Selective Redox Activation of H₂ or O₂ in a [NiRu] Complex by Aromatic Ligand Effects

Abstract

We present two closely related series of a [NiFe] hydrogenase analogue. Based on a [NiRu] core, these complexes demonstrate inactivity, H2 activation, or O2 activation depending only on the nature of the Ru-coordinated aromatic ligand. It is demonstrated that even small changes made to this aromatic ligand can modulate the catalytic activity of the complex. Structural, electrochemical, kinetic, and thermodynamic studies reveal that differences in activation and binding modes of the substrates, combined with differences in σ donation and lability of the aromatic ligands, result in abrupt changes in catalytic activity.

H2 and O2 activation by [NiFe]hydrogenases – Insights from model complexes

“…To facilitate the quantitative observation of activation of H 2 and O 2 by a Ni II Ru II complex, we systematically varied the σ-donation and π-accepting abilities of Ru's supporting ligand (Fig. 15) [18]. The Lewis acidity of the Ru center, which is controlled by the σ-donation and π-accepting abilities of this induction ligand, can be indirectly estimated based on its redox potential (Ru II /Ru I ).…”

“…Activation of H 2 and O 2 by Ni II Ru II complexes (n = 1 for cyclopentadienyl-derivarive ligands, n = 2 for benzene-derivative ligands) based on redox potential of Ru II /Ru I of Ni-SIa model [18]. Specifically, π-back donation to the induction ligand increases the Lewis acidity in the Ru center, while σ-donation from the induction ligand increases the Lewis basicity of the aqua ligand (Lewis ligand), so that both processes function adequately to spur the heterolytic cleavage of H 2 .…”

“…Fig. 17 No reactivity of a Ni II Ru II complex that has a pentamethylcyclopentadienyl ligand towards H 2 or hydride reagent (NaBH 4 ) [18].…”

“…Activation of O 2 by Ni II Ru II complexes based on redox potential of Ru II /Ru I of Ni-SIa model [18]. (Fig.…”

“…Relationship between log k 2 and redox potential of Ru II /Ru I of Ni II Ru II complexes [18]. Relationship between log k 2 and pK a of aqua ligand of Ni II Ru II complexes [18].…”