Carbamate Complex Research Articles

Terminal dysprosium and holmium organoimides.

Terminal rare-earth-metal imide complexes TptBu,MeLn(NC6H3iPr2-2,6)(dmap) of the mid-late rare-earth elements dysprosium and holmium were synthesized via double methane elimination of Lewis acid stabilized dialkyl precursors TptBu,MeLnMe(GaMe4) with primary aniline derivative H2NC6H3iPr2-2,6 (H2NAriPr). Exploiting the weaker Ln-CH3⋯[GaMe3] interaction compared to the aluminium congener, addition of the aniline derivative leads to the mixed methyl/anilido species TptBu,MeLnMe(HNAriPr) which readily eliminate methane after being exposed to the Lewis base DMAP ([double bond, length as m-dash]N,N-dimethyl-4-aminopyridine). Under the same conditions, [AlMe3]-stabilized dimethyl rare-earth-metal complexes transform immediately to Lewis acid bridged imides TptBu,MeLn(μ2-NC6H3Me2-2,6)(μ2-Me)AlMe2 (Ln = Dy, Ho). DMAP/THF donor exchange is accomplished by treatment of TptBu,MeLn(NC6H3iPr2-2,6)(dmap) with 9-BBN in THF while the terminal imides readily insert carbon dioxide to afford carbamate complexes.

A Cavity-Shaped Gold(I) Fragment Enables CO2 Insertion into Au-OH and Au-NH Bonds.

A cavity-shaped linear gold(I) hydroxide complex acts as a platform to access unusual gold monomeric species. Notably, this sterically crowded gold fragment enables the trapping of CO2 via insertion into Au-OH and Au-NH bonds to form unprecedented monomeric gold(I) carbonate and carbamate complexes. In addition, we succeeded in the identification of the first gold(I) terminal hydride bearing a phosphine ligand. The basic nature of the Au(I)-hydroxide moiety is also explored through the reactivity toward other molecules containing acidic protons such as trifluoromethanesulfonic acid and terminal alkynes.

Enhanced sulfidation of chrysocolla with ammonium carbamate and its effect on flotation

In this study, flotation experiments, zeta potential, XPS, AFM, SEM-EDS, and contact angle measurements were performed to study the influence of ammonium carbamate (CH6N2O2) on the sulfidation flotation of chrysocolla. The results of the sulfidation flotation experiments showed that the recovery of chrysocolla increased more than 40% on the optimal condition after adding ammonium carbamate. In addition, the zeta potential of samples with ammonium carbamate was clearly higher than ores for pH > 6, which was due to the complexation reaction between ammonium carbamate and copper ion on the surface of chrysocolla samples. The activity of copper adsorption has also been improved. Furthermore, the XPS data indicated that the content of Cu-S compounds on the mineral surface has been significantly enhanced after ammonium carbamate complex sulfidation. The chemical analysis of the solution led to the same conclusion. The AFM results showed that ammonium carbamate had a positive impact on the adsorption of minerals surface, and increased the flotation recovery. It can be deduced from the SEM-EDS analysis that the surface of chrysocolla better combined with S–, and more Cu-S components were generated on the surface, which led to 1.04% increase of S atomic concentration. Finally, the contact angle measurements showed that the water contact angle of chrysocolla after adding ammonium carbamate could reach 90.4°, which proved that the sulfidation improved the floatability of the chrysocolla sample.

An Aluminium Imide as a Transfer Agent for the [NR]2- Function via Metathesis Chemistry.

