Synthesis, characterization, and reactivity of neutral and cationic Pd-C,N,N pincer complexes

Article abstract of DOI:10.1002/ejic.200500479

The ortho-palladation of the iminophosphane ligand 6-phenyl-2-[(2,6- diisopropylphenyl)imino]pyridine (HL) with Pd(OAc)₂ and PdCl ₂(PhCN)₂ in benzene yields the neutral Pd-C,N,N pincer complexes Pd(OAc)(κ³-C,N,N

Full text of DOI:10.1002/ejic.200500479

FULL PAPER
DOI: 10.1002/ejic.200500479
Synthesis, Characterization, and Reactivity of Neutral and Cationic Pd–C,N,N
Pincer Complexes
Claudio Bianchini,[a] Géraldine Lenoble,[a] Werner Oberhauser,*[a] Sébastien Parisel,[a] and
Fabrizio Zanobini[a]
Keywords: Pd pincer / NMR spectroscopy / IR spectroscopy / Secondary phosphanes / Suzuki reaction
The ortho-palladation of the iminophosphane ligand 6-
phenyl-2-[(2,6-diisopropylphenyl)imino]pyridine (HL) with
Pd(OAc)2 and PdCl2(PhCN)2 in benzene yields the neutral
Pd–C,N,N pincer complexes Pd(OAc)(κ3-C,N,N-L) (1) and
been characterized by multinuclear NMR and IR spec-
troscopy. The solid-state structures of 1 and 2 have been de-
termined by single-crystal X-ray diffraction techniques. Both
the neutral compounds 1 and 2 and the cationic derivatives
PdCl(κ3-C,N,N-L) (2), respectively. In the presence of Na- 3, 4, and 5 were tested as catalyst precursors for the Suzuki
BArЈ4 [ArЈ = 3,5-(CF3)2C6H3], 2 reacts in CH2Cl2 with MeCN,
cross-coupling of 4-bromo- and 4-chloroacetophenone with
phenylboronic acid.
PPh3, or PH[o-MeO(C6H4)]2 to give the cationic palladium(II
)
pincer complexes [Pd(CH3CN)(κ3-C,N,N-L)]BArЈ4 (3),
[Pd(PPh3)(κ3-C,N,N-L)]BArЈ4 (4) and {Pd[PH(o-MeOC6H4)2]-
(κ3-C,N,N-L)}BArЈ4 (5), respectively. Complexes 1–5 have
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
phosphane-free catalysts for the Suzuki reaction of bro-
moarenes and chloroarenes, while the C,N- and C,O-palla-
dacycles b–f in conjunction with either secondary bulky
phosphanes[4] or N-heterocyclic carbenes[5] are very active
catalytic systems for the Suzuki reaction of chloroarenes.
The phosphinite P,C,P pincer complex i described by
Bedford exhibits a good activity for bromoarenes and con-
stitutes a successful example of the application of a terdent-
ate palladium(ii) pincer complex in a Suzuki reaction.[6]
Terdentate Pd–C,N,N pincer complexes have also been used
to catalyze Heck and Heck-type reactions.[7]
The ligands that have been employed so far for the syn-
thesis of Pd–C,N,N pincer complexes are shown in
Scheme 2.[8] A common structural motif to most ligands is
a planar assembly of nitrogen donor atoms from either pyr-
idine rings or imine groups, yet the combination of both
moieties in the same molecule has never been tested in pal-
ladium ortho-metallation.
Aimed at filling this gap, we decided to study the coordi-
nation chemistry of the (imino)pyridine ligand 6-phenyl-2-
[(2,6-diisopropylphenyl)imino]pyridine (HL) (Scheme 3)
that has been successfully employed to oligomerize ethylene
in conjunction with CoCl2 and MAO.[9] As a result, both
neutral and cationic PdII–C,N,N pincer complexes have
been obtained and fully characterized. A preliminary study
of the performance of these complexes in Suzuki cross-
coupling reactions of 4-bromo- and 4-chloroacetophenone
with phenylboronic acid has been carried out and is herein
reported.
Palladacycles constitute a numerous and thoroughly in-
vestigated class of organometallics commonly stabilized by
four-electron (bidentate) or six-electron (tridentate) donor
ligands.[1] The synthesis of palladacycles is relatively facile
and the modulation of their electronic and steric properties
can be achieved by varying (i) the size of the metallacyclic
ring, (ii) the nature of the metallated carbon atom (ali-
phatic, aromatic, vinylic), (iii) the type of donor atoms (N,
P, S, O) in the supporting ligand, and (iv) the nature of the
co-ligands. Proper combinations of these factors determine
whether dinuclear, mononuclear, neutral, or cationic com-
pounds are formed.
Herrmann’s discovery in 1995 that palladacycles can be
effective catalysts for Heck coupling reactions of aryl ha-
lides has stimulated much research aimed at using these or-
ganometallics in C–C bond-forming processes.[2] The most
important applications reported so far include Heck coup-
ling, Suzuki and Stille cross-couplings, and Sonogashira re-
actions.[1a] Some of the most active palladacycle catalysts
for Suzuki coupling reactions are reported in Scheme 1.
The C,N-palladacycles g and h reported by Milstein[3a]
and Nájera,[3b] respectively, are the only really efficient
[a] ICCOM-CNR, Area della Ricerca di Firenze,
Via Madonna del Piano, 50019 Sesto Fiorentino (Firenze), Italy
Fax: +39-055-522-5203
E-mail: Werner.oberhauser@iccom.cnr.it
4794
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Eur. J. Inorg. Chem. 2005, 4794–4800

Synthesis, Characterization, and Reactivity of Pd–C,N,N Pincer Complexes
FULL PAPER
Scheme 1.
