Well-defined bisMETAMORPhos PdI-PdI complex: Synthesis, structural characterization, and reactivity

Article abstract of DOI:10.1021/om5010622

The formation of a bisMETAMORPhos PN-bridged dimeric Pd^I complex (3) from ligand 1 and Pd(dba)₂ is described. The addition of 1 to Pd(dba)₂ initially leads to the formation of Pd⁰ complex 2, which has a highly distorted tetrahedral environment and binds two neutral ligands 1. Complex 2 converts to {Pd^I}₂ complex 3 upon heating. Complex 3 consists of a completely flat Pd-Pd core, with a Pd-Pd bond length of 2.6199(4) ?, and the Pd centers display a highly distorted square planar coordination environment. The formation of complex 3 from 2 is suggested to proceed via an in situ comproportionation pathway. Initial decoordination of one ligand from 2 followed by oxidative addition of one neutral coordinated ligand arm leads to a 1-Pd^IIH complex. Insertion of free dba into the Pd-H bond generates a 1-Pd^IIdba complex that releases 1,5-diphenylpent-1-en-3-one via intra- or intermolecular protonolysis. Concomitantly, comproportionation with 1-Pd⁰ yields 3. Complex 3 was found to function as a precatalyst in the Suzuki-Miyaura cross-coupling of p-chloroacetophenone with good conversions.

Full text of DOI:10.1021/om5010622

Article
pubs.acs.org/Organometallics
I
I
Well-Defined BisMETAMORPhos Pd −Pd Complex: Synthesis,
Structural Characterization, and Reactivity
Sander Oldenhof, Martin Lutz, Bas de Bruin, Jarl Ivar van der Vlugt, and Joost N. H. Reek*
†
‡
†
†
,†
†
Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
‡
Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The
Netherlands
*
S Supporting Information
ABSTRACT: The formation of a bisMETAMORPhos PN-
I
bridged dimeric Pd complex (3) from ligand 1 and Pd(dba)2
is described. The addition of 1 to Pd(dba) initially leads to
2
0
the formation of Pd complex 2, which has a highly distorted
tetrahedral environment and binds two neutral ligands 1.
I
Complex 2 converts to {Pd } complex 3 upon heating.
2
Complex 3 consists of a completely flat Pd−Pd core, with a
Pd−Pd bond length of 2.6199(4) Å, and the Pd centers display
a highly distorted square planar coordination environment.
The formation of complex 3 from 2 is suggested to proceed via
an in situ comproportionation pathway. Initial decoordination of one ligand from 2 followed by oxidative addition of one neutral
II
II
coordinated ligand arm leads to a 1-Pd H complex. Insertion of free dba into the Pd−H bond generates a 1-Pd dba complex that
0
releases 1,5-diphenylpent-1-en-3-one via intra- or intermolecular protonolysis. Concomitantly, comproportionation with 1-Pd
yields 3. Complex 3 was found to function as a precatalyst in the Suzuki−Miyaura cross-coupling of p-chloroacetophenone with
good conversions.
INTRODUCTION
■
Palladium is one of the most successfully applied transition
metals in the field of homogeneous catalysis and is best known
for its reactivity in cross-coupling involving C−C bond
formation (for example in Suzuki−Miyaura and Sonogashira
1
reactions). The applied palladium (pre)catalysts typically are
0
II
in the Pd or Pd oxidation states, while also complexes with
III
IV
Pd and Pd oxidation states have recently received substantial
2
attention. Complexes with the interesting but relatively rare
I
Pd oxidation state are stable only as closed-shell dinuclear
I
I
I
I
I
Figure 1. Formation of {Pd } complexes via comproportionation of
{
Pd } complexes containing a Pd −Pd bond. The first {Pd }
2
2
2
II
0
Pd with Pd (A), bimetallic reductive elimination (B), or photo-
chemically induced Pd−C homolysis (C); dba = dibenzylideneace-
tone.
complex was prepared in 1942 and fully characterized in 1981
3
by single-crystal X-ray diffraction. These complexes are
typically obtained via comproportionation of Pd and Pd0
II
4
precursors (Figure 1, route A). Besides the simple
combination of Pd and Pd precursors, in situ generation of
Figure 1). Ozerov et al. showed the formation of a (PNP-PdI)2
II
0
0
II
pincer complex via photochemically induced homolytic
the two oxidation states starting with a single Pd or Pd
precursor has also been described. For instance, starting with a
Pd precursor, the in situ oxidation of Pd with allyl halides or
II
splitting of a Pd −alkyl bond, leading to the formation of
I
0
II
alkyl radicals and mononuclear PNP-Pd · species, which
undergo homocoupling to form higher alkyl chains and a
propargyl halides has successfully been applied to generate
I
6b
I
4d,g,5
0
(PNP-Pd ) complex (route C Figure 1).
