A Spectroscopic Criterion for Identifying the Degree of Ground-Level Near-Degeneracy Derived from Effective Hamiltonian Analyses of Three-Coordinate Iron Complexes.

The fascinating magnetic and catalytic properties of coordinatively unsaturated 3d metal complexes are a manifestation of their electronic structures, in particular their nearly doubly or triply degenerate orbital ground levels. Here, we propose a criterion to determine the degree of degeneracy of this class of complexes based on their experimentally accessible magnetic anisotropy (parametrized by the electron spin - and zero-field splitting (ZFS)-tensors). The criterion is derived from a comprehensive spectroscopic and theoretical study in the trigonal planar iron(0) complex, [(IMes)Fe(dvtms)] (IMes = 1,3-di(2',4',6'-trimethylphenyl)imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane, ).

Three Distinct Oxidation States (II/II, II/III, and III/III) of Diorganocopper Complexes.

In this report, we present a structurally and spectroscopically characterized diorganocopper system in three distinct oxidation states: [CuCu] (), [CuCu] (), and [CuCu] (). These states are stabilized by a macrocyclic ligand scaffold featuring two square-planar coordination {C N }. We have analyzed the geometric and electronic structures using X-ray diffraction (XRD) and multiple spectroscopic methods including nuclear magnetic resonance (NMR), UV-vis, and electron paramagnetic resonance (EPR) spectroscopies, in combination with density functional theory (DFT) calculations.

Isolation and characterization of a triplet nitrene.

Nitrene radical compounds are short-lived intermediates in a variety of nitrogen-involved transformations. They feature either a singlet or a triplet ground state, depending on the electronic properties of the substituents. Triplet nitrenes are highly reactive and their isolation in the condensed phase under ambient conditions is challenging.

Insights into dioxygen binding on metal centers: an multireference electronic structure analysis.

Why does binding of dioxygen (O) to metal centers, the initial step of O storage, transportation, and activation, almost inevitably induce metal-to-O single-electron transfer and generate superoxo (O˙) species, instead of genuine O02 adducts? To address this question, this study describes highly correlated wavefunction-based calculations using CASSCF/NEVPT2 (CASSCF = complete active space self-consistent field, and NEVPT2 = -electron valence state second-order perturbation theory) approaches to explore the electronic-structure evolution of O association on Fe(II)(BDPP) (HBDPP = 2,6-bis((2-()-diphenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) and Co(II)(BDPP) to produce = 3 Fe(III)(BDPP)(O˙) (1) and Co(III)(BDPP)(O˙) (2). CASSCF/NEVPT2 calculations suggest that the processes furnishing 1 and 2 feature an avoided crossing resulting from interactions of two diabatic curves, of which one is characterized as Co(II) and Fe(II) centers interacting with a triplet O ligand and the other as Co(III) and Fe(III) centers bound to a superoxo ligand. In both cases, the avoided crossing induces a one-electron transfer from the divalent metal center to the incoming O ligand and leads to formation of trivalent metal-O˙ complexes.

Synthesis and Characterization of Bridging-Diazene Diiron Half-Sandwich Complexes: The Role of Sulfur Hydrogen Bonding.

We report two bridging-diazene diiron complexes [Cp*Fe(8-quinolinethiolate)](μ-NH) () and [Cp*Fe(1,2-CyPCHS)](μ-NH) (), synthesized by the reaction of hydrazine with the corresponding thiolate-based iron half-sandwich complex, [Cp*Fe(8-quinolinethiolate)] () and Cp*Fe(1,2-CyPCHS) (). Crystallographic analysis reveals that the thiolate sites in and can engage in N-H···S hydrogen bonding with the diazene protons. is thermally stable in both solid and solution states, allowing for one-electron oxidation to afford a cationic diazene radical complex [] at room temperature.

A Mechanistic Spectrum of O-H Bond Cleavage Observed for Reactions of Phenols with a Manganese Superoxo Complex.

