Bimetallamacrocycles involving tetrakis(diphenylphosphinoalkylthio)tetrathiafulvalene

Article abstract of DOI:10.1016/j.jorganchem.2009.04.006

Two novel tetrathiafulvalene (TTF) ligands, substituted by four diphenylphosphinoalkylthio groups, have been synthesized and characterized. Their redox properties, determined by cyclic voltammetry, have been compared with their precursors and discussed. T

Full text of DOI:10.1016/j.jorganchem.2009.04.006

Journal of Organometallic Chemistry 694 (2009) 2531–2535
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Bimetallamacrocycles involving tetrakis(diphenylphosphinoalkylthio)
tetrathiafulvalene
*
Grégory Gachot, Pascal Pellon, Thierry Roisnel, Dominique Lorcy
Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, Bât 10A, 35042 Rennes cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel tetrathiafulvalene (TTF) ligands, substituted by four diphenylphosphinoalkylthio groups, have
been synthesized and characterized. Their redox properties, determined by cyclic voltammetry, have
been compared with their precursors and discussed. The ability of these redox active ligands to react with
two equivalent of cis-W(CO)4(C5H11N)2 is presented. X-ray crystal structure of a bis 13-metallamacrocy-
cle is reported together with its redox behaviour.
Received 13 March 2009
Received in revised form 6 April 2009
Accepted 7 April 2009
Available online 17 April 2009
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Tetrathiafulvalene
Diphosphine ligands
Metallamacrocycle
Tungsten
1. Introduction
Therefore, we decided to investigate the behaviour of tetrakis
substituted (diphenylphosphinoalkylthio)-TTF towards W(CO)4
Formation of large metallamacrocycles based on transition metal
complexes with diphosphine ligands remains an important
synthetic challenge [1]. One of the strategies developed to reach
fragments and their ability to form metallamacrocycles using alkyl
chain of similar length as the ones involved in the formation of the
17- and 19-membered metallamacrocycles [7]. Two types of metal-
lamacrocycles can be envisioned starting from these tetra substi-
tuted TTF (Chart 2), either the phosphino groups coordinate the
tungsten atom in a similar way as the one observed from the bis
substituted TTF, to afford a bis 17- or 19-membered metallamacro-
cycles (way a), or two phosphino groups on the same dithiole ring
coordinate the metallic fragment (way b). Herein, we report the
synthesis of the tetrakisphosphino ligand 1 and 2 where the phos-
phine moieties are linked to the donor core through a thiopropyl or
a thiobutyl alkyl chain and the influence of this alkyl chain on the
formation of the metallamacrocycles.
such compounds involves the coordination of a bidentate
diphosphine ligand to the transition metal center [1]. Note however
that with this approach, most of the -diphosphine ligands with a
a,x-
a,x
flexible backbone between the two phosphorus atoms are more
likely to bridge two metals rather than to form a chelate ring afford-
ing oligomeric or polymeric structures [2]. Association of an electro-
active ligand such as a tetrathiafulvalene core (TTF) and transition
metals within a metallamacrocycle has been scarcely described so
far [3,4] even if TTF has been incorporated in various molecular
and supramolecular systems [5]. In continuation of our work on
the formation of hybrid organic–inorganic building blocks using
mono [6] and bis phosphino-TTF [7] as the electroactive ligand,
we decided to investigate the formation of large bimetallacycles
using tetrakis substituted (diphenylphosphinoalkylthio)-TTF as
starting material. Indeed, we have recently described the formation
of redox active 17- and 19-membered metallamacrocycles thanks to
the chelating ability of bis(diphenylphosphinoalkylthio)-TTF to-
wards M(CO)4 fragments (M = Mo, W) (Chart 1) [7]. It is worth men-
tioning that due to (i) the possible cis/trans isomerization of the TTF
core, (ii) the possible cis/trans coordination of the two P atoms
around the metallic fragment and (iii) the trans TTF as an element
of planar chirality, six stereoisomers were obtained [7].
2. Results and discussion
The synthesis of the ligands 1 and 2 was realized according to
the chemical pathway depicted in Scheme 1 starting from the tetra-
kis(cyanoethylthio)-TTF 3 [8]. Deprotection of the thiolate was
achieved in DMF using a base such as cesium carbonate at 70 °C
during 3 h instead of the cesium hydroxide usually used for this
type of deprotection. Indeed, it has to be mentioned that the use
of cesium hydroxide lead to a mixture of mono, bis and tetradepro-
tected derivatives. In order to prepare the tetrakis(diphenylphosph-
inopropylthio)-TTF 1 we added 3-iodopropylphosphine-borane in
the medium while for the synthesis of tetrakis(diphenylphosphin-
obutylthio)TTF 2, 4-bromobutylphosphine-borane was added [9].
