Mononuclear and tetranuclear palladacycles with terdentate [C,N,N] and [C,N,O] Schiff base ligands. C-H versus C-Br activation reactions

Article abstract of DOI:10.1016/j.ica.2011.01.027

Reaction of the Schiff base ligands 2-Br-4,5-(OCH₂O)C ₆H₂C(H)NCH₂CH₂NMe₂ (a) and 4,5-(OCH₂CH₂)C₆H₃C(H)NCH ₂CH₂NMe₂ (b) with Pd(OAc)₂ or K ₂[PdCl₄] leads to the mononuclear cyclometallated compounds [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH ₂CH₂NMe₂-C6,N,N}(OCOMe)] (1a) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)NCH ₂CH₂NMe₂-C6,N,N}(Cl)] (1b), derived from C-H activation at the C6 carbon. Treatment of a with Pd₂(dba)₃ gave [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH ₂CH₂NMe₂-C2,N,N}(Br)] (2a), via C-Br activation. The metathesis reaction of 1a with aqueous sodium chloride gave [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH ₂NMe₂-C6,N,N}(Cl)] (3a), with exchange of the acetate group by a chloride ligand. Treatment of the cyclometallated monomers 1a-3a with PPh₃ in a 1:1 molar ratio yielded the mononuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH ₂NMe₂-C6,N}(L)(PPh₃)] (L: OAc, 4a; Cl, 5a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH ₂NMe₂-C2,N}(Br)(PPh₃)] (6a), with Pd-NMe ₂ bond cleavage. However, treatment of a solution of 3a or 2a with silver trifluoromethanesulfonate, followed by reaction with PPh₃ in acetone yielded the cyclometallated complexes [Pd{2-Br-4,5-(OCH ₂O)C₆HC(H)NCH₂CH₂NMe ₂-C6,N,N}(PPh₃)][CF₃SO₃] (7a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH ₂NMe₂-C2,N,N}(PPh₃)][CF₃SO ₃] (8a), respectively, where the Pd-NMe₂ bond was retained. The reaction of the ligands 2-Br-4,5-(OCH₂O)C ₆H₂C(H)N(2′-OH-5′-^tBuC ₆H₃) (c) and 4,5-(OCH₂CH₂)C ₆H₃C(H)N(2′-OH-5′-^tBuC ₆H₃) (d) with Pd(OAc)₂ gave the tetranuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(2′-O- 5′-^tBuC₆H₃)-C6,N,O}]₄ (1c) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H) N(2′-O-5′-^tBuC₆H₃)-C6,N,O}] ₄ (1d), respectively. Treatment of 1c with PPh₃ in 1:4 molar ratio, gave the mononuclear species [Pd{2-Br-4,5-(OCH₂O)C ₆HC(H)N(2′-(O)-5′-^tBuC₆H ₃)-C6,N,O}(PPh₃)] (2c) with opening of the polynuclear structure after P-O_bridging bond cleavage. The structure of compounds 2a, 1c and 1d has been determined by X-ray diffraction analysis.

Full text of DOI:10.1016/j.ica.2011.01.027

Inorganica Chimica Acta 370 (2011) 89–97
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Mononuclear and tetranuclear palladacycles with terdentate [C,N,N] and [C,N,O]
Schiff base ligands. C–H versus C–Br activation reactions
a
Leticia Naya a, Digna Vázquez-García a, Margarita López-Torres a, Alberto Fernández a, , Antonio Rodríguez ,
⇑
Nina Gómez-Blanco a, José M. Vila b, , Jesús J. Fernández a
⇑
a Departamento de Química Fundamental, Universidade da Coruña, 15008 A Coruña, Spain
b Departamento de Química Inorgánica, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2010
Received in revised form 22 December 2010
Accepted 11 January 2011
Available online 31 January 2011
Reaction of the Schiff base ligands 2-Br-4,5-(OCH2O)C6H2C(H)@NCH2CH2NMe2 (a) and 4,5-(OCH2CH2)-
C6H3C(H)@NCH2CH2NMe2 (b) with Pd(OAc)2 or K2[PdCl4] leads to the mononuclear cyclometallated
compounds [Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2–C6,N,N}(OCOMe)] (1a) and [Pd{4,5-(OCH2-
CH2)C6H2C(H)@NCH2CH2NMe2–C6,N,N}(Cl)] (1b), derived from C–H activation at the C6 carbon. Treat-
ment of a with Pd2(dba)3 gave [Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2–C2,N,N}(Br)] (2a), via C–Br
activation.
Keywords:
The metathesis reaction of 1a with aqueous sodium chloride gave [Pd{2-Br-4,5-(OCH2O)C6H-
C(H)@NCH2CH2NMe2–C6,N,N}(Cl)] (3a), with exchange of the acetate group by a chloride ligand. Treat-
ment of the cyclometallated monomers 1a–3a with PPh3 in a 1:1 molar ratio yielded the mononuclear
complexes [Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2–C6,N}(L)(PPh3)] (L: OAc, 4a; Cl, 5a) and
[Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2–C2,N}(Br)(PPh3)] (6a), with Pd–NMe2 bond cleavage. How-
ever, treatment of a solution of 3a or 2a with silver trifluoromethanesulfonate, followed by reaction with
PPh3 in acetone yielded the cyclometallated complexes [Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2–
C6,N,N}(PPh3)][CF3SO3] (7a) and [Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2–C2,N,N}(PPh3)][CF3SO3] (8a),
respectively, where the Pd–NMe2 bond was retained.
Palladium
Schiff base
C–H activation
C–Br activation
Monophosphine
X-ray diffraction
The reaction of the ligands 2-Br-4,5-(OCH2O)C6H2C(H)@N(20-OH-50-tBuC6H3) (c) and 4,5-(OCH2CH2)-
C6H3C(H)@N(20-OH-50-tBuC6H3) (d) with Pd(OAc)2 gave the tetranuclear complexes [Pd{2-Br-4,
5-(OCH2O)C6HC(H)@N(20-O-50-tBuC6H3)–C6,N,O}]4 (1c) and [Pd{4,5-(OCH2CH2)C6H2C(H)@N(20-O-50-tBu-
C6H3)-C6,N,O}]4 (1d), respectively. Treatment of 1c with PPh3 in 1:4 molar ratio, gave the mononuclear
species [Pd{2-Br-4,5-(OCH2O)C6HC(H)@N(20-(O)-50-tBuC6H3)–C6,N,O}(PPh3)] (2c) with opening of the
polynuclear structure after P–Obridging bond cleavage.
The structure of compounds 2a, 1c and 1d has been determined by X-ray diffraction analysis.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
be classified according to the metal, to the donor atom, or to che-
late ring size.
Since their discovery, in the mid-1960s [1,2], cyclometallated
compounds have represented a highly interesting research topic,
owing not only to their importance as organometallic compounds,
but also due to their enormous potential use as chiral auxiliaries
[3,4], as efficient intermediate materials in catalytic and synthetic
processes [5–9] or in the synthesis of new compounds with inter-
esting mesogenic [10,11] and luminescent and electronic proper-
ties [12–15], as well as their potential use in medicine and
biology [16–18]. The variety of cyclometallated compounds is such
that, in agreement with the well established definition, they may
We have studied the influence of different substituents adjacent
to the carbon atom where metallation is possible [19–23]. The sim-
plest case is when only one ortho C–H bond is present, but when
there is more than one possible metallation site on the ligand the
question of regioselectivity arises as is depicted in Fig. 1. A meth-
oxy group at the C3 atom hinders metallation by palladium(II) at
the C2 atom (i), whereas the less sterically demanding methyl
group at the C3 position allows palladation at C2 (ii). The directing
effect of different cyclic substituents depends on ring size; benzo-
dioxane derivatives gave only the ortho-metallation reaction at the
C6 atom (iii), whereas piperonal derivatives afforded a mixture of
the two possible isomers (iv). When two different groups (C–H
and C–halogen) occupy the ortho carbons, the situation is rendered
⇑
Corresponding authors.
E-mail address: qiluaafl@udc.es (A. Fernández).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.027

90
L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
O
OMe
OMe
O
O
MeO
Me
Pd
O
H
X
Pd
Pd
N
N
N
N
ii
N
iv
iii
v
i
Fig. 1. Regioselectivity of cyclometallation reactions.
still holds (d 7.06, 6.46) and the H(6) singlet is absent, in agreement
with metallation at the C6 carbon.
O
O
O
O
O
O
The C(2)–Br bond in ligand a could be activated by treatment
with tris(dibenzilideneacetone)dipalladium(0) in toluene at 80 °C
for 4 h. The oxidative addition reaction afforded [Pd{4-5-
(OCH2O)C6H2C(H)@NCH2CH2NMe2–C2,N,N}(Br)] 2a. The 1H NMR
spectrum of 2a showed two singlets for the aromatic protons, at
d 7.51 and 6.61, assigned to the H(6) and H(3) proton atoms,
respectively, confirming metallation at the C(2) atom.
