Cyclopalladation of 3-methoxyimino-2-phenyl-3H-indoles

Article abstract of DOI:10.1016/j.jorganchem.2008.05.043

The direct cyclopalladation of 3-methoxyimino-2-(4-chlorophenyl)-3H-indole (1a) and 3-methoxyimino-2-phenyl-3H-indole (1b) results in the regioselective activation of the ortho σ[C(sp², phenyl)-H] bond affording (μ-OAc)₂[Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}]₂ (2) {R = Cl (2a) or H (2b)} that contain a central Pd(μ-OAc)₂Pd core. Compounds 2a and 2b reacted with triphenylphosphine (in a molar ratio PPh₃:2 = 2) giving [Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}(OAc)(PPh₃)] (3) {R = Cl (3a) or H (3b)}. Treatment of 2a or 2b with a slight excess of LiCl in acetone produced the metathesis of the bridging ligands and the formation of (μ-Cl)₂[Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}]₂ (4) {R = Cl (4a) or H (4b)} with a central Pd(μ-Cl)₂Pd moiety. The reactions of 4a or 4b with deuterated pyridine (py-d₅) or triphenylphosphine gave the monomeric derivatives [Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}Cl(L)] with R = Cl or H and L = py-d₅ (5) or PPh₃ (6). The crystal structure of 6b·1/2CH₂Cl₂ confirmed the mode of binding of the ligand, the nature of the metallated carbon atom and a trans-arrangement of the phosphine ligand and the heterocyclic nitrogen. Theoretical calculations on the free ligands are also reported and have allowed the rationalization of the regioselectivity of the cyclopalladation process.

Full text of DOI:10.1016/j.jorganchem.2008.05.043

Journal of Organometallic Chemistry 693 (2008) 2877–2886
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cyclopalladation of 3-methoxyimino-2-phenyl-3H-indoles
b
a
a
c
Concepción López a, , Asensio González , Carlos Moya , Ramon Bosque , Xavier Solans ,
*
Mercè Font-Bardía c
a Departament de Química Inorgànica, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain
b Laboratori de Química Orgánica, Facultat de Farmacia, Universitat de Barcelona, Pl, Pius XII s/n, E-08028 Barcelona, Spain
c Departament de Cristalꢀlografia Mineralogía i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The direct cyclopalladation of 3-methoxyimino-2-(4-chlorophenyl)-3H-indole (1a) and 3-methoxyimino-
2-phenyl-3H-indole (1b) results in the regioselective activation of the ortho
affording (
-OAc)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}]2 (2) {R = Cl (2a) or H (2b)} that contain a
central ‘‘Pd(
r
[C(sp2, phenyl)-H] bond
Received 17 March 2008
Received in revised form 30 May 2008
Accepted 30 May 2008
l
l
-OAc)2Pd” core. Compounds 2a and 2b reacted with triphenylphosphine (in a molar ratio
Available online 7 June 2008
PPh3:2 = 2) giving [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}(OAc)(PPh3)] (3) {R = Cl (3a) or H (3b)}. Treat-
ment of 2a or 2b with a slight excess of LiCl in acetone produced the metathesis of the bridging ligands
Keywords:
and the formation of (
central ‘‘Pd( -Cl)2Pd” moiety. The reactions of 4a or 4b with deuterated pyridine (py-d5) or triphenyl-
l
-Cl)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}]2 (4) {R = Cl (4a) or H (4b)} with a
Cyclopalladation
Activation of C–H bonds
Oximes
l
phosphine gave the monomeric derivatives [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}Cl(L)] with R = Cl
or H and L = py-d5 (5) or PPh3 (6). The crystal structure of 6bꢀ1/2CH2Cl2 confirmed the mode of binding
of the ligand, the nature of the metallated carbon atom and a trans-arrangement of the phosphine ligand
and the heterocyclic nitrogen. Theoretical calculations on the free ligands are also reported and have
allowed the rationalization of the regioselectivity of the cyclopalladation process.
Ó 2008 Elsevier B.V. All rights reserved.
Heterocycles
1. Introduction
the study of the cyclometallation of more complex ligands with
two different functional groups and a greater number of
r(C–H)
The synthesis and study of the reactivity and applications of
cyclopalladated compounds containing N-donor ligands is one of
the most attractive areas of organometallic chemistry [1]. Most
of the cyclopalladation reactions described so far involved the acti-
bonds susceptible to be metallated is not common. It is also note-
worthy that: (a) palladium chemistry of indole derivatives is of
interest for catalysis, medicinal and synthetic chemistry [5], (b)
oxime palladacycles are used in homogeneous catalysis [6] and
(c) the regioselective palladation of oximes [1a,6b] is useful in
the preparation of natural products [6b]. In this paper we present
a new family of ligands, containing simultaneously the indole moi-
ety and the oxime functional group, and a study of their reactivity
towards palladium(II). The new ligands (1) (Fig. 1) can exhibit two
different configurations (E and Z, Fig. 1) and may bind to the metal
through two different nitrogen donor atoms.
vation of a
r(C–H) bond of organic compounds containing a nitro-
gen atom of either a functional group (i.e. amines, imines, oximes,
etc.) or a heterocyclic system. It has been reported that when this
type of ligand has two or more
allate, the reaction proceeds with a high degree of regioselectivity
[2,3]. The preferential activation of one of the (C–H) bonds of the
r(C–H) bonds susceptible to met-
r
ligand is dependent on a wide variety of factors such as the nature
and hybridization of the carbon atom, and the relative orientation
between the nitrogen atom and the
r
(C–H) bond in the precursor.
2. Results and discussion
Furthermore, for Schiff bases R-CH = N-R0 containing a
r
(Csp2–H)
bond susceptible to metallation in the two substituents (R and
R0), the formation of the palladacycles containing the >C@N– func-
tional group in the new ring is strongly preferred (endo effect) [2].
Most of the work described so far is focused on monofunctional
organic ligands or compounds bearing two identical functional
groups. Examples of cyclopalladation of oximes, benzimidazole,
benzothiazole and benzoxazole have been reported [4]. However,
2.1. The ligands
The new indole derivatives 1a (R = Cl) and 1b (R = H) have been
prepared using a two-step straightforward sequence of reactions
(Scheme 1), which consisted of the synthesis of the 3-hydroxyi-
minoindole derivatives previously described [7,8] followed by
alkylation of the oxime group.
The procedure used for the alkylation of the precursors
(3-hydroxyiminoindole derivatives) is based on that described by
* Corresponding author.
E-mail address: conchi.lopez@qi.ub.es (C. López).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.05.043

2878
C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
ring around the C2–C10 bond and this suggested that the species
present in solution is the E isomer. In order to confirm this hypoth-
esis, we decided to undertake theoretical calculations for the Z and
E isomers of 1a and 1b using the AM1 program [10] implemented
in the SPARTAN 5.0 package [11]. The most relevant results obtained
from this study are: (a) in optimized geometries of the E and Z iso-
mers of 1a and 1b, the phenyl ring adopts different orientations
(Fig. 2) and (b) the total energy of the Z isomer is {1.89 Kcal/mol
(for 1a) and 1.99 Kcal/mol (for 1b)} greater than that of the E iso-
mer. In view of these results we postulate that 1a and 1b adopt
the E configuration in solution.
