Reactivities of d0 transition metal complexes toward oxygen: Synthetic and mechanistic studies

Abstract

Transition metals such as Fe in porphyrin complexes are known to bind or react with O2, and such reactions are critical to many biological functions and catalytic oxidation using O2. The transition metals in these reactions often contain valence d electrons, and oxidation of metals is an important step. In recent years, reactions of O2 with d0 transition metal complexes such as Hf(NR2)4 (R = alkyl) have been used to make metal oxide thin films as insulating gate materials in new microelectronic devices. This feature article discusses our recent studies of such reactions and the formation of TiO2 thin films. In contrast to the reactions of many dn complexes where metals are often oxidized, reactions of d0 complexes such as Hf(NMe2)4 and Ta(NMe2)4(SiR3) with O2 usually lead to the oxidation of ligands, forming, e.g., -ONMe2 and -OSiR3 from -NMe2 and -SiR3 ligands, respectively. Mechanistic and theoretical studies of these reactions have revealed pathways in the formation of the metal oxide thin films as microelectronic materials.