Base-promoted aryl carbon-iodine and carbon-bromine bond cleavage with rhodium porphyrin complexes: Scope and mechanism

Article abstract of DOI:10.1021/om300441p

Base-promoted aryl carbon-iodine and carbon-bromine bond (Ar-X, X = I, Br) cleavage by rhodium porphyrin complexes was achieved to give the rhodium(III) porphyrin aryls Rh(ttp)Ar (ttp = tetra-p-tolylporphyrinato dianion). Mechanistic studies showed that Rh^II₂(ttp)₂ is the intermediate for Ar-X (X = I, Br) cleavage. The Ar-X cleavage process goes through a rhodium(II) porphyrin radical mediated ipso-substitution mechanism.

Full text of DOI:10.1021/om300441p

Article
pubs.acs.org/Organometallics
Base-Promoted Aryl Carbon−Iodine and Carbon−Bromine Bond
Cleavage with Rhodium Porphyrin Complexes: Scope and
Mechanism
Ying Ying Qian and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China
S
* Supporting Information
ABSTRACT: Base-promoted aryl carbon−iodine and carbon−bromine
bond (Ar−X, X = I, Br) cleavage by rhodium porphyrin complexes was
achieved to give the rhodium(III) porphyrin aryls Rh(ttp)Ar (ttp =
tetra-p-tolylporphyrinato dianion). Mechanistic studies showed that RhII (ttp)2 is the intermediate for Ar−X (X = I, Br) cleavage.
2
The Ar−X cleavage process goes through a rhodium(II) porphyrin radical mediated ipso-substitution mechanism.
dimethylphenyliminoethyl]pyridine) has been reported to
undergo chlorine atom abstraction with chlorobenzene to
give LCoIICl and a phenyl radical. The phenyl radical combines
with another LCoI(N2) to give LCoIIPh.9 In addition to the CoI
metalloradical, [CoII(CN)5]3− reacts with 2-iodopyridine to
give cobalt(III) 2-pyridyl and cobalt(III) iodide complexes. It
was suggested that the [CoII(CN)5]3− first abstracts an iodine
atom to give [ICoIII(CN)5]3−. Then, the released pyridyl radical
combines with another [CoII(CN)5]3− to afford [(2-pyridyl)-
CoIII(CN)5]3−.10
INTRODUCTION
■
Aryl carbon−halogen bond (Ar−X, X = I, Br) cleavage is very
important in organic synthesis.1 Aryl halides are common
starting materials in transition-metal-catalyzed cross-coupling
reactions. The Ar−X cleavage step has been reported to be the
rate-limiting step in some catalyses.2 Ar−X cleavage by
transition-metal complexes is also a key step in the hydro-
dehalogenation of polyhalogenated aromatics.3
Four main types of mechanisms have been identified for the
Ar−X cleavage with transition-metal complexes: (1) oxidative
addition, (2) nucleophilic aromatic substitution, (3) direct
halogen atom abstraction, and (4) ipso substitution.
The radical ipso substitution of aryl halides by transition-
metal radicals was first reported by Chan’s group.11 IrII (ttp)2
2
Oxidative addition is the widely reported mechanism for Ar−
X cleavage with group 8,4 9,5 and 106 transition-metal com-
plexes. Oxidative addition of Ar−X to a group 10 transition-
metal center has been widely used in cross-coupling reactions.
For a typical Suzuki−Miyaura cross-coupling reaction, the first
step is the oxidative addition of Ar−X on a Pd(0) complex to
give a PdIIArX intermediate. The PdII intermediate then goes
through transmetalation and reductive elimination to afford the
coupling product.6 Ar−X (X = Cl, Br I) cleavage of 2-(2-
halophenyl)pyridine and 10-halobenzo[h]quinoline has also
been reported to take place with [RhI(PPh3)2(acetone)2]+ via
oxidative addition.5c
(ttp = tetra-p-tolylporphyrinato dianion) is formed from the
reduction of IrIII(ttp)(CO)Cl by base through ligand
substitution of OH− followed by reductive dimerization.
IrII(ttp) radical, which is in equilibrium with IrII (ttp)2, then
2
attacks the ipso carbon of aryl halides, followed by elimination
of the halogen atom to give IrIII(ttp)Ar. The halogen atom
further combines with another IrII(ttp) radical to give
IrIII(ttp)X, which is recycled to IrII(ttp) by base (Scheme 1).11
Scheme 1. Ipso-Substitution Mechanism of Ar−X Cleavage
by Iridium Porphyrins
Nucleophilic aromatic substitution (SNAr) of Ar−X by
transition-metal complexes has been less frequently reported
and usually involves electron-deficient aryl halides such as
fluorobenzenes.7 Cp*Rh(PMe3)H− undergoes uncleophilic
aromatic substitution with aryl fluorides to give the rhodium
aryls and fluoride ion.7
Direct halogen atom abstraction involves a metalloradical.
Ar−X cleavage has been reported through halogen atom
abstraction by various metalloradical complexes.8 The
[Cp*TiIII−NPtBu3]+ metalloradical undergoes halogen
atom abstraction with PhX to give [Cp*(X)TiIV−NPtBu3]+
and a phenyl radical.8a Ar−Br has also been cleaved by bromine
atom abstraction with the triplet excited state of the tetrakis(μ-
pyrophosphito)diplatinum(II) tetraanion.8c Apart from tita-
nium and platinum metalloradicals, LCoI(N2) (L = 2.6-bis[2,6-
As part of our systematic studies of Ar−X cleavage by group
9 metalloporphyrins, we now report extended studies, including
Received: May 21, 2012
Published: July 24, 2012
© 2012 American Chemical Society
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the reaction scope and detailed mechanistic studies, of base-
Table 2. Optimization of Base-Promoted Ph−I Cleavage
promoted Ar−X (X = Br, I) cleavage with RhIII(ttp)Cl.
RESULTS AND DISCUSSION
■
Base Promotion Effect of Ar−X Cleavage. Initially,
bromobenzene reacted with Rh(ttp)Cl (1a) in the absence of
base in benzene at 120 °C to give only a 29% yield of
Rh(ttp)Ph (Table 1, entry 1). Rh(ttp)Cl (1a) was not
a
t
entry
base
amt of BuOH, equiv
time, days
yield of 3a, %
b
1
K2CO3
KOH
KOH
50
50
1
1
2
46
63
c
2
c
3
85
Table 1. Optimization of Base-Promoted Ph−Br Cleavage
a
b
c
Isolated yield. Rh(ttp)I (1c) was isolated in 18% yield. Rh(ttp)I
(1c) was observed by TLC in the course of the reaction, and it was
completely consumed upon prolonged heating to give 3a.
Table 3. Substrate Scope of Ar−I Cleavage
a
t
entry
base
amt of BuOH, equiv
time
yield of 3a, %
b
1
3 days
1 day
18 h
18 h
18 h
7 h
29
53
45
82
88
70
68
c
2
KOAc
K2CO3
K2CO3
K2CO3
KOH
d
3
d
4
50
50
de
,
5
6
7
d
d
a
b
entry
FG
time
3 (yield, %)
KOH
50
7 h
1
2
3
4
5
OMe (4b)
Me (4c)
Br (4d)
1 day
1 day
4 h
3b (74)
3c (78)
3d (71)
3e (65)
3f (64)
a
b
Isolated yield. Rh(ttp)Cl (1a) (22%) and Rh(ttp)Br (1b) (25%)
c
d
were isolated. Rh(ttp)Br (1b) (45%) was isolated. Rh(ttp)Br (1b)
was observed by TLC in the course of the reaction, and it was
completely consumed upon prolonged heating to give 3a. Solvent-
free conditions in PhBr (600 equiv).
Cl (4e)
1 day
3 h
e
NO2 (4f)
a
Rh(ttp)I (1c) was observed by TLC in the course of the reaction, and
it was completely consumed upon prolonged heating to give
b
Rh(ttp)Ar. Isolated yield.
completely consumed and was recovered in 22% yield together
with Rh(ttp)Br (1b), isolated in 25% yield. With a base added,
such as KOAc and K2CO3, the reactions were promoted and
required less than 1 day to complete and gave 53% and 45%
yields of Rh(ttp)Ph (3a), respectively (Table 1, entries 2 and
3). The yield of Rh(ttp)Ph (3a) was improved to 70% within
7 h when the strong base KOH was applied.
