Synthesis of Low-Valent Nickel Complexes in Aqueous Media, Mechanistic Insights, and Selected Applications
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The synthesis of nickel(0) complexes usually requires the employment of strong reducing agents, including powerful hydride donors such as LiHBEt3, LiAlH4, and DIBAL-H. Herein, we have reduced the Ni(II) complex [(dippe)NiCl2] (1a) at room temperature by using KOH in aqueous media to yield the low-valent complex [Ni(dippe)2] (4a) as the main product, along with the formation of dippeO2. In order to gain some insight into the reaction mechanism, a series of intermediates were isolated and characterized at different reaction stages. As a result, both Ni(II) hydroxo-bridge (2b) and hydride (3b) complexes were identified as key intermediates. Additionally, the use of water as a hydrogen source in nickel-mediated processes was also investigated and successfully applied to the hydrodefluorination, hydrodesulfurization, and hydrogenation of selected organic substrates.
