Preparations of Saturated N-P-N Type Secondary Phosphine Oxides and their Applications in Cross-Coupling Reactions

Article abstract of DOI:10.1002/jccs.201500445

A series of cyclohexane-1,2-diamine (3a-3d) and benzene-1,2-diamine derivatives (3e-3h) were pre- pared. Followed by hydrolysis, the reaction of 3a-3c with PCl₃ successfully led to the formation of cor- responding metastable saturated heteroato

Full text of DOI:10.1002/jccs.201500445

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Preparations of Saturated N-P-N Type Secondary Phosphine Oxides and their
Applications in Cross-Coupling Reactions
Yu-Chang Chang, Ya-Han Liang and Fung-E Hong*
Department of Chemistry, National Chung Hsing University, Taichung 40227, Taiwan
(Received: Nov. 4, 2015; Accepted: Feb. 2, 2016; Published Online: Apr. 5, 2016; DOI: 10.1002/jccs.201500445)
A series of cyclohexane-1,2-diamine (3a-3d) and benzene-1,2-diamine derivatives (3e-3h) were pre-
pared. Followed by hydrolysis, the reaction of 3a-3c with PCl3 successfully led to the formation of cor-
responding metastable saturated heteroatom-substituted secondary phosphine oxides (HASPO 4a-4c),
a tautomer of the saturated heteroatom-substituted phosphinous acid (HAPA). Whereas ambient-stable
diamine-coordinated palladium complexes were obtained, HAPA-coordinated palladium complexes
were not successfully synthesized. The molecular structures of HASPO 4c, Pd(OAc)2(3a), PdBr2(3b)
and Pd(OAc)2(3c) and [Cu(NO3)(3d)+][NO3 ] were determined by single-crystal X-ray diffraction
-
method. Catalysis of in-situ Suzuki-Miyaura cross-coupling reactions for aryl bromides and
phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at
60 °C is the combination of 2 mmol% 3a/3.0 mmol KOH/1.0 mL 1,4-dioxane /1 mmol% Pd(OAc)2.
Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor-
mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl
bromides were observed while using 4-bromoanisole and styrene as substrates. The optimized condi-
tion for Heck reaction at 100 °C is 3 mmol% 3d/3.0 mmol CsF/1.0 mL toluene/3 mmol% Pd(OAc)2. In
general, cyclohexane-1,2- diamine derivatives exhibited better catalytic properties than those of ben-
zene-1,2-diamines.
Keywords: 1,2-diamines; Secondary phosphine oxides; Suzuki reactions; Heck reactions.
INTRODUCTION
Palladium-catalyzed cross-coupling reactions such as
fects through alternating the electron-withdrawing/donat-
ing substituents and the steric property ushered by the three
substituents.12-14 In addition to phosphines, 1,2-diamino-
ethane derivatives represent a series of well-known bi-
dentate ligands, which are inexpensive, easily accessible,
environmentally benign and substituent-tunable (Figure 1).
Applications of 1,2-diaminoethane-coordinated copper
complexes to catalyze coupling reactions between aryl
halides and amines were reported with good efficiencies by
Buchwald et al.15-19
Suzuki-Miyaura and Heck reactions provide chemists with
readily accessible toolkits to make carbon-carbon bond un-
der mild conditions. The central part of cross-coupling
methodology lies in the linking of an electropositive car-
bon moiety with an electronegative carbon or heteroatom
fragment (e.g. aryl halide with arylboronic acid for
Suzuki-Miyaura reaction). The first literature addressing
Suzuki-Miyaura and Heck catalytic cross-coupling reac-
tions can be traced back to 19791,2 and 19713-1972,4 re-
spectively. Among all the methods of C-C bond formation,
Suzuki-Miyaura cross-coupling reaction is regarded as one
of the most frequently used tool.5-7 For Heck reaction, the
construction of new C-C single bond between organic ha-
lide/triflate and olefin can be accomplished even at room
temperature.8-10
The progresses of Suzuki-Miyaura and Heck reac-
tions heavily rely on the development of ancillary ligands.11
Trialkyl or aryl phosphines have long been the ligands of
choice due to their readily tunable electronic and steric ef-
Fig. 1. Acyclic and cyclic 1,2-diaminoethane deriva-
tives.
* Corresponding author. Email: fehong@dragon.nchu.edu.tw
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201500445
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Chang et al.
In Suzuki-Miyaura or Heck cross-coupling reactions,
Utilizing the molecular backbone of diamine31,32 or
diimine,33-36 the synthetic protocols of heteroatom-substi-
tuted N-P-N type secondary phosphine oxides (HASPO) or
saturated diaminochlorophosphane/unsaturated diamino-
chlorophospholene (HASPO precursor) have been estab-
lished. A series of N-P-N/O-P-O type HASPO were shown
in Figure 2.37 By combining tert-butyl substituted N-P-N
type SPO with Pd(dba)2 as the catalytic system, good per-
formances were observed in Suzuki-Miyaura reaction as
well as in amination reaction even with less reactive aryl
chloride.31 Furthermore, Ackermann et al. firstly applied
saturated O-P-O type HASPO to Kumada-Corriu reaction
for inactivated aryl heteroaryl tosylates.38 Asymmetric
HASPO has also been synthesized and applied to asymmet-
ric catalytic reactions.39
the use of diamine20-25 or diimine26-29 as ancillary ligands
have been reported. In most cases, elevated temperature is
required to achieve high catalytic yield. For Suzuki-
Miyaura cross-coupling to be efficiently carried out at
room temperature, electron-donating groups should be
functionalized on 1,4-diazabutadiene.29 Recently, palla-
dium complexes chelated by cyclic 1,2-diaminoethane and
1,2-diiminoethane derivatives with benzyl substituents on
nitrogen atoms were employed as pre-catalysts in palla-
dium-catalyzed Suzuki-Miyaura cross-coupling reactions
with fair efficiencies by Franzén et al. (Scheme 1).22,30 It
was found that the catalytic performance of diamines are
generally better than that of diimines. Nevertheless, it re-
mains plenty of room for improvement in this system since
harsh condition, high reaction temperature and long reac-
tion hours (i.e. 120 °C and 24 hrs), is typically required.
Penta-valent secondary phosphine oxide (R’R”PH
(=O), SPO) is the tautomer of tri-valent phosphinous acid
(R’R”POH, PA).40 The latter can be used as a coordinating
ligand via its lone-pair electrons. SPO-to-PA tautomeri-
zation is a chemical equilibrium normally favorable to the
SPO form.41 It can be balanced to PA tautomer in the pres-
ence of transition-metal fragment (Scheme 2).42 SPO be-
haves as pre-ligand in a catalytic reaction,39 and one merit
of employing it lies in its air- and moisture-stability.32,37,43-48
Li et al. firstly showed that air-stable SPO (R2P(O)H: R =
-tBu) is an efficient pre-ligand for C-C, C-N and C-S
cross-coupling bond formation for inactivated aryl chlo-
rides, aryl bromides, olefins, amines, and thiols, given that
elevated temperature is normally required.47-49
Cyclic 1,2-diaminoethane and 1,2-diimino-
ethane derivatives chelated palladium com-
plexes
Scheme 1
The tautomerization of phosphinous acid
and its coordinated metal complex
Scheme 2
Fig. 2. Selected heteroatom-substituted secondary phosphine oxides (HASPO) from the literature.31,37,38
354
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Cross-coupling Reactions
In this study, we explored the use of diamines as pre-
Preparation of cyclic diamines (3a-3h) and
heteroatom substituted secondary phos-
phine oxides (HASPO 4a-4c). See Ref. 30
for the detail of the preparations of 3a and
3b
Scheme 3
cursors to develop a series of saturated HASPO pre-
ligands. The capacities of saturated/unsaturated cyclic
diamines and the given HASPOs as ligands for Suzuki-
Miyaura and Heck reactions were subsequently investi-
gated. Attempts to synthesize saturated HAPA-coordinated
palladium complexes were made but the diamine-coordi-
nated complexes were obtained. Therefore, the coordina-
tion chemistry of these diamine ligands toward palladium
and copper sources was further investigated. Finally, the
optimized reaction conditions for in-situ Suzuki-Miyaura
and Heck cross-coupling catalytic reactions were screened
for diamine ligands.
