Development of Functionalized N-Heterocyclic Carbene Ligands and Their Transition Metal Complexes

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C_2-Symmetric chiral bidentate NHC ligand precursors with o-xylylene framework and their Mo and Pd complexes were synthesized from chiral 1,2-bis(1-hydroxypropyl)benzene. Asymmetric allylic alkylation reaction using dimethyl malonate catalyzed by Pd complexes generated from the ligand precursors gave the corresponding product in good yield and enantioselectivity. Indenyl-functionalized BEt_3-adduct NHCs were prepared by the reaction of imidazolium pro-ligands with LiBEt_3H. This compound was converted into the indenyl-coordinate molybdenum complex dangling the NHC・BEt_3 moiety as a substituent. The stepwise coordination of NHC afforded a chelate-type mononuclear complex as well as a bimetallic complex.