SYNTHESES AND CHARACTERIZATION OF BINUCLEAR MANGANESE(III,IV) AND MANGANESE(IV,IV) COMPLEXES WITH LIGANDS RELATED TO TRIS(2-PYRIDYLMETHYL)AMINE

The syntheses and spectral, electrochemical, magnetic, and catalytic properties of some new bis(μ-oxo)dimanganese(III, IV) and -(IV, IV) dimers employing a single tetradentate ligand per manganese are reported. The crystal structure of [(Ll)Mn–O2– Mn(Ll)](ClO4)3•(CH3CN), where Ll is (2-(2-pyridyl)ethyl)bis(2-pyridylmethyl)amine, has been established by X-ray diffraction techniques. The complex, of formula [Mn2C38H40N8O2]Cl3O12•CH3CN, crystallizes in the triclinic space group with two independent molecules in a cell of dimensions a = 10.093 (1) Å, b = 12.223 (2) Å, c = 19.625 (2) Å, a = 84.10 (1)°, β = 85.71 (1)°, and γ = 68.468 (9)°. The structure was solved by direct methods and refined by least-squares techniques to a final agreement factor R = 0.0567 based on 6499 independently observed reñections. The complex [(L3)Mn–O2–Mn(L3)](ClO4)4, where L3 is ((6-methyl-2-pyridyl)methyl)(2-(2-pyridyl)ethyI)(2-pyridylmethyl)amine, of formula [Mn2C40H44NgO2](ClO4)4, crystallizes in the monoclinic space group P21/n with two molecules in a cell of dimensions a = 12.927 (9) Å, b = 14.277 (7) Å, c = 13.344 (7) Å, and β = 107.62 (5)°. The structure was solved by direct methods and refined to a final value of R = 0.0867 based on 601 observed independent intensities. The magnetic properties of the III/IV complexes are consistent with a doublet ground state, the observed J values being larger (in magnitude) than those for other reported complexes of this type. The IV/IV complex has a singlet ground state, with 2J = -262 cm−1. The EPR spectra of the III/IV complexes are similar to those observed in related species. The cyclic voltammograms of these and related complexes all show two quasi-reversible waves corresponding to III/IV ↔ III/III at 0.219–0.444 V and III/IV ↔ IV/IV at 1.038–1.277 V relative to Ag/AgCl in acetonitrile solvent. These complexes have been shown to preferentially catalyze the epoxidation of cyclohexene using iodosobenzene as the primary oxidant. © 1990, American Chemical Society. All rights reserved.