The reactivity of the Tm(II) complex 1 was also investigated towards CO2 as divalent lanthanide complexes have been reported to yield oxalate and/or carbonate complexes upon reduction of CO2. The reaction of 1 with excess CO2 led to the formation of the carbonate complex 4 (Scheme 2) isolated in 72% yield. Its IR spectrum features a strong absorption band at 1430 cm -1 , assigned to C-O stretching in the coordinated carbonate ligand. The 1 H NMR spectra of 4 at variable temperatures (Figure ) show multiple broad, overlapping and paramagnetically shifted resonances as a sign of restricted free rotation of the Cp ttt ligands. 22b Scheme 2. Reaction of 1 with CO2 leading to the formation of the carbonate complex 4.