Fullerenes as ligands

A common route to the synthesis of complexes involving fullerenes as ligands is by displacement of other ligands, typically those weakly coordinated to metals. For example, the platinum complex shown in Figure 13-35 can be formed by the displacement of ethylene ... 

The following is a comprehensive smwey of the chemistry of macrocycles comprised entirely of phenyl and acetylenic moieties. Although over fom" decades old, this area of research has come into its own just in the last few years. Widespread interest in the field has been spurred by recent discoveries utilizing these compoimds as ligands for organometallic chemistry, hosts for binding guest molecules, models of synthetic carbon allotropes, and precursors to fullerenes and other carbon-rich materials. This review will discuss the preparation of a tremendous variety of novel structm-es and detail the development of versatile synthetic methods for macro cycle construction. 

As immense pi systems, fullerenes were recognized early as ligands to transition metals. Fullerene-metal compounds have been prepared for a variety of metals. These compounds fall into several structural types ... 

The elution of [60]- and [70]fullerenes was measured in water-methanol as a function of temperature on a poly(octadecylsiloxane) phase.67 The retention was shown to be dependent on the surface tension of the stationary phase through a simple geometrical model in which the solute formed a cavity in the stationary phase. In affinity chromatography, it was demonstrated that low ligand density may be a requirement for specificity of binding.68... 

As seen, fullerenes behave as unsaturated ligands. Hence it is expected that coordination to metal fragments might saturate (at least partially) their electron-affinity. Hence it is expected that the electron-withdrawing ability of fullerenes is lowered after complexation with respect to that in their free state. 

Heating 26 with an excess of PPhj under pressure in chlorobenzene leads to the loss of one coordination site. One more Os-Os bond is broken upon formation of the complex Os3(CO)6(CNR)(p3-CNCH2QH4)-(PPh3)(p-PPh2)(p-T r -C6o) [74], The T r binding mode observed in this complex is very unusual for Cg0. One further example, where can act as a four-electron ligand is the fullerene carbido pentaosmium cluster complex 28 shown in Scheme 7.13 [75,76], The ri T -complex 28 is formed in a mixture with the normal T r r carbido pentaosmium complex 27. The two complexes can be converted into one another at elevated temperatures. 

Cyclic silylphosphanes, see Silylphosphanes, phosphorus-rich, cyclic Cyclic sulfur-nitrogen compounds, see Sulfur-nitrogen compounds, cyclic Cyclic trithiolate ligand, 38 8-9 Cyclic voltammetry A. chroococcum Fd 1, 38 130-131 fullerene adducts, 44 19 nickel(ll) macrocyclic complexes, 44 112 Rieske proteins, 47 138, 139 Cyclidenes, as cobalt complex ligands, 44 282-284... 

A few other interesting molecular architectures exhibiting uncharacteristic electrochemical behavior have been constructed on the basis of the methanofullerene building block. These include two methanofullerene-substituted bipyridine ligands complexed to rhenium and ruthenium ((35) and (36) in Fig. 17), which were prepared as possible candidates for photoinduced electron transfer processes [138]. In addition, three fullerene crown ether conjugates ((38), (39), and (40) in Fig. 18) have... 

Since the first report of a complex involving a direct metal-to-Ceo bond, (Ph3P)2 Pt( 7 -C6o)/ numerous studies have established that the fullerene Ceo acts as a moderately electronegative alkene in coordinating to electron-rich metal centers. In many cases the Ceo ligand is subject to relatively facile displacement when the complex is in solution however, the zerovalent, octahedral complexes M(CO)3(dppe)(Cgo) [M = Mo, W dppe = l,2-bis(diphenylphosphino)ethane] display outstanding stability even under severe conditions. The overall time needed to prepare these complexes from commercially available M(CO)g is dramatically reduced by adopting a biphasic procedure for the synthesis of the precursor M(CO)4(dppe), which was first described for the preparation of Mo(CO)4 (dppe). Here details are presented for the biphasic synthesis of W(CO)4(dppe) and for its use in the preparation of W(CO)3(dppe)(Cgo)-... 

The synthesis and structures of transition metal complexes of anionic cyclo-polypnictogen ligands, e.g. cyclo-P5, are discussed in Section 7.2.1 and 11.2. An exciting recent development involves the use of these complexes as building blocks for the construction of novel supramolecular assemblies, including one-dimensional (ID) and two-dimensional (2D) polymers and even soluble spherical fullerene-like aggregates.Complexes that have been used for this... 

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