Unusual (fulvene)chromiumcarbonyl complexes

Article abstract of DOI:10.1016/j.inoche.2004.05.015

The preparation and characterization of several new and unusual (fulvene)chromiumcarbonyl complexes is reported. η⁶-Phenyl- coordinated iso-(6,6-diphenylfulvene)Cr(CO)₃ (1) is obtained by treatment of (η⁶-benzophenone)Cr(CO)₃ with cyclopentadiene. Tricarbonyl(1-fulvenyl-4,6,8-trimethylazulene)chromium(0) (3) is the first transition metal complex containing a tricyclic fulvenylazulene ligand. P-Coordination without participation of the fulvene ring system has been achieved in the complex (6,6-dimethyl-1-diphenylphosphinofulvene)Cr(CO) ₅ (4).

Full text of DOI:10.1016/j.inoche.2004.05.015

Inorganic Chemistry Communications 7 (2004) 899–902
www.elsevier.com/locate/inoche
Unusual (fulvene)chromiumcarbonyl complexes
*
Frank T. Edelmann
Chemisches Institut der Otto-von-Guericke-Universit€at Magdeburg, Universit€atsplatz 2, D-39106 Magdeburg, Germany
Received 26 February 2004; accepted 16 May 2004
Available online 17 June 2004
Abstract
The preparation and characterization of several new and unusual (fulvene)chromiumcarbonyl complexes is reported. g6-Phenyl-
coordinated iso-(6,6-diphenylfulvene)Cr(CO)3 (1) is obtained by treatment of (g6-benzophenone)Cr(CO)3 with cyclopentadiene.
Tricarbonyl(1-fulvenyl-4,6,8-trimethylazulene)chromium(0) (3) is the first transition metal complex containing a tricyclic fulve-
nylazulene ligand. P-Coordination without participation of the fulvene ring system has been achieved in the complex (6,6-dimethyl-
1-diphenylphosphinofulvene)Cr(CO)5 (4).
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Fulvenes; Fulvene complexes; Chromium complexes; Azulene; Carbonyl complexes
1. Introduction
True iso-(6,6-diphenylfulvene)Cr(CO)3 (1) has never
been prepared until now.
The organometallic chemistry of pentafulvenes has
recently gained renewed interest as fulvenes have been
found to be highly versatile starting materials for the
preparation of catalytically active metallocenes. Various
olefin polymerization catalysts have been prepared from
fulvenes such as 6,6-dimethylfulvene or 6-dimethylami-
nofulvene [1–4]. (Fulvene)Cr(CO)3 complexes form a
well-established group of transition metal fulvene de-
rivatives. Since their discovery by Fischer and Semm-
linger [5] more than 40 years ago these compounds have
been extensively investigated using spectroscopic as well
as X-ray crystallographic techniques [6]. The longest
known representative, (6,6-diphenylfulvene)Cr(CO)3,
was first postulated on the basis of its IR data to have
the g6-phenyl-coordinated structure 1, but spectroscopic
and X-ray studies have later established the fulvene ring
coordinated structure 2 (Scheme 1) [7–9]. In fact, this
coordination mode represents the only type of (ful-
vene)chromiumcarbonyl complexes known thus far.
We report here the preparation and characterization
of 1 as well as the first Cr(CO)3 complex containing a
fulvenylazulene ligand. In addition, the new complex
(6,6-dimethyl-1-diphenylphosphinofulvene)Cr(CO)5 (4)
is described, which represents yet another unprece-
dented coordination mode in (fulvene)chromiumcar-
bonyl chemistry.
2. Results and discussion
The synthesis of iso-(6,6-diphenylfulvene)Cr(CO)3 (1)
was achieved according to Scheme 2 by condensation of
(g6-benzophenone)Cr(CO)3 with cyclopentadiene in the
presence of NaOEt.
Compound 1 forms an orange solid, which dissolves
in various organic solvents with a blood-red color. The
g6-phenyl coordination was unambiguously verified by
1
the H NMR data.
1-Fulvenylazulene (Scheme 3) is an interesting poly-
cyclic hydrocarbon which combines two pentafulvene
ring systems in one molecule. According to Hafner and
Bernhard [10], this unusual tricyclic olefin is readily
made via base-catalyzed condensation of azulene-1-al-
dehyde with cyclopentadiene. Formally, a reactive
* Corresponding author. Tel.: +49-391-6718327; fax: +49-391-
6712933.
E-mail address: frank.edelmann@vst.uni-magdeburg.de (F.T. Edel-
mann).
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.05.015

