Complexing ability of the versatile, redox-active, 3-[3-(diphenylphosphino)propylthio]-3′,4,4′-trimethyl- tetrathiafulvalene ligand

Article abstract of DOI:10.1021/ic026186f

The synthesis of a ligand containing as an electroactive core a tetrathiafulvalene moiety, 3-[3-(diphenylphosphino)- propylthio]-3′,4,4′-trimethyl-tetrathiafulvalene, is reported. Its versatile ability to act as a bidentate or a monodentate ligand, as demonstrated by the metal carbonyl complexes obtained, is described. The novel cis-Mo(CO)₄(P-TTF)₂ 4 and cis-W(CO)₄(P,S-TTF) 6 complexes have been characterized by X-ray diffraction analyses and cyclic voltammetry measurements. Within complex 4, no significant influence of the two electroactive ligands on the molybdenum center was detected, whereas, in complex 6, a weak influence of the TTF redox-active core can be observed on the redox behavior of the metal center.

Full text of DOI:10.1021/ic026186f

Inorg. Chem. 2003, 42, 2056−2060
Complexing Ability of the Versatile, Redox-Active,
3-[3-(Diphenylphosphino)propylthio]-3′,4,4′-trimethyl-tetrathiafulvalene
Ligand
Pascal Pellon, Gre´gory Gachot, Je´rome Le Bris, Ste´phane Marchin, Roger Carlier, and
Dominique Lorcy*
Synthe`se et Electrosynthe`se Organiques, UMR CNRS 6510, UniVersite´ de Rennes 1,
campus de Beaulieu, 35042 Rennes cedex, France
Received November 18, 2002
The synthesis of a ligand containing as an electroactive core a tetrathiafulvalene moiety, 3-[3-(diphenylphosphino)-
propylthio]-3′,4,4′-trimethyl-tetrathiafulvalene, is reported. Its versatile ability to act as a bidentate or a monodentate
ligand, as demonstrated by the metal carbonyl complexes obtained, is described. The novel cis-Mo(CO)4(P-TTF)2
4 and cis-W(CO)4(P,S-TTF) 6 complexes have been characterized by X-ray diffraction analyses and cyclic voltammetry
measurements. Within complex 4, no significant influence of the two electroactive ligands on the molybdenum
center was detected, whereas, in complex 6, a weak influence of the TTF redox-active core can be observed on
the redox behavior of the metal center.
Introduction
synthesis of phosphino ligands containing TTF where the
phosphorus atom is connected to the donor core through a
flexible propylthio spacer group.11 Complexes with such
ligands have not yet been described probably owing to the
presence of a mixture of two isomers (Z/E) in these bis-
functionalized TTFs. Herein we report the synthesis of a
single-substituted ligand containing the redox-active TTF
moiety together with its metal carbonyl complexes with the
Mo(CO)4 and W(CO)4 fragments. The structural and electro-
chemical properties of these complexes are also presented.
Coordination of metals by electroactive ligands containing
tetrathiafulvalene (TTF) moieties has recently attracted
attention due to the potential applications of these novel
organic-inorganic hybrid building blocks.1-7 Association of
the TTFs to the metal can be realized through an intervening
coordination function such as phosphine substituents well-
known for their chelating ability toward various transition
metal derivatives.2-6 So far, the few examples of complexes
with TTF-functionalized phosphine ligands described have
involved the diphenylphosphino substituents (PPh2) directly
linked to the donor core.2-6,8-10 We recently described the
Experimental Section
1H NMR and 13C NMR spectra were recorded on Bruker ARX
200 or Bruker AC 300P spectrometers. Chemical shifts are reported
in parts per million referenced to TMS for 1H NMR and 13C NMR
and to H3PO4 for 31P NMR. Melting points were measured using
a Kofler hot stage apparatus. Elemental analyses results were
obtained from the Laboratoire Central de Microanalyse du CNRS,
Lyon. Mass spectra were recorded with a ZABSpec TOF instrument
by the Centre Re´gional de Mesures Physiques de l’Ouest, Rennes.
