Selectivity in C-Cl bond activation of dichloroarenes by photogenerated Cp*Re(CO)2: Combined experimental and DFT studies

Article abstract of DOI:10.1039/b410265g

The photochemical reaction of the d⁶ Re(i) complex Cp*Re(CO)₃ with several substituted dichloroarenes (1-R-2,4-dichlorobenzene; R = Me, OMe, CF₃ and F) yields the insertion products trans-Cp*Re(CO)₂(C₆H ₃ClR)Cl. The C-Cl bond activation of 2,4-dichloroanisole and 2,4-dichloro-1-fluorobenzene occurs at position 2 (ortho to the methoxy and fluoro substituents, respectively), whereas for 2,4-dichlorotoluene and 2,4-dichloro-1-trifluoromethylbenzene the C-Cl bond in position 4 (para to the Me and CF₃ groups, respectively) is cleaved. The products have been characterized by elemental analyses and spectroscopic techniques, and by X-ray crystallography for the complexes trans-Cp*Re(CO)₂(5-chloro-2- methoxyphenyl)Cl and trans-Cp*Re(CO)₂(3-chloro-4-methylphenyl) Cl. DFT(B3PW91) calculations have been carried out to explain the selectivity observed in the isolated insertion products. It is shown that the Re-aryl bond dissociation energy is stronger in the observed isomer. This is analyzed as originating from a combination of electronic and steric factors.

Full text of DOI:10.1039/b410265g

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P A P E R
Selectivity in C–Cl bond activation of dichloroarenes by
photogenerated Cp*Re(CO)2: combined experimental and
DFT studies
Alvaro Aballay,a Eric Clot,b Odile Eisenstein,*b Maria Teresa Garland,c Fernando Godoy,a
˜
A. Hugo Klahn,*a Juan Carlos Munozc and Beatriz Oelckersa
a Instituto de Quimica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059 Valparaiso,
Chile. E-mail: hklahn@ucv.cl
b
`
Laboratoire de Structure et Dynamique des Systemes Moleculaires et Solides (CNRS UMR
5636), Universite Montpellier 2, Case courrier 14, 34095 Montpellier cedex 5, France.
´
´
E-mail: odile.eisenstein@univ-montp2.fr
c CIMAT, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Casilla 653
Santiago, Chile
Received (in Montpellier, France) 5th July 2004, Accepted 13th September 2004
First published as an Advance Article on the web 9th December 2004
The photochemical reaction of the d6 Re(I) complex Cp*Re(CO)3 with several substituted dichloroarenes
(1-R-2,4-dichlorobenzene; R = Me, OMe, CF3 and F) yields the insertion products trans-
Cp*Re(CO)2(C6H3ClR)Cl. The C–Cl bond activation of 2,4-dichloroanisole and 2,4-dichloro-1-
fluorobenzene occurs at position 2 (ortho to the methoxy and fluoro substituents, respectively), whereas for
2,4-dichlorotoluene and 2,4-dichloro-1-trifluoromethylbenzene the C–Cl bond in position 4 (para to the Me
and CF3 groups, respectively) is cleaved. The products have been characterized by elemental analyses and
spectroscopic techniques, and by X-ray crystallography for the complexes trans-Cp*Re(CO)2(5-chloro-2-
methoxyphenyl)Cl and trans-Cp*Re(CO)2(3-chloro-4-methylphenyl)Cl. DFT(B3PW91) calculations have
been carried out to explain the selectivity observed in the isolated insertion products. It is shown that the
Re–aryl bond dissociation energy is stronger in the observed isomer. This is analyzed as originating from a
combination of electronic and steric factors.
RhL2HCl2 (L = PCy3, PPri3).20 In all cases, an almost
Introduction
quantitative yield of the corresponding arene was obtained
whatever the substitution pattern. However, while 3- and 4-
chlorotoluenes are almost equally reactive, affording toluene in
more than 90% yield, reaction of 2-chlorotoluene under the
same conditions produces toluene in 7% yield only. The
protecting steric factor of the methyl group was claimed to
be responsible for this result. However, no steric effects were
observed in the degradation reaction of 2-chlorotoluene and
2,6-dichlorotoluene catalyzed by (Cp*RhCl2)2, where Cp* =
Z5-C5Me5.21 In both cases, toluene was formed in high yields,
92% and 96%, respectively. Similarly, 2,3-dichloronitroben-
zene can be selectively dechlorinated by Pd(PPh3)4 to give
3-chloronitrobenzene in 94% yield.22 Recently, we have also
observed the selective insertion of the photogenerated fragment
Cp*Re(CO)2 into the C–Cl bonds of 2,4,5-trichloroanisole and
3,4,5-trichloro-1-trifluoromethylbenzene to form the com-
plexes Cp*Re(CO)2(arylCl)Cl, where arylCl = 4,5-dichloro-
2-methoxyphenyl and 2,3-dichloro-5-trifluoromethylphenyl,
respectively.23
To better understand these apparently contradictory results
we have studied the photochemical reactions of the d6 Re(I)
complex Cp*Re(CO)3 with several substituted dichloroarenes
(1-R-2,4-Cl2C6H3, R = Me, OMe, CF3 and F). Our goal is to
establish how the steric and/or electronic effects of the benzene
substituents influence the insertion of the photogenerated
rhenium fragment into the different C–Cl bonds of the sub-
strate. DFT calculations have been used to discuss the selec-
tivity observed in the isolated insertion products.
