Simultaneous observation of doubly and triply chloride bridged isomers of an electron-rich ruthenium dimer: Role of dimer geometry in determining reactivity

Article abstract of DOI:10.1021/om050195p

High-yield routes to the dimeric monocarbonyl complexes [RuCl ₂(PP)(CO)]₂ (3; PP = dcypb, 1,4-bis(dicyclohexylphosphino) butane) are established via (a) decarbonylation of mononuclear RuCl ₂(PP)(CO)₂ (4), (b) one-pot carbonylation-decarbonylation of RuCl(PP)(μ-Cl)₃Ru(PP)(N₂) (1), and, most conveniently, (c) phosphine exchange of RuCl₂(PPh₃) ₃ with dcypb, followed by a carbonylation-decarbonylation sequence as in (b), all three steps being carried out in a one-pot procedure. One or three isomers of 3 can be observed by NMR analysis, depending on the solvent medium. A mixture of [RuCl(PP)(CO)]₂(μ-Cl)₂ (transoid, 3a; cisoid, 3b) and ionic {[Ru(PP)(CO)]₂(μ-Cl)₃}Cl (3c) is present in benzene, chlorobenzene, or THF. In CH₂Cl₂ or CDCl₃, only 3c is observed. This represents the first Ru ₂X₄L₄ system (L = L, L′) in which three of the possible edge-bridging and face-bridging isomers can be simultaneously observed and in which their ratio can be manipulated. Reactivity studies indicate that the face-sharing isomer 3c is considerably more stable than its edge-sharing isomers. Transformations of 3 are significantly accelerated by introduction of a donor solvent (methanol, THF). Product identities were established by ¹H, ¹³C, and ³¹P NMR and IR spectroscopy, by microanalysis, and by X-ray crystallography (3a/3b, 3c, 4a/4b).

Full text of DOI:10.1021/om050195p

Organometallics 2005, 24, 4721-4728
4721
Simultaneous Observation of Doubly and Triply
Chloride Bridged Isomers of an Electron-Rich
Ruthenium Dimer: Role of Dimer Geometry in
Determining Reactivity
Samantha D. Drouin, Sebastien Monfette, Dino Amoroso, Glenn P. A. Yap, and
Deryn E. Fogg*
Center for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa,
Ottawa, Ontario, Canada K1N 6N5
Received March 15, 2005
High-yield routes to the dimeric monocarbonyl complexes [RuCl2(PP)(CO)]2 (3; PP ) dcypb,
1,4-bis(dicyclohexylphosphino)butane) are established via (a) decarbonylation of mononuclear
RuCl2(PP)(CO)2 (4), (b) one-pot carbonylation-decarbonylation of RuCl(PP)(µ-Cl)3Ru(PP)-
(N2) (1), and, most conveniently, (c) phosphine exchange of RuCl2(PPh3)3 with dcypb, followed
by a carbonylation-decarbonylation sequence as in (b), all three steps being carried out in
a one-pot procedure. One or three isomers of 3 can be observed by NMR analysis, depending
on the solvent medium. A mixture of [RuCl(PP)(CO)]2(µ-Cl)2 (transoid, 3a; cisoid, 3b) and
ionic {[Ru(PP)(CO)]2(µ-Cl)3}Cl (3c) is present in benzene, chlorobenzene, or THF. In CH2Cl2
or CDCl3, only 3c is observed. This represents the first Ru2X4L4 system (L ) L, L′) in which
three of the possible edge-bridging and face-bridging isomers can be simultaneously observed
and in which their ratio can be manipulated. Reactivity studies indicate that the face-sharing
isomer 3c is considerably more stable than its edge-sharing isomers. Transformations of 3
are significantly accelerated by introduction of a donor solvent (methanol, THF). Product
identities were established by 1H, 13C, and 31P NMR and IR spectroscopy, by microanalysis,
and by X-ray crystallography (3a/3b, 3c, 4a/4b).
Introduction
and amines.18 Our interest in strongly electron-donating
ligands such as alkylphosphines stems from their
capacity to enhance olefin binding and activation.19
Despite the potential for simultaneously enhancing
catalyst reactivity and complex stability, Ru carbonyl
complexes of chelating, electron-rich alkylphosphines
have been underinvestigated, relative to their arylphos-
phine analogues. We recently described20 the impressive
activity of monoruthenium complexes containing a
single CO group and an electron-rich dcypb ligand in
the hydrogenation of benzophenone, a challenging21,22a
diaryl ketone substrate. We now report that decarbon-
ylation of RuCl2(dcypb)(CO)2 (4) enables development
of convenient routes to dimeric 3, effective precursors20
to these hydrogenation catalysts.
Monocarbonyl complexes of ruthenium(II) support a
wide range of catalytic processes. A survey of recent
studies involving the well-known hydrido carbonyl
catalyst RuHCl(PCy3)2(CO), for example, reveals high
activity in olefin hydrogenation and isomerization,1-5
hydrovinylation,6-10 dehydrosilylation,11 silylative
coupling,12-17 and intermolecular coupling of alkenes
* To whom correspondence should be addressed. E-mail: dfogg@
science.uottawa.ca. Fax: (613) 562-5170.
(1) Dinger, M. B.; Mol, J. C. Eur. J. Inorg. Chem. 2003, 2827-2833.
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2002, 344, 153-155.
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Nolan, S. P. Organometallics 2001, 20, 794-797.
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Of fundamental interest is the observation of three
distinct structural isomers of 3: edge-sharing transoid
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Organometallics 2002, 21, 1042-1049.
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10.1021/om050195p CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/01/2005

4722 Organometallics, Vol. 24, No. 20, 2005
Drouin et al.
Table 1. 31P{1H} NMR Data for dcypb Complexesa
Scheme 1
chem shift (ppm) and
coupling constant (Hz)
complex
RuCl(dcypb)(µ-Cl)3Ru(dcypb)(N2) (1)25
60.1, 45.3 (AX, 2JPP ) 40);
49.1, 37.4 (AX, 2JPP ) 26)
59.6, 43.7 (AX, 2JPP ) 40);
50.4, 43.0 (AX, 2JPP ) 23)
RuCl(dcypb)(µ-Cl)3Ru(dcypb)(CO) (2)
transoid-[RuCl(dcypb)(CO)]2(µ-Cl)2 (3a) 40.6 (s) or 34.4 (s)
cisoid-[RuCl(dcypb)(CO)]2(µ-Cl)2 (3b)
[Ru(dcypb)(CO)]2(µ-Cl)3]Cl (3c)b
ccc-RuCl2(dcypb)(CO)2 (4a)
40.6 (s) or 34.4 (s)
55.3, 42.3 (AX, 2JPP ) 23)
39.4, 17.1 (AX, 2JPP ) 22)
13.8 (s)
tcc-RuCl2(dcypb)(CO)2 (4b)
a Values in C6D6 at 121 MHz. b In CDCl3: δP 50.8, 42.5 (AX,
2
2JPP ) 23 Hz); δC 200.3 (t, JPC ) 15 Hz).
systems and indeed very similar to that found for the
dinitrogen analogue 1 (for 31P NMR data, see Table 1).
