Tetranuclear complexes of PdII with tridentate [C,N,O] and [O,N,O] ligands: Synthesis, reactivity and structural isomerism

Article abstract of DOI:10.1002/ejic.200700478

Treatment of the Schiff base ligand 2,3,4-(MeO)₃-C ₆H₂C(H)=N[2-(OH)-5-tBuC₆H₃] (a) with palladium(II) acetate in toluene gave the cyclometallated complex [Pd{2,3,4-(MeO)₃C₆HC(H)=N(2-O-5-tBuC₆H ₃)}]₄ (1a) with the tridentate ligand [C,N,O]. The complex showed a tetranuclear arrangement of the cyclometallated monomers with a P ₄O₄ core. Reaction of 2,6-(Me)₂C ₆H₃C(H)=N[2-(OH)C₆H₄] (b) and 2,5-(Me)₂C₆H₃C(H)=N[2-(OH)C₆H ₄] (c) with palladium(II) acetate under similar conditions yielded the tetranuclear complexes [Pd{6-Me-2-CH₂C₆H ₃C(H)=N(2-OC₆H₄)}]₄ (1b) and [Pd{5-Me-2-CH₂C₆H₃C(H)=N(2-OC₆H ₄)}]₄ (1c), respectively, in which the tridentate [C,N,O] ligand is bound through the aliphatic methyl carbon. Treatment of 2,4-(Me) ₂-C₆H₃C(H)=N[2-(OH)C₆H₄] (d) with palladium(II) acetate yielded a mixture of isomers, [Pd{4-Me-2-CH ₂C₆H₃C(H)=N-(2-OC₆H ₄)}]_n[Pd{2,4-(Me)₂C₆H ₂C(H)=N(2-OC₆H₄)}]_4-n (n = 0-4), also bearing a tetranuclear structure. However, the tetramer was assembled by two types of mononuclear Pd(ligand) building blocks: the ligand is coordinated through the aliphatic methyl carbon in one and through the aromatic ortho carbon in the other. The crystal structure of one such isomer confirmed the spectroscopic data. Treatment of 2-(OH)-4,6-(MeO)₂C₆H ₂C(H)=N[2-(OH)C₆H₄] (e) and 2-(OH)C ₆H₄-C(H)=N[2-(OH)C₆H₄] (f) with palladium(II) acetate yielded the tetranuclear complexes [Pd{2-O-4,6-(MeO) ₂C₆H₂C(H)=N(2-OC₆H ₄)}]₄ (1e) and [Pd{2-OC₆H₄C(H)=N(2- OC₆H₄)}]₄ (1f), respectively, after double deprotonation of the ligand, which coordinates to the metal through the two phenoxy oxygen atoms and the imine nitrogen atom in these complexes. Reaction of compounds 1a-1f with tertiary phosphanes in acetone gave mono- and dinuclear complexes, after cleavage of the tetranuclear structure. In these complexes, the tertiary phosphane is bonded trans to the nitrogen atom. The crystal structures for 1a, 1c, 1e, 1d/1d′ are reported; they show the characteristic Pd ₄O4 core. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700478

FULL PAPER
DOI: 10.1002/ejic.200700478
Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands:
Synthesis, Reactivity and Structural Isomerism
Jesús J. Fernández,*[a] Alberto Fernández,[a] Digna Vázquez-García,[a]
Margarita López-Torres,[a] Antonio Suárez,[a] Nina Gómez-Blanco,[a] and José M. Vila*[b]
Keywords: Palladium / Cyclometallation / Metallacycles / Tridentate [C,N,O] ligands / C–H activation
Treatment of the Schiff base ligand 2,3,4-(MeO)3-
C6H2C(H)=N[2-(OH)-5-tBuC6H3] (a) with palladium(II) ace-
tate in toluene gave the cyclometallated complex [Pd{2,3,4-
(MeO)3C6HC(H)=N(2-O-5-tBuC6H3)}]4 (1a) with the triden-
tate ligand [C,N,O]. The complex showed a tetranuclear ar-
rangement of the cyclometallated monomers with a P4O4
core. Reaction of 2,6-(Me)2C6H3C(H)=N[2-(OH)C6H4] (b) and
2,5-(Me)2C6H3C(H)=N[2-(OH)C6H4] (c) with palladium(II)
acetate under similar conditions yielded the tetranuclear
complexes [Pd{6-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]4 (1b)
and [Pd{5-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]4 (1c), respec-
tively, in which the tridentate [C,N,O] ligand is bound
through the aliphatic methyl carbon. Treatment of 2,4-(Me)2-
C6H3C(H)=N[2-(OH)C6H4] (d) with palladium(II) acetate
yielded a mixture of isomers, [Pd{4-Me-2-CH2C6H3C(H)=N-
aliphatic methyl carbon in one and through the aromatic or-
tho carbon in the other. The crystal structure of one such iso-
mer confirmed the spectroscopic data. Treatment of 2-(OH)-
4,6-(MeO)2C6H2C(H)=N[2-(OH)C6H4] (e) and 2-(OH)C6H4-
C(H)=N[2-(OH)C6H4] (f) with palladium(II) acetate yielded
the tetranuclear complexes [Pd{2-O-4,6-(MeO)2C6H2C(H)=
N(2-OC6H4)}]4 (1e) and [Pd{2-OC6H4C(H)=N(2-OC6H4)}]4
(1f), respectively, after double deprotonation of the ligand,
which coordinates to the metal through the two phenoxy oxy-
gen atoms and the imine nitrogen atom in these complexes.
Reaction of compounds 1a–1f with tertiary phosphanes in
acetone gave mono- and dinuclear complexes, after cleavage
of the tetranuclear structure. In these complexes, the tertiary
phosphane is bonded trans to the nitrogen atom. The crystal
structures for 1a, 1c, 1e, 1d/1dЈ are reported; they show the
characteristic Pd4O4 core.
(2-OC6H4)}]n[Pd{2,4-(Me)2C6H2C(H)=N(2-OC6H4)}]4–n (n
=
0–4), also bearing a tetranuclear structure. However, the
tetramer was assembled by two types of mononuclear Pd(li-
gand) building blocks: the ligand is coordinated through the
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
planar palladium(II) units have been of great interest in
view of their potential applications.[25] Nevertheless, few ex-
amples of supramolecular species with cyclometallated
building blocks have been reported,[26–31] many of which
correspond to tetrameric assemblies derived from palladi-
um(II) cyclometallated complexes with [C,N,X] (X = O, S)
tridentate ligands. Thus, for the [C,N,S] species, thiosemi-
carbazones give tetranuclear structures with an eight-mem-
bered Pd4S4 core,[32–34] and tetranuclear cluster complexes
derived from benzothiazolines[35,36] are also known. As for
the [C,N,O] derivatives,[37–40] they also exhibit an analogous
tetranuclear structure with a Pd4O4 core. In order to attain
neutrality the ligand is usually deprotonated in the com-
plex, at the hydrazine nitrogen atom, at the benzothiazoline
nitrogen atom or at the phenol oxygen atom. Even when
there is no metal–carbon bond formation, the tetranuclear
structure is reached only after deprotonation, as has been
reported for a coordination compound derived from a
[N,N,S] ligand.[41]
Introduction
Cyclometallated compounds have been extensively sur-
veyed,[1–5] and they exhibit a good number of applications
related to organic as well as to organometallic compounds,
metallomesogens and catalytic materials;[6–13] they also pro-
mote unusual coordination environments.[14] The more
common cyclometallated complexes encountered in the lit-
erature are the palladium(II) five-membered ring species af-
ter activation of aromatic C(sp2) atoms. Analogous com-
pounds containing alkyl C(sp3)–Pd bonds are also known
although these are more scarce.[15–19]
On the other hand, the building of supramolecular as-
semblies has also attracted much attention in the past
years,[20–24] and among these, examples containing square-
[a] Departamento de Química Fundamental, Universidad de
La Coruña,
15071 La Coruña, Spain
Fax: +34-981-167065
E-mail: qiluaafl@udc.es
The purpose of this paper is twofold: first, to study the
activation of aromatic carbon atoms against aliphatic car-
bon atoms by checking the bonding possibilities of N-phe-
nol Schiff base ligands, and secondly, to determine the
[b] Departamento de Química Inorgánica, Universidad de
Santiago de Compostela,
15782 Santiago de Compostela, Spain
Fax: +34-981-595012
E-mail: qideport@usc.es
5408
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5408–5418

Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands
structural particularity of the resulting complexes in terms lation was not accomplished in any instance; the deproton-
of their polynuclear nature.
ation of both phenoxy groups favoured the coordination of
the ligands as [O,N,O]. In all the cases depicted above the
resulting products after palladation of the ligands were tet-
ranuclear compounds, irrespective of the metallated atom,
including the [O,N,O] bonded ligands.
