Aryl silanes functionality

We sought to examine the enzymatic dioxygenation of aryl silanes using a number of different aromatic dioxygenases in order to determine if such transformations were possible and to define the substrate-specificity profile. We were also motivated by the rich chemistry of silicon-based materials, which includes the hydrosilylation of alkenes and ketones, the addition of electrophiles to vinyl and allyl silanes, and palladium catalyzed cross-coupling of vinyl silanes with aryl halides (13). As a result, silyl functional cw-diols have potential as chiral intermediates for drug development, as polymer precursors/modifiers and as elements in non-linear optical materials. 

The aryl silane library was also screened for their ability to function as the sole carbon source for Ralstonia eutropha A5, a wild type strain expressing a biphenyl dioxygenase (BPO) enzyme. A number of silanes were observed to support growth, including diphenylsilanes and trialkoxysilanes. Overall the study indicated the feasibility of the enzymatic conversion of arylsilanes to a novel series of silane cw-dihydrodiols and catechols. Such compounds may find application as chiral polymer precursors, intermediates for natural product synthesis and other usefol materials. 

Besides the traditional coupling between alkenes and aryl (vinyl) halides, other functionalized aryl derivatives can also couple with alkenes in the Heck reaction, including aryl silanes,stannanes, bismuth, antimony,triflates, boric acid, phosphonic acid, carboxylic acid, and diazonium salt. ... 

While there is no simple rule about the structures found in a polymer, the most common polymers have only a few organic functional groups, that repeat over and over to make the macromolecules. Of the groups shown in Figure 1.3, alkanes, esters, urethanes, carbonates, aryls, silanes, amides, and imides are commonly found in the backbone of polymers. Alcohols, carboxylic acids, and amines are either reactive parts of monomers or can be found in polymer side groups. 

Palladium catalysed Hiyama-type cross-coupling reactions of benzylic phosphates (74) with the aryl-silane (75) afforded corresponding di-arylmethanes (76) (Scheme 21). The reaction tolerated either electron-donating or electron-withdrawing functional groups providing products (76) in high to excellent yields. ... 

In this chapter the structural and NMR spectroscopic features of stabihzed silylium ions are summarized. As already outlined and justified in the introductory paragraph this overview focuses on species, which are stabilized by interaction with aryl groups or by silane functionalities. Both modes of stabilization, intra- or intermo-lecularly, will be discussed here in comparison. In addition, the structures of... 

Shibata and co-workers have reported an effective protocol for the cyclization/hydrosilylation of functionalized eneallenes catalyzed by mononuclear rhodium carbonyl complexes.For example, reaction of tosylamide 13 (X = NTs, R = Me) with triethoxysilane catalyzed by Rh(acac)(GO)2 in toluene at 60 °G gave protected pyrrolidine 14 in 82% yield with >20 1 diastereoselectivity and with exclusive delivery of the silane to the G=G bond of the eneallene (Equation (10)). Whereas trimethoxysilane gave results comparable to those obtained with triethoxysilane, employment of dimethylphenylsilane or a trialkylsilane led to significantly diminished yields of 14. Although effective rhodium-catalyzed cyclization/hydrosilylation was restricted to eneallenes that possessed terminal disubstitution of the allene moiety, the protocol tolerated both alkyl and aryl substitution on the terminal alkyne carbon atom and was applicable to the synthesis of cyclopentanes, pyrrolidines, and tetrahydrofurans (Equation (10)). 

More recently, trifluoromethanesulfonic acid (triflic acid, TfOH) has been used to functionalize silanes by electrophilic substitution of aryl substituents62,63 (equation 35). The silyl triflates formed in this reaction are useful building blocks for a wide variety of products. Chlorosilanes can be obtained by treatment with lithium chloride (equation 36). 

Similarly, l-(phenoxyalkyl)benzotriazoles 456 can be lithiated to give the corresponding acyllithiums 457, which have been used for the preparation of alkanoyl silanes and functionalized ketones (Scheme 120)665. Hydrolysis of adducts 458 was performed in refluxing aqueous ethanol (50%) containing 5% of sulfuric acid for 10 min. For acyl silanes, milder reaction conditions were used. When 1,4-dibromobutane was used as dielectrophile, alkyl, aryl, alkenyl and alkynyl 1,4-diketones were prepared in 74-86% yield666. 

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). 

---