Synthesis, molecular, spectroscopic and catalytic characterization of ruthenium(II) complexes with pyridine-2-carboxylic acid derivatives ligands

Article abstract of DOI:10.1016/j.poly.2012.09.021

The ruthenium(II) complexes [RuH(CO)(6-OH-py-2-COO)(PPh₃) ₂] (1) and [Ru(3-OH-py-2-COO)₂(PPh₃) ₂] (2) have been prepared in the reactions of [RuHCl(CO)(PPh ₃)₃] and [RuCl₂

Full text of DOI:10.1016/j.poly.2012.09.021

Polyhedron 48 (2012) 21–30
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, molecular, spectroscopic and catalytic characterization of
ruthenium(II) complexes with pyridine-2-carboxylic acid derivatives ligands
b
a
b
J.G. Małecki a, , S. Krompiec , A. Maron , M. Penkala
⇑
´
a Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
b Department of Inorganic, Organometallic Chemistry and Catalysis, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2012
Accepted 3 September 2012
Available online 23 September 2012
The ruthenium(II) complexes [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2]
(2) have been prepared in the reactions of [RuHCl(CO)(PPh3)3] and [RuCl2(PPh3)3] with 6-hydroxy- and
3-hydroxypyridine-2-carboxylic acids. The complexes have been characterized by IR, UV–Vis, NMR spec-
troscopy and X-ray crystallography. Based on the crystal structures, computational investigations were
carried out in order to determine the electronic structures of the complexes. The electronic spectra were
calculated with the use of time-dependent DFT methods, and correlated with the molecular orbitals of
the complexes. The emission properties of the complexes have been examined and quantum efficiencies
equal to 0.084 for the hydride carbonyl complex (1) and 0.046 for complex (2) have been determined. The
catalytic activity in the reaction of the double bond migration in 4-allyloxybutan-1-ol for both the com-
plexes was tested. Under properly selected reaction conditions, complex (1) selectively catalyzes double
bond migration leading to 1-propenyloxyalcohol.
Keywords:
Ruthenium(II) complexes
Pyridine derivatives carboxylic acids
Absorption and emission electronic spectra
DFT
Catalysts for double bond migration
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
depending on the reaction conditions it may lead to two different
products: the double bond migration product or the cyclization
Phosphine ruthenium(II) complexes with N-heterocyclic ligands
have attracted the attention of scientists who concentrate on syn-
thetic aspects, structural and physicochemical properties, and
reactivity. Among the most interesting examples of this kind of
compound are the triarylphospine complexes with pyridine type
ligands, mainly due to their potential applications [1–5]. The de-
sign and modification of the coordination sphere of the ruthe-
nium(II) central ions by introduction of ligands is necessary to
realize high catalytic activity and selectivity, and to tune up their
spectroscopic properties, which also causes widespread interest
in this class of compounds [6,7]. It is well known that ligands con-
taining pyridine rings demonstrate distinctive physico-chemical
product. However, from an application point of view, selective syn-
thesis of enol ethers is especially interesting. In particular, 1-prope-
nyl ethers are used as monomers for cationic photopolymerization
[10].
Here, we present the synthesis, crystal, molecular and electronic
structures, and spectroscopic characterization of two ruthenium(II)
complexes with picolinic acid derivatives: 6-hydroxypicolinic acid
(6-OH-picH) and 3-hydroxypicolinic acid (3-OH-picH). The elec-
tronic structures of the complexes have been determined by den-
sity functional theory (DFT) and employed for the discussion of
bonding properties. DFT and TDDFT calculations were performed
to establish the nature of the orbitals involved in the transition pro-
cesses and to correlate the structural parameters with the spectro-
scopic properties of the complexes. The luminescent properties of
the complexes were examined and the quantum yields of the fluo-
rescence were determined. The obtained complexes were also
examined for their catalytic activity in double bond migration in
4-allyloxybutan-1-ol.
properties that are caused by a low lying unoccupied
p-molecular
orbital [8]. Azine ligands generally have energetically low lying
p-
antibonding orbitals, which can accept electrons from filled metal
d orbitals. As a consequence, they can exhibit charge transfer bands
with interesting spectroscopic properties in the visible region [7].
In the literature, many hydride complexes are described, which
effectively catalyze double bond migration [9]. However, so far
Ru(II) hydride complexes containing N,O-donor ligands have only
been tested as a catalysts for isomerization of allyloxyalcohols very
weakly, so the interest in this fields seems to be justified. The isom-
erization of allyloxybutanol has been choosen due to the fact that
2. Experimental
The [RuHCl(CO)(PPh3)3] and [RuCl2(PPh3)3] were synthesized by
a literature method [11,12]. All other reagents used for the synthe-
sis of the complexes were commercially available and have been
used without further purification.
⇑
Corresponding author. Tel.: +48 32 3591513.
