Understanding the alkaline stability of quaternary ammonium (QA) cations tethered to polymer backbones in anion-exchange membranes (AEMs) is crucial to advance the long-term performance of anion-exchange polyelectrolyte-based fuel cells and electrolyzers. A library of model QA cations with N-phenyl and N-benzyl tethers has been synthesized, and comparative alkaline degradation studies revealed that the former are much less stable toward hydroxide attack than their benzylic counterparts. Density functional theory (DFT) studies support the relative stability of the QA cations and demonstrate the critical effect of hydroxide solvation on alkaline stability as well as the degradation pathway. The 3-benzyl-3,6-diazaspiro[5.5]-undecane-6-ium (N-benzyl-ASU, 8) cation was found to be the most stable QA group, with a half-life of 2,595 h at 80 °C and 14,363 h at 60 °C in 3 M NaOD at a hydration number of 4.8, despite its N-phenyl-ASU counterpart (5) having a higher energy lowest unoccupied molecular orbital (LUMO); this suggests that the LUMO energy alone may not be an accurate indicator of alkaline stability. This study highlights the importance of considering the method of tethering the QA group to the polymer backbone and controlling the level of hydroxide hydration when developing QA cations for use in AEM-based devices. The structure-stability correlations arising from this work will inform the design of heteroatom donor-containing QA-based head groups with improved stability profiles.

Palladium nanoparticles stabilised by confinement in crosslinked amine-decorated, polymer immobilised ionic liquids catalyse the hydrolytic evolution of hydrogen from NaBH4 under mild conditions. A series of three PIIL supports NH2-ImxPIIL (x = 1, (2a); x = 2, (2b), x = 3, (2c); where x corresponds to the number of imidazolium cations in the repeat unit) were prepared with an increasing number of imidazolium cations such that bis(styryl)-based crosslinkers 1a and 1b contain one and two imidazolium cations, respectively, while 1c is a more extensive tris(styryl)-based crosslinker with three imidazolium cations. The composition of the support influences the performance of the corresponding PdNP@NH2-ImxPIILS (x = 1, (4a); x = 2, (4b); x = 3, (4c) as catalysts for the hydrolysis of NaBH4 and a comparison of the most efficient system against its unmodified counterpart (i.e. PdNP@H-Im2PIIL) confirmed that incorporation of the surface coordinated amine improved catalyst performance. Palladium nanoparticles stabilised by NH2-Im2PIIL were the most efficient catalyst and the maximum initial turnover frequency of 81 molH2.molPd-1.min-1 is higher than the 59 molH2.molPd-1.min˗1 and 32 molH2.molPd-1.min-1 obtained with PdNPs supported by NH2-Im1PIIL and NH2-Im3PIIL, respectively, as well as the 19 molH2.molPd-1.min-1 obtained with commercial 10 wt% Pd/C. The results of kinetic studies, apparent activation energies and deuterium isotope effects have been compared with those in the literature and support a mechanism involving rate limiting activation of an O-H bond in water. Catalyst reuses studies showed that PdNP@NH2-Im2PIIL recycled with remarkable efficiency as high conversions were maintained across five runs with the catalyst retaining over 92% of its initial activity, an improvement on the 70% retention of activity with palladium nanoparticles supported by linear amine-modified imidazolium-based polymer, which demonstrates the beneficial effect of introducing crosslinking

Palladium nanoparticles (PdNP) stabilised by confinement in crosslinked amine-decorated, polymer-immobilised ionic liquids (PIILs) catalyse the hydrolytic evolution of hydrogen from NaBH4 under mild conditions. A series of three PIIL supports NH2-ImxPIIL (x = 1, (2a); x = 2, (2b); x = 3, (2c), where x corresponds to the number of imidazolium cations in the repeat unit) were prepared with an increasing number of imidazolium cations such that bis(styryl)-based crosslinkers 1a and 1b contain one and two imidazolium cations, respectively, while 1c is a more extensive tris(styryl)-based crosslinker with three imidazolium cations. The composition of the support influences the performance of the corresponding polymer immobilised ionic liquid stabilised (PIILS) palladium nanoparticles, PdNP@NH2-ImxPIILS (x = 1, (4a); x = 2, (4b); x = 3, (4c)) as catalysts for the hydrolysis of NaBH4 and a comparison of the most efficient system against its unmodified counterpart (i.e., PdNP@H-Im2PIILS) confirmed that incorporation of the surface coordinated amine improved catalyst performance. Palladium nanoparticles stabilised by NH2-Im2PIIL was the most efficient catalyst and the maximum initial turnover frequency of 81 molH2 molPd-1 min-1 is higher than the 59 and 32 molH2 molPd-1 min-1 obtained with PdNPs supported by NH2-Im1PIIL and NH2-Im3PIIL, respectively, as well as the 19 molH2 molPd-1 min-1 obtained with commercial 10 wt.% Pd/C. The results of kinetic studies, apparent activation energies, and deuterium isotope effects have been compared with those in the literature and support a mechanism involving rate-limiting activation of an O-H bond in water. Catalyst reuse studies showed that PdNP@NH2-Im2PIILS recycled with remarkable efficiency as high conversions were maintained across five runs with the catalyst retaining over 92% of its initial activity, an improvement on the 70% retention of activity with palladium nanoparticles supported by linear amine-modified imidazolium-based polymer, which demonstrates the beneficial effect of introducing crosslinking.

