Rhodium-Catalyzed Double Alkyl-Oxygen Bond Cleavage: An Alkyl Transfer Reaction from Bis/Tris(o-alkyloxyphenyl)phosphine to Aryl Acids

Article abstract of DOI:10.1021/acs.organomet.6b00638

An unprecedented rhodium-catalyzed selective cleavage of double alkyl-oxygen bonds of bis/tris(o-alkyloxyphenyl)phosphine has been realized, in which P atom functions as a directing group and simple aryl acids are the methyl group acceptor to provide methyl esters and a quaternary phosphonium salt. The preliminary mechanism was investigated via an ¹⁸O labeling experiment and stoichiometric reaction between a Rh-A crystal and an aromatic acid.

Full text of DOI:10.1021/acs.organomet.6b00638

Article
pubs.acs.org/Organometallics
Rhodium-Catalyzed Double Alkyl-Oxygen Bond Cleavage: An Alkyl
Transfer Reaction from Bis/Tris(o‑alkyloxyphenyl)phosphine to Aryl
Acids
Hui Zhou,†,‡,§ Jinlong Zhang,†,§ Huameng Yang,† Chungu Xia,† and Gaoxi Jiang*,†
†State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical
Physics (LICP), Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
‡University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
S
* Supporting Information
ABSTRACT: An unprecedented rhodium-catalyzed selective
cleavage of double alkyl-oxygen bonds of bis/tris(o-
alkyloxyphenyl)phosphine has been realized, in which P
atom functions as a directing group and simple aryl acids are
the methyl group acceptor to provide methyl esters and a
quaternary phosphonium salt. The preliminary mechanism was
investigated via an 18O labeling experiment and stoichiometric
reaction between a Rh-A crystal and an aromatic acid.
and remains a significant challenge. Conventionally, an
he pinpoint cleavage of unactivated carbon−oxygen bonds
Tin aryl alkyl ethers ranks among the most powerful (over)stoichiometric amount of strong acid5 or base6 was
utilized as a reactant for the deprotection of phenol derivatives7
and other useful transformations.2 During the last decades,
considerable attempts have been executed toward transition-
metal pincer complexes. Shaw,8 Tolman,9 and Dunbar10 have
probed the possibilities that transition metals can insert into the
ArO−CH3 bond to activate alkyl ethers. In 1974, Shaw’s group
first demonstrated the O-metalation of 2-alkoxyphenylphos-
phines by platinum(II) halides to form O-metalated chelates by
heating the ligand with metals in xylene. In 1977, Ittel, Tolman,
and co-workers reported that the 2-naphthyl bis[bis-
(dimethylphosphino)ethane] hydride complex of Fe can
catalyze the C(sp3)−O splitting of ethyl acetate and methyl
dimethylphosphonite. In 1995, Dunbar et al. using tris(2,4,6-
trimethoxyphenyl)phosphine/rhodium(I) olefin or tris(2,4,6-
trimethoxyphenyl)phosphine/iridium(I) olefin complexes real-
ized the cleavage of the Me−O bond and a phosphonium salt
produced concurrently as byproduct (Scheme 1, b). Afterward,
further progress in this field was achieved by Milstein,11 Krogh-
Jespersen,12 Goldman,13 Agapie,14 Paneque,15 and other
researchers16 independently. For example, Milstein’s group
presented the metal insertion into the strong Me−O bond of
the aryl ether molecules with direct C−O activation by a Rh
pincer catalyst. Goldman’s group and the Paneque and
Carmona group developed the cleavage of ether C−O bonds
in aryl alkyl ethers by pincer iridium catalysts independently.
protocols in modern synthetic organic chemistry1 and has
extensive applications in biomass conversion.2 Consequently, a
variety of cross-coupling reactions1,3 and eliminations4 have
been widely explored through transition-metal-catalyzed Ar-
(sp2)−O bond cleavage (Scheme 1, a). In contrast, the selective
fission of the CH3(sp3)−O bond has been relatively unexplored
Scheme 1. Selective Cleavage of the C−O Bond in Aryl
Methyl Ether Derivatives
Received: August 9, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Agapie and co-workers systematically investigated the aryl ether
cleavage by group 9 and 10 transition metals involving
stoichiometric studies of selectivity and mechanism. However,
these methods always suffer from the use of stoichiometric
amounts of transition metals, such as Pd, Pt, and Ir compounds.
The catalytic approach for selective cleavage of the ArO−CH3
bond is still very rare. So far, only one catalytic protocol was
realized, by Arisawa and Yamaguchi in 2012.17 They described a
catalytic approach based on RhH(CO)(PPh3)3/dppe for the
cleavage of the Me(sp3)−O bond of aryl methyl ethers,
followed by the transfer of a methyl group to thioesters,
affording aryl esters and methyl sulfides (Scheme 1, c). Herein,
we report an unprecedented process for Rh2(OAc)4-catalyzed
cleavage of double alkyl-oxygen bonds in bis/tris(o-
alkyloxyphenyl)phosphine to give a quaternary phosphonium
salt,18 in which diverse simple aryl acids function as the alkyl
group acceptor to provide esters in high yields (Scheme 1, d).
This process does not need to add any additional phosphine
ligand and phosphine functions as a directing group in the
transition-metal catalysis.
Rh2(OAc)4 is the best catalyst, affording 3s in 98% yield
(entries 2−12). The same high yield (95%) was acquired when
the Rh2(OAc)4 loading was decreased from 10.0 mol % to 8.0
mol % (entry 13). Further decline of the catalyst loading was
detrimental to the reaction results (entry 14). The screening of
solvents revealed that cyclohexane was superiorer to the others
(entries 15−20).
With the optimized reaction conditions established, a variety
of simple aryl acids were employed as methyl acceptors to
evaluate the generality of the reaction (Scheme 2). This
Scheme 2. Esterification of Various Aryl Acids via Rh-
a
Catalyzed Cleavage of the Me−O Bond in (2-MeOPh)3P
Initially, the model reaction was carried out between 2,3,4,5-
tetrachlorobenzoic acid 1s and tris(o-methoxyphenyl)-
phosphine 2a to optimize the conditions (Table 1). When
the mixture of 1s and 2a was heated for 12 h in cyclohexane at
120 °C with Fe(acac)3 (10 mol %) as a catalyst under a
nitrogen atmosphere, surprisingly, methyl 2,3,4,5-tetrachlor-
obenzoate 3s was obtained with 20% yield (entry 1).
