Syntheses and characterizations of thiolato-functionalized N-heterocyclic carbene Pd(ii) complexes with normal and mesoionic binding modes

Article abstract of DOI:10.1039/c1dt10789e

The thiolato-bridged dimeric Pd(ii) NHC complex 1 has been synthesized from the reaction of thioester-functionalized imidazolium salt B and Pd(OAc) ₂. The isolation of its interesting constitutional isomer 2 bearing both classical C(2)-bound an

Full text of DOI:10.1039/c1dt10789e

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Volume 40 | Number 44 | 28 November 2011 | Pages 11645–11984
ISSN 1477-9226
COVER ARTICLE
Yuan and Huynh
Syntheses and characterizations of
thiolato-functionalized N-heterocyclic
carbene Pd(II) complexes with normal
and mesoionic binding modes
1477-9226(2011)40:44;1-O

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PAPER
Syntheses and characterizations of thiolato-functionalized N-heterocyclic
carbene Pd(II) complexes with normal and mesoionic binding modes†
Dan Yuan and Han Vinh Huynh*
Received 29th April 2011, Accepted 13th June 2011
DOI: 10.1039/c1dt10789e
The thiolato-bridged dimeric Pd(II) NHC complex 1 has been synthesized from the reaction of
thioester-functionalized imidazolium salt B and Pd(OAc)2. The isolation of its interesting
constitutional isomer 2 bearing both classical C(2)-bound and mesoionic C(4)-bound ligands
coordinating to two different metal centers in the same complex allowed for a direct comparison of
these isomeric carbenes. Reactivity studies of 1 with NaSCH(CH3)2 and NaBF4 afforded the
tetranuclear compound 3 with a [Pd4S4] macrocycle. All complexes have been fully characterized by
multinuclei NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis.
Imidazolin-4-ylidenes, as an important type of mesoionic (abnor-
mal) carbenes,9 have been a focus of recent academic research
Introduction
due to their interesting nature and unusual bonding situation.10
Comparative studies on the donor strengths of various ligands11
show that imidazolin-4-ylidenes are generally stronger donors
than their normal counterparts (imidazolin-2-ylidenes). It has
also been reported that the increased donicity has led to a
better catalytic performance of their complexes in comparison
to imidazolin-2-ylidene analogues.8b
As an extension of our previously reported methodology, we
herein report on the synthesis and structural characterization
of a thiolato-bridged [Pd2S2] imidazolin-2-ylidene complex (1)
from a thioester-functionalized imidazolium salt (B) via in situ
hydrolysis. Besides the expected dimeric complex obtained as
the major product, an interesting dinuclear hetero-bis(carbene)
isomer (2) was isolated that contains both normal and mesoionic
carbene ligands allowing for a direct comparison of these two
isomeric ligands and their influence on the metal center in the same
complex. The reaction of the dimeric major isomer (1) with sodium
isopropyl thiolate led to a rearrangement to a new tetranuclear
[Pd4S4] molecular rectangle (3) supported by carbene ligands and
two different m-thiolato bridges.
N-heterocyclic carbenes (NHCs) have been investigated with
great intensity due to their unique properties1 and the ease of
their preparation as well as modification. In particular, donor
functions can be introduced at the nitrogen atom of the het-
erocycle in a simple manner, and various complexes of donor-
functionalized NHCs and their use in catalysis have been explored
and recently reviewed.2 Functionalization with N-, O- and P-
donor groups have been frequently reported, whereas NHCs
bearing S-donors,3 including thiolato-NHCs,4 thioether-NHCs5
and thiophene-NHCs,6 are still less studied. Among these sulfur
functionalized NHCs, we are particularly interested in thiolato-
NHCs due to the versatile and diverse coordination chemistry of
the soft, electron rich and anionic thiolato ligands in general.7
Previously we reported a straightforward one-pot synthesis of a
thiolato-bridged [Pd2S2] benzimidazolin-2-ylidene complex from
an easily available thioester-functionalized benzimidazolium salt
via in situ hydrolysis,4a which removes the necessity of han-
dling air-sensitive precursors in comparison with other reported
procedures.4b–d Besides the thiolato-bridged Pd(II) benzimidazolin-
2-ylidene complex mentioned above, and to the best of our
knowledge, all other reported examples are based on saturated
5- or 6-membered N-heterocycles. Thiolato-NHCs based on
imidazole remain unexplored, which is particularly surprising,
since the majority of NHCs are derived from imidazoles.
