Multimetallic Cooperativity in Activation of Dinitrogen at Iron-Potassium Sites.

The reaction of soluble iron-oxygen-potassium assemblies with N gives insight into the mechanisms of multimetallic N coordination. We report a series of very electron-rich three-coordinate, β-diketiminate-supported iron(I) phenoxide complexes, which are metastable but have been characterized under Ar by both crystallography and solution methods. Both monomeric and dimeric Fe-OPh-K compounds have been characterized, and their iron environments are very similar in the solid and solution states.

Sensitivity of X-ray core spectroscopy to changes in metal ligation: a systematic study of low-coordinate, high-spin ferrous complexes.

In order to assess the sensitivity and complementarity of X-ray absorption and emission spectroscopies for determining changes in the metal ligation sphere, a systematic experimental and theoretical study of iron model complexes has been carried out. A series of high-spin ferrous complexes, in which the ligation sphere has been varied from a three-coordinate complex, [L(tBu)Fe(SPh)] (1) (where L(tBu) = bulky β-diketiminate ligand; SPh = phenyl thiolate) to four-coordinate complexes [L(tBu)Fe(SPh)(X)] (where X = CN(t)Bu (2); 1-methylimidazole (3); or N,N-dimethylformamide (DMF) (4)), has been investigated using a combination of Fe K-edge X-ray absorption (XAS) and Kβ X-ray emission (XES) spectroscopies. The Fe K XAS pre-edge and edge of all four complexes are consistent with a high-spin ferrous assignment, with the largest differences in the pre-edge intensities attributed to changes in covalency of the fourth coordination site.

Identification of a single light atom within a multinuclear metal cluster using valence-to-core X-ray emission spectroscopy.

Iron valence-to-core Fe Kβ X-ray emission spectroscopy (V2C XES) is established as a means to identify light atoms (C, N, O) within complex multimetallic frameworks. The ability to distinguish light atoms, particularly in the presence of heavier atoms, is a well-known limitation of both crystallography and EXAFS. Using the sensitivity of V2C XES to the ionization potential of the bound ligand, energetic shifts of ~10 eV in the ligand 2s ionization energies of bound C, N, and O may be observed.

Ligand dependence of binding to three-coordinate Fe(II) complexes.

A series of three- and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant of the neutral ligands and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in K(eq), which decrease in the order CN(t)Bu > pyridine >2-picoline > DMF > MeCN > THF > PPh(3).

Synthesis of a bulky bis(imino)pyridine compound: a methodology for systematic variation of steric bulk and energetic implications for metalation.

A new bis(imino)pyridine compound, 2,6-{(2,6-Me(2)-C(6)H(3))NC(t-Bu)}(2)C(5)H(3)N (), has been synthesized with t-butyl substituents on the imino carbon atoms. The stepwise synthetic method for assembly of this compound is novel. Compound and its synthetic precursor, mono(imino)pyridine , have been characterized using single-crystal X-ray diffraction.