Table 4. Substrate Scope of Ar−Br Cleavage
In order to increase the solubility of Rh(ttp)Cl and base in
t
benzene, BuOH was added as a phase transfer reagent. The
a
b
entry
FG
time, h
3 (yield, %)
yield of Rh(ttp)Ph (3a) was enhanced from 45% to 82% when
t
1
2
p-OMe (2b)
p-tBu (2g)
p-Me (2c)
p-F (2h)
8
2
3b (65)
3g (68)
3c (11)
3h (60)
3e (73)
3f (80)
3i (74)
3j (44)
50 equiv of BuOH was used together with K2CO3 (Table 1,
entry 4). However, the KOH/tBuOH combination gave little
improvement (Table 1, entry 7). The solvent-free conditions
gave almost the same reaction rate and product yield as with
10 equiv of PhBr (Table 1, entry 5). Therefore, 10 equiv of
K2CO3, 50 equiv of tBuOH, and 10 equiv of ArBr in benzene at
120 °C were chosen as the reaction conditions for further
studies.
c
3
2
4
5
6
7
8
8
p-Cl (2e)
22
24
24
24
p-NO2 (2f)
m-CF3 (2i)
m-OMe (2j)
a
When the optimized reaction conditions for Ar−Br cleavage
were applied to iodobenzene, only a 46% yield of Rh(ttp)Ph
(3a) was obtained, with an 18% yield of Rh(ttp)I (1c)
recovered after 1 day (Table 2, entry 1). However, when the
strong base KOH was applied, the yield of Rh(ttp)Ph (3a)
was enhanced to 63% without any Rh(ttp)I (1c) remaining
(Table 2, entry 2). Moreover, without tBuOH, the reaction was
slower but gave a higher yield of Rh(ttp)Ph (3a) (Table 2,
entries 2 and 3). Therefore, Rh(ttp)Cl with 10 equiv of KOH
and 10 equiv of ArI in benzene at 120 °C were used for Ar−I
cleavage studies.
Substrate Scope of Ar−X Cleavage. Aryl iodides and aryl
bromides bearing both electron-donating and -withdrawing
functional groups reacted well with Rh(ttp)Cl (Tables 3 and 4).
The electron-rich 4-iodoanisole and 4-iodotoluene reacted
with Rh(ttp)Cl to give 74% and 78% yields of the
Rh(ttp)Br (1b) was observed by TLC in the course of the reaction,
and it was completely consumed upon prolonged heating to give
Rh(ttp)Ar. Isolated yield. Rh(ttp)(p-Br)Bn (5) was isolated in 62%
b
c
yield.
corresponding Rh(ttp)Ar species 3b,c, respectively (Table 3,
entries 1 and 2). Electron-poor aryl iodides also reacted with
Rh(ttp)Cl to give good yields of 3d−f as well (Table 3, entries
3−5).
Various aryl bromides also reacted with Rh(ttp)Cl smoothly
to give the Ar−Br cleavage product Rh(ttp)Ar in good yields
(Table 4). Meta-substituted ArBr reacted as successfully as
para-substituted ArBr with Rh(ttp)Cl to give the corresponding
Rh(ttp)Ar species (Table 4, entries 7 and 8). However, 4-
bromotoluene with reactive benzylic C−H bonds gave both
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Ar−Br and benzylic C−H cleavage products (Table 4,
entry 3).12
High functional group compatibility was achieved for both
base-promoted Ar−I and Ar−Br cleavages. 4-Nitrobromoben-
zene and 4-nitroiodobenzene worked well with Rh(ttp)Cl as
well (Table 3, entry 5, and Table 4, entry 6). Aryl halides with
electron-donating or electron-withdrawing para functional
groups reacted more quickly than iodobenzene and bromo-
benzene. However, the meta-substituted aryl halides react more
slowly. 4-Bromoiodobenzene only gave the Ar−I cleavage
product Rh(ttp)(4-bromophenyl), likely due to the lower bond
dissociation energy of Ar−I (Table 3, entry 3).13 However,
most of the aryl iodides took a longer time than aryl bromides
to complete the reaction.
These base-promoted Ar−X cleavages further provide a facile
synthesis of rhodium porphyrin aryls. In contrast, the reported
synthesis of rhodium porphyrin aryls requires the treatment of
Rh(ttp)Cl with aryllithiums or Grignard reagents.14
X-ray Crystallographic Details. The structures of Rh-
(ttp)(4-bromophenyl)(MeOH) (3d·MeOH) and Rh(ttp)(4-
chlorophenyl) (3e) were further established by single-crystal
X-ray analysis, and some crystallographic data are summarized
in Table 5. These complexes crystallized in the monoclinic
space group P21/n. The molecular structures of the complexes
Figure 2. ORTEP presentation of Rh(ttp)(4-chlorophenyl) (3e) (30%
probability displacement ellipsoids). Hydrogen atoms are omitted for
clarity.
smaller than Rh2+ (ionic radii 86 pm).16 The Rh−C bond lengths
are 2.028 and 2.138 Å.17
Figures 3 and 4 give the conformations of porphyrins,
showing the displacement of the core atoms and of Rh from the
Table 5. Selected Crystallographic Data of Rh(ttp)(4-
bromophenyl)(MeOH) (3d·MeOH) and Rh(ttp)(4-
chlorophenyl) (3e)
Rh(ttp)(4-
bromophenyl)·MeOH
(3d·MeOH)
Rh(ttp)(4-
chlorophenyl) (3e)
cryst syst, space
group
monoclinic, P21/n
monoclinic, P21/n
Rh−C bond
2.028(8)
2.138(6)
length (Å)
Figure 3. Porphyrin conformation of Rh(ttp)(4-chlorophenyl) (3e).
24-atom least-squares plane of the porphyrin core (in pm;
negative values correspond to displacement toward the aryl
group). Absolute values of the angles between pyrrole rings and
the least-squares plane, angles between pyrrole rings and the
least-squares plane, and angles between phenyl substituents and
the least-squares plane are shown in boldface.
Figure 1. ORTEP presentation of Rh(ttp)(4-bromophenyl)(MeOH)
(3d·MeOH) (30% probability displacement ellipsoids). Hydrogen
atoms are omitted for clarity.
Mechanistic Studies. RhIII(ttp)Cl has been reported to
react with KOH in benzene to give RhIII(ttp)OH. RhIII(ttp)-
OH, being unstable, then rapidly decomposes to give
RhII (ttp)2 and H2O2.18a However, RhII (ttp)2 further reacts
3d·MeOH and 3e are shown in Figures 1 and 2, respectively.
Rh(ttp)(4-bromophenyl) (3d) was coordinated with a
MeOH molecule, which was used in the crystal growth.
3d·MeOH is a six-coordinated octahedral complex, while
complex 3e is five-coordinated in a square-pyramidal
geometry with the porphyrin ligand occupying the square-
planar position. The conformation of the porphyrin is
somewhat saddlelike.15 This is because Rh3+ (ionic radii 75 pm) is
2
2
with KOH to give RhI(ttp)−,19 which can be protonated with
water to form RhIII(ttp)H.20 These rhodium species can
interconvert and even equilibrate under basic conditions.
Therefore, to find the rhodium porphyrin species responsible
for the Ar−X cleavage step, we examined the relative reactivity
of the rhodium species toward bromobenzene and iodobenzene
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(Scheme 1), Scheme 3 illustrates the proposed mechanism for
Ar−X (X = Br, I) cleavage with Rh(ttp)Cl. Rh(ttp)Cl first
Scheme 3. Proposed Mechanism for Base-Promoted Ar−X
(X = Br, I) Cleavage with Rh(ttp)Cl
undergoes ligand substitution with KOH or −OH produced
from hydrolysis of K2CO3 with intrinsic water to give
Rh(ttp)OH, which then undergoes reductive dimerization to
give Rh2(ttp)2.18 Rh2(ttp)2 then reacts with ArX (X = I, Br) to
yield Rh(ttp)Ar and Rh(ttp)X. The stoichiometry of this step is
supported by the nearly 1:1 ratio of Rh(ttp)Ph and Rh(ttp)X
formed when Rh2(ttp)2 reacted with ArX separately (Table 6,
entries 1 and 4). Rh(ttp)X (X = I, Br), which is chemically
equivalent to Rh(ttp)Cl, recycles back to Rh2(ttp)2 by the
reaction with a base. The slower reaction rate and stronger base
required for ArI suggests the ligand substitution of Rh(ttp)I is
slower than that of Rh(ttp)Br, likely due to the lower
electrophilicity of the Rh center of Rh(ttp)I.11,21 When no
base was added, Rh(ttp)Cl reacts very slowly with residual
water in benzene to give Rh(ttp)OH, which then dimerizes to
afford Rh2(ttp)2 and further cleaves the Ar−Br bond.
