(η6-Biphenyl)tricarbonylchromium and μ- (η6:η6)-biphenyl-bis(tricarbonylchromium)

Article abstract of DOI:10.1107/S0108270104025958

The structural features of (η-Biphenyl)tricarbonylchromium and μ-(η⁶:η⁶)-biphenyl-bis(tricarbonylchromium was investigated using density functional theory and natural bonding orbital theory analyses. It was found that the compund has a typical piano-stool coordination about the Cr center and the dihedral angle betwwen the planes of the phenyl rings is 23.55 (5)°. It was also found that the corresponding angle in compound is 0° because the molecule occupies a crystallographic inversion center. The Cr atoms reside on opposite sides of the biphenyl ligand.

Full text of DOI:10.1107/S0108270104025958

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
biphenyl)tricarbonylchromium, (II), which we reported
previously (Czerwinski et al., 2003). We found that (II) reacts
with tert-butyllithium at 195 K in ether in a metal±halogen
exchange reaction that forms (I) in ꢁ10% yield after proton-
ation with methanol. In an effort to prepare an authentic
sample of (I) for comparison, a 1:1 mixture of biphenyl and
hexacarbonylchromium was re¯uxed in dibutyl ether/tetra-
hydrofuran (Nicholls & Whiting, 1959). Unexpectedly, the 1H
NMR spectrum of the resulting crude yellow solid showed that
the product was a mixture containing 70% of the desired
compound, (I), and 30% of ꢁ-(ꢀ6:ꢀ6)-biphenyl-bis(tricar-
bonylhexchromium), (III). Recrystallization from hexane/
ether led to the formation of some single crystals of (III) but
was not an ef®cient method for effecting complete separation
of the two compounds. However, they have markedly different
polarities and were readily separated using thin-layer chro-
matography (Top & Jaouen, 1979). Slow evaporation of a
hexane/ether solution of (I) led to single crystals suitable for
crystallographic analysis.
ISSN 0108-2701
(g6-Biphenyl)tricarbonylchromium
and l-(g6:g6)-biphenyl-bis(tri-
carbonylchromium)
Ilia A. Guzeia* and Curtis J. Czerwinskib
aChemistry Department, University of Wisconsin±Madison, 1101 University Ave.,
Madison, WI 53706, USA, and bDepartment of Chemistry, University of Wisconsin±
La Crosse, 1725 State Street, La Crosse, WI 54601, USA
Correspondence e-mail: iguzei@chem.wisc.edu
Received 13 September 2004
Accepted 13 October 2004
Online 11 November 2004
The title compounds, [Cr(C12H10)(CO)3] and [Cr2(C12H10)-
(CO)6], serve as a fundamental standard of comparison for
other mono- and polysubstituted (ꢀ6-biphenyl)tricarbonyl-
chromium compounds. (ꢀ6-Biphenyl)tricarbonylchromium
has a typical piano-stool coordination about the Cr center,
and the dihedral angle between the planes of the phenyl rings
is 23.55 (5)ꢀ. The corresponding angle in ꢁ-(ꢀ6:ꢀ6)-biphenyl-
bis(tricarbonylchromium) is 0ꢀ because the molecule occupies
a crystallographic inversion center; the Cr atoms reside on
opposite sides of the biphenyl ligand. Density functional
theory and natural bonding orbital theory analyses were used
to scrutinize the geometry of these and closely related
compounds to explain important structural features.
We also report the structure of (III) (Fig. 2), which crys-
tallizes in space group P21/c. We include atomic coordinates
for the monoclinic cell that were not reported in a previous
study, which showed that (III) crystallizes in two different
space groups, P1 and P21/c (Corradini & Allegra, 1960).
