We present an in-depth study of the sterically demanding Cp-synthon (8-H-GuaH)Li isolated from natural product guaiazulene (Gua) as a ligand transfer reagent towards late transition metal complex precursors. The synthesis and full characterization of selected, essentially unexplored homo- and heteroleptic 8-H-guaiazulenide complexes of iron, ruthenium, cobalt, rhodium, platinum, copper and zinc are discussed in detail. In order to demonstrate their potential in catalytic applications, [(GuaH)PtMe3 ] was selected. The latter proved an even higher catalytic activity in light induced olefin hydrosilylation at catalyst loads as low as 5â ppm than classical [CpPtMe3 ] in a typical test reaction of silicone elastomer fabrication. Our results demonstrate that traditional petrochemical based Cp metal chemistry and catalysis can be replaced, sometimes even outmatched by superior catalysts based on cheap building blocks from renewable feedstock.
The synthesis of new tetradentate dianionic N2O2 ligand juglophen (H2jp, 1) and its nickel(II) complex [Ni(jp)] (2) is reported. The unprecedented ligand synthesis is accomplished via oxidative coupling of 1,5-dihydroxynapthalene and o-phenylenediamine by hypervalent phenyliodine(III)-diacetate. Ligand 1 and complex 2 were characterized via NMR, IR, UV-Vis spectroscopy, mass spectrometry, cyclic voltammetry and by XRD analysis. In order to investigate the non-innocent character of ligand 1, [Ni(jp)] (2) was oxidized using AgPF6 to form [Ni(jp)]+ [PF6]- (3) whereas one-electron reduction with [Cp2Co] generated [Cp2Co]+[Ni(jp)]- (4). The paramagnetic nature of the oxidized and reduced species 3 and 4 was validated via EPR spectroscopy and further investigated pursuing DFT calculations at the PBE-D3(BJ)/def2-TZVPP level of theory. Predominantly ligand-centered SOMOs of 3 and 4 are allowing insight towards a deeper understanding of the redox behavior of [Ni(jp)] (2).
Laser-based surface processing is an established way for the maskless generation of surface structures and functionalities on a large variety of materials. Laser-driven periodic surface texturing and structuring of thin films is reported for metallic-, semiconductive-, and polymeric films. Here, we introduce subwavelength surface patterning of metal-organic thin films of [Mo2S4(S2CNnBu2)2], a MoS2 precursor. Accurate control of one- and two-dimensional (1D and 2D) periodic patterns is achieved on silicon wafers with a pulsed 532 nm ns laser. With suitable combinations of laser polarization, laser pulse energy, the thickness of the SiO2 passivation layer, and the MoS2 precursor's thin film thickness, high-quality 1D and 2D self-organized periodic structures are obtained in virtually unlimited areas. The material redistribution related to the pattern formation is thermally driven at low laser energies. Increasing pulse energies beyond a threshold level, in our experiments a factor of 2, fully converts the precursor to MoS2.
Herein we present the molecular structures of six neutral Lewis acid-base adducts of the Lewis superacid Al(N(C6F5)2)3 and its higher homolog Ga(N(C6F5)2)3 with the electron pair donors MeCN, CNtBu, THF and PMe3. The crystal structures reveal crucial structural changes compared to the free Lewis acids as a consequence of the adduct formation. Furthermore, we calculated the corresponding dissociation enthalpies of the adducts which lie between 69 and 141 kJ mol-1 and are therefore considerably lower compared to the values for the formation of the anionic fluoride or chloride metallates.
We report a new high-yield synthesis of so far not accessible tetraphenylphosphonium methylcarbonate Ph4P[OCO2Me] via solvothermal fluoride-induced demethylation and MeF elimination at Me2CO3 (DMC) by Ph4P-F, structurally characterized as λ5-fluorophosphoran by XRD. The synthetic value of Ph4P[OCO2Me] key compound for preparing nearly all kinds of other Ph4P[anion] salts with perfectly crystallizing (not symmetry frustrated) cation is demonstrated by examples beyond ionic liquid research: a complete set of silylchalcogenide salts Ph4P[ESiMe3] (E = S, Se, and Te) including the first example of a structurally characterized non-coordinating, naked [Te-SiMe3]- anion is presented. With this set of soft Lewis bases and metal organic Lewis acids [Cp3La] at hand, a comprehensive series of crystalline 1 : 1 lanthanate complexes Ph4P[Cp3La-ESiMe3] has been prepared. Their structural features and trends such as complexation induced Si-E bond elongation and a pronounced trend in La-E-Si bond angle contraction with E = S < Se < Te are discussed. Heteronuclear 1H, 13C, 29Si, and 139La NMR studies provide a set of 139La NMR shifts for homologs of heavy chalcogen-lanthanum complexes.