Composite anion exchange membranes (AEMs) based on poly(terphenylene piperidinium) (PTPiQA) and impregnated with varying loadings of quaternized graphene oxide (QGO) as filler were developed, and their properties as anion exchange membranes for use in water electrolysis (AEMWEs) and fuel cells (AEMFCs) were explored. This study investigates the trade-off between mechanical robustness, ionic conductivity, and alkaline stability in QGO-reinforced twisted polymer backbones. QGO synthesized by functionalization with ethylenediamine (EDA), followed by quaternization with glycidyl trimethylammonium chloride (GTMAC), was used as a filler for PTPiQA, and the properties of the resulting composites PTPiQA-QGO-X investigated as a function of QGO loading for X between 0.1 and 0.7 wt%. Among all compositions, PTPiQA-QGO-0.3% exhibited the highest OH− conductivity of 71.56 mS cm−1 at room temperature, attributed to enhanced ionic connectivity and water uptake. However, this increase in conductivity was accompanied by a slight decrease in ion exchange capacity (IEC) retention (91.8%) during an alkaline stability test in 1 M KOH at 60 °C for 336 h due to localized cation degradation. Mechanical testing revealed that PTPiQA-QGO-0.3% offered optimal dry and wet tensile strength (dry TS of 42.77 MPa and wet TS of 30.20 MPa), whereas higher QGO loadings yielded low mechanical strength. These findings highlight that 0.3 wt% QGO balances ion transport efficiency and mechanical strength, while higher loadings improve alkaline durability, compromising mechanical durability and guiding the rational design of AEMs for AEMWEs and AEMFCs.

Green hydrogen is a promising energy carrier as it has a high energy density, and it can be produced in high purity from water via electrolysis. While proton exchange membrane (PEM) electrolysers have been developed, they require noble metal catalysts to survive the corrosive acidic environment in the cell, hence the prohibitively high cost of this technology has hindered its commercial implementation. Anion exchange membrane (AEM) electrolysers are a rapidly improving technology, which combine the advantages of alkaline water and PEM electrolysers, i.e. they are compact, utilise cost effective non-noble metal catalysts and operate under mild conditions, making them viable alternatives to PEM. 1 The composition of the anion exchange polyelectrolytes (AEPs) used as membranes and ionomers in these devices can be fine-tuned to control ion conductivity, ion exchange capacity, and water uptake and swelling. 2 This requires careful design of the cationic head group, the polymer backbone, the tether and the co-monomer. Despite the advantages of AEM based devices, balancing the long-term thermal stability and efficiency of AEPs at high pH remains a major challenge which needs to be addressed if AEM electrolysers are to become commercially competitive with existing hydrogen production systems. 3-5 Building upon previous studies, which have demonstrated the choice of cation-polymer tether is a major component in controlling alkaline stability, this work explores a bottom-up approach to the design of a new subset of polystyrene based quaternary ammonium (QA) monomers for use as AEPs. 6 A series of QA monomers were prepared either by Buchwald-Hartwig amination or reductive amination, followed by cyclisation using 1,5-dibromopentane. Alkaline stability studies were carried out over 30 days at 80 °C, using 1 H NMR spectroscopy to monitor the extent of QA degradation. To rationalise the experimentally observed degradation, computational studies were conducted to investigate the potential degradation pathways at different hydration levels and determine the corresponding activation parameters. The calculated activation energies support the observed degradation trends, providing justification to the order of stability of QA monomers under chosen conditions. Analysis concluded that increasing the number of ‘spacer’ units between the phenyl ring of the styrene and the QA centre led to a dramatic improvement in alkaline stability, with the most stable QA monomers displaying half-lives competitive with the most stable head groups reported in the literature under the same conditions. Inclusion of the electronegative nitrogen in the tether was found to cause a decrease in stability, despite the group being a necessary component to synthesise polymerizable QA monomers. The most stable QA monomer, which has an impressive half-life in excess of 30,000 h at 80 °C in 3M NaOD, was selected for the synthesis of AEPs to ascertain their suitability for use in AEM electrolysers. H. D. Abruña, et al., J. Phys. Chem. C, 2023 , 127, 7901-7912 . X. Chu, Y. Shi, L. Liu, Y. Huang and N. Li, J. Mater. Chem. A , 2019 , 7, 7717-7727. M. G. Marino and K. D. Kreuer, ChemSusChem , 2015 , 8, 513-523 Y. M. Lee, et al., Angew. Chem. Int. Ed. , 2021 , 60, 19272-19280. G. W. Coates, et al., J. Org. Chem. , 2021 , 86, 254-264. S. Doherty et. al., J. Membr. Sci, Manuscript currently under review. Figure 1

