Organometallic chemistry in a conventional microwave oven: The facile synthesis of group 6 carbonyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.04.030

Syntheses proceeding by reflux may be improved, accelerated and simplified, by carrying out the reaction in a modified conventional microwave oven. To demonstrate the potential of this method, the synthesis of over 20 group 6 organometallic compounds is reported. Hexacarbonyls, most notably Mo(CO)₆, react with a range of mono, and bi, and tridentate ligands in a modified conventional microwave oven. They generally proceed without an inert atmosphere, yields are high and reaction times are short. For example, cis -[Mo(CO)₄(dppe)] is prepared in >95% yield in 20 min. Reaction of Mo(CO)₆ with dicyclopentadiene affords a simple one-step synthesis of [CpMo(CO)₃]₂ in >90% yield, which reacts further with alkynes in toluene to produce dimetallatetrahedrane derivatives, [Cp₂Mo₂(CO)₄ (μ-RC₂R)]; presumably via the in situ formation of air-sensitive [CpMo(CO)₂]₂. Dimolybdenum tetra-acetate is also prepared in 48% yield in 45 min, however, this reaction requires an inert atmosphere. While W(CO)₆ reacts rapidly with amines to give cis diamine adducts in high yields, direct reactions with phosphines are not so clean. Bis(phosphine) complexes are, however, cleanly formed when a small amount of piperidine is added to the reaction mixture, presumably via the bis(piperidine) complex cis-[W(CO)₄(pip)₂]. Reactions with Cr(CO)₆ generally require an inert atmosphere and proceed less cleanly, although the important synthon [Cr(CO)₅ Cl][NEt₄] was prepared in 30 min (74% yield), while [(η⁶-C₆H₅OMe)Cr(CO)₃] can be prepared in 45% after 4 h.

Full text of DOI:10.1016/j.jorganchem.2004.04.030

Journal of Organometallic Chemistry 689 (2004) 2429–2435
www.elsevier.com/locate/jorganchem
Organometallic chemistry in a conventional microwave oven:
the facile synthesis of group 6 carbonyl complexes
a,
a
Michael Ardon a,b, Graeme Hogarth *, Daniel T.W. Oscroft
a
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
b
Department of Inorganic and Analytical Chemistry, Hebrew University Jerusalem, IL-91904 Jerusalem, Israel
Received 5 March 2004; accepted 13 April 2004
Abstract
Syntheses proceeding by reflux may be improved, accelerated and simplified, by carrying out the reaction in a modified con-
ventional microwave oven. To demonstrate the potential of this method, the synthesis of over 20 group 6 organometallic compounds
is reported. Hexacarbonyls, most notably Mo(CO)6, react with a range of mono, and bi, and tridentate ligands in a modified
conventional microwave oven. They generally proceed without an inert atmosphere, yields are high and reaction times are short. For
example, cis-[Mo(CO)4(dppe)] is prepared in >95% yield in 20 min. Reaction of Mo(CO)6 with dicyclopentadiene affords a simple
one-step synthesis of [CpMo(CO)3]2 in >90% yield, which reacts further with alkynes in toluene to produce dimetallatetrahedrane
derivatives, [Cp2Mo2(CO)4(l-RC2R)]; presumably via the in situ formation of air-sensitive [CpMo(CO)2]2. Dimolybdenum tetra-
acetate is also prepared in 48% yield in 45 min, however, this reaction requires an inert atmosphere. While W(CO)6 reacts rapidly
with amines to give cis diamine adducts in high yields, direct reactions with phosphines are not so clean. Bis(phosphine) complexes
are, however, cleanly formed when a small amount of piperidine is added to the reaction mixture, presumably via the bis(piperidine)
complex cis-[W(CO)4(pip)2]. Reactions with Cr(CO)6 generally require an inert atmosphere and proceed less cleanly, although the
important synthon [Cr(CO)5Cl][NEt4] was prepared in 30 min (74% yield), while [(g6-C6H5OMe)Cr(CO)3] can be prepared in 45%
after 4 h.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Group 6; Microwave; Synthesis
1. Introduction
in certain catalytic reactions [8]. Perhaps more impres-
sively, recent work suggests that the enantioselectivity of
certain reactions may be altered by microwave heating
over the conventional thermal methods [9].
Over the past twenty years, the application of mi-
crowave irradiation towards the acceleration of a wide-
range of organic and inorganic reactions, has received
considerable attention [1–6]. The main benefit of this
approach is one of a timesaving nature. More recently,
however, a number of other interesting effects have been
observed. Reactions generally carried out in toxic or-
ganic solvents may, under microwave irradiation, occur
in water, thus allowing a greener approach [7], while the
use of especially high boiling solvents with high dielec-
tric loss tangents can negate the need for high pressures
The microwave acceleration of organometallic reac-
tions has been given relatively little attention, and in
most examples reported to-date, Teflon autoclaves were
utilized. Mingos and co-workers have reported the
synthesis of rhodium and iridium(I) di-olefin complexes
[10], [Cp2Rh]PF6 [10], [(g6-C6H6)Ru(l-Cl)]2 [10],
[IrCl(CO)(PPh3)] [11] and [RuCl(CO)(2,20-bipy)2]Cl
[11], while Danks and co-workers have reduced
1-azabuta-1,3-diene iron tricarbonyl complexes with
sodium borohydride [12], and prepared thiolate com-
plexes, [CpRu(dppm)(SR)], using a focused monomode
microwave reactor [13]. Most importantly to this work,
recently Green and co-workers have shown that group 6
metal carbonyls react with diamines and diphosphines
* Corresponding author. Tel.: +44-207-679-4664; fax: +44-207-380-
7463.
