Radicals from organohalides

Cobaloxime(I) generated by the electrochemical reductions of cobaloxime(III), the most simple model of vitamin Bi2, has been shown to catalyze radical cyclization of bromoacetals.307 Cobalt(I) species electrogenerated from [ConTPP] also catalyze the reductive cleavage of alkyl halides. This catalyst is much less stable than vitamin Bi2 derivatives.296 It has, however, been applied in the carboxylation of benzyl chloride and butyl halides with C02.308 Heterogeneous catalysis of organohalides reduction has also been studied at cobalt porphyrin-film modified electrodes,275,3 9-311 which have potential application in the electrochemical sensing of pollutants. 

In the first work on the PTC carbonylation of organohalides, Pd(PPh3)4 was used as a metal catalyst [110]. There are a number of other examples of the use of Pd° complexes in two-phase carbonylations. The selective formation of one of four possible products, including esters, depends mainly on the composition of the metal complex (e. g., Pd(PPh3)4 vs. Pd(dba)2) [129]. Radical intermediates may be involved in the formation of several of the products. Esters (e. g., benzyl phenylacetate from benzyl bromide) are the major products of the carbonylation of benzyl bromides using a zwitterionic rhodium catalyst [130]. 

The blossoming area of the suitability of the hypophosphorous acid and its derivatives as hydrogen donors comes from the crucial re-examination by Barton and Jaszberenyi s group of some very old radical reductions involving hypophosphorous acid.9 These workers seminal contribution to the use of water as a solvent for water-soluble organohalides to be reduced cleanly and... 

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