The “Green” Electrochemical Synthesis of Periodate

High‐grade periodate is relatively expensive, but is required for many sensitive applications such as the synthesis of active pharmaceutical ingredients. These high costs originate from using lead dioxide anodes in contemporary electrochemical methods and from expensive starting materials. A direct and cost‐efficient electrochemical synthesis of periodate from iodide, which is less costly and relies on a readily available starting material, is reported. The oxidation is conducted at boron‐doped diamond anodes, which are durable, metal‐free, and nontoxic. The avoidance of lead dioxide ultimately lowers the cost of purification and quality assurance. The electrolytic process was optimized by statistical methods and was scaled up in an electrolysis flow cell that enhanced the space–time yields by a cyclization protocol. An LC‐PDA analytical protocol was established enabling simple quantification of iodide, iodate, and periodate simultaneously with remarkable precision.     

Surface Activation of Pt Nanoparticles Synthesised by “Hot Injection” in the Presence of Oleylamine

Oleylamine (OA) based “hot injection” colloidal synthesis offers a versatile approach to the synthesis of highly monodisperse metallic and multi‐metallic alloyed nanostructures in the absence of potentially toxic and unstable phosphine compounds. For application in heterogeneous catalysis and electrocatalysis, the adsorbed OA species at the metal surfaces should be effectively removed without compromising the structure and composition of the nanostructures. Herein, we investigate the removal of OA from colloidal Pt nanoparticles through 1) “chemical methods” such as washing in acetic acid or ethanol, and ligand exchange with pyridine; and 2) thermal pre‐treatment between 185 and 400 °C in air, H₂ or Ar atmospheres. The electrochemical reactivity of Pt nanoparticles is acutely affected by the presence of surface organic impurities, making this material ideal for monitoring the effectiveness of OA removal. The results showed that thermal treatment in Ar at temperatures above 400 °C provides highly active particles, with reactivity comparable to the benchmark commercial catalyst, Pt/ETEK. The mechanism involved in thermal desorption of OA was also investigated by thermogravimetric analysis coupled to mass spectrometry (TGA‐MS). Oxidation of HCOOH and adsorbed CO in acidic solution were used as test reactions to assess the Pt electrocatalytic activity.     

Electrochemical Study of Dialcarb “Distillable” Room‐Temperature Ionic Liquids

Electrode‐dependent potential windows (see picture, GC=glassy carbon) are determined for five dialkylammonium carbamate (dialcarb) room‐temperature ionic liquids in a systematic study of their physical and electrochemical properties. The viscosity and conductivity of the dialcarb ionic liquids, which are “distillable” at low temperature, are comparable to those of some conventional room‐temperature ionic liquids.

     

Electrocatalytic Oxidation of Ethylene Glycol on Dispersed Pt: Determination of the Reaction Products

Comparative studies of electrocatalytic ethylene glycol oxidation on bulk and dispersed Pt in acidic aqueous solutions have been performed. A quantitative method has been developed to determine all organic oxidation products using high-performance liquid chromatography with appropriate derivatising reagents.     

Platinum Group Organometallics Based on “Pincer” Complexes: Sensors,Switches, and Catalysts

Since the first reports in the late 1970s on transition metal complexes containing pincer‐type ligands—named after the particular coordination mode of these ligands—these systems have attracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typically, such a ligand comprises an anionic aryl ring which is ortho,ortho‐disubstituted with heteroatom substituents, for example, CH₂NR₂, CH₂PR₂ or CH₂SR, which generally coordinate to the metal center, and therefore support the M−C σ bond. This commonly results in a terdentate and meridional coordination mode consisting of two metallacycles which share the M−C bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental understanding of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mechanistic elucidation of fundamental transformations (for example, C−C bond activation), the construction of the first metallodendrimers for sustainable homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous investigations. This review discusses the synthetic methodologies that are currently available for the preparation of platinum group metal complexes containing pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineering of sensors, switches, and catalysts.     

The Controlled Formation and Cleavage of an Intramolecular d8–d8 Pt–Pt Interaction in a Dinuclear Cycloplatinated Molecular “Pivot‐Hinge”

The bis(diphenylphosphino)methane (dppm)‐bridged dinuclear cycloplatinated complex {[Pt(L)]₂(μ‐dppm)}²⁺ (Pt₂ ? dppm; HL: 2‐phenyl‐6‐(1H‐pyrazol‐3‐yl)‐pyridine) demonstrates interesting reversible “pivot‐hinge”‐like intramolecular motions in response to the protonation/deprotonation of L. In its protonated “closed” configuration, the two platinum(II) centers are held in position by intramolecular d⁸–d⁸ Pt–Pt interaction. In its deprotonated “open” configuration, such Pt–Pt interaction is cleaved. To further understand the mechanism behind this hingelike motion, an analogous dinuclear cycloplatinated complex, {[Pt(L)]₂(μ‐dchpm)}²⁺ (Pt₂ ? dchpm) with bis(dicyclohexylphosphino)methane (dchpm) as the bridging ligand, was synthesized. From its protonation/deprotonation responses, it was revealed that aromatic π–π interactions between the phenyl moieties of the μ‐dppm and the deprotonated pyrazolyl rings of L was essential to the reversible cleavage of the intramolecular Pt–Pt interaction in Pt₂ ? dppm. In the case of Pt₂ ? dchpm, spectroscopic and spectrofluorometric titrations as well as X‐ray crystallography indicated that the distance between the two platinum(II) centers shrank upon deprotonation, thus causing a redshift in its room‐temperature triplet metal–metal‐to‐ligand charge‐transfer emission from 614 to 625 nm. Ab initio calculations revealed the presence of intramolecular hydrogen bonding between the deprotonated and negatively charged 1‐pyrazolyl‐N moiety and the methylene CH and phenyl C–H of the μ‐dppm. The “open” configuration of the deprotonated Pt₂ ? dppm was estimated to be 19 kcal mol^?1 more stable than its alternative “closed” configuration. On the other hand, the open configuration of the deprotonated Pt₂ ? dchpm was 6 kcal mol^?1 less stable than its alternative closed configuration.     