The transformation of chloroarenes mediated by transition
metal complexes is a field of major interest. Chloroarenes,
normally less reactive than their brominated and iodinated
counterparts, are nevertheless preferred precursors for C–C
coupling reactions (Heck, Suzuki, Sonogashira, Stille) because
of their much lower cost.1 Another application is halocarbon
degradation for environmental remediation.2 For these
reasons, considerable attention has been focused on the transi-
tion metal catalyzed dechlorination of aryl chlorides.3
A
large number of stoichiometric and catalytic reactions have
been reported, particularly with d8 and d10 transition metal
species,4–10 but fewer with d6 metal systems.11–13
Selective dechlorination of polychlorobenzene compounds
by homogeneous catalysis is highly dependent on the position
of the chlorine in the aromatic ring and also on the nature of
the catalyst. For example, 1,2,4-trichlorobenzene can be mono-
dehalogenated by RhH2Cl(PPri3)2
and RhCl(PPh3)3
14
15,16
to give exclusively 1,2-dichlorobenzene, whereas the
same substrate reacted with Ni(PEt3)4 produces only a
stable 2,5-dichlorophenyl nickel complex, trans-NiCl(2,5-
Cl2C6H3)(PEt3)2.4 On the other hand, several other complexes
of Pd(II),17 Ni(0),18 Ni(II),19 Ru(II)14 yield mixtures of dichloro-
benzene in the degradation of 1,2,4-trichlorobenzene. There is
little information on the dechlorination of substituted chloro-
arenes. Electron-donating (Me, OMe, NH2) or electron-with-
drawing (COOH, MeCO, CF3) groups have no effect on the
hydrogenolysis of 3- and 4-substituted chlorobenzenes using
T h i s j o u r n a l i s & T h e R o y a l S o c i e t y o f C h e m i s t r y a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 5
226
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1

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Results and discussion
Experimental results
The complexes of the general formula Cp*Re(CO)2
(C6H3ClR)Cl (R = OMe, F, CF3, Me), 1–4, were prepared
by UV irradiation (l = 350 nm) of Cp*Re(CO)3 in neat
2,4-dichlorotoluene,
2,4-dichloro-1-trifluoromethylbenzene
and 2,4-dichoro-1-fluorobenzene, or in a saturated hexane
solution of 2,4-dichloroanisole, as shown in Scheme 1. Much
longer irradiation times or irradiation at l = 300 nm did not
increase the yields of the products: instead, it led to the
additional formation of Cp*Re(CO)2Cl2.13 These complexes
were purified by column chromatography and isolated as red
microcrystalline solids after recrystallization from CH2Cl2 and
hexane. In all cases, the compounds were obtained as a single
isomer with the chloroaryl group trans to the chloride ligand.
These new complexes have been identified by IR, 1H NMR,
13C NMR, and mass spectroscopies, elemental analysis and, in
two cases, by X-ray crystallography (vide infra).
Fig.
1
Molecular structure of complex trans-Cp*Re(CO)2
[C6H3Cl(OCH3)]Cl (1) drawn with 50% probability displacement
ellipsoids. Only one independent molecule of the two present in the
crystal is shown.
The IR spectra of 1–4 exhibited two n(CO) absorptions
around 2040 and 1960 cmÀ1. The higher wavenumber stretch-
ing mode (ns) has a weaker intensity than the lower wavenum-
ber stretching mode (nas). Similar intensity patterns have been
observed in several other dicarbonyl rhenium complexes.13,24
The appearance of a single resonance for the CO groups in the
13C NMR spectra near 195 ppm is further evidence of the trans
2-position has been cleaved, whereas for complexes 3 and 4,
two aromatic protons are shifted to lower field as a result of the
cleavage of the C–Cl bond at position 4. This assignment was
confirmed by 1H–1H NOESY experiments on complexes 1 and
3. 1 showed a unique NOE interaction between the Cp*
protons and the lower field aromatic protons but 3 exhibited
two NOE interactions between the Cp* protons and the lower
field aromatic resonances, as expected. Additional experimen-
tal evidence for the cleavage of a C–halogen bond at the 2-
position was obtained from the photochemical reaction of
Cp*Re(CO)3 in a saturated solution of 2-bromo-4-chloroani-
sole. The product trans-Cp*Re(CO)2[C6H3Cl(OMe)]Br,
expected from the lower dissociation energy of the C–Br vs.
C–Cl bonds, shows almost identical aromatic chemical shifts as
observed for 1. The 19F NMR spectrum of complex 2 also
confirms the above assignment, since the resonance at d À78.6
ppm is in good agreement with reported values for similar
complexes containing an aryl ligand with ortho fluorine
groups.26 Furthermore, X-ray crystallographic analyses of 1
(Fig. 1) and 4 (Fig. 2) confirm cleavage of the C–Cl bond ortho
and para to the OMe and Me substituents, respectively. Table 1
reports crystal structure and refinement data and Table 2
shows selected bond distances and angles. In both complexes
the rhenium atoms are seven-coordinate, with the Cp* ligand
as a three-coordinate monoanion, and the overall geometry is
comparable to a four-legged piano stool, which is consistent
with a ReIII oxidation state. In general, bond distances and
angles for complexes 1 and 4 compare with those of trans-
Cp*Re(CO)2(2,3,4,5-Cl4C6H)Cl 13 and trans-Cp*Re(CO)2(4,5-
Cl2-2-OMeC6H2)Cl.23 The Re–Cp* (centroid) distance of 1.962
and 1.966 A for 1 and 4, respectively, as well as the C–O bond
lengths are similar to those determined in other cyclopentadie-
1
orientation of these ligands.13 The H NMR spectra of com-
plexes 1–4 supports the formation of only one insertion
product, since they exhibit a single resonance for the Cp*
ligand. In addition, 1 and 4 show resonances for the protons
of the OCH3 and CH3 substituents of the aryl ligand. In all
cases, the aromatic region clearly shows the presence of three
distinguishable proton environments with an integration ratio
of 1 : 1 : 1. Complexes 1–4 are stable in the solid state at room
temperature with respect to trans-cis isomerization. However,
some trans-cis interconversion takes place in CDCl3 solution
1
for 3 and 4 as shown by small intensity resonances in the H
NMR spectra (cis : trans ratio of 1 : 13 for 3 and 1 : 24 for 4,
obtained by integration of the Cp* resonances).
