Dichloro(diphosphine)(2-pyridyl-ketone)ruthenium(II) complexes

Article abstract of DOI:10.1139/v03-109

Described are the synthesis and characterization of Ru(II) complexes of the type RuCl₂L₂(N-O), where L₂ is either 1,4-bis(diphenylphosphino)butane (dppb) or (PPh₃)₂, and N-O represents chelated 2-benz

Full text of DOI:10.1139/v03-109

1263
Dichloro(diphosphine)(2-pyridyl-
ketone)ruthenium(II) complexes1
Salete L. Queiroz, Alzir A. Batista, Marcio P. de Araujo, Roberto C. Bianchini,
Glaucius Oliva, Javier Ellena, and Brian R. James
Abstract: Described are the synthesis and characterization of Ru(II) complexes of the type RuCl2L2(N-O), where L2 is
either 1,4-bis(diphenylphosphino)butane (dppb) or (PPh3)2, and N-O represents chelated 2-benzoylpyridine (2-bzpy) or
2-acetylpyridine (2-acpy); the Ru presursors used were [RuCl2(dppb)]2(µ-dppb) or RuCl2(PPh3)3. The crystal structure
of cis-RuCl2(dppb)(2-bzpy) is presented, and three other RuCl2L2(N-O) complexes with cis-chlorines are isolated and
characterized spectroscopically; of the trans-dichloro species, RuCl2(PPh3)2(N-O) complexes are isolated, while the cor-
responding dppb species are characterized in situ. In all cases, thermodynamically stable cis-complexes are formed
from initially formed trans-species.
Key words: ruthenium, phosphines, 2-benzoylpyridine, 2-acetylpyridine, X-ray structures.
Résumé : On décrit la synthèse et la caractérisation de complexes du Ru(II) du type RuCl2L2(N-O) dans lesquels L2 =
1,4-bis(diphénylphosphino)butane (dppb) ou (PPh3)2 et N-O = 2-benzoylpyridine (2-bzpy) ou 2-acétylpyridine (2-acpy)
chélatées; les complexes de Ru utilisés sont le [RuCl2(dppb)]2(µ-dppb) ou RuCl2(PPh3)3. On a déterminé la structure
cristalline du cis-RuCl2(dppb)(2-bzpy) et on a isolé trois autres complexes du RuCl2L2(N-O) portant des atomes de
chlore en cis et on les a caractérisés de façon spectroscopique; des espèces trans-dichlorées, les complexes
RuCl2(PPh3)2(N-O) ont été isolés alors que les espèces correspondantes du dppb ont été caractérisées in situ. Dans tous
les cas, les complexes cis thermodynamiquement stables se forment à partir des espèces trans obtenues initialement.
Mots clés : ruthénium, phosphines, 2-benzoylpyridine, 2-acétylpyridine, structures par diffraction des rayons X.
[Traduit par la Rédaction] Queiroz et al. 1269
Introduction
synthesis using 2-acetylpyridine (2) was repeated (1), and
the product was identified as RuCl2(PPh3)2(C5H4N-COMe)
containing an η2-N,O-bonded pyridylketone; the complex
was identified by C, H, N, and Cl analysis, molecular
Some 25 years ago, one of our groups published a paper
(1) that questioned a reported synthesis of [RuCl2(PPh3)2]2
from RuCl2(PPh3)3 using catalytic amounts of the 2-pyridyl-
ketones, C5H4N-COR (R = H, Me, Ph) (2). The reported
1
weight, H and 31P NMR, and IR data in the ν(CO) and
ν(Ru-Cl) regions: the 31P{1H} NMR AB pattern required the
complex to have cis-phosphines, while trans-chlorines were
“favoured slightly” based on the dominance of a single
325 cm–1 band in the 400–250 cm–1 IR region (1). An X-ray
analysis of the supposed [RuCl2(PPh3)2]2 complex was re-
ported “to be underway” (2); no X-ray structure was ever
published, but the authors of ref. 2 did agree that their prod-
uct was certainly not [RuCl2(PPh3)2]2.4
Received 20 March 2003. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 30 September 2003.
