Hydroformylation, ruthenium catalyzed early catalysts

Up to now, almost exclusively terminal olefins have been screened in ruthenium-catalyzed hydroformylation. One of the notable exceptions concerns early investigations of Knifton [115]. He used ruthenium carbonyl melt catalysts, wherein the ruthenium carbonyls are dispersed in quaternary phosphonium salts with a low melting point. By the addition of chelating N-donor ligands such as 2,2 -bipyridyl, -aldehydes came out. 

Ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [PBuJBr was reported by Knifton as early as in 1987 [2]. The author described a stabilization of the active ruthenium-carbonyl complex by the ionic medium. An increased catalyst lifetime at low synthesis gas pressures and higher temperatures was observed. 

As early as 1938, Roelen discovered the cobalt-catalyzed hydroformylation of olefins, then known as the oxo reaction, which allowed the synthesis of aldehydes by addition of carbon monoxide and hydrogen to alkenes. Not long after this discovery it was found that cobalt, rhodium, ruthenium and platinum are also suitable as catalysts. However, because of the considerable price advantage for large scale applications in industry, cobalt catalysts are mostly used. Rhodium complexes, however, are... 

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