Stereoselectivity in a chiral ruthenium ethylene hydride complex: Evidence of an agostic intermediate

Article abstract of DOI:10.1021/om060868j

Treatment of Ru(η⁶:η¹-Me₂NC ₆H₄C₆H₄PCy₂)Cl ₂ with MeLi resulted in the formation of Ru(η⁶: η¹-Me₂-NC₆H₄C₆H ₄PCy₂)Me₂, which reacted with Ph ₃CPF₆ to form the cationic olefin hydride complex [Ru-(η⁶:η¹-Me₂NC₆H ₄C₆H₄PCy₂)(H₂C=CH ₂)(H)]PF₆. The new complexes were characterized by spectroscopy and by X-ray crystallographic analysis. The diastereomeric olefin hydride complexes were observed to exhibit two fluxional processes: a facile olefin rotation and another process that results in the exchange of the hydride and olefin protons. As the rate of diastereomer interconversion is much slower than that of olefin insertion, our studies suggest that the latter exchange takes place through an agostic species which undergoes dynamic methyl rotation.

Full text of DOI:10.1021/om060868j

1738
Organometallics 2007, 26, 1738-1743
Stereoselectivity in a Chiral Ruthenium Ethylene Hydride Complex:
Evidence of an Agostic Intermediate
J. W. Faller* and Philip P. Fontaine
Yale UniVersity, P.O. Box 208107, New HaVen, Connecticut 06520-8107
ReceiVed September 22, 2006
Treatment of Ru(η6:η1-Me2NC6H4C6H4PCy2)Cl2 with MeLi resulted in the formation of Ru(η6:η1-Me2-
NC6H4C6H4PCy2)Me2, which reacted with Ph3CPF6 to form the cationic olefin hydride complex [Ru-
(η6:η1-Me2NC6H4C6H4PCy2)(H2CdCH2)(H)]PF6. The new complexes were characterized by spectroscopy
and by X-ray crystallographic analysis. The diastereomeric olefin hydride complexes were observed to
exhibit two fluxional processes: a facile olefin rotation and another process that results in the exchange
of the hydride and olefin protons. As the rate of diastereomer interconversion is much slower than that
of olefin insertion, our studies suggest that the latter exchange takes place through an agostic species
which undergoes dynamic methyl rotation.
of agostic ethyl species,5,17-38 and their importance in polymer-
ization reactions has been noted on several occasions.5,24,29,35,39,40
Owing to their anticipated tolerance of polar functional
groups, ruthenium complexes are sought which are capable of
Introduction
The insertion of olefins into metal-hydride bonds is of fun-
damental importance to several catalytic processes, including
olefin hydrogenations, isomerizations, and hydroformylations.
The barrier for olefin insertion into a metal-hydride bond is
generally quite low, lower than that for their insertion into a
metal-alkyl bond. Therefore, olefin hydride complexes are less
common than olefin alkyl complexes. Nevertheless, there are a
number of reported olefin hydride complexes, including those
with the olefin and hydride bound in a cis relationship. Such
olefin hydride complexes of several metals (Mo,1 Co,2-4 Rh,2,3,5,6
Ir,7 Os,7 Ru,7-13 Pt,14 Nb,15 and Ta16) are known, most of which
undergo reversible migratory insertion/â-hydride elimination
processes. For the ruthenium variants, however, there are only
three reported cases of a reversible migratory insertion process.9-11
Closely related to the classical, terminal hydride complexes are
the complexes containing a three-center-two-electron C-H-M
bond (an agostic interaction). There have also been many reports
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10.1021/om060868j CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/23/2007

A Chiral Ruthenium Ethylene Hydride Complex
Organometallics, Vol. 26, No. 7, 2007 1739
Scheme 1. Synthesis of 2 and 3
catalyzing Ziegler-Natta type polymerizations. Despite this,
there have only been a few reported ruthenium-catalyzed
polymerizations, and these have been restricted to ethylene.41-43
If such a catalyst were chiral, the added advantage of stereo-
selective polymerization would become feasible. On this basis,
and given the applicability of other olefin hydride complexes
to polymerization catalysis, we set out to prepare and study the
dynamics of a novel chiral ruthenium ethylene hydride complex.