Results and discussion
In addition, recent studies have revealed that imidazole-based
NHCs can also bind to the metal center through the C(4)
carbon (imidazolin-4-ylidene), instead of the usual C(2) carbon.8
Thioester-functionalized imidazolium salt
The ligand precursor B with a thioester function can be syn-
thesized from 1-mesitylimidazole in a 2-step sequence. Nucle-
ophilic substitution of bromoethyl-substituted A5i with 1.2 equiv
of KSCOCH3 in CH3CN afforded the thioester-functionalized
imidazolium salt B as a brown oil (Scheme 1). A base peak in the
ESI mass spectrum at m/z = 289 for the [M - Br]+ cation indicates
the formation of B. Compared to its precursor A, an upfield shift of
the signal for the a-methylene protons from 4.08 ppm to 3.48 ppm
Department of Chemistry, 3 Science Drive 3, National University of
Singapore, Singapore, 117543. E-mail: chmhhv@nus.edu.sg; Fax: +65
67791691; Tel: +65 65162670
† Electronic supplementary information (ESI) available. CCDC reference
numbers 824213–824215. For crystallographic data in CIF or other
electronic format, see DOI: 10.1039/c1dt10789e
11698 | Dalton Trans., 2011, 40, 11698–11703
This journal is
The Royal Society of Chemistry 2011
©

are more complicated and exhibit twice the number of signals
compared to those of its isomer 1. More importantly, a sharp
signal for the NCHN proton of the mesoionic carbene is still
1
observed downfield at 8.90 ppm in the H NMR spectrum. In
the 13C NMR spectrum, two downfield signals are observed for
the two inequivalent carbene donor atoms.8b The more downfield
resonance at 162.9 ppm is attributed to the normal C(2) carbene
carbon, while that at 139.8 ppm is assigned to the mesoionic C(4)
carbene carbon. Attempts to interconvert 1 into 2 by heating and
addition of excess base were met with no success and only led
to intractable decomposition products.8b A theoretically possible
third isomer bearing two mesoionic carbenes was not observed.
Single crystals of 1·C3H6O and 2·2CH2Cl2 were grown from
concentrated acetone and CH2Cl2 solutions, respectively, and their
molecular structures are depicted in Fig. 1 and 2. In complex 1,
each of the two Pd(II) centers is bound to one carbene, one bromido
and two m-thiolato ligands in a square planar fashion. The dihedral
angles between the two [PdCS2Br] coordination planes and the
carbene ring planes amount to 54.1(1)◦ and 57.8(1)◦, respectively,
which are substantially smaller than the ideal 90◦ expected
for a monodentate NHC ligand due to the chelation through
Scheme 1 Synthesis of imidazolium bromides A and B.
was observed, which further supports the successful replacement
of the bromide with the less electronegative thioester function.
Thiolato-bridged Pd(II) carbene complexes
Palladation by treating salt B with one equiv of Pd(OAc)2 in
DMSO at 80 ◦C overnight afforded a mixture of thiolato-bridged
dinuclear [Pd2S2] carbene complexes in an overall yield >72%
(Scheme 2). The formation of the thiolato-donor occurs through
in situ hydrolysis of the methyl-thioester-function by acetic acid
liberated from the imidazolium deprotonation step and the water
present in the wet DMSO solvent.4a Subsequent coordination to
two Pd(II) centers further stabilizes the highly nucleophilic sulfur
function leading to the formation of thiolato-bridged dinuclear
Pd(II) complexes.
˚
the thiolato function. The Pd1–S2 [2.3691(12) A] and Pd2–S1
˚
[2.3642(13) A] bonds trans to the carbene are significantly longer
˚
˚
than the Pd1–S1 [2.2887(12) A] and Pd2–S2 [2.2944(12) A] bonds
trans to the bromido ligand due to the strong trans influence of the
NHC. As observed for the benzimidazolin-2-ylidene analogue,4a
the [Pd2S2] core of 1 is significantly bent with a hinge angle of ca.
120.10(4)◦.
