The synthesis and characterization by X-ray crystallography of the complexes [Ir(cod)(py)(L)]PF6 (L = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (2); L = IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (3); L = ICy, 1,3-bis(cyclohexyl)imidazol-2-ylidene (4)) are reported. Complexes 2−4 have been employed as catalysts for transfer hydrogenation reactions from 2-propanol to a number of unsaturated substrates and their activity compared with that of the related cationic iridium(I) species [Ir(cod)(py)(SIMes)]PF6 (1), [Ir(cod)(py)(PCy3)]PF6 (5), and complexes formed in situ from [Ir(cod)(py)2]PF6 and diazabutadienes (RNCHCHNR, DAB-R; R = cyclohexyl, DAB-Cy; R = 2,4,6-trimethylphenyl, DAB-Mes; R = adamantyl, DAB-Ad; R = 2,4,6-trimethoxyphenyl, DAB-trimethoxyphenyl). All complexes tested were found to be active catalysts for transfer hydrogenation of ketones, with complex 4 displaying the highest activity. Complex 4 also exhibits moderate activity toward simple olefins and an aromatic nitro co...

Cationic iridium complexes bearing imidazol-2-ylidene ligands as transfer hydrogenation catalysts

A new palladium complex series with N-heterocyclic carbene (NHC), pyridine and phosphine ligands, PdCl2(L)NHC (2a–c)(L = NHC), PdCl2(L1)NHC(3a–c)(L1 = pyridine), PdCl2(L2)NHC(4a–c)(L2 = triphenylphosphine) was synthesised and fully characterized. The catalytic activities of these complexes were screened for the Sonogashira and Suzuki–Miyaura reactions between arylhalides and phenylacetylene, and phenylboronic acid, respectively. The results pointed out that the carbene/phosphine complexes 4a–c exhibited excellent catalytic activities as compared to 2a–c, 3a–c, and the well-known systems for the palladium-catalysed Sonogashira reaction. The reactivity of 4a–c in these preliminary Sonogashira coupling tests seems to be higher than that of previously reported catalytic systems based on Pd(NHC) moieties. These new palladium NHC complexes are among the first reported palladium catalysts that are efficient for catalysing the Sonogashira reaction from arylchloride substrates.

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Synthesis and catalytic applications of palladium N-heterocyclic carbene complexes as efficient pre-catalysts for Suzuki-Miyaura and Sonogashira coupling reactions

Current advances on ruthenium(II) N-heterocyclic carbenes in hydrogenation reactions

Amidinatogermylene Metal Complexes as Homogeneous Catalysts in Alcoholic Media

To achieve a systems-based approach to targeting the antioxidant pathway, 1,4-naphthoquinone annulated N-heterocyclic carbene (NHC) [bis(1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i)] [silver(i) dichloride] (1), [bis(1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i)] chloride (2), and 1,3-dimesityl-4,5-naphthoquino-imidazol-2-ylidene)-gold(i) chloride (3)) were designed, synthesized, and tested for biological activity in a series of human cancer cell lines. The solution phase of complexes 1-3 were assigned using several spectroscopy techniques, including NMR spectroscopic analysis. Complexes 1 and 3 were further characterized by single crystal X-ray diffraction analysis. Electrochemical and spectroelectrochemical studies revealed that quinone reductions are reversible and that the electrochemically generated semiquinone and quinone dianions are stable under these conditions. Complex 1, containing two NHC-quinone moieties (to accentuate exogenous ROS via redox cycling) centered around a Au(i) center (to inactivate thioredoxin reductase (TrxR) irreversibly), was found to inhibit cancer cell proliferation to a much greater extent than the individual components (i.e., Au(i)-NHC alone or naphthoquinone alone). Treatment of A549 lung cancer cells with 1 produced a 27-fold increase in exogenous reactive oxygen species (ROS) which was found to localize to the mitochondria. The inhibition of TrxR, an essential mediator of ROS homeostasis, was achieved in the same cell line at low administrated concentrations of 1. TrxR inhibition by 1 was similar to that of auranofin, a gold(i) containing complex known to inhibit TrxR irreversibly. Complex 1 was found to induce cell death via an apoptotic mechanism as confirmed by annexin-V staining. Complex 1 was demonstrated to be efficacious in zebrafish bearing A549 xenografts. These results provide support for the suggestion that a dual targeting approach that involves reducing ROS tolerance while concurrently increasing ROS production can perturb antioxidant homeostasis, enhance cancer cell death in vitro, and reduce tumor burden in vivo, as inferred from preliminary zebra fish model studies.

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Dual targeting of the cancer antioxidant network with 1,4-naphthoquinone fused Gold(i) N-heterocyclic carbene complexes.

Synthesis, characterization and the Suzuki-Miyaura coupling reactions of N-heterocyclic carbene-Pd(II)-pyridine (PEPPSI) complexes

Novel ruthenium(II)– N -heterocyclic carbene complexes; synthesis, characterization and catalytic application

A series of new air and moisture-stable PEPPSI complexes are developed and evaluated for their catalytic performance in Suzuki cross-coupling reactions.

Çağlar Şahin

Papers

Synthesis, characterization and the Suzuki-Miyaura coupling reactions of N-heterocyclic carbene-Pd(II)-pyridine (PEPPSI) complexes

Novel ruthenium(II)– N -heterocyclic carbene complexes; synthesis, characterization and catalytic application

Synthesis, Characterization and the Suzuki—Miyaura Coupling Reactions of N-Heterocyclic Carbene—Pd(II)—Pyridine (PEPPSI) Complexes.