Silyl functions

When phosphaalkynes are exposed to bis- and tris(diazo) compounds, bis- or tris(l,2,4-diazaphosphol-5-yl) compounds are formed that may be further converted into a variety of novel heterocyclic systems. For example, bis- and tris[diazo(tri-methylsilyl)methyl]phosphanes 237 and 240 afforded bis- and tris(diazaphospho-lyl)phosphanes 238 and 241 after cycloaddition with ferf-butylphosphaacetylene followed by a subsequent 1,5-silyl shift (Scheme 8.56) (300). Reaction with electrophilic halides at the /V-silyl functions allows the introduction of a heteroatom bridge between the diazaphosphole ring leading to polycyclic ring systems such as 239 and 242. 

Levisalles and co-workers466 and Wentrup and Dahn467 studied enoldiazonium ions generated under superacidic conditions. More recently Laali and coworkers468 have shown that the stability of enoldiazonium ions can be greatly enhanced by an a-silyl functionality. Equation (4.137) shows the characteristic diazonium ion products. 

A novel chemical functionalization method for MWCNTs through an oxidation and silylation process was reported in 2002. Purified and oxidatively functionalized MWCNTs were reacted with 3-mercaptopropyltrimethoxysilane, the CNT surface being joined to the organosilane moieties through OH groups [143], Similarly, MWCNTs were functionalized by KMn04 oxidation under PTC catalysis and subsequent reaction with the hydrolysis product of 3-methacryloxypropyltri-methoxysilane (3-MPTS) (Scheme 1.13). The O-silyl-functionalized MWCNTs were characterized by FT-IR spectroscopy and energy-dispersive spectroscopy... 

Scheme 17. 4-Deprotonation of gramine bearing a bulky N-silyl functionality.

Another well-established process available for the preparation of PC double bonds is related to the easy migration of phosphorus-bonded silyl functions toward an a-positioned, doubly bonded element such as N, O, or S [Eq. (4)]. By this silatropic movement the double bond is... 

In recent years, we have been investigating easy and economical functionalization of widely nsed carbon based polymers snch as polybntadienes. The preliminary results of these studies have led our group to discover a highly selective and mild synthetic route to silyl-functionalization of 1,2-polybutadienes (PBD) via Pt-nanocluster catalyzed hydrosilylation of olefin bonds. Unlike other catalytic systems, our system was found to be equally effective with all varieties of functional silanes such as halo-, alkyl-, aryl- and alkoxy- silanes affording high yields and selectivities. In addition, all the hydrosilylation reactions were found to be very clean with the ease of product separation and purifications (Scheme 2). 

Scheme 1. Synthesis of silyl-functionalized silyldiazoacetic esters ...

Half-Sandwich Tungsten Complexes with Silyl-Functionalized r -Cyclopentadienyl Ligand ... 

Isocyanatomethyl-dimethylmonomethoxy silane introduces a novel and versatile concept into silyl-functionalized polymer chemistry. 

Soai et al. [62a] first reported the use of sihca gel or alumina as a heterogeneous support for chiral catalysts in the enantioselective addition of dialkylzincs to aldehydes. Chiral N-alkyhrorephedrines (R = Me, Et, n-Pr) were immobilized covalently on (3-chloropropyl)silyl-functionalized alumina or silica gel via a nucleophilic substitution. However, the catalytic activities and enantioselectivities were only moderate (24—59% ee) in comparison with those of homogeneous and polymer-... 

Newly developed silicon hnkers such as 79 (Scheme 37) have been synthesized in fewer steps as compared with the earlier reported traceless linkers based on silyl functionalization. They allow for an easy binding to the support before performing the combinatorial synthesis [93, 94],... 

An alternative procedure for the preparation of diethyl cyanobenzylphosphonates uses the addition of diethyl trimethylsilyl phosphite to P-nitrostyrenes in the presence of TiCl4. The silyl functionality is transferred to the oxygen to form nitronates, which, in the presence of low-valence titanium generated in situ, are converted to diethyl cyanobenzylphosphonates in 74-91% yields (Scheme 6.19). s ... 

Intramolecular interactions between a silyl and an ester group are also characteristic of the mass spectral behaviour of the methyl esters of silylated hydroxycarboxylic acids, e.g. 130 (reaction 57)85. Transfer of the silyl function (130 - 131) is followed by an a-cleavage (131 - 132) and terminated by the expulsion of Me2HSiOMe (132 - 133). A similar reaction sequence is operative for the TMS analogue of 13086. 

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