RESULTS AND DISCUSSION
Preparation of cyclic diamines (3a-3h) and saturated
heteroatom-substituted secondary phosphine oxides
(HASPO 4a-4c)
Firstly, diimines (2a-2h) were prepared in good
yields from the reaction of cyclohexane-1,2-diamines or
benzene-1,2-diamines with two molar equivalents of the
corresponding benzaldehyde or picolinaldehyde (for the
synthesis of 3h) (Scheme 3). The reactions were carried out
at refluxed MeOH for 30 minutes. At 25 °C, 2.1 molar
equivalents of NaBH4 were added to the solution except in
the cases of 3e and 3f (LiAlH4 was used, refluxed at THF
for 12 hours). Then, the reaction mixture was refluxed for
another 15 minutes till the cease of released gas. Subse-
quently, the mixture was quenched by water and extracted
by CH2Cl2. Purified diamines (3a-3f) were collected after
column chromatography. Note here, in 3g only one amino
group was functionalized presumably due to severer steric
hindrance between the two bulky substituents inherent to
the structural rigidity of planar benzene-1,2-diamine. Fur-
ther reactions of 3a-3c with PCl3 in toluene and the pres-
ence of NEt3 at 0 °C for 3 hours presumably led to the
formation of precursors, 2-chloro-1,3,2-diazaphospholene.
The targeted saturated heteroatom-substituted sec-
ondary phosphine oxides (HASPO 4a-4c) were obtained
after the hydrolysis of the corresponding 3a-3c and thereaf-
ter workup (Scheme 3). Nevertheless, our attempts to syn-
thesize unsaturated HASPO 4e from benzene-1,2-diamine
3e were not successful due to its highly unstable nature. It
decomposed within 15 minutes at ambient temperature af-
ter workup. Hence, no further attempts for the synthesis of
HASPO from the benzene-1,2-diamines 3f-3h were pur-
sued. In addition to the structural rigidity of benzene-
1,2-diamine, the high chemical instability of (benzene-
1,2-diamine)-based unsaturated HASPO with respect to
the metastability of (cyclohexane-1,2-diamine)-based satu-
rated HASPO will be addressed in more details.
The structure of 4c was determined by X-ray diffrac-
tion method and was depicted in Figure 3. The bond length
of P(1)-O(1) is 1.605(4) Å, a typical double bond. The at-
oms, P(1), N(1), C(1), C(6), N(2), in the five-membered
ring are not co-planar. Rather, the shape is more like a cyc-
lopentane. Lone-pair electrons on the two nitrogen atoms
are pointing to the opposite directions with respect to the
five-membered ring. In the crystal structure of 4c, two sub-
stituents on nitrogen atoms have the potential to create se-
vere steric hindrance when phosphinous acid HAPA 4c’ co-
ordinates to transition metal fragments.
Several attempts to prepare saturated HAPA-coordi-
nated palladium complex were unsuccessful, and the fol-
lowed X-ray structural determination of these reaction
products were resolved as diamine-coordinated complexes.
Initially, monitored closely by 31P NMR, the reaction of
HASPO 4b with PdBr2 in THF at 60 °C was carried out for
12 hours (Scheme 4). The disappearance of characteristic
JP-H might indicate the conversion of HASPO 4b to its cor-
responding HAPA 4b’, and then to 4b’-coordinated palla-
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The formations of diamine-coordinated pal-
ladium complexes from different reactions
Scheme 4
Pd(OAc)2(3a), PdBr2(3b) and Pd(OAc)2(3c), respec-
tively. In Cambridge Structure Database (CSD),51,52 only
twelve diamine-coordinated palladium complexes were
found within the searching constraints of Pd(diamine), in
which diamine represents cyclohexane-1,2-diamine with
an extended alkyl group attached to each nitrogen sites on
the Pd-containing five-membered ring.53 In addition to
diamine ligand, other ancillary ligands coordinated to pal-
ladium center of the twelve hits are required to fulfill the
16-electron count of square planar d8-Pd(II) center. Among
them, three complexes (CSD Refcode: REWPIT, TUVGIB
and VOFSAL) are coordinated by another two chloride lig-
ands, respectively. The Pd-N bond lengths and N-Pd-N
bond angles of these three complexes are within 2.045~
2.069 Å and 83.46~84.88°, showing consistency with
Pd(OAc)2(3a), PdBr2(3b) and Pd(OAc)2(3c).
Fig. 3. Molecular structure of HASPO 4c. Some hy-
drogen atoms are omitted for clarity.
dium complex. Nevertheless, an unexpected 3b-coordi-
nated palladium complex (PdBr2(3b)) was obtained while
trying to grow crystals of product in THF solution. This
could be originated from the unstable nature of 4b’ caused
by the existence of trace amount of water during the re-
action or crystal-growing process. ORTEP diagram of
PdBr2(3b) is depicted in Figure 4b. It seems that the
endocyclic P-N or exocyclic P-O bond in unsaturated
HAPA were fragile. Similar reactions of 4a and 4c with
PdBr2 gave only the uncharacterized reaction mixtures to-
gether with the decomposed HASPO moieties.50 When
Pd(OAc)2, Pd(COD)Cl2 or Pd(dba)3 were employed as the
palladium sources in the related reactions with 4a, 4b or 4c,
similar uncharacterized reaction mixtures were obtained.
Moreover, the same structure of diamine-chelated palla-
dium complex could be obtained directly from the reaction
of the corresponding diamine 3b with PdBr2 (Scheme 4).
For the formation of diamine 3a- and 3c- coordinated
Pd(OAc)2 complexes, it is evidenced by the crystal struc-
tures of both Pd(OAc)2(3a) and Pd(OAc)2(3c) (Scheme
4).
Interestingly, substituents attached to the two endo-
cyclic nitrogen atoms in PdBr2(3b) and Pd(OAc)2(3c) are
in cis-relationship; however, they are in trans-relationship
in Pd(OAc)2(3a). Among those twelve crystal structures,
MAPBEM and ZOXFEX (CSD Refcode) are equipped
with a tetra-dentate diamine ligand. The remaining ten
crystal structures with the PdLn(diamine) (n = 1 or 2) for-
mula, only one structure (HECFEB) has its two substitu-
ents on the two endocyclic nitrogen atoms being in trans-
relationship. Note that cis-relationship would bear larger
intramolecular steric repulsion. Additionally, Pd(OAc)2(3a)
and Pd(OAc)2(3c) are the first two structures with two ace-
tate as coordinating ligands when compared to those twelve
The crystal structures of Pd(OAc)2(3a), PdBr2(3b)
and Pd(OAc)2(3c) reveal that they are all diamine chelated
palladium complexes. The bond lengths of Pd-N are in the
range of 2.025~2.081 Å. The bond angles of N(1)-Pd(1)-
N(2) are 84.48(11)°, 85.0(2)° and 84.12(7)° for
structures. For comparison with Buchwald’s work,15-18
a
blue diamine-chelated copper complex [Cu(NO3)(3d)+]
-
[NO3 ] was prepared from the reaction of 3d with Cu(NO3)2×
3H2O. Its crystal structure was shown in Figure 4d. Close
examination of the structure of [Cu(NO3)(3d)+][NO3 ] has
-
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Cross-coupling Reactions
Fig. 4. Molecular structures of (a) Pd(OAc)2(3a), (b) PdBr2(3b), (c) Pd(OAc)2(3c) and (d) [Cu(NO3)(3d)+][NO3 ]. Some
-
hydrogen atoms are omitted for clarity.
tive 31P NMR spectra, while nearly 40% 4b was disinte-
revealed that 3d acted as a tetra-dentate ligand. Two types
-
of NO3 are coexistence in a molecule: one acts as ligand
and the other as counterion. The bond lengths of Cu(1)-N
range from 1.985~2.013 Å. The bond distance of
Cu(1)-O(1) is 2.3887(12) Å. It is 2.472 Å for Cu(1)…O(6).
