Flexible coordination of diphosphine ligands leading to cis and trans Pd(0), Pd(II), and Rh(I) complexes

Article abstract of DOI:10.1021/ic5010566

A series of diphosphine ligands ⁱPr₂P-C ₆H₄-X-C₆H₄-PⁱPr ₂ (for ligand L¹, X = CH₂; for ligand L ², X = CH₂CH₂) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium(II), and rhodium(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium(II) complexes, with L¹ coordinating preferentially cis, while L² coordinates in a trans fashion. Coordination to Pd(0) leads to L¹Pd(dba) and L²Pd(dba), in which both ligands accommodate a P-M-P angle close to 120°. L² was found to coordinate cis in a rhodium(I) complex ([L²Rh(nbd)][BF₄], where nbd = norbornadiene).

Full text of DOI:10.1021/ic5010566

Article
pubs.acs.org/IC
Flexible Coordination of Diphosphine Ligands Leading to cis and
trans Pd(0), Pd(II), and Rh(I) Complexes
Cezar C. Comanescu and Vlad M. Iluc*
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
*
S Supporting Information
i
ABSTRACT: A series of diphosphine ligands Pr P−C H −
2
6
4
i
1
2
X−C H −P Pr (for ligand L , X = CH ; for ligand L , X =
CH CH ) was investigated to determine the preference for
6
4
2
2
2
2
cis/trans coordination to palladium(0), palladium(II), and
rhodium(I). Increasing the length of the bridging alkyl
backbone from one to two carbons changes the geometry of
1
the resulting palladium(II) complexes, with L coordinating
2
preferentially cis, while L coordinates in a trans fashion.
1
2
Coordination to Pd(0) leads to L Pd(dba) and L Pd(dba), in
which both ligands accommodate a P−M−P angle close to
2
2
1
20°. L was found to coordinate cis in a rhodium(I) complex ([L Rh(nbd)][BF ], where nbd = norbornadiene).
4
INTRODUCTION
The factors determining the coordination mode of certain
diphosphines are still intensely studied since they can bind
either cis or trans, depending on the reaction conditions.
■
Diphosphine ligands have played an important role in
organometallic chemistry, especially because of their ability to1
support metal complexes that are highly active in catalysis.
Most bidentate ligands have a strong preference toward cis
13,15−17
Although known for some time, ancillary ligand flexibility
features prominently in recent studies with some examples, in
which the ligand actively participates in the reactions of the
2
−6
2
5−30
coordination,
are known.
although examples of trans-chelating ligands
While cis-chelating diphosphines, with bite
metal, known as metal−ligand cooperation.
We became
7
−21
31−39
interested in studying flexible ligand backbones
and
22
angles of ∼90°, have been employed for many decades, the
first ligand designed to coordinate trans to a metal center dates
from 1976. Known as TRANSPHOS, it is still arguably the
diphosphine that received the most attention among trans-
decided to determine whether we can control the cis or trans
coordination preference of certain diphosphines. Therefore, we
i
i
synthesized the diphosphines Pr P−C H −X−C H −P Pr
2
6
4
6
4
2
1
2
(
for ligand L , X = CH ; for ligand L , X = CH CH ) derived
2 2 2
2
3
from modified pincer backbones that show cis and trans
coordination to different metal centers. In addition, the
resulting Pd(II) complexes behave as active catalysts in Suzuki
and Heck coupling reactions.
spanning ligands. Although it strongly prefers a trans
coordination, when it shows bite angles ranging from 168° to
76°, some examples of tetracoordinate and tricoordinate
1
complexes with smaller bite angles (ca. 105°) have been
2
4
reported. Cis coordination of TRANSPHOS is typically
accompanied by bending of the phenanthrene backbone, while
the methylene groups increase the ligand’s flexibility (see
Figure 1). As pointed out in a recent review, only a few
diphosphines are known to coordinate in a trans fashion with a
RESULTS AND DISCUSSION
■
Synthesis and Structural Characterization of Metal
Complexes. Recently, Piers and Parvez reported a new
i
diphosphine with a modified pincer backbone, Pr P(o-C H −
2
6
4
i
1
40−42
7
CH
2
−o′-C
6
H
4
)P Pr
2
(L ).
When employed in conjunction
P−M−P angle close to 180°.
with iridium, a double C−H activation leading to an Ir carbene
43
was observed. This ligand design was inspired by the
pioneering work of Floriani et al., who synthesized the phenyl
derivative and explored its reactivity with Ni, Pd, Pt, Fe, and Rh
44
precursors. We postulated that increasing the length of the
backbone might force the ligand to coordinate preferentially in
a trans fashion.
4
3
The diphosphine syntheses are straightforward and afford
products in high yields. Compound Pr P(o-C H −CH CH −
i
2
6
4
2
2
Received: May 9, 2014
Published: August 7, 2014
Figure 1. TRANSPHOS and its two coordination modes.
©
2014 American Chemical Society
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Scheme 1. Syntheses of Palladium Complexes
i
2
1
o′-C H )P Pr (L ) was synthesized from 2-bromomethyl-
NMR spectrum from −5.87 ppm (in L ) to 38.47 ppm (broad,
6
4
2
4
5,46
2
1
bromobenzene,
in 91% yield. L was structurally charac-
CD Cl ) for L PdCl and to 34.62 ppm in the case of
2
2
2
1
1
terized in the solid state by single-crystal X-ray diffraction (see
Figure SX24 in the Supporting Information).
The reaction between L or L and Pd(COD)Cl in THF at
room temperature for 2 h (Scheme 1) led to the precipitation
of L PdCl (i = 1 or 2), yellow compounds, which were isolated
in high yield. Analogously, the reaction between L and
Pd(OAc) in THF at room temperature for 2 h led to the
isolation of the corresponding palladium(II) acetate complexes,
L Pd(OAc) in high yield (Scheme 1). All four metal complexes
were characterized by single-crystal X-ray diffraction (Figures
−5). As expected, the two L complexes, L PdCl (Figure 2)
and L Pd(OAc) (Figure 3), show cis coordination of the
L Pd(OAc) . The solid-state molecular structures of L PdCl
2
2
1
and L Pd(OAc) show a square-planar geometry at Pd(II) with
the sum of angles around the metal center of ca. 360° (360.38°
and 360.90° for L Pd(OAc)
P(2) angles are 100.02(5)° in L PdCl
2
1
2
2
1
1
for L PdCl
). The P(1)−Pd−
2
2
i
1
and 101.06(3)° in
2
2
i
1
L Pd(OAc)
mode of L .
, which is consistent with the cis coordination
2
1
2
2
On the other hand, L coordinates in a trans fashion to
i
2
2
palladium(II), leading to L PdCl
(Figure 4) and L Pd(OAc)
Figure 5). A slight increase of the P−Pd−P angle, from
62.72(2)° in L PdCl to 163.31(6)° in L Pd(OAc) , was
2 2
observed, which was likely a consequence of the additional
steric bulk of the acetate ligands. The sum of angles around
Pd(II) is close to 360° in both complexes (361.54° for L PdCl
and 358.94° for L Pd(OAc) ), as expected for a square planar
2
2
2
(
1
2
2
1
1
2
2
1
2
diphosphine. The coordination of the diphosphine to the
2
Pd(II) center is accompanied by a downfield shift in the 31
P
2
2
2
geometry at the metal center (Figures 4 and 5).
In order to determine the influence of the metal oxidation
state on the resulting geometry, reactions between the two
diphosphines and Pd(dba) were carried out (Scheme 1).
2
Although the two diphosphines showed different coordination
modes with palladium(II), they both behave as wide-angle
ligands when coordinated to the Pd(dba) moiety, a
coordination mode enforced by the oxidation state of
1
palladium. The P−Pd−P angle is 113.33(5)° in L Pd(dba)
2
i
and 117.117(17)° in L Pd(dba). Both L Pd(dba) complexes
(
Figures 6 and 7) have the sum of angles around the metal
center close to 360°, as expected for a trigonal planar geometry
at palladium (if dba is considered to occupy only one
coordination site).
1
2
Figure 2. (Left) Molecular structure of L PdCl2 with thermal
ellipsoids at 50% probability. (Right) View showing the anagostic
interaction between H(1A)−Pd. All hydrogen atoms except those
involved in the anagostic interaction were omitted for clarity. Selected
bond distances: Pd−Cl(1) = 2.3765(13) Å, Pd−Cl(2) = 2.3559(13)
Å, Pd−P(1) = 2.3311(13) Å, Pd−P(2) = 2.2742(13) Å, Pd−H(1A) =
In order to determine whether L can adapt its coordination
in response to the presence of a cis enforcing ligand, the
2
reaction between L and [Rh(nbd) ][BF ] (where nbd = 1,5-
2
4
2
norbornadiene) was carried out and led to [L Rh(nbd)][BF ]
4
(
eq 1). Its solid-state molecular structure (Figure 8) was
determined by single crystal X-ray diffraction, which indicated
that the P−Rh−P angle is 103.74(2)°. A search in the
Cambridge Structural Database showed that this value is the
2
.393 Å, Pd−H(1B) = 4.014 Å. Selected bond angles: P(1)−Pd−
Cl(1) = 84.87(5)°, Cl(1)−Pd−Cl(2) = 88.40(5)°, Cl(2)−Pd−P(2) =
8
1
7.09(5)°, P(2)−Pd−P(1) = 100.02(5)°, Pd−H(1A)−C(1) =
40.76°.
+
second largest in [Rh(P−P)(nbd)] complexes (77 examples).
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1
Figure 3. (Left) Molecular structure of L Pd(OAc) with thermal ellipsoids at 50% probability. (Right) View showing the anagostic interaction
2
between H(1B)−Pd. Co-crystallized solvent molecules and all hydrogen atoms except those involved in the anagostic interaction were omitted for
clarity. Selected bond distances: P(1)−Pd = 2.2759(7) Å, Pd−O(51) = 2.0981(19) Å, Pd−O(61) = 2.0871(18) Å, Pd−P(2) = 2.2486(8) Å, Pd−
H(1B) = 2.615 Å, Pd−H(1A) = 4.070 Å. Selected bond angles: P(1)−Pd−O(51) = 83.67(6)°, O(51)−Pd−O(61) = 88.42(7)°, O(61)−Pd−P(2) =
87.75(6)°, P(2)−Pd−P(1) = 101.06(3)°, Pd−H(1A)−C(1) = 139.93°.
2
2
Figure 4. Molecular structure of L PdCl with thermal ellipsoids at
Figure 5. Molecular structure of L Pd(OAc) with thermal ellipsoids
2
2
5
0% probability showing the anagostic interaction H(1B)−Pd and
at 50% probability showing the anagostic interaction H(1A)−Pd. Co-
crystallized solvent molecules and all hydrogen atoms except those
involved in the anagostic interaction were omitted for clarity. Selected
bond angles: Pd(1)−O(1) = 2.032(2) Å, Pd(1)−P(1) = 2.3575(10)
Å, Pd1−H(1A) = 2.599 Å, Pd(1)−H(1B) = 4.091 Å. Selected bond
distances: O(1)−Pd(1)−P(1) = 89.10(7)°, P(1)−Pd(1)−O(1)# =
90.37(7)°, P(1)−Pd(1)−P(1)# = 163.31(6)°, Pd(1)−H(1A)−C(1) =
117.87°.
