Investigation of Commercial Graphenes.

For graphene to achieve its full scientific and commercial potential, reliable mass production of the material on the multi-tonne scale is essential. We have investigated five samples of graphene obtained from commercial sources that state they can supply the product on the tonne scale per annum. From electron microscopy at the micrometre to the nanometre scale, and neutron vibrational spectroscopy, we find that none of the materials examined were 100 % isolated graphene sheets. In all cases, there was a substantial content of graphite-like material. The samples exhibited varying oxygen contents, this could be present as carboxylic acid (although other oxygenates, quinones, phenols may also be present) or water. We emphasise that INS spectroscopy is particularly useful for the investigation of inorganic materials that will be used commercially: it provides atomic scale information from macroscopic (10's of g) amounts of sample, thus ensuring that the results are truly representative.

Alkali Metal Triphenyl- and Trihydridosilanides Stabilized by a Macrocyclic Polyamine Ligand.

Potassium silanide [KSiH3 ]∞ contains 4.2 wt % of hydrogen and has been intensely studied as hydrogen storage material. The macrocyclic ligand Me4 TACD (1,4,7,10-tetramethyl-1,4,7,10-tetraaminocyclododecane, L) stabilizes the full range of triphenylsilyl complexes [(L)MSiPh3 ]n (M=Li-Cs), which react with H2 or PhSiH3 to form molecular [(L)MSiH3 ]n that can be isolated in soluble form and fully characterized.

Hypervalent Hydrosilicates Connected to Light Alkali Metal Amides: Synthesis, Structure, and Hydrosilylation Catalysis.

When light alkali metal amides [M(Me3 TACD)]n (M=Li, Na, K; (Me3 TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) were treated with H2 SiPh2 in THF, [M{(H2 SiPh2 )Me3 TACD}(thf)x ] containing a pendant hypervalent dihydridosilicate were formed and characterized by elemental analysis, NMR/IR spectroscopy, and single-crystal X-ray crystallography. The lithium complex catalyzed the hydrosilylation of styrene derivatives under mild conditions with anti-Markovnikov regioselectivity.

The Nature of the Heavy Alkaline Earth Metal-Hydrogen Bond: Synthesis, Structure, and Reactivity of a Cationic Strontium Hydride Cluster.

The molecular strontium hydride [(Me3TACD)3Sr3(µ3-H)2][SiPh3] (2) was isolated as the dark red benzene solvate 2·C6H6 in 69% yield from the reaction of [Sr(SiPh3)2(thf)3] (1') with (Me3TACD)H (1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane). This reaction can be considered as a redox process, with the Brønsted acidic amine proton in (Me3TACD)H transformed into the hydride by the anion [SiPh3]-. Trace amounts of water resulted in the formation of [(Me3TACD)3Sr3(µ3-H)(µ3-OH)][SiPh3] (2*), which cocrystallized with 2. Single-crystal X-ray diffraction of 2 revealed a substitutional disorder of a bridging hydride with a hydroxide ligand. Hydride complex 2 was also obtained by hydrogenolysis of [(Me3TACD)Sr(SiPh3)] (3), although pure 3 proved difficult to isolate. In the presence of a 2-fold excess of (Me3TACD)H, the reaction with disilyl 1' gave [(Me3TACD)SiPh3] (4). Complex 2 underwent facile H/D exchange with D2 (1 bar), with the anion [SiPh3]- decomposing concurrently. In the reaction of 2 with 1,1-diphenylethylene (DPE), the anion [SiPh3]- was added to the C═C bond in DPE to give [(Me3TACD)3Sr3H2][Ph2CCH2SiPh3] (5), whereas the cationic cluster [(Me3TACD)3Sr3H2]+ remained unchanged. 9-Fluorenone underwent one-electron reduction with 2 to give the paramagnetic ketyl complex [{(Me3TACD)H}Sr(OC13H8•)2(thf)2] (6). These strontium compounds are structurally similar to the lighter calcium congeners, but more reactive, in particular with regard to fast H/D exchange and [SiPh3]- anion decomposition. DFT studies on the cationic hydride clusters suggest a more pronounced covalent character for strontium compared to calcium. Disilyl 1, strontium diketyl 6, and the calcium congener of 6, [{(Me3TACD)H}Ca(OC13H8·)2] (10), were also characterized by X-ray diffraction.