Once the ligands were completely characterized, we studied
their reactivity towards palladium(II). It should be noted that de-
spite compounds 1a and 1b have the E-configuration, examples
of the E/Z isomerizations of Schiff bases during the reaction with
transition metal salts or complexes have been reported [12] and
consequently the isomerization of the ligand can not be excluded.
Fig. 1. Two possible isomers of the ligands C6H4-4R-1-[C8H4N-30-NOMe] {R = Cl
(1a) or H (1b)} selected for this study.
Pfeiffer and Bauer [9] for the alkylation of indigo in a two-phase
system and it could be extended to the synthesis of related alkyl
derivatives.
Elemental analyses of 1a and 1b were consistent with the
proposed formulae and their mass spectra showed a peak at
m/z = 271.1 (for 1a) and at 237.1 (for 1b) that agree with those ex-
pected for the corresponding [M+H]+ cations.
2.2. Palladium(II) complexes
As mentioned above, in compounds 1a and 1b, two different
arrangements between the OMe group and the >C@N– bond of
the heterocycle, could be expected {(E) and (Z) isomers, Fig. 1}.
Their 1H NMR spectra showed a singlet due to the OMe unit cen-
tered at d = 4.34 ppm (for 1b) or at d = 4.32 ppm (for 1b). This sug-
gested that only one isomer was present in solution. For 1a, a set of
four doublets (of relative intensities 2:2:1:1) and two triplets
(whose integration corresponded to one proton each) were de-
tected in the range: 7.20–8.60 ppm. The most intense doublets
were assigned to the pairs of protons (H11 and H15) and (H12 and
H14). For 1b, one of these signals was more complex due to the
overlapping of the resonance of the H13 proton.
When the corresponding ligand (1a or 1b) was treated with the
equimolar amount of Pd(OAc)2 in a 10:1 mixture of acetic acid and
acetic anhydride under reflux for 3.5 h, the formation of metallic
palladium was observed. Filtration through Celite followed by con-
centration of the filtrate to dryness and the subsequent chromatog-
raphy on SiO2 column gave a deep-garnet solid in both cases
(hereinafter referred to as 2a and 2b, respectively) (Scheme 2).
Compounds 2a and 2b were characterized by elemental analyses,
mass spectrometry, infrared spectroscopy and mono- [1H and
13C{1H}] and two-dimensional [{1H–13C} heteronuclear correla-
tions HSQC and HMBC and {1H–1H} NOESY] NMR experiments.
The infrared spectra of 2a and 2b showed two bands at 1559 and
1410 cmꢁ1 (for 2a) or at 1572 and 1419 cmꢁ1 (for 2b) that were
indicative of the presence of the OAcꢁ ligand. The separation be-
tween these two absorptions, suggests, according to the bibliogra-
phy [13] that the OAcꢁ behaved as a (O,O0) bridging ligand.
The unequivocal assignment of the signals due to the 1H and 13
C
nuclei of the bicyclic system [(H5–H8) and (C2–C9), respectively]
required the use of two dimensional {1H–13C}-HSQC and HMBC
experiments. In particular, in the {1H–13C}-HMBC spectra the exis-
tence of a cross-peak between the signal arising from the H11 pro-
ton and those of the C12 carbon nuclei and quaternary C2 and C10
carbon atoms permitted the assignment of the chemical shift of
C2. The doublet at d = 8.02 ppm showed cross-peaks with two qua-
ternary carbons and none of them was coincident with C2. This
allowed us to assign this signal to the H5 proton of indole unit
and the resonances of the C3 and C4 carbon atoms. The identifica-
tion of the remaining signals detected in the 1H spectra of 1a and
1b was achieved with the aid of {1H–1H}-COSY and NOESY
experiments.
Elemental analyses of 2a and 2b were consistent with those ex-
pected for the di-
l-acetato bridged cyclopalladated complexes:
(l
-OAc)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}]2 and the mass
spectra showed a peak at m/z = 753.9 (for 2a) or 684.0 (for 2b),
which correspond to the [M-OAc]+ cations.
1H and 13C{1H} NMR studies of 2a and 2b in CDCl3 at room tem-
perature showed two sets of superimposed signals of relative
intensities 2.8:1.0 (for 2a) and 2.7:1.0 (for 2b), which could be
indicative of the presence of two isomeric species [hereinafter
referred to as 2aI and 2aII (for 2a) and 2bI and 2bII (for 2b)] in solu-
tion. Examples of the coexistence of two isomers of related dimeric
{1H–1H}-NOESY and ROESY spectra did not allow us to clarify
the configuration of the oxime. However, the use of molecular
models for the E and Z isomers of 1a and 1b, revealed that in the
Z isomer, the oxygen atom would be very close to the phenyl ring
and consequently this would reduce the free rotation of the phenyl
compounds (
viously [14–16].
l-OAc)2[Pd(j
2-C,N-ligand)]2 have been reported pre-
1H NMR spectra of 2a and 2b, showed that the chemical shifts of
the OMe protons were very similar to those of the corresponding
Scheme 1.

C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
2879
Fig. 3. Schematic view of the trans- isomers of cyclopalladated complexes
-OAc)2[Pd{
2-C,N-ligand}]2 with an open-book type structure and of the cis-
Fig. 2. Optimized geometries of the E and Z isomers of ligand 1a.
(l
j
isomers of these products.
ligand for all the isomers. This finding suggested that none of the
two donor atoms of oxime group was bound to the palladium(II)
in the pairs (2aI, 2aII) and (2bI, 2bII). In the 13C{1H} NMR spectra
of the major isomers (2aI, 2bI) the intensity of the signal from
the C15 atom decreased substantially and shifted towards low-field
(ca. 21 ppm) in relation to the corresponding free ligand. In addi-
tion, no evidences of any cross-peak between the resonance of
the C15 nuclei and those of the aromatic protons was detected in
the [1H–13C]-HSQC spectra of any of the isomers. According to
the literature [17], these findings suggested the existence of a
thus, we assumed that in these species the two halves were in a
trans-arrangement.
Most of the acetato-bridged cyclopalladated dimers described
before show a folded structure {commonly known as open-book
structure (Fig. 3)} in solution as well as in the solid state [14–
16,18]. On this basis, we assumed that in the major isomers (2aI
and 2bI) the relative orientation of the acetato ligands corresponds
to the open-book type with a C2 symmetry. {1H–1H} NOESY and
ROESY spectra of 2a and 2b did not provide evidences of the exis-
tence of any interconversion between 2aI or 2bI and the minor iso-
mers (2aII and 2bII, respectively). Moreover, the molar ratio
between the two isomers did not vary substantially when the spec-
trum was recorded with a Bruker 250 MHz instrument {molar
ratios 2aI:2aII = 2.76 and 2bI: 2bII = 2.70}.
r
(Pd–C15) bond in the complexes. In view of the results obtained
from the characterization data available, we concluded that in
2aI and 2bI the ligands behaved as a bidentate [C(sp2, phenyl),
ꢁ
Nindole
]
group. The studies of the reactivity of 2 (vide infra) al-
lowed us to confirm that in the minor isomers 2aII and 2bII the li-
gands exhibited the same hapticity and mode of binding than in 2aI
and 2bI.
