Reversible Uptake of CO₂ by Pincer Ligand Supported Dimetallynes

We report on the reversible uptake of carbon dioxide by dimetallynes featuring ancillary hemi-labile pincer ligands. Insertion into the Ge-Ge/Sn-Sn bonds yields species containing an E(CO₂ )E unit, with the mode of ligation of the CO₂ fragment determined crystallographically being found to be dependent on the identity of the Group 14 element. The thermodynamics of CO₂ uptake/loss can be established through VT NMR (ΔH°=+24.6(2.3) kJ mol^-1 , ΔS°=+64.9(3.8) J mol^-1  K^-1 , ΔG°₂₉₈ =+5.3(1.9) kJ mol^-1 for the loss of CO₂ in the Ge case), and the chemical consequences of reversibility demonstrated by thermodynamically-controlled exchange reactions.