This chapter contains sections titled: Oxygenases Catechol 1,2-Dioxygenase Introduction Iron(III) Complexes as Structural and Functional Models for Catechol 1,2-Dioxygenases Mononuclear Iron(III) Precursor Complexes Mononuclear Iron(III) Tetrachlorocatecholate Complexes as Biomimetic Models for Enzyme Substrate Adducts Reactivity Studies of Iron(III) Catecholate Complexes Quercetin 2,3-Dioxygenase Introduction Results Kinetic Studies Copper Complexes as Structural Models for the Active Site of Quercetinase Spectroscopic Studies References