Results and Discussion
The reaction of HL with Pd(OAc)2 and PdCl2(PhCN)2 in
refluxing benzene yields the yellow, air-stable, neutral ter-
dentate Pd–C,N,N pincer complexes Pd(OAc)L (1) and
PdClL (2) in fairly good yields (57 and 81%), respectively.
Complex 2 was transformed into the monocationic Pd–
C,N,N pincer compounds 3, 4, and 5 by scavenging the
chloride ion with NaBArЈ4 in the presence of MeCN, PPh3,
or PH(o-MeOC6H4)2. The synthesis of the latter com-
pounds was readily achieved by dissolving 2 in oxygen-free
dichloromethane and adding acetonitrile, PPh3, or the new
secondary monophosphane PH(o-MeOC6H4)2 (Scheme 3).
The cationic complexes were isolated in good yields, from
60–70%, as yellow, air- and moisture-stable solids. All our
attempts to isolate 3, 4, and 5 with chloride as the counter-
ion were unsuccessful.
The solid-state structures of 1 and 2 have been deter-
mined by a single-crystal X-ray diffraction analysis. Crystal-
lographic data as well as selected bond lengths and angles
of both compounds are reported in Tables 1 and 2, respec-
tively, while ORTEP illustrations are presented in Figure 1.
The asymmetric unit of 1 contains one molecule of the
neutral pincer complex, while that of 2 contains one mole-
cule of 2 together with one molecule of CH2Cl2 and half a
molecule of toluene located on an inversion center. Both
complexes exhibit a distorted square-planar coordination
geometry. The metal center in 1 deviates by 0.004(6) Å in
the direction of C(20) from the plane defined by the atoms
C(1), N(1), and N(2). From the analogous plane, 2 deviates
by 0.016(6) Å in the direction of C(23). In both structures,
the Pd atom is coordinated by nitrogen atoms from pyridine
and imine groups and by one carbon atom, C(1), from the
6-phenyl ring. The square-planar geometry is completed by
an oxygen atom, O(1) from an acetate ligand in 1, and by
a chloride atom in 2. The slightly longer Pd(1)–N(2) bond
in 1 as compared to 2 is probably due to a significant steric
interaction between the acetate unit and an isopropyl group
of the ligand [shortest O···H contact distance of 2.844 Å
between O(2) and H(21B)]. A longer Pd–Nimine distance in
1 was also inferred from the IR spectrum which shows a
less pronounced red shift of the C=N band in 1 (21 cm–1)
Scheme 2.
Scheme 3.
Eur. J. Inorg. Chem. 2005, 4794–4800
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C. Bianchini, G. Lenoble, W. Oberhauser, S. Parisel, F. Zanobini
FULL PAPER
Table 1. Crystallographic data for 1 and 2·CH2Cl2·0.5 C7H8.
1
2·CH2Cl2·0.5
C7H8
Empirical formula
Formula mass
Temperature [K]
Wavelength [Å]
Crystal system
Space group
a [Å]
C27H30N2O2Pd C29.5H33Cl3N2Pd
520.93
293(2)
0.71073
628.33
293(2)
0.71073
orthorhombic monoclinic
P212121
12.050(3)
13.909(15)
14.530(9)
90.0
2435(3)
4
P21/c
9.788(7)
12.924(2)
23.027(6)
91.97(3)
2911(2)
4
b [Å]
c [Å]
β [°]
V [Å3]
Z [g m–3]
Dcalcd. [gm–3]
1.421
1.434
0.933
Absorption coefficient [mm–1] 0.787
F(000)
Crystal size [mm]
1072
1284
0.70×0.28×0.250.4×0.2×0.2
θ range for data collection [°] 2.03–25.08
2.08–25.02
–11 Յ h Յ 11
0 Յ k Յ 15
0 Յ l Յ 27
5087
5087
1.012
Limiting indices
0 Յ h Յ 14
0 Յ k Յ 16
0 Յ l Յ 17
2427
Measured reflections
Unique reflections
2427
GOF on F2
1.066
Data/restraints/parameters
Final R indices [I Ͼ 2σ(I)]
2427/0/289
R1 = 0.0470,
5087/8/302
R1 = 0.0583,
wR2 = 0.1226 wR2 = 0.1291
R1 = 0.0555, R1 = 0.1474,
wR2 = 0.1281 wR2 = 0.1586
Largest diff. peak/hole [e·Å–3] 1.076/–1.271
0.762/–0.892
R indices (all data)
Table 2. Selected bond lengths [Å] and angles [°] for compounds 1
and 2·CH2Cl2·0.5 C7H8.
Figure 1. ORTEP representation (30% probability displacement el-
lipsoids) of compounds 1 (top) and 2 (bottom). Hydrogen atoms
as well as solvent molecules are omitted for clarity.
1
2·CH2Cl2·0.5 C7H8
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–C(1)
Pd(1)–O(1)
Pd(1)–Cl(1)
N(2)–C(12)
N(1)–Pd(1)–N(2)
N(1)–Pd(1)–C(1)
C(1)–Pd(1)–O(1)
N(1)–Pd(1)–O(1)
C(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
1.954(6)
2.184(6)
1.957(8)
2.051(6)
1.955(5)
2.156(6)
1.970(7)
expected, tilted with respect to the coordination plane,
showing a dihedral angle of 76.1(5)° and 85.8(4)° in 1 and
2, respectively, due to the pronounced steric repulsion be-
tween the coordinating acetate and an isopropyl group from
the ligand.