Impregnation of phosphine-decorated polymer-immobilized ionic liquid with the tetrachloroaurate anion results in reduction of the gold(III) to gold(I) with concomitant oxidation of the phosphine to its oxide. In situ reduction of the resulting precursor, AuCl@O = PPh2-PEGPIILS, generated the corresponding O = PPh2-PEGPIIL-stabilized AuNPs, AuNP@O = PPh2-PEGPIILS, which is a highly active and selective catalyst for the solvent-dependent partial reduction of nitrobenzene to N-phenylhydroxylamine in water and azoxybenzene in ethanol. The initial TOFs are comparable to those obtained with gold nanoparticles generated by reduction of tetrachloroaurate-impregnated phosphine oxide-decorated polymer-immobilized ionic liquid AuCl4@O = PPh2-PEGPIILS, i.e., the activity and selectivity profiles do not appear to depend on whether the AuNPs are generated from Au(III) or in situ-generated Au(I). In stark contrast, gold nanoparticles prepared by NaBH4 reduction of AuCl@PPh2-PEGPIILS based on gold(I) confined in phosphine-modified polymer-immobilized ionic liquid gave markedly lower initial TOFs. The use of dimethylamine borane (DMAB) as the hydrogen donor resulted in a substantial and dramatic enhancement in activity for reductions conducted in water compared with NaBH4 and the initial TOF of 20,400 mol nitrobenzene converted mol Au-1 h-1 obtained with AuNPs generated in situ from AuCl4@O = PPh2-PEGPIILS is among the highest to be reported for the metal nanoparticle catalyzed selective reduction of nitrobenzene to N-phenylhydroxylamine; this is a significant improvement on existing protocols, which should enable the partial selective reduction of nitroarenes to be conducted in water with a low catalyst loading under extremely mild conditions.

Ruthenium nanoparticles stabilised by an amine-modified Ordered Mesoporous Silica Immobilized Ionic Liquid (OMSIIL) are efficient catalysts for the partial reduction of nitrobenzene to hydrazobenzene with 100 % selectivity as well as the complete reduction to aniline. High selectivity for the partial reduction of nitrobenzene to hydrazobenzene was obtained when the reaction was conducted in ethanol with 0.5 mol% catalyst and NaBH4 as the hydrogen donor whereas aniline was obtained as the sole product in water when dimethylamine borane (DMAB) was used as the hydrogen donor. Interestingly, while a range of electron poor nitroarenes were reduced to the corresponding hydrazoarene with high selectivities and good conversions, nitroarenes substituted with electron donating groups resulted in complete reduction to the aniline. Composition-time profiles suggest that reductions conducted in ethanol with sodium borohydride occur via the condensation pathway while those conducted in water using dimethylamine borane as the hydrogen source may well go via the direct pathway. This is the first example of the selective reduction of nitrobenzene to hydrazobenzene using a ruthenium nanoparticle-based catalyst and the initial TOF of 320 mol nitrobenzene converted mol Ru-1 h-1 for the partial reduction of nitrobenzene to hydrazobenzene is markedly higher than previous literature reports. A study of the catalyst performance as a function of the surface modification revealed that each component has a direct and dramatic effect on the efficacy as RuNPs stabilised by COK-12 modified with imidazolium-based ionic liquid and a primary amine gave the highest conversion while selective removal of either component or replacement of the primary amine with a tertiary amine resulted in a marked reduction in efficiency. Ruthenium nanoparticles stabilised by ordered mesoporous silica, COK-12, decorated with an imidazolium based ionic liquid and an amine catalyses the partial reduction of nitrobenzene to hydrazobenzene with 100 % selectivity as well as the complete reduction to aniline. A survey of the substrate scope revealed that the partial reduction appeared to be restricted to nitroarenes substituted with an electron withdrawing group. image

