The cyclopalladation reaction of 2-phenylaniline revisited

Article abstract of DOI:10.1016/j.jorganchem.2004.07.067

2-Phenylaniline reacted with Pd(OAc)₂ in toluene at room temperature for 24 h in a one-to-one molar ratio and with the system PdCl ₂, NaCl and NaOAc in a 1 (2-phenylaniline):1 (PdCl₂):2 (NaCl):1 (NaOAc) molar ratio in methanol at room temperature for one week to give the dinuclear cyclopalladated compounds (μ-X)₂[Pd{κ ²-N2′,C1-2-(2′-NH₂C₆H ₄)C₆H₄}]₂ [1a (X = OAc) and 1b (X = Cl)] in high yield. Moreover, the reaction between 2-phenylaniline and Pd(OAc)₂ in one-to-one molar ratio in acid acetic at 60°C for 4 h, followed by a metathesis reaction with LiBr, allowed isolation of the dinuclear cyclopalladated compound (μ-Br)₂[Pd{κ²- N2′,C1-2-(2′-NH₂C₆H₄)C ₆H₄}]₂ (1c) in moderate yield. A parallel treatment, but using monodeuterated acetic acid (DOAc) as solvent in the cyclopalladation reaction, allowed isolation of a mixture of compounds 1c, 1c_d1 [Pd{κ²-N2′,C1-2-(2′-NH ₂C₆H₄)C₆H₄](μ-Br) ₂[Pd{κ²-N2′,C1-2-(2′-NH ₂C₆H₄)-3-d-C₆H₃] and 1c_d2 (μ-Br)₂[Pd{κ²-N2′,C1-2- (2′-NH₂C₆H₄)-3-d-C₆H ₃}]₂ in moderate yield and with a deuterium content of ca. 60%. 1a and 1b reacted with pyridine and PPh₃ affording the mononuclear cyclopalladated compounds [Pd{κ²-N2′,C1-2- (2′-NH₂C₆H₄)C₆H ₄}(X)(L)] [2a (X = OAc, L = py), 2b (X = Cl, L = py), 3a (X = OAc, L = PPh₃) and 3b (X = Cl, L = PPh₃)] in a yield from moderate to high. Furthermore, 1a reacted with Na(acac) ? H₂O to give the mononuclear cyclopalladated compound 4 [Pd{κ²- N2′,C1-2-(2′-NH₂C₆H₄)C ₆H₄}(acac)] in moderate yield. ¹H NMR studies in CDCl₃ solution of 2a, 2b, 3a, 3b and 4 showed that 2a and 3a presented an intramolecular hydrogen bond between the acetato ligand and the amino group, and were involved in a dynamic equilibrium with water present in the CDCl₃ solvent; and that the enantiomeric molecules of 2b and 4 were in a fast exchange at room temperature, while they were in a slow exchange for 2a, 3a and 3b. The X-ray crystal structures of 3b and 4 were determined. 3b crystallized in the triclinic space group P1? with a = 9.9170(10), b = 10.4750(10), c = 12.0890(10) A?, α = 98.610(10)°, β = 94.034(10)°and γ = 99.000(10)°and 4 in the monoclinic space group P2₁/a with a = 11.5900(10), b = 11.2730(10), c = 12.2150(10) A?, α = 90°, β = 107.6560(10)°and γ = 90°.

Full text of DOI:10.1016/j.jorganchem.2004.07.067

Journal of Organometallic Chemistry 690 (2005) 422–429
www.elsevier.com/locate/jorganchem
The cyclopalladation reaction of 2-phenylaniline revisited
a,
Joan Albert , Jaume Granell , Javier Zafrilla , Merce Font-Bardia , Xavier Solans
a
a
b
b
*
`
a
´ ` ´ `
Departament de Quımica Inorganica, Universitat de Barcelona, Martı i Franques, 1-11, 08028 Barcelona, Spain
`
b
´
`
Departament de Cristal Æ lografia, Mineralogia i Diposits Minerals, Universitat de Barcelona. Martı i Franques s/n, 08028 Barcelona, Spain
Received 15 June 2004; accepted 9 July 2004
Available online 22 October 2004
Abstract
2-Phenylaniline reacted with Pd(OAc)2 in toluene at room temperature for 24 h in a one-to-one molar ratio and with the system
PdCl2, NaCl and NaOAc in a 1 (2-phenylaniline):1 (PdCl2):2 (NaCl):1 (NaOAc) molar ratio in methanol at room temperature for
one week to give the dinuclear cyclopalladated compounds (l-X)2[Pd{j2-N20,C1-2-(20-NH2C6H4)C6H4}]2 [1a (X = OAc) and 1b
(X = Cl)] in high yield. Moreover, the reaction between 2-phenylaniline and Pd(OAc)2 in one-to-one molar ratio in acid acetic at
60 ꢀC for 4 h, followed by a metathesis reaction with LiBr, allowed isolation of the dinuclear cyclopalladated compound
(l-Br)2[Pd{j2-N20,C1-2-(20-NH2C6H4)C6H4}]2 (1c) in moderate yield. A parallel treatment, but using monodeuterated acetic acid
(DOAc) as solvent in the cyclopalladation reaction, allowed isolation of a mixture of compounds 1c, 1cd1 [Pd{j2-N20,C1-2-(20-
NH2C6H4)C6H4](l-Br)2[Pd{j2-N20,C1-2-(20-NH2C6H4)-3-
D
-C6H3] and 1cd2 (l-Br)2[Pd{j2-N20,C1-2-(20-NH2C6H4)-3-
D-C6H3}]2 in
moderate yield and with a deuterium content of ca. 60%. 1a and 1b reacted with pyridine and PPh3 affording the mononuclear cyclo-
palladated compounds [Pd{j2-N20,C1-2-(20-NH2C6H4)C6H4}(X)(L)] [2a (X = OAc, L = py), 2b (X = Cl, L = py), 3a (X = OAc,
L = PPh3) and 3b (X = Cl, L = PPh3)] in a yield from moderate to high. Furthermore, 1a reacted with Na(acac) Æ H2O to give
1
the mononuclear cyclopalladated compound 4 [Pd{j2-N20,C1-2-(20-NH2C6H4)C6H4}(acac)] in moderate yield. H NMR studies
in CDCl3 solution of 2a, 2b, 3a, 3b and 4 showed that 2a and 3a presented an intramolecular hydrogen bond between the acetato
ligand and the amino group, and were involved in a dynamic equilibrium with water present in the CDCl3 solvent; and that the
enantiomeric molecules of 2b and 4 were in a fast exchange at room temperature, while they were in a slow exchange for 2a, 3a
ꢀ
and 3b. The X-ray crystal structures of 3b and 4 were determined. 3b crystallized in the triclinic space group P1 with
˚
a = 9.9170(10), b = 10.4750(10), c = 12.0890(10) A, a = 98.610(10)ꢀ, b = 94.034(10)ꢀ and c = 99.000(10)ꢀ and 4 in the monoclinic
˚
space group P21/a with a = 11.5900(10), b = 11.2730(10), c = 12.2150(10) A, a = 90ꢀ, b = 107.6560(10)ꢀ and c = 90ꢀ.