Br
Br
OH
N
OH
N
N
N
NMe2
NMe2
t Bu
t Bu
c
d
b
a
The IR spectra for 1a, 2a and 1b showed the m(C@N) stretch at
lower frequency [42 (1a), 17 (2a) and 29 (1b) cmꢀ1] than the cor-
responding one in the free imines in accordance with nitrogen
coordination to metal centre [30]. This was supported by the up-
field shift of the HC@N resonance in the 1H NMR spectra, ca.
0.5 ppm [31]. The resonances ca. d 3.8 and 2.9 were assigned to
the C@NCH2 and CH2NMe2 protons atoms, respectively. A singlet
ca. d 2.7 ppm was assigned to the NMe2 protons and was shifted
to higher frequency ca. 0.5 ppm consequent upon coordination of
the amine nitrogen atom to palladium, confirming that the palla-
dium atom was bonded to a phenyl carbon atom, to the imine
and to the amine nitrogen atoms, yielding a compound with two
fused rings at the metal: a five-membered ring, the metallacycle,
and a six-membered coordination ring.
Fig. 2. Potentially terdentate ligands with two possible metallation sites.
even more complex and the reaction conditions often determine
the final product.
Potentially terdentate Schiff base ligands give rise to com-
pounds with two fused five-membered fused rings at the metal
centre and the nature of the products is determined by the donor
atoms involved, with [C,N,N] ligands yielding mononuclear com-
pounds, and [C,N,O] and [C,N,S] ligands giving mononuclear and
tetranuclear complexes as appropriate [24–29].
As a continuation of our research, in the present paper we report
the reactions of Pd(AcO)2 and [Pd2(dba)3] with terdentate [C,N,N]
and [C,N,O] Schiff base ligands (a–d) (Fig. 2) derived from the reac-
tion of 2-Br-4,5-(OCH2O)C6H2COH and 4,5-(OCH2CH2)C6H3COH,
with NH2CH2CH2NMe2 or NH2(20-OH-50-tBuC6H3).
These ligands are also interesting because metallation, via C–H
or C–Br activation, may proceed at either one of the two ortho posi-
tions on the phenyl ring. The reactivity of the complexes with tri-
phenylphosphine is also reported, putting forward the influence of
the second donor atom at the metal, nitrogen or oxygen, which
gives way to the different final species.
The 13C–{1H} NMR spectra of 1a and 2a confirmed the proposed
structures, showing a strong downfield shift of the C@N, C(6) (1a),
C(2) (2a) and C(1) carbon resonances ca. 10, 30, 30 and 10 ppm,
respectively, from those for the free ligand consequent upon met-
allation (see Section 3) [32,33]. The signal assigned to the NMe2
group was also shifted to higher frequency showing coordination
of the amino nitrogen atom. Formation of the coordination ring
was confirmed by the separation of the two methylene resonances
C@NCH2CH2NMe2 (ca. 10 ppm) as compared to the uncoordinated
ligand [34]. In the IR spectrum of 1a the strong bands assigned to
2. Results and discussion
the symmetric and asymmetric m(COO) vibrations were in agree-
ment with those expected for terminal acetate ligands [35], in
agreement with mononuclear complexes. This was confirmed by
the MS-FAB spectra, which showed a peak assigned to the mono-
nuclear [M]+ fragment [36,37] with the ligand as terdentate
[C,N,N]. The spectroscopic data was confirmed by the structural
determination of 2a by X-ray diffraction analysis (vide infra).
Reaction of 1a with aqueous sodium chloride gave [Pd{2-Br-4,5-
(OCH2O)-C6HC(H)@NCH2CH2NMe2–C6,N,N}(Cl)] 3a, with exchange
of the acetate group by a chloride ligand, which was fully charac-
terised. The IR and 1H NMR spectra were similar to those described
for 1a, with the most noticeable difference being the absence of
any acetate spectral data (see Section 3).
2.1. Cyclometallated complexes derived from [C,N,N] ligands
For the convenience of the reader the compounds and reactions
are shown in Schemes 1–3. The compounds described were charac-
terised by elemental analysis (C, H and N), by mass spectrometry,
and by IR and 1H, 31P–{1H} and (in part) 13C–{1H} NMR spectros-
copy (data in Section 3).
The Schiff base ligands a and b were prepared by reaction be-
tween N,N0-dimethylethylenediamine and 6-bromopiperonal or
2,3-dihydrobenzofuran-5-carboxaldehyde, as appropriate, as air-
stable oils, which were fully characterised (see Section 3).
Reaction of a and b with palladium acetate or potassium
tetrachloropalladate, afforded [Pd{2-Br-4,5-(OCH2O)C6HC(H)@N-
CH2CH2NMe2-C6,N,N}(OCOMe)] 1a and [Pd{4,5-(OCH2CH2)C6H2-
C(H)@NCH2CH2NMe2–C6,N,N}(Cl)] 1b, after C–H activation at the
C6 atom.
Treatment of the cyclometallated monomers 1a, 3a and 2a with
triphenylphosphine in a 1:1 molar ratio in acetone at room
temperature yielded the mononuclear complexes [Pd{2-Br-4,5-
(OCH2O)C6HC(H)@NCH2CH2NMe2–C6,N}(OCOMe)(PPh3)] 4a, Pd{2-
Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2–C6,N}(Cl)(PPh3)] 5a and
[Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2–C2,N}(Br)(PPh3)] 6a,
respectively.
The 1H NMR spectrum for 1a showed a singlet at d 6.61 assigned
to the H(3) proton, and absence of the H(6) signal, confirming met-
allation at C(6). In the 1H NMR spectrum of 1b the initial double
doublets [H(2) and H(3) protons] in the spectrum of the free ligand
The 31P–{1H} NMR spectrum showed a singlet resonance at d
35.80 (4a), 36.61 (5a) and 39.63 (6a), shifted to higher frequency

L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
91
O
O
O
O
PPh3
OAc
PPh3
Br
Br
Pd
Pd
Cl
N
N
NMe2
NMe2
4a
5a
v
iv
O
O
O
O
O
O
PPh3
NMe2
Cl
OAc
CF3SO3
vi
iii
Br
Br
Br
Pd
Pd
Pd
N
NMe2
N
N
NMe2
3a
1a
7a
i
O
4
O
5
3
6
2
1
Br
N
c
d
NMe2
a
ii
O
O
O
O
PPh3
Br
CF3SO3
vi
Pd
Pd
NMe2
N
NMe2
N
2a
8a
iv
O
O
PPh3
Br
Pd
N
NMe2
6a
Scheme 1. (i) Pd(OAc)2, toluene; (ii) Pd2(dba)3, toluene; (iii) NaCl, acetone/water; (iv): PPh3, CDCl3; (v): PPh3, acetone; (vi) AgCF3SO3, PPh3, acetone.
accordance with a N–Pd–P trans geometry, as we have observed
earlier in related complexes [21,22].
O
a
O
4
b
3
2
5
The spectrum for complex 6a at room temperature showed no
coupling of the HC@N and H(3) resonances with the 31P nucleus.
However, when the spectrum was recorded at 223 K two doublets
at 8.58 and 5.66 ppm could be assigned to the imine proton and to
the H(3) resonance, respectively, coupled to the 31P nucleus
(4JPH = 9.7 Hz, 4JPH3 = 4.5 Hz). A similar fluxional behaviour, due
to the uncoordinated amine nitrogen NMe2, has been previously
observed by us [24].
6
Cl
1
i
Pd
N
NMe2
N
c
d
NMe2
b
1b
Scheme 2. (i) K2[PdCl4], ethanol/water.
The NMe2 resonance in the 1H NMR spectra appeared ca. d 2.2
suggesting that the NMe2 group was not coordinated (2.29 ppm
for the non-coordinated ligand). Furthermore, in the 13C–{1H}
NMR spectra of complex 5a the resonance corresponding to the
NMe2 carbon appeared at 45.15 ppm (45.78 ppm for the non
coordinated ligand) and the separation of the two methylene reso-
nances C@NCH2CH2NMe2 (3 ppm) confirmed Pd–NMe2 bond cleav-
age. Thus, the Schiff base ligand was solely bonded to the metal
from the free phosphine spectrum, in agreement with phosphorous
coordination to metal centre [38].
In the 1H NMR spectra some of the proton resonances, OCH2O
(4a, 5a) and H(3) (6a), were shifted towards lower frequency by
ca. 1.4 ppm as compared to the parent cyclometallated complexes,
due to the shielding effect of the phenyl phosphine groups, in

92
L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
O
O
O
O
O
O
PPh3
O
Br
Br
Br
Pd
Pd
N
ii
O
N
OH
i
N
t Bu
t Bu
t Bu
4
c
2c
1c
a
7
O
O
4
b
5
3
2
6
1
Pd
N
OH
12
O
N
i
11
8
10
9
t Bu
t Bu
4
d
1d
Scheme 3. (i) Pd(OAc)2, toluene; (ii) PPh3 (1:4), acetone.
through the imine nitrogen and the phenyl carbon atoms in a
bidentate [C,N] fashion.
cmꢀ1, upon nitrogen coordination of the imine, and absence of
the (O–H) stretch, as compared to the free ligand [3393 (c) and
3359 (d) cmꢀ1], in accordance with loss of the –OH proton
[41,42]; absence of the (COO) bands precludes the formulation
of the species as dimers with bridging acetate units or as mono-
mers with a similar structure to 1a.
m
Furthermore, treatment of a solution of 3a or 2a with silver
trifluoromethanesulfonate, followed by reaction with triphenyl-
phosphine in acetone yielded the cyclometallated complexes
[Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2–C6,N,N}(PPh3)]
[CF3SO3] 7a and [Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2–
C2,N,N}(PPh3)][CF3SO3] 8a. Conductivity measurements in dry
acetonitrile solutions showed that complexes 7a and 8a were 1:1
electrolytes. The 1H NMR spectra showed the HC@N and the H(3)
(8a) resonances as doublets by coupling to the 31P nucleus with J
values of 9.7 and 4.5 Hz, respectively; and the 31P–{1H} NMR spec-
tra showed a singlet resonance ca. d 35 ppm; these findings were in
agreement with a phosphorous trans to nitrogen geometry. The
OCH2O (7a) and H(3) (8a) resonances, as well as the NMe2
resonance (d 2.02), were also shifted to lower frequency due to
shielding of the phosphine phenyl rings.