The bond angles are 81.63(6)°, 85.80(5)° and 82.75(5)° for
N(3)-Cu(1)-N(1), N(1)-Cu(1)-N(2), and N(2)-Cu(1)-N(4),
respectively.
grated to unspecified species. Obviously, 4a-4c are thermo-
dynamically metastable.
In addition, 31P NMR spectrum of HASPO 4a showed
up to 50% decomposition when dissolved in THF and
heated at 60 °C for 2 hours (the integration of peak at 20.8
ppm became smaller and two new peaks at 4.3 and -6.4
ppm appeared). In the same reaction conditions, quantita-
tive decomposition of 4b was observed by 31P NMR spec-
trum (peak at 22.3 ppm disappeared while two new peaks
showed at 5.2 and -6.8 ppm). As to 4c, 10% of thermal deg-
radation was recorded (peak at 19.4 ppm turned weaker in
intensity and new emerging peak showed at -6.60 ppm).
Instability of unsaturated HASPO 4e and
metastability of saturated HASPO 4a-4c
Saturated HASPO 4a-4c are metastable compounds
and will undergo decomposition slowly in ambient temper-
ature, while unsaturated HASPO 4e decomposed rather
quickly in 15 minutes after synthesized. HASPO 4a and 4c
are white solids, and 4b is yellow liquid. Being preserved
in nitrogen-filled vials at 4 °C for 10 months, about 20%
decomposition of 4a and 4c were observed by their respec-
1
According to H NMR spectra of 4a-4c collected after
heated for 2 hours, their respective diamine peaks were ob-
served. Since 4a-4b have been obtained and characterized,
we believe that the failure to obtain the HAPA 4a’-4b’ co-
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Chang et al.
ordinated palladium complexes mainly lies in the meta-
stability of HAPA 4a’-4c’. In summary, the ambient and
thermal stability is decreased in the order of HASPO/
HAPA 4c > 4a > 4b.
tions (c.f. entries 1 and 5; Entries 2 and 6). It is believed
that the structural flexibility of cyclohexyl backbone in
3a-3c makes the better chelation of palladium complexes
than diamines with benzene backbone, and results in the dif-
ferences in reactivity. When 3b/3c was employed as ligand
in entry 2 and 3, -OCH3/-CH3 groups introduced larger steric
hindrance; this could hamper the intermolecular interaction
between substrate and palladium (entry 1 vs. 2 and 3 in Table
1). In addition, the extremely low catalytic efficiency of
diamine 3d (entry 4) could be ascribed to the formation of
stable tetra-coordinated palladium complex.
Palladium-catalyzed Suzuki-Miyaura reactions using
diamines 3a-3h and HASPO 4a-4c as ligands
Palladium-catalyzed Suzuki-Miyaura cross-coupling
reactions of aryl halides and phenylboronic acid were car-
ried out by employing these newly-made diamines 3a-3h
and HASPO 4a-4c auxiliary ligands (Scheme 5). As re-
vealed, cyclohexane ring functionalized on the 1,2-diamine
ligands reinforces the chelating ability in providing flexi-
bility of the bidentate ligands. Several factors that affect the
efficiency of the reactions, including the palladium sources,
ligand-to-metal ratio, bases, temperature, reaction time,
solvent and concentration etc., had been screened to search
for the optimized condition for the reaction.
In entries 9, 10 and 11 in Table 1, HASPO 4a-4c were
used as pre-ligands. It was the HAPA-coordinated palla-
dium that was expected as catalytic active species. How-
ever, according to the thermal instability of HASPO 4a-4c
and the result of the reaction of HASPO with various palla-
dium sources discussed in the previous sections, HAPA
(HASPO tautomer) could degrade into diamine ligand.
Therefore, it could be diamines that play a major role in the
Suzuki-Miyaura coupling reaction. It could be evidenced
from the catalytic yield within the first half hour is quite
low (entries 9, 10 and 11). The possible route for the forma-
tion of diamine-Pd active species is HASPO-to-HAPA
tautomerization followed by the fast decomposition of
HAPAto diamine ligand at 60 °C. Compared to HASPO 4a,
the lower catalytic yield in the cases of HASPO 4b and 4c
may again correspond to the larger steric hindrance of lig-
ands and longer catalytic induction time. On the contrary,
the yield exceeded 99% after three hours for HASPO 4a
(entry 9 in Table 1).
Suzuki-Miyaura cross-coupling reactions of
arylbromides and phenylboronic acid cata-
lyzed by the combination of palladium salt
and ligand
Scheme 5
Firstly, in-situ Suzuki-Miyaura cross-coupling reac-
tions were carried out to examine the catalytic efficiencies
of these newly made ligands. The general procedure for the
Suzuki-Miyaura cross-coupling reactions under investiga-
tion is described below. A 20 mL Schlenk tube was placed
with 1.0 mmol of aryl halides, 1.5 mmol of phenylboronic
acid, 1.0 mol% of palladium salt and 1.0 mol% of ligand,
1.0 mL of solvent and 3.0 mmol of base. The mixture was
stirred at designated temperature and time depending on
the reactions executed. The conversion rate is decided from
Table 1. Suzuki-Miyaura coupling reactions employing various
ligands [a]
Entry
Ligand
Yield (0.5 h) [b]
Yield (3.0 h) [b]
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
65
9
50
-
-
-
-
-
13
-
-
99
99
99
0
53
70
54
13
99
23
55
1
the integration of H NMR peak of product against stan-
dard; while the isolated yield was determined after purified
by column chromatography.
As shown in Table 1, the conversions are almost
quantitatively in 3.0 hours for using 3a, 3b, 3c, HASPO 4a
as ligands from the preliminary screening (entries 1, 2, 3,
9). Here, 3a stands out as the best ligand while the reaction
time is reduced to 0.5 hour (entry 1). Therefore, 3a is cho-
sen as the ligand for the optimization of reaction condition
thereafter. It is worthy of noting that ligands with cyclo-
hexyl backbone performed more effectively than those
with benzene ring backbone in the Suzuki-Miyaura reac-
3g
3h
4a
4b
4c
9
10
11
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), phenyl
boronic acid (1.5 mmol), KOH (3.0 mmol), THF (1.0 mL),
Pd(OAc)2 (1.0 mol%), ligand (1.0 mol%), Pd:L = 1:1, 60 °C. [b]
Determined by 1H NMR.
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Cross-coupling Reactions
Among all the influential factors that affect the cata-
fortunately, no conversion could be observed for every
single case.
lytic efficiency of the cross-coupling reaction, the role
played by base probably is the most ambiguous factor.29,54,55
Thereby, the impact of different bases on the catalytic
yields was then investigated with 3a as ligand, and the re-
sults are shown in Table 2. Among all the bases examined,
it was found that KOH in THF is the most effective combi-
nation (Table 2, entry 1). Unexpectedly, other bases gave
poor catalytic yields.
For most cross-coupling reactions, the generation of
ionic intermediates are assumed in the catalytic cycle.
Thereby, polar solvent is a favourite choice since the solu-
bility of these species is highly related to the overall cata-
lytic performance. As shown in Table 4, the combination of
KOH with either toluene, THF or 1,4-dioxane led to excel-
lent results in 1 hour (entries 1-3 in Table 4). As a result,
1,4-dioxane was selected as solvent for searching the opti-
mal reaction conditions. Upon the metal-to-ligand ratio
was tuning to 1:2 or 1:3 in the reaction duration of 0.25
hour, the catalytic yield decreased in the later case (c.f. en-
tries 2 and 3 in Table 4). The poor performance of the later
case is understandable since excess ligand might retard the
formation of unsaturated active palladium species during
reaction. Similar catalytic performance of the first two
cases is worthy of noting. It is believed that the best combi-
nation of Pd(OAc)2/3a is still 1:1 because the 3a acts as a
bi-dentate ligand is revealed in the crystal structure. The
lower dosage of 3a is more atom economic. Moreover, the
optimized metal-to-ligand ratio is consistent with the
conventional observation for a bi-dentate ligand with
palladium source.
