Oxygen—nitrogen bonds sulfur halides

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). 

Nucleophiles can be classified according to the kind of atom that forms a new covalent bond. For example, the hydroxide ion in eq. 6.1 is an oxygen nucleophile. In the product, a new carbon-oxygen bond is formed. The most common nucleophiles are oxygen, nitrogen, sulfur, halogen, and carbon nucleophiles. Table 6.1 shows some examples of nucleophiles and the products that they form when they react with an alkyl halide. 

The chemistry of phosphorus and the heavier congeners is dominated by element to element (E-E) single bonds and, particularly in the case of phosphorus, the availability of l>d orbitals to form dir—pir double bonds with a variety of other atoms such as oxygen, nitrogen, and even sulfur. Orbital participation results in expanded octets as found in compounds such as PF5, SbCl5, X3P=0 (where X=F, Cl, Br, I), the phosphorus oxoadds and oxoanions, and a class of compounds called the phosphazenes. We will take up many of these cases as we encounter them in the appropriate sections under our usual survey of the hydrides, oxides and oxoacids, and halides. For now, however, let s take a quick look at the phosphazenes, formerly called the phosphonitriles, that contain both N and P atoms in the same molecule. 

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