Metal halogen interchange

The Union Carbide team also utilized the dilithiocarborane chemistry to produce carboranylenesiloxane polymers by the metal-halogen interchange reaction (Fig. 4) between dilithiocarboranes and dichlorosiloxanes.21 Polymers with molecular weights up to 52,000 were synthesized by this procedure. 

Figure 4 Reaction scheme for the metal-halogen interchange reaction between dilithiocarboranes and dichlorosiloxanes for the synthesis of carboranylenesiloxane polymers. (Adapted from ref. 23.)...

Test of these conclusions is obscured by the simultaneous operation of a metal-halogen interchange (c), which can be interpreted as a car-banion displacement at a halogen atom ... 

That a metal-halogen interchange, (c), does take place under conditions of the Wurtz reaction has been shown by the isolation of amyl iodide in 47% yield from the reaction of amyl sodium with methyl iodide.10... 

Alkenyl-lithiums, which can be prepared by metal-halogen interchange between an appropriate iodide and t-BuLi at — 78°C, undergo cyclizations on warming to room temperature before quenching with a proton source (equation 117) . This cyclization reaction has been extended for the construction of polycyclic alkanes by sequential polyolefinic cyclizations (tandem cyclizations). A propellane system could be constructed in a single step from his-intramolecular cyclization as shown in equation 118 . 

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