Electrocatalytic reduction of benzaldehyde to benzyl alcohol on Pd supported on carbon felt was conducted in the aqueous phase using a continuous flow fixed-bed reactor at room temperature and atmospheric pressure. Methanol, ethanol, or isopropanol was added to the electrolyte to study the impact of alcohol type and concentration on the rates of benzaldehyde electrocatalytic hydrogenation (ECH) and H2 evolution, which is the prevalent side reaction. Whereas the ECH rates and Faradaic efficiency decreased with increasing alcohol concentrations, H2 evolution rates remained constant. The impact of the alcohol on hydrogenation was greater as the length of the alcohol’s hydrocarbon chain increased. Increasing the benzaldehyde concentration allows for high ECH rates and high Faradaic efficiency. The reaction order increased from ∼0.13 to ∼0.66 with half-cell potential increasing from −650 to −1150 mV (vs Ag/AgCl). Kinetic analysis reveals that the changes in reaction order are due to changes in benzaldehyde (and H) surface coverages as a function of half-cell cathodic potential. Thus, the results shown here reveal how the performance of the continuous electrocatalytic operation is affected by the electrolyte composition and half-cell cathodic potential.

N-Heterocyclic carbene ligated copper complexes act as catalysts in a variety of reactions. A brief overview of this rich chemistry is given here. Of particular note is the ability of Cu(NHC) complexes to functionalize carbonyls, alkenes and alkynes. With growth in the number of Cu(NHC) derived complexes, the catalytic possibilities involving these complexes are ever growing. We feel the full potential of these (for the most part) simply accessed complexes has yet to be fully achieved. The litany of reactions which Cu(NHC) catalyst facilitate are outlined here

Electrocatalytic hydrogenation is a particularly attractive approach for converting the most unstable compounds in biogenic feedstocks at ambient conditions without external H2. Here, we synthesized a variety of carbon-supported transition metal catalysts and characterized their activity for the electrocatalytic hydrogenation of a series of model compounds and pyrolysis bio-oil. Carbonyl compounds, especially aromatic aldehydes, such as furfural and benzaldehyde, are particularly inclined to hydrogenation driven by an applied current. This was verified with pure solutions of the model compounds and with pyrolysis bio-oil, where we achieved stable and steady continuous operation on Pd. When optimal catalyst composition was chosen, the conversion of benzaldehyde shifted from alcohol production (e.g., on Pd and Cu) to dimerization (e.g., on Co, Ni, and Zn). Pd and Cu were shown to offer the best compromise between reaction rates and efficiency although, in general, base metals offer similar conversions but better efficiencies than noble metals. Thus, the present work offers foundational results and guidelines for choosing the optimal metal catalyst and the applied potential for processing organic feedstocks as a function of its composition.

Electrolysis flow reactors based on the filter-press architecture of redox flow batteries have proven to be effective and scalable toward the production of commercially relevant, pharmaceutical quantities of anilines (>500 kg/year) from halogen-, hydroxyl-, and carbonyl-substituted nitroarenes. Turbulent flow through the carbon felts on which the catalysts were supported facilitated scaling toward production levels because it conferred on the reactors scale-independent, plug flow-like residence time distributions and high mass transfer coefficients. Equipping the cells with microreference electrodes made it possible to transfer reaction conditions first developed in batch systems to the continuous flow reactors. The catalysts prepared by incipient wetness impregnation of metal salts into lightly oxidized carbon felt supports were readily generalizable.

Treatment of trans-[W(N2)2(dppe)(PEtNMePEt)] (dppe = Ph2PCH2CH2PPh2; PEtNMePEt = Et2PCH2N(Me)CH2PEt2) with 3 equiv of tetrafluoroboric acid (HBF4·Et2O) at −78 °C generated the seven-coordinate tungsten hydride trans-[W(N2)2(H)(dppe)(PEtNMePEt)][BF4]. At higher temperatures, protonation of a pendant amine is also observed, affording trans-[W(N2)2(H)(dppe)(PEtNMe(H)PEt)][BF4]2, with formation of the hydrazido complex [W(NNH2)(dppe)(PEtNMe(H)PEt)][BF4]2 as a minor product. A similar product mixture was obtained using triflic acid (HOTf). The protonated products are thermally sensitive and do not persist at ambient temperature. Upon acid addition to the carbonyl analogue cis-[W(CO)2(dppe)(PEtNMePEt)], the seven-coordinate carbonyl hydride complex trans-[W(CO)2(H)(dppe)(PEtNMe(H)PEt)][OTf]2 was generated. A mixed diphosphine complex without the pendant amine in the ligand backbone, trans-[W(N2)2(dppe)(depp)] (depp = Et2P(CH2)3PEt2), was synthesized and treated with HOTf, selectively generating a hydrazido complex, [W(NNH2)(OTf)(dppe)(depp)][OTf]. Computational analysis probed the proton affinity of three sites of protonation in these complexes: the metal, pendant amine, and N2 ligand. Room-temperature reactions with 100 equiv of HOTf produced NH4 + from reduction of the N2 ligand (electrons come from W). The addition of 100 equiv of HOTf to trans-[W(N2)2(dppe)(PEtNMePEt)] afforded 0.81 equiv of NH4 +, while 0.40 equiv of NH4 + was formed upon treatment of trans-[W(N2)2(dppe)(depp)] with HOTf, showing that the complexes containing proton relays produce more products of reduction of N2.

Several new phenolate complexes were prepared by reacting [Au(IPr)(OH)] (IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene) with phenols in solution. These complexes were also prepared by a new method. The precursor to the gold hydroxide [Au(IPr)Cl] was simply ground with KOH and the organic substrates. [Au(IPr)(R)] complexes that required heating in solution for extended periods of time were prepared using the grinding method in only minutes.

An even split: In sharp contrast with the general behavior of Pd0 complexes, [Pd(IPr)(PCy3)] is able to activate the HH bond. The resulting trans‐[Pd(H)2(IPr)(PCy3)] is the first isolated mononuclear dihydride palladium compound. Its formation is supported by multinuclear NMR spectroscopy, density functional calculations, and X‐ray diffraction studies. The stability and reactivity of this new species are examined.magnified image

The sterically crowded isoindoline pincer ligand, 6'-MeLH, prepared by condensation of 4-methyl-2-aminopyridine and phthalonitrile, exhibits very different reaction chemistry with Cd2+, Zn2+, and Pd2+. Three different ligand coordination modes are reported, each dependent upon choice of metal ion. This isoindoline binds to Cd2+ as a charge-neutral, zwitterionic, bidentate ligand using imine and pyridine nitrogen atoms to form the eight-coordinate fluxional complex, Cd(6'-MeLH)2(NO3)2. In the presence of Zn2+, however, loss of a pyridine arm occurs through solvolysis and tetrahedrally coordinated complexes are formed with coordination of pyrrole and pyridine nitrogen atoms. Reaction with Pd2+ produces the highly distorted, square planar complex Pd(6'-MeL)Cl in which a deprotonated isoindoline anion coordinates as a tridentate pyridinium NNC pincer ligand.