Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis, characterization and application as Suzuki-Miyaura coupling catalysts

Article abstract of DOI:10.1016/j.jorganchem.2011.12.021

Palladium(II) complexes of the general formulae [PdCl₂(PN)] and [Pd(Me)Cl(PN)] were obtained from bidentate ligands bearing phosphine and imine donor groups. The complexes were shown to be highly active catalysts for the Suzuki-Miyaura cross-coupling reaction. The complexes are tolerant of a wide variety of reaction conditions such as solvent, choice of base as well as substituents on both arylboronic acids and aryl halides.

Full text of DOI:10.1016/j.jorganchem.2011.12.021

Journal of Organometallic Chemistry 703 (2012) 34e42
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis,
characterization and application as SuzukieMiyaura coupling catalysts
,
,
Tebello Mahamo a c, Mokgolela M. Mogorosi a, John R. Moss a 1, Selwyn F. Mapolie b, J. Chris Slootweg c,
Koop Lammertsma c, Gregory S. Smith a
,
*
a Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
b Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag, Matieland, South Africa
c Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
a r t i c l e i n f o
a b s t r a c t
Palladium(II) complexes of the general formulae [PdCl2(P^N)] and [Pd(Me)Cl(P^N)] were obtained from
bidentate ligands bearing phosphine and imine donor groups. The complexes were shown to be highly
active catalysts for the SuzukieMiyaura cross-coupling reaction. The complexes are tolerant of a wide
variety of reaction conditions such as solvent, choice of base as well as substituents on both arylboronic
acids and aryl halides.
Article history:
Received 9 November 2011
Received in revised form
14 December 2011
Accepted 19 December 2011
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Arylboronic acids
Aryl halides
Suzuki-Miyaura coupling
Iminophosphines
Palladium(II) complexes
1. Introduction
organoborate substrate, and finally, reductive elimination to give
the target product and regeneration of the active species [2]. As
Transition metal-catalyzed CeC and CeX (X ¼ heteroatom)
bond forming reactions are a powerful synthetic tool in organic
chemistry. In this regard, palladium complexes form some of the
most versatile and useful catalysts in these organic trans-
formations. The facile interchange between the two stable oxida-
tion states, Pd(II) and Pd(0), and the compatibility of many
palladium compounds with most functional groups, are mainly
responsible for the rich chemistry enjoyed by palladium
compounds [1]. This facile interchange between the Pd(II)/Pd(0)
oxidation states is what most palladium-catalyzed CeC bond
forming reactions such as ethylene oligo/polymerization reactions,
SuzukieMiyaura, Heck and Negishi coupling reactions rely on.
The most common SuzukieMiyaura catalysts currently in use
are phosphine complexes with strong P-donors, owing to the
stability displayed by these complexes as well as the comparative
ease with which their properties can be modified. The coupling
pathway requires a sequential oxidative addition at an active Pd(0)
by an aryl halide, activation and transmetallation with the
such, a pre-catalyst such as Pd(PPh3)4 would need to enter the
catalytic cycle through two successive ligand dissociations to give
the 14-electron catalytically active complex Pd0(PPh3)2. Such low-
valent, low-coordinate palladium complexes are known to be
extremely unstable and their formation is energetically unfav-
ourable. One of the main challenges facing these catalyst systems is
therefore the facile decomposition and deactivation of such
complexes, which can lead to poor catalyst performance [2] thereby
making the use of high Pd loading (2e12 mol%) necessary [3e9]. It
is therefore desirable to design catalysts that are both chemically
stable and catalytically active. One way of achieving this is through
the use of hemilabile supporting ligands.
The concept of hemilability was introduced in the 1970’s by
Rauchfuss [10,11] to describe multidentate ligands that ‘would bind
well enough to the metal centre to allow isolation of the complex,
but would readily dissociate the hard end component thus gener-
ating a vacant site for substrate binding’ [12]. This is a particularly
desirable characteristic for complexes which might have applica-
tion in catalysis, and since the majority of metals used in such
systems are middle or late transition metals, it is usually the soft
donor atom which is continually bound to the metal centre [13]. An
important property of these ligands is that they can stabilize metal
* Corresponding author. Tel.: þ27 21 6505279; fax: þ27 21 6505195.
E-mail address: Gregory.Smith@uct.ac.za (G.S. Smith).
1
John R. Moss is deceased.
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.021

T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
35
ions in a variety of oxidation states and geometries, which normally
form during the catalytic cycle [10]. In addition, the hard donor
sites are weakly coordinated to the soft metal centre, and can be
easily dissociated in solution, affording a vacant site whenever
demanded, whereas the chelate effect confers stability to the
catalyst precursor in the absence of substrate [10] thereby pre-
venting catalyst decomposition/deactivation.
Over the past few decades, interest in metal complexes of this
type of ligands, which are essentially functionalized phosphine
ligands, and their role in catalysis has been steadily growing as the
different features associated with each donor atom confer unique
properties to their metal complexes [13e16]. Unlike homo-donor
chelate ligands, hetero-donor ligands have a distinct trans effect
which can play a role in controlling the selectivity/activity, espe-
cially in co- and/or homo-polymerization processes [17]. The
syntheses and reactivity/catalytic activity of complexes bearing
hemilabile ligands of the type P^N [10,18] and P^O [19] have been
widely reported.
N
R
N
R
N
R
Pd(COD)MeCl
DCM, r.t.
Pd(COD)Cl
DCM, r.t.
Cl
Cl
Me
Pd
Pd
P
P
PPh
Cl
Ph
Ph
2
1
3
R
Compound
Compound
Compound
Phenyl
4-Tolyl
2a
2b
2c
1a
1b
1c
1d
1e
3a
3b
3c
3d
3e
3-Pyridyl
2-Thionyl 2d
2-Furyl
2e
Scheme 1. Preparation of iminophosphine palladium dichloride (2ae2e) [29] and
chloromethyl complexes (3ae3e).
