Amidophosphine-stabilized palladium complexes catalyse Suzuki–Miyaura cross-couplings in aqueous media

Article abstract of DOI:10.1002/aoc.3539

We report a simple and efficient procedure for Suzuki–Miyaura reactions in aqueous media catalysed by amidophosphine-stabilized palladium complexes trans-{L³PPh₂}₂PdCl₂ (3), trans-{L³PPhtBu}₂PdCl₂ (4), [Pd(η³-C₃H₅)(L³PPh₂)Cl] (5) and {Pd[2-(Me₂NCH₂)C₆H₄](L³PPh₂)Cl} (6). The acidity of the NH proton in complexes 3, 4, 5, 6 plays an important role in their catalytic activity. In addition, the palladium complexes cis-{L¹PPh₂}PdCl₂ (1) and trans-{L²PPh₂}₂PdCl₂ (2) stabilized by phosphines containing Y,C,Y-chelating ligands L^{1 ,2} have also been found to be useful catalysts for Suzuki–Miyaura reactions in aqueous media. The method can be effectively applied to both activated and deactivated aryl bromides yielding high or moderate conversions. The catalytic activity of couplings performed in pure water increases when utilizing a Pd complex with more acidic NH protons. A decrease of palladium concentration from 1.0 to 0.5 mol% does not lead to a substantial loss of conversion. In addition, Pd complex 1 can be efficiently recovered using two-phase system extraction. Copyright

Full text of DOI:10.1002/aoc.3539

Full paper
Received: 7 March 2016
Revised: 25 April 2016
Accepted: 20 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3539
Amidophosphine-stabilized palladium
complexes catalyse Suzuki–Miyaura cross-
couplings in aqueous media
a
a
b
b
c
Josef Jansa , Tomáš Řezníček , Libor Dostál , Zdena Růžičková , Filip Bureš
b
and Roman Jambor *
We report a simple and efficient procedure for Suzuki–Miyaura reactions in aqueous media catalysed by amidophosphine-
3
3
3
3
stabilized palladium complexes trans-{L PPh } PdCl (3), trans-{L PPhtBu} PdCl (4), [Pd(η -C H )(L PPh )Cl] (5) and {Pd[2-
2
2
2
2
2
3
5
2
3
2 2 6 4 2
(Me
NCH )C H ](L PPh )Cl} (6). The acidity of the NH proton in complexes 3–6 plays an important role in their catalytic activity.
In addition, the palladium complexes cis-{L PPh }PdCl (1) and trans-{L PPh } PdCl (2) stabilized by phosphines containing Y,C,
1
2
2
2
2 2
2
1
,2
Y-chelating ligands L have also been found to be useful catalysts for Suzuki–Miyaura reactions in aqueous media. The method
can be effectively applied to both activated and deactivated aryl bromides yielding high or moderate conversions. The catalytic
activity of couplings performed in pure water increases when utilizing a Pd complex with more acidic NH protons. A decrease
of palladium concentration from 1.0 to 0.5 mol% does not lead to a substantial loss of conversion. In addition, Pd complex 1
can be efficiently recovered using two-phase system extraction. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: aqueous media; palladium; Suzuki–Miyaura; C C coupling
We therefore decided to expand the number of
Introduction
amidophosphine-stabilized palladium complexes and prepared
3
3
The palladium-catalysed Suzuki–Miyaura cross-coupling reaction
between organoboron compounds and organic halides is a very
powerful tool for forming carbon–carbon bonds
the following complexes: trans-{L PPh } PdCl (3), trans-{L PPh
2 2 2
3
3
(tBu)} PdCl (4), [Pd(η -C H )(L PPh )Cl] (5) and {Pd[2-(Me NCH )
2 2 3 5 2 2 2
3 3 3
[
1–3]
and this makes
C H ](L PPh )Cl} (6). As the phosphines L PPh and L PPh(tBu)
6 4 2 2
the Suzuki–Miyaura reaction very important not only in academic
contain the NH functionality potentially suitable for two-phase
system extraction, we started with the testing of all the complexes
1–6 in the Suzuki–Miyaura cross-coupling reaction in aqueous
media. A decrease of the palladium concentration from 1.0 to
0.5 mol% does not show substantial loss of conversion. Among
complexes 3–6, it turns out that the catalytic activity of couplings
in water increases when utilizing Pd complex 6 with more acidic
NH protons. The possible recovery of 1 from water has also been
tested and it is demonstrated that Pd complex 1 can be efficiently
recovered by two-phase system extraction to give water-soluble
complex 7.
[4–7]
research but also in industrial synthesis of fine chemicals
and
[
8]
highly complex pharmaceuticals as well as in the synthesis of
[
9]
functionalized π-conjugated systems. The wide application of
the reaction results from the broad functional group tolerance,
the commercial availability and low toxicity of the organoborons,
[
10]
and the mild reaction conditions applied. Research in the field
of the palladium-catalysed Suzuki–Miyaura cross-coupling reaction
is focused on so-called green chemistry, that includes the possibility
[
11–15]
of using water as a solvent.
However, an efficient Suzuki–
Miyaura protocol in aqueous media is often restricted due to
limited solubility and the decreased stability of the catalyst in
[16–18]
water.
Therefore, a way to improve the efficiency of Suzuki–
Miyaura catalysis in water is by the employment of hydrophilic
[19–24]
ligands.