The diastereomeric nature of this complex provides an insight
into the nature of the unobserved ethyl intermediate that is
formed. Thus, this report details the facile conversion of the
planar-chiral arene-tethered complex Ru(η6:η1-Me2NC6H4C6H4-
PCy2)Cl2 (1) into the dimethyl analogue Ru(η6:η1-Me2-
NC6H4C6H4PCy2)Me2 (2), which is then in turn converted to
[Ru(η6:η1-Me2NC6H4C6H4PCy2)(H2CdCH2)(H)]PF6 (3) upon
the addition of CPh3PF6. The synthesis of the chiral-at-metal 3
is stereoselective, with one of the isomers present in 86%
diastereomeric excess (de). The solid-state structure shows that
the η2-ethylene ligand is bound in the anti position relative to
the NMe2 group in the preferred diastereomer. NMR studies in
solution have suggested that two low-barrier dynamic processes
are occurring: an olefin rotation and an “in-place” methyl
rotation of an agostic intermediate.
Figure 1. ORTEP diagram of (S)-2.
Scheme 2. Proposed Mechanism for Formation of 3
Results and Discussion
The treatment of 1 with an excess of MeLi results in
conversion to the dimethyl analogue 2 in high yield (Scheme
1). This neutral complex is moderately stable and extremely
soluble in most organic solvents, including hydrocarbons.
Although crystals were not readily obtained, the X-ray structure
was obtained from a single crystal that was produced by slow
diffusion of Et2O into a benzene solution of 2. The structure
(Figure 1) shows the Ru-CMe distances to be very similar (2.137
and 2.144 Å) and much shorter with respect to the Ru-Cl
distances in 1 (2.401 and 2.419 Å). The Ru-P distance is also
slightly shorter for 2 than for 1.44 The diastereotopic nature of
to be initiated by hydrogen abstraction from one of the methyl
groups, forming a transient carbene species that undergoes an
insertion of the remaining methyl group, furnishing a 16-electron
ethyl intermediate. The formation of the ethylene hydride
complex would then result from a â-hydride elimination of this
1
ethyl species (Scheme 2).8,11 The room-temperature H NMR
of 3 shows a sharp and well-separated doublet at δ -8.61,
suggestive of a terminal hydride and not an agostic interaction.
The strong coupling through the metal center to the phosphorus
(2JH-P) of 38.9 Hz corroborates this interpretation.5
As 3 is both planar-chiral and chiral-at-metal, two diastere-
omers are possible. Indeed, while the synthesis of 3 results in
the preferential formation of one of these isomers, a small
amount (7%) of a minor isomer is observed. We have observed
in our prior work with this arene-tethered system that the planar
chiral ligand can exert a strong influence on controlling the
metal-centered chirality.44,45 Crystals suitable for X-ray diffrac-
tion were obtained by slow diffusion of Et2O into a CH2Cl2
solution of 3, and the solid-state structure shows the η2-ethylene
is bound anti with respect to the NMe2 group (Figure 2). This
isomer is expected to be the more stable of the two, as follows
from our previous studies that have shown the ability of the NMe2
1
the two methyl groups is evidenced by NMR, as the H NMR
spectrum shows two doublets at δ 0.91 and 0.63 (3JH-P ) 5.2
Hz) and the 13C NMR spectrum shows two doublets at δ -10.9
and -11.1 (2JC-P ) 4-5 Hz).
