Catalytic reactivity of the complexes [Pd{(Ph2P)2N(tBu)-P,P′}X2], X = Cl, Br, I, in the Suzuki-Miyaura C?C coupling reaction: Probing effects of the halogeno ligand X? and the ligand's tBu group

Article abstract of DOI:10.1016/j.jorganchem.2018.10.006

The synthesis, as well as the spectroscopic and structural characterization of three analogous palladium(II) complexes, [Pd{(Ph₂P)₂N(^tBu)-κ²P,P′}X₂], X = Cl, Br, I, is presented. X-ray crystallography studies revealed a similar square planar PdP₂X₂ first coordination sphere among the three complexes. The catalytic reactivity of these complexes was tested in the Suzuki-Miyaura coupling reaction, showing that the X = Cl, Br, complexes are more active than the X = I analogue. The differences in the catalytic reactivity within this series of complexes, as well as comparisons with similar palladium(II) catalysts reported in the literature, are discussed with respect to the different electronegativity of the three halogens and the strong +I inductive effect of the ligand's ^tBu group.

Full text of DOI:10.1016/j.jorganchem.2018.10.006

Accepted Manuscript
t
Catalytic reactivity of the complexes [Pd{(Ph P) N( Bu)-P,P´}X ], X = Cl, Br, I, in the
2
2
2
−
Suzuki-Miyaura C−C coupling reaction: Probing effects of the halogeno ligand X and
t
the ligand's Bu group
Polydoros-Chrysovalantis Ioannou, Cécile Arbez-Gindre, Maria Zoumpanioti,
Catherine P. Raptopoulou, Vassilis Psycharis, Ioannis D. Kostas, Panayotis Kyritsis
PII:
S0022-328X(18)30640-5
10.1016/j.jorganchem.2018.10.006
JOM 20591
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 19 July 2018
Revised Date: 27 September 2018
Accepted Date: 13 October 2018
Please cite this article as: P.-C. Ioannou, Cé. Arbez-Gindre, M. Zoumpanioti, C.P. Raptopoulou, V.
t
Psycharis, I.D. Kostas, P. Kyritsis, Catalytic reactivity of the complexes [Pd{(Ph P) N( Bu)-P,P´}X ],
2
2
2
−
X = Cl, Br, I, in the Suzuki-Miyaura C−C coupling reaction: Probing effects of the halogeno ligand X
t
and the ligand's Bu group, Journal of Organometallic Chemistry (2018), doi: https://doi.org/10.1016/
j.jorganchem.2018.10.006.
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ACCEPTED MANUSCRIPT
t
Catalytic reactivity of the complexes [Pd{(Ph P) N( Bu)-P,P´}X ], X = Cl,
2
2
2
Br, I, in the Suzuki-Miyaura C−C coupling reaction: Probing effects of the
−
t
halogeno ligand X and the ligand’s Bu group
a
b
b
Polydoros-Chrysovalantis Ioannou , Cécile Arbez-Gindre , Maria Zoumpanioti ,
c
c
b,∗
Catherine P. Raptopoulou , Vassilis Psycharis , Ioannis D. Kostas , Panayotis
a,*
Kyritsis
a
Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University
of Athens, Panepistimiopolis, Zografou, 15771 Athens, Greece
b
National Hellenic Research Foundation, Institute of Biology, Medicinal Chemistry and
Biotechnology, Vas. Constantinou 48, 11635 Athens, Greece
c
NCSR “Demokritos”, Institute of Advanced Materials, Physicochemical Processes,
Nanotechnology and Microsystems, 15310 Aghia Paraskevi Attikis, Greece
________________________________________________________________________________
ABSTRACT
The synthesis, as well as the spectroscopic and structural characterization of three analogous
t
2
palladium(II) complexes, [Pd{(Ph P) N( Bu)-κ P,P´}X ], X = Cl, Br, I, is presented. X-ray
2
2
2
crystallography studies revealed a similar square planar PdP X first coordination sphere among the
2
2
three complexes. The catalytic reactivity of these complexes was tested in the Suzuki-Miyaura
coupling reaction, showing that the X = Cl, Br, complexes are more active than the X = I analogue.
The differences in the catalytic reactivity within this series of complexes, as well as comparisons
with similar palladium(II) catalysts reported in the literature, are discussed with respect to the
different electronegativity of the three halogens and the strong +I inductive effect of the ligand’s
t
Bu group.
Keywords: Palladium(II) complex; Bis(phosphino)amine ligand; Suzuki-Miyaura cross-coupling;
Homogeneous catalysis; Crystal structure
________________________________________________________________________________
1. Introduction
The bis(phosphino)amine type of ligands, (R P) N(R′), constitute a distinct sub-family of
2
2
chelating diphosphine ligands coordinating to various transition metals in bidentate fashion [1-2].
