Optimised Syntheses of the Half-Sandwich Complexes FeCl(dppe)Cp?, FeCl(dppe)Cp, RuCl(dppe)Cp?, and RuCl(dppe)Cp

Article abstract of DOI:10.1071/CH16322

Thanks to their synthetic versatility, the half-sandwich metal chlorides MCl(dppe)(η5-C5R5) [M≤Fe, Ru; dppe≤1,2-bis(diphenylphosphino)ethane, R≤H (cyclopentadiene, Cp), CH3 (pentamethylcyclopentadiene, Cp?)] are staple starting materials in many organomet

Full text of DOI:10.1071/CH16322

CSIRO PUBLISHING
Aust. J. Chem.
Full Paper
http://dx.doi.org/10.1071/CH16322
Optimised Syntheses of the Half-Sandwich Complexes
FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*,
and RuCl(dppe)Cp
A
B
B
Josef B. G. Gluyas, Neil J. Brown, Julian D. Farmer,
and Paul J. Low
,
A C
A
School of Chemistry and Biochemistry, University of Western Australia,
5 Stirling Highway, Crawley, WA 6009, Australia.
3
B
Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK.
C
Corresponding author. Email: paul.low@uwa.edu.au
5
Thanks to their synthetic versatility, the half-sandwich metal chlorides MCl(dppe)(Z -C R ) [M ¼ Fe, Ru; dppe ¼ 1,2-bis
5
5
(
diphenylphosphino)ethane, R ¼ H (cyclopentadiene, Cp), CH (pentamethylcyclopentadiene, Cp*)] are staple starting
3
materials in many organometallic laboratories. Here we present an overview of the synthetic methods currently available
for FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl(dppe)Cp*, and RuCl(dppe)Cp, and describe in detail updated and optimised
multigram syntheses of all four compounds.
Manuscript received: 25 May 2016.
Manuscript accepted: 19 June 2016.
Published online: 28 July 2016
Introduction
Half-sandwich complexes are known for all of the d-block
generate and study mixed-valence complexes and electron-
[
36–40]
transfer phenomena.
The ability to systematically vary
[
1,2]
metals and most of those in the f-block.
These systems,
typified by complexes of the cyclopentadienyl ligand (Cp),
the nature of the metal and the steric and electronic properties
of the half-sandwich fragment has allowed detailed investiga-
tion of the electronic and spectroscopic properties of such
complexes. In this context, the compounds FeCl(dppe)Cp*,
5
Z -C H , and derivatives but also including a wide array of
5
5
cyclic hydrocarbons, have been fundamental to the development
of organometallic chemistry. Through decades of inspiring
work, half-sandwich compounds now find application in an
immense range of catalytic transformations, including olefin
7
RuCl(PPh ) Cp, RuCl(dppe)Cp*, MoBr(dppe)(Z -C H ), and
3
2
7 7
ReCl(NO)(PPh )Cp* (dppe ¼ 1,2-bis(diphenylphosphino)ethane,
3
5
Cp* ¼ pentamethylcyclopentadiene, Z -C (CH ) ), which are
5
3 5
[
3–6]
polymerisation
and asymmetric processes which take
considerably more electron-rich than similar half-sandwich
carbonyl complexes such as MCl(CO) Cp, MCl(CO) Cp*
advantage of chirality introduced through either substitution of a
chiral auxiliary at the periphery of the cyclic hydrocarbon, use of
chiral supporting ligands, or otherwise engineering asymmetry in
2
2
7
(M ¼ Fe, Ru), MoBr(CO) (Z -C H ), MCl(CO) Cp, MCl
2
7
7
3
(CO) Cp* (M ¼ Mo, W), have proven to be especially useful.
3
[7–12]
the supporting ligand environment.
The capacity to control
However, despite the demonstrable utility of both FeCl
(dppe)Cp* and RuCl(dppe)Cp* as valuable starting materials,
the closely related cyclopentadienyl derivatives FeCl(dppe)
shape, solubility, and supporting ligands of half-sandwich com-
poundshasledtofurtherdevelopments inthe use ofhalf-sandwich
[13,14]
compounds in biological and biomedical contexts,
[41]
[42]
including
Cp and RuCl(dppe)Cp, which offer intermediate electron
donor capacity and smaller steric bulk at the metal centre than
[15,16]
applications as enzyme inhibitors and metal-based drugs.
[
43–47]
The synthetic versatility of the generic half-sandwich plat-
form has seen these systems routinely applied as frameworks
upon which to support and further develop the chemistry of
the Cp* derivatives, have been less thoroughly exploited.
In part the restricted use of these compounds might be attributed
to the limitations in synthetic routes to them. Here we summarise
the known synthetic routes to the family of complexes MCl
[
17]
[18]
ligands such as carbenes
silyenes,
and vinylidenes,
the polyyndiyl and cumulene forms of linear C
silyls and
[19]
5
(dppe)(Z -C R ) (M ¼ Fe, Ru; R ¼ H (Cp), CH (Cp*)), and
n
5
5
3
5
fragments supported by ML (Z -C R ), and related frag-
ments. The ligand substitution chemistry that has been
developed on various half-sandwich complexes has led to their
describe in detail multigram scale procedures which afford these
compounds in two-pot processes from commercial FeCl ꢀ4H O
2
5 5
[20,21]
2
2
or RuCl ꢀxH O.
