Redox catalysis and reactivity of metalloporphyrines

Ab initio and density-functional theory (DFT) calculations on the Cu(II)-catalyzed rearrangement of quadricyclane to norbornadiene suggest that reaction proceeds via electron-transfer from the surface/CuSO4 to the hydrocarbon. The mechanisms of direct porphyrin metalation was investigated using density functional theory (DFT) calculations for the gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu and Zn. The related reaction of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. DFT calculations suggest that metalations with Fe, Co and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol−1, in a good agreement with the overall experimental activation energy of 31 kcal mol−1.