Hydroquinoid chromium complexes bearing an acyclic conjugated bridge: Chromium-templated synthesis, molecular structure, and haptotropic metal migration

Article abstract of DOI:10.1021/om100257x

The naphthohydroquinoid tricarbonyl chromium complexes 3 and 6, bearing a styryl or phenylazo moiety, have been synthesized and studied for the haptotropic metal migration along the extended π-system. Quantum chemical calculations suggested a feasible stepwise rearrangement of the Cr(CO) ₃ fragment from the hydroquinoid to the other terminal phenyl ring for the azo- rather than for the ethene-bridged system. An experimental and kinetic study of the ethene-bridged complex 3 revealed a haptotropic metal shift onto the adjacent naphthalene ring to give isomer 7 and suggested a competing intermolecular decomplexation-recomplexation pathway for the coordination of the terminal phenyl ring, affording bismetalated complexes 8 and 9. Attempts of a controlled metal migration in the azo complex analogue 6 under similar conditions were unsuccessful and resulted in partial decomposition.

Full text of DOI:10.1021/om100257x

6172 Organometallics 2010, 29, 6172–6185
DOI: 10.1021/om100257x
Hydroquinoid Chromium Complexes Bearing an Acyclic Conjugated
Bridge: Chromium-Templated Synthesis, Molecular Structure, and
Haptotropic Metal Migration
§
Peter Hegele,† Bindu Santhamma,†,4 Gregor Schnakenburg, Roland Frohlich, Olga Kataeva,
€
Martin Nieger,§,^ Konstantinos Kotsis, Frank Neese,* and Karl Heinz Dotz*
‡
,‡
,†
€
†
ꢀ
€
€
Kekule-Institut fur Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universitat Bonn,
Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany, ‡Institut fu€r Physikalische und Theoretische Chemie,
Rheinische Friedrich-Wilhelms-Universita€t Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany,
§Institut fu€r Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universita€t Bonn, Gerhard-Domagk-Strasse 1,
D-53121 Bonn, Germany, ^Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki,
P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014, Finland, Organisch-Chemisches Institut,
Westfa€lische Wilhelms-Universita€t Mu€nster, Corrensstrasse 40, D-48149 Mu€nster, Germany, and
4Cellular and Structural Biology, UT Health Science Center, San Antonio, Texas 78229, United States
Received April 1, 2010
The naphthohydroquinoid tricarbonyl chromium complexes 3 and 6, bearing a styryl or phenylazo
moiety, have been synthesized and studied for the haptotropic metal migration along the extended
π-system. Quantum chemical calculations suggested a feasible stepwise rearrangement of the Cr(CO)3
fragment from the hydroquinoid to the other terminal phenyl ring for the azo- rather than for the ethene-
bridged system. An experimental and kinetic study of the ethene-bridged complex 3revealed a haptotropic
metal shift onto the adjacent naphthalene ring to give isomer 7 and suggested a competing intermolecular
decomplexation-recomplexation pathway for the coordination of the terminal phenyl ring, affording
bismetalated complexes 8 and 9. Attempts of a controlled metal migration in the azo complex analogue 6
under similar conditions were unsuccessful and resulted in partial decomposition.
Introduction
attracted increasing interest.3,4 Experimental and theoretical
investigations have been undertaken to elucidate the mechanism
of this process. Theoretical studies on naphthalene tricarbonyl
chromium complexes suggested a metal shift along the periphery
of the π-system via a η4-coordinated trimethylene methane-like
transition state.5 An alternative scenario potentially leading to
Metal complexes bearing a ligand that offers more than a
single coordination mode may undergo an intramolecular metal
shift along the ligand platform. This process in which the metal
center remains permanently coordinated to the ligand during the
metal relocation is referred to as haptotropic metal migration.1
Since the first report of a reversible shift of a Cr(CO)3 fragment
along the platform of 2,3-dimethylnaphthalene,2 the rearrange-
ment of chromium fragments along arene platforms has
€
(4) For reviews on the haptotropic migration, see: (a) Dotz, K. H.
Angew. Chem., Int. Ed. Engl. 1984, 23, 587; Angew. Chem. 1984, 96, 573. (b)
Ustynyuk, N. A. Organomet. Chem. USSR 1989, 2, 20; Metalloorg. Khim.
1989, 2, 43; Chem. Abstr. 1989, 111, 115236. (c) Semmelhack, M. F. In
Comprehensive Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A.;
Wilkinson, G., Eds.; Pergamon Press: Oxford, UK, 1995; Vol. 12, Chapter 9, p
979. (d) Wulff, W. D. In Comprehensive Organometallic Chemistry II; Abel,
E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon Press: Oxford, UK, 1995;
Vol. 12, pp 469. (e) Morris, M. J. In Comprehensive Organometallic Chemistry
II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G.,Eds.; Pergamon: Oxford, UK,
*To whom correspondence should be addressed. E-mail: doetz@
uni-bonn.de; neese@thch.uni-bonn.de.
(1) Anh, N. T.; Elian, M.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100,110.
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69, 744; Chem. Abstr. 2000, 134, 178576. (h) Dotz, K. H.; Stendel, Jr., J. In
€
1555. (c) Cunningham, S. D.; Ofele, K.; Willeford, B. J. Am. Chem. Soc.
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8, 1751. (h) Oprunenko, Y. F.; Malyugina, S.; Nesterenko, P.; Mityuk, D.;
Malyshev, O. J. Organomet. Chem. 2000, 597, 42. (i) Jahr, H. C.; Nieger,
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Pfletschinger, A.; Ciupka, J.; Dolg, M.; Nieger, M.; Schnakenburg, G.; Frohlich,
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r
2010 American Chemical Society
pubs.acs.org/Organometallics
Published on Web 11/01/2010

Article
Organometallics, Vol. 29, No. 23, 2010 6173
the same final rearrangement products may follow an inter-
molecular decoordination-recoordination mechanism during
which the Cr(CO)3 fragment is a stabilized by a coordinating
solvent. Whereas an intermolecular reaction is favored by high
temperatures and by coordinating solvents such as THF,
DMSO, and toluene, an intramolecular pathway typically
results from kinetic reaction control using noncoordinating or
only moderately coordinating solvents such as alkanes, dialkyl
ethers, or octafluorotoluene.4c,j,k An intramolecular haptotropic
metal migration is expected to reveal first-order kinetics and,
moreover, can be corroborated by stereochemical criteria, i.e.,
conservation of enantiomeric or diastereomeric purity in the
resulting haptotropomer resulting from a complex precursor
bearing a chiral plane. Among a variety of transition metal
complexes studied in this context, most reports concentrated on
arene chromium complexes, reflecting their ease of preparation.
Beyond the direct complexation of the arene by Cr(CO)6 or
more elaborate Cr(CO)3 transfer reagents such as Cr(NH3)3-
(CO)3,6 which typically results in the formation of regioisomeric
complexes, the chromium-templated benzannulation of alkoxy-
(aryl)carbene chromium complexes provides a regioselective
labeling of a specific benzene ring in densely substituted fused
hydroquinoid tricarbonyl chromium complexes under mild
conditions4a,f,i,h,k,7 Apart from naphthalene complexes, more
extended π-platforms such as phenanthrenes, naphthobenzofur-
anes, and triphenylenes bearing various substitution patterns
have been investigated for their tendency of haptotropic metal
migration.3i,m,n A remarkable example is presented by an orga-
nometallic switch in which a reversible haptotropic migration
was tuned by an appropriate coligand sphere.3k,l,8 Besides
polycyclic arene platforms, metal shifts have also been observed
along nonaromatic conjugated π-systems for several transition
metals, including η2- and η4-iron complexes.9 Extending our
work on fused aromatic platforms we turned our attention to
acyclic π-linkers bridging two arene skeletons. Herein, we report
on benzene and hydroquinoid naphthalene platforms connected
by an ethene (-CHdCH-) or an azo (-NdN-) moiety and
their tendency for haptotropic migration of a Cr(CO)3 fragment.
Figure 1. Molecular structure of stilbene chromium carbene 2.
The numbering of atoms differs from that used in the NMR charac-
terization. Selected bond lengths (A) and angles: C(11)-Cr(1) =
2.083(7); {O(1)-C(11)-C(1)}-{C(16)-Cr(1)-C(17)} = 36ꢀ,
(phenyl)-(phenylene)=4ꢀ,{O(1)-C(11)-C(1)}-(phenylene)=27ꢀ.
ꢀ
˚
Scheme 1. Synthesis of Hydroquinoid Benzostilbene Cr(CO)3
Complex 3
molecular structure reveals a nearly coplanar stilbene moiety
with a torsion angle of 4.3ꢀ between the arene rings (Figure 1).
Upon warming with 3-hexyne in tert-butyl methyl ether to
60 ꢀC, chromium carbene 2 underwent a clean benzannulation
to give tricarbonyl{[η6-1,2,3,4,4a,8a]-1-tert-butyldimethylsily-
loxy-2,3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]naphtha-
lene}chromium (3) as a single regioisomer in 92% yield after
O-silylation (Scheme 1).
The synthesis of the azobenzene chromium carbene ana-
logues required a modification of the standard protocol due
to the thermolability of lithioazobenzenes above -78 ꢀC.11
This problem was overcome by a low-temperature (-100 ꢀC)
transmetalation by anhydrous zinc bromide to generate the
organozinc derivative.12,13 This protocol is also compatible with
alkyl and amino donor substituents in the arene, which may
compensate in part the electron deficiency caused by the azo
moiety. Addition of hexacarbonyl chromium and subsequent
O-alkylation of the resulting acyl chromate intermediate by the
more soluble triethyloxonium tetrafluoroborate afforded the
azobenzene-functionalized chromium carbenes 5a-c in mod-
erate to good yields (Scheme 2).
Results and Discussion
Synthesis of Hydroquinoid Benzostilbene and Benzoazobenzene
Cr(CO)3 Complexes. The regioselective labeling of hydroquinoid
benzostilbene and benzoazobenzene platforms by a Cr(CO)3
fragment is based on the chromium-templated benzannulation
of stilbene and azobenzene chromium carbenes. Lithiation
of (E)-1-bromo-4-styrylbenzene (1), which is accessible in a
Wittig reaction of benzyltriphenylphosphonium bromide and
4-bromobenzaldehyde,10 followed by addition to hexacarbonyl
chromium and O-methylation of the acyl chromate intermediate
afforded pentacarbonyl[methoxy(4-{(E)-20-phenylethenyl}phe-
nyl)carbene]chromium(0) (2) in 82% yield (Scheme 1). Its
(6) (a) Rausch, M. D.; Moser, G. A.; Zaiko, E. J.; Lipman, A. L., Jr.
J. Organomet. Chem. 1970, 23, 185. (b) Knox, G. R.; Leppard, D. G.; Pauson,
P. L.; Watts, W. E. J. Organomet. Chem. 1972, 34, 347. (c)Moser, G. A.;Rausch,
M. D. Synth. React. Inorg. Met.-Org. Chem. 1974, 4, 37. (d) Top, S.; Jaouen, G.
J. Organomet. Chem. 1979, 182, 381.
(7) For another recent review, see: Waters, M. L.; Wulff, W. D. In
Organic Reactions; Overman, L. E., Ed.; Hoboken, NJ, 2008; Vol. 70, pp 121.
€
(8) Jahr, H. C.; Nieger, M.; Dotz, K. H. Chem. Commun. 2003, 2866.
(9) (a) Foxman, B.; Marten, D.; Rosan, A.; Raghu, S.; Rosenblum,
M. J. Am. Chem. Soc. 1977, 99, 2160. (b) Whitlock, H. W., Jr.; Reich, C.;
Woessner, W. D. J. Am. Chem. Soc. 1971, 9, 2483. (c) Hafner, A.; von
Philipsborn, W.; Salzer, A. Angew. Chem., Int. Ed. 1985, 24, 126; Angew.
Chem. 1985, 97, 136.
(11) (a) Katritzky, A. R.; Wu, J.; Verin, S. V. Synthesis 1995, 651. (b)
Koꢁzlecki, T.; Syper, L.; Wilk, K. A. Synthesis 1997, 681.
(12) Santhamma, B. Unpublished results, 2007.
(13) Garlichs-Zschoche, F. A.; Dotz, K. H. Organometallics 2007, 26,
4535.
€
(10) Leung, S. H.; Angel, S. A. J. Chem. Educ. 2004, 81, 1492.