{
Pd } complexes.
Also the in situ oxidation of Pd with
2
2
The Pd−Pd bond in this type of complexes can infer
Cu- or Ag-salts has been reported to lead to the formation of
I
5g
interesting reactivity, in particular concerning the stoichio-
{
{
Pd } complexes. Other routes toward the formation of
2
6
b,7
I
metric activation of small molecules,
but catalytic
Pd } complexes involve bimetallic reductive elimination or
radical-type reactions. Brown et al. showed that bulky
phosphine ligands (P Bu ) coordinated to an iodide-bridged
Pd } complex enforce the bimetallic reductive elimination of
2
I
6
applications of {Pd } complexes are rare. To the best of our
2
t
3
II
{
Received: October 22, 2014
Published: November 26, 2014
2
I
biphenyl and the formation of a {Pd } complex (route B
2
©
2014 American Chemical Society
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Organometallics
Article
knowledge only two examples are known in which a {PdI}2
formation of a dinuclear PN-bridged Pd complex from 1 and
I
complex was found to be actively involved in a catalytic cycle.
Pd(dba) and propose a mechanism for its formation.
2
I
Allyl-bridged {Pd } complexes have been used in the catalytic
2
8
carboxylation of allylstannanes and allylboranes, and more
recently {(P Bu )Pd Br} was applied in catalytic halide
RESULTS AND DISCUSSION
Synthesis and Characterization of {Pd } Complex 3.
■
t
I
I
3
2
2
exchange of aryl iodides to bromides using tetrabutylammo-
The preparation of bisMETAMORPhos ligand 1 has previously
+
−
9
13a
nium bromide (Bu N Br ) as bromide source. In contrast to
4
been reported.
Ligand 1 contains two stereogenic
the scarce catalytic application of these complexes they have
phosphorus centers and is obtained selectively as a single
R/S
S/R
been often applied as efficient precatalysts for the in situ
diastereomer (mesomeric form P −P ). Addition of an
0
generation of highly reactive 12-electron LPd species active in
equimolar amount of 1 to a toluene suspension of bis-
4
d,10
I
cross-coupling reactions.
Two well-known {Pd } precata-
2
(dibenzylideneacetone)palladium(0) {Pd(dba)
} led to the
2
t
t
lysts are {(P Bu )PdBr} and Pd Cl(μ-Cl)P Bu (Bph-Me); see
3
2
2
2
formation of a single species with four nonequivalent
t
31
Figure 2. Bromide-bridged complex {(P Bu )PdBr} was first
3
2
phosphorus signals (AA′A″B system) observed with
P
NMR spectroscopy; see Scheme 1. Note that 0.5 equiv of
Scheme 1. Procedure for the Synthesis of Dinuclear
Complex 3, Involving Initial Formation of 2 from Pd(dba)2
and Ligand 1
I
t
Figure 2. {Pd } complexes {(P Bu )PdBr} and Pd Cl(μ-Cl)-
2
3
2
2
t
P Bu (Bph-Me), two precatalysts applied in cross-coupling reactions.
2
6a
prepared by Vilar, Mingos, et al. and recently experimentally
and computationally studied by Schoenebeck et al. in Suzuki
11
t
cross-coupling reactions, while [Pd Cl(μ-Cl)P Bu (Bph-Me)]
2
2
was prepared by Vilar and applied in amination reactions of aryl
4
c,12
chlorides.
We recently reported the reactivity of a xanthene-based
I
bisMETAMORPhos ligand (1) toward low-valent Ir (acac)-
13
I
(
cod) (see Figure 3a). The initial formation of 1-Ir involves
Pd(dba) still remains unreacted as a 1:1 ligand to metal ratio
2
was used, and thus a suspension of free Pd(dba) and 2 was
2
0
obtained. MS data confirm the formation of 1 -Pd complex 2
2
as the sole species. This species is suggested to have a distorted
tetrahedral geometry, perhaps better described as a trigonal
pyramidal geometry. Combined with the stereogenic nature of
the P donors, this geometry explains the observation of four
different P signals in the 31P NMR spectrum (see Scheme 1).
