Initiators sulfonyl halides

The initiator in ATRP is usually a low molecular weight activated organic halide (RX, R=aclivated alkyl, X=chlorine, bromine, iodine). However, organic pscudohalidcs (e.g, X=thiocyanatc, azide) and compounds with weak N-X (e.g. N-bromosuccinimide 7 ) or S-X (e.g. sulfonyl halides - see below) have been used. 

Besides radical additions to unsaturated C—C bonds (Section III.B.l) and sulfene reactions (see above), sulfonyl halides are able to furnish sulfones by nucleophilic substitution of halide by appropriate C-nucleophiles. Undesired radical reactions are suppressed by avoiding heat, irradiation, radical initiators, transition-element ion catalysis, and unsuitable halogens. However, a second type of undesired reaction can occur by transfer of halogen instead of sulfonyl groups283-286 (which becomes the main reaction, e.g. with sulfuryl chloride). Normally, both types of undesired side-reaction can be avoided by utilizing sulfonyl fluorides. 

The free radical additions of sulfonyl halides to alkenes, catalyzed by light or typical chemical radical initiators (In), were first investigated in the 1950s69. The products which are / -halo sulfones (22) were obtained via a chain reaction in which RSO j acts as the chain carrier, namely61-62,70,71... 

Sulfonyl halides add to double bonds, to give P-halo sulfones, in the presence of free-radical initiators or UV light. A particularly good catalyst is cuprous chlo-ride. Triple bonds behave similarly, to give P-halo-a,(3-unsaturated sulfones. 

Closely related is the reaction of tertiary amines with sulfonyl halides that contain an a hydrogen. In this case, the initial product is the highly reactive sulfene, which cannot be isolated but reacts further to give products, one of which may be the alkene that is the dimer of RCH. Reactions of sulfenes in situ are also common (e.g., see 16-62). 

Closely related is the reaction of tertiary amines with sulfonyl halides that contain an a hydrogen. In this case the initial product is the highly reactive sulfene, which cannot be... 

Perfluoroalkyl sulfonyl halides are also good photochemical sources of perfluoroalkyl radicals, and they may also be used under thermal-induction, with a radical initiator, to form Rj in a synthetically useful manner [62]. 

The products from ATRP will most likely contain metallic and halide impurities. The sulfonyl halide initiators for ATRP have considerable advantages over alkyl halides in cost and in operating with any monomer capable of undergoing ATRP. 

Many other functional groups are reduced by Sml. For example, sulfonyl halides are converted to disulfides. The reduction of nitro compounds by this reagent enables synthesis of 1,2-diamines based on a reaction sequence initiated by nitronate addition to aldimines, and in the presence of nitriles it furnishes amidines, and that of isothiocyanates in the presence of conjugated esters, the half thioamide derivatives of succinic esters. 

In this reaction, one polymer chain forms per molecule of the organic halide (initiator), while the metal complex serves as a catalyst or as an activator, which catalytically activates, or homolytically cleaves, the carbon—halogen terminal. Therefore, the initiating systems for the metal-catalyzed living radical polymerization consist of an initiator and a metal catalyst. The effective metal complexes include various late transition metals such as ruthenium, copper, iron, nickel, etc., while the initiators are haloesters, (haloalkyl)benzenes, sulfonyl halides, etc. (see below). They can control the polymerizations of various monomers including methacrylates, acrylates, styrenes, etc., most of which are radically polymerizable conjugated monomers. More detailed discussion will be found in the following sections of this paper for the scope and criteria of these components (initiators, metal catalysts, monomers, etc.). 

Sulfonyl halides, particularly arenesulfonyl halides, can afford radical species much faster than carbon halides by the assistance of a metal complex and efficiently add to olefins with little dimerization of sulfonyl radicals in comparison to carbon-centered radicals. Another feature of the compounds is that there is little effect of the substituents on the rate of addition to an olefin. These properties make sulfonyl halides an efficient and universal series of initiators for the metal-catalyzed living radical polymerizations of various monomers including methacrylates, acrylates, and styrenes (Figure g). 52.175-177... 

