Lewis acidity of carboxyethyltin chlorides, Cl3SnCH2CH2CO2R and Cl2Sn(CH2CH2CO2R)2

Abstract The Lewis acidity of estertin chlorides, Cl 3 SnCH 2 CH 2 CO 2 R (R = Me, Pr i , Ph and H) and Cl 2 Sn(CH 2 CH 2 CO 2 R) 2 (R = Me and Pr i ) has been investigated. Stability constants ( K 1 , K 2 and K 3 ) for adducts of these Lewis acids with nitrogen donors, e.g. D = bipy, phen, py, quinoline and aniline, have been determined in CH 2 Cl 2 solution at 25 ± 1°C by UV and IR methods. From comparisons of stability constants, the following conclusions can be made: (i) Cl 3 SnCH 2 CH 2 CO 2 Me appears as strong a Lewis acid as MeSnCl 3 towards bidentate ligands and a single py molecule (from K 1 values); (ii) Cl 3 SnCH 2 CH 2 CO 2 Me · D (D = monodentate ligand) is a poorer acceptor than MeSnCl 3 · D but comparable to Me 2 SnCl 2 (using K 2 and K 3 values) towards D, and (iii) Cl 2 Sn(CH 2 CH 2 CO 2 R) 2 is a weaker acceptor than Cl 2 SnMe 2 towards phen and bipy (from K 3 values). Qualitatively it was established that for Cl 3 SnCH 2 CH 2 CO 2 R, the sequence of acidity is R = Ph > Me > Pr i > H towards bipy. Adducts of Cl 3 SnCH 2 CH 2 CO 2 Me and Cl 2 Sn(CH 2 CH 2 CO 2 Me) 2 with phen and bipy have similar Mosbauer parameters to those for other phen and bipy adducts of organotin trichloride and diorganotin dichloride.