Copper-Catalyzed Oxidative Cross-Coupling of Electron-Deficient Polyfluorophenylboronate Esters with Terminal Alkynes

We report herein a mild procedure for the copper-catalyzed oxidative cross-coupling of electron-deficient polyfluorophenylboronate esters with terminal alkynes. This method displays good functional group tolerance and broad substrate scope, generating cross-coupled alkynyl(fluoro)arene products in moderate to excellent yields. Thus, it represents a simple alternative to the conventional Sonogashira reaction.     

Tetracationic Bis-Triarylborane 1,3-Butadiyne as a Combined Fluorimetric and Raman Probe for Simultaneous and Selective Sensing of Various DNA,RNA, and Proteins

A bis-triarylborane tetracation (4-Ar₂B-3,5-Me₂C₆H₂)-C≡C−C≡C-(3,5-Me₂C₆H₂-4-BAr₂ [Ar=(2,6-Me₂-4-NMe₃-C₆H₂)⁺] ( 2⁴⁺ ) shows distinctly different behaviour in its fluorimetric response than that of our recently published bis-triarylborane 5-(4-Ar₂B-3,5-Me₂C₆H₂)-2,2′-(C₄H₂S)₂–5′-(3,5-Me₂C₆H₂-4-BAr₂) ( 3⁴⁺ ). Single-crystal X-ray diffraction data on the neutral bis-triarylborane precursor 2 N confirm its rod-like dumbbell structure, which is shown to be important for DNA/RNA targeting and also for BSA protein binding. Fluorimetric titrations with DNA/RNA/BSA revealed the very strong affinity of 2⁴⁺ and indicated the importance of the properties of the linker connecting the two triarylboranes. Using the butadiyne rather than a bithiophene linker resulted in an opposite emission effect (quenching vs. enhancement), and 2⁴⁺ bound to BSA 100 times stronger than 3⁴⁺ . Moreover, 2⁴⁺ interacted strongly with ss-RNA, and circular dichroism (CD) results suggest ss-RNA chain-wrapping around the rod-like bis-triarylborane dumbbell structure like a thread around a spindle, a very unusual mode of binding of ss-RNA with small molecules. Furthermore, 2⁴⁺ yielded strong Raman/SERS signals, allowing DNA or protein detection at ca. 10 nm concentrations. The above observations, combined with low cytotoxicity, efficient human cell uptake and organelle-selective accumulation make such compounds intriguing novel lead structures for bio-oriented, dual fluorescence/Raman-based applications.     

Highly Stable,Readily Reducible,Fluorescent, Trifluoromethylated 9-Borafluorenes

Three different perfluoroalkylated borafluorenes ( ^F Bf ) were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo-aryl moieties. They differ with regard to the para substituents on their exo-aryl moieties, being a proton ( ^F Xyl^FBf , ^FXyl: 2,6-bis(trifluoromethyl)phenyl), a trifluoromethyl group ( ^F Mes^FBf , ^FMes: 2,4,6-tris(trifluoromethyl)phenyl) or a dimethylamino group ( p -NMe₂-^FXyl^FBf , p-NMe₂-^FXyl: 4-(dimethylamino)-2,6-bis(trifluoromethyl)phenyl), respectively. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron-deficient derivative ^F Mes^FBf was also chemically reduced and its radical anion isolated and characterized. Furthermore, all compounds exhibit very long fluorescent lifetimes of about 250 ns up to 1.6 μs; however, the underlying mechanisms responsible for this differ. The donor-substituted derivative p -NMe₂-^FXyl^FBf exhibits thermally activated delayed fluorescence (TADF) from a charge-transfer (CT) state, whereas the ^F Mes^FBf and ^F Xyl^FBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition-dipole moments.