Similar distorted tetrahedral geometries were previously
Figure 3. (a) Previously reported reactivity of bisMETAMORPhos 1
15
0
I
reported for (Xantphos) Pd complexes. Upon heating this
2
with Ir(acac)(cod) leading to the initial formation of 1-Ir followed by
III
reaction mixture at 75 °C for 24 h, species 2 converted to the
oxidative addition of the ligand to generate a 1-Ir -hydride complex.
I
new {Pd }2 complex 3. Brown crystals of 3·1.7(CH Cl )
Red indicates a neutral sulfonamide ligand arm; blue indicates an
anionic sulfonamide ligand arm. (b) Schematic presentation of a
2
2
suitable for single-crystal X-ray diffraction were obtained, which
confirmed the formation of a dinuclear Pd complex containing
I
I
dinuclear Rh complex prepared with METAMORPhos ligands.
two anionic PN bridging ligand moieties (see Figure 4 and
Scheme 1). Monitoring the reaction of 2 toward 3 in time using
P and H NMR spectroscopy revealed that complex 2 does
−
31
1
monodeprotonation of ligand 1 by acac and displacement of
acacH and cod, yielding a complex in which the ligand is
not directly convert to 3. Prior to the formation of 3 a complex
31
1
monoanionic. Upon standing, oxidative addition of the neutral
(3′) is observed that shows very similar P NMR and H NMR
III
ligand arm occurs, generating a 1-Ir -hydride complex wherein
signatures. Over time 3′ fully converts to complex 3. Therefore,
I
both ligand arms are deprotonated. Another interesting aspect
of METAMORPhos-type ligands is their tendency to form
dinuclear complexes, which has been shown by the generation
this intermediate 3′ is suggested to be a kinetic {Pd } product
2
wherein the xanthene fragments are oriented in a mutual syn
fashion, whereas complex 3 is the thermodynamic anti product
(see Supporting Information for spectral data and structures).
Complex 3 is located on a crystallographic inversion center and
has a Pd−Pd bond of 2.6199(4) Å, which is comparable with
I
14
of boat-shaped dinuclear Rh complexes (Figure 3b). With
these two characteristics of (bis)METAMORPhos ligands in
mind we envisioned them to be suitable for the formation of
I
0
I
16
{
Pd } complexes from a Pd precursor. Here we report the
Pd−Pd bond lengths in other reported {Pd } complexes. As
2
2
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I
Unlike many other {Pd } complexes reported in the literature,
2
complex 3 is remarkably stable toward O in the solid state and
2
18
can be stored for days without decomposition.
To investigate Pd−Pd interactions in complex 3, a
computational study was performed using DFT [BP86, def2-
SV(P)] using a slightly simplified model of ligand 1 (having R
n
=
Me instead of para- Bu-Ph; see Figure 3). The DFT structure
is very similar to the molecular structure determined by X-ray
diffraction (Figure 4). The calculated Pd−Pd and Pd−P bond
lengths of the optimized structure are only slightly longer
(
∼0.05−0.07 Å) than the corresponding experimental values
(
commonly observed). The DFT-calculated Pd−Pd Wiberg
bond order of 0.274 suggests a rather weak Pd−Pd bond, in
agreement with the rather long Pd−Pd bond length (see Table
1
). The difference in bridged and nonbridged Pd−P bonds is
also reflected by the Pd−P bond orders found.
a
Table 1. Selected (DFT-Calculated ) Bond Distances and
Wiberg Bond Orders
distance (Å), exptl/DFT
Wiberg BO
Pd−Pd
2.6199(4)/2.6910
2.149(2)/2.1556
2.2273(7)/2.2938
2.4118(8)/2.4624
0.274
0.450
0.771
0.571
Pd−N (bridging)
1
Pd−P (bridging)
1
Pd−P (nonbridging)
2
Figure 4. Top: X-ray structure of 3 top view; dotted lines indicate
hydrogen bonds. Bottom: Molecular structure of 3 side view. Partially
occupied CH Cl solvent molecules, hydrogen atoms, and a disordered
a
Turbomole BP86, def2-SV(P), analyzed with AOMix.
