Syntheses and crystal structures of ruthenium-salen complexes containing triphenylphosphine ligands

Article abstract of DOI:10.1515/znb-2011-0316

Treatment of [Ru(PPh₃)3Cl₂] with the Schiff base ligand H₂salen in THF at reflux afforded a neutral Ru ^IIIsalen complex [Ru^III(salen)(PPh₃)Cl] (1). Interaction of [RuHCl(CO)(PPh₃

Full text of DOI:10.1515/znb-2011-0316

324
Note
anistic investigations of proton-coupled multielectron
transfer reactions [11, 12]. To design rationally trans-
formations catalyzed by ruthenium-salen complexes,
the knowledge of their redox and structural proper-
ties is desirable [13]. A few ruthenium-salen com-
plexes containing carbene, nitride, nitrosyl, oxo, hy-
drate, carbonyl, and halide groups, which show cat-
alytic activity and wherein the ruthenium oxidation
states vary from +2 to +6, have been investigated
in recent years [14–18]. However, ruthenium-salen
complexes with triphenylphosphine ligands have been
less explored [18, 19]. We were therefore interested
in the reactions of salen derivatives with the typical
ruthenium(II) center starting from [Ru(PPh3)3Cl2] and
[RuHCl(CO)(PPh3)3], which resulted in the isolation
of ruthenium(III) and ruthenium(II)-salen complexes
stabilized by triphenylphosphine ligands. The initial
results including the structural characterization and
electrochemical properties of such ruthenium-salen
complexes are presented in this paper.
Syntheses and Crystal Structures
of Ruthenium-Salen Complexes
Containing Triphenylphosphine
Ligands
Yan Lia,b, Qing Maa,b, Hua-Tian Shib, Qun Chena,
and Qian-Feng Zhanga,b
a School of Chemistry and Chemical Engineering,
Changzhou University, Jiangsu 213164, P. R. China
b Institute of Molecular Engineering and Applied Chemistry,
Anhui University of Technology, Ma’anshan,
Anhui 243002, P. R. China
Reprint requests to Dr. Qian-Feng Zhang.
Fax: +86-555-2312041.
E-mail: zhangqf@ahut.edu.cn
Z. Naturforsch. 2011, 66b, 324 – 328;
received October 27, 2010
Treatment of [Ru(PPh3)3Cl2] with the Schiff base lig-
and H2salen in THF at reflux afforded a neutral RuIII
-
salen complex [RuIII(salen)(PPh3)Cl] (1). Interaction of
[RuHCl(CO)(PPh3)3] with H2salen under similar con-
ditions gave a neutral RuII-salen complex [RuII(salen-
NH)(PPh3)(CO)] (2). In its formation one of the imine
bonds was nucleophilically attacked by hydride to give a
mixed imine-amine ligand. The two complexes have been
spectroscopically characterized, and the crystal structures of
Experimental Section
General
All synthetic manipulations were carried out under dry ni-
trogen by standard Schlenk techniques. [Ru(PPh3)3Cl2] [20]
1 · 2CH2Cl2 and 2 · CH2Cl2 have been established by X-ray and [RuHCl(CO)(PPh3)3] [21] were prepared according
crystallography.
to the literature methods. The Schiff base ligand H2salen
(salen = NNꢀ-bis(salicylidene)-o-phenylenediamine dianion)
was synthesized by condensation of salicylaldehyde with o-
phenylenediamine in refluxing ethanol [22]. RuCl3 · 3H2O
was used as purchased from Pressure Chemical Co. Ltd.