Of these heterodentate ligands, those bearing phosphorus and
nitrogen as their donor atoms have emerged as an important class
complexes as air and moisture-stable crystalline solids in
moderate to good yields (65e79%). Similar trends are observed in
the characterization data of both the reported palladium dichlor-
ide [29] and palladium chloromethyl complexes (Table 1). In the 1H
NMR spectra of the chloromethyl complexes, the signals for the
of ligands [18]. The
a metal centre in a low oxidation state, while the nitrogen
p
-acceptor ability of the phosphine can stabilize
-donor
s
ability makes the metal centre more susceptible to oxidative
addition reactions. This electronic asymmetry can also be used to
optimize a ligand for a particular reaction by appropriate choice of
the nature of the donor atoms. For example, binding the phos-
phorus atom directly to a more electronegative atom such as
oxygen or nitrogen [18,20] will reduce its electron donating capa-
imine protons appear as singlets in the region
(Table 1). Upon ligand coordination there is an upfield shift from
8.98e9.05 ppm (observed in the free ligand) and this upfield shift
has been attributed to the conformational change that occurs in
the ligand upon chelation [15,19,21d]. similar trend was
observed for the dichloride complexes, where an upfield shift of
the signals for the imine protons to 8.52e8.84 ppm was observed
[29]. As in the dichloride complexes, downfield shift to
5.09e5.49 ppm is observed for the methylene protons (N-CH2eR)
d 8.16e8.80 ppm
d
A
bility while also enhancing its
hand, the presence of an imino rather than amino group will result
in a nitrogen donor atom of greater -donating capabilities [18,21].
p-acceptor capacity. On the other
d
d
a
Moreover, these types of ligand allow modulation of the steric
crowding around the metal centre through the simple variation of
the substituents on the imine and phosphine groups [22]. Recent
years have seen an increase in the amount of research on the
synthesis and application of iminophosphine complexes as cata-
lysts for coupling reactions and it has been found that these
complexes show great promise [9,23e28].
We recently reported the use of well-defined neutral imino-
phosphine Pd(II) complexes in ethylene oligomerization reactions
[29]. We, herein, report the use of these complexes with hemilabile
iminophosphine ligands as pre-catalysts in SuzukieMiyaura
coupling reactions using low catalyst loadings under relatively mild
reaction conditions. The tested complexes show tolerance of a wide
variety of conditions, including different solvents, bases, substituents
on both the phenylboronic acid and the aryl halides used.
d
upon chelation.
A
slightly bigger downfield shift (to
d
5.47e5.69 ppm) was observed for the same protons in the
palladium dichloride complexes due to the deshielding that occurs
for these protons when the adjacent imine group coordinates to
the metal centre. The deshielding is, therefore, more significant for
the palladium dichloride complexes as there is less electron
density on the metal centre in the dichloride complexes due to the
electronegative chlorido-ligands than there is in analogous palla-
dium chloromethyl complexes. For both the dichloride and chlor-
omethyl complexes, there is only a slight effect on the signals for
the thiophenyl and furfuryl protons, indicating that these groups
do not participate in coordinating to the metal centre. The signals
for the methyl protons in Pd-Me appear as doublets in the region
d
0.21e0.61 ppm, with coupling constants of 3JHP ¼ 2.4e3.2 Hz. As
a result of the different trans influence of the two donor atoms in
the ligands, the phosphine is expected to coordinate trans to the
chloride. This coordination mode is demonstrated by the small
coupling constants between the phosphorus and the Pd-Me
protons [15,30e32].
2. Results and discussion
2.1. Preparation of the iminophosphine ligands 1ae1e and
complexes 2ae2e
In the 13C NMR spectrum of the methylchloride complexes, the
signals for the imine carbons are found in the region
162.4e164.7 ppm (Table 1). This is a downfield shift from 160.6 to
161.4 ppm observed for the free ligands, further confirming the
coordination of the imine group to the metal centre [21d]. On the
contrary, there is an upfield shift of 1.5e3.2 ppm with respect to
the free ligand in the signals for the methylene carbons upon
coordination to the metal centre [33]. The signals for the Pd-Me
We recently reported the preparation and characterization of
the iminophosphine ligands 1ae1e as well as their palladium
dichloride complexes 2ae2e and the activity of these complexes as
pre-catalysts in ethylene oligomerisation reactions [29]. In this
report, we present the preparation and characterization of analo-
gous palladium chloromethyl complexes (3ae3e) based on the
same ligands and investigate the application of both types of
complexes in the SuzukieMiyaura reaction (Scheme 1).
occur as a singlet at
d 0.62e2.9 ppm, which is comparable to
similar complexes [30]. The downfield shift of the phosphine
signals from ꢀ13.4 to ꢀ14.5 ppm in the free ligands to
37.4e38.3 ppm in the 31P NMR spectra of the complexes reflects
the coordination of the phosphine to the palladium [15,34e36].
This downfield shift is slightly more significant for the
2.2. Preparation of the Pd(P^N)MeCl complexes 3ae3e
The reaction of Pd(COD)MeCl with the appropriate imino-
phosphine ligands gave the desired palladium methylchloride

36
T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
Table 1
Characterization data for the iminophosphine palladium chloromethyl complexes 3ae3e.a
2
1
1
2
N
R
(COD)Pd(Me)Cl
N
R
Cl
Me
Pd
PPh2
P
Ph2
Entry Complex
R
Yield nC
(%)
]
dH(PdeCH3) (ppm)
dH (H1) dH(H2)
dC(PdeCH3) dC(C1)
dC(C2) (ppm)
dP (ppm)
N
(cmꢀ1
)
(ppm)
(ppm)
(ppm)
(ppm)
1
2
3
4
5
3a
3b
3c
3d
3e
Phenyl
4-Tolyl
65
1638
(1636)
1638
(1635)
1635
(1634)
1637
(1634)
1637
(1635)
0.21 (d, 3J ¼ 3.2 Hz) 5.09 (s) 8.80 (s) 0.62 (s)
62.5 (65.2) 164.7 (d, 3J ¼ 5.0 Hz) (160.6) 38.3 (s) (ꢀ13.8)
66.6 (64.8) 162.4 (d, 3J ¼ 4.9 Hz) (160.3) 37.4 (s) (ꢀ13.6)
64.4 (62.4) 163.7 (d, 3J ¼ 5.1 Hz) (161.3) 37.6 (s) (ꢀ13.4)
61.5 (60.0) 163.4 (d, 3J ¼ 5.1 Hz) (160.8) 37.5 (s) (ꢀ14.5)
59.1 (57.1) 163.7 (d, 3J ¼ 5.1 Hz) (161.4) 37.4 (s) (ꢀ14.5)
(4.70)
(9.05)
79
0.56 (d, 3J ¼ 3.0 Hz) 5.40 (s) 8.16 (s) 2.3 (s)
(4.64)
(9.00)
3-Pyridyl 72
2-Thionyl 73
0.61 (d, 3J ¼ 3.0 Hz) 5.49 (s) 8.40 (s) 2.6 (s)
(4.63)
(8.98)
0.55 (d, 3J ¼ 2.9 Hz) 5.48 (s) 8.24 (s) 2.3 (s)
(4.87)
(9.01)
2-Furyl
71
0.56 (d, 3J ¼ 2.4 Hz) 5.47 (s) 8.24 (s) 2.9 (s)
(4.64)
(8.98)
a
Corresponding ligand data in parentheses.
chloromethyl complexes (51.0e52.1 ppm) than it is for the
dichloride complexes (44.2e49.7 ppm). In both cases, the pres-
ence of only one signal in the 31P NMR spectra indicates the
formation of only one product.