The dimethyl complex 2 is readily converted to Ru(η6:η1-
Me2NC6H4C6H4PCy2)(H2CdCH2)(H)]PF6 (3) upon the addition
of CPh3PF6 (Scheme 1). This reaction, which has been observed
for other ruthenium and osmium arene complexes, is believed
(41) James, B. R.; Markham, L. D. J. Catal. 1972, 27, 442-&.
(42) Komiya, S.; Yamamoto, A.; Ikeda, S. Bull. Chem. Soc. Jpn. 1975,
48, 101-107.
(43) Nomura, K.; Warit, S.; Imanishi, Y. Macromolecules 1999, 32,
4732-4734.
(44) Faller, J. W.; D’Alliessi, D. G. Organometallics 2003, 22, 2749-
(45) Faller, J. W.; Fontaine, P. P. Organometallics 2005, 24, 4132-
4138.
2757.

1740 Organometallics, Vol. 26, No. 7, 2007
Faller and Fontaine
Figure 3. Dynamic NMR of Hydride Region.
The room-temperature 1H and 13C NMR of 3 shows that there
is a fast rotation of the ethylene ligand, as evidenced by the
appearance of two olefinic proton resonances and one olefinic
1
carbon resonance. As these H NMR resonances are broad at
room temperature, the temperature was lowered, which resulted
in their sharpening. The low barrier associated with this process
was demonstrated by lowering the temperature to -80 °C, at
which point no decoalescence had occurred and there were still
two sharp resonances apparent. Therefore, the line broadening
at room temperature is due to another dynamic process. As
previously mentioned, at room temperature a doublet hydride
Figure 2. ORTEP diagram of (SRu,R)-3.
Table 1. Selected Distances and Angles for 3
molecule 1
molecule 2
1
resonance at δ -8.61 is apparent in the H NMR spectrum.
Distances (Å)
Ru-H1
Ru-C1
Ru-C2
Ru-P1
C1-C2
C2-H1a
1.48(3)
Ru-H1
Ru-C1
Ru-C2
Ru-P1
C1-C2
C2-H1a
1.52(3)
Closer examination revealed that this resonance is actually
slightly broad at room temperature. Cooling of the sample
produced sharpening of the resonance, and at -40 °C another
hydride resonance became apparent. This minor hydride reso-
nance corresponds to the minor isomer of 3, which is too broad
to be observed in the room-temperature spectrum (Figure 3).
The line broadening in the hydride resonances and the olefin
resonances is related, as was determined with an EXSY spec-
trum, which showed cross-peaks between the olefin and hydride
resonances, as well as between the two olefinic proton reso-
nances for the major isomer. That each of the five protons, four
from the ethylene ligand and the hydride, are exchanging is
indicative of the fast olefin rotation relative to a second dynamic
process that involves both the hydride and the olefin ligand.
The simplest possibility is a reversible migratory insertion
process, which would give rise to a 16-electron ethyl intermedi-
ate and which would allow the permutations of the observed
exchange process. A question arises, then, as to whether or not
two such diastereomers of 3 are able to interconvert, since the
intermediate of the migratory insertion process should provide
a pathway for the interconversion of the isomers. That is, the
inversion barriers for 16-electron arene ruthenium complexes
are believed to be quite low, generally substantially below 15
kcal/mol,46 and so the epimerization of the metal should be a
very facile process if there were an equilibrium with a
16-electron ethyl species. It should be noted that such an ethyl
species, which is depicted as being pyramidal in Scheme 3,
could also have a planar geometry, as the ground-state geom-
etries of 16-electron half-sandwich complexes are very sensitive
to the ligand architecture.46 In either case, the most important
feature is that an equilibrium with a 16-electron complex
containing a normal σ-bonded ethyl group should provide a path
for a rapid epimerization.
