INTRAMOLECULAR CO · · · H INTERACTION
21
Presumably, the observed variations in the IR
spectra of complexes I–IV originate from intramo-
lecular interaction of hydrogen atoms in the substituent
on the benzene ring (assuming appropriate geometry of
the substituent) with carbonyl groups in the tricar-
bonylchromium fragment (H-interaction). This
interaction makes the carbonyl groups in the com-
plexes nonequivalent and gives rise to a new CO
stretching vibration band in a low-frequency region
relative to that typical of benzene(tricarbonyl)chro-
mium (see table).
considerable shift of the carbonyl stretching vibration
band (see table) is related to high acidity of hydrogens
atoms in structures II and IV.
The position of the third carbonyl stretching vibra-
tion band may be used as a measure of the strength of
intramolecular interaction between hydrogen and car-
bonyl groups. Depending on proton activity of the
hydrogen atom, electron-donor center of the carbonyl
group involved in H-bonding may change.
Theoretically, both oxygen and carbon atoms, as well
as the π-bond, can act as proton acceptor.
Hydrogen atoms in the substituents in the arene
fragment of I–IV are activated as a result of transfer of
π-electron density or lone electron pair on the
heteroatom in the fragment Z toward the aromatic ring
which acts here as acceptor due to coordination to
metal. Electron density distribution in complexes I–IV
may be represented as follows.
EXPERIMENTAL
All syntheses and operations with complexes I–IV
were performed under argon. Tricarbonyl(methoxy-
benzene)chromium, tricarbonyl(N-methyl-N-propyl-
aniline)chromium, and tricarbonyl(1-phenylethanol)
chromium were synthesized by reaction of the
corresponding aromatic compound with hexacarbonyl-
chromium on heating in a boiling diethylene glycol
dimethyl ether–octane mixture (1:1) [7]; tricarbonyl(1-
phenylpropene)chromium was synthesized according
to the procedure described in [8].
δ _
δ _
C
O
CH2
CH3
Oδ
+
H δ
+
H
H δ
Cr
Cr
+
CO
CO
CO
CO
CO
CO
The purity of the products was checked by liquid
chromatography on a Knauer Smart Line chromato-
graph equipped with a UV-Vis detector (LED matrix)
and a 8×250-mm column; stationary phase Diasfer-
110-S16, 5 μm; eluent acetonitrile–water (84:16). The
IR spectra were measured in the range from 600 to
4000 cm–1 on a Perkin–Elmer spectrometer; samples
were dispersed in mineral oil and placed between NaCl
plates.
I
II
δ _
δ _
N(Pr) CH2
CH CH CH2
H δ
+
H δ
+
Cr
Cr
CO
CO
CO
CO
CO
III
CO
IV
REFERENCES
Alternative interaction of activated hydrogen atom
with chromium is excluded, for such interaction should
give rise to new carbonyl stretching vibration bands at
higher frequency [5].
1. Pauson, P.L., Organometallic Chemistry, London:
Edward Arnold, 1967.
2. Jackson, W.R. and McMullen, C.H., J. Chem. Soc., 1965,
As stated above, two carbonyl absorption bands are
present in the IR spectrum of benzene(tricarbonyl)
chromium [6]. Analogous pattern is observed for
tricarbonyl(toluene)chromium [5]. Hydrogen atoms in
the methyl group in the latter, despite proton activation
via π–σ conjugation with the aromatic ring, cannot
interact with carbonyl groups because of remoteness.
no. 2, p. 1170.
3. Halet, J.F., Saillard, J.-Y., Bertrand Caro, B., Le Bihan, J.-Y.,
Top, S., and Jaouen, G., J. Organomet. Chem., 1984,
vol. 267, no. 3, p. 37.
4. Maux, P., Saillard, J.Y., Grandjean, D., and Jaouen, G.,
J. Org. Chem., 1980, vol. 45, no. 22, p. 4524.
5. Aleksanyan, V.T. and Lokshin, B.V., Itogi nauki i
Arene (tricarbonyl)chromium complexes containing
a hydroxy group in the α-position with respect to the
aromatic ring or a methyl group at the double bond in
the β-position attract specific interest. In these cases
tekhniki, seriya: stroenie molekul
i khimicheskaya
svyaz’ (Advances in Science and Technics; Series
Structure of Molecules and Chemical Bond), Moscow:
VINITI, 1976.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 1 2010
Bodrikov
