Stable cationic and neutral ruthenabenzenes

Article abstract of DOI:10.1021/om800857k

Reversible protonation of the purple ruthenabenzofuran (or tethered ruthenacyclohexadiene) Ru[C₅H₂- (C0₂Me-2) (CO₂Me-4)(CHCO₂Me-5)](CO)(PPh₃)2 (1) with HBF₄OEt₂ gives

Full text of DOI:10.1021/om800857k

Organometallics 2009, 28, 567–572
567
Stable Cationic and Neutral Ruthenabenzenes
George R. Clark, Tamsin R. O’Neale, Warren R. Roper,* Deborah M. Tonei, and
L. James Wright*
Department of Chemistry, The UniVersity of Auckland, PriVate Bag 92019, Auckland, New Zealand
ReceiVed September 4, 2008
Reversible protonation of the purple ruthenabenzofuran (or tethered ruthenacyclohexadiene) Ru[C5H2-
(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) with HBF4 · OEt2 gives the structurally characterized
stable cationic tethered ruthenabenzene [Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)](CO)(PPh3)2]-
[(BF4)2H] (2), while the thermal reaction of 1 with HCl forms the stable neutral tethered ruthenabenzene
Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]Cl(PPh3)2 (3) as the major product. The cyclopentadienyl
complex Ru(η5-C5H2(CH2CO2Me-1)(CO2Me-2)(CO2Me-4)Cl(CO)(PPh3) (4), which is formed in this
reaction as a minor product, can be separated from 3 by chromatography. Treatment of the ruthenabenzene
3 with CNR (R ) p-tolyl) gives the purple ruthenabenzofuran (or tethered ruthenacyclohexadiene) complex
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CNR)(PPh3)2 (5), which is the isocyanide analogue of 1.
quently obtained by ligand substitution at ruthenium.8 These
compounds remain the only simple metallabenzenes that involve
a metal from the second transition series that are stable under
ambient conditions.
Introduction
Metallabenzenes are now a well-established class of orga-
nometallic compounds, and considerable attention has been
directed toward developing synthetic routes and studying the
reaction chemistry of these compounds.1 In addition, important
fundamental information has been provided by a number of
computational studies that have explored aspects of the syn-
theses, reactivity, decomposition pathways, and aromatic char-
acter of these materials.1,2 Despite this scrutiny, nearly all of
the reported metallabenzenes that are stable under ambient
conditions are confined to derivatives of the third-row transition
metals osmium, iridium, and platinum. Metallabenzenes or
metallabenzenoids of the first- or second-row transition metals
iron,3 chromium,4 and ruthenium5,6 have been proposed as
reactive intermediates, and the ruthenabenzene Ru[C(Ph)CH-
CHC(Ph)C(OEt)](CO)Cp, a related ruthenaphenoxide, and a
ruthenaphenanthrene oxide have been detected spectroscopically
at low temperatures.6 However, it was not until 2006 that the
first stable metallabenzene of a second-row transition metal was
isolated. In that year Jia, Xia, and co-workers reported the
synthesis and study of the ruthenabenzene [Ru[CHC(PPh3)-
CHC(PPh3)CH]Cl2(PPh3)2]Cl.7 This remarkable compound re-
mains mostly unchanged after heating in the solid state in air
at 100 °C for 5 h. It was proposed that the two bulky
triphenylphosphonium substituents on the ruthenabenzene ring
play an important role in stabilizing this compound as well as
the other related ruthenabenzene derivatives that were subse-
In this paper we now report (i) the synthesis of the stable
blue cationic tethered ruthenabenzene [Ru[C5H2(CO2Me-2)-
(CO2Me-4)(CH2CO2Me-5)](CO)(PPh3)2][(BF4)2H] (2) through pro-
tonation of the ruthenabenzofuran (or tethered ruthenacyclohexa-
diene) Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2
(1) with HBF4 · OEt2; (ii) the synthesis of the stable green neutral
tethered ruthenabenzene Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2-
Me-5)]Cl(PPh3)2 (3) through reaction of 1 with HCl in benzene/
methanol solution heated under reflux; (iii) isolation of the
cyclopentadienyl complex Ru(η5-C5H2(CH2CO2Me-1)(CO2Me-
2)(CO2Me-4)Cl(CO)(PPh3) (4) as a byproduct from the thermal
reaction of 1 with HCl; (iv) the conversion of 3 to the ruthenaben-
zofuran (or tethered ruthenacyclohexadiene) complex Ru[C5H2-
(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CNR)(PPh3)2 (5) through
treatment with p-tolylisocyanide, and (v) the crystal structures of
2, 4, and 5.