E-mail address: gmalecki@us.edu.pl (J.G. Małecki).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.09.021

22
J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
2.1. Synthesis of the complexes [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1)
and [Ru(3-OH-py-2-COO)2(PPh3)2] (2)
optimized molecular structure obtained corresponds to an energy
minimum, thus only positive frequencies were expected. The cal-
culations were performed using the DZVP basis set [18] with f
functions having exponents of 1.94722036 and 0.748930908 for
the ruthenium atom, and polarization functions for all other
The complex [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) was syn-
thesized by the reaction between [RuHCl(CO)(PPh3)3] (0.2 g,
2.0 ꢀ 10ꢁ4 mol) and 6-hydroxypyridine-2-carboxylic acid (0.031
g, 2.2 ꢀ 10ꢁ4 mol), and the complex [Ru(3-OH-py-2-COO)2(PPh3)2]
(2) was synthesized by the reaction between [RuCl2(PPh3)3] (0.2 g,
2.0 ꢀ 10ꢁ4 mol) and 3-hydroxypyridine-2-carboxylic acid (0.061 g,
4.4 ꢀ 10ꢁ4 mol). The mixtures of the compounds were refluxed in
methanol (60 mL) for 3 h. After this time, they were cooled and fil-
tered. Crystals suitable for X-ray crystal analysis were obtained by
slow evaporation of the reaction mixtures.
atoms: 6-31g⁄⁄
– phosphorus, carbon, nitrogen, oxygen and
6-31g – hydrogen. Natural bond orbital (NBO) calculations were
performed with the NBO code [19] included in GAUSSIAN09. The con-
tribution of a group to a molecular orbital was calculated using
Mulliken population analysis. GAUSSSUM 2.2 [20] was used to calcu-
late group contributions to the molecular orbitals and to prepare
the partial density of states (DOS) and overlap population density
of states (OPDOS) spectra. The DOS and OPDOS spectra were
created by convoluting the molecular orbital information with
GAUSSIAN curves of unit height and a FWHM of 0.3 eV.
(1): Yield 62%. IR (KBr, cmꢁ1): 3414
m
OH; 3053
as(COO); 1608
plane); 1433 Ph(P–Ph); 1382
plane); 692 d(C–C
m
ArH; 2785, 2673
(C=N); 1566 m(C@C)
s(COO); 1091
m
CH; 1946
m
(CO); 1911
m(Ru-H); 1629
m
m
;
1480, 1460 d(C–CH
m
m
in the
d(C–CH
plane); 744 d(C–C
;
in the
out of the
in the plane)
516 m(N;O;P–Ru).
1H NMR (400 MHz, CDCl3) d (ppm): 10.98 (s, OH),
2.4. Crystal structure determination and refinement
8.67 (s, py), 7.75–7.18 (m, PPh3, py), 6.84 (d, py), 6.38 (d, py),
-16.08 (t, J = 16.8 Hz, H(Ru)). 31P NMR (CDCl3) d (ppm): 39.07 (s,
PPh3). UV–Vis (methanol; k (nm)): 325, 275, 248, 227.
Crystals of [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-
OH-py-2-COO)2(PPh3)2] (2) were mounted in turn on an Xcalibur,
Atlas, Gemini Ultra Oxford Diffraction automatic diffractometer
equipped with a CCD detector, and used for data collection. X-ray
(2): Yield 74%. IR (KBr, cmꢁ1): 3411
m
OH; 3053
mPhH; 1636
m
as(COO); 1594 m(C
@
N); 1559
Ph(P–Ph); 1307, 1254
plane); 702, 694 d(C–C
m(C@C); 1480, 1465 d(C–CH
;
in the plane)
;
in the plane)
intensity data were collected with graphite monochromated MoK
a
1430, 1383
752 d(C–C
m
m
s(COO); 1093 d(C–CH
plane); 523 m
P–Ph.1H
radiation (k = 0.71073 Å) at a temperature 295.0(2) K, with the
x
out of the
in the
scan mode. Ewald sphere reflections were collected up to
2h = 50.10. The unit cell parameters were determined from the
least-squares refinement of the setting angles of the 19550 and
21168 strongest reflections for complexes (1) and (2), respectively.
Details concerning crystal data and refinement are gathered in Ta-
ble 1. Lorentz, polarization and empirical absorption corrections
NMR (CDCl3) d (ppm): 12.48 (s, OH), 7.99 (d, Hpy), 7.34 (t, Hpy),
7.19 (t, Hpy), 7.10–6.92 (m, PPh3). 31P NMR (CDCl3) d (ppm):
44.69 (s, PPh3). UV–Vis (methanol, k (nm)): 371, 306, 268, 207.
2.2. Physical measurements
using spherical harmonics, implemented in the SCALE3 ABSPACK scaling
Infrared spectra were recorded on a Perkin Elmer spectropho-
tometer in the spectral range 4000–450 cmꢁ1 using KBr pellets.
Electronic spectra were measured on a Lab Alliance UV–Vis 8500
spectrophotometer in the range 600–180 nm in methanol solution.
The 1H and 31P NMR spectra were obtained at room temperature in
CDCl3 and C6D6 using a Bruker Avance 400 MHz spectrometer.
Luminescence measurements were made in ethanolic solutions
on an F-2500 FL spectrophotometer at room temperature. Quan-
tum yields of fluorescence were calculated using follow equation:
algorithm [21], were applied. The structure was solved by the Patt-
erson method and subsequently completed by difference Fourier
recycling. All the non-hydrogen atoms were refined anisotropically
using the full-matrix, least-squares technique. Knowing about the
limits of Fourier synthesis and the problems in recognizing artifacts
in the immediate neighborhood of heavy atoms, it is doubtful if a
reliable position for the hydrogen atom bound to the Ru-atom could
be found in the difference Fourier map avoiding the danger of mis-
taking the effects of the series termination errors for a true atomic
position. In the studied complex, the Ru–H bond length of 1.23(9) Å
is short and though short distances are present in the Cambridge
Structural Database (CSD; ConQuest v. 1.14; 2012), the authors con-
sider this bond length as erroneous. The OLEX2 [22], SHELXS97 and
Gradsg2s
Us
¼
Ustd
Gradstdg2std
where Us is the quantum yield of the unknown sample; Ustd is the
quantum yield of naphthalene as a reference at 313 nm and is equal
to 0.21 [13]; Grads and Gradstd are the gradients from the plot of
integrated fluorescence intensity versus the solutions absorbance
SHELXL97 [23] programs were used for all the calculations. The atom-
ic scattering factors used were those incorporated in the computer
programs.
