Diruthenium dithiolato cyanides: Basic reactivity studies and a post hoc examination of nature's choice of Fe versus Ru for hydrogenogenesis

Article abstract of DOI:10.1021/ic051989z

The reaction of Ru₂(S₂C₃H ₆)(CO)₆ (1) with 2 equiv of Et₄NCN yielded (Et₄N)₂[Ru₂(S₂C₃H ₆)(CN)₂(CO)₄], (Et₄N) ₂[3], which was shown crystallographically to consist of a face-sharing bioctahedron with the cyanide ligands in the axial positions, trans to the Ru-Ru bond. Competition experiments showed that 1 underwent cyanation >100x more rapidly than the analogous Fe₂(S₂C ₃H₆)(CO)₆. Furthermore, Ru₂(S ₂C₃H₆)(CO)₆ underwent dicyanation faster than [Ru₂(S₂C₃H₆)(CN)(CO) ₅]^-, implicating a highly electrophilic intermediate [Ru₂(S₂C₃H₆)(μ-CO)(CN)(CO) ₅]^-. Ru₂(S₂C₃H ₆)(CO)₆ (1) is noticeably more basic than the diiron compound, as demonstrated by the generation of [Ru₂(S ₂C₃H₆)(μ-H)(CO)₆]⁺, [1H]⁺. In contrast to 1, the complex [1H]⁺ is unstable in MeCN solution and converts to [Ru₂(S₂C₃H ₆)(μ-H)(CO)₅(MeCN)]⁺. (Et₄N) ₂[3] was shown to protonate with HOAc (pK_a = 22.3, MeCN) and, slowly, with MeOH and H₂O. Dicyanide [3]^2- is stable toward excess acid, unlike the diiron complex; it slowly forms the coordination polymer [Ru₂(S₂C₃H₆)(μ-H)(CN) (CNH)(CO)₄]_n, which can be deprotonated with Et ₃N to regenerate [H3]^-. Electrochemical experiments demonstrate that [3H]^- catalyzes proton reduction at -1.8 V vs Ag/AgCl. In contrast to [3]^2-, the CO ligands in [3H]^- undergo displacement. For example, PMe₃ and [3H]^- react to produce [Ru₂(S₂C₃H₆)(μ-H)(CN) ₂(CO)₃(PMe₃)]^-. Oxidation of (Et₄N)₂[3] with 1 equiv of Cp₂Fe⁺ gave a mixture of [Ru₂(S₂C₃H ₆)(μ-CO)(CN)₃(CO)₃]^- and [Ru ₂(S₂C₃H₆)(CN)(CO)₅] ^-, via a proposed [Ru₂]₂(μ-CN) intermediate. Overall, the ruthenium analogues of the diiron dithiolates exhibit reactivity highly reminiscent of the diiron species, but the products are more robust and the catalytic properties appear to be less promising.

Full text of DOI:10.1021/ic051989z

Inorg. Chem. 2006, 45, 2406−2412
Diruthenium Dithiolato Cyanides: Basic Reactivity Studies and a Post
Hoc Examination of Nature’s Choice of Fe versus Ru for
Hydrogenogenesis
Aaron K. Justice, Rachel C. Linck, and Thomas B. Rauchfuss*
Department of Chemistry, UniVersity of Illinois at Urbana-Champaign, Illinois 61801
Received November 17, 2005
The reaction of Ru2(S2C3H6)(CO)6 (1) with 2 equiv of Et4NCN yielded (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4], (Et4N)2[3],
which was shown crystallographically to consist of a face-sharing bioctahedron with the cyanide ligands in the axial
positions, trans to the Ru
rapidly than the analogous Fe2(S2C3H6)(CO)6. Furthermore, Ru2(S2C3H6)(CO)6 underwent dicyanation faster than
[Ru2(S2C3H6)(CN)(CO)5]-, implicating a highly electrophilic intermediate [Ru2(S2C3H6)( -CO)(CN)(CO)5]-. Ru2(S2C3H6)-
(CO)6 (1) is noticeably more basic than the diiron compound, as demonstrated by the generation of [Ru2(S2C3H6)-
−Ru bond. Competition experiments showed that 1 underwent cyanation >100× more
µ
(µ µ-
-H)(CO)6]+, [1H]+. In contrast to 1, the complex [1H]+ is unstable in MeCN solution and converts to [Ru2(S2C3H6)(
H)(CO)5(MeCN)]+. (Et4N)2[3] was shown to protonate with HOAc (pKa
) 22.3, MeCN) and, slowly, with MeOH and
-
H2O. Dicyanide [3]2 is stable toward excess acid, unlike the diiron complex; it slowly forms the coordination
polymer [Ru2(S2C3H6)(
Electrochemical experiments demonstrate that [3H]- catalyzes proton reduction at
to [3]2-, the CO ligands in [3H]- undergo displacement. For example, PMe3 and [3H]- react to produce [Ru2-
(S2C3H6)(
-H)(CN)2(CO)3(PMe3)]-. Oxidation of (Et4N)2[3] with 1 equiv of Cp2Fe+ gave a mixture of [Ru2(S2C3H6)-
-CO)(CN)3(CO)3]- and [Ru2(S2C3H6)(CN)(CO)5]-, via a proposed [Ru2]2(
-CN) intermediate. Overall, the ruthenium
µ
-H)(CN)(CNH)(CO)4]n, which can be deprotonated with Et3N to regenerate [H3]-.
1.8 V vs Ag/AgCl. In contrast
−
µ
(µ
µ
analogues of the diiron dithiolates exhibit reactivity highly reminiscent of the diiron species, but the products are
more robust and the catalytic properties appear to be less promising.
Scheme 1
Introduction
In examining diruthenium dithiolato carbonyls, we sought
new insights into the reactivity of M2(SR)2(CO)6-xLx com-
plexes.1,2 This family of butterfly structures resembles the
active sites of the Fe-only hydrogenase (Fe H2-ase) enzymes.3
We recently described the use of diruthenium dithiolates to
generate the first M2(SR)n species bearing a terminal hydride,
which in turn was converted to an H2 adduct (Scheme 1).4
We now report the substitution, redox, and acid-base
behavior of Ru2(S2C3H6)(CO)6 and its derivatives. We focus
* To whom correspondence should be addressed. E-mail: rauchfuz@
uiuc.edu.
(1) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B. J. Am. Chem. Soc.
2001, 123, 9476-9477.
