Organotin-oxygen coordination

A mixture of ethyl bromosuccinate and tinfoil in the presence of catalysts was stirred for 4 h, for example, and the tinfoil soon disappeared from the reaction mixture in the process. A product was easily isolated as a solid form from the reaction mixture, and two crystalline diastereomeric species were obtained by fractional crystallization of the above product. Based on the IR spectra of the products, the author first proposed a five-membered ring structure for organotin compounds in which lone electron pair of carbonyl oxygen coordinates to a tin atom, as shown in Eq. (2.4). 

Few X-ray diffraction data are available for the organotin alkoxides. Trimethyltin methoxide in the crystal is a five-coordinate linear polymer 47,380 and both tin atoms in the methanol solvate, CH2(SnPh2OMe)2-MeOH, are five coordinate, one by intramolecular coordination, and the other by solvation 48.381 Dimethyltin dimethoxide 49,382 dimethyltin diphenoxide 50,383 and isopropyltin triisopropoxide 51384 are five-coordinate oxygen-bridged dimers. All these compounds are monomers in solution. 

C NMR spectra of organotin derivatives 36-38 and their autoassociated complexes (see Section 4.05.3.2.3) have been recorded and chemical shift shown to be diagnostic of coordination between the tin atom and oxygen of a carbonyl group of adjacent molecules <1995JPR242>. 

Radical reductions typically involve a hydrogen atom transfer from a suitable donor (organotin or silicon hydride) to an acceptor, commonly a radical intermediate generated a to a earbonyl. In eases where enantiomerieally pure products are desired, a chiral Lewis acid is employed in order to coordinate to the Lewis basic carbonyl oxygen(s) and provide faeial bias for the ensuing hydrogen atom transfer. 

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