Effect of axial ligands on iridium(III) porphyrin complexes towards catalytic carbene C–H insertions

Abstract

Direct C–H functionalization has continued to be a hot research topic in the recent decade because of the huge abundance of C–H bonds in organic molecules and the high atom-economy of this methodology. However, the high C–H bond energy and selectivity among primary / secondary / tertiary saturated C–H bonds in a single organic molecule remain the major challenges in achieving selective C–H functionalization with practical interest. In our endeavour of developing robust metalloporphyrin catalysts for selective carbene C–H insertion reactions, herein we present our work on the inter- and intramolecular carbene C–H insertions using iridium(III) porphyrin complexes as catalysts. The incorporation of carbon-based axial ligands, such as –Me, –Ph and –C≡CPh, was found to elevate the catalytic activity of iridium(III) porphyrin complexes towards inter- and intramolecular carbene C–H insertions. With the use of a D4-symmetric Halterman porphyrin ligand, enantioselective carbene C–H insertion was achieved to give the desired products in moderate to excellent isolated yields (up to 87%) with good to excellent enantioselectivity (up to 78% enantiomeric excess).