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A synthetic route has been developed for a series of 3d homobimetallic complexes of Mn, Fe, Co, Ni and Cu using three different pyridyldiimine (PDI) and pyridyldialdimine (PDAI) macrocyclic ligands with ring sizes of 18, 20 and 22 atoms. Crystallographic analyses indicate that while the distances between the metals can be modulated by the size of the macrocycle pocket, the flexibility in the alkyl linkers used to construct the macrocycles enables the ligand to adjust the orientation of the PD(A)I fragments in response to the geometry of the [M(2)(μ-Cl)(2)](2+) core, particularly with respect to Jahn-Teller distortions. Analyses by UV-Vis spectroscopy and SQUID magnetometry revealed deviations from the properties [M(2)(μ-Cl)(2)](2+)-containing complexes bound by standard mononucleating ligands, highlighting the ability of macrocycles to use ring-size to control the magnetic interactions of pseudo-octahedral, high-spin metal centers.

The power of oriented electrostatic fields (ESFs) to influence chemical bonding and reactivity is a phenomenon of rapidly growing interest. The presence of strong ESFs has recently been implicated as one of the most significant contributors to the activity of select enzymes, wherein alignment of a substrate's changing dipole moment with a strong, local electrostatic field has been shown to be responsible for the majority of the enzymatic rate enhancement. Outside of enzymology, researchers have studied the impacts of "internal" electrostatic fields

The effects of ligand structural variation on the ultrafast dynamics of a series of copper coordination complexes were investigated using polarization-dependent mid-IR pump probe spectroscopy and two-dimensional infrared (2DIR) spectroscopy. The series consists of three copper complexes [((R3)P(3)tren)Cu(II)N(3)]BAr(F)(4) (1(PR3) ,(R3)P(3)tren = tris[2-(phosphiniminato)ethyl]amine, BAr(F)(4) = tetrakis(pentafluorophenyl)borate) where the number of methyl and phenyl groups in the PR(3) ligand are systematically varied across the series (PR(3) = PMe(3), PMe(2)Ph, PMePh(2)). The asymmetric stretching mode of azide in the 1(PR3) series is used as a vibrational probe of the small molecule binding site. The results of the pump probe measurements indicate that the vibrational energy of azide dissipates through intramolecular pathways and that the bulkier phenyl groups lead to an increase in the spatial restriction of the diffusive reorientation of bound azide. From 2DIR experiments we characterize the spectral diffusion of the azide group and find that an increase in the number of phenyl groups maps to a broader inhomogeneous frequency distribution (Δ(2)). This indicates that an increase in the steric bulk of the secondary coordination sphere acts to create more distinct configurations in the local environment that are accessible to the azide group. This work demonstrates how ligand structural variation affects the ultrafast dynamics of a small molecular group bound to the metal center, which could provide insight into the structure-function relationship of the copper coordination complexes, and transition metal coordination complexes in general.

This report describes the first examples of unassisted C(sp)-C(sp

A series of tetradentate tris(phosphinimine) ligands (R3P3tren) was developed and bound to CuI to form the trigonal pyramidal, C3v-symmetric cuprous complexes [R3P3tren-Cu][BArF4] (1PR3) (PR3 = PMe3, PMe2Ph, PMePh2, PPh3, PMe2(NEt2), BArF4 = B(C6F5)4). Electrochemical studies on the CuI complexes were undertaken, and the permethylated analog, 1PMe3, was found to display an unprecedentedly cathodic CuI/CuII redox potential (−780 mV vs. Fc/Fc+ in isobutyronitrile). Elucidation of the electronic structures of 1PR3via density functional theory (DFT) studies revealed atypical valence manifold configurations, resulting from strongly σ-donating phosphinimine moieties in the xy-plane that destabilize 2e (dxy/dx2−y2) orbital sets and uniquely stabilized a1 (dz2) orbitals. Support is provided that the a1 stabilizations result from intramolecular electrostatic fields (ESFs) generated from cationic character on the phosphinimine moieties in R3P3tren. This view is corroborated via 1-dimensional electrostatic potential maps along the z-axes of 1PR3 and their isostructural analogues. Experimental validation of this computational model is provided upon oxidation of 1PMe3 to the cupric complex [Me3P3tren-Cu][OTf]2 (2PMe3), which displays a characteristic Jahn–Teller distortion in the form of a see-saw, pseudo-Cs-symmetric geometry. A systematic anodic shift in the potential of the CuI/CuII redox couple as the steric bulk in the secondary coordination sphere increases is explained through the complexes' diminishing ability to access the ideal Cs-symmetric geometry upon oxidation. The observations and calculations discussed in this work support the presence of internal electrostatic fields within the copper complexes, which subsequently influence the complexes' properties via a method orthogonal to classic ligand field tuning., Secondary coordination sphere electrostatic effects tune the valence manifolds of copper centers, impacting molecular geometries, photophysical properties, and redox potentials.

The use of oriented internal electrostatic fields in homogenous systems is rapidly gaining attention as a nonconventional design principle for imparting unusual properties and/or reactivity profiles on metal complexes and catalysts. Herein, a series of η1 cupric superoxide complexes bound by tris(phosphinimine) ligands (X-PhMe2P3tren) are reported. Across this series of complexes, the identity of the substituent at the 4 position of a phosphinimine phenyl group was modulated (X = NMe2, H, CF3). The X-PhMe2P3tren ligands impart systematic adjustments to the electronic and secondary coordination sphere electrostatic properties of the copper complexes while maintaining a consistent steric profile in the vicinity of the O2 binding pockets. Key differences in the thermal stabilities and proton-coupled electron transfer (PCET) kinetics were observed among the η1 cupric superoxide complexes, which are discussed in the context of both intra- and inter-molecular electrostatic interactions. Notably, the cupric superoxide complex that was most resistant to decomposition – [(CF3 PhMe2P3tren)CuII(O2•1–)]+ – displays markedly improved thermal stability compared to the Me3P3tren-bound cupric superoxide complex and can be observed as high as room temperature on a multi-minute timescale. Detailed kinetic and computational analyses suggest that the improved thermal stability in this context results from an electrosteric effect, in which the accumulation of cationic charge in the secondary coordination sphere slows bimolecular decomposition.

