Palladium(ii) complexes supported by PBP and POCOP pincer ligands: A comparison of their structure, properties and catalytic activity

Article abstract of DOI:10.1039/c9dt03954f

A Pd(ii) chloride complex supported by a Yamashita-Nozaki PBP pincer ligand, [C₆H₄-1,2-(NCH₂P^tBu₂)₂B]PdCl (1a), was synthesized. The structure, properties and catalytic activity of complex 1a were compared with those of the corresponding POCOP pincer complex [C₆H₃-2,6-(OP^tBu₂)₂]PdCl (2a). It was found that the Pd centre in complex 1a is more electron rich and easier to be oxidized than that in complex 2a; complex 1a is a much better catalyst for Suzuki-Miyaura cross-coupling reactions than complex 2a. Starting from complexes 1a and 2a, two series of Pd(ii) pincer complexes bearing a SH, BH₄, NCS, NCSe or N₃ covalent ligand, [C₆H₄-1,2-(NCH₂P^tBu₂)₂B]PdY (Y = SH, 1b; BH₄; 1c; NCS, 1d; NCSe, 1e; and N₃, 1f) and [C₆H₃-2,6-(OP^tBu₂)₂]PdY (Y = SH, 2b; BH₄, 2c; NCS, 2d; NCSe, 2e; and N₃, 2f), were synthesized and fully characterized. Single crystal X-ray diffraction analysis indicated that the Pd centre is less tightly chelated in PBP pincer complexes. The strong σ-donor ability of the PBP pincer ligand has little influence on the structure of the covalent ligand possessing both σ-donor and π-Acceptor properties. However, the stretching vibrational frequencies of NCS, NCSe and N₃ ligands and the coordination mode of the BH₄ ligand are significantly different in these two types of palladium pincer complexes.

Full text of DOI:10.1039/c9dt03954f

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PAPER
Palladium(II) complexes supported by PBP and
POCOP pincer ligands: a comparison of their
structure, properties and catalytic activity†
Cite this: Dalton Trans., 2019, 48,
17633
a
a
a
a
a
Yazhou Ding, Qiang-Qiang Ma, Jiaxin Kang, Jie Zhang, * Shujun Li
and
a,b
Xuenian Chen
*
t
A Pd(II) chloride complex supported by a Yamashita–Nozaki PBP pincer ligand, [C
6
H
4
-1,2-(NCH
2
P Bu
2
)
2
B]
PdCl (1a), was synthesized. The structure, properties and catalytic activity of complex 1a were compared
t
with those of the corresponding POCOP pincer complex [C
6
H
3
-2,6-(OP Bu
2
)
2
]PdCl (2a). It was found that
the Pd centre in complex 1a is more electron rich and easier to be oxidized than that in complex 2a;
complex 1a is a much better catalyst for Suzuki–Miyaura cross-coupling reactions than complex 2a.
Starting from complexes 1a and 2a, two series of Pd(II) pincer complexes bearing a SH, BH
4
, N
̲
CS, N
̲
CSe
B]PdY (Y = SH, 1b; BH , 1f)
3
, 2c; NCS, 2d; NCSe, 2e; and N , 2f), were synthesized and
t
or N
3
covalent ligand, [C
6
H
4
2 2
-1,2-(NCH P Bu )
2
4 3
; 1c; N̲CS, 1d; N̲CSe, 1e; and N
t
and [C
6
H
3
-2,6-(OP Bu
2
)
2
]PdY (Y = SH, 2b; BH
4
̲
̲
fully characterized. Single crystal X-ray diffraction analysis indicated that the Pd centre is less tightly che-
lated in PBP pincer complexes. The strong σ-donor ability of the PBP pincer ligand has little influence on
the structure of the covalent ligand possessing both σ-donor and π-acceptor properties. However, the
Received 8th October 2019,
Accepted 4th November 2019
DOI: 10.1039/c9dt03954f
3 4
stretching vibrational frequencies of N̲CS, N̲CSe and N ligands and the coordination mode of the BH
rsc.li/dalton
ligand are significantly different in these two types of palladium pincer complexes.
Nozaki PBP pincer ligand has never been reported before. It is
well known that palladium complexes are among the most
Introduction
The Yamashita–Nozaki diphosphino-boryl (Yamashita–Nozaki efficient and frequently used transition metal catalysts in
t
PBP) pincer ligands, o-C
6 4 2 2 2
H {N(CH PR )} BH (R = Bu, Ph, and organic synthesis; particularly, pincer ligated palladium com-
1
Cy), were first synthesized in 2009. Over the last ten years, plexes are effective and versatile catalysts for a variety of cross-
this specific type of boryl ligand and other closely related PBP coupling and related reactions.
1
0
or PAlP pincer ligands have been successfully coordinated to
Due to the strong σ-donor ability and trans-influence, boryl
2
3
3b,4
many transition metals including cobalt, nickel,
ruthe- ligands sometimes can significantly change the electronic
5
6
5d,e
1,6c,7
8
11
nium, rhodium, osmium,
iridium
and platinum. At structure of the coordinate transition metals. Consequently,
the same time, transition metal complexes based on this type transition metal complexes supported by a Yamashita–Nozaki
of pincer ligand have been effectively used as catalysts for PBP pincer ligand are expected to demonstrate remarkably
3
,4,5b,7–9
many chemical transformations.
However, to the best different catalytic activities compared with those supported by
of our knowledge, a palladium complex bearing a Yamashita– other pincer ligands with weaker σ-donor ability and trans-
influence. It is well-established that the trans-influence of the
boryl ligands can significantly increase the M–L bond
lengths. However, the impact of the strong σ-donor ability of
the boryl ligands on the structure, properties and coordination
mode of other ligands sited at the trans-position, particularly
for those possessing both σ-donor and π-acceptor properties,
has yet to be explored.
a
11
Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials,
Key Laboratory of Green Chemical Media and Reactions, Ministry of Education,
Collaborative Innovation Centre of Henan Province for Green Manufacturing of Fine
Chemicals, School of Chemistry and Chemical Engineering, Henan Normal
University, Xinxiang, Henan 453007, China. E-mail: jie.zhang@htu.edu.cn,
xnchen@htu.edu.cn
b
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou,
Transition metal complexes supported by bis(phosphinite)
pincer ligands (POCOP) have also received a great deal of atten-
tion in the fields of organometallic chemistry and catalysis
Henan 450001, China
†
Electronic supplementary information (ESI) available: Spectroscopic and some
experimental details. CCDC 1957714, 1957715 and 1957717–1957722. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
C9DT03954F
1
2
over the past two decades partly due to the straight forward
ligand synthesis and the delicate balance of ligand electronics
This journal is © The Royal Society of Chemistry 2019
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of this type of complex. Different from the PBP pincer ligand,
the σ-donor ability of the central carbon atom of the POCOP
pincer ligand is relatively weak. It is fundamentally important
to make a comparison of the structure, electronic properties
and catalytic activity of these two types of complexes. Based
t
on the pincer ligands o-C
m-C
6
H
4
{N(CH
2
P Bu
2
)}
2
BH and
t
6 4 2 2
H (OP Bu ) (POCOP), in the present work, two series of
−
−
−
−
palladium(II) pincer complexes with Cl , SH , BH , N
̲
4
−
−
N
(
̲
CSe or N
3
as the other covalent ligand, [C
6 4
H
t
NCH
2
P Bu
2
)
2
B]PdY (Y = Cl, 1a; SH, 1b; BH ; 1c; N̲
4
t
N
̲
CSe, 1e; and N , 1f) and [C H -2,6-(OP Bu ) ]PdY (Y = Cl, 2a;
3
6
3
2 2
SH, 2b; BH
4
3
, 2c; N ̲C S, 2d; N ̲C Se, 2e; and N , 2f), were syn-
thesized. The structure, reactivity, spectroscopic characteristics
and catalytic activity of these two types of complexes were
investigated and the impact of the boryl ligand on the struc-
ture of the other covalent ligand was explored.
