Pentacoordinated tin

The mechanism of the reaction was postulated as being either synchronous attack of the RO" ion (R = Me or H) at tin and breaking of the aryl-tin bond, or rapid formation of a pentacoordinate tin intermediate [ROMe3SnPh-] followed by rate-determining breaking of the aryl-tin bond. In either case the phenyl-carbanion could separate as such and then react rapidly with solvent, or it could react with solvent as it separated. 

Aspects of pentacoordinate tin compounds. A. Tzschach and K. Jurkschat, Comments Inorg. Chem., 1983,3,35-50 (55). 

Racemization of stannane 37 was also observed in donor solvents as shown in Table 2. Although stable for short periods in phenethylamine and acetonitrile, stannane 37 is appreciably racemized in DMSO, HMPA and especially MeOH. Pentacoordinated tin species are likely intermediates. Interestingly, exposure to HMPA leads to significant formation... 

The IR and Raman spectra of the thiophosphoric acid ester 14 are consistent with a polymeric structure including tetra- and pentacoordinated tin atoms128. 

Pentacoordinate tin complexes can also be isolated from the reaction of diphenyldichlorostannane with 4 (R = Pr, R = Me) (38). The structure of the Ph2SnCl2 complex 60 was shown to be very similar to that of 54 by X-ray crystallography. Thus, the geometry around... 

A 1,2-oxastannetanide, which is an example of an anionic pentacoordinate tin compound with a four-membered ring oxygen and one organic substituent in apical position, was prepared at room temperature by deprotonation of the corresponding / -hydroxystannane using KH in THF and 18-crown-6 (equation 59)76. The presence of a stannyl anion was evident by the appearance of a double quartet with Sp centers at —75.09 ppm... 

Hypervalent compounds with coordinative phosphorus —> tin bonds are rare. An intermolecular P —> Sn coordination in Me2ClSnCH2CH2PPh2 and its bromo-substituted analogue was suggested based on NMR and 119Sn Mossbauer spectroscopic data201,202. The X-ray crystal structure analyses showed pentacoordinate tin atoms with the phosphorus and the chlorine atoms located in axial positions203. The P —> Sn distance amounts to... 

Anionic spirocyclic pentacoordinate tin species having aromatic rings, namely bis(TDT) complexes 113a324 and 113b336, were prepared in high yields by addition of halide ion to bis(toluene-3,4-dithiolato)tin, Sn(TDT)2, (equation 21). 

High yields in some of these reactions indicate the formation of pentacoordinate tin intermediates whose structures may resemble 397820.821. 

TABLE 65. Some structural parameters for selected cationic intermolecular pentacoordinate tin complexes containing a [SnC3X2]+ moiety (X = O, N)... 

Two signals were observed as a result of tetra- and pentacoordinated tin atoms in the polymer matrix. 

Simple 2,2-dibutyl-l,3,2-dioxastannolanes form solid complexes of monomer units with certain nucleophiles, such as pyridine and dimethyl sulfoxide, that have 1 1 stoichiometry and pentacoordinate tin atoms.62 Such complexes are less stable for more-substituted stannylene acetals, such as those derived from carbohydrates.62 Unfortunately, the precise structures of these complexes have not yet been defined. Addition of nucleophiles to solutions of stannylene acetals in nonpolar solvents has been found to markedly increase the rates of reaction with electrophiles,63 and transient complexes of this type are likely intermediates. Similar rate enhancements were observed in reactions of tributylstannyl ethers.57 Tetrabu-tylammonium iodide was the nucleophile used first,57 but a wide variety of nucleophiles has been used subsequently tetraalkylammonium halides, jV-methylimidazole,18 and cesium fluoride64,65 have been used the most. Such nucleophilic solvents as N,N-dimethylformamide and ethers probably also act as added nucleophiles. As well as increasing the rates of reaction, in certain cases the added nucleophiles reverse the regioselectivity from that observed in nonpolar solvents.18,19... 

Almost aU these complexes had a hexacoordinated tin atom in octahedral environment. It is remarkable that only five intermolecular coordination compounds Me3SnX B (Cl, Br, I B = Py, PhNH2 ) containing pentacoordinated tin atom... 

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