The use of palladium has dominated the catalyst market because of its success in many organic reactions, particularly cross-couplings. The only limitations were high cost and limited abundance of the metal in nature. Now with the greater focus on cost, both in research and industry, as well as maintaining our natural resources for a healthy environment, chemists are exploring alternative low cost, naturally abundant elements for metal catalysed reactions. Nickel has stood out as the inexpensive, abundantly available and surprisingly versatile alternative to Palladium. This has led to a recent expansion in the use of nickel catalysts within the field of carbon-carbon and carbon-heteroatom cross-coupling reactions. Unfortunately, many of these Ni precursors are air/moisture sensitive or rely upon the inconvenient in-situ reduction of Ni(II) species.
A series of air-stable Josiphos nickel catalysts have recently been developed. These catalysts can easily undergo reductive elimination to facilitate the catalytically active Ni(0) species. The Josiphos nickel catalysts have been used in reactions with substituted aryl, heteroaryl halides and tosylates with ammonia to produce diverse aryl and heteroaryl amines1. A number of cross-coupling publications have described the successful use of the Josiphos family of nickel catalysts, especially with ammonia. The versatility and potential scalability of this series of nickel catalysts was demonstrated by monoarylation experiments using commercially available ammonia gas, ammonium salts or ammonia stock solutions2,3. This system can also catalyze the coupling of aryl chlorides with gaseous amines in the form of their hydrochloride salts3.
Listed below are the molecular structures of the commercially available Josiphos nickel catalysts.
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