Reaction of a rare and well-characterized Mn-superoxo species, Mn(BDPP)(O⋅) (1, HBDPP=2,6-bis((2-(S)-di(4-bromo)phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine), with 4-dimethylaminophenol at -80 °C proceeds via concerted proton electron transfer (CPET) to produce a Mn-hydroperoxo complex, Mn(BDPP)(OOH) (2), alongside 4-dimethylaminophenoxy radical; whereas, upon treatment with 4-nitrophenol, complex 1 undergoes a proton transfer process to afford a Mn-hydroperoxo complex, [Mn(BDPP)(OOH)] (3). Intriguingly, the reactions of 1 with 4-chlorophenol and 4-methoxyphenol follow two routes of CPET and sequential proton and electron transfer to furnish complex 2 in the end. UV-vis and EPR spectroscopic studies coupled with DFT calculations provided support for this wide mechanistic spectrum of activating various phenol O-H bonds by a single Mn-superoxo complex, 1.

Bimetallic H Addition and Intramolecular Caryl-H Activation Mediated by an Iron-Zinc Hydride.

Heteronuclear Fe(μ-H)Zn hydride Cp*Fe(1,2-CyPCH)HZnEt () undergoes reversible intramolecular C-H reductive elimination through coupling of the cyclometalated phosphinoaryl ligand and the hydride, giving rise to a formal Fe(0)-Zn(II) species. Addition of CO intercepts this equilibrium, affording Cp*(CyPPh)(CO)Fe-ZnEt that features a dative Fe-Zn bond. Significantly, this system achieves bimetallic H addition, as demonstrated by the transformation of the monohydride Fe(μ-H)Zn to a deuterated dihydride Fe-(μ-D)-Zn upon reaction with D.

An Isolable One-Coordinate Lead(I) Radical with Strong g-Factor Anisotropy.

Lead-based radicals in the oxidation state of +1 are elusive species and are highly challenging to isolate in the condensed phase. In this study, we present the synthesis and characterization of the first isolable free plumbylyne radical 2 bearing a one-coordinate Pb(I) atom. It reacts with an N-heterocyclic carbene (NHC) to afford a two-coordinate NHC-ligated Pb(I) radical 3.

Magneto-Structural Correlation of Five-Coordinate Trigonal Bipyramidal High Spin Cobalt(II) Complexes.

Here, we combined magnetometry, multi-frequency electronic paramagnetic resonance, and wave function based ab initio calculations to investigate magnetic properties of two high spin Co(II) complexes Co(BDPP) (BDPP=2,6-bis((2-(S)-di(4-R)phenylhydroxylmethyl-1-pyrrolidi-nyl)methyl)pyridine, R=H for 8; R=Bu for 9). Complexes 8 and 9 featuring effective D symmetry were found to possess D=24.0 and 32.

Unusual Electronic Structures of an Electron Transfer Series of [Cr(μ-η : η -N )Cr].

In dinitrogen (N ) fixation chemistry, bimetallic end-on bridging N complexes M(μ-η  : η -N )M can split N into terminal nitrides and hence attract great attention. To date, only 4d and 5d transition complexes, but none of 3d counterparts, could realize such a transformation. Likewise, complexes {[Cp*Cr(dmpe)] (μ-N )} (1-3) are incapable to cleave N , in contrast to their Mo congeners.

Triplet bismuthinidenes featuring unprecedented giant and positive zero field splittings.

Isolation of triplet pnictinidenes, which bear two unpaired electrons at the pnictogen centers, has long been a great challenge due to their intrinsic high reactivity. Herein, we report the syntheses and characterizations of two bismuthinidenes MFluind-Bi () and MFluind*-Bi () stabilized by sterically encumbered hydrindacene ligands. They were facilely prepared through reductions of the corresponding dichloride precursors with 2 molar equivalents of potassium graphite.

Synthesis, Structure and Reactivity of a Mononuclear N,N,O-Bound Fe(II) α-Keto-Acid Complex.

A bulky, tridentate phenolate ligand (Im NNO ) was used to synthesise the first example of a mononuclear, facial, N,N,O-bound iron(II) benzoylformate complex, [Fe(Im NNO )(BF)] (2). The X-ray crystal structure of 2 reveals that the iron centre is pentacoordinate (τ=0.5), with a vacant site located cis to the bidentate BF ligand.

A Discrete, Boron-Containing Triangular Triradical.

