The synthesis of [FeRu(CO)2(μ-CO)2(η-C 5H5)(η-C5Me5)] and convenient entries to its organometallic chemistry

Article abstract of DOI:10.1039/b414412k

The synthesis, fluxionality and reactivity of the heterobimetallic complex [FeRu(CO)₂(μ-CO)₂(η-C₅H ₅)(η-C₅Me₅)] (5) are described. Complex 5 exhibits enhanced photolytic reactivity towards alkynes compared to its homometallic analogues, forming the dimetallacyclopentenone complexes [FeRu(CO)(μ-CO){μ-η¹:η ³-C(O)CR″CR′}(η-C₅H ₅)-(η-C₅Me₅)] (9, R′ = R″ = H; 10, R′ = R″ = CO₂Me; 11, R′ = H, R″ = CMe₂OH). Prolonged photolysis with diphenylethyne gives the dimetallatetrahedrane complex [FeRu(μ-CO)(μ-η²:η ²-CPhCPh)(η-C₅H₅)(η-C ₅Me₅)] (17), which contains the first iron-ruthenium double bond. Complexes containing a number of organic fragments can be synthesised using 9, 10 and 11. Heating a solution of 10 gave the alkenylidene complex [FeRu(CO)₂(μ-CO){μ-η¹:η ¹-C=C(CO₂Me)₃}(η-C₅H ₅)(η-C₅Me₅)] (23) through an unusual methylcarboxylate migration. Protonation and then addition of hydride to 9 gives the ethylidene complex [FeRu(CO)₂(μ-CO)(μ-CHCH ₃)(η-C₅H₅)(η-C₅Me ₅)] (27) via the ionic vinyl species [FeRu(CO) ₂(μ-CO)(μ-η¹:η²CH=CH ₂)(η-C₅H₅)(η-C₅Me ₅)][BF₄] (25). Compound 25 exhibits cis/trans isomerisation at room temperature. Protonation of 11 gives the allenyl species [FeRu(CO)₂(μ-CO)(μ-η¹:η ²-CH=C=CMe₂)(η-C₅H ₅)(η-C₅Me₅)][BF₄] (30). Compound 30 exist as three isomers, two cis and one trans. The two cis isomers are shown to be interconverting by σ-π isomerisation. The solid state structures of 5, 11, 12, 17, 23, 25 and 30 were established by X-ray crystallography and are discussed.

Full text of DOI:10.1039/b414412k

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F U L L P A P E R
The synthesis of [FeRu(CO)2(l-CO)2(g-C5H5)(g-C5Me5)] and
convenient entries to its organometallic chemistry
James N. L. Dennett, Selby A. R. Knox,* Kirsty M. Anderson, Jonathan P. H. Charmant and
A. Guy Orpen
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS.
E-mail: selby.knox@bris.ac.uk; Fax: +44 (0)117 929 0509; Tel: +44 (0)117 928 7650
Received 17th September 2004, Accepted 5th November 2004
First published as an Advance Article on the web 29th November 2004
The synthesis, fluxionality and reactivity of the heterobimetallic complex [FeRu(CO)2(l-CO)2(g-C5H5)(g-C5Me5)] (5)
are described. Complex 5 exhibits enhanced photolytic reactivity towards alkynes compared to its homometallic
1
3
analogues, forming the dimetallacyclopentenone complexes [FeRu(CO)(l-CO){l-g :g -C(O)CRꢀꢀCRꢀ}(g-C5H5)-
(g-C5Me5)] (9, Rꢀ = Rꢀꢀ = H; 10, Rꢀ = Rꢀꢀ = CO2Me; 11, Rꢀ = H, Rꢀꢀ = CMe2OH). Prolonged photolysis with
2
2
diphenylethyne gives the dimetallatetrahedrane complex [FeRu(l-CO)(l-g :g -CPhCPh)(g-C5H5)(g-C5Me5)] (17),
which contains the first iron–ruthenium double bond. Complexes containing a number of organic fragments can be
1
1
synthesised using 9, 10 and 11. Heating a solution of 10 gave the alkenylidene complex [FeRu(CO)2(l-CO){l-g :g -
=
C C(CO2Me)2}(g-C5H5)(g-C5Me5)] (23) through an unusual methylcarboxylate migration. Protonation and then
addition of hydride to 9 gives the ethylidene complex [FeRu(CO)2(l-CO)(l-CHCH3)(g-C5H5)(g-C5Me5)] (27) via the
1
2
=
ionic vinyl species [FeRu(CO)2(l-CO)(l-g :g -CH CH2)(g-C5H5)(g-C5Me5)][BF4] (25). Compound 25 exhibits
1
2
cis/trans isomerisation at room temperature. Protonation of 11 gives the allenyl species [FeRu(CO)2(l-CO)(l-g :g -
= =
CH C CMe2)(g-C5H5)(g-C5Me5)][BF4] (30). Compound 30 exist as three isomers, two cis and one trans. The two cis
isomers are shown to be interconverting by r–p isomerisation. The solid state structures of 5, 11, 12, 17, 23, 25 and 30
were established by X-ray crystallography and are discussed.
tem. Elemental analyses were performed by the Microanalytical
Laboratory of the School of Chemistry, University of Bristol.
Introduction
Bimetallic complexes have for a number of years served as
[Fe2(CO)4(g-C5H5)2] (4) and [RuI(CO)2(g-C5Me5)] (7) were
models for catalytic processes occurring at bulk metal surfaces.1
prepared using literature methods.6,7 Tetrafluoroboric acid–
More recently they have been employed in their own right as
diethyl ether complex, sodium borohydride, 2-methyl-3-butyn-2-
homogeneous catalysts,2 the two metal centres providing the
ol (Aldrich), diphenylethyne and dimethyl acetylenedicarboxy-
intriguing possibility of cooperative reactivity.3 In addition,
late (Lancaster) were used as supplied.
heterobimetallic complexes offer the possibility of combining
Ethyne (BOC) was purified by passing through an acetone/
2b,4
the catalytic features of two different metal centres.
solid CO2 trap, concentrated sulfuric acid, calcium hydroxide
and then calcium carbonate.
We have used the complexes [MMꢀ(CO)4(g-C5H5)(g-C5R5)]
(1, M = Mꢀ = Ru, R = H; 2, M = Mꢀ = Ru, R = Me;
3, M = Fe, Mꢀ = Ru, R = H; 4, M = Mꢀ = Fe, R = H) as an
excellent entry into the study of the behaviour of small organic
molecules in bimetallic systems.5 Interestingly, the chemistry
of asymmetric systems does not always fall between that of
its symmetric counterparts. For example, the Fe–Ru species 3
exhibits enhanced reactivity towards alkynes compared to the
Structure determinations for compounds 5, 11, 12, 17, 23, 25
and 30
Details of the structural analyses carried out on these com-
pounds are given in Table 1. X-Ray diffraction measurements
were made at low temperature using Bruker-AXS SMART8,9 (5,
12, 17, 23, 25 and 30) and P410 (11) diffractometers on single
crystals coated in vacuum grease and mounted on glass fibres.
For compounds 5, 12, 17, 23, 25 and 30, absorption cor-
rections were applied using SADABS.11 For compound 11 an
absorption correction was applied on the basis of psi-scan data.12
All structures were solved and refined by standard methods
using SHELXTL software.12 Extinction coefficients were refined
where appropriate.
5e
homobimetallic species 1 and 4.
Herein we report an extension of our studies to the mixed
iron–ruthenium cyclopentadienyl pentamethylcyclopentadienyl
complex [FeRu(CO)2(l-CO)2(g-C5H5)(g-C5Me5)] (5).
Experimental
General techniques
All reactions and general manipulations were carried out under
nitrogen, using solvents dried by distillation from an appropriate
drying agent.
