Palladium-Catalyzed Reductive Cross-Coupling Reaction of Aryl Chromium(0) Fischer Carbene Complexes with Aryl Iodides

Article abstract of DOI:10.1021/acs.organomet.7b00657

The first palladium-catalyzed reductive cross-couplings of aryl chromium(0) carbene complexes with aryl iodides have been realized. This coupling reaction shows excellent functional group tolerance and high efficiency. Mechanistically, aryl chromium(0) carbene complexes undergo transmetalation with arylpalladium species to generate palladium(II) carbene intermediates, which is followed by migratory insertion. The catalytic cycle is then completed by hydrogen transfer and reductive elimination. Consistent with the mechanistic hypothesis, density functional theory (DFT) calculations support the involvement of a palladium carbene intermediate, and carbene migratory insertion is a facile step with an energy barrier of 5.1 kcal/mol. The carbene transfer step and the hydrogen transfer step are confirmed as the rate-limiting steps in the catalytic cycle.

Full text of DOI:10.1021/acs.organomet.7b00657

Article
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Cite This: Organometallics XXXX, XXX, XXX-XXX
Palladium-Catalyzed Reductive Cross-Coupling Reaction of Aryl
Chromium(0) Fischer Carbene Complexes with Aryl Iodides
Kang Wang,† Yu Lu,‡ Fangdong Hu,† Jinghui Yang,† Yan Zhang,† Zhi-Xiang Wang,*,‡
and Jianbo Wang*,†
†Beijing National Laboratory of Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering
of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, People’s Republic of China
‡School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049,
People’s Republic of China
S
* Supporting Information
ABSTRACT: The first palladium-catalyzed reductive cross-couplings of
aryl chromium(0) carbene complexes with aryl iodides have been realized.
This coupling reaction shows excellent functional group tolerance and high
efficiency. Mechanistically, aryl chromium(0) carbene complexes undergo
transmetalation with arylpalladium species to generate palladium(II) carbene
intermediates, which is followed by migratory insertion. The catalytic cycle is
then completed by hydrogen transfer and reductive elimination. Consistent
with the mechanistic hypothesis, density functional theory (DFT) calcu-
lations support the involvement of a palladium carbene intermediate, and
carbene migratory insertion is a facile step with an energy barrier of 5.1 kcal/mol. The carbene transfer step and the hydrogen
transfer step are confirmed as the rate-limiting steps in the catalytic cycle.
Scheme 1. Pd-Catalyzed Reaction of Chromium(0) Fischer
Carbene Complexes through Carbene Transfer
INTRODUCTION
■
Group 6 Fischer carbene complexes, as represented by
chromium(0) Fischer carbenes, have been extensively studied
over the decades, and they have been proven to be valuable in
organic chemistry.1 In general, the metal carbonyl fragments of
these complexes can be viewed as functional groups to activate
the carbenic carbon to an electrophilic center, similar to the
case for a carbon in a carbonyl group.2 The chromium(0)
Fischer carbene complexes react with both nucleophiles and
electrophiles or undergo cycloaddition reactions with alkenes or
alkynes to form cyclic compounds.3,4 These transformations
have found wide applications in synthetic organic chemistry due
to the versatile chemical properties of the group 6 Fischer
carbene complexes.
More importantly, the transfer of carbene ligands from the
group 6 Fischer carbene complexes to other transition-metal
centers, in particular the late transition metals, can generate
new carbene complexes and thus significantly alter the chemical
behavior of Fischer carbene complexes. Traditionally, the car-
bene ligand transfer from group 6 metals to other stoichio-
metric transition metal species has been known for a long time.5
The seminal work by Sierra and co-workers on palladium-
catalyzed self-dimerization of chromium(0) carbene complexes
demonstrated potential applications of catalytic carbene trans-
fer reactions with catalytic amounts of palladium catalyst.6,7 Pre-
vious experimental and mechanistic investigations have revealed
that Pd(0) catalysts are highly efficient in catalyzing carbene
transfer processes. As shown in Scheme 1a, the carbene ligand
of Cr(0) carbene complexes undergoes two sequential trans-
metalations to the palladium(0) catalyst via dimetallacyclopropane
intermediate A. The final dimerization product is formed through
reductive elimination of a Pd(0) bis-carbene species.
Carbene transfer processes of chromium(0) Fischer carbene
complexes are also known for other transition-metal catalysts,
such as copper,8 nickel,9 rhodium,10 and gold,11 allowing for the
efficient construction of various structures. However, in con-
trast to the rich chemical properties of chromium(0) Fischer
carbene complexes, the scope of transformations based on
metal-catalyzed carbene transfer processes is still rather limited.
Received: August 30, 2017
© XXXX American Chemical Society
A
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a
To the best of our knowledge, the catalytic cross-coupling
reaction of chromium(0) Fischer carbene complexes with other
cross-coupling partners based on a transition-metal-catalyzed car-
bene transfer process has not yet been extensively explored.12,14j,k
We and others have recently developed the transition-metal-
catalyzed cross-coupling reaction of metal carbene species through
migratory insertion, which has been demonstrated to be a
powerful strategy for C−C bond formation (Scheme 1b).13,14
Both stable diazo compounds and nonstabilized diazo com-
pounds generated in situ from N-tosyl hydrazones have been
utilized as carbene precursors in these transformations. In the
reaction mechanism, the palladium carbene species B under-
goes migratory insertion to generate a C−C bond, followed by
various reactions. These types of coupling reactions are quite
general, and a series of cross-couplings under transition-metal
catalysis, especially under palladium catalysis, has been estab-
lished.
Table 1. Optimization of the Reaction Conditions
base
(equiv)
R3SiH
(equiv)
yield
b
entry 1a:2a
solvent
T (°C)
(%)
1
2
3
4
5
6
7
8
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
Et3N (2)
Et3N (2)
Et3N (2)
Et3N (2)
Et3N (2)
Et3N (2)
Et3N (2)
Et3N (2)
DCE
THF
PhMe
Et3SiH (1.2)
Et3SiH (1.2)
Et3SiH (1.2)
80
80
80
80
70
90
70
70
31
15
28
5
dioxane Et3SiH (1.2)
DCE
DCE
DCE
DCE
Et3SiH (1.2)
Et3SiH (1.2)
Et3SiH (2.0)
38
33
45
64
Ph2MeSiH
(2.0)
In connection to our interest in catalytic carbene-coupling
transformations, we envisioned the possibility of using chro-
mium(0) carbene complexes as metal carbene precursors in
transition-metal-catalyzed carbene cross-coupling involving
migratory insertion (Scheme 1c). Thus, a chromium(0) Fischer
carbene complex is expected to undergo carbene transfer with
the aryl palladium(II) intermediate C to form Pd(II) carbene
intermediate D, which then undergoes migratory insertion
to afford cross-coupling products. The realization of such a
transformation should significantly expand the realm of catalytic
carbene transfer reactions of Fischer carbene complexes as well
as carbene-based coupling reactions. We have recently reported
the palladium-catalyzed coupling of vinyl chromium(0) car-
benes with 2-iodophenols and 2-iodoanilines proceeding via
a carbene transfer process.14j Herein we further report our
experimental and mechanistic study on palladium-catalyzed
reductive coupling of aryl iodides with aryl chromium(0)
carbenes along the migratory insertion coupling reaction.