Fig. 1 Thermal ellipsoid plots of complex 1a at the 50% probability
level (for clarity, the hydrogen atoms and solvent molecules in the
lattice have been omitted, and the phenyl and tert-butyl groups have
been simplified). The selected bond lengths (Å) and angles (°): Pd1–B1,
1.972(4); Pd1–Cl1, 2.4448(11); Pd1–P1, 2.3282(11); Pd1–P2, 2.3374(10);
N1–B1–Pd1, 127.3(3); N2–B1–Pd1, 127.3(3); N1–B1–N2, 105.5(3); P1–
Pd1–P2, 155.61(4); B1–Pd1–Cl1, 177.07(16).
Results and discussion
Structure, properties and catalytic activity of [C
6
H
4
-1,2-
t
t
(
NCH P Bu ) B]PdCl (1a) and [C H -2,6-(OP Bu ) ]PdCl (2a)
2
2 2
6
3
2 2
Complex 1a was further characterized by HRMS, elemental
analysis and X-ray crystallography. Crystals of 1a used for the
X-ray diffraction analysis were obtained from CH Cl /n-hexane
2 2
Synthesis, characterization and crystal structure. Complex 2a
was first prepared by Koridze and co-workers in 31% isolated
yield by the reaction between Pd(PhCN) Cl and 1,3-bis(di-tert-
butylphosphinito)benzene in 2-methoxyethanol under reflux
2
2
solution at room temperature; 1a co-crystallized with the
solvent molecules (CH Cl and n-hexane). The single crystal
2
2
1
3
conditions. Guan and co-workers improved this method by
using PdCl as the palladium source and THF as the solvent;
a was isolated in 80% yield and the molecular structure of
structure of 1a is shown in Fig. 1 with the selected bond
lengths and angles listed. A distorted square planar geometry
for the palladium centre was observed in the molecule of 1a as
expected. The sum of the three bond angles around the boron
atom in the molecule of 1a is 360°; therefore, the boron atom
2
2
1
4
this complex was determined. In the present work, 2a was
prepared by following Guan’s improved method but Pd(cod)
Cl
2
was used as the palladium source. Complex 1a was pre-
2
is sp hybridised. The Pd–Cl bond length in 1a (2.4448(11) Å)
t
pared by the reaction of o-C H {N(CH P Bu )} BH with 1 equiv.
6
4
2
2 2
is much longer than that in the corresponding POCOP pincer
of Pd(cod)Cl
2
in THF at room temperature; 1a was isolated as a
14
complex 2a (2.3813(8) Å) due to the trans-influence of the
colourless crystalline solid in 80% yield. The syntheses of 1a
and 2a are summarized in Scheme 1.
boryl ligand. The Pd–P bond lengths in 1a (2.3282(11) and
2
.3374(10) Å) are also much longer than those in 2a (2.2926(7)
1
13
1
31
1
11
The H, C{ H}, P{ H} and B NMR spectra of complex
14
and 2.2954(7) Å). This indicates that the palladium centre is
less tightly chelated by the phosphorus atoms of the
Yamashita–Nozaki PBP pincer ligand compared with the
POCOP pincer ligand.
1
a (ESI, Fig. S1–S4†) were in good agreement with the structure
1
1
shown in Scheme 1. The B NMR resonance of 1a (39.0 ppm)
was similar to those of the corresponding Yamashita–Nozaki
PBP Ni and Pt complexes.
3
b,4,8
31
1
The P{ H} NMR spectrum of
Natural population analysis (NPA) and cyclic voltammetry
study of 1a and 2a. Based on the molecular structures obtained
using the X-ray crystallography technique, natural population
analyses (NPA) for complexes 1a and 2a were carried out using
Gaussian 09 program. The calculated NPA charges are pro-
vided in the ESI (Fig. S5†). It can be seen that the palladium
centre in complex 1a (NPA charge, −0.25) is more electron-rich
than that in 2a (NPA charge, −0.19). As a result, palladium(II)
supported by a Yamashita–Nozaki PBP pincer ligand should
be easier to be oxidized than that ligated by the corresponding
POCOP pincer ligand. To confirm this, cyclic voltammetry
measurements of complexes 1a and 2a were carried out. The
results are provided in the ESI (Fig. S6†). It can be seen from
Fig. S6† that both 1a and 2a underwent irreversible oxidation
under these conditions and 1a is easier to be oxidized as
expected.
t
1
a showed a singlet, indicating that the two CH P Bu arms
2 2
are equivalent in solutions.
Scheme 1 Syntheses of complexes 1a and 2a.
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Catalytic activity of 1a and 2a towards the Suzuki–Miyaura
cross-coupling reaction. The two palladium centres in com-
plexes 1a and 2a are significantly different: the former is more
electron rich and less tightly chelated by the pincer backbone.
Furthermore, the Pd–Cl bond length in 1a is much longer
than that in 2a, implying a weaker Pd–Cl bond in 1a. As a
result, these two types of complexes are expected to show
different catalytic activities for a given reaction. Palladium
complexes are well-known catalysts for the Suzuki–Miyaura
1
0,15
cross-coupling reaction.
Specifically, some POCOP pincer
Fig. 2 Cross-coupling of PhI with organic boronic acids (TOFs are cal-
palladium complexes were previously used to catalyse the culated from the isolated yields).
1
6
couplings of phenylboronic acid with bromobenzene and
1
7
4
-bromoacetophenone.
Complexes 1a and 2a were then used, respectively, to cata- suggested by Redóna for the cross-coupling of phenylboronic
lyse the cross-coupling of C X (X = Cl, Br, and I) with p-Me- acid with bromobenzene catalysed by other POCOP pincer pal-
B(OH) in toluene in the presence of K
6
H
5
1
6
C
6
H
4
2
3 4
PO . To better ladium complexes. The high catalytic activity of 1a for this
evaluate the activity, 0.1 mol% of catalyst was used under the type of reaction may be related to its electron rich Pd centre
same conditions for both the reactions. The results are listed which makes the oxidative addition process easier. Detailed
in Table 1.
It can be seen from Table 1 that 1a is far more active than
a in catalysing the cross-coupling of aryl halides with
p-methyl phenylboronic acid. At 80 °C, a turnover frequency
mechanistic investigation is in progress in our laboratory.
2
Reactions of 1a and 2a with NaSH, and the properties and
t
TOF) of 582 h− was achieved using 1a as the catalyst for the
coupling of PhI with p-Me-C B(OH) , and it is much higher
than that of 2a under the same conditions (71 h ).
