Thiocarbarmoyl-assisted formation of a new type of α-and β-isomer paddlewheel Pd24+ compounds. Synthesis, characterization, and crystal structures of [Pd(η1-SCNMe 2)(η2-Tp)(PPh3)]

Article abstract of DOI:10.1021/om100558m

The reaction of the doubly thiocarbamoyl-bridged boat-form complex [Pd(PPh₃)(Cl)]₂(μ-SCNMe₂)₂, 1, with dithio (SS) and tris(pyrazoyl-1-yl)borate (Tp) ligands produces the monomer η¹-thiocarbamoyl complexes [Pd(PPh₃) (η¹-CSNMe₂)(η²-SS)] (SS = Et ₂NCS₂, 2a; (EtO)₂PS₂, 2b) and [Pd(PPh₃)(η¹-CSNMe₂)(η²-Tp)] , 3, respectively. Treatment of 1 with dialkyldithiocarbonate, ROCS ₂^-, yields Fischer-type carbene complexes [Pd(PPh ₃){η¹-C(SR)(NMe₂)}(η²-S ₂CO)] (R = Me, 4a; Et, 4b). The carbene complexes 4a and 4b are formed via alkyl migration of the alkyldithiocarbonate ligand to the thiocarbamoyl ligand. The organometallic α-isomer paddlewheel-type Pd ₂⁴⁺ dipalladium complex without axial ligation, [Pd ₂(μ-Hdppa)₂(μ-SCNMe₂)₂][Cl] ₂, 5, is prepared by the reaction of Hdppa (Hdppa = bis(diphenylphosphino)amine) with 1. Treatment of 5 with anionic oxygen, nitrogen, or carbon reagents (KOH, NaN₃, NaNH₂, NaCCH), instead of forming axial ligation complex, yields the deprotonation of the Hdppa ligand of 5 to obtain the α-isomer paddlewheel Pd₂ ⁴⁺ complex [Pd₂(μ-dppa)₂(μ-SCNMe ₂)₂], 6. Protonation of 6 by HBF₄ or HCl gave 5 quantitatively as the BF₄^- and Cl^- salts, respectively. In the reaction of 5 with KTp, instead of forming a Tp-Pd complex, complex 6 was formed. The β-isomer paddlewheel complexes containing a Pd₂⁴⁺ core, [Pd(η²-dithio)] ₂(μ-dppa)(μ-SCNMe₂) (dithio = S₂P(OEt) ₂, 7a; S₂COEt, 7b; S₂CNC₄H ₈, 7c), are prepared by reactions of 5 with various dithio ligands, [NH₄][S₂P(OEt)₂], [K][S₂COEt], and [NH₄][S₂CNC₄H₈], in methanol at ambient temperature, respectively. X-ray structures of the new type of α-and β-paddlewheel Pd₂⁴⁺ species have been determined.

Full text of DOI:10.1021/om100558m

Organometallics 2010, 29, 3397–3403 3397
DOI: 10.1021/om100558m
Thiocarbarmoyl-Assisted Formation of a New Type of r- and β-Isomer
Paddlewheel Pd24þ Compounds. Synthesis, Characterization, and
Crystal Structures of [Pd(η1-SCNMe2)(η2-Tp)(PPh3)],
[Pd2(μ-Hdppa)2(μ-SCNMe2)2][Cl]2, [Pd2(μ-dppa)2(μ-SCNMe2)2],
and [Pd{η2-S2P(OEt)2}]2(μ-dppa)(μ-SCNMe2)
Kuang-Hway Yih*,† and Gene-Hsiang Lee‡
†Department of Applied Cosmetology, Hungkuang University Shalu, Taichung, Taiwan 433,
Republic of China, and Instrumentation Center, College of Science, National Taiwan University,
Taiwan, Republic of China
‡
Received June 6, 2010
The reaction of the doubly thiocarbamoyl-bridged boat-form complex [Pd(PPh3)(Cl)]2-
(μ-SCNMe2)2, 1, with dithio (SS) and tris(pyrazoyl-1-yl)borate (Tp) ligands produces the monomer
η1-thiocarbamoyl complexes [Pd(PPh3)(η1-CSNMe2)(η2-SS)] (SS = Et2NCS2, 2a; (EtO)2PS2, 2b)
and [Pd(PPh3)(η1-CSNMe2)(η2-Tp)], 3, respectively. Treatment of 1 with dialkyldithiocarbonate,
ROCS2-, yields Fischer-type carbene complexes [Pd(PPh3){η1-C(SR)(NMe2)}(η2-S2CO)] (R = Me,
4a; Et, 4b). The carbene complexes 4a and 4b are formed via alkyl migration of the alkyldithio-
4þ
carbonate ligand to the thiocarbamoyl ligand. The organometallic R-isomer paddlewheel-type Pd2
dipalladium complex without axial ligation, [Pd2(μ-Hdppa)2(μ-SCNMe2)2][Cl]2, 5, is prepared by the
reaction of Hdppa (Hdppa = bis(diphenylphosphino)amine) with 1. Treatment of 5 with anionic
oxygen, nitrogen, or carbon reagents (KOH, NaN3, NaNH2, NaCCH), instead of forming axial
ligation complex, yields the deprotonation of the Hdppa ligand of 5 to obtain the R-isomer
paddlewheel Pd24þ complex [Pd2(μ-dppa)2(μ-SCNMe2)2], 6. Protonation of 6 by HBF4 or HCl gave
-
5 quantitatively as the BF4 and Cl- salts, respectively. In the reaction of 5 with KTp, instead of
forming a Tp-Pd complex, complex 6 was formed. The β-isomer paddlewheel complexes containing a
Pd24þ core, [Pd(η2-dithio)]2(μ-dppa)(μ-SCNMe2) (dithio = S2P(OEt)2, 7a; S2COEt, 7b; S2CNC4H8,
7c), are prepared by reactions of 5 with various dithio ligands, [NH4][S2P(OEt)2], [K][S2COEt], and
[NH4][S2CNC4H8], in methanol at ambient temperature, respectively. X-ray structures of the new
type of R- and β-paddlewheel Pd24þ species have been determined.
