Facile η5-η3 hapticity interconversion in pentamethylcyclopentadienyl ruthenium(ii) complexes containing a phenylmethallyl ("open indenyl") ligand

Article abstract of DOI:10.1039/c1dt11436k

The indenyl effect has been introduced to pentadienyl ("open cyclopentadienyl") chemistry by preparation of the phenylmethallyl ("open indenyl") ligand oInd^Me. The reaction of its potassium salt K(oInd^Me) with [(η⁵-C ₅Me₅)RuCl]₄ afforded the sandwich complex [(η⁵-C₅Me₅)Ru(η⁵-oInd ^Me)] (1), which, upon treatment with PMe₃, CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily underwent η⁵- η³ hapticity interconversion and formed the complexes [(η⁵-C₅Me₅)Ru(η³-oInd ^Me)(L)] (2, L = PMe₃; 3, L = CO; 4, L = CN-o-Xy). In these complexes, the η³-bound phenylmethallyl ligand adopts an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the PMe₃ complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction was monitored by NMR spectroscopy at 50 °C to determine a first order rate constant of k _{323 K} = 6.57 × 10^-6 (± 0.02 × 10 ^-6) s^-1 and an activation barrier of ΔG° = 26.8 kcal mol^-1. DFT calculations afforded a stabilization of syn-2 and syn-3 by ΔG₂₉₈ = -1.54 and -1.74 kcal mol^-1 over the respective anti-isomer.

Full text of DOI:10.1039/c1dt11436k

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PAPER
Facile g5–g3 hapticity interconversion in pentamethylcyclopentadienyl
ruthenium(II) complexes containing a phenylmethallyl (“open indenyl”)
ligand†‡
`
`
Andreas Glo¨ckner, Oscar Arias, Thomas Bannenberg, Constantin G. Daniliuc, Peter G. Jones and
Matthias Tamm*
Received 27th June 2011, Accepted 22nd August 2011
DOI: 10.1039/c1dt11436k
The indenyl effect has been introduced to pentadienyl (“open cyclopentadienyl”) chemistry by
preparation of the phenylmethallyl (“open indenyl”) ligand oIndMe. The reaction of its potassium salt
5
5
5
K(oIndMe) with [(h -C5Me5)RuCl]4 afforded the sandwich complex [(h -C5Me5)Ru(h -oIndMe)] (1),
which, upon treatment with PMe3, CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily
5
3
5
3
underwent h –h hapticity interconversion and formed the complexes [(h -C5Me5)Ru(h -oIndMe)(L)] (2,
3
L = PMe3; 3, L = CO; 4, L = CN-o-Xy). In these complexes, the h -bound phenylmethallyl ligand adopts
an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the
PMe3 complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction
was monitored by NMR spectroscopy at 50 ◦C to determine a first order rate constant of k323 K = 6.57 ¥
10-6
(
0.02 ¥ 10-6) s-1 and an activation barrier of DG◦ = 26.8 kcal mol-1. DFT calculations afforded a
stabilization of syn-2 and syn-3 by DG298 = -1.54 and -1.74 kcal mol-1 over the respective anti-isomer.
Introduction
Over the last three decades, pentadienyl (“open cyclopentadienyl”)
complexes have received considerable attention, in particular
because of their stronger binding, vs. Cp, to transition metals, as
for instance demonstrated by the stability of base-free 14-electron
Fig. 1 Pentadienyl (open cyclopentadienyl, oCp), heteropentadienyl and
phenylallyl (open indenyl, oInd) ligands.
open titanocenes,1 but nonetheless higher reactivity in compar-
ison with the corresponding cyclopentadienyl complexes.2 More
recently, heteropentadienyl ligands were developed (Fig. 1) that
display a rich coordination chemistry and lead to metal complexes
with enhanced reactivity, arising from their intriguing ability to
For Cp complexes, benzannulation represents an alternative
method of weakening metal-carbon bonds, and the resulting
indenyl complexes often show enhanced ligand substitution rates
5
3
switch easily between various possible bonding modes (h , h or
5
3
1
5
3
by providing an associative pathway that involves h to h
h ). Thereby, h to h hapticity interconversion is particularly
facile, since the interaction between the metal atom and the C–
X p-bond is usually relatively weak, providing the possibility to
reversibly open a free coordination site for substrate addition and
activation.3 Pentadienyl ligands are also able to adopt a variety
of bonding modes,2 which also explains their reactivity in alkyne
coupling reactions,4 but in comparison hapticity interconversion
generally appears to be less facile.3
3
rearrangement (“indenyl effect”).5 Stabilization of the h -indenyl
intermediates can be ascribed to partial rearomatization of the
unperturbed annulated benzene ring, and this principle should
also apply to analogous phenylallyl ligands that can be classified
as open indenyl (oInd) ligands (Fig. 1). To the best of our
knowledge, however, the indenyl effect has not been adapted to the
chemistry of open cyclopentadienyl (oCp) ligands, and, stimulated
by our investigation of cycloheptatrienyl-pentadienyl zirconium
compexes,6 we aimed to design more labile pentadienyl ligands by
benzannulation. Since 2,4-dimethylpentadienyl (2,4-C7H11) repre-
sents the most widely used pentadienyl ligand in organotransition
metal chemistry,2 we chose to study the coordination chemistry
of the open indenyl ligand oIndMe (Fig. 1), in which the methyl
substituent should also help to keep this phenylmethallyl ligand
in the preferred U-conformation with an anti-orientation of
the methyl and phenyl groups.7 In view of the importance of
Institut fu¨r Anorganische und Analytische Chemie, Technische Univer-
sita¨t Braunschweig, Hagenring 30, D-38106, Braunschweig, Germany.
