
- Dyotropic-like photorearrangement in a phosphazane cage
Supramolecular chemistry, the subfield that studies intermolecular recognition, was brought to general attention in 1987 by the Nobel committee. Since then, new types of crown ethers, cryptands, and ever more elegant host-guest complexes have been reported in the literature.
Recently, inorganic chemists have developed macrocyclic ligands whose chemistry is akin to that of the organic counterpart, providing to the field new avenues to explore. At present, most of these inorganic complexes are frameworks made of P-N bonds. Adding to the field, the groups of Drs. D. S. Wright and A. Steiner respectively at the University of Cambridge and Liverpool (UK) discovered that phosphazane cage [PNtBu]4 (1α in the picture) rearranges into the highly strained isomer 1β, upon UV light irradiation.
According to calculations, photoisomerization starts with a P-N bond rupture and proceeds through a triplet intermediate, a singlet zwitterion, and a subsequent intramolecular cycloaddition. Overall, however, the reaction is reminiscent of the dyotropic rearrangement observed in organic chemistry, where two σ-bonds migrate (see picture) in regioselective fashion.
The discovery, unique on its own, demonstrates the feasibility to reproduce the regioselectivity of organic photochemistry in P-N macrocycles, opening up exciting possibilities in novel cage systems design, and perhaps generalize the approach to other main group frameworks, such as Si-N.
[“The Regioselective Photochemical Rearrangement of a-[PNtBu]4”, H. Bladt, S. Gonzalez Calera, J. M. Goodman, R. J. Less, V. Naseri, A. Steiner, D. S. Wright, Chem. Comm. 2009, 6637-6639.]
Posted by Alberto 
Posted by Alberto 
Posted by Alberto 
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