Superstable palladium(0) complex as an air-and thermostable catalyst for Suzuki coupling reactions

Article abstract of DOI:10.1002/ejoc.201403214

An unprecedentedly thermo-and air-stable Pd0 complex from readily available electron-poor trifluoromethylated phosphine was serendipitously discovered. As detailed and comparative DFT calculations indicate, the stability of the complex is associated with unusually strong ligand-ligand noncovalent interactions. The unique stability and the presence of hydrophobic structural elements of the complex offer several practical advantages, which were exploited in catalytic Suzuki-Miyaura coupling reactions.

Full text of DOI:10.1002/ejoc.201403214

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SHORT COMMUNICATION
DOI: 10.1002/ejoc.201403214
Superstable Palladium(0) Complex as an Air- and Thermostable Catalyst for
Suzuki Coupling Reactions
Alexandra Jakab,[a] Zoltán Dalicsek,*[b] Tamás Holczbauer,[a] Andrea Hamza,[a]
Imre Pápai,*[a] Zoltán Finta,[c] Géza Timári,[d] and Tibor Soós*[a]
Keywords: Noncovalent interactions / Cross-coupling / Fluorinated ligands / Electron-deficient compounds / Palladium
An unprecedentedly thermo- and air-stable Pd0 complex
from readily available electron-poor trifluoromethylated
noncovalent interactions. The unique stability and the pres-
ence of hydrophobic structural elements of the complex offer
phosphine was serendipitously discovered. As detailed and several practical advantages, which were exploited in cata-
comparative DFT calculations indicate, the stability of the
complex is associated with unusually strong ligand–ligand
lytic Suzuki–Miyaura coupling reactions.
persion interactions can induce counterintuitive steric ef-
fects in bulky carbene analogues.[6] Additional examples re-
veal that secondary interactions can decisively affect chemi-
cal structure and reactivity. After introducing several tert-
butyl groups, dispersion forces astonishingly overcome the
lability of an elongated covalent bond in hexaphenyl eth-
ane.[7] Moreover, frustrated Lewis pairs, sterically over-
crowded Lewis pairs unable to form a dative complex, still
generate highly reactive bifunctional encounter complexes
by attractive noncovalent interactions.[8]
These examples stretch the boundaries of current para-
digms and illuminate the need to locate and recognize ad-
ditional structural elements exerting extended intramolecu-
lar attractions to advance the understanding of chemical
bond and reactivity further.
Herein, we report our serendipitous finding of an un-
precedentedly stable Pd0 phosphine complex[9] in which un-
usually strong noncovalent interactions between the elec-
tron-poor, CF3-tagged phosphine ligands contribute sub-
stantially to the overall stability of the complex. This sta-
bility could be of a great practical advantage in palladium
catalysis, which was demonstrated in Suzuki–Miyaura cou-
pling reactions.
Introduction
Attractive noncovalent interactions play a fundamental
role in determining and maintaining the three-dimensional
structure of large molecules, such as proteins and supra-
molecular architectures.[1,2] They are also known to govern
selective processes, such as molecular recognition and ste-
reocontrol of organic reactions.[3] The influence exerted by
these ubiquitous interactions can vary greatly, as their over-
all contribution spans a wide energy range. With regard to
molecules with low molecular weights, it was established
that they are ancillary contributors that determine the over-
all molecular structure, shape, and behavior. As a result,
the relevance of secondary interactions within molecules,
especially intramolecular dispersion interactions, is often
neglected. Nevertheless, there is growing recent evidence
showing that extended attractive dispersion forces do play
an important, even decisive, role in molecular chemistry by
assisting or counteracting the effect of primary chemical
bonds or steric repulsion.
