Tetranuclear rhodium clusters

Related substitution patterns are observed in tetranuclear cobalt and rhodium clusters. Thus, the small ligand, P(OMe) (L), occupies axial sites in [Co,(CO)1 L ] (x = 1,2) (17) whereas steric effects become important witfi (OPh) and the isomers shown in Fig. 2 are obtained with tetrarhodium derivatives. 

The tetranuclear rhodium cluster Rh4(CO),2 has also been reported to catalyze the hydrocarbonylation of acrylic acid derivatives with isopropanol as hydrogen donor. As a typical example, ethyl acrylate reacts with CO and isopropanol... 

For tetranuclear cluster complexes, three stmcture types are observed tetrahedral open tetrahedral (butterfly) or square planar, for typical total valence electron counts of 60, 62, and 64, respectively. The earliest tetracarbonyl cluster complexes known were Co4(CO)22, and the rhodium and iridium analogues. The... 

In mixed metal clusters, redistributions can occur in the mass spectrometer so that the highest observed peak arises from such a product. This is clearly exemplified by the heterometallic dodecacarbonyls containing metals of the cobalt triad. The thermal stability of this series of clusters decreases as the rhodium content increases and facile redistributions result in the formation of tetranuclear species containing less rhodium the very thermally stable Q I CO) does not rearrange184. ... 

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

The reaction of M3(CO)12 with both open-chain and cyclic poly-alkenes has attracted some attention, especially in the case of Ru3(CO)i2. In most of the examples reported, the organic fragment bonds to the metal framework in such a way as to interact with more than one of the three metal atoms (68-77). There are some exceptions to this general statement, however. One is the reaction of Ru3(CO)j 2 with cyclopentadiene, in which a mononuclear complex is obtained (78). In other cases, tetranuclear and hexanuclear compounds are obtained (79 81). Cluster breakdown has also been observed in the case of a rhodium complex upon reaction with ethylene (55) as shown in Fig. 3. 

Our approach to the preparation of new imido clusters of rhodium consists of the reactions of equimolar quantities of [ Rh( -Cl)(diolefin) 2] with a solution, prepared in situ, by the addition of butyl lithium to ara-toluidine in a 2 1 molar ratio in diethyl ether. At first glance, a hypothetical trinuclear cluster of formulation [Rh3(/i-N-p-tolyl)2(diolefin)3] could be expected from these reactions on the basis of the formation the isoelectronic thiolate complexes [Rh3(//-SPh)2(diolefin)3]+. However, unexpectedly, the results of these one-pot reactions were the formation of the novel tetranuclear clusters [Rli4( u-N-/7-tolyl)2(diolefin)4] diolefin = 1,5-cyclooctadiene (cod) (1), tetrafluorobenzobarrelene (tfb) (2), isolated as dark-red crystalline solids in good yields. 

Neutral and anionic organoimidoimido clusters of rhodium)I) with diolefin and carbonyl ligands are accessible and stable. The diolefin neutral compounds [Rh4(/i-N-/7-tolyl)2(diolefin)4] are a convenient entry into this chemistry for which the synthetic route is an apparently simple replacement reaction, but the reproducibility of the results requires a careful technique. These tetranuclear compounds contain a trimetallic triangular cluster face capped on both sides by two pnra-toly-limido ligands and a further rhodium fragment coordinated to a para-to y ring in a 7 -fashion, giving an overall valence electron count of 64e. 

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