at the excitation wavelength and gs and gstd are the refractive indi-
ces of the solvents. The samples were prepared with an absorbance
less than 0.1 the excitation wavelengths in order to minimize re-
absorption effects and avoid inner-filter effects, which may perturb
the quantum yields values. The solvent (ethanol) used in the mea-
surements was spectroscopic grade and checked for background
fluorescence.
2.5. Catalytic tests
2.5.1. Allyl substrates
4-Allyloxybutan-1-ol was prepared according to the procedure
described in the literature [24].
2.3. DFT calculations
2.5.2. Isomerization of 4-allyloxybutan-1-ol
4-Allyloxybutan-1-ol (2 mmol) and [Ru] (0.01 mmol) were
stirred with a magnetic stirrer and heated in an oil bath at
100, 110, 120 or 130 °C for 3–24 h under an argon atmosphere
(see Table 5). The post-reaction mixture was analyzed using the
1H NMR technique at room temperature in C6D6 using a Bruker
Avance 400 MHz spectrometer. The choice of NMR solvent was
crucial, because cyclization of HO(CH2)4OCH@CHCH3 occurs rap-
idly in the NMR tube, even if CDCl3 contains only trace amounts
of HCl.
The calculations were carried out using the GAUSSIAN09 [14] pro-
gram. The B3LYP/DZVP level of the theory was used to fully opti-
mize the gas phase molecular geometries of the singlet ground
state of complexes (1) and (2) [15,16] and the TD-DFT (time depen-
dent density functional theory) method [17] was employed to cal-
culate the electronic absorption spectra of the complexes in the
solvent PCM (polarizable continuum model) model. For each com-
pound a frequency calculation was carried out, verifying that the

J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
23
Table 1
pling with the two trans phosphorus atoms (JHP = 16.80 Hz). In the
31P NMR spectra of complexes (1) and (2) singlets at 39.07 and
44.69 ppm are visible. The presence of magnetically equivalent
phosphorus atoms in the spectra of complexes proves the equiva-
lence of the phosphine groups in their structures.
In the IR spectra, ring C@N stretching modes of pyridine deriva-
tive ligands are observed at 1608 cmꢁ1 for complex (1) and
1594 cmꢁ1 for complex (2). The asymmetric and symmetric
stretches of COOꢁ groups gave bands with maxima at 1629,
1636 cmꢁ1 and 1382, 1306 cm–1, respectively. The carboxyl group
stretches in the free ligands are observed at 1715, 1331 cmꢁ1 for
6-OHpicH and 1702, 1322 cmꢁ1 for 3-OHpicH. The considerable dif-
Crystal data and structure refinement details of the [RuH(CO)(6-OH-py-2-
COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2) complexes.
(1)
(2)
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C
43H35NO4P2Ru
C48H38N2O6P2Ru
901.81
295.0(2)
monoclinic
P21/n
792.73
295.0(2)
orthorhombic
P212121
11.9875(10)
15.5353(12)
19.5857(19)
90.00
90.00
90.00
3647.4(5)
4
1.444
0.562
1624
0.19 ꢀ 0.11 ꢀ 0.10
3.35–25.05
ꢁ14 6 h 6 14,
ꢁ18 6 k 6 18,
ꢁ23 6 l 6 17
19550
12.1088(4)
27.8177(11)
12.5325(5)
90.00
90.487(3)
90.00
4221.3(3)
4
1.419
ference between mas and ms is indicative of a strong coordination of
the carboxyl oxygen to the ruthenium(II) acceptor centre. The IR
spectrum of complex (1) presents a strong C„O band and the Ru–
H stretching band at 1911 and 1946 cmꢁ1, respectively, and the val-
c
(°)
Volume (Å3)
Z
Calculated density (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
ues of their frequencies are decreased compared to the
stretching bands in the parent [RuHCl(CO)(PPh3)3] complex, in
which these stretching modes are present at 1922 and 2020 cmꢁ1
mCO and mRu–H
)
0.499
1848
,
Crystal dimensions (mm)
q Range for data collection (°)
Index ranges
0.43 ꢀ 0.10 ꢀ 0.08
3.35–25.05
ꢁ14 6 h 6 14,
ꢁ33 6 k 6 32,
ꢁ14 6 h 6 14,
21168
respectively. The decrease is caused by the donor–acceptor proper-
ties of 6-OHpicH and is connected with delivering electron density
by backbonding to the carbonyl ligand. The experimental and calcu-
lated IR spectra of the complexes are presented in Fig. 1.
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
)
6389 (0.0804)
6389/0/465
1.035
7336 (0.0326)
7336/0/534
1.044
3.2. Molecular structures
Final R indices [I > 2
r
(I)]
R1 = 0.0480,
wR2 = 0.1034
R1 = 0.0862,
wR2 = 0.1408
1.090/ꢁ1.185
R1 = 0.0320,
wR2 = 0.0732
R1 = 0.0463,
wR2 = 0.0801
0.468/ꢁ0.424
Crystals of the complexes suitable for single crystal X-ray analy-
ses were obtained by slow evaporation of the reaction mixtures.