Dedicated to John Harrod, a close friend and colleague of
one of us (BRJ) for 43 years; John physically handed me my
first sample of RuCl3·3H2O in Jack Halpern’s laboratory at
UBC in 1960.
S.L. Queiroz.2 Instituto de Química de São Carlos,
Universidade de São Paulo, CP 780, 13560–970, São Carlos,
SP, Brazil.
A.A. Batista and M.P. de Araujo. Departamento de
Química, Universidade Federal de São Carlos, CP 676,
13565–905, São Carlos, SP, Brazil.
This present paper reports on the synthesis and structural
characterization of the complex, cis-RuCl2(dppb)(2-benzoyl-
pyridine), where dppb = 1,4-bis(diphenylphosphino)butane;
data on the corresponding trans-isomer, and on the analo-
gous 2-acetylpyridine species, are presented also. The
bis(triphenylphosphine) complexes containing these 2-
pyridylketones are also described. It should be noted that 2-
benzoylpyridine (2-bzpy) is also called 2-pyridylphenyl-
ketone (3); we use the former-type nomenclature throughout
this paper.
2-Pyridylketone complexes of transition metals have been
known since the 1960s, particularly the 2-bzpy ligand sys-
tems (4). More recent interest in such ligands has generally
focussed on bioinorganic model systems or their hemi-labile
character for use in catalysis. Structural work describing
bidentate, N,O-bonded 2-bzpy includes that on mono- and
R.C. Bianchini, G. Oliva, and J. Ellena. Instituto de Fisica
e Química de São Carlos, Universidade de São Paulo, Av.
Dr. Carlos Botelho, 1465, CP 13560–970, São Carlos, SP,
Brazil.
B.R. James.3 Chemistry Department, University of British
Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
1This article is part of a Special Issue dedicated to Professor
John Harrod.
2Corresponding author (e-mail: salete@iqsc.usp.br).
3Corresponding author (e-mail: brj@chem.ubc.ca).
4K. Vrieze. Personal communication to BRJ, 1979.
Can. J. Chem. 81: 1263–1269 (2003)
doi: 10.1139/V03-109
© 2003 NRC Canada

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Can. J. Chem. Vol. 81, 2003
bis-(2-bzpy) complexes of Zn(II) in relation to models for
alcohol-dehydrogenases (3), and that on Cu(I) complexes
(5), while the first structural work involving Ru species was
that describing an η2-N,O-bonded 2-pyridylketone moiety of
an ONNS-bonded thiosemicarbazone of 2,6-diacetylpyridine
bonded to Ru(II) (6). Very recent reports on Ru complexes
have described the structures of [Ru(PMe3)2(CO)(COMe)(2-
bzpy)]BPh4 (7), [Ru(2,2′-bipyridine)2(2-bzpy)][PF6]2 (8),
and RuCl2(DMSO)2(2-acpy), where 2-acpy is 2-acetyl-
pyridine (9). Complexes such as [Ru(NH3)4(N-O)][BF4]2,
where N-O = 2-bzpy or 2-acpy, have been isolated and char-
acterized spectroscopically (10). Structurally characterized
complexes of other platinum metals containing 2-
pyridylketones have been reported, for example, [Pd(η1,η2-
C8H12OMe)(2-bzpy)]BF4 (11), and several cationic chloror-
hodium(III) complexes containing 2-bzpy (4).
More generally, our earlier collaborative studies have de-
veloped methods for synthesizing cis- and trans-
RuCl2(dppb)L2 and the corresponding bis(triphenylphos-
phine) complexes, where L = a N-donor or L2 = a bidentate,
N,N-donor, with a basic interest in their potential as hydro-
genation catalysts (12, 13), and so extension to N,O-donor
systems allows us also to obtain a broader data base for such
complexes, as well as to comment more definitively on the
nature of the RuCl2(PPh3)2(2-acetylpyridine) species isolated
in 1978 (1).
