Enantiospecific Synthesis\nof Planar Chiral Rhodium\nand Iridium Cyclopentadienyl Complexes: Enabling Streamlined and Computer-Guided\nAccess to Highly Selective Catalysts for Asymmetric C–H Functionalizations

Chiral cyclopentadienyl\n(Cp<sup>X</sup>) metal complexes\nare frequently\nused in asymmetric catalysis by virtue of their high reactivity and\nselectivity. Planar-chiral-only rhodium and iridium cyclopentadienyl\ncomplexes are particularly promising due to unrestricted chemical\nspace for Cp<sup>X</sup> ligand design while retaining structural\nsimplicity. However, they are currently still niche because of a lack\nof efficient synthetic strategies that avoid lengthy chiral auxiliary\nroutes or chiral preparatory HPLC resolution of the complexes. To\nstreamline access to such planar-chiral-only Cp<sup>X</sup>-metal\ncomplexes, we designed a straightforward, highly enantiospecific,\npoint-to-planar chirality transfer complexation via facially selective\nconcerted-metalation-deprotonation between metal-carboxylate precursor\n[M(olefin)<sub>2</sub>OAc]<sub>2</sub> and a chiral cyclopentadiene.\nThis entirely avoids the typical stereoablative complexation of an\nachiral cyclopentadienyl anion that detrimentally yields a racemate.\nExploiting the described enantiospecific complexation protocol and\na simple divergent synthetic route to suitable chiral cyclopentadienes,\nwe generated a structurally diverse library of new planar chiral Cp-Rh(I),\nCp-Ir(I), Cp-Rh(III), and Cp-Ir(III) complexes. Moreover, the enantiospecific\ncomplexation step can be concatenated with a preceding Au-catalyzed\ncyclization in an efficient one-pot process that likely involves an\nelaborate point-to-axial-to-point-to-planar chirality transfer. Guided\nby computational selectivity predictions, the structure of a Cp<sup>X</sup>-Rh complex in our library was tuned to optimize reactivity\nand selectivity in the asymmetric C–H functionalization of\na benzamide with various challenging alkenes. With an optimized Cp<sup>X</sup>-Rh complex in hand, we showcased its excellent catalytic\nperformance and high selectivity for refractory alkene substrates\nthat reacted in poor selectivity with previous Cp<sup>X</sup>-Rh catalysts.