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 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.