In the IR spectra of the complexes, the peaks for the imine bond
occur in the region 1635e1638 cmꢀ1, which is a slight hyp-
sochrombic shift with respect to the free ligands
(1634e1636 cmꢀ1). In contrast, the palladium dichloride complexes
showed a distinct bathochromic shift of between 8 and 11 cmꢀ1
with respect to the free ligands, which is typical for coordinated
imines of this type [30,37,38].
coordination mode of these types of ligands. Selected structural
data are listed in Table 2.
The X-ray crystal structure confirms the cis orientation of
the phosphine and the methyl groups around the metal centre.
The complex displays a distorted square planar arrangement
around the metal centre. Further, as expected, the iminophos-
phine ligand coordinates in a bidentate fashion to the palladium
centre, with the phosphine end of the ligand coordinated trans to
the chloride ligand. The ligand forms a puckered chelate ring
with the palladium centre, in which the ]CHC6H4 unit lies
above the Pd(P,N)MeCl plane with the torsion angle Pd(1)eP(1)e
C(16)eC(11) being 38.89 (17)ꢁ. The bite angle N(1)ePd(1)eP1 of
87.45 (5)ꢁ deviates slightly from the expected 90ꢁ angle, which
can be attributed to the steric strain imposed by the 6-membered
chelate ring N(1)ePd(1)eP(1)eC(16)eC(11)eC(10) that is formed
upon coordination to the palladium centre. This reduction in the
bite angle of N(1)ePd(1)eP(1) as well as the compensatory
increase in the N(1)ePd(1)eCl(1) angle has been observed in
other palladium methylhalide complexes of iminophosphines
[15,21,33,39e41]. The remaining two angles around the palla-
dium centre are close to the expected 90ꢁ, i.e 89.79 (6)ꢁ and
89.18 (6) for C(1)ePd(1)eP(1) and C(1)ePd(1)eCl(1) respectively.
These values are in good agreement with those obtained for
similar complexes [31,42,43].
2.3. X-ray structure of 3b
The solid-state structure of complex 3b (Fig. 1) was determined
by X-ray diffraction analysis in order to complete the character-
ization of the complex and to gain further insight into the
Table 2
Selected bond ligands (Å) and angles (ꢁ) for 3b.
Bond lengths
Pd(1)eCl(1)
Pd(1)eP(1)
Pd(1)eN(1)
Pd(1)eC(1)
P(1)eC(16)
P(4)eC(11)
2.3985(6)
2.1846(5)
2.1595(16)
2.0586(19)
1.8255(19)
1.824(3)
N(1)eC(10)
1.278(2)
N(1)eC(2)
1.484(2)
Bond angles
P(1)ePd(1)eCl(1)
N(1)ePd(1)e(Cl(1)
C(1)ePd(1)eCl(1)
N(1)ePd(1)eP(1)
C(1)ePd(1)eP(1)
C(1)ePd(1)eN(1)
177.15(2)
93.85(5)
89.18(6)
87.45(5)
89.79(6)
173.39(7)
Fig. 1. Molecular structure of 3b showing the atomic numbering scheme.

T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
37
2.4. SuzukieMiyaura coupling reactions
nanoclusters that have low stability. These clusters eventually
aggregate to form palladium black. Therefore, lowering palladium
concentration in the reaction mixture favours oxidative addition of
the aryl bromide to the Pd(0) species over cluster formation and
subsequent catalyst deactivation [44a]. This result is of particular
importance because the use of low catalyst loading is beneficial
only when high reaction rates accompanied by almost complete
conversions are observed. Otherwise expensive and time-
consuming procedures for product separation and purification
would be necessary, negating the beneficial effects of using low
catalyst loading.
Complex 2d was used in preliminary testing in order to optimize
reaction conditions (temperature, nature of base, solvent, catalyst
loading). The coupling of bromobenzene and phenylboronic acid
was chosen as the model reaction and all reactions were carried out
under aerobic conditions. Secondly, complexes 2b, 2d, 2e and 3b
were evaluated for activity in SuzukieMiyaura coupling reactions
to test the effect of palladium precursor (2b and 3b) and substitu-
ents (2b, 2d and 2e) that may influence the second coordination
sphere of the metal centre.
The data in Table 3 show the results obtained from the coupling
of bromobenzene with phenylboronic acid under different reaction
conditions when complex 2d was used as the pre-catalyst. The
complex is active even at temperatures as low as 85 ꢁC (entry 1,
Table 3), with almost complete conversion (94%) being obtained in
3 h. Increasing the temperature to 100 ꢁC (entry 2, Table 3) results
in an increase in reaction rate, and 92% conversion is reached in 1 h
(compared to 77% obtained after 1 h at 85 ꢁC) and 97% conversion at
the end of 3 h. Increasing the temperature beyond 100 ꢁC (entries 3
and 4, Table 3) does not have a significant beneficial effect on
catalyst performance, although complete conversion is reached
within 2.5 h at 140 ꢁC. At 110 ꢁC, 90% and 98% conversion were
reached within 1 h and 3 h respectively. In all cases, most conver-
sion occurs in the first hour of the reaction, with ꢂ90% conversion
being reached within an hour at 100 ꢁC and 110 ꢁC. Based on the
reactions obtained from the temperature study, all subsequent
reactions were carried out at 100 ꢁC.
Entries 1, 5 and 6 show the effect of catalyst loading on the
performance of complex 2d. The best performance is obtained
when 0.1 mol% Pd is used. Increasing catalyst loading to 1.0 and
5.0 mol% Pd (entries 5 and 6) results in catalyst decomposition
(shown by formation of palladium black) within the first 5 min and
1 min, respectively. This observation is in agreement with those by
de Vries [44] Rothenberg [45,46] and others [47,48], that only
homeopathic amounts of palladium (typically 0.01e0.1 mol%) are
needed for cross-coupling reactions. This is attributed to the fact
that once palladium has been reduced to Pd(0), it forms
Entries 2 and 7e11 in Table 3 highlight the effect of various bases
on the catalytic performance of complex 2d. K2CO3, the relatively
cheap and easy to handle base chosen for the preliminary investi-
gations, turned out to be one of the most efficient, along with KOH
(entry 7), Cs2CO3 (entry 10) and NaOH (entry 11), which gave
conversions in excess of 96% in 3 h or less. When these bases were
used, conversions in excess of 80% were obtained as early in the
reaction as 40 min, with 91% conversion being reached in this time
when Cs2CO3 was used as base. In contrast, the organic base, NaOAc
(entry 8) as well as Na2CO3 (entry 9) performed poorly, with only
42% and 29% conversion, respectively, obtained after 24 h of reac-
tion. Interestingly, comparing entries 2 and 9, but also 7 and 11,
a ‘potassium effect’ [25] becomes evident. It seems that the cation
plays an important role in determining the efficiency of the base to
activate the boronic acid as previously reported [25,49e51].
