Hydroformylation, ruthenium catalyzed linearity

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... 

Knifton has also shown (36 - 38,40) that nitrogen- or phosphorus-ligand modified ruthenium complexes, in a phosphonium salt matrix, can conveniently catalyze the hydroformylation of terminal alkenes with high selec-tivities in linear oxo products. Usually selectivities better than 80% were achieved. In the best case (160°C, 95 bar. CO/H2= 1/2) a linearity in nonanol of 94% was obtained starting from [Ru3(CO),2], 2,2 -bipyridine. and [PBu4]Br. The main products were alcohols and not aldehydes. However, it is often difficult to reduce the isomerization of oct-l-ene as well as its hydrogenation. The [Ru3(CO),2l/2,2 -bipyridine (bipy) system has been extensively explored. Two equilibria have been proposed to account for the infrared data and the effects of the bipy ligand [eqs. (8) and (9)]. 

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 ... 

---