We recently reported the presence of strong, local electrostatic fields in the secondary coordination sphere of a phosphinimine-decorated CuI complex, [(P3tren)CuI]+ (1). Here, we show that the low-temperature oxygenation of 1 yields a long-lived, three-fold symmetric η1-cupric superoxide complex, [(P3tren)CuII(O2)]+ (2). This latter complex was shown to abstract hydrogen atoms from 2,6-di-tert-butyl-4-methoxy phenol (KIE = 3.0 ± 0.3) and oxidize a cuprous tris(2-pyridylmethyl)amine complex to form a heteroleptic di(cupric)-μ-1,2-peroxide complex (4). The thermal stability of 2 was observed to be uncommonly high for sterically unprotected cupric superoxide complexes in this geometry (t1/2 = 10.4 h at -85 °C). Density functional theory (DFT) calculations implicate a unique electrostatic stabilization of the π*v orbital of the O2 unit, and the thermal stability of 2 is discussed in the context of the CuI/II redox potential of 1, the steric bulk in the complex’s secondary coordination sphere, and intramolecular electrostatic interactions.

This report describes an isostructural series of dinuclear iron, cobalt, and nickel complexes bound by a redox-active macrocyclic ligand. The series spans five redox levels (34–38 e–/cluster core),...

This work provides new routes for the conversion of U(iv) into U(vi) bis(imido) complexes and offers new information on the manner in which the U(vi) compounds form. Many compounds from the series described by the general formula U(NR)2(EPh)2(L)2 (R = 2,6-diisopropylphenyl, tert-butyl; E = S, Se, Te; L = py, EPh) were synthesized via oxidation of an in situ generated U(iv) amido-imido species with Ph2E2. This synthetic sequence provides a general route into bis(imido) U(vi) chalcogenolate complexes, circumventing the need to perform problematic salt metathesis reactions on U(vi) iodides. Investigation into the speciation of the U(iv) complexes that form prior to oxidation found a significant dependence on the identity of the ancillary ligands, with tBu2bpy forming the isolable imido-(bis)amido complex, U(NDipp)(NHDipp)2(tBu2bpy)2. Together, these data are consistent with the view that the bis(imido) U(vi) motif - much like the uranyl ion, UO22+- is a thermodynamic sink into which simple ligand frameworks are unable to prevent uranium from falling when in the presence of a suitable retinue of imido proligands.

Low-nuclearity nitrides of the late transition metals are rare and reactive molecular species, with little experimental precedent. The first putative examples of dicobalt bridging nitrides, [(nPDI2)Co2(μ-N)(PMe3)2][OTf]3 (n[Co2N]3+; PDI = pyridyldiimine; n = 2 or 3, representing the length of the aliphatic chain linking PDI imino groups), were reported recently and shown to undergo a range of intramolecular reaction pathways, including N-H bond formation, C-H bond insertion, and P═N bond formation at the bridging nitride. The specific mode of reactivity changed with the phase of the reaction and the size of the macrocycle used to support the transient species. The present contribution offers a computational investigation into both the geometric and electronic structures of these nitrides as well as the factors governing their reaction selectivity. The compounds n[Co2N]3+ exhibit μ-N-based lowest unoccupied molecular orbitals (LUMOs) that are consistent with subvalent, electrophilic nitrides. The specific orientations of the LUMOs induce ring-size-dependent stereoelectronic effects, thereby causing the product selectivity observed experimentally. Notably, the nitrides also exhibit a degree of nucleophilicity at μ-N by way of a high-energy, μ-N-based lone pair. This ambiphilic character appears to be a direct result of the constrained environment imposed by the folded-ligand geometries of n[Co2N]3+. When combined with the experimental findings, these data led to the conclusion that the folded-ligand isomers are the reactive species and that the constrained geometry imposed by the macrocyclic ligand plays an important role in controlling the reaction outcome.

Cluster complexes have attracted interest for decades due to their promise of drawing analogies to metallic surfaces and metalloenzyme active sites, but only recently have chemists started to develop ligand scaffolds that are specifically designed to support multinuclear transition metal cores. Such ligands not only hold multiple metal centers in close proximity but also allow for fine-tuning of their electronic structures and surrounding steric environments. This Feature Article highlights ligand designs that allow for cooperative small molecule activation at cluster complexes, with a particular focus on complexes that contain metal-metal bonds. Two useful ligand-design elements have emerged from this work: a degree of geometric flexibility, which allows for novel small molecule activation modes, and the use of redox-active ligands to provide electronic flexibility to the cluster core. The authors have incorporated these factors into a unique class of dinucleating macrocycles ((n)PDI(2)). Redox-active fragments in (n)PDI(2) mimic the weak-overlap covalent bonding that is characteristic of M–M interactions, and aliphatic linkers in the ligand backbone provide geometric flexiblity, allowing for interconversion between a range of geometries as the dinuclear core responds to the requirements of various small molecule substrates. The union of these design elements appears to be a powerful combination for analogizing critical aspects of heterogeneous and metalloenzyme catalysts.

A series of 2,6-diiminopyridine-derived macrocyclic ligands have been synthesized via [2+2] condensation around alkaline earth metal triflate salts. The inclusion of a tert-butyl group at the 4-position of the pyridine ring of the macrocyclic synthons results in macrocyclic complexes that are soluble in common organic solvents, thereby enabling a systematic comparison of the physical properties of the complexes by NMR spectroscopy, mass spectrometry, solution-phase UV-Vis spectroscopy, cyclic voltammetry and single-crystal X-ray crystallography. Solid-state structures determined crystallographically demonstrate increased twisting in the ligand, concurrent with either a decrease in ion size or an increase in macrocycle ring size (18, 20, or 22 membered rings). The degree of folding and twisting within the macrocycle can be quantified using parameters derived from the N(pyr)-M-N(pyr) bond angle and the relative orientation of the pyridinediimine (PDI) and pyridinedialdimine (PDAI) fragments to each other within the solid state structures. Cyclic voltammetry and UV-Vis spectroscopy were used to compare the relative energies of the imine π* orbital of the redox active PDI and PDAI components in the macrocycle when coordinated to redox inactive metals. Both methods indicate the change from a methyl to hydrogen substitution on the imine carbon lowers the energy of the ligand π* system.

