Experimental and Theoretical Study on the Role of Monomeric vs Dimeric Rhodium Oxazolidinone Norbornadiene Complexes in Catalytic Asymmetric 1,2- and 1,4-Additions

Manuel Kirchhof,Deven P Estes,Angelika Baro,Michal Nowakowski,Katrin Gugeler,Karina Abitaev,Alina Bauer,Bernd Plietker,Thomas Sottmann,Yaseen Qawasmi,Johannes Kästner,Mark R Ringenberg,Marc Schnierle,Wolfgang Frey,Felix Richard Fischer,Matthias Bauer,Sonia Alvarez-Barcia,Sabine Laschat

doi:10.1021/acs.organomet.0c00310

Manuel Kirchhof, Deven P Estes + Show 16 more

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https://doi.org/10.1021/acs.organomet.0c00310

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Abstract

The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to N-tosylimines and 1,4-add...

Highlights

The pioneering discovery by Hayashi, Carreira, and Grützmacher that chiral alkene and diene ligands enable efficient stereocontrol in asymmetric catalysis has delivered highly attractive alternatives to well-known chiral phosphorus and nitrogen ligands.[1−4] A large variety of chiral diene ligands has been developed since .[4,5] The scope of Rh, Ir, or Pdcatalyzed reactions has been expanded from 1,2- and 1,4additions at electron-poor double bonds[6] to reductions,[7] cycloadditions,[8] isomerizations, rearrangements,[9] and carbene insertions into B−H bonds[10] among others.[11]
We found that, when employing slightly polar and diastereomerically pure norbornadiene oxazolidinone ligands, the catalytic reactions were sluggish in dioxane and almost ceased in toluene, while microemulsions markedly improved the conversion and enantioselectivity as well as reaction rate
We report for the first time an assessment of the catalytic performance of a series of structurally similar Rh complexes, which differ in their aggregation state and nuclearity

Summary

Introduction

The pioneering discovery by Hayashi, Carreira, and Grützmacher that chiral alkene and diene ligands enable efficient stereocontrol in asymmetric catalysis has delivered highly attractive alternatives to well-known chiral phosphorus and nitrogen ligands.[1−4] A large variety of chiral diene ligands has been developed since .[4,5] The scope of Rh-, Ir-, or Pdcatalyzed reactions has been expanded from 1,2- and 1,4additions at electron-poor double bonds[6] to reductions,[7] cycloadditions,[8] isomerizations, rearrangements,[9] and carbene insertions into B−H bonds[10] among others.[11] As far as Rh Ir) catalysis are concerned, the majority of studies has dealt with dinuclear catalyst precursors [Rh(diene*)Cl]2 or [(Ir(diene*)Cl]2, while less work has been carried out with mononuclear Rh complexes. Tetraphenylborates[15] and binaphthyldiamines.[16] Alternatively, tridentate chiral diene−phosphine ligands have been employed, where the phosphine moiety is tethered via an electron-deficient alkene to the diene, resulting in a chelating coordination mode that stabilizes the active cationic Rh(I) catalyst.[17]

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