Compounds 1–5 have been characterized in solution by
multinuclear 1D and homo- and heteronuclear correlated
2D NMR spectroscopy.[10a] 13C{1H} NMR spectroscopy
has proved to be a useful technique to elucidate the solution
structure of all compounds, especially to assess the presence
of a Pd–C bond involving the phenyl ring attached at the
6-position of the pyridine unit.[10b–10e] Significant 13C NMR
chemical shifts, namely those pertaining to the C-1, C-2,
2.295(2)
1.286(9)
77.4(2)
81.6(3)
1.262(10)
77.7(3)
81.8(3)
98.7(3)
171.5(3)
97.6(2)
177.9(2)
as compared to 2 (30 cm–1). The Pd(1)–C(1) bond lengths
of either structure [1.957(8) Å in 1 and 1.970(7) Å in 2]
match well the values reported for other pincer PdII sys-
tems.[8a,8c,8d,8f,8h,8i] The two bite angles [N(1)–Pd(1)–C(1):
81.8(3)° in 1; 81.6(3)° in 2; N(1)–Pd(1)–N(2): 77.7(3)° in 1;
77.4(2)° in 2] are comparable in either structure, while the
coordination angle N(1)–Pd(1)–O(1) of 171.5(3)° in 1 and
the coordination angle N(1)–Pd(1)–Cl(1) of 177.9(2)° in 2
are significantly different. Indeed, 1 shows a deviation of
the bonded oxygen atom O(1) by 0.292(17) Å from the
plane defined by C(1), N(1), and N(2) in the direction of
C(23), while 2 exhibits a deviation of Cl(1) by 0.111(16) Å
from the analogous plane in the direction of C(23). In both
crystal structures, the 2,6-(diisopropyl)phenyl moiety is, as
Table 3. Selected 13C{1H} chemical shifts for HL and for com-
pounds 1–5.
C-1 (2JC,P [Hz])
C-2 (3JC,P [Hz])
C-4
C-12
HL
1
127.67
153.22
153.16
153.17
150.22 (4.9)
151.98 (5.4)
129.69
135.80
137.71
136.73
124.88
125.15
128.03
126.72
126.54
168.50
172.30
172.70
176.43
178.30
177.40
2
3
136.08
4
140.21 (10.5)
136.72 (10.5)
5
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Synthesis, Characterization, and Reactivity of Pd–C,N,N Pincer Complexes
FULL PAPER
1
Table 4. Selected H chemical shifts for HL and for compounds 1–5.
2-H (multiplicity)
3-H (multiplicity)
4-H (multiplicity)
5-H (multiplicity)
13-H (multiplicity)
4
4
4
4
4
([3JH,H, JH,H, JP,H [Hz])
(3JH,H, JH,H [Hz])
(3JH,H, JH,H [Hz])
(3JH,H, JH,H [Hz])
HL
1
7.54 (t)
(7.4)
7.48 (tt)
(7.2, 1.2)
7.08 (td)
(7.4, 1.6)
7.15 (td)
(7.4, 1.7)
7.21 (td)
(7.5, 1.2)
6.52 (td)
(8.1, 1.6)
6.74 (td)
(7.7, 1.5)
7.54 (t)
(7.4)
8.18 (d)
2.38 (s)
2.19 (s)
2.21 (s)
2.24 (s)
2.10 (s)
2.27 (s)
(7.2, 1.4)
7.33 (dd)
(6.6, 1.5)
7.84 (dd)
(7.4, 1.6)
7.40 (dd)
(7.6, 1.5)
7.43 (dd)
(7.7, 1.6)
7.44 (dd)
(7.8, 1.5)
7.19 (dd)
(7.5, 1.2)
7.41 (dd)
(7.4, 1.7)
6.99 (dd)
(7.6, 1.1)
6.32 (ddd)
(8.1, 0.9, 5.3)
6.24 (ddd)
(7.8, 1.0, 5.3)
7.02 (td)
(7.5, 1.4)
7.11 (td)
(7.4, 1.5)
7.13 (td)
(7.6, 1.6)
6.99 (td)
(7.5, 0.8)
7.06 (td)
(7.4, 1.0)
2
3
4
5
and C-4 carbon atoms from the phenyl ring and to the im- Table 5. Suzuki coupling of 4-bromo- and 4-chloroacetopheneone
with phenylboronic acid in the presence of 1, 2, 3, 4 and 5.
ine carbon atom C-12 are reported in Table 3, which also
provides 13C NMR spectroscopic data for the free ligand.
In line with the literature, the signals of C-1 and C-2 are
shifted down-field as compared to the free ligand, while the
Entry[a] Complex Substrate [Pd] [%]
Time [h] TON[b]
1
2
3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
1.0
1.0
0.01
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.01
0.01
1.0
0.01
0.01
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
2
4
4
2
4
4
2
4
2
4
2
2
4
2
2
4
8
8
8
8
4
8
4
8
64
89
70
25
99
31
83
85
13
2
signal of C-4 is shifted up-field.[10e] The J(C,P) coupling
4
1
constants of 4.9 Hz in 4 and 5.4 Hz in 5 provide further
evidence for ortho-palladation involving the 6-phenyl ring.
The coordination of the imine nitrogen atom to the PdII
center can be safely assessed on the basis of the down-field
shift of the imine carbon signal of C-12.
5
1
6[c]
7
1
2
8
9
2
3
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3
46
The H NMR spectra of 1–5 are fully consistent with
4
100
6200
8900
98
3400
9700
0
17
2
14
17
ortho-palladation of the 6-phenyl ring (Table 4).