2.172(3)
2.176(3)
2.2894(9)
1.398(5)
2.23
2.188(3)
2.190(3)
2.2866(9)
1.395(5)
2.31
Angles (deg)
H1-Ru-P1
C1-Ru-P1
C2-Ru-P1
78(1)
91.79(11)
108.01(10)
H1-Ru-P1
C1-Ru-P1
C2-Ru-P1
79(1)
91.66(10)
107.22(10)
a These distances correspond to through-space distances, not bond lengths.
substituent to direct the larger ligand into the anti binding site,
owing to the unfavorable steric interactions that would result
from syn coordination.
The X-ray analysis showed that 3 crystallized in the P21/c
space group, with two molecules in the asymmetric unit cell.
The differences between the two molecules are very minor,
differing in the conformations of the cyclohexyl groups, and
only slight variations are observed in the bond lengths and angles
(Table 1). The structure shows that the η2-ethylene is in fact
disposed nearly trans to the phosphine. Whereas the accuracy
associated with the location of hydrides by X-ray analysis is
low, the position of the hydride could be refined and appears
to be in unusually close proximity to the phosphine; the latter
is evidenced from the small P-Ru-H bond angle (78 and 79°
for the respective molecules). The C-Ru bonds for the
η2-ethylene ligand are essentially equivalent in both molecules
(2.172 and 2.176 Å in one case and 2.188 and 2.190 Å for the
other), illustrating that the bonding to the olefin ligand is not
significantly asymmetric. The observed Ru-H distances (1.52
and 1.48 Å, respectively, but perhaps longer in reality) are
somewhat shorter than is usually observed, although an even
shorter Ru-H distance (1.44 Å) has been reported.11 The C-C
bond distances of the η2-ethylene ligand are 1.398 and 1.395 Å
for the two molecules, and the distances from the hydride to
the adjacent carbon are 2.308 and 2.232 Å, respectively.
Therefore, the solid-state structure, like the solution structure,
appears to be a classical olefin hydride complex and not an
agostic ethyl complex.
No exchange was observed between the two diastereomers
in EXSY spectra. In addition, the interconversion of the two
diastereomers would result in the broadening of all of the
resonances in the NMR spectrum. However, only the olefin and
(46) Ward, T. R.; Schafer, O.; Daul, C.; Hofmann, P. Organometallics
1997, 16, 3207-3215.

A Chiral Ruthenium Ethylene Hydride Complex
Organometallics, Vol. 26, No. 7, 2007 1741
Scheme 3. Interconversion of Diastereomers of 3 via a
Pyramidal Ethyl Species
hydride resonances become broad, while the remaining reso-
nances for the distinct diastereomers remain sharp throughout
the dynamic temperature range (up to 75 °C, indicating a barrier
of >20 kcal mol-1 for the interconversion of the two isomers).
The free energies of activation for the dynamic processes of 3
were calculated from the line broadening in the 1H NMR
spectrum. For the major isomer, a barrier (∆Gq) of 15.2 kcal/
mol was calculated, while for the minor isomer ∆Gq ) 13.0
kcal/mol. This corresponds to rates of 40 and 176 s-1 at 25 °C,
respectively, and therefore, the calculated ratio of rates is only
4.4:1, while the ratio of concentrations of isomers is ∼13:1.
Furthermore, crystallization provides crystals of a single isomer,
as shown in Figure 2. The NMR spectrum taken immediately
upon dissolution of the crystals shows a preponderance of a
single isomer (∼98%) which equilibrated with a half-life on
the order of 10 min, indicating an epimerization barrier of ∼22
kcal mol-1. (Owing to the small percentage of the minor isomer
an accurate value for the barrier was not obtained.) In any case,
it is clear from all this evidence that the dynamic processes
observed by NMR are not leading to the rapid interconver-
sion of the two diastereomers.