Results and Discussion
The ligands employed provide several coordination ap-
proaches as a function of the substitution pattern of the
phenyl ring. Thus, only a, c, d and f have available aromatic
sp2 carbon atoms suitable for metallation, as well as MeO,
Me and OH substituents liable to carbon–metal and oxy-
gen–metal bond formation. On the other hand, b and e may
bind to the metal only through the MeO or OH groups;
accordingly, different alternatives of palladation were
found. Hence, in a the metal atom was found to be bonded
exclusively through the C-6 atom, with no sign of metalla-
tion of the C-2 methoxy group, resulting in the formation
of a five-membered palladated ring. For b and c, either the
C-2 Me group or the C-6 Me group was metallated to
render a six-membered palladated ring in each case. Metal-
lation of the C-6 carbon atom in ligand c was not observed,
quite possibly because of the steric hindrance imposed by
the neighbouring C-5 Me group. The reaction of ligand d
with palladium acetate provided a mixture of products, one
rendering metallation at the aromatic C-6 atom, and an-
other one at the aliphatic C-2 Me group, yielding –CH2–
Pd bond formation. Most outstanding for the tetranuclear
structure of the d species was that, as opposed to the
For the convenience of the reader the compounds and
[C,N,S] or [C,N,O] tetramers previously reported where the reactions are shown in Schemes 1, 2, 3 and 4. The com-
four cyclometallated moieties were identical, the present pounds described in this paper were characterized by ele-
1
case poses an unprecedented example of a tetranuclear mental analysis (C, H, N), by IR and H, 31P{1H} NMR
structure with two distinct palladated groups having five spectroscopy, and, in part, by FAB mass spectrometry and
and six-membered metallated rings. As for e and f, C-metal- single-crystal X-ray diffraction (Experimental Section).
Scheme 1. (i) Pd(AcO)2, (toluene); (ii) PPh3 (acetone, 1:4 molar ratio); (iii) diphosphane (acetone, 1:2 molar ratio).
Eur. J. Inorg. Chem. 2007, 5408–5418
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5409

J. J. Fernández, J. M. Vila et al.
FULL PAPER
The reaction of a with palladium(II) acetate in toluene Table 1. Selected bond lengths [Å] and angles [°] for complex 1a.
at 60 °C gave [Pd{2,3,4-(MeO)3C6HC(H)=N(2-O-5-
Pd1–C1
Pd1–N1
Pd1–O1
Pd1–O9
Pd2–C21
Pd2–N2
Pd2–O5
Pd2–O13
1.958(14) Pd3–C41
1.967(10) Pd3–N3
1.966(13)
1.953(10)
2.047(8)
2.134(8)
1.953(13)
1.961(10)
2.034(8)
2.138(9)
3.4120(14)
82.4(5)
96.8(4)
81.8(4)
99.1(3)
82.2(5)
tBuC6H3)}]4 (1a) as an air-stable solid, which was fully
characterized. The IR spectrum showed the shift of the
ν(C=N) stretch toward lower wavenumbers from the free
ligand value, because of nitrogen coordination of the
imine,[42,43] and the absence of the ν(O–H) stretch, as com-
pared to the ligand (3427 cm–1), in accordance with loss of
the –OH proton. In the 1H NMR spectrum the HC=N and
5-H resonances were high-field shifted, as compared to the
uncoordinated ligand, by 1.43 and 0.9 ppm, respectively;
the low δ values in these cases were due to the structure of
the complexes, which puts the HC=N and 5-H protons in
the proximity of the shielding zone of the phenyl rings of a
neighbouring metallated ligand.[32,33,37,39] Likewise, absence
2.144(9)
2.045(8)
Pd3–O5
Pd3–O9
1.965(13) Pd4–C61
1.951(10) Pd4–N4
2.122(8)
2.052(9)
Pd4–O1
Pd4–O13
Pd1–Pd2
3.3776(14) Pd3–Pd4
C1–Pd1–N1
C1–Pd1–O9
N1–Pd1–O1
O9–Pd1–O1
C21–Pd2–N2
C21–Pd2–O13
N2–Pd2–O5
O13–Pd2–O5
Pd4–O1–Pd1
Pd1–O9–Pd3
82.6(6)
96.6(5)
81.6(4)
99.3(3)
82.8(5)
96.8(5)
81.5(4)
99.0(3)
115.4(4)
119.0(4)
N3–Pd3–C41
C41–Pd3–O5
N3–Pd3–O9
O5–Pd3–O9
C61–Pd4–N4
C61–Pd4–O1
N4–Pd4–O13
O1–Pd4–O13
Pd3–O5–Pd2
Pd2–O13–Pd4
96.0(5)
81.7(4)
100.0(3)
116.0(4)
114.5(4)
1
of the OH resonance in the H NMR spectrum confirmed
deprotonation.
The FAB mass spectra showed the cluster of peaks char-
acteristic of the [MH]+ fragment centred at 1792 uma; the
isotopic pattern was in good agreement with the tetrameric
formulation.
Crystal Structure of 1a
Suitable crystals were grown by slowly evaporating chlo-
roform from a solution. Crystal data are given in Table 1.
The ORTEP illustration of complex 1a·H2O is shown in
Figure 1. The core of the tetrameric molecule consists of an
eight-membered ring of alternating palladium and oxygen
atoms. 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 ligand monomer, in a slightly
distorted square-planar arrangement. The mean deviations
from the least-squares plane are: Pd1, C1, N1, O1, O9,
0.0215 Å; Pd2, C21, N2, O5, O13, 0.0208 Å; Pd3, C41, N3,
O5, O9, 0.0166 Å; Pd4, C69, N4, O1, O13, 0.0300 Å. The
bond lengths at palladium are within the expected val-
ues.[37–40] The resulting cluster has approximate C2 sym-
metry; the C2 axis is perpendicular to and bisects Pd1···Pd2
and Pd3···Pd4. The Pd1···Pd2 and Pd3···Pd4 distances of
3.378(1) and 3.412(1) Å, respectively, preclude any Pd–Pd
interactions. Two of the quasi-planar Pd ligand units are
parallel and almost orthogonal to the other two parallel
monomer moieties.
Figure 1. Molecular structure of [Pd{2,3,4-(MeO)3C6HC(H)=N(2-
O-5-tBuC6H3)}]4 (1a). tBu groups have been omitted for clarity.
Ellipsoids drawn at 40% level.
= 3.4 and 10.7 Hz, respectively), and the 31P{1H} NMR
Treatment of 1a with triphenylphosphane or diphospha- spectrum showed the phosphorus resonance as a singlet at
nes (dppm, dppe) gave the mononuclear [Pd{2,3,4-(MeO)3- δ = 34.2 ppm; these findings were in agreement with an ar-
C6HC(H)=N(2-O-5-tBuC6H3)}(PPh3)] (2a) or dinuclear rangement in which the phosphorus atom is trans to the
[{Pd(2,3,4-{MeO}3C6HC{H}=N{2-O-5-tBuC6H3})}2(µ- nitrogen atom.[44–47] The HC=N proton resonance, at δ =
PPh2CH2PPh2)] (3a) and [{Pd(2,3,4-{MeO}3C6HC{H}= 8.14 ppm, showed a smaller high-field shift than that in
N{2-O-5-tBuC6H3})}2{µ-PPh2(CH2)2PPh2}] (4a) species, as compound 1a, as compared to the free ligand, in agreement
air-stable solids, which were fully characterized (Experimen- with the opening of the polynuclear structure.[39] Only one
tal Section), with opening of the polynuclear structure after singlet was observed in the 31P{1H} NMR spectra of 3a
P–Obridging bond cleavage; the Pd–Ochelating bond remained and 4a for the two equivalent phosphorus nuclei.
