Copper porphyrin catalyzed esterification of C(sp3)-H via a cross-dehydrogenative coupling reaction

Article abstract of DOI:10.1039/c6nj03876j

The crystal structure of 5,10,15,20-tetra(ethoxycarbonyl)porphyrin copper(ii) showed that its central copper has a six-coordinate structure. An efficient copper porphyrin-catalyzed cross-dehydrogenative coupling (CDC) esterification reaction between C(sp<

Full text of DOI:10.1039/c6nj03876j

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Copper Porphyrin Catalyzed Esterification of C (sp3)−H via Cross-
Dehydrogenative Coupling Reaction
Hua-Hua Wanga, Wei-Hong Wena, Huai-Bo Zoub, Fan Chenga, Atif Alia, Lei Shic, Hai-Yang Liua*, Chi-
Kwong Changd*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
The crystal structure of 5,10,15,20-tetra(ethoxycarbonyl)porphyrin copper(II) showed its centeral copper was a six-
coordinate structure. An efficient copper porphyrin-catalyzed cross-dehydrogenative coupling (CDC) esterification reaction
between C(sp3) − H and carboxylic acids using di-tert-butyl peroxide (DTBP) as the oxidant was established. Kinetic isotope
www.rsc.org/
effect (KIE) indicated that C(sp3)
−
H
bond cleavage was the rate-determining step of this CDC reaction.
were proved more efficient.25 The esterification may be
Introduction
complete in 12 hours
H
O
O
O
DTBP, Fe(acac)3 (20 mol %)
O
(1)
(2)
The cross-dehydrogenative coupling (CDC) reaction is
a
n
H
+
O
n
R
O
R
O
120 °C, 24 h
O
convenient synthetic protocol for direct C-H functionalization
including the formation of C−C and C−X (X = O, S, N, etc.)
bonds.1-6 The most important characteristic of the CDC
reaction is that there is no needs of pre-functionalization of
starting materials, which makes it a more environmentally
friendly and atom economical process.7-10 In the past years,
much progress has been made in the C−C bond construcꢀon by
using different hybrid C−H (sp to sp3) substrates via the CDC
reaction.11-13 C−O bond formaꢀon is another important
application of the CDC reaction. It may afford alcohol, ether
and ester compounds depending on the substrates used. Due
to wide applicability of esters as building blocks in organic
synthesis, the preparation of esters via the CDC reaction has
also gained much attention recently.14-21 As compared to
traditional method for ester preparation, the CDC reaction has
the advantage of using alkanes instead of alcohol substrates.
Alcohols are more expensive than alkanes, and some alcohols
are not commercially available. More importantly,
esterification of C–H bonds adjacent to a heteroatom may
provide diverse, biologically active esters such as artemisinin,
and sanguiin H-5 drugs.22, 23 In 2014, Pan’s group developed an
Fe-catalyzed CDC esterificaꢀon of C−H adjacent to an oxygen
atom for the synthesis of α-acyloxy ethers (Scheme 1, eq 1).24
While Cu-catalyzed CDC reactions using TBHP as an oxidant
O
O
O
H
TBHP, Cu(acac)2 (2.75 mol %)
120 °C, 12 h
O
n
H
+
O
n
R
O
R
O
O
Transition metal catalyzed CDC reaction
O
O
O
H
TBHP, Bu4NI (20 mol %)
O
O
(3)
n
H
+
O
n
R
O
R
O
EtOAC, 80 °C, 12 h
Transition metal free CDC reaction
Scheme 1. Examples of esterification of C(sp3)-H for the synthesis of α-acyloxy
ethers by CDC reaction
with a lower catalyst concentration (2.75 mol %) (Scheme 1, eq
2). It is noteworthy that Bu4NI may also be used as the catalyst
for the CDC esterification reaction (Scheme 1, eq 3).26
Metalloporphyrins are a class of versatile catalysts having the
capability to functionalize saturated C–H bonds via several
28
well-defined atom/group transfer processes,27,
such as
oxene,29 nitrene,30 and carbene31 C–H insertions. Although
many examples proved metal porphyrins were efficient
catalysts for C–H functionalization, the application of metal
porphyrins in CDC reactions is rare. The only example we can
find is Guo’s report about copper porphyrin-catalyzed
oxidative C(sp)−H coupling of terminal alkynes.32
Recently, we focused on the synthesis and application of
5,10,15,20-tetra-(ethoxylcarbonyl)porphyrin (TECP).33 Our
improved synthesis method is as simple as the synthesis of TPP.
