Fong Sheen Kuan

Synthesis and structures of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the α,ω-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me3SiCH2)Cl2Sn(CH2)nSnCl2(CH2SiMe3) (13, n = 5; 14, n = 6; 15, n = 7; 16, n = 8; 17, n = 10; 18, n = 12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me3SiCH2)(O)Sn(CH2)nSn(O)(CH2SiMe3)]m (19, n = 5; 20, n = 6; 21, n = 7; 22, n = 8; 23, n = 10; 24; n = 12) is reported. The reaction of the diorganodichlorostannanes 13–18 with the corresponding diorganotin oxides 19–24 provided the spacer-bridged tetraorganodistannoxanes {[(Me3SiCH2)ClSn(CH2)nSnCl(CH2SiMe3)]O}4 (25, n = 5; 26, n = 6; 27, n = 7; 28, n = 8; 29, n = 10; 30, n = 12). Compounds 13–30 have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds 25, 27, 29 and 30 have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all n in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7 A (for 25, n = 5) to approx. 15 A (for 30, n = 12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length n.

A novel route for the preparation of dimeric tetraorganodistannoxanes

The reaction of polymeric diorganotin oxides, (R2SnO)n (R=Me, Et, n-Bu, n-Oct, c-Hex, i-Pr, Ph), with saturated aqueous NH4X (X=F, Cl, Br, I, OAc) in refluxing 1,4-dioxane afforded in high yields dimeric tetraorganodistannoxanes, [R2(X)SnOSn(X)R2]2, and in a few cases diorganotin dihalides or diacetates, R2SnX2. The reported method appears suitable for the synthesis of fluorinated tetraorganodistannoxanes. Identification of [R2(OH)SnOSn(X)R2]2 (R=n-Bu; X=Cl, Br) and [R2(OH)SnOSn(X)R2] [R2(X)SnOSn(X)R2] suggest a serial substitution mechanism starting from [R2(OH)SnOSn(OH)R2]2. X-ray crystal structure determinations are reported for [Me2(AcO)SnOSn(OAc)Me2]2 (29a), [i-Pr2(Br)SnOSn(Br)i-Pr2]2 (20a), [c-Hex2(F)SnOSn(F)c-Hex2]2 (5a) and [c-Hex2(F)SnOSn(Cl)c-Hex2]2 (36), respectively. These show the presence of a central (R2Sn)2O2 core that is connected, via the oxygen atoms, to R2Sn entities. Acetate (29a) or halides (5a, 20a, 36) complete the coordination about the tin centres.