Synthesis and protonation studies of Cp*Os(dppe)H: Kinetic versus thermodynamic control

Article abstract of DOI:10.1021/om8000235

The previously undescribed complex Cp*Os(dppe)H was synthesized starting from either K₂OsX₆ salts or H ₂OsBr₆ and characterized together with its precursors Cp*Os(COD)X (X = Cl, Br). Protonation of 1 by HBF

Full text of DOI:10.1021/om8000235

Organometallics 2008, 27, 3307–3311
3307
Synthesis and Protonation Studies of Cp*Os(dppe)H: Kinetic versus
Thermodynamic Control
Pavel A. Dub,†,‡ Natalia V. Belkova,*,† Konstantin A. Lyssenko,† Gleb A. Silantyev,†
Lina M. Epstein,† Elena S. Shubina,† Jean-Claude Daran,‡ and Rinaldo Poli*,‡
A. N. NesmeyanoV Institute of Organoelement Compounds, Russian Academy of Sciences, 28 VaViloV
Street, 119991 Moscow, Russian Federation, and Laboratoire de Chimie de Coordination, UPR CNRS
8241 lie´e par conVention a` l’UniVersite´ Paul Sabatier et a` l’Institut National Polytechnique de Toulouse,
205 Route de Narbonne, 31077 Toulouse Cedex, France
ReceiVed January 9, 2008
(1) through Cp*Os(COD)X (X ) Cl, Br) intermediates and the
results of its protonation by HBF4 · Et2O in CD2Cl2. An
improved preparation of the K2OsX6 precursors is also described.
(a) Synthesis of Cp*Os(dppe)H. An apparently easy syn-
thetic route (“one-pot” procedure, use of nontoxic potassium
osmate, K2OsO2(OH)4, and aqueous ethanol, higher yield) was
reported recently6 for the synthesis of some C5R5-containing
(R ) H, Me) osmium complexes (Scheme 1, X ) Cl). However,
the presumed identity of intermediates A and B in Scheme 1
was not confirmed. Upon repeating this procedure, we found
that the addition of EtOH allows reduction of the reflux time to
20 min for the complete conversion of K2OsO2(OH)4 to species
A.7 In addition, we have confirmed the identity of intermediate
Summary: The preViously undescribed complex Cp*Os(dppe)H
was synthesized starting from either K2OsX6 salts or H2OsBr6
and characterized together with its precursors Cp*Os(COD)X
(X ) Cl, Br). Protonation of 1 by HBF4 · Et2O was studied in
CD2Cl2 at 193 K and was found to lead exclusiVely to
cis-[Cp*Os(dppe)(H)2]+BF4-, which irreVersibly transforms
-
into trans-[Cp*Os(dppe)(H)2]+BF4 aboVe 230 K.
A considerable amount of information has been accumulated
since the 1980s on proton transfer to transition metal hydrides.
Classical polyhydrides may be obtained indirectly through initial,
kinetically favored proton transfer at the hydride site, followed
by rearrangement of the dihydrogen intermediate to the ther-
modynamically more stable polyhydride.1 However, the question
of how the nature of the metal center and the electronic and
steric properties of the ligands in its coordination sphere affect
the choice of the kinetic protonation site (metal or hydride) is
not yet fully understood. Thus, for the recently studied
Cp*M(dppe)H complexes (M ) Fe,2 Ru3) proton transfer yields
initially (η2-H2)-complexes, which convert quantitatively into
the corresponding trans-dihydrides upon warming. This isomer-
ization process involves ligand reorganization without interme-
diates.4 Notably, no stationary point was found corresponding
to a putative cis-dihydride isomer.
8
A as K2OsCl6 and B as Cp*Os(COD)Cl, 2,9 as well as
structurally characterized the latter by X-ray diffraction (Figure
1). However, compound 2 could not be obtained in acceptable
yields in our hands. A significant amount of K2OsCl6, insoluble
in EtOH, often remained unreacted.
