Werner Salt as Nickel and Ammonia Source for Photochemical Synthesis of Primary Aryl Amines.

Cheap, stable and easy-to-handle Werner ammine salts have been known for more than a century; but they have been rarely used in organic synthesis. Herein, we report that the Werner hexammine complex [Ni(NH3 )6 ]Cl2 can be used as both a nitrogen and a catalytic nickel source that allow for the efficient amination of aryl chlorides in the presence of a catalytic amount of bipyridine ligand under the irradiation of 390-395 nm light without the need of any additional catalysts. More than 80 aryl chlorides, including more than 20 drug molecules, were aminated, demonstrating the practicality and generality of this method in synthetic chemistry. A slow NH3 release mechanism is in operation, obviating the problem of catalyst poisoning. Still interestingly, we show that the Werner salt can be easily recovered and reused, solving the problem of difficult recovery of transition metal nickel catalysts. The protocol thus provides an efficient new strategy for the synthesis of primary aryl amines.

Ni-Catalyzed Photochemical C-N Coupling of Amides with (Hetero)aryl Chlorides.

This paper reports a photochemical C-N coupling of abundant, but less reactive aryl chlorides, with structurally diverse primary and secondary amides by Ni-mediated without an external photocatalyst. Under the irradiation of light (390-395 nm) with a soluble organic amine as the base, the reaction allows for the successful transformation of (hetero)aryl chlorides to a wide range of N-aryl amides. More than 60 examples are shown, demonstrating the feasibility and applicability of this protocol in organic synthesis. Mechanic studies indicate that this amidation proceeds via a Ni(I)-Ni(III) catalytic cycle.

General Method for the Amination of Aryl Halides with Primary and Secondary Alkyl Amines via Nickel Photocatalysis.

The Buchwald-Hartwig C-N coupling reaction has been ranked as one of the 20 most frequently used reactions in medicinal chemistry. Owing to its much lower cost and higher reactivity toward less reactive aryl chlorides than palladium, the C-N coupling reaction catalyzed by Ni-based catalysts has received a great deal of attention. However, there appear to be no universal, practical Ni catalytic systems so far that could enable the coupling of electron-rich and electron-poor aryl halides with both primary and secondary alkyl amines. In this study, it is reported that a Ni(II)-bipyridine complex catalyzes efficient C-N coupling of aryl chlorides and bromides with various primary and secondary alkyl amines under direct excitation with light. Intramolecular C-N coupling is also demonstrated. The feasibility and applicability of the protocol in organic synthesis is attested by more than 200 examples.