Syntheses and molecular structures of 6-halogeno-pyridin-2-olate complexes with the diruthenium(2+) core

Article abstract of DOI:10.1016/j.ica.2005.07.023

The complexes [Ru₂(CO)₅(μ-FpyO)₂] ₂ (1), [Ru₂(CO)₄(μ-ClpyO)₂] ₂ (2), and [Ru₂(CO)₄(μ-BrpyO) ₂]₂ (3) were prepared from Ru₃(CO)₁₂ and 6-fluoro-2-hydroxypyridine (FpyOH), 6-chloro-2-hydroxypyridine (ClpyOH) and 6-bromo-2-hydroxypyridine (BrpyOH), respectively, in hot toluene. Compounds 1-3 are coordination dimers with a cyclo-RuORuO motif. By carrying out the reaction in hot methanol, the dinuclear complexes [Ru₂(CO) ₄(μ-ClpyO)₂(CH₃OH)] (4) and [Ru ₂(CO)₄(μ-BrpyO)₂(CH₃OH)] (5), respectively, were obtained. Treatment of 2 and 3 with triphenylphosphane provided the complexes [Ru₂(CO)₄(μ-ClpyO) ₂(PPh₃)] (6) and [Ru₂(CO)₄(μ- BrpyO)₂(PPh₃)] (7), respectively. The solid-state structures of complexes 1, 2, 4, 6, and 7 were determined by single crystal X-ray diffraction. In all cases, a head-head coordination of the two 6-halopyridinolate ligands at the Ru22+ core was found. In all chlorine- or bromine-containing complexes, the axial coordination site at the ruthenium atom neighbored by two Cl or Br atoms remains unoccupied due to steric shielding by the halogen atom. In the fluoropyridinolate complex 1, the same coordination site is occupied by a carbonyl ligand.

Full text of DOI:10.1016/j.ica.2005.07.023

Inorganica Chimica Acta 359 (2006) 970–977
www.elsevier.com/locate/ica
Syntheses and molecular structures of
6-halogeno-pyridin-2-olate complexes with the diruthenium(2+) core
a
b
a,
*
Lutz Scha¨ffler , Bernhard Muller , Gerhard Maas
¨
a
Abteilung Organische Chemie I, Universita¨t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
b
Sektion Ro¨ntgenbeugung, Universita¨t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Received 15 June 2005; accepted 16 July 2005
Available online 30 August 2005
Ruthenium and Osmium Chemistry Topical Issue
Abstract
The complexes [Ru2(CO)5(l-FpyO)2]2 (1), [Ru2(CO)4(l-ClpyO)2]2 (2), and [Ru2(CO)4(l-BrpyO)2]2 (3) were prepared from
Ru3(CO)12 and 6-fluoro-2-hydroxypyridine (FpyOH), 6-chloro-2-hydroxypyridine (ClpyOH) and 6-bromo-2-hydroxypyridine
(BrpyOH), respectively, in hot toluene. Compounds 1–3 are coordination dimers with a cyclo-RuORuO motif. By carrying out
the reaction in hot methanol, the dinuclear complexes [Ru2(CO)4(l-ClpyO)2(CH3OH)] (4) and [Ru2(CO)4(l-BrpyO)2(CH3OH)]
(5), respectively, were obtained. Treatment of 2 and 3 with triphenylphosphane provided the complexes [Ru2(CO)4(l-
ClpyO)2(PPh3)] (6) and [Ru2(CO)4(l-BrpyO)2(PPh3)] (7), respectively. The solid-state structures of complexes 1, 2, 4, 6, and 7 were
determined by single crystal X-ray diffraction. In all cases, a head–head coordination of the two 6-halopyridinolate ligands at the
2þ
Ru2 core was found. In all chlorine- or bromine-containing complexes, the axial coordination site at the ruthenium atom neigh-
bored by two Cl or Br atoms remains unoccupied due to steric shielding by the halogen atom. In the fluoropyridinolate complex 1,
the same coordination site is occupied by a carbonyl ligand.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Dinuclear complexes; Pyridonate ligand; Ruthenium compounds; X-ray crystal structures
1. Introduction
generated the complex [Ru2(CO)4(l-pyO)2]n (pyO = 2-
pyridinolate) as a coordination polymer, which was
found to be insoluble in all common solvents with no Le-
wis base properties but could be depolymerized by the
addition of donor ligands such as carbon monoxide, ace-
tonitrile, triphenylphosphane, triphenyl phosphite, and
2-hydroxypyridine [1,2]. Recently, we have found that
the reaction of Ru3(CO)12 with 6-methyl- or 6-phenyl-
2-hydroxypyridine provides complexes that are different
in composition and structure from the desired complexes
[Ru2(CO)4(l-MepyO)2] and [Ru2(CO)4(l-PhpyO)2] [3].