A detailed mechanistic study by density functional theory
(DFT) calculations supports the involvement of palladium-
(II) carbene as the reactive intermediate, which undergoes a
facile migratory insertion step with a very low energy barrier
(5.1 kcal/mol).
9
1.5:1 BnMe2N
(2)
DCE
DCE
DCE
DCE
DCE
Ph2MeSiH
(2.0)
70
70
70
70
70
76
12
15
0
10
11
12
13
1.5:1 Et2NH (2)
Ph2MeSiH
(2.0)
1.5:1
Ph2MeSiH
(2.0)
1.5:1 BnMe2N
(2)
c
1.5:1 Et2NH (2)
Ph2MeSiD
(2.0)
72
a
If not otherwise noted, reaction conditions are as follows: 1a
(0.10 mmol), 2a (0.10 mmol), Pd(PPh3)4 (5 mol %), Et3N (2 equiv),
and Et3SiH (1.2 equiv) in a solvent stirred at 80 °C for 5 h. The yields
refer to the products isolated by silica gel column chromatography.
b
c
1
>99 atom % D was observed in the H NMR spectrum.
decreased yields without amine (entry 11) and that no reductive
product was obtained in the absence of phenylmethylsilane
(entry 12). The deuterated product 3a (>99% D) was isolated
in 72% yield (entry 13), suggesting that diphenylmethylsilane
served as the hydride source in the catalytic cycle. According to
these control experiments, we could presume that the reductive
coupling reaction could be promoted in the presence of amine,
probably due to its coordination to dissociated Cr(CO)5 to
accelerate the carbene transfer process.12d
Under the same reaction conditions, the scope of this trans-
formation was first explored by using various aryl chromium(0)
carbene complexes 1a−p (Scheme 2). We found that the reac-
tion shows an obvious dependence on the electronic properties
of the substituents on the para position. The reactions with
substrates bearing electron-donating groups, such as a methoxy
group (3b), methyl group (3c) could give higher yields in
comparison to those with electron-withdrawing substituents,
chloro group (3e), fluoro group (3f), and trifluoromethyl group
(3g). The reactions with the substrates bearing meta and ortho
substituents gave the products in moderate yields (3h−k). The
reactions with carbene substrates bearing a naphthyl group (3l),
furyl group (3m), and thienyl group (3n) also proceeded
smoothly to afford the coupling products. Finally, the reactions
with chromium(0) carbenes bearing ethoxyl and benzyloxy
groups afforded the corresponding products 3o,p in 77% and
64% yields, respectively.
RESULTS AND DISCUSSION
■
Reaction Optimization and Scope. At the outset, the
complex pentacarbonyl (methoxy)(phenyl)carbene chromi-
um(0) (1a) was selected as a model compound to react with
biphenyl iodide (2a) with Et3SiH as the reductant. We were
delighted to find that, in the presence of 5 mol % Pd(PPh3)4
and 2 equiv of Et3N, the expected product 4-(methoxy-
(phenyl)methyl)-1,1′-biphenyl (3a) could be isolated in 31%
yield (Table 1, entry 1). To optimize the reaction conditions, a
series of solvents were then tested with Pd(PPh3)4 as the
catalyst (entries 2−4); however, the best result was observed
from the reaction run in 1,2-dichloroethane (DCE) solvent
(entry 1). Slightly improved results could be obtained by carry-
ing out the reaction at lower temperature and with increased
loading of the reductant Et3SiH (entries 5−7). Furthermore,
diphenylmethylsilane was found to be a better reductant than
Et3SiH, which could give the product in 64% yield (entry 8).
Finally, by screening the amine bases and adjusting the sub-
strate ratio, the reaction could be further improved to afford the
product in 76% yield (entry 9). We also carried out control
experiments to test the roles of both amines and silanes. These
showed that the reductive product could be obtained in
Next, the scope of aryl iodides was investigated (Scheme 3).
A series of aryl iodides 2b−l bearing both electron-withdrawing
and electron-donating groups were found to be compatible with
this protocol. Functional groups, such as a methyloxycarbonyl
group (4c), cyano group (4d), and carbonyl groups (4e,f), are
B
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Scheme 2. Scope of Aryl Chromium(0) Carbene Complexes
in Pd-Catalyzed Reductive Coupling with Aryl Iodide
Scheme 4. Proposed Possible Pathways
a
a
Reaction conditions: 1a−p (0.30 mmol), 2a (0.20 mmol), Pd(PPh3)4
(5 mol %), Me2BnN (2 equiv) and Ph2MeSiH (2 equiv) stirred at
70 °C for 5 h. All of the yields refer to the products isolated with silica
gel column chromatography.
intermediate C undergoes a migratory insertion step to afford
the alkyl palladium species D.15 Ligand exchange with hydro-
silane16 and subsequent reductive elimination afford the final
product F and regenerate the Pd(0) catalytic species A.
An alternative mechanism is also possible (Scheme 4, path b).
The nucleophilic attack of Ph2MeSiH to the chromium carbene
complex generates the alkyl chromium species G.17 This then
undergoes transmetalation with the aryl palladium species B to
afford palladium species H. Finally, reductive elimination of H
produces the product F and releases the Pd(0) species for the
next catalytic cycle.
Scheme 3. Scope of Aryl Iodides in Pd-Catalyzed Reductive
Coupling Reactions with a Phenyl Chromium(0) Carbene
Complex
a
To identify which mechanism in Scheme 4 is more reason-
able, mechanistic experiments were carried out (Scheme 5).
