Beyond S and Se: Electrocatalytic Hydrogen Production by Tellurolate-Bridged Co(III)-Mn(I) Heterodinuclear Complexes

In the pursuit of efficient electrocatalysts for the hydrogen evolution reaction (HER), a series of manganese and cobalt heterodinuclear complexes have been synthesized and characterized that have a stark resemblance with the [NiFe]-hydrogenase active site structure. Irradiation of [Mn₂(CO)₁₀] in the presence of 1.5 eq of [NaEPh] [E = S, Se, Te] followed by reaction with [Cp*CoCl]₂ led to the formation of half-sandwiched trichalcogenate-bridged heterodinuclear complexes [{Mn(CO)₃}(μ-EPh)₃(CoCp*)] [E = S (C1); Se (C2) and Te (C3)]. The reaction of these heterodinuclear trichalcogenate-bridged complexes with [LiBH₄·THF] yielded the corresponding dichalcogenate hydride-bridged heterobimetallic complexes [(CO)₃Mn(μ-EPh)₂(μ-H)(CoCp*)] [E = S (C5); Se (C6) and Te (C7)], which closely imitate the Ni-R intermediate of [NiFe]-hydrogenase. The resultant complexes (C5-C7) displayed impressive H₂ production in DMF in the presence of HBF₄, whereas the Te-based complex (C7) showcased the highest TON (184 h^-1) with an impressive Faradaic efficiency of >98%. The DFT investigations revealed a unique role of bridging chalcogens in catalysis, wherein, depending on the identity of the chalcogen (S, Se, or Te), protonation could occur via two distinct routes. This study represents a rare example of the full trio of S/Se/Te-based heterodinuclear complexes whose electrocatalytic HER activity has been probed under analogous conditions.