Molybdenum complexes trimeric

Only metal complexes of cycloarsathianes have been structurally characterized, and these include a tetramer (EtAsS)4 (as ruthenium complex) and the methyl cychc oligomers (MeAsS) with n = 4, 5, and 6 (as chromium and molybdenum complexes), e.g. (58) the later starting from a trimer-tetramer equilibrinm mixture (MeAsS) , n = 3 and 4 60 -pjjg structure of the pentamer complex is shown here. 

Oxidations of the molybdenum(IV) trimer M03O4 by [IrCle] and [Fe(phen)3] are inhibited by H indicating initial proton dissociation from the molybdenum complex. No mixed-valence species are detected and the product with [Fe(phen)3] is Mo(VI), while with [IrCle] , Mo(V) is produced. The difference is accounted for in terms of an inner-sphere mechanism for the latter reagent. Activation parameters are similar to those of substitution of SCN or M03O4 . 

Despite the proposal239 in 1929 that molybdenum(IV) complexes such as Mo304(C204)3+ contains an Mo304 4+ core, it was some 50 years later that the significance of trimeric molybdenum clusters was clearly appreciated. Three types of Mo3 cluster have been... 

Examples are listed in Table 8.7 for various numbers of bonds (x) between the double bonds. For the compounds with x = 6, the formation of the 7-membered ring is the preferred reaction. For x >6, the polymer is the favoured product. For x = 4 there is a remarkable variation in behaviour with the catalyst no reaction is observed with the molybdenum carbene catalyst, but with the rhodium complex there is 86% conversion of substrate in 72 h to products consisting of about 5% of cyclic dimer , 4% of cyclic trimer and 91% of linear oligomers (M = 1815). In the early stages of reaction the products are mainly the cyclic species but these undergo ROMP once their equilibrium concentration has been exceeded. With the ruthenium complex as initiator the kinetics of ROMP are less favourable and the products after 72 h consist of 25% cyclic dimer, 17% cyclic trimer and 58 % of linear oligomers (Marciniec 1995a). 

Interest in metal complexes containing polyfluoroalkyl- and polyfluoro-aryl-acetylenes as ligands has continued to be high, and has included compounds of platinum, palladium, gold, iridium, rhodium, - ruthenium, cobalt, - - nickel, molybdenum, and iron. These are reviewed in detail elsewhere in the Report (see Chapter 5). Such complexes may acquire usefulness for organic synthesis in due course thus significant amounts of hexakis(trifiuoromethyl)benzene are formed when perfluorobut-2-yne is incorporated into certain cobalt and nickel complexes. Similarly, the interesting compound hexakis(pentafluorophenyl)benzene was isolated in 40—70% yield hy trimerization of perfluorodiphenylacetylene over 7C-cyclopentadienylrhodium dicarbonyl in toluene. ... 

This synthesis of chromium(ll) acetate ean be eombined with other syntheses to create projects with broader enquiries. In our laboratory class, it is paired with the synthesis of copper(ll) acetate, another acetate-bridged, dimeric complex in which there is a magnetic interaction between the metal centers. Similarly, it could be paired with the synthesis of molybdenum(ll) acetate, Mo2(02CCH3)4, a quadmply metal-metal bonded compound. The stmctural diversity of metal acetates could also be explored by combining this synthesis with that of Cr30(02CCH3)6 or other trimeric basic metal acetates, which are known for many of the transition metals. ... 

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