Palladium(II) and Platinum(II) Tetramethyltetrapyridinoporphyrazine Complexes: Redox Properties and Interactions with Cysteine and Histidine

Cyclic voltammetry and spectroelectrochemistry studies are reported for the tetramethyl- tetrapyridinoporphyrazine complexes N,N′,N″,N‴-tetramethyltetra-2,3-pyridinoporphyrazine palladium(II) (1a), N,N′,N″,N‴-tetramethyltetra-3,4-pyridinoporphyrazine palladium(II) (1b), N,N′,N″,N‴-tetramethyltetra-2,3-pyridinoporphyrazine platinum(II) (2a) and N,N′,N″,N‴-tetramethyltetra-3,4-pyridinoporphyrazine platinum(II) (2b). Cyclic voltammetry on Pt disc electrodes showed two reductions. The first reduction was assigned to one-electron transfer to the ring with the formation of a monoanion species. All the tetramethyltetrapyridinoporphyrazine complexes are readily reduced to the monoanion species in the presence of histidine or cysteine. The rate constants for the interaction of complexes 1a, 1b, 2a and 2b with histidine and cysteine range from ~2 × 10−3 to 0.26 dm 3 mol −1 s −1.