6174 Organometallics, Vol. 29, No. 23, 2010
Hegele et al.
Scheme 2. Synthesis of Azobenzene Chromium Carbenes 5a-c
conditions by variation of temperature, time, and concentra-
tion. As expected, the conversion of the “kinetic” starting
material 3 increased with increasing temperature (80 ꢀC) and
prolonged reaction time in favor of mononuclear complexes 7
and 8; however, this is accompanied by increased decomposi-
tion, as indicated by formation of Cr(CO)6. The formation of
the naphthalene rearrangement product 7 (60% yield) could be
optimized by a combination of relatively short reaction time
(1 h) and slightly increased temperature (80 ꢀC). An increase of
concentration did not reveal significant changes of the product
distribution.
The parallel formation of mono- and dinuclear rearrange-
ment products indicates that competing mechanisms are opera-
tive. In order to examine the influence of Cr(CO)3 coordination
of the terminal phenyl ring on the metal shift within the
naphthalene moiety, we first concentrated on binuclear com-
plex 9. Sufficient amounts of this compound were obtained by
direct complexation of the kinetic benzannulation product 3 by
the Cr(CO)3 transfer reagent Cr(CO)3(NH3)3 in diethyl ether
using boron trifluoride etherate as an assisting Lewis acid. After
chromatographic purification complex 9 was isolated in mod-
erate yield of 54% along with its regioisomer 10 formed as a
minor product (36%). Attempts to induce a haptotropic metal
shift within the naphthalene skeleton of complex 9 failed under
our standard conditions (di-n-butyl ether, 80 ꢀC) and resulted in
predominating decomplexation.
While the formation of mononuclear complexes 7 and 8
might a priori be compatible with an intramolecular hapto-
tropic metal migration, the minor binuclear byproducts 9 and
10 formed along with significant amounts of hexacarbonyl
chromium are indicative for a competing intermolecular sce-
nario such as a decomplexation-recomplexation sequence.
The product distribution outlined in Scheme 4 suggests that
intermolecular reactions gain importance with longer reaction
times, higher temperatures, and higher concentrations. Due to
the diversity of the product pattern, we tried to separate the
overall reaction into individual steps of metal migration and to
study them in more detail. On the basis of previous obser-
vations4,5 the first metal shift is expected to occur within the
naphthalene moiety, modifying the “kinetic” benzannulation
product 3 into its “thermodynamic” haptotropomer 7. This
idea was corroborated by a kinetic 1H NMR study carried out
at 70 ꢀC to minimize subsequent rearrangement or decomposi-
tion. Octafluorotoluene was chosen as an electron-poor sol-
vent unable to stabilize Cr(CO)3 fragments and thus to assist
an intermolecular metal shift. The relative concentrations of
the haptotropomers were determined on the basis of the
resonance integrals of the naphthalene hydrogen atoms of
complex 3 relative to those of complex 7, which appear shifted
2.0-2.5 ppm to higher field (Scheme 5).
Benzannulation of azobenzene-based chromium carbenes
5a-c by 3-hexyne under our standard conditions followed
by naphthol protection afforded the hydroquinoid diazoar-
ene Cr(CO)3 complexes 6a-c in moderate to good yields
(Scheme 3).
Thermal Metal Rearrangement: Haptotropic Metal Migra-
tion versus Intermolecular Metal Shift. Benzoazobenzene Cr-
(CO)3 Complex. The intramolecular mobility of the Cr(CO)3
fragment was first studied for the azobenzene benzannulation
product 6a. A degassed solution of complex 6a in di-n-butyl
ether was first warmed to 70 ꢀC under an argon atmosphere.
Then the temperature was increased by 10 ꢀC after every 30 min,
and the progress of the reaction was monitored by IR spectros-
copy. No metal migration was observed even after a total
reaction time of 5 h while the temperature was increased to
120 ꢀC. We speculated that the incorporation of the electron-
withdrawing azo group deactivates the naphthalene system by
increasing the activation barrier for haptotropic migration of
the Cr(CO)3 fragment. Thus, we aimed at a compensation of the
electron deficiency imposed by the azo group by donor sub-
stitution of the terminal phenyl ring. However, no indication of
a metal shift was observed either for the methyl or the dimethyl-
amino derivative 6b or 6c under the aforementioned conditions.
Instead, all these reactions resulted in decomplexation and
further decomposition.
Benzostilbene Cr(CO)3 Complexes. The haptotropic migra-
tion studies were then extended to the stilbene benzannulation
product. In a separate series of experiments, solutions of com-
plex 3 in di-n-butyl ether were warmed within a temperature
range from 65 to 90 ꢀC, while the metal shift was continuously
monitored by IR spectroscopy over a period of 3 h. We identi-
fied only a small temperature window of 75-80 ꢀC in which
metal migration occurred reasonably fast without dominating
decomposition, as indicated by increasing formation of hexa-
carbonyl chromium. Even within this temperature window we
observed the formation of a complex product pattern consisting
of two pairs of mono- and bis-Cr(CO)3 complexes (Scheme 4).
At 75 ꢀC unreacted starting material 3 and its rearrangement
product 7 bearing the metal fragment on the adjacent naphtha-
lene ring appeared as the major products. Isomer 8 with the
coordinated terminal phenyl ring was formed in up to 10%
yield. Surprisingly, also small amounts (4-5%) of binuclear
complexes 9 and 10 were observed bearing chromium fragments
on both the naphthalene moiety and the phenyl ring. In an
attempt to rationalize these results, we modified the reaction
The ln[c/c0] versus time plot reveals a first-order kinetics
consistent with an intramolecular haptotropic migration of the
Cr(CO)3 fragment. The resulting rate constant of k = 5.6 ꢀ
10-3 s-1 exceeds that observed for comparable naphthalene
complexes3l,14 by 1 order of magnitude, resulting in a free
enthalpy of activation of ΔG‡ = 23.7 kcal/mol, which is lowered
by ca. 10%, respectively. Both parameters resemble those
obtained for phenanthrene complex analogues,5d revealing the
influence of the more extended π-system.
To get insight into the putative second individual migration
step, the rearrangement from haptotropomer 7 to complex 8,
€
€
(14) Dotz, K. H.; Szesni, N.; Nieger, M.; Nattinen, K. J. Organomet.
Chem. 2003, 671, 58.