Subsequently, several palladium complexes were
screened for Suzuki-Miyaura reaction (diamine 3a as
ligand). The best result was obtained when Pd(OAc)2 was
used (entry 1 in Table 3) because the di-valent Pd(OAc)2 is
easier to be reduced to Pd(0) in the presence of elec-
tron-rich ligand.56 Unexpectedly, poor performance was
observed for a zero-valent palladium source, Pd2(dba)3
(Entry 4 in Table 3). The same reactions were carried out
with various copper salts of CuI, CuBr, Cu(OAc)2 and CuI2
in the copper-to-3a ratio of 1:1 at 60 °C for 12 hours. Un-
Table 2. Suzuki-Miyaura coupling reactions employing various
bases [a]
Entry
Ligand
Yield (0.5 h) [b]
Yield (1.0 h) [b]
1
2
3
4
5
6
7
8
9
KOH
NaOH
65
0
0
5
0
0
0
0
0
2
95
2
5
8
0
3
0
0
2
2
Zero-valent palladium complex is the active species
for the cross-coupling reaction.57 Besides, the induction
time for the reduction of higher valent palladium center is
of crucial importance to the overall catalytic performance.
As a result, the induction time of the Suzuki-Miyaura reac-
tion was examined by monitoring the 1H NMR conversion
yield by using the reaction condition of 1 mol% of 3a/1
mol% of Pd(OAc)2/3 eq. KOH/1 mL 1,4-dioxane at 60 °C.
NaOtBu
K2CO3
KOtBu
Cs2CO3
CsF
Na2CO3
KF
K3PO4×nH2O
10
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), phenyl
boronic acid (1.5 mmol), base (3.0 mmol), THF (1.0 mL),
Pd(OAc)2 (1.0 mol%), 3a (1.0 mol%), Pd:L = 1:1, 60 °C. [b]
Determined by 1H NMR.
Table 4. Suzuki-Miyaura coupling reactions employing various
solvents [a]
Entry
Ligand
Yield (0.25 h) [b] Yield (3.0 h) [b]
Table 3. Suzuki-Miyaura coupling reactions employing various
palladium sources [a]
1
2
3
4
5
6
7
8
9
1,4-dioxane
1,4-dioxane
1,4-dioxane
Toluene
THF
DMF
MeOH
H2O
DMSO
95
96c
84d
56
35
8
99
-
-
99
65
15
22
21
0
Entry
Ligand
Yield (0.5 h) [b] Yield (3.0 h) [b]
1
2
3
4
5
6
Pd(OAc)2
Pd(COD)Cl2
PdBr2
65
50
13
15
12
1
95
61
27
22
15
1
Pd2(dba)3
16
13
0
[Pd(Cl)( 3-C3H5)]2
PdCl2
[a] Reaction condition: 4-bromoanisole (1.0 mmol), phenylboronic
acid (1.5 mmol), KOH (3.0 mmol), THF (1 mL), palladium
source (1.0 mol%), 3a (1.0 mol%), Pd:L = 1:1, 60 °C. [b]
Determined by 1H NMR.
[a] Reaction condition: 4-bromoanisole (1.0 mmol), phenylboronic
acid (1.5 mmol), KOH (3.0 mmol), THF (1 mL), palladium
source (1.0 mol%), 3a (1.0 mol%), Pd:L = 1:1, 60 °C. [b]
Determined by 1H NMR.
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Article
Chang et al.
It was found that the conversion yield was 89% in the first 3
minutes and it reached to 99% within 30 minutes (Figure
5). The observation showed that 3a/Pd(OAc)2 is an effi-
cient catalytic system for Suzuki-Miyaura cross-coupling
reactions.
performance of 3a is less efficient in the cases of aryl chlo-
rides than those of aryl bromides (supporting information).
Palladium-catalyzed Heck reactions using diamine
3a-3d as ligands
Having been demonstrated in the previous section,
diamine 3a-3d are more effective ligands than 3e-3h in the
Suzuki-Miyaura reactions. Factors such as ligand type, pal-
ladium source, palladium-to-ligand ratio, temperature,
base and solvent system strongly influence the catalytic
yield of a cross-coupling reaction. Moreover, Heck reac-
tion normally requires more severe reaction condition than
that of Suzuki reaction.58,59 Since high temperature is often
required for good catalytic performance, diamine 3a-3d
were employed for Heck reactions at 100 °C with DMF as
solvent (Scheme 6). To compare our results with the pub-
lished work of Hayashi,60 similar procedure were carried
out and described below. A 20 mL Schlenk tube was
charged with 1.0 mmol of substituted bromobenzene, 1.2
mmol of styrene, 3.0 mmol of base, 3.0 mol% of palladium
The scope of this Suzuki-Miyaura coupling reaction
using various aryl bromides was examined (Table 5). When
1-bromo-2-methylbenzene was used and catalysed by 2
mol% Pd(OAc)2 for 3 hours, moderate catalytic yield of
65% was obtained (entry 1). Worse yield was shown if
2-bromo-1,3,5-trimethylbenzene was chosen as aryl halide
(21% in entry 2). Obviously, steric hindrance caused by ad-
jacent methyl groups in 2-bromo-1,3,5-trimethylbenzene is
believed to be the cause of low catalytic yield. For elec-
tron-rich or deficient aryl bromides shown in entry 3-5, the
reactions gave the corresponding products in good yield.
Poor yield were observed in the cases having aldehyde, ni-
tro, amino or olefin substituents on the para-position of
benzene ring (entry 7, 8 and 9). For substrate with nitrile or
hydroxyl substituents, excellent results were obtained (en-
tries 10 and 11). Rather poor performances were observed
for heterocyclic aryl halides (entry 12, 13 and 14). The co-
ordination of heteroatom of aryl bromides to the catalytic
palladium centre reduces the reactivity of the active
species.
Conventionally, aryl chlorides are less reactive than
aryl bromides towards Suzuki-Miyaura coupling reaction.
It is due to the higher barrier height is estimated for Ar-Cl
bond breaking.57 Nevertheless, the low-cost aryl chloride
makes them attractive reaction species. The optimized re-
action conditions using 3a as auxiliary ligand in Suzuki-
Miyaura reaction for aryl chlorides were carried out. The
Fig. 5. The conversion rate of Suzuki-Miyaura reac-
tion monitored by 1H NMR.
360
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Cross-coupling Reactions
salt and 3.0 mol% of 3a-3d as catalyst precursors. The re-
action mixture was stirred at 100 °C and designated reac-
tion time. Work-up process was then followed. Due to
steric hindrance, the formation of trans-1,2-disubstituted
ethylene shall be the major product than its cis-counterpart.
Meanwhile, the 1,1’-disubstituted ethylene is also ex-
pected as a minor side product.
dioxane or toluene (entry 1 or 2 in Table 9). Moderate
yields (75% or 74%) were obtained for reducing the reac-
Table 6. Effect of various ligands in Heck reaction [a]
Entry
Ligand
NMR conv. (%)b
1
2
3
4
3a
3b
3c
3d
41
43
58
68
Moderate yields were obtained from preliminary
screening for diamine 3a-3d (Table 6). Interestingly, the
performance of 3d is the best among all four ligands (entry
4 in Table 6). However, 3a performs poorly in Suzuki-
Miyaura reaction (entry 4 in Table 1). Based on our screen-
ing tests, 3d was chosen as the ligand for investigating the
optimized reaction condition thereafter. Note that the con-
formation of 3d has the capacity to act as a tetra-dentate
ligand. At high reaction temperature, the energy is possible
high enough to break the pyridyl-Pd bonds and to regener-
ate active palladium center.