All non-hydrogen atoms were assigned anisotropic thermal
parameters and refined without positional restraints. With
the exception of cyclopentadienyl hydrogen atoms, hydrogens
bonded to metal-bound carbon atoms were located in the elec-
tron density difference map and refined with appropriate C–H
bond distance restraints. Hydroxyl and methyl hydrogen atoms
were located using rotating group refinements and constrained
to idealised C–H or O–H bond distances. All other hydrogen
atoms were constrained to ideal geometries. All hydrogens were
assigned isotropic displacement parameters equal to 1.5 times
(methyl and hydroxyl) or 1.2 times (all other hydrogen atoms)
the equivalent Uiso of their parent atom.
Photolysis reactions were carried out in silica glass tubes held
ca. 20 cm from a 500W mercury vapour lamp as a source
of UV radiation. Column chromatography was performed on
alumina (Brockmann activity II). IR spectra were recorded
using a Perkin-Elmer 1710 Fourier Transform Spectrometer
using calcium fluoride cells of 1 mm path length. EI and FAB
mass spectra were recorded using a Fisons Autospec instrument.
Proton and 13C NMR spectra were recorded on JEOL D 270,
GX 400 and Lambda 300 spectrometers operated in Fourier
Transform mode, with field maintained by an external lock sys-
CCDC reference numbers 250405–250411.
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
6 3
©

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stallographic data in CIF or other electronic format.
Preparation of [FeRu(CO)4(g-C5H5)(g-C5Me5)] (5)
Mercury (30 cm3) was added to a 3-neck 500 cm3 amalgam flask
fitted with an overhead stirrer. Sodium (3 g) was added in small
portions. A solution of [Fe2(CO)4(g-C5H5)2] (4) (3 g, 8.47 mmol
in 250 cm3 of tetrahydrofuran) was added and the mixture
stirred for 2 h. The solution of Na[Fe(CO)2(g-C5H5)] (6) was
filtered through a ground glass sinter and then cooled to −78 ◦C.
[RuI(CO)2(g-C5Me5)] (7) (5.74 g, 13.67 mmol) was added and
the solution allowed to warm over 1 h. Chromatography gave
two bands. The first, eluted with dichloromethane–hexane (5
: 95), gave small amounts (ca. 50 mg) of [Hg{Ru(CO)2(g-
1
C5Me5)}2] (33), identified by IR and H NMR spectroscopy.13
The second band, eluted with dichloromethane–hexane (7 :
93), gave 5.18 g of the crude product [FeRu(CO)4(g-C5H5)(g-
C5Me5)] (5). Recrystallisation from hexane gave 3.16 g of pure
[FeRu(CO)4(g-C5H5)(g-C5Me5)] (5) (49%).
Reaction of [FeRu(CO)4(g-C5H5)(g-C5Me5)] (5) with ethyne
under UV irradiation
A toluene (120 cm3) solution of 5 (0.8 g, 1.70 mmol) was placed
in a quartz tube. The solution was purged with ethyne and irra-
diated with UV light overnight (16 h). The solvent was removed
in vacuo and the residue washed with pentane. The residue was
then dissolved in dichloromethane (50 cm3) and filtered through
a ground glass sinter. After removal of the solvent on a rotary
evaporator and drying in vacuo, crude [FeRu(CO)(l-CO){l-
1
3
g :g -C(O)CHCH}(g-C5H5)(g-C5Me5)] (9) (780 mg, 95%) was
obtained. In subsequent reactions, crude 9 proved sufficiently
pure. Analytically pure 9 could be obtained through chromatog-
raphy (elution with dichloromethane gave a green band) and
then crystallisation (layering a thf solution of 9 with hexane),
although this lowered yields considerably (22%).
Reaction of [FeRu(CO)4(g-C5H5)(g-C5Me5)] (5) with dimethyl
acetylenedicarboxylate under UV irradiation
A toluene (100 cm3) solution of 5 (0.4 g, 0.85 mmol) was
placed in a quartz tube fitted with a nitrogen purge. An excess
of dimethyl acetylenedicarboxylate (0.5 cm3, 4.07 mmol) was
added. The solution was irradiated with UV light for 6 h.
Chromatography (elution with mixtures of dichloromethane–
hexane 3 : 2 to 4 : 1) gave a dark green band. Rechromatography
of this band yielded three bands. The first two contained
1
3
mixtures of cis and trans isomers of [FeRu(CO)(l-CO){l-g :g -
C(O)C(CO2Me)C(CO2Me)}(g-C5H5)(g-C5Me5)] (10). The third
also contained 10, but showed evidence (IR, 1H NMR and
2
4
mass spectrometry) for the presence of [FeRu(CO){l-g :g -
C4(CO2Me)4}(g-C5H5)(g-C5Me5)] (16). All three bands were
dark green and eluted with dichloromethane–hexane mixtures of
3 : 1, 9 : 2 and 1 : 0 respectively. Recrystallisation of the material
from each of these bands by layering saturated dichloromethane
solutions with hexane gave dark green crystalline 10 in a
combined yield of 160 mg (32%), plus, in the case of the last
band, a small amount (5 mg, 1%) of 16.
Reaction of [FeRu(CO)4(g-C5H5)(g-C5Me5)] (5) with 2-methyl
3-butyn-2-ol under UV irradiation
An excess of 2-methyl 3-butyn-2-ol (0.51 cm3, 5.17 mmol) was
added to a toluene (100 cm3) solution of 5 (0.5 g, 1.06 mmol)
in a quartz UV tube. The solution was irradiated with UV
light for 21 h, after which time the solvent was removed on a
rotary evaporator. Chromatography gave two main bands. The
first eluted with a 1 : 1 mixture of dichloromethane–hexane.
2
4
This red band proved to be [FeRu(CO){l-g :g -C(CMe2OH)-
CHCHC(CMe2OH)}(g-C5H5)(g-C5Me5)] (12) in 23% (138 mg)
yield. Red crystals of 12 were grown by layering a saturated
6 4
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3

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Reaction of [FeRu(CO)(l-CO){l-g1:g3-C(O)C(CMe2OH)CH}-
(g-C5H5)(g-C5Me5)] (11) with tetrafluoroboric acid–diethyl
etherate
dichloromethane solution with hexane. The second band
was dark green and required a solvent mixture of acetone–
dichloromethane (1 : 10) to elute from the column. This gave
1
3
100 mg (18%) of [FeRu(CO)(l-CO){l-g :g -C(O)C(CMe2OH)-
CH}(g-C5H5)(g-C5Me5)] (11). Dark green crystals of 11 were
grown by slow evaporation of a diethyl ether solution of 11.
An improved yield of 11 (190 mg, 33%) could be obtained by
using only a slight excess of 2-methyl 3-butyn-2-ol (0.11 cm3,
1.14 mmol).
Excess tetrafluoroboric acid–diethyl etherate (3 drops) was
added to a thf (10 cm3) solution of 11 (0.175 g, 0.33 mmol).
The solution changed colour from dark green to orange. The
solvent was reduced to ca. 3 cm3 in vacuo. On addition of diethyl
ether (25 cm3) an orange precipitate was formed. Removal of the
supernatant solution and recrystallisation from CD3NO2/Et2O
1
2
gave 140 mg (71%) of red crystalline [FeRu(CO)2(l-CO)(l-g :g -
Reaction of [FeRu(CO)4(g-C5H5)(g-C5Me5)] (5) with diphenyl-
ethyne under UV irradiation
= =
CH C CMe2)(g-C5H5)(g-C5Me5)][BF4] (30).
Diphenylethyne (1.32 g, 7.44 mmol) was added to a toluene
(150 cm3) solution of 5 (0.70 g, 1.48 mmol). The solution was
purged with nitrogen and irradiated with UV light for two days,
after which time the solvent was removed in vacuo. The resulting
black oil was dissolved in hexane (50 cm3) and cooled in an ice
bath. A black precipitate of [FeRu(l-CO)(l-g :g -CPhCPh)(g-
C5H5)(g-C5Me5)] (17) began to appear, which was collected using
a sinter funnel in 34% yield (285 mg). Crystals for an X-ray
diffraction study were grown by slow evaporation of a solution
of 17 in diethyl ether.
