Linkage isomerism in thiophene cyclometallated palladium(ii) complexes. Crystal and molecular structure of the isomers Pd{n-SC4H 2C(H)=NCy}-(O2CMe-O)(PPh3)l (n = 3, 4)

Article abstract of DOI:10.1002/zaac.200600371

Treatment of 2-SC₄H₃C(H)=NCy, a, or 3-SC ₄H₃C(H)= NCy, b, with palladium(II) acetate in toluene gave the dinuclear cyclometallated complexes [Pd{n-SC₄H ₂C(H)=NCy}(O₂CMe)]₂ (n = 5, 1a; n = 3, 1b; n = 4, 1b′), the latter two as a 1:1 mixture of linkage isomers, whose subsequent reactions produced isomeric mixtures in all cases. Reaction of 1a and 1b, 1b′ with aqueous sodium chloride or bromide yielded the corresponding halide-bridged complexes [Pd{n-SC₄H₂C(H)=NCy}(X)] ₂ (n = 5: X = Cl, 2a; X = Br, 3a; n = 3,4: X = Cl, 2b, 2b′; X = Br, 3b, 3b′) after metathesis. Reactions of the dinuclear compounds with tertiary phosphines in the appropriate molar ratio gave the mononuclear [Pd{n-SC₄H₂C(H)=NCy}(Cl)(PPh₃)] (n = 5, 6a; n = 3, 4 4b, 4b′) and [Pd{5-SC₄H₂C(H)=NCy} {(Ph ₂PCH₂CH₂)₂PPh-P,P,P}](Cl), (5a), and the dinuclear [{Pd[5-SC₄H₂C(H)=NCy](O₂CMe)} ₂-{μ-Ph₂P(CH₂)_nPPh₂}] (n = 2, 7a; n = 3, 8a; n = 4, 9a) complexes. The X-ray crystal structure of complex 4b, 4b′ is described, establishing the presence of two isomers in the crystal lattice.

Full text of DOI:10.1002/zaac.200600371

DOI: 10.1002/zaac.200600371
Linkage Isomerism in Thiophene Cyclometallated Palladium(II) Complexes.
Crystal and Molecular Structure of the Isomers [Pd{n-SC4H2C(H)؍NCy}-
(O2CMe-O)(PPh3)] (n ؍ 3, 4)
a
a
b
a
a
a
a,
´
´
´
Luis A. Adrio , Jose M. Antelo , Alberto Fernandez , M Teresa Pereira , Mercedes Tato , and Jose M. Vila *
a
´
´
Santiago de Compostela/Spain, Universidad de Santiago de Compostela, Departamento de Quımica Inorganica
b
´
A Corun˜a, Spain, Universidad de A Corun˜a, Departamento de Quımica Fundamental
Received December 28th, 2006.
Dedicated to Professor Joachim Strähle on the Occasion of his 70th Birthday
Abstract. Treatment of 2-SC4H3C(H)ϭNCy, a, or 3-SC4H3C(H)ϭ
NCy, b, with palladium(II) acetate in toluene gave the dinuclear
cyclometallated complexes [Pd{n-SC4H2C(H)ϭNCy}(O2CMe)]2
(n ϭ 5, 1a; n ϭ 3, 1b; n ϭ 4, 1bЈ), the latter two as a 1:1 mixture
of linkage isomers, whose subsequent reactions produced isomeric
mixtures in all cases. Reaction of 1a and 1b, 1bЈ with aqueous so-
dium chloride or bromide yielded the corresponding halide-bridged
complexes [Pd{n-SC4H2C(H)ϭNCy}(X)]2 (n ϭ 5: X ϭ Cl, 2a;
X ϭ Br, 3a; n ϭ 3,4: X ϭ Cl, 2b, 2bЈ; X ϭ Br, 3b, 3bЈ) after
metathesis. Reactions of the dinuclear compounds with tertiary
phosphines in the appropriate molar ratio gave the mononuclear
[Pd{n-SC4H2C(H)ϭNCy}(Cl)(PPh3)] (n ϭ 5, 6a; n ϭ 3, 4 4b, 4bЈ)
and [Pd{5-SC4H2C(H)ϭNCy}{(Ph2PCH2CH2)2PPh-P,P,P}](Cl),
(5a), and the dinuclear [{Pd[5-SC4H2C(H)ϭNCy](O2CMe)}2-
{µϪPh2P(CH2)nPPh2}] (n ϭ 2, 7a; n ϭ 3, 8a; n ϭ 4, 9a) complexes.
The X-ray crystal structure of complex 4b, 4bЈ is described,
establishing the presence of two isomers in the crystal lattice.
Keywords: Palladium; Cyclometallation; C-H activation; Isome-
rism; Phosphines
1 Introduction
no substituents at the imine nitrogen atom are to the best
of our knowledge outstanding, more so when the question
of regioselectivity arises, as is the case of ligand b described
below, where metallation may come about through the C2
or C5 atoms. In previous findings [13a] where more than
one metallation site was possible only one species was ob-
tained, namely that pertaining to the metallation of the car-
bon atom in ortho to the sulfur atom, with the alleged isom-
erism being due only to the cis or trans arrangement of
the ligands at palladium; this was also the case for related
platinocycles with an unsubstituted imine carbon atom [15].