Benzyl bromide (5a) and phenyl chromium(0) carbene 1a
were employed as the substrates (Scheme 5a). We reasoned
Scheme 5. Mechanistic Experiments
a
Reaction conditions: 1a (0.30 mmol), 2b−l (0.20 mmol), Pd(PPh3)4
(5 mol %), Me2BnN (2 equiv) and Ph2MeSiH (2 equiv) stirred at
70 °C for 5 h. All of the yields refer to the products isolated by silica
gel column chromatography.
tolerated, and the reactions afford the desired products in excel-
lent yields. Moreover, a naphthyl group (4i), thienyl group (4j),
and dibenzofuranyl group (4k) also tolerate the reaction condi-
tions to give the corresponding coupling products in good yields.
Mechanistic Considerations. We speculated that this
reductive coupling reaction may proceed by two different mech-
anisms. The first possible mechanism involves the palladium
carbene intermediate as we originally proposed (Scheme 4,
path a). Thus, upon oxidative addition of catalytic palladium(0)
species A to aryl iodide, the generated aryl palladium species B
reacts with phenyl chromium(0) carbene to give the Pd car-
bene intermediate C through carbene transfer. The carbene
C
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that if 1a reacts with the benzyl palladium species to generate a
Pd carbene (path a), subsequent β-hydride elimination would
produce the vinyl ether products; however, if the reaction
proceeds through path b, there should be no intermediate
leading to the formation of β-H elimination vinyl ether prod-
ucts. Indeed, we could observe a 7% yield of the vinyl ether
products with a 2.7:1 Z:E isomer ratio, together with large
amounts of self-dimerization products (Scheme 5a, condition A).
Changing the base from Me2BnN to K2CO3, we could obtain
the vinyl ethers in slightly improved yield (Scheme 5a, condi-
tion B). In both cases, the product 6c which should be formed
through path b was not observed.
Moreover, the benzyl bromide palladium species 5b was able
to react with phenyl chromium(0) carbene 1a (Scheme 5b).
The reaction gives the vinyl ethers in excellent yields with the
same 2.7:1 Z:E ratio, which further confirms the formation of
Pd carbene intermediate C and the migratory insertion/β-H
elimination mechanism (i.e., path a). Thus, all of the experi-
mental observations seem to support the assumption that this
coupling reaction undergoes the Pd(II) carbene pathway.
During the reaction scope study, significant electronic effects
of the substituents of the chromium(0) carbene species were
observed. Since such information should provide valuable insights
into the reaction mechanism, we then proceeded to study the
electronic effects of the reaction in detail with a Hammett
linear free energy correlation (Scheme 6). Thus, the relative
rate constants were measured over a range of aryl chromium(0)
carbene species bearing para substituents on the aromatic ring.
The Hammett correlation analysis of the data showed a nega-
tive reaction constant with a substantially large value (ρ = −2.93).
This substantial negative ρ value indicates that there should be
a significantly positive charge buildup at the carbenic carbon of
the chromium carbene during the reaction process.
This Hammett correlation result is consistent with the mech-
anism involving path a as shown in Scheme 4, in which the
Cr(0) carbene reacts with the aryl palladium(II) intermediate
via a carbene transfer reaction to form Pd(II) carbene inter-
mediate C. In this process, the carbenic ligand transfer from the
zerovalent chromium(0) center to a positively charged Pd(II)
species would make the carbenic carbon more electron defi-
cient. Thus, the electron-donating group on the aryl ring of
Cr(0) carbene should favor such a carbene transfer process.
Moreover, because of the electron-accepting nature of the
carbene ligand of the Pd carbene intermediate according to
earlier studies by Sierra and co-workers,18 the increased elec-
tron density on the aryl ring would stabilize the Pd carbene
intermediate C. In the case of path b, the nucleophilic attack
of Ph2MeSiH to the chromium carbene complex should be
favored by electron-withdrawing substituents on the aromatic
ring, while the following transmetalation step might be less
significantly affected by the electronic substituents because
the aromatic ring is attached to an sp3 carbon. Overall, if the
reaction follows the mechanism of path b, the electronic effects
would be expected to be either opposite (a positive ρ value) or
trivial (a very small ρ value), which is in contradiction with the
experimental observation. Consequently, the Hammett corre-
lation experiment supports that the reaction more likely follows
the mechanism of path a.
Computational Study. To gain further insights into the
reaction mechanism, we performed a DFT mechanistic study
using Gaussian 0919,20 to locate the pathway of the representa-
tive reaction shown in Table 1. It has been reported that the
active catalyst in palladium-catalyzed C−C couplings was often
a monophosphine palladium species, when a bulky phosphine
ligand was applied.21−23 Accordingly, we used PdPPh3 as the
active catalyst in mechanistic computations. On the other hand,
we further considered the possibility of using a bis-phosphine
palladium complex as an active catalyst to mediate the reaction,
but it is unlikely, as detailed in Figure S5 in the Supporting
Information. In an analysis of our computed energetic results,
Scheme 7 sketches the catalytic cycle of the transformation,
Scheme 6. Electronic Effects of the Reaction: Hammett
Linear Free Energy Correlation Study
Scheme 7. Computationally Proposed Catalytic Cycle ([Si] =
SiPh2Me)
which comprises five steps: namely, oxidative addition (step 1),
carbene transfer (step 2), migratory insertion (step 3), hydro-
gen transfer (step 4), and reductive elimination (step 5).
Figure 1 shows the free energy profile for steps 1−3 of the
catalytic cycle, with the optimized geometries displayed in
D
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Figure S6 in the Supporting Information. The reaction begins
with the oxidative addition of biphenyl iodide (2a) to PdPPh3,
which could proceed via two possible pathways. Along the black
pathway, the iodide atom of 2a first binds to the Pd center of
PdPPh3, giving the intermediate IM1, followed by migration of
the biphenyl group to the Pd center via the transition state TS1,
leading to the addition intermediate IM2 with a broken C−I
bond. Alternatively, 2a first coordinates to the active catalyst,
resulting in the π complex IM1′, which then passes TS1′ to
break the C−I bond, giving IM2′. The trans effect between the
biphenylyl group and PPh3 ligand makes IM2′ 10.8 kcal/mol
less stable than IM2, but it can isomerize to IM2 easily with a
barrier of 5.5 kcal/mol (isoTS). On comparison of the two
pathways, the blue pathway is kinetically more favorable. Over-
all, the oxidative addition is thermodynamically favorable by
26.0 kcal/mol.