H(2B)-Pd. All hydrogen atoms except those involved in the anagostic
interaction were omitted for clarity. Selected bond distances: Pd−
Cl(1) = 2.3146(6) Å, Pd−Cl(2) = 2.3049(6) Å, Pd−P(1) = 2.3372(6)
Å, Pd−P(2) = 2.3483(6) Å, Pd−H(1A) = 4.169 Å, Pd−H(1B) = 2.788
Å, Pd−H(2A) = 3.979 Å, Pd−H(2B) = 2.523 Å. Selected bond angles:
P(2)−Pd−Cl(1) = 88.75(2)°, Cl(1)−Pd−P(1) = 92.67(2)°, P(2)−
Pd−Cl(2) = 93.47(2)°, Cl(2)−Pd−P(1) = 86.65(2)°, P(1)−Pd−P(2)
=
162.72(2)°, Pd−H(1B)−C(1) = 113.63°, Pd−H(2B)−C(2) =
124.41°.
We became interested to determine the geometry of
palladium(0) complexes in the absence of dba. Reactions of
i
L PdCl (i = 1, 2) with either Mg/THF at room temperature
2
overnight or with LiBEt H for 4 h led to palladium(0)
3
complexes (Scheme 2). The same product was obtained
independently of the reduction method used, as confirmed by
1
31
13
H, P, and C NMR spectroscopy. X-ray crystallography
2
established that reduction of L PdCl yields a monomeric
complex, L Pd (Figure 9). Because L cannot accommodate a
2
2
1
trans-spanning geometry, a dimeric palladium(0) complex,
1
[
1
L Pd] , was formed (Figure 10). The P−Pd−P angles are
2
67.87(9)°, 170.82(9)°, 166.68(9)°, and 172.81(9)° for the
two similar units in [L Pd] , while in the monomeric L Pd, the
1
2
These angles range from 73.69° in [Rh(2-phosphino-2,3-
2
47
dihydrobenzo-[d][1,3]oxaphosphole)(nbd)][BF ] to 104.52°
corresponding P−Pd−P angle is 163.38(2)°.
4
iPr
17
in [( DPDBFphos)Rh(nbd)][BF ]. The value of the P−
Anagostic Interactions. All palladium complexes de-
scribed above exhibit anagostic interactions. Anagostic
4
2
metal−P angle changed by ca. 15° from L Pd(dba) to
2
31
103
48
[
1
L Rh(nbd)][BF ]. The P− Rh coupling constant of
interactions refer to any M−H−C interactions that are not
4
4
9,50
19.6 Hz is in agreement with previously reported values for
agostic
and are special cases of hydrogen bonding. The
7
wide-angle diphosphine ligands.
metal complexes featuring such interactions have a relatively
8
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1
2
Figure 6. Molecular structure of L Pd(dba) with thermal ellipsoids at
0% probability. Most hydrogen atoms were omitted for clarity.
Selected bond distances: Pd−P(1) = 2.3953(13) Å, Pd−P(2) =
.3337(13) Å, Pd−C(51) = 2.155(4) Å; Pd−C(52) = 2.144(4) Å.
Selected bond angles: P(1)−Pd−P(2) = 113.33(5)°, P(1)−Pd−C(51)
104.70(12)°, C(51)−Pd−C(52) = 38.74(16)°, C(52)−Pd−P(2) =
03.68(13)°.
Figure 8. Molecular structure of [L Rh(nbd)][BF ] with thermal
4
5
ellipsoids at 50% probability. Most hydrogen atoms and the
counterion were omitted for clarity. Selected bond distances: Rh−
C(51) = 2.169(2) Å, Rh−C(52) = 2.191(2) Å, Rh−C(54) = 2.225(2)
Å, Rh−C(55) = 2.206(2) Å, Rh−P(1) = 2.3548(6) Å, Rh−P(2) =
2
=
1
2
.4349(6) Å. Selected bond angle: P(1)−Rh−P(2) = 103.74(2)°.
i
Scheme 2. Reduction of L PdCl (i = 1, 2)
2
The effect of the anagostic interaction is dependent on the X
2
Figure 7. Molecular structure of L Pd(dba) with thermal ellipsoids at
0% probability. Most hydrogen atoms were omitted for clarity.
Selected bond distances: Pd−P(1) = 2.3390(5) Å, Pd−P(2) =
.3473(5) Å, Pd−C(51) = 2.1432(18) Å, Pd−C(52) = 2.1333(15) Å.
ligand coordinated to the metal center of interest, as the
5
−
CH COO group induces a larger splitting of the chemical
3
−
shifts for the two protons than Cl , and also on the solvent
2
used (different shifts are recorded for the H
and Hexo in
Selected bond angles: P(1)−Pd−P(2) = 117.117(17)°, P(2)−Pd−
C(52) = 100.28(7)°, P(2)−Pd−C(51) = 139.15(5)°, C(51)−Pd−
C(52) = 38.88(8)°, C(51)−Pd−P(1) = 103.73(5)°.
endo
1
L Pd(OAc) in CD Cl versus C D ). As a consequence, in
2
2
2
6
6
1
L Pd(OAc) , the exoproton has a chemical shift at 3.88 ppm as
2
a doublet due to H−H coupling (J = 20 Hz), while the
HH
long M−H distance (2.3−2.9 Å), a large M−H−C angle (110−
endohydrogen is shifted to 8.05 ppm (dt, J = 20 Hz, JHP =
HH
1
70°), and show an unusual shift of several ppm downfield
2.86 Hz; see Figure 11).
1
1
from the uncoordinated CH of the ligand precursor in their H
The backbone methylene protons of L appear as a triplet in
5
1−53
1
NMR spectra.
Anagostic interactions are usually associated
its H NMR spectrum at 5.16 ppm, due to their coupling with
8
31
with d metal centers, which are square planar prior to the
interaction, and are critically dependent on the metal center, as
Bergman and co-workers showed in their investigations on
the two equivalent P nuclei (J
= 4.05 Hz). Upon
HP
1
1
coordination to palladium(II) (in L PdCl and L Pd(OAc) ),
2
2
the two protons are not equivalent anymore and their chemical
shift is significantly different (see Table 1): the exoproton,
which is further away from palladium, shows a relatively close
5
1,54
Rh(I) complexes.
Bergman’s group conducted a theoretical
study to elucidate the origin of the anagostic interaction and
found that it can vary from purely electrostatic (hydrogen
bonding, extreme case) to an electrostatic−partially covalent
chemical shift to that of the corresponding proton in the free
1
ligand: 4.07 ppm (d, JH−H = 11.9 Hz) in L PdCl , while the
2
51
interaction (stronger interaction, shorter M−H distances).
endoproton, because of its interaction with palladium, shows a
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2
Figure 9. Molecular structure of L Pd with thermal ellipsoids at 50%
probability showing the anagostic interactions H(1A)−Pd and
H(2A)−Pd. All hydrogen atoms except those involved in the anagostic
interaction were omitted for clarity. Selected bond distances: Pd−P(1)
1
1
Figure 11. H NMR (C D ) spectrum of L Pd(OAc) depicting the
6
6
2
=
2.2659(7) Å, Pd−P(2) = 2.2623(7) Å, Pd−H(1A) = 2.59 Å, Pd−
anagostic interaction in the two insets (downfield, endo proton;
upfield, exo proton).
H(1B) = 3.97 Å, Pd−H(2A) = 2.62 Å, Pd−H(2B) = 3.98 Å. Selected
bond angles: P(1)−Pd−P(2) = 163.38(2)°, Pd−H(1A)−C(1) =
120.53°, Pd−H(2A)−C(2) = 122.60°.
Table 1. Chemical Shift (ppm) and Distances to Palladium
for the Protons Involved in Anagostic Interactions
endo δ
(ppm)
exo δ
(ppm)
Pd−H endo
Pd−H exo
metal complex
(Å)
(Å)
1
L PdCl
6.93
8.05
5.15
5.33
5.85
4.07
3.88
2.97
3.08
2.54
2.39
2.59
4.01
4.09
2
1
L Pd(OAc)
2
2
2
L PdCl
2.52, 2.78
2.59
3.97, 4.16
4.09
2
2
L Pd(OAc)
2
L Pd
2.59, 2.62
2.57, 2.76
3.97, 3.98
4.08, 4.21
2
L Pd(p-C H −
4.56, 4.11 2.90, 2.80
6
4
NO )Br
2
1
Figure 10. Molecular structure of [L Pd] with thermal ellipsoids at
2
50% probability (only one of the crystallographically independent
molecules in the unit cell is shown). Most hydrogen atoms were
omitted for clarity. Selected bond distances: Pd(1)−P(1) =
2
.2691(15) Å, Pd(2)−P(2) = 2.2710(15) Å. Selected bond angles:
P(1)−Pd(1)−P(1)# = 167.87(9)°; P(2)−Pd(2)−P(2)# = 170.82(9)°.
2
Figure 12. Calculated energies for the different conformations of L as
a ligand for palladium(II).
downfield shift at 6.93 ppm (dt, JHH = 11.9 Hz and JHP = 2.1
Hz).
mol) to 120° (+4.8 kcal/mol), the angle usually observed for
trigonal planar Pd(0) complexes.
2
DFT Calculations. The ability of L to accommodate both
cis and trans isomers was investigated using density functional
theory (DFT). The intermediate structures were optimized for
C−C Cross-Coupling Reactions. Palladium complexes
supported by bidentate phosphines, including trans-spanning
2
3,55
L PdCl2 constraining only the P−Pd−P angle at values
ligands,
were reported to be active catalysts in C−C cross
between 90 and 180° in 5° increments. Then, a single-point
coupling reactions. In order to determine whether the flexibility
energy was calculated for each conformer of the ligand by
of the ligand coordination is important to catalytic activity, the
1
2
1
2
removing the PdCl group (Figure 12). The difference between
reactivity of L Pd(OAc) , L Pd(OAc) , L PdCl , and L PdCl
2
2 2 2 2
the two conformers resulting from the cis-L PdCl and trans-
was tested in the coupling of aryl halides with phenyl boronic
acid (Table 2). Although aryl chlorides are unreactive (see
entries 13 and 14 in Table 2), all four palladium complexes
catalyzed the coupling of aryl bromides and iodides (see entries
2
2
L PdCl isomers is only 12.4 kcal/mol, in agreement with the
2
2
observed ability of this ligand to adopt both conformations
Figure 12). The energy drops rapidly from 90° (+12.4 kcal/
(
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1
Table 2. Suzuki Coupling Reactions Using L PdCl and
Carrying out the Suzuki coupling reaction of phenylboronic
2
2
L PdCl as Precatalysts
acid with p-nitrobromobenzene in 1,4-dioxane, using 1%
2
2
L PdCl and conditions similar to those previously described
2
led to 61.5% conversion to 4-nitrobiphenyl when one drop of
Hg was added to the reaction mixture prior to heating.
Although a drop in yield is apparent, the reaction was not shut
down, indicating that the likely mechanism of catalysis is
homogeneous. These findings agree with the accepted view of a
homogeneous mechanism for C−C cross-coupling reactions
that is operating even in the case of nanoparticulate
entry
substrate
precatalyst
time (h)
yield (%)
1
1
2
3
4
5
6
7
8
9
p-Br−C H −COCH
L PdCl
12
12
6
84
74
82
74
78
61
91
92
63
56
77
62
0
6
4
3
3
2
2
p-Br−C H −COCH
L PdCl
6
4
2
1
59−64
p-Br−C H −NO
L PdCl
palladium.