For studies on the subject of ruthenium-catalyzed car-
bene transfer reactions with diazo compounds, we be-
came interested recently in dinuclear ruthenium(I,I)
2þ
compounds in which the Ru2 core is bridged by two
6-substituted pyridin-2-olate (2-pyridonate) ligands. So
far, only complexes of this type containing the parent
2-pyridonate ligand have been reported. Thus, the reac-
tion of 2-hydroxypyridine with Ru3(CO)12 in hot toluene
2þ
In contrast to the current situation with Ru2 com-
*
Corresponding author. Tel.: +49 731 50 22790; fax: +49 731 50
plexes, a number of 6-R-pyridonate (RpyO, R = Me,
22803.
4þ
5þ
F, Cl, Br) complexes with the Ru2 and Ru2 core,
E-mail addresses: lutz.schaeffler@uni-ulm.de (L. Scha¨ffler),
having the general composition [Ru2(l-RpyO)4] [4–8]
gerhard.maas@uni-ulm.de (G. Maas).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.07.023

L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
971
and [Ru2(l-RpyO)4X] (see, e.g. [7,9–11]), respectively,
2.2. Preparation of bis(l-6-fluoropyridin-2-olato-
have been synthesized and structurally characterized.
In this communication, we report on the synthesis
1jO:2jN)-pentacarbonyl-1j2C:2j3C–diruthenium(Ru–
Ru) dimer, [Ru2(CO)5(l-FpyO)2]2 (1)
2þ
and structure determination of the first Ru2 complexes
with 6-halogeno-pyridin-2-olate ligands. Because of the
unsymmetrically bridging pyridonate ligands, the two
regioisomers1 I and II can be expected, to which we refer
here as the head–head (or 0,2) and the head–tail (or 1,1)
isomer, respectively. For complexes of the type [Ru2(l-
RpyO)4] and [Ru2(l-RpyO)4X] (R = Me, Hal), the three
possible regioisomers (0,4, 1,3, 2,2) have all been ob-
tained, and it has been stated that no general criteria ex-
ist to predict the preferred arrangement in an individual
case [7]. For the Ru22þ=bisð6-halogeno-pyridin-2-olateÞ
complexes reported here, the head–head (or 0,2) regio-
isomer I was obtained uniformly.
A solution of Ru3(CO)12 (100 mg, 0.16 mmol) and
6-fluoro-2-hydroxypyridine (53 mg, 0.47 mmol) in tolu-
ene (10 ml) was heated at reflux for 5 h. Crystals started
to appear at the end of the reaction. After cooling to r.t.,
the orange-yellow precipitate was filtered off, washed
with a small volume of cold toluene, and dried at
0.001 mbar. Yield: 72 mg (0.064 mmol, 54% based on
Ru). Decomposition of the complex, indicated by color
change to brown and black, started above 235 ꢁC. The
complex is air-sensitive and was stored, therefore, at
8 ꢁC under argon. IR (KBr): 2035 s, 1998 s, 1991 s,
1951 s, 1927 s, 1621 s, 1551 m, 1433 s, 1347 m, 1246
m, 1028 s, 785 m, 573 w cmꢀ1 1H NMR (CD3CN):
.
d = 6.13 (ddd, JH,H = 7.5, 0.9 Hz, jJH,Fj = 1.9 Hz, 5-
Hpy), 6.19 (d, JH,H = 8.3 Hz, long-range coupling not
resolved, 3-Hpy), 7.47 (dt, JH,H ꢁ JH,F ꢁ 8.6 Hz,
JH,H = 7.6 Hz, 4-Hpy). 13C NMR (CD3CN): d = 93.32
Hal
N
O
Hal
N
O
CO
L
CO
O
O
N
Hal
(JC,F = 30.7 Hz), 111.94 (JC,F = 4.4 Hz), 142.5 (JC,F
=
L
N
Ru
Ru
L
C
Ru
Ru
L
Hal
C
11.7 Hz), 164.39 (JC,F = 249.6 Hz), 175.73 (JC,F = 5.1
Hz), 202.48, 204.62 (d, JC,F = 5.1 Hz). MS (MALDI-
TOF, dithranol): m/z = 1136.3 (M+), 1050.5 (M+ ꢀ 3
CO). Anal. Calc. for C30H12F4N4O14Ru4 (1132.7): C,
31.81; H, 1.07; N, 4.95. Found: C, 31.62; H, 1.19; N,
4.98%.
O
O
C
O
C
O
C
O
C
O
II
I
2.3. Preparation of bis(l-6-chloropyridin-2-olato-
1jO:2jN)-tetracarbonyl-1j2C:2j2C–diruthenium(Ru–
Ru) dimer, [Ru2(CO)4(l-ClpyO)2]2 (2)
2. Experimental
2.1. General remarks
A solution of Ru3(CO)12 (100 mg, 0.16 mmol) and
6-chloro-2-hydroxypyridine (61 mg, 0.47 mmol) in tolu-
ene (10 ml) was heated at reflux for 2.5 h. After cooling
to r.t., the red precipitate was filtered off, washed with a
small volume of cold toluene, and dried at 0.001 mbar.
