Visible-light photolysis of [FeCp(η6-toluene)][PF6] as a clean, convenient and general route to iron-vinylidene and iron-acetylide complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.09.061

Visible-light photolysis of the cheap starting material [FeCp(η⁶-toluene)][PF₆] (Cp{double bond, long}η⁵-C₅H₅) using a simple 100-W globe in the presence of diphenyldiphosphinoethane (dppe) and termin

Full text of DOI:10.1016/j.jorganchem.2008.09.061

Journal of Organometallic Chemistry 694 (2009) 1219–1222
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Visible-light photolysis of [FeCp(
g
6-toluene)][PF6] as a clean, convenient
and general route to iron-vinylidene and iron-acetylide complexes
*
Cátia Ornelas, Jaime Ruiz, Didier Astruc
Institut des Sciences Moléculaires, UMR CNRS N° 5255, Université Bordeaux1, 33405 Talence Cedex, France
a r t i c l e i n f o
a b s t r a c t
Visible-light photolysis of the cheap starting material [FeCp(g g
6-toluene)][PF6] (Cp@ 5-C5H5) using a sim-
Article history:
Received 28 August 2008
Received in revised form 29 September
2008
Accepted 30 September 2008
Available online 8 October 2008
ple 100-W globe in the presence of diphenyldiphosphinoethane (dppe) and terminal alkynes cleanly
yields the vinylidene complexes [FeCp(dppe)(@C@CHR)][PF6] and, upon further deprotonation, the
iron-alkynyl complexes; the reaction is extended to ferrocenylacetylene to yield a bimetallic complex.
Ó 2008 Elsevier B.V. All rights reserved.
This communication is dedicated to our
friend Professor Dr. Chris Elschenbroich, an
outstanding organometallic chemist,
teacher and book author, at the occasion of
his retirement.
Keywords:
Vinylidene
Carbene
Acetylide
Photolysis
Iron
Sandwich complex
1. Introduction
and average–valence compounds [9,10]. Iron-vinylidene and alke-
nylidene complexes [Cp*Fe(dppe)(@C@CHR)][PF6] (with Cp*@g5
-
In organoiron chemistry [1], the sandwich complexes [FeCp(g6
-
C5Me5), synthesized and studied by the group of Lapinte, are a very
interesting organometallic family that has been used as mimics of
molecular wires [10]. The parent complexes [CpFe(dp-
pe)(@C@CHR)][PF6] are also known but require a long, multi-step
synthesis [11].
arene)][PF6] [2] occupy a large place because of their facile single-
step large-scale synthesis from ferrocene and further iron-induced
aromatic transformation [3]. Another application of these sand-
wich compounds is the visible-light photolysis, a source of the
12-electron fragment CpFe+ leading, in CH2Cl2, to arene exchange
and, in MeCN, to the synthesis of the piano–stool complexes
[CpFeL2(MeCN)][PF6] [4]. We now find that, if the visible-light pho-
2. Results and discussion
tolysis of [FeCp(g
6-toluene)][PF6] using simply a 100-W globe is
Our first synthetic attempt was carried out using trimethylsilyl-
carried out in CH2Cl2 in the presence of dppe and a terminal alkyne,
(i) the vinylidene complex [FeCp(dppe)(@C@CHR)][PF6] is directly
formed in high yield ; (ii) this reaction is clean and general, (iii)
it is extended to 1,4-bis(ethynyl)benzene and ethynylferrocene;
(iv) the mono- and bimetallic iron-vinylidene complexes are
deprotonated to the neutral iron-alkynyl complexes.
Vinylidene complexes are an important class of organometallic
complexes [5] that has been known for a long time and is involved
in organometallic hydrocarbon transformation [6,7], catalysis [8]
and molecular electronic of carbon chains [9] including mixed-
acetylene. The CH2Cl2 solution of [FeCp(g
6-toluene)][PF6], 1, was
irradiated with visible light overnight, and the solution changed
from yellow to brown. After removal of CH2Cl2 and toluene in va-
cuo, [CpFe(dppe){@C@CH(SiMe3)}][PF6], 2, was the only remaining
reaction product. Its 31P NMR spectrum showed, besides the PF6
peaks, only one peak at 97.0 ppm, confirming the consumption of
dppe with a 1:1 stoichiometry. The brown iron-vinylidene complex
2 was deprotonated and deprotected to give the corresponding red
iron-alkynyl complex 3 in THF using stoichiometric amounts of t-
BuOK and n-Bu4NF. The complex 3 was then separated from KPF6
formed by extraction with ether or dichloromethane, and obtained
in 99% yield (Scheme 1).
* Corresponding author.
E-mail address: d.astruc@ism.u-bordeaux1.fr (D. Astruc).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.061

