Structural and electrochemical study of metal carbonyl complexes with chelating bis- and tetrakis(diphenylphosphino)tetrathiafulvalenes

Article abstract of DOI:10.1016/S0022-328X(01)01249-9

Several mono- and bimetallic complexes involving organometallic fragments such as M(CO)₄ (M = Mo, W), Re(CO)₃Cl and Fe(CO)₃ coordinated to the chelating diphosphine 3,4-dimethyl-3′,4′-bis(diphenylphosphino)tetrathiafulvalene (P2) or tetraphosphine tetrakis(diphenylphosphino)tetrathiafulvalene (P4) have been synthesized and characterized. X-ray diffraction structures have been determined for P4[W(CO)₄]₂, P2Re(CO)₃Cl, P2Fe(CO)₃ and P4[Fe(CO)₃]₂. Octahedral geometrics around the metallic center are observed for the tungsten and rhenium complexes, with a fac arrangement of the ligands for the latter, whereas slightly distorted trigonal bipyramid are found for both iron counter parts. Although the complexes are more difficult to oxidize than the corresponding free phosphines, as evidenced by cyclic voltammetry measurements, the first oxidation potentials remain in the usual range, thus offering the opportunity to generate stable radical cation salts. In the case of Fe complexes, the first oxidation wave corresponds to the formation of paramagnetic d⁷ Fe(I) species, whereas in the Mo, W and Re complexes the metallic center is much more difficult to oxidize than the TTF core.

Full text of DOI:10.1016/S0022-328X(01)01249-9

Journal of Organometallic Chemistry 643–644 (2002) 292–300
www.elsevier.com/locate/jorganchem
Structural and electrochemical study of metal carbonyl complexes
with chelating bis- and
tetrakis(diphenylphosphino)tetrathiafulvalenes
Narcis Avarvari, David Martin, Marc Fourmigue´ *
‘Sciences Mole´culaires aux Interfaces’, CNRS FRE 2068, Institut Jean Rouxel, 2, rue de la Houssinie`re, BP32229,
44322 Nantes Cedex 3, France
Received 10 July 2001; accepted 11 September 2001
Dedicated to Professor Franc¸ois Mathey on the occasion of his 60th birthday
Abstract
Several mono- and bimetallic complexes involving organometallic fragments such as M(CO)4 (M=Mo, W), Re(CO)3Cl and
Fe(CO)3 coordinated to the chelating diphosphine 3,4-dimethyl-3%,4%-bis(diphenylphosphino)tetrathiafulvalene (P2) or tetraphos-
phine tetrakis(diphenylphosphino)tetrathiafulvalene (P4) have been synthesized and characterized. X-ray diffraction structures
have been determined for P4[W(CO)4]2, P2Re(CO)3Cl, P2Fe(CO)3 and P4[Fe(CO)3]2. Octahedral geometries around the metallic
center are observed for the tungsten and rhenium complexes, with a fac arrangement of the ligands for the latter, whereas slightly
distorted trigonal bipyramid are found for both iron counter parts. Although the complexes are more difficult to oxidize than the
corresponding free phosphines, as evidenced by cyclic voltammetry measurements, the first oxidation potentials remain in the
usual range, thus offering the opportunity to generate stable radical cation salts. In the case of Fe complexes, the first oxidation
wave corresponds to the formation of paramagnetic d7 Fe(I) species, whereas in the Mo, W and Re complexes the metallic center
is much more difficult to oxidize than the TTF core. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Tetrathiafulvalene; Phosphines; Metal carbonyl complexes; Crystal structures; Electrochemistry
1. Introduction
[5] or tetrakis(diphenylphosphino)tetrathiafulvalene
(hereafter P4) [6], or by the insertion of a spacer
between the PPh2 and the TTF moieties [7].
Chelating diphosphines such as bis(diphenylphos-
phino)methane (dppm) or bis(diphenylphosphino)-
ethane (dppe) are well known for the stabilization of
metal complexes in various oxidation states [1,2]. Their
derivatization with redox active molecules such as fer-
rocene [3] or tetrathiafulvalene opens new routes to-
ward the elaboration of hybrid molecules associating
open-shell species of organic and inorganic character.