Herein we report the first examples of Schiff base thio-
phene palladacyles which demonstrate that absence of
bulky groups at the imine carbon atom are unneeded to
establish palladation of the organic moiety, as was found
for the related platinocycles [15], and that regioselectivity
allows formation of species holding different metallated
carbon atoms thus giving rise to linkage isomerism in these
complexes. Moreover, the 1:1 mixture of isomers derived
from ligand b proved to be inseparable to the point that
both moieties co-crystallized in an unprecedented structure
that deemed indistinguishable the two isomers throughout
the crystal array.
Cyclometallation, of which palladacycles constitute a more
than fair percentage, represents a flourishing topic in
organometallic chemistry for which several reviews have ap-
peared [1Ϫ5]. Most significant amongst their characteristics
are the outstanding applications they show, such as their
use as intermediates in organic and organometallic syn-
thesis [5, 6], the design of liquid crystals [7] or their pharma-
cological usage [8] inclusive of their antitumoral activities
[9Ϫ12].
Although many organic ligands are known to undergo
metallation by palladium the majority hold phenyl rings,
with cyclometallated heterocycles being more scarce. In the
case of thiophene derivatives the presence of the N,N-di-
methyl group at the CϭX (X ϭ S, Se) atom has proven to
be a good substituent that promotes cyclometallation; thus,
thiophene palladacycles have been reported for N,N-di-
methylthiophene- carboseleno and thioamides [13], as well
as for thienylbipyridine [14]. Nevertheless, similar pal-
ladium species with thiophene Schiff base ligands bearing
* Prof. Dr. J. M. Vila
2 Experimental Section
´
´
Departamento de Quımica Inorganica
Universidad de Santiago de Compostela
E-15782 Santiago de Compostela / Spain
Fax: ϩ34/981-595012
General procedures
Solvents were purified by standard methods [16]. Chemicals
were reagent grade. Palladium(II) acetate was purchased from
E-mail: qideport@usc.es
734
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 633, 734Ϫ740

Linkage Isomerism in Thiophene Cyclometallated Palladium(II) Complexes
5.4), 6.90 (s, 1H, H3), 6.85 (d, 1H, H5, 3J(H4H5) 5.4), 6.77 (s, 1H, H5), 3.05,
Alfa Products. The phosphines, PPh3, Ph2P(CH2)2PPh2,
Ph2P(CH2)3PPh2, Ph2P(CH2)4PPh2, and thallium acetylacetonate,
Tl(acac), were purchased from Aldrich-Chemie. Microanalyses
3.1 (m, HipsoCy), 2.17, 2.13 (s, 3H, O2CMe). FAB-MS: m/z 715 [M]ϩ.
Preparation of [Pd{5-SC4H2C(H)؍NCy}(Cl)]2 (2a). To a solution
of 1a (100 mg, 0.14 mmol) in 25 cm3 of acetone, an aqueous solu-
tion of sodium bromide (ca. 10Ϫ2 M) was added and the mixture
stirred at room temperature for 3 h, after which water was added
and the solid formed was filtered off and dried in vacuo. Yield:
691 mg, 74 %. Anal. Found: C 39.4; H 4.2; N 4.1; S 9.4;
C22H28Cl2N2S2Pd2 (668.35 g/mol) requires C 39.5; H 4.2; N 4.2;
S 9.6 %.
´
were carried out at the Servicio de Analisis Elemental at the Univ-
ersidad of Santiago de Compostela using a Carlo Erba Elemental
Analyzer Model EA1108. IR spectra were recorded as Nujol mulls
or KBr discs with a Perkin-Elmer 1330, with a IR-FT Mattson
Model Cygnus-100 and with a Bruker Model IFS-66V spectropho-
tometers. NMR spectra were obtained as CDCl3 solutions and ref-
erenced to SiMe4 (1H) or H3PO4 (31P {1H}) and were recorded
with Bruker AMX 300, AMX 500 and WM250 spectrometers. All
chemical shifts are reported downfield from standards. The FAB
mass spectra were recorded with a Fisons Quatro mass spec-
trometer with a Cs ion gun; 3-nitrobenzyl alcohol was used as the
matrix.
IR (cmϪ1): ν(CϭN) 1613m, ν(PdϪCl) 290m, 246m. 1H NMR (CDCl3,
δ ppm, J Hz): 7.71 (s, 1H, HCϭN), 7.36 (d, 1H, H3, 3J(H3H4) 4.9), 7.12 (d,
1H, H4, 3J(H3H4) 4.9), 3.56 (m, HipsoCy). FAB-MS: m/z 668 [M]ϩ.
Compounds 3a, 2b and 3b were prepared analogously.
[Pd{5-SC4H2C(H)؍NCy}(Br)]2 (3a). Yield: 763 mg, 72 %. Anal.
Found: C 34.7; H 3.6; N 3.7; S 8.3; C22H28Br2N2S2Pd2 (757.25 g/
mol) requires C 34.9; H 3.7; N 3.7; S 8.5 %.