For the minor isomers (2aII and 2bII) most of the signals ap-
peared duplicated in the 1H NMR spectra and the chemical shifts
of the resonances from the methyl protons of the OAcꢁ ligand were
very similar to those reported previously for cyclopalladated com-
It is well-known that the dimeric cyclopalladated complexes (
l-
OAc)2[Pd(
j
2-C,N-ligand)]2 may exhibit different isomeric forms
plexes (l-OAc)2[Pd(j
2-C,N-ligand)]2 with a cis-arrangement of the
[14–16,18]. In these isomers, the two halves of the molecule could
be in a trans- or cis-arrangement (Fig. 3). It has been reported that
for the trans-isomers the resonance of the methyl groups of the
bridging ligands appear as one singlet, but it splits into two singlets
in the cis-isomers [14,15]. For 2aI and 2bI, one singlet [at 2.29 (for
2aI) or 2.26 ppm (for 2bI)] was observed in the 1H NMR spectra;
two halves of the molecule [14,15].
On the other hand, the 31P{1H} NMR spectra recorded after the
addition of PPh3 to a solution of 2a or 2b in CDCl3 (in a PPh3:Pd
molar ratio = 2) showed only a singlet at d = 42.5 and 43.7 ppm
for 2a and 2b, respectively. Besides, only a single set of signals
Scheme 2.

2880
C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
was observed in the 1H NMR spectra and the resonance of the pro-
tons of the OAcꢁ ligand appeared as a singlet at higher fields than
in 2a and 2b. This could be attributed to the proximity of the phe-
nyl rings. All these findings indicate that the two isomeric species
present in solution gave the same final products (3a or 3b). These
products were identified as [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NO-
Me)}(OAc)(PPh3)] {R = Cl (3a) or H (3b)} (Scheme 2). These results
confirmed that the nature of the metallated carbon is identical in
the two pairs of isomers {(2aI, 2aII) and (2bI, 2bII)}.
Similar results were obtained when this reaction was per-
formed using the crude of the reaction obtained (before the
work-up of the column), but in this case it was necessary to filter
the solution through Celite. In these cases, 1H and 31P{1H} NMR
spectra obtained were identical to of pure 2a or 2b. This is a proof
of the inexistence of any other type of palladacycle in the crude of
the reaction and indicates that the formation of 2 is regioselective.
Treatment of 2 with a slight excess of LiCl in acetone produced
Table 1
Selected bond lengths (in Å) and angles (°) for the two non-equivalent molecules (I
and II) found in the crystal structure of compound 6bꢀ1/2CH2Cl2 (standard deviations
are given in parenthesis)
Molecule I
Molecule II
Bond lengths
Pd(1)–C(11)
Pd(1)–N(11)
Pd(1)–P(1)
2.008(4)
2.105(3)
2.2627(19)
2.3636(15)
1.444(5)
1.464(5)
1.320(5)
1.451(5)
1.438(5)
1.393(6)
1.404(7)
1.355(7)
1.384(6)
1.399(6)
1.414(5)
1.301(5)
1.376(5)
1.419(6)
Pd(2)–C(21)
Pd(2)–N(21)
Pd(2)–P(2)
2.014(4)
2.113(3)
2.2702(16)
2.363(3)
1.432(5)
1.445(5)
1.332(5)
1.487(5)
1.447(6)
1.406(6)
1.342(7)
1.396(7)
1.395(7)
1.373(6)
1.434(5)
1.277(5)
1.388(4)
1.404(6)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
C(11)–C(16)
C(16)–C(17)
N(11)–C(17)
C(17)–C(18)
C(18)–C(19)
C(19)–C(110)
C(110)–C(111)
C(111)–C(112)
C(112)–C(113)
C(113)–C(114)
C(114)–N(11)
C(18)–N(12)
N(12)–O(11)
O(11)–C(115)
C(21)–C(26)
C(26)–C(27)
N(21)–C(27)
C(27)–C(28)
C(28)–C(29)
C(29)–C(210)
C(210)–C(211)
C(211)–C(212)
C(212)–C(213)
C(213)–C(214)
C(214)–N(21)
C(28)–N(22)
N(22)–O(21)
O(21)–C(215)
the formation of the di-
l-chloro-bridged cyclopalladated deriva-
tives
(l
-Cl)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}]2 {R = Cl
(4a) or H (4b)} (Scheme 2). Elemental analyses of 4a and 4b were
consistent with the proposed formulae and the mass spectra
showed the peak due to the corresponding cation [M-Cl]+ (at m/
z = 788.9 and 690.9 for 4a and 4b, respectively). Unfortunately,
the low solubility of 4a and 4b in most of the common solvents
used for NMR studies (i.e. acetone-d6, CDCl3, CD2Cl2) did not allow
us to characterize them in solution. However, the addition of a few
drops of deuterated pyridine (py-d5) to a suspension of 4a or 4b in
CDCl3, produced the complete dissolution of the palladium(II)
complex and the 1H NMR spectra of the resulting deep-garnet solu-
Bond angles
Cl(1)–Pd(1)–P(1)
P(1)–Pd(1)–C(11)
C(11)–Pd(1)–N(11)
N(1)–Pd(1)–Cl(1)
Pd(1)–N(11)–C(17)
Pd(1)–N(11)–C(114)
Pd(1)–C(11)–C(16)
C(11)–C(16)–C(17)
C(16)–C(17)–N(11)
N(11)–C(17)–C(18)
C(17)–C(18)–C(19)
C(18)–C(19)–C(114)
C(18)–N(12)–O(11)
N(12)–O(11)–C(115)
92.17(6)
93.63(12)
81.45(15)
93.41(10)
113.1(3)
138.9(3)
111.6(3)
116.3(3)
116.0(3)
110.2(3)
105.5(3)
105.9(3)
110.7(3)
111.2(4)
Cl(2)–Pd(2)–P(2)
90.40(7)
95.29(13)
80.94(15)
93.41(11)
112.3(2)
108.9(3)
113.7(3)
114.6(3)
118.3(3)
109.5(3)
105.2(3)
107.0(3)
113.7(3)
110.7(4)
P(2)–Pd(2)–C(21)
C(21)–Pd(2)–N(21)
N(21)–Pd(2)–Cl(2)
Pd(2)–N(11)–C(27)
Pd(2)–N(21)–C(214)
Pd(2)–C(21)–C(26)
C(21)–C(26)–C(27)
C(26)–C(27)–N(21)
N(21)–C(27)–C(28)
C(27)–C(28)–C(29)
C(28)–C(29)–C(214)
C(28)–N(22)–O(21)
N(22)–O(21)–C(215)
tions indicated the presence of the monomeric derivatives [Pd{j2
-
C,N-C6H3-4R-1-(C8H4N-30-NOMe)}Cl(py-d5)] {R = Cl (5a) or H (5b)}
(Scheme 2).
