Acyclic Carbene Complexes Research Articles

Transition-metal acyclic carbene complexes: building blocks for luminescent, stimuli-responsive, bioactive materials and catalysts

Acyclic carbene complexes exhibit exceptional performance and functional properties comparable to their NHC counterparts, and their environmentally sensitive open acyclic carbene structure makes them ideal for developing smart materials and sensors.

Development of Dual Phosphorescent Materials Based on Multiple Stimuli-Responsive Ir(III) Acyclic Carbene Complexes

A new series of Ir(III) carbene complexes with luminescent mechanochromism derived from trans–cis isomerization has been developed. Through the introduction of π-conjugating groups into the acyclic...

Luminescent monomeric and dimeric Ru(ii) acyclic carbene complexes as selective sensors for NH3/amine vapor and humidity.

A new class of luminescent bis(bipyridyl) Ru(ii) pyridyl acyclic carbene complexes with environmentally-sensitive dimerization equilibrium have been developed. Owing to the involvement of the orbitals of the diaminocarbene ligand in the emissive excited state, the phosphorescence properties of these complexes are strongly affected by H-bonding interactions with various H-bonding donor/acceptor molecules. With the remarkable differences in the emission properties of the monomer, dimer, and H-bonded amine adducts together with the change of the dimerization equilibrium, these complexes can be used as luminescent gas sensors for humidity, ammonia, and amine vapors. With the responses to amines and humidity and the corresponding change in the luminescence properties, a proof-of-principle for binary optical data storage with a reversible concealment process has been described.

Mechanochemical changes on cyclometalated Ir(iii) acyclic carbene complexes – design and tuning of luminescent mechanochromic transition metal complexes

A new class of luminescent cyclometalated Ir(iii) complexes with readily tunable mechanochromic properties derived from the mechanically induced trans-to-cis isomerization have been developed.

Synthesis, structure and cytotoxicity of cyclic (alkyl)(amino) carbene and acyclic carbene complexes of group 11 metals.

A series of complexes of cyclic (alkyl)(amino)carbene (CAAC) complexes of copper, silver and gold have been investigated for their antiproliferative properties. A second series of acyclic carbene (ACC) complexes of gold(i) were prepared by nucleophilic attack on isocyanide complexes by amines and amino esters, to give (ACC)AuCl, [(ACC)Au(PTA)]+ (PTA = triazaphosphaadamantane), as well as mixed-carbene compounds [(CAAC)Au(ACC)]+. Representative complexes were characterised by X-ray diffraction which confirmed the mononuclear linear structures without close intermolecular contacts or aurophilic interactions. The redox properties of these complexes have been determined. The compounds were tested against a panel of human cancer cell lines including leukemia (HL 60), breast adenocarcinoma cells (MCF-7) and human lung adenocarcinoma epithelial cell lines (A549), which show varying degrees of cisplatin resistance. The pro-ligand iminium salts and the PTA complexes were non-toxic. By contrast, the CAAC complexes show high cytotoxicity, with IC50 values in the sub-micromolar to ∼100 nanomolar range, even against cisplatin-insensitive MCF-7 and A549 cells. Cationic bis-carbene complexes [(Me2CAAC)2M]+ (6-8, M = Cu, Ag and Au) proved particularly effective. The mechanism of cell growth control by these complexes remains to be established, although possible modes of action such as inhibition of thioredoxin reductase (TrxR), which is a common pathway for gold NHC compounds, or the formation of reactive oxygen species (ROS) through redox processes, could be ruled out as primary pathways.

(C^Npz^C)AuIII complexes of acyclic carbene ligands: synthesis and anticancer properties.

A series of cyclometallated gold(iii) complexes supported by pyrazine-based (C^Npz^C)-type pincer ligands were synthesized via two different pathways. Nucleophilic attack on the isocyanide complex [(C^Npz^C)Au(C[triple bond, length as m-dash]NC6H3Me2-2,6)]SbF6 (2) gave [(C^Npz^C)Au(ACC)]SbF6 complexes with aniline (4·SbF6), adamantylamine (5), glycine ethyl ester (6), alanine methyl ester (7), valine methyl ester (8), phenylglycine methyl ester (9) and methionine methyl ester (10) substituents (ACC = acyclic carbene). The pathway via isocyanide insertion into gold-amide bonds was also investigated; e.g. the reaction of xylyl isocyanide with (C^Npz^C)AuNHPh followed by protonation with HBF4·OEt2 gave the acyclic carbene complex 4·BF4. To the best of our knowledge compounds 6-10 represent the first examples of gold(iii) acyclic carbene complexes bearing amino acid functions. The compounds provide a versatile platform for the study of the anti-proliferative properties of gold(iii) complexes. Tests against human adenoma-type lung cancer cells identified 5, 6, 7 and 10 as particularly promising and demonstrate the synthetic flexibility of acyclic carbene complexes and the potential of that class of compounds for anticancer applications. Compared to cisplatin, amino ester-containing ACC complexes showed improved selectivity for MCF-7 breast cancer cells over that for healthy fibroblasts.

Synthesis and Properties of Hydrazino Amino Acyclic Carbenes of Gold(I), Platinum(II), Palladium(II) and Rhodium(III)

AbstractThe nucleophilic addition of protected and substituted hydrazine derivatives to isonitrile complexes of gold(I), platinum(II), palladium(II) and rhodium(III) provides the corresponding hydrazino amino acyclic carbene complexes. These are characterized by their spectroscopic data, four different X‐ray single crystal structure analyses and their catalytic activity in the gold(I)‐catalyzed cycloisomerization of N‐propargylcarboxamides to alkylideneoxazolines is investigated.magnified image

Deconstructing Selectivity in the Gold-Promoted Cyclization of Alkynyl Benzothioamides to Six-Membered Mesoionic Carbene or Acyclic Carbene Complexes

We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by AuI and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au–C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom.