A Readily Available Chiral Ag-Based N-Heterocyclic Carbene Complex for Use in Efficient and Highly Enantioselective Ru-Catalyzed Olefin Metathesis and Cu-Catalyzed Allylic Alkylation Reactions

A new chiral bidentate N-heterocyclic carbene (NHC) ligand has been designed and synthesized.
The NHC ligand bears a chiral diamine backbone and an achiral biphenol group; upon metal complexation
(derived from Ag(I), Ru(II), or Cu(II)), the diamine moiety induces >98% diastereoselectivity such that the
biaryl unit coordinates to the metal center to afford the desired complex as a single atropisomer. Because
the ligand does not require optically pure biaryl amino alcohols, its synthesis is significantly shorter and
simpler than the related first generation ligands bearing a chiral binaphthyl-based amino alcohol. The chiral
NHC ligand can be used in the preparation of highly effective Ru- and Cu-based complexes (prepared and
used in situ from the Ag(I) carbene) that promote enantioselective olefin metathesis and allylic alkylations
with scope that is improved from previously reported protocols. In many cases, transformations promoted
by the chiral NHC-based complexes proceed with higher enantioselectivity and reactivity than was observed
with previously reported complexes.