ꢁ 2004 Elsevier B.V. All rights reserved.
Keywords: Cyclometallation; 2-Phenylaniline; Palladium
1. Introduction
cyclopalladation reaction [10] and the E ! Z isomeriza-
tion of exo-cyclopalladated imines [11]. Furthermore, an
intramolecular C–H bond activation of a biphenyl
group in a palladium(II) centre has been proposed in a
catalytic cycle that transforms a C–H bond in a C–C
bond [12].
In spite of these precedents, little attention has been
focused on the synthesis, structure, and dynamic behav-
iour of di- and mono-nuclear cyclopalladated com-
pounds containing a biphenyl cyclopalladated unit.
Furthermore, it is well known that cyclopalladation of
Cyclopalladated compounds containing a biphenyl
cyclopalladated unit have previously been used as start-
ing materials in organic and organometallic synthesis [1–
8], as precursors of catalytic species in C–C and C–N
coupling reactions [9] and in cyclopalladation reactions
to address questions such as the regioselectivity of the
*
Corresponding author. Tel.: +34 93 4021271; fax: +34 93 4907725.
E-mail address: joan.albert@qi.ub.es (J. Albert).
0022-328X/$ - see front matter ꢁ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.067

J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
423
primary amines in high yield is a challenging problem
[13]. These precedents prompted us to reinvestigate the
cyclopalladation reaction of 2-phenylaniline, which we
reported previously in a moderate yield of ca. 50% [14].
2. Results and discussion
Fig. 1. Lettering of the protons of the biphenyl cyclopalladated unit.
Scheme 1 shows the di- and mono-nuclear cyclopalla-
dated compounds discussed in this paper, and Fig. 1 the
letters assigned to the protons of their biphenyl cyclo-
palladated unit in regard to the discussion that follows.
Notably, compounds 1a and 1b were obtained in 85%
and 75% yield, respectively, by treating 2-phenylaniline
with palladium(II) acetate in toluene at room tempera-
ture for 24 h in a one to one–one molar ratio and by
treating the system 2-phenylaniline/PdCl2/NaCl/NaOAc
in a molar ratio of 1/1/2/1 in methanol at room temper-
ature for one week. In both cases, 1a and 1b precipitated
in the reaction medium, were isolated by filtration and
purified by washing with adequate solvents. It should
be noted that 1a was isolated as an addition compound
of formula 1a Æ 0.8 toluene and that the attempts to elim-
inate the toluene retained for 1a were not successful. In
addition, the reaction between 2-phenylaniline and pal-
ladium(II) acetate in one-to-one molar ratio in acetic
acid at 60 ꢀC for 4 h, followed by a metathesis reaction
with LiBr, allowed the isolation of compound 1c in a
moderate yield of 39%. It should be noted that the cyclo-
palladation reaction (ii) of Scheme 1 is the first example
of a cyclopalladation reaction of a primary amine,
which proceeds in good yield, that uses as palladating
agent the system PdCl2/NaCl/NaOAc.
Compounds 1 were only slightly soluble in common
organic solvents, but compound 1c was soluble in
Scheme 1. (i) 2-phenylaniline/ Pd(OAc)2, molar ratio = 1:1, toluene, room temperature, 24 h. (ii) 2-phenylaniline/PdCl2/NaCl/NaOAc, molar
ratio = 1:1:2:1, MeOH, room temperature, 1 week. (iii) (a) 2-phenylaniline/ Pd(OAc)2, molar ratio = 1:1, acetic acid, 60 ꢀC, 4 h, (b) LiBr (excess),
acetone, room temperature, 45 min, (c) Purification by column chromatography: stationary phase, SiO2; mobile phase, CHCl3/MeOH (100/6). (iv) (a)
2-phenylaniline/Pd(OAc)2, molar ratio = 1:1, monodeuterated acetic acid (DOAc), 60 ꢀC, 4 h, (b) LiBr (excess)/acetone, room temperature, 45 min,
(c) purification by column chromatography: stationary phase, SiO2; mobile phase, CHCl3/MeOH (100/6). (v) py-d5 (excess), CDCl3, room
temperature. (vi) L = py (excess) or PPh3 (molar ratio 1/PPh3 = 1:2), acetone, room temperature, 3 h. (vii) Na(acac) Æ H2O (excess), acetone, room
temperature, 3 h.

