# Isomerization pathway of a C–C sigma bond in a bis(octaazamacrocycle)dinickel(II) complex activated by deprotonation: a DFT study

## TL;DR

This study explores how a C–C sigma bond in a nickel complex changes shape when a proton is removed, using computational methods.

## Contribution

The paper presents a detailed DFT-based isomerization pathway for a dinickel(II) complex activated by deprotonation.

## Key findings

- Deprotonation of a bridging carbon enables a geometry twist from anti to syn.
- Intermediate geometries were identified through potential energy surface scans.
- Protonated forms of intermediates were analyzed to understand the isomerization mechanism.

## Abstract

The anti (a) to syn (s) isomerization pathway of the deprotonated form of the dimer with two nickel(II) 15-membered octaazamacrocyclic units connected via a carbon–carbon (C–C) σ bond was investigated. For the initial anti (a) structure, a deprotonation of one of the bridging (sp3 hybridized) carbon atoms is suggested to allow for an a to s geometry twist. A 360° scan around the bridging C–C dihedral angle was performed first to find an intermediate geometry. Subsequently, the isomerization pathway was explored via individual steps using a series of mode redundant geometry optimizations (internal coordinates potential energy surface scans) and geometry relaxations leading to the s structure. The prominent geometries (intermediates) of the isomerization pathway are chosen and compared to the a and s structures, and geometry relaxations of the protonated forms of selected intermediates are considered.

The online version contains supplementary material available at 10.1007/s00214-024-03100-5.