Results and discussion
Synthesis, structure and fluxionality of [FeRu(CO)4(g-C5H5)(g-
C5Me5)] (5)
2
2
The obvious route to 5 mirrors the synthesis of 3, i.e. reaction
of Na[Fe(CO)2(g-C5H5)] (6) with [RuI(CO)2(g-C5Me5)] (7). This
method was successful and gave good crystalline yields (49%)
(Scheme 1). A slight deficit of 7 was used to ensure its
complete consumption, as trace amounts of 7 proved hard to
separate from the product. Crystalline 5 proved air stable for
months, while solutions were stable under inert atmosphere for
several days, but decomposed within hours in air. Physical and
spectroscopic data are given in Tables 2 and 3.
Thermolysis of [FeRu(CO)(l-CO){l-g1:g3-C(O)C(CO2Me)-
C(CO2Me)}(g-C5H5)(g-C5Me5)] (10)
A toluene (100 cm3) solution of 10 (0.110 g, 0.188 mmol) was
heated to reflux for 0.5 h. The solution changed colour from
dark green to red. Removal of the solvent gave a red residue. This
residue was washed with hexane (4 × 5 cm3) until the solvent
started to become slightly red and then dried under reduced
Molecular structure of [FeRu(CO)2(l-CO)2(g-C5H5)(g-C5Me5)]
(5). The solid state structure of 5 is shown in Fig. 1 and
pertinent bond lengths are given in Table 4. The molecular
core consists of two metal atoms bridged symmetrically by
two carbonyl ligands. A pentamethylcyclopentadienyl ligand
and a cyclopentadienyl ligand are bound to a ruthenium atom
and an iron atom respectively, and lie trans to each other.
1
1
=
pressure, giving [FeRu(CO)2(l-CO){l-g :g -C C(CO2Me)2}(g-
C5H5)(g-C5Me5)] (23) in 60% (66 mg) yield. Analytically pure
dendritic crystals of 23 were grown by slow evaporation of a
diethyl ether solution. Crystals suitable for an X-ray diffraction
study were grown through layering a saturated dichloromethane
solution of 23 with hexane.
˚
The iron–ruthenium bond length is 2.652(1) A, slightly longer
˚
5e
than the iron–ruthenium bond length in 3 {2.626(1) A}, but
almost exactly halfway between the metal–metal distances in 4
{2.534(2) A} and [Ru2(CO)4(g-C5Me5)2] (8) {2.752(1) A}.15 The
complex lies along a crystallographic mirror plane that coincides
with the Fe–Ru bond and bisects the cyclopentadienyl and
pentamethylcyclopentadienyl ligands. Consequently the torsion
angle between the terminal carbonyl ligands along the metal–
metal bond is exactly 180◦. The terminal carbonyl ligands also
lie in the mirror plane. The Fe–CO and Ru–CO distances are
almost identical to those found in the diiron and diruthenium
systems. The metal–bridging carbonyl distances are slightly
˚
˚
Reaction of [FeRu(CO)(l-CO){l-g1:g3-C(O)CHCH}(g-C5H5)-
(g-C5Me5)] (9) with tetrafluoroboric acid–diethyl etherate
Excess tetrafluoroboric acid–diethyl etherate (5 drops) was
added to a thf (10 cm3) solution of 9 (0.18 g, 0.38 mmol). An
instant colour change was observed, the dark green solution
becoming orange. The solvent volume was reduced to ca. 3 cm3
in vacuo and on addition of diethyl ether (15 cm3) an orange pre-
cipitate was formed. After removal of the supernatant solution,
washing the precipitate with another 15 cm3 of diethyl ether
and drying in vacuo, 0.144 g (80%) of [FeRu(CO)2(l-CO)(l-
˚
˚
shorter for the ruthenium {2.002(2) A compared with 2.04(1) A}
˚
and slightly longer for iron {1.958(2) A compared with 1.82(4)
˚
1
2
and 1.87(4) A} when compared to the diruthenium and diiron
=
g :g -CH CH2)(g-C5H5)(g-C5Me5)][BF4] (25) was obtained as
an orange powder. Crystals of 25 were grown by layering a
saturated dichloromethane solution with diethyl ether.
systems.
Solution IR spectra of 5 reveal that both cis and trans
isomers are present in solution, the proportion of each isomer
being solvent dependent. In non-polar hexane two terminal
carbonyl stretches and one bridging carbonyl stretch are seen
at 1997(w), 1940(vs) and 1779(vs) cm−1 respectively, indicating
a preference for the trans isomer. In dichloromethane, three
carbonyl stretches are again seen, at 1987(m), 1942(s) and
1760(s) cm−1, but, the relative intensity of the highest energy
stretch has increased considerably, indicating the ratio of cis
to trans isomer has increased. The preference for the trans
isomer is presumably steric, to prevent interactions between the
cyclopentadienyl rings.
1
2
=
Reaction of [FeRu(CO)2(l-CO)(l-g :g -CH CH2)(g-C5H5)(g-
C5Me5)][BF4] (25) with sodium borohydride
A ten-fold excess of sodium borohydride (0.3 g, 7.9 mmol) was
added to an acetone (50 cm3) solution of 25 (0.40 g, 0.72 mmol).
The solution was stirred for 1 h and the solvent then removed in
vacuo. The product was extracted into dichloromethane (50 cm3)
and filtered through a sinter funnel. Chromatography gave three
bands. The first band eluted with dichloromethane–hexane (5 :
95) and gave a small amount (<5 mg) of [Ru2(CO)2(l-CO)(l-
CHMe)(g-C5Me5)2] (29), characterised by IR spectroscopy.14
The second band (red) eluted with dichloromethane–hexane
(1 : 4) and gave 56 mg (17%) of trans-[FeRu(CO)2(l-CO)(l-
CHMe)(g-C5H5)(g-C5Me5)] (27). The third band (red/orange)
eluted with dichloromethane–hexane (3 : 7) and gave 57 mg
(17%) of cis-[FeRu(CO)2(l-CO)(l-CHMe)(g-C5H5)(g-C5Me5)]
(27).
1
1H and 13C-{ H} NMR studies revealed complex 5 to be highly
fluxional at room temperature. Two signals corresponding to
the cyclopentadienyl and pentamethylcyclopentadienyl ligands
1
are seen in the H NMR spectrum at room temperature. The
1
room temperature 13C-{ H} NMR spectrum shows three signals
corresponding to the ring carbons of the pentamethylcyclopen-
tadienyl and cyclopentadienyl ligands and the carbons of the
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
6 5

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Scheme 1 Synthesis and reactivity towards alkynes of complex 5.
Table 2 Analytical and physical data for new compounds
Analysisa
C(%)
Complex
Colour
M. Wt.b
H(%)
[FeRu(CO)4(g-C5H5)(g-C5Me5)]
5
9
D. red, purple 470(470)c
48.76(48.63) 4.43(4.29)
Black/d. green 412(468)c,d 51.76(51.40) 4.70(4.74)
1
3
[FeRu(CO)(l-CO){l-g :g -C(O)CHCH}(g-C5H5)(g-C5Me5)]
1
3
[FeRu(CO)(l-CO){l-g :g -C(O)C(CO2Me)C(CO2Me)}(g-C5H5)(g-C5Me5)]
10 D. green
584(584)c
49.46(49.41) 4.69(4.49)
52.39(52.58) 5.28(5.37)
56.61(56.42) 6.50(6.56)
1
3
[FeRu(CO)(l-CO){l-g :g -C(O)C(CMe2OH)CH}(g-C5H5)(g-C5Me5)]
11 Black/d. green 497(525)e
12 D. red
2
4
[FeRu(CO){l-g :g -C(CMe2OH)CHCHC(CMe2OH)}(g-C5H5)(g-C5Me5)]
553(554)
670(670)c
564(564)
528(584)d
2
4
[FeRu(CO){l-g :g -C(CO2Me)C(CO2Me)C(CO2Me)C(CO2Me)}(g-C5H5)(g-C5Me5)] 16 D. green
2
2
[FeRu(l-CO)(l-g :g -CPhCPh)(g-C5H5)(g-C5Me5)]
17 Black
23 Red
25 Orange
27 Orange
30 Red
60.32(63.83) 5.27(5.32)
49.17(49.41) 4.57(4.49)
1
1
=
[FeRu(CO)2(l-CO){l-g :g -C C(CO2Me)2}(g-C5H5)(g-C5Me5)]
1
2
[FeRu(CO)2(l-CO)(l-g :g -CH CH2)(g-C5H5)(g-C5Me5)][BF4]
[FeRu(CO)2(l-CO)(l-CHMe)(g-C5H5)(g-C5Me5)]
469(556)c,f 42.61(43.27) 4.17(4.18)
=
442(470)e
509(596)c,f 46.07(46.41) 4.76(4.57)
51.62(51.18) 5.31(5.15)
1
2
=
=
[FeRu(CO)2(l-CO)(l-g :g -CH
C CMe2)(g-C5H5)(g-C5Me5)][BF4]
a Calculated values in parentheses. b EI mass spectrum unless otherwise stated. c FAB mass spectrum. d M+ − 2CO. e M+ − CO. f M+ − BF4.
methyl groups on the pentamethylcyclopentadienyl respectively.