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Organometallics, Vol. 29, No. 23, 2010 6175
Scheme 3. Benzannulation of Azobenzene Chromium Carbenes 5a-c
Scheme 4. Product Distribution of the Thermal Metal Rearrangement of Stilbene Benzannulation Product 3
bearing the Cr(CO)3 fragment on the terminal phenyl ring, we
warmed complex 7 both in di-n-butyl ether and in octafluor-
otoluene and monitored both processes by IR and NMR spec-
troscopy, respectively, in a temperature range of 70-80 ꢀC.
Both experiments did not reveal any indication of a controlled
metal migration and, instead, finally resulted in decomposition
of the starting material. We speculate that the chromium arene
interaction is destabilized when the metal fragment leaves its
position above the center of the less substituted naphthalene
ring, moving toward the π-periphery, and that the further
migration to the olefinic CdC bond cannot compete with
alternative pathways finally resulting in decomplexation.
Molecular Structures of Mono- and Bimetallic Benzostil-
bene Complexes 3 and 7-10 and Azobenzene Complex 6b. The
molecular structures of both the benzannulation products and
their rearrangement products arising from a shift of the Cr(CO)3
fragment have been established by X-ray diffraction. The
“kinetic” benzostilbene and azobenzene complexes 3 and 6b
reveal an eclipsed conformation of the Cr(CO)3 tripod that is
slightly shifted toward the periphery of the hydroquinoid ring. A
similar, but more pronounced dislocation is observed for hap-
totropomer 7, in which the metal fragment distinctly points
away from the ring junction and, moreover, adopts a staggered
conformation, which also occurs in the phenyl-coordinated
isomer 8. While an only minor deviation from coplanarity of
the naphthalene and benzene platforms (ca. 8ꢀ) is found for
complexes 6b, 7, and 8, the distortion of the extended π-system
increases to 30ꢀ in the “kinetic” benzannulation product 3. A
considerable deviation of the skeleton of fused arenes from
coplanarity has been found to hamper efficient haptotropic

6176 Organometallics, Vol. 29, No. 23, 2010
Hegele et al.
Scheme 5. Kinetic Plots for the Rearrangement of Complex 3 to Haptotropomer 7
Figure 3. Molecular structure of benzoazobenzene complex 6b.
Figure 2. Molecular structure of benzostilbene complex 3. The
numbering of atoms differs from that used in the NMR character-
ization. Selected bond lengths (A) and angles (deg) (323 K): Cr-
C(1)=2.2465(18), Cr-C(2)=2.2501(18), Cr-C(3)=2.2268(18),
Cr-C(4) = 2.2570(19), Cr-C(5) = 2.2985(18), Cr-C(10) =
2.2525(18); plane (phenyl)-(naphthalene) = 30.
ꢀ
˚
Selected bond lengths (A) and angles (deg): C(1)-Cr=2.262(3),
C(2)-Cr=2.276(3), C(3)-Cr=2.235(2), C(4)-Cr=2.248(2),
C(4A)-Cr = 2.272(3), C(8A)-Cr = 2.239(3); plane (phenyl)-
(naphthalene) = 8.
ꢀ
˚
Quantum Chemical Calculations. Calibration. To ensure
the reliability of density functional theory (DFT) and, in
particular, the BP86 functional15 for the study of hapto-
tropic rearrangements in arene Cr(CO)3 complexes, sin-
gle-point calculations of the reaction system shown in
Scheme 6 have been performed using different quantum
chemical ab initio approaches ranging from the SCF to the
highly correlated and accurate CCSD(T) level.16 The DFT
hybrid and double-hybrid functionals B3LYP17 and
B2PLYP18 were also tested for their ability to reproduce
the CCSD(T) results.
metal migration and to favor decomplexation; however, this
argument does not hold for arene complexes bearing a more
flexible alkene or azo π-bridge. The molecular structures of
mononuclear arene complexes 3, 6b, 7, and 8 are shown in
Figures 2-5.
In the binuclear complex 9 the angle between the two arene
platforms (11ꢀ) resembles that observed for the mononuclear
complexes 6b, 7, and 8. The Cr(CO)3 fragments reveal an anti
conformation and an eclipsed conformation for the Cr1
tripod within the naphthalene and a staggered one for the
Cr2 tripod within the benzene moieties, as encountered
separately in complexes 3 and 8, respectively. In complex
10 the syn conformation of both staggered metal fragments
results in a considerable distortion of the extended π-skele-
ton, as indicated by an angle of 42ꢀ between the benzene and
naphthalene planes. The molecular structures of the binu-
clear arene complexes 9 and 10 are depicted in Figures 6 and 7.
(15) (a) Perdew, J. P. Phys. Rev. B 1986, 33, 8822. (b) Becke, A. D.
Phys. Rev. A 1988, 38, 3098.
(16) Wennmohs, F.; Neese, F. Chem. Phys. 2008, 343, 217.
(17) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Stephens, P. J.;
Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98,
11623. (c) Lee, C; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(18) Grimme, S. J. Chem. Phys. 2006, 124, 34108.

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Organometallics, Vol. 29, No. 23, 2010 6177
Figure 6. Molecular structure of benzostilbene complex 9. The
numbering of atoms differs from that used in the NMR character-
ꢀ
˚
Figure 4. Molecular structure of benzostilbene complex 7. The
numbering of atoms differs from that used in the NMR characteriza-
tion. Selected bond lengths (A) and angles (deg): Cr-C(5) =
2.325(3), Cr-C(6) = 2.205(3), Cr-C(7) = 2.213(3), Cr-C(8) =
2.238(3), Cr-C(9) = 2.209(3), Cr-C(10) = 2.322(3); plane
(phenyl)-(naphthalene) = 9.
ization. Selected bond lengths (A) and angles (deg): C(1)-Cr(1) =
2.269(3), C(2)-Cr(1) = 2.258(3), C(3)-Cr(1) = 2.233(3), C(4)-
Cr(1)=2.243(3), C(5)-Cr(1)=2.280(3), C(10)-Cr(1) = 2.273(3),
C(24)-Cr(2)=2.241(3), C(25)-Cr(2)=2.223(3), C(26)-Cr(2) =
2.221(4), C(27)-Cr(2)=2.199(4), C(28)-Cr(2)=2.215(3), C(29)-
Cr(2) = 2.206(3); (phenyl)-(naphthalene) = 11.
ꢀ
˚
Figure 5. Molecular structure of benzostilbene complex 8. Selected
Figure 7. Molecular structure of benzostilbene complex 10. Selected
˚
00
ꢀ
˚
bond lengths (A) and angles (deg): C(1 )-Cr(1) = 2.227(2),
C(200)-Cr(1)=2.211(3), C(300)-Cr(1)=2.208(3), C(400)-Cr(1)=
2.210(3), C(500)-Cr(1)=2.203(3), C(600)-Cr(1)=2.194(3) ; plane
(phenyl)-(naphthalene) = 9.
bond lengths (A) and angles (deg): C(4A)-Cr(1)=2.284(3), C(5)-
Cr(1) = 2.224(3), C(6)-Cr(1) = 2.233(4), C(7)-Cr(1) = 2.239(4),
C(8)-Cr(1) = 2.202(4), C(8A)-Cr(1) = 2.275(3), C(100)-Cr(2) =
2.238(3), C(200)-Cr(2) = 2.200(4), C(300)-Cr(2) 2.211(4), C(400)-
Cr(2)=2.225(4), C(500)-Cr(2)=2.209(4), C(600)-Cr(2)=2.210(3);
(phenyl)-(naphthalene)=42.
The DFT calculations are in excellent agreement with the
ab initio wave function-based quantum chemical calculations
(Table 1). The difference between BP8615 and B3LYP17 is
marginal. B2PLYP18 performs also well but, as expected, reveals
a more pronounced basis set dependence than the standard DFT
functionals. As the error of the reaction enthalpy, calculated with
the BP86 functional15 relative to the ab initio methods, is very
small, we felt confident with the DFT results and applied this
method for the following study.
Scheme 6. Haptotropic Migration of the Cr(CO)3 Fragment in a
Model Naphthohydroquinone Complex (BP86/TZVP structures)
Geometric Structures and Comparison to the Experiments.
For the computational study of the target systems we have made
a few minor approximations to the computational model. The
hydroquinoid ring has been substituted with two methoxy and
two methyl groups, while more bulky substituents (a methoxy, a
OTBDMS group, and two ethyl groups) have been used in the
experimental study. Moreover, we optimized the structures of
the most stable conformation of the Cr(CO)3 tripod with respect
to the central bond C4a-C8a, consistent with the previous
study.5d In the experimental study, exclusively the E-derivatives
of the benzostilbene and benzoazobenzene Cr(CO)3 complexes
were observed. In agreement with this finding, their calculated
structures are 4.6-18.7 and 0.6-16.0 kcal/mol lower in energy
than their respective Z-isomers.
For both the benzostilbene (I, II, III, IV) and the benzoa-
zobenzene complex (V, VI, VII, VIII) four minima along the
haptotropic migration pathway could be located, as shown in
Figures 8 and 9, respectively. These four structures correspond
to the coordination of the Cr(CO)3 fragment to one of the three

