Dimolybdenum carboxylates with

Tetrakis-/i-(carboxylato)-dimolybdenum(II) complexes have been obtained by only one general route, namely by the direct interaction of carboxylic acids with molybdenum hexacarbonyl.8 This reaction requires elevated reaction temperatures and prolonged reaction times. These same compounds are obtained in comparable or better yields by the brief reaction of tetrachloro- or tetrabromotetrakis(tributylphosphine)dimolybdenum(II) with alkyl- or aryl-carboxylic acids in refluxing benzene. The bis-/i-(arylcarboxylato) complexes... 

The chemistry of ditungsten paddlewheel compounds is substantially less developed than the periodically related dichromium and dimolybdenum analogs. This is in part due to the increased susceptibility of the W2 core to reaction with Oj and in part to the increased difficulty in synthesizing the tetracarhoxylate analogs. One of the most commonly used methods is the reaction of WCl and the sodium carhoxylate with Na/Hg in THF (Eq. (6.2)) [12]. While this route works for a number of carboxylates, Wj(02CCH3)4 has to be prepared by metathesis of... 

In 1960, Wilkinson discovered that several carboxylic acids, HO2CR, react with molybdenum hexacarbonyl, Mo(CO)e, at elevated temperatures to form complexes of the type Mo(02CR)2 . The tme nature of these bright yellow molyb-denum(II) complexes was established in 1964 with the publication by Lawton and Mason of the X-ray crystal stmcture of tetra(acetato)dimolybdenum, which is depicted schematically in Fig. 1The Mo—Mo distance of 2.11A is considerably shorter than the Mo—Mo distance of 2.78 A in molybdenum metal, and this fact is evidence that the Mo—Mo bond in Mo2(02CCH3)4 has considerable multiple bond character. 

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