E-mail: m.tamm@tu-bs.de; Fax: +49 531-391-5309; Tel: +49 531-391-5387
† Dedicated to Professor Richard D. Ernst on the occasion of his 60th
birthday.
‡ Electronic supplementary information (ESI) available: Details of the
kinetic NMR study and the electronic structure calculations. CCDC
reference numbers 832071–832074. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt11436k
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allyl ruthenium species in catalytic allylation and C–C bond
formation,8 the preparation of Ru complexes containing the ligand
5
oIndMe bound in an h -fashion were targeted first, and these results,
along with studies of potential hapticity interconversions in these
systems, are presented in this contribution.
Results and discussion
Ligand synthesis
5
5
Scheme 2 Synthesis of [(h -C5Me5)Ru(h -oIndMe)] (1) and the haptictiy
switch of the open indenyl ligand upon addition of a ligand L.
NMR studies involving the lithium and potassium salts of the
phenylmethallyl anion oIndMe have been published previously.9
Likewise, the reaction of phenyl magnesium bromide with isobu-
tyraldehyde afforded a mixture of phenyl-2-methylpropenes on a
multigram scale from inexpensive, commercially available starting-
materials (Scheme 1).9b In our hands, this isobutene mixture was
readily deprotonated by adopting the general procedure for the
preparation of pentadienyl anions,10 and 2-methyl-1-phenylallyl
(phenylmethallyl) potassium, K(oIndMe), was isolated as a bright
orange, pyrophoric powder in good yield (see Experimental section
for further details).
the metal-bound pentadienyl system. In addition, six instead of
formerly four resonances can be assigned to the phenyl carbon
atoms in the 13C NMR spectrum.
An X-ray diffraction study of 1 confirmed the presence of a
half-open ruthenocene, in which the oIndMe ligand displays a h -
5
coordination mode (Fig. 2), albeit in a markedly distorted fashion
˚
with the Ru–C distances ranging from 2.178(3) A (Ru–C3) to
˚
2.312(3) A (Ru–C5). Despite this slight slippage of the Ru atom
towards the allylic moiety (C1–C3), significant interaction with the
C4 and C5 carbon atoms is indicated by a considerable bending
of the phenyl group towards the metal atom; the resulting fold
angle, which has also been used to describe structural distortions
in indenyl complexes,14 between the planes containing C1–C3
and C4–C9 is 14.8◦. In addition, phenyl coordination leads to
a noticeable perturbation of the electron delocalization within the
six-membered ring as revealed by a pronounced bond alternation,
e.g. with C–C bond lengths of 1.365(5), 1.416(5) and 1.351(5)
˚
A within the C6–C7–C8–C9 moiety. The crystal structure of
5
5
Scheme 1 Synthesis of phenylmethallyl potassium, K(oIndMe). Reagents
and conditions: (a) 1. Et2O, 0 ◦C → reflux, overnight; 2. HCl; 3.
KHSO4/MgSO4. (b) KOtBu/nBuLi, -78 ◦C.
the related indenyl complex [(h -C5Me5)Ru(h -C9H7)] displays a
similar, but slightly higher degree of bond alternation.15
K(oIndMe) is indefinitely storable under an inert atmosphere
(N2), and its THF solutions are stable for at least 24 h. The NMR
spectroscopic data are in agreement with earlier studies,9 which
suggested that the anion is held in the required U-conformation
(corresponding to an anti-orientation of the phenyl ring with
respect to the methyl substituent) in a similar fashion to that
described for the 2,4-dimethylpentadienyl anion.7 Accordingly,
the methyl group can be expected to be essential for the for-
5
mation of h -oIndMe complexes, since the related unsubstituted
phenylallyl anion adopts an S-conformation (corresponding to a
3
syn-orientation),11 and coordinates as an h -allyl ligand in several
Fig. 2 ORTEP diagram of 1 with thermal displacement parameters drawn
◦
examples.12
˚
at 30% probability. Selected bond lengths (A) and angles ( ): Ru–C(C5Me5)
2.161(3)–2.210(3), Ru–C1 2.199(3), Ru–C2 2.179(3), Ru–C3 2.178(3),
Ru–C4 2.216(3), Ru–C5 2.312(3), C1–C2 1.425(5), C2–C3 1.420(5),
C3–C4 1.442(5), C4–C5 1.445(5), C5–C6 1.430(5), C6–C7 1.365(5),
C7–C8 1.416(5), C8–C9 1.351(5), C4–C9 1.447(5); C1–C2–C3 121.9(3),
C2–C3–C4 127.2(3), C3–C4–C5 122.8(3).
