DECONVOLUTING STERIC AND ELECTRONIC SUBSTITUENT EFFECTS ON THE PROPERTIES OF LINEAR OLIGOSTANNANES - SYNTHESIS AND CHARACTERIZATION OF A NEW SERIES INCORPORATING THE (BU2SN)-SN-T GROUP

The synthesis and full characterization, including detailed Sn-119 NMR analysis, of the new series of oligostannanes Bu2Sn)-Sn-t-[(Bu2Sn)-Sn -n](n)-(SnBu2CH2CH2OEt)-C-n (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 (Bu2Sn)-Sn-t group are reported. Comparison of this new spectroscopic database, in particular, electron ic spectra and Sn-119 NMR parameters, with those obtained for known an alogous per-n-butylated derivatives, including the three compounds Bu2 Sn)-Sn-n-[(Bu2Sn)-Sn-n](n)-(SnBu2CH2CH2OEt)-C-n (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 ster ic interactions between substituents on adjacent tin atoms. Accordingl y, dramatic perturbations that are observed in the (1)J(Sn-119-Sn-119) values for Sn-Sn bonds that incorporate the (Bu2Sn)-Sn-t group in the se compounds, relative to the per-n-butyl derivatives, are proposed to arise from an electronic effect of the tert-butyl substituent.