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

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.