The application of the same strategy to the preparation of
the bromide compound, Cp*Os(COD)Br (3), by using HBr
instead of HCl (Scheme 1, X ) Br) turned out to be quite
straightforward, faster (ca. 3 h for Br vs 30 h for Cl), and
reproducible. The brown-black residue obtained from potassium
osmate and concentrated HBr corresponds to K2OsBr6. This
procedure yields the hexabromoosmate(IV) salt in good yields,
being considerably more convenient than those reported in the
literature.7,10 However the overall route suffers from a quite
low yield of compound 3.
Thus, despite the appealing use of the nontoxic potassium
osmate as a starting material, both chloro and bromo synthetic
pathways to Cp*Os(dppe)X complexes do not appear sufficiently
efficient; therefore the original, Girolami’s protocol11,12 (Scheme
2) was used in our further work. However, our improved
syntheses of K2OsX6 (X ) Cl, Br) may become advantageous
for other synthetic applications.
From this point of view the protonation of the yet unreported
Cp*Os(dppe)H complex would be of special interest because
it would complete the series of group 8 Cp*M(dppe)H com-
plexes and because of the reported5 ability of some CpOs(P-P)H
complexes [P-P ) dppm, dppe, dppp] to form cis-dihydrides
[CpOs(P-P)(H)2]+ upon protonation by HBF4 · Et2O at -78 °C
in CD2Cl2. Herein, we report the preparation of Cp*Os(dppe)H
* Corresponding authors. Tel: +7-499-1356448. Fax: +7-499-1355085.
E-mail: nataliabelk@ineos.ac.ru.
† A. N. Nesmeyanov Institute of Organoelement Compounds.
‡ UPR CNRS 8241.
(1) (a) Parkin, G.; Bercaw, J. E. J. Chem. Soc., Chem. Commun. 1989,
255–257. (b) Chinn, M. S.; Heinekey, D. M. J. Am. Chem. Soc. 1990, 112,
5166–5175. (c) Jia, G.; Lough, A. J.; Morris, R. H. Organometallics 1992,
11, 161–171. (d) Hamon, P.; Toupet, L.; Hamon, J.-R.; Lapinte, C.
Organometallics 1992, 11, 1429–1431. (e) Hamon, J. R.; Hamon, P.; Toupet,
L.; Costuas, K.; Saillard, J. Y. C. R. Chim. 2002, 5, 89–98.
(2) Belkova, N. V.; Revin, P. O.; Epstein, L. M.; Vorontsov, E. V.;
Bakhmutov, V. I.; Shubina, E. S.; Collange, E.; Poli, R. J. Am. Chem. Soc.
2003, 125, 11106–11115.
(6) Perkins, G. J.; Bruce, M. I.; Skelton, B. W.; White, A. H. Inorg.
Chim. Acta 2006, 359, 2644–2649.
(7) The same is true for the OsO4 reduction by concentrated HCl, which
is usually done in the presence of Fe(II) [ Dwyer, F. P.; Hogarth, J. W.
Inorg. Synth. 1957, 5, 206. ], but could be facilitated by addition of
EtOHGilchrist, R. Bur. Stand. J. Res. 1932, 9, 282. Turner, A. G.; Clifford,
A. F.; Ramachandra; Rao, C. N. Anal. Chem. 1958, 30, 1708–1709.
(8) See Supplementary Information for details.
(3) Belkova, N. V.; Dub, P. A.; Baya, M.; Houghton, J. Inorg. Chim.
Acta 2007, 360, 149–162.
(9) Liles, D. C.; Shaver, A.; Singleton, E.; Wiege, M. B. J. Organomet.
Chem. 1985, 288, C33–C36.
(4) Baya, M.; Maresca, O.; Poli, R.; Coppel, Y.; Maseras, F.; Lledo´s,
A.; Belkova, N. V.; Dub, P. A.; Epstein, L. M.; Shubina, E. S. Inorg. Chem.
2006, 45, 10248–10262.
(10) Lott, K. A. K.; Symons, M. C. R. J. Chem. Soc. 1960, 973–976.