Scheme 2 Synthesis of dinuclear Pd2S2 complexes 1 and 2.
The expected dimeric complex 1 was obtained in a yield of
44% after purification by column chromatography as a yellow
powder, soluble in CH2Cl2, CHCl3, acetone, DMSO, and DMF,
but insoluble in less polar solvents such as hexane and diethyl
ether. Its formation was confirmed by 1H NMR, which shows the
absence of the NCHN and the thioester protons. Upon complex
formation, the protons of the methylene group adjacent to the
nitrogen become diastereotopic with chemical shifts of 4.44 and
4.32 ppm. Likewise, the methylene protons of the bridge adjacent
to the sulfur also give rise to two diastereotopic signals at 3.66 and
1.93 ppm. The carbene carbon resonates at 163.8 ppm in the 13
C
NMR spectrum, which is as expected more highfield than that of
similar compounds bearing saturated4c or benzannulated NHCs.4a
A peak in the ESI mass spectrum at m/z = 782 for the mono-cation
[M - Br]+ also supports the formation of 1.
Fig. 1 Molecular structure of 1·C3H6O showing 50% probability ellip-
soids; hydrogen atoms and the acetone molecule are omitted for clarity.
◦
˚
Selected bond lengths [A] and bond angles [ ]: Pd1–C1 1.980(5), Pd1–S1
2.2887(12), Pd1–S2 2.3691(12), Pd1–Br1 2.4472(7), Pd2–C15 1.973(5),
Pd2–S2 2.2944(12), Pd2–S1 2.3642(13), Pd2–Br2 2.4340(7); C1–Pd1–S1
89.17(13), S1–Pd1–S2 81.05(4), S2–Pd1–Br1 97.36(3), Br1–Pd1–C1
92.49(13), C1–Pd1–S2 170.15(13), S1–Pd1–Br1 172.10(4), C15–Pd2–S2
89.72(13), S2–Pd2–S1 81.04(4), S1–Pd2–Br2 96.58(4), Br2–Pd2–C15
92.95(13), C15–Pd2–S1 170.37(13), S2–Pd2–Br2 171.50(4), Pd1–S1–Pd2
82.52(4), Pd1–S2–Pd2 82.29(4).
Besides the expected product 1, its interesting constitutional
isomer 2 bearing one imidazolin-2-ylidene and one mesoionic
imidazolin-4-ylidene ligand was isolated in a yield of 28% (Scheme
2). Compared to 1, the two NHCs in 2 adopt different coordination
modes: one is bound to the Pd center via C(2) (normal bonding
mode), while the other one coordinates via C(4) (mesoionic or
abnormal bonding mode). The formation of the mesoionic carbene
by competing deprotonation at C(4) probably helps to reduce
the steric congestion caused by the bulky mesityl substituent. As
direct isomers, complexes 1 and 2 cannot be differentiated by mass
spectrometry. On the other hand, the formation of 2 is evidenced by
NMR spectroscopy, which reveals distinct differences to complex
1. Due to the unsymmetrical nature of compound 2 as a result
The molecular structure of 2·2CH2Cl2 shown in Fig. 2 unam-
biguously confirmed the structure suggested by NMR spectra,
which shows that one carbene ligand is bound to the palladium
via the C(2) carbon while the other ligand is bound through the
C(4) carbon. To the best of our knowledge, complex 2 is the first
example of a dinuclear complex, in which a normal NHC and
its mesoionic isomer are coordinating two different metal centers
1
of two different carbene ligands, its H and 13C NMR spectra
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 11698–11703 | 11699
©

Fig. 2 Molecular structure of 2·2CH2Cl2 showing 50% probability ellip-
soids; hydrogen atoms and the CH2Cl2 mol◦ecules are omitted for clarity.
˚
Selected bond lengths [A] and bond angles [ ]: Pd1–C1 1.990(11), Pd1–S1
2.297(3), Pd1–S2 2.351(3), Pd1–Br1 2.4466(14), Pd2–C15 1.992(11),
Pd2–S2 2.266(3), Pd2–S1 2.378(3), Pd2–Br2 2.4490(15); C1–Pd1–S1
90.7(3), S1–Pd1–S2 79.67(10), S2–Pd1–Br1 95.98(8), Br1–Pd1–C1 93.6(3),
C1–Pd1–S2 170.4(3), S1–Pd1–Br1 174.40(9), C15–Pd2–S2 93.5(3),
S2–Pd2–S1 79.73(10), S1–Pd2–Br2 95.80(8), Br2–Pd2–C15 91.5(3),
C15–Pd2–S1 170.9(3), S2–Pd2–Br2 172.82(9), Pd1–S1–Pd2 82.19(9),
Pd1–S2–Pd2 83.47(10).