Complex (1) crystallizes in the orthorhombic P212121 space group
and complex (2) in the monoclinic P21/n space group. The molecular
structures of the complexes are shown in Fig. 2. Selected bond
lengths and angles are listed in Table 2. The Ru–C bond distance
(1.829(11) Å) is normal for a monomeric Ru(II) carbonyl complex
(the distances generally range from 1.74 to 1.98 Å). The Ru–P, Ru–
N and Ru–C distances are normal and comparable with distances
in other ruthenium complexes containing N-heterocyclic ligands.
The C(1)–O(1) bond shows some shortening in comparison with
typical distances for CO substituents, but similar distances can be
found in several compounds [24–35]. The ruthenium central ions
in the complexes have a disordered octahedral environment. In
both complexes, the largest deviations from the expected 90° bond
angle come from the bite angles of pyridine-2-carboxylic acid deriv-
atives, equal to 75.1(4)° and 78.29(7)°, 78.65(7)° in complexes (1)
and (2), respectively. The mutually trans configuration of the car-
bonyl and carboxyl groups in the structure of (1) is preferred due
to the strong donor property of the COOꢁ moiety. In complex (1),
the hydride ligand is in a trans position to the pyridine nitrogen do-
nor and the differences between the Ru(1)–N(1) bond lengths in
complexes (1) and (2) are, to a certain degree, connected to the trans
effect of the hydride ligand.
R indices (all data)
Largest diff. peak and hole (e Åꢁ3
)
2.5.3. Isolation of the pure 1-propenyl derivative (only when
conversion of the allyl substrate was practically quantitative)
The post-reaction mixture was diluted with 10 cm3 of hexane,
filtered and then 20 mg of activated carbon (Norit CN-1, Acros;
1 g/10 mg Ru) was added. The suspension was stirred for 2 h, fil-
tered and volatile residues were evaporated on a rotary evaporator.
The isomerization products, practically ruthenium-free (<0.1 ppm
Ru), were obtained in 95% yield.
(E) and (Z)-HOCH2CH2CH2CH2OCH = CHCH3: 1H NMR (400 MHz,
C6D6) d (ppm): 1.40–1.59 (m, 8H), 1.45 (dd, 3H, J = 1.6, J = 6.7 Hz),
1.69 (dd, 3H, J = 1.7, J = 6.8 Hz) 2.29–2.37 (m, 2H), 3.37–3.45 (m,
8H), 4.37 (dq, 1H, J = 6.7, J = 13.1 Hz), 4.72 (dq, 1H, J = 6.7,
J = 12.6 Hz), 5.80 (dq, 1H, J = 1.7, J = 6.2 Hz), 6.18 (dq, 1H, J = 1.5,
J = 12.6 Hz). 13C NMR (100 MHz, C6D6) d (ppm) = 9.5, 12.7, 26.2,
26.7, 29.5, 29.7, 62.2, 68.9, 71.9, 98.2, 100.7, 146.1, 147.2.
3. Results and discussion
In complex (2), the phosphines are in a cis conformation, with
the P(1)–Ru(1)–P(2) angle being equal to 95.70(2)°, greater than
the expected 90°. This distortion is probably connected to the steric
3.1. Spectroscopic characterization of the complexes
The 1H NMR spectra of the complexes show a set of signals cor-
responding to the PPh3 and picolinic acid derivative ligands. Com-
plexation with ruthenium(II) induces shielding effects for all
hydrogen atoms of the picolinic acid derivative ligand molecules
compared to the free ligand spectra. The weak signals of the hydro-
xyl group are observed as singlets at 10.98 ppm for complex (1)
and 12.48 ppm for complex (2). The signals of the phosphine phe-
nyl and pyridine rings are given in the Experimental section. Addi-
tionally, in the spectrum of complex (1) a signal at high field
(ꢁ16.08 ppm) is visible, which indicates the presence of the hy-
dride ligand coordinated to the ruthenium central ion. The shift
of the signal is due to the shielding effect of the metal and to the
charge of the hydride ion. The Ru–H signal is a triplet due to cou-
interaction between the bulky PPh3 ligands and p–p stacking inter-
actions between the phosphine phenyl and pyridine rings. The
phosphine ligands in the complex (2) are equivalent and have
the same environment, which is reflected in the 31P NMR spectrum.
In the complex (1), the P–Ru–P angle is lower than 180 °, being
equal to 174.00(13)°.
The conformations of the complexes molecules are stabilized by
intra- and inter-molecular weak hydrogen bonds, details of which
are collected in Table 3, and additionally by some electronic inter-
actions (p–p stacking) between PPh3 phenyl and pyridine rings.
Fig. 3 presents the alignment of the centroids of the pyridine and
phosphine phenyl rings. The plane–to–plane distances between
the phosphine phenyl centroids, determined by C(20)–C(25) and

24
J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
Fig. 1. The experimental and calculated IR spectra of the [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2) complexes.
C(26)–C(31) carbons, and the pyridine rings are equal to 3.76 and
3.75 Å in complex (1), indicating weak stacking interactions.
3.3. Electronic structure
p–p
A similar arrangement between the phosphine phenyl and pyridine
rings occurs in the structure of complex (2), where the distances
between the phenyl rings C(13)–C(18) and C(31)–C(36) and the
pyridine centroids are 3.83 and 3.57 Å.