(11) Gross, C. L.; Girolami, G. S. Organometallics 1996, 15, 5359–
5367.
(5) Jia, G.; Ng, W. S.; Yao, J.; Lau, Ch.-P.; Chen, Y. Organometallics
1996, 15, 5039–5045.
(12) Gross, C. L.; Brumaghim, J. L.; Girolami, G. S. Organometallics
2007, 26, 2258–2265.
10.1021/om8000235 CCC: $40.75
2008 American Chemical Society
Publication on Web 05/30/2008

3308 Organometallics, Vol. 27, No. 13, 2008
Notes
Scheme 1
Compound Cp*Os(dppe)H (1)17 (Figure 2) also adopts a
Scheme 2
three-legged piano stool geometry, the H and dppe ligands taking
the place of the halogen and COD ligands in the above-described
structures. Curiously, except for the P-Os-P angle, which is
much narrower (by almost 6°), the bond distances and angles
are almost identical to those of the previously reported
Cp*Ru(dppe)H compound.8,18 Another feature of this structure
is a short contact (2.32 Å) between Os-H and one ortho-CH
proton (bonded to atom C4),19 which gives rise to the negative
1H NOE and the cross-peak in the 2D (1H-1H) ROESY spectra
in solution.8
The new osmium(II) hydride complex Cp*Os(dppe)H (1) was
obtained as a green-yellow solid in 73% yield by treatment of
Cp*Os(dppe)X (with X ) either Cl or Br) with MeONa/MeOH.
The main NMR spectroscopic features of 1 are given in Table
1.13 Like its ruthenium analogue Cp*Ru(dppe)H,3 compound 1
is not stable in dichloromethane at ambient temperature,
undergoing H/Cl exchange with the solvent to yield
Cp*Os(dppe)Cl.14 However, no exchange occurs at measurable
rates at low temperatures.
(b) X-ray Analyses. The geometry of Cp*Os(COD)X (X )
Cl, 2; Br, 3) is identical to that of the Cp*Ru(COD)Cl
analogue,15 with the halogen atom and the centers of the two
COD double bonds occupying the basal position of a “three-
legged piano stool” (Figure 1). Whereas the M-CNT distance
is statistically longer for the Os-Cl compound, the M-Cl and
M-C (COD) distances are statistically shorter for osmium
relative to the Ru analogue.8 The reported covalent radii are
sensibly similar (Os, 1.28 Å; Ru, 1.26 Å).16 The longer C-C
distances for the coordinated COD double bonds (averages of
1.417(17) Å for Os and 1.388(8) Å for Ru) suggest that Os is
capable of stronger M-COD π back-bonding.
(c) Protonation of Cp*Os(dppe)H. The protonation of
Cp*Os(dppe)H by strong acids was monitored in CD2Cl2 by
1H and 31P{1H} NMR spectroscopy at low temperatures, where
no H/Cl exchange with the solvent occurs. The addition of 1
equiv of HBF4 · Et2O at 193 K led to the complete disappearance
of the starting material and to the quantitative appearance of a
new poorly resolved triplet resonance at -13.34, which becomes
much better resolved at 233 K with 2JH-P ) 10 Hz (Figure 3).8
Its 2JH-P value, together with the T1min value (186 ms at 220 K
and 500 MHz), the overall resonance shape, and temperature-
dependent behavior8 similar to that reported for the related
[CpOs(P-P)H2]+ and [Cp*Ir(dmpm)H2]2+ complexes,5,20 sug-
gests the formulation of the new compound as cis-
[Cp*Os(dppe)(H)2]+BF4- (cis-1H+, Table 1).21 Application of
the method of Halpern et al.22 gives an H-H distance of 1.56
Figure 1. Molecular structures of Cp*Os(COD)Cl (2) and Cp*Os(COD)Br (3) (30% probability level). Key bond lengths (Å) and angles
(deg): 2, Os-Cl, 2.456(2); Os-CNT, 1.925(4); Os-Cav 2.181(10); CNT-Os-Cl, 110.8(1); Cl-Os-C(11), 79.9(3); Cl-Os-C(12), 115.2(2);
Cl-Os-C(15), 119.5(2); Cl-Os-C(16), 81.0(3); 3, Os-Br, 2.5780(8); Os-CNT, 1.912(4); Os-Cav 2.173(9); CNT-Os-Br, 110.7(1);
Br-Os-C(11), 78.0(2); Br-Os-C(12), 112.9(3); 122.2(2); Br-Os-C(16), 83.8(2).
