Diruthenium carboxylates

Reaction of Os3(CO)i2 with a hexane solution of 2,2-dimethyl-3,5-heptanedionate (thdH) in a sealed autoclave at 190 °C leads to the tetraosmium chain complex Os2(CO)s(thd)2 2 294. Treatment of this compound with carbon monoxide yields the diosmium complex 295. In an investigation of the catalytic activity of diruthenium carboxylate complexes in the water-gas shift and Reppe olefin carbonylation rections, the trifluoroacetate compounds 296... 

Mixed-valence Ru"-Ru" paddlewheel carboxylate complexes also have potential for oxidation reactions after incorporation in a microporous lattice with porphyrinic ligands. This MOF can be used for oxidation of alcohols and for hydrogenation of ethylene. Both the porosity of the lattice and the abihty of the diruthenium centers to chemisorb dioxygen are essential for the performance of the catalyst [62, 64]. 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Rhodium-based catalysis suffers from the high cost of the metal and quite often from a lack of stereoselectivity. This justifies the search for alternative catalysts. In this context, ruthenium-based catalysts look rather attractive nowadays, although still poorly documented. Recently, diruthenium(II,II) tetracarboxylates [42], polymeric and dimeric diruthenium(I,I) dicarboxylates [43], ruthenacarbor-ane clusters [44], and hydride and silyl ruthenium complexes [45 a] and Ru porphyrins [45 b] have been introduced as efficient cyclopropanation catalysts, superior to the Ru(II,III) complex Ru2(OAc)4Cl investigated earlier [7]. In terms of efficiency, electrophilicity, regio- and (partly) stereoselectivity, the most efficient ruthenium-based catalysts compare rather well with the rhodium(II) carboxylates. The ruthenium systems tested so far seem to display a slightly lower level of activity but are somewhat more discriminating in competitive reactions, which apparently could be due to the formation of less electrophilic carbenoid species. This point is probably related to the observation that some ruthenium complexes competitively catalyze both olefin cyclopropanation and olefin metathesis [46], which is at variance with what is observed with the rhodium catalysts. 

The catalytic activity of low-valent ruthenium species in carbene-transfer reactions is only beginning to emerge. The ruthenium(O) cluster RujCCO), catalyzed formation of ethyl 2-butyloxycyclopropane-l-carboxylate from ethyl diazoacetate and butyl vinyl ether (65 °C, excess of alkene, 0.5 mol% of catalyst yield 65%), but seems not to have been further utilized. The ruthenacarborane clusters 6 and 7 as well as the polymeric diacetatotetracarbonyl-diruthenium (8) have catalytic activity comparable to that of rhodium(II) carboxylates for the cyclopropanation of simple alkenes, cycloalkenes, 1,3-dienes, enol ethers, and styrene with diazoacetic esters. Catalyst 8 also proved exceptionally suitable for the cyclopropanation using a-diazo-a-trialkylsilylacetic esters. ... 

A screening of ruthenium(II) carboxylates and several ruthenium(II) chloride complexes has identified tetrakis(trifluoroacetato)diruthenium as an excellent catalyst for the cyclo-propanation of cyclooctene with ethyl diazoacetate (60°C, excess of alkene, 0.75 mol% of catalyst yield of ethyl bicyclo[6.1,0]nonane-9-carboxylate 99% endojexo 1.65)." With several other ruthenium(II) complexes, ring-opening metathesis polymerization of cyclooctene competes strongly with the cyclopropanation reaction. 

The absence of mesomorphism in these compounds was explained on the basis of space-filling requirements. Thus, the intercalation of pyrazine between the binuclear units creates free volume which needs to be filled to obtain a stable, condensed phase when the carboxylates bear only one chain, the interdimeric space is likely filled by the aliphatic chains belonging to a different polymeric chain, giving rise to a crossed structure which prevents the formation of a columnar mesophase. However, as will be seen later, liquid-crystalline behavior was induced in the case of mixed-valence diruthenium(II,III) carboxylate complexes with bulky equatorial Kgands bearing two and three aliphatic chains as with such ligands, it was possible to fill the interdimeric space and thus to induce a thermotropic columnar mesophase. Very recently, the synthesis, characterization, and mesomorphic properties of pyrazine-polymerized divalent rhodium benzoates have also been reported (99). " Most of these compounds exhibit columnar (Colh, Coir, CoIn) and cubic mesophases with melting transition temperatures close to, or even below, room temperature. 

The trifluoroacetate analogue of [Ru2(02CR)2(C0)4]n was synthesized by Petrukhina et al. [68]. These were obtained by gas phase sublimation of the crude product from the reaction of Ru3(CO)i2 and trifluoroacetic acid in a DCM/benzene mixture. The solid state study of [Ru2(02CCF3)2(C0)5]2 (2) (Scheme 3) reveals a dimer of dimer structure. Petrukhina and Davies also reported a variety of mixed carbonyl/fluorinated benzoates of diruthenium(l,l) obtained via melt reactions of Ru3(CO)i2 with appropriate carboxylic acids (3-9) [69]. Compounds 3-6 show a... 

Ru/ Most diruthenium paddlewheels contain Ru " cores, which are formally mixed-valent, Ru(II)Ru(III). These cores are delocalized with Ru(2.5)Ru(2.5) oxidation states [44]. Two other redox states of the diruthenium core, Ru and RUj, have also been isolated, though only for a subset of the ligands listed above for Ru. Generally, RUj paddlewheels have weaker donors, for example, carboxylates and amidates, while Ru paddlewheels have more electron-rich donors, for example, amidinates and aminopyridinates. 

Another direction has been to develop heterogeneous applications of diruthenium paddlewheels [97]. By using multitopic carboxylate ligands, for example, 1,4-benzenedicarboxyate, RUj tetracar-boxylates are assembled into microporous networks. Interesting applications such as the catalytic hydrogenation of alkenes, the oxidation of primary aliphatic alcohols, and photocatalytic hydrogen production from water have been reported [98-101]. 

A wide series of diruthenium (II, II) tetracarboxylates of general formula [Ru2(jU-02CC H2 +i)4] has been made by the Grenoble group the carboxylate substituents include linear alkyl chains ( =4-19), unsaturated chains, and fluori-nated chains [51],... 

The structure and electrochemistry of a number of diruthenium(ll, lll) tetrametallocene carboxylates have been studied in a general paper, which examines the coordination chemistry of ferrocene and ruthenocene bis-carbox-... 

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