Measuring Metal-Metal Communication in a Series of Ketimide-Bridged [Fe 2 ] 6+ Complexes.

Reaction of Fe(acac) 3 with 3 equiv of Li[N═C(R)Ph] (R = Ph, t Bu) results in the formation of the [Fe 2 ] 6+ complexes, [Fe 2 (μ-N═C(R)Ph) 2 (N═C(R)Ph) 4 ] (R = Ph, 1 ; t Bu, 2 ), in low to moderate yields. Reaction of FeCl 2 with 6 equiv of Li(N═C 13 H 8 ) (HN═C 13 H 8 = 9-fluorenone imine) results in the formation of [Li(THF) 2 ] 2 [Fe(N═C 13 H 8 ) 4 ] ( 3 ) in good yield. Subsequent oxidation of 3 with ca. 0.8 equiv of I 2 generates the [Fe 2 ] 6+ complex, [Fe 2 (μ-N═C 13 H 8 ) 2 (N═C 13 H 8 ) 4 ] ( 4 ), along with free fluorenyl ketazine. Complexes 1 , 2 , and 4 were characterized by 1 H NMR spectroscopy, X-ray crystallography, 57 Fe Mössbauer spectroscopy, and SQUID magnetometry. The Fe-Fe distances in 1 , 2 , and 4 range from 2.803(7) to 2.925(1) Å, indicating that no direct Fe-Fe interaction is present in these complexes. The 57 Fe Mössbauer spectra for complexes 1 , 2 , and 4 are all consistent with the presence of symmetry-equivalent high-spin Fe 3+ centers. Finally, all three complexes exhibit a similar degree of antiferromagnetic coupling between the metal centers ( J = -26 to -30 cm -1 ), as ascertained by SQUID magnetometry.