1
structures of [C
6
H
4
-1,2-(NCH
]PdSH (2b)
In order to further explore the electron richness of the Pd
2
P Bu
2
)
2
B]PdSH (1b) and [C
6
H
3
-
(
t
2 2
2,6-(OP Bu )
6
H
4
2
−
1
Using 0.002 mol% of 1a as the catalyst, we then investigated centres ligated by the PBP and POCOP pincer frameworks, we
the cross-coupling of iodobenzene with other organic boronic decided to compare the mercapto complexes. The reaction of
acids in the presence of K
are shown in Fig. 2. Complex 1a is a very effective catalyst for produce complex 2b in good yield. In the present work, we
Suzuki–Miyaura cross-coupling reactions.
reacted 1a with 5 equiv. of NaSH in THF/methanol (5 : 1) at
3 4
PO
in toluene at 80 °C. The results 2a with 2 equiv. of NaSH in THF under reflux conditions can
1
8
The above coupling reactions were also performed in the room temperature; complex 1b was prepared in 40% yield
presence of elemental mercury. It was proved that the existence (Scheme 2). For the synthesis of POCOP pincer group 10 metal
of Hg had no influence on the coupling reactions. Therefore, mercapto complexes, good yields can be achieved by decreas-
1
9
the active catalysts are most probably the pincer ligated Pd(II) ing the amounts of NaSH used. However, for the present
species. The reactions are likely to follow the well-established reaction of 1a with NaSH, 1b was always obtained in low yields
oxidative addition, transmetallation and reductive elimination in THF/methanol no matter how much NaSH was used. When
1
5
mechanism in which Pd(II)/Pd(IV) species are involved as pure THF was used as the solvent, the expected product could
not be obtained. Complex 1b was isolated as an air/moisture
sensitive colourless crystalline solid and fully characterized by
multinuclear NMR, HRMS, FTIR and X-ray crystallography.
1
13
1
31
1
11
Table 1 Cross-coupling of C
6
H
5
X with p-Me-C
6
H
4
B(OH)
2
catalysed by
The H, C{ H}, P{ H} and B NMR spectra of complex
a
1a and 2a
1
b are provided in the ESI (Fig. S7–S10†). The NMR spectra
supported the structure of 1b and this is shown in Scheme 2.
Time
(h)
Temperature
(°C)
Conversion
(%)
Yield
(%)
TOF
−
1
[
Pd]
X
(h
)
1
1
1
2
2
2
a
a
a
a
a
a
Cl
Br
I
Cl
Br
I
2
2
0.5
2
2
110
80
80
110
80
80
30
27
95
97
Trace
40
41
100
100
10
43
51
143
582
<10
60
2
47
71
a
Conversions are based on the GC analysis results; yields are based on
the amounts of the isolated products; TOFs are calculated from the iso-
lated yields.
Scheme 2 Formation of complexes 1b and 2b.
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1
8
Similar to 2b and other POCOP pincer metal mercapto com- cules. Similar results were obtained for the POCOP pincer
2
0
20b
plexes, the resonance of the mercapto proton in complex 1b nickel mercapto complexes.
appeared at a relatively high field (−0.69 ppm) as a triplet.
However, a smaller coupling constant (JH–P = 7.7 Hz) was
observed for 1b than that for 2b (JH–P = 10.3 Hz). The P{ H}
NMR spectrum of 1b showed a singlet as expected.
Reactions of 1a and 2a with boron hydrides, and the
1
8
31
1
t
properties and structures of [C
6
H
4
-1,2-(NCH
2 2 2 4
P Bu ) B]PdBH
t
(
1c) and [C H -2,6-(OP Bu ) ]PdBH (2c)
6
3
2 2
4
Single crystals of complex 1b suitable for X-ray diffraction
analysis were obtained from benzene/n-hexane solution at
room temperature; 1b co-crystallized with benzene. The mole-
cular structure of 1b is shown in Fig. 3 along with the selected
bond lengths and angles. The geometries of the PBP pincer
backbone and the palladium centre in complex 1b are similar
to those of 1a. The Pd–S bond length in 1b (2.4409(11) Å) is
The coordination mode of the BH −
ligand in a transition
4
metal tetrahydroborate complex can be monodentate, biden-
tate or tridentate depending on the nature of the transition
2
1
metal centre. We previously obtained complex 2c as a colour-
less air/moisture sensitive solid by the reaction of the POCOP
1
8
−
pincer palladium thiolate complex with THF·BH
3
.
The BH
4
1
1
8
ligand in 2c adopts a η -HBH
3
coordination mode. Since the
much longer than that in 2b (2.3691(15) Å) because of the
trans-influence of the boryl ligand. The Pd–P bond lengths in
palladium centre ligated by a Yamashita–Nozaki PBP pincer
ligand is significantly different from that ligated by a POCOP
1
b (2.3391(9) and 2.3361(10) Å) are also much longer that
−
1
8
pincer ligand, the coordination mode of the BH
4
ligand in a
those in 2b (2.2934(13) and 2.2923(13) Å). Therefore, the pal-
ladium centre is also less tightly chelated by the Bu P arms of
2
t
PBP pincer palladium tetrahydroborate complex may be
different from that in a POCOP pincer complex. We then
the pincer backbone in 1b compared with 2b. The compara-
tively longer Pd–P and Pd–S bond lengths in 1b are consistent
with the smaller H–P coupling constant observed in the NMR
experiment for this complex.
treated complex 1a with 5 equiv. of NaBH
temperature; complex 1c was obtained in good yield
Scheme 3). Complex 1c was isolated as a colourless solid and
4
in THF at room
(
fully characterized by multinuclear NMR, FTIR, HRMS and
X-ray crystal diffraction analysis. This complex is also very air/
moisture sensitive especially in solutions. A PBP pincer cobalt
The solid state FTIR spectrum of complex 1b (ESI,
−
1
Fig. S11†) showed a weak absorption at 2585 cm corres-
ponding to the S–H stretching vibration. This stretching fre-
−
1 18
4
complex bearing a BH ligand was previously reported by
quency is slightly lower than that of 2b (2587 cm ).
3
a
Peters and his co-worker. However, this cobalt tetrahydrido-
borate complex is supported by a PBP hydridoborane pincer
ligand, which is slightly different from complex 1c.
Natural population analyses (NPA) for complexes 1b and 2b
were also carried out based on the X-ray crystallography data.
The calculated NPA charges are included in the ESI (Fig. S12†).
Similar to the chloride complexes (1a vs. 2a), the palladium
centre in complex 1b (NPA charge, −0.35) is more electron-rich
than that in 2b (NPA charge, −0.29). The mercapto protons in
both 1b and 2b (NPA charge, 0.10) are far less positive than
the hydrocarbon protons (NPA charge, 0.19–0.24) in the mole-
The NMR spectra of 1c (ESI, Fig. S13–S16†) were consistent
1
1
with the structure shown in Scheme 3. The B NMR resonance
of the BH moiety in 1c appeared as a quintet at −36.4 ppm
4
with a B–H coupling constant of 83 Hz. The coupling constant
in 1c is similar to that in 2c (82 Hz), however, the resonance
1
8
shifts to downfield slightly compared with 2c (−39.8 ppm).
