Sulfoxide Complexes of the Transition Metals

An excellent review article (460) has covered much of the literature concerning Me2SO complexes of the transition metals up to 1969. In consequence, only the major points prior to this period will be discussed, together with more recent developments and comments on complexes of the higher sulfoxides. 

Complexes of 3d transition metals with adenine (Ad) and/or the mono-deprotonated anion (Ad-) or adenosine (Ado) were prepared by refluxing a mixture of Ad or Ado with the appropriate hydrate metal perchlorate dissolved in triethylorthoformate and ethanol. Both the syntheses 3 and characterization , have been described previously. Hydrated metal perchlorates, adenine, and adenosine used in electrochemical experiments were used as received from Aldrich. All electrochemical experiments were performed in dimethyl sulfoxide (Me2S0) (Aldrich) containing 0.1 M tetra-butylammonium perchlorate (TBAP) (Eastman Kodak). Me2S0 was purified by fractional crystallization using a method similar to that described for purification of pyridine s. s recrystallized and dried in vacuo... 

Colona and coworkers oxidized a variety of alkyl aryl and heterocyclic sulfides to the sulfoxides using t-butyl hydroperoxide and a catalytic amount of a complex (97) derived from a transition metal and the imines of L-amino acids. Of the metals (M = TiO, Mo02, VO, Cu, Co, Fe), titanium gave the highest e.e. (21%), but molybdenum was the most efficient catalyst. The sulfoxides were accompanied by considerable sulfone125. 

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. 

Oxidation reactions are not limited to those that occur at a carbon centre. The perfluorinated Ni(F-acac)2-benzene-CgFi7Br system described above was also active for the oxidation of sulfides to sulfoxides and sulfones [28], A sacrificial aldehyde is required as co-reductant, but the reaction may be tuned by changing the quantity of this aldehyde. If 1.6 equivalents of aldehyde are used, the sulfoxide is obtained, whereas higher quantities (5 equivalents) lead to sulfones. Fluorous-soluble transition metal porphyrin complexes also catalyse the oxidation of sulfides in the presence of oxygen and 2,2-dimethylpropanal [29],... 

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