NMR spectra were recorded on a Bruker ALX 300 spectrom-
eter operating at 300 and 121.5 MHz for 1H and 31P, respec-
tively. Chemical shifts (δ, ppm) were reported with refer-
ence to SiMe4 (1H) and H3PO4 (31P). Infrared spectra (KBr)
were recorded on a Perkin-Elmer 16 PC FT-IR spectropho-
tometer with use of pressed KBr pellets, and positive FAB
mass spectra were recorded on a Finnigan TSQ 7000 spec-
trometer. The magnetic moment of the solid sample was mea-
sured by a Sherwood magnetic susceptibility balance at room
temperature. Cyclic voltammetry was performed on a CHI
660 electrochemical analyzer. A standard three-electrode cell
was used with a glassy carbon working electrode, a platinum
counter electrode and an Ag/AgCl reference electrode un-
Key words: Ruthenium, Schiff Base Ligand, Salen,
Synthesis, Crystal Structure
Introduction
Ruthenium complexes are currently investigated
because of their interesting structural, electrochem-
ical, catalytic, and biological properties [1–5] in-
cluding research of ruthenium complexes contain-
ing diimino tetradentate Schiff bases, such as salen
and salophen ligands [6, 7]. It has been noted that
manganese-salen complexes can be widely used as cat-
alysts for alkene epoxidation [8]. Recently, a num-
ber of ruthenium-salen complexes have also been
found to be active catalysts in various chemical trans-
formations [9, 10]. In particular, ruthenium macro-
cyclic complexes which are stable towards demeta-
lation have been found to show a reversible electro-
◦
der nitrogen atmosphere at 25 C. Formal potentials (Eo)
were measured in CH2Cl2 solutions with 0.1 M [nBu4N]PF6
as supporting electrolyte and reported with reference to the
ferrocenium-ferrocene couple (Cp2Fe+/0). In the −1.2 to
chemistry and provide good model systems for mech- +1.2 V region, a potential scan rate of 50 mV s−1 was used.
c
0932–0776 / 11 / 0300–0324 $ 06.00 ꢀ 2011 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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Note
325
Table 1. Crystallographic data and experimental details for
[RuIII(salen)(PPh3)Cl] · 2CH2Cl2 (1 · 2CH2Cl2) and [RuII-
(salen-NH)(PPh3)(CO)] · CH2Cl2 (2 · CH2Cl2).
The solvent was evaporated in vacuo, and the residue was
washed with diethyl ether and hexane. Recrystallization
from CH2Cl2/hexane afforded yellow crystals of 2 · CH2Cl2
within three days. Yield: 250 mg, 45 % (based on Ru). –
1H NMR (300 MHz, CDCl3): δ = 4.06 (d, J = 2.6 Hz, 2H,
CH2), 432 (br, 1H, NH), 531 (s, 2H, CH2Cl2), 7.11 – 7.93 (m,
27H, Ph), 882 (s, 1H, HC=N) ppm. – 31P NMR (300 MHz,
CDCl3): δ = −3.46 ppm. – IR (KBr disc, cm−1): ν(N-H)
3251 (w), ν(C≡O) 1947 (vs), ν(C=N) 1594 (s). – MS (FAB):
m/z = 707 [M]+, 679 [M-CO]+, 445 [M-PPh3]+. – Anal.
for C39H31N2O3PRu · (CH2Cl2): calcd. C 60.61, H 4.20,
N 3.53; found C 60.23, H 4.11, N 3.49.
Compound
1 · 2CH2Cl2
2 · CH2Cl2
Empirical formula
Formula weight
Crystal system
Space group
C40H33N2O2Cl5PRu C40H33N2O3Cl2PRu
882.97
monoclinic
P21/n
13.1127(3)
18.3256(4)
16.9880(4)
90
105.247(1)
90
3938.50(16)
4
792.62
triclinic
¯
P1
˚
a, A
9.2591(2)
12.2474(3)
17.3529(4)
69.718(1)
79.291(1)
74.753(1)
1771.07(7)
2
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
3
˚
V, A
X-Ray crystallography
Z
Dcalc, g cm−3
Temperature K
F(000), e
1.49
296(2)
1788
1.49
296(2)
808
Crystallographic data and experimental details for
[RuIII(salen)(PPh3)Cl] · 2CH2Cl2 (1 · 2CH2Cl2) and [RuII-
(salen-NH)(PPh3)(CO)]· CH2Cl2 (2 · CH2Cl2) are summa-
rized in Table 1. Intensity data were collected on a
Bruker SMART APEX 2000 CCD diffractometer using
µ(MoKα ) mm−1
0.8
0.7
Total / indep. refl. / Rint 38059 / 9060 / 0.022 32997 / 8111 / 0.026
Ref. parameters
460
441
R1a / wR2b [I ≥ 2σ(I)] 0.0343 / 0.0854
0.0359 / 0.0925
0.0421 / 0.0964
1.04
+1.00 / −0.94
˚
graphite-monochromatized MoKα radiation (λ = 0.71073 A)
R1a / wR2b (all data)
0.0466 / 0.0951
at 293(2) K. The collected frames were processed with the
software SAINT [23]. The data were corrected for absorption
using the program SADABS [24]. The structures were solved
by Direct Methods and refined by full-matrix least-squares
on F2 using the SHELXTL software package [25, 26]. All
non-hydrogen atoms were refined anisotropically. The po-
sitions of all hydrogen atoms were generated geometrically
Goodness of fit (GoF)c 1.03
∆ρfin (max / min), +0.64 / −0.61
−3
˚
e A
R1 = ΣꢁFo| − |Fcꢁ/Σ|Fo|; wR2 = [Σw(Fo − Fc2)2
/
a
b
2
Σw(Fo ) ]
2 2 1/2, w = [σ2(Fo2) + (AP)2 + BP]−1, where P =
2
2
2
(Max(Fo ,0)+2Fc )/3; c GoF = [Σw(Fo −Fc2)2 / (nobs
−
n
param)]1/2
.