6
4
2
2
2
p-Br−C H −NO
L PdCl
6
In order to determine whether the phosphines may dissociate
6
4
2
2
1
1
2
C H Br
L PdCl
3
during catalysis, the reaction of L PdCl or L PdCl with 2
6
5
2
2 2
2
C H Br
L PdCl
3
equiv of BF at ambient temperature for 3 h in THF was carried
6
5
2
3
1
p-I−C H −NO
L PdCl
5
out. Although no considerable decomposition was observed,
the results are consistent with the possibility that each
phosphine may dissociate during catalysis; for instance,
6
4
2
2
2
p-I−C H −NO
L PdCl
5
6
4
2
2
1
C H I
6
L PdCl
3
5
2
2
1
10
11
12
13
14
C H I
6
L PdCl
3
5
2
L PdCl is still ∼80% present in the resulting mixture, in the
2
1
2
p-I−C H −OCH
L PdCl
17
17
8
6
4
3
3
2
2
2
2
case of L PdCl treatment with BF .
2
3
2
2
p-I−C H −OCH
L PdCl
6
4
In order to probe whether L undergoes a trans−cis
1
p-Cl−C H −CH
L PdCl
6
4
3
isomerization during catalysis, the stoichiometric reaction
between L Pd and p-nitrobromobenzene was carried out and
2
p-Cl−C H −CH
L PdCl
8
0
2
6
4
3
2
led to the formation of trans-L Pd(p-C H −NO )Br, in which
6
4
2
2
L retains the trans coordination to the palladium center (P−
1
−12 in Table 2). Attempts to use K CO instead of the
2
3
Pd−P angle is 162.84(2)°). (The molecular structure of
stronger base Cs CO led to lower yields (25%−30% lower, on
2
3
56−59
2
L Pd(p-C H −NO )Br is shown in Figure 13.) The oxidative
average). As previously reported,
catalyst loadings higher
6
4
2
addition to a trans spanning Pd-diphosphine complexes leading
also to a trans Pd(II) complex is a rare event and is associated
with isomerization. For instance, complexes of the type
[(Xantphos)Pd(Aryl)]X (X = halide) show trans coordination,
although the ligand itself is known to exhibit both cis and trans
than 0.1 mol % led to a lower turnover frequency (TOF),
bercause of catalyst deactivation. It is likely that palladium
nanoparticles form and agglomerate since the formation of
palladium black is observed.
The same four palladium complexes also act as precatalysts in
the Heck coupling of aryl halides with n-butyl acrylate (Table
65−67
coordination.
Thiel et al. reacted Xantphos with Pd(dba)
2
3
). In addition to the results presented in Table 3, the coupling
and 4-trifluoromethyl-bromobenzene to obtain trans-
(Xantphos)Pd(4-trifluoromethylphenyl)(Br), which features a
of 1-hexene with 4-nitro-1-iodobenzene in 3 h (same
conditions as above), catalyzed by L PdCl , led to the expected
product in 61% yield.
2
68
P−Pd−P angle of 153.07(3)°. Similarly, treatment of
2
Xantphos with Pd (dba) and 4-bromobenzonitrile led to
2
3
In order to determine whether the reaction proceeds
heterogeneously and the homogeneous catalysts lead to the
formation of colloidal particles, a mercury test was conducted.
trans-(Xantphos)Pd(4-cyanophenyl)Br, which was character-
ized crystallographically and a large P−Pd−P angle of 150.7°
66
was found by Yin and Buchwald. Van Leeuwen et al.
1
2
Table 3. Heck Coupling Results Using L PdCl and L PdCl as Catalysts
2
2
entry
substrate
precatalyst
time (h)
yield(%)
1
1
2
3
4
5
6
7
8
9
p-Br−C H −COCH
L PdCl
4
4
4
4
8
8
3
3
4
4
4
4
8
8
63
78
91
84
92
79
88
92
97
91
92
88
87
73
6
4
3
3
2
2
p-Br−C H −COCH
L PdCl
6
4
2
1
p-Br−C H −NO
L PdCl
6
4
2
2
3
3
2
2
p-Br−C H −NO
L PdCl
6
4
2
1
p-Br−C H −CH
L PdCl
6
4
2
2
p-Br−C H −CH
L PdCl
6
4
2
1
p-I−C H −NO
L PdCl
6
4
2
2
2
p-I−C H −NO
L PdCl
6
4
2
2
1
p-I−C H −OCH
L PdCl
6
4
3
3
2
2
1
1
1
1
1
0
1
2
3
4
p-I−C H −OCH
L PdCl
6
4
2
1
p-I−C H −CH
L PdCl
6
4
3
2
2
p-I−C H −CH
L PdCl
6
4
3
2
1
p-Br−C H −OCH
L PdCl
6
4
3
3
2
2
p-Br−C H −OCH
L PdCl2
6
4
8
522
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
2
2
(
L PdCl , L Pd(OAc) ). However, the same ligand can
2 2
coordinate as a wide-angle ligand to palladium(0) in order to
2
accommodate a trigonal planar geometry in L Pd(dba), in
which case the dba molecule plays an important role as a
spectator ligand. Comparison of metrical parameters obtained
from X-ray crystal structures for palladium complexes (see
Table 4) is in agreement with these observations. Aside from
3
1
1
Table 4. Comparison of Metrical Parameters and P{ H}
1
2
NMR Chemical Shifts of L and L Complexes
metal complex
Pd−P (Å)
P−Pd−P (°) 31P NMR shift
1
L PdCl
2.3311(13), 2.2742(13)
2.3372(6), 2.3483(6)
2.2759(7), 2.2486(8)
2.3575(10)
100.02(5)
162.72(2)
101.06(3)
163.31(6)
113.33(5)
117.117(17)
38.47
28.64
2
2
L PdCl
2
1
L Pd(OAc)
34.62
2
2
L Pd(OAc)
18.31
2
1
L Pd(dba)
2.3953(13), 2.3337(13)
2.3390(5), 2.3473(5)
21.53, 20.69
32.89, 19.48
2
L Pd(dba)
2
Figure 13. Molecular structure of L Pd(p-C H −NO )Br with thermal
6
4
2
the large difference in P−Pd−P angles between cis and trans
ellipsoids at 50% probability. Most hydrogen atoms were omitted for
1
complexes, palladium(II) complexes supported by L show
clarity. Selected bond distances: Pd−P(1) = 2.3331(6) Å, Pd−P(2) =
shorter Pd−P distances than the corresponding complexes
2
.3377(6) Å, Pd−Br = 2.5221(3) Å, Pd−C(51) = 2.021(2) Å, Pd−
2
supported by L ; however, these differences are small. On the
H(1A) = 2.766 Å, Pd−H(2A) = 2.576 Å. Selected bond angles: P(1)−
Pd−P(2) = 162.84(2)°, Br−Pd−C(51) = 172.48(7)°, P(1)−Pd−Br =
31
other hand, P NMR chemical shifts are not predictive and do
not even differentiate between palladium(0) and palladium(II)
9
8
4.458(16)°, P(2)−Pd−Br = 86.236(18)°, P(1)−Pd−C(51) =
6.07(7)°, P(2)−Pd−C(51) = 95.48(6)°.
2
complexes. The flexibility of L is apparent in its coordination
to rhodium(I), when cis coordination is observed with a large
P−Rh−P angle of 103.75(2)°. In addition, the palladium(II)
complexes synthesized herein proved to be active catalysts in
Heck and Suzuki C−C couplings, achieving yields in the range
of 60%−99%, with the activated aryl iodides giving the fastest
and highest conversions among the tested substrates.
synthesized a series of ligands derived from Xantphos and
characterized the neutral complexes (L−L)Pd(4-C H CN)(Br)
6
4
(
L−L is the diphosphine ligand) obtained by reacting the
diphosphine with {[(o-tolyl) P]Pd(4-C H CN)Br} . It was
3
6
4
2
found that the P−Pd−P angles lie in the range of 150.4°−
1
55.0°, confirming the strong preference of the Xantphos motif
EXPERIMENTAL SECTION
■
67
toward trans coordination. Attempts to monitor the oxidative
addition step by NMR spectroscopy did not lead to additional
information since the stoichiometric reaction is almost
complete by the time an NMR instrument was reached.
General Remarks. Experiments were performed under a dry
nitrogen atmosphere using GloveBox techniques. Solvents were dried
by passing through a column of activated alumina, followed by storage
under dinitrogen. All commercial chemicals were used as received,
unless specified otherwise. (COD)PdCl2 and Pd(OAc)2 were
purchased from Sigma−Aldrich. Deuterated solvents were obtained
from Cambridge Isotope Laboratories. CD Cl and CDCl were dried
2
Although the flexibility of L to adopt various coordination
modes may still be important in other reactions, the results of
the cross-coupling experiments show that both palladium
2
2
3
over molecular sieved, while C D was dried by stirring over dry CaH
1
2
6
6
2
complexes, L PdCl and L PdCl , display similar activity. These
1
2
2
and filtered prior to use. L and 1,2-bis(2-bromophenyl)ethane were
results are in agreement with the findings from DFT
43,45,46
synthesized following a reported procedure.
NMR spectra were
calculations and indicate that the energy necessary to switch
recorded on a Varian 300 or Bruker 400 spectrometer at ambient
2
between cis and trans coordination modes for L is likely
probe temperature, unless otherwise indicated. Chemical shifts are
1
smaller than the activation barrier for the turnover-limiting step
in these reactions. However, based on results from the reaction
reported in ppm, relative to residual internal protonated solvent for H
and 13C{ H} NMR spectra or with respect to a Me Si standard, when
1
4
1
2
using CDCl for the coupling experiments. ESI-MS were recorded at
of L PdCl or L PdCl with 2 equiv of BF , it is also possible
3
2
2
3
the ND Mass Spectrometry (MS) & Proteomics Facility at the
University of Notre Dame. CHN analyses were performed on a CE-
that the phosphine dissociates during catalysis. Since large
colloidal particles do not form (Hg test) and the ligands are
chelating, it is likely that complete dissociation of the
diphosphines does not occur appreciably.
