Activation and deactivation of a robust immobilized Cp*Ir-transfer hydrogenation catalyst: a multielement in situ X-ray absorption spectroscopy study.

A highly robust immobilized [Cp*IrCl2]2 precatalyst on Wang resin for transfer hydrogenation, which can be recycled up to 30 times, was studied using a novel combination of X-ray absorption spectroscopy (XAS) at Ir L3-edge, Cl K-edge, and K K-edge. These culminate in in situ XAS experiments that link structural changes of the Ir complex with its catalytic activity and its deactivation. Mercury poisoning and "hot filtration" experiments ruled out leached Ir as the active catalyst. Spectroscopic evidence indicates the exchange of one chloride ligand with an alkoxide to generate the active precatalyst. The exchange of the second chloride ligand, however, leads to a potassium alkoxide-iridate species as the deactivated form of this immobilized catalyst. These findings could be widely applicable to the many homogeneous transfer hydrogenation catalysts with Cp*IrCl substructure.

Mechanistic and cytotoxicity studies of group IV ß-diketonate complexes.

Group IV metal complexes have previously shown promise as novel anticancer agents. Here, we discuss the mechanistic and cytotoxic nature of a series of group IV ß-diketonate coordination complexes. Clear evidence that the ligands are exchangeable on the metal centre and that the ß-diketonate ligands can act as potential drug delivery vehicles of the group IV metal ions was obtained. When evaluated for the cytotoxicity against human colon adenocarcinoma (HT-29) and human breast adenocarcinoma (MCF-7) cell lines, a general trend of decreasing potency down the group IV metals was observed. The most promising results obtained were for the hafnium complexes, with the tris diphenyl ß-diketonate hafnium complex exhibiting IC50 values of 4.9 ± 0.9 µM and 3.2 ± 0.3 µM against HT-29 and MCF-7, respectively, which are comparable with the activity of cisplatin against the same cell lines. This tri ß-diketonate hafnium complex is the first to show potent in vitro cytotoxic activity. The results reported show that ligand design has a significant effect on the cytotoxic potential of the complexes, and that these group IV complexes warrant further evaluation as novel metal-containing anticancer agents.

Rhodium, iridium, and ruthenium half-sandwich picolinamide complexes as anticancer agents.

Novel rhodium, iridium, and ruthenium half-sandwich complexes containing (N,N)-bound picolinamide ligands have been prepared for use as anticancer agents. The complexes show promising cytotoxicities, with the presence, position, and number of halides having a significant effect on the corresponding IC50 values. One ruthenium complex was found to be more cytotoxic than cisplatin on HT-29 and MCF-7 cells after 5 days and 1 h, respectively, and it remains active with MCF-7 cells even under hypoxic conditions, making it a promising candidate for in vivo studies.

A robust method to heterogenise and recycle group 9 catalysts.

This paper provides a viable, reproducible and robust method for immobilising hydroxyl tethered iridium-rhodium complexes. The materials have been shown to be both effective and recyclable in the process of catalytic transfer hydrogenation with minimal metal leaching.

Enhanced cytotoxicity of silver complexes bearing bidentate N-heterocyclic carbene ligands.

A diverse library of cationic silver complexes bearing bis(N-heterocyclic carbene) ligands have been prepared which exhibit cytotoxicity comparable to cisplatin against the adenocarcinomas MCF7 and DLD1. Bidentate ligands show enhanced cytotoxicity over monodentate and macrocyclic ligands.