Chiral ferrocene-based phosphine-imine and sulfur-imine ligands for palladium-catalyzed asymmetric allylic alkylation of cycloalkenyl esters

Fluorine in metal-catalyzed asymmetric transformations: the lightest halogen causing a massive effect

This review aims at providing an overview of the most significant applications of fluorine-containing ligands reported in the literature starting from 2001 until mid-2021. The ligands are classified according to the nature of the donor atoms involved. This review highlights both metal-ligand interactions and the structure-reactivity relationships resulting from the presence of the fluorine atom or fluorine-containing substituents on chiral catalysts.

Electrochemical evidence of intramolecular electronic communication in Zr and Hf phthalocyanines bearing ferrocene-containing β-diketonato axial ligands: structure of [PcHf(FcCOCHCOC6H5)2]

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

Metal-catalyzed enantioselective allylation in asymmetric synthesis

Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction. The reaction may tolerate a broad range of functional groups and has been applied successfully to the synthesis of many natural products and new chiral compounds.

Recent Applications of Chiral Ferrocene Ligands in Asymmetric Catalysis

Despite the impressive progress achieved in asymmetric catalysis during the last decade, an increasing number of new catalysts, ligands, and applications are reported every year to satisfy the need to embrace a wider range of reactions and to improve the efficiency of existing processes. Because of their availability, unique stereochemical aspects, and wide variety of coordination modes and possibilities for the fine-tuning of the steric and electronic properties, ferrocene-based ligands constitute one of the most versatile ligand architectures in the current scenario of asymmetric catalysis. Over the last few years ferrocene catalysts have been successfully applied in an amazing variety of enantioselective processes. This Review documents these recent advances, with special emphasis on the most innovative asymmetric processes and the development of novel, efficient types of ferrocene ligands.

Diastereoselective Addition of Enantiopure Lithium tert-Butylsulfinylferrocene to Imines

(S)-tert-Butylsulfinylferrocene was submitted to ortho-metalation, and the corresponding lithium derivative was trapped by alkyl or aryl imines bearing various electron-withdrawing groups on the nitrogen atom (Ts, Dpp, Boc). New aminosulfoxides were obtained with complete diastereocontrol when Dpp or Boc groups were used. The absolute configuration (SS,SFc,S) has been determined by single-crystal X-ray analysis and chemical correlation. An unusual pseudocyclic boatlike transition state has been proposed to explain the stereochemical course of this reaction.