Mechanistic Aspects of Aryl-Halide Oxidative Addition, Coordination Chemistry, and Ring-Walking by Palladium

Article abstract of DOI:10.1002/chem.201501580

This contribution describes the reactivity of a zero-valent palladium phosphine complex with substrates that contain both an aryl halide moiety and an unsaturated carbon-carbon bond. Although η²-coordination of the metal center to a C=C or C≡C unit is kinetically favored, aryl halide bond activation is favored thermodynamically. These quantitative transformations proceed under mild reaction conditions in solution or in the solid state. Kinetic measurements indicate that formation of η²-coordination complexes are not nonproductive side-equilibria, but observable (and in several cases even isolated) intermediates en route to aryl halide bond cleavage. At the same time, DFT calculations show that the reaction with palladium may proceed through a dissociation-oxidative addition mechanism rather than through a haptotropic intramolecular process (i.e., ring walking). Furthermore, the transition state involves coordination of a third phosphine to the palladium center, which is lost during the oxidative addition as the C-halide bond is being broken. Interestingly, selective activation of aryl halides has been demonstrated by adding reactive aryl halides to the η²-coordination complexes. The product distribution can be controlled by the concentration of the reactants and/or the presence of excess phosphine.

Full text of DOI:10.1002/chem.201501580

DOI: 10.1002/chem.201501580
Full Paper
&
Coordination Chemistry
Mechanistic Aspects of Aryl–Halide Oxidative Addition,
Coordination Chemistry, and Ring-Walking by Palladium
Olena V. Zenkina,[a, c] Ori Gidron,[a] Linda J. W. Shimon,[b] Mark A. Iron,[b] and
Milko E. van der Boom*[a]
Abstract: This contribution describes the reactivity of a zero-
valent palladium phosphine complex with substrates that
contain both an aryl halide moiety and an unsaturated
carbon–carbon bond. Although h2-coordination of the metal
center to a C=C or CꢀC unit is kinetically favored, aryl halide
bond activation is favored thermodynamically. These quanti-
tative transformations proceed under mild reaction condi-
tions in solution or in the solid state. Kinetic measurements
indicate that formation of h2-coordination complexes are
not nonproductive side-equilibria, but observable (and in
several cases even isolated) intermediates en route to aryl
halide bond cleavage. At the same time, DFT calculations
show that the reaction with palladium may proceed through
a dissociation–oxidative addition mechanism rather than
through a haptotropic intramolecular process (i.e., ring walk-
ing). Furthermore, the transition state involves coordination
of a third phosphine to the palladium center, which is lost
during the oxidative addition as the CÀhalide bond is being
broken. Interestingly, selective activation of aryl halides has
been demonstrated by adding reactive aryl halides to the
h2-coordination complexes. The product distribution can be
controlled by the concentration of the reactants and/or the
presence of excess phosphine.
Introduction
We have demonstrated that the reaction of [Ni(PEt3)4] and
[Pt(PEt3)4] with halogenated substrates results in h2-coordina-
tion to a C=C or N=N moiety followed by an intramolecular
aryl halide bond activation process.[5] Despite the similar reac-
tion pathways for these first- and third-row complexes, the
rate-determining step is different. The nature of the aryl halide
plays an important role in the platinum system, whereas the
ring-walking of the metal center over the p system of the sub-
strate is the slow step with nickel. These observations led to
the selective activation by the nickel system of a strong arylÀ
Br bond in the presence of a much more reactive arylÀI
bond[5b] (bond dissociation energies (BDE) of PhÀBr=(80Æ
2) kcalmolÀ1 and PhÀI=(65Æ2) kcalmolÀ1[6]).
Palladium-based catalysts are of prime importance for the for-
mation of carbon–carbon and other bonds under mild and ho-
mogeneous reaction conditions.[1] Numerous experimental[2]
and theoretical studies[2b,3] have been devoted to the mecha-
nistic and application aspects of such reactions. Metal-mediat-
ed processes often require substrates with several reactive
moieties, such as aryl halides and carbon–carbon multiple
bonds. The relative reactivity of a metal center with diverse
functional groups present in a system is one of the many fac-
tors that can play a role in the product distribution.[4] A funda-
mental understanding of the mechanism of competing pro-
cesses and the processes themselves might lead to the design
of new, useful reactions with high selectivity. Studies related to
the interaction and reactivity of halogenated and unsaturated
substrates with transition metals can provide clues on how to
improve the efficiency of palladium-catalyzed reactions.
There is ample evidence for haptotropic arrangements in
the literature.[7] Intramolecular pathways were observed in the
1960s by Basolo[8] and still generate much interest.[9] Dçtz and
Jahr observed the haptotropic migration of a chromium com-
plex along the extended p system of fused arenes.[10] Weisheit
et al. examined the related (4,4’-dibromotolane)platinum(0) di-
phoshine complex and observed an initial coordination to the
central CꢀC bond followed by CÀBr oxidative addition.[11] Weak
interactions between saturated hydrocarbons and metal com-
plexes have been observed as well.[4e,12] However, the use of in-
tramolecular reaction channels to selectively functionalize
a compound is rare.[13] Yokozawa and Yokoyama demonstrated
that the nickel-catalyzed formation of p-conjugated polymers
involves an intramolecular process coupled with selective aryl
halide bond cleavage.[14] Kiriy and co-workers observed the mi-
gration of a nickel(0) complex along a thiophene p-system in
the Kumada catalyst transfer polycondensation of thiophene-
[a] Prof. O. V. Zenkina, Dr. O. Gidron, Prof. M. E. van der Boom
Department of Organic Chemistry
The Weizmann Institute of Science, 76100 Rehovot (Israel)
E-mail: milko.vanderboom@weizmann.ac.il
[b] Dr. L. J. W. Shimon, Dr. M. A. Iron
Department of Chemical Research Support
The Weizmann Institute of Science, 76100 Rehovot (Israel)
[c] Prof. O. V. Zenkina
Current address: Faculty of Science
University of Ontario Institute of Technology, Oshawa, ON (Canada)
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/chem.201501580.
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based oligomers.[15] Likewise, Nebra et al. observed the shift of
a rhodium fragment between the arms of a bimetallic (1,3-bis-
(thiophosphinoyl)indenyl)palladium complex across the ligand
p system.[16]
tures as observed for structurally related nickel and platinum
complexes.[5b,d] Van Koten reported the formation and physico-
chemical properties of a series of structurally similar nitrogen-
based pincer complexes.[17] In addition, the molecular struc-
One of the questions that remain is whether the reaction of
[Pd(PEt3)4] with halogenated substrates will reflect that of plati-
num or nickel; will the rate-determining step be similar to the
platinum or nickel system and can we control the selectivity of
the reaction? In this study, we observed that h2-coordination
of [Pd(PEt3)2] to a C=C or a CꢀC moiety is kinetically favored
and followed by a rate-determining aryl halide bond activation.
This process proceeds quantitatively in solution and in the
solid state (CÀC bond formation by Pt0 in the solid state has
been previously observed[13]). Herein, we present a combined
experimental and computational study that involves variable-
temperature NMR spectroscopy,
tures of complexes 3Br and 3ꢀBr were unambiguously verified by
¼
single-crystal X-ray structure determination (Figure 1). Regard-
less of the nature of the aryl halide (Br, I) and unsaturated
moiety (C=C, CꢀC), selective h2-coordination of the metal
center to compounds 1, with release of two equivalents of
PEt3, is the kinetically preferred process. This process is fol-
lowed by a slower transformation to afford the thermodynami-
cally favored products of aryl halide bond activation (3).
The X-ray analysis of complex 2Bꢀr reveals a metal–ligand ar-
rangement that reflects some features of a metallocyclopro-
pene system (Figure 1, top left).[1c,18] The coordination of the
competition/cross-over experi-
ments, and density functional
theory (DFT) calculations.
Results and Discussion
The reaction of compounds
1 with an equimolar amount of
Scheme 1. Selective formation of palladium complexes 2 by h2-coordination of compounds 1 followed by metal
insertion into the aryl halide bond (3).
[Pd(PEt3)4] in an organic solvent
(e.g., toluene, THF, acetone) re-
sults in the quantitative forma-
tion of complexes 2 (Scheme 1).
The formation of these com-
plexes was carried out at tem-
peratures below À308C lest the
reaction continue to oxidative
addition products 3. h2-Coordi-
nation of the metal center to the
C=C or CꢀC moieties of com-
pounds 1 is evident from the
1H,13C{1H}, and 31P{1H} NMR spec-
troscopy data and the X-ray
structure
of
complex
2Bꢀr
(Figure 1, left; the superscript
identifies the halide and the sub-
script gives the bond order of
the carbon–carbon bridge). Pro-
longed reaction times at elevat-
ed temperatures result in the
quantitative formation of com-
plexes 3 by insertion of the
metal center into the aryl halide
bond (Scheme 1). These com-
plexes were isolated and charac-
terized by using a combination
of NMR spectroscopy, elemental
Figure 1. ORTEP diagrams of complexes 2Bꢀr (top left), 3Bꢀr (top right) and 3Br (bottom) with thermal ellipsoids set at
¼
the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond length [Š] and angles [o] for 2ꢀBr
(there are two molecules of 2Bꢀr per asymmetric unit): Pd1ÀC7 2.060(2), Pd1ÀC8 2.064(2), Pd1ÀP1 2.3170(5), Pd1À
analysis, and high-resolution P2 2.3170(5), C8ÀC7 1.282(3), C8ÀC9 1.448(3), C1ÀC7 1.453(3), C4ÀBr1 1.910(2); C7-Pd1-P2 146.36(6), C7-Pd1-C8
mass spectroscopy. The palladi-
36.23(8), C7-Pd1-P1 109.27(6), C8-Pd1-P2 110.13(6), P2-Pd1-P1 104.37(2); for 3Bꢀr (there are two molecules of 3ꢀBr per
asymmetric unit): Pd1ÀBr1 2.513(1), Pd1ÀP2 2.321(1), Pd1ÀP1 2.325(1), Pd1ÀC1 2.011(4), C6ÀC7 1.436(5), C7ÀC8
um complexes obtained herein
1.200(5), C8ÀC9 1.426(5); C1-Pd1-Br1 178.3(1), P2-Pd1-P1 171.20(4), C1-Pd1-P1 90.4(1); for 3Br: Pd1ÀBr1 2.515(1),
¼
(see the Experimental Section)
Pd1ÀP2 2.322(2), Pd1ÀP3 2.316(3), Pd1ÀC1 1.997(9), C4ÀC7 1.46(1), C7ÀC8 1.33(1), C8ÀC9 1.44(1); C1-Pd1-Br1
have similar spectroscopic fea- 175.4(2), P2-Pd1-P3 170.1(1), C1-Pd1-P3 89.2(2).