It was recently pinpointed that aromatic π–π interactions
contributed markedly to the formation of an 18-electron
palladium–phosphine complex.[4] Furthermore, CH–π and
CF–π type interactions can drive the formation of struc-
tural isomers of carbene–palladium complexes,[5] and dis-
Results and Discussion
[a] Institute of Organic Chemistry, Research Centre for Natural
Sciences, Hungarian Academy of Sciences,
P.O. Box 286, 1519 Budapest, Hungary
E-mail: soos.tibor@ttk.mta.hu
Recently, we developed a practical and cost-saving tag-
ging approach for organocatalyst immobilization that takes
advantage of the hydrophobicity of the shortest fluorous
group, the trifluoromethyl group.[10] As a continuation of
this effort, we became interested in extending our recycling
approach and in synthesizing the trifluoromethylated ana-
logue of Pd(P)4 (P = PPh3). This latter complex is still con-
sidered as the workhorse of the palladium-catalyzed cross-
coupling reactions,[11] although myriad of more active cata-
www.ttk.mta.hu/organo
[b] H4Sep Ltd.,
Berlini út. 47–49, 1045 Budapest, Hungary
[c] Zentiva Group
a.s. U Kabelovny 130, 10237 Prague 10, Czech Republic
[d] Sanofi Újpest,
Tó u. 1–5. 1045 Budapest, Hungary
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403214.
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Z. Dalicsek, I. Pápai, T. Soós et al.
SHORT COMMUNICATION
lyst have been developed over the last two decades.[12] Espe-
cially, the fine-chemical industry relies on this catalyst ow-
ing to its favorable cost/reactivity relationship and easy ac-
cessibility.[13] Nevertheless, there are several technical prob-
lems associated with the usage of Pd(P)4; its air and ther-
mosensitivity and its propensity to degrade easily upon
storage. Additionally, often-observed catalyst degradation
that occurs during cross-coupling reactions necessitates the
employment of relatively high catalyst loadings and impairs
the efficient separation of metal impurities from the prod-
uct.
For the sake of catalyst recycling and removal, we se-
lected the P[3,5-(CF3)2C6H3]3 (1) ligand (also denoted as
PF) to replace P, in Pd0 complexes. Our “a priori” ligand
choice could be underpinned only by its hydrophobic char-
acter, as the poor σ-donor nature of phosphine 1 is appar-
ently the opposite of the current trend in ligand develop-
ment for palladium-catalyzed cross-coupling applications.
Nevertheless, recent reports[14–17] have validated the effi-
ciency of electron-deficient phosphine ligands in various
palladium-catalyzed reactions. In those examples, the li-
gands made the metal center more electron-deficient and
had an accelerating effect on the rate of reductive elimi-
nation[14] or on the concerted metalation–deprotonation
step.[15]
Figure 1. ORTEP style diagram of the measured X-ray structure of
complex 2. Displacement ellipsoids are drawn at the 30% prob-
ability level. Hydrogen atoms are omitted for clarity.
For the synthesis of the envisioned trifluoromethylated room temperature, the sample preserved its bright-yellow
variant of Pd(P)4, the previously developed protocol was color, which was a good indicator of the quality and struc-
employed.[18] Accordingly, the addition of 1 (5 equiv.) to tural integrity of the Pd0 complex. An additional GLP-con-
PdCl2 in DMSO was followed by reduction with hydrazine trolled stability test (40 °C and 75% humidity) demon-
hydrate at 120 °C (Scheme 1).
strated that complex 2 could be stored in an open vial for
a longer period of time (for years) without any detectable
degradation or decomposition (color; 1H NMR, 19F NMR,
and 31P NMR spectroscopy data; and catalytic efficiency).
We also experienced a similar trend in complex stability
at higher temperature. Whereas nonfluorinated Pd(P)4 de-
composed in air at 98 °C in a differential scanning calorim-
etry analysis, fluorinated 2 had a significantly higher de-
composition point (170 °C) and a rather high melting point
(m.p. 225 °C) under an atmosphere of N2. The stability of
the complex, however, was not confined to the solid phase.
Solution-phase NMR studies indicated the nondissociative
Scheme 1. Synthesis of moisture- and air-stable fluorinated Pd0 cat-
alyst 2.
Resulting bright-yellow Pd0 complex 2 was isolated and nature of complex 2 in [D8]THF at ambient temperature.
characterized by NMR spectroscopy. Subsequently, the The 31P NMR spectra of the complex consisted of a single
combination of several analytical methods was used to de- signal and no formation of a tetrakis complex was observed
termine the structure and stoichiometry of complex 2. Al- if phosphine 1 was added to the solution of complex 2. It
though elemental analysis failed owing to the incomplete is also important to note that the presence of fluorine atoms
combustion of the highly fluorinated compound, an unex- influences the solubility profile of the Pd0 complex. Com-
pected 1:3 molar ratio of palladium and phosphorus was pound 2 is practically insoluble in most classical solvents
indicated by microwave plasma–atomic emission spec- (e.g., chloroform, hexanes, alcohols) at room temperature,
troscopy (MP-AES). The same stoichiometry was rein- but it is well soluble in THF.
forced by the MALDI-TOF MS measurements. Finally, the
The above data clearly indicate that the introduction of
structure and stoichiometry of 2 were unequivocally deter- CF3 groups into the meta positions of ligand P results in
mined by single-crystal X-ray diffraction (Figure 1) com- an unexpected and significant change in complex stability.
bined with phase identification and characterization of the To probe the origin of this enhanced stability, comparative
isolated sample by powder diffraction.
