SOLID-STATE AND SOLUTION STRUCTURAL INVESTIGATION OF HOMOLEPTIC TIN(IV) ALKOXIDE COMPOUNDS .1. SN(O-TERT-BU)4 AND [SN(O-ISO-PR)4.HO-ISO-PR]2

The crystal and molecular structures of Sn(O-t-Bu)4 and [Sn(O-i-Pr)4.HO-i-Pr]2 have been determined by single-crystal X-ray diffraction. Sn(O-t-Bu)4 crystallizes in the monoclinic crystal system with space group C2/c, where a = 17.382(6) angstrom, b = 8.742(2) angstrom, c = 15.518(5) angstrom, beta = 116.44(1)-degrees, Z = 4, and R = 2.5%. Sn(O-t-Bu)4 is monomeric in the solid state, with a distorted tetrahedral tin coordination environment. [Sn(O-i-Pr)4.HO-i-Pr]2 crystallizes in the monoclinic crystal system with space group P2(1)/n, where a = 11.808(3) angstrom, b = 14.356(3) angstrom, c = 12.380(2) angstrom, beta = 95.27(2)-degrees, Z = 2, and R = 4.9%. [Sn(O-i-Pr)4.HO-i-Pr]2 exhibits an edge-shared, bi-octahedral structure in the solid state that is distorted due to the presence of asymmetric hydrogen bonding between axially coordinated alcohol ligands and an isopropoxide ligand. C-13 NMR and IR spectroscopic data have been recorded for Sn(O-t-Bu)4 and Sn(O-t-Bu-d9)4 to establish criteria for unambiguous identification of solution structures of tin (IV) alkoxides. It is demonstrated that the two-bond 2J-C-13-O-Sn-119 coupling constant is larger for terminal alkoxide ligands than for mu-2-alkoxide bridges, and the nu(Sn-O) stretching frequency has been assigned. The dynamic solution behaviour of [Sn(O-i-Pr)4.HO-i-Pr]2 has been studied using variable temperature H-1 and C-13 NMR spectroscopy. The data obtained are consistent with a process that involves rapid reversible dissociation of isopropanol at room temperature. Upon cooling, the equilibrium concentration of the species with coordinated alcohol increases, and the molecule undergoes rapid intramolecular proton transfer (DELTA-G not-equal < 11.9 kcal mol-1). Upon further cooling, the C-13 NMR data are consistent wit a solution structure analogous to that found in the solid state.