Results and Discussion
In a recent paper we described the synthesis and some reaction
chemistry of the osmabenzofuran Os[C7H2O(OMe-7)(CO2Me-
4)(Ph-1)(Ph-2)](CS)(PPh3)2.9 The case for considering this com-
pound as an osmabenzofuran with delocalized bonding was
developed on the basis of spectroscopic, structural, and reactivity
data. One of the important reactions this compound undergoes is
protonation of C6 in the osmafuran ring to form the cationic,
tethered osmabenzene [Os[C5H(CH2CO2Me-5)(CO2Me-4)(Ph-
1)(Ph-2)](CS)(PPh3)2]+ (see Chart 1).9 A ruthenium complex,
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1), that
has the same basic metallabicyclic skeleton as this osmabenzofuran
and can also be considered as a ruthenabenzofuran9 (see Chart 2
and discussion below) has been reported to form through reaction
* Corresponding authors. E-mail: lj.wright@auckland.ac.nz; w.roper@
auckland.ac.nz.
(1) For example see: (a) Bleeke, J. R. Chem. ReV. 2001, 101, 1205. (b)
Landorf, C. W.; Haley, M. M. Angew. Chem., Int. Ed. 2006, 45, 3914. (c)
Wright, L. J. J. Chem. Soc., Dalton Trans. 2006, 1821, and references
therein.
(2) (a) Ferna´ndez, I.; Frenking, G. Chem.-Eur. J. 2007, 13, 5873. (b)
Zhu, J.; Jia, G.; Lin, Z. Organometallics 2007, 26, 1986.
(3) Ferede, R.; Allison, N. T. Organometallics 1983, 2, 463.
(4) Sivavec, T. M.; Katz, T. J. Tetrahedron Lett. 1985, 26, 2159.
(5) Yang, J.; Yin, J.; Abboud, K. A.; Jones, W. M. Organometallics
1994, 13, 971.
(6) Yang, J.; Jones, W. M.; Dixon, J. K.; Allison, N. T. J. Am. Chem.
Soc. 1995, 117, 9776.
(7) Zhang, H.; Xia, H.; He, G.; Wen, T.; Gong, L.; Jia, G. Angew. Chem.,
Int. Ed. 2006, 45, 2920.
(8) Zhang, H.; Feng, L.; Gong, L.; Wu, L.; He, G.; Wen, T.; Yang, F.;
Xia, H. Organometallics 2007, 26, 2705.
(9) Clark, G. R.; Johns, P. M.; Roper, W. R.; Wright, L. J. Organome-
tallics 2006, 25, 1771.
10.1021/om800857k CCC: $40.75
2009 American Chemical Society
Publication on Web 12/11/2008

568 Organometallics, Vol. 28, No. 2, 2009
Clark et al.
Chart 1
Scheme 1. Synthesis of the Tethered Metallabenzenes 2 and
3 and Formation of the Ruthenabenzofuran 5
Chart 2
between RuH2(CO)(PPh3)3 and methyl propiolate.10,11 We therefore
investigated the reactions of 1 with acid to determine whether a
related protonation reaction would occur at C6 in the ruthenafuran
ring, thereby leading to the formation of a tethered ruthenabenzene.
On treatment of a toluene solution of purple Ru[C5H2-
(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) with
HBF4 · OEt2, the solution immediately turns dark blue, and dark
blue crystals of the cationic, tethered ruthenabenzene [Ru[C5H2-
(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)](CO)(PPh3)2][(BF4)2H]
(2) are deposited from solution (see Scheme 1). Although 2
can be successfully recrystallized from dichloromethane/toluene,
this protonation reaction is readily reversed, and addition of
bases such as NEt3 to dichloromethane solutions of this product
causes immediate reversion back to 1. Complex 2, which is
stable in solution at 25 °C for days, has been thoroughly
characterized, including by a crystal structure determination (see
below). Characterizing data for 2 as well as 3-5 are collected
in the Experimental Section, and the numbering scheme used
for the NMR assignments is given in Scheme 1. In the 1H NMR
spectrum of 2, H1 appears as a doublet (4JH1H3 ) 2.4 Hz) at
14.97 ppm. Resonances in this downfield region are typically
observed for protons attached to the metal-bound carbon atoms
of metallabenzenes,1 and the signal for the two equivalent RuCH
atoms in the stable ruthenabenzene [Ru[CHC(PPh3)CHC-
(PPh3)CH]Cl2(PPh3)2]Cl appears at 17.5 ppm.7 H3 (8.83 ppm)
in 2 appears in the aromatic region, and the two protons attached
to C6 are observed at 2.73 ppm (cf. 6.06 ppm in 1), consistent
with saturation of this ring carbon atom. In the 13C NMR
The crystal structure of complex 2 was determined, and the
structure of the cationic ruthenium complex is shown in Figure
1 (crystal data for 2 as well as for 4 and 5 are given in the
Supporting Information). The geometry about Ru is ap-
proximately octahedral, and the six atoms of the ruthenabenzene
ring (Ru, C1-C5) and the three atoms of the tethering arm (C6,
C7, and O6) are all essentially coplanar (maximum deviation
from the mean plane through all nine atoms is 0.072 Å). The
Ru-C1 and Ru-C5 distances are 1.933(4) and 2.045(5) Å,
respectively. The trans-influence of the CO ligand is probably
the main factor responsible for the greater length of the Ru-C5
bond. The C-C distances within the ruthenabenzene ring of 2
(C1-C2, 1.404(6); C2-C3, 1.383(7); C3-C4, 1.413(7); C4-C5,
spectrum of 2, C1 and C5 appear as triplets at 290.8 (2JCP
)
6.1 Hz) and 283.6 (2JCP ) 7.7 Hz) ppm, respectively, positions
that are very similar to that reported for the two equivalent RuC
atoms in the ruthenabenzene [Ru[CHC(PPh3)CHC(PPh3)CH]-
Cl2(PPh3)2]Cl (284.3 ppm).7 C6 is observed at 52.3 ppm (cf.