Compound (III) has attracted attention recently in electro-
chemical reactions leading to substituted biphenyl compounds
(Rieke et al., 1992), and substituted variations of (III) have
been the subject of crystallographic studies related to the
electrochemistry (Pierce & Geiger, 1994) and novel coupling
reactions (Rosemunch et al., 1991; Uemura et al., 1994) of
(arene)tricarbonylchromium compounds.
Comment
As part of an ongoing study of ortho-substituted (biphenyl)-
tricarbonylchromium compounds, we became interested in
(ꢀ6-biphenyl)tricarbonylchromium, (I), since it is the simplest
unsubstituted version of all other mono- or polysubstituted
compounds in the series. Recently, polysubstituted analogs of
(I) have been used in stereoselective syntheses of biologically
important molecules (Kamikawa et al., 2003; Fogel et al., 2001)
and metal carbene benzannulation reactions (Kretschik et al.,
1996), and the (ꢀ6-biphenyl)dicarbonylchromium fragment
has been incorporated into Fischer carbene complexes (Merlic
et al., 1992). Surprisingly, the solid-state structure of the
unsubstituted analog (I) has not been reported to date, though
several methods for its synthesis have been described
previously (Fischer et al., 1959; Ercoli et al., 1959; Rieke et al.,
1982). The importance of this compound as a fundamental
standard of comparison for other mono- and polysubstituted
(ꢀ6-biphenyl)tricarbonylchromium compounds prompted us
to explore the solid-state structure of (I), which is reported
here.
Because of the importance of (I) and (III), we scrutinized
their solid-state geometries and performed density functional
theory (DFT) studies of (I) and (III), referred to as (I)-DFT
and (III)-DFT, respectively, and of [Cr(ꢀ6-C6H6)(CO)3], (IV),
Figure 1
The molecular structure of (I). Displacement ellipsoids are shown at the
50% probability level.
We ®rst became interested in (I) (Fig. 1) because it relates
to the structure of the brominated analog (ꢀ6-2-bromo-1,10-
Acta Cryst. (2004). C60, m615±m617
DOI: 10.1107/S0108270104025958
# 2004 International Union of Crystallography m615

metal-organic compounds
between the phenyl rings in these compounds are different.
The PhÐPh dihedral angles in (I) and (I)-DFT differ
dramatically (Table 1), but the value in (I)-DFT is closer to the
theoretical value of the dihedral angle in free biphenyl
(40.84ꢀ). In the solid-state structure of (III), the molecule
occupies a crystallographic inversion center, which results in a
torsion angle of 0ꢀ between the phenyl rings.
Experimental
A mixture of hexacarbonylchromium (0.900 g, 4.09 mmol) and bi-
phenyl (0.680 g, 4.02 mmol) in di-n-butyl ether (30 ml) and tetra-
hydrofuran (3 ml) was degassed and heated at re¯ux for 24 h under a
nitrogen atmosphere. Tetrahydrofuran, di-n-butyl ether and the
remaining unreacted hexacarbonylchromium were removed by
vacuum distillation. Puri®cation of the remaining yellow residue by
preparative thin-layer chromatography (silica gel, 2:1 hexane/diethyl
ether) gave a yellow band (RF = 0.35) from which (I) was isolated as a
yellow air-stable solid (0.722 g, 62% yield based on biphenyl) and an
orange band (RF = 0.15) from which (III) was isolated as a yellow air-
stable solid (0.192 g, 11% yield based on biphenyl). Crystals of (I)
were obtained by slow evaporation of a 3:1 hexane/ether solution and
crystals of (III) were obtained by slow evaporation of a 1:1 hexane/
ether solution.
Figure 2
The molecular structure of (III). Displacement ellipsoids are shown at the
50% probability level. [Symmetry code: (A) 1 x; y; z.]
with GAUSSIAN98 (Frisch et al., 1998). Selected geometric
parameters are presented in Table 1, while selected bond
lengths are tabulated in Tables 2 and 3. Literature data for the
relevant bond distances in related complexes reported to the
Cambridge Structural Database (Allen, 2002) were previously
compiled and analyzed by us (Czerwinski et al., 2003).
