Iron(II) Complexes Featuring a Redox-Active Dihydrazonopyrrole Ligand.

Nature uses control of the secondary coordination sphere to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that more typically engage in one electron redox processes.

Heterocyclic-Additive-Activated Dinuclear Dysprosium Electrocatalysts for Heterogeneous Water Oxidation.

Heterogeneous catalysis based on air-stable lanthanide complexes is relatively rare, especially for electrochemical water oxidation and reduction. Therefore, it is highly desired to investigate the synergy caused by cocatalysts on the lanthanide complex family for heterogeneous catalysis because of their structural diversity, air/moisture insensitivity, and easy preparation under an air atmosphere. Two mononuclear and three dinuclear dysprosium complexes containing a series of Schiff-base ligands have been demonstrated as robust electrocatalysts for triggering heterogeneous water oxidation in alkaline solution, in which the complex [Dy(hmb)(OAc)]·MeCN() was revealed to have the best activity toward heterogeneous water oxidation among all five complexes in the present study.

Structure and magnetic properties of a novel heteroheptanuclear metal string complex [NiRuNi(μ-teptra)(NCS)](PF).

We report the synthesis of a novel heteroheptanuclear metal string complex (HMSC) [NiRuNi(μ-teptra)(NCS)](PF) 1 supported by tetra-pyridyl-tri-amine (Hteptra) ligands. We employed X-ray diffraction and other spectroscopic techniques to characterize the complex. The observed remarkably short Ru-Ru distance of 2.

Reversible homolytic activation of water metal-ligand cooperativity in a T-shaped Ni(ii) complex.

A T-shaped Ni(ii) complex [DHPy]Ni has been prepared and characterized. EPR spectra and DFT calculations of this complex suggest that the electronic structure is best described as a high-spin Ni(ii) center antiferromagnetically coupled with a ligand-based radical. This complex reacts with water at room temperature to generate the dimeric complex [DHPy]Ni(μ-OH)Ni[DHPyH] which has been thoroughly characterized by SXRD, NMR, IR and deuterium-labeling experiments.

Imidazole for Pyridine Substitution Leads to Enhanced Activity Under Milder Conditions in Cobalt Water Oxidation Electrocatalysis.

A previously reported cobalt complex featuring a tetraimidazolyl-substituted pyridine chelate is an active water oxidation electrocatalyst with moderate overpotential at pH 7. While this complex decomposes rapidly to a less-active species under electrocatalytic conditions, detailed electrochemical studies support the agency of an initial molecular catalyst. Cyclic voltammetry measurements confirm that the imidazolyl donors result in a more electron-rich Co center when compared with previous pyridine-based systems.

Redox Activity, Ligand Protonation, and Variable Coordination Modes of Diimino-Pyrrole Complexes of Palladium.

Ligand-based functionality is a prominent method of increasing the reactivity or stability of metal centers in coordination chemistry. Some of the most successful catalysts use ligand-based redox activity, pendant protons, or hemilability in order to specifically accelerate catalysis. Here we report the diimino-pyrrole ligand DIPyH (DIPy = 2,5-bis( N-cyclohexyl-1-( p-tolyl)methanimine)pyrrolide), which exhibits all three of these ligand properties.

Ligand-Based Storage of Protons and Electrons in Dihydrazonopyrrole Complexes of Nickel.

A newly developed dihydrazonopyrrole ligand and corresponding Ni complexes have been synthesized and thoroughly characterized. Electrochemical studies and chemical reactivity tests show that these complexes can reversibly store both electrons and protons, or equivalently H-atoms, via ligand-based events. The stored H-atom equivalent can be transferred to small molecules such as acetonitrile or oxygen.

Third-Generation Light-Driven Symmetric Molecular Motors.

Symmetric molecular motors based on two overcrowded alkenes with a notable absence of a stereogenic center show potential to function as novel mechanical systems in the development of more advanced nanomachines offering controlled motion over surfaces. Elucidation of the key parameters and limitations of these third-generation motors is essential for the design of optimized molecular machines based on light-driven rotary motion. Herein we demonstrate the thermal and photochemical rotational behavior of a series of third-generation light-driven molecular motors.

Locked synchronous rotor motion in a molecular motor.

Biological molecular motors translate their local directional motion into ordered movement of other parts of the system to empower controlled mechanical functions. The design of analogous geared systems that couple motion in a directional manner, which is pivotal for molecular machinery operating at the nanoscale, remains highly challenging. Here, we report a molecular rotary motor that translates light-driven unidirectional rotary motion to controlled movement of a connected biaryl rotor.

Stable, crystalline boron complexes with mono-, di- and trianionic formazanate ligands.

Redox-active formazanate ligands are emerging as tunable electron-reservoirs in coordination chemistry. Here we show that boron diphenyl complexes with formazanate ligands, despite their (formal) negative charge, can be further reduced by up to two electrons. A combined crystallographic, spectroscopic and computational study establishes that formazanate ligands are stable in mono-, di- and trianionic form.

Spin-Crossover in a Pseudo-tetrahedral Bis(formazanate) Iron Complex.

Spin-crossover in a pseudo-tetrahedral bis(formazanate) iron(II) complex (1) is described. Structural, magnetic, and spectroscopic analyses indicate that this compound undergoes thermal switching between an S=0 and an S=2 state, which is very rare in four-coordinate complexes. The transition to the high-spin state is accompanied by an increase in Fe-N bond lengths and a concomitant contraction of intraligand N-N bonds.

Enantiopure Functional Molecular Motors Obtained by a Switchable Chiral-Resolution Process.

