Catalytic oxygenation of sp3 "C-H" bonds with Ir(III) complexes of chelating triazoles and mesoionic carbenes.
Cp*-Ir(III) complexes with additional chelating ligands are known active pre-catalysts for the oxygenation of C-H bonds. We present here eight examples of such complexes where the denticity of the chelating ligands has been varied from the well-known 2,2'-bpy through pyridyl-triazole, bi-triazole to ligands containing pyridyl-triazolylidene, triazolyl-triazolylidene and bi-triazolylidenes. Additionally, we also compare the catalytic results to complexes containing chelating cyclometallated ligands with additional triazole or triazolylidene donors. Single crystal X-ray structural data are presented for all the new complexes that contain one or more triazolylidene donors of the mesoionic carbene type. We present the first example of a metal complex containing a chelating triazole-triazolylidene ligand. The results of the catalytic screening show that complexes containing unsymmetrical donors of the pyridyl-triazole or pyridyl-triazolylidene types are the most potent pre-catalysts for the C-H oxygenation of cyclooctane in the presence of either m-CPBA or NaIO4 as a sacrificial oxidant. These pre-catalysts can also be used to oxygenate C-H bonds in other substrates such as fluorene and ethyl benzene. The most potent pre-catalysts presented here work with a lower catalyst loading and under milder conditions while delivering better product yields in comparison with related literature known Ir(III) pre-catalysts. These results thus point to the potential of ligands with unsymmetrical donors obtained through the click reaction in oxidation catalysis.
Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, D-14195, Berlin, Germany. biprajit.sarkar@fu-berlin.de.
Stephan
S
Hohloch
Selina
S
Kaiser
Fenja Leena
FL
Duecker
Aljoša
A
Bolje
Ramananda
R
Maity
Janez
J
Košmrlj
Biprajit
B
Sarkar