Nickel-Catalyzed Kharasch Addition Reaction

It has also been shown that Ni complexes can successfully carry out intramolecular or intermolecular electroreductive addition of alkyl radicals to activated olefins. Thus bicyelic ketones 78 and 80 are conveniently prepared in good yields from 2-bromoalkyl-2-cyclohexenone 77 and 3-bromoalkyl-2-cyclohexenone 79, respectively [25]. Alkyl bromides also react with a,) -unsaturated esters and nitriles to give 1,4-addition products in moderate yields [26]. 

6]C1 (81) (referred to as Ni(NCN)Cl) was reported to be an excellent catalyst for the Kharasch addition reaction. 

For instance, over 90% of 1 1 alkene CCU adduct was obtained in 15 min at room temperature during the reaction of methyl methacrylate with excess CCI4 in the presence of 5 mol% Ni(NCN)Cl in acetonitrile. Considering that NiCl2(PPh3)2 catalyzes the addition of polyhaloalkanes to 1-hexene in low yields only at 140 C 

The mechanism takes a different course with more acidic compounds such as )5-keto ester 7a (p/fa = 10). Mn(IlI) enolate 8a forms rapidly and reversibly. The rate-determining step is cyclization of the double bond to the Mn(lll) enolate of 8a with loss of Mn(ll) to give cyclohexanealkyl radical 11a, without the intermediacy of acyclic radical 9a, which is oxidized by Cu(OAc)2 to generate 71% of 12a. Similar mechanisms are operable with very acidic 1,3-diketones Mn(acac)j is stable and isolable. 

2 Initiation, Termination, Solvents and Common Side Reactions 

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Among the various oxidation states of nickel (0— IV), Ni(II) and Ni(0) are the most stable. There have been only a limited number of examples of nickel-catalyzed Kharasch addition reactions, in contrast to those of ruthenium, iron, and copper, probably be-... 

Pandarus and Zargarian developed propane-1,3-diol-based diphosphinite pincer nickel(III) complex 135 as a catalyst for Kharasch additions of olefins with CCI4 [154,155]. Only 0.1 mol% of the complex catalyzed the reaction of several olefins, such as styrene, methyl (meth)acrylate, acrolein, or acrylonitrile, in 65-97% yield. 

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