Synthesis and structures of all possible Cr(CO)3 complexes of triptycene

Article abstract of DOI:10.1021/om9703705

Mono-, bis-, and tris(tricarbonylchromium) complexes of triptycene were synthesized by the reaction of triptycene with Cr(CO)₆. The stereochemistry of the two isomeric bimetallic complexes of C_s and C_2v symmetries was dete

Full text of DOI:10.1021/om9703705

4
012
Organometallics 1997, 16, 4012-4015
Notes
Syn th esis a n d Str u ctu r es of All P ossible Cr (CO)3
Com p lexes of Tr ip tycen e
Shinji Toyota,* Hironobu Okuhara, and Michinori Oh ki
Department of Chemistry, Faculty of Science, Okayama University of Science, Ridaicho,
Okayama 700, J apan
Received May 2, 1997X
Summary: Mono-, bis-, and tris(tricarbonylchromium)
complexes of triptycene were synthesized by the reaction
of triptycene with Cr(CO)6. The stereochemistry of the
two isomeric bimetallic complexes of Cs and C2v sym-
metries was determined from the NMR spectra. X-ray
structures of the bimetallic (Cs) and trimetallic complexes
are presented.
the other forms 4 of Cs symmetry, these being stereoi-
somers (Scheme 1). Only 4 can accommodate one more
Cr(CO) group on the uncoordinated benzene to form
3
the 1:3 complex (n ) 3) 5, which is of C3h symmetry.
These Trip-[Cr(CO)3]n complexes were synthesized
by the treatment of triptycene with an excess amount
of Cr(CO)6, and all of them could be separated by
chromatography. The structure and stereochemistry of
the complexes are discussed on the basis of NMR spectra
and X-ray analyses.
Arene-tricarbonylchromium complexes, with two or
more aromatic rings participating in the complexation,
are of interest in view of their stereochemistry and
physical properties.1-4 A π complex of triptycene, which
possesses three benzene rings, with a mono(tricarbon-
ylchromium) (Trip-Cr(CO)3, 2) was reported by two
groups in the early 1970s,5 and its X-ray structure was
Exp er im en ta l Section
1
H NMR spectra were measured on a Varian Gemini-300
,6
spectrometer at 300 MHz and 13C NMR spectra on a J EOL
GSX-400 spectrometer at 100 MHz. Melting points are
uncorrected and were measured in a sealed tube under a
nitrogen atmosphere. Elemental analyses were performed
with a Perkin Elmer 240C analyzer. IR spectra were mea-
sured on a Hitachi I-2000 spectrometer, and only the absorp-
tions due to carbonyl stretching are described below. UV
spectra were recorded with a Hitachi U-2000 spectrophotom-
eter for chloroform solutions. Mass spectra were measured
by a J EOL J MS-DX303 spectrometer. Hexacarbonylchromium
was purchased from Strem Chemicals Inc. Triptycene was
synthesized by the Diels-Alder reaction of anthracene with
7
later established by Mislow et al. Because 2 possesses
two metal-free benzene rings, a triptycene molecule is
expected, in principle, to form a complex containing two
or three metals. Although the authors of ref 5 pointed
out the possibility of the formation of such complexes,
no experimental evidence has been reported so far to
our knowledge.
The molecular symmetry and stereochemistry of
Trip-[Cr(CO)3]n (n ) 1,2,3) complexes are worth men-
tioning. The symmetry of metal-free triptycene (1) is
lowered from D3h to Cs by the complexation of the first
Cr(CO)3 group.8 In the 1:1 complex (n ) 1) 2, complex-
ation of the second metal may occur at two possible
coordination sites: one forms 3 of C2v symmetry, and
benzyne, generated from anthranilic acid and isopentyl nitrite,
by a standard method.9
,10
3
Solutions of the Cr(CO) complexes
were handled under dimmed light to prevent decomposition.
Chromatography and recrystallization were carried out under
ambient conditions with commercially available solvents
without further purification.
X
Abstract published in Advance ACS Abstracts, August 1, 1997.
6
Rea ction of Tr ip tycen e w ith Cr (CO) . Caution: This
reaction should be carried out under a hood because of
(1) (a) Davis, R.; Kane-Maguire, L. A. P. In Comprehensive Orga-
nometallic Chemistry; Wilkinson, G., Stone, F. A. G., Abel, E. W., Eds.;
Pergamon Press: Oxford, 1984; Vol. 3, Chapter 26.2. (b) Morris, M. J .
In Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
A. G., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 5, Chapter
evolution of CO gas. This procedure is basically the same as
5,7
the literature method.
Triptycene (400 mg, 1.57 mmol) and
1
.78 g (8.10 mmol) of Cr(CO) were dissolved in 60 mL of
6
8
.
(
2) Sneeden, R. P. A. Organochromium Compounds; Academic
Press: New York, 1975.
3) Pauson, P. L. In Dictionary of Organometallic Compounds, 2nd
ed.; Chapman & Hall: New York, 1995; Vol. 1, p 963.
4) (a) Elschenbroich, C.; Schneider, J .; W u¨ nsch, M.; Pierre, J .-L.;
degassed dibutyl ether in a flask protected from light by
aluminum foil. The mixture was heated under reflux for 45 h
under a nitrogen atmosphere. At the beginning of the reaction,
(
6
some Cr(CO) sublimed at a condenser, and this was returned
(
Baret, P.; Chautemps, P. Chem. Ber. 1988, 121, 177. (b) Merkert, J .
W.; Geiger, W. E.; Paddon-Raw, M. N.; Oliver, A. M.; Rheingold, A. L.
Organometallics 1992, 11, 4109. (c) M u¨ ller, T. J . J .; Lindner, H. J .
Chem. Ber. 1996, 129, 607. (d) Elschenbroich, C.; K u¨ hlkamp, P.;
Behrendt, A.; Harms, K. Chem. Ber. 1996, 129, 859.
to the flask by adding a minimum volume of solvent from the
top of the condenser as necessary. After the reaction mixture
was cooled to room temperature, the undissolved green solids
were removed by filtration. The solvent was evaporated, and
the yellow residue was submitted to chromatography on silica
(5) Pohl, R. L.; Willeford, B. R. J . Organomet. Chem. 1970, 23, C45.
6) Moser, G. A.; Rausch, M. D. Synth. React. Inorg. Metal-Org.
(
Chem. 1974, 4, 37.
7) Gancarz, R. A.; Blount, J . F.; Mislow, K. Organometallics 1985,
, 2028.
8) For the description of the symmetry of the complexes, the
anisotropy of the Cr(CO)
group is ignored.
(
(9) Friedman, L.; Logullo, F. M. J . Org. Chem. 1969, 34, 3089.
(10) For a recent example of the triptycene synthesis, see: Toyota,
S.; Watanabe, Y.; Yoshida, H.; Oh ki, M. Bull. Chem. Soc. J pn. 1995,
68, 2751.
4
(
3
S0276-7333(97)00370-1 CCC: $14.00 © 1997 American Chemical Society

Notes
Organometallics, Vol. 16, No. 18, 1997 4013
Sch em e 1
Ta ble 1. Cr ysta l a n d Str u ctu r e An a lysis Da ta of
Com p ou n d s 4 a n d 5
4
5
chemical formula
fw
C26H14O6Cr2‚C6H6
604.50
C29H14O9Cr3‚C6H6
740.53
cryst size, mm
cryst syst
space group
a, Å
0.33 × 0.23 × 0.50
monoclinic
P21/c
0.28 × 0.23 × 0.23
monoclinic
P21/c
14.393(3)
12.300(7)
16.012(4)
101.32(2)
2779(1)
10.478(2)
14.156(2)
21.158(1)
100.180(8)
3088.9(6)
4
h
s
b, Å
c, Å
â, deg
V, Å3
Z
4
Dcalc, g/cm3
1.444
1.592
-
1
µ (Mo KR), cm
scan rate, deg min
in ω)
68.18
90.50
-
1
12.0
10.0
(
scan width, deg in ω 1.57 + 0.30 tan θ
0.89 + 0.30 tan θ
120.2
4821
2
θmax, deg
120.1
4367
no. of unique data
no. of data used
no. of variables
R(F)
Rw(F)
GOF
v
s
2972 (Fo > 1.0σ(F)) 3048 (Fo > 1.5σ(F))
418
0.077
0.076
2.73
485
0.055
0.058
1.92
+
(FAB) C29
H
14
O
9
Cr
3
(MH ) calcd m/ e 662.8932, found m/ e
6
2
62.8960. Anal. Calcd for C29
.72. Found: C, 57.06; H, 2.60.