Molecular switches, rotors, and motors play an important role in the development of nano-machines and devices, as well as responsive and adaptive functional materials. For unidirectional rotors based on chiral overcrowded alkenes, their stereochemical homogeneity is of crucial importance. Herein, a method to obtain new and functionalizable overcrowded alkenes in enantiopure form is presented.

Reduction of (Formazanate)boron Difluoride Provides Evidence for an N-Heterocyclic B(I) Carbenoid Intermediate.

Despite the current interest in structure and reactivity of sub-valent main group compounds, neutral boron analogues of N-heterocyclic carbenes have been elusive due to their high reactivity. Here we provide evidence that 2-electron reduction of a (formazanate)BF2 precursor leads to NaF elimination and formation of an N-heterocyclic boron carbenoid, and describe the formation of a series of unusual BN heterocycles that result from trapping of this fragment. Subsequent chemical oxidation by XeF2 demonstrates that the trapped (formazanate)B fragment retains carbenoid character and regenerates the boron difluoride starting material in good yield.

Formazanate ligands as structurally versatile, redox-active analogues of β-diketiminates in zinc chemistry.

A range of tetrahedral bis(formazanate)zinc complexes with different steric and electronic properties of the formazanate ligands were synthesized. The solid-state structures for several of these were determined by X-ray crystallography, which showed that complexes with symmetrical, unhindered ligands prefer coordination to the zinc center via the terminal N atoms of the NNCNN ligand backbone. Steric or electronic modifications can override this preference and give rise to solid-state structures in which the formazanate ligand forms a 5-membered chelate by binding to the metal center via an internal N atom.

Alkali metal salts of formazanate ligands: diverse coordination modes as a result of the nitrogen-rich [NNCNN] ligand backbone.

Alkali metal salts of redox-active formazanate ligands were prepared, and their structures in the solid-state and in solution are determined. The nitrogen-rich [NNCNN] backbone of formazanates results in a varied coordination chemistry, with both the internal and terminal nitrogen atoms available for bonding with the alkali metal. The potassium salt K[PhNNC(p-tol)NNPh]·2THF (1-K) is dimeric in the solid state and even in THF solution, as a result of the K atom bridging via interaction with a terminal N atom and the aromatic ring of a second unit.

Alkene isomerisation catalysed by a ruthenium PNN pincer complex.

The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable-temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex.

CO₂ fixation by dicopper(II) complexes in hypodentate framework of N₈O₂.

A new ligand with N8O2 donors containing three potential metal-binding sites (H₂L) and its tricopper(II) complex 1 are synthesized. The tricopper species is found to be formed from a hypodentate dicopper(II) complex 2 in basic solutions. Complex 2 may be isolated from the reaction of H₂L with a copper source under acidic conditions.

The formazanate ligand as an electron reservoir: bis(formazanate) zinc complexes isolated in three redox states.

The synthesis of bis(formazanate) zinc complexes is described. These complexes have well-behaved redox-chemistry, with the ligands functioning as a reversible electron reservoir. This allows the synthesis of bis(formazanate) zinc compounds in three redox states in which the formazanate ligands are reduced to "metallaverdazyl" radicals.

Kinetic and mechanistic studies of geometrical isomerism in neutral square-planar methylpalladium complexes bearing unsymmetrical bidentate ligands of alpha-aminoaldimines.

A series of hemilabile ligands of alpha-aminoaldimines and their methylpalladium complexes have been prepared and characterized. Neutral square-planar methylpalladium complexes in the form of [R(1)R(2)NCMe(2)CH horizontal lineNR]Pd(Me)Cl (R = Me, R(1) = R(2) = Me (3a); R = Me, R(1) = R(2) = Et (3b); R = Et, R(1) = R(2) = Me (4a); R = (n)Pr, R(1) = R(2) = Me (5a); R = (i)Pr, R(1) = R(2) = Me (6a); R = (i)Pr, R(1) = R(2) = Et (6b); R = (i)Pr, (R(1), R(2)) = c-C(4)H(8) (6c); R = (i)Pr, R(1) = (i)Pr, R(2) = H (6d); R = (i)Pr, R(1) = (t)Bu, R(2) = H (6e); R = (t)Bu, R(1) = R(2) = Me (7a); R = (t)Bu, R(1) = R(2) = Et (7b); R = (t)Bu, (R(1), R(2)) = c-C(4)H(8) (7c); R = (t)Bu, R(1) = (i)Pr, R(2) = H (7d); R = (t)Bu, R(1) = (t)Bu, R(2) = H (7e); R = Ph, R(1) = R(2) = Me (8a); R = Ph, R(1) = R(2) = Et (8b)) show geometrical isomerism. The relative ratios of trans/cis isomers appear to be predominated by the steric hindrance between the Pd-bound methyl group and imino or amino substituents (R and R(1) and R(2)).

Unsymmetrical bidentate ligands of alpha-aminoaldimines leading to sterically controlled selectivity of geometrical isomerism in square planar coordination.

New alpha-aminoaldimines with the formula of Et(2)NCMe(2)CH[double bond, length as m-dash]NR (R = (i)Pr, (t)Bu, Ph) and their dichloro or diacetato complexes of Ni, Pd, Pt are prepared and structurally characterized. A nickel complex is in a distorted tetrahedral configuration, and the Pd and Pt complexes () are of square planar form. The alpha-aminoaldimines can chelate to the metal in a C(2)-unsymmetric bidentate motif through the hetero functionalities of amine and imine, which show comparable trans influence.