Water‐Soluble Luminescent Cyclometalated Gold(III) Complexes with cis‐Chelating Bis(N‐Heterocyclic Carbene) Ligands: Synthesis and Photophysical Properties

Abstract

A new class of cyclometalated Au(III) complexes containing various bidentate C-deprotonated C^N and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized and characterized. These are the first examples of Au(III) complexes supported by cis-chelating bis-NHC ligands. [Au(C^N)(bis-NHC)] complexes display emission in solutions under degassed condition at room temperature with emission maxima (λmax ) at 498-633 nm and emission quantum yields of up to 10.1 %. The emissions are assigned to triplet intraligand (IL) π→π* transitions of C^N ligands. The Au(III) complex containing a C^N (C-deprotonated naphthalene-substituted quinoline) ligand with extended π-conjugation exhibits prompt fluorescence and phosphorescence of comparable intensity with λmax at 454 and 611 nm respectively. With sulfonate-functionalized bis-NHC ligand, four water-soluble luminescent Au(III) complexes, including those displaying both fluorescence and phosphorescence, were prepared. They show similar photophysical properties in water when compared with their counterparts in acetonitrile. The long phosphorescence lifetime of the water-soluble AuIII complex with C-deprotonated naphthalene-substituted quinoline ligand renders it to function as ratiometric sensor for oxygen. Inhibitory activity of one of these water-soluble Au(III) complexes towards deubiquitinase (DUB) UCHL3 has been investigated; this complex also displayed a significant inhibitory activity with IC50 value of 0.15 μM.

Cyclometalated Gold(III) Complexes: Synthesis, Reactivity, and Physicochemical Properties

“…[80] An analogous series of compounds (83)(84)(85)w as obtained by Venkatesan and coworkers by using terminal alkynes in the presence of Et 3 Nand ac atalytic amount of CuI to attain the required ligand exchange (method B, Scheme 20). [80] An analogous series of compounds (83)(84)(85)w as obtained by Venkatesan and coworkers by using terminal alkynes in the presence of Et 3 Nand ac atalytic amount of CuI to attain the required ligand exchange (method B, Scheme 20).…”

“…[84] Complexes of type 89 show luminescence in solution (CH 3 CN) at room temperature with quantum yields of up to about 10 %. [84] Complexes of type 89 show luminescence in solution (CH 3 CN) at room temperature with quantum yields of up to about 10 %.…”

“…Second, strong s-donors generally enhance the splitting of non-emissive d-d states.I nf act, luminescent cyclometalated Ir III and Pt II dicyano complexes are known [82] but the luminescent [(C^N)Au III ]dicyano complexes 86-88 were reported only recently (Scheme 21). [83] These complexes were easily prepared by the reaction of the corresponding Au III dichloro precursors with NaBu 4 CN in MeCN/MeOH solvent mixtures.Unlike for the diaryl (74 and 75)a nd dialkynyl complexes (80)(81)(82)(83)(84)(85), where electronic tuning was required to obtain stable complexes,all of these compounds are stable and easy to handle.E ach complex shows ad ifferent emission maximum, which signalizes the participation of the C^N ligand in the excited state and the minimal involvement of the cyanide ligand, in sharp contrast to the behavior observed for Ir III and Pt II dicyano complexes.Although the compounds are only weak emitters in solution, PL quantum yields of up to 30 %w ere achieved in PMMA films,m aking these complexes apotential alternative to the less stable diaryl and dialkynyl Au III complexes shown in Schemes 18 and 20.…”

“…In 2014, Che and co-workers achieved the synthesis of the cyclometalated [(C^N)Au(NHC) 2 ]c omplexes 89 and 90 by transmetalation of the corresponding [(C^N)AuCl 2 ]p recursors with (NHC)Ag I salts (Scheme 22). [84] Complexes of type 89 show luminescence in solution (CH 3 CN) at room temperature with quantum yields of up to about 10 %. As in the previous cases,t he emissions were assigned to at riplet intraligand 3 IL(p-p*) transition of the…”

Multi-functional bis(alkynyl)gold(iii) N⁁C complexes with distinct mechanochromic luminescence and electroluminescence properties

“…Similar emission behavior has also been observed in other gold( iii ) complexes. 16 The lower-energy vibronic emission band at ca. 545 nm with vibrational progressional spacings of about 1200 cm –1 was found to have a long emission lifetime of ca.…”