2
The large number of complexes [M{(R P) N(R′)-κ P,P′}X ], M = Ni, Pd, Pt; X = Cl, Br, I, bearing
2
2
2
this type of ligands, has been recently reviewed [2]. A search in the Cambridge Structural Database
(
[
CSD) [3] revealed a host of structurally characterized complexes containing X = Cl, i.e.
2
Pd{(R P) N(R′)-κ P,P′}Cl ] [4]. On the other hand, the analogous complexes containing X = Br, I,
2
2
2
i
2
are rather scarce (vide infra), despite the fact that the complex [Pd{Ph PN( Pr)P(Ph)(Me)-κ P,P´}I ]
2
2
was reported more than 20 years ago [5].
2
Complexes of the [Pd{(R P) N(R′)-κ P,P′}Cl ] type have been employed as catalysts in the
2
2
2
Suzuki-Miyaura or Heck C−C coupling reaction [4e,j,x,y,z]. In recent work reported by some of us,
2
the complexes [Pd{(Ph P) N(CH ) Si(OCH ) -κ P,P´}X ], X = Cl, Br [6], I [7], have been
2
2
2 3
3 3
2
immobilized onto STx-1 montmorillonite clay and the free and anchored complexes investigated as
homogeneous and heterogenized catalysts, in the Suzuki-Miyaura coupling reaction. The catalytic
reactivity of the latter three complexes has also been explored in the hydroalkoxycarbonylation
∗
Corresponding authors.
E-mail addresses: ikostas@eie.gr (I.D. Kostas); kyritsis@chem.uoa.gr (P. Kyritsis)
1

ACCEPTED MANUSCRIPT
reaction [7]. Very recently, Balakrishna and co-workers reported the immobilization of
2
[
Pd{(Ph P) N(CH ) Si(OCH ) -κ P,P´}Cl ] onto graphene oxide, and the investigation of the
2
2
2 3
3 3
2
catalytic reactivity of both free and anchored complexes in Suzuki–Miyaura, Ullmann coupling and
cyanation reactions [8].
2
Furthermore, the analogous nickel(II) complex, [Ni{(Ph P) N(CH ) Si(OCH ) -κ P,P´}Cl ], was
2
2
2 3
3 3
2
immobilized onto SBA-15 mesoporous molecular sieves by some of us, thus affording an
heterogenized Kumada coupling catalyst [9]. The catalytic reactivity in the same reaction was
2
earlier also reported for the complexes [Ni{(Ph P) N(S-CHMePh)-κ P,P´}X ], X = Cl, Br [10]. In
2
2
2
2
addition, other nickel(II) complexes of the type [Ni{(R P) N(R′)}-κ P,P
′
}X ], X = Cl, Br, have
2
2
2
been shown to catalyse the polymerization [11] or oligomerization [12-15] of ethene, as well as the
vinyl type polymerization of norbornene [16, 17]. Along these lines, chromium complexes bearing
(
R P) N(R′) ligands are also known to be active catalysts in the oligomerization of olefins [18].
2 2
Based on the above, it is of importance to investigate the structural or electronic factors affecting
2
the catalytic reactivity of complexes [Pd{(R P) N(R′)-κ P,P′}X ]. For instance, possible effects of
2
2
2
−
the identity of the halogeno X ligands need to be explored. For that purpose, in this work, the three
analogous complexes [Pd{(Ph P) N( Bu)-κ P,P´}X ], X = Cl, Br, I, which, in the following, are
t
2
2
2
2
referred to as [Pd(P,P)X ], were synthesized and comparatively investigated by X-ray
2
crystallography and spectroscopic methods. Despite the large number of structurally characterized
2
complexes [M{(R P) N(R′)-κ P,P
′
}X2],
M
=
Ni [4x,z, 9-17,19], Pd [4-8], Pt
2
2
[
4a,b,c,d,e,f,g,h,k,s,u,w,aa, 20], reported in the literature, a search in the CSD [3] confirmed that
t
structurally characterized complexes of this type, bearing the (R P) N( Bu) ligand, have not yet
2
2
been reported. This ligand [21] has been employed, along with other similar ligands, for the
2
+
synthesis of chromium(I) complexes of the type [Cr(CO) {(R P) N(R′)-κ P,P´}] , which were used
4
2
2
as pre-catalysts for the selective oligomerization of ethylene [22]. The same ligand has also been
used for the investigation of ruthenium-catalyzed aromatic amine alkylation of anilines [23].
t
2
Moreover, recently, the complex [Fe{(Ph P) N( Bu)-κ P,P´}(Cp)(H)] has been employed to
2
2
investigate hydride transfer reactions [24].