˚
(Csp3 -H = 0.97, Csp2 -H = 0.93 and N-H = 0.86 A), assigned
isotropic displacement parameters, and allowed to ride on
their respective parent carbon or nitrogen atoms before the
final cycle of least-squares refinement.
Elemental analyses were carried out using a Perkin-Elmer
2400 CHN analyzer.
CCDC 795838 and 795839 contain the supplementary
crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data request/cif.
III
Synthesis of [Ru (salen)(PPh )Cl] · 2CH Cl
3
2
2
(1 · 2CH Cl )
2
2
A
mixture of H2salen (85 mg, 0.75 mmol) and
[Ru(PPh3)3Cl2] (671 mg, 0.70 mmol) in THF (40 mL) was
refluxed with stirring for 4 h, during which time there was a
color change from reddish brown to green. The solvent was
evaporated in vacuo, and the residue was washed with diethyl
ether and hexane. Recrystallization from CH2Cl2/hexane
afforded green crystals of 1 · 2CH2Cl2 within five days.
Yield: 413 mg, 67 % (based on Ru). – IR (KBr disc,
cm−1): ν (C=N) 1591 (s). – MS (FAB): m/z = 711 [M]+,
676 [M-Cl]+, 449 [M-PPh3]+. – µeff = 1.94 µB. – Anal.
for C38H27N2O2ClPRu· 2CH2Cl2: calcd. C 54.41, H 3.77,
N 3.17; found C 54.12, H 3.70, N 3.13.
Results and Discussion
Treatment of [Ru(PPh3)3Cl2] with the Schiff base
ligand H2salen in THF at reflux afforded a neutral
RuIII-salen complex [RuIII(salen)(PPh3)Cl] (1) as a
green crystalline solid, while interaction of [RuHCl-
(CO)(PPh3)3] with H2salen under similar conditions
gave a neutral RuII-salen complex [RuII(salen-NH)-
(PPh3)(CO)] (2) as a yellow crystalline solid, as illus-
trated in Scheme 1. The former was formed by dis-
placement of one chloride and two PPh3 ligands in
the ruthenium starting material with ruthenium(II) be-
ing oxidized to ruthenium(III), and the deprotonated
salen2− group coordinated to the [RuCl(PPh3)]2+
species. The latter was similarly formed from the [Ru-
II
Synthesis of [Ru (salen-NH)(PPh )(CO)] · CH Cl
3
2
2
(2 · CH Cl )
2
2
A
mixture of H2salen (85 mg, 0.75 mmol) and
[RuHCl(CO)(PPh3)3] (666 mg, 0.70 mmol) in THF (40 mL)
was refluxed with stirring for 6 h, during which time
there was a color change from reddish grey to yellow. (CO)(PPh3)]2+ species coordinating with the deproto-
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326
Note
˚
Table 2. Selected bond lengths (A) and angles (deg) for
1 · 2CH2Cl2.
Ru(1)–N(1)
Ru(1)–O(1)
Ru(1)–P(1)
1.9990(19)
2.0069(17)
2.3440(6)
Ru(1)–N(2)
Ru(1)–O(2)
Ru(1)–Cl(1)
2.0082(19)
2.0055(16)
2.4460(6)
N(1)–Ru(1)–N(2)
N(1)–Ru(1)–O(1)
O(1)–Ru(1)–N(2) 173.79(7)
O(1)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
81.80(8)
92.04(8)
O(1)–Ru(1)–O(2)
N(1)–Ru(1)–O(2) 170.68(8)
O(2)–Ru(1)–N(2)
O(2)–Ru(1)–P(1)
N(2)–Ru(1)–P(1)
93.89(7)
92.32(7)
90.22(5)
91.99(6)
88.01(5)
97.16(6)
N(1)–Ru(1)–Cl(1) 86.97(6)
O(1)–Ru(1)–Cl(1) 89.17(5)
P(1)–Ru(1)–Cl(1) 175.08(2)
N(2)–Ru(1)–Cl(1) 91.25(6)
O(2)–Ru(1)–Cl(1) 85.94(5)
Scheme 1.
