Symmetry-Breaking Charge-Transfer Chromophore Interactions Supported by Carbon Nanodots

Carbon dots (CDs) and their derivatives are useful platforms for studying electron-donor/acceptor interactions and dynamics therein. Herein, we couple amorphous CDs with phthalocyanines (Pcs) that act as electron donors with a large extended π-surface and intense absorption across the visible range of the solar spectrum. Investigations of the intercomponent interactions by means of steady-state and pump-probe transient absorption spectroscopy reveal symmetry-breaking charge transfer/separation and recombination dynamics within pairs of phthalocyanines. The CDs facilitate the electronic interactions between the phthalocyanines. Thus, our findings suggest that CDs could be used to support electronic couplings in multichromophoric systems and further increase their applicability in organic electronics, photonics, and artificial photosynthesis.     

Synthesis of β-Ketoiminato Copper(II) Complexes and Their Use in Copper Deposition

The template synthesis of ethylenediamine ( 1 ) with 2-acetylcyclopentanone ( 2 ) and [Cu(OAc)₂ · H₂O] ( 5 ) produced [Cu(1-(2-cC₅H₆(O))C(Me)NCH₂)₂)] ( 6 ) in 82 % yield. Reaction of 5 with bis(benzoylacetone)diethylenetriamine ( 7 , = L H)^[1] gave [Cu(μ-OAc)( L )(H₂O)]₂ ( 8 ). The solid-state structures of 6 and 8 were determined confirming that 8 possesses intra- and intermolecular hydrogen bonds resulting in a dimer formation. The thermal behavior of 6 – 8 was studied by TG and TG-MS. Under oxygen CuO was formed, whereas under Ar Cu/Cu₂O ( 6 ) or Cu ( 8 ) was obtained. Complex 6 was used as CVD precursor for Cu and Cu-oxide deposition (substrate temp., 400–500 °C, N₂, 60 mL · min^–1; O₂, 60 mL · min^–1; pressure, 0.87–1.5 mbar). The as-obtained deposits show separated particles of different appearance at the substrate surface as evidenced by SEM. Non-volatile 8 was applied as spin-coating precursor for Cu and CuO formation [conc. 0.25 mol · L^–1; volume 0.2 mL; 3000 rpm; depos. time 2 min; heating rate 50 K · min^–1; holding time 60 min (Ar), 120 min (air) at 800 °C]. The samples on silicon consist of granulated particles (Ar) or are non-dense with a grainy topography (air). EDX and XPS measurements confirmed the formation of Cu (Ar) or CuO (O₂) with up to 13 mol-% C impurity.     

RuII and RuIII Chloronitrile Complexes: Synthesis,Reaction Chemistry,Solid State Structure,and (Spectro)Electrochemical Behavior

The synthesis of [Ti₆O₄(OiPr)₈(O₂CPh)₈] ( 3 ) and [RuCl(N≡CR)₅][RuCl₄(N≡CR)₂] ( 4a , R = Me; 4b , R = Ph), [Ru(N≡CPh)₆][RuCl₄(N≡CPh)₂] ( 5 ) and [H₃O][RuCl₄(N≡CMe)₂] ( 7a ) is discussed. Crystallization of 5 from CH₂Cl₂ gave trans-[RuCl₂(N≡CPh)₄] ( 6 ). The solid-state structures of 3 , 4a , b , 5 , 6 and 7a are reported. Complex 4b forms a 3D network, while 6 displays a 2D structure, due to π-interactions between the benzonitrile ligands. The (spectro)electrochemical behavior of 4a , b and 6 was studied at 25 and –72 °C and the results thereof are compared with [NEt₄][RuCl₄(N≡CMe)₂] ( 7b ) and [RuCl(N≡CPh)₅][PF₆] ( 8 ). The electrochemical response of the cation and the anion in 4a , b are independent from each other. [RuCl(N≡CR)₅]⁺ possesses one reversible Ru^II/Ru^III process. However, [RuCl₄(N≡CMe)₂]^– was shown to be prone to ligand exchange and disproportionation upon formation of either a Ru^IV and Ru^II species at 25 °C, while at –72 °C the rapid conversion of the electrochemically formed species is hindered. In situ IR and UV/Vis/NIR studies confirmed the respective disproportionation reaction products of the aforementioned oxidation and reduction, respectively.     

