Syntheses, structural determinations of [Ru(ROCS2) 2(PPh3)2]+/0 pairs, and kinetic analyses of thermal reactions involving transient trans-[Ru( iPrOCS2)2(PPh3)2] species (ROCS2- = ethyl- or isopropyldithiocarbonate and PPh3 = triphenylphosphine)

Article abstract of DOI:10.1021/ic051487l

Controlled-potential electrochemical oxidation of cis-[Ru(ROCS ₂)₂(PPh₃)₂] (R = Et, ⁱPr) yielded corresponding Ru(III) complexes, and the crystal structures of cis-[Ru(ROCS₂)₂(PPh₃)₂] and trans-[Ru(ROCS₂)₂(PPh₃)₂](PF ₆) were determined. Both pairs of complexes exhibited almost identical coordination structures. The Ru-P distances in trans-[Ru ^III(ROCS₂)₂(PPh₃) ₂](PF₆) [2.436(3)-2.443(3) A] were significantly longer than those in cis-[Ru^II(ROCS₂)₂- (PPh₃)₂] [2.306(1)-2.315(2) A]: the smaller ionic radius of Ru(III) than that of Ru(II) stabilizes the trans conformation for the Ru(III) complex due to the steric requirement of bulky phosphine ligands while mutual trans influence by the phosphine ligands induces significant elongation of the Ru^III-P bonds. Cyclic voltammograms of the cis-[Ru(ROCS ₂)₂-(PPh₃)₂] and trans-[Ru(ROCS ₂)₂(PPh₃)₂]⁺ complexes in dichloromethane solution exhibited typical dual redox signals corresponding to the cis-[Ru(ROCS₂)₂(PPh₃)₂] ^+/0 (ca. +0.15 and +0.10 V vs ferrocenium/ferrocene couple for R = Et and ⁱPr, respectively) and to trans-[Ru(ROCS₂) ₂(PPh₃)₂]^+/0 (-0.05 and -0.15 V vs ferrocenium/ferrocene for R = Et and ⁱPr, respectively) couples. Analyses on the basis of the Nicholson and Shain's method revealed that the thermal disappearance rate of transient trans-[Ru(ROCS₂) ₂(PPh₃)₂] was dependent on the concentration of PPh₃ in the bulk: the rate constant for the intramolecular isomerization reaction of trans-[Ru(ⁱPrOCS₂) ₂(PPh₃)₂] was determined as 0.338 ± 0.004 s^-1 at 298.3 K (ΔH* = 41.8 ± 1.5 kJ mol ^-1 and ΔS* = -114 ± 7 J mol^-1 K ^-1), while the dissociation rate constant of coordinated PPh ₃ from the trans-[Ru(ⁱPrOCS₂) ₂(PPh₃)₂] species was estimated as 0.113 ± 0.008 s^-1 at 298.3 K (ΔH* = 97.6 ± 0.8 kJ mol^-1 and ΔS* = 64 ± 3 J mol^-1 K ^-1), by monitoring the EC reaction (electrode reaction followed by chemical processes) at different concentrations of PPh₃ in the bulk. It was found that the trans to cis isomerization reaction takes place via the partial dissociation of ⁱPrOCS₂^- from Ru(II), contrary to the previous claim that it takes place by the twist mechanism.

Full text of DOI:10.1021/ic051487l

Inorg. Chem. 2006, 45, 1349−1355
+/
0
Syntheses, Structural Determinations of [Ru(ROCS2)2(PPh3)2]
Pairs,
and Kinetic Analyses of Thermal Reactions Involving Transient
-
trans-[Ru(iPrOCS2)2(PPh3)2] Species (ROCS2
) Ethyl- or
Isopropyldithiocarbonate and PPh3
) Triphenylphosphine)
Kyoko Noda,† Yuko Ohuchi,† Akira Hashimoto,† Masayuki Fujiki,† Sumitaka Itoh,† Satoshi Iwatsuki,‡
Toshiaki Noda,† Takayoshi Suzuki,*,§ Kazuo Kashiwabara,† and Hideo D. Takagi*,†
Graduate School of Science and Research Center for Materials Science, Nagoya UniVersity,
Furocho, Chikusa, Nagoya 464-8602, Japan, Department of Chemistry, Waseda UniVersity,
Ookubo, Shinjuku 169-8555, Japan, and Department of Chemistry, Graduate School of Science,
Osaka UniVersity, Toyonaka 560-0043, Japan
Received August 31, 2005
Controlled-potential electrochemical oxidation of cis-[Ru(ROCS2)2(PPh3)2] (R
complexes, and the crystal structures of cis-[Ru(ROCS2)2(PPh3)2] and trans-[Ru(ROCS2)2(PPh3)2](PF6) were
determined. Both pairs of complexes exhibited almost identical coordination structures. The Ru P distances in
trans-[RuIII(ROCS2)2(PPh3)2](PF6) [2.436(3) 2.443(3) Å] were significantly longer than those in cis-[RuII(ROCS2)2-
(PPh3)2] [2.306(1) 2.315(2) Å]: the smaller ionic radius of Ru(III) than that of Ru(II) stabilizes the trans conformation
)
Et, iPr) yielded corresponding Ru(III)
−
−
−
for the Ru(III) complex due to the steric requirement of bulky phosphine ligands while mutual trans influence by the
phosphine ligands induces significant elongation of the RuIII-P bonds. Cyclic voltammograms of the cis-[Ru(ROCS2)2-
(PPh3)2] and trans-[Ru(ROCS2)2(PPh3)2]+ complexes in dichloromethane solution exhibited typical dual redox signals
0
corresponding to the cis-[Ru(ROCS2)2(PPh3)2]+/ (ca.