119 ppm in 1), again consistent with saturation of this carbon
atom.
Figure 1. Molecular structure of the ruthenium cation of 2 with
thermal ellipsoids at the 50% probability level. Selected distances
[Å]: Ru-C1 1.933(4), Ru-C5 2.045(5), Ru-C13 1.941(5), Ru-O6
2.216(3), C1-C2 1.404(6), C2-C3 1.383(7), C3-C4 1.413(7),
C4-C5 1.374(7), C5-C6 1.518(7), C6-C7 1.504(8), O6-C7
1.231(7).
(10) Yamazaki, H.; Aoki, K. J. Organomet. Chem. 1976, 122, C54.
(11) Bruce, M. I.; Hall, B. C.; Skelton, B. W.; Tiekink, E. R. T.; White,
A. H.; Zaitseva, N. N. Aust. J. Chem. 2000, 53, 99.

Stable Cationic and Neutral Ruthenabenzenes
Organometallics, Vol. 28, No. 2, 2009 569
1.374(7) Å) are close to those found in benzene (1.390 Å)12
and show relatively little alternation. The C5-C6 and C6-C7
distances (1.518(7) and 1.504(8) Å, respectively) in 2 are
significantly longer than the corresponding distances in 1
(1.384(8) and 1.41(1) Å), consistent with saturation of C6. The
counteranion in the crystal is comprised of the very unusual
[(BF4)2H]- ion. The fluorine atoms in one of the [BF4]- groups
(the one involving B2) in this counteranion are disordered
between two slightly different positions, and the half-weighted
sets of atoms used in the refinement are labeled F5a-F8a and
-
F5b-F8b. In each orientation of the disordered BF4 unit one
fluorine atom (F8a or F8b) makes a close approach to F4 of
-
the other ordered BF4 (B1) unit, with F4 · · · F8a ) 2.597 Å
and F4 · · · F8b ) 2.750 Å. Both these distances are longer than
the F-H · · · F distance of 2.49 Å in crystalline hydrogen
fluoride,13 but both are considerably shorter than the sum of
the van der Waals radii for two fluorine atoms (ca. 2.94 Å)14
and are therefore consistent with a hydrogen bond between F4
and F8a/b. Furthermore, the B1-F4 distance (1.428(10) Å) is
longer than the other three B1-F distances (B1-F1, 1.361(9);
B1-F2, 1.366(8); B1-F3, 1.379(9) Å), and likewise the
B2-F8a and B2-F8b distances are longer than the other B2-F
distances. In the difference Fourier map there is a peak between
F4 and the disordered atoms F8a and F8b. However, the position
of this peak was not sufficiently reliable to justify its inclusion
as a hydrogen atom in the least-squares refinement. Although
this putative hydrogen atom was not located in the crystal
structure determination, its presence can be inferred from the
structural features noted above. In the 19F NMR spectrum of 2
only one sharp resonance at -154.49 ppm is observed,
indicating that in solution equilibration of the positions of all
fluorine atoms occurs rapidly on the NMR time scale.
In an attempt to prepare a neutral ruthenabenzene, the reaction
of 1 with HCl was investigated. It was found that on heating 1
under reflux for 4.5 h in benzene/methanol that contains a small
amount of trimethylsilyl chloride (a convenient way of introduc-
ing nonaqueous HCl to the system) while irradiating the mixture
with visible light, the solution slowly changes color from purple
to bright green. After purification of the reaction products by
column chromatography two products were obtained, the green
Figure 2. Molecular structure of 4 with thermal ellipsoids at the
50% probability level. Selected distances [Å]: Ru-C13 1.8729(18),
Ru-C1 2.2942(17), Ru-C2 2.2069(17), Ru-C3 2.1808(17),
Ru-C4 2.2222(16), Ru-C5 2.3113(16), Ru-P 2.3260(4), Ru-Cl
2.3914(4), C5-C6 1.499(2), C6-C7 1.528(3).