Compound (I)
The CrÐC(O), CrÐC(Ph) and CrÐcentroid(Ph) distances
in (I) and (III) are in excellent agreement with one another,
the corresponding parameters in (II) and the literature data
for related complexes. Interestingly, in the structures of
(I)-DFT, (III)-DFT and (IV) optimized at the B3LYP/
LANL2DZ level of theory, the CrÐC(O) distances are
Crystal data
3
[Cr(C12H10)(CO)3]
Mr = 290.23
Dx = 1.560 Mg m
Mo Kꢃ radiation
Cell parameters from 8453
re¯ections
Monoclinic, P21=n
Ê
a = 12.3982 (5) A
ꢄ = 2.6±26.4ꢀ
ꢁ = 0.92 mm
T = 100 (2) K
Ê
b = 7.1029 (3) A
1
Ê
c = 14.8428 (6) A
ꢂ = 108.969 (1)ꢀ
V = 1236.12 (9) A
Z = 4
Ê
shorter (by 0.01±0.02 A) than those in (I) and (III), while the
3
Ê
Block, yellow
0.38 Â 0.32 Â 0.28 mm
Ê
CrÐC(Ph) distances are longer (by almost 0.1 A) than the
respective bond lengths in (I) and (III), a very substantial
difference. It is noteworthy that the natural atomic charges of
the Cr centers in (I)-DFT, (III)-DFT and (IV) are 0.87 in all
three cases, a result not intuitively obvious since the formal
metal oxidation state in these compounds is zero. The natural
bond theory analysis revealed that the hybridization of the Cr
atoms is sd2 in (I)-DFT and (III)-DFT, and sp0.5d4.5 in (IV),
indicating contribution of the p orbitals in the latter case.
However, it is not clear why the hybridization states would
differ in these compounds.
Data collection
Bruker SMART CCD area-detector
diffractometer
' and ! scans
Absorption correction: multi-scan
(SADABS; Bruker, 2000±2003)
Tmin = 0.720, Tmax = 0.782
13 192 measured re¯ections
2526 independent re¯ections
2384 re¯ections with I > 2ꢅ(I)
Rint = 0.021
ꢄmax = 26.4ꢀ
h = 15 ! 15
k = 8 ! 8
l = 18 ! 18
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.025
wR(F2) = 0.072
S = 1.07
2526 re¯ections
w = 1/[ꢅ2(F2o) + (0.0425P)2
+ 0.6246P]
The CÐC distances in the ligated ring of the solid-state
Ê
structures of (I) and (III) [1.412 (12) and 1.414 (11) A,
respectively] are, as expected, longer than those of an ideal
benzene molecule. The corresponding value in (IV) is
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max = 0.001
3
Ê
Áꢆmax = 0.35 e A
3
Ê
0.24 e A
172 parameters
H-atom parameters constrained
Áꢆmin
=
Ê
1.415 (11) A, con®rming that the CrÐC interactions in all
three cases are similar. Calculating the average CÐC distances
in the coordinated rings in (I)-DFT and (IV) may be
misleading since the theoretical geometries indicate alter-
Table 1
Geometric parameters (A, ) for (I), (I)-DFT, (III), (III)-DFT and (IV).
ꢀ
Ê
Ê
nating bond lengths (1.43 and 1.42 A) in all three cases.
