Chiral Cyclopentadienyl Ligands: Design, Syntheses, and Applications in Asymmetric Catalysis

Abstract

The creation of new chiral ligands capable of providing high stereocontrol in metal-catalyzed reactions is crucial in modern organic synthesis.The production of bioactive molecules as single enantiomers is increasingly required, and asymmetric catalysis with metal complexes constitutes one of the most efficient synthetic strategies to access optically active compounds.H erein we offer ah istorical overview on the development of chiral derivatives of the ubiquitous cyclopentadienyl ligand (Cp X ), and detail their successful application in abroad range of metal-catalyzed transformations.Those include the functionalization of challenging C À Hb onds and beyond, giving access to an extensive catalogue of valuable chiral molecules.Acritical comparison of the existing ligand families,their design, synthesis,and complexation to different metals is also provided. In addition, future researchdirections are discussed to further enhance the performance and application of Cp X ligands in enantioselective catalysis.

Rhodium(III)-Catalyzed Enantioselective Benzamidation of Cyclopropenes

“…Chiral transition-metal cyclopentadienyl (Cp x ) complexes have emerged as powerful stereodirecting catalysts in enantioselective C-H functionalization transformations, 12 and a variety of chiral Cp x complexes have been synthesized and successfully applied in asymmetric reactions. 13,14 In 2017, Rovis et al reported the diastereoselective benzamidation of cyclopropenes with aryl hydroxamates using a bulky nonchiral Rh(III)-indene complex.…”

Chiral Bicyclo[2.2.2]octane‐Fused CpRh Complexes: Synthesis and Potential Use in Asymmetric C−H Activation

“…Notably, Group 9 cyclopentadienylmetal (CpM III , M=Co, Rh and Ir)‐catalyzed asymmetric C−H activation [2] has achieved great success by using chiral Cp ligands, [3] artificial metalloenzymes, [4] achiral CpM in combination with chiral carboxylic acids or chiral sulfonates, [5] or chiral transient directing groups [6] . So far, the use of CpM catalysts derived from chiral Cp ligands has become one of the most general and effective methods to realize asymmetric C−H activation [3a] . Since the pioneering work by Cramer, [7] diverse chiral Cp ligands have been revealed, including cyclohexane‐fused Cp I , [7–8] binaphthyl Cp II , [9, 10] spirobiindanyl Cp III , [11, 12] biphenyl Cp IV , [13] piperidine‐fused Cp V , [14, 15] cyclopentane‐fused Cp VI , [16] and ferrocenyl Cp VII [17] (Figure 1).…”

Rhodium Catalysts with a Chiral Cyclopentadienyl Ligand Derived from Natural R‐Myrtenal

“…Rhodium catalysts with chiral cyclopentadienyl ligands have recently attracted a lot of attention thanks to their successful application in C-H activation reactions. [1][2][3][4][5][6] The most explored catalysts of this type are the binaphthyl derivatives 1 developed by Cramer et al and You et al, [7][8][9][10][11] the amino acid derivatives 2 developed by Antonchik and Waldmann et al, [12] the streptavidine-docked derivatives 3 developed by Ward and Rovis et al, [13,14] as well as some others [15][16][17][18][19][20] (Scheme 1). A wide application of these catalysts is still somewhat limited by their multistep synthesis involving rather expensive starting materials and reagents.…”

“…Rhodium catalysts with chiral cyclopentadienyl ligands have recently attracted a lot of attention thanks to their successful application in C–H activation reactions . The most explored catalysts of this type are the binaphthyl derivatives 1 developed by Cramer et al and You et al, the amino acid derivatives 2 developed by Antonchik and Waldmann et al, the streptavidine‐docked derivatives 3 developed by Ward and Rovis et al,, as well as some others (Scheme ).…”