The insertion product of the rhenium fragment Cp*Re(CO)2
into one of the two distinct C–Cl bonds of the dichloroarene
was assigned by comparing the chemical shifts of the aromatic
protons of the chloroaryl ligand of the resulting oxidative
addition product to the aromatic proton chemical shifts of
the free substrate. Insertion of the rhenium fragment is ex-
pected to unshield the protons at the ortho position.25,26 For
complexes 1 and 2, only one aromatic proton resonance is
shifted to lower field, indicating that the C–Cl bond at the
Fig. 2 Molecular structure of complex trans-Cp*Re(CO)2
(C6H3ClCH3)Cl (4) drawn with 50% probability displacement
ellipsoids.
Scheme 1 Products from the irradiation of Cp*Re(CO)3 at l = 350
nm in the presence of different dichlorobenzene compounds.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1
227

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Table 1 Crystallographic data for 1 and 4
Table
3
Relative energy (DE/kJ molÀ1
)
of CpRe(CO)2(2-R-5-
ClC6H3)Cl, ortho, relative to CpRe(CO)2(4-R-3-ClC6H3)Cl, para.
Bond dissociation energies (BDE in kJ molÀ1) of C–Cl in 1-R-2,4-
Cl2C6H3 and Re–C in CpRe(CO)2(C6H3ClR)Cl.a
1
4
Formula
MW/g molÀ1
Temperature/K
Crystal system
Space group
a/A
C19H21Cl2O3Re
559.46
297(2)
C19H21Cl2O2Re
538.46
297(2)
BDE(Cl–C) BDE(Cl–C) BDE(Re–C) BDE(Re–C)
ortho
R
DEb
ortho
para
para
Monoclinic
P21/c
Orthorhombic
Pca21
CF3
F
À14.2 377.7
+21.9 387.9
À22.5 387.8
387.7
388.3
389.4
391.3
212.4
258.0
210.5
245.0
236.4
236.4
234.6
238.2
28.259(3)
8.4639(7)
16.7535(15)
100.4730(10)
3940.3(6)
4
14.0448(12)
8.5444(7)
15.8837(14)
—
b/A
c/A
Me
OMe +10.0 388.1
b/1
a
Here ortho (resp. para) indicates that the carbon of the C–Cl and
b
U/A3
1906.1(3)
4
1.876
Re–C bonds is ortho (resp. para) to R. A positive value for DE
corresponds to a higher stability of the ortho isomer.
Z
r
calcd/g cmÀ3
1.869
6.453
m/mmÀ1
6.663
13222
Reflections collected
Unique reflections
R(int)
27851
8817
4302
0.039
nicely agree with the experimental observations. The OMe and
F substituents direct the insertion into the ortho C–Cl bond
whereas Me and CF3 show a preference for insertion into the
para C–Cl bond. The differences in energy are small, showing a
subtle influence of the substituent on the insertion pattern. No
attempt was made to locate the transition states for insertion so
that these computational results only reflect the stability pre-
ferences of the two possible insertion products. The calcula-
tions were also limited to the observed trans isomers. A study
of the reaction energy profile such as the one performed on the
insertion of CpRe(CO)2 into the C–H bond of hydrofluoro-
benzene systems28 will be necessary to fully analyze the factors
that control the formation of the regioisomers; this will be
carried out in future work.
The calculated geometries (Table 4) of the complexes are in
good agreement with the structural data measured by X-ray
crystallography (Table 2). The overall piano-stool structure is
well reproduced with average angles of 1451 and 981 for C(aryl)–
Re–Cl and C(O)–Re–C(O), respectively. The phenyl ring is
parallel to the Cp ring in all cases. The bond distances are also
in good agreement with the experimental values. For instance,
in the case of the OMe group ortho to the Re fragment, 1, and
the associated calculated model, the Re–C(aryl) bond is 2.198
A (calcd) versus 2.189(7) A (exp.). In the case of the Me group
para to the rhenium fragment, 4, the Re–C(aryl) bond is 2.193
A (calcd), which is longer than the experimental value of
2.174(8) A, but still within the experimental limits taking into
account the e.s.d.
0.0621
0.0434
R1 (I 4 2sI)
wR2 (I 4 2sI)
R1 (all data)
wR2 (all data)
0.0287
0.0546
0.0997
0.0649
0.1108
0.0373
0.0579
nyl rhenium complexes. The OC–Re–CO interbond angles of
99.31 for 1 and 99.51 for 4, clearly establish the trans orien-
tation of these ligands and are quite similar to those observed
in several similar complexes.13,23
The most interesting feature is the selective insertion of the
rhenium fragment into a C–Cl bond as a function of the
substituent in position 1 in the 2,4-dichloroarenes. Fluoro
and methoxy groups direct the C–Cl bond activation towards
the 2-position, whereas methyl and trifluoromethyl substitu-
ents direct the reaction towards the 4-position. The ortho
directing effect appears to be similar to that found in the
C–H activation of hydrofluorobenzene systems by the same
metal fragment.25,26 We did not attempt to identify any
products that could be formed by C–H bond activation or
Z2-coordination of the dichloroarene, even though we have
experimental evidence for Z2-coordination of chlorobenzenes
to rhenium in the complexes Cp*Re(CO)2(5,6-Z2-1,2,4-
Cl3C6H3) and Cp*Re(CO)2(5,6-Z2-1,2,3,4-Cl4C6H2).27
Computational studies
The calculations show only a moderate influence of the
nature of R on the metric parameters. However, an interesting
trend appears when comparing the ortho and para regioisomers
(Table 4). For any R substituent, the Re–C(aryl) bond is
shorter when R is in the para position, the difference in bond
length being negligible in the case of R = F. This trend can be
better explained on steric grounds, which are especially im-
portant for CH3 and CF3 and minimal in the case of F. It thus
appears that the Re–C(aryl) bond length is not a good para-
meter to account for the structural preferences.
