Auto-association in organometallic compounds: a nuclear magnetic double resonance study of methyl- and n-butyl-tin alkoxides

Abstract

Tin-119 chemical shifts determined by ¹H–{¹¹⁹Sn} double resonance have been used as a probe to investigate tie auto-associative equilibria of representative simple methyl- and related n-butyl-tin alkoxides, R¹_4–n(OR²)_n(R¹= Me and Buⁿ). It is concluded that the O → Sn co-ordinate bond strengths. ΔH, for the dimerisation of the monomers are ⩽ca. 20, ca. 35. and ca. 50 kJ mol^–1 for n= 1, 2, and 3 respectively and that for the association of the dimers they are < ca. 10 and ⩽ca. 25 kJ mol^–1 for n= 2 and 3 respectively, consistent with the expected changes in the Lewis acidity of the tin atom. The equilibria are strongly dependent on the steric effects of the alkoxide groups. The changes in tin nuclear shielding observed are briefly discussed in terms of current theories.