Enhancement of Stannylene Character in Stannole Dianion Equivalents Evidenced by NMR and Mössbauer Spectroscopy and Theoretical Studies of Newly Synthesized Silyl-Substituted Dilithiostannoles

Abstract

Dilithiostannoles, which are aromatic tin-containing ring compounds, were proposed to have stannylene character, as judged from their NMR analysis. We herein report on the synthesis of silyl-substituted dilithiostannoles, which were characterized by NMR spectroscopy and X-ray diffraction analysis. The silyl-substituted derivatives also exhibit features characteristic of aromatic dilithiostannoles such as 7Li NMR signals at high-field area and no C–C bond alternation in the stannole rings. Theoretical calculations and the 119Sn NMR chemical shifts revealed that the stannylene character in the silyl-substituted dilithiostannoles is enhanced due to greater interaction between 5p (Sn) and LUMO (butadiene) in comparison to those in alkyl and aryl derivatives. The 119Sn Mössbauer spectra of dilithiostannoles were measured for the first time, indicating that each of the tin atoms in dilithiostannoles can be characterized as having Sn(II) character.