Silyl-Hydrosilane Exchange at a Magnesium Triphenylsilyl Complex Supported by a Cyclen-Derived NNNN-Type Macrocyclic Ligand.

The magnesium triphenylsilyl complex [(Me3TACD)Mg(SiPh3)] (2) was synthesized from magnesium bis(triphenylsilyl) [Mg(SiPh3)2(THF)2]·THF (1; THF = tetrahydrofuran) and the NNNN-type macrocyclic amidotriamine proligand (Me3TACD)H ((Me3TACD)H = Me3[12]aneN4 = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane). Treating 2 with AlR3 (R = Me, Et) gave the magnesium triphenylsilyl complexes with "blocked" amido function [(Me3TACD·AlR3)Mg(SiPh3)] (3a: R = Me; 3b: R = Et). Instead of forming a Mg-H bond upon reaction with dihydrogen or hydrosilanes, 2 and 3a,b underwent rapid silyl-silane exchange with hydrosilanes. Treating the ethyl complex [(Me3TACD·AlEt3)MgEt] with H3SiPh gave [(Me3TACD·AlEt3)MgH] (4), albeit not in a reproducible manner. The silyl-hydrosilane exchange allows access to other magnesium silyls of the type [(Me3TACD)Mg(SiR'3)] (5a: SiR'3 = SiH2Ph; 5b: SiR'3 = SiHPh2) and [(Me3TACD·AlR3)Mg(SiR'3)] (6a: SiR'3 = SiH2Ph, R = Me; 6b: SiR'3 = SiH2Ph, R = Et; 7a: SiR'3 = SiHPh2, R = Me; 7b: SiR'3 = SiHPh2, R = Et). The reaction of 2 with H2SiMePh in THF at room temperature resulted in an equilibrium (Keq ≈ 1). Protonolysis of 2 with Brønsted acids (HX) 2,5-di-tert-butylphenol, phenylacetylene, acetophenone, aniline, and triethylammonium chloride each gave a compound [(Me3TACD)Mg(X)] with the conjugated base coordinated at the magnesium along with HSiPh3. The magnesium silyls 1, 2, and 7b as well as the magnesium hydride 4 contain a distorted square-pyramidal magnesium center according to single-crystal X-ray diffraction.

Molecular Calcium Hydride: Dicalcium Trihydride Cation Stabilized by a Neutral NNNN-Type Macrocyclic Ligand.

Hydrogenolysis of bis(triphenylsilyl)calcium containing the neutral NNNN-type macrocyclic amine ligand Me4TACD [Ca(Me4TACD)(SiPh3)2] (2), gave the cationic dinuclear calcium hydride [Ca2H3(Me4TACD)2](SiPh3) (3), characterized by NMR spectroscopy, single-crystal X-ray analysis, and DFT calculations. Compound 3 reacted with deuterium to give the deuteride [D3]-3.

Formation of a Cationic Calcium Hydride Cluster with a "Naked" Triphenylsilyl Anion by Hydrogenolysis of Bis(triphenylsilyl)calcium.

Protonolysis of bis(triphenylsilyl)calcium [Ca(SiPh3)2(THF)4] (1; THF = tetrahydrofuran) with the NNNN-type macrocyclic amido triamine (Me3TACD)H (TACD = 1,4,7-triazacyclododecane) gave the heteroleptic calcium complex [Ca(Me3TACD)SiPh3] (2) in quantitative yield. Hydrogenolysis of 2 gave the cationic tricalcium dihydride cluster [Ca3H2(Me3TACD)3](+)(SiPh3)(-)·2THF (4a) in high yield with concomitant formation of HSiPh3. In the crystal, 4a consists of a cluster cation and a free triphenylsilyl anion. (1)H NMR spectroscopy and deuterium labeling experiments confirmed the selective cleavage of dihydrogen by the highly polar Ca-Si bond in 1.

