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A series of group 8 transition metal complexes of new tridentate phosphine ligands with Fe, Ru, and Os were prepared. The new complexes were characterized by multinuclear NMR spectroscopy and X-ray crystallography.

The complex Ti[OGeiPr3]4 (1), prepared via the reaction of Ti(OiPr)4 with iPr3GeOH, represents a useful structural and spectroscopic model for titanium–germanium species dispersed onto silica. This precursor was used to introduce site-isolated Ti(IV) centers onto the surface of a mesoporous SBA15 support via the thermolytic molecular precursor method. The local environments of the supported materials (TiGe3SBA15 and calcined TiGe3SBA15-O2) were studied by various spectroscopic methods, including X-ray absorption spectroscopy. These materials are active catalysts for the epoxidation of cyclic and terminal olefins with alkyl hydroperoxides under anhydrous conditions. Compared to catalysts synthesized from siloxide-only precursors, the new catalysts produce 2–3 times more product after 9 h under identical reaction conditions for the epoxidations of cyclohexene and 1-octene. The new materials did not significantly leach under reaction conditions.

The catalytic cleavage of two C-C single bonds is achieved by treatment of the hydrocarbon substrate spiro[bicyclo[2.2.1]hept-2-ene-7,1'-cyclopropane] with Pt(II) catalysts such as (Me2bpy)PtPh(NTf2) (Me2bpy = 4,4'-dimethyl-2,2'-bipyridine, NTf2(-) = N(SO2CF3)2(-)). The surprising rearrangement product 1,2,4,7,7a-pentahydroindene is generated in good yield. The mechanism of C-C bond activation is investigated using NMR spectroscopy, electrospray ionization mass spectrometry, and deuterium labeling, along with density functional theory calculations. These studies support an unusual catalytic mechanism in which an initial masked C-H bond activation initiates successive C-C bond cleavage events.

Reactions of the di(tert-butylphosphino)ethane complex (dtbpe)Rh(CH2Ph) with Ph2SiH2 and Et2SiH2 resulted in isolation of (dtbpe)Rh(H)2(SiBnPh2) (1; Bn = CH2Ph) and (dtbpe)Rh(H)2(SiBnEt2) (2), respectively. Both 1 and 2 feature strong interactions between the rhodium hydride and silyl ligands, as indicated by large 2JSiH values (44.4 and 52.1 Hz). The reaction of (dtbpm)Rh(CH2Ph) (dtbpm = di(tert-butylphosphino)methane) with Mes2SiH2 gave the pseudo-three-coordinate Rh complex (dtbpm)Rh(SiHMes2) (3), which is stabilized in the solid state by agostic interactions between the rhodium center and two C–H bonds of a methyl substituent on the mesityl group. The analogous germanium compound (dtbpm)Rh(GeHMes2) (4) is also accessible. Complex 3 readily undergoes reactions with diphenylacetylene, phenylacetylene, and 2-butyne to give the silaallyl complexes (dtbpm)Rh[Si(CPh═CHPh)Mes2] (5), (dtbpm)Rh[Si(CH═CHPh)Mes2] (7), and (dtbpm)Rh(Si(CMe═CHMe)Mes2) (8) via net insertions into the Si–H bond. The germaallyl compl...

The highly sensitive technique of microchip capillary electrophoresis (μCE) with laser-induced fluorescence (LIF) detection is under development for future in situ spaceflight missions to search for the organic chemical signatures of life. One fluorescent probe that enables this technology for amine, amino acid, and dipeptide analysis is 3-carboxy-6,8-difluoro-7-hydroxycoumarin (Pacific Blue™, PB) succinimidyl ester. Of particular importance is the hydrolysis of PB succinimidyl ester, which precludes long-term aqueous storage during spaceflight and therefore has a significant impact on instrument design and operation. As such, it is important to characterize the chemical stability of this dye to hydrolysis prior to spaceflight. Here, we study the hydrolysis kinetics of the PB succinimidyl ester at pH values between 3 and 10.5 using μCE-LIF. The PB succinimidyl ester has the longest lifetime at pH 4 (7.3 ± 0.1 h), with dramatically shorter half-lives in the basic pH regime. This work represents a first step in the full characterization of this fluorescent probe for spaceflight applications.

Hydridosilicate anions ([ArSiH(4)](-) and [SiH(6)](2-)) were stabilized as ligands in diruthenium Si-H σ-complexes [{(PhBP(Ph(3))Ru}(2)(μ-Cl)(μ-η(3),η(3)-H(4)SiAr)] (Ar = 2-MeOC(6)H(4), Mes, Ph) and [{(PhBP(Ph)(3))Ru}(2)(μ-η(4),η(4)-H(6)Si)] (see picture). These complexes were formed under mild conditions and characterized by single-crystal X-ray diffraction (see picture), NMR and IR spectroscopy, and computational techniques.

Complexes [PhBP_3]RuH(η^3-H_2SiRR′) (RR′ = Me,Ph, 1a; RR′ = Ph_2, 1b; RR′ = Et_2, 1c) react with XylNC to form carbene complexes [PhBP_3]Ru(H)═[C(H)(N(Xyl)(η^2-H–SiRR′))] (2a–c; previously reported for 2a,b). Reactions of 1a–c with XylNC were further investigated to assess how metal complexes with multiple M–H–Si bonds can mediate transformations of unsaturated substrates. Complex 2a eliminates an N-methylsilacycloindoline product (3a) that results from hydrosilylation, hydrogenation, and benzylic C–H activation of XylNC. Turnover was achieved in a pseudocatalytic manner by careful control of the reaction conditions. Complex 1c mediates a catalytic isocyanide reductive coupling to furnish an alkene product (4) in a transformation that has precedent only in stoichiometric processes. The formations of 3a and 4 were investigated with deuterium labeling experiments, KIE and other kinetic studies, and by examining the reactivity of XylNC with an η^3-H_2SiMeMes complex (1d) to form a C–H activated complex (6). Complex 6 serves as a model for an intermediate in the formation of 3a, and NMR investigations at −30 °C reveal that 6 forms via a carbene complex (1d) that isomerizes to aminomethyl complex 7d. These investigations reveal that the formations of 3a and 4 involve multiple 4-, 5-, and 6-coordinate silicon species with 0, 1, 2, or 3 Ru–H–Si bonds. These mechanisms demonstrate exceptionally intricate roles for silicon in transition-metal-catalyzed reactions with a silane reagent.

