Carbon-hydrogen bond activation of arenes by a [bis(oxazolinyl)phenyl]- rhodium(III) acetate complex

Article abstract of DOI:10.1002/ejic.200601085

Thermolysis of the rhodium(III) complex [(dm-Phebox-dm)-Rh(OAc) ₂(H₂O)] [1; dm-Phebox-dm = 2,6-bis(4,4-dimethyloxazolinyl) phenyl] in various arenes results in the formation of the corresponding aryl complexes [(dm-Phebox-dm)Rh(Ar) (κ²-OAc)] [Ar = C ₆H₅ (2), 3,5-Me₂C₆H₃ (3), 3,4-Me₂C₆H₃ (4), C₆H₄Me (5), C₆H₄CF₃ (6), C₆H₄OMe (7), C₆H₄COMe (8), C₆H₄Cl (9)]. The reaction of 1 with monosubstituted benzenes such as toluene, anisole, acetophenone, trifluorotoluene, and chlorobenzene produces a mixture of meta- and para-activated complexes, the ratio of which depends on the substituents on the benzene ring. The relative rate of the reaction of 1 with monosubstituted benzenes C₆H₅X was determined to be: X = OMe (1.8) > COMe (1.6) > CF₃ (1.2), Cl (1.2) > CH₃ (1). The acetato ligand of 1 appears to be essential for C-H bond activation of arenes as no reaction of the Rh^III complex [(dm-Phebox-dm)RhCl ₂(H₂O)] is observed in chlorobenzene at 120°C. The first-order rate constants obtained by thermolysis of 1 in [D ₈]toluene at 97.1-116.5°C yielded the following activation parameters: ΔH? = 22(2) kcalmol^-1 ΔS? = -24(5) calmol^-1 K^-1. The kinetic isotope effect for the C-H bond activation of toluene by 1 was determined to be k_H/k _D = 5.4 at 100 °C. These data suggest that the rate-determining step involves the C-H bond cleavage with a rigid, cyclic transition structure. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200601085

FULL PAPER
DOI: 10.1002/ejic.200601085
Carbon–Hydrogen Bond Activation of Arenes by a [Bis(oxazolinyl)phenyl]-
rhodium(III) Acetate Complex
Jun-ichi Ito[a] and Hisao Nishiyama*[a]
Keywords: C–H activation / Arenes / Rhodium / Substituent effects
Thermolysis of the rhodium(III) complex [(dm-Phebox-dm)-
Rh(OAc)2(H2O)] [1; dm-Phebox-dm = 2,6-bis(4,4-dimethylox-
(1.2) Ͼ CH3 (1). The acetato ligand of 1 appears to be essen-
tial for C–H bond activation of arenes as no reaction of the
azolinyl)phenyl] in various arenes results in the formation of RhIII complex [(dm-Phebox-dm)RhCl2(H2O)] is observed in
the corresponding aryl complexes [(dm-Phebox-dm)Rh(Ar)
(κ2-OAc)] [Ar = C6H5 (2), 3,5-Me2C6H3 (3), 3,4-Me2C6H3 (4),
C6H4Me (5), C6H4CF3 (6), C6H4OMe (7), C6H4COMe (8),
C6H4Cl (9)]. The reaction of 1 with monosubstituted ben-
zenes such as toluene, anisole, acetophenone, trifluorotol-
uene, and chlorobenzene produces a mixture of meta- and
para-activated complexes, the ratio of which depends on the
substituents on the benzene ring. The relative rate of the re-
chlorobenzene at 120 °C. The first-order rate constants ob-
tained by thermolysis of 1 in [D8]toluene at 97.1–116.5 °C
yielded the following activation parameters: ∆H‡
=
22(2) kcalmol–1, ∆S‡ = –24(5) calmol–1 K–1. The kinetic iso-
tope effect for the C–H bond activation of toluene by 1 was
determined to be kH/kD = 5.4 at 100 °C. These data suggest
that the rate-determining step involves the C–H bond cleav-
age with a rigid, cyclic transition structure.
action of 1 with monosubstituted benzenes C6H5X was deter- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
mined to be: X = OMe (1.8) Ͼ COMe (1.6) Ͼ CF3 (1.2), Cl
Germany, 2007)
have reported the intramolecular C–H bond activation of
{Cp*M} (M = Rh, Ir) species.[7] Such base-assisted C–H
bond activation is very attractive as an alternative mecha-
nism to oxidative addition. In this context, the RhIII com-
plexes [(Phebox)Rh(OAc)2(H2O)] [Phebox = 2,6-bis(oxazol-
inyl)phenyl],[8] which possess an RhIII center and meridio-
nal stereochemistry, could be expected to combine the func-
tions of a Lewis acid for coordination of the substrate and
a base to act as a proton acceptor during the C–H bond
cleavage step (Scheme 2). The RhIII acetate complex would
therefore provide different information regarding the coor-
dination chemistry in the meridional reaction field com-
pared with the structurally related Rh and Ir complexes
having a phosphane-based ligand (PCP- and PNP-type li-
Introduction
Intermolecular C–H bond activation has been considered
to be an essential step for functionalization of unreactive
hydrocarbons due to their relatively high dissociation ener-
gies.[1] Such transformations are attractive from a synthetic
point of view due to the possibility of using simple and
naturally abundant compounds to provide more useful and
complex products.[2] Thus far, a number of studies have fo-
cused on the mechanism involving oxidative addition, σ-
bond metathesis, 1,2-addition, and electrophilic acti-
vation.[3] Recently, electron-deficient Pd complexes bearing
acetato ligands have been found to be reactive for inter- and
intramolecular C–H bond activation and have been applied
to a suitable precursor for catalytic reactions.[4] Further-
more, computational studies of the C–H bond activation by
Pd(OAc)2 and related complexes have suggested a mecha-
nism whereby the acetato ligand assists the heterolytic
cleavage through a six-membered cyclic transition state, as
shown in Scheme 1.[5] Although Rh and Ir complexes have
been known to undergo oxidative addition to the electron-
rich metal center for some time,[3] only very recently have
Periana and co-workers reported the C–H bond cleavage of
arenes by the action of the alkoxy ligands of the IrIII com-
plexes [Ir(acac)2(OR)L].[6] Similarly, Davies and co-workers
Scheme 1.
