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

Two nickel complexes supported by tridentate NS 2 ligands, [Ni 2 ( κ ‐ N , S , S , S′ ‐N Ph {CH 2 (MeC 6 H 2 R′)S} 2 ) 2 ] ( 1 ; R′=3,5‐(CF 3 ) 2 C 6 H 3 ) and [Ni 2 ( κ ‐ N , S , S , S′ ‐N iBu {CH 2 C 6 H 4 S} 2 ) 2 ] ( 2 ), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid‐state structure of 1 reveals that the [Ni 2 (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 CF 3 COOH at −1.93 (overpotential of 1.04 V, with i cat / i p ≈21.8) and −1.47 V (overpotential of 580 mV, with i cat / i p ≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni 2 (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 [Ni 2 (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.