Considering the interest in processes related to hydrogen storage such as CO2 hydrogenation and formic acid (FA) decomposition, we have synthesized a set of Ir, Rh, or Ru complexes to be tested as versatile precatalysts in these reactions. In relation with the formation of H2 from FA, the possible applicability of these complexes in the transfer hydrogenation (TH) of challenging substrates as quinoline derivatives using FA/formate as hydrogen donor has also been addressed. Bearing in mind the importance of secondary coordination sphere interactions, N,N′ ligands containing NH2 groups, coordinated or not to the metal center, were used. The general formula of the new complexes are [(p-cymene)­RuCl­(N,N′)]­X, X = Cl–, BF4 – and [Cp*MCl­(N,N′)]­Cl, M = Rh, Ir, where the N,N′ ligands are 8-aminoquinoline (HL1), 6-pyridyl-2,4-diamine-1,3,5-triazine (L2) and 5-amino-1,10-phenanthroline (L3). Some complexes are not active or catalyze only one process. However, the complexes [Cp*MCl­(HL1)]Cl with M = Rh, Ir are versatile catalysts that are active in hydrogenation of quinolines, FA decomposition, and also in CO2 hydrogenation with the iridium derivative being more active and robust. The CO2 hydrogenation takes place in mild conditions using only 5 bar of pressure of each gas (CO2 and H2). The behavior of some precatalysts in D2O and after the addition of 9 equiv of HCO2Na (pseudocatalytic conditions) has been studied in detail and mechanisms for the FA decomposition and the hydrogenation of CO2 have been proposed. For the Ru, Ir, or Rh complexes with ligand HL1, the amido species with the deprotonated ligand are observed. In the case of ruthenium, the formate complex is also detected. For the iridium derivative, both the amido intermediate and the hydrido species have been observed. This hydrido complex undergoes a process of umpolung D+↔ Ir–D. All in all, the results of this work reflect the active role of −NH2 in the transfer of H+.

Herein, we harness the combination of two photocatalytic reactions, promoted by new Ir(iii) photosensitizers, for the direct access to 3-thiocyanato indoles from indolines in a one-pot process.

Five new RuII polypyridyl complexes bearing N‐(arylsulfonyl)‐8‐amidoquinolate ligands and three of their biscyclometalated IrIII congeners have been prepared and employed as photocatalysts (PCs) in the photooxidation of benzylamines with O2. In particular, the new RuII complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non‐emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S0←T1 energy values. Moreover, the RuII complexes, despite being non‐emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron‐withdrawing group (‐CF3) on the arene ring of the N‐(arylsulfonyl)‐8‐amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The IrIII analogues are considerably more photosensitive and consequently less efficient photosensitizers (PSs).

No abstract