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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).

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...

The mono- and dianions of CO2 (i.e., CO2− and CO22−) have been studied for decades as both fundamentally important oxycarbanions (anions containing only C and O atoms) and as critical species in CO2 reduction and fixation chemistry. However, CO2 anions are highly unstable and difficult to study. As such, examples of stable compounds containing these ions are extremely limited; the unadulterated alkali salts of CO2 (i.e., MCO2, M2CO2, M = alkali metal) decompose rapidly above 15 K, for example. Herein we report the chemical reduction of a cyclic (alkyl)(amino) carbene (CAAC) adduct of CO2 at room temperature by alkali metals, which results in the formation of CAAC-stabilized alkali CO2− and CO22− clusters. One-electron reduction of CAAC–CO2 adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals [M(CAAC–CO2)]n (M = Li, Na, K, 2–4) analogous to the alkali CO2− radical, and two-electron alkali metal reduction affords dianionic clusters of the general formula [M2(CAAC–CO2)]n (5–8) with reduced CO2 units which are structurally analogous to the carbonite anion CO22−. It is notable that crystalline clusters of these alkali–CO2 salts may also be isolated via the “one-pot” reaction of free CO2 with free CAAC followed by the addition of alkali metals – a process which does not occur in the absence of carbene. Each of the products 2–8 was investigated using a combination of experimental and theoretical methods.

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 ...

The exceptionally π-basic metal fragments {MoTp-(NO)(DMAP)} and {WTp(NO)(PMe(3))} (Tp = tris(pyrazolyl)borate; DMAP = 4-(N,N-dimethylamino)pyridine) form thermally stable η(2)-coordinated complexes with a variety of electron-deficient arenes. The tolerance of substituted arenes with fluorine-containing electron withdrawing groups (EWG; −F, −CF(3), −SF(5)) is examined for both the molybdenum and tungsten systems. When the EWG contains a π bond (nitriles, aldehydes, ketones, ester), η(2) coordination occurs predominantly on the nonaromatic functional group. However, complexation of the tungsten complex with trimethyl orthobenzoate (PhC(OMe)(3)) followed by hydrolysis allows access to an η(2)-coordinated arene with an ester substituent. In general, the tungsten system tolerates sulfur-based withdrawing groups well (e.g., PhSO(2)Ph, MeSO(2)Ph), and the integration of multiple electron-withdrawing groups on a benzene ring further enhances the π-back-bonding interaction between the metal and aromatic ligand. While the molybdenum system did not form stable η(2)-arene complexes with the sulfones or ortho esters, it was capable of forming rare examples of stable η(2)-coordinated arene complexes with a range of fluorinated benzenes (e.g., fluorobenzene, difluorobenzenes). In contrast to what has been observed for the tungsten system, these complexes formed without interference of C–H or C–F insertion.

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.

Dihapto-coordinate 1,2-dihydropyridine complexes of the metal fragment {WTp(NO)(PMe(3))} (Tp = tris(pyrazolyl)borate), derived from pyridine, are demonstrated to undergo protonation at C6 followed by regioselective amination at C5 with a variety of primary and secondary amines. The addition takes place stereoselectively anti to the metal center, producing exclusively cis-disubstituted products. The resulting 1,2,5,6-tetrahydropyridines can be successfully liberated by oxidation, providing a route to novel molecules of potential medicinal interest.

A second-row transition metal complex {MoTp(NO)(DMAP)} (DMAP = 4-(dimethylamino)pyridine; Tp = tris(pyrazolyl)borate) is shown to form dihapto-coordinate complexes with a range of substituted pyrid...

The complex MoTp(NO)(DMAP)(η2-naphthalene) (1; DMAP = 4-(dimethylamino)pyridine; Tp = tris(pyrazolyl)borate) is demonstrated to undergo Michael–Michael ring-closure (MIMIRC) reactions promoted by t...

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...

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...

