ReOCl3(PPh3)2] as a substrate for the synthesis of the rhenium(I) carbonyl complexes [Re(CO)2(OAc)(PPh 3)2] and [ReCl(CO)3(PPh3) 2

Article abstract of DOI:10.1016/j.jorganchem.2013.03.001

New preparative methods have been developed for the synthesis of the rhenium(I) carbonyl complexes [Re(CO)₂(OAc)(PPh₃) ₂] (1) and [ReCl(CO)₃(PPh₃)₂] (2). Acetic anhydride was decarbonylated during the course of its reaction with [ReOCl₃(PPh₃)₂], resulting in the formation of the rhenium(I) carbonyl complex [Re(CO)₂(OAc)(PPh₃) ₂] (1), which was subsequently converted almost quantitatively to [ReCl(CO)₃(PPh₃)₂] (2) via the decarbonylation of its acetate group under acidic conditions.

Full text of DOI:10.1016/j.jorganchem.2013.03.001

Journal of Organometallic Chemistry 733 (2013) 60e62
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Note
[ReOCl3(PPh3)2] as a substrate for the synthesis of the rhenium(I) carbonyl
complexes [Re(CO)2(OAc)(PPh3)2] and [ReCl(CO)3(PPh3)2]
*
Monika K. Krawczyk , Marta S. Krawczyk, Mi1osz Siczek, Tadeusz Lis
Faculty of Chemistry, University of Wrocław, F. Joliot-Curie St. 14, Wrocław 50-383, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
New preparative methods have been developed for the synthesis of the rhenium(I) carbonyl complexes
[Re(CO)2(OAc)(PPh3)2] (1) and [ReCl(CO)3(PPh3)2] (2). Acetic anhydride was decarbonylated during the
course of its reaction with [ReOCl3(PPh3)2], resulting in the formation of the rhenium(I) carbonyl
complex [Re(CO)2(OAc)(PPh3)2] (1), which was subsequently converted almost quantitatively to
[ReCl(CO)3(PPh3)2] (2) via the decarbonylation of its acetate group under acidic conditions.
Ó 2013 Elsevier B.V. All rights reserved.
Received 28 November 2012
Received in revised form
26 February 2013
Accepted 1 March 2013
Keywords:
Rhenium carbonyl complex
Acetic anhydride
Decarbonylation
1. Introduction
PPh3 [6]. For the second of these methods, [Re(CO)3H(PPh3)2] was
reacted with hydrogen chloride in benzene to give complex 2 [7]. In
[Re2(CO)10] is a common precursor for the construction of a
variety of different rhenium carbonyl complexes and can be ob-
tained from the reaction of Re2O7 or perrhenate salts with CO under
high pressure and temperature conditions or from the reaction of
(NH4)[ReO4] with CO (at atmospheric pressure) followed by a
reduction reaction with (i-Bu)2AlH [1]. [Re(CO)5X] (where X ¼ Cl or
Br) is another common starting material for the preparation of
rhenium carbonyl complexes [2].
[Re(CO)2(OAc)(PPh3)2] (1) and [ReCl(CO)3(PPh3)2] (2) are well-
known carbonyl complexes of rhenium. To date, three different
methods have been reported in the literature for the synthesis of 1
[3,4]. According to the first of these procedures, the treatment of
[Re(CO)2(NHCOR)(PPh3)2] (where R ¼ C6H5 or p-MeC6H4) with a
mixture of triethylamine and water in the presence of air gave
complex 1 [3]. In the second of these reports, the reaction of
[Re(CO)2H(PPh3)3] with acetic acid provided complex 1 [3]. In the
third of these methods, [Re2H8(PPh3)4] was refluxed in a mixture of
glacial acetic acid and acetic anhydride (10:1 e v/v) to give complex
1 [4]. Complex 2 has been structurally characterized [5] and three
different methods have been reported in the literature for its
preparation [6e8]. According to the first of these procedures,
complex 2 was prepared from the reaction of [Re(CO)6]ClO4 with
the third of these methods, complex 2 was prepared from the re-
action of [ReOCl3(PPh3)2] with PPh3 whilst a stream of CO was
passed through the reaction mixture [8].
