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We show how to improve the yield of MeX from CH4 activation catalysts from 12% to 90% through the use of “capping arene” ligands. Four (FP)RhIII(Me)(TFA)2 {FP = “capping arene” ligands, including 8...

Two-electron reduction of carbene-supported 9-bromo-9-borafluorenes with excess KC8 , Na, or Li-naphthalenide affords six N-heterocyclic carbene (NHC)- or cyclic(alkyl)(amino) carbene (CAAC)-stabilized borafluorene anions (3-8)-the first isolated and structurally authenticated examples of the elusive 9-carbene-9-borafluorene monoanion. The electronic structure, bonding, and aromaticity of the boracyclic anions were comprehensively investigated via computational studies. Compounds 5 and 8 react with metal halides via salt elimination to give new B-E (E=Au, Se, Ge)-containing materials (9-12). Upon reaction with diketones, the carbene ligand cleanly dissociates from 5 or 8 to yield new B-O containing spirocycles (13-14) that cannot be easily obtained using "normal" valent borafluorene compounds. Collectively, these results support the notion that carbene-stabilized monoanionic borafluorenes may serve as a new platform for the one-step construction of higher-value boracyclic materials.

We report a combined experimental and computational study focused on the mechanism of oxidative conversion of benzene and ethylene to styrene using [(η2-C2H4)2Rh(μ-OAc)]2 as the catalyst precursor ...

A common feature of d- and p-block elements is that they participate in multiple bonding. In contrast, the synthesis of compounds containing homo- or hetero-nuclear multiple bonds involving s-block elements is extremely rare. Herein, we report the synthesis, molecular structure, and computational analysis of a beryllium imido (Be=N) complex (2), which was prepared via oxidation of a molecular Be0 precursor (1) with trimethylsilyl azide Me3 SiN3 (TMS-N3 ). Notably, compound 2 features the shortest known Be=N bond (1.464 A) to date. This represents the first compound with an s-block metal-nitrogen multiple bond. All compounds were characterized experimentally with multi-nuclear NMR spectroscopy (1 H, 13 C, 9 Be) and single-crystal X-ray diffraction studies. The bonding situation was analyzed with density functional theory (DFT) calculations, which supports the existence of π-bonding between beryllium and nitrogen.

The synthesis and thermal redox chemistry of the first antimony (Sb)– and bismuth (Bi)–phosphaketene adducts are described. When diphenylpnictogen chloride [Ph2PnCl (Pn = Sb or Bi)] is reacted with sodium 2-phosphaethynolate [Na[OCP]·(dioxane)x], tetraphenyldipnictogen (Ph2Pn–PnPh2) compounds are produced, and an insoluble precipitate forms from solution. In contrast, when the N-heterocyclic carbene adduct (NHC)–PnPh2Cl is combined with [Na[OCP]·(dioxane)x], Sb– and Bi–phosphaketene complexes are isolated. Thus, NHC serves as an essential mediator for the reaction. Immediately after the formation of an intermediary pnictogen–phosphaketene NHC adduct [NHC–PnPh2(PCO)], the NHC ligand transfers from the Pn center to the phosphaketene carbon atom, forming NHC–C(O)P-PnPh2 [Pn = Sb (3) or Bi (4)]. In the solid state, 3 and 4 are dimeric with short intermolecular Pn–Pn interactions. When compounds 3 and 4 are heated in THF at 90 and 70 °C, respectively, the pnictogen center PnIII is thermally reduced to PnII to form tetraphenyldipnictines (Ph2Pn–PnPh2) and an unusual bis-carbene-supported OCP salt, [(NHC)2OCP][OCP] (5). The formation of compound 5 and Ph2Pn–PnPh2 from 3 or 4 is unique in comparison to the known thermal reactivity for group 14 carbene–phosphaketene complexes, further highlighting the diverse reactivity of [OCP]− with main-group elements. All new compounds have been fully characterized by single-crystal X-ray diffraction, multinuclear NMR spectroscopy (1H, 13C, and 31P), infrared spectroscopy, and elemental analysis (1, 2, and 5). The electronic structure of 5 and the mechanism of formation were investigated using density functional theory (DFT)., An N-heterocyclic carbene (NHC) was used to support the otherwise unstable Ph2Sb—P=C=O and Ph2Bi—P=C=O moieties. Exploration of the thermal chemistry of these NHC−phosphaketene adducts reveals the formation of the salt [NHC2OCP][OCP]. This present work demonstrates the thermal chemistry of the 2-phospaethynolate anion with heavier pnictogens (Sb and Bi).

