Convenient in situ generation of a chiral bis-N-heterocyclic carbene palladium catalyst and its application in enantioselective synthesis

Abstract

To simplify catalytic reactions employing chelating bisNHC–metal complexes, studies were conducted to elucidate conditions for the in situ generation of a chiral chelating bisNHC–palladium catalyst from the corresponding diimidazolium salt. The method provides a convenient entry to catalytic reactions and eliminates catalyst preparation steps. In addition to the in situ prepared catalyst, for comparative purposes, isolable species were synthesized and characterized by NMR spectroscopy, combustion analysis, and single-crystal X-ray diffraction. Employing C2-symmetric ligands derived from trans-9,10-Dihydro-9,10-EthanoAnthracene-11,12-diyl (DEA) and trans-9,10-Dihydro-9,10-EthanoAnthracene-11,12-diylMethanediyl (DEAM), diNHC–Pd complexes were synthesized and tested for activity in enantioselective arylboronic acid addition to cyclic enones.