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Mixing two volatile molybdenum(vi) compounds results in an eutectic which significantly lowers the melting point of the individual components, without reducing their volatility.

N-Heterocyclic carbenes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene 1a (IMes) or 1,3-bis(2,6-di-iso-propylphenyl)imidazolidene 1b (SIPr)] react with the polarized alkenes 2 and 4 to form the crystalline betaines 3a, 3b, and 5a. Furthermore, a one-pot reaction between an aldehyde, malononitrile, and an imidazolium salt of an N-heterocyclic carbene has been developed for the efficient preparation of betaine 5a without isolation of the free carbene. Full characterization data, including X-ray crystal structures, is reported for the three synthesized betaines. The structures of the betaines 3a, 3b, and 5a shed new light on the initial products formed in the reactions between N-heterocyclic carbenes and compounds containing polarized double bonds.

1,3-Dichloro-1,3-bis(dimethylamino)propenium salts react with primary amines to give different products depending on the structure of the amine. Reactions in which the primary amine is bonded to a tertiary carbon (tert-butylamine and 1-adamantylamine) result in 1,1-bis(dimethylamino)-3,3-bis(alkylamino)propenium salts which form via a 1,3-dimethylamino shift. In contrast, the reactions in which the primary amine is bonded to a secondary carbon (cyclohexylamine, cyclopentylamine, and sec-butylamine) result in 1-(ylidene)amino-1,3-bis(dimethylamino)propenium salts which form via an intramolecular hydride shift. All of the synthesized compounds have been fully characterized using spectroscopic methods, including single crystal X-ray diffraction. Finally, the mechanisms of the intramolecular rearrangements have been investigated computationally at the ωB97X-D/6-311G(d,p) level of theory, suggesting that the reactions proceed through putative keteniminium species.

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi4 chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

Nonconventional oil products (Access Western Blend [dilbit], Western Canadian Select [dilsynbit], and Synthetic Bitumen [synbit]) and a conventional crude (Heidrun) were naturally weathered on sea water under spring (April-May) and summer (July-August) conditions to improve our understanding of the effects of climatic parameters (air and water temperature, wind speed, and light intensity [solar radiation]) on their density and viscosity. The physical properties data, from each experiment, was fitted to a previously developed hyperbolic function that captured different rates of changes in densities and viscosities of the oils due to preferential weathering of the diluent portion of the diluted bitumen products. A combination of multiple correlation and regression analysis of experimental data over two seasons revealed that there were significant (p

Canadian bitumen is too viscous to transport by rail and pipeline to markets. One approach to solve this viscosity issue is to dilute the bitumen with a thinning agent to meet transport specifications, but the addition of diluent underutilizes pipeline capacity and increases production cost. A second approach involves the partial refinement of bitumen to produce synthetic crude, which better utilizes pipeline capacity; however, capital and operational costs are high. A third alternative is a new technology that involves wrapping bitumen in a polymer layer to form a solid “puck” termed Canapux, but transportation of this product to coastal ports is limited to rail. Also, greenhouse gas emissions are greater when oil is transported by rail rather than pipeline. In the end, a variety of bitumen products will be transported in Canada, but not all of these products will respond to remediation equally when spilled. In order to ensure effective spill contingency planning, we recommend that engineered bitumen products have physical properties that are resilient to change, within the range of typical response times, after a spill.

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.

Lawesson's reagent (LR) has been shown to react with the N-heterocyclic carbenes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)] to give adducts of the general form NHC·P(S)2-C6H4OCH3. Full characterizations, including X-ray crystal structures, are provided. The reaction of Woollins' reagent (WR) with IMes gave the known selanone, (IMes)Se.

The title compound was isolated as a by-product from a reaction incorporating 2,4,6-tri­methyl­benzoic acid under basic conditions., The title compound, C20H22O3, was formed in the reaction between 2,4,6-tri­methyl­benzoic acid and N,N-diiso­propyl­ethyl­amine in the presence of 1,3-di­chloro-1,3-bis­(di­methyl­amino)­propenium hydrogen dichloride, and was recrystallized from diethyl ether solution. It is the first exclusively alkyl-substituted benzoic anhydride to have been structurally characterized. The asymmetric unit consists of a half mol­ecule, the other half of which is generated by twofold rotation symmetry; the dihedral angle between the symmetry-related aromatic rings is 54.97 (3)°. The geometric parameters of the aromatic ring are typical of those for 2,4,6-tri­methyl­phenyl substituted groups. The C=O and C—O bond lengths are 1.1934 (12) and 1.3958 (11) Å, respectively, and the angle between these three atoms (O=C—O) is 121.24 (9)°. In the crystal, mol­ecules are linked by weak C—H⋯O hydrogen bonds and C—H⋯π inter­actions. The packing features wavy chains that extend parallel to [001].