+
0.15 and
+
0.10 V vs ferrocenium/ferrocene couple for R
)
Et and Pr, respectively) and to trans-[Ru(ROCS2)2(PPh3)2]+/
(
−0.05 and 0.15 V vs ferrocenium/ferrocene for
−
i
0
i
R
)
Et and Pr, respectively) couples. Analyses on the basis of the Nicholson and Shain’s method revealed that
the thermal disappearance rate of transient trans-[Ru(ROCS2)2(PPh3)2] was dependent on the concentration of
PPh3 in the bulk: the rate constant for the intramolecular isomerization reaction of trans-[Ru(iPrOCS2)2(PPh3)2] was
1
1
1
determined as 0.338
±
0.004 s- at 298.3 K (
∆
H*
)
41.8
±
1.5 kJ mol- and
∆
S* ) −114
±
7 J mol- K-1),
while the dissociation rate constant of coordinated PPh3 from the trans-[Ru(iPrOCS2)2(PPh3)2] species was estimated
1
1
1
as 0.113
±
0.008 s- at 298.3 K (
∆
H*
)
97.6
±
0.8 kJ mol- and
∆S*
)
64
±
3 J mol- K-1), by monitoring the
EC reaction (electrode reaction followed by chemical processes) at different concentrations of PPh3 in the bulk. It
i
-
was found that the trans to cis isomerization reaction takes place via the partial dissociation of PrOCS2 from
Ru(II), contrary to the previous claim that it takes place by the twist mechanism.
Introduction
atom increases has been related to both ground-state and
transition-state characteristics.1,2 Therefore, trans influence
and trans effect are not necessarily related to each other: to
understand these two phenomena it is necessary to examine
the metal-ligand bond lengths and lability of metal com-
plexes with a series of ligands possessing different donor/
acceptor properties.
Historically, the trans influence by which a metal to ligand
bond trans to the particular donor atom suffers from
elongation has been suggested to be related to the ground-
state property inherent in such complexes, while the trans
effect by which lability of a ligand trans to a particular donor
* To whom correspondence should be addressed. E-mail: suzuki@
chem.sci.osaka-u.ac.jp (T.S.), H.D.Takagi@nagoya-u.jp (H.D.T.).
† Nagoya University.
(1) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd ed.;
Butterworth-Heinemann: Oxford, U.K., 1997.
(2) Huheey, J. E. Inorganic Chemistry, 2nd ed.; Harper & Row: New
York, 1978.
‡ Waseda University.
§ Osaka University.
10.1021/ic051487l CCC: $33.50
Published on Web 01/12/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 3, 2006 1349

Noda et al.
diethyl ether. Anal. Calcd for C44H44O2S4P2Ru: C, 58.97; H, 4.95.
Found: C, 59.26; H, 4.95. 1H NMR (CDCl3, 303 K, 400 MHz): δ
1.17-2.26 (m, -CH3), 5.16 (m, -CH-), and 7.07-7.23 (m,
-C6H5). UV-vis (CH2Cl2, rt, λmax): 376 nm.
[Ru(ROCS2)2(PPh3)2](PF6). The crude EtOCS2 complex was
prepared by the modification of the reported method6 as follows:
recrystallized [Ru(EtOCS2)2(PPh3)2] was dissolved in acetone
containing 0.1 mol kg-1 NH4PF6, and electrolytically oxidized at
1.41 V vs ferrocenium/ferrocene couple by using a carbon fiber
electrode as the anode. After completion of the electrolysis solvent
was removed under reduced pressure, and an excess amount of
aqueous NH4PF6 solution was added. The product was filtered and
washed with water. The resulting crude green solid was recrystal-
We have recently reported a series of studies concerning
the trans influence and trans effect in various [Co(dtc)2(P-
ligand)2]+ complexes (dtc- ) N,N-dimethyldithiocarbamate
and P-ligand ) unidentate ligand with a phosphorus donor
atom),3,4 in which we pointed out that the simple parametric
descriptions of the donor and acceptor properties of P-ligands
postulated by Giering and co-workers5 cannot explain the
strengths of various CoIII-P bonds estimated from the
spectrophotometric method. To extend understandings of the
effect by spectator ligands as well as the nature of phosphorus
ligands, we examined the structures and isomerization
reactions of [Ru(ROCS2)2(PPh3)2]+/0 complexes in this study,
the former of which has never been reported in previous
studies.6
lized from dichloromethane/diethyl ether. Anal. Calcd for C45.7
47.4O2S4P3RuF6Cl7.4 ([Ru(EtOCS2)2(PPh3)2](PF6)‚3.7CH2Cl2): C,
41.35; H, 3.60. Found: C, 41.21; H, 3.40. UV-vis (CH2Cl2, rt,
-
H
As for the reactions of [Ru/Os(ROCS2)2(PPh3)2] com-
plexes,6,7 Chakravorty and co-workers reported “probable”
cis to trans isomerization rate constant, and they claimed
that the reaction proceeds through the twist mechanism.
However, a calculation on the basis of the AOM (angular
overlap model) indicates that the twist mechanism is not
likely to take place for second- and third-row transition metal
complexes with large ligand fields.3,4 In addition, our
previous results for Co(III) species3,4 strongly indicate that
the dissociation of coordinated ligands is significant even
for d6-Ru(II) species, by considering the trans influence/trans
effect of PPh3 and the effect of the spectator ligand.
Therefore, it is necessary to reinvestigate the reactions in
more detail so as to determine the exact reaction mechanism.