4
40 Elemental Analyzer.
2
−1
Synthesis of L . 12.8 g (37.64 mmol, 340.06 g mol ) of 1,2-bis(2-
46
bromophenyl)ethane was dissolved in 40 mL of Et O, and 47.05 mL
of BuLi 1.6 M (75.28 mmol) was added dropwise to the cooled
2
n
CONCLUSIONS
New palladium(0) and palladium(II) complexes supported by
solution. After stirring for 3 h at −78 °C, the conversion to the
■
corresponding dilithiated species was complete. Then, 12 mL of
i
1
2
Pr PCl (75.28 mmol) was added dropwise to the stirring solution and
2
the bidentate ligands L and L and a rhodium(I) complex
2
1
allowed to react overnight. The volatiles were removed under reduced
supported by L were synthesized and characterized. While L
1
pressure and the residue was dissolved in CH Cl . The solution was
2 2
has a preference for cis coordination to palladium(II) (L PdCl ,
2
filtered through Celite and concentrated under reduced pressure. The
product was isolated after crystallization from this concentrated
1
L Pd(OAc) ), it is flexible enough to adopt a wide angle upon
2
1
coordination to palladium(0) (L Pd(dba)), as a response to the
CH Cl2 solution at −35 °C. The reaction afforded 1,2-bis(2-
2
geometry enforced by the oxidation state of the metal. In
2
(
diisopropylphosphanyl)phenyl)ethane (L ) in 94% yield, 15.6 g
(35.38 mmol, 414.55 g mol ). Analytically pure L was obtained by
2
−1
2
contrast, L exhibits a strong preference for trans coordination
to palladium(II) and leads to square planar complexes
recrystallization from a saturated CH Cl solution at −35 °C, in 87%
2
2
8
523
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
2
−1
1
yield, producing 12.76 g of L (30.78 mmol, 4140.55 g mol ). H
MHz, C D ) δ 145.00 (t, J = 6.9 Hz, ArC), 133.41 (t, JCP = 18.7 Hz,
6
6
CP
NMR (300 MHz, C D ): δ 7.62 (ddd, J = 10.0, JHH = 5.5, JHH = 1.9
ArC), 131.67 (t, JCP = 3.9 Hz, ArC), 130.98 (s, ArC), 130.25 (s, ArC),
6
6
HP
Hz, 2H, ArH), 7.41−7.36 (m, 2H, ArH), 7.21 (td, J = 9.9 Hz, JHH
=
125.89 (t, JCP = 3.1 Hz, ArC), 40.51 (t, JCP = 4.3 Hz, −CH −), 26.56
HP
2
2
.1 Hz, 2H, ArH), 7.13 (td, J = 9.9, J = 2.1 Hz, 2H, ArH), 3.69 (t,
(t, JCP = 10.4 Hz, −CH(CH ) ), 24.14−23.83 (m, −CH(CH ) ), 19.25
HP
HH
3
2
3 2
3
1
JHP = 1.7 Hz, 4H, −CH −CH −), 2.02 (heptd, J = 9.3 Hz, JHH = 3.0
(d, JCP = 6.35 Hz, −CH(CH ) ), 19.03 (s, −CH(CH ) ). P NMR
2
2
HP
3
2
3 2
+
Hz, 4H, −CH(CH ) ), 1.17 (dd, J = 19.8, 9.3 Hz, 6H, −CH(CH ) ),
(121 MHz, C D ): δ 28.64 (s). MS (QTOF) m/z: C H P Pd ,
3
2
3
2
6 6 26 41 2
13
−
0
.98 (dd, J = 15.4, 9.3 Hz, 6H, −CH(CH ) ). C NMR (75 MHz,
C D ): δ 149.81 (d, J = 26.0 Hz, ArC), 134.52 (d, J = 20.0 Hz,
519.13 (expected 519.67, loss Cl and HCl). Anal. Calcd for
C H Cl P Pd: C, 52.76; H, 6.81. Found: C, 52.55; H, 6.64.
3
2
6
6
CP
CP
26 40
2 2
1
ArC), 132.79 (d, J = 3.0 Hz, ArC), 130.21 (m, Ar, ArC), 129.21 (s,
Synthesis of L Pd(OAc) . In a 20-mL scintillation vial, 240 mg of
CP
2
L1 (C H P , 400.53 g mol , 0.60 mmol) was dissolved in a
−1
CH, ArC), 125.88 (s, CH, ArC), 38.20 (dd, JCP = 2.53, 23.12 Hz,
25
38 2
−
CH −CH −), 24.82 (d, J = 13.8 Hz, −CH(CH ) ), 20.70 (d, J
=
minimum amount of THF and left stirring for 5 min at RT.
2
2
CP
3
2
CP
2
0.2 Hz, −CH(CH ) ), 19.75 (d, J = 10.9 Hz, −CH(CH ) ), 16.21
Independently, 131 mg of Pd(OAc) (98% purity, 0.57 mmol, 224.51
3
2
CP
3
2
2
3
1
−1
(s, −CH(CH ) ), 15.07 (d, J = 3.2 Hz, −CH(CH ) ). P NMR
(121 MHz, C D ) δ −6.81.
g mol ) was suspended in THF and stirred for 5 min prior to addition
to the L solution. The reaction turns yellow within 5 min (the
Pd(OAc) suspension is orange and the L solution is colorless) and
3
2
CP
3 2
1
6
6
1
1
1
Synthesis of L PdCl . In a 20-mL scintillation vial, 240 mg of L
2
2
−
1
(
C H P , 400.53 g mol , 0.60 mmol) was dissolved in a minimum
aliquots of the reaction mixture show that the reaction is complete
25
38 2
1
31
1
amount of THF and left stirring for 5 min at room temperature (RT).
after 2 h (by H and P NMR). The slight excess of L used (5%) was
removed at the end of the reaction by n-pentane trituration (3 times)
and removal of the n-pentane solution. After removal of the volatiles
−1
Independently, 165 mg of Pd(COD)Cl (99% purity, 285.51 g mol ,
2
0.57 mmol) was suspended in THF and stirred for 2 min prior to
1
1
addition to the L solution. The reaction turns yellow within 15 min
and aliquots of the reaction mixture show that the reaction is complete
after 2 h (by H and P NMR). The slight excess of L used (5%) was
removed at the end of the reaction by n-pentane trituration (3 times)
and removal of the n-pentane solution. After removing the volatiles
under reduced pressure, 331 mg L Pd(OAc) (C H O P Pd, 0.53
mmol 625.03 g mol ) was obtained in 93% yield. Recrystallization of
L Pd(OAc)2 can be achieved by layering a saturated CH Cl or
2
29 44
4 2
−
1
1
31
1
1
2
2
toluene solution with a small amount of n-pentane at −35 °C, in 76%
1
yield. This method allowed growing single crystals. H NMR (300
1
under reduced pressure for 1 h, 326 mg of L PdCl (C H Cl P Pd,
MHz, C D ): δ 8.04 (dt, J = 14.9, 2.3 Hz, 1H, backbone −CH(H)-,
2
25 38
2
2
6
6
−1
1
5
77.85 g mol , 0.56 mmol) was obtained in 99% yield. L PdCl is
endo), 7.15−7.07 (m, 2H, ArH), 6.97 (td, J = 7.3, 1.9 Hz, 4H, ArH),
6.83 (t, J = 7.4 Hz, 2H, ArH), 3.89 (d, J = 15.0 Hz, 1H, backbone
−CH(H)−, exo), 3.09−2.74 (m, 2H, −CH(CH ) ), 2.14 (s, 6H,
2
insoluble in n-pentane, so trituration led to no product loss.
1
Recrystallization of L PdCl can be performed by layering a saturated
CH Cl solution with a small amount of n-pentane at −35 °C, in 86%
yield. H NMR (400 MHz, CD Cl ): δ 7.59 (t, J = 6.3 Hz, 2H,
2
3 2
2
2
−CH COO), 1.67 (dd, J = 16.2, 7.0 Hz, 6H, −CH(CH ) ), 1.30 (d, J
3
3 2
1
2
2
HP
= 3.1 Hz, 2H, −CH(CH ) ), 1.17 (dd, J = 14.0, 5.4 Hz, 6H,
3 2
ArH), 7.56 (dd, JHP = 5.9, JHH = 3.5 Hz, 2H, ArH), 7.50 (t, JHP = 6.0
Hz, 2H, ArH), 7.39 (tt, JHP = 6.0, JHH = 1.1 Hz, 2H, ArH), 6.95 (dt,
JHH = 11.9, JHP = 2.1 Hz, endo backbone −CH −), 4.11 (d, J = 11.9
−CH(CH ) )), 1.05 (dd, J = 16.5, 7.0 Hz, 6H, −CH(CH ) )), 0.67
3
2
3 2
13
(d, J = 8.0 Hz, 6H, −CH(CH ) ). C NMR (75 MHz, CDCl ): δ
176.74 (s, CH COO), 145.83 (d, J = 11.8 Hz, ArC), 133.00 (d, JCP
3
2
3
2
HH
3
CP
=
Hz, exo backbone −CH −), 3.79 (dq, J = 11.6, 5.8 Hz, 2H,
8.2 Hz, ArC), 131.70 (s, ArC), 131.07 (d, JCP = 2.0 Hz, ArC), 127.37
(d, JCP = 38.3 Hz, ArC), 125.85 (d, JCP = 6.6 Hz, ArC), 42.66 (t, JCP
10.1 Hz, backbone −CH −), 25.61 (d, J = 28.6 Hz, −CH(CH ) ),
2
−
CH(CH ) ), 2.08−1.61 (br s, 2H, −CH(CH ) ), 1.57 (dd, J = 12.2,
=
3
2
3 2
5
.7 Hz, 6H, −CH(CH ) ), 1.44 (d, J = 6.6 Hz, 6H, −CH(CH ) ), 1.36
3
2
3
2
2
CP
3 2
(
dd, J = 14.0, 5.2 Hz, 6H, −CH(CH ) ), 0.92 (br s, 6H, −CH(CH ) ).
24.65 (d, J = 24.1 Hz, −CH(CH ) ), 24.03 (s, −CH(CH ) ), 20.75
3
2
3
2
CP
3
2
3 2
1
3
C NMR (75 MHz, CD Cl ): δ 145.44 (d, J = 12.28 Hz, ArC),
(s, CH COO), 20.68 (s, −CH(CH ) ), 19.84 (s, −CH(CH ) ), 19.45
2
2
CP
3
3
2
3 2
31
1
1
41.37 (br s, ArC), 133.37 (d, JCP = 8.1 Hz, ArC), 131.90 (s, ArC),
31.55 (d, JCP = 1.7 Hz, ArC), 126.98 (d, JCP = 6.5 Hz, ArC), 44.09 (t,
(s, −CH(CH ) ). P NMR (121 MHz, C D ): 34.62 (br s). MS
3 2 6 6
(QTOF) m/z: C25H P Pd , 505.12 (loss AcO , AcOH, expected
+
−
39 2
JCP = 10.4 Hz, backbone −CH −), 29.32 (s, −CH(CH ) ), 28.90 (s,
505.00). Anal. Calcd for C29
H
44
O
P
4
2
Pd: C, 55.73; H, 7.10. Found: C,
2
3 2
−
CH(CH ) ), 25.55 (d, J = 2.1 Hz, −CH(CH ) ), 25.25 (d, J
=
55.02; H, 7.02.
Synthesis of L Pd(OAc)
3
2
CP
3
2
CP
2
0
.9 Hz, −CH(CH ) ), 21.50 (br s, −CH(CH ) ), 21.33 (d, J = 2.9
2
. In a 20-mL scintillation vial, 248 mg of
3
2
3
2
CP
L2 (C26
H
P
, 414.55 g mol , 0.60 mmol) was dissolved in a
minimum amount of THF and left stirring for 15 min at RT.
Independently, 131 mg of Pd(OAc) (98% purity, 0.57 mmol, 224.51
g mol ) was suspended in THF and stirred for 5 min prior to addition
−1
Hz, −CH(CH ) ), 20.83 (d, J = 1.4 Hz, −CH(CH ) ). In H-coupled
40
2
3
2
CP
3 2
1
3
C, the backbone −CH − appears as a triplet at 44.05 ppm J
=
2
CH
31
1
25.95 Hz (spectrum taken on a Varian 300, 14 000 scans). P NMR
2
+
−1
(
121 MHz, CD Cl ): δ 38.47 (br s). MS (QTOF) m/z: C H P Pd ,
2 2 25 39 2
−
2
5
05.65 (expected 505.12, loss of −Cl and −HCl). Anal. Calcd for
to the L solution. The reaction turns yellow within 5 min (Pd(OAc)
2
2
C H Cl P Pd: C, 51.96; H, 6.63. Found: C, 52.08; H, 6.72.
suspension is orange, and the L solution is colorless, slightly turbid)
and aliquots of the reaction mixture show that the reaction is complete
2
5
38
2 2
2
2
Synthesis of L PdCl . In a 20-mL scintillation vial, 250 mg of L
2
2
−
1
1
31
2
(C H P , 414.55 g mol , 0.60 mmol) was dissolved in a minimum
after 2 h (by H and P NMR). The slight excess of L used (5%) was
6
40 2
amount of THF and left stirring for 5 min at RT. Independently, 132
removed at the end of the reaction by n-pentane trituration (3 times)
and removal of the n-pentane solution. After removal of the volatiles
−
1
mg of Pd(OAc) 98% (224.51 g mol , 0.59 mmol) was suspended in
2
2
2
THF and stirred for 2 min prior to dropwise addition to the L
under reduced pressure, 357 mg L Pd(OAc)
2
(C30
H
46
O
4
P
2
Pd, 0.53
−1
solution. The reaction turns yellow within 10 min and aliquots of the
mmol, 639.06 g mol ) was obtained in 98% yield. Recrystallization of
1
2
reaction mixture show that the reaction is complete after 2 h (by H
L Pd(OAc)
2
can be achieved by slow vapor diffusion of diethyl ether
and 31P NMR). The slight excess of L used (5%) was removed at the
end of the reaction by n-pentane trituration (3 times) and removal of
the n-pentane solution. After removal of the volatiles under reduced
2
or hexanes into a saturated toluene solution at −35 °C, in 86% yield.