[a] Department of Applied Chemistry, Graduate School of Engi-
neering, Nagoya University,
Chikusa, Nagoya 464-8603, Japan
Fax: +81-52-789-3209
E-mail: hnishi@apchem.nagoya-u.ac.jp
Scheme 2.
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1114–1119

C–H Bond Activation of Arenes
FULL PAPER
gands).[9] We report herein an intermolecular C–H bond The Rh(1)–C(19) bond length of 1.993(2) Å is comparable
activation reaction of simple arenes to a (Phebox)RhIII ace- to those in other arylRhIII complexes.[10] The κ2-acetato li-
tate complex.
gand makes the Rh center saturated.
Results and Discussion
When a solution of the RhIII acetate complex [(dm-Phe-
box-dm)Rh(OAc)2(H2O)] [1; dm-Phebox-dm = 2,6-bis(4,4-
dimethyloxazolinyl)phenyl][8b] in benzene was heated at
90 °C for 144 h, C–H bond activation took place to produce
the novel phenylrhodium(III) complex [(dm-Phebox-dm)-
Rh(Ph)(κ2-OAc)] (2) in 60% isolated yield (Scheme 3).
Thermolysis of 1 in m- and o-xylenes also gave the corre-
sponding arylRhIII complexes [(dm-Phebox-dm)Rh(Ar)(κ2-
OAc)] [Ar = 3,5-Me2C6H3 (3), 3,4-Me2C6H3 (4)] in 56%
and 64% yields, respectively (Scheme 3). Since products
arising from ortho-C–H bond activation of xylenes were not
detected, the regioselectivity of the reactions must be
strongly affected by the steric hindrance in the coordination
environment of the Phebox ligand. The authentic phenyl
Figure 1. Molecular structure of 3 with ellipsoids at the 40% prob-
ability level (one of the molecules in the unit cell has been omitted
for clarity). Selected bond lengths [Å] and angles [°]: Rh(1)–C(1)
1.919(2), Rh(1)–C(19) 1.993(2), Rh(1)–O(3) 2.2687(16), Rh(1)–
O(4) 2.2673(16), Rh(1)–N(1) 2.0753(18), Rh(1)–N(2) 2.0580(18);
N(2)–Rh(1)–N(1) 158.72(7), C(20)–C(19)–Rh(1) 128.83(17), C(24)–
complex 2 could be synthesized in 82% yield by treating 1 C(19)–Rh(1) 113.55(17).
with PhB(OH)2.
Since the substituent on the benzene ring has been shown
to affect the selectivity of C–H bond activation, we exam-
ined the reactivity of 1 toward the monosubstituted ben-
zenes C6H5X (X = Me, CF3, OMe, COMe, Cl; Scheme 4).
Thermolysis of 1 in toluene resulted in the formation of
para- and meta-tolyl complexes 5p and 5m in 64% isolated
yield in a 1:1.4 ratio, respectively. We did not detect the
ortho-C–H activated product, as observed in the reaction of
xylenes. We also prepared the authentic tolyl complex 5p as
a single isomer by the reaction of 1 with p-tolylboronic acid
(Figure 2). A similar C–H bond activation of electron-de-
ficient C6H5CF3 took place to produce a 1:7.8 mixture of
6p and 6m, respectively, in 76% yield. In the cases of anisole
and acetophenone, the formation of para- and meta-acti-
vated complexes was observed. This suggests that precoor-
Scheme 3.
An X-ray analysis of 3 confirmed its structure as an
arylRhIII complex (Figure 1). The orientation of the aryl
ligand is perpendicular to the Phebox plane [C(1)–Rh(1)–
C(19) 91.81(9)°]. The difference in angles around the ipso-
carbon atom of the aryl ligand [C(20)–C(19)–Rh(1)
128.83(17), C(24)–C(19)–Rh(1) 113.55(17)°] indicates that
the aryl ring is bent slightly towards the acetato ligand,
probably due to steric repulsion with the Phebox ligand. Scheme 4.
Eur. J. Inorg. Chem. 2007, 1114–1119
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1115

J. Ito, H. Nishiyama
FULL PAPER
dination of the carbonyl and methoxy groups to the Rh
Thermolysis of 1 in a 1:1 mixture of toluene and [D8]-
center is not important for the selectivity of the C–H bond toluene at 100 °C resulted in formation of the C–H- and
1
activation.[11] Reaction of 1 with C6H5Cl produced the C–D-activated complexes 5 and [D7]5. H NMR analysis
para- and meta-activated complexes 9p and 9m. The C–Cl revealed that the kinetic isotope effect is 5.4. This large
bond-activated complex was not detected in the (Phebox)- value suggests that the C–H bond cleavage is the rate-de-
Rh system.[12] Selectivity for the para position in preference termining step. Additionally, the rate constants obtained in
to the meta position was observed for electron-rich toluene the range of 97.1–116.5 °C yielded the following activation
and anisole, whereas the inverse selectivity was observed for parameters: ∆H‡
=
22Ϯ2 kcalmol–1 and ∆S‡
=
electron-deficient trifluorotoluene and acetophenone. This –24Ϯ5 calmol–1 K–1. The relatively large and negative
tendency is due to electrophilic aromatic substitution reac- value of the activation entropy suggests a rigid transition
tions. It is noteworthy that interconversion between 5p and state.[15]
5m is inhibited, as shown by no observation of isomeriza-
tion of 5p in toluene at 120 °C for 24 h.
We also checked the reaction of the RhIII complex [(dm-
Phebox-dm)RhCl2(H2O)] with chlorobenzene. When a solu-
tion of the complex in chlorobenzene was heated at 120 °C
for 40 h, no reaction was observed. This result clearly indi-
cates that the acetato ligand in 1 is essential for C–H bond
activation.
