A Bulky m‐Terphenyl Cyclopentadienyl Ligand and Its Alkali‐Metal Complexes

The synthesis of the new m ‐terphenyl‐substituted cyclopentadienyl ligand precursor 1‐cyclopentadiene‐2,6‐bis(2,4,6‐trimethylphenyl)benzene (Ter^MesCpH) is described. The synthesis proceeds through the reaction of Ter^MesLi with cobaltocenium iodide, followed by oxidation of the intermediate cobalt(I) species to give the corresponding cyclopentadiene as a mixture of isomers. The preparation and spectroscopic properties of the alkali‐metal salts (Li–Cs) is described, as well as structural information obtained by X‐ray diffraction studies for the lithium, potassium, and cesium analogues. Crystallographic data demonstrate the ability of these new ligands to act as monoanionic chelates by forming metal complexes with Cp–M–Ar bonding environments.     

Noble‐Metal‐Free Janus‐like Structures by Cation Exchange for Z‐Scheme Photocatalytic Water Splitting under Broadband Light Irradiation

Z‐scheme water splitting is a promising approach based on high‐performance photocatalysis by harvesting broadband solar energy. Its efficiency depends on the well‐defined interfaces between two semiconductors for the charge kinetics and their exposed surfaces for chemical reactions. Herein, we report a facile cation‐exchange approach to obtain compounds with both properties without the need for noble metals by forming Janus‐like structures consisting of γ‐MnS and Cu₇S₄ with high‐quality interfaces. The Janus‐like γ‐MnS/Cu₇S₄ structures displayed dramatically enhanced photocatalytic hydrogen production rates of up to 718 μmol g⁻¹ h⁻¹ under full‐spectrum irradiation. Upon further integration with an MnO_x oxygen‐evolution cocatalyst, overall water splitting was accomplished with the Janus structures. This work provides insight into the surface and interface design of hybrid photocatalysts, and offers a noble‐metal‐free approach to broadband photocatalytic hydrogen production.     

Phosphine‐Initiated Cation Exchange for Precisely Tailoring Composition and Properties of Semiconductor Nanostructures: Old Concept,New Applications

Phosphine‐initiated cation exchange is a well‐known inorganic chemistry reaction. In this work, different phosphines have been used to modulate the thermodynamic and kinetic parameters of the cation exchange reaction to synthesize complex semiconductor nanostructures. Besides preserving the original shape and size, phosphine‐initiated cation exchange reactions show potential to precisely tune the crystallinity and composition of metal/semiconductor core–shell and doped nanocrystals. Furthermore, systematic studies on different phosphines and on the elementary reaction mechanisms have been performed.     

Alkali‐Metal‐Mediated Magnesiations of an N‐Heterocyclic Carbene: Normal,Abnormal, and “Paranormal” Reactivity in a Single Tritopic Molecule

Herein the sodium alkylmagnesium amide [Na₄Mg₂(TMP)₆(nBu)₂] (TMP=2,2,6,6‐tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N‐heterocyclic carbene (NHC) IPr [1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]. Remarkably, magnesiation of IPr occurs at the para‐position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr²⁻. Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr⁻ monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali‐metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC.     

Structural and Magnetic Diversity in Alkali‐Metal Manganate Chemistry: Evaluating Donor and Alkali‐Metal Effects in Co‐complexation Processes

By exploring co‐complexation reactions between the manganese alkyl Mn(CH₂SiMe₃)₂ and the heavier alkali‐metal alkyls M(CH₂SiMe₃) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4‐dioxane, and 1,4‐diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali‐metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X‐ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA)₂MMn(CH₂SiMe₃)₃] (M=Na, 3 ; M=K, 4 ) to dimers [{KMn(CH₂SiMe₃)₃?C₆H₆}₂] ( 2 ) and [{NaMn(CH₂SiMe₃)₃}₂(dioxane)₇] ( 5 ); and to more complex supramolecular networks [{NaMn(CH₂SiMe₃)₃}_∞] ( 1 ) and [{Na₂Mn₂(CH₂SiMe₃)₆(DABCO)₂}_∞] ( 7 )). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4‐dioxane, as 1 produces coordination adduct 5 , while 2 forms heteroleptic [{(dioxane)₆K₂Mn₂(CH₂SiMe₃)₄(O(CH₂)₂OCH=CH₂)₂}_∞] ( 6 ) containing two alkoxide–vinyl anions resulting from α‐metalation and ring opening of dioxane. Compounds 6 and 7 , containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways.     

Four‐State Molecular Shuttling of [2]Rotaxanes in Response to Acid/Base and Alkali‐Metal Cation Stimuli

In this study, we synthesized [2]rotaxanes possessing three recognition sites—a dialkylammonium, an alkylarylamine, and a tetra(ethylene glycol) stations—in their dumbbell‐like axle component and dibenzo[24]crown‐8 (DB24C8) as their macrocyclic component. These [2]rotaxanes behaved as four‐state molecular shuttles: i) under acidic conditions, the DB24C8 unit encircled both the dialkylammonium and alkylarylammonium stations; ii) under neutral conditions, the dialkylammonium unit was the predominant station for the DB24C8 component; iii) under basic conditions, when both ammonium centers were deprotonated, the alkylarylamine unit became a suitable station for the DB24C8 component; and iv) under basic conditions in the presence of an alkali‐metal cation, the tetra(ethylene glycol) unit recognized the DB24C8 component through cooperative binding of the alkali‐metal ion. In addition, we observed that the [2]rotaxanes exhibited selective recognition for metal cations. These shuttling motions of the macrocyclic component proceeded reversibly.     

Solid‐Phase Synthesis of 2‐Alkenamides from Polystyrene‐Supported α‐Selenocarboxylic Acids

The polystyrene‐supported α‐selenoacetic acid and α‐selenopropionic acid were prepared and used for the synthesis of 2‐alkenamides from primary and secondary amines in good yields and high purities.     

Anisotropic Metal Deposition on TiO2 Particles by Electric‐Field‐Induced Charge Separation

Deposition of metals on TiO₂ semiconductor particles (M‐TiO₂) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site‐selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M‐TiO₂ particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high‐performance designer catalyst particles, for example for photosplitting of water.