1
H NMR (300 MHz, C D ): δ 7.38 (ddd, J = 7.6, 3.4, 1.7 Hz, 2H,
6 6
ArH), 7.23 (td, J = 7.3, 1.1 Hz, 2H, ArH), 7.13 (dtd, J = 4.8, 3.4, 1.5
Hz, 2H, ArH), 7.04 (t, J = 7.4 Hz, 2H, ArH), 5.41−5.26 (m, 2H,
−CH −, endo), 3.15−3.00 (m, 2H, −CH −, exo), 2.46 (dt, J = 13.8,
2
−1
pressure, 324 mg L PdCl2 (C H Cl P Pd, 591.87 g mol , 0.54
26
40
2 2
2
mmol) was obtained in 95% yield. Recrystallization of L PdCl was
achieved by layering a saturated toluene solution of L PdCl with n-
2
2
2
2
6.7 Hz, 2H, −CH(CH ) ), 2.29−2.15 (m, 2H, −CH(CH ) ), 1.91 (s,
2
3
2
3 2
pentane at −35 °C, in 81% overall yield. This method allowed growing
6H, CH COO−), 1.75 (dd, J = 16.1, 8.6 Hz, 6H, −CH(CH ) ), 1.42
3
3 2
1
single crystals. H NMR (300 MHz, C D ): δ 7.29 (dtd, J = 4.8, 3.9,
(dd, J = 14.7, 7.3 Hz, 6H, −CH(CH ) ), 0.94 (dd, J = 14.6, 7.3 Hz,
6
6
3 2
13
1
5
.0 Hz, 2H, ArH), 7.24−7.15 (m, 4H, ArH), 7.02−6.94 (m, 2H, ArH),
6H, −CH(CH ) ), 0.67 (dd, J = 12.7, 6.4 Hz, 6H, −CH(CH ) ). C
3
2
3 2
.23−5.07 (m, 2H, endo −CH − backbone), 3.20−3.01 (m, 2H,
NMR (75 MHz, C D ): δ 176.16 (s, CH COO−), 147.82 (t, J = 7.2
2
6
6
3
CP
−
CH(CH ) ), 3.04−2.89 (m, 2H, exo backbone −CH −), 2.77−2.60
Hz, ArC), 132.64 (s, ArC), 132.25 (t, J = 3.8 Hz, ArC), 130.49 (s,
3
2
2
CP
(
m, 2H, −CH(CH ) ), 1.83 (td, J = 9.8, 7.6 Hz, 6H, −CH(CH ) ),
ArC), 127.30 (t, JCP = 14.3 Hz, ArC), 125.70 (t, JCP = 2.7 Hz, ArC),
41.55 (t, JCP = 4.3 Hz, backbone −CH −), 24.41 (t, J = 10.1 Hz,
3
2
3 2
1
.25 (q, J = 7.5 Hz, 6H, −CH(CH ) ), 1.16 (dd, J = 13.1, 6.5 Hz, 6H,
3
2
2
CP
13
−
CH(CH ) ), 0.90 (q, J = 7.2 Hz, 6H, −CH(CH ) ). C NMR (75
−CH(CH ) ), 23.86 (s, −CH COO), 22.77 (t, J = 11.1 Hz,
3
2
3
2
3
2
3
CP
8
524
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
−
CH(CH ) ), 19.79 (s, −CH(CH ) ), 19.10 (m, −CH(CH ) ), 18.99
(dd, J = 15.1, 7.6 Hz, 4H, ArH), 7.00 (t, J = 7.3 Hz, 2H, ArH), 6.95 (d,
J = 4.5 Hz, 1H, −CHCH−CO coordinated, dba), 6.91−6.83 (m,
2H, ArH), 6.66 (d, J = 15.28 Hz, 1H, ArH), 6.63 (d, J = 3.8 Hz, 1H,
−CHCH-CO coordinated, dba), 4.85−4.77 (m,1H, backbone
−CH −), 4.73 (t, J = 11.2 Hz, 1H, backbone −CH −), 4.64−4.55
3
2
3
2
3 2
31
(
s, −CH(CH ) ), 16.94 (s, −CH(CH ) ). P NMR (121 MHz,
3
2
3 2
C D ): δ 18.31 (s). Anal. Calcd for C H O P Pd: C, 56.38; H, 7.26.
6
6
30 46
4 2
Found: C, 56.61; H, 7.16.
1
Synthesis of L Pd(dba). In a 20-mL scintillation vial, 240 mg of
2
2
1
−1
L (C H P , 400.53 g mol , 0.60 mmol) was dissolved in THF and
(m, 1H, backbone −CH −), 3.52 (dd, J = 14.5, 7.2 Hz, 1H, backbone
25
38
2
2
1
left stirring for 5 min at RT. Over the stirring L solution, 344 mg
Pd(dba) (0.60 mmol, 575.00 g mol ) suspended in THF were added
dropwise. The reaction turns dark orange and aliquots of the reaction
mixture show that the reaction is incomplete after 12 h (by H and
NMR). After an additional 24 h, the volatiles were removed under
reduced pressure and multiple triturations (hexanes and Et O) were
−CH −), 2.44−2.26 (m, 2H, −CH(CH ) ), 1.95−1.80 (m, 1H,
2
3 2
−1
−CH(CH ) ), 1.71 (dd, J = 18.1, 7.3 Hz, 3H, −CH(CH ) ), 1.33 (t, J
2
3
2
3 2
= 7.7 Hz, 3H, −CH(CH ) ), 1.22 (dd, J = 11.8, 5.6 Hz, 1H,
3
2
1
31
P
−CH(CH ) ), 1.05 (dd, J = 16.3, 6.9 Hz, 6H, −CH(CH ) ), 0.92 (dd,
3
2
3 2
J = 16.14, 6.65 Hz, 3H, −CH(CH ) ), 0.61 (dd, J = 16.76, 6.76 Hz,
3
2
3
1
6H, −CH(CH ) ), 0.45 (dd, J = 17.7, 6.6 Hz, 3H, −CH(CH ) ).
NMR (202 MHz, toluene-d , 260 K): δ 32.89 (br s), 19.48 (d, J
8.0 Hz). C NMR (101 MHz, toluene-d , 260 K): δ 186.10 (t, J
P
=
=
2
3
2
3 2
1
carried out to obtain L Pd(dba) in 53% yield (0.32 mmol, 234 mg).
8
PP
1
−1
13
L Pd(dba) (C H OP Pd, 741.23 g mol ) was crystallized from a
42
52
2
8
CP
toluene solution layered with diethyl ether. Traces of uncoordinated
dba could be observed by H NMR spectroscopy in the aryl region. H
4.1 Hz, CO), 149.25 (d, J = 15.0 Hz, ArC), 145.00 (d, JCP = 6.4
CP
1
1
Hz, ArC), 142.74 (d, J = 13.2 Hz, ArC), 142.51 (s, ArC), 141.84 (d,
CP
NMR (500 MHz, C D 279 K): δ 7.97 (d, J = 15.2 Hz, 1H, −CH
JCP = 12.9 Hz, ArC), 137.84 (s, ArC), 136.40 (s, ArC), 136.31 (d, JCP =
6
6,
CH−CO uncoordinated, dba), 7.48 (dd, J = 19.6, 6.5 Hz, 2H, ArH),
18.6 Hz, ArC), 135.01 (s, ArC), 132.55 (s, −CHCH−CO
uncoordinated, dba), 131.14 (s, −CHCH−CO uncoordinated,
dba), 130.90 (d, J = 16.1 Hz, ArC), 130.19 (d, J = 5.6 Hz,
7
.39 (s, 1H, ArH), 7.25−7.17 (m, 2H, ArH), 7.17−6.95 (m, 12H,
ArH), 6.93−6.86 (m, 1H, −CHCH−CO uncoordinated, dba),
.83−6.73 (m, 2H, backbone −CH(H)− and ArH), 5.36 (br s, 1H,
CHCH−CO coordinated, dba), 4.76 (br s, 1H, −CHCH−CO
CP
CP
6
−
-CHCH−CO coordinated, dba), 130.19−130.12 (m, ArC), 129.39
(s, ArC), 129.01 (s, ArC), 128.83 (s, ArC), 128.57 (s, ArC), 128.35 (s,
ArC), 128.09 (s, ArC), 127.99 (s, ArC), 127.73 (s, ArC), 126.73 (s,
ArC), 125.72 (s, ArC), 125.69 (s, ArC), 125.09 (d, JCP = 2.4 Hz, ArC),
124.49 (d, JCP = 2.4 Hz, −CHCH−CO coordinated, dba), 121.45
(s, ArC), 75.48 (dd, J = 16.8, J = 5.6 Hz, backbone −CH −), 64.74
coordinated, dba), 3.00 (d, J = 13.1 Hz, 1H, backbone −CH(H)−),
1
−
4
−
5
−
1
.88−1.78 (m, 1H, −CH(CH ) ), 1.54 (dd, J = 14.1, 5.0 Hz, 3H,
3
2
CH(CH ) ), 1.46−1.32 (m, 1H, −CH(CH ) ), 1.27 (dd, J = 16.3,
3
2
3 2
.9 Hz, 3H, −CH(CH ) ), 1.17 (dd, J = 16.5, 6.3 Hz, 3H,
3
2
CP
CP
2
CH(CH ) ), 1.13−1.07 (m, 3H, −CH(CH ) ), 1.01 (dd, J = 17.9,
(dd, JCP = 25.8, JCP = 2.6 Hz, backbone −CH −), 41.06 (d, J = 7.9
3
2
3
2
2
CP
.4 Hz, 3H, −CH(CH ) ), 0.86 (m, 1H, −CH(CH ) ),0.69 (s, 1H,
Hz, −CH(CH ) ), 38.20 (d, J = 18.7 Hz, −CH(CH ) ), 24.73 (dd,
3
2
3
2
3
2
CP
3 2
CH(CH ) ), 0.55 (t, J = 7.5 Hz, 3H, −CH(CH ) ), 0.25 (dd, J =
J
= 15.7, 7.0 Hz, −CH(CH ) ), 24.29 (d, J = 17.2 Hz,
3
2
3
2
CP
3
2
CP
6.4, 6.4 Hz, 3H, −CH(CH ) ), 0.10 (dd, J = 15.2, 6.3 Hz, 3H,
−CH(CH ) ), 21.55 (d, J = 15.8 Hz, −CH(CH ) ), 20.61 (s,
3
2
3
2
CP
3 2
31
−
6
CH(CH ) ). P NMR (162 MHz, C D , 279 K): δ 21.53 (d, J
.5 Hz), 20.69 (s, br). C NMR (126 MHz, C D , 279 K): δ 187.96
=
−CH(CH ) ), 19.77 (s, −CH(CH ) ), 19.66 (d, J = 9.5 Hz,
3
2
6
6
PP
3
2
3
2
CP
13
−CH(CH ) ), 19.16 (d, J = 6.3 Hz, −CH(CH ) ), 19.01 (d, J
=
6
6
3
2
CP
3
2
CP
(
1
dd, JCP = 2.21, 3.01 Hz, CO), 148.28 (d, J = 16.7 Hz, ArC),
7.3 Hz, −CH(CH ) ), 18.13 (d, J = 15.5 Hz, −CH(CH ) ), 15.43
CP
3
2
CP
3 2
47.55 (d, J = 16.9 Hz, ArC), 145.31 (d, J = 6.6 Hz, ArC), 142.64
(d, J = 7.1 Hz, −CH(CH ) ). Anal. Calcd for C H OP Pd: C,
CP
CP
CP
3
2
43 54
2
(
s, ArC), 137.92 (s, ArC); 136.90 (s, ArC), 133.26 (s, ArC), 132.59 (d,
68.38; H, 7.21. Found: C, 68.58; H, 7.20.