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C–C bond formation. In this study, we investigate C–C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au2(μ-CH3)(PMe2Ar′)2][NTf2], [Au2(μ-CH3)(XPhos)2][NTf2], and [Au2(μ-CH3)(tBuXPhos)2][NTf2] {Ar′ = C6H3-2,6-(C6H3-2,6-Me)2, C6H3-2,6-(C6H2-2,4,6-Me)2, C6H3-2,6-(C6H3-2,6-iPr)2, or C6H3-2,6-(C6H2-2,4,6-iPr)2; XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; tBuXPhos = 2-di-tert-butylphosphino-2′,4′,6′-triisopropylbiphenyl; NTf2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH3)L and Au(L)(NTf2) {L = phosphines listed above}. For [Au2(μ-CH3)(XPhos)2][NTf2] and [Au2(μ-CH3)(tBuXPhos)2][NTf2], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au2(μ-CH3)(PMe2Ar′)2][NTf2] increases as the steric bulk of the phosphine substituent Ar′ decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C–C coupling likely involves (1) cleavage of [Au2(μ-CH3)(PMe2Ar′)2][NTf2] to form Au(PR2Ar′)(NTf2) and Au(CH3)(PMe2Ar′), (2) phosphine migration from a second equivalent of [Au2(μ-CH3)(PMe2Ar′)2][NTf2] aided by binding of the Lewis acidic [Au(PMe2Ar′)]+, formed in step 1, to produce [Au2(CH3)(PMe2Ar′)][NTf2] and [Au2(PMe2Ar′)]+, and (3) recombination of [Au2(CH3)(PMe2Ar′)][NTf2] and Au(CH3)(PMe2Ar′) to eliminate ethane.

Electrochemical methods are coupled with chemical oxidant-based analytical strategies to evaluate the oxidative reactivity of the platinum(II) diimine complex (bpy)PtII(CH3)2 (bpy = 2,2′-bipyridine...

Hydrogen–deuterium exchange (H/D exchange) is a method commonly used for studying catalytic activation of C–H(D) bonds by transition metal complexes. In this study, a series of additives were studi...

Charge-separated metal-organic frameworks (MOFs) are a unique class of MOFs that can possess added properties originating from the exposed ionic species. A new charge-separated MOF, namely, UNM-6 synthesized from a tetrahedral borate ligand and Co2+ cation is reported herein. UNM-6 crystalizes into the highly symmetric P43n space group with fourfold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO3 - anions within the crystal structure. These NO3 - ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co2+ ) and Lewis base (anions) pairs within the pores and potentially cooperative catalytic activities. For example, UNM-6-Br, the MOF after anion exchange with Br- anions, displays high catalytic activity and stability in reactions of CO2 chemical fixation into cyclic carbonates.

Emissive β-diketones (bdks) and difluoroboron complexes (BF2bdks) exhibit multi-stimuli responsive luminescence, including solvatochromism, viscochromism, aggregation induced emission, thermal and mechanochromic luminescence, halochromism and pH sensing. In this study, a series of six-membered heterocycle-substituted (piperidine, morpholine, 1-methyl piperazine) bdk ligands and boron complexes were synthesized, and their luminescent properties were investigated. All the compounds exhibited red-shifted emission in more polar solvents due to intramolecular charge transfer as well as higher emission intensity in more viscous environments. In response to solubility changes in water/tetrahydrofuran mixtures, while the piperazine bdk ligand showed aggregation caused quenching, the piperidine and morpholine bdks displayed enhanced emission upon aggregation. In the solid state, all ligands exhibited mechanochromism. More dramatic halochromism was observed for the piperidine boron dye spin cast film. In solution, for the boron dyes under varying pH values (1-13), different protonated and deprotonated forms were analyzed according to the measured emission spectra. Graphical abstract Multi-stimuli responsive luminescent properties were investigated for the six-membered heterocycle-substituted β-diketone ligands and difluoroboron complexes.

Key steps in the functionalization of an unactivated arene often involve its dihaptocoordination by a transition metal followed by insertion into the C-H bond. However, rarely are the η2-arene and aryl hydride species in measurable equilibrium. In this study, the benzene/phenyl hydride equilibrium is explored for the {WTp(NO)(PBu3)} (Bu = n-butyl; Tp = trispyrazoylborate) system as a function of temperature, solvent, ancillary ligand, and arene substituent. Both face-flip and ring-walk isomerizations are identified through spin-saturation exchange measurements, which both appear to operate through scission of a C-H bond. The effect of either an electron-donating or electron-withdrawing substituent is to increase the stability of both arene and aryl hydride isomers. Crystal structures, electrochemical measurements, and extensive NMR data further support these findings. Static density functional theory calculations of the benzene-to-phenyl hydride landscape suggest a single linear sequence for this transformation involving a sigma complex and oxidative cleavage transition state. Static DFT calculations also identified an η2-coordinated benzene complex in which the arene is held more loosely than in the ground state, primarily through dispersion forces. Although a single reaction pathway was identified by static calculations, quasiclassical direct dynamics simulations identified a network of several reaction pathways connecting the η2-benzene and phenyl hydride isomers, due to the relatively flat energy landscape.

Herein, we describe the syntheses and structural characterization of bis(carbene)- and tris(carbene)-stabilized organomagnesium cations. The reaction of the N-heterocyclic carbene (NHC) stabilized ...

