Solid-State Photocyclodimerization of 1-Thiocoumarin (= 2H-1-Benzothiopyran-2-one)

Irradiation (λ > 390 nm) of 2H-1-benzothiopyran-2-one ( 1 ) in the solid state affords selectively 6aα,6bα,12bα,12cα -tetrahydrocyclobuta[1,2-c:4,3-c′]bis[1]benzothiopyran -6,7-dione ( 2 ), the head-to-head (HH) cis-cisoid-cis-dimer, while irradiation of 1 in the solid state using shorter wavelengths (λ > 340 nm) affords a mixture of all four cis-fused tricyclic dimers 2 – 5 . These results represent a novel wavelength effect in solid-state photochemistry.     

Green chemistry and sustainability metrics in the pharmaceutical manufacturing sector

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Non-aqueous electrolytes for isotachophoresis of weak bases and its application to the comprehensive preconcentration of the 20 proteinogenic amino acids in column-coupling ITP/CE–MS

Isotachophoresis (ITP) has long been used alone but also as a preconcentration technique for capillary electrophoresis (CE). Unfortunately, up to now, its application is restricted to relatively strong acids and bases as either the degree of (de)protonation is too low or the water dissociation is too high, evoking zone electrophoresis. With the comprehensive ITP analysis of all 20 proteinogenic amino acids as model analytes, we, here, show that non–aqueous ITP using dimethylsulfoxide as a solvent solves this ITP shortcoming. Dimethylsulfoxide changes the pH regime of analytes and electrolytes but, more importantly, strongly reduces the proton mobility by prohibiting hydrogen bonds and thus, the so-called Zundel–Eigen–Zundel electrical conduction mechanism of flipping hydrogen bonds. The effects are demonstrated in an electrolyte system with taurine or H⁺ as terminator, and imidazole as leader together with strong acids such as oxalic and even trifluoroacetic acid as counterions, both impossible to use in aqueous solution. Mass spectrometric as well as capacitively coupled contactless conductivity detection (C⁴D) are used to follow the ITP processes. To demonstrate the preconcentration capabilities of ITP in a two-dimensional set-up, we, here, also demonstrate that our non-aqueous ITP method can be combined with capillary electrophoresis–mass spectrometry in a column-coupling system using a hybrid approach of capillaries coupled to a microfluidic interface. For this, C⁴D was optimized for on-chip detection with the electrodes aligned on top of a thin glass lid of the microfluidic chip.     

Copper(I)‐Catalyzed Regioselective Addition of Nucleophilic Silicon Across Terminal and Internal Carbon–Carbon Triple Bonds

The copper(I) alkoxide‐catalyzed release of a silicon‐based cuprate reagent from a silicon–boron pronucleophile is applied to the addition across carbon–carbon triple bonds. Commercially available CuBr?Me₂S was found to be a general precatalyst that secures high regiocontrol for both aryl‐ and alkyl‐substituted terminal as well as internal alkynes. The solvent greatly influences the regioisomeric ratio, favoring the linear regioisomer with terminal acceptors. This facile protocol even allows for the transformation of internal acceptors with remarkable levels of regio‐ and diastereocontrol.     

A Combined Spectroscopic and Theoretical Study on a Ruthenium Complex Featuring a π-Extended dppz Ligand for Light-Driven Accumulation of Multiple Reducing Equivalents

The design of photoactive systems capable of storing and relaying multiple electrons is highly demanded in the field of artificial photosynthesis, where transformations of interest rely on multielectronic redox processes. The photophysical properties of the ruthenium photosensitizer [(bpy)₂Ru( oxim-dppqp )]²⁺ ( Ru ), storing two electrons coupled to two protons on the π-extended oxim-dppqp ligand under light-driven conditions, are investigated by means of excitation wavelength-dependent resonance Raman and transient absorption spectroscopies, in combination with time-dependent density functional theory; the results are discussed in comparison to the parent [(bpy)₂Ru(dppz)]²⁺ and [(bpy)₂Ru( oxo-dppqp )]²⁺ complexes. In addition, this study provides in-depth insights on the impact of protonation or of accumulation of multiple reducing equivalents on the reactive excited states.     

Pyrimidoquinazolinophenanthroline Opens Next Chapter in Design of Bridging Ligands for Artificial Photosynthesis**

The synthesis and detailed characterization of a new Ru polypyridine complex containing a heteroditopic bridging ligand with previously unexplored metal-metal distances is presented. Due to the twisted geometry of the novel ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)₃]²⁺ (bpy=2,2'-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier orbitals, apparent by, for example, luminescence quenching. Thus, the new bridging ligand motif offers electronic properties, which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru−Rh complex, visible light-driven reduction of NAD⁺ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.     

Photocatalytic Reduction of Nicotinamide Co-factor by Perylene Sensitized RhIII Complexes**

The ambitious goal of artificial photosynthesis is to develop active systems that mimic nature and use light to split water into hydrogen and oxygen. Intramolecular design concepts are particularly promising. Herein, we firstly present an intramolecular photocatalyst integrating a perylene-based light-harvesting moiety and a catalytic rhodium center ( Rh^IIIphenPer ). The excited-state dynamics were investigated by means of steady-state and time-resolved absorption and emission spectroscopy. The studies reveal that photoexcitation of Rh^IIIphenPer yields the formation of a charge-separated intermediate, namely Rh^IIphenPer ⋅ ⁺ , that results in a catalytically active species in the presence of protons.