4
Of particular relevance to confirm the occurrence of or-
tho-metallation are the multiplicities of the resonances of
the 6-phenyl ring. Indeed, the signals of 2-H and 5-H ap-
pear as a doublet of doublet and 3-H and 4-H show a trip-
let of doublet, while the free ligand exhibits a doublet for
the ortho protons 1-H and 5-H, triplets for 2-H and 4-H
and a triplet of triplet for the para proton 3-H. The small
4JP,H coupling constant of 5.3 Hz observed for 2-H in the
1H NMR spectra of compounds 4 and 5 is consistent with
the coordination of PPh3 and HP[o-MeO(C6H4)]2. The co-
ordination of the imine nitrogen atom to the palladium
atom is confirmed by an up-field shift of the methylimine
resonance (13-H), as compared to the free ligand.
Compounds 1–5 have been tested as catalyst precursors
for the Suzuki cross-coupling reaction of 4-bromo- and 4-
chloroacetophenone with phenylboronic acid in the pres-
ence of Cs2CO3 as the basic co-reagent in 1,4-dioxane at
100 °C (Scheme 4). This catalytic protocol is rather com-
mon for Suzuki reactions leading to selective production of
the unsymmetrically substituted biaryl.[1a,1b] Selected results
are given in Table 5.
4
5
5
5
Pd(OAc)2
1
2
3
4
4
5
5
57
61
86
[a] Catalytic conditions: 2×10–6 mol of Pd precatalyst, 2×10–4 mol
of substrate, 3 ×10–4 mol of phenylboronic acid, 6 ×10–4 mol of
Cs2CO3, T: 100 °C, solvent: 1,4-dioxane (15 mL). [b] TON deter-
1
mined by H NMR in CDCl3. [c] 1,4-Dioxane/water (14:1, v:v).
the low catalytic activity observed in a water/dioxane mix-
ture (Entry 6). Examination of withdrawn samples showed
the formation of the biaryl product after only 5 min. Unlike
the reaction catalyzed by Pd(OAc)2, no Pd metal precipi-
tation was observed using 1–5 as the catalyst precursors. In
situ NMR experiments showed the absence of free phos-
phane ligands during the reaction catalyzed by 4 and 5.
In line with the results reported in the literature, 4-bro-
moacetophenone is much more reactive than the analogous
chloro derivative, due to the lower bond strength of Ar–Br
as compared to Ar–Cl.[11] The coupling of 4-bromoace-
Scheme 4.
All catalytic coupling reactions were carried out under tophenone with phenylboronic acid is catalyzed by both the
an inert gas in freshly distilled 1,4-dioxane in order to avoid phosphane-free precursors 1, 2, and 3 and the phosphane-
the risk of imine hydrolysis, which may be responsible for modified precursors 4 and 5. However, the latter form much
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C. Bianchini, G. Lenoble, W. Oberhauser, S. Parisel, F. Zanobini
FULL PAPER
experiments, such as 1H COSY, 1H NOESY, and 1H-13C corre-
lations using degassed nonspinning samples. All the 2D NMR
spectra were recorded with a Bruker Avance DRX-400 instrument
using pulse sequences suitable for phase-sensitive representations
using TPPI. The 1H-13C correlations were recorded using an
HMQC sequence with decoupling during acquisition. GC analyses
were performed with a Shimadzu GC-14A gas chromatograph
equipped with a flame ionization detector and a 30 m (0.25 mm
i.d., 0.25 μm film thickness) SPB-1 Supelco fused silica capillary
column. GC-MS analyses were performed with a Shimadzu QP
more active catalysts, which has been previously observed
and attributed to the formation of coordinatively unsatu-
rated (phosphane)Pd0 catalysts.[1b] As a general trend, the
cationic precursors originate more efficient catalysts.
In the Suzuki cross-coupling of 4-chloroacetophenone
only the monophosphane-modified precursors 4 and 5 have
shown a significant activity.[12] Interestingly, the catalyst
modified with the secondary phosphane PH(o-MeOC6H4)2
is the most active with both 4-bromo- and 4-chloroaceto-
phenone, which is consistent with Indolese’s finding that 5000 apparatus equipped with a column identical to that used for
GC analysis.
bulky secondary monophosphanes in conjunction with Pd–
C,N or Pd–C,O palladacycles provide powerful systems for
Suzuki and Heck reactions.[4] Indeed, most of the really ef-
ficient catalytic systems for Suzuki cross-coupling contain
bulky monophosphanes,[12] hemilable P–O[13] and P–N li-
gands,[14] and 1,3-disubstituted imidazol-2-ylidenes.[15]
In the case of 5, an in situ NMR study under catalytic
conditions has shown the occurrence of phosphane depro-
tonation to give various unidentified phosphido–palladium
species, which might be responsible for the high catalytic
activity.
Catalytic Reactions: 1,4-Dioxane (15 mL) was degassed in a round-
bottomed flask by means of vacuum/nitrogen cycles. To this solvent
were added 4-bromoacetophenone or 4-chloroacetophenone
(2×10–4 mol), phenylboronic acid (36 mg, 3×10–4 mol), CsCO3
(115 mg, 6×10–4 mol) and the appropriate precatalyst
(2×10–6 mol) at room temperature under nitrogen. The resulting
suspension was heated under nitrogen to 100 °C with stirring to
give a clear solution. Heating was continued for the desired time.
Then, the solution was cooled to room temperature and ethyl ace-
tate (15 mL) was added. The solid products were removed from the
solution by filtration and the organic layer was washed with water
(three 30 mL portions) to remove CsCO3. The aqueous layer was
extracted three times with ethyl acetate. The combined organic lay-
ers were washed with brine, dried with MgSO4 and concentrated
to yield a pale yellow solid. The yield of the product was deter-
Conclusions
New PdII–C,N,N pincer complexes have been synthe-
sized and fully characterized in both the solid state and
solution. As a probe reaction to test their potential in
1
mined by H NMR in CDCl3.
