Base-promoted selective activation of benzylic carbon-hydrogen bonds of toluenes with rhodium(III) porphyrin chloride: Synthetic scopes and mechanism

Article abstract of DOI:10.1002/jccs.201200635

Toluenes underwent base-promoted selective benzylic carbon-hydrogen bond activation (CHA) with rhodium porphyrin chlorides (Rh(por)Cl). In the absence of nucleophilic base, both aryl and benzylic rhodium porphyrins were formed. In the presence of nucleophilic base, the selectivity, rates and functional group compatibilities of benzylic activation reactions were enhanced. K ₂CO₃ was found to be the optimal base to achieve the best yields. Ortho-, meta- and para-substituted toluenes in the presence of K ₂CO₃ yielded the corresponding rhodium porphyrin benzyls in high yields both in solvent-free conditions and in benzene solvent. Mechanistically, in the absence of nucleophilic base, a cationic rhodium(III) porphyrin species together with some rhodium(II) porphyrin are the most likely intermediates to account both the aryl and benzylic CHA. In the presence of a base, Rh(por)OH is generated by ligand substitution with Rh(por)Cl and rapidly undergoes reduction to give rhodium(II) porphyin dimer and H₂O ₂. The key rhodium porphyrin intermediates for benzylic CHA were found to be rhodium(II) porphyrin dimer and hydrides as observed by ¹H NMR spectroscopy, which underwent parallel benzylic CHA reactions with the rhodium(II) porphyrin dimer being the more reactive intermediate.

Full text of DOI:10.1002/jccs.201200635

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Base-Promoted Selective Activation of Benzylic Carbon-Hydrogen Bonds of Toluenes
with Rhodium(III) Porphyrin Chloride: Synthetic Scopes and Mechanism
Kwong Shing Choi, Peng Fai Chiu, Chung Sum Chan and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong,
People’s Republic of China
(Received: Dec. 7, 2012; Accepted: Feb. 18, 2013; Published Online: ??; DOI: 10.1002/jccs.201200635)
Toluenes underwent base-promoted selective benzylic carbon-hydrogen bond activation (CHA) with rho-
dium porphyrin chlorides (Rh(por)Cl). In the absence of nucleophilic base, both aryl and benzylic rho-
dium porphyrins were formed. In the presence of nucleophilic base, the selectivity, rates and functional
group compatibilities of benzylic activation reactions were enhanced. K2CO3 was found to be the optimal
base to achieve the best yields. Ortho-, meta- and para-substituted toluenes in the presence of K2CO3
yielded the corresponding rhodium porphyrin benzyls in high yields both in solvent-free conditions and in
benzene solvent. Mechanistically, in the absence of nucleophilic base, a cationic rhodium(III) porphyrin
species together with some rhodium(II) porphyrin are the most likely intermediates to account both the
aryl and benzylic CHA. In the presence of a base, Rh(por)OH is generated by ligand substitution with
Rh(por)Cl and rapidly undergoes reduction to give rhodium(II) porphyin dimer and H2O2. The key rho-
dium porphyrin intermediates for benzylic CHA were found to be rhodium(II) porphyrin dimer and hy-
drides as observed by 1H NMR spectroscopy, which underwent parallel benzylic CHA reactions with the
rhodium(II) porphyrin dimer being the more reactive intermediate.
Keywords: Benzylic; Carbon-hydrogen bond activation; Toluene; Rhodium(III); Porphyrin.
INTRODUCTION
Recent interests in carbon-hydrogen bond activation
that a nucleophilic base can accelerate the rate and enhance
the selectivities of these types of bond activation reac-
tions.4,6,9b To identify the synthetic scopes and gain further
mechanistic understanding of the base-promoted benzylic
CHA by rhodium(III) porphyrin chloride, we have under-
taken an extensive study and now report the results.
(CHA) by transition metal complexes (M) both in stoichio-
metric and catalytic applications in organic synthesis have
ushered intensive research for functional group compati-
ble, mild and selective processes.1 Late transition metal
complexes are more appealing than their early transition
metal counterparts due to broader functional group com-
patibilities.2 Often, the rates and yields of these CHA reac-
tions are enhanced significantly in the presence of bases,
which can play the role in abstracting the acidic hydrogens
of the C-H bonds, especially upon coordination to the metal
centers.3
Scheme I Base-Promoted Benzylic CHA
RESULTS AND DISCUSSION
Temperature Dependent CHA Selectivity
We have been interested in the chemistries of alkyl,4
aryl,5 benzylic6 and aldehydic7 carbon-hydrogen bond acti-
vation, and silicon-hydrogen activation8 with both rho-
dium(III) and iridium(III) porphyrin chlorides complexes.9
These types of metalloporphyrins are unique due to the ap-
parent steric difficulty of cis-coordination of a substrate to
a five coordinate metalloporphyrin complex in the course
of activation and the relative electronic inaccessibility of
an oxidative addition intermediate that requires a formal
M(V) oxidation state. We have also recently discovered
Initially, rhodium(III) tetrakis(4-tolyl)porphyrin chlo-
ride (Rh(ttp)Cl) was found to react with toluene in sol-
vent-free conditions at 120 oC in 3 days to give a mixture of
3-tolyl and 4-tolyl as well as benzylic rhodium porphyrin
complexes (Table 1, entry 2). Prolonged heating at 120 oC
for 7 days produced similar product yields and poor selec-
tivities (Table 1, entry 3). The absence of Rh(ttp)(2-tolyl) is
likely due to the steric hindrance of an adjacent methyl
group of toluene. To our surprise, the reaction at 200 oC
generated only Rh(ttp)Bn in 65% yield (Table 1, entry 4).
Special Issue Dedicated to Prof. Yu Wang in Honor of Her 70th Birthday
* Corresponding author. Tel: +852-3943-6376; Fax: +852-2603-5057; Email: ksc@cuhk.edu.hk
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Article
Choi et al.
in BnCHA were observed with the addition of other inor-
ganic nucleophilic bases (Table 2). Stronger bases such
NaOH, KOH, K3PO4, K2CO3, NaOPh and KHCO3 (10
equiv) were in general very effective promoter to yield
Rh(ttp)Bn selectively in high yields in 30 to 600 minutes
with K2CO3 being the most effective one both in terms of
rate enhancement and highest product yield (Table 2,
entris 1-7). Weaker bases such as NaOAc, KOAc and
(CH3)3CCO2Na were also effective but required longer re-
action times (Table 2, entries 8 to 10). However, when
NaHSO4 was added, only Rh(ttp)(4-tolyl) and Rh(ttp)(3-
tolyl) was formed (Table 2, entry 11). The absence of
Rh(ttp)Bn is likely due to the non-nucleophilic nature of
Table 1. Temperature Effect on CHA of Toluene with Rh(ttp)Cl
N2
temp, time
Rh(ttp)Cl
+
Rh(ttp)Bn
+
Rh(ttp)(4-tolyl)
+
Rh(ttp)(3-tolyl)
1
2
3
Yield /%a
2
Entry
Temp /oC
Time /d
1
3
1
2
3
4
60
3
3
7
1
No rxn
26
120
120
200
26
28
65
13
14
14
a Estimated from the integration of the reaction mixture after
chromatography by 1H NMR spectroscopy.
The selective formation of the apparently less stable
Rh(ttp)Bn was favored at high temperature, as Rh-Ar has a
stronger Rh-C bond.10 Since both Rh(ttp)(4-tolyl) and
Rh(ttp)Bn were stable in toluene at an elevated temperature
of 200 oC for 2 days without any interconversion (Scheme
II), BnCHA and ArCHA products are not formed from con-
secutive, but from concurrent pathways. The lack of inter-
conversion between Rh(ttp)(4-tolyl) and Rh(ttp)Bn likely
originates from the absence of a kinetically accessible
cis-coordination site and the steric hindrance of these large
benzyl and tolyl groups. Since Rh(ttp)Cl did not react at 60
oC in 3 days (Table1, entry 1), the K2CO3-promoted
BnCHA required at least 120 oC in 30 min.
-
HSO4 to stabilize the more cationic Rh(ttp)HSO4 that fa-
vors an electrophilic aromatic substitution. Indeed, a
cationic Rh porphyrin, such as Rh(oep)ClO4 is reported to
undergo SEAr with arenes.11
Besides the basicity, the size of cation and possibly
the apparent solubility of bases also affect the rates of
BnCHA. The rate of BnCHA was slower when NaOH was
added compared with KOH (Table 2, entries 1 and 2), simi-
lar to the reactivity of NaOAc versus KOAc (Table 2,
entries 8 and 9). Also, Na2CO3 was observed to be less sol-
uble in the reaction mixture compared with K2CO3. There-
fore K2CO3 was found to be the optimal base.
K2CO3 Loading
The loading of K2CO3 was further optimized. Both 1
and 5 equivalents of K2CO3 required extended reaction
time of more than 4 hours and produced lower yields of
Scheme II No Interconversion of Rh Complexes
Table 2. Base Effect on BnCHA
Base-Promoting Effect
pKa of
Entry
Base
conjugated Time /min Yields /%
acid12
With the reported base-promoted CHA by transition
metal complexes,3 we then explored the effect of added lig-
ands and bases. Coordinating ligands, such as Ph3P and
pyridine, did not produce any CHA products due to forma-
tion of coordination complexes that shut down the CHA re-
action completely. Indeed, (Ph3P)Rh(ttp)Cl was isolated in
52% yield. The non-coordinating base 2,6-di-tert-butyl-
pyridine (30 equiv) proved to be a somewhat effective but
non selective promoter, as Rh(ttp)Bn and Rh(ttp)(4-tolyl)
were obtained in 46 and 18% yields, respectively, after 3
days at 120 oC.
1
2
3
4
5
6
7
8
NaOH
KOH
K3PO4
Na2CO3
K2CO3
NaOPh
KHCO3
NaOAc
KOAc
13.8
13.5
12.3
10.3
10.3
9.90
6.35
4.76
4.76
4.76
1.99
45
60
60
600
30
60
600
60
45
60
480
79
94
77
79
97
93
94
84
84
74
42a
9
10
11
(CH3)3CCOO-Na+
NaHSO4
a as a mixture of Rh(ttp)(4-tolyl) (2) and Rh(ttp)(3-tolyl) (3).