1
intact in all cases. The H NMR spectrum of 2a showed
The reaction of b and c with palladium(II) acetate in
the resonances of the 5-H and HC=N protons as doublets, toluene at 60 °C gave the tetranuclear complexes [Pd{6-Me-
coupled to the 31P nucleus of the phosphane ligand (JH,P 2-CH2C6H3C(H)=N(2-OC6H4)}]4 (1b) and [Pd{5-Me-2-
5410
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Eur. J. Inorg. Chem. 2007, 5408–5418

Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands
Scheme 2. (i) Pd(AcO)2, (toluene); (ii) PPh3 (acetone, 1:4 molar ratio); (iii) diphosphane (acetone, 1:2 molar ratio).
CH2C6H3C(H)=N(2-OC6H4)}]4 (1c), respectively, as air- yields 2c in solution. The presence of weak and poorly re-
stable solids which were fully characterized (Experimental solved signals has been observed earlier in a similar com-
Section). Bonding of the metal was attained through a plex.[37]
methyl group in both cases; the integration for the multiplet
The synthesis of 1c is one of the rare examples where
1
signals in the H NMR spectrum of 1c showed that the C- activation of an aliphatic carbon, rather than an aromatic
6 atom was not metallated. The spectroscopic data was in carbon, is preferred for metallation.[15–19] This is particu-
agreement with nitrogen coordination of the C=N group larly interesting because activation of the aliphatic carbon
and deprotonation of the phenoxy group, vide supra implies the formation of a six-membered chelate ring as op-
(Scheme 2, see the Experimental Section). The resonances posed to the more stable five-membered one.
at δ ≈ 3.5 ppm and δ ≈ 2.5 ppm were assigned to the AB
system of the two nonequivalent methylene protons (JH,H
= 13.6 and 14.1 Hz for 1b and 1c, respectively). Their dia-
stereotopic nature follows from the tetrameric structure of
Crystal Structure of 1c
the complex, which renders both methylene protons, on
Suitable crystals were grown by slowly evaporating chlo-
either side of the metallated moiety, magnetically nonequiv- roform from a solution. Crystal data are given in Table 2.
alent (see the crystal structure of 1c). The singlet resonance The ORTEP illustration of complex 1c is shown in Figure 2.
at δ = 2.28 ppm (1b) and δ = 2.44 ppm (1c) were assigned Compound 1c shows as tetranuclear structure with a Pd4O4
to the nonmetallated methyl groups. An interesting feature core similar to that described for 1a; the most noticeable
1
in the H NMR spectrum of 1c is the presence of weak difference being the metallated carbon, which in this case
signals, four low-intensity doublets ascribed to the 11-H was an sp3 CH2 carbon as opposed to the aromatic sp2
and CH2 protons were identified, which could be indicative carbon atom in 1a. The coordination geometry about the
of the presence of other species in solution. However, we palladium atoms is slightly distorted square-planar. The
were unable to isolate the minor components of the mixture mean deviations from the least-squares plane are: Pd1, C14,
by column chromatography or by any other methods. The N1, O1, O2, 0.0271 Å; Pd2, C34, N2, O2, O1#1, 0.0342 Å.
1H NMR spectrum of 1c recorded at 323 K displayed the The bond lengths and angles are in the range of those pre-
same weak signals with no appreciable difference in either viously reported.[16,18,37–40] Another central feature of this
the chemical shift or in the relative intensities. When 1c was complex is the planar disposition of the six-membered cy-
treated with triphenylphosphane to give the mononuclear clometallated ring.
complex 2c, vide infra, only the signals corresponding to
Several structures of cyclometallated complexes derived
this complex appeared in its spectrum; this seems to suggest from Schiff bases in which the ligand is coordinated
that the weak resonances mentioned above could be due to through a CH2 carbon have been described previously;
a different grouping of the cyclometallated monomer frag- however, with the exception of a recent example reported
ments in the polynuclear structure, which when cleaved only by us,[48] in the remaining cases the six-membered cyclo-
Eur. J. Inorg. Chem. 2007, 5408–5418
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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J. J. Fernández, J. M. Vila et al.
FULL PAPER
Table 2. Selected bond lengths [Å] and angles [°] for complex 1c.
a complex mixture, as an outcome of which only five par-
tially overlapped doublets, of the ten required, were as-
signed to the CH2 protons at δ ≈ 3.5–4.0 ppm. The signals
corresponded to the isomers bearing a metallated methyl
group, [Pd{4-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]n[Pd{2,4-
(Me)2C6H2C(H)=N(2-OC6H4)}]4–n (n = 1, 3, 4) and two
isomers with n = 2, depending on whether the two cyclo-
metallated monomers [Pd{4-Me-2-CH2C6H3C(H)=N(2-
OC6H4)}] were opposite or adjacent in the tetranuclear ar-
rangement (a sixth isomer is possible when metallation is
through the C-6 carbon atom: [Pd{2,4-(Me)2C6H2C-
(H)=N(2-OC6H4)}(PPh3)]4). Surprisingly, the 1H NMR
spectrum recorded in a donor solvent such as [D6]dmso
showed two singlet signals at δ = 8.82 ppm and δ =
8.41 ppm assigned to two chemically different HC=N pro-
tons, putting forward the existence of only two species in
the solution in the aftermath of the tetranuclear structure
break-up caused by coordination of the solvent, which
yielded the mononuclear fragments [Pd{4-Me-2-CH2C6-
H3C(H)=N(2-OC6H4)}([D6]dmso)], 1d(dmso), and [Pd{2,4-
Pd1–C14
Pd1–N1
Pd1–O1
Pd1–O2
Pd1–Pd1#1
N1–Pd1–C14
N1–Pd1–O1
C14–Pd1–O2
O2–Pd1–O1
Pd1–O2–Pd2
1.985(9)
1.976(6)
2.123(5)
2.077(6)
3.2441(12)
95.1(3)
82.1(2)
89.6(3)
93.2(2)
119.3(3)
Pd2–C34
Pd2–N2
Pd2–O2
Pd2–O1#1
Pd2–Pd2#1
N2–Pd2–C34
N2–Pd2–O2
C34–Pd2–O1#1
O1#1–Pd2–O2
Pd2#1–O1–Pd1
1.997(10)
1.967(7)
2.124(5)
2.057(6)
3.2241(12)
95.3(4)
82.0(2)
88.8(3)
93.9(2)
120.3(3)
Symmetry transformations used to generate equivalent atoms:
# 1 – x – 1/2, –y + 1/2, z
(Me)2C6H2C(H)=N(2-OC6H4)}([D6]dmso)],
1dЈ(dmso),
with C(sp3)–Pd and C(sp2)–Pd bonds, respectively (see
Scheme 3). Hence, only one singlet was observed for the
CH2 protons at 3.26 ppm, as opposed to the AB system in
the tetranuclear structure, vide supra. The relative molar
ratio of the complexes in solution was 1:0.5 [1d(dmso)/
1dЈ(dmso)]. Regardless of the reaction time and tempera-
ture used in the synthesis, the final relative molar ratio re-
Figure 2. Molecular structure of [Pd{5-Me-2-CH2C6H3C(H)=N(2-
OC6H4)}]4 (1c). Ellipsoids drawn at the 40% level.
metallated ring showed a nonplanar geometry with a boat- mained unchanged.
like structure.[16,18,49–53] We believe that in 1c the tetranu-
clear structure brings close two of the cyclometallated li-
gands, thus imposing planarity of the ring in order to avoid
mutual steric repulsion.
Treatment of 1b and 1c with triphenylphosphane yielded
the mononuclear complexes 2b and 2c, respectively, upon
cleavage of the P–Obridging bond. The 1H NMR spectra
showed a doublet resonance assigned to the two equivalent
CH2 protons, consequent on splitting of the tetranuclear
structure, coupled to the 31P nucleus, δ = 2.96 ppm (3JP,H
=
5.8 Hz) and δ = 2.93 ppm (3JP,H = 5.8 Hz) for 2b and 2c,
respectively.