This communication describes the C–C bond activation of acetonitrile and the trapping of the methyl and cyanide fragments by macrocyclic, dicobalt complexes. Both products display unique structural features as a result of the constraints imposed by the macrocycle. The bridged species [((3)PDI(2))Co(2)(μ-CN)(PMe(3))(2)][OTf] ([Co(2)CN](+)) exhibits atypical Co–CN–Co binding, and upon either phosphine dissociation or oxidation, the flexible ligand framework is able to switch between different binding modes of μ-cyanide. Further, the bridging methyl species [((3)PDI(2))Co(2)(μ-CH(3))(PMe(3))][OTf] ([Co(2)CH(3)](+)) is the first structurally characterized dicobalt complex with a bridging methyl group.

Herein is described a mechanistic study of a palladium-catalyzed cross-coupling of aryl Grignard reagents to fluoroarenes that proceeds via a low-energy heterobimetallic oxidative addition pathway. Traditional oxidative additions of aryl chlorides to Pd complexes are known to be orders of magnitude faster than with aryl fluorides, and many palladium catalysts do not activate aryl fluorides at all. The experimental and computational studies outlined herein, however, support the view that at elevated Grignard : ArX ratios (i.e. 2.5 : 1) a Pd-Mg heterobimetallic mechanism predominates, leading to a remarkable decrease in the energy required for Ar-F bond activation. The heterobimetallic transition state for C-X bond cleavage is proposed to involve simultaneous Pd backbonding to the arene and Lewis acid activation of the halide by Mg to create a low-energy transition state for oxidative addition. The insights gained from this computational study led to the development of a phosphine ligand that was shown to be similarly competent for Ar-F bond activation.

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N–H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N–H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E–H bonds (E = B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH(3) in high yield through a reaction that engages the redox-activity of the ligand during PCET.

Pincer ligands have a remarkable ability to impart control over small molecule activation chemistry and catalytic activity; therefore, the design of new pincer ligands and the exploration of their reactivity profiles continues to be a frontier in synthetic inorganic chemistry. In this work, a novel, monoanionic NNN pincer ligand containing two phosphinimine donors was used to create a series of mononuclear Ni complexes. Ligand metallation in the presence of NaOPh yielded a nickel phenoxide complex that was used to form a mononuclear hydride complex on treatment with pinacolborane. Attempts at ligand metallation with NaN(SiMe(3))(2) resulted in the activation of both phosphinimine methyl groups to yield an anionic, cis-dialkyl product, in which dissociation of one phosphinimine nitrogen leads to retention of a square planar coordination environment about Ni. Protonolysis of this dialkyl species generated a monoalkyl product that retained the 4-membered metallacycle. The insertion of 2,6-dimethylphenyl isocyanide (xylNC) into this nickel metallacycle, followed by proton transfer, generated a new five-membered nickel metallacycle. Kinetic studies suggested rate-limiting proton transfer (KIE ≥ 3.9±0.5) from the α-methylene unit of the putative iminoacyl intermediate.

A novel approach to produce chiral diaryl sulfoxides from aryl benzyl sulfoxides and aryl bromides via an enantioselective arylation of aryl sulfenate anions is reported. A (JosiPhos)Pd-based catalyst successfully promotes the asymmetric arylation reaction with good functional group compatibility. A wide range of enantioenriched diaryl, aryl heteroaryl, and even diheteroaryl sulfoxides were generated. Many of the sulfoxides prepared herein would be difficult to prepare via classic enantioselective oxidation of sulfides, including Ph(Ph-d5)SO (90% ee, 95% yield). A DFT-based computational study suggested that chiral induction originates from two primary factors: (i) both a kinetic and a thermodynamic preference for oxidative addition that places the bromide trans to the JosiPhos-diarylphosphine moiety and (ii) Curtin-Hammett-type control over the interconversion between O- and S-bound isomers of palladium sulfenate species following rapid interconversion between re- and si-bound transmetalation products, re/si-Pd-OSPh (re/si-PdO-trans). Fil: Jia, Tiezheng. University of Pennsylvania; Estados Unidos Fil: Zhang, Mengnan. University of Pennsylvania; Estados Unidos Fil: McCollom, Samuel P.. University of Pennsylvania; Estados Unidos Fil: Bellomo Peraza, Ana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias ; Argentina Fil: Montel, Sonia. University of Pennsylvania; Estados Unidos Fil: Mao, Jianyou. Nanjing Tech University; República de China Fil: Dreher, Spencer D.. Merck & Company; Estados Unidos Fil: Welch, Christopher J.. Merck & Company; Estados Unidos Fil: Regalado, Erik L.. Merck & Company; Estados Unidos Fil: Williamson, R. Thomas. Merck & Company; Estados Unidos Fil: Manor, Brian C.. Merck & Company; Estados Unidos Fil: Tomson, Neil C.. University of Pennsylvania; Estados Unidos Fil: Walsh, Patrick J.. University of Pennsylvania; Estados Unidos