2,7-Diazapyrene and 2,9-diazaperopyrene tetraalkynes (12 and 13) as well as related non-N-doped pyrene and peropyrene tetraalkynes (14 and 15) of the same shape were used as polyaromatic templates in their metalation by [Co2(CO)8]. Isolated cobalt-rich [(12, 13, 14, 15)Co8(CO)24] clusters were characterized by means of NMR, IR, UV-Vis spectroscopy and X-ray crystallography. Their thermogravimetric behaviour and products of solid-state pyrolysis (SSP) were investigated by TGA, DSC, and scanning electron microscopy (SEM). Despite the same precursor shape, different carbon nanoparticles and nanotubes were formed depending on the extension of the π-system and nitrogen content of the precursors. Diazapyrene and diazaperopyrene complexes formed cauliflower-shaped nanoparticles, and the pyrene complex formed spherical nanoparticles and the peropyrene complex led to multi-walled carbon nanotubes. These results elucidate that the carbon to cobalt ratio and the nitrogen dopant in the precursor have a significant impact on the products of the pyrolysis reaction.
ConspectusOne of the constant challenges of synthetic chemistry is the molecular design and synthesis of nonionic, metal-free superbases as chemically stable neutral organic compounds of moderate molecular weight, intrinsically high thermodynamic basicity, adaptable kinetic basicity, and weak or tunable nucleophilicity at their nitrogen, phosphorus, or carbon basicity centers. Such superbases can catalyze numerous reactions, ranging from C-C bond formation to cycloadditions and polymerization, to name just a few. Additional benefits of organic superbases, as opposed to their inorganic counterparts, are their solubility in organic reaction media, mild reaction conditions, and higher selectivity. Approaching such superbasic compounds remains a continuous challenge. However, recent advances in synthetic methodology and theoretical understanding have resulted in new design principles and synthetic strategies toward superbases. Our computational contributions have demonstrated that the gas-phase basicity region of 350 kcal mol-1 and even beyond is easily reachable by organosuperbases. However, despite record-high basicities, the physical limitations of many of these compounds become quickly evident. The typically large molecular weight of these molecules and their sensitivity to ordinary reaction conditions prevent them from being practical, even though their preparation is often not too difficult. Thus, obviously structural limitations with respect to molecular weight and structural complexity must be imposed on the design of new synthetically useful organic superbases, but strategies for increasing their basicity remain important.The contemporary design of novel organic superbases is illustrated by phosphazenyl phosphanes displaying gas-phase basicities (GB) above 300 kcal mol-1 but having molecular weights well below 1000 g·mol-1. This approach is based on a reconsideration of phosphorus(III) compounds, which goes along with increasing their stability in solution. Another example is the preparation of carbodiphosphoranes incorporating pyrrolidine, tetramethylguanidine, or hexamethylphosphazene as a substituent. With gas-phase proton affinities of up to 300 kcal mol-1, they are among the top nonionic carbon bases on the basicity scale. Remarkably, the high basicity of these compounds is achieved at molecular weights of around 600 g·mol-1. Another approach to achieving high basicity through the cooperative effect of multiple intramolecular hydrogen bonding, which increases the stabilization of conjugate acids, has recently been confirmed.This Account focuses on our efforts to produce superbasic molecules that embody many desirable traits, but other groups' approaches will also be discussed. We reveal the crucial structural features of superbases and place them on known basicity scales. We discuss the emerging potential and current limits of their application and give a general outlook into the future.
