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(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.