Trimethyltin fluoride

The development of the hypervalency concept was discussed in general. This model was concerned with the group 14 elements . The ability of the tin atom to expand the coordination sphere in organotin compounds was established in the early 1960s, when an oligomeric structure was suggested for trimethyltin fluoride and trimethyltin carboxylates" on the basis of IR data. It should be pointed out that the trimethyltin chloride-pyridine adduct was the first pentacoordinate organotin compound structurally characterized by X-ray diffraction in 1963". ... 

Trimethyltin fluoride exists in the crystal as a polymer with a structure close to A. The Mc ,Sn units are planar, and the non-linear Sn-F-Sn bridges are somewhat asymmetric, with Sn-F distances ca. 210 and 220-260 pm, respectively.57 This structure is not easily disrupted, and trimethyltin fluoride, like the the other lower trialkyltin fluorides, is insoluble in unreactive organic solvents. The solid state 119Sn NMR spectrum shows effectively equal coupling to the two adjacent fluorine atoms with (SnF) 1300 Hz.58... 

A modified protocol has been developed involving less hazardous trimethyltin fluoride (Scheme 5.8.11). 

The trimethyltin fluoride is generated in situ or can be added initially. The advantage of this reagent is that it is less volatile than trimethyltin chloride, not easily absorbed through the skin and can be filtered off at the end of the reaction, rather than distributed in both the organic and aqueous waste streams. 

The last two derivatives to yield to synthetic efforts were 98 and 99. For the former, several approaches have been described. A classical one starts with the commercial product 109, which was converted to 98 via the intermediate halogenoethenes 110 and 111 [62], and a modem one starts from l,l-dihromo-2,2-difluoroethene (112), which was either metalated to the alkali derivative 113 or the tin compound 114 (Scheme 2-11). Loss of alkali fluoride or trimethyltin fluoride (by flash vacuum pyrolysis) then leads to the desired 98 [63]. 

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. 

The methyl group of 56a is abstracted after addition of Ph3CBAr 4 (Ar = 3,5-(CF3)2C6H3) to produce the salt 58 after abstraction of the benzyl group of 56e with BfCeFsls, the arene adduct 61 is formed. 56e forms also a stable, tetrahedral 14-electron compound with pyridine. This adduct formation with the Lewis base causes a noticeable elongation of the Fe-C bond length compared to that of parent compound 56e [210.7(2) vs. 204.14(18) pm]. Furthermore, alkyl complexes 56 serve as precursors for discrete iron(n) fluorides by reaction with trimethyltin fluoride. " ... 

Further information was obtained from a study of the infrared spectra in the potassium bromide region. Trimethyltin compounds normally give rise to two Sn—C vibrations at about 500 and 550 cm, belonging to the symmetrical and the asymmetrical Sn—C stretching vibrations of tetrahedral molecules, respectively 103, 104). Only one band (near 550 cm ) is expected, however, for the planar (CH3)3Sn configuration. Thus absence of the 500 cm band in trimethyltin fluoride and acylates 103) has been used as evidence for the occurrence of planar (CH3)3Sn ions in these compounds. 

Thus, for example, trimethyltin fluoride has the chain structure shown in Fig. 20 (a), in which each tin atom is five-coordinate o. ... 

Figure 24. The structure of the trimethyltin fluoride polymer. (After H. C. Clark, R. J. O Brien and J. Trotter, J. Chem. Soc., 1964,2332).

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