of amine with NaBH4 and CO2, resulted in a significant increase of selectivity to formamide. However, no effect was noted for [IL]BF4 and [IL]PF6. Monitoring the reaction course in time using 1H NMR brought about new insight into the role of BH3 in the reduction of CO2 and the functionalization of amines. The formation of N-methylaniline - borane intermediate was evidenced.

Highly Efficient Thiolate-Based Ionic Liquid Catalysts for Reduction of CO2: Selective N-Functionalization of Amines to Form N-Formamides and N-Methylamines

Developing efficient catalysts to convert CO2 into value-added chemicals is valuable for reducing carbon emissions. Herein, a kind of novel thiolate-based ionic liquid with sulfur as the active site was designed and synthesized, which served as highly efficient catalyst for the reductive N-functionalization of CO2 by amines and hydrosilane. By adjusting the CO2 pressure, various N-formamides and N-methylamines were selectively obtained in high yields. Remarkably, at the catalyst loading of 0.1 mol %, the N-formylation reaction of N-methylaniline exhibited an impressive turnover frequency (TOF) up to 600 h-1, which could be attributed to the roles of the ionic liquids in activating hydrosilane and amine. In addition, control experiments and NMR monitoring experiments provided evidence that the reduction of CO2 by hydrosilane yielded formoxysilane intermediates that subsequently reacted with amines to form N-formylated products. Alternatively, the formoxysilane intermediates could further react with hydrosilane and amine to produce 4-electron-reduced aminal products. These aminal products served as crucial intermediates in the N-methylation reactions.

Manganese-Catalyzed Mono-N-Methylation of Aliphatic Primary Amines without the Requirement of External High-Hydrogen Pressure

The synthesis of mono-N-methylated aliphatic primary amines has traditionally been challenging, requiring noble metal catalysts and high-pressure H2 for achieving satisfactory yields and selectivity. Herein, we developed an approach for the selective coupling of methanol and aliphatic primary amines, without high-pressure hydrogen, using a manganese-based catalyst. Remarkably, up to 98 % yields with broad substrate scope were achieved at low catalyst loadings. Notably, due to the weak base-catalyzed alcoholysis of formamide intermediates, our novel protocol not only obviates the addition of high-pressure H2 but also prevents side secondary N-methylation, supported by control experiments and density functional theory calculations.

Switching the hydrogenation selectivity of urea derivatives via subtly tuning the amount and type of additive in the catalyst system

Catalytic hydrogenation of urea derivatives is considered to be one of the most feasible methods for indirect reduction functionalization of CO2 and synthesis of valuable chemicals and fuels. Among value-added products, methylamines, formamides and methanol are highly attractive as important industrial raw materials. Herein, we report the highly selective catalytic hydrogenation of urea derivatives to N-monomethylamines for the first time. More importantly, two- and six-electron reduction products can be switched on/off by subtly tuning 0.5 mol% KOtBu (2% to 1.5%): when the molar ratio of KOtBu/(PPh3)3RuCl2 exceeds 2.0, it is favorable for the formation of two-electron reduction products (N-formamides), while when it is below 2.0, the two-electron reduction products are further hydrogenated to six-electron reduction products (N-monomethylamines and methanol). Furthermore, changing the type of additive can also regulate this interesting selectivity. Control experiments showed that this selectivity is achieved by regulating the acid-base environment of the reaction to control the fate of the common hemiaminal intermediate. A feasible mechanism is proposed based on mechanistic experiments and characterization. This method has the advantages of being simple, universal and highly efficient, and opens up a new synthesis strategy for the utilization of renewable carbon sources.