The thermal decomposition of gallium nitrate hydrate, Ga(NO3)3·9H2O, was studied using visual observation, thermogravimetric analysis coupled with mass spectrometry, and X-ray crystallography. A decomposition scheme involving compounds containing the [Ga13(OH)24(OH2)24]15+ polycation, in addition to gaseous water and hydrogen nitrate, is proposed.

Over the last ten years, Professor Jason Clyburne’s research has explored many different topics, but all are linked by the themes of unusual chemistry and interesting material properties. His lab is situated at Saint Mary’s University in Halifax, Nova Scotia, and he is the chair of Environmental Science with a cross-appointment in chemistry. Students often drop by to chat, and this review is an example of the type of discussion that occurs when he is trying to recruit them into his group. It is written in the form of a discussion between myself, a B.Sc. student, and Professor Clyburne, and it focuses on his interests in synthetic main group and materials chemistry. The general discussion includes asides and references to other work, to provide context. 1 Introduction 2 N-Heterocyclic Carbenes 3 Ionic Liquids 4 Reactions in Ionic Liquids 5 CO2 Capture with Ionic Liquids 6 Halide and Pseudo-Halide Adducts of CO2 7 Chemical Capture of CO2 8 Conclusion and Closing Remarks

This study examines the use of chemical dispersant to treat an oil spill after the initial release. The natural and chemically enhanced dispersion of four oil products (dilbit, dilynbit, synbit and conventional crude) were investigated in a wave tank. Experiments were conducted in spring and summer to capture the impact of temperature, and the conditions in the tank were of breaking waves with a wave height of 0.4 m. The results showed that natural dispersion effectiveness (DE) was less than 10%. But the application of dispersant increased the DE by an order of magnitude with a statistically significant level (p &lt, 0.05). Season (spring versus summer) had an effect on chemical DE of all oils, except for the conventional oil. Thus, the DE of dilbit products is highly dependent on the season/temperature. A model was fitted to the DE as a function of oil viscosity for the chemically dispersed oil, and the correlation was found to be very good. The model was then combined with a previous model compiled by the author predicting oil viscosity as a function of time, to produce a model that predicts the DE as function of time. Such a relation could be used for responders tackling oil spills.

In this paper we describe the synthesis, characterization, and X-ray crystal structures of two ligands, diethyl-N,N'-bis(p-tolyl)malonimidate and 1,3-bis(dimethylamino)-N,N'-bis(p-tolyl)propanediimidate. Their corresponding rhodium(i) dicarbonyl, dimethylaluminium, and bis-ligated zinc complexes have also been prepared and characterized. The donor properties of the ligands have been studied and have been compared to those of the traditional anionic N,N'-chelating ligand nacnac.

Lawesson's reagent (LR) has been shown to react with the N-heterocyclic carbenes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)] to give adducts of the general form NHC·P(S)2-C6H4OCH3. Full characterizations, including X-ray crystal structures, are provided. The reaction of Woollins' reagent (WR) with IMes gave the known selanone, (IMes)Se.

Global demand for petroleum keeps increasing while traditional supplies decline. One alternative to the use of conventional crude oils is the utilization of Canadian bitumen. Raw bitumen is a dense, viscous, semi-liquid that is diluted with lighter crude oil to permit its transport through pipelines to terminals where it can then be shipped to global markets. When spilled, it naturally weathers to its original form and becomes dense enough to sink in aquatic systems. This severely limits oil spill recovery and remediation options. Here we report on the application of charred hay as a method for modifying the surface behavior of bitumen in aquatic environments. Waste or surplus hay is abundant in North America. Its surface can easily be modified through charring and/or chemical treatment. We have characterized the modified and charred hay using solid-state NMR, contact angle measurements and infrared spectroscopy. Tests of these materials to treat spilled bitumen in model aquatic systems have been undertaken. Our results indicate that bitumen spills on water will retain their buoyancy for longer periods after treatment with charred hay, or charred hay coated with calcium oxide, improving recovery options.

