Stereoelectronic Tuning of Bioinspired Nonheme Iron(IV)-Oxo Species by Amide Groups in Primary and Secondary Coordination Spheres for Selective Oxygenation Reactions.

Two mononuclear iron(II) complexes, [(6-amide-BPMEN)Fe](OTf) () and [(6-amide-Me-BPMEN)Fe(OTf)](OTf) (), supported by two BPMEN-derived (BPMEN = ,-dimethyl-,-bis(pyridine-2-yl-methyl)ethane-1,2-diamine) ligands bearing one or two amide functionalities have been isolated to study their reactivity in the oxygenation of C-H and C═C bonds using isopropyl 2-iodoxybenzoate (Pr-IBX ester) as the oxidant. Both and contain six-coordinate high-spin iron(II) centers in the solid state and in solution. The 6-amide-BPMEN ligand stabilizes an = 1 iron(IV)-oxo intermediate, [(6-amide-BPMEN)Fe(O)] ().

Influence of intrinsic spin ordering in LaSrCoFeO and BaSrCoFeO towards electrocatalysis of oxygen redox reaction in solid oxide cell.

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O is associated with singlet oxygen in HO/OH), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction).

Oxygenolytic cleavage of 1,2-diols with dioxygen by a mononuclear nonheme iron complex: Mimicking the reaction of myo-inositol oxygenase.

A mononuclear iron(II) complex, [(Tp)Fe(OTf)(CHCN)] (1) (Tp = hydrotris(3,5-diphenylpyrazol-1-yl)borate, OTf = triflate) has been isolated and its efficiency toward the aliphatic CC bond cleavage reaction of 1,2-diols with dioxygen has been investigated. Separate reactions between 1 and different 1,2-diolates form the corresponding iron(II)-diolate complexes in solution. While the iron(II) complex of the tetradentate TPA (tris(2-pyridylmethyl)amine) ligand is not efficient in affecting the CC cleavage of 1,2-diol with dioxygen, complex 1 displays catalytic activity to afford carboxylic acid and aldehyde.

Electrochemical generation of high-valent oxo-manganese complexes featuring an anionic N5 ligand and their role in O-O bond formation.

Generation of high-valent oxomanganese complexes through controlled removal of protons and electrons from low-valent congeners is a crucial step toward the synthesis of functional analogues of the native oxygen evolving complex (OEC). In-depth studies of the water oxidation activity of such biomimetic compounds help in understanding the mechanism of O-O bond formation presumably occurring in the last step of the photosynthetic cycle. Scarce reports of reactive high-valent oxomanganese complexes underscore the impetus for the present work, wherein we report the electrochemical generation of the non-heme oxomanganese(IV) species [(dpaq)Mn(O)] (2) through a proton-coupled electron transfer (PCET) process from the hydroxomanganese complex [(dpaq)Mn(OH)]ClO (1).

3D Cyclophane for the Selective Conversion of Epoxide to Cyclic Carbonate.

A novel three-dimensional (3D) cyclophane molecule was synthesized and fully characterized. Cyclophane , which can form a N heterocyclic carbene, was tested for conversion of certain epoxides (-) [scheme 2] to cyclic carbonates in the presence of CO. Propylene oxide () was found to have more reactivity with cyclophane compared to the other epoxides.

A Theoretical Account of the Coupling between Metal- and Ligand-centred Spins.

This study addresses the magnetic interaction between paramagnetic metal ions and the radical ligands taking the [Cu (hfac) (imVDZ)] and [M (hfac) (pyDTDA)] (imVDZ=1,5-dimethyl-3-(1-methyl-2-imidazolyl)-6-oxoverdazyl; hfac=(1,1,1,5,5,5)hexafluroacetylacetonate; pyDTDA=4-(2'-pyridyl)-1,2,3,5-dithiadiazolyl), (M=Cu, Ni, Co, Fe, Mn) compounds as reference systems. The coupling between the metal and ligand spins is quantified in terms of the exchange coupling constant (J) in the platform of density functional theory (DFT) and the wave function-based complete active space self-consistent field (CASSCF) method. Application of DFT and broken symmetry (BS) formalism results ferromagnetic coupling for all the transition metal complexes except the Mn(II) complex.

Dioxygen Activation and Mandelate Decarboxylation by Iron(II) Complexes of N4 Ligands: Evidence for Dioxygen-Derived Intermediates from Cobalt Analogues.

The isolation, characterization, and dioxygen reactivity of monomeric [(TPA)M(mandelate)] (M = Fe, ; Co, ) and dimeric [(BPMEN)M(μ-mandelate)] (M = Fe, ; Co, ) (TPA = tris(2-pyridylmethyl)amine and BPMEN = ,-dimethyl-,-bis(pyridin-2-yl-methyl)ethane-1,2-diamine) complexes are reported. The iron(II)- and cobalt(II)-mandelate complexes react with dioxygen to afford benzaldehyde and benzoic acid in a 1:1 ratio. In the reactions, one oxygen atom from dioxygen is incorporated into benzoic acid, but benzaldehyde does not derive any oxygen atom from dioxygen.

Selective oxygenation of C-H and CC bonds with HO by high-spin cobalt(II)-carboxylate complexes.

Four cobalt(II)-carboxylate complexes [(6-Me-TPA)Co(benzoate)](BPh) (1), [(6-Me-TPA)Co(benzilate)](ClO) (2), [(6-Me-TPA)Co(mandelate)](BPh) (3), and [(6-Me-TPA)Co(MPA)](BPh) (4) (HMPA = 2-methoxy-2-phenylacetic acid) of the 6-Me-TPA (tris((6-methylpyridin-2-yl)methyl)amine) ligand were isolated to investigate their ability in HO-dependent selective oxygenation of C-H and CC bonds. All six-coordinate complexes contain a high-spin cobalt(II) center. While the cobalt(II) complexes are inert toward dioxygen, each of these complexes reacts readily with hydrogen peroxide to form a diamagnetic cobalt(III) species, which decays with time leading to the oxidation of the methyl groups on the pyridine rings of the supporting ligand.