This kind of porphyrin has a flat plane, and its metal complex
proved more robust in catalytic oxidation reactions.34 Here we
wish to report the CDC esterification of C(sp3)−H and
carboxylic acids by using Cu, Ni, Pd, Ag and Zn TECP complex
(
Scheme 2) as the catalysts. Preliminary results showed only
CuTECP exhibited high efficiency in the CDC esterification
reaction with very low catalyst concentration (0.5 mol %) and
much less reaction time (4 h, the highest yield up to 92%).
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O
O
Table 1. Selected bond distances and bond angels for CuTECP
Bond distances (Å)
N1‒Cu11
O1A‒Cu11
2.011(2)
N2‒Cu11
2.027(2)
N
N
O
O
O1B‒Cu11
2.06071(18)
O
O
2.6071(18)
M
Bond angels (deg)
N1‒Cu1‒N11
N2‒Cu1‒N11
N21‒Cu1‒N1
O1A‒Cu1‒O1B
180.0
90.52(8)
90.52(8)
180.0
N21‒Cu1‒N11
N2‒Cu1‒N1
N21‒Cu1‒N2
89.48(8)
89.48(8)
180.0
N
N
O
O
M = Ni, NiTECP M = Cu, CuTECP
M = Pd, PdTECP M = Ag, AgTECP
M = Zn, ZnTECP
11-X, 2-Y, -Z
Scheme 2. Molecule structure of metal TECP
Results and discussion
Crystal structure of CuTECP
The X-ray diffraction analysis reveals that the structure of
CuTECP crystallizes in the P-1 space group of the triclinic
system with one formula unit in a cell, no solvent molecule. All
crystallographically independent atoms are in general
positions with exception of the Cu atom, which lies on the
crystallographic center of inversion. The 24-membered
macrocyclic core of the porphyrin is coplanar, and the
displacement of each atom in the equatorial mean plane is
within 0.0311 Å. The six-coordinated copper atom is located
at the center of this almost perfectly planar porphyrin
macrocycle and bonded to four nitrogen and two oxygen
atoms to construct an octahedron (Figure 1). The Cu–N bond
lengths range from 2.011(2) to 2.027(2) Å with an average
value of 2.019(2) Å (Table 1), which is analogous to that found
in the literature.35 There are weak interactions between the
carbonyl oxygen atom and the Cu centre with a distance of
2.6071(19) Å, which is comparable to those found for related
weak Cu-O interactions.35 The axial two oxygen atoms (O1A
and O1B) site the opposite position of the copper atom Cu1,
the angle of O1A-Cu1-O1B is 180°.
Figure 2. 1D chain polymer connected by Cu-O interactions
Figure 3. Packing diagram of CuTECP with the dashed lines representing
hydrogen-bonding
Based on the above description, we have considered that
CuTECP forms one-dimensional long-chain structure through
weak intermolecular Cu-O interactions
(Figure 2). This
observation was comparable to our preview reported about
ZnTECP.33 The distance between two neighbouring CuTECP
planes is 3.3867 Å with a plane dihedral angle of 0°. There is a
partial overlap between the two adjacent CuTECP planes,
indicating the existence of π-π stacking interactions.