Perfluoroalkanesulfonyl halides 1-35 and 1-36 induced controlled polymerization of styrene and MMA in the presence of copper catalysts, although the initiation efficiency is lower.177 With the alkanesulfo-nyl halides 1-35 and 1-36, decomposition by loss of S02 from the initial sulfonyl radical occurs to give a perfluoroalkyl radical, which then adds to the monomer to initiate the polymerization. 

In addition to the carbon-centered radical initiators, arenesulfonyl halides are simple and efficient functionalized initiators by introducing a variety of functional termini conjugation between the aryl and the sulfonyl groups is absent (FI-51 to FI-58 Figure 14).175 Typically, a series of monosubstituted derivatives (FI-51) are commercially available and afford hydroxyl, carboxyl, nitro, and halo groups in living... 

Figure 14. Sulfonyl halide and conventional radical functional initiators.

Disulfonyl halides such as MI-22 to MI-26 are effective bifunctional initiators for various monomers including methacrylates, acrylates, and styrenes, because the sulfonyl halide part, as pointed out for their monofunctional versions, can induce fast initiation without a bimolecular termination reaction between the sulfonyl radicals.240-343... 

The initiation step in ATRP involves homolytic cleavage of an activated halogen-containing compound and subsequent addition of this radical to the monomer as shown in Scheme 23. The fragment that is retained at the a-end of the polymer can be composed of functional groups that are tolerant to the ATRP catalyst and propagating chain end. Two main classes of functionalized initiators have been reported, activated alkyl halides and sulfonyl halides. 

Sulfonyl halides have also proven to be effective initiators for the polymerization of styrenes, methacrylates, and acrylates by... 

Well-controlled polymerizations of a large number of monomers have been obtained in copper-catalyzed ATRP with sulfonyl halides as initiators, which yield a much faster rate of initiation than monomer propagation. For example, the apparent rate constants of initiation with sulfonyl chlorides are about four (for styrene and methacrylates) and three (for acrylates) orders of magnitude higher than those for propagation (Matyjaszewski and Xia, 2001). 

General Discussion. Various kinetic and reactivity studies have been performed using TsBr alone or in comparison with other arene sulfonyl halides. Most of the literature describes the use of this reagent to initiate free radical ring formation, predominantly for five-membered ring systems. There are, however, reports of its use in vinyl sulfone and thiolsulfonate formation and in halogenation reactions. 

Another advantage of ATRP is a multitude of commercially available initiators. Nearly all compounds with halogen atoms activated by the presence of 3-carbonyl, phenyl, vinyl or cyano groups have been used as efficient initiators. Also compounds with a weak halogen-heteroatom bond can be used, such as sulfonyl halides [31]. Small molecule initiators can carry additional functionalities, a few examples are shown in Scheme 9, the functionality is incorporated at the residual chain end. 

Thus, the initiating systems for the living polymerization consist of a halogenated initiator and a transition metal complex. The effective metal complexes for the catalysis now include various early and late transition metals as reviewed in this chapter, while the initiators are typically polyhaloalkanes, a-haloesters, (a-haloalkyl)benzenes, and sulfonyl halides. The metal-catalyzed polymerization can control the reactions of a... 

Another innovative approach to initiating the polymerization of acrylic structural adhesives is illustrated by a family of adhesives that uses the adherend surface itself as part of the chemical reaction that generates the free radical initiator. The compositions contain an acidic material, a sulfonyl halide group, and a transition metal compound. Upon contact with a metal surface such as iron, zinc, copper, cadmium, and their alloys, the components react with the metal surface through a free radical pathway, producing effective initiators for the polymerization of the acrylic monomers. Later extensions of this concept provide two-part adhesives employing... 

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