The development of effective CO2 capture technologies with low environmental impacts has been the focus of much recent research. Additionally, consideration is being given as to how CO2 sorbent systems may be applied to small-scale CO2 capture. After developing a useful CO2 capture system using the simple amine diethylenetriamine (DETA), we decided to investigate how the nitrate salt of DETA, [DETAH]NO3, with a reported high affinity for CO2 and exhibiting many of the ideal characteristics of an ionic liquid, would compare to DETA in terms of its performance as a CO2 sorbent. As a first step, [DETAH]NO3 was prepared and characterized using X-ray crystallography. For the CO2 capture studies, polyethylene glycol (PEG 200) was chosen as the solvent because of its nonreactivity toward the sorbent and CO2 as well as its low volatility and toxicity. Solutions of both DETA and [DETAH]NO3 in PEG 200 were found to perform optimally at a concentration of roughly 10% (v/v). [DETAH]NO3 proved slightly better for CO2 ...

Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4 N]HCO3 . The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2 . Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4 N]O2 CCH3 and therefore not representative of the bulk powder from the synthesis.

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs. peerReviewed

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.

Canada's production, transport, and sale of diluted bitumen (dilbit) products are expected to increase by a million barrels per day over the next decade. The anticipated growth in oil production and transport increases the risk of oil spills in aquatic areas and places greater demands on oil spill capabilities to respond to spills, which have raised stakeholder concerns. Current oil spill models only predict the transport of bitumen blends that are used in contingency plans and oil spill response strategies, rather than changes in the oil's physical properties that are relevant to spill response. We conducted weathering studies of five oil products (two conventional oils and three bitumen blends) in the Department of Fisheries and Oceans' flume tank. We also considered two initial oil slick thicknesses, 4.0 mm and 7.0 mm. We found that there is a major difference in the time evolution of oil properties (density and viscosity), raising doubts on weathering models that do not consider the thickness of oil. We also developed empirical expressions for the evolution of the density and viscosity of these oil products. The findings from the 4.0 mm results were incorporated with data from the literature to provide an update on the factors to consider during the decision making for spills of diluted bitumen products. The matrix indicated that most response options, including chemical dispersants, work much more effectively within 48 hours of the initiation of weathering. After this window of opportunity closes, natural attenuation or in situ burning is the only option remaining, but containment of oil is a limiting factor for in situ burning.

We report on the synthesis and structural features of NMe2-modified β-diketiminate-supported boron difluoride compounds (LArBF2: LAr=[HC(NAr)2(CNMe2)2]–; LPh: Ar=Ph; LTol: Ar=p-tolyl; LXyl: Ar=m-xylyl). The title compounds were prepared in moderate yields (~65%) by insitu deprotonation of the corresponding ligands LArH using KH, followed by the addition of BF3OEt2. According to solid-state and theoretical analyses of the BF2 compounds, the lone pair at each NMe2 group is involved in electron delocalization within the central BC3N2 ring. As a result, the N-aryl substituents sterically clash with the NMe2 groups, causing this central ring to pucker. Several attempts were made to prepare heavy analogues (e.g. LArBX2, X=Cl, Br, I) but only unidentifiable product mixtures were observed. It appears that the observed steric clash between the N-aryl substituents and the NMe2 groups prevented the formation of these heavy analogues.

Cyanide Hitches a Ride Cyanide is a by-product of the biosynthesis of ethylene in plants and it has been somewhat puzzling how the ion is safely removed before it can shut down enzymatic pathways by coordination to catalytic iron centers. A proposed mechanism has implicated the cyanoformate ion—essentially, a weak adduct of cyanide and carbon dioxide—as the initial product, although its lifetime was uncertain. Murphy et al. (p. 75 ; see the Perspective by Alabugin and Mohamed ) crystallized this previously elusive adduct and found that its solution-phase stability varies inversely with the dielectric properties of the medium. The results bolster a picture in which the adduct shuttles the cyanide away from the hydrophobic confines of the enzyme before releasing the cyanide into the more polar aqueous surroundings.

