Synthesis of Pyrimidines and 1,3,5‐Triazines via Cobalt‐Catalyzed Dehydrogenative Coupling in Air

Abstract Cobalt (II) complexes bearing tetrazine and pyridine‐based tridentate ligands have been developed and evaluated as efficient catalysts for the sustainable synthesis of N‐heterocycles, specifically pyrimidines and triazines, using readily available alcohols as substrates. The catalytic system demonstrates the potential of first‐row transition metals as viable alternatives to precious metal catalysts in heteroaromatic construction. A key feature of these complexes is the tetrazine moiety,─N═N─ unit, which plays a pivotal role in facilitating the catalytic transformations. Mechanistic investigations, including control experiments, reveal that the tetrazine functionality directly influences substrate activation and intermediate stabilization, thereby accelerating the bond‐forming steps leading to heterocycle formation. Importantly, the developed methodology proceeds under phosphine‐free conditions, addressing limitations associated with conventional phosphine ligands, such as sensitivity to air and environmental concerns. This approach highlights an atom‐economic and environmentally benign pathway to valuable heteroaromatic frameworks with broad relevance to pharmaceuticals, agrochemicals, and functional materials. Collectively, these results establish tetrazine‐based cobalt complexes as a promising class of catalysts that combine sustainability, efficiency, and versatility, thereby expanding the toolbox for N‐heterocycle synthesis and opening avenues for future applications in green and scalable synthetic methodologies.