Multi-electron redox reactivity of a samarium(ii) hydrido complex

Area of Science:

• Organometallic Chemistry
• Rare-Earth Chemistry
• Inorganic Chemistry

Background:

• Low-valent molecular rare-earth metal hydrides are scarce, primarily limited to Ytterbium(II) and Europium(II) centers.
• The synthesis and reactivity of such compounds are crucial for understanding f-element chemistry and developing new catalytic systems.

Purpose of the Study:

• To report the first synthesis of a divalent samarium(II) hydride complex.
• To investigate the reactivity of this novel complex with small molecules like CO2 and CS2.
• To explore the mechanistic pathways involved in the observed reactions.

Main Methods:

• Synthesis of a divalent samarium(II) alkyl complex, followed by hydrogenolysis to yield the target hydride.
• Reactions of the samarium(II) hydride complex with carbon dioxide and carbon disulfide.
• Characterization of the resulting samarium(III) complexes using analytical techniques.
• Density Functional Theory (DFT) calculations to elucidate reaction mechanisms.

Main Results:

• The first divalent samarium(II) hydride complex, [(CpAr5)SmII(μ-H)(DABCO)]2, was successfully synthesized using a super-bulky penta-arylcyclopentadienyl ligand.
• The complex exhibited multi-electron redox activity, reacting with CO2 to form a samarium(III) mixed-bis-formate/carbonate complex via hydride insertion and reductive disproportionation.
• Reaction with CS2 resulted in a four-electron reduction, yielding a samarium(III) bis-trithiocarbonate complex.

Conclusions:

• The successful synthesis of the divalent samarium(II) hydride complex broadens the scope of known low-valent rare-earth metal hydrides.
• The observed reactivity highlights the potential of samarium complexes in multi-electron redox processes and small molecule activation.
• Mechanistic insights gained from DFT calculations provide a deeper understanding of the reaction pathways involving samarium hydrides.