The Pd‐Co/rGO Catalyzed Buchwald–Hartwig Amination of N ‐Protected‐5‐Bromoindoles: A Green Approach to Functionalized Indoles With Photophysical Insights

To develop sustainable catalysts for C─N bond‐forming reactions, a series of Pd‐Co bimetallic alloy nanocatalysts supported on reduced graphene oxide (Pd‐Co@rGO) were synthesized. The synthesis utilized a clean chemical reduction method employing the environmentally friendly reagent ascorbic acid. Varying the starting material ratios allowed the preparation of catalysts with different metal weight percentages (wt% Pd and Co), facilitating the optimization of catalytic performance. Characterization (XRD, SEM, HR‐TEM, and AFM) confirmed the material's architecture. The Pd‐Co@rGO catalyst achieves high efficiency due to the synergistic electronic and geometric enhancement from the Co‐Pd alloying and the rGO support, which ensures uniform dispersion and optimal surface area. This robust and highly efficient platform successfully promoted the Buchwald–Hartwig amination of N ‐protected‐5‐bromoindole derivatives with a variety of primary (including heteroaryl) and secondary amines, affording the corresponding N ‐protected‐5‐amino‐1 H‐ indoles in good to excellent yields. The photophysical properties of the title compounds ( 5a–p ) were investigated in a chloroform solution at a concentration of 1 × 10 − 5 mol L −1 . Among all synthesized compounds, the N ‐benzyl, biphenylbenzyl, naphthyl, and nitro‐substituted indole derivatives ( 5c , 5e , and 5j ) exhibited the most intense absorption and emission maxima.