410
P. P. Roma´ nczyk and S. S. Kurek
1 Introduction
Molecular electrochemistry addresses redox behaviour and transformation of
molecules initiated by electron transfer (ET). Understanding the electronic and structural factors affected by the changes in both first and second coordination spheres
of a metal–ligand system, and the effects of local environment (dielectric medium
and specific interactions) that govern the ability of transition metal complexes to
undergo ET processes, is of great importance in organic and inorganic redox chemistry and catalysis, in artificial and biological systems. In this contribution, we focus
on computational protocols that use DFT combined with continuum solvation models
allowing accurate (to 0.05 V) prediction of redox potentials. After brief introduction to modelling approaches, we discuss selected examples of mono- and dinuclear
complexes, including ferrocene—an internal redox potential standard in non-aqueous
electrochemistry, (bio)catalytically relevant Mo, W, Cu or Fe systems, and mixedvalent (MV) compounds with interesting and unexpected electronic properties, for
which results of DFT computations successfully match experimental properties. The
chapter also covers the second coordination sphere and H-bonding effects on reduction potential and the problem of electronic coupling in MV compounds assessed
based on electrochemical measurements. The last part of the chapter describes ETtriggered bond-breaking processes and elucidation of possible reaction pathways
with the use of computations. Case studies on Mo and W nitrosyl alkoxide scorpionates are reviewed to show how molecular electrocatalysis of polychlorinated
alkanes dehalogenation and its inhibition can be controlled by non-covalent interactions, like C−H· · ·O hydrogen and/or halogen bonding, and dispersion forces,
bringing about activation of polyhalogenated alkanes and giving rise to enhanced
rates of electron transfer. Revealing the relationship of described systems with some
enzyme-mimicking activity is significant for the rational designing of new electrocatalysts.
2 DFT Modelling of Redox Potentials
Redox potential, a characteristic property of a given metal–ligand system, can be
controlled by introducing changes in the first and second coordination spheres, and
the local environment—solvent, ions and molecules present in the solution. The
prediction of accurate redox potentials is important in elucidating catalytic reaction
mechanisms, catalyst designing, and in modelling of active sites in metalloenzymes.
The use of the approach based on the DFT combined with implicit solvent models that
started with the 2002 Friesner and Baik paper [1] has recently been reviewed [2, 3],
and here, it will only be briefly outlined, followed by the discussion of selected
examples involving transition metal systems.
P. P. Roma´ nczyk and S. S. Kurek
1 Introduction
Molecular electrochemistry addresses redox behaviour and transformation of
molecules initiated by electron transfer (ET). Understanding the electronic and structural factors affected by the changes in both first and second coordination spheres
of a metal–ligand system, and the effects of local environment (dielectric medium
and specific interactions) that govern the ability of transition metal complexes to
undergo ET processes, is of great importance in organic and inorganic redox chemistry and catalysis, in artificial and biological systems. In this contribution, we focus
on computational protocols that use DFT combined with continuum solvation models
allowing accurate (to 0.05 V) prediction of redox potentials. After brief introduction to modelling approaches, we discuss selected examples of mono- and dinuclear
complexes, including ferrocene—an internal redox potential standard in non-aqueous
electrochemistry, (bio)catalytically relevant Mo, W, Cu or Fe systems, and mixedvalent (MV) compounds with interesting and unexpected electronic properties, for
which results of DFT computations successfully match experimental properties. The
chapter also covers the second coordination sphere and H-bonding effects on reduction potential and the problem of electronic coupling in MV compounds assessed
based on electrochemical measurements. The last part of the chapter describes ETtriggered bond-breaking processes and elucidation of possible reaction pathways
with the use of computations. Case studies on Mo and W nitrosyl alkoxide scorpionates are reviewed to show how molecular electrocatalysis of polychlorinated
alkanes dehalogenation and its inhibition can be controlled by non-covalent interactions, like C−H· · ·O hydrogen and/or halogen bonding, and dispersion forces,
bringing about activation of polyhalogenated alkanes and giving rise to enhanced
rates of electron transfer. Revealing the relationship of described systems with some
enzyme-mimicking activity is significant for the rational designing of new electrocatalysts.
2 DFT Modelling of Redox Potentials
Redox potential, a characteristic property of a given metal–ligand system, can be
controlled by introducing changes in the first and second coordination spheres, and
the local environment—solvent, ions and molecules present in the solution. The
prediction of accurate redox potentials is important in elucidating catalytic reaction
mechanisms, catalyst designing, and in modelling of active sites in metalloenzymes.
The use of the approach based on the DFT combined with implicit solvent models that
started with the 2002 Friesner and Baik paper [1] has recently been reviewed [2, 3],
and here, it will only be briefly outlined, followed by the discussion of selected
examples involving transition metal systems.