Coordination of the amine nitrogen to palladium was confirmed
by the low-field shift of the NMe2 resonance in the 13C–{1H} NMR
spectra, assigned ca. d 48.3, similar to the value found for 1a and
2a, and by the separation of the two methylene resonances
C@NCH2CH2NMe2 [10 ppm (7a) 15 ppm (8a)]. Thus, the palladium
metal centre was coordinated to both the imine and amine nitro-
gen atoms, with the phosphine ligand occupying the fourth coordi-
nation site, left vacant after halide abstraction.
m
In the 1H NMR spectra the absence of the OH resonance con-
firmed deprotonation. All the resonances were high-field shifted
as compared to the uncoordinated ligands (see data in Section 3)
and they were in agreement with metallation of the ligand and
with coordination of the palladium atom via the imine nitrogen
atom. The most noticeable shift concerned the HC@N and the
OCH2O (1c) and OCH2CH2 (1d) resonances, due to the structure
of the complex in which these protons are in the proximity of
the shielding area of the phenyl rings of a neighbouring metallated
ligand [43,44].
The OCH2O resonance (1c) appeared as two doublets at 5.69,
5.34 [2J(HH) = 1.4] and the OCH2CH2 resonance (1d) as four multi-
plets 4.18, 3.94 [CHa2], 2.79, 2.49 [CHb2] showing the non-equiva-
lence of these protons due to the tetrameric structure of the
complexes.
The 13C–{1H} NMR spectrum of 1d confirmed the proposed
structure, showing a strong downfield shift of the metallated and
C1 carbon resonances ca. 27.8 and 11.1 ppm, respectively, from
those for the free imine consequent upon metallation (see Section
3). The resonance assigned to the C(12)–O carbon was shifted to
higher frequency ca. 11.20 ppm upon Pd–O bond formation.
The FAB mass spectra of 1c and 1d showed the cluster of peaks
characteristic of the [M]+ and the [MH]+ fragment centred at 1921
and 1598 amu; the isotopic pattern was in good agreement with
the tetrameric formulation. The resolution of the molecular struc-
tures for both compounds (vide infra) confirmed the proposed
structures.
2.2. Cyclometallated complexes derived from [C,N,O] ligands
Ligands c and d were prepared by reaction of 6-bromopiperonal
and 2,3-dihydrobenzofuran-5-carboxaldehyde with 2-amino-4-
tert-butylphenol, respectively, as air-stable solids, which were fully
characterised (see Section 3).
Treatment of c and d with palladium(II) acetate in dry toluene
at 60 °C gave tetranuclear complexes [Pd{2-Br-4,5-(OCH2O)C6HC-
(H)@N(20-O-50-tBuC6H3)–C6,N,O}]4 1c and [Pd{4,5-(OCH2CH2)C6H2-
C(H)@N(20-O-50-tBuC6H3)–C6,N,O}]4 1d, after C–H activation
at the C6 carbon, ortho to the OCH2O or OCH2CH2 groups, in a sim-
ilar manner to previous findings for related [C,N,O] ligands
[25,39,40].
Treatment of 1c with triphenylphosphine in 1:4 molar ratio,
gave the mononuclear species [Pd{2-Br-4,5-(OCH2O)C6HC(H)@
N(20-(O)-50-tBuC6H3)–C6,N,O}(PPh3)] 2c, with opening of the poly-
nuclear structure after P–Obridging bond cleavage.
The 1H NMR spectrum of 2c showed the HC@N resonance as a
doublet coupled to the 31P nucleus and the 31P–{1H} NMR spec-
trum showed a singlet resonance at d 27.68, in accordance with a
phosphorous-to-nitrogen trans geometry. The shielding effect of
The IR spectra showed the shift of the
m(C@N) stretch towards
lower wavenumbers, from the free ligand value, 29(1c), 47(1d)

L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
93
the adjacent phenyl phosphine groups gave a low frequency shift
of the OCH2O resonance.
The HC@N proton resonance at 8.28 ppm showed a smaller
high-field shift than in compound 1c, in agreement with opening
of the polynuclear structure [45]. This was supported by the pres-
2.3.1. Molecular structure of complex 2a
Suitable crystals of compound 2a were grown from slowly
evaporating a dichloromethane/n-hexane solution.
The palladium metal centre is bonded to the ligand through the
C(2) carbon atom of the phenyl ring, the imine N(1) and the amine
N(2) nitrogen atoms, and to the Br(1) bromide ligand. The angles
between adjacent atoms in the coordination sphere of palladium
are close to the expected value of 90°, with the most noticeable dis-
tortions corresponding to the N(1)–Pd(1)–C(2) and N(1)–Pd(1)–
N(2) bond angles of 81.3(2) and 82.1(1), respectively. The sum of
the angles about palladium is approximately 360°.
ence of only one methylene resonance OCH2O,
a singlet at
4.72 ppm, as opposed to the two doublets present in the spectrum
of 1c.
Absence of the OH resonance in the 1H NMR spectrum con-
firmed deprotonation and was in agreement with Pd–Ochelating
bonding. The strength of this bond was put forward in the reaction
with excess of triphenylphosphine, which only yielded compound
2c; this contrasts with the facile breakage of the Pd–O bond ob-
served by us in semicarbazone compounds [46,47].
2.3. X-Ray diffraction analysis
The molecular structures for 2a, 1c and 1d were determined.
The labelling schemes for the compounds are shown in Figs. 3–5.
The crystals consist of discrete molecules, separated by normal
van der Waals distances. Crystallographic data and selected inter-
atomic distances and angles are listed in Tables 1–3.
Fig. 5. Molecular structure of [Pd{4,5-(OCH2CH2)C6H2C(H) = N(20-O-50-tBuC6H3)-
C6,N,O}]4 (1d), with labelling scheme. tBu groups, hydrogen atoms and the CHCl3
solvent molecules have been omitted for clarity.
Table 1
Crystal and structure refinement data for complexes 2a, 1c and 1d.
Fig. 3. Molecular structure of [Pd{4-5-(OCH2O)C6H2C(H) = NCH2CH2NMe2-
C2,N,N}(Br)] (2a), with labelling scheme. Hydrogen atoms have been omitted for
clarity.
2a
1cꢁ4CHCl3
1dꢁ4CHCl3
Formula
Mr
T (K)
k (Å)
C12H15BrN2O2Pd C76H68Br4Cl12N4O12Pd4 C80H80Cl12N4O8Pd4
405.57
293(2)
0.71073
2399.98
293(2)
0.71073
tetragonal
I41/a
2076.48
293(2)
0.71073
tetragonal
I41/a
Crystal system monoclinic
Space group P 21/c
Cell dimensions
a (Å)
b (Å)
13.140(2)
6.955(4)
16.587(2)
90
23.308(1)
23.308(1)
15.812(1)
90
22.826(2)
22.826(2)
18.018(2)
90
c (Å)
a
(°)
b (°)
110.854(2)
90
1416.6(3)
4
90
90
8590.5(7)
4
1.856
3.118
90
90
c
(°)
V (Å3)
9387.9(16)
4
1.469
1.145
Z
Dcalc. (Mg/m3) 1.902
l
(mmꢀ1
)
4.166
Crystal size
(mm)
0.30 ꢂ 0.20 ꢂ 0.20 0.15 ꢂ 0.15 ꢂ 0.08
0.36 ꢂ 0.25 ꢂ 0.15
2hmaximum (°) 53.98
Independent 3068
56.66
5360 (Rint = 0.1542)
50.00
4110
reflections (Rint = 0.0420)
(Rint = 0.0880)
0.920
0.0770
0.2162
S
1.040
(I)] 0.0365
0.0814
0.991
0.0688
0.2314
R [F, I > 2
r
wR [F2, all
data]
Fig. 4. Molecular structure of [Pd{2-Br-4,5-(OCH2O)C6HC(H) = N(20-O-50-tBuC6H3)-
C6,N,O}]4 (1c), with labelling scheme. tBu groups, hydrogen atoms and the CHCl3
solvent molecules have been omitted for clarity.