The reactions of a terminal aluminium imide with a range of oxygen-containing substrates have been probed with a view to developing its use as a novel main group transfer agent for the [NR]2- fragment. We demonstrate transfer of the imide moiety to [N2 ], [CO] and [Ph(H)C] units driven thermodynamically by Al-O bond formation. N2 O reacts rapidly to generate the organoazide DippN3 (Dipp=2,6-i Pr2 C6 H3 ), while CO2 (under dilute reaction conditions) yields the corresponding isocyanate, DippNCO. Mechanistic studies, using both experimental and quantum chemical techniques, identify a carbamate complex K2 [(NON)Al-{κ2 -(N,O)-N(Dipp)CO2 }]2 (formed via [2+2] cycloaddition) as an intermediate in the formation of DippNCO, and also in an alternative reaction leading to the generation of the amino-dicarboxylate complex K2 [(NON)Al{κ2 -(O,O')-(O2 C)2 N-(Dipp)}] (via the take-up of a second equivalent of CO2 ). In the case of benzaldehyde, a similar [2+2] cycloaddition process generates the metallacyclic hemi-aminal complex, Kn [(NON)Al{κ2 -(N,O)-(N(Dipp)C(Ph)(H)O}]n . Extrusion of the imine, PhC(H)NDipp, via cyclo-reversion is disfavoured thermally, due to the high energy of the putative aluminium oxide co-product, K2 [(NON)Al(O)]2 . However, addition of CO2 allows the imine to be released, driven by the formation of the thermodynamically more stable aluminium carbonate co-product, K2 [(NON)Al(κ2 -(O,O')-CO3 )]2 .

Syntheses and ligand exchange experiments of N,N-dialkylcarbamate bridged {Al3(μ3-O)}7+ complexes

A series of N,N-dialkylcarbamate bridged {Al3(μ3-O)}7+ complexes is synthesized by targeted hydolyses of aluminum N,N-dialkylcarbamates.

Direct synthesis of cyanate anion from dinitrogen catalysed by molybdenum complexes bearing pincer-type ligand

Dinitrogen is an abundant and promising material for valuable organonitrogen compounds containing carbon–nitrogen bonds. Direct synthetic methods for preparing organonitrogen compounds from dinitrogen as a starting reagent under mild reaction conditions give insight into the sustainable production of valuable organonitrogen compounds with reduced fossil fuel consumption. Here we report the catalytic reaction for the formation of cyanate anion (NCO−) from dinitrogen under ambient reaction conditions. A molybdenum–carbamate complex bearing a pyridine-based 2,6-bis(di-tert-butylphosphinomethyl)pyridine (PNP)-pincer ligand is synthesized from the reaction of a molybdenum–nitride complex with phenyl chloroformate. The conversion between the molybdenum–carbamate complex and the molybdenum–nitride complex under ambient reaction conditions is achieved. The use of samarium diiodide (SmI2) as a reductant promotes the formation of NCO− from the molybdenum–carbamate complex as a key step. As a result, we demonstrate a synthetic cycle for NCO− from dinitrogen mediated by the molybdenum–PNP complexes in two steps. Based on this synthetic cycle, we achieve the catalytic synthesis of NCO− from dinitrogen under ambient reaction conditions.

Cover Feature: N‐Aryl and N‐Alkyl Carbamates from 1 Atmosphere of CO2 (Chem. Eur. J. 72/2021)

We have successfully isolated the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1, phen=1,10-phenanthroline), which is an intermediate in the Zn(OAc)2/phen-catalyzed synthesis of organic carbamates from CO2, amines, and Si(OMe)4. By analyzing the reaction mechanism based on the reactivity of 1 and DFT calculations, we improved the catalytic system and synthesized various organic carbamates—including polyurethane raw materials—by using CO2 at 1 atm. More information can be found in the Full Paper by J.-C. Choi et al. (DOI: 10.1002/chem.202103587).

N-Aryl and N-Alkyl Carbamates from 1 Atmosphere of CO2.

We have successfully isolated and characterized the zinc carbamate complex (phen)Zn(OAc)(OC(=O)NHPh) (1; phen=1,10-phenanthroline), formed as an intermediate during the Zn(OAc)2 /phen-catalyzed synthesis of organic carbamates from CO2 , amines, and the reusable reactant Si(OMe)4 . Density functional theory calculations revealed that the direct reaction of 1 with Si(OMe)4 proceeds via a five-coordinate silicon intermediate, forming organic carbamates. Based on these results, the catalytic system was improved by using Si(OMe)4 as the reaction solvent and additives like KOMe and KF, which promote the formation of the five-coordinated silicon species. This sustainable and effective method can be used to synthesize various N-aryl and N-alkyl carbamates, including industrially important polyurethane raw materials, starting from CO2 under atmospheric pressure.