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi4 chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

The hydrogen isotopes deuterium (D) and tritium (T) have become essential tools in chemistry, biology and medicine1. Beyond their widespread use in spectroscopy, mass spectrometry and mechanistic and pharmacokinetic studies, there has been considerable interest in incorporating deuterium into drug molecules1. Deutetrabenazine, a deuterated drug that is promising for the treatment of Huntington's disease2, was recently approved by the United States' Food and Drug Administration. The deuterium kinetic isotope effect, which compares the rate of a chemical reaction for a compound with that for its deuterated counterpart, can be substantial1,3,4. The strategic replacement of hydrogen with deuterium can affect both the rate of metabolism and the distribution of metabolites for a compound5, improving the efficacy and safety of a drug. The pharmacokinetics of a deuterated compound depends on the location(s) of deuterium. Although methods are available for deuterium incorporation at both early and late stages of the synthesis of a drug6,7, these processes are often unselective and the stereoisotopic purity can be difficult to measure7,8. Here we describe the preparation of stereoselectively deuterated building blocks for pharmaceutical research. As a proof of concept, we demonstrate a four-step conversion of benzene to cyclohexene with varying degrees of deuterium incorporation, via binding to a tungsten complex. Using different combinations of deuterated and proteated acid and hydride reagents, the deuterated positions on the cyclohexene ring can be controlled precisely. In total, 52 unique stereoisotopomers of cyclohexene are available, in the form of ten different isotopologues. This concept can be extended to prepare discrete stereoisotopomers of functionalized cyclohexenes. Such systematic methods for the preparation of pharmacologically active compounds as discrete stereoisotopomers could improve the pharmacological and toxicological properties of drugs and provide mechanistic information related to their distribution and metabolism in the body.

Interest in beryllium, the lightest member of group 2 elements, has grown substantially within the synthetic community. Herein, we report the synthesis and crystal structure of a heteroleptic haloberyllium borohydride bis(1-isopropyl-3-methyl-benzimidazol-2-ylidene)methane ‘carbodicarbene’ (CDC) complex [(CDC)BeCl(BH4)]. Crystallographic data: Triclinic space group P1̅, a = 8.8695(14), b = 12.394(2), c = 16.844(3) Å, α = 102.395(4), β = 96.456(4), γ = 99.164(4)°, wR2 (all data) = 0.2706 for 6720 unique data and 357 refined parameters.

Previously, we reported an iron(III) complex with 6,6′-([2,2′-bipyridine]-6,6′-diyl)bis(2,4-ditertbutyl-phenol) as a ligand (Fe(tbudhbpy)Cl, 1) as catalytically competent for the electrochemical re...

A detailed investigation was conducted on the reaction of a 1,1'-bi-2-naphthol-coumarin-based fluorescent probe with amino acids. On the basis of the studies, including fluorescence spectroscopy, 1H NMR, UV-vis, mass spectroscopy, single-crystal X-ray analysis, and molecular modeling, it was found that the distinctively different fluorescent responses of the probe toward the amino acid at the two excitation wavelengths are due to two different reaction pathways that generate different intermediates and products.

We describe a novel method to synthesize 2,5-dialkyl-4,6,7-tricyanoindole derivatives from a base-catalyzed reaction of 1,3-diketones with fumaronitrile. The reaction proceeds by the condensation o...

A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multielectron redox processes that are both metal- and ligand-centered. Reduction of (PPClP)CoCl2 (1) with excess magnesium affords the CoICoI N-heterocyclic phosphido (NHP-)-bridged symmetric dimer [(μ-PPP)Co]2 (2). Two-electron oxidation of 2 with FcPF6 generates an asymmetrically bridged dication [(μ-PPP)Co]2[PF6]2 (3) in which the oxidation has occurred in a delocalized fashion throughout the Co2P2 core. In contrast, [(μ-PPP)Co]2+ (5), which can be generated either by one-electron oxidation of 2 with FcPF6 or comportionation of 2 and 3, features an asymmetric geometry and localized mixed valence. Treatment of 1 with the milder reductants CoCp2 and KBEt3H does not lead to formation of 2, 3, or 5 but instead generates dimeric species [(PPP)CoCl]2 (6) and [(PPP)CoH]2 (7). Unlike 2-5, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex 6 and 7 are connected solely by NHP- ligands that bridge the two (PPP)Co fragments.

The alkaline-earth elements (Be, Mg, Ca, Sr, and Ba) strongly favor the formation of diamagnetic compounds in the +2 oxidation state. Herein we report a paramagnetic beryllium radical cation, [(CAA...

The synthesis and reactivity study of the first isolable boraphosphaketene, cyclic(alkyl)(amino) carbene (CAAC)-borafluorene-P=C=O (2), is described. Photolysis of compound 2 results in the formation of CAAC-stabilized BP-doped phenanthryne (3) through tandem decarbonylation, monoatomic phosphide insertion, and ring-expansion. Notably, while BN-doped phenanthryne was previously discussed as a reactive intermediate which could not be isolated, the heavier BP-doped analogue exhibits remarkable solution and solid-state stability. The reactivity of 2 with stable carbenes was also explored. Addition of CAAC to 2 led to migration of the original CAAC ligand from boron to phosphorus and coordination of the added CAAC to carbon, affording compound 4. Reaction of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (NHC) with 2 resulted in N-C bond activation to give the unusual spiro-heterocyclic compound (5).

