Organoiron chemistry. Annual survey for the year 1992

Kerber, Robert C.

doi:10.1016/0022-328x(94)88091-3

Cited by 4 publications

(1 citation statement)

References 531 publications

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“…However, a more than qualitative characterization of ligand effects is often difficult. Ligand effects on structure and reactivity can be probed by transition metal NMR spectroscopy, as we have reported for a variety of cases: 59 Co, , 103 Rh, − 55 Mn, , and 57 Fe. − Cyclopentadienyl complexes of group VIII transition metals are vital in several important stoichiometric and catalytic reactions, and annually many synthetic applications are published. , Cyclopentadienyliron complexes in particular have attracted considerable interest as stoichiometric reagents in stereoselective reactions …”

Section: Introductionmentioning

confidence: 99%

⁵⁷Fe NMR Study of Ligand Effects in Cyclopentadienyliron Complexes

et al. 1996

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The first systematic 57Fe NMR study of ligand effects in cyclopentadienyliron complexes is presented. Four series encompassing a total of 35 compounds have been studied. Among the compounds are five new ring-substituted complexes with the formula (C5H4Y)Fe(CO)(PPh3)(Me), Y = Me, SiMe3, NEt2, I, and Ph. The crystal structure of (C5H4I)Fe(CO)(PPh3)(Me) (32) was determined. For the series CpFe(CO)2R (type I), 57Fe shielding was found to decrease with the bulkiness of the alkyl ligand R and to correlate with the CO-insertion rate of the complex. In type III complexes CpFe(CO)(L)(COMe), L = PR3, and CO, it is again the steric requirement of the ligand L that dominates the 57Fe chemical shift which increases with larger cone angles (θ). In contrast, a strong electronic effect was found for type II complexes CpFe(CO)(PPh3)X, X = H, Me, and I. Ligands with higher electronegativity induce a shift of the 57Fe resonance to higher frequencies. In the complexes (C5H4Y)Fe(CO)(PPh3)(Me), Y = Me, H, SiMe3, NEt2, I, Ph, COOMe, and COiPr (type IV), again electronic effects are dominant, whereby electron acceptor substituents (e.g. Y = COiPr, COOMe) cause a deshielding of the iron nucleus, relative to complexes with electron donor substituents (e.g. Y = Me, H, SiMe3). Dominant electronic ligand effects in type IV complexes are also apparent from the correlation of δ(57Fe) with the electronic substituent parameter σI. The 57Fe chemical shift is shown to be very sensitive to changes in the ligand sphere, and the effects are discussed in terms of the paramagnetic shielding constant (σpara). The 1 J(57Fe,13C) coupling constants and longitudinal relaxation times T 1 of 57Fe in selected complexes have been determined and ligand effects are discussed.

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