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palladium moiety induces significant lengthening of the CꢀC
bond (C7ÀC8=1.282 Š). This value falls between a triple and
a double carbon–carbon bond. For example, the C=C bond
length in trans-1,2-bis(4-pyridyl)ethylene is 1.333 Š,[19] whereas
the CꢀC bond length of complex 3Bꢀr is 1.201 Š (vide infra).
Complex 2Bꢀr exhibits a nearly planar geometry around the
metal center (mean deviation from the Pd1-P1-P2-C7-C8) plane
of 0.0011 Š) and angles of 104.36 and 36.238 for P1-Pd1-P2
and C7-Pd1-C8, respectively. The aromatic rings of the ligand
are bent away from the Pd by approximately 358: C1-C7-C8=
142.848 and C9-C8-C7=148.38. One can pass a plane through
the PdP2C4 core, and there are angles of 37.4 and 55.28 be-
tween this plane and planes through the C6Br and Py rings, re-
spectively. The main impetus behind this geometry is probably
the dominant p backbonding. The structure of the oxidative
3Br in the presence of excess of tetrabutylammonium iodide re-
¼
sulted in the formation of complex 3Br (94%) as the major
¼
product. Only 6% halide exchange (3I ) was observed by using
¼
1H and 31P{1H} NMR spectroscopy, which could also have taken
place after the formation of complex 3Br. Some halide ex-
¼
change (4%) was observed upon treatment of complex 3Br
¼
with tetrabutylammonium iodide under the same reaction con-
ditions. This observation essentially rules out the formation of
transient, cationic complexes. Formation of ionic bromide
would have resulted in significant halide scrambling.[23]
Table 1. Reaction rates of the formation of complexes 3 from complexes
2.
Entry
Reaction
T
[K]
[2]
PEt3
Solvent
k
addition products 3Br and 3ꢀBr show typical square-planar geo-
[a]
[mm] [equiv]
[”10À5 sÀ1
]
¼
metries around the d8 metal centers, which are directly
s bonded to the arene (Figure 1, top right).[5b,17] Formation of
the arene–metal bond does not significantly affect the bond
lengths of the ligand, in which the carbon–carbon bonds are
in the appropriate range for a conjugated aromatic system.
Is the formation of the h2-coordination complexes 2 a non-
productive side-equilibrium or a step on the reaction coordi-
nate? The formation of complexes 3 from the kinetic products
(2) could involve either inter- or intramolecular pathways. It is
plausible that the h2-coordination complexes (2) are in equilib-
rium with the free ligands (1) and [Pd(PEt3)2]. In time, such
highly reactive 14-electron species would cleave the aryl halide
bond and result in the formation of observed complexes 3. Al-
ternatively, the metal center could shift over the p-conjugated
system of the ligand towards the aryl halide bond (i.e., ring-
walking).[5b,15a,20] In a third scenario, the kinetic products might
rearrange by a cascade of reactions that involve the formation
of transient bimetallic complexes.[21]
1
2
3
4
5
6
7
8
2Br!3Br
297 74
297 74
297 19
291 19
291 19
303 43
303 43
303 21
303 43
226 19
226 19
226 19
226 74
235 19
235 19
235 85
235 19
2
2
2
2
10
0
0
0
10
2
2
10
2
2
2
[D8]toluene
[D6]acetone 5.4
6.1
¼
¼
2Br!3Br
¼
¼
2Br!3Br
[D8]toluene
[D8]toluene
[D8]toluene
[D8]toluene
THF
[D8]toluene
[D8]toluene
[D8]toluene
5.8
3.3
2.7
7.6
6.3
7.2
7.3
6.1
¼
¼
2Br!3Br
¼
¼
2Br!3Br
¼
¼
2Bꢀr!3Bꢀr
2Bꢀr!3Bꢀr
2Bꢀr!3Bꢀr
2Bꢀr!3Bꢀr
2I !3I
9
10
11
12
13
14
15
16
17
¼
¼
2I !3I
[D6]acetone 7.0
¼
¼
2I !3I
[D8]toluene
[D8]toluene
[D8]toluene
[D6]acetone 3.9
[D8]toluene
[D8]toluene
6.5
6.2
4.9
¼
¼
2I !3I
¼
¼
2Iꢀ!3Iꢀ
2Iꢀ!3Iꢀ
2Iꢀ!3Iꢀ
2Iꢀ!3Iꢀ
2
10
5.0
5.1
[a] These values were derived by using 31P{1H} NMR spectroscopy by
using first-order linear fits with R2 >0.99.
Several observations point towards a concerted oxidative
addition process as the rate-determining step for the bromo
derivatives (i.e., reactions 2Br!3Br and 2ꢀBr!3Bꢀr). We monitored
All four processes (2!3) are concentration independent
(Table 2, entries 1, 3 and 6, 8) and obey first-order kinetics in
h2-coordination complexes 2. The activation parameters de-
rived from Eyring plots (Figure 2) are listed in Table 2. The dif-
ferences between the bromo (2Br!3Br, 2ꢀBr!3ꢀBr) and iodo de-
¼
¼
the formation of thermodynamically favored complexes 3 by
using 31P{1H} NMR spectroscopy at various temperatures. The
transformations of the iodo derivatives (2I !3I and 2ꢀI !3ꢀI )
¼
¼
rivatives (2I !3I , 2ꢀI !3Iꢀ) reflects, as noted above, the large
¼
¼
¼
¼
proceed under conditions (TꢁÀ488C) at which the bromo de-
role of the halide in the overall process. The nearly identical ac-
rivatives (2Br, 2Bꢀr) are stable. The reactivity differences are sig-
tivation parameters of the C=C (2Br!3Br, 2I !3I ) and CꢀC
¼
¼
¼
¼
¼
nificant (DTꢂ608C) and indicate that the rate-determining
(2Bꢀr!3ꢀBr, 2ꢀI !3ꢀI ) systems with the same halide indicate a simi-
lar reaction profile and that the character of these carbon–
carbon bonds does not play a significant role in controlling
the overall reactivity. The near-zero entropy values further indi-
cate that metal–ligand dissociation is not part of the rate-de-
termining step. An intramolecular process or a dissociation
step followed by a rate-determining oxidative addition could
explain our observations. However, the negligible effect of the
solvent polarity or the presence of PEt3 rules against the for-
mation of unsaturated palladium intermediates formed by
a dissociation process. A process involving the formation of bi-
metallic complexes would most probably also be affected by
both solvent polarity and by the presence of phosphine, and
would likely not follow first-order kinetics in the metal com-
plex. In addition, the quantitative thermolysis of complex 2ꢀBr
step for the transformations 2Br!3Br and 2ꢀBr!3ꢀBr are related
¼
¼
to the cleavage of the aryl halide bond (c.f. BDEs of PhÀBr=
(80Æ2) kcalmolÀ1 and PhÀI=(65Æ2) kcalmolÀ1).[6] The h2-coor-
dination of the metal center is not likely to be drastically af-
fected by the electronic difference between the two halides
(c.f. Hammett constant sp: I=0.18, Br=0.23).[22] The solvent
polarity does not affect the reaction kinetics (Table 1, entries 1,
2: ktoluene/kacetone for 2Br!3Br ꢂ1.1 and entries 6, 7: ktoluene/kTHF for
¼
¼
2Bꢀr!3Bꢀr ꢂ1.2). These reactions are also barely affected by the
presence of 0 to 10 equivalents of PEt3 (Table 1, entries 4, 5: k2/
k10 for 2Br!3Br ꢂ1.2 and entries 6, 9: k0/k10 for 2ꢀBr!3Bꢀr ꢂ1.0).
¼
¼
Therefore, it is plausible that a nonpolar, concerted transition
state with two PEt3 ligands bound to the metal center is in-
volved in the slow step. Indeed, performing the reaction 2Br!
¼
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Table 2. Activation parameters (in [D8]toluene) derived from the Eyring
plots in Figure 2.
X=Br
X=I
CH=CH
CꢀC
CH=CH
CꢀC
[c]
[d]
2Br!3Br[a]
2Bꢀr!3Bꢀr[b]
2I !3I
2Iꢀ!3Iꢀ
¼
¼
¼
¼
DH° [kcalmolÀ1
DS° [e.u.]
]
23.5Æ1.9
1.3Æ6.6
23.1Æ1.9
22.7Æ2.0
À2.3Æ6.8
23.4Æ2.0
15.9Æ1.05
À6.9Æ4.6
16.2Æ1.05
19.2Æ0.9
4.3Æ3.7
17.9Æ0.9
Scheme 2. Exclusive formation of complexes 3 (from 2) in the presence of
compound 4 (X=Br or I). All experiments were performed in the presence
of 12 equivalents of PEt3.