Yield: 118 mg (0.10 mmol, 88% based on Ru). Decom-
position of the complex started at 328 ꢁC. IR (KBr):
2035 s, 1991 s, 1958 s, 1938 s, 1601 m, 1463 s, 1433 s,
1330 m, 1177 m, 1015 m, 931 m, 785 m cmꢀ1. MS
(MALDI-TOF, dithranol): m/z = 1114.5 (M+ ꢀ CO).
Anal. Calc. for C28H12Cl4N4O12Ru4 (1142.5): C, 29.44;
H, 1.06; N, 4.90. Found: C, 29.43; H, 1.13; N, 4.83%.
All solvents were distilled prior to use. 6-Fluoro- [12]
and 6-bromo-2-hydroxypyridine [13] were prepared by
published procedures, 6-chloro-2-hydroxypyridine was
purchased and used as received. Nuclear magnetic reso-
nance spectra in solution were recorded using a Bruker
DRX 400 spectrometer (1H: 400.13 MHz, 13C:
1
100.62 MHz, 19F: 376.47 MHz). H NMR spectra were
referenced to TMS, 13C NMR spectra to the solvent sig-
nal (d(CDCl3) = 77.0, d(CD3CN) = 118.26 ppm), and
19F spectra to external CFCl3 (d = 0 ppm). IR spectra:
Bruker Vector 22 FTIR; Mass spectra: MALDI: Bruker
Daltonic Reflex III; ESI: Waters micromass ZMD. The
reported m/z values for complexes 1–7 refer to the most
intense peak of a multiple-line isotope pattern; the
experimental and calculated intensity distribution agree
with each other. Microanalyses were carried out with a
Heraeus CHN–O–Rapid instrument in the Division of
Analytical Chemistry, University of Ulm.
2.4. Preparation of bis(l-6-bromopyridin-2-olato-
1jO:2jN)-tetracarbonyl-1j2C:2j2C–diruthenium(Ru–
Ru) dimer, [Ru2(CO)4(l-BrpyO)2]2 (3)
The same procedure as in Section 2.3, but with
6-bromopyridine (81.6 mg, 0.47 mmol), furnished a red
solid, which started to decompose at 312 ꢁC; yield:
129 mg (0.098 mmol, 83% based on Ru). IR (KBr):
2033 s, 1989 s, 1955 s, 1935 s, 1602 m, 1461 s, 1426 s,
1
This term, well established in organic chemistry, has been applied
appropriately by Cotton et al. to characterize these types of isomeric
complexes; see [6].
1398 m, 1331 m, 1173 w, 1011 w, 903 w, 781 w cmꢀ1
.

972
L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
MS (MALDI-TOF, dithranol): m/z = 1295.5 (M+ ꢀ
CO). Anal. Calc. for C28H12Br4N4O12Ru4 (1320.3): C,
25.47; H, 0.92; N, 4.24. Found: C, 25.58; H, 0.98; N,
4.26%.
homogeneous yellow solution had formed (ca. 30 min).
It was passed over a plug of silica gel (Si60, 0.063–
0.2 mm, 1 g) in order to remove any trace of 2, evapo-
rated to dryness, and the remaining orange-yellow solid
was dried at 0.001 mbar. Yield: 41.7 mg (50 lmol, quan-
titative based on PPh3); m.p. 199 ꢁC. 1H NMR (CDCl3):
d = 6.10 (d, J = 8.6 Hz, 2H), 6.39 (d, J = 7.3 Hz, 2H),
7.16 (dd, J = 8.6, 7.3 Hz, 2H), 7.39–7.49 (m, 9 H),
7.59–7.63 (m, 6H). 13C NMR (CDCl3): d = 110.10,
113.95, 128.32 (d, JC,P = 9.5 Hz), 130.32, 130.35,
131.59 (d, JC,P = 40.2 Hz), 133.82 (d, JC,P = 10.1 Hz),
139.13, 147.15, 172.91, 172.92, 200.40 (d, JC,P = 6.6 Hz),
201.88 (d, JC,P = 6.6 Hz). IR (KBr): 2036 s, 1987 s, 1958
s, 1926 s, 1600 m, 1528 w, 1472 s, 1451 m, 1435 m, 1094
w, 1010 w, 694 w cmꢀ1. MS (ESI): m/z = 834.6 (M+).
Anal. Calc. for C32H21Cl2N2O6PRu2 (833.54): C,
46.11; H, 2.54; N, 3.36. Found: C, 45.90; H, 2.64; N,
3.32%.
2.5. Preparation of bis(l-6-chloropyridin-2-olato-
1jO:2jN)-methanol-1jO-tetracarbonyl-1j2C:2j2C–
diruthenium(Ru–Ru) dimer, [Ru2(CO)4(CH3OH)(l-
ClpyO)2]2 (4)
A solution of Ru3(CO)12 (100 mg, 0.16 mmol) and
6-chloro-2-hydroxypyridine (61 mg, 0.47 mmol) in
methanol (10 ml) was heated at reflux for 48 h. After
cooling to r.t., the red precipitate was filtered off, washed
with a little cold methanol, and dried at 0.001 mbar.
