Octamethylcyclotetrasilazane, OMCTS

As already discussed in Section 2.2, crystalline dimethylsilanediol 53 can be prepared by hydrolysis from hexamethylcyclotrisilazane 51, from dimethoxydimethyl-silane [40], and from octamethylcyclotetrasilazane (OMCTS) 52. The most simple preparation of 53 is, however, controlled hydrolysis of dimethyldichlorosilane 48 in the presence of (NH4)2C03 or triethylamine [41]. Likewise, hydrolysis of hexam-ethylcyclotrisiloxane 54 and of octamethylcyclotetrasiloxane 55 eventually gives rise to dimethylsilanediol 53. In all these reactions the intermediacy of the very reactive dimethylsilanone 110 has been assumed, which can be generated by pyrolytic [42, 43] and chemical methods [44—46] and which cyclizes or polymerizes much more rapidly, e.g. in contact with traces of alkali from ordinary laboratory or even Pyrex glassware [40, 47] to 54, 55, and 56 than trimethylsilanol 4 polymerizes to hexamethyldisiloxane 7. Compound 111 is readily converted into dimethylsilanone 110 and MesSil 17 [46] (Scheme 3.6). 

Since HMDS boils at I26°C, and the least reactive silylated 2- H)-pyridinone (27) has to be heated to a much higher temperature to effect conversion, 27 is reacted with the stable crystalline and commercially available octamethylcyclotetrasilazane (OMCTS) (157) (melting point = 97°C, boiling point = 225°C) (57M11) to afford activated dimeric intermediates such as 158, which can be aminated at 180-200°C in the presence of... 

To investigate the ring contraction of octamethylcyclotetrasilazane (OMCTS) quantum chemical studies have been carried out (Gaussian98, B3LYP, 6-3IG ). 

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