As a continuation of our research activities regarding the evaluation of P,N-containing ligands
towards Pd-catalyzed coupling reactions [6, 7, 25], the complexes [Pd(P,P)X ], X = Cl, Br, I,
2
exhibiting a similar PdP X first coordination, were investigated as catalysts in the Suzuki-Miyaura
2
2
−
C−C coupling reaction. Our previous work has shown that the identity of X affects the catalytic
reactivity of the complexes, since complexes bearing X = Cl, Br, are more active than the
corresponding complex with X = I [6, 7]. Therefore, we sought to confirm this effect, but, in
addition, to assess the importance of the R′ group’s nature, which is expected to affect the electronic
and, possibly, catalytic properties of such complexes. For this purpose, comparisons are made with
2
t
other [Pd{(R P) N(R′)}-κ P,P
′
}X ] complexes, in order to assess whether the Bu group, which
2
2
2
exhibits a strong +I inductive effect, may confer an increased catalytic reactivity.
2. Results and Discussion
2.1. Synthesis and spectroscopic characterization of palladium(II) complexes
t
The (Ph P) N( Bu) ligand [21] was reacted, in a 1:1 stoichiometry, with a dichloromethane
2
2
solution of [Pd(cod)X ] (cod = 1,5-cyclooctadiene), X = Cl, Br, affording the complexes
2
[
Pd(P,P)X ], X = Cl, Br (Scheme 1). Complex [Pd(P,P)I ] was prepared by adding an excess of
2
2
−
NaI to complex [Pd(P,P)Cl ], in acetone, in order for the Cl ligand of the latter complex to be
substituted by I (Scheme 1). All complexes were characterized by IR and H and P NMR
spectroscopies (see spectra in Supporting Information). Based on comparisons with similar
2
−
1
31
palladium(II) complexes reported in the literature [4a,c,d,h,u,x,y,z], the IR peaks of [Pd(P,P)X ], X
2
−1
=
1
Cl, Br, I, at 870, 872, 867 cm , respectively, are assigned to ν(P-N-P), and those at 1437, 1434,
434 cm , respectively, to the ν(P-Ph). These data provide evidence that the conformation of the P-
−1
N-P backbone in the three complexes is similar, which is also supported by X-ray crystallography
2

ACCEPTED MANUSCRIPT
31
studies (vide infra). The presence of a lone singlet in the P NMR spectra of [Pd(P,P)X ], X = Cl,
2
Br, I, at δ 33.12, 30.96 and 25.09 ppm, respectively, as well as the absence of the signal at δ 57.8
t
ppm corresponding to the (Ph P) N( Bu) ligand [21], provides a clear evidence that, in all
2
2
complexes, the ligand coordinates to palladium(II) via both P atoms, which are equivalent to each
other, confirming similar observations recently reported for the analogous three complexes
2
[
Pd{(Ph P) N(CH ) Si(OCH ) -κ P,P´}X ], X = Cl, Br [6], I [7]. Positive ESI-MS spectra of
2
2
2 3
3 3
2
+
+
complexes showed bands corresponding exactly to [M–X] and [M+Na] (see experimental section
and also in SI).
Scheme 1. Synthesis of complexes [Pd(P,P)X ], X = Cl, Br, I.
2
2.2. Crystal structures
Suitable crystals suitable for X-ray crystallographic studies of all complexes were obtained by
the layering method, employing a solvent mixture of dichloromethane/n-hexane (1:3 by volume).
The structure of complexes [Pd(P,P)X ] (X = Cl, Br, I) (Fig. 1) contains discrete molecules (except
2
for the X = Cl complex which, in addition, contains a CH Cl lattice molecule per formula unit)
2
2
exhibiting a distorted square planar PdP X core. Palladium(II) is coordinated to the (P,P) chelating
2
2
ligand, forming a four-membered Pd–P–N–P ring. In all cases, the PdP X core is planar, showing
2
2
small mean deviation from the best plane defined by the Pd, P1, P2, X1 and X2 atoms (0.056 for Cl,
.081 for Br and 0.034 for I), with the P1 atom exhibiting the largest deviation (0.08 and 0.11 Å for
0
X = Cl, Br, respectively) and P2 atom (0.05 Å) for X = I. The four-membered Pd–P1–N–P2 ring is
planar, with the mean deviation from the best plane defined by these four atoms being 0.016, 0.023
and 0.056 Å for X = Cl, Br, I, respectively.