Scandium Reduced Arene Complex: Protonation and Reaction with Azobenzene.

The reactivity of the reduced anthracene complex of scandium [Li(thf)3][Sc{N(tBu)Xy}2(anth)] (2‐anth‐Li) (Xy=3,5‐Me2C6H3; anth=C14H10 2−, thf=tetrahydrofuran) toward Brønsted acid [NEt3H][BPh4] and azobenzene is reported. While a stepwise protonation of 2‐anth‐Li with two equivalents of [NEt3H][BPh4] afforded the scandium cation [Sc{N(tBu)Xy}2(thf)2][BPh4] (3), reduction of azobenzene gave a thermolabile, anionic scandium reduced azobenzene complex [Li(thf)][Sc{N(tBu)Xy}2(η 2‐PhNNPh)] (4), which slowly lost one of the anilide ligands to form the neutral scandium azobenzene complex dimer [Sc{N(tBu)Xy}(μ‐η 2:η 2‐Ph2N2)]2 (5). Exposure of 3 to CO2 produced the scandium carbamate complex [Sc{κ2‐O2CN(tBu)(Xy)}2][BPh4] (6) as a result of CO2 insertion into the Sc−N bonds. In an attempt to prepare scandium hydrides, the reaction of 3 with the hydride sources LiAlH4 and Na[BEt3H] led to the terminal aluminum hydride [AlH{N(tBu)Xy}2(thf)] (7) and the scandium n‐butoxide [Sc{N(tBu)(Xy)}2(μ‐OnBu)] (8) after Sc/Al transmetalation and nucleophilic ring‐opening of THF, respectively. All reported compounds isolated in moderate to good yields were fully characterized.

Carbon Dioxide Activation by a Palladium Terminal Imido Complex

We recently reported the first example of a palladium(ii) terminal imido complex. We proposed that this complex features exceptional high nucleophilicity at the nitrogen atom and a peculiar zwitterionic electronic structure with an anti-bonding highest-occupied molecular orbital (HOMO). This complex swiftly activated moderately acidic CH, OH, and NH bonds and also reacted with dihydrogen. However, unambiguous nucleophilic reactivity with substrates not featuring a hydrogen atom could not be observed. Herein, we now show that this nucleophilic complex also reacts with CO2 to give a ring-strained four-membered palladium(ii) carbamate complex. Remarkably, the same product is obtained in the reaction of the related bisamido complex, albeit at a slower reaction rate. Density functional theory calculations indicate that the addition of CO2 does not proceed via initial 1,2-addition across the Pd–N bond, but instead through nucleophilic attack by the imido (amido respectively) nitrogen atom.

Preparation of silvered polyimide film from silver carbamate complex using CO₂, amine, and alcohol

Abstract Silver diethylcarbamate, used as a silver precursor, can be prepared in a halogen-free manner using inexpensive and readily available reagents such as amines, alcohols, and carbon dioxide. Using silver diethylcarbamate, flexible polyimide films with a highly conductive and reflective surface were prepared. Silver diethylcarbamate can produce uniform silver nanoparticles (NPs) by low temperature thermosetting (125 °C) without the need for a reducing agent. Further heat treatments up to 300 °C resulted in partial surface aggregation of the silver metal particles, yielding a silvered polyimide film. The reflectivity and electrical conductivity of the metallic surface were similar to those of pure silver. The metalized films also retained the characteristic mechanical properties of the polymer substrate, and appropriate thermal properties. Therefore, these films could be used over a wide temperature range for various applications

Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes

New diamagnetic nickel(II) complexes based on an unsymmetrical (1-(3-((ditert-butylphosphino)methyl)phenyl)-N,N-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by 1H, 31P{1H}, and 13C{1H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX2 (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl4 to olefins. The reaction of the hydroxo complex (8) and the amido complex (11) with CO2 produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (10). The methyl (13), phenyl (14), and p-tolylacetylide (15) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric ar...

