Electronic and Steric Tuning of Catalytic H2 Evolution by Cobalt Complexes with Pentadentate Polypyridyl-Amine Ligands

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The Webster Group and collaborators report structural modifications of molecular cobalt catalysts that provide important insights into the structure–function relationship for the hydrogen evolution reaction. Despite a slight structural difference of the introduced isoquinoline group, the cobalt complex [Co(DPA-1-MPI)(H2O)](PF6)3 is ∼32 times as active as [Co(DPA-3-MPI)(H2O)](PF6)3 in photocatalytic H2 production. Density functional theory calculations show that the protonation of CoI to yield the CoIII–H species is energetically more favorable for [Co(DPA-1-MPI)(H2O)](PF6)3 than that of [Co(DPA-3-MPI)(H2O)](PF6)3. The presence of a planar conjugate bipyridyl unit is a key feature for stabilizing low valent CoI species toward proton binding. These studies were conducted in collaboration with Professor Xuan Zhao (The University of Memphis).

 

P. Wang, G. Liang, M. R. Reddy, M. Long, K. Driskill, C. Lyons, B. Donnadieu, J. C. Bollinger, C. E. Webster, X. Zhao. "Electronic and Steric Tuning of Catalytic H2 Evolution by Cobalt Complexes with Pentadentate Polypyridyl-Amine Ligands" J. Am. Chem.Soc., 2018, 140, 29, 9219-9229.


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