Cyclometallated compounds. XIII. Cyclopalladation of 2-phenoxypyridine and structurally-related compounds

Article abstract of DOI:10.1016/S0022-328X(98)01203-0

2-Phenoxypyridine and 2-phenylsulfanylpyridine are cyclopalladated readily by palladium acetate to give six-membered metallocycles. Extension to the three isomeric bis(2-pyridyloxy)benzenes leads to a new series of doubly-cyclopalladated compounds. In contrast, 3-6-diphenoxypyridazine and 4-6-diphenoxypyrimidine only undergo monopalladation, whilst their sulfur analogues are resistant to cyclopalladation. All cyclometallated compounds are converted to their acetylacetonate derivatives and the X-ray crystal structure of one of these is described.

Full text of DOI:10.1016/S0022-328X(98)01203-0

Journal of Organometallic Chemistry 579 (1999) 97–105
Cyclometallated compounds. XIII. Cyclopalladation of
2-phenoxypyridine and structurally-related compounds
Duncan J. de Geest, Brendan J. O’Keefe, Peter J. Steel *
Department of Chemistry, Uni6ersity of Canterbury, Christchurch, New Zealand
Received 30 October 1998
Abstract
2-Phenoxypyridine and 2-phenylsulfanylpyridine are cyclopalladated readily by palladium acetate to give six-membered
metallocycles. Extension to the three isomeric bis(2-pyridyloxy)benzenes leads to a new series of doubly-cyclopalladated
compounds. In contrast, 3-6-diphenoxypyridazine and 4-6-diphenoxypyrimidine only undergo monopalladation, whilst their sulfur
analogues are resistant to cyclopalladation. All cyclometallated compounds are converted to their acetylacetonate derivatives and
the X-ray crystal structure of one of these is described. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Cyclometallation reactions; Palladium complexes; Acetylacetonate complexes; Crystal structure
2-phenoxypyridine (2) and 2-phenylsulfanylpyridine (3).
Furthermore, we have incorporated these structural
motifs into ligands potentially capable of undergoing
double cyclopalladations and report the reactions of the
three isomeric bis(2-pyridyloxy)benzenes (4–6) and the
pyridazine and pyrimidine derivatives (7–10). All the
cyclopalladated compounds have been converted to
their acac derivatives and the structure of one of these
has been determined by single crystal X-ray
crystallography.
1. Introduction
Cyclopalladated compounds have attracted renewed
interest in recent years as metallomesogens [1]. In par-
ticular, acetylacetonate (acac) derivatives of various
cyclopalladated ligands, including doubly-metallated
examples, have been the subject of several recent studies
[2]. The vast majority of cyclopalladated compounds
contain a five-membered metallocycle [3]. However,
six-membered palladocycles are known, as exemplified
by the cyclopalladation of 2-benzylpyridine (1) [4], in a
less facile reaction than that of 2-phenylpyridine, which
produces a five-membered ring.
Since cyclopalladation of such ligands is well known
to proceed via an electrophilic substitution process [5],
it was felt that replacement of the methylene spacer of
1 by an oxygen, or sulfur, atom would activate the
phenyl ring towards electrophilic substitution, thereby
promoting the formation of a six-membered palladocy-
cle. We thus report the cyclopalladation reactions of
* Corresponding author. Tel.: +64-3-3642432; fax: +64-3-
3642110.
E-mail address: p.steel@chem.canterbury.ac.nz (P.J. Steel)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01203-0

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D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
2. Results and discussion
monomeric palladium acac complex, 15, albeit in rather
1
poor yield (Scheme 1). The H- and 13C-NMR spectra
Cyclopalladations are usually carried out by reaction
of the ligand with either lithium tetrachloropalladate or
palladium acetate. Upon reaction with lithium tetra-
chloropalladate in methanol, 2-phenoxypyridine (2)
gave a coordination complex, rather than a cyclopalla-
dated compound [6]. However, reaction with palladium
acetate in acetic acid at room temperature proceeded
smoothly to give the acetate-bridged cyclopalladated
dimer 11, in 69% yield. Ligand metathesis of 11 with
excess lithium chloride gave the chloro-bridged dimer,
12, in good yield, and this, in turn, was converted to the
mononuclear acac complex, 13, by reaction with
sodium acac (Scheme 1).
were assigned completely by a combination of one- and
two-dimensional NMR techniques.
Having established that both 2 and 3 can be cyclo-
palladated with the formation of six-membered metallo-
cyclic rings, consideration was given to the
incorporation of two of these structural motifs within
individual ligands, which would, therefore, be poten-
tially capable of undergoing double cyclopalladation
reactions. Doubly cyclopalladated compounds have
been the subject of much study in recent years [9,10],
with particular interest in compounds containing a
doubly-palladated benzene ring [11]. The three isomeric
bis(2-pyridyloxy)benzenes (4–6) are each potentially ca-
pable of undergoing such double metallations of a
benzene ring. We have described previously the synthe-
sis and coordination chemistry of these three ligands
[12,13] and have now examined their cyclopalladation
chemistry.
Complete assignment of the 1H-NMR spectrum of 13
was complicated by the overlap of the resonances for
H-5, H-4% and H-5%. This problem was overcome conve-
niently by the use of 1D-TOCSY experiments, which
enable the resolution of signals within isolated spin
systems [7]. Thus, irradiation of the doublet at 8.81
ppm (assigned to H-6) provided the entry into the
pyridyl ring spin system, allowing the assignment of the
triplet at 7.08 ppm to H-5. Similarly, irradiations of the
signals due to H6% (6.98 ppm) and H3% (7.62 ppm), with
short mixing times, resulted in magnetisation transfer
only to the adjacent protons H-5% and H4%, respectively.
The 13C-NMR spectrum of 13 was assigned subse-
quently by means of an HMQC experiment (see Section
4).