A new transition-metal-free synthetic method for C–O coupling between various aryl halides and alkoxides is described. This type of transformation is typically accomplished using palladium catalysts containing a specialized phosphine ligand. The reactions reported here can be performed under mild, ambient conditions using certain potassium alkoxides and a range of aryl halides, with iodide and bromide derivatives giving the best results. A likely mechanistic pathway involves the in situ generation of an aryne intermediate, and directing groups on the aryl ring inductively control regioselectivity.

The synthesis of discrete, cationic binuclear μ-aryl dicopper complexes [Cu2(μ-η(1):η(1)-Ar)DPFN]X (Ar = C6H5, 3,5-(CF3)2C6H3, and C6F5; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine; X = BAr4(-) and NTf2(-); Tf = SO2CF3) was achieved by treatment of a dicopper complex [Cu2(μ-η(1):η(1)-NCCH3)DPFN]X2 (X = PF6(-) and NTf2(-)) with tetraarylborates. Structural characterization revealed symmetrically bridging aryl groups, and (1)H NMR spectroscopy evidenced the same structure in solution at 24 °C. Electrochemical investigation of the resulting arylcopper complexes uncovered reversible redox events that led to the synthesis and isolation of a rare mixed-valence organocopper complex [Cu2(μ-η(1):η(1)-Ph)DPFN](NTf2)2 in high yield. The solid-state structure of the mixed-valence μ-phenyl complex exhibits inequivalent copper centers, despite a short Cu···Cu distance. Electronic and variable-temperature electron paramagnetic resonance spectroscopy of the mixed-valence μ-phenyl complex suggest that the degree of spin localization is temperature-dependent, with a high degree of spin localization observed at lower temperatures. Electronic structure calculations agree with the experimental results and suggest that the spin is localized almost entirely on one metal center.

Z-type interactions between bis(perfluorophenyl)zinc and platinum(II) diaryl complexes supported by 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), and bis(dimethylphosphino)ethane (dmpe) ligands are reported. In the solid state, the nature of the Pt–Zn interaction depends on the bidentate ligand; the phen-supported complex exhibits an unsupported Pt–Zn bond, while the dmpe derivative features additional bridging aryl interactions. A strongly accelerated rate of reductive elimination is observed for phen- and bpy-supported complexes, while aryl exchange between Pt and Zn is observed for the dmpe complex.

A new transition-metal-free synthetic method for C–O coupling between various aryl halides and alkoxides is described. This type of transformation is typically accomplished using palladium catalysts containing a specialized phosphine ligand. The reactions reported here can be performed under mild, ambient conditions using certain potassium alkoxides and a range of aryl halides, with iodide and bromide derivatives giving the best results. A likely mechanistic pathway involves the in situ generation of an aryne intermediate, and directing groups on the aryl ring inductively control regioselectivity.

© 2015 American Chemical Society. Localized orbital bonding analysis (LOBA) was employed to probe the oxidation state in cobalt-bis(diaryldithiolene)-catalyzed proton reduction in nonaqueous media. LOBA calculations provide both the oxidation state and chemically intuitive views of bonding in cobalt-bis(diaryldithiolene) species and therefore allow characterization of the role of the redox non-innocent dithiolene ligand. LOBA results show that the reduction of the monoanion species [1Br]-is metal-centered and gives a cobalt(II) ion species, [1Br]2-, coordinated to two dianionic ene-1,2-dithiolates. This electronic configuration is in agreement with the solution magnetic moment observed for the analogous salt [1F]2-(μeff= 2.39 μB). Protonation of [1Br]2-yields the cobalt(III)-hydride [1Br(CoH)]-species in which the Co-H bond is computed to be highly covalent (Löwdin populations close to 0.50 on cobalt and hydrogen atoms). Further reduction of [1Br(CoH)]-forms a more basic cobalt(II)-H intermediate [1Br(CoH)]2-(S = 0) from which protonation at sulfur gives a S-H bond syn to the Co-H bond. Formation of a cobalt-dihydrogen [1Br(CoH2)]-intermediate is calculated to occur via a homocoupling (H•+ H•→ H2) step with a free energy of activation of 5.9 kcal/mol in solution (via C-PCM approach).

Cobalt metaphosphate Co(PO3)2 nanoparticles are prepared via the thermolytic molecular precursor (TMP) method. A Ni form electrode decorated with Co(PO3)2 nanoparticles is evaluated as an anode for water oxidation electrocatalysis in pH 6.4 phosphate-buffered water. Catalytic onset occurs at an overpotential of ca. 310 mV, which is 100 mV lower than that observed for Co3O4 nanoparticles, with a comparable surface area under identical conditions. A per-metal turnover frequency (TOF) of 0.10–0.21 s−1 is observed at an overpotential, η, of 440 mV, which is comparable to the highest rate reported for a first-row metal heterogeneous catalyst. Post-catalytic characterization of the catalyst resting state by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy reveals that surface rearrangement occurs, resulting in an oxide-like surface overlayer.

