Solid-Phase Synthesis as a Platform for the Discovery of New Ruthenium Complexes for Efficient Release of Photocaged Ligands with Visible Light

Ruthenium-based
photocaging groups have important applications as biological tools
and show great potential as therapeutics. A method was developed to
rapidly synthesize, screen, and identify ruthenium-based caging groups
that release nitriles upon irradiation with visible light. A diverse
library of tetra- and pentadentate ligands was synthesized on polystyrene
resin. Ruthenium complexes of the general formula [Ru­(L)­(MeCN)n]m+ (n = 1–3, m = 1–2) were generated
from these ligands on solid phase and then cleaved from resin for
photochemical analysis. Data indicate a wide range of spectral tuning
and reactivity with visible light. Three complexes that showed strong
absorbance in the visible range were synthesized by solution phase
for comparison. Photochemical behavior of solution- and solid-phase
complexes was in good agreement, confirming that the library approach
is useful in identifying candidates with desired photoreactivity in
short order, avoiding time-consuming chromatography and compound purification.