Combined Spectroscopic and Electrochemical Detection of a NiI⋅⋅⋅HN Bonding Interaction with Relevance to Electrocatalytic H2 Production. Issue 29 (3rd June 2015)

• Record Type: Journal Article
• Authors: Kochem, Amélie; O'Hagan, Molly; Wiedner, Eric S.; van Gastel, Maurice
• Is Part Of: Chemistry. Volume 21:Issue 29(2015)
• Page Start: 10338
• Page End: 10347
• Publication Date: 2015-06-03
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201500954
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The [Ni(P<sup>R</sup><sub>2</sub>N<sup>R′</sup><sub>2</sub>)<sub>2</sub>]<sup>2+</sup> family of complexes are exceptionally active catalysts for proton reduction to H<sub>2</sub>. In this manuscript, we explore the first protonation step of the proposed catalytic cycle by using a catalytically inactive Ni<sup>I</sup> complex possessing a sterically demanding variation of the ligand. Due to the paramagnetic nature of the Ni<sup>I</sup> oxidation state, the protonated Ni<sup>I</sup> intermediate has been characterized through a combination of cyclic voltammetry, electron nuclear double resonance (ENDOR) spectroscopy, and hyperfine sublevel correlation (HYSCORE) spectroscopy. Both the electrochemical and spectroscopic studies indicate that the Ni<sup>I</sup> complex is protonated at a pendant amine that is <italic>endo</italic> to Ni, which suggests the presence of an intramolecular Ni<sup>I</sup><bold>⋅⋅⋅</bold>HN bonding interaction. Using density functional theory, the hydrogen bond was found to involve three doubly‐occupied, localized molecular orbitals: the 3d<sub>xz</sub>, 3d<inline-formula><alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgj1d0p6sj3" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:09476539:media:CHEM201500954:tex2gif-inf-7" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext> </mml:mtext><mml:mrow><mml:mtext>z</mml:mtext><mml:msup><mml:mtext> </mml:mtext><mml:mrow><mml:mtext>2</mml:mtext></mml:mrow></mml:msup></mml:mrow></mml:msub></mml:math></alternatives></inline-formula>, and 3d<sub>yz</sub> orbitals of nickel. These studies provide the first direct experimental evidence for this critical catalytic intermediate, and implications for catalytic H<sub>2</sub> production are discussed.</p> </abstract>