DG°
[kcalmolÀ1
]
298K
[a] T=284–301 K. [b] T=293–313 K. [c] T=213–239 K. [d] T=225–250 K.
Table 3. Crossover experiments for complexes 2 in the presence of p-
CF3PhX (X=Br (4Br) or X=I (4I)) and varying concentrations of added PEt3
(in [D8]toluene at RT for ꢂ10 h, see the Experimental section).
Entry
Reaction
[2]
[CF3PhX]
PEt3
Ratio
[mm]
[mm]
[equiv]
3:5 [%]
1
2
3
4
5
6
7
8
2Br!3Br
8.5
8.5
8.3
8.3
7.9
7.9
8.0
8.0
5.7
5.7
4.3
4.3
4.3
4.3
4.3
4.3
0
12
0
12
2
12
2
12
84:16
100:0
70:30
100:0
73:27
100:0
66:34
97:3
¼
¼
2Br!3Br
¼
¼
2Bꢀr!3Bꢀr
2Bꢀr!3Bꢀr
2I !3I
¼
¼
2I !3I
¼
¼
2Iꢀ!3Iꢀ
2Iꢀ!3Iꢀ
2
Figure 2. Eyring plots of the conversion of 2Br!3Br (red line, , R =0.980;
*
observed during the formation of complex 3Br from 2Br in the
presence of PhBr.
¼
¼
19 mm) and 2Bꢀr!3Bꢀr (black line, È, R2 =0.970; 42.8 mm); 2I !3I (red line,
,
¼
¼
&
¼
¼
R2 =0.987; 19 mm) and 2Iꢀ!3Iꢀ (black line, , R2 =0.989; 19 mm). 31P{1H} NMR
spectroscopy in [D8]toluene was used for all experiments (Figure S1 in the
Supporting Information).
The cross-over of [Pd(PEt3)2] with the more reactive 4Br and
4I might involve PEt3 dissociation from the h2-coordination
complexes (2) followed by reaction of compounds 4Br or 4I
with transient unsaturated species. Formation of complexes 3
is observed in high yield (>97%) by blocking such a potential
intermolecular pathway with the excess of PEt3, whereas an in-
tramolecular route would not be affected (Table 3, entries 2, 4,
6, 8).
as a powder at 408C to give complex 3Bꢀr also supports an in-
tramolecular pathway. This relatively slow solid-state process
takes 24 d to reach completion.
To unambiguously verify the presence of an intramolecular
reaction channel, we used NMR spectroscopy to follow the
conversion of the h2-coordination complexes (2) into com-
plexes 3 in the presence of p-CF3PhBr (4Br) or p-CF3PhI (4I; see
Scheme 2). The strongly electron-withdrawing CF3 unit makes
these substrates highly susceptible to activation by palladium.
Plotting the CBr 13C{1H} NMR shifts versus the Hammett con-
stant predicts that the arylÀBr and arylÀI bonds of compounds
4Br and 4I would be much more reactive than those of com-
pounds 1 with the same halide (Figure S2 in the Supporting In-
formation). Transfer of the metal center to compounds 4Br and
4I to afford complexes 5Br and 5I, respectively, was observed
(15–35%) in parallel to the formation of complexes 3 (Table 3,
entries 1, 3, 5, 7). Importantly, these competitive reactions are
almost completely suppressed by the presence of 12 equiva-
lents of PEt3 (Table 3, entries 2, 4, 6, 8). Thus, this is a unique
example in which the selectivity of aryl bond activation can be
controlled simply by the addition of excess PEt3. This clearly
demonstrates that the two competing aryl halide bond activa-
tion processes proceed by different routes. Selective cleavage
of a strong bond by a late-transition metal in the presence of
a weaker one is rare.[4h,5b,24] In addition, no metal transfer was
This hypothesis is further supported by the reactivity of
complex 6, which does not contain an aryl halide moiety
(Scheme 3). This complex was prepared in situ by the addition
of compound 7 to [Pd(PEt3)4]. The subsequent reaction with
CF3PhBr (4Br) in the presence of PEt3 resulted in quantitative
formation of complex 5Br and compound 7. Following the for-
mation of 5Br (Figure 3), second-order kinetics are observed for
this reaction (6+4Br!5Br +7), which is significantly slowed (by
ꢂ3) by the presence of excess PEt3. These observations imply
that the 2!3 transformations involve a different pathway, in
which we hypothesize that the [Pd(PEt3)2] moiety ring-walks
from the C=C or CꢀC moiety through a haptotropic rearrange-
ment followed by metal insertion into the aryl halide bond.
This latter step is rate determining and proceeds via a nonpolar
concerted transition state for the aryl-bromide systems (2Br!
¼
3Br, 2Bꢀr!3Bꢀr). Wu et al. observed their nickel(0) catalysts jump-
¼
ing between adjacent, but nonconjugated, thiophene rings
during Grignard metathesis chain-growth polymerization of
poly(bithienylmethylene)s.[25] It is conceivable that something
similar is happening here and is suppressed by the added
phosphine.
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ring-walk from the C=C/CꢀC bond along the ligand p system
to arrive at the CÀX bond to be activated, or it can dissociate
from the C=C/CꢀC bond, either as-is (i.e., as [Pd(PEt3)2]) or with
the assistance of one to two free phosphine ligands. In the
second option, the free metal center would “float” around in
solution until it encounters a CÀX bond to react with. Key en-
ergies along each pathway are given in Table 4 and the various
structures are depicted in Scheme 4. For all four systems,
TS(9–3) is significantly lower in energy than TS(2–3) within the
temperature range of 225 to 403 K. See Supporting Informa-
tion (Table S2) for free energies at different temperatures. Note
that although TS(9–3) increases with temperature, TS(2–3) de-
creases, albeit only very slightly (c.f. ꢂÀ0.3 kcalmolÀ1 for
TS(2–3) versus ꢂ4 kcalmolÀ1 for TS(9–3) over this temperature
range). Part of this is because of the much weaker coordina-
Scheme 3. Cross-over reaction of complex 6 with 4Br.
Table 4. Key energies (DG298,sol [kcalmolÀ1], CP-CCSD(T)/cc-pVDZ-PP+
DEM06/TZVP//DF-M06-LD3/def2-SVP) along the possible pathways for oxida-
tive addition from complexes 2. Energies are relative to 2 and are not
corrected for concentration (see Table S1 in the Supporting Information).
2Br
2I
2Bꢀr
21.7 (23.6)[a]
30.9
34.9
10.2
27.7
17.7
18.2
2ꢀI
16.5 (17.6)[a]
22.5
35.5
6.2
27.4
15.8
19.0
20.6
À1.1
À3.4
À23.2
¼
¼
Figure 3. Phosphine effect on the palladium transfer reaction: 6+4Br
!
5Br +7 with 1/[5Br] as a function of time. The 31P{1H} NMR spectroscopy
TS(9–3)
TS(2–3)
TS(2–1)
9
22.8
31.7
22.2
17.5
24.1
23.2
follow-up measurements were performed in [D8]toluene at 273 K in pres-
ence of two equivalents of PEt3 (blue line, k=1.4”10À4 mÀ1 À1, R2 =0.994)
s
1.3[b]
À4.3[b]
and in the presence of 12 equivalents of PEt3 (red line, k=3.9”10À5 mÀ1 sÀ1
R2 =0.988).
,
TS(2–8)
10.2
9.1
20.3
26.6
0.1
À1.2
À21.3
10.4
19.9
20.9
32.4
8
2!1+112
2!10+PEt3
2+PEt3!1+113
2+2PEt3!1+114
3
21.0
To get a better understanding of the reaction mechanism,
0.7
À1.9
À3.2
À21.7
the reaction was studied computationally at the CP-CCSD(T)/
À0.5
À22.6
SMD
M06=TZVP
cc-pVDZ-PP+DE
//DF-M06-LD3/def2-SVP level of theory
(see the Computational Methods section for full details), in
which frequencies were scaled by 0.9958 as recommended by
Kesharwani et al.[26] Following convention, free energies are
typically given at “standard
[a] Including the exergonic dissociation of PdP3. [b] Third phosphine not
coordinated (see text).
state” (i.e., 1 atm at 298.15 K);
the corrections for concentration
(DGcorr, see the Computational
Details section for details) are
given in Table S1 for typical con-
centrations used experimentally
(i.e., 19 and 74 mm at 298.15 K).
Table 4 lists key energies at
298.15 K during the reaction,
whereas other experimentally
used temperatures are consid-
ered in Table S2 in the Support-
ing Information. For complexes
2Br and 2Bꢀr, the optimized com-
¼
plexes and transition states
along the reaction pathway are
shown in Figures 4 and 5, re-
spectively; the iodo analogues
are very similar in appearance.
As noted above, there are two
Figure 4. DFT-optimized structures for the reaction of bromostilbazole 2Br; for clarity, the Br superscript and = sub-
conceivable reaction mecha-
¼
nisms. The metal center can script are not shown. The iodostilbazole analogues are very similar.
