Crystal Structure and Magnetic Characterization of Three-Coordinate [M{N(SiMe3)2}2(PCyp3)] Complexes with M = MnII, FeII, and CoII(Cyp = Cyclopentyl)

A low-coordinate iron organoazide complex

A labile organoazide iron complex is reported. Under ambient conditions, the azide adduct is subject to a dissociation equilibrium in solution, yet also undergoes intramolecular C-H bond amination. Single-crystal irradiation of the azide at 80 K leads to partial N2-extrusion and formation of a putative imido iron intermediate, which was computationally identified as a highly covalent {FeNR}8 species.

Slow magnetic relaxation in a trigonal-planar mononuclear Fe(II) complex

Based on a β-diketiminate ligand, an iron(III) tetrahedral high-spin complex, [LFeIII(Cl)2] (1), and an iron(II) high-spin triangular planar complex, [LFeIICl] (2), have been synthesized and structurally characterized. Also, complex 1...

Paramagnetic 7Li NMR Shifts and Magnetic Properties of Divalent Transition Metal Silylamide Ate Complexes [LiM{N(SiMe3)2}3] (M2+ = Mn, Fe, Co)

⁷Li NMR shifts and magnetic properties have been determined for three so-called ate complexes [LiM{N(SiMe₃)₂}₃] (M²⁺ = Mn, Fe, Co; e.g., named lithium-tris(bis(trimethylsilylamide))-manganate(II) in accordance with a formally negative charge assigned to the complex fragment [M{N(SiMe₃)₂}₃]^-, which comprises the transition metal). They are formed by addition reactions of LiN(SiMe₃)₂ and [M{N(SiMe₃)₂}₂] and stabilized by Lewis base/Lewis acid interactions. The results are compared to those of the related "ion-separated" complexes [Li(15-crown-5)][M{N(SiMe₃)₂}₃]. The ate complexes with the lithium atoms connected to the 3d metal atoms manganese, iron, or cobalt via μ₂ nitrogen bridges reveal strong ⁷Li NMR paramagnetic shifts of about -75, 125, and 171 ppm, respectively, whereas the shifts for the lithium ions coordinated by the 15-crown-5 ether are close to zero. The observed trends of the ⁷Li NMR shifts are confirmed by density-functional theory calculations. The magnetic dc and ac properties display distinct differences for the six compounds under investigation. Both manganese compounds, [LiMn{N(SiMe₃)₂}₃] and [Li(15-crown-5)][Mn{N(SiMe₃)₂}₃], display almost pure and ideal spin-only paramagnetic behavior of a 3d⁵ high-spin complex. In this respect slightly unexpected, both complexes show slow relaxation behavior at low temperatures under applied dc fields, which is especially pronounced for the ate complex [LiMn{N(SiMe₃)₂}₃]. Dc magnetic properties of the iron complexes reveal moderate g-factor anisotropies with small values of the axial magnetic anisotropy parameter D and a larger E (transversal anisotropy). Both complexes display at low temperatures and, under external dc fields of up to 5000 Oe, only weak ac signals with no maxima in the frequency range from 1 to 1500 s^-1. In contrast, the two cobalt complexes display strong g-factor anisotropies with large values of D and E. In addition, in both cases, the ac measurements at low temperatures and applied dc fields reveal two, in terms of their frequency range, well separated relaxation processes with maxima lying for the most part outside of the measurement range between 1 and 1500 s^-1.

Lateral Metallation and Redistribution Reactions of Sodium Ferrates Containing Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilide Ligands

Alkali‐metal ferrates containing amide groups have emerged as regioselective bases capable of promoting Fe−H exchanges of aromatic substrates. Advancing this area of heterobimetallic chemistry, a new series of sodium ferrates is introduced incorporating the bulky arylsilyl amido ligand N(SiMe₃)(Dipp) (Dipp=2,6‐iPr₂‐C₆H₃). Influenced by the large steric demands imposed by this amide, transamination of [NaFe(HMDS)₃] (HMDS=N(SiMe₃)₂) with an excess of HN(SiMe₃)(Dipp) led to the isolation of heteroleptic [Na(HMDS)₂Fe{N(SiMe₃)Dipp}]_∞ (1) resulting from the exchange of just one HMDS group. An alternative co‐complexation approach, combining the homometallic metal amides [NaN(SiMe₃)Dipp] and [Fe{N(SiMe₃)Dipp}₂] induces lateral metallation of one Me arm from the SiMe₃ group in the iron amide furnishing tetrameric [NaFe{N(SiCH₂Me₂)Dipp}{N(SiMe₃)Dipp}]₄ (2). Reactivity studies support that this deprotonation is driven by the steric incompatibility of the single metal amides rather than the basic capability of the sodium reagent. Displaying synergistic reactivity, heteroleptic sodium ferrate 1 can selectively promote ferration of pentafluorobenzene using one of its HMDS arms to give heterotrileptic [Na{N(SiMe₃)Dipp}(HMDS)Fe(C₆F₅)]_∞ (4). Attempts to deprotonate less activated pyridine led to the isolation of NaHMDS and heteroleptic Fe(II) amide [(py)Fe{N(SiMe₃)Dipp}(HMDS)] (5), resulting from an alternative redistribution process which is favoured by the Lewis donor ability of this substrate.