To understand the regiochemistry, we compared the Re–C
bond dissociation energy (BDE) with the corresponding C–Cl
BDE in the original R-substituted dichloroarene molecules
(Table 3). Without exception, the Re–C bond is stronger in
the rhenium complex that is preferred experimentally by 7 to 20
kJ molÀ1. However, the pattern is less clear in the reactant. The
radical C6H3ClRd is more stable when the carbon bearing the
radical center is ortho to R (Table 3) because this allows a
greater distance between the two large groups R and Cl.
Therefore, in the case of OMe the weaker C–Cl bond is
cleaved. In the case of Me and CF3, the strongest C–Cl bond
is cleaved while there is almost no difference between the two
C–Cl bond dissociation energies in the case of F. The small
differences in the C–Cl BDEs indicate that the two isomeric
R-substituted chlorophenyl radicals have similar energies.
Insertion products of the CpRe(CO)2 fragment into the C–Cl
bond of 1-R-2,4-Cl2C6H3 were optimized with DFT(B3PW91)
calculations. The relative energies of the products (Table 3)
Table 2 Selected bond lengths (A) and angles (1) for 1 and 4
1aa
1ba
4
Re–C(Cp*)
Re–C(2)
Re(1)–C(3)
2.348(7)
2.355(7)
2.325(5)
2.275(6)
2.261(6)
2.317(7)
2.345(5)
1.966
2.298(7)
2.261(7)
2.289(7)
2.344(7)
1.964
2.303(7)
2.252(7)
2.271(6)
2.342(6)
1.960
Re(1)–C(4)
Re(1)–C(5)
Re(1)–centroid Cp*
Re(1)–C(CO)
Re(1)–C(CO)
Re(1)–C(11)
Re(1)–Cl(1)
C(18)–O(1)
C(19)–O(2)
C(18)–Re(1)–C(19)
C(11)–Re(1)–Cl(1)
a
1.925(8)
1.968(8)
2.189(7)
2.4804(19)
1.148(9)
1.131(9)
99.3(3)
1.908(8)
1.960(9)
2.185(6)
2.4723(19)
1.145(9)
1.133(9)
1.926(7)
1.948(7)
2.174(8)
2.4717(13)
1.145(7)
1.135(8)
99.5(3)
100.4(3)
143.26(17)
144.07(17)
143.5(2)
Two independent molecules of 1 are found in the unit cell and labeled
as 1a and 1b.
228
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1

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Table 4 Selected bond distances (A) and angles (degrees) for trans-CpRe(CO)2(2-R-5-ClC6H3)Cl (ortho) and trans-CpRe(CO)2(4-R-3-ClC6H3)Cl
(para) computed at the B3PW91 level. The numbering scheme is the same as the one used for the X-ray structures. The antisymmetric, nas(CO),
and symmetric, ns(CO), unscaled stretching frequencies (cmÀ1) are also given.
OMe
Me
F
CF3
ortho
para
2.343
ortho
para
2.339
ortho
para
2.333
ortho
para
2.321
Re–C1
Re–C5
Re–C4
2.267
2.257
2.263
2.257
2.307
2.370
2.198
1.977
1.925
2.503
1.149
1.155
2.333
2.310
2.187
1.937
1.962
2.511
1.154
1.150
2.299
2.377
2.221
1.976
1.922
2.498
1.150
1.155
2.330
2.310
2.193
1.940
1.960
2.510
1.153
1.150
2.304
2.371
2.193
1.978
1.927
2.498
1.148
1.155
2.332
2.318
2.192
1.944
1.957
2.509
1.153
1.151
2.300
2.380
2.226
1.981
1.926
2.500
1.147
1.154
2.329
2.329
2.191
1.947
1.955
2.508
1.152
1.150
Re–C11
Re–C18
Re–C19
Re–Cl1
C18–O1
C19–O2
C18–Re–C19
C11–Re–Cl1
nas(CO)
ns(CO)
98.7
98.8
96.4
99.1
99.3
99.1
96.7
99.4
144.6
2074.7
2140.8
144.7
2077.7
2134.6
144.6
2075.4
2135.8
144.9
2080.2
2135.5
144.1
2079.6
2146.5
144.9
2082.2
2136.3
145.5
2080.2
2149.1
144.8
2084.9
2138.5
Therefore, the energy preference for one of the two Re–aryl
isomers can only come from the interaction between rhenium
and aryl radicals. This is illustrated by the significantly differ-
ent Re–C BDE values for the two isomers. The Re–C bond is
stronger for the preferred product, which comes from a
combination of electronic and steric factors. It has been shown
that the Re–C bond is significantly strengthened by the pre-
sence of an ortho fluorine.25 The electronegative OMe group
induces similar effect. The CF3 group does not stabilize the
neighbouring Re–C bond (the electronegative atom should be
directly bonded to the aryl ring). In contrast, the steric
influence of CF3 destabilizes the isomer where CF3 is ortho
to the rhenium fragment. This leads to a weaker Re–C in this
nonobserved isomer. The situation is similar with CH3. This
analysis shows how electronic and steric factors combine to
control the nature of the final isomer. We have calculated the
symmetrical and antisymmetrical n(CO) stretching frequencies
(Table 4). The relative frequencies do not correlate in a clear
manner with the relative BDE, thus showing that the strength
of the Re–C bond is not related with the electron-donating
and/or -releasing ability of C6H3ClR. This contrasts with the
systematic relationship found between H–C and M–C bond
energies.25,28–32 This shows that the bond energy relationship
H–C/M–C cannot be generalized to Y–C/M–C with Y a H
and further studies are needed.