The reactivity of the terminal zirconium(iv) oxo complex, O Created by potrace 1.16, written by Peter Selinger 2001-2019 Zr(MesNPiPr2)3CoCNtBu (2), is explored, revealing unique redox activity imparted by the pendent redox active cobalt(i) center. Oxo complex 2 can be chemically reduced using Na/Hg or Ph3C• to afford the ZrIV/Co0 complexes [(μ-Na)OZr(MesNPiPr2)3CoCNtBu]2 (3) and Ph3COZr(MesNPiPr2)3CoCNtBu (4), respectively. Based on the cyclic voltammogram of 2, Ph3˙ should not be sufficiently reducing to achieve the chemical reduction of 2, but sufficient driving force for the reaction is provided by the nucleophilicity of the terminal oxo fragment and its affinity to bind Ph3C+. Accordingly, 2 reacts readily with [Ph3C][BPh4] and Ph3CCl to afford [Ph3COZr(MesNPiPr2)3CoCNtBu][BPh4] ([5][BPh4]) and Ph3COZr(MesNPiPr2)3CoCl (6), respectively. The chemical oxidation of 2 is also investigated, revealing that oxidation of 2 is accompanied by immediate hydrogen atom abstraction to afford the hydroxide complex [HOZr(MesNPiPr2)3CoCNtBu]+ ([9]+). Thus it is posited that the transient [OZr(MesNPiPr2)3CoCNtBu]+ [2]+ cation generated upon oxidation combines the basicity of a nucleophilic early metal oxo fragment with the oxidizing power of the appended cobalt center to facilitate H-atom abstraction., Bimetallic cooperativity is demonstrated with a Co/Zr complex featuring both nucleophilic Zr(iv) oxo and redox active Co sites.

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.

Reactions are described for complexes of the form WTp(NO)(PMe(3))(η(2)-arene) and various amines, where the arene is benzene or benzene with an electron-withdrawing substituent (CF(3), SO(2)Ph, SO(2)Me). The arene complex is first protonated to form an η(2)-arenium species, which then selectively adds the amine. The resulting η(2)-5-amino-1,3-cyclohexadiene complexes can then be subjected to the same sequence with a second nucleophile to form 3-aminocyclohexene complexes, where up to three stereocenters originate from the arene carbons. Alternatively, 1,3-cyclohexadiene complexes containing an ester group at the 5 position (also prepared from an arene) can be treated with acid followed by an amine to form trisubstituted 3-aminocyclohexenes. When the amine is primary, ring closure can occur to form a cis-fused bicyclic γ-lactam. Highly functionalized cyclohexenes can be liberated from the tungsten through oxidative decomplexation. The potential utility of this methodology is demonstrated in the synthesis of the alkaloid γ-lycorane. An enantioenriched synthesis of a lactam precursor to γ-lycorane is also described. This compound is prepared from an enantioenriched version of the tungsten benzene complex. Regio- and stereochemical assignments for the reported compounds are supported by detailed 2D-NMR analysis and 13 molecular structure determinations (SC-XRD).

The 2-phosphaethynolate (OCP) anion has found versatile applications across the periodic table but remains underexplored in group 2 chemistry due to challenges in isolating thermally stable complexes. By rationally modifying their coordination environments using 1,3-dialkyl-substituted N-heterocyclic carbenes (NHCs), we have now isolated and characterized thermally stable, structurally diverse, and hydrocarbon soluble magnesium phosphaethynolate complexes (2, 4Me, and 8-10), including the novel phosphaethynolate Grignard reagent (2iPr). The methylmagnesium phosphaethynolate and magnesium diphosphaethynolate complexes readily activate dioxane with subsequent H-atom abstraction to form [(NHC)MgX(μ-OEt)]2 [X = Me (3) or OCP (8 and 9)] complexes. Their reactivities increased with the Lewis acidity of the Mg2+ cation and may be attenuated by Lewis base saturation or a slight increase in carbene sterics. Solvent effects were also investigated and led to the surreptitious isolation of an ether-free sodium phosphaethynolate (NHC)3Na(OCP) (6), which is soluble in aromatic hydrocarbons and can be independently prepared by the reaction of NHC and [Na(dioxane)2][OCP] in toluene. Under forcing conditions (105 °C, 3 days), the magnesium diphosphaethynolate complex (NHC)3Mg(OCP)2 (10) decomposes to a mixture of organophosphorus complexes, among which a thermal decarbonylation product [(NHC)2PI][OCP] (11) was isolated.