Several different Re-mediated decarbonylation reactions have
been reported in the literature for the formation of rhenium
carbonyl complexes from mixtures of carboxylic acids and anhy-
drides, with examples including the reaction of [N(C4H9)4]2[Re2Cl8]
with trifluoroacetic acid and trifluoroacetic anhydride (20:1 e v/v)
[9] or the reactions of the hydridophosphine rhenium complexes
with carboxylic acid and anhydrides (10:1 e v/v) [4].
Herein, we report the development of a novel preparative
method for the one-pot synthesis of [Re(CO)2(OAc)(PPh3)2] (1), as
well as a novel method for the synthesis of [ReCl(CO)3(PPh3)2] (2)
(Scheme 1).
2. Results and discussion
The reaction of [ReOCl3(PPh3)2] [10] with acetic anhydride and
triphenylphosphine resulted in the formation of
a rhenium
carbonyl complex of the formula [Re(CO)2(OAc)(PPh3)2] [3,4] (1),
which precipitated from the reaction mixture during the course
of the reaction. 31P{1H} NMR analysis of a sample collected from
the reaction mixture revealed the presence of a peak corre-
sponding to OPPh3
(
d
¼ 28.55 ppm), which indicated that tri-
phenylphosphine was behaving as a reducing agent in this
reaction. Mechanistically, the formation of 1 was attributed to the
rhenium-mediated decarbonylation of acetic anhydride. Thus, a
* Corresponding author. Tel.: þ48 713757338.
E-mail addresses: monika.krawczyk@chem.uni.wroc.pl, monikakrawczyk.k@
gmail.com (M.K. Krawczyk).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.001

M.K. Krawczyk et al. / Journal of Organometallic Chemistry 733 (2013) 60e62
61
Scheme 1. Reaction pathway for synthesis of [Re(CO)2(OAc)(PPh3)2] (1) and [ReCl(CO)3(PPh3)2] (2).
rhenium atom from [ReOCl3(PPh3)2] or another Re complex
derived from [ReOCl3(PPh3)2] inserts into the C(O)eO bond of
acetic anhydride, leading to the formation of an acyleRe species.
Subsequent elimination of a methyl group from the acyl group
attached to the Re atom would then occur to form a ReCO unit,
what was strongly supported by the isolation of (PMePh3)2[ReCl6]
(3) from the reaction mixture.
[ReCl(CO)3(PPh3)2] (2). To monitor this reaction, a solution of 35%
(v/v) DCl in D2O was added in a step-wise manner to a solution of
[Re(CO)2(OAc)(PPh3)2] (1) (130 mg, 0.16 mmol) in CD2Cl2 in a NMR
tube and the corresponding 1H and 31P{1H} NMR spectra were
recorded. Initially, 1 mL of the 35% (v/v) solution of DCl in D2O was
added to the CD2Cl2 solution of 1. The 31P{1H} NMR spectrum of
the mixture revealed the occurrence of peaks corresponding to 2
(at 9.56 ppm), as well as OPPh3 or a transition complex with co-
ordinated OPPh3 (at 27.79 ppm) and 1 (at 32.95 ppm). The cor-
responding 1H NMR spectrum of the mixture revealed signals
corresponded to 2 and OPPh3, as well as additional peaks that
were attributed to an unknown paramagnetic compound.
