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The development of efficient catalysts for the dehydrogenation of formic acid (FA) through molecular level control and precise regulation remains challenging. Herein, we report the newly developed complexes of iridium and ruthenium with nitrogen‐rich ligand for aqueous FA dehydrogenation. The Cp*Ir complex 1 (Cp*=cyclopentadienyl) and Ru(p‐cym) complex 2 (p‐cym=p‐Cymene) were synthesized and fully characterized. The single crystal structures of these complexes have a typical piano‐stool structure. A turnover frequency of 12468 h−1 was achieved for FA dehydrogenation at 90 °C by using complex 1 bearing 3,3'‐diamino‐5,5'‐bis(1H‐1,2,4‐triazole) (DABT). The effects of pH, temperature, concentration of formic acid and amount of catalyst on the reaction kinetics were studied in detail. Kinetic isotope effect (KIE) experiments and 1H NMR detection of reaction revealed that a plausible mechanism involves the decarboxylation of formate and the formation of H2. More importantly, the influence of H2O and H+ was involved in the rate‐determining step. This study demonstrated the effectiveness of nitrogen‐rich ligand for FA dehydrogenation, which would contribute to the development of new and effective hydrogen release systems. [ABSTRACT FROM AUTHOR]

Interconversion between CO 2 + H 2 and FA/formate is the most promising strategy for the fixation of carbon dioxide and reversible hydrogen storage; however, FA dehydrogenation and CO 2 hydrogenation are usually studied separately using different catalysts for each reaction. This report describes of the catalysis of [Cp*Ir(N∧N)(X)] n + (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; X = Cl, n = 0; X = H 2 O, n = 1) bearing a proton-responsive N∧N pyridylpyrrole ligand for both reactions. Complex 2-H 2 O catalyzes FA dehydrogenation at 90 °C with a TOF max of 45 900 h -1 . Its catalysis is more active in aqueous solution than in neat solution under base-free conditions. These complexes also catalyze CO 2 hydrogenation in the presence of base to formate under atmospheric pressure (CO 2 /H 2 = 0.05 MPa/0.05 MPa) at 25 °C with a TOF value of 4.5 h -1 in aqueous solution and with a TOF value of 29 h -1 in a methanol/H 2 O mixture solvent. The possible mechanism is proposed by intermediate characterization and KIE experiments. The extraordinary activity of these complexes are mainly attributed to the metal-ligand cooperative effect of the the pyrrole group to accept a proton in the dehydrogenation of formic acid and assist cooperative heterolytic H-H bond cleavage in CO 2 hydrogenation.

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH 4 ][(UO 2 ) 3 (HTTDS)(H 2 O)] (1), [(UO 2 ) 4 (HTTDS) 2 ](HIM) 6 (2, IM=imidazole), [(UO 2 ) 4 (TTDS)(H 2 O) 2 (Phen) 2 ] (3, Phen=1,10-phenanthroline), [Zn(H 2 O) 4 ] 0.5 [(UO 2 ) 3 (HTTDS)(H 2 O) 4 ] (4), and {(UO 2 ) 2 [Zn(H 2 O) 3 ] 2 (TTDS)} (5), {Zn(UO 2 ) 2 (H 2 O)(Dib) 0.5 (HDib)(HTTDS)} (6, Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO 2 ) 4 [Cu 3 (u 3 -OH)(H 2 O) 7 ](TTDS) 2 } (7) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H 8 TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO 7 pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO 2 ] 2+ units as co-ligands. The second metal centers were introduced in the syntheses of 4-7, and in all cases, they are part of the final structures, either as a counterion (4) or as a component of framework (5-7). Interesting, in 7, a rare polyoxometalate [Cu 3 (μ 3 -OH)O 7 (O 2 CR) 4 ] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO 2 ) 2 (O 2 CR) 4 ] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail., (© 2021 Wiley-VCH GmbH.)