Introduction
hydro-2H-pyrimido[1,2-a]pyrimidinate)5 bridging ligands.
4þ
R-Isomers were reported for the paddlewheel-type Pd2
3
complexes Pd(DPhBz)4 (DPhBz = N,N0-diphenylbenzami-
Paddlewheel-type metal complexes with bridging ligands
are a remarkable and important new class of homogeneous
catalysts.1 The R-isomer paddlewheel-type dipalladium com-
plexes without axial ligation are known in pyt (pyridine-
2-thionate),2 dpb (N,N0-diphenylbenzamidinate),3 mhp
(6-methyl-2-hydroxypyridinate),4 and hpp (1,3,4,6,7,8-hexa-
6
dinate), Pd2(TPG)4 (TPG = N,N,N0-triphenylguanidinate),
and Pt2(DArF)47 (DArF = diarylformamidinate), whereas
the β-isomers were reported for [Pd(TBT)]2(μ-acetate)2
(TBT = tolylbenzothiazole)8 and Pd2[μ-(C6X4)PPh2]2(μ-
O2CR)2. All four ligands in the R-isomer bridge the dimetal
unit to form a paddlewheel, and in the β-isomer, two brid-
ging and two chelating ligands coordinate to the metal
centers. Notably, these dipalladium complexes can be stabi-
lized by these bridging ligands with N, O, or S atoms,
and no metal-carbon bonded R-, β-isomer paddlewheel-
type dipalladium complexes have been synthesized and
characterized.
*Corresponding author. E-mail: khyih@sunrise.hk.edu.tw. Tel: 886-
4-26318652. Fax: 886-4-26321046.
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r
2010 American Chemical Society
Published on Web 07/12/2010
pubs.acs.org/Organometallics

3398 Organometallics, Vol. 29, No. 15, 2010
Yih and Lee
Scheme 1
All the characterized Pd(I) complexes are diamagnetic and
have at least dinuclear,9 side-by-side,10 or A-frame11 struc-
tures with a metal-metal bond, which allows the coupling of
the unpaired electron on each metal. The Pd24þ paddlewheel
complexes with d8 configurations of each Pd atom lead to a
Pd-Pd bond order of zero.
ligands in dichloromethane at ambient temperature pro-
duced the monomer η1-thiocarbamoyl complexes [Pd(PPh3)-
(η1-CSNMe2)(η2-SS)] (SS = Et2NCS2, 2a; (EtO)2PS2, 2b)
with 85% and 87% isolated yield (Scheme 1). Complexes 2a
and 2b can also be obtained from the reaction of [Pd-
(PPh3)2(η2-SCNMe2)][PF6]12a with dithio ligands, respec-
tively. In the reaction of 1 and tris(pyrazoyl-1-yl)borate,
the η1-thiocarbamoyl complex [Pd(PPh3)(η1-CSNMe2)(η2-
Tp)], 3, is produced with 80% isolated yield. Treatment of 1
with alkyldithiocarbonate, ROCS2-, yields Fischer-type
carbene complexes [Pd(PPh3){η1-C(SR)(NMe2)}(η2-S2CO)]
(R = Me, 4a; Et, 4b) with 72% and 75% isolated yield. No
dinuclear Fischer-type carbene complexes have been found
in the reaction. Fischer-type carbene complexes can also be
synthesized by the reaction of [Pd(PPh3)2(η1-SCNMe2)-
(Cl)]12b or [Pd(PPh3)2(η2-SCNMe2)][PF6] with alkyldithio-
carbonate ligands in methanol. Complexes 4a and 4b both
include a dithiocarbonate group, S2CO2-. Dithiocarbonate
metal complexes have previously been prepared by a variety
of synthetic routes including reactions of metal carbonyl
sulfide complexes with COS,14 reactions of metal carbon
disulfide complexes with dioxygen,15 dealkylation,16 iodide
abstraction,17 and hydrolysis18 of alkoxydithiocarbamate
metal complexes. Syntheses of carbene complexes by the
reaction of Pd thiocarbamoyl and thio ester complexes with
In an early study,12 variable-temperature 1H and 31P
NMR experiments of the thiocarbamoyl-Pd complex show
the sulfur-assisted dissociation reaction to form mono- and
dinuclear thiocarbamoyl-Pd complexes. In this paper, we
report the synthesis, characterization, electronic spectra, and
X-ray crystal structure analyses of a new type of R- and
4þ
β-isomer paddlewheel Pd2 compound formed in a thio-
carbamoyl-assisted mechanism.
Results and Discussion
Syntheses. Thiocarbamoyl chloride, Me2NC(S)Cl, has
been used to prepare the Pd-carbon complex [Pd(PPh3)2-
(η1-SCNMe2)(Cl)]13a and the intermolecular dissociation
reaction of complex [Pd(PPh3)2(η1-SCNMe2)(Cl)], forming
the doubly thiocarbamoyl-bridged boat-form dipalladium
complex [Pd(PPh3)(Cl)]2(μ-SCNMe2)2, 1.13b Treatment of 1
with diethyldithiocarbamate and diethyldithiophosphate
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Turner, G.. K. J. Chem. Soc., Chem. Commun. 1975, 615. (c) Werner, H.;
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Orlandini, A.; Scapacci, G. J. Chem. Soc., Dalton Trans. 1989, 211.