Further enhancements in selectivity, rate, and yields
2
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Benzylic CHA of Toluenes with Rh(por)Cl
Table 3. Loading Effect of K2CO3
Rh(ttp)Bn (Table 3, entries 1 and 2). 10 to 100 equivalents
of K2CO3 were equally efficient. Alower loading of K2CO3
gave a slower reaction with a lower yield and a higher load-
ing (up to 100 equivalents) resulted in little improved reac-
tion efficiency. Therefore, 10 equivalents of K2CO3 were
therefore employed for further studies.
120 oC, N2
Rh(ttp)Cl
+
BnH
Rh(ttp)Bn
K2CO3, time
Entry
Equiv of K2CO3
Time /min
Yields /%
1
2
3
4
5
1
5
10
20
100
840
240
30
30
30
69
77
97
97
96
Scope of Substrates
To examine the substrate scope of toluene, the opti-
mized base-promoted reaction conditions were applied to
various substituted toluenes. Generally, high yields of rho-
dium porphyrin benzyls were obtained in the presence of
K2CO3 or NaOH (Table 4). The basic reaction conditions
were also more functional group compatible (Columns A
and B versus C). Even the coordinating CN and redox ac-
tive NO2 groups were amenable (Table 4, columns A, en-
tries 7 and 8; 12 and 13). We do not understand the very
slow reaction and lower yield observed for 4-fluorotoluene
(Table 4, entry 6) presumably some C-F cleavage might
have occurred.13 More sterically hindered toluenes (ortho
and meta positions) were also applicable in the base-pro-
moted BnCHA but required longer times (Table 4, entries
10 and 11). Slightly lower yields of Rh(ttp)FG-Bn were ob-
tained for the ortho-substituted toluenes (Table 4, entries
11-13) and were attributed to steric hindrance.
o
KOH in toluene or benzene at 120 C for 1 day, we rea-
soned that some of the intermediates generated might be
base-labile to undergo decomposition. Rh(ttp)H is a possi-
ble intermediate and can be converted into Rh(ttp)- by pro-
ton abstraction in the presence of a stronger base and then
likely undergoes thermal decomposition. This aspect will
be discussed in details in the mechanistic studies section.
Porphyrin Effect
Both electron-rich and -deficient rhodium porphyrin
chlorides were examined (Table 5). The reactivity follows
the order of electron-deficient rhodium porphyrin chlo-
rides: bocp > ttp > tdbpp. (bocp = 2,3,7,8,12,13,17,18-
octachloro-5,10,15,20-tetrakis(p-tert-butylphenyl)porphy
rinato dianion, tdbpp = 5,10,15,20-tetrakis(3,5-di-tert-
butylphenyl)porphyrinato dianon). The product yields of
Rh(por)Bn were all high with a slightly lower yield for
The stronger base, NaOH, produced lower product
yields in most substrates with similar rates compared to that
of K2CO3. Since Rh(ttp)Bn was found to be stable towards
Table 4. Base Effect of Solvent-free Benzylic CHA of Toluenes
10 equiv of Base
Rh(ttp)Cl + 4-FG-BnH
Rh(ttp)(4-FG-Bn)
120 oC, N2, time
A (K2CO3)
B (NaOH)
C (No base)
Entry
FG
Time/min
Yield (%)
Time/min
Yield (%)
Time/d
Yield (%)
1
2
3
4
5
6
7
8
4-OMe
4-tBu
4-Me
H
30
45
45
30
240
15
60
30
60
120
90
90
90
1a (92)
1b (98)
1c (90)
1 (97)
1d (64)
1e (39)b
1f (83)
1g (98)
1h (67)
1i (81)
1j (73)
1k (81)
1l (84)
30
45
45
45
240
1a (98)
1b (82)
1c (77)
1 (79)
2
2
1a (78)
1b (84)
3
3
1 (26)a
1d (72)
4-F
1d (60)
4-CHO
4-CN
4-NO2
3,5-Me2
3-Me
2-Me
2-CN
2-NO2
3
1
3
No rxn
Decompo.
1h (35)
45
45
1g (75)
1h (55)
9
10
11
12
13
a 2 and 3 were also obtained in 26% and 13% respectively.
b 1c was also obtained in 31%.
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Table 5. Porphyrin Effect on Benzylic CHA
Table 6. Benzylic CHA of Toluenes in Benzene Solvent
120 oC, N2, time
120 oC, PhH, N2, time
Rh(por)Bn
Rh(por)Cl
+
BnH
Rh(ttp)(4-FG-Bn)
+
4-FG-BnH
Rh(ttp)Cl
NaOH (10 equiv)
K2CO3 (10 equiv)
Yieldsa /%
Entry
Por
Time /min
Yields /%
Entry
FG
Time /h
1
2
3
tdbpp
ttp
bocp
120
45
15
89
94
86
1
2
3
4
5
6
7
8
4-OMe
4-tBu
4-Me
H
1.5
2
2
1.5
7
2
1.5
2.5
5
5
4
76
65
68
75
55
68
70
54
64
64
77
71
4-F
4-CN
4-NO2
3,5-Me2
3-Me
2-Me
2-CN
2-NO2
Rh(bocp)Bn. The faster rate for Rh(bocp)Cl might be due
to the faster ligand substitution with NaOH. (See mecha-
nistic studies below.)
9
10
11
12
In Benzene Solvent
The reactions were also successful in benzene solvent
with 10 equivalents of various 4-substituted toluenes used
but with slightly lower efficiency. (Table 6) Longer reac-
tion times of 90 minutes were required and slightly lower
product yields were obtained.
4
a isolated yields.
Table 7. Selected Bond Lengths and Bond Angles of Rh(ttp)Bn
Complexes
X-ray Structures
The collection and processing parameters of single-
crystal data for complexes 1h-k are given in the Supporting
Information (CCDC 923670-923673). The X-ray structure
of 1b and 1d have been reported previously.18 Table 7 lists
selected bond lengths and angles. The bond lengths of
Rh-Ca and the bond angles of Rh-Ca-Cb are similar to the
reported bond lengths of Rh-Ca and bond angles of Rh-
Ca-Cb in Rh(ttp)Bn (2.064 Å and 115.8o)7 and the Rh-
Ca-Cb angles are not affected by the substituents (Table 7).
As a representative, Figure 1 shows the molecular structure
of Rh(ttp)(3,5-Me2-Bn) (1h) (30% thermal ellipsoids).
Mechanistic Studies
Rh-Ca-Cb bond angle
Entry
FG
Rh-Ca length /Å
/deg
1
2
3
4
5
6
4-tBu, 1b
4-F, 1d
3,5-Me2, 1h
3-Me, 1i
2-Me, 1j
2-CN, 1k
2.079(6)
2.072(5)
2.057(4)
2.056(9)
2.066(8)
2.053(6)
116.3(4)
115.8(3)
115.4(3)
116.2(6)
118.1(6)
115.1(4)
the ArCHA reactions. Since these aryl complexes do not
convert into the benzyl complex even at 200 oC, independ-
ent parallel pathways exist for the aryl and benzyl CHA re-
actions. We suggest that Rh(ttp)H and Rh2(ttp)2 are viable
intermediates in the BnCHA as they are known intermedi-
ate in CHA.4,14 Indeed independent experiments of Rh(ttp)H
and Rh2(ttp)2 with toluene, both gave Rh(ttp)Bn in high
yields of 68% and 70%, respectively in 1 h and support
their possible intermediacy (Scheme III).
No Base. In the absence of base, 3- and 4-tolyl
Rh(ttp) complexes, typical of SEAr sustitution products,
formed and this suggests the generation of a cationic
Rh(ttp)+ likely in the form of ion pair as an intermediate for
Scheme III Benzylic CHA with RhII and RhIIIH
Base Enhancement. To gain some insight into the
high yielding base-promoted BnCHA, the reaction of tolu-
ene (10 equiv) with Rh(ttp)Cl in benzene-d6 with 10 equiv
Fig. 1. ORTEP drawing of Rh(ttp)(3,5-Me2-Bn) (1h)
(30% probability displacement ellipsoids).
4
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Benzylic CHA of Toluenes with Rh(por)Cl
Table 8. K2CO3-Promoted Conversion of Rh(ttp)H to Rh2(ttp)2
of K2CO3 in a sealed NMR tube was monitored in the
1
K2CO3
course of 12 h by H NMR spectroscopy (For reaction
2Rh(ttp)H
Rh2(ttp)2
120 oC, C6D6
progess, see Figure S7 and Table S2). Initially, Rh(ttp)Cl
slowly disappeared with the formation of Rh2(ttp)2 and
then Rh(ttp)H which are both slowly converted to Rh(ttp)Bn.
Rh2(ttp)2 and Rh(ttp)H are therefore likely intermediates.15
In fact, Rh2(ttp)2 can exist in small amount with Rh(ttp)H in
benzene or can equilibrate with Rh(ttp)H in benzene under
an atmosphere of H2.14,16 Indeed, Rh(ttp)H at 120 oC after 2
hours gave about 2% of Rh2(ttp)2 (Table 8, entries 1 and 2).
Yield of Yield of
Time /h Rh(ttp)H Rh2(ttp)2
Total
yields /%
Entry
K2CO3
/%
/%
1
2
3
4
---
---
10 equiv
10 equiv
0
2
0
1
100
97
100
81
nil
2
nil
6
100
99
100
87
Scheme IV Benzylic CHA in benzene
Table 9. Reactivity on Benzylic CHA of Rhodium Porphyrin
Complexes
K2CO3 (10 equiv)
Rh(ttp)X
+
Rh(ttp)Bn
BnH
120 oC, 15 min, C6D6
The base-promoted conversion of Rh(ttp)H into
Rh2(ttp)2 was observed as well. K2CO3 in benzene pro-
moted the conversion of Rh(ttp)H into Rh2(ttp)2 in 6% very
[Rh(ttp)X]
/M
[Rh(ttp)Bn] :
[Rh(ttp)X] at 15 min
Entry
X
[PhCH3] /M
1
2
3
Cl
H
Rh(ttp)
0.01
0.01
0.005
0.1
0.1
0.1
0.18
0.12
2.10
o
slowly at 120 C after 1 hour (Table 8, entries 3 and 4).
