Phosphane-free C-C Heck couplings catalyzed by Pd(II) fluorinated aniline complexes of the type trans-[PdCl2(NH2ArF) 2]

Article abstract of DOI:10.1016/j.molcata.2005.11.020

A series of palladium fluoro-aniline complexes of the trans-[PdCl ₂(NH₂Ar^F)₂] type were synthesized in good yields by direct reaction of trans-[PdCl₂(C₆H ₅CN)] with Ar^FNH₂; Ar^F = C ₆H₃-2,3-F₂ (1), C₆H ₃-2,5-F₂ (2), C₆H₃-3,4-F₂ (3), C₆H₃-3,5-F₂ (4), C₆H ₂-2,3,4-F₃ (5), C₆H₂-2,3,6-F ₃ (6), C₆H₂-2,4,5-F₃ (7), C ₆H₂-2,4,6-F₃ (8), C₆F ₄-4-H (9), C₆F₅ (10). The crystal structures of complexes 3, 4 and 5 were determined. Heck coupling reactions were carried out using complexes 1-10 as catalysts in order to examine the effect of the fluorinated anilines in the reaction of bromobenzene and styrene.

Full text of DOI:10.1016/j.molcata.2005.11.020

Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
Phosphane-free C–C Heck couplings catalyzed by Pd(II) fluorinated
aniline complexes of the type trans-[PdCl2(NH2ArF)2]
1
´
´
Oscar Baldovino-Pantaleon, Joaquın Barroso-Flores, J.A. Cogordan ,
∗
´
´
´
Simon Hernandez-Ortega, Ruben A. Toscano, David Morales-Morales
Instituto de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Cd. Universitaria, Circuito Exterior Coyoaca´n, 04510 Me´xico, D.F., Me´xico
Received 4 October 2005; received in revised form 15 November 2005; accepted 15 November 2005
Available online 27 December 2005
Abstract
A series of palladium fluoro-aniline complexes of the trans-[PdCl2(NH2ArF)2] type were synthesized in good yields by direct reaction of
trans-[PdCl2(C6H5CN)] with ArFNH2; ArF = C6H3-2,3-F2 (1), C6H3-2,5-F2 (2), C6H3-3,4-F2 (3), C6H3-3,5-F2 (4), C6H2-2,3,4-F3 (5), C6H2-2,3,6-
F3 (6), C6H2-2,4,5-F3 (7), C6H2-2,4,6-F3 (8), C6F4-4-H (9), C6F5 (10). The crystal structures of complexes 3, 4 and 5 were determined. Heck
coupling reactions were carried out using complexes 1–10 as catalysts in order to examine the effect of the fluorinated anilines in the reaction of
bromobenzene and styrene.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Aniline ligands; Fluorinated amines; Heck reaction; C–C coupling reactions; Fluorinated amine complexes; Palladium complexes; Crystal structures;
Catalysis
1. Introduction
of active complexes as potential catalysts in industrial relevant
transformations [3], we report here our findings in the use of
a very simple, easy to synthesize series of complexes of the
type trans-[PdCl2(NH2ArF)2] based on fluorinated anilines for
the potential tuning of the electronics. The identification of the
electronic effects of the different fluorinated aniline palladium
complexes over the reactivity of these palladium complexes in
the Heck catalytic reaction of bromobenzene and styrene will be
discussed.
Palladium catalyzed C–C coupling reactions have been rec-
ognized as power tools in multiple organic transformations, from
these the Heck reaction has become a corner stone in modern
organic synthesis [1]. This reaction consists in the coupling of a
halo compound with an alkene. The importance of this reaction
has transcended its applications in the laboratory and become
of main interest at the industrial level [2]. The different cat-
alysts employed to carry out this reaction have also evolved
to achieve a better understanding of the factors that influence
activity, selectivity and stability. Thus, in recent years, several
groups have been involved in the design of ligands able to tol-
erate an oxidizing atmosphere, allowing Heck couplings in a
more efficient manner employing cheap reagent grade start-
ing materials. The use of cheap, easy to synthesize catalysts
such that the synthesis of the catalyst will not represent a chal-
lenge but an advantage has become a main research challenge.
Thus, given our continuous interest in the design and synthesis
2. Experimental
2.1. Materials and methods
Unless stated otherwise, all reactions were carried out under
an atmosphere of dinitrogen using conventional Schlenk glass-
ware. Solvents were dried using established procedures and
distilled under dinitrogen immediately prior to use. The IR spec-
tra were recorded on a Nicolet-Magna 750 FT-IR spectrometer
as KBr pellets. The 1H NMR (300 MHz) spectra were recorded
on a JEOL GX300 spectrometer. Chemical shifts are reported in
ppm down field of TMS using the solvent (CDCl3) as an internal
standard. 19F{1H} spectra were recorded with proton decou-
pling and are reported in ppm using C6F6 as external standard.