The IR spectrum of 2 exhibits a single band for
terminally bound CO at 1940 cm-1, a location ca. 40
cm-1 lower in energy than that reported for the corre-
sponding dppb complex (dppb ) 1,4-bis(diphenylphos-
phino)butane),26 consistent with the greater electron
density on the metal in 2. The identity of 2 is further
supported by microanalysis, though measurement of the
13C NMR spectrum was impeded by low solubility.
and cisoid [RuCl(dcypb)(CO)]2(µ-Cl)2 (3a and 3b, re-
spectively), and face-sharing ionic {[Ru(dcypb)(CO)]2(µ-
Cl)3}Cl (3c). These complexes represent incipient sources
of coordinatively unsaturated RuCl2L2(CO), the acces-
sibility of which depends on the lability of the dative
chloride bonds that enable bridging. The catalytic
activity of such coordinatively saturated dimers is thus
(presuming inner-sphere catalysis) a function of the ease
and rapidity with which they can release the mono-
nuclear species. Some of the best examples of chloride-
bridged dimers that exhibit potent catalytic activity are
the Noyori hydrogenation catalyst, formulated as Ru2-
Cl4(binap)2(NEt3) or NH2Et2{[RuCl(binap)]2(µ-Cl)3},22
and Wilkinson’s dimer, [Rh(PPh3)2]2(µ-Cl)2. In olefin
metathesis, triply chloride bridged dimers function as
catalytic sinks,23 although related, doubly bridged spe-
cies can exhibit high activity.24 The accessibility of three
geometrically distinct dimeric species in the present
work permits direct examination of the influence of
dimer geometry on reactivity. The profound influence
of solvent on both stability and preferred geometry, in
turn, has potentially important implications for reactiv-
ity and catalysis.
Puerta, Caulton, and co-workers have discussed the
difficulty of restraining carbonylation in the synthesis
of highly reactive RuX2L2(CO) complexes.27 Synthesis
of 3 presents a parallel problem, differing only in the
fact that the cis disposition of the chloride ligands
(imposed by cis chelation of the diphosphine ligand)
facilitates dimerization. In either case, a limitation on
the source of CO is essential: hence, in earlier work,
we resorted to synthesis of 3 via phosphine exchange
of RuCl2(PPh3)2(CO)(DMF) with dcypb.20 We were
prompted to examine decarbonylation of 4 as a poten-
tially more convenient route to 3 by the serendipitous
crystallization of the latter (as edge-sharing isomers 3a/
3b; vide infra) from benzene solutions of 4 that had been
left to stand for several weeks under N2. X-ray-quality
crystals of mononuclear 4a/4b were obtained from the
same solution over a shorter period: at no point were
signals for 3 observable by 31P NMR analysis of the
mother solution. Precedent exists for photochemical
scissionofRuII-CObondsonirradiationwithultraviolet28-30
or, more rarely, visible28 light. Formation of 3 is
consistent with the pathway shown in Scheme 2, in
which an equilibrium involving loss and recapture of a
CO ligand is disrupted by partial loss of CO from
solution. Such a mechanism underlies the well-estab-
lished isomerization of RuCl2L2(CO)2 complexes,28,31,32
as well as the dimerization chemistry.
Results and Discussion
Routes to [RuCl2(dcypb)(CO)]2 (3). Mononuclear
RuCl2(dcypb)(CO)2 (4) is accessible in near-quantitative
yields by carbonylation of dinuclear RuCl(dcypb)(µ-
Cl)3Ru(dcypb)(N2) (1) under 1 atm of carbon monoxide.25
The reaction is presumed to proceed via RuCl(dcypb)-
(µ-Cl)3Ru(dcypb)(CO) (2) and [RuCl2(dcypb)(CO)]2 (3;
one isomer is shown in Scheme 1). In an attempt to
arrest substitution at the stage of 3, we used a high-
vacuum line equipped with a digital Baratron capaci-
tance manometer to introduce CO in stoichiometric
amounts. These efforts were thwarted by the poor
solubility of 1, which results in a mixture that includes
unreacted 1, 2, and overcarbonylation products 4. The
identity of 2 was confirmed by its independent synthesis
via reaction of 1 with gaseous formaldehyde: this
complex gives rise to two pairs of 31P NMR doublets, in
a pattern characteristic26 of RuCl(PP)(µ-Cl)3Ru(PP)(L)
(26) Joshi, A. M.; Thorburn, I. S.; Rettig, S. J.; James, B. R. Inorg.
Chim. Acta 1992, 198-200, 283-296.
(27) Marchenko, A. V.; Huffman, J. C.; Valerga, P.; Jimenez Tenorio,
M.; Puerta, M. C.; Caulton, K. G. Inorg. Chem. 2001, 40, 6444-6450.
(28) Barnard, C. F. J.; Daniels, J. A.; Jeffery, J.; Mawby, R. J. J.
Chem. Soc., Dalton Trans. 1976, 953-961.
(29) Barnard, C. F. J.; Daniels, J. A.; Jeffery, J.; Mawby, R. J. J.
Chem. Soc., Dalton Trans. 1976, 1861-1864.
(30) Deacon, G. B.; Kepert, C. M.; Sahely, N.; Skelton, B. W.; Spiccia,
L.; Thomas, N. C.; White, A. H. J. Chem. Soc., Dalton Trans. 1999,
275-277.
(31) Krassowski, D. W.; Nelson, J. H.; Brower, K. R.; Hauenstein,
D.; Jacobson, R. A. Inorg. Chem. 1988, 27, 4294-307.
(32) The tcc isomer 4b is stable in CHCl3 at 22 °C but slowly
isomerizes to ccc-4a in benzene or, more rapidly, in THF (90% 4a after
24 h in THF, +10% of an unknown byproduct at δP 20 ppm; 10% 4a
after 18 h in C6D6). Isomer 4a does not isomerize within 24 h in these
solvents.
(23) (a) Amoroso, D.; Yap, G. P. A.; Fogg, D. E. Organometallics
2002, 21, 3335-3343. (b) Amoroso, D.; Snelgrove, J. L.; Conrad, J. C.;
Drouin, S. D.; Yap, G. P. A.; Fogg, D. E. Adv. Synth. Catal. 2002, 344,
757-763.
(24) (a) Volland, M. A. O.; Hansen, S. M.; Rominger, F.; Hofmann,
P. Organometallics 2004, 23, 800-816. (b) Hansen, S. M.; Volland, M.
A. O.; Rominger, F.; Eisentrager, F.; Hofmann, P. Angew. Chem., Int.
Ed. 1999, 38, 1273-1276.
(25) Amoroso, D.; Yap, G. P. A.; Fogg, D. E. Can. J. Chem. 2001,
79, 958-963.