E-mail addresses: ardon@vms.huji.ac.il (M. Ardon), g.hogarth@
ucl.ac.uk (G. Hogarth).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.04.030

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M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
to give tetracarbonyl products, [M(CO)4L] (L ¼ en,
bipy, dppm, dppe), with significant rate enhancements
of the thermal reactions [14].
Over the past decade we have developed a range of
microwave accelerated syntheses of group 6 carbonyl
complexes, based predominantly on molybdenum but
also including tungsten and chromium. All proceed in a
modified conventional microwave oven at atmospheric
pressure, and generally without need for an inert at-
mosphere. Prompted by the report of Green and co-
workers [14], and the continuing interest in group 6
carbonyl chemistry both at a research and teaching le-
vel, we herein describe details of our successful synthetic
procedures.
Carrying out microwave reactions in Teflon auto-
claves requires specialist laboratory equipment and such
closed systems present dangers due to the high pressures
generated. Further, assigning the specific effect of mi-
crowave irradiation on the reaction acceleration versus a
conventional open reflux system is difficult due to the
major pressure and temperature differences between the
two. In an open system, Mingos [15] and others [16–18]
have clearly shown that the rate enhancement results
from the coupling of solvents with high dielectric loss
tangents with the microwave’s irradiation, resulting in
super-heating, thereby leading directly to reaction ac-
celeration. This potential use of simple, safe and cost
effective microwave-accelerated syntheses of organome-
tallic complexes has hardly been explored.
Our interest in the microwave acceleration of orga-
nometallic reactions started following the realization
that many important organometallic reactions are ex-
cluded from undergraduate laboratories by time con-
straints. For example, there is a wealth of metal
carbonyl chemistry that is rarely explored at this level
due to both the constraints of time and the need for an
inert atmosphere (often due to the air-sensitivity of in-
termediate products). Thus in 1990, we first prepared the
important synthon, cis-[Mo(CO)4(pip)2], in 80–90%
yield over 30–40 min, and this was successfully turned
into an undergraduate experiment, the details of which
we have recently reported [19].
2. Results and discussion
In a conventional microwave oven, Mo(CO)6 reacts
smoothly with a range of mono- and bidentate amines
and phosphines to give tetracarbonyl complexes in good
to excellent yields (Fig. 1). With PPh3, the final product
is dependent upon the stoichiometry of the reaction;
with one equivalent of phosphine, monosubstituted
[Mo(CO)5(PPh3)] is isolated in 85% yield, along with a
small amount (10%) of trans-[Mo(CO)4(PPh3)2], which
is the only product (70%) with two equivalents of
phosphine. The cis isomer cannot be prepared directly in
the microwave oven, but is readily isolated upon addi-
tion of PPh3 to cis-[Mo(CO)4(pip)2] in refluxing di-
chloromethane. Microwave-accelerated syntheses of the
tetracarbonyls, [Mo(CO)4(bipy)], [Mo(CO)4(dppm)] and
[Mo(CO)4(dppe)] in a closed system have previously
been reported by Green and co-workers [14], reaction
N
O
O
CO
N
4
Mo
CO
OC
OC
Mo
Mo
CO
OC
CO
N
CO
CO
N
Mo
Mo
Mo
OC
OC
OC
OC
CO
CO
Mo
CO
Mo
CO
CO
Ph
P
2
OC
OC
N
OC
OC
P
CO
N
Ph
2
CO
Mo
OC
OC
CO
CO
CO
Ph
P
2
Mo
CO
OC
OC
P
N
Ph
2
CO
N
Mo
OC
OC
PPh
PPh
3
3
CO
CO
CO
Mo
PPh
OC
OC
CO
Mo
CO
OC
OC
CO
3
Fig. 1. Microwave accelerated reactions of Mo(CO)6.

M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
2431
times being 30 s. While our synthetic procedure, as ex-
pected, takes longer (15–20 min) yields are higher for the
diphosphine complexes and comparable for 2,20-bipy.
The dimeric molybdenum(I) cyclopentadienyl com-
plexes are important organometallic reagents and there
are two syntheses of [CpMo(CO)3]2 in Inorganic Syn-
thesis [20]. The first requires the preparation of sodium
cyclopentadienide and it subsequent reaction with
Mo(CO)6 to give Na[CpMo(CO)3], which is subse-
quently oxidised by iron(III) ammonium sulfate. In the
second, the tris(acetonitrile) complex [Mo(CO)3-
(MeCN)3] is first prepared, upon reflux of Mo(CO)6 in
acetonitrile for 4 h, and this is then reacted with freshly
distilled cyclopentadiene at reflux for a further 2 h.
While both routes offer high yields (89–98%) and can be
scaled up to generate 40–80 g of product, they suffer
from requiring a number of steps which must be carried
out under an inert atmosphere and involve potentially
chemistry. Its synthesis typically involves heating
Mo(CO)6 and acetic acid for 20 h, in order to obtain a
37% yield [22]. In the absence of an inert atmosphere,
all of our attempts to generate [Mo2(l-O2CMe)4] in
the microwave failed. However, under argon, we were
successful in getting a 48% yield with minimal work-up
in just 45 min (Fig. 1). This then provides a sim-
ple, relatively high yielding, route to this important
starting material in both research and undergraduate
laboratories.
