Silylation of aromatic compound

The iridium complex [lr(OMe)(cod)2] with 4,4 -di-tert-butyl-2,2 -bipyridine (dtbpy) or 2,9-diisopropyl-l,10-phenanthroline (dipphen) as ligand shows a catalytic activity for aromatic C—H silylation of aromatic compounds by disilane [60]. The reac-hon of 1,2-dimethylbenzene 135 with l,2-di-tert-butyl-l,l,2,2,-tetrafluorodisilane... 

Ishikawa found the Ni(PEt3)4-catalyzed silylation of aromatic compounds with 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene, providing the l-(di-ethylarylsilyl)-2-(diethylsilyl)benzene in high yields (Eq. 44) [89]. In the case of the reaction of mesitylene, interestingly, the sp3 C-H bond adds to the disilacy-clobutene, albeit in low yield (28% yield) [89]. Platinum(O) complexes are also applicable to this silylation reaction as the catalyst [90]. 

Direct silylation of aromatic compounds is carried out with 1,2-di-tert-butyl-1,1,2,2-tetrafluorodisilane (165) that serves as a silylating reagent in the presence of an iridium catalyst [60]. For example, the Irotalyzed C-H activation reaction of o-xylene selectively proceeds at the aromatic C-H bond rather than the benzylic one to give 166 in a high yield (Scheme 5.43). The synthetic utility of the products... 

Lcad(rV) trifluoroacetate is a strong electrophilic and oxidizing reagent It IS a valuable reagent for the hydroxylatton of aromatic compounds [5S, 59] Lead(IV) trifluoroacetate also reacts with silylated benzenes with the exclusive formation of the corresponding trifluoroacetate esters [59] (equation 28)... 

HydrosilyUitwn The reductive silylation of aromatic carbonyl compounds and esters is catalyzed by (CgFj)3B at room temperature (9 examples, 80-96%). Aldehydes react faster. 

The polymerization of aromatic diamines with acid chlorides in solution works well.7 914 35 The basicity of the aromatic diamine is low and acid binding can be achieved with several compounds and even solvents such as TV-methylpyrrolidonc (NMP) and dimethylacetamide (DMAc). The all-para aromatic amide poly(p-phenyleneterephthalamide) can be synthesized in DM Ac.7,9,14 To prevent precipitation of the polymer, a salt such as calcium chloride or lithium chloride can be added. It is also possible to react the acid chloride with a silylated diamine ... 

The method was also applied to the benzoylation of other aromatic compounds (Tab. 7.7). The benzoylation of benzene itself, volatile and less reactive, seemed more difficult to perform (Tab. 7.7, entry 4). Silyl-substituted aromatics reacted by ipso Si-substitution [77], and were less volatile. With trimethylsilylbenzene, benzoylation occurred with an overall yield higher than for benzene, but the competitive H-substitu-tion was also observed (entry 5). 

We know that reduction potentials of arylsilanes are less negative than those of the corresponding aromatic compounds without silyl substituents (Sect. 2.2.1). The effect of silyl groups to facilitate the electron transfer to the neigbouring aromatic group is explained in terms of p interaction. For example, half wave reduction potentials of naphthylsilanes are less negative than that of... 

The direct silylation of arenes through C—H bond activation provides an attractive route for the synthesis of useful aromatic compounds [64]. Vaska s complex was the first of the iridium catalysts to be reported for activation of the C—H bond in benzene by Si—H of pentamethyldisiloxane to yield phenylsubstituted siloxane [65]. However, a very attractive method for the aromatic C—H silylation with disilanes has been recently reported by the groups of Ishiyama and Miyaura [66-68]. 

Scheme 54 Photoreaction of aromatic carbonyl compounds with p,p-dimethyl ketene silyl acetals.

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