Table 1. Selected NMR (1H 500.33 MHz, 31P{1H} 202.5 MHz) Data for Cp*OsH(dppe) and cis- and trans-[Cp*OsH2(dppe)]BF4 Generated in
Situ in CD2Cl2 at 193 K
1
cis-1H+
trans-1H+
2
2
1H
1H
1H
-17.19 (t, JH-P) 27 Hz, 1H, Os-H)
1.92 (s, 15H, Cp*)
-13.34 (bt, JH-P ) 10 Hz, 2H, Os-H)
1.51 (s, 15H, C5Me5)
-13.32 (t, 2JH-P ) 35 Hz, 2H, Os-H)
1.72 (s, 15H, C5Me5)
1.89-2.06 (2 H, -CHA-CHA-),
2.08 2.26 (2 H, -CHB-CHB-)
51.9 (s)
2.02-2.25 (m, 2H, -CHA-CHA-),
2.65-2.88 (m, 2H, -CHB-CHB-)
41.8 (s)
2.32 (vd, 2JH-P ) 10 Hz, 4H, -CH2-CH2-)
31P{1H}
32.2 (s)

Notes
Organometallics, Vol. 27, No. 13, 2008 3309
Figure 2. Molecular structure of Cp*Os(dppe)H (1) (30% probability level). Key bond lengths (Å) and angles (deg): Os-H 1.56; Os-CNT
1.90(3); Os-P(1) 2.2357(9); Os-P(2) 2.2302(10); CNT-Os-H 119(3); CNT-Os-P(1) 134.0(4); CNT-Os-P(2) 135(2); P(1)-M-P(2)
78.0(2).
(QMEC) between the two hydride ligands.24 The temperature-
dependent chemical shift and line broadening for this resonance
(see the figure in the Supporting Information) are reminiscent
of those of complex cis-[CpOs(dppm)H2]+, for which QMEC
was shown20 as the responsible cause. The similarity in the
structure and NMR behavior suggests that QMEC could also
be operative in cis-[Cp*Os(dppe)H2]+.
When the temperature was raised to 293 K, the above-
described hydride signals of cis-1H+ disappeared and were
replaced by a new hydride triplet at δ -13.15 (2JH-P ) 35 Hz);
see Figure 3. The signal of trans-1D+ is only slightly shifted to
strong field (∆δ ) -0.01 ppm).8 The spectral properties allow
the new product to be formulated as trans-[Cp*Os-
(dppe)(H)2]BF4 (trans-1H+) (Table 1).25 The relatively large
Figure 3. 1H NMR (500.33 MHz) spectra (hydride region) of
2JH-P coupling constant is very similar to those observed for
[Cp*OsH2(dppe)]BF4; 233 K, CD2Cl2: (a) generated in situ by
mixing at 193 K, (b) same sample after warming to 298 K.
(13) The infrared spectrum (Nujol mull) of 1 contains a strong band at
2008 cm-1 due to the Os-H stretch, this frequency being considerably
Å in cis-1H+, close to the values of 1.6 Å calculated for cis-
[CpOs(dppe)(H)2]+ (240 ms at 500 MHz and 218 K)28 and of
1.49 Å derived from T1min data (145 ms at 240 K, 500 MHz)
higher than those of the Ru and Fe analogues (νRuH ) 1914 cm-1, νFeH
)
1839 cm-1).
(14) The rate of this exchange is essentially identical to that of the Ru
analogue (about 16% in 1 h at 300 K for Os, vs 15% for Ru), the pseudo-
first-order rate constant being 7.7 × 10-5 s-1 at T ) 300 K.