DFT calculations were performed for the series of Pd(P)n
Besides the stoichiometry, the most unusual and peculiar and Pd(PF)n complexes (n = 1–4). We used a dispersion-
characteristic of complex 2 was its high air and thermosta- corrected density functional (B3LYP-D3) in these calcula-
bility.[19] After prolonged exposure to air and moisture at tions to account reasonably for medium- and long-range
2
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Superstable Pd0 Complex for Suzuki Coupling Reactions
noncovalent interactions.[20] The dissociation energies of the
P and PF phosphine ligand were computed for these series,
and the results are presented in Figure 2.
Figure 3. Optimized structures of the Pd(PF)2 and Pd(PF)3 com-
plexes. Interligand aryl–aryl contacts are highlighted by red arrows
(P and T refer to parallel and T-shape arrangement of the interac-
tion aryl groups). All hydrogen atoms are omitted for clarity.
Figure 2. Variation of ligand dissociation energies computed for
Pd(P)n and Pd(PF)n complexes.
The nature and strength of intermolecular aryl–aryl con-
tacts were further analyzed by considering arene dimer
models, as depicted in Figure 4. In these models, the inter-
acting CF3-substituted benzene molecules are in the same
arrangements as they appear in the Pd(PF)3 complex.[21]
The computed interaction energies in these arene dimers are
–7.9 and –3.5 kcalmol–1 (for model-1 and model-2, respec-
tively), which suggests that the P-type aryl–aryl interactions
represent considerably stronger stabilizing effects, but the
contribution of T-type interactions is appreciable as
well.[26,27] These contacts are illustrated by noncovalent in-
teraction plots in Figure 4.[28] We find that the attractive
feature of these contacts is predominantly due to dispersion
interactions.[21,29] Intermolecular attractive forces are also
present in the Pd(P)3 and Pd(P)4 complexes through
Ph···Ph contacts, but they are much weaker, as revealed by
the interaction energies of relevant benzene dimer models
(–2.7 and –2.5 kcalmol–1 for P- and T-type dimers). These
results suggest that the enhanced stability of the Pd(PF)3
complex 2 is thus related to stabilizing interligand noncova-
lent interactions, which are found to be particularly strong
between CF3-substituted aryl groups.
In line with previous calculations,[4] the phosphine disso-
ciation energies were predicted to decrease gradually in the
Pd(P)n series, which was born out by the trend obtained for
the equilibrium Pd–P bond lengths as well (they became
longer with increasing number of coordinated phosphine
ligands).[21] In contrast, the computed dissociation energies
tended to increase along the Pd(PF)n series; they reached a
maximum at n = 3, and the coordination of the fourth
phosphine was found to be weaker again.
Calculations predicted practically identical metal–ligand
bond strengths in the Pd(P) and Pd(PF) monophosphine
species, and this indicates that the overall stabilization effect
of the two components of the Pd–phosphine bond (ligand-
to-metal σ donation and metal-to-ligand π backdonation)
is very similar in the two systems. The relative stabilities
of the diphosphine complexes, however, differ notably [by
7 kcalmol–1 in favor of Pd(PF)2]. Interestingly, the Pd(PF)2
complex has a bent equilibrium structure (PdP2 was found
to be linear);[4,21] this points to significant attractive aryl–
aryl interactions between the two PF phosphine ligands
(Figure 3, a).[22] Structural analysis revealed that in these
aryl–aryl contacts, a CF3 group interacts with the π system
of a neighboring aryl unit.[23] The interacting aryl groups
display either parallel (stacking) or T-shape arrangements,
as highlighted in Figure 3 (a). These structural motifs can
be identified in the Pd(PF)3 complex 2 as well (Figure 3,
b);[24] this implies a high degree of shape complementarity
between the diphosphine complex and the PF phosphine
(1). This allows facile coordination of the third ligand and
favorable ligand–ligand interactions to yield remarkable
stabilization for the Pd(PF)3 complex 2.[25] The formation
of the Pd(PF)4 tetrakis complex was predicted to be thermo-
dynamically feasible [the computed phosphine dissociation
energy is clearly larger than that of Pd(P)4]; however, the
coordination of the fourth trifluoromethylated phosphine is
Figure 4. Truncated models of P- and T-type aryl···aryl interactions
in Pd(PF)3. Carbon atoms bound to phosphorus in Pd(PF)3 are
marked by asterisks. Green regions between the arene molecules
represent stabilizing noncovalent interactions.