Therefore, Rh(ttp)H undergoes slow conversion into and
likely in equilibration with Rh2(ttp)2 under both thermal
and basic reaction conditions as the hydrogenation of
Rh2(ttp)2 into Rh(ttp)H is known.17 We do not understand
the detailed mechanism of this base-promoted dehydro-
genation of Rh(ttp)H at this stage and will be a subject of
further study.
of toluene with Rh(ttp)Cl were measured by competition
experiments with an equimolar mixture of solvent toluene
and toluene-d8. At 120 oC, without any base, (kH/kD)obs were
measured to be 6.6 for ArCHA (indistinguishable between
para and meta) and 4.1 for BnCHA. The isotope ratios were
calculated from the integration of the benzylic and aryl pro-
tons. With K2CO3 added, (kH/kD)obs was found to be 4.0. No
benzyl exchange occurred under the same basic conditions
in one hour, as Rh(ttp)Bn did not react with toluene-d8 to
give any Rh(ttp)Bn-d7. These values suggested that the
CHA steps were involved in or prior to the rate-determin-
ing step in the reactions. Furthermore, when NaOH was
added, (kH/kD)obs was found to be 4.3. Both the (kH/kD)obs
values in the K2CO3 and NaOH experiments were similar.
Therefore, the nature of a base has no significant effect on
the nature of transition state in the BnCHA steps.
Since independent reactions of Rh(ttp)H and Rh2(ttp)2
with toluene with K2CO3 added gave Rh(ttp)Bn in high
yields of 68% and 70%, respectively in 1 h (Scheme III).
Both Rh2(ttp)2 and Rh(ttp)H are the viable intermediates.
As Rh(ttp)H and Rh2(ttp)2 are shown to equilibrate (Table
8), we have to examine whether only one or both activate(s)
the C-H bond by their relative reactivity.
The relative reactivities of Rh2(ttp)2, Rh(ttp)H and
Rh(ttp)Cl in BnCHA in the presence of K2CO3 (10 equiv)
were measured by the amount of Rh(ttp)Bn formed in the
first 15 minutes of the reaction (Table 9). The relative reac-
tivities are about: 12 (Rh2(ttp)2) : 1 (Rh(ttp)H) : 1 (Rh(ttp)Cl).
Rh2(ttp)2 is the most reactive species (Table 9). As the reac-
tivity difference is not very large, we still could not con-
clude that both are direct intermediates. We turned our fo-
cus to the magnitude of kinetic isotope effect to probe the
nature of the transition states in the reactions with Rh(ttp)Cl,
Rh(ttp)H and Rh2(ttp)2.
ArCHA
With the help of the KIE and the formation of both
Rh(ttp)Ar (Ar = 3- and 4-tolyl), we reason that the ArCHA
operates by an SEAr mechanism (Scheme V). It is possible
that initially Rh(ttp)Cl ionizes into a Rh(ttp)+ which is then
coordinated by the p-orbitals of toluene. Subsequently, the
ArCHA occurs with a rate-limiting aromatic C-H cleavage
step. The BnCHA, however, goes through different mecha-
Isotope Effect
The observed isotope effects (kH/kD)obs for the BnCHA
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Article
Choi et al.
Table 10. Temperature Dependent Kinetic Isotope Effect of
K2CO3-promoted BnCHA
Aromatic and Benzylic CHA of Toluene
with Rh(ttp)Cl
Scheme V
K2CO3 (10 equiv)
1 h, temp, N2,
Rh(ttp)X
+
C6H5CH3 / C6D5CD3
1:1
Rh(ttp)Bn / Rh(ttp)Bn-d7
Total yields
a
Entry Rh(ttp)X
Temp /oC
(kH/kD)obs
/%
1
2
3
4
5
6
7
8
Rh(ttp)Cl
Rh(ttp)Cl
Rh(ttp)Cl
Rh(ttp)Cl
Rh2(ttp)2
Rh2(ttp)2
Rh(ttp)H
Rh(ttp)H
120
150
180
200
120
200
120
200
4.0 0.1b
4.5 0.1
4.8 0.1
5.4 0.1
6.7 0.2c
5.8 0.1
4.1 0.1
5.3 0.1
91%
88%
88%
85%
74%
68%
71%
68%
nisms either via coordination of the benzylic C-H to
Rh(ttp)+ followed by subsequent Cl- deprotonation to yield
Rh(ttp)Bn via an ionic pathway as we previously pro-
posed.18 Alternatively, some extent of ligand substitution
with water to yield Rh(ttp)OH can happen to yield Rh2(ttp)2
and Rh(ttp)H. (See discussion below.)
a Determined by 1H NMR. b 4.0 from mass spectrometry.
c 6.7 from mass spectrometry.
Temperature Effect on KIE
We focused our effort on the nature of the transition
states of K2CO3-promoted BnCHA as the reactions are
much more selective and broader in scope. The values of
BnCHA with toluene to give Rh(ttp)Bn and Rh(ttp)H. Both
RhII (ttp)2 and Rh(ttp)H now exist in solution.Rh(ttp)H can
2
undergo thermal or base-promoted dehydrogenation to
yield some RhII (ttp)2. The concentration of RhII (ttp)2 de-
0
temperature dependent KIE from 120 to 200 C obtained
2
2
from the BnCHA of toluene with Rh(ttp)Cl, Rh2(ttp)2, and
Rh(ttp)H in the presence of K2CO3 (10 equiv) are very re-
vealing (Table 10). For Rh(ttp)Cl and Rh(ttp)H (Table 10,
entries 1-4 and 7-8), the KIEs unusually increased with
temperature and is significant with a fairly large change in
magnitude. For Rh2(ttp)2, the opposite trend and a large dif-
ference were also observed. Both a change of mechanism
or a change of major reaction pathway for parallel reactions
for three rhodium porphyrin complexes can account the
trends. We argue for the latter proposal since it is more con-
sistent with the equilibrating mixture of Rh(ttp)H and
Rh2(ttp)2 as possible intermediates.
pends on temperature and base used. A stronger base may
competitive depronate the weakly acidic Rh(ttp)H to form
Rh(ttp)- which precipitates in solution and undergoes ther-
mal decomposition. We rationalize that two parallel
BnCHA reactions19 with Rh2(ttp)2 and Rh(ttp)H exist and
can account the increasing KIEs with temperature. The
KIE value of 6.7 for Rh2(ttp)2 at 120 oC (Table 10, entry 5)
supports the bimetalloradical activation with RhII(ttp) hav-
ing a linear transition state (TS) in the cleavage of the
benzylic C-H bond (Scheme V, Figure 2a). Such bimetal-
loradical activation mechanism of toluene by rhodium(II)
porphyrin has been well-established by Wayland and co-
Proposed Mechanism
o
workers to have a KIE value of 6.5 at 80 C.17 The lower
Based on the above findings and our latest under-
standings of rhodium porphyrin chemistries, Scheme VI il-
lustrates the reaction pathways that is different from our
previous one.18 Initially, Rh(ttp)Cl undergoes a ligand sub-
stitution with KOH or K2CO3 to give Rh(ttp)CO3K (or
Rh(ttp)OK after decarboxylation or Rh(ttp)OH after pro-
tonation of Rh(ttp)OK with residual water in solvent or re-
agent), which is then reduced to yield the metal-metal
bonded dimer of RhII2 (ttp)2 as we have reported earlier.
RhII2 (ttp)2 having a fairly weak Rh-Rh bond of about 16
kcal/mol, can dissociate into the RhII(ttp) monomer as a
metalloradical in solution.
KIE value of 5.6 at 200 oC is attributed to the Arrhenius be-
havior with a smaller energy level difference of ground and
transition states at a higher temperature (Table 10, entry
6).20
RhIII(por)H Sigma Bond Metathesis. For the
BnCHAwith Rh(ttp)H at 120oC, the observed KIE value of
4.1 (Table 3, entry 7), is consistent with a bent TS20 associ-
ated with a sigma bond metathesis process (Scheme VI,
Figure 2b) since the proposed TS of the reaction of
Rh(ttp)Me with toluene to give methane and Rh(ttp)Bn is
elucidated to be a bent one based on the observed KIE of
2.7 at 150 oC. The slightly higher KIE at 120 oC can be ac-
counted by the parallel metalloradical pathway as a small
RhII(por) Bimetalloradical Pathway. RhII (ttp)2 or
2
more correctly RhII(ttp) then undergoes a bimetalloradical
6
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Benzylic CHA of Toluenes with Rh(por)Cl
Table 11. Competition Experiments of Electronic Effect on
BnCHA
Scheme VI Parallel Base-Promoted BnCHA of Tolu-
ene
120 oC, PhH, N2, 1h
Rh(ttp)Cl
+
4-FG-BnH / BnH
1: 1
Rh(ttp)(4-FG-Bn) / Rh(ttp)Bn
K2CO3 (10 equiv)
a
Entry
p-FG
sp
log k(HFG/HH)
1
2
3
4
5
6
OMe
tBu
F
CHO
CN
NO2
-0.27
-0.15
1.5
0.47
0.71
0.81
0.60
-0.55
0.39
0.66
0.81
0.87
a sp: para-substituent constant.
amount of RhII2(ttp)2 is present. At 200 C with K2CO3
o
equiv of K2CO3 at 120 °C for 1 h. Figure 3 shows that a
nonlinear free energy relationship in the Hammett plot us-
ing the substituent constant sp.21 As the para substituent be-
came more electron donating, the rate decreased (NO2 to
CN, CHO, F and tBu). The more electron-rich substituent
(OMe), however, yielded a higher rate resulting in a rate in-
version point. We interpret that the BnCHA reaction does
not operate in a single step that depends on the substituent
electronic effect. Rather, both Rh(ttp)H and Rh2(ttp)2 exert
different electronic influence on the parallel activation re-
actions.
added, a much higher KIE of 5.3 was measured (Table 3,
entry 8) and can be reasoned with a larger contribution of
parallel bimetalloradical CHA with a higher concentration
of Rh2(ttp)2 .
