A gold(I)
complex bearing an imidazo[1,5-a]pyridin-3-ylidene
ligand with a 2,2′-bipyridine moiety at the C5 position was
prepared as a template for constructing heterobimetallic cooperative
catalysts. In situ generated gold–zinc bimetallic
systems enabled intermolecular nucleophilic anti-addition
of O-nucleophiles such as carboxylic acids and phenols
toward nonactivated internal alkynes. DFT calculations supported the
proposed cooperative action of the cationic gold atom and the zinc
salt site for activating the alkyne and the carboxylic acid, respectively.
Nickel-catalyzed reductive homo-coupling of aryl ethers has been achieved with Mg(anthracene)(thf)3 as a readily available low-cost reductant. DFT calculations provided a rationale for the specific efficiency of the diorganomagnesium-type two-electron reducing agent. The calculations showed that the dianionic anthracene-9,10-diyl ligand reduces the two aryl ether substrates resulting in the homo-coupling reaction through supplying the electrons to the Ni-Mg bimetallic system to form organomagnesium nickel(0)-ate complexes, which cause two sequential C–O bond cleavage reactions. The calculations also showed cooperative actions of Lewis-acidic magnesium atoms and electron-rich nickel atoms in the C–O cleavage reactions.
Numerous
remarkable reactions based on electrochemical carboxylations
using CO2 have recently attracted considerable attention.
In contrast to more recent examples, the electrochemical carboxylation
of naphthalene had already been established in 1959, whereby a dearomative
dicarboxylation selectively produces 1,4-dicarboxylated 1,4-dihydronaphthalene
derivatives. Here, we report that the use of electron-deficient naphthalene
derivatives in the presence of a redox mediator such as p-terphenyl and H2O under CO2 bubbling affords trans-1,2-disubstituted 1,2-dihydronaphthalene derivatives.
Silver complexes with 5‐(4‐(tert‐butyl)‐1H‐imidazol‐1‐yl)‐imidazo[1,5‐a]pyridin‐3‐ylidene ligands were synthesized as metal‐imidazole acid‐base cooperative catalysts. Single crystal XRD analysis revealed that the silver atom was located in the vicinity of the imidazole ring and that cationic silver complexes formed dimers through coordination between the silver metal and the imidazole pendant. These cationic silver complexes served as catalysts for cyclization of alkyne‐tethered carboxylic acids. NMR experiments indicated that the dimeric cationic silver complex dissociated to a monomer upon protonation of the imidazole moiety, resulting in coordination of an acetonitrile to the silver atom. DFT calculations supported the acid‐base cooperative action of the silver‐imidazole for the efficient alkyne‐carboxylic acid cyclization.
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