We have also explored the microwave-accelerated
reactions of W(CO)6 and to a lesser extent Cr(CO)6
(Fig. 2). Simple amine derivatives of W(CO)6 are easily
prepared in a manner analogous to that described above
for molybdenum, although yields are generally lower
(35–85%) and reaction times longer (1–2 h). These dif-
ferences are primarily due to the lower reactivity of
W(CO)6 vs Mo(CO)6, however, the propensity of tung-
sten to undergo oxidation also lowers the yields since the
reactions were carried out in air.
Direct reactions of phosphines with W(CO)6 were
very disappointing, large amounts of unreacted W(CO)6
remaining even after 2 h at reflux. However, we were
able to prepare [W(CO)4(PPh3)2] and [W(CO)4(dppm)]
in 96% and 68% yield respectively and in just 20 min,
simply by adding a few drops of piperidine to the re-
action mixture. The exact role of the piperidine was not
explored, but it seems logical that cis-[W(CO)4(pip)2] is
initially formed and then the amines are replaced by the
phosphine(s). This would also account for the mixture
of cis and trans isomers of [W(CO)4(PPh3)2] which is
hazardous
reagents.
An
early
synthesis
of
[CpMo(CO)3]2 involved the direct reaction of Mo(CO)6
vapour and cyclopentadiene at 250 °C gave the desired
product in 30% yield [21]. We have now found that in
the microwave oven, unpurified dicyclopentadiene reacts
with Mo(CO)6 in air to give [CpMo(CO)3]2 in 94% yield
after 1 h (Fig. 1) which is an important starting material
for a wide-range of molybdenum chemistry.
In all the reactions described above an inert atmo-
sphere is not necessary and, along with the timesaving,
this makes these syntheses particularly appealing.
Dimolybdenum tetra-acetate, [Mo2(l-O2CMe)4], is an-
other important starting material in molybdenum
N
CO
OC
OC
W
N
MeO
CO
Cr
OC
CO
OC
N
CO
N
-
OC
OC
W
CO
Cl
CO
CO
Cr
OC
OC
CO
M
CO
CO
CO
OC
OC
CO
N
N
CO
CO
CO
N
Cr
OC
OC
Mo
CO
OC
OC
CO
CO
W
Ph2
P
PPh3
W
PPh3
OC
OC
P
CO
PPh3
CO
CO
Ph2
+
OC
OC
OC
OC
W
CO
CO
PPh3
Fig. 2. Microwave accelerated reactions of Cr(CO)6 and W(CO)6.

2432
M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
formed. Further, as piperidine is released in the later
step, the process is apparently catalytic, although again
we have not fully explored this. Green and co-workers
have prepared [W(CO)4(dppm)], in comparable yields,
directly from the diphosphine and W(CO)6 via a mi-
crowave-accelerated process in a closed system [14]. It
may be that the temperatures required for carbonyl
substitution by a diphosphine are achievable under these
conditions, but are not easily generated in the open
system.
An attempt to prepare [CpW(CO)3]2 was not very
successful. Heating W(CO)6 and dicyclopentadiene for
90 min gave a brown solution from which small
amounts only of the desired product were isolated after
work-up and addition of piperidine had little effect to
the reaction.
Reactions carried out with Cr(CO)6 were of mixed
success (Fig. 2). Under an argon atmosphere, reaction
with NEt4Cl proceeded smoothly to afford
[Cr(CO)5Cl][NEt4] cleanly and in high yields (74%). The
only reaction of Cr(CO)6 to proceed in air was that with
piperidine which yielded [Cr(CO)5(pip)] after 40 min.
The isolated yield of the latter was modest (15%),
however, this is primarily due to the difficulty in sepa-
ration from the diglyme.
Arene chromium tricarbonyl complexes have a wide
range of applications and are important organometallic
synthons. Reaction of Cr(CO)6 with most arenes is,
however, notoriously slow and requires high tempera-
tures. Our initial experiments with mesitylene were dis-
appointing, and while some reaction did occur, it was
very slow and separation of the product from the dig-
lyme and unreacted hexacarbonyl. Using anisole gave
somewhat better results. Refluxing under an argon
blanket for 4 h (against the 24 h reported in the litera-
ture) gave [(g6-C6H5OMe)Cr(CO)3] in 45% yield, and
further work may be warranted in this area.
phine complex cis-[Mo(CO)2(dppm)(dppe)] can also be
formed (52%), shown to be the cis isomer by 31P NMR
spectroscopy. Dark brown cis-[Mo(CO)2(bipy)2] also
results from [Mo(CO)4(bipy)], although the reaction is
slower (90 min).
As mentioned above, dimeric cyclopentadienyl
molybdenum tricarbonyl complexes, [(g5-C5R5)Mo-
(CO)3]2, are important starting materials for a wide-
range of organomolybdenum chemistry, in both high
and low oxidation states. Much of this work involves the
initial generation of the triply-bonded tetracarbonyl
[(g5-C5R5)Mo(CO)2]2, a transformation which requires
high temperatures. For example, [CpMo(CO)2]2 is gen-
erated from [CpMo(CO)3]2 upon reflux in diglyme for
1.5–3 h while purging the solution with nitrogen. Our
attempts to carry out this transformation in the micro-
wave cavity under a static nitrogen atmosphere were not
successful, possibly since the diglyme was not dry.