3
2
[22–25]
use as building blocks in supramolecular architectures
and
[26,27]
surface-supported nanoarchitectures,
for the investigation of non-linear optical properties.
synthetic versatility is augmented by well defined one-electron
redox processes which opens a range of further possibili-
ties for use of these systems as platforms through which to
and as frameworks
[
28–33]
Results and Discussion
The
FeCl(dppe)Cp*
[
34,35]
The iron complex FeCl(dppe)Cp* was first prepared in the late
[
48]
1980s by Lapinte and co-workers.
In this early report
Journal compilation � CSIRO 2016
www.publish.csiro.au/journals/ajc

B
J. B. G. Gluyas et al.
colloidal potassium (generated using high intensity ultrasound)
was treated with a mixture of pentamethylcyclopentadiene and
per mole, prices from Sigma Aldrich.) Recently, a single crystal
X-ray diffraction study identified [FeCl (dppe)] as a coordina-
tion polymer, rather than the often presumed molecular species,
2
n
[
FeCl (dppe)] in a toluene/tetrahydrofuran mixture and
2
n
[
54]
allowed to react under ultrasonic irradiation for 30 min at
108C. An otherwise identical reaction conducted at 508C
FeCl (dppe).
2
ꢁ
Here, the following method is proposed (Scheme 1a). Potas-
sium pentamethylcyclopentadienide is produced in situ by
reaction of pentamethylcyclopentadiene with potassium metal
yielded the corresponding iron hydride FeH(dppe)Cp*. An
alternative procedure involving reaction of lithium penta-
methylcyclopentadienide with [FeCl (dppe)] in tetrahydro-
[
53]
in refluxing toluene,
and precipitates from the reaction as a
2
n
furan under reflux (1 h) or at room temperature (overnight)
affording FeCl(dppe)Cp* in 85 % isolated yield was later
fine white powder. The potassium pentamethylcyclopentadie-
nide so produced is not isolated, but rather the reaction mixture
is allowed to cool, diluted with a further portion of toluene, and
[49]
described. Similar reactions provide a general entry point to
5
[44,54]
FeCl(PMe ) (Z -C R ) (C R ¼ C H (Cp), C H (CH ) (Cp’),
treated with thoroughly dried [FeCl (dppe)] .
n
Following
3
2
5
5
5
5
5
5
5
4
3
2
[
50]
C (CH ) (Cp*)) complexes.
5
overnight reaction at room temperature, the workup involves a
simple filtration, removal of solvent, and crystallisation
(dichloromethane/n-pentane) of the residue. The target complex
is obtained in high yield (78 %, relative to K) in a 7.7 mmol
reaction as the dichloromethane solvate. Conducting the addi-
tion of [FeCl (dppe)] initially at ꢁ788C did not improve the
3 5
Most recently, Liddle and colleagues have explored the
synthetic chemistry associated with the preparation of a wide
5
range of half-sandwich FeCl(dppe)(Z -C R ) compounds
5
5
(
C R ¼ C H (Cp), C (CH ) (Cp*), C H SiMe , C H (SiMe ) ,
5
5
5
5
5
3 5
5
4
3
5
3
3 2
t
[51]
and C H ( Bu) ). In this case FeCl(dppe)Cp* was synthesised
5 3 2
2
n
(
73 %) by a 1 : 1 reaction of potassium pentamethylcyclopenta-
yield.
dienide with [FeCl (dppe)] in toluene (ꢁ788C - r.t., 18 h),
2
n
FeCl(dppe)Cp
The synthesis of FeCl(dppe)Cp was first reported in 1969 from
although only generalised reaction conditions were given for the
series of half-sandwich complexes reported. The reaction temper-
ature was noted as being important for achieving the reported
yields, with formation of ferrocenes and free 1,2-bis(diphenylpho-
sphino)ethane from ligand scrambling processes being problem-
atic in reactions conducted at room temperature, but being largely
eliminated in reactions carried out initially at ꢁ788C.
[
55,56]
the reaction of FeCl(CO) Cp
with 1,2-bis(diphenylpho-
sphino)ethane in benzene under UV irradiation, and isolated in
2
[
57]
45 % yield.
an alternative synthesis of FeCl(dppe)Cp from [FeCl (dppe)]n
Several years later Mays and Sears developed
2
and thallium cyclopentadienide in a reaction conducted in
benzene. Workup involved chromatographic purification to
remove ferrocene, which is the main by-product of the
A more convenient laboratory preparation of FeCl(dppe)Cp*
would avoid the use of ultrasonic irradiation, and the isolation
[
52]
[41]
and manipulation of air sensitive lithium
potassium
or pyrophoric
pentamethylcyclopentadienides, while taking
advantage of the ready availability of [FeCl (dppe)] . Although
reaction.