The proposed mechanism for C–H bond activation of
arenes by 1 is illustrated in Scheme 5. We have demon-
strated previously that the coordination site of H2O in
[(Phebox)RhCl2(H2O)] plays the role as the Lewis acidic po-
sition.[16] We therefore presume that a coordinatively unsat-
urated intermediate A with a vacant site can be formed by
dissociation of H2O. According to the final geometry of the
aryl complexes, isomerization to B might be important to
accept the arene molecule. The negative activation entropy
Figure 2. Molecular structure of 5p with ellipsoids at the 40% suggests that the C–H bond of arenes is cleaved though a
rate-determining six-centered transition state C.[5,7b] How-
probability level (one of the molecules in the unit cell has been
omitted for clarity). Selected bond lengths [Å] and angles [°]:
ever, we cannot rule out mechanisms involving σ-bond me-
Rh(1)–C(1) 1.912(2), Rh(1)–C(19) 2.005(2), Rh(1)–O(3) 2.2843(17),
Rh(1)–O(4) 2.2328(18), Rh(1)–N(1) 2.0526(19), Rh(1)–N(2)
2.0592(19); N(1)–Rh(1)–N(2) 159.00(8), C(20)–C(19)–Rh(1)
tathesis and oxidative hydrogen migration, which require
the four-centered transition state D.[3,17]
128.69(19), C(24)–C(19)–Rh(1) 113.81(19).
The substituent effect for C–H bond activation of mono-
substituted benzenes was determined by competition reac-
Conclusion
tions between two different aromatic compounds. The rela-
We have found intermolecular C–H bond activation of
tive rate of reaction of 1 with C6H5X decreased in the fol- various arenes by the structurally well-defined RhIII acetate
lowing sequence: OMe (1.8) Ͼ COMe (1.6) Ͼ CF3 (1.2), Cl complex 1, where the acetato ligand acts as a proton ac-
(1.2) Ͼ CH3 (1); no correlation with Hammett’s σ values ceptor. A large kinetic isotope effect and negative entropy
was observed. This result is inconsistent with electrophilic were found in this system. X-ray analysis of 3 has revealed
C–H bond activation, where the ρ values have been deter- a molecular structure with the aryl ligand at the apical posi-
2–
mined in the cases of PtCl6 and [(OEP)RhCl] (OEP = tion and a κ2-acetato ligand. Further detailed mechanistic
octaethylporphyrinato).[13,14]
and derivatization studies of arenes are in progress.
Scheme 5.
1116
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1114–1119

C–H Bond Activation of Arenes
FULL PAPER
196.8 (d, JRh,C = 29.6 Hz) ppm. C28H35N2O4Rh (566.49): calcd. C
59.37, H 6.23, N 4.95; found C 58.75, H 6.19, N 4.28.
Experimental Section
General Procedures: 1H and 13C NMR spectra were obtained at
25 °C with a Varian Mercury 300 spectrometer. 1H NMR chemical
shifts are reported relative to the singlet at δ = 7.26 ppm for chloro-
form or δ = 7.16 ppm for benzene. 13C NMR spectra are reported
in terms of chemical shifts relative to the triplet at δ = 77.0 ppm
for CDCl3 or δ = 128.0 ppm for C6D6 as an internal standard.
IR spectra were recorded with a JASCO FT/IR-230 spectrometer.
Elemental analysis was performed with a Perkin–Elmer 2400II.
[(dm-Phebox-dm)Rh(OAc)2(H2O)] (1) and [(dm-Phebox-dm)Rh-
(Cl)2(H2O)] were prepared according to a literature procedure.[8b]
Reaction of 1 with Toluene: Complex 1 (27 mg 0.050 mmol) was
dissolved in toluene (10 mL) in a 20-mL Schlenk tube under argon
and the solution was stirred at 115 °C for 144 h. The reaction mix-
ture was purified by column chromatography on silica gel with
ethyl acetate as eluent to give [(dm-Phebox-dm)Rh(C6H4Me)(κ2-
1
OAc)] (5; 22 mg, 78%) as a yellow solid. The H NMR spectrum
of the crude product revealed the formation of 5p and 5m in a
1.0:1.4 ratio. Complex 5p was alternatively synthesized by treat-
ment of 1 (54 mg, 0.10 mmol) with (p-C6H4Me)B(OH)2 (30 mg,
0.20 mmol) in toluene (2 mL) at 90 °C for 16 h. Workup as de-
scribed above gave complex 5p (36 mg, 65%). 5p: 1H NMR
(300 MHz, CDCl3, room temp.): δ = 0.99 (s, 6 H, Phebox-Me), 1.37
(s, 6 H, Phebox-Me), 2.06 (s, 3 H, OAc), 2.14, (s, 3 H, C6H4Me),
2.55 (s, 3,5-Me), 4.23 (d, JH,H = 8.4 Hz, 2 H, Phebox-CH2), 4.33
