Spectral study of the dioxygen and carbonyl adducts of ferrous porphyrins ligated by neutral S-donors

A series of the six-coordinated ferrous porphyrin complexes (L)Fe(II)TPP(O2) and (L)Fe(II)TPP(CO) (L, (CH3)2S, or C2H5SH, TPP, meso-tetraphenylporphyrin dianion) was prepared. UV–vis and FTIR spectroscopy were applied to follow the reaction of O2 and CO adducts of Fe(II) porphyrins with neutral thiol and thioether. Using sublimed layers methodology and low temperature technique, as well as isotope substitution, the formation of six-coordinate complexes was monitored in situ. The comparison of CO and O2 stretching frequencies of thiol and thioether adducts indicates that the degree of electron donation is similar for these ligands. The complexes of Me2S and EtSH with Fe(TPP)(O2) are stable at 150 K and slowly decompose at elevated temperatures. In contrast, the carbonyl complexes of Fe(Por) with Me2S and EtSH are relatively stable and retain six-coordination at room temperature. The electronic effects of axial S-donor ligands on the coordinated O2 and CO are discussed and compared with the effects of N- and O-donors.