∗
Corresponding author. Tel.: +52 555 622 4514; fax: +52 555 616 2217.
E-mail addresses: cogordan@servidor.unam.mx (J.A. Cogordan),
damor@servidor.unam.mx (D. Morales-Morales).
1
J.A. Cogordan is responsible for the theoretical calculations.
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.11.020

66
O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
3J = 8.25, 7.7 Hz, 2H, H5), 6.45 (dd, J = 8.25 Hz, 2H, H4), 5.46
(br, 4H, N–H). 19F{1H} NMR (DMSO-d6): δ −141.20 (m, F2),
−162.52 (m, F3). FT-IR (KBr, cm−1): ν (N–H) 3250.50(m),
3167.40(m), 3100.69(s), δ (N–H) 1577.38(m), 1510.63(s). MS-
FAB+: m/z 436 (M+, 2%), Elemental analysis calculated for
[C12H10F4N2Cl2Pd]calcd. %:C, 33.09;H, 2.31;foundC, 34.08;
H, 2.38.
Elemental analyses were determined on a Perkin-Elmer 240.
Positive-ion FAB mass spectra were recorded on a JEOL JMS-
SX102A mass spectrometer operated at an accelerating voltage
of 10 kV. Samples were desorbed from a nitrobenzyl alcohol
(NBA) matrix using 3 keV xenon atoms. Mass measurements in
FAB are performed at a resolution of 3000 using magnetic field
scans and the matrix ions as the reference material or, alterna-
tively, by electric field scans with the sample peak bracketed
by two (polyethylene glycol or cesium iodide) reference ions.
GC–MS analyses were performed on an Agilent 6890N GC with
a 30.0 m DB-1MS capillary column coupled to an Agilent 5973
Inert Mass Selective detector. Melting points were determined in
a MEL-TEMP capillary melting pointapparatus andarereported
without correction.
2.2.2. Synthesis of trans-[Pd(Cl)2(NH2C6H3-2,5-F2)2] (2)
Yellow solid, yield 106 mg (93.3%), mp 215–217 ◦C. 1H
NMR (DMSO-d6): δ 6.97 (m, 2H, H6), 6.50 (m, 2H, H4), 6.25
(m, 2H, H3), 5.46 (br, 4H, N–H); 19F{1H} NMR (DMSO-d6): δ
−119.45 (m, F5), −141.29 (m, F2). FT-IR (KBr, cm−1): ν (N–H)
3237.45(m), 3177.10(m), 3102.41(m); δ(N–H) 1576.70(m),
1510.24(s). MS-FAB+: m/z 436(M+, 7%). Elemental analysis
for [C12H10F4N2 Cl2Pd] calcd. %: C, 33.09; H, 2.31; found C,
32.43; H, 2.38.
PdCl2 and fluorinated anilines were obtained commercially
from Aldrich Chem. Co. Compound trans-[PdCl2(C6H5CN)]
[4], was synthesized according to the published procedures.
2.2. General procedure for the synthesis of the complexes
trans-[PdCl2(NH2ArF)2]
2.2.3. Synthesis of trans-[Pd(Cl)2(NH2C6H3-3,4-F2)2] (3)
1
Yellow solid, yield 93.3 mg (83.7%); mp 297–299 ◦C. H
NMR (DMSO-d6): δ 7.35–7.20 (m, 2H, H2), 7.06 (m, 2H, H6),
6.45–6.29 (m, 2H, H3), 5.24 (br, 4H, N–H); 19F{1H} NMR
(DMSO-d6): δ −139.65 (m, F4), −156.63 (m, F3). FT-IR (KBr,
cm−1): ν (N–H) 3289.59(m), 3203.72(s), 3116.51(m), δ (N–H)
1569.32(m), 1520.91(s). MS-FAB+: m/z 436 (M+, 10%). Ele-
mental analysis for [C12H10F4N2Cl2Pd] calcd. %: C, 33.09; H,
2.31; found C, 33.92; H, 2.37.
All the complexes were obtained using the same experimental
procedure. As a representative example, the synthesis of trans-
[Pd(Cl)2(NH2C6H4-2,3-F2)2] (1) is described (Scheme 1).
2.2.1. Synthesis of trans-[Pd(Cl)2(NH2C6H3-2,3-F2)2] (1)
A solution, 15 mL ethanol of [PdCl2(C6H5CN)] (100 mg,
0.26 mmol, 1 equiv) was added to a 15 mL ethanol solution with
68 mg (0.52 mmol, 2.0 equiv) of 2,3-fluoroaniline. The mixture
was reflux 8 h. After this time, the hot solution was filtrated and
the solvent removed under vacuum. Yellow crystalline power
was obtained in good yield. The single crystals suitable for X-
ray diffraction studies were obtained from CH2Cl2–MeOH (1:1)
solution. Yellow solid, yield 98 mg (87%), mp 215–217 ◦C. 1H
2.2.4. Synthesis of trans-[Pd(Cl)2(NH2C6H3-3,5-F2)2] (4)
Yellow solid, yield 100 mg (88%), mp 305–307 ◦C. 1H NMR
(DMSO-d6): δ 7.21–6.89 (br, 4H, H2,6), 6.14 (d, J = 8.52 Hz, 2H,
H4). 19F{1H} NMR (DMSO-d6): δ −111.97 (t, J = 8.5 Hz, F3,5).
