Nickel catalysts play a central role in many synthetic transformations ranging from carbon-carbon cross coupling reactions to the reduction of electron-rich carbon bonds with Raney nickel.  These nickel catalysts span a range of oxidation states: Nickel (0), nickel (II), nickel (III) and nickel (IV). The Ni catalysts available for immediate purchase are aluminum nickel (Al Ni) alloys, ammonium nickel hydrates, Ni COD, Ni halides (chlorides, bromides, fluorides and iodides), Ni cyclopentadienyls, nickel metal, nickel acac。