Deca-Arylsamarocene: An Unusually Inert Sm(II) Sandwich Complex

Samarocene sandwich complexes with superbulky penta-arylcyclopentadienyl ligands have been prepared and were structurally characterized: [(4-EtC6H4)(5)C-5](2)Sm (1) and [(4-iPrC(6)H(4))(5)C-5](2)Sm (2). Analogous to the previously reported synthesis of [(4-nBuC(6)H(4))(5)C-5](2)Sm, reaction of (DMAT)(2)center dot Sm(THF)(2) (DMAT = 2-Me2N-alpha-Me3Si-benzyl) and the appropriate Ar5C5H ligand gave 1 (66% yield) and 2 (59% yield). In contrast to the high reactivity of Cp*Sm-2, complex 1 has been shown to be surprisingly stable toward reaction with a large variety of reagents. Even under forcing conditions, no reaction with N-2, CO, CO2, pyrazine, trans-stilbene, pyridine, P-4, and benzophenone was observed. Complex 1 reacts with cuminil ArC(O)C(O)Ar (Ar = 4-iPrC(6)H(4)) to yield the Sm(III) sandwich complex [(4-EtC6H4)(5)C-5](2)Sm[ArC(O)C(O)Ar] (3), which could be isolated in 83% yield as a dark-red crystalline material. Complex 2 reacts with oxygen in the presence of phenazine to yield the bimetallic Sm(III) complex [(4-iPrC(6)H(4))(5)C5Sm(eta(1)-phenazine)]2(mu:eta(2)-eta(2)-O-2)(2) (4) in 25% yield as dark-red crystals. The unusually high redox-stability of deca-arylsamarocenes originates from steric hindrance of the Sm metal center.