Trinuclear ruthenium clusters bonding

A trinuclear ruthenium cluster blocked by three pentamethylcydopentadienyl ligands showed a unique reaction environment for C-C bond cleavage. C-C bonds in cydopentadiene and branched alkane are easily cleaved on the triruthenium cluster, giving organo(methylidyne)triruthenium complexes. For example, cydopentadiene coordinates to the trinuclear Ru cluster and cleaves a C-C bond to form ruthenacy-... 

Oxidative addition of hydrogen [reactions (3.55)-(3.57)] to clusters may change the multiplicity of M — M bonds, or cause their breaking. Most often, however, this process is accompanied by dissociation of a Lewis base and, in such cases, of course, the skeleton of the cluster does not change. Oxidative addition and reductive elimination of trinuclear ruthenium clusters have been investigated. Based on the kinetic equation, activation parameters, and isotope effects, the pathway for the reversible reaction... 

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). 

Photochemical Activation. Coordinative unsaturated fragments may also be produced by photolytic reactions. In presence of UV-irradiation metal carbonyl compounds lose sequentially CO-ligands. Electron-deficient, solvent coordinated species produced in this way may combine with inactivated metal complexes via the formation of donor-acceptor metal-metal bonds. Iron, ruthenium, and osmium trinuclear carbonyl clusters may be prepared by this way ... 

So far the discussion has concentrated on the reactions of symmetric 1,3-diynes with trinuclear ruthenium and osmium clusters. Related reactions occur with asymmetric diynes. For example, the reaction of [Ru3(CO)8(/tt-dppm)2] with HC CC CSiMes in thf gives [Ru3(/t-H)(CO)s(/r-dppm)2(/t3-7 --L-C2C GSiMe3)] 263 via the oxidative addition of the terminal C CH component of the diynyl ligand across one of the dppm-bridged Ru-Ru bonds. 

This account makes a few references to the related clusters that have fused-ring cyclopentadienyl derivatives, such as indenyl, azulene, and acenaphthylene, in addition to the cyclopentadienyl clusters with common CsRs groups. Some interesting trinuclear ruthenium complexes are also referred to even though they have no metal-metal bonds in the molecule. 

Au-B bonds are also present in metal clusters with intersticial or peripheral boron atoms. An example is the cluster [Fe4(CO)12BH(AuPPh3)2], which was prepared by reaction of [AuCl(PPh3)] with the carbonyl iron dihydride. With the oxonium salt the reaction proceeds to the trinuclear gold derivative [Fe4(CO)12B(AuPPh3)3] (357).2063-2070 The ruthenium analogues and complexes with other ligands have been also synthesized as, for example, (358).2071-2079... 

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. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

There are few reports of reactions between alkynes and trinuclear clusters of metals other than iron, ruthenium, or osmium. Some rhodium, platinum, and mixed-metal clusters undergo metal-metal bond rupture in reactions with alkynes (54-56), while in other cases the alkyne coordinates to the trinuclear unit without causing any major changes in framework geometry (56-59), as illustrated in Eq. (3). 

Fe3(CO)i2] was expected, but whereas reactions of the iron cluster normally lead to cleavage of the trimeric unit, the ruthenium analog seems to give stable trinuclear species. This was correlated with an increase in the stability of metal-metal bonds on descending the transition metal triad. For instance, when R = Et, Bu" or -in the case of osmium, Ph, the reaction in benzene or toluene under reflux affords [M3(CO)io( -H)(//-SR)] (M = Ru, Os) complexes. The structure of [Os3(CO)io(//-H)(/i-SEt)], synthesized in octane under reflux, has been reported. ... 

The heterometallic derivative Fe2(GO)6(Se)2 /x-HGG(GGMe) Os3(GO)io and its ruthenium homolog Fe2(GO)6(Se)2 /x-HGG(GGMe) Ru3(GO)io both contain an alkyne bound in parallel fashion to the trinuclear cluster and also show Se-G bonds. ... 

The simplest bonding mode found in trinuclear hydrocarbon-substituted clusters of osmium and ruthenium is the 7 -vinyl coordination in which one carbon center is formally cr-bound to one metal atom in the triangular core and the alkene/alkyne unit is formally vr-bound to an adjacent metal, so that the ligand donates three electrons to the cluster. Vinyl complexes are generally prepared by alkyne insertion into [Os3(/U-H)2(GO)io] or by the oxidative addition of an alkene to [Os3(GO)io(NGMe)2l or [Os3(GO)i2], and may be considered to be intermediates in reactions to other hydrocarbon-containing cluster products. A list of reported 77 -vinyl- and the related 77 -acetylide-substituted complexes is presented in Table 1. The related 77 -vinylidene-substituted clusters, in which one carbon atom of the ligand is cr-bonded to two metal centers and the alkene unit is formally vr-bound to the third metal center, can be prepared by the thermal conversion of an 77 -vinyl cluster (Scheme 3). The 77 -vinylidene formally donates four electrons to the cluster core. 

The chemistry of ruthenium carbonyl clusters is littered with instances where the simple trinuclear cluster acts as a catalyst. The list is lengthened by a study showing direct carbonylation of a C-H bond in a benzene ring of 2-phenyloxazo-lines catalysed by Ru3(CO)i2. 

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