CO]+ and [M–PPh3]+ with the characteristic isotopic
distribution patterns.
The crystal structures of 1 · 2CH2Cl2 and 2 · CH2Cl2
have been determined by X-ray crystallography. The
molecular structure of [RuIII(salen)(PPh3)Cl] (1) is
shown in Fig. 1, and selected bond lengths and bond
angles are given in Table 2. The geometry around
the ruthenium atom is pseudo-octahedral with chlo-
ride and PPh3 ligands in a mutually trans orien-
tation, as indicated by the P(1)–Ru(1)–Cl(1) bond
angle of 175.08(2)◦. As expected, the N2O2 entity
of the coordinated Schiff base lies in the equato-
rial plane. The Ru–O bond lengths of Ru(1)–O(1) =
˚
˚
2.0069(17) A and Ru(1)–O(2) = 2.0055(16) A, and the
˚
Ru–N bond lengths of Ru(1)–N(1) = 1.9990(19) A and
Ru(1)–N(2) = 2.0082(19) A found for complex 1 are
within the ranges found in other related Ru(III) com-
plexes [14–19]. The Ru–Cl bond length of 2.4460(6) A
and the Ru–P bond length of 2.3440(6) A are
˚
Fig. 1. Molecular structure of [RuIII(salen)(PPh3)Cl] (1), in
the crystal.
˚
nated (salen-NH)2− group in which one of the imine
bonds was nucleophilically attacked by hydride to re-
sult in the formation of a mixed imine-amine ligand.
The IR spectra of 1 and 2 clearly show strong bands
at 1591 and 1594 cm−1, respectively, which may be
attributed to theν(C=N) absorptions. The weak band
at 3251 cm−1 in the IR spectrum of 2 may be ten-
˚
consistent with reported values [18, 19]. The bond
angles of 170.68(8) and 173.79(7)◦ observed for
N(1)–Ru(1)–O(2) and N(2)–Ru(1)–O(1), respectively,
indicate a distortion from the ideal octahedral
geometry.
Fig. 2 shows the molecular structure of [RuII(salen-
tatively assigned to theν(NH) absorption. The C≡O NH)(PPh3)(CO)] (2), and selected bond lengths and
stretching vibration mode was found at 1947 cm−1 in bond angles are listed in Table 3. The molecule of 2
the IR spectrum of 2. The effective magnetic moment also adopts an approximately octahedral coordination
µ
eff of 1.94 µB at r. t. is consistent with a ruthenium(III) around the ruthenium center as in 1, but the positions
formulation for 1 [18]. In the 1H NMR spectrum of 2, trans to the carbonyl and PPh3 groups are occupied
two 1H signals at δ = 4.32 and 8.82 ppm are assigned by one hydroxyl and one imine moiety, respec-
to the protons of the amine NH and imine HC=N moi- tively, indicated by the O(3)–Ru(1)–C(1) bond angle
eties, respectively. The 31P{ H} NMR spectrum of 2 of 176.51(9)◦ and the N(2)–Ru(1)–P(1) bond angle
1
shows a singlet at δ = −3.46 ppm, which is down- of 178.42(6)◦, with the carbonyl and the phosphine
field from that of the free PPh3 ligand. The positive units cis to each other [C(1)–Ru(1)–P(1) = 89.00(8)◦].
ion FAB mass spectra of 1 and 2 display the peaks cor- Obviously, the main change in the structure of the
responding to the molecular ions [M]+, [M–Cl]+/[M– salen unit comes from the coexistence of aminic and
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327
˚
˚
Table 3. Selected bond lengths (A) and angles (deg) for
length (1.833(3) A) in 2 is in good agreement with
that in [Ru(3,5-t-Bu2salen)(CO)2] · 3MeOH [3,5-t-
Bu2salen = NNꢀ(di-3,5-di-t-butyl-2-oxybenzylidene)-
2 · CH2Cl2.
Ru(1)–N(1)
Ru(1)–C(1)
Ru(1)–O(3)
C(1)–O(1)
2.120(2)
1.833(3)
2.0892(18)
1.151(3)
Ru(1)–N(2)
Ru(1)–O(2)
Ru(1)–P(1)
2.068(2)
2.0552(17)
2.3447(6)
˚
cyclohexane-1,2-diamine] (av. 1.874(2) A), [Ru(3-t-
Bu-salen)(CO)2] [3-t-Bu-salen = NNꢀ(di-3-t-butyl-
2-oxybenzylidene)cyclohexane-1,2-diamine]
1.881(3) A) [28], and [Ru(2-Br-salen)(CO)(MeIm)]
(av.