Scheme 3 Synthesis of the tetranuclear macrocycle 3.
two inequivalent groups of NHC ligands in this complex. The
splitting patterns of the methylene groups and their assignment are
complicated not only due to diastereotopicity, but also accidental
overlap with signals arising from methyl groups. As expected, two
carbene signals are observed at 169.1 and 166.5 ppm, respectively,
in the 13C NMR spectrum.
within the same complex. In principle, this allows for a direct
comparison of the two isomeric binding modes and their impact
on bond parameters around each metal center.
The molecular structure of 3 was finally confirmed by X-ray
analysis on single crystals obtained from a concentrated mixed
acetone/toluene solution (Fig. 3). Each of the four Pd(II) centers
is coordinated by one carbene and three m-thiolato donors in a
square-planar fashion.
Apparently, the bromido ligand in 1 was first replaced with
one isopropyl thiolato ligand accompanied by the precipitation
of NaBr. The new highly nucleophilic thiolato ligand replaces a
second bromido ligand of another Pd(II) center leading to a rear-
rangement of one Pd–S bond and subsequent dimerization to yield
tetranuclear 3. Similar to a previously reported benzimidazolin-
2-ylidene Pd4 species,4a there is an eight-membered [Pd4S4]
The two Pd–Ccarbene distances are essentially the same [1.990(11)
˚
and 1.992(11) A]. As expected, and as a result of the strong NHC
˚
˚
trans influences, the Pd1–S2 [2.351(3) A] and Pd2–S1 [2.378(3) A]
bonds trans to the carbenes are significantly longer than the
˚
˚
Pd1–S1 [2.297(3) A] and Pd2–S2 [2.266(3) A] bonds trans to
the bromido ligands. Notably, the Pd2–S1 bond [2.378(3) A]
˚
trans to the mesoionic carbene is longer than the Pd1–S2 bond
˚
[2.351(3) A] trans to the normal carbene, suggesting a stronger
trans influence of C(4)-bound carbenes.12 In addition, the Pd2–S2
˚
bond [2.266(3) A] cis to the mesoionic carbene is shorter than the
˚
Pd1–S1 bond [2.297(3) A] cis to the normal one. On the other
˚
˚
hand, the Pd–Br bond lengths [2.4490(15) A and 2.4466(14) A]
are essentially the same. The dihedral angles between the two
[PdCS2Br] coordination planes and the two carbene ring planes
are also significantly different. Due to the reduced steric crowding
around the mesoionic carbene, this angle has decreased to 31.3(3)◦,
whereas that of the classical isomer amounts to 50.7(3)◦. The hinge
angle of the [Pd2S2] core in 2, similar to that of 1 (vide supra), is
ca. 119.0(1)◦.
˚
macrocycle with almost the same dimensions of [4.6421(24) A
˚
¥ 4.6617(24) A]. The two bridging isopropyl thiolato ligands are
found at opposite sides of this macrocycle, which in turn results
in two different sets of carbene donors trans to these isopropyl
thiolato ligands (Fig. 3, lower depiction). As expected, the Pd–S
bonds trans to the carbenes are longer than those in cis positions
due to the strong trans influence of the carbenes. The formal
replacement of two terminal bromido ligands by one bridging
thiolato ligand with concurrent rearrangement to a species of
higher nuclearity is an interesting reaction that can be exploited
as an entry to metallo-based supramolecular chemistry.
