Kharasch-like reaction

Mo(CO)6 was also used to catalyze Kharasch addition reactions of tetrachloro-methane or trichloroacetates to terminal olefins in acetonitrile (Fig. 38) [218]. A precomplexation like for Cr(CO)6 was not necessary. The ligand exchange... 

The catalytic aryl coupling reaction called the Kharasch-Grignard reaction consists of the rapid formation of biphenyl by the addition of an organic halide to a mixture of phenyl magnesium bromide and a trace amount of a transition metal halide. A Tc-complex mechanism from this reaction has been proposed, as shown in Fig. 7-17. According to this mechanism an organic halide most likely attacks the metal atom in [7-25] or [7-26]. ... 

In 1933, M. S. Kharasch and F. W. Mayo found that some additions of HBr (but not HC1 or HI) to alkenes gave products that were opposite to those expected from Markovnikov s rule. These anti-Markovnikov reactions were most likely when the reagents or solvents came from old supplies that had accumulated peroxides from exposure to the air. Peroxides give rise to free radicals that initiate the addition, causing it to occur by a radical mechanism. The oxygen-oxygen bond in peroxides is rather weak, so it can break to give two alkoxy radicals. 

There are numerous publications on the improvements to the Kharasch reaction. The primary method for improvement was the introduction of more sophisticated initiators (instead of peroxides [22-26, 37]). It was shown that various Red-Ox type initiators, like metal salts in different oxidation states (Cu", Cu ", Fe ", etc.), salts with organic acids (Co acetoacetate, Mn stearate), and a metal carbonyl - Fe(CO)5 give adducts with practical yields [38, 39] and allow to carry the reaction at near room temperatures (Fig. 30). 

Telomer mixtures can be separated by rectification. Congeners containing up to 15 C atoms can be easily prepared this way [57]. Formation of telomers of general formula C H2 2Cl4 with n - 20-50 was reported [58]. The Kharasch reaction with CCI4 yields ot,ot,ot,y-tetrachloroalkanes, while telomerization opens a way to a,a,a,co-tetrachloroalkanes. In the beginning free-radical initiators like azo-(bis)-diisobutyronitrile or benzoyl peroxide [57-60] were used later, metal complexes became popular. 

Preliminary work by Gutsche and Kharasch showed that under conditions in which a metaUocarbene was likely to be formed (e.g., EDA, Cu ), reaction commenced with electrophilic addition of the carbonyl oxygen atom, giving complex product mixtures dominated by enol ethers [179, 180]. In other words, the main adducts were products of formal O-H insertion via the enol tautomer of the... 

According to Ketley, in the first step solvents like ethanol acting as weak ligands or additives will cause the opening of the chloride bridges of the Kharasch complex a (reaction 91), resulting in the formation of complex b under a positive... 

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