Carbonyltungsten(0) complexes of acryloylferrocene: Synthesis and characterization

Article abstract of DOI:10.1016/j.jorganchem.2006.04.003

Photolysis of hexacarbonyltungsten(0) in the presence of acryloylferrocene in n-hexane solution at 10 °C yields pentacarbonyl(η²-acryloylferrocene)tungsten(0) (1) as the only photo-substitution product, different from the general reaction patte

Full text of DOI:10.1016/j.jorganchem.2006.04.003

Journal of Organometallic Chemistry 691 (2006) 3293–3297
www.elsevier.com/locate/jorganchem
Carbonyltungsten(0) complexes of acryloylferrocene: Synthesis
and characterization
¨
*
Dilek Ayßse Bo g˘ a, Saim Ozkar
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Received 25 January 2006; received in revised form 28 March 2006; accepted 9 April 2006
Available online 19 April 2006
Abstract
2
Photolysis of hexacarbonyltungsten(0) in the presence of acryloylferrocene in n-hexane solution at 10 °C yields pentacarbonyl(g -
acryloylferrocene)tungsten(0) (1) as the only photo-substitution product, different from the general reaction pattern observed for the
2
Group 6 metal carbonyls with other olefins. W(CO)
5
(g -acryloylferrocene) (1) decomposes in solution to the parent hexacarbonyltung-
sten(0) and free acryloylferrocene. Trimethylphosphite was introduced as ligand into the molecule to increase the stability. The photolysis
of pentacarbonyl(trimethylphosphite)tungsten(0) in the presence of acryloylferrocene in n-hexane solution at 10 °C yields only cis-
2
2
4 3 3
W(CO) [P(OCH ) ](g -acryloylferrocene) (2) as the monosubstitution product. Both g -acryloylferrocene complexes (1 and 2) could
be isolated and characterized by MS, IR and NMR spectroscopy. The trimethylphosphite complex (2) is found to be even less stable
2
than W(CO) (g -acryloylferrocene) (1).
5
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Tungstencarbonyl; Acryloylferrocene; Trimethylphosphite; Photolysis; Substitution
1
. Introduction
cene which has been recently isolated [10]. Acryloylferro-
cene is an olefin bearing a carbonyl group in addition to
the ferrocenyl unit. This carbonyl group may additionally
interact with the transition metal atom to which the olefin
ligand is already coordinated through its C@C bond.
Therefore, this potential feature of acryloylferrocene
prompted us to investigate its carbonylmetal complexes.
Olefin-substituted metal carbonyls are relevant to the
homogeneous photocatalytic processes [11] such as isomer-
ization [12], hydrogenation [13], and hydrosilylation [14] of
mono- and diolefins. Olefin-substituted Group 6 metal car-
bonyls are conveniently accessible from the parent M(CO)6
complexes (M = Cr, Mo, W) by means of photolytic CO
displacement in the presence of olefins: ethene and linear
alkenes [15–19], cycloalkenes [19–21], a,b-unsaturated
esters [22] and tetracyanoethene [23]. A recent kinetic study
Ferrocene [1] has been used in the synthesis of many new
materials having interesting properties [2,3]. For instance,
molecules containing ferrocene units have been used as
homogeneous catalysts [3], molecular sensors [4], molecular
magnets [5], non-linear optic materials [6], and liquid crys-
tals [7]. The presence of ferrocene in a molecule is expected
to influence its electron transfer ability [8]. For example,
introducing the ferrocenyl group into an olefin ligand is
expected to influence the stability and catalytic properties
of its complexes with the transition metal. Vinylferrocene
has already been employed as an olefin ligand containing
a ferrocenyl unit [9]. However, Group 6 metal carbonyl
complexes of the type M(CO) (g -vinylferrocene) have
been found to be unstable [9]. Another potential olefinic
ligand containing a ferrocenyl substituent is acryloylferro-
2
5
[24] on the photochemical conversion of W(CO) into a
6
2
trans-W(CO) (g -olefin) complex using E-cyclooctene as
4
2
*
a model olefin owing to its extraordinary coordination
Corresponding author. Tel.: +90 312 210 3212; fax: +90 312 210 3200.
¨
properties [25] showed that the photolysis of M(CO) in
E-mail address: sozkar@metu.edu.tr (S. Ozkar).