cis-RuCl2(dppb)(2-bzpy) (cis-1)
cis-1 was prepared by stirring [RuCl2(dppb)]2(µ-dppb)
(97 mg, 0.06 mmol) and 2-bzpy (60 mg, 0.32 mmol) in C6H6
(8 mL) at r.t. for 2 h. The resulting blue solution was re-
duced in volume to ~1 mL, when Et2O was added to precipi-
tate a blue solid that was collected, washed with hexanes and
Et2O, and dried under vacuum. Yield: 70%. UV–vis: 300
(9685), 620 (3370), 720 sh (2010). Anal. calcd. for
C40H37NOP2Cl2Ru: C 62.47, H 4.87, N 1.83; found: C 62.8,
H 5.1, N, 1.5. Crystals suitable for X-ray analysis were
grown by evaporation of a CH2Cl2–Et2O–MeOH solution of
the complex. trans-1 was generated in situ in a NMR tube in
C6D6 from a rapid reaction of [RuCl2(dppb)]2(µ-dppb) with
excess 2-bzpy (see Results and discussion).
cis-RuCl2(dppb)(2-acpy) (cis-2)
cis-2 was made by refluxing [RuCl2(dppb)]2(µ-dppb)
(97 mg, 0.06 mmol) and 2-acpy (0.1 mL, 0.89 mmol) in
C6H6 (8 mL) for 48 h. The resulting purple precipitate was
collected, washed with Et2O, and dried under vacuum.
Yield: 75%. UV–vis: 340 sh (2780), 557 (3175), 655 sh
(1690). Anal. calcd. for C35H35NOP2Cl2Ru: C 58.41, H 4.91,
N 1.95; found: C 57.9, H 4.9, N, 1.8. trans-2 was generated
in situ as described for trans-1, but using excess 2-acpy (see
Results and discussion).
Experimental
trans-RuCl2(PPh3)2(2-acpy) (trans-3)
trans-3 was prepared by dissolving RuCl2(PPh3)3
(100 mg, 0.10 mmol) and 2-acpy (0.014 mL, 0.12 mmol) in
CH2Cl2 (5 mL) at r.t. The solution immediately changed
from brown to blue, when the volume was rapidly reduced
to ~1 mL; hexanes was then added to precipitate a blue solid
that was collected, washed with hexanes, and dried under
vacuum. Yield: 68%. UV–vis: 376 (1705), 604 (1970). Anal.
calcd. for C43H37NOP2Cl2Ru: C 63.16, H 4.56, N 1.71;
found: C 62.4, H 5.0, N 1.3.
General
Synthetic procedures were performed using standard
Schlenk techniques under dry Ar because solutions of the
precursor complexes [RuCl2(dppb)]2(µ-dppb) (14, 15) and
RuCl2(PPh3)3 (16) are air-sensitive. Common chemicals used
were of reagent grade quality (Aldrich). Tetrabutylammon-
ium perchlorate (TBAP) from Fluka was recrystallized from
EtOH–H2O, and dried under vacuum at 80 °C (caution!).
Reagent grade solvents (Merck) were appropriately distilled,
dried, and stored over Linde 4 Å molecular sieves.
IR spectra (in cm–1) were recorded as CsI pellets on a
Bomen–Michelson 102 instrument, and UV–vis spectra in
CH2Cl2, given as λmax or sh = shoulder in nm (ε, in M–1 cm–1),
on an HP 8452A spectrophotometer. NMR spectra were re-
corded on a Bruker 400 MHz spectrometer (400 MHz for
1H, 100.6 MHz for 13C, 162 MHz for 31P) at room tempera-
cis-RuCl2(PPh3)2(2-acpy) (cis-3)
cis-3 was prepared by stirring RuCl2(PPh3)3 (50 mg,
0.05 mmol) and 2-acpy (0.014 mL, 0.12 mmol) in CH2Cl2
(5 mL) for 12 h at r.t. The volume of the resulting purple so-
lution was reduced to ~1 mL and hexanes was added to pre-
cipitate a purple solid that was collected, washed with Et2O,
and dried under vacuum. Yield: 70%. UV–vis: 346 sh
(4900), 554 (5200), 680 sh (2250). Anal. calcd. for
C43H37NOP2Cl2Ru: C 63.16, H 4.56, N 1.71; found: C 62.8,
H 4.7, N 1.8.