2
2
butylphenyl group on sulfonamide are omitted for clarity. Symmetry
The bridging Pd−P bond has a bond order of 0.771, while
1
operation a: 0.5 − x, 1.5 − y, 1 − z. Selected bond lengths (Å) Pd −
1
the nonbridging Pd−P bond has a significantly lower bond
2
Pd
2.6199(4), Pd −P 2.2273(7), Pd −N 2.149(2), P −N
1
(a)
1
1
1
1
1
1
order of 0.570 (see Table 1), in accordance with a longer Pd−
1
.670(2), N −S 1.588(2), Pd −P 2.4118(8), P −N 1.709(3), N −
2
1
1
1
2
2
2
2
P
and shorter Pd−P bond (both calculated and exper-
2
1
S 1.639(3), S −O 1.437(2), S −O 1.452(2), S −O 1.435(3), S −
1
2
1
3
2
4
2
imental). Seven frontier molecular orbitals (FMOs) were found
predominately centered at the Pd atoms; see Supporting
Information.
O 1.430(3), N ···O 2.677(4). Selected angles (deg): P −Pd −P
5
2
3a
1
1
2
1
02.57(3), P −Pd −N 103.24(6), N −Pd −Pd 83.19(6), Pd −
2
1
1a
1a
1
1a
1a
Pd −P 71.34(2), P −Pd −Pd 172.87(2), P −Pd −N 153.74(7).
1
1
2
1
1a
1
1
1a
Proposed Mechanism for Formation of Complex 3.
I
0
The formation of Pd dimer 3 solely from a Pd precursor
a consequence of its centrosymmetry, the two xanthene
fragments are in a mutual anti configuration. This symmetry
is retained in solution on the NMR time scale, leading to a
II
strongly suggests the in situ generation of a transient 1-Pd
species, followed by comproportionation with a suitable Pd
complex. In line with previously observed reactivity for Ir, we
hypothesized the formation of a 1-Pd H species via the
0
13
3
1
relatively simple P NMR spectrum with two AA′BB′ signals.
The P−N bond length of the bridging P−N ligand moiety is
slightly smaller [P −N : 1.670(2) Å] compared to the
II
decoordination of one equivalent of neutral ligand 1 from
complex 2, followed by oxidative addition of a neutral ligand
arm; see Scheme 2. Variable-temperature NMR experiments
1
1
H
nonbridged P−N bond [P −N : 1.709(3) Å]. A significant
2
2
difference in bond length between Pd −P and Pd −P
1
1
1
2
were performed with complex 2 in toluene-d to investigate
8
(
2.2273(7) and 2.4118(8) Å, respectively) was observed,
whether a Pd-hydride species could be detected. However, no
which is ascribed to the trans influence of the Pd−Pd
1
1
6d,17
hydride signal was detected in the H NMR spectrum down to
bond.
The short interatomic distance between the
−
60 ppm in the temperature range 213−363 K. The steady-
nitrogen of the nonbridging ligand arm (N ) and the oxygen
2
of the bridging sulfonamide unit [O3(a)] suggests the presence
of an intramolecular N−H···O hydrogen bond (red dotted line
at the top of Figure 4). The angles in the core bimetallic
skeleton (∠P −Pd −P 102.57(3)°; ∠P −Pd −N
Scheme 2. Formation of Complex 3 from 2 via
Comproportionation of Transient 1-Pd -H with Pd
II
0
1
1
2
2
1
1a
1
7
03.24(6)°; ∠N −Pd −Pd 83.19(6)°; ∠Pd −Pd −P
1
a
1
1a
1a
1
1
1.34(2)°) deviate significantly from 90°, indicating that the
palladium atom is in a highly distorted square planar geometry
= 360.34(9)°]. The six-membered Pd−P−N−Pd−P−
[∑
angles
N ring is essentially flat with a puckering amplitude of only
.1801(16) Å. This is in sharp contrast with dinuclear rhodium
complexes with bisMETAMORPhos that display boat-like-
0
14
shaped geometries. The formation of 3 was also synthetically
I
confirmed by a substitution reaction with {Pd } precursor
2
[
Pd (CH CN) ][BF ] and with two equivalents of ligand 1 in
2 3 6 4 2
the presence of a base (triethylamine or sodium acetate).
