Acyclic Boryl Complexes of Copper(I).

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH2 }2 CH2 , Dipp=2,6-iPr2 C6 H3 ) with B2 (OMe)4 provided access to (6-Dipp)CuB(OMe)2 via σ-bond metathesis. (6-Dipp)CuB(OMe)2 was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2 (OMe)4 . Alongside π-insertion, (6-Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe2 , a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin.

Optimised graphite/carbon black loading of recycled PLA for the production of low-cost conductive filament and its application to the detection of ß-estradiol in environmental samples.

The production, optimisation, physicochemical, and electroanalytical characterisation of a low-cost electrically conductive additive manufacturing filament made with recycled poly(lactic acid) (rPLA), castor oil, carbon black, and graphite (CB-G/PLA) is reported. Through optimising the carbon black and graphite loading, the best ratio for conductivity, low material cost, and printability was found to be 60% carbon black to 40% graphite. The maximum composition within the rPLA with 10 wt% castor oil was found to be an overall nanocarbon loading of 35 wt% which produced a price of less than £0.01 per electrode whilst still offering excellent low-temperature flexibility and reproducible printing. The additive manufactured electrodes produced from this filament offered excellent electrochemical performance, with a heterogeneous electron (charge) transfer rate constant, k0 calculated to be (2.6 ± 0.1) × 10-3 cm s-1 compared to (0.46 ± 0.03) × 10-3 cm s-1 for the commercial PLA benchmark. The additive manufactured electrodes were applied to the determination of ß-estradiol, achieving a sensitivity of 400 nA µM-1, a limit of quantification of 70 nM, and a limit of detection of 21 nM, which compared excellently to other reports in the literature. The system was then applied to the detection of ß-estradiol within four real water samples, including tap, bottled, river, and lake water, where recoveries between 95 and 109% were obtained. Due to the ability to create high-performance filament at a low material cost (£0.06 per gram) and through the use of more sustainable materials such as recycled polymers, bio-based plasticisers, and naturally occurring graphite, additive manufacturing will have a permanent place within the electroanalysis arsenal in the future.

Exploring the Role of the Connection Length of Screen-Printed Electrodes towards the Hydrogen and Oxygen Evolution Reactions.

Zero-emission hydrogen and oxygen production are critical for the UK to reach net-zero greenhouse gasses by 2050. Electrochemical techniques such as water splitting (electrolysis) coupled with renewables energy can provide a unique approach to achieving zero emissions. Many studies exploring electrocatalysts need to "electrically wire" to their material to measure their performance, which usually involves immobilization upon a solid electrode. We demonstrate that significant differences in the calculated onset potential for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be observed when using screen-printed electrodes (SPEs) of differing connection lengths which are immobilized with a range of electrocatalysts. This can lead to false improvements in the reported performance of different electrocatalysts and poor comparisons between the literature. Through the use of electrochemical impedance spectroscopy, uncompensated ohmic resistance can be overcome providing more accurate Tafel analysis.

Reduction of Na+ within a {Mg2 Na2 } Assembly.

Ionic compounds containing sodium cations are notable for their stability and resistance to redox reactivity unless highly reducing electrical potentials are applied. Here we report that treatment of a low oxidation state {Mg2 Na2 } species with non-reducible organic bases induces the spontaneous and completely selective extrusion of sodium metal and oxidation of the MgI centers to the more conventional MgII state. Although these processes are also characterized by a structural reorganisation of the initially chelated diamide spectator ligand, computational quantum chemical studies indicate that intramolecular electron transfer is abetted by the frontier molecular orbitals (HOMO/LUMO) of the {Mg2 Na2 } ensemble, which arise exclusively from the 3s valence atomic orbitals of the constituent sodium and magnesium atoms.

Experimental and Computational Studies on the Acetate-Assisted C-H Activation of N-Aryl Imidazolium Salts at Rhodium and Iridium: A Chloride Additive Changes the Selectivity of C-H Activation.

