Reductive Cleavage of Dioxygen Mediated by a Lewis Superacidic Bis(borane).

The bis-(borane) -{(CF)B}CF () reacts with dioxygen in the presence of decamethylferrocene (FeCp*, Cp* = pentamethylcyclopentadienyl) to deliver the salt [(μ-OH)-{B-(CF)}CF]-[FeCp*] () featuring a hydroxide sequestered by the two adjacent boron atoms. Mechanistic investigations of this formal 4-electron reduction of O suggest that it goes through the formation of a superoxide adduct [-O], which evolves through disproportionation into O and a peroxo-adduct [-O]. Upon coordination of another equivalent of , the thus-generated 4-fold boron-sequestered peroxide {[]-O} undergoes homolytic O-O bond cleavage to yield a pair of oxyl radicals [-O].

A non-innocent, π-extended N-heterobicyclic carbene-thiolate ligand.

A bidentate NHC-thiolate ligand based on the imidazo[1,5-]pyridine scaffold and featuring an extended π-system is described. It is derived from a readily available zwitterionic precursor and the chemistry of the corresponding homoleptic Ni(II) complex is investigated.

Elucidating the Correlation Between the Redox Potential, Spin State, and Crystal Structure in a Series of Ferrous Complexes with Redox-Active Ligands.

Accurately predicting the spin crossover (SCO) temperature (T) in spin crossover compounds remains a significant challenge due to their extreme sensitivity to minor variations in ligand and crystal structure. In this study, we uncover a critical link between the redox potential of ligands and SCO behavior within Hofmann-type clathrates {Fe(R-pbpy⁺)₂[μ₂-M(CN)₄]₂} (R = electron-donating or electron-withdrawing groups, M = Pd or Pt). Through precise tuning of the ligands' electronic properties, we establish a correlation between redox potential, space group, and SCO temperature, explained by an adaptation of Marcus theory of electron transfer.

σ-BH activation of NHC → BH fragments in dinuclear Cu complexes.

We explored herein the coordination properties of the bis(phosphine)NHC → BH ligand toward cationic and neutral Cu centres. The synthesis of three dinuclear Cu complexes featuring σ-BH interactions is reported. Noticeably, in each Cu complex, a BH moiety bridges two Cu centres two σ-BH interactions in a μ-ηη BH coordination mode.

Utility of 6-aza-2-thiothymine in the synthesis of novel [1,2,4]triazolo[4,3-][1,2,4]triazin-7-one derivatives: synthesis, structure elucidation, molecular docking and anti-lung cancer activity.

Using 6-aza-2-thiothymine (ATT) as a suitable precursor, a novel series of [1,2,4]triazolo[4,3-][1,2,4]triazin-7-one derivatives (7a-j) was prepared by refluxing 6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2)-one (3) with hydrazonoyl halides (1a-j) in chloroform in the presence of triethylamine. The structures of the newly synthesized compounds 7a-j were confirmed using spectral data, elemental analyses, and single-crystal X-ray diffraction results. All the synthesized triazolotriazin-7-one derivatives (7a-j) were evaluated as anti-cancer agents against PC3 (prostate cell line), A549 (lung carcinoma), PACA2 (pancreatic cancer cell line) and BJ1 (normal skin fibroblast) cell lines using MTT assay.

Synthesis and characterization of heptacoordinated molybdenum(II) complexes supported with 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligands.

Functional pincer ligands that engage in metal-ligand cooperativity and/or are capable of redox non-innocence have found a great deal of success in catalysis. These two properties may be found in metal complexes of the 2,6-bis(pyrazol-3-yl)pyridine (bpp) ligands. With this goal in mind, we have attempted the coordination of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine (LCF3) and its Bu analogue 2,6-bis(5--butylpyrazol-3-yl)pyridine (LtBu) to Mo(0) by reactions with mixed phosphine/carbonyl complexes [Mo(CO)(MeCN)(PMePh)] 1-3 (1 ≤ ≤ 3).

Electron-Transfer-Induced Structural Modification in a Thermochromic Hofmann Clathrate Derivative.

This study explores a Hofmann-type clathrate, {Fe(2,4-(OCH)-bpy)(HO)[μ-Pt(CN)][μ-Pt(CN)]·4HO}, which exhibits a thermally activated electron transfer (ET) without spin crossover. Synthesized as microcrystalline powders and single crystals, this compound reveals significant structural changes upon variation of the temperature, including alterations in the iron coordination sphere due to the large movement of the bipyridinium ligand. These changes correlate with a thermochromic hysteretic transition from yellow to orange.

Reactivity of metal hydrides with CO: going beyond formate with a high-valent cationic pentahydride Mo(vi) complex.