IR (cmϪ1): ν(CϭN) 1614m. 1H NMR (CDCl3, δ ppm, J Hz): 7.76 (s, 1H,
HCϭN), 7.36 (d, 1H, H3, 3J(H3H4) 4.9), 7.23 (d, 1H, H4, 3J(H3H4) 4.9),
3.73 (m, HipsoCy). FAB-MS: m/z 757 [M]ϩ.
Syntheses
Preparation of 2-SC4H3C(H)؍NCy (a). Thiophen-2-carboxyal-
dehyde (4 g, 35.7 mol) and cyclohexylamine (3.9 g, 39.2 mmol) were
refluxed together in chloroform (25 cm3) in a Dean-Strak apparatus
for 4 h, after which the solvent was removed under vacuum to give
a dark-yellow oily liquid, which was dried under vacuum. Yield:
656 mg, 95 %. Anal. Found: C 68.2; H 7.7; N 7.3; S 16.5; C11H15NS
(193.3 g/mol) requires C 68.4; H 7.8; N 7.3; S 16.6 %.
[Pd{n-SC4H2C(H)؍NCy}(Cl)]2 (n ؍ 3, 2b; n ؍ 4, 2bЈ). Yield:
730 mg, 78 %. Anal. Found: C 39.3; H 4.1; N 4.1; S 9.5;
C22H28Cl2N2S2Pd2 (668.35 g/mol) requires C 39.5; H 4.2; N 4.2;
S 9.6 %.
IR (cmϪ1): ν(CϭN) 1612m, ν(PdϪCl) 287m, 241m. 1H NMR (CDCl3,
δ ppm, J Hz): 7.76, 7.65 (s, 1H, HCϭN), 7.03 (d, 1H, H4, 3J(H4H5) 5.3),
6.95 (s, 1H, H3), 6.84 (d, 1H, H5, 3J(H4H5) 5.3), 6.75 (s, 1H, H5), 3.85 (m,
HipsoCy). FAB-MS: m/z 668 [M]ϩ.
IR (cmϪ1): ν(CϭN) 1632s. 1H NMR (CDCl3, δ ppm, J Hz): 8.39 (s, 1H,
HCϭN), 7.35, 7.28, 7.05 (ABX, 3H, H2, H3, H4, [3J(H2H3) 4.9, 3J(H3H4)
4.5, 4J(H2H4) 1.1]), 3.16 (m, HipsoCy). FAB-MS: m/z 193 [M]ϩ.
Ligand b was prepared similarly.
[Pd{n-SC4H2C(H)؍NCy}(Br)]2 (n ؍ 3, 3b; n ؍ 4, 3bЈ). Yield:
859 mg, 72 %. Anal. Found: C 34.6; H 3.6; N 3.7; S 8.4;
C22H28Br2N2S2Pd2 (757.25 g/mol) requires C 34.9; H 3.7; N 3.7;
S 8.5 %.
IR (cmϪ1): ν(CϭN) 1620m. 1H NMR (CDCl3, δ ppm, J Hz): 7.66, 7.58 (s,
1H, HCϭN), 7.05 (d, 1H, H4, 3J(H4H5) 5.3), 7.0 (s, 1H, H3), 6.95 (d, 1H,
H5, 3J(H4H5) 5.3), 6.88 (s, 1H, H5), 3.85 (m, HipsoCy). FAB-MS: m/z 757
[M]ϩ.
3-SC4H3C(H)؍NCy (b). Yield: 663 mg, 96 %. Anal. Found: C 68.1;
H 7.8; N 7.2; S 16.4; C11H15NS (193.3 g/mol) requires C 68.4; H
7.8; N 7.3; S 16.6 %.
IR (cmϪ1): ν(CϭN) 1636s. 1H NMR (CDCl3, δ ppm, J Hz): 8.31 (s, 1H,
HCϭN), 7.55, 7.53, 7.29 (ABX, 3H, H2, H4, H5, [4J(H2H4) 1.1, 4J(H2H5)
2.9, 3J(H4H5) 5.1]), 3.12 (m, HipsoCy). FAB-MS: m/z 193 [M]ϩ.
Preparation of [Pd{5-SC4H2C(H)؍NCy}(O2CMe)]2 (1a). 2-
SC4H3C(H)ϭNCy (0.27 g, 1.3 mmol) and palladium(II) acetate
(0.3 g, 1.3 mmol) were added to 25 cm3 of dry toluene to give a
yellow solution which was heated at 80 °C for 3 h under argon.
After cooling to room temperature the solution was filtered to elim-
inate the small amount of black palladium formed. The solvent
was removed under vacuum to give an orange solid which was
chromatographed on a column packed with silica gel. Elution with
dichloromethane / methanol (1 %) afforded the final product after
concentration, which was recrystallized from chloroform/n-hexane.
Yield: 288 mg, 62 %. Anal. Found: C 43.5; H 4.9; N 3.8; S 8.9;
C26H34N2O4S2Pd2 (715.53 g/mol) requires C 43.6; H 4.8; N 3.9;
S 9.0 %.
Preparation of [Pd{5-SC4H2C(H)؍NCy}(MeCOCHCOMe-O,O)]
(4a). The chloro-bridged complex, 2a, (20 mg, 0.03 mmol) and thal-
lium acetylacetonate (18 mg, 0.16 mmol) were stirred together in
chloroform (25 cm3) at room temperature for 2 h. The resulting
mixture was chromatographed on a column packed with silica gel.