[
53]
6
The arene(cyclopentadienyl) iron complex [FeCp(Z -
C H CH )]PF can be obtained by ligand exchange reactions
6
2
n
5
3
6
[
58]
[
FeCl (dppe) ] is commonly prepared from reaction of anhy-
2 n
of ferrocene with toluene
19-electron radical FeCp(Z -C H CH ) by Na:Hg amalgam.
and reduced to the highly reactive
[59]
2
[
41,51]
6
drous FeCl with 1,2-bis(diphenylphosphino)ethane it has
been recently shown that [FeCl (dppe)] can be conveniently
2
6
5
3
During the course of an exploration of a wide range of reactions
6
2
n
synthesised in high yield (,80 %) by treatment of FeCl ꢀ4H O
in which the toluene ligand is displaced from FeCp(Z -C H CH )
2
2
6
5
3
with 1,2-bis(diphenylphosphino)ethane in acetone/chloroform
it was found that reaction with 1,2-bis(diphenylphosphino)ethane
gave either FeH(dppe)Cp (56 %, from reactions in THF) or FeCl
(dppe)Cp (30%, from reactions in CH Cl ), although limited
[
44,54]
mixtures
considerably greater cost, of anhydrous FeCl (As of March
thereby avoiding the tedious preparation, or
2
2
2
2
016, FeCl ꢀ4H O costs ,A$65 per mole and FeCl ,A$390
synthetic details were given. In a similar study detailing
2
2
2
(a)
(b)
(c)
FeCI ·4H O
RuCI ·3H O
RuCI ·3H O
2
2
3
2
3
2
CpH, PPh3
(
Ph P) (μ-CH CH )
Cp∗ H
2
2
2
2
[
FeCI (dppe)]
[RuCp∗ Cl2]n
2
n
Ru Cl
Ph P
3
PPh3
C R M
(Ph P) (μ-CH CH )
5
5
2
2
2
2
(
Ph P) (μ-CH CH )
2
2
2
2
R
R
R
R
R ϭ CH , M ϭ K
3
R
Fe Cl R ϭ H, M ϭ Li
PPh2
Ru Cl
PPh2
Ru Cl
PPh2
Ph P
Ph P
Ph P
2
2
2
Scheme 1. Syntheses of (a) FeCl(dppe)Cp* and FeCl(dppe)Cp, (b) RuCl(dppe)Cp*, and (c) RuCl(dppe)Cp.

Optimised Syntheses of Half-Sandwich Complexes
C
investigations of the scope and the mechanism of the reactions of
(COD¼ 1,5-cyclooctadiene,
from RuCl ꢀxH O, triphenylphosphine, and pentamethylcyclo-
3
2
[66]
[
CpFe(COD)][Li(TMEDA)]
pentadiene, in a manner entirely analogous to the synthesis of
[67]
TMEDA ¼ tetramethylethylenediamine) with benzyl halo-
RuCl(PPh ) Cp. Incontrast the group of Suzuki and Moro-oka
3 2
[60]
gens, FeCl(dppe)Cp was observed in ,2 % conversion follow-
reacted oligomeric [RuCl Cp*] , obtained from direct reaction of
2 n
ing reaction with C H CH Cl in the presence of 1,2-bis
(diphenylphosphino)ethane, the major product being identified
as Fe(CH C H )(dppe)Cp.
RuCl ꢀxH O and pentamethylcyclopentadiene in refluxing meth-
6
5
2
3
68]
2
[
[69]
anol or ethanol, with 1,2-bis(diphenylphosphino)ethane in
ethanol (room temperature) to give the target compound RuCl
2
6 5
[69]
(dppe)Cp* in 41 % yield.
More recently, several groups have reported syntheses of
FeCl(dppe)Cp using methods closely related to that originally
The product obtained from the reaction of RuCl ꢀxH O with
3
2
[
41]
described by Mays and Sears,
and involve treatment of
[43,51]
pentamethylcyclopentadiene in alcohol solvents is often
described as either a dimer [RuCl Cp*] , or the oligomeric (or
[
FeCl (dppe)] with a metal cyclopentadienide (M ¼ Li
2
44]
n
2
2
[
or Tl ) in an aromatic solvent. Two points are worth highlight-
ing from these more modern investigations: as detailed in the
discussion of FeCl(dppe)Cp* one report notes that conduction of
the reaction initially at ꢁ788C suppresses the formation of
polymeric) form [RuCl Cp*] . In the course of their investiga-
2 n
tions, the Suzuki and Moro-oka group noted the synthesis of this
key reagent [RuCl Cp*] (x ¼ 2 or n) was sensitive to the nature
2
x
[
69]
of the solvent used in the preparation; similar observations on
the composition of this material and the formation of deca-
methylruthenocene as a by-product having also been made by
[
51]
ferrocene derivatives; the use of a sub-stoichiometric amount
of thallium cyclopentadienide also limits the formation of
ferrocene, with the excess [FeCl (dppe) ] being readily
[
68]
Tilley et al.
optimised the synthesis of [RuCl Cp*] , noting that the use of
Later, Koelle and Kossakowski explored and
2
2 n
removed by filtration together with thallium chloride from the
2
2
[44]
reaction mixture during workup.
