Selectivity of tungsten mediated dinitrogen splitting <i>vs.</i> proton reduction

Abstract

Mo complexes are currently the most active catalysts for nitrogen fixation under ambient conditions. In comparison, tungsten platforms are scarcely examined. For active catalysts, the control of N₂ <i>vs.</i> proton reduction selectivities remains a difficult task. We here present N₂ splitting using a tungsten pincer platform, which has been proposed as the key reaction for catalytic nitrogen fixation. Starting from [WCl₃(PNP)] (PNP = N(CH₂CH₂P<i>t</i>Bu₂)₂), the activation of N₂ enabled the isolation of the dinitrogen bridged redox series [(N₂){WCl(PNP)}₂]^0/+/2+. Protonation of the neutral complex results either in the formation of a nitride [W(N)Cl(<i>H</i>PNP)]⁺ or H₂ evolution and oxidation of the W₂N₂ core, respectively, depending on the acid and reaction conditions. Examination of the nitrogen splitting <i>vs.</i> proton reduction selectivity emphasizes the role of hydrogen bonding of the conjugate base with the protonated intermediates and provides guidelines for nitrogen fixation.