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than coordination to a C=C or
CꢀC bond (in this order). Like-
wise, the BO is lower for Pd than
for Pt or Ni; conversely, the BO
of the C=C/CꢀC bond is higher
for Pd than for the other two
metals, and in the case of ben-
zene approaches the BO of free
benzene. In fact, the BOs barely
(if at all) reflect the formation of
a PdÀC bonds in the (h2-are-
ne)Pd complexes. In addition,
the MÀC bonds are stronger in
the acetylene complexes than in
the ethylene complexes and are
weakest in the benzene com-
plexes. In the benzene–Pd com-
plex the bonds are very weak,
and this is reflected in the fact
that the energies of 8, in which
the metal is bound to the
phenyl ring (with the exception
of 8Br), are close to the bridge-
Figure 5. DFT-optimized structures for the reaction of bromotolan 2Bꢀr; for clarity, the Br superscript and ꢀ sub-
script are not shown.
tion of Pd to an arene p system than Ni or Pt (see below for
discussion). Previous studies on the related platinum and
nickel complexes[5b,d] show a preference for ring-walking over
dissociation of the metal fragment. The weaker coordination to
the aromatic p system means that the metal center is more
likely to dissociate and coordinate a third phosphine, and in all
four systems this is a favorable process on par with returning
to the central C=C or CꢀC bond (c.f. 8 and 2+PEt3!1+113 in
Table 4). As indicated for TS(9–3) in Table 4, the activation bar-
rier is not necessarily from the bridge complexes (2) but in cer-
tain cases from 1+113. In cases for which the latter is exergon-
ic, one needs to subtract this energy from the transition state
(i.e., reaction barrier) height.
dissociation energies. From the estimates of the importance of
all donor!acceptor interactions in the natural bond order
(NBO) basis (Table S4 in the Supporting Information), the im-
portance of the L!M and M!L interactions are an order of
magnitude smaller for the benzene complexes than for ethyl-
ene or acetylene. Moreover, note that the L!M interactions in-
volve the metal s orbital; this orbital is much higher in energy
(Table S5 in the Supporting Information) for Pd than for Ni or
Pt. As noted above, metal coordination to acetylene is stronger
than to ethylene. This is reflected in the results for the stilba-
zole (1X ) and tolan (1Xꢀ) systems. Although there is little differ-
¼
ence in the dissociation energies of either 113 or 114 from the
bridge complexes (2), the transition states for 113 dissociation
(TS(2–1)) and transfer to the ring (TS(2–8)) are significantly
higher in the tolan systems. This reflects the need to break the
stronger Pd–acetylene bond. This mirrors previous experimen-
tal observations[27] and the strength of the platinum–ligand
bond must in part be ascribed to relativistic effects.[28]
Coordination of the palladium center to the ligands (1)
seems to be significantly weaker than coordination of nickel or
platinum,[5b,d] and this is would appear to have a dramatic in-
fluence on the reaction chemistry. The coordination of a metal
center to a p bond was examined for the model [M(PH3)2] (M=
Ni, Pd, Pt) systems with ethylene, acetylene, and benzene.
From the bond orders (BOs; Table S3 in the Supporting Infor-
mation), it is clear that coordination of a metal center to an
arene (i.e., formation of an h2-C6H6 complex) is less favorable
Should the coordination complexes 2, 9, and 10 be de-
scribed as dative complexes (i.e., with a k !Pd bond) or as
metallacycles? These are the two extremes of the Dewar–
Chatt–Duncanson model of alkene and acetylene complexes,[29]
whereas most complexes lies somewhere in the middle. If one
considers the bond lengths of these complexes (Tables S8–S11
in the Supporting Information) or the bond indices of the
model complexes (Table S3 in the Supporting Information),
one notes that, for palladium, the coordinated C=C/CꢀC bonds
are intermediate between these two extremes. From the bond
orders of the model complexes, nickel and platinum lie much
further towards the metallacycle description. In the benzene
coordination complexes (8 and the model complexes), there is
much less loss of C=C bonding character and these complexes
probably are best described as dative complexes rather than
as metallacycles.
Scheme 4. Structures in the DFT study in which the wavy bond indicates var-
iation in the bridging bond (i.e., CꢀC or CH=CH) and X=Br or I.
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Dissociation of PdP2 from 2 is not favorable and in all four
cases involves reaction energies of DG298 ꢂ18 to 21 kcalmolÀ1
(Table 4). For the stilbazole systems, there is a barrier slightly
higher in energy than the products, but the more strongly
bound tolan ligands have a considerably higher dissociation
barrier. This reflects the stronger coordination of acetylene to
a metal center than ethylene (see above). However, this disso-
ciation process can perhaps be assisted by coordination of an
additional, third phosphine ligand prior to dissociation. For the
tolan systems, tris-phosphine complexes (9) were found, al-
though their formation is endergonic (Table 4), whereas in the
stilbazole systems the third phosphine will not remain coordi-
nated to the metal center. In the model Pd–acetylene and Pd–
ethylene complexes, the M!L interactions are very similar, yet
in the former there are significantly stronger L!M interactions
(Table S4 in the Supporting Information). One would thus
expect that the increased electron density on the metal center
would make coordination of the third phosphine less favor-
able. On the other hand, the acetylene can accept more elec-
tron density than ethylene, which thereby facilitates coordina-
tion of the third phosphine. However, if one considers the orbi-
tal energies of the model Pd complexes (Table S5 in the Sup-
porting Information), one notes that the orbitals in the acety-
lene complex are systematically lower in energy and thus
closer to the energy of the lone pair on the phosphine (for
PH3, EHOMO =À6.859 eV, primarily composed of the lone pair on
P); this would result in a better electronic interaction and,
therefore, 9Xꢀ complexes can be found even though phosphine
coordination is unfavorable. Nonetheless, the dissociation of
113 is practically isoergonic relative to 2. For the stilbazole
complexes, this reaction is slightly endergonic, consistent with
the observation that 2 are isolated experimentally. For the
tolan systems, the energies are slightly exergonic or endergon-
bazole or tolan ligand due to weak p interactions with the aro-
matic p system or because of the solvation cage. When p-
CF3PhBr (4Br) or p-CF3PhI (4I) is added to the reaction mixture
(i.e., the crossover experiments), some crossover is observed
(16–34%; see Table 3). This is consistent with the dissociative
mechanism found, but does not explain why crossover is sup-
pressed when a large excess of phosphine is added.
In a previous study on the Sonogashira reaction, it was
found that perfluoroaryl halides may react in an SNAr fashion
with phosphines to give PV products akin to oxidative addi-
tion.[30] This was also observed experimentally by Dardonville
and Brun when they reacted (p-BrPh)2CO with (n-C5H11)3P in
toluene at reflux.[31] With the more activating CF3 group (sp =
0.54 for CF3 and 0.43 for COPh[22]), one might expect the reac-
tion of 4 with the smaller phosphine to be faster at lower tem-
peratures. When large quantities of phosphine were added to
the reaction mixture, the crossover of the stilbazole/tolan com-
plexes was suppressed, and one possible explanation could be
that the reaction of 4 with the free phosphine would sequester
it and prevent its reaction with the Pd complex. The reaction
of PhX and p-CF3PhX (X=Br, I) with PEt3 was examined
(Table S6 in the Supporting Information). Oxidative addition-
like transition states were found for each aryl halide. Although
these transition states are too high for the reaction to be feasi-
ble at room temperature, the reactions in each case are exer-
gonic, so if such a reaction were to occur, through a different,
yet-to-be-determined mechanism, then the aryl halide would
be sequestered from the reaction and could not react with the
palladium complex. In cases in which a large excess of phos-
phine is added, the sequestering of the aryl halide would be
faster and, therefore, in this case crossover would not be ob-
served. Nevertheless, when p-CF3PhX and PEt3 are mixed under
the reaction conditions, no reaction is observed.
ic depending on the solvation approximation used (SMD or
SMD
M06=TZVP
DE
, see the Computational Methods section for details),
Summary and Conclusions
which clearly highlights the small error one must remember
exists even with the best computational methods. In addition,
if one considers the correction for concentration (Table S1 in
the Supporting Information), then these reactions are slightly
endergonic; this is appropriate because the bridge complexes
(2) are observed experimentally and, in one case (2Bꢀr), isolated
at low temperatures.
The reactivity towards stilbazole-based ligands of the final
member of the Group 10 [M(PEt3)4] family has been explored.
Previous studies on platinum and nickel systems have been re-
ported.[5b,d] In all three cases, the metal center first coordinates
to an unsaturated moiety (C=C, N=N, or CꢀC) prior to the acti-
vation of an arylÀBr or arylÀI bond.[5a,b,d] In contrast to platinum
and nickel, the coordination of palladium to the ligand p
system is weak and this has a significant impact on the com-
plex reactivity. Theoretical studies on the reactivity indicate
a phosphine-assisted dissociation–reassociation mechanism via
a transition state with three phosphine ligands on the metal
center. This transition state is special in that three phosphines
are coordinated to the metal center, whereas other related sys-
tems typically only involve two. However, the experimental
data points towards a ring-walking—or at least a nondissocia-
tive—process; the rate of the reaction is independent of the
concentration of the complex or phosphine in the system. The
reason for this apparent discrepancy is not obvious, but it
highlights the complexity of modeling the processes involved
in aryl halide bond activation. Despite the generally similar be-
havior of the three metals, varying reactivity is observed in this
For cases in which complexes 2 are thermalized in the ab-
sence of phosphine, even though a phosphine-assisted disso-
ciative mechanism is favored, a reaction may still be possible.
For the iodo complexes, TS(2–3) may still be energetically
achievable (Table 4). It is also possible that complexes 2 could
lose a phosphine ligand, which would then assist another mol-
ecule of 2 to react. The energies for this process (Table 4) show
that this is possible for the tolan complexes, but not for the
stilbazole complexes. This is consistent with the stronger L!M
donation in the tolan complexes, which would help stabilize
the complex when the phosphine dissociates.
Even though the experiments indicate that a dissociative
mechanism is less likely (no effect of the concentration of the
phosphine or complex on the reaction rate), it is still possible
that the free 113 moiety does not wander too far from its stil-
Chem. Eur. J. 2015, 21, 16113 – 16125
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2
08C): AB system: dA =13.5 ppm (1P, J(P,P)=16.1 Hz), dB =12.0 ppm
system, which is closely related to the strength and nature of
the metal–ligand interaction, particularly with the ligand p
system, and it is the middle member of this family that be-
haves differently from its two brothers.