Reactions of the cationic ruthenium silylene complexes [Cp*(PiPr3)Ru(H)2(═SiRR′)][B(C6F5)4] (R = Mes, R′ = H, 1; R = R′ = Ph, 2) with alkenes, alkynes, ketones, and Lewis bases were explored. Addition of 1-hexene, 3,3-dimethylbut-1-ene, styrene, and cyclopentene to 1 afforded the disubstituted silylene products [Cp*(PiPr3)Ru(H)2(═SiMesR)][B(C6F5)4] (R = Hex, 3; R = CH2CH2tBu, 4; R = CH2CH2Ph, 5; R = C5H9, 6). Analogous reactions with 2-butyne and 3,3-dimethylbut-1-yne yielded the vinyl-substituted silylene complexes [Cp*(PiPr3)Ru(H)2(═Si(CR═CHR′)Mes)][B(C6F)4] (R = R′ = Me, 7; R = H, R′ = tBu, 8). Complex 1 undergoes reactions with ketones to give the heteroatom-substituted silylene complexes [Cp*(PiPr3)Ru(H)2(═Si(OCHPhR)Mes)][B(C6F)4] (R = Ph, 9; R = Me, 10). Interestingly, complexes 3–8 display a weak interaction between the hydride ligands and the silicon center, while 9 and 10 exhibit a relatively large interaction (as determined by 2JSiH values). The reaction of isocyanates with 1 resulted in the sil...

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.

Titanium/AlPO materials were prepared by grafting a titanium alkoxide (titanium isopropoxide) onto a mesoporous aluminophosphate. The structures of the surface-bound titanium species were investigated by UV–vis, FTIR, MAS NMR, and XANES/EXAFS spectroscopies. The titanium anchoring occurs by reaction between the alkoxide precursor and surface Al–OH and P–OH groups of the AlPO support. The titanium species exist in isolated tetrahedral coordination environments, and as oligomerized species. The catalysts prepared are selective and active for the liquid-phase epoxidation of cyclohexene in the presence of TBHP. The observed activities and selectivities were comparable with those obtained for similarly prepared titanium/SBA-15 samples of similar Ti content (but higher BET surface area).

The transport properties of a junction consisting of small donor-acceptor molecules bound to Au electrodes are studied and understood in terms of its hybrid donor-acceptor-electrode interfaces. A newly synthesized donor-acceptor molecule consisting of a bithiophene donor and a naphthalenediimide acceptor separated by a conjugated phenylacetylene bridge and a nonconjugated end group shows rectification in the reverse polarization, behavior opposite to that observed in mesoscopic p-n junctions. Solution-based spectroscopic measurements demonstrate that the molecule retains many of its original constituent properties, suggesting a weak hybridization between the wave functions of the donor and acceptor moieties, even in the presence of a conjugated bridge. Differential conductance measurements for biases as high as 1.5 V are reported and indicate a large asymmetry in the orbital contributions to transport arising from disproportionate electronic coupling at anode-donor and acceptor-cathode interfaces. A semi-empirical single Lorentzian coherent transport model, developed from experimental data and density functional theory based calculations, is found to explain the inverse rectification.

The Ti-based heterogeneous catalysts TiSBA15, BucapTiSBA15, TS-1, and [Ti,Al]-MFI were investigated with respect to controlling factors for the competitive decomposition of aqueous H2O2 during selective catalytic oxidations. DRUV–vis spectroscopy revealed that the titanium species in these materials exist mainly in isolated, tetrahedral coordination environments. The observed rates of H2O2 decomposition at 65 °C in acetonitrile decreased in the following order: BucapTiSBA15 > TiSBA15 and TS-1 > [Ti,Al]-MFI. The decompositions of H2O2 were also monitored in the presence of inorganic additives and Bronsted acids and bases, in benzene/aqueous biphasic solutions. Significant retardation of the decomposition rates with the KH2PO4 additive was found with TiSBA15, which suggests that the KH2PO4 stabilizer may be useful for optimization of hydrogen peroxide efficiency in catalytic oxidations. DRUV–vis spectroscopy was employed to identify possible catalytically active intermediates, proposed to be Ti(IV)(OOH) spe...

The controlled synthesis of e-Co, CoO, and Co3O4 nanoparticles with the same stabilizers and with nearly identical particle size and shape allows comparisons of the inherent catalytic properties of these materials in the oxygen evolution reaction (OER). The nanoparticle electrodes exhibit relatively low overpotentials and very similar catalytic activities under basic conditions. The latter observation indicates that all three catalysts operate with similar catalytic mechanisms.

The ruthenium triflate complex Cp*(PiPr3)RuOTf (1) was generated from the reaction of Cp*(PiPr3)RuCl with Me3SiOTf in dibutyl ether. Complex 1 reacted with primary and secondary silanes to produce a family of Ru(IV) silyl dihydride complexes of the type Cp*(PiPr3)Ru(H)2(SiRR′OTf) (3–12). Structural analyses of complexes 8 (R = R′ = Ph) and 12 (R = R′ = fluorenyl) revealed the presence of a tetrahedral silicon center and a four-legged piano stool geometry about ruthenium. Anion abstraction from Cp*(PiPr3)Ru(H)2(SiHROTf) by [Et3Si·toluene][B(C6F5)4] afforded hydrogen-substituted cationic ruthenium silylene complexes [Cp*(PiPr3)Ru(H)2(═SiHR)][B(C6F5)4] (R = Mes (13), R = Si(SiMe3) (14)) that display a significant Ru–H···Si interaction, as indicated by relatively large 2JSiH coupling constants (2JSiH = 58.2 Hz (13), 2JSiH = 37.1 Hz (14)). The syntheses of secondary silylene complexes [Cp*(PiPr3)Ru(H)2(═SiRR′)][B(C6F5)4] (R = R′ = Ph (15); R = Ph, R′ = Me (16), R = R′ = fluorenyl (17)) were also achieved by an...