We have recently prepared the Pd complexes cis-{L PPh
1
* Correspondence to: Roman Jambor, Department of General and Inorganic
Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská
573, CZ-532 10 Pardubice, Czech Republic. E-mail: roman.jambor@upce.cz
2
}PdCl
(2) containing different Y,C,Y
2
2
(
2 2 2
1) and trans-{L PPh } PdCl
1
ꢀ
2
pincer-type ligands
L
(2,6-(Me
2
NCH
2
)
2
C
6 3
H )
and
L
(2,6-
ꢀ
[25]
(tBuOCH
2
)
2
6 3
C H )
(Fig. 1).
Recently, Baysal and co-workers re-
a Research Institute for Organic Syntheses (VUOS), Rybitví 296, CZ-533 54,
Pardubice-Rybitví, Czech Republic
3
3
ported the synthesis of cis-{L PPh
2
}
2
PdCl
2
, where L is (2,6-iPr
2
ꢀ
(C H )NH) (Fig. 1), and showed its suitability for Suzuki–Miyaura
6
3
[26]
3
b Department of General and Inorganic Chemistry, Faculty of Chemical Technology,
University of Pardubice, Studentská 573, CZ-532 10, Pardubice, Czech Republic
cross-coupling reactions. Ligand L with NH moiety and similarly
the presence of the NMe functional group in 1 could be suitable
2
for two-phase system extraction, while 2 contains OtBu group that
c Institute of Organic Chemistry and Technology, Faculty of Chemical Technology,
may render the complex soluble in water.
University of Pardubice, Studentská 573, CZ-532 10, Pardubice, Czech Republic
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

J. Jansa et al.
Figure 1. Potentially suitable complexes for two-phase system extraction.
Figure 2. PovRay view of 3. Hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (°): Pd1–Cl1 2.3014(8), Pd1–P1
Results and discussion
2.3124(4), P1–N1 1.6901(14), Cl1–Pd1–P1 89.70(1).
Synthesis and characterization of complexes 1–6
[
25]
Complexes 1 and 2 were prepared according to the literature.
Complexes 3 and 4, obtained by the reaction of PdCl with
and L PPh(tBu) (Scheme 1) were prepared to study the ef-
fect of the steric shielding of the phosphorus atom on the catalytic
[
27]
2
the P-N single bond (Σcov P,N = 1.73 Å) and P=N double bond
3
3
[
27]
L PPh
2
(
(
Σ
cov P,N = 1.63 Å) and is longer than in [(Ph
CH ) ] (1.6603(18) Å), where lone electron pair of phosphorus
atom is used in P=S covalent bond instead of P→Pd donation in
. The NH protons are involved in hydrogen bonding with Cl atoms
2 6 4
P S)NHC H –4-CH
[26]
3 2
3
activity. It is worth mentioning that cis-{L PPh
2
}
2
PdCl
with (cod)PdCl
the structure of the complex has not been determined so far.
2
has already
3
[26]
been prepared by the reaction of L PPh
2
2
,
but
3
with NH Cl bond distance of 3.193 Å.
3
1
The P NMR spectra of 3 and 4 show a signal at 61.8 ppm (3) and
9.9 ppm (4) that is shifted downfield compared to starting
Complexes 5 and 6 were prepared by the cleavage reaction of
3
6
dimeric [(η -C
3
H
5
)Pd-(μ-Cl)]
2 2 2 6 4 2
and [{2-(Me NCH )C H }Pd-(μ-Cl)] by
3
[26]
3
3
phosphines L PPh
2
(45.5 ppm) and L PPh(tBu) (54.9 ppm). The
phosphine L PPh
2
(Scheme 2).
3
1
31
P NMR signal found for 3 is similar to that of its cis-isomer
The P NMR spectra of 5 and 6 show a signal at 61.5 ppm (5) and
71.9 ppm (6) that is shifted downfield when compared to the
3
[26]
1
cis-{L PPh } PdCl (64.1 ppm). The H NMR spectra of 3 and 4
2
2
2
3
[26]
1
show the presence of four doublets at 0.88, 1.03, 1.23 and 1.34
starting phosphine L PPh (45.5 ppm). The H NMR spectra of
2
3
ppm of CH groups of ligand L in 3 (1.01, 1.16, 1.23 and 1.46
3
5 and 6 show the presence of a doublet at 0.91 ppm of CH groups
in 5 (0.89 in 6) and signals of CH groups at 3.24 ppm of iPr moiety of
ligand L in 5 (3.81 in 6). The H NMR spectra also reveal the doublet
of the P NH group of ligand L at 4.33 ppm in 5 (6.40 ppm in 6) with
coupling constant J( P, H) = 6 Hz for 5 ( J( P, H) = 7 Hz for 6)
that is shifted downfield when compared to that found for free
In addition, the signals at 1.14,
2.36, 3.29 and 4.46 ppm define the presence of the Pd(η -C H )
3
ppm for 4) and two septets of CH groups at 3.24 and 3.43 ppm in
1
3
1
3
(3.81 and 3.86 ppm in 4). The H NMR spectra also reveal the dou-
3
3
blet of the P NH group of ligand L in 3 at 5.76 ppm (5.57 ppm for 4)
with coupling constant J( P, H) = 6 Hz for 3 ( J( P, H) = 5 Hz for
) that is shifted downfield when compare to the value found in
free phosphine L PPh (3.78 ppm) and L PPh(tBu) (4.08 ppm).