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), styrene (1.2
mmol), K2CO3 (3.0 mmol), DMF (1 mL), Pd(OAc)2 (3.0 mol%),
ligand (3.0 mol%), Pd:L = 1:1, 100 °C, 12 h; [b] Determined by
1H NMR.
Table 7. Effect of various bases in Heck reaction [a]
Entry
Ligand
NMR conv. (%)b
1
2
3
4
5
6
7
8
NaOH
KOH
47
15
18
68
28
79
36
50
61
82
41
NaOtBu
K2CO3
In Heck reaction, base assists the release of hydrogen
halide (HX) during the reductive elimination process in or-
der to speed up the overall catalytic cycle. The screening of
bases was pursued and results are shown in Table 7. It
showed that CsF in DMF was the most effective combina-
tion (entry 10 in Table 7). Contrarily, two effective bases in
Heck reaction, KOH and NaOtBu, performed poorly. The
results highlight again that base is one of the most unpre-
dictable factors in cross-coupling reactions.
KOtBu
Cs2CO3
Na2CO3
KF
K3PO4×nH2O
CsF
9
10
11
CsOH×H2O
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), styrene (1.2
mmol), base (3.0 mmol), DMF (1 mL), Pd(OAc)2 (3.0 mol%), 3d
(3.0 mol%), Pd:L = 1:1, 100 °C, 12 h; [b] Determined by 1H
NMR.
The screening of palladium sources was pursued in
this section. The results showed that Pd(OAc)2 was the best
choice as in the Suzuki-Miyaura reaction (Table 8). Em-
ploying Pd(OAc)2 as the palladium source, minor reduc-
tion in yield was observed when the reaction time was re-
duced to 3 hours in DMF (entry 2 in Table 8). With PdX2 (X
= Cl or Br), greater reduction in yield was observed (entry 4
or 5 in Table 8). Our screening showed that 3d/DMF/
CsF/Pd(OAc)2 is the best combination for Heck reactions
performed herein. However, it is still of interests to locate
the suitable solvent system for diamine 3d in the Heck
reactions.
Table 8. Effect of various bases in Heck reaction [a]
Entry
Ligand
NMR conv. (%)b
1
2
3
4
5
6
[Pd(Cl)(h3-C3H5)]2
Pd(OAc)2
Pd(COD)Cl2
PdBr2
80 (69)
82 (74)
75 (52)
78 (23)
79 (8)
PdCl2
Pd2dba3
69 (40)
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), styrene (1.2
mmol), CsF (3.0 mmol), DMF (1 mL), palladium salt (3.0 mol%),
3d (3.0 mol%), Pd:L = 1:1, 100 °C. [b] The conversion was
determined by 1H NMR after 12 hours (in parentheses, 3 hours in
toluene).
Excellent yield (> 99%) was obtained for the reaction
carried out at 100 °C for 12 hours using either in 1,4-
Heck reaction of 4-bromoanisole and styrene
Scheme 6
J. Chin. Chem. Soc. 2016, 63, 353-367
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361

Article
Chang et al.
Table 9. Effect of the solvent in Heck reactions [a] NMR
conversion yields are in %
Entry
Ligand
NMR conv. [b] conv. [c] conv. [d]
1
2
3
4
1,4-dioxane
toluene
DMF
99
99
82
25
75
74
-
31
45
-
DMSO
-
-
[a] Reaction conditions: 4-bromoanisole (1.0 mmol), styrene (1.2
mmol), K2CO3 (3.0 mmol), solvent (1 mL), Pd(OAc)2 (3.0
mol%), ligand (3.0 mol%), Pd:L = 1:1, 100 °C, 12 h; [b]
Determined by 1H NMR, 100 °C, 12 h; [c] Determined by 1H
NMR, 100 °C, 3 h; [d] Determined by 1H NMR, 60 °C, 12 h.
tion time to 3 hours. Similarly, when lowering the tempera-
ture to 60 °C for 12 hours, the Heck reactions showed
worse NMR conversion yield than reducing the reaction
time (c.f. compare the forth and fifth columns in Table 9). It
reveals that the reaction temperature is a more important
factor than the duration of reaction time. Thereafter, tolu-
ene was chosen as the solvent for the optimization of reac-
tion condition. In summary, the optimized reaction condi-
tion for Heck reaction in this study is 3d/CsF/Pd(OAc)2/ to-
luene.
thesizing HAPA-coordinated palladium complexes were
made as our first step, but the instability of HAPA did not
allow us to precede further characterizations. Interestingly,
ambient stable diamine-coordinated palladium complexes
were successfully obtained from the reaction of HASPO
with PdBr2. As a result, the coordinating ability of our
diamine ligands toward palladium and copper were investi-
gated herein. Three diamine-coordinated palladium com-
plexes (Pd(OAc)2(3a), PdBr2(3b), Pd(OAc)2(3c)) and
The scope of this Heck coupling reaction using vari-
ous aryl bromides was examined using the optimized con-
dition (Table 10). Fair efficiencies were obtained for aryl
bromides with either electron-withdrawing or -donating
group substituents reacted in 1 mL toluene at 100 °C for 6
hours (entries 1-6 in Table 10). Small amount of side
products either from self-coupling of arylbromide or
1,1’-disubstituted ethylene were observed, thus also less-
ens the conversion rate of the target compound. Moderate
performance was observed in the case of 4-bromoben-
zonitrile although the reaction time was prolonged to 12
hours (entry 7 in Table 10). Rather poor result was obtained
for heterocyclic case such as 2-bromopyridine (entry 8 in
Table 10).
one copper complex ([Cu(NO3)(3d)+][NO3 ]) were synthe-
-
sized and characterized by X-ray diffraction method.
Furthermore, in-situ Suzuki-Miyaura and Heck
cross-coupling catalytic reactions were carried out for
diamine in order to expand the usage of diamine ligands.
The functionalized cyclohexyl and benzyl frameworks
force the two amino groups residing on the neighboring po-
sitions, a plus for chelating a metal center. Preliminary re-
sults showed that 1,2-diamino derivatives with cyclohexyl
backbone, 3a-3c, perform better than their benzene coun-
terparts, 3e-3h, partly due to the electron-donating nature
of alkyl substituent. These diamine ligands can be applied
to Suzuki-Miyaura reaction at 60 °C to achieve high cata-
lytic yield. Moreover, using HASPO 4a-4c as ancillary lig-
ands, Suzuki-Miyaura cross-coupling reactions were con-
ducted giving rise to very low catalytic yield within the first
half hour. Besides, high temperature is required for cata-
lytic Heck reactions. Moderate catalytic performance em-
CONCLUSION
Aiming at developing new HASPO pre-ligands for
palladium-catalyzed Suzuki-Miyaura cross-coupling and
Heck reactions, we have demonstrated the preparation,
characterization and reactivity studies of cyclic 1,2-di-
amino derivatives and N-P-N type heteroatom-substituted
secondary phosphine oxides (HASPO). HASPO can tauto-
merize to heteroatom-substituted phosphinous acid (HAPA,
the genuine ligand for metal-coordination). Crystal struc-
ture of HASPO 4c was well resolved. Efforts toward syn-
362
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Cross-coupling Reactions
ploying aryl halides as substrates is provided in the sup-
porting information.
17.54 mmol), and 2-pyridinecarboxaldehyde (1d) (1.68 mL,
17.54 mmol) were used. Good qualities of 3b and 3c could be ob-
tained from participation directly. Recrystallization of 3b-3d by
ethyl acetate and CH2Cl2 gave good qualities of products without
further separation by column chromatography. The yields of puri-
fied 3b (pale yellow liquid), 3c (white solid), and 3d (yellow
solid) are 98% (3.04 g, 8.58 mmol), 62% (2.06 g, 5.44 mmol),
90% (2.88 g, 7.89 mmol), respectively.