6178 Organometallics, Vol. 29, No. 23, 2010
Hegele et al.
aromatic rings or to the bridging CdC or NdN double bonds.
Experimental X-ray data are available for isomers I, II, IV, and
V but not for III and VII, where the metal fragment is located
above the central CdC or NdN bond, respectively. The
calculated Cr-Carene, Cr-Ccarbonyl, and C-O bond lengths
for the Cr(CO)3 fragment of the benzostilbene and benzoazo-
benzene complexes for all minimum energy structures are
compiled in Tables 2 and 3 and compared to the available
experimental data.
structure of Cr(CO)3-benzoazobenzene complex 6b the Cr-C4a
˚
bond is shorter than calculated (2.27 to 2.30 A) and the Cr-C2
distance is longer compared to the calculated Cr-C2 distance in
Table 2. Calculated (I, II, III, IV) and Experimentally Observed
˚
(3, 6b, 7, 8) Cr-Carene Bond Lengths (in A) of the Benzostilbene
and the Benzoazobenzene Complexes (Calculated and Experi-
mental Minimum Structures)
bond
Cr(CO)3-benzostilbene
Cr(CO)3-benzoazobenzene
The calculated Cr-C4a and Cr-C8a distances (Table 2) are
longer than the other Cr-C distances in the same arene ring
ring Aa
calcd (I)
exptl (3)
calcd (V)
exptl (6b)
˚
˚
(a difference of 0.05-0.08 A for ring A and 0.08-0.15 A for
ring B). The calculated structure of ring B of the Cr(CO)3-
benzostilbene derivative is in excellent agreement with the
experimental data. The structure of ring A agrees well with the
calculated structure; however small differences between experi-
mentally and theoretically determined distances are observed.
For Cr(CO)3-benzostilbene and Cr(CO)3-benzoazobenzene
complexes 3 and 6b the experimental Cr-C8a distance is shorter
Cr-C1
Cr-C2
Cr-C3
Cr-C4
Cr-C4a
Cr-C8a
2.24
2.24
2.24
2.24
2.31
2.32
2.25
2.25
2.23
2.26
2.30
2.25
2.23
2.24
2.24
2.25
2.30
2.30
2.26
2.28
2.23
2.24
2.27
2.24
ring Bb
calcd (II)
exptl (7)
calcd (VI)
Cr-C4a
Cr-C5
Cr-C6
Cr-C7
Cr-C8
Cr-C8a
2.35
2.22
2.21
2.26
2.21
2.34
2.32
2.20
2.21
2.24
2.21
2.32
2.35
2.23
2.21
2.23
2.20
2.35
˚
than the calculated one (experimental 2.25 and 2.24 A and
˚
theory 2.32 and 2.30 A, respectively) and is similar to most other
C-C bond lengths in the arene ring. In the experimental
Table 1. Comparison of Reaction Energies, ΔE, Calculated by ab
Initio and DFT Quantum Chemical Methods for the Migration of
the Cr(CO)3 Fragment along the Model Naphthohydroquinone
Skeletona,b
DBc
calcd (III)
calcd (VII)
Cr - C10
Cr - C20
Cr - N10
Cr - N20
C10 - C20
N10 - N20
2.30
2.20
1.91
2.28
method
ΔE (kcal/mol)
1.41
restricted Hartree-Fock (RHF)
-6.9
1.34
NCPF/116
CPF/119
QCISD(T)20
CCSD(T)
BP86
-6.3
ring Cd
calcd (IV)
exptl (8)
calcd (VIII)
-6.3
-6.0
Cr-C100
Cr-C200
Cr-C300
Cr-C400
Cr-C500
Cr-C600
2.29
2.22
2.24
2.22
2.24
2.22
2.24
2.21
2.21
2.20
2.21
2.21
2.26
2.22
2.24
2.22
2.24
2.22
-6.0
-6.3
B3LYP
B2PLYP
-6.4 (-6.3)
-5.5 (-6.6)
a A def2-TZVP basis set21 is applied at the metal atom and the newly
developed bn-ANO-DZP basis set22 on all the other atoms. b The values
with the larger def2-TZVPP basis set21 are given in parentheses.
a Complexation of ring A. b Complexation of ring B. c Complexation
of the double bond. d Complexation of ring C.
Figure 8. Calculated minimum energy structures for the haptotropic metal migration of the Cr(CO)3 benzostilbene complex.

Article
Organometallics, Vol. 29, No. 23, 2010 6179
Figure 9. Calculated minimum energy structures for the haptotropic metal migration of the Cr(CO)3 benzoazobenzene complex.
Table 3. Calculated and Experimental Cr-Ccarbonyl and C-O
Bond Lengths (in A) for the Cr(CO)3 Fragment Coordinated to
Rings A, B, and C or to the Central CdC and the NdN Bridges,
Respectively
in accordance with the larger complexation (binding) energy
of the Cr(CO)3 fragment to the benzene system (∼45 kcal/
mol, BSSE corrected) compared to the hydroquinone system (42
kcal/mol).
˚
The calculated Cr-Ccarbonyl and C-O bond distances
within the Cr(CO)3 fragment are in excellent agreement with
the available X-ray data (Table 3). These distances are
essentially independent of the positioning of the Cr(CO)3
fragment on the arene skeleton.
Cr(CO)3-benzostilbene
calcd exptl
Cr(CO)3-benzoazobenzene
calcd exptl
average Cr-C (CO)
average Cr-C (CO)
1.84 (V) 1.84 (6b)
1.85 (VI)
ring A
ring B
ring C
CdC
1.84 (I)
1.83 (3)
1.84 (7)
1.83 (8)
The extended aromatic skeletons in all calculated structures
are essentially planar except for structures III and VII, in which
the Cr(CO)3 fragment is located above the CdC or NdN
double bonds, respectively. The available experimental molecu-
lar structures of complexes 7 and 8 reveal essentially coplanar
arene platforms with the benzene ring twisted by ca. 8ꢀ relative to
the naphthalene moiety. In contrast, however, the X-ray struc-
ture of complex 3, bearing the metal-coordinated hydroquinoid
ring, shows a considerably increased angle of 30ꢀ between
both aromatic ring systems. Consequently, the incorporation
of another Cr(CO)3 fragment coordinated to ring C further
increases the twisting of the extended π-skeleton by ca. 12ꢀ, as
observed for the binuclear complex 10 (for the crystal struc-
tures of 3 and 10, see Figures 2 and 6).
1.84 (II)
1.84 (IV)
1.83 (III)
1.85 (VIII)
NdN
1.84 (VII)
average C-O
average C-O
ring A
ring B
ring C
CdC
1.17 (I)
1.15 (3)
1.15 (7)
1.16 (8)
1.16 (V)
1.16 (VI)
1.16 (VIII)
1.16 (6b)
1.17 (II)
1.17 (IV)
1.17 (III)
NdN
1.17 (VII)
˚
ring A (2.28 to 2.24 A), shifting the metal fragment from above
the center toward the periphery (toward above bond C2-C3) of
the coordinated hydroquinoid ring. A similar dislocation
(toward above bond C6-C7 of ring B; see Figure 9) is calculated
and experimentally observed for haptotropomer 7. In contrast,
the Cr-Carene distances within ring C are almost equal, except
Transition States. The calculated transition states for the
metal migration in the benzostilbene and the benzoazobenzene
complexes are represented in Figures 10 and 11, respectively. In
general, both systems behave analogously, revealing three transi-
tion states separating four minima. As previously reported
for the naphthalene Cr(CO)3 system,3m,5 the migration of
the chromium fragment from ring A to ring B does not take a
least motion pathway (crossing the middle of the carbon-
carbon bond common to two fused six-membered rings) but
rather proceeds along the π-ligand periphery with a η4-
trimethylenemethane-like complex transition state, IX and XII,
respectively. Both transition states reveal one short Cr-C8a
00
˚
the Cr-C1 distance of 2.29 A, which exceeds the other Cr-C
˚
bond lengths (average value 2.23 A) for the benzostilbene, and of
˚
˚
2.26 A (compared to a mean distance of 2.23 A) for the
azobenzene system (Table 3). The Cr-Carene bonds in ring C
are, on average, shorter than those in rings A and B, which is
(19) (a) Ahlrichs, R.; Scharf, P.; Ehrhardt, C. J. Chem. Phys. 1985, 82,
890. (b) Ahlrichs, R.; Scharf, P. In Ab Initio Methods in Quantum
Chemistry; Lawley, K. P., Ed.; Wiley: New York, 1987; Vol. 1, p 501.
(20) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. J. Chem.
Phys. 1987, 87, 5968.
(21) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 7,
3297.
(22) Neese, F. Unpublished.
˚
(or Cr-C4a) distance of 2.17 (or 2.16) A (in agreement with
previous studies3) along with the other three Cr-C distances of
˚
2.50-2.66 A for Cr-C4a, Cr-C1, Cr-C8 and Cr-C4,
Cr-C5, Cr-C8a, respectively.

6180 Organometallics, Vol. 29, No. 23, 2010
Hegele et al.
Figure 10. Calculated transition-state structures IX-XI for the tricarbonyl chromium benzostilbene system.
Figure 11. Calculated transition state structures XII-XIV for the tricarbonyl chromium benzoazobenzene system.
In all calculated transition-state structures, the extended
π-arene skeletons are essentially planar except for XIII,
characterizing the migration of the metal fragment from ring
B to the NdN double bond, where a significant twist has
been calculated. This transition-state structure has the metal
much closer to the NdN bond than observed for the
corresponding transition state of the benzostilbene system
(compare XIII in Figure 11 with X in Figure 10 and see
Table 4 for the bond distances between the metal and the
carbon or nitrogen atoms of the CdC or NdN bonds).
In contrast, the structures calculated for the final migration
step from the double bond to ring C are very similar for the ben-
zostilbene and benzoazobenzene systems. Again the Cr-N20
distance is smaller than the corresponding Cr-C20 distance in
the stilbene system. The Cr-CO bonds apparently become
slightly stronger in the transition states, as indicated by the
shorter calculated Cr-C distances (average values 1.82 A in
the transition states of both systems (Table 5) in comparison to
˚
˚
˚
1.84 A for benzostilbene and 1.85 A for benzoazobenzene
(Table 3)).
Energetics. According to our calculations the overall
haptotropic migration of the Cr(CO)3 fragment along the
extended arene platform is endothermic by 6.7 kcal/mol for
the benzostilbene system, but exothermic (-11.0 kcal/mol)
for the benzoazobenzene complex, suggesting that the nature
of the acyclic bridge has a major impact on the course of the