Along these lines, several tetrathiafulvalenyl phosphines
have already been described [4], either by functionaliza-
tion of the TTF p-redox core by one, two or four
diphenylphosphino moieties, as in 3,4-dimethyl-3%,4%-
bis(diphenylphosphino)tetrathiafulvalene (hereafter P2)
In this paper, we investigate the coordination chem-
istry of these di- and tetraphosphines with Groups
VI–VIII transition metal carbonyl fragments. The com-
plexes of P2 and P4 with the organometallic fragments
Mo(CO)4, W(CO)4, Re(CO)3Cl and Fe(CO)3 will be
described as well as their structural and electrochemical
properties. Of specific interest are the relative redox
potentials of these hybrid molecules where both the
TTF p-redox core and the metal fragment are suscepti-
ble to oxidation to open-shell species.
* Corresponding author. Tel.: +33-240-373915; fax: +33-240-
373995.
E-mail address: fourmigue@cnrs-imn.fr (M. Fourmigue´).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01249-9

N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
293
2. Results and discussion
three absorption bands in the carbonyl region, a signa-
ture of a fac isomer while only two bands are usually
encountered with the mer isomer [10]. This stereochem-
istry is further substantiated by the presence of a single
peak in the 31P-NMR spectrum and by its X-ray crystal
structure (see below). Similarly, the iron complex
[P2][Fe(CO)3] exhibits, as expected, an unique reso-
nance in 31P-NMR. The carbonyl carbon atoms res-
onate as a triplet in 13C-NMR, thus proving their
equivalence in solution, at the NMR time scale. The
flexibility of the coordination sphere around a pentaco-
ordinated iron center is a well-known phenomenon [11]
relying on the easy interconversion between a trigonal
bipyramidal geometry and a square planar pyramidal
one. Infrared spectrum shows the three characteristic
bands of a L2Fe(CO)3 complex type, where L2 is a
chelating ligand [12]. A single crystal X-ray measure-
ment, discussed below, definitely proved the structure
of the complex in solid state.
As their P2 counter parts, the bimetallic complexes
[P4][Mo(CO)4]2 and [P4][W(CO)4]2 show also the four
IR absorptions characteristic of a tetracarbonyl unit
with a cis arrangement of phosphines and wavelengths
very close to those of the corresponding monometallic
complexes. The bimetallic complex [P4][W(CO)4]2 was
also characterized by X-ray diffraction. On the other
hand, four bands were observed in the IR spectrum of
[P4][Re(CO)3Cl]2. Together with the observation of two
peaks in 31P-NMR (see Section 4), these results indicate
that two diastereoisomers were formed simultaneously
in the case of this bimetallic complex. This is not
surprising, since one can expect the chlorine ligands to
adopt both cis and trans positions relative to the TTF
plane in a bis( fac) arrangement around the two metal-
lic centers. On the other hand, the bimetallic iron
complex [P4][Fe(CO)3]2 presents only one isomer in
solution, as attested by 31P- and 13C-NMR spectra. The
infrared spectrum, measured in KBr, shows three ab-
sorption bands, as in the P2 counter part. An X-ray
diffraction experiment allowed us to characterize the
bimetallic complex in solid state.
2.1. Synthesis and characterizations
The complexes were obtained in good yields as or-
ange–red crystalline air-stable solids upon reaction of
P2 or P4 with, respectively, one or two equivalents of
the desired metallic precursors, i.e. cis-[M(CO)4-
(piperidine)2] (M=Mo, W), Re(CO)5Cl and Fe2(CO)9
(Scheme 1). Both monometallic [P2][Mo(CO)4] and
[P2][W(CO)4] complexes show the four absorptions
characteristic of a tetracarbonyl unit with a cis arrange-
ment of phosphines in the IR spectrum [8], while 31P-
NMR spectra display a singlet indicative of equivalent
phosphorus environments. In all the complexes studied
the phosphorus atoms resonate at lower field than the
free phosphines in 31P-NMR, which is a general ten-
dency within this class of compounds [9]. In 13C-NMR
spectrum of [P2][W(CO)4], we can clearly observe the
resonance of two different types of CO, the axial and
the equatorial ones, with the corresponding coupling
constants. This observation proves the rigidity in solu-
tion of the coordination sphere of the tungsten center.
