Atom transfer radical addition ATRA

The addition of halocarbons (RX) across alkene double bonds in a radical chain process, the Kharasch reaction (Scheme 9.29),261 has been known to organic chemistry since 1932. The overall process can be catalyzed by transition metal complexes (Mt"-X) it is then called Atom Transfer Radical Addition (ATRA) (Scheme 9.30).262... 

Scheme 9.30 Atom Transfer Radical Addition (ATRA)...

Carbon-carbon bond formation is a fundamental reaction in organic synthesis [1, 2,3,4], One way to form such a bond and, thus, extend a carbon chain is by the addition of a polyhalogenated alkane to an alkene to form a 1 1 adduct, as shown in Scheme 1. This reaction was first reported in the 1940s and today is known as the Kharasch addition or atom transfer radical addition (ATRA) [5,6], Historically, Kharasch addition reactions were conducted in the presence of radical initiators or... 

This catalytic sequence is known as Kharasch addition or atom transfer radical addition (ATRA) [4]. Various polyhalogenated compounds such as CCI4 and CCI3CO2R are used as the organic halides, and transition metal salts or complexes are used as the catalyst [3]. Intramolecular version of the Kharasch addition reaction (atom transfer radical cyclization, ATRC) has opened novel synthetic protocols to the synthesis of carbocyde or heterocyles catalyzed by transition metals [5-7], and this has become a very important field in free radical cydization in organic synthesis. Transition metal-catalyzed Kharasch reactions sometimes afford telomers or poly-... 

Metal-catalyzed living radical polymerization can be traced back to metal-catalyzed radical addition reactions to alkenes, sometimes collectively called Kharasch or atom-transfer radical addition (ATRA) reactions in organic chemistry (Scheme 2).33 Thus, a... 

A soluble dendritic Ni catalyst for the atom-transfer radical addition (ATRA, i.e., polyhalogenated alkane addition to olefins, the Kharasch addition) was described by van Leeuwen and van Koten et al. in 1994 [17]. GO and G1 carbosilane den-drimers, fimctionalized with NGN pincer-nickel(II) groups, were synthesized and applied as homogeneous catalysts for the addihon of organic halides to alkenes [Eq. (7)]. 

The name of ATRP originates from atom transfer radical addition (ATRA), the formation of an adduct (P—CH2—CHR —X) with a halogen in the presence of a metal catalyst. 

In recent years, transition metal mediated free radical processes have gained in importance. In particular the Kharasch addition to olefins such as atom transfer radical addition (ATRA) and atom transfer radical cyclisation (ATRC) and its extension to olefin polymerisation known as atom transfer radical polymerisation (ATRP) have been reported with a wide range of metal catalysts. 

A parallel development was initiated by the first publications from Sawamoto and Matyjaszweski. They reported independently on the transition-metal-catalyzed polymerization of various vinyl monomers (14,15). The technique, which was termed atom transfer radical polymerization (ATRP), uses an activated alkyl halide as initiator, and a transition-metal complex in its lower oxidation state as the catalyst. Similar to the nitroxide-mediated polymerization, ATRP is based on the reversible termination of growing radicals. ATRP was developed as an extension of atom transfer radical addition (ATRA), the so-called Kharasch reaction (16). ATRP turned out to be a versatile technique for the controlled polymerization of styrene derivatives, acrylates, methacrylates, etc. Because of the use of activated alkyl halides as initiators, the introduction of functional endgroups in the polymer chain turned out to be easy (17-22). Although many different transition metals have been used in ATRP, by far the most frequently used metal is copper. Nitrogen-based ligands, eg substituted bipyridines (14), alkyl pyridinimine (Schiff s base) (23), and multidentate tertiary alkyl amines (24), are used to solubilize the metal salt and to adjust its redox potential in order to match the requirements for an ATRP catalyst. In conjunction with copper, the most powerful ligand at present is probably tris[2-(dimethylamino)ethyl)]amine (Mee-TREN) (25). 

ATRP is an extension of atom transfer radical addition (ATRA), which is a well-known method of carbon-carbon bond formation (catalyzed by transition metal complexes) in organic synthesis. ATRP also has roots in the transition metal catalyzed telomerization reactions (Boutevin,... 

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