Doubly and Triply Cl Bridged Isomers of a Ru Dimer
Organometallics, Vol. 24, No. 20, 2005 4723
Scheme 2
one-pot carbonylation-decarbonylation sequence. By
stirring 1 under CO in methanol at room temperature
and then heating the reaction to reflux under N2, we
were able to isolate clean 3 in >80% yield from 1. The
one-pot procedure can be extended to include prepara-
tion of 1 via an initial step involving phosphine ex-
change of dcypb with the precursor RuCl2(PPh3)3 (Scheme
3; 72% overall yield). This last modification is particu-
larly convenient, in that it enables synthesis of 3 from
a commonly used and commercially available precursor,
through a three-step reaction sequence, without isola-
tion of intermediates 1 or 4.
Thermolytic cleavage of metal-carbonyl bonds is
more common, though isolated yields of the target
dimers are quite variable (6-94%) for RuCl2L2(CO)2
precursors (L2 ) 2 PMeiPr2,27 2 PMe2Ph,28 2 PMePh2,31
dtbpe,33 dppe;34 dtbpe ) 1,2-bis(di-tert-butylphosphino)-
ethane, dppe ) 1,2-bis(diphenylphosphino)ethane). In
the extreme (as in ctc RuCl2(PMe2Ph)2(CO)2), the M-CO
bonds are not thermally labile,28 owing to the low trans
effect of chloride. In both 4a and 4b, reactivity is
amplified by the positioning of at least one CO ligand
trans to a labilizing phosphine functionality. Accord-
ingly, 4 is readily converted into dimeric 3 in refluxing
methanol and isolated in ca. 80% yield (as the ionic
isomer 3c; vide infra) by crystallization from benzene.
Of interest, particularly given the high yield of 3, is the
observation of 31P NMR singlets at 23.7 and 24.0 ppm
(1:1 CH2Cl2:MeOH; 25% of total integration) prior to
crystallization. An inert-atmosphere MALDI mass spec-
trum of the crude reaction mixture is indistinguishable
from a composite spectrum of 3 + isolated 4: each shows
an isotope pattern corresponding to the cation of 3c and
signals for [4 - Cl - CO] and [4 - (CO)2]. We have been
unable so far to isolate these intermediates, but their
apparent lability, inferred from the high yields of clean
3, and the MALDI evidence indicating a common core
with 4, point toward a species such as RuCl2(PP)(CO)-
(MeOH) (5) or possibly (by analogy to recent dtbpe
chemistry)35 {[Ru(dcypb)(CO)]2(µ-Cl)3}[RuCl3(PP)(CO)].
Formation of a solvento species of type 5 was proposed
in earlier work34 on the basis of IR evidence; however,
addition of MeOH to CD2Cl2 solutions of 3c causes no
change to the 31P NMR spectrum, suggesting that 5 may
be too labile for direct observation. We regard an
alternative assignment as coordinatively unsaturated
RuCl2(dcypb)(CO) as improbable, in view of the ease
with which the latter species may be expected to
dimerize in solution. Pulsed gradient spin-echo (PGSE)
diffusion studies show that “RuCl2(dtbpe)(CO)” (pre-
pared by vacuum thermolysis of RuCl2(dtbpe)(CO)2)
exists as a dimer in solution, despite X-ray evidence for
the monomeric structure in the solid state.35
Scheme 3
Relationship between Edge-Sharing and Face-
Sharing Bioctahedra. An unexpected feature of this
chemistry is the accessibility of three isomeric forms of
3 (a-c; Chart 1), the ratio of which is strongly solvent
dependent.37 We were particularly interested in the
energetic relationship between the edge- and face-
sharing forms of 3, given the prevalence of the chloride-
bridged structural motif in ruthenium chemistry,38 and
the solvent dependence common in catalysis via such
species.39,40
Chart 1
Complex 3 exists as a single isomer in chloroform or
methylene chloride, as we originally reported: key
characterization data include an AX pattern in the 31
P
NMR spectrum and a triplet for the CO ligands in the
13C NMR spectrum. NMR, IR, and mass spectrometric
data do not distinguish, however, between the edge-
sharing dimer originally proposed (3d, Chart 1)20 and
the ionic, face-sharing isomer 3c. We can now unam-
biguously identify the species present in CH2Cl2 as 3c,
on the basis of experiments involving exchange of the
(37) It will be noted that none of the isomers shown for 3 in Chart
1 include a structure in which a CO ligand is trans to phosphine. Such
a configuration is disfavored by the high trans effects of both of these
ligand types (its appearance in 4a and 4b reflects the even greater
thermodynamic undesirability of an alternative containing mutually
trans carbonyl groups). We exclude this structural possibility for 3 on
the basis of 31P NMR chemical shift data (as well as signal multiplici-
ties). As Table 1 indicates, those complexes containing mutually trans
carbonyl and phosphine ligands are characterized by an unusually
high-field 31P NMR chemical shift, which affords a useful spectroscopic
handle for structural elucidation and assignment.
(38) Seddon, E. A.; Seddon, K. R. The Chemistry of Ruthenium;
Elsevier: Amsterdam, 1984.
(39) Bianchini, C.; Barbaro, P.; Scapacci, G.; Zanobini, F. Organo-
metallics 2000, 19, 2450-2461.
(40) See, for example: (a) Nkosi, B. S.; Coville, H. J.; Albers, M. O.;
Gordon, C.; Viney, M.; Singleton, E. J. Organomet. Chem. 1990, 386,
111-119. (b) Fogg, D. E.; James, B. R.; Kilner, M. Inorg. Chim. Acta
1994, 222, 85-90. (c) Zanetti, N. C.; Spindler, F.; Spencer, J.; Togni,
A.; Rihs, G. Organometallics 1996, 15, 860-866.
The success of the methanolic thermolysis route36
enabled us to prepare 3 from N2-bound dimer 1 via a
(33) Gottschalk-Gaudig, T.; Folting, K.; Caulton, K. G. Inorg. Chem.
1999, 38, 5241-5245.
(34) Grocott, S. C.; Wild, S. B. Inorg. Chem. 1982, 21, 3535-3540.
(35) Goicoechea, J. M.; Mahon, M. F.; Whittlesey, M. K.; Kumar, P.
G. A.; Pregosin, P. S. Dalton Trans. 2005, 588-597.
(36) Although control experiments carried out under an N2 atmo-
sphere confirm that carbon monoxide, rather than methanol, is the
source of the CO ligand in 3, use of methanol is critical for clean
reaction. Thermolysis in ethanol, THF, benzene, or toluene results in
contamination by varying amounts of an unknown byproduct, char-
acterized by a 31P NMR singlet at 20 ppm. (Observation of this
byproduct in aromatic solvents precludes assignment as a solvento
species such as 5; vide infra.)

4724 Organometallics, Vol. 24, No. 20, 2005
Drouin et al.
chloride counterion with TlPF6. This reaction effects
quantitative conversion to 3c‚PF6 (isolated in 81% yield)
with no change in the AX pattern for 3c. The face-
sharing structure is confirmed by X-ray analysis.
