Enantiospecific Synthesis of Planar Chiral Rhodium and Iridium Cyclopentadienyl Complexes: Enabling Streamlined and Computer-Guided Access to Highly Selective Catalysts for Asymmetric C–H Functionalizations
Sebastian Young Ye, Aragorn Laverny, Matthew D. Wodrich, Rubén Laplaza, Farzaneh Fadaei‐Tirani, Rosario Scopelliti, Clémence Corminbœuf, Nicolai Cramer
Abstract
High Resolution Image Download MS PowerPoint Slide Chiral cyclopentadienyl (Cp X ) metal complexes are frequently used in asymmetric catalysis by virtue of their high reactivity and selectivity. Planar-chiral-only rhodium and iridium cyclopentadienyl complexes are particularly promising due to unrestricted chemical space for Cp X ligand design while retaining structural simplicity. However, they are currently still niche because of a lack of efficient synthetic strategies that avoid lengthy chiral auxiliary routes or chiral preparatory HPLC resolution of the complexes. To streamline access to such planar-chiral-only Cp X -metal complexes, we designed a straightforward, highly enantiospecific, point-to-planar chirality transfer complexation via facially selective concerted-metalation-deprotonation between metal-carboxylate precursor [M(olefin) 2 OAc] 2 and a chiral cyclopentadiene. This entirely avoids the typical stereoablative complexation of an achiral cyclopentadienyl anion that detrimentally yields a racemate. Exploiting the described enantiospecific complexation protocol and a simple divergent synthetic route to suitable chiral cyclopentadienes, we generated a structurally diverse library of new planar chiral Cp-Rh(I), Cp-Ir(I), Cp-Rh(III), and Cp-Ir(III) complexes. Moreover, the enantiospecific complexation step can be concatenated with a preceding Au-catalyzed cyclization in an efficient one-pot process that likely involves an elaborate point-to-axial-to-point-to-planar chirality transfer. Guided by computational selectivity predictions, the structure of a Cp X -Rh complex in our library was tuned to optimize reactivity and selectivity in the asymmetric C–H functionalization of a benzamide with various challenging alkenes. With an optimized Cp X -Rh complex in hand, we showcased its excellent catalytic performance and high selectivity for refractory alkene substrates that reacted in poor selectivity with previous Cp X -Rh catalysts.