Compound
(I)
(III)
(I)-DFT
1.831 (1)
2.229 (15) 2.219 (11) 2.320 (17) 2.318 (15) 2.317 (7)
(III)-DFT (IV)
1.832 (3) 1.832
The ipso-CÐipso-C distances in (I), (II), (III), (I)-DFT,
(III)-DFT and the free biphenyl molecule optimized at the
B3LYP/6-311++G** level of theory are 1.488 (2), 1.497 (3),
1.493 (3), 1.488, 1.486 and 1.486 A, respectively, and are not
statistically different, despite the fact that the dihedral angles
CrÐC(O)
CrÐC(Ph)
CrÐcentroid(Ph) 1.725 (2)
(Ph)CÐC(Ph)
Ph±Ph angle
1.843 (8)
1.851 (3)
1.710 (2)
1.493 (3)
0.0
1.830
1.488
37.4
1.827
1.486
30.9
1.82
1.488 (2)
23.55 (5)
Ê
ꢂ
m616 Guzei and Czerwinski
[Cr(C12H10)(CO)3] and [Cr2(C12H10)(CO)6]
Acta Cryst. (2004). C60, m615±m617

metal-organic compounds
Table 2
Selected interatomic distances (A) for (I).
All H atoms were included in the structure-factor calculations at
idealized positions and were allowed to ride on their neighboring
atoms with relative isotropic displacement coef®cients.
Ê
CrÐC15
CrÐC14
CrÐC13
CrÐC5
CrÐC6
1.8374 (15)
1.8393 (15)
1.8518 (15)
2.2148 (14)
2.2240 (14)
CrÐC3
CrÐC2
CrÐC4
CrÐC1
2.2250 (14)
2.2252 (14)
2.2259 (14)
2.2592 (14)
For both compounds, data collection: SMART (Bruker, 2000±
2003); cell re®nement: SAINT (Bruker, 2000±2003); data reduction:
SAINT; program(s) used to solve structure: SHELXTL (Bruker,
2000±2003); program(s) used to re®ne structure: SHELXTL; mol-
ecular graphics: SHELXTL; software used to prepare material for
publication: SHELXTL.
CJC acknowledges the University of Wisconsin±La Crosse
Faculty Research Grant Program.
Compound (III)
Crystal data
3
[Cr2(C12H10)(CO)6]
Mr = 426.26
Dx = 1.780 Mg m
Mo Kꢃ radiation
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: AV1212). Services for accessing these data are
described at the back of the journal.
Monoclinic, P21=c
Cell parameters from 4396
re¯ections
Ê
a = 10.7256 (12) A
b = 10.6894 (12) A
ꢄ = 2±25ꢀ
Ê
1
Ê
c = 7.1789 (8) A
ꢁ = 1.40 mm
T = 100 (2) K
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ꢂ = 104.875 (2)ꢀ
V = 795.48 (15) A
Z = 2
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Ê
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Bruker SMART CCD 1000 area-
detector diffractometer
! scans
Absorption correction: multi-scan
(SADABS; Bruker, 2000±2003)
Tmin = 0.625, Tmax = 0.671
7141 measured re¯ections
1943 independent re¯ections
1838 re¯ections with I > 2ꢅ(I)
Rint = 0.025
ꢄmax = 28.3ꢀ
h = 14 ! 14
k = 14 ! 13
l = 9 ! 9
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.032
wR(F2) = 0.091
S = 1.09
1943 re¯ections
w = 1/[ꢅ2(F2o) + (0.0539P)2
+ 0.5575P]
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max < 0.001
3
Ê
Áꢆmax = 0.51 e A
3
Ê
0.35 e A
118 parameters
H-atom parameters constrained
Áꢆmin
=
Table 3
Selected interatomic distances (A) for (III).
Ê
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Cr1ÐC9
Cr1ÐC8
Cr1ÐC7
Cr1ÐC3
Cr1ÐC5
1.8484 (18)
1.8507 (18)
1.8549 (19)
2.2070 (18)
2.2137 (18)
Cr1ÐC6
Cr1ÐC2
Cr1ÐC4
Cr1ÐC1
2.2150 (17)
2.2201 (17)
2.2207 (18)
2.2384 (17)
ꢂ
Acta Cryst. (2004). C60, m615±m617
Guzei and Czerwinski
[Cr(C12H10)(CO)3] and [Cr2(C12H10)(CO)6] m617