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Z.R. Ratko6ic et al. / Journal of Organometallic Chemistry 637–639 (2001) 813–819
of such species. The suitable selection of the coordinated
ligand in the Cr(II)L reagents stops the reaction either
at the radical stage or lets it proceed to form the alcohol.
Further studies are in progress in our laboratories to
prepare additional new ferrocenylketyl radicals as well as
to characterise them by using X-ray techniques.
atmosphere; eluent Et2O–hexane=1:1(v/v)). The spots
were evaluated at first under Ar taking into account the
oxygen sensitivity properties of the radicals. Subse-
quently, the plates were oxidised by standing on air and
visualised with UV light. The Rf values of the ketones and
the radicals were roughly the same, but the colour of the
spots was different. After oxidation the colour of the
radicals (orange) changed to that of the ketones (red).
The corresponding alcohols have a different colour
(yellow) and Rf.
3. Experimental
3.1. Chemicals
3.4. UV–6is measurements
All ferrocenyl ketones used for reactions were pre-
pared by a procedure described earlier [8]. Chromium(II)
acetate hydrate [Cr(OAc)2·H2O]2 as well as the chromiu-
m(II) complexes were prepared by us using essentially the
literature protocols [10d]. Ligands as glycine, DL-alanine,
imino-diacetate and ethylenediaminetetra-acetate were
purchased from Aldrich Chemical Company. The 1,3-
propanediamine-N,N%-diace-
tic-N,N%-dipropionate was prepared at the Department
of Chemistry, University of Kragujevac. All other
reagents were purchased from Merck Company.
The amounts of reagents used for the preparation of
the Cr(II)L complexes were calculated [12a], using the
reported formation constants [12b] and considering the
actual pH value.
A 1.00 cm quartz cell was closed by means of silicon-
rubber caps and flushed with Ar, using hypodermic
needles as inlet and outlet. Ethereal solutions of 2a–e
were added through a hypodermic needle from a specially
designed storing vessel (similar to a Schlenk tube). The
cell was then closed under a small overpressure of Ar and
placed into the spectrophotometer (HP8453). After
recording the spectra the solvent was evaporated and the
residue was oxidised by air. After it the sample was
dissolved in Et2O and the spectra recorded again. These
spectra were found identical to those of the ketones
(1a–e). The samples were also checked by TLC and only
the ketones could be detected.
1
3.5. H-NMR measurements
3.2. Preparation of ferrocenylketyl radicals
1H-NMR spectra were recorded with a Bruker AM 360
spectrometer (1H 360 MHz) in CDCl3. From the ethereal
solution of 2a–e the solvent was evaporated by an Ar
stream and the residue was dissolved in CDCl3. (Slow
decomposition of the radicals was observed in CDCl3 in
contrary to Et2O.) All the samples showed strong para-
magnetic line broadenings. After oxidation of the sam-
ples by air only the spectra of ketones 1a–e were
observed. No alcohols could be detected by TLC in these
samples.
Chromium(II) ethylenediaminetetra-acetate, [Cr(II)-
(EDTA)]2−, was prepared from Na2EDTA·2H2O (1.12
g, 3 mmol), KOH (2.46 mol dm−3, 1.3 cm3, 3.2 mmol)
and [Cr(OAc)2·H2O]2 (0.47 g, 2.5 mmol Cr(II)) in a
mixture of H2O (20 cm3) and DMF (15 cm3) (pH 5.5,
checked by pH-potentiometry) under Ar using standard
Schlenk technique at room temperature. The red chromi-
um(II) acetate was completely dissolved only after the
addition of the ligand, with blue colour. Ferrocenyl
ketone (1a–e, 1 mmol) was dissolved in DMF (5 cm3)
and this solution after deoxygenation was added to the
complex in one portion. The colour of the solution slowly
(2–3 h) changed from blue to deep violet. The reaction
vessel was then kept under a slight overpressure of Ar,
and stirring was continued for 6 h. After this period the
solution was extracted (3×15 cm3) with Et2O under Ar
atmosphere. The organic phase was washed (3×10 cm3)
with deoxygenated water, then dried over anhydrous
Na2SO4, subsequently the solvent was evaporated under
reduced pressure and an orange residue was obtained,
which changed colour (to red) upon exposition to air.
Yields are shown in Table 1.
3.6. EPR measurements
X-band EPR spectra (9.50 GHz) were recorded at 298
K with a Bruker 200D SCR spectrometer. The ethereal
solutions of 2a–e were evaporated and the solid residues
were dissolved in toluene. The purity of the samples was
checked by TLC before and after the measurements.
Acknowledgements
Financial support of this work is provided by the
Hungarian OTKA (contract No. T33130) and FKFP
0308/2000 Projects, as well as the (Italian) Ministry of
University and Research (MURST). The Ja´nos Bo´lyai
Research Scholarship for K.M. is also acknowledged.
3.3. Separations on TLC
The reaction mixtures were analysed by TLC (DC-Fer-
tigplatten, Kieselgel 60 F254 (Merck-5719) under Ar