(b) Bianchini, C.; Meli, A. Inorg. Chem. 1987, 26, 4268. (c) Bianchini, C.;
Mealli, C.; Meli, A.; Sabat, M. J. Chem. Soc., Chem. Commun. 1985, 1024.
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Article
Organometallics, Vol. 29, No. 15, 2010 3399
Scheme 2
electrophiles have been reported.19 To our knowledge, our
discussion here of the formation of dithiocarbonate carbene
complexes via cleavage of the bridging S-Pd bond to form
a monomer alkyldithiocarbonate-Pd complex followed
by alkyl migration of the alkyldithiocarbonate ligand to
the thiocarbamoyl ligand has not been reported in the
literature.
prepare an axial ligation dinuclear compound or an A-frame
dinuclear complex from the reaction of 5 with KSCN,
PhCtCH, or S8 gave no reaction.
In order to synthesize different bridging ligands of paddle-
wheel-type Pd24þ complexes, some doubly nitrogen-bridged
boat-form dipalladium complexes of the type [Pd(PPh3)-
(X)]2(μ-L)2 (X=Cl, Br; L=4-methylpyridine-2-yl, 3-hydro-
xypyridine-2-yl, 3-aminopyridine-2-yl, pyrimidine-5-yl, thi-
azoline-2-yl, phenyloxythiocarbonyl)20 similar to complex 1
Treatment of 1 with Hdppa (Hdppa = {bis(diphenylphos-
phino)amine}) in dichloromethane at ambient temperature
causes displacement of both chloride and triphenylpho-
sphine ligands from palladium to give a novel paddlewheel-
4þ
have been prepared, and no paddlewheel-type Pd2 com-
plexes without exogenous ligation, [Pd2(μ-dppa)2(μ-N)2]-
[Cl]2, were obtained. To our knowledge, thiocarbamoyl-
assisted formation of new R- and β-isomer paddlewheel-type
Pd24þ complexes is the first example in the literature.
NMR Spectroscopy. The 1H, 31P{1H}, and 13C{1H} NMR
spectra of complexes 2a,b and 4a,b are compared to our
previous reports12a,b to confirm the formula. Complex 3
shows broad singlets for CH of pyrazole protons; because
of fast intramolecular exchange of the pyrazolyl groups, the
five-membered-ring inversion is too fast on the NMR time
scale. The 1H NMR spectra of R-isomers 5 and 6 in CDCl3
solution show two singlet resonances for the methyl groups
of the thiocarbamoyl ligands in the region of δ values from
1.54 to 2.15 ppm and the corresponding 13C{1H} NMR
signals from δ 38.3 to δ 54.9. The low-field section of the
13C{1H} NMR spectra consists of one sharp resonance
attributable on intensity grounds to the thiocarbamoyl
carbon atom in the region from δ 242 to δ 245. The 31P{1H}
NMR spectra of 5 and 6 show singlet resonance at δ 58.2 and
50.1, respectively.
4þ
type Pd2 complex without exogenous ligation, [Pd2(μ-
dppa)2(μ-SCNMe2)2][Cl]2, 5, in 82% isolated yield (Scheme 2).
Reaction of 5 with KOH, NaN3, NaCCH, or NaNH2 in
methanol yields neither an axial ligation dinuclear com-
pound nor a face-to-face dinuclear complex, but forms the
deprotonated Hdppa ligand in 5 to form the Pd24þ complex
[Pd2(μ-dppa)2(μ-SCNMe2)2], 6, with 75-98% isolated yield.
Protonation of 6 by HBF4 or HCl give 5 quantitatively as the
BF4- and Cl- salts, respectively. The phenomena also take
place in the reaction of 5 with KTp. Treatment of 5 with
various dithio ligands [NH4][S2P(OEt)2], [K][S2COEt], and
[NH4][S2CNC4H8] in methanol at ambient temperature un-
dergoes a deprotonation reaction on two Hdppa to form 6
first and then replacement of one Hdppa and one thio-
4þ
carbamoyl ligand to give the β-isomer paddlewheel Pd2
complexes [Pd{η2-S2P(OEt)2}]2(μ-dppa)(μ-SCNMe2), 7a,
[Pd(η2-S2COEt)]2(μ-dppa)(μ-SCNMe2), 7b, and [Pd(η2-S2C-
NC4H8)]2(μ-dppa)(μ-SCNMe2), 7c, in 75%, 82%, and 88%
isolated yield, respectively (Scheme 2). These air-stable and
yellow or red compounds are obtained in high yields and are
easily soluble in chlorinated or polar solvents but rather
insoluble in nonpolar solvents. No appreciable decomposi-
tion of these isolated products was observed even upon
prolonged standing of the precipitates in air. An attempt to
The 1H NMR spectra of β-isomers 7a, 7b, and 7c in CDCl3
solution also show two singlet resonances for the methyl
groups of the thiocarbamoyl ligands in the region of δ values
(20) (a) Wang, H. F.; Yih, K. H.; Huang., K. F.; Kwan., C. C.; Lee.,
G. H. J. Chin. Chem. Soc. 2009, 56, 718. (b) Yih, K. H.; Lee., G. H. J. Chin.
Chem. Soc. 2008, 55, 109. (c) Yih, K. H.; Lee., G. H.; Wang, H. F. J. Chin.
Chem. Soc. 2007, 54, 553.