FT-IR (KBr, cm−1): ν (N–H) 3288.43(m), 3192.34(s), 3114(m),
δ (N–H) 1608.00(s), 1572.35(w), 1478.85(m). MS-FAB+: m/z
399 (M+ − Cl 3%). Elemental analysis for [C12H10F4N2Cl2Pd]
calcd. %: C, 33.09; H, 2.31; found C, 34.01; H, 2.38.
3
NMR (DMSO-d6): δ 6.82 (dd, J = 7.7 Hz, 2H, H6), 6.54 (t,
2.2.5. Synthesis of trans-[Pd(Cl)2(NH2C6H2-2,3,4-F3)2]
(5)
Yellow solid, yield 104 mg (85%), mp 248–250 ◦C. 1H NMR
(DMSO-d6): δ 6.95 (m, 2H, H6), 6.52 (br, 2H, H5), 5.28 (br,
4H, N–H). 19F{1H} NMR (DMSO-d6): δ −153.99 (m, F4),
−157.63 (m, F2), −163.43 (m, F3). FT-IR (KBr, cm−1) ν (N–H)
3233.05(w), 3176.06(m), 3105.84(m), δ (N–H) 1575.65(m),
1507.42(s). MS-FAB+: m/z 436 (M+ − Cl, 3%). Elemental anal-
ysis for [C12H8F6N2Cl2Pd] calcd. %: C, 30.57; H, 1.71; found
C, 31.49; H, 1.75.
2.2.6. Synthesis of trans-[Pd(Cl)2(NH2C6H2-2,3,6-F3)2]
(6)
Yellow solid, yield 110 mg (90%), mp 255–257 ◦C. 1H NMR
(DMSO-d6): δ 6.88 (m, 2H, H4), 6.50 (m, 2H, H5). 19F{1H}
NMR (DMSO-d6): δ −131.60 (m, F6), −139.92 (m, F3),
−151.85 (m, F2). FT-IR (KBr, cm−1): ν (N–H) 3186.78(m),
3116.05(m); δ (N–H) 1625.12(w), 1577.57(m), 1515.70(s).
MS-FAB+: m/z 436 (M+ − Cl, 4%). Elemental analysis for
Scheme 1. Reactions for the synthesis of the complexes trans-
[PdCl2(NH2ArF)2].

O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
67
[C12H8F6N2Cl2Pd] calcd. %: C, 30.57; H, 1.71; found C, 30.11;
H, 1.74.
2.2.7. Synthesis of trans-[Pd(Cl)2(NH2C6H2-2,4,5-F3)2]
(7)
Yellow solid, yield 100 mg (82%), mp 258–260 ◦C. 1H NMR
(DMSO-d6): δ 7.27 (m, 2H, H6), 6.72 (m, 2H, H3), 5.25 (br,
4H, N–H). 19F{1H} NMR (DMSO-d6): δ −137.24 (m, F2),
−144.41 (m, F4) −153.54 (m, F5). FT-IR (KBr, cm−1): ν (N–H)
3227.79(m), 3175.29(m), 3106.59(m), δ (N–H) 1574.47(m),
1524.81(s). MS-FAB+: m/z 437 (M+ − Cl, 3%). Elemental anal-
ysis for [C12H8F6N2Cl2Pd] calcd. %: C, 30.57; H, 1.71; found
C, 31.24; H, 1.75.
Scheme 2. The palladium catalyzed Heck coupling reaction using trans-
[PdCl2(NH2ArF)2] as catalyst.
2.4. Data collection and refinement for
trans-[Pd(Cl)2(NH2C6H3-3,4-F2)2] (3),
trans-[Pd(Cl)2(NH2C6H3-3,5-F2)2] (4) and
trans-[Pd(Cl)2(NH2C6H2-2,3,4-F3)2] (5)
2.2.8. Synthesis of trans-[Pd(Cl)2(NH2C6H2-2,4,6-F3)2]
(8)
Yellow solid, yield 107 mg (88%), mp 206–208 ◦C. 1H
NMR (DMSO-d6): δ 6.98 (t, J = 8.25Hz, H3,5), 5.02 (s,
4H, N–H). 19F{1H} NMR (DMSO-d6): δ −127.42 (t,
J = 8.46 Hz, F4), −129.37 (d, J = 8.46 Hz, F2,6). FT-IR (KBr,
cm−1): ν (N–H) 3267.77(w), 3192.82(m), 3120.48(m). δ
(N–H) 1624.26(m), 1572.37(w), 1509.27(m), 1459.64(w). MS-
FAB+: m/z 437 (M+ − Cl, 1.5%). Elemental analysis for
[C12H8F6N2Cl2Pd] calcd. %: C, 30.57; H, 1.71; found C, 30.92;
H, 1.73.