Preparation of an open indenyl ruthenium(II) complex
Since many cyclopentadienyl-ruthenium sandwich complexes in-
corporating a broad variety of pentadienyl and heteropentadienyl
ligands are known,13 the preparation of the corresponding half-
open ruthenocene [(h -C5Me5)Ru(h -oIndMe)] (1) was attempted
5
5
Overall, the structural features resemble those found in
5
5
by the transmetallation reaction of tetrameric [(h -C5Me5)RuCl]4
related half-open ruthenocenes containing the (h -C5Me5)Ru
with four equivalents of K(oIndMe) (Scheme 2). Complex 1 could
be isolated after sublimation as an orange-red solid in 55% yield.
NMR spectroscopy clearly established the coordination of oIndMe
fragment.13b,c,g,i Similarly, the two ligands in 1 are reasonably
coplanar, with a tilt angle of 5.6◦ between the planes containing the
metal-bound carbon atoms. Although the metal–carbon distances
for the two ligands are comparable, the Ru atom is located much
as an h -pentadienyl ligand, since, for instance, the 1H NMR
5
˚
spectrum exhibits two distinct peaks for the ortho-hydrogen atoms
of the phenyl ring, whereby an extreme upfield shift from 6.42 to
2.89 ppm is observed for the phenyl CH group forming part of
closer to the plane of the acyclic ligand (1.616 versus 1.821 A) as
expected for a wider, open p-system.2 In 1, this opening is more
pronounced than observed in the related 2,4-dimethylpentadienyl
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5
5
complex [(h -C5Me5)Ru(h -2,4-C7H11)] as indicated by a larger
separation between the two terminal carbon atoms C1 and C5
13i
˚
(2.868 versus 2.783 A). It should also be noted that the open
indenyl coordination motif in 1 is related to that in a number
5
of cymantrene-based molecules containing h -hydronapthalenyl
ligands.16 In these cases, however, the presence of a bridging
CH2 unit at the electronically open edge affords smaller C–C
5
16c
˚
separations, e.g. 2.393 A for [Mn(h -C10H9)(CO)3]. In contrast
to 1, these complexes are not prepared by direct incorporation
of the hydronapthalenyl ligand, but generally from nucleophilic
attack of [Mn(h -C10H8)(CO3)]+ (h -C10H8 = naphthalene), which
6
6
is also a well-established method for the preparation of related
5
open cymantrenes of the type [Mn(h -cyclo-dienyl)(CO3)].2c
g5 to g3 hapticity interconversion
The sandwich complex 1 obeys the 18-electron rule, and con-
sequently, coordination of additional ligands to the ruthenium
atom is not possible unless the open indenyl ligand switches its
Fig. 3 ORTEP diagram of anti-2 with thermal displacement parameters
drawn at 50% probability. Selected bond lengths (A) and angles ( ):
Ru–C(C5Me5) 2.218(3)–2.256(3), Ru–C1 2.186(2), Ru–C2 2.122(2), Ru–C3
2.208(2), Ru–P 2.2955(6); C1–C2–C3 118.9(2).
5
3
◦
hapticity from an h to an h coordination mode. The 16-electron
intermediate would then provide a vacant coordination site for
an incoming substrate. Such an interconversion was observed
˚
5
5
for the related oxapentadienyl complex [(h -C5Me5)Ru(h -2,4-
C6OH9)] (2,4-C6OH9 = 2,4-dimethyloxapentadienyl), in which
the C–O p-bond coordination is broken upon reaction with
either PMe3 or CO under reflux for at least 6 h, affording the
complexes [(h -C5Me5)Ru(h -2,4-C6OH9)(L)] (L = PMe3, CO).13h
It is noteworthy that the PMe3 product was reportedto have limited
stability, whereas the reaction with CO did not lead to complete
conversion. In our hands, addition of one equivalent of PMe3
5
3
5
5
to [(h -C5Me5)Ru(h -oIndMe)] (1) at room temperature resulted
in a color change from orange to yellow within a few minutes
1
(Scheme 2). 31P{ H} NMR spectroscopy clearly confirmed PMe3
coordination and formation of complex 2 by a downfield shift
from -60.1 ppm for the free phosphine to 6.3 ppm. In addition,
the 1H and 13C NMR spectra display a number of couplings with
1
the 31P nucleus. Consequently, the H NMR spectrum exhibits a
single broad resonance (6.9–7.0 ppm) in the aromatic region for
the five H atoms of the displaced, uncoordinated phenyl group.
Similar observations were made upon reaction of 1 with carbon
monoxide or 2,6-dimethylphenyl isocyanide (CN-o-Xy), and the
spectroscopic data together with the elemental analyses are in
full agreement with the clean formation of [(h -C5Me5)Ru(h -
oInd)(L)] (2, L = PMe3; 3, L = CO; 4, L = CN-o-Xy) (Scheme
2, see Experimental section for details).
