Molecular Level Insights into the Chemical Reactivity of Metal Porphyrins and Iodine at the Solution/Solid Interface

Highly oxidized metalloporphyrins (MP) exhibit unusual electronic properties and unique reactivities and are known to serve as intermediates in a number of biological reactions. Of special interest are MP systems that can electronically communicate during the oxidative processes. Model synthetic porphyrins substituted with first row transition metals can react with dihalides and undergo metal oxidation or form MP p-cation radicals. MP dimers that are covalently connected by short alkane or alkene bridges exhibit electronic coupling between the macrocycles which can strongly influence the outcome of the oxidation reaction by dihalides. Metal surfaces also can serve as a conduit for electron transfer and promote cooperative behavior during reactions between adsorbed MP and axial ligands. In this contribution, we present STM experimental results and supporting theoretical calculations of the reactions dynamics of I 2 and metal (Co, Zn, and Ni) porphyrins adsorbed on metallic supports. Single molecule level STM imaging was accomplished in-situ under ambient solution conditions. We uncovered unusual surface chemistry and surface modulated cooperativity in the redox reactions. Computations corroborate our experimental findings. The high-resolution images obtained for these reactions at the single molecule level combined with theoretical studies offer insights into surface redox chemistry, surface cooperativity, and surface-driven catalysis.