The content of the reaction mixture was monitored throughout
the reaction using 1H and 31P{1H} NMR spectroscopy
(Supplementary data). During the course of the reaction, portions
of 0.5 mL of the reaction mixture were removed from the reaction
and quickly evaporated to dryness under an atmosphere of N2
before being dissolved in CD2Cl2 for NMR analysis. Several different
transition complexes were formed during the course of the reac-
tion. Following 5 min of the reaction, 31P{1H} NMR analysis
revealed the presence of peaks corresponding to [ReOCl3(PPh3)2]
(ꢀ18.54 ppm), PPh3 (ꢀ5.05 ppm), and OPPh3 (28.55 ppm). The
observation of peaks at ꢀ1.9, 8.0, 8.2, 8.3, 8.8, 9.0, 10.4, and
14.8 ppm in the 1H NMR spectrum suggested the formation of
paramagnetic transition complex or complexes. Interestingly, all of
these signals disappeared at the same time following 1.5e2.5 h of
the reaction. Following 15 min of the reaction, several additional
peaks were observed, including (i) peaks corresponding to
[Re(OAc)(CO)2(PPh3)2] (1) at 0.46 ppm in the 1H NMR spectrum and
at 32.95 ppm in the 31P{1H} NMR spectrum; and (ii) peaks corre-
sponding to another paramagnetic complex or complexes at 8.7,
10.9, and 11.3 ppm in the 1H NMR spectrum, and ꢀ182.9, ꢀ150.3,
and 40.2 ppm in the 31P{1H} NMR spectrum. These signals could
still be observed following 20 h of the reaction. The complete
disappearance of peaks corresponding to the substrate
[ReOCl3(PPh3)2] was observed following 35 min of the reaction.
Following 36 h of the reaction, peaks corresponding to complex 1,
Following the addition of a further 2 mL of the 35% (v/v) solution of
DCl in D2O, the signal corresponding to 1 in the 31P{1H} NMR
spectrum disappeared. Following 5 h of the reaction, the 31P{1H}
NMR spectrum revealed an increase in the intensity of the peak
corresponding to 2 (at 9.56 ppm) compared with the peak at
27.79 ppm (corresponding to the transition complex with coor-
dinated OPPh3) with a ratio of 2.7:1 between the two peaks,
respectively. Following 36 h of the reaction, however, the ratio had
changed to become 3:1, and after 60 h, only the peak corre-
sponding to 2 was observed.
As mentioned earlier, the salt (PMePh3)2[ReCl6] (3) is another
product from the reaction of [ReOCl3(PPh3)2] with acetic anhy-
dride. This compound has previously been obtained from the re-
action of (PMePh3)Cl with K2[ReCl6] [11]. 3 crystal reported here is
a polymorph of the one reported previously in the literature [11].
The crystals of
3
consist of
a
centrosymmetric hexa-
chloridorhenate(IV) anion and (PMePh3)þ cations (Fig. 1,
Supplementary data). The geometry of the anion could be best
described as a slightly distorted octahedron. All of the crystallo-
graphically independent ReeCl bond lengths [2.3540(11)e
þ
ꢀ
ꢀ
PMePh3 (22.19 ppm), OPPh3 (28.55 ppm) and PPh3 (ꢀ5.05 ppm)
2.3630(13) A] are similar to the value of 2.3545(9) A reported for
K2[ReCl6] [11,12]. The geometry of the (PMePh3)þ cation in 3 is
similar to that reported previously in the literature [11]. Two
rotamers of the (PMePh3)þ ion are observed in the crystal, how-
ever, which differ from each another in terms of the spatial
arrangement of one of their aromatic rings, which result in dis-
order over the two positions (with occupancies 0.616(9) and
0.384(9)). The crystals of 3 possess a layered architecture formed
through a network of CeH/Cl hydrogen bonds. The cations are
arranged in double layers separated by monolayers of anions that
are parallel to the (001) plane (Fig. 2, Supplementary data).
could all be observed in the 31P{1H} NMR spectrum. Complex 1
began to precipitate from the reaction mixture following 1 h of the
reaction. Following 42 h of the reaction, peaks corresponding to
traces of [ReCl(CO)3(PPh3)2] (2) were identified in the 31P{1H} NMR
spectrum. Following 70 h of the reaction, only signals corre-
þ
sponding to OPPh3, PPh3, PMePh3 and traces of 2 could be
detected in the 31P{1H} NMR spectrum of the reaction solution,
because complex 1 had precipitated completely from the solution.
In conclusion, the NMR spectra revealed that the synthesis of 1 was
accompanied by a number of complex processes.