6
0
022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.003

¨
D.A. Bo g˘ a, S. Ozkar / Journal of Organometallic Chemistry 691 (2006) 3293–3297
3294
2
the presence of an olefin is expected to yield the stable final
2.2. W(CO) (g -acryloylferrocene) (1)
5
2
product trans-M(CO) (g -olefin) through the intermediate
4
2
2
2
M(CO) (g -olefin) and cis-M(CO) (g -olefin) complexes.
Indeed, with a few exceptions, trans-M(CO) (g -olefin)
A solution of 0.48 g (1.4 mmol) W(CO)6 and 0.33 g
(1.4 mmol) acryloylferrocene in n-hexane (150 mL) was
irradiated at 10 °C until the starting material was no longer
observed in the IR spectrum (ca. 4 h). When the reaction
was complete, volatiles were evaporated under vacuum
and the dark red residue dissolved in n-hexane, and the
solution was left overnight at ꢀ35 °C. The red precipitate
was separated from the supernatant solution and dried
under vacuum (0.2 g, 26% yield). Anal. Calc. for
C H O WFe (M = 563.9): C, 38.30; H, 2.13. Found: C,
5
4
2
2
4
2
is always found to be the final product of the photosubsti-
tution of CO in the Group 6 metal carbonyls in the pres-
ence of excess olefin. In the case of tetracyanoethene [23]
and Z-cyclooctene with chromium [20], and vinylferrocene
with all three metals [9], the photosubstitution stops at the
2
first step, forming M(CO) (g -olefin). Here, we report the
5
photolysis of hexacarbonyltungsten(0) in the presence of
acryloylferrocene (acfc). Photo-substitution yields only
1
8
12
6
2
+
pentacarbonyl(g -acryloylferrocene)tungsten(0), W(CO) -
(
38.85; H, 2.26%. MS: m/z 563.9 (M ). IR (m(CO), n-hex-
ane): 2091, 2013, 1975, 1956, 1655 cm (CO of the acfc
5
2
ꢀ1
g -acfc) (1), as the final product, which was isolated from
the reaction solution and characterized by using IR, MS,
ligand); (m(CO), KBr pellet): 2084, 1970 (sh), 1960, 1943,
ꢀ
1
and NMR spectroscopy and elemental analysis.
1921, 1640 cm (CO of the acfc ligand). Raman (m(CO),
2
ꢀ1
1
Since W(CO) (g -acfc) (1) appears to be unstable,
solid): 2084, 2008, 1964, 1945 and 1918 cm . H NMR
5
particularly in solution, we attempted to stabilize the tung-
sten–acryloylferrocene complex by introducing trim-
ethylphosphite into the molecule. For this purpose, cis-
(d ppm, rel. to TMS, in CD Cl ): 4.99 (m, H2), 4.95 (m,
H7), 4.94 (m, H5), 4.71 (m, H3), 4.66 (m, H4), 4.30 (s,
2
2
0
0
0
H1 -H5 ), 4.14 (d, H8, J
= 17.9 Hz) and 3.80 (d,
H7–H8
2
13
W(CO) [P(OCH ) ](g -acfc) (2) was synthesized from the
H8 , J
0
¼ 12:6 HzÞ. C NMR (d ppm, rel. to TMS,
4
3 3
H7–H8
irradiation of W(CO) [P(OCH ) ] and acryloylferrocene
in CD Cl ): 202.4 (CO trans to acfc), 195.2 (CO cis to acfc),
2 2
5
3 3
1
in n-hexane at 10 °C and characterized by MS, IR, H
194.4 (C6, CO of acfc ligand), 78.94 (C1), 73.50 (C3), 73.13
1
3
31
0 0
NMR, C NMR and P NMR spectroscopies.
(C4), 70.56 (C1 -C5 ), 70.28 (C7), 69.86 (C2), 69.33 (C8),
68.63 (C5).
2
. Experimental
2
2
.3. cis-W(CO) [P(OCH ) ](g -acryloylferrocene) (2)
4
3 3
2
.1. General remarks
A solution of 0.63 g (1.4 mmol) W(CO) [P(OCH ) ] and
5
3 3
All reactions and manipulations were carried out either
0.33 g (1.4 mmol) acryloylferrocene in n-hexane (150 mL)
was irradiated at 10 °C until the starting material was no
longer observed in the IR spectrum (ca. 4 h). After the
reaction was completed the solvent was evaporated in vac-
uum. The solid residue was dissolved in n-hexane and the
solution was left overnight at ꢀ35 °C. A red precipitate
was separated from the supernatant solution and dried
in a vacuum or under a dry and oxygen-free nitrogen atmo-
sphere. Solvents were distilled after refluxing over metallic
sodium or phosphorous pentoxide for 3–4 days and stored
under nitrogen until used.
