Ruthenium production, aqueous base

While the decomposition products of molybdenum-based initiators may conveniently be removed as molybdates after any metathesis reaction by addition of aqueous base, ruthenium tends to form RUO2, a black insoluble product. The removal of decomposed Ru-sites from any product is best performed by the use of a water-soluble phosphine such as tris(hydroxymethyl)phosphine [182]. Alternatively, addition of triphenylphosphinoxide or DMSO followed by filtration over sihca was reported to be advantageous [183]. For purposes of completeness, the investigations of the actual catalytic cycle in the reaction of Cl2Ru(CHPh)(PCy3)2 with cyclic olefins carried out with substituted cyclobutenes shall be mentioned [184]. 

Furthermore, the utilization of preformed films of polypyrrole functionalized by suitable monomeric ruthenium complexes allows the circumvention of problems due to the moderate stability of these complexes to aerial oxidation when free in solution. A similar CO/HCOO-selectivity with regards to the substitution of the V-pyrrole-bpy ligand by an electron-with-drawing group is retained in those composite materials.98 The related osmium-based redox-active polymer [Os°(bpy)(CO)2] was prepared, and is also an excellent electrocatalyst for the reduction of C02 in aqueous media.99 However, the selectivity toward CO vs. HCOO- production is lower. 

One of the few examples of ruthenium-based systems is the RuCh 3 H20/dide-cyldimethylammonium bromide combination reported by Sasson and coworkers [121]. This system catalyzes the selective oxidation of a variety of alcohols, at high (625 1) substrate catalyst ratios, in an aqueous/organic biphasic system. However, 3-6 equiv. of H2O2 were required, reflecting the propensity of mthenium for catalyzing the non-productive decomposition of H2O2. 

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