In addition to these findings, we found that acetate group in 1
could be efficiently decarbonylated under acidic conditions. The
treatment of a dichloromethane solution of 1 with concentrated
hydrochloric acid led to the formation of crystalline complex 2. It
was assumed that the Re(OAc) unit in 1 was converted to an acyle
Re species under the acidic conditions and subsequently trans-
formed via the elimination of the methyl group to give
3. Experimental
3.1. General experimental
Data for the single crystals of 1 and 2 were collected on an
Xcalibur four-circle diffractometer with Mo
Ka
radiation

62
M.K. Krawczyk et al. / Journal of Organometallic Chemistry 733 (2013) 60e62
ꢀ
(
l
¼ 0.71073 A) and a Ruby charge coupled device detector [13]. The
powder diffractograms for the crystals of 1 and 2 were recorded on
a D8 ADVANCE powder diffractometer with Cu K radiation
¼ 1.5418 A) and a Vantec detector, and the results were compared
collected and allowed to stand. Crystallization subsequently occurred
from the organic phase to give the desired product [ReCl(CO)3(PPh3)2]
(2) as orange-red crystals in near quantitative yield.
Consideration of the unit-cell dimensions of these single crys-
tals and analysis of the solution of their crystal structure revealed
that these crystals were the same as those reported by Flörke and
Haupt [5]. Furthermore, the powder diffractogram of this product
was in agreement with calculated on the basis of the single X-ray
diffraction data of 2. ICP analysis: Calcd. for C39H30O3P2ClRe
(830.26 g/mol): Re, 22.43%; P, 7.46%; Found: Re, 21.82% P, 7.27%; 1H
a
ꢀ
(l
with those calculated from the crystal structure data of the
monocrystals of 1 and 2. The infrared (IR) and Fourier-transform
infrared (FTIR) spectra were recorded on a Bruker Vertex 70 FTIR
spectrometer (Bruker) as KBr discs (IR) or nujol mulls (FTIR). The 1H
NMR (300 MHz), 13C{1H} NMR (75 MHz) and 31P{1H} NMR
(121 MHz) spectra of the samples were recorded on an AMX Bruker
300 MHz NMR spectrometer (Bruker). The chemical shifts have
been reported in ppm relative to the residual peak of the deuterated
solvent for the 1H and 13C{1H} NMR spectra. For the 31P{1H} NMR,
the chemical shifts have been reported relative to the resonance
peak of an external 85% aqueous H3PO4 solution. Elemental ana-
lyses were carried out on an elemental analyzer CHNS Vario EL III,
Elemental Analysensysteme GmbH. Inductively coupled plasma
(ICP) analyses were conducted on an ARL Model 3410 ICP spec-
trometer (Fisons Instruments).
NMR (300 MHz, CD2Cl2)
d
: 7.44 (m, 18H, PPh3), 7.68 (m, 12H, PPh3);
13C{1H} NMR (75 MHz, CD2Cl2)
d
: 128.75 (t, m-carbon atoms of the
phenyl groups), 130.73 (s, p-carbon atoms of the phenyl groups),
134.27 (t, o-carbon atoms of the phenyl groups), 134.79 (t, i-carbon
atoms of the phenyl groups), 193.49 (s, carbon of CO), 196.08 (s,
carbon of CO), 201.55 (s, carbon of CO); 31P{1H} NMR (121 MHz,
CD2Cl2)
FTIR (nujol): 454 (w), 420 (w) cmꢀ1
(w), 236 (w), 192 (w) cmꢀ1
d
: 9.56 (s); IR (KBr):
n
(CO) 2046 (w), 1954 (s), 1904 (s) cmꢀ1
(ReeCl) 377 (w), 320 (w), 276
;
;
n
.
[ReOCl3(PPh3)2] was prepared according to a procedure previ-
ously reported in the literature [10]. All of the other materials used
in this study were obtained commercially and used without further
purification.
