Anthony F. Masters

Ionic‐Liquid‐Mediated Active‐Site Control of MoS2 for the Electrocatalytic Hydrogen Evolution Reaction

The layered crystal MoS(2) has been proposed as an alternative to noble metals as the electrocatalyst for the hydrogen evolution reaction (HER). However, the activity of this catalyst is limited by the number of available edge sites. It was previously shown that, by using an imidazolium ionic liquid as synthesis medium, nanometre-size crystal layers of MoS(2) can be prepared which exhibit a very high number of active edge sites as well as a de-layered morphology, both of which contribute to HER electrocatalytic activity. Herein, it is examined how to control these features synthetically by using a range of ionic liquids as synthesis media. Non-coordinating ILs with a planar heterocyclic cation produced MoS(2) with the de-layered morphology, which was subsequently shown to be highly advantageous for HER electrocatalytic activity. The results furthermore suggest that the crystallinity, and in turn the catalytic activity, of the MoS(2) layers can be improved by employing an IL with specific solvation properties. These results provide the basis for a synthetic strategy for increasing the HER electrocatalytic activity of MoS(2) by tuning its crystal properties, and thus improving its potential for use in hydrogen production technologies.

Structural features of ionic liquids: consequences for material preparation and organic reactivity

Ionic liquids have been proposed as functional replacements for harmful and hazardous volatile organic solvents. However, limiting their use in this way does not fully explore the potential chemical benefits of their solvating properties, which stem from the inherent differences between ionic liquids and single molecule solvents. These differences can be used to facilitate alternative and improved reaction outcomes. This review will highlight a range of examples, involving materials preparation and organic synthesis, in which substantial progress towards the understanding and targeted application of ionic liquids is demonstrated. In addition, a number of studies will be cited where unanticipated outcomes have been observed and the relationships between these outcomes and ionic liquid structural effects will be analysed, casting new light onto these studies.

Models of surface-confined metallocene derivatives

Abstract The silsesquioxane [((C6H11)7Si7O9)(OH)3] (LH3) was reacted with [M(C5H5)2Cl2] (M = Ti, Zr, Hf) and with [Ti(C5H5)Cl3]. The reaction with [Ti(C5H5)Cl3] produced [Ti(C5H5)L], whereas the reaction with [Ti(C5H5)2Cl2] produced a mixture of [Ti(C5H5)L]n. (n = 1, 2) as determined by NMR spectroscopy. Only [Ti(C5H5)L] could be isolated from the mixture. The reaction with [M(C5H5)2Cl2] (M = Zr, Hf) produced oligomeric species which contained no cyclopentadienyl ligands and which were formulated as containing trimeric [M3L4Cl]− anions on the basis of analytical and spectroscopic data.

The chemistry of cobalt acetate—IV. The isolation and crystal structure of the symmetric cubane, tetrakis[(μ-acetato)(μ3-oxo) (pyridine)cobalt(III)] · chloroform solvate, [Co4(μ3-O)4(μ-CH3CO2)4(C5H5N)in4] · 5CHCl3 and of the dicationic partial cubane, trimeric, [(μ-acetato)(acetato)tris(μ-hdyroxy(μ3-oxo) hexakispyridinetricobalt(III)]hexafluorophosphate · water solvate, [Co3(μ3-O)(μ-OH)3(μ-CH3CO2(CH3CO2(C5H5N)6[PF6]2 · 2H2O

Abstract The isolation from “cobalt(III) acetate” and characterisation by single crystal X-ray diffraction (refined to R = 0.087, Rw = 0.084) of the symmetric neutral cubane, [Co4(μ3-O)4(μ-CH3CO2)4(C5H5N)4], and of the hexafluorophosphate salt (refined to R = 0.078, Rw = 0.073) of the trimeric dication, the partial cubane, [Co3(μ3-OH)3(μ-CH3CO2)(CH3CO2(C5H5N)6]2+, are reported. The cubane crystallises as its chloroform solvate, [Co4(μ3-O)4(μ-CH3CO2)4(C5H5N)4] · 5CHCl3, whilst the partial cubane crystallises as its water solvate, [Co3(μ3-O)(μ-OH)3(μ-CH3CO2)(CH3CO2)(C5H5N)6][PF6]2 · 2H2O. The cubane and partial cubane dication have average Co ··· Co distances of 2.818(8), 2.683(6) and 2.918(6), 2.767(5) A, respectively, and average Co—μ3-O distances of 1.86 and 1.91 A, respectively.

