Complex amidinium-carboxylate interfaces

Tab. 17.4 Rates for unimolecular and bimolecular electron transfer for DeDp-ApAe complexes with amidinium-carboxylate interfaces.

An alternative approach for the study of PCET across amidinium-carboxylate interfaces relies on the formation of ternary complexes such as that shown for 16 [141]. A N-propylisonicotinamidine serves as a ditopic spacer between a Zn tetra-phenylporphyrin donor and 3,4-dinitrobenzoate acceptor. The PCET assembly is afforded by the axial coordination of the pyridyl group to the Zn porphyrin (Ka = 1-9 X 10 M 2 in CH2CI2). A benefit of this approach is a significantly reduced synthetic investment required for the incorporation of Dp/Ap into the assembly. Moreover, the system is highly modular and the De porphyrin can be... 

As previously shown, /V, A-dimetylan i I i ne acts as an electron donor toward the electronically excited Ru(II) tris(dipirydyl) complex (Bock et al. 1979). Recently, this complex was juxtaposed to N,N -dimethy laniline via a salt bridge (Deng et al. 1997 Kirby et al. 1997 Roberts et al. 1997). Supramolecular assemblies have been prepared in which an electron may transfer from A.A-dimethylaniline to the electronically excited Ru(II) tris(dipyridyl) acceptor through the intervening amidinium-carboxylate salt bridge interface (Scheme 5-15). 

The effect of the salt bridge on electron transfer can be determined directly by a comparative kinetics study of a D—[amidinium-carboxylate]—A complex and its switched interface D—[carboxylate-amidinium]—A congener. We have reported such a study for a supramolecular series of complexes where the donor is a ruthenium(II) polypyridyl with one bipyridine (bpy) ligand modified by either amidinium or carboxylate and the acceptor is the complementarity modified 3,5-dinitrobenzene (DNB) [162, 163]. The same donor-acceptor pair bridged by a symmetrical dicarboxylic acid interface has also been examined. 

---