Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

Abstract

Abstract. Even though the existence of 1,2,3-triazoles has been known for more than a century, the recent discovery of a copper(I) catalyzed version of this reaction has attributed unprecedented importance to these compounds. Coordination and organometallic chemists have benefited from this modular synthetic route, and have accessed ligands based on both the triazoles as well as the triazolylidenes. The wide variation of steric and electronic properties that can be achieved for this ligand class has made them useful for generating metal complexes

A DFT Study on the Redox Active Behavior of Carbene and Pyridine Ligands in the Oxidative and Reductive Quenching Cycles of Ruthenium Photoredox Catalysts

“…Twelve structurally related octahedral ruthenium photoredox catalysts, shown in Figure 3, have been systematically investigated in this computational study. The three distinct groups investigated included four homoleptic pyridine/carbene complexes with bpy, py-NHC, py-aNHC (prefix a denotes "abnormal" [63]), and py-MIC ligands ( Figure 3a); six heteroleptic systems with two bpy and one carbene-containing ligand ( Figure 3b); and two of the investigated systems, 11 and 12, displayed tridentate polypyridine/carbene ligands bound in facial and meridional fashions, respectively. To analyze the electronic structure changes and redox energetics along the photoredox quenching cycles of these systems, presented above universally for [Ru(bpy) 3 ] 2+ through Figure 1, we computed the four stationary points determining the cycles, including the ground state species, S 0 , the triplet 3 MLCT state, T 1 , the reduced (doublet) state, D red , and the oxidized (doublet) state, D ox , of all the complexes displayed in Figure 3.…”

Intermolecular C−C Coupling between 1‐Methyl‐1,2,3‐Triazole and 2,2′‐Bipyridine or 1,10‐Phenanthroline in MoII Complexes

“…The reaction described above is intermolecular yielding a bimetallic complex (Scheme a), in contrast with the formation of imidazol‐2‐yl complexes (Scheme b) or monometallic dearomatized C−C coupling products (Scheme c) obtained from the deprotonation of analogous bipy or 4,4′‐dihalo‐2,2′‐bipy derivatives, respectively, bearing a N ‐methylimidazole instead of the triazole ligand . In addition, note that once the C5−H group has been deprotonated the intermolecular nucleophilic attack onto a bipy ligand is preferred over the isomerization from N‐ to C‐coordination of the so formed triazolide ligand (in a similar way to the one depicted in Scheme b), despite the fact that 1,2,3‐triazole ligands have been regarded as much weaker donors than N‐methylimidazole ,. Nucleophilic additions to Mo‐coordinated η 3 ‐allyl groups are well‐known reactions .…”

“…The Cu‐catalyzed alkyne–azide cycloaddition (CuAAC) reaction allowed the regioselective formation of 1,4‐disubstituted 1,2,3‐triazoles, and later, the Ru‐catalyzed version was disclosed to yield, also regioselectively, the 1,5‐disubstituted derivatives . 1,2,3‐Triazole species are potentially versatile ligands offering several donor sites for metal coordination, so they may act as polydentate and bridging ligands, allowing the preparation of polymeric coordination compounds . On the other hand, in recent years a great number of bi and polydentate ligands containing the 1,2,3‐triazole unit have been synthesized, and their metal complexes have shown potential applications in a wide range of areas such as materials science, ion sensing, medicinal chemistry, and catalysis …”

Aminotriazole Mn(I) Complexes as Effective Catalysts for Transfer Hydrogenation of Ketones

“…The use of picolylamine as ligand resulted in a highly active catalyst that performs comparably to well‐known Ruthenium‐based systems (Scheme ) ,. Based on this literature precedence, we envisaged triazole derivatives as attractive alternative N‐donor units to pyridine compounds to be used as bidentate ligands for Mn‐catalysis . The synthesis of triazoles takes advantage of the modularity of Cu‐catalyzed azide‐alkyne cycloaddition (click chemistry), an extremely powerful synthetic tool when it comes to generate molecular complexity .…”