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 .