Yield: 72 mg (0.12 mmol, 51% based on Ru). When
the complex was heated, extrusion of a liquid was ob-
served at ꢂ235 ꢁC, and a color change to silver-black
above 326 ꢁC. 1H NMR (CDCl3): d = 3.48 (s, 3 H),
3.50 (s, 3H), 6.47 (d, J = 7.1 Hz, 1H), 6.66 (d, J = 8.6
Hz, 1H), 6.74 (d, J = 7.3 Hz, 1H), 7.25 (d, 1H, partly
covered by residual solvent signal), 7.35 (pseudo-t,
J1 + J2 = 15.6 Hz, 1H), 7.60 (pseudo-t, J1 + J2 =
15.9 Hz, 1H). IR (KBr): 2044 s, 1991 s, 1963 s, 1601 s,
2.8. Preparation of bis(l-6-bromopyridin-2-olato-
1jO:2jN)-tetracarbonyl-1j2C:2j2C–
triphenylphosphane-1jP–diruthenium(Ru–Ru),
[Ru2(CO)4(l-BrpyO)2(PPh3)] (7)
1531 m, 1465 s, 1167 m, 1025 m, 1013 m, 789 m cmꢀ1
.
The same procedure as described in Section 2.7 was
carried out with complex 3 (34.3 mg, 26 lmol) and
furnished 46.1 mg (50 lmol, quantitative based on
PPh3) of an orange-yellow solid; m.p. 223–224.5 ꢁC.
1H NMR (CDCl3): d = 6.10 (dd, J = 8.5, 0.8 Hz,
2H), 6.52 (dd, J = 7.3, 0.8 Hz, 2H), 7.06 (dd,
J = 8.5, 7.3 Hz, 2H), 7.38–7.46 (m, 9H), 7.59–7.63
(m, 6H). 13C NMR (CDCl3): d = 114.09, 114.27,
128.32 (d, JC,P = 9.5 Hz), 130.30, 130.32, 131.66 (d,
JC,P = 39.5 Hz), 133.84 (d, JC,P = 10.2 Hz), 138.14,
139.16, 174.00, 174.02, 200.63 (d, JC,P = 7.3 Hz),
201.97 (d, JC,P = 6.6 Hz). IR (KBr): 2033 s, 1989 s,
1956 s, 1928 s, 1603 s, 1522 m, 1469 s, 1447 m,
1387 w, 1362 w, 1188 w, 1094 w, 1006 w, 906 w,
694 m, 570 w. Anal. Calc. for C32H21Br2N2O6PRu2
(922.44): C, 41.67; H, 2.29; N, 3.04. Found: C,
41.44; H, 2.24; N, 2.92%. MS (ESI): m/z = 945.7
(M+ + Na), 923.5 (M+).
MS (ESI): m/z = 594.5 (C14H6Cl2N2O6Ru2 + Na). MS
(MALDI-TOF, dithranol): m/z = 1117.5 (2 Æ C14H6Cl2-
N2O6Ru2 ꢀ CO). Anal. Calc. for C30H20Cl4N4O14Ru4
(1206.6): C, 29.86; H, 1.67; N, 4.64. Found: C, 29.85;
H, 1.72; N, 4.62%.
2.6. Preparation of bis(l-6-bromopyridin-2-olato-
1jO:2jN)-methanol-1jO-tetracarbonyl-1j2C:2j2C–
diruthenium(Ru–Ru), [Ru2(l-
BrpyO)2(CO)4(CH3OH)]2 (5)
Following the procedure given in Section 2.5, but
with 6-bromo-2-hydroxypyridine (81.6 mmol, 0.47
mmol) and a reaction time of 36 h, 91 mg (0.13 mmol,
56% based on Ru) of a red solid was obtained, which
decomposed above 300 ꢁC. IR (KBr): 2032 s, 1989 s,
1954 s, 1936 s, 1602 s, 1523 m, 1461 s, 1427 s, 1331 m,
1174 m, 1011 m, 904 m, 791 m, 781 m cmꢀ1. MS (MAL-
DI-TOF, dithranol): m/z = 1292.6 (M+ ꢀ 2CH3OH ꢀ
CO). Anal. Calc. for C30H20Br4N4 O14Ru4 (1384.4): C,
26.03; H, 1.46; N, 4.05. Found: C, 25.80; H, 1.22; N,
4.13%.
