Pairwise H₂/D₂ Exchange and H₂ Substitution at a Bimetallic Dinickel(II) Complex Featuring Two Terminal Hydrides

Abstract

A compartmental ligand scaffold HL with two β-diketiminato binding sites spanned by a pyrazolate bridge gave a series of dinuclear nickel(II) dihydride complexes M[LNi(H)], M = Na (Na·2) and K (K·2), which were isolated after reacting the precursor complex [LNi(μ-Br)] (1) with MHBEt (M = Na and K). Crystallographic characterization showed the two hydride ligands to be directed into the bimetallic pocket, closely interacting with the alkali metal cation. Treatment of K·2 with dibenzo(18-crown-6) led to the separated ion pair [LNi(H)][K(DB18C6)] (2[K(DB18C6)]). Reaction of Na·2 or K·2 with D was investigated by a suite of H andH NMR experiments, revealing an unusual pairwise H/D exchange process that synchronously involves both Ni-H moieties without H/D scrambling. A mechanistic picture was provided by DFT calculations which suggested facile recombination of the two terminal hydrides within the bimetallic cleft, with a moderate enthalpic barrier of ∼62 kJ/mol, to give H and an antiferromagnetically coupled [LNi] species. This was confirmed by SQUID monitoring during H release from solid 2[K(DB18C6)]. Interaction with the Lewis acid cation (Na or K) significantly stabilizes the dihydride core. Kinetic data for the M[L(Ni-H)] → H transition derived from 2D H EXSY spectra confirmed first-order dependence of H release on M·2 concentration and a strong effect of the alkali metal cation M. Treating [LNi(D)] with phenylacetylene led to D and dinickel(II) complex 3 with a twice reduced styrene-1,2-diyl bridging unit in the bimetallic pocket. Complexes [LNi(H)] having two adjacent terminal hydrides thus represent a masked version of a highly reactive dinickel(I) core. Storing two reducing equivalents in adjacent metal hydrides that evolve H upon substrate binding is reminiscent of the proposed N binding step at the FeMo cofactor of nitrogenase, suggesting the use of the present bimetallic scaffold for reductive bioinspired activation of a range of inert small molecules.

Two-dimensional amorphous NiO as a plasmonic photocatalyst for solar H2 evolution

“…They should be associated with the bound H atoms on Ni metal atoms 26 . In detail, they are respectively terminal and internal Ni–H groups 27 , 28 . Internal Ni–H groups are much more than terminal ones, suggesting that H atoms have been doped into the NiO lattices.…”

Membrane Inlet Mass Spectrometry: A Powerful Tool for Algal Research

“…In microalgae, the electron donor to the [Fe-Fe] H 2 ase is ferredoxin (Florin et al, 2001), which can be reduced by the photosynthetic electron transport chain or by fermentative pathways (Catalanotti et al, 2013). Experimentally, H 2 production can be measured by different techniques, including modified O 2 electrodes (Wang, 1980;Godaux et al, 2015), gas chromatography (Hunt and Smith, 1961;Nagy et al, 2018), nuclear magnetic resonance spectroscopy (NMR) (Xu et al, 2016;Manz et al, 2017), or MIMS. Among these techniques, MIMS and modified O 2 electrodes allow in vivo quantitative measurement of hydrogen in a time-resolved manner.…”

Ligand Protonation Triggers H2 Release from a Dinickel Dihydride Complex to Give a Doubly “T”‐Shaped Dinickel(I) Metallodiradical

“…176.8(1) and 176.2(1)°). Comparison of the molecular structures of K[LNi I 2 ] ( 2 K ) and K[L(Ni II ‐H) 2 ] ( 1 K ) shows that the most conspicuous difference is the position of the K + cation: In 1 K the K + is located within the plane defined by the pyrazolate‐bridged dinickel dihydride core and in between the two flanking aryl rings of the 2,6‐disopropylphenyl (dipp) substituents at distances indicative of cation‐π interactions [18a] . In contrast, in 2 K the K + is located above the pyrazolate [20] and is additionally ligated by four THF molecules (the structure of 2 Na is very similar, but the Na + has only two THF ligands; Figure S9).…”