Polar aprotic solvents like THF, DMF and dioxane are often used
for coupling reactions as they allow for the best solubility of both
the substrates and the catalysts. As a result, high conversions with
high selectivities (depending on the choice of ligand) can be ob-
tained under mild conditions. A study of solvent effects on the
activity of complex 2d revealed that while the reaction proceeds
well in toluene (entry 2) and 1,4-dioxane (entry 12), catalytic
performance is greatly affected in DMF and even more so in
acetonitrile (entries 13 and 14). Scrivanti and co-workers [25] re-
ported that no catalytic activity was observed when they used the
hetero-donor P^O complex [PdCl2{8-(di-tertbutylphosphinooxy)
quinoline)}] as a pre-catalyst for Suzuki- Miyaura coupling in DMF.
They attributed the lack of catalytic activity in this solvent to
a possible mechanism whereby these solvents could activate
a process such as ligand hydrolysis leading to catalyst decomposi-
tion. Since in our case catalytic activity is just slowed down and not
completely suppressed, this mode of catalyst deactivation is not
operative. A possible explanation could be that, since both aceto-
nitrile and DMF are basic solvents with N-donor atoms, they could
compete with the imine moiety of the ligand in coordinating to the
palladium centre and the resultant complexes could be less active
than the iminophosphine complex. This possibility is further sup-
ported by the fact that in DMF, which is less basic than acetonitrile
due to conjugation, and therefore less available for coordination,
the reaction proceeds to almost complete conversion (94% after
24 h), whereas in acetonitrile only 52% conversion is obtained in the
same period. The reaction in 1,4-dioxane proceeds at a much higher
rate than it does in DMF and the same logic can be applied to
explain this. Since the oxygen donor atoms in dioxane are a harder
base than the nitrogen donor atom in DMF, this solvent is less likely
to coordinate to the palladium centre and therefore it is less likely
to interfere with catalyst performance.
Table 3
Influence of temperature, base, solvent and catalyst loading on the activity of 2d.a
Entry Mol% Pd Conditions Time (h) Solvent
Base
Conversion %b
1
2
0.1
0.1
0.1
0.1
1.0
5.0
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
85 ꢁC
3
3
3
2.5
3
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KOH
NaOAc
Na2CO3 29
Cs2CO3
NaOH
94
97
98
100
91
72
100 ꢁC
110 ꢁC
140 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
100 ꢁC
3
4e
5
6
7
8
9
10
11
12
13
14
15d
3
1.5
98
42
24
24
1.5
1.5
3
24
24
24
98
95
97
95c
52
4
1,4-Dioxane K2CO3
DMF K2CO3
Acetonitrile K2CO3
Toluene K2CO3
Nobre and Monteiro [23] reported the use of Pd(OAc)2 in
combination with iminophosphine ligands (2-diphenylphosphino-
benzylidene)-2-methylpropan-2-amine or (2-diphenylphosphino-
benzylidene)-2,6-diisopropylaniline as catalysts for the coupling of
phenylboronic acid and 4-bromotoluene. They also observed that
for this catalyst system, dioxane and toluene were the best solvents
(with 72% conversion being obtained for both solvents at 50 ꢁC and
a
Conditions: Solvent (15 ml), aryl halide (5.0 mmol), phenylboronic acid
(7.5 mmol), base (10.0 mmol).
b
Determined by GC with n-decane as internal standard.
38% conversion observed after 3 h.
0.1 mol% Hg with respect to bromobenzene.
Reaction done in a sealed tube.
c
d
e

38
T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
1 mol% Pd). Poor results were obtained when acetonitrile was used
[23]. The activity of complex 2d compares generally favourably
with other hetero-donor palladium complexes reported for
SuzukieMiyaura coupling [9,23,25,26] with lower catalyst loading
and shorter reaction times required, while high reaction rates are
maintained. It is important to note that the majority of imini-
phosphine palladium(II) complexes reported for SuzukieMiyaura
coupling reactions bear ligands with aryl groups on the imine
nitrogen [23ꢀ25] while the complexes in this report bear ligands
with benzyl, fyrfuryl and thiophenyl groups on the imine nitrogen.
The presence of the methylene group seems to enhance the cata-
lytic activity of these complexes, possibly due to the reduced steric
crowding in these complexes. Improved conversions and activities
are achieved while milder reactions conditions are employed
compared to the previously reported complexes.
Finally, to determine whether the catalytic species is the
molecular iminophosphine palladium complex or nanoparticles
(colloids or nanoclusters), a mercury poisoning test was carried out
by adding mercury to the reaction mixture before the catalytic test
was performed. Mercury is known to form an amalgam with Pd(0)
species, blocking active sites on catalytically active nanoparticles.
The results from the mercury test (entry 15) show an almost
complete suppression of catalytic activity in the presence of
mercury, indicating that the probability of the actual active species
in these reactions being a form of nanoparticles (colloids, nano-
clusters, etc) can not be excluded. It should be noted, however, that
not only colloidal Pd(0) but also molecular Pd(0) complexes have
been reported to be destroyed by elemental mercury [52,53]. It is
clear that our iminophosphine ligands are capable of stabilizing the
active catalyst.
Next we set out to investigate different aryl halides and
substituted phenylboronic acids as substrates under the optimized
conditions determined in the preliminary study for 2d (0.1 mol% Pd,
K2CO3, toluene, 100 ꢁC; see Table 4). In palladium-catalyzed
coupling reactions, oxidative addition to a Pd(0) species is often
the rate-determining step in the catalytic cycle [54], and the rela-
tive reactivity typically decreases in the order of I > OTf > Br >> Cl
because of the different C-X dissociation energies, (e.g. CeI 240 kJ/
mol to CeCl 339 kJ/mol). However, for some catalyst systems,
a reversal of reactivity between aryl bromides and aryl halides has
been reported, as in these cases, transmetalation of the Pd(II)-X
species is the rate-determining step. Smith and co-workers [55]
carried out mechanistic studies of the Suzuki coupling in the
production of the drug trityl losartan, an angiotensin II receptor
antagonist used for the treatment of high blood pressure, in which
they determined that the rate-determining step depends on the
identity of the aryl halide. They found that when using aryl
bromide, oxidative addition was rate-determining since the
coupling rate was strongly dependant on the concentrations of the
catalyst and the aryl bromide but independent of the aryl boronic
acid. In contrast, when aryl iodide was used as substrate, the
coupling rate was found to be proportional to the concentrations of
the catalyst and the aryl boronic acid but independent of the
concentration of iodotoluene, i.e., the transmetalation was rate-
determining. This observation has been attributed to the strength
of the Pd(II)-X bond in the products of the oxidative addition step
[56e58], and was supported by density functional theory calcula-
tions for the Stille cross-coupling reaction, which showed that the
overall activation barriers for the transmetalation process increase
in the order: X ¼ Cl < Br < I [56]. Comparing the efficiency of the
different aryl halides as substrates in this reaction reveals that the
best results are obtained when bromobenzene is used (entry 3) and
the poorest results are obtained when chlorobenzene is used as
substrate (entry 2). Although a slower reaction rate (compared to
bromobenzene) is observed when iodobenzene is used as the
substrate (entry 1), the reaction proceeds almost to completion
after 24 h (97%).
