Synthesis, Isomerization and Electrocatalytic Properties of Thiolate‐Bridged Dicobalt Hydride Complexes with Different Substituents

Abstract

Through different pathways, two unsaturated thiolate‐bridged CoIICoII complexes [Cp*Co(µ‐SR)2CoCp*] (1, R = Ph; 3, R = iPr, Cp* = η5‐C5Me5) were successfully synthesized. Interaction of complexes 1 or 3 with HBF4 resulted in oxidative addition to give the corresponding thiolate‐bridged CoIIICoIII hydride bridged complexes 4[BF4] and 5[BF4]. 1H NMR spectroscopic results indicate there exist two conformational isomers after protonation, in which the substituents on the thiolate ligands arranged in a symmetric or unsymmetric geometry. Interestingly, major sym‐4[BF4] can irreversibly convert into minor unsym‐4[BF4] at 30 °C evidenced by time‐dependent 1H NMR spectroscopy. Surprisingly, two isomers of 5[BF4] remain a dynamic equilibrium from –80 to 30 °C corroborated by variable‐temperature 1H NMR spectra. Furthermore, these thiolate‐bridged dicobalt hydride complexes are proved to be catalysts for electrocatalytic proton reduction by cyclic voltammetry. Notably, complex 5[BF4] exhibits better catalytic activity, which highlights the importance of the flexibility of the auxiliary ligand.