Bonds to Silicon

Substituted 1,3-diphosphorinans (19) or diphospholans (20) are the products resulting from reactions between alkali-metal (M) phosphides such as 

MPhP(CH2) PPhM, where n =2 or 3, and diorganodichlorosilanes.258 Similar ring-closure reactions occur with tin and aluminium organodichlorides. 

A new disilylphosphine (21) is produced by the reaction between bromine or iodine and potassium phenyl(trimethylsilyl)phosphide in benzene solution 259 on changing the solvent to THF, the reaction becomes more complex but the diphosphane (22) can be isolated. The latter is also the product from trimethylsilylation of dipotassium phenylphosphide.260 

Bonds to Fluorine.—Phosphorus (m) Compounds. SCF wavefunctions for PF allow estimation of the dissociation enthalpy (4.7 eV), the dipole moment (0.6 D), and the P—F distance (1.58 A), etc.,261 while the emission spectra of the species produced by the action of microwave discharges on HPF2 and PF3 may be analysed in terms of the PF diatomic.262 Experimental data for the e.s.r. parameters of the PF2 radical263 and those calculated by ab initio methods264 are in good agreement. 

Robinet, J.-F. Labarre, and C. Leibovici, Chem. Phys. Letters, 1974, 26, 203. 

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Considerable literature is currently available about these species. The review by Raabe and Michl in 1985 on Multiple Bonding to Silicon 6 is certainly the most detailed and complete reference to the topic to that date. Subsequently a number of other reviews that provide additional details of more limited areas of the field have been written by Brook and Baines,7 Cowley and Norman,8 Gordon,9 Shklover et al.,w Grev,11 and Lickiss.12 In addition, much information is to be found in The Chemistry of Organic Silicon Compounds edited by Patai and Rappoport,13 especially in chapters 2, 3, 8, 15, and 17. 

Figure 2. Variation of oxidation number of silicon with step and variation of number of oxygens bonded to silicon with step in direct or elemental-silicon process for (EtOJ Si.

G. Raabe, J. Michl, Multiple Bonds to Silicon, in S. Patai, Z. Rappoport (eds.), The Chemistry of Organic Silicon Compounds, John Wiley Sons, Chichester 1989, pp. 1015. 

Dienes bonded to silicones to give products stable to hydrolysis are available in a wide variety of combinations, from the distillable l,3-bis(isoprenyl)-l,l,3,3-tetramethyldisiloxane to high polymers with dozens of diene groups attached [23], Diels-Alder cycloadditions may be performed with dieno-philes. Maleic anhydride adds almost quantitatively to the conjugated diene system, giving easy access to a siloxane species of considerable industrial importance [24]. 

Evidently, it is favorable for dihydridesiloxanes to attract terminal allyl groups rather than NH-group bonded to silicon atoms, surrounded with organic radicals under the conditions of polyhydrosilylation reactions. That leads to formation of macromolecules with linear structure (scheme 2) [6]. 

Figure 7.12 shows the FI traces taken from the 2D plots at 7.3, 3.0 and Oppm. The aromatic resonances at 7.3 ppm (bottom trace in Figure 7.12) are very well resolved, while the aliphatic and vinyl protons of cod ligand (middle trace) are broad and hidden in the baseline. The upper trace, taken at Oppm, represents the pure signal of methyl proton bonded to silicon residue. Despite the fact that 2D CRAMPS experiment enabled us roughly to assign the position of cod protons, the exact chemical shifts of other hydrogens remain equivocal. 

H MAS NMR clearly shows five signals at 0.8, 1.9, 4.4, 10.1 and 12.1 ppm. The signals at 0.8, 1.9 and 4.4 are assigned to alkyl fragments bonded to silicon atoms, residual silanol groups on the silica surface and to silicon hydride species, respectively. The two downfield signals at 10.1 and 12.1 ppm are an indication of the presence of two types of zirconium hydride surface species [111]. DQ rotor-synchronized 2D H MAS NMR was used to discriminate these zirconium hydride... 

Linford, M. R. and Chidsey, . E. D. Alkyl monolayers covalently bonded to silicon surfaces. Journal of the American Chemical Society 115, 12631 (1993). 

The ideal surface for contact with human blood is the surface of blood vessels, and the immediate surface contains heparinoid complexes. Heparin, a negatively charged polysaccharide, has been bonded to silicon rubber and other polymers. In one procedure, a quaternary ammonium compound is first adsorbed on die polymer substrate and heparin is 111 turn adsorbed on the positively charged surface. Chemical bonding of heparin has also been achieved. Such surfaces do not cause clotting of contacted blood. 

Polymer structures that hold silanols at the interface. Good examples of hydrolytically stable crosslinked structures are silica and silicate rocks. Although every oxane bond in these structures is hydrolyzable, a silicate rock is quite resistant to water. Each silicon is bonded to four oxygens under equilibrium conditions with a favorable equilibrium constant for bond retention. The probability that all four bonds to silicon can hydrolyze simultaneously to release soluble silicic acid is extremely remote. With sensitive enough analytical techniques it is possible to identify soluble silica as it -leaches from rocks, but an individual rock will survive in water for thousands of years. 

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