Complex 2d is tolerant of both electron-withdrawing and
electron-donating groups on the aryl bromide. The best results
were obtained when highly electron-deficient aryl bromides such
as 2-bromobenzonitrile (entry 6) and 4-bromobenzaldehyde (entry
4) were used. 100% conversion was reached within 50 min for both
substrates. Using relatively electron-rich aryl bromides slows down
the rate of reaction (entries 5 and 7), with the poorest results (80%
conversion after 24 h) obtained when 4-bromobenzyl bromide was
used as substrate (entry 5). The complex also shows tolerance for
electron withdrawing and electron donating substituents on phe-
nylboronic acid. Good conversions were obtained in cases where 3-
chloro- and 3-methoxy-substituted phenylboronic acids were used.
In the case of 2-methoxyphenylboronic acid, only moderate
conversion was obtained, and this could be due to steric effects
resulting from the close proximity of the methoxy group to the
boronic acid moiety. Very little conversion was obtained when 3,4-
(methylenedioxy)phenylboronic acid was used with only 15%
conversion being observed after 24 h with 3-thiopheneboronic acid
as substrate resulting in only 6% of the desired product, possibly
due to poisoning of the active catalytic species by substrates with
donor sites.
2.5. Catalytic activity of complexes 2b, 2d, 2e and 3d
A comparative study of catalytic activity involving complexes
2b, 2d, 2e and 3d was carried out to determine the effects of
palladium precursor as well as ligand substituents using conditions
optimized for 2d (see Table 5). Comparing the results obtained for
2d and 3d (entries 2 and 4) indicates that the methyl chloride
complex is slightly more active than its dichloride counterpart.
Under the same reaction conditions 100% conversion is reached
within 90 min with the methyl chloride complex (3d) while only
96% conversion (same time) is achieved with the dichloride
complex (2d) in 90 min and 97% after 3 h. Furthermore, comparing
the results obtained for 2b, 2d and 2e (entries 1e3) shows that
having a ligand bearing a donor atom in the second coordination
sphere of the metal centre has a beneficial influence on the catalytic
activity of the complex. Of the three complexes, complex 2e,
bearing the furyl substituent gave the best results, with 100%
conversion being obtained in 30 min while 2b and 2d gave 96%
conversion over the same period. In all cases, good turnover
numbers (>960 mol/mol Pd) and turnover frequencies (>1920 mol/
mol Pd/h) were observed.
3. Conclusions
In conclusion, several new chloromethyl palladium complexes
based on iminophosphine ligands recently reported by us were
prepared and characterized. A selection of these complexes as
well as the dichloride complexes was tested for activity in
SuzukieMiyaura coupling reactions. An extensive study on the
scope of these complexes was performed. They were found to be
compatible with a wide range of reaction conditions as well as
functional groups on both the aryl halides and the arylboronic
acids. The results show that for these iminophosphine complexes,
low catalyst loadings are required while high conversions and
short reaction times are maintained. In addition, having a substit-
uent bearing a donor atom on the imine moiety was found to
enhance catalytic activity. Palladium methyl chloride complexes
were found to be more active than their palladium dichloride
counterparts. A distinct halide effect was observed, as well as
a
reversal in reactivity pattern between bromobenzene and
iodobenzene.

Table 4
SuzukieMiyaura coupling of various aryl halides with phenylboronic acids using complex 2d.a
Entry
1
Ar-X
Ar0-B(OH)2
Mol% Pd
0.1
Time
3 h
%Conv.b
66d
%Yieldc
54
2
3
4
0.1
0.1
0.1
24 h
27
97
16
90
95
3 h
50 min
100
5
6
0.1
0.1
24 h
80
73
96
50 min
100
7
8
0.1
0.1
2 h
100
19
93
24 h
NDe
9
0.1
2 h
92
87
10
11
12
0.1
0.1
1.5 h
24 h
100
15
96
NDe
0.1
0.1
24 h
24 h
6
NDe
51
13
63
a
Conditions: Solvent (15 ml), aryl halide (5.0 mmol), phenylboronic acid (7.5 mmol), base (10.0 mmol).
Determined by GC with n-decane as internal standard.
b
c
Isolated yields. Products were characterized by mass spectrometry and for entry 5, the product was also characterized by 1H NMR spectroscopy.
d
e
97% conversion observed after 24 h.
Product was not isolated.

40
T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
Table 5
4.2.1. Preparation of [Pd(C26H22NP)(Me)Cl (3a)
Catalytic activity of complexes 2b, 2d, 2e and 3d for the coupling of bromobenzene
Complex 3a was prepared by the reaction of Pd(COD)(Me)Cl
(0.30 g, 1.13 mmol) with 1a (0.42 g, 1.13 mmol) and the product was
obtained as a pale yellow powder (0.39 g, 65%). M.p. 169e171 ꢁC. IR
and phenylboronic acid.a
(KBr): 1638 cmꢀ1 C]N). 1H NMR (400 MHz, CDCl3): 0.21 (d,
(n
3JHP ¼ 3.2 Hz, 3H; Pd-CH3), 5.09 (s, 2H; N-CH2eR), 7.13 (dd, 3JHH ¼ 7.7,
10.5Hz,1H;Ar-H), 7.18e7.23(m, 8H;Ar-H),7.34(m,1H;Ar-H), 7.46 (dt,
3JHH ¼ 2.3,7.6Hz, 4H;Ar-H), 7.53(m, 2H; Ar-H), 7.71(brt, 3JHH ¼ 7.5 Hz,
Entry
Catalyst
Mol% Pd
Conversion %b
TONf,h
TOFg,h
3
3
1H; Ar-H), 7.82 (br t, JHH ¼ 7.5 Hz, 1H; Ar-H), 7.94 (dd, JHH ¼ 4.3,
6.3 Hz, 1H; Ar-H), 8.80 (s, 1H; H-imine). 13C NMR (100.6 MHz, CDCl3):
0.62 (s; Pd-CH3), 62.5 (s; N-CH2eR), 124.4 (s; Ar-C), 124.7 (d,
JCP ¼ 7.6 Hz; Ar-C),127.8 (s; Ar-C),128.3 (s; Ar-C),129.5 (d, JCP ¼ 8.8 Hz;
Ar-C),130.1 (d, JCP ¼ 11.9 Hz; Ar-C),132.4 (s; Ar-C),134.3 (s; Ar-C),134.8
(d, JCP ¼ 12.1 Hz; Ar-C), 135.5 (s; Ar-C), 136.0 (d, JCP ¼ 13.6 Hz; Ar-C),
137.4 (s; Ar-C), 138.0 (s; Ar-C), 138.5 (d, JCP ¼ 8.3 Hz; Ar-C), 164.7 (d,
3JCP ¼ 5.0 Hz; C-imine). 31P NMR (161.9 MHz, CDCl3): 38.3 (s). EI-MS:
m/z 501.10 [M ꢀ Cl]þ. Anal. Calc. forC27H25ClNOPPd(536.34): C, 60.46;
H, 4.70; N, 2.61. Found: C, 60.91; H, 4.43; N, 2.87.
