Mixed phosphine/N-heterocyclic carbene palladium complexes: Synthesis, characterization and catalytic use in aqueous Suzuki-Miyaura reactions

Article abstract of DOI:10.1039/c2dt32858e

A series of N-heterocyclic carbene (NHC)/PR₃ palladium(ii) and palladium(0) complexes has been synthesized and fully characterized. X-ray crystallographic data have allowed comparison of ligand steric properties. The NHC ligand was found to vary its steric properties as a function of the phosphine co-ligand. These complexes display interesting catalytic properties in the Suzuki-Miyaura reaction performed in aqueous media. The pre-catalyst [PdCl₂(IPr)(XPhos)] (IPr = N,N′-bis-(2,6-diisopropylphenyl) imidazol-2-ylidene; XPhos = 2-dicyclohexylphosphino-2′,4′,6′- triisopropylbiphenyl) was found to be the most efficient system, promoting the coupling of a wide range of aryl chlorides with boronic acids in aqueous media with a typical catalyst loading of 0.03 mol%.

Full text of DOI:10.1039/c2dt32858e

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Mixed phosphine/N-heterocyclic carbene palladium
complexes: synthesis, characterization and catalytic use
in aqueous Suzuki–Miyaura reactions†
Cite this: DOI: 10.1039/c2dt32858e
Thibault E. Schmid, Dale C. Jones, Olivier Songis, Olivier Diebolt, Marc R. L. Furst,
Alexandra M. Z. Slawin and Catherine S. J. Cazin*
3
A series of N-heterocyclic carbene (NHC)/PR palladium(II) and palladium(0) complexes has been syn-
thesized and fully characterized. X-ray crystallographic data have allowed comparison of ligand steric
properties. The NHC ligand was found to vary its steric properties as a function of the phosphine co-
ligand. These complexes display interesting catalytic properties in the Suzuki–Miyaura reaction performed
Received 28th November 2012,
Accepted 3rd January 2013
2
in aqueous media. The pre-catalyst [PdCl (IPr)(XPhos)] (IPr = N,N’-bis-(2,6-diisopropylphenyl)imidazol-2-
ylidene; XPhos = 2-dicyclohexylphosphino-2’,4’,6’-triisopropylbiphenyl) was found to be the most
efficient system, promoting the coupling of a wide range of aryl chlorides with boronic acids in aqueous
media with a typical catalyst loading of 0.03 mol%.
DOI: 10.1039/c2dt32858e
www.rsc.org/dalton
area of research primary resides in the potential of palladium
Introduction
cross-coupling catalysis to create C–C linkages required to gene-
1
4
The 2010 Nobel Prize in Chemistry was awarded to Heck, rate novel bioactive molecules. In this context, NHC-based
Negishi and Suzuki for their seminal contributions to the field systems have shown promising, but these studies are plagued
1
15
of C–C bond formation using palladium catalysis. Recent by the need of very high catalyst loadings. As part of our
developments in palladium-mediated cross-coupling catalysis program exploring ligand synergism in catalysis, we wished to
have led to unprecedented advances in natural product, probe such potentially beneficial effects using PR /NHC mixed
3
2
,3
polymer and pharmaceutical compound syntheses. Among systems in the Suzuki–Miyaura reaction conducted in aqueous
cross-coupling reactions, the Suzuki–Miyaura reaction is one media. Herein, we report the synthesis and full characteriz-
4
of the most popular and successful cross-coupling protocols,
ation of well-defined mixed tertiary phosphine/NHC palladium
allowing the efficient synthesis of pharmaceutically relevant systems and their corresponding catalytic performance in
biaryl compounds from non-toxic and versatile starting aqueous Suzuki–Miyaura reactions.
5
materials. During the last decade, a major advance has been
the development of catalysts enabling the coupling of boronic
6
acids with chlorinated compounds. Electron-rich phosphi-
6
b,e,f
7
nes
palladium catalyst modifiers in cross-coupling. Combining
both classes of ligands on the same metal has lead to highly Synthesis and characterization of [PdCl (IPr){P(R R′)}]
and N-heterocyclic carbenes (NHC) have been used as
8
,9
Results and discussion
2
2
1
0,11
active and stable catalysts.
The growing interest in sustain- complexes
able development has triggered tremendous research activity
in catalysis conducted in non-traditional media. In particu-
A series of [PdCl
phenyl)imidazol-2-ylidene) complexes was straightforwardly
synthesized by cleavage of [Pd(μ-Cl)(Cl)(IPr)] (1) with a ter-
2
tiary phosphine. To test the generality of the method, several
tertiary phosphine ligands possessing varied steric and elec-
tronic properties were selected and subjected to these reaction
conditions (Scheme 1). As IPr-based complexes have proven
best for the Suzuki–Miyaura coupling,
2 2
(IPr){P(R R′)}] (IPr = N,N′-bis-(2,6-diisopropyl-
1
2
lar, work has focused on the development of Suzuki–Miyaura
16
1
3
coupling systems carried out in water. The interest in this
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST,
UK. E-mail: cc111@st-andrews.ac.uk; Fax: +44 (0) 1334 463808
†
Electronic supplementary information (ESI) available: Experimental details,
8c,17,18a
the IPr ligand
kinetic experiments, NMR spectra, %VBur and mapping. CCDC 871882 2a,
was selected as the NHC of choice for the present study. Com-
plexes 2a–g are easily obtained in microanalytically pure form
and in good to excellent yields (Scheme 1).
8
71883 2b, 871884 2c, 871885 2d, 910518 2e, 871887 2f, 871888 2g, 913234 5 and
71889 6. For ESI and crystallographic data in CIF or other electronic format see
8
DOI: 10.1039/c2dt32858e
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The aromatic protons of the phosphine appear as sharp resonances suggested a restricted rotation of the phosphine
signals for complexes 2a, b, d, f and 2g whereas complexes 2c ligand. This could be explained by the steric bulk of tri(o-tolyl)-
and 2e show broad resonances. The broadness of the phosphine for complex 2c. In the case of 2e, a palladium–
6
e
arene interaction would explain a restricted rotation. Variable
Temperature (VT) NMR experiments were carried out in
2 2 4
C D Cl at 298, 323, 348 and 373 K (see ESI†). A sharpening of
1
the peaks was observed upon heating, permitting correct H
NMR assignments. Samples were then left to cool and again
analyzed by NMR. The observed spectra were identical to the
initial ones recorded at 298 K, confirming that these com-
plexes conserved their integrity throughout the experiment.