Elution with dichloromethane/chloroform (3:1) gave a yellow resi-
due after concentration, which was recrystallised from dichloro-
methane/hexane to give the required complex as a yellow solid.
Yield: 203 mg, 85 %. Anal. Found: C 48.1; H 5.2; N 3.5; S 8.0;
C16H21NO2SPd (397.83 g/mol) requires C 48.3; H 5.3; N 3.5; S
8.1 %.
IR (cmϪ1): ν(CϭN) 1600m, acac: ν(CϪC) 1576s, ν(CϪO) 1518s. 1H NMR
(CDCl3, δ ppm, J Hz): 7.73 (s, 1H, HCϭN), 7.09 (d, 1H, H3, 3J(H3H4) 4.9),
6.96 (d, 1H, H4, 3J(H3H4) 4.9), 5.34 (s, 1H, CH), 3.54 (m, HipsoCy), 2.05 (s,
3H, CMe), 2.01 (s, 3H, CMe). FAB-MS: m/z 398 [M]ϩ.
IR (cmϪ1): ν(CϭN) 1608m, νas(COO) 1580m, νs(COO) 1518m. 1H NMR
(CDCl3, δ ppm, J Hz): 7.87 (s, 1H, HCϭN), 7.36 (d, 1H, H3, 3J(H3H4) 4.9),
7.23 (d, 1H, H4, 3J(H3H4) 4.9), 3.58 (m, HipsoCy), 1.94 (s, 3H, O2CMe).
FAB-MS: m/z 715 [M]ϩ.
Preparation of [Pd{5-SC4H2C(H)؍NCy}{(Ph2PCH2CH2)2PPh-
P,P,P}](Cl) (5a). To a solution of 1a (21 mg, 0.03 mmol) in acetone
(15 cm3) (Ph2PCH2CH2)2PPh (16 mg, 0.06 mmol) was added. The
resulting mixture was stirred at room temperature for 24 h after
which the complex was then precipitated out by addition of water,
filtered off, dried in vacuo and recrystallized from dichloromethane/
n-hexane. Yield: 395 mg, 79 %. Anal. Found: C 64.7; H 5.6; N 1.7;
S 3.8; C45H47NP3SPd (833.27 g/mol) requires C 64.9; H 5.7; N 1.7;
S 3.9 %.
Compiund 1b was synthesized in a similar fashion as a mixture
of isomers.
[Pd{n-SC4H2C(H)؍NCy}(O2CMe)]2 (n ؍ 3, 1b; n ؍ 4, 1bЈ). Yield:
340 mg, 73 %. Anal. Found: C 43.5; H 4.6; N 3.8; S 9.0;
C26H34N2O4S2Pd2 (715.53 g/mol) requires C 43.6; H 4.8; N 3.9;
S 9.0 %.
IR (cmϪ1): ν(CϭN) 1610m, νas(COO) 1575m, νs(COO) 1417m. 1H NMR
(CDCl3, δ ppm, J Hz): 7.27, 7.25 (s, 1H, HCϭN), 6.96 (d, 1H, H4, 3J(H4H5)
Z. Anorg. Allg. Chem. 2007, 734Ϫ740
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
735

´
L. A. Adrio, J. M. Antelo, A. Fernandez, M. T. Pereira, M. Tato, J. M. Vila
IR (cmϪ1): ν(CϭN) 1618m. 1H NMR (CDCl3, δ ppm, J Hz): 7.93 (s, 1H,
perature X-ray data were collected in the θ range 1.84 to 28.28° on
a Siemens Smart CCD diffractometer by the omega/2-theta scan
method, using monochromated Mo-Kα radiation. Of the 9858 re-
flections measured, all of which were corrected for Lorentz and
polarisation effects and for absorption by semi-empirical methods
based on symmetry-equivalent and repeated reflections, 5963 inde-
pendent reflections exceeded the significance level IFI/σIFI > 4.0.
The structure was solved by direct methods and refined by full
matrix least squares on F2. Hydrogen atoms were included in calcu-
lated positions and refined in riding mode.
HCϭN), 7.01 (dd, 1H, H3, 4J(PH) 5.7, 3J(H3H4) 4.9), 3.58 (m, HipsoCy).
31P {1H} NMR (CDCl3, δ ppm, J Hz): 91.7 (t, 1P, J(PP) 27.1), 41.4 (d, 2P,
J(PP) 27.1). FAB-MS: m/z 833 [M]ϩ.
Preparation of [Pd{5-SC4H2C(H)؍NCy}(Cl)(PPh3)] (6a). To 2a,
(50 mg, 0.075 mmol) in dichloromethane (15 cm3), PPh3 (39 mg,
0.15 mmol) was added in a halide-bridged complex/phosphine 1:2
molar ratio. The mixture was stirred for 4 h, filtered over celite to
remove Pd(0), and the solvent eliminated under reduced pressure.
The residue was recrystallised from dichloromethane/hexane. Yield:
79 mg, 88 %. Anal. Found:
C29H29ClNPPdS (596.46 g/mol) requires C 58.4; H 4.9; N 2.4; S
5.4 %.
