Synthesis and Reactivity of Low-Coordinate Iron(II) Fluoride Complexes and Their Use in the Catalytic Hydrodefluorination of Fluorocarbons

A Bis-Cyclopentadienyl Ligand-Supported Di-Iron Trihydride Motif as a Synthon for Access to Heterobimetallic Trinuclear Complexes

Herein, we report the synthesis of a flexible bis-cyclopentadienyl ligand L (the doubly deprotonated form of H2L (1,3-bis(2,4-di-tert-butylcyclopentadienyldimethylsilyl)benzene)), demonstrating its ability to stabilize a series of di-iron hydrido complexes. Notably, this ligand facilitates the isolation of an unprecedented anionic cyclopentadienyl ligand-supported di-iron trihydride complex, LFe2(μ-H)3Li(THF) (2), functioning as a synthon for the [Fe2(μ-H)3]- core and providing access to heterobimetallic complexes 4-6 with coinage metals.

Unlocking the Metalation Applications of TMP-powered Fe and Co(II) bis(amides): Synthesis, Structure and Mechanistic Insights

Typified by LiTMP and TMPMgCl.LiCl, (TMP=2,2,6,6-tetramethylpiperidide), s-block metal amides have found widespread applications in arene deprotonative metalation. On the contrary, transition metal amides lack sufficient basicity to activate these substrates. Breaking new ground in this field, here we present the synthesis and full characterisation of earth-abundant transition metals M(TMP)2 (M=Fe, Co). Uncovering a new reactivity profile towards fluoroarenes, these amide complexes can promote direct M-H exchange processes regioselectively using one or two of their basic amide arms. Remarkably, even when using a perfluorinated substrate, selective C-H metalation occurs leaving C-F bonds intact. Their kinetic basicity can be boosted by LiCl or NBu4Cl additives which enables formation of kinetically activated ate species. Combining spectroscopic and structural studies with DFT calculations, mechanistic insights have been gained on how these low polarity metalation processes take place. M(TMP)2 can also be used to access ferrocene and cobaltocene by direct deprotonation of cyclopentadiene and undergo efficient CO2 insertion of both amide groups under mild reaction conditions.

Mononuclear Four-Coordinate Bis-Fluoride Bis-NHC Complexes of Chromium(II), Iron(II), and Cobalt(II)

The reaction between silylamido complexes of Cr(II), Fe(II), and Co(II) and IMes·2HF salt in the presence of IMes (IMes = 1,3-dimesitylimidazol-2-ylidene) led to isolation of Cr(IMes)2F2 (2-Cr), Fe(IMes)2F2 (2-Fe), and Co(IMes)2F2 (2-Co). X-ray structural studies revealed that 2-Cr adopts square planar geometry, while 2-Fe and 2-Co have distorted tetrahedral geometry. Magnetic susceptibility studies of 2-Cr, 2-Fe, and 2-Co were consistent with high-spin complexes, S = 2 for 2-Cr/2-Fe and S = 3/2 for 2-Co. We demonstrated that fluoride can be successfully exchanged for cyanide and azide using trimethylsilyl cyanide and trimethylsilyl azide (3-Fe and 4-Fe). DFT studies suggest that the preference of 2-Cr to adopt square planar geometry over tetrahedral is due to its d4 metal center, where four electrons fill the lower-lying d-orbitals.

Evidence for a High-Valent Iron-Fluoride That Mediates Oxidative C(sp3)-H Fluorination

[Fe^II(NCCH₃)(NTB)](OTf)₂ (NTB = tris(2-benzimidazoylmethyl)amine, OTf = trifluoromethanesulfonate) was reacted with difluoro(phenyl)-λ³-iodane (PhIF₂) in the presence of a variety of saturated hydrocarbons, resulting in the oxidative fluorination of the hydrocarbons in moderate-to-good yields. Kinetic and product analysis point towards a hydrogen atom transfer oxidation prior to fluorine radical rebound to form the fluorinated product. The combined evidence supports the formation of a formally Fe^IV(F)₂ oxidant that performs hydrogen atom transfer followed by the formation of a dimeric μ-F-(Fe^III)₂ product that is a plausible fluorine atom transfer rebound reagent. This approach mimics the heme paradigm for hydrocarbon hydroxylation, opening up avenues for oxidative hydrocarbon halogenation.

Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an S = 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 ab initio 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. These are strongly coupled to give an S total = 3 ground state with substantial magnetic anisotropy, and the merits of both localized and delocalized spin models are discussed. The dynamic nature of the sites is dependent on crystal packing, as shown by changes during a phase transformation that occurs near 160 K. The change in dynamics of the hydride motion leads to insight into its influence on the electronic structure. The accumulated data indicate that the two sites can trade geometries by rotating the hydrides, at a rate that is rapid above the phase transition temperature but slow below it. This small movement of the hydrides causes large changes in the ligand field because they are strong-field ligands. This suggests that hydrides could be useful in catalysis not only due to their reactivity, but also due to their ability to rapidly modulate the local electronic structure and spin states at metal sites.

Regioselective Transfer Hydrogenative Defluorination of Polyfluoroarenes Catalyzed by Bifunctional Azairidacycle

The catalytic hydrodefluorination (HDF) with a bifunctional azairidacycle using HCOOK was examined for cyano- and chloro-substituted fluoroarenes, including penta- and tetrafluorobenzonitriles, tetrafluoroterephthalonitrile, tetrafluorophthalonitrile, 3-chloro-2,4,5,6-tetrafluoropyridine, and 4-cyano-2,3,5,6-tetrafluoropyridine. The reaction was performed in the presence of a controlled amount of HCOOK with a substrate/catalyst ratio (S/C) of 100 in a 1:1 mixture of 1,2-dimethoxyethane (DME) and H2O at an ambient temperature of 30 °C to obtain partially fluorinated compounds with satisfactory regioselectivities. The C–F bond cleavage proceeded favorably at the para position of substituents other than fluorine, which is in consonance with the nucleophilic aromatic substitution mechanism. In the HDF of tetrafluoroterephthalonitrile and 4-cyano-2,3,5,6-tetrafluoropyridine, which do not contain a fluorine atom at the para position of the cyano group, the double defluorination occurred solely at the 2- and 5-positions, as confirmed by X-ray crystallography. The HDF of 3-chloro-2,4,5,6-tetrafluoropyridine gave preference to the C–F bond cleavage over the C–Cl bond cleavage, unlike the dehalogenation pathway via electron-transfer radical anion fragmentation. In addition, new azairidacycles with an electron-donating methoxy substituent on the C–N chelating ligand were synthesized and served as a catalyst precursor (0.2 mol%) for the transfer hydrogenative defluorination of pentafluoropyridine, leading to 2,3,5,6-tetrafluoropyridine with up to a turnover number (TON) of 418.

Visible-light-induced defluorinative carbonylative coupling of alkyl iodides with α-trifluoromethyl substituted styrenes

A visible-light-mediated defluorinative carbonylative cross-coupling of alkyl iodides with α-trifluoromethyl styrenes has been developed. The reaction occurs at room temperature under blue light irradiation, and various gem-difluoroalkenes were obtained in moderate to good yields. Synthetic transformations of the obtained product were performed as well.

Slow magnetic relaxation in a trigonal-planar mononuclear Fe(II) complex

Based on a β-diketiminate ligand, an iron(III) tetrahedral high-spin complex, [LFeIII(Cl)2] (1), and an iron(II) high-spin triangular planar complex, [LFeIICl] (2), have been synthesized and structurally characterized. Also, complex 1...

Significant Role of Oxygen Dopants in Photocatalytic PFCA Degradation over h-BN

The activation of the C(sp³)-F bond is extremely difficult due to its unreactive nature. The importance of this bond activation is recently highlighted because extensive distribution of perfluorocarboxylic acids (PFCAs) (C_nF_2n+1COOH) has emerged as a challenging environmental issue. Photocatalytic degradation of PFCAs over a few semiconducting light absorbers is known to remove these water and soil resilient contaminants but with limited efficiency. This work reports density functional theory calculations, through which we present a detailed mechanistic study of photocatalytic degradation of CF₃COOH (the shortest member of the PFCA family) over hexagonal boron nitride (h-BN). Our results clearly demonstrate that the existence of point defects is necessary to activate the h-BN plane for photocatalytic dissociation of the C-F bond. Specifically, we show that vacancies create strong Lewis acid or base sites (B or N vacancy, respectively) that facilitate the activation of the C(sp³)-F bond considerably. Furthermore, this study presents vivid theoretical evidence for the significant role of oxygen dopants, which mitigate the strength of the active sites and promote PFCA degradation over h-BN. Our calculations suggest that while the very stable intermediates generated during the reaction, in the case of h-BN with B or N vacancies, practically poison the catalyst, oxygen dopants make the degradation much more plausible and controllable. This work thus provides both an explanation for recently observed photocatalytic activity of h-BN to decompose PFCAs and valuable insights for exploring defected two-dimensional materials for activating and removing the fluorine-containing contaminants from water and soil.

