Study on the transannular bond formation and hypercoordination in tin and germanium spirometallocanes

D(CH₂CH₂S)₂MSNH(C₆H₄) (M = Ge, Sn; D = O, S) spirocycles were synthesized to analyze the influence of the decrease of the radius of the metal and the change of the hardness of donor atom on the strength of the transannular bond and the hypercoordination of group 14 elements. The compounds were characterized by IR, Raman and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy, EI mass spectrometry and elemental analysis. Monocrystal X-ray diffraction analyses were made for the germanium compounds. The germaspirocycles were five-coordinated and had distorted trigonal bipyramid geometry. In contrast with most of the reported analogous germocanes, the transannular bond is stronger when the donor atom is oxygen, rather than sulfur. O(CH₂CH₂S)₂GeSNH(C₆H₄) exhibits an intramolecular hydrogen bond formation between the amine group and the transannular oxygen. The presence of this hydrogen bond determines whether the sulfur (O?Ge–S) or the nitrogen (S?Ge–N) of the five-member ring is the axial atom. According to the ¹¹⁹Sn chemical shift, both stannospirocycles were five-coordinated and therefore the presence of the transannular interaction in solution could be suggested.