(15) Serron, S. A.; Luo, L.; Li, C.; Cucullu; M, E.; Stevens, E. D.; Nolan,
S. P. Organometallics 1995, 14, 5290–5297.
for cis-[Cp*Ir(dmpm)(H)2]2+ 20
. On the other hand, much smaller
T1min values were measured for the related dihydrogen com-
plexes [Cp*Fe(dppe)(H2)]+ (9.6 ms at 400 MHz)2 and
[Cp*Ru(dppe)(H2)]+ (19.3 ms at 500 MHz).3
(16) WebElements, the periodic table on the Internet, URL: http://
www.webelements.com/.
(17) The Cp* ligand is found disordered with two different orientations
with 0.58 and 0.42 occupancies; the position of the hydride ligand was
refined in isotropic approximation in a riding model. See the Supporting
Information for further details.
The protonation of 1 by 98% CF3SO3D at 200 K led to the
appearance of a new triplet resonance at -13.41 ppm (2JH-P
)
10 Hz) attributed to cis-[Cp*Os(dppe)(H)(D)]+CF3SO3 (cis-
1D+). Interestingly, besides this resonance the signal of cis-
1H+ was also observed.8 Correspondingly, two singlets appear
in the 31P{1H} specrum at 41.8 and 41.7 ppm, which were
observed as a doublet and triplet (JP-H ) 10 Hz) in noncoupled
31P spectra. The chemical shift difference between the hydride
signals of the two isotopomers is quite high (∆δ ) -0.08 ppm),
whereas the resonances of other hydrogen atoms are the same
for both complexes. The 2H NMR spectrum of the above-
mentioned mixture features a single resonance at -13.18 ppm
(∆δ ) 15 Hz). The 3:1 ratio cis-1D+:cis-1H+ was determined
from inverse-gated 31P{1H} spectra.23
-
(18) Guan, H.; Iimura, M.; Magee, M. P.; Norton, J. R.; Zhu, G. J. Am.
Chem. Soc. 2005, 127, 7805–7814.
(19) With normalization of the C-H length to the ideal value of 1.08
Å. This r(HH) value is certainly overestimated since M-H bond lengths
are usually underestimated in X-ray.
(20) Pons, V.; Heinekey, D. M. J. Am. Chem. Soc. 2003, 125, 8428–
8429.
(21) IR spectra (CH2Cl2) at 200 K show full disappearance of the νOsH
band at 2035 cm-1 (ε/L mol-1 cm-1 ) 84) of the starting hydride 1 and
appearance of two new bands at 2126 (ε ) 29) and 2177 (ε ) 16) cm-1 of
cis-1H+.
(22) (a) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am.
Chem. Soc. 1991, 113, 4173–4184. (b) Bayse, C. A.; Luck, R. L.; Schelter,
E. J. Inorg. Chem. 2001, 40, 3463–3467.
The observation of a simple triplet for the HH′PP′ spin system
could be rationalized in several different ways: on the basis of
(23) The addition of the extra proton could be explained by the exchange
of o-CH of the phenyl ring of the dppe ligand and the osmium-bound
deuterium via an electrophilic substitution on the arene ring (the cationic
dihydride serves as acid).
a rapid exchange of the two hydride environments; the JHP
)
JH′P′ and JHP′ ) JH′P could be accidentally degenerate; the JPP
could be very large, leading to a virtual triplet; or JHH′ could be
very large because of quantum mechanical exchange coupling
(24) Sabo-Etienne, S.; Chaudret, B. Chem. ReV. 1998, 98, 2077–2092.
(25) IR spectrum of trans-1H+ (CH2Cl2) at 200 K features two νOsH
bands at 2053 (ε/L mol-1 cm-1 ) 25) and 2102 (ε ) 41) cm-1
.

3310 Organometallics, Vol. 27, No. 13, 2008
Notes
by calculations of different models for Cp*Fe(dppe)H.29 On
the other hand, the trans form is energetically stabilized
relative to the cis isomer to a greater extent for the Cp*
system than for Cp one, for either steric or electronic reasons
or both, rendering the isomerization process irreversible like
for the Fe and Ru analogues.
