ELECTROCHEMISTRY OF NONPLANAR ZINC(II) TETRAKIS(PENTAFLUOROPHENYL)PORPHYRINS

The reduction potentials for the zinc derivatives of three nonplanar tetrakis(pentafluorophenyl)porphyrins, TFPPX(8) (X = Cl, Br, Me), have been measured by cyclic voltammetry in 0.1 M (TBA)PF6/CH2Cl2 solution. E(degrees)' values (V vs AgCl/Ag): ZnTFPPCl8 (2+/+ = 1.57; +/0 = 1.63; 0/- = -0.47; -/2- = -0.75); ZnTFPPBr8 (2+/+ = 1.53; +/0 = 1.57; 0/- = -0.48; -/2- = 0.76); ZnTFPPMe(8) (2+/+ = 0.99; +/0 = 0.97; 0/- = -1.14; -/2- = -1.52 (Ep). The experimentally determined trends in the electrochemical behavior of these porphyrins are in agreement with the prediction that the D-4h --> D-2 distortion of the macrocycle destabilizes the HOMOs (a(1u), a(2u) --> a, b(1)) more than the LUMOs (e(g) --> b(2), b(3)). The instabilities of the pi-radical cations, ZnTFPPX(8)(+), relative to ZnTFPPX(8) and ZnTFPPX(8)(2+) (K-disp = 12 +/- 5 (X = Cl); 5 +/- 3 (X = Br); 0.4 +/- 1 (X = Me)), are related to the effects of electron withdrawal at the meso positions as well as porphyrin distortion on the relative energies of the a(a(1u)) and b(1)(a(2u)) orbitals.