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Stable Divalent Triarylstannates R3SnLi Derived from 2‑[(Dimethylamino)methyl]phenyllithium and SnCl2 or R2Sn

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posted on 08.06.2015, 00:00 authored by Johann T. B. H. Jastrzebski, Mayra van Klaveren, Gerard van Koten
The triarylstannate lithium compound [{κ1-C-(2-Me2NCH2C6H4)2}­{κ2-C, N-(2-Me2NCH2C6H4)}­SnLi­(THF)2] (3a) was obtained in 63% yield from the reaction of 2-Me2NCH2C6H4Li (1) with SnCl2 in THF. Quantitative formation of 3a was also observed on reacting 1 with [κ2-C, N-(2-Me2NCH2C6H4)2Sn] (2). Removal of one THF molecule occurred when 3a was kept in vacuo; this process afforded [{κ1-C-(2-Me2NCH2C6H4)}­{κ2-C, N-(2-Me2NCH2C6H4)2}­SnLi­(THF)2] (3b). Also, THF-free (2-Me2NCH2C6H4)3SnLi (3c) is likewise accessible. In the solid state (X-ray) both 3a and 3b are monomeric; notable structural features are the Sn–Li distances (2.860(6) and 2.72(2) Å, respectively) and the distortion of the tetrahedral geometry at Sn in the direction of a trigonal pyramidal one. In 3a, one of the 2-Me2NCH2C6H4 anions is C-bonded to Sn, while N-coordination occurs to Li; in 3b, two of the three 2-Me2NCH2C6H4 anions are κ2-C,N bonded. 1H, 13C, 119Sn, and 7Li NMR spectroscopic studies of the species 3 in toluene showed that both 3a and 3b are monomeric in solution; at temperatures below 253 K, via both the 119Sn and 7Li NMR spectra (toluene-d8), the 119Sn–7Li coupling (289 Hz) is nicely resolved. The exchange of aryl groupings (vide infra) as well as between coordinated and free-NMe2 substituents remains fast on the NMR time scale at 183 K. 2D 1H–1H EXSY spectroscopy confirmed that the 2-Me2NCH2C6H4 groups present in stannate 3b and bisaryltin­(II) 2 undergo chemical exchange. The 2D 7Li–7Li EXSY spectrum points to the occurrence of chemical exchange of the lithium atoms of stannate 3b and aryllithium 1.