Metal sulfur—oxygen bonds

The 2-pyridyl sulfones have been activated with Sm(OTf)3 in toluene at 70 °C. The reaction also proceeds in refluxing methylene chloride, albeit with slightly diminished yields (Scheme 4.56) [308]. The mechanism has not been studied in either case, but activation has been suggested to involve the complexation of the metal ion with the pyridyl nitrogen and one of the sulfur oxygens, followed by the cleavage of the Cl—S bond leading to an oxacarbenium ion, for the pyridyl sulfones. 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

Facile isocyanide insertion reactions into metal-carbon, -nitrogen, -sulfur, -oxygen, - hydride, and - halide bonds have been found to readily occur. The insertion into metal-hydrides to give stable formimidines is particularly noteworthy since corresponding formyls (—CHO) are exceptionally difficult to synthesize and tend to be very unstable. There is a great deal of interest in carbon monoxide reductions, and the instability of the intermediate reduction products has made a study of the reduction process extremely difficult. Recently, however, the interaction of isocyanides with zirconium hydrides has allowed the isolation of the individual reduction steps of the isocyanide which has provided a model study for carbon monoxide reduction (39). 

Into Metal-Nitrogen, -Oxygen, and - Sulfur Bonds... 

The platinum metal chalcogenides in general are easier to prepare than the corresponding oxides. Whereas special conditions of temperature and pressure are required to prepare many of the oxides, the platinum metals react most readily with S, Se, and Te. A number of additional differences concerning the chemistry of the chalcogenides and the oxides are summarized as follows The metal—sulfur (selenium, tellurium) bond has considerably more covalent character than the metal-oxygen bond and, therefore, there are important differences in the structure types of the compounds formed. Whereas there may be considerable similarity between oxides and fluorides, the structural chemistry of the sulfides tends to be more closely related to that of the chlorides. The latter compounds... 

Sulfur dioxide insertion is not limited to metal-carbon a bonds, although M—C is by far the most common substrate involved. Reactions have been reported which lead to insertion of SOa metal-carbon TT (or polyhapto) bonds 26, 102, 130-132), as well as transition metal-transition metal 112), transition metal-Group IVB metal 14, 19), and metal-oxygen 9,58) linkages. Moreover, reaction (8) (97) where M = Rh... 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

The question of the similarities and differences between the metal-oxygen bond and the metal-sulfur bond is fundamental in geochemistry, and relates to the lithophile versus chalcophile nature of particular elements. A full discussion is presented in Chapter 8. 

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