Article
Organometallics, Vol. 29, No. 23, 2010 6181
˚
Table 4. Cr-C Bond Lengths (in A) of the Calculated Transition-
State Structures in the Benzostilbene and the Benzoazobenzene
Series
Table 6. Reaction and Activation Energies (in kcal/mol) for the
Haptotropic Cr(CO)3 Migration in Benzostilbene and Benzoa-
zobenzene Complexesa
bond
TSa
calculated bond lengths
Cr(CO)3-benzostilbene Cr(CO)3-benzoazobenzene
Cr(CO)3-benzostilbene Cr(CO)3-benzoazobenzene
ΔE
ΔE1
ΔE
ΔE1
ring A f ring B
Cr-C8a
Cr-C4a
Cr-C1
ring A f ring B
ring B f CdC
ring B f NdN
CdC f C
-1.5
14.1
13.3
5.5
-2.1
-6.4
2.17
2.66
2.56
2.50
2.62
2.16
5.5
4.3
-19.3
-12.1
Cr-C8
NdN f C
-11.3
-8.9
Cr-C4
Cr-C5
2.53
2.55
1
Ea
1
Ea
Ea
Ea
ring B f CdC
Cr-C7
ring A f ring B
ring B f CdC
ring B f NdN
CdC f C
27.5
20.8
35.1
15.1
27.5
26.3
12.5
24.1
2.20
2.54
2.19
2.93
Cr-C8
13.7
Cr-C6
10.2
8.2
Cr-C10
NdN f C
21.2
ring B f NdN
Cr-C7
a ΔE1 and Ea denote the reaction and activation energies, respec-
tively; the zero vibrational energies (ZVE) are added to the DFT
energies.
1
2.34
2.27
2.39
2.04
Cr-C6
Cr-N10
Cr-N20
azobenzene complex (see Table 7 and Figure 12), suggesting
that the NdN bridge is suited to favor the metal shift within
the naphthalene moiety over the CdC linker. The calculated
ΔG‡ value for the benzostilbene system, corrected to the
experimental temperature, is 26.8 kcal/mol, which is in good
agreement with the experimental value of ΔG‡ = 23.7 kcal/mol
obtained from the kinetic study at 70 ꢀC in C6F5CF3. Solvent
effects have not been considered in this study. The barrier for the
naphthalene complex (calculated value ΔG‡ ∼30 kcal/mol) is in
the same range, indicating an only minor influence of the styryl
extension on the activation barrier. (2) The putative metal shift
from the non-hydroquinoid naphthalene ring to the terminal
benzene ring is supposed to proceed via intermediates III
(VII), which are 9.6 kcal/mol (8.2 kcal/mol) lower in energy in
the benzostilbene (benzoazobenzene) series than the calculated
transition-state energies for the metal shift from ring B to the
respective double bond (see Figure 12 and Table 6).
CdC f C
Cr-C1000
Cr-C200
Cr-C6
2.18
2.76
2.34
2.54
1.38
Cr-C200
C10-C20
NdN f C
Cr-C100
Cr-N20
2.16
2.66
2.38
2.55
1.29
Cr-C600
Cr-C200
N10-N20
a TS = transition state.
˚
Table 5. Cr-C and C-O Bond Lengths (in A) of the Calculated
Transition-State Structures within the Cr(CO)3 Fragment
calculated bond lengths
TSa
Cr(CO)3-benzostilbene Cr(CO)3-benzoazobenzene
Importantly, the highest barrier in each series refers to the
initial metal migration from ring A to ring B. Thus, the calcula-
tions suggest that, if the initial migration is kinetically feasible,
the subsequent steps should be feasible as well, resulting in
a complete intramolecular migration along the extended
π-platform. The absence of any detected intermediate with the
metal fragment coordinated to the double-bond bridge might be
explained by (a) a low transition state for the final metal shift
onto ring C, which is energetically uphill with respect to the
starting material in the benzostilbene case, or (b) alternative
competing pathways characterized by lower barriers, which
have not been included in the calculations but might be opera-
tive especially in the benzoazobenzene system, revealing an
average Cr-C (CO)
ring A f ring B
ring B f CdC
ring B f NdN
CdC f C
1.81
1.82
1.82
1.83
1.82
NdN f C
1.82
average C-O
ring A f ring B
ring B f CdC
ring B f NdN
CdC f C
NdN f C
a TS = transition state.
1.17
1.17
1.17
1.17
1.17
1.17
1
activation energy, Ea , of 24.1 kcal/mol for the metal migration
onto ring C (see Table 6 and Figure 12).
reaction. In the benzostilbene series the intermediates B and
III are energetically uphill with respect to both the starting
material A and the putative final rearrangement product C.
In the benzoazobenzene series, however, the energies of the
respective intermediates range between those of the starting
and the final complexes A and C. The metal shift involves
two major steps: (1) The migration within the naphthalene
part is endothermic by 13.3 kcal/mol in the benzostilbene
system but exothermic by -6.4 kcal/mol for the benzoazo-
benzene complex. The activation barrier for the haptotropic
metal migration from ring A to ring B amounts to 35.1 kcal/
mol for the benzostilbene complex and 27.5 kcal/mol for the
From an experimental point of view, the reaction produces not
only mononuclear but also binuclear complexes that were
trapped and structurally investigated. The bimetallic complexes
may be generally formed in two ways: (a) by initial dissociation of
the Cr(CO)3 fragment from one of the intermediates, temporary
stabilization by the solvent or another donor ligand, and sub-
sequent recoordination to another aromatic ring or (b) by direct
bimolecular transfer of the Cr(CO)3 fragment between two
monometallic complexes. No experimental evidence is presently
available to favor one mechanism over the other. However, cal-
culations of the disproportionation reaction indicate for the
benzostilbene system that a reaction between two molecules of

6182 Organometallics, Vol. 29, No. 23, 2010
Table 7. Crystallographic Data and Details of Refinement for 2, 3(223 K), 3 (123 K), and 7
Hegele et al.
2
3(223K)
3(123 K)
7
empirical formula
fw [g/mol]
wavelength
T [K]
C21H14CrO6
414.32
0.71073
123
C32H38CrO5Si
582.71
0.71073
C32H38CrO5Si
582.71
0.71073
C34H43CrO5.5Si
619.77
0.71073
223
123
223
cryst syst
space group
orthorhombic
P212121 (#19)
7.3508(13)
11.578(5)
44.049(8)
90
monoclinic
P2/c (#13)
14.898(1)
12.022(1)
17.710(1)
90
104.62(1)
90
3069.2(4)
4
1.261
monoclinic
P2/c (#13)
14.8276(4)
11.9847(3)
17.5574(5)
90
104.178(2)
90
3024.99(14)
4
1.280
monoclinic
P21/c (#14)
9.006(1)
15.916(1)
23.474(1)
90
100.45(1)
90
3308.9(4)
4
1.244
˚
a [A]
˚
b [A]
˚
c [A]
R [deg]
β [deg]
γ [deg]
90
90
3
˚
volume [A ]
Z
3748.9(19)
8
1.468
0.646
1696
0.50 ꢀ 0.14 ꢀ 0.03
1.85 to 28.00
-9 e h e 9
-15 e k e 15
-58 e l e 58
22 481
8556
0.2056
505/1
calcd density [g/cm3]
absorp coeff [mm-1
F(000)
]
0.449
1232
0.455
1232
0.421
1316
cryst size [mm3]
θ range [deg]
limiting indices
0.40 ꢀ 0.30 ꢀ 0.10
1.69 to 30.49
-19 e h e 21
-17 e k e 15
-25 e l e 19
22 032
9300
0.058
360/0
R1 = 0.0515
wR2 = 0.1118
R1 = 0.1180
wR2 = 0.1328
1.017
0.40 ꢀ 0.30 ꢀ 0.10
2.94 to 27.47
-17 e h e 19
-15 e k e 15
-22 e l e 22
17 938
6738
0.0279
353/0
R1 = 0.0329
wR2 = 0.0795
R1 = 0.0544
wR2 = 0.0855
0.963
0.25 ꢀ 0.25 ꢀ 0.05
1.55 to 27.84
-9 e h e 11
-17 e k e 20
-30 e l e 23
21 567
7812
0.077
395/3
R1 = 0.0606
wR2 = 0.1083
R1 = 0.1305
wR2 = 0.1268
1.010
collected reflns
unique reflns
R (int)
params/restraints
R indices for (I > 2σ(I ))
R1 = 0.0658
wR2 = 0.1340
R1 = 0.1445
wR2 = 0.1536
0.759
R indices (all data)
goodness-of-fit on F2
largest diff peak and
0.65/-1.287
0.434/-0.385
0.308/-0.298
0.373/-0.410
-3
˚
hole [e A
]
on the hydroquinoid ring are readily accessible via chromium-
templated benzannulation of stilbene and azobenzene chromium
carbenes. A quantum chemical study suggests for the benzoa-
zobenzene system that a stepwise haptotropic migration of the
Cr(CO)3 fragment along the extended π-system to the other
terminal phenyl ring may be feasible according to the calculated
activation barriers provided that the initial metal shift within the
naphthalene moiety (V f VI) characterized by the highest
activation barrier in the metal shift sequence can be realized
under the reaction conditions. In contrast, the respective
rearrangements in the benzostilbene series result in transition
states, intermediates, and a product higher in energy than the
starting material.
The experimental study within the benzostilbene series
reveals that the initial metal migration requires a small
temperature window of 75-80 ꢀC and is complicated by
competing pathways even under these optimized conditions.
It affords the regioisomers expected for an intramolecular
sliding of the Cr(CO)3 fragment along the conjugated
π-platform. An intramolecular mechanism for the initial hap-
totropic metal migration from the hydroquinoid to the
adjacent naphthalene ring (3 f 7) is supported by a kinetic
NMR study. The product pattern experimentally observed
for this process also includes minor amounts of complex 8
bearing a coordinated terminal phenyl ring as well as of
binuclear complexes 10 and 11, which indicates competing
intermolecular pathways.
Figure 12. Energy diagram for the haptotropic rearrangement in
Cr(CO)3-benzostilbene and Cr(CO)3-benzoazobenzene complexes.
The zero vibrational energies (ZVE) are added to the DFT energies.
All energies are relative to the energy of the complex bearing
the metal fragment coordinated to ring A. A: Coordination via
hydroquinoid naphthalene ring. B: Coordination via nonhydro-
quinoid naphthalene ring. C: Coordination via benzene ring.
3 (metal above ring A) or 7 (metal above ring B) leading to a
metal-free arene ligand and a bimetallic complex would be
energetically downhill by 7-8 kcal/mol, while disproportiona-
tion of complex 8 bearing the Cr(CO)3 fragment above ring C
results in a thermoneutral process. Thus, the computational
study is consistent with the experiment demonstrating that the
disproportionation reactions are energetically feasible.
A subsequent controlled haptotropic metal migration
from the naphthalene to the terminal phenyl ring via the
acyclic conjugated bridge could not be confirmed experi-
mentally. Quantum chemical calculations indicate that the
metal fragments become kinetically labile while traversing
Conclusions
Hydroquinoid benzostilbene and benzoazobenzene
Cr(CO)3 complexes bearing the metal label selectively