Calculations using the density functional theory (DFT) method
of GAUSSIAN-09 were carried out to obtain an insight into the elec-
tronic structures and bonding properties of the complexes. Before
the calculations, their geometries were optimized in singlet states

J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
25
Fig. 2. Molecular structures of the [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2) complexes. Hydrogen atoms (bonding with carbons) are
omitted for clarity.

26
J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
Table 2
Selected bond lengths (Å) and angles (°) for the [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2) complexes with the optimized geometry values.
(1)
(2)
exp
calc
exp
calc
Bond lengths (Å)
C(1)–O(1)
1.119(15)
1.829(11)
2.169(11)
2.149(9)
2.352(3)
2.338(3)
1.23(9)
1.163
1.860
2.290
2.159
2.429
2.429
1.615
N(1)–Ru(1)
N(2)–Ru(1)
O(1)–Ru(1)
O(4)–Ru(1)
P(1)–Ru(1)
P(2)–Ru(1)
2.109(2)
2.103(2)
2.0970(16)
2.1059(16)
2.3363(7)
2.3328(7)
2.140
2.140
2.135
2.135
2.428
2.428
C(1)–Ru(1)
N(1)–Ru(1)
O(2)–Ru(1)
P(1)–Ru(1)
P(2)–Ru(1)
Ru(1)–H(1)
Angles (°)
C(1)–Ru(1)–H(1)
C(1)–Ru(1)–N(1)
C(1)–Ru(1)–O(2)
C(1)–Ru(1)–P(1)
C(1)–Ru(1)–P(2)
N(1)–Ru(1)–H(1)
N(1)–Ru(1)–P(1)
N(1)–Ru(1)–P(2)
O(2)–Ru(1)–H(1)
O(2)–Ru(1)–N(1)
O(2)–Ru(1)–P(1)
O(2)–Ru(1)–P(2)
P(1)–Ru(1)–H(1)
P(2)–Ru(1)–H(1)
P(2)–Ru(1)–P(1)
O(1)–C(1)–Ru(1)
92(4)
89.13
101.78
175.94
91.76
91.76
169.10
96.25
96.24
94.94
74.16
88.72
88.73
83.28
83.28
166.05
178.59
O(1)–Ru(1)–N(2)
O(1)–Ru(1)–O(4)
N(2)–Ru(1)–O(4)
O(1)–Ru(1)–N(1)
N(2)–Ru(1)–N(1)
O(4)–Ru(1)–N(1)
O(1)–Ru(1)–P(2)
N(2)–Ru(1)–P(2)
O(4)–Ru(1)–P(2)
N(1)–Ru(1)–P(2)
O(1)–Ru(1)–P(1)
N(2)–Ru(1)–P(1)
O(4)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
P(2)–Ru(1)–P(1)
91.28(8)
167.01(7)
78.29(7)
78.65(7)
84.73(8)
92.57(7)
88.31(5)
173.68(7)
101.21(5)
89.00(6)
99.70(5)
90.59(7)
88.24(5)
174.99(6)
95.70(2)
93.65
168.77
77.90
77.90
83.42
93.64
87.70
172.13
99.69
89.30
99.69
89.30
87.71
172.13
98.13
102.9(5)
177.0(5)
88.4(4)
88.7(4)
165(4)
94.3(3)
91.5(3)
90(4)
75.1(4)
89.6(3)
93.5(3)
83(4)
92(4)
174.00(13)
178.5(13)
Table 3
the donations from the pyridine derivative ligands to the ruthe-
nium central ions have values of 336.17 and 394.11 kcal/mol, and
the back donations are only equal to 26.64 and 36.30 kcal/mol in
Hydrogen bonds for the [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-
COO)2(PPh3)2] (2) complexes (Å and °).
D–Hꢂ ꢂ ꢂA
(1)
C(5)–H(5). . .O(3)#1
C(39)–H(39). . .O(2)
O(4)–H(4A). . .O(3)#1
d(D–H)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
<(DHA)
complexes (1) and (2), respectively. These data confirm strong
r-
donor and weak -acceptor properties of hydroxypicolinic acids
p
0.93
0.93
0.82
2.58
2.45
2.08
3.229(17)
3.122(18)
2.617(13)
127.6
129.1
123.2
as ligands. In the analyses it was found that the picolinic acid deriv-
atives donor ligands do not show covalent bonding with ruthenium.
Coulomb-type interactions between the ruthenium central ions and
these ligands are clearly visible in the calculated Wiberg bond indi-
ces, whose values are considerably lower than one. The Ru–N and
Ru–O bond indices are 0.35 and 0.40 in complex (1), and in complex
(2) a similar value of 0.44 is obtained. The Ru–P bond orders are also
smaller than 1 (near to 0.7). For the carbonyl group of complex (1),
three natural bond orbitals were detected for the C–O bond, and one
for the Ru–C bond. The Ru–C bond orbitals are polarized towards
the carbon atom, and the C–O bond orbitals are polarized towards
the oxygen end. The oxygen atom of the carbonyl ligand has one
lone pair (LP) orbital. The Wiberg index of the CO bond in the com-
plex is reduced (by 0.20) with respect to free CO (WCO = 2.23). The
charge on the carbonyl group, calculated simply by summing the
individual charges on the carbon and oxygen atoms, is equal to
0.201.
