Organosilicon Spacers

A different strategy from the above consists in the incorporation of silylamino groups on ferrocene. Condensation of such difunctional reagents with disilanols leads to the formation of polymers where the ferrocene groups are separated by organosilicon spacers [28] (Fig. 8.7). 

Figure 3. Half-shell structure model for organosilicon compounds with different spacers along the C3 symmetric substituent axis and dihedral angles go(X3Y-YX3) determined for the molecular skeletons.

The distance-dependent Pauling bond orders range from 1.00 in hexamethyldisilane with a SiSi bond of 235 pm in length (Fig. 4 standard d(l)) to 0.26 for hexakis(rert.butyl)disilane with an extremely elongated spacer distance of 270 pm between its bulky Si(C(CH3)3)3 half-shells [6b]. To rationalize the sometimes considerably weakened SiSi bonds - hexakis(rm.butyl)disilane does not dissociate into two radicals -, it has been proposed [6b,7] that additional attractive van der Waals interactions within the hydrocarbon wrapping contribute to the bonding within the respective organosilicon molecules. This assumption is further supported by the structure of hexakis(trimethylsilyl)disilane (Fig. 2), in which (presumably due to the considerable polarization Si -C5e-H5 calculated [5b]) extremely short non-bonded C(H3)-- (H3)C distances of only 352 pm are found. 

The structural comparison of the C3-symmetric skeletons of the organosilicon (halfshell (spacer) half-shell) molecules (Figure 8a) provides a rational criterion for steric overcrowdedness Obviously, at distances Y Y below 333 pm different dihedral angles a)(Xo,Y YX3) between the half-shell substituents are observed, whereas above 414 pm they are identical. The accompanying torsion D3d — D3 within the molecular skeleton is therefore a criterion for steric overcrowding48. 

Organosilicones are favourable in a broad variety of industrial applications primarily because of their unique smface active properties. Especially in the case of aqueous applications the hydrophilically substituted trisiloxane derivatives are good wetting agents. Usually, the molecule consists of a lyophobic trisiloxane moiety attached directly to an alkyl spacer group via a silicon-carbon bond. This spacer group carries on the other side a nonionic or an ionic hydrophilic part. 

The idea of this method is clear in Figure 8. This method was used in the study [40]. Organosilicon derivative of phenylboronic acid was used as a modifier of silica, while bis-NAD 1 and bis-NAD II were used as spacers. Residues of phenylboronic acid were supposed to be separated by 0.7 and 1.5nm respectively. The stationary phase obtained exhibits higher retention of spacer used in comparison with other related biopolymers. Evidently, this method is appropriate only for the preparation of bonded layers with a low density of bonded groups. 

Fig. IS. Organosilicon model compounds with spacers of different lengths between two bulky half-shell substituents with threefold axes overlap criterion based on deviating dihedral angles and intramolecular (as well as peripheral) van der Waals bonding [22],...

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