While 3c is the only species observed in CHCl3 or CH2-
Cl2, two other isomers are also evident in benzene,
chlorobenzene, or THF. These are identified as the
neutral, edge-sharing dimers transoid 3a and cisoid 3b,
also characterized by X-ray analysis following seren-
dipitous crystallization from solutions of 4, as noted
above. 31P NMR spectra of 3 in C6D6 thus reveal two
1:1 singlets (40.6, 34.4 ppm; Table 1) due to the edge-
sharing dimers, as well as the AX spin system due to
3c, integration of which is affected by precipitation. In
chlorobenzene (in which all three isomers are soluble),
their ratio is 1:1:10. We note that the related [RuClL2-
(CO)]2(µ-Cl)2 dimers (L2 ) dtbpe or 2 PMeiPr2)27,33 are
also observed in two isomeric forms. The dtbpe chem-
istry affords a mixture of cisoid and transoid isomers,
as deduced by the observation of two 31P NMR sin-
glets.33,41 For the PMeiPr2 species, an AB pattern is
accompanied (though apparently not invariably)42 by a
singlet presumably due to a cisoid or transoid iso-
mer;27,42 the AB pattern was assigned to an isomer
isostructural with 3d,27 though a cationic complex of the
type 3c could also account for this set of signals. In some
instances, observation of a single infrared ν(CO) stretch-
ing band is adduced as evidence for a C2h, rather than
a C2v, structure (thus 3a, rather than 3b).31,34 However,
mixtures of such isomers in some cases give rise to a
single ν(CO) band,27,33 as indeed is observed for 3.
31P EXSY analysis of 3 in C6D6 revealed a correlation
between the signals for 3a and 3b, indicating that the
edge-sharing isomers are related by a chemical equi-
librium.43 No correlation of these signals with those due
to 3c is evident, indicating that the edge-face inter-
conversion is slow on the NMR time scale. Chemical
evidence, however, confirms that all three isomers exist
in equilibrium (Scheme 4). This evidence includes (a)
the 1H NMR nor the IR spectra differ appreciably among
isomers 3a-c. 13C NMR data for 3a and 3b in C6D6
could not be obtained, owing to crystallization of 3c over
several hours in solution, which rapidly depletes the
solute concentration.
Attempts to quantify the energy barriers relating
3a-c by variable-temperature 31P NMR experiments in
chlorobenzene were hampered by the low solubility of
3c, which unexpectedly precipitated at elevated tem-
peratures. The complexity of the NMR spectrum, result-
ing from dynamic exchange between four sites with
mutual coupling between two (PA and PB of 3c), exceeds
current capabilities for line shape analysis. Some insight
can be gleaned from reactivity studies, however. Com-
plex 3c is considerably less reactive than its edge-
sharing isomers, as indeed the EXSY data suggest. It
is air-stable in solution in CDCl3 over a period of weeks
and remarkably resistant to reaction with carbon mon-
oxide: carbonylation of 3c (as a homogeneous solution
in CDCl3) required 4 days for complete conversion to 4
at 22 °C. The robustness of the Ru2(µ-Cl3) entity is
implied by a number of other reports. Dimer 6, for
example (PP ) (R,R)-3-benzyl-2,4-bis(diphenylphosphi-
no)pentane; Scheme 5), requires several hours to convert
into edge-sharing 7a even at 90 °C in neat DMSO,39
while the vinylidene complex {[Ru(dcypb)(dCd
CHtBu)]2(µ-Cl3)}Cl is only ca. 30% converted to mono-
nuclear species after 48 h under CO in refluxing
chlorobenzene.44 As noted in the Introduction, the triply
bridged alkylidene complexes RuCl(PP)(µ-Cl3)Ru(PP)-
(dCHR) represent a catalyst sink in olefin metathesis:
these species react very sluggishly even toward the
strained, notoriously reactive monomer norbornene,23
in sharp contrast to the high ROMP activity reported
by Hofmann et al. for the doubly bridged {[Ru(PP)-
(CHR)]2(µ-Cl2)}2+ complexes.24 Illustrative of the ther-
modynamic stability of the Ru2(µ-Cl)3 moiety is the very
high efficiency of routes to such species from a range of
precursors, including edge-bridged dimers.45-47 Severin
has contrasted the irreversibility of this reaction with
the lability of the corresponding MM′(µ-Cl)2 products,46
while Caulton and co-workers have likewise noted that
M2(µ-Cl2) units readily undergo bridge-cleaving reac-
tions.48
Scheme 4
Scheme 5
quantitative crystallization of 3c from benzene solutions
containing all three species, (b) observation of all three
species by 31P NMR analysis on redissolving 3c in THF
or chlorobenzene, (c) complete transformation of 3a/3b
into 3c on stripping off the solvent and redissolving in
CDCl3, and (d) quantitative transformation of 3a-c into
3c‚PF6 by reaction with TlPF6, as noted above. Neither
Consistent with the higher reactivity of the edge-
bridged dimers 3a and 3b is the accelerated rate of
carbonylation of 3 in THF, in which all three isomers
(44) Drouin, S. D.; Foucault, H. M.; Yap, G. P. A.; Fogg, D. E.
Organometallics 2004, 23, 2583-2590.
(41) Recent attempts to isolate the dimeric species instead led to
crystallographic characterization of [Ru2(µ-Cl)3(CO)2(PP)2][RuCl3(CO)-
(PP)],35 again pointing toward the thermodynamic stability of the face-
bridged structural motif.
(42) Bustelo, E.; Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. J.
Chem. Soc., Dalton Trans. 1999, 2399-2404.
(43) The EXSY experiment also reveals site exchange between the
inequivalent phosphines of 3c, probably owing to motion of the flexible
dcypb backbone.
(45) Quebatte, L.; Scopelliti, R.; Severin, K. Angew. Chem. Int. Ed.
2004, 43, 1520-1524.
(46) Severin, K. Chem. Eur. J. 2002, 8, 1514-1518. The catalytic
data of ref 45 suggest, however, that heterometallic MM′(µ-Cl)3 dimers
may be more labile.
(47) Gauthier, S.; Quebatte, L.; Scopelliti, R.; Severin, K. Chem. Eur.
J. 2004, 10, 2811-2821.
(48) Coalter, J. N.; Huffman, J. C.; Streib, W. E.; Caulton, K. G.
Inorg. Chem. 2000, 39, 3757-3764.

Doubly and Triply Cl Bridged Isomers of a Ru Dimer
Organometallics, Vol. 24, No. 20, 2005 4725
are present, vs CDCl3 or CH2Cl2 solutions, which
contain only 3c. Use of alcohol solvents similarly
promotes reaction: in both cases, formation of 4 is
complete within hours, as compared to the time scale
of days in CDCl3 noted above. Despite this evidence of
their capacity to destabilize the Ru2(µ-Cl3) moiety,
MeOH and THF appear too labile as ligands toward 3
to permit direct observation of the solvento species by
NMR analysis. Thus, in THF, only signals for 3a-c are
evident; in 1:1 CD2Cl2-MeOH, only 3c is observed
(although signals at ca. 23 ppm appear on heating the
latter; vide supra). Face-sharing dimers, including the
Noyori catalyst described above, have long been known
to exhibit amplified hydrogenation activity in the pres-
ence of alcohols.22,39,40 Bianchini’s group has correlated
this effect with transformation into edge-sharing dimers
(e.g. 7b, Scheme 5) in methanolic solutions: notably,
the triply bridged structure was regenerated on removal
of solvent.39 While equilibria between trichloro- and
dichloro-bridged species have also been noted in pyri-
dine49 (and use of acetonitrile solvent transforms the
dimers into mononuclear species),39,50 the coordinating
power of such donors tends to inhibit catalysis. The
activating effect of alcohol (co)solvents may thus be due,
at least in part, to their capacity to disrupt the triply
bridged unit via formation of labile Ru-O(H)R bonds.