Syntheses
homogeneous catalysis, these complexes have been em- PH(o-CH3OC6H4)2: The bis(o-methoxyphenyl)phosphane oxide
HPO(o-CH3OC6H4)2 was synthesized as described in the litera-
ture.[18] The subsequent reduction of the phosphane oxide was per-
formed applying a protocol similar to that published by Vine-
yard.[19] HSiCl3 (12.1 mL, 120.0 mmol) was added to a solution
of bis(o-methoxyphenyl)phosphane oxide (10.48 g, 40.0 mmol) and
triethylamine (16.7 mL, 120.0 mmol) in acetonitrile (250 mL) at
room temperature. The reaction mixture was refluxed for 8 h. Af-
terwards, the solution was cooled to 0 °C and a solution of KOH
(40 g) in water (150 mL) was slowly added to the reaction mixture.
An off-white solid precipitated that was, however, dissolved at the
end of the addition to form a clear two-phase system. The organic
phase was separated and the solvent was removed under reduced
pressure. The crude product was washed with degassed ethanol
(30 mL) and the product was filtered off and dried in a stream of
nitrogen. Yield: 7.19 g (73%). C14H14O2P (245.1): calcd. C 68.60,
H 5.71; found C 68.20; H 5.60. 1H NMR (200.13 MHz, CDCl3,
ployed as catalyst precursors for cross-coupling reactions
of 4-bromo- and 4-chloroacetophenone with phenylboronic
acid to give 4-acetylbiphenyl. Only the phosphane-modified
complexes have shown significant activity. This activity,
however, is far lower than the most active catalysts reported
in the literature.
Experimental Section
General: All manipulations were carried out under nitrogen using
Schlenk-type techniques. All the solid compounds were collected
on sintered-glass frits and washed with appropriate solvents before
[16]
being dried in a stream of nitrogen. PdCl2(C6H5CN)2
and
NaB[C6H3(CF3)2]4 (NaBArЈ4)[17] were prepared according to litera-
ture methods. The ligands (2,6-diisopropylphenyl)[1-(6-phenylpyri-
din-2-yl)ethylidene]amine (HL) and 1-(6-phenylpyridin-2-yl)ethan-
one were prepared as reported in the literature.[9] The solvents were
distilled under nitrogen from Na (n-pentane, diethyl ether, benzene)
or CaH2 (CH2Cl2). All the other reagents and solvents were used
as purchased from commercial suppliers. Deuterated solvents for
NMR measurements were dried with molecular sieves. Elemental
analyses were performed with a Carlo Erba Model 1106 elemental
analyzer. Infrared spectra were recorded with an FT-IR Spectrum
1
294 K): δ = 3.78 (s, 6 H, OCH3), 5.23 (d, JH,P = 229 Hz, 1 H,
PH), 6.80–7.40 (m, 8 H, C6H4) ppm. 31P{1H} NMR (81.01 MHz,
CDCl3, 294 K): δ = –71.70 (s) ppm.
[6-C6H4-py-2-C(Me)=N(2,6-iPr2C6H3)]PdOAc (1): The ligand HL
(300 mg, 0.84 mmol) and Pd(OAc)2 (190 mg, 0.84 mmol) were dis-
solved in degassed benzene (30 mL). The resultant red solution was
heated at 60 °C for 16 h. Afterwards, this solution was filtered
through Celite and concentrated to 2 mL. To this solution diethyl
ether (15 mL) was added to precipitate a yellow-green compound,
which was filtered off and dried in a stream of nitrogen. Yield:
1
GX instrument. H, 13C{1H}, and 31P{1H} NMR spectra were re-
corded at 200.13, 50.32, and 81.01 MHz, respectively, with a Bruker
ACP-200 spectrometer or at 400.13, 100.62, and 161.98 MHz, 250 mg (57%). C27H30N2O2Pd (520.69): calcd. C 62.28, H 5.76, N
respectively, with a Bruker Avance DRX-400 spectrometer. Chemi-
cal shifts are reported in ppm (δ) with reference to either TMS as
an internal standard [1H and 13C{1H} NMR spectra] or 85%
H3PO4 as an external standard [31P{1H} NMR spectra]. The as-
signment of 1H and 13C signals was based on 1D and 2D NMR
5.38; found C 62.10, H 5.55, N 5.10. 1H NMR (400.13 MHz,
3
CDCl3, 294 K): δ = 1.15 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2], 1.40
3
[d, JH,H = 6.8 Hz, 6 H, CH(CH3)2], 1.75 [s, 3 H, CH3CO2], 2.19
3
[s, 3 H, 13-H], 3.17 [sept, JH,H = 6.8 Hz, 2 H, CH(CH3)2], 7.02
3
4
3
(td, JH,H = 7.5, JH,H = 1.4 Hz, 1 H, 4-H), 7.08 (td, JH,H = 7.4,
4798
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2005, 4794–4800

Synthesis, Characterization, and Reactivity of Pd–C,N,N Pincer Complexes
FULL PAPER
3
4
4JH,H = 1.6 Hz, 1 H, 3-H), 7.19 (dd, JH,H = 7.5, JH,H = 1.2 Hz, 7), 176.43 (C-12) ppm. IR (KBr): ν = 1609 (C=N), 2327 (C–N),
˜
3
1 H, 2-H), 7.22–7.29 (m, 3 H, 16–18-H), 7.33 (dd, JH,H = 6.6,
2300 (C–N) cm–1.
