Structure and reactivity of the first-row d-block metal-superoxo complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-07, Vol.48 (26), p.9469-9489
• Main Authors: Fukuzumi, Shunichi, Lee, Yong-Min, Nam, Wonwoo
• Format: Article
• Language: English
• Subjects: Catalysis; Chromium; Cobalt; Coordination compounds; Copper; Electron transfer; Electrons; Iron; Manganese; Nickel; Reactivity; Scandium; Superoxide dismutase; Titanium; Transition metals; Triflic acid; Vanadium; Zinc
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt01402k

In the first-row of d-block metals, ten elements are included, such as scandium (Sc, 3d 1 ), titanium (Ti, 3d 2 ), vanadium (V, 3d 3 ), chromium (Cr, 3d 5 4s 1 ), manganese (Mn, 3d 5 ), iron (Fe, 3d 6 ), cobalt (Co, 3d 7 ), nickel (Ni, 3d 8 ), copper (Cu, 3d 10 4s 1 ) and zinc (Zn, 3d 10 ). The synthesis, characterization, and reactivity of first-row d-block metal-superoxo complexes are discussed together with the structures of the end-on (η 1 ) and side-on (η 2 ) metal-superoxo complexes in this review article. Electron transfer from electron donors to O 2 is enhanced by binding of Sc 3+ to produce an end-on type Sc( iii )-superoxo complex. Metal-superoxo complexes such as Ti( iv )-superoxo, oxovanadium( v )-superoxo, Cr( iii )-superoxo, Fe( iii )-superoxo, Co( iii )-superoxo, Ni( iii )-superoxo and Cu( ii )-superoxo species generally undergo hydrogen atom transfer reactions. A Cr( iii )-superoxo complex undergoes not only hydrogen atom transfer but also oxygen atom transfer reactions. In the presence of protons ( e.g. , trifluoromethanesulfonic acid, HOTf), much enhanced acid catalysis was observed in oxygen atom transfer reactions from a nonheme Cr( iii )-superoxo complex, [(Cl)(TMC)Cr III (O 2 )] + , to thioanisole. The enhanced reactivity of [(Cl)(TMC)Cr III (O 2 )] + by HOTf results from proton-coupled electron transfer (PCET) from electron donors, including thioanisole, to [(Cl)(TMC)Cr III (O 2 )] + . A manganese( iv )-superoxo complex plays a very important role in thermal and photoinduced dioxygen activation by a Mn( iii ) corrolazine complex. A metal-superoxide complex using the last element in the first-row of transition metals, that is a Zn( ii )-superoxide complex, is produced to accelerate the reduction of O 2 &z.rad; − in a SOD (superoxide dismutase) model. This review discusses the structure and reactivity of metal-superoxo complexes covering all ten first-row d-block metals from Sc to Zn.