New potential (P,S)-ligands containing tetrathiafulvalene

Article abstract of DOI:10.1039/b005835l

The synthesis of novel (P,S)-ligands containing tetrathiafulvalene (TTF) from preformed TTF derivatives is reported. These compounds were prepared by using borane as protecting group for the phosphine. The electrochemical properties of these new ligands are presented. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b005835l

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New potential (P,S)-ligands containing tetrathiafulvalene
Pascal Pellon, Emilie Brulé, Nathalie Bellec, Karine Chamontin and Dominique Lorcy*
Synthèse et Electrosynthèse Organiques, UMR CNRS 6510, Université de Rennes 1,
campus de Beaulieu, 35042 Rennes cedex, France
1
Received (in Cambridge, UK) 19th July 2000, Accepted 25th September 2000
First published as an Advance Article on the web 8th November 2000
The synthesis of novel (P,S)-ligands containing tetrathiafulvalene (TTF) from preformed TTF derivatives is reported.
These compounds were prepared by using borane as protecting group for the phosphine. The electrochemical
properties of these new ligands are presented.
Among the various functionalized tetrathiafulvalenes (TTFs)
described in the literature1 only a few examples of these
organic donors are substituted with coordination functions.2–6
From the viewpoint of molecular materials, phosphine sub-
stituents, thanks to their chelating ability towards low- and
high-oxidation-state transition metal derivatives, offer the possi-
bility of forming organic–inorganic hybrid building blocks.6,7
Association of the TTFs, well known for their redox properties,
with one or more appropriate metals will lead to a hybrid mole-
cule with multiple redox sites. Various potential applications
can be considered for these hybrid molecules such as in molecu-
lar materials or in catalytic activity.2,7 The TTF-functionalized
phosphine ligands described so far involved one or more
diphenylphosphino substituents directly linked to the donor
core (1–3).2–6 Our goal was to introduce a spacer between the
phosphine–borane substituents was realized starting either
from dibromo-TTF 4 or bis(cyanoethylthio)-TTF 5 as outlined
in Scheme 1.13,† It is worth noting that 4 is less stable and more
difficult to purify than 5. Nevertheless, addition of the
lithium salt of diphenylphosphine–borane, Ph2P(Li)BH3, to 4
at low temperature afforded bisphosphine–borane TTF 6.
Bis(cyanoethylthio)-TTF 5 was used as the precursor in our
second approach for the synthesis of compound 6. Becher
and co-workers have recently demonstrated that the use of
cyanoethyl-protected TTF-thiolate is an efficient building block
for the preparation of a wide range of TTF derivatives as well
as dendritic compounds or cyclophanes containing one or two
TTF units.14 The advantage of bis(cyanoethylthio)-TTF 5 is not
only connected with its stability when compared with 4 but also
to the fact that deprotection of one thiolate group can be select-
ively achieved.14 Depending on the amount of the base used
either the mono- or the bis-thiolate TTF was generated in the
medium, and can futher react with various electrophiles. In
order to prepare bisphosphine–borane-TTF we chose 3-iodo-
propyl(diphenyl)phosphine which was prepared by action of
Ph2P(Li)BH3 on 1,3-diiodopropane in tetrahydrofuran (THF)
at Ϫ80 ЊC under argon (Scheme 1).
Bis(cyanoethylthio)-TTF 5 in the presence of two equivalents
of caesium hydroxide yielded the dithiolate; reaction of
this intermediate with iodopropyl(diphenyl)phosphine–borane
afforded the TTF 6 in good yield. As it has been pointed out
by Becher, deprotection of one thiolate can be performed with
one equivalent of caesium hydroxide. Actually, we used that
possibility in order to prepare the mono(phosphino–borane)-
substituted TTF 8 (Scheme 2). After the addition of base, the
thiolate generated in situ reacted with iodomethane and the
TTF 7 was obtained. Then treatment of this TTF with another
equivalent of caesium hydroxide, followed by the addition of
iodopropyl(diphenyl)phosphine–borane, led to the TTF 8.
Phosphine–borane-TTFs 6 and 8, due to their stability, can
be stored as precursors for further work. Decomplexation of
phosphine–borane complexes in the presence of 1,4-diazabi-
cyclo[2.2.2]octane (DABCO) under inert atmosphere gave the
phosphine derivatives 9 and 10 in good yields (Scheme 3).12
These phosphine ligands are moderately air stable in solution.