2.9. X-ray crystal structure determination for complexes
1, 2, 4, 6, and 7
Single crystals of 1 were obtained as follows: A part
of the boiling reaction solution (toluene, see Section
2.2) was separated after a reaction time of 4 h, filtered
hot, and was cooled slowly (10 ꢁC/h) from ꢂ100 ꢁC to
r.t. The yellow rod-shaped crystals of 1 were separated
manually from the orange crystals of unreacted
Ru3(CO)12. Block-shaped red crystals of 2 were ob-
tained by filtration of the hot reaction solution (toluene)
to separate already precipitated product, cooling, and
crystallization at 8 ꢁC during three days. Dark-red pris-
2.7. Preparation of bis(l-6-chloropyridin-2-olato-
1jO:2jN)-tetracarbonyl-1j2C:2j2C–
triphenylphosphane-1jP–diruthenium(Ru–Ru),
[Ru2(CO)4(l-ClpyO)2(PPh3)] (6)
Complex 2 (29.7 mg, 26 lmol) was suspended in a
solution of triphenylphosphane (13.1 mg, 50 lmol) and
CH2Cl2 (1 ml), and the mixture was stirred until a

L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
973
Table 1
Summary of crystallographic data and structure refinement for compounds 1, 2, 4, 6, and 7
1
2
4
6
7
a
a
Empirical formula
C30H12F4N4O14Ru4 C28H12Cl4N4O12Ru4 (C15H10Cl2N2O7Ru2)2 C32H21Cl2N2O6P1Ru2 C32H21Br2N2O6P1Ru2
Æ 0.5C6H12
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
1132.72
190(2)
0.23 · 0.10 · 0.08
monoclinic
P21/n
8.585(1)
12.973(1)
15.610(2)
90
100.82(2)
90
1707.5(4)
2
2.203
1.83
1088
1142.50
193(2)
0.31 · 0.19 · 0.15
monoclinic
1206.58
190(2)
0.38 · 0.23 · 0.15
orthorhombic
Pbca
875.60
193(2)
0.31 · 0.23 · 0.15
triclinic
922.44
193(2)
0.27 · 0.19 · 0.12
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
˚
a (A)
8.376(1)
9.592(2)
11.855(2)
98.83(2)
100.79(2)
109.36(2)
858.6(2)
1
29.391(2)
15.498(2)
8.512(6)
90
90
90
3877.4(6)
4
2.067
1.87
2336
9.646(1)
10.262(1)
18.920(2)
100.66(1)
102.79(1)
98.68(1)
1758.4(3)
2
13.962(1)
14.989(1)
24.077(2)
82.60(1)
88.25(1)
76.96(1)
4868.0(7)
6
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
qcalc (g cmꢀ3
)
2.21
2.11
548
1.654
1.10
872
1.888
3.49
2688
l(Mo Ka) (cmꢀ1
F(000)
)
h Range (ꢁ)
Index ranges
2.06–25.97
ꢀ9 6 h 6 9
ꢀ15 6 k 6 15
ꢀ19 6 l 6 19
13139
2.31–26.11
ꢀ10 6 h 6 10
ꢀ11 6 k 6 11
ꢀ14 6 l 6 14
12141
1.91–24.09
ꢀ32 6 h 6 33
ꢀ17 6 k 6 17
ꢀ9 6 l 6 9
23592
2.12–25.98
ꢀ10 6 h 6 10
ꢀ12 6 k 6 12
ꢀ22 6 l 6 23
13847
1.92–25.94
ꢀ17 6 h 6 17
ꢀ18 6 k 6 18
ꢀ29 6 l 6 29
38546
Reflections collected
Independent
3108 (0.0335)
3126 (0.0289)
2959 (0.0447)
6387 (0.0261)
17671 (0.0451)
reflections (Rint
Completeness to
hmax (%)
)
92.8
91.4
96.4
92.7
93.0
Absorption correction
numerical
3126/0/235
1.179
numerical
17671/0/1216
Data/restraints/parametersb 3108/0/253
2959/0/258
1.041
0.0217, 0.0591
6387/0/433
0.939
0.0226, 0.0524
Goodness-of-fit on F2
Final R indices
0.880
0.0201, 0.0407
0.0220, 0.0625
0.0285, 0.0513
0.0536, 0.0561
0.74, ꢀ0.71
c
[I > 2r(I)]: R1, wR2
R indices (all data):
R1, wR2
0.0312, 0.0426
0.0282, 0.0750
0.0264, 0.0604
0.0308, 0.0548
c
Largest difference
peak and hole (e A
0.53, ꢀ0.46
0.52, ꢀ0.98
0.346, ꢀ0.49
0.477, ꢀ0.44
ꢀ3
˚
)
a
In the solid state, the complex exists as a centrosymmetric coordination dimer.
b
c
Refinement based on F2 values.
2
2 1=2
R1 = RiFoj ꢀ jFci/RjFoj; wR2 ¼ ½RðwðF 2o ꢀ F c2Þ Þ=RwðF o2Þ ꢃ
.
matic crystals of 4 were grown from methanol by using
the same procedure as before. Crystallization from hot
cyclohexane afforded ruby-red crystals of 6 Æ 0.5C6H12
and orange-yellow crystals of 7.
thermal vibration; therefore, the derived bond lengths
and angles are not reasonable. Software for all calcula-
tions: SHELX-97 [14]; molecule plots: ORTEP-3 [15]. Crys-
tallographic data and details of the refinement for all
structures are given in Table 1.