Fig. 4 ORTEP diagram of anti-3 with thermal displacement parameters
◦
˚
drawn at 50% probability. Selected bond lengths (A) and angles ( ):
Ru–C(C5Me5) 2.2071(18)–2.2772(18), Ru–C1 2.218(2), Ru–C2 2.1653(18),
Ru–C3 2.2204(17), Ru–C21 1.855(2), C21–O 1.159(3); Ru–C21–O
175.54(18), C1–C2–C3 120.39(17).
5
3
X-ray diffraction analyses of crystals of 2 and 3 confirmed
5
3
19
5
3
˚
that the open indenyl ligand has undergone an h –h hapticity
interconversion (Fig. 3 and 4), and the phenyl ring, which has
preserved its anti-orientation, now clearly tilts out of the allylic
plane with an increase of the absolute C1–C2–C3–C4 torsion
angle from 4.5◦ in 1 to 60.6◦ and 49.9◦ in 2 and 3, respectively.
The additional ligand is located next to the open edge of the allyl
moiety corresponding to the expected exo-conformation based on
Ph2-C3H3)(PPh3)] (Ru–P = 2.329(2) A), and [(h -C5H5)Ru(h -2-
18c
˚
Me-C3H4)(CO)] (Ru–C = 1.841(4) A).
It is remarkable how readily the open indenyl complex 1 is
able to provide the 16-electron (h -C5Me5)Ru-allyl complex frag-
5
5
5
ment, since the related pentadienyl complex [(h -C5Me5)Ru(h -
2,4-C7H11)] does not react with PMe3 or CO, even under reflux
conditions.13h Additionally, although photoelectron spectroscopy
and theoretical studies suggested that the metal-pentadienyl is
generally stronger than the metal-heteropentadienyl bond,20 thus
providing a greater reactivity for the latter, we have apparently
managed to reverse the usual order.3 Undoubtedly, the enhanced
reactivity of 1 can be ascribed to rearomatization as the main driv-
detailed studies on d6-[(h -C5H5)M(h -allyl)(L)] complexes (L =
CO, PR3), which revealed that the exo-isomer is usually more stable
than the endo-isomer.17,18 The Ru–L bond distances, at 2.2955(6)
5
3
˚
and 1.855(2) A for the PMe3 and the CO adduct, respectively, are
5
3
in line with those reported for the complexes [(h -C5Me5)Ru(h -
2,4-C6OH9)(PPh3)] (Ru–P = 2.3205(8) A),13h [(h -C5H5)Ru(h -1,1-
ing force upon ligand addition and concomitant h –h hapticity
5
3
5
3
˚
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interconversion. Therefore, the use of open indenyl ligands such
as oIndMe offers an alternative and facile access to coordinatively
unsaturated cyclopentadienyl-allyl ruthenium(II) species, which
are otherwise generated by stepwise methods, e.g. by reduction
phenyl group, the structural parameters of syn-2 and anti-2 are
very similar.
Since the anti to syn isomerization proceeds slowly at room
temperature, this process can conveniently be followed by NMR
spectroscopy. Thus, a sample of anti-2 in C6D6 was sealed in an
NMR tube, heated at 50◦ C (323 K) for 21 days and regularly
monitored by 31P and 1H NMR spectroscopy (see Electronic
supplementary information for details‡). As expected, a new
signal at 11.4 ppm in the 31P NMR assigned to syn-2 became
predominant, while the resonance of anti-2 at 6.3 ppm decreased
over time (Fig. 6). After 14 days, about 98% of the original isomer
was converted, as determined by integration of the respective
resonances. Since no further increase of the syn/anti ratio of
98 : 2 was observed for another seven days, we assume that this
distribution represents the equilibrated system.
5
3
of Ru(IV) precursors such as [(h -C5Me5)Ru((h -allyl)X2] (X = Cl,
Br).21
Study of anti to syn isomerization
3
In the solid state, the h -oIndMe ligand in the PMe3 and CO com-
plex 2 and 3 displayed the original anti-orientation of the methyl
and phenyl substituents, and NMR spectroscopic characterization
indicated the (almost) exclusive formation of these isomers as the
kinetic products.22 When we checked sealed NMR samples after
about half a year at room temperature, no changes were observed
for the CO complex 3, whereas the 1H, 13C and 31P NMR spectra
of the phosphine congener 2 revealed the presence of considerable
amounts of an additional species.
Heating this sample for several days eventually resulted in the
disappearance of the peaks assigned to the original product and in
the predominant formation of a new compound (Scheme 3). We
were able to grow crystals suitable for X-ray diffraction analysis
from this sample, and the resulting molecular structure is shown
in Fig. 5. In contrast to anti-2 (vide supra, Fig. 3), the phenyl
group now points away from the PMe3 ligand and adopts a syn-
orientation with respect to the methyl group, while preserving
the exo-conformation. In analogy to various experimental and
theoretical studies on syn-anti isomerization in palladium, nickel
or ruthenium complexes,23 formation of the isomer syn-[(h -
5
3
1
C5Me5)Ru(h -oIndMe)(PMe3)] (syn-2) can be rationalized by a h -
oIndMe intermediate with an Ru–C3 bond that allows rotation
around the C2–C3 bond. Apart from the different position of the
Fig. 6 Change of the proportion of anti-2 and syn-2 in C6D6 at 50 ◦C
monitored by 31P NMR spectroscopy over a period of 21 days.