2
(1P, J(P,P)=16.0 Hz); HRMS (FD-TOF): m/z calcd for C25H40BrNP2Pd:
603.0851; found: 603.0842.
Formation of 2I
¼
[Pd(PEt3)4] (8.0 mg, 0.014 mmol) was dissolved in [D8]toluene
(0.3 mL), loaded in a 5 mm screw-cap NMR tube equipped with
a septum, and cooled to À808C. Subsequently, a solution of (E)-4-
Experimental Section
General procedures
(4-iodostyryl)pyridine (1I ; 4.0 mg, 0.013 mmol) in [D8]toluene
¼
All reactions were carried out in an N2-filled M. Braun glovebox
with H2O and O2 levels <2 ppm. Solvents were reagent grade or
better and dried, distilled, and degassed before being introduced
into the glovebox, in which they were stored over activated 4 Š
(0.4 mL) was added dropwise. The tube was immediately shaken
and transferred into
a
precooled (À808C) NMR machine.
31P{1H} NMR spectroscopy indicated the quantitative formation of
complex 2I after ꢂ5 min. Performing this reaction at À478C also
¼
molecular sieves. Ligands 1, 7, complex 3Br, and [Pd(PEt3)4] (114)
resulted in the formation of complex 2I , which selectively convert-
¼
¼
were prepared according to published procedures.[32]
ed to complex 3I (see below). Therefore, complex 2I was charac-
¼
¼
terized by using NMR spectroscopy in the presence of PEt3
(2 equiv). 1H NMR ([D6]acetone, À808C): d=8.57 (brs, 1H; PyrH),
8.11 (brs, 2H; PyrH), 7.82 (d, J=7.8 Hz, 1H; PyrH), 7.59–7.43 (brm,
2H; ArH), 7.00 (brs, 2H; ArH), 4.45 (m, 1H; CH=CH), 4.34 (m, 1H;
CH=CH), 1.52–1.42 (m, 12H; PCH2CH3), 0.87 ppm (m, 18H;
PCH2CH3); 31P{1H} NMR ([D8]toluene): AB system: dA =13.43 ppm
(1P, 2J(P,P)=17.2 Hz), dB =12.10 ppm (1P, 2J(P,P)=17.2 Hz).
Analysis
Mass spectrometry was carried out by using a Micromass Platform
ZQ 4000 instrument, a Waters Micromass GCT Premier mass spec-
trometer, or a Q-TOF Waters-Micromass high-resolution mass spec-
trometer. Elemental analyses were performed by H. Kolbe, Mikro-
analytisches Laboratorium, Germany. The 1H, 13C{1H}, 19F{1H}, and
31P{1H} NMR spectra were recorded at 400.19, 100.6, 376.48, and
161.9 MHz, respectively, by using a Bruker AMX400NMR spectrom-
eter or at 500.132, 125.77, 470.5, and 202.46 MHz, respectively, by
using a Bruker Avance 500NMR spectrometer. All chemical shifts
Formation of 2Bꢀr
A solution of [Pd(PEt3)4] (121 mg, 0.21 mmol) in THF (4 mL) was
1
slowly added to
a
stirred solution of 4-((4-bromophe-
(d) are reported in ppm and coupling constants (J) in Hz. The H
nyl)ethynyl)pyridine (1Bꢀr; 54 mg, 0.21 mmol) in THF (3 mL). All vola-
tiles were removed under vacuum after 15 min. Washing the resi-
due with pentane (1”3 mL) afforded complex 2Bꢀr (80% yield). Sub-
sequently, the yellow solid was dissolved in Et2O (1 mL), followed
by the addition of pentane (3 mL), and allowed to crystallize at
and 13C{1H} NMR chemical shifts are reported relative to tetrame-
thylsilane. 31P{1H} NMR chemical shifts are given relative to 85%
H3PO4 in D2O at d=0.0 (external reference), with shifts downfield
of the reference considered positive. 19F{1H} NMR spectra were ref-
erenced to an external standard of C6F6 at d=À162.9 ppm. All
measurements were carried out at 298 K unless stated otherwise.
Assignments in the 1H and 13C{1H} NMR spectra were made by
1
3
À308C under N2. H NMR ([D6]acetone): d=8.39 (d, J(H,H)=6.1 Hz,
2H; PyrH), 7.45 (d, 3J(H,H)=8.4 Hz, 2H; ArH), 7.22 (d, 3J(H,H)=
8.1 Hz, 2H; ArH), 7.13 (d, J(H,H)=7.0 Hz, 2H; ArH), 1.56–1.68 (m,
12H; PCH2CH3), 0.97–1.07 ppm (m, 18H; PCH2CH3); 13C{1H} NMR
([D6]acetone): d=149.3 (s), 147.0 (dd, Cq, J(P,C)=14.3 Hz, J(P,C)=
8.6 Hz), 136.5 (dd, Cq, 3J(P,C)=14.0 Hz, 3J(P,C)=8.8 Hz), 131.1 (s),
3
1
using H{31P} and 13C-DEPT-135 NMR spectroscopy.
3
3
Formation of 2Br
¼
2
2
129.5 (s), 124.4 (dd, Cq, J(P,C)=66.7 Hz, J(P,C)=4.1 Hz; CꢀC), 121.3
(s), 121.0 (dd, Cq, 2J(P,C)=4.1 Hz; CꢀC), 118.1 (s, Cq), 19.3 (dd,
1J(P,C)=29.8 Hz, 3J(P,C)=15.7 Hz; PCH2CH3) 8.5 ppm (d, 2J(P,C)=
9.1 Hz; PCH2CH3); 31P{1H} NMR ([D8]toluene): d=16.75 (d, 1P,
[Pd(PEt3)4] (30 mg, 0.052 mmol) was dissolved in [D8]toluene
(0.3 mL) and loaded into a 5 mm screw-cap NMR tube. Subse-
quently, a solution of (E)-4-(4-bromostyryl)pyridine (1Br; 14 mg,
¼
0.054 mmol) in [D8]toluene (0.4 mL) was added at À808C. The tube
was immediately sealed, shaken, and transferred into the pre-
cooled NMR machine at À808C. Quantitative formation of complex
2J(P,P)=5.1 Hz), 15.29 ppm (d, 1P, J(P,P)=5.0 Hz); HRMS (FD-TOF):
2
m/z calcd for C25H39NBrP2Pd: 601.0695; found: 601.0679 [M+H]+;
elemental analysis calcd (%): C 49.97, H 6.37, N 2.33; found: C
50.65, H 6.17, N 2.49.
2Br and PEt3 (2 equiv) was observed by using 31P{1H} NMR spectros-
¼
copy. This compound is stable in solution for at least 10 h at 08C.
Compound 2Br was isolated by removing all the volatiles in vacuo
¼
at 08C and washing the residue with cold pentane (2 mL, À408C)
to give a light yellow powder (96% yield). Performing this reaction
at +11 8C also resulted in the quantitative formation of complex
Formation of 2Iꢀ
A
solution of [Pd(PEt3)4] (9.0 mg, 0.016 mmol) in [D8]toluene
2Br. However, prolonged reaction times at this temperature result-
(0.3 mL) was slowly added to a stirred solution of 4-((4-iodophe-
nyl)ethynyl)pyridine (1ꢀI ; 4.7 mg, 0.015 mmol) in [D8]toluene
(0.4 mL) at À608C. The quantitative formation of compound 2ꢀI
was observed after ꢂ20 min by using 31P{1H} NMR spectroscopy at
this temperature. No intermediates were observed. 1H NMR
([D8]toluene, À638C): d=8.49 (d, 3J(H,H)=5.9 Hz, 2H; PyrH), 7.27
(d, 3J(H,H)=8.2 Hz, 2H; ArH), 7.05 (d, 3J(H,H)=5.5 Hz, 2H; ArH),
6.98 (d, 3J(H,H)=8.1 Hz, 2H; ArH), 1.25–1.16 (m, 12H; PCH2CH3),
0.82–0.76 ppm (m, 18H; PCH2CH3); 13C{1H} NMR ([D6]acetone,
À638C): d=149.2, 146.8 (dd, br, Cq), 137.1, 136.4 (dd, br, Cq), 129.8,
¼
ed in the formation of complex 3Br (e.g., 49% conversion after
¼
1
3
17.5 h). H NMR ([D6]acetone, 08C): d=8.12 (d, J(H,H)=5.8 Hz, 2H;
PyrH), 7.24 (d, 3J(H,H)=8.4 Hz, 2H; ArH), 7.13 (d, 3J(H,H)=7.6 Hz,
2H; ArH), 6.99 (d, 3J(H,H)=4.7 Hz, 2H; ArH), 4.49 (m, 3J(P,H)=
23.2 Hz, 3J(P,H)=6.5 Hz, 3J(H,H)=6.1 Hz, 1H; CH=CH), 4.36 (m,
3
3
3J(P,H)=22.6 Hz, J(P,H)=6.4 Hz, J(H,H)=7.0 Hz, 1H; CH=CH), 1.42
(m, 12H; PCH2CH3), 0.88 ppm (m, 18H; PCH2CH3); 13C{1H} NMR
([D6]acetone, 08C): d=154.4 (Cq, s), 149.3, 146.2 (Cq, s), 131.1, 126.5,
119.1, 115.3 (Cq; CÀBr), 59.9 (dd, 2J(P,C)=25.8 Hz, 2J(P,C)=3.9 Hz;
CH=CH), 59.5 (dd, 2J(P,C)=23.3 Hz, 2J(P,C)=5.0 Hz; CH=CH), 18.7
(m; PCH2CH3), 9.7 ppm (m; PCH2CH3); 31P{1H} NMR ([D8]toluene,
2
2
125.1 (dd, Cq, J(P,C)=68.3 Hz, J(P,C)=4.0 Hz; CꢀC), 122.1 (dd, Cq,
2
2J(P,C)=64.8 Hz, J(P,C)=4.2 Hz; CꢀC), 121.5, 89.3 (s, Cq; CÀI), 18.6
Chem. Eur. J. 2015, 21, 16113 – 16125
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(m, PCH2CH3), 8.5 ppm (m, PCH2CH3); 31P{1H} NMR ([D8]toluene): d=
16.01 (d, 1P, J(P,P)=4.8 Hz), 14.6 ppm (d, 1P, J(P,P)=4.8 Hz).