The reactivity of ketenylidenetriphenylphosphorane (1) with the protic reagents 2,4,6-trimethylphenol (7), 2,6-di-tert-butyl-4-methylphenol (8), and diphenylamine (9) has been explored. Three novel carbonyl-stabilized ylides have been synthesized and characterized. Crystal structures were obtained for Ph3PCHC(O)O(C6H2Me3) (11), Ph3PCHC(O)O(C6H2t-Bu2Me) (12), and Ph3PCHC(O)NPh2 (13), respectively. These products were then methylated in an attempt to develop a new route to low-valent carbon compounds. Crystals of [Ph3PCH(CH3)C(O)O(C6H2Me3)]I (14) were isolated and characterized but this route did not prove to be synthetically useful, at least toward the goal of preparing low-valent carbon-centered materials. Finally, 1 was also reacted with the bulky tin reagent, bis[bis(trimethylsilyl)amido]tin(II), in the presence of 2,4,6-trimethylphenol. A complex mixture of products was obtained, from which crystals of an unusual chelated tin compound (15) were isolated and characterized using X-ray crystallog...

We have performed a survey of carbon dioxide capture in phosphonium-based ionic liquids and end-capped polyethylene glycol using DETA (DETA = diethylenetriamine) as a model absorbent. The carbon dioxide adduct of DETA is zwitterionic and forms readily in both ionic and polymeric media. Crystals of the adduct have been isolated, and its X-ray crystal structure is reported. The adduct is hygroscopic and decomposes with heating, with the onset of decomposition occurring at ∼85 °C. Computational studies were performed examining possible structures for the adducts formed between DETA and CO2 in the gas phase. Also described is a study of the thermal stability of phosphonium ionic liquids and selected polymeric solvents under neutral and oxidizing conditions. Heat capacity measurements were also performed on a number of ionic liquids.

The organometallic dianions diethyltetrachlorodizincate, [Et(Cl)Zn(μ-Cl)2Zn(Cl)Et], and ethyltribromozincate, [EtZnBr3], have been isolated from reaction mixtures containing diethylzinc and a tetra...

A carbene transfer agent, 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene-silver(I)chloride ([IMes]AgCl), was treated with various osmium clusters. Reaction of ([IMes]AgCl) with [Os3(μ-H)2(CO)10] gave [Os3(μ-H)(μ-Cl)(CO)9(IMes)] (1), an osmium N-heterocyclic carbene complex. The reaction of ([IMes]AgCl) with the cluster [Os3(CO)10(CH3CN)2] yielded two products, [Os3(μ-Cl)(CO)10(μ-Ag(IMes)] (2) and [(IMes-H)][Os3(μ-Cl)(CO)10](μ4-Ag)[Os3(μ-Cl)(CO)10] (3). Compound (2) is a heterobimetallic carbene complex resulting from the complete incorporation of ([IMes]AgCl). Transmetalation using [(IMes)AgCl] and the cluster [Os4(μ-H)4(CO)12] in the presence of trimethylamine-N-oxide resulted in the formation of [Os4(μ-H)4(CO)11(n·IMes)] (4), where (n denotes normal carbene bonding, i.e., through C2). [Os4(μ-H)4(CO)10(IMes)2] (5) was formed using the activated cluster [Os4(μ-H)4(CO)10(CH3CN)2] and [(IMes)AgCl]. Compound (5) was found to be sensitive to silica gel column chromatography in the presence of dichlorometha...

Phosphonium ionic liquids (PhosILs), most notably tetradecyl(trihexyl)phosphonium decanoate (PhosIL-C(9)H(1)9COO), are solvents for bases such as Grignard reagents, isocyanides, Wittig reagents (phosphoranes), and N-heterocyclic carbenes (NHCs). The stability of the organometallic species in PhosIL solution is anion dependent. Small bases, such as hydroxide, react with the phosphonium ions and promote C-H exchange as suggested by deuterium-labeling studies. A method to dry and purify the ionic liquids is described and this step is important for the successful use of basic reagents in PhosIL. NHCs have been generated in PhosIL, and these persistent solutions catalyze organic transformations such as the benzoin condensation and the Kumada-Corriu cross-coupling reaction. Phosphoranes were generated in PhosIL, and their reactivity with various organic reagents was also tested. Inter-ion contacts involving tetraalkylphosphonium ions have been assessed, and the crystal structure of [(n-C(4)H(90)(4)P][CH(3)CO(2).CH(3)CO(2)H] has been determined to aid the discussion. Decomposition of organometallic compounds may also proceed through electron-transfer processes that, inter alia, may lead to decomposition of the IL, and hence the electrochemistry of some representative phosphonium and imidazolium ions has been studied. A radical derived from the electrochemical reduction of an imidazolium ion has been characterized by electron paramagnetic resonance spectroscopy.

