Hypercoordinated oxazoline and ethyl pyridyl organotin compounds: potential routes to stable polystannanes

Abstract

Tetraorganotin chelating tin (IV) compounds containing a rigid (10) and a semi-flexible (18) oxazoline ligand were synthesized by a reaction between the lithiated oxazoline and Ph3SnCl in good yields. Conversion into their corresponding dihalide species by reaction with two equivalents of bromine was undertaken to yield the dibromide species, 13 and 20 respectively. X-ray crystallography of these compounds revealed relatively short tin-nitrogen bond distances (10:2.762 13: 2.383, 18: 3.234 Å). These all fall within the Van der Waal radii of a tin-nitrogen bond and all adopt a distorted trigonal bipyramidal geometry in the solid state. Compounds 13 and 20 were converted into the corresponding dihydrides by reaction with NaBH4. Polymerization of the corresponding tin dihydrides produced low molecular weight polymers, 10,100 Da for the rigid species (16) and 3,200 Da for the semi-flexible tin species (22). A tetraorganotin compound containing a chelating ethyl pyridyl ligand (23) was synthesized by reacting 2-vinyl pyridine with triphenyltin hydride via a hydrostannylation reaction which was further reacted with two equivalents of bromine to yield the dibromide species (24). The X-ray crystallographic data of 23 and 24 showed relatively short Sn-N bond lengths of 2.888(2) Å and 2.363(5) Å respectively. Compound 24 will be investigated in the future for the stabilization of polystannanes following the synthesis of the dihydride species.

Synthesis and Properties of Hypercoordinate Stannanes and Polystannanes

“…Unpublished worked by a previous student, demonstrated the solid-state structure of compound 7 by obtaining a crystal suitable for single crystal x-ray diffraction. 46 It was found that there were two unique molecules of 7 within the unit cell, slightly different in bond lengths and angles (Figure 39a, c). This was compared to the optimized structures of the two conformers of 7…”

“…The dibromide stannane intermediate, 7, was synthesized according to unpublished work by Desiree Bender. 46 This was achieved via bromination with the dropwise addition of 2 molar equivalents of Br2 to a solution of 2 in C6H6 at 0 ℃ (Scheme 11). Compound 7 was preferentially synthesized through bromination reaction rather than chlorination because upon reaction with 1.0 M solution of HCl/Et2O, the result is an insoluble product, which is most likely the formation of a salt formed via the protonation of the nitrogen atom of the pyridine ring.…”

“…Although the sensitivity of the Previous unpublished work from our group demonstrated the solid-state structure of compound 2 by obtaining a crystal suitable for single crystal X-ray diffraction. 46 It was found that there was one unique molecule of 2 within the unit cell, and this was compared to calculated data (Figure 38, Table 2). The experimental bond distance between Sn1-N1 was found to be 2.888 Å and calculated to be 2.887 Å, showing to be relatively close.…”