Subsequent to the oxidative addition, step 2 transfers the car-
bene moiety (Ph−C−OMe) of the Cr(0) Fischer carbene 1a to
the palladium center of IM2. To begin with, the formal CrC
bond of the Cr(0) carbene 1a coordinates to the Pd(II) center
of IM2 by crossing TS2, resulting in the dimetallacyclopropane
intermediate IM3.18 After the Cr(CO)5 moiety leaves from
IM3 via crossing a barrier of 6.4 kcal/mol (TS3), the inter-
mediate IM4 is formed. IM4 features palladium carbene
character with a PdC bond length of 1.991 Å, even shorter
than that (2.005 Å) in the X-ray structure of a well-recognized
palladium carbene complex.24 Previously, we have also char-
acterized the metal carbene character of similar palladium com-
plexes.21 Overall, relative to IM2, the carbene transfer over-
comes a barrier of 26.7 kcal/mol (TS3) and is slightly end-
ergonic by 2.3 kcal/mol. Note that the process from IM2 to
IM4 releases Cr(CO)5, which can be stabilized by forming the
complex 1p with the base Me2BnN. The formation of 1p drives
IM4 down by 10.6 kcal/mol; thus, the amine benefits the reac-
tion by stabilizing the unstable Cr(CO)5 moiety. The palladium
carbene IM4 is also not stable, easily undergoing migratory
insertion by striding a low barrier of 5.1 kcal/mol (TS4), giving
the 21.5 kcal/mol more stable intermediate IM5. The facile
migratory insertion of IM4 is consistent with our previous DFT
calculations for the palladium carbenes generated from different
precusors.21
The pathway for steps 4 and 5 of the catalytic cycle is shown
in Figure 2, with optimized structures included in Figure S7 in
the Supporting Information. Subsequent to the formation of
stable IM5, hydrosilane [Si]H ([Si] = SiPh2Me) reacts with
IM5. To deliver the product 3a, the hydrogen of [Si]H should
transfer to the carbene carbon of IM5 for depalladation.
We first considered a stepwise mechanism, proceeding via σ-bond
metathesis between Si−H and Pd−I bonds, followed by reduc-
tive elimination to form a C−H bond to produce 3a. A transi-
tion state (TS5′) describing the D to E process in path b
(Scheme 4) could be located, but the barrier (42.1 kcal/mol,
TS5′ relative to IM5) for the metathesis is obviously too high,
considering that the reaction could be performed at 70 °C.
Another pathway starting from IM4 was also found to be
unlikely (see Figure S8 in the Supporting Information). Instead,
a mechanism described by TS5 is much more favorable, TS5
being 14.3 kcal/mol lower than TS5′. As depicted by the opti-
mized structure of TS5, hydrogen transfer, depalladation, and
Pd−Si bond formation take place concertedly. The short Pd−H
distance (1.639 Å) indicates that the hydrogen transfer is facil-
itated by the Pd center. A similar mechanism has been reported
previously, but the favorability of the mechanism depends on
catalytic systems.25 Relative to IM5, the hydrogen transfer spans
a barrier of 27.9 kcal/mol and is exergonic by 16.2 kcal/mol.
After hydrogen transfer to deliver the product 3a, the result-
ing IM6 undergoes reductive elimination via TS6, followed
by dissociation to release [Si]I byproduct and regenerate
PdPPh3.When Figures 1 and 2 are combined, carbene transfer
with a barrier of 26.7 kcal/mol and hydrogen transfer with a
barrier of 27.9 kcal/mol are the rate-determining steps of the
transformation. The barriers are somewhat high but are in the
reasonable range, considering the fact that the transformations
were required to be run at elevated temperature.
Figure 1. Free energy profile for steps 1−3 of the catalytic cycle.
E
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Figure 2. Free energy profile for steps 4 and 5 of the catalytic cycle. The key bond length in the optimized structure of TS5 is given in angstroms,
and the trivial hydrogen atoms in TS5 are omitted for clarity.
were obtained on an Agilent 7890A/5975C instrument, and HRMS
were obtained on a Bruker APEX IV FTMS apparatus. All of the
starting materials were purchased and used without further purification
(PE, petroleum ether; EA, ethyl acetate). The chromium(0) Fischer
carbene complexes were prepared according to the literature proce-
dure: 2a,c,i,j,k;26a 2b,d−h;26b 2l,m;26c 2n;26d 2p,q.7d
With regard to path b in Scheme 4, we considered the sub-
process along the path: 1a + [Si]H → G + [Si]+ (Scheme 4,
path b). The step is endergonic by 32.2 kcal/mol, indicating
that it has a kinetic barrier at least higher than 32.2 kcal/mol,
which is higher than the rate-determining barrier of 27.9 kcal/mol
for path a. Therefore, the mechanism via path b can be ruled out.
Typical Experimental Procedure for the Pd-Catalyzed
Reductive Cross-Coupling Reactions of Aryl Iodides with
Aryl Chromium(0) Fischer Carbene Complexes. Aryl chromi-
um(0) carbene complex 1a (93.6 mg, 0.30 mmol), 4-biphenyl iodide
(2a) (56.0 mg, 0.20 mmol), and Pd(PPh3)4 (11.6 mg, 5 mol %) were
successively placed in a 10 mL Schlenk reaction flask. The reaction
flask was then degassed and charged with N2 three times, and 1,2-di-
chloroethane (2 mL) was introduced using a syringe. After that,
Me2BnN (30.1 μL, 2 equiv) and Ph2MeSiH (42.1 μL, 2 equiv) were
then added to the solution. The resulting solution was then stirred at
60 °C for 3 h. After completion of the reaction, the mixture was cooled
to room temperature, filtered through a short plug of silica gel, and
washed with the eluent (petroleum ether/EtOAc 30/1). Solvent was
then removed in vacuo to provide a crude mixture, which was purified
by silica gel column chromatography to afford the pure product.
4-(Methoxy(phenyl)methyl)-1,1′-biphenyl (3a):27 yield 76% (41.6 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
CONCLUSION
■
We have developed the first reductive cross-coupling of aryl
chromium(0) Fischer carbene complexes with aryl iodide using
hydrosilane as the hydrogen source. The implication of this
study is that aryl chromium(0) carbene complexes could be
considered as versatile Pd carbene precursors for catalytic cross-
coupling reactions through a migratory insertion step. The
computational studies support our original hypothesis that the
Pd carbene formation and its migratory insertion are involved
in this catalytic cycle. Furthermore, the DFT calculations fur-
ther confirm that carbene transfer and hydrogen transfer are the
rate-limiting steps of the catalytic cycle. This work should open
up new opportunities for palladium-catalyzed transformations
of chromium(0) Fischer carbenes based on Pd carbene migratory
insertion. Further exploration of the transition-metal-catalyzed
cross-coupling reactions of chromium(0) carbene complexes
are currently underway in our laboratories.
