Borate Iron Research Articles

The Properties of Hydrotris(3‐mesitylpyrazol‐1‐yl) Borate Iron(II) Complexes with Aryl Carboxylate Co‐ligands – Stabilization of an Iron(III) Alkylperoxide

AbstractThrough the reaction of [TpMesFeCl] with different benzoic acids, namely salicylic acid (HOBzo−OH), m‐chloro benzoic acid (HOBzm−Cl), p‐dimethylamino benzoic acid (OBzp−N(Me)2) and benzoic acid itself, in the presence of triethylamine corresponding complexes [TpMesFeOBzR] with varying residues R could be isolated and fully characterized (including paramagnetic NMR spectroscopy, elemental analysis, IR, cyclic voltammetry). From acetonitrile solutions they crystallized as acetonitrile adducts [TpMesFe(NCMe)OBzR], which indicates, that a coordination and activation of an exogeneous substrate is principally possible. While no reactivity towards O2 could be observed, in contact with tBuOOH all complexes were found to form iron(III) tert‐butylperoxide complexes [TpMesFe(OBzR)(OOtBu)], as evidenced by UV‐vis, EPR and Raman spectroscopy. Through UV‐vis studies it was shown, that both the formation rate and the stability of [TpMesFe(OBzR)(OOtBu)] are influenced by the basicity of the benzoate co‐ligands, which is determined by the substituents. An extraordinarily high stability was observed for the salicylate representative, which, however, cannot be explained on basis of such electronic effects; other potential stabilizing factors that may play an important role are discussed.

Dioxygenation of cysteamine to hypotaurine at a tris(pyrazolyl)borate iron(ii) unit - cysteamine dioxygenase mimicking?

A novel complex Tp(Me,Ph)Fe(SCH2CH2NH2) has been synthesized as a speculative model for ADO. Indeed its reaction with O2 led to the dioxygenation of the S atom and thus to hypotaurine. This finding may allow us to draw conclusions on the constitution of the ADO active site, whose structure is still unknown.

Low-Coordinate Iron(II) Complexes of a Bulky Bis(carbene)borate Ligand

The bulky bis(carbene)borate ligand H2B(tBuIm)2– allows for the synthesis of three- and four-coordinate iron(II) complexes, including heteroleptic H2B(tBuIm)2FeN(TMS)2 and homoleptic [H2B(tBuIm)2]2Fe. The magnetic properties of these coordinatively unsaturated complexes have been characterized by SQUID magnetometry, but no evidence of single-molecule magnet behavior is observed, despite large negative uniaxial zero field splitting. The three-coordinate complex H2B(tBuIm)2FeN(TMS)2 serves as a precursor for the synthesis of the four-coordinate mixed carbene complex H2B(tBuIm)2(iPr2Im)FeCl, which has a coordination environment similar to that found in tris(carbene)borate iron(II) chloride complexes. Despite this similarity, attempts to prepare the corresponding iron(IV) nitride were unsuccessful, suggesting that subtle structural factors are critical to stabilizing this species.

On the analogy in evolution processes and the behavior of a magnetically ordered systems

Common regularities in the biology evolution and the magnetization processes of magnetically ordered materials have been demonstrated. The arrays of the experimental data have been accumulated in the registration process of a weak polarization-optical response of borate iron at the presence of external magnetic field. It is shown that the magnetic behavior of response in some respects analogous to processes in biologically systems, such as differentiation, convergence, the development of clones, etc. It is predicted the existence of the weaving development that combines the characteristics of the processes of differentiation and convergence. More detail are considered the phenomenon nie the branch points; it is shown the possibility of the acceleration, retardation, and wavelike development. The proposed approach may be useful for comparison, the study and predict development scenarios for actual organized systems of various natures (ecological, social, financial, informative etc.), and high degree of hierarchical complexity.

ChemInform Abstract: The Structure and Reactivity of Iron Nitride Complexes

AbstractReview: 67 refs.

The structure and reactivity of iron nitride complexes

The structure and reactivity of discrete iron nitride complexes is described. Six-coordinate, four-fold symmetric nitrides are thermally unstable, and have been characterized at cryogenic temperatures by an arsenal of spectroscopic methods. By contrast, four-coordinate, three-fold symmetric iron nitrides can be prepared at room temperature. A range of diamagnetic iron(IV) nitrides have been reported and in some cases, isolated. Among these are the isolable, yet reactive, tris(carbene)borate iron(IV) nitrides. These complexes can effect two-electron nitrogen atom transfer to a range of substrates, in some cases with complete atom transfer occuring through Fe-N bond cleavage. These nitrides are also active in single electron pathways, including the synthesis of ammonia by a mechanism involving hydrogen atom transfer to the nitride ligand. One-electron oxidation of a tris(carbene)borate iron(IV) nitride leads to an isolable iron(V) complex that is unusually reactive for a metal nitride.

Nitrogen Atom Transfer from Iron(IV) Nitrido Complexes: A Dual-Nature Transition State for Atom Transfer

The mechanism of nitrogen atom transfer from four-coordinate tris(carbene)borate iron(IV) nitrido complexes to phosphines and phosphites has been investigated. In the absence of limiting steric effects, the rate of nitrogen atom transfer to phosphines increases with decreasing phosphine σ-basicity. This trend has been quantified by a Hammett study with para-substituted triarylphosphines, and is contrary to the expectations of an electrophilic nitrido ligand. On the basis of electronic structure calculations, a dual-nature transition state for nitrogen atom transfer is proposed, in which a key interaction involves the transfer of electron density from the nitrido highest occupied molecular orbital (HOMO) to the phosphine lowest unoccupied molecular orbital (LUMO). Compared to analogous atom transfer reactions from a 5d metal, these results show how the electronic plasticity of a 3d metal results in rapid atom transfer from pseudotetrahedral late metal complexes.