Crystalline red–orange prisms for 3, 4 and 5 were grown inde-
pendently from DMSO (3), DMF (4) and from a CH2Cl2/MeOH
solvent system for 5, and mounted on glass fibers. In all cases,
the X-ray intensity data were measured at 293 or 291 K on a
Bruker SMART APEX CCD-based X-ray diffractometer sys-
˚
tem equipped with a Mo-target X-ray tube (λ = 0.71073 A). The
detector was placed at a distance of 4.837 cm from the crystals in
all cases. A total of 1800 frames were collected with a scan width
of 0.3◦ in ω and an exposure time of 10 s/frame. The frames were
integrated with the Bruker SAINT software package [5] using a
narrow-frame integration algorithm. The integration of the data
was done using a monoclinic unit cell in all cases, except for
complex 4, where a triclinic cell was used to yield a total of
15787, 4707 and 6152 reflections for 3, 4 and 5, respectively,
2.2.9. Synthesis of trans-[Pd(Cl)2(NH2C6F4-4-H)2] (9)
Yellow solid, yield: 72 mg (53%); mp 215–217 ◦C. 1H
NMR (DMSO-d6): δ = 6.69 (t, J = 10.72 Hz, 2H, H4), 5.91
(br, 4H, N–H). 19F{1H} NMR (DMSO-d6): δ −143.03 (m,
F2,6), −161.93 (m, F3,5). FT-IR (KBr, cm−1): ν (N–H)
3187.49(m), 3114.41(m); δ (N–H) 1653.16(w), 1577.59(w),
1529.34(s). MS-FAB+: m/z 507 (M+, 4%). Elemental analysis
for [C12H6F8N2Cl2Pd] calcd. %: C, 28.40; H, 1.19; Found C,
27.85; H, 1.24.
◦
˚
to a maximum 2θ angle of 50.00 (0.93 A resolution), of which
4193 (3), 2014 (4) and 1379 (5) were independent. Analysis of
the data showed in all cases negligible decays during data col-
lections. The structures were solved by Patterson method using
SHELXS-97 [6] program. The remaining atoms were located via
a few cycles of least squares refinements and difference Fourier
maps, using the space group C2(1)/c and P2(1)/c with Z = 2 and
4 for 3 and 5, respectively, and P-1 with Z = 2 for 4. Hydrogen
atoms were input at calculated positions, and allowed to ride
on the atoms to which they are attached. Thermal parameters
were refined for hydrogen atoms on the phenyl groups using a
2.2.10. Synthesis of trans-[Pd(Cl)2(NH2C6F5)2] (10)
Yellow solid, yield 100 mg (70%), mp 215–217 ◦C.
19F{1H} NMR (DMSO-d6): δ −162.52 (m, F2,6), −166.74
(t, F4), −178.85 (m, F3,5). FT-IR (KBr, cm−1): ν (N–H)
3189.61(w), 3109.28(w); δ (N–H) 1602.96(m), 1525.09(s).
MS-FAB+: m/z 573 (M+ − 2Cl, 2%). Elemental analysis for
[C12H4F10N2Cl2Pd] calcd. %: C, 26.52; H, 0.74; found: C,
26.73; H, 0.75.
˚
Ueq = 1.2 A to precedent atom in all cases. For all complexes,
the final cycle of refinement was carried out on all non-zero data
using SHELXL-97 [6] and anisotropic thermal parameters for
all non-hydrogen atoms. The details of structure determinations
2.3. General procedure for the catalytic reactions
˚
are given in Table 1 and selected bond lengths (A) and angles
A DMF solution (5 mL) of 50.0 mmol of halobenzene,
60.0 mmol of styrene and the prescribed amount of catalyst was
introduced into a Schlenk tube in the open air. The tube was
charged with a magnetic stir bar and an equimolar amount of
base, sealed and fully immersed in a 160 ◦C silicon oil bath.
After the prescribed reaction time (2 h), the mixture was cooled
to room temperature and the organic phase analyzed by gas chro-
matography (GC–MS) (Scheme 2).
(◦) are given in Tables 2–4, respectively. Numbering of atoms is
shown in Figs. 1–3, respectively, (ORTEP) [7].