(d, JH,H = 8.4 Hz, 2 H, Phebox-CH2), 6.57 (d, JH,H = 8.0 Hz, 2 H,
C6H4Me), 6.61 (d, JH,H = 8.0 Hz, 2 H, C6H4Me), 6.69 (s, 1 H,4-
H) ppm. 13C NMR (75 MHz, CDCl3, room temp.): δ = 19.09, 20.67
(C6H4Me), 24.48 (OAc), 27.11, 27.23, 65.18, 81.87, 122.4–139.6,
140.8 (d, JRh,H = 31.9 Hz, Cipso), 170.9 (JRh,C = 5.2 Hz), 183.5
(OAc), 196.7 (JRh,C = 29.6 Hz) ppm. 5m: 1H NMR (300 MHz,
CDCl3, room temp.): δ = 0.99 (s, 6 H, Phebox-Me), 1.38 (s, 6 H,
Phebox-Me), 2.06 (s, 3 H, OAc), 2.13, (s, 3 H, C6H4Me), 2.55 (s,
3,5-Me), 4.23 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2), 4.33 (d, JH,H
= 8.1 Hz, 2 H, Phebox-CH2), 6.27 (d, JH,H = 7.6 Hz, 1 H,
Reaction of 1 with Benzene: Complex 1 (27 mg, 0.050 mmol) was
dissolved in benzene (5 mL) in a 20-mL Schlenk tube under argon
and the solution was stirred at 90 °C for 144 h. After removal of
the solvent, the yellow residue was purified by column chromatog-
raphy on silica gel with ethyl acetate/MeOH (10:1) as eluent to
give [(dm-Phebox-dm)Rh(Ph)(κ2-OAc)] (2; 17 mg, 62%) as a yellow
solid. Complex 2 was alternatively synthesized by treatment of 1
(54 mg, 0.10 mmol) with PhB(OH)2 (27 mg, 0.22 mmol) in toluene
(2 mL) at 70 °C for 46 h. Workup as described above gave 2 (44 mg,
1
0.082 mmol, 82%). H NMR (300 MHz, CDCl3, room temp.): δ =
0.97 (s, 6 H, Phebox-Me), 1.39 (s, 6 H, Phebox-Me), 2.07 (s, 3 H,
OAc), 2.56 (d, JH,H = 0.6 Hz, 6 H, 3,5-Me), 4.23 (d, JH,H = 8.2 Hz,
2 H, Phebox-CH2), 4.33 (d, JH,H = 8.2 Hz, 2 H, Phebox-CH2),
6.69–6.79 (m, 6 H, C6H5 and 4-H) ppm. 13C NMR (75 MHz,
CDCl3, room temp.): δ = 19.08, 24.45 (OAc), 27.01, 27.19, 65.18,
C6H4Me), 6.50 (d, JH,H = 7.6 Hz, 1 H, C6H4Me), 6.60 (t, JH,H
=
81.87, 121.5, 125.3, 126.1, 126.7, 134.1, 139.7, 146.0 (d, JRh,C
=
7.6 Hz, 1 H, C6H4Me), 6.69 (s, 1 H), 6.87 (s, 1 H, C6H4Me) ppm.
13C NMR (75 MHz, CDCl3, room temp.): δ = 19.09, 21.67
(C6H4Me), 24.48 (OAc), 27.05, 27.17, 65.21, 81.87, 122.4–139.60,
145.8 (d, JRh,C = 31.4 Hz, Cipso), 170.9 (d, JRh,C = 5.2 Hz), 183.5
(OAc), 196.6 (d, JRh,C = 29.6 Hz) ppm. C27H33N2O4Rh (552.47):
calcd. C 58.70, H 6.02, N 5.07; found C 58.83, H 5.98, N 4.96.
31.9 Hz, Cipso), 171.0 (d, JRh,C = 5.2 Hz), 183.5 (OAc), 196.5 (d,
JRh,C = 29.6 Hz) ppm. C26H31N2O4Rh (538.44): calcd. C 58.00, H
5.80, N 5.20; found C 58.11, H 5.67, N 5.07.
Reaction of 1 with m-Xylene: Complex 1 (54 mg 0.10 mmol) was
dissolved in m-xylene (10 mL) in a 20-mL Schlenk tube under ar-
gon and the solution was stirred at 140 °C for 60 h. The reaction
mixture was purified by column chromatography on silica gel with
ethyl acetate as eluent to give [(dm-Phebox-dm)Rh(3,5-
Me2C6H3)(κ2-OAc)] (3; 32 mg, 56%) as a yellow solid. 1H NMR
(300 MHz, CDCl3, room temp.): δ = 1.00 (s, 6 H, Phebox-Me), 1.38
(s, 6 H, Phebox-Me), 2.05 (s, 3 H, OAc), 2.06 (s, 6 H), 2.55 (s, 6
Reaction of 1 with α,α,α-Trifluorotoluene: Complex 1 (27 mg
0.050 mmol) was dissolved in α,α,α-trifluorotoluene (3 mL) in a 20-
mL Schlenk tube under argon and the solution was stirred at
100 °C for 140 h. The reaction mixture was purified by column
chromatography on silica gel with ethyl acetate as eluent to give
[(dm-Phebox-dm)Rh(C6H4CF3)(κ2-OAc)] (6; 23 mg, 76%) as a yel-
H), 4.24 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2), 4.33 (d, JH,H
=
1
low solid. The H NMR spectrum of the crude products revealed
8.4 Hz, 2 H, Phebox-CH2), 6.32 (s, 1 H, C6H3Me2), 6.38 (s, 2 H,
C6H3Me2), 6.68 (s, 1 H, 4-H) ppm. 13C NMR (75 MHz, CDCl3,
room temp.): δ = 19.08, 21.52, 24.47 (OAc), 27.06, 27.14, 65.23,
81.84, 123.6, 126.0, 126.7, 131.6, 131.6, 133.9, 139.5, 145.6 (d, JRh,C
= 31.4 Hz, Cipso), 170.9 (d, JRh,C = 5.7 Hz), 183.3 (OAc), 196.7 (d,
JRh,C = 29.6 Hz) ppm. C28H35N2O4Rh (566.49): calcd. C 59.37, H
6.23, N 4.95; found C 59.34, H 6.33, N 4.46.
the formation of 6p and 6m in a ratio of 1:7.8. 6p: 1H NMR
(300 MHz, CDCl3, room temp.): δ = 0.94 (s, 6 H, Phebox-Me), 1.39
(s, 6 H, Phebox-Me), 2.06 (s, 3 H, OAc), 2.57 (s, 3,5-Me), 4.25 (d,
JH,H = 8.4 Hz, 2 H, Phebox-CH2), 4.35 (d, JH,H = 8.4 Hz, 2 H,
Phebox-CH2), 6.74 (s, 1 H, 4-H), 6.77–6.97 (4 H, C6H4CF3) ppm.
