We report a study of Zn(2+) by Cd(2+) cation exchange (CE) in colloidal ZnSe nanocrystals (NCs). Our results reveal that CE in ZnSe NCs is a thermally activated isotropic process. The CE efficiency (i.e., fraction of Cd(2+) ions originally in solution, Cdsol, that is incorporated in the ZnSe NC) increases with temperature and depends also on the Cdsol/ZnSe ratio. Interestingly, the reaction temperature can be used as a sensitive parameter to tailor both the composition and the elemental distribution profile of the product (Zn,Cd)Se NCs. At 150 °C ZnSe/CdSe core/shell hetero-NCs (HNCs) are obtained, while higher temperatures (200 and 220 °C) produce (Zn1-xCdx)Se gradient alloy NCs, with increasingly smoother gradients as the temperature increases, until homogeneous alloy NCs are obtained at T ≥ 240 °C. Remarkably, sequential heating (150 °C followed by 220 °C) leads to ZnSe/CdSe core/shell HNCs with thicker shells, rather than (Zn1-xCdx)Se gradient alloy NCs. Thermal treatment at 250 °C converts the ZnSe/CdSe core/shell HNCs into (Zn1-xCdx)Se homogeneous alloy NCs, while preserving the NC shape. A mechanism for the cation exchange in ZnSe NCs is proposed, in which fast CE takes place at the NC surface, and is followed by relatively slower thermally activated solid-state cation diffusion, which is mediated by Frenkel defects. The findings presented here demonstrate that cation exchange in colloidal ZnSe NCs provides a very sensitive tool to tailor the nature and localization regime of the electron and hole wave functions and the optoelectronic properties of colloidal ZnSe-CdSe NCs.

A computationally guided synthetic route to a free silanide derived from tris(3‐methylindol‐2‐yl)methane ([(tmim)Si]−) through nucleophilic substitution on the SiII precursor (Idipp)SiCl2 is reported (Idipp=2,3‐dihydro‐1,3‐bis(2,6‐diisopropylphenyl)‐1H‐imidazol‐2‐ylidene). This approach circumvents the need for strained tetrahedral silanes as synthetic intermediates. Computational investigations show that the electron‐donating properties of [(tmim)Si]− are close to those of PMe3. Experimentally, the [(tmim)Si]− anion is shown to undergo clean complexation to the base metal salts CuCl and FeCl2, demonstrating the potential utility as a supporting ligand.

Compounds of main‐group elements such as silicon are attractive candidates for green and inexpensive catalysts. For them to compete with state‐of‐the‐art transition‐metal complexes, new reactivity modes must be unlocked and controlled, which can be achieved through strain. Using a tris(2‐skatyl)methylphosphonium ([TSMPH3]+) scaffold, we prepared the strained cationic silane [TSMPSiH]+. In stark contrast with the generally hydridic Si−H bond character, it is acidic with an experimental pKaDMSO within 4.7–8.1, lower than in phenol, benzoic acid, and the few hydrosilanes with reported pKa values. We show that ring strain significantly contributes to this unusual acidity along with inductive and electrostatic effects. The conjugate base, TSMPSi, activates a THF molecule in the presence of CH‐acids to generate a highly fluxional alkoxysilane via trace amounts of [TSMPSiH]+ functioning as a strain‐release Lewis acid. This reaction involves a formal oxidation‐state change from SiII to SiIV, presenting intriguing similarities with transition‐metal‐mediated processes.

Mononuclear, coordinatively unsaturated rhenium(V) dioxo species of the type XReO2 (X = Me, substituted cyclopentadienyl) have long been postulated as intermediates in rhenium-catalyzed deoxydehydration, but their characterization was precluded because of aggregation into dimeric or oligomeric structures. Using the bulky 1,2,4-tri-tert-butylcyclopentadienyl (Cp(ttt)) ligand, the rhenium(V) dioxo species (Cp(ttt))ReO2 could now be observed, in equilibrium with the dimeric form [(Cp(ttt))Re(O)μ-O]2, and characterized by NMR, IR, and UV-vis spectroscopies, as well as electrospray ionization mass spectrometry. (Cp(ttt))ReO2 is shown to be the primary product of reduction of the rhenium(VII) complex (Cp(ttt))ReO3 with PPh3 and demonstrated to react with ethylene glycol significantly faster than its dimeric counterpart, supporting its role as an intermediate in rhenium-catalyzed deoxydehydration reactions.

The ability of the bis(imidazolyl)ketone ligand BMIK (bis(1-methyl-4,5-diphenylimidazolyl)ketone) to function as a redox active ligand has been investigated. The reduction of [M(BMIK)Cl] (M = Fe and Zn) complexes resulted in a pinacol-type coupling to form dinuclear complexes featuring very weak and abnormally elongated C-C bonds (1.729(5) and 1.708(3) Å for Fe and Zn, respectively). Oxidation of these complexes using ferrocenium in the presence of Cl ions regenerated the original [M(BMIK)Cl] complexes, showing the reversibility of the coupling process. This makes it a potentially interesting approach for the storage of electrons and application of the BMIK ligand as a redox active ligand.