Maximum
q
0.480
1.031
1.395
(e A3)

94
L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
Table 2
OCH2O group [C(4), C(5), O(1), O(2), C(12)] are 0.0087, 0.0045
and 0.0365 Å, respectively; with angles planes under 4.5°. As ex-
pected the coordination ring Pd(1), N(1), C(8), C(9), N(2), shows
large deviations from planarity with C(8) and N(2) lying above
the last square plane and C(9) below.
Selected bond distances (Å) and angles (°) for
complex 2a.
2a
Pd(1)–N(1)
Pd(1)–C(2)
Pd(1)–N(2)
Pd(1)–Br(1)
N(1)–C(7)
N(1)–C(8)
N(2)–C(9)
C(1)–C(2)
1.975(3)
1.993(4)
2.177(3)
2.4309(6)
1.284(5)
1.451(5)
1.471(6)
1.415(6)
1.443(5)
1.508(6)
81.3(2)
2.3.2. Molecular structure of complex 1c and 1d
Suitable crystals of compounds 1c and 1d were grown from
slowly evaporating chloroform/n-hexane solutions.
The core of the tetrameric molecule consists of an eight-mem-
bered ring of alternating palladium and oxygen atoms. The asym-
metric unit contains a quarter of the molecule and the complete
molecule is generated by a rotoinversion fourfold axis which
crosses through the middle of the Pd4O4 core.
Each palladium atom is bonded to the ligand through an aryl
carbon, a C@N nitrogen and a phenoxy oxygen atom, and also to
a bridging oxygen atom of a neighbouring cyclometallated moiety.
Thus, each palladium atom belongs to two fused five-membered
rings, which are planar and coplanar with the phenol ring, the met-
allated phenyl ring and the OCH2O or the OCH2CH2 ring. Two of the
quasi-planar Pd ligand units are parallel and almost orthogonal to
the other two parallel monomer moieties.
C(1)–C(7)
C(8)–C(9)
N(1)–Pd(1)–C(2)
N(1)–Pd(1)–N(2)
C(2)–Pd(1)–N(2)
C(2)–Pd(1)–Br(1)
N(2)–Pd(1)–Br(1)
C(1)–C(2)–Pd(1)
C(2)–C(1)–C(7)
N(1)–C(7)–C(1)
C(7)–N(1)–Pd(1)
C(8)–N(1)–Pd(1)
82.1(1)
163.2(2)
98.2(1)
98.4(1)
111.4(3)
115.0(4)
114.9(4)
117.4(3)
118.2(3)
The Pd–C and the Pd–N bond lengths are consistent with those
found in related complexes [39–42]. The trans-lengthening influ-
ence of the a-bonded carbon is clearly illustrated by the lengthen-
Table 3
Selected bond distances (Å) and angles (°) for complexes 1c and 1d.
ing of the palladium–oxygen distance trans to carbon, relative to
trans to nitrogen: 2.107(6) versus 2.035(6) 1c, and 2.137 (6) versus
2.025 (6) 1d. A characteristic of the coordinated ligand is the short-
ening of the O(1)–C(9) (1c) and the O(1)–C(13) (1d) bond distances
of 1.36(1) and 1.33(1) Å, respectively, as compared to values re-
ported previously for uncoordinated phenols [53] [1.411(5) Å in
N-(2-hydroxyphenyl-2-hydroxyaniline].
The sum of the angles at palladium is ca. 360°, with the only
noteworthy deviations being the somewhat reduced N(1)–Pd(1)–
C(6) and N(1)–Pd(1)–O(1) angles of 82.8(4) (1c, 1d) and 81.7(3)
(1c), 81.1(3) (1d), respectively consequent upon chelation.
1c
1d
Pd(1)–N(1)
Pd(1)–C(6)
Pd(1)–O(1)
Pd(1)–O(1A)
N(1)–C(7)
N(1)–C(8)
O(1)–C(9)
O(1)–C(13)
C(1)–C(6)
1.942(8)
1.951(10)
2.107(6)
2.035(6)
1.30(1)
1.932(8)
1.950(9)
2.137(6)
2.025(6)
1.28(1)
1.43(1)
1.36(1)
1.43(1)
1.33(1)
1.44(1)
1.43(1)
1.45(1)
1.45(1)
1.39(1)
C(1)–C(7)
C(8)–C(9)
C(8)–C(13)
1.39(1)
N(1)–Pd(1)–C(6)
N(1)–Pd(1)–O(1)
O(1)–Pd(1)–O(1A)
O(1A)–Pd(1)–C(6)
C(1)–C(6)–Pd(1)
C(6)–C(1)–C(7)
N(1)–C(7)–C(1)
C(7)–N(1)–Pd(1)
C(8)–N(1)–Pd(1)
82.8(4)
81.7(3)
97.6(2)
82.4(4)
81.1(3)
98.1(2)
3. Conclusion
97.9(3)
98.3(4)
The terdentate Schiff base ligands a–d are readily cyclometallat-
ed by palladium(II) salts. However, whilst the terdentate [C,N,N] li-
gands, a and b, gave mononuclear complexes, the analogous
[C,N,O] ligands, c and d, gave tetranuclear species after double
deprotonation of the ligand at a phenyl carbon atom and at the –
OH phenol oxygen; in all cases Pd(II) selectively activates the
C(6)–H bond. In order to metallate the C2 position an oxidative
addition reaction with Pd2(dba)3 was necessary. The nature of
the second donor atom, nitrogen (a and b) or oxygen (c and d),
as appropriate, determines the reactivity of the cyclometallated
complexes towards triphenylphosphine. Thus, treatment of 1a,
2a or 3a with triphenylphosphine gives cleavage of the Pd–NMe2
bond, whilst treatment of the tetranuclear complex 1c with tri-
phenylphosphine produces opening of the polynuclear structure
after P–Obridging bond cleavage. Nevertheless, the P–Ochelating bond
remained unaltered even when a large excess of the phosphine
was used, putting forward the higher stability of the [Pd,N,C,C,O]
ring as compared to the [Pd,N,C,C,N] one.
111.7(7)
113.3(9)
114.7(1)
117.3(7)
115.3(6)
111.5(8)
112.8(9)
116.2(9)
116.7(7)
114.5(6)
Symmetry transformations used to generate equivalent atoms: 1c: ꢀy + 5/4,
x ꢀ 3/4, ꢀz + 5/4; 1d: y ꢀ 1/4, ꢀx + 5/4, ꢀz + 1/4.
The Pd(1)–N(1) 1.975(3) Å and Pd(1)–N(2) 2.177(3) Å bond
lengths are similar to others reported for related complexes
[24,26,48,49]; the greater bond distance of the latter reflects the
stronger trans influence of the carbon C(2) atom as compared to
the bromine Br(1) atom. The Pd(1)–C(2) bond length of
1.993(4) Å, shorter than the expected value of 2.081 Å (based on
the sum of the covalent radii for carbon(sp2) and palladium,
0.771 and 1.31 Å, respectively), is consistent with those found in
related complexes [24,26,48,49]. The Pd(1)–Br(1) bond length of
2.4309(6) Å is in accordance with the value found earlier in related
cyclometallated compounds [24,50–52].
4. Experimental
The geometry at palladium is planar [mean deviation from the
least square plane for, Pd(1), C(2), N(1), N(2), Br(1), of 0.0271 Å].
Except for the coordination ring, the cyclopalladated moiety is
nearly planar. The mean deviation from the least squares planes
determined for the metallacycle [Pd(1), C(2), C(1), C(7), N(1)], the
metallated phenyl ring [C(1), C(2), C(3), C(4), C(5), C(6)] and the
4.1. General remarks
Safety note: Solvents were purified by standard methods [54].
Chemicals were reagent grade and were purchased from Aldrich-
Chemie. Microanalyses were carried out using
a Carlo Erba

L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
95
Elemental Analyser, Model 1108. IR spectra were recorded as KBr
discs on a Satellite FTIR. NMR spectra were obtained as CDCl3
and CD3SOCD3 solutions and referenced to SiMe4 (1H, 13C–{1H})
{1H} (300 MHz, CDCl3, d ppm, J Hz): d = 163.30 [s, C4], 156.46 [s,
C@N], 149.52 [s, C12], 142.92 [s, C9], 135.23 [s, C7], 130.98 [s, C3],
129.24, 128.18 [s, C5/C1], 125.07 [s, C10], 124.70 [s, C6], 114.05 [s,
or 85% H3PO4
(
31P–{1H}) and were recorded on a Bruker AV-300F
C8], 112.57 [s, C11], 109.46 [s, C2], 71.99 [s, CHa ], 34.36 [s,
2
or AC-500F spectrometer. All chemical shifts were reported down-
field from standards. The FAB mass spectra were recorded using a
FISONS Quatro mass spectrometer with a Cs ion gun; 3-nitrobenzyl
alcohol was used as the matrix.
C(CH3)3], 31.56 [s, C(CH3)3], 31.48 [s, CHb].