No carbonyl resonances were observed at room temperature.
At low temperature (−60 ◦C) the spectra are more compli-
cated. The 1H NMR spectrum shows a single broad resonance
at d 4.70 (5H) for the cyclopentadienyl protons and two
overlapping broad signals at d 1.80 and 1.70 corresponding to
the methyls on the pentamethylcyclopentadienyl ligand. The low
To summarise, complex 5 is fluxional at room temperature
17,5c
like its dimetallic analogues 4 and 2.
Two linked fluxional
processes are occurring, cis/trans isomerisation and carbonyl
exchange, shown in Scheme 2.
Several routes into the organic chemistry of 5 were ex-
plored. Photolysis with alkynes to form dimetallacyclopenta-
1
3
dienyl complexes [FeRu(CO)(l-CO){l-g :g -C(O)CRꢀꢀCRꢀ)(g-
C5H5)(g-C5Me5)] (9, Rꢀ = Rꢀꢀ = H; 10, Rꢀ = Rꢀꢀ = CO2Me; 11,
Rꢀ = H, Rꢀꢀ = CMe2OH) proved the best method and is detailed
below. Other routes aimed at functionalisation of a carbonyl
ligand, through sequential reaction with nucleophiles, then base
or acid, led to decomposition.
1
temperature 13C-{ H} NMR spectrum shows two signals for the
carbons of the methyl groups of the pentamethylcyclopentadi-
enyl ligand at d 9.37 and 8.62, and another two for the ring
carbons of the cyclopentadienyl ligand. Only one resonance is
seen for the ring carbons of the pentamethylcyclopentadienyl,
the signal of the major isomer presumably obscuring that of the
minor form. This behaviour suggests that cis/trans isomerisation
is no longer occurring. If complex 5 were completely static at this
point, six resonances for the carbonyl ligand carbons would be
expected. However, only three are seen, at d 267.0 (2 × l-CO),
211.6 (Fe–CO) and 200.1 (Ru–CO), thought to belong to the cis
isomer. A broad signal at ca. d 238 is also seen, thought to be due
to the carbonyl carbons of the trans isomer, indicating carbonyl
ligand interconversion is still occurring at this temperature. This
assumes that carbonyl ligand interconversion is a lower energy
process in the trans isomer than the cis isomer, as established by
Cotton et al. for 4.16
Characterisation of the new heterobimetallic complexes
proved straightforward through comparison of data with those
for their Fe2Cp2 and Ru2Cp*2 analogues. Physical and spectro-
scopic data for all the new compounds are given in Tables 2
and 3. In a number of the new complexes, the orientation of the
pentamethylcyclopentadienyl and cyclopentadienyl rings gave
rise to cis and trans isomers. These were distinguished primarily
on the basis of their IR spectra. The isomer ratios did not
affect the chemistry of these complexes and in the interests
of conciseness will not be discussed. However, in some cases
fluxional processes were observed and in these instances the
assignment of isomers is pertinent.
6 6
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3

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D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
6 7

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In the reaction of 5 with the terminal alkyne 2-methyl 3-
butyn-2-ol, alkyne–carbonyl linkage occurs so that the organic
substituent occupies the Rꢀꢀ position in the resulting dimetalla-
cyclopentadienyl. This is in agreement with the behaviour of the
5e,18
other bimetallic systems.
The reasons for this are thought
to be steric, with the organic group (CMe2OH) occupying the
sterically less demanding environment.
The solid state structure of 11 was determined by an X-ray
diffraction study. The structure is shown in Fig. 2 and relevant
bond lengths are given in Table 5.
Fig. 1 Molecular structure of 5. Hydrogen atoms have been omitted
for clarity. Thermal ellipsoids are drawn at the 50% probability level.
˚
Table 4 Selected bond lengths (A) for 5
Ru(1)–C(1)
Ru(1)–C(10)
Ru(1)–C(12)
Ru(1)–Fe(2)
C(12)–O(12)
2.262(2)
2.022(2)
1.875(3)
2.652(1)
1.149(3)
Fe(2)–C(7)
2.127(3)
1.958(2)
1.745(3)
1.171(2)
1.155(4)
Fe(2)–C(10)
Fe(2)–C(11)
C(10)–O(10)
C(11)–O(11)
Fig. 2 Molecular structure of 11. Cyclopentadienyl, hydroxyl and
methyl hydrogen atoms have been omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level.
Molecular structure of [FeRu(CO)(l-CO){l-g1:g3-C(O)C-
(CMe2OH)CH}(g-C5H5)(g-C5Me5)] (11). The solid state
structure of 11 shows that the ketonic group is bound to the
iron centre. This is in accord with the structure assigned on the
1
basis of its 13C-{ H} NMR spectrum. The Fe–Ru bond length
˚
˚
in 11 is 2.64499(7) A, comparable to that of 5 {2.652(1) A}.
The bridging carbonyl ligand shows metal–carbon distances
typical of Fe–l-C(O) and Ru–l-C(O) distances and the Ru–
C(2)–O(2) and Fe–C(2)–O(2) angles reveal the carbonyl double
bond is not bent away from the large Cp* ligand. The C3 unit
Scheme 2 The fluxional processes occurring in complex 5.
3
of the dimetallacyclopentenone ring is clearly bound in g -
fashion to the iron atom. The r-bound ketonic carbon {C(5)}
Synthesis of dimetallacyclopentenone complexes
˚
has an Fe–C bond distance of 1.896(4) A. The p-bound olefinic
An interesting contrast exists between the homobimetallic 1, 4
and 2 and the heterobimetallic system 3, with regard to their
reactivity towards alkynes. Both classes form dimetallacyclo-
pentenone compounds on photolysis with alkynes, but the
homobimetallic systems generally require longer reaction times
carbons C(3) and C(4) show Fe–C distances of 2.024(4) and
˚
2.067(4) A respectively. Complex 11 has a cis orientation of
cyclopentadienyl rings.
The general procedure for these photolysis reactions involves
the use of an excess of the alkyne. This gave rise to additional
products in the reactions of 5 with dimethyl acetylenedicarbo-
xylate and 2-methyl 3-butyn-2-ol. One of these was identified
5e
and give lower yields than the heterobimetallic 3. Indeed, in
the case of the Ru2Cp2 system, the reaction is restricted to
diphenylethyne. Complex 5 reacts with a variety of alkynes
(ethyne, dimethyl acetylenedicarboxylate, 2-methyl 3-butyn-2-
ol) in much the same way as 3, giving the dimetallacyclo-
2
4
as the metallacyclopentadiene complex [FeRu(CO){l-g :g -C-
(CMe2OH)CHCHC(CMe2OH)}(g-C5H5)(g-C5Me5)] (12) for-
med through loss of three carbonyl ligands and linkage of two
alkyne molecules in a tail-to-tail manner. A similar multiple
alkyne insertion is seen in a minor product of the prolonged
1
3
pentenone species [FeRu(CO)(l-CO){l-g :g -C(O)CRꢀꢀCRꢀ}(g-
C5H5)(g-C5Me5)] (9, Rꢀ = Rꢀꢀ = H; 10, Rꢀ = Rꢀꢀ = CO2Me; 11,
Rꢀ = H, Rꢀꢀ = CMe2OH) in reasonable reaction times and yields
(Scheme 1).