The bulky m-terphenyl phenol Ar*OH 1 (Ar* = C6H3-2,6-Mes2, Mes = 2,4,6-trimethylphenyl) was synthesized via the treatment of Ar*Li with nitrobenzene. The phenol 1 is prepared in modest to good yield using this method. Attempts were also made to prepare 1 through oxidation of the bulky boronic acid Ar*B(OH)2with Oxone®, but this reaction was not suitable for preparative-scale reactions. Side products of the reaction between Ar*Li and nitrobenzene were identified as Ar*[N(O)Ph] and [C6H5N(O)]2and were characterized by X-ray crystallography and EPR spectroscopy. A variety of main-group and transition-metal complexes of Ar*OH were prepared, namely Sn(OAr*)2, Ge(OAr*)2, [N(SiMe3)2]Ge(OAr*), [Me2Al(OAr*)]2, and Ti(NMe2)(OAr*)2. All compounds were characterized spectroscopically and most were studied by single-crystal X-ray diffraction as well.Key words: m-terphenyl, main-group compounds, X-ray crystallography, multinuclear NMR spectroscopy, EPR spectroscopy.

The osmium cluster [Os4(μ-H)4(CO)11(IMes)] (1·nIMes) was prepared by treatment of IMesAgCl with [Os4(μ-H)4(CO)12]. The product of this reaction is believed to be the first tetranuclear NHC cluster compound. Thermolysis of this complex in benzene at reflux resulted in exhaustive dehydrogenation of an o-methyl group on IMes, partial dehydrogenation of benzene, and subsequent coupling of the two unsaturated fragments to produce 2. The abnormal NHC complex (1·aIMes) was also isolated. All compounds were characterized by spectroscopic studies and confirmed by X-ray crystallography.

The P,P-chelated heteroleptic complex bis[bis(diisopropylphosphino)amido]indium chloride [(i-Pr2P)2N]2InCl was prepared in high yield by treating InCl3 with 2 equiv of (i-Pr2P)2NLi in Et2O/tetrahydrofuran solution. Samples of [(i-Pr2P)2N]2InCl in a pentane slurry, a CH2Cl2 solution, or in the solid state were exposed to CO2, resulting in the insertion of CO2 into two of the four M-P bonds to produce [O2CP(i-Pr2)NP(i-Pr2)]2InCl in each case. Compounds were characterized by multinuclear NMR and IR spectroscopy, as well as single-crystal X-ray diffraction. ReactIR solution studies show that the reaction is complete in less than 1 min at room temperature in solution and in less than 2 h in the solid-gas reaction. The CO2 complex is stable up to at least 60 °C under vacuum, but the starting material is regenerated with concomitant loss of carbon dioxide upon heating above 75 °C. The compound [(i-Pr2P)2N]2InCl also reacts with CS2 to give a complicated mixture of products, one of which was identified as the CS2 cleavage product [S═P(i-Pr2)NP(i-Pr2)]2InCl]2(μ-Cl)[μ-(i-Pr2P)2N)].

RADMAP, an open source program, allows for rapid analysis and visualization of the earliest stages of reactions between any molecule and a monoatomic probe (i.e., H*, H(+), H(-), Br*, or any other monoatomic species) using ab initio methods. This program creates non-planar potential energy surfaces of the initial interaction between a molecule of interest and the monoatomic probe. These surfaces can be used to both predict the site of addition as well as provide a qualitative estimate for the relative proportion of the formation of adducts; therefore, it gives insight into both the reactivity and the kinetic stability of a molecule. The program presents a way to quickly predict the number of signals anticipated in transverse field muon spin resonance spectra as well as their relative intensities.

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.

A series of N-heterocyclic carbene (NHC)AgCl complexes [NHC = SIMes (1), IPr (2), SIPr (3), IPrMe (4), IMe (5), ICy (6), IAd (7), IsB (8), IDD (9), and TPh (10)] have been synthesized through reaction of the imidazolium chloride salts with Ag2O or by direct metalation of the corresponding imidazol-2-ylidene carbene in the presence of AgCl. All silver(I) complexes [(SIMes)AgCl] (11), [(IPr)AgCl] (12), [(SIPr)AgCl] (13), [(IPrMe)AgCl] (14), [(IMe)AgCl] (15), [(ICy)AgCl] (16), [(IAd)AgCl] (17), [(IsB)AgCl] (18), [(IDD)AgCl] (19), and [(TPh)AgCl] (20) have been spectroscopically and structurally characterized. The structure of these silver complexes is dependent on the halide and the solvent used for the synthesis. Adjusting these parameters has led to the previously reported complex, [(IMes)2Ag]+[AgCl2]- (21), and to a new silver complex, [(IMes)2Ag]+2[Ag4I6]2- (22).

