Factors That Determine the Mechanism of NO Activation by Metal Complexes of Biological and Environmental Relevance



This account presents a sampling of kinetic and mechanistic investigations on the activation of nitric oxide (NO) by metal complexes of biological and environmental importance. Throughout the review the main emphasis falls on the finding and characterization of factors that control the dynamics of NO–metal interactions in which the metal centers serve as coordination and electron-transfer mediators. On the basis of the systems surveyed, several important aspects concerning the mechanism of NO activation processes have been evaluated and are discussed in detail. They involve the effect of (i) chemical properties of the reaction medium, (ii) electronic nature of the leaving ligand, (iii) environment of the coligands, and (iv) steric hindrance around the metal active center, on the reversible binding of NO to metal complexes, as well as on the electronic nature and reactivity of metal activated forms of nitric oxide in the resulting nitrosyl products. The conclusions drawn from the work summarized in this review, along with a comparison with data available for other related systems, add a valuable piece to the puzzle of the complex mechanistic picture that describes the process of metal-assisted activation of nitric oxide.