Metal–organic frameworks (MOFs) are an emerging class of microporous materials that have potential applications in a wide range of areas. As a subclass of MOFs, ionic MOFs, especially charge-separa...

Two vanadium(III) complexes, CztBu(PyriPr)2VCl2 (1) and CztBu(PyriPr)2V(N3)2 (2), were synthesized and characterized. Chemical reduction of both 1 and 2 gives the thermally stable nitrido-bridged vanadium(IV) dimer complex, [{CztBu(PyriPr)2}V]2(μ-N)2 (3), which is a rare example of a dimeric vanadium(IV) complex bridged by two nitrido ligands. The nitride ligands of 3 are unreactive due to the well-protected environment provided by the pincer ligand and its substituents, as is supported by its X-ray crystal structure and further described by DFT calculations.

Earth-abundant transition-metal catalysts capable of reducing CO2 to useful products have been gaining attention to meet increasing energy demands and address concerns of rising CO2 emissions. Grou...

Shear-induced crystallization of dyes in the amorphous state is an effective strategy for generating higher energy emission after mechanical perturbation—a rare phenomenon in mechanoresponsive mate...

Luminescent β-diketones (bdks) and difluoroboron coordinated complexes (BF₂bdks) exhibit many environment-sensitive properties, such as solvatochromism, viscochromism, aggregation-induced emission (AIE), and thermal and mechanochromic luminescence (ML). In a previous study, an azepane-substituted bdk ligand (L1) and boron dye (D1) showed noteworthy luminescence properties but low quantum yields (Φ, L1: 0.26; D1: 0.02) due to free intramolecular bond rotation and twisted intramolecular charge transfer state formation with associated nonradiative decay. Thus, in order to improve the quantum yields, an azepane-substituted bdk ligand (L2) and boron complex (D2) with restricted C–C bond rotation were synthesized, and various luminescence properties were investigated. Restricting bond rotation blue-shifted absorptions and emissions, increased lifetimes, and greatly improved quantum yields (Φ, L2: 0.47; D2: 0.83). Excited state density functional theory calculations displayed twisted geometries for L1 and D1 but more planar geometries for L2 and D2. All compounds showed red-shifted emissions in more polar solvents. For viscochromism, L1 and D1 exhibited higher emission intensity in more viscous media. However, L2 and D2 did not show dramatic viscochromism, substantiating the relation between viscosity sensitivity and intramolecular bond twisting. Additionally, while both ligands showed quenched emission upon aggregation, the dyes exhibited AIE regardless of bond restriction. Thermal and ML studies showed a more dramatic emission shift for L2 than L1 between thermally annealed and melt-quenched states. In summary, the quantum yields of the azepane-substituted bdk ligand and boron dye were successfully improved by restricting the intramolecular C–C bond rotation, making various luminescence properties more promising for environment-sensitive applications.

The first examples of N-heterocyclic carbene (NHC) and cyclic(alkyl)(amino) carbene (CAAC) stabilized borepinium and borafluorenium heterocycles are reported herein. The optical properties of the heterocyclic borenium cations were tuned by varying the Lewis base and by changing the number of atoms in the ring. More importantly, functionalizing the cationic boron ring system in the NHC-borafluorenium cation affords a temperature-sensitive molecule with reversible colorimetric "turn off/turn on" properties in solution. Notably, this is the first report of thermochromism in these cationic species. This property, which is mediated by an intermolecular boron-oxygen bond equilibrium, was examined in detail by X-ray crystallography, variable temperature-UV/Vis absorption spectroscopy (VT-UV/Vis), and density functional theory (DFT).

Recent synthetic efforts have uncovered several bond activation pathways mediated by beryllium. Having the highest charge density and electronegativity, the chemistry of beryllium often diverges from that of its heavier alkaline earth metal congeners. Herein, we report the synthesis of a new carbodicarbene beryllacycle (2). Compound 2 converts to 3 via an unprecedented cyclic(alkyl)(amino) carbene (CAAC)-promoted ring expansion reaction (RER). While CAAC activates a carbon-beryllium bond, N-heterocyclic carbene (NHC) coordinates to beryllium to give the tetracoordinate complex 4, which contains the longest carbeneC-Be bond to date at 1.856(4) A. All of the compounds were fully characterized by X-ray crystallography, Fourier transform infrared spectroscopy, and 1H, 13C, and 9Be NMR spectroscopy. The ring expansion mechanism was modeled with both NHC and CAAC using density functional theory calculations. While the activation energy for the observed beryllium ring expansion with CAAC was found to be 14 kJ mol-1, the energy barrier for the hypothetical NHC RER is significantly higher (199.1 kJ mol-1).

We report the synthesis and characterization of novel anionic arylfluoroborate, three-coordinate ligated arylcopper(I) and cationic ligated copper(I) complexes. We show through in situ 19F NMR monitoring that neutral arylboronate ester is more kinetically competent than anionic arylfluoroborate for transmetalation with (PN)CuF (PN = o-(di-tert-butylphosphino)-N,N-dimethylaniline). The transmetalation of the neutral arylboronate ester proceeds via a two-step process involving a cationic copper(I) species wherein an anionic arylfluoroborate is generated in situ as a competent aryl group transferring reagent.