The structural data provided by X-ray for complex 2[21]
likely hindered kinetically, as it requires substantial struc- are in good agreement with the computed geometries. Both
tural reorganization of the coordination sphere of the ex- P- and T-type intramolecular aryl–aryl contacts can be
tremely stable Pd(PF)3 species. These results provide ration- readily identified in the X-ray structure. Furthermore, the
ale for the experimental observation of triphosphine com- neighboring molecules in the crystal interact predominantly
plex Pd(PF)3 as opposed to Pd(P)4.
through intermolecular CF···π interactions; however, F···F
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Z. Dalicsek, I. Pápai, T. Soós et al.
SHORT COMMUNICATION
contacts are also present. These interactions are responsible palladium complex [presumably the Pd(PF)2 species] is
for the stability of the crystal lattice of 2.
stable under the applied conditions.[31] Finally, the orange
Owing to the unique physicochemical properties of com- color, the common earmark of the workup procedure of the
plex 2, promising catalytic performance was expected and Suzuki reactions, was not present during chromatography
synthetic efforts were then directed to this end. We were of the reaction mixture, and the original catalyst could be
particularly interested in catalyst robustness in terms of de- isolated.
composition under the catalytic conditions, which is still a
Subsequently, extensive solvent screening was performed
challenge in palladium catalysis, and it is an important de- for the above model reaction, which revealed the general
sign criteria that impacts the overall utility of a given palla- applicability of catalyst 2 in safer solvents, classified as
dium complex in industry. As a model reaction, the Suzuki– class II and class III in industry[32] (Table 2.). We also
Miyaura cross-coupling[30] of 2-bromopyridine (3a) with an showed that alternative solvents,[33] such as methylal and
easily available boronic acid coupling partner, electron-rich ethylal, could be used efficiently at lower temperatures (40–
dioxaborolane 4a, was chosen. Although poor catalytic per- 85 °C), an observation that reinforced the importance of
formance was obtained at lower temperature, excellent re- catalyst solubility in the applied solvents. Ultimately, the
sults were realized under more forcing conditions (Table 1, base screening indicated that both K2CO3 and K3PO4 could
entry 5). The requirement for elevated temperatures stems be employed with almost the same efficiency in the coupling
from the increased stability of the catalyst toward ligand reactions.
dissociation; however, the low reactivity was also related to
the poor solubility of complex 2 in the applied aqueous
methanol solvent system (it starts to dissolve only at 70 °C).
Table 2. Solvent screening in the Suzuki reactions of 2-bromopyr-
idine with dioxaborolane 4a.[a]
However, the catalyst loading could be reduced to 0.02 mol-
% or even lower, and the reaction still had reasonable con-
versions within 1 h and reached an appreciable turnover fre-
quency (TOF) of 4450 h–1.