The solid state FTIR spectrum of 1c (ESI, Fig. S17†) supported
2
a η -H
2
2 2
BH coordination mode. The strong absorptions at
370 and 2408 cm− can be assigned to the terminal B–H
stretching vibrations; the broad band at 1808 cm is related
to the bridging B–H stretching vibrations; the BH defor-
1
−
1
2
−
1
mation mode appears at 1181 cm . All of these IR absorptions
are typical of a bidentate BH4− ligand
21a
and are comparable
Fig. 3 Thermal ellipsoid plots of complex 1b at the 50% probability
level (for clarity, the hydrogen atoms except that attached to the
sulphur atom and solvent molecules in the lattice have been omitted,
and the phenyl and tert-butyl groups have been simplified). The selected
bond lengths (Å) and angles (°): Pd1–B1, 1.997(4); Pd1–S1, 2.4409(11);
Pd1–P1, 2.3391(9); Pd1–P2, 2.3361(10); N1–B1–Pd1, 127.3(3); N2–B1–
Pd1, 127.3(3); N1–B1–N2, 105.3(3); P1–Pd1–P2, 155.03(4); B1–Pd1–S1,
1
78.55(13).
Scheme 3 Formation of complexes 1c and 2c.
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2
to those of other pincer metal complexes with a η -H
2
BH
2
Multinuclear NMR, FTIR, HRMS, elemental analysis and X-ray
crystallography were used to characterize these products.
Crystals of 1d and 2d suitable for X-ray diffraction analysis
2
2
ligand.
Efforts were made to obtain single crystals of 1c in order to
−
further confirm the coordination mode of the BH
4
2 2
ligand. were obtained from CH Cl /n-hexane solutions at room temp-
Unfortunately, 1c failed to be isolated in any pure crystalline erature. The X-ray diffraction experiments indicated that the
−
form; this complex decomposes slowly in solutions. SCN anion coordinates to the palladium centre in the isothio-
Interestingly, crystals quickly developed in a diethyl ether solu- cyanate mode (N ̲C S) in both 1d and 2d. The structures of 1d
tion of 1c containing a small amount of 1a. X-ray diffraction and 2d are shown in Fig. 4 and 5, respectively, along with the
analysis indicated that these crystals were formed by the co- selected bond lengths and angles. Similar to complexes 1a and
crystallization of 1c and 1a. Only one molecule was found in 1b, the trans-influence of the boryl ligand makes the Pd–N
the lattice. Of the four coordinate sites of the palladium centre bond length in 1d (2.130(3) Å) much longer than that in 2d
in this molecule found in the lattice, three were occupied by (2.061(3) Å). However, the bond lengths and angles of the iso-
the tridentate PBP pincer ligand and the fourth was occupied thiocyanate ligand in 1d and 2d are comparable.
by 76% of B and 24% of Cl. The B and Cl atoms were in substi-
2
3
−
tutional disorder. The four H atoms of the BH
4
group in the
molecule of 1c were clearly located in the Fourier map and
quite similar Pd⋯H distances (2.04(6) and 2.00(6) Å) in the
two Pd–H–B bridges were observed. As a result, the X-ray crys-
2
tallography experiment also supported a η -H
2
BH
2
coordi-
−
nation mode for the BH4 ligand in 1c. The co-crystallization
and substitutional disorder made the crystallographic data
unpublishable. However, the molecular image of 1c based on
these data is included in the ESI (Fig. S18†) along with the
selected bond lengths and angles.
Reactions of 1a and 2a with KSCN, and the properties and
t
structures of [C H -1,2-(NCH P Bu ) B]PdN
̲
6
4
2
2 2
6
3
t
Fig. 4 Thermal ellipsoid plots of complex 1d at the 50% probability
level (two independent molecules were found in the lattice; only one is
2
2 2
,6-(OP Bu ) ]PdN̲CS (2d)
The above experimental results indicate that the coordination shown here; for clarity, the hydrogen atoms have been omitted, and the
−
mode of the BH
4
ligand in complex 1c is different from that phenyl and tert-butyl groups have been simplified). The selected bond
lengths (Å) and angles (°): Pd1–B1, 1.967(4); Pd1–N5, 2.130(3); Pd1–P1,
.3415(9); Pd1–P2, 2.3411(9); N5–C25, 1.163(5); C25–S1, 1.633(4); N1–
2
1
of 2c (η -H BH vs. η -HBH ). This prompted us to explore
other ligands with more than one coordination mode, particu-
larly for those possessing both σ-donor and π-acceptor pro-
2
2
3
2
B1–Pd1, 127.7(3); N2–B1–Pd1, 127.4(3); N1–B1–N2, 104.9(3); P1–Pd1–
P2, 156.33(3); B1–Pd1–N5, 177.84(15); Pd1–N5–C25, 162.1(3); N5–C25–
perties. The different electron richness of the palladium S1, 178.2(4).
centres may influence the structure, properties and coordi-
nation mode of this type of ligand.
The SCN− anion can coordinate to a metal centre either in
the thiocyanate form (S
̲C N) or in the isothiocyanate form
(N ̲C S). We treated complexes 1a and 2a, respectively, with 5
equiv. of KSCN in THF at room temperature; some air stable
crystalline solids (1d and 2d) were obtained (Scheme 4).
Fig. 5 Thermal ellipsoid plots of complex 2d at the 50% probability
level (for clarity, the hydrogen atoms have been omitted, and the phenyl
and tert-butyl groups have been simplified). The selected bond lengths
(
(
Å) and angles (°): Pd1–C1, 1.986(3); Pd1–N1, 2.061(3); Pd1–P1, 2.2965
8); Pd1–P2, 2.3012(8); N1–C23, 1.146(4); C23–S1, 1.630(4); P1–Pd1–P2,
160.45(3); C1–Pd1–N1, 178.26(13); Pd1–N1–C23, 170.4(3); N1–C23–S1,
Scheme 4 Formation of complexes 1d and 2d.
179.9(4).
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The NMR and FTIR spectra of 1d and 2d are included in
the ESI (Fig. S19–S27†). All of the NMR spectra displayed the
expected resonances for 1d and 2d. The FTIR spectra showed
that the
(
N ̲C S stretching vibrational frequency of 1d
2090 cm− ) is much lower than that of 2d (2104 cm ),
1
−1
although the structure of the NCS moiety in 1d and 2d is not
̲
influenced significantly by the boryl ligand located at the
trans-position as indicated by the X-ray diffraction study. The
FTIR observation is consistent with the fact that the palladium
centre in 1d is more electron rich than that in 2d. The stretch-
ing vibrational frequencies of the isothiocyanate groups in 1d
and 2d are also in conformity with those of other transition
2
4
metal complexes bearing isothiocyanate ligands.
