The electronic effects in the (diimine)Pd-(II)-catalysed aerobic oxidation of alcohols were investigated from the viewpoint of both the catalyst and the alcohol. A −push±pull× mechanism is operative, where both electron-donating substituents on the benzyl alcohol (1 À 0.58) and electron-withdrawing groups on the 4,4'-disubstituted-2,2'-bipyridine ligand (1 0.18) increase the reaction rate. The results indicate partial reduction of the palladium centre in the transition state of the rate-limiting step.

No abstract

The steric influence of substituents on the 2-and 9-positions of phenanthroline in the (2,9-R 2 -1,10-phenanthroline)palladium(II)-catalyzed aerobic oxidation of 2-hexanol was investigated by means of high throughput experimentation. (Neocuproine)Pd-(OAc) 2 (R CH 3 ) was found to be a highly active catalyst for alcohol oxidation in 1 : 1 water/DMSO mixtures. The catalyst is unique in that it tolerates water, polar co-solvents and a wide variety of functional groups in the alcohol. Turn-over frequencies of > 1500 h À1 were achieved and a series of alcohols was oxidised with 0.1 to 0.5 mol % of catalyst.

The hydrogenation of three different pharmaceutical nitro-containing compounds has been studied using high-throughput experimentation (HTE) methods. Significant improvements to the existing reactions were obtained for two of the examples. Each reaction exhibits distinct features regarding activity and chemoselectivity. The best catalyst and reaction conditions found were remarkably different for each of the reactions. For one of the reactions, larger-scale studies are presented, which show that the screening reactions provided a fast and reliable indicator of the most promising reaction conditions.

No abstract