Copper iodide nanoparticles supported on modified graphene-based nanocomposite catalyzed CO2 conversion into oxazolidinone derivatives

We report on the preparation of copper iodide nanoparticles (NPs) immobilized on vitamin B3-modified graphene (CuI/GO-VB) nanocomposite and its application for the synthesis of oxazolidinone compounds using a remarkable carboxylative cyclization method via the reaction of arylacetylene, aldehyde and benzylamine derivatives under an atmospheric pressure of CO2 gas. The CuI/GO-VB catalyst was prepared from graphene oxide (GO), vitamin B3 (VB) and CuI using a two-step procedure; firstly graphene-based composite (GO-VB) was synthesized by the reaction of GO and nicotinoyl chloride, followed by the immobilization of CuI NPs on GO-VB. The CuI/GO-VB nanocomposite was fully identified with X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The catalytic performance of the CuI/GO-VB heterogeneous catalyst was investigated in carboxylative cyclization for the synthesis of oxazolidinone compounds under an atmospheric pressure of CO2 gas at 100οC in solvent-, base-, and additive-free conditions; the corresponding oxazolidinone compounds were obtained in 79-94% yield. The hot filtration results indicated that CuI/GO-VB nanocomposite was a heterogeneous catalyst and showed a good reusability for 5 runs without a significant decrease in its catalytic performance.

Bis(N-Heterocyclic Carbene) Manganese(I) Complexes in Catalytic N-Formylation/N-Methylation of Amines Using Carbon Dioxide and Phenylsilane

A series of six Mn(I) complexes with general formula [MnBr(bisNHC)(CO)3 ], having a bidentate bis(N-heterocyclic carbene) ligand (bisNHC), has been developed by varying the bridging group between the NHC donors, the nitrogen wingtip substituents and the heterocyclic ring. The synthesis of the complexes has been accomplished by in situ transmetalation of the bisNHC from the corresponding silver(I) complexes. Removal of the bromide anion affords the corresponding solvento complexes [Mn(bisNHC)(CO)3 (CH3 CN)](BF4 ). The influence of the bisNHC structure on its electron donor ability has been evaluated by FTIR and 13 C NMR spectroscopy, both in the neutral and cationic complexes. Finally, the isolated Mn(I)-bisNHC complexes have been employed as homogeneous catalysts in the reductive N-formylation and N-methylation of amines with CO2 as C1 source and phenylsilane as reducing agent, showing a high selectivity for the N-methylated product. Preliminary mechanistic investigations suggest that, in the adopted reaction conditions, the formylated product can be formed via different reaction pathways, either metal-catalyzed or not, while the methylation reaction requires the use of the Mn(I) catalyst.

A complete series of N-heterocyclic tetrylenes (Si-Pb) with a 1,1'-ferrocenediyl backbone enabled by 1,3,2-diazaborolyl N-substituents

The use of bulky 1,3,2-diazaborolyl N-substituents has allowed the synthesis of the complete series of ferrocene-based N-heterocyclic tetrylenes fc[(N{B})2E] (fc = 1,1'-ferrocenediyl, {B} = (HCNC6H3-2,6-iPr2)2B, E = Si-Pb). The silylene fc[(N{B})2Si] is inert towards NH3, CO2 or N2O under ambient conditions and thus significantly less reactive than the N-aryl homologue fc[(NC6H3-2,6-iPr2)2Si]. In accord with its higher reactivity, computational results indicate a more pronounced ambiphilicity of fc[(NC6H3-2,6-iPr2)2Si]. Our computational investigation of the model compound fc[(NBMe2)2Si] suggests that silylenes of this type may be superior to fc[(NC6H3-2,6-iPr2)2Si] in terms of ambiphilicity.

