The Chemistry of Sulfoxide Complexes

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. 

In the chemistry of main-group element sulfoxide complexes, a relationship between Aj/(S=0) and the enthalpy of formation of the sulfoxide complex has been derived (159). The applicability of the equation has only been examined for O-l SO complexes, and the constraints on using Ai (S=0) as a measure of metal-ligand bond strength should be borne in mind during its application. 

This powerful dehydrating agent was initially used in the preparation of nickel sulfoxide complexes (244), but has found wider application in the chemistry of lanthanide sulfoxide complexes (189). 

A review on the chemistry of low-valent titanium has appeared which deals with some aspects of the chemistry of titanium sulfoxide complexes (397). Titanyl complexes of the type [Ti0L5][C104]2 have... 

Much of the chemistry of palladium and platinum sulfoxide complexes has been discussed in previous sections and so only additional salient points will be mentioned here. A complete listing of all palladium and platinum sulfoxide complexes prepared would require a review article in itself. 

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). 

In general, the chemistry of fluoro-l,3,5-triazines resembles that of the chloro derivatives, and therefore will not be discussed in detail. There is evidence that cyanuric fluoride is less reactive than cyanuric chloride in reaction with aniline (76CCC3378). Chambers et al. have reported the isolation of a stable anion cr- complex from the reaction of cyanuric fluoride and cesium fluoride (equation 32) (77JCS(Pl)l605). Such species are believed to be intermediates in the formation of (68) from cyanuric fluoride and perfluoropropene (equation 33). Olah et al. have shown that cyanuric fluoride deoxygenates sulfoxides efficiently (equation 34) (80S221). 

In contrast, the chemistry of the oxidation of a primary alcohol to an aldehyde differs sharply from the oxidation of an aldehyde to a carboxylic acid (case (b)). Advantage, in this case, must be taken of the difference in the mechanisms of these steps. Among the reagents which can effectively oxidize alcohols and remain rather inert toward aldehydes are pyridinium chlorochro-mate (a chromium trioxide-hydrogen chloride complex of pyridine) or dimethyl sulfoxide-Lewis acid. 

In some of the more complex molecules, there are instances in which the low energy chromophore is probably not localized on the sulfoxide, yet the sulfinyl (SO) group is involved in the observed transformations. Some attempt will be made to differentiate photochemical reactions of molecules that merely happen to contain a sulfinyl group and those for which the sulfoxide is the critical functional group and/or chromophore. Section IX is reserved for the chemistry of ketosulfoxides in which the chemistry is clearly carbonyl but the reaction involves of sulfinyl site. The photochemistry of sulfenic esters (R-S-0-R ) appears throughout the text, particularly in Section III—the discussion of sulfoxide a-cleavage reactions. A short additional section on these sulfoxide isomers is also included at the end. 

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