The reaction of 1b with the tertiary diphosphane
Ph2P(CH2)2PPh2 (dppe) gave the dinuclear cyclometallated
complex, [{Pd(6-Me-2-CH2C6H3C{H}=N{2-OC6H4})}2{µ-
PPh2(CH2)2PPh2}] (3b), which was fully characterized. The
1H NMR spectrum showed only one set of signals for the
two cyclometallated moieties, and a singlet at δ = 33.2 ppm
in the 31P{1H} NMR spectrum was assigned to the two
equivalent phosphorus nuclei.
Scheme 3. (i) Pd(AcO)2, (toluene); (ii) PPh3 (acetone, 1:4 molar ra-
tio).
We suggest that in nondonor solvents such as chloro-
Treatment of d with palladium(II) acetate, under the form the [Pd{4-Me-2-CH2C6H3C(H)=N(2-OC6H4)}] and
same conditions as those used for the synthesis of 1a–1c, [Pd{2,4-(Me)2C6H2C(H)=N(2-OC6H4)}] building blocks
yielded a mixture of isomers, [Pd{4-Me-2-CH2C6H3C- were randomly arranged into tetranuclear moieties. There-
(H)=N(2-OC6H4)}]n and [Pd{2,4-(Me)2C6H2C(H)=N(2- fore, four isomers were present in the solution (vide supra),
OC6H4)}]4–n (n = 0–4), featuring dissimilar cyclometallated in addition to the two “pure” complexes [Pd{4-Me-2-
units arising from the different metallation site chosen by CH2C6H3C(H)=N(2-OC6H4)}]4 and [Pd{2,4-(Me)2C6H2C-
the metal: aromatic sp2 phenyl carbon atoms or aliphatic (H)=N(2-OC6H4)}]4. However, when the mixture was dis-
sp3 methyl carbon atoms. The 1H NMR spectrum in CDCl3 solved in a donor solvent the tetranuclear structure was
showed extended overlapping of the signals as expected for cleaved, and the two distinct mononuclear moieties could
5412
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5408–5418

Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands
be isolated. Another approach to the separation of the mo- found to be disordered, the major component (70%) corre-
nonuclear isomers was treatment of the complex mixture sponded to a ligand coordinated through the C7A methyl-
with triphenylphosphane in acetone, which yielded com- ene carbon and the minor component through the C6B aro-
plexes [Pd{4-Me-2-CH2C6H3C(H)=N(2-OC6H4)}(PPh3)] matic carbon. The ligand coordinated to Pd2 was also dis-
(2d) and [Pd{2,4-(Me)2C6H2C(H)=N(2-OC6H4)}(PPh3)] ordered (50% for each component) and coordinated
(2dЈ), which were fully characterized (Experimental Sec- through the C26B aromatic or the C27A aliphatic carbon
tion). The above-mentioned assumption was confirmed by atoms, respectively, for each component.
the crystal structure of one of the isomers.
Crystal Structure of the Mixture of [Pd{4-Me-2-
CH2C6H3C(H)=N(2-OC6H4)}]3[Pd{2,4-(Me)2-
C6H2C(H)=N(2-OC6H4)}]
Crystal data are given in Table 3, and the ORTEP illus-
tration is shown in Figure 3. A single crystal was isolated
from a chloroform solution of the mixture of isomers and
its resolved crystal and molecular structure showed the
characteristic tetranuclear arrangement described for 1a
and 1c bearing a central Pd4O4 core. Each palladium atom
was coordinated to the ligand d through the C=N nitrogen,
and to two phenoxy oxygen atoms, one of the latter two
pertaining to a neighbouring metallated unit. However, the
fourth coordination position was occupied by the C46 aro-
matic carbon for the Pd3 atom and by the C67 methylene
carbon atom for Pd4. The ligand coordinated to Pd1 was
Table 3. Selected bond lengths [Å] and angles [°] for complex 1d/dЈ.
Pd1–C7A
Pd1–N1
Pd1–C6B
Pd1–O4
Pd1–O1
Pd2–C26B
Pd2–N2
Pd2–C27A
Pd2–O3
Pd2–O2
1.941(10)
1.962(5)
1.99(3)
Pd3–C46
Pd3–N3
Pd3–O1
Pd3–O3
Pd4–C67
Pd4–N4
Pd4–O2
Pd4–O4
1.948(5)
1.954(4)
2.067(4)
2.142(4)
1.976(6)
1.978(5)
2.063(4)
2.124(4)
Figure 3. Molecular structure of the mixture of [Pd{4-Me-2-
CH2C6H3C(H)=N(2-OC6H4)}]n and [Pd{2,4-(Me)2C6H2C(H)=N-
(2-OC6H4)}]4–n (n = 3). Minor components of the disordered struc-
ture have been omitted for clarity. Ellipsoids drawn at the 40%
level.
2.052(4)
2.140(4)
1.926(16)
1.976(4)
2.006(10)
2.034(3)
2.136(4)
3.4385(9)
90.8(3)
86.0(6)
92.3(3)
97.1(6)
81.93(18)
95.02(17)
75.7(5)
96.4(3)
106.7(5)
86.3(3)
The reaction of e and f with palladium(II) acetate in tol-
uene gave the non-cyclometallated complexes [Pd{2-O-4,6-
Pd1–Pd2
Pd3–Pd4
3.2368(9)
81.8(2)
98.7(2)
80.93(15)
98.64(14)
93.9(2)
C7A–Pd1–N1
N1–Pd1–C6B
C7A–Pd1–O4
C6B–Pd1–O4
N1–Pd1–O1
O4–Pd1–O1
C26B–Pd2–N2
N2–Pd2–C27A
C26B–Pd2–O3
C27A–Pd2–O3
N2–Pd2–O2
O3–Pd2–O2
C46–Pd3–N3
C46–Pd3–O1
N3–Pd3–O3
O1–Pd3–O3
C67–Pd4–N4
C67–Pd4–O2
N4–Pd4–O4
O2–Pd4–O4
Pd3–O1–Pd1
Pd4–O2–Pd2
Pd2–O3–Pd3
Pd1–O4–Pd4
(MeO)2C6H2C(H)=N(2-OC6H4)}]4 (1e)
and [Pd{2-
OC6H4C(H)=N(2-OC6H4)}]4 (1f) as yellow and red air-
stable solids, respectively. The IR spectroscopic data was in
good agreement with nitrogen coordination of the im-
ine,[42,43] and absence of the ν(O–H) bands, indicated
double deprotonation of the ligands; the latter was con-
firmed by the absence of the OH resonances in the 1H
NMR spectra. While the 1H NMR spectrum for 1e showed
a high-field shift of the HC=N resonance (δ = 1.19 ppm),
similar to that observed for 1a–1c, the HC=N resonance for
89.8(2)
82.40(18)
93.96(15)
123.8(2)
119.15(19)
116.79(17)
115.5(2)
81.65(18)
95.74(15)
Scheme 4. (i) Pd(AcO)2, (toluene); (ii) PPh3 (acetone, 1:4 molar ratio).
Eur. J. Inorg. Chem. 2007, 5408–5418
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5413

J. J. Fernández, J. M. Vila et al.
FULL PAPER
1f appeared at δ = 8.94 ppm (shifted by 0.24 ppm), putting right angles. Bond lengths and angles are within the ex-
forward that the HC=N proton was not in the shielding pected values.[16,18,37–40]
area of the phenyl ring of an adjacent metallated ligand,
probably because of cleavage of the tetranuclear structure
caused by the coordination of [D6]dmso used as the NMR
Table 4. Selected bond lengths [Å] and angles [°] for complex 1e.
solvent (vide supra). The IR, NMR and mass spectra of
these complexes did not definitely establish their tetranu-
clear nature; nevertheless, resolution of the molecular struc-
ture of 1e evidenced the tetrameric arrangement of the pal-
ladated fragments (Scheme 4).
