Deconvoluting Steric and Electronic Substituent Effects on the Properties of Linear Oligostannanes: Synthesis and Characterization of a New Series Incorporating the Bu t 2 Sn Group

The synthesis and full characterization, including detailed 119 Sn NMR analysis, of the new series of oligostannanes X−Bu n 2 Sn−[Bu n 2 Sn] m −Bu t 2 Sn−[Bu n 2 Sn] n −SnBu n 2 CH 2 CH 2 OEt ( 1a, X = 2-ethoxyethyl, m = n = 0; 2a, X = Bu n, m = 0, n = 1; 3a, X = 2-ethoxyethyl, m = n = 1; 4a, X = Bu n, m = 1, n = 2; 5a, X = 2-ethoxyethyl, m = n = 2; 6a, X = 2-ethoxyethyl, m = n = 3) that incorporate a single Bu t 2 Sn group are reported. Comparison of this new spectroscopic database, in particular, electronic spectra and 119 Sn NMR parameters, with those obtained for known analogous per- n -butylated derivatives, including the three compounds EtOCH 2 CH 2 Bu n 2 Sn−[Bu n 2 Sn] n −SnBu n 2 CH 2 CH 2 OEt ( 1c ( n = 1), 2c ( n = 2), and 3c ( n = 3)), which are prepared for the first time in pure form, suggest that 1a − 6a are free of structural distortions caused by steric interactions between substituents on adjacent tin atoms. Accordingly, dramatic perturbations that are observed in the 1 J ( 119 Sn− 119 Sn) values for Sn−Sn bonds that incorporate the Bu t 2 Sn group in these compounds, relative to the per- n -butyl derivatives, are proposed to arise from an electronic effect of the tert -butyl substituent.