1H NMR (C6D6): d=8.69 (d, 3J(H,H)=6.0 Hz, 2H; PyrH), 7.48 (d,
2
2
3
3J(H,H)=7.6 Hz, 2H; PyrH), 7.28 (d, J(H,H)=7.3 Hz, 2H; PyrH), 7.17
(d, 3J(H,H)=16.2 Hz, 2H; CH=CH), 7.01 (d, 3J(H,H)=6.0 Hz, 2H;
ArH), 6.90 (d, 3J(H,H)=16.2 Hz, 2H; CH=CH), 1.73 (m, 12H;
PCH2CH3), 1.02 ppm (m, 18H; PCH2CH3); 13C{1H} NMR (C6D6): d=
Formation of 3Br
¼
This is a modification of a previously reported procedure.[32b] A so-
lution of [Pd(PEt3)4] (39 mg, 0.067 mmol) in THF (2 mL) was added
3
161.4 (t, Cq, J(P,C)=9.5 Hz), 144.5 (s, Cq), 137.1, 135.8, 133.5, 128.5,
1
126.0, 123.9, 120.3, 16.5, (t, J(P,C)=27.0 Hz; PCH2CH3), 8.0 ppm (s;
solution of (E)-4-(4-bromostyryl)pyridine (1Br; 17 mg,
PCH2CH3); 31P{1H} NMR (C6D6): d=11.43 ppm (s, 2P); MS (ES+): m/z
calcd for C25H41NPdP2I: 650.08; found: 649.88 [M+H]+; elemental
analysis calcd (%): C 46.20, H 6.20, N 2.16; found: C 46.28, H 6.41,
N 1.86.
to
a
¼
0.065 mmol) in THF (2 mL) at RT. After 12 h, the volatiles were re-
moved under vacuum and the residue was then washed with cold
pentane (2 mL, À408C). The resulting solid was recrystallized from
THF/pentane (1:10 v/v) to yield complex 3Br. Colorless crystals were
¼
obtained upon slow evaporation of the solvent at RT (90% yield).
Formation of 3Bꢀr
Follow-up 31P{1H} NMR spectroscopy of a solution of complex 2Br
¼
A solution of complex 2Bꢀr (18 mg, 0.030 mmol) in THF (0.7 mL) was
heated in a sealed screw-cap NMR tube to 408C. All volatiles were
removed after 12 h under vacuum. Washing the residue with cold
pentane (À308C, 1”0.5 mL) gave pure complex 3Bꢀr (90% yield).
Subsequently, the residue was dissolved in a mixture of Et2O
(0.5 mL) and hexane (1 mL), which resulted in the formation of X-
ray quality crystals after 24 h at RT. A solution of complex 2ꢀBr
(18 mg, 0.030 mmol) in [D8]toluene (0.7 mL; 43 mm) was loaded in
a 5 mm screw-cap NMR tube. The reaction progress was monitored
by using 31P{1H} NMR spectroscopy to show the selective formation
of complex 3Bꢀr and concurrent disappearance of complex 2Bꢀr at
various temperatures. No intermediates were observed. First-order
linear fits afforded the following values: k293K =2.6”10À5 sÀ1, R2 =
(74 mm) in [D8]toluene at 248C showed the formation of complex
3Br and the concurrent disappearance of complex 2Br. No inter-
¼
¼
mediates were observed. After ꢂ11 h, 75% of the starting material
(2Br) was selectively converted into complex 3Br. The reaction rate
¼
¼
was independent of solvent polarity (toluene vs. acetone) and con-
centration (see Table 1 for details). Monitoring the transformation
of 2Br!3Br at various temperatures in [D8]toluene afforded the fol-
¼
¼
lowing first-order rate constants for a concentration of 19 mm:
k
k
284K =1.0”10À5 sÀ1
291K =3.3”10À5 sÀ1
,
,
R2 =0.998;
R2 =0.997;
k
k
287K =1.6”10À5 sÀ1
301K =1.2”10À4 sÀ1
,
,
R2 =0.998;
R2 =0.994.
1H NMR (C6D6): d=8.57 (d, 3J(H,H)=6.1 Hz, 2H; PyrH), 7.43 (d,
3J(H,H)=7.8 Hz, 2H; ArH), 7.17 (d, 3J(H,H)=7.8 Hz, 2H; ArH), 7.06
(d, 3J(H,H)=16.3 Hz, 1H; CH=CH), 6.88 (d, 3J(H,H)=6.1 Hz, 2H;
ArH), 6.78 (d, 3J(H,H)=16.3 Hz, 1H; CH=CH), 1.53 (m, 12H;
PCH2CH3), 0.92 ppm (m, 18H; PCH2CH3); 13C{1H} NMR (C6D6): d=
159.7 (t, 2J(P,C)=6.0 Hz), 150.8, 144.7, 137.4 (t, 3J=4.1 Hz), 133.8,
131.0, 126.3, 123.9, 120.6, 15.3 (t, 1J(P,C)=13.2 Hz; PCH2CH3),
8.2 ppm (s, PCH2CH3); 31P{1H} NMR (C6D6): d=12.52 ppm (s, 2P); MS
(ES+): m/z calcd for C25H41NPdP2Br: 603.08; found: 604.54 [M+H]+.
0.999;
0.997;
k
k
298K =4.1”10À5 sÀ1
,
R2 =0.997;
k
k
303K =7.6”10À5 sÀ1
313K =2.9”10À4 sÀ1
,
,
R2 =
R2 =
308K =2.1”10À4 sÀ1 R2 =0.999;
0.998. The reaction rate was independent of solvent polarity (tolu-
ene vs. THF) and concentration (see Table 1 for details). 1H NMR
(C6D6): d=8.52 (d, 3J(H,H)=5.9 Hz, 2H; PyrH), 7.43–7.48 (m, 4H;
ArH), 7.17–7.18 (d, 3J(H,H)=5.9 Hz, 2H; ArH), 1.56–1.63 (m, 12H;
PCH2CH3), 0.96–1.03 ppm (m, 18H; PCH2CH3); 13C{1H} NMR (C6D6):
d=161.5 (t, Cq, 2J(P,C)=11.1 Hz), 150.4, 137.3 (t, 3J(P,C)=7.7 Hz),
131.6 (s, Cq), 130.7 (s, C), 125.3 (s), 116.3 (s, Cq), 95.4 (s, Cq; CꢀC),
86.5 (s, Cq; CꢀC), 15.2 (t, 1J(P,C)=26.4 Hz; PCH2CH3), 8.2 ppm (s;
PCH2CH3); 31P{1H} NMR ([D8]toluene): d=12.20 ppm (s, 2P); elemen-
tal analysis calcd (%) for C25H38BrNP2Pd: C 49.97, H 6.37, N 2.33;
found: C 50.08, H 6.49, N, 2.30; HRMS (FD-TOF): m/z calcd:
601.0695; found: 601.0684.
Formation of 3Br from 2Br in the presence of tetrabutylammo-
¼
¼
nium iodide
A solution of complex 2Br (5.0 mg, 0.0083 mmol) and tetrabutylam-
¼
monium iodide (3.1 mg, 0.0084 mmol) in [D8]toluene (0.7 mL) was
stirred at 208C for 12 h. 31P{1H} NMR spectroscopy indicated full
conversion of the starting material (2Br) into two new complexes
¼
3Br (94%) and 3I (6%). Complexes 3Br and 3I were identified by
¼
¼
¼
¼
the addition of authentic samples to the reaction mixture. Reacting
Solid-state formation of 3ꢀBr
complex 3Br (5.0 mg, 0.0083 mmol) in [D8]toluene (0.7 mL) with tet-
¼
A yellow powder of complex 2Bꢀr (54 mg, 0.090 mmol) was heated
in the absence of light at 408C under N2. After 16 d, a sample was
rabutylammonium iodide (3.1 mg, 0.0084 mmol) also resulted in
the formation of complex 3I (4%) after 14 h, as determined by
¼
1
analyzed by using H and 31P{1H} NMR spectroscopy in [D8]toluene
using 31P{1H} NMR spectroscopy.
showing 85% conversion of complex 2Bꢀr to complex 3ꢀBr. Quantita-
tive formation of complex 3Bꢀr was observed after 24 d.
Formation of 3I
¼
A [D8]toluene solution of complex 2I (19 mm) was monitored by
Formation of 3Iꢀ
¼
using 31P{1H} NMR spectroscopy at À478C to show the quantitative
formation of complex 3I and the concurrent disappearance of
A solution of [Pd(PEt3)4] (9.0 mg, 0.016 mmol) in [D8]toluene
¼
complex 2I (k226K =6.1”10À5 sÀ1, R2 =0.997). Formation of complex
(0.3 mL) was slowly added to a solution of compound 1Iꢀ (4.7 mg,
0.015 mmol) in [D8]toluene (0.4 mL) at RT. Removal of all volatiles
after 14 h under vacuum and subsequent washing of the residue
with cold pentane (1 mL, À308C) gave complex 3Iꢀ (94% yield). A
solution of complex 2Iꢀ (8.6 mg, 0.013) in [D8]toluene (0.7 mL,
19 mm) was loaded in a 5 mm screw-cap NMR tube. The reaction
progress was monitored by using 31P{1H} NMR spectroscopy to
show the selective formation of complex 3Iꢀ and concurrent disap-
pearance of complex 2Iꢀ at various temperatures. No intermediates
were observed. The reaction rate was independent of solvent po-
larity (toluene vs. acetone) and concentration (see Table 1 for de-
¼
3I became visible after ꢂ15 min. After ꢂ10 h, 90% conversion of
¼
the starting material (2I ) was observed. The volatiles were re-
¼
moved under vacuum after an additional reaction time of 4 h.