However, we have successfully trapped this reactive in-
termediate in a number of cases. Thus, heating toluene
solutions of [(g5-C5H4R)Mo(CO)3]2 (R ¼ H, Me, But)
with a three-fold excess of PhC2Ph for 2 h gave the
dimetallatetrahedrane complexes [(g5-C5H4R)2Mo2-
(CO)4(l-PhC2Ph)] in moderate yields (39–46%) after
work-up (Fig. 3). In a similar fashion, thermolysis of
[(g5-C5H4Me)Mo(CO)3]2 and excess nitrobenzene in
toluene for 1 h afforded a mixture of molybdenum(V)
complexes [(g5-C5H4Me)MoO(l-NPh)]2 and [(g5-
C5H4Me)2Mo2O2(l-NPh)(l-O)], in yields comparable
with those in the literature [23].
These experiments demonstrate that the unsaturated,
air-sensitive, molybdenum–molybdenum triply bonded
complexes, [(g5-C5H4R)Mo(CO)2]2, can be prepared in
air and reacted in situ in the microwave cavity. This
allows some quite difficult chemistry to be carried out in
an inexpensive and convenient manner. Further, the
reactions proceed rapidly in toluene, a solvent with a
low dielectric loss tangent and one, which while widely
used in organometallic chemistry, is not usually associ-
ated with microwave-accelerated reactions.
Microwave-accelerated organomolybdenum chemis-
try is not simply limited to the use of Mo(CO)6 (Fig. 3).
Diphosphine complexes [Mo(CO)4(dppm)] and [Mo-
(CO)4(dppe)] both react cleanly with more diphosphine
to produce cis-[Mo(CO)2(dppm)2] and cis-[Mo(CO)2-
63%) over 40 min, and in this way the mixed diphos-
In conclusion we have demonstrated the simple and
often high yielding syntheses of a range of group 6
carbonyl complexes in a modified commercial micro-
Ph
Ph
CO
CO
Ph
OC
CO
O
R
Me
CO
R
CO
N
Mo
Mo
Mo
Mo
Mo
Mo
E
R
Me
OC
OC
R
OC
OC
O
E =O, NPh
L
Mo
CO
Ph2P
Ph2
L
L
L
L
L
CO
CO
P
PPh2
CO
Mo
CO
Mo
CO
P
Ph2
CO
CO
L-L = 2,2'-bipy, dppm, dppe
Fig. 3. Further microwave accelerated reactions of molybdenum carbonyls.

M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
2433
wave oven. The rate acceleration as compared to con-
ventional methods allows many of these preparations to
become the domain of the teaching laboratory, this be-
ing further enhanced by the negation in many instances
of the need of an inert atmosphere. Microwave-en-
hanced reactions work best for Mo(CO)6 in line with the
established order of reactivity of the group 6 carbonyls;
Mo > W ꢀ Cr [34]. A further important advantage of the
microwave-accelerated approach using group 6 hexa-
carbonyls is that in no instance was sublimation of the
parent carbonyl a problem. This is often the case in
conventional systems in which sublimation can lead to
the blocking of the condenser, a potentially hazardous
process.
cis-[Mo(CO)4(pip)2] (2.54 g, 83%). IR(CH2Cl2): 2013m,
1934s, 1887vs, 1819s cmꢂ1
.
[Mo(CO)4(2,20-bipy)] [25] – A diglyme (12.5 cm3)
and thf (5 cm3) solution of Mo(CO)6 (2.03 g, 7.69 mmol)
and 2,20-bipyridine (1.45 g, 9.28 mmol) was heated for
20 min to give a bright red precipitate. This was filtered,
washed with hexane (2 ꢁ 10 cm3) and air dried to yield
[Mo(CO)4(2,20bipy)] (2.63 g, 94%). IR(CH2Cl2): 2015m,
1906vs, 1877s, 1831m cmꢂ1
.
[Mo(CO)4(1,10-phen)] [25] – A diglyme (15 cm3)
and thf (6 cm3) solution of Mo(CO)6 (2.00 g, 7.58 mmol)
and 1,10-phenanthroline (3.01 g, 16.7 mmol) was heated
for 15 min to give a bright red precipitate. This was
filtered, washed with hexane (5 ꢁ 10 cm3) and air dried
to yield [Mo(CO)4(1,10-phen)] (2.68 g, 91%) as a dark
orange solid. IR(CH2Cl2): 2015s, 1905vs, 1877s, 1831m
3. Experimental
cmꢂ1
.
cis-[Mo(CO)4(py)2] [26] – A diglyme (12.5 cm3) and
thf (5 cm3) solution of Mo(CO)6 (2.08 g, 7.91 mmol) and
an excess of pyridine (3.6 cm3) was heated for 20 min,
affording a bright orange solution. Cooling in ice bath
gave a yellow precipitate. This was filtered, washed with
hexane (3 ꢁ 10 cm3) and air dried to yield cis-
[Mo(CO)4(py)2] (1.45 g, 50%). IR(CH2Cl2): 2014m,
3.1. General
All reactions were carried out in a PROLINE pro-
gram 1250 750 W microwave oven modified as shown. A
hole bored in the top of the oven allowed connection of
a water condenser to the reaction flask. Two holes bored
in the side were fitted with a U-tube connected to a cold
water supply. The rate of reflux could then be moder-
ated by adjusting the volume of water in the cavity by
moving the U-tube in or out. All reactions were carried
out in air in a 100 ml round bottomed flask. A more
detailed description of this apparatus has recently been
published [18]. Solvents were used as supplied except for
the toluene (distilled over sodium).