(19) Dobrzynski, E. D.; Angelici, R. J. Inorg. Chem. 1975, 14, 1513.

3400 Organometallics, Vol. 29, No. 15, 2010
Yih and Lee
Figure 1. ORTEP drawing with 30% thermal ellipsoids and
atom-numbering scheme for the cationic complex [Pd(PPh3)(η1-
2
˚
SCNMe2)(η -Tp)], 3. Selected bond distances (A) and angles
(deg): Pd(1)-C(1) 1.980(3), Pd(1)-N(4) 2.101(2), Pd(1)-N(2)
2.138(2), Pd(1)-P(1) 2.2725(7), S(1)-C(1) 1.676(3), N(1)-
C(1) 1.318(4), C(1)-Pd(1)-N(4) 88.63(11), C(1)-Pd(1)-N(2)
170.64(11),N(4)-Pd(1)-N(2) 88.29(9), C(1)-Pd(1)-P(1) 88.75(8),
N(4)-Pd(1)-P(1) 176.27(7), N(2)-Pd(1)-P(1) 94.71(7).
Figure 2. ORTEP drawing with 50% thermal ellipsoids and
atom-numbering scheme for the cationic complex [Pd2(μ-
dppa)2(μ-SCNMe2)2][Cl]2, 5. Selected bond distances (A) and
angles (deg): Pd(1)-C(1A) 2.000(4), Pd(1)-P(1) 2.3283(11),
Pd(1)-P(2A) 2.3303(11), Pd(1)-S(1) 2.4321(10), Pd(1)-Pd(1A)
2.6908(6), S(1)-C(1) 1.732(4), C(1A)-Pd(1)-P(1) 89.56(12),
P(1)-Pd(1)-P(2A) 173.41(4), C(1A)-Pd(1)-S(1) 154.85(12),
P(1)-Pd(1)-S(1) 93.29(4), P(2A)-Pd(1)-S(1) 89.53(4), C(1A)-
Pd(1)-Pd(1A) 82.13(12).
˚
from 2.80 to 3.28 ppm and the corresponding 13C{1H} NMR
signals from δ 41.3 to δ 50.1 ppm. The low-field section of the
13C{1H} NMR spectra consist of one resonance attributable
on intensity grounds to the thiocarbamoyl carbon atom in
the region from δ 231.6 to δ 242.0 ppm. The 31P{1H} NMR
spectra of 7a, 7b, and 7c show two doublet resonances
attributed to the different chemical environment of the two
phosphorus atoms of the dppa ligand and two singlet
resonances for two (EtO)2PS2 ligands of 7a.
X-ray Single-Crystal Structures of 3, 5, 6, and 7a. The novel
complexes 3, 5, 6, and 7a were analyzed by X-ray diffraction
studies and are shown in Figures 1-4, respectively.
In Figure 1, the X-ray diffraction study of 3 reveals a
square-planar geometry for palladium with the poly-
(pyrazol-1-yl)borate ligands in bidentate mode, and the
uncoordinated pyrazole group lies above the coordination
plane. The poly(pyrazol-1-yl)borate ligands form a chelate
angle of 88.29(9)o and adopt a boat-form conformation for
the six-membered PdN4B ring. In complex 3, the Pd(1)-C(1),
Pd(1)-N(2), and Pd(1)-N(4) bond distances (1.980(3),
˚
2.101(2), and 2.138(2) A) are consistent with the values
Figure 3. ORTEP drawing with 50% thermal ellipsoids and
atom-numbering scheme for the complex [Pd2(μ-dppa)2(μ-
SCNMe2)2], 6. ORTEP view of molecule 6 looking along the
Pd-Pd bond, emphasizing the eclipsed geometry of the two
reported for PdII-C and Pd-N systems. The Pd(1)-N(2)
distance (trans to carbon) is slightly longer than Pd(1)-N(4)
(trans to phosphorus) because of the higher trans influence
induced by the thiocarbamoyl group than the triphenylpho-
sphine group. The N(2)-Pd-N(4) bond angle (88.29(9)o)
is larger than that reported for the same ligand in Pd(3-
C10H6CH2NMe)(η2-Tp) (85.52(8)o),21a Pd{2-CH2C6H4-
P(o-tolyl)2}(η2-Tp) (86.3(1)o), Pd(C6H4C5H4N)(η2-Tp)
(85.7(3)o),21b and PdPh(PPh3)(η2-Tp) (87.1(3)o) but smaller
than that of Pd(allyl)(η2-Tp)21c (92.2(3)o).
˚
PdL4 units. Selected bond distances (A) and angles (deg):
Pd(1)-C(1A) 1.998(5), Pd(1)-P(2A) 2.3409(13), Pd(1)-P(1)
2.3446(13), Pd(1)-S(1) 2.4330(13), Pd(1)-Pd(1A) 2.7113(8),
S(1)-C(1) 1.733(5), C(1A)-Pd(1)-P(2A) 90.93(14), C(1A)-
Pd(1)-P(1) 88.17(14), P(2A)-Pd(1)-P(1) 176.49(5), C(1A)-
Pd(1)-S(1) 154.34(15), P(2A)-Pd(1)-S(1) 89.82(5), P(1)-
Pd(1)-S(1) 92.45(5).
In each complex 5 and 6, the two palladium atoms are
bridged by two dppa and two thiocarbamoyl ligands, result-
ing in a paddlewheel-type structure; no axial coordination of
any kind has been found within the molecule or in the lattice.
