Cooperative Sulfur Transformations at a Dinickel Site: A Metal Bridging Sulfur Radical and Its H-Atom Abstraction Thermochemistry.

ABSTRACT: Starting from the dinickel(II) dihydride complex [ML(Ni-H)₂] (1^M), where L^3- is a bis(tridentate) pyrazolate-bridged bis(β-diketiminato) ligand and M⁺ is Na⁺ or K⁺, a series of complexes [KLNi₂(S₂)] (2^K), [MLNi₂S] (3^M), [LNi₂(SMe)] (4), and [LNi₂(SH)] (5) has been prepared. The μ-sulfido complexes 3^M can be reversibly oxidized at E_1/2 = -1.17 V (in THF; vs Fc⁺/Fc) to give [LNi₂(S^•)] (6) featuring a bridging S-radical. 6 has been comprehensively characterized, including by X-ray diffraction, SQUID magnetometry, EPR and XAS/XES spectroscopies, and DFT calculations. The pK_a of the μ-hydrosulfido complex 5 in THF is 30.8 ± 0.4, which defines a S-H bond dissociation free energy (BDFE) of 75.1 ± 1.0 kcal mol^-1. 6 reacts with H atom donors such as TEMPO-H and xanthene to give 5, while 5 reacts with 2,4,6-tri(tert-butyl)phenoxy radical in a reverse H atom transfer to generate 6. These findings provide the first full characterization of a genuine M-(μ-S^•-)-M complex and provide insights into its proton-coupled electron transfer (PCET) reactivity, which is of interest in view of the prominence of M-(μ-SH/μ-S)-M units in biological systems and heterogeneous catalysis.

SUBMITTER: Tagliavini V 

PROVIDER: S-EPMC11345757 | biostudies-literature | 2024 Aug

REPOSITORIES: biostudies-literature