NMR spectrum a singlet at 21.55 ppm is observed for the two
equivalent phosphorus atoms.
The other product formed during the synthesis of 3 from 1
was the cyclopentadienyl complex Ru(η5-C5H2(CH2CO2Me-
1)(CO2Me-2)(CO2Me-4)Cl(CO)(PPh3) (4) (see Scheme 1). If
the reaction conditions described above were changed so that
the acid used was concentrated aqueous HCl and the solution
was not irradiated with visible light, the ratio of 3 to 4 in the
crude product was close to 1.0 (as estimated by NMR
spectroscopy). We do not have any direct evidence relating to
the mechanism by which 3 and 4 are formed from 1, but a
plausible sequence involves protonation of C6 in 1 followed
either by (i) loss of CO from the resulting cationic intermediate
and coordination of chloride to give 3 (irradiation with visible
light could facilitate CO dissociation leading to increased yields
of 3) or (ii) the coupling of C1 and C5 in the cationic
intermediate to give an η1-cyclopentadienyl complex, which then
rearranges with coordination of chloride to give the η5-
cyclopentadienyl complex 4. There is ample evidence for the
transformation of metallabenzenes into cyclopentadienyl com-
plexes,1 and this metallabenzene decomposition route has been
studied by computational methods.15
The characterizing spectroscopic data relating to 4 are
collected in the Experimental Section and are mostly unremark-
able. In the 1H NMR spectrum the two inequivalent protons on
C6 are observed as doublets at 2.88 and 3.91 ppm, with geminal
HH coupling constants of 17.8 Hz. In the 13C NMR spectrum
the saturated carbon atom C6 appears at 32.6 ppm. The crystal
structure of 4 was determined, and the molecular structure is
shown in Figure 2. The carbon atoms C2-4 of the π-bound
cyclopentadienyl ligand make slightly closer approaches to
ruthenium than C1 and C5. The atoms C6 and C7 that formed
part of the five-membered ruthenacyclic ring in 1 are found
within the CH2CO2Me substituent on the cyclopentadienyl ring
in 4.
neutral
(CH2CO2Me-5)]Cl(PPh3)2 (3), in 78% yield, and the yellow
cyclopentadienyl complex
Ru(η5-C5H2(CH2CO2Me-1)-
ruthenabenzene
Ru[C5H2(CO2Me-2)(CO2Me-4)-
(CO2Me-2)(CO2Me-4)Cl(CO)(PPh3) (4) in ca. 10% yield (see
Scheme 1). The ruthenabenzene 3 is remarkably stable in
solutions that contain traces of HCl, even at elevated temper-
atures, as is indicated by the synthetic procedure described
above. We were not able to obtain the crystal structure of 3
because of the difficulty in obtaining single crystals suitable
for X-ray diffraction studies; however, the spectroscopic and
analytical data confirm the ruthenabenzene formulation. In the
1H NMR spectrum of 3, H1 appears as a doublet of triplets at
3
16.45 ppm (4JHH ) 2.7, JHP ) 3.0 Hz), H3 is observed as a
doublet at 8.76 ppm (4JHH ) 2.4 Hz), and the two protons on
C6 appear as a singlet at 3.19 ppm. In the 13C NMR spectrum
the two metal-bound carbon atoms again appear as triplets at
characteristically low field values (C1, 287.8 (2JCP ) 12.6 Hz);
C5, 289.3 (2JCP ) 10.6 Hz) ppm), and the other ruthenabenzene
ring carbon atoms have resonances in the aromatic region. The
methylene carbon C6 is observed at 56.2 ppm, and in the 31P
Although the ruthenabenzene 3 is very stable in solutions
that contain traces of HCl, addition of the base NEt3 or 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) results in the complete
conversion of 3 to intractable mixtures of products. In contrast,
treatment of a dichloromethane solution of 3 with CO (1 atm
pressure, ambient temperature) rapidly results in the regeneration
of 1 (see Scheme 1). The overall outcome of this reaction is
(12) Piermarini, G. J.; Mighell, A. D.; Weir, C. E.; Block, S. Science
1969, 165, 1250.
(13) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements;
Pergamon Press, 1989, ISBN 0-08-022057-6.
(14) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(15) Iron, M. A.; Lucassen, A. C. B.; Cohen, H.; van der Boom, M. E.;
Martin, J. M. L. J. Am. Chem. Soc. 2004, 126, 11699.

570 Organometallics, Vol. 28, No. 2, 2009
Clark et al.
about the Ru-C5 vector, and the angle between the two mean
planes is 9.6°.