Reactions of 1a and 2a with KSeCN, and the properties and
t
structures of [C
6
H
4
-1,2-(NCH
2 2 2
P Bu ) B]PdN̲CSe (1e) and
t
[C
6
H
3
-2,6-(OP Bu
2
)
2
]PdNCSe (2e)
̲
Fig. 6 Thermal ellipsoid plots of complex 1e at the 50% probability
level (two independent molecules were found in the lattice; only one is
shown here; for clarity, the hydrogen atoms have been omitted, and the
phenyl and tert-butyl groups have been simplified). The selected bond
Similar to the SCN− anion, the SeCN− anion can also coordi-
nate to a metal centre in two different modes: selenocyanate
mode and isoselenocyanate mode. We reacted 1a and 2a, lengths (Å) and angles (°): Pd1–B1, 1.985(7); Pd1–N3, 2.143(6); Pd1–P1,
2
.3338(16); Pd1–P2, 2.3319(16); N3–C9, 1.126(10); C9–Se1, 1.809(7);
respectively, with 5 equiv. of KSeCN in THF at room tempera-
ture; the isoselenocyanate complexes 1e and 2e were isolated
in moderate yields as air/moisture sensitive solids (Scheme 5).
Both 1e and 2e were fully characterized by using multinuclear
NMR, FTIR, HRMS and X-ray crystallography. It should be
N1–B1–Pd1, 128.1(5); N2–B1–Pd1, 126.4(5); N1–B1–N2, 105.5(5); P1–
Pd1–P2, 155.68(6); B1–Pd1–N3, 178.8(3); Pd1–N3–C9, 171.9(6); N3–
C9–Se1, 177.4(7).
−
pointed out that the SeCN anion also coordinates in the iso-
selenocyanate mode in both 1e and 2e.
The NMR and FTIR spectra of 1e and 2e (ESI, Fig. S28–
S36†) supported their structures depicted in Scheme 5. The
N ̲C Se stretching vibrational absorption of 1e appeared at
−1
−1
2
080 cm while that of 2e appeared at 2108 cm in the FTIR
spectra. These results are similar to those for the isothio-
cyanate complexes (1d vs. 2d). The stretching vibrational fre-
quencies of the isoselenocyanate groups in 1e and 2e are also
in conformity with those of other transition metal complexes
2
4b,25
bearing isoselenocyanate ligands.
Crystals suitable for X-ray diffraction analysis were obtained
from benzene (for 1e) or dichloromethane (for 2e) solution at
−
10 °C. The diffraction experiments were performed at room
Fig. 7 Thermal ellipsoid plots of complex 2e at the 50% probability
level (for clarity, the hydrogen atoms have been omitted, and the phenyl
and tert-butyl groups have been simplified). The selected bond lengths
temperature. The molecular structures of 1e and 2e are pre-
sented in Fig. 6 and 7, respectively, along with the selected
bond lengths and angles. The Pd–N bond length in 1e (2.143 (Å) and angles (°): Pd1–C1, 1.984(2); Pd1–N1, 2.057(2); Pd1–P1, 2.2958
6); Pd1–P2, 2.2971(6); N1–C23, 1.149(4); C23–Se1, 1.779(2); P1–Pd1–
(
P2, 160.39(2); C1–Pd1–N1, 178.35(10); Pd1–N1–C23, 170.4(2); N1–C23–
Se1, 178.7(3).
(
6) Å) is much longer than that in 2e (2.057(2) Å) because of
the trans-influence of the boryl ligand. The Pd–P bond lengths
in 1e (2.3338(16) and 2.3319(16) Å) are also longer than those
in 2e (2.2958(6) and 2.2971(6) Å). Again, the structures of the
isoselenocyanate ligands in 1e and 2e are quite similar; the
bond lengths and angles are not significantly influenced by
the PBP and POCOP pincer backbones, the σ-donation abilities
of which are quite different.
Scheme 5 Formation of complexes 1e and 2e.
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Reactions of 1a and 2a with NaN
3
, and the properties and
t
structures of [C H -1,2-(NCH P Bu ) B]PdN (1f) and [C H -
6
4
2
2 2
3
6
3
t
2
2 2 3
,6-(OP Bu ) ]PdN (2f)
To further explore the interactions of ligands possessing both
σ-donor and π-acceptor properties with the palladium centres
supported by the above PBP and POCOP pincer backbones,
complexes 1a and 2a were treated, respectively, with 5 equiv. of
NaN
ligated palladium complexes bearing an azide covalent ligand
1f and 2f) were obtained in moderate yields (Scheme 6).
3
in methanol solutions at room temperature; pincer
(
Complexes 1f and 2f are air/moisture sensitive colourless to
light yellow solids; they were recrystallized in toluene solutions
and fully characterized by multinuclear NMR, FTIR, HRMS
and single crystal X-ray diffraction analysis. The NMR and
FTIR spectra of 1f and 2f are provided in the ESI (Fig. S37–
Fig. 9 Thermal ellipsoid plots of complex 2f at the 50% probability level
(the azide group is in disorder; for clarity, the hydrogen atoms have
been omitted, and the phenyl and tert-butyl groups have been sim-
plified). The selected bond lengths (Å) and angles (°): Pd1–C1, 1.989(2);
Pd1–N1A, 2.126(6); Pd1–P1, 2.3005(5); Pd1–P2, 2.2996(5); N1A–N2,
S45†). The NMR spectra were in good agreement with the 1.127(7); N2–N3A, 1.134(11); P1–Pd1–P2, 160.269(19); C1–Pd1–N1A,
169.8(2); Pd1–N1A–N2, 136.6(5); N1A–N2–N3A, 174.8(6).
structures of 1f and 2f illustrated in Scheme 6. As expected, the
−
1
N3 asymmetric stretching frequency of 1f (2038 cm ) is 14
−
1
wavenumbers lower than that of 2f (2052 cm ). The asym-
metric stretching vibrational frequencies of the azide groups
in 1f and 2f are also in conformity with those of other tran-
2
4a
sition metal complexes bearing azide ligands.
The crystal structures of complexes 1f and 2f are presented
in Fig. 8 and 9, respectively. The selected bond lengths and
angles are also listed. The PBP pincer framework of 1f is
similar to that of 1a. The B–N bond length in 1f (2.187(3) Å) is
much longer than that in 2f (2.126(6) Å). The Pd–P bond
lengths in 1f (2.3380(7) and 2.3351(7) Å) are also longer than
those in 2f (2.3005(5) and 2.2996(5) Å). The bond lengths and
angles of the azide ligand in 1f and 2f are comparable
although the FTIR spectra displayed a smaller asymmetric
stretching vibrational absorption for the azide ligand in
complex 1f. All of these observations are similar to the isothio-
cyanate and isoselenocyanate complexes (1d vs. 2d and 1e vs.
Scheme 6 Formation of complexes 1f and 2f.
2e).