Similar behavior involving water as a transient donor
may possibly account for the recent observation that
catalysis via MM′(µ-Cl)3 dimers is faster in “wet” organic
solvents.47 Conversely, the reactivity (and, by extension,
the catalytic activity) of such dimeric species can be
expected to be at a minimum in media such as neat
CHCl3 and CH2Cl2, in which the unreactive, triply
bridged isomer is strongly preferred.
Figure 1. ORTEP diagram for [RuCl(dcypb)(CO)]2(µ-Cl)2
(3a/3b). Thermal ellipsoids are shown at the 30% prob-
ability level; hydrogen atoms are omitted for clarity. The
predominantly chloride site shown for Cl(1) has a true
occupancy of 70% Cl. Selected bond lengths (Å) and angles
(deg): Ru-P(1), 2.3336(15); Ru-P(2), 2.3645(14); Ru-Cl-
(2), 2.4643(13); P(1)-Ru-Cl(2), 173.27(5); Cl(2)-Ru-Cl-
(2A), 80.91(4); P(2)-Ru-Cl(2A), 168.83(5); Ru-Cl(2)-
Ru(A), 99.09(4); P(1)-Ru-P(2), 98.61(5).
Molecular Structures of 3a/3b, 3c, and 4a/4b.
ORTEP representations, with relevant bond lengths and
angles, are shown for 3a/3b and 3c in Figures 1 and 2
and for 4a/4b in Figure 3. Bond distances and angles
for 3c are given in Table 2. The coordination about each
Ru center is distorted octahedral. Complexes 3a/3b and
3c are edge-sharing and face-sharing bioctahedra, con-
taining two metal centers bridged by two and three
chloride ligands, respectively. Structures 3a/3b and 4a/
4b are located around a crystallographic center of
symmetry, and the terminal Cl(1) and CO ligands are
mutually disordered. Consequently, the X-ray data do
not distinguish between transoid and cisoid isomers 3a
and 3b (as also noted for the edge-sharing dimer [RuCl-
(PtBu2Me)2(CO)]2(µ-Cl)227) or between ccc-4a and tcc-4b,
and bond distances and angles involving the disordered
atoms are not meaningful.
Figure 2. ORTEP diagram for {[Ru(dcypb)(CO)]2(µ-Cl)3}-
Cl (3c). Thermal ellipsoids are shown at the 30% prob-
ability level; hydrogen atoms, chloride counterion, and
cocrystallized solvent molecules are omitted for clarity.
Selected bond lengths and angles are summarized in Table
2.
are isostructural with 3a or 3b, though [RuCl(NN)-
(CO)]2(µ-Cl)2 (NN ) phen, di-2-pyridyl ketone)30 reveals
a structure corresponding to 3d. The face-sharing
structural motif is considerably more common. Finally,
4a is one of a small class of Ru(II) bis-CO compounds
containing cis phosphines;33,34,55,56 two other complexes
of this type have been characterized crystallographi-
cally.33,57
A search of the Cambridge Crystallographic Database
suggests that the unsupported, edge-bridged structural
motif represented by [RuCl2LL′L′′](µ-Cl)2 (where any of
L, L′, and L′′ may be identical) is rather rare: only a
handful of examples are found,27,30,33,51-54 most of which
(49) MacFarlane, K. S.; Thorburn, I. S.; Cyr, P. W.; Chau, D. E. K.
Y.; Rettig, S. J.; James, B. R. Inorg. Chim. Acta 1998, 270, 130-144.
(50) Fogg, D. E.; James, B. R. Inorg. Chem. 1997, 36, 1961-1966.
(51) Chung, M.-K.; Ferguson, G.; Robertson, V.; Schlaf, M. Can. J.
Chem. 2001, 79, 949-957.
The increased splay of the bridging chlorides in 3a/
3b vs 3c (Ru-Cl(2)-Ru(A) ) 99.09(4)° vs a range of
(55) Whittlesey, M. K.; Perutz, R. N.; Virrels, I. G.; George, M. W.
Organometallics 1997, 16, 268-274.
(56) Mague, J. T.; Mitchener, J. P. Inorg. Chem. 1972, 11, 2714-
2720.
(57) De Araujo, M. P.; Porcu, O. M.; Batista, A. A.; Oliva, G.; Souza,
D. H. F.; Bonfadini, M.; Nascimento, O. R. J. Coord. Chem. 2001, 54,
81-94.
(52) Teulon, P.; Roziere, J. J. Organomet. Chem. 1981, 214, 391-
397.
(53) Southern, T. G.; Dixneuf, P. H.; Le Marouille, J.-Y.; Grandjean,
D. Inorg. Chem. 1979, 18, 2987-2991.
(54) Cotton, F. A.; Matusz, M.; Torralba, R. C. Inorg. Chem. 1989,
28, 1516-1520.

4726 Organometallics, Vol. 24, No. 20, 2005
Drouin et al.
solution, enabling examination of the relationship be-
tween bridging geometry and reactivity. Face-sharing
{[Ru(dcypb)(CO)]2(µ-Cl)3}Cl (3c) is quite unreactive,
relative to its edge-bridged isomers, as evidenced by its
stability toward air and its slow rate of carbonylation.
These observations are of broader interest in context of
catalysis mediated by Ru2(µ-Cl)3 species. Dimerization
can, of course, provide a resting state in catalysis (i.e. a
“protected” reservoir of the catalytically active mono-
mer). Alternatively, however, it may represent a deac-
tivation pathway, or catalyst sink. The catalytic utility
of a coordinatively saturated dimer will in general be
limited by its kinetic capacity to provide a binding site
via liberation of the coordinatively unsaturated mono-
mer. The higher reactivity of edge-bridged dimers thus
reflects the greater lability of the bridging chloride
donors. Conversely, the stability of the Ru2(µ-Cl)3 unit
may point toward a general obstacle in catalysis medi-
ated by such dimers. The capacity of labile donors such
as alcohols or ethers to disrupt the triply bridged unit
suggests a straightforward means of amplifying reactiv-
ity, as well as a partial explanation for the solvent
dependence of catalysis mediated by such species.
Figure 3. ORTEP diagram for RuCl2(dcypb)(CO)2 (4a/4b).