The synthesis of 2,9-diaza-1,3,8,10-tetratriflato-dibenzoperylene (DDP 3 a) and corresponding 2,9-dimethyl-1,3,8,10-tetratriflato-dibenzoperylene (DBP 3 b) has been developed at multigram scale via reduction of one of the industrially most important high-performance dyes, perylene-3,4,9,10-tetracarboxylic diimide (PTCDI), and of the corresponding dihydroxy peropyrenequinone precursor. The focus of this paper is on the reactivity pattern of 3 a as key intermediate towards highly functionalized 2,9-diazadibenzopyrelenes (DDPs) obtained via catalytic substitution of four triflate by aryl, heteroaryl, alkynyl, aminyl, and O-phosphanyl substituents. The influence of electron-donating substituents (OSiMe3 , OPt-Bu2 , N-piperidinyl), electron-withdrawing (OTf, 3,5-bis-trifluoromethyl-phenyl), and of electron-rich π-conjugated (2-thienyl, 4-tert-butylphenyl, trimethylsilyl-ethynyl) substituents on optoelectronic and structural properties of these functionalized DDPs has been investigated via XRD analyses, UV/Vis, PL spectroscopy, and by electroanalytical CV. These results were correlated to results of DFT and TD-DFT calculations. Thus, functionalized DPPs with easily tunable HOMO and LUMO energies and gap became available via a new and reliable synthetic strategy starting from readily available PTCDI.
The chromophore class of 1,3,8,10-tetrasubstituted peropyrenes was effectively synthesized from peropyrenequinone via a Zn-mediated reductive aromatization approach. In one step, a symmetric functionalization of the peropyrene backbone introducing silylethers (2,3), pivaloyl (4), triflyl (5) and also phosphinite (6) groups was established. Furthermore, the potential of using 4 and 5 in transition metal catalysed cross couplings was explored leading to 1,3,8,10-tetraaryl (8-11) and tetraalkynyl (7) peropyrenes. The influence of various substituents on the optoelectronic properties of these π-system extended peropyrenes was investigated in solid state by means of X-ray crystallography, in solution by means of UV-Vis and fluorescence spectroscopy and by their redox properties studied via cyclic voltammetry. By comparison with DFT and TD-DFT calculations, it could be elucidated that introduction of a broad variety of substituents in such versatile one or two step procedures leads to peropyrenes with easily tunable HOMO and LUMO energies ranging in a gap window of 0.8 eV. The frontier molecular orbital energies identify the target molecules as promising candidates for hole transporting semiconductors.
Crystallography, X-Ray , Catalysis , Density Functional Theory , Oxidation-Reduction
This research presents the highly regioselective syntheses of 1,2-dicarboxylated cyclopentadienide salts [Cat]2 [C5 H3 (CO2 )2 H] by reaction of a variety of organic cation methylcarbonate salts [Cat]OCO2 Me (Cat=NR4 + , PR4 + , Im+ ) with cyclopentadiene (CpH) or by simply reacting organic cation cyclopentadienides Cat[Cp] (Cat=NR4 + , PR4 + , Im+ ) with CO2 . One characteristic feature of these dianionic ligands is the acidic proton delocalized in an intramolecular hydrogen bridge (IHB) between the two carboxyl groups, as studied by 1 Hâ NMR spectroscopy and XRD analyses. The reaction cannot be stopped after the first carboxylation. Therefore, we propose a Kolbe-Schmitt phenol-carboxylation related mechanism where the acidic proton of the monocarboxylic acid intermediate plays an ortho-directing and CO2 activating role for the second kinetically accelerated CO2 addition step exclusively in ortho position. The same and related thiocarboxylates [Cat]2 [C5 H3 (COS)2 H] are obtained by reaction of COS with Cat[Cp] (Cat=NR4 + , PR4 + , Im+ ). A preliminary study on [Cat]2 [C5 H3 (CO2 )2 H] reveals, that its soft and hard coordination sites can selectively be addressed by soft Lewis acids (Mo0 , Ru2+ ) and hard Lewis acids (Al3+ , La3+ ).