(2)
O(3)–H(3A). . .O(2)
O(6)–H(6). . .O(5)
C(24)–H(24). . .O(1)
C(26)–H(26). . .O(4)
C(32)–H(32). . .O(4)
C(45)–H(45). . .O(2)#2
C(48)–H(48). . .O(1)
0.82
0.82
0.93
0.93
0.93
0.93
0.93
1.83
1.84
2.25
2.60
2.25
2.47
2.44
2.564(3)
2.567(3)
3.120(4)
3.407(4)
3.138(3)
3.344(4)
3.261(4)
147.6
146.8
156.4
145.9
159.1
156.2
147.3
Symmetry transformations used to generate equivalent atoms: #1: 1 ꢁ x, ꢁ1/2 + y,
3/2 ꢁ z; #2: 1/2 + x, 1/2 ꢁ y, ꢁ1/2 + z.
using the DFT method with the B3LYP functional. In general, the
predicted bond lengths and angles are in agreement with the val-
ues based on the X-ray crystal structure data, and the general
trends observed in the experimental data are reproduced in the
calculations (Table 2). The maximum differences between experi-
mental and calculated geometries are in the Ru(1)–N(1) bond
length in complex (1) (0.12 Å) and in ruthenium–phosphines
bonds, by about 0.1 Å. The experimental and calculated angles be-
tween the PPh3 ligands in complex (1) differ by about 8° and the
differences in geometries of complex (2) do not exceed 3°.
The interactions between the ligands and the central ions man-
ifest themselves in charges on the complex metal ions. The metal
ions in the complexes are formally in the second oxidation state,
but the calculated natural charges are considerably lower than 2+,
and are equal to ꢁ0.748 and ꢁ0.024 for complexes (1) and (2),
respectively. The natural charges indicate that donations from the
ligands to the central ions have the advantage over the back dona-
tions from the metal to the ligands. The NBO analyses (Second Order
Perturbation Theory Analysis of Fock Matrix in NBO Basis) show that
Analysis of the frontier molecular orbitals is useful for under-
standing the spectroscopic properties, such as electronic absorp-
tion and emission spectra of complexes. The densities of states
(DOS) in terms of Mulliken population analysis were calculated
using the GAUSSSUM program and Fig. 4 presents the composition
of the fragment orbitals contributing to the molecular orbitals. As
can be seen in the DOS diagrams of the complexes, the dRu orbitals
play a significant role in the frontier HOMOs of the complexes with
a contribution of the picolinic acid derivatives and, in the case of
complex (1), PPh3 ligands. The contributions of the d ruthenium
orbitals in occupied molecular orbitals (HOMO–HOMO ꢁ 2) are in
the range 59–70% in complex (1) and 75–78% in complex (2). The
3-OH-picH ligand contributes in a wider range in the HOMOs than
6-OH-picH. In HOMO ꢁ 1 and HOMO ꢁ 2 for the electronic struc-
ture of complex (1)
p orbitals of the carbonyl group are noted,
which affects the luminescent properties of the complex.

J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
27
localized on the d ruthenium orbitals with an admixture of the
p
orbitals of the picolinic acid derivatives ligands and the LUMOs
are localized on the pyridine derivative ligands, the transitions
above 300 nm have metal–ligand charge transfer character. The
bands observed at 275, 248 and 268 nm have also been attributed
to MLCT transitions, but with an admixture of LLCT character. The
highest energy bands with maxima at 227 and 207 nm are attrib-
uted to transitions of ligand–ligand charge transfer type (p–
p⁄).
The emission characteristics of the complexes have been pre-
pared in optically diluted ethanolic solutions at room temperature.
The measurement of the quantum yields have been examined by a
comparative method using naphthalene in ethanol as a standard
(UST = 0.21). The solutions of complexes (1) and (2) have been ex-
cited at wavelengths equal to 322 and 304 nm and the emissions
maxima are observed at 381 and 344 nm, respectively. The quan-
tum efficiencies are equal to 0.084 for complex (1) and 0.046 for
complex (2). The emissions originating from the lowest energy me-
tal to ligand charge transfer states, derived from the excitations
involving dRu
?
p⁄
transitions, are observed. The assignments
ligand
are supported by the analysis of the frontier orbitals of the com-
plexes showing a partial contribution of ligand nature, and the
transitions calculated in this energy range have MLCT character
(see Table 4) and proceed between the frontier HOMOs and
LUMO + 1/+2 for complex (1) and between the frontier HOMOs
and LUMO + 5/+6 for complex (2). As shown in Fig. 5, the fluores-
cence of complex (1) is stronger than that of complex (2), which
is related to the differences in their electronic structures. Moreover
in the HOMO ꢁ 1 and HOMO ꢁ 2 of complex (1) the carbonyl li-
gand plays a significant role, and transitions from these orbitals
to LUMO and LUMO + 1/+2 are calculated in the energy range close
to the excitation (italic lines in Table 4).
3.5. Catalytic activity
The synthesized hydride complex (1) turned out to be an active
catalyst for double bond migration in 4-allyloxybutan-1-ol
(Scheme 1 and Table 5). Complex (2) was completely inactive: nei-
ther isomerization nor cyclization of allyloxyalcohol was catalyzed
(after 3 h at 120 °C the conversion was 0%). Probably this is due to
the fact that the only labile ligands in complex (2) are PPh3 which
are insufficient to generate an active form of the catalyst for the
double bond migration.
Fig. 3. The
p-stacking interactions in the molecules of the [RuH(CO)(6-OH-py-2-
COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2) complexes.
