Diketonate complexes, osmium

There is a wide range of diketonates, such as Ru(acac)3, with octahedral coordination [133b] (they do not seem, however, to be oxidized to the +4 state this is possible with osmium) similarly several salts of the tris(oxalato) complex Ru(C204)3 have been isolated. 

As might be expected for chelating 0,0 donor ligands it is the intermediate trivalent state of osmium which is stabilized by /J-diketonates (as is the case for catechols, p. 597, and tropolonato complexes, p. 597). In the presence of rc-acceptor chelates such as bipy, phen and terpy the II state is favoured, while with halides the IV state is preferred. The apparent absence of an osmyl complex, e.g. 0s02acac2, is surprising. 

Diarylacetylenes are converted in 55-90% yields into a-diketones by refluxing for 2-7 h with thallium trinitrate in glyme solutions containing perchloric acid [413. Other oxidants capable of achieving the same oxidation are ozone [84], selenium dioxide [509], zinc dichromate [660], molybdenum peroxo complex with HMPA [534], potassium permanganate in buffered solutions [848, 856, 864,1117], zinc permanganate [898], osmium tetroxide with potassium chlorate [717], ruthenium tetroxide and sodium hypochlorite or periodate [938], dimethyl sulfoxide and iV-bromosuccin-imide [997], and iodosobenzene in the presence of a ruthenium catalyst [787] (equation 143). 

Ruthenium(III), d, is ruthenium s most stable oxidation state and resembles rhodium(III) and iridium(III) more than osmium(III). The salts inelude the halides, hydroxides, and oxides RuCls SHaO is most important because it is a good starting material for other compounds and reacts readily with olefins and phosphines. Complexes of this oxidation state are known with water, eyanide, oxygenated organies, sueh as diketones and earboxylates, pyridines, earbonyls, ey-elopentadienyls, phosphine, and arsine ligands. A notable differenee between ruthenium(II) and ruthenium(III) is the absenee of ruthenium(III) nitrosyl complexes. 

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