In addition to the above description, hydrogen bonding is also
an important aspect for constructed formation 3D
supramolecular network. There are two hydrogen-bonding
interactions among the molecules of CuTECP (Figure 3). One
hydrogen bond formed by methylene hydrogen and carbonyl
oxygen atom between two adjacent copper porphyrin moieties
between two coordination polymer chains and the other one
formed between pyrrole hydrogen atom of one polymer chain
and coordinated carbonyl oxygen atom of another polymer
chain.
Cross-dehydrogenative coupling
The optimization of reaction conditions was initiated by
examining the coupling of benzoic acid (
in the presence of CuTECP and DTBP at 120
product isolated detected to be -acyloxy ether (1a). When the
1) with 1,4-dioxane (
a)
°C (Scheme 3). The
α
concentration of CuTECP was 0.1 mol % (vs benzoic acid), 1a
was obtained with an isolated yield of 72% (Table 2, entry 1).
When the concentration of CuTECP increased to 0.5 mol %, the
yield of 1a increased up to 80% (Table 2, entry 2). With the
Figure 1. ORTEP plots of CuTECP (showing 50% probability thermal displacement
ellipsoids, hydrogen atoms omitted for clarity)
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further increase in the concentration of CuTECP to 1.0 mol %,
nearly no improvement of the 1a yield could be observed (81%;
Table 2, entry 3). Significant decrease in the yield of 1a was
observed with 3 or 4 equiv of DTBP (Table 2, entry 4 and 5),
this may be due to oxidative decomposition of the catalyst. To
further confirm this, stability study was carried out. The
catalyst solution at different concentration(0.1 mol %, 0.5 mol %
and 1.0 mol %, vs 0.5 mmol) were incubated with the same
amount DTBP (1.0 mmol) at 120 °C for 5 min to check the
catalyst decomposition and the results are showed in Figure
S1-S3 (Supporting Information). When the catalyst amount of
CuTECP less than 0.1 mol % (vs 0.5 mmol), it would undergoes
Scheme 3. The CDC esterificaꢀon of C−H adjacent to an oxygen atom for the synthesis
of α-acyloxy ethers
CuTECP (0.5 mol %)
DTBP (2 equiv)
O
O
O
Ar COOH
+
O
120 oC, 4 h
Ar
O
O
2-20
a
2a-20a
O
O
O
O
O
OMe O
O
MeO
O
O
O
O
O
O
a
complete oxidative degradation. When the catalyst
MeO
MeO
concentration were more than 0.5 mol % (vs 0.5 mmol), after
reaction there are still significant amount of catalyst as
indicated by UV-Vis spectra. Also, the colour of solution would
change from red to green. The green compound might be the
hydroxyporphyrin or polypyrrole derivatives formed by
oxidation of catalyst itself.36-38 Among other tested normal
oxidants such as TBHP (70% in H2O), PhIO, m-CPBA, H2O2 (30%
in H2O) and PhI(OAc)2 (Table 2, entry 6-9), only TBHP worked
with a low yield of 1a (28%, Table 1, entry 6). We carried out
the reaction using Ni, Pd, Ag and Zn TTECP complexes as
catalysts under same reaction conditions, only traces of 1a
were detected (Table 2, entry 10-13). When cupric acetate
monohydrate used as catalyst, obtained a moderate yield of 1a
(57%, Table 2, entry 14). Furthermore, the reaction could not
proceed without the use of CuTECP catalyst or DTBP oxidant
2a 92%
OMe O
3a 89%
OMe O
4a 83%
O
OMe O
O
O
O
O
O
O
O
OMe
MeO
OMe
7a 84%
5a 72%
6a 60%
O
O
O
O
O
O
O
O
O
O
O
O
O
9a 81%
10a 74%
8a 84%
O
O
O
O
O
O
O
O
O
O
O
F
Br
13a 68%
12a 79%
11a 78%
O
O
O
O
O
O
O
O
O
O
O
O
O
O2N
NC
F3C
16a N.D.