Analytical grade and deuterated solvents, ferrocene,
acryloyl chloride, trimethylaluminum, ethylaluminumdi-
chloride, trimethylphosphite and hexacarbonyltungsten(0)
were purchased from Aldrich Chemical Co. Ltd., Dorset,
England, and used as received. The thermal reactions and
other treatments of organometallic compounds such as
purification and crystallization were followed by taking
IR spectra from solutions on a Perkin–Elmer 16 PC FT-
IR spectrometer. NMR spectra were recorded on a Bruker
+
under vacuum. (0.14 g, 15% yield). MS: m/z 660.0 (M ).
ꢀ
1
IR(n-hexane) m(CO) = 2051, 1966, 1944, 1926, 1652 cm
1
(CO of the acfc ligand). H NMR (d ppm, rel. to TMS,
in CD Cl ): 4.92 (H2), 4.78 (H7), 4.59 (H3), 4.55 (H4),
2
2
0
0
4.51 (H8), 4.24 (s, H1 –H5 ), 4.18 (H5), 3.68 (d,
P(OCH ) , J( P– C) = 14 Hz), 3.56 (H8 ). C NMR (d
3
1
13
0
13
3
3
ppm, rel. to TMS, in CD Cl ): 198.1 (s, C6, CO of acfc
2
2
1
13
31 13
Avance DPX 400 (400.1 MHz for H; 100.6 MHz for C;
ligand), 207.3 (d, CO trans to acfc, J( P– C) = 16.4 Hz),
204.5 (d, CO trans to trimethylphosphite, J( P– C)
3
1
31 13
1
61.3 MHz for P). TMS was used as internal reference for
H and C NMR chemical shifts. H PO (85%, in a glass
1
13
= 27.3 Hz), 197.4 (d, CO cis to acfc and P(OCH ) ,
3
4
3 3
3
1
31 13
capillary) was used as reference for P NMR chemical
shifts. FAB-MS was done on a Fisons VG Autospec with
m-nitrobenzylalcohol as matrix. Elemental analyses were
performed on a LECO CHNS-932 instrument at METU
Central Laboratory.
J( P– C) = 11.0), 197.0 (d, CO cis to acfc and
P(OCH ) , J( P– C) = 10.9 Hz), 80.0 (C1), 72.64 (C2),
3
1
13
3
3
0
0
72.42 (C5), 70.31 (C1 –C5 ), 69.87 (C3), 69.34 (C4), 69.03
3
1
13
(C7), 62.49 (C8), 52.85 (d, P(OCH ) , J( P– C)
3
3
3
1
= 5.4 Hz). P NMR (d ppm, rel. to H PO , in CD Cl ):
3
4
2
2
Photochemical reactions were carried out in an immer-
sion-well apparatus [26] (solidex glass, k > 280 nm) by
using a Hanau TQ 150 high pressure mercury lamp, which
was cooled by circulating water. Acryloylferrocene [10] and
W(CO) [P(OCH ) ] [27] were prepared according to the lit-
146.1.
3. Results and discussion
Irradiation of W(CO) in the presence of acryloylferro-
5
3 3
6
erature procedures.
cene (acfc) in n-hexane at 10 °C results in nearly complete

¨
D.A. Bo g˘ a, S. Ozkar / Journal of Organometallic Chemistry 691 (2006) 3293–3297
3295
2
conversion into W(CO) (g -acfc) (1), Scheme 1, which was
Fig. 1 shows the IR spectrum of 1 in the CO stretching
5
isolated and characterized by elemental analysis, MS, IR,
Raman, H and C NMR spectroscopy.
region. The observation of four prominent bands and one
1
13
weak absorption indicates that the W(CO) skeleton in 1 with
5
the single-face p-alkene ligand (by disregarding the substitu-
ent effect on its symmetry) has a C2v symmetry with five IR-
active CO stretching modes: 3A , B , B [28]. The two very
1
1
2
strong bands in the spectrum are readily assigned to the B1
and B modes. All five CO stretching bands of the W(CO)
2
5
unit are also observable in the Raman spectrum. The IR spec-
ꢀ
1
trum also shows an absorption band at 1655 cm (in n-hex-
ꢀ
1
ane) or 1640 cm (in KBr) due the carbonyl group of the
acryloylferrocene ligand in 1. The same absorption is
ꢀ1
observed at 1665 cm for the free acryloylferrocene in n-hex-
ane. This relatively small shift in the CO stretching frequency
is indicative for the coordination of acryloylferrocene to tung-
sten through the C@C bond, not through the carbonyl group.
