Application of Manganese Pincer Complexes for Hydrogenation and Dehydrogenation Reactions

On the way towards sustainable and green chemistry, scientists found a key technology which allows chemical transformations to proceed with minimum waste generation and energy consumption. The key is transition metal catalysis which is also attractive from an economical point of view. At the end of 19th century, Alfred Werner defined basics of coordination chemistry which were significant for the development of transition metal catalysis. In the 1930s, the Oxo Process, in which olefins react with syngas to produce linear and branched aldehydes, was developed by Otto Roelen. The reaction is still widely used and allows to produce millions metric tons of oxo chemicals. A following milestone in transition metal catalysis occurred in the 1950s when the Wacker Process was developed. The reaction allows to oxidize olefins to aldehydes and ketones with the use of PdCl2 as catalyst. Many other reactions were developed involving transition metal catalysis, including important processes such as C-C bond formations, site selective C-H bond activation, arylation of amines and alcohols and others which have been also applied in industrial processes to obtain bulk chemicals, fine chemicals and polymers. Another indicator highlighting the importance of homogeneous transition metal catalysis is the acknowledgement by the Noble Prize committee. Thus, in 2001, the Nobel Prize in chemistry was awarded jointly to William S. Knowles, Ryoji Noyori and K. Barry Sharpless for their work on transition metal catalysed asymmetric hydrogenation and oxidation reactions. Later in 2005, Yves 0Chauvin, Robert H. Grubbs and Richard R. Schrock were selected for the Noble Prize in chemistry for their work on the development of the metathesis reaction in organic synthesis. And finally, recent Noble Prize in chemistry in 2010 was awarded to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for palladium-catalysed cross coupling reactions in organic synthesis. Until recently, reports featuring homogeneous transition metal catalysis were focused on using rare and expensive metals. The application of noble metals raises major concern, as they are toxic and consequently they produce toxic waste. And to their low availability (listed as critical raw materials for European Union), noble metals require difficult extraction from the Earths crust.