Article
Organometallics, Vol. 29, No. 23, 2010 6183
Table 8. Crystallographic Data and Details of Refinement for 6b, 8, 9, and 10
6b
8
9
10
empirical formula
fw [g/mol]
wavelength
T [K]
C
612.75
0.71073
123
triclinic
P1 (#2)
32H40CrN2O5Si
C32H38CrO5Si
582.71
0.71073
123
triclinic
P1 (#2)
11.5676(4)
13.7999(4)
21.5818(7)
88.1781(16)
75.4222(16)
67.0976(17)
3062.92(17)
4
1.264
0.450
1232
0.44 ꢀ 0.40 ꢀ 0.36
1.61 to 27.50
-15eh e 15-17ek
e 17-27el e 28
35 335
14 035
0.0630
719/5
R1 = 0.0517
wR2 = 0.1259
R1 = 0.0969
wR2 = 0.1409
0.960
C35H38Cr2O8Si
718.74
0.71073
123
triclinic
P1 (#2)
8.5910(2)
9.8163(3)
20.8240(7)
80.0285(10)
86.8668(10)
81.2150(17)
1708.59(9)
2
1.397
0.721
748
0.32 ꢀ 0.24 ꢀ 0.08
2.62 to 28.00
-10eh e 11-12ek
e 12-27el e 26
17 188
8213
0.0558
423/26
R1 = 0.0515
wR2 = 0.0962
R1 = 0.1140
wR2 = 0.1206
0.902
C78H94Cr4O17Si2
1567.71
0.71073
123
cryst syst
space group
monoclinic
P21/c (#14)
15.2728(6)
11.1828(7)
23.2046(11)
90
102.001(3)
90
3876.6(3)
2
1.343
˚
a [A]
9.3080(6)
9.9851(6)
18.7963(14)
91.533(5)
92.188(6)
111.237(5)
1625.58(19)
2
1.252
0.429
648
0.40 ꢀ 0.20 ꢀ 0.10
2.17 to 26.00
-12eh e 11-12ek
e 12-23el e 23
12 138
6099
0.0389
386/5
R1 = 0.0441
wR2 = 0.1190
R1 = 0.0605
wR2 = 0.1235
1.090
˚
b [A]
˚
c [A]
R [deg]
β [deg]
γ [deg]
3
˚
volume [A ]
Z
calcd density [g/cm3]
absorp coeff [mm-1
F(000)
]
0.642
1644
cryst size [mm3]
θ range [deg]
limiting indices
0.24 ꢀ 0.12 ꢀ 0.08
2.72 to 27.49
-19eh e 19-13ek
e 14-21el e 30
21 437
8858
0.0724
496/57
R1 = 0.0503
wR2 = 0.1094
R1 = 0.1336
wR2 = 0.1299
0.889
collected reflns
unique reflns
R(int)
params/restraints
R indices for (I > 2σ(I ))
R indices (all data)
goodness-of-fit on F2
largest diff peak and hole [e A
-3
˚
]
0.540/-0.557
0.761/-0.661
0.566/-0.767
0.508/-0.760
the CdC or NdN double bonds. They may be cleaved under
the reaction conditions and coordinated to mononuclear
complexes, resulting in minor amounts of binuclear bypro-
ducts. Despite encouraging theoretical studies, no controlled
metal migration was observed for the respective benzoazo-
benzene Cr(CO)3 complex 6b, which may reflect the electron-
deficient azobenzene moiety.
3J = 7.55 Hz, 2H, H-8/80), 7.56 (m, 4H, H-2/20/3/30). 13C NMR
(DEPT 135, 75 MHz, CDCl3): δ 67.18 (OCH3), 125.32, 126.08,
126.79, 127.34, 128.25, 128.79, 131.16 (Ar-CH, CdCH), 136.78,
140.22, 151.98 (Ar-C), 216.39 (cis-CO), 224.00 (trans-CO), 345.14
(CrdC). FT-IR (cm-1, PE): νCO 2062 (m, A1), 1954 (vs, E). MS
(EI): (Mþ) m/z (%) 414.0 (8), 386.0 (29), 358.0 (25), 330.0 (19),
302.0 (4), 274.0 (17), 219.9 (100). HR-MS: calcd for C32H38CrO5Si
- 4CO 302.0399, found 302.0405.
Tricarbonyl{[η6-1,2,3,4,4a,8a]-1-tert-butyldimethylsilyloxy-2,
3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]naphthalene}chromium-
(0) (3). A solution of 2 (420 mg, 1 mmol) and 3-hexyne (0.45 mL,
4 mmol) in 40 mL of tert-butylmethyl ether was degassed by three
freeze-pump-thaw cycles and warmed to 55 ꢀC for 80 min. After
cooling to 0 ꢀC, triethylamine (0.28 mL, 2 mmol) followed by tert-
butyldimethylsilyl trifluoromethanesulfonate (0.35 mL, 2 mmol)
were added, and the reaction mixture was stirred for a further
60 min while the temperature was allowed to warm to room
temperature. The solvent was removed under reduced pressure,
and the residue was purified by column chromatography (petro-
leum ether/dichloromethane, 2:1) to yield 540 mg (0.93 mmol,
91.8%) of 3 as a red solid.
Experimental Section
All operations involving organometallic compounds were car-
ried out under argon using round-bottom flasks (rearrangement of
tricarbonylchromium complexes in preparative scale). Solvents
were predistilled, dried using standard methods, saturated, and
stored under argon. The solvent used for the kinetic NMR study of
the haptotropic rearrangement (octafluorotoluene, Acros) was
degassed by three freeze, pump, and thaw cycles. Merck silica gel
(0.040-0.063 mm) was used for chromatographic purification.
Given yields refer to pure products. 1H and 13C NMR spectra of
the purified complexes were recorded at 25 ꢀC (298 K) using Bruker
DRX-300, -400, and -500 instruments. FT-IR: Nicolet Magna 550.
MS (EI): Thermo Finnigan MAT 95 XL.
1H NMR (300 MHz, CDCl3): δ 0.30 (s, 3H, SiCH3), 0.35 (s,
3H, SiCH3), 1.06 (s, 9H, SiC(CH3)3), 1.21-1.27 (m, 6H,
CH2CH3), 2.50-2.80 (m, 4H, CH2CH3), 3.90 (s, 3H, OCH3),
7.00 (d, 3J = 16.42 Hz, 1H, CdC-H), 7.11 (d, 3J = 16.42 Hz,
1H, CdC-H), 7.21 (t, 3J = 7.08 Hz, 1H, H-400), 7.30 (“t”, 3J =
7.46 Hz, 2H, H-300/500), 7.45 (d, 3J = 7.37 Hz, 2H, H-200/600), 7.62
(d, 3J = 9.06 Hz, 1H, H-5), 7.70 (d, 3J = 9.06 Hz, 1H, H-6), 7.77
(s, 1H, H-8). 13C NMR (DEPT 135, 75 MHz, CDCl3): δ -0.00
(SiCH3), -0.87 (SiCH3), 17.46 (CH2CH3), 18.72 (CH2CH3),
20.99 (SiC(CH3)3), 22.19 (CH2CH3), 23.29 (CH2CH3), 28.02
(SiC(CH3)3), 65.76 (OCH3), 98.09, 101.56, 104.19, 109.18
(Ar-C), 123.99, 124.12, 126.32, 126.73, 127.28, 128.19,
128.77, 130.59 (Ar-CH, CdCH), 130.65, 131.10, 135.17,
136.68 (Ar-C), 234.03 (CO). FT-IR (cm-1, PE): νCO 1959 (vs,
A1), 1897, 1884 (s, E). MS (EI): (Mþ) m/z (%) 582.1 (5), 526.1
(5), 498.1 (65), 446.2 (100). HR-MS: calcd for C32H38CrO5Si
582.1894, found 582.1896.
Pentacarbonyl[methoxy(4-{(E)-20-phenylethenyl}phenyl)-
carbene]chromium(0) (2). A 2.2 mL (5.5 mmol) portion of an
n-butyllithium (2.5 mol in n-hexane) solution was slowly added to
a solution of 1.3 g (5 mmol) of 4-bromostilbene in 80 mL of
diethyl ether precooled to 0 ꢀC. The reaction mixture was stirred
for 60 min. Then 1.54 g (7 mmol) of hexacarbonylchromium was
added, and the mixture was stirred for a further 90 min. After
addition of 1 mL (8 mmol) of methyl trifluoromethanesulfonate
the solvent was removed under reduced pressure after 15 min, and
the residue was purified by column chromatography (petroleum
ether/dichloromethane, 2:1) toyield1.69 g (4.1 mmol, 81.6%) of2
as a brown solid.
1H NMR (300 MHz, CDCl3): δ 4.82 (s, 3H, OCH3), 7.13 (d,
3J=16.52 Hz, 1H, CdC-H), 7.25 (d, 3J=16.52 Hz, 1H, CdC-H),
3
7.32 (t, J=7.08 Hz, 1H, H-10), 7.41 (m, 2H, H-9/90), 7.50 (d,

