Pentamethylcyclopentadienyl Ir(III) metallacycles: recent developments in catalysis
Iridium (III) metallacycles have been applied successfully in organic transformations and in processes relevant to energy and environmental sciences. The ongoing interest for these complexes and their corresponding catalysts has led to new developments taking a strong advantage of the properties imparted by the chelate carboligand. Recent publications in this field are highlighted in order to underline the usefulness of such catalysts in oxygen and hydrogen production as well as for hydrodefluorination and hydrosilylation reactions for the synthesis of bulk and fine chemicals.
Over the past decade, transition-metal-catalysed C-H activation has allowed various ortho-selective C-C and C-X bond-forming reactions through in situ generation of metallacycle intermediates (1). Although C-H activation and its applications have been quite developed for ruthenium and rhodium, they have been far less studied for iridium, which has nevertheless attracted a rising interest in the past years (1). Since the 1960’s, the cyclometallation reaction has provided an easy access to original organometallic compounds bearing a metal-carbon σ bond as part of one chelate carboligand (2). The C-H (or C-C) bond activation required by the cyclometallation process is assisted intramolecularly by coordination of a directing donor atom (for example N, P, O or C). As a result, complexes bearing such ligands are displaying increased stability with exclusive reactivity. Recently, half-sandwich (i.e. pentamethylcyclopentadienyl, Cp*) iridium (III) metallacycles have demonstrated a great potential in homogeneous catalysis and displayed significant activities for a range of organic reactions. In two recent reviews, the applications of Cp* iridium(I ...