Silanones generation

The platinum complex [ Pt(dmpe) 2( X-H)2](OTf)2 can catalyze the generation of silanones from secondary silanols under very mild conditions (at room tempera-... 

Schemes 6-31 Pt(ll)-catalyzed generation of silanones and the proposed mechanism...

More recently, Belzner et al. reported a new type of oxygen transfer reaction from isocyanates to bis[2-(dimethylaminomethyl)phenyl]silylene (8)18 which was thermally generated from the corresponding cyclotrisilane 7, and they obtained some convincing results of the involvement of silanone 9 (Scheme 3). However, they found that silanone 9 is not stable enough to be isolated. Only cyclic di- and trisiloxanes 10 and 11 (i.e., the cyclic dimer and trimer of the silanone 9) were obtained together with the corresponding isonitrile as other main products when... 

Silanoncs (R2Si=0). As already written above, an attempt to prepare a four membered silaoxetane ring has not been very successful because of its instability but these reactions have been used conveniently to generate silanone S. 

A siloxetane 526 as an intermediate from a [2 + 2] cycloaddition of silene 241 with acetone has been formulated by lshikawa134. It extrudes a silanone equivalent to give the vinyl ether 527. The second regioisomeric silene 242 generated together with 241 by photolysis of 240 undergoes an ene reaction instead (equation 179)134. 

Evidence for the formation of silanones depends on two types of experiments. In the first, silanones are generated as unstable intermediates in reactions, and their formation is inferred from the isolation of trapping products with suitable substrates. The second approach is based on their generation in a low temperature matrix and their characterization by infrared spectroscopy which reveals v(si=o) at ca 1200 cm-1. These two groups of experiments are described below. 

When a mixture of methylsilane (or dimethylsilane) deposited with ozone in an argon matrix at 17 K was photolyzed, the corresponding silanone, MeHSi=0 (or Me2Si=0), was generated and characterized by their infrared spectra. In the case of the parent silane, H3SiH, a similar photolytic reaction with ozone in an Ar matrix led to the identification of SiO, H2Si=0 (2), (HO)HSi=0 (silanoic acid) and (HO)2Si=0 (silicic acid)18. 

Most recently, Milstein and coworkers reported a new type of homogeneous catalytic reaction that generates silanones from secondary silanols under extremely mild conditions. The platinum complex (dmpe)Pt(Me)OTf) (27) (dmpe = Me2PCH2CH2PMe2, OTf = OSO2CF3 was treated with an equimolar amount of the silanol, (i-PrhSilKOII) (28), in acetone to yield a new dimeric hydrido-bridged complex 29 and the trimer 30 of diisopropylsilanone, 31 (Scheme 12)29. 

The generation of methane in the reaction was evidenced by the 111 NMR spectrum of the reaction mixture. It was also shown that the newly obtained complex 29 reacts catalytically with silanol 28 to give the trimer 30 (presumably from trimerization of 31) with the evolution of hydrogen gas. In the presence of MesSiOMe the same reaction resulted in the formation of an insertion product of the intermediate silanone 31 as shown in the lower part of Scheme 12. The proposed catalytic cycle for the dehydrogenation of 28 with 29 is shown in Scheme 13. It should be noted, however, that spectroscopic evidence for the proposed silanones was not presented. 

In analogy to the reaction of decamethylsilicocene 41 with carbon dioxide leading to the generation of intermediary silanone 44, silicocene 41 was allowed to react with carbon oxysulfide under very mild conditions (—78 °C/toluene) to give the corresponding 1,3,2,4-dithiadisiletane derivative 81, a formal head-to-tail [2 + 2] cycloaddition reaction product of the initially formed silanethione 80 (Scheme 29)41b. 

In recent years remarkable progress has been made in the chemistry of organosilicon compounds containing a double bond to group 14 and group 15 elements. The reaction of a silylene-isocyanide complex with nitrile oxide generated the intermediate silanone, which with phenyl isothiocyanate afforded 1,3,2-oxathiasiletane 63, which is sensitive to hydrolysis (Equation 10) <2000CL244>. 

Besides olygomerization, one of the typical reactions of silanones is the insertion into Si-O or other polar bonds [1]. So the cathodic generation of diphenylsilanone was performed using hexamethyldisiloxane (HMDS) as a silanone trap. The reduction of O2 dissolved to saturation in a 0.1 M solution of BU4NPF6 in DMF or THF in the presence of Ph2Si(OMe)2 and HMDS resulted in formation of an insertion product — 1,1,1,5,5,5-hexamethyl-3,3-diphenyltrisiloxane (Scheme 2). With permethylcyclosiloxanes D (n = 3, 4), used as trapping molecules instead of HMDS, corresponding cyclic products with extended cycles, D D 2, were obtained. The results of siloxane... 

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