The tetrakis(phosphine borane)-TTFs 4 and 5 were obtained as air
* Corresponding author. Fax: +33 2 23 23 67 38.
E-mail address: dominique.lorcy@univ-rennes1.fr (D. Lorcy).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.04.006

2532
G. Gachot et al. / Journal of Organometallic Chemistry 694 (2009) 2531–2535
Table 1
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
Ph2PM(CO)4PPh2
(CH2)n
S
Oxidation peak potentials in V vs. SCE, Pt working electrode and 31P chemical shifts in
S
S
M = W, Mo
Me
S
CDCl3 for compounds 1–6.
S
TTF(SR)4
d
31P ppm
TTF-(SR)4
S
S
S
S
S-(CH2)n
Me
R, compound
E1pa=E1pc
E2pa=E2pc
TTF cis/trans
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
0.61*
0.58*
0.86*
0.84*
17-membered metallamacrocycle (n = 3)
19-membered metallamacrocycle (n = 4)
–(CH2)3-PPh2
–(CH2)4-PPh2
1
2
À16.7
À16.4
1 n = 3
2 n = 4
–(CH2)2-CN 3
–(CH2)3-PPh2BH3
–(CH2)4-PPh2BH3
0.71/0.63
0.59/0.51
0.55/0.49
0.62/0.54
0.99/0.88
0.95/0.87
0.90/0.82
0.97*
4
5
15.9
15.9
8
Chart 1.
Metallamacrocyle 6
*
Irreversible process.
W(CO)4
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
dino ligands can be replaced by other ligands such as two diphenyl
phosphino moieties [10]. As mentioned earlier, for mono and bis
substituted phosphino-TTF derivatives, the metal carbonyl com-
plexation can be realized, directly from the phosphine-borane
TTF complexes [6,7], in a one-pot procedure by a two-step chemi-
cal synthesis: (i) decomplexation of the phosphine borane and (ii)
addition of cis-W(CO)4(C5H10NH)2 in the medium. Using this one-
pot procedure, one avoids any undesired oxidation of the phos-
phine groups. According to this strategy, we first studied TTF 1 as
starting material and deprotected the phosphine groups by heating
TTF 1 in the presence of four equivalents of DABCO at 50 °C for 4 h
in dry and degassed toluene. Addition of two equivalents of cis-
W(CO)4(C5H10NH)2 in the medium followed by the heating of the
solution for 2 h at 90 °C allowed us to isolate after column chroma-
tography upon silica gel, besides polymeric derivatives, one com-
pound in 33% yield. Analysis of this compound by 31P NMR in
CDCl3 reveals one singlet at 8 ppm associated with a small doublet
due to the coupling of the phosphorus atom with the 183W isotope.
The presence of only one singlet suggests the formation of a sym-
metrical molecule and the coupling constant observed J1PW = 231 Hz
is characteristic for the presence of cis-P–W–P isomer [11,12]. Slow
diffusion of methanol into a dichloromethane solution of this
derivative allowed us to obtain crystals suitable for X-ray structure
analysis. The crystal structure determination reveals that a bime-
tallic complex is formed and that two 13-membered metallamac-
rocycles are formed and connected by the TTF core (way b, Chart
2), as the two phosphine groups on one dithiole ring of the TTF
are coordinated to the metal center (Scheme 2). This complex 6
crystallizes in the monoclinic system, space group P21/n with the
complex located on an inversion center and one CH2Cl2 molecule
in general position. The molecular structure of this bimetallic com-
pound 6 is represented in Figs. 1 and 2 and selected bond lengths
and angles are listed in Table 2.
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
S
S
S
S
W(CO)4
W(CO)4
n = 3, 4
S
S
S
S
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
n = 3, 4
W(CO)4
Way a
Way b
Chart 2.
stable derivatives in 73% and 68% yield, respectively. Deprotection
of the phosphines was realized by heating a solution of the tetra-
kis(phosphineborane)-TTF 4 and 5 in toluene under inert atmo-
sphere at 50 °C for 5 h in the presence of four equivalents of
DABCO.
After filtration
on celite,
the
tetrakis(diph-
enylphosphinoalkylthio)-TTF 1 and 2 were obtained in 71% and
68% yield, respectively. Note that these derivatives 1 and 2 are eas-
ily transformed, upon air exposure, into the corresponding phos-
phine oxides. Therefore, deprotection of the phosphine was
performed in order to characterized by 1H and 31P NMR these TTFs
and to analyze their redox properties.