Hammett Studies
In order to gain some mechanistic understandings of
the toluene electronic effect of CHA, the Hammett plot was
constructed from a series of competition experiments using
an equimolar mixture of 4-substituted (FG) toluene and to-
luene in reacting with Rh(ttp)Cl and K2CO3 (10 equiv) at
120 °C in 1 h in benzene (Table 11). The ratios were kinetic
ones, as no Rh(ttp)(4-F-Bn) 1d was formed when Rh(ttp)Bn
1 was reacted with 4-fluorotoluene in benzene with 10
CONCLUSIONS
In summary, nucleophilic base such as K2CO3 was
found to enhance the BnCHAof toluenes both in rate, func-
tional comaptiblity and yield. The enhancements are due to
the more facile ligand substituion of Rh(ttp)Cl with hy-
droxide to yield Rh(ttp)OH and then RhII(ttp). RhII(ttp) ac-
tivate the benzylic C-H bonds of toluenes in a bimetal-
loradical mechanism to give Rh(ttp)Bns and Rh(ttp)H.
Rh(ttp)H can also undergo a slower sigma bond metathesis
type BnCHA. The thermal and/or base-promoted dehydro-
Fig. 2. Transition State Structures for Benzylic CHA.
genation of Rh(ttp)H back to a small amount of RhII (ttp)2
2
can rationalize the equilibrating mixture of RhII and RhIIIH
and the temperature dependent KIEs with the unusual in-
creasing KIEs with temperature for RhIIIH.
EXPERIMENTAL
Unless otherwise noted, all reagents were purchased from
commercial suppliers and directly used without further purifica-
tion. Hexane was distilled from anhydrous calcium chloride. Ben-
zene and toluene were distilled from sodium. Thin layer chroma-
tography was performed on pre-coated silica gel 60 F254 plates.
Fig. 3. Hammett plot of BnCHA of Toluenes with
Rh(ttp)Cl.
J. Chin. Chem. Soc. 2013, 60, 000-000
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7

Article
Choi et al.
Silica gel (Merck, 70-230 mesh) were used for column chroma-
tography.
Anal Calcd. for C55H43N4Rh: C, 76.56; H, 5.02; N, 6.49. Found C,
76.09; H, 5.06; N, 6.45.
1H NMR and 13C NMR spectra were recorded on a Bruker
DPX-300 at 300 MHz and 75 MHz respectively. Chemical Shifts
were referenced with the residual solvent protons in C6D6 (d =
7.15 ppm), CDCl3 (d = 7.26 ppm) or tetramethylsilane (d = 0.00
ppm) in 1H NMR spectra and CDCl3 (d = 77.16 ppm) in 13C NMR
spectra as the internal standards. Chemical shifts (d) were re-
ported as part per million (ppm) in (d) scale downfield from TMS.
Coupling constants (J) were reported in Hertz (Hz). High resolu-
tion mass spectra (HRMS) were recorded on a ThermoFinnigan
MAT 95 XL mass spectrometer. Fast atom bombardment spectra
were performed with 3-nitrobenzyl alcohol (NBA) as the matrix.
All samples for combustion analyses were recrystallized from
CH2Cl2/MeOH and vacuum dried at room temperature for at least
2 days before submission.
Synthsis of (5,10,15,20-tetratolylporphyrinato)(3-tol-
yl)rhodium(III), [Rh(ttp)(3-tolyl)] (3). Rh(ttp)Cl (20.0 mg,
0.025 mmol) was mixed with (3-tolylmagnesium bromide (0.25
mmol) in THF (1.5 mL) at 120 oC under N2 for 30 min with the re-
action tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(3-tolyl) (3) (14.0 mg,
0.016 mmol, 65%) as a red solid. Rf = 0.55 (hexane/CH2Cl2 =
1:1). 1H NMR (CDCl3, 300 MHz) d 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) d 20.36, 21.88, 121.60, 123.19, 123.55, 125.93, 127.75,
129.77, 131.92, 132.98, 134.12, 134.51, 137.58, 139.51, 143.41.
HRMS (FABMS): Calcd for (C55H43N4Rh)+: m/z 862.2537.
Found: m/z 862.2508.
The synthesis of Rh(ttp)Cl, Rh(ttp)H and Rh2(ttp)2 follows
a literature method.22,23
Reaction of Rh(ttp)Cl with Toluene. Rh(ttp)Cl (30.0 mg,
0.037 mmol) and toluene (1.5 mL) were degassed in a Telfon-
stoppered tube for three freeze-thaw-pump cycles and heated at
120 oC under N2 for 3 d with the reaction tube covered by alumi-
num foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1). Three
CHA products 1, 2 and 3 with the same Rf = 0.55 (hexane/CH2Cl2
= 1:1) were collected in one portion (24.9 mg) and the ratio was
General Procedure for the Reactions of Rh(ttp)Cl
with Toluene and Various Ligands/Bases
Addition of 1 equiv of PPh3. Rh(ttp)Cl (30.0 mg, 0.037
mmol), PPh3 (9.7 mg, 0.037 mmol) and toluene (1.5 mL) were de-
o
gassed for three freeze-thaw-pump cycles and heated at 120 C
under N2 for 3 d with the reaction tube covered by aluminum foil.
No CHA product was observed.
Addition of 30 equiv of Pyridine. Rh(ttp)Cl (30.0 mg,
0.037 mmol), pyridine (90 mL, 88.2 mg, 1.12 mmol) and toluene
(1.5 mL) were degassed for three freeze-thaw-pump cycles and
heated at 120 oC under N2 for 3 d with the reaction tube covered
by aluminum foil. No CHA product was observed.
1
determined by H NMR analysis from the integration of the
benzylic and aromatic protons as Rh(ttp)Bn (1)13 (26%), Rh(ttp)
(4-tolyl) (2) (26%), and Rh(ttp)(3-tolyl) (3) (13%). The com-
plexes 2 and 3 were further synthesized independently.24
Synthesis of (5,10,15,20-tetratolylporphyrinato)(4-tol-
yl)rhodium(III), [Rh(ttp)(4-tolyl)] (2). Rh(ttp)Cl (20.0 mg,
0.025 mmol) was mixed with (4-tolylmagnesium bromide (0.25
mmol) in THF (1.5 mL) at 120 oC under N2 for 30 min with the re-
action tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-tolyl) (2) (20.0 mg,
0.023 mmol, 93%) as a red solid. Rf = 0.55 (hexane/CH2Cl2 =
1:1). 1H NMR (CDCl3, 300 MHz) d 0.17 (d, 2 H, J = 6.9 Hz), 1.08
(s, 3 H), 2.69 (s, 12 H), 4.61 (d, 2 H, J = 8.4 Hz), 7.52 (t, 8 H, J =
6.0 Hz), 8.01 (d, 4 H, J = 8.7 Hz), 8.05 (d, 4H, J = 8.6 Hz), 8.75 (s,
8 H). 13C NMR (CDCl3, 75 MHz) d 19.15, 21.68, 120.79 (d, 1JRh-C
= 37.6 Hz), 122.98, 125.06, 127.13, 127.54, 128.36, 129.52,
131.75, 133.94, 134.30, 137.38, 139.27, 143.20. HRMS (FABMS):
Calcd. for (C55H43N4Rh)+: m/z 862.2537. Found: m/z 862.2578.
Addition of 30 equiv of 2,6-Di-tert-butylpyridine.
Rh(ttp)Cl (30.0 mg, 0.037 mmol), 2,6-di-tert-butylpyridine (251
mL, 214.3 mg, 1.12 mmol) and toluene (1.5 mL) were degassed
for three freeze-thaw-pump cycles and heated at 120 oC under N2
for 3 d with the reaction tube covered by aluminum foil. The sol-
vent was then removed in vacuum and the red crude mixture was
isolated by column chromatography on silica gel eluting with a
solvent mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)Bn (1)
(14.8 mg, 0.017 mmol, 46%) and Rh(ttp)(4-tolyl) (2) (5.8 mg,
0.0067 mmol, 18%).
Addition of 10 equiv of NaOH. Rh(ttp)Cl (30.0 mg, 0.037
mmol) and 10 equiv of NaOH (14.9 mg, 0.37 mmol) and toluene
(1.5 mL) were degassed for three freeze-thaw-pump cycles and
heated at 120 oC under N2 for 45 min with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
8
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Benzylic CHA of Toluenes with Rh(por)Cl
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)Bn (1) (25.3 mg, 0.035 mmol, 79%).
Addition of 10 equiv of KOH. Rh(ttp)Cl (30.0 mg, 0.037
mmol), 10 equiv of KOH (20.9 mg, 0.37 mmol) and toluene (1.5
mL) were degassed for three freeze-thaw-pump cycles and heated
at 120 oC under N2 for 1 h with the reaction tube covered by alu-
minum foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
Rh(ttp)Bn (1) (30.1 mg, 0.035 mmol, 94%).
num foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
Rh(ttp)Bn (1) (30.1 mg, 0.035 mmol, 77%).
Addition of 10 equiv of NaOAc. Rh(ttp)Cl (20.0 mg,
0.025 mmol), NaOAc (20 mg, 0.25 mmol) and toluene (1.5 mL)
were degassed for three freeze-thaw-pump cycles and heated at
120 oC under N2 for 1 h with the reaction tube covered by alumi-
num foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
Rh(ttp)Bn (1) (18.0 mg, 0.021 mmol, 84%).
Addition of 10 equiv of K3PO4. Rh(ttp)Cl (30.0 mg, 0.037
mmol) and 10 equiv of K3PO4 (85.6 mg, 0.37 mmol) and toluene
(1.5 mL) were degassed for three freeze-thaw-pump cycles and
heated at 120 oC under N2 for 1 h with the reaction tube covered
by aluminum foil. The solvent was then removed in vacuum and
the red crude mixture was isolated by column chromatography on
silica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1)
to give Rh(ttp)Bn (1) (24.7 mg, 0.029 mmol, 77%).