Rapid Iron(III)-Fluoride-Mediated Hydrogen Atom Transfer

We anticipate high-valent metal-fluoride species will be highly effective hydrogen atom transfer (HAT) oxidants because of the magnitude of the H-F bond (in the product) that drives HAT oxidation. We prepared a dimeric Fe^III (F)-F-Fe^III (F) complex (1) by reacting [Fe^II (NCCH₃ )₂ (TPA)](ClO₄ )₂ (TPA=tris(2-pyridylmethyl)amine) with difluoro(phenyl)-λ³ -iodane (difluoroiodobenzene). 1 was a sluggish oxidant, however, it was readily activated by reaction with Lewis or Brønsted acids to yield a monomeric [Fe^III (TPA)(F)(X)]⁺ complex (2) where X=F/OTf. 1 and 2 were characterized using NMR, EPR, UV/Vis, and FT-IR spectroscopies and mass spectrometry. 2 was a remarkably reactive Fe^III reagent for oxidative C-H activation, demonstrating reaction rates for hydrocarbon HAT comparable to the most reactive Fe^III and Fe^IV oxidants.

Catalytic Hydrodefluorination via Oxidative Addition, Ligand Metathesis, and Reductive Elimination at Bi(I)/Bi(III) Centers

Herein, we report a hydrodefluorination reaction of polyfluoroarenes catalyzed by bismuthinidenes, Phebox-Bi(I) and OMe-Phebox-Bi(I). Mechanistic studies on the elementary steps support a Bi(I)/Bi(III) redox cycle that comprises C(sp²)-F oxidative addition, F/H ligand metathesis, and C(sp²)-H reductive elimination. Isolation and characterization of a cationic Phebox-Bi(III)(4-tetrafluoropyridyl) triflate manifests the feasible oxidative addition of Phebox-Bi(I) into the C(sp²)-F bond. Spectroscopic evidence was provided for the formation of a transient Phebox-Bi(III)(4-tetrafluoropyridyl) hydride during catalysis, which decomposes at low temperature to afford the corresponding C(sp²)-H bond while regenerating the propagating Phebox-Bi(I). This protocol represents a distinct catalytic example where a main-group center performs three elementary organometallic steps in a low-valent redox manifold.

Bipyridinium and Phenanthrolinium Dications for Metal-Free Hydrodefluorination: Distinctive Carbon-Based Reactivity

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications is reported. Calculations of Hydride Ion Affinity (HIA) values indicate high carbon-based Lewis acidity at the ortho and para positions. This arises in part from extensive LUMO delocalization across the aromatic backbones. Species [C₁₀ H₆ R₂ N₂ CH₂ CH₂ ]²⁺ (R=H [1 a]²⁺ , Me [1 f]²⁺ , tBu [1 g]²⁺ ), and [C₁₂ H₄ R₄ N₂ CH₂ CH₂ ]²⁺ (R=H [2 a]²⁺ , Me [2 b]²⁺ ) were prepared and evaluated for use in the initiation of hydrodefluorination (HDF) catalysis. Compound [2 a]²⁺ proved highly effective towards generating catalytically active silylium cations via Lewis acid-mediated hydride abstraction from silane. This enabled the HDF of a range of aryl- and alkyl- substituted sp³ (C-F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis-2,4,6-(CF₃ )₃ C₆ H₉ . The dications are shown to act as hydride acceptors with the isolation of neutral species C₁₆ H₁₄ N₂ (3 a) and C₁₆ H₁₀ Me₄ N₂ (3 b) and monocationic species [C₁₄ H₁₃ N₂ ]⁺ ([4 a]⁺ ) and [C₁₈ H₂₁ N₂ ]+ ([4 b]⁺ ). Experimental and computational data provide further support that the dications are initiators in the generation of silylium cations.

Facilitating the Ferration of Aromatic Substrates through Intramolecular Sodium Mediation

Exploiting cooperative effects between Na and FeII centres present in tris(amide) ferrate complexes has led to the chemoselective ferration of pentafluorobenzene, benzene, toluene, anisole, and pyridine being realised at room temperature. The importance of this bimetallic partnership is demonstrated by neither the relevant sodium amide (NaHMDS or NaTMP) nor the FeII amide Fe(HMDS)2 efficiently metallating these substrates under the conditions of this study. By combining NMR studies with the isolation of key intermediates and DFT calculations, we offer a possible mechanism for how these reactions take place, uncovering a surprising reaction pathway in which the metals cooperate in a synchronised manner. Although the isolated products are formally the result of Fe-H exchange, theoretical calculations indicate that the aromatic substrates undergo Na-H exchange followed by fast intramolecular transmetallation to Fe, thus stabilizing the newly generated aryl fragment.

