Conformational Effects of [Ni₂(μ‐ArS)₂] Cores on Their Electrocatalytic Activity

Abstract

Two nickel complexes supported by tridentate NS2 ligands, [Ni2(κ‐N,S,S,S′‐NPh{CH2(MeC6H2R′)S}2)2] (1; R′=3,5‐(CF3)2C6H3) and [Ni2(κ‐N,S,S,S′‐NiBu{CH2C6H4S}2)2] (2), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid‐state structure of 1 reveals that the [Ni2(μ‐ArS)2] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF3COOH at −1.93 (overpotential of 1.04 V, with icat/ip≈21.8) and −1.47 V (overpotential of 580 mV, with icat/ip≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni2(μ‐ArS)2] core, which allows proximity of the two Ni⋅⋅⋅Ni centers at 2.730(8) Å; thus possibly favoring H+ reduction. In contrast, the planar [Ni2(μ‐ArS)2] core of 2 results in a Ni⋅⋅⋅Ni distance of 3.364(4) Å and is unstable in the presence of acid.

A Ditopic Phosphane‐decorated Benzenedithiol as Scaffold for Di‐ and Trinuclear Complexes of Group‐10 Metals and Gold

“…In regard of the very close energies (the triplet lies Ͻ0.1 kcal•mol -1 below the singlet state), safe assignment of the electronic ground state is currently unfeasible and requires further investigation. A reversible metal-centered reduction had previously also been established for a related mononuclear complex [Ni(dppf)(bdt)] (dppf = 1,1-bis-diphenylphosphinoferrocene, bdt = benzenedithiolate) [11] and for dinickel complexes [Ni 2 (NR{CH 2 (MeC 6 H 2 R')S} 2 ) 2 ] [12] featuring structurally related N,S,S-coordinated amino-dithiolato ligands. The redox behavior of the latter complements that of 8 in that the aminedecorated dithiolato-ligands render oxidation toward higher oxidized forms electrochemically reversible, whereas the soft phosphine donors in 8 render further reduction of an initially formed Ni II /Ni I complex to a Ni I /Ni I complex (quasi)reversible.…”