Possible Mechanism for Ar−X Cleavage. The possibility
of the four plausible mechanisms for Ar−X cleavage, oxidative
addition, nucleophilic aromatic substitution, direct halogen atom
abstraction ,and ipso substitution, is discussed below (Scheme 4).
Oxidative addition is not likely for a metalloporphyrin, because the
syn addition to the planar metalloporphyrin to form a stable six-
coordinated syn intermediate is highly sterically demanding.
Moreover, the highly elusive Rh(IV) porphyrin complex is difficult
to generate (Scheme 4, eq i).22 The nucleophilic aromatic
substitution mechanism with RhI(ttp)− and aryl halide involves a
negatively charged intermediate (Scheme 4, eq ii). However, the
reaction rate between RhI(ttp)− and PhBr was very slow (Table 6,
entry 3). A nucleophilic aromatic substitution mechanism is
thus unlikely. The direct halogen atom abstraction mechanism
(Scheme 4, eq iii) and ipso-substitution mechanism (Scheme 4, eq
iv) both involve a metalloradical as an intermediate. For the direct
halogen atom abstraction mechanism, an aryl radical is generated
during the reaction. On the other hand, a halogen radical is formed
when the ipso substitution is operating.
Figure 4. Porphyrin conformation of Rh(ttp)(4-bromophenyl) (3d).
Table 6. Reactivity of Rhodium Porphyrin Species with PhBr
and PhI
Rh(ttp)X
a
entry Rh(ttp)X′
time
PhX
yield of 3a, %
(yield, %)
b
1
2
3
4
5
Rh2(ttp)2
Rh(ttp)H
Rh(ttp)−
Rh2(ttp)2
5 min
1 day
1 day
5 min
1 day
PhBr
PhBr
PhBr
PhI
37
17
6
1b (34)
c
30
23
1c (30)
Rh(ttp)H
PhI
a
b
Isolated yield. Calculated from the ratio of integration of the pyrrole
c
peak of Rh(ttp)Br with that of Rh(ttp)Ph. Calculated from the ratio
of integration of the pyrrole peak of Rh(ttp)I with that of Rh(ttp)Ph.
(Table 6). RhII (ttp)2 reacted with both bromobenzene and
2
iodobenzene rapidly over 5 min and gave a total yield of
rhodium porphyrin complexes (Table 6, entries 1 and 4) close
to the yield of Rh(ttp)Ph obtained with RhIII(ttp)Cl (Table 1,
entry 4, and Table 2, entry 3). However, only around a 20%
yield of Rh(ttp)Ph was obtained after 1 day when RhIII(ttp)H
and RhI(ttp)− were reacted with halobenzenes (Table 6, entries
2, 3, and 5). Therefore, RhII (ttp)2 is the most possible
2
intermediate for both Ar−Br and Ar−I cleavage because it
reacted the fastest among the three probable intermediates.
Aryl halides can in principle undergo nucleophilic aromatic
substitution with RhI(ttp)− to form benzyne intermediates. This
possibility is excluded on the basis of the regioselectivity of the
reaction. Had the elimination−addition benzyne mechanism
indeed operated, the reaction of RhI(ttp)− with aryl halides
would have yielded two regioisomers in a 1:1 ratio (Scheme 2).
From the reaction of Rh2(ttp)2 with PhBr, the yields of
Rh(ttp)Ph (3a) and Rh(ttp)Br (1b) were 37% and 34%,
respectively (Table 6, entry 1). The slightly higher yield of
Rh(ttp)Ph (3a) in comparison with that of Rh(ttp)Br (1b)
indicates that a halogen atom leakage reaction has occurred and
is consistent with the ipso-substitution mechanism. Further-
more, when Rh2(ttp)2 reacted with 4-bromoanisole, Rh(ttp)(4-
methoxyphenyl) (3b) and Rh(ttp)Br (1b) were formed in 40%
and 36% yields, respectively, with 2% of PhBr detected by GC-
MS as the bromine leakage product, which subsequently reacts
with benzene solvent (eq 1). No biaryl, which can be formed by
the coupling reaction of an aryl radical, was detected.
Therefore, the halogen radical is identified as an intermediate
formed from the Ar−X cleavage reaction.
Scheme 2. Ar−X Cleavage via a Benzyne Mechanism
Furthermore, the halogen atom abstraction mechanism is not
valid, since when an equimolar mixture of para- and meta-
substituted ArX reacted with Rh(ttp)Cl, Rh(ttp)C6H4(p-FG)
Proposed Mechanism. On the basis of the mechanism
proposed for Ar−X (X = Br, I) cleavage with Ir(ttp)(CO)Cl
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Scheme 4. Possible Mechanisms for Ar−X (X = Br, I) Cleavage
para-substituted ArX (X = Br, I) should promote the reaction
rate, since the Rh(ttp)−cyclohexadienyl radical intermediate
can be stabilized by both electron-withdrawing and electron-
donating p-FGs through resonance and inductive effects.10,24
First, to ensure no exchange between Rh(ttp)Ar and ArX, an
exchange reaction was carried out to confirm that the product
ratio is the kinetic ratio. Rh(ttp)Ph was reacted with 4-
bromoanisole under the reaction conditions for 3 days; a 90%
isolated yield of Rh(ttp)Ph was recovered and no Rh(ttp)(4-
methoxyphenyl) was observed (eq 4). Thus, no exchange of
Rh(ttp)Ph occurred. Then, an equimolar mixture of para-
substituted ArBr and PhBr was reacted with Rh(ttp)Cl (Table 7)
by competition experiments. The product ratio was obtained by
was obtained as the major product (eqs 2 and 3). The product
ratio should be near 1:1 for a halogen atom abstraction
mechanism, since the position of FG does not affect the Ar−X
bond strength much. The results support the ipso-substitution
mechanism, because only the p-FGs but not the m-FGs stabilize
the Rh(ttp)−cyclohexadienyl radical intermediate by a
resonance interaction (Scheme 5).
Table 7. Competition Reaction between Substituted ArBr
and PhBr with Rh(ttp)Cl
Scheme 5. Rh(ttp)−Cyclohexadienyl Radical Stabilized by
p-FG
a
b
0
a
entry
FG
3b−h:3a
total yield, %
σp
log(kFG/kH)
1
2
3
4
5
OMe (2b)
tBu (2g)
F (2h)
6.3:1.0
2.2:1.0
2.4:1.0
4.2:1.0
8.8:1.0
76
77
71
57
76
−0.27
−0.15
0.06
0.799
0.342
0.380
0.623
0.944
Cl (2e)
0.23
NO2 (2f)
0.78
a
Ratio of Rh(ttp)C6H4(p-FG) and Rh(ttp)Ph in the crude product
obtained by H NMR spectroscopy. Hammett constant.25
b
1
determining the ratio Rh(ttp)C6H4(p-FG):Rh(ttp)Ph in the
1
crude reaction product by H NMR spectroscopy. A V-shaped
Hammett plot was obtained in Figure 5. The competition
reactions between an equimolar mixture of para-substituted
ArI and PhI with Rh(ttp)Cl and K2CO3 were also carried out
(Table 8). A V-shaped Hammett plot was also obtained
(Figure 6). The V-shaped Hammett plots indicate that ArX
(X = Br, I) with both electron-donating and electron-
withdrawing groups react faster than PhX (X = Br, I),
supporting the ipso-substitution mechanism for Ar−X
cleavage with Rh(ttp)Cl.
To further validate the ipso-substitution mechanism, competi-
tion reactions between an equimolar mixture of para-substituted
ArX (X = Br, I) and PhX (X = Br, I) with Rh(ttp)Cl and KOH
or K2CO3 were carried out to obtain the Hammett plot. For the
halogen atom abstraction mechanism, an increased reactivity
trend from electron-rich aryl halides to electron-poor aryl
halides should be observed.23 However, for the ipso-
substitution mechanism, both electron-rich and electron-poor
Metalloradical ipso substitution is an energetically lower
energy reaction pathway than direct halogen atom abstraction.