The data also differ from those found for cis-{L PPh } PdCl
2
31
1
2
31
1
2
31
1
2
31
1
4
3
[26]
3
3
[26]
2
phosphine L PPh (3.78 ppm).
2
3
[26]
2
3
2
2
3 5
where one doublet at 1.17 ppm of CH groups, one septet of CH
3
group in 5.
1
groups of the iPr moiety at 3.09 ppm and the doublet of the P NH
The H NMR data thus provide evidence of different acidity of
PNH atom in the Pd(II) complexes 3–6 and define decreasing acidity
of NH atom in the sequence 6 > 3 > 4 > 5. Since complex 2 is par-
tially soluble in water due to the presence of the ethereal OtBu
groups and complexes 1, 3–6 contain functional groups potentially
suitable for two-phase system extraction, we started with the test-
ing of all the complexes 1–6 in Suzuki–Miyaura cross-coupling reac-
tions in aqueous media.
3
group of ligand L at 6.10 ppm are observed. The data, however,
suggest the existence of highly symmetric arrangement of the Pd
atom in 3 and 4. To establish unambiguously the structure of
prepared complexes, X-ray structural analysis of complex 3 was
carried out.
Single crystals of 3 suitable for X-ray diffraction analysis were
2
obtained from saturated Et O–hexane solution. The molecular
structure of 3 is shown in Fig. 2. The crystal data and structure
refinement are given in Table 1.
The coordination number of the Pd atom in 3 is four with mutu-
Catalytic activity of 1–6 in Suzuki–Miyaura cross-coupling re-
actions in aqueous media
3
ally trans coordinated phosphines L PPh
2
and chlorine atoms Cl1
and Cl1a. The P1-N1 bond distance (1.6901(14) Å) varies between
All prepared Pd(II) complexes 1–6 were used as catalysts in the
[
28–33]
Suzuki–Miyaura
reaction between 4-nitrobenzene bromide
and phenylboronic acid (Scheme 3). The cross-coupling reactions
were carried out under aqueous conditions (EtOH–water or water)
involving Pd(II) catalysts 1–6 (1 mol%)/Na
argon.
2
CO
The reactions were monitored using GC analysis and
the results are summarized in Table 2. Commercially available
(PPh PdCl ] was used as a standard.
The systems EtOH–H O in 4:1 and 2:1 ratios and pure water were
3
system under
[
34,35]
[
3 2
)
2
2
tested as aqueous media. 4-Nitrobiphenyl is detected as a major
product in all tested aqueous media. As a general trend, compound
5 with weakly acidic NH group shows lower catalytic activity in pure
3
Scheme 1. Synthesis of complexes trans-{L PPh(R)}
2
PdCl
2
(R = Ph (3); tBu (4)).
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Efficient catalysts for Suzuki–Miyaura reaction in aqueous media
2
Table 1. Crystal data and structure refinement for 3 and 7·H O·0.5EtOH
3
7·H
2
O·0.5EtOH
PPdꢁH Oꢁ0.5C
Yellow
Triclinic
C
48
H
56Cl
2
N
2
P
2
Pd
24
C H
30Cl
2
N
2
2
2 6
H O
Empirical formula
Colour
Yellow
Triclinic
Crystal system
Space group
a (Å)
b (Å)
c (Å)
P
ꢀ1
P
ꢀ1
9.5870(4)
13.7651(12)
14.7880(10)
15.1400(10)
72.578(5)
74.261(5)
75.084(4)
2
11.1420(4)
11.7201(5)
82.641(3)
69.695(4)
74.079(3)
1
α (°)
β (°)
γ (°)
Z
ꢀ
1
μ (mm
(Mg m
)
0.635
1.037
ꢀ
3
D
x
)
1.325
1.510
Crystal size (mm)
Crystal shape
θ range (°)
0.48 × 0.33 × 0.21
Block
0.46 × 0.36 × 0.18
Block
1.9–27.5
1.4–27.5
a
a
Tmin, Tmax
0.873, 0.958
0.688, 0.861
No. of reflections measured
No. of unique reflections; Rint
No. of observed ref. [I > 2σ(I)]
No. of parameters
22 068
5162; 0.0356
4659
57 780
12 705; 0.0364
10 195
250
614
b
Final R [I > 2σ(I)]
0.0232
0.0446
b
wR2 (all data)
0.0586
0.1248
a
Correction by SORTAV program.
h
i
h
i
ꢀ
ꢁ
ꢀ
ꢁ
1=2
ꢀ
ꢁ
ꢀ
ꢁ
1=2
b
2
2
c
2
2
2
2
o
2
c
2
Definitions: RðFÞ ¼ ∑jjFoj ꢀ jFcjj=∑jFoj, wR2 ¼ ∑w F ꢀ F =∑w F
, S ¼ ∑w F ꢀ F
= Nreflns ꢀ Nparams
, weighting scheme w =
o
o
ꢂ
ꢂ
2
2
ꢀ1
2
o
2
2
o
2
o
2
o
ꢂ
ꢂ
[σ (F
o
) + (w
1
P) + w
2
P] , P = [max(F
, 0) + 2F
c
]/3, Rint ¼ ∑ F ꢀ F ðmeanÞ =∑F (summation is carried out only where more than one symmetry
equivalent is averaged).
