Monosilylated precursor

When the monosilylated precursor 26 was reacted in a similar manner with LiBH4 according to Scheme 11, the resulting product was the solvent-free lithium borate salt 27 (74% yield). This compound could be recrystallized from -hexane. 

The cyclohexyl-substituted analog of 40, [Et3NH] [ (c-CeHi 1)781701 i(OSi-Me3) 2Al] (44), was synthesized independently in our laboratory by dehydrochlorination of the monosilylated precursor 12 with anhydrous AICI3 in the presence of triethylamine (Scheme 13). A comparison of the X-ray crystal structures of... 

A series of ferrasilsesquioxanes stabilized by phosphine ligands has been prepared and characterized by Baker et al Reactions of the iron(II) precursor FeCl2(dcpe) (dcpe = bis(dicyclohexylphosphino)ethane) with 2 or the monosilylated precursor (c-C5H9)7Si70g(0SiMe3)(0FI)2 (38) afforded the (dcpe)iron(II)-silsesquioxane... 

PMOs from Mixtures of Bis- or Multi-Silylated and Monosilylated Precursors... 

Scheme 11 Self association through H-bonds between adenine-containing and thymine-containing monosilylated precursors...

The polymeric silica materials derived from silylated aryl iodides have been prepared via sol-gel processes, either by the hydrolytic polycondensation of a bis-silylated monomer or by the co-gelification of a monosilylated precursor with tetraethyl orthosilicate [113]. These silica-supported aryl iodides have been successfully applied as supported catalysts in the a-tosyloxylation of aliphatic ketones in the presence of m-chloroperbenzoic acid as an oxidant, with the corresponding a-tosyloxyketones obtained in moderate to good isolated yields. The supported catalysts can be recycled by a simple filtration [113]. 

The fulvene route was also successfully employed in the preparation of a compound, which can be regarded as one of the most advanced molecular models for a catalytically active titanium center on a silica surface. When Cp Ti(C5Me4CH2) was reacted with the monosilylated silsesquioxane precursor 12 in refluxing toluene a color change from deep purple to amber was observed. Crystallization afforded a bright-yellow material, which was subsequently shown to be the novel mo o(pentamethyleyclopentadienyl) titanium(IV) silsesquioxane complex 126 (69% yield). Its formation is illustrated schematically in Scheme 42. 

The first silsesquioxane derivative of copper was made in our laboratory according to Scheme 65. The reaction of the monosilylated disilanol precursor 12 with tetrameric copper(I)-r-butoxide in a molar ratio of 2 1 afforded the colorless copper(I) silsesquioxane complex 187, in which the CU4O4 core of copper(I)-t-but-oxide is retained. 

Kevin J. Quinn of the College of the Holy Cross chose (Organic Lett. 2005, 7, 1243) a complementary approach in his synthesis of rollicosin. The symmetrical diol 4 is also available from carbohydrate precursors. Monosilylation followed by esterification with acryloyl chloride gave 5. Exposure of 5 to the Grubbs catalyst in the presence of 6 led, by ring-closing metathesis and cross metathesis, to the y-lactonc 7. Note that 5-lactone formation did not compete ... 

As illustrated in Scheme 6, monosilylation of the aliphatic diamine nitrogen atoms and subsequent reaction with the dianhydride yields a polyimide precursor devoid of free carboxylic acid groups, a poly(amic trimethylsilyl ester)... 

The synthesis of L-daunosamine began with the condensation of trans-crotonaldehyde (56) with dibenzylhydrazine (Scheme 17). Sharpless asymmetric dihydroxylation of the resulting ( )-a, (3-unsaturated hydrazone 57 afforded the syn-diol 58 (70% yield, 89% ee by HPLC), and silylation with chlorodimethyl-vinylsilane then provided the radical cyclization precursor 59 in 98% yield. In the key step, exposure to thiyl radicals generated from PhSH and AIBN led to radical cyclization of dibenzylhydrazone 59. The unstable cyclic intermediate was then directly treated with fluoride to afford vinyl adduct 60 in 77% yield (dr 91 9, H NMR). In control experiments with corresponding monosilyl derivatives, the (3-O-silyl... 

The development of organosilicon chemistry makes it possible to synthesize a very large family of monosilylated R Si(OR)3 precursors. The R group can be chosen with very different architectures and functions and with a high stability of the Si-C link. This chemistry has been widely developed and several applications and fundamental results have already been published in specific reviews [47, 48]. We just briefly mention below some aspects of these materials in relation to the field of nanosciences. 

The formation of stable iV,0-acetal TMS ethers, which are excellent precursors of V-acyliminium ions, is easily achieved by DIBAL reduction of V-acylamides followed by in situ protection with TMSOTf/pyridine (eq 39). 2,6-Lutidine has also been used as base. The DIBAL reduction-TMSOTf/pyridine silylation sequence has also been applied to the formation of monosilyl... 

Surface-functionalized ionosilicas are generally synthesized either via postsynthesis grafting or hydrolysis-cocondensation reactions involving trialkoxysily-lated ionic precursors. Scheme 16.5 illustrates the two different synthetic methods involving a monosilylated imidazolium precursor 3-methyl-l-(3-(trie-thoxysilyl)propyl)-imidazolium chloride. 

The use of ionic precursors in template-directed hydrolysis-polycondensation reactions clearly indicated a strong contribution of the precursor toward the formation of structured mesophases, based on ionic precursor-surfactant interactions. The work of Che and coworkers beautifully illustrates that templating methods involving surfactant-precursor ion pairs allow accessing highly structured siuface-functionalized silica materials. However, this work exclusively focused on the use of monosilylated costructure-directing agents and the formation of siuface-fimctionalized mesoporous silica phases. 

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