Reversible Uptake of CO 2 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(CO 2 )E unit, with the mode of ligation of the CO 2 fragment determined crystallographically being found to be dependent on the identity of the Group 14 element. The thermodynamics of CO 2 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 CO 2 in the Ge case), and the chemical consequences of reversibility demonstrated by thermodynamically-controlled exchange reactions.