Table 2. Catalytic activity of 1–6 in Suzuki–Miyaura cross-coupling re-
actions in aqueous media
Catalyst
2
EtOH–H O (4:1)
2
EtOH–H O (2:1)
2
H O
a
Conversion (%)
100
97
96
[
3 2 2
(PPh ) PdCl ]
1
9
5
97
99
95
96
97
99
99
99
98
99
76
99
2
3
4
5
6
97
99
99
97
99
a
Calculated from GC-MS analysis.
Scheme 2. Synthesis of compounds 5 and 6.
water than the other complexes, and, as a result, complex 5 was not
tested further.
Therefore, complexes 1–4 and 6 were used as the catalysts in the
[28–33]
Suzuki–Miyaura reaction
between 4′-substituted phenyl bro-
mides and 4-substituted phenylboronic acids (Scheme 4). The
cross-coupling reactions were carried out in water with 1.0 mol%
of the palladium complexes. The reactions were monitored using
GC analysis and the results are summarized in Table 3. Commer-
3 2 2
cially available [(PPh ) PdCl ] was used as a standard (for the results
Scheme 3. Suzuki–Miyaura cross-coupling reaction in aqueous media.
of the Suzuki–Miyaura reaction between 4-chlorobenzonitrile and
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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J. Jansa et al.
Scheme 5. Synthesis of ionic Pd complex 7 and its regeneration to neutral
compound 1.
Scheme 4. Suzuki–Miyaura cross-coupling reactions in water.
phenylboronic acid, see Scheme S1 and Table S1 in the supporting
information).
characterized using NMR spectroscopy in D O and the structure
2
was determined using X-ray diffraction analysis.
31
Aryl bromides featuring either electron-donating (NMe ) or
The P NMR spectrum of 7 shows a signal at 18.4 ppm which is
2
[
25]
electron-withdrawing (NO ) substituents were screened. 4,4′-
comparable with the signal found for neutral complex 1 (19.4)
but is shifted downfield when compared with the free phosphine
2
Disubstituted biphenyls are detected as major products in all cases.
As a general trend, compounds 1–4 and 6 show higher catalytic ac-
tivities in all examined reactions than commercially available
1
[25]
1
L PPh (16.5 ppm). The H NMR spectrum of 7 reveals an AB spin
2
system (δ 3.25, δ 3.75) with J being 12 Hz and a broad singlet at
A
B
AB
[
(PPh ) PdCl ]. Similarly, complex 1 having cis arrangement of chlo-
2
4.19 ppm for CH N groups and two signals at 2.73 and 2.76 ppm for
3
2
2
1
1
rine atoms shows lower catalytic activities in all examined reactions
the CH groups of ligand L . In addition, the H NMR spectrum also
3
than complexes 2–4 having trans arrangement. Complex 4 featur-
ing bulkier phosphine L PPh(tBu) shows higher catalytic activity
reveals a signal of NH group at 4.28 ppm. This pattern indicates the
3
presence of two inequivalent CH NMe moieties. While the first one
2
2
than 3. As expected, the Suzuki–Miyaura reaction carried out with
the electron-rich N,N-dimethyl-4-bromoaniline affords lower yields
of between 62 and 75%, with the highest activity observed for com-
plex 6 where corresponding turnover number (TON) and turnover
coordinates the palladium atom to provide P,N-chelating mode of
1
phosphine L PPh similar to 1, the second CH NMe group is pro-
2
2
2
tonated to give CH NHMe moiety in 7. As a result, the palladium
2
2
ionic compound 7 consisting of cis-{[2-(Me NHCH )-6-(Me NCH )
2
2
2
2
ꢀ
1
frequency (TOF) are 75 and 6.3 h (0.1 mol% Pd, 75% yield at
0°C for 6 h, see Table S2 in supporting information). Decrease of
C H ]Ph P}PdCl cation and chloride anion is properly soluble in
6 3 2 2
water.
8
palladium concentration from 1.0 to 0.5 mol% does not show a sub-
stantial loss of conversion (Table 3). Calculated TON (198) and TOF
The molecular structure of 7 was also confirmed using X-ray dif-
fraction techniques and is depicted in Fig. 3 together with selected
bond distances and angles. The crystal data and structure refine-
ment are given in Table 1.
ꢀ
1
(33 h ) (0.05 mol% of 1, 99% yield at 80°C for 6 h, see Table S2
in supporting information) are, however, lower than those reported
in Suzuki–Miyaura coupling reactions catalysed by Pd hybrid on
graphene oxide.
The coordination number of Pd(II) is four in 7 with mutual cis
[11,12]
arrangement of phosphorus P1 and nitrogen N1 of the (k NP)-coor-
2
1
dinated phosphine L PPh and chlorine Cl1 and Cl2 atoms in 7. The
2
cis atoms define angles of P1–Pd1–N1 = 94.14(12)° and Cl1–Pd1–
Cl2 = 87.32(4)°, and there is a distortion of ideal square-planar
geometry resulting from the ring strain of the six-membered
metallacycle Pd1–P1–C1–C2–C7–N1. The Pd1-P1 bond distance in
7 of 2.2522(10) Å is similar to those observed in phosphine and
Two-phase separation of 1: synthesis of 7
The possible recovery of 1-6 from water was also tested. These at-
tempts were successful for compound 1 only. The aqueous phase
was acidified using HCl to pH around 5 after the Suzuki–Miyaura re-
action followed by extraction with EtOAc. The organic layers were
dried and subjected to GC analysis, while the aqueous phase was
[
36–49]
phosphite complexes of Pd(II) (2.2–2.4 Å)
and in neutral com-
[
25]
plex 1 (2.2543(9) Å).