1
The H NMR spectrum of 1 in CD Cl shows three mul-
2
2
tiplets at 4.95, 4.14 and 3.80 ppm due to the olefinic pro-
tons of the acryloylferrocene ligand. Compared to the
free acryloylferrocene molecule (6.85, 6.40 and 5.73 ppm,
respectively), the relatively large shift of the olefinic proton
signals toward higher magnetic field (Dd = 1.90, 2.26 and
1.93 ppm, respectively) indicates the coordination of acry-
loylferrocene to the metal through its C@C double bond.
1
The H NMR spectrum of 1 also exhibits four multiplets
and a singlet due to the hydrogen atoms of the substituted
and unsubstituted cyclopentadienyl ring, respectively.
Although the cyclopentadienyl ring protons experience
only slight changes in their chemical shifts upon coordina-
tion, the substituted cyclopentadienyl ring looses its sym-
metry plane upon coordination, so that the four
hydrogen atoms are different in the acfc ligand of 1.
Scheme 1. Photolysis of W(CO)
hexane solution in the presence of acryloylferrocene (acfc).
6 5 3 3
or W(CO) [P(OCH ) ] at 10 °C in n-
0
.90
.85
.80
0
0
0.75
0.70
0
.65
.60
.55
0
0
0.50
0.45
0
.40
.35
.30
0
0
0.25
0.20
0.15
2
000
1800
-1
Wavenumbers(cm )
2
ꢀ1
ꢀ1
; a shoulder at about 1970 cm ,
Fig. 1. Part of the IR spectrum of W(CO)
5
(g -acfc) (1), recorded from KBr pellet, showing m(CO) bands (2084 cm , A
1
ꢀ ꢀ1 ꢀ1 ꢀ1
1
1 1 2 1
A ; 1960 cm , B ; 1943 cm , B ; 1921 cm , A and 1640 cm , CO group of the acfc ligand).

¨
D.A. Bo g˘ a, S. Ozkar / Journal of Organometallic Chemistry 691 (2006) 3293–3297
3296
1
3
The C NMR spectrum of 1 in CD Cl gives two sig-
1.88 and 2.1 ppm, respectively), indicating the coordination
2
2
nals for the CO ligands, one signal due to the carbonyl car-
bon of the acfc ligand, two signals for the olefinic carbon
atoms, and six signals for the ferrocenyl unit. The appear-
ance of only one signal for the four equatorial CO groups
suggests that the molecule is fluxional with respect to rota-
tion about the metal–alkene bond axis. Compared to the
of acryloylferrocene through the C@C bond.
1
3
The C NMR spectrum of 2 in CD Cl exhibits four
2
2
doublets and one singlet in carbonyl region. The singlet
at 198.1 ppm can readily be assigned to the carbonyl car-
bon of the acryloylferrocene ligand. The four doublets
3
1
13
(because of P– C coupling) are due to the four different
1
3
C NMR spectrum of the free acryloylferrocene molecule,
CO ligands in 2. The doublet at the highest chemical shift
3
1
13
the coordination shifts of the olefinic carbons are Dd = 63.1
and 57.4 ppm, respectively, while the shift of the carbonyl
carbon of the ligand in 1 is Dd = 2.6 ppm. The large coor-
dination shift of the olefinic carbon signals supports the
coordination of acryloyferrocene to the metal through its
C@C double bond. The signals of the cyclopentadienyl
carbons show only slight changes upon coordination.