In this article, (1) we report successful isolation and crystal
structures of both d5-Ru(III) and d6-Ru(II) complexes for the
first time and (2) the trans to cis isomerization process in
the Ru(II) species was reanalyzed as the EC reaction by
varying the concentration of PPh3 in the bulk. The structures
and reactivity of the d5-Ru(III) and d6-Ru(II) species were
discussed on the basis of the trans influence/trans effect of
the phosphine ligand.
λ
max): 731, 445, 367, and ∼250 nm.
[Ru(iPrOCS2)2(PPh3)2](PF6) was obtained by the reaction of
the Ru(II) complex with Ce(IV). To a solution containing 0.2 mol
of [Ru(iPrOCS2)2(PPh3)2] and 2.18 mol of NH4PF6 in acetone/
dichloromethane (5:1 v/v) was added 30 mL of aqueous solution
of ceric ammonium nitrate (50 mmol kg-1), and the mixture was
stirred for 10 min. The crude product was filtered out and washed
with water. Deep green crystals were obtained by recrystallization
of the crude product from dichloromethane/diethyl ether. Anal.
Calcd for C44H46O3S4P3F6Ru ([Ru(iPrOCS2)2(PPh3)2](PF6)‚H2O): C,
49.90; H, 4.38. Found: C, 50.05; H, 4.16. UV-vis (CH2Cl2, rt,
λmax): 734, ∼555, 455, 369, and ∼250 nm.
Other Chemicals. Triphenylphosphine, PPh3, was recrystallized
twice from methanol/diethyl ether and dried under vacuum for 10
h at 70 °C. Tetra-n-butylammonium hexafluorophosphate, TBAPF6,
was recrystallized 3 times from ethanol/water and dried at 100 °C
for 10 h in a vacuum oven. Dichloromethane, which was used as
the solvent, was dried over molecular sieves 4A, followed by
distillation.
Crystallography.8 The X-ray diffraction data for the EtOCS2
complexes were collected at 23 °C on an automated Rigaku AFC-
5R four-circle diffractometer. On the other hand, the data for the
iPrOCS2 complexes were obtained at -73(2) °C on a Rigaku Raxis-
rapid imaging plate detector. A graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å) was used for all measurements. The
structures were solved by the direct method using SIR92 program9
and refined on F2 (with all independent reflections) using the
SHELXL97 program.10 All non-hydrogen atoms were refined
anisotropically, and H atoms were introduced theoretically and
treated by riding models, except for those of the solvent molecules
of crystallization in [Ru(iPrOCS2)2(PPh3)2](PF6)‚0.5CH2Cl2‚0.5CH3-
CN.8
Experimental Section
[Ru(ROCS2)2(PPh3)2]. The crude compounds were prepared by
the literature method.6,8 The resulting EtOCS2 complex, [Ru-
(EtOCS2)2(PPh3)2], was recrystallized by the vapor phase diffusion
of diethyl ether into dichloromethane solution, affording orange
plate crystals. Anal. Calcd for C42H40O2S4P2Ru: C, 58.11; H, 4.64.
Found: C, 58.04; H, 4.50. 1H NMR (CDCl3, 303 K, 400 MHz): δ
1.22 (t, -CH3), 4.25 (q, -CH2-), and 7.08-7.24 (m, -C6H5).
UV-vis (CH2Cl2, rt (room temperature), λmax): 376 nm. Red block
The crystallographic data are summarized in Table 1.
Spectrometric and Electrochemical Measurements. 1H NMR
spectra of samples in deuterated chloroform solution were recorded
by a Bruker AMX-400WB spectrometer. The UV-vis absorption
spectra were recorded by a Jasco V-570 spectrophotometer.
An attempt to estimate the rates for isomerization reactions by
means of the stopped-flow method was not successful: the spectral
change was too small for the reliable determination of the
isomerization rate constants. In addition, it was hardly possible to
isolate redox and following isomerization processes after complete
redox reactions by counter reagents when optimized experimental
i
crystals of the PrOCS2 complex, [Ru(iPrOCS2)2(PPh3)2], were
obtained by recrystallization from dichloromethane/acetonitrile/
(3) Iwatsuki, S.; Suzuki, T.; Hasegawa, A.; Funahashi, S.; Kashiwabara,
K.; Takagi, H. D. J. Chem. Soc., Dalton Trans. 2002, 3593.
(4) Iwatsuki, S.; Kashiwamura, S.; Kashiwabara, K.; Suzuki, T.; Takagi,
H. D. Dalton Trans. 2003, 2280.
(5) (a) Rahman, Md. M.; Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P.
Organometallics 1989, 8, 1. (b) Liu, H.-Y.; Eriks, K.; Prock, A.;
Giering, W. P. Organometallics 1990, 9, 1758.
(6) Bag, N.; Lahiri, G. K.; Chakravorty, A. J. Chem. Soc., Dalton Trans.
1990, 1557.
(7) (a) Pramanik, A.; Bag, N.; Ray, D.; Lahiri, G. K.; Chakravorty, A.
Inorg. Chem. 1991, 30, 410. (b) Pramanik, A.; Bag, N.; Chakravorty,
A. J. Chem. Soc., Dalton Trans. 1993, 237.
(9) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(10) Sheldrich, G. M. SHELXL97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(8) See Supporting Information for full details.