The Ru-C1 (1.986(3) Å) and Ru-C5 (2.092(4) Å) distances
in 5 are both slightly longer than the corresponding distances
in the cationic tethered ruthenabenzene 2 (1.933(4) and 2.045(5)
Å, respectively), and the trans-influence of the CNR ligand is
probably mostly responsible for the longer Ru-C(5). The C-C
distances within the six-membered ruthenacyclic ring of 5 show
considerably more alternation in length (C1-C2, 1.368(5);
C2-C3, 1.437(5); C3-C4, 1.376(5); C4-C5, 1.475(5) Å) than
do the corresponding distances in 2. Nevertheless, the first three
distances still all fall within the range observed for other
metallabenzenes,1 although the C4-C5 distance is closer to
values normally associated with C-C single bonds. The C5-C6
(1.376(5) Å) and C6-C7 (1.437(5) Å) distances are also close
to those commonly observed in aromatic systems. The bonding
in the bicyclic ring system of 5 can be discussed in terms of
the three valence bond structures 5A-5C depicted in Chart 2.
Three corresponding valence bond structures were used to
discuss the bonding in the related osmabenzofuran Os[C7H2O-
(OMe-7)(CO2Me-4)(Ph-1)(Ph-2)](CS)(PPh3)2.9 The alternation
of the C-C distances in the ruthenabicyclic ring system of 5
points to a major contribution from valence bond structure 5C.
However, the C-C distances involving C1-4 and C5-7, which
all fall within the normal aromatic range, indicate some
contribution from 5A and 5B. This is supported by the 1H and
13C NMR chemical shifts of the ring atoms, which are consistent
with a degree of delocalization within the ruthenabicyclic
system. Accordingly, we favor a delocalized ruthenabenzofuran
description for the bonding in 5 (and 19) rather than an
alternative tethered ruthenacyclohexadiene description with
localized double bonds.
Figure 3. Molecular structure of 5 with thermal ellipsoids at the
50% probability level. Selected distances [Å]: Ru-C1 1.986(3),
Ru-C5 2.092(4), Ru-C13 1.954(4), Ru-O5 2.266(2), C1-C2
1.368(5), C2-C3 1.437(5), C3-C4 1.376(5), C4-C5 1.475(5),
C5-C6 1.376(5), C6-C7 1.437(5), O5-C7 1.242(4).
that the chloride ligand is substituted by CO and one of the
protons on C6 is lost in a process that is formally the reverse
of the reaction in which 3 is formed from 1. We do not have
any evidence that indicates whether substitution of chloride by
CO occurs before or after the proton is lost from C6 during the
reaction in which 1 is regenerated from 3. In an analogous
manner, treatment of 3 with p-tolylisocyanide gives the purple
isocyanide-containing ruthenabenzofuran (or tethered ruthena-
cyclohexadiene) Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)]-
(CNR)(PPh3)2 (5) (see Scheme 1). In the IR spectrum of 5 ν(CN)
is observed at 2060 cm-1. As might be expected, the 1H and 13
C
NMR spectra of 5 are similar to the corresponding spectra obtained
1
for 1. In the H NMR spectrum of 5 H1 is observed at the low
Concluding Remarks
field position of 12.40 ppm (cf. 11.67 ppm in 1), H6 is observed
at 6.17 ppm (cf. 6.08 in 1), and H3 is obscured by the PPh3
Tethered ruthenabenzenes are accessible through protonation
ofC6inthefive-memberedruthenacyclicringofRu[C5H2(CO2Me-
2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1). Thus, treatment
of 1 with HBF4 · OEt2 yields the blue cationic tethered ruthen-
resonances (7.26-7.46 ppm), as is the case for H3 in 1. In the 13
C
NMR spectrum of 5, C1 and C5 are observed at the low field
positions of 245.0 and 232.8 ppm, respectively (cf. 232.9 and 227.0,
respectively, in 1). The resonances of the other carbon atoms in
the six-membered metallacyclic ring all appear in the aromatic
region at 127.8 (C2), 147.4 (C3), and 121.1 (C4) ppm (cf. 128.5,
147.3, and 122.2 ppm, respectively, in 1). The resonance for C6
(117.1 ppm) also falls in the aromatic region (cf. 119.1 ppm in 1).
It is noteworthy that the chemical shifts of H1 and C1/5 in 5 (and
1) (ca. 12 and 235 ppm, respectively) are midway between the
chemical shifts of the corresponding atoms in the ruthenabenzenes
2, 3, and [Ru[CHC(PPh3)CHC(PPh3)CH]Cl2(PPh3)2]Cl7 (ca. 16 and
280 ppm, respectively) and the chemical shifts of the corresponding
atoms in simple, nonconjugated vinyl derivatives of ruthenium that
bear bis(triphenylphosphine) and carbonyl or isocyanide ligands
(ca. 8 and 175 ppm, respectively).16
abenzene
[Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]-
(CO)(PPh3)2][(BF4)2H] (2), while treatment with HCl gives the
green neutral tethered ruthenabenzene Ru[C5H2(CO2Me-
2)(CO2Me-4)(CH2CO2Me-5)]Cl(PPh3)2 (3). Both these ruthen-
abenzenes are stable in solution, and remarkably, 3 survives
mostly unchanged on heating under reflux for several hours in
a toluene/methanol solution that contains traces of HCl. Since
calculations have shown that the coupling of the two metal-
bound carbon atoms in simple metallabenzene models to give
cyclopentadienyl ligands is a relatively low energy process for
second-row transition metal derivatives,15 the tethering arms and/
or the methyl ester ring substituents in 2 and 3 probably provide
important stabilizing effects.
