NUCLEAR-MAGNETIC-RESONANCE STUDIES AND STRUCTURAL INVESTIGATIONS OF THE CHEMISTRY OF ORGANOTIN COMPOUNDS .1. SN-119 NMR-STUDIES OF THE PYRAZINE ADDUCTS OF SOME ORGANOTIN COMPOUNDS

A procedure is described for the analysis of the concentration dependence of NMR chemical shift data on the chemical equilibria present in solution. This procedure has been used to study the equilibrium between SnMe3Cl and 4-methylpyridine in benzene, and the values obtained for the thermodynamic parameters are in good agreement with those previously determined by a calorimetric method. The equilibria of the adduct formation reactions of SnPh2Cl2, SnPh2Br2 and SnPh2I2 with pyrazine in chloroform and acetonitrile have also been investigated. In chloroform solution, both 1:1 and 1:2 (M:L) adducts are formed, whereas only 1:1 adducts are formed in acetonitrile under the experimental conditions used. For all three organotin compounds the interactions are relatively weak. The Lewis acidity of the SnPh2X2 organotin species decreases in the order Cl > Br > I. © 1990.