Chromatography was carried out on deactivated
alumina (6% w/w distilled water) wet packed with light-
petroleum. The solution to be separated was added to
alumina (3–5 g) and the solvent removed under reduced
pressure. The resulting solids were then deposited on top
of the prepared column and separation effected by elu-
tion with progressively more polar solvents.
IR spectra were recorded on a Nicolet 205 FTIR
spectrometer. NMR spectra were recorded on Bruker
AMX400 and Avance500 spectrometers and internally
referenced to residual solvent peaks (1H, 13C) or exter-
nally to P(OMe)3 (31P). Mass spectra were recorded on
VG 7070 high resolution and VG Analytical ZAB2F
spectrometers and elemental analyses were performed in
house.
1939s, 1893vs, 1832s cmꢂ1
.
[Mo(CO)5(PPh3)] [27] – A diglyme (15 cm3) and
thf (6 cm3) solution of Mo(CO)6 (1.02 g, 3.86 mmol) and
PPh3 (1.23 g, 4.69 mmol) was heated for 40 min, which
upon cooling in an ice bath lead to the deposition of a
yellow precipitate. This was filtered, washed with hexane
(3 ꢁ 10 cm3) and air dried to yield trans-
[Mo(CO)4(PPh3)2] (0.29 g, 10%). Removal of thf and
hexane from the washings under reduced pressure and
further cooling of the remaining solution in an ice bath
lead to the formation of a pale brown precipitate which
was filtered washed with cold hexane (2 ꢁ 10 cm3) and
air dried to yield [Mo(CO)5(PPh3)] (1.62 g, 85%).
IR(CH2Cl2): 2073s, 1946vs cmꢂ1
.
trans-[Mo(CO)4(PPh3)2] [27] – A diglyme (15 cm3)
and thf (6 cm3) solution of Mo(CO)6 (1.01 g, 3.83 mmol)
and PPh3 (2.39 g, 9.11 mmol) was heated for 80 min, and
upon cooling in an ice bath lead to the deposition of a
pale brown precipitate. This was filtered, washed with
hexane (2 ꢁ 10 cm3) and air dried to yield trans-
[Mo(CO)4(PPh3)2] (1.94 g, 70%). IR(CH2Cl2): 1953m,
1896vs cmꢂ1
.
[Mo(CO)4(dppm)] [28] – A diglyme (15 cm3) and
thf (6 cm3) solution of Mo(CO)6 (1.00 g, 3.78 mmol) and
dppm (1.75 g, 4.56 mmol) was heated for 20 min. Upon
cooling an orange precipitate resulted which was fil-
tered, washed with hexane (2 ꢁ 10 cm3) and air dried to
yield [Mo(CO)4(dppm)] (2.24 g, 87%). IR(CH2Cl2):
3.2. Syntheses
cis-[Mo(CO)4(NHC5H10)2] [24] – A diglyme (12.5
cm3) and thf (5 cm3) solution of Mo(CO)6 (2.15 g, 8.14
mmol) and an excess of piperidine (5 cm3) was heated
for 40 min, which upon cooling lead to the deposition
of a yellow crystalline solid. This was filtered, washed
with hexane (2 ꢁ 10 cm3) and air dried to yield
2022s, 1913vs, 1881s cmꢂ1
.
[Mo(CO)4(dppe)] [28] – A diglyme (15 cm3) and thf
(6 cm3) solution of Mo(CO)6 (1.00 g, 3.78 mmol) and
dppe (1.81 g, 4.54 mmol) was heated for 20 min. Upon

2434
M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
cooling a yellow precipitate resulted which was filtered,
washed with hexane (2 ꢁ 10 cm3) and air dried to yield
[Mo(CO)4(dppe)] (2.19 g, 96%). IR(CH2Cl2): 2021s,
was filtered, washed with hexane (3 ꢁ 10 cm3) and air
dried to yield cis-[Mo(CO)2(dppm)(dppe)] (0.65 g, 52%)
as a light yellow powder. IR(CH2Cl2): 1856vs, 1784s
cmꢂ1; 1H NMR (acetone-d6): d 8.08–6.93 (m, Ph, 28H),
6.85 (t, J 6.8, 2H, Ph), 6.83 (t, J 7.8, 2H, Ph), 6.48 (t, J
6.4, 2H, Ph), 6.40 (t, J 8.5, 2H, Ph), 6.29 (t, J 8.2, 2H,
Ph), 6.21 (t, J 7.7, 2H, Ph), 4.82 (m, 1H, PCH2P), 3.99
(dt, J 15.7, 8.6, 1H, PCH2P), 3.53 (dd, J 33.0, 4.1, 2H,
1911vs, 1884s cmꢂ1
.
[CpMo(CO)3]2 [19] – A diglyme (25 cm3) solution of
Mo(CO)6 (1.00 g, 3.78 mmol) and dicyclopentadiene (1
cm3, 7.56 mmol) was heated for 1 h. The reaction mix-
ture turned purple and was cooled in an ice bath. Dis-
tilled water (25 cm3) was added to give a fine precipitate.