The Pd−P and Pd−X bond lengths, listed in Table 1, are typical of similar complexes reported in
the literature [4-8]. As expected, the Pd−X bond lengths follow the trend Pd−I > Pd−Br > Pd−Cl,
with average values 2.64, 2.48 and 2.36 Å, respectively. The Pd−P bond lengths are shorter than the
Pd−X ones, with average values 2.205, 2.214 and 2.232 Ǻ for X = Cl, Br, I, respectively. The P-Pd-
o
P endocyclic angle of the three complexes is rather conserved at ca. 71 , confirming earlier
observations on similar literature complexes [4-8]. Furthermore, the P1-N-P2 angles of the three
complexes are also similar (Table 1), in agreement with their similar ν(P-N-P) IR transitions (vide
supra).
3

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Figure 1. Partially labeled ORTEP plots for the molecular structure of the complexes [Pd(P,P)X2],
X = Cl, Br, I (from left to right). Color code: Pd olive green, Cl yellow, Br orange, I brown, N blue,
P cyan, C grey. The thermal ellipsoids are plotted at a probability level of 50%.
Table 1. Selected bond angles and lengths of complexes [Pd(P,P)X ], X = Cl, Br, I.
2
X
Bond angles (°)
X1−Pd−X2 X1−Pd−P1 X2−Pd−P2 P1−Pd−P2 Pd−P1−N Pd−P2−N P1−N−P2
Cl
Br
I
95.63(4)
94.66(1)
95.22(1)
95.14(3)
97.39(2)
96.06(1)
97.99(3)
96.90(2)
97.53(1)
71.34(3)
71.36(3)
71.23(2)
95.31(9)
95.04(9)
95.02(6)
95.46(9)
95.30(8)
94.58(6)
97.82(14)
98.16(13)
98.36(8)
Bond lengths (Å)
Pd−X1
Pd−X2
Pd−P1
Pd−P2
P1−N
P2−N
Cl
Br
I
2.3569(8) 2.3654(9) 2.2055(8) 2.2048(8)
2.4754(4) 2.4802(4) 2.2181(7) 2.2105(8)
2.6408(2) 2.6482(2) 2.2294(5) 2.2342(5)
1.708(3)
1.709(2)
1.713(2)
1.704(3)
1.709(3)
1.722(2)
2.3. Catalytic activity in Suzuki Miyaura cross-coupling
Proper base selection and optimization of palladium(II) complex efficiency were performed in
the Suzuki-Miyaura coupling of the deactivated 4-bromoanisole with phenylboronic acid in DMF as
a solvent at 80 ºC for 2 h, using a relatively low palladium loading (0.1 mol%) (Table 2).
Complexes [Pd(P,P)Cl ] and [Pd(P,P)Br ] afforded a higher conversion to 4-methoxybiphenyl
2
2
compared to [Pd(P,P)I ] by using K PO as a base (compare entries 1–3). These two more active
2
3
4
catalysts were further evaluated using K CO or Cs CO as a base, showing that the conversion rate
2
3
2
3
decreases in the order Cs CO > K CO > K PO (compare entries 1, 4, 5 for [Pd(P,P)Cl ], and
2
3
2
3
3
4
2
entries 2, 6, 7 for [Pd(P,P)Br ], but also that [Pd(P,P)Br ] is only very slightly more active than
2
2
[
Pd(P,P)Cl ] (compare entries 4 vs 6 and 5 vs 7). Thus, the most efficient combination of
2
catalyst/base was found to be [Pd(P,P)Br ]/Cs CO affording 95% conversion into the biaryl (entry
2
2
3
7). The conversion was also high (89%) just after 1 h of reaction time (entry 8).
4

ACCEPTED MANUSCRIPT
Table 2. Optimization of palladium(II) catalyst and base selection for the Suzuki-Miyaura coupling
a
of 4-bromoanisole with phenylboronic acid.
b
Entry Complex
Base
Time
h)
Conversion (%)
ArPh PhPh
c
d
(
1
2
3
4
5
6
7
8
[Pd(P,P)Cl2]
[Pd(P,P)Br2]
[Pd(P,P)I2]
[Pd(P,P)Cl2]
[Pd(P,P)Cl2]
[Pd(P,P)Br2]
[Pd(P,P)Br2]
[Pd(P,P)Br2]
K PO4
2
2
2
2
2
2
2
1
81
85
76
90
94
91
95
89
1
1
1
<1
1
<1
1
<1
3
K PO4
3
K PO4
3
K CO3
2
Cs CO3
2
K CO3
2
Cs CO3
2
Cs CO3
2
a
Reaction conditions: 4-MeO-C H -Br (125 µL, 1.0 mmol), PhB(OH) (183 mg, 1.5 mmol), base
6
4
2
(2.0 mmol), dodecane (70 µL, 0.3 mmol), 0.5 mM solution of catalyst in DMF (2 mL, 1.0 µmol), 80
ºC, argon.
b
Determined by GC (dodecane as internal standard).