424
J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
acetone. Compounds 1a and 1b gave satisfactory elemen-
tal analyses, IR and FAB+. In the IR of 1a, the asymmet-
ric and symmetric stretchings of the carboxylate groups
appeared at 1581 and 1419 cmꢀ1, respectively, indicating
that the acetato ligands presented a bidentate bridging
coordination mode [15] and in the FAB+ of compounds
1, one of the most intense peaks was [My + H+ ꢀ HX],
[y = 1a (X = OAc), y = 1b (X = Cl) or y = 1c (X = Br)],
according to their dinuclear structure [16]. In addition,
suspensions of compounds 1 in CDCl3 reacted with an
excess of py-d5 affording yellow solutions whose 1H
NMR spectra at 200 MHz showed the quantitative for-
mation of the mononuclear cyclopalladated compounds
20. Thus, according to the cis arrangement between the
py-d5 ligand and the palladated phenyl ring and the struc-
ture of compounds 20, their a proton resonated at low fre-
quencies (6.52, 6.48 and 6.47 ppm, respectively) and
appeared as a doublet (3JHH = 7–8 Hz) due to their cou-
It should be noted that the presence of deuterium
atoms in the three position of the palladated phenyl ring
of the molecules, which constitute sample A, showed that
the C–H bond activation step of the cyclopalladation
reaction of 2-phenylaniline was a reversible process. Fur-
thermore, these findings were consistent with an intramo-
lecular mode for the C–H bond activation, in accordance
with the general mechanism accepted for the cyclometal-
lation reaction [17]. It should be noted that studies on the
cyclopalladation reaction of benzylamine in monodeuter-
ated acetic acid using as metallating agent palladium(II)
acetate also showed that the C–H bond activation step
of this reaction is a reversible process and proceeds in
an intramolecular mode [18].
In order to fully characterize compounds 1a and 1b,
they were transformed by splitting reactions in the
mononuclear cyclopalladated compounds 2a, 2b, 3a
and 3b. Furthermore, 1a was transformed into the
mononuclear compound 4 by a reaction between 1a
and an excess of Na(acac) Æ H2O. Compounds 2a, 2b,
3a, 3b and 4 were obtained in moderate to high yields,
were soluble in CHCl3 and acetone and gave satisfac-
1
pling with the b proton [10,11,14]. Furthermore, H–1H
COSY and NOESY experiments at 500 MHz allowed
the assignment of the a–e protons in compound 2c0.
In order to elucidate whether theC–H activation step of
the cyclopalladation reaction was a reversible process, 2-
phenylaniline was treated with palladium(II) acetate in a
one-to-one molar ratio in monodeuterated acetic acid
(DOAc) at 60 ꢀC for 24 h, followed by a metathesis reac-
tion with LiBr. This procedure allowed the isolation of
sample A in a yield of 45%. Sample A was a mixture of
compounds 1c, 1cd1 and 1cd2. This was inferred from the
1H NMR at 500 MHz of solution B, which presented the
signals corresponding to compounds 2c0 and 2cd0 . Solu-
tionBwasobtainedbytreatingasuspensionofA inCDCl3
with py-d5. It should be noted that the 1H NMR in perdeu-
terated acetic acid of 2-phenylaniline demonstrated that 2-
phenylaniline was in the form 2-PhC6H4ND2 in this
1
tory elemental analyses, IR, FAB+ and H NMR. In
the IR of 2a and 3a, the difference in the wave numbers
of the asymmetric and symmetric stretchings of their
carboxylate group, indicated that the acetato ligand
presented a monodentate coordination mode [15]. In
the FAB+ of 2a, 2b, 3a, 3b and 4, the base peak was
[My + H+ ꢀ HX], [y = 2a or 3a (X = OAc), y = 2b or
3b (X = Cl), and y = 4 (X = acac)], according to their
mononuclear structure [16]. Furthermore, 1H–1H
COSY and NOESY experiments at 500 MHz for com-
pounds 2a, 2b, 3a and 3b allowed the assignment of the
most informative aromatic protons. Thus, according to
the cis arrangement between their pyridine or triphe-
nylphosphine ligand and their palladated phenyl ring
and to their structure [10,11,14,19], the a proton of
compounds 2a, 2b, 3a and 3b resonated at low frequen-
cies (6.54, 6.53, 6.41 and 6.50 ppm, respectively) and
appeared as a doublet for 2a and 2b, due to the cou-
pling of the b proton with the a proton, and as a triplet
for 3a and 3b, due to the coupling of the b proton and
the phosphorus nucleus with the a proton. Moreover,
for compounds 3a and 3b, the coupling constant be-
tween the phosphorus nucleus and the a proton (7–8
Hz) was consistent with a cis arrangement between
the triphenylphosphine ligand and the palladated phe-
nyl ring. In addition, the chemical shift of the phos-
phorus nucleus of 3a (34.25 ppm) and 3b (35.12
ppm) was in the interval expected for a cyclopalladated
compound of general formula trans-N,P-[Pd(C,N)X-
(PPh3)] (X = OAc, Cl or Br) with a six-membered pal-
ladacycle [10,11,14,20–22].
1
solvent, but the H NMR of solution B showed that the
amino groups of sample A did not present deuterium.
Thisresult suggestedthat the aminogroupsofsampleA ex-
changed D by H with water molecules present in the
1
acetone solvent used in its preparation. In the H NMR
at 500 MHz of solution B, the decrease of the intensity
of the signal of the d proton in relation to the intensity of
the remaining aromatic protons, demonstrated that deute-
rium atoms were incorporated at the 3 position of the
metallated phenyl ring. Thus, applying Eq. (1), in which
vð2c0dÞ and r were the mole fraction of compound 2cd0
and the ratio between the integrals of the d and e protons,
it was found that the molar fraction of compound 2c0d in
solution B was ca. 0.6. The mole fraction of 2c0d in solution
B was thereafter assumed to be the deuterium content of
samples A (ca. 60%); because the splitting reaction with
py-d5, which transforms sample A into solution B, should
affect neither the Pd–C r bonds nor the C–D r bonds of
sample A.