15a 34%
(
Table 2, entry 15 and 16).
14a 72%
O
O
O
O
O
O
Table 2. Optimization of reaction conditionsa
N
O
O
O
H
O
O
O
O
entry
1
catalyst (mol %)
CuTECP (0.1)
CuTECP (0.5)
CuTECP (1.0)
CuTECP (0.5)
CuTECP (0.5)
CuTECP (0.5)
CuTECP (0.5)
CuTECP (0.5)
CuTECP (0.5)
NiTECP (0.5)
PdTECP (0.5)
AgTECP (0.5)
ZnTECP (0.5)
Cu(OAc)2·H2O (0.5)
CuTECP (0.5)
oxidant (equiv)
DTBP (2.0)
DTBP (2.0)
DTBP (2.0)
DTBP (3.0)
DTBP (4.0)
TBHP (2.0)
m-CPBA (2.0)
H2O2 (2.0)
yield, %b
72
17a 64%
18a 27%
19a 80%
O
O
O
O
O
2
80
O
(cinnamic acid)
O
O
3
81
O
O
O
4
74
22a 31%
21a N.D.
20a 35%
5
62
Scheme 4. Coupling of 1,4-dioxane with substituted benzoic acids. Isolated yield
based on carboxylic acid.
6
28
7
N.D.
N.D.
N.D.
trace
trace
trace
trace
57
With the optimized reaction conditions (Table 2, entry 2),
subsequently we explored the benzoic acid scope of this
CuTECP-catalyzed CDC esterification reaction. Notably, the acid
reagents may not be consumed completely due to their
different reactivity within the same reaction time frame here.
As shown in Scheme 4, the reaction has a broad scope of
benzoic acid derivatives bearing different groups such as
methoxy, methyl, tert-butyl, phenyl, fluoro and bromo, giving
8
9
PhI(OAc)2 (2.0)
DTBP (2.0)
DTBP (2.0)
DTBP (2.0)
DTBP (2.0)
DTBP (2.0)
10
11
12
13
14
15
16
N.D.
N.D.
DTBP (2.0)
good to excellent yields of 60−92% (2a-13a). All of ortho-,
aReaction condition: benzoic acid (0.5 mmol), 1,4-dioxane (1 mL), catalyst,
meta-, and para-substituted benzoic acids could work in this
system. Slightly lower yields were observed in the case of
ortho-substituted benzoic acids in comparison to their para
b
oxidant, 120 °C, 4 h. Isolated yield based on carboxylic acid. DTBP = di-tert-butyl
peroxide. TBHP
= tert-butyl hydroperoxide (70% in H2O). m-CPBA = 3-
chloroperbenzoic acid. H2O2 (30% in H2O). PhI(OAc)2 = iodosobenzene diacetate.
and meta analogues, possibly due to steric hindrance (2a-4a,
9a and 10a). Variation of substituents on the aromatic ring
showed obvious effects on the reaction efficiency. The
reaction with benzoic acids substituted with a 4-methoxy
group afforded the expected product with an excellent yield
(
2a, 92%). The electronic effect of the substituents has no
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significant influence on the yield of product, as it observed olefination of cyclohexane occurs first followed by the
from the good yield of 12a (79%) bearing fluorine group. On construction of an allylic ester C−O bond or a reverse sequence
the other hand, 4-bromobenzoic acid substrate just afforded operates. To reveal the exact sequence, two independent
the corresponding product 13a with 68% yield. It was observed reactions carried out. When using cyclohexene as substrate, it
that the presence of 4-trifluoromethyl and 4-cyano in the gave 2f smoothly. While when a presynthesized intermediate
carboxylic acid substrate could also afforded the expected cyclohexyl 4-methoxybenzoate was further treated under the
product 14a (72%) and 15a (34%) smoothly. Thus, nitro- reaction conditions (Scheme S1, see Supporting Information),
benzoic acid could not afford the expected product (16a
)
it failed to give 2f. This indicated that the dehydrogenative
perhaps due to its electronic effect. Similar results also olefination of cyclohexane occurs before the formation of
observed for the previously reported transition metal- allylic ester C−O bond. Similar phenomenon had also been
catalyzed CDC reactions.24, 25. This is quite different from non- observed previously.18
metal catalyzed CDC reaction in which nitro-substituted
aromatic acid could still give good yield of product.26
CuTECP (0.5 mol %)
DTBP (2 equiv)
O
O
O
+
MeO
MeO
H Sub.