1
2
3
4
2b
2d
2e
3b
0.1
0.1
0.1
0.1
98c
96d
100
96e
980
960
1000
960
1960
1920
2000
1920
a
Conditions: Solvent (10 ml), aryl halide (5.0 mmol), phenylboronic acid
(7.5 mmol), base (10.0 mmol), 0.1 mol% Pd, time (30 min).
b
Determined by GC with n-decane as internal standard.
100% conversion obtained after 40 min.
97% conversion obtained after 3 h.
100% conversion obtained after 1.5 h.
TON: mol of aryl bromide converted/mol catalyst.
TOF: mol of aryl bromide converted/mol catalyst per hour.
TON and TOF values at 30 min of reaction.
c
d
e
f
g
h
4.2.2. Preparation of [Pd(C27H24NP)(Me)Cl (3b)
Complex 3b was prepared by the reaction of 1b (0.42 g,
1.07 mmol) and Pd(COD)(Me)Cl (0.28 g, 1.07 mmol) and the product
was obtained as a pale yellow solid (0.47 g, 79%). M.p. 122e124 ꢁC
4. Experimental
(decomp.). IR (KBr): 1638 cmꢀ1 C]N). 1H NMR (400 MHz, CDCl3):
(n
4.1. General remarks
0.56 (d, 3JHP ¼ 2.9 Hz, 3H; Pd-CH3), 2.36 (s, 3H; Ar-CH3), 5.40 (s, 2H;
N-CH2eR), 6.91 (d, 3JHH ¼ 7.7 Hz, 2H; Ar-H), 7.02 (m, 1H; Ar-H), 7.08
(br s,1H; Ar-H), 7.10 (d, 4JHH ¼ 5.9 Hz, 2H; Ar-H), 7.14 (d, 4JHH ¼ 5.1 Hz,
3H; Ar-H), 7.26 (t, 3JHH ¼ 7.2 Hz, 4H; Ar-H), 7.40 (t, 3JHH ¼ 7.2 Hz, 3H;
Ar-H), 7.47 (dd, 3JHH ¼ 4.1 Hz, 7.5 Hz,1H; Ar-H), 7.55 (t, 3JHH ¼ 7.4 Hz,
1H; Ar-H), 8.16 (s,1H; H-imine). 13C NMR (100.6 MHz, CDCl3): 2.3 (s;
Pd-CH3), 21.2 (s; Ar-CH3), 66.6 (s; N-CH2eR),126.8 (s; Ar-C),127.2 (s;
Ar-C),127.3 (s; Ar-C),127.5 (s; Ar-C),127.8 (d, JCP ¼ 5.9 Hz; Ar-C),128.0
(s; Ar-C), 128.1 (s; Ar-C), 128.2 (s; Ar-C), 128.6 (d, JCP ¼ 11.1, Ar-C),
128.8 (s; Ar-C),129.4 (d, JCP ¼ 13.6 Hz; Ar-C),129.7 (s; Ar-C),129.9 (s;
Ar-C), 130.7 (s; Ar-C), 130.8 (d, JCP ¼ 2.0 Hz; Ar-C), 131.3 (d,
JCP ¼ 1.3 Hz; Ar-C),131.8 (s; Ar-C),131.9 (d, JCP ¼ 6.8 Hz; Ar-C),132.2 (s;
Ar-C), 132.3 (s; Ar-C), 133.6 (d, JCP ¼ 5.5 Hz; Ar-C), 133.9 (d,
JCP ¼ 12.4 Hz; Ar-C),137.0 (s; Ar-C),137.4 (d, JCP ¼ 14.3 Hz; Ar-C),162.4
(d, 3JCP ¼ 4.9 Hz; C-imine). 31P NMR (161.9 MHz, CDCl3): 37.4 (s). EI-
MS: m/z 514.10 [M ꢀ Cl]þ. Anal. Calc. for C28H27ClNPPd (536.34): C,
61.10; H, 4.94; N, 2.54. Found: C, 61.54; H, 4.61; N, 2.49.
All reactions were carried out under nitrogen or argon atmo-
sphere using a dual vacuum/nitrogen line and standard Schlenk
techniques unless otherwise stated. Solvents were dried and purified
by refluxing under argon in the presence of a suitable drying agent.