(2) (a) Borg, S. J.; Behrsing, T.; Best, S. P.; Razavet, M.; Liu, X.; Pickett,
C. J. J. Am. Chem. Soc. 2004, 126, 16988-16999. (b) Mejia-
Rodriguez, R.; Chong, D.; Reibenspies, J. H.; Soriaga, M. P.;
Darensbourg, M. Y. J. Am. Chem. Soc. 2004, 126, 12004-12014.
(3) (a) Frey, M. ChemBioChem 2002, 3, 153-160. (b) Cammack, R.; Frey,
M.; Robson, R. Hydrogen as a Fuel: Learning from Nature; Taylor
& Francis: London, 2001.
on the propanedithiolate complexes because they sterically
resembles the dithiolate cofactor in the enzyme.5
2406 Inorganic Chemistry, Vol. 45, No. 6, 2006
10.1021/ic051989z CCC: $33.50
© 2006 American Chemical Society
Published on Web 02/28/2006

Diruthenium Dithiolato Cyanides
Scheme 2
Using diruthenium dithiolates, we have addressed certain
anomalies arising from our studies on the corresponding
diiron dithiolates. We previously reported that the dicyanation
of Fe2(SR)2(CO)6 proceeds more rapidly than the cyanation
of [Fe2(SR)2(CN)(CO)5]-,6 and questions arose about the
generality of this highly unusual behavior. The instability
of [Fe2(SR)2(CN)2(CO)4]2- upon treatment with excess acid
is well-known,7,8 but the decomposition pathway has re-
mained unexplained. Finally, the diiron complexes are
unstable toward oxidation,7 at least in the absence of trapping
ligands9 and we sought insights into the relevant redox
events, including the possible isolation of a mixed-valence
intermediate. Studies on the ruthenium analogues provide
insights relevant to all of these questions. Mononuclear Ru-
SR-CN compounds have been previously described by Liaw
and co-workers.10 The preparative results are summarized
in Scheme 2.
be applied to the synthesis of the 1,3-propanedithiolate, Ru2-
(S2C3H6)(CO)6 (1). Yields are 30-40% based on hydrated
ruthenium trichloride.
Cyanation of M2(S2C3H6)(CO)6 (M ) Fe, Ru). Slow
addition of 1 equiv of Et4NCN to a dilute MeCN solution
of 1 efficiently gave Et4N[Ru2(S2C3H6)(CN)(CO)5], Et4N-
[2]. We obtained substantial amounts of the corresponding
dicyanide (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4] ((Et4N)2[3]) when
the Et4NCN was added rapidly or when concentrated
solutions of 1 were used. With two or more equivalents of
Et4NCN, 1 converted cleanly to the dicyanide (Et4N)2[3];
no evidence was ever obtained for formation of the tricyanide
[Ru2(S2C3H6)(CN)3(CO)3]3-. The tendency of 1 to give the
dicyanide [3]2- even upon treatment with substoichiometric
amounts of cyanide is reminiscent of the behavior of related
diiron dithiolato complexes.6,13
The mechanism for dicyanation does not entail two
consecutive CN- for CO substitutions,6 i.e., Et4N[2] is not
an intermediate in the formation of dicyanide (Et4N)2[3]
under preparative conditions. This point was proven by
treatment of an equimolar mixture of 1 and Et4N[2] with 2
equiv of Et4NCN to give (Et4N)2[3], leaving unreacted Et4N-
[2]. Complete conversion of 1 occurred. The same result was
obtained using 13CN-labeled Et4N[2], the 13C-labeled species
remained unreacted (eq 1).
Results
Ru2(S2C3H6)(CO)6. Cabeza and co-workers prepared the
dithiolato complex Ru2(S2C6H4)(CO)6 via the Zn reduction
of carbonylated solutions of ruthenium chloride in the
presence of the benzene-1,2-dithiol.11 Key to their methodol-
ogy is the reductive carbonylation of Ru(III) to produce Ru-
(II) chloro-carbonyls.12 We found that Cabeza’s method could
+2CN-
-w2CO
[Ru2(S2C3H6)(13CN)(CO)5]-
(4) Justice, A. K.; Linck, R. C.; Rauchfuss, T. B.; Wilson, S. R. J. Am.
Chem. Soc. 2004, 126, 13214-13215.
Ru2(S2C3H6)(CO)6
(5) Nicolet, Y.; de Lacey, A. L.; Vernede, X.; Fernandez, V. M.;
Hatchikian, E. C.; Fontecilla-Camps, J. C. J. Am. Chem. Soc. 2001,
123, 1596-1601.
[Ru2(S2C3H6)(13CN)(CO)5]-
(1)
[Ru2(S2C3H6)(CN)2(CO)4]2-
(6) Gloaguen, F.; Lawrence, J. D.; Schmidt, M.; Wilson, S. R.; Rauchfuss,
T. B. J. Am. Chem. Soc. 2001, 123, 12518-12527.
(7) Schmidt, M.; Contakes, S. M.; Rauchfuss, T. B. J. Am. Chem. Soc.
1999, 121, 9736-9737.
(100%)
Of course, Et4N[2] does react with Et4NCN to give (Et4N)2-
[3], but this reaction is clearly slower than the conversion 1
+ 2 Et4NCN f (Et4N)2[3].
Comparative Cyanation of 1 and its Diiron Analogue.
We probed the relative reactivity of the diiron and diruthe-
(8) Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Yarbrough, J. C.;
Darensbourg, M. Y. J. Am. Chem. Soc. 2001, 123, 9710-9711.
(9) Boyke, C. A.; van der Vlugt, J. I.; Rauchfuss, T. B.; Wilson, S. R.;
Zampella, G.; De Gioia, L. J. Am. Chem. Soc. 2005, 127, 11010-
11018.
(10) Chen, C.-H.; Wang, L.-C.; Liaw, W. F. J. Chin. Chem. Soc. 2004,
51, 1121-1126.
(11) (a) Cabeza, J. A.; Martinez-Garcia, M. A.; Riera, V.; Ardura, D.;
Garcia-Granda, S. Organometallics 1998, 17, 1471-1477. (b) Cabeza,
J. A.; Martinez-Garcia, M. A.; Riera, V.; Ardura, D.; Garcia-Granda,
S.; Van der Maelen, J. F. Eur. J. Inorg. Chem. 1999, 1133-1139.
(12) Hill, A. F. Angew. Chem., Int. Ed. 2000, 39, 130-134.
(13) Lyon, E. J.; Georgakaki, I. P.; Reibenspies, J. H.; Darensbourg, M.
Y. J. Am. Chem. Soc. 2001, 123, 3268-3278.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2407

Justice et al.