Disubstituted and trisubstituted benzoic acids also worked well
in the reaction and gave the desired products (5a 7a).
120 oC, 4 h
R
OH
−
b-i
2
2b-2i
To prove the synthetic utility of the method, we had examined
other types of acid substrates for this oxidative esterification
reaction. Hydrocinnamic acid (17) and 3-phenoxypropanoic
acid (19) worked well and gave the corresponding product 17a
and 19a with 64% and 80% yield respectively. This indicated
O
O
O
O
O
O
N
H
O
O
O
MeO
MeO
MeO
2c N.D.
2b 45%
2d N.D.
O
O
O
O
O
O
O
O
that fat acid might work in this reaction. Benzoylglycine (18
)
MeO
MeO
MeO
gave 18a with a significant lower yield (27%) due to the
2f 23%
2g 15%
2e N.D.
electronic effects. It is noteworthy that furan-3-carboxylic acid
(
21) even gave no detectable product. This may be due to
O
O
O
MeO
O
O
coordination interaction between copper central metal and
furan oxygen, which reducing the catalyst activity. This maybe
proved by IR spectra of stoichiometric mixture of 21 and
CuTECP (Figure S4, see Supporting Information). In far-infrared
wavelength number area, axial Cu-O (552 cm-1) coordination
O
MeO
2h
2i
N.D.
N.D.
Scheme 5. Copper porphyrin-catalyzed CDC esterification of other C(sp3)−H substrates
with p-anisic acid. Isolated yield based on p-anisic acid.
bond vibration could be observed clearly.
A similar
observation had been reported by Chaudhuri et al.25 In
addition, 1-naphthoic acid (20) also gave much lower yield
(35%) of product 20a. When cinnamic acid (22) used as
substrate, decarboxylative alkenylation of cyclic ether
observed. The reaction gave 31% yield of 22a as identified by
its 1H NMR and 13C NMR spectra. This is similar to the iron-
catalyzed alkenylation of cyclic ethers.16
After testing the CDC reaction with the symmetric 1,4-dioxane,
we tried to extend the substrate scope to the other C(sp3)−H
substrates (Scheme 5). Consistent with the literature,6 the
coupling of 4-methoxybenzoic acid and 1,3-dioxolane (b) gave
no expected product 1,3-dioxolan-2-yl 4-methoxybenzoate but
1,3-dioxolan-4-yl 4-methoxybenzoate (2b) in 45% yield, which
1
was identified by its H NMR and 13C NMR spectra. Thereafter,
the scope of this protocol was evaluated using other C(sp3)−H
substrates
methoxybenzoic acid. Disappointingly, tetrahydrofuran (
pyrrolidine ( ), tetrahydropyran ( ), toluene ( ), and 1,3-
benzodioxole ( ) did not react with 4-methoxylbenzoic acid
under the current conditions as indicated with no
corresponding product (2c 2e 2h and 2i) could be detected.
