Synthesis And Electrochemical Characterization Of Acetylacetone (Acac) And Ethyl Acetate (Ea) Appended Beta-Trisubstituted Push-Pull Porphyrins: Formation Of Electronically Communicating Porphyrin Dimers

Two new families of "push-pull" tetraphenylporphyrins with one acetylacetone (acac) or ethyl acetate (EA) moiety at a beta-pyrrole position of the macrocycle and two Br or Ph substituents at the antipodal beta-positions were synthesized and structurally, spectroscopically, and electrochemically characterized. The examined porphyrins are represented as MTPP(R)(2)acac and MTPP(R)(2)EA (where R = Br or Ph and M = H-2, Co, Ni, Cu, or Zn). NiTPP(Br)(2)acac exhibits an extremely nonplanar conformation (Delta 24 = 0.44 angstrom, Delta C-beta = 0.82 angstrom), while H2TPP(Br)(2)EA and ZnTPP(Ph)(2)EA exhibit a quasi-planar conformation. All of the synthesized acac-appended porphyrins show a keto-enol tautomerism in solution, which results in formation of hydrogen bonded dimers as evidenced by H-1 NMR and mass spectrometry. Dimers were also detected under the electrochemical conditions for the dibromo derivatives but not the diphenyl substituted porphyrins. A facile stepwise and reversible electrogeneration of the electronically communicating porphyrin dimers is observed for MTPP(Br)(2)acac where M = Cu-II, Ni-II, or Zn-II.