Reactions of Dicarbonyl(η⁵-Cyclopentadienyl)Iron(II)-Complexes of Two Cyclic Enol Ethers with Selected Nucleophiles

References

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• Booysen , J. F. , Bredenkamp , M. W. and Holzapfel , C. W. unpublished results
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• When samples of 1 2 were dissolved in deuterated solvents (DMSO—d 6, acetone—d 6 and CD3NO2) for nmr, without first drying the solvents (4Å molecular sieves), the rapid development of the hydroxy—aldehydes 3 4, respectively, at the expense of the parent compounds were observed
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• Chromatography of 15 at -10°C over deoxygenated silica gel with THF/CH2Cl2 (3:7–10:0) led to its hydrolysis yielding the hydroxy—aldehyde 3 (68%) m.p. 85–89°C; v max (THF) 3472 (OH), 2028 and 1974 (metal C[dbnd]O) and 1658 cm−1 (aldehyde C[dbnd]O); δH 1,7–2,6 (m, 4H, H-2, H-3′s and OH), 3,47 (bs, 2H, H-4′s), 4,75 (s, 5H, Cp) and 9,22 (bs, 1H, H-1); δC 30,88 (d, C-2), 37,99 (t, C-3), 64,99 (t, C-4), 87,47 (d, Cp), 197,53 (d, C-1) and 217,03 (s, C[dbnd]O); m/z 264 (M+, 3), 208 (M+-2CO, 38), 163 (C5H5FeCH2CO+, 56), 121 (C5H5Fe, 100) and 71 (C4H7O+, 87)
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• Chromatography of 16 at -10°C over deoxygenated silica gel with THF/CH2Cl2 (3:7–7:3) led to its hydrolysis yielding the hydroxy—aldehyde 4 (64%) v max (THF) 3497 (OH), 2015 and 1963 (metal C[dbnd]O) and 1653 cm−1 (aldehyde C[dbnd]O); δH (CDCl3/CS2, 1:4) 1,56 (bs, 4H, H-3′s and H-4′s), 2,25 (bs, 2H, H-2 and OH), 3,55 (bs, 2H, H-5′s), 4,79 (s, 5H, Cp) and 9,29 (s, 1H, H-1); δC (CDCl3/CS2, 1:4) 29,23 (d, C-2), 33,51 and 34,87 (2xt, C-3 and C-4), 60,92 (t, C-5), 86,38 (d, Cp), 194,95 (d, C-1) and 217,02 (s, C[dbnd]O)
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• The unusual prevalence of the hydroxy-aldehydes 3 4 at the expense of the corresponding cyclic hemiacetals, and the allylic rearrangment of 6 to the sterically more crowded 5 may possibly be ascribed to the thermodynamic stability gained when Fp is α with respect to a carbonyl group. This situation allows resonance stabilisation of the highly polar C—Fp—bond
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• Fish , R. W. , Giering , W. P. , Marten , D. and Rosenblum , M. 1976 . J. Organomet. Chem. , 105 : 101 There is no precedent for 13C-nmr chemical shifts of Cp(CO)Fe-η3-complexes. The 13C-nmr spectrum of7 has only one iron—complexed carbonyl resonance, and the chemical shifts of the terminal carbon atoms of the η3—complexed moiety are significantly shielded relative to the central carbon atom. The same relative shift pattern is observed in the 1H-nmr spectra. This phenomenum is also observed in the carbon spectra of Fe(CO)3I—η3—complexes, Randall, E. W., Rosenberg, E. and Milone, L., J. Chem. Soc., Dalton Trans., 1973, 1672, and in neutral η3—metal complexes in general, Chisholm, M. H. and Godleski, S., “Progress in Inorganic Chemistry”, Vol. 20, Editor: Lippard, S. J., John Wiley and Sons, New York, 1976, pp. 366–70, The single I.R.—band for the iron—complexed carbonyl and the chemical shifts and coupling constants of the η3—complexed protons are in good agreement with the examples cited in
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• Basolo , F. 1985 . Inorg. Chim. Acta , 100 : 33 Such mechanisms, in which a η5—complexed cyclopentadienyl derivative withdraws two electrons from the central metal atom to accommodate another electron pair at the metal atom in a transition state, has been postulated for associative substitution reactions. The central metal atom thus maintains 18—electrons in its valence shell throughout the rearrangement/substitution process
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