The value of Pd1-N1 bond length being
evaporated. The residue was dissolved in D
2
O and characterized
2.097(3) Å defines a strong coordination of N to Pd atom and is
comparable to those found in similar monomeric N-coordinated
3
1
using P NMR spectroscopy, where a signal at 18.4 ppm is detected
and assigned to complex 7. Compound 7 can be also prepared by
the reaction of 1 with 1 eq. of HCl (Scheme 5) and it was
[
43–55]
Pd complexes (2.073–2.155 Å).
The second nitrogen atom
1
N2 of L PPh
2
is protonated providing palladium cation cis-{[2-
Table 3. Catalytic activity of 1–4 and 6 in Suzuki–Miyaura cross-coupling reactions in H
2
O
Catalyst
R′ = NO
2
R′ = NO
2
R′ = NO
2
R′ = NO
2
R′ = NMe
2
R′ = NO
2
R = CF
3
R = Ph
R = CHO
R = H
R = H
R = H
a
Conversion (%)
b
4
7
5
35
34
96
19
46
[
3 2 2
(PPh ) PdCl ]
b
1
6
72
85
81
88
83
71
89
89
93
81
99
99
98
99
99
62
65
69
67
75
99
b
2
3
4
6
88
81
84
83
96
b
90
b
93
b
91
a
Calculated from GC-MS analysis.
b
0.5 mol% of palladium complex.
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Appl. Organometal. Chem. (2016)

Efficient catalysts for Suzuki–Miyaura reaction in aqueous media
2 2 6 3 2 2
(Me NCH )C H ]Ph P}PdCl cation and chloride anion. Catalytic ac-
tivity of 7 is similar to that of its neutral precursor 1 due to an easy
regeneration of complex 1 from 7 under basic conditions (water
solution of Na CO ). Studies of possible separation of 7 for testing
2 3
in consecutive runs are of our current interest.
Experimental
General methods
3
Starting phosphine L PPh
2
and compounds 1 and 2 were
Figure 3. (A) PovRay view of 7. Hydrogen atoms, H
molecules are omitted for clarity. Selected bond distances (Å) and angles
°): Pd1–N1 2.097(3), Pd1–P1 2.2522(10), Pd1–Cl1 2.3038(10), Pd1–Cl2
2
O and ethanol
[25,26,56]
synthesized according to the literature.
di-μ-chloro-bis(η -allyl)dipalladium(II) and di-μ-chloro-bis[2-[(N,N-
Starting PdCl2,
3
(
dimethylamino)methyl]phenyl-C,N]dipalladium(II) were purchased
2.3749(11), N1–Pd1–P1 94.14(10), N1–Pd1–Cl1 177.65(10), P1–Pd1–Cl1
6.59(4), N1–Pd1–Cl2 92.00(10), P1–Pd1–Cl2 173.77(4), Cl1–Pd1–Cl2 87.32
8
from Sigma Aldrich and used as received. Starting Ph PCl and
2
(4). (B) Hydrogen bonding in the crystal structure of 7.
(tBu)PhPCl were purchased from ABCR and used as received. All re-
actions were carried out under argon atmosphere, using standard
Schlenk techniques. Solvents were dried by standard methods
1
13
31
and distilled prior to use. H NMR, C NMR and P NMR spectra
were acquired with a Bruker Avance 500 spectrometer in C D or
6
6
1
D O. Appropriate chemical shifts were calibrated on: H, residual
2
13
peak of C D (7.15 ppm); C, residual peak of C D (128.00 ppm);
6
6
6 6
3
1
(
Me
2
NHCH
2
)-6-(Me
2
NCH
2
)C
6
H
3
]Ph
2
P}PdCl
2
, that is compensated by
P, external H PO (0.00 ppm).
3 4
ꢀ
Cl anion. The Me
2
NH atom is also involved in hydrogen bonding
with the chloride anion of another molecule of 7 (Fig. 3).
3
Complex 7 as a water-soluble Pd complex was also tested as a
catalyst in the Suzuki–Miyaura reaction between 4′-substituted
phenyl bromides and 4-substituted phenylboronic acids (Scheme 4)
Preparation of L PPh(tBu)
An amount of 2.6 ml of 1.6 M n-BuLi was added dropwise to an Et O
2
3
(
10 ml) solution of L H (0.75 g, 4.2 mmol) at ꢀ80°C and the solution
in water involving Pd(II) catalyst 7 (1%)/Na CO3 system under
2
was stirred for 30 min at room temperature. (tBu)PhPCl (0.80 ml, 4.2
argon. The reactions were monitored using GC analysis and the re-
sults are similar to those for the neutral precursor 1 (Table 3). These
results may suggest an easy regeneration of complex 1 from 7
under these conditions (water solution of Na CO ; Scheme 5).