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Figure 5. Hammett plot of base-promoted Ar−Br cleavage using the Hammett constants.
Table 8. Competition Reaction between Substituted ArI and
PhI with Rh(ttp)Cl
Scheme 6. Comparison of the Mechanisms with Rhodium
and Iridium Porphyrin Complexes
a
b
0
a
entry
FG
3b−f:3a
total yield, %
σp
log(kFG/kH)
1
2
3
4
OMe (4b)
Me (4c)
Cl (4e)
9.1:1.0
2.6:1.0
4.8:1.0
68
69
67
69
−0.27
−0.17
0.23
0.959
0.415
0.681
1.26
NO2 (4f)
18.2:1.0
0.78
a
Ratio of Rh(ttp)C6H4(p-FG) and Rh(ttp)Ph in the crude product
b
25
1
EXPERIMENTAL SECTION
obtained by H NMR spectroscopy. Hammett constant.
■
General Procedure. Unless otherwise specified, all reagents were
purchased from commercial suppliers and used without further
purification. Hexane for chromatography was distilled from anhydrous
calcium chloride. Benzene and benzene-d6 were distilled from sodium
and were stored in a Teflon-screw-capped tube under nitrogen prior to
use. All reactions were carried out without light irradiation by
wrapping with aluminum foil. The reaction mixtures in Teflon-screw-
capped tubes were heated in heat blocks on heaters. Rh(ttp)Cl
(1a),17a,27 Rh2(ttp)2,28 Rh(ttp)H,29 and Rh(ttp)−Na+ 29 were prepared
according to literature procedures. Thin-layer chromatography (TLC)
was performed on precoated silica gel 60 F254 plates. Silica gel
(Merck, 70−230 and 230−400 mesh) was used for column
chromatography in air. Single crystals of 3d,e for X-ray crystallography
were grown from CH2Cl2/MeOH or from CHCl3/MeOH via slow
evaporation.
The π character of the CC bond in an aromatic ring
(∼30 kcal/mol)26 is weaker than that of Ar−X (X = Br,
∼80 kcal/mol; X = I, ∼65 kcal/mol). Therefore, the rate-limiting
step is likely metalloradical attack at the ipso carbon to break the
weaker bond and results in a resonance-stabilized intermediate
in which a much weaker Ar−X bond can then occur to form
M(por)Ar (M = Rh, Ir) and halogen radical (Scheme 6).
CONCLUSION
■
Both Ar−Br and Ar−I can be successfully cleaved with Rh(ttp)Cl
in the presence of base to give Rh(ttp)Ar in good yields. Rh2(ttp)2
was the proposed intermediate to cleave the Ar−X bond
(X = Br, I). The ipso-substitution mechanism for both Ar−Br
and Ar−I cleavage is operating.
Experimental Instrumentation. 1H NMR spectra were recorded
on a Bruker DPX-300 (300 MHz) or Bruker AvanceIII 400
(400 MHz) spectrometer. 13C NMR spectra were recorded on a
Figure 6. Hammett plot of base-promoted Ar−I cleavage using the Hammett constants.
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Bruker DPX-300 (75 MHz), Bruker AvanceIII 400 (100 MHz), or
Bruker AvanceIII 700 (176 MHz) spectrometer. Spectra were
referenced internally to the residual proton resonance in CDCl3 (δ
0.123 mmol), tBuOH (0.06 mL, 0.632 mmol), and PhBr (2a; 0.013 mL,
0.123 mmol) were added in benzene (1.0 mL). The red mixture was
degassed for three freeze−thaw−pump cycles, purged with N2, and
heated at 120 °C under N2 for 18 h. Excess benzene was removed by
vacuum distillation. The red residue was purified by column
chromatography on silica gel with a solvent mixture of hexane and
CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a; 8.3 mg, 0.010 mmol,
82%) was collected.
(e). Reaction of Rh(ttp)Cl with K2CO3 and tert-Butyl Alcohol
in PhBr. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg,
0.123 mmol), and tBuOH (0.06 mL, 0.632 mmol) were added in PhBr
(1.0 mL, 9.462 mmol). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2 for
18 h. Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a;
8.9 mg, 0.010 mmol, 88%) was collected.
(f). Reaction of Rh(ttp)Cl with PhBr and KOH. Rh(ttp)Cl (1a;
10.0 mg, 0.012 mmol), KOH (6.7 mg, 0.119 mmol), and PhBr (2a;
0.013 mL, 0.123 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged
with N2, and heated at 120 °C under N2 for 7 h. Excess benzene was
removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of hexane
and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a; 7.1 mg,
0.008 mmol, 70%) was collected.
(g). Reaction of Rh(ttp)Cl with PhBr, KOH, and tert-Butyl Alcohol.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (6.7 mg, 0.119 mmol),
tBuOH (0.06 mL, 0.632 mmol), and PhBr (2a; 0.013 mL, 0.123 mmol)
were added in benzene (1.0 mL). The red mixture was degassed for three
freeze−thaw−pump cycles, purged with N2, and heated at 120 °C under
N2 for 7 h. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)Ph (3a; 6.9 mg, 0.008 mmol, 68%) was collected.
Optimization of Base-Promoted Ph−I Cleavage by Rh(ttp)Cl.
(a). Reaction of Rh(ttp)Cl with PhI, K2CO3 and tert-Butyl Alcohol.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg, 0.123 mmol),
tBuOH (0.06 mL, 0.632 mmol), and PhI (4a; 0.014 mL, 0.124 mmol)
were added in benzene (1.0 mL). The red mixture was degassed for
three freeze−thaw−pump cycles, purged with N2, and heated at 120 °C
under N2 for 1 day. Excess benzene was removed by vacuum distillation.
The red residue was purified by column chromatography on silica gel with
a solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)I20a (1c; 1.9 mg, 0.002 mmol, 18%) and Rh(ttp)Ph (3a) (4.7 mg,
0.006 mmol, 46%) were collected.
1
7.26 ppm) or with tetramethylsilane (TMS, δ 0.00 ppm) in H NMR
spectra as the internal standard and in C6D6 (δ 128.06 ppm) or CDCl3
(δ 77.16 ppm) in 13C NMR spectra as internal standard. 19F NMR
spectra were recorded on a Varian XL-400 spectrometer at 376 MHz.
Chemical shifts were referenced with external standard fluorine in
C6H5CF3 using a sealed melting point tube that was placed into the
NMR tube (δ 0.00 ppm). Chemical shifts (δ) are reported in parts per
million (ppm). Coupling constants (J) are reported in hertz (Hz).
High-resolution mass spectra (HRMS) were obtained on a
ThermoFinnigan MAT 95 XL mass spectrometer in fast atom
bombardment (FAB) mode using 3-nitrobenzyl alcohol (NBA) matrix
and CH2Cl2 as the solvent or in electrospray ionization (ESI) mode
using MeOH/CH2Cl2 (1/1) as the solvent.
GC-MS analysis was conducted on a GCMS-QP2010 Plus system
using an Rtx-5MS column (30 m × 0.25 mm). The details of the GC
program are as follows. The column oven temperature and injection
temperature were 50.0 and 250.0 °C. Helium was used as the carrier
gas. The flow control mode was chosen as linear velocity (36.3 cm s−1)
with a pressure of 53.5 kPa. The total flow, column flow, and purge
flow were 24.0, 1.0, and 3.0 mL min−1, respectively. Split mode
injection with split ratio 20.0 was applied. After injection, the column
oven temperature was kept at 50.0 °C for 5 min and then the
temperature was elevated at a rate of 20.0 °C min−1 for 10 min until
250.0 °C. The temperature of 250.0 °C was kept for 5 min.