Addition of 10 equiv of KOAc. Rh(ttp)Cl (20.0 mg, 0.025
mmol), KOAc (25 mg, 0.25 mmol) and toluene (1.5 mL) were de-
o
gassed for three freeze-thaw-pump cycles and heated at 120 C
under N2 for 45 min with the reaction tube covered by aluminum
foil. The solvent was then removed in vacuum and the red crude
mixture was isolated by column chromatography on silica gel
eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
Rh(ttp)Bn (1) (18.0 mg, 0.021 mmol, 84%).
Addition of 10 equiv of (CH3)3CCOO-Na+. Rh(ttp)Cl
(20.0 mg, 0.025 mmol), (CH3)3CCOO-Na+ (31 mg, 0.25 mmol)
and toluene (1.5 mL) were degassed for three freeze-thaw-pump
Addition of 10 equiv of Na2CO3. Rh(ttp)Cl (20.0 mg,
0.025 mmol) and 10 equiv of Na2CO3 (26.5 mg, 0.25 mmol) and
toluene (1.5 mL) were degassed for three freeze-thaw-pump cy-
o
cles and heated at 120 C under N2 for 10 h with the reaction
tube covered by aluminum foil. The solvent was then removed in
vacuum and the red crude mixture was isolated by column chro-
matography on silica gel eluting with a solvent mixture of hex-
ane: CH2Cl2 (1:1) to give Rh(ttp)Bn (1) (17.0 mg, 0.020 mmol,
79%).
o
cycles and heated at 120 C under N2 for 1 h with the reaction
tube covered by aluminum foil. The solvent was then removed in
vacuum and the red crude mixture was isolated by column chro-
matography on silica gel eluting with a solvent mixture of hex-
ane: CH2Cl2 (1:1) to give Rh(ttp)Bn (1) (16.0 mg, 0.019 mmol,
74%).
Addition of 10 equiv of K2CO3. Rh(ttp)Cl (30.0 mg, 0.037
mmol), 10 equiv of K2CO3 (51.1 mg, 0.37 mmol) and toluene (1.5
mL) were degassed for three freeze-thaw-pump cycles and heated
at 120 oC under N2 for 30 min with the reaction tube covered by
aluminum foil. The solvent was then removed in vacuum and the
red crude mixture was isolated by column chromatography on sil-
ica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to
give Rh(ttp)Bn (1) (30.2 mg, 0.035 mmol, 94%).
Addition of 10 equiv of NaHSO4. Rh(ttp)Cl (20.0 mg,
0.025 mmol), NaHSO4 (30 mg, 0.25 mmol) and toluene (1.5 mL)
were degassed for three freeze-thaw-pump cycles and heated at
120 oC under N2 for 8 h with the reaction tube covered by alumi-
num foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
the mixture of Rh(ttp)(4-tolyl) (2) and Rh(ttp)(3-tolyl) (3) (9.0
mg, 0.010 mmol, 42%).
Addition of 10 equiv of NaOPh. Rh(ttp)Cl (20.0 mg,
0.025 mmol), 10 equiv of NaOPh (29 mg, 0.25 mmol) and toluene
(1.5 mL) were degassed for three freeze-thaw-pump cycles and
heated at 120 oC under N2 for 1 h with the reaction tube covered
by aluminum foil. The solvent was then removed in vacuum and
the red crude mixture was isolated by column chromatography on
silica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1)
to give Rh(ttp)Bn (1) (20.0 mg, 0.023 mmol, 93%).
Addition of 10 equiv of K2CO3 in Benzene as Solvent.
Rh(ttp)Cl (30.0 mg, 0.037 mmol), 10 equiv of K2CO3 (51.1 mg,
0.37 mmol), toluene (40 mL, 3.4 mg, 0.37 mmol) and benzene (1.5
mL) were degassed for three freeze-thaw-pump cycles and heated
at 120 oC under N2 for 1.5 h with the reaction tube covered by alu-
minum foil. The solvent was then removed in vacuum and the red
crude mixture was isolated by column chromatography on silica
gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1) to give
Rh(ttp)Bn (1) (24.0 mg, 0.028 mmol, 75%).
Addition of 10 equiv of KHCO3. Rh(ttp)Cl (30.0 mg,
0.037 mmol), KHCO3 (37.2 mg, 0.37 mmol) and toluene (1.5 mL)
were degassed for three freeze-thaw-pump cycles and heated at
120 oC under N2 for 1 h with the reaction tube covered by alumi-
J. Chin. Chem. Soc. 2013, 60, 000-000
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9

Article
Choi et al.
General Procedure for the Reactions of Rh(ttp)Cl
with Various Substituted Toluenes
the reaction tube covered by aluminum foil. The solvent was then
removed in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-tBu-Bn) (1b) (15.0 mg,
0.016 mmol, 74%).
Reactions of Rh(ttp)Cl with 4-Methylanisole. Rh(ttp)Cl
(30.0 mg, 0.037 mmol), 10 equiv of K2CO3 (51.1 mg, 0.37 mmol)
were mixed with 4-methylanisole (1.5 mL) at 120 oC under N2 for
30 min with the reaction tube covered by aluminum foil. The sol-
vent was then removed in vacuum and the red crude mixture was
isolated by column chromatography on silica gel eluting with a
solvent mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-OMe-
Bn) (1a) (30.5 mg, 0.034 mmol, 92%) as a red solid. Rf = 0.35
(hexane/CH2Cl2 = 1:1). 1H NMR (CDCl3, 300 MHz) d -3.77 (d, 2
H, J = 3.6 Hz), 2.70 (s, 12 H), 2.92 (d, 2 H, J = 8.4 Hz), 3.43 (s, 3
H), 5.42 (d, 2 H, J = 8.4 Hz), 7.54 (d, 8 H, J = 7.8 Hz), 7.98 (dd, 4
H, J = 2.1, 7.4 Hz), 8.07 (dd, 4 H, J = 2.4, 7.2 Hz), 8.67 (s, 8 H).
HRMS (FABMS): Calcd for (C56H45N4ORh)+: m/z 892.2643.
Found: m/z 892.2589. Anal Calcd. for C56H45N4ORh: C, 75.33; H,
5.10; N, 6.27. Found C, 74.87; H, 5.27; N, 5.99.
Reaction of Rh(ttp)Cl with p-Xylene. Rh(ttp)Cl (30.0 mg,
0.037 mmol), K2CO3 (51.1 mg, 0.37 mmol) and p-xylene (1.5
mL) were heated at 120 oC for 45 min with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)(4-Me-Bn) (1c) (29.3 mg, 0.033 mmol, 90%)
as a red solid. Rf = 0.65 (hexane:CH2Cl2 = 1:1). 1H NMR (CDCl3,
300 MHz) d -3.77 (d, 2H, J = 3.6 Hz), 1.68 (s, 3 H), 2.70 (s, 12 H),
2.87 (d, 2 H, J = 7.8 Hz), 5.66 (d, 2 H, J = 7.8 Hz), 7.54 (dd, 8 H, J
= 2.1, 6.8 Hz), 7.96 (dd, 4 H, J = 2.1, 7.1 Hz), 8.07 (dd, 4 H, J =
2.1, 7.7 Hz), 8.67 (s, 8 H). HRMS (FABMS): Calcd for
(C56H45N4Rh)+: m/z 876.2694. Found: m/z 876.2667. Anal Calcd.
for C56H45N4Rh: C, 76.70; H, 5.17; N, 6.39. Found C, 76.64; H,
5.28; N, 6.06.
Addition of 10 equiv of 4-Methylanisole in Benzene as
Solvent. Rh(ttp)Cl (30.0 mg, 0.037 mmol), K2CO3 (51.1 mg, 0.37
mmol) and 4-methylanisole (47 mL, 45.4 mg, 0.37mmol) and ben-
zene (1.5 mL) were heated at 120 oC with for 1.5 h with the reac-
tion tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-OMe-Bn) (1a) (25.2
mg, 0.028 mmol, 76%).
Addition of 10 equiv of p-Xylene in Benzene as Solvent.
Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol)
and p-xylene (31 mL, 26.5 mg, 0.25 mmol) and benzene (1.5 mL)
were heated at 120 oC with for 1.5 h with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)(4-Me-Bn) (1c) (15.0 mg, 0.017 mmol, 68%).
Reactions of Rh(ttp)Cl with 4-Fluorotoluene. Rh(ttp)Cl
(30.0 mg, 0.037 mmol), K2CO3 (51.1 mg, 0.37 mmol) and 4-fluo-
rotoluene (1.5 mL) were heated at 120 oC under N2 for 4 h with the
reaction tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-F-Bn) (1d) (20.9 mg,
0.024 mmol, 64%) as a red solid. Rf = 0.60 (hexane/ CH2Cl2 =
1:1). 1H NMR (CDCl3, 300 MHz) d -3.83 (d, 2 H, J = 3.9 Hz), 2.70
(s, 12 H), 2.89 (dd, 2 H, J = 2.7, 5.7 Hz,), 5.55 (t, 2 H, J = 8.7 Hz),
7.55 (t, 8 H, J = 6.6 Hz), 7.98 (dd, 4 H, J = 2.1, 8.0 Hz), 8.06 (d, 4
H, J = 1.2, 8.0 Hz), 8.68 (s, 8 H). 13C NMR (CDCl3, 75 MHz) d
Reactions of Rh(ttp)Cl with 4-tert-Butyltoluene. Rh(ttp)Cl
(30.0 mg, 0.037 mmol), 10 equiv of K2CO3 (51.1 mg, 0.37 mmol)
was mixed with 4-tert-butyltoluene (1.5 mL) at 120 oC under N2
for 45 min with the reaction tube covered by aluminum foil. The
solvent was then removed in vacuum and the red crude mixture
was isolated by column chromatography on silica gel eluting with
a solvent mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-tBu-
Bn) (1b) (33.4 mg, 0.036 mmol, 98%) as a red solid. Rf = 0.75
(hexane/CH2Cl2 = 1:1). 1H NMR (CDCl3, 300 MHz) d -3.79 (d, 2
H, J = 3.6 Hz), 0.96 (s, 9 H), 2.70 (s, 12 H), 2.93 (d, 2 H, J = 8.1
Hz), 5.89 (d, 2 H, J = 8.4 Hz), 7.54 (t, 8 H, J = 6.0 Hz), 8.04 (t, 8 H,
J = 7.9 Hz), 8.65 (s, 8 H). 13C NMR (CDCl3, 75 MHz) d 13.00 (d,
1JRh-C = 26.6 Hz), 21.91, 31.01, 34.48, 122.75, 113.30, 124.47,
127.60, 131.68, 134.13, 134.23, 137.41, 139.76, 143.49, 146.20.
