Isolation of (CO)1– and (CO2)1– Radical Complexes of Rare Earths via Ln(NR2)3/K Reduction and [K2(18-crown-6)2]2+ Oligomerization

Deep-blue solutions of Y2+ formed from Y­(NR2)3 (R = SiMe3) and excess potassium in the presence of 18-crown-6 at −45 °C under vacuum in diethyl ether react with CO at −78 °C to form colorless crystals of the (CO)1– radical complex, {[(R2N)3Y­(μ-CO)2]­[K2(18-crown-6)2]}n, 1. The polymeric structure contains trigonal bipyramidal [(R2N)3Y­(μ-CO)2]2– units with axial (CO)1– ligands linked by [K2(18-crown-6)2]2+ dications. Byproducts such as the ynediolate, [(R2N)3Y]2(μ-OCCO)­{[K­(18-crown-6)]2(18-crown-6)}, 2, in which two (CO)1– anions are coupled to form (OCCO)2–, and the insertion/rearrangement product, {(R2N)2Y­[OC­(CH2)­Si­(Me2)­NSiMe3]}­[K­(18-crown-6)], 3, are common in these reactions that give variable results depending on the specific reaction conditions. The CO reduction in the presence of THF forms a solvated variant of 2, the ynediolate [(R2N)3Y]2(μ-OCCO)­[K­(18-crown-6)­(THF)2]2, 2a. CO2 reacts analogously with Y2+ to form the (CO2)1– radical complex, {[(R2N)3Y­(μ-CO2)2]­[K2(18-crown-6)2]}n, 4, that has a structure similar to that of 1. Analogous (CO)1– and (OCCO)2– complexes of lutetium were isolated using Lu­(NR2)3/K/18-crown-6: {[(R2N)3Lu­(μ-CO)2]­[K2(18-crown-6)2]}n, 5, [(R2N)3Lu]2(μ-OCCO)­{[K­(18-crown-6)]2(18-crown-6)}, 6, and [(R2N)3Lu]2(μ-OCCO)­[K­(18-crown-6)­(Et2O)2]2, 6a.