o
ture (r.t., ~20 C) in CH2Cl2 or CD2Cl2. Residual solvent
proton, solvent carbon, or external P(OMe)3 (31P, δ 141.00
relative to 85% aq. H3PO4) were used as references. Cyclic
and differential pulse voltammetries were carried out at r.t.
in freshly distilled CH2Cl2 containing 0.1 M TBAP, using a
PAR model 273A potentiostat/galvanostat with an
EG&G/PARC model 175 universal programmer as a sweep
generator. A three-electrode system with resistance compen-
sation was used throughout, the working and auxiliary elec-
trodes being a stationary Pt foil and a Pt wire, respectively.
The reference electrode was Ag/AgCl in a Luggin capillary
in the CH2Cl2 medium, in which ferrocene is oxidized at
0.43 V (Fc+/Fc); all potentials are reported with respect to
the Ag/AgCl electrode. Elemental analyses were performed
at the Institute of Chemistry of the University of São Paulo.
trans-RuCl2(PPh3)2(2-bzpy) (trans-4)
trans-4 is formed immediately on mixing RuCl2(PPh3)3
(200 mg, 0.20 mmol) and 2-bzpy (57.2 mg, 0.31 mmol) in
CH2Cl2 (5 mL) at r.t. The volume of the blue solution was
reduced to ~1 mL, and Et2O was added to give a blue solid
that was collected, washed with Et2O, and dried under vac-
uum. Yield: 62%. UV–vis: 280 sh (2520), 670 (5025). Anal.
calcd. for C48H39NOP2Cl2Ru: C 65.53, H 4.47, N 1.59;
found: C 65.15, H 4.6, N 1.6.
© 2003 NRC Canada

Queiroz et al.
1265
Table 1. 31P{1H} NMR, electrochemical, and IR data for complexes 1–4.
Complex
δA and δX
2JAX (Hz)
E1/2 (V)
ν(CO), ν(Ru-Cl) (cm–1)
RuCl2(dppb)(2-bzpy) (trans-(1))
RuCl2(dppb)(2-bzpy) (cis-(1))
RuCl2(dppb)(2-acpy) (trans-(2))
RuCl2(dppb)(2-acpy) (cis-(2))
RuCl2(PPh3)2(2-acpy) (trans-(3))
RuCl2(PPh3)2(2-acpy) (cis-(3))
RuCl2(PPh3)2(2-bzpy) (trans-(4))
RuCl2(PPh3)2(2-bzpy) (cis-(4))
51.1, 43.3
44.7, 40.1
50.0, 43.0
46.3, 41.1
48.4, 39.5
45.5, 40.1
49.1, 39.1
43.8, 39.2
43.70
38.47
44.00
38.55
35.60
33.54
35.28
34.17
0.70
1591, 256 and 227
0.68
0.60
0.68
0.60
0.68
1580, 262 and 235
1617, 325
1575, 250 and 224
1588, 329
1589, 314 and 281
cis-RuCl2(PPh3)2(2-bzpy) (cis-4)
Results and discussion
The RuCl2(dppb)(2-bzpy) complex (1) is isolated from a
cis-4 was prepared as described for trans-4, but the reac-
tant solution was left for 6 h at r.t. Yield: 65%. UV–vis: 292
(10 900), 604 (4045), 720 sh (2350). Anal. calcd. for
C48H39NOP2Cl2Ru: C 65.53, H 4.47, N, 1.59; found: C 65.5,
H 4.6, N 1.7.
simple, h, r.t. reaction of excess 2-bzpy with
2
[RuCl2(dppb)]2(µ-dppb), as outlined in eq. [1]. The structure
of 1, presented as an ORTEP in Fig. 1 (23), reveals the
Ru(II) ion in a distorted octahedral environment, with cis-
chlorines, one trans to a P atom of chelated dppb, and one
trans to the O atom of chelated 2-bzpy, whose N atom is
trans to the second P atom. The asymmetric unit consists of
one molecule of cis-1 and a MeOH solvent. Throughout the
paper, the cis- and trans-nomenclature refers to the arrange-
ment of chlorine ligands.