The corresponding [P2][Re(CO)3Cl] complex exhibits
2.2. X-ray structures
Scheme 1.
[P4][W(CO)4]2 crystallizes as a toluene solvate in the
monoclinic system, space group P21/c, with one
molecule located on the inversion center, one toluene
molecule disordered on an inversion center and one
toluene molecule in general position in the unit cell.
Bond lengths within the coordination sphere of the W
atom (Table 1) are in the usual range as are the bond
lengths within the TTF core. An ORTEP view with
partial numbering scheme is given in Fig. 1. The metal–
carbon bonds trans to phosphorus are slightly shorter
Table 1
Selected bond lengths and bond angles in [P4][W(CO)4]2[toluene]3
Bond lengths
W(1)ꢀP(1)
W(1)ꢀP(2)
W(1)ꢀC(1)
W(1)ꢀC(2)
W(1)ꢀC(3)
2.4872(8)
2.4749(7)
1.993(3)
2.033(3)
2.023(3)
W(1)ꢀC(4)
C(1)ꢀO(1)
C(2)ꢀO(2)
C(3)ꢀO(3)
C(4)ꢀO(4)
1.988(3)
1.153(4)
1.141(4)
1.145(4)
1.151(4)
Bond angles
P(1)ꢀW(1)ꢀP(2)
,
than those of cis, the average difference being 0.038 A.
79.97(2)
The dithiole rings are not folded along the S···S hinge

294
N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
[P2][Re(CO)3Cl] crystallizes in the orthorhombic sys-
tem, space group Pna21, with two crystallographically
independent and two toluene molecules in the unit cell
(Fig. 3). Both molecules are almost identical and ap-
pear to correspond to each other through a pseudo-in-
version center while the toluene molecules do not. Bond
lengths and angles in the coordination sphere of the Re
atom are collected in Table 2. The structure reveals a
facial arrangement for the carbonyl groups consistent
with the structural assignment from IR studies [16]. The
metallacycle is folded by 23.2(4)° along the P···P hinge
while the TTF core is also affected since the dithiole
ring bearing the two diphenylphosphino groups is
folded by 24(1)° along the S···S hinge. This folding of
the dithiole ring has been often observed in several P2
and P4 complexes [6,17] and illustrates the flexibility of
the TTF core.
Fig. 1. ORTEP view of the bimetallic complex [P4][W(CO)4]2.
Suitable X-ray diffraction crystals of [P2][Fe(CO)3]
were obtained by recrystallization in hexane. The struc-
ture was solved in the orthorhombic system, space
group Pbca, with two crystallographically independent
molecules and one molecule of hexane located on an
inversion center. Thus, the complex crystallized as a
solvate with one molecule of hexane to four molecules
of complex. The solvent is located in the structure
between the planes defined by the donors. No short
intermolecular van der Waals S···S contacts are ob-
served within these planes. Bond lengths and angles in
the coordination sphere of Fe are listed in Table 3. An
ORTEP representation of one (Fe1) of the two indepen-
dent molecules of complex is shown in Fig. 4. The
coordination geometry around the metallic center is of
distorted trigonal bipyramid (tbp) type, with the
diphosphine occupying one axial and one equatorial
Fig. 2. Side view of [P4][W(CO)4]2 showing the folding of the
metallacycle along the P···P hinge.
Fig. 3. ORTEP view of [P2][Re(CO)3Cl]. The phenyl rings have been
omitted for clarity.
