Platinum Metals Review - Volume 49, Issue 4, 2005

The asymmetric reduction of carbonyl, C=O, groups for the production of enantiomerically pure secondary alcohols is a reaction of fundamental importance in modern synthetic chemistry. This reaction can be performed in a number of ways. Asymmetric chemocatalysis (1) and the often complementary biocatalysis offer solutions to the stereoselective reduction of C=O groups. These two techniques have found wide industrial application (2). In the mid 1990s, two new ruthenium systems based on dihydrogen or transfer hydrogenation for asymmetric reduction of prochiral ketones were developed by Professors Noyori and Ikariya. These systems enable catalytic asymmetric reduction to provide a route for the generation of enantiomerically pure secondary alcohols in a highly efficient, simple and economic way (3). This paper describes some robust and cost-effective chemocatalytic technology for asymmetric ketone reduction, using ruthenium catalysts with diphosphine ligands.

It is proposed that 3400 ± 50 K is probably closer to the melting point of pure osmium than the value of 3300 K for impure metal which is usually quoted.

Comparisons are made between platinum-copper and platinum-ruthenium alloys used for jewellery to evaluate the effects of casting variables. The effects of flask temperatures, investments, and centrifugal speeds on microstructure, percentage fill, and porosity were examined over a range of temperatures. Optimum conditions and materials for successful casting of high quality platinum jewellery alloys, using a Hot Platinum induction melting and casting machine, are described. Suitable choice of investment materials and rotational speeds produced good grid fills with Pt-5%Cu and Pt-5%Ru alloys. Metal porosity was more difficult to control, due to the inherently chaotic nature of the casting process, but casting into a relatively cool mould minimised the probability of bad porosity for both alloys. Pt-5%Ru was found to be successful as a casting alloy when used with induction melting technology. It displayed superior uniformity, hardness and colour, compared with cast Pt-5%Cu alloy.

A review of recently published aspects on ruthenium complexes with nucleophilic N-heterocyclic carbene (NHC) ligands is presented here, in continuation of a paper published in the July issue of this Journal, that covered initial work and subsequent main developments in this chemistry. In Part II selected applications of these complexes as pre-catalysts in metathesis reactions are highlighted. Particular attention is paid to metathesis in room temperature ionic liquids as the solvents, asymmetric catalysis, and in situ generated, very active catalytic systems based on NHC-platinum group metals. Most NHC-platinum group metal complexes are useful as highly active and selective pre-catalysts for fundamental chemical transformations.