Dihydroguaiazulenide Complexes and Catalysts of Group 8-12 Transition Metals: Ligands from Renewable Feedstock Replace, even Outmatch Petrochemical Based Cyclopentadienyl Chemistry.

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 5 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.

Heavy silylchalcogenido lanthanates synthesis Ph4P[Cp3La-ESiMe3] (E = S, Se, and Te) via fluoride-induced demethylation of dimethylcarbonate to Ph4P[OCO2Me] key intermediate.

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.

Rylene- and diaza-rylene-derived cobalt clusters for solid-state pyrolysis towards undoped and N-doped carbon nanoparticles.

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.

Tetrasubstituted Peropyrenes Formed by Reductive Aromatization: Synthesis, Functionalization and Characterization.

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.

Highly Selective Ortho-Directed Dicarboxylation of Cyclopentadiene by Methylcarbonates and CO2 or COS - First Insight into Co-ordination Chemistry of New Ambident Ligands.

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 H 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+ ).

Access to Functionalized Pyrenes, Peropyrenes, Terropyrenes, and Quarterropyrenes via Reductive Aromatization.

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 80 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.

Chalcogenido-Dimethylgallates and -Indates DMPyr2 [Me2 M(µ2 -E)]2 (M=Ga, In; E=S, Se): Building Blocks for Higher and Lower Order Chalcogenidoindates.

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.

A Series of Homoleptic Linear Trimethylsilylchalcogenido Cuprates, Argentates and Aurates Cat[Me3SiE-M-ESiMe3] (M = Cu, Ag, Au; E = S, Se).

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.

Kekulene: On-Surface Synthesis, Orbital Structure, and Aromatic Stabilization.

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.

Homoleptic trimethylsilylchalcogenolato zincates [Zn(ESiMe3)3]- and stannanides [Sn(ESiMe3)3]- (E = S, Se): precursors in solution-based low-temperature binary metal chalcogenide and Cu2ZnSnS4 (CZTS) synthesis.

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.

On-Surface Synthesis and Characterization of a Cycloarene: C108 Graphene Ring.

The synthesis of cycloarenes in solution is challenging because of their low solubility and the often hindered cyclodehydrogenation reaction of their nonplanar precursors. Using an alternative on-surface synthesis protocol, we achieved an unprecedented double-stranded hexagonal cycloarene containing 108 sp2 carbon atoms. Its synthesis is based on hierarchical Ullmann coupling and cyclodehydrogenation of a specially designed precursor on a Au(111) surface. The structure and other properties of the cycloarene are investigated by scanning tunneling microscopy/spectroscopy, atomic force microscopy, and density functional theory calculations.

Homoleptic Group 13 Trimethylsilylchalcogenolato Metalates [M(ESiMe3)4]- (M = Ga, In; E = S, Se): Metastable Precursors for Low-Temperature Syntheses of Chalcogenide-Based Materials.

We communicate the synthesis and full characterization of so far unknown tetrakis(trimethylsilylsulfido) and -(trimethylsilylselenido) gallates and indates in form of their organic salts Cat+[M(ESiMe3)4]- (M = Ga, In; E = S, Se; Cat = dimethylpyrrolidinium (DMPyr+), Ph4P+, (dppe)2Cu+, (dmpe)2Cu+). These thermally metastable silylchalcogenolatometalates can act as modular precursors for an ionic-liquid- or organic-solution-based low-temperature synthesis of multinary metal chalcogenide materials such as the CIGS species Cu(InxGa1-x)(SySe1-y)2.

Systematic study on anion-cation interactions via doubly ionic H-bonds in 1,3-dimethylimidazolium salts comprising chalcogenolate anions MMIm [ER] (E = S, Se; R = H, tBu, SiMe3).

We present convenient syntheses of so far inaccessible, crystalline and highly pure 1,3-dialkylimidazolium salts with extremely nucleophilic thiolate and selenolate anions [ER]- (R = H, tBu, SiMe3). While non existent for E = O, the title compounds exist as slightly less basic E = S and Se homologues. The anion cation H-bond interactions in the crystalline state have been studied systematically in six related ionic compounds of varying anion basicity and steric bulk, namely MMIm [SH] (1), MMIm [StBu] (2), and MMIm [SSiMe3] (3), as well as MMIm [SeH] (4), MMIm [SetBu] (5) and MMIm [SeSiMe3] (6). The chalcogenolate title compounds 3, 5, and 6 are prepared by the newly introduced method of desilylation of Me3Si-ER (E = S, Se) by the super-nucleophile MMIm [StBu] (2), which is easily accessible via deprotonation of HStBu with in situ generated NHC 1,3-dimethylimidazolidin-2-ylidene. Focus is put on the role of the most acidic imidazolium proton C2-H as structural director and as 1H NMR shift indicator. These salts show an unusually high volatility and tendency to sublime under vacuum without irreversible decay.

Ferrocenyl-sulfonium ionic liquids - synthesis, characterization and electrochemistry.

New ferrocenylsulfonium cation based ionic liquids were prepared by direct alkylation of the corresponding ferrocenyl-based thioethers with N-alkylbis(trifluoromethanesulfonyl)imides (R'TFSI). This convenient direct access to organometallic sulfonium bis(trifluoromethanesulfonyl)imide (TFSI) salts without the need for ion exchange was chosen in order to obtain highly pure and reversibly redox active room temperature ILs in many cases. In other cases the anion cation interaction in the solid state was studied by XRD analyses. Moreover a diferrocenylmethylsulfonium tetrafluoroborate with two redox active centers was synthesized. The redox chemistry of these sulfonium salts was investigated via cyclic voltammetry. Furthermore, UV-Vis spectra and thermoanalytical data are discussed. The electron-withdrawing sulfonium group is directly bonded to the ferrocenyl unit, therefore this cationic group influences the potential of these ionic liquids in a more pronounced way than being anchored to the ferrocenyl unit via an organic spacer. With their low absorbance in the visible light and reversible, tunable redox potential, these room temperature ILs open perspectives as redox mediators in dye sensitized solar cells (DSSCs), as redox electrolytes in supercapacitors or as overcharge protection additives in batteries.

Synthesis of Adjacent Quaternary Stereocenters by Catalytic Asymmetric Allylboration.

Allylboration of ketones with γ-disubstituted allylboronic acids is performed in the presence of chiral BINOL derivatives. The reaction is suitable for single-step creation of adjacent quaternary stereocenters with high selectivity. We show that, with an appropriate choice of the chiral catalyst and the stereoisomeric prenyl substrate, full control of the stereo- and enantioselectivity is possible in the reaction.