Unlocking the Nucleophilic Functionalization Potential of a Natural Asphalt: Grafting a Pd(0)–Diethanolamine Complex as a Recyclable Catalyst for Upgrading Biaryl Synthesis

This study introduces a novel method for functionalizing natural asphalt, presenting new opportunities for upgrading asphaltenes from road to a catalyst. The process utilizes a metal-free sonobromination technique in acetic acid to incorporate carbon–halogen substituents onto natural asphalt. These sites are then targeted by nucleophilic substitution with diethanolamine, followed by complexation with Pd(0) to create a unique palladium complex grafted onto natural asphalt. This stabilized complex serves as a heterogeneous and recoverable catalyst in the Suzuki reaction. This complex facilitates the reaction between aryl boronic acids and various ortho-, meta-, and para-substituted aryl halides under mild conditions using polyethylene glycol-400 as the green solvent. The reaction conversion rate is significantly influenced by the leaving group ability of the halides and the electronic and steric effects of the substituents on both reactants. This environmentally friendly process offers a broad substrate scope (24 examples) and achieves excellent yields of biphenyl derivatives. Notably, it employs a naturally derived catalytic support, underscoring its sustainability. This research potentially unlocks the bonding of nucleophiles to the natural asphalt for developing novel functional materials from this renewable resource.