Studies of catalytic benzene alkenylation using different diimine ligated Rh(I) acetate complexes and Cu(OAc)2 as the oxidant revealed statistically identical results in terms of activity and product selectivity. Under ethylene pressure, two representative diimine ligated rhodium(I) acetate complexes were demonstrated to exchange the diimine ligand with ethylene rapidly to form [Rh(μ-OAc)(η2-C2H4)2]2 and free diimine. Thus, it was concluded that diimine ligands are not likely coordinated to the active Rh catalysts under catalytic conditions. At 150 °C under catalytic conditions using commercial Cu(OAc)2 as the oxidant, [Rh(μ-OAc)(η2-C2H4)2]2 undergoes rapid decomposition to form catalytically inactive and insoluble Rh species, followed by gradual dissolution of the insoluble Rh to form the soluble Rh, which is active for styrene production. Thus, the observed induction period under some conditions is likely due to the formation of insoluble Rh (rapid), followed by redissolution of the Rh (slow). The Rh de...

Oxygen reduction is a critical half reaction in renewable fuel cell development and a key step in the development of aerobic oxidation reactions. Herein, we report rapid two-electron O2 reduction by a d0 ZrIV center with an appended redox-active Co-I site serving as an electron reservoir. The early/late heterobimetallic Zr/Co complex (THF)Zr(MesNP iPr2)3CoCN tBu (1) reacts readily with O2 and O atom transfer reagents to generate reactive oxygenated species including terminal peroxo and oxo complexes, (O2)Zr(MesNP iPr2)3CoCN tBu (2) and O≡Zr(MesNP iPr2)3CoCN tBu (3). The bimetallic Zr/Co complex provides a new cooperative synthetic pathway to promote multielectron redox processes such as oxygen reduction, with each metal playing a distinct role as a substrate binding site or redox mediator.

In the past two decades, the organometallic chemistry of the alkaline earth elements has experienced a renaissance due in part to developments in ligand stabilization strategies. In order to expand the scope of redox chemistry known for magnesium and beryllium, we have synthesized a set of reduced magnesium and beryllium complexes and compared their resulting structural and electronic properties. The carbene-coordinated alkaline earth-halides, (Et2CAAC)MgBr2 (1), (SIPr)MgBr2 (2), (Et2CAAC)BeCl2 (3), and (SIPr)BeCl2 (4) [Et2CAAC = diethyl cyclic(alkyl)(amino) carbene; SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazole-2-ylidene] were combined with an α-diimine [2,2-bipyridine (bpy) or bis(2,6-diisopropylphenyl)-1,4-diazabutadiene (DippDAB)] and the appropriate stoichiometric amount of potassium graphite to form singly- and doubly-reduced compounds (Et2CAAC)MgBr(DippDAB) (5), (Et2CAAC)MgBr(bpy) (6), (Et2CAAC)Mg(DippDAB) (7), (Et2CAAC)Be(bpy) (8), and (SIPr)Be(bpy) (9). The doubly-reduced compounds 7-9 exhibit substantial π-bonding interactions across the diimine core, metal center, and π-acidic carbene. Each complex was fully characterized by UV-vis, FT-IR, X-ray crystallography, 1H, 13C, and 9Be NMR, or EPR where applicable. We use these compounds to highlight the differences in the organometallic chemistry of the lightest alkaline earth metals, magnesium and beryllium, in an otherwise identical chemical environment.

Carbenes are known to activate carbon dioxide to form zwitterionic adducts. Their inherent metal-free redox activity remains understudied. Herein, we demonstrate that zwitterionic adducts of carbon dioxide formed with cyclic(alkyl)(amino) carbenes are not only redox active, but they can mediate the stoichiometric reductive disproportionation of carbon dioxide to carbon monoxide and carbonate. Infrared spectroelectrochemical experiments show that the reaction proceeds through an intermediate radical anion formed by one-electron reduction, ultimately generating a ketene product and carbonate in the absence of additional organic or inorganic reagents.

The dihapto-coordination of benzene to the π-basic fragment {TpW(NO)(PMe3)} (Tp = hydridotris(pyrazolyl)-borate) enhances the basicity of the arene ligand to the point that it can be protonated with a mild Bronsted acid (diphenylammonium triflate; p Ka ∼ 1). The resulting η2-benzenium complex reacts with a wide range of nucleophiles including protected enolates, cyanide, amines, methoxide, and aromatic nucleophiles to form 5-substituted 3,4-η2-1,3-cyclohexadiene complexes in good yield (42-70%). These coordinated dienes were successfully taken through a second protonation and nucleophilic addition with a similar scope of nucleophiles (54-80%). The resulting cis-3,4- and cis-3,6-disubstituted η2-cyclohexene complexes were prepared with high regio- and stereocontrol, as governed by the asymmetric nature of π-allyl intermediates. In some cases, a diene linkage isomerization from 3,4-η2 to 1,2-η2 could be effected with a redox catalyst, and reactions of the latter species led to cis-3,5-disubstituted cyclohexene products exclusively. Oxidative decomplexation afforded the free cyclohexene products in moderate yield (37-68%). Additionally, when a single enantiomer of the chiral dearomatization agent was used, the elaborated cyclohexenes were able to be synthesized in enantioenriched forms (86-90% enantiomeric excess). Full characterization of 40 new compounds is provided that includes two-dimensional NMR, IR, electrochemical and in some cases crystallographic data.