Data collection was performed on an image-plate dif-
fractometer (Stoe IPDS) using monochromated Mo Ka
˚
radiation (k = 0.71073 A). For 2 and 6, the positions of
the Ru atoms were extracted from a sharpened Patter-
son map, all other structures were completely solved
with direct methods. All structures were refined using
a full-matrix least-squares method. Hydrogen atom
positions were calculated geometrically and treated as
riding on their bond neighbors in the refinement proce-
dure. The position of the methanolic OH proton of 4
was located in a difference Fourier map and was refined
freely. The positions of the carbon atoms of the cyclo-
hexane molecule present in the unit cell of 6 were not
well defined and the atoms showed large ellipsoids of
3. Results and discussion
The syntheses carried out during this study are put
together in Scheme 1. Heating of Ru3(CO)12 with three
molar amounts of 6-fluoro-, 6-chloro- or 6-bromo-
2-hydroxypyridine in boiling toluene furnished the
complexes [Ru2(CO)5(l-FpyO)2]2 (1), [Ru2(CO)4
(l-ClpyO)2]2 (2) and [Ru2(CO)4(l-BrpyO)2]2 (3),
respectively, all of which started to separate already
from the hot reaction solution. In contrast to the latter
two, complex 1 deteriorates when exposed to air for an

974
L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
CO CO
O
N
L
toluene, rfx,
2.5−5 h
X
X
N
O
Ru
Ru
OC
Ru3(CO)12
+
OC
CO
CO
L
N
Ru Ru
O
O
N
X
X
N
OH
X
CO CO
X = F, Cl, Br
1: X = F, L = CO
2: X = Cl, L = none
3: X = Br, L = none
X = Cl, Br
CH3OH, rfx,
36−48 h
X = Cl, Br PPh3,
CH2Cl2, r.t.
X
N
O
X
N
O
CO
P
CO
CO
Ru
O
CO
CH3
Ru
Ru
Ru
O
H
X
X
N
N
O
CO CO
CO CO
4: X = Cl
5: X = Br
6: X = Cl
7: X = Br
Scheme 1.
extended period of time; the orange color of the solid
starts to darken after one day and turns into black
after several days. All three complexes are barely solu-
ble in the common non-polar organic solvents, but
have a higher solubility in donor solvents such as
DMSO or acetonitrile: in each case, ꢂ50 mg of the
complex can be dissolved in 1 ml of acetonitrile. These
solubility characteristics are a consequence of the solid-
state structures of 1–3 which, according to X-ray struc-
ture analysis of 1 and 2 (vide infra), exist as centrosym-
metric coordination dimers made up from two
dinuclear monomers and held together by two Ru–O
contacts. The coordination dimers are also detected
in the MALDI mass spectra. Solvents with Lewis-base
properties can easily split up the dimers, thereby
replacing the axial Ru–O coordination by a donor mol-
ecule. Thus, the reported NMR spectra of 1, recorded
in CD3CN solution (see Section 2), are in fact those
of [Ru2(CO)4(CD3CN)2(l-FpyO)2]; the observation of
only two 13C signals for the carbonyl groups, one of
which shows a JC,F coupling of 5.1 Hz, most likely ex-
cludes the alternative complex [Ru2(CO)5(CD3CN)-
(l-FpyO)2] which should give rise to at least three
CO signals in the 13C NMR spectrum. The axial site
at the second ruthenium atom is occupied by a car-
bonyl ligand in 1 but remains empty in 2 and 3.
dine in hot methanol furnished the methanol adducts 4
and 5, and brief treatment of coordination dimers 2
and 3 with PPh3 at 20 ꢁC afforded the ‘‘monomeric’’ com-
plexes 6 and 7 which are well soluble in common solvents
such as chloroform, toluene, and acetonitrile. Com-
pound 4 was sparingly soluble in chloroform, while 5
was virtually insoluble. Remarkably, the 1H NMR spec-
trum of 4 in CDCl3 showed two sets of signals for the
pyridonate rings. This magnetic non-equivalence of the
Fig. 1. Molecular structure of 1 in the crystal. Ellipsoids of thermal
vibration are shown at the 30% probability level. The coordination
dimer has a crystallographic center of symmetry. Geometry of the
The formation of a coordination dimer can also be
suppressed in the presence of the two-electron donor li-
gands, methanol and triphenylphosphane. Thus, the
reaction of Ru3(CO)12 with 6-chloro- or 6-bromopyri-
0
˚
˚
RuORuO core: Ru2–O4 2.137(2) A, Ru2–O4 2.283(2) A, O4–Ru2–O4
75.53(7)ꢁ, Ru2–O4–Ru20 104.47 (7)ꢁ, O4–Ru2–O40–Ru20 0.0ꢁ.

L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
975
two pyridonate ligands is due to the formation of a cen-
trosymmetric dimer [Ru2(CO)4(CH3OH)(l-HalpyO)2]2
maintained by two O–Hꢄ ꢄ ꢄO hydrogen bonds involving
the methanol ligand and one pyridonate ring, as was re-
vealed by X-ray structure determination (vide infra,
Fig. 3). This dimer is obviously stable in CDCl3 solution,
but not under mass spectrometry conditions: The ESI-
MS spectrum of 4 shows a peak corresponding to the
‘‘monomeric’’ dinuclear complex without the methanol
ligand, and the MALDI mass spectra of 4 and 5 closely
resemble those of the coordination dimers 2 and 3,
respectively.