2
4.3. Synthesis of the cyclopalladated complexes
4.3.1. Pd{2-Br-4,5-(OCH2O)C6HC(H) = NCH2CH2NMe2-C6,N,N}
4.2. Syntheses of the ligands
(OCOMe) (1a)
A
pressure tube containing 2-Br-4,5-(OCH2O)C6H2C(H) =
4.2.1. 2-Br-4,5-(OCH2O)C6H2C(H)@NCH2CH2NMe2 (a)
NCH2CH2NMe2 (a) (0.306 g, 1.023 mmol), palladium(II) acetate
(0.200 g, 1.341 mmol) and 20 cm3 of dry toluene was sealed under
argon. The mixture was heated for 24 h at 60 °C. The brown solid
was filtered off, and dried under vacuum. Yield: 51%. Anal. Calc.
for C14H17N2O4BrPd: C, 36.3; H, 3.7; N, 6.0. Found: C, 36.4; H,
2-Br-4,5-(OCH2O)C6H2COH (0.510 g, 2.227 mmol) and NH2CH2
CH2NMe2 (0.202 g, 2.293 mmol) were added to 50 cm3 of dry chlo-
roform. The mixture was heated under reflux in a Dean-Stark appa-
ratus for 8 h. After cooling to room temperature, the solvent was
evaporated to give
a
brown oil. Yield: 80%. Anal. Calc. for
3.6; N, 6.0. IR: m(C@N) 1592sh,s, mas(COO) 1567s, ms(COO)
C
12H15N2O2Br: C, 48.2; H, 5.0; N, 9.4. Found: C, 48.3; H, 5.0; N,
1331 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 8.13 [t,
1H, Hi, 4J(HiHc) = 1.5], 6.61 [s, 1H, H3], 5.96 [s, 2H, OCH2O], 3.79
9.3. IR:
m
(C@N) 1634 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm,
J Hz): d = 8.53 [t, 1H, Hi, 4J(HiHc) = 1.3], 7.47 [s, 1H, H6], 6.95 [s,
[dt, 2H, CHc2, 3J(HcHd) = 6.0], 2.95 [t, 2H, CHd], 2.72 [s, 6H, NMe2],
2
1H, H3], 6.01 [s, 2H, OCH2O], 3.72 [dt, 2H, CHc , 3J(HcHd) = 7.3],
2.06 [s, 3H, OCOMe]. RMN 13C–{1H} (500 MHz, CDCl3, d ppm,
J Hz): d = 179.82 [s, CH3COO], 172.68 [s, C@N], 152.37 [s, C4],
150.82 [s, C5], 141.84 [s, C1], 130.99 [s, C6], 114.46 [s, C2], 108.53
[s, C3], 101.47 [s, OCH2O], 65.82 [s, CHd], 53.72 [s, CHc ], 48.01 [s,
2
2.62 [t, 2H, CH2d], 2.29 [s, 6H, NMe2]. RMN 13C–{1H} (500 MHz,
CDCl3, d ppm, J Hz): d = 160.29 [s, C@N], 150.36 [s, C4], 147.80 [s,
C5], 128.52 [s, C1], 117.22 [s, C2], 112.50 [s, C3], 107.75 [s, C6],
2
2
101.08 [s, OCH2O], 60.08, 59.42 [s, CHc /CH2d], 45.79 [s, NMe2].
NMe2], 23.40 [s, CH3COO]. MS-FAB: m/z = 463.0 [M]+, 405.0 [M-
2
OAc]+.
4.2.2. 4,5-(OCH2CH2)C6H3C(H) = NCH2CH2NMe2 (b)
Schiff base ligand b was prepared following a similar procedure
that a but using 4,5-(OCH2CH2)C6H3COH to give an orange oil.
Yield: 89%. Anal. Calc. for C13H18N2O: C, 71.5; H, 8.3; N, 12.8. Found:
4.3.2. Pd{4,5-(OCH2CH2)C6H2C(H) = NCH2CH2NMe2-C6,N,N}(Cl) (1b)
To a stirred solution of potassium tetrachloropalladate (0.617 g,
1.892 mmol) in water (6 cm3) ethanol (20 cm3) was added. The ob-
tained fined and yellow suspension of potassium tetrachloropalla-
date was treated with 4,5-(OCH2CH2)C6H3C(H) = NCH2CH2NMe2
(b) (0.413 g, 1.892 mmol). The mixture was stirred for 76 h at room
temperature. The yellow precipitate was filtered off and dried in
vacuo. Yield: 29%. Anal. Calc. for C13H17N2OClPd : C, 43.5; H, 7.8;
C, 71.6; H, 8.4; N, 12.8. IR:
m
(C@N) 1646 m cmꢀ1. RMN 1H
(300 MHz, CDCl3, d ppm, J Hz): d = 8.03 [s, 1H, Hi], 7.50 [s, 1H,
H6], 7.24 [dd, 1H, H2, 3J(H2H3) = 8.2, 4J(H2H6) = 1.1], 6.60 [d, 1H,
H3], 4.39 [t, 2H, CH2a , 3J(HaHb) = 8.8], 3.54 [dt, 2H, CHc2,
3J(HcHd) = 7.3, 4J(HiHc) = 1.1], 3.00 [t, 2H, CH2b], 2.47 [t, 2H, CH2d],
2.15 [s, 6H, NMe2].
N, 4.8. Found: C, 43.4; H, 7.7; N, 4.7. IR:
m .
(C@N) 1614s cmꢀ1
RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 7.79 [t, 1H, Hi,
4J(HiHa) = 1.3], 7.06 [d, 1H, H2, 3J(H2H3) = 8.0], 6.46 [d, 1H, H3],
4.52 [t, 2H, CHa2, 3J(HaHb) = 8.8], 3.80 [dt, 2H, CHc2, 3J(HcHd) = 6.0],
3.58 [t, 2H, CHb], 2.91 [t, 2H, CHd], 2.67 [s, 6H, NMe2]. MS-FAB:
4.2.3. 2-Br-4,5-(OCH2O)C6H2C(H) = N(20-OH-50-tBuC6H3) (c)
2-Br-4,5-(OCH2O)C6H2COH (1.000 g, 4.366 mmol) and NH2(20-
OH-50-tBuC6H3) (0.722 g, 4.366 mmol) were added to 50 cm3 of
dry chloroform. The mixture was heated under reflux in a Dean-
Stark apparatus for 8 h. After cooling to room temperature, the sol-
vent was evaporated to give a yellow solid. Yield: 94%. Anal. Calc.
for C18H18NO3Br: C, 57.5; H, 4.8; N, 3.7. Found: C, 57.3; H, 4.7; N,
2
2
m/z = 359.1 [MH]+, 323.0 [MH-Cl]+.
4.3.3. Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2-C2,N,N}(Br) (2a)
A
pressure tube containing 2-Br-4,5-(OCH2O)C6H2C(H)@
3.7. IR:
m
(C@N) 1617 m,
m
(OH) 3393 h cmꢀ1. RMN 1H (300 MHz,
NCH2CH2NMe2 (a) (0.143 g, 0.478 mmol), tris(dibenzylideneace-
tone)dipalladium(0) (0.200 g, 0.218 mmol) and 50 cm3 of dry tolu-
ene was sealed under argon. The mixture was heated for 4 h at
80 °C. After cooling to room temperature the solution was filtered
through Celite to remove the black palladium formed. The solvent
was removed under vacuum to give a brown oil which was recrys-
tallized from ether, filtered off and dried Yield: 70%. Anal. Calc. for
CDCl3, d ppm, J Hz): d = 8.95 [s, 1H, OH] (resonance taken from a
spectrum recorded in DMSO-d6), 8.97 [s, 1H, Hi], 7.68 [s, 1H, H6],
7.07 [s, 1H, H3], 7.29 [d, 1H, H8, 4J(H8H10) = 2.2], 7.26 [dd, 1H,
H10
,
3J(H10H11) = 8.4], 6.96 [d, 1H, H11], 6.07 [s, 2H, OCH2O], 1.36
[s, 9H, tBu]. RMN 13C–{1H} (300 MHz, CDCl3,
d
ppm, J Hz):
d = 155.10 [s, C@N], 151.08 [s, C4], 149.84 [s, C12], 147.96 [s, C5],
143.10 [s, C9], 134.73 [s, C7], 128.39 [s, C1], 126.12 [s, C10],
119.07 [s, C2], 114.42 [s, C8], 112.88 [s, C3/C11], 107.37 [s, C6],
102.34 [s, OCH2O], 34.34 [s, C(CH3)3], 31.52 [s, C(CH3)3].
C
12H15N2O2BrPd: C, 35.5; H, 3.7; N, 6.9. Found: C, 35.4; H, 3.6; N,
6.8. IR: m
(C@N) 1617 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm,
J Hz): d = 7.81 [t, 1H, Hi, 4J(HiHc) = 1.4], 7.51 [s, 1H, H6], 6.76 [s,
1H, H3], 5.91 [s, 2H, OCH2O], 3.85 [dt, 2H, CHc , 3J(HcHd) = 6.0],
2
4.2.4. 4,5-(OCH2CH2)C6H3C(H) = N(20-OH-50-tBuC6H3) (d)
2.91 [t, 2H, CHd], 2.73 [s, 6H, NMe2]. RMN 13C–{1H} (500 MHz,
2
Schiff base ligand d were prepared following a similar proce-
dure that c but using 4,5-(OCH2CH2)C6H3COH to give a brown so-
lid. Yield: 97%. Anal. Calc. for: C19H21NO2: C, 77.3; H, 7.2; N, 4.7.