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II
state concentration of such a 1-Pd -hydride species might be
complex 3 shows activity in the Suzuki−Miyaura cross-coupling
of p-chloroacetophenone. In a 2-propanol/THF mixture at 70
°C and 0.5 mol % catalyst loading, 87% conversion was
obtained after 6.5 h with preformed complex 3 (Table 2, entry
too low to be detected, which could potentially be explained by
an immediate follow-up reaction of the formed 1-Pd -hydride
species. Protonolysis of the Pd−H bond by the NH of ligand 1
leads to the formation of H ; such reactivity was previously
However, when 3 was prepared in a
sealed NMR tube, no H could be observed by H NMR
spectroscopy, which rules out the direct protonolysis of the
II
2
III 13a,b
described with 1-Ir H.
Table 2. Suzuki-Miyaura Cross-coupling with Various Pd-
1
a
2
complexes
Pd−H bond with the ligand; see Scheme 2.
0
Notably, using the alternative Pd precursor tetrakis-
(
triphenylphosphine)palladium, Pd(PPh ) , also generated
3 4
species 2 upon reaction with two equivalents of 1, but in this
case the formation of 3 could not be observed upon heating.
Interestingly, 3 was formed when the reaction of 1 with
Pd(PPh ) was performed in the presence of one equivalent of
b
entry
catalyst
conversion % (1 h)
1
2
3
87 (25.1)
71 (11.2)
<1
3
4
dba, which hints at an important role of dba in the sequence of
reaction steps leading to formation of complex 3. Analysis of
the crude reaction mixture by mass spectrometry (CSI+)
Pd(dba)
3/1
/1
2
c
3
a
Reaction conditions: catalyst 0.5 mol %, 2-propanol (0.75 mL), 1.1
equiv of KO Bu (1 M in THF), 6.5 h at 70 °C. Conversions were
determined by GC-MC and H NMR. Reaction was performed with
II
t
b
indicates the presence of a 1-Pd dba intermediate at m/z
+
1
c
1
1
190.30727 (m/z calcd for C H N O P PdS [M] :
6
4
64
2
5
2
2
1
the addition of 1 equiv of 1.
190.271 99). H NMR spectroscopy of the reaction mixture
also provided support for such a 1-Pd dba species (see
II
19
Supporting Information). Furthermore, NMR analysis of the
reaction mixture after prolonged heating (65 °C, 40 h) showed
the formation of 1,5-diphenylpent-1-en-3-one, which is the
product of protonolysis of a Pd−dba bond; see Supporting
Information. This compound was also detected by GC-MS,
with an overall conversion of 20% dba (theoretical yield: 25%).
These combined observations are in agreement with the
proposed reaction mechanism shown in Scheme 3. Initial
1). In situ formation of 3 resulted in slightly lower conversion
(71%), Table 2, entry 2. The difference in conversion between
well-defined and in situ generated catalyst is even more
pronounced after 1 h (25.1% vs 11.2% for 3 and Pd(dba) /1,
2
respectively). This suggests that the initial formation of 3 is
required to obtain high catalytic activities. Addition of one
equivalent of 1 to the reaction mixture led to complete loss of
catalytic activity. This inhibition effect was previously observed
for the (Xantphos)Pd-catalyzed amination of aryl bromides due
15
Scheme 3. Proposed Mechanism for the Formation of
Complex 3
to the formation of (Xantphos) Pd. If complex 3 is directly
2
involved in the catalysis, it is unlikely that the addition of
exogenous ligand would inhibit the catalytic activity. Therefore,
we consider it most likely that 3 acts as precatalyst for the
0
generation of a mononuclear 1-Pd complex, concomitant with
II
the formation of 1-Pd . Further studies on the reactivity of
complex 3 are currently ongoing.