Washing the residue with cold pentane (1 mL, À408C) gave com-
plex 3I (94%). Performing this reaction at various temperatures af-
¼
forded the following first-order rate constants: k213K =5.9”10À6 sÀ1
,
R2 =0.994; k219K =1.6”10À5 sÀ1, R2 =0.994; k226K =6.1”10À5 sÀ1, R2 =
0.991;
232K =1.9”10À4 sÀ1 R2 =0.997; 232K =3.3”10À4 sÀ1 R2 =
k
,
k
,
0.989. The reaction rate was independent of solvent polarity (tolu-
ene vs. acetone) and concentration (see Table 1 for details).
Chem. Eur. J. 2015, 21, 16113 – 16125
www.chemeurj.org
16121
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Competition experiments of 2I with 1-iodo-4-(trifluorome-
thyl)benzene (4I)
tails). First-order linear fits afforded the following values: k225K
=
¼
9.4”10À6 sÀ1, R2 =0.998; k240K =1.4”10À5 sÀ1, R2 =0.990; k230K =3.1”
10À5 sÀ1
,
R2 =0.998;
k
235K =4.9”10À5 sÀ1
,
R2 =0.998;
k250K =8.4
A cold solution of complex 2I (3.6 mg, 0.0055 mmol) in the pres-
”10À4 sÀ1, R2 =0.996. This transformation (2ꢀI !3ꢀI ) was also moni-
¼
ence of PEt3 (2 equiv) in [D8]toluene (0.3 mL) was mixed with a solu-
tion of 1-iodo-4-(trifluoromethyl)benzene (4I; 0.8 mg, 0.003 mmol)
in [D8]toluene (0.4 mL) at À608C. The reaction mixture was kept at
this temperature for 6 h and then allowed to reach RT. 31P{1H} NMR
analysis revealed full conversion of complex 2I into complexes 3I
tored at 225 K in [D8]toluene with a lower concentration of com-
plex 2Iꢀ (3 mm, k=1.1”10À5, R2 =0.999). H NMR (C6D6): d=8.31 (d,
1
3J(H,H)=4.6 Hz, 2H; PyrH), 7.2 (m, 4H; ArH), 6.95 (d, 3J(H,H)=
5.9 Hz, 2H; ArH), 1.47–1.44 (m, 12H; PCH2CH3), 0.81–0.75 ppm (m,
18H; PCH2CH3); 13C{1H} NMR (C6D6): d=162.8 (t, Cq, J(P,C)=9.5 Hz),
2
¼
¼
(73%) and 5I (27%). These products were identified by addition of
149.9, 137.0 (t, 3J(P,C)=8.0 Hz), 133.4 (s, Cq), 130.2 (s), 125.0 (s),
115.9 (s, Cq), 94.8 (s, Cq; CꢀC), 85.3 (s, Cq; CꢀC), 15.8 (t, 1J(P,C)=
27.6 Hz; PCH2CH3), 7.5 ppm (s; PCH2CH3); 31P{1H} NMR ([D8]toluene):
d=11.38 ppm (s, 2P). HRMS (ESI+): m/z calcd for C25H39NP2IPd:
648.0648; found: 648.0645 [M+H]+.
authentic samples to the product solution. Quantitative formation
of complex 3I was observed when this reaction was carried out in
¼
the presence of PEt3 (12 equiv, 8 mg, 0.07 mmol).
Competition experiments of 2Bꢀr with 1-bromo-4-(trifluorome-
thyl)benzene (4Br)
Formation of 6
A
cold solution of complex 2Bꢀr (3.5 mg, 0.0058 mmol) in
[Pd(PEt3)4] (38 mg, 0.066 mmol) was dissolved in toluene (2 mL)
and added dropwise to a solution of (E)-4-styrylpyridine (7; 10 mg,
0.055 mmol) in toluene (3 mL) at RT. All the volatiles were removed
[D8]toluene (0.3 mL) was mixed with a cold solution of 1-bromo-4-
(trifluoromethyl)benzene (4Br; 0.70 mg, 0.0031 mmol) in [D8]toluene
(0.4 mL) at À608C. The reaction mixture was kept at this tempera-
ture for 15 min and then allowed to reach RT. 31P{1H} NMR analysis
after ꢂ10 h, revealed the quantitative transformation of the start-
ing materials into complex 3Bꢀr (70%) and complex 5Br (30%). These
complexes were identified by the addition of authentic samples to
the reaction mixture. When this reaction was repeated with the ad-
dition of PEt3 (12 equiv, 8.0 mg, 0.067 mmol), quantitative forma-
tion of complex 3Bꢀr was observed by using 31P{1H} NMR spectrosco-
py.
1
in vacuo after 6 h to give a light yellow residue. H NMR spectros-
copy revealed the formation of complex 6 (88%) and unreacted
ligand 7 (12%). H and 13C{1H} NMR spectra were recorded at 08C
1
to reduce line broadness. 1H NMR ([D6]acetone, 08C): d=8.12 (d,
3J(H,H)=6.0 Hz, 2H; PyrH), 7.20 (d, J(H,H)=7.9 Hz, 2H; ArH), 7.10
3
3
3
(t, J(H,H)=7.6 Hz, 2H; ArH), 7.01 (d, J(H,H)=4.7 Hz, 2H; ArH), 7.01
(t, 3J(H,H)=7.0 Hz, 1H; ArH), 4.52 (m, 3J(P,H)=16.8 Hz, 3J(P,H)=
6.6 Hz, 3J(H,H)=6.1 Hz, 1H; CH=CH), 4.42 (m, 3J(P,H)=16.8 Hz,
3J(P,H)=6.5 Hz, 3J(H,H)=6.0 Hz, 1H; CH=CH), 1.54–1.34 (m, 12H;
PCH2CH3), 0.88 ppm (m, 18H; PCH2CH3); 13C{1H} NMR ([D6]acetone,
08C): d=154.3 (dd, Cq, 3J(P,C)=5.6, 3J(P,C)=2.6 Hz), 150.2, 146.3
Competition experiments of 2Iꢀ with 1-iodo-4-(trifluorome-
thyl)benzene (4I)
3
3
(dd, Cq, J(P,C)=6.1 Hz, J(P,C)=1.3 Hz), 128.9 (s), 126.0 (s), 122.6 (s),
118.5 (s), 60.7 (dd, 2J(P,C)=25.6 Hz, 2J(P,C)=3.9 Hz; CH=CH) 59.4
(dd, 2J(P,C)=22.7 Hz, 2J(P,C)=5.1 Hz), 18.1 (t, 1J(P,C)=12.0 Hz;
PCH2CH3), 8.2 ppm (d, 2J(P,C)=3.0 Hz; PCH2CH3); 31P{1H} NMR
A cold solution of complex 2Iꢀ (3.6 mg, 0.0056 mmol) in the pres-
ence of PEt3 (2 equiv) in [D8]toluene (0.3 mL) was mixed with
a cold solution of 1-iodo-4-(trifluoromethyl)benzene (4I; 0.8 mg,
0.003 mmol) in [D8]toluene (0.4 mL) at À608C. The reaction mixture
was kept at this temperature for 6 h and then allowed to reach RT.
31P{1H} NMR spectroscopy revealed full conversion of complex 2ꢀI
and the formation of complexes 3Iꢀ (66%) and 5I (34%). On per-
forming this reaction with the addition of PEt3 (12 equiv, 8 mg,
0.07 mmol), formation of complexes 3Iꢀ (97%) and 5I (3%) was ob-
servable by 1 H, 19F{1H}, and 31P{1H} NMR spectroscopy. These com-
plexes were identified by the addition of authentic samples to the
reaction mixture.
2
([D8]toluene): AB system dA =17.30 ppm (1P, J(P,P)=18.0 Hz), dB =
15.42 ppm (1P, 2J(P,P)=18.1 Hz).
Competition experiments for 2Br with 1-bromo-4-(trifluoro-
methyl)benzene (4Br)
¼
A
cold solution of complex 2Br (3.6 mg, 0.0060 mmol) in
¼
[D8]toluene (0.3 mL) was mixed with a cold solution of 1-bromo-4-
(trifluoromethyl)benzene (4Br; 0.8 mg, 0.004 mmol) in [D8]toluene
(0.4 mL) at À608C. The reaction mixture was kept at this tempera-
ture for 15 min and then allowed to reach RT. 19F{1H} and
31P{1H} NMR analysis after ꢂ10 h stirring at RT revealed the quanti-
tative transformation of complex 2Br into complexes 3Br (84%) and
Competition experiments of 6 with 1-bromo-4-(trifluorome-
thyl)benzene (4Br)
¼
¼
5Br (16%), respectively. These products were identified by the addi-
tion of authentic samples to the product solution. Complex 3Br was
the only observable product when this reaction was performed
with the addition of PEt3 (12 equiv; 8.5 mg, 0.072 mmol). The PEt3
was first mixed with a solution containing compound 4Br.
A solution of complex 6 (4.5 mg, 0.0086 mmol) and PEt3 (2 equiv)
of in [D8]toluene (0.3 mL) was mixed with a solution of 1-bromo-4-
(trifluoromethyl)benzene (4Br; 2.0 mg, 0.0088 mmol) in [D8]toluene
(0.4 mL) at À308C. 1H and 31P{1H} NMR spectroscopy showed the
formation of compound 7 and complex 5Br in 95% yield.