With the aim to study the reactivity of such dimers toward
external thiolato ligands, the major dimeric isomer 1 was treated
with two equiv sodium isopropyl thiolate. Initially, a simple
bromido–thiolato ligand exchange was expected that should give
rise to the dimers X or X¢. Although the bromido ligands were
indeed abstracted, a tetra-palladium species was formed instead
(Scheme 3). Reaction optimization via counteranion exchange
using NaBF4 resulted in the isolation of the tetranuclear [Pd4S4]
macrocyclic compound 3, which was obtained as a yellow powder
soluble in CH2Cl2, CHCl3, acetone, CH3CN, but insoluble in
diethyl ether, toluene or hexane. In its ESI spectrum, a dicationic
base peak at m/z = 779 was assigned to the [M - 2BF4]2+ fragment.
Moreover, a smaller signal at m/z = 1644 assignable to the [M -
BF4]+ monocation was observed as well. The 1H NMR spectrum
shows two sets of signal in the aromatic region, suggesting
Conclusions
In summary, we have presented the first synthesis of cis-chelating
thiolato/imidazolin-2-ylidene complexes via a simple in situ
hydrolysis and palladation protocol of a thioester-functionalized
imidazolium bromide salt B. In addition to the desired dimeric
Pd(II) complex 1 containing two normal carbenes, its interesting
isomer 2 bearing both normal and mesoionic carbenes has
been isolated as well. The formation of the latter resulted from
competing deprotonation at C(4) instead of C(2) probably due
11700 | Dalton Trans., 2011, 40, 11698–11703
This journal is
The Royal Society of Chemistry 2011
©

synthesis of thiolato-functionalized NHC complexes to different
transition metals. Furthermore, work is underway to exploit the
bromido/thiolato ligand exchange reaction for the controlled
synthesis of higher metallo-aggregates.
Experimental section
General considerations
Unless otherwise noted, all operations were performed without
taking precautions to exclude air and moisture, and all solvents
and chemicals were used as received. Compound A was syn-
thesized according to a reported procedure.5i 1H and 13C NMR
spectra were recorded on a Bruker ACF 300 spectrometer or
AMX 500 spectrophotometer, and the chemical shifts (d) were
internally referenced to the residual solvent signals relative to
tetramethylsilane (1H, 13C). ESI mass spectra were measured using
a Finnigan MAT LCQ spectrometer. Elemental analyses were
performed on a Perkin–Elmer PE 2400 elemental analyzer at the
Department of Chemistry, National University of Singapore.
Syntheses
Thioester imidazolium salt (B). A mixture of salt A (374 mg,
1 mmol) and KSCOCH3 (137 mg, 1.2 mmol) in CH3CN (10 ml)
was stirred at ambient temperature overnight. The resulting
suspension was filtered and the solvent of the filtrate was removed
to yield the product as brown oil quantitatively (369 mg, 1 mmol).
1H NMR (300 MHz, DMSO-d6): d 10.06 (s, 1 H, NCHN), 8.01 (s,
1 H, NCHCHN), 7.16 (t, 1 H, NCHCHN), 6.94 (s, 2 H, Ar–H),
4.88 (t, 3J(H,H) = 6.1 Hz, 2 H, NCH2), 3.48 (t, 3J(H,H) = 6.1 Hz,
2 H, CH2S), 2.27 (s, 3 H, COCH3), 2.28 (s, 3 H, p-CH3), 2.02 (s,
6 H, 2 ¥ o-CH3). 13C{ H} NMR (75.47 MHz, DMSO-d6): 195.0
1
Fig. 3 Molecular structure of compound 3·2C7H8 (upper: top view;
(s, CO), 141.5 (s, NCHN), 138.3, 134.5, 131.0, 130.1, 124.4, 123.3
(s, Ar–C), 49.8 (s, NCH2), 30.9 (s, CH3), 30.1 (s, CH2S), 21.4 (s,
p-CH3), 17.9 (s, o-CH3). MS (ESI): m/z = 289 [M - Br]+.