The influence of the substituents on the redox properties of the
TTFs 1–5 has been studied by cyclic voltammetry. The oxidation
peak potentials of the various TTFs are collected in Table 1. In both
series it can be noticed that the effect of the diphenylphosphine-
borane group or the diphenylphosphine one decreases with the
length of the alkyl chain. Indeed, in both cases, the butyl deriva-
tives, TTF 2 and 5, are easier to oxidize than the propyl derivatives,
TTF 1 and 4. However the electron withdrawing effect of these two
groups is less important than the one of the cyanoethyl group. The
lack of reversibility observed for the TTFs 1 and 2 was attributed to
the presence of the phosphines substituents and to their reducing
character towards the generated mono and biscationic species in
the medium.
Within this complex, the phosphines are cis coordinated to the
metal center and this confirms the cis-P–W–P structure deduced
from the 31P NMR spectrum. The TTF moiety is not planar and
the dithiole rings are folded along the SÁÁÁS vector with an angle
of 20° and adopts a chair conformation. Analysis of the bond
lengths of the TTF core shows that the TTF is under the neutral
In order to form metal carbonyl complexes with these TTF li-
gands, we used cis-W(CO)4(C5H10NH)2 where the two labile piperi-
H3B
Ph2P-(CH2)n-S
BH3
S-(CH2)n-PPh2
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
NC(CH2)2S
S(CH2)2CN
S
S
S
S
S
S
S
S
Cs2CO3, DMF
Br(CH2)nPPh2BH3
DABCO
S
S
S
S
Ph2P-(CH2)n-S
S-(CH2)n-PPh2
NC(CH2)2S
S(CH2)2CN
Ph2P-(CH2)n-S
H3B
S-(CH2)n-PPh2
BH3
4 n = 3
1 n = 3
2 n = 4
3
5 n = 4
Scheme 1.

G. Gachot et al. / Journal of Organometallic Chemistry 694 (2009) 2531–2535
2533
(CO)4
W
Ph2P
PPh2
(CH2)3
H3B
BH3
(CH2)3
S
S
Ph2P-(CH2)3-S
S-(CH2)3-PPh2
S
S
S
S
S
1) DABCO
2) cis-W(CO)4(C5H10NH)2
S
S
S
S
S
Ph2P-(CH2)3-S
H3B
S-(CH2)3-PPh2
BH3
(CH2)3 (CH2)3
Ph2P
PPh2
4
W
(CO)4
6
Fig. 3. Cyclic voltammogram of complex 6.
Scheme 2.
Ph
Ph
P
Ph
Ph
(OC)4W
Ph
P
P
S
S
S
S
C62
O4
C4
W(CO)4
Ph
C61
C60
O2
C2
S60
C51
C52
S50
S61
S51
P
Ph
C50
O1
C63
C53
Ph
C1
C3
P2
P1
P2
C70
S50
O3
[P4][W(CO)4]2
W1
C1
O1
O3
W1
C70
S61
C53
C63
P1
C50
C51
C60
C61
C3
C2
C4
S51
Chart 3.
C52
O2
S60
O4
C62
derivatives coordinated to W(CO)4 fragment [13], which indicates
that the two 13-membered metallamacrocycles are not con-
strained. No short SÁÁÁS contacts are observed between neighboring
complex 6 in the solid state presumably due to the huge steric hin-
drance of the two metallacycles fused to the TTF core (Fig. 2).
It is interesting to note that using TTF 2, with the longer butyl
arms, as starting material and following the same experimental
procedure, that is decomplexation of the phosphine and addition
of two equivalents of cis-W(CO)4(C5H10NH)2 in the medium, we
did not isolate a monomeric structure. Instead, analysis by 31P
NMR, of the different fractions obtained after chromatographic
separation, reveals the presence of numerous signals attributed
to polymeric derivatives resulting from presumably intra and
intermolecular complexation.
Fig. 1. ORTEP view of TTF complex 6 showing the atom labeling (50% probability
ellipsoids). Phenyl rings and hydrogen atoms are omitted for clarity.
