Hydrides electron paramagnetic resonance

The isomerization of 5-vinyl-2-norbornene to 5-ethylidene-2-norbornene has been performed using a catalytic system consisting of an alkali metal hydride and an amine. The activity of the alkali metal hydride increased with increasing size of the alkali metal KH > NaH > LiH. Among the various amines tested, only aliphatic 1,2-diamines exhibited the activity for the isomerization. Electron paramagnetic resonance (EPR) and UV-visible spectroscopic experiments on the active species suggest that the isomerization of 5-vinyl-2-norbornene proceeds through a radical mechanism.167... 

Few paramagnetic hydrides are known and even fewer have been studied by Electron Paramagnetic Resonance. For example, [TiH2Cp2] and TaH2(dmpe)2Cl2 have been examined in this way. 

The reduction of cyanocobalamin gives three possible oxidation states for the cobalt atom (Fig. 2). Electron spin resonance studies with Bi2-r reveals that this molecule is the only paramagnetic species giving a spectrum expected for a tetragonal low spin Co(II) complex. Controlled potential reduction of cyanocobalamin to Bi2-r proves that this reduction involves one electron, and further reduction of Bi2-r to B12-S requires a second single electron (16—19). At one time B12-S was considered to be a hydride of Co(III), but controlled potential coulometry experiments provided evidence against a stable hydride species (16). However, these experimental data do not exclude the possibility of a stable Co(III) hydride as the functional species in enzyme catalyzed oxidation reduction reactions. 

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