CDCl3, d ppm, J Hz): d = 170.64 [s, C@N], 153.92 [s, C4], 148.44 [s,
C5], 144.52 [s, C2], 141.10 [s, C1], 118.59 [s, C3], 107.55 [s, C6],
100.77 [s, OCH2O], 63.73 [s, CHd], 52.91 [s, CHc ], 48.54 [s, NMe2].
2
2
Found: C, 77.2; H, 7.1; N, 4.8. IR:
m
(C@N) 1625 m,
m
(OH) 3359sh
MS-FAB: m/z = 405.9 [M]+.
cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 8.64 [s, 1H, OH]
(resonance taken from a spectrum recorded in DMSO-d6), 8.61 [s,
1H, Hi], 7.89 [s, 1H, H6], 7.65 [dd, 1H, H2, 3J(H2H3) = 8.2,
4.3.4. Pd{2-Br-4,5-(OCH2O)C6HC(H) = NCH2CH2NMe2-C6,N,N}(Cl)
(3a)
4J(H2H6) = 1.4], 7.27 [d, 1H, H8, 4J(H8H10) = 2.3], 7.21 [dd, 1H, H10
,
A solution of 1a (0.169 g, 0.366 mmol) in 15 cm3 of acetone was
treated with a saturated solution of NaCl in ca. 20 cm3 of water. The
pale brown precipitate formed was filtered off, washed with water
3J(H10H11) = 8.4], 6.94 [d, 1H, H11], 6.88 [d, 1H, H3], 4.68 [t, 2H,
b
CHa2, 3J(HaHb) = 8.7], 3.29 [t, 2H, CH2], 1.35 [s, 9H, Bu]. RMN 13C–
t

96
L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
and dried under vacuum. Yield: 70%. Anal. Calc. for
12H14N2O2ClBrPd: C, 32.7; H, 3.2; N, 6.4. Found: C, 32.5; H, 3.1;
4.3.9. Pd{4-5-(OCH2O)C6H2C(H)@NCH2CH2NMe2-C2,N,N}(PPh3)
[CF3SO3] (8a)
Compound 8a was obtained as a yellow solid, following a sim-
ilar procedure that 7a but using 2a as starting material.
Yield: 82%. Anal. Calc. for C31H30N2O5F3SPPd: C, 50.5; H, 4.1; N,
C
N, 6.3. IR:
m
(C@N) 1612 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d
ppm, J Hz): d = 8.24 [t, 1H, Hi, 4J(HiHc) = 1.5], 6.65 [s, 1H, H3], 6.03
[s, 2H, OCH2O], 3.84 [dt, 2H, CHc , 3J(HcHd) = 6.1], 2.93 [t, 2H, CHd2,
2
3J(HcHd) = 6.1], 2.71 [s, 6H, NMe2]. MS-FAB: m/z = 325.0 [MHꢀCl]+.
3.8. Found: C, 50.6; H, 4.1; N, 3.7. IR: m(C@N) 1581w, m(CF3SO3)
1264sh, 1030s, 1224sh, 1153 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d
ppm, J Hz): d = 8.28 [d, 1H, Hi, 4J(PHi) = 9.7], 6.91 [s, 1H, H6], 5.72 [s,
2H, OCH2O], 5.68 [d, 1H, H3, 4J(PH3) = 4.5], 4.07 [b, 2H, CHc2], 3.02 [t,
2H, CH2d, 3J(HcHd) = 6.0], 2.02 [s, 6H, NMe2]. RMN 31P–{1H}
4.3.5. Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2-C6,N}(OCOMe)
(PPh3) (4a)
In a NMR tube a solution of 1a (0.0088 g, 0.0217 mmol) in deu-
terate chloroform, was treated with PPh3 (0.0057 g, 0.0217 mmol).
RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 8.49 [s, 1H, Hi], 6.56 [s,
1H, H3], 4.63 [s, 2H, OCH2O], 3.67 [t, 2H, CHc2, 3J(HcHd) = 6.6], 2.88
(300 MHz, CDCl3,
d
ppm, J Hz): d = 39.06 [s]. RMN 13C–{1H}
(300 MHz, CDCl3, d ppm, J Hz): d = 174.72 [d, C@N, 3J(PC@N) = 3.3],
150.49 [d, C4, 4J(PC4) = 7.5], 147.85 [C5, 5J(PC5) = 5.6], 145.12 [s, C2],
143.14 [s, C1], 118.65 [d, C3, 3J(PC3) = 10.9], 109.72 [s, C6], 101.02
[s, OCH2O], 66.78 [s, CHd], 51.78 [s, CHc ], 48.32 [s, NMe2]. P-phenyl:
[m, 2H, CHd], 2.68 [s, 3H, OCOMe], 2.28 [s, 6H, NMe2]. RMN 31P–
2
{1H} (300 MHz, CDCl3, d ppm, J Hz): d = 35.80 [s].
2
2
135.28 [d, Co, 2J(PCo) = 12.6], 132.16 [d, Cp, 4J(PCp) = 2.2], 129.20 [d,
Ci, 1J(PCi) = 47.9], 129.29 [d, Cm, 3J(PCm) = 10.7]. MS-FAB: m/
z = 587.1 [M]+. Specific molar conductivity, Km = 109.3 ohmꢀ1 cm2
molꢀ1 (in acetonitrile).
4.3.6. Pd{2-Br-4,5-(OCH2O)C6HC(H)@NCH2CH2NMe2-C6,N}(Cl)(PPh3)
(5a)
PPh3 (0.037 g, 0.084 mmol) was added to a suspension of 3a
(0.022 g, 0.0784 mmol) in acetone (15 cm3). The mixture was stir-
red for 24 h and solvent removed to give a yellow solid which was
dried in vacuo. Yield: 38%. Anal. Calc. for C30H29N2O2PBrClPd: C,
4.3.10. [Pd{2-Br-4,5-(OCH2O)C6HC(H)@N(20-O-50-tBuC6H3)-C6,N,O}]4
(1c)
51.3; H, 4.2; N, 3.9. Found: C, 51.4; H, 4.1; N, 3.7. IR:
m
(C@N)
A pressure tube containing 2-Br-4,5-(OCH2O)C6H2C(H) = N(20-
OH-50-tBuC6H3) (0.167 g, 0.445 mmol), palladium(II) acetate
(0.100 g, 0.445 mmol) and 20 cm3 of dry toluene was sealed under
argon. The resulting mixture was heated at 60 °C for 24 h. After cool-
ing to room temperature the solution was filtered through Celite to
remove the small amount of black palladium formed. The solvent
was removed under vacuum to give a red oil, which was recrystal-
lized from dichloromethane/hexane to give the desired product as
a red solid. Yield: 37%. Anal. Calc. for C72H64N4O12Br4Pd4: C, 44.9;
1614w cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 8.51 [s,
1H, Hi], 6.57 [s, 1H, H3], 4.60 [s, 2H, OCH2O], 3.99 [b, 2H, CHc ],
2
2.73 [b, 2H, CHd], 2.29 [s, 6H, NMe2]. RMN 31P–{1H} (300 MHz,
2
CDCl3, d ppm, J Hz): d = 36.61 [s]. RMN 13C–{1H} (500 MHz, CDCl3,
d ppm, J Hz): d = 176.99 [s, C@N], 146.97 [s, C4], 149.40 [s, C5],
139.50 [s, C1], 132.94 [s, C6], 115.88 [s, C2], 109.36 [s, C3], 99.12
[s, OCH2O], 58.96 [s, CHd], 55.98 [s, CHc ], 45.15 [s, NMe2]. P-phenyl:
2
2
134.45 [d, Co, 2J(PCo) = 13.5], 131.97 [d, Cp, 4J(PCp) = 2.7], 130.75 [d,
Ci, 1J(PCi) = 46.5], 128.53 [d, Cm, 3J(PCm) = 12.2]. MS-FAB: m/
z = 667.0 [MHꢀCl]+.
H, 3.4; N, 2.9. Found: C, 45.0; H, 3.2; N, 2.8. IR:
m
(C@N) 1588 m cmꢀ1
.
RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 7.79 [s, 1H, Hi], 7.22 [d,
1H, H11, ,
3J(H10H11) = 8.8], 6.99 [dd, 1H, H10 4J(H8H10) = 2.2], 6.63
4.3.7. Pd{4-5-(OCH2O)C6H2C(H) = NCH2CH2NMe2-C2,N}(Br)(PPh3)
(6a)
[d, 1H, H8], 6.37 [s, 1H, H3], 5.69, 5.34 [d, 2H, OCH2O, gemJ(HH) = 1.4],
1.21 [s, 9H, tBu]. MS-FAB: m/z = 1921.8 [M]+.
Compound 6a was obtained following a similar procedure that
4a but using 2a as starting material.
