Nitrone [2]rotaxanes: Simultaneous chemical protection and electrochemical activation of a functional group

D'Souza, Daniel, Leigh, David, Mottier, Loic, Mullen, Kathleen, Paolucci, Francesco, Teat, Simon, & Zhang, Songwei (2010) Nitrone [2]rotaxanes: Simultaneous chemical protection and electrochemical activation of a functional group. Journal of the American Chemical Society, 132(27), pp. 9465-9470.

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We report on the use of the hydrogen bond accepting properties of neutral nitrone moieties to prepare benzylic-amide-macrocycle-containing [2]rotaxanes in yields as high as 70 %. X-Ray crystallography shows the presence of up to four intercomponent hydrogen bonds between the amide groups of the macrocycle and the two nitrone groups of the thread. Dynamic 1H NMR studies of the rates of macrocycle pirouetting in nonpolar solutions indicate that amide-nitrone hydrogen bonds are particularly strong, ~1.3 and ~0.2 kcal mol-1 stronger than similar amide-ester and amide-amide interactions, respectively. In addition to polarizing the N-O bond through hydrogen bonding, the rotaxane structure affects the chemistry of the nitrone groups in two significant ways: The intercomponent hydrogen bonding activates the nitrone groups to electrochemical reduction, a one electron reduction of the rotaxane being stablized by a remarkable 400 mV (8.1 kcal mol-1) with respect to the same process in the thread; encapsulation, however, protects the same functional groups from chemical reduction with an external reagent (and slows down electron transfer to and from the electroactive groups in cyclicvoltammetry experiments). Mechanical interlocking with a hydrogen bonding molecular sheath thus provides a route to an encapsulated polarized functional group and radical anions of significant kinetic and thermodynamic stability.

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ID Code: 45195
Item Type: Journal Article
Refereed: Yes
DOI: 10.1021/ja1034683
ISSN: 0002-7863
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000)
Australian and New Zealand Standard Research Classification > BIOLOGICAL SCIENCES (060000)
Australian and New Zealand Standard Research Classification > ENGINEERING (090000)
Copyright Owner: Copyright 2010 American Chemical Society
Deposited On: 24 Aug 2011 22:17
Last Modified: 14 Jul 2014 23:38

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