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

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journal contribution
posted on 24.06.1997, 00:00 by Zhaomin Hou, Yugen Zhang, Takashi Yoshimura, Yasuo Wakatsuki
Reaction of (C5Me5)2Sm(THF)2 with 1 equiv of ArOH (Ar = C6H2tBu2-2,6-R-4, R = H, Me, tBu) or Sm(OAr)2(THF)3 in toluene gave almost quantitatively the corresponding heteroleptic unsolvated dimeric Sm(II) complexes [(C5Me5)Sm(μ-OAr)]2 (Ar = C6H2tBu2-2,6-R-4, R = H (1a), Me (1b), tBu (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 1ac afforded the corresponding HMPA-coordinated monomeric complexes (C5Me5)Sm(OAr)(HMPA)2 (2ac) in 90−94% isolated yields. Air-oxidation of 1c yielded an orange-red Sm(III) complex, (C5Me5)2Sm(OAr) (3, Ar = C6H2tBu3-2,4,6), in which an agostic interaction between the central Sm(III) ion and an ortho-tBu methyl group was observed. Reaction of 1ac with 2 equiv of C5Me5K in THF yielded the polymeric Sm(II) complexes [(μ,η5-C5Me5)Sm(OAr)(μ,η5-C5Me5)K(THF)2] (4ac), in which the “(C5Me5)K(THF)2” unit acted as a neutral coordination ligand. Metathesis reaction of (ArO)2Sm(THF)3 with C5Me5K or (C5Me5)2Sm(THF)2 with ArOK also gave 4ac in excellent yields. In the solid state, the ArO ligand of 4b (Ar = C6H2tBu2-2,6-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-tBu methyl group of the ArO ligand was observed. Reaction of 4ac with 2 equiv of HMPA in THF yielded 2ac in 90−95% isolated yields.