Whereas for ligand e coordination is only possible Pd2–O10
through the phenoxy oxygen atoms, ligand f holds two co-
ordination sites, the C-6 carbon and the phenoxy oxygen
atoms; however, regardless of the reaction conditions used,
the cyclometallated complex was not obtained in any case.
Pd1–O1
Pd1–O2
Pd1–O14
Pd1–N1
Pd2–O5
Pd2–O6
1.965(4)
2.013(4)
2.074(4)
1.940(4)
1.953(4)
1.999(3)
2.068(4)
1.940(4)
3.0695(8)
95.05(16
83.87(16)
87.81(15)
93.25(14)
94.98(17)
84.50(16)
87.90(14)
92.62(14)
121.28(17)
116.87(17)
Pd3–O9
Pd3–O10
Pd3–O2
Pd3–N3
Pd4–O13
Pd4–O14
Pd4–O6
Pd4–N4
1.953(4)
2.008(4)
2.076(3)
1.940(4)
1.953(4)
2.031(3)
2.057(4)
1.933(4)
3.1011(7)
95.33(16)
83.96(16)
86.65(14)
94.10(14)
95.28(16)
83.89(16)
86.32(15)
94.51(14)
120.78(18)
118.98(17)
Pd2–N2
Pd1–Pd2
N1–Pd1–O1
N1–Pd1–O2
O1–Pd1–O14
O2–Pd1–O14
N2–Pd2–O5
N2–Pd2–O6
O5–Pd2–O10
O6–Pd2–O10
Pd3–Pd4
N3–Pd3–O9
N3–Pd3–O10
O9–Pd3–O2
O10–Pd3–O2
N4–Pd4–O13
N4–Pd4–O14
O13–Pd4–O6
O14–Pd4–O6
Pd3–O10–Pd2
Pd4–O14–Pd1
Crystal Structure of 1e·2CH2Cl2
Suitable crystals were grown by slowly evaporating Pd1–O2–Pd3
dichloromethane from a solution. Crystal data are given in
Pd2–O6–Pd4
Table 4, and the ORTEP illustration of complex 1e is shown
in Figure 4. The molecular structure of 1e·2CH2Cl2 showed
a [Pd(ligand)]4 tetrameric structure, in which each palla-
The reaction of 1e and 1f with triphenylphosphane
dium atom was coordinated in a slightly distorted square- yielded the mononuclear complexes [Pd{2-O-4,6-(MeO)2-
planar geometry through the two deprotonated phenoxy C6H2C(H)=N(2-OC6H4)}(PPh3)] (2e) and [Pd{2-OC6H4C-
oxygen atoms, the C=N nitrogen and an oxygen atom from (H)=N(2-OC6H4)}(PPh3)] (2f) after cleavage of the tetranu-
another Pd(ligand) unit. The mean deviations from the le- clear structure, as air-stable solids, which were fully charac-
ast-squares plane are: Pd1, O1, O2, O14, N1, 0.0091 Å; terized. The 31P NMR spectroscopic data were in accord-
Pd2, O5, O6, O10, N2, 0.0015 Å; Pd3, O2, O9, O10, N3, ance with an arrangement in which the phosphorus atom is
0.0285 Å; Pd4, O6, O13, O14, N4, 0.0074 Å. The core was trans to the nitrogen atom. Contrary to the case of five-
formed by an eight-membered Pd4O4 ring of similar geome- membered ring palladacycles, the 3-H protons and (in 2e)
try to those described above. Each palladium atom belongs the C-4 MeO group were not affected by shielding from the
to two fused five- and six-membered rings, which are phosphane phenyl rings; expansion of the metallated ring to
planar, and coplanar with the two phenol rings. The four six members places these nuclei away form the appropriate
units are arranged as parallel pairs in two sets at nearly shielding zone.
Figure 4. Molecular structure of [Pd{2-O-4,6-(MeO)2C6H2C(H)=N(2-OC6H4)}]4, (1e). Ellipsoids drawn at the 40% level.
5414
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Eur. J. Inorg. Chem. 2007, 5408–5418

Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands
1
6.7, N 6.1. IR: ν = 3375 (s, νO–H), 1608 (sh, νC=N) cm–1. H NMR
˜
Conclusions
3
(200 MHz, CDCl3): δ = 2.41, 2.59 (s, 6 H, Me), 6.95 (dt, JH,H
7.5 Hz, JH,H = 1.2 Hz, 1 H), 7.06 (dd, JH,H = 8.0 Hz, JH,H
1.2 Hz, 1 H), 7.3 (m, 5 H), 7.91 (s, 6-H), 8.9 (s, 1 H, Hi), 9.8 (br, 1
H, OH) ppm.
=
=
4
3
4
We have shown that Schiff base ligands derived from 2-
aminophenol offer different bonding modes to palladi-
um(II) because of the various donor atoms they possess,
behaving as tridentate [C,N,O] or [O,N,O] ligands. In all
cases, tetranuclear compounds were formed upon reaction
of the ligand with the metal salt through metallation of a
substituted phenyl ring. As with the tridentate [C,N,S] thio-
semicarbazones, formation of the central eight-membered
Pd4O4 core seems to favour tetranuclear clusters, as op-
posed to the dinuclear moieties obtained from didentate
[C,N] Schiff bases. Where choice was possible, five-mem-
bered ring metallacycles were preferred over six-membered
ones; nevertheless, the latter may be obtained when substit-
uents hinder attack of the metal atom on the phenyl ring.
In the case of ligand d, where metallation may proceed
through a phenyl or a methyl carbon atom, mixed five- and
six-membered palladated moieties build up the tetrameric
structure, thus constituting an unprecedented example of a
tetranuclear cyclopalladated compound.
2,4-(Me)2C6H3C(H)=N[2-(OH)C6H4] (d): Yield: 1589 mg, 97%.
C15H15NO (225.12): calcd. C 79.9, H 6.7, N 6.2; found C 79.4, H
1
6.4, N 6.1. IR: ν = 3043 (m, νO–H), 1619 (s, νC=N) cm–1. H NMR
˜
(200 MHz, CDCl3): δ = 2.40, 2.61 (s, 6 H, Me), 6.5 (br, 1 H, OH),
3
3
6.94 (t, JH,H = 7.6 Hz, 1 H), 7.3 (m, 5 H), 7.91 (d, JH6,H5
=
7.8 Hz, 1 H, 6-H), 8.97 (s, 1 H, Hi) ppm.
Schiff base e was prepared similarly as a yellow solid.
2-(OH)-4,6-(MeO)2C6H2C(H)=N[2-(OH)C6H4]
(e):
Yield:
1523 mg, 93%. C15H15NO4 (273.10): calcd. C 65.9, H 5.5, N 5.1;
found C 65.8, H 5.5, N 5.1. IR: ν = 3430 (m, νO–H), 3385 (sh),
˜
1625 (sh, m, νC=N) cm–1. H NMR (200 MHz, CDCl3): δ = 3.85,
1
3.84 (s, 6 H, MeO), 5.6 (br, 1 H, OH), 5.9, 6.1 (s, 2 H, 3-H, 5-H),
7.0 (m, 4 H), 8.9 (s, 1 H, Hi), 10.8 (br, 1 H, OH) ppm.
Schiff base f was prepared similarly as a red solid.
2-(OH)C6H4C(H)=N[2-(OH)C6H4] (f): Yield: 1176 mg, 92%.
C13H11NO2 (213.08): calcd. C 73.2, H 5.2, N 6.6; found C 73.1, H
5.0, N 6.3. IR: ν = 3500 (m, νO–H), 1630 (m, νC=N) cm–1. 1H NMR
˜
(200 MHz, CDCl3): δ = 5.7 (br, 1 H, OH), 7.2 (m, 8 H), 8.7 (s, 1
H, Hi), 12.2 (br, 1 H, OH) ppm.