3
4
4JH,H = 1.5 Hz, 1 H, 5-H), 7.35 (dd, JH,H = 6.1, JH,H = 0.9 Hz,
{[6-C6H4-py-2-C(Me)=N(2,6-iPr2C6H3)]Pd[P(C6H5)]3}BArЈ4
(4):
3
4
1 H, 10-H), 7.73 (dd, JH,H = 8.4, JH,H = 0.9 Hz, 1 H, 8-H), 7.94
Compound 2 (80 mg, 0.16 mmol) and PPh3 (40 mg, 0.16 mmol)
were dissolved in degassed CH2Cl2 (20 mL). To this yellow solution
NaBArЈ4 (170 mg, 0.19 mmol) was added. During a reaction time
of 3 h, NaCl was formed, which was removed by filtration through
Celite. The clear yellow solution was then concentrated to 2 mL
and n-hexane was added to precipitate a yellow product, which was
filtered off and dried in a stream of nitrogen. Yield: 160 mg
(62.7%). C75H54BF24N2PPd (1586.78): calcd. C 56.77, H 3.40, N
1.76; found C 56.62, H 3.55, N 1.84. 1H NMR (400.13 MHz,
(t, JH,H = 7.7 Hz, 1 H, 9-H) ppm. 13C{1H} NMR (100.62 MHz,
3
CDCl3, 294 K):
δ = 17.59 (C-13), 23.25 (CH3CO2), 23.72
[CH(CH3)2], 23.87 [CH(CH3)2], 28.71 [CH(CH3)2], 121.05 (C-8),
121.07 (C-10), 123.48 (C-16, C-18), 124.01 (C-5), 124.88 (C-4),
126.92 (C-17), 130.85 (C-3), 135.80 (C-2), 138.72 (C-15, C-19),
139.47 (C-9), 141.02 (C-14), 146.83 (C-6), 153.20 (C-11), 153.22 (C-
1), 165.34 (C-7), 172.30 (C-12), 176.81 (CH3COO) ppm. IR (KBr):
ν = 1617 (C=N), 1717 (C=O) cm–1.
˜
3
[6-C6H4-py-2-C(Me)=N(2,6-iPr2C6H3)]PdCl (2): The ligand HL
(150 mg, 0.42 mmol) and PdCl2(C6H5CN)2 (160 mg, 0.42 mmol)
were dissolved in benzene (20 mL) at room temperature. The
orange suspension was refluxed for 12 h. During this time a yellow
precipitate formed. The suspension was concentrated to dryness
and the yellow powder was suspended in diethyl ether and filtered
off, washed several times with diethyl ether and then dried in a
stream of nitrogen. Yield: 180 mg (86.1%). C25H27ClN2Pd
(497.14): calcd. C 60.40, H 5.43, N 5.63; found C 60.62, H 5.57, N
CDCl3, 294 K): δ = 0.79 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2], 1.01
[d, 3JH,H = 6.8 Hz, 6 H, CH(CH3)2], 2.10 (s, 3 H, 13-H), 2.86 [sept,
3JH,H = 6.8 Hz, 2 H, CH(CH3)2], 6.32 (ddd, JH,H = 8.1, JH,P
=
3
3
5.3, 4JH,H = 0.8 Hz, 1 H, 2-H), 6.52 (td, 3JH,H = 8.1, 4JH,H = 1.6 Hz,
3
1 H, 3-H), 6.88 (d, JH,H = 7.8 Hz, 2 H, 16-H, 18-H), 6.99 (td,
3JH,H = 7,5, JH,H = 0.8 Hz, 1 H, 4-H), 7.15 (t, JH,H = 7.8 Hz, 1
4
3
H, 17-H), 7.23 (m, 12 H, o+m-PPh3), 7.41 (m, 3 H, p-PPh3), 7.43
3
4
(dd, JH,H = 7.7, JH,H = 1.6 Hz, 1 H, 5-H), 7.52 (d, 1 H, 10-H),
7.53 {br. s, 4 H, p-B[C6H3(CF3)2]4}, 7.74 {m, 8 H, o-B[C6H3-
1
3
3
3
5.70. H NMR (400.13 MHz, CDCl3, 294 K): δ = 1.16 [d, JH,H
=
(CF3)2]4}, 7.88 (t, JH,H = 8.2 Hz, 1 H, 9-H), 7.89 (d, JH,H =
3
6.9 Hz, 6 H, CH(CH3)2], 1.40 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2], 8.2 Hz, 1 H, 8-H) ppm. 13C{1H} NMR (100.62 MHz, CDCl3,
3
2.21 (s, 3 H, 13-H), 3.06 [sept, JH,H = 7.0 Hz, 2 H, CH(CH3)2],
294 K): δ = 18.90 (C-13), 22.71 [CH(CH3)2], 23.50 [CH(CH3)2],
28.73 [CH(CH3)2], 117.50 [p-C6H3(CF3)2], 122.10 (C-8), 122.60 (C-
3
4
3
7.11(td, JH,H = 7.4, JH,H = 1.5 Hz, 1 H, 4-H), 7.15 (td, JH,H
=
4
1
7.4, JH,H = 1.7 Hz, 1 H, 3-H), 7.23–7.30 (m, 3 H, 16–18-H), 7.41 10), 124.20 (C-16, C-18), 124.50 (q, JCF = 272.6 Hz, CF3), 125.80
3
4
3
3
(dd, JH,H = 7.4, JH,H = 1.7 Hz, 1 H, 2-H), 7.53 (dd, JH,H = 7.8,
(C-5), 126.72 (C-4), 128.0 (p-PPh3), 128.80 (d, JC,P = 10.8 Hz, m-
4JH,H = 0.9 Hz, 1 H, 10-H), 7.75 (dd, JH,H = 8.3, JH,H = 0.7 Hz, PPh3), 128.80 (q, 2JC,P = 32.5 Hz, CCF3), 128.90 (C-17), 128.90 (d,
3
4
3
4
1 H, 8-H), 7.84 (dd, JH,H = 7.4, JH,H = 1.6 Hz, 1 H, 5-H), 7.99
1JC,P = 49.8 Hz, ipso-PPh3), 130.90 (d, 4JC,P = 4.5 Hz, C-3), 131.50
(o-PPh3), 134.80 [o-C6H3(CF3)2], 137.80 (C-15, C-19), 140.21 (d,
(t, JH,H = 7.8 Hz, 1 H, 9-H) ppm. 13C{1H} NMR (100.62 MHz,
3
CDCl3, 294 K): δ = 17.40 (C-13), 23.47 [CH(CH3)2], 24.02 3JC,P = 10.5 Hz, C-2), 141.80 (C-9), 142.80 (C-14), 148.10 (C-6),
2
1
[CH(CH3)2], 28.74 [CH(CH3)2], 120.71 (C-8), 121.0 (C-10), 123.50
150.22 (d, JC,P = 4.9 Hz, C-1), 151.98 (C-11), 161.80 (q, JC,B =
(C-16, C-18), 124.31 (C-5), 125.15 (C-4), 127.20 (C-17), 131.0 (C-
49.5 Hz,
ipso-CB),
164.20
(C-7),
178.30
(C-12) ppm.
