Tuning Ligand Effects
and Probing the Inner-Workings
of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made
Properties
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Abstract
Activating chemical bonds through
external triggers and understanding
the underlying mechanism are at the heart of developing molecules
with catalytic and switchable functions. Thermal, photochemical, and
electrochemical bond activation pathways are useful for many chemical
reactions. In this Article, a series of Ru<sup>II</sup> complexes
containing a bidentate and a tripodal ligand were synthesized. Starting
from all-pyridine complex <b>1</b><sup>2+</sup>, the pyridines
were stepwise substituted with “click” triazoles (<b>2</b><sup>2+</sup>–<b>7</b><sup>2+</sup>). Whereas
the thermo- and photoreactivity of <b>1</b><sup>2+</sup> are
due to steric repulsion within the equatorial plane of the complex, <b>3</b><sup>2+</sup>–<b>6</b><sup>2+</sup> are reactive
because of triazoles in axial positions, and <b>4</b><sup>2+</sup> shows unprecedented photoreactivity. Complexes that feature neither
steric interactions nor axial triazoles (<b>2</b><sup>2+</sup> and <b>7</b><sup>2+</sup>) do not show any reactivity. Furthermore,
a redox-triggered conversion mechanism was discovered in <b>1</b><sup>2+</sup>, <b>3</b><sup>2+</sup>, and <b>4</b><sup>2+</sup>. We show here ligand design principles required to convert
a completely inert molecule to a reactive one and vice versa, and
provide mechanistic insights into their functioning. The results presented
here will likely have consequences for developing a future generation
of catalysts, sensors, and molecular switches