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The reactivity of bidentate AuIII–Cl species, [(C^N)AuCl2], with a bisphosphine or carbon donor ligands results in reductive elimination. Combined experimental and computational investigations lead to the first evidence of a direct intramolecular C(sp2)–N(sp2) bond formation from a monomeric [(C^N)AuCl2] gold(iii) complex. We show that bidentate ligated Au(iii) systems bypass transmetallation to form C(sp2)–N(sp2) species and NHC–Au–Cl. Mechanistic investigations of the reported transformation reveal a ligand-induced reductive elimination via a key AuIII intermediate. Kinetic studies of the reaction support a second-order rate process. [ABSTRACT FROM AUTHOR]

The reactivity of tetrachloroauric acid (HAuCl4) with readily accessible bidentate N-donor ligands affords N,N-ligated Au(iii) center complexes. These compounds are useful precursors of stable catalysts, anticancer agents, and building blocks for materials. This report provides detailed insight into intermediates, equilibria, the counter anion effect, and structural variability, using spectroscopy, crystallography and computational tools. Novel mixed-valence Au(i) and Au(iii) complexes [Au(o-phen)Cl2]2[AuCl2][AuCl4] and [Au(o-phen)Cl2][AuCl2] having AuCl2− and AuCl4− anions linearly arranged in the axial sites of the square-planar Au(o-phen)Cl2 cation were discovered. Other competing side products of the reaction studied revealed protonated N,N-bidentate ligands with AuCl4− anions. Quantitative variable temperature NMR studies reveal that for a mixture of target Au(iii) salt and the protonated ligand, the reaction favors the irreversible formation of the side product. Using a rapid (30 min) temperature controlled protocol, the desired coordinated species is accessible in respectable yields while avoiding side products. [ABSTRACT FROM AUTHOR]

Herein is reported the synthesis of two Au(III) complexes bearing the (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (R,R-QuinoxP*) or (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxaline (S,S-QuinoxP*) ligands. By reacting two stoichiometric equivalents of HAuCl4.3H2O to one equivalent of the corresponding QuinoxP* ligand, (R,R)-(–)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (1) and (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) were formed, respectively, in moderate yields. The structure of (S,S)-(+)-2,3-Bis(tert-butylmethylphosphino)quinoxalinedichlorogold(III) tetrachloroaurates(III) (2) was further confirmed by X-ray crystallography. The antiproliferative activities of the two compounds were evaluated in a panel of cell lines and exhibited promising results comparable to auranofin and cisplatin with IC50 values between 1.08 and 4.83 µM. It is noteworthy that in comparison to other platinum and ruthenium enantiomeric complexes, the two enantiomers (1 and 2) do not exhibit different cytotoxic effects. The compounds exhibited stability in biologically relevant media over 48 h as well as inert reactivity to excess glutathione at 37 °C. These results demonstrate that the Au(III) atom, stabilized by the QuinoxP* ligand, can provide exciting compounds for novel anticancer drugs. These complexes provide a new scaffold to further develop a robust and diverse library of chiral phosphorus Au(III) complexes. [ABSTRACT FROM AUTHOR]

Glioblastoma multiforme (GBM) is the most lethal brain cancer subtype, often advanced by the time of initial diagnosis. Existing treatment modalities including surgery, chemotherapy and radiation have been stymied by recurrence, metastasis, drug resistance and brain targetability. Here, we report a geometrically distinct Au(i) complex ligated by N^N-bidentate ligands and supported by a N-heterocyclic ligand that modulates mitochondrial morphology to inhibit GBM in vitro and in vivo . This work benefits from the facile preparation of anti-GBM Au(i)-NHC complexes., Competing Interests: Samuel G. Awuah reports that financial support was provided by University of Kentucky. Samuel G. Awuah reports a relationship with University of Kentucky that includes funding grants. Samuel G. Awuah has patents pending in the University of Kentucky Research Foundation., (This journal is © The Royal Society of Chemistry.)

The anti-breast cancer stem cell (CSC) properties of a series of gold(i) complexes comprising various non-steroidal anti-inflammatory drugs (NSAIDs) and triphenylphosphine 1-8 are reported. The most effective gold(i)-NSAID complex 1, containing indomethacin, exhibits greater potency for breast CSCs than bulk breast cancer cells (up to 80-fold). Furthermore, 1 reduces mammosphere viability to a better extent than a panel of clinically used breast cancer drugs and salinomycin, an established anti-breast CSC agent. Mechanistic studies suggest 1-induced breast CSC death results from breast CSC entry, cytoplasm localisation, an increase in intracellular reactive oxygen species levels, cyclooxygenase-2 downregulation and inhibition, and apoptosis. Remarkably, 1 also significantly inhibits tumour growth in a murine metastatic triple-negative breast cancer model. To the best of our knowledge, 1 is the first gold complex of any geometry or oxidation state to demonstrate anti-breast CSC properties., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Imidazolium salts are common building blocks for functional materials and in the synthesis of N-heterocyclic carbene (NHC) as σ-donor ligands for stable metal complexes. The title salt, 1,3-bis-(4-hy-droxy-phen-yl)-1 H -imidazol-3-ium chloride (IOH·Cl), C 15 H 13 N 2 O 2 + ·Cl - a two-step procedure involving a di-aza-butadiene precursor followed by ring closure using tri-methylchloro-silane and paraformaldehyde. The structure of IOH·Cl consists of a central planar imidazolium ring (r.m.s. deviation = 0.0015 Å), with out-of-plane phenolic side arms. The dihedral angles between the 4-hy-droxy-phenyl substituents and the imidazole ring are 55.27 (7) and 48.85 (11)°. In the crystal, O-H⋯Cl hydrogen bonds connect the distal hy-droxy groups and Cl via a two-step procedure involving a di-aza-butadiene precursor followed by ring closure using tri-methylchloro-silane and paraformaldehyde. The structure of IOH·Cl consists of a central planar imidazolium ring (r.m.s. deviation = 0.0015 Å), with out-of-plane phenolic side arms. The dihedral angles between the 4-hy-droxy-phenyl substituents and the imidazole ring are 55.27 (7) and 48.85 (11)°. In the crystal, O-H⋯Cl hydrogen bonds connect the distal hy-droxy groups and Cl - anions in adjacent asymmetric units, one related by inversion (- x  + 1, - y  + 1, - z  + 1) and one by the n -glide ( x  - , - y  + , z  - ), with donor-acceptor distances of 2.977 (2) and 3.0130 (18) Å, respectively. The phenolic rings are each π-π stacked with their respective inversion-related [(- x  + 1, - y  + 1, - z  + 1) and (- x , - y  + 1, - z  + 1)] counterparts, with inter-planar distances of 3.560 (3) and 3.778 (3) Å. The only other noteworthy inter-molecular inter-action is an O⋯O (not hydrogen bonded) close contact of 2.999 (3) Å between crystallographically different hy-droxy O atoms on translationally adjacent mol-ecules ( x  + 1, y , x  + 1).

The reactivity of bidentate AuIII-Cl species, [(C^N)AuCl2], with a bisphosphine or carbon donor ligands results in reductive elimination. Combined experimental and computational investigations lead to the first evidence of a direct intramolecular C(sp2)-N(sp2) bond formation from a monomeric [(C^N)AuCl2] gold(iii) complex. We show that bidentate ligated Au(iii) systems bypass transmetallation to form C(sp2)-N(sp2) species and NHC-Au-Cl. Mechanistic investigations of the reported transformation reveal a ligand-induced reductive elimination via a key AuIII intermediate. Kinetic studies of the reaction support a second-order rate process.