Electrochemical behavior of metallocenium cations encapsulated by a tetrahedral supramolecular capsule

INOR 220

Bryan E. F. Tiedemann, tmann@berkeley.edu1, Burak Ulgut, bu22@cornell.edu2, Héctor D. Abruña, hda1@cornell.edu2, and Kenneth N. Raymond, raymond@socrates.berkeley.edu1. (1) Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720-1460, (2) Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853-1301
The self-assembled [Ga4L6]12- supramolecular cluster (H4L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) binds a variety of monocationic guests within its hydrophobic cavity, forming 1:1 host-guest complexes. In particular, many cationic sandwich complexes such as [Cp2Co]+ have relatively high affinities for the host cavity, exhibiting large binding constants (Kb ~ 104 – 105 M-1). In contrast, binding constants are much smaller for neutral analogs such as ferrocene, with host-guest complex concentrations typically too low to detect via 1H NMR. Host-guest complexes featuring G+ = [Cp2Co]+, [Cp*2Co]+, and [Cp*2Fe]+ (Cp* = pentamethylcyclopentadienyl) encapsulated within [Ga4L6]12- were prepared, and the G+/0 redox couples were investigated by cyclic voltammetry in DMF. For all three host-guest systems, a single (quasi)reversible wave was observed, with E1/2 shifted cathodically vs. free guest. This shift implies encapsulation preferentially stabilizes the cation over the neutral species, and titration of [Ga4L6]12- with Cp*2Fe allowed Kb(G0) to be computed from the dependence of E1/2 on guest concentration.

 

Frontiers of Inorganic Chemistry: The Gray Areas
7:00 PM-10:00 PM, Sunday, 10 September 2006 Moscone Center -- Hall D, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, 11 September 2006 Moscone Center -- Hall D, Sci-Mix

Division of Inorganic Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006