Metal sulfur—nitrogen bonds

Table 9 Examples of Triorganotin and Triorganolead Compounds Containing Metal-Oxygen, -Sulfur or -Nitrogen bonds Exhibiting One-dimensional Associated Structures...

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... 

Metallaheterocycles with the metal atom capable of supporting a carbon-metal double bond, and with oxygen, nitrogen, sulfur, or selenium as the second heteroatom are the only structures capable of full conjugation. These compounds show furan-like aromaticity with the heteroatom /i-electrons participating. No examples of this type of ring system were uncovered, undoubtedly due to the stability of the metalla-carbon double bonds required for their formation. 

Although the bis(dithiocarbamate) complexes of Fe(II) are relatively unstable to air oxidation, early studies (12, 15) produced stable adducts of NO and CO. Both 5-coordinate [Fe(NO)(I dtc)2] and 6-coordinate [Fe(NO)2(R2dtc)2] complexes are known. There has been considerable interest in the mode of attachment of the NO molecule, as there are six possibilities (see Scheme 4). (A) and (B) represent valence-bond structures of the linear Fe-NO bond. Structure (C) involves a symmetric Fe-NO TT-bond. Structure D illustrates the bent mode of attachment, in which nitrosyl is coordinated to the metal through the nitrogen atom, but the Fe-NO bond-angle differs greatly from 180°. Structures (E) and (F) are valence-bond formalisms of an unsymmetrical, metal-NO 7r-bond. The structure of [Fe(NO)(R2dtc)2] (R = Me or Et) has been shown (230,231) to be square pyramidal, with four sulfur atoms in... 

A second approach has been developed for preparing linkage isomers— that of deliberately modifying the bonding characteristics of the central metal ion through coordination with ligands such as triphenylarsine in this way the palladium(II) complexes of nitrogen- and sulfur-bonded thiocyanate have been obtained 8). 

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