Cyclometalated Mono‐ and Dinuclear Ir^III Complexes with “Click”‐Derived Triazoles and Mesoionic Carbenes

Abstract

Orthometalation at Ir(III) centers is usually facile, and such orthometalated complexes often display intriguing electronic and catalytic properties. By using a central phenyl ring as C-H activation sites, we present here mono- and dinuclear Ir(III) complexes with "click"-derived 1,2,3-triazole and 1,2,3-triazol-5-ylidene ligands, in which the wingtip phenyl groups in the aforementioned ligands are additionally orthometalated and bind as carbanionic donors to the Ir(III) centers. Structural characterization of the complexes reveal a piano stool-type of coordination around the metal centers with the "click"-derived ligands bound either with C^N or C^C donor sets to the Ir(III) centers. Furthermore, whereas bond localization is observed within the 1,2,3-triazole ligands, a more delocalized situation is found in their 1,2,3-triazol-5-ylidene counterparts. All complexes were subjected to catalytic tests for the transfer hydrogenation of benzaldehyde and acetophenone. The dinuclear complexes turned out to be more active than their mononuclear counterparts. We present here the first examples of stable, isomer-pure, dinuclear cyclometalated Ir(III) complexes with poly-mesoionic-carbene ligands.

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

“…The solid‐state structures of complexes 8 – 12 were determined by single‐crystal X‐ray diffraction analyses and confirmed the connectivity pattern deduced from NMR spectroscopy. All complexes show the typical three‐legged piano‐stool geometry around the iridium center as expected for this type of half‐sandwich iridium complexes . Representative molecular structures of complexes 8b , 9a – b and 10 are shown in Figure (see Supporting Information for the structures of complexes 8d , 8e , 9c , 11 , 12a , and 12b ).…”

“…Selected bond lengths and angles are listed in Table . Bond lengths and angles around the iridium center are unsurprising for complexes 8b , 9a – b (Table ) and also for all structures reported in the supporting information, revealing no significant differences to reported triazolylidene iridium(III) complexes . In contrast, the bonding in complex 10 deviates considerably.…”

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

“…A few examples of di‐ and trinuclear iridium(III) complexes as well as trinuclear iridium(I) complexes appeared recently in the literature. [97f], Most of these complexes are based on ligand types L23 , L28 , and L30 . Additionally, there are a few other examples of dinuclear iridium(III) complexes.…”

“…Intriguingly, the cyclometalated complex displayed cooperative effects in the aforementioned transfer hydrogenation reaction. [100a] Attempts were made to synthesize a tri‐cyclometalated iridium(III) complex by making use of the ligand L28 . However, in this case, no cyclometalation was observed, with the central iridium(III) atoms binding only through the triazolylidene donors to form the trinuclear complex 99 .…”

Base free transfer hydrogenation using a covalent triazine framework based catalyst

“…Ir complexes involving a N-heterocycle carbene ligand, [5][6][7][8][9][10][11][12][13][14][15][16] or halfsandwich complexes with a Cp* ligand [17][18][19][20][21][22] Recently, Porous Organic Frameworks (POFs) have been gaining attention within catalytic and other applications. 56,57 Covalent Triazine Frameworks (CTFs), a subclass of POFs, are highly porous and stable solids made by trimerisation of aromatic nitriles.…”