In order to account for these observations, we propose an
equilibrium between the terminal ethylene hydride complex and
an agostic ethyl species, rather than a 16-electron species with
a normal σ-bound ethyl group. This accounts for the observed
lack of interconversion between the two diastereomers, since
the agostic interaction avoids the coordinative unsaturation that
would lead to fast epimerization. Also, these proposed inter-
mediates can still give rise to the exchange of the olefin and
hydride protons, through an “in-place walking” mechanism in
which the methyl group retains contact with the metal center
throughout the dynamic process.5,27,47-49 This process (Figure
4), when coupled with the faster olefin rotation, would lead to
the exchange behavior observed in the present case. It should
be noted that the formation of a true 16-electron σ-ethyl inter-
mediate cannot be unequivocally ruled out. For example, if the
formation of such an intermediate had a high energy approaching
that of the transition state, then similar rates might be observed.
Nevertheless, upon consideration of other analyses3 of this type
of problem, we feel the more likely explanation of the high
Figure 4. Dynamic Behavior of 3.
barrier for epimerization involves an agostic rather than a 16-
electron species.
The processes discussed here have analogues in the [(C5H5)-
(L)Co-CH2CH2-H]+ case studied by Brookhart et al., who
have proposed that, for agostic complexes that exhibit such
dynamic behavior, it is usually the case that the isomerization
of the metal complex Via a 16-electron ethyl intermediate is
significantly slower than both olefin rotation and methyl
rotation.27 The cobalt complexes differ in that the agostic ethyl
is the stable form, rather than the ethylene hydride found for 3.
The situation is that it is often difficult to distinguish between
the processes; that is, dynamic methyl rotation of an agostic
interaction versus migratory insertion to yield a 16-electron ethyl
species versus inversion at the metal center. One exception is
the report by Spencer et al., in which the rate of inversion of
the metal chirality, stemming from the formation of a 16-electron
ethyl intermediate, was directly measured by following the
averaging of diastereotopic methyl groups with L ) Me2PPh
by NMR.23 In Spencer’s case it was also observed that the
formation of the 16-electron ethyl and inversion of the cobalt
metal center was a higher barrier process (13.4 kcal mol-1) than
the process which resulted in the exchange of terminal and
bridging methyl resonances (9.6 kcal/mol). One should note that
it is also difficult to disentangle the actual rate of inversion of a
pyramidal intermediate from the rate of formation of the 16-
electron pyramidal intermediate. Hence, the barrier to inversion
could be a component of the total. Brookhart determined an
inversion barrier of ∼3 kcal mol-1 in an analogous case.27 In
the present case, the planar chirality of the arene-tethered ligand
makes the overall inversion process easily distinguishable from
the other processes. Specifically, olefin rotation has a very low
barrier and the formation of an agostic species does not result
in the epimerization of 3, whereas the formation of a normal
σ-ethyl intermediate would provide a rapid epimerization route.
(47) Green, M. L. H.; Wong, L. L. J. Chem. Soc., Chem. Commun. 1988,
677-679.
(48) Bercaw, J. E.; Burger, B. J.; Green, M. L. H.; Santarsiero, B. D.;
Sella, A.; Trimmer, M. S.; Wong, L. L. J. Chem. Soc., Chem. Commun.
1989, 734-736.
Conclusions
The planar chiral dichloride complex 1 has been converted
into the dimethyl analogue 2, which was subsequently converted
(49) Casey, C. P.; Yi, C. S. Organometallics 1991, 10, 33-35.

1742 Organometallics, Vol. 26, No. 7, 2007
Faller and Fontaine
Table 2. Crystallographic Data
into a cationic ethylene hydride complex 3. The latter reaction
is stereoselective, as the product 3 forms in 86% de. The identity
2
3
of both derivatives has been established by H, 31P, and 13C
1
color, shape
empirical formula
formula wt
Mo KR radiation/Å
T /K
yellow, block
C28H42NPRu
524.69
0.710 73
173
yellow, block
C28H41F6NP2Ru
668.65
0.710 73
173
NMR, along with X-ray crystallography. The metal-centered
chirality in 3 is effectively controlled by the planar chirality of
the arene-tethered ligand and, more specifically, the directing
influence of the NMe2 group. Both the solid-state and solution
structures are suggestive of a classical, terminal hydride species.
