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

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.