Table 2
Selected bond distances and bond angles in [P2][Re(CO)3Cl][toluene]
Bond lengths
Re(1A)ꢀP(1A)
Re(1A)ꢀP(2A)
Re(1A)ꢀCl(1A)
Re(1A)ꢀC(1A)
Re(1A)ꢀC(2A)
Re(1A)ꢀC(3A)
C(1A)ꢀO(1A)
C(2A)ꢀO(2A)
C(3A)ꢀO(3A)
2.459(4) Re(1B)ꢀP(1B)
2.455(4) Re(1B)ꢀP(2B)
2.502(4) Re(1B)ꢀCl(1B)
2.451(4)
2.447(4)
2.492(4)
1.97(2)
1.89(2)
1.83(2)
1.16(2)
1.21(2)
1.21(2)
Table 3
1.93(2)
1.89(2)
1.80(2)
1.12(2)
1.21(2)
1.21(2)
Re(1B)ꢀC(1B)
Re(1B)ꢀC(2B)
Re(1B)ꢀC(3B)
C(1B)ꢀO(1B)
C(2B)ꢀO(2B)
C(3B)ꢀO(3B)
Selected bond distances and bond angles in [P2][Fe(CO)3][hexane]1/4
Bond lengths
Fe(1)ꢀC(33)
Fe(1)ꢀC(34)
Fe(1)ꢀC(35)
Fe(1)ꢀP(1)
Fe(1)ꢀP(2)
C(33)ꢀO(1)
C(34)ꢀO(2)
C(35)ꢀO(3)
1.757(6)
1.752(6)
1.756(5)
2.213(1)
2.184(1)
1.158(5)
1.158(5)
1.145(4)
Fe(2)ꢀC(68)
Fe(2)ꢀC(69)
Fe(2)ꢀC(70)
Fe(2)ꢀP(3)
Fe(2)ꢀP(4)
C(68)ꢀO(4)
C(69)ꢀO(5)
C(70)ꢀO(6)
1.749(6)
1.737(6)
1.746(6)
2.195(1)
2.215(1)
1.153(6)
1.161(5)
1.154(5)
Bond angles
P(1A)ꢀRe(1A)ꢀP(2A) 80.89(12) P(1B)ꢀRe(1B)ꢀP(2B) 81.00(12)
while the metallacycles C2P2W are folded by 17.37(8)°,
as already observed in the few W(CO)4 complexes with
conjugated chelating diphosphines such as the tetrakis-
(diphenylphosphino)benzene-bis(tetracarbonyltungsten)
complex [13]. In Fig. 2 we present a side view of the
molecule, allowing the easy observation of this distor-
tion. A similar folding (15–17°) is also found in the
corresponding molybdenum complex [13] as well as in
monometallic complexes with 1,2-bis(diphenylphos-
phino)ethylene [14] or 1,2-bis(diphenylphosphino)-
propene [15].
Bond angles
C(33)ꢀFe(1)ꢀC(34) 122.3(2)
C(68)ꢀFe(2)ꢀC(69)
C(68)ꢀFe(2)ꢀC(70)
C(69)ꢀFe(2)ꢀC(70) 115.2(2)
89.3(3)
95.6(3)
C(33)ꢀFe(1)ꢀC(35)
C(34)ꢀFe(1)ꢀC(35)
C(33)ꢀFe(1)ꢀP(1)
C(34)ꢀFe(1)ꢀP(1)
C(35)ꢀFe(1)ꢀP(1)
C(33)ꢀFe(1)ꢀP(2)
C(34)ꢀFe(1)ꢀP(2)
C(35)ꢀFe(1)ꢀP(2)
P(1)ꢀFe(1)ꢀP(2)
93.6(2)
90.0(2)
91.71(15) C(68)ꢀFe(2)ꢀP(3)
89.06(15) C(69)ꢀFe(2)ꢀP(3)
174.29(16) C(70)ꢀFe(2)ꢀP(3)
106.21(16) C(68)ꢀFe(2)ꢀP(4)
131.36(18) C(69)ꢀFe(2)ꢀP(4)
90.08(16) C(70)ꢀFe(2)ꢀP(4)
85.01(17)
130.90(18)
113.86(18)
170.37(17)
94.15(19)
91.06(17)
85.95(4)
86.32(4)
P(3)ꢀFe(2)ꢀP(4)

N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
295
influence of the complexation on the TTF core. A much
larger difference between the two independent
molecules Fe1 and Fe2 can be observed when taking
into account the second distortion. Indeed, values of
21.1(1)° (Fe1) and 10.2(1)° (Fe2) for the folding angles
along the P···P hinge support this difference and sug-
gest a certain flexibility of the five-membered ring
metallacycle. Finally we note that the axial FeꢀP bonds
Fig. 4. ORTEP view of [P2][Fe(CO)3]. The phenyl rings have been
omitted for clarity.
