Novel Heteroleptic Samarium(II) Complexes Bearing both Aryloxide and Pentamethylcyclopentadienide Ligands

Reaction of (C 5 Me 5 ) 2 Sm(THF) 2 with 1 equiv of ArOH (Ar = C 6 H 2 t Bu 2 -2,6-R-4, R = H, Me, t Bu) or Sm(OAr) 2 (THF) 3 in toluene gave almost quantitatively the corresponding heteroleptic unsolvated dimeric Sm(II) complexes [(C 5 Me 5 )Sm(μ-OAr)] 2 (Ar = C 6 H 2 t Bu 2 -2,6-R-4, R = H ( 1a ), Me ( 1b ), t Bu ( 1c )). These heteroleptic complexes are stable in toluene solution and did not undergo ligand redistribution. Addition of 4 equiv of hexamethylphosphoric triamide (HMPA) to a THF solution of 1a − c afforded the corresponding HMPA-coordinated monomeric complexes (C 5 Me 5 )Sm(OAr)(HMPA) 2 ( 2a − c ) in 90−94% isolated yields. Air-oxidation of 1c yielded an orange-red Sm(III) complex, (C 5 Me 5 ) 2 Sm(OAr) ( 3, Ar = C 6 H 2 t Bu 3 -2,4,6), in which an agostic interaction between the central Sm(III) ion and an ortho - t Bu methyl group was observed. Reaction of 1a − c with 2 equiv of C 5 Me 5 K in THF yielded the polymeric Sm(II) complexes [(μ,η 5 -C 5 Me 5 )Sm(OAr)(μ,η 5 -C 5 Me 5 )K(THF) 2 ] ∞ ( 4a − c ), in which the “(C 5 Me 5 )K(THF) 2 ” unit acted as a neutral coordination ligand. Metathesis reaction of (ArO) 2 Sm(THF) 3 with C 5 Me 5 K or (C 5 Me 5 ) 2 Sm(THF) 2 with ArOK also gave 4a − c in excellent yields. In the solid state, the ArO ligand of 4b (Ar = C 6 H 2 t Bu 2 -2,6-Me-4) was severely bent toward the central Sm atom (∠Sm−O−Ar 126.7(5)°) and an agostic interaction between the Sm atom and an ortho - t Bu methyl group of the ArO ligand was observed. Reaction of 4a − c with 2 equiv of HMPA in THF yielded 2a − c in 90−95% isolated yields.