Reaction of the corresponding thioether, 3, with pal-
ladium acetate in acetic acid at room temperature, or
under reflux, failed to produce the desired acetate-
bridged dimer. However, reaction with palladium ac-
etate in benzene, under conditions described recently
for the cyclopalladation of primary and secondary ben-
zylamines [8], successfully induced cyclopalladation, to
give, following acetate–chloride exchange, a chloro-
bridged dimer 14, in reasonable yield. Subsequent lig-
and exchange of 14 with thallium acac gave the
Reaction of 1,2-bis(2-pyridyloxy)benzene (4) with
two equivalents of palladium acetate in refluxing acetic
acid gave a product, in 67% yield, within which the
central benzene ring is doubly metallated. Whereas
single-metallation reactions using palladium acetate
lead to acetate-bridged dimeric products [14], the prod-
ucts resulting from double-metallation of a ligand are
represented usually as polymeric species. However, we
have shown recently that this is not necessarily so and
that tetranuclear molecular structures can be formed
[14]. In the present example, we believe that the
product, 16, exists as a tetranuclear dimer with the two
ligand components being bridged by four acetate lig-
ands (Scheme 2). Direct ligand exchange of 16 with
acetylacetone, in the presence of triethylamine, gave the
dipalladium acac complex, 17, in 72% yield. The FAB
mass spectrum of this compound showed a strong
cluster of peaks centred around m/z=674 a.m.u., with
the correct isotopic distribution for two palladium
1
atoms. The H- and 13C-NMR spectra were completely
assigned by a combination of one- and two-dimensional
techniques (see Section 4).
Whereas the ortho isomer (4) can only undergo cy-
clometallation in the 3- and 6-positions, the meta iso-
mer (5) has two possible modes of reaction: either single
metallation in the 2-position, with tridentate coordina-
tion involving both of the pyridyl rings, or double
metallation in the 4- and 6-positions. For related com-
pounds, both modes of reaction are known [15]. In the
event, reaction of the meta isomer, 5, with two equiva-
lents of palladium acetate in acetic acid, at room tem-
perature, gave the 4,6-dicyclopalladated complex, 18, in
modest yield. Again, we believe that this complex is a
tetranuclear dimer with four bridging acetate ligands.
The cleft-shaped topology of such a species would be
similar to that of a doubly-cyclopalladated product
Scheme 1.

D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
99
Scheme 2.
from reaction of 1,3-bis(1-ethylbenzimidazol-2-yl)-
benzene, which has recently been crystallographically
characterised [16]. Ligand metathesis of 18 with excess
lithium chloride gave the corresponding chloro-bridged
complex in 74% yield, and this was, in turn, converted
into the dipalladium acac complex 19. This compound
was characterised fully by elemental analysis, mass
spectrometry, infrared and NMR spectroscopy (see Sec-
tion 4).
Reaction of the para-isomer 6 with two equivalents
of palladium acetate in acetic acid, at room tempera-
ture, gave a doubly-palladated complex. This ligand
can also undergo double metallation to give two possi-
ble regioisomers, depending upon whether it reacts in
the 2- and 3-positions or the 2- and 5-positions. By
analogy with our recently reported product from the
double palladation of 1,4-bis(benzothiazol-2-yl)benzene
[14], we believe that this complex has the box-shaped
tetranuclear structure (20) shown in Scheme 2, with
palladation occurring in the 2- and 5-positions, for
steric reasons. This is supported by the FAB mass
spectrum which shows a highest-mass cluster of peaks
centred around 1186 a.m.u., with a Pd4 isotopic distri-
bution. Ligand metathesis of 20 with excess lithium
chloride gave a chloro-bridged complex, in 92% yield,
which in turn was converted into the monomeric dipal-
ladium acac complex, 21. This complex is insoluble in
common NMR solvents.
series, the binucleating ligands have utilised a phenyl
ring as the central component, with two appended
heterocycles. An alternative approach to new doubly-
cyclopalladated compounds would be to use a heterocy-
cle as the central component with two attached
phenoxy groups. This is the case with the four ligands
(7–10), containing central pyridazine and pyrimidine
cores with two suitably placed phenoxy or phenylsul-
fanyl substituents. Previously, we have shown that di-
azines with two directly attached phenyl rings can be
made to undergo double cyclopalladations [17].
The two pyridazine derivatives, (7) and (8), were
prepared from 3,6-dichloropyridazine according to lit-
erature procedures [18,19]. Reaction of the pyridazine
bis-ether, 7, with one equivalent of palladium acetate in
benzene gave the acetate-bridged dimer, [Pd(7–
H)OAc]2, which, after metathesis to the corresponding
chloride and acac exchange, gave the mononuclear
This series of doubly-cyclopalladated complexes rep-
resents the first examples of double cyclopalladation
with the formation of two six-membered rings, unsup-
ported by additional donor groups [15]. Within this
Scheme 3.

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D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
˚
from the plane being 0.023(4) A for C1%A. The six-
membered metallocycles each exist in a shallow boat
conformation: Pd1 and O3 are 0.640(2) and 0.368(3)
˚
A, respectively, above the meanplane defined by N2,
C3, C1% and C2%; and Pd1A and O3A are 0.656(2)
˚
and 0.347(3) A, respectively, above the meanplane
defined by N2A, C3A, C1%A and C2%A. The cy-
clometallated phenyl ring is inclined to the pyridazine
ring at an angle of 38.6° in one molecule and at 37.0°
in the other.
The palladium atoms have approximately square
planar coordination to the CNO2 donor set (Fig. 1)
and the Pd–C, Pd–N bond lengths are similar to
those in related cyclopalladated complexes which in-
corporate a nitrogen donor in a five-membered metal-
locycle
[21].
The
geometries
of
the
two
acetylacetonate subunits are very similar to those that
have been determined for related structures [21]. Of
particular note is the difference in the Pd–O bond
lengths, with those trans to carbon being significantly
longer than those trans to nitrogen, this variation be-
ing consistent with those seen in related structures
and a reflection of the different trans influences of
carbanion and nitrogen donors [21]. This complex
represents the first example of a crystallographically
characterised structure incorporating a bidentate lig-
and with a nitrogen donor in a six-membered metal-
locycle formed from palladation of an aryl ring.