The results presented in Table 5 show that the obtained hydride
complex (1) is an active double bond migration catalyst. The best
result was obtained after 3 h at 120 °C (95% conversion, 100%
yield). A similiar result was obtained at 110 °C, however it was nec-
essary to run the reaction for 24 h. Although the conversion was
quantitative, the yield was 93%. The results in Table 2 clearly indi-
cate that rising the temperature up to 130 °C or prolongation of the
reaction time at 120 °C for over 3 h leads to the formation of un-
wanted intermolecular addition (polymerization) products, ob-
served in the post-reaction mixture. On the other hand, lowering
the temperature below 120 °C causes dramatic conversion loss
(after 3 h at 100 °C only 8% conversion is obtained). It is notewor-
thy that the advantage of complex (1) is its selectivity. It does not
catalyze cyclization of 4-allyloxybutan-1-ol to a cyclic acetal –
which could be expected.
According to us, double bond migration in 4-allyloxybutan-1-ol
occurs via the classic mechanism of Ru–H addition–elimination
[38]. Moreover, in the case of these allyl compounds creation of ex-
tra-hydride ligands is possible due to the presence of an OH group
in this molecule [39]. Previously, we excluded a hydride mecha-
nism for consequent cyclization and polymerization of allyloxybut-
anol. In these reactions we postulate that transition metal
complexes are playing the role of Lewis acid type catalysts for in-
tra- (cyclization) or inter-molecular (polymerization) addition of
The orbitals of the picolinic acid derivatives mainly contribute in
the frontier LUMO orbitals: LUMO to LUMO + 2, and for complex (2)
2
in LUMO + 6. In the case of complex (1), the ruthenium dx 2 orbi-
ꢁy
2
tal plays a role in LUMO + 1 (17%), the dz orbitals participate in
LUMO + 14/+18 (31%/24%) and the carbonyl ligand is involved in
LUMO + 16/+18 orbitals (74%, 48%). In complex (2) the contribution
of the ruthenium d orbitals in the LUMO to LUMO + 2 range is smal-
ler than in complex (1), but the ruthenium dz2 orbitals contribute in
higher unoccupied orbitals: LUMO + 5 (13%) and LUMO + 15 (38%).
3.4. Electronic spectra
The UV–Vis spectra of the studied complexes are similar and the
maxima are located at 325, 275, 248, 227 and 371, 306, 268, and
207 nm for (1) and (2), respectively. The theoretical absorption
spectra of the complexes were obtained from the calculation of
the singlet excited states with TD-DFT at the B3LYP/DZVP/6-
31g++ level in the methanol solvent phase. Computation of 100 ex-
cited states of the complexes allowed for the interpretation of the
experimental spectra. Selected transitions, assigned to the absorp-
tion bands, are shown in Table 4. The first bands have HOMO ?
LUMO/L + 1 character. Taking into account that the HOMOs are

28
J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
Fig. 4. The density-of-states diagrams for [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2).
an OH group to the double bond [39]. Thus, it is suitable to obtain a
1-propenyl derivative via isomerization of the appropriate allyl
hydroxyalkyl ether. In this case the pure, practically ruthenium-
free, 1-propenyl product was obtained using the method previ-
ously described in the literature, i.e. adsorption of Ru compounds
and impurities on activated carbon [36–38].
and phosphorus nuclear magnetic resonance, electronic absorption
and emission spectroscopy, and X-ray crystallography. The cata-
lytic activities of the complexes have been examined for the double
bond migration in 4-allyloxybutan-1-ol. The complex [RuH
(CO)(6-OH-py-2-COO)(PPh3)2] (1) was obtained from the reaction
between [RuHCl(CO)(PPh3)3] and an equivalent amount of 6-
hydroxypyridine-2-carboxylic acid, and the complex [Ru(3-OH-
py-2-COO)2(PPh3)2] (2) was synthesized from the [RuCl2(PPh3)3]
parent complex and a double stoichiometric amount of 3-hydroxy-
pyridine-2-carboxylic acid. In the crystal structure of the com-
plexes, some types of non-covalent interactions between
aromatic rings have been found. The electronic structures of the
complexes have been determined using the density functional the-
ory (DFT) method, and employed for discussion of their properties.
4. Conclusions
Summarizing, two new ruthenium(II) complexes with picolinic
acid derivatives, 6-hydroxypyridine-2-carboxylic acid and 3-
hydroxypyridine-2-carboxylic acid, functioning as N,O-donor li-
gands were synthesized and characterized by infra red, proton

J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
29
Table 4
The electronic transitions for complexes (1) and (2) calculated with the B3LYP functional by the TD-DFT method.
k (nm)
f
Transitions
Character
Exp (nm)
325
(1)
354.3
350.3
324.3
315.2
306.1
290.3
283.2
267.7
262.0
248.5
236.3
231.8
227.7
224.1
0.0534
0.1404
0.0
HOMO ? LUMO (98%)
HOMO ? L + 1 (80%)
H ꢁ 1 ? LUMO (98%)
dRu ?
p⁄
d
Ru ? ꢁ OHpicH
p⁄PPh3/dRu
dRu
dRu
dRu
dRu
dRu
dRu
?
?
?
?
?