The 31P{1H} NMR, IR, and electrochemical data for com-
plexes 1–4 are summarized in Table 1; H and 13C NMR
1
data spectra were measured, and the more significant find-
ings are presented in the Results and discussion text.
X-ray crystallography of cis-RuCl2(dppb)(2-bzpy)
(cis-1)
A prismatic crystal was used in the single-crystal, X-ray
diffraction experiment, measurements being made on an
Enraf-Nonius CAD-4 diffractometer with graphite
monochromated Mo Kα (λ = 0.71073 Å) radiation. Crystal
and structure refinement data for cis-1 are summarized in
Table 2.5 One standard reflection measured every 30 min
was used to apply a decay correction, the maximum decay
being 1%. The data collection and reduction were performed
with the programs CAD-4 (17) and XCAD-4 (18), respec-
tively.
[1]
The structure was solved by direct methods with
SHELXS-86 (19), and the model refined by full-matrix
least-squares on F2 by means of SHELXL-97 (20). After in-
clusion of the complete complex in the refinement, the dif-
ference Fourier map showed two peaks that were interpreted
as a MeOH solvent. All the H atoms were stereochemically
positioned and refined with the riding model (20), with the
C—H bond lengths in the aromatics rings, CH2 and CH3
groups, being set equal to 0.93, 0.97, and 0.96 Å, respec-
tively. Once the complete isotropic model was obtained, an
empirical absorption correction (21) was applied (minimum
and maximum transmission factors were 0.9039 and 0.8469,
respectively), after which all non-H atoms were refined
anisotropically. The H atoms of the aromatic rings and CH2
were set isotropic with a thermal parameter 20% greater
than the equivalent isotropic displacement parameter of the
C atom to which each one is bonded; this percentage was set
to 50% for the H atoms of the Me group. The atomic scatter-
ing factors were taken from ref. 22.
Relevant interatomic distances and angles are listed in
Table 3. The Ru—Cl (avg 2.427 Å), Ru—N (2.126 Å), and
Ru—P (avg 2.289 Å) bond lengths observed are within the
normal, well-established range for those in Ru(II) complexes
(12, 13, 24). The Ru—N bond is ~0.07 Å shorter than that in
[Ru(PMe3)2(CO)(COMe)(2-bzpy)]+ where the N atom is
trans to CO (7), but is ~0.08 Å longer than that in [Ru(2,2′-
bipyridine)2(2-bzpy)]2+ where the N atom is trans to a
bipyridine-N (8); the expected trans influence (8, 25) is evi-
dent. The Ru—O bond length of 2.035(3) Å is the shortest
found in the three Ru-(2-bzpy) complexes: trans to the
COMe group in the monocation, the Ru—O length is
2.226(4) Å (7), while trans to a bipyridyl-N the value is
2.058 Å (8). Ru—N and Ru—O bond distances in trans-
RuCl2(DMSO)2(2-acpy), where both N and O are trans to S-
bonded DMSO, are 2.122(3) and 2.084(3) Å, respectively
5 Supplementary data (full crystal data and details on data collection and refinement have been deposited along with tables of atomic coordi-
nates, anisotropic thermal parameters, all bond lengths and angles, and torsion angles) may be purchased from the Depository of Unpub-
lished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0S2, Canada
(http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC 208536 contains the supplementary data for
this paper. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge, U.K.; fax +44 1223 336033; or deposit @ccdc.cam.ac.uk).
© 2003 NRC Canada

1266
Can. J. Chem. Vol. 81, 2003
Table 2. Crystal data and structure refinement for RuCl2(dppb)(2-bzpy).
