Coinage metal complexes of N‐heterocyclic carbene bearing nitrile functionalization: Synthesis and photophysical properties

N-Heterocyclic Carbene-Borane Adducts with Chiral (R)-Chloroethyl and Vinyl Substituents

This research provides how chiral imidazolium salts {1,3-bis[1'-chloro-1'-phenylpropan-2'-yl]-imidazolium} (1a) and enantiopure {1,3-bis[(R)-1-chlorobutan-2-yl]-imidazolium} [1b] can be utilized in diverse synthetic pathways to obtain new carbene-borane adducts (2a-2d): {1,3-bis[1'-chloro-1'-phenylpropan-2'-yl]-imidazolyl-2-ylidene-borane} (2a), {1,3-bis[(Z)-1'-phenylpropen-2'-yl]-imidazolyl-2-ylidene-borane} (2b), {1,3-bis[(R)-1-chlorobutan-2-yl]-imidazolyl-2-ylidene-borane} (2c), and {1,3-bis[but-1-en-2-yl]-imidazolyl-2-ylidene-borane} (2d). The carbene-borane adducts were synthesized and characterized by 13C, 1H, and 11B nuclear magnetic resonance spectroscopy and time-of-flight mass spectrometry. The X-ray crystal analyses of compounds 2a and 2b were performed, and to understand the structure and interactions of 2a, a computational study was carried out. The effect of N-substituents in the NHC-borane adducts was clearly observed in the C-B bond lengths obtained by single-crystal X-ray diffraction, where the C-B bond is longer for adducts with N-(R)-chloroethyl substituents than for vinyl substituents. The analysis of the reduced density gradient and the bond critical point calculations of 2a showed intramolecular proton-hydride and Cl···N interactions. These chiral imidazolium salts could have applicability in the development of new materials and possibly in pharmaceutical research.

Acridine N-Heterocyclic Carbene Gold(I) Compounds: Tuning from Yellow to Blue Luminescence

The synthesis and the luminescence features of three gold(I)-N-heterocyclic carbene (NHC) complexes are presented to study how the n-alkyl group can influence the luminescence properties in the crystalline state. The mononuclear gold(I)-NHC complexes, [(L¹ )Au(Cl)] (1), [(L² )Au(Cl)] (2), and [(L³ )Au(Cl)] (3) were isolated from the reactions between [(tht)AuCl] and corresponding NHC ligand precursors, [N-(9-acridinyl)-N'-(n-butyl)-imidazolium chloride, (L¹ .HCl)], [N-(9-acridinyl)-N'-(n-pentyl)-imidazolium chloride, (L² .HCl)] and [N-(9-acridinyl)-N'-(n-hexyl)-imidazolium chloride, (L³ .HCl)]. Their single-crystal X-ray analysis reveals the influence of the n-alkyl groups on solid-state packing. A comparison of the luminescence features of 1-3 with n-alkyl substituents is explored. The molecules 1-3 depicted blue emission in the solution state, while the yellow emission (for 1), greenish-yellow emission (for 2), and blue emission (for 3) in the crystalline phase. This paradigm emission shift arises from n-butyl to n-pentyl and n-hexyl in the crystalline state due to the carbon-carbon rotation of the n-alkyl group, which tends to promote unusual solid packing. Hence n-alkyl group adds a novel emission property in the crystalline state. Density Functional Theory and Time-Dependent Density Functional Theory calculations were carried out for monomeric complex, N-(9-acridinyl)-N'-(n-heptyl)imidazole-2-ylidene gold(I) chloride and dimeric complex, N-(9-acridinyl)-N'-(n-heptyl)imidazole-2-ylidene gold(I) chloride to understand the structural and electronic properties.

Antiproliferative Activity of Functionalized Histidine-derived Au(I) bis-NHC Complexes for Bioconjugation

A series of histidine derived Au(I) bis-NHC complexes bearing different ester, amide and carboxylic acid functionalities as well as wingtip substituents is synthesized and characterized. The stability in aqueous media, in vitro cytotoxicity in a set of cancer cell lines (MCF7, PC3 and A2780/A2780cisR) along with the cellular uptake are evaluated. Stability tests suggest hydrolysis of the ester within 8 h, which might lead to deactivation. Furthermore, the bis-NHC system shows a sufficient stability against cysteine and the thiol containing peptide GSH. The benzyl ester and amide show the highest activity comparable to the benchmark compound cisplatin, with the ester only displaying a slightly lower cytotoxicity than the amide. A cellular uptake study revealed that the benzyl ester and the amide could have different intracellular distribution profiles but both complexes induce perturbations of the cellular physiological processes. The simple modifiability and high stability of the complexes provides a promising system for upcoming post modifications to enable targeted cancer therapy.