Both phosphine TTF 9 and 10 exhibit similar phosphorus
chemical shifts (δP Ϫ16.4 ppm). This chemical shift is close
phosphorus atom and the TTF and to form a potentially
bidentate ligand by adding a sulfide function. Indeed, ambi-
dentate ligands such as (P,S) ones, due to the different lability
of the phosphorus–metal and sulfur–metal bond, have been
recently investigated in catalytic asymmetric reactions.8–10 In
this paper, we describe the synthesis of new ligands containing
the redox-active TTF moiety together with their electrochemical
properties.
Results and discussion
In order to build these new ligands we used preformed TTF
derivatives and then we functionalized these donors with the
appropriate substituents. The use of phosphine–borane com-
plexes in the synthesis of phosphino-TTF presents several
advantages. On one hand, these complexes are very stable com-
pared with phosphine derivatives, not sensitive towards the
usual oxidizing or electrophilic reagents10 and very easy to use
in organic synthesis.11 On the other hand, decomplexation of
phosphine–borane is simply realized using a soft method
which does not interact with the TTF core.12 The grafting of
† As details of compound 5 have not yet been published, its data are
reported below: yield 70%; mp 174 ЊC; Rf (SiO2; CH2Cl2) 0.56; δH (200
MHz; CDCl3) 2.18 (s, 6H), 2.65 (t, 4H), 2.95 (t, 4H); δC (75 MHz;
CDCl3) 16.23, 19.12, 31.47, 109.40, 116.90, 118.27, 139.12; MS (EI)
401.949 (Mϩ) (Found: C, 41.84; H, 3.44; N, 6.54; S, 47.56. C14H14N2S6
requires C, 41.75; H, 3.50; N, 6.95; S, 47.80%).
DOI: 10.1039/b005835l
J. Chem. Soc., Perkin Trans. 1, 2000, 4409–4412
This journal is © The Royal Society of Chemistry 2000
4409

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Scheme 1 Reagents and conditions: i, Ph2P(Li)BH3, THF, Ϫ80 ЊC; ii, CsOHؒH2O (2.1 equiv.); iii, I(CH2)3PBH3Ph2.
Table 1 CV data, E in V vs. SCE, Pt working electrode with 0.1 M
n-Bu4NPF6, scanning rate 100 mV sϪ1 in CH2Cl2
1
2
Compound
Epa
Epa
∆E (mV)
DMBMT-TTF
0.43
0.39
0.40
0.49
0.44
0.81
0.83
380
440
440
370
400
6
8
0.84
9
0.86a
0.84a
10
a Quasi-irreversible process.
Our synthetic approach allowed us to prepare P,S hybrid
ligands containing TTF with a propyl chain between the sulfur
atom and the phosphorus one. The scope of this synthesis can
now be broadened to related P,S ligands by the introduction of
a cyclic or aliphatic bridging chain of variable length. The next
step of this work will be to study the ability of these ligands
to coordinate different metals. Application of these ligands
can be easily foreseen for molecular materials and/or catalytic
activities. Within this framework, and depending on the metal
centre coordinated, we can tune the redox properties of the
TTF. This can be achieved by substituting these donors by
either electron-donating or -withdrawing groups instead of
the methyl one.
Scheme 2 Reagents and conditions: i, CsOHؒH2O (1 equiv.); ii, MeI;
iii, I(CH2)3PBH3Ph2.
Experimental
Mps were measured on a Kofler hot-stage apparatus and are
uncorrected. Elemental analyses were performed at the
Laboratoire Central de Microanalyse du CNRS, Lyon. 1H
NMR and 13C NMR spectra were recorded on Bruker ARX
200 or Bruker AC 300P spectrometers. Chemical shifts are
quoted in parts per million (ppm) referenced to tetramethyl-
silane for 1H NMR and 13C NMR and to H3PO4 for 31P NMR.
Coupling constants (J) are reported in Hertz. Mass spectra
were recorded with a Varian MAT 311 instrument by the
Centre Régional de Mesures Physiques de l’Ouest, Rennes.
THF was distilled from sodium–benzophenone. Methanol
was dried over calcium. Toluene was dried over sodium wire.
Chromatography was performed using silica gel Merck 60 (70–
260 mesh). CV was carried out on a 10Ϫ3 M solution of TTF
derivatives in dichloromethane, containing 1.0 M n-Bu4NPF6 as
the supporting electrolyte. Voltammograms were recorded at
0.1 V sϪ1 at a platinum disk electrode (A = 1 mm2). The poten-
tials were measured versus Saturated Calomel Electrode (SCE).