Empirical formula
C40H37Cl2NOP2Ru·CH3OH
Formula weight
Temperature (K)
Crystal system
813.66
293(2)
Triclinic
P1
Space group
Unit cell dimensions
a (Å)
b (Å)
10.917(2)
11.446(2)
15.667(3)
86.06(1)
74.41(1)
80.93(1)
1861.3(7)
2
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Z
Density (calculated) (Mg m–3)
Absorption coefficient (mm–1)
F(000)
1.452
0.687
836
Crystal size (mm3)
θ range for data collection (°)
Index ranges
0.25 × 0.19 × 0.15
1 ≤ θ ≤ 25
–12 ≤ h ≤ 12, –12 ≤ k ≤ 12, 0 ≤ l ≤ 17
1
Decay of standard
Reflections collected
Independent/observed reflections
Completeness to θ = 25° (%)
Data/parameters
6237
6237 (R(int) = 0.00)/4424 (I > 2σ(I))
95.4
6237/444
Goodness-of-fit on F2
SHELXL-97 weight parameters
Final R indices (I > 2σ(I))
R indices (all data)
Extinction coefficient
Largest diff. peak and holea (e Å–3)
1.041
0.0750, 0.0
R1 = 0.0453, wR2 = 0.1199
R1 = 0.0770, wR2 = 0.1317
0.0002(6)
0.915 and –1.040
aAt ~1 Å from the Ru atom.
(9). The Ru—O bond in cis-1 is also shorter than that found
for the acetylpyridine moiety of an ONNS-bonded
thiosemicarbazone at Ru(II) (2.232 Å) (6) and for the coor-
dinated acetone of RuCl2(CO)(PPh3)2(acetone), 2.194 Å
(26); the small value is readily rationalized in that in cis-1,
the coordinated ketone moiety is trans to chloride, a π-do-
nor, while in the other systems the ketone group is trans to
PPh3 (26) and an imine N atom (6), both π-acceptors. The
bite angle of the benzoylpyridine ligand in cis-1 (76.7(1)°) is
close to those found, for example, in the other Ru-(2-bzpy)
(7, 8) and Ru-(2-acpy) (9) complexes; the essential planarity
of the five-membered chelate ring, with an approximate 45°
twist of the benzoyl-phenyl from the planarity, is similar to
those noted for the other two 2-bzpy complexes (7, 8). The
structure of the “cis-RuCl2(dppb)” component of cis-1 is
very similar to that in cis-RuCl2(dppb)(N-N) complexes,
where N-N = 2,2′-bipyridine or 1,10-phenanthroline (12).
Table 1 lists some spectroscopic and electrochemical data
for cis-1 and the other 2-pyridylketone complexes studied in
this work. The solution NMR data imply the solid state
structure is maintained in solution: the 31P{1H} NMR AX
pattern does not itself distinguish between cis-1 and trans-1
(see below), but two strong ν(Ru-Cl) bands in the IR spec-
trum are consistent with cis-geometry. We have recently es-
tablished for Ru(II)-dppb species (with 18 data points) an
inverse dependence of the 31P shifts on Ru—P bond length
(12); the data for cis-1 fit well with this correlation and im-
ply that the δ values of 44.7 and 40.1 refer to P(1) and P(2),
respectively. 1H NMR data confirm the presence of one
bzpy ligand per dppb, while the coordination shift of the HN
atom adjacent to the N atom (δ 8.68 → 9.03) and that of
ν(C=O) (1668 → 1591 cm–1) again show both O- and N-co-
ordination of bzpy. The lower ν(C=O) value in the Ru(II)
species vs. values for the Zn(II) complexes (~1620 cm–1) (3)
is consistent with the presence of significant Ru → carbonyl
π-backbonding (27). A coordination shift of the 13C reso-
nance of the C=O group (δ 193.8 → 206.1) is also evident.
The blue colour of cis-1 is manifested in an absorption
maximum at 620 nm with a shoulder at 720 nm, while the
CV reveals a reversible redox process (ipa/ipc ≅ 1) with E1/2
=
0.70 V, the process being confirmed by differential pulse
voltammetry. The RuIII/RuII couple is ~10 mV more positive
that for the structurally similar cis-RuCl2(dppb)(bipy) (12),
showing relative stabilization of the lower valence state by
substitution of a 2-pyridyl by a benzoyl moiety.
Synthesis of the 2-acetylpyridine (2-acpy) analogue (cis-
2) is as for cis-1, but requires the use of reflux conditions.