Synthesis and Spectroscopic and Magnetic Characterization of Tris(3,5-dimethylpyrazol-1-yl)borate Iron Tricyanide Building Blocks, a Cluster, and a One-Dimensional Chain of Squares

The synthesis and spectroscopic and magnetic characterization of several hydridotris(3,5-dimethylpyrazol-1yl)borate (Tp*) iron(II) and iron(III) tricyanide complexes, a rectangular cluster, and a one-dimensional chain of squares are described. Treatment of [NEt4][(Tp*)Fe(III)(CN)3] (3) with manganese(II) triflate in dimethylformamide (DMF) affords rectangular clusters (6, {[(Tp)Fe(CN)2(mu-CN)Mn(DMF)4]2[OTf]2}.2DMF), while tosylate salts afford one-dimensional networks (5, {Mn(II)(DMF)2(mu-OTs)(mu-NC)2(NC)Fe(III)(Tp*)}n) containing embedded [(Tp*)2Fe(III)2Mn(II)2(CN)6]2+ clusters via in situ trapping; the cluster and network crystallize in the monoclinic (6, P2(1)/n) and triclinic (5, P1) space groups, respectively. The 1-D network (5) appears to be derived from {cis-(mu-O3SC6H4Me)2Mn(II)(DMF)4}n (4, P2(1)/n), which is obtained via crystallization of Mn(OTs)2 from DMF/Et2O mixtures. For 4, magnetic studies indicate that the Mn(II) centers are magnetically isolated, with calculated J, g, and theta constants of 6.7 x 10(-3) cm(-1), 2.03, and -0.52 K. Additional magnetic studies of 5 and 6 indicate that the [(Tp*)Fe(III)(CN)3]- centers are highly anisotropic (g = 2.9) and are antiferromagnetically coupled to adjacent Mn(II) centers. For 5 and 6, fitting of the chiT vs T data via the Curie-Weiss expression affords Curie (6.25 and 10.8 cm(3) K mol(-1)) and Weiss (-14.37 and -8.80 K) constants that are consistent with antiferromagnetically coupled low-spin Fe(III) and high-spin Mn(II) centers; least-squares fitting of the chiT vs T data using molecular field theory affords g(avg.), J1, J2, and J' values of 2.25, -1.72, -0.58, and -0.12 cm(-1) for 5. Overall, bridging tosylates appear to be poor communicators of spin information. For 6, the g, J1, and J2 (2.15, -2.02, and -0.78 cm(-1)) values were obtained via least-squares fitting of the chiT vs T data using an expression derived using the Kambe vector coupling method; simulations of the data via MAGPACK afford g(avg.) and J(iso) values of 2.1 and -2.1 cm(-1).

The first example of a structurally characterized octahedral hydrotris(pyrazolyl)borate iron methyl complex

The one-step synthesis of the known acetyl complex κ 3-TpFe(CO)(PMe 3)(COMe) ( 1, 78% yield) is achieved by reaction of cis, trans-Fe(CO) 2(PMe 3) 2MeI with potassium hydrotris(pyrazolyl)borate (KTp), in CH 2Cl 2 at room temperature. This reaction is specific to the parent Tp ligand. Visible light irradiation of 1 in toluene for 1 h afforded the first octahedral methyl–iron complex featuring the hydrotris(pyrazolyl)borate ligand TpFe(CO)(PMe 3)Me ( 2) in 80% yield. Compound 2 has been fully characterized by elemental analysis, IR, NMR spectroscopies, cyclic voltammetry and by an X-ray diffraction analysis. A comparison of steric and electronic properties is made with those of related cyclopentadienyl (Cp, Cp*, C 5Ph 5) complexes, and suggests that relative donating abilities follow the trend Cp, Cp*, C 5Ph 5>Tp, and structural comparisons indicate that Tp is the most sterically demanding ligand.

Tris(mercaptoimidazolyl)hydroborato complexes of cobalt and iron, [Tm Ph] 2M (M=Fe, Co): structural comparisons with their tris(pyrazolyl)hydroborato counterparts

The tris(mercaptophenylimidazolyl)borate iron and cobalt complexes [Tm Ph] 2M (M=Fe, Co) have been synthesized by reaction of [Tm Ph]Tl with MI 2. Structural characterization by X-ray diffraction demonstrates that the potentially tridentate [Tm Ph] ligand binds through only two sulfur donors in these ‘sandwich’ complexes and that the ‘tetrahedral’ metal centers supplement the bonding by interactions with the two B–H groups. Comparison of the structures of [Tm Ph] 2M (M=Fe, Co) with the related tris(pyrazolyl)borate [Tp Ph] 2M counterparts indicates that the tris(mercaptoimidazolyl) ligand favors lower primary coordination numbers in divalent metal complexes. The trivalent complexes, {[Tp Ph] 2Fe}[ClO 4] and {[pzBm Me] 2Co}I, however, exhibit octahedral coordination, with the ligands binding using their full complement of donor atoms.