Exploiting Orthogonal C–C Cross-Coupling Reactions for Chemistry-on-the-Complex: Modular Assembly of 2,6-Di(quinolin-8-yl)pyridine Ruthenium(II) Photosensitizer Triads

In this work, we present a concise modular assembly strategy using one universal heteroleptic 2,6-di(quinolin-8-yl)pyridine-based ruthenium(II) complex as a starting building block. Extending the concept from established ligand modifications and subsequent complexation (<i>classical route</i>), the later appearing chemistry-on-the-complex methodology was used for late-stage syntheses, <i>i.e.</i>, assembling discrete building blocks to molecular architectures (here: dyad and triads). We focused on Suzuki-Miyaura and Sonogashira cross-couplings as two of the best-known C-C bond forming reactions. Both were performed on one building block complex bearing a bromine and TIPS-protected alkyne for functional group interconversion (bromine to TMS-protected alkyne, a benzyl azide, or a boronic acid pinacol ester moiety with ≥95% isolated yield and simple purification) as well as building block assemblies using both a triarylamine-based donor and a naphthalene diimide-based acceptor in up to 86% isolated yield. Additionally, the developed purification <i>via</i> automated flash chromatography is simple compared to tedious manual chromatography for ruthenium(II)-based substrates in the <i>classical route</i>. Based on the preliminary characterization by steady-state spectroscopy, the observed emission quenching in the triad (55%) serves as an entry to rationally optimize the modular units <i>via</i> chemistry-on-the-complex to elucidate energy and electron transfer.