Coupling product.
Homo-coupling by-product.
c
d
Catalysis by complex [Pd(P,P)Br ] (0.1 mol%) was then performed for a variety of electron-rich
2
and electron-poor aryl bromides in DMF/Cs CO at 80 ºC for 1 h, affording conversions to biaryls
2
3
–1
in the range 75–89% with TOFs 750–890 h (Scheme 2, Table 3). Conversion to unsubstituted
biphenyl as homo-coupling by-product was usually less than 1%. Purification of the products was
achieved by column chromatography affording isolated yields up to 80%.
Scheme 2. Suzuki-Miyaura cross-coupling.
–
The observed effect of the catalytic reactivity clearly exerted by the halogeno ligand X
(significantly higher reactivity for X = Cl, Br complexes over the X = I analogue), is in agreement
with similar observations concerning the analogous complexes [Pd{(Ph P) N(CH ) Si(OCH ) -
2
2
2 3
3 3
2
κ P,P´}X ], X = Cl, Br [6], I [7]. As already stated for these complexes [7], the different
2
electronegativity of the corresponding halogen could have a significant effect on catalytic reactivity,
since the larger electron density of palladium(II) in the X = Cl, Br, complexes, due to the higher
electronegativity of chlorine and bromine compared to that of iodine, is expected to facilitate
reduction to palladium(0), to which oxidative addition of the aryl bromide takes place, further
promoting, this way, the catalytic cycle.
The reaction conditions employed in the catalytic experiments presented in Tables 2 and 3
(
catalyst loading 0.1 mol% Pd, 80 ºC) can be considered to be relatively mild compared to similar
palladium(II) catalysts containing R′ moieties with aromatic groups, using more drastic conditions
1.0 mol% Pd loading, 80 ºC) [4e,x,y,z]. Furthermore, it should be noted that temperatures between
(
9
i
0-110 ºC were used for a similar catalyst at 0.1 mol% Pd loading bearing R′ = Pr, [4j]. Although
direct comparisons between the above catalytic systems cannot be made because of the different
t
reaction conditions, the observed reactivity of our catalysts bearing R′ = Bu, combined with the
i
reported one for the catalyst containing R′ = Pr [4j], provides evidence that the strong +I inductive
i
t
effect exerted by the Pr and Bu groups is favorable. The latter may enhance the catalytic reactivity
of the corresponding palladium(II) complexes, possibly due to the fact that the (Ph P) N(R′), R′ =
2
2
5

ACCEPTED MANUSCRIPT
i
t
Pr, Bu, ligands increase the electron density of palladium(II) and, hence, favour its reduction to
palladium(0) (vide supra).
Table 3. Suzuki-Miyaura coupling of aryl bromides with phenylboronic acid catalyzed by
a
[Pd(P,P)Br2].
b
–1 c
d
Entry
ArBr
Coupling product
Conversion (%) TOF (h ) Yield (%)
1
7
5
750
66
2
3
8
2
820
760
890
890
72
65
78
79
76
89
89
e
4
5
6
7
9
9
790
890
70
78
7
8
8
9
88
88
87
89
880
880
870
890
80
79
78
80
PhCO
1
1
0
1
a
Reaction conditions: ArBr (1.0 mmol), PhB(OH) (183 mg, 1.5 mmol), Cs CO (652 mg, 2.0
2
2
3
mmol), dodecane (70 µL, 0.3 mmol), 0.5 mM solution of [Pd(P,P)Br ] in DMF (2 mL, 1.0 µmol),
2
8
0 ºC, 1 h, argon.
b
Conversion to coupling product as determined by GC (dodecane as internal standard).
TOF = Turnover Frequency (moles of aryl bromide transformed to biphenyl per mole of Pd per
c
hour).
d
Isolated yield by column chromatography.