Homoleptic quasilinear metal(i/ii) silylamides of Cr-Co with phenyl and allyl functions - impact of the oxidation state on secondary ligand interactions

Herein we describe the synthesis and characterization of a variety of new quasilinear metal(i/ii) silylamides of the type [M(N(Dipp)SiR₃)₂]^0,- (M = Cr-Co) with different silyl substituents (SiR₃ = SiPh_3-nMe_n (n = 1-3), SiMe₂(allyl)). By comparison of the solid state structures we show that in the case of phenyl substituents secondary metal-ligand interactions are suppressed upon reduction of the metal. Introduction of an allyl substituted silylamide gives divalent complexes with additional metal-π-alkene interactions with only weak activation of the C[double bond, length as m-dash]C bond but substantial bending of the principal N-M-N axis. 1e^--reduction makes cobalt a more strongly bound alkene substituent, whereas for chromium, reduction and intermolecular dimerisation of the allyl unit are observed. It thus indicates that the general view of low-coordinate 3d-metal ions as electron deficient seems not to apply to anionic metal(i) complexes. Additionally, the obtained cobalt(i) complexes are reacted with an aryl azide giving trigonal imido metal complexes. These can be regarded as rare examples of high-spin imido cobalt compounds from their structural and solution magnetic features.

A Molecular Low-Coordinate [Fe-S-Fe] Unit in Three Oxidation States

A [Fe-S-Fe] subunit with a single sulfide bridging two low-coordinate iron ions is the supposed active site of the iron-molybdenum co-factor (FeMoco) of nitrogenase. Here we report a dinuclear monosulfido bridged diiron(II) complex with a similar complex geometry that can be oxidized stepwise to diiron(II/III) and diiron(III/III) complexes while retaining the [Fe-S-Fe] core. The series of complexes has been characterized crystallographically, and electronic structures have been studied using, inter alia, 57 Fe Mössbauer spectroscopy and SQUID magnetometry. Further, cleavage of the [Fe-S-Fe] unit by CS2 is presented.

Pogo-Stick Iron and Cobalt Complexes: Synthesis, Structures, and Magnetic Properties

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(μ-I)]₂ (1-M, M = Fe, Co; Cp' = η⁵-1,2,4-tri-tert-butylcyclopentadienyl) with [Im^DippNLi]₂ (Im^DippN = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal half-sandwich compounds [Cp'M(NIm^Dipp)] (2-M, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool. Complex 2-Co can also be prepared by an acid-base reaction between [Cp'Co{N(SiMe₃)₂}] (3-Co) and Im^DippNH. The electronic and magnetic properties of 2-M and 3-Co were probed by ⁵⁷Fe Mössbauer spectroscopy (M = Fe), X-band EPR spectroscopy (M = Co), and solid-state magnetic susceptibility measurements. In particular, the central metal atom adopts a high-spin (S = 2) state in 2-Fe, while the cobalt complex 2-Co represents a rare example of a Co(II) species with a coordination number different from six displaying a low-spin to high-spin spin-crossover (SCO) behavior. The experimental observations are complemented by DFT calculations.

Magnetic anisotropy in trigonal planar Fe(ii) bis(trimethylsilyl)amido complexes of the type [Fe{N(SiMe3)2}2L]-experiment and theory

Systematic ac (alternating current) magnetic investigations on four new trigonal planar high-spin Fe2+ complexes [Fe{N(SiMe3)2}2L] reveal that complexes which comprise a phosphine or arsine type ligand (L = PPh3, PMe3 and AsPh3) display slow magnetic relaxation at temperatures below 8 K under applied dc (direct current) fields, whereas a complex with a phosphine oxide ligand (L = OPPh3) does not. Accordingly, the parameters characteristic for magnetic anisotropy, derived both from dc magnetic measurements and quantum chemical calculations, reveal distinct differences for these two types of complexes. Extensive ab initio calculations of multi-reference wave function type were performed on the four new complexes listed above and the related reported ones with L = py, thf and PCy3 in order to get a reasonable description of the local electronic states involved in the magnetic relaxation. These calculations confirm that strong spin-orbit effects generate the magnetic anisotropy of complexes with L = PPh3, PMe3, AsPh3 and PCy3. On the other hand, the complexes with L = OPPh3, py and THF exhibit only small spin-orbit splittings, consistent with the fast relaxation found experimentally.

C-Halide bond cleavage by a two-coordinate iron(i) complex

The two-coordinate iron(i) complex [Fe^I(N(SiMe₃)₂)₂]⁻ is highly efficient in the cleavage of C-halide bonds.

ortho-Phenyl dialkylphosphonium sulfonate compounds: two rotamers in equilibrium

Two known and two new ortho-phenyl phosphonium–sulfonate compounds have been synthesized and analyzed in solution and in the solid state.