Optimization of Base-Promoted Ph−Br Cleavage by Rh-
(ttp)Cl. (a). Reaction of Rh(ttp)Cl with PhBr. Rh(ttp)Cl (1a; 10.0 mg,
0.012 mmol) and PhBr (2a; 0.013 mL, 0.123 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 3 days. Excess benzene was removed by vacuum distillation. The
red residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent . Red solid
Rh(ttp)Br (1b; 2.5 mg, 0.003 mmol, 25%), Rh(ttp)Cl (1a; 2.2 mg,
0.003 mmol, 22%), and Rh(ttp)Ph (3a; 2.9 mg, 0.003 mmol, 29%)
were collected. Rh(ttp)Br (1b): Rf = 0.30 (CH2Cl2 = 100%); 1H NMR
(CDCl3, 300 MHz) δ 2.71 (s, 12 H), 7.55 (t, 8 H, J = 6.3 Hz), 8.10 (d,
8 H, J = 8.1 Hz), 8.93 (s, 8 H); 13C NMR (CDCl3, 75 MHz) δ 21.89,
127.58, 127.92, 132.88, 134.09, 134.97, 137.63, 143.66; calcd for
(C48H36N4BrRh)+ m/z 850.1173, found m/z 850.1116. Rh(ttp)Ph
(3a): Rf = 0.50 (hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 300 MHz) δ
0.26 (d, 2 H, J = 8.1 Hz), 2.69 (s, 12 H), 4.76 (dt, 2H, J = 1.2, 7.8 Hz),
5.23 (t, 1 H, J = 7.8 Hz), 7.52 (t, 8 H, J = 7.3 Hz), 8.00 (dd, 4 H, J =
2.1, 8.9 Hz), 8.06 (dd, 4 H, J = 2.2, 8.7 Hz), 8.76 (s, 8 H); 13C NMR
(CDCl3, 75 MHz) δ 21.88, 120.68, 123.21, 124.22, 127.76, 129.11,
131.98, 134.11, 134.52, 137.62, 139.43, 143.39; calcd for
(C54H41N4Rh)+ m/z 848.2381, found m/z 848.2360.
(b). Reaction of Rh(ttp)Cl with PhI, KOH, and tert-Butyl Alcohol.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol),
tBuOH (0.06 mL, 0.632 mmol), and PhI (4a; 0.014 mL, 0.124 mmol)
(b). Reaction of Rh(ttp)Cl with PhBr and KOAc. Rh(ttp)Cl (1a;
10.0 mg, 0.012 mmol), KOAc (12.2 mg, 0.124 mmol), and PhBr (2a;
0.013 mL, 0.123 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged
with N2, and heated at 120 °C under N2 for 1 day. Excess benzene was
removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of
hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Br (1b; 4.5 mg,
0.005 mmol, 45%) and Rh(ttp)Ph (3a; 5.4 mg, 0.005 mmol, 53%)
were collected.
(c). Reaction of Rh(ttp)Cl with PhBr and K2CO3. Rh(ttp)Cl (1a;
10.0 mg, 0.012 mmol), K2CO3 (17.0 mg, 0.123 mmol), and PhBr (2a;
0.013 mL, 0.123 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged
with N2, and heated at 120 °C under N2 for 18 h. Excess benzene was
removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of hexane
and CH2Cl2 (1/1). Red solid Rh(ttp)Ph (3a; 4.6 mg, 0.005 mmol,
45%) was collected.
were added in benzene (1.0 mL). The red mixture was degassed for
three freeze−thaw−pump cycles, purged with N2, and heated at
120 °C under N2 for 1 day. Excess benzene was removed by vacuum
distillation. The red residue was purified by column chromatography
on silica gel with a solvent mixture of hexane and CH2Cl2 (1/1) as
eluent. Red solid Rh(ttp)Ph (3a; 6.4 mg, 0.008 mmol, 63%) was
collected.
(c). Reaction of Rh(ttp)Cl with PhI and KOH. Rh(ttp)Cl (1a;
10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol), and PhI (4a;
0.014 mL, 0.124 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged
with N2, and heated at 120 °C under N2 for 2 days. Excess benzene
was removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of
hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a; 8.6 mg,
0.010 mmol, 85%) was collected.
Substrate Scope of Base-Promoted Ar−I Cleavage by
Rh(ttp)Cl. (a). Reaction of Rh(ttp)Cl with 4-Iodoanisole and KOH.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol),
and 4-iodoanisole (4b; 29.1 mg, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
(d). Reaction of Rh(ttp)Cl with PhBr, K2CO3 and tert-Butyl
Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg,
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cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methoxyphenyl) (3b; 7.8 mg, 0.009 mmol, 74%) was collected.
Rh(ttp)(4-methoxyphenyl) (3b): Rf = 0.68 (hexane/CH2Cl2 1/1); 1H
NMR (CDCl3, 400 MHz) δ 0.15 (d, 2 H, J = 7.9 Hz), 2.69 (s, 12 H),
2.77 (s, 3 H), 4.44 (d, 2 H, J = 9.1 Hz), 7.53 (t, 8 H, J = 6.6 Hz), 8.01
(d, 4 H, J = 7.4 Hz), 8.06 (d, 4 H, J = 7.4 Hz), 8.76 (s, 8 H); 13C NMR
(CDCl3, 176 MHz) δ 21.69, 54.15, 110.01, 122.96, 127.53, 128.44,
131.75, 133.92, 134.29, 137.40, 139.22, 143.18, 153.96; calcd for
(C55H43N4ORh)+ m/z 878.2486, found m/z 878.2489.
Substrate Scope of Base-Promoted Ar−Br Cleavage by
Rh(ttp)Cl. (a). Reaction of Rh(ttp)Cl with 4-Bromoanisole, K2CO3,
and tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 4-
bromoanisole (2b; 0.015 mL, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 8 h. Excess
benzene was removed by vacuum distillation. The red residue was
purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methoxyphenyl) (3b; 6.8 mg, 0.008 mmol, 65%) was collected.
(b). Reaction of Rh(ttp)Cl with 4-Bromo-tert-butylbenzene,
K2CO3, and tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg,
(b). Reaction of Rh(ttp)Cl with 4-Iodotoluene and KOH. Rh(ttp)
Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol), and 4-
iodotoluene (4c; 27.1 mg, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methylphenyl)27b (3c; 8.1 mg, 0.009 mmol, 78%) was collected.
(c). Reaction of Rh(ttp)Cl with 4-Bromoiodobenzene and KOH.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol),
and 4-bromoiodobenzene (4d; 35.0 mg, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 4 h. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(4-bromophenyl) (3d; 7.9 mg, 0.009 mmol, 71%) was
collected. Rh(ttp)(4-bromophenyl) (3d): Rf = 0.68 (hexane/CH2Cl2
t
0.012 mmol), K2CO3 (17.0 mg, 0.123 mmol), BuOH (0.06 mL,
0.632 mmol), and 4-bromo-tert-butylbenzene (2g; 0.021 mL, 0.124 mmol)
were added in benzene (1.0 mL). The red mixture was degassed for
three freeze−thaw−pump cycles, purged with N2, and heated at 120
°C under N2 for 2 h. Excess benzene was removed by vacuum
distillation. The red residue was purified by column chromatography
on silica gel with a solvent mixture of hexane and CH2Cl2 (1/1) as
eluent. Red solid Rh(ttp)(4-tert-butylphenyl) (3g; 7.4 mg, 0.008
mmol, 68%) was collected. Rh(ttp)(4-tert-butylphenyl) (3g): Rf = 0.68
(hexane/CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ 0.23 (d, 2 H,J
= 8.5 Hz), 0.35 (s, 9 H), 2.70 (s, 12 H), 4.80 (d, 2 H, J = 8.8 Hz), 7.53
(t, 8 H, J = 6.4 Hz), 8.03 (d, 4 H, J = 7.2 Hz), 8.08 (d, 4 H, J = 7.5
Hz), 8.78 (s, 8 H); 13C NMR (CDCl3, 100 MHz) δ 21.69, 30.72,
32.60, 121.39, 123.00, 127.53, 127.89, 131.72, 133.86, 134.29, 137.39,
139.32, 142.67, 143.24; calcd for (C58H49N4Rh)+ m/z 904.3007, found
m/z 904.2996.
