Electrochemical and spectroscopic studies of poly(diethoxyphosphoryl)porphyrins

Abstract

The synthesis and electrochemical characterization of two related series of porphyrins bearing diethoxyphosphoryl groups are reported. One group of compounds is represented as (T( p-R)PP)M where R = phos = P(O)(OEt) 2 and M = Zn(II) or H 2 while the other is represented as (di( p-R)Pdi(phos)P)M where R = P(O)(OEt) 2, H or CH 3 and M = Zn(II) or H 2. Each porphyrin was investigated by electrochemistry and thin-layer spectroelectrochemistry in CH 2Cl 2, CDCl 3, CHCl 3 or PhCN containing tetra- n-butylammonium perchlorate (TBAP) as supporting electrolyte. The highly electron-withdrawing P(O)(OEt) 2 groups lead to easier reductions and harder oxidations than the two comparison compounds, (TPP)Zn and (TPP)H 2 where TPP = the dianion of the tetraphenylporphyrin. The P(O)(OEt) 2 groups located on the two meso-positions of the porphyrin macrocycle in (di( p-R)Pdi(phos)P)M or on the para-positions of the substituted phenyl groups in (T( p-R)PP)M can also bind to the Zn(II) ion of another porphyrin in solution, leading to the formation of aggregates which was both concentration and solvent dependent as determined by UV–visible spectroscopy and electrochemistry. Binding constants for addition of triphenylphosphine oxide (PPh 3O) to the zinc porphyrins were also measured in CDCl 3 and ranged from log K = 1.7 to 3.1 for formation of the five-coordinate complex. The comparison of X-ray diffraction data for the investigated diethoxyphosphoryl-substituted porphyrin (diPdi(phos)P)H 2 and its Zn complex showed that the metallation induces almost no change in the geometry of the porphyrin macrocycle, but plays the key role in the process of supramolecular assembling.