Other related structures incorporate tridentate metal-
lated ligands [22], or result from aliphatic palladation
[23], or both [24].
A significant feature of the structure is the highly
encumbered environment of the non-coordinated ni-
trogen (N1) of the pyridazine ring (Fig. 1). In order
to undergo double cyclometallation the corresponding
nitrogen in the monopalladated intermediate must
first coordinate to a second palladium atom. We rea-
soned that this was a probable explanation for the
resistance of 7 towards double metallation and there-
fore felt more optimistic that the pyrimidine ana-
logues, (9) and (10), would be more amenable to
double metallation. Thus, these two new ligands were
synthesised, in yields of 89 and 47%, from 4,6-
dichloropyrimidine, by reaction with two equivalents
of phenoxide and thiophenoxide, respectively.
Fig. 1. Perspective view and atom labelling of one of the two
independent molecules of 22. Selected bond lengths (A) and angles (°)
for the Pd1 [and Pd1A] molecule: Pd1–C2% 1.972(3) [1.974(3)], Pd1–
N2 2.012(2) [2.006(2)], Pd–O1 2.080(2) [2.076(2)], Pd–O2 2.032(2)
[2.018(2)]; C2%–Pd1–N2 87.3(2) [87.6(1)], O1–Pd1–O2 91.66(8)
[91.92(7)], C3–O3–C1% 119.5(2) [120.7(2)].
˚
complex 22, in good yield (Scheme 3). This monopal-
ladated complex was again characterised fully by
standard NMR techniques. A number of attempts
were made to doubly-metallate 7 with palladium ac-
etate (in a variety of solvents and under a range of
reaction conditions), but these invariably gave only
the singly-cyclopalladated product. This is despite the
fact that a pyridazine subunit is well-known to act as
a good bridging component in the formation of binu-
clear metal coordination complexes [20]. Furthermore,
all attempts to react the sulfur analogue (8) with pal-
ladium acetate, in either acetic acid or benzene, failed
to produce even a singly-cyclopalladated product. In
view of these findings, it was decided to perform a
single crystal X-ray structure determination of 22, in
order to examine its exact structure in more detail.
The cyclopalladated acac complex of 3,6-diphe-
noxypyridazine crystallises in the orthorhombic space
group P212121, with two independent molecules of 22
in the asymmetric unit. Fig. 1 shows a perspective
view and atom labelling of the structure of one of the
molecules, with selected interatomic distances and an-
gles. The two independent molecules have similar
bonding geometries, but differ in the conformations
of the non-metallated phenoxy substituents. Specifi-
cally, the phenoxy and pyridazine ring meanplanes
are inclined at an angle of 72.7° in the molecule
shown but at an angle of 63.7° in the other molecule
in the asymmetric unit.
Despite our optimism that double metallation
might occur, these two ligands behaved similarly to
their pyridazine analogues. Thus, the diphenoxy
derivative (9) reacted with palladium acetate in ben-
zene to give, after conversion to the chloride deriva-
tive and ligand exchange, the mononuclear acac
derivative 23, the NMR spectra of which were as-
signed fully (Scheme 3). Once again, all attempts to
induce double palladation proved unsuccessful, as did
attempts to cyclometallate the sulfur analogue 10.
The four phenyl and two pyridazine rings are each
essentially planar, with the maximum displacement

D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
101
3. Concluding comments
4. Experimental
In this study we have shown that 2-phe-
noxypyridine (2) and its sulfur analogue (3) readily
undergo cyclopalladation to produce complexes con-
taining six-membered metallocycles. Furthermore, all
three bis(2-pyridyloxy)benzenes (4–6) have been dou-
bly-cyclometallated. Such compounds are of consider-
able topical interest [9–11] and these represent the
first examples of doubly cyclometallated compounds
with two six-membered metallocycles. In contrast, the
diphenoxy-pyridazine (7) and -pyrimidine (9) only un-
dergo monometallation, whilst their sulfur analogues,
(8) and (10) are resistant to cyclopalladation. In all
cases, the cyclometallated products have been con-
verted to their acac derivatives, as such compounds
have been shown recently to be interesting metallome-
sogens [2].
4.1. Ligand preparations and NMR spectra
2-Phenoxypyridine (2) was prepared by the reaction
of phenol with 2-bromopyridine in the presence of
anhydrous potassium carbonate, as previously reported
1
[26]. Mp 41.5–43.5°C. H-NMR (CDCl3): l 6.90 (d,
1H, H-3), 6.99 (t, 1H, H-5), 7.14 (d, 2H, H-2% and H-6%),
7.20 (t, 1H, H-4%), 7.40 (t, 2H, H-3% and H-5%), 7.68 (t,
1H, H-4), 8.20 (d, 1H, H-6). 13C-NMR (CDCl3): l
111.47 (C-3), 118.41 (C-5), 121.12 (C-2% and C-6%),
124.62 (C-4%), 129.65 (C-3% and C-5%), 139.36 (C-4),
147.74 (C-6), 154.11 (C-1%), 163.72 (C-2).
2-Phenylsulfanylpyridine (3) was prepared by the
reaction of thiophenol with 2-chloropyridine in the
presence of triethylamine, as previously described [27].
1H-NMR (CDCl3): l 6.87 (d, 1H, H-3), 6.98 (t, 1H,
H-5), 7.41 (m, 3H, H-3%, H-4% and H-5%), 7.42 (t, 1H,
H-4), 7.59 (d, 2H, H-2% and H-6%), 8.41 (d, 1H, H-6).
13C-NMR (CDCl3): l 119.77 (C-5), 121.20 (C-3), 128.98
(C-4%), 129.52 (C-3% and C-5%), 130.88 (C-1%), 134.83
(C-2% and C-6%), 136.61 (C-4), 149.44 (C-6), 161.40 (C-2).