methylbenzene and 2,4-dichloro-1-fluorobenzene were used as
received (Aldrich). 2-Bromo-4-chloroanisole and 2,4-dichloro-
anisole were prepared in 85–90% yield from the corresponding
phenols by Williamson syntheses.34 Infrared spectra were
recorded in solution (CaF2 cell) on a Perkin Elmer FT-1605
spectrophotometer, 1H and 13C NMR spectra on Bruker
AVANCE 400 and AMX 500 instruments. All 1H NMR
chemical shifts were referenced using the chemical shifts of
residual solvent, 13C chemical shifts to solvent peaks and 19F
chemical shifts to C6F6 at À162.9. Mass spectra were obtained
at the Laboratorio de Servicios Analıticos, Universidad Cato-
´ ´
lica de Valparaıso, and the Chemistry Department of the
´
University of York, on a Shimadzu GC-MSA and a VG
Autospec instrument, respectively, under electron impact mode
at 70 eV. Elemental analyses were obtained at the Centro de
´ ´
Instrumentacion, Pontificia Universidad Catolica de Chile,
Santiago, Chile.
Photolysis of Cp*Re(CO)3 in the presence of chlorinated
substrates: general procedure
All reactions were carried out under nitrogen at room tem-
perature in a Pyrex tube (25 cm long, 1.5 cm external diameter)
fitted with a rubber septum. Cp*Re(CO)3 (typically 50–150
mg) was dissolved in 15–20 ml of the chlorinated solvent (for
2,4-dichlorotoluene,
2,4-dichloro-1-trifluoromethylbenzene,
and 2,4-dichloro-1-fluorobenzene) or in 20 ml of a saturated
solution of the solid chlorinated compound (for 2-bromo-4-
chloroanisole and 2,4-dichloroanisole). Solutions were irra-
diated at 350 nm for the time indicated below in a Rayonet
RPR-100 photochemical reactor to give yellow to greenish-
brown solutions. Solvent was removed under vacuum and the
residue was chromatographed on silica gel 60 (Fluka).
Conclusion
The photogenerated Cp*Re(CO)2 fragment inserts specifically
in one of the C–Cl bonds of substituted dichloroarenes of
general formula 1-R-2,4-Cl2C6H3. In the case of R = F and
OMe, the metal fragment inserts in the C–Cl bond ortho to R.
In the case of R = Me and CF3, the metal fragment inserts in
the C–Cl para to R. DFT calculations show that the observed
compound is the more stable regioisomer. The calculations
also show that the observed regioisomer corresponds to the
stronger Re–C bond and not necessarily to the more stable
C6H3ClR organic radical. In the case of R = F and OMe,
the substituent strengthens an ortho Re–C bond. Such
strengthening does not occur when R = CH3 or CF3 and
steric factors disfavor the presence of a large metal fragment
adjacent to R.
trans-Cp*Re(CO)2[C6H3Cl(OCH3)]Cl. (1) Irradiation time:
15 h. Cp*Re(CO)3: 600 mg, 1.48 mmol. Following the general
procedure, elution with hexane gave a mixture of reusable
unreacted Cp*Re(CO)3 and 2,4-dichloroanisole. Hexane–
CH2Cl2 (3 : 1) eluted orange 1, contaminated with traces of
trans-Cp*Re(CO)2Cl2. 1 was isolated as pure orange crystals
by layering a concentrated CH2Cl2 solution with hexane (yield
68 mg, 0.12 mmol, 8% conversion). IR (CH2Cl2) n(CO)/cmÀ1
:
2040 s and 1954 vs; 1H NMR (CDCl3) d: 1.71 (s, 15H), 3.80 (s,
3H), 6.73 (d, 1H, J = 8.6 Hz), 7.10 (dd, 1H, J = 8.6, 2.5 Hz),
7.65 (d, 1H, J = 2.5 Hz); 13C–{1H} NMR (CDCl3) d: 9.49 (C5
Me5), 55.45 (OCH3), 103.64 (C5Me5); 110.79 [C6H3Cl(OCH3)],
120.07, 126.11, 126.63, 145.61, 162.65 [C6H3Cl(OCH3)],
195.36 (CO); mass spectrum (based on 187Re/35Cl) m/z:
554 [M]+, 526 [M À CO]+, 498 [M À 2CO]+, 356
Experimental
Methods and materials
All reactions were carried out under nitrogen using standard
Schlenk techniques. Cp*Re(CO)3 was prepared as previously
described.33 2,4-Dichlorotoluene, 2,4-dichloro-1-trifluoro-
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1
229

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1
[M À 2CO À C6H3Cl(OCH3)]+.
Anal.