The inefficient catalytic performance can be attri-
buted to the thermal instability of HASPO/HAPA 4a-4c
ligand system evidenced by the NMR specptra. In addition,
decomposition of HASPO 4a-4c was also observed after
long-term storage in nitrogen-filled vials at 4 °C. The
exocyclic P-OH or endocyclic P-N single bonds in HAPAis
fragile in 60 °C and the compounds decomposed into their
corresponding 1,2-diamines.
‡ Spectroscopic data for 3a. 1H NMR(CDCl3, /ppm): 7.31
(t, J = 2.8 Hz, 8H, Ar), 7.24 (t, J = 2.8 Hz, 2H, Ar), 3.90 (d, J =
12.8 Hz, 2H, Benzylic), 3.65 (d, J = 13.2 Hz, 2H, Benzylic), 2.26
(d, J = 4.4 Hz, 2H), 2.16 (d, J = 12.0 Hz, 2H), 1.80 (b, 2H), 1.72 (d,
J = 9.2 Hz, 2H), 1.23 (t, J = 10.8 Hz, 2H), 1.04 (d, J = 9.6 Hz, 2H);
13C NMR(CDCl3, /ppm): 141.0, 128.2, 128.0, 126.6 (Aromatic),
60.8 (Benzylic), 50.8 (CH), 31.5 (CH2), 25.0 (CH2). ‡ Spectro-
scopic data for 3b. 1H NMR(CDCl3, /ppm): 7.28 (d, J = 7.6 Hz,
2H, Ar), 7.21 (t, J = 7.6 Hz, 2H, Ar), 6.90 (t, J = 7.6 Hz, 2H, Ar),
6.82 (d, J = 8.0 Hz, 2H, Ar), 3.92 (d, J = 13.2 Hz, 2H, Benzylic),
3.72 (s, 6H, OMe), 3.64 (d, J = 13.2 Hz, 2H, Benzylic), 2.38 (b,
2H), 2.26 (d, J = 4.8 Hz, 2H), 2.14 (d, J = 12.0 Hz, 2H), 1.71 (d, J
= 8.0 Hz, 2H), 1.23 (t, J = 10.8 Hz, 2H), 1.09 (d, J = 9.2 Hz, 2H);
13C NMR(CDCl3, /ppm): 157.4, 129.3, 129.1, 127.7, 120.2, 109.9
(Aromatic), 60.8 (Benzylic), 55.0 (OMe), 45.8 (CH), 31.4 (CH2),
25.0(CH2). ‡ Spectroscopic data for 3d. 1H NMR(CDCl3, /ppm):
8.51 (d, J = 4.0 Hz, 2H, Ar), 7.61 (t, J = 8.0 Hz, 2H, Ar), 7.38 (d, J
= 8.0 Hz, 2H, Ar), 7.12 (d, J = 8.0 Hz, 2H, Ar), 4.02 (d, J = 12.8
Hz, 2H, Benzylic), 3.83 (d, J = 13.2 Hz, 2H, Benzylic), 2.30 (d, J
= 4.4 Hz, 2H), 2.23 (b, 2H), 2.13 (d, J = 11.6 Hz, 2H), 1.71 (d, J =
EXPERIMENTAL
General procedure: All reactions were carried out under a
nitrogen atmosphere using standard Schlenk techniques or in a ni-
trogen-flushed glove box. Freshly distilled solvents were used.
All processes of separations of the products were performed by
Centrifugal Thin Layer Chromatography (CTLC, Chromatotron,
Harrison model 8924) or column chromatography. GC-MS analy-
sis was performed on an Agilent 5890 gas chromatograph (Restek
Rtx-5MS fused silica capillary column: 30 m, 0.25 mm, 0.5 mm)
with an AgilentÒ 5972 mass selective detector. Routine 1H NMR
spectra were recorded on a Varian-400 spectrometer at 399.760
MHz. The chemical shifts are reported in ppm relative to internal
standards TMS (d = 0.0). 31P and 13C NMR spectra were recorded
at 161.8 and 100.5 MHz, respectively. The chemical shifts for the
former and the latter are reported in ppm relative to internal stan-
dards H3PO4 (d = 0.0) and CHCl3 (d = 77), respectively. Mass
spectra were recorded on JOEL JMS-SX/SX 102A GC/MS/MS
spectrometer.
7.2 Hz, 2H), 1.22 (t, J = 8.2 Hz, 2H), 1.08 (t, J = 10.4 Hz, 2H); 13
C
General procedure for the synthesis of 3a-3d: Into a 100
mL three neck round flask with stir bar was placed (+/-)-trans-
1,2-diaminocyclohexane (1.00 g, 8.77 mmol) and 15 mL MeOH.
The solution was stirred under refluxed before 2 molar equiva-
lents of benzaldehyde (1a) (1.78 mL, 17.54 mmol) was added.
The formation of 2a was observable within 30 minutes of
refluxing. It was then allowed to cool to 25 °C before 2.1 molar
equivalents of NaBH4 (0.70 g, 18.41 mmol) was added. The solu-
tion was allowed to reflux further for 15~30 minutes till the ceas-
ing of bubbling. Again, the solution was allowed to cool to 25 °C
and then 5 mL of H2O was added to quench the reaction. Pale yel-
low solid was extracted by CH2Cl2 from separatory funnel. Sub-
sequently, the separation of pure product was performed by col-
umn chromatography. The yield of isolated 3a is 70% (1.80 g,
6.12 mmol).
NMR (CDCl3, /ppm): 160.6, 149.0, 136.4, 122.3, 121.7 (Aro-
matic), 61.3 (Benzylic), 52.5, 31.5, 25.0.
General procedure for the synthesis of 3e-3f: Into a 100
mL three-neck round flask with stir bar was placed o-phenyl-
enediamine (1.08 g, 10.0 mmol) and 15 mL MeOH. The solution
was stirred under refluxed before 2 molar equivalents of benzal-
dehyde (1a) (2.04 mL, 20.0 mmol) was added. The formation of
2e was noticed within 30 minutes of refluxing. It was allowed to
cool to 25 °C before 4.0 molar equivalents of LiAlH4 (1.52 g, 40.0
mmol) and 20 mL of THF were added. The solution was allowed
to reflux further for another 12 hours. Again, the solution was al-
lowed to cool to 25 °C and then ether acetate and 5 mL of H2O
were added to quench the reaction. More ether acetate was added
and yellow liquid was extracted by ether acetate from separatory
funnel. Subsequently, the separation of pure product was per-
formed by column chromatography. The yield of isolated 3e (yel-
low solid) is 60% (2.72 g, 20.0 mmol). Similar procedures were
applied to the preparation of 3f. The corresponding starting mate-
Similar procedures were applied to the preparations of
3b-3d. The corresponding starting materials, 2-methoxybenzal-
dehyde (1b) (2.39 g, 17.54 mmol), mesitaldehyde (1c) (2.59 g,
J. Chin. Chem. Soc. 2016, 63, 353-367
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363

Article
Chang et al.
rial, 2-methoxybenzaldehyde (1b) (2.72 g, 20.0 mmol), was used.
The yield of isolated 3f (yellow solid) is 40% (1.39 g, 3.99 mmol).
tate and water were added and the organic phase was collected
from separatory funnel. Subsequently, the separation of pure
product was performed by column chromatography. The yield of
isolated 4a (white solid) is 58% (0.79 g, 2.32 mmol).