Similarly, the addition of PPh3 to suspensions of 4a or 4b (in a
molar ratio PPh3:4 = 2) in CH2Cl2 produced the splitting of the
‘‘Pd(l-Cl)2Pd” bridges and the formation of [Pd{j
2-C,N-C6H3-4R-
1-(C8H4N-30-NOMe)}Cl(PPh3)] {R = Cl (6a) or H (6b)} (Scheme 2).
Compounds 6a and 6b were characterized by elemental analyses,
mass spectrometry, infrared spectroscopy and mono- and two-
dimensional NMR spectra. The most relevant feature observed in
the 1H NMR spectra of 6a (or 6b) is the downfield shift of the signal
arising from the H8 proton when compared with that of 3a (or 3b).
This variation could be attributed to the proximity between the C8–
H8 bond and the chloride ligand (we will return to this point later
on). The position of the signals observed in the 31P{1H} NMR spec-
tra of 6a and 6b in CDCl3 {d = 44.2 (for 6a) and 45.8 ppm (for 6b)} is
consistent with data reported for related palladacycles of general
palladated complexes of the type [Pd(
j
2-C,N-ligand)Cl(PPh3)]
[2d,4b,16,19,20]. The values of the bond angles: P(1)–Pd(1)–C(11)
and P(1)–Pd(1)–C(21) {93.63(12)° and 95.29(13)°, respectively},
indicate that the phosphine ligand is in a cis-arrangement to the
metallated carbon which is in good agreement with the transpho-
bia effect [20].
Each one of the two molecules of 6b contain a [6.5.5.6] tetracy-
clic system formed by the indole unit, a five-membered palladacy-
cle and the phenyl ring. The indole and the phenyl rings of the
2-phenylindole unit are practically coplanar {angles between these
planes are 1.0(3)° (in I) and 1.9(3)° (in II)}. The metallacycles are
practically planar and form angles of 5.1(2)° (in I) and 2.6(2)° (in
II) with the phenyl ring attached to them.
formula [Pd(j
2-C,N-ligand)Cl(PPh3)] [19] in which the phosphine
is in a cis-arrangement to the metallated carbon atom and this is
in good agreement with the so-called transphobia effect [20].
The values of the torsion angles O(11)–N(12)–C(18)–C(17) and
O(21)–N(22)–C(28)–C(27) (178.10° and 179.17°, respectively) indi-
cate that in I and II the oxime moiety adopts the E configuration.
For this arrangement of substituents: (a) the nitrogen atoms
2.3. Crystal and molecular structure of 6bꢀ1/2CH2Cl2
The structure features two non-equivalent molecules of [Pd{j2
-
C,N-C6H4-1-(C8H4N-30-NOMe)}Cl(PPh3)] 6b (hereinafter referred to
as I and II) and CH2Cl2. A selection of bond lengths and angles is
presented in Table 1 and the ORTEP plot of molecule I is depicted
in Fig. 4.
{N(12) in I or N(22) in II} are close to the r(C–H) bonds of the ortho
site of phenyl unit and (b) the distance between the oxygen atom
O(1) {or O(2)} and the C(110)–H(110) {or the C(210)–H(210)} bond
(2.47 Å and 2.46 Å) suggests a weak C–HꢀꢀꢀO hydrogen bond.
On the other hand, the separation between the chloride ligand
{Cl(1) or Cl(2)} and the C–H bond of the nearest site of the indole
ring {C(113)–H(113) and C(213)–H(213) in molecules I and II}
(2.63 and 2.51 Å in I and II, respectively) is smaller than the sum
of their van der Waals radii {Cl (1.75 Å) and H (1.20 Å)} [21], thus
indicating an intramolecular non-conventional weak hydrogen
bond (C–HꢀꢀꢀCl). This interaction could be the cause of the down-
field shift detected for the H8 proton of 6a and 6b, when compared
with its position in 3a and 3b, respectively.
In molecules I and II the palladium atoms {Pd(1) and Pd(2),
respectively} are located in a slightly distorted square-planar envi-
ronment and they are bound to the heterocyclic nitrogen {N(11) (in
I) and N(21) (in II)}, the ortho carbon atom {C(11) and C(21) in I
and II, respectively} of the indole moiety, thus confirming that
the mode of binding of 1b is [C(sp2,phenyl), Nindole]ꢁ. One chloride
{Cl(1) or Cl(2)} and a phosphorus atom {P(1) and P(2), respectively}
fulfill the coordination sphere. Bond lengths and angles around the
palladium(II) atoms are similar to those reported for most cyclo-

C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
2881
Fig. 4. ORTEP plot of molecule I found in the crystal structure of compound 6bꢀ1/2CH2Cl2. Hydrogen atoms as well as the molecule of CH2Cl2 have been omitted for clarity.
In the crystal, molecules I and II are associated in a head to tail
arrangement (Fig. 5) in such a way that the C(232)–H(232) bond of
the smaller ring strain of the five-membered palladacycles com-
pared to that of the four-membered metallacycles.
the phosphine ligand of II is close to the
of a neighbouring molecule I [22]. This distribution of molecules,
interactions [23], leads to a chain that stacks
p system of the indole unit
2.4. Conclusions
connected by CHꢀꢀꢀ
p
along the b-axis {[010] plane}.
The results presented here show that the cyclopalladation of the
two 3-methoxyimino-2-phenyl-3H-indole compounds (1a and 1b)
is regioselective and gives five-membered metallacycles contain-
Since: (a) it is well-known that in the cyclopalladation of N-do-
nor ligands, the metallacycle formation requires the coordination
of the nitrogen ligands followed by the electrophilic attack of the
palladium(II) species formed to the carbon atom [12a,24] and (b)
the ligands under study contain two different nitrogen atoms
ing simultaneously a
r(Pd–Nindole) and a r
[Pd–C(sp2,phenyl)]
bond in which the oxime unit exhibits the E form. Furthermore,
theoretical calculations have allowed us to rationalize the prefer-
ential formation of these five-membered palladacycles and the
optimized geometries of the two forms of the ligands reveal that
in the E form of 1a and 1b: (a) the oxygen of the =NOMe moiety
is close to one of hydrogen atoms of the indole ring and (b) the
nitrogen is proximal to a hydrogen of the phenyl ring. The crystal
structure of 6bꢀ1/2CH2Cl2 showed that this arrangement of groups
prevails in the palladacycles allowing the existence of weak
C–HꢀꢀꢀX (X = O and N) interactions.
(Nindole and Noxime), the first key point to rationalize the formation
ꢁ
of the new palladacycles with a bidentate [C(sp2,phenyl), Nindole
]
ligand should be related to the coordination abilities of the two
nitrogen atoms. The use of molecular models as well as the opti-
mized geometries of the free ligands in the E and Z forms (Fig. 2)
suggested that the accesibility of the palladium to the oxime nitro-
gen would be more hindered than for the heterocyclic nitrogen. In
addition, molecular orbital calculations for 1a and 1b in the E and Z
forms revealed that in both cases the HOMO orbital (Fig 6) is a
Finally, due to the ongoing interest of oxime ligands, their pal-
ladium(II) derivatives or their analogues with indole units in
homogeneous catalysis and organic synthesis [5,6], the new com-
pounds presented in this work appear to be excellent candidates
for further studies in these fields.
combination of the atomic orbitals of the Nindole atom and p-bond-
ing orbitals of the indole ring and the phenyl unit. Besides, the
comparison of the Mulliken charges on the two nitrogen atoms
indicates that the Nindole has higher electronic density than the
Noxime atom [25]. All these findings suggest that the binding of
the ligand to the palladium would occur preferentially through
the Nindole atom and this reduces to two the number of possible
metallacycles.