The X-ray crystal structure of compounds 3b and 4
was determined. Figs. 2 and 3 show the X-ray molecular
structures of 3b and 4 and the labels of selected atoms
vð2c0dÞ ¼ 1 ꢀ r
ð1Þ

J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
425
sent in the unit cell of 3b (Z = 2) and two pairs of enan-
tiomeric molecules were present in the unit cell of 4
(Z = 4).
The structures consisted of discrete molecules sepa-
rated by van der Waals distances and presented neither
hydrogen bonds nor p–p stacking interactions between
neighbouring molecules [23]. The distances and angles
around the palladium atoms were in the usual intervals
[21,24,25]. The palladium atoms presented a distorted
square planar coordination. Thus, for 3b, the deviation
of C(12) from the plane formed by N, Pd, P and Cl
˚
was ꢀ0.108(4) A and for 4, the deviation of O(1) from
the plane formed by N, Pd, O(2) and C(13) was
˚
ꢀ0.215(3) A. In both cases, the six-membered palladacy-
cle was nonplanar and the palladium atom and the met-
allated carbon atom were out of the plane formed by the
other four atoms of the metallacycle. This was inferred
for 3b by the torsion angles N–C(1)–C(6)–C(7), C(12)–
(C7)–C(6)–C(1) and Pd–C(12)–C(7)–C(6), which were
0.3(5)ꢀ, 38.0(5)ꢀ and ꢀ5.4(5)ꢀ, respectively; and for 4,
by the torsion angles N–C(6)–C(12)–C(11), C(6)–
C(11)–C(12)–C(13) and C(11)–C(12)–C(13)–Pd; which
were ꢀ1.6(7)ꢀ, ꢀ30.5(7)ꢀ and 5.2(7)ꢀ, respectively. It
should be noted that the nonplanar structure of the
six-membered palladacycle is the origin of the chirality
in this kind of compounds. In addition, for compound
4, the six-membered metallacycle formed by the acetyl-
acetonate ligand and the palladium atom was planar
since the torsion angles Pd–O(2)–C(3)–C(2), O(1)–Pd–
O(2)–C(3) and O(2)–C(3)–C(2)–C(1) were ꢀ0.5(7)ꢀ,
5.3(4)ꢀ and ꢀ3.7(9)ꢀ, respectively. For compound 4,
and according to the trans influence of the coordinated
ligands to the palladium atom, the Pd–O(1) distance
Fig. 2. X-ray molecular structure of compound 3b.
˚
[2.093(4) A] was larger than the Pd–O(2) distance
˚
[1.993(3) A]. Furthermore, comparing 3b and 4, the
Fig. 3. X-ray molecular structure of compound 4.
˚
Pd–N distance [2.115(3) A] and the Pd–C(12) distance
˚
[2.021(4) A] for 3b were larger than the Pd–N distance
Table 1
Selected bond distances and angles for compounds 3b and 4
˚
˚
[1.995(4) A] and the Pd–C(13) distance [1.969(6) A] for
4, due to the greater trans influence of the P and Cl
atoms in relation to the O(2) and O(1) atoms, respec-
tively [26].
3b
4
Pd–C(12)
Pd–N
Pd–P
2.021(4)
2.115(3)
Pd–C(13)
Pd–N
1.969(6)
1.995(4)
1.993(3)
In a previous paper [14], we reported the X-ray crystal
structure of the mononuclear compound [Pd{j2-N20,C1-
2-(20-NH2C6H4)C6H4}Br(PPh3)] (compound 3c); which
is identical to compound 3b, but it presents as unidentate
anionic ligand a bromo ligand. It should be noted that
there were no significant differences between the crystal
structures of compounds 3c and 3b, both crystallized in
2.2490(9)
2.4056(11)
84.38(13)
92.52(11)
176.62(8)
171.40(11)
87.35(9)
Pd–O(2)
Pd–O(1)
Pd–Cl
2.093(4)
86.4(2)
C(12)–Pd–N
C(12)–Pd–P
N–Pd–P
C(13)–Pd–N
C(13)–Pd–O(2)
N–Pd–O(2)
C(13)–Pd–O(1)
N–Pd–O(1)
O(2)–Pd–O(1)
C(6)–N–Pd
92.72(19)
178.52(12)
173.33(18)
89.38(16)
91.62(15)
114.9(3)
C(12)–Pd–Cl
N–Pd–Cl
P–Pd–Cl
C(1)–N–Pd
95.80(4)
107.5(2)
ꢀ
the triclinic space group P1 and the distances and angles
were quite similar for both compounds, but in 3c the dis-
˚
Distances in A and angles in ꢀ.
˚
tance Pd–Br was 2.5399(7) A and in 3b the distance
˚
Pd–Cl was 2.4056(11) A.
1
We note that in the room temperature H NMR at
for the following discussion, and Table 1 gives selected
bond distances and angles. 3b crystallized in the triclinic
200 MHz of compounds 2b and 4, the protons of the
amino group appeared as a broad A2 spin system, cen-
tred at 5.77 ppm for 2b and at 4.92 ppm for 4. This
ꢀ
space group P1 and 4 in the monoclinic space group
P21/a. Thus, a pair of enantiomeric molecules was pre-

426
J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
result indicated a fast exchange between their enantio-
meric molecules. In contrast, in the same conditions,
the protons of the amino group of 3b produced a broad
AB spin system, centred at 4.97 ppm, due to a slow ex-
change between their enantiomeric molecules. These re-
sults agreed with previous studies on the dynamic
behaviour of nonplanar six-membered palladacyles,
which related the rate of transformation between their
enantiomeric conformations with the volume of the
ancillary ligands coordinated to the metal centre [27].