Encouraged by the rudimentary result, examination of other
transition metals disclosed that an amount of 10.0 mol % of
a
Table 1. Optimization of the Reaction Conditions
b
entry
cat. (mol %)
solvent
yield (%)
20
1
Fe(acac)3 (10)
AgOTf (10)
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
toluene
a
Reaction conditions: a mixture of 1 (0.1 mmol), 2a (0.12 mmol), and
2
Rh2(OAc)4 (8.0 mol %) in cyclohexane (1.0 M) at 120 °C for 12 h
3
Sc(OTf)3 (10)
Ni(acac)2 (10)
Ni(OAc)2 (10)
PdCl2 (10)
22
34
13
21
52
48
65
76
85
98
b
under a nitrogen atmosphere. Isolated yield.
4
5
6
Rh2(OAc)4-catalyzed process was able to introduce the methyl
group to a wide range of mono- and polysubstituted aromatic
acids from 2a successfully. The results showed that acids
bearing substituents, such as methoxyl, dimethylamino, methyl,
halogen, trifluoromethyl, and nitro groups, are excellent
reaction partners to form the corresponding methyl esters
with 63−93% yields regardless of its position (3a−l). For
disubstituted acids, the reactions proceeded smoothly to afford
the desired esters in 80−88% yields (3m−q). The trisubstituted
acid 1r underwent the methyl transfer reaction to generate 3r
with 75% yield. Notably, besides 1s, the tetrasubstituted acid 1t
was also examined under the optimized reaction condition, and
it was compatible for this transformation to result in 3t in 61%
yield.
7
Pd(OAc)2 (10)
Pd(OTf)2 (10)
Pd2(dba)3 (10)
Pd2(allyl)2Cl2 (10)
[Rh(cod)Cl]2 (10)
Rh2(OAc)4 (10)
Rh2(OAc)4 (8)
Rh2(OAc)4 (5)
Rh2(OAc)4 (8)
Rh2(OAc)4 (8)
Rh2(OAc)4 (8)
Rh2(OAc)4 (8)
Rh2(OAc)4 (8)
Rh2(OAc)4 (8)
8
9
10
11
12
13
14
15
16
17
18
19
20
c
95 (91)
68
85
DCE
64
dioxane
89
ether
87
AcOEt
87
CH3CN
40
Next, we investigated the analogues of 2a for the trans-
formation (Scheme 3). The reaction between 1i and tri-o-
ethyoxyl-substituted 2b occurred readily and gave rise to the
ethyl benzoate 3ib and phosphonium salt and its isomer18 (P-
IV) in 72% and 70% yield at 160 °C respectively (eq 1, (i)), but
a
Reaction conditions: a mixture of 1s (0.1 mmol), 2a (0.12 mmol),
and catalyst in solvent (1.0 mL) at 120 °C for 12 h under a nitrogen
b
c
atmosphere. Determined by GC analysis using a standard. Yield of
isolated product is given in parentheses.
B
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 3. Utilization of Other N,P-Containing Compounds
2b−f
Scheme 4. Preliminary Mechanistic Studies: (a) 18O
-Labeling Experiment between 1a and 2a-18O (30% 18O); (b)
Identification of Phosphonium Salts by Rh2(OAc)4 or
[Rh(COD)Cl]2; (c) Stoichiometric Reaction between Rh-A
and 1i; (d) Examination of the Reactivity of P-II
the much bulkier isopropyl group was completely unreactive
(eq 1, (ii)). No reaction occurred with mono-o-methyoxyl-
substituted substrate 2d as reactant at 120 °C, and a less than
30% conversion was observed at 160 °C (eq 2). Using di-o-
methyoxyl-substituted substrate 2e reacted with 1i at 160 °C
facilitated smoothly 3i and salt P-I in 87% and 86% yields,
respectively, which indicated that the existence of two methoxyl
groups was crucial to the high reactivity and total completion of
the methyl group transfer process (eq 3). In contrast, tris(o-
methoxyphenyl)amine 2f failed to undergo the reaction under
the current conditions, most likely caused by the low chelation
potency and poor nucleophilic attack ability of the N atom to
the rhodium center, in contrast to the P atom (eq 4), which
indicated that the chelation between the phosphorus atom and
rhodium might switch the activation of the Me−O bond.
In order to gain insight into the mechanistic details of this
alky group transfer process, several preliminary experiments
were performed, and outcomes are outlined in Scheme 4. An
isotopic labeling experiment with 18O-labeled phosphine
2a-18O (30%-18O) prepared and employed as reaction partner
afforded 3a exclusively, without formation of 18O-labeled ester
3a-18O (Scheme 4, a). The result confirms undoubtedly that
the process underwent selective cleavage of the Me−O bond
rather than the Ar−O bond of tris(o-methoxyphenyl)-
phosphine. Furthermore, in the presence of Rh2(OAc)4,
[Rh(cod)Cl]2, or Rh-A as catalyst P-containing salt P-III was
isolated in 89%, 77%, and 80% yields, respectively, and
structurally identified as a quaternary phosphonium salt
(Scheme 4, b). After failing to prepare a single crystal of
Rh2(OAc)4 with 2a, we used [Rh(cod)Cl]2 to react with 2a
(Scheme 4, c). Fortunately, a single crystal of Rh-A of the
[Rh(cod)Cl]2/(2-MeOPh)3P complex was synthesized success-
fully.19 The stoichiometric reaction between Rh-A and 1i under
standard conditions resulted in 3i in 85% yield and P-III in
82% yield, while the salt P-II was also isolated in 5% yield. On
employing P-II as methylating agent instead of 2a, a trace of
the desired ester product was obtained (Scheme 4, d).
Although the mechanism of this catalytic transformation is
not completely clear yet, on the basis of the above-mentioned
observations, a possible reaction process is postulated in
Scheme 5. Stable compound Rh-B formed smoothly by the
coordination of Rh2(OAc)2 with a phosphine atom, then was
protonated by acidic reactant to form Rh-C, which transformed
into Rh-D via fast oxidative addition of the Me−O bond to the
Rh center, followed by acid anion nucleophilic attack to give
methyl aromatic esters and Rh-E separately. The compound
Rh-E underwent protonation, oxidative addition, and nucleo-
Scheme 5. Postulated Mechanism
C
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
6.80 (m, 4H), 6.73−6.64 (m, 2H), 3.74 (s, 6H); 13C NMR (100 MHz,
CDCl3) δ = 161.33, 136.50, 134.11, 133.81, 130.08, 128.51−128.00,
125.20, 120.90, 110.20, 77.34, 77.02, 76.70, 55.66; 31P NMR (100
MHz, CDCl3) δ = −27.88.
philic attack by a phosphine atom, resulting in the
phosphonium salt P-III.