Table 1. Suzuki reactions of 2-bromopyridine with dioxaborolane
4a.[a]
Entry
Solvent[b]
Base
T [°C]
Conv.[c] [%]
1
2
3
4
5
6
7
8
EtOH[d]
DMF
K2CO3
K3PO4
K3PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
K2CO3
K3PO4
K3PO4
110
110
130
110
90
90
110
90
Ͼ99
Ͼ99 (88)
97 (76)
Ͼ99 (95)
NMP
DMSO[d]
MEK[d]
89
85
85
90
85
97
93
99
MIBK[d]
THF[d]
2-MeTHF[d]
1,3-dioxalane
glycerol-formal
methylal
ethylal
Entry Catalyst [mol-%]
T [°C]
Conv.[b]
Yield[c] [%]
9
75
110
40
1
2
3
4
5
6
7
8
9
0.33
0.33
0.33
0.33
0.33
0.66
1.3
25
50
70
0
5
24
–
–
10
11
12
16
47
88
87
89
89
39
85
90
60
110
110
110
110
110
Ͼ99
Ͼ99
Ͼ99
91
[a] Reaction conditions:
A mixture of 2-bromopyridine (3a,
1 mmol), dioxaborolane 4a (1.5 equiv.), 2 (0.33 mol-%), and base
(2 equiv.) in solvent (5 mL) was stirred and heated in a test vial for
1 h. [b] NMP = N-methylpyrrolidone, MEK = methyl ethyl ketone,
MIBK = methyl isobutyl ketone. [c] Conversion after 24 h was de-
termined by GC analysis of the crude mixture by using octadecane
as an internal standard; conversion after 3 h is given in parenthesis.
[d] Organic solvent/water (10:1) mixture was used.
0.02
0.007
50
[a] Reaction conditions: A mixture of 2-bromopyridine (1 mmol),
dioxaborolane 4a (1.5 equiv.), 2 (0.33 mol-%), and K2CO3 (2 equiv.)
in MeOH/H2O (10:1) was stirred and heated in a test vial for 1 h.
[b] Conversion was determined by GC analysis of the crude mixture
by using octadecane as an internal standard. [c] Yield of isolated
product.
To gauge the generality of catalyst 2 in Suzuki–Miyaura
reactions, a broad range of coupling reactions toward un-
symmetrical biphenyls and N-containing heterocyclic bi-
Surprisingly, even at higher temperatures (e.g., 110 °C), aryls were investigated (Table 3).
no decomposition of catalyst 2 could be detected visually.
Gratifyingly, all these transformations proceeded
Thus, the formation and occurrence of any palladium nano- smoothly within 1 h under the previously developed reac-
particles during the reaction was negligible (if any). tion conditions. Borolanes bearing electron-donating sub-
Furthermore, no palladium black formation occurred, and stituents gave slightly improved yields in the coupling reac-
the reaction mixture remained bright-yellow after the cou- tions, but electron-withdrawing substituents did not impair
pling reaction. These intriguing results highlight the ther- the yields significantly. By using nonactivated aryl bromide
mal robustness of the complex under forcing catalytic con- 10, bromoisoquinoline 8, and indole derivative 6, near
ditions and indicate that the catalytically active form of the quantitative yields were achieved, which confirmed the ap-
4
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Superstable Pd0 Complex for Suzuki Coupling Reactions
Table 3. Suzuki reactions of aryl bromides with dioxaborol- actions conditions, the coupling of 4a with more challeng-
anes.[a], [34]
.
ing 2-chloropyridine (3b) was realized, and the product was
obtained in excellent yield within only 5 min in a microwave
reactor (Table 3, entry 21). Under the same microwave con-
ditions, other dioxaborolanes were treated with 3b to pro-
vide the products in good to excellent yields (Table S4, Sup-
porting Information).
Exploiting further the potential arising from the stability
of complex 2, an advantageous formula was prepared by
mixing 2 with potassium carbonate and the additive dppb
and pressing the mixture into disk-shaped tablets (Fig-
ure 5). These catalyst tablets with a well-defined catalyst
loading enabled the coupling reactions to be performed in
a more user friendly manner, not only in terms of dosage,
but also in terms of the visual indication of the reaction
progress.[36]
Figure 5. Reaction conditions for the Suzuki reaction by using pre-
formed (0.05–3 mol-%) catalyst tablets: “1 ps. Suzuki tablet (1 mol-
%)” was added to a stirred solution of 3a (1 mmol) and 4b
(1.1 equiv.) in MeOH/H2O (10:1), and the mixture was heated at
110 °C for 1 h.
Ultimately, an additional feature of catalyst 2 was uti-
lized for synthetic applications. Owing to its enhanced
hydrophobic nature, catalyst 2 could be adsorptively sup-
ported onto corundum.[10] Although this immobilization is
of a physical type, the catalyst could not be washed off from
the solid support with aqueous methanol rinsing at 110 °C.
This immobilized system was then applied as a catalyst bed
in continuous flow Suzuki reactions (Figure 6.). In the pres-
ence of cesium carbonate, a simple protocol allowed the
generation of biaryls 5d and 5e in good yields without
washing the catalyst from the column.[21] These preliminary
results demonstrate another particularly attractive attribute
of complex 2.