The major changes are in the length of the Pd-Pd and P-N
bond distances, but the overall structures do not differ signi-
ficantly. The Pd24þ electronic configurations of 5 (Figure 2)
and 6 (Figure 3) have a bond order of zero. The Pd-Pd
(21) (a) Valk, J. M.; Maassarani, F.; Van der Sluis, P.; Spek, A. L.;
Boersma, J.; Van Koten, G. Organometallics 1994, 13, 2320. (b) Canty,
A. J.; Hoare, J. L.; Skelton, B. W; White, A. H.; Van Koten, G. J. Organomet.
Chem. 1998, 552, 23. (c) Canty, A. J.; Jin, H.; Roberts, A. S.; Traill, P. R.;
Skelton, B. W.; White, A. H. J. Organomet. Chem. 1995, 489, 153.

Article
Organometallics, Vol. 29, No. 15, 2010 3401
of the carbon than the sulfur atom of the thiocarbamoyl
˚
ligand. The P-NH bond distances (1.657(3) and 1.669(4) A
in complex 5) are longer than the P-N bond distances (in the
˚
range 1.596(3)-1.629(4) A in complexes 6 and 7a), due to the
delocalization of electron density of the dppa ligand in
complexes 6 and 7a.
IR, MS, and UV-Vis Spectroscopy. Spectroscopic and
analytical data of 2-7 were obtained. In the infrared spectra
of 2-4, the C-N stretches for the SCNMe2 group are in the
region 1429-1437 cm-1, typical for an η1-bound SCNMe2
group24 with a partial multiple C-N bond of the thiocarba-
moyl ligand. In the infrared spectra of 5-7, the C-N stre-
tches for the SCNMe2 group are in the region 1536-1556
cm-1, typical for an η2-bridging-bound SCNMe2 group with
partial multiple C-N bonds of the thiocarbamoyl ligand.
The peaks at 1520 and 1526 cm-1 in the IR spectra of 4a and
4b indicate a delocalized C(SR)NMe2 group. The IR spectra
of 4a and 4b show the CdO stretching band of the coordi-
nated carbonate ligand at 1680, 1612 and at 1683, 1618 cm-1
,
respectively, which are indicative of a chelate dithiocarbo-
nate ligand.14-18 In the FAB mass spectra, base peaks with
the typical Pd isotope distribution are in agreement with the
[M]þ molecular masses of 2-7, respectively.
Figure 4. ORTEP drawing with 50% thermal ellipsoids and
atom-numbering scheme for the complex [Pd2{η2-S2P(OEt)2}2]-
(μ-dppa)(μ-SCNMe2), 7a. Selected bond distances (A) and
angles (deg): Pd(1)-C(1) 1.983(4), Pd(1)-P(3) 2.2780(10),
Pd(1)-S(3) 2.4063(10), Pd(1)-S(2) 2.4418(10), Pd(1)-P(1)
2.9290(11), Pd(1)-Pd(2) 3.2279(4), C(1)-Pd(1)-P(3) 84.99(11),
C(1)-Pd(1)-S(3) 177.16(11), P(3)-Pd(1)-S(3) 97.16(4), C(1)-
Pd(1)-S(2) 94.73(11), P(3)-Pd(1)-S(2) 177.67(4), S(3)-Pd(1)-
S(2) 83.20(4).
˚
The UV-visible absorption spectra for R-isomers 5and 6and
β-isomers 7a-care obtained. The absorption bands were shown
at 406 nm (ε 850 M-1 cm-1) for 5, 445 nm (ε 406 M-1 cm-1) for
6, 439 nm (ε 4993 M-1 cm-1) for 7a, 445 nm (ε 5790 M-1 cm-1
)
for 7b, and 383 nm (ε 3740 M-1 cm-1) for 7c. Such an
absorption is similar to that of [PdII(bridge)4PdII]-type com-
plexes, since similar absorptions are also found in [Pd2(mhp)4]
(ca. 370 nm, ε = 2200),4 [Pd2(CH3CSS)4] (397 nm, ε = 2290),25
[Pd2(form)4] (492 nm, ε = 2600),26 [Pd2(μ-dbp)4] (500 nm, ε =
2500),3 and [Pd2(pyt)4] (430 nm, ε = 2150).2
˚
distance of 2.6908(6) A in 5 is slightly shorter, by ca. 0.0258
˚
˚
A, than that in 6 (2.7166(6) A). The crystal structure of 6 has
been shown to possess an eclipsed geometry. The Pd-Pd
˚
distance of 6 is 0.326 A longer than the shortest Pd-Pd
distance ever reported for any type complex in Pd2(hpp)4Cl2
and 0.229 A longer than that in Pd-Pd-NCCH3.
Conclusion
22
˚
The doubly thiocarbamoyl-bridged complex 1 is a good
starting material for the preparation of paddlewheel dipal-
ladium complexes. We employed Hdppa and three different
dithio ligands to investigate the new R- and β-isomer paddle-
4þ
The metal-carbon-bonded β-isomer paddlewheel Pd2
complex 7a has also been investigated by X-ray crystallo-
graphy. In Figure 4, one dppa and one thiocarbamoyl
bridging ligand are cis to each other, with the remaining
two dithio ions acting as bidentate chelating ligands, which
forms four-membered rings with separate palladium atoms.
The thiocarbamoyl ligand shows a strong tendency to adopt
bidentate coordination because of the ability of the amino
lone pair to contribute via conjugation to the metal-ligand
bonding.23 There are no formal metal-metal bonds in these
4þ
wheel Pd2 complexes, respectively. The monodentate an-
ionic oxygen, nitrogen, or carbon ligand improves the for-
4þ
mation of R-isomer paddlewheel-type Pd2 dipalladium
complexes without axial ligation, whereas the bidentate
anionic dithio ligands improve the formation of β-isomer
paddlewheel-type Pd2 dipalladium complexes. The thio-
4þ
carbamoyl ligand shows a strong tendency to adopt biden-
tate coordination because of the ability of the amino lone
pair to contribute via conjugation to the metal-ligand
bonding.