1
‡ Spectroscopic data for 3e. H NMR(CDCl3, /ppm):
7.40-7.25 (m, 10H, Ar), 6.80-6.70 (m, 4H, Ar), 4.32 (s, 4H,
Benzylic), 3.65(b, 2H); 13C NMR(CDCl3, /ppm): 139.4, 137.1,
128.6, 127.8, 127.2, 119.4, 111.9 (Aromatic), 48.7 (Benzylic). ‡
Similar procedures were applied to the preparations of 4b
and 4c from corresponding 3b (1.42 g, 4.0 mmol) and 3c (1.51 g,
4.0 mmol). The yields of purified 4b (yellow liquid) and 4c (white
solid) are 35% (0.56 g, 1.40 mmol) and 75% (1.27 g, 3.00 mmol),
1
Spectroscopic data for 3f. H NMR(CDCl3, /ppm): 7.31-7.23
(m, 4H, Ar), 6.93-6.88 (m, 4H, Ar), 6.77-6.71 (m, 4H, Ar), 4.31
(s, 4H, Benzylic), 3.88 (b, 2H), 3.83 (s, 6H, OMe); 13C NMR
(CDCl3, /ppm): 157.4, 137.6, 129.1, 128.2, 127.5, 120.5, 119.2,
112.4, 110.2 (Aromatic), 55.2 (Benzylic), 44.1 (OMe).
1
respectively. ‡ Spectroscopic data for 4a. H NMR(CDCl3,
/ppm): 7.52 (d, JP-H = 604.7 Hz, 1H, P-H), 7.41 (d, J = 10.0 Hz,
2H, Ar), 7.34-7.22 (m, 8H, Ar), 4.40-4.04 (m, 4H, Benzylic),
3.00-2.80 (m, 2H), 1.84-1.66 (m, 4H), 1.26-1.01 (m, 4H); 13C
NMR (CDCl3, /ppm): 138.3,138.1, 128.5, 128.4, 128.1, 127.9,
127.3, 127.2 (Aromatic), 63.1, 62.7 (Benzylic), 46.5, 45.9 (CH),
29.3, 28.6 (CH2), 24.1, 24.0 (CH2); 31P NMR(CDCl3, /ppm): 20.8
General procedure for the synthesis of 3g-3h: Similar
procedures for the preparation of 3f are applicable for making 3g
and 3h. The corresponding 2-pyridinecarboxaldehyde (1d) (2.14
g, 20.0 mmol) was firstly used to prepare 2h. Further reaction
with NaBH4 (0.79 g, 21.0 mmol) and workup followed to produce
3h (yellow solid) in 35% yield (1.02 g, 3.52 mmol). Similar pro-
cedures were applied to the preparation of 3g. The corresponding
mesitaldehyde (1c) (2.95 mL, 20.0 mmol) was used. Due to se-
vere steric hindrance, only one side of amine is formed. The yield
of isolated 3g (yellow solid) is 68% (1.63 g, 6.79 mmol).
‡ Spectroscopic data for 3g. 1H NMR(CDCl3, /ppm): 6.94
(s, 2H, Ar), 6.93 (d, J = 4.0 Hz, 1H, Ar), 6.86 (d, J = 8.0 Hz, 1H,
Ar), 6.74 (d, J = 4.0 Hz, 2H, Ar), 4.22 (s, 2H, Benzylic), 3.23 (b,
3H), 2.39 (s, 6H), 2.33 (s, 3H); 13C NMR(CDCl3, /ppm): 138.0,
137.6, 137.2, 134.2, 132.3, 129.0, 120.6, 118.5, 116.1, 111.3, (Ar-
omatic), 42.5 (Benzylic), 20.9 (Mes), 19.4 (Mes). ‡ Spectro-
scopic data for 3h. 1H NMR (CDCl3, /ppm): 8.59 (d, J = 4.2 Hz,
2H, Ar), 7.63 (t, J = 7.6 Hz, 2H, Ar), 7.36 (d, J = 7.6 Hz, 2H, Ar),
7.17 (t, J = 6.0 Hz, 2H, Ar), 6.75 (quin., J = 4.0 Hz, 2H, Ar), 6.66
(quin., J = 4.0 Hz, 2H, Ar), 4.55 (b, 2H), 4.49 (s, 2H, Benzylic);
13C NMR(CDCl3, /ppm): 158.8, 149.2, 136.9, 136.6, 122.0,
121.6, 119.3, 112.1 (Aromatic), 49.8 (Benzylic).
1
(d, JP-H = 605.8 Hz). ‡ Spectroscopic data for 4b. H NMR
(CDCl3, /ppm): 7.39 (d, JP-H = 614.7 Hz, 1H, P-H), 7.41 (q, J = 7.2
Hz, 2H, Ar), 7.23 (quin. J = 8.4 Hz, 2H, Ar), 6.95-6.82 (m, 4H,
Ar), 4.54 (t, J = 15.2 Hz, 1H, Benzylic), 4.35 (q, J = 8.4 Hz, 1H,
Benzylic), 4.19 (t., J = 16.8 Hz, 1H, Benzylic), 3.87 (d, J = 13.2
Hz, 1H, Benzylic), 3.83 (s, 3H, OMe), 3.81 (s, 3H, OMe), 3.04 (t,
J = 11.4 Hz, 1H), 2.79 (t, J = 10.2 Hz, 1H), 2.01 (d, J = 10.4 Hz,
1H), 1.88 (d, J = 11.4 Hz, 1H), 1.70 (t, J = 12.8 Hz, 2H), 1.29-1.14
(m, 3H), 1.07-1.01 (m, 1H); 13C NMR(CDCl3, /ppm): 157.0,
156.9, 129.8, 128.9, 128.4, 128.0, 127.6, 126.2, 120.3, 120.1,
110.1, 110.0 (Aromatic), 64.4, 62.4 (Benzylic), 55.1, 55.0 (OMe),
41.2, 10.1 (CH), 29.4, 28.5 (CH2), 24.3, 24.1 (CH2); 31P NMR
(CDCl3, /ppm): 22.3 (d, JP-H = 615.0 Hz). ‡ Spectroscopic data
1
for 4c. H NMR (CDCl3, /ppm): 6.57 (d, JP-H = 609.2 Hz, 1H,
P-H), 6.79 (s, 2H, Ar), 6.79 (s, 2H, Ar), 4.17-4.08 (m, 2H,
Benzylic), 3.95-3.86 (m, 2H, Benzylic), 3.11 (t, J = 10.4 Hz, 1H),
2.85 (t, J = 9.8 Hz, 1H), 2.36 (s, 6H), 2.33 (s, 6H), 2.22 (s, 3H),
2.21 (s, 3H), 2.01 (d, J = 10.4 Hz, 1H), 2.07 (d, J = 11.2 Hz, 1H),
1.96 (s, 1H), 1.79 (s,1H), 1.35-1.15 (m, 5 H); 13C NMR (CDCl3,
/ppm): 137.9, 137.7, 137.5, 137.0, 129.8, 129.4, 129.2, 129.1 (Ar-
omatic), 66.1, 63.7 (Benzylic), 42.8, 41.7 (CH), 29.3, 28.9 (CH2),
24.4, 24.3, (CH2), 20.9, 20.8 (Mes), 20.3, 20.2 (Mes); 31P NMR
(CDCl3, /ppm): 19.4 (d, JP-H = 609.6 Hz). Compound 4c has been
communicated elsewhere.
General procedure for the synthesis of 4a-4c: The proce-
dures for the preparation of 4a-4c were modified from literature.32
Into a 100 mL round flask with stir bar was placed 3a (1.17 g, 4.0
mmol). The air was pumped out and backfilled with nitrogen gas
before 8 mL of toluene was added. Three molar equivalents of
triethylamine (1.66 mL, 12.0 mmol) was injected and then the
flask was placed in ice-water bath. Under nitrogen, 5 mL of tolu-
ene and 1.5 molar equivalents of phosphorus trichloride (0.35
mL, 6.0 mmol) were added to another 100 mL flask. At 0 °C, the
content of the latter flask was transferred to the first one slowly
through cannular needle and stirred for 3 hours at that tempera-
ture. Certain amount of hexane was added to salt out ionic com-
pounds. Participate was filtrated out and followed by hydrolysis
of the filtrated solution with water for 5 minutes. More ether ace-
General procedure for the synthesis of Pd(OAc)2 (3a) and
Pd(OAc)2 (3c): Into a 10 mL Schlenk flask was placed 3a (0.035 g,
0.1 mmol) and Pd(OAc)2 (0.022 g, 0.1 mmol) with 1 mLof CH2Cl2.