3. Experimental
3.1. Materials and methods
After the coordination of the palladium to the Nindole atom of 1a
or 1b, the activation of the
cycles with a
{Pd–Csp2,phenyl)} bond, which are more stable
than those arising from the metallation of the indole unit due to
r
[C(sp2,phenyl)-H] bond gives pallada-
2-(4-Chlorophenyl)indole and 2-phenylindole, tricaprylmethy-
lammonium chloride (Aliquat336), Pd(OAc)2, LiCl and PPh3, glacial
acetic acid and acetic anhydride were obtained from commercial
r

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C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
Fig. 5. Schematic view of the relative arrangement of the two non-equivalent molecules of 6b in the crystal. The molecules of CH2Cl2 are shown but hydrogen atoms have
been omitted for clarity.
3.2. Preparation of the compounds
3.2.1. Synthesis of C6H4-4R-1-(C8H4N-30-NOH) {R = Cl or H)}
The synthesis of these products was previously described but
the procedure used in this work is not identical to that reported be-
fore [7]. 3-Hydroxyimino-2-(4-chlorophenyl)-3H-indole was pre-
pared as follows: 0.81 g (1.2 ꢂ 10ꢁ2 mol) of NaNO2 was added
under continuous stirring to a solution containing 2-(4-chloro-
phenyl)indole (2.50 g, 1.1 ꢂ 10ꢁ2 mol), acetic acid (20 mL) and
dimethylformamide (8 mL). The resulting solution was stirred at
room temperature for 3 h and then poured onto 100 mL of H2O.
The solid formed was collected by filtration, washed with water
and dried in vacuum. Yield: 2.68 g (95%).
Fig. 6. HOMO orbitals of the E and Z isomers of ligand 1a.
sources and used as received. Solvents were dried and distilled be-
fore use [26]. Elemental analyses were carried out at the Serveis de
Recursos Cientifics i Tècnics (Universitat Rovira i Virgili). Mass spec-
tra (ESI+) were performed at the Servei d’Espectrometria de Masses
(Universitat de Barcelona). Infrared spectra were obtained with a
Nicolet 400FTIR instrument using KBr pellets. Routine 1H and
13C{1H} NMR spectra were recorded with a Mercury-400 MHz
3-Hydroxyimino-2-phenyl-3H-indole was prepared similarly,
but in this case starting material was 2-phenylindole. Yield:
2.26 g (96%). These precursors were used in the next step without
any further purification.
3.2.2. Synthesis of C6H4-4R-1-(C8H4N-30-NOMe) {R = Cl (1a) or H (1b)}
Compound 1a was prepared as follows: to a solution containing
3-hydroxyimino-2-(4-chlorophenyl)-3H-indole (1.10 g, 4.28 ꢂ
10ꢁ3 mol), Aliquat 336 (800 mg, 1.9 ꢂ 10ꢁ3 mol) and NaOH
(12 mL of a 40% solution) in CH2Cl2 (125 mL), methyl iodide
(2.28 g, 1 mL, 16 ꢂ 10ꢁ3 mol) was added. The reaction mixture
was stirred at room temperature for 24 h. After this period water
(75 mL) was added and the resulting solution was transferred to
a separating funnel. The organic layer was separated and the aque-
ous one was afterwards extracted with 20 mL of CH2Cl2. The
combined organic extracts were dried over Na2SO4, filtered and
instrument. 31P{1H} NMR spectra were recorded with
a
Varian-Unity-300 instrument using P(OMe)3 as reference [d(31P) =
140.17 ppm]. High resolution 1H NMR spectra and the two-dimen-
sional [{1H–1H}-NOESY, ROESY and COSY and {1H–13C}-HSQC and
HMBC] experiments were registered with a Varian VRX-500 or a
Bruker Avance DMX-500 MHz instruments at 298 K. The chemical
shifts (d) are given in ppm and the coupling constants (J) in Hz.
Except where quoted, the solvent for the NMR experiments was
CDCl3 (99.9%) and SiMe4 was used as reference.

C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
2883
concentrated. Further purification by flash chromatography on
neutral alumina using diethylether as eluant produced the release
of an orange band that was collected and concentrated to dryness
on a rotary evaporator giving 1a. This product was collected and
dried in vacuum for one day. Yield: 0.97 g (84%)}.
d = 65.3(OMe), 170.5(C2), 156.1(C3), 136.9(C4), 127.3(C5),
132.5(C6), 128.6(C7), 124.7(C8), 119.0(C9), 151.0(C10), 131.9(C11),
132.4(C12), 124.7(C13), 131.9(C14), 150.9(C15), 24.91[CH3(OAc)]
and 182.1(>CO2(OAc)]; for 2aII (selected data): 65.3(OMe), 24.9
and 25.3[CH3(OAc)], 181.3 and 183.0 [>CO2(OAc)]. For 2b: Elemen-
tal analyses calc. for C32H25N4O4Pd2: C, 51.77; H, 3.39; N, 7.55.
Found: C, 51.59; H, 3.45; N, 7.42%. MS (ESI+): m/z = 684.0 [M-
OAc]+. IR data: 2963(m), 1608(s), 1572(s, OAc), 1502(m),
1442(m), 1422(s, OAc), 1409(s), 1260)s), 1140(s), 1031(s),
961(m), 805(m), 748(s). Solution studies: two isomers (2bI and
2bII coexisted in a 2.7:1.0 ratio) in CDCl3 at room temperature.
1H-NMR data for 2bI [27]: d = 2.20[s, 6H, CH3(OAc)], 4.29[s, 6H,
OMe], 7.56[d, 2H, J = 7.6, 2H5], 7.16[td, 2H, J = 7.6 and 1.0, 2H6],
7.02[td, 2H, J = 7.6 and 1.0, 2H7], 7.29[d, 2H, J = 7.6, 2H8], 7.49[dd,
2H, J = 8.0 and 1.0, 2H11], 6.48[dd, 2H, J = 8.0 and 1.0, 2H12],
6.22[d, 2H, J = 8.0, 2H13] and 7.16[d, 2H, 2H14]; for 2bII (in this case
most of the signals appeared duplicated suggesting that the two
halves were not equivalent) d = 2.28[s, 3H, OAc], 2.14[s, 3H, OAc],
4.26[br.s, 6H, OMe], 7.68[d, 2H, J = 7.6, 2H5], 6.82[br., 2H, 2H6],
7.18 [br, 2H, J = 7.2 and 1.0, 2H8], 7.45[br., 2H, J = 8.0 and 1.0,
2H11], 6.31–6.41[2 br.d, 4H, J = 8.0 and 1.0, 2H12 and 2H13] [30],
6.80[br.s, 2H, 2H14], (the resonances due to H7 were partially
masked by the signals due to solvent and the major isomer, respec-
tively) [30]. 13C{1H} NMR data for 2bI [27]: d = 65.6(OMe),
171.4(C2), 154.2(C3), 138.0(C4), 127.0(C5), 134.2(C6), 129.4(C7),
Ligand 1b was isolated as a deep-orange solid with the same
procedure as that described for 1a but using 3-hydroxyimino-2-
phenyl-3H-indole (0.89 g, 4 ꢂ 10ꢁ3 mol) as starting material. Yield:
0.90 g (95%). Characterization data for 1a: Elemental analyses calc.
