Mechanistic study of the bismuth mediated fluorination of arylboronic esters and further rational design.

Density functional theory (DFT) calculations have been performed to gain insight into the catalytic mechanism of the bismuth redox catalyzed fluorination of arylboronic esters to deliver the widely used arylfluoride compounds (Science 2020, 367, 313-317). The study reveals that the whole catalysis can be characterized via three stages: (i) transmetallation generates the Bi(iii) intermediate 5, capitalizing on the use of KF as an activator. (ii) 5 then reacts with the electrophilic fluorination reagent 1-fluoro-2,6-dichloropyridinium 4via oxidative addition to give the Bi(v) intermediate IM4A. (iii) IM4A undergoes a reductive elimination step to yield aryl fluoride compounds and regenerates the bismuth catalyst for the next catalytic cycle. Each stage is kinetically and thermodynamically feasible. The transmetallation step, with a barrier of 25.4 kcal mol-1, is predicted to be the rate-determining step (RDS) during the whole catalytic cycle. Furthermore, based on a mechanistic study, new catalysts with the framework of tethered bis-anionic ligands were designed, which will help to improve current catalytic systems and develop new bismuth mediated fluorination of arylboronic esters.

A Bis-(carbone) Pincer Ligand and Its Coordinative Behavior toward Multi-Metallic Configurations.

Carbones are divalent carbon(0) species that contain two lone pairs of electrons. Herein, we have prepared the first known stable and isolable free bis-(carbone) pincer framework with a well-defined solid-state structure. This bis-(carbone) ligand is an effective scaffold for forming monometallic (Ni and Pd) and trinuclear heterometallic complexes with Au-Pd-Au, Au-Ni-Au, and Cu-Ni-Cu configurations. Sophisticated quantum-theoretical analyses found that the metal-metal interactions are too weak to play a significant role in upholding these multi-metallic configurations; rather, the four lone pairs of electrons within the bis-(carbone) framework are the main contributors to the stability of the complexes.

Synthesis, characterization, and photoluminescence properties of three two-dimensional lanthanide-containing Dawson-type polyoxometalates.

Three [α2-P2W17O61]10--based lanthanide-containing polyoxometalates (LCPs) [N(CH3)4]3H8{Ln(H2O)7[Ln(H2O)3Ln(H2O)4(α2-P2W17O61)2]}·48H2O [Ln = La3+ (1), Ce3+ (2), and Pr3+ (3)] were successfully obtained by the reaction of a trivacant Dawson-type precursor [P2W15O56]12- and lanthanide ions under hydrothermal conditions. The compounds 1-3 were fully characterized by single-crystal X-ray diffraction and a series of analytical methods, including elemental analyses, powder X-ray diffraction (PXRD), IR spectroscopy, Raman spectroscopy, UV/vis diffuse reflectance spectroscopy, and thermogravimetric analysis (TGA). Single-crystal X-ray diffraction analyses indicated that 1-3 were isostructural and exhibited a 2D network architecture through the alternative connection of [α2-P2W17O61]10- and lanthanide ions. The photoluminescence properties of 1-3 were investigated at room temperature, and 3 displayed the characteristic emissions of a Pr3+ emitting center, indicating that POMs can transfer energy and sensitize Pr3+ emissions. The reason for the weak emission intensity of Pr3+ emitting ions was because the radiationless losses via a charge-transfer Pr → W state negatively affected the emission of the Pr3+ ions in LCPs.

Well-tuned white-light-emitting behaviours in multicenter-Ln polyoxometalate derivatives: A photoluminescence property and energy transfer pathway study.

White light-emitting diodes (WLEDs) are of scientific significance in terms of their wide applications, and few uminescent materials based on white-light-emitting polyoxometalate (POM) derivatives have been reported till now. Herein, a series of organic chromophores modified POM derivatives [N(CH3)4]3K2Ln(C7H5O2)(H2O)2(α-PW11O39)]·11H2O (Ln3+ = Eu3+ (1), Tb3+ (2), Tm3+ (3), Lu3+ (4)) and multicenter-Ln analogues [N(CH3)4]3K2EuxTbyTm1-x-y(C7H5O2)(H2O)2(α-PW11O39)·11H2O (5-11) were synthesized successfully and were characterized by various physico-chemical analysis. The investigations indicate the white-light-emitting behavior can be well tuned by adjusting the molar ratio of Eu3+/Tb3+/Tm3+ = 0.06:0.10:0.84 in 9. The energy transfer process from organic benzoic and POM ligands to Eu3+, Tb3+ and Tm3+ emitting centers were detected through time-resolved emission spectroscopy (TRES) and the comparison of excitation of single-, double-, treble-Ln3+ mixed, indicating the energy can transfer from the photoexcitation O → M LMCT state of POM components and π → π* transition of organic ligand to sensitize the emissions of Ln3+ ions via intramolecular energy transition mechanism. The energy transfer between Eu3+ and Tb3+, Tm3+ and Eu3+, Tm3+ and Tb3+ ions also have been recorded and carefully studied by TRES and variations of Tm3+ luminescence lifetime in this context, and the results show a low-effectively process of energy transfer between Tm3+/Eu3+, Tm3+/Tb3+ ions and a relatively good energy transfer efficiency between Eu3+/Tb3+ ions.

Elucidating white light emissions in Tm3+/Dy3+ codoped polyoxometalates: a color tuning and energy transfer mechanism study.

The double-tartaric bridging Tm-substituted POM derivative [N(CH3)4]6K3H7[Tm(C4H2O6)(α-PW11O39)]2·27H2O (1) was successfully synthesized and well characterized by various physico-chemical analyses. Furthermore, the mixed Dy3+/Tm3+ ion-based POM derivatives [N(CH3)4]6K3H7[DyxTm1-x(C4H2O6)(α-PW11O39)]2·27H2O (3-8) were first synthesized and confirmed by PXRD and IR spectra, indicating compounds 3-8 are isomorphic with 1. The detailed analyses of Ln-O-W bond angle and coordinated aqua ligands around emitting Ln3+ ions have revealed that the mentioned negative factors do not effectively affect the luminescence of emitting Ln3+ ions in 1-8. Investigations of PL emissions reveal that 3-8 can display color-tunable PL properties, emitting color from blue to white to yellow. The study of time-resolved emission spectroscopy of 6 indicates the energy can transfer from the LMCT excited state of POM fragments to Tm3+ and/or Dy3+ ions. Furthermore, the decreased luminescent lifetime of Tm3+ ions in 3-8 reasonably verifies the energy transfer from Tm3+ to Dy3+ ions to efficiently facilitate emissions of the Dy3+ centre.