Proton loss transition metal complexes

In an aquo-complex, loss of protons from the coordinated water molecules can occur, as with hydrated non-transition metal ions (p. 45). To prevent proton loss by aquo complexes, therefore, acid must usually be added. It is for these conditions that redox potentials in Chapter 4 are usually quoted. Thus, in acid solutions, we have... 

Transition metal complexes can promote reactions by organizing and binding substrates. We have already seen this in terms of metal-directed reactions. Another important function is the supply of a coordinated nucleophile for the reaction, which is incorporated in the product. We have already seen a coordinated nucleophile at work in the reaction discussed above of Co— OH with NO+ nucleophiles, which are electron-rich entities, are best represented in coordination chemistry by coordinated hydroxide ion, formed by proton loss from a water molecule this is a common ligand in metal complexes. Normally, water dissociates only to a very limited extent, via... 

Attack by proton donors R3SnNMe2+ HX->R3SnX-hMe2NH (X = NR 2, PR 2, AsR. OH, OR, SR, Halogen, transition metal complex, carbon acid ). This has an enormous range. Carbon acids include hydrocarbons such as alkynes and cyclopentadiene. The reactions are aided by the loss of volatile dimethylamine. 

Exchange reactions of aromatic compounds catalyzed by base are also well-documented. The generation of benzyne intermediates by loss of HX (or DX) from haloaromatics in the presence of a strong base such as NH2 (or NDi) is responsible for H—D exchange. Complexation of aromatics to zero-valent transition metals to give complexes such as 7i-C6H6Cr(CO)3 enhances the acidity of the protons of the complexed aromatic and permits base-catalyzed exchange. 

Route I (oxidative addition) involves a concerted oxidative addition process with the formation of metal-hydride species A. Alternatively, an electrophilic attack by the metal center on the aryl ip o-carbon may afford a metal arenium (Wheland) complex B followed by proton loss. In the agostic C-H bond activation route, the six-membered transition state C including a hydrogen-metal interaction has been found to initiate the C-H activation process, leading to an agostic intermediate D and acting simultaneously as an intramolecular base for deprotonation. 

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