The cationic molybdenum pentahydride complex [MoH(depe)] (depe = 1,2-bis(diethylphosphino)ethane) is shown to undergo two consecutive reactions with carbon dioxide. In the initial, room-temperature process, classical insertion of CO into a metal-hydride bond is observed, resulting in the formation of the expected formate complex, [MoH(HCOO)(depe)]. Further reactivity is triggered at temperature above 100 °C.

Influence of triphosphine ligand coordination geometry in Mn(I) hydride complexes [(PPP)(CO)MnH] on their kinetic hydricity.

Octahedral Mn(I) complexes bearing tridentate donor ligands [(LL'L'')(CO)MnX] have recently emerged as major players in catalytic (de)hydrogenation processes. While most of these systems are still based on structurally rigid pincer scaffolds imposing a meridional coordination mode, for some more flexible tridentate ligands a facial arrangement of donor moieties becomes possible. Accordingly, the geometry of the corresponding Mn(I) hydrides [(LL'L'')(CO)MnH] directly involved in the catalytic processes, namely the nature of the donor extremity located in the -position of the hydride (CO and L for - and -configurations, respectively) may influence their hydride transfer ability.

Low-valent group 6 metals/Al(CF) donor-acceptor systems for CO activation and cleavage.

Donor-acceptor systems for CO activation combining a formally zero-valent group 6 metal as the donor with the Lewis acid Al(CF) (AlCF) are reported. They were obtained from AlCF adducts of N-complexes by N-to-CO substitution. One species was capable of C-O cleavage.

Gradual spin crossover behavior encompasing room temperature in an iron(II) complex based on a heteroscorpionate ligand.

In this paper, we report the synthesis of six novel triazole-based heteroscorpionate ligands based on heterocycle metathesis reactions and their iron(II) complexes. Single crystal structure analyses were performed, the spectroscopic and magnetic properties of the obtained complexes were studied and their spin crossover-structural relationships were compared to those obtained for their pyrazole-based analogues reported in the literature. In particular, the amino derivative complex bis[hydrobis(pyrazol-1-yl)(3-amino-1,2,4-triazol-1-yl)]iron(II) obtained by post-synthetic catalytic nitro-group reduction under pressure of hydrogen in an autoclave presents a scarce gradual spin crossover behavior at room temperature.

Borohydride Compounds Catalyze the Selective 4e Reduction of CO with 9-BBN.

The selective double hydroboration of CO into bis(boryl)acetal (BBA) is a challenging yet appealing reduction process since BBA can be used as a versatile C and C sources for the synthesis of value-added products. In the present study, we demonstrate that simple borohydride compounds are efficient and selective catalysts for the synthesis of BBA when using 9-borabicyclo(3.3.

Combining electron transfer, spin crossover, and redox properties in metal-organic frameworks.

Hofmann coordination polymers (CPs) that couple the well-studied spin transition of the Fe central ion with electron-responsive ligands provide an innovative strategy toward multifunctional metal-organic frameworks (MOFs). Here, we developed a 2D planar network consisting of metal-cyanide-metal sheets in an unusual coordination mode, brought about by infinitely π-stacked redox-active bipyridinium derivatives as axial ligands. The obtained family of materials show vivid thermochromism attributed to electron transfer and/or electronic spin state change processes that can occur either independently or concomitantly.

Hofmann Clathrates: A "Blue Box" Approach to Modulate Spin-Crossover Properties.

Hofmann coordination polymers (CPs) with cationic ligands provide an innovative strategy for recognizing π-electron-rich aromatic molecules - similar to the "little blue box". In this study, we demonstrate that hydroquinone molecules can be incorporated into these coordination polymers when redox-active bipyridinium derivatives are used as axial ligands. The insertion leads to a significant structural modification, resulting in a shift of the spin transition by 150 K and an approximate 23 % increase in volume, caused by the strong donor-acceptor π-π stacking interaction formed between the ligands and the guest molecule.

Coordination of Al(CF) B(CF) on group 6 end-on dinitrogen complexes: chemical and structural divergences.

The coordination of the Lewis superacid tris(pentafluorophenyl)alane (AlCF) to phosphine-supported, group 6 bis(dinitrogen) complexes [ML(N)] is explored, with M = Cr, Mo or W and L = dppe (1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), dmpe (1,2-bis(dimethylphosphino)ethane) or 2 × PMePh. Akin to tris(pentafluorophenyl)borane (BCF), AlCF can form 1 : 1 adducts by coordination to one distal nitrogen of general formula -[ML(N){(μ-η:η-N)Al(CF)}]. The boron and aluminium adducts are structurally similar, showing a comparable level of N push-pull activation.

Single electron reduction of NHC-CO-borane compounds.