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C. Ornelas et al. / Journal of Organometallic Chemistry 694 (2009) 1219–1222
CH3
hνvis
R
+
-
+
-
+
Fe
C
C
PF6
PF6
CH3
+
H
C
C R
Fe
Ph2P
dppe
H
PPh2
R = SiMe3
CH2Cl2
2
1
t-BuOK
TBAF
THF, RT
K+PF6
-
+
SiFMe3
t-BuOH
+
+
Fe
C
C
H
Ph2P
PPh2
3
Scheme 1. Example of the visible-light generation of the 12-electron fragment CpFe+ from [FeCp( 6-toluene)][PF6] for the clean synthesis, in the presence of a terminal
g
alkyne, of vinylidene and alkynyl complexes.
Similarly, the brown bimetallic vinylidene complexes 4 and 6
were synthesized starting from 1,4-bis(ethynyl)benzene and ethy-
nylferrocene, respectively. These complexes were also similarly
deprotonated to quantitatively yield the corresponding brown
alkynyl complexes 5 and 7 (Schemes 2 and 3). The complex 7
was characterized by standard spectroscopic and analytical tech-
niques including the expected IR and 31P NMR spectra (see Table
1 and end of this article) and mass spectrometry showing its
molecular peaks at 1162.23 (Calc. for C72H62P4Fe2: 1162.86).
The vinylidene and alkynyl complexes were also characterized
by cyclic voltammetry in dichloromethane [10,12]. The monoalky-
In conclusion, a new, general route to iron-vinylidene and iron-
alkynyl complexes has been disclosed and shown to be general and
quantitative in a single-step by visible-light photolysis in dichloro-
methane of the cheap, easily available starting material [FeCp(g6
-
toluene)][PF6] in the presence of terminal alkynes.
3. Spectroscopic and analytical data
3.1. CpFe(dppe)C„CH, 3
1H NMR (CDCl3, 300 MHz): 7.90–7.14 (m, 20H, arom. CH of
dppe), 4.21 (s, 5H, Cp), 2.72 and 2.26 (m, 4H, CH2CH2 of dppe),
1.86 (s, 1H, C„CH). 13C NMR (CDCl3, 75.0 MHz): 142.4–127.1
*
nyl complex 3 shows a reversible redox wave at 160 mV vs. FeCp2
that corresponds to the oxidation of FeII to FeIII of the iron-alkynyl
complex. The symmetrical bisalkynyl complex 5 presents two
reversible redox waves at 0 and 210 mV vs. FeCp2*, the difference
of 210 mV between these two waves indicating a high electronic
communication between the two metal centers that sharply con-
trasts with the lack of wave splitting observed in 1,4-bis(ferrocen-
ylethynyl)benzene [12].
(arom. of dppe), 112.1(Cb), 105.7 (C ), 79.6 (Cp), 28.3 (CH2 of dppe).
a
31P NMR (CDCl3, 121 MHz): 106.4 (Fe-dppe). MS (ESI m/z), Calc. for
C33H30P2Fe: 544.4. Found: M+ 545.0. Anal. Calc. for C33H30P2Fe: C,
72.81; H, 5.55. Found: C, 72.47; H, 5.41%. Infrared t .
C„C: 1918 cmÀ1
3.2. 1,4-(CpFe(dppe)C„C)2C6H4, 5
The alkynyl complex CpFe(dppe)C„C–Fc, 7, shows two com-
*
1H NMR (CDCl3, 300 MHz): 7.89–7.20 (m, 20H, arom. CH of
dppe), 6.11 (s, 4H, CH of benzene bridge), 4.19 (s, 10H, Cp), 2.56
and 2.16 (m, 4H, CH2CH2 of dppe). 13C NMR (CDCl3, 75.0 MHz):
pletely reversible redox waves at 0 mV and 650 mV vs. FeCp2
.
The first redox wave at 0 mV corresponds to the oxidation of the
iron-alkynyl complex to the mixed-valence [13] complex 7+ that
has been reported by Sato [14], and the second wave corresponds
to the oxidation of FeII to FeIII of the ferrocenyl group.
142.4–120.1 (arom.), 111.6 (Cb), 103.7 (C ), 76.6 (Cp), 28.1
a
(CH2 of dppe). 31P NMR (CDCl3, 121 MHz): 106.6 (Fe-dppe).
H
C
-
(PF6 )2
C
H
+
Fe
C
C
h
νvis
Ph2P
PPh2
+
-
2
PF6
CH3
+
Fe
dppe
+
C
C
Fe
CH2Cl2
- 2 PhCH3
PPh2
4
H
C
Ph2P
1
C
H
t
-BuOK
Fe
THF, RT
K+PF
+ 2
-
t
-BuOH
+ 2
6
Fe
C
C
C
C
PPh2
Ph2P
PPh2
Ph2P
5
Scheme 2. Visible-light photolytic synthesis of binuclear vinylidene and alkynyl complexes from the precursor complex [FeCp(g
6-toluene)][PF6].