As previously observed with bis-functionalized TTFs, all the
TTFs synthesized and described below are present as two
isomers (Z/E) which were observed by 1H and 13C NMR
spectroscopy but not separated (only the E isomers are pre-
sented in the Schemes).15 Light petroleum (LP) refers to the
fraction with distillation range 40–60 ЊC.
Scheme 3 Reagents and conditions: i, DABCO.
to that observed for P,S ligands such as 2,5-bis[2-
(diphenylphosphino)ethyl]thiophene (δP Ϫ16.6 ppm).9
The donor abilities of these TTFs were studied by cyclic
voltammetry (CV). It is worth noting that the presence of
the phosphine–borane on the side-chain slightly increases the
donor ability of the TTF core. This could be explained by a
possible complexation of the exocyclic sulfurs with the borane
which would deactivate the withdrawing effect of the sulfur.
The more anodic oxidation potentials for the dimethylbis-
(methylthio)-TTF (DMBMT-TTF) are in favour with this
hypothesis. CV data for TTFs 6, 8–10 and DMBMT-TTF are
collated in Table 1.
4410
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Iodopropyl(diphenyl)phosphine–borane
3-[3-(Boranatodiphenylphosphino)propylthio]-4,4Ј-dimethyl-3Ј-
(methylthio)tetrathiafulvalene 8
A mixture of PPh3ؒBH3 (2.76 g, 10 mmol), lithium divided in
small pieces (140 mg, 20 mmol) and 20 mL of freshly distilled
THF was vigorously stirred under argon for 5 h. After cooling
To a solution of the TTF 7 (363 mg, 1 mmol) in 20 mL of DMF
was added, under argon, a solution of CsOHؒH2O (0.2 g, 1.2
mmol) in 5 mL of MeOH. The mixture was stirred for 30 min
at RT after which 3-iodopropyl(diphenyl)phosphine–borane
(368 mg, 1 mmol) was added. Stirring was continued for 1 h.
Solvents were removed by rotary evaporation, and the residue
was extracted with CH2Cl2 and washed with water. Chromato-
graphy over silica gel (2:1 CH2Cl2–LP) afforded title fulvalene 8
(0.5 g, 91%) as an orange powder, mp 99–100 ЊC; Rf 0.61; δH
(200 MHz; CDCl3) 0.60–1.40 (3H), 2.02 (m, 2H), 2.22 (s, 3H),
2.31 (s, 3H), 2.48 (m, 2H), 2.49 (s, 3H), 2.94 (t, 2H), 7.65–7.89
(m, 10H); δC (50 MHz; CDCl3) 15.65, 15.90, 19.79, 23.78, 24.88,
t
of the mixture at 0 ЊC in a ice-bath, BuCl (1.1 mL, 10 mmol)
was added slowly. The solution was stirred for another hour at
RT. This solution was added to a solution of 1,3-diiodopropane
(1.19 mL, 10 mmol) in 20 mL of dried THF at Ϫ80 ЊC and
the mixture was allowed to warm to RT over a period of 12 h.
Acidic hydrolysis with 1 M HCl, extraction with CH2Cl2, and
purification by chromatography over silica gel (2:1 CH2Cl2–
LP) afforded 3-iodopropyl(diphenyl)phosphine–borane (0.48 g,
30%) as a white powder, mp < 40 ЊC; Rf 0.68; δH (200 MHz;
CDCl3) 0.60–1.30 (m, 3H), 2.00 (m, 2H), 2.34 (m, 2H), 3.22
(t, 2H, J 6.8), 7.26–7.74 (m, 10H); δP (121 MHz; CDCl3)
15.55; δC (50 MHz; CDCl3) 8.07, 27.51, 27.56, 129.59, 129.60,
132.04, 132.76 (Found: [M Ϫ H]ϩ, 367.0281. C15H18BP requires
m/z, 367.0287).
37.28, 108 (br, 2C), 118.6, 121.6, 129.35, 129.47, 131.78, 132.52,
ϩ
134.10, 136.16; δP (121 MHz; CDCl3) 16.33 (Found: M
,
᝽
550.0337. C24H28BPS6 requires M, 550.0351. Found: C, 52.27;
H, 4.95; P, 5.67; S, 34.17. C24H28BPS6 requires C, 52.35; H, 5.12;
P, 5.62; S, 34.93%).