Heating on a steam bath for 20 min resulted in aggre-
gation of the precipitate and made filtration easier. The
purple solid was filtered and washed with hexane (2 ꢁ 10
cm3) and air dried to yield [CpMo(CO)3]2 (0.87 g, 94%).
PCH2CH2P), 3.53 (dd, J 39.3, 5.0, 2H, PCH2CH2P); 31
P
NMR (acetone-d6): 71.2 (ddd, J 91, 26, 7), 55.2 (ddd, J
22, 18, 7), 17.4 (ddd, J 91, 26, 22), )1.8 (dt, J 26, 26, 18).
[Cp2Mo2(CO)4(l-PhC2Ph)] [30] – A toluene (25
cm3) solution of [CpMo(CO)3]2 (0.30 g, 0.61 mmol) and
diphenylacetylene (0.33 g, 1.85 mmol) was heated for 2
h. The reaction mixture was cooled in an ice bath and
filtered. The toluene was removed under reduced pres-
sure and the remaining solid was washed with hexane
(5 ꢁ 10 cm3) and air dried to yield [Cp2Mo2(CO)4(l-
PhC2Ph)] (0.16 g, 39%) as a red solid. IR(CH2Cl2):
1988s, 1923vs, 1839s cmꢂ1; 1H NMR (CDCl3): d 7.23 (t,
J 7.6, 4H, Ph), 7.10 (t, J 7.6, 2H, Ph), 7.06 (d, J 7.6, 4H,
Ph), 5.18 (s, 10H, Cp).
IR(CH2Cl2): 2014m, 1958vs, 1912s, 1900sh cmꢂ1 1H
;
NMR (CDCl3): d 5.31 (s, 10H).
[Mo2(l-O2CMe)4] [22] – Under an argon atmo-
sphere, a diglyme (40 cm3) solution of Mo(CO)6 (1.00 g,
3.77 mmol) and acetic acid (1 cm3) was heated for 45
min. After cooling to room temperature the bright yel-
low precipitate was filtered, washed with acetone (2 ꢁ 20
cm3) and air dried to yield [Mo2(l-O2CMe)4] (0.39 g,
48%).
cis-[Mo(CO)2(2,20-bipy)2] [29] – A diglyme (20 cm3)
solution of [Mo(CO)4(2,20-bipy)] (0.53 g, 1.46 mmol)
and 2,20-bipy (0.49 g, 3.13 mmol) was heated for 90 min.
The reaction mixture turned black. Upon cooling a
black-brown precipitate resulted, which was quickly
filtered and washed thoroughly with hexane until the
washings were no longer red. The remaining brown solid
was air dried to yield trans-[Mo(CO)2(2,20-bipy)2] (0.36
[(g5-C5H4Me)2Mo2(CO)4(l-PhC2Ph)] [30] – A
toluene (25 cm3) solution of [(g5-C5H4Me)Mo(CO)3]2
(0.30 g, 0.58 mmol) and diphenylacetylene (0.31 g, 1.74
mmol) was heated for 2 h. The reaction mixture was
cooled in an ice bath and filtered. The toluene was re-
moved under reduced pressure and the remaining solid
was washed with hexane (5 ꢁ 10 cm3) and air dried to
yield [(g5-C5H4Me)2Mo2(CO)4(l-PhC2Ph)] (0.16 g,
40%) as a red solid. IR(CH2Cl2): 1982s, 1914vs, 1834s
g, 53%). IR(KBr): 1776s, 1735s cmꢂ1
.
cis-[Mo(CO)2(dppm)2] [29] – A diglyme (25 cm3)
solution of [Mo(CO)4(dppm)] (1.00 g, 1.69 mmol) and
dppm (0.78 g, 2.03 mmol) was heated for 40 min. Upon
cooling in an ice bath a brown precipitate resulted which
was filtered, washed with hexane (3 ꢁ 10 cm3) and air
dried to yield cis-[Mo(CO)2(dppm)2] (0.98 g, 63%) as a
cmꢂ1
.
[(g5-C5H4Me)2Mo2O2(l-O)(l-NPh)] and ½ðg5-
C5H4Me)MoO(l-NPh)]2 [23] – A toluene (25 cm3)
solution of [(g5-C5H4Me)Mo(CO)3]2 (1.00 g, 1.95
mmol) and nitrobenzene (0.50 cm3) was heated for 1 h
producing a dark yellow solution. The toluene was re-
moved under reduced pressure and the solid was washed
with hexane (2 ꢁ 10 cm3). Chromatography was carried
out. Eluting with light petroleum–dichloromethane (4:1)
yellow powder. IR(CH2Cl2): 1859vs, 1790s cmꢂ1 1H
;
NMR (acetone-d6): d 7.94–7.05 (m, 32H, Ph), 6.83 (t, J
7.4, 4H, Ph), 6.68 (t, J 7.3, 4H, Ph), 4.78 (m, 4H, CH2);
31P NMR (acetone-d6) 18.3 (d, J 5.5), 2.3 (d, J 5.5).
cis-[Mo(CO)2(dppe)2] [29] – A diglyme (25 cm3)
solution of [Mo(CO)4(dppe)] (1.00 g, 1.65 mmol) and
dppe (0.78 g, 1.96 mmol) was heated for 40 min. Upon
cooling in an ice bath a yellow precipitate resulted which
was filtered, washed with hexane (3 ꢁ 10 cm3) and air
dried to yield cis-[Mo(CO)2(dppe)2] (0.83 g, 45%) as a
gave
a
yellow band which afforded [(g5-
C5H4Me)MoO(l-NPh)]2 (0.17 g, 18%), while eluting
with light petroleum–dichloromethane (3:7) gave an
orange band which afforded [(g5-C5H4Me)2Mo2O2(l-
O)(l-NPh)] (0.09 g, 8%).