C. Ornelas et al. / Journal of Organometallic Chemistry 694 (2009) 1219–1222
1221
-
H
PF6
+
Fe
C
C
hνvis
Ph2P
PPh2
+
-
Fe
PF6
CH3
+
Fe
Fe
dppe
CH2Cl2
6
- PhCH3
1
t-BuOK
THF, RT
Fe
C
C
K+PF6
+
-
t-BuOH
+
Ph2P
Fe
PPh2
7
Scheme 3. Visible-light photolytic synthesis of ferrocenylvinylidene and alkynyl complexes from the precursor complex [FeCp(g
6-toluene)][PF6].
Table 1
Electrochemical, I.R. and P NMR data of the complexes 2–7.
Complex
Cyclic voltammetrya
I.R.
31P NMR
1st E1/2 (mV)
2nd E1/2 (mV)
tCC
tPF6
dppm (dppe)
dppm (PF6)
Vinilidene complexes
2
4
6
825
800
510
1025
1020
690
1642
1632
1967
839
839
839
97.0
92.4
93.5
À144.1
À144.1
À144.1
Alkynyl complexes
3
5
7
160
0
0
–
210
650
1918
2060
2066
–
–
–
106.4
106.6
106.4
–
–
–
E1/2 = (Epa+Epc)/2 vs. FeCp2 (in V). Electrolyte: [n-Bu4N][PF6] 0.1 M; working and counter electrodes: Pt; reference electrode: Ag; internal reference: FeCp2*; scan rate:
a
*
0.200 VsÀ1; 20 °C.
(MALDI-TOF; m/z). Calc. for C72H62P4Fe2: 1162.85. Found: M+
[2] (a) M.L.H. Green, L. Pratt, G. Wilkinson, J. Chem. Soc. (1960) 989–992;
(b) A.N. Nesmeyanov, N.A. Vol’kenau, I.N. Bolesova, Tetrahedron Lett. (1963)
1725–1728;
1162.23. Anal. Calc. for C72H62P4Fe2: C, 74.37; H, 5.37. Found: C,
73.93; H, 5.32%. Infrared
t .
C„C: 2060 cmÀ1
(c) I.U. Khand, P.L. Pauson, W.E. Watt, J. Chem. Soc. (1968) 2257–2260;
(d) For the various reports on the synthesis of [FeCp(
g
6-toluene)][PF6] based
on the reaction between ferrocene and AlCl3 in the presence of Al powder in
refluxing toluene, see Ref. [3b, p. 4040].
3.3. CpFe(dppe)C„C-Fc, 7 (Fc = ferrocenyl)
[3] (a) A.S. Abd-El-Aziz, S. Bernardin, Coord. Chem. Rev. 203 (2000) 219–267;
(b) D. Astruc, Tetrahedron 39 (1983) 4027–4095. Tetrahedron Report N° 157.
[4] D. Catheline, D. Astruc, J. Organomet. Chem. 248 (1983) C9–C12;
T.P. Gill, K.R. Mann, Inorg. Chem. 22 (1983) 1986–1991;
D. Catheline, D. Astruc, Organometallics 3 (1984) 1094–1100;
J. Ruiz, D. Astruc, Inorg. Chim. Acta 361 (2008) 1–4;
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[5] M.I. Bruce, Chem. Rev. 91 (1991) 197–257.
[6] J.P. Selegue, Organometallics 1 (1982) 217–218;
1H NMR (CDCl3, 300 MHz): 7.74–7.20 (m, 20H, arom. CH of
dppe), 4.21 (s, 5H, Cp), 3.77–3.65 (m, 9H, Cp of Fc), 2.75 and 2.38
(m, 4H, CH2CH2 of dppe). 13C NMR (CDCl3, 75.0 MHz): 142.4–
127.4 (arom.), 79.0 (Cp), 73.4–65.8 (Cp of Fc), 25.6 (CH2 of dppe).
31P NMR (CDCl3, 121 MHz): 106.4 (Fe-dppe). Anal. Calc. for
C43H38P2Fe2: C, 70.90; H, 5.26. Found: C, 70.56; H, 5.21%. Infrared
t
C„C: 2066 cmÀ1
.
H. Werner, Chem. Commun. (1997) 903–904;
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492–501.
Acknowledgments
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3974–3975.
We are grateful to Fundação para a Ciência e a Tecnologia (FCT),
Portugal (Ph.D. grant to CO), the Institut Universitaire de France
(IUF, DA), the CNRS and the Université Bordeaux I for financial
support.
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