The long‐sought carbene–bismuthinidene, (CAAC)Bi(Ph), has been synthesized. Notably, this represents both the first example of a carbene‐stabilized subvalent bismuth complex and the extension of the carbene‐pnictinidene concept to a non‐toxic metallic element (Bi). The bonding has been investigated by single‐crystal X‐ray diffraction studies and DFT calculations. This report also highlights the hitherto unknown reducing and ligand transfer capability of a beryllium(0) complex.

Emissive β-diketones (bdks) and difluoroboron complexes (BF2 bdks) show multi-stimuli responsive luminescence in both solution and the solid state. A series of bdk ligands and boron coordinated dyes were synthesized with different cyclic amine substituents in the 4-position to explore ring size effects on various luminescent properties, including solvatochromism, viscochromism, aggregation-induced emission (AIE), mechanochromic luminescence (ML) and halochromism. Red-shifted absorption and emission were observed in CH2 Cl2 for both bdk ligands and boron dyes with increasing substituent ring size. The compounds displayed bathochromic emission in more polar solvents, and higher fluorescence intensity in more viscous media. The AIE compounds exhibited enhanced emission when aggregated. For solid-state properties, a large emission wavelength shift was shown for the piperidine substituted bdk after melt quenching on weighing paper. Large blue-shifted emissions were observed in all the boron dye spin cast films after trifluoroacetic acid vapor annealing, and the original emissions were partially recovered after triethylamine vapor treatment.

Substantial progress has been made in the coordination chemistry of main-group elements with neutral donor ligands, largely ushered in by the development of stable N-heterocyclic carbenes (NHCs). There is growing interest in the synthesis of well-defined coordination compounds containing s-block metals; however, examples of molecular compounds containing “normal” NHCs bound to magnesium remain relatively understudied. We report that NHCs react with magnesium halides, MgX2 (X = Cl, Br, I), to afford (IPr)MgCl2(THF) (1), [(IPr)MgCl2]2 (2), (sIPr)2MgCl2 (3), (sIPr)2MgBr2 (4), and (sIPr)2MgI2 (5), where IPr is 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidine and sIPr is 1,3-diisopropyl-4,5-dimethylimidizol-2-ylidine. Using the IPr ligand, weak NHC coordination and dynamic interaction with THF are observed in solution. In contrast, the coordination of two sIPr ligands results in higher purity, enhanced stability, and no observation of THF coordination. Dual carbene complexation with commercially available Mgn...

Herein we report the synthesis and characterization of dinuclear magnesium-hydride complexes, [(IiPrMe2)Mg(μ-H)(HMDS)]2 [4, IiPrMe2 = N,N'-diisopropyl-2,3-dimethylimidazol-2-ylidine, HMDS = bis(trimethylsilyl)amide] and [(IiPrMe2)Mg(μ-H)(ASCP)]2 (5, ASCP = 2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl). Compounds 4 and 5 exhibit the lowest nuclearity of any carbene-magnesium hydride complex to date.

The first examples of pyrene-fused Janus-type N-heterocyclic germylenes (NHGe) are reported. Remarkably, the pyrene linker and the germanium containing rings are extremely twisted, with "twist angles" up to 64°. Coordination of a Lewis base modifies the twisting of pyrene to an overall bent core (141° bend angle).

We report a trinuclear copper(II) complex, [(DAM)Cu3(μ3-O)][Cl]4 (1, DAM = dodecaaza macrotetracycle), as a homogeneous electrocatalyst for water oxidation to dioxygen in phosphate-buffered solutions at pH 7.0, 8.1, and 11.5. Electrocatalytic water oxidation at pH 7 occurs at an overpotential of 550 mV with a turnover frequency of ∼19 s–1 at 1.5 V vs NHE. Controlled potential electrolysis (CPE) experiments at pH 11.5 over 3 h at 1.2 V and at pH 8.1 for 40 min at 1.37 V vs NHE confirm the evolution of dioxygen with Faradaic efficiencies of 81% and 45%, respectively. Rinse tests conducted after CPE studies provide evidence for the homogeneous nature of the catalysis. The linear dependence of the current density on the catalyst concentration indicates a likely first-order dependence on the Cu precatalyst 1, while kinetic isotope studies (H2O versus D2O) point to involvement of a proton in or preceding the rate-determining step. Rotating ring-disk electrode measurements at pH 8.1 and 11.2 show no evidence of H2O2 formation and support selectivity to form dioxygen. Freeze-quench electron paramagnetic resonance studies during electrolysis provide evidence for the formation of a molecular copper intermediate. Experimental and computational studies support a key role of the phosphate as an acceptor base. Moreover, density functional theory calculations highlight the importance of second-sphere interactions and the role of the nitrogen-based ligands to facilitate proton transfer processes.

