Tin-chalcogen double bonds

Similarly, stannanethione 166 and stannaneselone 168 kinetically stabilized by Tbt and Ditp groups have Sn chemical shifts of 531 and 440 ppm, respectively. Kuchta and Parkin have reported the synthesis of stable terminal chalcogenido complexes of tin 193 (Scheme 58), and the chemical shifts for the central tin atom appears at a much higher field, i.e. —303 ppm (193a, X=S) and —444 ppm (193b, X=Se). This clearly shows that the thermodynamically stabilized tin-chalcogen double bonds in 193 (X=S, Se) are electronically perturbed to a great extent. 

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