Metal-ligand exchange

The case studies below will provide selected examples of calorimetric studies carried out on metal-ligand exchange reactions of phosphorous-based ligands (such as phosphines, phosphite, A -pyrrolyl-phosphines) and N-heterocyclic carbene ligands (NHCs) as well as addition reactions relevant to catalytic transformations, involving metals such as ruthenium, rhodium,platinum,and molybdenum. ... 

In addition to the mechanism of metal-ligand exchange, the affinity of lead for different types of ligands is of interest. Lead s toxicity and the variety of... 

It is driven by a metal-centred redox process, beginning with oxidative addition of the halide substrate to the metal, ligand exchange and then reductive elimination leading to product formation as shown below ... 

A further complication in the identification of target sites and chemical forms of metals is the kinetic lability of coordinate covalent bonds. Metal ligands exchange rapidly in and out of the coordination sphere, in particular for first-row transition metals. This kinetic lability varies between metals, and, as indicated above, is influenced by the nature of the ligand, whether mono- or multidentate, and by the pH and ionic strength of its immediate environment. Copper, for example, forms relatively low affinity complexes with albumin or amino acids, but is tightly bound to ceruloplasmin. Similarly, mercury and cadmium form kinetically labile complexes with amino acids, glutathione, or albumin, but more stable chelates with metallothionein. 

Theory, experiment and reaction rates a personal view . J. Reedijk (2008) Platinum Metals Rev., vol. 52, p. 2 - Metal-ligand exchange kinetics in platinum and ruthenium complexes. Significance for effectiveness as anticancer drugs . 

Abstract Many metal compounds are known to be useful in medicinal applications, and from these the many anticancer Pt(II) and Ru(n)/Ru(ni) compounds are a special class, as they show a particular metal-ligand exchange behavior. In fact these compounds often do have ligand exchange kinetics in the same ordo of magnitude as the division of (tumor) cells, which make them suitable candidates to interfere with this process. The present chapter discusses this class of compounds with a focus on the mechanism of action of cisplatin and related Pt and Ru compounds. 

Benzeneselenol as a representative selenol is a colorless liquid of greater acidity than benzenethiol (p a = 5.9 (PhSeH) 6.5 (PhSH)). The bond energy of Se-H is 73 kcal/mol, is smaller than S-H (87 kcal/mol) [82]. These properties may contribute to the efficiency in the oxidative addition of selenols to low-valent transition metals, ligand-exchange reaction between high-valent transition metal complexes and selenols, and protonation process of carbon-metal bonds. Indeed, several transition metal complexes catalyze the highly selective hydrothiolation of alkynes and allenes. 

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