6m: 1H NMR (300 MHz, CDCl3, room temp.): δ = 0.94 (s, 6 H,
Phebox-Me), 1.39 (s, 6 H, Phebox-Me), 2.06 (s, 3 H, OAc), 2.57 (s,
3,5-Me), 4.25 (d, JH,H = 8.4 Hz, 2 H, Phebox-CH2), 4.35 (d, JH,H
= 8.4 Hz, 2 H, Phebox-CH2), 6.74 (s, 1 H, 4-H), 6.77–6.97 (3 H,
C6H4CF3), 7.18 (s, 1 H, C6H4CF3) ppm. 13C NMR (75 MHz,
CDCl3, room temp.): δ = 19.11, 24.45 (OAc), 26.99, 27.23, 65.23,
81.94, 118.5 (q, JC,F = 4.1 Hz), 124.4 (q, JC,F = 269.9 Hz), 127.0
(q, JC,F = 31.4 Hz), 130.4 (q, JC,F = 2.9 Hz), 134.3, 140.1, 147.4 (d,
JRh,C = 31.9 Hz, Cipso), 171.1 (d, JRh,C = 5.1 Hz), 184.1 (OAc),
195.6 (d, JRh,C = 29.1 Hz) ppm. C27H30F3N2O4Rh (606.44): calcd.
C 53.47, H 4.99, N 4.62; found C 54.13, H 5.27, N 3.85.
Reaction of 1 with o-Xylene: Complex 1 (27 mg 0.050 mmol) was
dissolved in o-xylene (2 mL) in a 20-mL Schlenk tube under argon
and the solution was stirred at 140 °C for 36 h. The reaction mix-
ture was purified by column chromatography on silica gel with
ethyl acetate as eluent to give [(dm-Phebox-dm)Rh(3,4-
Me2C6H3)(κ2-OAc)] (4; 24 mg, 86%) as a yellow solid. 1H NMR
(300 MHz, CDCl3, room temp.): δ = 1.01 (s, 6 H, Phebox-Me), 1.38
(s, 6 H, Phebox-Me), 2.06 (m, 9 H, OAc and C6H3Me2), 2.55 (d,
JH,H = 0.6 Hz, 6 H), 4.23 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2),
4.33 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2), 6.17 (d, JH,H = 7.8 Hz,
1 H, C6H3Me2), 6.48 (d, JH,H = 7.8 Hz, 1 H, C6H3Me2), 6.68 (m, Reaction of 1 with Anisole: Complex 1 (27 mg 0.050 mmol) was
1 H, 4-H), 6.76 (s, 1 H, C6H3Me2) ppm. 13C NMR (75 MHz,
CDCl3, room temp.): δ = 19.05, 19.08, 19.90, 24.52 (OAc), 27.17,
65.19, 81.84, 125.9, 126.7, 126.8 (d, JRh,H = 1.1 Hz), 129.1, 131.4,
133.0, 134.9 (d, JRh,C = 1.1 Hz), 139.5 (d, JRh,C = 1.1 Hz), 141.2
(d, JRh,C = 32.0 Hz, Cipso), 170.9 (d, JRh,C = 5.7 Hz), 183.4 (OAc),
dissolved in anisole (3 mL) in a 20-mL Schlenk tube under argon
and the solution was stirred at 120 °C for 44 h. The reaction mix-
ture was purified by column chromatography on silica gel with
ethyl acetate as eluent to give [(dm-Phebox-dm)Rh(C6H4OMe)(κ2-
1
OAc)] (7; 20 mg, 70%) as a yellow solid. The H NMR spectrum
Eur. J. Inorg. Chem. 2007, 1114–1119
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1117

J. Ito, H. Nishiyama
FULL PAPER
of the crude products revealed the formation of 7p and 7m in a 1:1
ratio. 7p: H NMR (300 MHz, CDCl3, room temp.): δ = 0.98 (s, 6
temp.): δ = 0.81 (s, 6 H, Phebox-Me), 1.16 (s, 6 H, Phebox-Me),
2.16 (s, 3 H, OAc), 2.45 (s, 6 H, 3,5-Me), 3.40 (d, JH,H = 8.1 Hz,
Phebox-CH2), 3.52 (d, JH,H = 8.1 Hz, Phebox-CH2), 6.47 (s, 1 H,
4-H), 6.61 (t, JH,H = 7.8 Hz, 2 H, C6H4Cl), 6.84 (d, JH,H = 7.8 Hz,
2 H, C6H4Cl), 6.97 (d, JH,H = 7.8 Hz, 2 H, C6H4Cl), 7.46 (s, 1 H,
C6H4Cl) ppm. 13C NMR (75 MHz, C6D6, room temp.): δ = 19.35,
1
H, Phebox-Me), 1.38 (s, 6 H, Phebox-Me), 2.05 (s, 3 H, OAc), 2.55
(s, 3,5-Me), 3.64 (s, 3 H, OMe), 4.23 (d, JH,H = 8.1 Hz, 2 H, Phe-
box-CH2), 4.33 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2), 6.42 (d, JH,H
= 7.8 Hz, 2 H, C6H4OMe), 6.60 (d, JH,H = 7.8 Hz, 2 H, C6H4OMe),
6.69 (s, 1 H, 4-H) ppm. 13C NMR (75 MHz, CDCl3, room temp.): 25.04 (OAc), 27.04, 27.34, 65.45, 81.90, 122.5–140.1, 150.4 (d, JRh,C
δ = 19.10, 24.47 (OAc), 27.03, 27.23, 55.07 (OMe), 65.16, 81.88,
111.5, 126.0, 126.7, 133.3 (d, JRh,C = 33.1 Hz, Cipso), 133.9, 139.6,
= 32.6 Hz, Cipso), 171.5 (d, JRh,C = 5.2 Hz), 184.1, 198.1 (d, JRh,C
= 28.0 Hz) ppm. C26H30ClN2O4Rh (572.89): calcd. C 54.51, H
5.28, N 4.89; found C 54.66, H 5.18, N 4.72.