4þ
Pd2 complexes; the bridging bulky dppa molecules easily
force apart the chelating groups, resulting in the Pd-Pd
separation of 3.2279(4) A in 7a. The dihedral angle between
˚
the PdCPS2 and PdPS3 coordination planes of 7a is 45°,
which is considerably greater than the 24° angle found in the
benzoxazole and benzothiazole complexes,8 indicating much
greater steric repulsion in the present cases. In complex 7a,
the three planes of PdPS3, Pd2CS, and PdCPS2 lie in a
distorted square plane. A least-squares plane calculation
revealed the planarity of the three planes of 7a (largest
Experimental Section
Materials. All manipulations were performed under nitro-
gen using vacuum-line, drybox, and standard Schlenk techni-
ques. NMR spectra were recorded on a Bruker AM-500 WB
˚
deviation 0.0132-0.0722 A). In complex 7a, the Pd(1)-S(3)
(24) Gal, A. W.; Ambrosius, H. P. M. M.; Van der Ploeg, A. F. J. M.;
Bposman, W. P. J. Organomet. Chem. 1978, 149, 81.
(25) Iovesana, O.; Bellitto, C.; Flamini, A.; Zanazzi, P. F. Inorg.
˚
bond distance, 2.4063(10) A, is longer than the Pd(2)-S(5)
bond distance, 2.3439(11) A, due to the higher trans influence
˚
Chem. 1979, 18, 2258.
(26) (a) Cotton, F. A.; Gruhn, N. E.; Gu, J.; Huang, P.; Lichtenberger,
D. L.; Murillo, C. A.; Van Dorn, L. O.; Wilkinson, C. C. Science 2002, 298,
1971. (b) Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Timmons, D. J.;
Wilkinson, C. C. J. Am. Chem. Soc. 2002, 124, 9249. (c) Berry, J. F.; Cotton,
F. A.; Huang, P.; Murillo, C. A. J. Chem. Soc., Dalton Trans. 2003, 1218.
(22) Murahashi, T.; Otani, T.; Mochizuki, E.; Kai, Y.; Kurosawa, H.
J. Am. Chem. Soc. 1998, 120, 4536.
(23) Anderson, S.; Cook, D. J.; Hill, A. F. Organometallics 2001, 20,
2468.

3402 Organometallics, Vol. 29, No. 15, 2010
Yih and Lee
FT-NMR spectrometer and are reported in units of δ (ppm)
with residual protons in the solvent as an internal standard
(CDCl3, δ 7.24; CD3CN, δ 1.93; C6D6, δ 7.15; C2D6CO, δ 2.04).
IR spectra were measured on a Nicolet Avator 320 instru-
ment and were referenced to a polystyrene standard, using cells
equipped with calcium fluoride windows. Mass spectra were
recorded on a JEOL SX-102A spectrometer. Solvents were dried
and deoxygenated by refluxing over the appropriate reagents
before use. n-Hexane, diethyl ether, THF, and benzene were
distilled from sodium-benzophenone. Acetonitrile and dichloro-
methane were distilled from calcium hydride, and methanol was
distilled from magnesium. All other solvents and reagents were
of reagent grade and were used as received. Elemental analyses
and X-ray diffraction studies were carried out at the Regional
Center of Analytical Instrumentation located at the National
Taiwan University. PdCl2 and Hdppa were purchased from
Strem Chemical. KOH, NaN3, NaNH2, and NaCCH were
purchased from TCI. NH4S2P(OEt)2, KS2COEt, and NH4S2-
CNC4H8 were purchased from Merck.
(20 mL) with continuous stirring under a stream of dry nitrogen
was added NH4S2P(OEt)2 (0.406 g, 2.0 mmol). The color of the
solution changed from red to yellow immediately, and a yellow
precipitate was formed. The precipitate was collected by filtra-
tion (G4), washed with n-hexane (2 ꢀ 10 mL), and then dried in
vacuo to yield 0.792 g (75%) of [Pd{η2-S2P(OEt)2}]2(μ-dppa)-
(μ-SCNMe2), 7a. Further purification was accomplished by
recrystallization from 1:10 CH2Cl2/n-hexane. Spectroscopic
data of 7a are as follows: IR (KBr, νCN/cm-1): 1556(m). 31P{1H}
NMR (202 MHz, CDCl3, 298 K): δ 31.3, 50.7 (d, dppa, 2JP-P
=
21 Hz), 101.2, 111.4 (s, PS2). 1H NMR (500 MHz, CDCl3, 298
K): δ 1.15, 1.29 (br, 12H, OCH2CH3), 3.10, 3.28 (s, 6H, NCH3),
3.86, 4.11 (br, 8H, OCH2), 7.11-8.25 (m, 20H, Ph). 13C{1H}
NMR (125 MHz, CDCl3, 298 K): δ 15.8 (s, OCH2CH3), 42.1,
47.3 (s, NCH3), 61.8, 63.0 (br, OCH2), 127.9-140.8 (m, C of Ph),
242.0 (s, NCS). MS (FAB, NBA, m/z): 1056.8 (Mþ). Anal. Calcd
for C35H46N2O4P4Pd2S5: C, 39.82; H, 4.39; N, 2.65. Found: C,
39.84; H, 4.46; N, 2.60.
