Bridging hydrogen exchange

Similar bridging hydrogen exchange processes have been observed for neutral and cationic (zj -allyL/i-IIjMD, complexes 25 (Scheme 3)23.58,63 j ny of these complexes are prepared by the protonation of the corresponding anionic or neutral (/j4-dicnc)MLn complexes 26 (see Section V.C.l). Migration of the metal about a cyclic ) -allyl ligand (i.e. 25a to 25b) is proposed to involve an (/j" -diene)MLn hydride intermediate/transition state 27. 

Covalent. Formed by most of the non-metals and transition metals. This class includes such diverse compounds as methane, CH4 and iron carbonyl hydride, H2Fe(CO)4. In many compounds the hydrogen atoms act as bridges. Where there are more than one hydride sites there is often hydrogen exchange between the sites. Hydrogens may be inside metal clusters. 

Proton Abstraction. Although the exopolyhedral hydrogens of nido and arachno boranes are generally considered hydridic, the bridge hydrogens are acidic as first demonstrated by titration of and deuterium exchange (71). Some typical reactions are... 

Adsorption of nonionic compounds on subsurface solid phases is subject to a series of mechanisms such as protonation, water bridging, cation bridging, ligand exchange, hydrogen bonding, and van der Waals interactions. Hasset and Banwart (1989) consider that the sorption of nonpolar organics by soils is due to enthalpy-related and entropy-related adsorption forces. 

Deuterium exchange studies on decaborane and other boranes indicate acidic character of bridge hydrogens. They react with bases undergoing proton abstraction reactions ... 

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