Following the established treatment for a first-order reaction
proceeding to equilibrium,24 a plot ln(Asyn-2,•-Asyn-2,t) against time
confirmed the isomerization to be a first-order process with a rate
constant of k323 K = 6.57 ¥ 10-6 ( 0.02 ¥ 10-6) s-1,25 corresponding to
a half-life of 29.3 h and a free activation energy of DG◦ = 26.8 kcal
mol-1 at T = 323 K (Fig. 7).
Scheme 3 Slow isomerization of anti-2 to syn-2.
Fig. 7 First-order kinetic plot for the conversion of anti-2 to syn-2 in
C6D6 at 50 ◦C monitored by 31P NMR spectroscopy.
To assess the different stabilities of the anti- and syn-isomers,
DFT calculations employing the M06 functional were carried out
for 2 and 3 (Table 1). Although the thermodynamic preference for
the syn-isomer, with DG298 = -1.54 (2) and -1.74 kcal mol-1 (3), is
Fig. 5 ORTEP diagram of syn-2 with thermal displacement parame-
˚
ters drawn at 50% probability. Selected bond lengths (A) and angles
(◦): Ru–C(C5Me5) 2.2055(13)–2.2837(14), Ru–C1 2.1672(14), Ru–C2
2.1308(13), Ru–C3 2.2439(13), Ru–P 2.2953(4); C1–C2–C3 114.73(13).
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Table 1 M06 energies and enthalpies (in kcal mol-1) for the anti to syn
isomerization of complexes 2 and 3a
assignment of signals was supported by 2D experiments (COSY,
HSQC, HMBC, NOESY). A Bruker Vertex 70 spectrometer
was used for recording the IR spectra. Elemental analyses were
performed by combustion and gas chromatographical analysis
with an Elementar varioMICRO instrument. The mixture of the
isomers 2-methyl-1-phenyl-1-propene and 2-methyl-3-phenyl-1-
Complex
DEel
DE0
DH298
DG298
2 (L = PMe3)
3 (L = CO)
-1.30
-1.45
-1.36
-1.51
-1.40
-1.39
-1.54
-1.74
5
propene was prepared according to the literature,9b as was [(h -
a DEel: zero-point uncorrected electronic energies, DE0: relative energies at
0 K, DH298: enthalpies at 298 K, DG298: Gibbs free energies at 298 K.
C5Me5)RuCl]4.30 All other reagents were obtained commercially
and used as received.
fairly low in both cases, these calculations confirm that the anti-
isomers are only the kinetic products, which can be expected to
isomerize slowly to the syn-product, as observed for the phosphine
species 2. The Gibbs–Helmholtz equation (DG298 = -RTlnK)
affords an equilibrium constant of K298 K = csyn/canti = 13.4, which
corresponds to 93% conversion and is in good agreement with
the experimentally derived value of K323 K = 49 (based on 98%
conversion, vide supra).
X-ray diffraction studies
Data were recorded at 100 K on Oxford Diffraction diffractome-
ters using monochromated Mo-Ka or mirror-focussed Cu-Ka
radiation. The structures were refined anisotropically using the
SHELXL-97 program.31 Hydrogen atoms were either (i) located
and refined isotropically (H1A, H1B, H3, and for 1 H5; in some
cases with constraints to C–H bond lengths); (ii) included as
idealized methyl groups allowed to rotate but not tip or (iii) placed
geometrically and allowed to ride on their attached carbon atoms.
For compound 3, the Flack parameter refined to 0.000(8). Crystal
and structure refinement data are summarized in Table 2.
The disparate behaviour of the CO congener 3, which does not
rearrange to a syn-isomer at room temperature, could be ascribed
to a higher activation barrier, since a stronger p-acceptor can be
3
1
3
expected to disfavour the h -h -h process,23i,26 whereas a strong
1
s-donor such as PMe3 should stabilize the h -oIndMe intermediate
(or transition state). In addition, the different steric properties
of the PMe3 and CO ligands (see Fig. 3 and 4) might have a
considerable impact on the rates of the anti to syn isomerization.
