13C−119Sn Correlation NMR in Solution and Solid-State CP/MAS NMR of Bis(tributylstannyl(IV)) O-5,6-Isopropylidene-l-(+)-ascorbate

Abstract

Various NMR correlation techniques, 1H−13C HMQC, 1H−13C HMBC, 1H−119Sn HMQC with gradient enhancement, and 13C−119Sn HMQC, enabled a full resonance assignment and the solution structure elucidation of bis(tributylstannyl(IV)) l-(+)-ascorbate (1) and O-5,6-isopropylidene-l-(+)-ascorbate (2) in deuteriochloroform. Double heteronuclear 13C−119Sn HMQC spectroscopy appeared indispensable for discriminating between 2J(13C−O−119Sn) and 3J(13CC−O−119Sn) coupling pathways involving quaternary carbon atoms and provided useful information about the relative magnitudes of 2J(13C−119Sn) and 3J(13C−119Sn) coupling constants, as they turned out to have an uncommon coupling size sequence. While the tin atoms in compounds 1 and 2 are four-coordinate in solution, 117Sn CP/MAS NMR reveals that compound 2 has one four-coordinate and one five-coordinate tin atom in the solid state.