Redox-Switchable Complexes Based on Nanographene-NHCs.

A series of rhodium and iridium complexes with a N-heterocyclic carbene (NHC) ligand decorated with a perylene-diimide-pyrene moiety are described. Electrochemical studies reveal that the complexes can undergo two successive one-electron reduction events, associated to the reduction of the PDI moiety attached to the NHC ligand. The reduction of the ligand produces a significant increase on its electron-donating character, as observed from the infrared spectroelectrochemical studies. The rhodium complex was tested in the [3+2] cycloaddition of diphenylcyclopropenone and methylphenylacetylene, where it displayed a redox-switchable behavior. The neutral complex showed moderate activity, which was suppressed when the catalyst was reduced.

Redox-Switchable Cycloisomerization of Alkynoic Acids with Napthalenediimide-Derived N-Heterocyclic Carbene Complexes.

Two naphthalene-diimide (NDI) bis-imidazolium salts have been used as N-heterocyclic carbene (NHC) precursors for the preparation of NDI-functionalized complexes of rhodium and iridium of general formula [MCl(NDI-NHC)(COD)] (M=Rh, Ir; NDI-NHC=NDI-functionalized NHC ligand). Comparison of the IR spectra of the complexes [IrCl(NDI-NHC)(CO)2 ] and their related one- and two-electron reduced forms, reveal that each one-electron reduction produces a decrease of the average ν(CO) of 9-10 cm-1 , indicating a significant enhancement of the electron-richness of the metal. The [MCl(NDI-NHC)(COD)] complexes were tested in the catalytic cycloisomerization of alkynoic acids. The one-electron reduced forms showed greatly enhanced activities. For the cyclization of 5-hexynoic acid, the two-electron reduction of the ligand produced further enhancement of the catalytic activity, therefore showing that the catalyst can switch between three redox species with three distinct catalytic activities.

Metal organic framework top-down and bottom-up patterning techniques.

Metal organic frameworks (MOFs) have recently attracted considerable research interest in several fields from coordination chemistry and materials science to engineering and medicine not only due to energy and environmental issues but also due to the need for new paradigms of efficiency and sustainability according to the requirements of the 21st century global society. Because of their crystalline and organic-inorganic nature, they are able to crystallize constituting intergrown architectures ductile enough to be patterned, with the use of appropriate techniques, as nano- and micro-devices with multiple applications. This perspective comprehensively summarizes the recent state of the art in the use of top-down and bottom-up methodologies to create MOF structures with a defined pattern at the nano- and micro-scale.