Cluster chemistry trinuclear complexes

Mo, W) are very useful reagents in organometallic chemistry, in particular for the formation of metal-metal bonded complexes. This is illustrated below by the high-yield synthesis of a heterotrinuclear complex having a linear M— Pt—M core, Section C. The trinuclear complexes M—M —M react with tertiary phosphines3,4 to give heterotetranuclear clusters M2M 2( 7-C5H5)2 (CO)6(PR3)2 and details of the synthesis of two of these (M = Mo M = Pd, Pt) are presented in Section D. 

Nickel forms organometallic clusters with three to six metal atoms. Among these some unusual structures and bonding situations occur which were mentioned in Chapter 2. The cluster chemistry of palladium is rather poor, and the outstanding features of platinum are a considerable number of trinuclear heterometallic complexes and the chimney-like structures of the clusters [Pt3(C0)g]. ... 

Rhenium occupies a very important place in the development of the chemistry of complexes containing metal metal double, triple and quadruple bonds. This chemistry involves coordination complexes that contain pairs or trinuclear clusters of rhenium atoms and has been surveyed in a recent monograph entitled Multiple Bonds Between Metal Atoms .5 This source, which covers the literature up to early 1981, has also been invaluable in preparing the present review and can be consulted for a more complete and detailed coverage of these classes of complexes. 

Given the well documented role of homolytic M-M bond cleavage in photoreactions of dinuclear carbonyls, a logical hypothesis for the photofragmentations of trinuclear complexes would be to follow a similar path to give a diradical. Indeed such an intermediate is attractive in the context that the lower quantum yields could be attributed to rapid recombination of the radicals held together by the rest of the cluster. However, experiments with added chlorocarbons in Ru3(CO)i2 photolysis solutions have shown that a trappable diradical is not an intermediate in the photoreaction chemistry, but instead the intermediate formed is susceptible to trapping by two electron donors (i.e., Lewis base nucleophiles) (eq. 13) [17,20,48-50]. 

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

As mentioned previously, one of the more interesting developments in the chemistry of Wn has been the synthesis and the characterization of dinuclear complexes containing W—W double bonds and trinuclear clusters containing W—W single bonds. 

It is in this oxidation state that the known chemistry of the two elements is most different. For rhenium di- and trinuclear cluster species predominate (Section 18-D-5), whereas for Tc there are only a few Tc and no Tc3+ complexes. Mononuclear Tc3+ species do occur. The only simple [MXJ3- complex known for either element is the [Tc(NCS)6]3 ion, but the mer-MCl3(PR3)3, MCl3py3, and [MX2(LL)2]+ complexes with X = halide, NCS , or MeS" and LL a diphosphine or diarsine are important.41 Some of these complexes can be reduced with retention of structure in the II and even I oxidation states.42... 

Halides are known to labilize CO ligands in trinuclear ruthenium clusters. For a survey of these reactions see G. Lavigne in The Chemistry of Metal Cluster Complexes, D.F. Shriver, H.D. Kaesz and R.D. Adams (eds), VCH, New York, 1990, p. 201. 

The most extensive studies of the chemistiy of cluster complexes have been associated with the trinuclear cluster unit, as may be anticipated. A wide range of substitution reactions has been demonstrated for both Ru3(CO)i2 and Os3(CO)i2, with the full range of ligands normally employed in the study of metal carbonyl chemistry. In genera 1, the trinuclear osmium cluster is more readily maintained, ruthenium often giving rise to cluster breakdown, yielding mononuclear and binu-clear adducts. This reflects the increased bond enei of the metal-metal bond on descending the triad (see Table X later in this section). 

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