Ruthenium II Carboxylate Complexes

667cm-1. The 13CNMR spectrum of the enriched species in CD2C12 at — 90 °C displays a downiield carbide resonance at 477.9 and terminal CO resonances at 222.8 and 220.0 in a ratio of 1 6 6. This anion is protonated first on the Fe—Fe skeleton and next on an Fe—C bond.2 Alkylation occurs on the carbide,8 and reaction with Fe2(CO)9 produces a five-iron carbide anion. In a strongly acidic medium, the carbide ligand is converted to CH. 7 

Ceriotti, P. Chini, G. Longoni, and G. Piro, Gazz. Chim. Ital., 112, 353 (1982). 

Shriver and M. A. Drezdzon, The Manipulation of Air Sensitive Compounds, Wiley-Int rscience, New York, 1986. 

Snbmitted by MICHEL O. ALBERS, ERIC SINGLETON, and JANET E. 

Carboxylate anions are versatile ligands that are found in a variety of coordination modes including unidentate, chelate, and a number of bis(monodentate) bridging modes.1 Such versatility makes the chemistry of carboxylate complexes particularly interesting. It is now also apparent that the diverse catalytic activity shown by many metal carboxylates may be rationalized in terms of the chemistry of the carboxylato ligand.2 In general though, few rational syntheses of metal carboxylates are known.1 This 

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Finally, of note is the hydrogenation of a,/J-unsaturated carboxylic acids. This may be accomplished in a highly diastereoselective manner by the use of ruthenium(II)-BINAP complexes (equation 88)351. The chemical yields are high (83-99%) and the reaction occurs in up to 97% ee. This type of hydrogenation has been used as the key step in a synthesis of building blocks for protease inhibitors and has been performed on a 100 g scale352. 

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. 

Ru-vinylidene complexes can be easily prepared by reaction of low-valent ruthenium complexes with terminal acetylenes. Treatment of the Ru(ii) complex 117 with phenylacetylene gave the Ru(iv)-vinylidene complex 118 in 88% yield (Scheme 41 ).60 The reaction of 118 with C02 in the presence of Et3N afforded selectively the Ru-carboxylate complex 120, probably via the terminal alkynide intermediate 119. 

Ruthenium bipyridyl complexes are suitable photosensitizers because then-excited states have a long lifetime and the oxidized Ru(III) center has a longterm chemical stability. Therefore, Ru bipyridyl complexes have been studied intensively as photosensitizers for homogeneous photocatalytic reactions and dye-sensitization systems. The Ru bipyridyl complex, bis(2,2 -bipyridine)(2,2 -bipyri-dine-4, 4,-dicarboxylate)ruthenium(II), having carboxyl groups as anchors to the semiconductor surface was synthesized and single-crystal Ti02 photoelectrodes sensitized by this Ru complex were studied in 1979 and 1980 [5,6]. 

Considerable variation in stereocontrol can also occur, depending on the catalyst employed (equation 125). In general, the various rhodium(II) carboxylates and palladium catalysts show little stereocontrol in intermolecular cyclopropanation162,175. Rhodium(II) acetamides and copper catalysts favour the formation of more stable trans (anti) cyclopropanes162166. The ruthenium bis(oxazolinyl)pyridine catalyst [Ru(pybox-ip)] provides extremely high trans selectivity in the cyclopropanation of styrene with ethyl diazoacetate43. Furthermore, rhodium or osmium porphyrin complexes 140 are selective catalysts... 

Cleavage of Ru—CH3 bonds by acids has been used by Werner et al. for the selective introduction of small molecules at the ruthenium center. Addition of HBF4 to complex 33, in the presence of carbon monoxide or ethylene, allows the coordination of these molecules in complexes 48,49, and 50 (43). Complexes of type 33 give carboxylate complexes 34,35, and 38 on treatment with carboxylic acids (42,43). A bis(alkyl)ruthenium(II) complex (52) was also obtained by addition of PMe3 to the ethylene complex 51 (24,26). 

Combination of silicon hydrides with catalytic amounts of a ruthenium(II) complex in tetrahydrofuran, chloroform or benzene has afforded a new reducing system capable of efficient reduction of a,p-unsatu-rated carboxylic acids, esters, amides, etc. Addition of a weak proton source, such as a sterically hindered phenol significantly increases reaction rates. The ruthenium mixture was found to exhibit the same regioselectivity observed with the above-described palladium systems. 

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