2
JCP = 10.4 Hz, ArC), 131.92 (d, JCP = 5.0 Hz, ArC), 131.51 (d, JCP
=
Synthesis of [L Rh(nbd)]BF . In a 20-mL scintillation vial, 33 mg
4
2
−1
5
.8 Hz, −CHCH−CO uncoordinated, dba), 130.48 (s, −CH
of L (C H P , 414.55 g mol , 0.08 mmol) was dissolved in a
26 40 2
CH−CO uncoordinated, dba),), 130.19 (s, ArC), 130.07 (d, J = 22.3
minimum amount of THF and cooled at −60 °C in the cold well.
CP
Hz, ArC), 129.22 (s, ArC), 128.97 (s, −CHCH−CO coordinated,
Independently, 30 mg of [Rh(nbd) ]BF (99% purity, 0.08 mmol, 375
2
4
−1
dba), 128.90 (d, J = 8.0 Hz, ArC), 128.73 (s, ArC), 128.66 (s, ArC),
g mol ) was suspended in THF and stirred for 5 min prior to addition
to the L solution. The color of the solution changed from orange-red
(suspension of Rh precursor is red) to light orange and finally yellow
CP
2
1
1
1
28.24 (s, ArC), 128.01 (s, ArC), 127.86 (s, ArC), 126.55 (s, ArC),
26.01 (s, ArC), 125.60 (s, ArC), 125.44 (s, ArC), 124.75 (s, ArC),
24.51 (s, ArC), 124.42 (s, −CHCH−CO coordinated, dba), 64.37
+
after stirring for 1 h and subsequent warming up to RT. Trituration
(
d, J = 24.0 Hz, backbone −CH −), 36.78 (dd, J = 18.2, 13.9 Hz,
with n-pentane was repeated twice in order to remove any impurities.
PC
2
CP
2
−
CH(CH ) ), 26.29 (dd, J = 12.3, 4.7 Hz, −CH(CH ) ), 25.05 (d,
After solvent removal and trituration, the [L Rh(nbd)]BF
3
2
CP
3
2
4
−
1
J
= 14.4 Hz, −CH(CH ) ), 23.72 (d, J = 16.6 Hz, −CH(CH ) ),
(C H BF P Rh, 50 mg, 696.39 g mol ) yield was 91%.
Recrystallization of [L Rh(nbd)]BF can be achieved by slow vapor
CP
3
2
CP
3
2
33 48 4 2
2
2
1.83 (d, J = 10.3 Hz, −CH(CH ) ), 20.11 (d, J = 6.4 Hz,
CP
3
2
CP
4
−
CH(CH ) ), 19.01 (d, J = 5.6 Hz, −CH(CH ) ), 18.91 (s,
diffusion of hexanes into a saturated CH Cl solution at −35 °C,
3
2
CP
3
2
2
2
1
−
CH(CH ) )), 18.80 (d, J = 6.9 Hz, −CH(CH ) ), 18.26 (d, J
=
isolated yield = 73%. H NMR (500 MHz, CD Cl ) δ 7.45−6.80 (m,
3
2
CP
3
2
CP
2
2
8
.8 Hz, −CH(CH ) ), 17.33 (d, J = 6.8 Hz, −CH(CH ) ), 16.01 (d,
10H, ArH 8H and 2H −CH(H)−CH(H)−), 5.07 (s, 4H, −CH−,
nbd), 4.05 (s, 2H, −CH−, nbd), 4.04−3.84 (m, 2H, −CH(H)−
CH(H)−), 3.52−2.96 (m, 2H, −CH(CH ) ), 2.84−2.44 (m, 2H,
3
2
CP
3 2
+
JCP = 7.2 Hz, −CH(CH ) ). MS (QTOF) m/z: C H P Pd , 507.12
3
2
25 39 2
(
expected 507.57, loss of dba). Anal. Calcd for C H OP Pd: C,
42 52 2
3 2
6
8.06; H, 7.07. Found: C, 67.98; H, 6.93.
−CH(CH ) ), 2.40−2.00 (m, 2H, −CH −, nbd), 1.85−1.65 (m, 3H,
3
2
2
2
Synthesis of L Pd(dba). In a 20-mL scintillation vial, 248 mg of
−CH(CH ) ), 1.45 (s, 9H, −CH(CH ) ), 1.17−0.89 (m, 6H,
3
2
3 2
L2 (C H P , 414.55 g mol , 0.60 mmol) was dissolved in a
−1
−CH(CH ) ), 0.83−0.41 (m, 6H, −CH(CH ) ). C NMR (126
13
26
40
2
3
2
3 2
minimum amount of THF and left stirring for 5 min at RT. 344 mg
MHz, CD Cl ): δ 144.28 (s, ArC), 132.50 (s, ArC), 130.74 (s, ArC),
2 2
−
1
Pd(dba) (0.60 mmol, 575.00 g mol ) suspended in THF was added
130.46 (s, ArC), 127.39 (s, ArC), 126.37 (s, ArC), 72.69 (s, nbdC),
70.83 (s, nbdC), 68.31 (s, nbdC), 52.29 (s, nbdC), 36.14 (s, backbone
−CH −CH −), 23.70 (d, J = 18.8 Hz, −CH(CH ) ), 21.74 (s,
2
2
dropwise to the stirring L solution. The reaction turns dark orange
and aliquots of the reaction mixture show that the reaction is
2
2
CP
3 2
1
31
incomplete after 12 h (by H and P NMR). After an additional 24 h,
−CH(CH ) ), 20.94 (s, −CH(CH ) ), 20.48 (s, −CH(CH ) ), 20.13
3
2
3
2
3 2
31
the volatiles were removed under reduced pressure and multiple
(s, −CH(CH ) ), 17.77 (s, −CH(CH ) ). P NMR (202 MHz,
3
2
3 2
2
19
triturations (hexanes and Et O) were carried out to obtain L Pd(dba)
CD Cl ) δ 21.98 (d, J = 119.6 Hz). F NMR (471 MHz, CD Cl )
2
2 2 RhP 2 2
2
+
in 42% yield (0.25 mmol, 186 mg). L Pd(dba) (C H OP Pd, 755.26
δ −158.76 (s). MS (QTOF) m/z: C H P Rh , 609.20 (expected
− +
43
54
2
33 48 2
−1
g mol ) was crystallized from a toluene solution layered with diethyl
609.22, loss of BF ); C H P Rh , 517.00 (expected 517.16,
4 26 40 2
1
ether. Traces of uncoordinated dba could be observed by H NMR
additional loss of nbd ligand). Anal. Calcd for C H BF P Rh·
33 48 4 2
1
spectroscopy in the aryl region. The room temperature H NMR was
0.5CH Cl : C, 54.82, H, 6.63. Found: C, 54.70, H, 6.59.
2 2
1
1
1
broad in C D . H NMR (400 MHz, toluene-d , 260 K) δ 7.80−7.74
Synthesis of [L Pd] . To a solution of 58 mg of L PdCl
2 2
1
6
6
8
−
(
1
m, 1H, −CHCH−CO uncoordinated, dba), 7.42 (t, J = 7.6 Hz,
(C H Cl P Pd, MW: 577.85 g mol , 0.10 mmol) in THF, a
25 38 2 2
H, −CHCH−CO uncoordinated, dba), 7.37 (d, J = 7.2 Hz, 2H,
suspension of Mg (6 mg, 250% of the stoichiometric amount, 0.25
mmol) in THF was added at ambient temperature and stirred
ArH), 7.25 (d, J = 7.5 Hz, 2H, ArH), 7.21−7.11 (m, 5H, ArH), 7.06
8
525
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
overnight. The reaction mixture turned orange-gray; then, it was
filtered over Celite and the volatiles were removed under reduced
pressure. The same product could be obtained from the reaction of
ArH), 7.30−7.18 (m, 4H, ArH), 7.14−7.07 (m, 1H, ArH), 6.90 (ddd, J
= 8.8, 4.8, 1.1 Hz, 1H, ArH), 6.74 (t, J = 7.4 Hz, 1H, Ar), 6.10 (d, J =
8.5 Hz, 1H, ArH), 4.56 (t, J = 12.1 Hz, 1H, −CH(H)−CH −), 4.11
2
1
L PdCl with 1.5 or 2 equiv Li[(C H ) BH] at low temperature (−80
(m, 1H, −CH(H)−CH(H)−), 3.68−3.52 (m, 1H, −CH(CH ) ),
2
2
5
3
3 2
°
C) for 4 h and allowing the reaction mixture to warm up to RT,
3.38−3.26 (m, 1H, −CH(CH ) ), 2.90 (td, J = 12.5, 6.8 Hz, 1H,
3
2
followed by a similar workup. Using 1 equiv of Li(C H ) BH, the
−CH(H)−CH(H)−), 2.80 (td, J = 12.8, 6.7 Hz, 1H, −CH(H)−
CH −), 1.81 (dd, J = 20.3, 7.4 Hz, 3H, −CH(CH ) ), 1.76 (d, J = 3.3
2
5 3
1
major product (65% by NMR spectroscopy) is still [L Pd] , but there
is evidence of an unsymmetrical side-product (2 doublets in the
2
2
3 2
31
P
Hz, 1H, −CH(CH ) ), 1.48 (dd, J = 15.9, 7.2 Hz, 3H, −CH(CH ) ),
3
2
3 2
NMR spectrum). The orange powder was washed three times with n-
pentane, and the volatiles were removed under reduced pressure. The
product was recrystallized from a saturated n-pentane solution in 74%
1.36−1.24 (m, 4H, −CH(CH ) and −CH(CH ) ), 1.15 (ddd, J =
3
2
3 2
10.0, 7.3, 0.8 Hz, 3H, −CH(CH ) ), 1.00−0.91 (m, 3H, −CH-
3
2
(CH ) ), 0.71 (ddd, J = 12.3, 7.5, 1.2 Hz, 3H, −CH(CH ) ), 0.37−
3
2
3 2
1
yield, as an orange crystalline powder. H NMR (300 MHz, C D ): δ
0.29 (m, 3H, −CH(CH ) ), 0.22 (dd, J = 14.4, 7.2 Hz, 3H,
6
6
3 2
13
7
1
2
1
−
.36 (s, 2H, backbone −CH −), 7.27 (m, 4H, ArH), 7.06 (td, J = 7.6,
−CH(CH ) ). C NMR (101 MHz, C D ) δ 165.67 (dd, J = 6.2,
2
3
2
6
6
CP
.2 Hz, 2H, ArH), 6.97 (td, J = 7.5, 1.3 Hz, 2H, ArH), 2.24−2.10 (m,
2.5 Hz, ArC), 145.55 (t, J = 1.8 Hz, ArC), 144.77 (d, JCP = 12.3 Hz,
CP
H, −CH(CH ) ), 2.06−1.93 (m, 2H, −CH(CH ) ), 1.49 (dd, J =
ArC), 143.04 (d, JCP = 12.5 Hz, ArC), 138.49 (dd, JCP = 5.1, 2.0 Hz,
ArC), 136.30 (d, JCP = 1.3 Hz, ArC), 135.85 (dd, JCP = 4.6, 3.0 Hz,
ArC), 131.72 (d, JCP = 7.6 Hz, ArC), 131.57 (s, ArC), 131.53 (s, ArC),
131.24 (s, ArC), 130.74 (d, JCP = 7.6 Hz, ArC), 130.59 (d, JCP = 2.4
Hz, ArC), 130.35 (d, JCP = 1.7 Hz, ArC), 129.82 (d, JCP = 1.8 Hz,
ArC), 126.06 (dd, JCP = 18.3, 5.5 Hz, ArC), 121.26 (s, ArC), 118.79 (s,
ArC), 40.33 (d, JCP = 11.8 Hz, −CH −CH −), 38.61 (d, J = 9.6 Hz,
3
2
3
2
5.6, 7.0 Hz, 6H, −CH(CH ) ), 1.28 (ddd, J = 14.2, 13.8, 6.9 Hz, 12H,
3
2
13
CH(CH ) ), 0.79 (dd, J = 15.0, 7.0 Hz, 6H, −CH(CH ) ).
