Structural and spectroscopic characterization of an Fe(VI) bis(imido) complex.

High-valent iron species are key intermediates in oxidative biological processes, but hexavalent complexes apart from the ferrate ion are exceedingly rare. Here, we report the synthesis and structural and spectroscopic characterization of a stable Fe(VI) complex () prepared by facile one-electron oxidation of an Fe(V) bis(imido) (). Single-crystal x-ray diffraction of and revealed four-coordinate Fe centers with an unusual "seesaw" geometry.

Stabilization of the Dinitrogen Analogue, Phosphorus Nitride.

The N analogue phosphorus nitride (PN) was the first phosphorus-containing compound to be detected in the interstellar medium; however, this thermodynamically unstable compound has a fleeting existence on Earth. Here, we show that reductive coupling of iron(IV) nitride and molybdenum(VI) phosphide complexes assembles PN as a bridging ligand in a structurally characterized bimetallic complex. Reaction with C≡N Bu releases the mononuclear complex [(NN)Mo-PN], NN = [(MeSiNCHCH)N]), which undergoes light-induced linkage isomerization to provide [(NN)Mo-NP], as revealed by photocrystallography.

Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance.

A low-coordinate, high spin ( = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the = 3/2 surface, oxidative addition to an η-allyl intermediate only occurs on the = 1/2 surface.

Strong π-Backbonding Enables Record Magnetic Exchange Coupling Through Cyanide.

The paramagnetic cyano-bridged complex PhB(BuIm)Fe-NC-Mo(NBuAr) (Ar = 3,5-MeCH) is readily assembled from a new four-coordinate, high-spin ( = 2) iron(II) monocyanide complex and the three-coordinate molybdenum(III) complex Mo(NBuAr). X-ray diffraction and IR spectroscopy reveal that delocalization of unpaired electron density into the cyanide π* orbitals leads to a reduction of the C-N bond order. Direct current (dc) magnetic susceptibility measurements, supported by electronic structure calculations, demonstrate the presence of strong antiferromagnetic exchange between spin centers, with a coupling constant of = -122(2) cm.

A Dimeric Hydride-Bridged Complex with Geometrically Distinct Iron Centers Giving Rise to an = 3 Ground State.

Structural and spectroscopic characterization of the dimeric iron hydride complex [PhB(BuIm)FeH] reveals an unusual structure in which a tetrahedral iron(II) site ( = 2) is connected to a square planar iron(II) site ( = 1) by two bridging hydride ligands. Magnetic susceptibility reveals strong ferromagnetic coupling between iron centers, with a coupling constant of = +110(12) cm, to give an = 3 ground state. High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy confirms this model.

Two-state reactivity in C-H activation by a four-coordinate iron(0) complex.

The ground state structure of [PhB(BuIm)Fe(CO)] is trigonal pyramidal (S = 1), with a thermally accessible square planar (S = 0) geometry. Experimentally calibrated electronic structure calculations provide evidence for two-state reactivity, with C-H oxidative addition on the singlet surface providing an iron(ii) product (S = 0).

Arrested α-hydride migration activates a phosphido ligand for C-H insertion.

Bulky tris(carbene)borate ligands provide access to high spin iron(ii) phosphido complexes. The complex PhB(MesIm)FeP(H)Ph is thermally unstable, and [PPh] group insertion into a C-H bond of the supporting ligand is observed. An arrested α-hydride migration mechanism suggests increased nucleophilicity of the phosphorus atom facilitates [PPh] group transfer reactivity.