Herein we report a versatile concept for the synthesis of fourfold functionalized, soluble pyrenes, peropyrenes, terropyrenes, and quarterropyrenes. They were obtained by a modular stepwise approach towards the rylene scaffold via Suzuki-Miyaura cross coupling, oxidative cyclodehydrogenation in the presence of caesium hydroxide under air, and finally zinc-mediated reductive silylation. The silylated reaction products were characterized by X-ray crystallography. The first example of a synthesized and crystallized quarterropyrene is presented and its oxidation reaction investigated. The functionalized ropyrenes were systematically characterized by means of UV/Vis-NIR and photoluminescence spectroscopy showing a bathochromic shift of 80â nm per naphthalene unit and a nearly linear increase of the extinction coefficients. Cyclic voltammograms and DFT calculations identify them as electron-rich dyes and show a narrowing of the electrochemically determined HOMO-LUMO gap and lower oxidation potentials for the higher homologues.
This minireview describes two strategically different and unexplored approaches to use ionic liquids (IL) containing weakly solvated and highly reactive chalcogenide anions [E-SiMe3 ]- and [E-H]- of the heavy chalcogens (E=S, Se, Te) in materials synthesis near room temperature. The first strategy involves the synthesis of unprecedented trimethylsilyl chalcogenido metalates Cat+ [M(E-SiMe3 )n ]- (Cat=organic IL cation) of main group and transition metals (M=Ga, In, Sn, Zn, Cu, Ag, Au). These fully characterized homoleptic metalates serve as thermally metastable precursors in low-temperature syntheses of binary, ternary and even quaternary chalcogenide materials such as CIGS and CZTS relevant for semiconductor and photovoltaics (PV) applications. Furthermore, thermally and protolytically metastable coinage metalates Cat+ [M(ESiMe3 )2 ]- (M=Cu, Ag, Au; E=S, Se) are accessible. Finally, the use of precursors BMPyr[E-SiMe3 ] (E=Se,Te; BMPyr=1-butyl-1-methylpyrrolidinium) as sources of activated selenium and tellurium in the synthesis of high-grade thermoelectric nanoparticles Bi2 Se3 and Bi2 Te3 is shortly highlighted. The second synthesis strategy involves the metalation of ionic liquids Cat[S-H] and Cat[Se-H] by protolytically highly active metal alkyls or amides Rn M. This rather general approach towards unknown chalcogenido metalates Catm [Rn-1 M(E)]m (E=S, Se) will be demonstrated in a research paper following this short review head-to-tail.
Metalation of the anions in the ionic liquids DMPyr[SH] and DMPyr[SeH] (DMPyr=1,1-dimethylpyrrolidinium) by trimethylgallium and trimethylindium is investigated. The reaction proceeds via pre-coordination of [EH]- , methane elimination and formation of an unprecedented series of chalcogenido metalates DMPyr2 [Me2 M(µ2 -E)]2 (M=Ga, In; E=S, Se). These show the presences of dinuclear dianions with four-membered ring structures displaying highly nucleophilic bridging chalcogenide ligands in their crystallographically determined molecular structures. Some representative reactions of these building blocks with amphoteric electrophiles were studied: Addition of two equivalents of E(SiMe3 )2 (E=S, Se) to the indates DMPyr2 [Me2 In(µ2 -S)]2 and DMPyr2 [Me2 In(µ2 -Se)]2 leads to a cleavage of the ring, E silylation and formation of mononuclear, monoanionic indates DMPyr[Me2 In(SSiMe3 )2 ], DMPyr[Me2 In(SeSiMe3 )2 ], and even a mixed sulfido-selenido dimethylindate DMPyr[Me2 In(SSiMe3 )(SeSiMe3 )]. Reaction of DMPyr2 [Me2 In(µ2 -S)]2 with two equivalents of Lewis acid Me3 In leads to charge delocalization, ring expansion and formation of six-membered ring DMPyr3 [Me2 In(µ2 -S-InMe3 )]3 . The latter is a key intermediate in the formation of dianionic sulfidoindate DMPyr2 [(Me2 In)6 (µ3 -S)4 ] displaying an unusual inverse heteroadamantane cage structure with four capping sulfido ligands.