The carbon dioxide radical anion [CO˙] is a highly reactive species of fundamental and synthetic interest. However, the direct one-electron reduction of CO to generate [CO˙] occurs at very negative reduction potentials, which is often a limiting factor for applications. Here, we show that NHC-CO-BR species - generated from the Frustrated Lewis Pair (FLP)-type activation of CO by N-heterocyclic carbenes (NHCs) and boranes (BR) - undergo single electron reduction at a less negative potential than free CO.

Structure and Synthesis of Vindolicine and Derivatives.

This article describes the reaction of vindoline with formaldehyde and trimethyl orthoformate to prepare vindolicine, tris-vindolicinyl methane and higher molecular weight homologues. The synthesis of 10-formyl vindoline as an intermediate allowed further exploration of its chemistry, in particular the reaction with acetone which yielded a symmetrical dimer, which was further reacted with vindoline to give molecules containing three and four vindoline units. These molecules were characterized by NMR and for some of them (vindolicine, 10-formyl vindoline, 10-(1'-(but-1'-en-3'-one))-vindoline) by X-ray crystallography.

Two active species from a single metal halide precursor: a case study of highly productive Mn-catalyzed dehydrogenation of amine-boranes intermolecular bimetallic cooperation.

Metal-metal cooperation for inert bond activation is a ubiquitous concept in coordination chemistry and catalysis. While the great majority of such transformations proceed intramolecular mode in binuclear complexes, to date only a few examples of intermolecular small molecule activation using usually bimetallic frustrated Lewis pairs (M⋯M') have been reported. We introduce herein an alternative approach for the intermolecular bimetallic cooperativity observed in the catalytic dehydrogenation of amine-boranes, in which the concomitant activation of N-H and B-H bonds of the substrate the synergetic action of Lewis acidic (M) and basic hydride (M-H) metal species derived from the same mononuclear complex (M-Br).

Mechanochemical Studies on Coupling of Hydrazines and Hydrazine Amides with Phenolic and Furanyl Aldehydes-Hydrazones with Antileishmanial and Antibacterial Activities.

Hydrazone compounds represent an important area of research that includes, among others, synthetic approaches and biological studies. A series of 17 hydrazones have been synthesized by mechanochemical means. The fragments chosen were phenolic and furanyl aldehydes coupled with 12 heterocyclic hydrazines or hydrazinamides.

An Experimental and Computational Investigation Rules Out Direct Nucleophilic Addition on the N Ligand in Manganese Dinitrogen Complex [Cp(CO) Mn(N )].

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO) Mn(N )] (1, Cp=η -cyclopentadienyl, C H ) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N )MnCOPh]Li (3) that is stable only below -40 °C.

Synthesis and Coordination of a Bisphosphine-[NHC-borane] Compound: A Ligand Framework for Bimetallic Structure Featuring a Boron-Bridging Moiety.

We report herein the synthesis of a bisphosphine-[NHC-BH] compound and its coordination toward gold. The ligand is shown to support a bimetallic structure bisphosphine-[NHC-BH](AuCl). The abstraction of one chloride from the gold metal center triggers the activation of a BH fragment, leading to the reductive elimination of H and the formation of a dicationic Au complex featuring Au centers at the +0.

Assessing Combinations of B(C F ) and N -Derived Molybdenum Nitrido Complexes for Heterolytic Bond Activation.

Two different dinitrogen-derived molybdenum nitrido complexes varying by their geometry, ligand spheres and oxidations states were shown to engage their N ligand in dative bonding with the strong Lewis acid B(C F ) . The stable adducts were assessed for frustrated Lewis pair-type heterolytic E-H bond splitting of hydrosilanes (E=Si) and HB(C F ) . Whereas Si-H bond activation was achieved, HB(C F ) was shown to substitute B(C F ) in a quantitative or equilibrated fashion, depending on the nature of the nitrido complex.

Design of Anti-infectious Agents from Lawsone in a Three-Component Reaction with Aldehydes and Isocyanides.

The first effective synthetic approach to naphthofuroquinones via a reaction involving lawsone, various aldehydes, and three isocyanides under microwave irradiation afforded derivatives in moderate to good yields. In addition, for less-reactive aldehydes, two naphtho-enaminodione quinones were obtained for the first time, as result of condensation between lawsone and isocyanides. X-ray structure determination for and 2D-NMR spectra of confirmed the obtained structures.

Pressure Tuning of Coupled Structural and Spin State Transitions in the Molecular Complex [Fe(HB(pz))(phen)].

The large volume change, which accompanies the molecular spin crossover (SCO) phenomenon in some transition metal complexes, prompts frequently the coupling of the SCO with other instabilities. Understanding the driving mechanism(s) of such coupled phase transitions is not only important for fundamental reasons but also provides scope for the development of multifunctional materials. The general theoretical expectation is that the coupling has elastic origin, and the sequence of transitions can be tuned by an externally applied pressure, but dedicated experiments remain scarce.