Two novel tris(tert-butoxy)siloxy palladium(II) complexes of the form (4,4′-di-tert-butyl-2,2′-bipyridyl)Pd[OSi(OtBu)3](R) were synthesized (1, R = OSi(OtBu)3 and 2, R = CH3). The structures of these compounds were determined by multinuclear NMR spectroscopy and single crystal X-ray diffraction. The solid-state thermolytic chemistry of 1 and 2 was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These compounds were covalently grafted onto the surface of mesoporous silica (SBA15) under mild, nonaqueous conditions to generate supported Pd(II) centers. Reactions of 1 and 2 with the surface Si–OH groups occurs selectively through the -OSi(OtBu)3 ligand with elimination of HOSi(OtBu)3. The new materials, designated Pd(1)SBA15 and Pd(2)SBA15, were characterized using N2 porosimetry, TGA, powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). The coordination environments of the supported Pd centers were investiga...

Site-isolated Ta(V) centers were introduced onto the surface of a mesoporous SBA-15 support via the thermolytic molecular precursor method. After thermal treatment under oxygen, the resulting Si-OH and Ta-OH sites of TaSBA15-O(2)were modified with a series of trimethyl group 14 species, Me(3)E-, by treatment with Me(3)E-NMe(2) (E = Si, Ge, Sn) reagents. The resulting surface-modified catalysts (Me(3)E)(cap)TaSBA15 exhibit a significantly increased rate of cyclohexene epoxidation with H(2)O(2) as an oxidant, and provided a decreased amount of allylic oxidation products with respect to the unmodified material, TaSBA15-O(2). The rate of nonproductive H(2)O(2) decomposition, as monitored via (1)H NMR spectroscopy, significantly decreased after the surface modification. The structure of the TaSBA15 catalysts and potential Ta(V) epoxidation intermediates (formed upon treatment of Ta(V) materials with H(2)O(2)) were probed using UV-visible absorbance and diffuse-reflectance UV-visible spectroscopy. A Ta(V)(η(2)-O(2)) intermediate species is proposed for the TaSBA15-O(2), (Me(3)Si)(cap)TaSBA15, and (Me(3)Ge)(cap)TaSBA15 catalysts, while intermediate species for the (Me(3)Sn)(cap)TaSBA15 catalysts could not be characterized.

Site-isolated Ti(IV) centers were introduced onto the surface of a mesoporous SBA-15 support via the thermolytic molecular precursor method. Prior to thermal treatment to generate Ti−OH sites, residual silanol groups were capped via reaction with Me2N-SiMe3 to give TiMecapSBA15. After low temperature treatment in oxygen, the resulting Ti−OH sites of TiMecapSBA15-O2 were modified by reaction with a series of protic reagents: phenol, pentafluorophenol, acetic acid, and trifluoroacetic acid. The structure of the resulting TiSBA15 catalysts and the Ti(IV) epoxidation intermediates (formed upon treatment of Ti(IV) materials with TBHP or H2O2) were probed using diffuse-reflectance UV−visible spectroscopy and infrared spectroscopy. A titanium-hydroperoxo species similar to that found in TS-1 is proposed for all catalysts. Samples modified with phenol and pentafluorophenol exhibited conversions of 1-octene that are 20 to 50% higher than those for TiMecapSBA15-O2, without a significant drop in selectivity for the ...

The dichloride complex Cp∗(Am)WCl 2 ( 1 , Am = [(iPrN) 2 CMe] − ) reacted with the primary silanes PhSiH 3 , ( p -tolyl)SiH 3 , (3,5-xylyl)SiH 3 , and (C 6 F 5 )SiH 3 to produce the W(VI) (silyl)trihydrides Cp∗(Am)W(H) 3 (SiHPhCl) ( 2 ), Cp∗(Am)W(H) 3 (SiHTolylCl) ( 3 ), Cp∗(Am)W(H) 3 (SiHXylylCl) ( 4 ), and Cp∗(Am)W(H) 3 [SiH(C 6 F 5 )Cl] ( 5 ). In an analogous manner, 1 reacted with PhSiH 2 Cl to give Cp∗(Am)W(H) 3 (SiPhCl 2 ) ( 6 ). Complex 6 can alternatively be quantitatively produced from the reaction of 2 with Ph 3 CCl. NMR spectroscopic studies and X-ray crystallography reveal an interligand H⋯Si interaction between one W–H and the chlorosilyl group, which is further supported by DFT calculations.

The hydroarylation of unactivated olefins effected by Pt(II) precatalysts was found to proceed through the in situ production of protic acid followed by a Friedel−Crafts mechanism. The reaction was...

Trimeric diphenylanthracene macrocycles were synthesized via the zirconocene-mediated coupling of 9,10-bis-[4-trimethylsilyl(ethynyl)phenyl]anthracene. The macrocycles feature a strained architecture due to orientation of the anthracene units into the plane of the macrocycle. The demetalated cyclophane exhibits a considerably higher flexibility in solution, while the zirconocene-containing macrocycle is quite rigid.

Complexes of Ru(II) containing the pincer ligand [−N(2-PPh2-4-Me-C6H3)2] (PNPPh) were prepared. The complex (PNPPhH)RuCl2 (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNPPhH)Ru(OTf)2 (2). Complex 1 was also treated with an excess of NaBH4 to give a bimetallic complex [(PNPPh)RuH3]2 (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.

Efforts to install the bis(8-quinolyl)methylsilyl (Me-NSiN; 1 = Me-NSiNH) and bis(8-quinolyl)phenylsilyl (Ph-NSiN; 2 = Ph-NSiNH) ligands onto nickel are described. Reaction of 1 with NiCl2(DME) and...