CONCLUSIONS
■
The versatile coordination chemistry of bisMETAMORPhos
0
ligand 1 with the Pd precursor Pd(dba) is discussed. Initially,
2
0
displacement of the dba ligand results in formation of Pd
0
complex 2 (1 -Pd ) , which contains four magnetically
2
2
3
1
inequivalent phosphorus atoms according to P NMRI
spectroscopy. In time, a unique PN-bridged dinuclear Pd
complex (3) is obtained as the thermodynamic product. This
species displays a completely flat Pd−Pd core, with a Pd−Pd
bond length of 2.6199(4) Å. The formation of complex 3 from
2
is suggested to proceed via an in situ comproportionation
pathway. This route involves (1) decoordination of one ligand
decoordination of one equivalent of 1 from complex 2 and
in 2, followed by oxidative addition of one coordinated ligand
II
subsequent oxidative addition of one ligand arm leads to
arm to generate a 1-Pd -hydride complex; (2) reaction of this
II
II
II
formation of the transient 1-Pd -hydride species. Immediate
1-Pd -hydride species with free dba to yield a 1-Pd dba
II
1
insertion of dba into the Pd−H bond generates 1-Pd dba.
complex, which was detected by H NMR and mass
Protonolysis (intra- or intermolecular) of the Pd−dba bond by
the acidic sulfonamide N−H of the bis-METAMORPhos ligand
generates 1,5-diphenylpent-1-en-3-one and a coordinately
spectrometry; (3) intra- or intermolecular protonolysis of the
Pd−dba bond to release 1,5-diphenylpent-1-en-3-one, which is
1
observed by H NMR and GC-MS, concomitant with
II
0
0
unsaturated Pd species, which couples with (1)Pd (liberated
comproportionation with 1-Pd to generate 3. Complex 3
I
from 2) to produce the final {Pd } complex 3.
Reactivity of Complex 3. Dinuclear {Pd } complexes
was applied in the Suzuki−Miyaura coupling reaction of p-
chloroacetophenone, and good conversion was obtained.
Complex 3 is most likely not directly involved in catalysis but
serves as a precatalyst for the catalytically active species.
2
I
2
have previously been successfully applied as precatalysts in
Suzuki−Miyaura cross-coupling reactions of aryl chlorides. Also
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twice with pentane (3 × 10 mL), and collected (yield: 45%). 31P{ H}
1
EXPERIMENTAL SECTION
■
NMR (162 MHz, CD Cl ): δ 39.62 (AA′BB′, J = 37.1, 10.0, 3.3 Hz,
2
2
General Procedures. All reactions were carried out in dry
glassware under a nitrogen atmosphere using standard Schlenk
techniques unless stated otherwise. Toluene, pentane, and THF
were distilled from sodium under dinitrogen, ACN was distilled from
CaH under nitrogen, and CH Cl was collected from an MB SPS-800.
1
2
P), 22.27 (AA′BB′, J = 37.2, 10.2, 3.8 Hz, 2P). H NMR (400 MHz,
CD Cl ): δ 10.26 (t, J = 8.5 Hz, 2H), 8.24−8.13 (m, 2H), 7.81−7.42
2
2
(
8
(
m, 2H), 7.63−7.50 (m, 4H), 7.30−6.55 (m, 24H), 6.92−6.70 (m,
H), 6.70−6.57 (m, 6H), 6.39 (m, 4H), 6.16 (t, J = 7.6 Hz, 2H), 4.5
br s, 1H), 2.72−2.60 (m, 4H), 2.61−2.52 (m, 4H), 1.75 (s, 6H),
2
2
2
Deuterated solvents were degassed by four freeze−pump−thaw cycles
1
1
.67−1.48 (m, 8H), 1.46−1.26 (m, 8H), 1.20 (s, 6H), 1.00−0.92 (m,
and dried over molecular sieves (4 Å). NMR spectra were measured
1 31 13 1
2H). H{ P} NMR (400 MHz, CD Cl ): δ 8.92. C{ H} NMR
1
13
31
2
2
on a Bruker AMX 400 ( H: 400.1 MHz, C: 100.6 MHz, and P:
(
101 MHz, CD Cl ): δ 154.44 (d, J = 4.7 Hz, Cquat), 152.85 (d, J = 7.4
Hz, Cquat), 148.38 (s, Cquat), 146.28 (s, Cquat), 142.31 (s, Cquat), 140.55
2 2
1
1
