Triorganotin fluorides

Preparation, characterization, and properties of silicon-containing triorganotin fluorides, both symmetrical and unsymmetrical, were investigated. It was observed that introduction of a trimethylsilyl group in the alkyl chain results in a considerable enhancement of solubility in various nonpolar solvents including dense carbon dioxide. 

Certain triorganotin fluorides are known to be effective vis-cosifiers for nonpolar solvents. Dunn and Oldfield (1 ) have studied the solution properties of tri-n-butyltin fluoride (BUF) in various organic solvents. They reported that, among n-alkanes, BUF dissolves only in n-hexane and not in n-heptane. This... 

Triorganotin Fluoride. Fluorination of triorganotin bromide was carried out by an excess of ammonium fluoride at 120°C for one hour. 

Synthesis and Characterization. Tris(trimethylsilylpropyl)tin fluoride (PTF) and tris(trimethylsilylmethyl)tin fluoride (MTF) were synthesized according to scheme A (Figure 1) while scheme B (Figure 1) was followed in the synthesis of dibutyl-(trimethylsilylpropyl)tin fluoride (BTF). MTF has been reported in the literature (6) however, it was synthesized to compare its solution properties with the other two novel compounds. The steps involved in these syntheses were straight-forward and thus need no elaboration. In the synthesis of BTF, the unsymmetrical triorganotin fluoride, bromination of tetraorganotin compound resulted... 

Figure 1. Schemes for the synthesis of silicon containing triorganotin fluorides.

Viscosity Behavior. The polymeric nature of triorganotin fluorides dissolved in nonpolar solvents is outlined in the introduction. As a result of the transient polymer formation, these solutions exhibit nonlinear concentration vs. viscosity curves. 

Solubilities of Silicon Containing Triorganotin Fluorides at 25°C Solvent... 

Triorganotin fluorides can be prepared by the use of new fluorinating systems. 18-Crown-6 or dibenzo-24-crown-8 can act as solid-liquid phase transfer catalysts for CsF. Trialkyltin mercaptides can be fluorodestannylated by CsF in the presence of crown ethers or alkyl bromides358 ... 

In the condensed phase Me3SiF molecules show no intermolecular interactions, while the same germanium derivatives are associated as a dimer due to intermolecular F Ge coordination. According to the tendency for tetrahedral main-group 14 elements to expand the coordination sphere, organotin fluorides show a strong tendency to associate in the solid state and even in triorganotin fluorides the tin atom is five-coordinate A common feature of this class of compounds in the solid state is coordination expansion of the tin atom due to hypervalent interaction, which in turn often results in formation of polymeric materials. 

Triorganotin fluorides form polymeric chains in the solid state. The tin atom is five-coordinate and has trigonal bipyramidal geometry, with the halogen atoms in axial positions. 

Some triorganotin fluorides have been found to be monomeric, 120, and the bond length of 1.961 A in trimesityltin fluoride has been suggested as a standard value for the single covalent Sn-F bond [346]. 

Except for the unusually high value initially reported for tricyclohexyltin fluoride (Sn-F 2.45 A) [347], in other monomeric triorganotin fluorides the observed Sn-F interatomic distances are similar (see Table 3.12). It was recently demonstrated that this figure is wrong, that the correct value is 2.051 A, and that the structure is asymmetric, with a second, dative Sn — F intermolecular bond of 2.303 A [348]. In trimethyltin fluoride a bent chain structure was reported in an early determination of crystal structure [349]. The Sn-F bond lengths, however, differ very little. 

---