1
eluent, Rf = 0.40); white oil; H NMR (400 MHz, CDCl3) δ 3.41
(s, 3H), 5.28 (s, 1H), 7.26−7.28 (m, 1H), 7.32−7.36 (m, 3H),
7.38−7.43 (m, 6H), 7.53−7.57 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 57.1, 85.2, 127.0, 127.1, 127.2, 127.3, 127.6, 128.0 128.5,
128.8, 140.4, 140.9, 141.2, 142.0.
4-(Methoxy(phenyl)methyl)-1,1′-biphenyl (deuterated) (3a′):
yield 72% (41.6 mg, purified by silica gel column chromatography
using PE/EA 40/1 as eluent, Rf = 0.40); white oil; 1H NMR (400 MHz,
CDCl3) δ 3.41 (s, 3H), 7.25−7.26 (m, 1H), 7.32−7.36 (m, 3H),
7.38−7.43 (m, 6H), 7.54−7.57 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 57.1, 126.9, 127.1, 127.2, 127.3, 127.3, 127.6, 128.5, 128.8,
140.4, 140.9, 141.1, 142.0.
EXPERIMENTAL SECTION
■
General Information. All reactions were performed under a
nitrogen atmosphere in oven-dried reaction flasks. All solvents were
freshly distilled and degassed according to ref 31. The boiling point of
petroleum ether was between 60 and 70 °C. Commercially available
reagents were used as received. For chromatography, 200−300 mesh
silica gel (Qingdao, China) was used. 1H NMR spectra were recorded
on a Bruker ARX 400 spectrometer (400 MHz); 13C NMR spectra
were recorded on a Bruker ARX 400 spectrometer (100 MHz). The
data for NMR spectra are reported as follows: chemical shifts (δ)
are reported in ppm, and coupling constants (J) are in hertz (Hz).
IR spectra were recorded on a Nicolet 5MX-S infrared spectrometer and
are reported in terms of frequency of absorption (cm−1). Mass spectra
4-(Methoxy(4-methoxyphenyl)methyl)-1,1′-biphenyl (3b): yield
85% (51.7 mg, purified by silica gel column chromatography using
PE/EA 20/1 as eluent, Rf = 0.35); white oil; IR (film): 2926, 1937,
1
1510, 1454, 1244, 851, 734, 700 cm−1; H NMR (400 MHz, CDCl3)
δ 3.40 (s, 3H), 3.78 (s, 3H), 5.25 (s, 1H), 6.88 (d, J = 8.7 Hz, 2H),
7.29 (d, J = 8.8 Hz, 2H), 7.32−7.34 (m, 1H), 7.40−7.43 (m, 4H),
F
DOI: 10.1021/acs.organomet.7b00657
Organometallics XXXX, XXX, XXX−XXX

Organometallics
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7.54−7.58 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 55.3, 57.0, 84.8,
113.9, 127.1, 127.2, 127.2, 128.3, 128.7, 134.0, 134.2, 140.3, 140.9,
141.5, 159.1; HRMS (ESI) m/z calcd for C21H20O2Na (M + Na)+
327.1361, found 327.1356.
4-(Methoxy(2-methoxyphenyl)methyl)-1,1′-biphenyl (3j): yield
51% (31.0 mg, purified by silica gel column chromatography using
PE/EA 20/1 as eluent, Rf = 0.35); white oil; IR (film): 2925, 2895,
1935, 1587, 1488, 1091, 757, 698 cm−1;1H NMR (400 MHz, CDCl3)
δ 3.41 (s, 3H), 3.82 (s, 3H), 5.73 (s, 1H), 6.86−6.88(m, 1H),
6.97−7.01 (m, 1H), 7.31−7.33 (m, 1H), 7.39−7.46 (m, 5H),
7.50−7.51 (m, 2H), 7.53−7.57 (m, 3H); 13C NMR (100 MHz,
CDCl3) δ 55.5, 57.1, 78.5, 110.6, 120.8, 126.8, 126.8, 126.9, 127.1,
127.4, 128.4, 128.7, 130.5, 140.0, 141.1, 141.2, 156.7; HRMS (ESI)
m/z calcd for C21H20O2Na (M + Na)+ 327.1356, found 327.1360.
4-(Methoxy(o-tolyl)methyl)-1,1′-biphenyl (3k): yield 55% (31.7 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
eluent, Rf = 0.45); white oi; IR (film): 2957, 2911, 1946, 1600, 1479,
4-(Methoxy(p-tolyl)methyl)-1,1′-biphenyl (3c): yield 90% (51.9 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
eluent, Rf = 0.40); white oil; IR (film): 2939, 2982, 1941, 1599, 1512,
1
1091, 800, 697 cm−1; H NMR (400 MHz, CDCl3) δ 2.31 (s, 3H),
3.38 (s, 3H), 5.24 (s, 1H), 7.14−7.22 (m, 2H), 7.25−7.27 (m, 2H),
7.28−7.31 (m, 1H), 7.37−7.41 (m, 4H), 7.52−7.56 (m, 4H); 13C
NMR (100 MHz, CDCl3) δ 21.2, 57.1, 85.1, 127.0, 127.1, 127.2, 127.3,
127.3, 128.8, 129.2, 137.3, 139.1, 140.3, 141.0, 141.5; HRMS (ESI)
m/z calcd for C21H20ONa (M + Na)+ 311.1406, found 311.1414.
4,4″-(Bethoxymethylene)di-1,1′-biphenyl (3d): yield 72% (50.5 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
eluent, Rf = 0.40); white solid; IR (film): 2952, 2926, 1939, 1593,
1
1179, 1080, 761, 693 cm−1; H NMR (400 MHz, CDCl3) δ 2.30,
(s, 3H), 3.41 (s, 3H), 5.45 (s, 1H), 7.18−7.20 (m, 1H), 7.32−7.48
(m, 8H), 7.53−7.57 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 19.5,
57.2, 82.4, 126.1, 126.8, 127.1, 127.3, 127.5, 128.0, 128.8, 130.6, 134.0,
135.9, 139.5, 140.0, 140.4, 140.9; HRMS (ESI) m/z calcd for
C21H20ONa (M + Na)+ 311.1406, found 311.1404.
1
1487, 1090, 759, 695 cm−1; H NMR (400 MHz, CDCl3) δ 3.44
(s, 3H), 5.33 (s, 1H), 7.30−7.34 (m, 2H), 7.39−7.41 (m, 3H),
7.43−7.46 (m, 5H), 7.56−7.58 (m, 8H); 13C NMR (100 MHz,
CDCl3) δ 57.2, 85.0, 127.1, 127.3, 127.4, 128.8, 130.1, 140.5, 140.9,
141.1; HRMS (ESI) m/z calcd for C26H22ONa (M + Na)+ 373.1563,
found 373.1568.
