Alison J. Edwards

β-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

The preparation and characterization of a series of magnesium(II) iodide complexes incorporating beta-diketiminate ligands of varying steric bulk and denticity, namely, [(ArNCMe)(2)CH](-) (Ar=phenyl, ((Ph)Nacnac), mesityl ((Mes)Nacnac), or 2,6-diisopropylphenyl (Dipp, (Dipp)Nacnac)), [(DippNCtBu)(2)CH](-) ((tBu)Nacnac), and [(DippNCMe)(Me(2)NCH(2)CH(2)NCMe)CH](-) ((Dmeda)Nacnac) are reported. The complexes [((Ph)Nacnac)MgI(OEt(2))], [((Mes)Nacnac)MgI(OEt(2))], [((Dmeda)Nacnac)MgI(OEt(2))], [((Mes)Nacnac)MgI(thf)], [((Dipp)Nacnac)MgI(thf)], [((tBu)Nacnac)MgI], and [((tBu)Nacnac)MgI(DMAP)] (DMAP=4-dimethylaminopyridine) were shown to be monomeric by X-ray crystallography. In addition, the related beta-diketiminato beryllium and calcium iodide complexes, [((Mes)Nacnac)BeI] and [{((Dipp)Nacnac)CaI(OEt(2))}(2)] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, [((Mes)Nacnac)MgMg((Mes)Nacnac)] and [((tBu)Nacnac)MgMg((tBu)Nacnac)]. The reduction of a 1:1 mixture of [((Dipp)Nacnac)MgI(OEt(2))] and [((Mes)Nacnac)MgI(OEt(2))] with potassium gave a low yield of the crystallographically characterized complex [((Dipp)Nacnac)Mg(mu-H)(mu-I)Mg((Mes)Nacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of [((Mes)Nacnac)BeI], [{((Dipp)Nacnac)CaI(OEt(2))}(2)], or [{((tBu)Nacnac)CaI(thf)}(2)] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes [((Mes)Nacnac)MgMg((Mes)Nacnac)] and [((tBu)Nacnac)MgMg((tBu)Nacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes [((Mes)Nacnac)Mg(L)Mg(L)((Mes)Nacnac)] (L=THF or DMAP), [((Mes)Nacnac)Mg(mu-AdN(6)Ad)Mg((Mes)Nacnac)] (Ad=1-adamantyl), [((tBu)Nacnac)Mg(mu-AdN(6)Ad)Mg((tBu)Nacnac)], and [((Mes)Nacnac)Mg(mu-tBu(2)N(2)C(2)O(2))Mg((Mes)Nacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of [((tBu)Nacnac)Mg(mu-H)(2)Mg((tBu)Nacnac)] has shown the compound to have different structural and physical properties to [((tBu)Nacnac)MgMg((tBu)Nacnac)]. Treatment of the former with DMAP has given [((tBu)Nacnac)Mg(H)(DMAP)], the X-ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare [((Mes)Nacnac)Mg(mu-H)(2)Mg((Mes)Nacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, [((Mes)Nacnac)MgMg((Mes)Nacnac)] confirmed that the compound is devoid of hydride ligands.

Plasmonic twinned silver nanoparticles with molecular precision

Determining the structures of nanoparticles at atomic resolution is vital to understand their structure–property correlations. Large metal nanoparticles with core diameter beyond 2 nm have, to date, eluded characterization by single-crystal X-ray analysis. Here we report the chemical syntheses and structures of two giant thiolated Ag nanoparticles containing 136 and 374 Ag atoms (that is, up to 3 nm core diameter). As the largest thiolated metal nanoparticles crystallographically determined so far, these Ag nanoparticles enter the truly metallic regime with the emergence of surface plasmon resonance. As miniatures of fivefold twinned nanostructures, these structures demonstrate a subtle distortion within fivefold twinned nanostructures of face-centred cubic metals. The Ag nanoparticles reported in this work serve as excellent models to understand the detailed structure distortion within twinned metal nanostructures and also how silver nanoparticles can span from the molecular to the metallic regime.

Chemoenzymatic methods for the enantioselective preparation of sesquiterpenoid natural products from aromatic precursors

The enantiomerically pure cis-1,2-dihydrocatechols 2, which are generated by enzymatic dihydroxylation of the corresponding aromatic, engage in regio- and stereo-controlled Diels-Alder cycloaddition reactions to give a range of synthetically useful bicyclo[2.2.2]octenes. Certain examples of the latter type of compound have been used as starting materials in the synthesis of the sesquiterpenoids (−)-patchoulenone and (−)-hirsutene.

Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball

The syntheses of the first rhombicuboctahedral copper polyhydride complexes [Cu28 (H)15 (S2 CNR)12 ]PF6 (NR=N(n) Pr2 or aza-15-crown-5) are reported. These complexes were analyzed by single-crystal X-ray and one by neutron diffraction. The core of each copper hydride nanoparticle comprises one central interstitial hydride and eight outer-triangular-face-capping hydrides. A further six face-truncating hydrides form an unprecedented bridge between the inner and outer copper atom arrays. The irregular inner Cu4 tetrahedron is encapsulated within the Cu24 rhombicuboctahedral cage, which is further enclosed by an array of twelve dithiocarbamate ligands that subtends the truncated octahedron of 24 sulfur atoms, which is concentric with the Cu24 rhombicuboctahedron and Cu4 tetrahedron about the innermost hydride. For these compounds, an intriguing, albeit limited, H2 evolution was observed at room temperature, which is accompanied by formation of the known ion [Cu8 (H)(S2 CNR)6 ](+) upon exposure of solutions to sunlight, under mild thermolytic conditions, and on reaction with weak (or strong) acids.

Hydrido copper clusters supported by dithiocarbamates: oxidative hydride removal and neutron diffraction analysis of [Cu7(H){S2C(aza-15-crown-5)}6].

Reactions of Cu(I) salts with Na(S(2)CR) (R = N(n)Pr(2), NEt(2), aza-15-crown-5), and (Bu(4)N)(BH(4)) in an 8:6:1 ratio in CH(3)CN solution at room temperature yield the monocationic hydride-centered octanuclear Cu(I) clusters, [Cu(8)(H){S(2)CR}(6)](PF(6)) (R = N(n)Pr(2), 1(H); NEt(2), 2(H); aza-15-crown-5, 3(H)). Further reactions of [Cu(8)(H){S(2)CR}(6)](PF(6)) with 1 equiv of (Bu(4)N)(BH(4)) produced neutral heptanuclear copper clusters, [Cu(7)(H){S(2)CR}(6)] (R = N(n)Pr(2), 4(H); NEt(2), 5(H); aza-15-crown-5, 6(H)) and clusters 4-6 can also be generated from the reaction of Cu(BF(4))(2), Na(S(2)CR), and (Bu(4)N)(BH(4)) in a 7:6:8 molar ratio in CH(3)CN. Reformation of cationic Cu(I)(8) clusters by adding 1 equiv of Cu(I) salt to the neutral Cu(7) clusters in solution is observed. Intriguingly, the central hydride in [Cu(8)(H){S(2)CN(n)Pr(2)}(6)](PF(6)) can be oxidatively removed as H(2) by Ce(NO(3))(6)(2-) to yield [Cu(II)(S(2)CN(n)Pr(2))(2)] exploiting the redox-tolerant nature of dithiocarbamates. Regeneration of hydride-centered octanuclear copper clusters from the [Cu(II)(S(2)CN(n)Pr(2))(2)] can be achieved by reaction with Cu(I) ions and borohydride. The hydride release and regeneration of Cu(I)(8) was monitored by UV-visible titration experiments. To our knowledge, this is the first time that hydride encapsulated within a copper cluster can be released as H(2) via chemical means. All complexes have been fully characterized by (1)H NMR, FT-IR, UV-vis, and elemental analysis, and molecular structures of 1(H), 2(H), and 6(H) were clearly established by single-crystal X-ray diffraction. Both 1(H) and 2(H) exhibit a tetracapped tetrahedral Cu(8) skeleton, which is inscribed within a S(12) icosahedron constituted by six dialkyl dithiocarbamate ligands in a tetrametallic-tetraconnective (μ(2), μ(2)) bonding mode. The copper framework of 6(H) is a tricapped distorted tetrahedron in which the four-coordinate hydride is demonstrated to occupy the central site by single crystal neutron diffraction. Compounds 1-3 exhibit a yellow emission in both the solid state and in solution under UV irradiation at 77 K, and the structureless emission is assigned as a (3)metal to ligand charge transfer (MLCT) excited state. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on model compounds match the experimental structures and provide rationalization of their bonding and optical properties.

Diffuse X-ray scattering from benzil, C14H10O2: analysis via automatic refinement of a Monte Carlo model

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in benzil, diphenylethanedione, C(6)H(5)-CO-CO-C(6)H(5). A model involving 13 parameters consisting of 11 intermolecular force constants, a single intramolecular torsional force constant and a local Debye-Waller factor was refined to give an agreement factor, R = [summation operator omega(Delta I)(2)/summation operator omega I(obs)(2)](1/2), of 14.5% for 101,324 data points. The model was purely thermal in nature. The analysis has shown that the diffuse lines, which feature so prominently in the observed diffraction patterns, are due to strong longitudinal displacement correlations. These are transmitted from molecule to molecule via a network of contacts involving hydrogen bonding of an O atom on one molecule and the para H atom of the phenyl ring of a neighbouring molecule. The analysis also allowed the determination of a torsional force constant for rotations about the single bonds in the molecule. This is the first diffuse scattering study in which measurement of such internal molecular torsion forces has been attempted.

Neutron Diffraction – Recent Applications to Chemical Structure Determination

A brief introduction to the capabilities of the modern Laue neutron diffraction technique is given, and recent examples of successful solutions of structural problems are highlighted.