1350 Inorganic Chemistry, Vol. 45, No. 3, 2006

[Ru(ROCS2)2(PPh3)2]+/0 Pairs
Table 1. Crystallographic Data
param
[Ru(EtOCS2)2(PPh3)2]
[Ru(EtOCS2)2(PPh3)2](PF6)
[Ru(iPrOCS2)2(PPh3)2]
[Ru(iPrOCS2)2(PPh3)2](PF6)
geometry, solvate
formula
fw
cryst syst
space group, Z
a/Å
cis-, none
C42H40O2P2RuS4
867.99
monoclinic
P21/c, 8
11.870(2)
36.585(4)
20.122(2)
90
101.346(9)
90
8568(2)
1.346
trans-, none
C42H40F6O2P3RuS4
1012.96
orthorhombic
P212121, 4
18.622(4)
21.445(6)
11.089(5)
90
90
90
4428(2)
1.519
0.712
cis-, 0.5CH2Cl2‚ 0.5CH3CN
trans-, H2O
C44H46F6O3P3RuS4
1059.03
triclinic
C45.5H46.5ClN0.5O2P2RuS4
959.03
monoclinic
P21/c, 8
12.052(5)
36.352(14)
20.134(9)
90
100.55(2)
90
8672(6)
1.469
P1h, 2
11.336(7)
11.415(8)
19.347(13)
76.77(5)
75.76(5)
76.49(5)
2320(3)
1.516
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
D
calcd/Mg m-3
µ(Mo KR)/mm-1
R1a (obsd)b
0.669
0.053
0.210
0.728
0.044
0.125
0.684
0.074
0.224
0.043
0.123
wR2c (all)
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b Fo > 2σ(Fo ). c wR2 ) [∑w(|Fo| - |Fc|)2/∑|Fo| ]1/2
.
2
2
2
conditions were chosen. Therefore, the method established by
Nicholson and Shain11 was used for the determination of the rate
constants of the thermal isomerization process that follows the
electrochemical reduction of Ru(III) species (EC process).
Ru(1)-S(6) angles are 96.92(8) and 95.04(7)°, respectively,
while the P(1)-Ru(1)-S(7) angle is acute at 86.32(7)°.
Similarly, P(2)-Ru(1)-S(6) and P(2)-Ru(1)-S(2) angles
are larger than the right angle, although the P(2)-Ru(1)-
S(1) angle is 86.48(7)°. For the other crystallographically
independent molecule, similar features were observed in their
bond angles around Ru(51).8 Therefore, the two S atoms trans
to the PPh3 ligands are pushed away from the ordinary
octahedral apexes by two bulky PPh3 ligands: the P(1)-
Ru(1)-P(2) angle is as wide as 102.17(6)°, although each
one of the phenyl rings on two PPh3 ligands stack through
the space to avoid further repulsion between these two
unidentate ligands (Figure 1a). The bite angles of two
The electrochemical measurements and electrolyses of Ru(II)
complexes were carried out by a BAS 100B electrochemical
analyzer with a glassy carbon disk or fiber as the working electrode,
a platinum wire counter electrode, and a Ag/AgNO3 reference
electrode (0.01 mol kg-1 AgNO3 and 0.1 mol kg-1 tetra-n-
butylammonium perchlorate in acetonitrile). The temperature of the
sample solutions was controlled by circulation of thermostated
water. The voltammograms were recorded in reference to the
ferrocenium/ferrocene couple. Kinetic measurements, on the basis
of the Nicholson and Shain’s method,11 were carried out by varying
the scanning rate (five different rates from 100 to 1000 mV s-1
were employed) at each temperature. Two electrochemical cells
with isothermal and nonisothermal configurations were employed
for the measurements, to examine the reversibility of the electrode
process.12-14 Since the estimated rate constants by using two
different cells were identical with each other within the experimental
uncertainty, the rate constants for the chemical process that followed
the redox reaction at the electrode were confidently determined.
-
EtOCS2 ligands are in the range 71.39(6)-71.81(9)°.
In the complex of trans-[Ru(EtOCS2)2(PPh3)2](PF6) the
RuIII-S distances are 2.361(2)-2.372(3) Å that are some
0.028 Å shorter than that for the average RuII-S distances
located at the mutually trans positions: this difference may
be taken as the difference in the ionic radii for Ru(II) and
Ru(III). The two phosphorus atoms are located along the
straight P-Ru-P axis, while four S atoms are positioned in
Results and Discussion
-
the equatorial plane. The bite angles of two EtOCS2 ions
Crystal Structures. The crystal structures of all four
are 73.12(10) and 73.17(10)°.
complexesof[Ru(ROCS2)2(PPh3)2]and[Ru(ROCS2)2(PPh3)2]-
The most striking feature observed in the crystal structures
of these two complexes in different oxidation states is that
the RuIII-P distances in trans-[Ru(EtOCS2)2(PPh3)2](PF6)
[2.441(3) and 2.443(3) Å] are longer than the RuII-P
distances in cis-[Ru(EtOCS2)2(PPh3)2] [2.309(2)-2.315(2) Å]
by ca. 0.13 Å. Similarly large differences in the MII/III-P
distances were also observed in the analogous pairs of
osmium complexes: cis-[OsII(MeOCS2)2(PPh3)2] (average
2.303(3) Å) vs trans-[OsIII(MeOCS2)2(PPh3)2](PF6) (2.449-
(2) Å) and cis-[OsII(Et2NCS2)2(PPh3)2] (average 2.317(6) Å)
vs trans-[OsIII(Et2NCS2)2(PPh3)2](PF6) (2.439(3) Å).7 In those
studies the trans isomers of the Os(II) complexes were
isolated and the crystal structures were also analyzed; the
OsII-P distances in trans-[OsII(MeOCS2)2(PPh3)2] and trans-
[OsII(Et2NCS2)2(PPh3)2] were determined as 2.365(2) and
2.337(8) Å, respectively.7 This indicated that the reduction
of Os center (from OsIII to OsII) in the same coordination
environments made remarkable shortening of the OsIII/II-P
i
(PF6) (R ) Et or Pr) have been determined,8 and the
molecular structures of the EtOCS2 complexes are illustrated
i
in Figure 1 (those of the PrOCS2 complexes are shown in
Figure S1 in the Supporting Information). In [Ru(EtOCS2)2-
(PPh3)2], the RuII-S distances for the S atoms located at
mutually trans positions to the other S atom are 2.385(2)-
2.401(2) Å, while those for the S atoms that are trans to the
P atoms are 2.448(2)-2.463(2) Å. Therefore, it appears that
there is a significant trans influence by the coordinated P
atoms. On the other hand, the P(1)-Ru(1)-S(2) and P(1)-
(11) (a) Bard, A. J.; Faulkner, L. R. Electrochemical Methods; John Wiley
and Sons: New York, 1980. (b) Nicholson, R. S.; Shain, I. Anal. Chem.