4-((4-Chlorophenyl)(methoxy)methyl)-1,1′-biphenyl (3e): yield
62% (38.2 mg, purified by silica gel column chromatography using
PE/EA 40/1 as eluent, Rf = 0.40); yellow oil; IR (film): 2957, 2918,
1940, 1593, 1487, 1089, 763, 697 cm−1; 1H NMR (400 MHz, CDCl3)
δ 3.39 (s, 3H), 5.25 (s, 1H), 7.30−7.31 (m, 4H), 7.36−7.43 (m, 5H),
7.54−7.57 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 57.1, 84.5, 127.1,
127.3, 127.3, 128.3, 128.6, 128.7, 128.8, 133.3, 134.3, 140.7, 140.7,
140.8; HRMS (ESI) m/z calcd for C20H17ClONa (M + Na)+
331.0860, found 331.0869.
4-((4-Fluorophenyl)(methoxy)methyl)-1,1′-biphenyl (3f): yield
42% (24.6 mg, purified by silica gel column chromatography using
PE/EA 40/1 as eluent, Rf = 0.40); yellow oil; IR (film): 2959, 2925,
1601, 1507, 1229, 1086, 835, 754 cm−1; 1H NMR (400 MHz, CDCl3)
δ 3.39 (s, 3H), 5.26 (s, 1H), 7.00−7.04 (m, 2H), 7.32−7.36 (m, 3H),
7.37−7.44 (m, 4H), 7.54−7.57 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 57.0, 84.5, 115.4 (d, JF = 21.5 Hz), 127.1, 127.3 (d, JF =
3.0 Hz), 127.3, 128.6 (d, JF = 8.1 Hz), 128.8, 134.3, 137.9 (d, JF =
3.0 Hz), 140.6, 140.8, 140.9, 162.4 (d, JF = 245.8 Hz); HRMS (ESI)
m/z calcd for C20H17FONa (M + Na)+ 315.1156, found 315.1160.
4-(Methoxy(4-(trifluoromethyl)phenyl)methyl)-1,1′-biphenyl
(3g): yield 42% (28.8 mg, purified by silica gel column chromatog-
raphy using PE/EA 40/1 as eluent, Rf = 0.40); white oil; IR (film):
3022, 2929, 1939, 1556, 1485, 1325, 1078, 758, 698 cm−1;1H NMR
(400 MHz, CDCl3) δ 3.46 (s, 3H), 5.45 (s, 1H), 7.41−7.48 (m, 5H),
7.54−7.57 (m, 4H), 7.50−7.58 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 57.1, 85.3, 125.0, 125.8, 126.0, 126.2, 127.1, 127.2, 127.4,
128.0, 128.8, 139.4, 140.5, 140.9, 141.1; HRMS (ESI) m/z calcd for
C21H17F3ONa (M + Na)+ 365.1123, found 365.1131.
4-(Methoxy(3-methoxyphenyl)methyl)-1,1′-biphenyl (3h): yield
79% (48.1 mg, purified by silica gel column chromatography using
PE/EA 20/1 as eluent, Rf = 0.30); white oil; IR (film): 2953, 2918,
2826, 1596, 1487, 1289, 1257, 1094, 1042 cm−1; 1H NMR (400 MHz,
CDCl3) δ 3.42 (s, 3H), 3.80 (s, 3H), 5.26 (s, 1H), 6.79−6.82 (m, 1H),
6.96−6.98 (m, 2H), 7.25−7.26 (m, 1H), 7.32−7.34 (m, 1H), 7.40−
7.43 (m, 4H), 7.53−7.57 (m, 4H); 13C NMR (100 MHz, CDCl3) δ
55.2, 57.1, 85.1, 112.4, 112.9, 119.4, 127.1, 127.2, 127.2, 127.3, 128.7,
129.5, 140.4, 140.9, 141.1, 143.6, 159.8; HRMS (ESI) m/z calcd for
C21H20O2Na (M + Na)+ 327.1356, found 327.1360.
2-([1,1′-Biphenyl]-4-yl(methoxy)methyl)naphthalene (3l): yield
56% (36.3 mg, purified by silica gel column chromatography using
PE/EA 40/1 as eluent, Rf = 0.45); white solid; IR (film): 2951, 2911,
1
2357, 1603, 1485, 1445, 1111, 817, 746 cm−1; H NMR (400 MHz,
CDCl3) δ 3.47 (s, 3H), 5.46 (s, 1H), 7.32−7.34, (m, 1H), 7.40−7.42
(m, 2H), 7.45−7.48 (m, 5H), 7.55−7.57 (m, 4H), 7.80−7.88 (m, 4H);
13C NMR (100 MHz, CDCl3) δ 57.1, 85.3, 125.0, 125.8, 125.9, 126.2,
127.1, 127.2, 127.3, 127.5, 127.7, 128.0, 128.4, 128.8, 133.0, 133.3,
139.4, 140.5, 140.9, 141.1; HRMS (ESI) m/z calcd for C24H20ONa
(M + Na)+ 347.1406, found 347.1400.
3-([1,1′-Biphenyl]-4-yl(methoxy)methyl)furan (3m): yield 65%
(34.4 mg, purified by silica gel column chromatography using
PE/EA 30/1 as eluent, Rf = 0.45); yellow oil; IR (film): 2955, 2911,
1
2359, 1588, 1481, 1452, 1096, 871, 753 cm−1; H NMR (400 MHz,
CDCl3) δ 3.38 (s, 3H), 5.24 (s, 1H), 6.36 (d, J = 1.1, 1H), 7.32
(m, 1H), 7.35 (m, 1H), 7.38−7.39 (m, 1H), 7.42−7.45 (m, 4H),
7.58−7.60 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 56.7, 78.1, 109.4,
117.8, 127.0, 127.1, 127.2, 127.3, 127.3 128.8, 140.1, 140.2, 140.7,
140.8, 143.4; HRMS (ESI) m/z calcd for C18H16O2Na (M + Na)+
287.1043, found 287.1048.