In conclusion, an unprecedented rhodium-catalyzed cleavage
reaction of double alkyl-oxygen bonds of bis/tris(o-
alkyloxyphenyl)phosphine was realized, in which simple aryl
acids function as the alkyl group acceptors to give an array of
esters and phosphonium salts.18 The preliminary mechanism
investigation by 18O-labeling experiment indicated that the
selective cleavage of double alkyl-oxygen bonds might take
place via protonation of a rhodium/substrate complex followed
by nucleophilic substitution to complete the whole process.
This transformation presents a new activation model for stable
sp3-carbon−oxygen bonds. The further investigation on other
simple aryl alkyl ethers instead of special bis/tris(o-
alkyloxyphenyl)phosphine is ongoing in our group.
Synthesis of Tris(2-methoxyphenyl)amine (2f). To a three-
necked flask fitted with a reflux condenser, thermometer, and nitrogen
purge line was added o-anisidine (0.64 g, 5.2 mmol), o-iodoanisole (2.3
g, 10 mmol), ball-milled K2CO3 (3 g), spongy copper powder (0.64 g),
and nitrobenzene (2 g). The flask was then heated at reflux for about 3
h under a nitrogen purge. When the reaction was complete
(monitored by TLC), the mixture was poured into saturated NH4Cl
(aq); then the aqueous phase was extracted with ethyl acetate (3 × 30
mL), and the combined organic layers were dried over anhydrous
MgSO4, filtered, and concentrated by rotary evaporation. The crude
product was then recrystallized from acetone to obtain the desired
1
compound 2f. Yield: 1.15 g (65% yield), white solid. H NMR (400
MHz, CDCl3) δ = 7.05 (ddd, J = 8.1, 6.3, 2.7 Hz, 3H), 6.85 (ddd, J =
7.1, 6.4, 4.4 Hz, 9H), 3.59 (s, 9H); 13C NMR (100 MHz, CDCl3) δ =
153.11, 137.76, 124.50, 123.73, 120.64, 112.59, 77.36, 77.04, 76.73,
55.76, 55.72.
EXPERIMENTAL SECTION
■
Materials and Methods. All nonaqueous manipulations were
carried out under an inert N2 (g) atmosphere using standard Schlenk
techniques. Reactions were monitored using thin-layer chromatog-
raphy (TLC) on silica gel plates. Visualization of the developed plates
was performed under UV light (254 nm) or KMnO4 stain. Silica gel
flash column chromatography was performed on Synthware 40−63
μm silica gel. All NMR spectra were run at 400 MHz (1H NMR) or
Synthesis of 18O-Labeled Triphenylphosphine (2a-18O).
Procedure 1: A Schlenk tube was charged with PhI (0.2 g, 10
mmol), Cu(OH)2 (4.9 mg, 0.05 mmol), glycolic acid (22.8 mg, 0.3
mmol), NaOH (240 mg, 6.0 mmol), and DMSO/H2O (1.0 mL/1.0
mL). The mixture was stirred at 120 °C for 6 h under Ar. The reaction
mixture was allowed to cool to room temperature, poured into water
(3 mL), and then acidified to pH = 1 with 2 N HCl. The aqueous
phase was extracted twice with EA, and the combined organic layer
was washed with H2O and brine, dried over anhydrous Na2SO4, and
concentrated under vacuum. Purification of the crude product by silica
gel column chromatography (EtOAc/n-hexane) afforded the phenol in
up to 99% yield. Procedure 2: The phenol (0.56 g, 6 mmol) was added
to a two-necked flask with K2CO3 (12 mmol, 2 equiv) as the
dehydrogenating base in DMF (10 mL); then MeI (3 equiv) was
added, and the reaction mixture was stirred for 8 h. Et2O (30 mL) was
added to the mixture, and the organic phases were washed with water,
then dried over anhydrous Na2SO4, and concentrated by rotary (under
low temperature) to gain the crude product. The pure methyl ether
was obtained in 92% yield by silica gel column chromatography.
Procedure 3: TMEDA (15 mmol, 0.15 equiv) was added to a hexane
solution of n-butyllithium (1.6 M, 3.1 mL, 5 mmol) slowly via syringe
at 0 °C under an argon atmosphere. The reaction mixture was stirred
at 60 °C for 18 h, and a copious amount of precipitate was produced.
18O-Labeled ether (5.1 mmol) was then added to the reaction mixture
100 MHz (13C NMR/31P NMR) in CDCl3 or d6-DMSO solution. H
1
NMR spectra were internally referenced to tetramethylsilane. 13C
NMR spectra were internally referenced to the residual solvent signal.
High-resolution mass spectra (HRMS) were recorded on a Bruker
MicrOTOF-QII mass instrument (ESI). Unless otherwise indicated,
starting catalysts and materials were obtained from Sigma-Aldrich,
TCI, Alfa Aesar, Adamas, or Acros Co. Ltd. Moreover, commercially
available reagents were used without additional purification.
Phosphines 1 and 2 and amine 3 with different substituents were
prepared according to literature procedures.
Synthesis of (2-Methoxyphenyl)diphenylphosphane (2d). A
solution of 2-bromo benzylmethyl ether (0.94 g, 5 mmol) in dry THF
was dropped into a suspension of magnesium (0.12 g) in THF (6 mL)
previously activated with iodine. The mixture was refluxed until
magnesium disappeared, a solution of chlorodiphenylphosphine (0.89
g, 4.0 mmol, 0.8 equiv) in dry THF (1 mL) was added at room
temperature, and the reaction mixture was then heated to reflux for 1
h. After cooling, the mixture was poured into a mixture of ice (ca. 5 g)
and HCl (6 mL, 1 N) and stirred until magnesium dissolution. The
aqueous phase was extracted with Et2O (3 × 30 mL), the combined
organic layers were dried over anhydrous Na2SO4, and the solvent was
removed under reduced pressure. The residue was recrystallized with
MeOH to obtain the desired compound 2d. Yield: 1.0 g (85%), white
crystals: 1H NMR (400 MHz, CDCl3) δ = 7.38−7.26 (m, 11H), 6.94−
6.82 (m, 2H), 6.71−6.65 (m, 1H), 3.75 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ = 161.23, 161.08, 136.79, 136.69, 133.98, 133.78, 133.63,
130.32, 128.55, 128.37, 128.30, 125.71, 125.59, 121.03, 110.25, 110.23,
77.36, 77.04, 76.72, 55.70, 55.66; 31P NMR (100 MHz, CDCl3) δ =
−16.77.