Heterobimetallic Hydrides with a Germanium(II)-Zinc Bond

In the presence of TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine), zinc dihydride reacted with germanium(II) compounds (BDI-H)Ge (1) and [(BDI)Ge][B(3,5-(CF3 )2 C6 H3 )4 ] (3) (BDI-H = HC{(C=CH2 )(CMe)(NAr)2 }, BDI = [HC(CMeNAr)2 ]; Ar = 2,6-i Pr2 C6 H3 ) by formal insertion of the germanium(II) center into the Zn-H bond of polymeric [ZnH2 ]n to give neutral and cationic zincagermane with a H-Ge-Zn-H core [(BDI-H)Ge(H)-(H)Zn(tmeda)] (2) and [(BDI)Ge(H)-(H)Zn(tmeda)][B(3,5-(CF3 )2 C6 H3 )4 ] (4), respectively. Compound 2 eliminated [ZnH2 ] giving diamido germylene 1 at 60 °C. Compound 2 and deuterated analogue 2-d2 exchanged with [ZnH2 ]n and [ZnD2 ]n in the presence of TMEDA to give a mixture of 2 and 2-d2 . Compounds 2 and 4 reacted with carbon dioxide (1 bar) at room temperature to form zincagermane diformate [(BDI-H)Ge(OCHO)-(OCHO)Zn(tmeda)] (5) and formate bridged digermylene [({BDI}Ge)2 (μ-OCHO)]+ [B(C6 H3 (CF3 )2 )4 ] (6) along with zinc formate [(tmeda)Zn(μ-OCHO)3 Zn(tmeda)][B(C6 H3 (CF3 )2 )4 ] (7), respectively. The hydridic nature of the Ge-H and Zn-H bonds in 2 and 4 was probed by reactions with Brönsted and Lewis acids.

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.

Highly Selective Monomethylation of Amines with CO2 /H2 via Ag/Al2 O3 as a Catalyst

The selective synthesis of monomethylated amines with CO₂ is particularly challenging because the formation of tertiary amines is thermodynamically more favorable. Herein, a new strategy for the controllable synthesis of N-monomethylated amines from primary amines and CO₂ /H₂ is explored. First-principle calculations reveal that the dissociation of H₂ via an heterolytic route reduces the reactivity of methylated amines and thus inhibit successive methylation. In situ DRIFTS proves the process of formation and decomposition of ammonium salt by secondary amine reversible binding with H⁺ on the Ag/Al₂ O₃ catalyst, thereby reducing its reactivity. Meanwhile, the energy barrier for the rate-determining step of monomethylation was much lower than that of overmethylation (0.34 eV vs. 0.58 eV) means amines monomethylation in preference to successive methylation. Under optimal reaction conditions, a variety of amines were converted to the corresponding monomethylated amines in good to excellent yields, and more than 90 % yield of product was obtained.

A versatile way for the synthesis of monomethylamines by reduction of N-substituted carbonylimidazoles with the NaBH4/I2 system

An economical and versatile protocol for the one-pot synthesis of monomethylamines by reduction of N-substituted carbonylimidazoles with NaBH₄/I₂ in THF at reflux temperature is described. This method used no special catalyst and various monomethylamines can be easily obtained in moderate to good yields from a wide range of raw materials including amines (primary amines and secondary amines), carboxylic acids and isocyanates. Besides, an interesting reduction selectivity was observed. Exploration of the reaction process shows that it undergoes a two-step pathway via a formamide intermediate and the reduction of the formamide intermediate to monomethylamine as the rate-determining step. This work can contribute significantly expanding the applications of N-substituted carbonylimidazoles.

One-Pot Reductive Methylation of Nitro- and Amino-Substituted (Hetero)Aromatics with DMSO/HCOOH: Concise Synthesis of Fluorescent Dimethylamino-Functionalized Bibenzothiazole Ligands with Tunable Emission Color upon Complexation

