Silicon ligands halides

Like in the hydrolytic way, the knowledge of mechanisms is made difficult by the conplicated nature of molecular precursors. First, one has to bear in mind that rapid scrambling of ligands (halide, alkoxide, carboxylate, etc.) takes place around metal and semi-metal centers even at room temperature (Eq. 26.10). For instance, a mixture of metal (or silicon) chloride and metal (or silicon) alkoxide rapidly leads to a mixture of chloroalkoxides, which are the actual precursors (Moedritzer, 1971). 

The catalytic cycle was devised relying on a ligand exchange between the iron complex and a chlorosilane, regenerating the iron (111) halide due to the more oxophilic character of the silicon (Scheme 34). 

Si H M agostic interactions in silylamido complexes have been extensively studied to date. The earlier examples were prepared by halide displacement in the coordination sphere of a metal by a silylated amide, which puts severe limitations on the nature of the substituents at silicon (usually, robust methyl groups are used). More recently, a new route to p-agostic silylamides based on the direct coupling of silanes with imido ligands was discovered that allows one to trace the effect of substitution at silicon on the extent of the Si-H bond complexation (vide infra). 

Fig. 5 Relationship between the amount of graft polymers and Mn of free polymers. The graft polymerization was carried out under various conditions on silicon wafer (squares), silica particles with varying diameter (d = 12, 130, 290, 740, 1550 nm) (circles), and silica monolith with 50-nm mesopores (triangles). Two types of immobilized initiators, 2 and 5 (n = 6 and R" = CH3) in Fig. 2, two types of copper halides, CuBr and CnCl, and two types of ligands, spartein (Sp) and dipyridyl derivatives (4,4 -diheptyl-2,2 -dipyridyl (dHbipy) and 4,4 -dinonyl-2,2 -dipyridyl (dNbipy)), were used...

A decrease in the barrier for ligand exchange on going from the germanium derivatives to the corresponding silicon ones when all other factors remain the same (Table 35) is indicative of the higher configurational stability of the five-coordinate Ge halides under... 

---