A dinucleating macrocyclic ligand with two redox-active, pyridyldiimine components was shown to undergo reversible ligand folding to accommodate various substitution patterns, metal ion spin states, and degrees of Fe-Fe bonding within the cluster. An unfolded-ligand geometry with a rectangular Fe2(μ-Cl)2 core and an Fe-Fe distance of 3.3262(5) A served as a direct precursor to two different folded-ligand complexes. Chemical reduction in the presence of PPh3 resulted in a diamagnetic, folded ligand complex with an Fe-Fe bonding interaction (dFe-Fe = 2.7096(17) A) between two intermediate spin (SFe = 1) Fe(II) centers. Ligand folding was also induced through anion exchange on the unfolded-ligand species, producing a complex with three PhS- ligands and a temperature-dependent Fe-Fe distance. In this latter example, the weak ligand field of the thiolate ligands led to a product with weakly coupled, high-spin Fe(II) ions (SFe = 2; J = -50.1 cm-1) that form a bonding interaction in the ground state and a nonbonding interaction in the excited state(s), as determined by SQUID magnetometry and variable temperature crystallography. Finally, both folded-ligand complexes were shown to reform an unfolded-ligand geometry through convergent syntheses of a complex with an Fe-Fe bonded Fe2(μ-SPh)2 core (dFe-Fe = 2.7320(11) A). Experimentally validated DFT calculations were used to investigate the electronic structures of all species as a way to understand the origin of Fe-Fe bonding interactions, the extent of ligand reduction, and the nature of the spin systems that result from multiple, weakly interacting spin centers.

This work provides new routes for the conversion of U(iv) into U(vi) bis(imido) complexes and offers new information on the manner in which the U(vi) compounds form. Many compounds from the series described by the general formula U(NR)

Metal-catalyzed carbon-carbon bond-forming reactions are a mainstay in the synthesis of pharmaceutical agents. A long-standing problem plaguing the field of transition metal catalyzed C-H functionalization chemistry is control of selectivity among inequivalent C-H bonds in organic reactants. Herein we advance an approach to direct site selectivity in the arylation of 2-benzylfurans founded on the idea that modulation of cooperativity in bimetallic catalysts can enable navigation of selectivity. The bimetallic catalysts introduced herein exert a high degree of control, leading to divergent site-selective arylation reactions of both sp(2) and sp(3) C-H bonds of 2-benzylfurans. It is proposed that the selectivity is governed by cation-π interactions, which can be modulated by choice of base and accompanying additives [MN(SiMe3)2, M = K or Li·12-crown-4].

Reaction of [Pd(IPr)(2)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and O-2 leads to the surprising discovery that at low temperature the initial reaction product is a highly labile peroxide complex cis-[Pd(IPr)(2)(eta(2)-O-2)]. At temperatures greater than or similar to -40 degrees C, cis-[Pd(IPr)(2)(eta(2)-O-2)] adds a second O-2 to form trans-[Pd(IPr)(2)(eta(1)-O-2)(2)]. Squid magnetometry and EPR studies yield data that are consistent with a singlet diradical ground state with a thermally accessible triplet state for this unique bis-superoxide complex. In addition to reaction with O-2 , cis-[Pd(IPr)(2)(eta(2)-O-2)] reacts at low temperature with H2O in methanol/ether solution to form trans-[Pd(IPr)(2)(OH)(OOH)]. The crystal structure of trans-[Pd(IPr)(2)(OOH) (OH)] is reported. Neither reaction with O-2 nor reaction with H2O occurs under comparable conditions for cis-[Pd(IMes)(2)(eta(2)-O-2)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). The increased reactivity of cis-[Pd(IPr)(2)(eta(2)-O-2)] is attributed to the enthalpy of binding of O-2 to [Pd(IPr)(2)] (-14.5 +/- 1.0 kcal/mol) that is approximately one-half that of [Pd(IMes)(2)] (-27.9 +/- 1.5 kcal/mol). Computational studies identify the cause as interligand repulsion forcing a wider C-Pd-C angle and tilting of the NHC plane in cis-[Pd(IPr)(2)(eta(2)-O-2)]. Arene-arene interactions are more favorable and serve to further stabilize. cis-[Pd(IMes)(2)(eta(2)-O-2)]. Inclusion of dispersion effects in DFT calculations leads to improved agreement between experimental and computational enthalpies of O-2 binding. A complete reaction diagram is constructed for formation of trans-[Pd(IPr)(2)(eta(1)-O-2)(2)] and leads to the conclusion that kinetic factors inhibit formation of trans-[Pd(IMes)(2)(eta(1)-O-2)(2)] at the low temperatures at which it is thermodynamically favored. Failure to detect the predicted T-shaped intermediate trans-[Pd(NHC)(2)(eta(1)-O-2)] for either NHC = IMes or IPr is attributed to dynamic effects. A partial potential energy diagram for initial binding of O-2 is constructed. A range of low-energy pathways at different angles of approach are present and blur the distinction between pure "side-on" or "end-on" trajectories for oxygen binding.

Reaction of [Pd(IPr)

Three [Me2NN]Cu(η2-L2) complexes (Me2NN = HC[C(Me)NAr]2; L2 = PhNO (2), (3), PhCH 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 CH2 (4); Ar = 2,6-Me2-C6H3; ArF = 3,5-(CF3)2-C6H3) have been studied by Cu K-edge X-ray absorption spectroscopy, as well as single- and multi-reference computational methods (DFT, TD-DFT, CASSCF, MRCI, and OVB). The study was extended to a range of both known and theoretical compounds bearing 2p-element donors as a means of deriving a consistent view of how the pre-edge transition energy responds in systems with significant ground state covalency. The ground state electronic structures of many of the compounds under investigation were found to be strongly influenced by correlation effects, resulting in ground state descriptions with majority contributions from a configuration comprised of a Cu(ii) metal center anti-ferromagentically coupled to radical anion O2, PhNO, and ligands. In contrast, the styrene complex 4, which displays a Cu K pre-edge transition despite its formal d10 electron configuration, exhibits what can best be described as a Cu(i):(styrene)0 ground state with strong π-backbonding. The Cu K pre-edge features for these complexes increase in energy from 1 to 4, a trend that was tracked to the percent Cu(ii)-character in the ground state. The unexpected shift to higher pre-edge transition energies with decreasing charge on copper (QCu) contributed to an assignment of the pre-edge features for these species as arising from metal-to-ligand charge transfer instead of the traditional Cu1s → Cu3d designation.

