Mn(II), Fe(II), and Co(II) Aryloxides: Steric and Dispersion Effects and the Thermal Rearrangement of a Cobalt Aryloxide to a Co(II) Semiquinone Complex

[Image: see text] A series of Mn(II), Fe(II), and Co(II) bisaryloxide dimers ([M(OC(6)H(2)-2,4,6-Cy(3))(2)](2) {M = Mn (1), Fe (2), and Co (3)} were synthesized by the addition of 2,4,6-tricyclohexylphenol (HOC(6)H(2)-2,4,6-Cy(3)) to the silyl amido dimers [M(N(SiMe(3))(2))(2)](2) (M = Mn, Fe, Co; Cy = cyclohexyl). An unexpected and unique Co(II) phenoxide derivative (4), [Co(OC(6)H(2)-2,4,6-Cy(3))(O(2)C(6)H-3,5,6-Cy(3))](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 −OC(6)H(3)-2,6-Pr(i)(2) (Pr(i) = isopropyl), which is sterically similar to −OC(6)H(2)-2,4,6-Cy(3) but produces fewer close H···H interactions, gave the trimeric species [M(OC(6)H(3)-2,6-Pr(i)(2))(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 −OC(6)H(3)-2,6-Pr(i)(2) ligand and the lower stabilization it produces.