Regio- and Stereoselective Thianthrenation of Olefins To Access Versatile Alkenyl Electrophiles

Herein, we report a regioselective alkenyl electrophile synthesis from unactivated olefins that is based on a direct and regioselective C−H thianthrenation reaction. The selectivity is proposed to arise from an unusual inverse-electron-demand hetero-Diels–Alder reaction. The alkenyl sulfonium salts can serve as electrophiles in palladium- and ruthenium-catalyzed cross-coupling reactions to make alkenyl C−C, C−Cl, C−Br, and C−SCF₃ bonds with stereoretention.     

Tapered copolymers of styrene and 4-vinylbenzocyclobutene via carbanionic polymerization for crosslinkable polymer films

Well-defined polystyrene homopolymers with surface-adhesive triethoxysilyl end group were synthesized via living carbanionic polymerization, epoxide end-functionalization and subsequent hydrosilylation with triethoxysilane. Grafting-to performance of polymers with various molecular weight (M_n = 3000–14,000 g mol⁻¹) to a silicon surface was examined in dependence of reaction time, polymer concentration, solvent and number of alkoxysilyl end groups. Crosslinkable polymers for surface modification were synthesized by statistical carbanionic copolymerization of 4-vinylbenzocyclobutene (4-VBCB) and styrene, followed by epoxide end-functionalization and triethoxysilane modification (M_n = 4000–14,000 g mol⁻¹). The copolymers were characterized by ¹H-NMR, THF-SEC, and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry. In situ ¹H-NMR kinetic studies in cyclohexane-d₁₂ provided information regarding the monomer gradient in the polymer chains, with styrene being the more reactive monomer (r_s = 2.75, r_4-VBCB = 0.23). Thin polymer films on silicon wafers were prepared by grafting-to surface modification under conditions derived for the polystyrene homopolymer. The traceless, thermally induced crosslinking reaction of the benzocyclobutene units was studied by DSC in bulk as well as in 3–6 nm thick polymer films. Crosslinked films were analyzed by atomic force microscopy, ellipsometry, and nanoindentation, showing smooth polymer films with an increased modulus. © 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 181–192     

Synthesis of the 8,19-Epoxysteroid Eurysterol A

We report the first chemical synthesis of eurysterol A, a cytotoxic and antifungal marine steroidal sulfate with a unique C8−C19 oxy-bridged cholestane skeleton. After C19 hydroxylation of cholesteryl acetate, used as an inexpensive commercial starting material, the challenging oxidative functionalization of ring B was achieved by two different routes to set up a 5α-hydroxy-7-en-6-one moiety. As a key step, an intramolecular oxa-Michael addition was exploited to close the oxy-bridge (8β,19-epoxy unit). DFT calculations show this reversible transformation being exergonic by about −30 kJ mol⁻¹. Along the optimized (scalable) synthetic sequence, the target natural product was obtained in only 11 steps in 5 % overall yield. In addition, an access to (isomeric) 7β,19-epoxy steroids with a previously unknown pentacyclic ring system was discovered.     

Pentafluoroethylaluminates: A Combined Synthetic,Spectroscopic, and Structural Study

Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C₂F₅)₄]⁻ were obtained from AlCl₃ and LiC₂F₅. They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C₂F₅)₄]⁻ ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF₃) under formation of [(C₂F₅)_4−nAlF_n]⁻ (n=1–4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C₂F₅)AlF₃]⁻ ion was structurally characterized.