Entry 8 in Table 1.
e
6

ACCEPTED MANUSCRIPT
3. Conclusions
t
2
Three analogous palladium(II) complexes, namely [Pd{(Ph P) N( Bu)-κ P,P´}X ], X = Cl, Br, I,
2
2
2
were structurally and spectroscopically characterized. The fact that these complexes contain a
similar square planar PdP X first coordination sphere allows the assessment of the effects on their
2
2
−
catalytic reactivity of the halogeno X within a series of structurally similar catalysts. The
complexes containing X = Cl, Br, are more active catalysts in the Suzuki-Miyaura coupling
reaction, confirming recent observations on the catalytic reactivity within the series
2
[
Pd{(Ph P) N(CH ) Si(OCH ) -κ P,P´}X ], X = Cl, Br [6], I [7]. The different electronegativity of
2
2
2 3
3 3
2
the three halogens may be the critical factor for the observed differences. In addition, comparisons
concerning the catalytic reactivity of similar palladium(II) complexes provide some evidence of
t
increased reactivity when R′ = Bu, possibly due to its strong +I inductive effect.
4. Experimental section
4.1. General
The synthetic work was carried out under inert conditions, using Schlenk techniques. The
solvents were dried and distilled according to procedures reported in the literature [26]. The
t
(
Ph P) N( Bu) ligand [21] and the [Pd(cod)X ] complexes, X = Cl, Br, (cod = 1,5-cyclooctadiene)
2 2 2
[
27] were synthesized according to literature procedures. All other chemicals were commercially
available. FT-IR spectra (average of 50 scans) were recorded at room temperature on a Shimadzu
IR Affinity-1 spectrophotometer. Pellets of the specimens were prepared after mixing with dry KBr.
1
31
H and P NMR solution spectra (CDCl ) were acquired on a Varian 300 or 600 MHz
3
1
spectrometer. Chemical shift values in H NMR spectra were referenced internally to the residual
solvent resonance, and the P spectra were referenced to external 85% H PO in H O. Gas
3
1
3
4
2
chromatography was undertaken using a Hewlett-Packard (HP) Model GC-6890 equipped with FID
with a HP-5 capillary column (30 m × 0.32 mm i.d., 0.25 µm film thickness). Inlets and Detector
temperature was kept constant at 260 and 300 °C, respectively. The oven temperature was held at
60 °C for 3 min and then raised with a rate of 10 °C/min to 260 °C, under constant flow (0.6
mL/min). Spectra analysis was done using HP ChemStation. HRMS were obtained by using a
Thermo Scientific LTQ Orbitrap Velos (ESI) spectrometer.
4.2. Palladium dichloro{N,N-bis(diphenylphosphanyl)tert-butylamine}, [Pd(P,P)Cl2]
[
Pd(cod)Cl ] (0.097 g, 0.340 mmol) was dissolved in dichloromethane (10 mL) at room
2
t
temperature. Addition of the (Ph P) N( Bu) ligand (0.150 g, 0.340 mmol) afforded a yellow
2
2
solution, which was stirred at room temperature for 24 h and subsequently concentrated to 2 mL.
Addition of 5 mL n-hexane afforded 0.190 g of a yellow powder, which was filtrated and dried
−1
under vacuum (90% yield), m.p. (dec.) 164–170 ºC. IR (KBr, cm ): 509 (s), 521 (s), 567 (s), 596
m), 693 (s), 711 (m) ,748 (s), 870 (s) ν(P-N-P), 1008 (s), 1100 (s), 1176 (s), 1222 (s), 1248 (s),
(
1
1
311 (s), 1372 (s), 1402 (s), 1437 (s) ν(P-Ph), 1481 (s). H NMR (600 MHz, CDCl ): δ 8.23–8.19
3
t
31
1
(m, 8H, Ar), 7.66–7.65 (m, 4H, Ar), 7.61–7.59 (m, 8H, Ar), 0.99 (s, 9H, Bu). P{ H} NMR (121.5
+
MHz, CDCl ): δ 33.12. HRMS (positive ESI-MS): calcd for C H ClNP Pd [M–Cl] 582.0493,
found 582.0504; calcd for C H Cl NNaP Pd [M+Na] 640.0079, found 640.0083.
3
28 29
2
+
2
8
29
2
2
4.3. Palladium dibromo{N,N-bis(diphenylphosphanyl)tert-butylamine}, [Pd(P,P)Br2]
t
By reacting [Pd(cod)Br ] (0.042 g, 0.132 mmol) with the (Ph P) N( Bu) ligand (0.050 g, 0.132
2
2
2
mmol), employing the procedure described above, [Pd(P,P)Br ] was afforded as 0.060 g of a
2
−1
yellow powder (76% yield), m.p. (dec.) > 200 ºC. IR (KBr, cm ): 506 (s), 523 (m), 565 (s), 595
(m), 691 (s), 709 (m) ,744 (s), 872 (s) ν(P-N-P), 997 (s), 1092 (s), 1176 (m), 1225 (s), 1247 (s),
7

ACCEPTED MANUSCRIPT
1
1
8
308 (s), 1375 (m), 1434 (s) ν(P-Ph), 1457 (s), 1478 (s). H NMR (600 MHz, CDCl ): δ 8.23 (m,
3
t
31
1
H, Ar), 7.68–7.65 (m, 4H, Ar), 7.61–7.59 (m, 8H, Ar), 0.99 (s, 9H, Bu). P{ H} NMR (121.5
+
MHz, CDCl ): δ 30.96. HRMS (positive ESI-MS): calcd for C H BrNP Pd [M–Br] 625.9988,
3
28 29
2
+
found 625.9997; calcd for C H Br NNaP Pd [M+Na] 727.9069, found 727.9077.