HRMS (FABMS): Calcd for (C59H51N4Rh)+: m/z 918.3163.
Found: m/z 918.3139. Anal Calcd. for C59H51N4Rh: C, 77.11; H,
5.59; N, 6.09. Found C, 76.66; H, 5.65; N, 5.91.
1
1
11.43 (d, JRh-C = 27.3 Hz), 21.89, 112.96 (d, JC-F = 20.9 Hz),
122.83, 126.08, 126.18, 127.78, 131.83, 134.16, 134.21, 137.52,
139.61, 143.45. HRMS (FABMS): Calcd for (C55H42FN4Rh)+: m/z
880.2443. Found: m/z 880.2426. Anal Calcd. for C55H42FN4Rh: C,
74.61; H, 5.07; N, 6.39. Found C, 74.99; H, 4.81; N, 6.36.
Addition of 10 equiv of 4-Fluorotoluene in Benzene as
Solvent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25
Addition of 10 equiv of 4-tert-Butyltoluene in Benzene
as Solvent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg,
0.25 mmol) and 4-tert-butyltoluene (43 mL, 37 mg, 0.25 mmol)
and benzene (1.5 mL) were heated at 120 oC with for 1.5 h with
10
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Benzylic CHA of Toluenes with Rh(por)Cl
mmol) and 4-fluorotoluene (28 mL, 28 mg, 0.25 mmol) and ben-
zene (1.5 mL) were heated at 120 oC with for 1.5 h with the reac-
tion tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-F-Bn) (1d) (12.0 mg,
0.014 mmol, 55%).
as Solvent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg,
0.25 mmol) and 4-methylbenzonitrile (30 mL, 28 mg, 0.25 mmol)
and benzene (1.5 mL) were heated at 120 oC with for 1.5 h with
the reaction tube covered by aluminum foil. The solvent was then
removed in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-CN-Bn) (1f) (15.0 mg,
0.017 mmol, 68%).
Reactions of Rh(ttp)Cl with p-Tolualdehyde. Rh(ttp)Cl
(30.0 mg, 0.037 mmol), 10 equiv of K2CO3 (51.1 mg, 0.37 mmol)
were mixed with p-tolualdehyde (1.5 mL) at 120 oC under N2 for
15 min with the reaction tube covered by aluminum foil. The sol-
vent was then removed in vacuum and the red crude mixture was
isolated by column chromatography on silica gel eluting with a
solvent mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-CHO-
Bn) (1e)7 (12.9 mg, 0.014 mmol, 39%) as a red solid. Rf = 0.30
(hexane/CH2Cl2 = 1:1). 1H NMR (CDCl3, 300 MHz) d -3.81 (d, 2
H, J = 3.9 Hz), 2.70 (s, 12 H), 2.97 (d, 2 H, J = 7.5 Hz), 6.35 (d, 2
H, J = 7.2 Hz), 7.55 (d, 8 H, J = 6.3 Hz), 7.95 (d, 4 H, J = 7.8 Hz),
8.05 (d, 4 H, J = 7.2 Hz), 8.70 (s, 8 H), 9.43 (s, 1 H). Rh(ttp)(4-
Me-Bn) (1c) (10.1 mg, 0.012 mmol, 31%) was also obtained.
Addition of 10 equiv of p-Tolualdehyde in Benzene as
Solvent. Rh(ttp)Cl (30.0 mg, 0.037 mmol), K2CO3 (51.1 mg, 0.37
mmol) and p-tolualdehyde (43 mL, 44.7 mg, 0.37mmol) and ben-
zene (1.5 mL) were heated at 120 oC with for 1.5 h with the reac-
tion tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-CHO-Bn) (1e) (27.0
mg, 0.028 mmol, 75%) and Rh(ttp)(4-Me-Bn) (1c) (only ob-
served in NMR of the crude reaction mixture).
Reactions of Rh(ttp)Cl with 4-Nitrotoluene. Rh(ttp)Cl
(30.0 mg, 0.037 mmol), K2CO3 (51.1 mg, 0.37 mmol) and 4-nitro-
toluene (1.5 mL) were heated at 120 oC for 30 min with the reac-
tion tube covered by aluminum foil. The solvent was then re-
moved in vacuum and the red crude mixture was isolated by col-
umn chromatography on silica gel eluting with a solvent mixture
of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-NO2-Bn) (1g) (33.0
mg, 0.036 mmol, 98%) as a red solid. Rf = 0.40 (hexane/ CH2Cl2 =
1:1). 1H NMR (CDCl3, 300 MHz) d -3.84 (d, 2 H, J = 3.9 Hz), 2.71
(s, 12 H), 2.90 (d, 2 H, J = 8.7 Hz), 6.69 (d, 2 H, J = 8.7 Hz), 7.56
(t, 8 H, J = 7.5 Hz), 7.95 (d, 4 H, J = 7.1 Hz), 8.05 (d, 4 H, J = 7.5
Hz), 8.71 (s, 8 H). 13C NMR (CDCl3, 75 MHz) d 8.50 (d, 1JRh-C
=
28.4 Hz), 21.88, 31.28, 121.32, 123.09, 124.79, 127.91, 132.11,
134.11, 134.21, 137.76, 139.27, 143.42, 150.74. HRMS (FABMS):
Calcd for (C55H42N5O2Rh)+: m/z 907.2388. Found: m/z 907.2430.
Addition of 10 equiv of 4-Nitrotoluene in Benzene as
Solvent. Rh(ttp)Cl (30.0 mg, 0.037 mmol), K2CO3 (51.5 mg, 0.37
mmol) and 4-nitrotoluene (51.1 mg, 0.37 mmol) and benzene (1.5
mL) were heated at 120 oC with for 1.5 h with the reaction tube
covered by aluminum foil. The solvent was then removed in vac-
uum and the red crude mixture was isolated by column chroma-
tography on silica gel eluting with a solvent mixture of hexane:
CH2Cl2 (1:1) to give Rh(ttp)(4-NO2-Bn) (1g) (23.6 mg, 0.026
mmol, 70%).
Reactions of Rh(ttp)Cl with 4-Methylbenzonitrile.
Rh(ttp)Cl (30.0 mg, 0.037 mmol), K2CO3 (51.1 mg, 0.37 mmol)
and 4-methylbenzonitrile (1.5 mL) were heated at 120 oC for 1 h.
with the reaction tube covered by aluminum foil. The solvent was
then removed in vacuum and the red crude mixture was isolated
by column chromatography on silica gel eluting with a solvent
mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(4-CN-Bn) (1f)
(27.4 mg, 0.031 mmol, 83%) as a red solid. Rf = 0.30 (hexane/
CH2Cl2 = 1:1).1H NMR (CDCl3, 300 MHz) d -3.87 (d, 2 H, J = 3.9
Hz), 2.71 (s, 12 H), 2.90 (d, 2 H, J = 8.4 Hz), 6.11 (d, 2 H, J = 8.1
Hz), 7.57 (t, 8 H, J = 8.4 Hz), 7.93 (dd, 4 H, J = 1.5, 8.3 Hz), 8.03
(dd, 4 H, J = 1.2, 7.7 Hz), 8.90 (s, 8 H). 13C NMR (CDCl3, 75
MHz) d 9.27 (d, 1JRh-C = 28.0 Hz), 21.89, 106.25, 120.01, 122.98,
124.92, 127.89, 129.69, 132.04, 134.12, 134.29, 137.32, 139.32,
143.39. HRMS (FABMS): Calcd for (C56H42N5Rh)+: m/z 887.2490.
Found: m/z 887.2487.
Reactions of Rh(ttp)Cl with Mesitylene. Rh(ttp)Cl (20.0
mg, 0.025 mmol), K2CO3 (51.1 mg, 0.37 mmol) and mesitylene
(1.5 mL) were heated at 120 oC for 1 h with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)(3,5-Me2-Bn) (1h) (15.0 mg, 0.017 mmol,
67%) as a red solid. Rf = 0.55 (hexane/ CH2Cl2 = 1:1). 1H NMR
(CDCl3, 300 MHz) d -3.81 (d, 2 H, J = 3.9 Hz), 1.56 (s, 6 H), 2.56
(s, 2 H), 2.70 (s, 12 H), 6.08 (s, 1 H), 7.54 (t, 8 H, J = 6.6 Hz), 8.00
(dd, 4 H, J = 1.8, 7.5 Hz), 8.05 (dd, 4 H, J = 2.1, 8.6 Hz), 8.68 (s, 8
H). HRMS (FABMS): Calcd for (C57H47N4Rh)+: m/z 890.2850.
Found: m/z 890.2824. Anal Calcd. for C57H47N4Rh: C, 76.84; H,
5.32; N, 6.29. Found C, 76.71; H, 5.31; N, 6.17.
Addition of 10 equiv of 4-Methylbenzonitrile in Benzene
Addition of 10 equiv of Mesitylene in Benzene as Sol-
J. Chin. Chem. Soc. 2013, 60, 000-000
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11

Article
Choi et al.
vent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25
mmol) and mesitylene (47 mL, 45.4 mg, 0.25 mmol) and benzene
(1.5 mL) were heated at 120 oC with for 2.5 h with the reaction
tube covered by aluminum foil. The solvent was then removed in
vacuum and the red crude mixture was isolated by column chro-
matography on silica gel eluting with a solvent mixture of hexane:
CH2Cl2 (1:1) to give Rh(ttp)(3,5-Me2-Bn) (1h) (12.0 mg, 0.013
mmol, 54%).
