Synthesis and molecular structure of chiral metallo-based sterically overcrowded alkenes

Article abstract of DOI:10.1016/S0040-4020(02)00090-X

A four step synthesis of pyridyl-2-yl-thioxanthen-9-ylidene-isoquinolines is described. The corresponding palladium complexes are the first examples of a novel class of chiral, metallo-based, sterically overcrowded alkenes. The crystal and molecular structure of the palladium dichloride complex shows an anti-folded helical configuration with significant distortion of the central olefinic bond.

Full text of DOI:10.1016/S0040-4020(02)00090-X

TETRAHEDRON
Pergamon
Tetrahedron 58 42002) 2183±2188
Synthesis and molecular structure of chiral metallo-based
sterically overcrowded alkenes
Matthijs K. J. ter Wiel, Auke Meetsma and Ben L. Feringap
Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4,
9747 AG Groningen, The Netherlands
Received 12 September 2001; accepted 24 January 2002
AbstractÐA four step synthesis of pyridyl-2-yl-thioxanthen-9-ylidene-isoquinolines is described. The corresponding palladium complexes
are the ®rst examples of a novel class of chiral, metallo-based, sterically overcrowded alkenes. The crystal and molecular structure of the
palladium dichloride complex shows an anti-folded helical con®guration with signi®cant distortion of the central ole®nic bond. q 2002
Elsevier Science Ltd. All rights reserved.
1. Introduction
racemization barriers and both the aryl-X and aryl-Y bond
lengths in symmetric7 and non-symmetric inherently5
dissymmetric alkenes 4Fig. 1).5,7
The development of organic materials for optical data
storage and molecular optical devices whose properties
can be modulated by light has attracted considerable interest
in recent years.1 The efforts in our groupwere focused on
the synthesis of helically shaped-sterically overcrowded
alkenes. The intriguing thermochromic, photochromic and
stereochemical properties associated with these chiral
compounds have resulted in chiroptical molecular
switches2,3 and the ®rst light-driven molecular motor.4,5
The properties of molecules to be used in optical memory
devices should meet three basic requirements: 4a) thermal
stability of both isomers, 4b) a repeatable switching cycle
without loss of activity, 4c) ready detectability of both
forms.
Figure 1. Structures of symmetrically and inherently dissymmetric over-
crowded alkenes.
Recently we reported the ®rst metallo-based overcrowded
alkene8 and it was shown that the isomerization barrier
increased considerably when the aryl-Y covalent bond in
1 was replaced by a metal ion coordinated to two pyridine
moieties as in complex 3.
The photochemical process in chiroptical molecular
switches, based on sterically overcrowded alkenes, pertains
to the bistability of the cis- and trans-`pseudo-enantiomeric'
forms6 of such helical compounds. Stereospeci®c inter-
conversion between `pseudo-enantiomers' with M-helicity
and P-helicity can be achieved by irradiation with light
of different wavelengths. Selectivity in the switching
process is accomplished by incorporation of electron
donating and withdrawing substituents within the
molecule.3
In order to combine the advantage of the larger racemization
barrier expected for the metallo-based overcrowded alkenes
and the possibility to tune the wavelength of the photo-
isomerization process and the selectivity in the chiroptical
switches, a novel class of metallo-based molecular switches
was envisioned. Towards this goal we report here the
synthesis and structural analysis of a chiral-helical shaped-
metallo-based overcrowded alkene.
Essential for the thermal stability of both stereoisomers, and
as a consequence the possibility to repeat the switching
cycle, is the presence of a high racemization barrier. It
was shown that a remarkable correlation exists between
2. Results and discussion
Keywords: alkenes; chiral compounds; molecular switches.
Corresponding author. Tel.: 131-50-3634278; fax: 131-50-3634296;
e-mail: feringa@chem.rug.nl
p
The palladium complexes 4 were chosen as the target
structures 4Fig. 2). Compared to structure 2 the upper
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020402)00090-X

2184
M. K. J. ter Wiel et al. / Tetrahedron 58 -2002) 2183±2188
method of choice is a gem-dichloride coupling reaction
which requires lower half thioxanthones 6 and for the
upper half 7 4Scheme 1).
Initially the synthesis of 7 was attempted by addition of
isoquinoline 8 to 42-pyridinylmethyl)lithium 9. However,
this coupling reaction gave 7 in very low yield 4Scheme 2).
