Organosilanes Organosilicon compounds

It is the purpose of this chapter to review selectively the advances in the synthetic applications of organosilicon compounds, excluding those organosilanes covered in other chapters. Since the publication of The Chemistry of Organic Silicon Compounds, two monographs1,2 and several reviews3-5 have been published, as have three conference proceedings6-8 and a symposium-in-print 9. 

The classical procedure of resolution through diastereomer formation and separation, widely applied in organic chemistry (43), was first applied to silicon compounds by Sommer. (-)-Menthol proved to be a convenient resolving agent for organosilicon compounds. Using this method, acyclic and cyclic organosilanes have been resolved, as detailed in the sequel. 

The chemistry of organosilicon compounds has expanded with the use of transition metals. Both catalytic processes (179) and the chemistry of silicon transition metal compounds (180) have been developed. Catalytic reactions of organosilanes and more recently, reactions of silyl-transition metal complexes have already found interesting applications in organic synthesis (80,181,182). 

Chiral organosilanes have been shown to undergo stereospecific catalytic reactions leading to the preparation of optically active silyl-transition metal complexes. We first discuss the stereochemistry and mechanism of transition metal catalyzed reactions of organosilicon compounds. Then the stereochemistry of chiral organosilyl-transition metal complexes are described. The chemistry of optically active silyl- and germyl-transition metals has been the subject of a recent review (12), and we concentrate here on mechanistic implications, especially in the field of homogeneous catalytic reactions. 

The stability of pentacoordinate phosphorus compounds has been discussed in terms of apicophilicity of the ligands. The isomerization of these compounds arises from intramolecular ligand permutation via Berry pseudo-rotation or turnstile rotation. It is of interest to know whether the concepts developed in the field of phosphorus chemistry are applicable or not to related organosilicon compounds. It is the aim of this Section to critically review recent studies of the dynamic stereochemistry of pentacoordinate organosilanes. 

The photochemistry of organosilicon compounds has been extensively investigated not only from synthetic and mechanistic perspectives, but also with the intent of determining characteristic chemical and physical properties. Very recently, Steinmetz reviewed the area of organosilane photochemistry in which he focused on the reactivities of mono-, di-, tri-, and polysilanes. The most interesting and important point of that review is the differences in the reactivity that exist between organosilicon compounds and the corresponding all-carbon compounds. 

Pentacoordinated silicate TASF, one of the best activators of organosilicon compounds in the Pd-catalyzed cross-coupUng reaction as we have seen, is found to be involved in the coupling reaction with aryl hahdes in the absence of other organosilanes to give methylated arenes (Scheme 1A)S Recently, DeShong and co-workers also reported that tetrabutylammonium triphenyldifluorosilicate, another pentacoordinated silicate, is applicable for the phenylation of allyl benzoates and aryl haUdes in the presence of a palladium catalyst. 

The fundamental work of Sommer and his coworkers on the stereochemistry of organosilicon compounds originated from the preparation of optically pure methyl-a-naphthylphenylsilane (XII) and closely related compounds, which were obtained via fractional crystallization of diastereomeric menthoxymethyl-a-naphthylphenylsilane [61]. However, few examples of the preparation of optically active organosilanes either by kinetic resolution or by asymmetric synthesis have been recorded so far in... 

Reduction to Alcohols. The organosilane-mediated reduction of ketones to secondary alcohols has been shown to occur under a wide variety of conditions. Only those reactions that are of high yield and of a more practical nature are mentioned here. As with aldehydes, ketones do not normally react spontaneously with organosilicon hydrides to form alcohols. The exceptional behavior of some organocobalt cluster complex carbonyl compounds was noted previously. Introduction of acids or other electrophilic species that are capable of coordination with the carbonyl oxygen enables reduction to occur by transfer of silyl hydride to the polarized carbonyl carbon (Eq. 2). This permits facile, chemoselective reduction of many ketones to alcohols. 

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