[Fe2[(SCH2)2NR](CN)2(CO)4] for R ) Me14 and H.15 The
Ru-Ru bond distance (2.67 Å) and the average Ru-S
distance (2.42 Å) are similar to those distances in 1, which
was also characterized crystallographically (Table 1). The
Ru-CN distances are 2.04 Å, ca. 0.2 Å longer than the Ru-
CO distances of 1.87 Å. Analogous to the corresponding
diiron system, the Ru-CO distances are ∼0.05 Å shorter in
(PPN)2[3] than in 1.
[Ru2(S2C3H6)(µ-H)(CO)6]+. Compound 1 was found to
protonate to give a stable hydride, in contrast to the
corresponding diiron hexacarbonyl.16 Thus, the addition of
HOTf to a CH2Cl2 solution of 1 caused the νCO bands to
shift by ∼50 cm-1 toward higher energy, as seen for the
Figure 1. Molecular structure of the dianion of (PPN)2[Ru2(S2C3H6)(CN)2-
(CO)4]‚MeCN with the thermal ellipsoids at the 35% probability level. H
atoms are omitted for clarity.
1
substituted diiron systems.16 The H NMR spectrum of the
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Ru2(S2C3H6)(Co)6 (1) the anion in (PPN)2[Ru2(S2C3H6)(CN)2(CO)4],
(PPN)2[3]
resulting solution exhibited a hydride signal at δ -12.66.
The addition of hexanes to such solutions precipitated [1H]-
OTf. [1H]+ was easily deprotonated by weak bases such as
THF. The related hydride [Ru2(S2C6H4)(µ-H)(CO)6]+ is
apparently11 less stable than the propanedithiolato derivative
described above.
(PPN)2[3]
Ru(1)-Ru(2)
(1)
2.6667(7)
2.4205(11)
2.4206(11)
2.4195(12)
2.4142(12)
1.861(4)
Ru-Ru
2.6743(13)
2.396
1.941
Ru(1)-S(1)
Ru(1)-S(2)
Ru(2)-S(1)
Ru(2)-S(2)
Ru(1)-C(2)
Ru(1)-C(3)
Ru(2)-C(5)
Ru(2)-C(6)
Ru(1)-C(1)
Ru(2)-C(4)
Ru-S(av)
Ru-CO(axial,av)
Ru-CO(basal,av)
1.912
Treatment of [1H]+ with 1 equiv of Et4NCN and PMe3
resulted in the deprotonation of [1H]+. After it stood in a
MeCN solution, [1H]OTf underwent monosubstitution to
1.879(4)
1.857(5)
1.894(4)
2.048(4)
1
give [Ru2(S2C3H6)(µ-H)(CO)5(NCMe)]OTf. An in situ H
2.032(4)
NMR experiment showed the formation of a kinetic isomer
(δ -12.8) followed over the course of several hours by the
appearance of a second isomer (δ -17.64). In the absence
of acids, MeCN solutions of 1 are stable.
[Ru2(S2C3H6)(µ-H)(CN)2(CO)4]-. The increased basicity
of the Ru-Ru versus Fe-Fe bonds is particularly evident
for dianion [3]2-, which has a pKa greater than 22 indicated
by its ability to deprotonate HOAc in MeCN solution.17
Water and MeOH are also sufficiently acidic to protonate
the dicyanide, although this conversion required several
minutes at ambient temperatures.
Ru(1)-S(1)-Ru(2)
Ru(1)-S(2)-Ru(2)
66.87(3)
66.95(3)
Ru-S-Ru
67.84(3)
154.80(11)
151.78(11)
Ru-Ru-CO(1)
Ru(2)-Ru(1)-C(1) 149.87(11) Ru-Ru-CO(5)
Ru(1)-Ru(2)-C(4) 147.47(12) Ru-Ru-CO(basal,av.) 101.25
Ru(1)-Ru(2)-C(5) 99.10(12)
Ru(1)-Ru(2)-C(6) 104.93(13)
Ru(2)-Ru(1)-C(2) 102.79(13)
Ru(2)-Ru(1)-C(3) 101.25(12)
nium complexes toward cyanide through competition experi-
ments. Treatment of a 1:1 mixture of Fe2(S2C3H6)(CO)6 and
1 with 2 equiv Et4NCN produced exclusively [3]2-, leaving
unreacted Fe2(S2C3H6)(CO)6 (Scheme 2). In a more stringent
competition experiment, 2 equiv of Et4NCN was added to a
solution of 5 equiv of Fe2(S2C3H6)(CO)6 and 1 equiv of 1.
Again, IR spectroscopic and extractive workup indicated
complete conversion of 1 to [3]2-, leaving Fe2(S2C3H6)(CO)6
unaffected (eq 2).
The addition of 1 equiv of TsOH (p-MeC6H4SO3H, pKa
) 8.0 in MeCN) to aqueous or MeCN solutions of (Et4N)2-
[3], followed by the addition of large organic cations, yielded
+
crystalline salts (e.g., A[3H] where A ) PPN+, PPh4 , and
Et4N+). The νCO bands for [3H]- occur at ca. 50 cm-1 higher
energy than its conjugate base, as is typical.8,18 The 1H NMR
spectrum indicates the presence of two isomers in the ratio
1.0:0.75. This isomer ratio remains unchanged over the
course of several hours at room temperature in MeCN
solution. Two major isomers were previously observed in
the 1H NMR spectrum of [Fe2(S2C3H6)(µ-H)(CN)2(CO)4]-.8
Given its greater basicity, [3]2- was tested for its ability to
deprotonate [Fe2(S2C3H6)(µ-H)(CN)2(CO)4]-. No reaction
was observed for an equimolar solution of [3]2- and [Fe2-
+2CN-
-w2CO
5Fe2(S2C3H6)(CO)6
Ru2(S2C3H6)(CO)6
5Fe2(S2C3H6)(CO)6
(2)
[Ru2(S2C3H6)(CN)2(CO)4]2-
(100%)
As a control experiment, we confirmed that (Et4N)2[Fe2-
(S2C3H6)(CN)2(CO)4] did not react with 1, i.e., the product
ratio from the competition experiment reflects relative rates
of the cyanation.
Characterization of [Ru2(S2C3H6)(CN)2(CO)4]2-. The
(Et4N)2[3] salt is soluble in polar organic solvents, as well
as water, producing air-sensitive yellow solutions. The solid-
state structure of (PPN)2[3] (PPN ) N(PPh3)2) was deter-
mined via single-crystal X-ray diffraction (Figure 1, Table
1). A conventional butterfly structure is evident; both cyanide
ligands are trans to the Ru-Ru bond as seen for (Et4N)2-
(14) Lawrence, J. D.; Li, H.; Rauchfuss, T. B.; Be´nard, M.; Rohmer, M.-
M. Angew Chem., Int. Ed. 2001, 40, 1768-1771.
(15) Li, H.; Rauchfuss, T. B. J. Am. Chem. Soc. 2002, 124, 726-727.
