Metal sulfoxidation

Formation of C-C Bonds by Addition of Metalated Sulfoxides or Sulfoximides to Carbonyl Groups... 

This review is intended as an account of the coordination chemistry of both dimethyl sulfoxide and the higher sulfoxides, with particular reference to the mode of bonding and the extent to which this affects the chemistry of transition-metal sulfoxide complexes. No attempt has been made to provide an exhaustive listing of all known sulfoxide complexes, many of which contain coordinated sulfoxide moieties only coincidentally to their other important functions. 

In order to understand the bonding in transition-metal sulfoxide complexes, it is necessary to summarize the physical data available in the literature and so determine what constraints are necessary in any bonding model. An understanding of the factors affecting the bonding in these complexes is essential if further developments are to be made in the chemistry of transition-metal sulfoxide complexes. 

Undoubtedly, one of the major interests in platinum-metal sulfoxide chemistry is the synthesis and use of O-bonded sulfoxide complexes as reactive intermediates in synthetic and catalytic chemistry. The chemistry of such weakly bonded intermediates has recently been reviewed (142). 

We have mentioned previously (see Section 3.1) the easy formation of a double bond by sulfoxide pyrolysis. Associated with an alkylative step of a metallated sulfoxide, the sequence is of great value in alkene synthesis [44U, 441], as in the one-pot reaction given here. 

G. Solladie, Formation of C-C Bonds by Addition to Carbonyl Groups (0=0) - Metalated Sulfoxides or Sulfoximides, in Methoden Org. Chem. (Houben-Weyl) 4th ed., 1952, Stereoselective Synthesis (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), Vol. E21b, 1793, Georg Thieme Verlag, Stuttgart, 1995. 

Also, coordination compounds and metal carbonyls are able to undergo a PET, resulting in initiating radicals [63]. Recently investigated examples are iron chloride based ammonium salts [149], vanadium(V) organo-metallic complexes [150], and metal sulfoxide complexes [151]. However, the polymerization efficiency of some systems is only low due to redox reactions between the central metal ion and the growing polymer radical, and the low quantum yields of PET. 

It is possible to prepare block copolymers by free-radical initiation, as R. B. Seymour, G. A. Stahl, D. R. Owent, and H. Wood discuss in their chapter. Methyl methacrylate macroradicals were made with peroxide and azo initiators in diluents, and different vinyl monomers were polymerized onto them. Block copolymers of two ethylene imines, one having a long (lauroyl) side chain and one with a short (propionyl) side chain were synthesized by M. H. Litt and T. Matsuda in a two-step cationic polymerization process. Block and random copolymers of episulfides were prepared by E. Cernia, A. Roggero, A. Mazzei, and M. Bruzzone using anionic catalysts of metalated sulfoxides and sulfones. 

Henbest and Trocha-Grimshaw have shown that sulfoxides may be oxidized to sulfones in the presence of iridium and rhodium complexes [139, 140]. Oxidations were studied by passing air through a solution of the sulfoxide in hot wopropanol containing 10% water in the presence of the catalyst. Sulfones were formed when chlorides of iridium or rhodium were used while chlorides of ruthenium, osmium and palladium were not effective. Under reaction conditions the chlorides should be converted wholly or partly to metal sulfoxide complexes. 

The reaction of 149 with 127 might be a direct conjugate addition. An alternative mechanism would be a 1,2-addition to the enone from the a-carbon of the metallated sulfoxide followed by an anion accelerated oxy-Cope rearrangment. Evaluate this possibility using a stereochemical analysis of each step of the reaction. (Juvabione-20)... 

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