Scheme 3
For all the previously reported examples of [CpOs-
(P-P)H2]+ complexes, as well as for the [Cp*Os-
(dppe)H2]+ complex described here, a classical cis-dihydride
structure is generated without the observation of a nonclas-
sical isomer (dihydrogen complex). This behavior is different
from that of the Fe and Ru analogues, whose protonation
systematically affords dihydrogen complexes as intermediates
and trans-dihydride isomers as thermodynamically stable
products, without the observation of intermediate cis-dihy-
dride isomers.1d,2,3,29,30 The increase of the relative energy
of the metal d electrons upon descending the group desta-
bilizes a dihydrogen structure M(η2-H2), through a better
back-donation to the σ* orbital of the dihydrogen ligand,
relative to the classical cis-dihydride isomer, and also helps
the direct transfer of the proton to the metal.
Although formation of the cis-dihydride can be formally
regarded as a result of proton transfer to the metal atom, it
is more likely that the initial proton attack takes place at the
hydride site, as it does in the case of (η2-H2)-complexes’
formation for the corresponding Fe and Ru complexes.1d,2,3
The nonclassical (η2-H2)-like structure could be a transition
state for this proton transfer reaction or be generated as a
short-lived intermediate, then collapsing to the classical cis-
dihydride with a very low activation barrier. The latter
scenario was found by DFT calculations for the
Cp*Mo(dppe)H3 protonation, although a nonclassical inter-
mediate could not be observed under any experimental
conditions.31 The former one was suggested for the
Cp*W(dppe)H3 protonation, where the initial H-bonding
interaction involves an important contribution from the metal
atom.32 Studies of hydrogen bonding and proton transfer from
weaker acids to Cp*Os(dppe)H are underway, aiming to shed
more light on the ground-state properties of this hydride and
the details of the proton transfer mechanism.
trans-[CpOs(P-P)(H)2]+5 and for trans-[CpOs(LL′)H2]+ (LL′
)
(PR3)2, (CO)(PiPr3)).26 The T1min of trans-[Cp*Os-
(dppe)(H)2]+ (530 ms at 500 MHz) may be compared with that
measured for complex trans-[CpOs(dppe)(H)2]+ (610 ms at 300
MHz).5 Cooling the sample again to 233 K does not result in
any further change, showing that the cis-trans isomerization
is irreversible. When the HBF4 · Et2O addition (ca. 1 equiv) was
carried out at room temperature, the nearly quantitative forma-
tion of the trans isomer was immediately observed; the traces
of cis-1H+ completely disappeared within 10 min.27
Thus, the protonation of compound 1 by HBF4 · Et2O
occurs as shown in Scheme 3. Complex cis-1H+ is the kinetic
product formed selectively at low temperatures (193 K) and
isomerizes quantitatively to trans-1H+ at higher temperature.
We cannot exclude that the minor amount of trans-1H+
observed in the low-temperature protonation process derives
from a direct protonation at the metal site, but we consider
it more likely that this isomer derives from the isomerization
of the cis kinetic product due to the occasional warming of
the sample during the transfer into the NMR probe. This
amount, in fact, was not perfectly reproducible in different
experiments but always remained <2%; see Figure 3. For
other related protonation studies, a greater amount of trans
isomer is obtained directly by low-temperature protonation:
the cis/trans ratios observed for protonation at -78 °C were
24:1 for [CpOs(dppm)H2]+, 1:3 for [CpOs(dppe)H2]+, and
1:3 for [CpOs(dppp)H2]+ (changing to 10:1, 1:70, and 100%
trans, respectively, upon warming to room temperature).5 The
10:1 ratio for the dppm derivative at room temperature was
also obtained upon generating the complex by a different
route (reaction of CpOs(dppm)Br with Na[BArF*4] under H2,
where ArF* ) 3,5-(CF3)2C6H3),28 indicating the presence of
a reversible equilibrium in that case. Thus, the Cp* system
differs from the Cp analogues in two ways: protonation of
the monohydride complex yields the cis isomer selectiVely
at low temperature, and the higher temperature rearrangement
to the trans isomer is quantitatiVe. Our previous results on
the kinetics of the (η2-H2) f (H)2 isomerization for the
In summary, the protonation of the new osmium hydride
Cp*Os(dppe)H (1) by HBF4 · Et2O in CD2Cl2 was found to lead
at low temperatures essentially exclusively to cis-[Cp*Os-
(dppe)(H)2]+BF4-, which then quantitatively transforms into
trans-[Cp*Os(dppe)(H)2]+BF4- above 230 K. The comparison
with the previously reported protonation of less sterically
hindered Cp analogues suggests an important difference: a
competitive direct proton attack at the metal center, yielding
the trans-dihydride species, is possible for the sterically less
hindered Cp system, but is blocked for the Cp* system.
