ELECTROCHEMISTRY AND SPECTRAL CHARACTERIZATION OF OXIDIZED AND REDUCED (TPPBRX)FECL WHERE TPPBRX IS THE DIANION OF BETA-BROMINATED-PYRROLE TETRAPHENYLPORPHYRIN AND X VARIES FROM 0 TO 8

The electrochemistry and spectroelectrochemistry of (TPPBrx)FeCl (TPPB rx is the dianion of beta-brominated-pyrrole tetraphenylporphyrin and x = 0-8) were examined in PhCN containing tetra-n-butylammonium perchl orate (TBAP) as supporting electrolyte. Each compound undergoes two re versible to quasireversible one-electron oxidations and either three o r four reductions within the potential limits of the solvent. The two oxidations occur at the conjugated porphyrin pi ring system, and Delta E(1/2) between these two electrode reactions increases as the molecul e becomes more distorted. The overall reduction of each compound invol ves the stepwise electrogeneration of an iron(II), iron(I), and iron(I ) pi anion radical. An equilibrium between chloride-bound and chloride -free iron(II) forms of the porphyrin is observed with association of the anionic ligand being favored for compounds with x > 5. Singly redu ced (TPPBrx)FeCl (x = 0 to x = 6) forms both mono- and bis-CO adducts in CH2Cl2. Only the mono-CO adduct is observed for (TPPBr7)FeCl, and t here is no binding at all of CO to (TPPBr8)FeCl. The nu(CO) of both th e mono- and bis-adducts increases with increase in the number of Br gr oups, but in a nonlinear fashion which is explained in terms of two co mpeting effects. One is the electron-withdrawing affinity of the Br su bstitutents and the other the nonplanarity of the macrocycle.