The solid-state structures of complexes 1, 2, 4, 6, and
7 were determined by single-crystal X-ray diffraction
analysis. Molecule plots are shown in Figs. 1–5. Selected
data of the bond geometry are assembled in Table 2. All
complexes feature the head–head (0,2) arrangement of
the two pyridonate ligands, i.e., both halogen substitu-
ents at C-6 of the two pyridonate rings are neighboring
the axial coordination site of the same ruthenium atom.
The intramolecular Clꢄ ꢄ ꢄCl and Brꢄ ꢄ ꢄBr contacts are
somewhat shorter than the sum of van der Waals radii
˚
˚
(3.60 A for Clꢄ ꢄ ꢄCl, 4.00 A for Brꢄ ꢄ ꢄBr), while the
Fꢄ ꢄ ꢄF distance in 1 is distinctly larger than this sum
˚
(3.742 vs. 2.80 A). As a consequence, the axial coordina-
tion site at the ruthenium atom having the halogen
neighbors remains unoccupied in the chloro-(2, 4, 6)
and bromo-(7) complexes, while in fluoro-complex 1,
the small carbonyl ligand can be accommodated at this
Fig. 2. Molecular structure of 2 in the crystal. Ellipsoids of thermal
vibration are shown at the 30% probability level. The coordination
dimer has a crystallographic center of symmetry. Geometry of the
0
˚
˚
RuORuO core: Ru2–O4 2.141(2) A, Ru2–O4 2.227(2) A, O4–Ru2–
O40 78.24(10)ꢁ, Ru2–O4–Ru20 101.76(10)ꢁ, O4–Ru2–O40–Ru20 0.0ꢁ.
Fig. 4. Molecular structure of 6 in the crystal. Ellipsoids of thermal
vibration are shown at the 30% probability level.
Fig. 3. Molecular structure of 4 in the crystal. Ellipsoids of thermal
vibration are shown at the 30% probability level. The hydrogen-
bonded dimer has a crystallographic center of symmetry.
Fig. 5. Molecular structure of 7 in the crystal. Ellipsoids of thermal
vibration are shown at the 30% probability level.

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L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
Table 2
Selected values of the bond geometry of compounds 1, 2, 4, 6, and 7
Hal
N
O
CO
CO
O
L2 Ru
N
Ru L1
Hal
C
O
C
O
1
2
4
6
7b
Hal
L1
L2
F
Cl
Opya
Cl
HOCH3
Cl
PPh3
Br
PPh3
Opya
CO
˚
Bond lengths (A)
Ru–Ru
Ru–N
2.6393(4)
2.6081(8)
2.6281(3)
2.6627(6)
2.6620(5)–2.6738(5)
2.139(3)–2.168(3)
2.083(2)–2.114(3)
1.839(5)–1.862(5)
1.362(5)–1.378(4)
1.278(4)–1.294(5)
1.362(5)–1.378(4)
3.699–3.726
2.169(2), 2.183(2)
2.091(2), 2.137(2)
1.840(3)–1.886(3)
1.331(4), 1.368(3)
1.273(3), 1.302(3)
2.119(3), 2.175(3)
2.099(2), 2.141(2)
1.843(4)–1.861(4)
1.351(5), 1.354(5)
1.300(4), 1.315(4)
2.154(2), 2.157(2)
2.098(2), 2.117(2)
1.839(3)–1.850(3)
1.361(4), 1.363(3)
1.290(3), 1.295(3)
2.142(2), 2.167(2)
2.109(2), 2.120(2)
1.844(3)–1.853(3)
1.347(3), 1.355(3)
1.285(3), 1.290(3)
Ru–O
Ru–Ccarbonyl
N–C(–O)
(N–)C–O
Halꢄ ꢄ ꢄHalc
Ru–L1
Ru–L2
3.742
2.283(2)
1.990(3)
3.484
2.227(2)
3.387
2.198(2)
3.534
2.414(1)
2.387(1)–2.391(1)
Bond angles (ꢁ)
RuO,O–RuN,N–N
RuO,O–RuN,N–Ccarbonyl
RuN,N–RuO,O–Ccarbonyl
RuN,N–RuO,O–O
N–Ru–N
81.07(6), 82.42(6)
89.66(9), 89.95(9)
94.81(9), 95.94(9)
81.65(5), 83.11(5)
86.05(8)
83.05(8), 84.08(8)
92.94(12), 95.87(13)
93.62(11), 94.13(11)
82.38(6), 85.33(7)
87.58(12)
83.54(6), 85.42(6)
93.37(11), 94.25(11)
96.04(11), 96.21(11)
82.43(5), 85.21(5)
87.06(6)
82.62(5), 84.62(5)
92.80(3), 95.92(8)
93.01(8), 93.79(7)
81.04(5), 83.32(4)
86.54(7)
83.30(8)–85.35(8)
92.89(11)–94.30(12)
92.34(11)–96.36(11)
80.12(6)–84.38(7)
87.38(11)–91.40(12)
168.97(3)–173.40(3)
Ru–Ru–L1
153.63(5)
158.25(7)
161.63(7)
167.84(2)
Torsion angles (ꢁ)
N–Ru–Ru–O
27.9(1), 28.2(1)
13.2(3), 15.3(3)
30.1(1)
19.0(1), 24.5(1)
2.2(4), 11.9(4)
26.1(2)
16.1(1), 19.3(1)
ꢀ0.6(3), 8.4(3)
19.0(1)
22.0(1), 23.6(1)
0.3(3), 17.6(3)
25.99(3)
15.4(1)–17.1(1)
22.9(1)–27.3(1)
1.7(5)–7.1(5),
8.5(5)–16.6(4)
21.4(2)–27.1(2)
Ru–N–C–O
C–Ru–Ru–Cd
a
Centrosymmetric dimer with cyclo-RuORuO core.