5.11; N: 6.33.
Addition of 10 equiv of o-Xylene in Benzene as Solvent.
Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol)
and o-xylene (30 mL, 26.5 mg, 0.25 mmol) and benzene (1.5 mL)
were heated at 120 oC with for 5 h with the reaction tube covered
by aluminum foil. The solvent was then removed in vacuum and
the red crude mixture was isolated by column chromatography on
silica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1)
to give Rh(ttp)(2-Me-Bn) (1j) (14 mg, 0.016 mmol, 64%).
Reaction of Rh(ttp)Cl with 2-Methylbenzonitrile.
Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol)
and 2-methylbenzonitrile (1.5 mL) were heated at 120 oC for 1.5 h
with the reaction tube covered by aluminum foil. The solvent was
then removed in vacuum and the red crude mixture was isolated
by column chromatography on silica gel eluting with a solvent
mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(2-CN-Bn) (1k)
(29.3 mg, 0.033 mmol, 81%) as a red solid. Rf = 0.66 (hex-
ane:CH2Cl2 = 1:1). 1H NMR (CDCl3, 300 MHz) d -3.56 (d, J = 4.2
Hz, 2 H), 2.62 (d, J = 7.5 Hz, 1 H), 2.70 (s, 12 H), 5.98 (t, J = 7.7
Hz, 1 H), 6.17 (d, J = 7.5 Hz, 1 H), 6.40 (t, J = 7.4 Hz, 1 H), 7.54
(d, J = 7.5 Hz, 4 H), 7.59 (d, J = 7.5 Hz, 4 H), 8.05 (d, J = 7.8 Hz, 4
H), 8.08 (d, J = 7.8 Hz, 4 H), 8.73 (s, 8 H). 13C NMR (CDCl3, 75
MHz) d -5.2 (d, 1JRh-C = 28.7 Hz), 21.69, 106.76, 115.11, 122.76,
123.58, 126.09, 127.58, 129.61, 130.58, 131.80, 134.06, 137.32,
139.35, 143.46, 145.54. HRMS (FABMS): Calcd for
(C56H42N5Rh)+: m/z 887.2490. Found: m/z 887.2478. Anal Calcd.
for C56H42N5Rh: C, 76.70; H, 5.17; N, 6.39. Found: C, 76.60; H,
5.11; N: 6.33.
Reaction of Rh(ttp)Cl with m-Xylene. Rh(ttp)Cl (20.0
mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol) and m-xylene
(1.5 mL) were heated at 120 oC for 2 h with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)(3-Me-Bn) (1i) (17.7 mg, 0.020 mmol, 81%)
as a red solid. Rf = 0.51 (hexane:CH2Cl2 = 1:1). 1H NMR (CDCl3,
300 MHz) d -3.79 (d, J = 3.9 Hz, 2 H), 1.58 (s, 3 H), 2.63 (s, 1 H),
2.64 (s, 1 H), 2.70 (s, 12 H), 2.80 (d, J = 8.1 Hz, 1 H), 5.77 (t, J =
7.7 Hz, 1 H), 6.32 (d, J = 7.8 Hz, 1 H), 7.53 (d, J = 5.7 Hz, 4 H),
7.55 (d, J = 5.7 Hz, 4 H), 8.00 (dd, J = 2.6, 5.9 Hz, 4 H), 8.06 (dd, J
= 2.4, 5.1 Hz, 4 H), 8.67 (s, 8 H). HRMS (FABMS): Calcd for
(C56H45N4Rh)+: m/z 876.2694. Found: m/z 876.2682. Anal Calcd.
for C56H45N4Rh: C, 76.70; H, 5.17; N, 6.39. Found: C, 76.42; H,
5.09; N: 6.37.
Addition of 10 equiv of m-Xylene in Benzene as Solvent.
Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol)
and m-xylene (31 mL, 26.5 mg, 0.25 mmol) and benzene (1.5 mL)
were heated at 120 oC with for 5 h with the reaction tube covered
by aluminum foil. The solvent was then removed in vacuum and
the red crude mixture was isolated by column chromatography on
silica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1)
to give Rh(ttp)(3-Me-Bn) (1i) (14.0 mg, 0.016 mmol, 64%).
Reaction of Rh(ttp)Cl with o-Xylene. Rh(ttp)Cl (20.0 mg,
0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol) and o-xylene (1.5
mL) were heated at 120 oC for 1.5 h with the reaction tube covered
by aluminum foil. The solvent was then removed in vacuum and
the red crude mixture was isolated by column chromatography on
silica gel eluting with a solvent mixture of hexane: CH2Cl2 (1:1)
to give Rh(ttp)(2-Me-Bn) (1j) (16 mg, 0.018 mmol, 73%) as a red
Addition of 10 equiv of 2-Methylbenzonitrile in Benzene
as Solvent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg,
0.25 mmol) and 2-methylbenzonitrile (30 mL, 29.3 mg, 0.25
mmol) and benzene (1.5 mL) were heated at 120 oC with for 4 h
with the reaction tube covered by aluminum foil. The solvent was
then removed in vacuum and the red crude mixture was isolated
by column chromatography on silica gel eluting with a solvent
mixture of hexane: CH2Cl2 (1:1) to give Rh(ttp)(2-CN-Bn) (1k)
(17.0 mg, 0.019 mmol, 77%).
Reaction of Rh(ttp)Cl with 2-Nitrotoluene. Rh(ttp)Cl
(20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25 mmol) and 2-nitro-
toluene (1.5 mL) were heated at 120 oC for 1.5 h with the reaction
tube covered by aluminum foil. The solvent was then removed in
vacuum and the red crude mixture was isolated by column chro-
matography on silica gel eluting with a solvent mixture of hexane:
CH2Cl2 (1:1) to give Rh(ttp)(2-CN-Bn) (1l) (19.1 mg, 0.021
mmol, 84%) as a red solid. Rf = 0.30 (hexane:CH2Cl2 = 1:1). 1H
NMR (CDCl3, 300 MHz) d -3.19 (br, 2 H), 2.51 (d, J = 6.9 Hz, 1
H), 2.71 (s, 12 H), 5.87 (t, J = 7.5 Hz, 1 H), 6.40 (t, J = 7.4 Hz, 1
1
solid. Rf = 0.66 (hexane:CH2Cl2 = 1:1). H NMR (CDCl3, 300
MHz) d -3.57 (d, J = 3.6 Hz, 2 H), -0.91 (s, 3 H), 2.56 (d, J = 7.5
Hz, 1 H), 2.70 (s, 12 H), 5.66 (t, J = 7.5 Hz, 1 H), 5.72 (d, J = 7.8
Hz, 1 H), 6.31 (t, J = 7.2 Hz, 1 H), 7.53 (d, J = 3.3 Hz, 4 H), 7.54
(d, J = 1.8 Hz, 4 H), 7.96 (dd, J = 1.7, 7.7 Hz, 4 H), 8.05 (dd, J =
2.1, 7.4 Hz, 4 H), 8.67 (s, 8 H). HRMS (FABMS): Calcd for
(C56H45N4Rh)+: m/z 876.2694. Found: m/z 876.2703. Anal Calcd.
for C56H45N4Rh: C, 76.70; H, 5.17; N, 6.39. Found: C, 76.60; H,
12
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Benzylic CHA of Toluenes with Rh(por)Cl
H), 6.61 (d, J = 8.0 Hz, 1 H), 7.53 (d, J = 7.8 Hz, 4 H), 7.59 (d, J =
7.8 Hz, 4 H), 8.01 (dd, J = 1.4, 7.7 Hz, 4 H), 8.12 (dd, J = 1.5, 7.5
Hz, 4 H), 8.74 (s, 8 H).13C NMR (CDCl3, 75 MHz) d -2.83 (d,
1JRh-C = 28.4 Hz), 21.55, 122.51, 123.47, 123.75, 127.37, 127.49,
128.99, 129.88, 131.61, 133.88, 137.17, 138.34, 139.17, 143.25.
HRMS (FABMS): Calcd for (C55H42N5O2Rh)+: m/z 907.2388.
Found: m/z 907.2396.
of benzylic proton = 1.610, the integration of pyrrole signal was
set as 8.000) and the isotope ratio of 2 and 3 to 2-d7 and 3-d7 to be
6.6 (integration of aromatic proton = 2.607 with the integration of
pyrrole signal was set as 8.000) by integration of 1H NMR. The
results were the average of at least two runs of experiments.
Those isotope ratios were confirmed by FABMS and measured to
be 4.1.
Addition of 10 equiv of 2-Nitrotoluene in Benzene as
Solvent. Rh(ttp)Cl (20.0 mg, 0.025 mmol), K2CO3 (34.5 mg, 0.25
mmol) and 2-nitrotoluene (34.5 mg, 0.25mmol) and benzene (1.5
mL) were heated at 120 oC with for 4 h with the reaction tube cov-
ered by aluminum foil. The solvent was then removed in vacuum
and the red crude mixture was isolated by column chromatogra-
phy on silica gel eluting with a solvent mixture of hexane: CH2Cl2
(1:1) to give Rh(ttp)(2-CN-Bn) (1l) (16 mg, 0.018 mmol, 71%).
NMR Tube Experiment: Reaction of Rh(ttp)Cl with To-
luene. Rh(ttp)Cl (8 mg, 0.010 mmol), toluene (11 µL, 0.10
mmol), K2CO3 (14 mg, 0.10 mmol) and benzene-d6 (0.50 mL)
were degassed for three freeze-thaw-pump cycles in a Telfon
screw capped NMR tube and then flame-sealed under vacuum.
The reaction mixture was covered by aluminium foil and heated
at 120 oC in an oil bath. In the course of reaction, the amount of
Rh(ttp)Cl was decreasing, both Rh(ttp)H and Rh2(ttp)2 were ob-
served during the reaction. After 12 h, Rh(ttp)Bn (89%, NMR
yield) was observed.
