Silicon boron-nitrogen bonds

Boron—nitrogen coordination polymers, with ferrocene, 6, 208 Boron nucleophiles, in conjugate additions asymmetric 1,4-additions, 10, 388 mechanisms, 10, 384 to nitroolehns, 10, 388 to a,/3-unsaturated amides, 10, 386 to a,/3-unsaturated esters, 10, 386 to a,/3-unsaturated ketones, 10, 384 Boron-silicon bonds, addition to alkenes, 10, 760 to alkynes, 10, 758 to allenes, 10, 760 to carbenoids, 10, 766 to 1,3-dienes, 10, 762 to isocyanides, 10, 765... 

We are investigating a series of reactions of aminopyridines and aminopyrimidines and main group compounds. These heterocycles can form adducts with both kinds of nitrogen atoms pyridinic or anilinic. Bonding of several aminopyridines to heteroatoms such as boron, silicon, or phosphorus gives polyfunctional molecules rich in lone pairs and therefore candidates to be used as ligands. 

The Miedema modeP describes bonding in intermetallic, ordered compounds of metallic elements. In addition to the metallic elements the model also includes the elements hydrogen, boron, carbon, nitrogen, silicon, and phosphorus in their metallic... 

Boron and carbon form infinite arrays with three and four electrons per atom contributing to the bonding, but nitrogen forms the diatomic dinitrogen molecule which is held in the solid by weak van der Waals forces. Aluminium is a metal and is more easily melted than is boron. Silicon-silicon bonds are weaker than C-C bonds. White phosphorus has molecules held in the solid by stronger van der Waals forces than the diatomic molecules of Nj. 

It is believed that most of the transition metals are complexed to nitrogen donors, such as are found in amino acids or derivatives of chlorophyll, and that the metals with high ionic potentials, such as beryllium, boron, germanium, titanium, gallium, and major elements such as aluminum and silicon, may be bonded to oxygen donors of degraded lignin. 

In contrast, use of metalloid elements, such as silicon, tin antimony or boron, which can form weak covalent bonds with oxygen, nitrogen or sulfur substituents during the course of the reaction, results in templated products that may be obtained metal-free by simple hydrolysis. These covalent template reactions (the M—X bond is essentially covalent in these cases) also have the advantage that the... 

In nonoxide ceramics, nitrogen (N) or carbon (C) takes the place of oxygen in combination with silicon or boron. Specific substances are boron nitride (BN), boron carbide (B4C), the silicon borides (SiB4 and SiBg), silicon nitride (SisN4), and silicon carbide (SiC). All of these compounds possess strong, short covalent bonds. They are hard and strong, but brittle. Table 22.5 lists the enthalpies of the chemical bonds in these compounds. 

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