(c). Reaction of Rh(ttp)Cl with 4-Bromotoluene, K2CO3, and tert-
Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 4-
1
1/1); H NMR (CDCl3, 400 MHz) δ 0.10 (d, 2 H, J = 7.6 Hz), 2.70
bromotoluene (2c; 0.015 mL, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 2 h. Excess
benzene was removed by vacuum distillation. The red residue was
purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methylphenyl) (3c; 1.1 mg, 0.001 mmol, 11%) and Rh(ttp)(p-Br)Bn
(5; 7.0 mg, 0.007 mmol, 62%) were collected. Rh(ttp)(p-Br)Bn (5):
(s, 12 H), 4.90 (d, 2 H, J = 8.8 Hz), 7.54 (t, 8 H, J = 5.5 Hz), 8.00 (d, 4
H, J = 7.2 Hz), 8.06 (d, 4 H, J = 7.0 Hz), 8.78 (s, 8 H); 13C NMR
(CDCl3, 176 MHz) δ 21.69, 115.01, 123.02, 126.59, 127.59, 130.26,
131.87, 133.89, 134.28, 137.53, 139.03, 143.09; calcd for
(C54H40BrN4Rh)+ m/z 926.1486, found m/z 926.1493.
(d). Reaction of Rh(ttp)Cl with 4-Chloroiodobenzene and KOH.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol),
and 4-chloroiodobenzene (4e; 29.6 mg, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 1 day. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(4-chlorophenyl) (3e; 6.9 mg, 0.008 mmol, 65%) was
collected. Rh(ttp)(4-chlorophenyl) (3e): Rf = 0.68 (hexane/CH2Cl2
1
Rf = 0.45 (hexane/CH2Cl2 2/1); H NMR (CDCl3, 300 MHz) δ
−3.86 (d, 2 H, J = 3.6 Hz), 2.71 (s, 12 H), 2.77 (d, 2 H, J = 8.4 Hz),
5.95 (d, 2 H, J = 8.1 Hz), 7.56 (t, 8 H, J = 7.8 Hz), 7.96 (dd, 4 H, J =
1.8, 7.2 Hz), 8.06 (d, 4 H, J = 8.4 Hz), 8.70 (s, 8 H); 13C NMR (C6D6,
75 MHz) δ 10.56, (1JRh−C = 27.2 Hz), 21.89, 117.35, 122.88, 126.44,
127.79, 129.18, 131.92, 134.19, 134.26, 137.55, 139.55, 143.45; calcd
for (C55H42N4BrRh)+ m/z 940.1642, found m/z 940.1628.
(d). Reaction of Rh(ttp)Cl with 4-Bromofluorobenzene, K2CO3,
1
1/1); H NMR (CDCl3, 400 MHz) δ 0.16 (d, 2 H, J = 8.8 Hz), 2.70
and tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(s, 12 H), 4.78 (d, 2 H, J = 8.8 Hz), 7.54 (t, 8 H, J = 6.0 Hz), 8.00 (d, 4
H, J = 4.5 Hz), 8.07 (d, 4 H, J = 4.6 Hz), 8.79 (s, 8 H); 13C NMR
(CDCl3, 176 MHz) δ 21.69, 123.02, 123.73, 126.81, 127.59, 129.64,
131.87, 133.89, 134.27, 137.53, 139.04, 143.10; calcd for
(C54H40ClN4Rh)+ m/z 882.1991, found m/z 882.1990.
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 4-
bromofluorobenzene (2h; 0.014 mL, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 8 h. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(4-fluorophenyl) (3h; 6.2 mg, 0.007 mmol, 60%) was
collected. Rh(ttp)(4-fluorophenyl) (3h): Rf = 0.58 (hexane/CH2Cl2
(e). Reaction of Rh(ttp)Cl with 4-Nitroiodobenzene and KOH.
Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg, 0.125 mmol),
and 4-nitroiodobenzene (4f; 30.8 mg, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 3 h. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(4-nitrophenyl) (3f; 6.9 mg, 0.008 mmol, 64%) was collected.
Rh(ttp)(4-nitrophenyl) (3f): Rf = 0.68 (hexane/CH2Cl2 1/1); 1H
NMR (CDCl3, 400 MHz) δ 0.37 (d, 2 H, J = 8.2 Hz), 2.70 (s, 12 H),
5.61 (d, 2 H, J = 9.1 Hz), 7.55 (t, 8 H, J = 5.9 Hz), 8.00 (d, 4 H, J = 7.2
Hz), 8.06 (d, 4 H, J = 7.1 Hz), 8.83 (s, 8 H); 13C NMR (CDCl3, 176
MHz) δ 21.69, 117.68, 123.13, 124.95, 127.69, 129.13, 132.07, 133.88,
134.26, 137.72, 138.78, 143.02; calcd for (C54H40N5O2Rh)+ m/z
893.2232, found m/z 893.2230.
1
4
2/1); H NMR (CDCl3, 300 MHz) δ 0.16 (dd, 2 H, JH−F = 1.8, J =
8.9 Hz), 2.69 (s, 12 H), 4.55 (dd, 1 H, 3JH−F = 8.6, J = 8.9 Hz), 7.54 (d,
2 H, J = 6.3 Hz), 7.99 (dd, 4 H, J = 2.2, 8.5 Hz), 8.02 (dd, 4 H, J = 2.2,
8.7 Hz), 8.74 (s, 8 H); 19F NMR (C6H5CF3, 376 MHz) δ −62.84 (s,
1F); calcd for (C54H40N4FRh)+ m/z 876.2238, found m/z 866.2287.
(e). Reaction of Rh(ttp)Cl with 4-Bromochlorobenzene, K2CO3,
and tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
(17.0 mg, 0.123 mmol), tBuOH (0.06 mL, 0.632 mmol), and
4-bromochlorobenzene (2e; 23.7 mg, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 22 h. Excess benzene was removed by vacuum distillation. The red
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residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(4-chlorophenyl) (3e; 7.7 mg, 0.009 mmol, 73%) was
collected.
(c). Reaction of Rh(ttp)− with PhBr. Rh(ttp)− (9.3 mg, 0.012 mmol)
and PhBr (2a; 0.013 mL, 0.123 mmol) were added in benzene (1.0
mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day. Excess
benzene was removed by vacuum distillation. The red residue was
purified by column chromatography on silica gel with a solvent mixture
of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a; 0.6
mg, 0.001 mmol, 6%) was collected.
(d). Reaction of Rh2(ttp)2 with PhI. Rh2(ttp)2 (9.3 mg, 0.006 mmol)
and PhI (4a; 0.013 mL, 0.123 mmol) were added in benzene (1.0 mL).
The red mixture was degassed for three freeze−thaw−pump cycles,
purged with N2, and heated at 120 °C under N2 for 5 min. Excess
benzene was removed by vacuum distillation. The red residue was purified
by column chromatography on silica gel with a solvent mixture of hexane
and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)I (1c; 3.2 mg, 0.004 mmol,
30%) and Rh(ttp)Ph (3a; 3.1 mg, 0.004 mmol, 30%) were collected.
(e). Reaction of Rh(ttp)H with PhI. Rh(ttp)H (9.3 mg, 0.012 mmol)
and PhI (4a; 0.013 mL, 0.123 mmol) were added in benzene (1.0 mL).
The red mixture was degassed for three freeze−thaw−pump cycles,
purged with N2, and heated at 120 °C under N2 for 1 day. Excess benzene
was removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of hexane and
CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Ph (3a; 2.3 mg, 0.003 mmol,
23%) was collected.
Reaction of Rh2(ttp)2 with 4-Bromoanisole. Rh2(ttp)2 (9.3 mg,
0.006 mmol) and 4-bromoanisole (4a; 0.015 mL, 0.123 mmol) were
added in benzene (1.0 mL). The red mixture was degassed for three
freeze−thaw−pump cycles, purged with N2, and heated at 120 °C
under N2 for 5 min. Excess benzene was removed by vacuum
distillation and was analyzed by GC-MS. PhBr (2a; 0.0002 mnol, 2%)
was determined by GC-MS with naphthalene as internal standard. The
red residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)Br (1b; 3.7 mg, 0.004 mmol, 36%) and Rh(ttp)Ph (3a; 4.0 mg,
0.005 mmol, 40%) were collected.
(f). Reaction of Rh(ttp)Cl with 4-Bromonitrobenzene, K2CO3, and
tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 4-
bromonitrobenzene (2f; 25.0 mg, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 24 h. Excess
benzene was removed by vacuum distillation. The red residue was
purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
nitrophenyl) (3f; 8.6 mg, 0.010 mmol, 80%) was collected.
