Trinuclear metal carbonyls

The reaction between a trinuclear metal carbonyl cluster and trimetbyl amine borane has been investigated (41) and here the cluster anion functions as a Lewis base toward the boron atom, forming a B—O covalent bond (see Carbonyls). Molecular orbital calculations, supported by stmctural characterization, show that coordination of the amine borane causes small changes in the trinuclear framework. 

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. 

Quite a number of dinuclear, and three trinuclear, metal carbonyls have received some study with respect to photoinduced metal-metal bond cleavage. Some typical systems are given in Table 15.98-108) First, consider Mn2(CO)io which is perhaps... 

Table 7. Two-electron reduction potential for selected bi- and trinuclear metal-carbonyl complexes (V relative to the SCE obtained from reactivity studies).

As with dinudear metal carbonyls ( 13.2.4.2.) the prevalent mode of photoreaction of trinuclear metal-carbonyl complexes is cleavage of a metal-metal bond. Subsequent decay of the bond-cleaved intermediate can yield fragmentation or substitution of the complex. These reactions are discussed in 13.3. 

This contribution is a report on progress in the authors laboratory in the field of solid-gas reactions involving trinuclear metal carbonyl clusters of osmium as solid substrates. 

The (MM) of polynuclear carbonyls have been assigned for a number of compounds, and the MM stretching force constants obtained from normal coordinate analysis have been used to discuss the nature of the M-M bond. Figure 111-57 shows the Raman spectra of Mn2(CO),o, MnRe(CO),o, and Re2(CO)ii, obtained by Quicksall and Spiro. Risen and co-workers" " carried out normal coordinate analyses on many dinuclear and trinuclear metal carbonyls. Table 111-61 lists the observed r(MM) and the corresponding force constants obtained by these and other workers. It is noted that the MM... 

Although a metal ion usually serves as a matrix for the synthesis of organic products, in this case there is a kind of functional work exchange between partners, with L27 assembling the trinuclear metal carbonyl cluster from mononuclear Ni(CO)4- The cluster is isolated as a nickel complex incorporating the L27 template. 

Controlled electron-transfer chain catalysed nucleophilic substitution reactions of di- and trinuclear metal carbonyls allows sequential and regioselective coordination of polydentate ligands. This type of reaction has been illustrated by the syntheses of (tCFg)3C3]Co3(C0)g L > (n = 1-3 L =... 

Reaction of the manganese and rhenium carbonyls, M2(CO)10, with Ru3(CO)12 or Os3(CO)12 in a 3 1 ratio yields the products [M(CO)5]2M (CO)4, with M = Re or Mn, M = Ru or Os. These are considered to be linear trinuclear metal systems. The only other trinuclear carbonyl derivative isolated is OsCo2(CO)n, obtained as one of a number of compounds from the reaction of Co2(CO)8 with H2Os(CO)4. No structural data are available for this compound (241). 

Unlike most metal complexes containing the fa c-(diim i n c) Re1 (CO). unit, which are typically highly luminescent in solution, trinuclear rhenium carbonyl compounds 7 and 8 (see Fig. 11a) show only weak luminescence ( em = 0.0015) in CH3CN at room temperature [36], The quenching appears to occur via intramolecular... 

The first experiments which were carried out in the author s laboratory on organometallic phase-transfer catalysis were concerned with the reduction of nitrobenzenes (4) to anilines (5) by triiron dodecacarbonyl. Such a conversion was reported to occur in benzene containing methanol at reflux for 10-17 h, with the hydridoundecacarbonyltriferrate anion as the likely key intermediate (16). It was our expectation that the trinuclear iron hydride should be generated by phase-transfer catalysis and if so, effect reduction of nitro compounds (4) under exceedingly mild conditions. Indeed this was the case, as illustrated by the results shown in Table I (17). Not only is the reaction complete in 2 h or less using sodium hydroxide as the aqueous phase, benzene as the organic phase, and benzyltrieth-ylammonium chloride as the phase-transfer catalyst, but it occurs at room temperature and requires less metal carbonyl than when the reaction was... 

For the mononuclear and dinuclear compounds, except V(CO)6, the mnnber of valence electrons per metal atom is 18. The EAN (effective atomic number) of the metal is the number of electrons of the d" configuration added to twice the number of CO groups, one electron being further added in the case of metal-metal bonded dinuclear systems. For trinuclear, tetranuclear, and hexanuclear compoimds (metal-carbonyl clusters), the cluster valence electron counting is 48, 60, and 86, respectively. As the [K(cryptand 2.2.2)] derivative. As the tetraalkylammonium derivative. As the tetrachloroaluminate. 

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