Homometallic

Homometallic and Heterometallic Transition Metal Allenyl Complexes Synthesis,... 

Reactions of clusters with mononuclear or dinuclear metal complexes frequently provide a method of expanding the metal core nuclearity under controlled conditions. The majority of medium- and high-nuclearity homometallic clusters has been prepared from lower-nuclearity cluster precursors by thermolyses ("heat-it-and-hope ) reactions. This is less true of the heterometallic clusters in this... 

Ligand fluxionality on metal clusters has been the subject of many studies, the majority of reports focusing on carbonyl migration on homometallic tri- and... 

Relatively few investigations involving palladium carbonyl clusters have been carried out, partly because palladium per se does not form stable, discrete homometallic carbonyl clusters at room temperature in either solid or solution states.114,917-922 Nevertheless, solution-phase palladium carbonyl complexes have been synthesized with other stabilizing ligands (e.g., phosphines),105,923 and carbon monoxide readily absorbs on palladium surfaces.924 Moreover, gas-phase [Pd3(CO)n]-anions (n = 1-6) have been generated and their binding energies determined via the collision-induced dissociation method.925... 

Figure 7.13 The evolution along the series of lanthanides of the sum of Ln-0 bond lengths in homometallic [Ln2] complexes for each crystallographic site. The solid lines...

Figure 7.15 Superposition of the ESI mass spectrograms of the [Ce2], [Er2] and [CeEr] complexes, emphasizing the absence of the characteristic peaks from any of the homometallic analogues on the graph from the heterometallic species.

The bond lengths and angles of the TTF moiety are close to those reported for the noncoordinated neutral unit, indicating that organic molecule is neutral. The complexes reach the nanometric scale, the length of the molecules is equal to 38.25 A ( 4 nm). The shortest intermolecular S---S contacts are equal to 3.9768(35) A for homometallic complex and 3.9456(16) A for heterometallic. 

In addition to these homometallic (rhodium) clusters, several hetero-metallic clusters of the type [M M CO o]2, where M and M1 are each different metals selected from the Co, Rh, Ir triad (jc = 1-11), have been described and claimed to be useful catalysts in the reaction between carbon monoxide and hydrogen to produce oxygenated products (68, 69). These complexes can be prepared from the heterometallic dodecacar-bonyl complexes, [MuM (CO)12] (M, M1 = Co, Rh, or Ir y = 1-3), by simply mixing the appropriate dodecacarbonyl species in THF under nitrogen and then adding water (70). They can be isolated by adding a suitable cation e.g., Al3+, Mg2+, Ca2+, etc. 

In a more general context, metal carbonyls on zeolites can be a unique way to prepare highly dispersed metal catalysts. In the present work, this is especially the case for iron as no other mild methods are operative. It is expected that the method could be applied to the preparation of bi- and polymetallic catalysts even though the starting material are not bi- or polymetallic clusters, but more conveniently homometallic clusters. 

Compared to the wealth of data concerning the solid- and solution-state structures of lithium (di)organophosphides, reports of heavier alkali metal analogues are sparse. Indeed, the first crystallographic study of a homometallic heavier alkali metal (di)organophosphide complex was reported only in 1990 (67) and the majority of such complexes have been reported in the past 3 years. Interest in these complexes stems mainly from their enhanced reactivity in comparison to equivalent lithium complexes, which is particularly useful for the synthesis of alkaline earth, lanthanide, and actinide organophosphide complexes. 

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