One-pot reductive N,N-dimethylation of suitable nitro- and amino-substituted (hetero)arenes can be achieved using a DMSO/HCOOH/Et₃N system acting as a low-cost but efficient reducing and methylating agent. The transformation of heteroaryl-amines can be accelerated by using dimethyl sulfoxide/oxalyl chloride or chloromethyl methyl sulfide as the source of active CH₃SCH₂⁺ species, while the exclusion of HCOOH in the initial stage of the reaction allows avoiding N-formamides as resting intermediates. The developed procedures are applicable in multigram-scale synthesis, and because of the lower electrophilicity of CH₃SCH₂⁺, they also work in pathological cases, where common methylating agents provide N,N-dimethylated products in no yield or inferior yields due to concomitant side reactions. The method is particularly useful in one-pot reductive transformation of 2-H-nitrobenzazoles to corresponding N,N-dimethylamino-substituted heteroarenes. These, upon Cu(II)-catalyzed oxidative homocoupling, afford 2,2'-bibenzazoles substituted with dimethylamino groups as charge-transfer N^N ligands with intensive absorption/emission in the visible region. The fluorescence of NMe₂-functionalized bibenzothiazoles remains intensive even upon complexation with ZnCl₂, while emission maxima are bathochromically shifted from the green/yellow to orange/red spectral region, making these small-molecule fluorophores, exhibiting large emission quantum yields and Stokes shifts, an attractive platform for the construction of various functional dyes and light-harvesting materials with tunable emission color upon complexation.

Amino-based covalent organic frameworks for a wide range of functional modification

A versatile protocol for modification of amino-based COFs with desired functionalities was developed via transforming the unreachable amino groups into imine, thiourea, amide and azo-based functional groups.

Additive-free selective methylation of secondary amines with formic acid over a Pd/In2O3 catalyst

Formic acid is the sole carbon and hydrogen source in the additive-free catalytic methylation of amines.

Mesoionic N-heterocyclic olefin catalysed reductive functionalization of CO2 for consecutive N-methylation of amines

A mesoionic N-heterocyclic olefin (mNHO) was introduced as a metal-free catalyst for the reductive functionalization of CO2 leading to consecutive double N-methylation of primary amines in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN). A wide range of secondary amines and primary amines were successfully methylated under mild conditions. The catalyst sustained over six successive cycles of N-methylation of secondary amines without compromising its activity, which encouraged us to check its efficacy towards double N-methylation of primary amines. Moreover, this method was utilized for the synthesis of two commercially available drug molecules. A detailed mechanistic cycle was proposed by performing a series of control reactions along with the successful characterisation of active catalytic intermediates either by single-crystal X-ray study or by NMR spectroscopic studies in association with DFT calculations.

N-Dimethylation and N-Functionalization of Amines Using Ru Nanoparticle Catalysts and Formaldehyde or Functional Aldehydes as the Carbon Source

N-methylated amines are essential bioactive compounds and have been widely used in the fine and bulk chemical industries, as well as in pharmaceuticals, agrochemicals, and dyes. Developing green, efficient, and low-cost catalysts for methylation of amines by using efficient and easily accessible methylating reagents is highly desired yet remains a significant challenge. Herein, we report the selective N-dimethylation of different functional amines with different functional aldehydes under easy-to-handle and industrially applicable conditions using carbon-supported Ru nanoparticles (Ru/C) as a heterogeneous catalyst. A broad spectrum of amines could be efficiently converted to their corresponding N,N-dimethyl amines with good compatibility of various functional groups. This method is widely applicable to N-dimethylation of primary amines including aromatic, aliphatic amines with formaldehyde, and synthesis of tertiary amines from primary, secondary amines with different functional aldehydes. The advantage of this newly described method includes operational simplicity, high turnover number, the ready availability of the catalyst, and good functional group compatibility. This Ru/C catalyzed N-dimethylation reaction possibly proceeds through a two-step N-methylation reaction process.