(16) Fauvel, K.; Mathieu, R.; Poilblanc, R. Inorg. Chem. 1976, 15, 976-
978.
(17) Izutsu, K. Acid-Base Dissociation Constants in Dipolar Aprotic
SolVents; Blackwell Scientific Publications: Oxford, U.K., 1990.
(18) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B.; Be´nard, M.; Rohmer,
M.-M. Inorg. Chem. 2002, 41, 6573-6582.
2408 Inorganic Chemistry, Vol. 45, No. 6, 2006

Diruthenium Dithiolato Cyanides
(S2C3H6)(µ-H)(CN)2(CO)4]-. When an equimolar solution of
[Fe2(S2C3H6)(CN)2(CO)4]2- and [3]2- was treated with 1
equiv of HOTs, the two dimetallic complexes protonated to
the same extent, despite the extreme difference in their
basicity. The slow rate of proton transfer between metal
hydrides is well-known,19 so product distribution is a result
of the rate of protonation, not the basicity of the metal-
metal bond.
[Ru2(S2C3H6)(µ-H)(CN)(CNH)(CO)4]n. The addition of
two or more equivalents of HOTs to solutions of (Et4N)2[3]
resulted in rapid formation of Et4N[3H], followed by the
slower precipitation of a yellow solid. The IR spectrum of
this precipitate is consistent with [Ru2(S2C3H6)(µ-H)(CN)-
(CNH)(CO)4]n, (3H2)n. Relative to Et4N[3H], the νCO and
a preparative scale experiment, treatment of (Et4N)2[3] with
1 equiv Cp2FePF6 resulted in complete consumption of the
starting materials. ESI-MS and IR analysis indicates that the
major CN-containing products are [2]- and [Ru2(S2C3H6)-
(µ-CO)(CN)3(CO)3]-, resulting from disproportionation (eq
4).
[Ru2(S2C3H6)(CN)2(CO)4]2-
([3]2-)
+ Cp2Fe+ f 0.5[Ru2(S2C3H6)
[Ru (S C H )(CN)(CO) ]-
-
(µ-CO)(CN)3(CO)3] + 0.5
+
2
2
3
6
5
([2]-)
Cp2Fe (4)
The tricyanide was independently generated utilizing a
protocol recently published for [Fe2(S2C2H4)(µ-CO)(CN)3-
(CO)3]-.9 Thus [3]2- was oxidized by the simultaneous
addition of 2 equiv of Cp2Fe+ and 1 equiv of Et4NCN. The
product distribution in eq 4 is consistent with an initially
formed radical, [Ru2(S2C3H6)(CN)2(CO)4]-, which suffers
nucleophilic attack by [Ru2(S2C3H6)(CN)2(CO)4]2- to form
a µ-CN-linked Ru4 species.
ν
CN bands of (3H2)n are shifted toward higher energy by 10
and 35 cm-1, respectively. The fact that protonation induces
a greater shift in νCN than νCO is consistent with protonation
at cyanide. The addition of Et3N converted (3H2)n back into
[3H]-, signaled by the formation of a homogeneous solution
and the appearance of IR bands at the appropriate positions.
We propose that (3H2)n is a hydrogen-bonded polymer
consisting of RuCNH‚‚‚NCRu linkages. Consistent with this
proposal, the presence of NEt4Cl, a source of the hydrogen-
bond acceptor Cl-, prevents precipitation. The IR spectrum
of the resulting solution matches well that for solid (3H2)n.
Treatment of [3H]- with a 1.0 M solution of DCl produced
the corresponding solid (3HD)n, [Ru2(S2C3H6)(µ-H)(CN)-
(CND)(CO)4]. Neutralization of this solid with Et3N regener-
ated [3H]-, with no evidence of H-D exchange between
the Ru-H-Ru and RuCN-D sites (eq 3), and there is no
evidence for exchange between [3H]- and free Et3ND+ in
MeCN.
Cyclic voltammetry revealed [3]2- an irreversible oxidation
wave at 19 mV, and protonation of the Ru-Ru bond causes
a loss of the oxidation wave and the appearance of an
irreversible wave at approximately -1.8 V. Upon addition
of 5 and 10 equiv HOTs, the reduction current increases,
indicative of the catalytic reduction of protons.1 The electrode
became coated during the course of the electrolysis experi-
ments, probably because of the formation of (3H)n.
Discussion
Compared to the analogous diiron dithiolates, Ru2(S2C3H6)-
(CO)6 is more susceptible to attack by both nucleophilic and
electrophilic reagents. Both features can be rationalized on
the basis of electronic and molecular structures. The high
basicity of the Ru-Ru bond conforms with the well-known
trend that second-row metals are stronger Brønsted bases
than analogous complexes of first-row metals.20 The en-
hanced electrophilicity of Ru2(S2C3H6)(CO)6 was demon-
strated by competition experiments. Relative to the analogous
diiron system, Ru2(S2C3H6)(CO)6 reacts >100× faster with
cyanide. We attribute this increased electrophilicity to the
greater size of ruthenium, which facilitates associative
reactions. As in the analogous diiron compound, only two
cyanide ligands could be installed.
The cyanation is characterized by two unusual findings.
First, the monocyanide [Ru2(S2C3H6)(CN)(CO)5]- is not an
intermediate in the dicyanation. This result is understandable
since this monocyanide is isoelectronic to the hexacarbonyl
except that it is anionic, which would be expected to inhibit
cyanation. The fact that dicyanation of the hexacarbonyl is
faster than monocyanation requires a more complex explana-
tion. It is known that ligand substitution is associative,21 and
the initial product could reasonably be [Ru2(S2C3H6)(µ-CO)-
Ru2(S2C3H6)(µ-H)(CN)(CND)(CO)4 N
Ru2(S2C3H6)(µ-D)(CN)(CNH)(CO)4 (3)
Treatment of MeCN solutions of [3H]- with ONMe3 and
PMe3 smoothly yielded [Ru2(S2C3H6)(µ-H)(CN)2(CO)4-x
-
(PMe3)x]- (x ) 1, 2). On the basis of 31P and H NMR
measurements, we determined that the monophosphine
complex, [Ru2(S2C3H6)(µ-H)(CN)2(CO)3(PMe3)]-, formed as
a single isomer.
