Effect of Thiolate vs. Nitrogen-Base Ligands on O2 Stretching Frequencies of (Oxytetraphenylporphyrinato)cobalt

Article abstract of DOI:10.1021/ja00309a017

The resonance Raman spectra of model compounds of oxycytochrome P-450, K^Cr (K^Cr: potassium 18-crown-6-ether) and its 18O2 analogue were located at 1122 and 1058 cm^-1, respectively, in CH2Cl2 solution at ca. 185 K with 457.9-nm excitation.The ν(16O2) of this compound is lower by 22 cm^-1 than that of a model compound of oxyhemoglobin, Co(TPP)(1-Melm)16O2 (1144 cm^-1), measured under similar conditions.The observed shift has been attributed to the presence of lone-pair electrons on the thiolate sulfur atom which donate extra electron density to dioxygen via ? overlap.The ν(O2) of K^Cr and its 18O2 analogue are observed at 1120 and 1055 cm^-1, respectively, by 476.5-nm excitation.The small shift of ν(O2) observed by replacing the SC6H5^- with SCH2C6H5^- ion indicates that the degree of total electron donation to dioxygen via ? and ? overlap is similar for these two compounds.When a CH2Cl2 solution of crystalline K^Cr(HSC6H5) is saturated with dioxygen at ca. 185 K and warmed to ca. 225 K, a new ν(O2) band appears at 1137 cm^-1 which is assigned to .The electronic spectrum of K^Cr in CH2Cl2 solution exhibits the α and β bands at 620 and 522 nm, respectively, and a split Soret band at 468 and 423 nm.The excitation profile of the ν(O2) (1122 cm^-1) suggests that the 468-nm component contains substantial Co-O2 character.