7-CO-ORDINATE DIOXYGEN ADDUCT OF IRON(II) WITH SPIN-TRIPLET GROUND-STATE

Recent studies of synthetic models for hemoproteins demonstrated the importance of steric effects on the reversibility of the uptake of dioxygen. In the absence of steric protection of 1 face of the porphyrin, it was suggested that an intermediate in the irreversible autoxidation to Fe3+ products may be a binuclear species, but information on such species is lacking. The isolation of a product of the oxygenation of a 6 co-ordinate Fe3+ complex having properties consistent with a dioxygen-bridged binuclear structure is reported here. Oxygenation of cis-[Fe(bt)2(NCS)2] (bt = 2,2''-bi-2-thiazoline) in non-aqueous solvents yields a product having properties consistent with a binuclear structure in which 7 co-ordinate Fe2+ in the triplet ground state are bridged by singlet dioxygen.