The electronic environment around the carbene carbon
remains relatively constant across the series of complexes of
2
type 2, the carbenic carbon C presenting a chemical shift
2
within a narrow range of 170–174 ppm. The important
J
CP
2 2
Scheme 1 Synthesis of [PdCl (IPr){P(R R’)}] complexes.
coupling constant (180 to 197 Hz) is characteristic of the trans
1
8
position of the phosphorus ligand with respect to the NHC.
4
5
The imidazole backbone carbon atoms, C and C , appear as a
13
1
31
1
Table 1 Selected C–{ H} and P–{ H} NMR data for complexes 2a–g (δ in
4
31
1
doublet (120–125.1 ppm,
JCP = 5.1–5.7 Hz). P–{ H} NMR
a
ppm, J in Hz)
spectra of all complexes interestingly showed sharp singlets
shifted downfield when compared to the free phosphine at
4
5
31
C C
C
carbene
P
13
1
room temperature. Table 1 summarizes selected C–{ H} and
4
2
2
Complex (PR R′)
δ
C
J
CP
δ
C
J
CP
δ
P
31
1
P–{ H} NMR data associated with complexes 2a–g.
Structural features for complexes 2a–g were unambiguously
22.0 determined by single crystal X-ray diffraction studies. Graphi-
cal representations are provided in Fig. 1 with selected bond
distances and angles presented in Table 2. Complexes of type
42.5 2 show a slightly distorted square planar geometry, with angles
(
(
(
(
(
(
(
2a) (PPh
3
)
)
124.4
124.1
124.5
124.0
124.3
124.0
124.1
5.7
5.2
5.6
5.1
5.3
5.3
5.4
171.1
174.5
170.9
171.9
173.7
174.1
174.0
199.2
182.4
197.1
181.9
186.9
187.8
187.4
20.4
1
9
2b) (PCy
3
2c) (P(o-tolyl)
2d) (P(Ad)
3
)
19.2
28.6
25.8
n
2
( Bu))
2e) (PCy (o-biph))
2
2f) (XPhos)
2g) (SPhos)
43.3
between adjacent ligands ranging from 88.40(5)° to 94.26(7)°,
displaying a trans configuration of the phosphine ligand to the
N-heterocyclic carbene. The Pd–Cl bond distances of these
a 13
1
31
1
C–{ H} spectra were recorded in CDCl
3
;
P–{ H} spectra were
recorded in CD Cl . NMR were recorded at 298 K.
2
2
n
Fig. 1 Molecular representations of [PdCl
2
(IPr)(PPh
3
)] (2a), [PdCl
2
(IPr)(PCy
3
)] (2b), [PdCl
2
(IPr){P(o-tolyl)
Cl
3
}] (2c), [PdCl
2
(IPr){P(1-Ad)
2
( Bu)}] (2d), [PdCl
2
(IPr){PCy
2
-
(
o-biphenyl)}] (2e), [PdCl (IPr)(XPhos)] (2f) and [PdCl
2
2
(IPr)(SPhos)] (2g). Solvent molecule (CH
2
2
for 2c and 2f) and hydrogen atoms are omitted for clarity.
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Table 2 Selected bond lengths (Å) and angles (°) (esd) and %VBur values
n
2
a PPh
3
2b PCy
3
2c P(o-tol)
3
2d P(Ad)
2
( Bu)
2
2e PCy (o-biph)
2f XPhos
2g SPhos
Pd–C
Pd–P
Pd–Cl1
Pd–Cl2
C–Pd–P
C–Pd–Cl1
C–Pd–Cl2
P–Pd–Cl1
P–Pd–Cl2
Cl1–Pd–Cl2
2.032(5)
2.3054(13)
2.2849(13)
2.2873(14)
173.95(14)
87.30(13)
92.57(13)
87.06(5)
93.11(5)
179.06(6)
34.3
2.034(5)
2.3344(12)
2.3067(13)
2.3136(13)
174.84(14)
88.79(13)
89.47(13)
92.32(5)
89.56(4)
177.58(5)
32.1
2.032(6)
2.040(8)
2.036(3)
2.3359(10)
2.3132(10)
2.2930(10)
173.19(9)
85.75(9)
92.82(9)
87.46(4)
93.98(4)
178.48(4)
33.7
2.055(5)
2.3211(14)
2.3133(13)
2.3027(12)
178.24(14)
90.76(13)
88.24(13)
89.89(5)
91.08(5)
178.38(5)
33.8
2.054(3)
2.3319(9)
2.3160(9)
2.2932(9)
174.73(9)
88.61(9)
91.46(9)
91.20(3)
88.74(3)
179.87(4)
32.3
2.3547(15)
2.3002(15)
2.3127(15)
175.67(18)
90.73(15)
88.89(15)
92.37(5)
88.40(5)
172.97(7)
32.8
2.3671(19)
2.3248(19)
2.293(2)
177.2(2)
88.4(2)
86.6(2)
94.26(7)
90.69(7)
174.28(7)
33.2
a
NHC %VBur
a
PR
3
%VBur
31.8
35.2
39.0
37.2
38.0
36.2
35.6
a
When two independent structures were found in single crystal X-ray diffraction experiments, %VBur were calculated for both. For clarity, only
one value is given. Full details can be found in the ESI.
complexes fall between the values found for the Pd–(μ-Cl) and
Pd–Cl distances of the parent dimer [Pd(μ-Cl)Cl(IPr)] : (Pd–
2
1
6
(
μ-Cl) = 2.4029(9) Å, Pd–Cl = 2.2715(9) Å).
On the other hand, these Pd–Cl distances are similar to
1
8a
those found for phosphite analogues [PdCl (IPr){P(OR) }].
2
3
The Pd–P bond distances found in complexes of type 2 are
longer than those found in phosphite-containing Pd(II) com-
1
8b
plexes, a similar trend previously observed with Ru species.
Buried volumes (%VBur) calculated using the SambVca appli-
2
0
cation show that the NHC ligand adapts its bulkiness to the Fig. 2 Molecular representation of [Pd(μ-Cl)Cl(SPhos)]
2
(5). Selected bond dis-
1
8a
tances (Å) and angles (°): Pd1–P1 2.247(3); Pd–Cl1 2.329(3); Pd–Cl2 2.283(3).
phosphine occupying a relative trans position.
value for the NHC %VBur is calculated in the PPh
complex 2a (34.3 for the NHC moiety, 31.8 for the phosphine).
