Ligand Assisted CO2 Activation and Catalytic Valorization by an NHI-Stabilized Stannylene

Abstract

The aryl(imino)stannylene MesTer[N(IDipp)]Sn could be obtained by treating NHILi (NHI=N(IDipp), IDipp=C[N-(2,6-iPr2C6H3)CH]2) with MesTerSnCl (MesTer=2,6-Mes2C6H3) and offers a unique reactivity pattern compared to conventional single site tetrylene catalyzed CO2 reduction reactions. The Sn(II) center, stabilized by the NHI ligand enabled the sequestration and valorization of CO2 to C1 feedstock stoichiometrically, as well as catalytically, utilizing HBpin (pin=pinacolato) as reductant. The experimental comparison with aryl(amido)stannylene MesTer(NPh2)Sn and aryl(phosphinidene)stannylene MesTer[P(IDipp)]Sn, as well as computational analysis, rationalize the electronic features and key role of the NHI ligand in the CO2 reduction process. In case of the phosphorus congener, Sn−P bonding with pronounced double-bond character is obtained, which prevents swift dissociation, thus preventing CO2 uptake. Instead, hard/soft mismatch between tin and the NHI induces zwitterionic and single-bond character, switching on the intermediate dissociation of Sn(II)/NHI, followed by a tin hydride mediated reduction step, and thus allows for efficient catalysis under mild conditions.