Tetrahydrofuran was distilled from sodium-benzophenone. Metha-
nol was distilled from calcium. Toluene was dried over sodium
wire. Chromatography was performed using silica gel Merck 60
(70-260 mesh). Mo(CO)6 and 1,4-diazabicyclo[2.2.2]octane (DAB-
CO) were purchased from ACROS organics. W(CO)6 was pur-
* Author to whom correspondence should be addressed. E-mail:
dominique.Lorcy@univ-rennes1.fr.
(1) Tanaka, H.; Okano, Y.; Kobayashi, H.; Susuki, W.; Kobayashi, A.
Science 2001, 291, 285 and references cited therein.
(2) Fourmigue´, M.; Batail, P. Bull. Soc. Chim. Fr. 1992, 129, 29.
(3) Fourmigue´, M.; Uzelmeier, C. E.; Boubekeur, K.; Bartley, S. L.;
Dunbar, K. R. J. Organomet. Chem. 1997, 529, 343.
(4) Uzelmeier, C. E.; Bartley, S. L.; Fourmigue´, M.; Rogers, R.;
Grandinetti, G.; Dunbar, K. R. Inorg. Chem. 1998, 37, 6706.
(5) Smucker, B. W.; Dunbar, K. R. J. Chem. Soc., Dalton Trans. 2000,
1309.
(6) Cerrada, E.; Diaz, C.; Diaz, M. C.; Hursthouse, M. B.; Laguna, M.;
Light, M. E. J. Chem. Soc., Dalton Trans. 2002, 1104.
(7) Iwashori, F.; Gohlen, S.; Ouahab, L.; Carlier, R.; Sutter, J. P. Inorg.
Chem. 2001, 40, 6541.
(8) Fourmigue´, M.; Batail, P. J. Chem. Soc., Chem. Commun. 1991, 1370.
(9) Fourmigue´, M.; Huang, Y. S. Organometallics 1993, 12, 797.
(10) Gerson, F.; Lampretch, A.; Fourmigue´, M. J. Chem. Soc., Perkin Trans.
2 1996, 1.
(11) Pellon, P.; Brule´, E.; Bellec, N.; Chamontin, K.; Lorcy, D. J. Chem.
Soc., Perkin. Trans. 1 2000, 4409.
2056 Inorganic Chemistry, Vol. 42, No. 6, 2003
10.1021/ic026186f CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/14/2003

A Redox-ActiWe Substituted TetrathiafulWalene Ligand
Scheme 1
chased from Aldrich. M(CO)4(NHC5H10)2 were prepared from
M(CO)6 according to a published procedure.12 Cyclic voltammetry
was carried out on a 10-3 M solution of TTF derivatives in
dichloromethane, containing 1 M NBu4PF6 as the supporting
electrolyte. Voltammograms were recorded at 0.1 V s-1 at a
platinum disk electrode (A ) 1 mm2). The potentials were measured
versus a saturated calomel electrode. Single-crystal diffraction data
were collected on a Kappa diffractometer equipped with a CCD
detector from the Centre de Diffractome´trie X, Universite´ de Rennes
1, France.
3-[3-(Boranatodiphenylphosphino)propylthio]-3′,4,4′-trimethyl-
TTF 2. To a solution of cyanoethylthiotrimethyl-TTF 1 (800 mg,
2.4 mmol) in 20 mL of DMF was added under argon a solution of
CsOH and H2O (410 mg, 2.4 mmol) in 5 mL of MeOH. The mixture
was allowed to stir for 30 min at rt, after which 3-chloropropyl-
diphenylphosphine-borane (670 mg, 2.4 mmol) 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. Chro-
matography over silica gel (4:1 CH2Cl2/PE) afforded 2 (692 mg,
56%) as an orange powder. Mp: 162 °C. δH (200 MHz; CDCl3):
0.60-1.50 (m, 3H); 1.87 (m, 2H); 1.96 (s, 6H); 2.08 (s, 3H); 2.33
(m, 2H); 2.80 (t, 2H); 7.30-7.82 (m, 10H). δP (121 MHz;
CDCl3): 16.6. δC (75 MHz; CDCl3): 13.9, 15.8, 23.7, 24.9, 38.0,
118.9, 123.2, 128.9, 129.2, 129.4, 130.0, 131.7, 132.4, 132.6, 136.2.