3
mmol) was added to the resulting Et O solution (10 ml) of L Li
2
precooled to ꢀ80°C and stirred for an additional 3 h. The suspen-
sion was filtered and Et O solution was evaporated to give a light
2
2
3
3
1
yellow oil of L PPh(tBu). Yield 1.6 g (87%). H NMR (C D , 500
MHz, δ, ppm): 1.01 (s, 9H, Bu), 1.69 (d, 12H, J
6
6
t
= 6.8 Hz, CHCH3),
H–H
3
.58 (m, 2H, CHCH ), 4.08 (d, 1H, NH), 6.82 (t, 1H, J
= 6.8 Hz,
3
H–H
Conclusions
ArH), 6.98–7.25 (m, 4H, ArH), 7.41 (d, 2H, J
= 6.8 Hz, ArH), 7.54
H–H
31
(
t, 1H, JH–H = 6.8 Hz, ArH); P NMR (C D , 202 MHz, δ, ppm): 54.9.
6 6
In summary, we report a simple and efficient procedure for Suzuki–
Miyaura reactions catalysed by palladium complexes 1–6 contain-
ing functional groups potentially useful for two-phase system
extraction. In this study, aqueous media and green solvents were
used instead of toxic organic solvents. It was demonstrated that
the NH proton acidity in amidophosphine-stabilized Pd complexes
Anal. Calcd for C H NP (341.47) (%): C, 77.38; H, 9.45. Found (%):
22 32
C, 77.42; H, 9.47.
3
Preparation of trans-{(L PPh ) PdCl } (3)
2
2
2
3
3–6 may tune their catalytic activity (Scheme S3 in supporting
PdCl (0.2 g, 1.1 mmol) was added to a solution of L PPh (0.79 g,
2 2
3
information). Complex 4 featuring bulkier phosphine L PPh(tBu)
showed higher catalytic activities than analogous compound 3
containing phosphine L PPh . In addition, palladium complexes 1
2.20 mmol) in tetrahydrofuran (THF; 20 ml) and the suspension
was stirred for 1 day. The suspension was filtered and the solvent
evaporated. The resulting orange solid was washed with hexane
(3 ml) to afford a yellow-orange powder of 3. Yield 0.93 g (94%);
3
2
and 2 stabilized by phosphines containing Y,C,Y-chelating ligands
1,2
1
L
have also been found to be useful catalysts for Suzuki–Miyaura
m.p. 249–250°C. H NMR (C D , 500MHz, δ, ppm): 0.88 (d, 3H, J
6
6
H–H
reaction in aqueous media. The method can be effectively applied
to both activated and deactivated aryl bromides yielding high or
moderate conversions. Decrease of palladium concentration from
= 6.8 Hz, CH ), 1.03 (d, 3H, J
= 6.8 Hz, CH ), 1.23 (d, 3H, J
= 6.8 Hz, CH ), 3.24 (m, 1H, CH), 3.43
3
=
3
H–H
3
H–H
6.8 Hz, CH ), 1.34 (d, 3H, J
3
H–H
(m, 1H, CH), 5.76 (d, 1H, NH, JH–P = 6 Hz), 6.93–7.15 (m, 3H, ArH),
7.21–7.32 (m, 6H, ArH) 7.45–7.58 (m, 4H, ArH). C NMR (C D , 125
6 6
13
1.0 to 0.5 mol% did not show substantial loss of conversion. The
possible recovery of 1–6 from water has also been tested. These at-
tempts were successful for compound 1 only. Therefore, the aque-
ous phase containing complex 1 was acidified by HCl to pH around
MHz, δ, ppm): 23.8 (CH(CH
3 2 3 2 3 2
) ), 24.3 (CH(CH ) ), 26.4 (CH(CH ) ),
28.1 (CH(CH ), 146.5 (C-1), 136.2 (C-2 and C-6), 124.4 (C-3 and C-
3 2
)
5), 122.8 (C-4), 136.6 (d, J31P13C = 46.3 Hz, i-carbons of phenyls),
133.2 (d, J31P13C = 15.0 Hz, o-carbons of phenyls), 131.4 (s, p-carbons
of phenyls), 125.9 (d, J31P13C = 10.0 Hz, m-carbons of phenyls).
5
and the presence of an ionic complex 7 was observed. Com-
pound 7 was quantitatively prepared by the reaction of 1 with 1
eq. of HCl and was characterized using NMR spectroscopy in D
and X-ray diffraction analysis. These data provided evidence
of the ionic nature of 7 consisting of cis-{[2-(Me NHCH )-6-
31
P
2
O
NMR (CDCl
Cl
63.49; H, 6.04.
3
,
202 MHz, δ, ppm): 61.8. Anal. Calcd for
C
48
H
56
N
2
2
P
2
Pd (900.27) (%): C, 64.04; H, 6.27. Found (%): C,
2
2
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

J. Jansa et al.
3
Preparation of trans-{[(L PPh(tBu)]
2 2
PdCl } (4)