for C15H11ClN2O: C, 66.55; H, 4.10; N, 10.35. Found: C, 66.47; H,
4.15; N, 10.12%. MS (ESI+): m/z = 271.1 [M+H]+. IR data: 2937(m),
1592(s), 1479(m), 1442(m), 1402(s), 1270(w), 1094(s), 1027(s),
951(m), 835(m) and 755(s). 1H NMR data [27]: d = 4.34[s, 3H,
OMe], 8.02[d, 1H, J = 7.5, H5], 7.24[td, J = 7.5 and 1.0, H6], 7.40[td,
1H, J = 7.5 and 1.0, H7], 7.53[d, 1H, J = 7.5, H8], 8.26[dd, 2H, J = 9.2
and 2.0, H11 and H15], 7.44[dd, 2H, J = 9.2 and 2.0, H12 and H14].
13C{1H} NMR data [27]: d = 65.1(OMe), 165.2(C2), 157.4(C3),
138.4(C4), 127.6(C5), 132.2(C6), 126.3(C7), 121.2(C8), 122.8(C9),
155.1(C10), 131.7(C11 and C15), 132.4(C12 and C14) and 123.3(C13).
For 1b: Elemental analyses calc. for C15H12N2O: C, 76.25; H, 5.12;
N, 11.86. Found: C, 76.12; H, 5.055; N, 11.72%. MS (ESI+): m/z =
237.10[M+H]+. IR data: 2940(m), 1602(s), 1512(m), 1436(m),
1349(s), 1270(w), 1107(s), 1028(s), 954(m), and 755(s). 1H-NMR
data [27]: d = 4.32[s, 3H, OMe], 8.02[d, 1H, J = 7.7, H5], 7.23[td,
J = 7.7 and 1.5, H6], 7.44[td, 1H, J = 7.7 and 1.5, H7] [28],
7.55[d,1H, J = 7.7, H8] [28], 8.23[dd, 2H, J = 9.2 and 2.0, H11 and
H15], 7.48–7.60[br.m, 3H, H12, H13 and H14]. 13C{1H} NMR data
[27]: d = 65.2(OMe), 166.1(C2), 154.5(C3), 139.2(C4), 127.6(C5),
132.6(C6), 131.3(C7), 121.4(C8), 122.6(C9), 155.6(C10), 130.2(C11
and C15), 128.8(C12 and C14) and 127.9(C13).
125.7(C8),
118.9(C9),
153.1(C10),
131.6(C11),
138.3(C12),
and
130.5(C13),
125.8(C14),
152.7(C15),
25.0[CH3(OAc)]
181.9(>CO2(OAc)]; for 2aII (selected data): 65.3(OMe), 24.7 and
25.2[CH3(OAc)], 181.40 and 183.2 [>CO2(OAc)].
3.2.4. Synthesis of [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-
NOMe)}(OAc)(PPh3)] {R = Cl (3a) or H (3b)}
3.2.3. Synthesis of (
l
-OAc)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-
NOMe)}]2 {R = Cl (2a) or H (2b)}
These compounds were prepared as follows: 2 ꢂ 10ꢁ5 mol of 2a
(16 mg) or 2b (15 mg) was dissolved in 0.7 mL of CDCl3 and then
11 mg of PPh3 (4 ꢂ 10ꢁ5 mol) was added and the resulting solution
was analyzed by 1H and 31P{1H} NMR. Concentration to dryness
lead a purple solid that was collected and dried in vacuum for 3
days. Yields: 23 mg (82%) for 3a and 21 mg (79%) for 3b. Character-
ization data for 3a: Elemental analyses calc. for C35H28ClN2O3PPd:
C, 60.27; H, 4.05; N, 4.02. Found: C, 60.05; H, 3.98; N, 3.93%. MS
(ESI+): m/z = 638.4 [M-OAc]+. 1H NMR data [27]: d = 4.30[s, 3H,
OMe], 7.90[d, 1H, J = 7.1, H5], 7.13[td, 1H, J = 7.2, and 1.5 H6],
7.80[d, 1H, J = 7.1 and 1.0, H8], 8.12[dd, 1H, J = 8.0 and 1.0, H11],
6.83[dd, 1H, J = 8.0 and 1.0, H12], 6.41[d, 1H, H14], 1.30 [s, 3H,
CH3(OAc)] and 7.20–7.60 (br.m. 16 H, H7 and aromatic protons of
the PPh3 ligand). For 3b: Elemental analyses calc. for C35H29
N2O2PPd: C, 63.40; H, 4.41; N, 4.23. Found: C, 63.29; H, 4.32; N,
4.11%. MS (ESI+): m/z = 603.1 [M-OAc]+. 1H NMR data [27]:
d = 4.34[s, 3H, OMe], 7.92[d, 1H, J = 7.1, H5], 7.11[td, 1H, J = 7.1,
and 1.0 H6], 7.84[d, 1H, J = 7.1 and 1.0, H8], 8.16[dd, 1H, J = 8.0
and 1.0, H11], 6.80–6.84[br.m, 2H, H12 and H13], 6.45[d, 1H, H14],
1.32[s, 3H, CH3(OAc)] and 7.20–7.60 (br.m. 16 H, H7 and aromatic
protons of the PPh3 ligand). 31P{1H} NMR data d = 42.5.
Compound 1a (294 mg, 1.09 ꢂ 10ꢁ3 mol) or 1b (257 mg,
1.09 ꢂ 10ꢁ3 mol) was dissolved in a mixture of glacial acetic acid
and acetic anhydride (10:1), then 245 mg (1.09 ꢂ 10ꢁ3 mol) of
Pd(OAc)2 was added. The reaction mixture was heated at 90 °C
for 3.5 h and then allowed to cool at room temperature. The result-
ing deep-brown mixture was filtered through Celite and the filtrate
was concentrated to dryness on a rotary evaporator. Afterwards
the nearly black solution was dissolved in the minimum amount
of CH2Cl2 and passed through a SiO2 column (2.0 cm ꢂ 6.5 cm).
The column was first eluted with CH2Cl2 to remove traces (8 mg)
of a minor pale yellow by-product. The subsequent elution with
a CH2Cl2:MeOH mixture (100:0.25) produced the release of a gar-
net band that was collected and concentrated to dryness on a ro-
tary evaporator giving 2a and 2b, respectively. The deep-red
solid formed was collected and dried in vacuum for one day.