(g). Reaction of Rh(ttp)Cl with 3-Bromobenzotrifluoride, K2CO3,
and tert-Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 3-
bromobenzotrifluoride (2i; 0.017 mL, 0.124 mmol) were added in
benzene (1.0 mL). The red mixture was degassed for three freeze−
thaw−pump cycles, purged with N2, and heated at 120 °C under N2
for 24 h. Excess benzene was removed by vacuum distillation. The red
residue was purified by column chromatography on silica gel with a
solvent mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid
Rh(ttp)(3-trifluoromethylphenyl) (3i; 8.1 mg, 0.009 mmol, 74%) was
collected. Rh(ttp)(3-trifluoromethylphenyl) (3i): Rf = 0.68 (hexane/
CH2Cl2 1/1); 1H NMR (CDCl3, 400 MHz) δ 0.40 (s, 1 H), 0.43 (d, 1
H, J = 8.4 Hz), 2.70 (s, 12 H), 4.84 (t, 1 H, J = 7.9 Hz), 5.48 (d, 1 H,
J = 7.4 Hz), 7.54 (t, 8 H, J = 6.4 Hz), 8.00 (d, 4 H, J = 8.4 Hz), 8.08
(d, 4 H, J = 8.4 Hz), 8.80 (s, 8 H); 13C NMR (CDCl3, 176 MHz) δ
21.69, 53.87, 107.34, 113.24, 121.32, 123.17, 125.80, 126.17, 127.57,
131.79, 134.14, 137.43, 139.20, 143.19, 153.61; calcd for
(C55H40F3N4Rh)+ m/z 917.2333, found m/z 917.2326.
(h). Reaction of Rh(ttp)Cl with 3-Bromoanisole, K2CO3, and tert-
Butyl Alcohol. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 3-
Competition Reactions of Meta- and Para-Substituted ArX
with Rh(ttp)Cl. (a). Competition Reaction of 4-Bromoanisole and
3-Bromoanisole with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg,
bromoanisole (2j; 0.017 mL, 0.124 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 24 h. Excess
benzene was removed by vacuum distillation. The red residue was
purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(3-
methoxyphenyl) (3j; 4.6 mg, 0.005 mmol, 44%) was collected.
t
0.012 mmol), K2CO3 (17.0 mg, 0.123 mmol), BuOH (0.06 mL,
0.632 mmol), 4-bromoanisole (2b; 0.008 mL, 0.060 mmol), and 3-
bromoanisole (2j; 0.008 mL, 0.060 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methoxyphenyl) (3b; 7.4 mg, 0.008 mmol, 70%) and Rh(ttp)(3-
methoxyphenyl) (3j; 0.4 mg, 0.0005 mmol, 4%) (ratio 17.5:1) were
collected in a single fraction. The ratio was determined by the ratio of
meta aryl proton signals of the two products by 1H NMR
spectroscopy.
1
Rh(ttp)(3-methoxyphenyl) (3j): Rf = 0.68 (hexane/CH2Cl2 1/1); H
NMR (CDCl3, 400 MHz) δ 0.39 (s, 1 H), 0.43 (d, 1 H, J = 8.4 Hz),
1.49 (s, 3 H), 2.70 (s, 12 H), 4.83 (t, 1 H, J = 7.9 Hz), 5.47 (d, 1 H, J =
7.4 Hz), 7.54 (t, 8 H, J = 6.5 Hz), 8.00 (d, 4 H, J = 7.2 Hz), 8.07 (d, 4
H, J = 4.4 Hz), 8.79 (s, 8 H); 13C NMR (CDCl3, 100 MHz) δ 21.68,
117.57, 123.12, 123.60, 125.03, 125.22, 125.40, 127.61, 131.91, 132.45,
133.87, 134.30, 137.54, 139.06, 143.16; calcd for (C55H43N4ORh)+ m/
z 878.2486, found m/z 878.2481.
Reactivity of Rhodium Porphyrin Species with PhBr and PhI.
(a). Reaction of Rh2(ttp)2 with PhBr. Rh2(ttp)2 (9.3 mg, 0.006 mmol)
and PhBr (2a; 0.013 mL, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 5 min.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)Br
(1b; 3.5 mg, 0.004 mmol, 34%) and Rh(ttp)Ph (3a; 3.8 mg, 0.004
mmol, 37%) were collected.
(b). Reaction of Rh(ttp)H with PhBr. Rh(ttp)H (9.3 mg,
0.012 mmol) and PhBr (2a; 0.013 mL, 0.123 mmol) were added
in benzene (1.0 mL). The red mixture was degassed for three
freeze−thaw−pump cycles, purged with N2, and heated at 120 °C
under N2 for 1 day. Excess benzene was removed by vacuum
distillation. The red residue was purified by column chromatog-
raphy on silica gel with a solvent mixture of hexane and CH2Cl2
(1/1) as eluent. Red solid Rh(ttp)Ph (3a; 1.7 mg, 0.002 mmol, 17%)
was collected.
(b). Competition Reaction of 4-Iodotoluene and 3-Iodotoluene
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (7.0 mg,
0.124 mmol), 4-iodotoluene (4c; 26.8 mg, 0.123 mmol), and 3-
iodotoluene (; 26.8 mg, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methylphenyl) (3c; 4.1 mg, 0.005 mmol, 40%) and Rh(ttp)(3-
methylphenyl) (3k; 2.0 mg, 0.002 mmol, 19%) (ratio 2.1:1) were
collected in a single fraction. The ratio was determined by the ratio of
meta aryl proton signals of the two products by 1H NMR
spectroscopy. Rh(ttp)(3-methylphenyl) (3k): Rf = 0.55 (hexane/
CH2Cl2 1/1); 1H NMR (CDCl3, 300 MHz) δ 0.01 (s, 1 H), 0.13 (d, 1
H, J = 8.0 Hz), 2.69 (s, 12 H), 4.64 (t, 1 H, J = 7.5 Hz), 5.04 (d, 1 H,
J = 6.8 Hz), 7.53 (t, 8 H, J = 5.9 Hz), 8.02 (dd, 4 H, J = 2.2, 8.6 Hz),
8.07 (dd, 4 H, J = 2.4, 7.9 Hz), 8.75 (s, 8 H); 13C NMR (CDCl3, 75
MHz) δ 20.36, 21.88, 121.60, 123.19, 123.55, 125.93, 127.75, 129.77,
5460
dx.doi.org/10.1021/om300441p | Organometallics 2012, 31, 5452−5462

Organometallics
Article
131.92, 132.98, 134.12, 137.58, 139.51, 143.41; calcd for
(C55H43N4Rh)+ m/z 862.2537, found m/z 862.2508.
4-bromonitrobenzene (2f; 12.5 mg, 0.062 mmol), and bromobenzene
(2a; 0.007 mL, 0.062 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged with
N2, and heated at 120 °C under N2 for 1 day. Excess benzene was
removed by vacuum distillation. The red residue was purified by column
chromatography on silica gel with a solvent mixture of hexane and
CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-nitrophenyl) (3f; 7.5 mg,
0.008 mmol, 68%) and Rh(ttp)Ph (3a; 0.8 mg, 0.001 mmol, 8%) (ratio
8.8:1) were collected in a single fraction. The ratio was determined by the
ratio of meta aryl proton signals of the two products by 1H NMR
spectroscopy.
Competition Reactions of Para-Substituted ArBr and PhBr
with Rh(ttp)Cl. (a). Control Experiment of Rh(ttp)Ph with 4-
Bromoanisole. Rh(ttp)Ph (3a; 10.0 mg, 0.012 mmol) K2CO3
t
(17.0 mg, 0.123 mmol), BuOH (0.06 mL, 0.632 mmol), and 4-
bromoanisole (2b; 0.015 mL, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 3 days.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Rh(ttp)Ph (3a; 9.0 mg,
0.011 mmol, 90%) was recovered.