2
4
photolysis of 4 with ethyne, the complex [Fe2(CO){l-g :g -
CHCHCHCH)}(g-C5H5)2] (13).18
By comparison with dimetallacyclopentenone complexes de-
rived from 4, it is clear the low field resonances in the 13C-{ H}
1
˚
Table 5 Selected bond lengths (A) for 11
NMR spectra of 9–11 (between d 226.0 and 239.5) indicate the
ketonic groups are bound to the iron centre. Ketonic groups in
Ru2Cp*2 systems reside at higher field. Resonances around d 200
indicate the terminal carbonyl ligand is bound to the ruthenium.
This is not wholly expected as it requires the double bond of the
ketenyl group to p bond to the iron atom and not the more
electron rich ruthenium, which would provide better p back-
donation. There is no obvious explanation for this behaviour.
Ru–C(1)
Ru–C(2)
Ru–(C3)
Ru–Fe
C(1)–O(1)
C(2)–O(2)
C(6)–O(4)
1.840(5)
2.028(4)
2.047(4)
2.64499(7)
1.149(6)
1.193(5)
1.429(6)
Fe–C(2)
Fe–C(3)
Fe–C(4)
Fe–C(5)
C(5)–O(3)
C(3)–C(4)
C(4)–C(5)
1.898(4)
2.024(4)
2.067(4)
1.896(4)
1.197(5)
1.402(5)
1.440(6)
6 8
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3

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The 1H NMR spectrum of 12 shows a broad resonance
at d 2.19 (2H) corresponding to the two hydroxide protons.
The two metallacyclopentadiene protons (Ha) are seen as a
hump on the side of the cyclopentadienyl resonance at ca. d
4.84. The combined relative intensity of these peaks is 7H,
indicating this is the case. This compares well with the diiron
The structure of 12 suggested the additional product formed
in the reaction of 5 with dimethyl acetylenedicarboxylate was
2
4
also a metallacyclopentadiene complex, [FeRu(CO){l-g :g -C-
(CO2Me)C(CO2Me)C(CO2Me)C(CO2Me)}(g-C5H5)(g-C5Me5)]
(16). The low yield of 16 precluded its full characterisation,
but evidence for its identity was obtained, including mass spe-
2
4
1
complex 13 and the diruthenium species [Ru2(CO){l-g :g -
ctrometric, H NMR and IR spectroscopic data. Interestingly,
C(Me)CHC(CO2Me)C(CO2Me)}(g-C5H5)2] (14).18,19 The 13C-
the IR spectrum of 16 showed a semi-bridging carbonyl absorp-
1
{ H} NMR spectrum shows a terminal carbonyl carbon at d
tion at 1913 cm−1, unlike that of 12.
222.0, indicating it is located at the Fe–Cp centre. The carbons
of the metallacyclopentadiene ring are found at d 177.5 (l-C) and
d 90.1 (CH). The IR spectrum of 12 showed a single terminal
carbonyl stretch at 1952(s) cm−1.
The formation of these metallacyclopentadiene species could
be minimised by using only a slight excess of the alkyne.
Synthesis of a dimetallatetrahedrane complex
An X-ray diffraction study was undertaken to confirm the
relative positions of the CMe2OH groups and the metallacy-
clopentadiene protons (Ha).
Photolysis of 5 with diphenylethyne initially proved disappoint-
ing. Products thought to be dimetallacyclopentenone species
were seen, but complete characterisation proved impossible
due to contamination by 5 and other products. However, on
prolonged photolysis with a large excess of diphenylacetylene,
one product could be isolated. Spectroscopic data showed it
Molecular structure of [FeRu(CO){l-g2:g4-C(CMe2OH)CH-
CH C(CMe2OH)}(g-C5H5)(g-C5Me5)] (12). The structure of
12 is shown in Fig. 3 and pertinent bond lengths are given in
2
2
was the dimetallatetrahedrane complex [FeRu(l-CO)(l-g :g -
CPhCPh)(g-C5H5)(g-C5Me5)] (17) (Scheme 1). An IR spectrum
of the product showed one bridging carbonyl absorption at
˚
Table 6. The Fe–Ru bond length in 12 is 2.674(6) A, slightly
˚
longer than that of 5 {2.652(1) A}. The molecular structure
shows the two bulky CMe2OH groups are attached to the
bridging carbons of the metallacyclopentadiene ring. These
sites are the most sterically demanding. The reasons for this
orientation lie in the carbon–carbon bond formation process
that occurs between the two incoming alkyne units, bond
formation occurring between the least sterically hindered ends
of the alkyne units, i.e. the CH units. This is in accord with the
alkyne linking reactions seen for the diruthenium tetrahedrane
1
1736 cm−1. 13C-{ H} NMR spectroscopy showed resonances
due to one cyclopentadienyl ligand, one pentamethylcyclopen-
tadienyl ligand and two distinct phenyl groups. In addition
to these signals, resonances at d 269.0, 143.4 and 143.3
were seen, attributed to a bridging carbonyl ligand and two
bridging alkyne carbons. These values compare well with
those for the known diruthenium tetrahedrane complexes
2
2
2
2
[Ru2(l-CO)(l-g :g -CPhCPh)(g-C5H5)2] (18) and [Ru2(l-CO)(l-
2 2
complex [Ru2(l-CO){l-g :g -C(CF3)C(CF3)}(g-C5H5)2] (15).20
21,5c
g :g -CPhCPh)(g-C5H5)(g-C5Me5)] (19).
A subsequent X-ray
diffraction study showed the structure to be that of 17. However,
a satisfactory elemental analysis was not obtained. This was
attributed to the relative instability of complex 17, which was
found to gradually decompose as a solid even under nitrogen.
Molecular structure of [FeRu(l-CO)(l-g2:g2-CPhCPh)(g-C5-
H5)(g-C5Me5)] (17). The solid state structure of 17 is shown in
Fig. 4 and significant bond lengths are given in Table 7.
Fig. 3 Molecular structure of 12. Cyclopentadienyl, hydroxyl and
methyl hydrogen atoms have been omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level.
The terminal carbonyl ligand lies in a plane bisecting the C(3)–
C(4) bond and stands on the same side of the metal–metal bond
as the metallacyclopentadiene unit, trans to the pentamethyl-
cyclopentadienyl ligand. This is in contrast to the analogous
Ru2Cp2 metallacyclopentadienes in which the majority have the
CO ligand semi-bridging the metal centres, on the opposite side
of the metal–metal bond to the metallacyclopentadiene. The
metallacyclopentadiene ring is non-planar, with the iron atom
out of the C(2)–C(3)–C(4)–C(5) plane by 18.8◦.
Fig. 4 Molecular structure of 17. Hydrogen atoms have been omitted
for clarity. Thermal ellipsoids are drawn at the 50% probability level.
˚
Table 6 Selected bond lengths (A) for 12
The structure of 17 is similar to those of the diruthenium com-
plexes 18 and 19. The iron–ruthenium bond length of 2.4018(9)
Fe(1)–Ru(1)
Fe(1)–C(1)
Fe(1)–C(2)
2.674(6)
1.727(4)
2.002(3)
Ru(1)–C(2)
Ru(1)–C(3)
C(1)–O(1)
2.139(3)
2.140(3)
1.166(4)
˚
A is significantly shorter than a typical iron–ruthenium single
˚
bond, including that of 5 {2.652(1) A}, suggesting complex 17
has the first example of an iron–ruthenium double bond in
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
6 9

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˚
Table 7 Selected bond lengths (A) for 17
to involve a zwitterionic l-cyclopropenyl intermediate and a
similar process would be envisaged in our system (Scheme 4).