3,3Ј-Bis[3-(boranatodiphenylphosphino)propylthio]-4,4Ј-
dimethyltetrathiafulvalene 6
3,3Ј-Bis[3-(diphenylphosphino)propylthio]-4,4Ј-dimethyltetra-
thiafulvalene 9
From the bisbromo-TTF 4. A mixture of PPh3ؒBH3 (276 mg,
1 mmol), lithium divided in small pieces (14 mg, 2 mmol) and
2 mL of freshly distilled THF was vigorously stirred under
argon for 5 h at RT. After cooling of the mixture at 0 ЊC in a ice-
To a solution of the TTF 6 (201 mg, 0.5 mmol) in 20 mL of
dried, degassed toluene was added, under argon, DABCO
(112 mg, 1 mmol). The mixture was stirred for 3–4 h at 50 ЊC.
The reaction was followed by TLC. Toluene was evaporated off
with a vacuum pump, and the residue was chromatographed
under inert atmosphere with degassed solvents to afford the
TTF 9 as an orange oil (224 mg, 60%), Rf (SiO2; 2:1 CH2-
Cl2–LP) 0.62; δH (200 MHz; CDCl3) 1.62–1.80 (m, 4H), 2.04
(s, 6H), 2.13 (m, 4H), 2.80 (t, 4H), 7.30–7.75 (m, 20H); δC (50
MHz; CDCl3) 15.42, 26.17, 26.92, 37.10, 108.33, 119.08,
128.53, 128.55, 130.88, 132.72, 135.14; δP (121 MHz; CDCl3)
Ϫ16.47 (Found: [M ϩ H]ϩ, 749.0851. C38H39P2S6 requires m/z,
749.0854).
t
bath, BuCl (110 µL, 1 mmol) was slowly added. The solution
was stirred for another hour at RT, then was added to a solution
of the dibromo-TTF 413 (269 mg, 0.5 mmol) in 5 mL of dried
THF at Ϫ80 ЊC. The mixture was allowed to reach RT
and was stirred overnight. Acidic hydrolysis, extraction with
CH2Cl2, rotary evaporation, and purification over silica gel (2:1
CH2Cl2–LP) afforded title fulvalene 6 (0.16 g, 21%) as a yellow
powder.
From the bis(cyanoethylthio)-TTF 5. To a solution of the
bis(cyanoethylthio)-TTF 5 (402 mg, 1 mmol) in 20 mL of DMF
was added under argon a solution of CsOHؒH2O (353 mg, 2.1
mmol) in 5 mL of MeOH. The mixture was stirred for 30 min at
RT, after which 3-iodopropyl(diphenyl)phosphine–borane (736
mg, 2 mmol) was added. Stirring was continued for 1 h. Sol-
vents were removed by rotary evaporation, and the residue was
extracted with CH2Cl2 and washed with water. Chromato-
graphy over silica gel (2:1 CH2Cl2–LP) afforded title fulvalene
6 (0.48 g, 62%) as a yellow powder, mp 183–184 ЊC; Rf 0.53;
δH (200 MHz; CDCl3) 0.67–1.25 (m, 6H), 1.72–1.91 (m, 4H),
2.05 (s, 6H), 2.25–2.39 (m, 4H), 2.76 (t, 4H), 7.43–7.70 (m,
20H); δP (121 MHz; CDCl3) 16.68; δC (75 MHz; CDCl3) 15.87,
23.76, 24.93, 37.37, 108.0, 118.3, 129.34, 129.49, 131.75, 132.54,
3-[3-Diphenylphosphino)propylthio]-4,4Ј-dimethyl-3Ј-(methyl-
thio)tetrathiafulvalene 10
Same procedure as for 9, applied to 8. The TTF 10 was
obtained as an orange oil (235 mg, 88%), Rf (SiO2; 2:1 CH2Cl2–
LP) 0.75; δH (300 MHz; CDCl3) 1.72 (m, 2H), 2.04 (s, 3H), 2.12
(s, 3H), 2.13 (m, 2H), 2.31 (s, 3H), 2.80 (t, 2H), 7.22–7.36
(m, 10H); δC (50 MHz; CDCl3) 15.61, 15.80, 19.76, 26.60, 27.34,
37.51, 108.50, 109.00, 119.52, 121.25, 128.97, 129.05, 133.12,
134.06, 135.49, 138.72; δP (121 MHz; CDCl3) Ϫ16.43 (Found:
M
᝽
ϩ, 536.0019. C24H25PS6 requires M, 536.0018).
References
136.22 (Found: M ϩ, 776.1442. C38H44B2P2S6 requires M,
᝽
1 G. Schukat and E. Fanghänel, Sulfur Rep., 1996, 18, 1.
2 M. Fourmigué and P. Batail, J. Chem. Soc., Chem. Commun., 1991,
1370.