[Pd(η2-S2COEt)]2(μ-dppa)(μ-SCNMe2), 7b. The synthesis
and workup were similar to those used in the preparation of
complex 7a. The complex [Pd(η2-S2COEt)]2(μ-dppa)(μ-SCNMe2),
7b, was isolated in 82% yield as a yellow microcrystalline solid.
Spectroscopic data of 7b are as follows: IR (KBr, νCN/cm-1):
1554(m). 31P{1H} NMR (202 MHz, CDCl3, 298 K): δ 57.6, 67.4
(d, dppa, 2JP-P = 76 Hz). 1H NMR (500 MHz, CDCl3, 298 K): δ
1.54 (s, 6H, OCH2CH3), 2.79, 3.07 (s, 6H, NCH3), 4.52 (br, 4H,
OCH2), 7.08-8.38 (m, 20H, Ph). 13C{1H} NMR (125 MHz,
CDCl3, 298 K): δ 13.8 (s, OCH2CH3), 41.6, 50.1 (s, NCH3), 67.2,
67.6 (s, OCH2), 127.2-132.8 (m, C of Ph), 231.6 (s, NCS). MS
(FAB, NBA, m/z): 926.8 (Mþ). Anal. Calcd for C33H36N2O2-
P2Pd2S5: C, 42.72; H, 3.91; N, 3.02. Found: C, 42.78; H, 4.00;
N, 2.98.
[Pd(PPh3)(η1-SCNMe2)(η2-Tp)], 3. CH2Cl2 (20 mL) was
added to a flask (100 mL) containing 1 (0.984 g, 1.0 mmol)
and KTp (0.277 g, 1.1 mmol). The solution was stirred for 3 h.
The mixture was filtered by filtration (G4) with Celite; then
n-hexane (30 mL) was added to the solution, and a light yellow
precipitate was formed. The precipitate was collected by filtra-
tion (G4), washed with n-hexane (2 ꢀ 10 mL), and then dried in
vacuo, yielding 0.535 g (80%) of 3. Spectroscopic data for 3:
31P{1H} NMR: δ 31.1 (s, PPh3). 1H NMR: δ 3.10, 3.28 (s, 6H,
NMe), 6.09 (br, 3H, 4-H of pyrazole), 7.05, 7.82 (br, 6H, 3,5-H
of pyrazole), 7.27-7.67 (m, 15H, PPh3). 13C{1H} NMR: δ 42.1,
45.5 (s, NCH3), 128.5 (m, o-C of Ph), 131.1 (s, 4-C of pyrazole),
131.8 (m, p-C of Ph), 132.0 (s, 5-C of pyrazole), 134.2 (m, m-C of
Ph), 135.6 (s, 3-C of pyrazole). MS (FAB, NBA, m/z): 668 (Mþ),
601 (Mþ - pyrazole). Anal. Calcd for C30H30BN7PSPd: C,
53.87; H, 4.52; N, 14.66. Found: C, 54.01; H, 4.41; N, 14.58.
[Pd2(μ-Hdppa)2(μ-SCNMe2)2][Cl]2, 5. CH2Cl2 (10 mL) was
added to a mixture of Hdppa (0.384 g, 1.0 mmol) and complex
[Pd(PPh3)(Cl)]2(μ-SCNMe2)2, 1 (0.984 g, 1.0 mmol). After 10
min, a yellow solid was formed, which was isolated by filtration
(G4), washed with n-hexane (2 ꢀ 10 mL), and subsequently
dried under vacuum, yielding 1.009 g (82%) of [Pd2(μ-Hdppa)2-
(μ-SCNMe2)2][Cl]2, 5. Spectroscopic data of 5 are as follows: IR
(KBr, νCN/cm-1): 1550(m). 31P{1H} NMR (202 MHz, CDCl3,
298 K): δ 58.2 (s, Hdppa). 1H NMR (500 MHz, CDCl3, 298 K):
δ 1.55, 2.11 (s, 12H, NCH3), 5.74 (s, 2H, NH), 7.11-8.71 (m,
40H, Ph). 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 48.1, 54.9
(s, NCH3), 127.9-133.2 (m, C of Ph), 245.0 (s, NCS). MS (FAB,
NBA, m/z): 1159 (Mþ - 2Cl). Anal. Calcd for C54H54Cl2N4-
P4S2Pd2: C, 52.70; H, 4.42; N, 4.55. Found: C, 52.82; H, 4.46;
N, 4.38.
[Pd2(μ-dppa)2(μ-SCNMe2)2], 6. A solution of [Pd2(μ-Hdppa)2-
(μ-SCNMe2)2][Cl]2, 5 (1.059 g, 1.0 mmol), in MeOH (20 mL) was
treated with KOH (0.138 g, 3.0 mmol) at ambient temperature.
Instantly, the reaction mixture turned red. After 10 min of stirring, a
red precipitate was formed. The precipitate was collected by
filtration (G4), washed with n-hexane (2 ꢀ 10 mL), and dried in
vacuo to yield 1.136 g (98%) of [Pd2(μ-dppa)2(μ-SCNMe2)2], 6.
Spectroscopic data of 6 are as follows: IR (KBr, νCN/cm-1):
1536(m). 31P{1H} NMR (202 MHz, CD3OD, 298 K): δ 50.1. 1H
NMR (500 MHz, CD3OD, 298 K): δ 1.54, 2.16 (s, 12H, NCH3),
7.11-8.71 (m, 20H, Ph). 13C{1H} NMR (125 MHz, CD3OD, 298
K): δ 38.3, 49.5 (s, NCH3), 127.9-133.2 (m, C of Ph), 243.0 (s,
NCS). MS (FAB, NBA, m/z): 1159 (Mþ). Anal. Calcd for
C54H52N4P4S2Pd2: C, 56.01; H, 4.53; N, 4.84. Found: C, 56.22;
H, 4.51; N, 4.78.