However, all five carbon atoms of the substituted cyclopen-
tadienyl ring become different upon coordination of
acryloylferrocene.
of 207.3 ppm with J( P– C) = 16.4 Hz is assigned to the
CO trans to the acfc ligand. The doublet at 204.5 ppm with
3
1
13
the largest P– C coupling constant of 27.3 Hz is assigned
to the CO ligand trans to the trimethylphosphite. The other
3
1
13
two doublets at 197.4 and 197.0 ppm with P– C coupling
constants of 11.0 and 10.9 Hz, respectively, are assigned to
the CO ligands trans to each other (cis to both acfc and
3
1
13
P(OCH ) ). The doublet at 52.85 ppm with the P– C
3
3
coupling constant of 6 Hz is due to the P(OCH ) ligand.
3
3
The olefinic carbon atoms give two signals at 69.03 and
62.49 ppm which have been shifted by Dd = 64.4 and
64.2 ppm, respectively, compared to the free acryloylferro-
cene. The large coordination shift of the olefinic carbon sig-
nals supports the coordination of acryloyferrocene to the
metal through its C@C double bond. The ferrocenyl part
gives five signals for the five different carbon atoms of
the substituted cyclopentadienyl ring and one signal for
the five equal carbon atoms of the unsubstituted cyclopen-
tadienyl ring. The signals of the cyclopentadienyl ring car-
bons show only slight changes upon coordination to
tungsten through the C@C bond.
The higher kinetic lability of 2 as compared to 1 can be
ascribed to steric crowding. Thus, introducing a donor/
acceptor ligand into the molecule does not provide addi-
tional stability for the tungsten–olefin bond in the case of
acryloylferrocene.
Photolysis of an n-hexane solution of hexacarbonyltung-
sten(0) in the presence of acryloylferrocene gives only the
monosubstitution product. The photosubstitution of one
CO group in W(CO) by acryloylferrocene is the only reac-
6
tion in this photolysis and continues practically until the
complete conversion of W(CO) to the mono-substitution
6
product. Prolonged irradiation of the solution does not
give any further CO substitution; it causes rather 1 to
1
3
decompose slowly. C NMR and IR spectra show the slow
formation of W(CO) and free acryloylferrocene when the
6
complex 1 left in solution. This observation indicates that 1
is labile in solution and decomposes into hexacarbonyl-
tungsten(0) and acryloylferrocene.
With the anticipation that introducing a different ligand
into the carbonyl-olefin–metal complex may strengthen the
2
metal–olefin bond, cis-W(CO) [P(OCH ) ](g -acfc) (2) was
4
3 3
synthesized. Irradiation of W(CO) [P(OCH ) ] [27] in the
In both complexes 1 and 2, the acfc ligand is bonded to
the metal only through the C@C bond. There is no indica-
tion that acryloylferrocene interacts with the metal through
its CO group.
5
3 3
presence of acryloylferrocene in n-hexane at 10 °C yields
the complex 2 (Scheme 1), which was isolated and charac-
1
13
31
terized by using IR, MS, H,
C and
P NMR
spectroscopies.
In general, the carbonylmetal complexes of acryloylfer-
rocene are labile in solution. Attempts to prepare the chro-
mium and molybdenum analogs failed. Together with the
large coordination shifts of the olefinic carbon and proton
signals in 1 and 2, this lability may be considered as an
indication for the activation of the acryloylferrocene
C@C bond upon coordination to a transition metal.
The IR spectrum of 2 taken in n-hexane exhibits four
strong absorption bands for CO stretching. The observa-
tion of four bands indicates a cis arrangement for the
W(CO) moiety, which has then a C local symmetry with
4
s
0 00
3
A + A CO stretching modes [28]. The IR spectrum also
ꢀ
1
shows an absorption band at 1652 cm due the carbonyl
group of the acfc ligand in complex 2. This relatively small
shift in the CO stretching frequency compared to the free
acryloylferrocene (1665 cm ) is also indicative for the
coordination of acryloylferrocene to the tungsten through
Acknowledgement
ꢀ1
Partial support of this work by Scientific and Technical
Research Council of Turkey (TBAG-2320) and Turkish
Academy of Sciences is gratefully acknowledged.
C@C bond.
1
The H NMR spectrum of 2 in CD Cl shows a doublet
2
2
for the P(OCH ) ligand, three multiplets for the olefinic
3
3
protons, four signals for the hydrogen atoms of the substi-
tuted cyclopentadienyl and a singlet for the hydrogen
atoms of the unsubstituted cyclopentadienyl ring. Com-
pared to the free acryloylferrocene, the signals of olefinic
protons show a remarkable coordination shift (Dd = 1.91,
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