Abstract
Well-defined low-valent molecular rare-earth metal hydrides are rare, and limited to Yb(2+) and Eu(2+) centers. Here, we report the first example of the divalent samarium(ii) hydrido complex [(Cp(Ar5))Sm(II)(μ-H)(DABCO)](2) (4) (Cp(Ar5) = C(5)Ar(5), Ar = 3,5-(i)Pr(2)-C(6)H(3); DABCO = 1,4-diazabicyclooctane) supported by a super-bulky penta-arylcyclopentadienyl ligand, resulting from the hydrogenolysis of the samarium(ii) alkyl complex [(Cp(Ar5))Sm(II){CH(SiMe(3))(2)}(DABCO)] (3). Complex 4 exhibits multi-electron redox reactivity toward a variety of substrates. Exposure of complex 4 to CO(2) results in the formation of the trivalent samarium(iii) mixed-bis-formate/carbonate complex [(Cp(Ar5))Sm(III)(μ-η(2):η(1)-O(2)CH)(μ-η(2):η(2)-CO(3))(μ-η(1):η(1)-O(2)CH)Sm(III)(Cp(Ar5))(DABCO)] (8), mediated by hydride insertion and reductive disproportionation reactions. Complex 4 shows four-electron reduction toward four equivalents of CS(2) to afford the trivalent samarium(iii) bis-trithiocarbonate complex [(Cp(Ar5))Sm(III)(μ-η(2):η(2)-CS(3))(DABCO)](2) (9). A mechanistic study of the formation of complex 8 was carried out using DFT calculations.