A perfluoroalkyl ketone-based molecular probe was found to show highly enantioselective fluorescent enhancement in the fluorous phase when treated with an amino alcohol generated from the asymmetric reaction of a meso-epoxide with an alkyl amine. The two enantiomeric probes (R)- and (S)-2 were used to screen catalysts for this asymmetric reaction. The use of the probe in the fluorous phase allowed the fluorescent sensing of the products to be conducted away from the other reaction components with minimized interference. It was further found that when (R)- or (S)-2 was used to determine the enantiomeric composition of the amino alcohol product, there was a large nonlinear effect. That is, only when one enantiomer of the substrate was in excess was there a large fluorescence enhancement for the chirality-matched probe-substrate interaction. This allowed the racemic probe rac-2 to be used to evaluate the asymmetric induction in the catalyst screening. The catalyst screening using the fluorescent probes led to the discovery of a more enantioselective and efficient method for the desymmetrization of 1,2-epoxycyclohexane with iPrNH2 to form the corresponding chiral amino alcohol. This work presents a novel method to conduct catalyst screening for asymmetric synthesis and has potential to become a high-throughput process.

We report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)‐stabilized bismuth complexes, which feature low‐coordinate cationic bismuth centers with C=Bi multiple‐bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6] (8) and [(CDC)BiBr2(THF)2][SbF6] (11), dications [(CDC)Bi(Ph)][SbF6]2 (9) and [(CDC)BiBr(THF)3][NTf2]2 (12), and trication [(CDC)2Bi][NTf2]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C⇉ Bi double dative bonds and thus represent unprecedented bismaalkene cations. The synthesis of these species highlights a unique non‐reductive route to C−Bi π‐bonding character. The CDC‐[Bi] complexes (7–13) were compared with related NHC‐[Bi] complexes (1, 3–6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low‐coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry., Unprecedented low‐coordinate carbodicarbene bismaalkene cations have been prepared which feature C⇉ Bi double dative bonds. The synthesis of these compounds represents a unique non‐reductive route to C=Bi double‐bond character.

A one-pot synthetic procedure for a series of bimetallic Nb/M complexes, Cl–Nb(iPrNPPh2)3M–X (M = Fe (2), Ni (4), Cu (5)), is described. A similar procedure aimed at synthesizing a Nb/Co analogue instead affords iPrN═Nb(iPrNPPh2)2(μ-PPh2)Co–I (3) through cleavage of one phosphinoamide P–N bond under reducing conditions. Complexes 4 and 5 are found to have short Nb-M distances, corresponding to unusual metal–metal bonds between Nb and these first row transition metals. For comparison, a series of heterobimetallic O≡Nb(iPrNPPh2)3M–X complexes (M = Fe (7), Co (8), Ni (9), Cu (10)) was synthesized. In these complexes, the NbV center is engaged in sufficient π-bonding to the terminal oxo ligand to remove the driving force for direct metal–metal interactions. A comparison of the cyclic voltammograms of 2 and 4–10 reveals that the presence of a second metal shifts the redox potentials of both Nb and the late metal center anodically, even when direct metal–metal interactions are not present.

The sterically bulky compounds N,N′-bismesityl phenanthrene-9,10-diimine [1] and imine–nitrone [2] were synthesized. To the best of our knowledge, this is the first report of the synthesis of a bulky steric imine–nitrone accessed from the secondary ketimine using urea hydrogen peroxide over methyltrioxorhenium catalyst. Purified compounds were characterized using 1H and 13C NMR, high-resolution mass spectrometry, and infrared spectrometry. We report the first crystal structure of compound 1. Detailed IR bands of compounds 1 and 2 were assigned by comparing experimentally measured spectra to individually animated modes of quantum mechanically computed spectra. We believe these compounds may be of use as bidentate ligands in the synthesis of novel organometallic compounds. The asymmetric N and O coordination sites of compound 2 might impart interesting electronic effects to organometallic compounds compared to the symmetric N,N′-coordination sites of compound 1.

Interactions between a nitro group and an aromatic ring have been identified as an important aspect within the solid-state structures of many energetic materials. We investigated nitro-aromatic interactions within a molecular “torsion balance”, both in solid-state as well as in solution. Our balance features a Troger’s base and a nitroalkene functionality substituted at 1 and 8 positions of a naphthalene ring. Because of restricted rotation around a biaryl axis, the balance can adapt two principal atropisomeric conformations: folded and unfolded. Intramolecular nitro-aromatic interactions are feasible only in the folded state. A torsion balance containing a highly electron deficient aromatic ring crystallized in the folded state leading to the formation of a short (

The new iron(IV) nitride complex PhB(iPr2Im)3Fe≡N reacts with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) to provide PhB(iPr2Im)3Fe(CN)(N2)(BAC). This unusual example of a four-electron reaction involves carbon atom transfer from BAC to create a cyanide ligand along with the alkyne iPr2N-C≡C-NiPr2. The iron complex is in equilibrium with an N2-free species. Further reaction with CO leads to formation of a CO analogue, which can be independently prepared using NaCN as the cyanide source, while reaction with B(C6F5)3 provides the cyanoborane derivative.