2-([1,1′-Biphenyl]-4-yl(methoxy)methyl)thiophene (3n): yield
60% (33.6 mg, purified by silica gel column chromatography using
PE/EA 40/1 as eluent, Rf = 0.40); yellow oil; IR (film): 2955, 2920,
2365, 1588, 1481, 1081, 756, 701 cm−1; 1H NMR (400 MHz, CDCl3)
δ 3.43 (s, 3H), 5.52 (s, 1H), 6.88−6.89 (m, 1H), 6.93−6.95 (m, 1H),
7.29−7.42 (m, 2H), 7.44−7.49 (m, 4H), 7.58−7.60 (m, 4H); 13C
NMR (100 MHz, CDCl3) δ 57.0, 81.2, 125.4, 125.6, 126.5, 127.1,
127.3, 127.3, 127.3, 128.8, 129.4, 140.3, 140.8, 140.8, 146.1; HRMS
(ESI) m/z calcd for C18H16OSNa (M + Na)+ 303.0814, found
303.0822.
4-(Ethoxy(phenyl)methyl)-1,1′-biphenyl (3o): yield 77% (44.4 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
eluent, Rf = 0.45); white oil; IR (film): 3062, 3019, 2360, 1600, 1488,
1
1188, 1102, 768, 734 cm−1; H NMR (400 MHz, CDCl3) δ 1.28
(t, J = 7.0 Hz, 3H), 3.55 (q, J = 7.0 Hz, 2H), 5.39 (s, 1H), 7.24−7.26
(m, 1H), 7.30−7.34 (m, 3H), 7.38−7.42 (m, 6H), 7.52−7.56 (m, 4H);
13C NMR (100 MHz, CDCl3) δ 15.4, 64.7, 83.3, 127.0, 127.1, 127.2,
127.2, 127.4, 127.5, 128.5, 128.8, 140.3, 141.0, 141.7, 142.5; HRMS
(ESI) m/z calcd for C21H20ONa (M + Na)+ 311.1407, found
311.1412.
4-((Benzyloxy)(phenyl)methyl)-1,1′-biphenyl (3p): yield 64% (44.9
mg, purified by silica gel column chromatography using PE/EA 40/1
as eluent, Rf = 0.40); white oil; IR (film): 2954, 2920, 1609, 1501,
1448, 1089, 1058, 761, 695 cm−1; 1H NMR (400 MHz, CDCl3) δ 4.58
(s, 2H), 5.49 (s, 1H), 7.28−7.31 (m, 2H), 7.32−7.38 (m, 7H),
7.40−7.46 (m, 6H), 7.54−7.58 (m, 4H); 13C NMR (100 MHz, CDCl3)
δ 70.6, 82.3, 127.1, 127.2, 127.2, 127.3, 127.6, 127.6, 127.8, 128.2, 128.4,
128.5, 128.8, 138.4, 140.4, 140.9, 141.2, 142.1; HRMS (ESI) m/z calcd
for C26H22ONa (M + Na)+ 373.1563, found 373.1566.
4-((3-Chlorophenyl)(methoxy)methyl)-1,1′-biphenyl (3i): Yie ld
56% (34.6 mg, purified by silica gel column chromatography using
PE/EA 40/1 as eluent, Rf = 0.35); yellow oil; IR (film): 2951, 2908,
1
1590, 1494, 1191, 1105, 764 cm−1; H NMR (400 MHz, CDCl3) δ
3.41 (s, 3H), 5.25 (s, 1H), 7.24−7.27(m, 3H), 7.33−7.35 (m, 1H),
7.38−7.44 (m, 5H), 7.55−7.57 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 57.1, 84.6, 125.0, 126.9, 127.1, 127.3, 127.4, 127.7, 128.8,
129.7, 134.4, 140.4, 140.7, 144.2; HRMS (ESI) m/z calcd for
C20H17ClONa (M + Na)+ 331.0860, found 331.0874.
1-(tert-Butyl)-4-(methoxy(phenyl)methyl)benzene (4a):27 yield
65% (31.0 mg, purified by silica gel column chromatography using
G
DOI: 10.1021/acs.organomet.7b00657
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
PE/EA 40/1 as eluent, Rf = 0.45); white oil; H NMR (400 MHz,
CDCl3) δ 1.29 (s, 9H), 3.38 (s, 3H), 5.22 (s, 1H), 7.24−7.27 (m, 3H),
7.32−7.35 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 32.6, 35.7, 58.3,
86.5, 126.5, 127.8, 128.1, 128.6, 129.6, 140.3, 143.4, 151.5.
1939, 1596, 1487, 1095, 736, 699 cm−1; 1H NMR (400 MHz, CDCl3)
δ 3.48 (s, 3H), 5.98 (s, 1H), 7.21−7.26 (m, 2H), 7.30−7.34 (m, 3H),
7.52−7.55 (m, 3H), 7.58−7.60 (m, 2H), 7.83 (d, J = 7.6 Hz, 1H), 7.91
(d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 57.3, 79.7, 111.8,
119.7, 120.7, 122.8, 123.1, 124.3, 124.6, 126.3, 126.9, 127.1, 127.6,
128.4, 134.0, 141.3, 153.7, 156.2; HRMS (ESI) m/z calcd for
C20H16O2Na (M + Na)+: 311.1043, found 311.1040.
1-Methoxy-4-(methoxy(phenyl)methyl)benzene (4b):27 yield 74%
(31.4 mg, purified by silica gel column chromatography using PE/EA
20/1 as eluent, Rf = 0.35); white oil; H NMR (400 MHz, CDCl3) δ
1
3.36 (s, 3H), 3.78 (s, 3H), 5.20 (s, 1H), 6.84−6.86 (m, 2H), 7.24−
7.26 (m, 3H), 7.32−7.33 (m, 4H); 13C NMR (100 MHz, CDCl3) δ
55.3, 56.9, 85.0, 113.8, 126.8, 127.3, 128.3, 128.4, 134.3, 142.3, 159.0.
Methyl 4-(methoxy(phenyl)methyl)benzoate (4c):28 yield 65%
(31.2 mg, purified by silica gel column chromatography using PE/EA
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.7b00657.
■
S
1
40/1 as eluent, Rf = 0.40); white oil; H NMR (400 MHz, CDCl3) δ
1
3.39 (s, 3H), 3.89 (s, 3H), 5.28 (s, 1H), 7.32−7.33 (m, 4H), 7.43
(d, J = 8.3 Hz, 2H), 7.99 (d, J = 8.3 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 52.1, 57.1, 85.0, 126.7, 127.0, 127.8, 128.6, 129.3, 129.8,
141.3, 147.3, 166.9.
Experimental procedures, characterization data, H and
13C NMR spectra, and DFT calculation details (PDF)
Cartesian coordinates for calculated structures (XYZ)
4-(Methoxy(phenyl)methyl)benzonitrile (4d):27 yield 50% (20.7 mg,
purified by silica gel column chromatography using PE/EA 30/1 as
AUTHOR INFORMATION
Corresponding Authors
*E-mail for Z.-X.W.: zxwang@ucas.ac.cn.