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F.T. Edelmann / Inorganic Chemistry Communications 7 (2004) 899–902
THF according Scheme 4 led to the formation of a
single product 3, which was isolated in 51% yield in the
form of permanganate-colored crystals. The coordina-
tion site of the tricarbonylchromium group was clearly
1
established by H NMR data of 3.
Finally, another novel coordination mode in (ful-
vene)chromiumcarbonyl complexes, i.e., P-coordination
without participation of the fulvene ring system, has
been achieved in the complex (6,6-dimethyl-1-diphe-
nylphosphinofulvene)Cr(CO)5 (4). The phosphine-
substituted fulvene ligand is accessible through
condensation of diphenylphosphinocyclopentadiene
with acetone in the presence of a strong base [13].
Treatment of 6,6-dimethyl-1-diphenylphosphinofulvene
with (MeCN)3Cr(CO)3 in THF gave an unseparable
mixture of fulvene-coordinated Cr(CO)3 complex and P-
coordinated Cr(CO)5 derivative. While the former could
not be isolated in a pure state, it was possible to prepare
pure P-coordinated (6,6-dimethyl-1-diphenylphosphi-
nofulvene)Cr(CO)5 (4) by the reaction of the ligand with
freshly prepared Cr(CO)5(THF) according to Scheme 5.
The product was isolated in 36% yield in the form of
bright yellow, air-sensitive crystals.
Scheme 1. Structures of iso-(6,6-diphenylfulvene)Cr(CO)3 (1) and (6,6-
diphenylfulvene)Cr(CO)3 (2).
Scheme 2. Synthesis of iso-(6,6-diphenylfulvene)Cr(CO)3 (1).
In summarizing these results, we have demonstrated
that besides the normal (g6-fulvene)Cr(CO)3 coordina-
tion mode involving the fulvene ring systems other types
of (fulvene)chromiumcarbonyl compounds can be real-
ized. These include especially the g6-phenyl coordina-
tion of a phenyl substituent and the P-coordination of a
diorganophosphine unit, in both cases without partici-
pation of the pentafulvene ring system. In addition, the
first chromiumcarbonyl derivative of a 1-fulvenylazu-
lene ligand has been synthesized.
Scheme 3. Resonance structures of 1-fulvenylazulene.
Cr(CO)3 fragment should have the choice between two
fulvene units in this ligand. However, the resonance
forms depicted in Scheme 3 clearly indicate that the
pendant fulvene substituent has a higher electron density
than the fulvene unit within the azulene part of the
molecule and should therefore be favored as complex-
ation site.
Since the parent 1-fulvenylazulene is very susceptible
to polymerization, we chose the more stable 1-fulvenyl-
4,6,8-trimethylazulene [10] as starting material. Treat-
ment of this ligand with (MeCN)3Cr(CO)3 [11,12] in
Scheme 5. Preparation of (6,6-dimethyl-1-diphenylphosphinoful-
vene)Cr(CO)5 (4).
Scheme 4. Formation of (1-fulvenyl-4,6,8-trimethylazulene)Cr(CO)3 (3).