The redox properties of the bis(13-membered metallacycle) 6
obtained from 1 was studied by cyclic voltammetry. Two oxidation
waves are observed, the first one is reversible and corresponds to
the oxidation of the TTF in its radical cation while the second pro-
cess is not fully reversible (Fig. 3). Actually, the latter is due to the
concomitant oxidation of TTF radical cation into the dication and
the oxidation of the two metallic centers. This process is not fully
reversible due to the loss of carbonyl ligands on the metallic cen-
ter. It is interesting to note that, due to the presence of the propyl-
thio spacer group, the first redox potential of the TTF is not
modified by the presence of the two W(CO)4 fragments coordi-
nated to the phosphino groups. This result strongly differs from
what was observed with the tetrakis(diphenylphosphino)TTF,
noted P4, in the bimetallic [P4][W(CO)4]2 where the phosphorus
atoms are directly linked to the donor core (Chart 3) [12]. In this
case a strong anodic shift of the first oxidation is observed
(+400 mV) due to strong interactions between the TTF core and
the metallic fragment.
Fig. 2. Side views of TTF complex 6 showing the steric hindrance around the TTF
core. Hydrogen atoms are omitted for clarity.
Table 2
Selected bond lengths (Å) and angles (°) for complex 6.
Bond lengths
P1ÀW1
P2ÀW1
W1ÀC1
W1ÀC2
W1ÀC3
W1ÀC4
2.5424(15)
2.5377(14)
2.021(6)
1.983(6)
1.966(7)
2.016(7)
C1ÀO1
C2ÀO2
C3ÀO3
C4ÀO4
C70ÀC70
1.141(7)
1.162(7)
1.153(8)
1.145(8)
1.346(12)
Bond angles
P2ÀW1ÀP1
C60ÀP2ÀW1
C50ÀP1ÀW1
94.11(5)
116.62(18)
116.68(17)
C53ÀC63ÀS60
C63ÀC53ÀS50
122.9(4)
123.9(4)
3. Conclusions
In summary, we described the synthesis of a novel family of tet-
radentate phosphino-TTFs where the phosphino moieties are linked
to the donor core through a propylthio or a butylthio spacer group.
Depending on the length of this spacer, a dinuclear tungsten com-
plex has been formed, as evidenced by X-ray structure analysis,
state. As seen in Table 2, The W–P distances and P–W–P interligand
angles are in the usual range for non cyclic bisdiphenylphosphine

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G. Gachot et al. / Journal of Organometallic Chemistry 694 (2009) 2531–2535
Table 3
through the coordination of the two phosphino groups on the same
dithiole ring to a metallic W(CO)4 fragment. The redox properties of
this electroactive bis 13-membered metallamacrocycles were
determined and comparison with those of the starting ligand shows
that the presence of these two metallamacrocycles does influence
the electron donating ability of the TTF.
Crystal data and structure refinement parameters for complex 6.
Structure parameter
(Complex 6).(CH2Cl2)2
Empirical formula
Molecular weight
Cryst system
Space group
a (Å)
C76H68Cl4O8P4S8W2
1999.16
Monoclinic
P21/n
10.278(5)
19.724(5)
20.301(5)
90
b (Å)
c (Å)
4. Experimental
a
(°)
b (°)
94.707(5)
90
4102(2)
293(2)
4.1. General
c
(°)
V (Å3)
1H NMR and 31P NMR spectra were recorded on Bruker AC 300P
or ARX 200 spectrometers. Chemical shifts are reported in ppm ref-
erenced to TMS for 1H NMR and to H3PO4 for 31P NMR. Melting
points were measured using a Kofler hot stage apparatus. Mass
spectra were performed by the Centre Régional de Mesures Phy-
siques de l’Ouest, Rennes. Methanol was distilled from calcium
and dichloromethane from P2O5. Chromatography was performed
using silica gel Merck 60 (70–260 mesh). The tetrakis(cyanoethyl-
thio)-TTF 3 was prepared according to previously published proce-
T (K)
Z
2
Dcalc (g/cm3)
1.619
3.266
16 664
9377(0.0282)
8003
0.0448, 0.1074
0.0543, 0.1123
1.139
l
(mmÀ1
)
Total reflections
Unique data (Rint
Obs reflections (I > 2
R1, wR2
R1, wR2 (all data)
Goodness-of-fit (GoF)
)
r(I))
dures [8]. Cis-W(CO)4(NC5H11 2 was prepared from W(CO)6
)
according to published procedure [10]. Cyclic voltammetry were
carried out on a 10À3 M solution of the derivatives in dichloro-
methane, containing a 0.1 M nBu4NPF6 as the supporting electro-
lyte. Voltammograms were recorded at 0.1 V sÀ1 at a platinum
disk electrode (A = 1 mm2). The potentials were measured versus
Saturated Calomel Electrode.
