Ni(II) complexes for hydrogen oxidation and hydrogen production: An ab-initio molecular dynamics investigation

We present a detailed theoretical study of [Ni(P ^R ₂N ^R' ₂) ₂] ²⁺ electrocatalysts for H ₂ oxidation and H ₂ formation developed at the EFRC Center for Molecular Electrocatalysis at PNNL. P ^R ₂N ^R' ₂ denotes cyclic diphosphine ligands that incorporate an amine base in each ligand chelate ring. Density functional theory-based calculations and hybrid QM/MM molecular dynamics simulations have been employed to efficiently map the complex chemistry of these catalysts. Results are rationalized in terms of the P and N substituents and their capability to tune the pK _a of the pendant amines and the hydricity of the metal center. A detailed analysis of the conformational dynamics of the reaction intermediates and their role on the catalytic activity is also presented, along with a discussion on the role of solvent (acetonitrile) and of small amounts of water, which have been shown to have a dramatic effect on rates of H ₂ production.