4.3.11. [Pd{4,5-(OCH2CH2)C6H2C(H) = N(20-O-50-tBuC6H3)-C6,N,O}]4
(1d)
RMN 1H (300 MHz, CDCl3, d ppm, J Hz, T = 223 K): d = 8.58 [d,
1H, Hi, 4J(PHi) = 8.2], 6.94 [s, 1H, H6], 5.75 [s, 2H, OCH2O], 5.66 [d,
1H, 4J(PH3) = 3.8], 4.26 [b, 2H, CH2c ], 3.05 [b, 2H, CHd2], 2.04 [b, 6H,
NMe2]. RMN 31P–{1H} (300 MHz, CDCl3, d ppm, J Hz): d = 39.63 [s].
A
pressure tube containing 4,5-(OCH2CH2)C6H3C(H) = NCH2
CH2NMe2 (0.131 g, 0.445 mmol), palladium(II) acetate (0.100 g,
0.445 mmol) and 20 cm3 of dry toluene was sealed under argon.
The resulting mixture was heated at 60 °C for 5 days. After cooling
to room temperature the solution was filtered through Celite to re-
move the small amount of black palladium formed. The solvent
was removed under vacuum to give a red oil, which was chromato-
graphed on a column packed with silica gel. Elution with dichloro-
methane afforded a red oil after solvent removal, which was
recrystallized from dichloromethane/ hexane to give the desired
product as a red solid. Yield: 61%. Anal. Calc. for C76H76N4O8Pd4:
4.3.8. Pd{2-Br-4,5-(OCH2O)C6HC(H) = NCH2CH2NMe2-C6,N,N}(PPh3)
[CF3SO3] (7a)
A solution of 3a (0.054 g, 0.122 mmol) in acetone (15 cm3) was
treated
with
silver
trifluoromethanesulfonate
(0.031 g,
0.122 mmol) and stirred for 1 h. The resulting solution was filtered
through Celite to remove the AgCl precipitate. PPh3 (0.032 g,
0.122 mmol) was added to the filtrate, the solution stirred another
24 h and the solvent removed to give a brown solid which was
recrystallized from dichloromethane/ hexane. Yield: 73%. Anal.
Calc. for C31H29N2O5F3PSBrPd: C, 45.6; H, 3.6; N, 3.4. Found: C,
C, 57.1; H, 4.8; N, 3.5. Found: C, 57.3; H, 4.7; N, 3.4. IR: m(C@N)
1578s cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 7.34 [d,
1H, H2, 3J(H2H3) = 7.9], 6.27 [d, 1H, H3], 7.14 [s, 1H, Hi], 6.97 [dd,
45.4; H, 3.5; N, 3.3. IR:
m
(C@N) 1585w,
m
(CF3SO3) 1264s, 1030s,
1H, H10,
3J(H10H11) = 8.3, 4J(H8H10) = 2.2], 6.86 [d, 1H, H11], 6.64
1227s, 1155 m cmꢀ1. RMN 1H (300 MHz, CDCl3, d ppm, J Hz):
d = 8.61 [d, 1H, Hi, 4J(PHi) = 9.7], 6.60 [s, 1H, H3], 4.55 [s, 2H,
OCH2O], 4.09 [b, 2H, CHc ], 3.10 [t, 2H, CHd, 3J(HcHd) = 6.0], 2.02
[d, 1H, H8], 4.18, 3.94 [m, 2H, CHa ], 2.79, 2.49 [m, 2H, CHb], 1.23
2
2
[s, 9H, tBu]. RMN 13C–{1H} (500 MHz, CDCl3,
d
ppm, J Hz):
d = 163.67 [s, C4], 160.72 [s, C12], 157.20 [s, C@N], 152.57 [s, C6],
143.80 [s, C9], 139.72 [s, C1], 136.03 [s, C7], 133.95 [s, C5], 129.07
[s, C3], 126.21 [s, C10], 122.46 [s, C8], 111.61 [s, C11], 104.38 [s,
2
2
[s, 6H, NMe2]. RMN 31P–{1H} (300 MHz, CDCl3, d ppm, J Hz):
d = 33.17 [s]. RMN 13C–{1H} (500 MHz, CDCl3,
d ppm, J Hz):
d = 175.24 [d, C@N, 3J(PC@N) = 3.5], 150.64, 150.20 [s, d, C5/C4,
J(PC) = 2.6], 142.47 [s, C1], 132.87 [s, C6], 116.93 [s, C2], 110.27 [s,
C3], 99.31 [s, OCH2O], 67.54 [s, CHd], 52.96 [s, CHc ], 48.49 [s,
C2], 71.93 [s, CHa ], 34.04 [s, C(CH3)3], 31.31 [s, C(CH3)3], 28.66 [s,
2
CHb2]. MS-FAB: m/z = 1598.1 [MH]+.
2
2
NMe2]. P-phenyl: 134.35 [d, Co, 2J(PCo) = 12.6], 131.68 [d, Cp,
4J(PCp) = 2.2], 131.74 [d, Ci, 1J(PCi) = 50.9], 128.87 [d, Cm,
3J(PCm) = 11.1]. MS-FAB: m/z = 665.0 [MH]+. Specific molar conduc-
tivity, Km = 117.8 ohmꢀ1 cm2 molꢀ1 (in acetonitrile).
4.3.12. [Pd{2-Br-4,5-(OCH2O)C6HC(H) = N(20-(O)-50-tBuC6H3)-
C6,N,O}(PPh3)] (2c)
PPh3 (0.016 g, 0.062 mmol) was added to a suspension of 1c
(0.030 g, 0.016 mmol) in acetone (15 cm3). The mixture was stirred

L. Naya et al. / Inorganica Chimica Acta 370 (2011) 89–97
97
[8] M. Weck, C.W. Jones, Inorg. Chem. 46 (2007) 1865.
[9] R. Johansson, O.L. Wendt, Dalton Trans. 488 (2007).
[10] M. Marcos, in: J.L. Serrano (Ed.), Metallomesogens. Synthesis, Properties and
Applications, VCH, Weinheim, 1996.
[11] D. Pucci, G. Barneiro, A. Bellusci, A. Crispini, M. Ghedini, J. Organomet. Chem.
691 (2006) 1138.
[12] M.l.S. Lowry, S. Bernhard, Chem. Eur. J. 12 (2006) 7970.
[13] M. Ghedini, I. Aiello, A. Crispini, A. Golemme, M. La Deda, D. Pucci, Coord.
Chem. Rev. 250 (2006) 1373.
[14] S.C.F. Kui, I.H.T. Sham, C.C.C. Cheung, C.-W. Ma, B. Pan, N. Zhu, C.M. Che, W.-F.
Fu, Chem. Eur. J. 13 (2007) 417.
[15] L.-L. Wu, C.-H. Yang, I.-W. Sun, S.-Y. Chu, P.-C. Kao, H.-H. Huang,
Organometallics 26 (2007) 2017.
[16] A. Habtemariam, B. Watchman, B.S. Potter, R. Palmer, S. Parsons, A. Parkin, P.J.
Sadler, J. Chem. Soc., Dalton Trans. 1306 (2001).
[17] A. Gómez-Quiroga, C. Navarro-Ranninger, Coord. Chem. Rev. 248 (2004) 119.
[18] J. Ruiz, J. Lorenzo, L. Sanglas, N. Cutillas, C. Vicente, M.D. Villa, F.X. Avilés, G.
López, V. Moreno, J. Pérez, D. Bautista, Inorg. Chem. 45 (2006) 6347.
[19] J.M. Vila, M.T. Pereira, E. Gayoso, M. Gayoso, Transition Met. Chem. 311 (1986)
342.
[20] B. Teijido, A. Fernández, M. López-Torres, S. Castro-Juiz, A. Suárez, J.M.
Ortigueira, J.M. Vila, J.J. Fernández, J. Organomet. Chem. 598 (2000) 71.
[21] S. Castro-Juiz, M. López-Torres, A. Fernández, R. Mosteiro, A. Suárez, J.M. Vila,
J.J. Fernández, Polyhedron 20 (2001) 2945.
for 24 h and the solvent removed to give a violet solid which was
recrystallized from acetone/hexane. The solution was filtered, sol-
vent removed at reduced pressure and the desired product obtained
as a violet solid. Yield: 24%. Anal. Calc. for C36H31NO3BrPPd: C, 58.2;
H, 4.2; N, 1.9. Found: C, 58.0; H, 4.3; N, 1.8. IR: m .
(C@N) 1582 m cmꢀ1
RMN 1H (300 MHz, CDCl3, d ppm, J Hz): d = 8.28 [b, 1H, Hi], 7.01 [d,
1H, H8, 4J(H8H10) = 2.3], 6.95 [dd, 1H, H10, 3J(H10H11) = 8.8], 6.47 [s,
t
1H, H3], 6.28 [d, 1H, H11], 4.73 [s, 2H, OCH2O], 1.25 [s, 9H, Bu].
RMN 31P–{1H} (300 MHz, CDCl3, d ppm, J Hz): d = 29.57 [s]. RMN
13C–{1H} (500 MHz, CDCl3, d ppm, J Hz): d = 171.25 [s, C12], 155.76
[s, C@N], 151.18 [s, C4], 148.90 [s, C5], 146.45 [s, C9], 137.25 [s, C1],
135.22 [s, C7], 132.94 [s, C6], 127.98 [s, C10], 120.74 [s, C8], 114.99
[s, C2], 111.79 [s, C11], 108.82 [s, C3], 99.18 [s, OCH2O], 33.86 [s,
C(CH3)3], 31.55 [s, C(CH3)3]. P-phenyl: 132.12 [d, Co, 2J(PCo) = 9.9],
131.97 [d, Cp, 4J(PCp) = 2.7], 128.454 [d, Cm, 3J(PCm) = 12.1]. MS-
FAB: m/z = 743.0 [MH]+.