A series of oligothiophene-perfluoro-9-heterofluorene donor-acceptor (DA) compounds was synthesized via a combination of nucleophilic aromatic substitution (S(N)Ar(F)) and palladium coupling reactions. These compounds are of interest as possible building blocks for materials with useful electron transport properties, since they possess relatively low LUMO energy levels of -3.3 to -3.6 eV (as determined by differential pulse voltammetry). The HOMO-LUMO energy gaps, as determined by UV-vis spectroscopy, range between 2.4 and 2.5 eV, and photoluminescence emission spectra reveal lambda(ems) values in the range of 480-600 nm (corresponding to yellow-orange emission). Dilute solution-state photoluminescence quantum yields were significantly lower than those of the pure acceptor heterofluorenes (0.02-0.38 for the DA compounds vs approximately 1 for the pure acceptors), and notable solvatochromism in the fluorescence suggests emission from a charge-separated state. Theoretical calculations show that HOMO-level electron density is more localized on the thiophene fragment, while the LUMO level electron density is mostly associated with the electron-deficient portion of the molecule. Photovoltaic (PV) devices based on DA/poly-3-hexylthiophene (P3HT) blends exhibit improved performance over P3HT-only devices, suggesting the ability of these DA compounds to transport electrons in the solid state.

International audience; Sn two-step: Dehydrocoupling of stannanes by the d0 complex [Cp2(Cl)HfH] preferentially occurs by two successive reactions (see scheme): -bond metathesis to form [Cp2(Cl)Hf(SnH3)] and subsequent stannylene transfer into the Cp2(Cl)HfSnH3 bond. [Cp2(Cl)Hf(SnH3)] readily isomerizes to a species possessing a reactive stannylene unit, [Cp2(Cl)Hf(-H)SnH2], thus making the stannylene-transfer reaction energetically feasible.

Reactions of PNP-supported silylene complexes [(PNP)(H)Ir═SiRR′][B(C6F5)4] (R = R′ = Ph (1) and R = H, R′ = Mes (2)) with Lewis bases, carbonyl compounds, alcohols, and amines were investigated. Addition of DMAP (4-dimethylaminopyridine) to 1 and 2 produced base-stabilized silylene complexes [(PNP)(H)IrSiRR′(DMAP)][B(C6F5)4] (R = R′ = Ph (3) and R = H, R′ = Mes (4)). Reactions of 2 with benzophenone and benzaldehyde afforded the products of stoichiometric hydrosilylation, heteroatom-substituted silylene complexes [(PNP)(H)Ir═SiMes(OCH(Ph)(R))][B(C6F5)4] (R = Ph (5) and R = H (6)). Complex 1 reacted with DMF or benzophenone, and 2 reacted with DMF, to afford base-stabilized silylene complexes of the type [(PNP)(H)IrSiRR′(B)][B(C6F5)4] (R = H, R′ = Mes, B = DMF (7); R = R′ = Ph, B = DMF (8) and O═CPh2 (9)). In contrast, treatment of 1 with acetophenone afforded {(PNPH)IrH[SiPh2(OC(═CH2)Ph)]}[B(C6F5)4] (10), from activation of a C−H bond at the α-carbon position of acetophenone. Reactions of alcohols and ami...

The platinum ethylene complexes (PyPyr)Pt(C2H4)Cl (1) and (PyPyr)Pt(C2H4)OTf (4) (PyPyr = 3,5-diphenyl-2-(2-pyridyl)pyrrolide) were treated with 1 equiv of LiN(SiMe3)2, LiNiPr2, and LiNH(o-xylyl) to produce the platinum complexes (PyPyr)PtH[η2-CH2═CHN(SiMe3)2] (5), (PyPyr)Pt[κ2C,N-(CH2CH2NiPr2)] (6), and (PyPyr)Pt{κ2C,N-[CH2CH2NH(o-xylyl)]} (7), respectively. X-ray crystallography reveals that 7 adopts a square-planar geometry at the platinum center and the azaplatinacyclobutane ring displays a puckering of the β-carbon out of planarity by 0.270 A. Thermolysis of 5 and 7 at 60 °C for 16 h releases the vinylamines (CH2═CH)N(SiMe3)2 and (CH2═CH)NH(o-xylyl), respectively. Heating 5 and 7 under 1 atm of H2 at 60 °C releases the ethylamines EtN(SiMe3)2 and EtNH(o-xylyl), respectively. Addition of PiPr3 to 7 produces (PyPyr)Pt(PiPr3)[CH2CH2NH(o-xylyl)] (8) in 95% yield, while additions of 1 equiv of a Lewis base (L) to 1 result in displacement of ethylene to give (PyPyr)Pt(L)Cl (L = NEt3 (9), NH2Ph (10), PiPr3 ...

Bipolar molecules incorporating donor and acceptor components within a single molecule create exciting device opportunities due to their possible use as nanoscale p-n heterojunctions. Here we report a direct characterization of the internal electronic structure of a single bipolar molecular heterojunction, including subnanometer features of the intramolecular donor-acceptor interface. Angstrom-resolved scanning tunneling spectroscopy was used to map the energy levels and spatial extent of molecular orbitals across the surface of an individual bipolar molecule, bithiophene naphthalene diimide (BND). We find that individual BND molecules exhibit type II heterojunction behavior with orbital energy shifts occurring over subnanometer intramolecular interface distances. Comparison of this behavior with first-principles theoretical modeling provides new insights into the optimization of these molecular systems.

Transport fluctuations and variations in a series of metal-molecule-metal junctions were quantified through measurements of their thermopower. Thiol bound aromatic molecules of various lengths and degrees of freedom were chosen to understand the magnitude and origins of the variations. Junction thermopower was determined by measuring the voltage difference across molecules trapped between two gold contacts held at different temperatures. While any given measurement was remarkably stable, the breadth of distributions from repeated measurements implies variations in the offset of the highest occupied molecular orbital (HOMO) relative to the Fermi Energy of the contacts, similar in magnitude to the nominal offset itself. Statistical analysis of data shows that these variations are born at the junction formation, increase with molecular length, and are dominated by variations in contact geometry and orbital hybridization, as well as intermolecular interactions.

