Complexes of Ni(i): a "rare" oxidation state of growing importance.

Nickel plays an important role in areas as diverse as metallurgy, magnetism and biology as well as in chemical applications such as the catalytic transformation of organic substrates. Despite nickel's importance, the investigation of its compounds in various oxidation states remains uneven and those in the +1 oxidation are less common than those in the neighboring 0 and +2 oxidation states. Nonetheless, in recent years, the volume of work on Ni(i) complexes has increased to the extent that they can be no longer regarded as rare. This review focuses on the syntheses and structures of Ni(i) complexes and shows that they display a range of structures, reactivity and magnetic behavior that places them in the forefront of current nickel chemistry research.