Anal. Calcd for C24H28BPS5: C, 55.59; H, 5.44; S, 30.91. Found:
C, 55.19; H, 5.20; S, 31.08.
3-[3-(Diphenylphosphino)propylthio]-3′,4,4′-trimethyl-TTF 3.
To a solution of TTF 2 (519 mg, 1 mmol) in 30 mL of dried,
degassed toluene was added under argon DABCO (112 mg, 1
mmol). The mixture was stirred for about 4 h at 50 °C. The reaction
was followed by TLC. The solution was filtrated through a silica
gel column with degassed toluene. Toluene was evaporated with a
vacuum pump to afford TTF 3 (394 mg, 78%) as an orange powder.
Mp: 93 °C. δH (200 MHz; CDCl3): 1.72 (m, 2H); 1.94 (s, 6H);
2.03 (s, 3H); 2.12 (m, 2H); 2.80 (t, 2H); 7.30-7.55 (m, 10H). δP
(121 MHz; CDCl3): -16.4. δC (75 MHz; CDCl3) 13.8, 15.4, 26.2,
26.9, 37.1, 106.0, 110.2, 119.0, 122.8, 128.5, 128.6, 132.6, 132.8,
135.2, 138.3.
cis-Mo(CO)4(P-TTF)2 4. To a solution of the TTF 2 (519 mg,
1 mmol) in 10 mL of dried, degassed toluene was added under
argon DABCO (112 mg, 1 mmol). The mixture was stirred for 4 h
at 50 °C, after which the Mo(CO)4(NHC5H10)2 (0.5 mmol, 188 mg)
in 10 mL of degassed CH2Cl2 was added and stirring was continued
for 15 min. Solvent was removed, and the residue was extracted
with CH2Cl2 and washed with water. Chromatography over silica
gel (4:1 CH2Cl2/PE) afforded the complex 4 (243 mg, 20%) as an
orange powder. δH (200 MHz; CDCl3): 1.37 (m, 4H); 1.91 (s, 12H);
1.96 (s, 6H); 1.98 (m, 4H); 2.47 (t, 4H); 7.25-7.40 (m, 20H). δP
(121 MHz; CDCl3): 26.6. Found: M+•, 1217.9453. HRMS: calcd
for C52H50MoO4P2S10 1217.9446, found 1217.9453. Anal. Calcd
for C52H50MoO4P2S10: C, 51.3; H, 4.14; S, 24.88; P, 5.08. Found:
C, 51.7; H, 4.37; S, 24.84; P, 4.92.
cis-W(CO)4(NHC5H10)(P-TTF) 5. To a solution of TTF 2 (519
mg, 1 mmol) in 10 mL of dried, degassed toluene was added under
argon DABCO (112 mg, 1 mmol). The mixture was stirred for 4 h
at 50 °C, after which the W(CO)4(NHC5H10)2 (464 mg, 1 mmol)
in 10 mL of degassed CH2Cl2 was added. Stirring was continued
for 15 min, and the solvent was evaporated. The residue was
extracted with CH2Cl2 and washed with water. The organic layer
was dried over Na2SO4, and evaporation of the solvent gave the
complex 5 as an orange powder. δH (200 MHz; CDCl3): 1.58 (m,
4H); 1.70 (m, 2H); 1.88 (m, 2H); 1.96 (s, 6H); 2.03 (s, 3H); 2.12
(m, 2H); 2.68 (m, 4H); 2.78 (m, 2H); 2.86 (br, 1H); 7.18-7.63
(m, 10H). δP (121 MHz; CDCl3): 22.0. HRMS: calcd for C33H36-
NO4PS5W 885.0487, found 885.0491.
cis-W(CO)4(P,S-TTF) 6. To a solution of TTF 2 (519 mg, 1
mmol) in 10 mL of dried, degassed toluene was added DABCO
(112 mg, 1 mmol) under argon. The mixture was stirred for 4 h at
50 °C, after which the W(CO)4(NHC5H10)2 (464 mg, 1 mmol) in
10 mL of degassed CH2Cl2 was added. The reaction mixture was
stirred for 15 min, and the solvent was removed under reduced
pressure. The residue was extracted with CH2Cl2, washed with
water, and dried over Na2SO4. The residue was chromatographed
over silica gel (4:1 CH2Cl2/PE) and afforded the complex 6 (648
mg, 81%) as an orange powder. Mp: 180 °C. δH (200 MHz;
CDCl3): 1.92 (s, 6H); 2.05 (m, 2H); 2.16 (s, 3H); 2.56 (m, 2H);
3.22 (m, 2H); 7.20-7.60 (m, 10H). δP (121 MHz; CDCl3): 2.4.