The diiron complexes [Fe(2)(CO)(6)(1,8-S(2)-2,4,5,7-Cl(4)C(10)H(2))] (3), [Fe(2)(CO)(6)(1,8-S(2)C(10)H(6))] (4), and [Fe(2)(CO)(6)(1,8-S(2)-2,7-tBu(2)C(10)H(4))] (5) were synthesized in moderate yield from naphthalene-1,8-dithiols and [Fe(3)(CO)(12)]. They were characterized by IR, (1)H and (13)C NMR spectroscopy and 3 and 4 were characterized by X-ray crystallography. They contain a butterfly Fe(2)S(2) core with Fe-Fe distances of 2.529(1) (3) and 2.506(1) A (4). Cyclic voltammetry (CH(2)Cl(2)/nBu(4)PF(6)) revealed two one-electron reductions, at potentials more positive than those for the related [Fe(2)(CO)(6)(S(CH(2))(3)S)] (1), and one one-electron oxidation. The first reduction of the electron poor 3 (-1.60 V vs Fc/Fc(+)) is 240 mV more positive than the first reduction of the electron rich 5 (-1.84 V). Electrochemical studies revealed that 3-5 facilitate the proton reduction of p-toluenesulfonic acid. The rates of catalysis, with a 95% confidence limit, are 2.4+/-0.8 (1), 5.2+/-0.8 (3), 3.1+/-1.1 (4), 2.9+/-0.6 (5), and 4.5+/-0.2 h(-1) for the related [Fe(2)(CO)(6)(1,2-S(2)C(6)H(4))]. The rates were determined by bulk electrolysis at -1.70 V (Fc/Fc(+)), which correspond to an overpotential of 1.05 V for p-toluenesulfonic acid.

The rhodium and iridium complexes [(tBu2bpy)2M(μ-Cl)]2 (M = Rh (1), Ir (2)) containing the bidentate tBu2bpy (4,4′-di-tert-butyl-2,2′-bipyridyl) ligand were prepared. Dimeric complexes 1 and 2 react with HSiPh3 to give [(tBu2bpy)MH(SiPh3)(μ-Cl)]2 in good yields (M = Rh (3) 92%, Ir (4) 90%). Addition of PiPr3 to 3 or 4 gave monomeric crystalline complexes of the type (tBu2bpy)MH(SiPh3)Cl(PiPr3) (M = Rh (7) and Ir (8)), which adopt a slightly distorted octahedral coordination geometry with the tBu2bpy ligand occupying sites trans to the hydride and chloride ligands, as determined by X-ray crystallography. Salt metathesis reactions of 7 and 8 produced (tBu2bpy)MH(SiPh3)(R)PiPr3 as monomeric octahedral complexes with the tBu2bpy ligand occupying sites trans to the hydride and R substituents (M = Rh, R = H (11) and M = Ir, R = H (12), Me (14), and Ph (15)). Salt metathesis reactions with 3 and 4 also generated the dimeric, dicationic complexes [(tBu2bpy)M(SiPh3)(μ-H)]2[B(C6F5)4]2, where M = Rh (16) or Ir (17)....

New rhodium and iridium complexes containing the bidentate ligand 3,5-diphenyl-2-(2-pyridyl)pyrrolide (PyPyr) were prepared. The bis(ethylene) complex (PyPyr)Rh(C(2)H(4))(2) (3) reacted with HSiEt(3), HSiPh(3), and HSi(t)BuPh(2) to produce the 16-electron Rh(V) bis(silyl)dihydrides (PyPyr)Rh(H)(2)(SiEt(3))(2) (8), (PyPyr)Rh(H)(2)(SiPh(3))(2) (9), and (PyPyr)Rh(H)(2)(Si(t)BuPh(2))(2) (10), respectively. The analogous Ir(V) bis(silyl)dihyride (PyPyr)Ir(H)(2)(SiPh(3))(2) (11) has also been synthesized. X-ray crystallography reveals that 9-11 adopt a coordination geometry best described as a bicapped tetrahedron. Silane elimination from 9 and 10 occurred in the presence of either HSiEt(3) or PPh(3). Mechanistic studies of the silane exchange process involving 10 and free HSiEt(3) (to give 8) indicate that this process occurs by rate-limiting reductive elimination of HSi(t)BuPh(2) from 10 to generate a 14-electron Rh(III) intermediate of the type (PyPyr)Rh(H)(Si(t)BuPh(2)).

Reaction of Cp*(iPr2MeP)RuCl (1) with 0.5 equiv of Mg(CH2Ph)2(THF)2 afforded the benzyl complex Cp*(iPr2MeP)Ru(η3-CH2Ph) (2). Complex 2 readily reacted with primary silanes H3SiR (R = trip, dmp, MesF; trip = 2,4,6-iPr3-C6H2, dmp = 2,6-Mes2-C6H3, MesF = 2,4,6-(CF3)3-C6H2) to liberate toluene and afford hydrogen-substituted silylene complexes Cp*(iPr2MeP)(H)Ru═SiH(R) [R = trip, 3; dmp, 4; MesF, 5]. Complexes 3−5 exhibit characteristic SiH 1H NMR resonances downfield of 8 ppm and very small 2JSiH coupling constants (8−10 Hz). The solid state structures of complexes 3 and 5 feature short Ru−Si distances of 2.205(1) and 2.1806(9) A, respectively, and planar silicon centers. In addition, the silylene complex Cp*(iPr2MeP)(H)Ru═SiPh(trip) (6) and the unusual, chlorine-substituted species Cp*(iPr2MeP)(H)Ru═SiCl(R) [R = trip, 7; dmp, 8] were prepared. Hydrogen-substituted ruthenium germylene complex Cp*(iPr2MeP)(H)Ru═GeH(trip) (9) was prepared similarly by reaction of 2 with tripGeH3. Complex 9 is the first structu...