776.1442. Found: C, 58.49; H, 5.70. B, 2.81; P, 7.40. C38H44-
B2P2S6 requires C, 58.76; H, 5.71; B, 2.78; P, 7.97%).
3 M. Fourmigué and P. Batail, Bull. Soc. Chim. Fr., 1992, 129, 29.
4 M. Fourmigué and Y. S. Huang, Organometallics, 1993, 12, 797.
5 F. Gerson, A. Lampretch and M. Fourmigué, J. Chem. Soc., Perkin
Trans. 2, 1996, 1.
6 M. Fourmigué, C. E. Uzelmeier, K. Boubekeur, S. L. Bartley and
K. R. Dunbar, J. Organomet. Chem., 1997, 529, 343.
7 B. W. Smucker and K. R. Dunbar, J. Chem. Soc., Dalton Trans.,
2000, 1309.
8 For examples of P,S ligands see: (a) E. Hauptman, P. J. Fagan
and W. Marshall, Organometallics, 1999, 18, 2061; (b) P. Barbaro,
A. Currao, J. Herrmann, R. Nesper, P. S. Pregosin and R.
Salzmann, Organometallics, 1996, 15, 1879; (c) A. R. Sanger, Can. J.
Chem., 1983, 61, 2214; (d) M. Hiraoka, A. Nishikawa, T. Morito
and K. Achiwa, Chem. Pharm. Bull., 1998, 46, 704; (e) S. Gladiali,
A. Dore and D. Fabbri, Tetrahedron: Asymmetry, 1994, 5, 1143;
( f ) J. Kang, S. H. Yu, J. I. Kim and G. H. Cho, Bull. Korean Chem.
Soc., 1995, 16, 439.
3-(2-Cyanoethylthio)-4,4Ј-dimethyl-3Ј-(methylthio)tetrathia-
fulvalene 7
To a solution of the bis(cyanoethylthio)-TTF 5 (1.0 g, 2.49
mmol) in 30 mL of DMF was added, under argon, a solution
of CsOHؒH2O (0.42 g, 2.49 mmol) in 5 mL of MeOH. The
mixture was stirred for 15 min at RT, after which CH3I (0.2 mL,
3.2 mmol) was added. Stirring was continued for 30 min. Sol-
vents were removed by rotary evaporation, and the residue was
extracted with CH2Cl2 and washed with water. Chromato-
graphy over silica gel (2:1 CH2Cl2–LP) afforded title compound
7 (0.6 g, 66%) as an orange powder, mp 101–102 ЊC; Rf 0.45;
δH (200 MHz; CDCl3) 2.19 (s, 3H), 2.25 (s, 3H), 2.38 (s, 3H),
2.71 (t, 2H), 3.00 (t, 2H); δC (75 MHz; CDCl3) 15.25, 15.64,
18.48, 19.42, 30.86, 107.26, 110.44, 116.20, 117.73, 120.86,
133.70, 138.55 (Found: C, 39.71; H, 3.45; N, 3.93; S, 52.84.
C12H13NS6 requires C, 39.64; H, 3.60; N, 3.85; S, 52.91%).
9 M. Alvarez, N. Lugan and R. Mathieu, Inorg. Chem., 1993, 32,
5652.
10 P. Pellon, Tetrahedron Lett., 1992, 33, 445.
J. Chem. Soc., Perkin Trans. 1, 2000, 4409–4412
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11 Y. Gourdel, A. Ghanimi, P. Pellon and M. Le Corre, Tetrahedron
Lett., 1993, 34, 1011.
12 H. Brisset, Y. Gourdel, P. Pellon and M. Le Corre, Tetrahedron
Lett., 1993, 34, 4523.
13 The general synthesis of TTFs starting from mesoionic dithioles was
described in these references: A. Souizi and A. Robert, Tetrahedron,
1984, 40, 1817; F. Bertho, A. Robert, P. Batail and P. Robin,
Tetrahedron, 1990, 46, 433.
14 N. Svenstrup, K. M. Rasmussen, T. K. Hansen and J. Becher,
Synthesis, 1994, 809; J. Lau, O. Simonsen and J. Becher, Synthesis,
1995, 521; K. B. Simonsen, N. Svenstrup, J. Lau, O. Simonsen,
P. Mrk, G. J. Kristensen and J. Becher, Synthesis, 1996, 407; J. Lau,
P. Blanchard, A. Riou, M. Jubault, M. P. Cava and J. Becher, J. Org.
Chem., 1997, 62, 4936.
15 A. Souizi, A. Robert, P. Batail and L. Ouahab, J. Org. Chem., 1987,
52, 1610.
4412
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