IR (cmϪ1): ν(CϭN) 1613m. 1H NMR (CDCl3, δ ppm, J Hz): 8.1 (d, 1H,
HCϭN, 4J(PH) 7.2), 6.95 (d, 1H, H4, 3J(H3H4) 5.1), 5.90 (dd, 1H, H3,
4J(PH) 5.5, 3J(H3H4) 5.1), 3.60 (m, HipsoCy). 31P {1H} NMR (CDCl3,
δ ppm): 26.6s FAB-MS: m/z 596 [M]ϩ.
C 58.1; H 4.7; N 2.3; S 5.3;
The two isomers 4b and 4bЈ crystallized with all their atoms occu-
pying the same crystallographic positions except C(1a), S(1a) and
C(2b), S(1b). In view of the close overlap between C(1a) and S(1b),
and C(2b) and S(1a) bond length restrains were imposed during
the refinement. The occupancies of the two pairs of positions were
tied to give an overall value of 1.0 and then refined giving values
of, approximately 0.5 for each component. All the measured reflec-
tions were corrected for Lorentz and polarization effects and for
absorption by semi-empirical methods based on symmetry-equiva-
lent and repeated reflections [Tmax/Tmin ϭ 0.7658 and 0.6889]. The
structure was solved by direct methods and refined by full matrix
least squares on F2. Hydrogen atoms were included in calculated
positions and refined in riding mode. Refinement converged at a
final R ϭ 0.0290 (wR2 ϭ 0.0719 for all 6574 data, 336 parameters,
mean and maximum δ/σ ϭ 0.000, 0.001) with allowance for ther-
mal anisotropy of all non-hydrogen atoms. Minimum and maxi-
Compound 4b was prepared analogously from 1b.
[Pd{n-SC4H2C(H)؍NCy}(O2CMe)(PPh3)] (n ؍ 3, 4b; n ؍ 4, 4bЈ)
Ϫ Yield: 882 mg, 79 %. Anal. Found: C 60.0; H 5.1; N 2.3; S 5.1;
C31H32NO2PSPd (620.3 g/mol) requires C 60.1; H 5.2; N 2.3; S
5.2 %.
IR (cmϪ1): ν(CϭN) 1615m, νas(COO) 1503m, νs(COO) 1387m. 1H NMR
(CDCl3, δ ppm, J Hz): 7.93, 7.86 (d, 1H, HCϭN, 4J(PH) 6.8), 7.01 (d, 1H,
H4, 3J(H4H5) 4.9), 6.90 (d, 1H, H3, 4J(PH) 5.2), 6.78 (d, 1H, H5, 3J(H4H5)
5.3), 6.72 (s, 1H, H5), 3.58 (m, HipsoCy), 2.10 (s, 3H, O2CMe). 31P {1H}
NMR (CDCl3, δ ppm): 34.7s, 34.1s.
mum final electron density Ϫ0.673 and 0.423 eAϪ3. The structure
˚
Preparation [{Pd[5-SC4H2C(H)؍NCy](O2CMe)}2{µ؊Ph2P(CH2)2-
PPh2-P,P}] (7a). 1,2-bis(diphenylphosphino)ethane (28 mg,
0.07 mmol) was added to a solution of complex 1a (50 mg,
0.07 mmol) in acetone (15 cm3). The mixture was stirred for 3 h,
and the resulting orange solid filtered off and dried. Yield:
solution and refinement were carried out using the program pack-
age SHELX-97 [17].
64 mg, 82 %. Anal. Found:
C 56.0; H 5.3; N 2.4; S 5.7;
C52H58N2O4P2Pd2S2 (1113.95 g/mol) requires C 56.1; H 5.3; N 2.5;
S 5.8 %.
IR (cmϪ1): ν(CϭN) 1618m, νas(COO) 1505m, νs(COO) 1390m. 1H NMR
(CDCl3, δ ppm): 7.84 (d, 1H, HCϭN, 4J(PH 7.7), 7.0 (d, 1H, H4, 3J(H3H4)
4.6), 5.97 (dd, 1H, H3, 4J(PH) 5.7, 3J(H3H4) 4.6), 3.65 (m, HipsoCy), 1.95
(s, 3H, O2CMe). 31P {1H} NMR (CDCl3, δ ppm): 26.6s.
Crystallographic data (excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
631115. Copies of the data can be obtained free of charge on appli-
cation to The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK.
Compounds 8a and 9a were prepared analogously.
Preparation of [{Pd[5-SC4H2C(H)؍NCy](O2CMe)}2{µ؊Ph2P-
(CH2)3PPh2-P,P}] (8a). Yield: 67 mg, 85 %. Anal. Found: C 56.2;
H 5.3; N 2.4; S 5.5; C53H60N2O4P2Pd2S2 (1127.97 g/mol) requires
C 56.4; H 5.4; N 2.5; S 5.7 %.