Addition of 10 equiv of K2CO3. Rh(ttp)Cl (30.0 mg, 0.037
mmol), a premixed equimolar solvent mixture of toluene/tolu-
ene-d8 (1.5 mL) and K2CO3 (51.1 mg, 0.37 mmol) were degassed
for three freeze-thaw-pump cycles in the Telfon-stopped tube.
The tube was covered by aluminum foil and heated to 120 oC un-
der N2 for 1 h. The isotope ratio of 1 to 1-d7 was determined to be
1
4.0 (benzylic CHA) by integration of H NMR (Integration of
benzylic proton (1.598) was used to calculate the ratio with the in-
tegration of pyrrole signal set as 8.000). The results were the aver-
age of at least two runs. The isotope ratio was also measured by
FABMS to be 4.0.
Temperature Dependent on Isotope Effect with
Rh(ttp)Cl
o
Kinetic Isotope Effect at 150 C. Rh(ttp)Cl (30.0 mg,
0.037 mmol), a premixed equimolar solvent mixture of toluene/
toluene-d8 (1.5 mL) and K2CO3 (51.1 mg, 0.37 mmol) were de-
gassed for three freeze-thaw-pump cycles in the Telfon-stopped
tube. The tube was covered by aluminum foil and heated to 150 oC
under N2 for 1 h. The isotope ratio of 1 to 1-d7 was determined to
be 4.5 (benzylic CHA) by integration of 1H NMR (Integration of
benzylic proton (1.636) was used to calculate the ratio with the in-
tegration of pyrrole signal set as 8.000). The results were the aver-
age of at least two runs.
NMR Tube Experiment: Dehydrogenation of
Rh(ttp)H
Thermal Dehydrogenation. Rh(ttp)H (3 mg, 0.004 mmol)
and benzene-d6 (0.50 mL) were degassed for three freeze-thaw-
pump cycles in a Telfon screw capped NMR tube and then flame-
sealed under vacuum. The reaction mixture was covered by alu-
minium foil and heated at120 oC in an oil bath. After 2 h, Rh2(ttp)2
(2%, NMR yield) was observed and Rh(ttp)H (97%, NMR yield)
was remained.
o
Kinetic Isotope Effect at 180 C. Rh(ttp)Cl (30.0 mg,
0.037 mmol), a premixed equimolar solvent mixture of toluene/
toluene-d8 (1.5 mL) and K2CO3 (51.1 mg, 0.37 mmol) were de-
gassed for three freeze-thaw-pump cycles in the Telfon-stopped
tube. The tube was covered by aluminum foil and heated to 180 oC
under N2 for 1 h. The isotope ratio of 1 to 1-d7 was determined to
be 4.8 (benzylic CHA) by integration of 1H NMR (Integration of
benzylic proton (1.652) was used to calculate the ratio with the in-
tegration of pyrrole signal set as 8.000). The results were the aver-
age of at least two runs.
Base-Promoted Dehydrogenation. Rh(ttp)H (3 mg, 0.004
mmol), K2CO3 (5.4mg, 0.040mmol) and benzene-d6 (0.50 mL)
were degassed for three freeze-thaw-pump cycles in a Telfon
screw capped NMR tube and then flame-sealed under vacuum.
The reaction mixture was covered by aluminium foil and heated
at 120 oC in an oil bath. After 1 h, Rh2(ttp)2 (6%, NMR yield) was
observed and Rh(ttp)H (81%, NMR yield) was remained.
Isotope Effects. A premixed equimolar solvent mixture of
toluene/toluene-d8 (total volume = 1.5 mL) and Rh(ttp)Cl (30.0
mg, 0.037 mmol) were degassed for three freeze-thaw-pump cy-
cles in the Telfon-stopped tube. The tube was covered by alumi-
num foil and heated to 120 oC under N2 for 3 d. The isotope ratio
of 1 to 1-d7 was determined to be 4.1 (benzylic CHA, integration
o
Kinetic Isotope Effect at 200 C. Rh(ttp)Cl (30.0 mg,
0.037 mmol), a premixed equimolar solvent mixture of toluene/
toluene-d8 (1.5 mL) and K2CO3 (51.1 mg, 0.37 mmol) were de-
gassed for three freeze-thaw-pump cycles in the Telfon-stopped
tube. The tube was covered by aluminum foil and heated to 200 oC
under N2 for 1 h. The isotope ratio of 1 to 1-d7 was determined to
be 5.4 (benzylic CHA) by integration of 1H NMR (Integration of
J. Chin. Chem. Soc. 2013, 60, 000-000
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.jccs.wiley-vch.de
13

Article
Choi et al.
benzylic proton (1.670) was used to calculate the ratio with the in-
tegration of pyrrole signal set as 8.000). The results were the aver-
age of at least two runs.
mixture of toluene (39.0 mL, 0.37 mmol) and 4-methylanisole
(47.0 mL, 0.37 mmol) and K2CO3 (51.1 mg, 0.37 mmol) in ben-
zene (2.0 mL) as the solvent were degassed for three freeze-
thaw-pump cycles and heated at 120 oC under N2 for 1 h in a Tef-
lon-stoppered tube. After the reaction was complete, the 1H NMR
spectrum of the crude reaction mixture was taken. The ratio of
k(HFG/HH) was calculated from the ratio of the benzylic protons
with reference to the pyrrole proton in the 1H NMR spectrum from
at least two runs. A series of experiments was carried out using
various functionalized toluenes of 4-tert-butyltoluene (64.0 mL,
0.37 mmol), 4-fluorotoluene (41.0 mL, 0.37 mmol), p-tolualde-
hyde (44.0 mL, 0.37 mmol), 4-methylbenzonitrile (44.0 mL, 0.37
mmol), and 4-nitrotoluene (51.1 mg, 0.37 mmol). The ratios of
k(HFG/HH) were calculated from the integration of the benzylic
Attempted H/D exchange. Rh(ttp)Bn (10.0 mg, 0.012
mmol), 10 equiv of K2CO3 (16.0 mg, 0.12 mmol) and toluene-d8
(1.5 mL) were degassed for three freezethaw-pump cycles and
heated at 120 oC under N2 for 1 h with the reaction tube covered
by aluminum foil to give only recovered Rh(ttp)Bn (8.0 mg,
0.0093 mmol, 80%).
Temperature Dependent on Isotope Effect with
Rh(ttp)H
Kinetic Isotope Effect at 120 oC. Rh(ttp)H (6 mg, 0.008
mmol), a premixed equimolar solvent mixture of toluene/tolu-
ene-d8 (1.0 mL) and K2CO3 (11 mg, 0.080 mmol) were heated at
120 oC under N2 for 1 h. The isotope ratio of 1 to 1-d7 was deter-
mined to be 4.1 (benzylic CHA) by integration of 1H NMR (Inte-
gration of benzylic proton (1.614) was used to calculate the ratio
with the integration of pyrrole signal set as 8.000).
Kinetic Isotope Effect at 200 oC with Addition of K2CO3.
Rh(ttp)H (6 mg, 0.008 mmol), a premixed equimolar solvent mix-
ture of toluene/ toluene-d8 (1.0 mL) and K2CO3 (11 mg, 0.080
mmol) were heated at 200 oC under N2 for 1 h. The isotope ratio of
1 to 1-d7 was determined to be 5.3 (benzylic CHA) by integration
of 1H NMR (Integration of benzylic proton (1.684) was used to
calculate the ratio with the integration of pyrrole signal set as
8.000).
1
protons in H NMR spectra. The results were the average of at
least two runs of experiments.
Attempted exchange
Rh(ttp)Bn (10.0 mg, 0.012 mmol), 10 equiv of K2CO3 (16.0
mg, 0.12 mmol) and 4-fluorotoluene (1.5 mL) were degassed for
three freeze-thaw-pump cycles and heated at 120 oC under N2 for
1 h to give only Rh(ttp)Bn (8.0 mg, 0.0093 mmol, 80%).
ACKNOWLEDGEMENTS
We thank the Research Grants Council of the
HKSAR, the People’s Republic of China (CUHK 400307)
and the Chinese University of Hong Kong for Collabora-
tion Funding with Taiwan for financial support. This article
is dedicated to Professor Y. Wang on the occasion of her
70th birthday.
Temperature Dependent on Isotope Effect with
Rh2(ttp)2
Kinetic Isotope Effect at 120 oC with Addition of K2CO3.
Rh2(ttp)2 (6 mg, 0.004 mmol), a premixed equimolar solvent mix-
ture of toluene/toluene-d8 (1.0 mL) and K2CO3 (5.4 mg, 0.040
mmol) were heated at 120 oC under N2 for 1 h. The isotope ratio of
1 to 1-d7 was determined to be 6.7 (benzylic CHA) by integration
of 1H NMR (Integration of benzylic proton (1.711) was used to
calculate the ratio with the integration of pyrrole signal set as
8.000). The results were the average of at least two runs. The iso-
tope ratio was also measured by FABMS to be 6.7.
Kinetic Isotope Effect at 200 oC with Addition of K2CO3.
Rh2(ttp)2 (8 mg, 0.005 mmol), a premixed equimolar solvent mix-
ture of toluene/toluene-d8 (1.0 mL) and K2CO3 (7.2 mg, 0.052
mmol) were heated at 200 oC under N2 for 1 h. The isotope ratio of
1 to 1-d7 was determined to be 5.6 (benzylic CHA) by integration
of 1H NMR (Integration of benzylic proton (1.699) was used to
calculate the ratio with the integration of pyrrole signal set as
8.000).
SUPPORTING INFORMATION
Text, tables, and figures of crystallographic data for
complexes 1h-k, 1H and 13C NMR spectra for 1a-k. This
material is available free of charge via the Internet at
http://onlinelibrary.wiley.com. CCDC 923670-923673 con-
tains the supplementary crystallographic data of 1h-k.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or on applica-
tion to the CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK; fax: (+44) 1223-336-033; or email: deposit@ccdc.
cam.ac.uk.
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J. Chin. Chem. Soc. 2013, 60, 000-000
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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