Abstract
The stoichiometry of the adducts formed by tributylphosphine (TBP) and tributylphosphine oxide (TBPO) with organotin halides in benzene was determined by 31P NMR spectroscopy and by calorimetry. Except for two cases, all adducts were found to have 1/1 stoichiometry. For the MeSnCl 3/TBP and the Me 2SnCl 2/TBPO systems there was evidence for a small amount of 1/2 adduct. Both techniques indicate no adduct formation between triorganotin halides and TBP, whereas the equilibrium constants for the 1/1 adducts of TBPO with triorganotin halides range from 150 to 300. With the diorgano- and monoorgano-tin halides, however, the equilibrium constants for 1/1 adduct formation with TBP are the same as or greater than those for TBPO. Enthalpy changes determined by calorimetry show the same reversal of basicity, which can be attributed to steric repulsions in the weakly acidic triorgano derivatives with TBP. These repulsions are overwehlmed by the greater intrinsic tin-phosphorus dative bond strength in the di- and mono-organotin halide adducts.
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