Silicon compounds in carbon-11 radiochemistry: present use and future perspectives

Positron emission tomography (PET) is a powerful functional imaging technique that requires the use of positron emitting nuclides. Carbon-11 (¹¹C) radionuclide has several advantages related to the ubiquity of carbon atoms in biomolecules and the conservation of pharmacological properties of the molecule upon isotopic exchange of carbon-12 with carbon-11. However, due to the short half-life of ¹¹C (20.4 minutes) and the low scale with which it is produced by the cyclotron (sub-nanomolar concentrations), quick, robust and chemospecific radiolabelling strategies are required to minimise activity loss during incorporation of the ¹¹C nuclide into the final product. To address some of the constraints of working with ¹¹C, the use of silicon-based chemistry for ¹¹C-labelling was proposed as a rapid and effective route for radiopharmaceutical production due to the broad applicability and high efficiency showed in organic chemistry. In the past years several organic chemistry methodologies have been successfully applied to ¹¹C-chemistry. In this short review, we examine silicon-based ¹¹C-chemistry, with a particular emphasis on the radiotracers that have been successfully produced and potential improvements to further expand the applicability of silicon in radiochemistry.

The use of silicon-based reagents and precursors for carbon-11 labelling has shown wide applicability and robustness with short reaction times using mild conditions. In this review, recent advances and future perspectives are examined.

Mechanism of iron complexes catalyzed in the N-formylation of amines with CO2 and H2: the superior performance of N-H ligand methylated complexes

CO2 hydrogenation into value-added chemicals not only offer an economically beneficial outlet but also help reduce the emission of greenhouse gases. Herein, the density functional theory (DFT) studies have been carried out on CO2 hydrogenation reaction for formamide production catalyzed by two different N-H ligand types of PNP iron catalysts. The results suggest that the whole mechanistic pathway has three parts: (i) precatalyst activation, (ii) hydrogenation of CO2 to generate formic acid (HCOOH), and (iii) amine thermal condensation to formamide with HCOOH. The lower turnover number (TON) of a bifunctional catalyst system in hydrogenating CO2 may attribute to the facile side-reaction between CO2 and bifunctional catalyst, which inhibits the generation of active species. Regarding the bifunctional catalyst system addressed in this work, we proposed a ligand participated mechanism due to the low pKa of the ligand N-H functional in the associated stage in the catalytic cycle. Remarkably, catalysts without the N-H ligand exhibit the significant transfer hydrogenation through the metal centered mechanism. Due to the excellent catalytic nature of the N-H ligand methylated catalyst, the N-H bond was not necessary for stabilizing the intermediate. Therefore, we confirmed that N-H ligand methylated catalysts allow for an efficient CO2 hydrogenation reaction compared to the bifunctional catalysts. Furthermore, the influence of Lewis acid and strong base on catalytic N-formylation were considered. Both significantly impact the catalytic performance. Moreover, the catalytic activity of PNMeP-based Mn, Fe and Ru complexes for CO2 hydrogenation to formamides was explored as well. The energetic span of Fe and Mn catalysts are much closer to the precious metal Ru, which indicates that such non-precious metal catalysts have potentially valuable applications.

Recent Representative Advances on the Synthesis and Reactivity of N-Heterocyclic-Carbene-Supported Zinc Complexes

The present account reviews the most recent noteworthy developments on the synthesis, structure and catalytic applications of Zn-NHC species, a class of complexes that have attracted attention over the past five to ten years due to their enhanced robustness and hydrolytic stability versus classical Zn organometallics. In particular, thanks to NHC stabilization, access to unprecedented Zn species were recently achieved, including two-coordinate Zn(II) organocations and thermally stable molecularly well-defined Zn hydride species, opening the way to effective Zn-mediated hydro-silylation/-boration catalysis of various unsaturated substrates under mild conditions. The potential of NHC-Zn species for the stabilization of unprecedented Zn species and use in various catalytic applications is only emerging and the vast array of readily available NHC structures should promote future developments of the field.

