Mild and Efficient Ni-Catalyzed Biaryl Synthesis with Polyfluoroaryl Magnesium Species: Verification of the Arrest State, Uncovering the Hidden Competitive Second Transmetalation and Ligand-Accelerated Highly Selective Monoarylation

Employing a nickel catalyst and electron-deficient polyfluoroaryl magnesium species, a highly selective monoarylation of polyfluoroarenes containing multiple identical coupling sites has been achieved for the first time, which represents a long-standing problem due to the competitive reactivity between the desired products and the starting polyfluoroarenes. Because of the negative fluorine effect, a surprisingly stable <i>cis</i> [Ni­(Ar^F4)₂(DPEPhos)] species <b>4</b> (Ar^F4 = 2,3,5,6-tetrafluorophenyl) confirmed by X-ray crystallography is isolated, which acts as catalyst arrest state as proven by a thermal decomposition test. Further retro-transmetalation experiments uncover a hidden secondary transmetalation between Ar^F4-Ni-Ph and excess Ar^F4-MgCl that competes with the desired but reluctant reductive elimination at the high-valent nickel center. Accordingly, through the cooperation of newly developed DMM-DPEPhos, and a dioxane-mediated Schlenk equilibrium with Grignard reagent, the formation of the corresponding arrest state is remarkably inhibited. An excellent coupling efficiency and an excellent monoarylation selectivity are therefore generally accomplished with a widespread electrophile scope and good functional group tolerance under mild conditions. Importantly, our novel method shows great power in the gram-scale synthesis of thienyl-2,3,5,6-tetrafluorophenyl units that represent key components in materials science

Sonogashira Couplings on the Surface of Montmorillonite-Supported Pd/Cu Nanoalloys

To explore the true identity of palladium-catalyzed Sonogashira coupling reaction, montmorillonite (MMT)-supported transition metal nanoparticles (MMT@M, M = Pd, Cu, Fe, and Ni) were prepared, characterized, and evaluated systematically. Among all MMT@M catalysts, MMT@Pd/Cu showed the highest activity, and it was successfully extended to 20 examples with 57%–97% yields. The morphology characterization of MMT@Pd/Cu revealed that the crystalline bimetallic particles were dispersed on a MMT layer as nanoalloy with diameters ranged from 10 to 11 nm. In situ IR analysis using CO as molecular probe and XPS characterization found that the surface of Pd/Cu particles consisted of both catalytic active sites of Pd(0) and Cu­(I). The experiments on the catalytic activities of MMT@M found that Pd/Cu catalyst system exhibited high activity only in nanoalloy form. Therefore, the Pd/Cu nanoalloy was identified as catalyst, on which the interatom Pd/Cu transmetalation between surfaces was proposed to be responsible for its synergistic activity

Privilege Ynone Synthesis via Palladium-Catalyzed Alkynylation of “Super-Active Esters”

A neat palladium-catalyzed alkynylation reaction was developed with “super-active ester” as the carbonyl electrophile, which provides a clean and efficient synthetic protocol for a broad array of ynone compounds under CO-, Cu-, ligand-, and base-free conditions. The superior activity of triazine ester was rationalized by the strong electron-withdrawing ability and the unique affinity of triazine on palladium. A mechanistic experiment clearly demonstrated that the N–Pd coordination of triazine plays a crucial role for the highly efficient C–O activation

Synthesis and Optical Properties of Donor–Acceptor-Type 1,3,5,9-Tetraarylpyrenes: Controlling Intramolecular Charge-Transfer Pathways by the Change of π‑Conjugation Directions for Emission Color Modulations