[a] Reaction conditions: A mixture of aryl halide (1 mmol), di-
oxaborolane (1.5 equiv.), 2 (0.33 mol-%), and K2CO3 (2 equiv.) in
MeOH/H2O (10:1) was stirred and heated in a test vial for 1–3 h
at 110 °C. [b] Yield of isolated product. [c] Reaction was performed
in a single-mode microwave reactor (Monowave 300) by using 2
(1 mol-%) and dppb (2 mol-%) as additives at 160 °C.
Figure 6. Flow reactions were performed by using a Syrris flow
chemistry instrument equipped with a back pressure regulator. The
catalyst bed was prepared from Al2O3 (5.7 g, 100–200 mesh, Ald-
rich) and catalyst 2 (64 mg, 1 mol-%), which were mixed and filled
into a thermoglass column. The reactions were conducted on a
1 mmol scale at 110 °C.
plicability and robustness of the catalyst. These examples
indicate the viability of the catalyst in typical industrial ap-
plications.[35]
Further exploration showed that the catalyst was not
compatible with an activated Cl substituent, as in 2-chloro-
pyridine owing to the electron-poor nature of the metal cen-
ter in complex 2. This limitation[35] triggered us to enhance
the reactivity and thermostability of the catalytic system
further. We found that the catalytic activity and stability of
complex 2 could be improved by using it in combination
Conclusions
In summary, we recognized that attractive noncovalent
with other phosphine ligands, but especially with 1,4-bis(di- ligand–ligand interactions in a trifluoromethylated Pd0
phenylphosphanyl)butane (dppb). After optimizing the re- phosphine complex can dramatically enhance the stability
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SHORT COMMUNICATION
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of the complex toward ligand dissociation. This “super-
stable” Pd0 system is a thermally, air, and moisture stable
tricoordinate complex, and it was shown to be an efficient
and robust promoter for Suzuki coupling reactions. Appli-
cation of additive ligands (e.g., dppb), a user-friendly for-
mulation, and simple immobilization techniques underline
the practicality of this catalyst. Our present results may en-
courage further investigations to gain more insight into the
role of stabilizing ligand–ligand interactions[37] in homogen-
eous transition-metal catalysis, which can advance the field
of catalyst developments further. Additional applications of
this Pd catalyst in various cross-coupling reactions and C–
H activations will be reported in due course.
[8]
[9]
[10]
[11]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, characterization data, spectroscopic
data, theoretical calculation details, and crystallographic data.
[12]
CCDC-995867 (for Lt1 of 2) and -995868 (for Lt2 of 2) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
[13]
[14]
[15]
The estimated annual usage is 10 tons.
T. S. is grateful to the Lendület Foundation for financial support.
This work was also supported by Hungarian Scientific Research
Fund (OTKA) (grant number K-81927). The authors thank Dr.
Mihály Braun for MP-AES measurements and Dr. Lajos Nagy for
MALDI-TOF MS measurements. The authors also thank Dr. Pe-
tra Bombicz, Dr. László Filák, and Norbert Koch for helpful dis-
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F
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6
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Superstable Pd0 Complex for Suzuki Coupling Reactions
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Received: September 15, 2014
Published Online: ᭿
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Pages: 8
Z. Dalicsek, I. Pápai, T. Soós et al.
SHORT COMMUNICATION
Superstable Palladium(0) Complex
A. Jakab, Z. Dalicsek,* T. Holczbauer,
A. Hamza, I. Pápai,* Z. Finta, G. Timári,
T. Soós* ............................................ 1–8
Superstable Palladium(0) Complex as an
Air- and Thermostable Catalyst for Suzuki
Coupling Reactions
An unprecedentedly thermo- and air-stable
Pd0 complex from readily available elec-
tron-poor trifluoromethylated phosphine is
reported. The stability of the complex is as-
sociated with unusually strong ligand–
ligand noncovalent interactions. The un-
ique stability of the complex and the pres-
ence of hydrophobic structural elements
are exploited in catalytic Suzuki–Miyaura
coupling reactions.
Keywords: Noncovalent interactions
Cross-coupling Fluorinated ligands
/
/
/
Electron-deficient compounds / Palladium
8
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