THE STRUCTURE OF 2,2-DIBUTYL-1,3,2-DIOXASTANNANE IN THE SOLID-STATE AND IN SOLUTION

Crystals of 2.2-dibutyl-1,3,2-dioxastannane (1) are orthorhombic, of space group Pnma, with a = 7.663(3), b 18.437(2), c = 9.277(4) angstrom, Z = 4, R = 0.0568 (R(w) = 0.0551) for 1183 independent reflections with I > 3-sigma(I). Compound 1 is a polymer in which each monomer unit is joined to the next by a four-membered (SnO)2 ring. The Sn-O bond lengths inside the monomer units average 2.04 angstrom while those between monomers average 2.57 angstrom. The mirror plane of the crystal contains the atoms in the four-membered rings and the other oxygen atoms. Two of the three remaining carbon atoms in the six-membered rings of the monomer units are close to the mirror plane. The other carbon atom is disordered above and below the plane. It was shown by Sn-119 NMR spectroscopy that solutions of 1 contain mixtures of oligomers that consist mainly of dimers, trimers, and tetramers in chloroform-d. DELTA-G0 values for dimer-trimer equilibria and dimer-tetramer equilibria of -2.5 and -1.5 kcal mol-1 were obtained from integration of low temperature Sn-119 NMR spectra. These values favour the higher oligomers slightly less than those for 2,2-dibutyl-1,3,2-dioxastannolane.