Deconvoluting Steric and Electronic Substituent Effects on the Properties of Linear Oligostannanes: Synthesis and Characterization of a New Series Incorporating the Bu^t₂Sn Group

Abstract

The synthesis and full characterization, including detailed 119Sn NMR analysis, of the new series of oligostannanes X−Bun2Sn−[Bun2Sn]m−But2Sn−[Bun2Sn]n−SnBun2CH2CH2OEt (1a, X = 2-ethoxyethyl, m = n = 0; 2a, X = Bun, m = 0, n = 1; 3a, X = 2-ethoxyethyl, m = n = 1; 4a, X = Bun, m = 1, n = 2; 5a, X = 2-ethoxyethyl, m = n = 2; 6a, X = 2-ethoxyethyl, m = n = 3) that incorporate a single But2Sn group are reported. Comparison of this new spectroscopic database, in particular, electronic spectra and 119Sn NMR parameters, with those obtained for known analogous per-n-butylated derivatives, including the three compounds EtOCH2CH2Bun2Sn−[Bun2Sn]n−SnBun2CH2CH2OEt (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 1J(119Sn−119Sn) values for Sn−Sn bonds that incorporate the But2Sn group in these compounds, relative to the per-n-butyl derivatives, are proposed to arise from an electronic effect of the tert-butyl substituent.