Complex 2b, featuring PCy , shows the smallest %VBur for the
The highest
3
-containing
dimer is shorter than the one found in the IPr/SPhos Pd(II)
complex 2g (2.247(3) Å for 5, 2.3319(9) for 2g) (Fig. 2).
21
3
carbene ligand (32.1), while 35.2 is calculated for the phos-
phine. If no drastic differences in sterics were observed with
the NHC ligands, the study brought in light the very different
steric environments displayed by the phosphines (see ESI†).
No clear trend with Pd–Ccarbene bond length and the %VBur or As [Pd(0)L
Synthesis of [Pd(IPr)(SPhos)] (6)
2
2
] (n = 1 or 2) complexes are believed to be the
n
σ donating properties of the phosphine ligands were observed, active species entering the catalytic cycle in cross coupling
suggesting that both trans-influence and steric properties do reactions, the synthesis of the mixed (NHC)/phosphine
have an effect.
complex [Pd(IPr)(SPhos)] (6) was investigated. This compound
3
was obtained using a one-pot reaction involving [Pd(η -allyl)Cl-
t
(
IPr)] 3, SPhos and KO Bu (Scheme 3). [Pd(IPr)(SPhos)] (6) pre-
sents similar NMR features as its Pd(II) analogues: the back-
2
Synthesis of [Pd(μ-Cl)(Cl)(SPhos)] (5)
4
5
4
bone carbons C and C appear as a doublet (125.1 ppm, JCP
=
In order to assess the synergy resulting from the presence of
mixed ligands, the phosphine-based dimer [Pd(μ-Cl)(Cl)-
17.2 Hz), the carbene carbon atom was shifted downfield
when compared to the Pd(II) compounds and presented a
(
SPhos)] (5) was synthesized (Scheme 2).
2
3
much lower coupling constant with the phosphorus atom
1
1
The P–{ H} NMR spectrum of the complex exhibits a
singlet at 53.3 ppm. The Pd–P bond distance observed in the
2
(
199.5 ppm, JCP = 84.5 Hz).
Scheme 2 Synthesis of [Pd(μ-Cl)Cl(SPhos)]
2
(5).
Scheme 3 Synthesis of [Pd(IPr)(SPhos)] (6).
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a
Table 3 Catalysts screening
Loading
(mol%)
b
Entry
Catalyst
Conv. (%)
1
2
3
4
5
6
7
8
9
[Pd(μ-Cl)(Cl)(IPr)]
2
1
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.1
0.1
0.1
0.5
0.5
0.1
0.1
37
22
c
[PdCl
[PdCl
[PdCl
[PdCl
[PdCl
[PdCl
[PdCl
[PdCl
[PdCl
2
2
2
2
2
2
2
2
2
(IPr)(PPh
(IPr)(PPh
3
)] 2a
)] 2a
)] 2b
)] 2b
3
42
c
(IPr)(PCy
(IPr)(PCy
3
6
3
19
43
22
>99
>99
>99
42
57
>99
96
Fig. 3 Molecular representation of [Pd(IPr)(SPhos)] (6). Selected bond distances
(IPr){P(o-tolyl) }] 2c
(IPr){P(1-Ad)
3
(Å) and angles (°): Pd–C: 2.022(8); Pd–P: 2.248(2); C–Pd–P: 172.9(2).
n
2
( Bu)}] 2d
(IPr){PCy (o-biphenyl)}] 2e
2
(IPr)(XPhos)] 2f
(IPr)(SPhos)] 2g
3
1
1
Finally, the P–{ H} NMR spectrum exhibits a sharp singlet
10
3
at 66.9 ppm. An X-ray diffraction study on single crystal was 11
[Pd(η -allyl)(Cl)(IPr)] 3
12
13
14
[PdCl (IPr)(3-chloropyridine)] 4
2
performed on 6. The molecular representation as well as
selected bond distances and angles are presented in Fig. 3.
This complex presents a slightly distorted linear geometry
and displays shorter Pd–C and Pd–P bond distances than its
[Pd(μ-Cl)(Cl)(SPhos)]
[Pd(IPr)(SPhos)] 6
2
5
a
Reaction conditions: 4-chlorotoluene (1 mmol), PhB(OH)
2
i
(
1.05 mmol), NaOH (1.5 mmol), catalyst 0.5–0.1 mol% Pd, H O : PrOH
2
b
corresponding Pd(II) complex. The %VBur associated with the (9 : 1) (0.5 mL), 80 °C, 14 h. Conversion to coupling product, based on
c
4-chlorotoluene, determined by GC (average of two runs). Performed
phosphine (36.3) varies only slightly from its Pd(II) counterpart
35.6), while the steric constrain of the NHC on the metal
in H O.
2
(
centre (43.9) is much larger in the absence of the chlorine
atoms (32.3 for the Pd(II) analogue). The steric mapping of the
Pd(0) clearly proves that the NHC ligand adapts its bulkiness
in order to occupy the maximum area around the dicoordi-
nated metal (see ESI†). This result further supports the non-
negligible flexibility of the NHC ligands.
cyclohexyl, tolyl and adamantyl phosphine-based complexes
a–d (Table 3, entries 3, 5–7). Noticeably, all biphenylphos-
phine-based catalysts led to complete conversion of the sub-
strates with only 0.1 mol% Pd, regardless of the type of
complexes (Table 3, entries 8–10 and 13–14).
2
2
Interestingly and not surprisingly, [PdCl (IPr)(SPhos)] (2g)
and its Pd(0) analogue led to similar conversions (Table 3,
entries 10 and 14), supporting the existence of the same active
species in the catalytic cycle. In order to study this case in
more details, a comparative reaction profiling was performed.
At 80 °C, a slight induction period was observed for the Pd(II)
Catalytic studies
In order to gauge the effect of this mixed ligation about palla-
dium, catalytic studies were performed in the Suzuki–Miyaura
reaction in water. The benchmark coupling of 4-chlorotoluene
with phenylboronic acid performed with a catalyst loading of
complex [PdCl
2
(IPr)(SPhos)] 2g whereas the Pd(0) species [Pd-
0
.5 mol% was first investigated. Since NaOH was found to be
(
IPr)(SPhos)] 6 reacted immediately (see ESI†). Considering the
the most efficient base in a previous study on carbene–phos-
phite Pd(II) pre-catalysts for Suzuki–Miyaura,
air-sensitive nature of 6 and the difficulty associated with its
handling, the remainder of this study was carried out with Pd
1
8a
the water-
soluble and inexpensive base was selected for the present
(
II) precursors.