However, the two diastereomers of 3 were seen to undergo a
dynamic process, with the barriers being 15.2 and 13.0 kcal/
mol for the major and minor species, respectively, which resulted
in the exchange of the hydride and olefin resonances in the 1H
NMR spectrum. It was observed that the diastereomers of 3 do
not interconvert Via the dynamic processes observed by line
broadening in the NMR, which is suggestive of an equilibrium
involving an agostic species. If a conventional 16-electron ethyl
species were involved, we would anticipate a barrier less than
the >22 kcal/mol we observe. That is, the continual agostic
contact to the ruthenium should slow the epimerization of the
metal center. We propose, then, that the aforementioned dynamic
NMR observations represent the barriers to the dynamic methyl
group rotation of an agostic interaction. Thus, this is an unusual
case where the barrier of such a process could be directly
determined, as the diastereomers observed in this system allow
for the various dynamic processes to be readily distinguishable.
cryst syst
space group
unit cell dimens
a/Å
b/Å
c/Å
monoclinic
P21/c (No. 14)
monoclinic
P21/c (No. 14)
9.9085 (2)
10.7654(2)
24.0370(5)
96.192(2)
2549.04(8)
4
13.1073(2)
22.3257(3)
20.0334(3)
94.5439(9)
5843.94(13)
8
â/deg
V/Å3
Z
D
calcd/g cm-3
1.367
6.93
1.520
7.03
µ/cm-1 (Mo KR)
cryst size/mm
total, unique no. of rflns
Rint
0.10 × 0.10 × 0.10 0.12 × 0.14 × 0.24
17 748, 6356
0.056
23 777, 14196
0.027
no. of obsd rflns (I > 3σ(I)) 4392
9329
709, 0
no. of params, restraints
280, 0
R,a Rw,b GOF
0.050, 0.063, 2.02
-1.98, 2.10
0.038, 0.040, 1.77
-0.57, 0.70
min, max resid
density/e Å-3
a R ) ∑||Fo| - |Fc||/∑|Fo|, for all I > 3σ(I). b Rw ) [∑[w(|Fo| - |Fc|)2]/
∑[w(Fo)2]]1/2
.
29.0 (d, JC-P ) 2.6 Hz), 28.1-27.7 (several superimposed
resonances), 27.3 (d, JC-P ) 2.6 Hz), 27.0 (d, JC-P ) 2.6 Hz) (CH2
cyclohexyl); -10.9 (d, JC-P ) 4.7 Hz), -11.1 (d, JC-P ) 4.0 Hz) (Ru-
CH3). 31P NMR (162 MHz): 58.0 (s).
Experimental Section
General Methods. All manipulations were carried out under a
nitrogen atmosphere using standard Schlenk techniques. CH2Cl2
and THF were dried by distillation over CaH and Na/benzophenone,
respectively, under a nitrogen atmosphere. Et2O was dried on an
alumina-based solvent purification system, and benzene was used
directly without drying. MeLi and CPh3PF6 were used as received
(Aldrich). Elemental analyses were carried out by Atlantic Micro-
labs. NMR spectra were recorded on a Bruker 400 MHz (operating
at 162 MHz for 31P and 100 MHz for 13C), or a Bruker 500 MHz
(operating at 202 MHz for 31P and 125 MHz for 13C). Chemical
shifts are reported in ppm relative to solvent peaks (1H), or an H3-
PO4 external standard.