1964, 36, 706.
(12) Yee, E. L.; Cave, R. J.; Guyer, K. L.; Tyma, P. D.; Weaver, M. J. J.
Am. Chem. Soc. 1979, 101, 1131.
(13) Criss, C. M.; Salomom, M. Physical Chemistry of Organic SolVent
Systems; Covington, A. K., Dickinson, T., Eds.; Plenum Press: New
York, 1973.
(14) Agar, J. N. AdV. Electrochem. Eng. 1963, 3, 31.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1351

Noda et al.
Figure 1. ORTEPs (30% probability level, hydrogen atoms omitted). Selected bond lengths (Å) and angles (deg) for (a) one of the crystallographically
independent complex molecules in cis-[Ru(EtOCS2)2(PPh3)2], Ru(1)-P(1) 2.315(2), Ru(1)-P(2) 2.309(2), Ru(1)-S(1) 2.452(2), Ru(1)-S(2) 2.397(2), Ru-
(1)-S(6) 2.385(2), Ru(1)-S(7) 2.463(2), P(1)-Ru(1)-P(2) 102.17(6), S(1)-Ru(1)-S(2) 71.81(9), and S(6)-Ru(1)-S(7) 71.39(6), and (b) the cationic
part in trans-[Ru(EtOCS2)2(PPh3)2](PF6), Ru(1)-P(1) 2.443(3), Ru(1)-P(2) 2.441(3), Ru(1)-S(1) 2.371(3), Ru(1)-S(2) 2.363(3), Ru(1)-S(6) 2.372(3),
Ru(1)-S(7) 2.361(2), P(1)-Ru(1)-P(2) 179.63(9), S(1)-Ru(1)-S(2) 73.12(10), and S(6)-Ru(1)-S(7) 73.17(10).
bonds as a result of a large augmentation of 5dπ-3dπ back-
bonding.7 In contrast, in the RuIII/II complexes having a
similar coordination environment, the Ru-P bonds were not
so sensitive to the oxidation state of Ru center; i.e., the
RuIII-P bonds in trans(P)-[RuCl2(O2CPh)(PPh3)2] (2.414 Å)
are comparable to the RuII-P bonds in trans(P)-[RuCl(CO)-
(O2CPh)(PPh3)2] (2.410 and 2.374 Å).15 A very recent
example of [RuII/III(dppbt-O2)2(dppbt)]-/0 (dppbt ) 2-(diphen-
ylphosphino)benzenethiolate; dppbt-O2 ) 2-(diphenylphos-
phino)benzenesulfinate) also showed similar RuII/III-P dis-
tances between the Ru(II) and Ru(III) complexes.16 Hence,
for the RuII/III-P bonds the contribution of 4dπ-3dπ back-
bonding remained unaltered by the difference in the oxidation
state of Ru center (e.g., Ru(II)-d5 or Ru(III)-d6). Although
we could not isolate (and, therefore, not determine the
structure of) the trans isomer of the Ru(II) complex, trans-
[RuII(EtOCS2)2(PPh3)2], it is, therefore, claimed that a
remarkable elongation of the RuIII-P bonds in trans-[RuIII-
(EtOCS2)2(PPh3)2](PF6) as compared to the RuII-P bonds
in cis-[RuII(EtOCS2)2(PPh3)2] results from a large mutual
trans influence of PPh3; it seems that the difference in the
degree of the 5dπ-3dπ and 4dπ-3dπ interaction originates
from the relativistic effect,2 which is effective especially for
the third-row transition elements such as Os.
structural features similar to those of the [Ru(EtOCS2)2-
(PPh3)2]+/0 complexes.8
Stability of the Transient trans-Ru(II) Species in
Dichloromethane. As a preliminary experiment, we exam-
ined the rate constant for the chemical process that followed
the electrochemical reduction of trans-[Ru(iPrOCS2)2-
(PPh3)2]+ at ambient temperature with varying the concentra-
tion of PPh3 in the bulk: the observed rate constant for the
thermal isomerization of trans-[Ru(iPrOCS2)2(PPh3)2] to cis-
[Ru(iPrOCS2)2(PPh3)2] (vide infra) decreased with increasing
[PPh3]free up to [PPh3]free ) 20 mmol kg-1, while further
addition of excess PPh3 in the bulk (>20 mmol kg-1)
gradually accelerated decomposition of trans-[Ru(iPrOCS2)2-
(PPh3)2], which was observed by the complete loss of typical
absorption bands of the expected product, cis-Ru(II). This
observation indicates that a large excess PPh3 in the bulk
induces decomposition of the transient trans-Ru(II) species,
while no appreciable degree of decomposition was observed
when less than 10 mmol kg-1 of free PPh3 was added.
