The Reactivity of Transition Metal Complexes with Small Molecules

The Reactivity of Transition Metal Complexes with Small Molecules 

From an energetic viewpoint, these reactions fuel a good number of biological functions which are responsible for biochemical reactions crucial to life . In common chemical processes, these reactions require the use of heterogeneous catalytic systems and drastic reaction conditions (pressures of 100 atm and temperatures around 400°C), whereas, at a cellular level, they proceed smoothly under ambient conditions (room temperature and 1 atm pressure). 

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In the oxidation reactions the problem of oxidant activation is frequently met (in the general case, activation of small molecules [5]). For example, comparatively low reactivity of 02, H202 and 03 under soft conditions requires their prior thermal or catalytic activation, for instance, with the help of transition metal complexes or irradiation. Activation of molecular oxygen by one-electron reduction consumes energy ... 

This chapter illustrates the complementarity of photochemical and radiation chemical techniques to elucidate elementary pathways in mechanistically rich systems. Some of the mechanistic conclusions that have resulted from these studies in aqueous media are presented. Extreme (both high and low) oxidation states of transition-metal complexes are included. Reactivity with respect to electron transfer reactions and small-molecule activation are addressed. 

An indirect yet powerful tool to monitor the metal adsorption sites is to study CO adsorption. CO is widely used as a probe molecule because of its low reactivity and quite sensitive vibrational frequency Small changes in the substrate electronic structure reflect into measurable changes in CO stretching frequency. The study of CO desorption temperature from a metal covered MgO film and of the IR bands associated to the formation of metal-carbonyl complexes provides an useful tool to identify the surface sites involved in the stabilization of the M-CO species [31]. However, for an atomistic view of the sites involved, it is essential to combine the experimental evidences with the results of ab initio calculations. Recently, this has been done for a series of transition metal atoms, Rh, Pd, and Ag, all belonging to the second transition series but characterized by quite different valence structures (Rh, d Pd, di° Ag, d si) [211,212]. 

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