Panneerselvam Murugesan, Jaccob Madhavan, Costa Luciano T
MolMod-CS-Instituto de Química, Universidade Federal Fluminense, Campos de Valonginho s/n, Centro, Niterói, Rio de Janeiro 24020-14, Brazil.
Programa de Engenharia Química (PEQ/COPPE), Universidade Federal do Rio de Janeiro (UFRJ), Moniz Aragão, Rio de Janeiro 21941-594, Brazil.
ACS Omega. 2024 Nov 26;9(49):48766-48780. doi: 10.1021/acsomega.4c03260. eCollection 2024 Dec 10.
In this study, comprehensive density functional theory calculations were conducted to investigate the molecular mechanism of electrocatalytic proton reduction using group 9 transition metal bpaqH (2-(bis(pyridin-2-ylmethyl)amino)--(quinolin-8-yl)acetamide) complexes. The goal was to explore how variations in the structural and electronic properties among the three metal centers might impact the catalytic activity. All three metal complexes were observed to share a similar mechanism, primarily characterized by three key steps: heterolytic cleavage of H (HEP), reduction protonation (RPP), and ligand-centered protonation (LCP). Among these steps, the heterolytic cleavage of H (HEP) displayed the highest activation barrier for cobalt, rhodium, and iridium catalysts compared to those of the RPP and LCP pathways. In the RPP pathway, hydrogen evolution occurred from the M-H intermediate using acetic acid as a proton donor at the open site. Conversely, in the LCP pathway, H-H bond formation took place between the hydride and the protonated bpaqH ligand, while the open site acted as the spectator. The enhanced activity of the cobalt complex stemmed from its robust σ-bond donation and higher hydride donor ability within the metal hydride species. Additionally, the cobalt complex demonstrated a necessary negative potential in the first (M) and second (M) reduction steps in both pathways. Notably, M-H exhibited a more crucial negative potential for the cobalt complex compared to those of the other two metal complexes. Through an examination of kinetics and thermodynamics in the RPP and LCP processes, it was established that cobalt and rhodium catalysts outperformed the iridium ligand scaffold in producing molecular hydrogen after substituting cobalt metal with rhodium and iridium centers. These findings distinctly highlight the lower-energy activation barrier associated with LCP compared to alternative pathways. Moreover, they offer insights into the potential energy landscape governing hydrogen evolution reactions involving group 9 transition metal-based molecular electrocatalysts.
在本研究中，进行了全面的密度泛函理论计算，以研究使用第9族过渡金属bpaqH（2 - （双（吡啶 - 2 - 基甲基）氨基） - （喹啉 - 8 - 基）乙酰胺）配合物进行电催化质子还原的分子机制。目的是探索三个金属中心之间结构和电子性质的变化如何影响催化活性。观察到所有三种金属配合物都具有相似的机制，主要特征为三个关键步骤：氢的异裂裂解（HEP）、还原质子化（RPP）和配体中心质子化（LCP）。在这些步骤中，与RPP和LCP途径相比，钴、铑和铱催化剂的氢异裂裂解（HEP）显示出最高的活化能垒。在RPP途径中，使用乙酸作为开放位点处的质子供体，从M - H中间体发生析氢反应。相反，在LCP途径中，氢化物与质子化的bpaqH配体之间形成H - H键，而开放位点起旁观者作用。钴配合物活性增强源于其在金属氢化物物种中强大的σ键供体作用和更高的氢化物供体能力。此外，钴配合物在两条途径的第一步（M）和第二步（M）还原步骤中都表现出必要的负电位。值得注意的是，与其他两种金属配合物相比，M - H对钴配合物表现出更关键的负电位。通过研究RPP和LCP过程中的动力学和热力学，发现用铑和铱中心取代钴金属后，钴和铑催化剂在产生分子氢方面优于铱配体支架。这些发现清楚地突出了与其他途径相比，LCP具有更低能量的活化能垒。此外，它们为涉及第9族过渡金属基分子电催化剂的析氢反应的势能面提供了见解。