The given ranges relate to the three independent molecules in the asymmetric unit of the crystal.
b
c
Intramolecular Halꢄ ꢄ ꢄHal distance.
d
The given torsion angles are those involving the two carbonyl groups that point downwards in Figs. 1–5.
site. Steric shielding of the axial site at ruthenium has
been observed before in the diruthenium(II,II) complex
(2,2)-tetrakis(6-chloropyridin-2-olato)diruthenium [7],
where pairs of the pyridonate ligands are in a trans ori-
entation (in contrast to the cis orientation in the present
complexes).
In complex 4, the axial coordination site at the O,O-
substituted ruthenium atom is occupied by a methanol
molecule. In the solid state, a centrosymmetric dimer ex-
ists which is held together by two O–Hꢄ ꢄ ꢄO hydrogen
bonds involving the OH function of methanol and a
pyridonate oxygen atom of a second dinuclear complex.
The hydrogen bond is almost linear: <(O–Hꢄ ꢄ ꢄO) =
The second ruthenium atom in complexes 1 and 2
completes its ligand sphere by axial coordination of a
pyridonate oxygen atom of a second dinuclear complex
molecule which in turn forms a Ru–O bond with the first
molecule. In this manner, a centrosymmetric dimer with
a planar cyclo-Ru–O-Ru–O core is built up (see Figs. 1
and 2 for details of the bond geometry). The axial Ru–O
˚
˚
166(4)ꢁ, d(O–H) = 0.92(5) A, d(Oꢄ ꢄ ꢄH) = 1.71(5) A,
˚
d(Oꢄ ꢄ ꢄO) = 2.610(3) A. Finally, the PPh3 complexes 6
and 7 exist as isolated dinuclear complexes. Notably,
the three P–CPh bonds are not in a fully staggered con-
formation with respect to the four equatorial ligands at
ruthenium; rather, one P–CPh bond is almost colinear
with a Ru–C or Ru–O bond (torsion angle in 6: C11–
Ru1–P–C27 5.0(2)ꢁ; in 7: O2–Ru1–P1–C27 5.1(2)ꢁ).
The Ru–Ru bond lengths in all five complexes are in
the range of single bonds; as Table 2 shows, the shortest
˚
bond is longer by 0.09–0.19 A than the equatorial Ru–O
bonds. This dimerization motif is not uncommon in the
structural chemistry of dinuclear ruthenium carboxylate
and pyridonate complexes [6,7,16].

L. Scha¨ffler et al. / Inorganica Chimica Acta 359 (2006) 970–977
977
˚
distance is found in the coordination dimer 2 (2.608 A)
Acknowledgments
and the longest one in the PPh3 complexes (2.663–
˚
2.674 A). For comparison, a Ru–Ru bond length of
This work was supported by the Deutsche For-
schungsgemeinschaft (Grant Ma 819/11-1). The support
and sponsorship rendered by COST Action D24 ‘‘Sus-
tainable Chemical Processes: Stereoselective Transition
Metal-Catalyzed Reactions’’ is gratefully acknowledged.
˚
2.7108(4) A was found in the unsubstituted pyridonate
complex [Ru2(CO)4(l-pyO)2(PPh3)2] bearing two axial
PPh3 ligands [17]. All complexes feature the expected
deviation from the fully eclipsed conformation around
the Ru–Ru bond (see torsion angles given in Table 2);
similar geometries have been observed in [Ru2(CO)4(l-
pyO)2L2], L = PPh3 [17] and 2-hydroxypyridine [2].
The torsion angles N–Ru–Ru–O and C–Ru–Ru–C are
larger in the fluoropyridonate complex 1 than in 2, 4,
6, and 7. Another remarkable difference is seen for the
torsion angles Ru–N–C–O, which are quite similar in
1 (13.2ꢁ and 15.3ꢁ) while in the other complexes one tor-
sion angle is close to 0ꢁ and the other is larger by ca. 8–
17ꢁ.
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– Program for the Solution and
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