X-r a y Cr ysta llogr a p h y. Crystals of 4 and 5 used for the
H
14
O
9
Cr
3
‚C
6 6
H : C, 56.76; H,
measurements were grown from benzene solutions. Reflection
data were collected on a Rigaku AFC7R diffractometer with
h
R
graphite-monochromated Cu K radiation (λ ) 1.541 78 Å) at
room temperature. The scan mode was the ω-2θ method. The
structure was solved by the direct method and refined by the
full-matrix least-squares method using the TEXSAN program.
Anisotropic thermal parameters were employed for nonhydro-
gen atoms. All hydrogen atoms were found in the e-map, and
the positional and thermal parameters of hydrogens in solvent
molecules were fixed during the refinement. No absorption
correction was employed. The reflection data were corrected
gel with 5:1 ethyl acetate-hexane eluent. Only 2 was satis-
factorily separated from the others as the first eluate. Com-
plexes 3-5 were separated by preparative HPLC with a
Chemcosolb Si column (5 µm, 10 mm L × 300 mm) eluted with
5
:1 ethyl acetate-hexane. After the elution of a trace amount
of triptycene (retention time 9 min), 2 (19 min), 4 (21 min),
and 5 (34 min) were eluted. 3 was eluted on switching the
eluent to ethyl acetate. Recrystallization of each complex from
benzene-hexane gave pure material as yellow crystals con-
taining benzene molecules, the yields being 20, 5, 23, and 40%
for 2-5, respectively.
for Lorentz and polarization effects and secondary extinction.
2
The function minimized was ∑[w(|F
|F
Table 1.
o
| - |F
c
|) ], where w )
2
-1
[σ
c
o
|] . Additional crystal and analysis data are listed in
6
The spectroscopic data for tricarbonyl(η -triptycene)chro-
mium(0) (2) were identical with those reported in the
5
-7,11
literature.
Resu lts a n d Discu ssion
6
6
µ-(η :η -Tr ip tycen e)bis[tr ica r bon ylch r om iu m (0)] (C2v
3): mp 220-227 °C dec; H NMR (CDCl
m, 4H), 5.66 (m, 4H), 7.22 (m, 2H), 7.36 (C
C NMR (CDCl
C H ), 142.1, 231.6; IR (Nujol, cm ) 1972, 1952, 1880, 1866
6 6
)
1
Triptycene was heated with 5 M hexacarbonylchro-
mium in dibutyl ether under reflux for 45 h under a
nitrogen atmosphere to give a mixture of complexes
(
3
) δ 4.89 (s, 2H), 5.08
), 7.40 (m, 2H);
) δ 49.4, 89.0, 90.3, 116.6, 122.4, 126.4, 128.3
(
6
H
6
1
3
3
-
1
(
(
2
-5. After the separation of 2 by chromatography on
CdO); UV (benzene, nm) 334.5 (log ꢀ ) 4.2); HRMS (FAB)
silica gel, the mixture of the other complexes could be
satisfactorily separated by HPLC. The isolated yields
of 2-5 were 20, 5, 23, and 40%, respectively. Each
complex was purified by recrystallization from benzene-
hexane to give yellow crystals, which were stable at
room temperature and decomposed at about 230 °C. In
solutions, the complexes slowly decomposed to the
metal-free triptycene under natural light.
+
C
26
H
14
O
6
Cr
2
(MH ) calcd m/ e 526.9679, found m/ e 526.9695.
Anal. Calcd for C26
C, 63.28; H, 3.19.