Figure 2. The chiral metallo-based overcrowded alkenes.
benzo[a]thioxanthene moiety is replaced by a pyridine and
isoquinoline moiety, connected by a methylene group, and
PdCl2, the bridging Y group. The structural features of this
system show that by incorporation of metal binding sites
control can be achieved of the conformation and the
dynamic processes by metal binding. It is anticipated that
by adding a metal to the ligand, the otherwise free rotation
of the ligating pyridine and isoquinoline moieties is
constrained and the position of these moieties is locked.
As a consequence, due to steric hindrance around the central
ole®nic bond, the whole complex is forced to adopt a helical
architecture.
Scheme 2. Attempted synthesis of 7 by addition of 42-pyridinylmethyl)-
lithium 9 to isoquinoline 8.
More ef®cient was a four step approach using Reissert
compound 10.15 Compound 10 could readily be prepared
from isoquinoline, benzoylchloride and KCN. Initially, 10
was deprotonated using NaH in dry toluene, but the use of
tBuOK in dry THF proved to be more ef®cient. The dark
blue±purple solution of deprotonated 10 was treated with
picolylchloride providing the Reissert compound 11 in
moderate yield together with 7. This prompted the develop-
ment of a more ef®cient route in which 11 was not isolated,
but immediately hydrolyzed under basic conditions giving 7
in good yield 4Scheme 3).
The key stepin the synthesis of overcrowded alkenes is the
formation of the central sterically hindered double bond
connecting upper and lower halves. The retrosynthetic
scheme below shows that the ligands 4, necessary for the
formation of Pd-complexes 4, are to be obtained by coupling
of a thioxanthene lower half and an upper half bearing the
coordinating heterocycles 4Scheme 1).
Scheme 3. Synthesis of 1-42-pyridinylmethyl)isoquinoline 7.
The thioxanthenes, prepared by standard procedures,3,16
were converted into the corresponding gem-dichlorides
12a±d by treatment with pure oxalyl chloride. These highly
moisture sensitive compounds were not isolated, but
immediately used in the subsequent reaction with 7. Re¯ux-
ing the gem-dichlorides 12a±c in p-xylene in the presence
of 7 afforded target compounds 5a±c 4Scheme 4).
Scheme 1. Retrosynthetic scheme for 4 based on the gem-dichloride
approach.
There are several methods for the synthesis of a sterically
hindered ole®nic bond: the McMurry coupling,9 the
Barton±Kellogg reaction,10,11 Peterson ole®nation,12 and
gem-dichloride coupling.13 When the ®rst of these are to
be employed, one would eventually need a ketone moiety
at the position at which double bond is to be formed both in
upper and lower halves leading to several coupling
products. The latter two methods require a methylene and
ketone moiety at these positions. Based upon our experience
with the total synthesis of other overcrowded alkenes14 the
Scheme 4. Synthesis of ligands 5a±c.

M. K. J. ter Wiel et al. / Tetrahedron 58 -2002) 2183±2188
2185
Whereas 5a could be isolated in 45% yield, yields dropped
considerably when a substituent was introduced in the thiox-
anthene. The alkene 5b with a methyl substituent was
obtained in 18% yield and the methoxy-substituted alkene
The X-ray structure clearly shows the non-planar, helical
shaped structure with folded upper and lower parts of the
molecule. The tri- and tetracyclic units on both sides of the
central double bond are positioned in opposite directions
4i.e. anti-folded). The central six-membered rings,
embedding the palladium and sulfur atom in the upper and
lower parts of the molecule, clearly have a boat conforma-
tion. This conformation is necessary to allow the aromatic
rings to adopt an anti-folded con®guration to diminish the
steric strain around the central double bond caused by peri-
hydrogen interactions between H2 and H27 and H13±H14 and
H18. The folded con®guration is also evident from the
torsion angles: C9±C10±C15±C1ˆ113.68; C2±C1±C15±
C10ˆ2115.78; C17±C16±C28±C27ˆ2135.88; C28±C16±
C17±C18ˆ137.48.
1
5c was isolated in only 1.5% yield. H NMR spectra of 5b
and 5c, indicated the presence of both the cis and trans
isomer as is evident from characteristic resonances of the
methyl 41.84 and 2.04 ppm) and methoxy groups 43.33 and
3.45 ppm). Both geometrical isomers are obtained in a one
to one ratio. Attempts to synthesize 5d failed as only starting
material could be isolated 4Scheme 4).