Experimental Section
General Procedures: Solvents were purified by standard methods.[54]
Chemicals were reagent grade. The phosphanes PPh3,
Ph2PCH2PPh2 (dppm) and Ph2P(CH2)2PPh2 (dppe) were pur-
chased from Aldrich Chemie. Microanalyses were carried out with
a Carlo Erba Elemental Analyzer, Model 1108. IR spectra were
recorded by using Nujol mulls or KBr discs with a Perkin–Elmer
1330 and a Mattson spectrophotometer. NMR spectra were ob-
tained in CDCl3 solutions and referenced to SiMe4 [1H, or 85%
H3PO4 31P{1H}]; they were recorded with a Bruker AC-2005 spec-
trometer. All chemical shifts were reported downfield from the
standards. The FAB mass spectra were recorded by using a Quatro
mass spectrometer with a Cs ion gun; 3-nitrobenzyl alcohol (3-
NBA) was used as the matrix.
[Pd{2,3,4-(MeO)3C6HC(H)=N(2-O-5-tBuC6H3)}]4 (1a): A pressure
tube containing 2,3,4-(MeO)3C6H2C(H)=N[2-(OH)-5-tBuC6H3]
(0.456 mg, 1.33 mmol), palladium acetate (0.300 g, 1.33 mmol) and
dry toluene (20 cm3) was sealed under argon. The resulting mixture
was heated at 60 °C for 24 h. After cooling to room temperature
the solution was filtered through Celite to remove the small amount
of black palladium formed. The solvent was removed under vac-
uum to give a red oil, which was recrystallized from dichlorometh-
ane/hexane to give the desired product as a red solid. Yield:
1191 mg, 50%. C80H92N4O16Pd4 (1791.28): calcd. C 53.6, H 5.2, N
3.1; found C 53.0, H 5.1, N 3.1. IR: ν = 1571 (sh, m, νC=N) cm–1.
˜
1H NMR (200 MHz, CDCl3): δ = 1.24 (s, 9 H, tBu), 3.38, 3.81,
4
4.03 (s, 9 H, MeO), 5.81 (s, 1 H, 5-H), 6.75 (d, JH8,H10 = 2.2 Hz,
1 H, 8-H), 6.99 (dd, 3JH10,H11 = 8.8 Hz, 4JH8,H10 = 2.2 Hz, 1 H, 10-
H), 7.35 (d, 1 H, 11-H), 7.54 (s, 1 H, Hi) ppm. FAB-MS: m/z =
1792 [MH]+, 896 [M/2]+.
Syntheses
2,3,4-(MeO)3C6H2C(H)=N[2-(OH)-5-tBuC6H3] (a): 2,3,4-(MeO)3-
C6H2COH (1.000 g, 6.06 mmol) was added to a solution of 2-
amino-4-tert-butylphenol (1.188 g, 6.06 mmol) in dry chloroform
(50 cm3). The solution was heated under reflux in a Dean–Stark
apparatus for 4 h. After cooling to room temperature the chloro-
form was removed, and a brown solid was obtained. Yield:
1850 mg, 89%. C20H25NO4 (343.18): calcd. C 69.9, H 7.3, N 4.1;
Compound 1b was prepared similarly as a brown solid.
[Pd{6-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]4 (1b): Yield: 98 mg,
30%. C60H52N4O4Pd4 (1318.75): calcd. C 54.4, H 4.3, N 4.2; found
C 53.9, H 4.1, N 4.1. IR: ν = 1583 (s, νC=N) cm–1. 1H NMR
˜
(200 MHz, CDCl3): δ = 2.28 (s, 3 H, Me), 2.60, 3.49 (d, Jgem(H,H)
=
13.6 Hz, 2 H, -CH2-), 6.51 (dt, 3JH9,H8 = 8.3 Hz, 3JH10,H9 = 7.2 Hz,
found C 68.5, H 7.0, N 3.8. IR: ν = 3427 (m, νO–H), 1589 (s, νC=N
)
˜
cm–1. 1H NMR (200 MHz, CDCl3): δ = 1.13 (s, 9 H, tBu), 3.92,
3
4JH11,H9 = 1.3 Hz, 1 H, 9-H), 6.80 (d, JH5,H4 = 7.6 Hz, 1 H, 5-H),
3
3
3.95, 4.02 (s, 9 H, MeO), 6.80 (d, JH5,H6 = 8.3 Hz, 1 H, 5-H), 7.92
6.86 (m, 2 H, 8-H, 4-H), 7.04 (d, JH4,H3 = 7.4 Hz, 1 H, 3-H), 7.5
3
(d, JH5,H6 = 8.3 Hz, 1 H, 6-H), 6.95 (d, 2JH,H = 8.3 Hz, 11 H), 7.4
3
3
4
(dt, JH10,H9 = 7.2 Hz, JH11,H10 = 8.3 Hz, JH10,H8 = 1.3 Hz, 1 H,
10-H), 7.84 (dd, 3JH11,H10 = 8.3 Hz, JH11,H9 = 1.3 Hz, 1 H, 11-H),
4
(m, 2 H, 8-H, 10-H), 8.76 (s, 1 H, OH) (resonance taken from a
spectrum recorded in [D6]dmso), 8.97 (s, 1 H, Hi) ppm. FAB-MS:
m/z = 344 [MH]+.
8.13 (s, 1H, Hi) ppm. FAB-MS: m/z = 331 [(M/4)H]+.
Compound 1c was prepared similarly as a red solid.
Schiff base ligands b–d were prepared similarly as brown solids.
2,6-(Me)2C6H3C(H)=N[2-(OH)C6H4] (b): Yield: 1214 mg, 89%.
[Pd{5-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]4 (1c): Yield: 40 mg,
45%. C60H52N4O4Pd4 (1318.75): calcd. C 54.4, H 4.3, N 4.2; found
C15H15NO (225.12): calcd. C 79.9, H 6.7, N 6.2; found C 68.5, H
C 54.2, H 4.3, N 4.1. IR: ν = 1582 (s, νC=N) cm–1. 1H NMR
˜
1
7.0, N 3.8. IR: ν = 3396 (m, νO–H), 1621 (s, νC=N) cm–1. H NMR
˜
(200 MHz, CDCl3): δ = 2.44 (s, 3 H, Me), 2.45 (d, Jgem(H,H)
=
(200 MHz, CDCl3) δ = 2.64 (s, 6 H, Me), 7.2 (m, 7 H), 9.1 (s, 1 H,
Hi), 10.8 (br, 1 H, OH) ppm.
14.1 Hz, 1 H, -CH2-), 3.59 (d, Jgem(H,H) = 14.1 Hz, 1 H, -CH2-),
3
4
6.50 (dt, JH9,H8 = 7.8 Hz, JH11,H9 = 0.9 Hz, 1 H, 9-H), 6.8 (m, 3
3
2,5-(Me)2C6H3C(H)=N[2-(OH)C6H4] (c): Yield: 1188 mg, 88%.
C15H15NO (225.12): calcd. C 79.9, H 6.7, N 6.2; found C 79.8, H
H), 7.2 (m, 3 H), 7.13 (s, 1 H, Hi), 7.74 (dd, JH11,H10 = 8.3 Hz,
4JH11,H9 = 0.9 Hz, 1 H, 11-H) ppm.
Eur. J. Inorg. Chem. 2007, 5408–5418
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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J. J. Fernández, J. M. Vila et al.
FULL PAPER
[Pd{4-Me-2-CH2C6H3C(H)=N(2-OC6H4)}]n[Pd{2,4-(Me)2C6H2C-
(H)=N(2-OC6H4)}]4–n (n = 0–4): The mixture was prepared by fol-
lowing a procedure similar to that used for 1a, but with reaction
times of 5 h, 24 h and 3 d and reaction temperatures of 40, 60 and
80 °C. The components of the mixture could not be separated by
column chromatography or by other methods. Yield: 30 mg, 30%.
C60H52N4O4Pd4 (1318.75): calcd. C 54.4, H 4.3, N 4.2; found C
(200 MHz, CDCl3): δ = 2.28 (s, 3 H, Me), 2.93 (d, 3JCH ,P = 5.8 Hz,
2
2 H, -CH2-), 6.43 (t, 3JH10,H9 = 7.5 Hz, 1 H, 10-H), 6.66 (d, 3JH3,H4
3
= 7.8 Hz, 1 H, 3-H), 6.89 (m, 2 H, 4-H, 11-H), 7.09 (t, JH9,H8
=
4
3
7.5 Hz, JH11,H9 = 1.5 Hz, 1 H, 9-H), 7.25 (d, JH9,H8 = 7.5 Hz, 1
H, 8-H), 7.27 (s, 1 H, 6-H), 8.32 (d, 4JH ,P = 12.7 Hz, 1 H, Hi) ppm.
i
31P{1H} NMR (80.96 MHz, CDCl3): δ = 33.8 (s) ppm. FAB-MS:
m/z = 592 [M]+.
