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

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.