lower: side view) showing 50% probability ellipsoids; hydrogen atoms,
-
the toluene molecules, BF4 counteranions, and mesityl groups are
omitted for clarity. Both N-substituents are omitted in the lower depic-
◦
˚
tion. Selected bond lengths [A] and bond angles [ ]: Pd1–C1 1.988(7),
Pd1–S2 2.3314(18), Pd1–S5 2.3917(18), Pd1–S1 2.3207(18), Pd2–S2
2.3336(18), Pd2–C15 1.991(7), Pd2–S3 2.3333(18), Pd2–S5 2.3656(17),
Pd3–S6 2.3939(18), Pd3–S3 2.3249(18), Pd3–C29 1.994(7), Pd3–S4
2.3267(18), Pd4–S1 2.3335(18), Pd4–S6 2.3703(18), Pd4–S4 2.3315(18),
Pd4–C43 1.989(7), S5–C57 1.851(8), S6–C60 1.849(8); C1–Pd1–S2 96.0(2),
S2–Pd1–S5 84.24(6), S5–Pd1–S1 93.86(6), S1–Pd1–C1 87.1(2), S2–Pd2–S5
84.24(6), S2–Pd2–C15 90.5(2), C15–Pd2–S3 89.3(2), S3–Pd2–S5
95.20(6), S6–Pd3–S4 83.85(6), S6–Pd3–S3 93.45(6), S3–Pd3–C29
87.5(2), C29–Pd3–S4 95.9(2), S1–Pd4–C43 88.6(2), S1–Pd4–S6 96.14(6),
S6–Pd4–S4 84.27(6), S4–Pd4–C43 90.6(2), Pd1–S2–Pd2 83.42(6),
Pd1–S5–Pd2 81.45(6), Pd1–S1–Pd4 105.39(7), Pd2–S3–Pd3 105.09(7),
Pd4–S6–Pd3 81.28(6), Pd4–S4–Pd3 83.54(6).
Dinuclear thiolato-bridged NHC complexes (1 & 2). A mixture
of salt B (506 mg, 1.37 mmol) and Pd(OAc)2 (307 mg, 1.37 mmol)
in DMSO (5 ml) was stirred at 80 ◦C overnight. The resulting
mixture was filtered and the solvent of the filtrate was removed by
vacuum distillation. The resulting residue was washed with H2O (3
¥ 20 ml) and diethyl ether (3 ¥ 20 ml). The product was purified by
chromatography on silica using ethyl acetate : hexane (0.8 : 1) (1,
261 mg, 0.303 mmol, 44%; 2, 167 mg, 0.194 mmol, 28%). Complex
1
3
1: H NMR (500 MHz, CDCl3): d 7.05 (d, J(H,H) = 1.9 Hz, 2
H, 2 ¥ NCHCHN), 6.98 (s, 2 H, Ar–H), 6.95 (s, 2 H, Ar–H),
6.80 (d, 3J(H,H) = 1.9 Hz, 2 H, 2 ¥ NCHCHN), 4.44 (ps-t, 2 H,
2 ¥ NCHH), 4.32 (ps-d, 2 H, 2 ¥ NCHH), 3.66 (ps-d, 2 H, 2 ¥
CHHS), 2.33 (s, 6 H, 2 ¥ p-CH3), 2.23 (s, 6 H, 2 ¥ o-CH3), 2.22
to steric reasons. The observed differences in bond parameters
around the two inequivalent Pd centers in a single complex is in
line with the view that mesoionic C(4)-bound carbenes are stronger
electron donors of greater trans influence than their direct C(2)-
bound classical analogues.
Metathesis reaction of the major isomer 1 with NaSCH(CH3)2
and NaBF4 led to rearrangement and dimerization to the
tetranuclear species 3 with a [Pd4S4] macrocycle. All complexes
have been fully characterized and their molecular structures
determined by X-ray diffraction analyses. Research in our lab is
currently on-going to extend the straightforward and promising
1
(s, 6 H, 2 ¥ o-CH3), 1.93 (ps-t, 2 H, 2 ¥ CHHS). 13C{ H} NMR
(125.77 MHz, CDCl3): 163.8 (s, NCN), 138.7, 135.8, 135.6, 134.9,
129.2, 129.0, 123.5, 120.9 (s, Ar–H), 56.0 (s, NCH2), 25.6 (s, CH2S),
21.2 (s, p-CH3), 19.3 (s, o-CH3), 19.1 (s, o-CH3). Anal. Calc. for
C28H34Br2N4Pd2S2: C, 38.95; H, 3.97; N, 6.49. Found: C, 39.06;
H, 3.84; N, 6.13%. MS (ESI): m/z = 782 [M - Br]+. Complex 2:
4
1H NMR (500 MHz, DMSO-d6): d 8.90 (d, J(H,H) = 1.9 Hz, 1
4
H, NCHN), 7.63 (d, J(H,H) = 1.9 Hz, 1 H, NCHCN), 7.34 (d,
3J(H,H) = 1.9 Hz, 1 H, NCHCHN), 7.09 (s, 2 H, Ar–H), 7.02 (s,
1 H, Ar–H), 6.97 (s, 1 H, Ar–H), 6.85 (d, 3J(H,H) = 1.9 Hz, 1 H,
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 11698–11703 | 11701
©

Table 1 Selected X-ray crystallographic data for complexes 1·C3H6O, 2·2CH2Cl2 and 3·2C7H8
1·C3H6O
2·2CH2Cl2
3·2C7H8
Formula
C28H34Br2N4Pd2S2·C3H6O
C28H34Br2N4Pd2S2·2CH2Cl2
C62H82B2F8N8Pd4S6·2C7H8
Formula weight
Color, habit
Cryst size/mm
T/K
921.41
1033.18
1915.20
Yellow, plate
0.32 ¥ 0.16 ¥ 0.08
100(2)
Yellow, plate
0.14 ¥ 0.12 ¥ 0.06
223(2)
Yellow, block
0.26 ¥ 0.26 ¥ 0.20
223(2)
Crystal system
Space group
Monoclinic
P21/c
17.718(2)
12.4490(18)
15.964(2)
90
103.858(3)
90
3418.7(8)
4
1.790
Mo-Ka
3.542
1.18–27.50
23 754
7836
Monoclinic
P21/n
16.9381(14)
8.9830(7)
24.9425(19)
90
91.468(2)
90
3793.9(5)
4
1.809
Mo-Ka
3.473
1.44–25.00
20 763
6686
Monoclinic
P21/n
15.3906(4)
24.2174(6)
24.4807(7)
90
90.7140(10)
90
9123.7(4)
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
Z
4
Dc/g cm-3
1.394
Mo-Ka
0.971
1.55–25.00
53 165
16 052
Radiation used
m/mm-1
q range/◦
Reflections collected
Independent reflections
R(int)
0.0483
0.1048
0.0546
Max., min. transmission
Final R indices [I > 2s(I)]
R indices (all data)
Goodness-of-fit on F2
0.7648, 0.3969
R1 = 0.0445, wR2 = 0.1082
R1 = 0.0596, wR2 = 0.1159
1.038
0.8187, 0.6420
R1 = 0.0776, wR2 = 0.1432
R1 = 0.1321, wR2 = 0.1591
1.079
0.8295, 0.7864
R1 = 0.0651, wR2 = 0.1743
R1 = 0.0859, wR2 = 0.1873
1.047
-3
˚
Peak/hole/e A
1.395/-1.757
1.011/-1.009
1.386/-0.892
NCHCHN), 4.70 (ps-d, 1 H, NCHH), 4.60 (ps-d, 1 H, NCHH),
4.19 (ps-t, 1 H, NCHH), 3.96 (ps-t, 1 H, NCHH), 3.46 (ps-d, 1 H,
CHHS), 3.19 (ps-d, 1 H, CHHS), 2.32 (s, 6 H, 2 ¥ p-CH3), 2.17 (s,
3 H, o-CH3), 2.15 (s, 3 H, o-CH3), 2.01 (s, 5 H, o-CH3 + CH2S),
19.8, 19.7, 19.1, 19.0, 14.8 (s, Ali-C). MS (ESI): m/z = 779 [M -
2BF4]2+, 1644 [M - BF4]+.
X-Ray diffraction studies
1
1.98 (s, 3 H, o-CH3). 13C{ H} NMR (125.77 MHz, DMSO-d6):
X-Ray data for 1·C3H6O, 2·2CH2Cl2 and 3·2C7H8 were collected
with a Bruker AXS SMART APEX diffractometer, using Mo-Ka
radiation at 100(2)K (for 1·C3H6O) or at 223(2)K (for 2·2CH2Cl2
and 3·2C7H8) with the SMART suite of Programs.13 Data were
processed and corrected for Lorentz and polarisation effects with
SAINT,14 and for absorption effects with SADABS.15 Structural
solution and refinement were carried out with the SHELXTL suite
of programs.16 The structure was solved by direct methods to locate
the heavy atoms, followed by difference maps for the light, non-
hydrogen atoms. All non-hydrogen atoms were generally given
anisotropic displacement parameters in the final model. All H-
atoms were put at calculated positions. A summary of the most
important crystallographic data is given in Table 1.