Combined experimental and computational mechanistic studies of the reactions of unsymmetrical, para-substituted N-aryl imidazolium salts, L2-R1,R2, at [MCl2Cp*]2 (M = Rh, Ir) in the presence of NaOAc are reported. These proceed via intermediate N-heterocyclic carbene complexes that then allow an internal competition between two differently substituted aryl rings toward C-H activation to be monitored. At 348 K in dichloroethane C-H activation of the aryl with the more electron-withdrawing substituents is generally favored. DFT calculations show similar barriers for proton transfer and dissociative HOAc/Cl- ligand substitution, with proton transfer favoring electron-donating substituents, and ligand substitution favoring electron-withdrawing substituents. Microkinetic simulations reproduce the experimental preference implying that the ligand substitution step dominates selectivity. For several substrates, notably L2-F,OMe and L2-F,H, running the C-H activation reactions at 298 K in the presence of added [Et4N]Cl reverses the selectivity. The greater availability of chloride in solution makes an alternative dissociative interchange ligand substitution mechanism accessible, leaving proton transfer as selectivity determining and so favoring electron-donating substituents. Our results highlight the potential importance of the ligand substitution step in the interpretation of substituent effects and demonstrate how a simple additive, [Et4N]Cl, can have a dramatic effect on selectivity by changing the mechanism of ligand substitution.

2D-Hexagonal Boron Nitride Screen-Printed Bulk-Modified Electrochemical Platforms Explored towards Oxygen Reduction Reactions.

A low-cost, scalable and reproducible approach for the mass production of screen-printed electrode (SPE) platforms that have varying percentage mass incorporations of 2D hexagonal boron nitride (2D-hBN) (2D-hBN/SPEs) is demonstrated herein. These novel 2D-hBN/SPEs are explored as a potential metal-free electrocatalysts towards oxygen reduction reactions (ORRs) within acidic media where their performance is evaluated. A 5% mass incorporation of 2D-hBN into the SPEs resulted in the most beneficial ORR catalysis, reducing the ORR onset potential by ca. 200 mV in comparison to bare/unmodified SPEs. Furthermore, an increase in the achievable current of 83% is also exhibited upon the utilisation of a 2D-hBN/SPE in comparison to its unmodified equivalent. The screen-printed fabrication approach replaces the less-reproducible and time-consuming drop-casting technique of 2D-hBN and provides an alternative approach for the large-scale manufacture of novel electrode platforms that can be utilised in a variety of applications.

Potassium Aluminyl Promoted Carbonylation of Ethene.

The potassium aluminyl [K{Al(NONDipp )}]2 ([NONDipp ]2- =[O{SiMe2 NDipp}2 ]2- , Dipp=2,6-iPr2 C6 H3 ) activates ethene towards carbonylation with CO under mild conditions. An isolated bis-aluminacyclopropane compound reacted with CO via carbonylation of an Al-C bond, followed by an intramolecular hydrogen shift to form K2 [Al(NONDipp )(µ-CH2 CH=CO-1κ2 C1,3 -2κO)Al(NONDipp )Et]. Restricting the chemistry to a mono-aluminium system allowed isolation of [Al(NONDipp )(CH2 CH2 CO-κ2 C1,3 )]- , which undergoes thermal isomerisation to form the [Al(NONDipp )(CH2 CH=CHO-κ2 C,O)]- anion. DFT calculations highlight the stabilising influence of incorporated benzene at multiple steps in the reaction pathways.

Reductive Dimerization of CO by a Na/Mg(I) Diamide.

Sodium reduction of [{SiNDipp}Mg] [{SiNDipp} = {CH2SiMe2N(Dipp)}2; Dipp = 2,6-i-Pr2C6H3] provides the Mg(I) species, [{SiNDipp}MgNa]2, in which the long Mg-Mg bond (>3.2 Å) is augmented by persistent Na-aryl interactions. Computational assessment indicates that this molecule is best considered to comprise a contiguous tetrametallic core, a viewpoint borne out by its reaction with CO, which results in ethynediolate formation mediated by the dissimilar metal centers.