1
Redox Properties of Substituted Diruthenium Dithi-
olates. Cyclic voltammetry indicates that compared to Fe2-
(S2C3H6)(CO)6, 1 is both more difficult to oxidize and more
difficult to reduce. The compound exhibits an irreversible
oxidation at +1.3 V and an irreversible reduction at -1.5 V
(vs Ag/AgCl, MeCN solution). For comparison, Fe2(S2C3H6)-
(CO)6 oxidizes at +1.2 V and reduces at -1.16 V. Upon
treatment of a solution of 1 with excess HOTf, the current
increases dramatically and the reduction potential shifts by
-0.10 to -1.60 V. We attribute these changes to the effect
of protonation and catalytic proton reduction catalyzed by
[1H]+.
CV experiments showed that MeCN solutions of (Et4N)2-
[3] oxidized irreversibly at the mild potential of 19 mV. In
(20) Moore, E. J.; Sullivan, J. M.; Norton, J. R. J. Am. Chem. Soc. 1986,
108, 2257-2263.
(21) Ellgen, P. C.; Gerlach, J. N. Inorg. Chem. 1973, 12, 2526-2532.
(19) Kramarz, K. W.; Norton, J. R. Prog. Inorg. Chem. 1994, 42, 1-65.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2409

Justice et al.
Scheme 3
(CN)(CO)6]- (Scheme 3). An analogous intermediate has
been detected in the cyanation of a diiron carbonyl containing
a specially modified thioether ligand.22 Pickett et al. showed
that the attacking cyanide in effect pushes a CO from a
terminal position into a bridging site, concomitant with loss
of the Fe-Fe bond. Apparently, this µ-CO species is more
electrophilic than either [Ru2(S2C3H6)(CO)6] or [Ru2(S2C3H6)-
(CN)(CO)5]-. Pickett et al. rationalized the high electrophi-
licity of the Fe2(µ-CO) intermediate as resulting from the
electron-withdrawing properties of the µ-carbonyl, which also
labilizes the trans terminal carbonyl.
[(C5R5)2RuII (µ-H)(CO)4]+ exhibit enhanced reactivity toward
2
nucleophiles relative to its conjugate base.28
One-electron oxidation of [Ru2(S2C3H6)(CN)2(CO)4]2-
initiates a multistep process that entails a bis(bimetallic)
intermediate, most likely containing a µ-CN linkage. Two-
electron oxidation of [Ru2(S2C3H6)(CN)2(CO)4]2- was dem-
onstrated by the synthesis of [Ru2(S2C3H6)(µ-CO)(CN)3-
(CO)4]-. In contrast, the active site of the Fe-only H2-ase,
which is buried near the center of globular proteins,29 does
form a stable S ) 1/2 state. Our quest for related mixed-
valence bimetallic dithiolates continues.
Because of a large overpotential, [Ru2(S2C3H6)(µ-H)(CN)2-
(CO)4]- is a poorer catalyst for hydrogen evolution relative
to the known diiron complexes. Despite the fact that Ru2-
(S2C3H6)(CO)6 readily protonates and lacks donor ligands,
this species is a poor catalyst for proton reduction, requiring
-1.6 V, compared to ca. -1.0 V for [Fe2(S2C3H6)(µ-H)-
(CN)(CO)4(PMe3)]. Our evidence indicates that iron com-
pounds are superior catalysts relative to the analogous
ruthenium compounds.
Evolutionarily optimized bioorganometallic enzymes have
evolved highly efficient mechanisms to accomplish some of
nature’s and synthetic chemistry’s most important reactions.
The conversion of protons and electrons to dihydrogen is
an example of a reaction that nature has perfected using
inexpensive, plentiful metals, such as iron. Using the more
reactive platinum group metals, the chemical industry
struggles to achieve such reactions with the same efficiency,
environmental-friendliness, and gentleness as the natural
systems. The results presented in this paper indicate that
platinum-group metal mimics of the Fe-only hydrogenase
active sites yield catalysts less effective for proton reduction,
although many aspects of the associated reactivity are quite
analogous.
A mechanism that rationalizes these results is presented
in Scheme 3.
Two isomers were observed for [Ru2(S2C3H6)(µ-H)(CN)2-
(CO)4]-, which presumably result from protonation of two
rotamers of the dicyanide conjugate base, as seen in the
protonation of the analogous diiron system.23 The low
rotational barriers in the 34e- species, Fe2(S2CnH2n)(CO)4L2,
allow rapid isomerization at room temperature,4,24 whereas
the rotational barriers are higher in the confacial bioctahedral
derivatives, [Fe2(S2CnH2n)(µ-X)(CO)6-xLx]z (X ) CO, SMe,
H).9,25 We obtained no evidence for protonation at a single
metal, as is implied in the Fe-only H2-ases. For related
cyclopentadienyl complexes, Angelici had also found that
protonation occurs at the Ru-Ru bond, not at a single metal
site, even in electronically unsymmetrical species.26
In contrast to the substitutional inertness of dicyanide [3]2-,
the carbonyl ligands in its conjugate acid [3H]- are readily
substituted by PMe3. Protonation-induced labilization of
carbonyl ligands has been observed previously in the case
of [Fe2(S2C3H6)(µ-H)(CO)4(PMe3)2]+, wherein MeCN dis-
places one CO ligand.27 Similarly, complexes of the type
(22) George, S. J.; Cui, Z.; Razavet, M.; Pickett, C. J. Chem.sEur. J. 2002,
8, 4037-4046.
(23) (a) Zhao, X.; Georgakaki, I. P.; Miller, M. L.; Mejia-Rodriguez, R.;
Chiang, C.-Y.; Darensbourg, M. Y. Inorg. Chem. 2002, 41, 3917-
3928. (b) Boyke, C. A.; Rauchfuss, T. B. In progress.
(24) Adams, R. D.; Cotton, F. A.; Cullen, W. R.; Hunter, D. L.; Mihichuk,
L. Inorg. Chem. 1975, 14, 1395-1399.
Experimental
General. Previous reports describe the general methods used in
this work.30 Zinc powder, 2-ethoxyethanol, 1,3-propanedithiolate,
Et4NCN, Et4NCl, and hydrated p-toluenesulfonic acid were obtained
(25) (a) Adams, R. D.; Kwon, O. S.; Smith, M. D. Israel J. Chem. 2001,
41, 197-206. (b) Georgakaki, I. P.; Miller, M. L.; Darensbourg, M.
Y. Inorg. Chem. 2003, 42, 2489-2494. (c) Boyke, C. A.; Rauchfuss,
T. B.; Wilson, S. R.; Rohmer, M.-M.; Benard, M. J. Am. Chem. Soc.
2004, 126, 15151-15160.