162.9 (s, NCN), 139.8 (s, NCCHN), 138.1, 136.3, 135.9, 135.7,
135.2, 134.9, 134.8, 134.6, 132.4, 129.5, 129.2, 129.1, 127.3, 124.4,
122.7 (s, Ar–H), 55.4 (s, NCH2), 54.8 (s, NCH2), 26.9 (s, CH2S),
23.3 (s, CH2S), 21.1 (s, p-CH3), 21.0 (s, p-CH3), 19.3 (s, o-CH3),
19.1 (s, o-CH3), 17.3 (s, o-CH3). Anal. Calc. for C28H34Br2N4Pd2S2:
C, 38.95; H, 3.97; N, 6.49. Found: C, 39.04; H, 4.03; N, 5.82%. MS
(ESI): m/z = 782 [M - Br]+.
Tetranuclear macrocyclic compound (3). A mixture of 2-
propanethiol (9.2 ml, 0.1 mmol) and NaOH aqueous solution
(16.0 ml, 0.1 mmol, 6.25 mol l-1) was stirred in degassed CH3CN for
0.5 h. Complex 1 (43 mg, 0.05 mmol) and NaBF4 (5 mg, 0.05 mmol)
were added to the mixture. After heating at 70 ◦C overnight, the
mixture was filtered over Celite. The solvent of the filtrate was
removed under vacuum to give a yellow solid. The compound was
recrystallized by slow evaporation of an acetone/toluene solution
(20 mg, 0.012 mmol, 46%). 1H NMR (500 MHz, CDCl3): d 7.35
(s, 2 H, Ar–H), 7.31 (s, 2 H, Ar–H), 6.99 (s, 2 H, Ar–H), 6.97 (s,
2 H, Ar–H), 6.91 (s, 2 H, Ar–H), 6.89 (s, 2 H, Ar–H), 6.84 (s, 2
H, Ar–H), 6.74 (s, 2 H, Ar–H), 4.91–4.84 (m, 4 H, 2 ¥ NCH2),
4.76 (m, 2 H, 2 ¥ NCHH), 4.49 (m, 2 H, 2 ¥ NCHH), 2.49 (m,
2 H, 2 ¥ SCH), 2.33 (s, 12 H, 4 ¥ Me), 2.16 (m, 16 H, 4 ¥ Me
+ 2 ¥ CH2S), 2.02 (s, 6 H, 2 ¥ Me), 1.98 (s, 6 H, 2 ¥ Me), 1.28
(m, 8 H, 2 ¥ Me + CH2S), 1.16 (m, 6 H, 2 ¥ Me), 0.93 (m, 2 H,
Acknowledgements
The authors thank the National University of Singapore for
financial support (WBS R-143-000-407-112). Technical support
from staff at the CMMAC of our department is appreciated. In
particular, we thank Ms Geok Kheng Tan, Ms Hong Yimian and
Prof. Lip Lin Koh for determining the X-ray molecular structures.
Notes and references
1 For a recent review, see: F. E. Hahn and M. C. Jahnke, Angew. Chem.,
Int. Ed., 2008, 47, 3122.
2 For a recent review, see: A. T. Normand and K. J. Cavell, Eur. J. Inorg.
Chem., 2008, 2781.
3 For a recent review, see: M. Bierenstiel and E. D. Cross, Coord. Chem.
Rev., 2011, 255, 574.
1
CH2S). 13C{ H} NMR (125.77 MHz, CDCl3): 169.1 (s, NCN),
166.5 (s, NCN), 140.4, 139.9, 136.1, 136.0, 135.96, 135.5, 135.2,
134.8, 130.2, 130.1, 130.0, 129.9, 124.2, 123.9, 122.8, 122.4 (s, Ar-
C), 55.9, 55.4, 39.5, 34.8, 32.6, 31.7, 30.2, 29.1, 23.4, 21.8, 21.7,
11702 | Dalton Trans., 2011, 40, 11698–11703
This journal is
The Royal Society of Chemistry 2011
©

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The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 11698–11703 | 11703
©