2
3
study. Pre-catalysts 2a and 2b were first tested in pure water
To test the limits of the biphenylphosphine-based com-
in reactions carried out for 14 hours at 80 °C (Table 3, entries
plexes, low catalyst loading (0.05–0.02 mol%) experiments were
performed (Table 4). At a catalyst loading of 500 ppm, mixed
NHC/Buchwald phosphine ligand based complexes 2e–g dis-
played higher activities than the corresponding dimer 5
2
and 4). The rapid formation of palladium black was observed
under these conditions, leading to limited conversions. Nolan
and co-workers have successfully performed Suzuki–Miyaura
couplings under mild conditions using technical grade isopro-
panol (containing amounts of water) as a solvent. Gratefully,
using isopropanol as an additive (H O : PrOH 9 : 1) resulted in
a drastic improvement of the activity of 2a and 2b (Table 3,
entries 3 and 5). The catalytic performance of our NHC/phos-
phine mixed system was then compared to that of the commer-
(
2
Table 4, entries 1–4). Decreasing the catalyst loading to
00 ppm (Table 4, entries 5–7), [PdCl (IPr)(XPhos)] (2f) was
8
a
2
i
2
found to be the best catalyst among the NHC/phosphine com-
plexes (TON of 4300) and was therefore selected to further
explore the scope of the Suzuki–Miyaura reaction under these
optimized reaction conditions.
1
6
3
cially available complexes [Pd(μ-Cl)(Cl)(IPr)] , (1), [Pd(η -
2
2
4
25
allyl)(Cl)(IPr)] (3), [PdCl
Buchwald phosphine-based dimer complex [Pd(μ-Cl)(Cl)-
SPhos)] (5). Only poor to moderate conversions were obtained
2
(IPr)(3-chloropyridine)] (4) and the
Scope of the reaction
(
2
with 0.5 mol% Pd of the commercially available systems 1, 3 In order to investigate the efficiency and versatility of
and 4 (Table 3, entries 1, 11 and 12) and with the phenyl, [PdCl (IPr)(XPhos)] 2f under aqueous conditions, various aryl
2
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a
Table 4 Low catalyst loading study
and provided quite different reaction outcomes: no starting
material could be observed by GC, but 2-phenylpyridine could
only be isolated in 48% yield, and 3-phenylpyridine was iso-
lated in quantitative yield in pure form using a simple
aqueous workup followed by a filtration through a pad of
silica. This reactivity difference could be explained by a more
facile dehalogenation of 2-chloropyridine under the catalytic
conditions, with 3-chloropyridine undergoing the Suzuki coup-
b
Load.
(mol%) (%)
Conv.
Entry Catalyst
TON
1
2
3
4
5
6
7
[PdCl
[PdCl
[PdCl
2
2
2
(IPr){PCy
(IPr)(XPhos)] 2f
(IPr)(SPhos)] 2g
2
(o-biphenyl)}] 2e 0.05
93
1860
>1980
0.05
0.05
0.05
>99
>99
51
36
86
>1980 ling at a higher rate. The hydrodehalogenation reaction has
[Pd(μ-Cl)(Cl)(SPhos)]
2
5
1020
1800
4300
2650
26
indeed been observed with NHC-based catalytic systems. Of
[PdCl
[PdCl
[PdCl
2
2
2
(IPr){PCy
(IPr)(XPhos)] 2f
(IPr)(SPhos)] 2g
2
(o-biphenyl)}] 2e 0.02
note, electron-poor substrates were found to give lower conver-
sions and require higher catalyst loadings than electron-rich
deactivated substrates.
0.02
0.02
53
a
Reaction conditions: 4-chlorotoluene (1 mmol), PhB(OH)
2
(
L
1.05 mmol), NaOH (1.5 mmol), pre-catalyst injected from a 0.01 mol
−
1
stock solutions (THF was used due to the poor solubility of the
i
catalyst in isopropanol), solvent: H
1
determined by GC (average of two runs).
2
O : PrOH, 9 : 1 (0.5 mL), 100 °C,
b
4 h. Conversion to coupling product, based on 4-chlorotoluene, Conclusions
In summary, a series of mixed NHC/tertiary phosphine palla-
dium complexes has been successfully synthesized and fully
characterized. The structural data emerging from single crystal
X-ray diffraction studies permit an analysis of ligand steric
properties. These palladium complexes were tested for catalytic
activity in the Suzuki–Miyaura cross-coupling in an aqueous
medium comprised of water–isopropanol as a 9 : 1 mixture,
using NaOH as the operational base. The best catalyst among
those examined is [PdCl (IPr)(XPhos)] (2f). This pre-catalyst
2
permits the successful synthesis of a broad range of biaryls
from aryl chlorides using a typical catalyst loading of
0.03 mol%. Sterically hindered biaryls, including tri-ortho-sub-
stituted species and terphenyls, were synthesized in high
yields from aryl chlorides and boronic acids. Further studies
aimed at exploring catalytic behaviour in aqueous media are
currently being studied in our laboratories.
Experimental section
General considerations
a
Scheme 4 Substrate scope using 2f (isolated yields; 0.06 mol% Pd used).
All reactions were performed under an inert atmosphere of
argon or nitrogen using standard Schlenk line and glovebox
techniques. Solvents were dispensed from a solvent purifi-
chlorides were reacted with a number of boronic acids cation system from Innovative Technology. Flash column
Scheme 4).
chromatography was performed on silica gel 60
Phenylboronic acid could be coupled in excellent yields (230–400 mesh). H, C{ H} and P–{ H} nuclear magnetic
(
1
13
1
31
1
with a number of deactivated aryl chloride substrates, namely, resonance (NMR) spectra were recorded on a Bruker AC300 or
methyl or methoxy groups in ortho, meta and para positions. on a Bruker Avance 400 Ultrashield spectrometer at 298 K
2
-Chloro-m-xylene as well as 9-chloroanthracene were also unless otherwise stated. All reagents and commercial catalysts
reacted with phenylboronic acid and reactions provided yields were purchased and used as received unless otherwise stated.
of 87% and 94%, respectively. Ortho-substituted boronic acids HRMS samples were submitted to EPSRC National Mass Spec-
and ortho-substituted aryl chlorides could be coupled to yield trometry Service Centre (http://www.swan.ac.uk/nmssc/index.
a number of bi- and tri-ortho-substituted biaryls as well as ter- html).
phenyl derivatives in good to quantitative yields. Finally, this
methodology also proved efficient for the coupling of hetero- type [PdCl (IPr)(PR R′)].
