Zusammenfassung
The diastereomers (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos) NCMe]X (X = I, PF6), 5:95, differing only in the metal configuration, were prepared from (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos)I] (95:5) in acetonitrile in the absence or presence of NH4PF6. The diastereomers interconverted by change of the Fe configuration in first-order reactions in CDCl3 at 293 K with half-lives of 216 min (iodide) and 96 ...
Zusammenfassung
The diastereomers (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos) NCMe]X (X = I, PF6), 5:95, differing only in the metal configuration, were prepared from (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos)I] (95:5) in acetonitrile in the absence or presence of NH4PF6. The diastereomers interconverted by change of the Fe configuration in first-order reactions in CDCl3 at 293 K with half-lives of 216 min (iodide) and 96 min (hexafluorophosphate) in an S(N)1-type dissociation of the MeCN ligand, followed by pyramidal inversion of the 16-electron intermediates (R-Fe, R-C)- and (S-Fe,R-C)-[CpFe(Prophos)](+) and recombination with MeCN. In the presence of phosphite ligands there was MeCN/ligand exchange, the kinetics of which was measured. The rates of the MeCN/phosphite exchange decreased with increasing cone angle for P(OCH2)(3)CMe: (101 degrees), P(OMe)(3) (107 degrees), and P(OPh)(3) (128 degrees). PPh3 (145 degrees) did not enter the vacant coordination site in the intermediates (R-Fe,R-C)- and (S-Fe,R-C)-[CpFe(Prophos)](+). Phosphines such as Ph2PCH2CH2PPh2 and PBu3 bound only loosely to the intermediates. The phosphite complexes (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos)P(OR)(3)]X were configurationally stable at the metal atom. In the MeCN/phosphite exchange reactions the diastereomeric ratio of the products was constant, explained by an equilibrium between the intermediates in an energy diagram in which the barrier for the unimolecular pyramidal inversion was lower than the barriers for the bimolecular reactions of the intermediates with the phosphite ligands. A correlation between the major diastereomers (S-Fe,R-C)-[CpFe(Prophos)NCMe]X (X = I, PF6) and the diastereomers of the phosphite complexes with the same relative configuration and the favored envelope conformation of the Fe-Prophos chelate ring was corroborated, and a new correlation with the P-P coupling constants of the Prophos ligand was established, including all the compounds of a former study.
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