It should be noted that at ꢀ60 ꢀC, the conversion be-
tween the enantiomeric molecules of 2b and 4 was
still in a fast exchange. This result contrasted with the
behaviour of mononuclear cyclopalladated compounds
containing a six-membered palladacycle derived from
2-benzylpyridine and 2-benzylbenzothiazole for which
the exchange between their enantiomeric molecules
was in a slow exchange at low temperature [27,28].
of the precedent discussion, the acetate anion should re-
main associated with the aqua complex II through hydro-
gen bonds. In support of the proposed behaviour of
compounds 2a and 3a in CDCl3 solution, it should be
noted that: (i) an intramolecular hydrogen bond between
an acetato ligand and a coordinated amino group to a pal-
ladium(II) centre has been determined by X-ray diffrac-
tion [22]; (ii) the chemical shift of the protons of the
aqua ligand of neutral organoaquopalladium(II) com-
plexes appears between 1.70 and 2.80 ppm, and; (iii) these
latter compounds experience a fast exchange between
coordinated water and free water [29].
3. Experimental
3.1. Instruments and reagents
1
It is noteworthy that in the room temperature H
Elemental analyses of C, H and N were performed with
an Eager 1108 microanalyzer. Infrared spectra were re-
corded on a Nicolet Impact-400 spectrophotometer using
pressed discs of dispersed samples of the compounds in
NMR at 200 MHz of 2a and 3a, the protons of the amino
group were not observed. Nevertheless, at 300 MHz and
at ꢀ60 ꢀC, they gave place to a broad AX spin system,
with the branches centred at 10.41 and 4.35 ppm for 2a
and at 8.83 and 4.54 ppm for 3a. In addition, the chemical
shift of the water present in the CDCl3 was 2.33 ppm for
the CDCl3 solution containing 2a and 2.72 ppm for the
CDCl3 solution containing 3a. Raising the temperature
for the CDCl3 solution containing 3a until 10 ꢀC, the sig-
nals of the amino protons broadened and were centred at
9.51 and 4.33 ppm and the chemical shift of the water pre-
sent in the CDCl3 moved to 1.71 ppm. Similar behaviour
was observed when the temperatureofthe CDCl3 solution
containing 2a was increased. These results were consistent
with: (i) a slow conversion between the enantiomeric mol-
ecules of 2a and 3a; (ii) the existence of an intramolecular
hydrogen bond between the amino group and the acetato
ligand of compounds 2a or 3a, and; (iii) the establishment
of the dynamic equilibrium shown in Fig. 4 between 2a or
3a and water present in the CDCl3 solvent. In addition,
the dependence of the chemical shift of the water present
in the CDCl3 solvent containing 2a or 3a with the temper-
ature indicated that, for the dynamic equilibrium shown
in Fig. 4, at low temperature the predominant species
was the aqua complex II while at high temperature it
was the acetato complex I. Note that for the consistency
1
KBr. H NMR spectra in CDCl3 were recorded at 500
MHz on a Bruker DMX 500 instrument, at 300 MHz
on a Varian 300 instrument and at 200 MHz on a Varian
Gemini-200 instrument. The 31P{1H} NMR spectra in
CHCl3 were recorded at 101.26 MHz in a Bruker DRX
250 instrument. Chemical shifts are reported in d values
(ppm) [relative to SiMe4 for 1H and 85% H3PO4 for 31P]
and coupling constants in Hz. FAB+ mass spectra were
obtained with a VG-Quatro Fisions instrument, using 3-
nitrobenzylalcohol as matrix. All chemicals and solvents
were of commercial grade and used as received, except
MeOH that was distilled over CaCl2 and toluene that
was distilled over sodium and benzophenone.
3.2. Synthesis of compounds 1 and sample A
1a: A suspension formed by 0.375 g (2.23 · 10ꢀ3 mol)
of 2-phenylaniline, 0.500 g (2.23 · 10ꢀ3 mol) of Pd(A-
cO)2 and 20 mL of toluene was stirred at room temper-
ature for 24 h. The precipitate was filtered, washed with
5 mL of diethylether and dried under vacuum. Yield:
85% (in relation to the isolated 1a Æ 0.8 toluene). Charac-
terization data: Anal. Calc. for C28H26N2O4Pd2 Æ 0.8 tol-
uene: C, 54.46; H, 4.41; N, 3.78. Found: C, 54.4; H, 4.6;
N, 3.7%. EM-FAB+ (Da/e) (selected data): [M + H+] =
667, [M + H+ ꢀ HOAc] = 607, [M + H+ ꢀ HOAc–
OAc]+ = 548, [M/2 ꢀ OAcꢀ + Pd] = 380. IR (cmꢀ1):
ma(COO) = 1581, ms(COO) = 1419, ma(NH2) = 3318,
ms(NH2) = 3269. 1b: A suspension formed by 0.239 g
(1.41 · 10ꢀ3 mol) of 2-phenylaniline, 0.250 g (1.41 ·
10ꢀ3 mol) of PdCl2, 0.164 g (2.82 · 10ꢀ3 mol) of NaCl,
0.115 g (1.41 · 10ꢀ3 mol) of NaOAc and 20 mL of
MeOH was stirred at room temperature for 1 week.
The precipitate was filtered, washed with 5 mL of water
Fig. 4. Dynamic equilibrium between compounds 2a (L = py) or 3a
(L = PPh3) and water present in CDCl3.

J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
427
3
m (2H, Hg and Hh); 7.11 td, JHH = 7.5, JHH = 1.5
4
and 5 mL of diethylether and dried under vacuum.
Yield: 75%. Characterization data: Anal. Calc. for
C24H20N2Cl2Pd2: C, 46.48; H, 3.25; N, 4.52. Found:
C, 46.3; H, 3.4; N, 4.4%. EM-FAB+ (Da/e) (selected
data): [M + H+] = 619, [M + H+ ꢀ HCl] = 583, [M/2 ꢀ
Clꢀ] = 274. IR (cmꢀ1): ma(NH2) = 3283, ms(NH2) = 3234.
1c: A suspension formed by 0.188 g (1.11 · 10ꢀ3 mol) of
2-phenylaniline, 0.250 g (1.11 · 10ꢀ3 mol) of Pd(AcO)2
and 20 mL of acetic acid was stirred at 60 ꢀC for 4 h.
