Photolytic water oxidation catalyzed by a molecular carbene iridium complex

Application of 1,2,3-triazolylidenes as versatile NHC-type ligands: synthesis, properties, and application in catalysis and beyond

“…For example, the iridium complexes 42 and 44 tolerate aqueous 1 M HCl for several days. 23,50 Under these conditions, no traces of triazolium salt are observed, demonstrating the high resistance of the M-C trz bond towards acidolysis. Hence, the C trz -Ir bond and also the iridium-75 pyridylidene bond are substantially more robust towards protonation than the C aryl -Ir bond.…”

“…Complex 42 featuring a monodentate carbene ligand is less soluble in water and achieves under dilute conditions a respectable 22,800 turnovers. 23 However, this TON is substantially lower than those from bidentate complexes such as 44 or 58, and conversion decreases markedly after consumption 25 of about 50% of sacrificial oxidant, suggesting only limited catalyst lifetime. Therefore, chelation seems to be important for generating robust water oxidation catalysts.…”

“…In this context, it is interesting to note that complex 48a displays activity similar to a mixture of CuCl and the mesoionic oxide 49a (cf Scheme 15) in the coupling of benzyl azide and 50 phenylacetylene. 23 The mesoionic oxide/CuCl mixture may be generated directly from 48a, a process that is not unlikely to occur under catalytic conditions. 55 Considering the popularity of palladium in cross-coupling reactions, and of aryl-aryl cross-coupling in particular, it is not surprising that many triazolylidene palladium complexes have been investigated as catalyst precursors for Suzuki-Miyaura cross-coupling.…”

“…One-pot syntheses of triazoles from an aniline starting material have been reported, 17,18 along with 10 syntheses utilizing alkyl azide where these azides are not isolated prior to the CuAAC process. 11,[19][20][21][22][23][24] Subsequent alkylation of the triazole with a suitable alkylating agent is generally selective and yields the 1,3,4-substituted triazolium salt (Scheme 1). Although triazolylidenes are a new class of NHC ligands, the variety of ligands that have been synthesised via the CuACC reaction is substantial.…”

Ligand Exchange and Redox Processes in Iridium Triazolylidene Complexes Relevant to Catalytic Water Oxidation

“…5 Over the last few years, iridium complexes have emerged as very powerful catalysts for this water oxidation process. [6][7][8][9][10][11][12][13][14][15][16][17][18] Depending on the ligand design, very high turnover numbers have been achieved. 19 Moreover, kinetic and mechanistic studies have provide increasingly compelling evidence that some complexes are precursors for homogeneous rather than heterogeneous [20][21][22] water oxidation catalysts and that the oxidation therefore occurs at an iridium center that is in a well-defined environment.…”