CO reductive oligomerization by a divalent thulium complex and CO(2)-induced functionalization

The divalent thulium complex [Tm(Cp(ttt))(2)] (Cp(ttt) = 1,2,4-tris(tert-butyl)cyclopentadienyl) reacts with CO to afford selective CO reductive dimerization and trimerization into ethynediolate (C(2)) and ketenecarboxylate (C(3)) complexes, respectively. DFT calculations were performed to shed light on the elementary steps of CO homologation and support a stepwise chain growth. The attempted decoordination of the ethynediolate fragment by treatment with Me(3)SiI led to dimerization and rearrangement into a 3,4-dihydroxyfuran-2-one complex. Investigation of the reactivity of the C(2) and C(3) complexes towards other electrophiles led to unusual functionalization reactions: while the reaction of the ketenecarboxylate C(3) complex with electrophiles yielded new multicarbon oxygenated complexes, the addition of CO(2) to the ethynediolate C(2) complex resulted in the formation of a very reactive intermediate, allowing C–H activation of aromatic solvents. This original intermolecular reactivity corresponds to an unprecedented functionalization of CO-derived ligands, which is induced by CO(2).