The transformations of Pt complex species in concentrated NaOH solutions (1−12 M) of Na 2 [PtCl 6 ] were studied with a combination of methods, including 195 Pt nuclear magnetic resonance, ultraviolet−visible, and Raman spectroscopy. The two-step process was observed under the following conditions: (1) formation of the [Pt(OH) 5 Cl] 2− anion that proceeds relatively fast even at room temperature and (2) further slow substitution of the last chlorido ligand with the formation of the [Pt(OH) 6 ] 2− anion. Overall, it was determined that the [PtCl 6 ] 2− to [Pt(OH) 6 ] 2− transformation (especially the first stage) is greatly accelerated under blue light (455 nm) irradiation. The structures of [Pt(OH)Cl 5 ] 2− and [Pt(OH) 5 Cl] 2− were determined using the single-crystal X-ray diffraction data of the corresponding salts isolated for the first time. Analysis of the [Pt(OH)Cl 5 ] 2− reactivity showed that under analogous conditions, its hydrolysis proceeds 2 orders of magnitude slower than that of [PtCl 6 ] 2− , indicating that the formation of [Pt(OH) 5 Cl] 2− from [PtCl 6 ] 2− (stage 1) does not follow a simple sequential substitution pattern. A model for [Pt(OH) 5 Cl] 2− anion formation that includes the competing reaction of direct Cl ligand substitution and the self-catalyzed secondorder reaction caused by a redox process is proposed. The influence of Pt speciation in alkaline solutions on the reductive behavior is shown, illustrating its impact on the preparation of Pt nanoparticles.

A mechanistic study of direct selective oxidation of benzylic C(sp 3 )À H groups with peracetic acid, catalyzed by palladium complexes with tripodal amino-tris(pyriylmethyl) ligands, is presented. The oxidation of arylalkanes having secondary and tertiary benzylic CÀ H groups, predominantly yields, depending on the substrate and conditions, either the corresponding ketones or alcohols. One of the three 2-pyriylmethyl moieties, which is pending in the starting catalyst, apparently, facilitates the active species formation and takes part in stabilization of the high-valent Pd center in the active species, occupying the axial coordination site of palladium. The catalytic, as well as isotopic labeling experiments, in combination with ESI-MS data and DFT calculations, point out palladium oxyl species as possible catalytically active sites, operating essentially via CÀ H abstraction/oxygen rebound pathway. For the ketones formation, OÀ H abstraction/в-scission mechanism has been proposed.ChemCatChem

A combination of the exceptional stability of fac-[Ir­(H2O)3(NO2)3] together with thermolability of nitro and aqua ligands and high solubility in various solvents makes it promising as a brand-new chlorine-free precursor of iridium for the preparation of heterogeneous catalysts. In the current work, a new technique of fac-[Ir­(H2O)3(NO2)3] preparation based on hydrothermal treatment of (NH4)3[Ir­(NO2)6] was developed. For this purpose, the influence of reaction parameters such as the reaction time, temperature, and pH of the solution on the process of hexanitroiridate salt hydrolysis was investigated. The synthesized fac-[Ir­(H2O)3(NO2)3] solution in this optimized way was used for the preparation of the series of Ir/g-C3N4 catalysts, which were evaluated in the water oxidation reaction with NaIO4 utilized as a sacrificial reagent. A 20-fold enhancement of the oxygen evolution reaction (OER) activity was found to take place under visible light (λ = 411 nm) illumination of the systems. The highest rate of the photoinduced OER per iridium center was achieved by the Ir0.005/g-C3N4 (air, 400°C) catalyst with an exceptional turnover frequency value of 967 min–1 approaching the activity of known homogeneous iridium OER catalysts. The leaching experiments have shown that aquated Ir species are generated in a solution after prolonged functioning of the catalysts. Despite this, in the closed system the photodriven OER activity persists at a steady-state level evidencing an equilibrium achieved between dissolved and anchored Ir species forming catalytic tandem with the g-C3N4.

No abstract