µ-(η :η -Tr ip tycen e)bis[tr ica r bon ylch r om iu m (0)] (C )
s
4): mp 230-237 °C dec; H NMR (CDCl
m, 2H), 5.21 (m, 2H), 5.67 (m, 2H), 5.80 (m, 2H), 7.14 (m,
H), 7.36 (C
9.9, 90.8, 91.3, 114.8, 115.5, 123.5, 126.5, 128.3 (C
32.2, 232.5; IR (Nujol, cm-1) 1978, 1956, 1900, 1884, 1856
H
14
O
6
Cr
2
6 6
‚C H : C, 63.58; H, 3.33. Found:
6
6
1
(
(
2
8
2
3
) δ 4.96 (s, 2H), 5.14
1
3
6
H
6
), 7.38 (m, 2H); C NMR (CDCl
3
) δ 49.5, 89.7,
6
H
6
), 142.4,
The new compounds, 3-5, gave satisfactory analytical
data, and their mass peaks (FAB) were consistent with
the expected molecular weights. The solutions show a
UV absorption at ca. 330 nm with a very broad shoulder
band in the visible region, attributable to the charge
transfer between the Cr atom and the benzene ligand.12
Characteristic IR bands due to carbonyl stretching were
observed in the range of 1850-1900 (symmetric) and
(
CdO); UV (benzene, nm) 327.5 (log ꢀ ) 4.3); HRMS (FAB)
+
C
26
H
14
O
6
Cr
2
(MH ) calcd m/ e 526.9679, found m/ e 526.9672.
Anal. Calcd for C26
C, 63.68; H, 3.27.
H
14
O
6
Cr
2
6 6
‚C H : C, 63.58; H, 3.33. Found:
6
6
6
µ -(η :η :η -Tr iptycen e)tr is[tr icar bon ylch r om iu m (0)] (5):
3
1
mp 227-233 °C dec; H NMR (CDCl
3
) δ 4.88 (s, 2H), 5.27 (m,
); C NMR (CDCl ) δ 47.4, 90.2,
1
3
6
9
1
H), 5.79 (m, 6H), 7.37 (C
1.2, 112.2, 128.3 (C ), 232.1; IR (Nujol, cm ) 1972, 1948,
874 (CdO); UV (benzene, nm) 333.5 (log ꢀ ) 4.4); HRMS
6
H
6
3
-
1
6
H
6
-
1 2
1940-1980 (asymmetric) cm
.
(
11) Vandenheuvel, W. J . A.; Walker, R. W.; Nagelberg, S. B.;
(12) Kanis, D. R.; Ratner, M. A.; Marks, T. J J . Am. Chem. Soc.
1994, 114, 10338.
Willeford, B. R. J . Organomet. Chem. 1980, 190, 73.

4
014 Organometallics, Vol. 16, No. 18, 1997
Notes
Ta ble 2. Selected Bon d Len gth s a n d Dih ed r a l
An gles in Com p ou n d s 4 a n d 5
4
5
Bond Lengths (Å)
Cr(1)-Cara
Cr(1)-CCO
Cr(2)-Car
Cr(2)-CCO
Cr(3)-Car
Cr(3)-CCO
2.207-2.245
2.199-2.242
1.838-1.844
2.236-2.186
1.817-1.842
2.195-2.235
1.822-1.842
1.38-1.42
b
1.79-1.82
2.192-2.236
1.81-1.83
Car-Car (coordinated)
1.37-1.43
1.36-1.41
Car-Car (uncoordinated)
Dihedral Angles (deg)c
Plane 1-Benzene 1
Plane 2-Benzene 2
Plane 3-Benzene 3
Plane 1-Plane 2
Plane 1-Plane 3
Plane 2-Plane 3
6.4
3.8
3.7
5.4
1.7
4.9
120.4
117.7
121.9
120.2
120.5
119.3
a
Aromatic carbons. b Carbonyl carbons. c Dihedral angles be-
tween average planes comprised of carbon atoms as follows. Plane
1
: C(10), C(4a), C(9a), C(9). Plane 2: C(10), C(10a), C(8a), C(9).
Plane 3: C(10), C(16), C(12), C(9). Benzene 1: C(1), C(2), C(3),
C(4), C(4a), C(9a). Benzene 2: C(5), C(6), C(7), C(8), C(8a), C(10a).
Benzene 3: C(11), C(12), C(13), C(14), C(15), C(16).
and selected structural parameters are given in Table
2
. As expected from the NMR data, 4 and 5 take
approximately Cs and C3h structures, respectively.
Structural features in each benzene-tricarbonylchro-
mium moiety are common with those of other ordinary
1
,2
complexes.
