Ketones, dimesityl reduction

Reductions of certain aromatic ketones with metal hydrides have been shown to involve radical intermediates formed by an electron-transfer mechanism (25). For example, the reaction of aluminum hydride with dimesityl ketone in THF produced a violet solution that gave an EPR spectrum indicative of the presence of a paramagnetic species. The paramagnetic species is an intermediate in the reduction of the ketone, and is believed to be a radical cation-radical anion pair (25). 

With compounds of rather negative reduction potential such as dimesityl-ketone or 2,2 -bipyridine the reaction produced only Ti(III) species in low amount. On the other hand, good n acceptors such as o-quinones or azo-con taining heterocycles yielded large amounts of Ti(IV) complexes of the anion radicals [89] according to Eq. (5) [88]. Similar Ti(IV) semiquinone complexes were reported from the reactions of photogenerated CpTiCl2 with o-quinones [90]. 

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