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.

A series of Mn(II), Fe(II), and Co(II) bisaryloxide dimers ([M(OCH-2,4,6-Cy)] {M = Mn (), Fe (), and Co ()} were synthesized by the addition of 2,4,6-tricyclohexylphenol (HOCH-2,4,6-Cy) to the silyl amido dimers [M(N(SiMe))] (M = Mn, Fe, Co; Cy = cyclohexyl). An unexpected and unique Co(II) phenoxide derivative (), [Co(OCH-2,4,6-Cy)(OCH-3,5,6-Cy)], was obtained via ligand rearrangement of at ca. 180 °C. This yielded in which there are two unchanged, bridging phenoxide ligands as well as a terminal bidentate semiquinone ligand bound to each cobalt. Complexes and 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 -OCH-2,6-Pr (Pr = isopropyl), which is sterically similar to -OCH-2,4,6-Cy but produces fewer close H···H interactions, gave the trimeric species [M(OCH-2,6-Pr)] {M = Fe () or Co ()} which feature a linear array of three metal atoms bridged by aryloxides. The higher association number in and in comparison to that of is due to the lower dispersion energy donor properties of the -OCH-2,6-Pr ligand and the lower stabilization it produces.