In elegant recent studies, the groups of Bouwman
methanol and a 2.5 fold excess of pentamethylcyclopentadiene
gave better yields of the less soluble oligomeric species
[RuCl Cp*] , while the use of ethanol led to greater proportions
[
61]
and
Whiteley have shown the thermal conversion of FeI(CO) Cp
[62]
2
2
n
to FeI(dppe)Cp in yields of 74% (0.2 mmol scale) to 48%
(8.2mmol scale), and taking advantage of the strong Fe–I bond
of the more soluble dimer [RuCl Cp*] with decamethylruthe-
2 2
nocene as a by-product in up to 30 % yield. The dimeric
[RuCl Cp*] obtained using ethanol as the solvent was
which hinders the formation of the cationic mono-carbonyl
substitution product [Fe(CO)(dppe)Cp]I. While this approach is
not suitable for the synthesis of the chloride complex FeCl(dppe)
Cp, which is the focus of this discussion, FeI(dppe)Cp displays
essentially identical reactivity to FeCl(dppe)Cp and thus is a
viable alternative entry into such half-sandwich systems.
2
2
described as redder in colour, more soluble and leading to
cleaner subsequent reactions. Reduction of the dimer with
cobaltocene gave the mixed valence dimer [(Cp*Ru) (m-Cl) ].
2
3
Both RuCl(dppe)Cp* and RuCl(PPh ) Cp* were synthesised by
reaction of the mixed valence compound with the appropriate
3
2
II
phosphine, the yield indicative of reaction of only the ‘Ru ’
Our efforts towards producing FeCl(dppe)Cp in a convenient
laboratory setting have considered approaches from [FeCl
[
70]
portion of the dimer.
(dppe)]n and metal cyclopentadienide sources. The use of
thallium cyclopentadienide in the manner originally described
Aside from a mention of the formation of RuCl(dppe)Cp* in
a study of the enthalpies of displacement of COD from RuCl
(COD)Cp* with a variety of bidentate phosphines and
[
41]
[44]
by Mays and Sears and later optimised is highly effective,
but the use of toxic thallium reagents is less than desirable.
Efforts to arrive at a synthetic method that takes advantage of an
in situ synthesis of an alkali metal cyclopentadienide (M ¼ Li,
Na, K) resulted in a maximum yield of 37 % from M ¼ Li.
Although isolating alkali metal organometallics is less conve-
nient than an in situ approach, lithium cyclopentadienide can be
handled without issue in a glovebox, is considerably less
sensitive to atmospheric exposure than the corresponding pyro-
[
71]
arsines,
step- and yield-wise, subsequent reports
small scale variations on the ligand exchange synthesis origi-
which is not an attractive synthetic procedure both
[
72–74]
have focussed on
[66]
nally described by Treichel and co-workers.
Seeking to develop a simplified, optimised, high yielding,
multigram procedure we reinvestigated the Tilley, Grubbs, and
Bercaw, and Suzuki and Moro-oka based procedures. Reaction
of ,2.8 equivalents of pentamethylcyclopentadiene with
RuCl ꢀxH O in methanol yielded the intermediate oligomeric
[63]
[64]
phoric sodium
and potassium
compounds, and naturally
3
2
avoids the toxicity issues associated with thallium compounds.
We therefore consider that on balance the route proposed by
ruthenium species [RuCl Cp*] as an insoluble brown powder,
2 n
which was freed of decamethylruthenocene by washing with
hexanes. Subsequent reaction of [RuCl Cp*] with 1,2-bis
[
51]
Liddle and co-workers
chemistry of FeCl(dppe)Cp. Solid samples of lithium cyclopen-
provides the best entry into the
2
n
(diphenylphosphino)ethane under reflux in ethanol
(Scheme 1b) allowed the isolation of RuCl(dppe)Cp*
in 87 % yield (relative to RuCl ꢀxH O, 12.1 mmol scale)
[65]
tadienide and [FeCl (dppe)] are prepared and isolated, the
2 n
solids are mixed in a Schlenk flask under nitrogen (a glovebox
3
2
greatly simplifies this procedure) and the flask cooled to ꢁ788C
by crystallisation directly from the reaction mixture. Thus the
target half-sandwich complex can be synthesised in a two pot,
two step reaction sequence directly from RuCl ꢀxH O avoiding
(dry ice/acetone). Dry toluene is added dropwise to the reaction
flask, which is then left to warm slowly to room temperature.
Workup consists of a simple filtration and crystallisation, and
affords the desired compound in 72 % yield from a 7.6 mmol
scale reaction (Scheme 1a).
3
2
any intermediate purification or chromatography.
RuCl(dppe)Cp
Three separate groups reported the synthesis of RuCl(dppe)Cp
[42,75,76]
RuCl(dppe)Cp*
nearly simultaneously in late 1979 and early 1980,
by
The complex RuCl(dppe)Cp* was reported essentially simulta-
neously by two independent research groups using different
approaches. Treichel et al. described a ligand exchange reaction
from 1,2-bis(diphenylphosphino)ethane and RuCl(PPh ) Cp*,
thermally driven phosphine exchange of 1,2-bis(diphenylpho-
sphino)ethane with RuCl(PPh ) Cp in refluxing benzene or
3
2
[42]
toluene in yields of ,80 %. Over the following years several
researchers have explored this ligand exchange synthesis with
3
2
[43,45,46,66,77–80]
the initial ruthenium complexbeing prepared ina one pot reaction
slight variations on the early procedures.