NMR (101 MHz, C D ): δ 151.60 (t, J = 9.0 Hz, ArC), 134.40 (t,
C
3
2
3 2
6
6
CP
JCP = 11.1 Hz, ArC), 132.88 (t, JCP = 2.6 Hz, ArC), 131.90 (s, ArC),
29.27 (s, ArC), 125.18 (t, JCP = 1.8 Hz, ArC), 43.11 (t, JCP = 11.4 Hz,
backbone −CH -), 28.68 (t, J = 7.5 Hz, −CH(CH ) ), 27.73 (t, J
1
2
CP
3
2
CP
2
2
CP
=
8.3 Hz, −CH(CH ) ), 22.59 (t, J = 7.2 Hz, −CH(CH ) ), 22.06
−CH −CH −), 29.03 (dd, J = 17.8, 4.3 Hz, −CH(CH ) ), 27.39
3
2
CP
3
2
2
2
CP
3 2
(
t, J = 6.4 Hz, −CH(CH ) ), 21.39 (t, J = 3.5 Hz, −CH(CH ) ),
(dd, J = 16.3, 2.6 Hz, −CH(CH ) ), 25.96 (dd, J = 18.4, 3.6 Hz,
CP
3
2
CP
3
2
CP
3
2
CP
31
2
2
5
1.09 (t, JCP = 4.3 Hz, −CH(CH ) ). P NMR (121 MHz, C D ): δ
−CH(CH ) ), 24.91 (d, J = 13.5 Hz, −CH(CH ) ), 23.61 (dd, J
=
3
2
6
6
3
2
CP
3
2
CP
8.88 (s). Anal. Calcd for C H P Pd : C, 59.23; H, 7.56. Found: C,
9.18; H, 7.48.
Synthesis of L Pd. To a THF solution of L PdCl (59 mg, 591.87
17.2, 3.1 Hz, −CH(CH ) ), 22.98 (d, J = 10.6 Hz, −CH(CH ) ),
50
76
4
2
3
2
CP
3 2
20.38 (s, −CH(CH ) ), 20.14 (dd, J = 6.4, 2.9 Hz, −CH(CH ) ),
3
2
CP
3 2
2
2
2
19.67 (dd, J = 3.2, 2.0 Hz, −CH(CH ) ), 19.41 (dd, J = 5.4, 3.0
CP
3
2
CP
−1
g mol , 0.10 mmol, C H Cl P Pd), a suspension of 6 mg of Mg in
Hz, −CH(CH ) ), 18.98 (dd, J = 6.0, 2.8 Hz, −CH(CH ) ), 17.70
26
40
2
2
3
2
CP
3 2
31
THF (0.25 mmol) was added dropwise at ambient temperature and
the mixture was stirred overnight. The solution turned gray-yellow and
it was filtered through a plug of Celite. The solution obtained was light
gray-yellow, and the volatiles were removed under reduced pressure.
After successive washings with n-pentane in order to remove traces of
THF, the product was recrystallized from a saturated n-pentane
(s, −CH(CH ) . P NMR (162 MHz, C D ) δ 28.55 (d, J = 399.6
3
2
6
6
PP
Hz), 21.23 (d, J = 399.5 Hz). Anal. Calcd for C H BrNO P Pd: C,
PP
32 44
2 2
53.16; H, 6.13; N 1.94. Found: C, 53.24; H, 6.19; N 1.906. 9
Representative Procedure for Suzuki Couplings. Cs CO
2
3
(196 mg, 0.6 mmol), phenylboronic acid (367 mg, 0.3 mmol),
bromoacetophenone (40 mg, 0.2 mmol), 1 mol % (relative to aryl
halide) of the Pd precatalyst, and the internal standard 1,3,5-
trimethoxybenzene (34 mg, 0.2 mmol) in 1,4-dioxane (1.4 mL)
were added to a flask equipped with a stir bar, under nitrogen
2
solution, affording L Pd as off-gray crystals (C H P Pd, 520.92 g
26
40 2
−1
2
mol , 52 mg) in 89% yield. Reaction of L PdCl with 1−2 equiv
2
Li(C H ) BH (−80 °C, 4 h) leads to the same product, in 83% yield.
2
5 3
1
H NMR: (300 MHz, C D ) δ 7.32−7.17 (m, 6H, ArH), 7.08 (td, J =
atmosphere. The solution was heated with stirring at 100 °C under N
6
6
2
1
7
.4, 1.5 Hz, 2H, ArH), 5.95−5.80 (m, 2H, backbone −CH −, endo),
for the specified period of time. After cooling, a H NMR spectrum of
2
2
.65−2.49 (m, 2H, backbone −CH −, exo), 2.18−2.06 (m, 2H,
the reaction mixture was acquired in CDCl . The yield was computed
2
3
1
−
CH(CH ) ), 1.98 (dt, J = 14.1, 7.0 Hz, 2H, −CH(CH ) ), 1.40 (dd,
as an average of two runs determined by H NMR spectroscopy using
3
2
3 2
J = 17.1, 6.8 Hz, 6H, −CH(CH ) ), 1.25 (dt, J = 14.6, 7.3 Hz, 12H,
an internal standard; only the trans isomer was observed. No increase
in yield was observed when the reaction mixture was stirred for longer
times.
3
2
13
−
CH(CH ) ), 0.83 (dd, J = 11.9, 6.7 Hz, 6H, −CH(CH ) ).
C
3
2
3 2
NMR: (75 MHz, C D ): δ 149.37 (t, J = 8.9 Hz, ArC), 132.59 (s,
6
6
CP
70
n
ipso, ArC), 132.53 (s, ArC), 132.16 (t, JCP = 3.3 Hz, ArC), 129.36 (s,
ArC), 125.68 (t, JCP = 1.8 Hz, ArC), 41.58 (t, JCP = 7.1 Hz, backbone
Representative Procedure for Heck Couplings.
Bu NBr
4
(13 mg, 0.041 mmol) and K CO (64 mg, 0.46 mmol), 1-bromo-4-
2
3
−
−
−
CH −), 28.44 (t, J = 7.0 Hz, −CH(CH ) ), 24.19 (t, J = 8.4 Hz,
nitrobenzene (84 mg, 0.41 mmol), and a 0.5 mL solution of 0.1 mol %
(relative to the aryl halide) Pd precatalyst in dimethylacetamide
(DMA), n-butyl acrylate (105.6 mg, 0.82 mmol), and the internal
standard (1,3,5-trimethoxybenzene, 69 mg, 0.41 mmol, as a 1.5 mL
2
CP
3
2
CP
CH(CH ) ), 21.67−21.36 (m, −CH(CH ) ), 21.24 (t, J = 5.9 Hz,
3
2
3
2
CP
31
CH(CH ) ), 18.31 (s, −CH(CH ) ). P NMR (121 MHz, C D ):
3
2
3
2
6
6
2
9.85 (s). Anal. Calcd for C H P Pd: C, 59.94; H, 7.74. Found: C,
26 40 2
5
9.61; H, 7.70.
Synthesis of L Pd(p-C H −NO )Br. 52 mg of L Pd (C H P Pd,
solution in DMA) were combined. The mixture was stirred under N
2
2
2
1
6
4
2
26 40 2
at 140 °C for the specified time. After cooling, a H NMR spectrum of
−1
5
20.97 g mol , 0.10 mmol) were mixed in toluene with 20 mg of 1-
the reaction mixture was acquired in CDCl . The yield was computed
3
−1
1
bromo-4-nitrobenzene (C H BrNO , 202.01 g mol , 0.10 mmol) and
stirred for 2 h at RT. The workup consisted solely of solvent removal
as an average of two runs determined by H NMR spectroscopy using
6
4
2
an internal standard; only the trans isomer was observed. No increase
in yield was observed when the reaction mixture was stirred for longer
times.
1
under reduced pressure and trituration with n-pentane. The H and
3
1
P NMR spectra showed the product to be pure. After
recrystallization out of a concentrated toluene solution layered with
X-ray Crystallography. The diffraction experiments were carried
out on a Bruker AXS SMART CCD three-circle diffractometer with a
sealed tube using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). The crystals were mounted on a plastic loop and used for
the diffraction experiments. Anisotropic thermal parameters were
refined for all non-hydrogen atoms. The hydrogens were placed
according to a riding model. Details of the crystal structures and
refinement data for complexes 1−10 are given in the Supporting
Information.
2
n-pentane, 62 mg of L PdBr(C H NO ) (C H BrNO P Pd, 722.98 g
6
4
2
32 44
2 2
−1
mol , 0.08 mmol) were isolated in 86% overall yield. This method
also afforded X-ray-quality crystals. A control experiment was also
carried out in order to follow the ligand dynamics during the oxidative
addition process. After 5 min, the conversion was found to be already
1
31
8
6%. The reaction was monitored by H and P spectroscopy, and
spectra were recorded every 15 min, up to 1 h when the reaction was
found to be virtually complete. Conversion: 86% (5 min); 95% (15
min); 96% (30 min); 97% (45 min); 98% (60 min). No intermediates
were observed throughout the experiment. 1H NMR (400 MHz,
C D ) δ 7.99 (dt, J = 8.5, 1.7 Hz, 1H, Ar), 7.75 (dd, J = 8.5, 2.7 Hz,
2
X-ray Crystal Structure of L . Single crystals were obtained as
colorless blocks from a concentrated n-pentane solution at −35 °C in
2
the glovebox. Crystal and refinement data for L : C H P ; M =
6
6
26 40
2
r
1H, ArH), 7.53 (dd, J = 8.5, 2.7 Hz, 1H, ArH), 7.43 (t, J = 7.4 Hz, 1H,
̅
414.52; triclinic; space group P1; a = 7.1305(9) Å; b = 7.2635(9) Å; c
8
526
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
−
−3
=
=
12.7304(17) Å; α = 88.779(2)°; β = 78.166(2)°; γ = 72.008(2)°; V
for all 8880 data. Residual electron density (e Å ) max/min: 0.254/
3
613.14(14) Å ; Z = 1; T = 100(2) K; λ = 0.71073 Å; μ = 0.187
−0.294.