δC (75 MHz; CDCl3): 13.8, 15.3, 23.1, 29.9, 43.3, 104.0, 113.9,
122.7, 122.9, 128.6, 130.1, 132.1, 134.9, 135.8, 136.3, 202.4.
HRMS: calcd for C28H25O4PS5W, 799.9604, found, 799.9598.
Results and Discussion
The new ligand was prepared from the preformed TTF
derivative 1 according to the chemical pathway described
in Scheme 1.13 This was realized in order to avoid the
presence of two TTF isomers (Z/E) as it was the case in our
previously published phosphino ligands containing tetrathia-
fulvalene (TTF).11 The cyanoethyl thiolate protecting group,
an efficient building block for the preparation of a wide range
of TTF derivatives,14 was cleaved with cesium hydroxide
and reacted with 3-chloropropyldiphenylphosphine-borane
leading to TTF 2 in good yield. As the other phosphine-
borane complexes, TTF 2 is stable and can be handled under
atmospheric conditions without any particular conditions.15,16
Decomplexation of phosphine borane can be realized using
a soft method, which does not interact with the TTF core,
such as treatment with DABCO under inert atmosphere to
afford TTF 3 in good yields.17
In order to form metal carbonyl complexes with this
ligand, we realized the synthesis of cis-M(CO)4L2 derivatives
(M ) Mo, W) according to the procedure described by
Darensbourg et al.12 Indeed the use of these disubstituted
metal derivatives with L ) piperidine allows the facile
(13) Bellec, N.; Lorcy, D. Tetrahedron Lett. 2001, 42, 3189.
(14) Simonsen, K. B.; Becher, J. Synlett 1997, 62, 1211 and references
therein.
(15) Pellon, P. Tetrahedron Lett. 1992, 33, 445.
(16) Gourdel, Y.; Ghanimi, A.; Pellon P.; Le Corre, M. Tetrahedron Lett.
1993, 34, 1011.
(17) Brisset, H.; Gourdel, Y.; Pellon, P.; Le Corre, M. Tetrahedron Lett.
1993, 34, 4523.
(12) Darensbourg, D.; Kump, R. L. Inorg. Chem. 1978, 17, 2680.
Inorganic Chemistry, Vol. 42, No. 6, 2003 2057

Pellon et al.
Figure 2. ORTEP view of complex 6 showing the atom labeling (50%
probability ellipsoids). Hydrogen atoms are omitted for clarity. Selected
bond lengths: W1-C2 1.940(6), W1-C4 1.995(5), W1-C1 2.002(6), W1-
C3 2.011(6), W1-P2 2.4959(12), W1-S3 2.5500(15), C11-C12 1.343-
(7), S3-C8 1.764(4), S3-C7 1.823(5).
Figure 1. ORTEP view of complex 4 showing the atom labeling (50%
probability ellipsoids). Hydrogen atoms are omitted for clarity. Selected
bond lengths: Mo1-C3 1.982(5), Mo1-C1 1.983(5), Mo1-C4 2.020(5),
Mo1-C2 2.046(5), Mo1-P2 2.5472(12), Mo1-P1 2.5535(11), C13-C14
1.345(8), S1-C10 1.771(6), S1-C9 1.829(5).
Scheme 3
Scheme 2
replacement of the two labile piperidino ligands by another
ligand such as the diphenylphosphinopropylthio TTF 3.
Then, to a solution of TTF 3 in CH2Cl2 was added 1 equiv
of cis-Mo(CO)4(piperidine)2, and the mixture was warmed.
labile ligand and replacing it by the thio ether function of
the already coordinated, via the phosphorus atom, TTF 3
inducing the formation of a six-membered metallocyclic ring.
