UC Davis

A series of Mn(II), Fe(II), and Co(II) bisaryloxide dimers ([M(OC₆H₂-2,4,6-Cy₃)₂]₂ {M = Mn (1), Fe (2), and Co (3)} were synthesized by the addition of 2,4,6-tricyclohexylphenol (HOC₆H₂-2,4,6-Cy₃) to the silyl amido dimers [M(N(SiMe₃)₂)₂]₂ (M = Mn, Fe, Co; Cy = cyclohexyl). An unexpected and unique Co(II) phenoxide derivative (4), [Co(OC₆H₂-2,4,6-Cy₃)(O₂C₆H-3,5,6-Cy₃)]₂, was obtained via ligand rearrangement of 3 at ca. 180 °C. This yielded 4 in which there are two unchanged, bridging phenoxide ligands as well as a terminal bidentate semiquinone ligand bound to each cobalt. Complexes 1 and 2 did not undergo such a rearrangement under the same conditions; both are thermally stable to temperatures exceeding 250 °C and feature numerous short-contact (<2.5 Å) H···H interactions consistent with the presence of dispersion stabilization. Use of the aryloxide ligand -OC₆H₃-2,6-Prⁱ₂ (Prⁱ = isopropyl), which is sterically similar to -OC₆H₂-2,4,6-Cy₃ but produces fewer close H···H interactions, gave the trimeric species [M(OC₆H₃-2,6-Prⁱ₂)₂]₃ {M = Fe (5) or Co (6)} which feature a linear array of three metal atoms bridged by aryloxides. The higher association number in 5 and 6 in comparison to that of 1-3 is due to the lower dispersion energy donor properties of the -OC₆H₃-2,6-Prⁱ₂ ligand and the lower stabilization it produces.