Thermal ellipsoids are shown at the 30% probability level;
solvate molecules and hydrogen atoms are omitted for
clarity. The predominantly chloride site shown as Cl(1) has
a true occupancy of 66% Cl. Selected bond lengths (Å) and
angles (deg): Ru-P(1), 2.4101(10); Ru-P(2), 2.4816(10);
Ru-Cl(2), 2.4350(10); P(1)-Ru-P(2), 100.50(3).
Table 2. Selected Bond Lengths (Å) and Angles
(deg) for Complex 3c
Bond Distances
Ru(1)-P(1)
Ru(1)-P(2)
Ru(2)-P(3)
Ru(2)-P(4)
Ru(1)-C(1)
Ru(2)-C(2)
C(1)-O(1)
2.335(4)
2.352(4)
2.346(4)
2.327(3)
1.856(15)
1.812(14)
1.124(14)
C(2)-O(2)
1.163(14)
2.478(3)
2.501(3)
2.481(3)
2.485(3)
2.463(3)
2.495(3)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-Cl(3)
Ru(2)-Cl(1)
Ru(2)-Cl(2)
Ru(2)-Cl(3)
Experimental Section
Unless otherwise stated, all operations were performed
under N2 using standard Schlenk or drybox techniques. Dry,
oxygen-free solvents were obtained using an Anhydrous
Engineering solvent purification system and stored over Linde
4 Å molecular sieves. CDCl3 and C6D6 were dried over
activated sieves (Linde 4 Å) and degassed by consecutive
freeze/pump/thaw cycles. Ru2Cl4(dcypb)2(N2) (1)25 was prepared
according to literature procedures. RuCl3‚3H2O was purchased
from Strem Chemicals. CO was obtained from Praxair and
used as received. NMR spectra were recorded on a Varian XL-
300 spectrometer or Bruker AMX-500 spectrometer. Peaks are
reported in ppm, relative to 85% H3PO4 (31P) or the deuterated
solvent (1H, 13C). Infrared spectra were recorded on a Bomem
MB100 IR spectrometer. Microanalytical data were obtained
using a Perkin-Elmer Series II CHNS/O instrument.
Attempted Stoichiometric Carbonylation of RuCl-
(dcypb)(µ-Cl)3Ru(dcypb)(N2) (1). Attempts to prepare 3 via
reaction of 1 with stoichiometric amounts of CO were unsuc-
cessful. In a representative procedure, 1 (23.0 mg, 18.1 µmol)
was suspended in 5.00 mL of C6D6, in a flask with total
internal volume 25.96 mL. The flask was connected to a high-
vacuum line equipped with a digital Baratron capacitance
manometer. The suspension was frozen with liquid nitrogen
and the flask evacuated to an ultimate vacuum of 38 Torr.
Carbon monoxide gas (32 Torr) was then transferred from a
glass bulb, following which the system was sealed and warmed
to 22 °C. The resulting suspension was stirred for 24 h, over
which time the suspension partially cleared, though some
orange-brown solid remained undissolved. 31P{1H} NMR analy-
sis of an aliquot at this time revealed the presence of 1 (∼5%
integrated intensity), 2 (5%), 4a (30%), 4b (30%), and un-
identified product(s) characterized by singlets at 22.7 and 22.8
ppm (30%). These integration ratios are not quantitatively
significant, owing to the presence of undissolved 1 and/or 2.
RuCl(dcypb)(µ-Cl)3Ru(dcypb)(CO) (2). Formaldehyde
gas, generated by heating paraformaldehyde at 180 °C under
a stream of N2, was bubbled through a suspension of 1 (50
mg, 0.79 µmol) in 10 mL of benzene. After 30 min, the supply
of formaldehyde was stopped, the system sealed, and the
suspension stirred for 24 h. Concentration and addition of
hexanes afforded an orange-brown solid which was filtered off,
washed with hexanes (3 × 5 mL), and dried under vacuum.
The poor solubility of the product in all organic solvents
Bond Angles
C(1)-Ru(1)-P(1)
C(1)-Ru(1)-P(2)
C(2)-Ru(2)-P(4)
91.2(4)
91.9(4)
90.4(4)
P(2)-Ru(1)-Cl(1)
P(1)-Ru(1)-Cl(3)
P(2)-Ru(1)-Cl(3)
96.09(12)
98.45(12)
95.53(12)
92.21(12)
92.1(4)
P(1)-Ru(1)-Cl(1) 171.52(12) P(1)-Ru(1)-P(2)
P(2)-Ru(1)-Cl(2) 172.02(13) C(2)-Ru(2)-P(3)
P(4)-Ru(2)-Cl(1) 171.32(12) O(1)-C(1)-Ru(1) 173.2(13(1)
P(3)-Ru(2)-Cl(3) 170.25(12) O(2)-C(2)-Ru(2) 175.4(12)
85.57(10)-85.83(10)°, respectively) reflects the greater
compactness of the face-sharing structure. This effect
is manifested in a significant decrease in the Ru-Ru
distance in 3c, relative to that in 3a/3b (3.384(4) Å vs
3.7730(13) Å). Structure 3c exhibits the compression of
cofacial Cl-Ru-Cl angles (76.93(11)-80.62(11)°) usual
for Ru2(µ-Cl)3 face-sharing bioctahedra;58 similarly,
P-Ru-P angles (average 92.7°) compare well with those
in face-bridged Ru2Cl5(dcypb)2 (average 94.4°)25 but are
significantly smaller than those for 3a/3b and 4a/4b
(98.61(5) and 100.50(3)°, respectively). Ru-Cl and Ru-P
bond lengths fall within the usual ranges.58 While C-O,
Ru-C, and Ru-Cl(1) bond distances for 3a/3b and 4a/
4b are obscured by Cl/CO disorder, C-O bond lengths
in 3c (average 1.144 Å) are comparable to those in
mer,cis-RuCl2(PPh2Me)3(CO)31 (1.167 Å) and ctc-
[RuCl2(PhCH2PPh2)2(CO)2] (1.13 Å).58c
Conclusions
The foregoing describes convenient routes into mono-
carbonyl ruthenium complexes containing the basic,
bulky diphosphine dcypb. Dimeric [RuCl2(PP)(CO)]2 can
be observed as three geometrically distinct isomers in
(58) (a) Cotton, F. A.; Torralba, R. C. Inorg. Chem. 1991, 30, 2196-
2207. (b) Rhodes, L. F.; Sorato, C.; Venanzi, L. M.; Bachechi, F. Inorg.
Chem. 1988, 27, 604-610. (c) Wilkes, L. M.; Nelson, J. H.; Mitchener,
J. P.; Babich, M. W.; Riley, W. C.; Helland, B. J.; Jacobson, R. A.;
Cheng, M. Y.; Seff, K.; McCusker, L. Inorg. Chem. 1982, 21, 1376-
1382.