The solution was concentrated under vacuum and the
residue was treated with 0.348 g (4.44 · 10ꢀ3 mol) of
LiBr and 10 mL of acetone. The suspension formed
was stirred at room temperature for 30 min. The result-
ing suspension was filtered, the solution concentrated
under vacuum and the residue eluted through a SiO2
column chromatography using as eluent CHCl3/MeOH
(100/6). The orange band was collected and concen-
trated under vacuum. Addition of 5 mL of diethylether
to the residue produced the precipitation of 1c that was
filtered and dried under vacuum. Yield: 39%. Character-
ization data: IR and EM-FAB+ were coincident with
those previously reported [14]. Sample A: A suspension
formed by 0.094 g (5.5 · 10ꢀ3 mol) of 2-phenylaniline,
0.125 g (5.5 · 10ꢀ3 mol) of Pd(OAc)2and 10 mL of
monodeuterated acetic acid was stirred at 60 ꢀC for 24
h. The solution was concentrated under vacuum and
the residue was treated with 0.174 g (2.0 · 10ꢀ3 mol)
of LiBr and 5 mL of acetone. The suspension formed
was stirred at room temperature for 30 min. The result-
ing suspension was filtered, the solution concentrated
under vacuum and the residue eluted through a SiO2
column chromatography using as eluent CHCl3/MeOH
(100/6). The orange band was collected and concen-
trated under vacuum. Addition of 5mL of diethylether
to the residue produced the precipitation of sample A
that was filtered and dried under vacuum. Yield: 45%.
3
(1H, Hc); 6.88 td, JHH = 7.5, JHH = 1.5 (1H, Hb),
4
3
7.47, br d, JHH = 8, (1H, Ha), 5.20 br s, (2H, NH2).
1
Solution B: Its H NMR spectrum is the addition of
1
1
1
the H NMR of 2c0 to the H NMR of 2c0d. The H
NMR of 2c0d is identical to that of compound 2c0, but
the d proton is absent and the c proton is a doublet.
3.4. Preparation of compounds 2
2a: A suspension formed by 0.150 (0.225 · 10ꢀ3 mol)
of 1a, 0.036 (0.450 · 10ꢀ3 mol) of pyridine and 20 mL of
acetone was stirred at room temperature for 3 h and the
solution formed was concentrated under vacuum. Addi-
tion of 5 mL of diethylether to the residue produced the
precipitation of 2a, which was filtered and dried under
vacuum. Yield: 59%. Characterization data: Anal. Calc.
for C19H18N2O2Pd: C, 55.29; H, 4.40; N, 6.79. Found:
C, 55.6; H, 4.2; N, 6.6%. EM-FAB+ (Da/e) (selected
data): [M + H+] = 413, [M + H+ ꢀ HOAc ] = 353,
[M + H+ ꢀ HOAc–py] = 274. IR (cmꢀ1): ma(NH2) =
3248, ms(NH2) = 3100, ma(COO) = 1581, ms(COO) =
3
1384. 1H NMR (500 MHz): 8.55 dd, JHH = 6.5
3
4
4JHH = 1.5 (2H, Hopy); 7.78 tt, JHH = 7.5 JHH = 1.5
3
(1H, Hppy); 7.57 dd, JHH = 7.3, JHH = 1.3 (1H, He);
4
3
7.44 dd, JHH = 7.5, JHH = 1.5 (1H, Hd); 7.35 dd,
4
3JHH = 7.5 JHH = 1.5 (1H, Hh); 7.29 td, JHH = 6.5
4
3
3
4
4JHH = 1.0 (2H, Hmpy); 7.23 td, JHH = 7.5 JHH = 1.0
3
4
(1H, Hf); 7.19 td JHH = 7.5 JHH = 1.5 (1H, Hg); 7.09
td, 3JHH = 7.3 4JHH = 1.0 (1H, Hc); 6.88 td,
4
3
3JHH = 7.5, JHH = 1.5 (1H, Hb); 6.54 dd, JHH = 8.0
4JHH = 1.0 (1H, Ha); 1.97 s (3H, OAc). 2b: A suspension
formed by 0.100 g (0.161 · 10ꢀ3 mol) of 1a, 0.025 g
(0.322 · 10ꢀ3 mol) of pyridine and 20 mL of acetone
was stirred at room temperature for 3 h and the solution
formed was concentrated under vacuum. Addition of 5
mL of diethylether to the residue produced the precipi-
tation of 2b, which was filtered and dried under vacuum.
Yield: 85%. Characterization data: Anal. Calc. for
C17H15N2ClPd: C, 54.64; H, 3.89; N, 7.20. Found: C,
54.2; H, 4.0; N, 7.1%. EM-FAB+ (Da/e) (selected data):
[M + H+] = 389, [M + H+ ꢀ HCl] = 353, [M + H+ ꢀ
HCl–py] = 274. IR (cmꢀ1): ma(NH2) = 3177, ms(NH2) =
3.3. Preparation of compounds 20 and solution B
A suspension formed by 0.010 g of the corresponding
compound 1 or of the sample A and 0.7 mL of CDCl3
was treated with 2 drops of py-d5 in a NMR tube and
shacked until a pale yellow solution was formed. Char-
1
3
acterization data: 2a0: H NMR (200 MHz): 7.52 dd,
3100. 1H NMR (500 MHz): 8.67 dd, JHH = 6.5
4
3
3
4
3JHH = 6.9 JHH = 1.9 (1H, He); 7.39 d, JHH = 7.6
4JHH = 1.5 (2H, Hopy); 7.76 tt, JHH = 7.5 JHH = 1.5
3
(1H, Hd); 7.32 d, JHH = 7.6 (1H, Hh); 7.25–7.08 (2H,
3
(1H, Hppy); 7.52 d, JHH = 7.0 (1H, He); 7.48 dd,
3JHH = 8.0 JHH = 1.5 (1H, Hd); 7.2–7.4 m (5H, Hf,
3
Hg and Hf); 7.04 t, JHH = 7.4 (1H, Hc); 6.83 t, JH–
3
4
3
H = 7.4 (1H, Hb); 6.52 d, JHH = 7.6 (1H, Ha); 1.94 s
3
Hg, Hh and Hmpy); 7.14 td, JHH = 7.5 JHH = 1.0
4
3
4
(3H, OAc). 2b0: 1H NMR (200 MHz): 7.55 d,
(1H, Hc); 6.91 td, JHH = 7.5 JHH = 1.5 (1H, Hb); 6.53
dd, 3JHH = 8.0 4JHH = 1.0 (1H, Ha); 5.77 br s (2H, NH2).