Most probably this is due to steric hindrance, since for
increasing substituent sizes in 5a±c yields dropconsider-
ably. It has been reported13c that the addition of base results
in increased yields in the gem-dichloride-coupling reac-
tions. The same reaction, performed with 7 and 12a in the
presence of piperidine, however, did not provide product 5a.
The bond length of the central double bond 4C15±C16,
Ê
1.348 A) in the Pd-complex is similar to values found for
other chiral overcrowded alkenes.3,7 However, the central
double bond is, compared to those in other chiroptical mole-
cular switches, considerably distorted: C1±C15±C16±
C28ˆ5.28; C1±C15±C16±C17ˆ2174.88; C10±C15±C16±
C17ˆ7.48; C10±C15±C16±C28ˆ2172.68.
The palladium complexes 4a and 4b were obtained quanti-
tatively by heating the ligand and PdCl2 for 2.5 h at 508C
and subsequently at room temperature overnight in aceto-
nitrile 4Scheme 5).
The bond lengths to palladium for the square planar
Ê
palladium complex 4Pd±N 2.014/2.023 A and Pd±Cl
Ê
bonds 2.284/2.290 A) can be considered normal and show
no strong deviation from values reported in literature for
other bipyridine complexes17 and the previously reported
metallo-based sterically overcrowded alkene.8
Both 4a and 4b are chiral compounds. The groups around
the central double bond are forced by steric interactions into
non-planar, helical orientation. The chirality in these
inherently dissymmetric alkenes therefore originates from
this helical shape of the molecule and is controlled by the
metal-coordination in the upper part which `locks' the
pyridine and isoquinoline moieties.
Scheme 5. Synthesis of palladium complexes 4a and 4b.
Pure palladium complexes 4a and 4b, showing low solu-
bility, were isolated as yellow/orange powders. Upon
complexation of PdCl2 to the ligands 5a and 5b, a shift of
1
approximately 0.4 ppm down®eld was observed in the H
3. Conclusion
NMR-spectrum for the pyridinic protons in the complexes
4a and 4b. Crystals of 4b suitable for X-ray analysis 4Fig. 3)
could be obtained by slow diffusion of acetonitrile in a
chloroform solution of this complex.
In conclusion, the ®rst chiral metallo-based sterically over-
crowded alkenes have successfully been synthesized. The
new methylene-bridged isoquinoline±pyridine moiety is
introduced as a bidentate metal binding site. The X-ray
analysis of the palladium complexe 4b clearly show the
helical shape. The resolution of these new chiral over-
crowded alkenes and photochemical behavior are subject
to current investigation.
4. Experimental
4.1. General
1H NMR data were recorded on a Varian VXR 300 or a
Varian Unity 500 4at 300, or 500 MHz, respectively). 13C
NMR data were recorded on a Varian VXR 300 or a Varian
Unity 500 4at 75.48 or 125.80 MHz, respectively). The
chemical shifts are denoted in 4units ppm) with the solvent
as an internal standard and converted to the TMS scale.
High Resolution Mass Spectra 4HRMS) were recorded on
Figure 3. A Pluton representation of the structure of complex 4b.

2186
M. K. J. ter Wiel et al. / Tetrahedron 58 -2002) 2183±2188
a AEI MS-902 mass spectrometer by electron impact 4EI)
and were performed by Mr A. Kiewiet. Elemental analyses
were performed in the microanalytical department of our
laboratory by Mr H. Draayer, Mr J. Ebels and Mr J.
Hommes. Melting points were taken on a Mettler FP-2 melt-
ing point apparatus, equipped with a Mettler FP-21 micro-
scope and are uncorrected. All chemicals were obtained
from Acros, Aldrich, or Merck. Solvents were dried using
standard procedures.
hexane/EtOAc/Et3Nˆ10:3:1, Rfˆ0.35) giving 7 as a yellow
oil 40.99 g, 4.5 mmol, 71%). 1H NMR 4300 MHz, CDCl3) d
4.84 4s, 2H), 7.05 4m, 1H), 7.15 4d, Jˆ8.1 Hz, 1H), 7.4±7.6
4m, 4H), 7.77 4d, Jˆ8.1 Hz, 1H), 8.27 4d, Jˆ8.4 Hz, 1H),
8.47 4d, Jˆ5.9 Hz, 1H), 8.53 4d, Jˆ4.0 Hz, 1H); 13C NMR
475.48 MHz, CDCl3) d 44.0 4t), 118.8 4d), 120.2 4d), 122.2
4d), 125.0 4d), 126.0 4d), 126.2 4d), 126.2 4s), 128.8 4d),
135.2 4d), 135.2 4s), 140.9 4d), 148.0 4d), 158.0 4s), 158.2
4s); m/z4EI, %)ˆ221 46), 220 4M1, 41), 219 4100), 218 419),
217 44), 191 43), 115 43), 110 45), 109.5 49), 109 44), 95.5
43), 51 43); HRMS: calcd for C15H12N2: 220.10004, found
220.09898.
