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Catalysts that allow for selective oxidation of organic compounds in solution are useful tools in chemical synthesis, waste remediation, and renewable energy storage schemes. Of these, iridium oxide and iridium-based molecular compounds are frequently employed as catalysts to oxidize substrates ranging from small organic molecules to water. Here, we study the mechanism and evaluate the potential of iridium-based catalysts for small molecule oxidation in wastewater treatment, using lactic acid as a substrate. By investigating the reaction products, kinetic isotope effects, and electrochemical properties of iridium oxide and a molecular analogue on a high surface area antimony-doped tin oxide (ATO) support, we find evidence for a new iridium-catalyzed pathway for lactic acid oxidation. Applying this at concentrations representative of effluent from dairy production processes, we show that iridium oxide can selectively remove small amounts of lactic acid from water by oxidizing it to CO2 with concomitant cat...

We describe a systematic method for the preparation and spectroscopic characterization of a CO2 molecule coordinated to an activated bisphenoidal nickel(I) compound containing a tetraazamacrocyclic ligand in the gas phase. The resulting complex was then structurally characterized by using mass-selected vibrational predissociation spectroscopy. The results indicate that a highly distorted CO2 molecule is bound to the metal center in an η(2)-C,O coordination mode, thus establishing an efficient and rational method for the preparation of metal-activated CO2 for further studies using ion chemistry techniques.

We report a heterogeneous cobalt–phosphine-based water oxidation catalyst that was produced by thermal synthesis, and can be easily and rapidly deposited onto a variety of substrates from a suspension. Application of the catalyst dramatically improved the oxygen evolution efficiency and corrosion-resistance of stainless steel, nickel and copper anodes in alkaline media. More than 20 g of catalyst was prepared in a single batch, and it was shown to be effective at surface loadings as low as 20 μg/cm2. The catalyst was investigated in three different systems: (1) An alkaline electrolyzer with stainless steel electrodes activated with the catalyst supported 120–200% of the current density of an unactivated but otherwise identical electrolyzer, over a range of applied potentials, and maintained this improved efficiency throughout 1495 h of continuous use in 1 M NaOH. (2) Copper anodes were activated and protected from corrosion in dilute sodium hydroxide for 8 h of electrolysis, before a steady decrease in pe...

A pentamethylcyclopentadienyl (Cp*) iridium water-oxidation precatalyst was modified to include a silatrane functional group for covalent attachment to metal oxide semiconductor surfaces. The heterogenized catalyst was found to perform electrochemically driven water oxidation at an overpotential of 462 mV with a turnover number of 304 and turnover frequency of 0.035 s^(–1) in a 0.1 M KNO3 electrolyte at pH 5.8. Computational modeling of the experimental IR spectra suggests that the catalyst retains its Cp* group during the first hour of catalysis and likely remains monomeric.

A pentamethylcyclopentadienyl-iridium complex containing a tricyclic, dianionic, tridentate, scorpionate (facial binding), mixed organic-inorganic ligand was synthesized and characterized by single-crystal X-ray crystallography, as well as polynuclear NMR, UV-vis, and IR spectroscopies. The central cycle of the tridentate ligand consists of a modified boroxine in which two of the boron centers are tetrahedral, anionic borates. The complex is stable to hydrolysis in aqueous solution for9 weeks at 25 °C but reacts with a 50 mM solution of sodium periodate within 12 s to form a periodate-driven oxygen evolution catalyst that has a turnover frquency of15 s(-1). However, the catalyst is almost completely deactivated within 5 min, achieving an average turnover number of ca. 2500 molecules of oxygen per atom of iridium. Nanoparticles were not observed on this time scale but did form within 4 h of catalyst activation under these experimental conditions. The parent complex was modeled using density functional theory, which accurately reflected the geometry of the complex and indicated significant interaction of iridium- and boracycle-centered orbitals.

We report that in the presence of trifluoroacetic acid primary phosphines undergo efficient addition to aldehydes to form the corresponding secondary phosphine oxides in 47−97% yield. This transformation is compatible with aryl and alkyl phosphines, as well as a broad range of aldehydes, including formaldehyde. By using 1,5-dialdehydes as reaction partners, the addition provides a straightforward route to bis(phosphine oxides), which are difficult to prepare by alternative methods. In the presence of boron trifluoride diethyl etherate as reagent, benzophenone was shown to couple to phenylphosphine and cyclohexylphosphine in 92% and 72% yield, respectively. Twenty-three examples are presented.

We report the thermal synthesis of a heterogeneous Co–phosphine-based water oxidation catalyst that can be easily coated onto a variety of substrates. The system is active in neutral water and performs best with borate as electrolyte, in which the onset of catalytic current occurs at 1.51 V vs. RHE, with a Tafel slope of 68 mV per decade. Stable water oxidation is observed for over 40 hours; including in seawater with borate electrolyte, in which the catalyst is selective for water oxidation over chloride (85% Faradaic efficiency). The organic portion of the catalyst appears to play a crucial role in catalytic activity.