Interestingly, this process does not occur in the Ru2Cp2 system
or the Fe2Cp2 system, suggesting the ability of the electron-
donating Cp* ligand is key in stabilising the metal-centred pos-
itive charge of the l-cyclopropenyl intermediate, 11. Complex
23 exists as a mixture of cis and trans isomers, the trans isomer
dominating even in polar solvents. Data for both isomers are
given in Tables 2 and 3. It was apparent from IR spectra taken
from samples of the refluxing toluene reaction solution that
the trans isomer is the only one present, implying it is strongly
favoured in less polar solvents. Exposure to a polar solvent
(dichloromethane) overnight resulted in some interconversion
of trans-23 to cis-23, but the trans isomer was still dominant.
Ru(1)–Fe(3)
Ru(1)–C(1)
Ru(1)–C(2)
Ru(1)–C(3)
C(2)–C(10)
2.4018(9)
1.955(4)
2.102(4)
2.096(4)
1.458(5)
Fe(3)–C(1)
Fe(3)–C(2)
Fe(3)–C(3)
C(3)–C(4)
C(2)–C(3)
1.913(4)
1.971(4)
1.990(4)
1.470(5)
1.325(5)
a bimetallic system. This situation is also necessary to satisfy
the 18-electron rule. However, although the alkyne C≡C bond
lies virtually perpendicular to the iron–ruthenium bond and is
clearly a four electron donor, the C≡C bond is only lengthened
˚
to 1.325(5) A. Also, the Ph–C≡C angle is only distorted from
linearity by 40.1◦ (to 139.9(2)◦). This suggests a carbon–carbon
double bond, so the situation is obviously more complex and
better thought of as a M2C2 delocalised unit. A slight distortion
from planarity is seen along the Cp–Fe–Ru–Cp* axis, but this
may be due to crystal packing forces.
1
The 13C-{ H} NMR spectrum of trans-23 shows a resonance
at d 313.4 for the l-C of the alkenylidene unit. Resonances are
also seen at d 258.5, 211.3 and 199.9 for one bridging and two
terminal carbonyl ligands. A peak is seen at d 137.6 for the
C(CO2Me)2 carbon. The cis isomer showed carbon resonances at
The Ru2Cp2 tetrahedrane complexes 18 and 19 are made
by photolysis of their respective dimetallacyclopentenone
=
d 313.4 and 136.7 for the l-C and C CR2 of the vinylidene unit.
1
3
complexes, [Ru2(CO)(l-CO){l-g :g -C(O)CPhCPh)(g-C5H5)(g-
A single crystal grown from a dichloromethane/hexane system
was shown by X-ray crystallography to have a cis orientation of
the cyclopentadienyl rings. However, the IR spectrum of the bulk
crystals in dichloromethane clearly suggested that the majority
were of the trans isomer, revealing absorptions at 2000(w),
1965(s), 1799(m) and 1703(m/w) cm−1.
C5R5)] (20, R = H; 21, R = Me).5d,21 Presumably, formation
1
3
of 17 proceeds via the acyl complex [FeRu(CO)(l-CO){l-g :g -
C(O)CPhCPh)(g-C5H5)(g-C5Me5)] (22).
Reactivity of dimetallacyclopentadienyl complexes 9–11
Dimetallacyclopentenone complexes are often useful precursors
of complexes containing small organic units such as alkenyl,
alkenylidene and allenyl. Complexes 9–11 formed a number of
such species through simple procedures such as thermolysis or
reaction with acid (Scheme 3).
1
1
=
Molecular structure of [FeRu(CO)2(l-CO){l-g :g -C C(CO2-
Me)2}(g-C5H5)(g-C5Me5)] (23). The molecular structure of
cis-23 is shown in Fig. 5. Bond lengths are given in Table 8.
˚
The Fe–Ru bond length of 2.6229(12) A is slightly shorter than
˚
that of 5 {2.652(1) A}. The alkenylidene ligand bridges the two
metal centres, with its double bond slightly bent away from the
ruthenium–pentamethylcyclopentadienyl centre, presumably for
Synthesis of an alkenylidene complex
˚
On heating a toluene solution of 10 to reflux, a colour change
from dark green to red was observed. One product was isolated
and crystallised, the vinylidene complex [FeRu(CO)2(l-CO){l-
steric reasons. The vinylidene double bond length is 1.317(9) A,
comparable to that in the diruthenium complex [Ru2(CO)2(l-
1
1
=
CO){l-g :g -C C(CO2Me)2}(g-C5H5)(g-C5Me5)] (24) {1.342(6)
1
1
˚
5d
=
g :g -C C(CO2Me)2}(g-C5H5)(g-C5Me5)] (23), the result of
alkyne–carbonyl bond cleavage and a CO2Me group migration.
A similar methylcarboxylate migration is seen in the Ru2CpCp*
system.5d The mechanism for this conversion was proposed
A}. The sums of the bond angles around each vinylidene
carbon are 359.7◦ {C(4)} and 362.9◦ {C(5)}, indicating both
are sp2 hybridised. The O–C–O planes of the CO2Me groups are
perpendicular to each other, dramatically reducing the steric
Scheme 3 Reactivity of dimetallacyclopentenone complexes 9–11.
7 0
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3

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sponding to two terminal and one bridging carbonyl ligand,
the relative intensities indicating that a cis and a trans isomer
of 25 are present in solution. The two isomers shown are
likely to be the most favoured forms of complex 25. An X-
ray crystallographic study showed the solid-state structure to
be cis-25 and is discussed later. In both isomers the vinyl lig-
and is p-bound to the ruthenium–pentamethylcyclopentadienyl
centre, as this more electron rich centre is a better p back-
donator than the iron–cyclopentadienyl centre. Also, the proton
situated on the bridging carbon of the vinyl unit (Ha) is syn
to the pentamethylcyclopentadienyl ligand on the ruthenium
atom, reducing unfavourable steric interactions between the
pentamethylcyclopentadienyl and the vinyl protons Hb and Hc.
1H NMR spectra show compound 25 is highly fluxional in
solution at room temperature. At −20 ◦C two sets of signals
are seen, corresponding to the cis and trans isomers. The
major and minor resonances for proton Ha are seen at d 9.33
and 10.65 respectively. Based on the solution IR spectrum
of 25 and comparison of the 1H NMR spectroscopic data
1
2
with those of the diruthenium species [Ru2(CO)2(l-CO)(l-g :g -
=
CHa CH2)(g-C5H5)2][BF4] (26) (proton Ha is found at higher
field in trans-26),22 the major isomer is assigned as trans. On
cooling the solution to −40 ◦C and then −60 ◦C, the Cp signals
of each isomer did not sharpen significantly when compared to
Scheme 4 Proposed mechanism of carboxylate group migration in the
conversion of 10 to 23.
◦
those at −20 C, indicating that the isomerisation process has
◦
slowed or even stopped at −20 C. However, the resolution of
the spectra at −40 ◦C and −60 ◦C became very poor. This was
attributed to solubility problems at low temperature in CD2Cl2.
At room temperature the Cp signals are almost coalesced with
resonances at d 5.51 and 5.50. This behaviour suggests that
compound 25 undergoes cis/trans isomerisation as its lowest
energy isomerisation process (Scheme 5). A r,p oscillation would
demand the presence of two cis isomers as the process does not
occur in trans isomers for steric reasons.
Fig. 5 Molecular structure of 23. Hydrogen atoms have been omitted
for clarity. Thermal ellipsoids are drawn at the 50% probability level.
˚
Table 8 Selected bond lengths (A) for 23
Scheme 5 cis/trans isomerisation in the vinyl complex cation of 25.