,
are slightly longer than the equatorial ones by 0.03 A
Table 4
,
(Fe1) and 0.02 A (Fe2), likely because of the weaker
Selected bond distances and bond angles in [P4][Fe(CO)3]2
p-retrodonation due to the axial CO. All the other
structural parameters are in the usual range and deserve
no special comments.
Bond lengths
FeꢀC(28)
FeꢀC(29)
FeꢀC(30)
FeꢀP(1)
1.771(3)
1.775(4)
1.773(4)
2.193(1)
FeꢀP(2)
2.214(1)
1.140(3)
1.153(4)
1.153(4)
In the case of bimetallic [P4][Fe(CO)3]2 we could
obtain suitable X-ray diffraction crystals by recrystal-
lization in acetonitrile or in toluene. We discuss here-
after only the structure of the complex recrystallized in
acetonitrile, whose quality is somewhat better than the
other one, in which disordered molecules of toluene are
present. Thus, the complex crystallizes in the triclinic
C(28)ꢀO(1)
C(29)ꢀO(2)
C(30)ꢀO(3)
Bond angles
C(28)ꢀFeꢀC(29)
C(28)ꢀFeꢀC(30)
C(29)ꢀFeꢀC(30)
C(28)ꢀFeꢀP(1)
C(29)ꢀFeꢀP(1)
91.01(15)
91.46(14)
119.77(15)
88.95(10)
119.39(11)
C(30)ꢀFeꢀP(1)
C(28)ꢀFeꢀP(2)
C(29)ꢀFeꢀP(2)
C(30)ꢀFeꢀP(2)
P(1)ꢀFeꢀP(2)
120.83(11)
175.58(9)
90.25(10)
91.59(9)
(
system, space group P1, with one independent molecule
86.74(4)
located on the inversion center. Bond lengths and an-
gles, among which those concerning the coordination
sphere of Fe are listed in Table 4, are in the usual
range. An ORTEP view of the molecular structure is
presented in Fig. 5. The TTF core is slightly distorted,
the folding angle along the S···S axis being 5.9(3)°. A
drastic decrease, down to 2.0(1)°, is observed for the
folding angle about the P···P axis, when comparing
with the monometallic complex described above. This
leads to an almost planar five-membered ring metalla-
cycle. The coordination geometry around the iron cen-
ter is almost a perfect trigonal bipyramid, since ~
amounts 0.91 (see above), with an axial and an equato-
rial phosphine. On the contrary, in the bimetallic com-
Fig. 5. ORTEP view of the bimetallic complex [P4][Fe(CO)3]2. The
phenyl rings have been omitted for clarity.
site. This situation is usually encountered within other
unsaturated cis diphosphine Fe(CO)3 complexes [18]. In
order to distinguish between the two possible limit cases
of a pentacoordinated iron center, one can simply apply
the ~ test [19], where ~=(h−i)/60. The parameters h
and i represent the largest angle and second largest
angle, respectively, around the metallic center. The
value of ~ ranges from 0, for a perfect square pyramid,
to 1 for a trigonal bipyramid. In our case ~(Fe1)=0.72
and ~(Fe2)=0.66, hence the ligands around Fe define a
distorted trigonal bipyramid geometry. A ~ value of the
same order of magnitude (0.76) was observed for
[C2H2(PPh2)2][Fe(CO)3] [18c], whereas in the saturated
counter part, (dppe)Fe(CO)3 (~=0.35), the iron center
is clearly in a distorted square pyramidal environment.
Another interesting point concerning our complex is, as
in the case of the rhenium complex discussed above, the
distortions from the planarity within the dithiole moiety
bearing the phosphine groups, along S···S and P···P
axes. The first one, with folding angles of 9.3(2)° for
S1···S2 (Fe1) and 13.5(2)° for S5···S6 (Fe2), shows the
plex
tetrakis(diphenylphosphino)benzene-bis(tricar-
bonyliron) [20], the geometry at Fe is intermediate
between trigonal bipyramidal and square pyramidal
(~=0.50).