2.5. Theoretical calculations
Geometry optimizations at the Restricted Hartree–Fock level
of theory were carried out using the Gaussian98 suite of

68
O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
Table 1
Crystal data and structure parameters for trans-[Pd(Cl)2(NH2C6H3-3,4-F2)2] (3), trans-[Pd(Cl)2(NH2C6H3-3,5-F2)2] (4) and trans-[Pd(Cl)2(NH2C6H2-2,3,4-F3)2]
(5)
Identification code
3
4
5
Empirical formula
Formula weight
C
16H22Cl2F4N2O2PdS2
C9H12ClF2N2OPd0.5
290.86
293(2)
C6H2ClF3NPd0.5
233.74
291(2)
591.78
293(2)
Temperature (K)
´
˚
Wavelength (A)
0.71073
Monoclinic
C2(1)/c
0.71073
Triclinic
P-1
0.71073
Monoclinic
P2(1)/c
Crystal system
Space group
´
´
´
˚
˚
˚
Unit cell dimensions
a = 10.763(1) A
a = 5.9282(5) A
a = 13.0625(8) A
α = 90◦
α = 94.267(2)◦
α = 90◦
´
´
´
˚
˚
˚
b = 15.098(1) A
b = 9.0285(8) A
b = 7.8514(5) A
β = 98.9030(10)◦
β = 94.152(1)◦
β = 99.050(2)◦
´
´
´
˚
˚
˚
c = 7.1598(4) A
c = 11.057(1) A
c = 7.7548(5) A
γ = 90◦
γ = 98.436(2)◦
γ = 90◦
3
˚
Volume (A )
1160.4(2)
575.24(9)
785.74(9)
Z
2
2
4
Density (calculated) (Mg/m3)
Absorption coefficient (mm−1
F(0 0 0)
1.694
1.256
592
1.679
1.093
292
1.976
1.579
448
)
Crystal size
0.316 mm × 0.310 mm × 0.146 mm
0.24 mm × 0.12 mm × 0.07 mm
0.38 mm × 0.35 mm × 0.07 mm
θ range for data collection (◦)
Index ranges
1.90–32.55
187–24.98
3.04–24.99
−16 ≤ h ≤ 16, −22 ≤ k ≤ 22, −10 ≤ l ≤ 10
15787
−7 ≤ h ≤ 7, −10 ≤ k ≤ 10, −13 ≤ l ≤ 13
4707
2014 [R(int) = 0.0334]
Analytical
0.9299 and 0.8186
Full-matrix least-squares on F2
2014/0/150
−15 ≤ h ≤ 15, −9 ≤ k ≤ 9, −9 ≤ l ≤ 9
6152
1379 [R(int) = 0.0292]
Integration
0.8896 and 0.5622
Full-matrix least-squares on F2
1379/0/111
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
4193 [R(int) = 0.0862]
Analytical: face-indexed
0.8404 and 0.6112
Full-matrix least-squares on F2
4193/0/143
1.017
0.997
1.001
R1 = 0.0397, wR2 = 0.0840
R1 = 0.0249, wR2 = 0.0527
R1 = 0.0393, wR2 = 0.1097
R1 = 0.0552, wR2 = 0.0905
R1 = 0.0262, wR2 = 0.0531
R1 = 0.0427, wR2 = 0.1137
−3
−3
−3
˚
˚
˚
Largest diff. peak and hole
1.023 and −0.434 eA
0.296 and −0.376 eA
0.769 and −1.068 eA
wR2 = [w((Fo)2 − (Fc)2) − w(Fo)2]1/2
.
|F −F |
o
c
R1 =
,
|F |
o
Table 4
Table 2
Selected bond lengths and angles for trans-[Pd(Cl)2(NH2C6H2-2,3,4-F3)2] (5)
Selected bond lengths and angles for trans-[Pd(Cl)2(NH2C6H3-3,4-F2)2] (3)
Angles (◦)
˚
Bond lengths (A)
Angles (◦)
˚
Bond lengths (A)
Pd(1) N(1)
Pd(1) N(1)#1
Pd(1) Cl(2)
2.052(4)
2.052(4)
2.2919(10)
N(1) Pd(1) N(1)#1
N(1) Pd(1) Cl(2)
N(1)#1 Pd(1) Cl(2)
N(1) Pd(1) Cl(2)#1
N(1)#1 Pd(1) Cl(2)#1
Cl(2) Pd(1) Cl(2)#1
180.00
Pd(1) N(1)
Pd(1) N(1)#1
Pd(1) Cl(1)
2.0461(19)
2.0461(19)
2.2989(6)
N(1) Pd(1) N(1)#1
N(1) Pd(1) Cl(1)
N(1)#1 Pd(1) Cl(1)
N(1) Pd(1) Cl(1)#1
N(1)#1 Pd(1) Cl(1)#1
Cl(1) Pd(1) Cl(1)#1
180.00
89.35(13)
90.65(13)
90.65(13)
89.35(13)
180.00
89.92(6)
90.08(6)
90.08(6)
89.92(6)
180.00
Pd(1) Cl(2)#1 2.2919(10)
Pd(1) Cl(1)#1 2.2989(6)
Symmetry transformations used to generate equivalent atoms: #1 −x + 1, y + 2,
−z.