Low-Coordinate Iron Chalcogenolates and Their Complexes with Diethyl Ether and Ammonia

Treatment of Fe{N(SiMe₃)₂}₂ with 2 equiv of the appropriate phenol or thiol affords the dimers {Fe(OC₆H₂-2,6-Bu^t₂-4-Me)₂}₂ (1) and {Fe(OC₆H₃-2,6-Bu^t₂)₂}₂ (2) or the monomeric Fe{SC₆H₃-2,6-(C₆H₃-2,6-Prⁱ₂)₂}₂ (3) in moderate to excellent yields. Recrystallization of 1 and 2 from diethyl ether gives the corresponding three-coordinate ether complexes Fe(OC₆H₃-2,6-Bu^t₂-4-Me)₂(OEt₂) (4) and Fe(OC₆H₃-2,6-Bu^t₂)₂(OEt₂) (5). In contrast, no diethyl ether complex is formed by the dithiolate 3. The ¹H NMR spectra of 4 and 5 show equilibria between the ether complexes and the base-free dimers. A comparison of these spectra with those of the dimeric 1 and 2 allows an unambiguous assignment of the paramagnetically shifted signals. Treatment of 1 with excess ammonia gives the tetrahedral diammine Fe(OC₆H₂-2,6-Bu^t₂-4-Me)₂(NH₃)₂ (6). Ammonia is strongly coordinated in 6, with no apparent loss of ammine ligand either in solution or upon heating under low pressure. In contrast, significantly weaker ammonia coordination is observed when dithiolate 3 is treated with excess ammonia, which gives the diammine Fe{SC₆H₃-2,6-(2,6-Prⁱ₂-C₆H₃)₂}₂(NH₃)₂ (7). Complex 7 readily loses ammonia either in solution or under reduced pressure to give the monoammine complex Fe{SC₆H₃-2,6-(2,6-Prⁱ₂-C₆H₃)₂}₂(NH₃) (8). The weak binding of ammonia by iron thiolate 7 reflects the likely behavior of the proposed iron-sulfur active site in nitrogenases, where release of ammonia is required to close the catalytic cycle.

Pd/Cu-Catalyzed Defluorinative Carbonylative Coupling of Aryl Iodides and gem-Difluoroalkenes: Efficient Synthesis of α-Fluorochalcones

An unprecedented and challenging defluorinative carbonylation was achieved. Enabled by a Pd/Cu cooperative catalyst system, the first example of defluorinative carbonylative coupling has been established. With gem-difluoroalkenes and aryl iodides as the substrates, this methodology offers flexible and facile access to privileged α-fluorochalcones under mild reaction conditions in moderate-to-excellent yields. Mechanistic studies indicated transmetalation between palladium and copper intermediates as a crucial step of the catalytic cycle.

Experimental and Computational Studies of the Iron-Catalyzed Selective and Controllable Defluorosilylation of Unactivated Aliphatic gem-Difluoroalkenes

The first iron-catalyzed defluorosilylation of unactivated gem-difluoroalkenes was developed, delivering gem-disilylated alkenes and (E)-silylated alkenes with excellent efficiency. This protocol features good functional group compatibility and excellent regio- and stereoselectivity, enabling the late-stage silylation of biologically relevant compounds, thus providing good opportunities for applications in medicinal chemistry. Preliminary mechanistic studies and DFT calculations reveal that a nucleophilic addition and elimination of the second C-F bond might be involved in the disilylation catalytic system, demonstrating unusual reactivity characteristics of iron catalysis.

Catalyst-Free Hydrodefluorination of Perfluoroarenes with NaBH4

Presented is an economical means of removing fluorine from various highly fluorinated arenes using NaBH₄. The procedure was adapted for different classes of perfluoroarenes. A novel isomer of an emerging class of organic dyes based on the carbazole phthalonitrile motif was succinctly synthesized in two steps from tetrafluorophthalonitrile, demonstrating the utility of the hydrodefluorination procedure. Initial exploration of the dye shows it to be photoactive and capable of facilitating contrathermodynamic styrenoid E/Z isomerization.