The syntheses and XRD molecular structures of a complete series of silylsulfido metalates Cat[M(SSiMe3)2] (M = Cu, Ag, Au) and corresponding silylselenido metalates Cat[M(SeSiMe3)2] (M = Cu, Ag, Au) comprising lattice stabilizing organic cations (Cat = Ph4P+ or PPN+) are reported. Much to our surprise these homoleptic cuprates, argentates, and aurates are stable enough to be isolated even in the absence of any strongly binding phosphines or N-heterocyclic carbenes as coligands. Their metal atoms are coordinated by two silylchalcogenido ligands in a linear fashion. The silyl moieties of all anions show an unexpected gauche conformation of the silyl substituents with respect to the central axis Si-[E-M-E]-Si in the solid state. The energetic preference for the gauche conformation is confirmed by quantum chemical calculations and amounts to about 2-6 kJ/mol, thus revealing a rather shallow potential mainly depending on electronic effects of the metal. Furthermore, 2D HMQC methods were applied to detect the otherwise nonobservable NMR shifts of the 29Si and 77Se nuclei of the silylselenido compounds. Preliminary investigations reveal that these thermally and protolytically labile chalcogenido metalates are valuable precursors for the precipitation of binary coinage metal chalcogenide nanoparticles from organic solution and for coinage metal cluster syntheses.
We revisit the question of kekulene's aromaticity by focusing on the electronic structure of its frontier orbitals as determined by angle-resolved photoemission spectroscopy. To this end, we have developed a specially designed precursor, 1,4,7(2,7)-triphenanthrenacyclononaphane-2,5,8-triene, which allows us to prepare sufficient quantities of kekulene of high purity directly on a Cu(111) surface, as confirmed by scanning tunneling microscopy. Supported by density functional calculations, we determine the orbital structure of kekulene's highest occupied molecular orbital by photoemission tomography. In agreement with a recent aromaticity assessment of kekulene based solely on C-C bond lengths, we conclude that the π-conjugation of kekulene is better described by the Clar model rather than a superaromatic model. Thus, by exploiting the capabilities of photoemission tomography, we shed light on the question which consequences aromaticity holds for the frontier electronic structure of a π-conjugated molecule.
A single thiocatecholate group has been combined with a phthalocyanine and used to coordinate a [Ni(dppe)]2+ fragment to give the unprecedented title complex [(dppe)Ni(S2PcH2)]. UV-Vis spectroscopy shows new strong transitions in the Q-band, which TDDFT calcualtions predict result from internal charge transfer processes. Insights are gained with respect to designing future photocatalytic systems.
A series of dinuclear copper(I) N,C,N- and P,C,P-carbodiphosphorane (CDP) complexes using multidentate ligands CDP(Py)2 (1) and (CDP(CH2PPh2)2 (13) have been isolated and characterized. Detailed structural information was gained by single-crystal XRD analyses of nine representative examples. The common structural motive is the central double ylidic carbon atom with its characteristic two lone pairs involved in the binding of two geminal L-Cu(I) fragments at Cu-Cu distances in the range 2.55-2.67 Å. In order to enhance conformational rigidity within the characteristic Cu-C-Cu triangle, two types of chelating side arms were symmetrically attached to each phosphorus atom: two 2-pyridyl functions in ligand CDP(Py)2 (1) and its dinuclear copper complexes 2-9 and 11, as well as two diphenylphosphinomethylene functions in ligand CDP(CH2PPh2)2 (13) and its di- and mononuclear complexes 14-18. Neutral complexes were typically obtained via the reaction of 1 with Cu(I) species CuCl, CuI, and CuSPh or via the salt elimination reaction of [(CuCl)2(CDP(Py)2] (2) with sodium carbazolate. Cationic Cu(I) complexes were prepared upon treating 1 with two equivalents of [Cu(NCMe)4]PF6, followed by the addition of either two equivalents of an aryl phosphine (PPh3, P(C6H4OMe)3) or one equivalent of bisphosphine ligands bis[(2-diphenylphosphino)phenyl] ether (DPEPhos), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (XantPhos), or 1,1'-bis(diphenyl-phosphino) ferrocene (dppf). For the first time, carbodiphosphorane CDP(CH2PPh2)2 (13) could be isolated upon treating its precursor [CH(dppm)2]Cl (12) with NaNH2 in liquid NH3. A protonated and a deprotonated derivative of ligand 13 were prepared, and their coordination was compared to neutral CDP ligand 13. NMR analysis and DFT calculations reveal that the most stable tautomer of 13 does not show a CDP (or carbone) structure in its uncoordinated base form. For most of the prepared complexes, photoluminescence upon irradiation with UV light at room temperature was observed. Quantum yields (ΦPL) were determined to be 36% for dicationic [(CuPPh3)2(CDP(Py)2)](PF6)2 (4) and 60% for neutral [(CuSPh)2(CDP(CH2PPh2)2] (16).
