ORGN 255 |
| The preparation, characterization and operation of two generations of the trivalent mechanically interlocked molecular machines – molecular elevators – have been investigated in order to compare and understand the properties and mechanisms of operation of these kinds of artificial machines as a prelude to optimizing their functional operations. We have modified the tritopic receptor in the molecular elevator first generation by introducing dioxynaphthalene π-electron-rich units onto their termini (Scheme). The extended aromatic ring system confers stronger electron-donating power compared with the simple benzo units. These additional structural features should direct and enhance the formation of [π-π] stacking and charge-transfer (CT) interactions with the electron-acceptor bipyridinium (BIPY2+) units. We report (1) the synthesis of two tris-crown ether derivatives containing catechol and 2,3-dioxynaphthalene π-electron-rich units, respectively, to give the first and second generations of the molecular machines that act like nanometer-scale elevators, (2) the elevators' characterization by mass spectrometry and 1H NMR spectroscopy and (3) acid-base switching processes by 1H NMR spectroscopy. Scheme. The trifurcated guest salt [2H3][PF6]6 and the tritopic host 1 in a CHCl3/MeCN solution (3.0 mL, 2:1) form a 1:1 adduct (superbundle) that was converted to the molecular elevator [4H3][PF6]9 in the reaction with (i) 3,5-di-tert-butylbenzylbromide, followed by (ii) counterion exchange (NH4PF6/MeOH/H2O). The same protocol, without 1, was used to synthesize the control compound [3H3][PF6]9.
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Molecular Recognition and Materials
1:00 PM-4:40 PM, Monday, 29 August 2005 Washington DC Convention Center -- 201, Oral
Division of Organic Chemistry |