3
ppm): 71.9. Anal. Calcd for C33H40ClN PPd (637.53) (%): C, 62.17; H,
6.32. Found (%): C, 62.01; H, 6.35.
3
PdCl (0.2 g, 1.1 mmol) was added to a solution of L PPh(tBu) (0.75
2
g, 2.20 mmol) in THF (20 ml) and the suspension was stirred for 1
day. The suspension was filtered and the solvent evaporated. The
resulting orange solid was washed with hexane (3 ml) to afford
Preparation of cis-{(2-(Me NHCH )-6-(Me NCH )C H )PPh ]
2 2 2 2 6 3 2
+
ꢀ
PdCl } Cl (7)
2
1
an orange powder of 4. Yield 0.95 g (94%); m.p. 219–220°C. H
A solution of 36% HCl (0.08 ml, 0.7 mmol) was added to a solution of
NMR (C
(
6
D
6
, 500MHz, δ, ppm): 1.01 (d, 3H, JH–H = 6.6 Hz, CH
d, 3H, JH–H = 6.6 Hz, CH ), 1.23 (d, 3H, JH–H = 6.6 Hz, CH ), 1.28 (d,
( Bu)), 1.46 (d, 3H, JH–H = 6.6 Hz, CH ), 3.81 (m,
H, CH), 3.86 (m, 1H, CH), 5.57 (d, 1H, JH–P = 5 Hz, NH), 6.98–7.19
3
), 1.16
1
(0.37 g, 0.68 mmol) in CH Cl (5 ml) and the mixture was stirred for
2 2
3
3
1
h until the precipitation of a yellow solid. Water (30 ml) was added
t
9H, JH–P = 7 Hz, CH
3
3
for two-phase extraction. The organic and water fractions were sep-
arated. The water was evaporated to yield a yellow solid that was
recrystallized from ethanol (10 ml). Slow evaporation of ethanol at
room temperature provided yellow crystals of 7 suitable for X-ray
1
13
(
m, 3H, ArH), 7.21–7.32 (m, 3H, ArH) 7.41–7.56 (m, 2H, ArH).
NMR (C , 125 MHz, δ, ppm): 23.7 (CH(CH ), 24.3 (CH(CH
4.4 (CH(CH ), 28.1 (CH(CH ), 28.4 (C(CH ), 29.7 (d, C(CH
C
6
D
6
3
)
2
3
)
2
),
d,
2
3 2
)
3 2
)
3
)
3
3
)
3
1
diffraction analysis. Yield 0.35 g (85%); m.p. 213–215°C. H NMR
J31P13C = 46.3 Hz), 147.5 (C-1), 135.6 (C-2 and C-6), 123.4 (C-3 and
C-5), 126.9 (C-4), 135.6 (d, J31P13C = 42.5 Hz, i-carbons of phenyls),
(
D2O, 400 MHz, δ, ppm): 2.73 (bs, 6H, JH–H = 6.2 Hz, NHCH ), 2.76
3
(
bs, 6H, NCH ), 3.50 (AB spin system δ 3.25 and δ 3.75, 2H, J
3
A
B
H–H
1
32.2 (d, J31P13C = 10.0 Hz, o-carbons of phenyls), 130.4 (s, p-carbons
=
5.8 Hz, CH N), 4.19 (bs, 2H, CH NH), 4.28 (bs, 1H, NHMe ), 7.37–
2 2 2
31
of phenyls), 126.9 (d, J31P13C = 11.0 Hz, m-carbons of phenyls).
P
13
7.56 (m, 13H, ArH). C NMR (D O, 100 MHz, δ, ppm): 42.0 (NHCH ),
2
3
NMR (C D , 202 MHz, δ, ppm): 69.9. Anal. Calcd for C H Cl N P Pd
6
6
44 64 2 2 2
4
2.9 (NCH ), 59.1 (CH N), 61.0 (CH NH), 68.0 (CH N, J = 14.0
3
2
2
2
31P13C
(860.26) (%): C, 61.43; H, 7.50. Found (%): C, 61.48; H, 7.54.
Hz), 141.7 (C-6), 140.2 (C-2), 132.5 (d, J31P13C = 48.0 Hz, C-1), 131.7
d, J31P13C = 10.0 Hz, C-3), 130.7 (C-5), 123.0 (C-4), 134.9 (d, J31P13C
48.3 Hz, i-carbons of phenyls), 133.3 (o-carbons of phenyls),
(
=
3
3
3 5 2
Preparation of [Pd(η -C H )(L PPh )Cl] (5)
31
130.1 (p-carbons of phenyls), 129.2 (m-carbons of phenyls).
P
3
Di-μ-chlorobis(η -allyl)dipalladium(II) (0.23 g, 0.62 mmol) was
NMR (D O, 162 MHz, δ, ppm): 18.4. Anal. Calcd for C24H30Cl N PPd
2
3 2
3
added to a solution of L PPh (0.44 g, 1.23 mmol) in CH Cl (15ml)
2
2
2
(590.26) (%): C, 48.84; H, 5.12. Found (%): C, 48.67; H, 5.45.
and the mixture was stirred for 1 day. Cloudy solution was filtrated,
the solvent was evaporated and the solid residuum was washed
with hexane (5 ml) to afford yellow crystals of 5. Yield 0.60 g
General procedure for Suzuki–Miyaura reaction
1
(
1
(
(
J
89%); m.p. 139–141°C. H NMR (C
2H, JH–H = 6.8 Hz, CH
D
6 6
, 500MHz, δ, ppm): 0.91 (d,
(anti)), 2.36
(anti)), 3.29 (d, 1H, JH–H = 5.5 Hz, CH
syn)), 3.42 (m, 2H, CH), 4.33 (s, 1H, JH–P = 6 Hz, NH), 4.46 (d, 1H,
H–H = 5.5 Hz, CH (syn)), 4.75–4.81 (m, 1H, CH (allyl)), 6.88 (d, 2H,
H–H = 6.8 Hz, ArH), 6.99–7.03 (m, 6H, ArH), 7.15–7.26 (m, 5H, ArH).