Synthesis of [Ru(η6:η1-NMe2C6H4C6H4PCy2)(η2-H2CdCH2)-
(H)]PF6 (3). A flame-dried flask was charged with 2 (102 mg, 0.194
mmol) and CPh3PF6 (73.3 mg, 0.189 mmol) and placed under a
nitrogen atmosphere. CH2Cl2 (5 mL) was added, and the solution
was stirred for 1/2 h, at which time it was removed and dried under
vacuum. Crystals (50.2 mg, 40%) were obtained by slow diffusion
of Et2O into a CH2Cl2 solution of the product, performed under a
nitrogen atmosphere in a Schlenk tube. Anal. Calcd for C28H41F6-
NP2Ru: C, 50.30; H, 6.18; N, 2.09. Found: C, 49.99; H, 6.20; N,
2.16. Data for the major isomer are as follows. 1H NMR (500 MHz,
25 °C, CD2Cl2): 7.68 (1H, m), 7.54 (1H, m), 7.48 (1H, m), 7.44
(1H, d, J ) 7.1 Hz), (CHarom); 6.24 (1H, dd, J ) 5.8, 1.2 Hz), 6.17
Synthesis of Ru(η6:η1-NMe2C6H4C6H4PCy2)Me2 (2). A flame-
dried flask was charged with 1 (102 mg, 0.180 mmol) and placed
under a nitrogen atmosphere. THF (5 mL) was then added, and
the solution was cooled to 0 °C, before the addition of MeLi (0.60
mL, 1.6 M in Et2O, 0.96 mmol). The resulting mixture was stirred
for 30 min at this temperature and was then warmed to room
temperature and stirred for an additional 30 min. The solvent was
then removed under vacuum, the residue was extracted with benzene
(4 × 10 mL), and the extracts were filtered through Celite. The
product was dried under vacuum and used directly (85.3 mg, 90%).
Anal. Calcd for C28H42NPRu‚1/2C6H6 : C, 66.05; H, 8.05; N, 2.48.
Found: C, 65.77; H, 8.21; N, 2.58. A crystal was obtained by slow
6
(1H, d, J ) 6.9 Hz), 6.10 (1H, t, J ) 5.8 Hz), 5.40 (1H, m), (CHη -
arene); 2.75 (2H, br, H2CdCH2); 2.72 (6H, s, N(CH3)2); 2.39 (1H,
m), 2.13 (1H, m) (CHcyclohexyl); 2.10 (2H, br, H2CdCH2); 1.97-
0.97 (18H, m), 0.79-0.63 (2H, m) (CH2 cyclohexyl); -8.61 (1H, d,
2JH-P ) 38.9 Hz, Ru-H). 13C NMR (125 MHz): 145.5 (d, JC-P
)
6
17.2 Hz, CCarom); 143.0 (d, JC-P ) 41.5 Hz, CParom); 135.7 (CNη -
6
arene); 131.1, 130.9, 130.3 (CHarom); 130.2 (CCη -arene); 128.7 (d, JC-P
) 6.4 Hz, CHarom); 100.8, 96.8 (d, JC-P ) 6.8 Hz), 95.5, 75.3 (d,
6
JC-P ) 6.4 Hz), (CHη -arene); 43.5 (N(CH3)2); 36.2 (d, JC-P ) 19.0
1
Hz), 34.6 (d, JC-P ) 33.6 Hz), (CHcyclohexyl); 33.7 (H2CdCH2); 29.4
diffusion of Et2O into a benzene solution. H NMR (400 MHz,
(d, JC-P ) 1.6 Hz), 28.4, 28.3 (d, JC-P ) 6.0 Hz), 27.6 (d, JC-P
)
C6D6): 7.37 (1H, m), 7.32 (1H, m), 7.09-7.04 (2H, m) (CHarom);
5.22 (1H, d, J ) 5.6 Hz), 5.03 (1H, d, J ) 5.6 Hz), 4.87 (1H, dd,
13.6 Hz), 27.4 (d, JC-P ) 8.2 Hz), 26.8, 26.3 (d, JC-P ) 13.6 Hz),
26.1, 26.0, 25.9 (CH2 cyclohexyl). 31P NMR (162 MHz) : 78.8 (s).
Data for the minor isomer (observable resonances) are as follows.