¼
X-ray crystallographic analysis
Competition experiments of 2Br with bromobenzene
¼
X-ray analysis of 2Br
¼
A
cold solution of complex 2Br (4.0 mg, 0.0066 mmol) in
¼
[D8]toluene (0.3 mL) was mixed with a cold solution of bromoben-
zene (0.6 mg, 0.004 mmol) in [D8]toluene (0.4 mL) at À608C. The
reaction mixture was kept at this temperature for 15 min and then
allowed to reach RT. 31P{1H} NMR analysis after ꢂ10 h revealed the
Crystal data: C25H38NBrP2Pd; colorless; prisms; 0.4”0.3”0.2 mmÀ3
;
¯
triclinic; P1; a=14.1542(2), b=14.5498(2), c=15.0008(1) Š; a=
67.7701(7), b=88.5428(6), g=72.7628(6)8; T=120(2) K; V=
2718.06(6) Š3; Z=4; Mr =600.81; m=2.283 mmÀ1
;
1calcd =
quantitative formation of complex 3Br.
1.47 mgmÀ3
.
¼
Chem. Eur. J. 2015, 21, 16113 – 16125
www.chemeurj.org
16122
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Data collection and processing: Nonius Kappa CCD diffractome-
ter; MoKa (l=0.71073 Š); graphite monochromator; À18ꢁhꢁ18,
À17ꢁkꢁ18, 0ꢁlꢁ19; frame scan width=1.08; scan speed 1.08
per 20 sec; typical peak mosaicity 0.528; 52926 reflections collect-
ed, 12397 independent reflections (Rint =0.036); 2qmax =54.948. The
data were processed with Denzo-Scalepack.
lar’s Minnesota-06 suite of functionals[36] (i.e., M06-L),[37] with an
empirical dispersion correction added,[38] specifically the third ver-
sion of Grimme’s dispersion;[38b] this combination is denoted as
M06-LD3.
When using a GGA functional, density fitting basis sets, specifically
the fitting sets generated by using the automatic generation algo-
rithm implemented in Gaussian 09, were used in order to speed up
the calculations.[39] In the thermochemical analyses, the frequencies
were scaled by the 0.9958 factor recommended by Kesharwani
et al.[26] and the different experimental temperatures were used as
applicable. Energies were calculated by using domain-based local
pair natural orbital coupled cluster with single and double excita-
tions and a quasi-perturbative triples treatment (DLPNO-CCSD(T))
calculations[40] with the resolution of identity chain of spheres ex-
change (RIJCOSX) approximation[41] used to increase the speed of
the calculations. Orbitals were localized according to the Pipek–
Mezey method.[42] The reliability of the DLPNO approximations has
recently been examined.[43] For geometry optimizations, the def2-
SVP basis set[44] was used, which includes a relativistic effective
core potential (RECP) on palladium, bromine, and iodine. The same
basis set and the def2-TZVP counterpart were used for all DFT cal-
culations. Ab initio calculations used the cc-pVDZ-PP and cc-pVTZ-
PP basis set-RECP combinations, which combine Dunning’s cc-
pVnZ basis sets[45] with Peterson’s basis set-RECP combinations for
the heavier elements.[46] Basis set superposition error (BSSE) correc-
tions were estimated by using the counterpoise correction (CP)
method suggested by Boys and Bernardi.[47] The correction is equal
to Equation 1:
Solution and refinement: The structure was solved by using direct
methods with SHELXS-97.[33] The full-matrix least-squares refine-
ment is based on F2 with SHELXL-13,[33] 541 parameters with 0 re-
straints, final R1 =0.0259 (based on F2) for data with I>2s(I) and
R1 =0.0356 on 12395 reflections, goodneÀss3-of-fit on F2 =1.088,
largest electron density peak=0.721 eŠ
and largest hole
À3
À0.600 eŠ
.
X-ray analysis of 3Br
¼
Crystal data: C25H40NBrP2Pd; colorless; prisms; 0.1”0.1”0.1 mmÀ3
orthorhombic; Pna2(1); a=15.962(3), b=14.889(3), c=11.611(2) Š;
T=120(2) K; Z=4; Mr =602.83; 1calcd
V=2759.4(9) Š3;
1.45 mgmÀ3; m=2.249 mmÀ1
;
=
.
Data collection and processing: Nonius KappaCCD diffractometer;
MoKa (l=0.71073 Š); graphite monochromator; 0ꢁhꢁ19, 0ꢁkꢁ
17, 0ꢁlꢁ13; 23256 reflections collected, 2641 independent reflec-
tions (Rint =0.0325); 2qmax =55.108. The data were processed with
Denzo-Scalepack.
Solution and refinement: The structure was solved by using direct
methods with SHELXT-13.[33] The full matrix least-squares refine-
ment is based on F2 with SHELXL-13,[33] 254 parameters with 3 re-
straints, final R1 =0.0457 (based on F2) for data with I>2s(I) and
R1 =0.0557 on 3308 reflections, goodness-of-fit on F2 =1.068, larg-
À3
DECP ¼ E ðABÞ À EAAðAÞ À EBBðBÞÀ
AB
est electrÀo3n density peak=1.681 eŠ
and largest hole=
AB
ð1Þ
Â
Ã
À1.083 eŠ
.
EAABðABÞ À EAABðAÞ þ EBABðABÞ À EBABðBÞ
X-ray analysis of 3ꢀBr
in which EYXðZÞ is the energy of fragment X calculated at the opti-
mized geometry of Y with the basis set of fragment Z. This was
done for M06 by using the “counterpoise” keyword in Gaussian 09
and according to the example in the orca users’ manual for the
other cases.
Crystal data: C25H38NBrP2Pd; colorless prisms; 0.6”0.2”0.2 mm3;
monoclinic, P21/c; a=15.713(3), b=28.456(6), c=13.812(3) Š; b=
115.80(3)8; T=120(2) K; V=5560(2) Š3; Z=8; Mr =600.81; 1calcd
=
1.435 mgmÀ3; m=2.232 mmÀ1
.
Data collection and processing: Nonius KappaCCD diffractometer;
MoKa (l=0.71073 Š); graphite monochromator; À20ꢁhꢁ18, 0ꢁ
kꢁ36, 0ꢁlꢁ17; frame scan width=0.78; scan speed 1.08 per 98 s;
typical peak mosaicity 0.698; 40653 reflections collected, 12606 in-
dependent reflections (Rint =0.065); 2qmax =54.968. The data were
processed with Denzo-Scalepack.
Bulk solvent effects were approximated by single-point energy cal-
culations by using a polarizable continuum model (PCM),[48] specifi-
cally the integral equation formalism model (IEF-PCM)[48a,b,49] with
toluene as the solvent, as in the experiments. Specifically, Truhlar’s
empirically parameterized version solvation model density (SMD)
was used.[50] Two methods for correcting for solvation were used
for the CCSD(T) calculations. The first is to correct the gas-phase
energies with the difference between the solution SMD-M06 and
Solution and refinement: The structure was solved by using direct
methods with SHELXT-13.[33] The full matrix least-squares refine-
ment is based on F2 with SHELXL-13,[33] 553 parameters with 0 re-
straints, final R1 =0.0465 (based on F2) for data with I>2s(I) and
gas-phase M06 energies using either the def2-SVP or def2-TZVP
SMD
M06=SVP
basis set; this is denoted as DE
or DEM06=TZVP<brtr>SMD, respec-
R1 =0.0772 on 12606 reflections, goodness-of-fit on F2 =1.029,
tively. The second is to apply the post-Hartree–Fock (HF) correla-
tion calculation to the SMD-HF orbitals; this is denoted as SMD-
À3
largest electron density peak=0.877 eŠ
and largest hole=
À3
CCSD(T). The difference in the energies between the three solva-
À0.739 eŠ
.
SMD
M06=TZVP
tion options is insignificant. The DE
results are presented in
CCDC 1413587–1413589 contain the supplementary crystallo-
graphic data for this paper. These data are provided free of charge
by The Cambridge Crystallographic Data Centre.
the paper whereas the SMD-CCSD(T) results, along with other
tested considered levels of theory, are presented in the Supporting
Information in Table S7; these include the M06 functional (the
hybrid version of M06L used for geometry optimizations),[51] the
DSD-PBEB95[52] double-hybrid functional[53] and second-order
Møller–Plesset (MP2)[54] (obtained as a byproduct of the CCSD(T)
calculation).
Computational details
All calculations used either Gaussian 09, Revision D.01[34] or
ORCA 3.0.2.[35] Geometry optimizations and DFT calculations were
done with the former, whereas single-point-energy double-hybrid
DFT and ab initio (see below) calculations were done with the
latter. Geometries were optimized with the local version of Truh-
In all DFT calculations run with Gaussian 09, an ultrafine (i.e.,
a pruned (99,590)) grid was used, which is especially critical for the
M06 suite of functionals.[55] For interpretative purposes, Mayer[56]
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Following convention, free energies are reported at standard state,
that is, 1 atm and 298.15 K. By redoing the thermochemical analy-
sis within Gaussian 09 at other temperatures, one can obtain the
free energies at different temperatures. The corrections for varying
concentrations can also be obtained;[60] details are provided in the
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This research was supported by the Helen and Martin Kimmel
Center for Molecular Design. We thank Dr. D. Freeman for the
preparation of various ligands. M.E.v.d.B. is the incumbent of
the Bruce Pearlman Chair in Synthetic Organic Chemistry.
Keywords: aryl halide activation
·
bond activation
·
coordination · rearrangement · palladium
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Received: April 22, 2015
Revised: July 17, 2015
Published online on September 18, 2015
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