2.3. Electrochemistry
Cyclic voltammetry data for all the complexes along
with those already published [6] for P2 and P4 are
given in Table 5. As a general remark, the donors
experience, especially for the first oxidation wave, a
strong anodic shift upon complexation comparing with
the free phosphines oxidation potentials. This means
that significant through space or through bond interac-
tions between the TTF core and the metallic fragment
occur. Nevertheless, these potentials are still below 1 V
and open the possibility of synthesizing, by electrocrys-
tallization, air-stable open-shell species bearing
organometallic fragments.
In Fig. 6, we have represented the cyclic voltammetry
curves for both mono- and bimetallic tungsten com-

296
N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
plexes. The molybdenum complexes show similar
curves. Two reversible one-electron TTF based redox
processes are observed for the monometallic P2W and
P2Mo complexes. Anodic shifts of 220 and 200 mV,
respectively, are noticed for the first oxidation poten-
tial, whereas the second one is less influenced by the
metallic fragment. A third oxidation weakly reversible
wave at about Eox= +1.25 V is observed. A better
reversibility is obtained at higher scan rates. This pro-
cess was assigned to an one-electron oxidation of the
Table 5
Cyclic voltammetry data
Compound
E1M (DE) E1TTF (DE) E2TTF (DE) E1M%
P2 a
0.27; r
0.33; r
0.81; r
0.73; r
P4 a
[P2][Fe(CO)3] a
[P4][Fe(CO)3]2
0.28 (112); r 0.68 (183); r 1.18 (165); r
0.31 (80); r 1.04; wr
a
[P2][Mo(CO)4] b
0.47 (60); r 0.85 (60); r 1.25; wr
0.71 (68); r 1.23; ir
0.49 (60); r 0.86 (64); qr 1.26; wr
0.73 (64); r 1.33; ir
0.52 (59); r 0.90 (59); r 1.64; ir
0.82 (60); r 1.15 (59); r 1.64; ir
a
[P4][Mo(CO)4]2
[P2][W(CO)4] b
Fig. 7. Cyclic voltammetry curves for [P2][Re(CO)3Cl] and
[P4][Re(CO)3Cl]2.
a
[P4][W(CO)4]2
[P2][Re(CO)3Cl] b
b
[P4][Re(CO)3Cl]2
metallic center, which is likely to be decomposed by
loss of carbonyl ligands upon oxidation. Electrochemi-
cal studies [21] dealing with [cis-P2M(CO)4] (M=Mo
or W) type complexes show that an irreversible one-
electron oxidation of the metal occurs at potentials
around +1.1 V and, accordingly, the instability of the
oxidized species relies on the fast dissociation of the
carbonyl ligands. In the case of bimetallic P4W2 and
P4Mo2 only the reversible wave corresponding to the
monoelectronic oxidation of TTF core in radical cation
is observed, with a strong anodic shift of 400 and 380
mV, respectively, versus free P4, which means a
roughly double influence upon complexation than in
the case of monometallic counter parts. Subsequently,
the oxidation of TTF+ to TTF2+ and that of M0 to
M+1 probably occurs at very close potentials, hence
only a broad irreversible oxidation wave is observed at
about +1.28 V.
Potentials are expressed in V vs. SCE and DE in mV. For the
reversible (r) and quasi-reversible (qr) processes the half-wave poten-
tials (E1/2) are given, whereas only the oxidation potentials (Eox) are
shown for the weak-reversible (wr) and irreversible (ir) processes. The
free phosphines oxidation potentials were taken from Ref. [6]. E1M
and E1M% refer to metal centered redox processes, whereas E1TTF and
E2TTF are related to the TTF framework.
a CH2Cl2, n-Bu4NPF6, 0.05 M, 100 mV s−1
b CH3CN, n-Bu4NPF6, 0.05 M, 100 mV s−1
.
.
The cyclic voltammetry curves corresponding to the
rhenium complexes are shown in Fig. 7. Two reversible
one-electron TTF based redox processes are observed
for both monometallic and bimetallic complexes.