(26) Nataro, C.; Angelici, R. J. Inorg. Chem. 1998, 37, 2975-2983.
(27) Zhao, X.; Chiang, C.-Y.; Miller, M. L.; Rampersad, M. V.; Darens-
bourg, M. Y. J. Am. Chem. Soc. 2003, 125, 518-524.
(28) (a) Ovchinnikov, M. V.; Wang, X.; Schultz, A. J.; Guzei, I. A.;
Angelici, R. J. Organometallics 2002, 21, 3292-3296. (b) Ovchin-
nikov, M. V.; Guzei, I. A.; Angelici, R. J. Organometallics 2001, 20,
691-696. (c) Ovchinnikov, M. V.; LeBlanc, E.; Guzei, I. A.; Angelici,
R. J. J. Am. Chem. Soc. 2001, 123, 11494-11495.
(29) Nicolet, Y.; Lemon, B. J.; Fontecilla-Camps, J. C.; Peters, J. W. Trends
Biochem. Sci. 2000, 25, 138-143.
2410 Inorganic Chemistry, Vol. 45, No. 6, 2006

Diruthenium Dithiolato Cyanides
from Aldrich; ONMe3 (Aldrich) was dried via benzene-water
azeotropic distillation, followed by repeated vacuum-sublimation
cycles; PMe3 was obtained from Strem. RuCl3‚3H2O was obtained
from Pressure Chemical Co, and FcPF6 was prepared by literature
methods.31
mixture was concentrated to 2 mL, and a yellow-orange product
precipitated upon the addition of 30 mL of Et2O. The product was
washed with 3 × 10 mL of Et2O and vacuum-dried. Yield: 0.230
1
g (75%). H NMR (acetone-d6): δ 1.4 (t, 24H, NCH2CH3), 1.9
(bs, 2H, SCH2CH2CH2S), 2.1 (bs, 4H, SCH2CH2CH2S), 3.5 (q, 16H,
NCH2CH3). 13C NMR (CD3OD, 20OC): δ 7.8 (q, 8C, NCH2CH3),
24.2 (bs, 2C, SCH2CH2CH2S), 35.5 (bs, 1C, SCH2CH2CH2S), 53.3
(t, 8C, NCH2CH3), 150 (2, 2C, RuCN), 207 (bs, 4C, RuCO). IR
(MeCN): νCN 2087, νCO 1978, 1938, 1899 cm-1. Anal. Found
(calcd): C, 40.58 (40.97); H, 6.11 (6.33); N, 7.43 (7.64).
Ru2(S2C3H6)(CO)6, 1. A dark brown suspension of 5 g (20.54
mmol) of RuCl3‚3H2O in 300 mL of 2-ethoxyethanol was warmed
to reflux, while being purged with CO for 3.5 h. The light yellow
solution was cooled to room temperature and treated with 1.15 mL
(11.4 mmol) of 1,3-propanedithiol, followed by 10 g (150 mmol)
of Zn powder. The mixture was warmed to reflux for 2 h, again
under a CO purge. After it was cooled to room temperature, the
mixture was poured into a beaker containing 1500 mL of H2O.
The resulting flocculent precipitate was collected by filtration on a
pad of Celite, where it was washed with 3 × 100 mL of H2O before
being air-dried. The yellow-orange product was extracted from the
Celite with 3 L of CH2Cl2, and the filtrate was evaporated under
vacuum. An extract of the residue in 8 mL of CH2Cl2 was loaded
onto a column of neutral alumina that was packed with hexane.
After the column was washed with hexane, a yellow band was
eluted with CH2Cl2. Crystals suitable for X-ray diffraction studies
were grown from hexane solution at -20 °C. Yield: 1.5 g (35%).
1H NMR (CDCl3): δ 2.2 (bs, 4H), 1.9 (bs, 2H). IR (hexane): νCO
2085, 2054, 2012, 2003, 1993 cm-1. Anal. Found (calcd): C, 22.82
(22.69); H, 1.19 (1.27).
(PPN)2[Ru2(S2C3H6)(CN)2(CO)4], (PPN)2[3]. This species was
prepared in a manner analogous to that for (Et4N)2[3], using PPNCN
in place of Et4NCN. Crystals suitable for X-ray diffraction analysis
were grown from a mixture of MeCN-hexanes-Et2O.
Competitive Cyanation of 1 and Fe2(S2C3H6)(CO)6. A red-
orange solution containing 0.081 g (0.210 mmol) of Fe2(S2C3H6)-
(CO)6 and 0.020 g (0.042 mmol) of 1 in 10 mL of MeCN was
treated with 0.013 g (0.084 mmol) of Et4NCN in 3 mL of MeCN.
IR (MeCN): νCN 2087, νCO 2074, 2034, 1994, 1979, 1939, 1900
cm-1
.
As a control experiment, a MeCN solution of (Et4N)[Fe2-
(S2C3H6)(CN)2(CO)4] and 1 was demonstrated to be stable for 12
h. A related competition experiment was also conducted on a 1:1
solution of 1 and Fe2(S2C3H6)(CO)6 with similar results.
Dicyanation of 1 in the Presence of Et4N[Ru2(S2C3H5)(13CN)-
(CO)5]. A solution of 0.032 g (0.0671 mmol) of 1 and 0.040 g
(0.067 mmol) of Et4N[Ru2(S2C3H6)(13CN)(CO)5] in 10 mL of
MeCN was shown to be stable by IR spectroscopy. To this solution
was added 0.022 g (0.134 mmol) of Et4NCN in 5 mL of MeCN.
IR (MeCN): νCN 2100, 2087, νCO 2045, 1985, 1978, 1963, 1938,
1925, 1900 cm-1. This corresponds to a mixture of unreacted Et4N-
[Ru2(S2C3H6)(13CN)(CO)5] and [3].
The complex Ru2(S2C2H4)(CO)6 was prepared analogously in a
1
28% yield. H NMR (C6D6): δ 1.44 (bs, 4H). IR (hexane): νCO
2087, 2056, 2014, 2005, 1995, 1966 cm-1. Anal. Found (calcd):
C, 21.23 (20.78); H, 0.54 (0.87).
[Ru2(S2C3H6)(µ-H)(CO)6]OTf, [1H]OTf. A yellow solution of
0.10 g (0.21 mmol) of 1 in 5 mL of CH2Cl2 was treated with 1.80
mL of a 0.113 M solution of HOTf in CH2Cl2. The solution was
concentrated to 2 mL, and the light-yellow product precipitated
upon addition of 30 mL of hexane. The sample was washed with
30 mL of hexane and dried under vacuum. Yield: 0.125 g (96%).
