Disiloxanediols

A further disiloxanediol, l,3-bis(dicyclopentenyl)-l,3-dimethyldihy-droxydisiloxane, is obtained by hydrolysis of the product obtained from... 

Disiloxanediols are sometimes obtained inadvertantly when the silanediol is desired, or appear as by-products of the latter. Synthesis of the lower members is often quite difficult, and careful control of pn and temperature was found necessary by Lucas and Martin (38) to prepare tetramethyldisiloxanediol. Frisch, Goodwin and Scott (19) obtained a number of divinyl- and diallyldisiloxanediols under conditions similar to those used for the preparation of the related silanediols. Robinson and Kipping (57) early obtained relatively stable disiloxanediols from silanediols by means of heat or acids. 

It is often difficult to control the condensation reactions of silanediols so that only a single reaction occurs to give the disiloxanediol, but the sterically hindered ferrocenyl substituted diol 34 can be condensed to give 35 in good yield (equation 12). If 35 is subject to similar conditions but for 2 h at reflux temperature, then further condensation reactions... 

The disiloxanediols 43251 and 44252 contain only intramolecular hydrogen bonds with an O N distance of 2.644 A in 43 and an O O distance of 2.899 A in 44. These disiloxane diols thus differ from the others in that discrete molecules with no significant intermolecular interactions are formed. They are also both unusual in that the Si—O—Si linkage in each is linear. In 44, the structure is distorted away from tetrahedral at the Si atoms towards a trigonal bipyramidal geometry by an additional coordination to a sulphoxide oxygen. 

A better control of the reaction products is achieved by starting the synthesis from dilithiated disiloxanediols. Cyclotrisiloxanes are formed upon reaction with halides such as BuSiFs (Eq. Six-membered ring systems containing heteroatoms are also accessible by this method. 

Reactions of 1,2-dichlorotetramethyldisilane with the siloxanediols according to Eq. 1 give the expected seven- to eleven-membered rings 1, II and III, cf [5, 6]. Reactions of 1,1,2,2-tetrachlorodimethyldisilane with one equivalent of siloxanediol give the monocyclic siloxanes IV, V, VI, VII (Scheme 1), for disiloxanediol (n = 1) as well with endocyclic as with exocyclic Si-Si, and for tri- and tetrasiloxanediol ( = 2, 3) with exocyclic Si-Si only. 

The reaction of 1,1,2,2-tetrachlorodimethyldisilane with two equivalents of siloxanediol gives in a similar way the bicyclic cyclosiloxanes VIII, IX, X, for disiloxanediol ( = 1) with endocyclic Si-Si only, and for tri- and tetrasiloxanediol (n = 2,3) exclusively with exocyclic Si-Si (Scheme 2). The cyclocondensation in the 1,1-position at Si-Si seems to be favored, especially for at least eight-membered rings. 

Since the spirocycles 1 with the siloxane structure as well as the bis-TCA-disiloxanediol 5, which is obtained from (HO)2TCA by heating between 80°C and 110°C in toluene solution as the condensation product, exhibited intense photoluminescence similar to the cyclobutenes described above, the perphenylated cyclotri- and -tetrasiloxane compounds were also investigated. 

Fig. 8. Photoluminescence excitation spectra of the stereoregular phenylcyclosiloxanes [PhSiO(OSiMc3)] where n = 4, 6, 8, and 12, together with the tetraphenyl-l,3-disiloxanediol, measured as solids (powder) at liquid nitrogen temperature, 7 = 77 K. Emission wavelength A = 505 nm, speetral bandwidth AA = I nm, edge filter (50% transmission at 495 nm). Legend D2 tetraphenyidisiloxanediol D4-DI2 - phenyleyelo-siloxane, ring sizes of n = 4-12.

The first type, 11, has been found in a l,3-dimethyl-2-oxa-l,3-disilacyclohexane-1,3-diol [24]. Type 12 has been found in l,l,3,3-tetra-wo-propyl-l,3-disiloxanediol, HOPr 2SiOSiPr 20H [25]. The third type, 13, is illustrated by the methyl [26], ethyl [27], -propyl [28], and phenyl derivatives. 

Quite in contrast to the alkoxides and simple silox-ides, related disiloxanediolate complexes of cerium(rv) form spontaneously upon treatment of cerium(III) precursors with... 

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