Yields: 302 mg (69%) for 2a and 243 mg (60%) for 2b. Characteriza-
tion data for 2a: Elemental analyses calc. for C32H23Cl2N4O4Pd2: C,
47.37; H, 2.86; N, 6.91. Found: C, 47.12; H, 3.00; N, 6.8%. MS (ESI+):
m/z = 753.9 [M-OAc]+. IR data: 2933(m), 1573(s), 2559(s, OAc),
1465(m), 1426(s, OAc), 1080(m), 1017(s), 752(m). Solution stud-
ies: two different isomers (2aI and 2aII coexisted in a 2.8:1.0 ratio)
in CDCl3 at room temperature. 1H NMR data for 2aI [27]: d = 2.29[s,
6H, 2CH3(OAc)], 4.37[s, 6H, 2OMe], 7.65[d, 2H, J = 7.2, 2H5], 7.13[td,
2H, J = 7.2 and 1.0, 2H6], 7.32[td, 2H, J = 7.2 and 1.0, H7], 7.30[d, 2H,
J = 7.2, 2H8], 7.43[dd, 2H, J = 8.0 and 1.0, 2H11], 6.52[dd, 2H, J = 8.0
and 1.0, 2H12], 6.60[d, 2H, J = 8.0, 2H14]; for 2aII: (in this case most
of the signals appeared duplicated suggesting that the two halves
were not equivalent) d = 2.13[s, 3H, OAc], 2.30[s, 3H, OAc],
4.36[br.s, 6H, OMe], 7.50 and 7.48[d, 2H, J = 7.2, 2H5], 7.18[br.,
2H, 2H6], 7.08 and 7.20[br., 2H, J = 7.2 and 1.0, 2H8], 6.77[br.d,
2H, J = 8.0 and 1.0, H12], 6.89[br.s, 2H, 2H14] [29], the resonances
due to H7 and H11 appeared partially masked by the signals due
to the same protons of 2aI. 13C{1H} NMR data for 2aI [27]:
3.2.5. Synthesis of (l
-Cl)2[Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}]2
{R = Cl (4a) or H (4b)}
To a solution containing 2.46 ꢂ 10ꢁ4 mol of 2a (200 mg) or 2b
(232 mg) in acetone (10 mL), LiCl (23 mg, 5.42 ꢂ 10ꢁ4 mol) was
added. The reaction mixture was stirred at 25 °C. The solid formed
was removed by filtration and air-dried. Yields: 153 mg (76%) and
132 mg (71%) for 4a and 4b, respectively. Characterization data for
4a: Elemental analyses calc. for C30H20Cl4N4O2Pd2: C, 43.77; H,
2.45; N, 6.81. Found: C, 43.70; H, 2.37; N, 6.59%. MS (ESI+): m/z =
788.9 [M-Cl]+. IR data: 2974(m), 1599(m), 1567(s), 1497(m),
1448(m), 1439(s), 1387(w), 1285(w), 1117(w), 1082(m), 1043(m)
1021(s), 968(w), 767(m), 756(m) and 486(w). For 4b: Elemental

2884
C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
analyses calc. for C32H22Cl2N4O2Pd2: C, 47.77; H, 2.94; N, 7.43.
Found: C, 47.85; H, 3.05; N, 7.35%. MS (ESI+): m/z = 690.9 [M-Cl]+.
IR data: 2970(m), 1588(m), 1492(m), 1402(s), 1250(m) 1138(m)
1028(m) 959(m), 792(w) and 740(m).
3.3. Crystallography
A prismatic crystal of 6bꢀ1/2CH2Cl2 (sizes in Table 2) was se-
lected and mounted on a Enraf-Nonius CAD4 four-circle diffrac-
tometer. Unit-cell parameters were determined from automatic
centering of 25 reflections (12° < h < 21°) and refined by least-
squares method. Intensities were collected with graphite mono-
3.2.6. Synthesis of [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}Cl(py-
d5)] {R = Cl (5a) or H (5b)}
These compounds were prepared in solution and characterized
by 1H NMR. 2 ꢂ 10ꢁ5 mol of the corresponding complex 4 [16 mg
(for 4a) or 15 mg (for 4b)] was suspended in 0.7 mL of CDCl3, then
two drops of deuterated pyridine (py-d5) were added and the mix-
ture was shaken for two minutes. After this period a deep-garnet
solution containing 5a or 5b was obtained. 1H-NMR data for 5a
[27]: d = 4.39[s, 3H, OMe], 7.95[d, 1H, J = 7.2, H5], 7.38[td, J = 7.2
and 1.0, H6], 7.20[td, 1H, J = 7.2 and 1.0, H7], 7.28[d, 1H, J = 7.2,
H8], 8.11[dd, 1H, J = 8.0 and 1.0, H11], 7.02[dd, 1H, J = 8.0 and 1.0,
H12], 7.21[d, 1H, H14]. For 5b [27]: d = 4.40[s, 3H, OMe], 8.02[d,
1H, J = 7.4, H5], 7.26[td, J = 7.4 and 1.0, H6], 7.42[td, 1H, J = 7.4
and 1.0, H7], 7.30[d,1H, J = 7.2, H8], 8.21[dd, 1H, J = 8.0 and 1.0,
H11] and 6.90–7.20[m, 3H, H12, H13 and H14].
chromatized Mo Ka radiation, using x/2h scan-technique. The
number of reflections measured in the range 2.14° 6 h 6 29.97°
was 17813, out of which 14109 were assumed as observed apply-
ing the condition I > 2r(I). Three reflections were measured every
two hours as orientation and intensity control, significant intensity
decay was not observed. Lorentz-polarization and absorption cor-
rections were made.
The structure was solved by direct methods, using the SHELXS
computer program [31] and refined by full-matrix least-squares
method with the SHELX-97 computer program [32] using 17813
reflections, (very negative intensities were not assumed). The
2
2 2
function minimized was
R
wjjFoj ꢁ jFcj j , where w = [
r
2(I) +
2
2
(0.0255P)2+5.5920P]ꢁ1, and P ¼ ðjFoj þ 2jFcj Þ=3; f, f0 and f00 were
taken from the bibliography [33]. All H atoms were computed
and refined, using a riding model, with an isotropic temperature
factor equal to 1.2 times the equivalent temperature factor of the
atom which are linked. The final R (on F) factor was 0.049, wR(on
|F|2) = 0.0794 and goodness-of-fit = 1.334 for all observed reflec-
tions. Number of refined parameters was 730. Max. shift/esd =
0.00, Mean shift/esd = 0.00. Maximum and minimum peaks in final
difference synthesis was 0.801 and ꢁ0.918 eÅꢁ3, respectively. Fur-
ther details concerning the solution and refinement of this crystal
structure are presented in Table 2.
3.2.7. Synthesis of [Pd{j2-C,N-C6H3-4R-1-(C8H4N-30-NOMe)}Cl(PPh3)]
{R = Cl (6a) or H (6b)}
A suspension of 1.00 ꢂ 10ꢁ4 mol of 4a (83 mg) or 4b (76 mg) in
CH2Cl2 (20 mL) was treated with PPh3 (53 mg, 2.0 ꢂ 10ꢁ4 mol). The
reaction mixture was strirred at 25 °C for 1 h and then filtered out.