(
c
-
i
)
as the cross-coupling partners with 4-
c
),
Figure 4. The stability of CuTECP (reaction condition: p-anisic acid (0.5 mmol), 1,4-
dioxane (1 mL), CuTECP (0.5 mol %), DTBP (2.0 equiv), 120 °C, 4 h)
d
e
h
i
To check the catalytic performance, stability of CuTECP in the
reaction was investigated by using p-anisic acid with 1,4-
dioxane substrates. UV-Vis spectra showed CuTECP nearly
decomposed completely after the reaction (Figure 4). To
investigate the details of000 copper porphyrin-catalyzed CDC
esterification of ethers with carboxylic acids, a series of control
experiments performed. No desired product was detected
when free radical scavenger 2,2,6,6-tetramethylpyridine N-
-
,
Anisole coupled with 4-methoxybenzoic acid to afford the
corresponding product (2g) with 15% yield. Interestingly, the
protocol was also successful for the esterification of
cyclohexane with 23% yield of 2f. The 2f is an olefinated
coupling product. When cyclohexane reacted with aromatic
acids, one may wonder whether the dehydrogenative
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oxide (TEMPO) or butylated hydroxytoluene (BHT) was added anhydrous sodium sulphate. Solvents removed in a rotary
to the reaction system. When p-anisic acid ( ) reacted with an evaporator under reduced pressure. Silica gel (100–200 mesh
equimolar mixture of 1,4-dioxane and 1,4-dioxane-d8 (Scheme size) used for the column chromatography. UV-Visible
2
6
), a significant kinetic isotope effect (KIE) was observed with absorption spectra measured on Hitachi 3900H in 1 cm optical
kH/kD = 2 (the KIE was determined by 1H NMR spectroscopy by path length quartz cell at room temperature. NMR spectra
analyzing the ratio of 1a and [D]1a). This indicates that were recorded in CDCl3 with tetramethylsilane as the internal
C(sp3)−H bond cleavage was involved in the rate-determining standard for H NMR (400 MHz) CDCl3 solvent as the internal
step, which is similar to previously published results.24
1
standard for 13C NMR (100 and 150 MHz). HR‒MS spectra
recorded on Bruker maxis impact mass spectrometer with an
ESI source.
Synthetic procedures
The synthesis of 5,10,15,20-tetrakis(ethoxycarbonyl)porphyrin
ligand
(TECP)
and
5,10,15,20-
tetrakis(ethoxycarbonyl)porphyrin Zinc(II) (ZnTECP) were
performed by our recently reported procedure33. The
metalloporphyrin
5,10,15,20-
(NiTECP),
Scheme 6. KIE studies
tetrakis(ethoxycarbonyl)porphyrin
nickel(II)
5,10,15,20-tetrakis(ethoxycarbonyl)porphyrin
palladium(II)
(PdTECP),
copper(II)
5,10,15,20-tetrakis(ethoxycarbonyl)porphyrin
(CuTECP) and 5,10,15,20-
tetrakis(ethoxycarbonyl)porphyrin Silver(II) (AgTECP) were
prepared using literature procedures39.
Synthesis of NiTECP: NiTECP was obtained by refluxing TECP with
Ni(OAc)2•4H2O in DMF solution for 2 h. Then it was diluted with
CH2Cl2 and washed with saturated aqueous solution of NaCl several
times. The organic layer was collected and dried over anhydrous
Na2SO4. The filtrate was concentrated and the crude product was
purified on silica gel (100‒200 mesh) using CH2Cl2 as eluent. Purple
crystal obtained after slow evaporation from CH2Cl2/hexane (1:4
v/v). Yield: 90%. 1H NMR (400 MHz, CDCl3) δ 9.39 (s, 8H), 4.90 (q, J =
6.9 Hz, 8H), 1.66 (t, J = 7.0 Hz, 12H). 13C NMR (150 MHz, CDCl3) δ
Scheme
7. Proposed mechanism of copper porphyrin catalyzed CDC 169.36, 141.08, 133.26, 110.07, 63.04, 14.57. HR‒MS calcd for
[M+H]+: C32H29N4NiO8 655.1333, found 655.1334.
esterification reaction
Synthesis of PdTECP: PdTECP was synthesized similar to the
procedure of NiTECP, except Pd(OAc)2 was used instead of
Ni(OAc)2•4H2O. Yield: 70%. 1H NMR (400 MHz, CDCl3) δ 9.45 (s,
8H), 5.09 (q, J = 7.1 Hz, 8H), 1.79 (t, J = 7.1 Hz, 12H). 13C NMR
(150 MHz, CDCl3) δ 170.16, 139.91, 131.29, 113.86, 63.43,
14.73. HR‒MS calcd for [M+H]+: C32H29N4O8Pd 703.1027, found
703.1020.
