In conclusion, the divalent thulium complex [Tm(Cp ttt )2] exhibits a rich reactivity towards CO and CO2 allowing the selective formation of carbonate (C1), ethynediolate (C2) and ketenecarboxylate (C3) complexes. The reactivity of the CO dimerization product 2 with external CO at room temperature is remarkable and proves the intermediacy of 2 in the formation of the ketenecarboxylate complex 3, which was also supported by DFT calculations. The reactivity of 2 and 3 was systematically investigated towards electrophiles leading to the following observations: (a) while 3 features an expected nucleophilic reactivity towards CO2, the addition of methyl iodide yields a C7 allene-tricarboxylate complex in which the C6O6 core is exclusively built from CO molecules; (b) the ethynediolate complex 2 shows unexpected reactivity towards CO2 and silylating agents. In the case of CO2, a highly reactive species is formed, which is able to induce an intermolecular C-H activation on the solvent. This novel reactivity opens new ways for the formation of multicarbon oxygenates by small molecule activation and the functionalization of CO and CO2