Highly active palladium and nickel catalysts for oxidative processes mediated by molecular oxygen

Abstract

In this thesis an optimization of the synthesis of five palladium pincer complexes and their application in different aerobic oxidative processes are presented. A CNC pincer type containing N-heterocyclic carbene moieties, two NCN pincers bearing pyrazole moieties and two PCP pincer complexes with phosphinite groups are prepared by short synthetic routes with moderate overall yields. The catalytic activity of the latter palladium pincer complexes is evaluated in several oxidative processes mediated solely by molecular oxygen, focusing on the use of environmentally friendly media. The palladacycles featured excellent catalytic activities in the aerobic oxidation of primary and secondary benzylic alcohols and methylene compounds, and in the copper-free oxidative homocoupling of arylacetylenes. Competitive yields, very low catalyst loadings and convenient reaction media are presented, thus achieving high TON and TOF values in the aforementioned oxidative processes. On the other hand, a new NCN pincer type ligand is synthesized and applied, in combination with palladium(II) or nickel(II) salts, to the aerobic oxidation of alcohols and methylene compounds. Excellent results (including high TON and TOF values) are obtained in the above oxidative processes. In addition, a new oxygen-mediated transformation, the oxidative cleavage of C-C triple bond, is carried out by using two exceptionally active catalytic systems based on the combination of nickel(II) bromide and triazole ligand.