The terminal imido complexes U(NDipp)Cl2(tppo)3 (tppo = triphenylphosphine oxide) and U(NDipp)Cl2(R2bpy)2 (Dipp = 2,6-iPr2-C6H3; R2bpy = 4,4′-R2-2,2′-bipyridyl; R = Me, tBu) contain reactive U N bonds, which undergo [2 + 2] cycloaddition reactions with the N–C multiple bonds of isocyanates and benzonitrile. These low valent imido complexes display a preference for forming cycloaddition products, in contrast to high valent bis(imido) complexes, which undergo imido group exchange when treated with isocyanates. This disparity suggests that the U(IV) NR linkage, already known to be more ionic than U(VI) NR bonds, is also weaker than its U(VI) congener. The cycloaddition products that were used in this qualitative bond strength analysis have been characterized by X-ray crystallography and NMR spectroscopy. Most importantly, U(NDipp)Cl2(tppo)3 and U(NDipp)Cl2(R2bpy) appear to be excellent synthetic precursors to new and intriguing organometallic uranium complexes.

Uranium tetrachloride undergoes facile reactions with 4,4'-dialkyl-2,2'-bipyridine, resulting in the generation of UCl4(R2bpy)2, R = Me, (t)Bu. These precursors, as well as the known UCl4(tppo)2 (tppo = triphenylphosphine oxide), react with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide the versatile uranium(IV) imido complexes, U(NDipp)Cl2(L)n (L = R2bpy, n = 2; L = tppo, n = 3). Interestingly, U(NDipp)Cl2(R2bpy)2 can be used to generate the uranium(V) and uranium(VI) bisimido compounds, U(NDipp)2X(R2bpy)2, X = Cl, Br, I, and U(NDipp)2I2((t)Bu2bpy), which establishes these uranium(IV) precursors as potential intermediates in the syntheses of high-valent bis(imido) complexes from UCl4. The monoimido species also react with 4-methylmorpholine-N-oxide to yield uranium(VI) oxo-imido products, U(NDipp)(O)Cl2(L)n (L = (t)Bu2bpy, n = 1; L = tppo, n = 2). The aforementioned molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent sources of U(IV), U(V), and U(VI) imido species.

Metal-catalyzed carbon–carbon bond-forming reactions are a mainstay in the synthesis of pharmaceutical agents. A long-standing problem plaguing the field of transition metal catalyzed C–H functionalization chemistry is control of selectivity among inequivalent C–H bonds in organic reactants. Herein we advance an approach to direct site selectivity in the arylation of 2-benzylfurans founded on the idea that modulation of cooperativity in bimetallic catalysts can enable navigation of selectivity. The bimetallic catalysts introduced herein exert a high degree of control, leading to divergent site-selective arylation reactions of both sp2 and sp3 C–H bonds of 2-benzylfurans. It is proposed that the selectivity is governed by cation−π interactions, which can be modulated by choice of base and accompanying additives [MN(SiMe3)2, M = K or Li·12-crown-4].

The redox-active bis(imino)acenapthene (BIAN) ligand was used to synthesize homoleptic aluminum, chromium, and gallium complexes of the general formula (BIAN)3M. The resulting compounds were characterized using X-ray crystallography, NMR, EPR, magnetic susceptibility and cyclic voltammetry measurements and modeled using both DFT and ab initio wavefunction calculations to compare the orbital contributions of main group elements and transition metals in ligand-based redox events. Complexes of this type have the potential to improve the energy density and electrolyte stability of grid-scale energy storage technologies, such as redox flow batteries, through thermodynamically-clustered redox events.

[(TMEDA)Co(NO)2][BPh4] reacts with Group 1 salts of various monoanionic ligands to yield four and five coordinate {Co(NO)2} 10 complexes. The synthesis of the four coordinate complex of the form [{LX} Co(NO)2] via salt-metathesis reactions of [(TMEDA)Co(NO)2][BPh4] with [{ArNC(Me)CHC(Me)NAr} Li(OEt2)] (Ar ¼ 2,6-di-iso-propylphenyl) is reported. In addition [(TMEDA)Co(NO)2][BPh4] reacts with either KTp * or a suite of cyclopentadienyllithium and cyclopentadienylsodium reagents, to generate the corresponding five coordinate [{L2X}Co(NO)2] complexes ({L2X ¼ C5H5, MeC5H4 ,C p *, t BuC5H4, Ph2CHC5H4 ,M e 3SiC5H4, t BuMe2SiC5H4, i Pr3SiC5H4, 1,3-( i Pr3Si)2C5H3 and Tp * ). In support of existing precedent, the four coordinate complex is a thermally robust and readily isolable species while five coordinate complexes are thermally unstable transient intermediates that may either undergo dissociation of an NO ligand or be trapped by alkenes to form the corresponding metal dinitrosoalkane complexes. These reactions demonstrate that [(TMEDA)Co(NO)2][BPh4] provides a versatile synthetic entry point to cobalt dinitrosyl complexes and obviates the need for the repeated use of nitric oxide in the preparation of dinitrosoalkane complexes of cobalt.

The discovery of a Nb(III)-mediated catalytic hydrogenation of internal alkynes to (Z)-alkenes that proceeds through an unprecedented mechanism is reported. The mechanistic proposal involves initial reduction of the alkyne by the Nb(III) complex (BDI)Nb(N(t)Bu)(CO)(2) to provide a Nb(V) metallacyclopropene, itself capable of σ-bond metathesis reactivity with H(2). The resulting alkenyl hydride species then undergoes reductive elimination to provide the (Z)-alkene product and regenerate a metal complex in the Nb(III) oxidation state. Support for the proposed mechanism is derived from (i) the dependence of the product selectivity on the relative concentrations of CO and H(2), (ii) the isolation of complexes closely related to those proposed to be part of the catalytic cycle, (iii) H/D crossover experiments, and (iv) DFT studies of multiple possible reaction pathways.