After purification, the solvents were transferred under vacuum into
a Teflon-valve storage vessel. All commercially available chemicals
were purchased from either SigmaeAldrich or Merck and used
without further purification. PdCl2 was obtained from Johnson
Matthey. 2-Diphenylphosphinobenzaldehyde [59], Pd(COD)Cl2 [60],
Pd(COD)MeCl [61], ligands 1ae1e [29] and complexes 2ae2e [29]
were all prepared using literature procedures. NMR spectra were
recorded on a Varian Mercury-300 MHz (1H: 300 MHz; 13C:
75.5 MHz; 31P: 121 MHz) or Varian Unity-400 MHz (1H: 400 MHz;
13C: 100.6 MHz; 31P: 161.9 MHz) spectrometer. 1H NMR spectra were
referenced internally using the residual protons in deuterated
solvents (CDCl3:
the internal standard tetramethylsilane (
were referenced internally to the deuterated solvent resonance
(CDCl3: 77.0; DMSO: 39.4) and the values are reported relative to
tetramethylsilane ( 0.00). All chemical shifts are quoted in (ppm)
d
7.27; DMSO:
d
2.50) and values reported relative to
d
0.00). 13C NMR spectra
4.2.3. Preparation of [Pd(C25H21N2P)(Me)Cl (3c)
d
d
Compound 3c was prepared by the reaction of Pd(COD)MeCl
(0.13 g, 0.50 mmol) and 1c (0.19 g, 0.5 mmol product was obtained
as a pale yellow powder (0.19 g, 72%). M.p. 180e182 ꢁC. IR (KBr):
d
d
and coupling constants, J, in Hertz (Hz). Melting points were deter-
mined on a Reichert-Jung Thermovar hotstage microscope and are
uncorrected. Infrared spectra were recorded on a Thermo Nicolet. FT-
IR instrument in the 4000e300 cmꢀ1 range using KBr discs. Micro-
analyses were determined using a Fisons EA 1108 CHNO-S instru-
ment. Mass spectrawere recordedon a Waters API Q-TOF Ultima (ESI,
70 eV). GC analyses were performed using a Varian 3900 gas chro-
matograph equipped with an FID and a 50 m ꢃ 0.20 mm HP-PONA
1635 cmꢀ1 C]N, imine). 1H NMR (400 MHz, CDCl3): 0.61 (d,
(n
3JHP ¼ 3.0 Hz, 3H; Pd-CH3), 5.49 (s, 2H; N-CH2eR), 7.09 (dd,
3JHH ¼ 7.4 Hz, 9.8 Hz, 1H; Ar-H), 7.14e7.17 (m, 5H; Ar-H), 7.39e7.41
(m, 4H; Ar-H), 7.46e7.49 (m, 3H; Ar-H), 7.60e7.62 (m, 1H, Ar-H),
3
7.65e7.66 (m, 1H; Ar-H), 8.00 (td, JHH ¼ 1.8 Hz, 7.8 Hz, 1H; Ar-H),
4
8.32 (d, JHH ¼ 2.2, Hz, 1H; Ar-H), 8.40 (s, 1H, H-imine), 8.51 (dd,
3JHH ¼ 1.6 Hz, 4.8 Hz,1H; Ar-H). 13C NMR ( 100.6 MHz, CDCl3): 2.6 (s;
Pd-CH3), 64.4 (s; N-CH2eR), 123.3 (s; Ar-C), 126.5 (s; Ar-C), 128.7 (d,
JCP ¼ 11.2 Hz; Ar-C), 130.4 (d, JCP ¼ 1.7 Hz; Ar-C), 131.1 (d,
JCP ¼ 2.3 Hz; Ar-C), 132.3 (d, JCP ¼ 6.7 Hz; Ar-C), 132.5 (s; Ar-C), 133.1
(d, JCP ¼ 12.4 Hz; Ar-C),133.8 (s; Ar-C), 133.9 (s; Ar-C), 134.1 (s; Ar-C),
136.1 (d, JCP ¼ 8.7 Hz; Ar-C), 137.4 (s; Ar-C), 149.0 (s; Ar-C), 150.4 (s;
Ar-C), 163.6 (d, 3JCP ¼ 4.8 Hz; C-imine). 31P NMR (161.9 MHz, CDCl3):
37.6 (s). EI-MS: m/z 501.11 [M ꢀ Cl]þ. Anal. Calc. for C26H24ClN2PPd
(537.33): C, 58.12; H, 4.50; N, 5.21. Found: C, 58.52; H, 4.56; N, 5.13.
column (0.50 mm film thickness).
4.2. General procedure for the preparation of palladium
chloromethyl complexes 3ae3e
To a solution of the appropriate ligand in CH2Cl2 (15 ml) was
added an equimolar amount of a Pd(COD)(Me)Cl solution in CH2Cl2
(15 ml). The reaction was stirred at room temperature for 15 h, after
which the solvent was reduced in vacuo and hexane was added to
precipitate the product. The resultant solid was washed with
hexane and then dried. The desired products were obtained as pale
yellow or off-white solids in moderate to good yields.
4.2.4. Preparation of [Pd(C24H20NPS)(Me)Cl (3d)
Complex 3d was prepared by the reaction of 1d (0.41 g,
1.07 mmol) and Pd(COD)(Me)Cl (0.28 g, 1.07 mmol) and the product

T. Mahamo et al. / Journal of Organometallic Chemistry 703 (2012) 34e42
41
was obtained as a pale yellow solid (0.42 g, 73%). M.p. 188e190 ꢁC.
IR (KBr): 1637 cmꢀ1 C]N). 1H NMR (400 MHz, CDCl3): 0.56 (d, 3H,
Table 6
Crystal and refinement data for 3b.
(n
3JHP ¼ 2.9 Hz, 3H; Pd-CH3), 5.48 (s, 2H; N-CH2eR), 6.36 (br s, 1H; H-
thiophene), 6.73 (d, 3JHH ¼ 2.6 Hz, 1H; H-thiophene), 7.10 (br s, 1H;
H-thiopehene), 7.16 (t, 3JHH ¼ 8.8 Hz, 1H; Ar-H), 7.29 (t, JHH ¼ 5.8 Hz,
4H; Ar-H), 7.39 (t, 3JHH ¼ 7.6 Hz, 4H; Ar-H), 7.48 (t, 3JHH ¼ 7.5 Hz, 3H;
Ar-H), 7.54e7.55 (m, 1H; Ar-H), 7.64 (t, 3JHH ¼ 7.3 Hz, 1H; Ar-H), 8.24
(br s, 1H; H-imine). 13C NMR ( 100.6 MHz, CDCl3): 2.3 (s; Pd-CH3),
61.5 (s; N-CH2eR), 123.9 (C-thiophene), 127.0 (C-thiophene), 127.7
(d, JCP ¼ 42.0 Hz; Ar-C), 128.3 (s; C-thiophene), 128.8 (s; Ar-C), 130.0
(d, JCP ¼ 11.3 Hz; Ar-C), 130.9 (d, JCP ¼ 2.1 Hz; Ar-C), 131.2 (d,
JCP ¼ 1.5 Hz; Ar-C), 132.4 (d, JCP ¼ 6.8 Hz; Ar-C), 133.7 (s; Ar-C), 134.2
(d, JCP ¼ 12.4 Hz; Ar-C), 135.9 (d, JCP ¼ 8.5 Hz; Ar-C), 137.3 (d,
JCP ¼ 14.4 Hz; Ar-C), 138.6 (s; C-thiopehene), 163.4 (d, 3JCP ¼ 5.1 Hz;
C-imine). 31P NMR (161.9 MHz, CDCl3): 37.5 (s). EI-MS: m/z 506.83
[M ꢀ Cl]þ. Anal. Calc. For C25H23ClNPPdS (542.37): C, 55.36; H, 4.27;
N, 2.58; S, 5.91. Found: C, 55.42; H, 4.25; N, 2.31; S, 5.87.