Theoretical calculations
All computations were performed using the density functional
method M06 as implemented in the Gaussian09 program.32 For
all main-group elements (C, H, P and O), the all-electron triple-z
basis set (6-311G**) was used,33 whereas for ruthenium a small-
core relativistic ECP together with the corresponding double-z
valence basis set was employed (Stuttgart RSC 1997 ECP).34
Conclusions
The phenylmethallyl ligand oIndMe was shown to be capable
5
of binding to transition metals in a h -fashion, as exemplified
5
5
by preparation of the half-open ruthenocene [(h -C5Me5)Ru(h -
oIndMe] (1). In analogy to indenyl complexes,4 this “open indenyl”
system is susceptible to ligand addition by undergoing a ready
2-Methyl-1-phenylallylpotassium, K(oIndMe
)
A suspension of potassium tert-butoxide (6.03 g, 53.7 mmol)
in 60 mL of pentane was prepared, and 2-methyl-1-phenyl-1-
propene/2-methyl-3-phenyl-1-propene (7.10 g, 53.7 mmol) was
added via a syringe. The mixture was cooled to -78 ◦C and n-
butyllithium (22.6 mL, 2.5 M, 56.5 mmol) in hexane was added
slowly and carefully. After stirring overnight, during which time
the mixture was allowed to warm up, the orange precipitate was
collected on a frit and washed with 2 ¥ 20 mL, 2 ¥ 15 mL and 3 ¥
10 mL of pentane. Finally, the bright orange, pyrophoric product
5
3
h to h hapticity interconversion, a reaction that has rarely been
observed for the corresponding pentadienyl (“open cyclopenta-
dienyl”) complexes. Thus, open indenyl complexes such as 1 can
be expected to exhibit interesting reactivity by providing a co-
ordinatively unsaturated cyclopentadienyl-allyl complex fragment
under mild conditions, and, for instance, C–C coupling reactions
with alkynes to form new pentadienyl or vinylidene species could
5
3
be envisaged.27,28 Furthermore, in view of the relevance of h –h
haptotropic rearrangements29 and of allyl ruthenium species as
intermediates in homogeneous catalysis,8 the use of open indenyl
complexes in organotransition metal catalysed reactions can be
anticipated.
1
was dried under vacuum (7.4 g, 81%). H NMR (400 MHz, d8-
THF, ambient): d = 6.63 (br s, 2 H, m-Phenyl), 6.42 (br s, 2 H,
o-Phenyl), 5.76 (t, 3JHH = 7.0 Hz, 1 H, para-phenyl), 3.81 (d, 4JHH
=
1.7 Hz, 1 H, H3), 3.38 (d, 2JHH = 2.5 Hz, 1 H, anti-H1), 3.21 (br
s, 1 H, syn-H1), 1.77 (s, 3 H, H10). 13C NMR (100 MHz, d8-THF,
ambient): d = 146.9 (C4), 143.1 (C2), 128.9 (br, m-Phenyl), 108.7
(p-Phenyl), 80.8 (C3), 73.6 (C1), 29.5 (C10). The hindered rotation
around the C3–C4 bond at room temperature results in a broad
resonance for the meta-carbon atom, whereas the ortho-carbon
atom is not observed. At 222 K four separate peaks (130, 128, 123
and 113 ppm) are detected. Because of the extreme air-sensitivity,
it was not possible to obtain an accurate elemental analysis.
Experimental section
All synthetic and spectroscopic manipulations were carried out
under an atmosphere of prepurified nitrogen, either in a Schlenk
apparatus or in a glovebox. Solvents were dried and deoxygenated
either by distillation under a nitrogen atmosphere from sodium
benzophenone ketyl (THF) or by an MBraun GmbH solvent
purification system (all other solvents). NMR spectra were
recorded on Bruker DPX 200, Bruker AV 300 and Bruker DRX
400 spectrometers. The chemical shifts are expressed in parts per
million (ppm) and are referenced to residual 1H of the solvent, the
13C resonance of the solvent, or external H3PO4. If required, the
[(g5-C5Me5)Ru(g5-oIndMe)] (1)
◦
At -78 C, a dark yellow solution of K(oIndMe) (0.188 g,
1.10 mmol) in 10 mL of THF was added dropwise with a syringe to
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Dalton Trans., 2011, 40, 11511–11518 | 11515
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Table 2 Crystal and structure refinement for compounds 1, 2 and 3
1
anti-2
anti-3
syn-2
Empirical formula
Formula weight
T/K
C20H26Ru
367.48
100(2)
1.54184
Monoclinic
P21/c
13.4601(2)
7.1135(1)
17.8388(2)
90
104.424(2)
90
1654.20(4)
4
C23H35PRu
443.55
100(2)
0.71073
Orthorhombic
Pccn
34.0568(14)
14.0658(6)
8.9452(4)
90
90
90
4285.1(3)
8
C21H26ORu
395.49
100(2)
1.54184
Orthorhombic
Pna21
11.5667(2)
12.0145(2)
13.0890(2)
90
C23H35PRu
443.55
100(2)
0.71073
Monoclinic
P21/n
8.3388(2)
17.1916(6)
15.4241(6)
90
105.443(4)
90
2131.33(12)
4
˚
Wavelength l/A
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
90
90
3
˚
Volume/A
Z
1818.95(5)
4
Reflections collected
Independent reflections
rc/g cm-3
20622
3419 [Rint = 0.0347]
1.476
7.572
0.0341
0.0903
1.077
108761
4371 [Rint = 0.1076]
1.375
0.810
0.0246
0.0265
0.849
0.472/-0.425
20543
4166 [Rint = 0.0436]
1.444
6.973
0.0193
0.0534
1.053
63644
4865 [Rint = 0.0349]
1.382
0.814
0.0188
0.0441
1.046
m/mm-1
R(Fo), [I > 2s(I)]
2
Rw (Fo
)
Goodness of fit on F2
-3
˚
Dr/e A
2.823/-0.808
0.319/-0.627
0.360/-0.345
5
a dark red suspension of [(h -C5Me5)RuCl]4 (0.300 g, 0.28 mmol)
in 30 mL of THF. After the slow warm-up and stirring for a total
time of 3.5 h, the solvent was removed from the dark red solution.
