Platinum Metals Review - Volume 52, Issue 2, 2008

The combination of focused microwave heating and encapsulated metal promoters (EnCat^TM) offers a safer, cleaner and more cost-effective solution to a wide range of catalyst-mediated reactions, some of which are not widely accessible to the bench chemist due to high hazard ratings. These include the palladium-catalysed Sonogashira cross-coupling, palladium-catalysed transfer hydrogenation, platinum-mediated hydrogenation and osmium tetroxide-catalysed dihydroxylation.

The paper critically presents various routes for immobilising ruthenium alkylidene complexes through their ligands. This part (Part I) describes immobilisation via coordinating/actor ligands (phosphane/alkylidene), and established ancillary ligands such as N-heterocyclic carbenes. Other ligands commonly encountered in immobilisation protocols, such as Schiff bases, arenes, anionic ligands and specifically tagged (ionic liquid tag, fluoro tag) substituents will be the topic of Part II. Selected applications of some of these ruthenium complexes in olefin metathesis reactions are highlighted where they are particularly advantageous.

A novel method of forming a palladised copper (Cu/Pd) interface of well defined structure is described. The CuPd alloy is straightforwardly obtained by immersing a copper substrate in acidic solutions of palladium salts. Depending on the composition of the salt/acid solution, the copper surface is virtually instantly covered with a CuPd deposit. With nitric and sulfuric acid solutions and the corresponding Pd(II)-based salt, the deposit is composed of nanoparticles of disordered CuPd alloy dispersed at the copper interface. The alloy-modified surface was successfully used as an efficient promoter of bond cleavage reactions, especially those of carbon–iodide and carbon–bromide bonds in alkyl halides. The catalytic activity is specifically characterised by a very large shift in potential as between the use of a regular glassy carbon surface and the palladised copper interface. With alkyl halides (RBr and RI), the shift toward less cathodic potentials is so large that it enables the one-electron cleavage of C–I and C–Br bonds. This method should enable the heterogeneous generation of free alkyl radicals as transients in electrochemical reactions. These novel cathodic materials could also be of considerable interest for the disposal of halogenated waste.

The usefulness of platinum as an electrochemical reference electrode was investigated. Well known redox systems with one-electron single or multiple redox waves, and two-electron multiple redox waves were used as test regimes. The effects on electrode performance of variables such as the solvent, the physical state of the electrolyte and its temperature were investigated. Cyclic voltammetry (CV) was used to derive kinetic parameters for comparison with corresponding measurements on traditional reference electrodes. The results indicate that Pt can be used as a reference electrode under specific conditions in which traditional reference electrodes cannot be used.

The year 2007 marked the centenary of the death of Dmitri Mendeleev (1834–1907). This article discusses how he and some of his predecessors accommodated the platinum group metals (pgms) in the Periodic Table, and it considers the placing of their three transuranic congeners: hassium (¹⁰⁸Hs), meitnerium (¹⁰⁹Mt) and darmstadtium (¹¹⁰Ds). Over twenty-five years ago McDonald and Hunt (1) wrote an excellent account of the pgms in their periodic context. This account is indebted to that work. The present article introduces new perspectives and shows some of the relevant tables. There are good books on the history of the Periodic Table, e.g. (2, 3) and other texts (4, 5) which provide a fuller picture than it is possible to give here.