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...

The preparation of the complex MoTp(NO)(DMAP)(4,5-η2-(2-trifluoromethyl)pyridine) (DMAP = 4-(dimethylamino)pyridine; Tp = tris(pyrazolyl)borate) is described. The CF3 substituent is found to preclude κ-N coordination, allowing for direct coordination without protection of the nitrogen. The dihapto-coordinate complex can be isolated as a single diastereomer, methylated, and reacted with a range of nucleophiles. Oxidative decomplexation affords the free dihydropyridines in good yield (75-90%). As a demonstration of synthetic utility, a series of novel bridgehead CF3-substituted isoquinuclidines was prepared from these decomplexed dihydropyridines.

An oxidant-initiated, substitution process for dihapto-coordinated ligands is described for the {MoTp(NO)(DMAP)} system. Complexes of the form MoTp(NO)(DMAP)(η2-alkene), MoTp(NO)(DMAP)(η2-ketone), ...

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.

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...

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.

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...

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.

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.

The reduction of the relatively inert carbon–oxygen bonds of CO2 to access useful CO2-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO2 and the MGE. Herein we report the first successful chemical reduction of CO2 at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO2 adduct (1) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO2)]n(M = Li, Na, K, 2-4) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M2(CAAC–CO2)]n (5-8). It is notable that these crystalline clusters of reduced CO2 may also be isolated via the “one-pot” reaction of free CO2 with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products 2-8 were investigated using a combination of experimental and theoretical methods.

The reduction of the relatively inert carbon–oxygen bonds of CO2to access useful CO2-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Achieving this reduction using earth-abundant main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere reactions and bond activation events between CO2and the MGE. Herein we report the first successful chemical reduction of a zwitterionic carbene-CO2adduct by either one or two equivalents of light alkali metals to form isolable, room-temperature-stable crystalline clusters exhibiting remarkably diverse electronic and structural characteristics. The reduction of a CAAC-CO2adduct [CAAC–CO2, 1, CAAC = cyclic (alkyl)(amino) carbene] with one equivalent of lithium, sodium or potassium metal yields the monoanionic radicals (THF)3Li2(CAAC–CO2)2(2), (THF)4Na4(CAAC–CO2)4(3), or (THF)4K4(CAAC–CO2)4(4). The reduction of 1by two or more equivalents of lithium, sodium, or potassium yields the open-shell, dianionic clusters (THF)2Li6(CAAC–CO2)3(5), Li12(CAAC–CO2)6(6), Na12(CAAC–CO2)6(7), and K10(CAAC–CO2)5(8). Each of the clusters was studied by a combination of X-ray crystallography, FTIR, UV-Vis, EPR and NMR spectroscopies, and theoretical calculations. The synthetic transformation described in this report results in the facile net reduction of CO2at room temperature by lithium, sodium, and potassium metal without the need for additional metallic promoters, catalysts, or reagents – a process which does not occur in the absence of carbene.

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 attachment of molecular catalysts to conductive supports for the preparation of solid-state anodes is important for the development of devices for electrocatalytic water oxidation. The preparation and characterization of three molecular cyclopentadienyl iridium(III) complexes, Cp*Ir(1-pyrenyl(2-pyridyl)ethanolate-κO,κN)Cl (1) (Cp* = pentamethylcyclopentadienyl), Cp*Ir(diphenyl(2-pyridyl)methanolate-κO,κN)Cl (2), and [Cp*Ir(4-(1-pyrenyl)-2,2′-bipyridine)Cl]Cl (3), as precursors for electrochemical water oxidation catalysts, are reported. These complexes contain aromatic groups that can be attached via noncovalent π-stacking to ordered mesoporous carbon (OMC). The resulting iridium-based OMC materials (Ir-1, Ir-2, and Ir-3) were tested for electrocatalytic water oxidation leading to turnover frequencies (TOFs) of 0.9–1.6 s−1 at an overpotential of 300 mV under acidic conditions. The stability of the materials is demonstrated by electrochemical cycling and X-ray absorption spectroscopy analysis before and after catalysis. Theoretical studies on the interactions between the molecular complexes and the OMC support provide insight onto the noncovalent binding and are in agreement with the experimental loadings.