54.3, H 4.3, N 4.0. IR: ν = 1598 (s, νC=N) cm–1. 1H NMR
˜
Compounds 2d and 2dЈ were prepared by a similar procedure to
the one described for 2a using as starting material the mixture of
isomers 1d/1dЈ. The compounds were obtained as a mixture [in a
1:0.5 (2d/2dЈ) molar ratio] from which the pure compounds could
not be isolated by column chromatography or by other methods.
(200 MHz, CDCl3): δ = 3.62 (d, Jgem(H,H) = 13.5 Hz, 1 H, -CH2-),
3.53 (d, Jgem(H,H) = 14.0 Hz, 1 H, -CH2-), 3.83 (d, Jgem(H,H)
=
13.0 Hz, 1 H, -CH2-), 3.84 (d, Jgem(H,H) = 14.0 Hz, 1 H, -CH2-),
3.92 (d, Jgem(H,H) = 13.7 Hz, 1 H, -CH2-) ppm. 1H NMR
(200 MHz, [D6]dmso): δ = 2.14 (s, 3 H, Me), 2.34, 2.35 (s, 6 H,
MeЈ), 3.26 (s, 2 H, -CH2-), 8.41 (s, 1 H, Hi), 8.82 (s, 1 H, Hi) ppm.
[Pd{4-Me-2-CH2C6H3C(H)=N(2-OC6H4)}(PPh3)]
(2d)
and
[Pd{2,4-(Me)2C6H2C(H)=N(2-OC6H4)}(PPh3)] (2dЈ): Yield: 23 mg,
Compound 1e was prepared similarly as a yellow solid.
50%. C33H29NOPPd (592.98): calcd. C 66.8, H 4.9, N 2.4; found
[Pd{2-O-4,6-(MeO)2C6H2C(H)=N(2-OC6H4)}]4
(1e):
Yield:
C 66.3, H 4.7, N 2.3. IR: ν = 1581 (s, νC=N) cm–1. 1H NMR
˜
117 mg, 75%. C60H52N4O16Pd4 (1510.75): calcd. C 47.7, H 3.5, N
(200 MHz, CDCl3): δ = 2.67 (s, 6 H, MeЈ), 2.25 (s, 3 H, Me), 2.93
1
3.7; found C 47.5, H 3.4, N 3.5. IR: ν = 1612 (s, νC=N) cm–1. H
(d, 3JCH ,P = 5.8 Hz, 2 H, -CH2-), 5.67 (d, 4JH5,P = 3.4 Hz, 1 H, 5Ј-
˜
2
4
4
NMR (200 MHz, CDCl3): δ = 3.70, 3.82 (s, 6 H, MeO), 5.57, 5.73
H), 8.20 (d, JH ,P = 10.3 Hz, 1 H, HiЈ), 8.32 (d, J
= 12.7 Hz,
Hi,P
i
(d, H5, 4JH5,H3 = 1.9 Hz, 2 H, 3-H), 6.59 (t, 3JH9,H8 = 7.5 Hz, 1 H,
1 H, Hi) ppm. 31P{1H} NMR (80.96 MHz, CDCl3): δ = 34.6 (2dЈ),
3
9-H), 7.09 (m, 2 H, 8-H, 10-H), 7.71 (s, 1 H, Hi), 8.33 (d, JH11,H10 33.8 (s) (2d) ppm.
= 8.3 Hz, 1 H, 11-H) ppm.
[Pd{2-O-4,6-(MeO)2C6H2C(H)=N(2-OC6H4)}(PPh3)] (2e): Yield:
Compound 1f was prepared similarly as a red solid. Different reac-
tion times (5 h, 24 h and 5 d) were used with similar yields.
29 mg, 60%. C33H28NO4PPd (639.97): calcd. C 61.9, H 4.4, N 2.2;
found C 61.5, H 4.1, N 2.0. IR: ν = 1611 (s, νC=N) cm–1. 1H NMR
˜
(200 MHz, CDCl3): δ = 3.67, 3.88 (s, 6 H, MeO), 5.63, 5.78 (d,
[Pd{2-OC6H4C(H)=N(2-OC6H4)}]4 (1f): Yield: 118 mg, 86%.
3
4JH5,H3 = 2.2 Hz, 2 H, 3-H, 5-H), 6.64 (t, JH10,H9 = 7.5 Hz, 1 H,
C52H36N4O8Pd4 (1270.75): calcd. C 49.2, H 2.8, N 4.4; found C
3
10-H), 6.90 (d, JH11,H10 = 7.5 Hz, 1 H, 11-H), 7.03 (t, 1 H, 9-H),
48.9, H 2.8, N 4.3. IR: ν = 1609 (s, νC=N) cm–1. 1H NMR
˜
3
4
7.72 (d, JH9,H8 = 8.3 Hz, 1 H, 8-H), 9.12 (d,
J
= 18.1 Hz, 1
3
3
Hi,P
(200 MHz, [D6]dmso): δ = 7.17 (m, JH10,H11 = 8.3 Hz, JH10,H9
=
H, Hi) ppm. 31P{1H} NMR (80.96 MHz, CDCl3): δ = 23.4 (s) ppm.
FAB-MS: m/z = 639 [M]+.
4
3
7.0 Hz, JH10,H8 = 1.3 Hz, 1 H, 10-H), 7.30 (m, JH,H = 8.0 Hz,
3JH,H = 6.8 Hz, JH,H = 1.3 Hz, 1 H), 7.34 (dd, H8, JH9,H8
=
4
3
3
4
8.3 Hz, 1 H), 7.57 (dd, JH,H = 8.7 Hz, JH,H = 1.3 Hz, 1 H), 7.60
(m, JH,H = 1.3 Hz, 1 H, 9-H), 7.93 (m, JH,H = 8.6 Hz, JH,H
6.8 Hz, JH,H = 1.8 Hz, 1 H), 8.18 (dd, JH,H = 8.0 Hz, JH,H
[Pd{2-OC6H4C(H)=N(2-OC6H4)}(PPh3)] (2f): Yield: 25 mg, 66%.
4
3
3
=
=
C31H24NO2PPd (579.92): calcd. C 64.2, H 2.4, N 4.2; found C 64.3,
4
3
4
H 2.3, N 4.0. IR: ν = 1603 (s, νC=N) cm–1. 1H NMR (200 MHz,
˜
3
1.8 Hz, 1 H), 8.33 (dd, 1 H, 11-H), 8.94 (1 H, Hi) ppm. FAB-MS: CDCl3): δ = 6.61 (d, JH5,H4 = 8.5 Hz, 1 H, 5-H), 6.7 (m, 2 H, 3-
m/z = 637 [M/2]+.
H, 10-H), 6.92 (dd, 3JH11,H10 = 8.3 Hz, JH11,H9 = 1.2 Hz, 1 H, 11-
3
3
3
H), 7.08 (dt, JH10,H9 = 6.9 Hz, JH9,H8 = 8.3 Hz, 1 H, 9-H), 7.22
[Pd{2,3,4-(MeO)3C6HC(H)=N(2-O-5-tBuC6H3)}(PPh3)] (2a): PPh3
(6.99 mg, 0.026 mmol) was added to a suspension of 1a (12 mg,
0.006 mmol) in acetone (15 cm3). The mixture was stirred for 12 h,
and the solvent was removed to give a violet solid, which was
recrystallized from acetone/hexane. Yield: 15 mg, 80%.