Co-crystallisation of octafluoronaphthalene (OFN) with trans-stilbene or trans-azobenzene from solutions yielded 1:1 molecular complexes, shown by single-crystal X-ray diffraction to contain infinite stacks of near-parallel and planar, alternating OFN and trans-stilbene or trans-azobenzene molecules.

Bis(di-i-propylphosphino)amine 1 reacts with B(C6F5)3 to form an adduct with concomitant N/P H-isomerization. This species reacts smoothly with carbon dioxide. An attempt to prepare an anionic derivative resulted in the formation of a novel heterocycle derived from the PNP ligand and B(C6F5)3.

2,4,6-Triphenylbenzaldehyde 1 undergoes a condensation reaction with 2-aminophenol to give N-(2′,4′,6′-triphenylbenzylidene)-2-iminophenol (TPIP) 2. The imine 2 can be reduced with NaBH4 in ethanol to form N-(2′,4′,6′-triphenylbenzyl)-2-aminophenol (TPAP) 3. Addition of trimethylaluminum to 2 or 3 results in the formation of the complexes TPIP-AlMe2·AlMe3 (4) or TPAP-AlMe2 (5). Compounds 2, 3, and 4 have been crystallographically characterized.Key words: N,O ligands, aluminum, m-terphenyl, Schiff bases, X-ray crystallography.

The reaction of trimethylaluminum with 2,4,6-triphenylbenzoic acid and the isoelectronic fluoren-9-one phenylhydrazone results in the formation of the dialkylaluminum complexes [(CH3)2Al{μ-O2CPh(Ph3)}]2 (4) and [Me2AlN(C6H5)NC13H8]2 (5). The synthesis of these complexes, as well as their spectroscopic and structural characterization are reported. X-ray crystallographic studies show that the carboxylato complex 4 adopts a dimeric structure containing an 8-membered O–Al–O–C core whereas the hydrazonato complex 5 likewise is dimeric in the solid state, but exhibits a 6-membered N–Al–N heterocyclic ring.

Hydrogen bonds are weak directional forces that are evident in a large number of chemical systems. Although they have been studied for over a century, the range of donor-acceptor pairs continues to be extended. Recently, isolable N-heterocyclic carbenes have been prepared and these molecules provide a novel route into a number of unusual hydrogen bonds. Here we briefly review structural studies on these interactions.

Pyridine, when allowed to react with chromic anhydride under strictly anhydrous conditions, gives the known, very air-sensitive, crystalline 2:1 Lewis acid–base complex 1. The crystal structure has now been successfully determined. When benzimidazole and three 2-alkyl-1H-benzimidazoles were treated with chromium trioxide in aqueous acetic acid, crystalline dichromate salts (2–5) were readily formed. These salts consist of dichromate anions linked to the cations by hydrogen bonds of the type N—H···O. The chromium atoms have distorted tetrahedral environments, with the Cr—O distances being typical for dichromate anions. In the cases of the 2-methyl and 2-ethyl salts, the anions are disordered about a centre of inversion. The hydrogen bonding arrangements are discussed and the structures are compared with other oxygenated chromium(VI) species. The dichromate salts are useful selective oxidants for a range of primary and secondary alcohols; examples of these reactions are reported.Key words: chromium(VI), pyridine – chromium trioxide complex, benzimidazolinium dichromate salts, controlled oxidation of alcohols.

Crystallographic studies of 2,6-bis(2,4,6-trimethylphenyl)-4-methyliodobenzene 1 and 2,6-diphenyl-4-methyliodobenzene 2 were performed and in both cases [CH3···I] interactions were identified. Theoretical calculation of the dipole moment of 1 and the partial charges of the iodine and methyl hydrogens were performed. These charges, although small, suggest that they are large enough to encourage the formation of weak dipole-dipole interactions in the absence of other stabilizing forces