A family of Ni(II) halide complexes of substituted aniline derivatives were prepared and studied via single-crystal X-ray diffraction and variable temperature magnetic measurements: [Ni(4-Mean)4Cl2] 1, [Ni(4-Clan)2Cl2(MeOH)2] 2, [Ni(4-Clan)2Br2(EtOH)2] 3, [Ni(4-Clan)4Br2] (4-Clan) 4, [Ni(4-Clan)2Br2(H2O)2] 5, [Ni(4-MeOan)2Br2(H2O)2] 6, [Ni(3-MeOan)4Cl2] 7, [Ni(3-MeOan)4Br2] 8, [Ni(4-MeOan)4Cl2] 9, [Ni(4-MeOan)4(H2O)2](Br)2 10, and [(4-MeOan)2(DMSO)4Ni](Br)2 11 (4-Mean = 4-methylaniline, 4-Clan = 4-chloroaniline, 3-MeOan = 3-methoxyaniline, 4-MeOan = 4-methoxyaniline). All complexes are six-coordinate, filling the coordination sphere with a combination of halide ions, aniline-based ligands and/or solvent molecules. The complexes demonstrate variable stability once removed from the mother liquor with loss of coordinated solvent molecules being common. Analysis of the magnetic properties of the compounds shows the presence of single-ion anisotropy, weak interactions, or a combination thereof.

The elastic moduli of amorphous and crystalline atomic layer-deposited Hf1-xZrxO2 (HZO, x = 0, 0.31, 0.46, 0.79, 1) films prepared with TaN electrodes on silicon substrates were investigated using picosecond acoustic measurements. The moduli of the amorphous films were observed to increase between 211 ± 6 GPa for pure HfO2 and 302 ± 9 GPa for pure ZrO2. In the crystalline films, it was found that the moduli increased upon increasing the zirconium composition from 248 ± 6 GPa for monoclinic HfO2 to 267 ± 9 GPa for tetragonal ZrO2. Positive deviations from this increase were observed for the Hf0.69Zr0.31O2 and Hf0.54Zr0.46O2 compositions, which were measured to have moduli of 264 ± 8 GPa and 274 ± 8 GPa, respectively. These two compositions contained the largest fractions of the ferroelectric orthorhombic phase, as assessed from polarization and diffraction data. The biaxial stress states of the crystalline films were characterized through sin2( ψ) x-ray diffraction analysis. The in-plane stresses were all found to be tensile and observed to increase with the increasing zirconium composition, between 2.54 ± 0.6 GPa for pure HfO2 and 5.22 ± 0.5 GPa for pure ZrO2. The stresses are consistent with large thermal expansion mismatches between the HZO films and silicon substrates. These results demonstrate a device-scale means to quantify biaxial stress for investigation on its effect on the ferroelectric properties of hafnia-based materials.

Lithium bis(diisopropylphosphino)amide LiN[P(i-Pr)2]2 reacts with SnCl2 or GeCl2·dioxane in the presence of excess n-BuLi to produce the bicyclic compounds {MN[P(i-Pr)2]2}2 (M = Sn, Ge) which feature Sn22+ or Ge22+ units bridged by phosphorus. When paired with B(C6F5)3 in THF, the Lewis-basic M22+ complexes participate in a THF ring-opening reaction. Quite surprisingly, in the absence of THF one para-F atom from B(C6F5)3 is activated and displaced to B while a new M–C bond is formed. Each of these complexes, as well as Cl2Sn{N[P(i-Pr)2]2}2 and {ClSnN[P(i-Pr)2]2}2 were characterized by a combination of multi-nuclear NMR spectroscopy and single-crystal X-ray diffraction.