Studies on the coordination of nitrosoarene (ArNO) ligands to late-transition metals are used to provide the first definition of the geometric, spectroscopic, and computational parameters associated with a PhNO electron-transfer series. Experimentally, the Pd complexes PdCl(2)(PhNO)(2), PdL(2)(PhNO)(2), and PdL(2)(TolNO) (L = CNAr(Dipp2); Ar(Dipp2) = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3)) are characterized as containing (PhNO)(0), (PhNO)(•1-), and (TolNO)(2-) ligands, respectively, and the structural and spectroscopic changes associated with this electron transfer series provide the basis for an extensive computational study of these and related ArNO-containing late-transition metal complexes. Most notable from the results is the unambiguous characterization of the ground state electronic structure of PdL(2)(PhNO)(2), found to be the first isolable, transition metal ion complex containing an η(1)-N-bound π-nitrosoarene radical anion. In addition to the electron transfer series, the synthesis and characterization of the Fe complex [Fe(TIM)(NCCH(3))(PhNO)][(PF(6))(2)] (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) allows for comparison of the geometric and spectroscopic features associated with metal-to-ligand π-backbonding as opposed to (PhNO)(•1-) formation. Throughout these series of complexes, the N-O, M-N, and C-N bond distances as well as the N-O stretching frequencies and the planarity of the ArNO ligands provided distinct parameters for each ligand oxidation state. Together, these data provide a delineation of the factors needed for evaluating the oxidation state of nitrosoarene ligands bound to transition metals in varying coordination modes.

We have investigated both the chemical reduction of (BDI)Nb(V) imido complexes (BDI = HC[C(Me)NAr](2); Ar = 2,6-(i)Pr(2)-C(6)H(3)) to the formal Nb(III) oxidation state and the ability of these Nb(III) complexes to behave as two-electron reductants. The reduction of the Nb(V) species was found to depend heavily on the nature of available supporting ligands, but the chemistry of the reduced compounds proceeded cleanly with a number of unsaturated organic reagents. Accordingly, the novel Nb(V) bis(imido) complexes supported by the monoazabutadiene (mad) ligand (mad)Nb(N(t)Bu)(NAr)(L') (L' = py, thf) were formed by either KC(8) reduction of (BDI)Nb(N(t)Bu)Cl(2)(py) in the absence of strong π-acids or by H(2) reduction of the Nb(V) dimethyl complex (BDI)Nb(N(t)Bu)Me(2) in THF. These products are likely formed though an intramolecular, 2 e(-) reductive C-N bond cleavage, as has been observed previously for related Group 4 systems, suggesting that transient Nb(III) intermediates were present in both cases. In the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), KC(8) reduction of (BDI)Nb(N(t)Bu)Cl(2)(py) was arrested at the Nb(IV) oxidation state to give (BDI)Nb(N(t)Bu)Cl(dmpe), which was characterized by solution-state EPR spectroscopy as a Nb-centered paramagnet with strong coupling to the two equivalent phosphorus nuclei (A(iso){(93)Nb} = 120.5×10(-4) cm(-1), A(iso){(31)P} = 31.0×10(-4) cm(-1), g(iso) = 1.9815). When strong π-acids were used to intercept the thermally unstable Nb(III) complex (BDI)Nb(N(t)Bu)(py) prior to reductive cleavage of the ligand C-N bond, the thermally stable Nb(III) species (BDI)Nb(N(t)Bu)(CX)(2)(L″) (X = O, L″ = py; X = NXyl, L″ = CNXyl; Xyl = 2,6-Me(2)-C(6)H(3)) were obtained in good yields. The Nb(III) complexes (BDI)Nb(N(t)Bu)py, (BDI)Nb(N(t)Bu)(CO)(2)(py) and (BDI)Nb(N(t)Bu)(CO)(2) were subsequently investigated for their ability to serve as two-electron reducing reagents for both metal-ligand multiple bond formation and for the reduction of organic π-systems. The reduction of mesityl azide by (BDI)Nb(N(t)Bu)(py) and diphenylsulfoxide by (BDI)Nb(N(t)Bu)(CO)(2) led to the monomeric bis(imido) and dimeric oxo complexes (BDI)Nb(N(t)Bu)(NMes)(py) and [(BDI)Nb(N(t)Bu)](2)(μ2-O)(2), respectively. MeLi addition to (BDI)Nb(N(t)Bu)(CO)(2)(py) resulted in the formation of a Nb-acylate via methide addition to one of the carbonyl carbons. The acylate product was revealed to have a short Nb-C(acylate) bond distance (2.059(4) Å), consistent with multiple Nb-C bond character resulting from Nb(III) back-bonding into the acylate carbon. The interaction of (BDI)Nb(N(t)Bu)(CO)(2) with two equivalents of 4,4'-dichlorobenzophenone resulted in the clean, quantitative formation of the corresponding pinacol coupling product, but introduction of the ketone in 1: 1 molar ratios resulted in mixtures of the pinacol product and the starting material, suggesting that ketone coordination to the Nb(III) complex may be reversible. Relatedly, addition of 1-phenyl-1-propyne to (BDI)Nb(N(t)Bu)(CO)(2) formed a thermally unstable 1: 1 Nb/alkyne complex, as characterized by NMR and IR spectroscopies; reaction of this species with HCl/MeOH yielded a 2: 1 mixture of 1-phenyl-1-propene and the free alkyne, suggesting a high degree of covalency in the Nb-C bonds.

In the title compound, C5HN7, the nitrile and azido substituents are close to being coplanar with the central ring. Molecules in the crystal are linkedviaan N—H...N hydrogen bond to a nitrile acceptor, forming a chain extending along thec-axis direction.