?
p⁄
0.002
H ꢁ 2 ? L + 1 (51%); HOMO ? L + 2 (18%)
H ꢁ 2 ? L + 1 (23%), HOMO ? L + 2 (45%)
H ꢁ 1 ? L + 2 (13%), HOMO ? L + 3 (67%)
HOMO ? L + 5 (93%)
p⁄OHpicH
0.0431
0.0158
0.0074
0.0137
0.0572
0.0074
0.0032
0.0042
0.0342
0.0452
p⁄PPh3/OHpicH
p⁄PPh3
p⁄PPh3/OHpicH
275
248
227
HOMO ? L + 6 (85%), HOMO ? L + 7 (12%)
H ꢁ 4 ? LUMO (75%), HOMO ? L + 7 (12%)
H ꢁ 10 ? LUMO (20%), HOMO ? L + 12 (56%)
H ꢁ 1 ? L + 9 (61%)
p⁄PPh3
PPh3
pPPh3
pPPh3 ?
p⁄
OHpicH
?
p⁄
OHpicH
dRu
/
pOHpicH
pOHpicH
pPPh3
pPPh3/OHpicH
?
p⁄
H ꢁ 1 ? L + 11 (69%)
?
p⁄PPh3
PPh3
H ꢁ 12 ? L + 1 (30%), H ꢁ 10 ? L + 1 (20%), H ꢁ 4 ? L + 2 (23%)
H ꢁ 6 ? L + 2 (26%), H ꢁ 1 ? L + 14 (15%)
?
p⁄
PPh3
?
p⁄
PPh3
(2)
413.7
411.6
359.7
306.1
304.2
303.8
279.7
271.6
249.2
248.0
247.8
238.9
0.0069
0.0035
0.0837
0.0031
0.0013
0.0009
0.0012
0.0016
0.0010
0.0203
0.0501
0.0238
HOMO ? L + 1 (88%)
dRu
dRu
dRu
dRu
dRu
dRu
dRu
dRu
?
?
?
?
?
?
?
?
p⁄
p⁄OHpicH
p⁄OHpicH
p⁄OPPHhp3i/cdHRu
p⁄
p⁄OHpicH
H ꢁ 1 ? L + 1 (66%), HOMO ? LUMO (18%)
H ꢁ 2 ? LUMO (59%), H ꢁ 1 ? L + 2 (14%)
H ꢁ 1 ? L + 3 (54%), H ꢁ 1 ? L + 5 (30%)
HOMO ? L + 6 (92%)
371
305
268
H ꢁ 1 ? L + 6 (91%)
HOMO ? L + 9 (96%)
p⁄OHpicH
HOMO ? L + 10 (77%)
HOMO ? L + 16 (84%)
p⁄OHpicH/PPh3
PPh3/OHpicH
pOHpicH
pOHpicH
pOHpicH
?
?
?
p⁄
H ꢁ 2 ? L + 11 (22%), H ꢁ 2 ? L + 13 (51%)
p⁄PPh3
H ꢁ 3 ? L + 2 (69%)
p⁄PPh3
PPh3
H ꢁ 5 ? L + 2 (50%), H ꢁ 2 ? L + 17 (14%)
pPPh3
?
p⁄
227
PPh3
Table 5
Isomerization of 4-allyloxybutan-1-ol to its 1-propenyl derivative catalyzed by
[RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1).
T (°C);
s
(h)
Conversion (%)
Yield (%)a
Z/E ratiob
100; 3
100; 6
110; 3
110; 6
110; 24
120; 3
120; 6
130; 3
130; 6
8
24
34
66
100
95
100
100
100
100
100
100
100
93
100
87
88
47/53
43/57
54/46
55/45
59/41
63/37
58/42
59/41
54/46
90
a
Yield of 4-(1-propenyloxy)butan-1-ol formation.
Determined by 1H NMR.
b
utan-1-ol. The lack of catalytic activity in the double bond migra-
tion reaction with complex (2) suggests the hydride and carbonyl
ligands are involved in the creation of the active form of the cata-
lyst for this type of reaction.
Fig. 5. Emission spectra of [RuH(CO)(6-OH-py-2-COO)(PPh3)2] (1) and [Ru(3-OH-
py-2-COO)2(PPh3)2] (2) complexes in ethanolic solutions.
Acknowledgements
(1)
O
O
HO
HO
The GAUSSIAN-09 calculations were carried out in the Wrocław
Centre for Networking and Supercomputing, WCSS, Wrocław, Po-
land, (http://www.wcss.wroc.pl). Mateusz Penkala is grateful for
a scholarship from the UPGOW project, co-financed by the Euro-
pean Social Fund.
Scheme 1. Isomerization of 4-allyloxybutan-1-ol catalyzed by [RuH(CO)(6-OH-py-
2-COO)(PPh3)2] (1).
The quantum efficiencies, examined by a comparative method
with naphthalene in ethanol as a standard (UST = 0.21), are equal
to 0.084 for the hydride carbonyl complex (1) and 0.046 for com-
plex (2). The differences in the luminescent properties of the com-
plexes have been correlated with their electronic structures and
referred to participation of the carbonyl ligand orbitals involved
in MLCT transitions.
Appendix A. Supplementary data
CCDC 854426 and 892040 contain the supplementary crystallo-
graphic data for the complexes [RuH(CO)(6-OH-py-2-COO)
(PPh3)2] (1) and [Ru(3-OH-py-2-COO)2(PPh3)2] (2). These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Complex (1) can be described as a highly active and selective
catalyst for the double bond migration reaction of 4-allyloxyb-

30
J.G. Małecki et al. / Polyhedron 48 (2012) 21–30
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