assigned to l(CÈH) of PPh . The two bands may possibly
[ReO I(PPh ) ]22 and [ReOI (PPh ) (EtO)]22 were prepared
3
2
3 2
2
3 2
correspond to unbound CÈH and to the CÈH involved in
by the respective literature procedures. All chemicals were of
at least reagent grade and used as supplied.
CÈHÉ É ÉO hydrogen bonding (shown in the crystal structure of
complex 3), respectively.
In the spectra of the two rhenium complexes the Re2O
stretch is seen as a strong band at 987 and 993 cm~1, respec-
tively. Bands assignable to the MÈN stretching vibrations
were found in the region from 350 to 450 cm~1. MÈCl stretch-
ing vibrations were also clearly seen in the spectra of the cor-
responding Pd and Pt complexes. In addition to the above,
trans-[Pd(PPh ) Cl(picOH)] Æ CHCl (1). To a stirred sus-
3 2
3
pension of trans-[Pd(PPh ) Cl ] (0.35 g, 0.5 mmol) in ethanol
3 2
2
(10 cm3) was added a methanolic suspension (4 cm3) of 3-
hydroxypicolinic acid (0.14 g, 1 mmol) and triethylamine (0.28
cm3, 2 mmol). The resulting yellow suspension was stirred for
three weeks. It was centrifuged and a yellow solid isolated,
washed with ethanol and dried over silica gel (yield of yellow
solid: 0.35 g, 0.44 mmol, 87%). Yellow crystals suitable for
X-ray di†raction were obtained by vapour di†usion of diethyl
PPh and bipy bands were observed in all the applicable
3
spectra.
The proposed formula for complexes 4 to 8 are based on
elemental analysis and spectroscopic data, considering analo-
gous complexes that have been reported5,17h19 for other
bidentate ligands. In complexes 4 and 5 two picOH~ ligands
are coordinated to palladium and platinum, respectively, but
in 4 a chlorine ligand is also bound to palladium as shown in
the infrared spectrum. Complex 4 has possibly either a
[4 ] 1] geometry or a square planar geometry involving a
monodentate picOH~ ligand. For the palladium and plati-
num complexes 6 and 7 containing 2,2@-bipyridine, cationic
species are proposed with a Cl~ counter-anion, since no
bands were found in the infrared or Raman spectra for the
MÈCl stretching vibration, clearly seen in the spectra of com-
plexes 1, 2 and 4 with a coordinated chlorine ion. Complexes
6 and 7 are analogous to the reported 6,7-dihydroxycoumarin
species.17 Complex 8 is analogous to the rhenium complexes
with maltol, tropolone or hydroxypyridinone ligands that
have been reported.18,19
ether into a solution of the compound in CHCl .
3
cis-[Pt(PPh ) Cl(picOH)] Æ CHCl (2). To a stirred suspen-
3 2
3
sion of cis-[Pt(PPh ) Cl ] (0.39 g, 0.5 mmol) in ethanol (10
3 2
2
cm3) was added a methanolic suspension (4 cm3) of 3-
hydroxypicolinic acid (0.14 g, 1 mmol) and triethylamine (0.28
cm3, 2 mmol). The resulting white suspension was stirred for
six days. It was centrifuged and an o†-white solid isolated,
washed with ethanol and dried over silica gel (yield of o†-
white solid: 0.41 g, 0.46 mmol, 92%). O†-white crystals suit-
able for X-ray di†raction were obtained by vapour di†usion of
diethyl ether into a solution of the compound in CHCl .
3
[ReOI (PPh )picOH)] (3).
A
suspension of [ReOI -
2
3
2
(PPh ) (EtO)] (0.31 g, 0.3 mmol) and 3-hydroxypicolinic acid
3 2
(0.04 g, 0.3 mmol) in acetone (10 cm3) was reÑuxed for 30 min.
1H and 13C-{1H} NMR spectra
The dark solution was placed in the fridge. After three weeks
dark green crystals were isolated, washed with acetone and
dried over silica gel. Dark green crystals suitable for X-ray
di†raction were obtained by vapour di†usion of diethyl ether
Proton and carbon NMR data and tentative assignments for
HpicOH and complexes 1, 2 and 3 are given in Table 4 (see
Fig. 1È3 for labelling). Protonation of the phenolic oxygen
into a solution of the compound in CHCl . Yield: 0.12 g, 0.14
atom (H ) of the picOH~ ligand is shown in the 1H NMR
3
OH
mmol, 46.7%.
spectra by signals at d 16.5 and 16.9, respectively for com-
plexes 1 and 2, and at d 10.6 for complex 3. Solution
13C-M1HN NMR spectra are of poor quality for most of the
complexes; CPMAS solid state NMR data were used to deter-
mine the peak positions for C and C . In comparison with
K[PdCl(picOH) ] Æ 2H O (4). A methanolic suspension (4
2
2
cm3) of 3-hydroxypicolinic acid (0.14 g, 1 mmol) was added to
an aqueous solution (10 cm3) of K [PdCl ] (0.14 g, 0.5 mmol)
5
7
HpicOH, the resonances of C and C are signiÐcantly shifted
2
4
6
7
and triethylamine (0.28 cm3, 2 mmol). The resulting yellow
suspension was stirred for one day. It was centrifuged and a
yellow solid isolated, washed with ethanol and dried over
silica gel. Yield: 0.18 g, 0.37 mmol, 73%.
in the spectra of the complexes, while the position of the phe-
nolic carbon atom C is little altered. This is consistent with
5
the N,O-chelation shown in the crystal structures of these
complexes.
[Pt(picOH) ] (5). A methanolic suspension (5 cm3) of 3-
2
Experimental
hydroxypicolinic acid (0.06 g, 0.4 mmol) was added to a meth-
anolic suspension (5 cm3) of K [PtCl ] (0.08 g, 0.2 mmol). The
2
4
resulting suspension was stirred for Ðve days. It was centri-
fuged and a yellow solution obtained. A yellow solid was iso-
lated from the solution after three days, washed with ethanol
and dried over silica gel. Yield 0.04 g, 0.08 mmol, 42.5%.
Preparation of complexes
The starting materials, trans-[Pd(PPh ) Cl ],20 cis-
3 2
2
or
[Pt(PPh ) Cl ],21
[M(bipy)Cl ]17
(M \ Pd
Pt),
3 2
2
2
Table 4 1H and 13C-M1HN NMR spectroscopic data for 3-hydroxypicolinic acid and its complexesa
Chemical shift (d)
Compound
H
H
H
H
C
C
C
C c
C
C c
2
3
4
OH
2
3
4
5
6
7
HpicOHb
8.1
8.4
8.3
8.0
7.8
d
d
7.9
6.7
7.0
7.1
È
132.1
135.0
135.9
130.7
129.7
128.1
127.3
128.1
129.4
128.0
127.1
127.2
159.4
161.5
163.4
156.7
133.4
138.3
138.4
140.1
164.5
169.6
169.4
172.3
1
2
3
16.5
16.9
10.6
7.4
a Spectra in CDCl solution unless otherwise stated. b In (CD ) SO solution. c CPMAS solid state NMR data. d Peak obscured.
3 2
3
New J. Chem., 2000, 24, 511È517
515
Quintal, Susana M. O.