N(1)–Ru(1)–N(2)
O(3)–Ru(1)–N(1)
O(3)–Ru(1)–N(2)
C(1)–Ru(1)–N(2)
C(1)–Ru(1)–O(3) 176.51(9)
C(1)–Ru(1)–P(1) 89.00(8)
N(2)–Ru(1)–P(1) 178.42(6)
N(1)–Ru(1)–P(1) 98.25(6)
80.17(8)
88.72(8)
85.49(7)
91.02(9)
O(2)–Ru(1)–N(1) 169.26(7)
˚
O(2)–Ru(1)–N(2)
C(1)–Ru(1)–N(1)
C(1)–Ru(1)–O(2)
O(2)–Ru(1)–O(3)
O(2)–Ru(1)–P(1)
O(3)–Ru(1)–P(1)
92.39(7)
90.58(10)
97.33(9)
82.94(7)
89.17(5)
94.49(5)
˚
(MeIm = N-methylimidazole) (1.846(13) A) [14],
but slightly shorter than that in cis-,cis[Ru{η2-
˚
N(O)C10H6)}2(CO)(PPh3)] (1.919(4) A) [29].
The cyclic voltammogram of 1 shows three re-
versible oxidation couples at E1/2 = 0.82, 0.58 and
−0.87 V, which are assigned to the metal-centered
RuIII-RuII couple, the ligand-centered oxidation, and
the metal-centered oxidation of RuIV-RuIII, respec-
tively. The RuIII-RuII potential for complex 2 (E1/2
=
0.94 V) is considerably larger than that for complex 1
(E1/2 = 0.82 V), indicative of the carbonyl stabiliza-
tion of the complex. It is also noted that the cyclic
voltammogram of 1 reveals two reversible couples
at 0.94 and 0.61 V assigned to the RuIII-RuII couple
and ligand-centered oxidation, respectively. Similar to
complex [Ru(salen)(NO)Cl] [13], the irreversible wave
at −0.91 V in complex 1 is assigned to the metal-
centered reduction of ruthenium(II).
In summary, the ruthenium(III)-salen complex
[RuIII(salen)(PPh3)Cl] (1) and the ruthenium(II)-salen
complex [RuII(salen-NH)(PPh3)(CO)] (2) with tri-
phenylphosphine ligands were synthesized and struc-
turally characterized along with spectroscopic and
electrochemical analyses. Formation of 1 involved the
oxidation of ruthenium(II) to ruthenium(III), and for-
mation of 2 involved the generation of a mixed imine-
amine ligand salen-NH, which is due to one of the
imine bonds being nucleophilically attacked by hy-
dride. It is interesting to note that the mixed imine-
amine ligand is twisted from the regular butterfly con-
formation of the salen ligand to a V-shaped conforma-
tion, which results in the carbonyl and the phosphine
ligands being cis to each other so as to avoid the ster-
ical crowding around the octahedral ruthenium center
in 2. The catalytic properties of these rutheniumsalen
complexes will be further investigated in our labora-
tory.
Fig. 2. Molecular structure of [RuII(salen-NH)(PPh3)(CO)]
(2), in the crystal.
iminic bonds. The torsion angle for the iminic bond
C(51)–N(2)–C(3)–C(46) is 177.7◦, while that for
the amine bond C(56)–N(1)–C(2)–C(66) is 58.1◦.
The mixed imine-amine ligand is twisted from the
regular butterfly conformation of the salen ligand to a
V-shaped conformation. The only similar example for
the salophen ligand is a dimeric aluminum-salophen
complex [27]. The hydrogen atoms on the newly
formed sp3 atoms [N(1) and C(2)] have enough space
in 2 and do not affect the relative orientation of phenyl
groups. The sterical crowding around the new sp3
atoms is relaxed by the V shape of the ligand so
that abnormal torsion angles around N(1) and C(2)
Acknowledgement
˚
are avoided. The Ru–P bond length of 2.3447(6) A
This project was supported by the Natural Science Foun-
dation of China (20771003) and the Program for New Cen-
tury Excellent Talents in University of China (NCET-06-
is comparable to that in other ruthenium phosphine
complexes such as [Ru(2-Br-salen)2(PPh3)2] [av.
˚
˚
2.403(2) A] [14] and 1 [2.3440(6) A]. The Ru–C bond 0556).
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