4.1.1. 2-Benzoyl-1-pyridin-2-ylmethyl-1,2-dihydro-iso-
quinoline-1-carbonitrile 011). To a re¯uxing solution of
10 42.08 g, 8.0 mmol) in dry toluene 430 ml) under a
nitrogen atmosphere was added NaH 40.72 g, 15.0 mmol,
50% dispersion in oil). The reaction mixture immediately
turned deepred. After re¯uxing for 3 min, picolylchloride
40.96 g, 7.5 mmol) in dry toluene 410 ml) was added where-
upon the reaction mixture was re¯uxed for 2 h. The reaction
mixture was then cooled to room temperature and a solution
of saturated NH4Cl 450 ml) was added. The reaction mixture
was extracted with CH2Cl2 42£50 ml), dried on Na2SO4,
®ltered and the organic layers were evaporated under
reduced pressure giving a brown oil. This oil was puri®ed
using column chromatography 4SiO2, hexane/EtOAc/
Et3Nˆ9:3:1, Rfˆ0.23) yielding the product as white crystals
which precipitated from the eluent 40.64 g, 1.8 mmol, 23%,
decomposition when T.1408C). 1H NMR 4300 MHz,
CDCl3) d 3.61 4d, Jˆ12.5 Hz, 1H), 3.88 4d, Jˆ12.5 Hz,
1H), 5.50 4d, Jˆ7.7 Hz, 1H), 6.33 4d, Jˆ8.1 Hz, 1H), 7.0±
7.6 4m, 12H), 8.35 4d, Jˆ4.8 Hz, 1H); 13C NMR
475.48 MHz, CDCl3) d 45.8, 60.4, 106.4, 117.7, 122.3,
124.9, 125.3, 126.5, 126.7, 127.9, 128.0, 128.5, 129.1,
129.4, 131.6, 133.3, 135.9, 149.1, 153.8, 169.4; m/z 4EI,
%)ˆ351 4M1, 0.5), 260 43), 259 413), 246 42), 220 47),
219 419), 218 44), 198 42), 197 410), 196 41), 169 43), 168
45), 154 42), 131 42), 106 48), 105 4100), 92 43), 78 43), 77
428), 76 42), 65 43), 51 45); m/z 4CI, %)ˆ354 45), 353 426),
352 4M1H1, 100), 326 46), 325 425), 222 411), 221 462),
139 48), 122 42), 105 46); Anal. Calcd: C, 78.60; H, 4.80; N,
12.00%; Found: C, 79.19; H, 4.86; N, 12.03%.
4.1.3. 1-0Pyridyl-2-yl-thioxanthen-9-ylidene-methyl)-iso-
quinoline 05a). In a magnetically stirred ¯ask under a
nitrogen atmosphere 6a 42.58 g, 12 mmol) was dissolved
in oxalyl chloride 450 ml). This mixture was re¯uxed for
3 h which resulted in a yellow solution. The oxalyl chloride
was removed under reduced pressure with an oil pump using
three liquid nitrogen traps. When the oxalyl chloride was
removed beige solid was obtained, which turned pink after
2.5 h in vacuo. Dry p-xylene 430 ml) was added giving a
pink solution, to which was added a solution of 7 42.68 g,
12 mmol) in dry p-xylene 420 ml) giving a dark green
mixture. This mixture was then re¯uxed overnight 418 h).