62.0 MHz) or on a Varian Mercury 300 ( H: 300.1 MHz)
spectrometer. High-resolution mass spectra were obtained on a
time-of-flight JEOL AccuTOF LC-plus mass spectrometer (JMS-
T100LP) equipped with a CSI or ESI source. Calculated spectra were
obtained with JEOL Isotopic Simulator (version 1.3.0.0). Geometry
optimizations were carried out with the Turbomole program
(
(
s, Cquat), 134.75 (s, Cquat), 134.13 (s, Cquat), 130.86 (s, CH), 130.04
s, CH), 129.87 (s, CH), 129.71 (s, Cquat), 129.47 (s, CH), 129.05 (s,
CH), 128.86 (s, CH), 128.77 (s, CH), 128.51 (s, CH), 128.38 (s,
CH), 128.18 (s, CH), 127.92 (s, CH), 127.42 (s, CH), 126.86 (s,
CH), 126.69 (s, CH), 126.51 (s, CH), 126.31 (s, CH), 125.81 (s,
CH), 125.45 (s, CH), 125.16 (s, CH), 124.18 (s, CH), 122.91 (d, J =
4.14 Hz, Cquat), 122.53 (d, J = 16.67 Hz, Cquat), 35.98 (s, Cquat), 35.88
s, CH ), 35.71 (s, CH ), 35.71 (s, CH ), 33.85 (s, CH ), 33.79 (s,
CH ), 31.15 (s, CH ), 22.93 (s, CH ), 22.73 (s, CH ), 22.64 (s, CH ),
4.08 (s, CH ), 14.02 (s, CH ). HR MS (CSI ): m/z calcd for
21a
21b
package,2 coupled to the PQS Baker optimizer
via the BOpt
1c
21d,e
package, at the spin unrestricted ri-DFT level using the BP86
2
2
1f
functional, the resolution-of-identity (ri) method, and the def2-
(
2
2
2
2
21g
21h
SV(P) basis set for the geometry optimizations. Wiberg
bond
2
3
3
2
2
+
orders were calculated from the Turbomole output files using the
1
3
3
21i,j
+
AOMix program.
C H N O P Pd S [M + Na] 1931.308 77, obsd 1931.314 34.
Anal. Calcd for C H N O P Pd S : C, 59.15; H, 5.17; N, 2.94.
94
98
4
10
4
2 4
Materials. All reagents were purchased from commercial suppliers
and used without further purification: Pd(dba)2 (Sigma-Aldrich),
94
98
4
10
4
2 4
Found: C, 59.08; H, 5.21; N, 2.94.
Pd(PPh3) (Strem Chemicals), trans,trans-dibenzylideneacetone
4
Suzuki−Miyaura Coupling. Complex 3 (1 μmol, 0.5 mol %) was
dissolved in 2-propanol (0.75 mL), and to this solution were added p-
chloroacetophenone (0.2 mmol, 25.9 μL), phenylboronic acid (1.2
(
Sigma-Aldrich), palladium(II)chloride (Sigma-Aldrich). Ligand 1
was prepared according to a literature procedure.
Preparation of Complex 2. Pd(dba) (16.9 mg, 1 equiv) and
13b
t
2
equiv, 29.3 mg), and 1 M KO Bu (0.22 mL, 1.1 equiv) in THF. The
ligand 1 (50.0 mg, 2 equiv) were dissolved in toluene (2 mL) and
stirred at room temperature for 30 min. The purple reaction mixture
was filtrated over Celite and concentrated to approximately 1 mL.
Pentane (8 mL) was added to precipitate out a yellow powder, which
reaction mixture was heated to 70 °C for 6.5 h, whereafter it was
cooled to room temperature and concentrated. Water (2 mL) was
added, and the product was extracted with diethyl ether (3 × 2 mL).
The organic fractions were combined and dried with MgSO , filtered,
4
was filtrated, washed twice with pentane (5 mL), and collected (yield:
and concentrated. The biphenyl product was obtained as a light yellow
6
3
9%). 31P{ H} NMR (162 MHz, toluene-d ): δ 53.31 (ddd, J = 99.5,
1
solid. H NMR (CDCl , 400 MHz): δ 8.04 (d, J = 8.3 Hz, 2H), 7.69
1
8
3
5.1, 20.1 Hz, 1P), 49.73 (ddd, J = 100.4, 96.9, 42.0 Hz, 1P), 45.61 (br
dd, J = 97.5, 35.2 Hz, 1P), 33.74 (ddd, J = 41.8, 20.4, 19.5, Hz, 1P). H
(d, J = 8.3 Hz, 2H), 7.65−7.62 (m, 2H), 7.52−7.40 (m, 3H), 2.65 (s,
1
+
3H). MS (EI, m/z): 196 (M ). These assignments matched with
2
0
NMR (400 MHz, toluene-d ): δ 8.92 (d, J = 25.6 Hz, 1H), 8.58 (m,
previously reported literature data.
