Recyclable Catalysts for Palladium‐Catalyzed CO Coupling Reactions, Buchwald–Hartwig Aminations, and Sonogashira Reactions

Abstract

Simply reuse: Homogeneous palladium catalysts are effective and attractive tools for advanced organic synthesis (see example). Compound 1 belongs to a new class of ligands that enable recycling of the precious‐metal catalyst directly from the reaction without any heterogenization.

Stable Mesoionic N‐Heterocyclic Olefins (mNHOs)

“…Upon mixing E with mNHO 2,t he clean and quantitative formation of NHO F and triazolium salt 1 was observed (see the Supporting Information). Furthermore,a ddition of mNHO 6 to 1 leads quantitatively and instantaneously to mNHO 2 and salt 5.Both competition experiments clearly establish the experimental basicity trend NHO (F) < mNHO (2/4) < mNHO (6).…”

“…As ar esult of the good stabilization of the positive charge by the aromatic imidazolium moiety,N HOs are highly polarized towards the exocyclicc arbon atom leading to strong s-donor properties,even exceeding those of NHCs. [4] So far NHOs and their derivatives,w hich can be considered as deoxy-Breslow type intermediates, [5] have found broad application in several fields such as transition metal and organo catalysis, [6] main-group [7] and coordination chemistry, [8] or polymer chemistry. [9,10] Besides Arduengotype N-heterocyclic carbenes, [11] abnormal N-heterocyclic carbenes (aNHC), [12] and mesoionic carbenes (MICs), 1H-1,2,3-triazol-5-ylidenes [13] have been shown to be isolable, stable and bottable carbenes with strong s-donor properties exceeding traditional NHCs.…”

Thermoregulated Aqueous Biphasic Catalysis of Sonogashira Reactions

“…[1][2][3][4][5][6] However, the main disadvantage of these homogeneous catalysts is the problem of separation and recycling the catalyst from the reaction mixture. To deal with this problem, a lot of strategies have been developed.…”

Synthesis of Phenols: Organophotoredox/Nickel Dual Catalytic Hydroxylation of Aryl Halides with Water

“…[1] Although phenols have been synthesized efficiently by different strategies, [2,3] one of the most attractive methods is the metal-catalyzed hydroxylation of aryl halides owing to the abundance of various haloarenes (Scheme 1A). [4] Thec oupling of hydroxide anions from strong inorganic bases with aryl halides under the catalysis of copper, [5] iron, [6] and palladium [7] has been successfully developed and is recognized as one of the most valuable approaches to phenols.H owever,t he use of strong inorganic bases or organic superbases [8] is problematic, especially for substrates bearing base-sensitive functionalities. To overcome this limitation, Fier and Maloney [5l, 7h] recently reported the palladium-and copper-catalyzed hydroxylation of aryl halides to access phenols with benzaldehyde oxime as the hydroxide surrogate and Cs 2 CO 3 as the base (Scheme 1A).…”