The reactions of carbamoylmethylphosphonates (CMP) and carbamoylmethylphosphine oxides (CMPO) with mercuric nitrate typically result in deprotonation of the methylene carbon atom spanning the phosphoryl and the amide carbonyl groups of the bifunctional ligand with concomitant formation of [Hg(L)](NO3) compounds containing a stable mercury-carbon σ bond. The resulting organometallic compounds form dimers [Hg(L)(NO3)]2 via bidentate interactions between the phosphoryl oxygen atom and carbonyl oxygen atom in one [Hg(L)]+ unit and the Hg(II) ion in the second [Hg(L)]+ unit. Additional examples of this general reactivity/structure pattern are reported herein. In contrast, in Hg(II) complexes of two CMPO derivatives, in which the amide N-atom is functionalized with a 2-methylpyridine group, the trifunctional phosphine oxides are observed to behave as neutral ligands forming complexes (L′)Hg (NO3)2.

Cyclic(alkyl)(amino) carbene (CAAC)-stabilized complexes of phosphorus, one of the lightest group 15 elements, are well-established and can often be obtained in high yields. In contrast, analogous CAAC compounds of bismuth, the heaviest nonradioactive member of group 15, are unknown. Indeed, reactivity increases as you descend the group, and as a result there are only a few examples of N-heterocyclic carbene (NHC)-bismuth complexes. Moreover, activated bismuth compounds often readily extrude bismuth metal, making isolation of stable complexes highly challenging. We report that CAACs react with phenylbismuth dichloride (PhBiCl2) to afford Et2CAAC-Bi(Ph)Cl2 and CyCAAC-Bi(Ph)Cl2. Significantly, these complexes represent the first structurally characterized examples of CAAC-coordination to bismuth. The CAAC-stabilized bismuth compounds can also be obtained from air-stable salts, [Et2CAAC-H]22+ [Cl2(Ph)Bi(μ-Cl2)Bi(Ph)Cl2]2– and [CyCAAC-H]22+ [Cl2(Ph)Bi(μ-Cl2)Bi(Ph)Cl2]2–, by deprotonation with potassium bis(tr...

The structure of the title compound, {(NH4)2[Cu(C2O4)2]}n, at 100 K has monoclinic (P21/c) symmetry with the CuIIatom on an inversion center. The compound has a polymeric structure due to long Cu...O interactions which create [Cu(C2O4)2] chains along theaaxis. The structure also displays intermolecular N—H...O hydrogen bonding, which links these chains into a three-dimensional network.

The bis(phosphino)amines (R2P)NH(PR′2) (R = R′ = isopropyl; R = R′ = phenyl; R = isopropyl, R′ = phenyl) react with ZnEt2 to form complexes with two different structural motifs, either the homoleptic monomeric P,P-chelates Zn[N(i-Pr2P)2]2 and Zn[N(i-Pr2P)(Ph2P)]2 or the heteroleptic dimeric Zn2N2P2 heterocycles {EtZn[N(PPh2)2]}2 and {EtZn[N(PPh2)(i-Pr2P)]}2. In two cases, CO2 reacts with these complexes to give adducts Zn[O2CP(i-Pr2)NP(i-Pr2)]2 and Zn[O2CP(i-Pr2)NPPh2][Ph2PN(i-Pr2P)]ZnEt2, similar to adducts formed from the reaction of CO2 with frustrated Lewis pairs (FLPs). In the other two cases, reaction with CO2 results in cleavage and rearrangement of the N–P bonds to give either N(PPh2)3 or Ph2P(iPr2P)NPPh2. The zinc complexes and their CO2 products were characterized with a combination of single crystal X-ray diffraction and multinuclear NMR spectroscopy.

The catalytic reactivity of the high-spin Mn(II) pyridinophane complexes [(Py2NR2)Mn(H2O)2]2+ (R = H, Me, tBu) towards O2 formation is reported. With small macrocycle N-substituents (R = H, Me), the complexes catalytically disproportionate H2O2 in aqueous solution. While this catalysis is shut down with a bulky substituent (R = tBu), the complex becomes active for electrocatalytic H2O oxidation in aqueous solution. Control experiments are in support of a homogeneous molecular catalyst and preliminary mechanistic studies suggest the catalyst is mononuclear. This ligand-controlled switch in catalytic reactivity has implications for the design of new manganese-based water oxidation catalysts.