The three isomeric bis(2-pyridyloxy)benzenes (4–6)
were prepared from reactions of 2-bromopyridine with
the appropriate dihydroxybenzene, as previously
Some years ago, we reported a detailed study of
1
the H- and 13C-NMR spectra of a series of 19 acac
complexes of various cyclometallated ligands [25]. We
showed that cyclopalladation leads to consistent
changes in certain chemical shifts for the complexes,
relative to those of the starting ligand. We showed
subsequently that these parameters can be diagnosti-
cally useful for distinguishing the regioselectivity of
cyclopalladation reactions for ligands that could po-
tentially react at either of two sites [17]. In the
present work, and in related studies [6,9], we have
extended our sample of cyclopalladated Pd(acac)
complexes to over 45 such compounds, thereby
refining these parameters.
Fig. 2 shows the average induced changes in chemi-
cal shift of the proton and carbon-13 signals resulting
from the introduction of the Pd(acac) substituent into
the ortho position of a phenyl ring of 45 nitrogen-
containing ligands. These values now reveal that the
most reliably diagnostic parameters correspond to H4%
in the 1H-NMR spectra, which consistently experi-
ences a 0.25 ppm upfield shift, and C5% in the 13C-
NMR spectra, which consistently moves upfield by
4.2 ppm.
1
described [12,13] 4: H-NMR (CDCl3) l: 6.70 (d, 2H,
H3%), 6.90 (t, 2H, H5%), 7.28 (s, 4H, H3-6), 7.56, (t, 2H,
H4%), 8.10 (d, 2H, H6%). 13C-NMR (CDCl3) l: 110.73
(C3%), 118.17 (C5%), 123.60 (C3,6), 125.73 (C4,5), 138.96
(C4%), 145.66 (C1,2), 147.31 (C6%), 163.06 (C2%). 5:
1H-NMR (CDCl3) l: 6.93 (d, 2H, H3%), 6.96 (s, 1H,
H2), 6.99 (dd, 2H, H4,6), 7.00 (t, 2H, H5%), 7.40 (t, 1H,
H5), 7.68 (t, 2H, H4%), 8.21 (d, 2H, H6%). 13C-NMR
(CDCl3) l: 111.48 (C3%), 113.88 (C2), 116.81 (C4,6),
118.56 (C5%), 129.92 (C4), 139.26 (C4%), 147.53 (C6%),
154.98 (C1,3), 163.07 (C2%). 6: 1H-NMR (CDCl3) l:
6.94 (d, 2H, H3%), 7.00 (t, 2H, H5%), 7.17 (s, 4H,
H2,3,5,6), 7.69 (t, 2H, H4%), 8.21 (d, 2H, H6%).
13C-NMR (CDCl3) l: 111.38 (C3%), 118.44 (C5%), 122.32
(C2,3,5,6), 139.41 (C4%), 147.63 (C6%), 150.58 (C1,4),
163.73 (C2%).
3,6-Diphenoxypyridazine (7) was prepared by the
reaction of two equivalents of sodium phenoxide with
3,6-dichloropyridazine as previously reported [18]. Mp
1
141.5-142°C (lit. [18] 140-141°C). H-NMR (CDCl3): l
7.17 (br t, 2H, H-4% and H-4¦), 7.18 (br d, 4H, H-2%,
H-6%, H-2¦ and H-6¦), 7.19 (br s, 2H, H-4 and H-5), 7.36
(br t, 4H, H-3%, H-5%, H-3¦ and H-5¦). 13C-NMR
(CDCl3): l 120.97 (C-2%, C-6%, C-2¦ and C-6¦), 121.75
(C-4 and C-5), 125.02 (C-4% and C-4¦), 129.56 (C-3%,
C-5%, C-3¦ and C-5¦), 153.52 (C-1% and C-1¦), 162.96
(C-3 and C-6).
3,6-Bis(phenylsulfanyl)pyridazine (8) was prepared by
the reaction of sodium thiophenoxide with 3,6-dichloro-
pyridazine in ethanol as previously reported
Fig. 2. Mean Pd(acac) induced chemical shift changes for 45 N-lig-
ands.

102
D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
[19]. Mp 79.5-80.5°C (lit. [19] 78°C). 1H-NMR (CDCl3):
l 6.82 (s, 2H, H-4 and H-5), 7.40 (m, 6H, H-3%, H-4%,
H-5%, H-3¦, H-4¦ and H-5¦), 7.57 (m, 4H, H-2%, H-6%,
H-2¦ and H-6¦). 13C-NMR (CDCl3): l 125.39 (C-4 and
C-5), 129.26 (C-1% and C-1¦), 129.55 (C-4% and C-4¦),
129.79 (C-3%, C-5%, C-3¦ and C-5¦), 134.95 (C-2%, C-6%,
C-2¦ and C-6¦), 162.20 (C-3 and C-6).
13C-NMR (CDCl3): l 111.91 (C-5), 127.28 (C-1% and
C-1¦), 129.76 (C-3%, C-5%, C-3¦ and C-5¦), 129.97 (C-4%
and C-4¦), 135.50 (C-2%, C-6%, C-2¦ and C-6%), 156.70
(C-2), 172.20 (C-4 and C-6).
4.2. Cyclopalladation reactions
4,6-Diphenoxypyrimidine (9): A mixture of phenol
(2.88 g, 3.1 mmol), potassium carbonate (2.81 g, 2.0
mmol) and 4,6-dichloropyrimidine (1.53 g, 1.0 mmol)
was heated at 160°C for 1 h after which it was allowed
to cool to room temperature. Water (10 cm3) and
aqueous potassium hydroxide (0.13 mol dm−3, 30 cm3)
were added and the suspension ultrasonicated to break
up the solid. The mixture was filtered and the solid
washed with water (50 cm3), then dried under reduced
pressure to give 9 in 89% yield. Mp 109–109.5°C. Anal.