Symmetry transformations used to generate equivalent atoms: #1 −x, −y, −z + 2.
programs [8]. For the fluorinated aniline ligands, a 6-311G**
basis set was used, whereas for the respective Pd complexes the
Effective Core Potential (ECP) approach was employed using
the Hay and Wadt ECP’s together with their corresponding basis
sets [9]. The ECP replaces the core electrons of the second
row atoms and heavier by a set of functions and operators that
simulate their effect on the valence electrons. This allows for
the use of larger computational resources in the description of
the valence electronic structure. A Natural Bond Orbital (NBO)
analysis [10] was carried out at the optimized structures in order
to asses the electron distribution over the molecules.
Table 3
Selected bond lengths and angles for trans-[Pd(Cl)2(NH2C6H3-3,5-F2)2] (4)
˚
Bond lengths (A)
Angles (◦)
Pd(1) N(1)
Pd(1) N(1)#1
Pd(1) Cl(1)
2.052(2)
2.052(2)
2.3047(6)
N(1) Pd(1) N(1)#1
N(1) Pd(1) Cl(1)
N(1)#1 Pd(1) Cl(1)
N(1) Pd(1) Cl(1)#1
N(1)#1 Pd(1) Cl(1)#1
Cl(1) Pd(1) Cl(1)#1
180.00(1)
90.30(6)
89.70(6)
89.70(6)
90.30(6)
180.00
Pd(1) Cl(1)#1 2.3047(6)
Symmetry transformations used to generate equivalent atoms: #1 −x + 1, y + 1,
−z + 1.

O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
69
Table 5
HOMO energies for the free aniline ligands (eV)
Disubstituted anilines
Trisubstituted anilines
Ligand
E HOMO (eV)
Ligand
E HOMO (eV)
1
2
3
4
−8.5874
−85994
−8.4985
−8.6963
5
6
7
8
−8.8582
−8.9570
−8.8677
−8.8337
Molecular conformations optimized with RHF method.
Fig. 1. An ORTEP representation of the structure of trans-[Pd(Cl)2(NH2C6H3-
3,4-F2)2] (3) at 50% probability showing the atom labeling scheme.
The energy of the LP (HOMO) decreases as its delocaliza-
tion over the aromatic ring increases. This delocalization of the
LP is largely favored by the presence of the electronegative flu-
orine atoms at meta- positions. In the case of the disubstituted
anilines it may be observed that the ortho- substitution has less
influence in the delocalization than the para- substitution, since
the energy difference for the HOMOs of ligands in 1 and 2 is
only slightly higher than 0.01 eV (regardless of the relative meta-
position in which the second Fluorine atom is located) and the
difference between the corresponding values for these ligands
and in 3 is approximately 10 times larger (0.1 eV). Having both
fluorine atoms at meta- positions (ligand in 4) lowers the energy
of the HOMO for the ligand by another 0.1 eV, approximately.
A similar trend may be found for the trisubstituted anilines. In
the case of ligands in 9 and 10 the values of the energies for
the HOMO are −9.3842 and −9.6179 eV, respectively, with a
difference of 0.23 eV which exhibits the larger delocalization in
ligand in complex 10 by having an extra fluorine atom in para-
position (Tables 5–7).
The delocalization of the LP over the aromatic ring modifies
its availability for coordination to the metallic center, which is
Fig. 2. An ORTEP representation of the structure of trans-[Pd(Cl)2(NH2C6H3-
3,5-F2)2] (4) at 50% probability showing the atom labeling scheme.
Table 6
Wiberg Pd N bond index for compounds 1 through 8
In Table 8 the energies for the HOMO in the free aniline lig-
ands are shown. According to the NBO analysis at the optimized
geometries the HOMO is constituted by the nitrogen’s lone pair
(LP) located at the 2pz Natural Atomic Orbital. This analysis
yielded the following relative order of energy for the HOMO:
Disubstituted anilines
Trisubstituted anilines
Compound
Pd N bond index
Compound
Pd N bond index
1
2
3
4
0.2922
0.2926
0.296
5
6
7
8
0.2957
0.3982
0.2918
0.279
0.2921
Disubstituted anilines: 4 < 2 < 1 < 3.
Trisubstituted anilines: 6 < 7 < 5 < 8.
Table 7
Wiberg bond indexes for the Pd Cl bond and the total index for the Pd atom
Compound
Pd Cl bond
index
Total Wiberg bond
index for Pd
Pd natural
charge
Disubstituted anilines
1
2
3
4
0.3897
1.434
1.0572
1.0536
1.0612
1.062
0.3905
0.3809
0.383
1.4368
1.4283
1.4238
Trisubstituted anilines
5
6
7
8
0.3893
1.4409
1.4273
1.4396
1.4318
1.0483
1.0629
1.0504
1.05975
0.3982
0.3897
0.3972
Fig. 3. An ORTEP representation of the structure of trans-[Pd(Cl)2(NH2C6H2-
2,3,4-F3)2] (5) at 50% probability showing the atom labeling scheme.