Design and Enantioselective Synthesis of Cashmeran Odorants by Using “Enol Catalysis”

Novel Cashmeran odorants were designed by molecular modeling. Their short syntheses involve a novel asymmetric Brønsted acid catalyzed Michael addition of unactivated α‐substituted ketones. This key transformation was realized by utilizing a new type of enol activation catalysis and affords different cyclic ketones bearing α‐quaternary stereocenters in good to excellent yields and with high enantioselectivity. Subsequent McMurry coupling and Saegusa–Ito oxidation furnished the enantiopure target odorants, one enantiomer of which indeed possesses the typical olfactory aspects of Cashmeran.     

Carbocatalysis: The State of “Metal‐Free” Catalysis

The rise in global demand for crucial chemical compounds has driven immense research in the fundamental science of catalysis. Graphene and its derivatives (chemically modified graphene, CMGs) have recently emerged as a new class of heterogeneous catalyst that promises economically viable and greener routes to these compounds. Although CMGs possess unique catalytic properties, the actual active sites are often points of discussion. Current minimal understanding on the possible effects of metallic impurities on the electrocatalytic performances of these CMGs calls forth the need to raise awareness on possible metallic impurities misrepresenting the actual chemical catalytic performances of the CMGs. This Minireview highlights the latest advances in the application of CMGs as catalysts, with an emphasis on the possible effects of metallic impurities on CMG catalysis.     

Reaction of “Non‐Symmetrical” 1,2,4‐Trithiolanes with [(phosphane)Pt0(η2‐nbe)] Complexes

Two unsymmetrical 1,2,4‐trithiolanes ( 1d and 1e ) were reacted with [Pt⁰(PPh₃)₂(η²‐nbe)] ( 6 ; nbe=norborn‐2‐ene) and [Pt⁰(dppn)(η²‐nbe)] ( 11 ; dppn=1,8‐bis(diphenylphosphanyl)naphthalene)), respectively. Their treatment with compound 6 resulted in the formation of six‐membered platinacycles of type 7 , which selectively underwent fragmentation into dithiolato complexes and thiobenzophenone ( 4b ). The isolation of the first stable C‐substituted member of this class of compounds (i.e., compound 7e ) permitted kinetic studies of this process by using UV/Vis spectroscopy. These results, together with DFT calculations, allowed us to propose a mechanism for the reactions of compound 6 with 1,2,4‐trithiolanes. In contrast, similar treatment of compound 11 with compounds 1d and 1e at room temperature did not result in any reaction. Heating the appropriate samples to 110 °C led to the formation of dithiolato complexes and η²‐thioketone compounds, thus pointing to a thermally induced [3+2]‐cycloreversion of the heterocycles as an initial step of the reaction.     

Deep Oxidation of Methane on a Pt/Si3N4 Catalyst

We have studied platinum catalysts supported on silicon nitride Si₃N₄ in the process of deep oxidation of methane. We have used transmission electron microscopy and X-ray photoelectron spectroscopy to study the surface properties of the Pt/Si₃N₄ samples before and after the catalytic reaction. We have established that the metallic platinum particles in freshly prepared systems are characterized by average sizes of 1.7-5.3 nm, while after the catalytic reaction we observe formation of Pt crystallites up to 30-70 nm in size. We hypothesize that the observed deactivation of platinum catalysts in deep oxidation of methane is connected with crystallization of the metallic particles and their entrainment with the reaction products during catalysis.     

Controllable Encapsulation of “Clean” Metal Clusters within MOFs through Kinetic Modulation: Towards Advanced Heterogeneous Nanocatalysts

Surfactant‐free tiny Pt clusters were successfully encapsulated within MOFs with controllable size and spatial distribution by a novel kinetically modulated one‐step strategy. Our synthesis relies on the rational manipulation of the reduction rate of Pt ions and/or the growth rate of MOFs by using H₂ as assistant reducing agent and/or acetic acid as MOF‐formation modulator. The as‐prepared Pt@MOF core–shell composites exhibited exceedingly high activity and excellent selectivity in the oxidation of alcohols as a result of the ultrafine “clean” Pt clusters, as well as interesting molecular‐sieving effects derived from the outer platinum‐free MOF shell.     

Synthesis of Mesoporous Platinum–Copper Films by Electrochemical Micelle Assembly and Their Electrochemical Applications

We have electrochemically synthesized mesoporous platinum–copper films with various compositions in an aqueous surfactant solution. By tuning the composition ratios of the platinum and copper sources in the precursor solutions, mesoporous bimetallic films with copper contents that dramatically change from 0 to 70 mol % can be successfully prepared. The obtained bimetallic films possess uniformly sized mesopores over the entire area. These mesoporous platinum–copper films are electrochemically active and show composition‐dependent catalytic activity and stability for the methanol oxidation reaction. The bimetallic mesoporous films are a promising new class of electrocatalyst for the future.