3JHH = 6.8 (1H, He); 7.40 dd, JHH = 7.0, JHH = 1.1
(1H, Hd); 7.1–7.3 m (3H, Hf, Hg and Hh); 7.07 td,
3
4
4
3
3JHH = 7.2, JHH = 1.0 (1H, Hc); 6.83 td, JH–H = 7.4,
3.5. Preparation of compounds 3
4JH–H = 1.3 (1H, Hb); 6.48 d, JHH = 7.6 (1H, Ha);
3
1
6.03 br s (2H, NH2). 2c0: H NMR (500 MHz): 7.60 d
3a: A suspension formed by 0.100 g (0.3 · 10ꢀ3 mol)
of 1a, 0.078 g (0.6 · 10ꢀ3 mol) of triphenylphosphine
and 20 mL of acetone was stirred at room temperature
3JHH = 7.0 Hz (1H, He), 7.47 dd, JHH = 8.0,
3
4JHH = 1.5 (1H, Hd); 7.23–7.27 m, (1H, Hf), 7.23–7.13

428
J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
for 3 h and the solution formed was concentrated under
vacuum. Addition of 5 mL of diethylether to the result-
ing residue produced the precipitation of 3a, which was
filtered and dried under vacuum. Yield = 74%. Charac-
terization data: Anal. Calc. for C32H28NO2PPd: C,
64.49; H, 4.74; N, 2.39. Found: C, 64.6; H, 4.8; N,
of 3b, which was filtered and dried under vacuum.
Yield = 60%. Characterization data: Anal. Calc. for
C30H25NClPPd: C, 62.96; H, 4.40; N, 2.45. Found: C,
63.3; H, 4.5; N, 2.5%. EM-FAB+ (Da/e) (selected data):
[M + H+ ꢀ HCl] = 536,
[M + H+ ꢀ HCl–phenylani-
line] = 367. IR (cmꢀ1): ma(NH2) = 3311, ms(NH2) = 3241,
1
2.4%.
EM-FAB+
(Da/e)
(selected
data):
m(q X-sensitive mode of coordinated PPh3) = 1097. H
NMR (500 MHz): 7.45 dd, JH–H = 7.5 JH–P = 12
[M + H+ ꢀ HOAc] = 536, [M + H+ ꢀ HOAc–phenylan-
iline] = 367. IR (cmꢀ1): IR (cmꢀ1): ma(NH2) = 3290
ms(NH2) = not observed; ma(COO) = 1581, ms(COO) =
1391, m(q X-sensitive mode of coordinated PPh3) =
3
3
3
(6H, HoPPh3); 7.34 td, JHH = 7.5 JHH = 2.0 (3H,
4
HpPPh3); 7.27–7.22 m, (10H, He, Hf, Hg, Hh, HmPPh3);
3
7.21 dd, JHH = 7.5 JHH = 1.0 (1H, Hd); 6.86 t,
4
1
3
1096. H NMR (500 MHz): 7.4–7.5 m, (6H, HoPPh3);
7.3–7.4 m, (3H, HpPPh3); 7.2–7.3 m, (11H, Hd, He, Hf,
3JHH = 7.7 (1H, Hc); 6.50 t, JHH = 4JHP = 7.0 (1H,
3
Ha); 6.44 t, JH–H = 7.5 (1H, Hb); 4.88 and 5.07 br sig-
3
Hg, Hh, HmPPh3); 6.86 t, JHH = 7.0 (1H, Hc); 6.45 t
nals, (2H, NH2). RMN 31P{1H} = 35.12 s.