An

D
J. B. G. Gluyas et al.
important point highlighted in two of these studies is that the
2
Instead, pure trans-RuCl (dppe) was isolated and identified by
2
2
1
31
side products RuCl (dppe) and [RuClCp] (Z -m -dppe) can be
H and P NMR spectroscopy of the precipitate formed in this
reaction. This is consistent with the early syntheses of trans-
2
2
2
2
2
isolated when the ligand exchange reaction is carried out using
[45]
[
80]
[88]
2
2
ꢁ10 mol-% excess of 1,2-bis(diphenylphosphino)ethane.
RuCl (dppe)
and the observations of side products in the
established phosphine exchange synthesis of RuCl(dppe)
2
The original Bruce report also notes formation of an initial
yellow precipitate which was discarded before the desired
[45,89]
Cp.
A revised synthesis of this material is described below.
In our hands, RuCl(dppe)Cp was best obtained following
[
reaction of RuCl(PPh ) Cp with 1,2-bis(diphenylphosphino)
[42]
product was isolated by crystallisation, suggesting that one or
both of the side products described by later researchers was also
formed in this early work. Interestingly, phosphine exchange
reactions of RuCl(PPh ) Cp with one equivalent of 1,2-bis
67]
3
2
ethane in a 1 : 1 ratio under reflux in toluene (94 % yield,
5.5 mmol scale, Scheme 1c). Workup consists of reduction of
the solution volume and addition of hexanes to precipitate the
product, which is recovered by a simple filtration. This proce-
3
2
(diphenylphosphino)methane (dppm) under conditions of high
concentration (0.1 M) in benzene leads to the mono-substituted
1
product RuCl(PPh )(k -dppm)Cp (dppm ¼ 1,1-bis(diphenyl-
dure is essentially very similar to the wealth of previous
[42,43,45,46,66,75–80]
3
[81]
phosphino)methane).
Presumably, competition with the
reports,
however taking care to employ the
liberated triphenylphosphine prevents the ligand exchange equi-
libria from shifting to the four membered chelate ring. In more
dilute solution (0.005 M), the competition with external triphe-
nylphosphine is less significant and RuCl(dppm)Cp is
correct stoichiometric ratio of ruthenium to phosphine allows
the product to be obtained in high yield and purity directly from
the reaction mixture.
[42,81]
obtained.
In contrast, the greater stability of the five-
trans-RuCl (dppe)
2
2
membered chelate in RuCl(dppe)Cp leads to ready formation
of this species from RuCl(PPh ) Cp and 1,2-bis(diphenylpho-
As noted above, attempts to synthesise RuCl(dppe)Cp directly
from RuCl ꢀxH O, cyclopentadiene and 1,2-bis(diphenylpho-
3
2
3
2
[42,43,45,46,66,75–80]
sphino)ethane under a range of concentrations.
As described below, the 1 : 1 reaction of RuCl(PPh ) Cp and
sphino)ethaneresultedintheisolationofpuretrans-RuCl (dppe) .
2
2
3
2
These findings are consistent with the early organometallic liter-
aturewhere the synthesisof trans-RuCl (dppe) isdescribedunder
1,2-bis(diphenylphosphino)ethane in refluxing toluene yields
only the desired complex RuCl(dppe)Cp (94% isolated yield,
2
2
[88]
very similar conditions. Accordingly a targeted synthesis of
trans-RuCl (dppe) was developed by addition of an ethanol
5
.5 mmol scale) even from relatively concentrated solutions.
Routes requiring milder conditions for the final step in the
2
2
solution of RuCl ꢀxH O to a solution of 1,2-bis(diphenylpho-
3
2
synthesis of RuCl(dppe)Cp exist; typically these involve dis-
placement of a more labile, unsaturated organic ligand from a
cyclopentadienyl ruthenium precursor. However, while the final
step in these syntheses is indeed mild, the production of the
labile precursors is decidedly non-trivial. The methods dis-
sphino)ethaneinarefluxingtetrahydrofuran/ethanolmixture. This
results in almost immediate formation of a yellow crystalline
precipitate, the reaction being complete within 10 min. Following
cooling of the reaction solution, trans-RuCl (dppe) can be
2
2
isolated in 88 % yield via simple filtration.
3
cussed include thermal decomposition of the Z -allyl ruthenium
3
complex RuCl(Me)(Z -C H )Cp in the presence of 1,2-bis
(
3
5
3
Conclusion
diphenylphosphino)ethane. The precursor RuCl(Me)(Z -
C H )Cp is produced by substitution of the corresponding
[82]
Robust, large scale, high yield syntheses for the widely used
5
3
5
3
dichloride RuCl (Z -C H )Cp with methyl lithium. In turn,
RuCl (Z -C H )Cp is obtained from oxidative addition of allyl
family of half-sandwich complexes MCl(dppe)(Z -C R ) (M ¼
5 5
2
3
5
3
2
3
5
Fe, Ru; R ¼ H (Cp), CH (Cp*)) obtained in two-pot processes
3
[
82]
chloride with RuCl(CO) Cp, carried out in decane at 1408C
from commercial FeCl ꢀ4H O or RuCl ꢀxH O have been
2
2
2
3
2
Further reports describe substitution of the cyclooctadiene
ligand of RuCl(COD)Cp by 1,2-bis(diphenylphosphino)ethane,
although the synthesis of RuCl(COD)Cp involves the use of
described in detail. These methods represent, in our hands, the
most convenient entry to the chemistry of these versatile
reagents and minimise the use of highly toxic (TlCp) or isolation
of highly pyrophoric (KCp*) compounds. The ready availability
of these MCl(dppe)Cp derivatives should see growth in the
interest in these compounds within the myriad of applications of
half-sandwich compounds and add further opportunities to
explore the electronic and steric effects of the ligand sphere in
[
83,84]
thallium cyclopentadienide and carbon tetrachloride,
þ
and
reaction of [RuCp(C H )] with a halide source, typically a
1
0 10
tetrabutylammonium halide, and 1,2-bis(diphenylphosphino)
[
85]
ethane.
