Synthesis and Properties of Hypercoordinate Stannanes and Polystannanes

Candidate: Gloria D'Amaral

Supervisor: Dr. Daniel Foucher

Abstract:
Asymmetric tetraorganotin (IV) compounds containing either a flexible propyl alcohol ligand (10) or a semi-flexible ethyl 2-pyridyl ligand (11) were synthesized in good yields via select hydrostannylation reactions. The triphenyl derivatives were converted in good yields to their dihalide stannane intermediates (6, 7), respectively, by mild sequential chlorination with HCl or by reaction with Br2. The dihalides were converted to reactive dihydride monomers (8, 9) by a reaction with LiAlH4 or NaBH4 in good yields. All stannane intermediates and monomers were fully characterized by NMR (1H, 13C, 119Sn) spectroscopy and high-resolution mass spectrometry. DFT calculations were also performed on the ethyl 2-pyridyl stannane intermediates 2 and 7, which revealed optimized structure geometry and electronic energies. From the three methods that were used, M05-2X-GD3 showed the lowest mean sum of squared distances (MSSD) value and the lowest electronic energies of the hypercoordinate structures. Polymerization of the corresponding dihydrides in the presence of both early and late transition metal catalysts produced moderate molecular weight polymers 10a and 11a. Compound 10a was cast onto a transparent film for the first time and was additionally coated on a PET film. While the cast film on PET showed good flexibility, an initial evaluation of its electronic properties using a 4-probe conductivity device revealed no intrinsic semi-conductivity. Optimization of the polymerization of 10a involved a catalyst screening, using alternative dehydrocoupling catalysts. A yield of 74 % was obtained when a lower (4 to 2 mol %) catalytic loading of RhCl(PPh3)3 was employed (10b). Evidence for a higher molecular weight polymer (based on retention volume) was determined when an early transition metal catalyst, ZrCp2Me2, was used (10d). A new ethyl 2-pyridyl iv containing polystannane 11a was synthesized with a Mw of 11,200 Da using RhCl(PPh3)3, and 119Sn NMR revealed the presence of both 4- and 5-coordinate Sn centers randomly distributed along the backbone. The pyridyl polystannane 11a was also shown to have semi-crystalline and crystalline properties by differential scanning calorimetry (DSC).