Despite the established high reducing character of Tm(II) complexes, no reaction of 1 was observed with either N2 or H2 and no traces of decomposition could be noticed upon heating a C6D6 solution of the complex at 80 °C for several days. This unusual stability contrasts with the reported reactivity of base-free samarocene [SmCp*2] (Cp* = h 5 -C5Me5) with N2. The bulky nature of the Cp ttt ligand is vital to kinetically stabilize the Tm(II) complex and avoid thermal decomposition, as observed when using the smaller Cp* or disubstituted 1,2-R2C5H3 (R = t Bu, SiMe3) ligands. Despite the steric protection imposed by the Cp ttt ligands, coordination of a Lewis base to the metal center has been achieved in related [Ln(Cp ttt )2] complexes (Ln = Yb and Sm). We therefore reasoned than the high reducing character of the Tm(II) center in 1 in addition to the oxophilic nature of f-elements 28 may lead to interesting reactivity towards the gaseous oxocarbons CO and CO2.