Conclusions
In conclusion, we have prepared and fully characterized two
series of palladium(II) complexes supported by PBP and
POCOP pincer ligands with Cl, SH, BH , N
̲
̲C Se or N as
3
4
t
the covalent ligand, [C
6
H
4
-1,2-(NCH
2 2 2
P Bu )
SH, 1b; BH ; 1c; NCS, 1d; N
4
̲
̲
3
6 3
H
t
(
̲
̲
2
2
4
and N
3
these two series of complexes have been investigated. The pal-
ladium centre is less tightly chelated and more electron rich in
Fig. 8 Thermal ellipsoid plots of complex 1f at the 50% probability level 1a–f compared with that in 2a–f. As expected, the strong trans-
(
for clarity, the hydrogen atoms have been omitted, and the phenyl and
influence of the boryl ligand makes the Pd–X (X = Cl, S, and N)
bond length in 1a, 1b and 1d–f much longer than that in 2a,
tert-butyl groups have been simplified). The selected bond lengths (Å)
and angles (°): Pd1–B1, 1.986(3); Pd1–N3, 2.187(3); Pd1–P1, 2.3380(7);
Pd1–P2, 2.3351(7); N3–N4, 1.094(5); N4–N5, 1.188(5); N1–B1–Pd1,
2b and 2d–f. However, the strong σ-donor ability of the boryl
ligand has very little influence on the structures of the covalent
1
26.6(2); N2–B1–Pd1, 126.8(2); N1–B1–N2, 106.5(2); P1–Pd1–P2, 155.72
(
2); B1–Pd1–N3, 174.31(15); Pd1–N3–N4, 136.6(4); N3–N4–N5, 178.0(5).
ligands even for those possessing both σ-donor and π-acceptor
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properties. Nevertheless, the stretching frequencies of the THF (30 mL) was added. After the mixture was refluxed for
CS, NCSe and N groups in complexes 1d–f are much lower 36 h and cooled to room temperature, it was filtered over
than those of complexes 2d–f; the coordination modes of the Cellite and concentrated under vacuum to yield the crude
N
̲
̲
3
1
BH
4
group in complexes 1c and 2c are different (η -HBH
3
vs. product, which was further purified by column chromato-
2
η -H BH ). Complex 1a is a much better catalyst for the graphy to give 2a as a white solid (442 mg, 82% yield). The
2
2
Suzuki–Miyaura cross-coupling reaction than 2a. A TOF value NMR spectra of 2a recorded in this work were in good agree-
of around 30 000 h− can be achieved with 20 ppm of 1a for ment with the literature value.
1
13,14
the cross-coupling between iodobenzene and organic boronic
acids at 80 °C.
Reaction of 1a with NaSH, and the synthesis and
t
characterization of [C H -1,2-(NCH P Bu ) B]PdSH (1b)
6
4
2
2 2
A mixture of 1a (29 mg, 0.05 mmol), NaSH (14 mg,
0.25 mmol), THF (10 mL) and methanol (2 mL) was stirred at
room temperature for 20 min. Then the insolubles were fil-
tered off; the resulting solution was pumped to dryness. The
residue was extracted with toluene (5 mL × 3). The removal of
toluene from the combined extractions produced the crude
product of 1b which was further purified by recrystallization in
benzene/n-hexane solution at −10 °C to give 1b as a colourless
Experimental
General information
All of the experiments were performed under a nitrogen atmo-
sphere and the standard Schlenk and glove-box techniques
were used. Solvents were degassed and dried before use. NMR
spectra were recorded using a Bruker Advance 600 or 400 MHz
spectrometer at room temperature. Chemical shift values were
1
crystalline solid (12 mg, 40% yield). H NMR (600 MHz,
1
referenced internally to the residual solvent resonances ( H
benzene-d , δ): 7.15–7.16 (m, 2H, ArH), 6.95–6.97 (m, 2H, ArH),
6
13
and C NMR) or externally to the resonances of standard
3
.65 (s, 4H, CH
SH, JH–P = 7.7 Hz). C{ H} NMR (151 MHz, benzene-d
38.8 (t, ArC, JC–P = 9.2 Hz), 119.1 (s, ArC), 110.0 (s, ArC), 40.9
t, CH , JC–P = 14.5 Hz), 35.7 (t, C(CH , JC–P = 6.5 Hz), 29.7 (t,
, JC–P = 3.4 Hz). P{ H} NMR (243 MHz, benzene-d , δ):
2
), 1.25–1.28 (m, 36H, C(CH
3
)
3
), −0.69 (t, 1H,
3
1
11
reagents ( P NMR: 85% H
3
PO
4
, 0 ppm; B NMR: BF
3
·Et
2
O,
13
1
6
, δ):
0
4
ppm). FTIR spectra were recorded in the range of
1
(
00–4000 cm− with a VECTOR 22 Bruker spectrophotometer
1
2
3 3
)
at room temperature. High resolution mass spectrometry
HRMS) was performed in the ESI mode by using a MicrOTOF
31
1
C(CH
3
)
3
6
(
11
92.9 (s). B NMR (193 MHz, benzene-d , δ): 41.5 (s). FTIR (KBr
6
mass spectrometer. GC-MS analyses were carried out by using
a SHIMADZU-(GCMS-QP2020) instrument. The pincer ligand
−1
disc): 2585 (w) cm
C
. HRMS (ESI): m/z calculated for
+
+
24
H
45BN
2
P
2
SPd + Na [M + Na] 595.1811, found 595.1852.
t
1a
t
26
precursors o-C H {N(CH P Bu )} BH and m-C H (OP Bu )
2 2
6
4
2
2
2
6
4
were prepared by following the published procedures.
Reaction of 1a with NaBH , and the synthesis and characteriz-
4
t
ation of [C H -1,2-(NCH P Bu ) B]PdBH (1c)
6
4
2
2 2
4
The synthesis and characterization of [C H -1,2-
6
4
A mixture of 1a (29 mg, 0.05 mmol), NaBH4 (10 mg,
.26 mmol) and THF (10 mL) was stirred at room temperature
A mixture of o-C H {N(CH P Bu )} BH (480 mg, 1.10 mmol), for 20 min. The insolubles were then filtered off and the result-
t
(
2 2 2
NCH P Bu ) B]PdCl (1a)
0
t
6
4
2
2 2
Pd(cod)Cl (314 mg, 1.10 mmol) and THF (20 mL) was stirred ing solution was pumped to dryness to give the crude product
2
at room temperature for 30 min; the volatiles were then of 1c, which was further purified by recrystallization in diethyl
removed under vacuum. The resulting residue was extracted ether solution at room temperature. Complex 1c was obtained
1
with hexanes (20 mL × 3). The solvents were then removed as a light yellow crystalline solid (22 mg, 78% yield). H NMR
from the combined extractions under vacuum and the crude (600 MHz, CD Cl , δ): 6.94–6.98 (m, 4H, ArH), 3.88 (s, 4H,
2
2
solid product was obtained. The product was further purified CH ), 1.39–1.42 (m, 36H, C(CH ) ), 0.34 (br q, 4H, BH , J
=
H–B
2
3 3
4
1
3
1
2 2
2 2
by recrystallization in CH Cl /n-hexane (1 : 1) solution at room 80.0 Hz). C{ H} NMR (151 MHz, CD Cl , δ): 138.5 (t, ArC,
temperature to give 1a as a colourless crystalline solid (506 mg, JC–P = 8.9 Hz), 119.1 (s, ArC), 109.4 (s, ArC), 40.2 (t, CH , J
=
=
B
2
C–P
1
8
0% yield). H NMR (600 MHz, CD Cl , δ): 7.94–7.97 (m, 4H, 13.9 Hz), 36.0 (t, C(CH ) , J
3 3 C–P 3 3 C–P
= 6.7 Hz), 29.8 (t, C(CH ) , J
2
2
1
3
1
31
1
11
ArH), 3.86 (s, 4H, CH
2
), 1.42–1.45 (m, 36H, C(CH
3
)
3
). C{ H} 3.5 Hz). P{ H} NMR (162 MHz, benzene-d , δ): 92.2 (s).
