Synthesis, electrochemistry and spectroelectrochemistry of tetraundecylporphyrins in nonaqueous media

Abstract

Six meso-substituted tetraundecylporphyrins were prepared in high yield using an improved synthetic method and then characterized by electrochemistry and spectroelectrochemistry as well as UV-vis, FTIR and NMR spectroscopy. The examined compounds are represented as (TUP)M where M = H2, ZnII, CuII, NiII, PdII or MnIIICl and TUP is the dianion of a porphyrin having undecyl groups (-CH2(CH2)9CH3) on the four meso-positions of the macrocycle. Two oxidations are observed for each compound in CH2Cl2 and PhCN containing 0.1 M TBAP, leading to the stepwise formation of π-cation radicals and dications. The free-base and MnIIICl derivatives undergo two reductions but only one reversible reduction is seen for the other porphyrins under the given solution conditions. Comparisons are made between the electrochemical behavior of the (TUP)M derivatives and two related series of porphyrins, (TPP)M and (OEP)M. The effect of substituents on the meso-positions of the TUP macrocycle is also discussed.