Synthesis of nitriles by catalytic dehydrogenation of amines using ruthenium complexes

Abstract

Nitriles represent one of the most important classes of organic compounds used as intermediates in the synthesis of biologically active compounds and pharmaceutical substances. Furthermore, they are also used in agrochemicals, herbicides, polymers, dyes and natural products, which are derived from amino acids in plants, arthropods, bacteria and fungi. Nitriles are also versatile intermediates in synthetic organic chemistry due to their easy conversion into amines, amides, carboxylic acids, aldehydes, esters, etc. The most common and well-known procedure for the preparation of nitriles is the nucleophilic displacement of substrates with suitable leaving groups such as halogen compounds, aryl sulphonates, alcohols, ester, ethers, nitro or amino compounds and diazonium salts with inorganic cyanide ions. The conventional methods and several other reported procedures such as dehydration of amides and aldoximes, condensation of carboxylic acids with NH3 and conversion of aldehydes, alcohols and esters, often require hazardous reagents, severe reaction conditions and/or produce stoichiometric waste. For example, the Rosenmund-von Braun and the Sandmeyer reaction require the use of stoichiometric amounts of CuCN and produce high amounts of CuCl as waste. To overcome some of these environmental related problems, catalytic methods such as direct conversion of primary amines to nitriles via dehydrogenation could be a viable alternative and clean route if a simple olefin is used as hydrogen acceptor. This procedure offers a mechanistically distinct and relatively benign pathway for nitrile synthesis. n catalysis, ruthenium complexes have been proved to be very efficient for transfer hydrogenation reactions. So considering this previous background, my work has been focused in the study of the catalytic mechanism of dehydrogenation of amines into the corresponding nitriles using different ruthenium complexes as catalysts. For that, I have synthesized 3 ruthenium complexes containing NHC ligands (imidazolylidenes in this case) with different electronic properties. The modulation of the electronic properties is introduced by changing the functional groups at 4 and 5 positions in the imidazol ring. The main purpose of this work was to study how the electronic density over the metal affects the effectiveness of the dehydrogenation of amines over a series of arenes with different functional groups.