Copper/chemistry , Luminescence , Phosphoranes/chemistry , Ligands , Phosphoranes/chemical synthesis , Quantum Theory , Spectrum Analysis , Temperature , X-Ray Diffraction
Previous reports in the literature describe that the crystallization of hexaphenyl carbodiphosphorane (CDPPh) from a variety of solvents gives a "bent" geometry for the P-C-P moiety as the solid-state molecular structure. However, a linear structure is observed when CDPPh is crystallized from benzene. Here, we report detailed spectroscopic and theoretical studies on the linear and bent structures. X-ray powder diffraction examinations show a phase transition of linear CDPPh upon the loss of co-crystallized benzene molecules, which is accompanied by the bending of the P-C-P unit. Studies on the linear and bent structures (i.e., X-ray powder diffraction, solid-state NMR, UV-vis spectroscopy, and IR spectroscopy) show significant differences in their properties. Investigations of the solid-state structures with density functional theory-based methods (PBE-D3) point toward subtle dispersion effects being responsible for this solvent-induced bond-bending isomerism in CDPPh.
Organic cation salts with homoleptic zincate and stannanide anions, Ph4P [Zn(ESiMe3)3] (E = S (1a), Se (1b)) and Cat [Sn(ESiMe3)3] (Cat = Ph4P+ (E = S (2a-Ph4P); Cat = PPN+ (E = S 2a-Ph4P, Se (2a)) are presented and structurally characterized. Efforts to isolate neutral thermally metastable stannane precursors [Sn(ESiMe3)4] (E = S (3), Se(4)) are reported as well. The thermal decomposition of the presented precursors to yield binary sulfides and selenides of zinc and tin is investigated. Furthermore, the potential of using the title anions as precursors in solution-based low-temperature synthesis of Cu2ZnSnS4 (CZTS) by coprecipitation with [Cu(tmtu)3]PF6 and subsequent annealing is discussed.
Phase-pure crystalline Bi2Se3 and Bi2Te3 nanoparticles are formed in reactions of [C4C1Im]3[Bi3I12] (C4C1Im = 1-butyl-3-methylimidazolium) with [C4C1Pyr][ESiMe3] (E = Se or Te; C4C1Pyr = 1-butyl-1-methylpyrrolidinium) in the ionic liquid (IL) [C4C1Im]I. The resulting crystalline tetradymite-type nanoparticles exhibit stoichiometric Bi:E (E = Se or Te) molar ratios (2:3). Because all synthetic steps were performed under strict inert gas conditions, the surfaces of the Bi2Se3 and Bi2Te3 nanoparticles are free of metal oxide species. As proven by infrared and X-ray photoelectron spectroscopy analyses, the nanoparticle surfaces reveal only minor organic contamination from solvent residues ([C4C1Im]I). The nanomaterials show high Seebeck coefficients of -124 µV K-1 (Bi2Se3) and -155 µV K-1 (Bi2Te3) and feature high electrical conductivities (328 and 946 S cm-1, respectively) at the highest tested temperature (240 °C). The corresponding thermal conductivities (0.8 and 2.3 W m-1 K-1, respectively, at 30 °C) are comparable to those of single crystals and recently reported ab initio calculations, which is in remarkable contrast to typical findings of nanograined bulk materials obtained from compacted nanoparticles. These findings emphasize the low level of impurities, surface contamination, and, in general, defects produced by the synthetic approach reported here. The figure of merit in the in-plane direction of the compacted pellets reached peak values 0.45 for Bi2Se3 and 0.4 for Bi2Te3.