8
1
7
3
5
H), 7.91 (dd, J = 11.1, 8.3 Hz, 4H), 7.47 (d, J = 8.2 Hz, 4H), 7.39−
.29 (m, 4H), 7.17−7.06 (m, 6H), 7.00−6.92 (m, 6H), 6.92−6.69 (m,
H), 6.64−6.52 (m, 4H), 6.54−6.43 (m, 8H), 6.15−6.06 (m, 4H),
.93 (t, J = 7.3 Hz, 2H), 5.49 (br s, 1H), 5.42 (t, J = 8.4 Hz, 2H), 5.18
ASSOCIATED CONTENT
■
*
S
Supporting Information
CIF file, H and 31P NMR of formation of 3 from 2 with
1
(
br s, 1H), 3.48 (d, J = 22.8 Hz, 1H) 2.63 (m, 2H), 2.42−2.29 (m,
intermediate product 3′, preparation of [Pd (CH CN) ][BF ] ,
4
0
1
H), 2.21 (m, 2H), 1.85 (s, 3H), 1.63 (s, 3H), 1.49−1.05 (m, 22H),
2
3
6
4 2
1
31
xyz/pbd file of 3, Wiberg bond orders, FMOs. This material is
.96−0.85 (m, 12H). H{ P} NMR (400 MHz, toluene-d ): δ 8.92 (s,
8
H), 8.58 (d, J = 7.7 Hz, 1H), 7.91 (dd, J = 11.1, 8.3 Hz, 4H), 7.47 (d,
available free of charge via the Internet at http://pubs.acs.org.
J = 8.2 Hz, 4H), 7.39−7.29 (m, 4H), 7.17−7.06 (m, 6H), 7.00−6.92
m, 6H), 6.92−6.69 (m, 3H), 6.64−6.52 (m, 4H), 6.54−6.43 (m, 8H),
.15−6.06 (m, 4H), 5.93 (t, J = 7.3 Hz, 2H), 5.49 (br s, 1H), 5.42 (d, J
8.2 Hz, 2H), 5.18 (br s, 1H), 3.48 (s, 1H) 2.63 (m, 2H), 2.42−2.29
m, 4H), 2.21 (m, 2H), 1.85 (s, 3H), 1.63 (s, 3H), 1.49−1.05 (m,
(
6
=
(
AUTHOR INFORMATION
Corresponding Author
E-mail: j.n.h.reek@uva.nl.
Notes
■
*
13
1
2
1
1
1
1
1
1
1
1
1
1
3
2H), 0.96−0.85 (m, 12H). C{ H} NMR (101 MHz, CD Cl ): δ
2
2
The authors declare no competing financial interest.
48.67 (s, C ), 147.68 (s, Cquat), 140.80 (s, Cquat), 136.17 (s, Cquat),
quat
35.29 (s, Cquat), 131.63 (s, CH), 131.31 (s, CH), 131.18 (s, CH),
30.84 (s, CH), 129.64 (s, CH), 129.58 (s, CH), 129.52 (s, CH),
29.43 (s, CH), 129.36 (s, CH), 129.30 (s, CH), 129.26 (s, CH),
29.06 (s, CH), 128,75 (s, CH), 128.56 (s, CH), 128.49 (s, CH),
28.37 (s, CH), 127. 55 (s, CH), 127. 36 (s, CH), 126.91 (s, CH),
26.70 (s, CH), 126.67 (s, CH), 126.52 (s, CH), 126.12 (s, CH),
25.90 (s, CH), 124.86 (s, Cquat), 124.47 (s, Cquat), 124.18 (s, CH),
23.88 (s, CH), 123.64 (s, CH), 123.44 (s, CH), 123.23 (s, Cquat),
22.82 (s, CH), 122.66 (s, Cquat), 36.26 (s, Cquat), 35.99 (s, Cquat),
5.85 (s, CH ), 35.81 (s, CH ), 35.74 (s, CH ), 33.76 (s, CH ), 33.65
ACKNOWLEDGMENTS
■
We kindly acknowledge NWO for financial support and Ed
Zuidinga for mass analysis. The X-ray diffractometer has been
financed by The Netherlands Organization for Scientific
Research (NWO).
REFERENCES
■
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