C38H38NO4PPd (710.11): calcd. C 64.3, H 5.4, N 1.9; found C 64.3,
3
3
3
(dt, JH5,H4 = 8.6 Hz, JH4,H3 = 6.8 Hz, JH4,H2 = 1.8 Hz, 1 H, 4-
3
4
H), 7.74 (dd, JH9,H8 = 8.3 Hz, JH10,H8 = 1.4 Hz, 1 H, 8-H), 8.61
(dd, JH ,P = 17.1 Hz, 1 H, Hi) ppm. 31P{1H} NMR (80.96 MHz,
4
CDCl3):i δ = 23.3 (s) ppm. FAB-MS: m/z = 579 [M]+.
Compounds 3a and 4a were obtained as violet solids by a similar
procedure, but with a 1:2 complex 1a/ diphosphane molar ratio.
H 5.3, N 1.8. IR: ν = 1544 (s, νC=N) cm–1. 1H NMR (200 MHz,
˜
CDCl3): δ = 1.27 (s, 9 H, tBu), 2.92, 3.73, 3.98 (s, 9 H, MeO), 5.49
[{Pd(2,3,4-{MeO}3 C6 HC{H}=N{2-O-5-tBuC6H3 })}2 (µ-
PPh2CH2PPh2)] (3a): Yield: 19 mg, 60 %. C65H68N2O8P2Pd2
(1280.03): calcd. C 60.9, H 5.3, N 2.2; found C 60.2, H 5.2, N 2.1.
(d, 4JH5,P = 3.4 Hz, 1 H, 5-H), 6.45 (d, 3JH10,H11 = 8.7 Hz, 1 H, 11-
3
4
H), 6.96 (dd, JH10,H11 = 8.7 Hz, JH8,H10 = 1.9 Hz, 1 H, 10-H),
4
4
7.05 (d, JH8,H10 = 1.9 Hz, 1 H, 8-H), 8.14 (d, JH ,P = 10.7 Hz, 1
1
IR: ν = 1544 (s, νC=N) cm–1. H NMR (200 MHz, CDCl3): δ = 1.32
i
˜
H, Hi) ppm. 31P{1H} NMR (80.96 MHz, CDCl3): δ = 34.2 (s) ppm.
(s, 9 H, tBu), 2.89, 3.70, 3.95 (s, 9 H, MeO), 5.39 (d, 4JH5,P = 4.3 Hz,
3
Compounds 2b–2f were prepared similarly as red or brown (2b)
solids.
1 H, 5-H), 6.46 (d, JH10,H11 = 9.2 Hz, 1 H, 11-H), 7.1 (m, 2 H, 10-
H, 8-H), 7.99 (d, JH ,P = 10.7 Hz, 1 H, Hi) ppm. 31P{1H} NMR
4
i
(80.96 MHz, CDCl3): δ = 25.6 (s) ppm.
[Pd{6-Me-2-CH2C6H3C(H)=N(2-OC6H4)}(PPh3)] (2b): Yield:
10 mg, 60%. C33H29NOPPd (592.98): calcd. C 66.8, H 4.9, N 2.4;
[{Pd(2,3,4-{MeO}3C6HC{H}=N{2-O-5-tBuC6H3})}2{µ-PPh2(CH2)
2PPh2}] (4a): Yield: 21 mg, 65 %. C66H70N2O8P2Pd2 (1294.06): calcd.
found C 66.5, H 4.7, N 2.3. IR: ν = 1581 (s, νC=N) cm–1. 1H NMR
˜
(200 MHz, CDCl3): δ = 2.55 (s, 3 H, Me), 2.96 (d, 3JCH ,P = 5.8 Hz,
C 61.3, H 5.4, N 2.1; found C 61.1, H 5.3, N 2.0. IR: ν = 1544 (s,
˜
2
2 H, -CH2-), 6.43 (t, 3JH10,H9 = 7.3 Hz, 1 H, 10-H), 6.52 (t, 4J
νC=N) cm–1. 1H NMR (200 MHz, CDCl3): δ = 1.30 (s, 9 H, tBu),
H5,CH2
3
= 4.4 Hz, 1 H, 2-H), 6.92 (m, 3 H), 7.09 (t, JH,H = 7.8 Hz, 1 H),
2.85, 3.72, 3.97 (s, 9 H, MeO), 5.38 (s, 1 H, 5-H), 6.51 (d, 3JH10,H11
=
4
3
4
8.69 (d, JH ,P
=
12.7 Hz,
1
H, Hi) ppm. 31P{1H} NMR 8.7 Hz, 1 H, 11-H), 7.01 (dd, JH10,H11 = 8.7 Hz, JH8,H10 = 1.9 Hz,
i
4
(80.96 MHz, CDCl3): δ = 33.4 (s) ppm.
1 H, 10-H), 7.09 (d, JH8,H10 = 1.9 Hz, 1 H, 11-H) ppm. 31P{1H}
NMR (80.96 MHz, CDCl3): δ = 35.0 (s) ppm.
[Pd{5-Me-2-CH2C6H3C(H)=N(2-OC6H4)}(PPh3)] (2c): Yield:
29 mg, 60%. C33H29NOPPd (592.98): calcd. C 66.8, H 4.9, N 2.4;
Compound 3b was obtained following a similar procedure as a brown
solid.
found C 66.4, H 4.8, N 2.3. IR: ν = 1581 (s, νC=N) cm–1. 1H NMR
˜
5416
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 5408–5418

Tetranuclear Complexes of PdII with Tridentate [C,N,O] and [O,N,O] Ligands
Table 5. Crystal and structure refinement data.
1a·H2O
1c
1d/dЈ
1e·4CH2Cl2
Chemical formula
Formula weight
T [°C]
C80H94N4O17Pd4
1809.19
293(2)
C60H52N4O4Pd4
1318.66
293(2)
C60H52N4O4Pd4
1318.66
293(2)
C64H60Cl8N4O16Pd4
1850.36
120(2)
λ
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
monoclinic
C2/c
23.371(1)
23.254(1)
30.721(1)
orthorhombic
Fdd2
9.311(2)
27.305(6)
39.281(8)
triclinic
P1
monoclinic
C12/c1
31.233(6)
17.500(3)
27.541(5)
¯
12.334(3)
13.728(3)
17.537(5)
75.770(4)
81.472(4)
81.208(4)
2825(1)
2
94.635(1)
113.864(3)
γ [°]
V [Å3]
16641(1)
8
1.444
56.58
53553
9986(4)
8
1.472
52.88
13766(4)
8
1.408
52.92
Z
µ [mm–1]
2θmax [°]
Refln. collected
1.300
52.88
31767
2611
77225
Refln. independent 19987 (Rint = 0.068)
2210 (Rint = 0.035)
0.0311
0.0808
11533 (Rint = 0.031)
0.0432
0.1332
14150 (Rint = 0.088)
0.0401
0.0969
[a]
R1
0.0598
0.1891
[b]
wR2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|, [FϾ4σ(F)]. [b] wR2 = [Σ[w(Fo2–Fc ) /Σw(Fo2)2]1/2, all data.
[{Pd(6-Me-2-CH2C6H3C{H}=N{2-OC6H4})}2{µ-PPh2(CH2)2PPh2}]
(3b): Yield: 23 mg, 70%. C56H50N2O2P2Pd2 (1057.80): calcd. C
Acknowledgments
63.6, H 4.8, N 2.6; found C 63.6, H 4.7, N 2.6. IR: ν = 1581 (s,
˜
We thank the Ministerio de Educación
CTQ2006-15621-C02-01/BQU) for financial support.
y Ciencia (Project
1
νC=N) cm–1. H NMR (200 MHz, CDCl3): δ = 2.55 (s, 3 H, Me),
3
3
2.90 (d, JCH ,P = 9.1 Hz, 2 H, -CH2-), 6.43 (t, JH10,H9 = 6.8 Hz,
2
4
3
1 H, 10-H), 6.74 (t, JH ,CH = 2.3 Hz, 1 H, 3-H), 6.84 (dd, JH,H
= 8.3 Hz, JH,H = 0.9 Hz, 1 H), 6.94 (d, JH,H = 4.9 Hz, 1 H), 7.10
(dt, JH,H = 8.3 Hz, JH,H = 1.4 Hz, 1 H), 8.71 (m, 1 H, Hi) ppm.
3
2
4
3
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Received: May 2, 2007
Published Online: October 4, 2007
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