3), 137.71 (C-2), 138.2 (C-15, C-19), 138.91 (C-9), 141.0 (C-14), 31P{1H}(161.98 MHz, CDCl3, 294 K): δ = 39.2 (s) ppm. IR (KBr):
147.0 (C-6), 152.98 (C-11), 153.15 (C-1), 165.20 (C-7), 172.70 (C- ν = 1608 (C=N) cm–1.
˜
12) ppm. IR (KBr): ν = 1612 (C=N) cm–1.
˜
{[6-C6H4-py-2-C(Me)=N(2,6-iPr2C6H3)]Pd[PH(o-MeOC6H4)]2}-
{[6-C6H4-py-2-C(Me)=N(2,6-iPr2C6H3)]Pd(NCCH3)}BArЈ4
(3): BArЈ4 (5): Compound 2 (100 mg, 0.22 mmol) and PH(o-MeO-
Compound 2 (60 mg, 0.12 mmol) was dissolved in a mixture of
dichloromethane (15 mL) and acetonitrile (1 mL). To this yellow
solution NaBArЈ4 (115 mg, 0.13 mmol) was added. The yellow
solution was stirred for 30 min. During this time NaCl precipitated,
which was removed by filtration through Celite. The clear yellow
solution was then concentrated to dryness. No recrystallization was
needed. Yield: 120 mg (73.0%). C59H39BF24N3Pd (1362.61): calcd.
C6H4)2(53 mg, 0.22 mmol) were dissolved in degassed CH2Cl2
(20 mL). To this yellow solution NaBArЈ4 (190 mg, 0.21 mmol) was
added. During a reaction time of 2 h NaCl was formed, which was
removed by filtration through Celite. The clear yellow solution was
then concentrated to 3 mL and n-hexane was added to precipitate
a bright yellow product, which was filtered off and dried in a
stream of nitrogen. Yield: 0.16 g, (60.0%). C71H54BF24N2O2PPd
(1570.71): calcd. C 54.29, H 3.44, N 1.78; found C 54.15, H 3.33,
1
C 52.00, H 2.86, N 3.08; found C 52.10, H 2.92, N 3.15. H NMR
3
1
3
(400.13 MHz, CDCl3, 294 K): δ = 1.19 [d, JH,H = 6.9 Hz, 6 H, N 1.67. H NMR (400.13 MHz, CDCl3, 294 K): δ = 0.85 [d, JH,H
3
3
CH(CH3)2], 1.30 [d, JH,H = 6.8 Hz, 6 H, CH(CH3)2], 2.00 (s, 3 H,
= 6.8 Hz, 6 H, CH(CH3)2], 1.06 [d, JH,H = 6.8 Hz, 6 H,
3
3
CH3CN), 2.24 (s, 3 H, 13-H), 2.95 [sept, JH,H = 6.8 Hz, 2 H,
CH(CH3)2], 2.27 (s, 3 H, 13-H), 2.86 [sept, JH,H = 6.8 Hz, 2 H,
3
4
1
CH(CH3)2], 6.99 (dd, JH,H = 7.6, JH,H = 1.1 Hz, 1 H, 2-H), 7.13 CH(CH3)2], 3.66 (s, 3 H, OCH3), 5.39 (d, JP,H = 381.5 Hz, 1 H,
3
4
3
4
(td, JH,H = 7.6, JH,H = 1.6 Hz, 1 H, 4-H), 7.21 (td, JH,H = 7.5,
PH), 6.24 (ddd, 3JH,H = 7.8, JH,H = 1.0, 4JPH = 5.3 Hz, 2-H), 6.74
4JH,H = 1.2 Hz, 1 H, 3-H), 7.28–7.35 (m, 3 H, 16–18-H), 7.40 (dd,
(td, JH,H = 7.7, JH,H = 1.5 Hz, 3-H), 6.84–6.95 (m, 6 H, m + o-
3
4
3JH,H = 7.6, 4JH,H = 1.5 Hz, 1 H, 5-H), 7.41 (dd, 3JH,H = 7.8, 4JH,H Anisyl), 7.06 (td, JH,H = 7.4, JH,H = 1.0 Hz, 1 H, 4-H), 7.22 (m,
3
4
= 0.9 Hz, 1 H, 10-H), 7.54 [br. s, 4 H, p- B[C6H3(CF3)2]4], 7.66 (dd,
2 H, 16-H, 18-H), 7.34 (m, 1 H, 17-H), 7.44 (dd, 3JH,H = 7.8, 4JH,H
4
3
4
5
3JH,H = 8.4, JH,H = 0.8 Hz, 1 H, 8-H), 7.73 [m, 8 H, o-
= 1.5 Hz, 1 H, 5-H), 7.46 (dt, JH,H = 8.7, JH,H = 1.0, JH,P =
3
B[C6H3(CF3)2]4], 7.83 (t, JH,H = 7.9 Hz, 1 H, 9-H) ppm. 13C{1H}
1.0 Hz, 1 H, 10-H), 7.50 (m, 2 H, p-Anisyl), 7.53 {m, 4 H, p-
NMR (100.12 MHz, CDCl3, 294 K): δ = 3.07 (CH3CN), 17.52 (C- B[C6H3(CF3)2]4}, 7.71 (dt, 3JH,H = 7.7, 4JH,H = 1.0, 5JH,P = 1.0 Hz,
3
13), 23.35 [CH(CH3)2], 23.94 [CH(CH3)2], 28.91 [CH(CH3)2],
118.21 [p-C6H3(CF3)2], 121.19 (CH3CN), 122.77 (C-8), 123.31 (C-
1 H, 8-H), 7.73 {m, 8 H, o-B[C6H3(CF3)2]4}, 7.81 (dd, JH,H
=
7.7, JH,H = 8.4 Hz, 1 H, 9-H) ppm. 13C{1H} NMR (100.62 MHz,
3
10), 124.96 (C-16, C-18), 125.28 (q, 1JC,F = 272.6 Hz, CF3), 126.70 CDCl3, 294 K): δ = 18.92 (C-13), 22.40 [CH(CH3)2], 23.98
2
2
(C-5), 128.03 (C-4), 129.01 (C-17), 129.71 (q, JC,P = 32.5 Hz,
