Ruthenium/phosphonium salt system

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)]. 

More than one decade after Parshall s work, Knifton demonstrated the crucial role played by the addition of quaternary phosphonium salts in the hydroformylation of internal olefins catalyzed by ruthenium melt [27]. In the system described, the anionic ruthenium cluster [HRu3(CO)jj] generated in situ from [RUO2], [Ru(OAc)2], or [Ru(acac)3] is the predominant metal carbonyl species in the reactant solutions. 

Ruthenium catalysts have also been applied as effective catalysts. The selective oxidation of 12 could be achieved by using terpyridine-derived ruthenium complexes, with catalyst loadings below 1 mol% and the addition of a phase transfer catalyst (PTC an ammonium, phosphonium, or sulfonium salt) in biphasic aqueous systems, but also in methanol without PTC, and without the need for adding... 

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