The crystal structure of 5 was determined, and the molecular
structure is shown in Figure 3. The same fused five- and six-
membered bicyclic ring system with Ru at a bridgehead position
that is present in 1 is also clearly evident in the structure of 5.
The atoms in the six-membered ruthenacyclic ring (Ru, C1-C5)
are essentially coplanar, with the maximum displacement from
the mean plane through these atoms being 0.064 Å. The atoms
in the five-membered ring (Ru, C5-C7, O5) are also coplanar
(maximum displacement from the mean plane through these five
atoms is 0.037 Å). The bicyclic ring system is folded slightly
Treatment of 3 with CN-p-tolyl causes HCl to be lost, and the
isocyanide-containing compound Ru[C5H2(CO2Me-2)(CO2Me-
4)(CHCO2Me-5)](CNR)(PPh3)2 (5) is formed. This is the isocya-
nide analogue of compound, 1. On the basis of the structural
and spectroscopic data for 5 (and 1) some delocalization of the
bonding within the fused ruthenabicyclic rings is apparent, and
we therefore favor the description of these compounds as
“ruthenabenzofurans”.
Experimental Section
General Comments. Standard laboratory procedures were
(16) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.
Organometallics 1996, 15, 1793.
followed, as have been described previously.16 The compound

Stable Cationic and Neutral Ruthenabenzenes
Organometallics, Vol. 28, No. 2, 2009 571
2,4
1,3
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) was
J
) 9.5 Hz, o-PPh3), 129.6 (s, p-PPh3), 131.4 (t′,
J
CP
) 43.4
CP
prepared according to the literature method.10
3,5
Hz, i-PPh3), 133.8 (t′,
J
) 10.7 Hz, m-PPh3), 150.7 (s, C3),
CP
2
Infrared spectra (4000-400 cm-1) were recorded as Nujol mulls
165.2 (s, C9), 166.1 (s, C11), 182.6 (s, C7), 287.8 (t, JCP ) 12.6
Hz, C1), 289.3 (t, 2JCP ) 10.6 Hz, C5). 31P NMR (CDCl3, δ): 21.55.
between KBr plates on a Perkin-Elmer Paragon 1000 spectrometer.
1
Ru[η5-C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]Cl(CO)(P-
Ph3) (4). Compound 4 can be obtained in low yield (ca. 10%) from
a fast moving band eluted from the column described in the
synthesis of 3 above. A higher yielding synthesis is as follows:
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) (0.200
g) and concentrated aqueous HCl (0.5 mL) were heated under reflux
in a mixture of benzene (25 mL) and methanol (6 mL) for 5 h.
After removal of the solvent under vacuum, the remaining crude
solid (a mixture of unchanged 1, 3, and 4 in approximately equal
amounts as determined by NMR spectroscopy) was dissolved in
dichloromethane and a small amount of ethanol added. Upon
removal of the dichloromethane under reduced pressure, 1 crystal-
lized from solution and was removed by filtration. Excess hexane
was added to the filtrate and the resulting solution left to stand for
16 h. During this time yellow crystals were deposited, and these
were collected by filtration. Recrystallization from dichloromethane/
hexane gave pure 4 as yellow crystals (0.030 g, 20%). Anal. Calc
for C31H28ClO7PRu: C, 54.75; H, 4.16. Found: C, 54.49; H, 4.37.
MS (m/z, FAB+, NBA): calcd for C31H2835ClO7P102Ru, 680.03047
and C31H2837ClO7P102Ru, 682.02752, found 680.03035 and 682.02890,
respectively. IR (cm-1): 1971 ν(CO); 1726, 1688, 1664 (CO2CH3).
NMR spectra were obtained on a Bruker DRX 400 at 25 °C. H,
13C, 19F, and31P NMR spectra were obtained operating at 400.1 (1H),
100.6 (13C), 376.5 (19F), and 162.0 (31P) MHz, respectively.
Resonances are quoted in ppm and 1H NMR spectra referenced to
either tetramethylsilane (0.00 ppm) or the proteo-impurity in the
solvent (7.25 ppm for CHCl3). 13C NMR spectra were referenced
to CDCl3 (77.0 ppm), 19F NMR spectra to CFCl3 (0.00 ppm), and
31P NMR spectra to 85% orthophosphoric acid (0.00 ppm) as an
external standard. Elemental analyses were obtained from the
Microanalytical Laboratory, University of Otago.
[Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)](CO)(PPh3)2]-
[(BF4)2H] (2). Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(P-
Ph3)2 (1) (0.100 g) was dissolved in toluene (5 mL) at room
temperature, giving a purple solution. HBF4 · Et2O (0.3 mL, 54%
w/w solution) was then slowly added, causing the formation of a
dark blue precipitate. This product was collected by filtration and
recrystallized from dichloromethane/toluene to give pure 2 as dark
blue crystals (0.042 g, 42%). Anal. Calc for C49H44O7P2RuB2F8 ·
(0.5CH2Cl2) · (2.4H2O): C, 50.93; H, 4.31. Found: C, 50.88; H,
4.21% (NMR spectroscopy showed the presence of ca. 0.5 molar
equiv of CH2Cl2 of crystallization as well as ca. 2 molar equiv of
water in the analytical sample. The crystal grown for X-ray
structural analysis contained 0.3 molar equiv of CH2Cl2, 2.4 molar
equiv of H2O, and 0.5 molar equiv of toluene). IR (cm-1): 1988
1H NMR (CDCl3, δ): 2.88 (d, 1H, JHH ) 17.8 Hz, H6), 3.31 (s,
2
3H, H10/H12/H13), 3.67 (s, 3H, H10/H12/H13), 3.78 (s, 3H, H10/
H12/H13), 3.91 (d, 1H, 2JHH ) 17.8 Hz, H6), 4.81 (d, 1H, 4JHH
)
1
4
ν(CO); 1711, 1631 (CO2CH3). H NMR (CDCl3, δ): 2.73 (s, 2H,
1.3 Hz, H1), 6.21 (d, 1H, JHH ) 1.3 Hz, H3), 7.19 - 7.54 (m,
15H, PPh3). 13C NMR (CDCl3, δ): 32.6 (s, C6), 51.8 (s, C10/C12/
C13), 52.09 (s, C10/C12/C13), 52.1 (s, C10/C12/C13), 79.4 (s, C2/
H6), 3.73 (s, 3H, H10), 3.83 (s, 3H, H12), 3.99 (s, 3H, H13),
7.15-7.54 (m, 30H, PPh3), 8.83 (d, 4JHH ) 2.2 Hz, 1H, H3), 14.97
4
(d, JHH ) 2.4 Hz, 1H, H1). 13C NMR (CDCl3, δ): 52.0 (s, C12),
2
C4/C5), 82.3 (d, JCP ) 9.1 Hz, C2/C4/C5), 88.1 (s, C3), 99.1 (s,
52.3 (s, C10), 53.2 (s, C6), 56.6 (s, C13), 129.1 (t′,16
J
CP
) 10.3
2,4
C1), 112.4 (s, C2/C4/C5), 128.4 (d, 2JCP ) 10.8 Hz, o-PPh3), 130.6
1,3
Hz, o-PPh3), 129.4 (t′,
J
CP
) 48.9 Hz, i-PPh3), 129.6 (s, C2),
1
3
(d, JCP ) 51.1 Hz, i-PPh3), 133.2 (s, p-PPh3), 133.5 (d, JCP
)
3,5
130.8 (s, C4), 131.9 (s, p-PPh3), 133.0 (t′,
J ) 11.3 Hz, m-PPh3),
CP
10.5 Hz, m-PPh3), 164.6 (s, C11/C9/C7), 165.4 (s, C11/C9/C7),
156.6 (s, C3), 163.9 (s, C9), 164.8 (s, C11), 185.9 (s, C7), 199.7
(t, 2JCP ) 14.4 Hz, C8), 283.6 (t, 2JCP ) 7.7 Hz, C5), 290.8 (t, 2JCP
) 6.1 Hz, C1). 31P NMR (CDCl3, δ): 29.81. 19F NMR (CDCl3, δ):
-154.49.
170.4 (s, C11/C9/C7), 200.7 (d, JCP ) 21.7 Hz, C8). 31P NMR
2
(CDCl3, δ): 47.16.
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CN-p-tolyl)-
(PPh3)2 (5). A solution of p-tolyl isocyanide (0.013 g) in
dichloromethane (3 mL) was added with stirring to a solution of
Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]Cl(PPh3)2 (3) (0.100
g) in dichloromethane (5 mL) at room temperature. The color of
the mixture turned instantly from green to dark purple-brown. After
5 min the solvent was removed under reduced pressure and the
residue subjected to column chromatography on silica gel using
dichloromethane/ethanol (100:2) as eluant. The major purple band
was collected and a purple solid obtained by removal of the
dichloromethane under reduced pressure. This was recrystallized
from dichloromethane/ethanol to yield pure 5 as purple crystals
(0.048 g, 48%). Anal. Calc for C56H49NO6P2Ru · (0.25CH2Cl2): C,
66.48; H, 4.91; N, 1.38. Found: C, 66.53; H, 4.88; N, 1.34. MS
(m/z, FAB+, NBA): calcd for C56H49NO6P2102Ru, 995.20786 and
C56H49NO6P2104Ru, 997.20894, found 995.20793 and 997.20918,
Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]Cl(PPh3)2 (3).
Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) (0.200
g) was heated under reflux in a solution of benzene (50 mL),
methanol (12 mL), and trimethylsilyl chloride (0.180 mL) contained
in a Pyrex flask illuminated with a 1000 W tungsten halogen lamp
positioned 15 cm away from the flask. After 2 h more trimethylsilyl
chloride (0.01 mL) was added to the flask, and the heating and
illumination continued for a further 2.5 h. Over the course of the
reaction the deep purple solution became bright green in color. The
solvent was removed under reduced pressure, and the residue was
dissolved in a minimum of the solvent mixture dichloromethane/
ethanol/trimethylsilyl chloride (100:2:0.05). This solution was then
purified by column chromatography on silica gel using a solution
of dichloromethane/ethanol/trimethylsilyl chloride (100:2:0.05) as
eluant. The band that appeared dark brown on the column but eluted
as a bright green solution was collected, and on removal to the
solvent 3 was obtained as a green solid (0.157 g, 78%). MS (m/z,
FAB+, NBA): calcd for C48H4335ClO6P2102Ru, 914.12669 and
C48H4335ClO6P2101Ru, 913.12792, found 914.12554, and 913.12946,
respectively. Satisfactory elemental analysis could not be obtained,
probably because of the small amounts of HCl that were required
to be present in solution to stabilize this product and the poor
crystallinity of solid samples. IR (cm-1): 1720, 1586 (CO2CH3).
1H NMR spectrum (CDCl3, δ): 3.19 (s, 2H, H6), 3.59 (s, 3H, H13)
3.63 (s, 3H, H12), 3.67 (s, 3H, H10), 7.20-7.38 (m, 30H, PPh3),
8.76 (d, 4JHH ) 2.4 Hz, 1H, H3), 16.45 (dt, 4JHH ) 2.7, 3JHP ) 3.0
Hz, 1H, H1). 13C NMR (CDCl3, δ): 50.6 (s, C12), 51.3 (s, C10),
53.5 (s, C13), 56.2 (s, C6), 124.3 (s, C4), 126.2 (s, C2), 127.4 (t′,
respectively. IR (cm-1): 2060 ν(CNR); 1714, 1577 (CO2CH3). H
NMR (CDCl3, δ): 2.27 (s, 3H, CNC6H4CH3), 3.20 (s, 3H, H13),
3.53 (s, 3H, H12), 3.66 (s, 3H, H10), 5.95 (d, JHH ) 8.3 Hz, 2H,
1
3
4
3
H14b), 6.17 (t, JHP ) 2.7 Hz, 1H, H6), 6.86 (d, JHH ) 8.2 Hz,
2H, H14c), 7.26 - 7.46 (m, 31H, PPh3, and H3), 12.40 (dt, 4JHH
)
1.8, 3JHP ) 1.7 Hz, 1H, H1). 13C NMR (CDCl3, δ): 21.1 (s, C15),
50.3 (s, C10), 50.6 (s, C12), 51.3 (s, C13), 117.1 (s, C6), 121.1 (s,
C4), 124.8 (s, C14b), 127.4 (t′,
2,4
J
CP
) 9.1 Hz, o-PPh3), 127.6 (s,
C14a), 127.8 (s, C2), 129.1 (s, C14c), 129.3 (s, p-PPh3), 133.1 (t′,
1,3
3,5
J
) 41.2 Hz, i-PPh3), 134.2 (t′,
J
CP
) 11.1 Hz, m-PPh3),
CP
136.3 (s, C14d), 147.4 (s, C3), 164.2 (s, C11), 168.6 (s, C9), 171.5
2
2
(t, JCP ) 15.1 Hz C8), 178.8 (s, C7), 232.8 (t, JCP ) 11.6 Hz,
C5), 245.0 (t, JCP ) 11.6 Hz, C1). 31P NMR (CDCl3, δ): 43.22.
2

572 Organometallics, Vol. 28, No. 2, 2009
Clark et al.
via the Internet at http://pubs.acs.org and from the Cambridge
Crystallographic Data Centre (fax: +44-1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk) as supple-
mentary publication nos. CCDC 699174-699176, respectively.
Acknowledgment. We thank the Foundation for Research,
Science and Technology for supporting this work through a
postdoctoral fellowship to D.M.T.
Supporting Information Available: Crystal and refinement data
in CIF format for compounds 2, 4, and 5 are available free of charge
OM800857K