Larger anodic shifts than in the case of Group VI metal
complexes discussed above characterize both Re com-
plexes versus the free ligands. This is not surprising,
since an electron poorer metallic fragment is coordi-
nated to the same TTF framework. Re(I) centers in
such a kind of environment are known to be hard to
oxidize. Reports in the literature [10a,16] mention that
the irreversible oxidation of fac-P2XRe(CO)3 complexes
arises at potentials around +1.4–1.6 V. This is in good
agreement with our curves, where a broad peak at
Fig. 6. Cyclic voltammetry curves for [P2][W(CO)4] and
[P4][W(CO)4]2.

N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
297
+1.64 V can be observed. Thus, if taking into account
the stability of these organo-rhenium fragments toward
oxidation, our complexes are potential good candidates
for electrocrystallization experiments where the metallic
center plays basically a structural role.
A much weaker reversibility for this redox process,
hence lower stability for the paramagnetic 17-electron
species, is observed when the cyclic voltammetry mea-
sure is performed in acetonitrile, certainly because of a
fast ligand exchange. Subsequently, the oxidation of the
TTF core in P4Fe2 appears to be quite difficult and
only weakly reversible. Conversely, more encouraging
electrochemical data are obtained for the monometallic
complex, since two reversible TTF based oxidation
steps are observed after the first metal based oxidation
wave generating a positive charged species. Therefore it
is not surprising to note a much larger anodic shift
versus free P2, than those observed for the Mo, W and
Re counter parts, for the one-electron oxidation of TTF
core in radical cation. However, a potential value of
+0.68 V remains in the usual range of TTF donors,
thus the obtention of mixed organic–organometallic
diradical species can be envisaged.
A very different electrochemical behavior, when com-
pared with the cases discussed above, is displayed by
the P2Fe and P4Fe2 complexes. It is well established
[22] that P2Fe(CO)3 complexes are readily oxidized in
non-coordinating solvents, such CH2Cl2, in a reversible
one-electron process to lead at a paramagnetic 17-elec-
tron species. The oxidation potentials range from 0.12
V when P2=dppe to 0.69 V for P2=[P(OPh)3]2, with a
peak separation DE of about 150–170 mV, and the
paramagnetic complexes have been evidenced by EPR
and IR measurements. A more exhaustive crystallo-
graphic, EPR and theoretical study [23] dealing with
[(PPh3)2Fe(CO)3]+ complex shows that the iron center
adopts a square pyramidal geometry in solution as well
as in solid state, with the unpaired electron located in
the Fe(d2z) orbital. Thus, the possibility to have para-
magnetic metallic centers in the vicinity of an organic
TTF based radical, within the P2Fe and P4Fe2 com-
plexes, appeared to us particularly interesting. The
cyclic voltammetry curves represented in Fig. 8 show,
as expected, a first reversible oxidation wave for both
complexes, relying on the generation of paramagnetic
d7 iron species. The corresponding potential values,
listed in Table 5, are in the usual range. In the case of
bimetallic P4Fe2 a concomitant one-electron oxidation
of both Fe centers is likely to occur, since no splitting,
even at very low scan rate, was observed for this wave.
3. Conclusions
The new synthesized organometallic TTF based com-
plexes appear to be interesting electro-active molecular
precursors. The organometallic fragments could either
play mainly a structural role (M=Mo, W, Re) or be
directly involved in the redox processes, thus competing
with the TTF core (M=Fe). Further work will be
devoted to the obtention, by electrocrystallization ex-
periments, of radical cation salts derived from these
precursors.
4. Experimental
4.1. General
P2 and P4 were prepared by published procedures
[5,6]. Re(CO)5Cl and Fe2(CO)9 were obtained from
Strem Chemicals and used as received. cis-
Mo(CO)4(piperidine)2 and cis-W(CO)4(piperidine)2
were prepared from Mo(CO)6 and W(CO)6 as described
elsewhere [24]. Dry toluene was obtained by distillation
from Na and dry CH2Cl2 by distillation from P2O5.
