A matrix of heterobimetallic complexes for interrogation of hydrogen evolution reaction electrocatalysts

Abstract

Nitrosyls as electron reservoirs guide protons to favorable sites in bimetallic HER catalysts.

Structural and Electronic Responses to the Three Redox Levels of Fe(NO)N2S2‐Fe(NO)2

“…[19][20][21] We introduced NO into models of the [FeFe]-hydrogenase enzyme active site with the expectation that it might reproduce the function of the electron reservoir [Fe 4 S 4 ]sub-cluster in the H-cluster.C learly the binding capability of the N 2 S 2 unit to both Fe(NO) and Fe(NO) 2 persists throught wo reductionsi ncreasing the overall electronc ount by two. The XRD analysis, solid-state structures, and IR data are consistentw ith data from EPR spectroscopy, magnetic susceptibility and computational modeling that define the electronic structures of theses pecies.…”

“…[12][13][14][15] In the latter,M eyer et al pre-sentedX -ray crystal structures in three redox levels. [19][20][21] Specifically,r edox reactivity in the NO of the Fe(NO)u nit might mimic the 4Fe4S cluster of the H-cluster.G enerally,t he diiron complex offers opportunity to examine the mutual influence of redox activeu nits as mediated by sulfur bridges.As indicated in Figure 1, multiple chemical routes led to the cationic,o xidized form, {Fe(NO)} 7 -{Fe(NO) 2 } 9 ,t hat is,1 + + or 1* + + , implicating particular thermodynamic stability and as elf-assembly process. [16] While mostly explored with M = Ni 2 + ,other dications such as [Fe(NO)] 2 + ,[Co(NO)] 2 + ,and [VO] 2 + are also included in this new class of metallo-ligands.…”

“…[17] An ACS-related structure, [Fe(NO)N 2 S 2 ·Fe(NO) 2 ] + /0 was revealed by us during studies of metallodithiolates as ligands in dinitrosyliron complexes, DNICs, Figure 1. [19][20][21] Specifically,r edox reactivity in the NO of the Fe(NO)u nit might mimic the 4Fe4S cluster of the H-cluster.G enerally,t he diiron complex offers opportunity to examine the mutual influence of redox activeu nits as mediated by sulfur bridges. [19][20][21] Specifically,r edox reactivity in the NO of the Fe(NO)u nit might mimic the 4Fe4S cluster of the H-cluster.G enerally,t he diiron complex offers opportunity to examine the mutual influence of redox activeu nits as mediated by sulfur bridges.…”

Interplay of hemilability and redox activity in models of hydrogenase active sites

“…Generally, the E and C steps alternate to avoid the accumulation of like charges (31,40). The likelihood of each C step is evaluated in our computations by comparing the acidities of the protonated species vs. the proton provider HOEt 2 + (as the acid is HBF 4• OEt 2 or HOEt 2• BF 4 ) (32,38). A positive ΔpK a (ΔpK a = pK a (CatH) − pK a ([HOEt 2 ] + ) indicates a thermodynamically favorable C step.…”

“…The calculations predict that second reduction event at −1.28 V (calculated) should produce the catalytic wave. However, this catalytic wave appears experimentally at approximately −0.70 V and the current increases with additional equivalents of HBF 4 •OEt 2 (38). The early appearance of the catalytic wave indicates that the second reduction in the mechanism is a proton-coupled electron transfer (PCET) as in an [ECEC] cycle.…”