Synthesis and properties of the dichloro [tetramethyl (trifluoromethyl)cyclopentadienyl]ruthenium dimer: X-ray structure of [M2(η5-C5Me4CF3)2Cl2(μ-Cl)2] (MRu, Rh)

Synthesis and Coordination Chemistry of Fluorinated Cyclopentadienyl Ligands

The incorporation of fluorinated substituents in cyclopentadienyl anions leads to distinct changes in the properties of the corresponding metal complexes, e.g., with regards to electrochemical properties or metal–ligand bonding energies. This review summarizes the synthetic challenges of the preparation and coordination of fluorinated cyclopentadienyl anions.

1 Introduction

2 Fluorinated Cyclopentadienyls

3 Cyclopentadienyls with One CF3 Group

4 Cyclopentadienyls with Four CF3 Groups

5 Cyclopentadienyls with Five CF3 Groups

6 Cyclopentadienyls with ‘Fluorous Ponytails’

7 Cyclopentadienyls with C6F5 Groups

8 Trends in Interaction Energies

9 Conclusion

Dehydration of (Perfluoroalkyl)tetramethylcyclopentenols

(Perfluoroalkyl) tetramethylcyclopentenols (alkyl = n-butyl, n-hexyl, n-octyl) were dehydrated to a complex mixture of endo, endo-(perfluoroalkyl) tetramethyl-cyclopentadienes and their endo-, exo-isomers. It was found in preliminary screening experiments that the best reagent for this transformation, giving an 89% yield of isomeric product mixture, was P₂O₅ in benzene at 80-90 °C. Products were characterized on the basis of their mass spectra and retention time information, and some peaks in the mass spectra were identified from their molecular fragments. Structures were assigned to the three most abundant products of (perfluorohexyl)tetramethylcyclopentenol dehydration. Formal dehydration kinetics showed a second order reaction in benzene but zeroth order with induction period in chlorobenzene, suggesting mass transfer limitations in the more polar chlorobenzene. Some of the products were formed by consecutive isomerization of the others, as shown by the kinetic analysis.

Synthesis of Rhodium Complexes with Novel Perfluoroalkyl Substituted Cyclopentadienyl Ligands

Mixtures of isomers of (perfluoroalkyl)tetramethylcyclopenta-1,3-dienes (CH3)4C5H(CF2)nCF3 (n = 3, 5, 7, 9) were synthesized as precursors of new cyclopentadienyl ligands for organotransition metal catalysis in fluorous biphase media and characterized by combination of GC-MS and 13C NMR spectroscopy. Rhodium(III) chloro complexes [Rh{(CH3)4C5(CF2)nCF3}Cl2]2 and rhodium(I) carbonyl complexes [Rh{(CH3)4C5(CF2)nCF3}(CO)2] were prepared from the cyclopentadienes and molecular structure of [Rh{(CH3)4C5(CF2)5CF3}Cl2]2 was determined by X-ray diffraction. The ligands are electronically close to the unsubstituted cyclopentadienyl as shown by values of carbonyl stretching frequencies in the carbonyl complexes. Neither carbonyl frequencies nor NMR chemical shifts of the complexes are substantially affected by the length of the perfluoroalkyl chain.