Facile procedure for producing silver nanocoated cotton gauze and antibacterial evaluation for biomedical applications

We present a rapid, simple, convenient and cost-effective method for producing nanosized stable silver particles on cotton fibers with complete control of the silver loading level using a thermal reducing silver carbamate complex. Cotton gauze was coated with silver 2-ethylhexylcarbamate solution. Silver nanoparticles on the cotton gauze were characterized by energy dispersive X-ray spectroscopy and X-ray diffraction. Particle size and lattice image of the silver nanoparticles were studied by scanning electron microscopy. The antibacterial activity of the silver coated cotton gauze against Escherichia coli and Staphylococcus aureus, whole blood clotting and physical properties including vertical wicking test, water retention time and absorption of 0.9 % (w/v) saline were studied. Silver coated cotton gauze showed a faster blood clotting rate than the untreated cotton gauze. Cotton gauzes treated with two different silver concentrations (0.01 %, 0.1 %) showed slightly better saline absorption and they had better vertical wicking and water retention time than pristine cotton gauze.

Surface modification of polyester fibers by thermal reduction with silver carbamate complexes

In this study, the surface of polyester fiber was modified by means of thermal treatment with a silver carbamate complex. We used scanning electron microscopy (SEM), an X-ray diffraction technique (XRD), and X-ray photoelectron spectroscopy (XPS) to allow a detailed characterization of the silver-coated polyethylene terephthalate (PET) fibers. The results revealed remarkable changes in the surface morphology and microstructure of the silver film after thermal reduction. On SEM, the silver nanoparticles (AgNPs) were seen to be uniformly and densely deposited on the fiber surface. The XRD pattern of the silver-coated fiber indicated that the film has a crystalline structure. A continuous layer of AgNPs, between 30 and 100 nm in size, was assembled on the PET fibers. The PET/Ag composite was found to impart high conductivity to the fibers, with an electrical resistivity as low as 0.12 kΩ·cm.

Synthesis and Reactivity of a Mixed-Sandwich Uranium(IV) Primary Amido Complex

Facile N–H bond activation of ammonia by the “tucked-in” mixed-sandwich complex U(η-COTTIPS2)(η5:κ1-C5Me4CH2) (1; COTTIPS2 = 1,4-{SiiPr3}2C8H6) yields a rare example of a primary amido complex, U(COTTIPS2)Cp*(NH2) (2). 2 reacts with CO2 to form the carbamate complex U(COTTIPS2)Cp*(κ2-O2CNH2) (3) and may be deprotonated with KH in the presence of 18-crown-6 to form the primary imido complex [U(COTTIPS2)Cp*(NH)][K(18C6)] (4). 2 and 3 have been crystallophically characterized by X-ray diffraction.

Preparation of sintered silver nanosheets by coating technique using silver carbamate complex

This study describes a coating technique approach for large-scale preparation of sintered silver nanosheets whose lateral dimensions were controlled in the thickness range of 50–65 nm. These procedures involved coating water-soluble poly (vinyl alcohol) (PVA) and silver 2-ethylhexylcarbamate (Ag-EHC), as well as thermal reduction of a silver precursor by heating at 150 °C, followed by dissolving away the PVA layer with alcoholic water. When the silver carbamate layer on the PVA layer was heated to 150 °C, the silver carbamate layer was thermally reduced and directed to grow into uniform sintered nanosheets with aspect ratios as high as 1000. The multi-stacked PVA/Ag structures and sintered silver nanosheets were confirmed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Measurements of the conductive property at room temperature indicated that these nanosheets were electrically continuous with a resistivity of approximately 7.3 × 10−6 Ω cm.

Structurally simple complexes of CO2.