Doubly and Triply Cl Bridged Isomers of a Ru Dimer
Organometallics, Vol. 24, No. 20, 2005 4727
Table 3. Summary of Crystallographic Data and Structure Refinement Details for
[RuCl(dcypb)(CO)]2(µ-Cl)2 (3a/3b), {[Ru(dcypb)(CO)]2(µ-Cl)3}Cl (3c), and RuCl2(dcypb)(CO)2 (4a/4b)
3a/3b
3c
4a/4b
empirical formula
formula wt
temp, K
C
58H104Cl4O2P4Ru2
C82H128Cl4O2P4Ru2
1613.66
C42H64Cl2O2P2Ru
834.84
1301.23
203(2)
0.710 73
monoclinic, C2/c
203(2)
203(2)
wavelength, Å
cryst syst, space group
unit cell dimens
a, Å
0.710 73
monoclinic, P21/n
0.710 73
orthorhombic, Pna21
26.508(3)
90
14.576(2)
109.078(2)
17.037(2)
90
6221.2(14)
4; 1.389
0.799
2736
0.1 × 0.1 × 0.1
1.62-28.84
-35 e h e 33
0 e k e 19
0 e l e 22
24 591/7487 (R(int) ) 0.1291)
28.84; 91.9
15.3703(19)
90
15.560(1)
90
11.522(1)
90
23.213(2)
90
4161.9(6)
4; 1.332
0.615
1760
0.2 × 0.2 × 0.2
1.75-28.82
0 e h e 20
0 e k e 15
-30 e l e 31
32 606/9930 (R(int) ) 0.0506)
28.82; 94.8
R, deg
b, Å
18.721(2)
â, deg
99.027(3)
c, Å
28.156(4)
γ, Å
90
V, Å3
8001.7(17)
Z; calcd density, g/cm3
abs coeff, mm-1
F(000)
4; 1.339
0.636
3408
cryst size, mm
θ range for data collecn. deg
limiting indices
0.05 × 0.05 × 0.05
1.31-20.81
-15 e h e 15
0 e k e 18
0 e l e 28
63 347/8378 (R(int) ) 0.4158)
20.81; 100.0
no. of rflns collected/unique
completeness to θ; %
abs cor
max, min transmission
refinement method
semiempirical from equivalents
0.928 076, 0.779 953
full-matrix least squares on F2
8378/0/399
0.928 077, 0.742 233
0.928 076, 0.731 149
no. of data/restraints/params
goodness of fit on F2
final R indices (I >2σ(I))a
R indices (all data)
7487/0/316
1.015
R1 ) 0.0567, wR2 ) 0.1016
R1 ) 0.1325, wR2 ) 0.1142
0.889, -1.025
9930/1/442
1.064
R1 ) 0.0449, wR2 ) 0.1040
R1 ) 0.0583, wR2 ) 0.1072
0.933, -0.904
1.002
R1 ) 0.0704, wR2 ) 0.1533
R1 ) 0.1639, wR2 ) 0.1935
0.865, -0.773
largest diff peak, hole, e/Å3
2
2
a Definitions of R indices: R1 ) ∑(Fo - Fc)/∑(Fo); wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]]1/2
.
precluded reprecipitation or measurement of the 13C NMR
is rapidly depleted by crystallization of 3c (identified by X-ray
diffraction), precluding measurement of the 13C{1H} NMR
spectrum. (iii) In chlorobenzene: 31P{1H} NMR (C6H5Cl, δ) 52.2
(d, 3c, 2JPP ) 25 Hz), 42.5 (d, 3c, 2JPP ) 25 Hz), 39.0 (s, 3a or
3b), 32.7 (s, 3a or 3b).
1
spectrum. Yield: 40 mg (80%). H NMR (CDCl3): δ 0.7-3.1
(br m, CH2, Cy of dcypb). 31P{1H} NMR (C6D6): δ 59.6 (d, 2JPP
) 40 Hz, 1P), 50.4 (d, 2JPP ) 23 Hz, 1P), 43.7 (d, 2JPP ) 40 Hz,
2
1P), 43.0 (d, JPP ) 23 Hz, 1P). IR (Nujol, cm-1): ν(CO) 1940
(m). Anal. Calcd for C57H104OCl4P4Ru2: C, 53.77; H, 8.23.
Found: C, 53.21; H, 8.27.
One-Pot Synthesis of 3c from RuCl2(PPh3)3. Addition
of solid dcypb (104 mg, 0.23 mmol) to a solution of RuCl2(PPh3)3
(200 mg, 0.21 mmol) in 5 mL of benzene caused an instanta-
neous color change from dark brown to green. The solution
was stirred under N2 for 8 h, following which MeOH (20 mL)
was added to the orange suspension and the atmosphere was
exchanged for CO. A clear yellow solution formed on stirring
overnight. This was heated to reflux under N2 for 8 h, stripped
of solvent, and taken up in benzene, from which clean 3c
crystallized as above. Yield after filtering and washing with
diethyl ether (5 × 5 mL): 99 mg (72%).
[RuCl(dcypb)(CO)]2(µ-Cl)2 (3).20 (a) An orange suspension
of 1 (50 mg, 0.039 mmol) in 20 mL of methanol was stirred
under 1 atm of CO for 18 h, following which the yellow-white
suspension (100% tcc 4b, as judged by 31P NMR analysis of
an aliquot in CDCl3) was heated to reflux under N2 for 16 h.
The solvent was then removed completely, and the residual
solid was taken up in benzene to crystallize 3c. This causes
the disappearance of “impurities”, possibly RuCl2(dcypb)(CO)-
(MeOH) (5), present in the crude mixture. 31P NMR in 1:1 CH2-
Cl2/MeOH: 23.7 (s), 24.0 ppm (s); 25% of total integration.
Inert-atmosphere MALDI MS (CH2Cl2; pyrene matrix): m/z
1264.9 (cation of 3c), 621.8 ([4 - (CO)2]), 614.8 ([4 - Cl - CO]).
Yield of 3c after washing with benzene (2 mL) and Et2O (4 ×
2 mL) and drying under vacuum: 42 mg (82%). A control
experiment carried out by refluxing 1 in MeOH under N2
showed no carbonylation.
{[Ru(dcypb)(CO)]2(µ-Cl)3}PF6 (3c(PF6)). A solution of
TlPF6 (20 mg, 0.059 mmol) in 2 mL of THF was added to a
suspension of 3 (75 mg, 0.12 mmol of Ru) in 6 mL of THF.
The suspension was stirred for 16 h and then filtered through
Celite and neutral alumina. The filtrate was concentrated and
Et2O added to precipitate a yellow solid. This was filtered off,
washed with Et2O and hexanes, and dried under vacuum.
Recrystallization from THF/Et2O afforded clean 3c(PF6).
Yield: 66 mg (81%). 31P{1H} NMR (acetone-d6, δ): 52.7 (d, 2JPP
) 24 Hz), 41.6 (d, 2JPP ) 24 Hz), -146.3 (sept, 1JPF ) 708 Hz).
1H NMR (acetone-d6, δ): 1.10-2.59 (br m, CH2, Cy of dcypb).