155.6, 170.9 (d, JRh,C = 5.3 Hz), 183.6 (OAc), 196.6 (d, JRh,C
=
1
29.0 Hz) ppm. 7m: H NMR (300 MHz, CDCl3, room temp.): δ =
0.99 (s, 6 H, Phebox-Me), 1.38 (s, 6 H, Phebox-Me), 2.05 (s, 3 H,
OAc), 2.54 (s, 3,5-Me), 3.61 (s, 3 H, OMe), 4.23 (d, JH,H = 8.1 Hz,
2 H, Phebox-CH2), 4.33 (d, JH,H = 8.1 Hz, 2 H, Phebox-CH2), 6.01
(m, 1 H, C6H4OMe), 6.27 (d, JH,H = 7.8 Hz, 1 H, C6H4OMe), 6.69
(t, JH,H = 7.8 Hz, 1 H, C6H4OMe), 6.69 (s, 1 H, 4-H), 6.77 (d, JH,H
= 7.8 Hz, 1 H, C6H4OMe) ppm. 13C NMR (75 MHz, CDCl3, room
temp.): δ = 19.10, 24.47 (OAc), 27.03, 27.23, 54.82 (OMe), 65.21,
81.88, 106.5, 120.0, 124.8, 126.2, 126.6, 127.0, 139.7, 148.0 (d, JRh,C
= 31.4 Hz, Cipso), 156.4, 170.9 (d, JRh,C = 5.2 Hz), 183.6 (OAc),
196.3 (d, JRh,C = 29.7 Hz) ppm. C27H33N2O5Rh (568.47): calcd. C
57.05, H 5.85, N 4.93; found C 56.85, H 5.76, N 4.72.
Competition Reaction: Complex 1 (16 mg, 0.030 mmol) was dis-
solved in a 1:1 molar mixture (4 mL) of toluene and C6H5X (X =
OMe, COMe, CF3, or Cl) under argon. The solution was stirred at
100 °C for 24 h and then passed through a short column. The rela-
tive ratio of products was determined on the basis of the 1H NMR
spectra in CDCl3.
Reaction of
1 with [D8]Toluene/Toluene: Complex 1 (11 mg
0.020 mmol) was dissolved in a 1:1 mixture of [D8]toluene and tolu-
ene (1 mL) in a 20-mL Schlenk tube under argon. The solution was
stirred at 100 °C for 40 h and then the solvent was removed under
1
reduced pressure. The H NMR spectrum of the resulting residue
revealed the formation of [D7]3 and 3 in a 5.4:1 ratio.
Reaction of 1 with Acetophenone: Complex 1 (27 mg 0.050 mmol)
was dissolved in acetophenone (3 mL) in a 20-mL Schlenk tube
under argon and the solution was stirred at 140 °C for 24 h. The
reaction mixture was purified by column chromatography on silica
gel with ethyl acetate as eluent to give [(dm-Phebox-dm)-
Rh(C6H4COMe)(κ2-OAc)] (8; 23 mg, 78%) as a yellow solid. The
1H NMR spectrum of the crude products revealed the formation
of 8p and 8m in a 1:4.5 ratio. 8p: 1H NMR (300 MHz, CDCl3,
room temp.): δ = 0.95 (s, 6 H, Phebox-Me), 1.39 (s, 6 H, Phebox-
Me), 2.07 (s, 3 H, OAc), 2.44 (s, 3 H, -COMe), 2.57 (s, 3,5-Me),
4.24 (d, JH,H = 8.5 Hz, 2 H, Phebox-CH2), 4.35 (d, JH,H = 8.5 Hz,
2 H, Phebox-CH2), 6.74 (s, 1 H, 4-H), 6.96 (d, JH,H = 8.0 Hz, 2
H), 7.31 (d, JH,H = 8.0 Hz, 2 H) ppm. 8m: 1H NMR (300 MHz,
CDCl3, room temp.): δ = 0.95 (s, 6 H, Phebox-Me), 1.39 (s, 6 H,
Phebox-Me), 2.07 (s, 3 H, OAc), 2.39 (s, 3 H, -COMe), 2.57 (s, 3,5-
Monitoring the Reaction of 1 with [D8]Toluene: Complex 1 (16.0 mg,
0.030 mmol) was dissolved in [D8]toluene (3 mL) under argon. The
solution (0.6 mL) was placed into an NMR tube and then the tube
was flame-sealed. The four samples were maintained in oil baths
at 97.1, 105.0, 111.3, and 116.5 °C. The reaction was monitored by
1H NMR spectroscopy by recording the signal of the methyl group.
The rate constants were estimated as 2.48(5)ϫ10–6 (97.1 °C),
4.13(5)ϫ10–6
(105.0 °C),
7.12(9)ϫ10–6
(111.3 °C),
and
1.21(1)ϫ10–5 s–1 (116.5 °C). The Eyring plot gave the following ac-
tivation parameters: ∆H‡
–24Ϯ5 calmol–1 K–1.
= =
22Ϯ2 kcalmol–1 and ∆S‡
X-ray Diffraction Study: Single crystals of 3 and 5p suitable for an
X-ray diffraction study were obtained from hexane/CH2Cl2 solu-
tions at room temperature. The diffraction data were collected with
a Bruker SMART APEX CCD diffractometer with graphite-mono-
chromated Mo-Kα radiation (λ = 0.71073 Å). An empirical absorp-
tion correction was applied with SADABS. The structure was
solved by direct methods and refined by full-matrix least squares
on F2 using SHELXTL. All non-hydrogen atoms of the rhodium
complex were refined with anisotropic displacement parameters.