The reaction mixture had turned overnight orange/red and a
solid had precipitated. After cooling to room temperature
the reaction mixture was diluted with CH2Cl2 4200 ml) and
extracted with 6 M HCl solution 43£200 ml). The red acid
layers were washed with CH2Cl2 42£100 ml) and then
neutralized with NaHCO3. Upon addition of the NaHCO3
a yellow/red suspension was obtained. This suspension was
extracted with CH2Cl2 43£250 ml). The combined organic
layers were dried on Na2SO4 and the solvent removed under
reduced pressure giving a red oil. The compound was puri-
®ed by column chromotography 4neutral Al2O3 activity V,
CH2Cl2, Rfˆ0.43). After evaporation of the CH2Cl2, 5a is
obtained as a white foam 42.26 g, 0.68 mmol, 45%, mp
1
191.5±192.08C). H NMR 4CDCl3, 300 MHz) d 6.64±6.69
4dt, Jˆ7.7, 1.1 Hz, 1H), 6.85±6.90 4dt, Jˆ7.5, 1.1 Hz, 1H),
6.94±7.00 4dt, Jˆ7.5, 1.1 Hz, 1H), 7.02±7.51 4m, 10H),
7.55±7.57 4d, Jˆ6.2 Hz, 2H), 7.68±7.66 4d, Jˆ8.1 Hz,
1H), 8.57±8.59 4td, Jˆ5.1, 1.3 Hz, 1H), 8.75±8.77 4d,
Jˆ5.1 Hz, 1H); 13C NMR 475.48 MHz, CDCl3) d 119.7
4d), 121.4 4d), 124.9 4d), 125.2 4d), 125.6 4d), 125.9 4d),
126.26 4d), 126.34 4d), 126.4 4d), 126.6 4d), 126.9 4d),
128.2 4d), 129.4 4d), 129.5 4d), 133.3 4s), 134.0 4s), 135.2
4s), 135.4 4d), 135.6 4s), 136.0 4s), 138.4 4s), 141.6 4d), 149.1
4d), 157.7 4s),158.9 4s); m/z 4EI, %)ˆ417 42), 416 49), 415
430), 414 4M1, 97), 413 4100), 412 46), 411 47), 410 43), 382
43), 381 47), 380 44), 379 47), 338 43), 337 48), 336 427), 308
43), 304 44), 287 45), 286 420), 207.5 44), 207 412), 206.5 43),
206 49), 205 46), 197 43), 190 45), 189 44), 149 43), 44 44);
HRMS: calcd for C28H18N2S: 414.11906, found 414.11856;
Anal. Calcd: C, 81.13; H, 4.38; N, 6.76%; Found: C, 80.71;
H, 4.46; N, 6.83%.
4.1.2. 1-02-Pyridinylmethyl)isoquinoline 07). Under a
nitrogen atmosphere 11 41.65 g, 6.3 mmol) was dissolved
in dry THF 430 ml) and then cooled to 2508C. At 2508C
the Reissert compound 1015 was deprotonated by dropwise
addition of a solution of KOtBu 40.52 g, 7.0 mmol) in dry
THF 430 ml). Already when the ®rst dropwas added the
mixture turned deep purple. After adding all of the
KOtBu, the reaction mixture was stirred for 1 h at 2408C.
Upon addition of picolylchloride 40.89 g, 7.0 mmol) the
reaction mixture slightly decolorized. After stirring for 1 h
at 2308C, the reaction mixture was allowed to reach room
temperature. The reaction mixture was then stirred for an
additional 2 h whereupon a solution of 2 M KOH in H2O/
EtOH 430 ml) was added. The now red/orange solution was
stirred overnight. The reaction mixture was acidi®ed with
2 M HCl solution 4100 ml), diluted with CH2Cl2 4100 ml)
and extracted with 2 M HCl 42£100 ml). The combined
acidic layers were neutralized with NaHCO3 and then
extracted with CH2Cl2 43£100 ml). The organic layers
were dried on Na2SO4, ®ltered and the solvent removed
under reduced pressure resulting in a yellow brownish oil.
This oil was puri®ed using column chromatography 4SiO2,
4.1.4. 1-[02-Methyl-thioxanthen-9-ylidene)-pyridin-2-yl]-
isoquinoline 05b). This compound was prepared using the
procedure for the synthesis of 1-4pyridyl-2-yl-thioxanthen-
9-ylidene-methyl)-isoquinoline 5a. Starting from 6b
40.41 g, 1.8 mmol) and 7 40.36 g, 1.6 mmol), the product
was obtained after column chromatography 4neutral Al2O3

M. K. J. ter Wiel et al. / Tetrahedron 58 -2002) 2183±2188
2187
activity V, CH2Cl2, Rfˆ0.45) as a white foam 40.12 g,
56.82; H, 3.07; N, 4.73; Pd, 17.98%; Found: C, 56.08; H,
3.10; N, 4.76; Pd 17.75%.