4.4. X-ray crystallographic study
[22] L. Naya, D. Vázquez-García, M. López-Torres, A. Fernández, J.M. Vila, N. Gómez-
Blanco, J.J. Fernández, J. Organomet. Chem. 693 (2008) 685.
[23] J.M. Vila, A. Suárez, M.T. Pereira, E. Gayoso, M. Gayoso, Polyhedron 6 (1987)
1003.
[24] A. Fernández, P. Uría, J.J. Fernández, M. López-Torres, A. Suárez, D. Vázquez-
García, M.T. Pereira, J.M. Vila, J. Organomet. Chem. 620 (2001) 8.
[25] A. Fernández, D. Vázquez-García, J.J. Fernández, M. López-Torres, A. Suárez, S.
Castro-Juíz, J.M. Vila, New J. Chem. 26 (2002) 398.
[26] A. Fernández, D. Vázquez-García, J.J. Fernández, M. López-Torres, A. Suárez,
J.M. Vila, J. Organomet. Chem. 690 (2005) 3669.
[27] J.J. Fernández, A. Fernández, D. Vázquez-García, M. López-Torres, A. Suárez, N.
Gómez-Blanco, J.M. Vila, Eur. J. Inorg. Chem. (2007) 5408.
[28] A. Amoedo, M. Graña, J. Martínez, M.T. Pereira, M. López-Torres, A. Fernández,
J.J. Fernández, J.M. Vila, Eur. J. Inorg. Chem. (2002) 613.
Three-dimensional, room temperature X-ray data were collected
on a Bruker Smart 1 K CCD and a Bruker X8 Apex diffractometeres
using graphite-monochromated Mo Ka radiation. All the measured
reflections were corrected for Lorentz and polarisation effects and
for absorption by semi-empirical methods based on symmetry-
equivalent and repeated reflections. The structures were solved by
direct methods and refined by full matrix least squares on F2. Hydro-
gen atoms were included in calculated positions and refined in rid-
ing mode. The chloroform solvent molecule in the crystal of
complex 1d were poorly defined and the Cl(1), Cl(2) and Cl(3) chlo-
rine atoms were disordered and, consequently, refined in two com-
plementary positions with occupancies of 56% and 44%. Disorder
also affected to the C(15), C(16) and C(17) carbon atoms of the
tert-butyl group; the refinement was carried out taking into account
two components with occupancies of approximately 80% and 20 %.
PLATON/SQUEEZE [55] was used to remove the effects of four ill de-
fined solvent molecules (four voids per unit cell, volume 1440 Å3,
15% of the total, electrons count 112) from the data. Refinement
converged with allowance for thermal anisotropy of all non-hydro-
gen atoms. The structure solution and refinement were carried out
using the program package SHELX-97 [56].
[29] J. Martínez, L. Adrio, J.M. Antelo, J.M. Ortigueira, M.T. Pereira, M. López-Torres,
J.M. Vila, J. Organomet. Chem. 691 (2006) 2891.
[30] H. Onoue, I. Moritani, J. Organomet. Chem. 43 (1972) 431.
[31] Y.A. Ustinyuk, V.A. Chertov, I.V. Barinov, J. Organomet. Chem. 29 (1971) C53.
[32] P.J. Steel, G.B. Caygill, J. Organomet. Chem. 327 (1987) 101.
[33] P. Dotta, P.G.A. Kumar, P.S. Pregosin, A. Albinati, S. Rizatto, Organometallics 23
(2004) 4247.
[34] A. Fernández, J.J. Fernández, M. López-Torres, A. Suárez, J.M. Ortigueira, J.M.
Vila, H. Adams, J. Organomet. Chem. 612 (2000) 85.
[35] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fifth ed., Wiley & Sons, New York, 1997.
[36] L. Tusek-Bozic, M. Curic, P. Traldi, Inorg. Chim. Acta 254 (1997) 49.
[37] L. Tusek-Bozic, M. Komac, M. Curic, A. Lycka, M. Dálpaos, V. Scarcia, A. Furlani,
Polyhedron 19 (2000) 937.
[38] P.S. Pregosin, R.W. Kuntz, in: P. Diehl, E. Fluck, R. Kosfeld (Eds.), 31P and 13C
NMR of Transition Metal Phosphine Complexes, Springer, Berlin, 1979.
[39] C. Chen, Y. Liu, S. Peng, S. Liu, J. Organomet. Chem. 698 (2004) 1806.
[40] H. Yang, M.A. Khan, K.M. Nicholas, J. Chem. Soc., Chem. Commun. (1992) 210.
[41] A. Fernández, D. Vázquez-García, J.J. Fernández, M. López-Torres, A. Suárez, S.
Castro-Juiz, J.M. Vila, New J. Chem. 26 (2002) 105.
Acknowledgements
We thank the Ministerio de Educación y Ciencia (Projects
CTQ2006-15621-C02-02/BQU, UDC, and CTQ2006-15621-C02-01/
BQU, USC) and the Xunta de Galicia (Ref. PGIDIT04PXI10301IF
and INCITE08E1R103020ES) for financial support.
[42] C. López, A. Caubet, S. Pérez, X. Solans, M. Font-Bardía, J. Organomet. Chem.
681 (2003) 82.
[43] J.M. Vila, M.T. Pereira, J.M. Ortigueira, M. López-Torres, D. Lata, M. Graña, A.
Suárez, J.J. Fernández, A. Fernández, J. Chem. Soc., Dalton Trans. (1999) 4193.
[44] D. Vázquez-García, A. Fernández, J.J. Fernández, M. López-Torres, A. Suárez,
J.M. Ortigueira, J.M. Vila, H. Adams, J. Organomet. Chem. 595 (2000) 199.
[45] J.J. Fernández, A. Fernández, D. Vázquez-García, M. López-Torres, A. Suárez,
J.M. Vila, Polyhedron 26 (2007) 4567.
Appendix A. Supplementary material
CCDC 769674, 769672 and 769673 contain the supplementary
crystallographic data for 2a, 1c and 1d, respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic 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.ica.2011.01.027.
[46] J.M. Vila, M. Gayoso, M.T. Pereira, M. López-Torres, J.J. Fernández, A. Fernández,
J.M. Ortigueira, J. Organomet. Chem. 532 (1997) 171.
[47] A. Fernández, M. López-Torres, A. Suárez, J.M. Ortigueira, M.T. Pereira, J.J.
Fernández, J.M. Vila, H. Adams, J. Organomet. Chem. 598 (2000) 1.
[48] G. García-Herbosa, A. Muñoz, D. Miguel, S. García Granda, Organometallics 13
(1994) 1775.
[49] F. Neve, A. Crispín, C. Di Pietro, S. Campagna, J. Organomet. Chem. 21 (2002)
3511.
[50] J.M. Vila, M. Gayoso, M.T. Pereira, J.M. Ortigueira, A. Fernández, N.A. Bailey, H.
Adams, Polyhedron 12 (1993) 171.
[51] J.M. Vila, J.M. Ortigueira, M. López-Torres, J.J. Fernández, A. Fernández, Acta
Crystallogr., Sect. C C55 (1999) 1646.
[52] G. Zhao, Q.G. Wang, T.C.W. Mak, Organometallics 17 (1998) 3437.
[53] Y. Elerman, A. Elmali, O. Atakol, I. Svoboda, Acta Crystallogr., Sect. C 51 (1995)
2344.
[54] W.L.F. Armarego, C.L.L. Chai, Purification of Laboratory Chemicals, fifth ed.,
Butterworth-Heinemann, Bodmin, 2003.
References
[1] J.P. Kleinmann, M. Dubeck, J. Am. Chem. Soc. 86 (1963) 1544.
[2] A.C. Cope, R.W. Siekman, J. Am. Chem. Soc. 87 (1965) 3272.
[3] S.P. Flanagan, R. Goddard, P.J. Guiry, Tetrahedron 61 (2005) 9808.
[4] L. Tang, Y. Zhang, L. Ding, Y. Li, K.-F. Mok, W.-C. Yeo, P.-H. Leung, Tetrahedron
Lett. 48 (2007) 33.
[5] S.-W. Lai, T.-C. Cheung, M.C.W. Chan, K.-K. Cheung, S.-M. Peng, C.-M. Che,
Inorg. Chem. 39 (2000) 255.
[6] J. Dupont, C.S. Consorti, J. Spencer, Chem. Rev. 105 (2005) 2527.
[7] H.-Y. Thu, W.-Y. Yu, C.-M. Che, J. Am. Chem. Soc. 128 (2006) 9048.
[55] A.L. Speck, Acta Crystallogr., Sect. A 46 (1990) C34.
[56] G.M. Sheldrick, SHELX-97, An Integrated System for Solving and Refining Crystal
Structures from Diffraction Data, University of Göttingen, Germany, 1997.