C-Si Bond cleavage

Based on the earlier work of Brook (7), a number of valuable reactions involving Si—C bond cleavage have been described. Both aromatic and... 

Example The molecular ion of l,2-bis(trimethylsiloxy)benzene, m/z 254, undergoes methyl loss by Si-C bond cleavage as typically observed for silanes (Fig. 6.48). Rearrangement of the [M-CHb] ion then yields [Si(Me)3], m/z 73 (base peak). This is not an ortho elimination with concomitant H transfer as defined in the strict sense, but the observed reaction is still specific for the orthoisomer. [190,203] In the spectra of the meta- and para-isomers the [Si(Me)3] ion is of lower abundance, the [M-CHb] ion representing the base peak in their spectra. Moreover, the m/z 73 ion is then generated directly from the molecular ion which is clearly different from the two-step pathway of the ortho-isomer. 

It is interesting to note that the fluoride ion-promoted Si-C bond cleavage of vinyl silanes is greatly facilitated by the presence of a hydroxyl group at the tetrahedral P-carbon atom [67]. 

It has also been mentioned in the literature that bis(trimethyl-silylbenzene)chromium, Cr(Tj6-C8H5SiMe3)2, undergoes rapid Si—C bond cleavage in absolute methanol at room temperature, in contrast to the inertness of the uncomplexed trimethylsilylbenzene in methanol (47). 

Ready cleavage of Si—C bonds was observed in reactions of allyltri-methylsilane with Pd(II) and Hg(II) compounds (92, 133, 169), and of alkynyltrimethylsilanes with Pt(II) complexes (126). Probably, in all cases 7r-complex formation occurs as an intermediate step, and this promotes Si—C bond cleavage. 

The products arising from the reaction of 431 with the alkyl-substituted silenes 149 and 150 suggest that the reaction occurs by a radical pathway, initiated by a homolytic Si—C bond cleavage of 431 and subsequent Si—Si bond formation giving the biradical 434. Intramolecular disproportionation of 434 gives 435, while 436 and 437 are the results of ring closure reactions without or with expulsion of tetramethylethene, respectively (equation 139)181. 

Decamethylsilicocene (82) can be regarded as an electron-rich silicon(II) compound containing a hypercoordinated silicon atom. The chemistry of 82 is determined by (a) the nucleophilicity of the silicon lone-pair (cr-donor function towards electrophiles, oxidative-addition processes) and (b) the weakness of the silicon-(cyclopentadienyl)carbon jr-bond rearrangement, Si—C bond cleavage). In the following section, the chem-... 

Pilcher, A. S. DeShong, P. Utilization of tetra-butylammonium triphenyldifluorosilicate as a fluoride source for Si-C bond cleavage. J. Org. Chem. 1996, 61, 6901-6905. 

The formation of this species cannot be explained on the basis of any other obvious mechanism. Neither does the initially considered alternative, a C—C bond cleavage of the silacyclobutane instead of a Si—C bond cleavage (77), account for the ethylation of silicon that occurs in this crucial test experiment [Eq. (26)]. 

This scheme was also used for the synthesis of a venlafaxine analogue containing a four-membered silacycle instead of a six-membered ring but Si-C bond cleavage with silacyclobutane ring opening took place in the amination step (Scheme 4) (04OM4987). 

As shown in Scheme 2, compounds 10 and 14 were additionally obtained by alternative methods involving Si-C bond cleavage reactions. These syntheses were performed in acetonitrile (10,14) or water (14) at room temperature. 

The diacetylide Me2Si(C=CPh)2 undergoes Si—C bond cleavage in reactions with Pt(C2H4)2(PR3) [R3 = (C6H,)3, MeBu-tj, PhPr-i2], in light petrol but at RT in under 2 h ... 

A precedent for this reaction is provided by the observation of organic products derived from Si C bond cleavage after autooxidation of other trialkylsilyl metal derivatives. In... 

The Si-C bond cleavage appears to proceed via the lutetium phenyl complex Cp 2LuPh. This is supported by the reaction of PhSil 13 with Cp 2LuPh, which results in the formation of benzene. A plausible reaction pathway is outlined in Scheme 291.604... 

The photochemical properties, and the excited states of polymeric polysilanes (R1R2Si)rt, investigated both in solution and in the solid state were described153. Reactions involved both Si-Si and Si-C bond cleavages. 

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