Alumanyl-Samarium(II): Synthesis, Characterization, and Reactivity Studies

Metal–metal bonded species involving lanthanides are intriguing but rare. The recently reported salt metathesis reaction of an Al anion and SmI2(thf)2 yields novel heterometallic compound possessing two distinctive Al–Sm bonds. Although the Al–Sm bonds were considerably long [3.518(1) and 3.543(1) Å], DFT calculations indicated polar character of the Alδ−–Smδ+ bonds. This is the first example of lanthanide species containing X-type Al ligands. Reactivity studies have demonstrated that the introduction of Sm(II) produces unique reactivity. The reaction with carbodiimide led to an insertion of carbodiimide into the Al–Sm bonds and reductive coupling of carbodiimide to create an oxalamidinate moiety, facilitated by Sm(II). Exposure of the Al–Sm–Al complex toward ethylene furnished a Sm(II) salt of anionic aluminacyclopropane that was spontaneously isomerized to a 1,4-dialuminacyclohexane derivative. The important role of Sm(II) to facilitate the ring expansion through an alkyl-relay mechanism was elucidated by DFT calculations.