General procedure for the synthesis of complexes of the
2
2
aromatic compounds, which are regarded as challenging sub-
Synthesis of complexes 2a–e. In a glovebox, a Schlenk flask
strates, as well as benzyl chloride. Notably, 2-chloropyridine was charged with [Pd(μ-Cl)(Cl)(IPr)]2 (200 mg, 0.177 mmol)
and 3-chloropyridine were reacted with phenylboronic acid and the appropriate phosphine (0.344 mmol) and closed with
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n
a septum. Outside the glovebox, CH
2
Cl
2
(3 mL) was injected
2 2
[PdCl (IPr){P(1-adamantyl) ( Bu)}] (2d). The procedure
through a septum and the reaction mixture was stirred at room yielded 221 mg (68%) of the analytically pure product as a
temperature until the solution became clear. The solvent was white powder. (CD Cl , 400 MHz, 278 K) δ (ppm) = 0.81 (t,
H–H = 7.3 Hz, 3H, CH
2
2
3
3
reduced in vacuo (1 mL) and absolute ethanol (3 mL) was
J
2 3
–CH ), 1.05 (d, JH–H = 6.7 Hz, 12H,
3
added. The solvent was reduced in vacuo until the appearance CH–CH ), 1.17–1.32 (m, 4H, CH ), 1.37 (d, J
= 6.7 Hz, 12H,
3
2
H–H
of a precipitate. The supernatant solution was removed and CH–CH
the resulting powder was dried under vacuum.
PdCl (IPr)(PPh )] (2a). The procedure yielded 272 mg (93%) CH–CH ), 7.12 (d, J = 1.4 Hz, 2H, H , H ), 7.31 (d, J
3
2
), 1.52–1.62 (m, 2H, CH ), 1.59 (br s, 12H, Ad-H), 1.77
(br s, 6H, Ad-H), 1.96–2.08 (m, 12H, Ad-H), 3.22 (br s, 4H,
4
5
3
[
= 7.7
2
3
3
H–H
13
3
1
of the analytically pure product as a microcrystalline yellow Hz, 4H, Ar CH), 7.44 (t, JH–H = 7.7 Hz, 2H, Ar CH). C–{ H}
1
powder. H NMR (CD
2
Cl
2
, 400 MHz, 298 K) δ (ppm) = 1.09 (d, NMR (CDCl
3
, 75.47 M Hz, 298 K) δ (ppm) = 14.1 (s, CH
3
), 15.3
= 13.3
3
3
JH–H = 6.7 Hz, 12H, CH–CH ), 1.31 (d, J
), 3.19 (sept, JH–H = 6.7 Hz, 4H, CH–CH
.6 Hz, 2H, H H ), 7.21–7.30 (m, 12H, CH PPh
m, 3H, CH PPh ), 7.40 (d, J
H–H = 7.8 Hz, 2H, Ar CH). C–{ H} NMR (CDCl
98 K) δ (ppm) = 23.1 (s, CH–CH ), 26.4 (s, CH–CH ), 28.8 (s, 129.7 (s, Ar CH), 135.8 (s, C ), 147.2 (s, C ), 171.9 (d, JC–P =
CH–CH ), 123.9 (s, CH), 124.4 (d, J
= 6.7 Hz, 12H, (d, JC–P = 19.5 Hz, CH ), 22.8 (s, CH–CH ), 25.4 (d, J
3
H–H
2
3
C–P
3
CH–CH
1
3
3
), 7.18 (d, J = Hz, CH
), 7.32–7.37 CH–CH
= 7.8 Hz, 4H, Ar CH), 7.58 (t, = 6.9 Hz, CH), 36.8 (s, CH ), 39.9 (s, CH ), 40.2 (d, J
2
), 26.7 (s, CH–CH
3 2
), 28.8 (s, CH), 28.9 (s, CH), 29.1 (s, CH ), 36.6 (d, JC–P
3
), 27.8 (d, JC–P = 8.9 Hz, CH), 28.8 (s,
4
5
3
3
1
(
= 11.5
C–P
3
H–H
13
2
2
4
3
1
IV
4
5
J
3
, 75.47 MHz, Hz, Ad C ), 123.4 (s, Ar CH), 124.0 (d, JC–P = 5.1 Hz, C , C ),
IV
IV
2
2
3
4
3
4
5
2
31
1
= 5.3 Hz, C C ), 127.7 181.9 Hz, C ). P–{ H} NMR (CD Cl ) δ (ppm) = 26.6. Anal.
2 2
3
C–P
(
1
1
{
C
d, J = 10.6 Hz, CH), 129.8 (d, JC–P = 2.3 Hz, CH), 129.9 (s, CH), calcd for C51
30.5 (d, JC–P = 44.5 Hz, C–P), 135.1 (d, JC–P = 10.6 Hz, CH), 66.15; H, 8.27; N, 3.14.
H
75
N
2
Cl
2
PPd: C, 66.26; H, 8.18; N, 3.03. Found: C,
1
IV
IV
2
2
31
35.7 (s, C ), 149.0 (s, C ), 171.1 (d, J
= 199.2 Hz, C ). P–
[PdCl (IPr){PCy (o-biphenyl)}] (2e). The procedure yielded
C–P
2
2
1
H} NMR (CD
Cl PPd: C, 65.26; H, 6.21; N, 3.38. Found: C, 65.42; H, powder. H NMR (C
0.79–1.17 (m, 10H, Cy), 1.09 (d, J
2 2
Cl ) δ (ppm) = 20.4. Anal. calcd for 268 mg (85%) of the analytically pure product as a yellow
1
45
H
51
N
2
2
2 2 4
D Cl , 300 MHz, 373 K) δ (ppm) =
3
6
.09; N, 3.54.
PdCl (IPr)(PCy
= 6.8 Hz, 12H, CH–CH3),
H–H
3
[
2
3
)] (2b). The procedure yielded 298 mg (99%) 1.36 (d, JH–H = 6.8 Hz, 12H, CH–CH
3
), 1.47–1.51 (m, 8H, Cy),
1.81–1.93 (m, 4H, Cy), 3.28 (sept, JH–H = 6.8 Hz, 4H, CH–CH ),
= 6.6 7.01–7.06 (m, 3H, Ar CH), 7.08 (m, 2H, H , H ), 7.17–7.38 (m,
1
3
of the analytically pure product as a colourless powder.
NMR (CD Cl , 400 MHz, 278 K) δ (ppm) = 1.06 (d, J
H
3
3
4
5
2
2
H–H
Hz, 12H, CH–CH
3
), 1.08 (br s, 8H, Cy CH
2
), 1.25–1.33 (m, 7H, 5H, Ar CH), 7.35 (m, 4H, Ar CH), 7.45–7.55 (m, 3H, Ar CH).