+
Cp*M(dppe)H2 (M ) Fe, Ru) systems3,4 revealed that the
high activation barrier renders this process too slow at
temperatures close to 200 K. At the same time, the proton
transfer reaction has a very low activation barrier so the
competitive direct proton attack at the metal site can occur
at low temperatures to give trans species for the less sterically
encumbered complexes. The sterically more crowded coor-
dination sphere, like that in Cp*M(dppe)H, blocks quite
efficiently the direct access of the metal site, as was shown
Acknowledgment. We thank the CNRS and the RFBR
(05-03-22001) for support through a France-Russia
(29) Belkova, N. V.; Collange, E.; Dub, P.; Epstein, L. M.; Lemenovskii,
D. A.; Lledo´s, A.; Maresca, O.; Maseras, F.; Poli, R.; Revin, P. O.; Shubina,
E. S.; Vorontsov, E. V. Chem.-Eur. J. 2005, 11, 873–888.
(30) Conroy-Lewis, F. M.; Simpson, S. J. J. Chem. Soc., Chem. Commun.
1987, 1675–6.
(26) (a) Wilczewski, J. J. Organomet. Chem. 1986, 317, 307–325. (b)
Esteruelas, N.; Gomez, A. V.; Lopez, A. M.; Oro, L. A. Organometallics
1996, 15, 878–881. (c) Rottink, M. R.; Angelici, R. J. J. Am. Chem. Soc.
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(31) Belkova, N. V.; Revin, P. O.; Besora, M.; Baya, M.; Epstein, L. M.;
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2006, 2192–2209.
(27) An 1H NMR monitoring of the isomerization process at 250 K gives
rates of (3.15 ( 0.02) × 10-4 and (3.14 ( 0.02) × 10-4 s-1 for the cis-
1H+ disappearance and trans-1H+ appearance, respectively.
(28) Egbert, J. D.; Bullock, R. M.; Heinekey, D. M. Organometallics
2007, 26, 2291–2295.
(32) (a) Andrieu, J.; Belkova, N. V.; Besora, M.; Collange, E.; Epstein,
L. M.; Lledo´s, A.; Poli, R.; Revin, P. O.; Shubina, E. S.; Vorontsov, E. V.
Russ. Chem. Bull. 2003, 52, 2679–2682. (b) Belkova, N. V.; Besora, M.;
Baya, M.; Dub, P. A.; Epstein, L. M.; Lledo´s, A.; Poli, R.; Revin, P. O.;.
Shubina, E. S. Manuscript in preparation.

Notes
Organometallics, Vol. 27, No. 13, 2008 3311
Supporting Information Available: Synthetic, spectroscopic,
crystallographic, and analytical data, variable-temperature NMR
spectra, and X-ray crystallographic files in CIF format. This material
is available free of charge via the Internet at http:/pubs.acs.org.
bilateral PICS grant. Support from the IUF (France) and
the RFBR (08-03-00464) and Division of Chemistry and
Material Sciences of RAS (Russia) is also gratefully
acknowledged. Thanks are expressed to Dr. Y. Coppel
(LCC CNRS) for assistance with the low-temperature
NMR measurements.
OM8000235