C19H21O3Cl2Re: C, 41.16; H, 3.82%; found: C, 41.18; H, 3.75.
calcd
for
(CH2Cl2) n(CO)/cmÀ1: 2034 s and 1955 vs; H NMR (CDCl3)
d: 1.72 (s, 15H), 2.33 (s, 3H), 6.96 (d, 1H, J = 7.7 Hz), 7.38 (dd,
1H, J = 7.7, 1.4 Hz), 7.55 (d, 1H, J = 1.4 Hz); 13C–{1H} NMR
(CDCl3) d: 9.74 (C5Me5), 19.83 (CH3), 103.80 (C5Me5); 124.71
[C6ClH3(CH3)], 131.90, 133.16, 135.23, 143.94, 145.26
(C6H3ClCH3), 197.29 (CO); mass spectrum (based on
187Re/35Cl) m/z: 538 [M]+, 510 [M À CO]+, 482 [M À 2CO]+,
trans-Cp*Re(CO)2[C6H3Cl(OCH3)]Br. Irradiation time: 6 h.
Cp*Re(CO)3: 150 mg, 0.37 mmol. Following the general
procedure, elution with hexane eluted a mixture of unreacted
Cp*Re(CO)3 and 2-bromo-4-chloroanisole. Hexane–CH2Cl2
356
[M À 2CO À (C6H3ClCH3)]+.
Anal.
calcd
for
(2 : 1)
eluted
reddish-orange
trans-Cp*Re(CO)2[C6H3-
C19H21O2Cl2Re: C, 42.38; H, 3.93%; found: C, 42.33; H, 3.88.
Cl(OCH3)]Br, contaminated with traces of trans-Cp*Re
(CO)2Br2. This complex was obtained pure as reddish-orange
crystals by layering a concentrated CH2Cl2 solution of the
impure solid with hexanes (yield 77 mg, 0.13 mmol). IR
(CH2Cl2) n(CO)/cmÀ1: 2034 s and 1951 vs; 1H NMR (CDCl3)
d: 1.77 (s, 15H), 3.77 (s, 3H), 6.72 (d, 1H, J = 8.6 Hz), 7.10 (dd,
1H, J = 8.6, 2.5 Hz), 7.64 (d, 1H, J = 2.5 Hz); 13C–{1H} NMR
(CDCl3) d: 9.93 (C5Me5), 55.47 (OCH3), 103.18 (C5Me5);
110.81, 118.67, 126.03, 126.60, 145.42, 162.82 [C6H3Cl
(OCH3)], 193.99 (CO); mass spectrum (based on 187Re/35Cl)
m/z: 598 [M]+, 570 [M À CO]+, 542 [M À 2CO]+. Anal. calcd
for C19H21O3BrClRe: C, 38.10; H, 3.53%; found: C, 37.94;
H, 3.41.
Crystal structure determination
X-Ray quality crystals of 1 and 4 were obtained by recrystalli-
zation from solutions in hexanes by slow cooling to À10 1C. A
summary of crystal data, data collection, and refinement
parameters for the structural analyses is given in Table 1.w
Crystals of 1 and 4 were glued to a glass fiber and mounted on
a Bruker SMART APEX diffractometer, equipped with a CCD
area detector. Data was collected using graphite-monochro-
mated MoKa radiation (l = 0.71073 A). Cell constants for 1
and 4 were obtained from the least-squares refinement of three-
dimensional centroids of 994 and 983 reflections, respectively,
in the range 4.761 r 2y r 50.081. Data were measured through
the use of CCD recording of o rotation frames (0.31 each). All
data were corrected for Lorentz and polarization effects.
Absorption corrections were applied using the SADABS rou-
tine.35 Both data were integrated with the Bruker SAINTPLUS
program.36
The structures were solved by Patterson, completed by
difference Fourier techniques and refined by full-matrix least-
squares on F2 (SHELXL-97)37 with initial isotropic, but sub-
sequent anisotropic thermal parameters. Hydrogens in 1 and 4
were included in calculated positions and refined riding on
carbon atoms with free isotropic displacement parameters.
Atomic scattering factors were used as implemented in the
program.
trans-Cp*Re(CO)2(C6H3ClF)Cl. (2) Irradiation time: 10 h.
Cp*Re(CO)3: 300 mg, 0.74 mmol. Following the general
procedure, elution with hexane eluted unreacted Cp*Re(CO)3
(205 mg, 0.51 mmol). Hexane–CH2Cl2 (5 : 1) eluted crude
yellow 2. This was crystallized by layering a concentrated
CH2Cl2 solution with hexanes to give pure 2 (yield 82 mg,
0.14 mmol, 60%). IR (CH2Cl2) n(CO)/cmÀ1: 2044 s and 1963
vs; 1H NMR (CDCl3) d: 1.78 (s, 15H), 6.95 (pst, 1H, Jap = 8.6
Hz), 7.10 (m, 1H), 7.62 (dd, 1H, JHF = 4.6 Hz, JHH = 2.5 Hz).
13C–{1H} NMR (CDCl3) d: 9.51 (d, JCF = 1 Hz, C5Me5),
103.99 (C5Me5); 115.03 (d, JCF = 36 Hz, C6H3ClF), 115.93
(d, JCF = 34 Hz, C6H3ClF), 127.45 (d, JCF = 9.5 Hz,
C6H3ClF), 129.28 (d, JCF = 2.5 Hz, C6H3ClF), 145.54
(d, JCF = 11 Hz, C6H3ClF), 166.92 (d, JCF = 234 Hz,
C6H3ClF), 194.39 (br s, CO); 19F NMR (CDCl3) d À78.62
(m); mass spectrum (based on 187Re/35Cl) m/z: 542 [M]+, 514
[M À CO]+, 486 [M À 2CO]+, 356 [M À 2CO À C6H3ClF]+.
Anal. calcd for C18H18O2Cl2FRe: C, 39.86; H, 3.34%; found:
C, 39.96; H, 3.19.