Cubic Co3O4 nanoparticles with average diameters of 5.9, 21.1, and 46.9 nm (hereafter small, medium, and large) have been synthesized and characterized by pXRD, TEM, and BET. The nanoparticles were loaded onto Ni foam supports for evaluation as anodes for water electrolysis in 1.0 M KOH. Current densities of 10 mA/cm2 were achieved at overpotentials of 328, 363, and 382 mV for anodes loaded with 1 mg/cm2 of small, medium, and large sized Co3O4 nanoparticles, respectively. The activity correlates with the BET surface area of the isolated particles. A plot of the electrochemical overpotential at 10 mA/cm2 against the log of the BET surface area gives a linear relation with a slope of −47 ± 7 mV/dec, showing unequivocally that the activity increase is a function of accessible catalyst surface area.

In this paper, a theoretical investigation of bond activations of PhSiH3, catalyzed by Cp2SmH, is proposed by examination of the energy profiles of these reactions. The formation of the minor and major products observed experimentally is rationalized. The experimentally proposed two-step mechanism, starting with a Si−C activation to give Cp2SmPh as an intermediate, is confirmed. The second step involves reaction of this intermediate with the Si−H bond of PhSiH3 to give Ph2SiH2 and regenerate the samarium hydride. The relative free enthalpy barriers of these two steps are in agreement with the lack of observation of any intermediate during the catalytic reaction. In addition to the main experimentally proposed mechanism, a second mechanism that involves two successive Si−H activations is proposed in order to account for the formation of byproducts. Theoretically, these two reactions are demonstrated to occur competitively, which explains the formation of secondary products arising from redistribution and d...

Complexes of Pt(IV) containing the bidentate ligand 3,5-diphenyl-2-(2-pyridyl)pyrrolide (PyPyr) were prepared. The ethylene complex PyPyrPt(C2H4)Cl (1) was treated with HSiEt3 or HSiEtMe2 to produce the Pt(IV) silyl dihydrides PyPyrPt(H)2SiEt3 (3) and PyPyrPt(H)2SiEtMe2 (4), respectively. The solid-state structure of 3, determined by X-ray crystallography, reveals a dimeric structure that forms via π-stacking between the PyPyr ligands. Addition of Lewis bases to 3 results in either coordination to generate an octahedral Lewis base adduct (with DMAP) or silane elimination to give square-planar Pt(II) Lewis base complexes (with phosphines). Complex 3 was also found to be an active hydrosilylation catalyst for the hydrosilylation of alkynes and terminal olefins with HSiEt3.

Reaction of 2 equivs of MesC[triple bond]CPh with Cp(2)Zr(eta(2)-Me(3)SiC[triple bond]CSiMe(3))(pyr) afforded the zirconacyclopentadiene Cp(2)Zr[2,5-Ph(2)-3,4-Mes(2)C(4)]. The regiochemistry of this isomer (betabeta with respect to the mesityl substituents) was determined through single-crystal X-ray analysis and 2D (NOESY, HSQC, HMBC) NMR experiments. This selectivity is attributed largely to a steric-based directing effect of the o-methyl ring substituents since coupling of 1,3-dimethyl-2-(phenylethynyl)benzene with zirconocene gave a single regioisomer (o-xylyl groups in both beta-positions) while coupling of 1,3-dimethyl-5-(phenylethynl)benzene gave a statistical distribution of zirconacyclopentadiene regioisomers. The coupling reaction of 2 equivs of MeC[triple bond]CMes or PrC[triple bond]CMes with Cp(2)Zr(eta(2)-Me(3)SiC[triple bond]CSiMe(3))(pyr) at ambient temperature gave the betabeta regioisomers, Cp(2)Zr[2,5-Me(2)-3,4-Mes(2)C(4)] and Cp(2)Zr[2,5-Pr(2)-3,4-Mes(2)C(4)], respectively, as the major products. Heating solutions of these zirconacycles at 80 degrees C for several hours resulted in an increase in the amount of the unsymmetrical product. For reaction mixtures of PrC[triple bond]CMes and Cp(2)Zr(eta(2)-Me(3)SiC[triple bond]CSiMe(3))(pyr) the major (and apparently thermodynamic) product under these reaction conditions was Cp(2)Zr[2,4-Mes(2)-3,5-Pr(2)C(4)]. The steric strain in the mesityl-substituted zirconacycles allowed for facile substitution reactions of MesC[triple bond]CPh or PrC[triple bond]CMes by less bulky alkynes (i.e., tolan and 3-hexyne) to give the unsymmetrical ziconacyclopentadienes Cp(2)Zr[2,4,5-Ph(3)-3-MesC(4)], Cp(2)Zr[2-Ph-3-Mes-4,5-Et(2)C(4)], and Cp(2)Zr[2-Pr-3-Mes-4,5-Ph(2)C(4)]. Reaction of a mesityl-terminated diyne containing a rigid dihexylfluorenylene spacer with zirconocene afforded poly(p-fluorenylenedienylene) after demetalation with benzoic acid.

Reaction of the zirconocene dichloride Cp′′Flu*ZrCl2 (Cp′′ = 1,3-(SiMe3)2C5H3, Flu* = C13Me9) with iBuLi (iBuLi = LiCH2CHMe2) resulted in elimination of isobutylene and formation of Cp′′(η5:η3-C13Me9H)ZrH (1-syn-1,2-DHF*D), possessing an η5:η3-dihydrofluorenediyl ligand derived from a metal-to-benzo ring hydride transfer. This species undergoes reversible hydride transfer and exists in equilibrium with only one of its three other possible isomers (1-syn-3,4-DHF*D). Compound 1-syn-1,2-DHF*D catalyzes the cyclization of 1,5-hexadiene to methylenecyclopentane, and its reaction with excess isobutylene leads to the elimination of isobutane and formation of the cyclometalated zirconocene isobutyl species (η5:η1-C5H3-1-SiMe2CH2-3-SiMe3)(η5-C13Me9)ZriBu (2). Reaction of Cp′′Flu′′ZrCl2 with iBuLi directly generated the cyclometalated zirconocene species (η5:η1-C5H3-1-SiMe2CH2-3-SiMe3)(η5-C13Me8H)ZriBu (3); however, reaction of the dichloride Cp′′Flu′′ZrCl2 with iBuLi in the presence of hydrogen generated the dihyd...