Therefore, we used experimental conditions 0 e [PPh3] e
10 mmol kg-1 to investigate the effect of free PPh3 in the
bulk on the thermal isomerization reactions of trans-[Ru-
(iPrOCS2)2(PPh3)2], to avoid appreciable amounts of decom-
position of the intermediate during the observation of the
isomerization process. As for trans-[Ru(EtOCS2)2(PPh3)2],
the decomposition induced by PPh3 in the bulk was the more
evident even at [PPh3] ) 10 mmol kg-1. Because of this
instability, it was not possible to examine the isomerization
kinetics involving transient trans-[Ru(EtOCS2)2(PPh3)2].
Results of the preliminary experiment indicate that the
decomposition of the transient trans-Ru(II) species induced
by excess PPh3 in the bulk is associative in nature, since
In conclusion, the mutual trans influence of PPh3 in the
Ru(III) complexes is as large as that in the analogous Ru(II)
complexes and the trans coordination geometry in [Ru-
(EtOCS2)2(PPh3)2](PF6) is caused essentially by the large
steric repulsion between two PPh3 and smaller ionic size of
Ru(III). Complexes of [Ru(iPrOCS2)2(PPh3)2]+/0 exhibited
(15) (a) McGuiggan, M. F.; Pignolet, L. H. Cryst. Struct. Commun. 1978,
7, 583. (b) McGuiggan, M. F.; Pignolet, L. H. Cryst. Struct. Commun.
1981, 10, 1227.
(16) Grapperhaus, C. A.; Poturovic, S.; Mashuta, M. S. Inorg. Chem. 2005,
44, 8185.
-
iPrOCS2- is somewhat more bulky compared with EtOCS2 .
On the other hand, cis-Ru(II) complexes are indefinitely
1352 Inorganic Chemistry, Vol. 45, No. 3, 2006

[Ru(ROCS2)2(PPh3)2]+/0 Pairs
Table 2. Isolated Values of k1, k3, and the Ratio of k2/k-1 at Various
Temperatures and the Activation Parameters for k1 and k3
T/Ka
102k1/s-1
k3/s-1
(k-1/k2)/kg mol-1 b
278.3
283.3
288.3
293.3
298.3
1.72 ( 1.44
2.63 ( 0.57
2.79 ( 0.72
5.63 ( 0.40
11.3 ( 0.8
0.077 ( 0.014
0.124 ( 0.006
0.182 ( 0.004
0.254 ( 0.002
0.338 ( 0.004
1210 ( 9800
363 ( 278
2750 ( 2690
2740 ( 728
2340 ( 734
Activation Parametersc
∆H* ) 97.6 ( 0.8 kJ mol-1; ∆S* ) 64 ( 3 J mol-1 K-1 for k1
∆H* ) 41.8 ( 1.5 kJ mol-1; ∆S* ) -114 ( 7 J mol-1 K-1 for k3
a Temperature was controlled by circulation of thermostated water within
(0.2 K. b Although errors for k-1/k2 at each temperature are very large,
the k1 and k3 (especially k3) values were not sensitive to the ratio of k-1/k2.
c The activation parameters were determined without using data obtained
at low temperatures (278.3 and 283.3 K).
apparent rate constant on the concentration of PPh3 in the
bulk may indicate the involvement of the dissociative
isomerization/decomposition process other than the intramo-
lecular isomerization process, as described by the following
equations:3,4,17
Figure 2. Dependence of kexp on [PPh3] at various temperatures. Curved
lines at each temperature represent the calculated points on the basis of the
data in Tables 2 and S4, by using eq 4. [RuIII] ) 1.0 mmol kg-1, and I )
0.1 mol kg-1 [TBAPF6].
trans-[Ru(iPrOCS2)2(PPh3)2] yk1z
k-1
[Ru(iPrOCS2)2(PPh3)] (SQPY) + PPh3 (1)
k2
98
stable in dichloromethane solution at room temperature and
decomposition was not induced for cis-Ru(II) complexes
even with a large excess of free PPh3 in the bulk.
[Ru(iPrOCS2)2(PPh3)] (SQPY)
decomposition/isomerization or/and side reactions (2)
Kinetic Analyses of the Thermal Reactions Involving
Transient trans-[Ru(iPrOCS2)2(PPh3)2] Species in Dichlo-
romethane. Reactions of the transient species, trans-[Ru-
(iPrOCS2)2(PPh3)2], produced by the electrochemical reduc-
tion of trans-[Ru(iPrOCS2)2(PPh3)2]+ were examined at
various temperatures. Chakravorty et al. postulated that the
disappearance of the transient [Ru(ROCS2)2(PPh3)2] com-
k3
9
trans-[Ru(iPrOCS2)2(PPh3)2]
8 cis-[Ru(iPrOCS2)2(PPh3)2]
(3)
The apparent rate constant, kexp, that corresponds to the
disappearance of transient trans-[Ru(iPrOCS2)2(PPh3)2] is
then expressed by eq 4, by assuming a steady state for the
five-coordinate pseudo-square pyramidal (SQPY ) C2V)
species,
i
plexes (R ) Me and Pr) produced at the electrode was
attributed only to the trans to cis isomerization process and
reported that the reactions proceeded through the intramo-
lecular twist mechanism without giving sufficient reasons:6
the reported activation parameters were ∆H* ) 46.6 kJ
mol-1, ∆S* ) -96.6 J mol-1 K-1, and k ) 0.15 s-1 (283
K) for R ) Me and 40.7 kJ mol-1, -122.6 J mol-1 K-1,
and k ) 0.095 s-1 (283 K) for R ) iPr. As discussed in our
previous articles,3,4 dissociation of coordinated phosphine
ligands may also have to be taken into account for the
complete analyses of such isomerization processes. There-
fore, we reinvestigated the trans to cis isomerization rate for
the [Ru(iPrOCS2)2(PPh3)2] complexes, by using the method
identical with that employed by Chakravorty et al. Cyclic
voltammograms exhibited by cis-[Ru(iPrOCS2)2(PPh3)2] and
trans-[Ru(iPrOCS2)2(PPh3)2]+ in dichloromethane were quite
similar to those reported by Chakravorty et al.6
As shown in Figure 2 (averaged values of rate constants
at each condition are summarized in Table S4 in the
Supporting Information), the rate constant for the chemical
process that followed the electrochemical reduction of trans-
[Ru(iPrOCS2)2(PPh3)2]+ decreased to a constant value at
higher concentration of added PPh3 (up to ca. 10 mmol kg-1,
as described in the previous section). Such a dependence of
d[trans-[Ru(iPrOCS2)2(PPh3)2]]
-
)
dt
kexp[trans-[Ru(iPrOCS2)2(PPh3)2]]
k2(k1 + k3) + k3k-1[PPh3]free
(k-1[PPh3]free + k2)
kexp
)
)
k1 + k3 + k3A[PPh3]free
(A[PPh3]free + 1)
(4)
where [PPh3]free is the concentration of excess free PPh3 in
the bulk and A ) k-1/k2. The curvature of the plots in Figure
2 indicates that the A value is in the order of 103, since
A[PPh3]free in the denominator is not significantly different
from unity when [PPh3]free ≈ 10 mmol kg-1. The results
obtained by the least-squares analyses are summarized in
Table 2. Since the dependency of k3 on the other rate
constants was small (as judged from the dependency factor
given by the “Sigma Plot” program), the activation param-
(17) Jordan, R. B. Reaction Mechanisms of Inorganic and Organometallic
Systems, 2nd ed.; Oxford Press: New York, 1998.