Ruthenium-Catalyzed Hydrodefluorination with Silane as the Directing and Reducing Group

We describe herein an efficient and selective Ru-catalyzed intramolecular HDF directed by a silyl group, which is readily installed, and removable and transformable following the HDF reaction. The hydrosilyl group in polyfluoroaryl silane acts not only as the directing group but also as the internal reductant, enabling precise control of the ortho-selectivity and avoiding overdefluorination. Mechanistic studies reveal a plausible catalytic cycle involving a Ru(IV)-aryne intermediate.

The electronic structure of a β-diketiminate manganese hydride dimer

The electronic structure of a dimeric manganese hydride catalyst supported by β-diketiminate ligands, [(2,6-iPr2PhBDI)Mn(μ-H)]2, was investigated with density functional theory. A triple bond between the manganese centres was anticipated from simple electron-counting rules; however, calculations revealed Mn-Mn Mayer bond orders of 0.21 and 0.27 for the ferromagnetically-coupled and antiferromagnetically-coupled extremes, respectively. In accordance with experimentally determined Heisenberg exchange coupling constants of -15 ± 0.1 cm-1 (SQUID) and -10.2 ± 0.7 cm-1 (EPR), the calculated J0 value of -10.9 cm-1 confirmed that the ground state involves antiferromagnetic coupling between high spin Mn(ii)-d5 centres. The effect of steric bulk on the bond order was examined via a model study with the least sterically-demanding version of the β-diketiminate ligand and was found to be negligible. Mixing between metal- and β-diketiminate-based orbitals was found to be responsible for the absence of a metal-metal multiple bond. The bridging hydrides give rise to a relatively close positioning of the metal centres, while bridging atoms possessing 2p orbitals result in longer Mn-Mn distances and more stable dimers. The synthesis and characterization of the bridging hydroxide variant, [(2,6-iPr2PhBDI)Mn(μ-OH)]2, provides experimental support for these assessments.

A Phosphine Functionalized β-Diketimine Ligand for the Synthesis of Manifold Metal Complexes

A bis(diphenyl)-phosphine functionalized β-diketimine (PNac-H) was synthesized as a flexible ligand for transition metal complexes. The newly designed ligand features symmetrically placed phosphine moieties around a β-diketimine unit, forming a PNNP-type pocket. Due to the hard and soft donor atoms (N vs. P) the ligand can stabilize various coordination polyhedra. A complete series ranging from coordination numbers 2 to 6 was realized. Linear, trigonal planar, square planar, tetrahedral, square pyramidal, and octahedral coordination arrangements containing the PNac-ligand around the metal center were observed by using suitable metal sources. Hereby, PNac-H or its anion PNac- acts as mono-, bi- and tetradendate ligand. Such a broad flexibility is unusual for a rigid tetradentate system. The structural motifs were realized by treatment of PNac-H with a series of late transition metal precursors, for example, silver, gold, nickel, copper, platinum, and rhodium. The new complexes have been fully characterized by single crystal X-ray diffraction, NMR, IR, UV/Vis spectroscopy, mass spectrometry as well as elemental analysis. Additionally, selected complexes were investigated regarding their photophysical properties. Thus, PNac-H proved to be an ideal ligand platform for the selective coordination and stabilization of various metal ions in diverse polyhedra and oxidation states.

Synthesis and Structure of Iron (II) Complexes of Functionalized 1,5-Diaza-3,7-Diphosphacyclooctanes

In order to synthesize new iron (II) complexes of 1,5-diaza-3,7-diphosphacyclooctanes with a wider variety of the substituents on ligands heteroatoms (including functionalized ones, namely, pyridyl groups) and co-ligands, it was found that these ligands with relatively small phenyl, benzyl, and pyridin-2-yl substituents on phosphorus atoms in acetonitrile formed bis-P,P-chelate cis-complexes [L₂Fe(CH₃CN)₂]²⁺ (BF₄)₂⁻, whereas P-mesityl-substituted ligand formed only monoligand P,P-complex [LFe(CH₃CN)₄]²⁺ (BF₄)₂⁻. 3,7-dibenzyl-1,5-di(1′-(R)-phenylethyl)-1,5-diaza-3,7-diphosphacyclooctane reacted with hexahydrate of iron (II) tetrafluoroborate in acetone to give an unusual bis-ligand cationic complex of the composition [L₂Fe(BF₄)]⁺ BF₄⁻, where two fluorine atoms of the tetrafluoroborate unit occupied two pseudo-equatorial positions at roughly octahedral iron ion, according to X-ray diffraction data. 1,5-diaza-3,7-diphosphacyclooctanes replaced tetrahydrofurane and one of the carbonyl ligands of cyclopentadienyldicarbonyl(tetrahydrofuran)iron (II) tetrafluoroborate to form heteroligand complexes [CpFeL(CO)]⁺BF₄⁻. The structural studies in the solid phase and in solutions showed that diazadiphosphacyclooctane ligands of all complexes adopted chair-boat conformations so that their nitrogen atoms were in close proximity to the central iron ion. The redox properties of the obtained complexes were performed by the cyclic voltammetry method.

