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

Through different pathways, two unsaturated thiolate-bridged Co(II)Co(II)complexes [Cp*Co(mu-SR)(2)CoCp*] (1, R = Ph;3, R =iPr, Cp* = eta(5)-C5Me5) were successfully synthesized. Interaction of complexes1or3with HBF(4)resulted in oxidative addition to give the corresponding thiolate-bridged Co(III)Co(III)hydride bridged complexes4[BF4]and5[BF4].H-1 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, majorsym-4[BF4]can irreversibly convert into minorunsym-4[BF4]at 30 degrees C evidenced by time-dependent(1)H NMR spectroscopy. Surprisingly, two isomers of5[BF4]remain a dynamic equilibrium from -80 to 30 degrees C corroborated by variable-temperature(1)H NMR spectra. Furthermore, these thiolate-bridged dicobalt hydride complexes are proved to be catalysts for electrocatalytic proton reduction by cyclic voltammetry. Notably, complex5[BF4]exhibits better catalytic activity, which highlights the importance of the flexibility of the auxiliary ligand.