Electrochemical Properties and Reactivity Study of [Mn(O)(μ-OR-Lewis Acid)] Cores.

A mononuclear manganese(V) oxo complex of a bis(amidate)bis(alkoxide) ligand, (NMe)[Mn(HMPAB)(O)] [; HHMPAB = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene], was synthesized and structurally characterized. A Mn-O distance of 1.566(4) Å was observed in the solid-state structure of , consistent with the Mn≡O formulation.

Oxygen Reduction Assisted by the Concert of Redox Activity and Proton Relay in a Cu(II) Complex.

A copper complex, [Cu(dpaq)](ClO) (), of a monoanionic pentadentate amidate ligand (dpaq) has been isolated and characterized to study its efficacy toward electrocatalytic reduction of oxygen in neutral aqueous medium. The Cu(II) mononuclear complex, poised in a distorted trigonal bipyramidal structure, reduces oxygen at an onset potential of 0.50 V vs RHE.

A High Spin Mn(IV)-Oxo Complex Generated via Stepwise Proton and Electron Transfer from Mn(III)-Hydroxo Precursor: Characterization and C-H Bond Cleavage Reactivity.

The oxomanganese(IV) complex [(dpaq)Mn(O)]-M (, M = redox-inactive metal ion, H-dpaq = 2-[bis(pyridin-2-ylmethyl)]amino--quinolin-8-ylacetamide), generated in the reaction of the precursor hydroxomanganese(III) complex with iodosylbenzene (PhIO) in the presence of redox-inactive metal triflates, has recently been reported. Herein the generation of the same oxomanganese(IV) species from using various combinations of protic acids and oxidants at 293 K is reported. The reaction of with triflic acid and the one-electron-oxidizing agent [Ru(bpy)] leads to the formation of the oxomanganese(IV) complex.

Highly Selective and Catalytic Oxygenations of C-H and C=C Bonds by a Mononuclear Nonheme High-Spin Iron(III)-Alkylperoxo Species.

The reactivity of a mononuclear high-spin iron(III)-alkylperoxo intermediate [Fe (t-BuL )(OOCm)(OH )] (2), generated from [Fe (t-BuL )(H O)(OTf)](OTf) (1) [t-BuL =1,1'-(((pyridin-2-ylmethyl)azanediyl)bis(ethane-2,1-diyl))bis(3-(tert-butyl)urea), OTf=trifluoromethanesulfonate] with cumyl hydroperoxide (CmOOH), toward the C-H and C=C bonds of hydrocarbons is reported. 2 oxygenates the strong C-H bonds of aliphatic substrates with high chemo- and stereoselectivity in the presence of 2,6-lutidine. While 2 itself is a sluggish oxidant, 2,6-lutidine assists the heterolytic O-O bond cleavage of the metal-bound alkylperoxo, giving rise to a reactive metal-based oxidant.

Ligand-induced symmetry breaking and concomitant blueshift in the emission wavelength of an octahedral chromium complex.

The resulting distortion of the octahedral symmetry of the complex [Cr(NH)] upon replacing the axial ligands with halides (i.e., weaker ligands) affects the stability of the doublet state with respect to that of the quartet ground state.

On exo-cyclic aromaticity.

The domain of aromaticity spans a wide range of molecules, from polycyclic aromatic hydrocarbons, heterocycles to all-metal systems. Here, in silico we demonstrate the aromaticity in CBF, extending beyond the limit of conventional aromatic molecules. This molecule gains the magic number of six π-electrons through an unusual electronic contribution from exo-cyclic atoms.

What Can We Learn from a Biomimetic Model of Nature's Oxygen-Evolving Complex?

A recently reported synthetic complex with a MnCaO core represents a remarkable structural mimic of the MnCaO cluster in the oxygen-evolving complex (OEC) of photosystem II (Zhang et al., Science 2015, 348, 690). Oxidized samples of the complex show electron paramagnetic resonance (EPR) signals at g ≈ 4.

Interpretation and Quantification of Magnetic Interaction through Spin Topology.

This work develops a formalism to quantify the interaction among unpaired spins from the ground state spin topology. Magnetic systems where the spins are coupled through direct exchange and superexchange are chosen as references. Starting from a general Hamiltonian, an effective Hamiltonian is obtained in terms of spin density which is utilized to compute exchange coupling constants in magnetic systems executing direct exchange.

Interplay among aromaticity, magnetism, and nonlinear optical response in all-metal aromatic systems.

All-metal aromatic molecules are the latest inclusion in the family of aromatic systems. Two different classes of all-metal aromatic clusters are primarily identified: one is aromatic only in the low spin state, and the other shows aromaticity even in high-spin situations. This observation prompts us to investigate the effect of spin multiplicity on aromaticity, taking Al(4)(2-), Te(2)As(2)(2-), and their copper complexes as reference systems.

Exchange interactions in systems with multiple magnetic sites.

Nonequivalent magnetic interactions in systems with multiple magnetic centers can be explored through a proper description of exchange coupling. The magnetic exchange coupling constant (J) in systems with two magnetic sites is reliably estimated using Heisenberg-Dirac-van Vleck (HDVV) model through broken symmetry approach (BS) within a density functional theory (DFT) framework. However, in case of systems with multiple magnetic centers, exchange coupling constants, evaluated through state-of-the-art techniques, are often found to be inadequate to produce a correct fingerprint of the nature of magnetic interactions therein.