The ORTEP of 6 is given in Figure 2. Within this complex
6 the W-P and S-W distances (W-P, 2.4959(12) Å; S-W,
2.5500(15) Å) are in the usual range with an interligand angle
of S-W-P 84.79(4)°. The 31P NMR spectra reveal a singlet
at (δ 2.4 ppm) at lower field than the signal observed for
the phosphorus atom of TTF 3 itself (δ -16.4 ppm). It is
worth noting that the synthesis of complexes 4 and 6 can be
realized in a one-pot procedure directly from TTF 2, by
performing the borane decomplexation and the addition of
cis-M(CO)4(piperidine)2 directly in the medium where the
TTF 3 was formed affording 4 in low yield (20%) and 6 in
good yield (81%).
1
After 15 min, analysis of the medium by H NMR and 31P
NMR reveals that the two piperidine ligands have been
replaced by two phosphino TTF 3 (Scheme 2). Chromato-
graphic separation of the reaction mixture on silica gel affords
the complex 4 as an orange crystalline solid. X-ray crystal
structure analysis demonstrates that two TTF 3 are indeed
coordinated to the metal center via the phosphorus atom (P-
TTF) and the molybdenum center is surrounded by two cis-
coordinated ligand 3 (Figure 1). Phosphorus-molybdenum
bond lengths are in the usual range (Mo-P1, 2.5472(12) Å;
Mo-P2, 2.5535(11) Å) with a P1-Mo-P2 interligand angle
of 100.26(4)°. One singlet is observed on the 31P NMR
spectra of 4, cis-Mo(CO)4(P-TTF 3)2, at (δ 26.6 ppm)
indicating equivalent phosphorus environments.
Contrariwise following the same experimental procedure
using the tungsten analogue, cis-W(CO)4(piperidine)2, analy-
sis of the medium by 1H NMR reveals that only one
piperidino ligand has been replaced by the phosphino TTF
3 affording the complex 5, cis-W(CO)4(piperidine)(P-TTF
3) (Scheme 3). This was confirmed by mass spectrometry.
Even when adding an excess of TTF 3 in the medium the
result remains unchanged. Actually it was already reported
that substitution of the second piperidino ligand needed more
rigorous conditions than in the corresponding molybdenum
species.12 After chromatography of the crude product on silica
gel column an orange crystalline air stable solid was obtained.
The crystal structure of this complex reveals that the
phosphorus and sulfur atoms (P,S-TTF) of the same ligand
3 are, this time, coordinated to the metal affording the
complex 6, cis-W(CO)4(P,S-TTF 3). Interestingly, the silica
gel is acid enough for displacing the remaining piperidino
Even if the mode of coordination is different, the solid
state packing of these two complexes (i.e., 4 and 6) reveals
alternate layers of organic and inorganic entities with a
distinct organization of the neutral TTF moieties. Within the
molybdenum complex 4 the two TTFs of the complex are
perpendicular to each other, and each TTF of two neighbor-
ing complexes is orthogonal with the shortest S‚‚‚S contact
being equal to 3.6 Å (Figure 3). Contrariwise with the
tungsten complex the organic parts form segregated stacks
with a crisscross overlap of one dithiole ring of the TTFs,
while the inorganic part forms also segregated stacks, the
shortest S‚‚‚S contact between two TTFs being equal to 3.7
Å (Figure 4).
The effect of ligand environment, especially of the TTF
core, on the redox properties of the bound metal ion was
studied by cyclic voltammetry. For that purpose we prepared
the metal carbonyl complexes Mo(CO)4(PPh3)2 and W(CO)4-
(PPh3)2. Furthermore, to analyze more precisely the influence
2058 Inorganic Chemistry, Vol. 42, No. 6, 2003

A Redox-ActiWe Substituted TetrathiafulWalene Ligand
Scheme 4
Table 1. Oxidation Peak Potentials in V vs SCE in CH2Cl2, Pt
Working Electrode, NBu4PF6
1
2
Epa1/Epc
Epa2/Epc
∆E(Epa2 - Epa1), mV
Mo(CO)4(PPh3)2
W(CO)4(PPh3)2
7
0.85/0.76
0.74a
0. 84a
TTF 2
TTF 3
Mo(CO)4(PTTF)2 4
W(CO)4(P,S TTF) 6
0.35/0.29
0.35/0.29
0.36/0.30
0.38/0.31
0.82/0.76
0.79/0.73
0.87/0.76
0.88/0.73
470
440
510
500
Figure 3. Crystal structure of complex 4 projection viewed along the a
axis.