Platinum and ruthenium nanoparticles stabilised by an amine modified polymer immobilised ionic liquid (MNP@NH2-PEGPIILS, M = Pt, Ru) catalyse the hydrolytic liberation of hydrogen from dimethylamine borane (DMAB), ammonia borane (AB) and NaBH4 under mild conditions. While RuNP@NH2-PEGPIILS and PtNP@NH2-PEGPIILS catalyse the hydrolytic evolution of hydrogen from NaBH4 with comparable initial TOFs of 6,250 molesH2.molcat−1.h−1 and 5,900 molesH2.molcat−1.h−1, respectively, based on the total metal content, RuNP@NH2-PEGPIILS is a markedly more efficient catalyst for the dehydrogenation of DMAB and AB than its platinum counterpart, as RuNP@NH2-PEGPIILS gave initial TOFs of 8,300 molesH2.molcat−1.h−1 and 21,200 molesH2.molcat−1.h−1, respectively, compared with 3,050 molesH2.molcat−1.h−1 and 8,500 molesH2.molcat−1.h−1, respectively, for PtNP@NH2-PEGPIILS. Gratifyingly, for each substrate tested RuNP@NH2-PEGPIILS and PtNP@NH2-PEGPIILS were markedly more active than commercial 5wt

RuNPs stabilised by a polymer immobilised ionic liquid derived from co-polymerisation of a PEG -substituted imidazolium-based styrene monomer and diphenyl(4-vinylphenyl)phosphine oxide, RuNP@O = PPh2-PEGPIILS, (2) is a remarkably efficient and selective catalyst for the hydrazine hydrate-mediated partial reduction of nitroarenes to the corresponding N-arylhydoxylamine. Near quantitative conversion to N-phenylhydroxylamine with > 99 % selectivity was obtained after only 2 h when the reaction was conducted at 25 degrees C in ethanol under an inert atmosphere using 0.1 mol% catalyst. Under these conditions, the composition-time profile showed that the reduction occurred via the direct path-way whereas reactions in air gave a mixture of azoxy-based products due to competing condensation resulting from reversible formation of N-phenylhydroxylamine. The initial TOF of 6,100 h(-1) obtained after 10 min at 40 degrees C with 0.1 mol% 2 is among the highest to be reported for the metal nanoparticle catal-ysed reduction of nitrobenzene to N-phenylhydroxylamine and a significant improvement on 5 wt% Ru/C which gave a modest conversion of 21 % (initial TOF = 240 h(-1)) to a mixture of N-phenylhydroxylamine and aniline. A broad range of substituted N-aryl and N-heteroaryl nitroarenes were reduced to the corre-sponding N-arylhydroxylamine in high yield and with excellent selectivity by adjusting the reaction times. However, reduction of electron rich amino-substituted nitroarenes was extremely slow and resulted in reduction to the aniline with no evidence for the corresponding hydroxylamine. Complete reduction of amino substituted nitroarene is proposed to be facilitated by amine-assisted elimination of hydroxide from the hydroxylamine to afford a readily reducible quinondiimine-derived iminium inter-mediate that reacts with a surface hydride to liberate the amine. Under optimum conditions the catalyst could be reused five times for the reduction of nitrobenzene to N-phenylhydroxylamine with no detect-able change in activity and only slight decrease in selectivity.

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO2 to formate; the initial TOF of 500 h-1 is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst.