Transport in metal-molecule-metal junctions is defined by the alignment and coupling of molecular orbitals with continuum electronic states in the metal contacts. Length-dependent changes in molecular orbital alignment and coupling with contact states were probed via measurements and comparisons of thermopower (S) of a series of phenylenes and alkanes with varying binding groups. S increases linearly with length for phenylenediames and phenylenedithiols while it decreases linearly in alkanedithiols. Comparison of these data suggests that the molecular backbone determines the length dependence of S, while the binding group determines the zero length or contact S. Transport in phenylenes was dominated by the highest occupied molecular orbital (HOMO), which aligns closer to the Fermi energy of the contacts as approximately L(-1), but becomes more decoupled from them as approximately e(-L). In contrast, the decreasing trend in S for alkanedithiols suggests that transmission is largely affected by gold-sulfur metal induced gap states residing between the HOMO and lowest unoccupied molecular orbital.

The reaction of one equiv of 1-alkynylphosphines, R2PC≡CR′ (R = Et, iPr, or Ph and R′ = Ph or Mes), with Cp2Zr(pyr)(η2-Me3SiC≡CSiMe3) resulted in formation of monoalkyne complexes. In the case where R = Et, iPr, or Ph and R′ = Ph, a “ligand free” zirconacyclopropene complex is produced. These complexes are stabilized by intermolecular donation of the phosphorus lone-pair in the dimeric complexes [Cp2Zr(η2-R2PC≡CPh)]2 (R = Et, iPr, or Ph). However, with R = Ph and R′ = Mes, the zirconocyclopropene-pyridine complex Cp2Zr(pyr)(η2-Ph2PC≡CMes) is formed. Homocoupling of the 1-alkynylphosphines was demonstrated by reaction of a second equiv of Ph2PC≡CPh with [Cp2Zr(η2-Ph2PC≡CPh)]2 to give the diphosphinozirconacyclopentadiene Cp2Zr[2,5-(Ph2P)2-3,4-Ph2C4] with high regioselectivity (77%). The zirconacyclopropene complexes also react with one equiv of PhC≡CPh or EtC≡CEt to give zirconacyclopentadienes in which the phosphino substituent preferentially adopts the 2-position (α) of the zirconacyclopentadiene ring. T...

Silicone nanospheres containing a variety of functional groups (pyridines, phosphines, thiols, amines, etc.) have been prepared by emulsion copolymerization of methyltrimethoxysilane, MeSi(OMe)3, and the functionalized monomer of interest, RSi(OMe)3. This procedure provides a reproducible synthesis of spherical particles in the 12−28 nm size regime as determined by transmission electron microscopy (TEM). The presence of the functional groups is supported by a combination of spectroscopic methods including DRUV−vis, DRIFTS, and NMR spectroscopy. Comonomer dispersity within the nanospheres was probed using elemental mapping techniques, and these support a homogeneous distribution of functional groups within the particles. Palladium(0) immobilization on phosphine-substituted nanospheres also results in a random distribution of the transition metal throughout the particles. Nanospheres containing multiple acid/base functionalities were also prepared, and these demonstrate functional group cooperativity based ...

Vanadium silyl complexes of the type Cp(dmpe)VSiHRR′ are formed by reaction of Cp(dmpe)VMe (1) with RR′SiH2 (2, R, R′ = Ph; 3, R = Mes, R′ = H) in benzene at room temperature with concomitant relea...

Two novel tris(tert-butoxy)siloxy complexes of Pt(II) and Pt(IV) were prepared in high yields, (cod)Pt[OSi(OtBu)3]2 (1; 87%; cod = 1,5-cyclooctadiene) and Me3Pt(tmeda)[OSi(OtBu)3] (2; 81%; tmeda = N,N,N′,N′-tetramethylethylenediamine). The structures of these compounds were determined by multinuclear NMR spectroscopy and by single-crystal X-ray analysis. The thermolytic chemistry of 1 and 2 in the solid state was studied by thermogravimetric analysis. The thermal decomposition of these complexes resulted in the formation of Pt metal, with the elimination of HOSi(OtBu)3. Precursors 1 and 2 react with the surface Si−OH groups of mesoporous SBA15 silica to generate surface-supported Pt centers. The coordination environments of the supported Pt centers in these new materials, termed Pt(II)SBA15 and Pt(IV)SBA15, were investigated using Fourier-transform infrared spectroscopy, X-ray absorption near-edge spectroscopy, and extended X-ray absorption fine structure analysis. These materials were also characterized ...

The Pt(II) complex (NSiN)PtCl (2; NSiN = bis(8-quinolyl)methylsilyl) was prepared from reaction of (COD)PtCl2, Qn2SiHMe (1) and excess NEt3 in dichloromethane. The X-ray structure of 2 confirms a square-planar geometry about platinum and a highly distorted tetrahedral geometry at Si. A series of thermally stable (NSiN)Pt(IV) compounds including (NSiN)PtH2(X) [X = Cl (5), OTf (10)] and (NSiN)PtMe2(X) [X = I (6), OTf (7)] were also synthesized. Five-coordinate Pt(IV) complexes of the type [(NSiN)PtR2][B(C6F5)4] (X = Me (9), H (11)] were generated by treatment of the corresponding triflato derivatives with 1 equiv of Li(Et2O)3[B(C6F5)4] in dichloromethane. A crystal structure of 9 reveals a square-pyramidal structure with an empty coordination site trans to silicon. Initial reactivity studies have shown that complex 9 is thermally and chemically robust.