All hydrogen atoms were located at calculated positions and refined
as rigid groups. Refinement details for 3: empirical formula:
C29.50H38.50N2O4Rh; Mr = 588.03; temperature: 153(2) K; crystal
Me), 4.24 (d, JH,H = 8.5 Hz, 2 H, Phebox-CH2), 4.35 (d, JH,H
8.5 Hz, 2 H, Phebox-CH2), 6.74 (s, 1 H, 4-H), 6.84 (t, JH,H
=
=
7.8 Hz,
1
H, C6H4COMe), 7.15 (d, JH,H
=
7.8 Hz,
1
H,
C6H4COMe), 7.23 (s, 1 H, C6H4COMe), 7.31 (d, JH,H = 7.8 Hz, 1
H, C6H4COMe) ppm. 13C NMR (75 MHz, CDCl3, room temp.): δ
= 19.11, 24.52 (OAc), 26.70 (COMe), 27.06, 27.33, 65.20, 81.92,
121.8, 125.1, 126.5, 126.6, 133.3, 139.5, 140.1, 146.7 (d, JRh,C
=
31.9 Hz, Cipso), 171.1 (d, JRh,C = 5.7 Hz), 184.0 (OAc), 195.9 (d,
JRh,C = 29.7 Hz), 199.0 (COMe) ppm. C28H33N2O5Rh (580.48):
calcd. C 57.93, H 5.73, N 4.83; found C 57.68, H 5.60, N 4.64.
¯
system: triclinic; space group: P1; a = 11.2915(5), b = 13.4972(7),
Reaction of 1 with Chlorobenzene: Complex 1 (27 mg 0.050 mmol)
was dissolved in chlorobenzene (5 mL) in a 20-mL Schlenk tube
under argon and the solution was stirred at 120 °C for 50 h. The
reaction mixture was purified by column chromatography on silica
gel with ethyl acetate as eluent to give [(dm-Phebox-dm)-
Rh(C6H4Cl)(κ2-OAc)] (9; 23 mg, 80%) as a yellow solid. The 1H
NMR spectrum of the crude products revealed the formation of 9p
c = 19.5574(9) Å, α = 96.8790(10), β = 103.3450(10), γ =
101.8940(10)°, V = 2793.7(2) Å3, Z = 4, ρcalcd. = 1.398 Mgm–3, µ
= 0.648 mm–1, F(000) = 1226, crystal size = 0.40ϫ0.40ϫ0.30 mm,
θ range = 1.74–27.53°; index ranges: –14 Յ h Յ 14, –16 Յ k Յ 17,
–25 Յ l Յ 21; reflections collected: 19914; independent reflections:
12803 [R(int) = 0.0187], completeness to θ = 27.53°: 99.2%; max/
min transmission: 1.000000/0.788581; data/restraints/parameters:
and 9m in a 1:2.2 ratio. 9p: 1H NMR (300 MHz, C6D6, room 12803/0/673; goodness-of-fit on F2: 1.030; final R indices [I Ͼ
temp.): δ = 0.78 (s, 6 H, Phebox-Me), 1.17 (s, 6 H, Phebox-Me),
2.16 (s, 3 H, OAc), 2.48 (s, 6 H, 3,5-Me), 3.43 (d, JH,H = 8.7 Hz,
Phebox-CH2), 3.55 (d, JH,H = 8.7 Hz, Phebox-CH2), 6.49 (s, 1 H,
4-H), 6.91 (d, JH,H = 8.3 Hz, 2 H, C6H4Cl), 7.08 (d, JH,H = 8.3 Hz,
2σ(I)]: R1 = 0.0343, wR2 = 0.0844; R indices (all data): R1 =
0.0438, wR2 = 0.0895; largest diff. peak/hole: 0.946/–0.363 eÅ–3.
Refinement details for 5p: empirical formula: C27H33N2O4Rh; Mr
= 552.46; temperature: 173(2) K; crystal system: triclinic; space
2 H, C6H4Cl) ppm. 13C NMR (75 MHz, C6D6, room temp.): δ = group: P1; a = 11.3424(5), b = 13.1787(6), c = 17.4623(8) Å, α =
¯
19.35, 25.04 (OAc), 27.10, 27.34, 65.45, 81.90, 122.5–140.0, 145.2
(d, JRh,C = 32.5 Hz, Cipso), 171.4 (d, JRh,C = 4.5 Hz), 184.1, 198.3
94.8920(10), β = 94.7150(10), γ = 102.4740(10)°, V = 2525.7(2) Å3,
Z = 4, ρcalcd. = 1.453 Mgm–3, µ = 0.711 mm–1, F(000) = 1144, crys-
(d, JRh,C = 28.0 Hz) ppm. 9m: 1H NMR (300 MHz, C6D6, room tal size = 0.30ϫ0.20ϫ0.10 mm, θ range = 1.18–27.51°; index ran-
1118
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1114–1119

C–H Bond Activation of Arenes
FULL PAPER
R. J. Nielsen, W. A. Goddard III, R. A. Periana, Organometal-
lics 2006, 25, 5173–5175.
[7] a) D. L. Davies, O. Al-Duaij, J. Fawcett, M. Giardiello, S. T.
Hilton, D. R. Russell, Dalton Trans. 2003, 4132–4139; b) D. L.
Davies, S. M. A. Donald, O. Al-Duaij, S. A. Macgregor, M.
Polleth, J. Am. Chem. Soc. 2006, 128, 4210–4211.
[8] a) Y. Kanazawa, Y. Tsuchiya, K. Kobayashi, T. Shiomi, J. Itoh,
M. Kikuchi, Y. Yamamoto, H. Nishiyama, Chem. Eur. J. 2006,
12, 63–71; b) J. Ito, T. Shiomi, H. Nishiyama, Adv. Synth. Ca-
tal. 2006, 348, 1235–1240.
[9] a) M. E. van der Boom, D. Milstein, Chem. Rev. 2003, 103,
1759–1792; b) M. Kanzelberger, B. Singh, M. Czerw, K.
