The formation of ethynediolate fragments upon reductive coupling of CO has been reported for a handful of low-valent f-block complexes, mostly based on U(III) metal centers, 16e,17f-j,17l and recently by Evans and co-workers upon treatment of in situ generated Ln(II) species or with The sensitivity of the corresponding ethynediolate products to thermolysis was found to be ligand dependent. 17g-i In the case of 2, no traces of decomposition could be detected upon heating a toluene solution of the complex at 100 °C for several days.