and stirred for 20−24 h. After cooling to −78 °C, 5 mL of THF and
PCl3 (1.5 mmol) were successively added, and the solution was stirred
for 3 h at this temperature, then allowed to warm to −10 °C. Then 2
mL of HCl (aq, 2 M) solution was added. The aqueous solution was
extracted with Et2O (3 × 30 mL), and the combined organic phases
were dried over anhydrous Na2SO4. The solvent was removed under
reduced pressure. The crude product was purified via silica gel column
chromatography to afford the desired product 2a-18O in 91% yield
(eluent, petroleum ether (PE)/EA = 20:1).
Synthesis of [Rh(cod)Cl]2/(2-MeOPh)3P Complex (Rh-A). To a
solution of the complex [RhCl(cod)]2 (100 mg, 0.203 mmol) in
acetone (5 mL) was added (2-MeOPh)3P 2a (2.0 equiv). The color of
the solution quickly changed from orange to yellow. The mixture was
stirred at room temperature and checked for completion by TLC.
After the solvent was removed in vacuo, the desired single-crystal Rh-
A was obtained: 1H NMR (400 MHz, CDCl3) δ = 7.35 (t, J = 7.7 Hz,
4H), 6.95 (t, J = 7.3 Hz, 4H), 6.83 (dd, J = 8.0, 4.0 Hz, 4H), 5.23 (s,
2H), 3.86 (s, 2H), 3.54 (d, J = 18.2 Hz, 9H), 2.36 (s, 4H), 2.01−1.79
(m, 4H); 13C NMR (100 MHz, CDCl3) δ = 160.43, 160.39, 131.17,
120.57, 120.47, 119.96, 119.54, 110.66, 110.62, 98.24, 77.45, 77.13,
76.82, 71.53, 55.12, 33.21, 29.19; 31P NMR (100 MHz, CDCl3) δ =
16.51, 15.60; HRMS (ESI) m/z [C29H34ClO3PRh + H]+ calcd
599.0989, found 599.0990.
Synthesis of Bis(2-methoxyphenyl)(phenyl)phosphane (2e).
To an ether solution (10 mL) of 1-bromo-2-methoxylbenzene (1.88 g,
10 mmol, 2.5 equiv) was added a hexane solution of n-butyllithium
(1.6 M, 6.4 mL, 10.2 mmol) at −78 °C. Then resulting solution was
warmed to 0 °C and stirred for 1 h until many white solid salts were
produced. THF (10 mL) was added to the reaction mixture, and the
mixture was cooled to −78 °C. Dichlorophenylphosphine (0.71 g, 4
mmol) was added to the reaction system slowly, and the mixture was
stirred for 1 h, gradually warmed to room temperature, and stirred
untilcompletion. After addition of a saturated solution of NH4Cl, the
mixture was extracted with ethyl acetate (EA). The organic layer was
washed with brine and dried with anhydrous Na2SO4. The solvent was
removed under reduced pressure. The residue was recrystallized with
EtOH to obtain the desired compound 2e. Yield: 1.2 g (95%), white
General Process for the Esterification of Various Aromatic
Acids (1a−t). To a flame-dried Schlenck tube charged with a
magnetic stir bar were added benzoic acid 1a−t (0.1 mmol), (2-
1
solid. H NMR (400 MHz, CDCl3) δ = 7.38−7.25 (m, 7H), 6.94−
D
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
MeOPh)3P 2a (0.12 mmol), and Rh2(OAc)4 (8.0 mol %) in 1.0 mL of
dry cyclohexane. The resulting suspension was stirred at 120 °C under
N2 for 12 h. When the reaction was complete (monitored by TLC),
the organic layer was separated and the aqueous layer was extracted
with EtOAc. The combined organic layers were dried (MgSO4),
filtered, concentrated in vacuo, and purified by flash chromatography
(1−5% ethyl acetate in petroleum ether) to afford pure products 3a−t
(58−91% yields).
Methyl benzoate (3a). This was prepared according to the
general procedure. Yield: 63%, colorless oil. 1H NMR (400 MHz,
CDCl3) δ = 8.08 (d, J = 7.4 Hz, 2H), 7.58 (t, J = 6.7 Hz, 1H), 7.47 (t, J
= 6.9 Hz, 2H), 3.95 (s, 3H); 13C NMR (100 MHz, CDCl3) δ =
167.11, 129.70, 129.41, 128.12, 77.40, 77.08, 76.76, 52.09.
1H), 7.75−7.65 (m, 2H), 3.97 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ = 165.90, 132.95, 131.79, 129.86, 127.57, 123.94, 77.36, 77.04, 76.73,
53.30.
Methyl 2,4-dichlorobenzoate (3m). This was prepared accord-
1
ing to the general procedure. Yield: 86%, colorless oil. H NMR (400
MHz, CDCl3) δ = 7.82 (d, J = 8.4 Hz, 1H), 7.48 (s, 1H), 7.31 (d, J =
8.4 Hz, 1H), 3.94 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 165.16,
138.32, 134.93, 132.53, 130.99, 128.13, 126.98, 77.41, 77.09, 76.77,
52.56.
Methyl 4-chloro-3-nitrobenzoate (3n). This was prepared
according to the general procedure. Yield: 87%, white solid. 1H
NMR (400 MHz, CDCl3) δ = 8.56 (s, 1H), 8.21 (d, J = 7.6 Hz, 1H),
7.70 (d, J = 8.4 Hz, 1H), 4.02 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
= 164.12, 133.54, 132.15, 131.54, 130.02, 126.51, 77.38, 77.06, 76.74,
52.91.
Methyl 4-methoxybenzoate (3b). This was prepared according
1
to the general procedure. Yield: 89%, colorless oil. H NMR (400
Methyl 3-chloro-4-nitrobenzoate (3o). This was prepared
according to the general procedure. Yield: 88%, light yellow solid.
