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

Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb and Eu centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(Cp)Sm(μ-H)(DABCO)] (4) (Cp = CAr, Ar = 3,5-Pr-CH; DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(Cp)Sm{CH(SiMe)}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates. Exposure of complex 4 to CO results in the formation of the trivalent samarium(iii) mixed-bis-formate/carbonate complex [(Cp)Sm(μ-η:η-OCH)(μ-η:η-CO)(μ-η:η-OCH)Sm(Cp)(DABCO)] (8), mediated by hydride insertion and reductive disproportionation reactions. Complex 4 shows four-electron reduction toward four equivalents of CS to afford the trivalent samarium(iii) bis-trithiocarbonate complex [(Cp)Sm(μ-η:η-CS)(DABCO)] (9). A mechanistic study of the formation of complex 8 was carried out using DFT calculations.