Computational details
All calculations were performed with the Gaussian98 set of
programs38 within the framework of hybrid DFT
(B3PW91),39,40 on the model systems CpRe(CO)2(C6H3ClR)Cl
(Cp = Z5-C5H5; R = F, OMe, Me, CF3). The rhenium atom
was represented by the relativistic effective core potential
(RECP) from the Stuttgart group (15 valence electrons) and
its associated (8s7p6d)/[6s5p3d] basis set,41 augmented by an f
polarization function (a = 0.869).42 The chlorine atoms were
represented by RECP from the Stuttgart group and the
associated basis set,43 augmented by a d polarization func-
tion.44 A 6-31G(d,p) basis set45 was used for all the remaining
atoms of the complex (C, H, O, F). Full optimizations of
geometry without any constraints were performed, followed by
analytical computation of the Hessian matrix to confirm the
nature of the located extrema as minima on the potential
energy surface. The arenes C6Cl2H3R and the radicals
CpRe(CO)2Cl and C6H3ClR (R = F, OMe, Me, CF3) were
optimized at the B3PW91 level (unrestricted formalism for
open-shell systems) to estimate the Re–C and C–Cl BDEs.
trans-Cp*Re(CO)2[C6H3Cl(CF3)]Cl. (3) Irradiation time:
14 h. Cp*Re(CO)3: 200 mg, 0.49 mmol. Following the general
procedure, elution with hexane gave 20 mg of a 1 : 2 mixture
(according to 1H NMR integration) of unreacted Cp*Re(CO)3
and Cp*2Re2(CO)5. Hexane–CH2Cl2 (2 : 1) eluted crude yellow
3. Pure 3 was obtained as a yellow microcrystalline powder by
layering a concentrated CH2Cl2 solution with hexane (yield 40
mg, 0.067 mmol, 14%). IR (CH2Cl2) n(CO)/cmÀ1: 2042 s and
1
1965 vs; H NMR (CDCl3) d: 1.76 (s, 15H), 7.38 (d, 1H, J =
7.9 Hz), 7.61 (dd, 1H, J = 7.9, 1 Hz), 7.75 (d, 1H, J = 1 Hz);
13C–{1H} NMR (CDCl3) d: 9.47 (C5Me5), 103.84 (C5Me5);
128.78, 143.48, 147.20 [C6H3Cl(CF3)], 196.86 (CO); other
aromatic and CF3 carbons could not be assigned due to
isomerization to the cis isomer; 19F NMR (CDCl3) d À62.54;
mass spectrum (based on 187Re/35Cl) m/z: 592 [M]+, 564
[M À CO]+, 536 [M À 2CO]+, 356 [M À 2CO À C6H3Cl
(CF3)]+. Anal. calcd for C19H18O2Cl2F3Re: C, 38.51; H,
3.04%; found: C, 38.50; H, 2.85.
Acknowledgements
We thank the Pontificia Universidad Catolica de Valparaıso
´ ´
(DI 125782/02) and FONDECYT (Chile) for financial support
(grant 1020655 and 7030107). B. O. acknowledges the Royal
Society of Chemistry/CONICYT exchange program. O. E.
thanks FONDECYT for an invited professorship to Pontificia
trans-Cp*Re(CO)2(C6H3ClCH3)Cl. (4) Irradiation time:
15 h. Cp*Re(CO)3: 900 mg, 2.22 mmol. Following the general
procedure, elution with hexane gave unreacted Cp*Re(CO)3
(840 mg, 2.07 mmol). Hexane–CH2Cl2 (5 : 1) eluted orange 4
contaminated with traces of trans-Cp*Re(CO)2Cl2. Pure 4 was
obtained as orange crystals by layering a concentrated CH2Cl2
solution with hexane (yield 30 mg, 0.056 mmol, 37%). IR
w CCDC reference numbers 244319 and 244320. See http://
www.rsc.org/suppdata/nj/b4/b410265g/ for crystallographic data in
.cif or other electronic format.
230
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1

View Article Online
Universidad Cato
´
lica de Valparaı
´
so. We also wish to thank
25 E. Clot, M. Besora, F. Maseras, C. Me
´
gret, O. Eisenstein, B.
Oelckers and R. N. Perutz, Chem. Commun., 2002, 490 and
references therein.
FONDAP (grant 1198002) and Fundacion Andes for financial
support for the purchase of the X-ray diffractometer (Con-
venio C-13575) and the NMR spectrometer (Convenio C-
13672). The donation of NH4ReO4 by MOLYMET-Chile
was greatly appreciated.
26 J. J. Carbo, O. Eisenstein, C. L. Higgitt, A. H. Klahn, F. Maseras,
B. Oelckers and R. N. Perutz, J. Chem. Soc., Dalton Trans., 2001,
1452.
27 A. Abalay, A. H. Klahn and B. Oelckers, unpublished results.
28 E. Clot, B. Oelckers, A. H. Klahn, O. Eisenstein and R. N. Perutz,
Dalton Trans., 2003, 4065.
29 (a) W. D. Jones and E. T. Hessel, J. Am. Chem. Soc., 1993, 115,
554; (b) D. D. Wick and W. D. Jones, Organometallics, 1999, 18,
495.
30 J. A. Martinho-Simoes and J. L. Beauchamp, Chem. Rev., 1990,
90, 629.
References
1
(a) F. Lemaitre and P. Harvey, J. Am. Chem. Soc., 2003, 125,
5511; (b) B. M. Choudary, S. Mahdi, N. S. Chowdari, M. L.
Kantam and B. Sreedar, J. Am. Chem. Soc., 2002, 124, 1427; (c) I.