(
However, the synthesis of this precursor [RuCp
þ
C H )] , among other difficulties, requires ruthenocene
10 10
[
86]
(involving a challenging synthesis itself)
rial and includes a 50 h reflux.
as a starting mate-
the chemistry of ML Cp’-derived complexes.
2
[87]
The most regularly used route to RuCl(dppe)Cp, based on the
procedures for ligand exchange from RuCl(PPh ) Cp developed
Experimental
3 2
[75]
[42]
General Conditions
by Bruce and co-workers, Davies and Scott,
[
and Treichel
is recognisably robust. However, we felt there
76]
and Komar,
All reactions were carried out under an atmosphere of dry argon
(FeCl(dppe)Cp*) or nitrogen (all other reactions) using standard
Schlenk techniques. Toluene and hexanes were dried by passage
over an alumina column, other solvents were standard reagent
grade and used as received. No special precautions were taken to
exclude air or moisture during workup except where otherwise
indicated. Commercial pentamethylcyclopentadiene was dis-
tilled before use, cyclopentadiene was freshly cracked from
may be a possibility of improving on the established thermal
phosphine exchange reaction of RuCl(PPh ) Cp and 1,2-bis
3
2
(diphenylphosphino)ethane and so explored the prospect of
reducing the number of steps and reagents required to make
the target complex. Thus, 1,2-bis(diphenylphosphino)ethane was
dissolved in an ethanol/tetrahydrofuran mixture at reflux, and a
mixture of freshly cracked cyclopentadiene and RuCl ꢀxH O was
3
2
[
90]
[67]
added in a steady stream. This method was intended to mimic that
dicyclopentadiene,
and RuCl(PPh ) Cp
and lithium
were synthesised according to literature
procedures. All other reagents were commercially available and
3
2
[
67]
[65]
used in the synthesis of RuCl(PPh ) Cp
(
and RuCl
however the desired product was not obtained.
cyclopentadienide
3
2
[66]
PPh ) Cp*,
3 2

Optimised Syntheses of Half-Sandwich Complexes
E
used as received. As the water content of RuCl varies and is
3
rise to very broad signals, providing little meaningful informa-
tion. Introduction of a reducing agent, cobaltocene, did not alter
the signal resolution and so these effects are presumably due to
difficult to accurately determine, all calculations were per-
formed assuming that the molecular formula is RuCl ꢀ3H O.
3
2
II
NMR spectra were recorded at 258C on a Bruker Avance III HD
6
some spin crossover to the high-spin d Fe form.
6
1
00 ( H 600.1 MHz, C 150.9 MHz, P 242.9 MHz) or a
13
31
[
65]
1
31
Synthesis of Lithium Cyclopentadienide
Varian Inova 300 ( H 300.2 MHz, P 121.5 MHz) spectrometer
using CDCl or C D as the solvent. Chemical shifts were
Warning: Although no difficulties have been encountered in the
preparation or handling of lithium cyclopentadienide, which is
considerably less reactive than the Na or K analogues, orga-
nolithiums should be regarded as air-sensitive, flammable, and
potentially pyrophoric materials. All manipulations of this
compound should be conducted under a rigorously anaerobic
environment, by a competent worker.
Cyclopentadiene (5.06 g, 76.6 mmol) was dissolved in
hexanes(120mL), the solution was cooledto08C (ice/saltcooling
bath) and n-butyl lithium (30.6 mL, 2.5M, 76.6 mmol of n-BuLi)
was added dropwise over a 10min period. The reaction mixture
quickly developed a thick white suspension, which was stirred for
18h and allowed to warm slowly to ambient temperature. The
product was isolated by filtration under Schlenk conditions,
washed with dry hexanes (3 ꢂ 50mL), and vacuum dried afford-
ing lithium cyclopentadienide as a white powder in 78% yield
(4.29 g, 59.6 mmol) which was transferred to a nitrogen filled
3
6 6
1
determined relative to internal residual solvent signals ( H,
1
3
C)
[91]
31
or external 85 % H PO ( P 0.0 ppm).
