Gold Complexes of an Alicyclic Indazole-Derived N-Heterocyclic Carbene: Syntheses, Characterizations, and Ligand Disproportionation

Sivaram, Haresh; Jothibasu, Ramasamy; Huynh, Han Vinh

doi:10.1021/om201268m

Cited by 36 publications

(32 citation statements)

References 56 publications

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“… 37 Although NHCs are regarded as stronger σ-donor ligands than phosphines and are expected to form stronger bonds to the metal center, ligand scrambling reaction products have already been observed upon crystallization. 38 , 39 …”

Section: Introductionmentioning

confidence: 99%

N-Heterocyclic Carbene Gold(I) Complexes: Mechanism of the Ligand Scrambling Reaction and Their Oxidation to Gold(III) in Aqueous Solutions

et al. 2020

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N -Heterocyclic carbene (NHC) gold(I) complexes offer great prospects in medicinal chemistry as antiproliferative, anticancer, and antibacterial agents. However, further development requires a thorough understanding of their reaction behavior in aqueous media. Herein, we report the conversion of the bromido[3-ethyl-4-(4-methoxyphenyl)-5-(2-methoxypyridin-5-yl)-1-propylimidazol-2-ylidene]gold(I) ((NHC)Au I Br, 1 ) complex in acetonitrile/water mixtures to the bis[3-ethyl-4-(4-methoxyphenyl)-5-(2-methoxypyridin-5-yl)-1-propylimidazol-2-ylidene]gold(I) ([(NHC) 2 Au I ] + , 7 ), which is subsequently oxidized to the dibromidobis[3-ethyl-4-(4-methoxyphenyl)-5-(2-methoxypyridin-5-yl)-1-propylimidazol-2-ylidene]gold(III) ([(NHC) 2 Au III Br 2 ] + , 9 ). By combining experimental data from HPLC, NMR, and (LC-)/HR-MS with computational results from DFT calculations, we outline a detailed ligand scrambling reaction mechanism. The key step is the formation of the stacked ((NHC)Au I Br) 2 dimer ( 2 ) that rearranges to the T-shaped intermediate Br(NHC) 2 Au I –Au I Br ( 3 ). The dissociation of Br – from 3 and recombination lead to (NHC) 2 Au I –Au I Br 2 ( 5 ) followed by the separation into [(NHC) 2 Au I ] + ( 7 ) and [Au I Br 2 ] − ( 8 ). [Au I Br 2 ] − is not stable in an aqueous environment and degrades in an internal redox reaction to Au 0 and Br 2 . The latter in turn oxidizes 7 to the gold(III) species 9 . The reported ligand rearrangement of the (NHC)Au I Br complex differs from that found for related silver(I) analogous. A detailed understanding of this scrambling mechanism is of utmost importance for the interpretation of their biological activity and will help to further optimize them for biomedical and other applications.

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Section: Introductionmentioning

confidence: 99%

N-Heterocyclic Carbene Gold(I) Complexes: Mechanism of the Ligand Scrambling Reaction and Their Oxidation to Gold(III) in Aqueous Solutions

et al. 2020

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“…As expected, 8-Mes is bulkier than 7-Mes (43.1), 17 but smaller % V bur values were also determined for 9-Mes (43.6) and 10-Mes (43.3) using their [AuCl(erNHC)] complexes. 18 As for other gold(I) erNHC complexes, ligand disproportionation 22,23 was not observed for complex 3 upon prolonged standing in solution.…”

Section: ■ Introductionmentioning

confidence: 99%

Gold(I) and Gold(III) Complexes of Expanded-Ring N-Heterocyclic Carbenes: Structure, Reactivity, and Catalytic Applications

et al. 2019

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The oxidative addition of bromine to homo-and heterobis(carbene) gold(I) complexes 1−6 containing expanded-ring Nheterocyclic carbene (erNHC) ligands was explored to prepare the first examples of gold(III) erNHC complexes. The use of stoichiometric amounts of bromine consistently gave clean gold-centered oxidations leading to the isolation of monocarbene and mixed carbene complexes of the type [AuBr 3 (erNHC)] (7−9) and trans-[AuBr 2 ( i Pr 2 -bimy)(erNHC)]-BF 4 (13−15), respectively. The use of excess bromine additionally led to ligand brominations in the monocarbene series affording [Au-Br 3 (erNHC Br2 )] complexes (10−12), while in the case of the heterobis-(carbene) series, tribromide complexes of the type trans-[AuBr 2 ( i Pr 2bimy)(erNHC)]Br 3 (16−18) were obtained instead. Comparison of the catalytic activities of all complexes in the hydroamination of alkynes revealed the superior performance of mono-erNHC complexes in all cases.

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“…Similarly another reagent Br-(CH 2 ) 4 -Br in acetonitrile is reported in good yield (Scheme-73) [87].…”

Section: Scheme-71mentioning

confidence: 98%

Synthesis of indazole motifs and their medicinal importance: An overview

Gaikwad¹,

Chapolikar²,

Devkate³

et al. 2015

European Journal of Medicinal Chemistry

283

115

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Gold Complexes of an Alicyclic Indazole-Derived N-Heterocyclic Carbene: Syntheses, Characterizations, and Ligand Disproportionation

Cited by 36 publications

References 56 publications

N-Heterocyclic Carbene Gold(I) Complexes: Mechanism of the Ligand Scrambling Reaction and Their Oxidation to Gold(III) in Aqueous Solutions

N-Heterocyclic Carbene Gold(I) Complexes: Mechanism of the Ligand Scrambling Reaction and Their Oxidation to Gold(III) in Aqueous Solutions

Gold(I) and Gold(III) Complexes of Expanded-Ring N-Heterocyclic Carbenes: Structure, Reactivity, and Catalytic Applications

Synthesis of indazole motifs and their medicinal importance: An overview

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