The Cr atom lies almost above the center
of the benzene ring, with an interatomic Cr-C distance
of 2.19-2.24 Å for each coordinating benzene. The three
carbonyl groups bonded to the chromium atom take a
staggered conformation, such that one of the CO groups
is farthest from the bridgehead carbons: for example,
C(1)-C(9a), C(2)-C(3), and C(4)-C(4a) bonds are bi-
sected by the carbonyls in benzene 1. The preference
for this conformation is attributed to the avoidance of
steric interactions between the carbonyl groups and
another adjacent benzene ring.
There are no observable changes in the bond distances
and the bond angles in the aromatic carbons due to the
complex formation. While all the complexed benzene
groups are virtually planar, the folding of the two
attached carbons, C(9) and C(10), from the benzene
plane toward the opposite side of the Cr(CO)3 group is
significant. The dihedral angles between the benzene
plane and the plane made of the bridgehead and the
attached aromatic carbons are 3.7-6.4° for the com-
plexed benzenes. The bending angle is largest at
benzene 1 in 4 among them because there is no Cr(CO)3
group, which prevents the deformation, between ben-
zenes 1 and 3. These values are larger than the
corresponding angle in the 1:1 complex 2, 3.0°.7
F igu r e 1. ORTEP drawings of 4 and 5 with thermal
ellipsoids at 50% probability (solvent molecules are not
shown).
1H NMR signals due to the protons in the complexed
benzeno groups are shifted upfield (ca. δ 5.2) compared
with those in the metal-free ones (ca. δ 7.3). The upfield
shift was also observed for the aromatic carbons by
about 30 ppm in 13C NMR spectra.
The stereochemistry of the two 1:2 complexes is
unambiguously determined by the signal pattern of the
1
13
H and C NMR. The two complexed benzeno groups
The deformations of the triptycene skeleton, widening
or narrowing of the notches between the three bridges,
are sometimes significant in the variously substituted
are magnetically equivalent in 3, whereas they are
nonequivalent in 4. As for the carbonyl carbon signals,
3
and 4 afford one and two signals, respectively, at ca.
32 ppm. These findings indicate that 3 has a higher
1
3
triptycenes we have studied. As shown in Table 2,
2
C2v symmetry with an additional symmetrical plane
through the uncomplexed benzene ring compared with
(
13) Mikami, M.; Toriumu, K.; Konno, M.; Saito, Y. Acta Crystallogr.,
4
(Cs). On the other hand, in the 1:3 complex 5, all the
Sect. B 1975, 31, 2474. Toyota, S.; Endo, M.; Teruhi, M.; Noda, Y.;
Oh ki, M.; Yamasaki, M.; Shibahara, T. Bull. Chem. Soc. J pn. 1993, 66,
088. Toyota, S.; Miyasaka, T.; Matsumoto, Y.; Matsuo, T.; Oh ki, M.
Bull. Chem. Soc. J pn. 1994, 67, 1680. Oh ki, M.; Fujino I.; Kawaguchi,
D.; Chuda, K.; Moritaka, Y.; Yamamoto, Y.; Tsuda, S.; Akinaga, T.;
Aki, M.; Kojima, H.; Morita, N.; Sakurai, M.; Toyota, S.; Tanaka, Y.;
Tanuma, T.; Yamamoto, G. Bull. Chem. Soc. J pn. 1997, 70, 457.
benzeno groups are magnetically equivalent and so are
the carbonyl groups, consistent with C3h symmetry.
2
The structures of 4 and 5 were determined by X-ray
crystallography. Figure 1 shows the ORTEP drawings,

Notes
Organometallics, Vol. 16, No. 18, 1997 4015
the dihedral angle between planes 2 and 3 in 4 is a little
but significantly larger than 120°, the ideal value for
C3 symmetry, due to the compensation of the narrow
notch between planes 1 and 3. Because of the absence
of a Cr(CO)3 group in the notch between benzenes 1 and
Ack n ow led gm en t. The authors thank M. Aki and
N. Morita for their assistance in X-ray analysis.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and thermal parameters and complete bond distances and
angles for 4 and 5 (19 pages). Ordering information is given
on any current masthead page.
3
, benzene 3 is pushed away by the Cr(CO)3 group
bonded to benzene 2 to reduce the steric interaction.
This type of deformation is insignificant in 5 because
Cr(CO)3 groups lie in all notches.
OM9703705