a Irreversible process.
collected in Table 1 together with the data of TTF 2 and 3
as well as Mo(CO)4(PPh3)2, W(CO)4(PPh3)2, and 7 for
comparison. Complexes Mo(CO)4(PPh3)2, W(CO)4(PPh3)2,
and 7 exhibit one oxidation wave which is not fully reversible
in the case of the molybdenum complex and irreversible for
the tungsten complexes. The lack of reversibility of this
oxidation step is essentially due to the loss of carbonyl
ligands occurring during the process.
Concerning the complex cis-Mo(CO)4(P-TTF)2 4 two
oxidation waves are observed. The first reversible oxidation
step corresponds to the oxidation of the two TTFs in its
radical cations while the second oxidation process is due to
the concomitant oxidation of TTF radical cations into the
dications and the oxidation of the molybdenum center.
However, this process is not fully reversible due to the loss
2
of carbonyl ligands. The reduction wave observed at Epc
)
0.76 V is essentially due to the reduction of the TTF dications
into its radical cations. According to the value of the second
oxidation peak potential (Epa2 ) 0.87 V) and to the oxidation
of Mo(CO)4(PPh3)2 (Epa ) 0. 85 V), no significant influence
of the TTF core on the molybdenum center can be detected.
Similarly the redox behavior of the TTF core, within this
complex, is not influenced by the presence of the molybde-
num center.
The analysis of the redox behavior of W(CO)4(P,S-TTF)
6 indicates also two oxidation processes involving first the
reversible oxidation of the TTF and then the second oxidation
of the TTF together with the metal center. The first oxidation
step is a monoelectronic transfer, and an anodic shift of 30
mV is observed, compared with TTF 2, indicating that weak
interactions might occur between the TTF redox center and
the metal one. Considering the values of the oxidation
potential of 7 (Epa ) 0. 84 V) and the second oxidation peak
Figure 4. Crystal structure of complex 6: (a) projection onto the ac plane
showing the segregated stacks of organic and inorganic entities; (b)
projection onto the ab plane showing the crisscross overlap of the dithiole
moieties.
2
potential of 6 (Epa ) 0.88 V), an anodic shift of 40 mV is
observed for oxidation of the metal center. This confirms
that weak interactions occur between the TTF redox center
and the metal one either through space or through bond
interactions. This result differs from what was observed for
4 where the TTF was coordinated through the phosphorus
atom and a spacer involving four atoms (between the PPh2
and the TTF moieties), while in 6 the coordination through
the sulfur atom brings closer the TTF to the metal center.
of the TTF core in complex 6 we also prepared complex 7
from an analogue P,S bidentate ligand, the diphenyl[3-
(phenylthio)propyl]phospine (Ph2P(CH2)3SPh). Following the
experimental procedure we used for synthesizing complex
6, we reproduced the original P,S-metallocycle ring formation
with W(CO)4(piperidine)2 and obtained 7 (Scheme 4).
Oxidation peak potentials of the complexes 4 and 6 are
Inorganic Chemistry, Vol. 42, No. 6, 2003 2059

Pellon et al.
In summary we have prepared a new redox-active ligand
containing two binding sites through a phosphorus and sulfur
atoms. Depending on the metal used for the formation of
metal carbonyl complexes with this novel ligand, it acts either
as a monodentate (P) ligand or as a bidentate (P,S) ligand.
A weak influence of the TTF redox-active core on the redox
behavior of the metal center can be observed in the case of
the P,S coordination which brings nearer the TTF to the
metal. It will be of interest to study the chemical or
electrochemical oxidation of these complexes and to analyze
the influence of the organometallic fragments toward the
organization of the TTF radical cation moieties in the solid
state.
Acknowledgment. The authors are indebted to Thierry
Roisnel from the Centre de Diffractome´trie X, Universite´
de Rennes 1, for X-ray structural determinations and to Dr.
N. Bellec for useful discussions.
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes 4 and 6. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC026186F
2060 Inorganic Chemistry, Vol. 42, No. 6, 2003