Recently, we have witnessed significant progress with regard to the synthesis of molecular alkaline earth metal reagents and catalysts. To provide new precursors for light alkaline earth metal chemistry, molecular aryloxide and alkoxide complexes of beryllium and magnesium are reported. The reaction of beryllium chloride dietherate with two equivalents of 1,3-diisopropyl-4,5-dimethylimidizol-2-ylidine (sIPr) results in the formation of a bis(N-heterocyclic carbene) (NHC) beryllium dichloride complex, (sIPr)2BeCl2 (1). Compound 1 reacts with lithium diisopropylphenoxide (LiODipp) or sodium ethoxide (NaOEt) to form the terminal aryloxide (sIPr)Be(ODipp)2 (2) and alkoxide dimer [(sIPr)Be(OEt)Cl]2 (3), respectively. Compounds 2 and 3 represent the first beryllium alkoxide and aryloxide species supported by NHCs. Structurally related dimers of magnesium, [(sIPr)Mg(OEt)Brl]2 (4) and [(sIPr)Mg(OEt)Me]2 (5), were also prepared. Compounds 1-5 were characterized by single crystal X-ray diffraction studies, 1H, 13C, and 9Be NMR spectroscopy where applicable.

The reaction of (Me3Si)(i-Pr2P)NH with ZnEt2 gives the complex {[(Me3Si)(i-Pr2P)N]ZnEt}2, which was characterized by multinuclear NMR spectroscopy and X-ray crystallography. This Zn complex reacts with CO2 to give an adduct with the proposed formula of [(Me3Si)N(i-Pr2PCO2)]ZnEt that undergoes further transformation into the crystallographically characterized di-adduct [(Me3Si)N(i-Pr2PCO2)]2Zn, in addition to a Zn6 cluster containing both P–CO2 adducts and fragments of the isocyanate i-Pr2P–N C O. These reaction pathways have been separately observed in related group 2 and group 14 complexes, but not previously within the same molecule. Reactions with the related heteroallene CS2 were also examined. The free ligand (Me3Si)(i-Pr2P)NH reacts with CS2 to form a bright red, crystalline adduct (Me3Si)[P(i-Pr)2(CS2)]NH. This adduct was treated with ZnEt2 to provide the same product that is obtained from the reaction of {[(Me3Si)(i-Pr2P)N]ZnEt}2 with CS2, proposed to be a dithiocarbamate complex, with the CS2 bound to the N instead of the P atom.

In its neutral state, bis(diisopropylphosphino)amine HL reacts in equimolar amounts with the nickel halides NiCl2·6H2O, NiBr2, and NiI2in ethanol solutions to give the air- and moisture-stable P,P-chelated complexes (HL)NiX2(X = Cl, Br, I). Under similar conditions, complexes of the form (HL)2NiX2(X = BF4, NO3, ClO4) were prepared from 2:1 ligand-metal ratios of Ni(BF4)2{\textperiodcentered}6H2O, Ni(NO3)2{\textperiodcentered}6H2O, or Ni(ClO4)2{\textperiodcentered}6H2O. Deprotonation of the ligand with NaNH2followed by reaction with NiI2gives L2Ni when performed in Et2O, but leads to the co-crystal L2Ni{\textperiodcentered}2NCCHC(Me)NH2 when the solvent is acetonitrile. In addition to these Ni2+compounds, the Ni0complex (HL)2Ni can be prepared from a toluene solution of Ni(cod)2. Each complex has been characterized by a combination of IR and multi-nuclear NMR spectroscopies, as well as single-crystal X-ray diffraction. Electrochemical studies of the complexes revealed irreversible decomposition of the (HL)NiX2(X = Cl, Br, I) series, but electrocatalytic CO2reduction by the (HL)2NiX2(X = BF4, NO3, ClO4) compounds.