6184 Organometallics, Vol. 29, No. 23, 2010
Hegele et al.
General Procedure for the Haptotropic Rearrangement. A
solution of 3 (405 mg, 0.7 mmol) in 45 mL of di-n-butyl ether
was degassed by three freeze-pump-thaw cycles and was
warmed for 3 h at 80 ꢀC. The solvent was removed at reduced
pressure, and the residue was purified by column chromatogra-
phy (petroleum ether/dichloromethane, 1:1) to obtain a mixture
of 3 (24 mg, 0.04 mmol, 6%), 7 (85 mg, 0.15 mmol, 21%), 8
(113 mg, 0.19 mmol, 28%), 9 (40 mg, 0.06 mmol, 8%), and 10
(35 mg, 0.05 mmol, 7%).
PE): νCO 1978, 1957 (vs, A1), 1916, 1896, 1889, 1883 (s, E). MS (EI):
(Mþ) m/z (%) 718.1 (9), 634.1 (25), 582.1 (9), 498.1 (100), 446.2 (67).
HR-MS: calcd for C35H39Cr2O8Si 718.1146, found 718.1140.
Hexacarbonyl{η6:η6-[4a,5,6,7,8,8a:100,200,300,400,500,600]-1-tert-
butyldimethylsilyloxy-2,3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]-
naphthalene}bischromium(0) (10). 1H NMR (500 MHz, CDCl3):
δ 0.29 (3H, SiCH3), 0.32 (3H, SiCH3), 1.06 (t, 3J = 7.33 Hz, 3H,
3
CH2CH3), 1.18 (s, 9H, SiC(CH3)3), 1.21 (t, J = 6.86 Hz, 3H,
CH2CH3), 2.52-2.67 (m, 2H, CH2CH3), 2.80-2.88 (m, 2H,
CH2CH3), 3.99 (s, 3H, OCH3), 5.35 (“t”, J = 5.91 Hz, 1H,
H-400), 5.43 (d, 3J = 6.46 Hz, 1H, H-200/600), 5.47 (“t”, 3J = 7.17
Hz, 1H, H-300,H-500), 5.53 (d, 3J = 6.46 Hz, 1H, H-200/600), 5.58
(“t”, 3J = 7.41 Hz, 1H, H-300,H-500), 5.68 (d, 3J = 6.86 Hz, 1H,
H-6), 6.44 (s, 1H, H-8), 6.48 (d, 3J = 6.86 Hz, 1H, H-5), 6.60 (d,
Tricarbonyl{[η6-4a,5,6,7,8,8a]-1-tert-butyldimethylsilyloxy-2,
3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]naphthalene}chromium-
(0) (7). 1H NMR (500 MHz, CDCl3): δ 0.31 (s, 3H, SiCH3), 0.32
(s, 3H, SiCH3), 1.06 (t, 3J = 7.25 Hz, 3H, CH2CH3), 1.18 (s, 9H,
SiC(CH3)3), 1.20 (t, 3J = 7.33 Hz, 3H, CH2CH3), 2.58-2.70 (m,
2H, CH2CH3), 2.84-2.92 (m, 2H, CH2CH3), 4.00 (s, 3H, OCH3),
5.74 (d, 3J = 6.94 Hz, H-6), 6.49 (s, 1H, H-8), 6.50 (m, 1H, H-5),
6.80 (d, 3J = 16.16 Hz, 1H, CdC-H), 7.09 (d, 3J = 16.16 Hz, 1H,
CdC-H), 7.31 (t, 3J=7.41Hz,1H,H-400),7.39(“t”,3J=7.41Hz,
3
3J = 16.00 Hz, 1H, CdC-H), 6.68 (d, J = 16.00 Hz, 1H,
CdC-H). 13C NMR (125 MHz, CDCl3): δ -3.25 (SiCH3),
-2.74 (SiCH3), 14.28 (CH2CH3), 15.58 (CH2CH3), 18.83
(SiC(CH3)3), 20.21 (CH2CH3), 20.49 (CH2CH3), 25.98
(SiC(CH3)3), 62.06 (OCH3), 84.51, 86.21, 90.07, 90.66, 90.88,
91.50, 91.60, 92.28, 92.76, 122.65, 124.31, 127.14, 128.43, 132.26,
133.86, 135.76 (Ar-CH, CdCH), 232.13 (CO), 232.51 (CO).
FT-IR (cm-1, PE): νCO 1976, 1969 (vs, A1), 1917, 1909, 1886,
1896 (s, E). MS (EI): (Mþ) m/z (%) 718.0 (9), 634.1 (22), 582.1
(11), 498.1 (100), 446.2 (67). HR-MS: calcd for C35H39Cr2O8Si
718.1146, found 718.1131.
3
2H, H-300,500), 7.51 (d, J = 7.41 Hz, 2H, H-200/600). 13C NMR
(DEPT 135, 125 MHz, CDCl3): δ -3.22 (SiCH3), -2.64 (SiCH3),
14.33 (CH2CH3), 15.59 (CH2CH3), 18.83 (SiC(CH3)3), 20.17
(CH2CH3), 20.50 (CH2CH3), 26.02 (SiC(CH3)3), 62.03 (OCH3),
84.00, 86.45, 90.09 (Ar-CH), 100.04, 100.95, 103.98 (Ar-C),
125.77, 126.89, 128.50, 128.78, 131.01 (Ar-CH, CdCH), 132.01
(Ar-C), 135.26 (Ar-C), 135.99 (Ar-C), 144.06 (Ar-C), 146.77
(Ar-C), 232.53 (CO). FT-IR (cm-1, PE): νCO 1964 (vs, A1), 1901,
1889 (s, E). MS (EI): (Mþ) m/z (%) 582.2 (32), 526.2 (14), 498.2
(17), 446.2 (100). HR-MS: calcd for C32H38CrO5Si 582.1894, found
582.1891.
General Procedure for the Benzannulation of Azobenzene
Carbene Complexes. A solution of 4a (300 mg, 0.71 mmol) and
3-hexyne (230 mg, 2.84 mmol) in 10 mL of tert-butylmethyl ether
was degassed by three freeze-pump-thaw cycles and warmed at
60 ꢀC for 60 min. After cooling the reaction mixture to -20 ꢀC,
triethylamine (0.12 g, 1.27 mmol) and then tert-butyldimethylsilyl
trifluoromethanesulfonate (330 mg, 1.27 mmol) were added, and
the solution was stirred for 60 min while the temperature was
allowed to warm to room temperature. The solvent was removed
under reduced pressure, and the residue was purified by chroma-
tography on silica gel (petroleum ether/CH2Cl2, 2:1), affording 6a
as a dark brown solid (290 mg, 70%).
Tricarbonyl{[η6-100,200,300,400,500,600]-1-tert-butyldimethylsilyloxy-
2,3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]naphthalene}
1
chromium(0) (8). H NMR (500 MHz, CDCl3): δ 0.22 (s, 6H,
SiCH3), 1.12 (m, 3H, CH2CH3), 1.15 (s, 9H, SiC(CH3)3), 1.24 (m,
3H, CH2CH3), 2.81-2.89 (m, 4H, CH2CH3), 3.92 (s, 3H, OCH3),
5.31 (t, 3J = 6.23 Hz, 1H, H-400), 5.47 (“t”, 3J = 6.46 Hz, 2H, H-300/
500), 5.59 (d, 3J = 5.86 Hz, 2H, H-200/600), 6.72 (d, 3J = 16.14 Hz,
1H, CdC-H), 7.10 (d, 3J = 16.14 Hz, 1H, CdC-H), 7.66 (dd,
3J = 8.84 Hz, 4J = 1.64 Hz, 1H, H-6), 7.97 (d, 3J = 8.84 Hz, 1H,
Tricarbonyl{[η6-1,2,3,4,4a,8a]-1-tert-butyldimethylsilyloxy-
2,3-diethyl-4-ethoxy-7-[(E)-20-phenyldiazenyl]naphthalene}-
chromium(0) (6a). 1H NMR (300 MHz, CDCl3): δ 0.37 (s, 3H,
SiCH3), 0.41 (s, 3H, SiCH3),1.16(s, 9H, SiC(CH3)3), 1.38-1.32 (m,
6H, CH2CH3), 1.56 (t, 3J = 7.0 Hz, 3H, CH3), 2.96-2.51 (m, 4H,
CH2CH3), 4.06-3.98 (m, 1H, OCH2), 4.28-4.21 (m, 1H, OCH2),
7.56-7.48 (m, 3H, Ar-CH), 7.80 (d, 3J = 9.4 Hz, 1H, H-5), 7.96
(d, J = 7.1 Hz, 2H, Ar-CH), 8.07 (dd, 3J = 9.4 Hz, 4J = 1.5 Hz,
1H, H-6), 8.55 (d, 4J = 1.5 Hz, 1H, H-8). 13C NMR (DEPT 135, 75
MHz, CDCl3): δ -2.63 (SiCH3), -2.21 (SiCH3), 15.80 (CH2CH3),
14.91 (CH2CH3), 17.25 (OCH2CH3), 19.04 (SiC(CH3)3), 20.02
(CH2CH3), 21.78 (CH2CH3), 26.06 (SiC(CH3)3), 75.80 (OCH2-
CH3), 94.92, 103.66, 104.20, 110.98 (Ar-C), 121.31, 123.03, 124.33,
127.63 (Ar-CH), 127.85 (Ar-C), 129.14, 131.30 (Ar-CH),
133.89, 148.71, 152.31 (Ar-C), 233.58 (CO). FT-IR (cm-1, PE):
4
H-5), 8.04 (d, J = 1.64 Hz, 1H, H-8). 13C NMR (125 MHz,
CDCl3): δ -3.08 (SiCH3), -3.03 (SiCH3), 14.80 (CH2CH3), 14.83
(CH2CH3), 15.83 (CH2CH3), 15.87 (CH2CH3), 20.49 (SiC(CH3)3),
26.17 (SiC(CH3)3), 62.30 (OCH3), 90.65, 91.01, 92.77, 122.31,
122.54, 122.63, 122.79, 123.22,124.27,126.46,127.50, 128.22,
128.69, 129.20, 131.76, 137.51 (Ar-CH, CdCH), 232.93 (CO).
FT-IR (cm-1, PE):νCO 1971 (vs, A1), 1900 (s, E). MS (EI): (Mþ) m/
z (%) 582.2 (1), 498.2 (17), 446.2 (100).
Synthesis of Bischromium Complexes 9 and 10 by Direct
Complexation. A suspension of benzostilbene complex 3 (180
mg, 0.31 mmol) and boron trifluoride etherate (%, 0.13 mL, 0.34
mmol) in 20 mL of diethyl ether was stirred at ambient tem-
perature for 1 day. The solvent was removed at reduced pres-
sure, and the residue was purified by column chromatography
(petroleum ether/dichloromethane, 1:1) to obtain a mixture of 8
(120 mg, 0.17 mmol, 54%) and 9 (80 mg, 0.11 mmol, 36%).
Hexacarbonyl{η6:η6-[1,2,3,4,4a,8a:100,200,300,400,500,600]-1-tert-
butyldimethylsilyloxy-2,3-diethyl-4-methoxy-7-[(E)-20-phenylethenyl]-
ν
CO = 1957 (s, A1), 1894, 1886 (s, E). MS (EI): (Mþ) m/z (%) 598.1
(14), 514.1 (10), 462.2 (100). HR-MS (ESI pos.): calcd for
C31H38CrN2O5SiHþ 599.2028, found 599.2028.
Tricarbonyl{[η6-1,2,3,4,4a,8a]-1-tert-butyldimethylsilyloxy-
2,3-diethyl-4-ethoxy-7-[(E)-20-(400-methyl)phenyldiazenyl]naph-
thalene}chromium(0) (6b). Purification by chromatography on
silica gel (petroleum ether/CH2Cl2, 2:1) afforded 6b as a dark
brown solid in 84% yield.
1
naphthalene}bischromium(0) (9). H NMR (500 MHz, CDCl3): δ
0.36 (3H, SiCH3), 0.42 (3H, SiCH3), 1.15 (s, 9H, SiC(CH3)3),
1.34-1.30 (m, 6H, CH2CH3), 2.88-2.56 (m, 4H, CH2CH3), 3.98
(s, 3H, OCH3), 5.34 (“t”, 3J = 5.96 Hz, 1H, H-400), 5.45-5.48 (m,
2H, H-300/500),5.54(d,3J=6.56Hz,1H,H-200/600),5.60(d,3J=6.66
Hz, 1H, H-200/600), 6.68 (d, 3J = 16.24 Hz, CdC-H, 1H), 6.95 (d,
3J = 16.24 Hz, CdC-H, 1H), 7.60 (d, 3J = 9.14 Hz, H-6, 1H), 7.77
(d, 3J =9.14 Hz, H-5, 1H), 7.84 (s, H-8, 1H). 13CNMR(DEPT135,
125 MHz, CDCl3): δ -2.88 (SiCH3), -2.05 (SiCH3), 15.38
(CH2CH3), 16.89 (CH2CH3), 19.02 (SiC(CH3)3), 20.11 (CH2CH3),
21.40 (CH2CH3), 26.01 (SiC(CH3)3), 66.05 (OCH3), 90.60, 91.52,
92.40 (Ar-CH), 96.93, 102.12, 104.10, 104.64, 109.76 (Ar-C),
124.18, 125.43, 126.23, 126.75, 129.65 (Ar-CH, CdCH), 130.11,
1H NMR (300 MHz, CDCl3): δ 0.36 (s, 3H, -CH3), 0.41 (s,
3H, -CH3), 1.15 (s, 9H, -CH3), 1.38-1.31 (m, 6H, -CH3), 1.56
(t, J = 6.98 Hz, 3H, -CH3), 2.45 (s, 3H, --OCH3), 2.96-2.52
(m, 4H, -CH2), 4.05-3.95 (m, 1H, -OCH2), 4.27-4.19 (m, 1H,
3
-OCH2), 7.33 (m, 2H, ArH), 7.80 (d, J = 9.4 Hz, 1H, H-5),
7.86 (m, 2H, ArH), 8.07 (dd, 3J = 9.4 Hz, 4J = 1.7 Hz, 1H, H-6),
8.15 (d, 4J = 1.7 Hz, 1H, H-8). 13C NMR (DEPT 135, 75 MHz,
CDCl3): δ -2.63 (SiCH3), -2.19 (SiCH3), 14.92 (CH2CH3),
15.80 (CH2CH3), 17.23 (OCH2CH3), 19.05 (SiC(CH3)3), 20.05
(CH2CH3), 21.58 (-CH3), 21.76 (CH2CH3), 26.06 (SiC(CH3)3),
131.73, 133.26 (Ar-C), 232.70 (CO), 233.81 (CO). FT-IR (cm-1
,