Fe–C(1)
Fe–C(2)
Fe–C(4)
Fe–Ru
C(1)–O(1)
C(2)–O(2)
1.754(7)
1.951(6)
1.926(6)
2.6229(12)
1.150(8)
1.165(7)
Ru–C(3)
Ru–C(2)
Ru–C(4)
C(4)–C(5)
C(3)–O(3)
C(5)–C(6)
C(5)–C(8)
1.858(6)
2.014(6)
2.026(6)
1.317(9)
1.142(7)
1.461(9)
1.527(8)
1
2
=
Molecular structure of cis-[FeRu(CO)2(l-CO)(l-g :g -CH
CH2)(g-C5H5)(g-C5Me5)][BF4] (25). The molecular structure
of the vinyl complex cation of cis-25 is shown in Fig. 6. Bond
lengths are given in Table 9. The Fe–Ru bond length of 25 is
˚
˚
2.7009(4) A, longer than that of 5 {2.652(1) A}. A carbonyl
ligand bridges the two metal centres asymmetrically, with the
=
C O bond leaning slightly away from the iron cyclopentadienyl
interactions between them. This has an effect on the C(5)–
C(6) and C(5)–C(8) bond distances, the C(5)–C(6) length being
significantly shorter. There is probably some delocalisation over
C(4)–C(5)–C(6)–O(4), with the C(6)–O(4) p bond lying in the
plane of the C(4)–C(5) p bond. The C(8)–O(6) p bond lies
perpendicular to the C(4)–C(5) p bond and cannot interact in
this way.
centre. Two other carbonyl ligands are found, both terminal,
with one bound to the iron atom and one to the ruthenium
atom. Their bond distances and angles are unremarkable. The
vinyl ligand is orientated so that it is bound to the iron atom in a r
=
fashion and to the ruthenium atom in a p fashion. The vinyl C C
bond length is 1.378(4) A, indicating significant p back-donation
from the ruthenium–pentamethylcyclopentadienyl centre.
˚
Synthesis of a vinyl complex
Synthesis of an ethylidene complex
Addition of tetrafluoroboric acid–diethyl etherate to a thf solu-
The homobimetallic analogues of 25 react cleanly with hy-
dride to give l-ethylidene complexes, providing an entry point
into bimetallic alkylidene chemistry.22,23 The reaction proceeds
through nucleophilic attack at the methylene end of the
vinyl unit.
tion of 9 led to the precipitation of the vinyl compound
1
2
=
[FeRu(CO)2(l-CO)(l-g :g -CH CH2)(g-C5H5)(g-C5Me5)][BF4]
(25) through cleavage of the alkyne–carbonyl bond and
protonation of the alkyne.
The vinyl species 25 could exist as eight isomers, but only
two are seen. The IR spectrum of 25 has carbonyl stretching
frequencies at 2027 (m), 2006 (s) and 1855 (m) cm−1, corre-
Compound 25 reacts similarly with sodium borohydride in
acetone to give the l-ethylidene complex [FeRu(CO)2(l-CO)(l-
CHCH3)(g-C5H5)(g-C5Me5)] (27).
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
7 1

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pentamethylcyclopentadienyl resonances of the other isomers
and the solvent peak, whilst the other methyl signal is seen at d
2.71. The second isomer has cyclopentadienyl and pentamethyl-
cyclopentadienyl resonances at d 5.97 and 2.30 respectively. The
allenyl proton, Ha, is seen at d 10.68 and one methyl signal is
observed at d 2.53. Again, the other methyl signal is obscured
by solvent and pentamethylcyclopentadienyl resonances. The
third and least abundant isomer is detected only through its
cyclopentadienyl signal, which appears at d 6.05. Peaks due to
its methyl groups, Ha and pentamethylcyclopentadienyl protons
were either too weak to be observed or obscured by other peaks.
By comparison of the above data with those for the diruthe-
nium allenyl compound,24 the three isomers are thought to be
trans-30a, cis-30a and cis-30b in the ratio 15 : 10 : 1 at −60 ◦C. In
both trans and cis-30a, the allenyl ligand is p-bound to the
electron rich ruthenium–pentamethylcyclopentadienyl ligand, a
situation that would maximise the amount of p-back-donation.
The coalescence of the protons of the two cis isomers suggests
r-p isomerisation is occurring as shown in Scheme 6. A similar
situation is seen in the diruthenium system [Ru2(CO)2(l-CO)(l-
Fig. 6 Molecular structure of the complex cation of 25. Cyclopentadi-
enyl and methyl hydrogen atoms have been omitted for clarity. Thermal
ellipsoids are drawn at the 50% probability level.
1
2
= =
g :g -CH C CMe2)(g-C5H5)2][BF4] (31) and the diiron system
1
2
24,25
˚
Table 9 Selected bond lengths (A) for 25
= =
[Fe2(CO)6(l-SCMe3)(l-g :g -CH C CMe2)] (32).
Fe(1)–Ru(1)
Fe(1)–C(2)
Fe(1)–C(3)
Fe(1)–C(4)
C(2)–O(2)
C(4)–C(5)
2.7009(4)
1.767(3)
1.904(3)
1.941(2)
1.142(3)
1.378(4)
Ru(1)–C(1)
Ru(1)–C(3)
Ru(1)–C(4)
Ru(1)–C(5)
C(1)–O(1)
C(3)–O(3)
1.901(3)
2.113(2)
2.158(2)
2.294(3)
1.133(3)
1.160(3)
Two isomers of 27 are seen, arising from the orientations
of the cyclopentadienyl rings. By IR spectroscopy, these relate
to one cis and one trans isomer. The methyl group of the
ethylidene ligand is presumed to be anti to the pentamethylcy-
clopentadienyl ring in both isomers in order to eliminate any un-
favourable methyl–pentamethylcyclopentadienyl interactions.
Through comparison with trans-[Fe2(CO)2(l-CO)(l-CHMe)(g-
C5H5)2] (28) and trans-[Ru2(CO)2(l-CO)(l-CHMe)(g-C5Me5)2]
(29) this is confirmed. In trans-28, Ha is found at d 10.62,
whereas in trans-29, Ha resonates at d 8.45. In trans-27 Ha is
found at d 8.99, strongly suggesting that this proton resides
syn to the pentamethylcyclopentadienyl ligand and anti to
the cyclopentadienyl ligand. Similarly, the ethylidene methyl
resonance in trans-27 is found at d 3.19, which compares better
with trans-28 (d 3.19) than trans-29 (d 2.94).
Scheme 6 Isomers of the allenyl complex cation of 30.
Due to solubility restrictions, it was not possible to obtain
1
satisfactory low temperature 13C-{ H} NMR data. A room
1
temperature 13C-{ H} NMR spectrum in nitromethane showed
Synthesis of an allenyl complex
peaks due to only one isomer, proposed to be trans-30a.
Resonances are seen at d 240.7, 210.1 and 199.3 due to l-CO,
Fe–CO and Ru–CO respectively. The a, b and c carbons of the
Addition of tetrafluoroboric acid–diethyl etherate to a thf solu-
tion of 11 leads to cleavage of the alkyne–carbonyl bond and loss
of water to give the bridging allenyl compound [FeRu(CO)2(l-
=
=
allenyl unit CaH Cb CcMe2 are seen at d 143.1, 160.3 and 116.2
respectively. Two distinct methyl signals are seen at d 27.0 and
24.2. Signals due to the two cis isomers were not observed.
1
2
= =
CO)(l-g :g -CH C CMe2)(g-C5H5)(g-C5Me5)][BF4] (30). An
X-ray diffraction study was conducted and is discussed below.
It is clear from IR and NMR spectroscopy that 30 is highly
fluxional at room temperature. The IR spectrum of 30 at room
temperature suggests that a species with a trans arrangement
of the terminal carbonyl ligands is dominant, with carbonyl
stretches at 2028(w), 2007(s) and 1857(w) cm−1.
Molecular structure of trans-[FeRu(CO)2(l-CO)(l-g1:g2-
= =
CH C CMe2)(g-C5H5)(g-C5Me5)][BF4] (30a). The molecu-
lar structure of the allenyl complex cation of trans-30a is shown
in Fig. 7. Bond lengths are given in Table 10.