The reactivity of the reduced Zr/Co and Ti/Co complexes (THF)Zr(MesNPiPr2)3CoN2 (1, Mes = 2,4,6-trimethylphenyl) and (THF)Ti(XylNPiPr2)3CoN2 (7, Xyl = 3,5-dimethylphenyl) toward diaryl ketones is explored in an effort to gain mechanistic insight into C═O bond cleavage processes. Complex 1 reacts with 4,4′-dimethoxybenzophenone to generate ((p-OMeC6H4)2CO)Zr(MesNPiPr2)3CoN2 (2), which exists as a mixture of valence tautomers in solution that interconvert via electron transfer from Co–I to the Zr-bound ketone in 2S to form a Zr-bound ketyl radical in 2T. The geometry of 2 in the solid state is most consistent with the singlet ketone adduct tautomer 2S. Upon removal of the Co-bound N2 under vacuum, complex 2 cleanly coverts to the μ-oxo carbene product (η2-MesNPiPr2)Zr(MesNPiPr2)2(μ-O)Co═C(C6H4p-OMe)2 (5) at room temperature in solution. A diamagnetic intermediate, tentatively assigned as ketone-bridged species (η2-MesNPiPr2)Zr(MesNPiPr2)2Co(μ2,η1η2-OC(p-OMeC6H4)2) (6), is observed spectroscopically during t...

Five different coordination motifs were observed upon reaction of the simple group 13 Lewis acids MCl3 (M = In, Ga, Al, B) or BF3·Et2O with the ambidentate bis(diisopropylphosphino)amine ligand HN[P(i-Pr)2]2. In a 1:1 reaction mixture, the softer Lewis acids InCl3, GaCl3 and BCl3 coordinate to one of the two P atoms of the ligand. In contrast, AlCl3 and BF3 prefer coordination to the harder N atom. In all cases, the acidic N–H proton is shifted to P upon complexation with a metal. By altering the reaction stoichiometry, 2:1 metal–ligand complexes could be isolated for three of the combinations. BCl3 gives a bis-adduct via the two P atoms. GaCl3 produces a salt consisting of a [GaCl4]− anion and a P,P-chelated [LGaCl2]+ cation. Most unexpectedly, the reaction with InCl3 in methanol resulted in solvent deprotonation by the ligand to give two symmetric [(i-Pr2PH)2N]+ cations in which all the basic P sites are coordinated to H rather than the group 13 Lewis acid. These cations are balanced by the unique compl...

Strong spin-dependent delocalization (double exchange) was previously demonstrated for the complexes, NN-Bridge-SQ-Coiii(py)2Cat-Bridge-NN (where NN = S = 12 nitronylnitroxide, Bridge = 1,4-phenylene and single bond, SQ = S = 12 orthobenzosemiquinone, Coiii = low-spin d6 cobalt 3+, and Cat = diamagnetic catecholate). The mixed-valent S = 12 SQ-Coiii-Cat triad results in ferromagnetic alignment of localized (pinned) NN spins which are ∼22 A apart (Bridge = Ph). Herein, we report similar ferromagnetic coupling of localized verdazyl (Vdz) radical spins. The origin of the magnetic exchange results from a second order vibronic effect (pseudo Jahn-Teller effect) in [Vdz-diox-Ru(py)2-diox-Vdz]0, which possesses a diamagnetic [diox-Ru-diox]0 triad by virtue of strong antiferromagnetic SQ-Ruiii exchange.

N‐Heterocyclic carbene (NHC)‐ and cyclic (alkyl)(amino)carbene (CAAC)‐stabilized borafluorene radicals have been isolated and characterized by elemental analysis, single‐crystal X‐ray diffraction, UV/Vis absorption, cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies. Both the CAAC–borafluorene radical (2) and the NHC–borafluorene radical (4) have a considerable amount of spin density localized on the boron atoms (0.322 for 2 and 0.369 for 4). In compound 2, the unpaired electron is also partly delocalized over the CAAC ligand carbeneC and N atoms. However, the unpaired electron in compound 4 mainly resides throughout the borafluorene π‐system, with significantly less delocalization over the NHC ligand. These results highlight the Lewis base dependent electrostructural tuning of materials‐relevant radicals. Notably, this is the first report of crystalline borafluorene radicals, and these species exhibit remarkable solid‐state and solution stability., Crystalline, isolable borafluorene radicals that are stabilized by N‐heterocyclic carbene or cyclic (alkyl)(amino)carbene ligands have been synthesized. They exhibit remarkable solution and solid‐state stability and were characterized by elemental analysis, single‐crystal X‐ray diffraction, UV/Vis absorption, cyclic voltammetry, EPR spectroscopy, and theoretical studies.