3 4
Synthesis of [FeCl (dppe)]
2
n
Acetone (480 mL) was deoxygenated by sparging with nitrogen,
and FeCl ꢀ4H O (10.0 g, 50.5 mmol) was added giving a green
2
2
suspension. Separately, 1,2-bis(diphenylphosphino)ethane
(
20.2 g, 50.8 mmol) was dissolved in chloroform (120 mL) and
the solution also deoxygenated by sparging. The 1,2-bis
diphenylphosphino)ethane solution was then transferred into
(
the stirred FeCl ꢀ4H O mixture via cannula; during the addition
2
2
a white precipitate began to form almost immediately. This
reaction mixture was subsequently heated to reflux for 3 h after
which
a copious white precipitate had formed. The
precipitate was collected by filtration, washed with diethyl
ether (3 ꢂ 100 mL) and dried, first in air and then in a vacuum
desiccator for a minimum of 16 h, to afford [FeCl (dppe)] in
glovebox for subsequent manipulation.
d
(600.1MHz,
13
2
n
H
†
9
8 % yield as a free flowing cream powder (26.2 g, 49.9 mmol).
(CD SO) 5.33. d (150.9MHz, (CD SO) 103.0. The
C
3
)
2
3
)
2
C
[92]
NMR data are in agreement with the literature.
Synthesis of [FeCl(dppe)Cp*] ꢀ CH Cl
2
2
Synthesis of FeCl(dppe)Cp
Warning: Potassium pentamethylcyclopentadienide is a highly
[
53]
reactive material, spontaneously combustible in air.
The
Lithium cyclopentadienide (549 mg, 7.62 mmol) and
[FeCl (dppe)] (4.00 g, 7.62 mmol) were combined in a Schlenk
procedures described below are designed to avoid the isolation
of this compound and any exposure of this material to the
atmosphere must be avoided.
2
n
flask within a glove box, before being transferred to an efficient
Schlenk line to conduct the remainder of the experiment. The
flask containing the solid reagents was cooled to ꢁ788C (dry ice/
acetone cooling bath), and toluene (50 mL) was added dropwise
over 10 min to the stirred mixture. Upon completion of solvent
addition the cooling bath was left in place and the reaction
mixture, an off-white suspension, was allowed to stir and slowly
warm to room temperature over a period of 16h. After this time
the deep blue-black mixture was filtered through Celite and
washed through with dichloromethane (200 mL). The combined
washings were concentrated to dryness and the black residue
dissolved in the minimum volume of dichloromethane (,10mL)
and layered with n-pentane (,50 mL). This mixture was left
undisturbed overnight yielding blue-black crystals which were
recovered by decanting the liquors and washing with n-pentane to
afford FeCl(dppe)Cp as blue-black crystals in 72 % yield (3.05 g,
A mixture of potassium (300 mg, 7.67 mmol), pentamethyl-
cyclopentadiene (1.15 g, 8.44 mmol), and toluene (15 mL) was
heated to reflux until a fine white precipitate had formed and
pieces of potassium metal were no longer visible (,3 h).
Following cooling of the reaction mixture to ambient tempera-
ture, toluene (35 mL) was added followed by [FeCl (dppe)]
2
n
(4.31 g, 8.21 mmol) and the resulting dark mixture was stirred
for 16 h. Subsequently, the reaction mixture was filtered through
Celite and the filter cake was washed with toluene until the
washings were colourless (,60 mL). The combined filtrant and
washings were then concentrated to dryness, and the residue was
dissolved in the minimum volume of dichloromethane
(
,15 mL) and layered with n-pentane (,60 mL). This mixture
was left undisturbed overnight to afford large black crystals and
a fine brown powder, the crystals were recovered by decanting
the liquors and fine particles, and washing with n-pentane to
afford [FeCl(dppe)Cp*]ꢀCH Cl as black crystals in 78 % yield
5.49mmol). d
(m, 2H, dppe), 4.17 (s, 5H, C
(m, 2H, C ), 7.10 (m, 4H, C
H signal, 2H, C ), 7.24 (m, 4H, C
). d (242.9MHz, C ) 97.8. Found: C 67.23, H 5.32. Anal.
ClFe: C 67.11, H 5.27 %.
(600.1MHz, C D
) 2.02 (m, 2H, dppe), 2.34
), 6.93 (m, 4H, C ), 6.99
), 7.17 (m, partly obscured by
), 8.13 (m, 4 H,
H
6 6
H
H
6 5
5
5
H
H
6 5
2
2
6
5
(
3.74 g, 5.99 mmol). d (300.2 MHz, C D ) 1.34 (br s, 15H,
C
C
6
D
H
5
6
H
D
6 6
5
H
6 5
H
6 6
C (CH ) ), 1.83 (br s, 2H, dppe), 2.41 (br s, 2H, dppe), 4.27 (s,
3 5
6
5
P
5
2
d (121.5 MHz, C D ) 92.4. Found: C 62.29, H 5.82. Anal. Calc.
H, CH Cl ), 7.03–7.27 (m, 16H, C H ), 8.01 (br s, 4H, C H ).
Calc. for C31H P
29 2
2
2
6
5
6 5
P
6 6
Synthesis of RuCl(dppe)Cp*
for C H P ClFeꢀCH Cl : C 62.60, H 5.88 %.
