Hydroformylation, ruthenium catalyzed propene

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

The hydroformylation of alkenes to give linear aldehydes constitutes the most important homogeneously catalyzed process in industry today [51]. The hydroformylation of propene is especially important for the production of n-bu-tyraldehyde, which is used as a starting material for the manufacture of butanol and 2-ethylhexanol. Catalysts based on cobalt and rhodium have been the most intensively studied for the hydroformylation of alkenes, because they are industrially important catalysts. While ruthenium complexes have also been reported to be active catalysts, ruthenium offers few advantages over cobalt or... 

A comparison of Rh and Ru catalysts in the hydroformylation of linear butenes [4] or the strong electron-deficient substrate 3,3,3-trifluoropropene led to the conclusion that the latter are less active [5]. Moreover, in the hydroformylation of propene in comparison with Co and Rh catalysts, an inferior selectivity was noted [6]. In a competition experiment with the iridium-catalyzed hydroformylation of several a-olefins at 13 bar syngas pressure and 100 C, a related PPhj-modified Ru complex revealed no activity [7]. On the other hand, unmodified ruthenium based catalysts were shown to be more active than osmium complexes [8], thus the following rough order of reactivity results ... 

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