RuNPs stabilised by amino‐decorated imidazolium‐based polymer immobilized ionic liquids catalyse the dimethylamine borane mediated reduction of quinolines to 1,2‐dihydroquinoline (DHQ) and 1,2,3,4‐tetrahydroquinoline (THQ). Partial reduction of 3‐substituted quinolines to the corresponding 1,2‐dihydroquinoline was achieved with 100 % selectivity in toluene under mild conditions. This is the first report of the selective partial reduction of 3‐substituted quinolines to the corresponding 1,2‐dihydroquinolines with a heterogeneous nanoparticle‐based catalyst. A wide range of substituted quinolines have also been reduced to the corresponding 1,2,3,4‐tetrahydroquinoline with high selectivity and good yields by adjusting the reaction time. The 1,2‐dihydroquinolines readily release dihydrogen in toluene at 60 °C in the absence of catalyst with no evidence for disproportionation and as such are potential organo‐hydride reagents. The initial TOF of 610 mol quinoline converted mol Ru−1 h−1 for the reduction of quinoline is among the highest to be reported for a metal nanoparticle‐based catalyst and the conversion of 96 % obtained after 4 h at 65 °C is significantly higher than its platinum nanoparticle counterpart PtNP@NH2‐PEGPIILS as well as 5 wt/% Ru/C, which only reached 9 % and 11 % conversion, respectively, at the same time. Hot filtration experiments showed that the active species was heterogeneous.

Ruthenium nanoparticles stabilised by polymer immobilized ionic liquids catalyse the hydrolytic release of hydrogen from sodium borohydride. The composition of the polymer influences performance and ruthenium nanoparticles stabilised by an amine-decorated imidazolium-based polymer immobilised ionic liquid (RuNP@NH2-PIILS) was the most efficient with a maximum initial turnover frequency (TOF) of 177 moleH2. molRu- 1.min- 1, obtained at 30 degrees C with a catalyst loading of 0.08 mol%; markedly higher than that of 69 molH2. molRu- 1.min- 1 obtained with 5 wt% Ru/C and one of the highest to be reported for a RuNP catalyst. The apparent activation energy (Ea) of 38.9 kJ mol-1 for the hydrolysis of NaBH4 catalysed by RuNP@NH2-PIILS is lower than that for the other polymer immobilized ionic liquid stabilised RuNPs, which is consistent with its efficacy. Comparison of the initial rates of hydrolysis in H2O and D2O catalysed by RuNP@NH2-PIILS gave a primary kinetic isotope effect (kH/kD) of 2.3 which supports a mechanism involving rate limiting oxidative addition of one of the O-H bonds in a strongly hydrogen-bonded surface-coordinated [BH3H- ]--H2O ensemble. The involvement of a surface-coordinated borohydride is further supported by an inverse kinetic isotope effect of 0.65 obtained from a comparison of the initial rates for the hydrolysis of NaBH4 and NaBD4 under the conditions of catalysis i.e., at a high hydride/catalyst mole ratio. Interestingly though, when the comparison of the initial rates of hydrolysis of NaBH4 and NaBD4 was conducted in dilute solution with a hydride/catalyst mole ratio of 1 a kinetic isotope effect (kH/kD) of 2.72 was obtained; this would be more consistent with concerted activation of both an O-H and B-H bond in the rate limiting step, possibly via a concerted oxidative addition-hydride transfer in the surface-coordinated hydrogen-bonded ensemble. Catalyst stability and reuse studies showed that RuNP@NH2-PIILS retained 71% of its activity over five runs; the gradual drop in the initial TOF with run number appears to be due to passivation of the catalyst by the sodium borate by-product as well as an increase in viscosity of the reaction mixture rather than leaching of the catalyst.

Platinum nanoparticles stabilized by imidazolium‐based phosphine‐decorated Polymer Immobilized Ionic Liquids (PPh2‐PIIL) catalyze the hydrolytic evolution of hydrogen from sodium borohydride with remarkable efficiency, under mild conditions. The composition of the polymer influences efficiency with the catalyst based on a polyethylene glycol modified imidazolium monomer (PtNP@PPh2‐PEGPIILS) more active than its N‐alkylated counterpart (PtNP@PPh2‐N‐decylPIILS). The maximum initial TOF of 169 moleH2.molcat−1.min−1 obtained at 30 °C with a catalyst loading of 0.08 mol% is among the highest to be reported for the aqueous phase hydrolysis of sodium borohydride catalyzed by a PtNP‐based system. Kinetic studies revealed that the apparent activation energy (Ea) of 23.9 kJ mol−1 for the hydrolysis of NaBH4 catalyzed by PtNP@PPh2‐PEGPIILS is significantly lower than that of 35.6 kJ mol−1 for PtNP@PPh2‐N‐decylPIILS. Primary kinetic isotope effects kH/kD of 1.8 and 2.1 obtained with PtNP@PPh2‐PEGPIILS and PtNP@PPh2‐N‐decylPIILS, respectively, for the hydrolysis with D2O support a mechanism involving rate determining oxidative addition or σ‐bond metathesis of the O−H bond. Catalyst stability and reuse studies showed that PtNP@PPh2‐PEGPIILS retained 70 % of its activity across five runs; the gradual drop in conversion appears to be due to poisoning of the catalyst by the accumulated metaborate product as well as the increased viscosity of the reaction mixture.