70
O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
reflected in the Pd N bond index [11]. As it may be observed
in Table 3 the Pd N bond index becomes higher as the energy
of the HOMO of the ligand increases. As the Pd N bond index
increases the Pd Cl bond index decreases as a mean of pre-
serving the total bond index on the Pd atom. However, these
two effects are not mutually compensating and the total Wiberg
index for the Pd atom becomes larger as the Pd N bond index
increases. This is also reflected in the natural charge calculated
for the Pd atom (see Table 4).
It is possible to notice from Table 8 that the catalytic activity
of these complexes increases as the Pd N bond index increases.
According to the Heck’s reaction mechanism the first step in the
reaction herein studied would be the oxidative addition of bro-
mobenzene to the Pd complex. Thus, the energy of the HOMO
in the complexes is the optimal parameter to be analyzed against
the conversion yield. It is observed that the complex gets more
active towards oxidative addition as the energy of the HOMO in
the complex increases and as a consequence the catalytic activity
does too.
Table 8
Heck couplings of bromobenzene with trans-[PdCl2(NH2ArF)2] as catalyst
Entry
NH2ArF
E HOMO (eV)
% Conversiona
51.45
1
−10.3314
2
3
−10.2607
−10.1358
56.30
57.48
This is directly observed between complexes 9 and 10 in
which the presence of an extra fluorine in the para- position
increases the conversion yield from 41.62 to 51.3%.
4
5
−10.3279
−10.6887
45.20
64.33
3. Results and discussion
The reaction of two equivalents of the fluorinated ani-
lines with one equivalent of the palladium starting material
[PdCl2(C6H5CN)] under reflux afforded in good to excellent
yields the complexes trans-[PdCl2(NH2ArF)2] with ArFNH2;
ArF = C6H3-2,3-F2 (1), C6H3-2,5-F2 (2), C6H3-3,4-F2 (3),
C6H3-3,5-F2 (4), C6H2-2,3,4-F3 (5), C6H2-2,3,6-F3 (6), C6H2-
2,4,5-F3 (7), C6H2-2,4,6-F3 (8), C6F4-4-H (9), C6F5 (10), these
complexes were characterized by 1H NMR showing in all cases
the presence of the aromatic (except for the case of complex
10) and N–H protons. More informative results the analyses
by 19F NMR where the typical splittings for the presence of
the different susbstitutions in the fluorinated anilines moiety for
complexes 1 trough 10 are observed [12]. Infrared spectra of
these complexes in all cases reveal the N–H stretching and the
in-plane deformation frequencies to be located at about 3000 and
1500 cm−1, respectively. Analyses of the aniline compounds by
FAB+ spectrometry affords in most of the cases the molecular
ion minus a chloride [M+ − Cl], other important peaks include
the consecutive lost of chlorides. In all cases elemental analysis
are consistent with the proposed formulations.
6
−10.4068
59.10
7
8
−10.6462
−10.3132
52.32
47.48
Crystals suitable for single crystal X-ray diffraction analy-
ses (Table 1) were obtained for complexes 3, 4 and 5, being
the only difference the fluorinated substituent, the three struc-
tures share a number of common features. The palladium centers
are located into a square planar environment, having the fluori-
nated aniline ligands in a trans configuration and completing the
coordination sphere the two chlorides. Bond lengths and bond
angles in all three complexes are comparable to those found in
trans-[PdCl2(H2NC6H4-3-F)2] [13], the largest deviation from
the ideal bond angles being observed for complex 5 in N(1)-
Pd(1)-Cl(2) [89.35(13)]. It is interesting to notice that while
some fluorinated anilines have been extensibly used as precur-
9
51.3
10
41.62
Reaction conditions 50 mmol of halobenzene, 60 mmol of styrene, 60 mmol of
base, 4.0 × 10−5 mmol of catalyst and 5 mL of DMF, 2 h at 160 ◦C.
a
Yields obtained by GC are based on bromobenzene.

O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
71
sors for the synthesis of Schiff base ligands, crystallographically
characterized examples of transition metal complexes contain-
ing the bound aniline itself are rare [13,14].
with Pd(IV)/Pd(II) and Pd(II)/Pd(0) both being proposed at var-
ious times [16], however in this case given the type of species
involved we favor the Pd(0)/Pd(II) mechanism although the
precise mechanism of the catalytic reaction remains to be eluci-
dated.