Reduction of a Chelating Bis(NHC) Palladium(II) Complex to [{μ‐bis(NHC)}2Pd2H]+: A Terminal Hydride in a Binuclear Palladium(I) Species Formed under Catalytically Relevant Conditions

Catalytic processes featuring N-heterocyclic carbene (NHC) ligands have been extensively studied following the isolation of free imidazol-2-ylidenes An important reaction class is the base-assisted palladium-mediated C–C/N coupling, such as the Sonogashira, Buchwald–Hartwig, and Mizoroki–Heck reactions

Synthesis, Structure and Gas-Phase Reactivity of a Silver Hydride Complex [Ag3{(PPh2)2CH2}3(μ3-H)(μ3-Cl)]BF4†

Coinage metal hydrides continue to attract attention because of their interesting structural and physical properties, as well as for their role as reagents or intermediates in the transformation of organic substrates. For example, several copper hydride compounds have been structurally characterized and developed as catalysts for 1,4 reduction reactions of enones and for hydrocupration of alkynes. In contrast, whereas their heavier congeners have been implicated as reactive intermediates in oxidation and other reactions, and have been characterized in the gas phase, as well as by matrix isolation experiments, few silver and gold hydride compounds have been synthesized and structurally characterized by X-ray crystallography. We have been examining the role of coinage-metal cluster compounds in C C bond coupling reactions, click chemistry, and C X bond activation 8] of organic substrates. In our work, methods based on mass spectrometry (MS) are employed to explore cluster formation and reactivity, and to direct condensed phase synthesis and characterization of novel clusters. As part of this cluster chemistry program, we became interested in extending the method of generating bis(phosphino)-protected gold nanoclusters by sodium borohydride reduction of gold salts to generate related silver nanoclusters. Herein, we report on the serendipitous MSbased discovery of a novel silver hydride cluster, [Ag3HClL3] + (L = bis(phosphino) ligand), which has prompted its massspectrometry-directed synthesis and X-ray and neutron crystallographic structural characterization, which reveal a {Ag3(m3-H)(m3-Cl)} + core structure. 14] The gas-phase reactivity of this cluster is also explored. Electrospray ionization mass spectrometry (ESI-MS) analysis of methanol/chloroform solutions of silver(I) trifluoroacetate [Ag(tfa)] that had been treated with sodium borohydride in the presence of 1,1-bis(diphenylphosphino)methane (designated hereafter as L) showed evidence of the formation of silver hydride cluster cations (Figure 1; see also the Supporting Information, Figure S1), which, based on isotope patterns (Figures S2 and S3) and high resolution accurate mass measurements (Table S1), are formulated as: [Ag3HL3] , [Ag3HClL3] , [Ag3Cl2L3] + and [Ag10H8L6] . The species [Ag3H2L3] + was not observed in any of the spectra recorded. Replacing NaBH4 with sodium borodeuteride confirmed that NaBH4 is the source of the hydride in the clusters (for example, formation of [Ag3DL3] 2+ and not [Ag3HL3] ; Figures S4 and S5). The observation of abundant silver hydride cluster cations by ESI-MS encouraged us to refine the condensed-phase synthetic route (Supporting Information, Method A) to allow the isolation of a crystalline salt suitable for characterization by IR and H NMR spectroscopy (Figures S6 and S7, as well as supporting text), as well as structural determination by single-crystal X-ray diffraction and neutron diffraction. The presence of the abundant trinuclear silver hydride cluster ligated by the trifluoroacetate (tfa) anion, [Ag3H(tfa)L3] +

Synthesis, Structural Characterization, and Gas-Phase Unimolecular Reactivity of the Silver Hydride Nanocluster [Ag3((PPh2)2CH2)3(μ3-H)](BF4)2

A bis(diphenylphosphino)methane-ligated trinuclear silver hydride nanocluster, [Ag3((Ph2P)2CH2)3(μ3-H)](BF4)2, featuring three silver(I) ions coordinated to a μ3-hydride, and its deuteride analogue, [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2, have been isolated and structurally characterized using electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, NMR and IR spectroscopy. The position of the deuteride in [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2 was determined by neutron diffraction. ESI-MS of [Ag3L3(μ3-H/D)](BF4)2 [L = ((Ph2P)2CH2)2] produces [Ag3L3(μ3-H/D)](2+) and [Ag3L3(μ3-H/D)(BF4)](+). A rich gas-phase ion chemistry of [Ag3L3(μ3-H/D)](2+) is observed under conditions of collision-induced dissociation (CID) and electron-capture dissociation (ECD). CID gives rise to the following complementary ion pairs: [Ag3L2](+) and [L+(H/D)](+); [Ag2(H/D)L2](+) and [AgL](+); [Ag2(H/D)L](+) and [AgL2](+). ECD gives rise to a number of dissociation channels including loss of the bis(phosphine) ligand, fragmentation of a coordinated bis(phosphine) ligand via C-P bond activation, and loss of a hydrogen (deuterium) atom with concomitant formation of [Ag3L3](+). Under CID conditions, [Ag3L3(μ3-H/D)(BF4)](+) fragments via ligand loss, the combined loss of a ligand and [H,B,F4], and cluster fragmentation to give [Ag2(BF4)L2](+) and [Ag2(L-H)L](+) [where (L-H) = (Ph2P)2CH(-)].