Pentacoordinate tin complexes

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... 

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

The first tin hydride complex [Bu2Snl2H][Li] was recently synthesized. The observed upheld ii Sn chemical shift (-177.9 ppm in THF-rfg) and spin-spin coupling constants [ /( Sn— C) 498 Hz, /( Sn— H) 2318 Hz] as compared with those for Bu2SnIH (—76.3 ppm, 408 and 2060 Hz, respectively) strongly indicate the formation of a pentacoordinated tin complex. 

Treatment of allyl bromides with the complex obtained from tin(II) chloride and the disodium salt of diethyl 2,3-dihydroxybutanedioate gives an intermediate which reacts with aldehydes to provide homoallylic alcohols with 50-65% ee. Lower enantiomeric excesses were obtained with bulky aldehydes and for allylstannanes with y-substituents. Pentacoordinated allyltin complexes may be involved97. 

Various monocyclic and bicyclic pentacoordinate anionic germanium and tin complexes are known which possess bidentate dianionic oxo and related ligands, such as aliphatic or aromatic 1,2-diols, a-hydroxy carboxylic acids and their thio analogues (for early references see References 191, 307-309). Anionic mono- and bis-chelated germanium and... 

SCHEME 6. Relationship between trigonal bipyramid and rectangular pyramid for pentacoordinated spirocyclic germanium and tin complexes... 

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). 

Only recently, an aliphatic analogue of the pentacoordinate cationic tin complexes 461, the triorganotin iodide derivative 466, was obtained (equation 82)918. 

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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