3
13
1
Cy CH
2
), 1.36 (d,
J
H–H = 6.6 Hz, 12H, CH–CH
3
), 1.58 (br s,
3
C–{ H} NMR (CDCl , 75.47 MHz, 298 K) δ (ppm) = 22.8 (s,
2
3
1
5H, Cy CH ), 2.09 (dt, J
= 12.0 Hz, J
= 12.0 Hz, 3H, P– CH–CH ), 26.4 (s, Cy CH ), 26.5 (s, CH–CH ), 27.4 (s, Cy CH ),
2
H–P
H–H
3
2
3
2
3
CH), 3.18 (sept, JH–H = 6.6 Hz, 4H, CH–CH
3
), 7.11 (d, J = 1.6 27.6 (s, Cy CH
2
), 27.8 (s, Cy CH
2
), 28.7 (s, CH–CH
3
), 29.3 (d,
4
5
3
Hz, 2H, H , H ), 7.31 (d, JH–H = 7.6 Hz, 4H, Ar CH), 7.44 (t,
J
2 2
C–P = 5.2 Hz, Cy CH ), 30.7 (d, JC–P = 3.4 Hz, Cy CH ), 31.3 (d,
3
13
1
1
4
JH–H
00.62 MHz, 298 K) δ (ppm) = 22.9 (s, CH–CH
CH ), 26.6 (s, CH–CH ), 27.6 (d, JC–P = 10.5 Hz, Cy CH
s, CH–CH ), 29.3 (s, Cy CH ), 31.3 (d, J
=
7.6 Hz, 2H, Ar CH).
C–{ H} NMR (CDCl3,
JC–P = 25.2 Hz, Cy CH), 123.8 (s, Ar CH), 124.3 (d, JC–P
=
=
4
5
2
1
3
), 26.5 (s, Cy 5.2 Hz, C , C ), 125.7 (d, JC–P = 8.5 Hz, Ar CH), 126.5 (d, JC–P
), 28.7 31.4 Hz, C ), 126.6 (s, Ar CH), 128.4 (d, JC–P = 6.3 Hz, Ar CH),
= 20 Hz, P–CH), 129.8 (s, Ar CH), 130.0 (s, Ar CH), 131.4 (d, JC–P = 8.5 Hz, Ar
C–P
IV
2
3
2
1
(
3
2
4
4
5
IV
1
23.4 (s, Ar CH), 124.1 (d, JC–P = 5.3 Hz, C , C ), 129.7 (s, Ar CH), 135.3 (d, JC–P = 8.7 Hz, Ar CH), 135.9 (s, C ), 141.7 (s,
IV
IV
2
2
IV
IV
IV
2
CH), 135.7 (s, C ), 147.1 (s, C ), 174.5 (d, JC–P = 182.4 Hz, C ). C ), 145.9 (d, JC–P = 4.9 Hz, C ), 147.2 (s, C ), 173.69 (d, JC–P
3
1
1
2
31
1
P–{ H} NMR (CD Cl ) δ (ppm) = 22.1. Anal. calcd for = 186.9 Hz, C ). P–{ H} NMR (CD Cl ) δ (ppm) = 25.8. Anal.
2
2
2
2
C
8
45
H
69Cl
2
N
2
PPd: C, 63.86; H, 8.22; N, 3.31. Found: C, 63.74; H, calcd for C51
.29, N, 3.45. 66.84; H, 7.70; N, 3.14.
PdCl (IPr){P(o-tolyl) }] (2c). The procedure yielded 298 mg [PdCl (IPr)(XPhos)] (2f). In a glovebox, a Schlenk flask was
2 2
H67Cl N PPd: C, 66.84; H, 7.37; N, 3.06. Found C,
[
2
3
2
1
(97%) of the analytically pure product, as a yellow powder. H charged with [Pd(μ-Cl)(Cl)(IPr)]
2
(283 mg, 0.25 mmol), XPhos
3
NMR (C
Hz, 12H, CH–CH ), 1.25 (d, J
2 2 4
D Cl , 300 MHz, 348 K) δ (ppm) = 1.07 (d, JH–H = 6.7 (238.4 mg, 0.5 mmol) and THF (3 mL) was added. The reaction
3
= 6.7 Hz, 12H, CH–CH ), 1.87 mixture was stirred for 3 hours. The solvent was evaporated,
3
H–H
3
3
(br s, 9H, C–CH
3
), 3.22 (sept,
3 2 2
JH–H = 6.7 Hz, 4H, CH–CH ), the resulting solid dissolved in CH Cl (1 mL) and isopropanol
4
5
6
.94–7.03 (m, 7H, Ar CH), 7.13 (d, J = 1.3 Hz, 2H, H H ), 7.23 (3 mL) was then added. The volume was reduced in vacuo until
3
3
(br t, J
= 7.4 Hz, 4H, Ar CH), 7.38 (d, J
= 7.7 Hz, 4H, Ar the appearance of a precipitate, the suspension cooled to
H–H
H–H
3
13
1
CH), 7.56 (t, JH–H = 7.7 Hz, 2H, Ar CH). C–{ H} NMR (CDCl
5 MHz, 298 K) δ (ppm) = 22.7 (s, CH–CH ), 23.7 (br s, ing solid was dried under vacuum to give analytically pure 2f
C–CH ), 26.7 (s, CH–CH ), 28.8 (s, CH–CH ), 123.7 (s, Ar CH), (432 mg, 83%) as a pale yellow solid. H NMR (C D Cl ,
3
,
−15 °C and the supernatant solution was removed. The result-
7
3
1
3
3
3
2
2
4
4
4
5
1
24.5 (d, JC–P = 5.6 Hz, C C ), 124.8 (br s, Ar CH), 129.7 (br s, 300 MHz, 373 K) δ (ppm) = 0.59–0.80 (m, 3H, CH–CH
3
), 0.85
), 0.91–1.20 (m, 10H, Cy), 1.10
= 6.8 Hz, 12H, CH–CH ), 1.27–1.57 (m, 12H, Cy), 1.28
3
Ar CH), 130.0 (s, Ar CH), 131.1 (d, JC–P = 7.8 Hz, Ar CH), 133.1 (d, JH–H = 6.6 Hz, 6H, CH–CH
3
IV
IV
3
(br s, Ar CH), 135.7 (s, C ), 143.4 (d, J
= 7.3 Hz, C ), 147.4 (d, J
H–H
C–P
31
3
IV
2
2
1
3
3
(
s, C ), 170.9 (d, JC–P = 197.1 Hz, C ). P–{ H} NMR (CD
Cl PPd: C, 66.24; H, CH–CH
.40; N, 3.22. Found: C, 65.87; H, 6.79; N, 3.34.