1H NMR (400 MHz, CDCl3) δ = 8.22 (d, J = 1.7 Hz, 1H), 8.08 (dd, J
= 8.4, 1.7 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 4.00 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ = 164.09, 150.44, 134.36, 133.08, 128.76,
127.09, 125.39, 77.39, 77.07, 76.75, 53.07.
Methyl 3-bromo-4-chlorobenzoate (3p). This was prepared
according to the general procedure. Yield: 82%, colorless oil. 1H NMR
(400 MHz, CDCl3) δ = 8.32 (d, J = 1.9 Hz, 1H), 7.94 (dd, J = 8.4, 2.0
Hz, 1H), 7.56 (d, J = 8.4 Hz, 1H), 3.97 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ = 165.07, 139.52, 134.95, 129.95, 122.64, 77.36, 77.04,
76.72, 52.57.
Methyl 4-chloro-2-fluorobenzoate (3q). This was prepared
according to the general procedure. Yield: 80%, colorless oil. 1H NMR
(400 MHz, CDCl3) δ = 7.90 (t, J = 8.1 Hz, 1H), 7.24−7.14 (m, 2H),
3.94 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 164.01, 163.97,
163.07, 160.44, 139.94, 133.02, 77.40, 77.08, 76.76, 52.42.
Methyl 4-chloro-2,5-difluorobenzoate (3r). This was prepared
according to the general procedure. Yield: 75%, colorless oil. 1H NMR
(400 MHz, CDCl3) δ = 7.78−7.69 (m, 1H), 7.26 (dd, J = 9.1, 5.9 Hz,
1H), 3.96 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 163.04, 162.99,
158.60, 156.01, 155.21, 152.76, 119.03, 52.70.
MHz, CDCl3) δ = 7.99 (d, J = 8.5 Hz, 2H), 6.91 (d, J = 8.5 Hz, 2H),
3.88 (s, 3H), 3.84 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 166.88,
163.32, 131.59, 122.58, 113.59, 77.38, 77.06, 76.75, 55.41, 51.87.
Methyl 4-(dimethylamino)benzoate (3c). This was prepared
1
according to the general procedure. Yield: 89%, white solid. H NMR
(400 MHz, CDCl3) δ = 7.95 (d, J = 9.1 Hz, 2H), 6.69 (d, J = 9.0 Hz,
2H), 3.90 (s, 3H), 3.08 (s, 6H); 13C NMR (100 MHz, CDCl3) δ =
167.46, 153.25, 131.22, 116.96, 110.69, 77.38, 77.06, 76.74, 51.46,
40.01.
Methyl 4-methylbenzoate (3d). This was prepared according to
1
the general procedure. Yield: 85%, colorless oil. H NMR (400 MHz,
CDCl3) δ = 7.92 (d, J = 7.9 Hz, 2H), 7.23 (d, J = 7.9 Hz, 2H), 3.89 (s,
3H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 167.14, 143.50,
129.56, 129.03, 127.42, 77.33, 77.02, 76.70, 51.89, 21.60.
Methyl 2-chlorobenzoate (3e). This was prepared according to
1
the general procedure. Yield: 89%, colorless oil. H NMR (400 MHz,
CDCl3) δ = 7.84 (dd, J = 7.7, 1.6 Hz, 1H), 7.44 (dtd, J = 9.6, 8.0, 1.5
Hz, 2H), 7.32 (td, J = 7.5, 1.5 Hz, 1H), 3.95 (s, 3H); 13C NMR (100
MHz, CDCl3) δ = 166.12, 133.64, 131.37, 130.00, 77.44, 77.12, 76.80,
52.41.
Methyl 4-chlorobenzoate (3f). This was prepared according to
1
the general procedure. Yield: 93%, colorless oil. H NMR (400 MHz,
CDCl3) δ = 8.01 (d, J = 8.3 Hz, 2H), 7.45 (d, J = 8.2 Hz, 2H), 3.95 (s,
3H); 13C NMR (100 MHz, CDCl3) δ = 166.24, 139.37, 130.97,
128.71, 128.57, 77.36, 77.04, 76.73, 52.29.
Methyl 2,3,4,5-tetrachlorobenzoate (3s). This was prepared
1
according to the general procedure. Yield: 91%, white solid. H NMR
(400 MHz, CDCl3) δ = 7.86 (s, 1H), 3.99 (s, 3H); 13C NMR (100
MHz, CDCl3) δ = 164.04, 136.25, 135.07, 132.26, 131.83, 130.48,
129.63, 77.34, 77.02, 76.70, 53.07.
Methyl 4-bromobenzoate (3g). This was prepared according to
1
the general procedure. Yield: 83%, white solid. H NMR (400 MHz,
Methyl 2,4-dichloro-5-fluoro-3-nitrobenzoate (3t). This was
prepared according to the general procedure. Yield: 61%, white solid.
1H NMR (400 MHz, CDCl3) δ = 7.87−7.80 (m, 1H), 4.03−3.91 (m,
3H); 13C NMR (100 MHz, CDCl3) δ = 162.62, 157.60, 155.06,
130.64, 130.57, 119.98, 119.74, 77.33, 77.02, 76.70, 53.38.
CDCl3) δ = 7.94 (d, J = 7.7 Hz, 2H), 7.63 (d, J = 8.3 Hz, 2H), 3.96 (s,
3H); 13C NMR (100 MHz, CDCl3) δ = 166.40, 131.89, 131.72,
131.12, 129.03, 128.06, 77.34, 77.02, 76.71, 52.
Methyl 4-fluorobenzoate (3h). This was prepared according to
1
the general procedure. Yield: 70%, light yellow oil. H NMR (400
MHz, CDCl3) δ = 8.08−8.00 (m, 2H), 7.09 (dd, J = 9.6, 7.8 Hz, 2H),
3.90 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 166.00, 132.25,
132.16, 132.05, 131.93, 126.37, 52.06.
Methyl 4-iodobenzoate (3i). This was prepared according to the
general procedure. Yield: 91%, white solid. 1H NMR (400 MHz,
CDCl3) δ = 7.84 (d, J = 8.6 Hz, 2H), 7.78 (d, J = 8.6 Hz, 2H), 3.95 (s,
3H); 13C NMR (100 MHz, CDCl3) δ = 166.59, 137.72, 131.03,
129.59, 100.75, 77.37, 77.05, 76.74, 52.31.
