Carbon-atom clusters formation

The cohesive energy per carbon atom in a poly-yne ring is only 99.1 kcal/mol, clearly lower than the value in Cc. Anticipating a long and complicated route of formation when starting from graphite, in does not seem likely that any of the larger clusters observed experimentally would have a linear or cyclic chain structure. 

A much more detailed and time-dependent study of complex hydrocarbon and carbon cluster formation has been prepared by Bettens and Herbst,83 84 who considered the detailed growth of unsaturated hydrocarbons and clusters via ion-molecule and neutral-neutral processes under the conditions of both dense and diffuse interstellar clouds. In order to include molecules up to 64 carbon atoms in size, these authors increased the size of their gas-phase model to include approximately 10,000reactions. The products of many of the unstudied reactions have been estimated via simplified statistical (RRKM) calculations coupled with ab initio and semiempirical energy calculations. The simplified RRKM approach posits a transition state between complex and products even when no obvious potential barrier... 

The formation of boron-carbon bonds between the boron atoms of the clusters and carbon atoms of substituents has been described [51, 52]. These reactions have, however, not been used for the preparation of compounds useful for BNCT. Rather, the connection between the cluster and organic moieties via heteroatoms such as S, O, and N, has been achieved, and several compounds of interest to BNCT have been prepared by subsequent reactions on these heteroatoms. 

The chemistry of the carbidocarbonyl clusters of cobalt and rhodium (none is known for iridium) is predominantly the work of Italian school of the late Paolo Chini and colleagues. The first rhodium cluster of this type to be reported was [Rh6C(CO)ls]2, 24 (59), isolated as a minor by-product in the synthesis of [Rh7(CO)t6]3- (and originally misformulated as [Rh3(CO)l0]-). The formation of 24 resulted from the reaction of [Rh7(CO)l6]3- with chloroform (the source of the carbon atom), present as an impurity in the reaction solvent, and 24 is now synthesized by this reaction [Eq. (17)]. 

The reversible formation of a C-H bond by protonation of [HFe4C(CO)l2] to HFe4(CH)(CO)l2 (75, 7 7) is another instructive example of reactivity at the carbon atom. The exposed carbon atom in the anion proves to be a less basic site than is the methanol molecule, since the methylidyne cluster spontaneously deprotonates in methanol solution [Eq. (24)]. 

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