The solution was stirred at 25 °C for 12 hours. Yellow color and
column shape crystals were formed and determined by x-ray dif-
fraction methods as Pd(OAc)2 (3a). The same procedures are appli-
cable to the preparation of 3c_Pd from its corresponding 3c.
1
‡ Spectroscopic data for Pd(OAc)2(3a). H NMR (d6-
364
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J. Chin. Chem. Soc. 2016, 63, 353-367

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Cross-coupling Reactions
DMSO, /ppm): 7.86 (d, J = 7.6 Hz, 2H, Ar), 7.40~7.28 (m, 4H,
Ar), 6.92~6.75 (m, 4H, Ar), 6.17(q, J = 10.8 Hz, 1H, N-H), 4.54
(d, J = 11.6 Hz, 1H, N-H) 3.87~3.58 (m, 4H, Benzylic), 2.89~2.80
(m, 1H, cyclohexyl), 2.11~2.00 (m, 3H, cyclohexyl), 1.88 (s, 3H,
acetate), 1.84 (s, 3H, acetate), 1.54 (m, 2H, cyclohexyl), 1.23~
1.17 (m, 1H, cyclohexyl), 1.06~0.81 (m, 3H, cyclohexyl). 13C
NMR (CDCl3, /ppm): 174.9, 172.1, 152.3, 149.1, 137.0, 132.6,
130.1, 128.3, 127.5, 123.8, 123.0, 120.4, 66.0, 62.2, 57.3, 54.9,
49.1, 29.0, 24.6, 24.0, 23.7, 21.3. ‡ Spectroscopic data for
Pd(OAc)2 (3c). 1H NMR (CDCl3, /ppm): d = 7.76 (d, J = 10.4 Hz,
1H, N-H), 6.89 (s, 2H, Ar), 6.85 (s, 2H, Ar), 6.19~6.13 (m, 1H,
N-H), 4.36~4.30 (m, 1H, Benzylic), 4.12~4.07 (m, 1H, Benzylic),
3.84~3.78 (m, 2H, Benzylic and cyclohexyl), 3.61~3.58 (m, 1H,
Benzylic), 2.66~2.57 (m, 1H, cyclohexyl), 2.43 (s, 6H, CH3),
2.25 (s, 6H, CH3), 2.23 (s, 6H, CH3), 2.10~2.07 (m, 1H, cyclo-
hexyl), 1.97~1.92 (m, 1H, cyclohexyl), 1.85~1.78 (m, 1H, cyclo-
hexyl), 1.79 (s, 3H, acetate), 1.67 (d, J = 14.0 Hz, 1H, cyclo-
hexyl), 1.49 (d, J = 13.6 Hz, 1H, cyclohexyl), 1.25 (s, 3H, ace-
tate), 1.23~1.12 (m, 2H, cyclohexyl), 0.87~0.81 (m, 1H, cyclo-
hexyl). 13C NMR (CDCl3, /ppm): 180.6, 180.1, 138.5, 138.2,
137.6, 137.4, 129.8, 129.5, 128.2, 126.7, 67.5, 63.0, 51.6, 43.6,
32.4, 29.8, 24.8, 24.1, 22.9, 22.2, 20.9, 20.8, 20.6.
the aqueous layer was extracted with ethyl acetate (2 x 5 mL). The
combined organic layer was washed with brine and dried with an-
hydrous magnesium sulfate. The dried organic layer was concen-
trated in vacuo. The residue was purified by column chromatogra-
phy to give the desired product.
General procedure for Heck reactions: Schlenk tube was
charged with Pd(OAc)2 (0.03 mmol, 6.7 mg), 3a (0.03 mmol, 8.7
mg) and CsF (3.0 mmol, 0.456 g). This tube was subjected to vac-
uum for 10 minutes and then toluene (1 mL) was added. To this
mixture styrene (1.2 mmol, 0.137 mL) and aryl bromide (1.0
mmol) were added slowly with the help of syringe. The resulting
suspension was stirred at certain temperature for designated time.
After completion of reaction, the reaction was diluted with EtOAc
and filtered through a pad of Celite. The organic layer was then
extracted with ethylacetate (10 x 3 mL) and water. The organic
layer was collected separately and dried over anhydrous Na2SO4
and concentrated under reduced pressure to obtain crude residue.
The product was purified by flash chromatography (5% EtOAc/
hexane), which yielded the desired trans-stilbene.
X-ray crystallographic studies: Suitable crystals of
Pd(OAc)2 (3a), PdBr2 (3b), Pd(OAc)2 (3c), ([Cu(NO3)(3d)+]
-
[NO3 ]) and 4c were sealed in thin-walled glass capillaries under
General procedure for the synthesis of ([Cu(NO3)(3d)+]
[NO3-]): Into a 10 mL Schlenk flask was placed 3d (0.035 g, 0.1
mmol) and Cu(NO3)2×3H2O (0.022 g, 0.1 mmol) with 1 mL of
CH2Cl2. The solution was stirred at 25 °C for 12 hours. Participate
was filtrated out and clear blue solution was collected. Blue col-
ored cubic shape crystals were formed gradually from the solu-
tion. Its crystal structure was latterly determined by x-ray diffrac-
nitrogen atmosphere and mounted on a Bruker AXS SMART
1000 diffractometer. Intensity data were collected in 1350 frames
with increasing (width of 0.3° per frame). The absorption correc-
tion was based on the symmetry equivalent reflections using
SADABS program. The space group determination was based on
a check of the Laue symmetry and systematic absences, and was
confirmed using the structure solution. The structure was solved
by direct methods using a SHELXTL package.33 All non-H atoms
were located from successive Fourier maps and hydrogen atoms
were refined using a riding model. Anisotropic thermal parame-
ters were used for all non-H atoms, and fixed isotropic parameters
were used for H atoms.34 Crystallographic data for compounds
Pd(OAc)2(3a), PdBr2(3b), Pd(OAc)2(3c), ([Cu(NO3)(3d)+]
tion methods and assigned as ([Cu(NO3)(3d)+][NO3 ]). Since it is
-
a paramagnetic species, differentiable NMR spectra were not pos-
sible. The major mass pattern of ([Cu(NO3)(3d)+][NO3 ]) shows
-
the parent peak at m/z = 483 (P+) and the daughter peak at m/z =
+
+
421 (P-NO3 ) and m/z = 358 (P-2NO3 ).
General procedure for the Suzuki-Miyaura cross-cou-
pling reactions: Suzuki-Miyaura cross-coupling reactions were
performed according to the following procedures. The four reac-
tants, palladium salt, ligand, boronic acid and base, were placed
in a suitable oven-dried Schlenk flask. It was evacuated for 0.5
hour and backfilled with nitrogen gas before adding solvent and
aryl halide through a rubber septum. The aryl halides being solids
at room temperature were added prior to the evacuation/backfill
cycle. The flask was sealed with a rubber septum and the solution
was stirred at the required temperature for designated hours.
Then, the reaction mixture was diluted with ethyl acetate (3 mL)
and the cooled solution poured into a separatory funnel. The mix-
ture was washed with aqueous NaOH solution (1.0 M, 5 mL) and
-
[NO3 ]) and 4c are available from
SUPPORTING INFORMATION
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Center, CCDC no. 899551, 899552, 899553, 899554, and
899555 for compound Pd(OAc)2 (3a), PdBr2 (3b),
Pd(OAc)2 (3c), ([Cu(NO3)(3d)+][NO3 ]) and 4c, respec-
-
tively. Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.
J. Chin. Chem. Soc. 2016, 63, 353-367
© 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.jccs.wiley-vch.de
365

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