Heteronuclear clusters synthesis

Digermanium hexachloride, synthesis in electric discharge, 6 173, 272 Diglycolic acid, complex formation by, 3 276 Digold heteronuclear cluster compounds. X-ray crystallography, 39 358-362... 

The addition of transition metal fragments ML (L = two-electron donor ligand) across formally unsaturated metal-metal or metal-carbon bonds is a well-developed synthetic route to heteronuclear clusters (1,2,11,12,27) and has received theoretical justification from Hoffmann s isolobal principle (46). The addition of a PtL2 fragment across an M=M double bond may be considered as analogous to the reaction of a carbene with an olefin, resulting in a cyclopropane. The use of isolobal analogies in the directed synthesis of heteronuclear clusters has been reviewed (11,12,27). 

Although the vast majority of Group IB metal heteronuclear clusters have been synthesized using one of the generally applicable rational preparative procedures outlined in Sections II,A,1 and II,A,2, a number of such species have been obtained via routes for which the nature of the product cannot be predicted in advance or via procedures which have not been widely used. These other methods of synthesis are outlined in this section. 

Most heteronuclear clusters in which no ligands are attached to the Group IB metals were prepared using one of the few generally applicable rational methods that are currently available for the synthesis of these species. These preparative routes all involve the addition of Ag+, either to preformed cluster anions (98,118,123,190,192) or to neutral polynuclear (188) or dimeric (189,191) compounds. Equations (66) and (67) show examples (189,190). 

In search of an example for a heteronuclear cluster (CO)9Co3ER where E is a transition element with only one ligand R, the synthesis of the complex shown in Fig. 7, recently succeeded41. ... 

These homonuclear clusters are usually also obtained as by-products of the pho-tolytic synthesis of the heteronuclear cluster compounds (see Sec. 1.28.3). 

In initial studies on transition metal cluster chemistry synthetic work was frequently based on chance discoveries. However the explosive development of this branch of chemistry in the last fifteen years has also produced an accelerated evolution of cluster synthetical methods. On going from casual synthesis to tailored cluster synthesis, the systematic preparation of a great variety of homo and heteronuclear cluster compounds is already possible. 

A review article illustrates the use of W(CO)2(CR)Cp as precursor for the synthesis of heteronuclear cluster complexes in which the y3 CR ligand is often present.Addition of Fe2(CO)9 to Mo(CO)2(Ctol)Cp affords the y-alkylidyne... 

Whereas a large number of metal-sulfur clusters are present in nature, carbonyl clusters are exclusively products of chemical synthesis. They have been widely used in industrial catalytic processes17 and some of these processes are triggered by the redox aptitude of these species.lc g As for the metal-sulfur clusters, we will briefly discuss their structures and their propensity to donate/accept electrons in order of increasing nuclearity. We will consider only homonuclear and homoleptic metal-carbonyl derivatives. However, it is noted that heteronuclear derivatives are gaining considerable interest due to the synergistic effect of metal-metal bonds possessing a polar character.lc,ld... 

Fig. 1. Examples of the synthesis of heteronuclear gold cluster complexes by the reaction of Au(PPh3)Cl with transition metal anions.

Heteronuclear gold cluster compounds have, therefore, been proposed as potential precursors for the synthesis of selective catalysts and also as models of the modifications to the substrate that arise at a molecular level. Braunstein has reviewed in more detail the catalytic applications of gold-containing polymetallic systems (212). 

Furthermore, the photolysis of azido complexes can be used for the synthesis of heteronuclear gold cluster compounds, if a source for the heteroatom is present during the photolysis in form of a carbonyl or azido complex. ... 

In order to understand the growth of metal clusters in solution, one should start from a metal complex precursor, such as [My(CO)x], according to Eq. (1). The precursor can be generated in situ. The protocol synthesis of such a chemical precursor is represented by the flow-chart see Fig. 4 for the case of ruthenium-selenide. This flow chart summarizes the synthesis initially reported in 1991, " and it will be taken as the template for similar compounds. A careful follow-up of the reaction was made by means of the Indeed, following the synthesis without carbon, i.e., after step 3, a heteronuclear chemical precursor was identified Ru4Se2(CO)3(CO)g. The ongoing reaction under the boiling point of the solvent for 20 hours led to a complete pyrolysis of the heteronuclear molecular cluster compound to nanopowders of... 

The synthesis of several new heteronuclear hydrido carbonyl clusters have also been described. Reaction of PPH[FeH(CO)9] with M(C0)5THF (M = Or, Mo or W) yields [FeM(y-H)(CO)9] in which the H atom is presumed to bridge the Fe-M bond. Other Fe containing anionic heterometallic clusters reported in 1984 include [Fe0s3H(C0)i3]" and [FeaNKy 3-H) (y-CO) (CO) e Both... 

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