2
8
29
2
2
4.4. Palladium diiodo{N,N-bis(diphenylphosphanyl)tert-butylamine}, [Pd(P,P)I2]
Complex [Pd(P,P)Cl ] (0.070 g, 0.113 mmol) was dissolved at room temperature in aceton (10
2
mL), followed by the addition of NaI in stoichiometric excess (0.070 g, 0.452 mmol), affording a
dark yellow solution, which was stirred at room temperature for 24 h. The reaction mixture was
then concentrated to dryness and the solid residue was re-dissolved in dichloromethane (10 mL).
This solution was filtrated through celite in order to remove the remaining NaI or NaCl formed
during the reaction. The filtrate was concentrated to 4 mL, n-hexane (10 mL) were then added to
allow precipitation of the expected product, that was collected by filtration, and dried under vacuum
−1
to afford 0.060 g (67% yield) of a dark yellow powder, m.p. (dec.) > 200 ºC. IR (KBr, cm ): 506
(
s), 528 (m), 562 (s), 591 (m), 692 (s), 748 (s), 867 (s) ν(P-N-P), 995 (m), 1101 (s), 1097 (s), 1176
1
(s), 1224 (s), 1245 (s), 1307 (w), 1375 (m), 1434 (s) ν(P-Ph), 1457 (s), 1480 (s). H NMR (600
t
MHz, CDCl ): δ 8.23 (m, 8H, Ar), 7.68–7.65 (m, 4H, Ar), 7.61–7.59 (m, 8H, Ar), 0.96 (s, 9H, Bu).
3
3
1
1
P{ H} NMR (121.5 MHz, CDCl ): δ 25.09. HRMS (positive ESI-MS): calcd for C H INP Pd
3
28 29
2
+
+
[
M–I] 673.9849, found 673.9877; calcd for C H I NNaP Pd [M+Na] 823.8792, found 823.8830.
28 29 2 2
4.5. General experimental procedure for the Suzuki-Miyaura coupling
Aryl bromide (1.0 mmol), phenylboronic acid (0.183 g, 1.5 mmol), Cs CO (652 mg, 2.0 mmol),
2
3
palladium(II) complex [Pd(P,P)Br ] in DMF (0.5 mM, 2 mL, 1.0 µmol) and dodecane (70 µL, 0.3
2
mmol) as internal standard were stirred over a preheating oil bath at 80 °C under argon for 1 h.
After cooling to room temperature, addition of water (5 mL) and extraction with dichloromethane
(
2 × 10 mL), the organic layer was washed with brine (10 mL), dried over Na SO , filtered, passed
2 4
through celite and analyzed by GC. GC retention times were compared with those of authentic
samples. After evaporation of the any volatile residue, isolation of the pure biaryl was achieved by
column chromatography on silica gel using a mixture of hexane/AcOEt as eluent. All biaryls are
1
13
known compounds [25c], and were characterized by H and C NMR spectra.