3
6
39
2
2
2
The signals in the NMR spectra of [FeCl(dppe)Cp*]ꢀCH Cl
Pentamethylcyclopentadiene (4.0mL) was added to a suspension
2
2
are broad. This effect is minimised by the use of C D as the
6
of RuCl ꢀ3H O (3.16g, 12.1 mmol) in methanol (50 mL) and the
6
3
2
NMR solvent. Spectra recorded in CD Cl are broader, but the
2
mixture was heated to reflux for 6 h. Subsequent cooling, first to
ambient temperature and then to 08C, gave a black solid in a black
solution. The solid was isolated by filtration and washed with
2
key signals are still identifiable although naturally the solvent of
crystallisation (CH Cl ) is not. Spectra recorded in CDCl give
2
2
3
†
III
Failure to deoxygenate the solventsin this procedure will lead to brown colourationof the product, presumably due to the formation of Fe oxide species. Such
2 n
samples can be further utilised, although will result in lower yields of the relevant half-sandwich complex. The complex [FeCl (dppe)] should be stored under
inert atmosphere, prolonged storage in air results in a green colouration.

F
J. B. G. Gluyas et al.
methanol (50 mL) and then with hexanes until the washings were
colourless (,100 mL) affording 3.22 g of [RuCl Cp*] as a
brown powder after drying in air. This solid was dissolved in
ethanol (45 mL) along with 1,2-bis(diphenylphosphino)ethane
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2
n
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2
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mixture was heated to reflux for 18h, followed by cooling to
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[
[
[
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(
dppe)Cp* as red crystals (1.03 g, 1.54 mmol, 13%). Total yield
8
CDCl ) 1.43 (s, 15H, C (CH ) ), 2.13 (m, 2H, CH (dppe)), 2.67
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3
2
H
3
5
3 5
2
(m, 2H, CH (dppe)), 7.19 (m, 4H, aryl dppe), 7.30 (m, 4H, aryl
2
[
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[
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[
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Synthesis of RuCl(dppe)Cp
A mixture of RuCl(PPh ) Cp (4.00 g, 5.51 mmol), 1,2-bis
2
3
(
(
diphenylphosphino)ethane (2.18 g, 5.47 mmol), and toluene
50 mL) was heated to reflux for 20 h, allowed to cool to ambient
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[
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temperature, and concentrated to half of the original volume.
Hexanes (30 mL) was added to the resulting orange slurry and
the solids were collected by filtration, washed with hexanes
(
(
[
15] K. J. Kilpin, P. J. Dyson, Chem. Sci. 2013, 4, 1410. doi:10.1039/
C3SC22349C
30 mL) and diethylether (30 mL), and dried in air to afford RuCl
dppe)Cp in 94 % yield as a yellow-orange solid (3.08 g,
[
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OM049122G
[
5
.14 mmol).dH (300.2 MHz, CDCl ) 2.40 (m, 2H, CH ), 2.63
3 2
(
7
m, 2H, CH ), 4.54 (s, 5H, C H ), 7.13–7.19 (m, 4H, C H ),
6 5
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201000695
2
5
5
.24–7.31 (m, 8H, C H ), 7.38–7.42 (m, 4H, C H ), 7.87
6 5 6 5
(m, 4H, C H ). d (121.5 MHz, CDCl ) 80.7. Found: C 62.18,
H 4.94. Anal. Calc. for C H P ClRu: C 62.05, H 4.87 %.
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6
5
P
3
3
1
29
2
[
20] P. J. Low, M. I. Bruce, Adv. Organomet. Chem. 2001, 48, 71.
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Synthesis of trans-RuCl (dppe)
2
2
[
21] M. I. Bruce, P. J. Low, Adv. Organomet. Chem. 2004, 50, 179.
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A
mixture of 1,2-bis(diphenylphosphino)ethane (3.81 g,
.56mmol), ethanol (100 mL), and tetrahydrofuran (8mL) was
9
heated at high reflux until a colourless solution was obtained.
3419. doi:10.1039/B901649J
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3
2
2
193. doi:10.1021/IC902011V
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ethanol (10 mL) and the dark brown solution was allowed to cool
to room temperature before being added steadily dropwise over a
[
[
2
5
min period to the refluxing phosphine solution. Any remaining
RuCl ꢀ3H O in the dropping funnel was washed into the reaction
3
2
ˇ
P. St eˇ pni cˇ ka, G. S u¨ ss-Fink, B. Therrien, Organometallics 2009, 28,
mixture with a further 10 mL of ethanol and reflux was continued
for 10min until the reaction mixture consisted of a yellow pre-
cipitateina palebrownsolution. The precipitate was recovered by
filtration and washed with acetone (3 ꢂ 50 mL) to afford trans-
RuCl (dppe) in 88% yield as a bright yellow crystalline solid
4
350. doi:10.1021/OM900359J
[
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2
2
(
3.26 g, 3.37mmol). d (600.1 MHz, CDCl ) 2.74 (m, 8H, CH ),
3
S. Ababou-Girard, T. Roisnel, M. G. Humphrey, J. Phys. Chem. C
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2
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6 5 6 5
[
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6 5 P 3
5
2
48
4
2
Supplementary Material
Proton NMR spectra for FeCl(dppe)Cp*, FeCl(dppe)Cp, RuCl
(dppe)Cp*, RuCl(dppe)Cp, and trans-RuCl (dppe) are avail-
able on the Journal’s website.
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