Inorganic Chemistry, Vol. 45, No. 3, 2006 1353

Noda et al.
Scheme 1. Chemical Processes Observed after Reduction of trans-[RuIII(iPrOCS2)2(PPh3)2]+
eters for the k3 process were confidently determined as
∆H* ) 41.8 ( 1.5 kJ mol-1 and ∆S* ) -114 ( 7 J mol-1
K-1 by using data at T > 288 K (the activation parameters
estimated by using data obtained at all temperatures were
∆H* ) 48.4 ( 2.4 kJ mol-1 and ∆S* ) -91.2 ( 9 J mol-1
K-1, showing limited dependence of k3 on the other rate
constants). On the other hand, the k1 value became unreliable
at low temperatures since it depended largely on the k3 value.
The activation parameters for the k1 process were determined
as ∆H* ) 97.6 ( 0.8 kJ mol-1 and ∆S* ) 64 ( 3 J mol-1
K-1 (only data obtained at T g 288.3 K were used). The
values of k1 and k3 were 0.113 ( 0.008 s-1 and 0.338 (
0.004 s-1, respectively, for the reactions of transient trans-
[Ru(iPrOCS2)2(PPh3)2] at 25 °C (Scheme 1).
place for these Ru(II) complexes;3,4,18 the k2 process merely
leads to the decomposition of the five-coordinate species.
Although kinetic data reported for solvent exchange and
ligand substitution reactions are scarce, the ligand substitution
reactions in Ru(II) complexes have been considered to occur
through the dissociative interchange mechanism.19 The k1
value for the [Ru(iPrOCS2)2(PPh3)2] complex obtained in this
study is more than 10 times larger than the water exchange
rate constant in hexaaquaruthenium(II), 0.018 s-1 at 298 K.20
On the other hand, a trans-labilization effect by the coordina-
tion of η6-benzene in [Ru(η6-C6H6)(OH2)3]2+ was reported
by Merbach and co-workers, in which the water exchange
rate constant was accelerated to 11.5 ( 3.1 s-1 at 298 K.19b
It seems that the RuII-P bond energy is not small despite
the expected large mutual trans influence/trans effect of the
PPh3 ligand, since the dissociation rate constant of the PPh3
ligand coordinated at the mutually trans positions in trans-
[Ru(iPrOCS2)2(PPh3)2], k1, is not significantly large. Such a
stabilization of RuII-P bonds in trans-[Ru(iPrOCS2)2(PPh3)2]
may be explained either by the electronic sponge effect of
In the previous study, it was reported that the isomerization
process through the five coordinate intermediate was very
slow because of the high energy barrier for the [Co(dtc)2-
(P-ligands)2]+ complex (dtc ) N,N-dimethyldithiocarbamate,
and P-ligand ) unidentate phosphines or phosphites), on the
basis of the AOM calculation.3,4 Such a high activation
energy for the structural change from pseudo-square pyra-
midal structure (SQPY) to the pseudo-trigonal bipyramidal
transition state was explained by the relatively large π-acidity
of the ligands.18 Since the 10Dq value is somewhat larger
for [Ru(iPrOCS2)2(PPh3)] than that for [Co(dtc)2(P-ligand)2]+
and since the interelectronic repulsion parameters (Racah’s
B and C parameters) are significantly smaller for the
complexes of second-row transition metals, the activation
enthalpy expected for the change from the five-coordinate
pseudo-square pyramidal to pseudo-trigonal bipyramidal
structure should be much larger for [Ru(iPrOCS2)2(PPh3)2]
than that for the corresponding Co(III) complex with dtc-
ligands: isomerization through the k2 process does not take
-
the spectator ligand,3,4 iPrOCS2 , or by the intrinsic strength
of the RuII-P bond.