1
0.28 mmol, 18%, mp99.3±99.7 8C). H NMR 4300 MHz,
CDCl3) d 1.84 4s, 3H), 2.04 4s, 3H), 6.59±6.69 4m, 2H),
6.81±6.86 4t, Jˆ7.7 Hz, 1H), 6.90±7.54 4m, 33 H), 7.64±
7.66 4d, Jˆ8.1 Hz, 2H), 8.18 4br. s, 2H), 8.54±8.58 4m, 2H),
8.72 4m, 2H); 13C NMR 475.48 MHz, CDCl3) d 20.4, 20.7,
119.77, 119.84, 121.50, 121.60, 125.11, 125.22, 125.66,
125.74, 126.13, 126.42, 126.47, 126.52, 126.69, 127.06,
127.44, 127.67, 128.32, 129.29, 129.55, 129.71, 129.74,
130.05, 130.39, 130.71, 133.77, 134.48, 135.08, 135.22,
135.42, 135.57, 135.63, 135.80, 136.17, 136.20, 138.79,
141.49, 141.78, 149.10, 149.24, 157.88, 158.06, 159.10,
159.31; m/z 4EI, %)ˆ431 42), 430 49), 429 433), 428 4M1,
100), 427 482), 413 43), 411 42), 397 42), 396 44), 395 46),
394 43), 393 44), 379 42), 352 44), 351 411), 350 436), 349
42), 348 43), 334 42), 322 42), 318 42), 302 43), 301 47), 300
429), 299 43), 298 43), 282 43), 215 42), 214.5 46), 214 419),
213.5 43.6), 213 49), 212 42), 211 45), 210 42), 206.5 42), 206
45), 205.5 43), 205 46), 198.5 42), 198 42), 197.5 42), 197 42),
196 42), 190 44), 189 44); HRMS: calcd for C29H20N2S:
428.13471, found 428.13331; Anal. Calcd: C, 81.28; H,
4.70; N, 6.54%; Found: C, 80.56; H, 4.83; N, 6.46%.
4.1.7.
Dichloro[1-[02-methyl-thioxanthen-9-ylidene)-
pyridin-2-yl]-isoquinoline] palladium 04b). Ligand 5b
472.6 mg, 0.17 mmol) and an equimolor amount of PdCl2
425 mg, 0.17 mmol) were stirred for 2.5 h at 508C in CH3CN
415 ml) and then overnight at room temperature. The orange
suspension becomes bright yellow after 30 min at 508C.
After removal of the solvent the palladium complex 5b
1
was obtained quantitatively as a yellow powder. H NMR
4300 MHz, CDCl3) d 1.77 4s, 3H), 2.08 4s, 3H), 6.63±6.66
4t, Jˆ7.7 Hz, 1H), 6.75±6.78 4d, Jˆ7.7 Hz, 1H), 6.87 4s,
1H), 6.93±7.79 4m, 35H), 7.83±7.86 4d, Jˆ8.4 Hz, 2H),
9.00±9.02 4d, Jˆ2.3 Hz, 1H), 9.03±9.04 4d, Jˆ2.9 Hz,
1H), 9.14±9.15 4m, 2H); m/z 4DEI, %)ˆ610 40.1), 608
40.2), 606 40.3), 604 4M1, 0.2), 429 432), 428 4100), 427
488), 425 45), 351 435), 300 427), 214 416); m/z 4DCI,
%)ˆ628 42), 626 46), 624 49), 622 4M1NH41, 8), 431
410), 430 434), 429 4100); Anal. Calcd: C, 57.49; H, 3.33;
N, 4.62; Pd, 17.56%; Found: C, 56.22; H, 3.26; N, 4.54; Pd
17.31%.