Phosphine oxide-decorated polymer immobilized ionic liquid stabilized RuNPs catalyse the hydrogenation of aryl ketones with remarkable selectivity for the CO bond, complete hydrogenation to the cyclohexylalcohol and hydrogenation of levulinic acid to γ-valerolactone.

The Noyori-Ikariya (arene)Ru(II)/TsDPEN precatalyst has been anchored to amorphous silica and DAVISIL through the eta(6)-coordinated arene ligand via a straightforward synthesis and the derived systems, (arene)Ru(II)/TsDPEN@silica and (arene)Ru(II)/TsDPEN@DAVISIL, form highly efficient catalysts for the asymmetric transfer hydrogenation of a range of electron-rich and electron-poor aromatic ketones, giving good conversion and excellent ee's under mild reaction conditions. Moreover, catalyst generated in situ immediately prior to addition of substrate and hydrogen donor, by reaction of silica-supported [(arene)RuCl2](2) with (S,S)-TsDPEN, was as efficient as that generated from its preformed counterpart [(arene)Ru{(S,S)-TsDPEN}Cl]@silica. Gratifyingly, the initial TOFs (up to 1085 h(-1)) and ee's (96-97 %) obtained with these catalysts either rivalled or outperformed those previously reported for catalysts supported by either silica or polymer immobilized through one of the nitrogen atoms of TsDPEN. While the high ee's were also maintained during recycle studies, the conversion dropped steadily over the first three runs due to gradual leaching of the ruthenium.

The iridium-catalyzed C-H borylation of diethyl phenylphosphonate results in nonselective mono and bisborylation to afford a near statistical mixture of 3-, 3,5- and 4-boryl substituted aryl phosphonates whereas 3-substituted aryl phosphonates undergo highly regioselective C-H borylation to afford the corresponding meta-phosphonate substituted arylboronic esters as the sole product; the resulting boronic esters were used as nucleophilic reagents in a subsequent palladium-catalyzed Suzuki–Miyaura cross-coupling to generate a range of biarylmonophosphonates. Gratifyingly, the Suzuki–Miyaura cross-coupling can be conducted without purifying the boronic ester which greatly simplifies the synthetic procedure.

Gold nanoparticles stabilized by phosphine-decorated polymer immobilized ionic liquids (AuNP@PPh2-PIILP) is an extremely efficient multiproduct selective catalyst for the sodium borohydride-mediated reduction of nitrobenzene giving N-phenylhydroxylamine, azoxybenzene, or aniline as the sole product under mild conditions and a very low catalyst loading. The use of a single nanoparticle-based catalyst for the partial and complete reduction of nitroarenes to afford three different products with exceptionally high selectivities is unprecedented. Under optimum conditions, thermodynamically unfavorable N-phenylhydroxylamine can be obtained as the sole product in near quantitative yield in water, whereas a change in reaction solvent to ethanol results in a dramatic switch in selectivity to afford azoxybenzene. The key to obtaining such a high selectivity for N-phenylhydroxylamine is the use of a nitrogen atmosphere at room temperature as reactions conducted under an inert atmosphere occur via the direct pathway and are essentially irreversible, while reactions in air afford significant amounts of azoxy-based products by virtue of competing condensation due to reversible formation of N-phenylhydroxyl-amine. Ultimately, aniline can also be obtained quantitatively and selectively by adjusting the reaction temperature and time accordingly. Introduction of PEG onto the polyionic liquid resulted in a dramatic improvement in catalyst efficiency such that N-phenylhydroxylamine could be obtained with a turnover number (TON) of 100 000 (turnover frequency (TOF) of 73 000 h(-1), with >99% selectivity), azoxybenzene with a TON of 55 000 (TOF of 37 000 h(-1) with 100% selectivity), and aniline with a TON of 500 000 (TOF of 62 500 h(-1), with 100% selectivity). As the combination of ionic liquid and phosphine is required to achieve high activity and selectivity, further studies are currently underway to explore whether interfacial electronic effects influence adsorption and thereby selectivity and whether channeling of the substrate by the electrostatic potential around the AuNPs is responsible for the high activity. This is the first report of a AuNP-based system that can selectively reduce nitroarenes to either of two synthetically important intermediates as well as aniline and, in this regard, is an exciting discovery that will form the basis to develop a continuous flow process enabling facile scale-up.

