Substitution, cluster

In the tetranuclear clusters substitution reactions are complicated by the large number of different possible isomers. For instance, in the structure of Co4(CO)i2 there is the possibility of three different monosubstituted derivatives (apical, equatorial or axial), and seven different di-substituted isomers. It seems possible that the extensive use of 13C, and where appropriate 31P NMR66 could make an important contribution to this area. 

A number of cluster-substituted ketones and the aldehyde all reacted with the Et3SiH/CF3C02H to give the alkyl derivatives rather than the expected alcohols ... 

An exception wras the reaction of (OC)9Co3CCHCH3+PF6- with AT,A -di-methylaniline, in which the basic substrate abstracted a proton to give the vinyl-substituted cluster. The results of these reactions are summarized in Table XII. The (OC)9Co3CCHR+PF6 salts, like the cluster-substituted acylium ion, are rather weakly electrophilic. Although they alkylate N, N-... 

It seems clear that cluster-substituted carbonium ions are easily generated, are very stable thermally, and are of sufficient electrophilic reactivity to be useful in the synthesis of many new functional cluster compounds. Before we consider further their exceptional stability and the mode of their stabilization, it is of interest to mention some chemical consequences of the high stability of a positive charge generated a to the apical carbon atom of the (OC)9Co3C cluster. For instance, one might expect the addition of the positive part of an ionic or polar reagent, X+Y-, to the... 

All of the reactions of such vinylic derivatives that we have studied proceed in this manner (46). This reaction is of special utility in the generation of tertiary cluster-substituted carbonium ions ... 

Not only can existing structural motifs be modified by cluster substitution but completely new materials can be synthesized. (Zhou et al., 2004) employed an early transition-metal octahedral cluster with terminal cyano ligands, [Nb6Cli2(CN)6]4-(Figure 8.6, see also Section 3.3.5) in combination with a metal linker complex... 

The Rb902 cluster substituted by Cs atoms was found with a sample of arbitrary composition (Rb902).76(Csn03),24 (= Rb6.1Cs2.4O2). The X-ray pattern of this sample is indexed essentially on the basis of an enlarged unit cell of Rb902. Instead of a molar volume of 396 cm mol a value of 413 cm mol is found for the substituted Rb902. The additional 17 cm mol" correspond to a substitution of... 

Ni(CO)4 -H 4 PCCHaCHaCNla Ni4(CO)6[P(CH2CH2Clsr)3]4 -H 10 CO (27) The carbonyl clusters substituted by ligands with Group V donor atoms are listed in Table V along with their preparations and references to structural studies. 

Carbonyl Clusters Substituted by Ligands with an Organic n System... 

Clusters substituted with water or water fragments are known. The 58-electron anion [Re4(/ -H)3(/ 3-H)(CO)i2] (Fig. 8) reacts reversibly with a water molecule, which is probably coordinated as a bridging ligand. This complex is unstable above 270 K and gives a derivative with a triply bridging OFF, presumably via a tetrahy-dridic intermediate substituted with a water molecule coordinated to only one metal center. ... 

Instead, cyclopentadienyl tricobalt clusters substituted with the cyclic furyne... 

Coordination-dehydration reactions of propargyl alcohols have been followed in detail on triosmium clusters an example is given in Fig. 26.1 Protonation of triosmium clusters substituted with parallel alkynes leads to propargyl cationic derivatives which, in turn, can isomerize to allenylidene complexes. Fig. 27.1 ... 

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