The high melting points that these complexes exhibited (high
thermal stability) and the attention that palladium complexes
have attracted in the last years in the homogeneous catalysis
field prompted us to test their catalytic activity in the catalyzed
arylation of haloarenes (Heck reaction). Initial tests carrying out
the reaction of iodobenzene with styrene afforded in all cases
quantitative yields (6 h reaction time, 160 ◦C reaction temper-
ature), however more illustrative resulted the catalytic reaction
of bromobenzene with styrene, these experiments were carried
out under similar reaction conditions (2 h reaction time, 160 ◦C
reaction temperature) with all 10 complexes, resulting complex
5 to be the most reactive. This is curios considering the fact that
this results has been previously observed in a different reac-
tion (thiolation) catalyzed by NCN pincer Ni(II) complexes,
were the species [NiCl2{C5H3N-2,6-(CHNC6H2-2,3,4-F3)2}]
also resulted to be the more reactive in a similar series of com-
plexes (Scheme 3) [15].
The fact that these complexes are not sensitive to oxygen or
water allowed us to carry out all the experiments in the open
air using technical grade reagents. Although no clear trend is
observed regarding the fluorine content in the different com-
plexes it is clear that the particular substitution pattern of com-
plex 5 favors either more active or more stable species that in
turn may favor more the catalytic activity of the corresponding
complexes they form.
In order to shed some light in this respect we carried out
some theoretical calculations, the results obtained indicate that
the fluorinated aniline in complex 5 presents a strong electron
withdrawing substituent such that the electronic pair in the nitro-
gen is less available, this fact may in turn favor the formation
of stronger Pd N bonds. However, a quick analysis of the bond
distances of the crystal structures shown in the present paper
do not reveal considerable differences in bond distances with
respect to the different anilines (complexes 3, 4 and 5), however
this may also be a consequence of the packing of the different
molecules in the solid state. Thus, it seems that there is a subtle
balance between the electronics and sterics in the present cat-
alytic system that allows complex 5 to be the more active in the
arylation of iodo and bromo benzene with styrene.
In conclusion we have reported a high yield procedure for
the synthesis of fluorinated aniline-palladium complexes of the
type trans-[PdCl2(NH2ArF)2], these compounds efficiently cat-
alyzedtheHeckreactionofiodoandbromobenzenewithstyrene
in the complete absence of phosphines. It is noteworthy that the
attractive features of this catalytic system of good yields and air
and water stability and easiness for the synthesis of the catalytic
precursors approach those required for commercial viability and
opens future possibilities for its use in other palladium catalyzed
reactions, this research is currently under investigation.
Moreover, from the theoretical calculations the following
general principles may be observed, even when it is not possible
to obtain a strict relationship between the substitution pattern
on the ligand and the conversion. The catalytic activity tends
to increase as the energy of the HOMO increases. This in turn
increases with electron donation from the ligand to the metallic
center (this feature assessed by the Pd N Wiberg bond index).
This electron donation becomes larger as the lone pair from the
N atom in the ligand is less delocalized over the aromatic ring.
In order to prevent delocalization of the lone pair, and there-
fore increase the Pd N bond index in the complex, substitution
of the meta- positions with fluorine atoms, over the ortho- and
para-, will render the desired effect. Thus, from the present data
it seems that substitution of the meta- positions by a stronger
electron donor substituent would decrease even more the delo-
calization of the LP and this in turn would tend to increase the
yield in the catalytic transformation by an increase of the energy
of the HOMO in the Pd complex, activating it for the first step
of oxidative addition in the Heck reaction, these modifications
are currently under investigation.
Supplementary material
Supplementary data for complexes 3, 4 and 5 have been
deposited at the Cambridge Crystallographic Data Centre.
Copies of this information are available free of charge on
request from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: +44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk) quoting the
deposition numbers CCDC 281879 (3), CCDC 281878 (4) and
CCDC 281880 (5).
Experiments using chlorobenzene resulted only in traces of
the products probably as a consequence of the quick and clear
decomposition of the complexes in the reaction mixture to pal-
ladium black.
There has been a considerable debate in the literature about
the oxidation states of the species involved in the catalytic cycle
Acknowledgements
O. B.-P and J. B.-F would like to thank CONACYT for finan-
cial support. We would like to thank Chem. Eng. Luis Velasco
´
Ibarra and M.Sc. Francisco Javier Perez Flores, QFB. Ma del
´
˜
Rocıo Patino and Ma de las Nieves Zavala for their invalu-
able help in the running of the FAB+-Mass, IR and 19F{1H}
spectra, respectively. The support of this research by CONA-
CYT (J41206-Q) and DGAPA-UNAM (IN114605) is gratefully
acknowledged. We would like to thank DGSCA for generous
Scheme 3.

72
O. Baldovino-Pantaleo´n et al. / Journal of Molecular Catalysis A: Chemical 247 (2006) 65–72
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Special thanks to David Vazquez for keeping running the net-
´
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Prof. Keith Hollis for careful proof reading of the manuscript.
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