Chiral Cyclic Alkyl Amino Carbene (CAAC) Transition-Metal Complexes: Synthesis, Structural Analysis, and Evaluation in Asymmetric Catalysis
Adrien Madron du Vigné, Nicolai Cramer
Abstract
Despite recent advances in the field of cyclic alkyl amino carbenes (CAACs) including a few complementary synthetic strategies affording CAACs with various substitution patterns, the application potential of chiral CAACs to efficiently catalyze asymmetric organometallic transformations remains largely underdeveloped. Herein, we describe a convenient and robust route that incorporates common chiral primary amine allowing access of a broad range of chiral CAACs precursors. The corresponding transition-metal complexes with Cu, Au, Ru, Rh, Ir, and Pd were obtained in a straightforward manner. The steric parameters of the complexes were comprehensively collected by X-ray single-crystal analysis to serve as a source of information for further ligand design. The preliminary application potential of the copper CAAC complexes was tested in asymmetric conjugate borylation of an α,β-unsaturated ester providing 89:11 er, thus illustrating the potential of chiral CAACs in asymmetric catalysis.