2
Cl
2
)
(d, JH–H = 6.9 Hz, 6H, CH–CH
3
), 1.39 (d, JH–H = 6.6 Hz, 12H,
), 1.98 (br s, 3H, CH–CH ), 2.74 (sept, JH–H = 6.7 Hz,
2H, CH–CH ), 2.90 (sept, JH–H = 6.9 Hz, 1H, CH–CH3),
3
δ (ppm) = 19.2. Anal. calcd for C48
6
H
57
N
2
2
3
3
3
3
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3
3
.26 (sept, JH–H = 6.6 Hz, 4H, CH–CH
3
), 6.83–6.86 (m, 1H, Ar Ar CH), 7.39–7.50 (m, 6H, Ar CH), 7.91–7.97 (m, 2H, Ar CH).
1
3
1
CH), 6.95 (s, 2H, Ar CH), 6.98–7.07 (m, 1H, Ar CH), 7.09 (d,
H–P = 1.2 Hz, 2H, H , H ), 7.17 (m, 1H, Ar CH), 7.33 (d, JH–H 27.8 (d, JC–P = 11.2 Hz, Cy CH
7.7 Hz, 4H, Ar CH), 7.48 (t, JH–H = 7.7 Hz, 2H, Ar CH), CH ), 37.2 (d, JC–P = 25.5 Hz, Cy CH), 55.9 (s, O–CH ), 68.1
2 3
.82–7.90 (m, 1H, Ar CH). C–{ H} NMR (CDCl , 75 MHz, (s, C–OCH ), 104.3 (s, Ar CH), 118.2 (d, J
C–{ H} NMR (CD Cl , 75.5 MHz, 298 K) δ 26.5 (s, Cy CH ),
2
2
2
5
4
5
3
2
J
2
), 29.6 (s, Cy CH
2
), 31.7 (s, Cy
3
1
=
7
2
1
3
1
3
IV
= 2.2 Hz, Ar C ),
3
3
C–P
98 K) δ (ppm) = 22.8 (br s, CH–CH
3
3
), 24.2 (s, CH–CH ), 25.9 126.3 (d, JC–P = 10.3 Hz, Ar CH), 130.5 (s, Ar CH), 130.7 (d, JC–P
(
=
s, Cy CH
2
), 26.1 (s, CH–CH ), 26.7 (br s, CH–CH ), 27.0 (d, JC–P = 2.3 Hz, Ar CH), 133.9 (d, JC–P = 9.1 Hz, Ar CH), 135.9 (d, JC–P
3 3
IV
12.6 Hz, Cy CH ), 27.6 (d, JC–P = 10.8 Hz, Cy CH ), 28.8 (br s, = 9.0 Hz, Ar CH), 139.7 (d, J
= 4.4 Hz, Ar C ), 158.3 (s,
C–P
2
2
IV 31
1
CH–CH
3
(
1
1
1
1
(
6
3
), 29.9 (d, JC–P = 13.4 Hz, Cy CH
2
), 30.0 (br s, CH–CH
3
), Ar C ). P–{ H} NMR (CD
Pd : C, 53.12; H, 6.00. Found: C, 53.15; H, 6.11.
= 13.6 Hz, Ar CH), [Pd(IPr)(SPhos)] (6). In a glovebox, a flask was charged with
C–P
2 2
Cl ) δ (ppm) = 53.3. Anal. calcd for
4.5 (s, CH–CH
3
), 120.7 (br s, Ar CH), 123.4 (s, Ar CH), 124.0
C
52
H
70Cl
4
O
4
P
2
2
4
4
5
d, JC–P = 5.3 Hz, C , C ), 124.6 (d, J
IV
3
27.2 (d, JC–P = 2.0 Hz, Ar CH), 129.6 (s, Ar CH), 130.0 (s, C ), [Pd(η -allyl)(Cl)(IPr)] (150 mg, 0.262 mmol), SPhos (107.6 mg,
33.2 (d, JC–P = 6.1 Hz, Ar CH)), 135.8 (s, C ), 137.1 (s, C ), 0.262 mmol) and KO Bu (64.7 mg, 0.577 mmol). Toluene
39.0 (d, J
IV
IV
t
IV
IV
= 21.0 Hz, Ar CH), 142.7 (s, C ), 147.2 (s, C ), (3 mL) and isopropanol (3 mL) were then added. The reaction
C–P
IV
2
2
31
1
48.2 (s, C ), 174.1 (d,
Cl ) δ (ppm) = 42.5. Anal. calcd for C60
9.12; H, 8.22; N, 2.69. Found: C, 69.14; H, 7.92; N, 2.82.