Drying at 50 ◦C for 1.5 h and subsequent sublimation (0.1 mbar,
100 ◦C) yielded a red-orange solid (0.222 g, 54%). Single crystals
were obtained by slow sublimation in a sealed glass tube. 1H NMR
(400 MHz, C6D6, ambient): d = 6.93 (br d, 1 H, Phenyl), 6.84 (br
t, 1 H, Phenyl), 6.78 (br t, 1 H, Phenyl), 6.68 (t of t, 3JHH = 7.4 Hz,
4JHH = 0.9 Hz, 1 H, Phenyl), 5.22 (s, 1 H, H3), 2.89 (d, 3JHH = 5.1
Hz, 1 H, H5), 2.49 (d of d, 2JHH = 3.2 Hz, 4JHH = 0.9 Hz, 1 H, syn-
H1), 1.81 (s, 3 H, H10), 1.43 (s, 15 H, C5Me5), 0.48 (d, 2JHH = 3.1
Hz, 1 H, anti-H1). 13C NMR (100 MHz, C6D6, ambient): d = 137.5
(Phenyl), 127.9 (Phenyl), 125.2 (Phenyl), 118.7 (Phenyl), 100.9 (C2
or C4), 94.9 (C2 or C4), 85.3 (C5Me5), 85.0 (C3), 66.8 (C5), 44.3
(C1), 25.8 (C10), 10.0 (C5Me5). Elemental analysis (%): calculated
for C20H26Ru (366.68): C = 65.37, H = 7.13; found: C = 65.24, H =
7.06.
calculated for C23H35PRu (443.57): C = 62.28, H = 7.95; found: C =
62.29, H = 7.97.
Isomerization from anti-2 to syn-2
Isomerization was achieved by heating a sample of anti-2 to 50 ◦C
in either hexane or C6D6 over a period of 14 days. Single crystals
of syn-2 were obtained by cooling a saturated pentane solution to
-30 ◦C. 1H NMR (400 MHz, C6D6, ambient): d = 7.44 (d of m, 2
H, 3JHH = 7.8 Hz, o-Phenyl), 7.25 (m, 2 H, m-Phenyl), 7.08 (t of t
of br d 3JHH = 7.4 Hz, 4JHH = 1.3 Hz, 1 H, p-Phenyl), 2.25 (s, 3 H,
H10), 2.06 (d, 3JPH = 18.0 Hz, 1 H, H3), 1.79 (br d, 3JPH = 1.8 Hz,
1 H, syn-H1, 1.58 (d, 4JPH = 1.3 Hz, 15 H, C5Me5), 0.97 (d, 2JPH
=
7.2 Hz, 9 H, PMe3), 0.69 (d of m, 3JPH = 19.8 Hz, 1 H, anti-H1).
13C NMR (100 MHz, C6D6, ambient): 146.8 (s, ipso-Phenyl), 130.0
(o-Phenyl), 127.7 (m-Phenyl), 123.4 (p-Phenyl), 89.0 (d, 2JPC = 2.3
Hz, C5Me5), 79.3 (d, 2JPC = 2.7 Hz, C2), 49.9 (d, 2JPC = 5.4 Hz, C3),
33.1 (d, 2JPC = 7.1 Hz, C1), 22.2 (d, 3JPC = 1.6 Hz, C10), 18.8 (d,
1
1JPC = 26.1 Hz, PMe3), 11.0 (C5Me5). 31P{ H} NMR (161 MHz,
[(g5-C5Me5)Ru(g3-oIndMe)(PMe3)] (2)
C6D6, ambient): d = 11.3 (s, PMe3).