*E-mail for J.W.: wangjb@pku.edu.cn.
ORCID
Zhi-Xiang Wang: 0000-0001-5815-3032
Jianbo Wang: 0000-0002-0092-0937
Notes
■
1
eluent, Rf = 0.40); yellow oil; H NMR (400 MHz, CDCl3) δ 3.38
(s, 3H), 5.26 (s, 1H), 7.26−7.37 (m, 5H), 7.47 (d, J = 8.3 Hz, 2H),
7.61 (d, J = 8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 57.1, 84.7,
111.2, 118.8, 127.1, 127.3, 128.2, 128.7, 132.3, 140.7, 147.6.
1-(4-(Methoxy(phenyl)methyl)phenyl)ethanone (4e):27 yield 65%
(29.2 mg, purified by silica gel column chromatography using PE/EA
1
30/1 as eluent, Rf = 0.40); white oil; H NMR (400 MHz, CDCl3) δ
2.57 (s, 3H), 3.39 (s, 3H), 5.28 (s, 1H), 7.32−7.34 (m, 5H), 7.46
(d, J = 8.2 Hz, 2H), 7.91 (d, J = 8.2 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 26.6, 57.0, 85.2, 126.9, 127.5, 128.0, 128.4, 128.6, 136.5,
142.0, 147.6, 198.5.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
4-(Methoxy(phenyl)methyl)benzaldehyde (4f): yield 74% (31.1 mg,
purified by silica gel column chromatography using PE/EA 30/1 as
eluent, Rf = 0.40); yellow oil; IR (film): 2923, 2846, 2815, 1698, 1609,
1457, 1210, 1098, 802, 693 cm−1; 1H NMR (400 MHz, CDCl3) δ 3.40
(s, 3H), 5.30 (s, 1H), 7.26−7.29 (m, 1H), 7.29−7.34 (m, 4H), 7.53
(d, J = 8.1 Hz, 2H), 7.84 (d, J = 8.3 Hz, 2H), 9.98 (s, 1H); 13C NMR
(100 MHz, CDCl3) δ 57.1, 85.0, 127.0, 127.3, 128.0, 128.7, 129.9,
135.6, 141.0, 149.1, 191.9; HRMS (ESI) m/z calcd for C15H14O2Na
(M + Na)+ 249.0886, found 249.0889.
■
This project was supported by the National Basic Research
Program of China (973 Program, No. 2015CB856600) and the
Natural Science Foundation of China (Grants 21332002,
21472004, and 21573233 (to Z.X.-W.)).
REFERENCES
■
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1-(Methoxy(phenyl)methyl)-3-methylbenzene (4g):27 yield 90%
(38.2 mg, purified by silica gel column chromatography using PE/EA
(b) Wu, Y.-T.; Kurahashi, T.; de Meijere, A. J. Organomet. Chem. 2005,
690, 5900−5911. (c) Aumann, R. Eur. J. Org. Chem. 2000, 17−31.
(d) de Meijere, A.; Schirmer, H.; Duetsch, M. Angew. Chem., Int. Ed.
1
40/1 as eluent, Rf = 0.40); white oil; H NMR (400 MHz, CDCl3) δ
2000, 39, 3964−4002. (e) Barluenga, J.; Santamaría, J.; Tomas
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, M.
2.32 (s, 3H), 3.37 (s, 3H), 5.20 (s, 1H), 7.04−7.06 (m, 1H),
7.14−7.16 (m, 2H), 7.18−7.22 (m, 1H), 7.31−7.36 (m, 5H); 13C
NMR (100 MHz, CDCl3) δ 21.5, 57.0, 85.5, 124.0, 126.9, 127.4, 127.5,
128.3, 128.4, 128.6, 138.1, 142.0, 142.2.
Chem. Rev. 2004, 104, 2259−2283. (f) Dotz, H. K.; Stendel. Chem.
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(2) (a) Pfeiffer, J.; Nieger, M.; Dotz, K. H. Eur. J. Org. Chem. 1998,
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1-Methoxy-3-(methoxy(phenyl)methyl)benzene (4h):27 yield 80%
(31.4 mg, purified by silica gel column chromatography using PE/EA
1011−1022. (b) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; Muller, J.;
̈
Huttner, G.; Lorenz, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 564−
1
́
565. (c) Barluenga, J.; Trabanco, A. A.; Florez, J.; García-Granda, S.;
30/1 as eluent, Rf = 0.35); white oil; H NMR (400 MHz, CDCl3) δ
Martín, E. J. Am. Chem. Soc. 1996, 118, 13099−13100.
3.38 (s, 3H), 3.80 (s, 3H), 5.68 (s, 1H), 6.84−6.86 (m, 1H), 6.95−6.99
(m, 1H), 7.20−7.22 (m, 2H), 7.27−7.30 (m, 2H), 7.37−7.39 (m, 2H),
7.45−7.47 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 55.4, 57.1, 78.8,
110.6, 120.8, 126.8, 127.0, 127.1, 128.1, 128.3, 130.6, 142.1, 156.6.
2-(Methoxy(phenyl)methyl)naphthalene (4i):29 yield 61% (30.3 mg,
purified by silica gel column chromatography using PE/EA 40/1 as
(3) (a) Fischer, E. O.; Held, W.; Kreiβl, F. R.; Frank, A.; Huttner, G.
Chem. Ber. 1977, 110, 656−666. (b) Klabunde, U.; Fischer, E. O. J.
Am. Chem. Soc. 1967, 89, 7141−7142. (c) Hu, F.; Yang, J.; Xia, Y.; Ma,
C.; Zhang, Y.; Wang, J. Org. Chem. Front. 2015, 2, 1450−1456. (d) Hu,
F.; Yang, J.; Xia, Y.; Ma, C.; Xia, H.; Zhang, Y.; Wang, J.
Organometallics 2016, 35, 1409−1414. (e) Amin, S. R.; Sarkar, A.
Organometallics 1995, 14, 547−550. (f) Wulff, W. D.; Gilbertson, S. R.
1
eluent, Rf = 0.45); white solid; H NMR (400 MHz, CDCl3) δ 3.46
(s, 3H), 5.92 (s, 1H), 7.26−7.32 (m, 3H), 7.42−7.45 (m, 3H),
7.57−7.62 (m, 2H), 7.79−7.86 (m, 3H), 8.05−8.08 (m, 1H); 13C
NMR (100 MHz, CDCl3) δ 57.3, 83.3, 124.1, 125.3, 125.4, 125.5,
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