To a degassed solution of starting bromide (0.32 mmol) and bo-
ronic acid (0.32 mmol) in aqueous media (10 ml), Pd catalysts 1–6
3 2
), 1.14 (d, 1H, JH–H = 5.5 Hz, CH
d, 1H, JH–H = 5.5 Hz, CH
2
2
2 3
(0.003 mmol or 0.0015 mmol) and Na CO (34 mg, 0.32 mmol) were
added. The mixture was stirred for 6 h under argon at 80°C, and ex-
tracted with EtOAc (2 × 10 ml). The combined organic layers were
dried (Na SO ) and subjected to GC analysis (Tables 2 and 3).
2 4
2
J
1
3
6 6 3 2 3 2
C NMR (C D , 125 MHz, δ, ppm): 23.9 (CH(CH ) ), 29.2 (CH(CH ) ),
5
7.2 (Cterm(allyl)), 77.2 (Cterm(allyl)), 110.1 (Cmeso(allyl)), 147.4 (C-1),
Crystallography
Crystals suitable for X-ray analyses were grown from Et
136.9 (C-2 and C-6), 128.3 (C-3 and C-5), 123.5 (C-4), 130.6 (d,
J31P13C = 45.3 Hz, i-carbons of phenyls), 128.2 (d, J31P13C = 16.0 Hz,
2
O–hexane
o-carbons of phenyls), 127.9 (s, p-carbons of phenyls), 126.6 (d,
(
3) or H O–EtOH (7) solutions at room temperature. Compounds
2
31
6 6
J31P13C = 12.0 Hz, m-carbons of phenyls). P NMR (C D , 202 MHz,
crystallized as the corresponding solvate 7·H O·0.5EtOH. The in-
2
δ, ppm): 61.6. Anal. Calcd for C27
H, 6.11. Found (%): C, 59.82; H, 6.45.
H33ClNPPd (544.41) (%): C, 59.57;
tensity data for single crystals were measured with a four-circle
diffractometer KappaCCD with CCD area detector using
monochromatized Mo K radiation (λ = 0.71073 Å) at 150(2) K.
α
3
The crystallographic details are summarized in Table 1, and empir-
ical absorption corrections were applied (multiscan from symmetry-
Preparation of {Pd[2-(Me NCH )C H ](L PPh )Cl} (6)
2
2
6
4
2
Di-μ-chlorobis[2-[(dimethylamino)methyl]phenyl-C,N]dipalladium
related measurements). Data reductions were performed with
3
[57]
(
II) (0.6 g, 1.1 mmol) was added to a solution of L PPh (0.77 g, 2.1
DENZO-SMN.
The absorption was corrected by integration
2
[
58]
mmol) in CH Cl (15 ml) and the mixture was stirred for 1 day.
methods. Structures were solved by direct methods (Sir92) and
refined by full matrix least-squares based on F (SHELXL97).
2
2
2
[59]
Cloudy solution was filtrated, the solvent was evaporated and the
resulting product was washed with pentane (7 ml) to afford yellow
Hydrogen atoms were mostly localized on a difference Fourier
map and recalculated into idealized positions (riding model) and
assigned temperature factors H (H) = 1.2U (pivot atom) or
1
crystals of 6. Yield 1.25 g (92%); m.p. 141.3–143.1°C. H NMR (C D ,
6
6
5
00 MHz, 300 K, δ, ppm): 0.89 (d, 12H, JH–H = 6.2 Hz, CH ), 2.88 (d, 6H,
3
iso
eq
JH–P = 6.8 Hz, NCH ), 3.39 (m, 2H, CH), 4.04 (d, 2H, J
= 6.8 Hz,
1.5Ueq for the methyl moiety with C H = 0.96, 0.97 and 0.93 Å for
methyl, methylene and hydrogen atoms in aromatic ring moiety,
respectively. The structure of 7 contains disordered chloride anion
which was split into two positions with occupancy of 52:48; this dis-
order was modelled according to the position of residual electron
density maximum at the Fourier electron density map and treated
by standard Shelxl software instructions. The positions of the hy-
drogen atoms connected to the O1 atom (water molecule) were
fixed on places with appropriate hydrogen bond connectivity.
CCDC1448889 (for 3) and 1448890 (for 7) contain the supplementary
3
H–P
CH N), 6.25–6.32 (m, 4H, ArH), 6.40 (s, 1H, J
= 7 Hz, NH), 6.88–
2
H–P
7
.04 (m, 5H, ArH), 7.26–7.48 (m, 4H, ArH), 7.72 (dd,4H, JH–H = 6.2
1
3
Hz, ArH). C NMR (C
6
D
6
, 125 MHz, δ, ppm): 22.3 (CH(CH
3 2
) ), 29.2
(
CH(CH ), 50.6 (CH NCH
3
)
2
2
3
), 72.7 (CH NCH ), 147.3 (C-1), 136.7 (C-2
2
3
and C-6), 127.7 (C-3 and C-5), 123.8 (C-4), 130.8 (d, J31P13C = 47.3
Hz, i-carbons of phenyls), 128.1 (d, J31P13C = 12.0 Hz, o-carbons of
phenyls), 126.3 (s, p-carbons of phenyls), 122.9 (d, J31P13C = 12.0
Hz, m-carbons of phenyls), 122.6 (CArH), 126.3 (CArH), 134.4 (CArH),
[60]
31
1
6 6
37.2 (CArH), 148.1 (CArH), 150.9 (CArH). P NMR (C D , 202 MHz, δ,
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Efficient catalysts for Suzuki–Miyaura reaction in aqueous media
[
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