PdCl
charged with [Pd(μ-Cl)(Cl)(IPr)]
SPhos (205.3 mg, 0.5 mmol). THF (3 mL) was added and the NMR (C D , 400 MHz, 298 K) δ (ppm) = 0.94–1.64 (m, 22H,
JC–P = 187.8 Hz, C ). P–{ H} NMR mixture was stirred during 5 days at room temperature. The
CD
2
2
H
85Cl
2
N
2
PPd: C, solvent was evaporated under vacuum and isopropanol (2 mL)
was added. The resulting solid was collected by filtration and
[
2
(IPr)(SPhos)] (2g). In a glovebox, a Schlenk flask was washed with isopropanol (3 × 2 mL). The product was dried
1
2
(283 mg, 0.25 mmol) and under vacuum to afford 6 (88.5 mg, 37%) as a yellow solid. H
6
6
3
3
solution was stirred for 3 hours. Addition of pentane (15 mL) Cy), 1.23 (d,
led to a precipitate. The solid was collected by filtration and 6.8 Hz, 12H, CH–CH
washed with hexanes (10 mL), leading to the analytically pure CH–CH ), 3.14 (s, 6H, O–CH ), 6.28 (d, J
2
4
3 H–H
JH–H = 6.8 Hz, 12H, CH–CH ), 1.72 (d, J =
3
3
), 3.11 (sept,
J
H–H = 6.8 Hz, 4H,
3
= 8.5 Hz, 2H, Ar
3
3
H–H
1
4
5
g as a pale yellow solid (477 mg, 98%). H NMR (CD
00 MHz, 278 K) δ (ppm) = 0.69–0.92 (m, 6H, Cy), 0.93–1.05 (m, 8H, Ar CH), 9.00 (m, 1H, Ar CH). C–{ H} NMR (C D ,
2
Cl
2
,
CH), 6.53 (s, 2H, H , H ), 7.04–7.09 (m, 2H, Ar CH), 7.20–7.34
1
3
1
6 6
3
(
(
(
m, 4H, Cy), 1.06 (d, J
br s, 6H, Cy), 1.35 (d, JH–H = 6.6 Hz, 12H, CH–CH
br s, 4H, Cy), 1.71 (m, 2H, Cy), 3.19 (sept, JH–H = 6.7 Hz, 4H, (d, JC–P = 3.8 Hz, Cy-CH
= 6.9 Hz, 12H, CH–CH ), 1.28–1.42 100.6 MHz, 298 K) δ (ppm) = 24.0 (s, CH–CH ), 25.3 (s,
H–H
3
3
3
3
), 1.43–1.54 CH–CH
3
), 26.7 (Cy CH
2
2
), 27.4 (d, JC–P = 5.7 Hz, Cy CH ), 27.6
3
2
), 29.0 (s, CH–CH
3
), 31.8 (d, JC–P
=
3
1
CH–CH ), 3.52 (s, 6H, O–CH ), 6.50 (d, J
= 8.4 Hz, 2H, Ar 12.2 Hz, Cy CH ), 32.7 (d, J = 13.1 Hz, Cy CH ), 36.1 (d, J
3
3
H–H
2
C–P
2
C–P
3
CH), 6.77–6.82 (m, 1H, Ar CH), 7.04 (m, 1H, Ar CH), 7.14 (d, = 15 Hz, Cy CH), 55.1 (s, O–CH ), 103.6 (s, Ar CH), 120.7 (s, Ar
5
4
5
IV
4
2
H, JH–P = 1.2 Hz, H , H ), 7.19–7.30 (m, 2H, Ar CH), 7.34 (d, CH), 121.7 (s, C ), 123.3 (s, CH), 125.1 (d, JC–P = 17.2 Hz, C ,
3
5
JH–H = 7.7 Hz, 4H, Ar CH), 7.41–7.46 (m, 1H, Ar CH), 7.48 (t, C ), 128.7 (s, Ar CH), 129.0 (s, Ar CH), 132.3 (s, Ar CH), 137.7
H–H = 7.7 Hz, 2H, Ar CH). C–{ H} NMR (CDCl
98 K) δ (ppm) = 22.9 (s, CH–CH ), 26.1 (s, Cy CH ), 26.7 (s, C ), 146.4 (s, C ), 146.4 (d, JC–P = 43.0 Hz, Ar CH), 158.6 (s,
CH–CH ), 27.1 (d, J
3
13
1
IV
IV
J
3
, 75 MHz, (d, JC–P = 2.9 Hz, C ), 138.0 (d, JC–P = 15.0 Hz, C ), 138.2 (s,
IV
IV
2
3
2
2
2
IV
2
2
31
1
= 11.7 Hz, Cy CH ), 27.3 (d, J
= 12.1 C ), 199.5 (d, JC–P = 84.5 Hz, C ). P–{ H} NMR (C D ,
3
C–P
2
C
–
P
6
6
Hz, Cy CH
CH ), 31.9 (d, JC–P = 21.1 Hz, Cy CH), 55.0 (s, O–CH
Ar CH), 119.4 (s, C ), 123.4 (s, Ar CH), 124.1 (d, J
2 2 3
), 28.2 (s, Cy CH ), 28.7 (s, CH–CH ), 30.3 (s, Cy 121 MHz, 298 K) δ (ppm) = 66.9.
1
2
3
), 103.1 (s,
= 5.4 Hz,
IV
4
C–P
1
3
4
C , C ), 124.3 (d, JC–P = 14.2 Hz, Ar CH), 127.6 (d, JC–P = 33.2
IV
Hz, C ), 128.5 (s, Ar CH), 128.9 (s, Ar CH), 129.7 (s, Ar CH),
Acknowledgements
1
2
1
31.8 (d, J
= 5.7 Hz, Ar CH), 135.8 (s, Ar–C), 138.5 (d, JC–P =
C–P
IV
IV
.5 Hz, C ), 140.0 (d, JC–P = 21.2 Hz, Ar CH), 147.4 (s, C ), We thank the Royal Society (University Research Fellowship to
58.0 (s, C ), 175.0 (d,
IV
2
2
31
1
JC–P = 187.4 Hz, C ). P–{ H} NMR CSJC) for financial support. We are grateful to Umicore AG for
(CD Cl ) δ (ppm) = 43.3. Anal. calcd for C H Cl N PPd: C, generous gifts of palladium complexes and to the EPSRC
2 2 52 71 2 2
6
5.19; H, 7.33; N, 2.87. Found: C, 64.84; H, 7.67; N, 3.18.
Pd(μ-Cl)(Cl)(SPhos)] (5). A Schlenk flask was charged with
PdCl (NCPh) ] (200 mg, 0.52 mmol), SPhos (211.3 mg,
National Mass Spectrometry Service Centre HRMS analysis.
[
2
[
2
2
0
.515 mmol) and THF–toluene (2 mL, 1 : 1) was added. The
reaction mixture was stirred for 2 hours. The precipitate was
collected by filtration and washed with pentane (3 × 5 mL).
The resulting orange solid was dried under vacuum to afford
analytically pure 5 (250 mg, 83%) as an orange powder.
Notes and references
1 The announcement can be found on the Nobel Prize
official website: http://nobelprize.org/nobel_prizes/chem-
istry/laureates/2010/
1
H NMR (CD Cl , 300 MHz, 278 K) δ (ppm) = 1.05–1.33
2
2
(
1
m, 12H, Cy), 1.47–1.59 (m, 4H, Cy), 1.61–1–83 (m, 16H, Cy),
2 For a brief account of the importance of the chemistry see:
X.-F. Wu, P. Anbarasan, H. Neumann and M. Beller, Angew.
Chem., Int. Ed., 2010, 9047.
.88–2.07 (br s, 4H, Cy), 2.11–2.42 (m, 8H, Cy), 3.72 (s, 12H,
3
O–CH ), 6.69 (d, J
= 8.4 Hz, 4H, Ar CH), 7.06–7.09 (m, 2H,
H–H
3
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1
2
9 See ESI.†
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1 Complex 5 was crystallographically characterized in a
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This journal is © The Royal Society of Chemistry 2013
Dalton Trans.