3
3JHH = 4JPH = 7.0 (1H, Ha); 6.41 t, JHH = 7.5 (1H,
Hb); 1.64
s
(3H, OAc). RMN 31P{1H} (101.26
3.6. Preparation of compound 4
MHz) = 34.25 s. 3b: A suspension formed by 0.100 g
(0.16 · 10ꢀ3 mol) of 1b, 0.084 g (0.32 · 10ꢀ3 mol) of tri-
phenylphosphine and 20 mL of acetone was stirred at
room temperature for 3 h. The solution was concen-
trated under vacuum and the residue was eluted through
A suspension formed by 0.300 g (0.450 · 10ꢀ3 mol) of
compound 1a, 0.252 g (1.8 · 10ꢀ3 mol) of Na(acac) Æ
H2O and 20 mL of acetone was stirred at room temper-
ature for 1 h. The suspension was concentrated under
vacuum and the residue was eluted through a SiO2 col-
umn chromatography using as eluent CHCl3/MeOH
(100:10). The yellow band was collected and concen-
trated under vacuum. Addition of 5 mL of diethylether
a
SiO2 column chromatography using as eluent
CHCl3/MeOH (100:6). The orange band was collected
and concentrated under vacuum. Addition of 5 mL of
diethylether to the residue produced the precipitation
Table 2
Crystallographic data for 3b and 4
Compound
3b
4
Empirical formula
Formula weight
Temperature (K)
C
30H25ClNPPd
C17H17NO2Pd
373.72
293 (2)
572.33
293 (2)
0.71069
˚
Wavelength (A)
0.71069
Monoclinic, P21/a
ꢀ
Triclinic, P1
Crystal system, space group
Unit cell dimensions
˚
a (A)
9.9170(10)
10.4750(10)
12.0890(10)
98.610(10)
94.034(10)
99.000(10)
1220.7(2)
2
11.5900(10)
1.2730(10)
12.2150(10)
90
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
107.6560(10)
90
3
˚
Volume (A )
1520.8(2)
4
1.632
Z
DCalc (mg/m3)
1.557
0.995
580
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm)
)
1.223
752
0.1 · 0.1 · 0.2
1.71–31.62ꢀ
0 6 h 6 14
ꢀ15 6 k 6 15
ꢀ17 6 l 6 17
0.1 · 0.1 · 0.2
3.42–31.84ꢀ
ꢀ15 6 h 6 14
0 6 k 6 16
0 6 l 6 17
12664/3820 (0.0395)
Full-matrix least-squares on F2
3820/0/191
Theta range for data collection
Index ranges
Reflections collected/unique (Rint
Refinement method
)
11270/6458 (0.0284)
Full-matrix least-squares on F2
6458/0/368
Data/restraints/parameters
Goodness-of-fit on F2
1.142
R1 = 0.0532
1.095
R1 = 0.0565
Final R indices (I > 2r(I))
wR2 = 0.1444
R1 = 0.0652
wR2 = 0.1657
R1 = 0.1070
wR2 = 0.1849
R indices (all data)
wR2 = 0.1592
0.072(4)
Extinction coefficient
Largest different peak and hole (e A )
3
˚
0.810 and ꢀ0.659
0.631 and ꢀ1.352

J. Albert et al. / Journal of Organometallic Chemistry 690 (2005) 422–429
429
[2] M.S. Driver, J.F. Hartwig, J. Am. Chem. Soc. 117 (1995) 4708.
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14 (1995) 2214.
to the residue produced the precipitation of 4, which was
filtered and dried under vacuum. Yield = 46%. Charac-
terization data: Anal. Calc. for C17H17NO2Pd: C, 54.64;
H, 4.58; N, 3.75. Found: C, 54.3; H, 4.7; N, 3.7%.
EM-FAB+ (Da/e) (selected data): [M + H+] = 374,
[M + H+ ꢀ Hacac] = 273. IR (cmꢀ1): ma(NH) = 3283,
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(1995) 1005.
ms(NH) = 3191,
m(C:::C + C:::O) = 1588,
m(C:::O +
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(1994) 4751.
C:::C) = 1511, dd(CH3) = 1391, m(C–CH3 + C:::C) =
1264. 1H NMR (500 MHz): 7.57 d, 3JH–H = 8.0 (1H, He);
7.36–7.42 m, (2H, Hby Hd); 7.22–7.27 m, (1H, Hf); 7.1–
7.2 m, (4H, Ha, Hc, Hg y Hh), 5,30 (1H, HCH acac); 4.92 br
s (NH2), 1.99 and 1.94 s (6H, HMe acac).
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3.7. Crystal structures
´
[10] M. Benito, C. Lopez, X. Morvan, Polyhedron 18 (1999) 2583.
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Organomet. Chem. 545–546 (1997) 131.
Crystals for the X-ray molecular structure determina-
tion of 3b and 4 were obtained by slow evaporation of
the solvents of a solution of 3b in methanol/dichloro-
methane (1/1) and of a solution of 4 in dichloromethane.
In both cases a prismatic crystal was selected and
mounted on a MAR345 diffractometer with an image
plate detector. Intensities were collected with graphite-
monochromatized Mo Ka radiation. The structures
were solved by direct methods using the SHELXS [30]
computer program and refined by the full-matrix least
squares method, with the SHELXL 97 [31] computer pro-
gram. A summary of crystallographic data and some de-
tails of the refinement are given in Table 2.
[12] M. Miura, T. Tsuda, T. Satoh, S. Pivsa-Art, M. Nomura, J. Org.
Chem. 63 (1998) 5211.
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references therein.
´
[14] J. Albert, J. Granell, A. Luque, J. Mınguez, R. Moragas, M.
Font-Bardia, X. Solans, J. Organomet. Chem. 522 (1996) 87.
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232.
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P. Traldi, Inorg. Chim. Acta 161 (1989) 57.
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3225.
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´ ´ ´
Torres, A. Castin˜eiras, A. Suarez, J.J. Fernandez, A.F. Fernan-
dez, J. Organomet. Chem. 547 (1997) 297.
´
[20] J. Albert, M. Gomez, J. Granell, J. Sales, X. Solans, Organome-
4. Supplementary material
tallics 9 (1990) 1405.
[21] J. Albert, R.M. Ceder, M. Gomez, J. Granell, J. Sales, Organ-
´
Crystallographic data for the structural analyses of
3b and 4 have been deposited at the Cambridge Crystal-
lographic Data Centre, CCDC, Nos. 240805 for 3b and
240804 for 4. Copies of this information can be obtained
from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: 44-1233-336033; e-mail: depos-
it@ccdc.ac.uk or www.ccdc.cam.ac.uk).
ometallics 11 (1992) 1536.
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´
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´
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´ ´
Rodrıguez-Ramos, J.R. Masaguer, J.L. Garcıa-Ruano, X. Solans,
´
´
Organometallics 12 (1993) 4104.
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Metals, second ed., Wiley, New York, 1994, p. 6.
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(1986) 589.
Acknowledgements
We are grateful to the Ministerio de Ciencia y Tec-
´
nologıa and to the Generalitat de Catalunya for financial
support (Grants BQU2003-0096 and 2001SGR 00054).
[28] Y. Fuchita, K. Yoshinaga, H. Kusaba, M. Mori, K. Hiraki, K.
Takehara, Inorg. Chim. Acta 239 (1995) 125.
´
[29] C. Bartolome, P. Espinet, L. Vicente, F. Villafan˜e, Organometal-
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tion of Crystal Structures, University of Go¨ttingen, Germany,
1997.
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¨