1H NMR (CD2Cl2): δ 2.78 (t, 4H, SCH2), 2.29 (d, 2H, SCH2CH2-
CH2S), -12.66 (s, Ru-H-Ru). IR (CH2Cl2): νCO 2143, 2126, 2078
cm-1. When the same reaction was conducted in an MeCN solution,
after 48 h the spectrum changed to indicate a new species assigned
as [Ru2(S2C3H6)(µ-H)(CO)5(NCMe)]OTf. 1H NMR (MeCN-d3): δ
2.2 (t, 4H, SCH2), 1.95 (d, 2H, SCH2CH2CH2S), -17.6 (s, 1H,
Ru-H-Ru). IR (MeCN): νCO 2131, 2076, 2062, 2025 cm-1. ESI-
MS: m/z 490.9 ([Ru2(S2C3H6)(µ-H)(CO)5(MeCN)]+).
PPh4[Ru2(S2C3H6)(µ-H)(CN)2(CO)4], PPh4[3H]. An solution
of 0.25 g (0.341 mmol) of (Et4N)2[3] in 35 mL H2O was first treated
with 0.34 mL (0.341 mmol) of 1 M HCl and then added slowly to
a solution of 0.65 mg (1.71 mmol) of PPh4Cl in 10 mL of H2O.
The pale yellow precipitate was collected by filtration on a pad of
Celite and washed with 30 mL each of H2O and Et2O. The product
was extracted from the Celite with 10 mL of MeCN, and the extract
was concentrated to a volume of 1 mL. The product, which
precipitated upon addition of 30 mL of Et2O, was washed with 30
1
mL of Et2O and dried under vacuum. Yield: 0.21 mg (65%). H
NMR (DMSO-d6):
δ 7.9 (m, 20H, PPh4), 2.6 (m, 6H,
Et4N[Ru2(S2C3H6)(CN)(CO)5] Et4N[2]. A solution of 0.10 g
(0.21 mmol) of 1 in 6 mL of MeCN was treated dropwise with a
solution of 0.036 g (0.23 mmol) of Et4NCN in 4 mL of MeCN.
The solvent was removed from the yellow-orange solution. The
red-orange residue was extracted into 3 × 5 mL of THF, and this
extract was filtered through a pad of Celite. The solvent was reduced
to 1 mL; the mustard yellow product precipitated upon addition of
30 mL of hexane. The product was further washed with hexane
and dried under vacuum. Yield: 0.060 g (47%). 1H NMR (DMSO-
d6): δ 1.1 (t, 12H, NCH2CH3), 2.0 (bs, 2H, SCH2CH2CH2S), 2.1
(bs, 4H, SCH2CH2CH2S), 3.2 (q, 8H, NCH2CH3). IR (MeCN): νCN
2103, νCO 2046, 1988, 1965, 1925 cm-1. Anal. Found (calcd): C,
47.29 (48.76); H, 3.06 (3.35); N, 3.56 (3.45).
SCH2CH2CH2S), -12.8 (s, 1H, Ru-H-Ru), -14.2 (s, 1H, Ru-H-
Ru). IR (MeCN): νCN 2120, νCO 2057, 2037, 1991 cm-1. Anal.
Found (calcd): C, 33.28 (33.77); H, 4.67 (4.33); N, 4.37 (4.6).
Reaction of [3H]- with DCl. A solution of 0.005 g (0.0068
mmol) of (NEt4)2[3] in ∼1.0 mL of MeCN-d3 was treated with
0.26 mL (0.0068 mmol) of a 0.026 M solution of HOTs‚H2O in a
sealable NMR tube, using standard vacuum-line techniques, fol-
lowed by the addition of 140 µL (0.0136 mmol) of a 0.10 M
solution of DCl. The yellow precipitate redissolved upon addition
of 140 µL (0.0136 mmol) of 0.10 M NEt3 with no evidence for
deuteration of [3H]-.
[Ru2(S2C3H6)(µ-H)(CN)(CNH)(CO)4]n, [3H2]n. A solution of
0.050 g (0.0682 mmol) of Et4N[3H] in 5 mL of MeCN was treated
with 0.129 g (0.682 mmol) of HOTs‚H2O in 2 mL of MeCN. After
the solution was stirred for 24 h, the solvent was removed, leaving
(Et4N)2[Ru2(S2C3H6)(CN)2(CO)4], (Et4N)2[3]. A solution of 0.20
g (0.42 mmol) of 1 in 5 mL of MeCN was treated with a solution
of 0.14 g (0.90 mmol) of Et4NCN in 5 mL of MeCN. The reaction
a yellow solid. IR (KBr): νCN 2152, νCO 2064, 2045, 2003 cm-1
.
When the reaction was conducted in the presence of 0.110 g (0.682
mmol, 10 fold excess) of NEt4Cl, a homogeneous yellow solution
was obtained. IR (MeCN): νCN 2146, νCO 2065, 2050, 2007 cm-1
.
(30) Schwarz, D. E.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 2003,
42, 2410-2417.
(31) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-922.
Inorganic Chemistry, Vol. 45, No. 6, 2006 2411

Justice et al.
Table 2. Crystallographic Data
Ru2(S2C3H6)(CO)6
Et4N[Ru2(S2C3H6)(µ-H)(CN)2(CO)3(PMe3)]. A yellow solution
of 0.200 g (0.273 mmol) of (Et4N)2[3] in 10 mL of MeCN was
treated with 2.73 mL (0.273 mmol) of a 0.10 M HCl solution in
MeCN, followed by a solution of 0.020 g (0.273 mmol) of ONMe3
in 3 mL of MeCN, and then 0.55 mL (0.273 mmol) of a 0.5 M
solution of PMe3 was added. After the reaction was allowed to
proceed overnight, the solvent was removed in a vacuum. After it
was rinsed with ca. 30 mL of H2O, the residue was extracted into
2 mL of MeCN, and a yellow solid precipitated upon further
addition of Et2O. Yield: 0.122 g (68%). 1H NMR (MeCN-d3): δ
3.2 (q, 8H,NCH2CH3), 2.2 (bs, 4H, SCH2), 2.0 (bs, 2H, SCH2CH2),
1.5 (d, 9H, Ru-PMe3, JH-P ) 10 Hz), 1.2 (t, 12H, NCH2CH3),
-13.7 (d, 1H, Ru-H-Ru, JH-P ) 11 Hz). 31P NMR (MeCN-d3): δ
(PPN)2[Ru2(S2C3H6)
(CN)2(CO)4]‚MeCN (3)
(1)
chemical formula
temp (K)
cryst size (mm)
cryst syst
space group
a (Å)
C9H6O6Ru2S2
193 (2)
0.26 × 0.22 × 0.07
monoclinic
C2/m
16.643(9)
9.798(6)
9.177(5)
90
91.127(10)
90
1496.1 (14)
4
2.115
0.71073
0.9931/0.6569
C83H69N5O4P4Ru2S2
193(2)
0.44 × 0.22 × 0.06
monoclinic
P21/n
10.175(2)
52.898(12)
13.697(3)
90
94.099(9)
90
7344 (3)
4
1.439
0.71073
0.9652/0.8186
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
9.54 (s). IR (MeCN): νCN 2116, 2100, νCO 2033, 1972, 1951 cm-1
ESI-MS: m/z 522.0 ([Ru2(S2C3H6)(µ-H)(CN)2(CO)3(PMe3)]+).
