Clusters containing cyclopentadienyl ligands

Because compounds 4 and 33 are efficient catalyst precursors for the hydrogenation of diphenylacetylene and both contain an alkyne bound parallel to a metal-metal bond, E. Sappa and coworkers have made the hypothesis that clusters with an alkyne bound parallel to one edge of a triangular metal array could act as catalyst precursors or as intermediates in the hydrogenation of alkynes. - i In fact, the unsaturated binuclear complex [Ru2(Cp)2(//-Ph2C2)(CO)] (35), which has the alkyne bonded in a perpendicular mode to the metal-metal bond (Fig. 5), is a poor hydrogenation catalyst.  

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Analogous clusters containing cyclopentadienyl ligands have also been reported K. KKlausmeyer,... 

Metal dimers containing cyclopentadienyl ligands also can be separated to monomers with Hj as for (h -CjH5)2Cr2(CO) at 150 atm (15 MPa) and 70°C to yield HCr(CjHj-h )(CO)3. Mixed-metal hydride clusters may be synthesized from the H -assisted condensation of two different metal carbonyls. When Os3(CO),2 Or Ru3(CO),2 reacts with Ni2(C5Hj-h )2(CO)2 in the presence of at atm P, the mixed-metal clusters M3(ja-H)3Ni(C5H5-h5)(CO), [M = Ru (39%), Os (70%)] are formed l... 

All of these three classes can produce bridge-terminal and/or terminal-terminal exchange, depending upon the particular example in question. In comparison with binuclear complexes, the dissociation pathway of [( -C5H5)Cr(CO)3]2 has not been identified for any cluster. Since most of the dinuclear complexes studied contain cyclopentadienyl ligands which, whenever evidence can determine this, stay bound to one metal, it seems more appropriate to place their exchange processes in the third classification. 

In 1971 only two complexes of palladium(I) had been identified.65 Although the area has grown significantly, the relative paucity of palladium cluster compounds can be attributed, in part, to the surprising weakness of palladium-carbon monoxide bonds and in particular those where CO is bound terminally. In this chapter the chemistry of palladium(I) and clusters of palladium in other oxidation states will be considered. However, complexes containing organic ligands such as allyl and cyclopentadienyl will not be dealt with as this area has been reviewed recently in a companion volume.66... 

Finally, dinuclear Pd complexes can be prepared, which contain bridging cyclopentadienyl ligands (see Dinuclear Organometallic Cluster Complexes). WheuPdl/j -CsHsK ) -2-MeC3Hs) is reacted with two equivalents of phosphines or phosphites, dinuclear species Pd2(/r-C5H5)(/u,-2-MeC3H5)L2 are formed (equation 50). 

Finally, dinuclear Pd complexes can be prepared, which contain bridging cyclopentadienyl ligands see Dinuclear Organometallic Cluster Complexes Pdljj -CsHsXjj ... 

Cyclopentadienyl)tetranickel clusters have not, so far, been intensively studied. The simplest ( / -cyclopentadienyl)tetranickel cluster (NiCp)4, in spite of many efforts, has not been isolated. This unknown species would have the expected closed-shell 60-electron configuration and would be diamagnetic. Such 60-electron species are in fact known, for example (CpCo)4H4. The first (cyclopentadienyl)tetranickel cluster was obtained in the reaction of CpNiNO with LiAlH4/AlCl3 in THF solution at 20 The cluster contains three hydride ligands and has the composition... 

Many types of hydrocarbyi ligands are known for the triruthenium clusters containing a cyclopentadienyl ligand /it3-alkylidyne, /it-alkylidene, /tj-j/ -vinylidene, /t3-J7 ( )-alkyne, ... 

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