[(g5-C5Me5)Ru(g3-oIndMe)(CO)] (3)
Compound 1 (0.100 g, 0.27 mmol) was dissolved in 10 mL of
pentane. The addition of PMe3 (29 mL, 0.28 mmol) with a micro-
syringe resulted in a color change from dark orange to yellow
within 10 min. The solvent was removed in vacuo and a yellow
solid was isolated (0.077 g, 64%). Single cryst◦als were obtained
by cooling a saturated pentane solution to -15 C. 1H NMR (400
MHz, C6D6, ambient): d = 7.13–6.85 (br m, 5 H, Phenyl), 4.17
(s, 1 H, H3), 2.37 (m, 1 H, syn-H1), 2.03 (s, 3 H, H10), 1.68 (d,
Compound 1 (0.100 g, 0.27 mmol) was dissolved in 10 mL of
pentane. Then CO (0.6 bar) was bubbled through the solution for
one minute accompanied by a color change from dark orange to
yellow. Stirring was continued for another minute and the solvent
was subsequently removed under vacuum yielding a yellow solid
(77 mg, 71%). Single crystals were obtained by cooling a saturated
pentane solution to -15 ◦C. 1H NMR (400 MHz, C6D6, ambient):
d = 7.13–7.08 (br m, 4 H, Phenyl), 6.93–6.89 (br m, 1 H, Phenyl),
4.37 (s, 1 H, H3), 2.62 (m, 1 H, syn-H1), 2.60 (m, 1 H, anti-
H1), 1.68 (s, 3 H, H10), 1.64 (s, 15H, C5Me5). 13C NMR (100
MHz, C6D6, ambient): d = 209.2 (CO), 148.9 (ipso-Phenyl), 128.5
(Phenyl), 125.7 (Phenyl), 123.7 (Phenyl), 94.6 (C5Me5), 85.4 (C2),
58.2 (C3), 37.2 (C1), 26.1 (C10), 10.7 (C5Me5). Elemental analysis
4JPH = 1.2 Hz, 15 H, C5Me5), 1.43–1.38 (br d, JPH = 20.5 Hz, 1
3
H, anti-H1), 0.68 (d, JPH = 7.6 Hz, 9 H, PMe3). 13C NMR (100
2
3
MHz, C6D6, ambient): d = 152.1 (d, JPC = 9.6 Hz, ipso-Phenyl),
128.3 (Phenyl), 128.0 (Phenyl), 122.5 (Phenyl), 89.7 (d, 2JPC = 2.0
2
2
Hz, C5Me5), 76.1 (d, JPC = 2.0 Hz, C2), 50.2 (d, JPC = 6.0 Hz,
2
3
C3), 33.6 (d, JPC = 6.6 Hz, C1), 26.0 (d, JPC = 2.0 Hz, C10),
18.9 (d, 1JPC = 25.0 Hz, PMe3), 11.3 (C5Me5). 31P{ H} NMR (161
1
MHz, C6D6, ambient): d = 6.2 (s, PMe3). Elemental analysis (%):
11516 | Dalton Trans., 2011, 40, 11511–11518
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(%): calculated for C21H26ORu (395.50): C = 63.77, H = 6.63; found:
C = 63.96, H = 6.49. IR (Nujol): n(CO/cm-1) = 1946.
2009, 28, 3437; (e) A. B. Zaitsev, H. F. Caldwell, P. S. Pregosin and L.
F. Veiros, Chem.–Eur. J., 2009, 15, 6468.
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1967, 86, 1345; (b) R. Knorr and E. Lattke, Chem. Ber., 1981, 114,
2116; (c) R. Knorr, M. Hintermeyer-Hilpert and P. Bo¨hrer, Chem. Ber.,
1990, 123, 1137; (d) H. Balzer and S. Berger, Chem. Ber., 1992, 125,
733.
[(g5-C5Me5)Ru(g3-oIndMe)(CN-o-Xy)] (4)
Compound 1 (0.100 g, 0.27 mmol) was dissolved in 10 mL of
pentane. The addition of CN-o-Xy (0.035 g, 0.27 mmol) in 3 mL
of pentane with a pipette resulted in a color change from dark
orange to dark yellow within 5 min. The solvent was removed in
vacuo and the yellow solid was crystallized from pentane at -30 ◦C
(0.101 g, 74%). 1H NMR (400 MHz, C6D6, ambient): d = 7.03 (d
10 D. R. Wilson, L. Stahl and R. D. Ernst, Organomet. Synth., 1986, 3,
136.
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1634.
3
3
of m, JHH = 7.9 Hz, 2 H, Phenyl), 6.78 (t of br m, JHH = 7.7
3
Hz, 2 H, Phenyl), 6.70 (m, 3 H, Phenyl), 6.48 (t of m, JHH = 7.4
Hz, 1 H, Phenyl), 4.40 (s, 1 H, H3), 2.73 (m, 1 H, syn-H1), 2.55
(m, 1 H, anti-H1), 2.06 (s, 6 H, CH3), 1.92 (s, 3 H, H10), 1.81 (s,
15 H, C5Me5). 13C NMR (100 MHz, C6D6, ambient): d = 150.3
(ipso-Phenyl), 133.5 (ipso-Phenyl), 128.6 (Phenyl), 127.7 (Phenyl),
125.5 (Phenyl), 125.3 (Phenyl), 122.3 (Phenyl), 92.6 (C5Me5), 82.3
(C2), 57.0 (C3), 36.9 (C1), 27.0 (C10), 18.9 (CH3), 11.1 (C5Me5).
One carbon signal is probably hidden under the solvent peak;
the resonance for the isocyanide carbon atom was not observed.
Elemental analysis (%): calculated for C29H35NRu (498.67): C =
69.85, H = 7.07, N = 2.81; found: C = 69.97, H = 7.11, N = 2.88.
IR (ATR): n(CN/cm-1) = 2003.
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Acknowledgements
A.G. acknowledges Richard D. Ernst (University of Utah) for
his guidance, encouragement and continuous support, and also
thanks Greg Turpin for the many helpful discussions in the
Department of Chemistry at the University of Utah. This work
was supported by the Fonds der Chemischen Industrie.
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1 applies.
=
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