Krogh-Jespersen, A. S. Goldman, J. Am. Chem. Soc. 2000, 122,
11017–11018.
ges: –14 Յ h Յ 14, –17 Յ k Յ 16, –14 Յ l Յ 22; reflections col-
lected: 18003, independent reflections: 11516 [R(int) = 0.0353],
completeness to
θ = 27.51°: 99.3%; max/min transmission:
1.000000/0.735363; data/restraints/parameters: 11516/0/629; good-
ness-of-fit on F2: 0.983; final R indices [I Ͼ 2σ(I)]: R1 = 0.0320,
wR2 = 0.0788; R indices (all data): R1 = 0.0407, wR2 = 0.0872;
largest diff. peak/hole: 0.901 and –0.661 eÅ–3. CCDC-623906 and
-623907 contain the supplementary crystallographic data for com-
plexes 3 and 5p, respectively. These data can be obtained free of
charge from The Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/datarequest/cif.
[10] a) S. Gatard, R. Çelenligil-Çetin, C. Guo, B. M. Foxman, O. V.
Ozerov, J. Am. Chem. Soc. 2006, 128, 2808–2809; b) W. D.
Jones, F. J. Feher, Inorg. Chem. 1984, 23, 2376–2388; c) R. Co-
hen, M. E. van der Boom, L. J. W. Shimon, H. Rozenberg, D.
Milstein, J. Am. Chem. Soc. 2000, 122, 7723–7734.
Acknowledgments
This research was financially supported by a Grant-in-Aid for Sci-
entific Research from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan.
[11]
[12]
A. D. Ryabov, Chem. Rev. 1990, 90, 403–424.
For examples of C–H bond activation in preference to C–Cl
bond activation, see: a) Y. Fuchita, Y. Utsunomiya, M. Yasu-
take, J. Chem. Soc., Dalton Trans. 2001, 2330–2334; b) E. Ben-
Ari, M. Gandelman, H. Rozenberg, L. J. W. Shimon, D.
Milstein, J. Am. Chem. Soc. 2003, 125, 4714–4715; c) E. Ben-
Ari, R. Cohen, M. Gandelman, L. J. W. Shimon, J. M. L. Mar-
tin, D. Milstein, Organometallics 2006, 25, 3190–3210; d) L.
Fan, S. Parkin, O. V. Ozerov, J. Am. Chem. Soc. 2005, 127,
16772–16773; e) T. Ishiyama, J. Takagi, K. Ishida, N. Miyaura,
N. R. Anastasi, J. F. Hartwig, J. Am. Chem. Soc. 2002, 124,
390–391; f) G. A. Chotana, M. A. Rak, M. R. Smith III, J. Am.
Chem. Soc. 2005, 127, 10539–10544; g) J. Y. K. Tsang, M. S. A.
Buschhaus, P. Legzdins, B. O. Patrick, Organometallics 2006,
25, 4215–4225.
[1] S. J. Blanksby, G. B. Ellison, Acc. Chem. Res. 2003, 36, 255–
263.
[2] a) V. Ritleng, C. Sirlin, M. Pfeffer, Chem. Rev. 2002, 102, 1731–
1770; b) F. Kakiuchi, S. Murai, Acc. Chem. Res. 2002, 35, 826–
834; c) K. Godula, D. Sames, Science 2006, 312, 67–72; d) G.
Dyker, Angew. Chem. Int. Ed. 1999, 38, 1698–1712; e) T. Ishi-
yama, N. Miyaura, J. Organomet. Chem. 2003, 680, 3–11.
[3] a) B. A. Arndtsen, R. G. Bergman, T. A. Mobley, T. H. Pe-
terson, Acc. Chem. Res. 1995, 28, 154–162; b) J. A. Labinger,
J. E. Bercaw, Nature 2002, 417, 507–514; c) W. D. Jones, Acc.
Chem. Res. 2003, 36, 140–146.
[4] a) C. Jia, T. Kitamura, Y. Fujiwara, Acc. Chem. Res. 2001, 34,
633–639; b) L. V. Desai, K. L. Hull, M. S. Sanford, J. Am.
Chem. Soc. 2004, 126, 9542–9543; c) M. D. K. Boele, F. P. F.
Van Strijdonck, A. H. M. De Vries, P. C. J. Kamer, J. G.
De Vries, P. W. N. M. Van Leeuwen, J. Am. Chem. Soc. 2002,
124, 1586–1587.
[13] G. B. Shul’pin, G. V. Nizova, A. T. Nikitaev, J. Organomet.
Chem. 1984, 276, 115–153.
[14] Y. Aoyama, T. Yoshida, K. Sakurai, H. Ogoshi, Organometal-
lics 1986, 5, 168–173.
[5] a) B. Biswas, M. Sugimoto, S. Sakaki, Organometallics 2000,
19, 3895–3908; b) D. L. Davies, S. M. A. Donald, S. A. Mac-
gregor, J. Am. Chem. Soc. 2005, 127, 13754–13755; c) V. R.
Ziatdinov, J. Oxgaard, O. A. Mironov, K. J. H. Young, W. A.
Goddard III, R. A. Periana, J. Am. Chem. Soc. 2006, 128,
7404–7405.
[6] a) W. J. Tenn III, K. J. H. Young, G. Bhalla, J. Oxgaard, W. A.
Goddard III, R. A. Periana, J. Am. Chem. Soc. 2005, 127,
14172–14173; b) W. J. Tenn III, K. J. H. Young, J. Oxgaard,
[15] a) A. D. Ryabov, I. K. Sakodinskaya, A. K. Yatsimirsky, J.
Chem. Soc., Dalton Trans. 1985, 2629–2638; b) M. Gómez, J.
Granell, M. Martinez, Organometallics 1997, 16, 2539–2546.
[16] Y. Motoyama, M. Okano, H. Narusawa, N. Makihara, K.
Aoki, H. Nishiyama, Organometallics 2001, 20, 1580–1591.
[17] J. Oxgaard, R. P. Muller, W. A. Goddard III, R. A. Periana, J.
Am. Chem. Soc. 2004, 126, 352–363.
Received: November 6, 2006
Published Online: February 2, 2007
Eur. J. Inorg. Chem. 2007, 1114–1119
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1119