3.4. Synthesis of (PMePh3)2[ReCl6] (3)
The filtrate remaining of the reaction mixture from the synthesis
of 1 was decanted and slowly concentrated under an atmosphere of
nitrogen to give a grease-like material. This material was dissolved
in acetone and ultimately provided pale green crystals. ICP analysis:
Calcd. for C19H18PCl6Re (676.25 g/mol): Re, 27.54%; P, 4.58%; Found:
Re, 27.64%; P, 4.62%; Anal. Calcd.: Cl, 31.46%; Found: Cl, 30.37%; 1H
3.2. Synthesis of [Re(CO)2(OAc)(PPh3)2] (1)
The synthesis of 1 was conducted under an atmosphere of N2
using a standard Schlenk techniques. Acetic anhydride (6 mL) was
added to a mixture of [ReOCl3(PPh3)2] (490 mg, 0.59 mmol) and PPh3
(790 mg, 3.0 mmol), and the resulting mixture was heated at reflux
(140 ꢁC) with stirring for 70 h. The mixture was then cooled to
ambient temperature and filtered to give the crude product as a pale
brown solid. The crude product was washed several times with
hexane to remove any residual phosphine. The resulting brown
residue was then dissolved in CH2Cl2 and purified by column chro-
matography over neutral alumina using dichloromethane as the
eluent. The brown impurities remained on the column and a yellow
solution was collected. The solvent was then removed in vacuo to
give a yellowegreen solid, which was recrystallized from CH2Cl2 to
give the desired product as a crystalline solid (380 mg; 78% yield).
Consideration of the unit-cell dimensions of these single crystals and
an analysis of their general structure revealed that they were the
same as those reported by La Monica et al. [3] Furthermore, the
powder diffractogram of the product was in agreement with
calculated on the basis of the single X-ray diffraction data of 1. The
characterization data for [Re(CO)2(OAc)(PPh3)2] (1) were as follows.
Elemental analysis: Anal. Calcd. for C40H33O4P2Re (825.84 g/mol): C,
57.87%; H, 5.02%. Found: C, 58.17%; H, 4.03%. ICP analysis: Calcd. Re,
22.56%; P, 7.26%; Found: Re, 22.55%; P, 7.50%; 1H NMR (300 MHz,
NMR (300 MHz, CD2Cl2) d: 1.81 (s, 3H, CH3), 7.51 (m, 6H, hydrogen
atoms of the phenyl groups), 7.68 (m, 6H, hydrogen atoms of the
phenyl groups), 7.97 (m, 3H, hydrogen atoms of the phenyl groups);
13C{1H} NMR (75 MHz, CD2Cl2)
d
: 24.14 (s, carbon from the CH3
group), 122.89 (s), 122.60 (s), 136.60 (m), 155.26 (d), (carbon atoms
of the phenyl groups); 31P{1H} NMR (121 MHz, CD2Cl2)
d
: 60.21 (s)
þ
(this value differs from the expected value for a PMePh3 cation
[22.19 ppm] because of the paramagnetism of the [ReCl6]2ꢀ anion).
Appendix A. Supplementary data
CCDC 928677 contains the supplementary crystallographic data
for 3. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
References
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Chem. 112 (1976) 297.
CD2Cl2)
(75 MHz, CD2Cl2)
d
: 0.45 (s, 3H, CH3), 7.43 (m, 30H, PPh3); 13C{1H} NMR
: 23.97 (s, carbon of the CH3), 128.81 (t, m-carbon
d
atoms of the phenyl groups),130.60 (s, p-carbon atoms of the phenyl
groups),133.26 (t, i-carbon atoms of the phenyl groups),134.81 (t, o-
carbon atoms of the phenyl groups), 186.35 (s, carbon of the
carboxylate of the CH3CO2 group), 202.69 (s, carbon atoms of CO);
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1101.
31P-{1H} NMR (121 MHz, CD2Cl2)
1850 (s) cmꢀ1
(w), 418 (w), 297 (w), 263 (w), 235 (w), 218 (w), 199 (w) cmꢀ1
d
: 32.95 (s); IR (KBr):
n(CO) 1925 (s),
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;
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.
3.3. Synthesis of [ReCl(CO)3(PPh3)2] (2)
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Concentrated hydrochloric acid (1 mL) was added to a stirred so-
lution of [Re(CO)2(OAc)(PPh3)2] (1) (100 mg, 0.12 mmol) in CH2Cl2
(10 mL) at room temperature, resulting in the formation of a biphasic
mixture. The two phases were separated and the organic phase was
ꢁ