F.T. Edelmann / Inorganic Chemistry Communications 7 (2004) 899–902
901
3. Experimental
3.3. ð6,6-Dimethyl-1-diphenylphosphinofulveneÞCrðCOÞ5
ð4Þ
All reactions involving metal carbonyl complexes
were carried out under dry nitrogen using standard
Schlenk techniques. THF was dried over Na/benzo-
phenone and freshly distilled under nitrogen prior to
use. The starting materials (g6-benzophenone)Cr(CO)3
[14], 1-fulvenyl-4,6,8-trimethylazulene [10], (CH3CN)3
M(CO)3 (M ¼ Cr, Mo) [11,12] and 6,6-dimethyl-1-diphe-
nylphosphinofulvene [13] were prepared as described in
the literature. IR spectra: Perkin–Elmer spectrometer
180 and Bio-Rad FTS 7, Nujol mulls between KBr
disks. 1H NMR spectra: and Bruker AM-250 (250 MHz,
TMS ext., 25 °C).
An orange-yellow solution of Cr(CO)5(THF) was
freshly prepared by UV-irradiation (3 h) of a solution of
Cr(CO)6 (395 mg, 1.8 mmol) in THF (150 ml). 6,6-Di-
methyl-1-diphenylphosphinofulvene (500 mg, 1.7 mmol)
in THF (10 ml) was added and the reaction mixture was
stirred for 12 h. The solvent was removed in vacuo, the
solid residue was redissolved in toluene (15 ml) and
purified by column chromatography on silica gel (col-
umn: l ¼ 10 cm, £ ¼ 2:5 cm). After elution of a pale-
yellow band (unreacted ligand), the product was eluted
with toluene as a narrow orange band. Evaporation to
dryness left a sticky, orange-yellow residue, which
crystallized upon treatment with n-hexane (20 ml). 300
mg (36%) of 4 was isolated in the form of bright yellow
needles. M.p. 110 °C. Anal. Calc. for C25H19CrO5P
(482.4): C 62.25, H 3.97; found: C 62.86, H 4.22%. IR
3.1. iso-ðꢀ6-6,6-DiphenylfulveneÞCrðCOÞ3 ð1Þ
Sodium metal pieces (575 mg, 25 mmol) were dis-
solved in ethanol (50 ml). (g6-Benzophenone)Cr(CO)3
(2.70 g, 8.5 mmol) and freshly distilled cyclopentadiene
(2.0 g, 30 mmol) were added, and the mixture was stirred
at 40–45 °C for 3 h. The resulting deep red solution was
evaporated to dryness and the oily residue was extracted
with warm toluene (50 ml). After dilution with n-hexane,
the solution was subjected to column chromatography
on silica gel (column: l ¼ 20 cm, £ ¼ 6 cm). With the
use of toluene/n-hexane (1:5) as eluant, a yellow by-
product was first washed from the column. The desired
product followed as a red band using toluene/n-hexane
(1:1). M.p. 75 °C (dec.). Anal. Calc. for C21H14CrO3
(259.2): C 68.85, H 3.85; found: C 68.72, H 3.96%. IR
(KBr): (CO) 2057, 1976, 1941, 1922, 1908 cmꢀ1 1H
.
NMR (CDCl3): d 7.55–7.20 (m, 10H, C6H5); 6.75, 6.50,
6.25 (m, each 1H, fulvene ring); 2.09 (s, 6H, CH3) ppm.
31P NMR (CH2Cl2): d 40.9 ppm. 13C NMR (CDCl3): d
221.8 (COtrans), 216.8 (d, COcis, 2JCP ¼ 14 Hz), 155.2 (C-
6), 145.5 (very weak, C-5), 142.3 (d, C-2, J ¼ 14 Hz),
136.4 (d, C-1, J ¼ 83 Hz), 136.2 (C-3), 132.1 (d, o-C6H5,
J ¼ 10 Hz), 129.7 (p-C6H5), 129.4 (d, q-C6H5, J ¼ 57
Hz), 128.4 (d, m-C6H5, J ¼ 9 Hz), 122.0 (C-4), 23.4
(CH3) ppm.
1
(KBr): m(CO) 1960, 1888 cmꢀ1. H NMR (CDCl3): d
7.44 (m, 2H), 7.24 (m, 3H) (C6H5 uncoordinated); 6.76,
6.66, 6.47, 6.05 (d, each 1H, fulvene ring); 5.19 (d, 2H),
4.65 (q, 1H), 4.35 (t, 2H) (C6H5 coordinated) ppm.
3.2. ð1-Fulvenyl-4,6,8-trimethylazuleneÞCrðCOÞ3 ð3Þ
Acknowledgements
A solution of 1-fulvenyl-4,6,8-trimethylazulene (950
mg, 3.9 mmol) in THF (20 ml) was added to a stirred
suspension of (CH3CN)3Cr(CO)3 (1.0 g, 3.9 mmol) in
THF (50 ml), causing an intense deep purple color to
develop immediately. After stirring for 2 h at room
temperature, the solvent was removed in vacuo and the
residue was extracted with hot toluene (100 ml). The
extract was filtered, diluted with n-hexane (200 ml) and
kept at )30 °C for 24 h. The resulting crystals were
isolated by filtration and dried under vacuum to give 750
mg (51%) of 3 as glistening black needles. Solutions of 3
display a permanganate-like color. Anal. Calc. for
C22H18CrO3 (382.4): C 69.10, H 4.74; found: C 69.07, H
Thanks are due to the Deutsche Forschungsgemein-
schaft, the Fonds der Chemischen Industrie and the
€
Otto-von-Guericke-Universitat Magdeburg for financial
support of this work.
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