The NMR and IR spectroscopic data and CV data (Table 1)
are very similar to those of cis-1, and the structure is as-
sumed to be the same (type II as in Fig. 1, see below and
© 2003 NRC Canada

Queiroz et al.
1267
Fig. 1. ORTEP view of cis-RuCl2(dppb)(2-bzpy) (1), showing the atom labeling, with 30% probability ellipsoids.
also rxn. [1]). The Me resonance of the coordinated acetyl
group is seen at δ 2.10 (upfield shifted from that of the free
ligand at δ 2.71), while there is again a downfield shift
(δ 8.68 → 8.85) for HN. In contrast with cis-1, cis-2 is purple
and the solution spectrum shows an absorption maximum at
557 nm.
trans-dichloro species of this type invariably has a lower re-
duction potential than that of a corresponding cis-formulation
(12, 28, 29). Of note, a solution of the blue trans-3
isomerizes over time to the purple cis-species, a process
that can be readily monitored by CV (30) (cf. Fig. 2, t1/2
~
1
30 min at r.t.), 31P or H NMR, or by UV–vis spectroscopy.
trans-3 shows UV–vis absorption maxima at 376 and
604 nm, while cis-3 has a maximum at 554 and a shoulder at
~680 nm.
As described in the Experimental section, two complexes
with the formulation RuCl2(PPh3)2(2-acpy) (3) were isolated
from the same reaction precursor RuCl2(PPh3)3 but using
different timescales. A blue solid is obtained after a few
minutes, while a 12 h reaction time generates a purple solid,
and the complexes have different spectroscopic properties.
Three structural formulations are possible for the
bis(triphenylphosphine) species: I (with trans chlorines), and
II and III (with cis chlorines). The more stable, purple com-
plex has 31P NMR, IR, and CV data (Table 1) close to those
found for cis-1 and cis-2, and is thus assigned the cis-
dichloro geometry II (cf. rxn. [1]). The 1H NMR data (as for
cis-2) show an upfield shift for the Me (δ 2.71 → 2.41) and a
downfield shift for HN (δ 8.68 → 9.51). The 31P NMR data
of a solution of the blue complex show about a 9 ppm differ-
ence between the δA and δX values vs. ~5 ppm for the cis-
complexes, and the ν(Ru-Cl) region shows a single, sharp
band at 325 cm–1, findings that imply that the blue species is
trans-3. Of note, the 1H NMR shift for the Me is now
slightly downfield (δ 2.71 → 2.79), while that for HN is now
slightly upfield (δ 8.68 → 8.60). These shifts are the reverse
of those seen for the cis-complexes, and presumably reflect
that the acetyl is now trans to the π-acceptor PPh3 (structure
I) vs. the π-donor chloride ligand (structure II). Further, the
E1/2 value of trans-3 is 8–10 mV lower than those of the cis-
species, again consistent with the trans formulation, as a
cis- and trans-RuCl2(PPh3)2(2-bzpy)2 (4) are made simi-
larly to the 2-acpy analogues (3), the initially formed kinetic
product being the blue, trans-isomer, this then transforming
to an isolable, purple cis-isomer (Table 1). Whether cis-4 has
geometry II or III is unclear; the 31P NMR data are close to
those of the other cis species (of structure II), but the ν(Ru-
Cl) IR data are significantly different and may indicate
structure III.
cis-RuCl2(dppb)2(2-bzpy) (cis-1) was isolated after a 2 h
reaction time at r.t. (see above), but initially when the reac-
tants are mixed, the trans-isomer is detected by in situ 31P
NMR (see Fig. 3 and Table 1). Corresponding behaviour is
seen for the isolated cis- and in situ formed trans-
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Can. J. Chem. Vol. 81, 2003
Table 3. Selected bond lengths (Å) and angles (°) for
Fig. 2. Differential pulse voltammogram of cis- and trans-
RuCl2(PPh3)2(2-acpy) (3).
RuCl2(dppb)(2-bzpy), esds in parentheses.
