Organosamarium-Mediated Transformations of CO₂and COS:  Monoinsertion and Disproportionation Reactions and the Reductive Coupling of CO₂to [O₂CCO₂]²⁻

The reactivity of CO 2 and COS with divalent and trivalent organosamarium complexes has been investigated. (C 5 Me 5 ) 2 Sm(THF) 2 reductively couples CO 2 in THF at room temperature to form the oxalate complex, [(C 5 Me 5 ) 2 Sm] 2 (μ-η 2:η 2 -O 2 CCO 2 ), 1, in >90% yield. The metal centers in 1 are formally eight-coordinate. The reaction of COS with (C 5 Me 5 ) 2 Sm(THF) 2 is more complicated and generates a disproportionation product, (C 5 Me 5 ) 2 Sm(μ-η 2:η 1 -S 2 CO)Sm(C 5 Me 5 ) 2 (THF), 2, which has one (C 5 Me 5 ) 2 Sm unit involved in a four-membered ring, while the other (C 5 Me 5 ) 2 Sm unit is bound to THF and the oxygen of the S 2 CO ligand. CO 2 reacts with [(C 5 Me 5 ) 2 Sm] 2 (μ-η 1:η 1 -N 2 Ph 2 ) in >90% yield to form the asymmetrical monoinsertion product, (C 5 Me 5 ) 2 Sm[μ-η 2:η 1 -PhNN(CO 2 )Ph]Sm(C 5 Me 5 ) 2 (THF), 3 . One (C 5 Me 5 ) 2 Sm unit is involved in a five-membered ring, and the other is attached to THF and the other oxygen originating from CO 2 . 1 − 3 were characterized by analytical methods, X-ray diffraction, and NMR and IR spectroscopy.