Rapid antibiotic susceptibility testing using resazurin bulk modified screen-printed electrochemical sensing platforms.

Urinary tract infections (UTIs) are one of the most common types of bacterial infection. UTIs can be associated with multidrug resistant bacteria and current methods of determining an effective antibiotic for UTIs can take up to 48 hours, which increases the chances of a negative prognosis for the patient. In this paper we report for the first time, the fabrication of resazurin bulk modified screen-printed macroelectrodes (R-SPEs) demonstrating them to be effective platforms for the electrochemical detection of antibiotic susceptibility in complicated UTIs. Using differential pulse voltammetry (DPV), resazurin was able to be detected down to 15.6 µM. R-SPEs were utilised to conduct antibiotic susceptibility testing (AST) of E. coli (ATCC® 25922) to the antibiotic gentamicin sulphate using DPV to detect the relative concentrations of resazurin between antibiotic treated bacteria, and bacteria without antibiotic treatment. Using R-SPEs, antibiotic susceptibility was determined after a total elapsed time of 90 minutes including the inoculation of the artificial urine, preincubation and testing time. The use of electrochemistry as a phenotypic means of identifying an effective antibiotic to treat a complicated UTI offers a rapid and accurate alternative to culture based methods for AST with R-SPEs offering an inexpensive and simpler alternative to other AST methods utilising electrochemical based approaches.

Recent advances in 2D hexagonal boron nitride (2D-hBN) applied as the basis of electrochemical sensing platforms.

2D hexagonal boron nitride (2D-hBN) is a lesser utilised material than other 2D counterparts in electrochemistry due to initial reports of it being non-conductive. As we will demonstrate in this review, this common misconception is being challenged, and researchers are starting to utilise 2D-hBN in the field of electrochemistry, particularly as the basis of electroanalytical sensing platforms. In this critical review, we overview the use of 2D-hBN as an electroanalytical sensing platform summarising recent developments and trends and highlight future developments of this interesting, often overlooked, 2D material.

A Structurally Characterized Cobalt(I) σ-Alkane Complex.

A cobalt σ-alkane complex, [Co(Cy2 P(CH2 )4 PCy2 )(norbornane)][BArF 4 ], was synthesized by a single-crystal to single-crystal solid/gas hydrogenation from a norbornadiene precursor, and its structure was determined by X-ray crystallography. Magnetic data show this complex to be a triplet. Periodic DFT and electronic structure analyses revealed weak C-H→Co σ-interactions, augmented by dispersive stabilization between the alkane ligand and the anion microenvironment. The calculations are most consistent with a η1 :η1 -alkane binding mode.

Room Temperature Iron-Catalyzed Transfer Hydrogenation and Regioselective Deuteration of Carbon-Carbon Double Bonds.

An iron catalyst has been developed for the transfer hydrogenation of carbon-carbon multiple bonds. Using a well-defined ß-diketiminate iron(II) precatalyst, a sacrificial amine and a borane, even simple, unactivated alkenes such as 1-hexene undergo hydrogenation within 1 h at room temperature. Tuning the reagent stoichiometry allows for semi- and complete hydrogenation of terminal alkynes. It is also possible to hydrogenate aminoalkenes and aminoalkynes without poisoning the catalyst through competitive amine ligation. Furthermore, by exploiting the separate protic and hydridic nature of the reagents, it is possible to regioselectively prepare monoisotopically labeled products. DFT calculations define a mechanism for the transfer hydrogenation of propene with nBuNH2 and HBpin that involves the initial formation of an iron(II)-hydride active species, 1,2-insertion of propene, and rate-limiting protonolysis of the resultant alkyl by the amine N-H bond. This mechanism is fully consistent with the selective deuteration studies, although the calculations also highlight alkene hydroboration and amine-borane dehydrocoupling as competitive processes. This was resolved by reassessing the nature of the active transfer hydrogenation agent: experimentally, a gel is observed in catalysis, and calculations suggest this can be formulated as an oligomeric species comprising H-bonded amine-borane adducts. Gel formation serves to reduce the effective concentrations of free HBpin and nBuNH2 and so disfavors both hydroboration and dehydrocoupling while allowing alkene migratory insertion (and hence transfer hydrogenation) to dominate.