Combined with these observations and previous reports,18, 24
a
plausible mechanism for present copper porphyrin catalyzed
CDC esterification reaction might be depicted as Scheme 7
.
The reaction is likely to be initiated by Cu(II)-mediated
decomposition of DTBP to form tert-butyloxy radicals. The
abstraction of an α ethereal hydrogen from dioxane by tert-
butyloxy radical gives the radical intermediate
coupling of and leads to the formation of ester. When
cyclohexane was used as C(sp3)−H substrate, olefinaꢀon
happened followed by the formation of cyclohexene radical
the coupling of with leads to formation of product. The
(A). The
Synthesis of CuTECP: CuTECP was synthesized similar to the
A
C
procedure of NiTECP, except Cu(OAc)2•H2O was used instead of
Ni(OAc)2•4H2O. Yield: 92%. HR‒MS calcd for [M+H]+: C32H29CuN4O8
660.1276, found 660.1276.
B,
B
C
Synthesis of AgTECP: AgTECP was synthesized similar to the
procedure of NiTECP, except AgNO3 was used instead of
Ni(OAc)2•4H2O. Yield: 85%. HR‒MS calcd for [M+H]+: C32H29AgN4O8
704.1031, found 704.1038.
possible pathway for the cross-decarboxylative coupling
reaction shown at the lower side of Scheme 7. The 1,4-dioxane
radical attacks C-C double bond followed by the elimination of
carboxyl group to give the product.
Crystallography
Single-crystal X-ray diffraction data recorded on a Rigaku R-
AXIS SPIDER IP diffractometer with Cu Kα radiation using a ω
scan technique. The crystal kept at 150 K during data
collection. Using Olex240, the structure was solved with the
olex2.solve41 structure solution program using Charge Flipping
Experimental
Materials and methods
All the reagents were commercial grade and purified according
to the established procedures. Organic extracts dried over
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and refined with the olex2.refine41 refinement package using metal porphyrin-catalyzed C−O and C−C bond formaꢀon CDC
Gauss-Newton minimisation. All atoms except for hydrogen reactions are currently going on in our laboratory.
atoms were refined anisotropically.
Crystallographic description of CuTECP
660.14 g/mol), triclinic, space group P-1, a = 6.4200(5) Å, b =
8.6707(7) Å, c = 12.9072(10) Å, α = 85.111(7)°, β =
: C32H28CuN4O8 (M =
Acknowledgements
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (Nos. 21371059;
21671068)
88.215(6)°, γ = 83.692(6)°, V = 711.37(10) Å3, Z = 2, T = 150 K,
μ = 1.615 mm-1, ρcalc = 1.5408 g/cm3, F(000) = 340.1, 6928
reflections measured (11.92° ≤ 2θ ≤ 125.02°), 2249 unique
(Rint = 0.0440, Rsigma = 0.0416) which used in all calculations.
The final R1 was 0.0402 (I>=2σ (I)) and wR2 was 0.1343 (all
data). CCDC 1504785 for compound CuTECP contains the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
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O
O
O
O
O
O
DTBP, CuTECP(0.5 mol %)
120 °C, 4 h
O
N
N
N
OH
O
O
+
O
O
O
Cu
O
N
R
R
20 examples
Up to 92% yield
O
O
Copper porphyrin was an efficient catalyst for the direct esterification of C(sp3)−H bond using DTBP as oxidant.
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