In dipolar organic π-conjugated molecules, variable photophysical properties can be realized through efficient excited-state intramolecular charge transfer (ICT), which essentially depends on the π-conjugation patterns. Herein, we report a controllable regioselective strategy for synthesis and optical properties of two donor–acceptor (DA)-type 1,3,5,9-tetraarylpyrenes (i.e., 1,3-A/5,9-D (<b>4b</b>) and 1,3-D/5,9-A (<b>4c</b>)) by covalently integrating two phenyl rings and two <i>p</i>-OMe/CHO-substituted phenyl units into the 2-<i>tert</i>-butylpyrene building block, in which the two phenyl rings substituted at the 1,3-positions act as acceptors for <b>4b</b> or as donors for <b>4c</b> and the two <i>p</i>-OMe or <i>p</i>-CHO-substituted phenyl moieties substituted at the K-region of 5,9-positions act as donors for <b>4b</b> or as acceptors for <b>4c</b>, respectively. Density functional theory calculations on their frontier molecular orbitals and UV–vis absorption of S₀ → S₁ transition theoretically predicted that the change of π-conjugation directions in the two DA pyrenes could be realized through a variety of substitution patterns, implying that the dissimilar ground-state and excited-state electronic structures exist in each molecule. Their single-crystal X-ray analysis reveal their highly twisted conformations that are beneficial for inhibiting the π-aggregations, which are strikingly different from the normal 1,3,5,9-tetraphenylpyrenes (<b>4a</b>) and related 1,3,6,8-tetraarylpyrenes. Indeed, experimental investigations on their optical properties demonstrated that the excited-state ICT pathways can be successfully controlled by the change of π-conjugation directions through the variety of substitution positions, resulting in the modulations of emission color from deep-blue to green in solution. Moreover, for the present DA pyrenes, highly fluorescent emissions with moderate-to-high quantum yields both in the thin film and in the doped poly­(methyl methacrylate) film were obtained, suggesting them as promising emitting materials for the fabrication of organic light-emitting diodes

Synthesis and Optical Properties of Donor–Acceptor-Type 1,3,5,9-Tetraarylpyrenes: Controlling Intramolecular Charge-Transfer Pathways by the Change of π‑Conjugation Directions for Emission Color Modulations

In dipolar organic π-conjugated molecules, variable photophysical properties can be realized through efficient excited-state intramolecular charge transfer (ICT), which essentially depends on the π-conjugation patterns. Herein, we report a controllable regioselective strategy for synthesis and optical properties of two donor–acceptor (DA)-type 1,3,5,9-tetraarylpyrenes (i.e., 1,3-A/5,9-D (<b>4b</b>) and 1,3-D/5,9-A (<b>4c</b>)) by covalently integrating two phenyl rings and two <i>p</i>-OMe/CHO-substituted phenyl units into the 2-<i>tert</i>-butylpyrene building block, in which the two phenyl rings substituted at the 1,3-positions act as acceptors for <b>4b</b> or as donors for <b>4c</b> and the two <i>p</i>-OMe or <i>p</i>-CHO-substituted phenyl moieties substituted at the K-region of 5,9-positions act as donors for <b>4b</b> or as acceptors for <b>4c</b>, respectively. Density functional theory calculations on their frontier molecular orbitals and UV–vis absorption of S₀ → S₁ transition theoretically predicted that the change of π-conjugation directions in the two DA pyrenes could be realized through a variety of substitution patterns, implying that the dissimilar ground-state and excited-state electronic structures exist in each molecule. Their single-crystal X-ray analysis reveal their highly twisted conformations that are beneficial for inhibiting the π-aggregations, which are strikingly different from the normal 1,3,5,9-tetraphenylpyrenes (<b>4a</b>) and related 1,3,6,8-tetraarylpyrenes. Indeed, experimental investigations on their optical properties demonstrated that the excited-state ICT pathways can be successfully controlled by the change of π-conjugation directions through the variety of substitution positions, resulting in the modulations of emission color from deep-blue to green in solution. Moreover, for the present DA pyrenes, highly fluorescent emissions with moderate-to-high quantum yields both in the thin film and in the doped poly­(methyl methacrylate) film were obtained, suggesting them as promising emitting materials for the fabrication of organic light-emitting diodes