IR (cmϪ1): ν(CϭN) 1618m, νas(COO) 1501m, νs(COO) 1385m. 1H NMR
(CDCl3, δ ppm, J Hz): 1H NMR (CDCl3, δ ppm, J Hz): 7.95 (d, 1H,
HCϭN, 4J(PH 7.5), 6.8 (d, 1H, H4, 3J(H3H4) 4.8), 6.0 (dd, 1H, H3, 4J(PH)
5.2, 3J(H3H4) 4.8), 3.48 (m, HipsoCy), 1.90 (s, 3H, O2CMe). 31P {1H} NMR
(CDCl3, δ ppm): 23.5 s.
3 Results and Discussion
Synthesis and characterization
Preparation of [{Pd[5-SC4H2C(H)؍NCy](O2CMe)}2{µ؊Ph2P-
(CH2)4PPh2-P,P}] (9a). Yield: 63 mg, 79 %. Anal. Found: C 56.5;
H 5.4; N 2.4; S 5.6; C54H62N2O4P2Pd2S2 (1142.0 g/mol) requires C
56.8; H 5.5; N 2.5; S 5.6 %.
IR (cmϪ1): ν(CϭN) 1618m, νas(COO) 1504m, νs(COO) 1389m. 1H NMR
(CDCl3, δ ppm, J Hz): 7.93 (d, 1H, HCϭN, 4J(PH 7.8), 6.9 (d, 1H, H4,
3J(H3H4) 4.4), 6.01 (dd, 1H, H3, 4J(PH) 5.3, 3J(H3H4) 4.4), 3.6 (m,
HipsoCy), 1.89 (s, 3H, O2CMe). 31P {1H} NMR (CDCl3, δ ppm): 24.8 s.
The compounds and reactions are shown in Schemes 1 and
2. The compounds were characterized by elemental analysis
1
and by IR and by H and 31P {1H} NMR spectroscopy,
and (in part) by FAB mass spectrometry.
Treatment of 2-SC4H3C(H)ϭNCy, a, with palladium(II)
acetate in toluene at 80 °C for two hours gave a yellow crys-
talline solid identified as the cyclometallated product de-
rived from C-H activation at the 2-position, 1a. The 1H
NMR spectrum for 1a showed the absence of the ABX pat-
tern in the parent ligand; thus, two doublets at δ ϭ 7.23
and δ ϭ 7.36 were assigned to the AB system for the H3
Crystal structure
Crystals of complex 4b, 4bЈ were mounted on a glass fiber and
transferred to the diffractometer. Three-dimensional, room tem-
736
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Z. Anorg. Allg. Chem. 2007, 734Ϫ740

Linkage Isomerism in Thiophene Cyclometallated Palladium(II) Complexes
Scheme 1 (i) Pd(AcO)2 / Toluene; (ii) NaCl/ acetone/water; (iii) NaBr/ acetone/water; (iv) Tl(acac) / CHCl3; (v) (Ph2PCH2CH2)2PPh /
acetone; (vi) PPh3 / acetone; (vii) Ph2P(CH2)nPPh2 / acetone (n ϭ 2, 7a; n ϭ 3, 8a; n ϭ 4, 9a)
and H4 protons [3J(HH ϭ 4.9 Hz], respectively, with the
signal for the H2 nucleus absent upon metallation at C2. In
the IR spectra of the complexes the ν(CϭN) stretch ap-
peared at lower frequency than the corresponding one in
the free ligand in accordance with nitrogen coordination to
metal atom [18]. This was supported by the upfield shift of
the NMR signal for the HCϭN proton, ca. 1 ppm [19]. The
νas(COO) and νs(COO) values were consistent with bridg-
ing acetato groups [20], the singlet resonance at ca. 2.00 in
the 1H NMR spectra was assigned to the equivalent methyl
acetate protons, in agreement with a trans geometry of the
two cyclometallated moieties [21].
Treatment of 1a with an aqueous solution of sodium
chloride or bromide gave the chloro- or bromo-bridged di-
nuclear compounds 2a and 3a, respectively (see Experimen-
tal). The IR and NMR data was in accordance with absence
of the acetate ligands after metathesis; for 2a bands at 290
and 273 cmϪ1 were ascribed to the ν(Pd-Cl) stretches.
Reaction of the halide-bridged complexes 2a or 3a with
thallium 2,4-pentanedionate gave the soluble complex 4a as
an air-stable solid, which was fully characterized (see Ex-
perimental). The 1H NMR spectrum showed singlets ca.
δ ϭ 7.73 assigned to the HCϭN proton resonance. Singlet
resonances at δ ϭ 5.34 and at δ ϭ 2.05, δ ϭ 2.01 were
assigned to the CH and to the two non-equivalent methyl
groups, respectively.
