Carbenes generation hosts

The reactive behavior of a carbene within a molecular reaction vessel is expected to be very different from that of a carbene in any other reaction medium. Host vessels may have any variety of different channel or cavity sizes that can restrict the mobility of carbene guests and any other reaction partner that might also be included.54 One should even be able to generate, within the host domain, a carbene that has no intramolecular reaction pathways available. Situated like a model ship... 

The history of supramolecular carbene chemistry is not long. Preliminary trials, during the 1970s, involved the generation of carbenes in the presence of micelles, e.g., quaternary ammonium salts, and crown ethers.72 However, carbene host ICs were not formed, nor were they sought. Instead, these hosts enable phase transfer catalysis (PTC) of Lewis acid-Lewis base reactions, e.g., the SN2 reaction (Equation (1)). 

Adamantylidenes, when generated by photolysis of the corresponding diazirines incarcerated within an organic container, were found to behave differently from free carbenes and the chemistry ensuing was determined by the structure of the host-guest complexes. Thus, the substituent pattern on the adamantane skeleton affected the orientation of the carbene within the host cavity. ... 

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