Organic Electrochemistry: Molecular Syntheses with Potential

Efficient and selective molecular syntheses are paramount to inter alia biomolecular chemistry and material sciences as well as for practitioners in chemical, agrochemical, and pharmaceutical industries. Organic electrosynthesis has undergone a considerable renaissance and has thus in recent years emerged as an increasingly viable platform for the sustainable molecular assembly. In stark contrast to early strategies by innate reactivity, electrochemistry was recently merged with modern concepts of organic synthesis, such as transition-metal-catalyzed transformations for inter alia C-H functionalization and asymmetric catalysis. Herein, we highlight the unique potential of organic electrosynthesis for sustainable synthesis and catalysis, showcasing key aspects of exceptional selectivities, the synergism with photocatalysis, or dual electrocatalysis, and novel mechanisms in metallaelectrocatalysis until February of 2021.

A Stable N-Heterocyclic Silylene with a 1,1'-Ferrocenediyl Backbone

The N-heterocyclic silylene [{Fe(η5 -C5 H4 -NDipp)2 }Si] (1DippSi, Dipp=2,6-diisopropylphenyl) shows an excellent combination of pronounced thermal stability and high reactivity towards small molecules. It reacts readily with CO2 and N2 O, respectively affording (1DippSiO2 )2 C and (1DippSiO)2 as follow-up products of the silanone 1DippSiO. Its reactions with H2 O, NH3 , and FcPH2 (Fc=ferrocenyl) furnish the respective oxidative addition products 1DippSi(H)X (X=OH, NH2 , PHFc). Its reaction with H3 BNH3 unexpectedly results in B-H, instead of N-H, bond activation, affording 1DippSi(H)(BH2 NH3 ). DFT results suggest that dramatically different mechanisms are operative for these H-X insertions.

Selective synthesis of N-monomethyl amines with primary amines and nitro compounds

The development of the selective N-monomethylation of primary amines and nitro compounds by using various methylating agents, such as MeX, carbon dioxide, methanol, formaldehyde, formic acid and dimethyl carbonate.

Immobilized Zn(OAc)2 on bipyridine-based periodic mesoporous organosilica for N-formylation of amines with CO2 and hydrosilanes

Zn(OAc)₂ immobilized on bipyridine-based periodic mesoporous organosilica is a good catalyst for N-formylation of amines with CO₂ and PhSiH₃.

C-Methylenation of anilines and indoles with CO2 and hydrosilane using a pentanuclear zinc complex catalyst

The one-step C-methylenation of anilines and indoles with CO2 and phenylsilane was catalyzed by a pentanuclear ZnII complex to give diarylmethanes via geminal C-H and C-C bond formation. It is proposed that the zinc-hydride complex generated in situ is a catalytically active species and that bis(silyl)acetal is a key intermediate. When aniline was used as a substrate, both the C-methylenation and N-methylation proceeded.

What Fluorine Can Do in CO2 Chemistry: Applications from Homogeneous to Heterogeneous Systems

CO₂ chemistry including capture and fixation has attracted great attention towards the aim of reducing the consumption of fossil fuels and CO₂ accumulation in the atmosphere. "CO₂ -philic" materials are required to achieve good performance owing to the intrinsic properties of the CO₂ molecule, that is, thermodynamic stability and kinetic inertness. In this respect, fluorinated materials have been deployed in CO₂ capture (physical and chemical pathway) or fixation (thermo- and electrocatalytic procedure) with good performances, including homogeneous (e. g., ionic liquids and small organic molecules) and heterogeneous counterparts (e. g., carbons, porous organic polymers, covalent triazine frameworks, metal-organic frameworks, and membranes). In this Minireview, these works are summarized and analyzed from the aspects of (1) the strategy used for fluorine introduction, (2) characterization of the targeted materials, (3) performance of the fluorinated systems in CO₂ chemistry, and comparison with the nonfluorinated counterparts, (4) the role of fluorinated functionalities in the working procedure, and (5) the relationship between performance and structural/electronic properties of the materials. The systematic summary in this Minireview will open new opportunities in guiding the design of "CO₂ -philic" materials and pave the way to stimulate further progress in this field.