as an air-stable solid which was fully characterized. The
phosphorus resonances in the 31P {1H} NMR spectra of
the complex were downfield shifted from their values in the
free phosphine suggesting coordination of all the phos-
phorus atoms to the metal center. A triplet resonance at
δ ϭ 91.7 was assigned to the central 31P nucleus, which was
trans to the phenyl carbon atom, and a doublet signal at
δ ϭ 41.1 was assigned to the two equivalent mutually trans
phosphorus nuclei. The latter signal appeared at lower fre-
quency in accordance with the high trans influence of the
phosphine ligand [22]. The resonance of the proton in the
ortho position to the metallated carbon, H3, appeared as a
doublet of doublets showing coupling to the central 31P
atom [J(PH) 5.7 Hz]; no coupling was observed to the ter-
minal phosphorus nuclei. These data are in accordance with
a disposition in which the metalated ring is nearly perpen-
dicular to the plane defined by the three phosphorus atoms;
these observations were confirmed by selective decoupling
experiments. The absence of the ν(Pd-Cl) band in the IR
spectrum confirmed Pd-Cl bond cleavage upon coordi-
nation of the palladium atom to the three phosphorus
atoms. No noticeable shift of the ν(CϭN) stretching vi-
bration to lower wavenumbers [18] or upfield shift of the
1
HCϭN proton resonance in the H NMR spectra [19] was
observed indicating absence of palladiumϪnitrogen interac-
tion in solution. Conductivity measurements show the ex-
pected values for a 1:1 electrolyte [23].
Reaction of 1a or 2a with tertiary phosphines gave
mononuclear and dinuclear compounds. Thus, treatment of
Reaction of 2a with triphos in a water/acetone mixture
yielded the mononuclear cyclometallated complex [Pd{2-
SC4H2C(H)ϭNCy}{(Ph2PCH2CH2)2PPh-P, P, P }](Cl), (5a),
Z. Anorg. Allg. Chem. 2007, 734Ϫ740
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737

´
L. A. Adrio, J. M. Antelo, A. Fernandez, M. T. Pereira, M. Tato, J. M. Vila
Scheme 2 (i) Pd(AcO)2 / Toluene; (ii) NaX (X ϭ Cl, Br)/ acetone/water; (iii) PPh3 / acetone.
1a with Ph2P(CH2)nPPh2 in 1:2 molar ratio gave com-
pounds [{Pd[5-SC4H2C(H)ϭNCy](O2CMe)}2{µϪPh2P-
(CH2)nPPh2}] (n ϭ 2, 7a; n ϭ 3, 8a; n ϭ 4, 9a) as pure air-
NCy}(O2CMe)]2 (n ϭ 3, 1b; n ϭ 4, 1bЈ) in ca. 1:1 ratio as
determined by 1H NMR spectroscopy; attempts to separate
both isomers deemed unsuccessful. The 1H NMR spectrum
showed two doublets assigned to the AB pattern of the H4
and H5 protons for 1b, and two singlet resonances assigned
to the H3 and H5 protons for 1bЈ. Treatment of the acetato-
bridged compounds with aqueous sodium chloride or bro-
mide yielded the halide-bridged (2b, 2bЈ X ϭ Cl; 3b, 3bЈ
X ϭ Br) complexes (see Experimental Setion), whereas re-
action with triphenylphosphine gave 4b, 4bЈ with a terminal
acetato group; the spectroscopic data was in accordance
with a trans PϪPdϪN geometry.
Molecular structure of [Pd{n-SC4H2C(H)؍NCy}-
(O2CMe)(PPh3)] (n ؍ 3, 4b; n ؍ 4, 4bЈ). Suitable crystals
were grown by slowly evaporating a dichloromethane/n-
hexane solution of the complexes. The molecular structures
are illustrated in Figures 1 and 2. Crystal data are given in
Table 1 and selected bond distances and angles with esti-
mated standard deviations are shown in Table 2.
The crystal consists of discrete molecules separated by
van der Waals distances. The two isomers share the same
crystallographic position (except the sulfur and a carbon
atom, of the thiophene ring) with occupancies of approxi-
mately 50 % for each isomer. In both isomers the four-coor-
dinated paladium atom is bonded to one carbon atom (C(2)
and C(4) [27], for the isomers a and b, respectively) of the
thiophene ring and the imine nitrogen of the Schiff base
ligand, one monodentate acetate ligand and to the phos-
phorus atom of the triphenylphosphine ligand. The coordi-
stable solids, which were fully characterised (see Experimen-
1
tal section and Scheme 1). The H NMR spectra showed
the HCϭN resonance to higher frequency with respect to
1a, as a doublet owing to coupling to the phosphorus nu-
cleus. The H3 resonance was shifted to lower frequency by
ca. 1 ppm with respect to 1a, owing to shielding by the
phosphine phenyl rings, in accordance with a phosphorus
trans to nitrogen geometry. The 31P chemical shift values
were also consistent with a phosphorus trans to nitrogen
arrangement [22, 24Ϫ26]. Reaction of 2a and tri-
phenylphosphine produced the mononuclear compound 6a,
with the phosphorus ligand trans to the nitrogen atom
(see Experimental).
The chemical behavior of 3-SC4H3C(H)ϭNCy, b, was
very similar to that of ligand a, giving rise to the dinuclear,
1b, 2b, 3b, and mononuclear species, 4b, as air-stable prod-
ucts which were unequivocally determined (see Experimen-
tal Section for details of characterization) and shall not be
discussed in detail. However, it is most noteworthy to point
out that as opposed to ligand a, in the case b, there are two
possible positions for palladation giving rise to compounds
with the sulfur atom at the 3 (palladation at the Cortho to
sulfur) or 4 (palladation at the Cmeta to sulfur) sites, re-
sulting in the formation of two linkage isomers. Thus, reac-
tion of b and palladium acetate in toluene gave the di-
nuclear acetate-bridged complexes [Pd{n-SC4H2C(H)ϭ
738
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Z. Anorg. Allg. Chem. 2007, 734Ϫ740

Linkage Isomerism in Thiophene Cyclometallated Palladium(II) Complexes
Table 1 Crystal data and structure refinement data for compound
4b, 4bЈ.
