Nitrogen-bonded substituents

Depending on the steric bulk of the nitrogen bonded substituent, the reaction of 4 with pyridine-2-aldimines can also proceed by an intermolecular insertion of the silylene into the C-H bond of the acyclic CN group [19]. 

The enthalpies of formation of phenols with nitrogen-bonded substituents appear in Table 4. 

X-ray analysis of diaziridinone (25) gave an N—N bond length of 1.60 A, and an N—CO bond length of 1.325 A. The bonds from nitrogen to substituent form angles of 56° with the plane of the ring the substituents are trans to each other (78JOC922). 

Ring opening occurs mainly at the least hindered carbon-nitrogen bond, unless the more hindered is activated by unsaturation or aromatic substituents 53,101,102,108). 

Tables 15 and 16 show the absorption maxima of some metal complexes of benzothiazolyl-substituted formazans 230 and 231.283 The wavelengths are metal ion dependent, making formazans useful reagents for the identification of specific metal ions or the simultaneous determination of two ions. The wavelengths are much longer than those of the formazan anion (Table 14). The general trend for electron-rich substituents is toward a larger shift this is to be expected as it tends to enhance the aromatic character of the ring and increase the covalent character of the metal — nitrogen bond. The sharpness of the absorption band has been attributed to coordination to the heterocyclic nitrogen as in 232.57S...

H-NMR studies of oligocarbene Ru(II) complexes indicate a substantial barrier to rotation about the metal-carbene carbon and nitrogen-R bonds. This restricted rotation is thought to arise as a consequence of intramolecular non-bonding cis interactions of the carbene nitrogen-R substituents, and not because of any significant double bond character in ruthenium-carbene carbon (76). 

Effect of 2,6-substituents on the carbon-nitrogen bond cleavage rate in radical-zwitterions from 1 -benzyl-4-phenylpyridiniums in dimethylformamide at 25 °C. 

Substituents with Oxygen or Nitrogen Bonded to Ring Nitrogens... 

Wilcox and co-workers (145) reported that the stereoselectivity of 1,3-dipolar cycloaddition reactions can be controlled in a predictable manner when ion pairs are located at a proper position near the reaction site (Scheme 11.40). He has employed an A-phenylmaleimide substrate having a chiral center in the substituent at ortho position of the phenyl group. Due to serious steiic hindrance, this phenyl group suffers hindered rotation around the aryl-nitrogen bond (rotation barrier 22 kcal/mol). Four diastereomeric cycloadducts are possible in the cycloaddition step with a nitrile oxide. When the cycloaddition reaction is carried out in... 

Various addition reactions to the C = C bond have been studied by Barton and co-workers in the steroid series. Although the yields of products generally depend on the substituent, they are usually higher with oxygen-containing substituents, e.g. 17 (Y = OAc. OMe)34 and 18, and lower with nitrogen-containing substituents, e.g. 17 (Y = pyrrolidino).34" 37... 

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