4.2.3. Complex 6
To a solution of TTF 1 (310 mg, 0.24 mmol) in 25 ml of dried, de-
gassed toluene was added under argon DABCO (110 mg,
0.96 mmol). The mixture was stirred for 4 h at 50 °C after which
cis-W(CO)4(NHC5H10)2 (220 mg, 0.48 mmol) in 8 ml of degassed
CHCl3 was added. Stirring was continued for 2 h at 90 °C and then
the solvent was evaporated. The residue was extracted with CH2Cl2
and washed with water. The organic layer was dried over Na2SO4
and the solvent evaporated. Chromatography over silica gel (1:1
CH2Cl2/PE) gave the complex 6 as an orange powder in 33% yield.
Mp = 165 °C(dec); 1H NMR (200 MHz; CDCl3) 1.75 (m, 8H) ; 2.35
(m, 8H); 2.85 (t, J = 7.0 Hz, 8H); 7.30–7.50 (m, 40H); 31P NMR
4.2. Synthesis and characterization
4.2.1. 2,3,6,7-Tetrakis[4-(boronatodiphenylphosphino)alkylthio]
tetrathiafulvalene 4 and 5
To
a solution of tetrakiscyanoethylthio-TTF 3 (400 mg,
0.73 mmol) in 20 mL of DMF was added under argon a solution
of Cs2CO3, H2O (410 mg, 2.4 mmol). The mixture was allowed to
stir for 3 h at 70 °C after which, 3-iodopropyldiphenylphosphine-
borane (1 g, 3.65 mmol) for 4 or 4-bromobutyldiphenylphos-
phine-borane (1.2 g, 3.6 mmol) for 5 was added. The mixture was
stirred for 12 h and then the solvents were evaporated. The residue
was extracted with CH2Cl2 and washed with water. The organic
layer was dried over Na2SO4 and evaporated. Chromatography over
silica gel (4:1 CH2Cl2/PE) afforded 4 (690 mg, 73%) as an orange
powder or 5 as an orange thick oil (670 mg, 68%).
(121 MHz; CDCl3) d 8.0 (J1 = 231 Hz); IR (cmÀ1
)mC=O 1872, 1884,
PW
1907, 2013; HRMS: Calc. for C74H64O8P4S8W2: 1828.0337. Found:
1828.0280.
4.3. Crystallography
Single-crystal diffraction data were collected on Nonius Kap-
paCCD diffractometer (Centre de Diffractométrie X, Université de
Rennes, France). Details of the crystallographic are given in Table 3.
TTF 4 mp 82 °C; 1H NMR (200 MHz, CDCl3) d 0.2–1.8 (m, 12H);
1.85 (m, 8H); 2.30 (m, 8H); 2.90 (t, J = 7.1 Hz, 8H); 7.30–7.70 (m,
40H); 31P NMR (121 MHz, CDCl3)
d 15.9; HRMS: Calc. for
Appendix A. Supplementary material
C66H76B4P4S8 1292.3036. Found 1292.3046.
TTF 5 1H NMR (200 MHz, CDCl3) d 0.2–1.6 (m, 12H); 1.65 (m,
16H); 2.15 (m, 8H); 2.75 (t, J = 7.1 Hz, 8H); 7.30–7.80 (m, 40H);
31P NMR (121 MHz; CDCl3) d 15.8; HRMS: Calc. for C70H84B4P4S8
1348.3700. Found 1348.3724.
CCDC 723837 contains the supplementary crystallographic
data for complex 6. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.04.006.
4.2.2. 2,3,6,7-Tetrakis[3-diphenylphosphinoalkylthio]tetrathiafulvale-
ne 1 and 2
This procedure was realized in order to characterize by 1H and
31P NMR the TTF 1 and 2. The typical procedure is as followed. To a
solution of TTF 4 or 5 (0.1 mmol) in 10 ml of dried, degassed tolu-
ene was added under argon DABCO (0.4 mmol). The mixture was
stirred for 4 h at 50 °C after which the solution was filtered through
a silica gel column under inert atmosphere using dry and degassed
toluene as eluent. TTF 1 1H NMR (200 MHz; CDCl3) d 1.75 (m, 8H);
2.32 (m, 8H); 2.80 (t, J = 7.1 Hz, 8H); 7.30–7.70 (m, 40H); 31P NMR
(121 MHz; CDCl3) d À16.7. TTF 2 1H NMR (200 MHz; CDCl3) d 1.55
(m, 8H); 1.72 (m, 8H); 2.08 (m, 8H); 2.80 (t, J = 7.0 Hz, 8H); 7.20–
7.50 (m, 40H); 31P NMR (121 MHz; CDCl3) d À16.4.
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