REACTIONS AND PROPERTIES OF n BONDS

Most of the reactions and properties of 1-substituted imidazoles have been discussed earlier in this review. Apart from the utilization of the readily removable benzyl substituent in synthetic procedures leading to 2-substituted imidazoles, perhaps the mostexciting advances have stemmed from the reactions of the 1 -acylimidazoles (imidazolides) which are extremely reactive in such nucleophilic reactions as hydrolysis and alcoholysis.12 The use of such compounds as N,N -carbonyl-diimidazole in peptide synthesis is now commonplace. The silicon-nitrogen bond in N-trimethylsilylimidazoles is also extremely reactive, so reactive that it is attacked by a-halogenocarboxylic esters.361... 

Properties and Reactions. The stmcture of (aLkyl)imiQoboranes RB=NR is characterized by ahnear C—B—N—C geometry and a B—N bond order approaching three. Amino iminoboranes can be described usiag three resonance stmctures ... 

Reactions of Co-ordinated CO and Lewis Acid Adducts. The details of the preparation and properties of [Me3SiFe(COSiMe3XCO)3]2 (see Vol. 1, p. 139) have been published.The reaction of FeiCO) and MeC H N=PPh, in THF yields [Fe(CO)4(CNCftH4Me)], [Fe(CO)3(CNC6H4Me2], and Ph3PO (o-, m-, and p-isomers all isolated ). This is a rare example of deoxygenation of co-ordinated CO without M—C bond cleavage. The p-Me complexes can also be obtained from the reaction of Fe2(CO)g and p-MeC H N PPhj in benzene at room temperature. 

To understand Group 14 - and especially organosilicon - chemistry some comparisons between silicon and carbon have to be considered. There are two major properties that distinguish silicon from carbon. Silicon atoms are about 50 % larger than carbon atoms and this increased size will have some ramifications and consequences, such as lower barriers to silicon-element bond rotations and less stable n-bonds. Furthermore, the smaller Pauling electronegativity of silicon results in differently polar silicon-element bonds compared to carbon and thus will change its reactivity and enable reactions not possible in carbon chemistry. 

The synthesis and properties of cyclic hydrazine derivatives with N—N and N—S bonds have been investigated.119 The reaction of hydrazine-1,2-di-carboxylic esters with suiphanyl chlorides by a base-catalysed mechanism leads to the formation of six-, seven-, and eight-membered heterocycles. 

---