1H NMR (500 MHz, 25 °C, CD2Cl2): 6.34 (1H, t, J ) 6.0 Hz),
6.16 (2H, m, superimposed by major isomer), 4.35 (1H, d, J ) 6.0
6
J ) 5.6 Hz, 0.8 Hz), 4.49 (1H, tm, J ) 5.6 Hz), (CHη -arene); 2.50
(1H, m, CHcyclohexyl); 2.23 (6H, s, N(CH3)2); 2.14 (1H, m, CH
cyclohexyl); 2.03-1.07 (18H, m, CH2 cyclohexyl); 0.99 (1H, m, CH2
cyclohexyl); 0.91 (3H, d, J ) 5.2 Hz, Ru-CH3); 0.63 (3H, d, J )
5.2 Hz, Ru-CH3); 0.52 (1H, m, CH2 cyclohexyl). 13C NMR (126
MHz, C6D6): 147.9 (d, JC-P ) 22.0 Hz, CCarom); 147.0 (d, JC-P
6
6
Hz) (CH η -arene); 2.79 (6H, s, N(CH3)2, superimposed by major
isomer). 31P NMR (162 MHz): 78.2 (s).
)
35.3 Hz, CParom); 129.7 (CHarom); 128.6 (CNη -arene);
Structure Determination and Refinement. Crystals were
obtained by slow diffusion of diethyl ether into a methylene chloride
solution of complexes 2 and 3. Data were collected on a Nonius
KappaCCD (Mo KR radiation) diffractometer and the data pro-
128.4, 126.8 (d, JC-P ) 4.7 Hz), 122.2 (CHarom); 108.4 (d, JC-P
)
6
2.8 Hz, CCη -arene); 97.1 (d, JC-P ) 3.5 Hz), 86.9 (d, JC-P ) 5.3
6
Hz), 84.6, 75.3 (d, JC-P ) 13.5 Hz) (CHη -arene); 45.9 (N(CH3)2);
36.2 (d, J
) 16.7 Hz), 33.1 (d, JC-P ) 18.9 Hz) (CHcyclohexyl);
C-P

A Chiral Ruthenium Ethylene Hydride Complex
Organometallics, Vol. 26, No. 7, 2007 1743
cessed with Scalepack.50 The structures were solved by direct
methods (SIR92)51 and refined on F for all reflections.52 Non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters. Hydrogen atoms were included at calculated positions.
Relevant crystal and data parameters are presented in Table 2.
Structure Determination of 2. This structure determination was
straightforward, and the compound had crystallized in a monoclinic
cell with absences indicating a space group of P21/c.
c, which requires two independent molecules in the asymmetric
unit. The molecules are nearly identical, and only one of the cations
is shown in Figure 2. One of the SbF6 counterions showed a 3:1
disorder, which was modeled as a rotation about one F-Sb-F axis
of ∼45°.
Supporting Information Available: CIF files and tables giving
crystallographic data for compounds 2 and 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data for the structural analysis have also been
deposited with the Cambridge Crystallographic Data Centre: CCDC
Nos. 620863 and 620862 for compounds 2 and 3. Copies of this
information may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (int code)
+44(1223)336-033; e-mail, deposit@ccdc.cam.ac.uk; web, www:
http://www.ccdc.cam.ac.uk).
Structure Determination of 3. This structure determination was
straightforward and the compound had crystallized in a monoclinic
cell with Z ) 8 and with absences indicating a space group of P21/
(50) Minor, W., Otwinowski, Z., Eds. HKL2000 (Denzo-SMN) Software
Package. Processing of X-ray Diffraction Data Collected in Oscillation
Mode. Methods in Enzymology; Academic Press: New York, 1997;
Macromolecular Crystallography.
(51) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(52) TEXSAN for Windows version 1.06: Crystal Structure Analysis
Package; Molecular Structure Corp., The Woodlands, TX, 1997-1999.
OM060868J