4.6. X-ray crystallography
A crystal of [Pd(P,P)Cl ]·2CH Cl (0.14 × 0.21 × 0.45 mm) was mounted in air; crystals of
2
2
2
[
Pd(P,P)Br ] (0.11 × 0.11 × 0.25 mm) and [Pd(P,P)I ] (0.06 × 0.08 × 0.23 mm) were taken from
2
2
o
the mother liquor and immediately cooled to –113 C. Diffraction measurements were made on a
Rigaku R-AXIS SPIDER Image Plate diffractometer using graphite monochromated Mo Kα
radiation. Data collection (ω-scans) and processing (cell refinement, data reduction and Empirical
absorption correction) were performed using the CrystalClear program package [28]. Important
crystallographic data are listed in Table 4. The structures were solved by direct methods using
2
SHELXS-97 and refined by full-matrix least-squares techniques on F with SHELXL ver.2014/6
[
29]. Further experimental crystallographic details for [Pd(P,P)Cl ]·2CH Cl : 2θ
= 54°;
2
2
2
max
reflections collected/unique/used, 41955/7524 [R = 0.0241]/7524; 405 parameters refined;
int
3
(
∆/σ)max = 0.001; (∆ρ)max/(∆ρ)min = 0.526/-0.458 e/Å ; R1/wR2 (for all data), 0.0246/0.0645 and the
Flack parameter takes the value 0.01(3). Further experimental crystallographic details for
Pd(P,P)Br ]: 2θmax = 54°; reflections collected/unique/used, 29061/6109 [R = 0.0418]/6109; 387
[
2
int
3
parameters refined; (∆/σ)max = 0.001; (∆ρ)max/(∆ρ)min = 0.564/-0.902 e/Å ; R1/wR2 (for all data),
.0389/0.0775. Further experimental crystallographic details for [Pd(P,P)I ]: 2θ = 54°;
0
2
max
reflections collected/unique/used, 39517/6247 [Rint = 0.0261]/6247; 423 parameters refined;
3
(
∆/σ)max = 0.003; (∆ρ)max/(∆ρ)min = 1.190/-0.886 e/Å ; R1/wR2 (for all data), 0.0211/0.0424.
8

ACCEPTED MANUSCRIPT
Hydrogen atoms were located by difference maps and were refined isotropically or were introduced
at calculated positions as riding on bonded atoms. All non-hydrogen atoms were refined
anisotropically. The plots of the structures shown in Figure 1 were drawn using the Diamond 3
program package [30].
Table 4. Crystallographic data for complexes [Pd(P,P)X ], X = Cl, Br, I.
2
[
Pd(P,P)Cl ]·2CH Cl
[Pd(P,P)Br2]
[Pd(P,P)I2]
2
2
2
Formula
Fw
C H Cl NP Pd
788.61
C H Br NP Pd
707.68
C H I NP Pd
801.66
30
33
6
2
28 29
2
2
28 29 2
2
Space group
a (Å)
b (Å)
P2 2 2
P2 /n
P2 /n
1
1 1
1
1
10.7148(12)
15.2050(16)
21.201(3)
90.0
90.0
90.0
10.0400(2)
14.6240(3)
19.1974(4)
90.0
96.444(1)
90.0
10.6143(2)
15.1406(3)
17.8385(3)
90.0
90.121(1)
90.0
c (Å)
o
α ( )
o
β ( )
o
γ ( )
V (Å )
3
3454.0(7)
4
2800.85(10)
4
2866.76(9)
4
Z
T (ºC)
Radiation
24
Mo Kα
1.517
-113
Mo Kα
1.678
-113
Mo Kα
1.857
-3
ρcalcd (g cm
)
-1
µ (mm )
1.116
3.647
2.930
Reflections with I>2σ(I) 7325
5252
0.0307
0.0738
5823
a
R1
wR
0.0238
0.0640
0.0188
0.0415
a
2
a
2
o
2 2
2 2 1/2
o
2
2
o
2
R = Σ(|F |-|F |)/Σ(|F |) and wR = {Σ[w(F -F ) ]/Σ[w(F ) ]} , w = 1⁄[σ (F )+(αP) +bP]
1
o
c
o
2
c
2
2
and P = [max (F ,0)+2F ]/3. Α = 0.0409, b=0.99 for X = Cl; α = 0.0375, b = 3.12 for X = Br;
o
c
α = 0.0149, b = 2.83 for X = I.
Acknowledgements
This work was supported, in part, by the Special Account for Research Grants of the National
and Kapodistrian University of Athens. We thank Drs A. Grigoropoulos and I. Stamatopoulos for
helpful discussions and the reviewers of the manuscript for their constructive comments.
Appendix A. Supplementary data
The CCDC codes 1854977, 1854978, 1854979, for [Pd(P,P)X ], X = Cl, Br, I, respectively,
2
contain the supplementary crystallographic data. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. The
Supporting Information related to this article is available free of charge and contains copies of IR,
NMR and HRMS spectra of the three complexes.
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1

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Highlights
•
•
•
The synthesis and characterization of the analogous palladium(II) complexes
t
2
[
Pd{(Ph P) N( Bu)-κ P,P´}X ], X = Cl, Br, I, is presented.
2 2 2
The three complexes exhibit similar square planar first coordination spheres
and the expected differences in the Pd−X bond lengths.
−
t
The effects of the halogeno X ligands, as well as of the “P-N-P” ligand’s Bu
group, on the catalytic reactivity of the three complexes in the Suzuki-Miyaura
coupling reaction, were investigated.