Cubanes reactions with transition metal complexes

Desymmetrization to the co-kernel subgroups will become important in connection with the mechanism of reactions involving transition metal complexes as well as of highly symmetric organic molecules, such as cubane or tetrahedrane. A Table of Kernels and Co-Kernels is, therefore, included as Appendix B, but reference to it will be deferred until the the ideas developed in this chapter are extended beyond single atoms, first to diatomic and then to polyatomic molecules. 

Transition-metal complexes of [Sn( a3-NR)]4 cubanes have also been reported. The reaction of Fe2(CO)9 with [Sn( a3-NSiEt3)]4,8, produces the complex [Sn()a3-NSiEt3)]4-2Fe(CO)4,36, in 82% yield, even when an excess of Fe2(CO)9 is used. The presence of only two broad signals for the ethyl substituents in the NMR spectrum suggests that the iron centers scramble in solution, cf. 35. A series of related transition-metal complexes of 4 have been mentioned in reviews, however no details have been reported for the complexes 37a-d. ... 

Like protons, transition-metal ions are strongly acidic and they can, in principle, add to both the C—H and C—C bonds of alkanes. As already noted in the section on proton affinities (Table 1) strained cycloalkanes are intrinsically more basic than open-chain alkanes, and the reaction of cyclopropane with Pt((II) to form a platinacyclo-butane (equation 14) was the first reaction of a formally saturated hydrocarbon with a transition-metal ion . The driving force in this reaction is relief of the strain associated with the small ring. The resulting metallacyclobutane is essentially free of ring strain. Many low-valent transition-metal complexes have been found to react with cycloalkanes. Metal ions convet the strained hydrocarbons quadricyclane , cubane , bicyclo-[2.1.0]pentanes , bicyclo[3.1.0]hexanes , bicyclo[4.1.0]heptanes and bicyclo-butanes into less strained isomers (usually cyclohexanes). 

---