Pd-catalysed carbonylations of anilines in ionic liquids

Resumen

This thesis describes the study of several palladium catalysts with commercially available phosphorus and nitrogen donor ligands, either as sole ligand or in combination with N-heterocyclic carbenes. The palladium systems were applied in carbonylation of anilines for the formation of amides and ureas. The thesis is divided into four chapters. The first chapter is a brief introduction to the carbonylation chemisty of homogeneous palladium catalysts. Carbonylation reactions involving ionic liquids and SILP catalysts is also discussed. The second chapter deals with the formation of amides from anilines. A novel catalytic system is disclosed and a mechanism is proposed. The third chapter covers work on two catalytic systems for the formation of diphenyl urea involving ionic liquids as solvent and reaction facilitator. The fourth chapter describes the transfer of the ionic liquid mediated oxidative carbonylation of aniline into flow. Supported ionic liquid phase technology was applied for the heterogenization of the molecular catalyst. -Preparation of Benzamide by Carbonylation of Anilines- In this chapter, a previously unpublished palladium based catalytic system for the highly selective transformation of anilines into benzamides, is described. The reaction proceeded smoothly without the need for prior activation of the aniline. Notably, the catalytic system is additive free, robust and utilizes commercially available ligands. A wide range of primary anilines including sterically hindered substrates were efficiently converted into benzamides in high yield. Moreover, a catalytic cycle accounting for the cleavage of primary arylamine C-N bond in the transformation is presented. To the best of our knowledge this is the first example of catalytic C-N activation bond in the presence of palladium without prior activation of the aniline. -Palladium Catalysed Carbonylation of Aniline in Ionic Liquid- This chapter deals with the oxidative carbonylation of aniline in a biphasic ionic liquid/toluene system. An in-situ high-pressure NMR experiment was performed to shed light on the mechanism of the reaction. The spectroscopic experiment supports proposals in literature. A proposed intermediate was confirmed and information on the formation of this intermediate was obtained. The presence of ionic liquid in the reaction was observed to be crucial for the outcome of the reaction. Furthermore, the nature of the ionic liquid strongly influenced the reaction, as did the amount of ionic liquid in the reaction. Two hypotheses, with respect to the cause of this influence, were tested and the results are discussed. Selective oxidative carbonylation of aniline to diphenylurea was carried out in the presence of a catalytic system comprising of [PdCl2 (PPh3)2] and BMIM][Cl] with a TOF of 15600 per hour and 1900 per hour when benzoquinone or oxygen were used as oxidants, respectively. The TOF achieved with benzoquinone as oxidant was, to the best of our knowledge, the highest reported so far under mild reaction conditions (140 degrees Celsius and 10 bar). In order to investigate the influence of the ionic liquids, several cations and anions were applied. The best results were achieved with [BMIM][Br] while the employment of [BMIM][NTf2] drove a spontaneous product separation. Recycling experiments were conducted but loss of activity was observed after the first reuse. Decomposition of the catalyst was observed during workup but leaching of catalyst into the toluene phase can not be excluded as a cause for the unsuccessful recyclability. -Oxidative Carbonylationn of Aniline in Continuous Flow- Silicas with two different imidazoliums attached was prepare, characterized and applied as supports. The characterization of the supports indicated, that functionalisation mainly took place inside the pores, but to a lesser extent for dihydroimidazolium than for imidazolium. Under batch conditions, good activity and recyclability were obtained with SILP, while support impregnated only with the homogenous catalyst was not active. Continuous flow experiments were performed with the prepared SILP materials. Steady-state conditions were not obtained due to the deactivation of the catalyst under continuous flow conditions. Characterization of the catalyst material after reaction indicated leaching of both palladium and non-anchored IL during the reaction to be the cause of the deactivation of the SILP catalyst. Leaching of the catalytically active components of the SILP material was most likely caused by the large amounts of solvent passed over the catalyst. The partial miscibility of solvent and ionic liquid caused the removal of the of the ionic liquid layer, containing the active catalyst from the solid support, and thus deactivated the catlyst. In this perspective, the imidazolium functionalisation of the silica surface did not provide the anticipated anchoring of the non-covalently bound IL as leaching was observed regardless of the support material applied for the preparation of the SILP.