6
NMR (151 MHz, CD Cl , δ): 138.6 (t, ArC, J
= 9.1 Hz), 119.1 NMR (193 MHz, CD Cl , δ): 38.1 (s, N BPd), −36.4 (quin, BH ,
2
2
C–P
2
2
2
4
(
s, ArC), 109.4 (s, ArC), 40.0 (t, CH , J
= 14.7 Hz), 36.1 (t, JB–H = 80.0 Hz). FTIR (KBr disc): 2370 (s), 2408 (s), 1808 (br w),
2
C–P
3
1
1
−1
3 3 3 3
24 48 2 2 2
C(CH ) , JC–P = 6.4 Hz), 29.9 (t, C(CH ) , JC–P = 3.5 Hz). P{ H} 1181 (s) cm . HRMS (ESI): m/z calculated for C H B N P Pd +
1
1
+
+
NMR (162 MHz, benzene-d , δ): 89.0 (s). B NMR (128 MHz, H [M + H] 571.2541, found 571.2536.
6
benzene-d , δ): 39.0 (s). HRMS (ESI): m/z calculated for
6
+
+
Reaction of 1a with KSCN, and the synthesis and
C
24
H
2 2
44BClN P Pd + H [M + H] 570.1926, found 570.1924.
t
characterization of [C H -1,2-(NCH P Bu ) B]PdN̲CS (1d)
Anal. calcd for C H BClN P Pd: C, 50.11; H, 7.71. Found: C,
6
4
2
2 2
2
4
44
2 2
5
0.20; H, 7.83.
A mixture of 1a (29 mg, 0.05 mmol), KSCN (25 mg, 0.25 mmol)
and THF (10 mL) was stirred at room temperature for 25 min.
The insolubles were then filtered off and the resulting solution
t
Synthesis of [C H -2,6-(OP Bu ) ]PdCl (2a)
6
3
2 2
t
The ligand precursor m-C
6
H
4
(OP Bu
2
)
2
(400 mg, 1.00 mmol) was pumped to dryness to give the crude product of 1d, which
was mixed with Pd(cod)Cl2 (285 mg, 1.00 mmol) in a flask; was further purified by recrystallization in toluene solution at
17640 | Dalton Trans., 2019, 48, 17633–17643
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room temperature. Complex 1d was obtained as a yellow crys- solution was pumped to dryness to give the crude product of
1
talline solid (22 mg, 73% yield). H NMR (400 MHz, CD Cl , 2e, which was further purified by recrystallization in CH Cl
2
2
2
2
2
δ): 6.94–6.99 (m, 4H, ArH), 3.88 (s, 4H, CH ), 1.39–1.42 (m, solution at room temperature. Complex 2e was obtained as a
1
3
1
1
3
6H, C(CH
3
)
3
). C{ H} NMR (151 MHz, CD
2
Cl
2
, δ): 149.0 (s, colourless crystalline solid (19 mg, 63% yield). H NMR
= 7.2 Hz), 6.67
NCS), 138.6 (t, ArC, JC–P = 9.1 Hz), 119.3 (s, ArC), 109.5 (s, ArC), (600 MHz, benzene-d , δ): 6.88 (t, 1H, ArH, J
6
H–P
1
3
3
2
9.9 (t, CH ).
2
, JC–P = 14.7 Hz), 35.8 (t, C(CH
3
)
3
, JC–P = 6.8 Hz), (d, 2H, ArH, JH–P = 7.2 Hz), 1.26–1.28 (m, 36H, C(CH
3
)
3
C
3
1
1
1
9.7 (t, C(CH ) , JC–P = 3.6 Hz). P{ H} NMR (162 MHz, { H} NMR (151 MHz, CD Cl , δ): 167.8 (t, ArC, JC–P = 5.8 Hz),
3 3 2 2
benzene-d , δ): 90.2 (s). B NMR (128 MHz, benzene-d , 136.9 (t, ArC, JC–P = 14.2 Hz), 136.5 (t, NCS, JC–P = 3.2 Hz),
3 3
δ): 37.6 (s). FTIR (KBr disc): 2090 (s) cm . HRMS (ESI): m/z cal- 129.1 (s, ArC), 105.8 (t, ArC, JC–P = 7.0 Hz), 40.0 (t, C(CH ) , JC–P
1
1
6
6
−
1
+
+
31
1
culated for C25
93.1989.
H
44BN
3
P
2
SPd + H [M + H] 593.1989, found = 8.2 Hz), 27.9 (t, C(CH
3 3
) , JC–P = 3.6 Hz). P{ H} NMR
5
(243 MHz, benzene-d , δ): 204.1 (s). FTIR (KBr disc): 2108 (s)
cm . HRMS (ESI): m/z calculated for C23H39NO P SePd + H
2 2
6
−
1
+
Reaction of 2a with KSCN, and the synthesis and
+
[
M + H] 610.0725, found 610.0729.
t
characterization of [C
A mixture of 2a (108 mg, 0.20 mmol), KSCN (101 mg,
.00 mmol) and THF (20 mL) was stirred at room temperature
6 3 2 2
H -2,6-(OP Bu ) ]PdN̲CS (2d)
Reaction of 1a with NaN , and the synthesis and characteriz-
3
t
ation of [C H -1,2-(NCH P Bu ) B]PdN (1f)
6
4
2
2 2
3
1
for 2 h. The insolubles were then filtered off and the resulting A mixture of 1a (29 mg, 0.05 mmol), NaN (16 mg, 0.25 mmol)
3
solution was pumped to dryness to give the crude product of and methanol (10 mL) was stirred at room temperature for
2
d, which was further purified by recrystallization in CH
2
Cl
2
/
30 min. The solvent was then removed under vacuum. The
n-hexane (1 : 1) solution at room temperature. Complex 2d was residue was extracted with toluene (5 mL × 3). The removal of
obtained as a colourless crystalline solid (96 mg, 85% yield). toluene from the combined extractions followed by recrystalli-
1
H NMR (600 MHz, CDCl
3
, δ): 6.96 (t, 1H, ArH, JH–P = 8.0 Hz), zation in the same solvent at room temperature produced 1f as
1
6
.53 (d, 2H, ArH, J = 8.0 Hz), 1.39–1.41 (m, 36H, C(CH3)3). a light yellow crystalline solid (18 mg, 60% yield). H NMR
H–P
1
3
1
C{ H} NMR (151 MHz, CDCl
3
, δ): 167.7 (t, ArC, JC–P = 5.8 Hz), (400 MHz, CD
3
CN, δ): 6.99–7.03 (m, 2H, ArH), 6.93–6.96 (m,
, JH–P = 2.2 Hz), 1.37–1.41 (m, 36H,
= 7.9 Hz), 27.7 (t, C(CH ) ). C{ H} NMR (151 MHz, CD Cl , δ): 138.6 (t, ArC,
1
40.8 (s, NCS), 128.5 (s, ArC), 128.3 (t, ArC, JC–P = 2.8 Hz), 106.1 2H, ArH), 3.97 (t, 4H, CH
2
1
3
1
(t, ArC, JC–P = 7.2 Hz), 39.5 (t, C(CH ) , J
3 3 C–P
3 3
2
2
3
1
1
C(CH
1
3
)
3
, JC–P = 3.7 Hz). P{ H} NMR (243 MHz, CDCl
3
, δ):
JC–P = 9.1 Hz), 119.1 (s, ArC), 109.3 (s, ArC), 39.9 (t, CH
2
, JC–P
, JC–P
=
=
−
1
95.1 (s). FTIR (KBr disc): 2104 (s) cm . HRMS (ESI): m/z cal- 15.1 Hz), 35.7 (t, C(CH
3
)
3
, JC–P = 6.5 Hz), 29.6 (t, C(CH )
3 3
+
+
31
1
culated for C H NO P SPd + H [M + H] 562.1283, found 3.7 Hz). P{ H} NMR (162 MHz, benzene-d , δ): 89.5 (s).