Methyl 4-(trifluoromethyl)benzoate (3j). This was prepared
according to the general procedure. Yield: 58%, colorless oil. 1H NMR
(400 MHz, CDCl3) δ = 8.11 (d, J = 8.0 Hz, 2H), 7.66 (d, J = 8.0 Hz,
2H), 3.92 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 165.74, 134.50,
134.17, 133.30, 129.89, 125.29 (q, J = 3.8 Hz), 77.30, 76.98, 76.66,
52.36.
Ethyl 4-iodobenzoate (3ib). To a flame-dried Schlenck tube
charged with a magnetic stir bar were added benzoic acid 1a (0.1
mmol), (2-EtOPh)3P 2b (0.12 mmol), and Rh2(OAc)4 (8.0 mol %) in
1.0 mL of dry cyclohexane. The resulting suspension was stirred at 120
°C under N2 for 12 h. When the reaction was complete (monitored by
TLC), the organic layer was separated and the aqueous layer was
extracted with EtOAc. The combined organic layers were dried
(MgSO4), filtered, concentrated in vacuo, and purified by flash
chromatography (1−5% EA in PE) to afford pure product 3ib. Yield:
1
72%, colorless oil. H NMR (400 MHz, CDCl3) δ = 7.80 (d, J = 8.7
Hz, 2H), 7.75 (d, J = 8.6 Hz, 2H), 4.37 (q, J = 7.1 Hz, 2H), 1.39 (t, J =
7.1 Hz, 3H).
2-((2-Hydroxyphenyl)(methyl)(phenyl)phosphonio)-
phenolate (P-I). To a flame-dried Schlenck tube was added benzoic
acid 1i (0.3 mmol), bis(2-methoxyphenyl)(phenyl)phosphane 2e
(0.36 mmol), and Rh2(OAc)4 (8.0 mol %) in 3.0 mL of dry
cyclohexane. The resulting suspension was stirred at 160 °C under N2
for 12 h. When the reaction was complete (monitored by TLC), the
organic layer was concentrated in vacuo and purified by flash
chromatography (gradient: PE/EA = 20:1, EA, MeOH), to afford
the desired product 3i (87%) and P-I. Yield: 86%, light yellow solid.
1H NMR (400 MHz, DMSO) δ = 7.67 (dd, J = 20.5, 7.4 Hz, 6H), 7.36
Methyl 3-nitrobenzoate (3k). This was prepared according to
1
the general procedure. Yield: 81%, colorless oil. H NMR (400 MHz,
CDCl3) δ = 8.84 (s, 1H), 8.40 (dd, J = 19.0, 7.7 Hz, 2H), 7.68 (t, J =
7.9 Hz, 1H), 4.00 (s, 3H); 13C NMR (100 MHz, CDCl3) δ = 164.85,
148.19, 135.19, 131.79, 131.69, 129.61, 127.30, 124.46, 77.39, 77.08,
76.76, 52.75, 52.70.
Methyl 2-nitrobenzoate (3l). This was prepared according to the
general procedure. Yield: 85%, colorless oil. 1H NMR (400 MHz,
CDCl3) δ = 7.96 (dd, J = 7.7, 1.4 Hz, 1H), 7.79 (dd, J = 7.4, 1.7 Hz,
(t, J = 7.7 Hz, 2H), 6.88 (dd, J = 14.6, 7.6 Hz, 2H), 6.66 (t, J = 7.2 Hz,
E
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3H), 2.76 (d, J = 14.9 Hz, 3H); 13C NMR (101 MHz, DMSO) δ =
167.39, 167.23, 136.84, 136.21, 134.39, 134.28, 133.35, 132.62, 132.51,
131.71, 129.76, 129.63, 118.72, 116.38, 116.31, 116.15, 104.84, 103.91,
40.40, 40.18, 39.97, 39.76, 39.54; 31P NMR (101 MHz, DMSO) δ =
57.09, 56.33, 18.79, 16.51; HRMS (ESI) m/z [C19H17O2P + H]+ calcd.
309.1044, found 309.1040.
ACKNOWLEDGMENTS
■
Financial support from the Hundred Talent Program of
Chinese Academy of Sciences (CAS) and the Natural Science
Foundation of Jiangsu (Grant No. BK20151235) is gratefully
acknowledged.
2-((2-Hydroxyphenyl)(2-methoxyphenyl)(methyl)phos-
phonio)phenolate (P-III). To a flame-dried Schlenck tube were
added benzoic acid 1i (0.3 mmol), tris(2-methoxyphenyl)phosphane
2a (0.36 mmol), and Rh2(OAc)4 (8.0 mol %) in 3.0 mL of dry
cyclohexane. The resulting suspension was stirred at 120 °C under N2
for 12 h. When the reaction was complete (monitored by TLC), the
organic layer was concentrated in vacuo and purified by flash
chromatography (gradient: PE/EA = 20:1, EA, MeOH), to afford
the desired product 3i (93%) and P-III. Yield: 89%, light yellow solid.
1H NMR (400 MHz, DMSO) δ = 7.87−7.68 (m, 1H), 7.46−7.31 (m,
3H), 7.17 (dd, J = 12.1, 7.4 Hz, 2H), 6.99−6.54 (m, 6H), 3.76 (s, 3H),
2.71 (dd, J = 15.6, 8.4 Hz, 3H); 13C NMR (100 MHz, DMSO) δ =
173.36, 166.22, 165.95, 165.09, 161.93, 136.83, 135.22, 134.86, 134.05,
131.69, 121.93, 118.86, 117.91, 113.78, 109.53, 107.89, 105.11, 103.64,
101.90, 56.71, 52.28; 31P NMR(101 MHz, DMSO) δ = 18.50, 17.69;
HRMS (ESI) m/z [C20H19O3P + H]+ calcd 339.1150, found 339.1142.