Empirical formula
Formula weight
Temperature
C31H32NO2PPd S
620.01
293(2) K
˚
Wavelength
0.71073 A
Crystal system
Space group
Unit cell dimensions
triclinic
P 1
a ϭ 8.2478(1) A
b ϭ 11.4224(2) A
c ϭ 15.7151(1) A
¯
˚
α ϭ 80.449(1)°
β ϭ 88.429(1)°
γ ϭ 78.557(1)°
˚
˚
3
˚
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
θ range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to θ ϭ 28.28°
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff. peak and hole
1430.95(3) A
2
1.439 Mg/m3
0.805 mmϪ1
636
0.50 x 0.50 x 0.35 mm3
1.84 to 28.28°.
Ϫ10< h< 10, Ϫ15< k< 14, Ϫ20< l< 12
9858
6754 [R(int) ϭ 0.0146]
95.5 %
0.7658 and 0.6889
Full-matrix least-squares on F2
6754 / 6 / 336
1.025
R1 ϭ 0.0290, wR2 ϭ 0.0684
R1 ϭ 0.0361, wR2 ϭ 0.0719
0.423 and Ϫ0.673 e A
Figure 1 Molecular structure of [Pd{4-SC4H2C(H)ϭNCy}-
(O2CMe)(PPh3)] (4b), with labelling scheme. Hydrogen atoms have
been omitted for clarity.
Ϫ3
˚
˚
Table 2 Selected bond distances /A and angles /° for compound
4b, 4bЈ.
Pd(1)-N(1)
Pd(1)-O(1)
C(2/4)-Pd(1)-N(1)
N(1)-Pd(1)-P(3)
N(1)-Pd(1)-O(1)
2.118(2)
2.091(2)
80.34(8)
173.81(5)
93.19(5)
Pd(1)-C(2a/4b)
Pd(1)-P(1)
C(2/4)-Pd(1)-P(1)
C(2/4)-Pd(1)-O(1)
P(1)-Pd(1)-O(1)
1.990(2)
2.2487(6)
94.23(6)
172.25(8)
93.19(5)
˚
The Pd-C bond distance of 1.990(2) A is somewhat
shorter than the value predicted from the sum of the van
der Walls radii of palladium and carbon atoms [28] but
similar to values reported previously [13a, 29, 30] for ortho-
palladated thiophene rings. The Pd(1)-N(1) bond distance
˚
of 2.118(2) A is longer than the predicted value based on
the sum of the covalent radii of palladium atom an N(sp2)
radii [28] showing the high trans influence of the phosphine
phosphorus [31, 32]. The Pd(1)-P(1) bond distance of
˚
2.091(2) A is in agreement with the values previously re-
ported [31]. The Pd-O bond distance is also within the ex-
pected values [31Ϫ33].
Figure 2 Molecular structure of [Pd{3-SC4H2C(H)ϭNCy}-
(O2CMe)(PPh3)] (4bЈ), with labelling scheme. Hydrogen atoms have
been omitted for clarity.
The coordination sphere around palladium atom is
planar [mean deviation from the least square plane Pd(1),
˚
C(2/4), N(1), P(1), O1(1), (plane 1), of 0.0394 A] and ap-
proximately co-planar with the metallated ring [Pd(1), C(2/4),
˚
nation sphere of the palladium atom may be described as
slightly distorted square-planar. The angles between adjac-
ent atoms in the coordination sphere of palladium atom are
close to the expected value of 90° with the most noticeable
distortion corresponding to the bite angle C(2)/C(4)-Pd(1)-
N(1) of 80.34(8)°. The sum of the angles about palladium
is approximately 360°.
C(1), C(5), N(1); mean deviation 0.0329 A (plane 2)] and
with the thiophene ring [planes 3a and 3b, mean deviation
of 0.0178, 0.0213 A, for isomer a and b, respectively] (angles
between planes are: plane 1:2, 3.6°; plane 1:3a, 4.0°; 1:3b,
˚
4.3°; 2:3a, 2.9°; 2:3b, 3.4°).
No intra or intermolecular interactions were observed for
the thiophene sulfur.
Z. Anorg. Allg. Chem. 2007, 734Ϫ740
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www.zaac.wiley-vch.de
739

´
L. A. Adrio, J. M. Antelo, A. Fernandez, M. T. Pereira, M. Tato, J. M. Vila
´
Acknowledgments. We thank the Ministerio de Educacion y Ciencia
(Project CTQ2006-15621-C02-01/BQU) for financial support. L. A.
Adrio acknowledges a fellowship from the Xunta de Galicia and
[16] D. D. Perrin and W. L. F. Armarego, Purification of Labora-
tory Chemicals, Butterworth-Heinemann, London, 4th ed.,
1996.
´
J. M. Antelo acknowledges a fellowship from the Fundacion Gil
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and Refining Crystal Structures from Diffraction Data, Univer-
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