Calc. for C16H12N2O2: C, 72.72; H, 4.58; N, 10.60;
Found: C, 72.55; H, 4.42; N, 10.61%. Calc. for
C16H12N2O2: M+, 264.0899; Found (EI): M+,
264.0897. IR (KBr pellet): wmax 1606, 1579, 1562, 1489,
4.2.1. General procedures
Method A: A solution containing the ligand and one
or two equivalents of palladium acetate in glacial acetic
acid was stirred at room temperature for 24 h. The
acetic acid was then removed under reduced pressure.
The resultant m-acetato complex was then converted to
the m-chloro complex by stirring with an acetone/water
(60/40, v/v) solution containing excess lithium chloride
(four equivalents) for up to four days. The resultant
precipitate was filtered off and washed with acetone
then with ether.
Method B: A solution containing the ligand and one
or two equivalents of palladium acetate in glacial acetic
acid was refluxed for 17 h. The acetato palladium
complex was extracted by Soxhlet extraction with chlo-
roform. An acetone solution of the acetato palladium
complex and an excess of acetylacetone and triethyl-
amine was stirred for 16 h. The acetone was then
removed under reduced pressure. The residue was sus-
pended in water and the acac complex was filtered off.
Method C: A solution containing the ligand and one
or two equivalents of palladium acetate in benzene was
degassed by passing a stream of nitrogen through it for
5 min and then heated at 60°C under an atmosphere of
nitrogen for 24 h. The benzene was then removed under
reduced pressure and the residue taken up in chloro-
form and filtered. The filtrate was stripped of solvent
under reduced pressure and the residue stirred with an
acetone/water (60/40, v/v) solution containing excess
lithium chloride (four equivalents) for up to 4 days. The
resultant m-chloro palladium complex was filtered off
and washed with acetone then with ether.
Method D: Excess acetylacetone was added to a
freshly prepared solution of sodium methoxide in
methanol and the resultant solution of sodium acac was
added to a suspension of the m-chloro palladium com-
plex in methanol and the mixture stirred for one to four
days. The precipitated acac complex was filtered off
and washed with methanol and then with ether.
Method E: The chloro-bridged dimer was added to a
solution of two equivalents of thallium acac in
dichloromethane and the resultant solution stirred for
24 h. The precipitate of thallium chloride was filtered
off using a plug of anhydrous magnesium sulfate and
the dichloromethane removed from the filtrate under
reduced pressure. The residue was taken up in chloro-
form and vapour diffusion of petroleum ether into this
solution gave the acac complex, which was filtered off
and washed with pentane.
1456, 1382, 1240, 1219, 1207, 1152, 820, 763, 695 cm−1
.
1H-NMR (CDCl3): l 6.29 (s, 1H, H-5), 7.16 (d, 4H,
H-2%, H-6%, H-2¦ and H-6¦), 7.28 (t, 2H, H-4% and H-4¦),
7.44 (t, 4H, H-3%, H-5%, H-3¦ and H-5¦), 8.45 (s, 1H,
H-2). 13C-NMR (CDCl3): l 92.11 (C-5), 121.48 (C-2%,
C-6%, C-2¦ and C-6%), 125.90 (C-4% and C-4¦), 129.87
(C-3%, C-5%, C-3¦ and C-5¦), 152.43 (C-1% and C-1¦),
158.42 (C-2), 171.61 (C-4 and C-6).
4,6-Bis(phenylsulfanyl)pyrimidine (10): Thiophenol
(2.1 cm3, 2.0 mmol) was added to a freshly prepared
solution of sodium ethoxide (0.52 g sodium, 2.3 mmol)
in ethanol (20 cm3) and to the resultant solution was
added 4,6-dichloropyrimidine (1.5 g, 1.0 mmol) dis-
solved in ethanol (20 cm3). The reaction mixture was
stirred under reflux for 1 day after which it was allowed
to cool to room temperature and the precipitate of
sodium chloride removed by filtration. The filtrate was
chilled and the precipitate filtered off to give 10. The
filtrate was stripped of solvent and the residue taken up
in water (50 cm3). Aqueous sodium hydroxide (8 mol
dm−3, 5 cm3) was added and the solution extracted
with chloroform (3×25 cm3). The organic extracts
were combined, dried over magnesium sulfate and the
solvent removed under reduced pressure to give a
residue which crystallised upon standing overnight. The
supernatant was removed and the solid recrystallised
from ethanol to give additional 10. Total yield 47%.
Mp 116.5–117°C. Anal. Calc. for C16H12N2S2: C,
64.83; H, 4.08; N, 9.45; Found: C, 64.53; H, 3.91; N,
9.44%. Calc. for C16H12N2S2: M+, 296.0442; Found
(EI): M+, 296.0443. IR (KBr pellet): wmax 1530, 1494,
1
1474, 1427, 1281, 1082, 802, 748, 689 cm−1. H-NMR
(CDCl3): l 6.03 (s, 1H, H-5), 7.31 (t, 4H, H-3%, H-5%,
H-3¦ and H-5¦), 7.36 (t, 2H, H-4% and H-4¦), 7.41 (d,
4H, H-2%, H-6%, H-2¦ and H-6¦), 8.62 (s, 1H, H-2).

D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
103
4.2.2. Cyclopalladation of 2-phenoxypyridine (2)
4.2.4. Cyclopalladation of 1,2-bis(2-pyridyloxy)benzene
(4)
Method A gave [Pd(2-H)OAc]2, 11, in 69% yield. Mp
226-228°C. Anal. Calc. for C26H22N2O2Pd2: C, 46.52;
H, 3.03; N, 4.17; Found: C, 46.24; H, 3.10; N, 4.14%.
IR (KBr pellet): wmax 1610, 1583, 1568, 1478, 1454,
Method B gave [Pd2(4-2H)(OAc)2]2, 16, in 67% yield.
Mp\215°C (dec.). IR (KBr pellet): wmax 1578, 1475,
1
1420, 1375, 1298, 928, 772 cm−1. H-NMR (CDCl3):
1422, 1327, 1298, 1181, 775, 756 cm−1
.