[CH(CH3)2], 28.73 [CH(CH3)2], 55.70 (OCH3), 111.35 (d, JC,P
=
1
CCF3), 132.96 (C-3), 135.60 [o-C6H3(CF3)2], 136.08 (C-2), 138.87 4.7 Hz, o-Anisyl), 111.41 (d, JC,P = 54.5 Hz, ipso-Anisyl), 117.80
3
(C-15, C-19), 140.76 (C-14), 142.32 (C-9), 147.87 (C-6), 153.17 (C-
{p-[C6H3(CF3)2]}, 121.64 (d, JC,P = 4.7 Hz, m-Anisyl), 121.93 (C-
1), 154.39 (C-11), 162.68 (q, 1JC,B = 49.5 Hz, ipso-C–B), 167.36 (C-
8), 122.29 (C-10) 124.37 (C-17), 124.50 (d, 1JC,F = 272.6 Hz, CF3),
Eur. J. Inorg. Chem. 2005, 4794–4800
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4799

C. Bianchini, G. Lenoble, W. Oberhauser, S. Parisel, F. Zanobini
[8]
FULL PAPER
2
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125.89 (C-5), 126.54 (C-4), 127.96 (C-16, C-18), 128.80 (d, JC,F
=
32.5 Hz, CCF3), 129.50 (q, 2JC,F = 32.5 Hz, CCF3), 131.86 (d, 4JC,P
= 4.0 Hz, C-3), 134.80 {o-[C6H3(CF3)2]}, 135.57 (d, 3JC,P = 8.0 Hz,
3
m-Anisyl), 134.24 (p-Anisyl), 136.72 (d, JC,P = 10.5 Hz, C-2),
138.06 (C-15, C-19), 140.98 (C-14), 141.51 (C-9), 148.60 (C-6),
2
2
151.98 (d, JC,P = 5.4 Hz, C-1), 152.24 (C-11), 160.82 (d, JC,P
=
1
3.3 Hz, C–OCH3), 162.30 (q, JC,B = 49.5 Hz, ipso-C–B), 164.25
(C-7), 177.40 (C-12) ppm. 31P{1H}(161.98 MHz, CDCl3, 294 K):
δ –23.34 (s) ppm. IR (KBr): ν = 1607 (C=N) cm–1.
˜
X-ray Crystallographic Analysis of 1 and 2: Single crystals of both
compounds were obtained by slow diffusion of toluene at room
temperature into a saturated CH2Cl2 solution of 1 and 2, respec-
tively. Diffraction data were collected at room temperature with an
Enraf Nonius CAD4 automatic diffractometer with Mo-Kα radia-
tion (graphite monochromator). Unit cell parameters of both struc-
tures were determined from a least-squares refinement of the set-
ting angles of 25 carefully centered reflections. Crystal data and
data collection details are given in Table 1. Lorentz polarization
and absorption corrections were applied.[20a] Atomic scattering fac-
tors were taken from ref.[20b] and an anomalous dispersion correc-
tion, with a real and imaginary part, was applied.[20c] The structures
were solved by direct methods and refined by full-matrix F2 refine-
ment. While in 1 anisotropic thermal parameters were assigned to
all non-hydrogen atoms, in 2 only the disordered toluene molecule
was treated isotropically. In both structures, the hydrogen atoms
were introduced in their calculated positions, with thermal param-
eters 20% larger than those of the respective carbon atoms. All the
calculations were performed with a PC using the WINGX pack-
age[20d] with SIR-97,[20e] SHELX-97,[20f] and ORTEP-3 pro-
grams.[20g] CCDC-271410 (1), and -271409 (2) contain the supple-
mentary crystallographic data 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.
[9]
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[11]
[12]
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[14]
Acknowledgments
M. L. Clarke, D. J. Cole-Hamilton, J. D. Woollins, J. Chem.
Soc. Dalton Trans. 2001, 2721.
Thanks are due to the European Commission (Contract HPRN-
CT-2002-00196, PALLADIUM project) for financial support.
Thanks are also due to the Ente Cassa di Risparmio di Firenze for
a generous grant.
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Received: May 26, 2005
Published Online: October 11, 2005
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