As the replacement of a coordinated ligand through the
associative attack by free PPh3 leads to the decomposition
of these complexes with a more rapid rate (see previous
section), such a process involves the dissociation of coor-
dinated dithiocarbonate ligand (Scheme 1). According to the
second-order perturbation theory [symmetry rules and the
principle of the least motion ()PLM)],21 a mixing of A1g
and B1g states causes asymmetric elongation of RuII-S bonds
through the B1g mode of vibration, for the d6 configuration
(19) (a) Richens, D. T. The Chemistry of Aqua Ions; Wiley: New York,
1997. (b) Stebler-Rothlisberger, M.; Hummel, W.; Pittet, P.-A.; Burgi,
H.-B.; Ludi, A.; Merbacher, A. E. Inorg. Chem. 1988, 27, 1358.
(20) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transition
Metal Complexes, 2nd ed.; VCH: New York, 1991.
(18) (a) Vanquickenborne, L. G.; Pierloot, K. Inorg. Chem. 1981, 20, 3673.
(b) Vanquickenborne, L. G.; Pierloot, K. Inorg. Chem. 1984, 23, 1471.
1354 Inorganic Chemistry, Vol. 45, No. 3, 2006

[Ru(ROCS2)2(PPh3)2]+/0 Pairs
in the D2h symmetry. Incoming free PPh3 ligand at the xy
plane is expected to induce this mixing by lowering the
LUMO level. Such a process is the more favored by trans-
[Ru(EtOCS2)2(PPh3)2] than the iPr derivative, because of the
less steric hindrance of this dithiocarbonate ligand.
the RuII-S bond is expected to ramble through the low-
energy B1g mode of vibration, although the ligand may not
completely dissociate from the metal center (Scheme 1). A
rather large rate constant, k3 (small activation enthalpy),
together with the large negative activation entropy for this
process, strongly indicates that the intramolecular isomer-
ization reaction proceeds through the D2h f Cs structural
change (through the allowed B1g mode of partial dissociation
of one of the RuII-S bonds, according to the symmetry rules
and PLM as described above), for which the free energy
barrier should not be large since the resulting cis conforma-
tion is also in the pseudo-Cs symmetry. The large negative
activation entropy is attributed to the increased electrostric-
tion caused by the charge separation that occurs during this
process.
On the other hand, it was found that cis-Ru(II) complexes
are indefinitely stable in dichloromethane solution while
trans-Ru(III) complexes gradually decomposed at room
temperature, although it took more than 12 h before obvious
decomposition was observed for the latter complexes in
solution. It should also be noted that decomposition was not
induced for cis-Ru(II) complex even with excess free PPh3.
Since the dissociation of coordinated PPh3 is typical only
for the trans-Ru(II) and trans-Ru(III) species, it is concluded
that the dissociation of coordinated PPh3 from trans-Ru(II)
complex is a result of the trans effect. Therefore, the slow
dissociation of coordinated PPh3 from trans-[Ru(iPrOCS2)2-
(PPh3)2] under the conditions of [PPh3]free < 10 mmol kg-1
is considered to take place by the limiting dissociative
mechanism (destabilization of the ground state). The large
activation enthalpy and the large positive activation entropy
estimated for the k1 process support this conclusion.
For the k3 (isomerization) process, the activation entropy
was largely negative. The large negative entropy observed
for the k3 process in the case of trans-Ru(II) complex
indicates that the reaction proceeds through a transition state
with a larger polarity than in the ground state: a charge
separation process is invoked. As discussed above, the
dissociative isomerization pathway that involves the change
from pseudo-square planar to pseudo-trigonal bipyramidal
structure does not take place for Ru(II) (and Co(III)
complexes), since such a structural change requires rather
high energy (Scheme 1). On the other hand, it has been
known that the stability constants of the transition metal
complexes with dithiocarbonate and dithiocarbamate ligands
depend largely on the size and charge of the metal ion.22
Therefore, it is certain that the energy of the RuII-S bond is
much smaller than that for the CoIII-S bond. As a result,
Conclusion
Crystal structures of [Ru(EtOCS2)2(PPh3)2]+/0 and [Ru-
(iPrOCS2)2(PPh3)2]+/0 pairs were determined for the first time;
in the Ru(III) complexes the coordination structures around
Ru(III) were in the D2h symmetry with elongated RuIII-P
bonds because of the mutual trans influence, while two PPh3
molecules in the corresponding Ru(II) species were observed
at the cis positions. From the analyses of the EC reactions,
rate constants for the trans to cis isomerization in [Ru-
(iPrOCS2)2(PPh3)2] and the dissociation reaction of the
coordinated PPh3 ligand were isolated for the first time. It
was shown that the latter process takes place by the limiting
dissociative mechanism, while the former process proceeds
through dissociation of one of the RuII-S bonds. The slow
dissociative activation of PPh3 from transient trans-[Ru-
(iPrOCS2)2(PPh3)2] indicates the mild mutual trans effect in
d6-Ru(II), while the elongation of the Ru(III)-P bonds in
trans-[Ru(iPrOCS2)2(PPh3)2]+ was attributed to the mutual
trans influence since decomposition of this species was much
slower.
Supporting Information Available: Experimental procedures
including syntheses, crystallography, and spectroscopic measure-
ments of the complexes, ORTEPs, and UV-vis absorption spectra
(21) (a) Burdett, J. K. Molecular Shapes: Theoretical Models of Inorganic
Stereochemistry; John Wiley and Sons: New York, 1980. (b) Itoh,
S.; Kishikawa, N.; Suzuki, T.; Takagi, H. D. Dalton Trans. 2005, 1066
and references therein.
(22) Sillen, L. G. Stability Constants of Metal-Ion Complexes; Royal Society
of Chemistry: London, 1971.
i
of the PrOCS2 complexes and the table of rate constants at each
condition measured (PDF/CIF format). This material is available
free of charge via the Internet at http://pubs.acs.org.
IC051487L
Inorganic Chemistry, Vol. 45, No. 3, 2006 1355