P. Beletskoya and A. V. Cheprokov, Chem. Rev., 2000, 100, 3009
and references therein.
31 H. E. Bryndza, L. K. Fong, R. A. Paciello, W. Tam and J. E.
Bercaw, J. Am. Chem. Soc., 1987, 109, 1444.
2
3
A. Ghattas, R. Abu-Reziq, D. Avnir and J. Blum, Green Chem.,
2003, 5, 40.
32 P. L. Holland, R. A. Andersen, R. G. Bergman, J. Huang and
S. P. Nolan, J. Am. Chem. Soc., 1997, 119, 128000.
33 A. T. Patton, C. E. Strouse, C. B. Knobler and J. A. Gladysz, J.
Am. Chem. Soc., 1983, 105, 5804.
34 A. I. Vogel, Vogel’s Textbook of Practical Organic Chemistry,
Longman Group Limited, London, 4th edn., 1978, p. 754.
35 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
36 (a) SAINT+, version 6.01, Bruker AXS, Inc., Madison, WI,
USA, 2000; (b) SAINT, version 4.0, Bruker AXS, Inc., Madison,
WI, USA, 2000.
(a) V. V. Grushin and H. Alper, Chem. Rev., 1994, 94, 1047; (b) V.
V. Grushin and H. Alper, Top. Organomet. Chem., 1999, 3, 193.
D. R. Fahey and J. E. Mahan, J. Am. Chem. Soc., 1977, 99, 2501.
L. M. Alcazar-Roman and J. F. Hartwig, J. Am. Chem. Soc.,
2001, 123, 12905.
Y. Ben-David, M. Gozin, M. Portnoy and D. Milstein, J. Mol.
Catal., 1992, 73, 173.
C. M. King, R. B. King, N. K. Bhattacharyya and M. G. Newton,
J. Organomet. Chem., 2000, 600, 63.
4
5
6
7
8
9
37 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Gottingen, Germany, 1997.
Y. Akita, A. Inoue, K. Ishida, T. Terui and A. Ohta, Synth.
Commun., 1986, 16, 1067.
A. Zapf and M. Beller, Chem. Eur. J., 2001, 7, 2908.
¨
38 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr.,
R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.
Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala,
Q. Cui, K. Morokuma, P. Salvador, J. J. Dannenberg, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J.
Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. G. Johnson, W.
Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon,
E. S. Replogle and J. A. Pople, GAUSSIAN 98 (Revision A.11),
Gaussian, Inc., Pittsburgh, PA, 2001.
10 A. Spencer, J. Organomet. Chem., 1984, 270, 115.
11 C. Leiva and D. Sutton, Organometallics, 1998, 17, 4568.
12 M. E. Cucullu, S. P. Nolan, T. R. Belderrain and R. H. Grubbs,
Organometallics, 1999, 18, 1299.
13 A. H. Klahn, A. Toro, B. Oelckers, G. E. Buono-Core, V.
Manriquez and O. Wittke, Organometallics, 2000, 19, 2580.
14 J. Diaz, M. A. Esteruelas, J. Herrero, L. Moraleja and M. Olivan,
J. Catal., 2000, 195, 187.
15 M. A. Esteruelas, J. Herrero, F. M. Lopez, M. Martin and L. A.
Oro, Organometallics, 1999, 18, 1110.
16 M. A. Atienza, M. A. Esteruelas, M. Fernandez, J. Herrero and
M. Olivan, New J. Chem., 2001, 25, 775.
´
17 L. Lassova, H. K. Lee and T. S. A. Hor, J. Org. Chem., 1998, 63,
3538.
18 D. R. Fahey, J. Am. Chem. Soc., 1970, 92, 402.
19 M. Stiles, J. Org. Chem., 1994, 59, 5381.
20 V. V. Grushin and H. Alper, Organometallics, 1991, 10, 1620.
21 K.-I. Fujita, M. Owaki and R. Yamaguchi, Chem. Commun.,
2002, 2964.
39 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
40 J. P. Perdew and Y. Wang, Phys. Rev. B, 1992, 45, 13244.
41 D. Andrae, U. Ha
Theor. Chim. Acta, 1990, 77, 123.
42 A. W. Ehlers, M. Bohme, S. Dapprich, A. Gobbi, A. Hollwarth,
¨
ussermann, M. Dolg, H. Stoll and H. PreuX,
¨
¨
V. Jonas, K. F. Kohler, R. Stegmann, A. Veldkamp and G.
¨
Frenking, Chem. Phys. Lett., 1993, 208, 111.
22 A. Angeloff, J. J. Brunet, P. Legars, D. Neibecker and D. Souyri,
Tetrahedron Lett., 2001, 42, 2301.
43 A. Bergner, M. Dolg, W. Kuchle, H. Stoll and H. PreuX, Mol.
¨
23 A. Aballay, F. Godoy, G. E. Buono-Core, A. H. Klahn, B.
Oelckers, M. T. Garland and J. C. Munoz, J. Organomet. Chem.,
2003, 688, 168.
Phys., 1993, 30, 1431.
44 A. Hollwarth, H. Bohme, S. Dapprich, A. W. Ehlers, A. Gobbi, V.
¨
Jonas, K. F. Kohler, R. Stagmann, A. Veldkamp and G. Frenk-
¨
¨
24 F. W. B. Einstein, A. H. Klahn, D. Sutton and K. G. Tyers,
Organometallics, 1986, 5, 53 and references therein.
ing, Chem. Phys. Lett., 1993, 203, 237.
45 P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973, 28, 213.
N e w J . C h e m . , 2 0 0 5 , 2 9 , 2 2 6 – 2 3 1
231