[Pd(η2-S2CNC4H8)]2(μ-dppa)(μ-SCNMe2), 7c. The synthesis
and workup were similar to those used in the preparation
of complex 7a. The complex [Pd(η2-S2CNC4H8)]2(μ-dppa)(μ-
SCNMe2), 7c, was isolated in 88% yield as a yellow microcrys-
talline solid. Spectroscopic data of 7c are as follows: IR (KBr,
ν
CN/cm-1): 1554(m). 31P{1H} NMR (202 MHz, CDCl3, 298 K):
2
1
δ 55.9, 66.0 (d, dppa, JP-P = 80 Hz). H NMR (500 MHz,
CDCl3, 298 K): δ 1.84-1.95 (m, 8H, NCH2CH2), 2.80, 3.10 (s,
6H, NCH3), 3.94-3.77 (m, 8H, NH2), 7.01-8.42 (m, 20H, Ph).
13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 24.3, 24.6, 24.7,
24.8 (s, NCH2CH2), 41.3 (s, NCH3), 48.9, 49.1, 49.4, 49.8 (s,
NCH2), 127.0-132.8 (m, C of Ph), 205.2 (d, NCS2, 3JP-C = 25.8
Hz), 239.1 (s, NCS). MS (FAB, NBA, m/z): 979 (Mþ). Anal.
Calcd for C37H42N4P2Pd2S5: C, 45.44; H, 4.33; N, 5.73. Found:
C, 45.52; H, 4.46; N, 5.68.
Single-Crystal X-ray Diffraction Analyses of 3, 5, 6, and 7a.
Single crystals of 3, 5, 6, and 7a suitable for X-ray diffraction
analyses were grown by recrystallization from 20:1 n-hexane/
CH2Cl2. The diffraction data were collected at room tempera-
ture on an Enraf-Nonius CAD4 diffractometer equipped with
˚
graphite-monochromated Mo KR (λ = 0.71073 A) radiation.
The raw intensity data were converted to structure factor ampli-
tudes and their esd’s after corrections for scan speed, back-
ground, Lorentz, and polarization effects. An empirical absorp-
tion correction, based on the azimuthal scan data, was applied
to the data. Crystallographic computations were carried out on
a Microvax III computer using the NRCC-SDP-VAX structure
determination package.27
A suitable single crystal of 3 was mounted on the top of a glass
fiber with glue. Initial lattice parameters were determined from
24 accurately centered reflections with θ values in the range from
1.13° to 27.50°. Cell constants and other pertinent data were
collected. Reflection data were collected using the θ/2θ scan
method. The θ scan angle was determined for each reflection
Complex 6 can also be synthesized using the same procedure
by employing NaN3, NaNH2, NaCCH, or KTp with complex 5,
respectively.
(27) Gabe, E. J.; Lee, F. L.; Lepage, Y. In Crystallographic Comput-
ing 3; Sheldrick, G. M.; Kruger, C.; Goddard, R., Eds.; Clarendon Press:
Oxford, England, 1985; p 167.
[Pd{η2-S2P(OEt)2}]2(μ-dppa)(μ-SCNMe2), 7a. To [Pd2(μ-
dppa)2(μ-SCNMe2)2], 5 (1.159 g, 1.0 mmol), dissolved in MeOH

Article
Organometallics, Vol. 29, No. 15, 2010 3403
according to the equation 0.70 ( 0.35 tan θ. Three check
reflections were measured every 30 min throughout the data
collection and showed no apparent decay. The merging of
equivalent and duplicate reflections gave a total of 41 138 unique
measured data, of which 14 164 reflections with I > 2σ(I) were
considered observed. The first step of the structure solution used
the heavy-atom method (Patterson synthesis), which revealed
the positions of metal atoms. The remaining atoms were found
in a series of alternating difference Fourier maps and least-
squares refinements. The quantity minimized by the least-
squares program was w(|Fo| - |Fc|)2, where w is the weight of
a given operation. The analytical forms of the scattering factor
tables for the neutral atoms were used.28 The non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were in-
cluded in the structure factor calculations in their expected
positions on the basis of idealized bonding geometry but were
not refined in least-squares. All hydrogens were assigned iso-
˚
2
tropic thermal parameters 1-2 A larger than the equivalent Biso
value of the atom to which they were bonded. The final residuals
of this refinement were R = 0.040 and Rw = 0.092.
The procedures for 5, 6, and 7a were similar to those for 3. The
final residuals of this refinement were R = 0.050 and Rw
0.117 for 5, R = 0.054 and Rw = 0.119 for 6, and R = 0.041 and
=
R
w = 0.086 for 7a.
Acknowledgment. We thank the National Science
Council of Taiwan, Republic of China (project NSC98-
2113-M-241-001-MY2), for financial support and Mrs.
S.-L. Huang for carrying out NMR experiments.
Supporting Information Available: ORTEP diagrams and
tables of crystal, data collection, and refinement parameters, atomic
coordinates, bond distances and bond angles, and isotropic displa-
cement parameters for complexes 3, 5, 6, and 7a. This material is
available free of charge via the Internet at http://pubs.acs.org.
(28) (a) International Tables for X-ray Crystallography; Reidel:
Dordrecht, 1974; Vol. IV. (b) LePage, Y.; Gabe, E. J. Appl. Crystallogr.
1990, 23, 406.