2-((2-Ethoxyphenyl)(ethyl)(2-hydroxyphenyl)phosphonio)-
phenolate (P-IV). To a flame-dried Schlenck tube was added benzoic
acid 1i (0.3 mmol), tris(2-ethoxyphenyl)phosphane 2b (0.36 mmol),
and Rh2(OAc)4 (8.0 mol %) in 3.0 mL of dry cyclohexane. The
resulting suspension was stirred at 160 °C under N2 for 12 h. When
the reaction was complete (monitored by TLC), the organic layer was
concentrated in vacuo and purified by flash chromatography (gradient:
PE/EA = 20:1, EA, MeOH), to afford the desired product 3ib (72%)
and P-IV. Yield: 65%, light yellow solid. 1H NMR (400 MHz, DMSO)
δ 1H NMR (400 MHz, DMSO) δ 7.86−7.61 (m, 3H), 7.48−7.35 (m,
3H), 7.31−7.11 (m, 3H), 7.06−6.55 (m, 3H), 4.14−3.97 (m, 2H),
3.19−3.02 (2, 2H), 1.13 (dt, J = 21.5, 7.6 Hz, 3H), 0.97 (t, J = 6.9 Hz,
3H); 31P NMR (101 MHz, DMSO) δ = 25.30; HRMS (ESI) m/z
[C22H23O3P + H]+ calcd 367.1463, found 367.1453.
REFERENCES
■
(1) (a) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2011, 111, 1346−
1416. (b) Li, B.-J.; Yu, D.-G.; Sun, C.-L.; Shi, Z.-J. Chem. - Eur. J. 2011,
17, 1728−1759. (c) Cornella, J.; Zarate, C.; Martin, R. Chem. Soc. Rev.
2014, 43, 8081−8097. (d) Tobisu, M.; Chatani, N. Acc. Chem. Res.
2015, 48, 1717−1726. (e) Tollefson, E. J.; Hanna, L. E.; Jarvo, E. R.
Acc. Chem. Res. 2015, 48, 2344−2353.
(2) Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B.
M. Chem. Rev. 2010, 110, 3552−3599.
(3) Wenkert, E.; Michelotti, E. L.; Swindell, C. S. J. Am. Chem. Soc.
1979, 101, 2246−2247. (b) Dankwardt, J. W. Angew. Chem., Int. Ed.
2004, 43, 2428−2432. For selected examples of nickel-catalyzed
reactions, see: (c) Leiendecker, M.; Hsiao, C.-C.; Guo, L.; Alandini,
N.; Rueping, M. Angew. Chem., Int. Ed. 2014, 53, 12912−12915.
(d) Zhang, J.; Xu, J.; Sun, H.; Shen, Q.; Zhang, Y. Organometallics
2015, 34, 5792−5800. (e) Zhao, Y.; Snieckus, V. Org. Lett. 2015, 17,
4674−4677. (f) Tobisu, M.; Takahira, T.; Chatani, N. Org. Lett. 2015,
17, 4352−4355. (g) Nakamura, K.; Tobisu, M.; Chatani, N. Org. Lett.
2015, 17, 6142−6145. (h) Zarate, C.; Manzano, R.; Martin, R. J. Am.
Chem. Soc. 2015, 137, 6754−6757. (i) Ogawa, H.; Minami, H.; Ozaki,
T.; Komagawa, S.; Wang, C.; Uchiyama, M. Chem. - Eur. J. 2015, 21,
13904−13908. (j) Liu, X.; Hsiao, C.-C.; Kalvet, I.; Leiendecker, M.;
Guo, L.; Schoenebeck, F.; Rueping, M. Angew. Chem., Int. Ed. 2016, 55,
6093−6098. (k) Tobisu, M.; Takahira, T.; Morioka, T.; Chatani, C. J.
Am. Chem. Soc. 2016, 138, 6711−6714. For selected examples of
ruthenium-catalyzed reactions, see: (l) Kakiuchi, F.; Usui, M.; Ueno,
S.; Chatani, N.; Murai, S. J. Am. Chem. Soc. 2004, 126, 2706−2707.
(m) Ueno, S.; Mizushima, E.; Chatani, N.; Kakiuchi, F. J. Am. Chem.
Soc. 2006, 128, 16516−16517. (n) Zhao, Y.; Snieckus, V. J. Am. Chem.
Soc. 2014, 136, 11224−11227. For chromium-catalyzed reaction, see:
(o) Cong, X.; Tang, H.; Zeng, X. J. Am. Chem. Soc. 2015, 137, 14367−
14372. For iron-catalyzed reaction, see: (p) Agrawal, T.; Cook, S. P.
Org. Lett. 2014, 16, 5080−5083.
Stoichiometric Experiment between R-A and 1i. Rh-A (50
mg) and benzoic acid 1i (1.0 equiv) were added to a flame-dried
Schlenk tube with a magnetic stir bar in 1.5 mL of cyclohexane, which
was stirred at 120 °C for 12 h, resulting in 3i in 85% yield and P-II in
82% yield. Meanwhile the salt P-II was also isolated in 5% yield.
1
Compound P-II: H NMR (400 MHz, DMSO) δ = 7.85−7.70 (m,
́
(4) For selected examples, see: (a) Alvarez-Bercedo, P.; Martin, R. J.
ez-
3H), 7.24−7.13 (m, 3H), 7.13−7.07 (m, 3H), 6.97−6.85 (m, 3H),
3.79 (s, 6H), 2.63 (d, J = 15.2 Hz, 3H); 13C NMR (100 MHz, DMSO)
δ = 161.69, 161.66, 137.42, 137.40, 134.37, 134.28, 129.79, 129.77,
129.75, 122.19, 122.06, 112.70, 112.63, 106.46, 105.52, 56.27, 11.85,
11.23; 31P NMR (101 MHz, DMSO) δ = 20.09; HRMS (ESI) m/z
[C19H17O2P + H]+ calcd 309.1044, found 309.1040.
Am. Chem. Soc. 2010, 132, 17352−17353. (b) Cornella, J.; Gom
́
Bengoa, E.; Martin, R. J. Am. Chem. Soc. 2013, 135, 1997−2009.
(c) Tobisu, M.; Morioka, T.; Ohtsuki, A.; Chatani, N. Chem. Sci. 2015,
6, 3410−3414.
(5) For examples of using strong Lewis acids, see: (a) Kawamura, Y.;
Takatsuki, H.; Torii, F.; Horie, T. Bull. Chem. Soc. Jpn. 1994, 67, 511−
515. (b) Parker, K. A.; Petraitis, J. J. Tetrahedron Lett. 1981, 22, 397−
400. (c) Node, M.; Nishide, K.; Fuji, K.; Fujita, E. J. Org. Chem. 1980,
45, 4275−4277. (d) Vickery, E. H.; Pahler, L. F.; Eisenbraun, E. J. J.
Org. Chem. 1979, 44, 4444−4446. (e) Minamikawa, J.; Brossi, A.
Tetrahedron Lett. 1978, 19, 3085−3086. (f) Jung, M. E.; Lyster, M. A.