1H-NMR
2.04 (s, 3H, CH3COO), 2.22 (s, 3H, CH3COO),
6.36 (s, 2H, H-4, H-5), 6.71 (t, 2H, H-5%), 7.07 (d,
2H, H-3%), 7.57 (t, 2H, H-4%), 8.38 (d, 2H, H-6%). Lig-
and exchange gave Pd2(4–2H)(acac)2, 17, in 72%
yield. The solid was recrystallised by diffusion of pen-
tane into a chloroform solution of 17. Mp\215°C
(dec.). Anal. Calc. for C26H24N2O6Pd2 · CHCl3: C,
40.91; H, 3.18; N, 3.53; Found: C, 40.85; H, 2.84;
N, 3.64%. Calc. for C26H24N2O1606Pd108Pd: M+,
673.9705; Found (FAB): M+, 673.9708. IR (KBr pel-
let): wmax 1614, 1583, 1514, 1431, 1394, 1367, 1294,
(CDCl3): l 2.12 (s, 3H, CH3COO), 6.62 (d, 1H, H-6%),
6.63 (t, 1H, H-5), 6.66 (t, 1H, H-4%), 6.82 (d, 1H, H-3%),
6.86 (t, 1H, H-5%), 6.88 (d, 1H, H-3), 7.55 (t, 1H, 4),
8.02 (d, 1H, H-6). 13C-NMR (CDCl3):
l 24.53
(CH3COO), 114.29 (C-3), 115.18 (C-6%), 117.80 (C-5),
123.06 (C-4%), 124.90 (C-5%), 134.08 (C-3%), 139.80 (C-4),
148.82 (C-6), 149.30 (C-1%), 157.30 (C-2), 181.16
(CH3COO). Ligand exchange gave[Pd(2-H)Cl]2, 12, in
69%
yield.
Mp\300°C.
Anal.
Calc.
for
C22H16N2O2Cl2Pd2: C, 42.34; H, 2.58; N, 4.49: Cl,
11.36; Found: C, 42.49; H, 2.23; N, 4.27; Cl, 11.27%.
IR (KBr pellet): wmax 1610, 1577, 1480, 1454, 1437,
1424, 1313, 1302, 1184, 770, 749, 731 cm−1. This
complex is insoluble in common NMR solvents.
1
1022, 924, 772 cm−1. H-NMR (CDCl3): 2.03 (s, 6H,
acac–CH3), 2.08 (s, 6H, acac–CH3), 5.41 (s, 2H, acac-
CH), 7.08 (t, 2H, H-5%), 7.24 (s, 2H, H-4, H-5), 7.35 (d,
2H, H-3%), 7.83 (t, 2H, H-4%), 8.80 (d, 2H, H-6%). 13C-
NMR (CDCl3): 27.57 and 27.94 (acac–CH3), 100.29
(acac–CH), 115.06 (C-3%), 118.61 (C-5%), 119.12 (C-3,
C-6), 127.90 (C-4, C-5), 137.25 (C-1, C-2), 140.10 (C-
4%), 148.44 (C-6%), 158.19 (C-2%), 187.15 and 187.79
(acac–CO).
Method D then gave Pd(2-H)(acac), 13, in 43% yield.
Mp 133-135°C. Anal. Calc. for C16H15NO3Pd: C, 51.15;
H, 4.02; N, 3.73; Found: C, 50.89; H, 3.72; N, 3.84%.
IR (KBr pellet): wmax 1612, 1595, 1577, 1528, 1479,
1441, 1426, 1406, 1314, 1300, 761, 749, 732 cm−1
.
1H-NMR (CDCl3): l 2.04 (s, 3H, acac–CH3), 2.09 (s,
3H, acac–CH3), 5.42 (s, 1H, acac–CH), 6.98 (d, 1H,
H-6%), 7.06 (t, 1H, H-4%), 7.08 (t, 1H, H-5), 7.12 (t, 1H,
H-5%), 7.22 (d, 1H, H-3), 7.62 (d, 1H, H-3%), 7.82 (t, 1H,
H-4), 8.81 (d, 1H, H-6). 13C-NMR (CDCl3): l 27.58
and 27.95 (acac–CH3), 100.39 (acac–CH), 114.91 (C-
3), 115.47 (C-6%), 118.53 (C-5), 123.68 (C-4%), 125.65
(C-5%), 133.83 (C-3%), 140.27 (C-4), 148.22 (C-6), 187.02
and 188.12 (acac–CO).
4.2.5. Cyclopalladation of 1,3-bis(2-pyridyloxy)benzene
(5)
Method A gave [Pd2(5–2H)(OAc)2]2, 18, in 36%
yield. Mp\220°C (dec.). IR (KBr pellet): wmax
1612, 1566, 1477, 1421, 1294, 1242, 1123, 1028, 984,
777, 689 cm−1
.
1H-NMR (CDCl3): 1.97 (s,
3H, CH3COO), 2.20 (s, 3H, CH3COO), 6.13 (s,
1H, H-2), 6.47 (s, 1H, H-5), 6.69 (t, 2H, H-5%), 6.90
(d, 2H, H-3%), 7.66 (t, 2H, H-4%), 8.06 (d, 2H,
H-6%). Ligand exchange gave [Pd2(5-2H)Cl2]2 in
74% yield. Mp\240°C (dec.). IR (KBr pellet): wmax
1611, 1570, 1474, 1421, 1294, 1242, 1123, 982, 777
cm−1. Method D then gave Pd2(5–2H)(acac)2, 19, in
52% yield. The solid was recrystallised by diffusion of
pentane into a chloroform solution of 19. Mp 158–
160°C. Anal. Calc. for C26H24N2O6Pd2.CHCl3: C,
40.91; H, 3.18; N, 3.53; Found: C, 40.50; H, 2.93; N,
3.54%. Calc. for C26H24N2O1606Pd108Pd: M+, 673.9705;
Found (FAB): M+, 673.9687. IR (KBr pellet): wmax
4.2.3. Cyclopalladation of 2-phenylsulfanylpyridine (3)
Method C gave [Pd(3-H)Cl]2, 14, in 47% yield. IR
(KBr pellet): wmax 1587, 1551, 1458, 1431, 1421, 1157,
1020, 762, 746 cm−1. This complex is insoluble in
common NMR solvents.