The deep-red filtrate was concentrated to dryness on a rotary evap-
orator giving a deep-garnet solid that was later on dissolved in the
minimum amount of CH2Cl2 and passed through a short SiO2 col-
umn (2.5 cm ꢂ 5.0 cm). Elution with CH2Cl2 produced the release
of a red band that was collected and concentrated to dryness on
a rotary evaporator. The bright garnet solid formed was collected
and dried in vacuum for 2 days. Yields: 98 mg (71%) for 6a and
101 mg (70%) for 6bꢀ1/2CH2Cl2. Characterization data for 6a: Ele-
mental analyses calc. for C34H28ClN2OPPd: C, 59.28; H, 4.10; N,
4.07. Found: C, 59.39; H, 4.15; N, 4.27%. MS (ESI+): m/z = 687.0
[M-Cl]+. IR-data: 3055 and 3040(w), 1602(w), 1564(m), 1496(m),
1478(m), 1221(s), 1435(s), 1101(m), 1093(m), 1016(s), 973(m),
740(s), 702(m), 692(s), 535(s), 512(s) and 493(s). 1H NMR data
for 6a [27]: d = 4.41[s, 3H, OMe], 7.98[d, 1H, J = 7.2, H5], 7.22[td,
J = 7.2 and 1.0, H6], 7.39[td, 1H, J = 7.2 and 1.0, H7], 9.15[d, 1H,
J = 7.2, H8], 8.26[dd, 1H, J = 8.0 and 1.0, H11], 6.93[dd, 1H, J = 8.0
and 1.0, H12], 6.47[d, 1H, H14] and 7.40–7.50 and 7.60–7.75(2m,
15H, aromatic protons of the PPh3 ligand). 13C{1H}-NMR data
3.4. Theoretical studies. Computational details
Calculations were carried out at the AM1 computational level
[10] using the SPARTAN 5.0 package [11]. Geometry optimizations
were performed without symmetry restrictions.
Table 2
Crystal data and details of the refinement of the crystal structure of compound 6b ꢀ
1/2CH2Cl2
Crystal size (mm ꢂ mm ꢂ mm)
Empirical formula
Molecular weight
Crystal system
Space group
0.20 ꢂ 0.05 ꢂ 0.05
67H54Cl4N4O2P2Pd2
C
1363.68
Triclinic
3
[27]: 65.6(OMe), 173.7(d, JP–C = 3.6, C2), 159.1(C3), 140.1(C4),
ꢀ
3
123.4(C5), 132.8(C6), 126.9(C7), 123.8(C8), 121.9(d, JP–C = 4.2, C9),
P1
a (Å)
11.790(8)
153.6(C10), 130.6(C11), 136.8(C12), 130.2(C13), 124.7(C14), 151.7(d,
2JP–C = 9.3, C15) and four additional doublets centered at 128.1,
130.8, 131.2 and 135.0 due to 13C nuclei of the PPh3 ligand.
31P{1H} NMR data d = 44.2. For 6b: Elemental analyses calc. for
b (Å)
15.474(11)
c (Å)
18.681(9)
a
(°)
b (°)
(°)
108.32(5)
107.13(3)
91.89(4)
c
C
33H26ClN2OPPdꢀ1/2CH2Cl2: C, 59.01; H, 3.99; N, 4.11. Found: C,
T (K)
293(2)
58.97; H, 4.02; N, 4.03%. MS (ESI+): m/z = 687.0 [M-Cl]+. IR data:
3053(w), 3040(w), 2930(w), 1602(w) 1564(m), 1544(w), 1441(s),
1435(s), 1101(m), 1093(m), 1120(s), 773(m), 740(s), 703(m),
692(s), 534(s), 512(s) and 493(s). 1H NMR data for 6b [27]:
d = 4.41[s, 3H, OMe], 8.01[d, 1H, J = 7.2, H5], 7.20[td, J = 7.2 and
1.0, H6], 7.49[td, 1H, J = 7.2 and 1.0, H7], 9.17[d, 1H, J = 7.2, H8],
8.35[dd, 1H, J = 8.0 and 1.0, H11], 6.54[br., 2H, H13 and H14],
5.12[s, 1H, CH2Cl2] and 7.50–7.80(m, 15H, aromatic protons of
the PPh3 ligand). 13C{1H}-NMR data [27]: 65.9(OMe), 173.6(d,
3JP–C = 3.2, C2), 158.8(C3), 141.9(C4), 122.6(C5), 135.4(C6),
127.3(C7), 123.1(C8), 121.5((d, 3JP–C = 4.0, C9), 152.2(C10),
k (Å)
0.71073
3062(4)
V (Å3)
Z
2
Dcalc (Mg/m3)
1.479
0.862
l
(mmꢁ1
)
F (000)
1380
H
range for data collection (°)
from 2.14 to 29.97
17813
Number of collected reflections
Number of unique reflections [Rint
Completeness to
]
17813 [0.0443]
100.0%
H = 25.00°
Refinement method
Full-matrix least-squares on F2
17813
Number of data/restraints/parameters
Number of parameters
730
1.334
130.2(C11), 139.8(C12), 130.5(C13), 124.6(C14), 153.5(d, JP–C = 9.5,
3
Goodness-of-fit (GOF) on F2
C15) and four additional doublets centered at ca. 128.1, 130.8,
131.2 and 135.0 due to the 13C nuclei of the PPh3 ligand 31P{1H}
NMR data d = 45.8.
Final R indices [I > 2
r
(I)]
R1 = 0.0487, wR2 = 0.1005
R1 = 0.0794, wR2 = 0.1269
0.801 and ꢁ0.918
R indices (all data)
Largest difference peak and hole (e Åꢁ3
)

C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
2885
(b) A. García-Granados, P.E. López, E. Melguizo, A. Parra, Y. Simeó, J. Org. Chem.
72 (2007) 3500;
Acknowledgement
(c) T. Honda, T. Janosik, Y. Honda, J. Han, K.T. Liby, C.R. Williams, R.D. Couch,
A.C. Anderson, M.B. Sporn, G.W. Gribble, J. Med. Chem. 47 (2004) 4923;
(d) R. Chinchilla, C. Nájera, Chem. Rev. 107 (2007) 874.
[7] J. Schmitt, C. Perrin, M. Langlois, M. Suquet, Bull. Soc. Chim. Fr. (1969)
1227.
We are grateful to the Ministerio de Ciencia y Tecnología of Spain
and to the Generalitat de Catalunya for financial support (Grants:
CTQ2006-02390/BQU, CTQ2006-0207 and 2005SGR-0603).
[8] N. Campbell, R.C. Cooper, J. Chem. Soc. (1935) 1208.
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Appendix A. Supplementary data
CCDC 680983 contains the supplementary crystallographic data
for 6bꢀ1/2CH2Cl2. These data can be obtained free of charge from
the Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2008.05.043.
[13] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
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[27] Labelling of the atoms refers to those shown in scheme 2.
[28] This signal was partially masked by the resonances of the set of protons H12
,
H13 and H14
.
[29] This resonance was partially overlapped by the signals due to the H12 proton of
the major isomer (2aI) and those of the H6 protons of the two isomers.

2886
C. López et al. / Journal of Organometallic Chemistry 693 (2008) 2877–2886
[30] The resonances of these protons were partially masked by the signals due to
the same nuclei of the major isomer (2bI).
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