A neutral boron-containing triangular triradical based on a triptycene derivative has been designed and synthesized. Its structure, bonding and physical property have been studied by EPR spectroscopy, SQUID magnetometry and single crystal X-ray diffraction, as well as theoretical calculations. The triradical has a series of isosceles triangle conformations in the solution due to the Jahn-Teller distortion, leading to the splitting of the two low-lying doublet states.

Unusual Hydrogenation Reactivities of a Thiolate-Bridged Dicobalt μ-Nitride Featuring a Bent {Co-N-Co} Core.

Transition metal nitrides have received considerable attention owing to their crucial roles in nitrogen fixation and nitrogen atom transfer reactions. Compared to the early and middle transition metals, it is much more challenging to access late transition metal nitrides, especially cobalt in group 9. So far, only a handful of cobalt nitrides have been reported; consequently, their hydrogenation reactivity is largely unexplored.

Tracking an Fe (O) Intermediate for Water Oxidation in Water.

High-valent iron-oxo species are appealing for conducting O-O bond formation for water oxidation reactions. However, their high reactivity poses a great challenge to the dissection of their chemical transformations. Herein, we introduce an electron-rich and oxidation-resistant ligand, 2-[(2,2'-bipyridin)-6-yl]propan-2-ol to stabilize such fleeting intermediates.

Snapshots of Early-Stage Quantitative N Electrophilic Functionalization.

Electrophilic functionalization of N moieties in metal dinitrogen complexes typically initiates the catalytic synthesis of N-containing molecules directly from N. Despite intensive research in the last six decades, how to efficiently and even quantitatively convert N into diazenido and hydrazido species still poses a great challenge. In this regard, systematic and comprehensive investigations to elucidate the reaction intricacies are of profound significance.

Monosubstituted Doublet Sn(I) Radical Featuring Substantial Unquenched Orbital Angular Momentum.

Due to their intrinsic high reactivity, isolation of heavier analogues of carbynes remains a great challenge. Here, we report the synthesis and characterization of a neutral monosubstituted Sn(I) radical () supported by a sterically hindered hydrindacene ligand, which represents the first tin analogue of a free carbyne. Different from all Sn(I/III) species reported thus far, the presence of a sole Sn-C σ bond in renders the remaining two Sn 5p orbitals energetically almost degenerate, of which one is singly occupied and the other is empty.

Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an = 3 ground state.

Hydride complexes are important in catalysis and in iron-sulfur enzymes like nitrogenase, but the impact of hydride mobility on local iron spin states has been underexplored. We describe studies of a dimeric diiron(ii) hydride complex using X-ray and neutron crystallography, Mössbauer spectroscopy, magnetism, DFT, and calculations, which give insight into the dynamics and the electronic structure brought about by the hydrides. The two iron sites in the dimer have differing square-planar (intermediate-spin) and tetrahedral (high-spin) iron geometries, which are distinguished only by the hydride positions.

Signet-Ring-Shaped Octaphosphorus-Cobalt Complexes: Synthesis, Structure, and Functionalization Reactions with Carbene Analogs.

White phosphorus activation with low-valent metal species has proved to be very effective in converting P into small P-containing molecules with ≤ 4. Much less developed are metal-mediated P-coupling reactions that can yield selectively large polyphosphorus clusters. Herein, we report P-activation reactions with three-coordinate -heterocyclic carbene(NHC)-cobalt(0)-alkene complexes, which produce the P complexes of cobalt [(NHC)Co(μ-η:η-P)] (NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), ; 1,3-bis(2,6-diethylphenyl)imidazol-2-ylidene (IDep), ) in high yields.

Electronic structure analysis of electrochemical CO reduction by iron-porphyrins reveals basic requirements for design of catalysts bearing non-innocent ligands.

Electrocatalytic CO reduction is a possible solution to the increasing CO concentration in the earth's atmosphere, because it enables storage of energy while using the harmful CO feedstock as a starting material. Notably, iron(ii) tetraphenylporphyrin, [Fe(TPP)] (TPP = tetraphenylporphyrin tetra-anion diradical), and its derivatives have been established as one of the most promising families of homogeneous catalysts for CO reduction into CO. Our earlier work has demonstrated that [Fe(TPP)], a catalytically active species, is best described as an Fe(ii) center antiferromagnetically coupled with a TPP diradical.