Competition Reactions of Para-Substituted ArI and PhI with
Rh(ttp)Cl. (a). Competition Reaction of 4-Iodoanisole and PhI
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (6.9 mg,
0.123 mmol), 4-iodoanisole (4b; 28.8 mg, 0.123 mmol), and
iodobenzene (4a; 0.014 mL, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
methoxyphenyl) (3b; 6.6 mg, 0.008 mmol, 61%) and Rh(ttp)Ph (3a;
0.7 mg, 0.001 mmol, 7%) (ratio 9.1:1) were collected in a single
fraction. The ratio was determined by the ratio of meta aryl proton
(b). Competition Reaction of 4-Bromoanisole and PhBr with
Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg,
t
0.123 mmol), BuOH (0.06 mL, 0.632 mmol), 4-bromoanisole (2b;
0.008 mL, 0.060 mmol), and bromobenzene (2a; 0.007 mL, 0.060
mmol) were added in benzene (1.0 mL). The red mixture was
degassed for three freeze−thaw−pump cycles, purged with N2, and
heated at 120 °C under N2 for 1 day. Excess benzene was removed by
vacuum distillation. The red residue was purified by column
chromatography on silica gel with a solvent mixture of hexane and
CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-methoxyphenyl) (3b;
6.9 mg, 0.008 mmol, 66%) and Rh(ttp)Ph (3a; 1.1 mg, 0.001 mmol,
10%) (ratio 6.3:1) were collected in a single fraction. The ratio was
determined by the ratio of meta aryl proton signals of the two products
1
signals of the two products by H NMR spectroscopy.
(b). Competition Reaction of 4-Iodotoluene and PhI
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (6.9 mg,
0.123 mmol), 4-iodotoluene (4c; 26.8 mg, 0.123 mmol), and iodobenzene
(4a; 0.014 mL, 0.123 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged with N2,
and heated at 120 °C under N2 for 1 day. Excess benzene was removed by
vacuum distillation. The red residue was purified by column chromatog-
raphy on silica gel with a solvent mixture of hexane and CH2Cl2 (1/1) as
eluent. Red solid Rh(ttp)(4-methylphenyl) (3c; 5.3 mg, 0.006 mmol, 50%)
and Rh(ttp)Ph (3a; 2.0 mg, 0.002 mmol, 19%) (ratio 2.6:1) were collected
in a single fraction. The ratio was determined by the ratio of meta aryl
1
by H NMR spectroscopy.
(c). Competition Reaction of 4-Bromo-tert-butylbenzene and
PhBr with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
(17.0 mg, 0.123 mmol), tBuOH (0.06 mL, 0.632 mmol), 4-bromo-tert-
butylbenzene (2g; 0.011 mL, 0.062 mmol), and bromobenzene (2a;
0.007 mL, 0.062 mmol) were added in benzene (1.0 mL). The red
mixture was degassed for three freeze−thaw−pump cycles, purged
with N2, and heated at 120 °C under N2 for 1 day. Excess benzene was
removed by vacuum distillation. The red residue was purified by
column chromatography on silica gel with a solvent mixture of hexane
and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-tert-butylphenyl)
(3g; 6.0 mg, 0.007 mmol, 53%) and Rh(ttp)Ph (3a; 2.5 mg,
0.003 mmol, 24%) (ratio 2.2:1) were collected in a single fraction. The
ratio was determined by the ratio of meta aryl proton signals of the
1
proton signals of the two products by H NMR spectroscopy.
(c). Competition Reaction of 4-Chloroiodobenzene and PhI
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (6.9 mg,
0.123 mmol), 4-chloroiodobenzene (4e; 29.3 mg, 0.123 mmol), and
iodobenzene (4a; 0.014 mL, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
chlorophenyl) (3e; 6.1 mg, 0.007 mmol, 55%) and Rh(ttp)Ph (3a;
1.2 mg, 0.001 mmol, 12%) (ratio 4.8:1) were collected in a single
fraction. The ratio was determined by the ratio of meta aryl proton
1
two products by H NMR spectroscopy.
(d). Competition Reaction of 4-Bromofluorobenzene and PhBr
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg,
t
0.123 mmol), BuOH (0.06 mL, 0.632 mmol), 4-bromofluorobenzene
(2h; 0.007 mL, 0.062 mmol), and bromobenzene (2a; 0.007 mL, 0.062
mmol) were added in benzene (1.0 mL). The red mixture was degassed
for three freeze−thaw−pump cycles, purged with N2, and heated at
120 °C under N2 for 1 day. Excess benzene was removed by vacuum
distillation. The red residue was purified by column chromatography on
silica gel with a solvent mixture of hexane and CH2Cl2 (1/1) as eluent.
Red solid Rh(ttp)(4-fluorophenyl) (3h; 5.4 mg, 0.006 mmol, 50%) and
Rh(ttp)Ph (3a; 2.2 mg, 0.003 mmol, 21%) (ratio 2.4:1) were collected in
a single fraction. The ratio was determined by the ratio of meta aryl
1
signals of the two products by H NMR spectroscopy.
(d). Competition Reaction of 4-Nitroiodobenzene and PhI
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), KOH (6.9 mg,
0.123 mmol), 4-nitroiodobenzene (4f; 30.6 mg, 0.123 mmol), and
iodobenzene (4a; 0.014 mL, 0.123 mmol) were added in benzene
(1.0 mL). The red mixture was degassed for three freeze−thaw−pump
cycles, purged with N2, and heated at 120 °C under N2 for 1 day.
Excess benzene was removed by vacuum distillation. The red residue
was purified by column chromatography on silica gel with a solvent
mixture of hexane and CH2Cl2 (1/1) as eluent. Red solid Rh(ttp)(4-
nitrophenyl) (3f; 7.2 mg, 0.008 mmol, 65%) and Rh(ttp)Ph (3a; 0.4
mg, 0.0004 mmol, 4%) (ratio 18.2:1) were collected in a single
fraction. The ratio was determined by the ratio of meta aryl proton
1
proton signals of the two products by H NMR spectroscopy.
(e). Competition Reaction of 4-Bromochlorobenzene and PhBr
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3 (17.0 mg,
0.123 mmol), tBuOH (0.06 mL, 0.632 mmol), 4-bromochloro-
benzene (2e; 11.9 mg, 0.062 mmol), and bromobenzene (2a; 0.007 mL,
0.062 mmol) were added in benzene (1.0 mL). The red mixture was
degassed for three freeze−thaw−pump cycles, purged with N2, and heated
at 120 °C under N2 for 1 day. Excess benzene was removed by vacuum
distillation. The red residue was purified by column chromatography on
silica gel with a solvent mixture of hexane and CH2Cl2 (1/1) as eluent.
Red solid Rh(ttp)(4-chlorophenyl) (3e; 5.0 mg, 0.006 mmol, 46%) and
Rh(ttp)Ph (3a; 1.2 mg, 0.001 mmol, 11%) (ratio 4.2:1) were collected in
a single fraction. The ratio was determined by the ratio of meta aryl
1
signals of the two products by H NMR spectroscopy.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
proton signals of the two products by H NMR spectroscopy.
Tables, figures, and CIF files giving crystallographic data for
(f). Competition Reaction of 4-Bromonitrobenzene and PhBr
with Rh(ttp)Cl. Rh(ttp)Cl (1a; 10.0 mg, 0.012 mmol), K2CO3
(17.0 mg, 0.123 mmol), tBuOH (0.06 mL, 0.632 mmol),
1
Rh(ttp)Ar and H and 13C NMR spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
5461
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Organometallics
Article
(17) (a) Zhou, X.; Li, Q.; Mak, T. C. W.; Chan, K. S. Inorg. Chim.
Acta 1998, 270, 551−554. (b) Fleischer, E. B.; Lavallee, D. J. Am.
Chem. Soc. 1967, 89, 7132−7133.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ksc@cuhk.edu.hk.
(18) (a) Choi, K. S.; Lai, T. H.; Chan, K. S. Organometallics 2011, 30,
2633−2635. (b) Frary, F. C.; Nietz, A. H. J. Am. Chem. Soc. 1915, 37,
2268−2273. (c) Thomas, A. M., Jr. J. Chem. Eng. Data 1963, 8, 51−54.
(19) (a) Ni, Y.; Fitzgerald, J. P.; Carroll, P.; Wayland, B. B. Inorg.
Chem. 1994, 33, 2029−2035. (b) Wayland, B. B.; Balkus, K. J.; Farnos,
M. D. Organometallics 1989, 8, 950−955.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(20) (a) Wayland, B. B.; Voorhees, S. L. V.; Wilker, C. Inorg. Chem.
1986, 25, 4039−4042. (b) Ogoshi, H.; Setsune, J.; Yoshida, Z. J. Am.
Chem. Soc. 1977, 99, 3869−3870.
We thank the Research Grants Councils (No. 400308) and a
Special Equipment Grant (No. SEG/CUHK09) from the
University Grants Committee of Hong Kong SAR, People’s
Republic of China, for financial support.
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