The stoichiometry of organotin trihalides in solution

Abstract

The formation of Lewis acid-base adducts of the organotin trihalides, CH 3SnCl 3, C 4H 9SnCl 3, and C 6H 5SnCl 3, with acetonitrile, DMA, triphenylphosphine oxide (TPPO), and triethylphosphine oxide (TEPO) were studied by calorimetry and NMR spectroscopy. Schematic mapping of the calorimetry results for the TPPO adducts in benzene showed that the data are best fit by the assumption of simultaneous formation of 1 1 and 1 2 adducts. For the C 6H 5SnCl 3-TPPO system K 1 = 4.3 X 10 4, K 2 = 55, Δ H 1 = −13.3 kcal/mol, and Δ H 2 = −10.8 kcal/mol. These equilibrium constants correspond to 93% 1 1 adduct and 1 2 adduct at equilibrium after the acid and base are mixed in equimolar (0.1 M) concentrations. Thus, for this system and all others studied the 1 1 adduct predominates. Equilibrium constants for the formation of the 1 1 adducts were determined by 119Sn or 31P NMR spectroscopy from the shifts obtained in a series of equimolar mixtures of acid and base. These constants vary from approximately 1 for the acetonitile adducts to greater than 10 5 for TEPO and reveal the expected basicity order TEPO > TPPO > DMA > acetonitile.