J. Org. Chem. 1977, 42, 3761−3764. (g) McOmie, J. F. W.; West, D. E.
Organic Syntheses; Wiley: New York, 1973; Vol. V, p 412. For use of
protic acids, see:. (h) Kamal, A.; Gayatri, N. L. Tetrahedron Lett. 1996,
37, 3359−3362. (i) Li, G.; Patel, D.; Hruby, V. J. Tetrahedron Lett.
1993, 34, 5393−5396. (j) Kawasaki, I.; Matsuda, K.; Kaneko, T. Bull.
Chem. Soc. Jpn. 1971, 44, 1986−1987.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00638.
NMR spectra for all compounds and HRMS (ESI) for
new compounds Rh-A, P-I to P-IV (PDF)
(6) For examples of using nucleophilic metal salts in polar solvents at
high temperatures, see: (a) Chakraborti, A. K.; Nayak, M. K.; Sharma,
L. J. Org. Chem. 2002, 67, 1776−1780. (b) McCarthy, J. R.; Moore, J.
L.; Cregge, R. J. Tetrahedron Lett. 1978, 19, 5183−5186. (c) Feutrill,
G. I.; Mirrington, R. N. Tetrahedron Lett. 1970, 11, 1327−1328.
(7) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed., John Wiley: New York, 1999.
(8) (a) Jones, C. E.; Shaw, B. L.; Turtle, B. L. J. Chem. Soc., Dalton
Trans. 1974, 989−992. (b) Empsall, H. D.; Hyde, E. M.; Jones, C. E.;
Shaw, B. L. J. Chem. Soc., Dalton Trans. 1974, 1980−1983.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: gxjiang@licp.cas.cn.
Author Contributions
§H. Zhou and J. Zhang contributed equally to this work.
Notes
The authors declare no competing financial interest.
F
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(9) (a) Ittel, S. D.; Tolman, C. A.; English, A. D.; Jesson, I. P. J. Am.
Chem. Soc. 1978, 100, 7577−7585. (b) Tolman, C. A.; Ittel, S. D.;
English, A. D.; Jesson, J. P. J. Am. Chem. Soc. 1979, 101, 1742−1751.
(10) Dunbar, K. R.; Haefner, S. C.; Uzelmeizer, C. E.; Howard, A.
Inorg. Chim. Acta 1995, 240, 527−534.
(11) (a) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Vigalok, A.;
Milstein, D. Angew. Chem., Int. Ed. Engl. 1997, 36, 625−626. (b) van
der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Shimon, L. J. W.;
Milstein, D. J. Am. Chem. Soc. 1998, 120, 6531−6541. (c) van der
Boom, M. E.; Liou, S.-Y.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D.
Inorg. Chim. Acta 2004, 357, 4015−4023. (d) Weissman, H.; Shimon,
L. J. W.; Milstein, D. Organometallics 2004, 23, 3931−3940.
(12) (a) Choi, J.; Choliy, Y.; Zhang, X.; Emge, T. J.; Krogh-Jespersen,
K.; Goldman, A. S. J. Am. Chem. Soc. 2009, 131, 15627−15629.
(b) Kundu, S. K.; Choi, J.; Wang, D. Y.; Choliy, Y.; Emge, T. J.; Krogh-
Jespersen, K. J. Am. Chem. Soc. 2013, 135, 5127−5143.
(13) Haibach, M. C.; Lease, N.; Goldman, A. S. Angew. Chem., Int. Ed.
2014, 53, 10160−10163.
(14) Edouard, G. A.; Kelley, P.; Herbert, D. E.; Agapie, T.
Organometallics 2015, 34, 5254−5277.
(15) (a) Lara, P.; Paneque, M.; Poveda, M. L.; Salazar, V.; Santos, L.
L.; Carmona, E. J. Am. Chem. Soc. 2006, 128, 3512−3513. (b) Santos,
L. L.; Mereiter, K.; Paneque, M. Organometallics 2013, 32, 565−569.
(16) For other examples of pincer-ligand transition-metal complexes,
see: (a) Sun, J.-S.; Uzelmeier, C. E.; Ward, D. L.; Dunbar, K. R.
Polyhedron 1998, 17, 2049−2063. (b) Han, X.-H.; Yamamoto, Y. J.
Organomet. Chem. 1998, 561, 157−165. (c) Kataoka, Y.; Nakamura,
T.; Tani, K. Chem. Lett. 2003, 32, 66−67. (d) Shmidt, A. F.; Smirnov,
V. V. Kinet. Catal. 2005, 46, 495−501. (e) Zhu, Y.; Smith, D.; Herbert,
D.; Gatard, S.; Ozerov, O. Chem. Commun. 2012, 48, 218−220.
(f) Lao, D.-B.; Owens, A. C. E.; Heinekey, D. M.; Goldberg, K. I. ACS
Catal. 2013, 3, 2391−2396. (g) Miller, A. J. M.; Kaminsky, W.;
Goldberg, K. I. Organometallics 2014, 33, 1245−1252.
(17) Arisawa, M.; Nihei, Y.; Suzuki, T.; Yamaguchi, M. Org. Lett.
2012, 14, 855−857.
(18) (a) Ramirez, F.; Chen, E. H.; Dershowitz, S. J. Am. Chem. Soc.
1959, 81, 4338−4342. (b) Denney, D. B.; Felton, S. M. J. Am. Chem.
Soc. 1968, 90, 183−187. (c) Cooper, M. K.; Downes, J. M.;
Duclcworth, P. A.; Tiekink, E. R. T. Aust. J. Chem. 1992, 45, 595−
609. (d) Bestmann, H. J.; Fiirst, T. G.; Schier, A. Angew. Chem., Int. Ed.
Engl. 1993, 32, 1747−1750. (e) Moiseev, D. V.; Patrick, B. O.; James,
B. R.; Hu, T. Q. Inorg. Chim. Acta 2010, 363, 3569−3574.
(19) (a) Takeda, N.; Tagawa, T.; Unno, M. Heteroat. Chem. 2014, 25,
628−635. (b) X-ray crystallographic data for Rh-A have been
deposited in the Cambridge Crystallographic Data Centre database
(http://www.ccdc.cam.ac.uk/) under accession code CCDC 1442978.
G
DOI: 10.1021/acs.organomet.6b00638
Organometallics XXXX, XXX, XXX−XXX