Reductive Elimination at Carbon under Steric Control.

It has been previously demonstrated that stable singlet electrophilic carbenes can behave as metal surrogates in the activation of strong E-H bonds (E = H, B, N, Si, P), but it was believed that these activations only proceed through an irreversible activation barrier. Herein we show that, as is the case with transition metals, the steric environment can be used to promote reductive elimination at carbon centers.

Nanodiamond based surface modified screen-printed electrodes for the simultaneous voltammetric determination of dopamine and uric acid.

The electroanalytical detection of the neurotransmitter dopamine (DA) in the presence of uric acid (UA) is explored for the first time using commercially procured nanodiamonds (NDs). These are electrically wired via surface modification upon screen-printed graphite macroelectrodes (SPEs). The surface coverage of the NDs on the SPEs was explored in order to optimize electroanalytical outputs to result in well-resolved signals and in low limits of detection. The (electro)analytical outputs are observed to be more sensitive than those achieved at bare (unmodified) SPEs. Such responses, previously reported in the academic literature have been reported to be electrocatalytic and have been previously attributed to the presence of surface sp2 carbon and oxygenated species on the surface of the NDs. However, XPS analysis reveals the commercial NDs to be solely composed of nonconductive sp3 carbon. The low/negligible electroconductivity of the NDs was further confirmed when ND paste electrodes were fabricated and found to exhibit no electrochemical activity. The electroanalytical enhancement, when using NDs electronically wired upon SPEs, is attributed not to the NDs themselves being electrocatalytic, as reported previously, but rather changes in mass transport where the inert NDs block the underlying electroactive SPEs and create a random array of graphite microelectrodes. The electrode was applied to simultaneous sensing of DA and UA at pH 5.5. Figures of merit include (a) low working potentials of around 0.27 and 0.35 V (vs. Ag/AgCl); and (b) detection limits of 5.7 × 10-7 and 8.9 × 10-7 M for DA and UA, respectively. Graphical abstract The electroanalytical enhancement of screen-printed electrodes modified with inert/non-conductive nanodiamonds is due to a change in mass transfer where the inert nanodiamonds facilitate the production of a random microelectrode array.

A facile electrochemical intercalation and microwave assisted exfoliation methodology applied to screen-printed electrochemical-based sensing platforms to impart improved electroanalytical outputs.

Screen-printed electrodes (SPEs) are ubiquitous with the field of electrochemistry allowing researchers to translate sensors from the laboratory to the field. In this paper, we report an electrochemically driven intercalation process where an electrochemical reaction uses an electrolyte as a conductive medium as well as the intercalation source, which is followed by exfoliation and heating/drying via microwave irradiation, and applied to the working electrode of screen-printed electrodes/sensors (termed EDI-SPEs) for the first time. This novel methodology results in an increase of up to 85% of the sensor area (electrochemically active surface area, as evaluated using an outer-sphere redox probe). Upon further investigation, it is found that an increase in the electroactive area of the EDI-screen-printed based electrochemical sensing platforms is critically dependent upon the analyte and its associated electrochemical mechanism (i.e. adsorption vs. diffusion). Proof-of-concept for the electrochemical sensing of capsaicin, a measure of the hotness of chillies and chilli sauce, within both model aqueous solutions and a real sample (Tabasco sauce) is demonstrated in which the electroanalytical sensitivity (a plot of signal vs. concentration) is doubled when utilising EDI-SPEs over that of SPEs.

Pathway to a molecular calcium methyl.