Crown ether adducts of light alkali metal triphenylsilyls: synthesis, structure and hydrosilylation catalysis.

Alkali metal triphenylsilyls [Li(12-crown-4)SiPh3]·(thf)0.5 (2), [Na(15-crown-5)SiPh3]·(thf)0.5 (3) and [K(18-crown-6)SiPh3(thf)] (4) were synthesized using 1,1,1-trimethyl-2,2,2-triphenyldisilane (Ph3SiSiMe3) and isolated in high yields. Solid state structures were determined by single crystal X-ray diffraction. These alkali metal silyls catalyzed the regioselective hydrosilylation of 1,1-diphenylethylene to give the anti-Markovnikov product. The presence of crown ethers enhanced the reactivity of the metal silyls in hydrosilylation catalysis.

Hydrosilylation catalysis by an earth alkaline metal silyl: synthesis, characterization, and reactivity of bis(triphenylsilyl)calcium.

Bis(triphenylsilyl)calcium [Ca(SiPh3)2(thf)] obtained in high yield as a crystalline ether adduct catalyzes the hydrosilylation of activated C-C double bonds efficiently and regioselectively.

Calcium-mediated dearomatization, C-H bond activation, and allylation of alkylated and benzannulated pyridine derivatives.

A facile and general synthetic pathway for the production of dearomatized, allylated, and C-H bond activated pyridine derivatives is presented. Reaction of the corresponding derivative with the previously reported reagent bis(allyl)calcium, [Ca(C(3)H(5))(2)] (1), cleanly affords the product in high yield. The range of N-heterocyclic compounds studied comprised 2-picoline (2), 4-picoline (3), 2,6-lutidine (4), 4-tert-butylpyridine (5), 2,2'-bipyridine (6), acridine (7), quinoline (8), and isoquinoline (9). Depending on the substitution pattern of the pyridine derivative, either carbometalation or C-H bond activation products are obtained. In the absence of methyl groups ortho or para to the nitrogen atom, carbometalation leads to dearomatized products. C(sp(3))-H bond activation occurs at ortho and para situated methyl groups. Steric shielding of the 4-position in pyridine yields the ring-metalated product through C(sp(2))-H bond activation instead. The isolated compounds [Ca(2-CH(2)-C(5)H(4)N)(2)(THF)] (2b⋅(THF)), [Ca(4-CH(2)-C(5)H(4)N)(2)(THF)(2)] (3b⋅(THF)(2)), [Ca(2-CH(2)-C(5)H(3)N-6-CH(3))(2)(THF)(n)] (4b⋅(THF)(n); n=0, 0.75), [Ca{2-C(5)H(3)N-4-C(CH(3))(3)}(2)(THF)(2)] (5c⋅(THF)(2)), [Ca{4,4'-(C(3)H(5))(2)-(C(10)H(8)N(2))}(THF)] (6a⋅(THF)), [Ca(NC(13) H(9)-9-C(3)H(5))(2)(THF)] (7a⋅(THF)), [Ca(4-C(3) H(5)-C(9) H(7)N)(2)(THF)] (8b⋅(THF)), and [Ca(1-C(3)H(5)-C(9)H(7) N)(2)(THF)(3)] (9a⋅(THF)(3)) have been characterized by NMR spectroscopy and metal analysis. 9a⋅(THF)(4) and 4b⋅(THF)(3) were additionally characterized in the solid state by X-ray diffraction experiments. 4b⋅(THF)(3) shows an aza-allyl coordination mode in the solid state. Based on the results, mechanistic aspects are discussed in the context of previous findings.