−1
−3
2
mm ; d = 1.123 g cm ; 12 575 reflections collected; 2158 unique
X-ray Crystal Structure of [L Rh(nbd)]BF
4
. Single crystals were
calc
(
>
Rint = 0.0235); giving R = 0.0271, wR = 0.0706 for 2056 data with [I
obtained as yellow blocks from a concentrated DCM solution at −35
1
2
2
2σ(I)] and R = 0.0288, wR = 0.0721 for all 2158 data. Residual
°C in the glovebox. Crystal and refinement data for [L Rh(nbd)]BF
:
4
1
2
−
−3
electron density (e Å ) max/min: 0.366/−0.174.
C
33
H
48BF
4
P
2
Rh; M = 696.37; orthorhombic; space group Pbca; a =
r
1
X-ray Crystal Structure of L PdCl . Single crystals were obtained
17.0147(14) Å; b = 17.9627(15) Å; c = 20.3387(17) Å; α = 90°; β =
2
3
as yellow blocks from a concentrated dichloromethane (DCM)
solution layered with n-pentane at −35 °C in the glovebox. Crystal and
refinement data for L PdCl : C H Cl P Pd; M = 577.79;
90°; γ = 90°; V = 6216.1(9) Å ; Z = 8; T = 120(2) K; λ = 0.71073 Å; μ
−1
−3
= 0.699 mm ; dcalc = 1.488 g cm ; 52 131 reflections collected; 6222
1
unique (Rint = 0.0528); giving R = 0.0275, wR = 0.0588 for 4932 data
1
2
2
25 38
2
2
r
with [I > 2σ(I)] and R = 0.0437, wR = 0.0641 for all 6222 data.
monoclinic; space group P2(1)/n; a = 10.3224(8) Å; b =
5.9598(13) Å; c = 16.8281(14) Å; α = 90°; β = 102.4370(10)°; γ
1
2
−
−3
Residual electron density (e Å ) max/min: 0.659/−0.357.
X-ray Crystal Structure of [L Pd] . Single crystals were obtained
1
=
1
1
3
90°; V = 2707.3(4) Å ; Z = 4; T = 120(2) K; λ = 0.71073 Å; μ =
2
−1
−3
as red blocks from a concentrated n-pentane solution at −35 °C in the
.012 mm ; d = 1.418 g cm ; 34 014 reflections collected; 4763
calc
1
glovebox. Crystal and refinement data for [L Pd] : C H P Pd ; M =
unique (Rint = 0.0829); giving R = 0.0532, wR = 0.0866 for 4048 data
with [I > 2σ(I)] and R = 0.0687, wR = 0.0903 for all 4763 data.
Residual electron density (e Å ) max/min: 0.589/−0.686.
2
50 76
4
2
r
1
2
1
013.79; monoclinic; space group P2/n; a = 19.7619(12) Å; b =
1
2
−
−3
13.7004(9) Å; c = 19.9613(13) Å; α = 90°; β = 112.3640(10)°; γ =
3
1
90°; V = 4997.9(6) Å ; Z = 4; T = 120(2) K; λ = 0.71073 Å; μ = 0.879
X-ray Crystal Structure of L Pd(OAc) . Single crystals were
2
−1
−3
mm ; d = 1.347 g cm ; 62 041 reflections collected; 8823 unique
calc
obtained as yellow blocks from a concentrated DCM solution layered
with n-pentane at −35 °C in the glovebox. Crystal and refinement data
for L Pd(OAc) : C H Cl O P Pd; M = 709.91; monoclinic; space
group P2(1)/n; a = 9.3254(11) Å; b = 11.7802(13) Å; c = 30.612(4)
Å; α = 90°; β = 91.014(2)°; γ = 90°; V = 3362.4(7) Å ; Z = 4; T =
1
6
0
(
Rint = 0.0957); giving R = 0.0610, wR = 0.1128 for 6320 data with [I
1 2
1
> 2σ(I)] and R = 0.0927, wR = 0.1250 for all 8823 data. Residual
1 2
2
30 46
2
4
2
r
−
−3
electron density (e Å ) max/min: 3.044/−2.222.
2
3
X-ray Crystal Structure of L Pd. Single crystals were obtained as
−1
−3
gray blocks from a concentrated n-pentane at −35 °C in the glovebox.
20(2) K; λ = 0.71073 Å; μ = 0.837 mm ; d = 1.402 g cm ; 36
calc
2
Crystal and refinement data for L Pd: C H P Pd; M = 520.92;
26
40
2
r
69 reflections collected; 5908 unique (Rint = 0.0582); giving R =
1
monoclinic; space group P2(1)/c; a = 11.089(3) Å; b = 14.971(4) Å; c
.0320, wR = 0.0637 for 4685 data with [I > 2σ(I)] and R = 0.0496,
2
1
3
−
−3
= 15.505(4) Å; α = 90°; β = 102.693(4)°; γ = 90°; V = 2511.2(12) Å ;
wR = 0.0674 for all 5908 data. Residual electron density (e Å )
max/min: 0.384/−0.408.
−1
2
Z = 4; T = 120(2) K; λ = 0.71073 Å; μ = 0.877 mm ; d = 1.378 g
calc
−3
cm ; 33 869 reflections collected; 4417 unique (R = 0.0321); giving
2
int
X-ray Crystal Structure of L PdCl . Single crystals were obtained
2
R = 0.0212, wR = 0.0563 for 4120 data with [I > 2σ(I)] and R =
1
2
1
as yellow blocks from a concentrated toluene solution at −35 °C in the
glovebox. Crystal and refinement data for L PdCl : C H Cl P Pd; M
=
1
V = 2657.7(4) Å ; Z = 4; T = 120(2) K; λ = 0.71073 Å; μ = 1.032
mm ; d = 1.479 g cm ; 27 106 reflections collected; 4677 unique
−
0
.0235, wR = 0.0575 for all 4417 data. Residual electron density (e
2
2
2
26 40
2
2
r
−3
Å ) max/min: 0.379/−0.350.
591.82; monoclinic; space group P2(1)/n; a = 9.4720(7) Å; b =
2
X-ray Crystal Structure of L Pd(p-C H −NO )Br. Single crystals
6
4
2
3.5331(11) Å; c = 20.7908(18) Å; α = 90°; β = 94.265(2)°; γ = 90°;
were obtained from a concentrated toluene solution layered with n-
pentane at −35 °C in the glovebox. Crystal and refinement data for
3
−1
−3
2
calc
L Pd(p-C H −NO )Br: C H BrNO P Pd; M = 815.07; triclinic;
6
4
2
39 52
2
2
r
(Rint = 0.0411); giving R = 0.0231, wR = 0.0484 for 4015 data with [I
1 2
̅
space group P1; a = 10.9023(4) Å; b = 11.6680(4) Å; c = 16.3181(6)
>
2σ(I)] and R = 0.0321, wR = 0.0504 for all 4677 data. Residual
1 2
Å; α = 80.5340(10)°; β = 83.7490(10)°; γ = 68.3020(10)°; V =
3
−
−3
electron density (e Å ) max/min: 0.367/−0.349.
1
899.83(12) Å ; Z = 2; T = 120(2) K; λ = 0.71073 Å; μ = 1.658
2
X-ray Crystal Structure of L Pd(OAc) . Single crystals were
−1
−3
2
mm ; d = 1.425 g cm ; 20 759 reflections collected; 6678 unique
calc
obtained as orange blocks from a concentrated DCM solution at −35
(
Rint = 0.0243); giving R = 0.0261, wR = 0.0630 for 5973 data with [I
1 2
2
°
C in the glovebox. Crystal and refinement data for L Pd(OAc) :
2
> 2σ(I)] and R = 0.0312, wR = 0.0651 for all 6678 data. Residual
1 2
C H Cl O P Pd; M = 815.06; monoclinic; space group P2/n; a =
−
−3
38
55
2
4
2
r
electron density (e Å ) max/min: 0.793/−0.761.
1
1
0
0.4111(15) Å; b = 12.9808(18) Å; c = 14.580(2) Å; α = 90°; β =
DFT Calculations. DFT calculations were carried out using
Gaussian03 (revision D.02). The B3LYP (DFT) method was used to
carry out geometry optimizations on the model compounds specified
in the text, using the LANL2DZ basis set. The validity of the true
minima was checked by the absence of negative frequencies in the
energy Hessian.
3
02.458(2)°; γ = 90°; V = 1924.1(5) Å ; Z = 2; T = 120(2) K; λ =
−1
−3
.71073 Å; μ = 0.742 mm ; d = 1.407 g cm ; 28 610 reflections
calc
collected; 3391 unique (Rint = 0.0534); giving R = 0.0443, wR =
0
1
2
.0977 for 3106 data with [I > 2σ(I)] and R = 0.0495, wR = 0.1000
1 2
−
−3
for all 3391 data. Residual electron density (e Å ) max/min: 0.638/
0.997.
X-ray Crystal Structure of L Pd(dba). Single crystals were
−
1
ASSOCIATED CONTENT
Supporting Information
■
obtained as orange blocks from a concentrated diethyl ether solution
at −35 °C in the glovebox. Crystal and refinement data for L Pd(dba):
C H OP Pd; M = 741.18; monoclinic; space group P2(1)/n; a =
1
9
0
1
*
S
NMR spectra, crystallographic information (cif), and DFT
calculation details. This material is available free of charge via
the Internet at http://pubs.acs.org.
42
52
2
r
3.054(3) Å; b = 15.323(3) Å; c = 18.240(4) Å; α = 90°; β =
3
3.755(6)°; γ = 90°; V = 3640.5(14) Å ; Z = 4; T = 120(2) K; λ =
−1
−3
.71073 Å; μ = 0.629 mm ; d = 1.352 g cm ; 16 694 reflections
calc
collected; 6407 unique (Rint = 0.0669); giving R = 0.0493, wR =
AUTHOR INFORMATION
Corresponding Author
E-mail: viluc@nd.edu.
1
2
■
0
.1007 for 4631 data with [I > 2σ(I)] and R = 0.0801, wR = 0.1135
1 2
−
−3
for all 6407 data. Residual electron density (e Å ) max/min: 0.646/
0.868.
X-ray Crystal Structure of L Pd(dba). Single crystals were
*
−
2
Notes
obtained as orange blocks from a concentrated diethyl ether solution
The authors declare no competing financial interest.
at −35 °C in the freezer in the glovebox. Crystal and refinement data
2
for L Pd(dba): C H OP Pd; M = 755.20; monoclinic; space group
43
54
2
r
ACKNOWLEDGMENTS
■
P2(1); a = 9.8272(4) Å; b = 18.7287(9) Å; c = 10.3022(5) Å; α = 90°;
3
We gratefully acknowledge discussions with Dr. Allen Oliver
and funding from the University of Notre Dame (South Bend,
IN, USA). The MS results are supported by the National
Science Foundation (NSF) (under No. CHE-0741793).
β = 90.438(2)°; γ = 90°; V = 1896.07(15) Å ; Z = 2; T = 120(2) K; λ
−1
−3
=
0.71073 Å; μ = 0.606 mm ; d = 1.323 g cm ; 27 576 reflections
calc
collected; 8880 unique (Rint = 0.0275); giving R = 0.0217, wR =
1
2
0
.0453 for 8498 data with [I > 2σ(I)] and R = 0.0238, wR = 0.0462
1 2
8
527
dx.doi.org/10.1021/ic5010566 | Inorg. Chem. 2014, 53, 8517−8528

Inorganic Chemistry
Article
(
36) Zhang, W.-H.; Chien, S. W.; Hor, T. S. A. Coord. Chem. Rev.
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