The discovery that imido analogs of actinyl dioxo cations can be extended beyond uranium into the transuranic elements is presented. Synthesis of the Np(V) complex, Np(NDipp)2((t)Bu2bipy)2Cl (1), is achieved through treatment of a Np(IV) precursor with a bipyridine coligand and lithium-amide reagent. Complex 1 has been structurally characterized, analyzed by (1)H NMR and UV-vis-NIR spectroscopies, and the electronic structure evaluated by DFT calculations.

The title compound, C3H2N4O4, forms crystals with two molecules in the asymmetric unit which are conformationally similar. With the exception of the O atoms of the nitro groups, the molecules are essentially planar. In the crystal, adjacent molecules are associated by N—H...N hydrogen bonds involving the imidazole N—H donors and N-atom acceptors of the unsaturated nitrogen of neighboring rings, forming layers parallel to (010).

A correlation between the tungsten tin solid state bond distance (rWSn) and the solution state one-bond scalar coupling of tungsten to tin (1JWSn) is reported. This correlation was observed in hydrido- and chlorotungstenocene diorganostannyl chlorides (Cp2WXSnClR2, X = H (1), X = Cl (2)) with sterically demanding organic substituents (R = tBu (1a, 2a), Ph (1b, 2b)). The different steric demands of the organic substituents (tBu and Ph) force the complexes 1a and 1b (or 2a and 2b) to adopt at 190 K in the solid state different, single rotameric conformations. For 1a and 2a, the tBu substituents occupy the equatorial wedge of the tungstenocene, whereas for 1b and 2b the Ph substituents are rotated to place the chlorine in the equatorial wedge. Variable-temperature multinuclear NMR and density functional theory calculations at the B3LYP/LANL2DZ level indicate the possibility of low-lying conformational isomers for complexes 1b.

We have synthesized a series of lanthanide dithiocarbamate precursors for the synthesis of lanthanide sulfide materials and nanoparticles. Three dithiocarbamate complexes with europium, [Eu(S2CNRR‘)3L], where L = 1,10-phenanthroline, and R = methyl, R‘ = ethyl (1), R = R‘ = nPropyl (2), and R = R‘ = iButyl (3), as well as the lanthanide complexes, [Ln(S2CNR2)3 L], where R = ethyl, L = 1, 10-phenanthroline, and Ln = Nd (4), Sm (5), Gd (6), Ho (7), and Er (8), were synthesized and characterized by single-crystal X-ray diffraction, infrared, NMR, and UV−visible spectroscopy. We have used thermal analysis coupled with GC−MS and X-ray powder diffraction to determine the mechanism of decomposition. With R = Et, smaller Ln ions give lower precursor decomposition temperatures, consistent with the higher lattice energies of the product Ln sulfides. Because they are monomeric, and water- and air-stable, these compounds should be ideal precursors for forming LnS as nanoparticles and bulk materials.

Monometallic niobium arene complexes [Nb(BDI)(N(t)Bu)(R-C(6)H(5))] (2a: R = H and 2b: R = Me, BDI = N,N'-diisopropylbenzene-β-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)Nb(N(t)Bu)](2)(μ-RC(6)H(5))] (7a: R = H and 7b: R = Me) in solution. The kinetics of this reaction were followed by (1)H NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds 7a-b showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H(OEt(2))][B(C(6)F(5))(4)], resulting in the monoprotonated cationic inverted sandwich complex 8 [[(BDI(#))Nb(N(t)Bu)][(BDI)Nb(N(t)Bu)](μ-C(6)H(5))][B(C(6)F(5))(4)] and the dicationic complex 9 [[(BDI(#))Nb(N(t)Bu)](2)(μ-RC(6)H(5))][B(C(6)F(5))(4)](2) (BDI(#) = (ArNC(Me))(2)CH(2)). NMR, UV-vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb-arene interactions. The X-ray crystal structures, UV-vis spectra, arene (1)H NMR chemical shifts, and large J(CH) coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding π system of the arene ligands. However, Nb L(3,2)-edge XANES spectra and the lack of sp(3) hybridization of the arene carbons indicate that the Nb → arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d(2) electronic configurations are appropriate to describe the Nb atoms in all four complexes.

Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}(9) species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me(2)-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co-NO bonding interaction as a Co(II) (S(Co) = 3/2) metal center, antiferromagnetically coupled to a triplet NO(-) anion (S(NO) = 1), an interpretation of the electronic structure that was validated by ab initio multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant g-anisotropy in the S = ½ ground state, but the linear-response DFT performed poorly at calculating the g-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin-orbit coupling were required for obtaining accurate modeling of the molecular g-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (S(Ni) = 1) metal center antiferromagnetically coupled to an S(NO) = 1 NO(-). The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO(0) formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and ab initio computational methods for their ability to predict various spectroscopic and molecular features.

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.

