The preparation and characterization of structurally stable 5-coordinate polystannanes

Abstract

Tetraorganotin compounds [2-(MeOCH2)C6H4]SnR3 (R = Me, n-Bu, Ph) containing a C,O-chelating ligand were prepared in good yield from the reaction of the R3SnCl and [2-(MeOCH2)C6H4]Li. Tethered organotin compounds Ph3Sn(CH2)3OC6H4R (R = Ph, H, CF3, OCH3) were prepared in good yield from the hydrostannylation reactions of the corresponding vinyl ethers with Ph3SnH. Conversion of two organotin compounds to triorganotin chlorides and diorganotin chlorides, (Ph3-nClnSn(CH2)3OC6H4R; R = H, Ph: n = 1, 2), was successfully carried out and characterisation afforded by NMR spectroscopy. X-ray crystallographic studies revealed a tetrahedral geometry for the tetraorganotin Ph3Sn(CH2)3OC6H4CF3, while five-coordinate trigonal bipyramidal structures with relatively short Sn-O (2.7-2.8 Å) interactions were observed for both mono- (Ph2ClSn(CH2)3OC6H4R; R = H, Ph) and dichloride (PhCl2Sn(CH2)3OC6H4R; R = H, Ph) species. Penta-coordinate diorganotin dichlorides containing a C,N- chelating ligand[2-(Me2NCH2)C6H4]RSnCl2 (R = Me, n-Bu, Ph) or C,O- chelating ligand [2-(MeOCH2)C6H4]RSnCl2 (R = Me, n-Bu, Ph) were prepared by treating RSnCl3 with the lithiated salts [2-(Me2NCH2)C6H4]Li and [2-(MeOCH2)C6H4]Li respectively. Organotin chlorides were successfully reduced with LiAlH4 or NaBH4 to produce novel hydrides. Catalytic dehydrocoupling of diorganotin dihydrides to yield polystannanes was explored using a variety of dehydrocoupling catalysts such as Wilkinson’s catalyst, Cp2ZrMe2 or TMEDA. In almost every instance this resulted in the formation of yellow coloured gummy polymeric materials of moderate molecular weights (Mw = 1 × 104 - 1 × 105 Da) and PDI’s (1.3-2.0). The stability of polystannanes containing tethered O or C,N- or C,O-chelating ligands was investigated in both solid and in solution using NMR and UV-Vis spectroscopies. These studies revealed an enhanced stability to ambient light in the solid state and in solution in the dark when compared to known poly(dialkyl)stannanes.