The structure of the allenyl complex cation in 30a shows a
trans orientation of cyclopentadienyl rings. An iron–ruthenium
To understand which isomers were present and what fluxional
processes were occur◦ring, a low temperature 1H NMR study was
performed. At −60 C three cyclopentadienyl signals are seen
relating to three structural isomers of [FeRu(CO)2(l-CO)(l-
˚
bond length of 2.6831(8) A is unremarkable, being only slight
˚
longer than that of 5 {2.652(1) A}. The bridging carbonyl
=
C O bond is slightly bent away from the iron–cyclopentadienyl
g :g -CH C CMe2)(g-C5H5)(g-C5Me5)][BF4] (27) in the ratio
15 : 10 : 1. As the temperature is raised the two minor signals
begin to coalesce until at 40 ◦C only one signal is seen. The Cp
signal due to the major isomer remains unchanged throughout
this temperature range. At −60 ◦C, the major isomer has signals
at d 5.64 and 2.22, corresponding to the cyclopentadienyl and
pentamethylcyclopentadienyl ligands. A resonance at d 9.34 is
centre, with an Fe–C(2)–O(2) angle of 145.7(3)◦ compared to
131.5(3)◦ for Ru–C(2)–O(2). The allenyl unit {C(4)–C(5)–C(6)}
binds to the iron atom through C(4) in a r fashion and to the
ruthenium atom through C(4)–C(5) via a p interaction. The
1
2
= =
˚
double bond between C(4) and C(5) {1.368(4) A} is longer than
˚
that between C(5)–C(6) {1.323(4) A}, indicating significant p
back-donation from the ruthenium centre to the C(4)–C(5) p*
= =
= =
also seen, relating to Ha of the allenyl unit CHa C CMe2.
One of the methyl groups of the allenyl unit is obscured by the
orbitals. The allenyl C C C system is kinked away from the
metal centres partly in order to relieve steric strain between the
7 2
D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3

View Article Online
2 (a) P. Braunstein and J. Rose, Catalysis and Related Reactions
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4 (a) P. Braunstein and J. Rose, Heterometallic Clusters in Catalysis,
in Metal Clusters in Chemistry, ed.P. Braunstein, L. A. Oro and
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(b) S. A. R. Knox, Pure Appl. Chem., 1984, 56, 81; (c) J. N. Wilkinson,
PhD Thesis, University of Bristol, 1999; (d) P. J. King, S. A. R. Knox,
M. S. Legge, A. G. Orpen, J. N. Willinson and E. A. Hill, J. Chem.
Soc., Dalton Trans., 2000, 1547; (e) B. P. Gracey, S. A. R. Knox, K. A.
Macpherson, A. G. Orpen and S. R. Stobart, J. Chem. Soc., Dalton
Trans., 1985, 1935; (f) A. F. Dyke, S. A. R. Knox, P. J. Naish and
G. C. Taylor, J. Chem. Soc., Dalton Trans., 1988, 74.
6 R. B. King, Organometallic Syntheses, ed. J. J. Eisch and R. B. King,
Academic Press, New York and London, 1965, vol. 1, p. 114.
7 G. O. Nelson and C. E. Sumner, Organometallics, 1986, 5, 1983.
8 SMART diffractometer control software, Bruker Analytical X-ray
Instruments Inc., Madison, WI, 1998.
9 SAINT integration software, Siemens Analytical X-ray Instruments
Inc., Madison, WI, 1994.
Fig. 7 Molecular structure of the complex cation of 30. Cyclopentadi-
enyl and methyl hydrogen atoms have been omitted for clarity. Thermal
ellipsoids are drawn at the 50% probability level.
˚
Table 10 Selected bond lengths (A) for 30
Fe–Ru
2.6831(8)
1.760(4)
1.873(4)
1.950(3)
1.153(4)
1.368(4)
1.323(4)
1.504(5)
Ru–C(2)
Ru–C(3)
Ru–C(4)
Ru–C(5)
C(2)–O(2)
C(3)–O(3)
C(6)–C(8)
2.171(4)
1.881(4)
2.144(3)
2.198(3)
1.168(4)
1.150(4)
1.496(5)
Fe–C(1)
Fe–C(2)
Fe–C(4)
C(1)–O(1)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
10 XSCANS diffractometer control software, Bruker Analytical X-ray
Instruments Inc., Madison, WI, 1998.
11 G. M. Sheldrick, SADABS: A program for adsorption correction with
Siemens SMART system, University of Go¨ttingen, Germany, 1996.
12 SHELXTL program system version 5.1, Bruker Analytical X-ray
Instruments Inc., Madison, WI, 2001.
methyl groups and the carbonyl on the ruthenium atom, and
partly as a consequence of the changed hybridisation of the
carbon atoms due to back-bonding. Indeed the methyl group
{C(8)} is also bent away from the ruthenium-based carbonyl
ligand with a C(5)–C(6)–C(8) angle of 125.4(3)◦, compared to
118.5(3)◦ for C(5)–C(6)–C(7).
13 P. J. King and S. A. R. Knox, personal communication.
14 N. J. Forrow, PhD Thesis, University of Bristol, 1984.
15 (a) O. S. Mills, Acta Crystallogr., 1958, 11, 620; (b) A. Steiner, H.
Gornitzka, D. Stalke and F. T. Edelmann, J. Organomet. Chem.,
1992, 431, C21.
Conclusions
A good synthesis of the iron–ruthenium cyclopentadienyl–
pentamethylcyclopentadienyl complex [FeRu(CO)4(g-C5H5)(g-
C5Me5)] (5) has been established. The chemistry of 5 is
broadly similar to that of [FeRu(CO)4(g-C5H5)2] (3) and of
the diruthenium complex [Ru2(CO)4(g-C5H5)(g-C5Me5)] (2).
Through initial photolysis with alkynes and then subsequent
reactions, complex 5 provides access to and data on compounds
containing a variety of organic fragments, making them ripe for
further investigation.
The heightened reactivity of complex 5 under photolytic
conditions towards alkynes compared with its homometallic
analogues, illustrates the broader potential of mixed metal
systems to outperform their homometallic analogues.
Also, the unusual methylcarboxylate migration serves to show
how asymmetry in these bimetallic systems can lead to novel
reactivity.
16 J. G. Bullit, F. A. Cotton and T. J. Marks, Inorg. Chem., 1972, 11,
671.
17 P. McArdle, L. O’Neil and D. Cunningham, Organometallics, 1997,
16, 1335.
18 A. F. Dyke, S. A. R. Knox, P. J. Naish and G. E. Taylor, J. Chem.
Soc., Dalton Trans., 1982, 1297.
19 P. R. Rodenhurst, PhD Thesis, University of Bristol, 1993.
20 (a) S. M. Nicholls, PhD Thesis, University of Bristol, 1991; (b) L. A.
Brady, A. F. Dyke, S. E. Garner, V. Guerchais, S. A. R. Knox, J. P.
Maher, S. M. Nicholls and A. G. Orpen, J. Chem. Soc., Chem.
Commun., 1992, 310; (c) L. A. Brady, A. F. Dyke, S. E. Garner,
S. A. R. Knox, A. Irving, S. M. Nicholls and A. G. Orpen, J. Chem.
Soc., Dalton Trans., 1993, 487.
21 R. E. Colborn, A. F. Dyke, B. P. Gracey, S. A. R. Knox, K. A.
Macpherson, K. A. Mead and A. G. Orpen, J. Chem. Soc., Dalton
Trans., 1990, 761.
22 A. F. Dyke, S. A. R. Knox, M. J. Morris and P. J. Naish, J. Chem.
Soc., Dalton Trans., 1983, 1417.
23 A. F. Dyke, S. A. R. Knox, P. J. Naish and A. G. Orpen, J. Chem.
Soc., Chem. Commun., 1980, 441.
24 C. P. McArdle, PhD Thesis, University of Bristol, 1999.
25 D. Seyferth, G. B. Womack, C. M. Archer and J. C. Dewan,
Organometallics, 1989, 18, 430.
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D a l t o n T r a n s . , 2 0 0 5 , 6 3 – 7 3
7 3