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Published on: May 20, 2019
Cooperative Sulfur Transformations at a Dinickel Site: A Metal Bridging Sulfur Radical and Its H-Atom Abstraction
Valeria Tagliavini1, Peng-Cheng Duan1, Sayanti Chatterjee2,3
1Institute of Inorganic Chemistry, University of Göttingen, Tammannstr. 4, D-37077 Göttingen, Germany.
Abstract:
Starting from the dinickel(II) dihydride complex [ML(Ni-H)2] (1), where L3- is a bis(tridentate) pyrazolate-bridged bis(β-diketiminato) ligand and M+ is Na+ or K+, a series of complexes [KLNi(S2)] (2), [MLNi2S] (3), [LNi2(SMe)] (4), and [LNi2(SH)] (5) has been prepared. The μ-sulfido complexes 3 can be reversibly oxidized at E1/2 = -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 pKa 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.
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