Synthesis, characterization, X-ray structure, and mixed-valence states of trans-dichlorotin(IV)-5,10,15,20-tetraferrocenylporphyrin

Reaction between H₂TFcP (TFcP^2- is a dianion of 5,10,15,20-tetraferrocenylporphyrin) with tin(II) chloride results in formation of the trans-Cl₂SnTFcP complex, which was characterized by UV-vis, MCD, ¹H and ¹³C NMR, and APCI MS methods. X-ray single crystal analysis was used to determine the structure of the target compound. Crystallography reveals a very unusual α,α,β,β- conformation of the ferrocene groups and largely planar structure of the porphyrin macrocycle. Density functional theory calculations predict that the HOMO in trans-Cl₂SnTFcP is predominantly ferrocene centered, while LUMO is primarily localized over the porphyrin core. Redox properties of the trans-Cl₂SnTFcP complex were investigated using electrochemical (CV and DPV), spectroelectrochemical, and chemical oxidation approaches. Electrochemical experiments conducted in low-polarity solvent using non-coordinating electrolyte reveal the sequential oxidation of ferrocene substituents along with porphyrin-based single-electron oxidation and reduction processes. The first ferrocene oxidation process is separated by 130 mV from the next three ferrocene based oxidations, which are more closely spaced. Mixed-valence [trans-Cl₂SnTFcP]⁺ was generated in situ by spectroelectrochemical and chemical oxidation approaches and characterized by UV-vis-NIR spectroscopy.