A Dimeric Hydride-Bridged Complex with Geometrically Distinct Iron Centers Giving Rise to an S = 3 Ground State

Structural and spectroscopic characterization of the dimeric iron hydride complex [Ph₂B(^tBuIm)₂FeH]₂ reveals an unusual structure in which a tetrahedral iron(II) site (S = 2) is connected to a square planar iron(II) site (S = 1) by two bridging hydride ligands. Magnetic susceptibility reveals strong ferromagnetic coupling between iron centers, with a coupling constant of J = +110(12) cm^-1, to give an S = 3 ground state. High-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy confirms this model. A qualitative molecular orbital analysis of the electronic structure, as supported by electronic structure calculations, reveals that the observed spin configuration results from the orthogonal alignment of two geometrically distinct four-coordinate iron fragments held together by highly covalent hydride ligands.

Selective Copper Complex-Catalyzed Hydrodefluorination of Fluoroalkenes and Allyl Fluorides: A Tale of Two Mechanisms

The transition to more economically friendly small-chain fluorinated groups is leading to a resurgence in the synthesis and reactivity of fluoroalkenes. One versatile method to obtain a variety of commercially relevant hydrofluoroalkenes involves the catalytic hydrodefluorination (HDF) of fluoroalkenes using silanes. In this work it is shown that copper hydride complexes of tertiary phosphorus ligands (L) can be tuned to achieve selective multiple HDF of fluoroalkenes. In one example, HDF of the hexafluoropropene dimer affords a single isomer of heptafluoro-2-methylpentene in which five fluorines have been selectively replaced with hydrogens. DFT computational studies suggest a distinct HDF mechanisms for L₂CuH (bidentate or bulky monodentate phosphines) and L₃CuH (small cone angle monodentate phosphines) catalysts, allowing for stereocontrol of the HDF of trifluoroethylene.

Synthesis and Characterization of β-Diketimine Schiff Base Complexes with Ni(II) and Zn(II) Ions: Experimental and Theoretical Study

Schiff base diethyl 4,4-(pentane-2,4-diylidenebis(azanylylidene))benzoate (1) as a new ligand (L) was prepared by the reaction of acetylacetone with benzocaine in the ratio of 1 : 1. Two transition-metal complexes, [Ni(II)(LCl(HOEt))] (2) and [Zn(II)(LCl(HOEt))] (3), have been synthesized from metal salts with didentate Schiff base ligand (L) and characterized by elemental analyses, FT-IR, 1H NMR, 13C NMR UV-Vis spectroscopy, and magnetic susceptibility. The biological activity of the complexes was studied. In addition, the M06-2x density function theory method and the 6-31G(d) basic set were applied to determine the optimized structures of 1–3 and to determine their IR and 1H NMR, 13C NMR spectra theoretically. The data are in good agreement with the experimental results. The geometries of complexes 2 and 3 were determined to be square-planar for 2 and tetrahedral for 3.

Nonclassical Applications of closo-Carborane Anions: From Main Group Chemistry and Catalysis to Energy Storage

Classically closo-carborane anions, particularly [HCB₁₁H₁₁]^- and [HCB₉H₉]^-, and their derivatives have primarily been used as weakly coordinating anions to isolate reactive intermediates, platforms for stoichiometric and catalytic functionalization, counteranions for simple Lewis acid catalysis, and components of materials like liquid crystals. The aim of this article is to educate the reader on the contemporary nonclassical applications of these anions. Specifically, this review will cover new directions in main group catalysis utilized to achieve some of the most challenging catalytic reactions such as C-F, C-H, and C-C functionalizations that are difficult or impossible to realize with transition metals. In addition, the review will cover the utilization of the clusters as dianionic C σ-bound ligands for coordination chemistry, ligand substituents for coordination chemistry and advanced catalyst design, and covalently bound spectator substituents to stabilize radicals. Furthermore, their applications as solution-based and solid-state electrolytes for Li, Na, and Mg batteries will be discussed.