Deep-Cavity Cavitand Octa
Acid as a Hydrogen Donor:
Photofunctionalization with Nitrenes Generated from Azidoadamantanes
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Abstract
1-azidoadamantane and 2-azidoadamantane form a 1:1 complex
with
hosts octa acid (OA) and cucurbit[7]uril (CB7) in water. Isothermal
titration calorimetric measurements suggest these complexes to be
very stable in aqueous solution. The complexes have been characterized
by <sup>1</sup>H NMR in solution and by ESI-MS in gas phase. In both
phases, the complexes are stable. Irradiation of these complexes (λ
> 280 nm) results in nitrenes via the loss of nitrogen from the
guest
azidoadamantanes. The behavior of nitrenes within OA differs from
that in solution. Nitrenes included within octa acid attack one of
the four tertiary benzylic hydrogens present at the lower interior
part of OA. While in solution intramolecular insertion is preferred,
within OA intermolecular C–H insertion seems to be the choice.
When azidoadamantanes included in CB7 were irradiated (λ >
280
nm) the same products as in solution resulted but the host held them
tightly. Displacement of the product required the use of a higher
binding guest. In this case, no intermolecular C–H insertion
occurred. Difference in reactivity between OA and CB7 is the result
of the location of hydrogens; in OA they are in the interior of the
cavity where the nitrene is generated, and in CB7 they are at the
exterior. Reactivity of nitrenes within OA is different from that
of carbenes that do not react with the host