cis-[W(CO)4(NHC5H10)2] [26] – A diglyme (20
cm3) and thf (5 cm3) solution of W(CO)6 (2.00 g, 5.68
mmol) and an excess of piperidine (5 cm3) was heated
for 2 h. A yellow precipitate was formed upon cooling
which was filtered, washed with hexane (2 ꢁ 10 cm3) and
air dried to yield cis-[W(CO)4(pip)2] (0.93 g, 35%).
yellow powder. IR(CH2Cl2): 1851vs, 1783s cmꢂ1 1H
;
NMR (acetone-d6): d 7.81–7.05 (m, 36H, Ph), 6.83 (t, J
7.0, 2H, Ph), 6.21 (t, J 7.4, 2H, Ph), 3.49 (dd, J 40.1, 6.3,
4H, CH2), 3.49 (dd, J 32.4, 5.3, 4H, CH2); 31P NMR
(acetone-d6) 67.3 (t, J 13.1), 47.2 (t, J 13.1).
IR(CH2Cl2): 2007m, 1923s, 1870vs, 1815s cmꢂ1
.
cis-[Mo(CO)2(dppm)(dppe)] – A diglyme (25 cm3)
solution of [Mo(CO)4(dppm)] (0.80 g, 1.35 mmol) and
dppe (0.65 g, 1.63 mmol) was heated for 40 min. Upon
cooling in an ice bath a brown precipitate resulted which
[W(CO)4(2,20-bipy)] [27] – A diglyme (20 cm3) and
thf (5 cm3) solution of W(CO)6 (2.03 g, 5.77 mmol) and
2,20-bipyridine (1.09 g, 6.98 mmol) was heated for 80
min to give a bright red precipitate. This was filtered,

M. Ardon et al. / Journal of Organometallic Chemistry 689 (2004) 2429–2435
2435
washed with hexane (2 ꢁ 10 cm3) and air dried to yield
purchase of our first microwave oven and Mr. P.D.
Hayes for excellent technical support.
[W(CO)4(2,20bipy)] (1.02 g, 39%). IR(CH2Cl2): 2008m,
1976vs, 1893s, 1827m cmꢂ1
.
[W(CO)4(1,10-phen)] [27] – A diglyme (15 cm3) and
thf (6 cm3) solution of W(CO)6 (2.03 g, 5.77 mmol) and
1,10-phenanthroline (1.91 g, 10.6 mmol) was heated for
1 h to give a bright red precipitate. This was filtered,
washed with hexane (5 ꢁ 10 cm3) and air dried to yield
[W(CO)4(1,10-phen)] (2.33 g, 85%) as a dark orange
References
[1] R. Gedye, F. Smith, K. Westaway, H. Ali, L. Baldisera, L.
Laberge, J. Rousell, Tetrahedron Lett. 27 (1986) 279.
[2] R.J. Giguere, T.L. Bray, S.M. Duncan, Tetrahedron Lett. 27
(1986) 2945.
solid. IR(CH2Cl2): 2008s, 1894vs, 1875s, 1827m cmꢂ1
.
[3] S. Caddick, Tetrahedron 50 (1994) 10403.
[4] D.M.P. Mingos, D.R. Baghurst, Chem. Rev. 20 (1991) 1.
[5] A.G. Whittaker, D.M.P. Mingos, J. Microwave Power Electro-
mag. Energy 29 (1994) 195.
[W(CO)4(PPh3)2] [27] – To a diglyme (25 cm3)
solution of W(CO)6 (1.00 g, 2.84 mmol) and PPh3 (1.81
g, 6.90 mmol) was added a few drops of piperidine. This
was heated for 20 min. Upon cooling in an ice bath a
yellow precipitate was deposited. This was filtered, wa-
shed with hexane (2 ꢁ 10 cm3) and air dried to yield
[W(CO)4(PPh3)2] (2.23 g, 96%) as a mixture of cis and
trans isomers. IR(CH2Cl2): 2018m, 1939m, 1907sh,
[6] D.M.P. Mingos, Res. Chem. Intermed. 20 (1994) 85.
[7] A.G. Whittaker, Educ. Chem. (2002) 134.
[8] A.K. Bose, M.S. Manhas, S.N. Ganguly, A.H. Sharma, B.K.
Banik, Synthesis (2002) 1578.
[9] N. Kuhnert, T.N. Danks, Green Chem. 3 (2001) 68.
[10] D.R. Baghurst, D.M.P. Mingos, M.J. Watson, J. Organomet.
Chem. 368 (1989) C43.
1889vs cmꢂ1
.
[11] D.R. Baghurst, S.R. Cooper, D.L. Greene, D.M.P. Mingos, S.M.
Reynolds, Polyhedron 9 (1990) 893.
[W(CO)4(dppm)] [27] – To a diglyme (25 cm3) so-
lution of W(CO)6 (1.00 g, 3.78 mmol) and dppm (1.31 g,
3.41 mmol) was added a few drops of piperidine. This
was heated for 20 min. Upon cooling a yellow precipi-
tate resulted which was filtered, washed with hexane
(2 ꢁ 10 cm3) and air dried to yield [W(CO)4(dppm)]
[12] J. Akisanya, T.N. Danks, R.N. Garman, J. Organomet. Chem.