The ability to bind CO2 through the formation of low-energy, easily-broken, bonds could prove invaluable in a variety of chemical contexts. For example, weak bonds to CO2 would greatly decrease the cost of the energy-intensive sorbent-regeneration step common to most carbon capture technologies. Furthermore, exploration of this field could lead to the discovery of novel CO2 chemistry. Reduction of complexed carbon dioxide might generate chemical feedstocks for the preparation of value-added products, particularly transportation fuels or fuel precursors. Implementation on a large scale could help to drastically reduce CO2 concentrations in the atmosphere. However, literature examples of weakly bonded complexes of CO2 are relatively few and true coordination complexes to a 'naked' CO2 fragment are nearly unheard of. In this review article, a variety of complexes of CO2 featuring diverse binding modes and reactivity will be examined. Topics covered include: (A) inclusion complexes of CO2 in porous materials. (B) Zwitterionic carbamates produced from the reaction of CO2 with polyamines. (C) Carbamate salts produced from reaction of CO2 with two equivalents of an amine. (D) Insertion products of CO2 into acid-base adducts (e.g., metal complexes). (E) Lewis acid-base activated CO2, such as frustrated Lewis pair complexes. (F) Simple base-CO2 adducts, wherein the base-CO2 bond is the only interaction formed. Complexes in the last category are of particular interest, and include imidazol-2-carboxylates (N-heterocyclic carbene adducts of CO2) as well as a few other examples that lie outside NHC chemistry.

Molecular Dynamics Simulations of Proposed Intermediates in the CO2 + Aqueous Amine Reaction.

Ab initio molecular dynamics simulations of up to 210 ps have been performed on various aqueous intermediates postulated in the CO2 + amine reaction, important for CO2 capture. Observations of spontaneous deprotonation of aqueous carbamate zwitterions R1R2NHCOO(±) by bulk water (instead of additional amine, or via umbrella sampling) are reported apparently for the first time. Carbamic acid structures R1R2NCOOH were observed in some simulations, arising from zwitterions not via classical 1,3-H-shifts but via Grotthuss-style multiple-H(+) transfer pathways that involve bulk H2O and require carbamate anions R1R2NCOO(-) as an intermediate stage along the way. H(+)-bridging complexes, including not only Zundel ions [water·H(+)·water](+) but neutral carbamate complexes [carbamate(-)·H(+)·water], were observed in simulation. These results should assist efforts in improving underlying mechanisms for kinetic modeling.

Synthesis and Reactivity of Three-Coordinate (dtbpe)Rh Silylamides: CO2 Bond Cleavage by a Rhodium(I) Disilylamide

Rhodium(I) silylamide complexes supported by the 1,2-bis(di-tert-butylphosphino)ethane (dtbpe) ligand have been prepared and their structures and reactivity studied. Although the complexes degrade over time to release the corresponding silylamines, they react cleanly with silver(I) salts to transfer the amido group at ambient temperature. The bis(trimethylsilyl)amide complex (dtbpe)Rh–N(TMS)2 reacts with CO2 to form a carbamate complex that decomposes via loss of hexamethyldisiloxane to form a bis(μ-isocyanate) dimer, suggesting that silylamides may be useful nitrene-group and nitrogen-atom sources through selective N–Si bond cleavage.

Impact of water on CO2 capture by amino acid ionic liquids

The reversible capture of CO2 from fossil-fueled industries and the absorption of CO2 for natural-gas-sweetening purposes are industrial issues closely related to very important environmental, economical, and technological concerns. Biological amino acids can be used for task-specific ionic liquids for reversible CO2 capture. Several groups have reported efficient and reversible CO2 capture by such ionic liquids under rigorously dry conditions. However, we have observed that CO2 capture by amino acid ionic liquids is hugely impacted by the presence of water. In addition, the amino acid anions appear to play only a transitory role in the CO2 capture in the first minutes of exposure to a wet CO2 stream. Here, we studied the interaction of two ionic liquids—tetramethylammonium glycinate ([N1111][Gly]) and tetraethylammonium prolinate ([N2222][Pro])—with CO2 under wet conditions, by 13C-NMR. Results show that CO2 is initially captured in a carbamate form by the amine-functionalized anions of these salts. This capture mode is unambiguously confirmed by a single-crystal X-ray study of the CO2-ionic liquid complex. However, in solution, as additional CO2 is added, the carbamate releases the covalently bound CO2, and the CO2 remaining in solution shifts in form to an equilibrium mixture of carbonate and bicarbonate. Indeed, when the amount of CO2 present in the system exceeds about one-half mole per mole of ionic liquid present, the ionic liquid–carbamate complex is detected in only trace amounts, and the neutralized amino acids are readily identifiable by NMR.