Photocatalysis Enabling Acceptorless Dehydrogenation of Diaryl Hydrazines at Room Temperature

Abstract

Aromatic azo compounds are privileged structural motifs, and they exhibit a myriad of pharmaceutical as well as industrial applications. Here, we report a catalytic acceptorless dehydrogenation of diarylhydrazine derivatives to access a wide variety of aryl-azo compounds with the removal of molecular hydrogen as the sole byproduct. This distinctive reactivity has been achieved under dual catalytic conditions by merging the visible-light active [Ru(bpy) 3 ] 2+ as the photoredox catalyst and Co(dmgH) 2 (py)Cl as the proton-reduction catalyst. The reaction proceeds smoothly under very mild and benign conditions and operates at ambient temperature. This dual catalytic approach is highly compatible with many different functional groups and has a broad substrate scope. We have also demonstrated the reversible hydrogen storage and release phenomenon on hydrazobenzene/azobenzene couple to show the utility of these compounds as hydrogen storage materials. Further diversification of azobenzene was shown by a transitionmetal-catalyzed azo-group-directed ortho-C−H bond functionalization.

Chemoselective Hydrogenation of Nitroarenes Using an Air-Stable Base-Metal Catalyst

“… 34 The conditions appeared to be very close to those applied for nitroarene hydrogenation. The catalytic hydrogenation of azobenzene to hydrazobenzene was previously achieved using rare and expensive transition metals like Pd, 35 Pt, 36 and Ru. 37 …”

The Merger of Photoredox and Cobalt Catalysis

“…It should also be noted here that similar cooperative catalysis can facilitate the dehydrogenative coupling of two N-heterocycles by finely tuning the reaction conditions [79]. In addition to C-N bonds, N-N bonds were able to be desaturated to afford azobenzene derivatives by a cobaloxime/photoredox system [80].…”

Cross-Coupling Hydrogen Evolution Reactions

“…Balaraman 等 [65] 利用三联吡啶钌作为光催化剂, 钴 肟配合物 Co(dmgH) 2 (Py)Cl 作为产氢催化剂, 在可见光 照射下实现了二芳基肼类化合物的分子内放氢反应, 高 效制备了一系列二芳基偶氮类化合物(图 20). 此外, Sorensen 等 [66] 结合四丁基铵十聚钨酸盐(TBADT)和钴 肟产氢催化剂, 在近紫外光照的条件下对未活化的烷烃 和醇的分子内放氢反应进行了研究.…”