603 (2000) 240.
[13] N. Kuhnert, T.N. Danks, J. Chem. Res.-S (2002) 66.
[14] S.L. VanAtta, B.A. Duclos, D.B. Green, Organometallics 19
(2000) 2397.
[15] D.R. Baghurst, D.M.P. Mingos, J. Chem. Soc., Chem. Commun.
(1992) 674.
(1.32 g, 68%). IR(CH2Cl2): 2017s, 1904vs, 1874s cmꢂ1
.
[Cr(CO)5(NHC5H10)] [31] – A diglyme (12.5 cm3)
and thf (5 cm3) solution of Cr(CO)6 (1.00 g, 4.55 mmol)
and an excess of piperidine (2.5 cm3) was heated for 40
min. A green precipitate was formed upon cooling which
was filtered, washed with hexane (2 ꢁ 10 cm3) and air
dried to yield [Cr(CO)5(pip)] (0.18 g, 14%). IR(CH2Cl2):
[16] J.T.M. Linders, J.P. Kokje, M. Overhand, S.T. Lie, L. Maat,
Recueil des Travaux Chimique des Pays-Bas 107 (1988) 449.
[17] G. Bond, R.B. Moyes, S.D. Pollington, D.A. Whan, Chem. Ind.
(London) 18 (1991) 686.
[18] D.A.C. Stuerga, P. Gaillard, J. Microwave Power Electromag.
Energy 31 (1996) 87;
D.A.C. Stuerga, P. Gaillard, J. Microwave Power Electromag.
Energy 31 (1996) 101.
2065m, 1929vs cmꢂ1
.
[19] G. Hogarth, M. Ardon, P.D. Hayes, J. Chem. Educ. 79 (2002)
1249.
[Cr(CO)5Cl][NEt4] [32] – Under a nitrogen atmo-
sphere, a diglyme (20 cm3) and thf (20 cm3) solution of
Cr(CO)6 (4.00 g, 18.2 mmol) and Et4NCl ꢃ H2O (3.40 g,
18.5 mmol) was heated for 30 min. After cooling to
room temperature bright yellow crystals were filtered
off, washed with pentane (2 ꢁ 20 cm3) and air dried to
yield [Cr(CO)5Cl][NEt4] (4.80 g, 74%). IR(CH2Cl2)
[20] A.R. Manning, P. Hackett, R. Birdwhistell, P. Soye, Inorg. Synth.
28 (1990) 148;
M.D. Curtis, M.S. Hay, Inorg. Synth. 28 (1990) 150.
[21] G. Wilkinson, J. Am. Chem. Soc. 76 (1954) 209;
R.B. King, Organomet. Synth. 1 (1965) 109.
[22] A.B. Brignole, F.A. Cotton, Inorg. Synth. 13 (1972) 87.
[23] J. Fletcher, G. Hogarth, D.A. Tocher, J. Organomet. Chem. 403
(1991) 345.
2060s, 1926vs, 1854m cmꢂ1
.
[(g6-C6H5OMe)Cr(CO)3] [33] – Under an argon
atmosphere, a diglyme (20 cm3) and thf (20 cm3) solu-
tion of Cr(CO)6 (1.00 g, 4.55 mmol) and anisole (2 cm3)
were refluxed for 4 h to yield a yellow solution. After
filtration through Fuller’s earth and removal of solvents
and unreacted carbonyl under reduced pressure, ex-
traction and crystallization from pentane afforded [(g6-
C6H5OMe)Cr(CO)3] (0.50 g, 45%). IR(CH2Cl2) 1978m,
[24] D.J. Darensbourg, R.L. Kump, Inorg. Chem. 17 (1978) 2680.
[25] M.H.B. Stiddard, J. Chem. Soc. (1962) 4712.
[26] C.S. Kraihanzel, F.A. Cotton, Inorg. Chem. 2 (1963) 533.
[27] M. Graziani, F. Zingales, U. Belluco, Inorg. Chem. 6 (1967)
1582.
[28] S.O. Grim, W.L. Briggs, R.C. Barth, C.A. Tolman, J.P. Jesson,
Inorg. Chem. 13 (1974) 1095.
[29] M.H. Chisholm, J.A. Conner, J.C. Huffman, E.M. Korber, C.
Overton, Inorg. Chem. 23 (1984) 2298;
A.M. Bond, R. Colton, J.J. Jackowski, Inorg. Chem. 14 (1975)
274.
1906s cmꢂ1
.
[30] M.H. Chisholm, F.A. Cotton, J. Am. Chem. Soc. 100 (1978)
5768.
[31] A. Magee, C.N. Matthews, T.S. Wang, J.H. Wotiz, J. Am. Chem.
Soc. 83 (1961) 3200.
Acknowledgements
[32] M.J. Wovkulich, J.D. Atwood, Inorg. Synth. 23 (1985) 37.
[33] C.A.L. Mahaffy, P.L. Pauson, Inorg. Synth. 28 (1990) 136.
[34] J.R. Graham, R.J. Angelici, Inorg. Chem. 6 (1967) 2082.
We would like to thank Professor R.J.H. Clark for
generously funding the early stages of this work via