Method E then gave Pd(3-H)(acac), 15, in 20% yield.
Mp 199–200°C (dec.). Anal. Calc. for C16H15NO2SPd:
C, 49.05; H, 3.86; N, 3.58; Found: C, 48.81; H, 4.02; N,
3.55%. IR (KBr pellet): wmax 1592, 1559, 1511, 1420,
1
1394, 774, 745, 612 cm−1. H-NMR (CDCl3): l 2.00 (s,
3H, acac–CH3), 2.05 (s, 3H, acac–CH3), 5.42 (s, 1H,
acac–CH), 7.01 (t, 1H, H-5%), 7.07 (t, 1H, H-4%), 7.17 (t,
1H, H-5), 7.30 (d, 1H, H-6%), 7.44 (d, 1H, H-3%), 7.66 (t,
1H, H-4), 7.73 (d, 1H, H-3), 8.81 (d, 1H, H-6). 13C-
NMR (CDCl3): l 27.52 and 27.98 (acac–CH3), 100.34
(acac–CH), 121.56 (C-5), 124.64 (C-5%), 125.82 (C-3),
126.02 (C-4%), 126.83 (C-6%), 131.75 (C-2%), 135.75 (C-3%),
137.32 (C-4), 145.63 (C-1%), 153.77 (C-6), 158.68 (C-2),
186.57 and 187.92 (acac–CO).
1587, 1510, 1475, 1394, 1292, 1113, 984, 779, 746 cm−1
.
1H-NMR (CDCl3): 2.02 (s, 6H, acac–CH3), 2.09 (s,
6H, acac–CH3), 5.40 (s, 2H, acac–CH), 6.70 (s, 1H,
H-2), 7.05 (t, 2H, H-5%), 7.17 (d, 2H, H-3%), 7.67 (s, 1H,
H-5), 7.82 (t, 2H, H-4%), 8.78 (d, 2H, H6%). 13C-NMR
(CDCl3): 27.65 and 27.93 (acac–CH3), 100.18 (acac–
CH), 102.98 (C-2), 114.70 (C-3%), 118.43 (C-5%), 136.91
(C-5), 140.02 (C-4%), 148.52 (C-6%), 187.12 and 187.65
(acac–CO).

104
D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
4.2.6. Cyclopalladation of 1,4-bis(2-pyridyloxy)benzene
(6)
Method A gave [Pd2(6–2H)(OAc)2]2, 20, in 27%
yield. Mp\210°C (dec.). IR (KBr pellet): wmax 1582,
H-5%), 7.04 (d, 2H, H-2¦ and H-6¦), 7.32 (t, 1H, H-4¦),
7.47 (t, 2H, H-3¦ and H-5¦), 8.38 (s, 1H, H-2)] followed
by [Pd(9–H)Cl]2, in 37% overall yield. Mp 244–245°C
(dec.). Anal. Calc. for C32H22N4O4Cl2Pd2: C, 47.34; H,
2.74; N, 6.91; Found: C, 47.44; H, 2.80; N, 6.97%. IR
(KBr pellet): wmax 1611, 1585, 1572, 1547, 1491, 1468,
1479, 1427 1337, 1296, 1242, 1140, 899, 758, 673 cm−1
.
1H-NMR (CDCl3): 2.06 (s, 3H, CH3COO), 2.31 (s, 3H,
CH3COO), 6.22 (s, 2H, H-3, H-6), 6.63 (t, 2H, H-5%),
6.88 (d, 2H, H3%), 7.53 (t, 2H, H-4%), 8.19 (d, 2H, H-6%).
Ligand exchange gave [Pd2(6–2H)Cl2]2 in 92% yield.
Mp\230°C (dec.). IR (KBr pellet): wmax 1611, 1591,
1454, 1431, 1408, 1244, 1198, 758 cm−1 1H-NMR
.
(CDCl3): l 6.62 (s, 1H, H-5), 6.92 (d, 1H, H-6%), 6.95 (t,
1H, H-4%), 7.08 (t, 1H, H-5%), 7.14 (d, 2H, H-2¦ and
H-6¦), 7.34 (t, 1H, H-4¦), 7.41 (d, 1H, H-3%), 7.47 (t, 2H,
H-3¦ and H-5¦), 8.93 (s, 1H, H-2). 13C-NMR (CDCl3):
l 94.62 (C-5), 116.48 (C-6%), 121.32 (C-2¦ and C-6¦),
124.85 (C-4%), 126.30 (C-4¦), 126.63 (C-5%), 130.10 (C-3¦
and C-5¦), 136.80 (C-3¦), 160.00 (C-2).
1508, 1477, 1423, 1292, 1138, 1107, 893, 789 cm−1
.
Method D then gave Pd2(6–2H)(acac)2, 21, in 94%
yield. Mp \220°C (dec.). Anal. Calc. for
C26H24N2O6Pd2: C, 46.38; H, 3.59; N, 4.16; Found: C,
46.12; H, 3.46; N, 4.25%. IR (KBr pellet): wmax 1589,
1508, 1481, 1398, 1292, 1128, 1113, 1020, 893, 795, 771,
617 cm−1. This complex is insoluble in common NMR
solvents.
Method E then gave Pd(9-H)(acac), 23, in 62% yield.
