Hydrodefluorination mechanism

Several mechanisms are involved in the displacement of fluorine by hydrogen and these can be divided into two groups, namely radical-type and nucleophilic hydrodefluorinations. The most general is a radical mechanism involving reductive cleavage of the fluorine bond. Radical catalytic hydrogenolyses take place at the catalyst surface ... 

Gatalytic G-F activation has been demonstrated in several reactions. Most of the catalytic conversions involving the cleavage of a G-F bond achieve hydrodefluorination reactions (i.e., the replacement of fluorine by hydrogen) or cross-coupling reactions of fluorinated aromatics. Prominent exceptions consist of Murai s rhodium-catalyzed exchange reaction between fluorobenzenes (see Scheme 41) and a disilane as well as the amination of 2-fluoroni-trobenzene. At present, turnover numbers are invariably low and there are no detailed studies of kinetics and mechanism of catalytic G-F activation. 

A probable mechanism for the hydrodefluorination of the gm-difluoromethylene derivatives with lithium aluminium hydride, catalysed by ZnCl2 without ancillary ligands, in good to high yields has been suggested. ... 

Apart from olefin metathesis, the mechanisms of various [(NHC)Ru]-cat-alyzed reactions have been analyzed by DFT computations. Among them, the catalytic hydrodefluorination of fluoroarenes, the coupling of alcohols and amines, and the hydrogenation of ketones and esters have received... 

A recent theoretical and experimental study of Radius and co-workers described the catalytic cycle of [(IiPr)4Ni2(COD)] induced hydrodefluorination of polyfluoroaromatics using hydrosilanes as hydryde source. This study concluded that the mechanism for [NiL2] complexes remains unclear and non-general because neither the commonly accepted intramolecular concerted pathway, nor a nucleophilic mechanism of the metal base was valid for partially fluorinated arenes. 

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