The dimeric ß-diketiminato calcium hydride, [(BDI)CaH]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2), reacts with ZnMe2 to afford the bimetallic calcium zincate complex, [(BDI)Ca(µ-CH3)2Zn(µ-H)]2, which subsequently undergoes an intramolecular reaction to effect the formation of [(BDI)CaMe]2, a notable omission from the homologous series of ß-diketiminato alkylcalcium derivatives.

Alkali metal reduction of crown ether encapsulated alkali metal cations.

[{SiNDipp}BeClM]2 ({SiNDipp} = {CH2SiMe2N(Dipp)}2; M = Li, Na, K, Rb) are converted to ionic species by treatment with a crown ether. Whereas the lithium derivative reacts with Na or K to provide [{SiNDipp}BeCl]-[M(12-cr-4)2]+ (M = Na, K), the resultant sodium species is resistant to reduction by potassium. These observations are rationalised by a hybrid experimental/theoretical analysis.

[{SiNDipp}MgNa]2: A Potent Molecular Reducing Agent.

The bimetallic species, [{SiNDipp}MgNa]2 [{SiNDipp} = {CH2SiMe2N(Dipp)}2; (Dipp = 2,6-i-Pr2C6H3)], is shown to be a potent reducing agent, able to effect one- or two-electron reduction of either dioxygen, TEMPO, anthracene, benzophenone, or diphenylacetylene. In most cases, the bimetallic reaction products imply that the dissimilar alkaline metal centers react with a level of cooperativity. EPR analysis of the benzophenone-derived reaction and the concurrent isolation of [{SiNDipp}Mg(OCPh2)2], however, illustrate that treatment with such reducible, but O-basic, species can also result in reactivity in which the metals provide independent reaction products. The notable E-stereochemistry of the diphenylacetylene reduction product prompted a computational investigation of the PhC≡CPh addition. This analysis invokes a series of elementary steps that necessitate ring-opening via Mg+ → Na+ amido group migration of the SiNDipp ligand, providing insight into the previously observed lability of the bidentate dianion and its consequent proclivity toward macrocyclization.

The borylamino-diborata-allyl anion.

Reactions of ß-diketiminato alkaline earth alkyldiboranate derivatives [(BDI)Ae{pinBB(R)pin}] (BDI = HC{(Me)CNDipp}2; Dipp = 2,6-i-Pr2C6H3; Ae = Mg, R = n-Bu or Ae = Ca, R = n-hexyl) with t-BuNC provide access to the respective group 2 derivatives of unprecedented diborata-allyl, {(pinB)2CNBpin(t-Bu)}-, anions. Although the necessary mode of B-C bond cleavage implicated in these transformations could not be elucidated, further studies of the reactivity of magnesium triboranates toward isonitriles delivered a more general and rational synthetic access to analogous anionic moieties. Extending this latter reactivity to a less symmetric triboranate variant also provided an isomeric Mg-C-bonded dibora-alkyl species and sufficient experimental insight to prompt theoretical evaluation of this reactivity. DFT calculations, thus, support a reaction pathway predicated on initial RNC attack at a peripheral boron centre and the intermediacy of such dibora-alkyl intermediates.

The structures and reactivity of NHC-supported copper(i) triphenylgermyls.

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh3 complexes. Of these, (IPr)CuGePh3 (IPr = :C{N(2,6-iPr2C6H3)CH}2) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph3Ge]-. The Cu-Ge bond of (IPr)CuGePh3 underwent π-bond insertions with tBuNCS, CS2, and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh3 inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh3 compounds were validated as catalytic intermediates; addition of 10 mol% of NHC-copper(i) alkoxide to a mixture of triphenyl germane and a tin(iv) alkoxide resulted in a tin/germanium cross coupling with concomitant formation of alcohol. Moreover, a catalytic hydrogermylation of Michael acceptors was developed with Ph3GeH adding to 7 activated alkenes in good conversions and yields in the presence of 10 mol% of NHC-copper(i) alkoxide. In all cases, this reaction provided the ß-germylated substrate implicating nucleophilicity at germanium.