Empirical formula
Formula weight
T, K
C28H27ClNPPd
550.33
173(2)
0.71073
Monoclinic
P21/n
10.0673(8)
21.8872(18)
11.0593(9)
90
92.3710(10)
90
2434.8(3)
4
1.501
0.954
l, Å
Crystal system
Space group
a, Å
b, Å
c, Å
a
b
g
, deg
, deg
, deg
V, Å3
Z
Densitycalc, mg/mL
Absorption coefficient, mmꢀ1
F(000)
1120
Crystal size, mm
0.24 ꢃ 0.23 ꢃ 0.12
q
range for data collection, deg
1.86 to 27.14
Limiting indices
Reflections collected/unique
Completeness to
Max. and min. transmission
Refinement method
ꢀ12 ꢄ h ꢄ 12,ꢀ28 ꢄ k ꢄ 28,ꢀ14 ꢄ l ꢄ 14
38460/5380 [R(int) ¼ 0.0444]
27.14 (99.9%)
4.2.5. Preparation of [Pd(C24H20NOP)(Me)Cl (3e)
Complex 3e was prepared by the reaction of 1e (0.39 g,
1.07 mmol) and Pd(COD)(Me)Cl (0.28 g,1.07 mmol) and the product
was obtained as a pale yellow solid (0.40 g, 71%). M.p. 193e195 ꢁC.
q
0.8941 and 0.8034
Full-matrix least-squares on F2
5380/0/291
IR (KBr): 1637 cmꢀ1 C]N). 1H NMR (400 MHz, CDCl3): 0.56 (d,
(n
Data/restraints/parameters
Goodness-of-fit on F2
1.025
3JHP ¼ 2.4 Hz, 3H; Pd-CH3), 5.47 (s, 2H; N-CH2eR), 6.35 (br s, 1H; H-
Final R indices [I > 2
R indices (all data)
Largest diff. peak and hole
s(I)]
R1 ¼ 0.0238, wR2 ¼ 0.0546
R1 ¼ 0.0321, wR2 ¼ 0.0584
0.370 and ꢀ0.405 e Aꢀ3
furan), 6.72 (d, 3JHH ¼ 2.6 Hz, 1H; H-furan), 7.06 (1H, br s, H-furan),
3
7.15 (t, JHH ¼ 8.7 Hz, 1H; Ar-H), 7.26e7.29 (m, 4H; Ar-H), 7.38 (t,
3JHH ¼ 7.3 Hz, 4H; Ar-H), 7.48 (t, 3JHH ¼ 7.5 Hz, 3H; Ar-H), 7.56e7.58
3
(m, 1H; Ar-H), 7.62 (t, JHH ¼ 7.3 Hz, 1H; Ar-H), 8.24 (br s, 1H; H-
Oxford Cryostream cooling system (Oxford Cryostat). Cell refine-
ment and data reduction were performed using the program SAINT
[62]. The data were scaled and absorption corrections were per-
formed using SADABS [63]. The structure was solved by direct
methods using SHELXS-97 [63] and refined by full-matrix least-
squares methods based on F2 using SHELXL-97 [63] and using the
graphics interface program X-Seed [64]. The programs X-Seed and
POV-Ray [65] were both used to prepare molecular graphic images.
All non-hydrogen atoms were refined anisotropically. All hydrogen
atoms were positioned geometrically with C-H distances ranging
from 0.95 Å to 0.98 Å and refined as riding on their parent atoms,
with Uiso (H) ¼ 1.2e1.5 Ueq (C). The structure was successfully
refined to the R factor 0.0238. The parameters for crystal data
collection and structure refinements are in Table 6.
imine). 13C NMR (100.6 MHz, CDCl3): 2.9 (s; Pd-CH3), 59.1 (s; N-
CH2eR), 110.6 (s; C-furan), 111.3 (s; C-furan), 126.9 (d,
JCP ¼ 57.5 Hz; Ar-C), 128.2 (s; C-furan), 128.7 (d, JCP ¼ 11.2 Hz; Ar-C),
130.9 (d, JCP ¼ 2.0 Hz; Ar-C), 131.4 (d, JCP ¼ 1.7 Hz; Ar-C), 132.2 (d,
JCP ¼ 6.8 Hz; Ar-C), 133.5 (s; Ar-C), 134.1 (d, JCP ¼ 12.6 Hz; Ar-C),
135.9 (d, JCP ¼ 8.7 Hz; Ar-C), 136.0 (s; Ar-C), 142.8 (s; C-furan), 149.5
3
(s; Ar-C), 163.7 (d, JCP ¼ 5.1 Hz; C-imine). 31P NMR (161.9 MHz,
CDCl3): 37.4 (s). EI-MS: m/z 490.21 [M ꢀ Cl]þ. Anal. Calc. For
C25H23ClNOPPd (526.30): C, 57.05; H, 4.40; N, 2.66. Found: C, 57.56;
H, 4.39; N, 2.98.
4.3. SuzukieMiyaura coupling reactions
A 100 ml round bottom flask was fitted with a reflux condenser
and a magnetic stirrer bar. The flask was charged with toluene
(15 ml) and the appropriate amount of catalyst reagents and the
internal standard (n-Decane: 2.59 mmol). The contents were
thoroughly mixed and an initial sample (t0) was then taken. The
reaction flask was placed in an oil bath at the desired temperature
and the reaction mixture allowed to heat/reflux with stirring. A
sample was taken and analyzed every 10 min for the first hour and
every 30 min thereafter until t3h. In cases where conversion was not
complete after 3 h, the reaction mixture was then allowed to stir for
a total of 24 h. The reaction at 140 ꢁC was performed in a sealed
tube. All catalytic reactions were done under aerobic conditions.
Percentage conversions were determined by GC with n-decane as
the internal standard and the coupling products were characterized
by mass spectrometry (Table 4) as well as 1H NMR spectroscopy
(Entry 5, Table 4 only).
Acknowledgements
We gratefully thank the University of Cape Town, the National
Research Foundation (NRF) of South Africa, the Royal Netherlands
Academy of Arts and Sciences (KNAW) for a Carolina MacGillavry
PhD Fellowship (T.M.), and SASOL (M.M.M.) for financial support.
We thank the AngloPlatinum Corporation and Johnson Matthey for
the kind donation of metal salts.
Appendix A. Supplementary material
CCDC 819785 contains the supplementary crystallographic data
for complex 3b for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
4.4. X-ray data collection and structure refinement of
[Pd(C27H24NP)(Me)Cl (3b)
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