Palladium nanoparticles stabilized by lightly cross-linked phosphine-decorated polymer immobilized ionic liquids (PIIL) and their PEGylated counterparts (PEGPIIL) are highly effective catalysts for the aqueous phase hydrogenation and sodium borohydride-based reduction of a wide range of nitroaromatic and heteroaromatic compounds under mild conditions with low catalyst loadings. Introduction of extensive cross-linking with tris(4-vinylphenyl)phosphine to isolate the phosphine-based heteroatom and limit the number of surface Pd center dot center dot center dot P interactions did not have a significant influence on catalyst performance. Comparative testing revealed PdNPs immobilized on lightly cross-linked phsophine-decoarted PEGylated polymer to be a highly efficient catalyst for the aqueous phase reduction of nitroarenes with a TON of 36000 (TOF = 2580 h(-1)) for hydrogenation and a TON of 274 000 (TOF = 17 125 h(-1)) for transfer hydrogenation. Even though these reactions occur under diffusion control due the poor solubility of the substrate these values are the highest to be reported for the room temperature aqueous phase reduction of nitroarenes catalyzed by a nanoparticle-based system. A continuous flow reduction of nitrobenzene in a packed bed reactor operated over a period of 250 min with no sign of catalyst deactivation and the corresponding space-time-yield of 0.738 g L-1 min(-1) is a marked improvement on that of 0.384 g L-1 min(-1) obtained in batch. The same system also catalyzes a tandem Suzuki-Miyaura cross coupling-nitroarene reduction sequence to afford high yields of biaryl amine in an operationally straightforward single-pot procedure. This is a highly versatile protocol which will enable the aromatic nitro fragment to be introduced as a nitro-substituted aryl or heteroaryl halide and as such will lend itself to rapid diversification for the synthesis of a wide range of amines.

Palladium nanoparticles stabilized by heteroatom donor‐modified polystyrene‐based polymer immobilized ionic liquids (PdNP@HAD‐PIILP; HAD‐PPh2, OMe, NH2, CN, pyrrolidone) are highly efficient catalysts for the Suzuki‐Miyaura cross‐coupling in aqueous media under mild conditions. Catalyst modified with phosphine was consistently the most efficient as it gave high yields across a range of substrates under mild conditions at low catalyst loadings. Incorporation of polyethylene glycol into the phosphine modified immobilised ionic liquid support improved catalyst efficacy by improving dispersibility and facilitating access to the active site. Moreover, each of the heteroatom modified catalysts was more active than the corresponding unsubstituted imidazolium‐based polystyrene benchmark as well as commercial samples of Pd/C. Catalyst generated in situ from either [PdCl4]@PPh2‐PIILP or its PEGylated counterpart [PdCl4]@PPh2‐PEGPIILP, by reduction with phenylboronic acid, outperformed their pre‐formed counterparts for the vast majority of substrates examined. The turnover frequency of 16,300 h−1 obtained at room temperature is one of the highest to be reported for palladium nanoparticle‐catalysed Suzuki‐Miyaura cross‐coupling between 4‐bromoacetophenone and phenylboronic acid in aqueous media under such mild conditions.

Doherty, S., Knight, J. G., Backhouse, T., Bradford, A., Saunders, F., Bourne, R. A., Chamberlain, T. W., Stones, R., Clayton, A. and Lovelock, K. (2018) Highly efficient aqueous phase reduction of nitroarenes catalyzed by phosphine­ decorated polymer immobilized ionic liquid stabilized PdNPs. Catalysis Science & Technology, 8 (5). pp. 1454­1467. ISSN 2044­4761 doi: https://doi.org/10.1039/c7cy02557b Available at http://centaur.reading.ac.uk/75592/