Bond lengths (Å)
Ru—O(1)
Ru—N(1)
Ru—P(1)
Ru—P(2)
Ru—Cl(2)
Ru—Cl(1)
O(1)—C(5)
2.035(3)
2.126(4)
2.286(1)
2.292(1)
2.397(1)
2.458(1)
1.251(5)
1.327(6)
1.370(6)
N(1)—C(23)
N(1)—C(21)
Bond angles (°)
O(1)-Ru-N(1)
O(1)-Ru-P(1)
N(1)-Ru-P(1)
O(1)-Ru-P(2)
N(1)-Ru-P(2)
P(1)-Ru-P(2)
O(1)-Ru-Cl(2)
N(1)-Ru-Cl(2)
P(1)-Ru-Cl(2)
P(2)-Ru-Cl(2)
O(1)-Ru-Cl(1)
N(1)-Ru-Cl(1)
P(1)-Ru-Cl(1)
P(2)-Ru-Cl(1)
Cl(2)-Ru-Cl(1)
76.7(1)
95.19(9) C(111)-P(1)-Ru
92.4(1) C(1)-P(1)-Ru
91.99(9) C(221)-P(2)-C(211) 100.7(2)
167.3(1)
94.47(5) C(211)-P(2)-C(4)
170.15(9) C(221)-P(2)-Ru
93.6(1)
86.66(5) C(4)-P(2)-Ru
97.52(5) C(5)-O(1)-Ru
87.15(9) C(23)-N(1)-C(21)
C(121)-P(1)-Ru
119.8(2)
110.4(2)
119.1(2)
C(221)-P(2)-C(4)
100.1(2)
102.7(2)
120.7(1)
110.3(1)
119.5(2)
119.0(3)
117.2(4)
128.5(4)
113.9(3)
117.6(4)
118.1(4)
122.1(5)
112.6(4)
121.8(6)
Fig. 3. 31P{1H} NMR in C6H6 of a mixture of cis- and trans-
RuCl2(dppb)(2-bzpy) (1): top, “immediately” after mixing
[RuCl2(dppb)]2(µ-dppb) and 2-benzoylpyridine; bottom, after
25 min when just cis-1 is seen.
C(211)-P(2)-Ru
82.4(1)
C(23)-N(1)-Ru
173.64(4) C(21)-N(1)-Ru
91.35(4) O(1)-C(5)-C(21)
90.04(5) O(1)-C(5)-C(11)
C(121)-P(1)-C(111) 102.5(2)
C(121)-P(1)-C(1)
C(111)-P(1)-C(1)
N(1)-C(21)-C(26)
N(1)-C(21)-C(5)
N(1)-C(23)-C(24)
102.6(2)
99.4(2)
1
31P{1H} NMR (δA 43.6, δX 38.8; J = 35 Hz) and H NMR
data (δMe 2.40; δH 9.54, H adjacent to N) in CDCl3, and the
purple colour (1), are all consistent with a cis-3 formulation
(see Table 1). The only contrary evidence is the reported
single ν(Ru-Cl) value of 325 cm–1 (1) that pertains to trans-
3. It is evident that the spontaneous trans/cis isomerization
process was not recognized in the early work, and the data
reported in this current paper, especially with the X-ray
analysis for cis-1, characterize more completely the nature
of these Ru(II) 2-pyridylketone complexes.
Acknowledgements
We thank Conselho Nacional de Desenvolvimento
científico e Tecnológico (CNPq), Coordenação de Aper-
feiçoamento de Pessoal de Nível Superior (CAPES),
Financiadora de Estudos e Projetos (FINEP), and Fundação
de Amparo à Pesquisa do Estado de Sào Paulo (FAPESP) in
Brazil, and the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support. JE thanks
FAPESP for a postdoctoral fellowship.
RuCl2(dppb)2(2-acpy) (2) species (Table 1). The trans → cis
isomerization process is faster for all the systems in the
presence of sunlight; details of possible isomerization mech-
anisms (31) for these chelated six-coordinate complexes re-
main to be elucidated.
Reevaluation of the 1978 data for the reported
RuCl2(PPh3)2(2-acpy) complex 3 in this current paper (see
Introduction) can now be made. The previously reported r.t.
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