Article
Organometallics, Vol. 29, No. 23, 2010 6185
75.75 (OCH2), 95.21, 103.66, 104.12, 110.86 (Ar-C), 121.51,
123.05, 124.28, 126.90 (Ar-CH), 127.95 (Ar-C), 129.81 (Ar-
CH), 133.79, 141.98, 148.93, 150.68 (Ar-C), 233.66 (CO).
FT-IR (cm-1, PE): νCO 1961 (s, A1), 1901, 1888 (s, E). MS
(EI): (Mþ) m/z (%) 612.2 (20), 528.2 (30), 476.3 (100). HR-MS:
calcd for C32H40CrN2O5Si 612.2112, found 612.2136.
CCDC-769717 (2), CCDC-770726 (3(223K)), CCDC-717393
(3(123K)), CCDC-769720 (6b), CCDC-770727 (7), CCDC-
769718 (8), CCDC-769716 (9), and CCDC-769719 (10) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Computational Details. The ORCA electronic structure pro-
gram package25 was used for all quantum chemical calculations.
Minimum energy structures and transition states were opti-
mized with the BP86 functional11 in combination with the
Ahlrichs TZVP basis set for the Cr(CO)3 template and the
smaller SV(P) basis set for the arene system. The resolution-
of-the-identity RI approximation26 was used in the Split-RI-J
variant27 with the appropriate Coulomb fitting sets. The recently
implemented transition-state searcher of the ORCA package is
based on eigenvector following28 and is very efficient due to the use
of partial Hessians. Transition states and minima were verified
through frequency calculations that were performed by two-sided
differentiation of analytic gradients.
Tricarbonyl{[η6-1,2,3,4,4a,8a]-1-tert-butyldimethylsilyloxy-
2,3-diethyl-4-methoxy-7-[(E)-20-(400-N,N-dimethylamino)phenyl-
diazenyl]naphthalene}chromium(0) (6c). Purification by chroma-
tography on silica gel (petroleum ether/CH2Cl2, 2:1) afforded 6c
as a dark brown solid in 50% yield.
1H NMR (300 MHz, CDCl3): δ 0.38 (s, 3H, SiCH3), 0.43 (s,
3H, SiCH3), 1.15 (s, 9H, -CH3), 1.34 (q, J = 7.3 Hz, 6H, -CH3),
1.56 (t, J = 7 Hz, 3H, -CH3), 2.74-2.54 (m, 3H, -CH2), 2.95-
2.81 (m, 1H, -CH2), 3.11 (s, 6H, -N(CH3)2), 4.08-3.98 (m, 1H,
-CH2), 4.30-4.20 (m, 1H, -CH2), 6.80-6.75 (m, 2H, Ar-CH),
7.79 (d, J = 9.40 Hz, 1H, H-5), 7.93-7.88 (m, 2H, Ar-CH), 8.07
(dd, J = 9.40 Hz, J = 1.60 Hz, 1H, H-6), 8.37 (d, J = 1.60 Hz, 1H,
H-8). 13C NMR (DEPT 135, 75 MHz, CDCl3): δ -2.67 (SiCH3),
-2.09 (SiCH3), 15.01 (CH2CH3), 15.80 CH2CH3), 17.06 OCH2-
CH3), 19.06 (SiC(CH3)3), 20.14 CH2CH3), 21.68 CH2CH3), 26.11
SiC(CH3)3), 40.29 (-N(CH3)2), 75.50 (OCH2), 96.63, 103.56,
103.66, 110.20 (Ar-C), 111.52, 122.43, 123.64, 124.13, 125.27 (Ar-
CH), 128.46, 133.25, 143.66, 149.81, 152.67 (Ar-C), 234(CO). FT-
IR (cm-1, PE): νCO 1959 (s, A1), 1899, 1884 (s, E). MS (EI): (Mþ)
m/z (%) 641.2 (2), 557.2 (24), 505.2 (100), 476.2 (30). HR-MS (ESI
pos.): calcd for C33H43CrN3O5SiHþ 642.2450, found 642.2450.
Crystallography. The crystal structure determinations were
performed on a Nonius KappaCCD diffractometer at 123(2) K/
223(2) K for 3(223K), 3(123K), 7, 8, 9, and 10 and on a STOE IPDS
2T diffractometer at 123(2) K for 2 and 6b using Mo KR radiation
Acknowledgment. Financial support by the Deutsche
Forschungsgemeinschaft (SFB 624 “Templates”) and the
Fonds der Chemischen Industrie is gratefully acknowl-
edged. B.S. thanks the Alexander-von-Humboldt Foun-
dation for a postdoctoral research fellowship.
Supporting Information Available: 1H and 13C NMR spectra
of all complexes and crystallographic data of compounds 2, 3,
6b, 7, 8, 9, and 10 (CIF format) are available free of charge via
the Internet at http://pubs.acs.org.
˚
(λ = 0.71073 A). Crystal data, data collection parameters, and
results of the analyses are listed in Tables 7 and 8. Direct methods
(SHELXS-97)23 were used for structure solution, and refine-
ment was carried out using SHELXL-97 (full-matrix least-squares
on F2).24 Hydrogen atoms were refined using a riding model.
Note Added after ASAP Publication. This paper was pub-
lished on the Web on Nov 1, 2010, with errors in Table 7 and the
caption for Figure 2. The corrected version was reposted on Nov
5, 2010.
(23) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(24) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(25) Neese, F. ORCA-an ab Initio Density Functional and Semiem-
€
(26) (a) Vahtras, O.; Almlof, J.; Feyereisen, M. W. Chem. Phys. Lett.
€
1993, 213, 514. (b) Weigend, F.; Haser, M. Theor. Chem. Acc. 1997, 97, 331.
(c) Bernholdt, D. E.; Harrison, R. J. Chem. Phys. Lett. 1996, 250, 477.
(27) Neese, F. J. Comput. Chem. 2003, 24, 1740.
€
pirical Program Package, version 2.5-20.2007; Universitat Bonn: Bonn,
Germany, 2007.
(28) Baker, J. J. Comput. Chem. 1986, 7, 385.