Synthesis of a CrCoAPO-5(AFI) Molecular Sieve and Its Activity in Cyclohexane Oxidation in the Liquid Phase

A new CrCoAPO-5 was synthesized under hydrothermal conditions, characterised by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, energy dispersive X-ray analysis, thermogravimetric analysis, electron paramagnetic resonance and nitrogen physisorption. The CrCoAPO-5 showed catalytic activity in the liquid phase oxidation of cyclohexane at 115°C and 1 MPa of oxygen.

The Formation of High‐Order Polybromides in a Room‐Temperature Ionic Liquid: From Monoanions ([Br5]− to [Br11]−) to the Isolation of [PC16H36]2[Br24] as Determined by van der Waals Bonding Radii

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

Controlling Hydrolysis Reaction Rates with Binary Ionic Liquid Mixtures by Tuning Hydrogen-Bonding Interactions

The ability of a binary ionic liquid (IL) system consisting of a phosphonium transition state analogue (TSA) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf(2)]) to accelerate the rate of the well-studied hydrolysis of a tert-alkyl picolinium salt by influencing the solvent structure was investigated. A significant rate enhancement was observed in the presence of the TSA; however, comparison with other cations illustrated that this enhancement was not unique to the chosen TSA. Instead, the rate enhancements were correlated with the dilution of hydrogen bonding by the added cations. This phenomenon was further examined by the use of 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ([BMMIM][NTf(2)]) as a cosolvent and the use of Reichardts dye to measure the extent of hydrogen bonding on solutes in these systems. The rate increases are rationalized in terms of weaker hydrogen bonding from the solvent system to water.

The chemistry of cobalt acetate—III. The isolation and crystal structure characterisation of the mixed valence octacobalt oligomer, [Co8(O)4(CH3CO2)6(OMe)4]Cl4(OHn)4 · 6H2O (n = 1 or 2), derived from the preparation of cobalt(III) acetate

Abstract The mixed valence octacobalt oligomer, [Co 8 (O) 4 (CH 3 CO 2 ) 6 (OMe) 4 Cl 4 (OH n ) 4 ] ( n = 1 or 2), in which the Co 8 O 8 core defines a helical array of three condensed, face-sharing Co 4 O 4 cubanes, was isolated during the recrystallisation of crude “[Co(OAc) 3 ]” from methanol/dichloromethane/diethyl ether and its crystal structure determined.

Photocatalytic Hydrogen Evolution from Silica‐Templated Polymeric Graphitic Carbon Nitride–Is the Surface Area Important?

Low‐surface‐area, mesoporous silica‐templated polymeric graphitic carbon nitride (SBA–g‐C3N4), when irradiated with visible light, exhibits a greatly improved photocatalytic hydrogen evolution rate as compared to that of conventional bulk g‐C3N4 synthesized directly from the condensation of dicyandiamide. It also performs very similarly to high‐surface‐area mesoporous g‐C3N4 on a per‐unit mass basis. However, on the per‐unit area basis it greatly outperforms the other materials. The intrinsically high surface activity of SBA–g‐C3N4 was confirmed by using two different co‐catalysts, in situ photodeposited Pt and a structurally well‐defined molecular cobaloxime. Instead of the magnitude of the surface area as the dominant feature that determines activity, it was established that the high activity of SBA–g‐C3N4 results from a much higher number of delocalized electrons present and a suppressed recombination probability of photogenerated electron–hole pairs.

Reactions of p-coumaryl alcohol model compounds with dimethyl carbonate. Towards the upgrading of lignin building blocks

Cinnamyl alcohol 1 and 4-(3-hydroxypropyl)phenol 2, two compounds resembling the lignin building block p-coumaryl alcohol, can be selectively transformed into different products by catalytic methodologies based on dimethyl carbonate (DMC) as a green solvent/reagent. Selectivity can be tuned as a function of the reaction temperature and of the nature of the catalyst. Basic catalysts such as K2CO3, trioctylmethylphosphonium methylcarbonate ([P8881][CH3OCOO]), and CsF/αAl2O3 promote selective transesterification of the aliphatic hydroxyl group at 90 °C. However, amphoteric solids such as alkali metal-exchanged faujasites, NaX and NaY, selectively yield the corresponding alkyl ethers at higher temperatures (165–180 °C). The phenolic hydroxyl group of 2 can be methylated similarly with the faujasites at high temperatures. This preliminary screening for selectivity illustrates reactivity trends and delineates some of what might be among the most promising synthetic pathways to upgrade lignin-derived chemical building blocks.