Spectra in CDCl3 are identical with those for 3c, neglecting
the PF6 septet. IR (Nujol, cm-1): ν(CO) 1956 (s). Anal. Calcd
for C58H104O2Cl3P5F6Ru2: C, 49.38; H, 7.43. Found: C, 49.63;
H, 7.53.
(b) A solution of 4a/4b (95:5) (42 mg, 0.062 mmol) in 20 mL
of MeOH was refluxed under N2 for 16 h. The solvent was
removed under high vacuum to yield a yellow product consist-
ing of solely 3c (31P NMR). Clean 3c crystallized on taking up
the oil in benzene. Isolated yield: 31 mg (78%). The isomeric
form of 3 is solvent-dependent. (i) In CDCl3: 31P{1H} NMR
2
2
(CDCl3, δ) 50.8 (d, JPP ) 23 Hz, 3c), 42.5 (d, JPP ) 23 Hz,
3c); 13C{1H} NMR (CDCl3, δ) 200.3 (t, JPC ) 15 Hz, CO, 3c).
2
1H NMR (CDCl3, δ) 1.10-2.53 (br m, CH2, Cy of dcypb); IR
RuCl2(dcypb)(CO)2 (ccc, 4a; tcc, 4b). We earlier described
formation of a 1:4 mixture of 4a/4b by reaction of 1 with CO
in THF over 24 h.25 The same reaction in EtOH permits
isolation of 4b. Treatment of an orange suspension of 1 (50
mg, 0.039 mmol) in 20 mL of EtOH with CO caused a color
(Nujol, cm-1) ν(CO) 1958. (ii) In C6D6: 31P{1H} NMR (C6D6, δ)
2
2
55.3 (d, 3c, JPP ) 23 Hz), 42.3 (d, 3c, JPP ) 23 Hz), 40.6 (s,
3a or 3b), 34.4 (s, 3a or 3b). 1H NMR and IR spectra are
indistinguishable from those in (i). The concentration of solute

4728 Organometallics, Vol. 24, No. 20, 2005
Drouin et al.
change to pale yellow over 18 h at room temperature. The
reaction mixture was cooled to -35 °C, and the precipitate was
filtered off and washed with EtOH, Et2O, and then hexanes.
Yield of clean 4b after drying under vacuum: 20 mg (38%). A
second crop (1:9 mixture of 4a/4b) was obtained by concentra-
tion and addition of cold pentane. Yield after washing with
cold pentane and drying under vacuum: 29 mg (92% total).
Spectroscopic data (see Table 1) agree with values previously
reported.25 A 31P-31P EXSY experiment shows no correlation
between the two isomers.
Solvent Effects in Carbonylation of 3c. A solution of
cationic 3c (45 mg, 0.069 mmol Ru) in 10 mL of CHCl3 was
stirred under 1 atm of CO at room temperature. Complete
conversion to RuCl2(dcypb)(CO)2 required 4 days (31P NMR).
Concentration and addition of cold pentane produced a pale
yellow powder (95:5 4a/4b), which was filtered off, washed with
pentane, and dried under vacuum. Yield: 42 mg (89%). An
identical experiment carried out in 10 mL of THF or EtOH
showed complete conversion to 4 within 14 or 18 h, respec-
tively.
Crystallographic Analysis of [RuCl(dcypb)(CO)]2(µ-
Cl)2 (3a/3b), {[Ru(dcypb)(CO)]2(µ-Cl)3}Cl (3c), and RuCl2-
(dcypb)(CO)2 (4a/4b). X-ray-quality crystals of 3a/3b depos-
ited under an N2 atmosphere over 1 month from a benzene
solution of 4a and 4b (as judged by 31P{1H} NMR analysis,
which revealed no signals for 3a-c). Diffraction-quality crys-
tals of 4a/4b were obtained from the same solution over a
shorter period. Complex 3c spontaneously crystallized at room
temperature from a C6D6 solution containing 3a-c. Details
of crystal data and data refinement are collected in Table 3.
Appropriate crystals were selected, mounted on thin glass
fibers using viscous oil, and cooled to the data collection
temperature. Data were collected on a Bruker AX SMART 1k
CCD diffractometer using 0.3° ω scans at 0, 90, and 180° in φ.
Unit-cell parameters were determined from 60 data frames
collected at different sections of the Ewald sphere. Semiem-
pirical absorption corrections based on equivalent reflections
were applied.59 For 3c, no data were observed beyond 42° (2θ),
and the data set was truncated accordingly. Systematic
absences in the diffraction data and unit-cell parameters were
consistent with Cc and C2/c for 3a/3b, Pna21 and Pnma
(Pnam) for 4a/4b, and, uniquely, with space group P21/n (No.
14) for 3c. Solution in C2/c for 3a/3b and Pna21 for 4a/4b
yielded chemically reasonable and computationally stable
results of refinement. The packing diagram for 4a/4b did not
reveal any overlooked crystallographic symmetry, and the
absolute structure parameter refined to nil, indicating that
the true hand of the data had been determined. The structures
were solved by direct methods, completed with difference
Fourier syntheses, and refined with full-matrix least-squares
procedures based on F2. The compound molecule for 3a/3b is
located on a 2-fold axis, and a chloride ligand is found
disordered with a carbonyl ligand. A chloride ligand is likewise
found to be disordered in three positions with two carbonyl
ligands in 4a/4b. The disordered, artificially shortened car-
bonyl ligands were constrained with an idealized C-O bond
distance of 1.145 Å. The isotropic parameters were kept
identical for the same atoms in the different disordered
positions, and the site occupancies of each contributing
disordered position were refined to 72/28 for 3a/3b and 66/18/
16 for 4a/4b. Two symmetry-unique benzene solvent molecules
were found cocrystallized in 4a/4b. For 3c, a chloride coun-
terion and four cocrystallized benzene solvent molecules were
located in the asymmetric unit. To conserve a favorable data
to parameter ratio, all of the non-carbonyl carbon atoms in 3c
were refined isotropically and all phenyl groups were refined
as idealized, rigid, flat hexagons; all non-hydrogen, non-carbon
atoms and the carbonyl carbon atoms were refined with
anisotropic displacement coefficients. All hydrogen atoms were
treated as idealized contributions. All scattering factors are
contained in the SHELXTL 6.12 program library.60
Acknowledgment. This work was supported by the
Natural Sciences and Engineering Research Council of
Canada, the Canada Foundation for Innovation, and the
Ontario Innovation Trust.
Supporting Information Available: ORTEP diagrams
and tables of crystal data collection and refinement param-
eters, atomic coordinates, bond lengths and angles, anisotropic
displacement parameters, and hydrogen coordinates for 3a/
3b, 3c‚4C6H6, and 4a/4b‚2C6H6; crystal data are also available
as CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org. The supplementary crystal-
lographic data for this paper also appear in CCDC publications
# 264682 (3a/3b), 183209 (3c), and 264681 (4a/4b). These data
can be obtained free of charge from the Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
OM050195P
(60) Sheldrick, G. M. SHELXTL 6.12; Bruker AXS, Madison, WI,
2001.
(59) Blessing, R. Acta Crystallogr. 1995, A51, 33.