Synthesis of the complex (BDI)Nb(N(t)Bu)Cl(2)py (BDI = HC[C(Me)N(2,6-iPr(2)-C(6)H(3))](2)) was achieved in high yield following the treatment of Nb(N(t)Bu)Cl(3)py(2) with Li(BDI)(OEt(2)). Substitution of the chlorides for fluorides was effected by introducing 2.0 equiv of Me(3)SnF in toluene, providing the pyridine-coordinated difluoride complex (BDI)Nb(N(t)Bu)F(2)py in modest yield. The pyridine ligands from both halide compounds were removed by treatment of the pyridine adducts with B(C(6)F(5))(3), affording the Lewis base-free complexes (BDI)Nb(NtBu)X(2) (X = Cl, F). Additionally, the Lewis base-free dichlorides of the (t)Bu-imido and Ar-imido (Ar = 2,6-(i)Pr(2)-C(6)H(3)) complexes were obtained following treatment of Nb(NR)Cl(3)(dme) (R = tBu, Ar) with Li(BDI)(OEt(2)). The pyridine-coordinated dichloride was alkylated and arylated to form the dimethyl complex (BDI)Nb(N(t)Bu)Me(2) (described previously, see text) and the mono(p-tolyl) complex (BDI)Nb(N(t)Bu)Cl(p-tol), the latter of which was methylated with MeMgBr to yield the mixed alkyl/aryl complex (BDI)Nb(N(t)Bu)Me(p-tol) in good yield. A rare example of a Group 5 bis((t)Bu-imido) species was synthesized in good yield via treatment of (BDI)Nb(N(t)Bu)Cl(2)py with 2.0 equiv of LiNHtBu to form (BDI)Nb(NtBu)(2)py. Exchange of the coordinated pyridine ligand for either pyridine-d(5) or dmap (p-(dimethylamino)pyridine) was shown to occur through a dissociative mechanism, allowing for removal of the coordinated Lewis base by treatment with B(C(6)F(5))(3). The resulting average C(2v)-symmetric tetracoordinate bis(imido) complex (BDI)Nb(N(t)Bu)(2) was characterized in solution by NMR spectroscopy and observed to undergo clean thermal decomposition to yield (BDI(#))Nb(N(t)Bu)(NH(t)Bu) (BDI(#) = H(2)C=C(NAr)CH=C(NAr)Me) over several hours at room temperature. Treatment of the four-coordinate bis(imido) with (t)BuNCO resulted in clean [2 + 2] cycloaddition to yield an oxaazametallacyclobutane complex, which was further observed to extrude (t)BuN=C=N(t)Bu over 12 h at room temperature. The molecular structures of (BDI)Nb(N(t)Bu)Cl(2)py, (BDI)Nb(NAr)Cl(2), (BDI)Nb(N(t)Bu)Me(2), (BDI)Nb(N(t)Bu)Cl(p-tol), (BDI)Nb(N(t)Bu)(2)py, and (BDI)Nb(NtBu)(2)(dmap) were determined crystallographically. Finally, DFT (BP86) geometry optimization calculations on a model complex of the thermally unstable four-coordinate bis(imido) species allowed for identification of the orbital interactions leading to activation of the imido groups through mixing with the BDI frontier orbitals.

The reaction of carbon monoxide with a beta-diketiminato dimethyl niobium complex (BDI)Me2Nb(NtBu) is shown to lead to a variety of products whose distribution displays a remarkable dependence on the reaction conditions. Among these, the products of metal reduction, enediolate formation, and intramolecular C-H activation have been fully characterized. An investigation into the individual steps leading to these products points to a transient initial monoacyl complex, whose fate may be perturbed via reaction conditions to allow for control over the product distribution. Furthermore, the reaction of (BDI)Me2Nb(NCMe3) with XylNC (Xyl = 2,6-Me2C6H3) yields the eta2-ketimine complex (BDI)(Me2C=NXyl)Nb(NCMe3), whose characterization and reactivity enhance our understanding of the sequences involving CO.

Ammonia is naturally formed from the conversion of N2 from the atmosphere. A subsequent conversion of the produced ammonia promotes the generation of nitrogen-containing biomolecules. This natural process is carried out by anaerobic bacteria utilizing nitrogenase enzymes to catalyze the transformation. Though biological rates of nitrogen reduction are very slow, ammonia synthesis is carried out by the chemical industry using the Haber-Bosch process, which is a high-pressure, high-temperature, heterogeneous catalysis reaction. The ammonia synthesis reaction is active over Fe and Ru catalysts, though Fe is normally used industrially due to the lower cost. Both H2 and N2 must dissociate at the catalyst surface (Fe or Ru) before the reaction can proceed. Typical operating conditions are 350- 500oC, and 100-200 atm. Only about 15% ammonia conversion is obtained through the catalyst beds with large recycle, which makes the process very energetically inefficient. As a potential alternative, the electrochemical synthesis of NH3provides the most direct and theoretically most efficient process. DFT calculations by Norskov et al. predict that ammonia can be electrochemically synthesized at room temperature on Ru surfaces if protons are supplied at sufficiently negative potentials and hydrogen evolution is suppressed.1 The ammonia formation reaction can only occur in the absence of site-blocking adsorbates such as water or oxygen since they are a poison for NH3 catalysts. Marnellos et al. demonstrated the electrochemical synthesis of ammonia from H2 and N2 using high-temperature proton conductors at atmospheric pressures.2 However, though they reported that >78% of their electrochemically-pumped H2 was converted to NH3, they were limited by very low proton conductivity at 570oC. In fact, in order to get electrochemical NH3 production at greater rates, there is a pressing need to use electrolytes that show greater proton transport at reduced temperatures. Ideally, the temperature range should be high enough for fast kinetics and low enough to reduce NH3 decomposition, which can greatly enhance the viability of the electrochemical production of NH3. The work we are presenting involves the evaluation of the electrochemical synthesis of ammonia in different ionic liquids (IL) using a newly designed electrochemical system able to operate in a wide range of pressures (0 – 3,000 psi) and temperatures (-30 – 400 ºC). In addition, ionic liquids with different anions (i.e. triflamide and triflate) and cations (i.e.butylmethylpyrrolidinium and butylmethylimidazolium) have also been studied and their physicochemical and electrochemical properties characterized. As nitrogen is converted to ammonia during the electrochemical synthesis, ammonia solubility in the ionic liquid will play a very important role. Parameters such as conductivity and diffusion coefficient of the IL will be affected, which will greatly influence the production rate of the overall process. Consequently, we have carried out the physicochemical and electrochemical characterization of the selected ionic liquids with different ammonia compositions and the influence on the electrosynthesis process. As part of the obtained results, figure 1 shows cyclic voltammograms of butylmethylpyrrolidinium triflamide in presence of increasing ammonia compositions. Acknowledgement Financial support from the LANL LDRD-DR Program is gratefully acknowledged. References 1. Rod, T. H.; Logadottir, A.; Norskov, J. K., Ammonia synthesis at low temperatures. Journal of Chemical Physics 2000, 112(12), 5343-5347. 2. Marnellos, G.; Stoukides, M., Ammonia synthesis at atmospheric pressure. SCIENCE 1998, 282 (5386), 98-100.

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