Mp 202–206°C (dec.). Anal. Calc. for C21H18N2O4Pd:
C, 53.80; H, 3.87; N, 5.98; Found: C, 53.81; H, 4.16; N,
5.88%. IR (KBr pellet): wmax 1611, 1585, 1548, 1509,
1490. 1471, 1456, 1432, 1394, 1309, 1241, 1227, 1196,
4.2.7. Cyclopalladation of 3,6-diphenoxypyridazine (7)
Method C gave [Pd(7-H)OAc]2 [1H-NMR (CDCl3): l
1.68 (s, 3H, CH3COO), 6.70 (d, 1H, H-6%), 6.83 (t, 1H,
H-4%), 6.91 (t, 1H, H-5%), 6.95 (d, 3H, H-5, H-2¦ and
H-6¦), 7.11 (d, 1H, H-4), 7.16 (t, 1H, H-4¦), 7.17 (d, 1H,
H-3%), 7.33 (t, 2H, H-3¦ and H-5‘‘). 13C-NMR (CDCl3):
l 23.99 (CH3COO), 114.56 (C-6%), 120.22 (C-2¦ and
C-6¦), 123.20 (C-4%), 123.26 (C-5), 124.78 (C-5%), 124.89
(C-4), 125.02 (C-4¦), 129.55 (C-3¦ and C-5¦), 134.99
(C-3%), 180.01 (CH3COO)] followed by [Pd(7-H)Cl]2, in
63% overall yield. IR (KBr pellet): wmax 1491, 1441,
1425, 1418, 1279, 1180, 1163, 1111, 883, 764, 750, 689
cm−1. This complex is insoluble in common NMR
solvents.
749 cm−1 1H-NMR (CDCl3): l 1.90 (s, 3H, acac–
.
CH3), 2.09 (s, 3H, acac–CH3), 5.42 (s, 1H, acac–CH),
6.57 (s, 1H, H-5), 6.94 (d, 1H, H-6%), 7.10 (br t, 2H,
H-4% and H-5%), 7.17 (d, 2H, H-2¦ and H-6¦), 7.34 (t,
1H, H-4¦), 7.49 (t, 2H, H-3¦ and H-5¦), 7.65 (d, 1H,
H-3%), 9.19 (s, 1H, H-2). 13C-NMR (CDCl3): l 27.56
and 27.71 (acac–CH3), 93.97 (C-5), 100.44 (acac–CH),
115.53 (C-6%), 119.12 (C-2%), 121.39 (C-2¦ and C-6¦),
124.27 (C-4%), 125.86 (C-4¦), 126.52 (C-5%), 130.12 (C-3¦
and C-5¦), 133.70 (C-3%), 145.05 (C-1%), 152.08 (C-1¦),
158.91 (C-2), 187.00 and 188.13 (acac–CO).
4.3. X-ray crystallography
Method E then gave, in 87% yield, Pd(7–H)(acac),
22, as pale yellow crystals suitable for single crystal
X-ray structure determination. Mp 186–188°C. Anal.
Calc. for C21H18N2O4Pd: C, 53.80; H, 3.87; N, 5.98;
Found: C, 53.70; H, 3.84; N, 5.94%. IR (KBr pellet):
wmax 1593, 1570, 1514, 1458, 1443, 1420, 1394, 1269,
All measurements were made with a Siemens CCD
area detector using graphite monochromatized Mo-Ka
˚
(u=0.71073 A) radiation. Intensities were corrected for
Lorentz and polarization effects and for absorption.
The structure was solved by direct methods using
SHELXS [28], and refined on F2 using all data by full-
matrix least-squares procedures with SHELXS-96 [29].
All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were in-
cluded in calculated positions with isotropic displace-
ment parameters 1.3 times the isotropic equivalent of
their carrier carbons. The function minimised was
S w(F2o−F2c), with w=[|2(Fo2)+0.0413P2]−1, where
P=[max(Fo)2+2Fc2]/3.
1
1190, 1163, 754 cm−1. H-NMR (CDCl3): l 1.90 (s,
3H, acac–CH3), 2.03 (s, 3H, acac–CH3), 5.34 (s, 1H,
acac–CH), 6.96 (m, 1H, H-6%), 7.07 (m, 1H, H-5%), 7.10
(m, 1H, H-4%), 7.21 (m, 1H, H-4¦), 7.36 (d, 1H, H-5),
7.41 (m, 4H, H-2¦, H-3¦, H-5¦ and H-6¦), 7.44 (d, 1H,
H-4), 7.60 (m, 1H, H-3’). 13C-NMR (CDCl3): l 27.30
and 27.63 (acac–CH3), 100.08 (acac–CH), 115.13 (C-
6’), 120.58 (C-2%), 120.88 (C-2¦ and C-6¦), 123.58 (C-5),
124.34 (C-5%), 125.32 (C-4¦), 125.54 (C-4%), 125.60 (C-4),
129.48 (C-3¦ and C-5¦), 134.32 (C-3%), 150.86 (C-1%),
152.87 (C-1¦), 156.81 (C-3), 160.82 (C-6), 185.84 and
188.45 (acac–CO).
Crystal data for 22 at −130°C: C21H18N2O4Pd,
Mr=468.8, 0.53×0.35×0.13 mm, orthorhombic,
space group P212121, a=13.0994(3), b=14.4413(4),
3
˚
˚
c=20.1011(4) A, V=3902.6(2) A , F(000)=1888,
4.2.8. Cyclopalladation of 4,6-diphenoxypyrimidine (9)
Method C gave [Pd(9-H)OAc]2 [1H-NMR (CDCl3): l
2.10 (s, 3H, CH3COO), 6.23 (s, 1H, H-5), 6.71 (d, 1H,
H-6%), 6.84 (t, 1H, H-4%), 6.97 (d, 1H, H-3%), 7.02 (t, 1H,
Z=8, Dc=1.64 g cm−3, v(Mo–Ka)=1.48 mm−1
,
2qmax=53°, 509 parameters, S=1.07, wR2=0.0503 for
all 7048 unique data, R=0.0223 for 6837 data with
Fo\4|(Fo).

D.J. de Geest et al. / Journal of Organometallic Chemistry 579 (1999) 97–105
105
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