5
Found: C, 49.10; H, 7.03.
2
3
39
2
2
6
1
1
62.1284. Anal. calcd for C23
H
39NO
2
P
2
SPd: C, 49.16; H, 7.00.
B NMR (193 MHz, benzene-d
6
, δ): 39.8 (s). FTIR (KBr disc):
−
1
44 5 2
2038 (vs) cm . HRMS (ESI): m/z calculated for C24H N BP Pd
+
+
+
H [M + H] 582.2285, found 582.2288.
Reaction of 1a with KSeCN, and the synthesis and
characterization of [C H -1,2-(NCH P Bu ) B]PdN
t
̲
Reaction of 2a with NaN , and the synthesis and characteriz-
ation of [C H -2,6-(OP Bu ) ]PdN (2f)
6 3 2 2 3
6
4
2
2 2
3
t
0
3
(16 mg, 0.25 mmol)
for 30 min. The insolubles were then filtered off and the result- and methanol (10 mL) was stirred at room temperature for
ing solution was pumped to dryness to give the crude product 48 h. The solvent was then removed under vacuum. The
of 1e, which was further purified by recrystallization in residue was extracted with toluene (5 mL × 3). The removal of
benzene solution at room temperature. Complex 1e was toluene from the combined extractions followed by recrystalli-
obtained as a colourless crystalline solid (20 mg, 62% yield). zation in the same solvent at room temperature produced 2f as
1
1
H NMR (400 MHz, CD
H, CH ), 1.41–1.43 (m, 36H, C(CH
151 MHz, CD Cl , δ): 138.3 (t, ArC, J
2 2
Cl , δ): 6.97–7.02 (m, 4H, ArH), 3.91 (s, a colourless crystalline solid (17 mg, 64% yield). H NMR
1
3
1
4
(
2
3
)
3
3
). C{ H} NMR (600 MHz, CDCl , δ): 6.95 (t, 1H, ArH, JH–P = 8.0 Hz), 6.53 (d,
= 9.0 Hz), 129.8 (s, 2H, ArH, JH–P = 8.0 Hz), 1.40–1.43 (m, 36H, C(CH3)3). C{ H}
C–P
1
3
1
2
2
NCSe), 119.2 (s, ArC), 109.4 (s, ArC), 39.7 (t, CH
2
, JC–P
=
NMR (151 MHz, CDCl
3
, δ): 167.4 (t, ArC, JC–P = 5.8 Hz), 128.7
3
1
1
1
5.1 Hz), 35.7 (s, C(CH
3 3 3 3
) ), 29.6 (s, C(CH ) ). P{ H} NMR (t, ArC, JC–P = 3.8 Hz), 128.1 (s, ArC), 106.0 (t, ArC, JC–P = 7.5
1
1
(243 MHz, CD Cl , δ): 90.9 (s). B NMR (193 MHz, CD Cl , δ): Hz), 39.4 (t, C(CH ) , J
= 7.5 Hz), 27.6 (t, C(CH ) , J = 3.6
3 3 C–P
2
2
2
2
3 3 C–P
−
1
31
1
3
7.9 (s). FTIR (KBr disc): 2080 (s) cm . HRMS (ESI): m/z calcu- Hz). P{ H} NMR (243 MHz, CDCl
3
, δ): 192.7 (s). FTIR (KBr
+
+
−1
3 2
lated for C25H44BN P SePd + Na [M + Na] 657.1312, found disc): 2052 (vs) cm . HRMS (ESI): m/z calculated for
+
+
6
57.1353.
C H N O P Pd + H [M + H] 546.1633, found 546.1615.
22 39 3 2 2
Reaction of 2a with KSeCN, and the synthesis and
characterization of [C H -2,6-(OP Bu ) ]PdN̲CSe (2e)
6 3 2 2
General procedure for Suzuki–Miyaura coupling reactions
t
Iodobenzene or bromobenzene or chlorobenzene (0.30 mmol),
A mixture of 2a (27 mg, 0.05 mmol), KSeCN (36 mg, organic boronic acid (0.36 mmol) and K
3 4
PO (0.60 mmol) were
0
.25 mmol) and THF (10 mL) was stirred at room temperature mixed in a 10 mL Schlenk flask. Toluene (5 mL) containing 3 ×
−
4
−6
for 2 h. The insolubles were then filtered off and the resulting 10 or 6 × 10 mmol catalyst (1a or 2a) was added. The
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mixture was stirred at 80 or 110 °C; the reaction was monitored the crystallographic data and structure refinement for these
by using GC-MS. The reaction was stopped after 2 h or until complexes are provided in the ESI (Tables S1–S3†).
benzene halide was consumed completely. The solvent was
CCDC 1957714 (1a), 1957715 (1b), 1957717–1957719 (1d–f),
then removed under vacuum and the residue was separated by and 1957720–1957722 (2d–f)† contain the supplementary crys-
flash chromatography on silica gel using petroleum ether/ tallographic data for this paper.
EtOAc as the eluent. Conversions were calculated based on the
GC analysis results and TOFs were determined from the iso-
1
lated yields. The H NMR spectra of the isolated cross-coupling Conflicts of interest
products are provided in the ESI (Fig. S46–S49†). For the Hg
There are no conflicts to declare.
test experiment, PhI or PhBr was interacted with p-Me-C
6 4
H B
(
OH) at 80 °C in the presence of 2 drops of elemental mercury
2
under the same conditions. Each reaction was repeated for two
to three times and monitored by GC analysis.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (no. 21571052, U1804253 and 21771057).
Natural population analyses
Natural population analyses (NPA) for complexes 1a, 2a, 1b
2
7
and 2b were performed using Gaussian 09 program based on
the geometries obtained from the single crystal X-ray diffrac-
tion analysis results. The B3LYP functional was used with a
standard 6-31+G(d) basis set to optimize the geometries of all
the structures. The calculated NPA charges for the atoms in
the molecules of 1a, 2a, 1b and 2b are provided in the ESI
Notes and references
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atmosphere at a scan rate of 100 mV s . The sample concen-
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X-ray structure determination
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8,29
OLEX2.
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n-hexane and dichloromethane; complex 1b co-crystallized
with the solvent molecules of benzene. Both complexes 1d and
1
e crystallized as two independent molecules in the lattice.
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17642 | Dalton Trans., 2019, 48, 17633–17643
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Dalton Trans., 2019, 48, 17633–17643 | 17643