Synthesis and characterization of niobium(IV) porphyrins. Formation and spectroscopic properties of dioxygen adducts of niobium(IV) porphyrins

Abstract

The niobium(IV) porphyrins Nb^IV(X)₂(por) have been prepared from Nb^V(X)₃(por)[por = meso-tetraphenylporphinato (TPP), meso-tetra-m-tolylporphinato (TMTP), or meso-tetra-p-tolylporphinato (TPTP); X = Cl or Br]; irreversible oxygenation of these low-valent porphyrins yields adducts such as Nb^V(X)₂(O₂)(TPP) and e.s.r. and i.r. data show that the niobium–O₂ bonding in the dioxygen complexes is best described by the superoxide formalism.