4.1.5. 1-[02-Methoxy-thioxanthen-9-ylidene)-pyridin-2-
yl-methyl]-isoquinoline 05c). This compound was prepared
using the procedure for the synthesis of 5a. Starting from 6c
40.75 g, 3.1 mmol) and 7 40.68 g, 3.1 mmol), 5c is obtained
after column chromatography 4neutral Al2O3 activity V,
CH2Cl2, Rfˆ0.43) as a white foam 420 mg, 0.045 mmol,
4.2. Crystal structure determination 04b)
Crystals suitable for X-ray diffraction were grown by slow
diffusion of acetonitrile in a chloroform solution containing
the palladium complex 4b. C29H20Cl2N2PdS, bright orange/
yellow block-shaped crystal 40.08£0.15£0.45), triclinic,
1
1.5%, mp88.2±89.0 8C). H NMR 4CDCl3, 125.80 MHz)
Ê
Ê
space group P-1, aˆ9.29341) A, bˆ11.12441) A,
d 3.33 4bs, 3H), 3.45 4s, 3H), 6.47±6.49 4dd, Jˆ8.4,
2.6 Hz, 1H), 6.62±6.65 4dt, Jˆ7.4, 1.2 Hz, 1H), 6.74±7.72
4m, 26H), 8.17 4bs, 2H), 8.59±8.60 4d, Jˆ4.8 Hz, 1H),
8.65±8.66 4dd, Jˆ3.3, 1.1 Hz, 1H), 8.75 4s, 2H); 13C
NMR 4CDCl3, 500 MHz) d 54.4, 54.6, 111.7, 113.0,
114.7, 119.3, 119.4, 121.1, 122.2, 121.7, 124.0, 124.4,
124.7, 125.1, 125.6, 125.9, 126.0, 126.1, 126.2, 126.2,
126.5, 126.6, 126.7, 126.8, 126.9, 127.0, 127.8, 129.0,
129.1, 129.4, 133.5, 134.3, 134.6, 133.9, 135.1, 135.3,
135.6, 135.7, 136.0, 136.3, 138.3, 138.4, 141.1, 141.2,
141.2, 148.8, 157.0, 157.2, 157.5, 158.3, 158.7; m/z 4EI,
%)ˆ445 433), 444 4100, M1) 443 456), 429 410), 401 45),
400 46), 368 45), 367 413), 366 438), 351 45), 323 46), 317
46), 316 426), 222 417), 206 45), 200 47), 199 46).
Ê
cˆ13.20541) A, aˆ101.04347)8, bˆ92.15049)8, gˆ
105.46747)8, Vˆ1285.642) A , Zˆ2, dxˆ1.565 g cm23
.
X-Ray data were collected on an ENRAF±NONIUS
Ê 3
CAD4T [Mo Ka, Graphite monochromated, lˆ
Ê
0.71073 A, Qmaxˆ20.33; v-scan, Tˆ150 K]. The structure
was solved using Paterson methods 4DIRDIF) nd re®ned on
F2 4SHELXL-93). Hydrogen atoms were taken into account
at calculated positions. Final R value 0.0357 44830 re¯ec-
tions). Crystallographic data 4excluding structure factors)
for the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supple-
mentary publication no. CCDC 170549. Copies of the data
can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK 4fax: 144-1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk).
4.1.6. Dichloro[1-0pyridyl-2-yl-thioxanthen-9-ylidene-
methyl)-isoquinoline] palladium 04a). Ligand 5a
4150 mg, 0.36 mmol) and an equimolar amount of PdCl2
464 mg, 0.36 mmol) were stirred for 2.5 h at 508C in
CH3CN 415 ml) and then overnight at room temperature.
The orange suspension becomes bright yellow after
30 min at 508C. After removal of the solvent the palladium
complex 4a was obtained quantitatively as a yellow powder.
1H NMR 4300 MHz, CDCl3) d 6.66±6.69 4t, Jˆ7.7 Hz, 1H),
6.95±7.11 4m, 4H), 7.29±7.38 4m, 4H), 7.44±7.46 4d,
Jˆ7.7 Hz, 1H), 7.57±7.69 4m, 4H), 7.74±7.76 4d,
Jˆ8.1 Hz, 1H), 7.80±7.83 4d, Jˆ8.4 Hz, 1H), 9.02±9.04
4d, Jˆ6.2 Hz, 1H), 9.13±9.15 4d, Jˆ5.9 Hz, 1H); m/z
4DEI, %)ˆ594 42.1), 592 4M1, 3.0), 591 41.6), 590 42.3),
589 41.5), 555 41.2), 554 40.8), 521 40.8), 416 48), 415 432),
414 4100), 413 4100), 412 48), 411 411), 381 47), 379 48), 336
432); m/z 4DCI, %)ˆ614 40.7), 612 42.0), 610 4M1NH41, 3),
608 42.4), 417 410), 416 432), 415 4100); Anal. Calcd: C,
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