.
Z
densitycalcd (Mg m-3
)
µ(Mo KR) (mm-1
max/min.
)
Et4N[Ru2(S2C3H6)(µ-H)(CN)2(CO)2(PMe3)2]. A yellow solution
of 0.200 g (0.273 mmol) of (Et4N)2[3] in 10 mL of MeCN was
treated with 2.73 mL (0.273 mmol) of a 0.10 M HCl solution in
MeCN, followed by a solution of 0.041 g (0.546 mmol) of ONMe3
in 3 mL of MeCN and 2.2 mL (1.092 mmol) of a 0.50 M solution
of PMe3. After 24 h, the solvent was removed in a vacuum. After
it was rinsed with 30 mL of H2O, the residue was extracted into 2
mL of MeCN and diluted with Et2O to give a yellow solid. Yield:
transition
reflns
4070/1450
46029/12954
measured/independent
data/restraints/params
GOF on F2
1450/38/114
1.063
12954/85/930
0.884
0.0932
0.0431 (0.1035)
0.0653 (0.0753)
0.382/-0.489
Rint
0.0274
0.0180 (0.0219)
R1 [I > 2σ] (all data)a
wR2 [I > 2σ] (all data)b 0.0451 (0.0463)
max peak/hole (e-/Å3)
0.313/-0.402
1
0.164 g (72%). H NMR (MeCN-d3): δ 3.2 (q, 8H,NCH2CH3),
2.2 (bs, 4H, SCH2), 2.0 (bs, 2H, SCH2CH2), 1.5 (d, 9H, Ru-PMe3,
JH-P ) 11 Hz), 1.4 (d, 9H, Ru-PMe3, JH-P ) 10 Hz), 1.2 (t, 12H,
NCH2CH3), -13.1 (t, 1H, Ru-H-Ru, JH-P ) 11 Hz), -13.7 (t, 1H,
Ru-H-Ru, JH-P ) 11 Hz), -15.1 (t, 1H, Ru-H-Ru, JH-P ) 11 Hz),
-15.4 (t, 1H, Ru-H-Ru, JH-P ) 11 Hz). 31P NMR (MeCN-d3): δ
2
a R1 ) ∑|Fo| - |Fc|/∑|Fo|. b wR2 ) {[w(|Fo| - |Fc|)2]/∑[wFo ]}1/2
,
where w ) 1/σ2(Fo).
precipitated upon addition of 35 mL of Et2O. After a few hours at
room temperature, the product mixture became insoluble in MeCN.
IR (MeCN): νCN 2123, νCO 2059, 2016, 1979, 1902 cm-1. ESI-
MS: m/z 499.8 ([Ru2(S2C3H6)(µ-CO)(CN)3(CO)3]-).
9.47 (s), 5.12 (s). IR (MeCN): νCN 2090, νCO 1938, 1922 cm-1
ESI-MS: m/z 569.9 ([Ru2(S2C3H6)(µ-H)(CN)2(CO)2(PMe3)2]+).
.
Oxidation of (Et4N)2[Ru2(S2C3H6)(CN)2(CO)4] with FcPF6. A
solution of 0.050 g (0.027 mmol) of (Et4N)2[3] in 5 mL of MeCN
was cooled to -40 °C under a stream of CO and then treated with
0.009 g (0.027 mmol) of FcPF6 in 5 mL of MeCN. After resulting
solution was allowed to warm to room temperature, the solvent
was removed in vacuo, and the residue was rinsed with 3 × 10
mL of hexanes. The residue was extracted with 2 mL of MeCN,
and the addition of 35 mL of Et2O precipitated a solid, identified
spectroscopically as Et4N[Ru2(S2C3H6)(µ-CO)(CN)3(CO)3] (see next
preparation) and NEt4[2]. IR (MeCN): νCN 2125, 2102, νCO 2057,
2046, 2017, 1988, 1980, 1964, 1926, 1902 cm-1. ESI-MS: m/z
499.8 ([Ru2(S2C3H6)(µ-CO)(CN)3(CO)3]-), 475.8 ([Ru2(S2C3H6)-
(CN)(CO)5]-).
(Et4N)[Ru2(S2C3H6)(µ-CO)(CN)3(CO)3]. A solution of 0.050
g (0.027 mmol) of (Et4N)2[3] in 5 mL of MeCN was cooled to
-40 °C under a stream of CO and then treated simultaneously with
0.018 g (0.054 mmol) of FcPF6 in 5 mL of MeCN and 0.004 g
(0.027 mmol) of Et4NCN. The resulting dark yellow solution was
then allowed to warm to room temperature, and the solvent was
removed in vacuo. The residue was rinsed with 3 × 10 mL of
hexanes. The residue was extracted into 2 mL of MeCN and
Crystallography. Crystals were mounted to a thin glass fiber
using Paratone-N oil (Exxon). Data, collected at 198 K on a Siemens
CCD diffractometer, were filtered to remove statistical outliers. The
integration software (SAINT) was used to test for crystal decay as
a bilinear function of X-ray exposure time and sin(Θ). The data
were solved using SHELXTL by direct methods (Table 2); atomic
positions were deduced from an E map or by an unweighted
difference Fourier synthesis. H atom U’s were assigned as 1.2 Ueq
for adjacent C atoms. Non-H atoms were refined anisotropically.
Successful convergence of the full-matrix least-squares refinement
of F2 was indicated by the maximum shift/error for the final cycle.
Acknowledgment. This research was funded by the
Department of Energy. The authors would like to thank
Christine Boyke and Dorothy Loudermilk for their help in
making the cover graphics.
Supporting Information Available: X-ray crystallographic data
for 1 and (PPN)2[3]. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC051989Z
2412 Inorganic Chemistry, Vol. 45, No. 6, 2006