Nuclear magnetic resonance spectra were recorded in a
Bruker ARX 400 spectrometer operating at 400.13
1
MHz for H, 100.62 MHz for 13C and 161.97 MHz for
31P. Chemical shifts are expressed in parts per million
downfield from external Me4Si (1H and 13C) and 85%
H3PO4 (31P). Coupling constants J are expressed in Hz.
The following abbreviations are used: s, singlet; d,
doublet, t, triplet, m, multiplet, b, broad, v, virtual.
Mass spectra were performed in a HP 5989A spectrom-
eter in the EI mode, with an ionization energy of 70 eV.
Infrared spectra were measured in a FTIR Nicolet 20
SXC spectrometer. Elemental analyses were performed
Fig. 8. Cyclic voltammetry curves for [P2][Fe(CO)3] and
[P4][Fe(CO)3]2.

298
N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
by the ‘Service d’Analyse du CNRS’, at Gif-sur-Yvette,
France. Cyclic voltammetry experiments were per-
formed in a VPM potentiostat in dried CH3CN or
CH2Cl2 solutions of 0.05 M n-Bu4NPF6 as electrolyte
at room temperature (r.t.). A negligible difference of
about 10 mV was noticed between the potential values
measured in CH3CN and in CH2Cl2. A Pt working
electrode (diameter 1 mm), a Pt counter electrode and a
SCE reference electrode were used.
4.2.4. [Tetrakis(diphenylphosphino)tetrathiaful6alene]-
bis[tetracarbonyl(molybdenum)], [P4][Mo(CO)4]2
Mo(CO)4(piperidine)2 (250 mg, 0.66 mmol) and P4
(200 mg, 0.21 mmol) were dissolved in CH2Cl2 (30 ml)
and heated to reflux for 2.5 h. After cooling and MeOH
addition, the precipitated violet solid was filtered and
recrystallized from toluene to afford [P4][Mo(CO)4]2 as
violet crystals (214 mg, 74%). Anal. Calc. for
C62H40O8P4S4Mo2·(C7H8)3: C, 61.03; H, 3.95; P, 7.58; S,
7.85. Found: C, 61.17; H, 3.97; P, 7.52; S, 7.67%. IR
(KBr, cm−1): wCO 1884, 1911, 1932, 2023. 31P-NMR
4.2. Synthesis and characterization of complexes
1
(CDCl3): l 52.8. H-NMR (CD2Cl2): l 7.48 (bs, 24H,
H
meta, Hpara), 7.50–7.58 (m, 16H, Hortho).
4.2.1. [3,4-Bis(diphenylphosphino)-3%,4%-dimethyl-
tetrathiaful6alene]rheniumtricarbonyl-chloride,
[P2][Re(CO)3Cl]
4.2.5. [3,4-Bis(diphenylphosphino)-3%,4%-dimethyl-
tetrathiaful6alene][tetracarbonyl]tungsten, [P2][W(CO)4]
W(CO)4(piperidine)2 (152 mg, 0.33 mmol) and P2
(200 mg, 0.33 mmol) were dissolved in CH2Cl2 (25 ml)
and the solution warmed to reflux for 2.5 h. After
cooling and slow MeOH diffusion, violet crystals were
filtered (232 mg, 78%). Anal. Calc. for C32H26P2O4S4W:
C, 48.22; H, 2.92; S, 14.30. Found: C, 48.26; H, 2.90; S,
13.23%. IR (KBr, cm−1): wCO 1879, 1901, 1920, 2021.
P2 (300 mg, 0.5 mmol) in dry toluene (50 ml) and
Re(CO)5Cl (180 mg, 0.5 mmol) were heated under
reflux for 2 days. After cooling at 0 °C, the orange
microcrystals were filtered and recrystallized from tolu-
ene to afford [P2][Re(CO)3Cl] as orange crystals (339
mg, 75%). Anal. Calc. for C35H26ClP2O3Re·C7H8: C,
50.52; H, 3.43; P, 6.20; S, 12.84. Found: C, 50.08; H,
3.37; P, 7.29; S, 12.81%. IR (KBr, cm−1): wCO 1916,
1949, 2028. 31P-NMR (CDCl3): l 22.9. 1H-NMR
(CDCl3): l 7.35–7.51 (m, 12H, Hmeta, Hpara), 7.71–7.85
(m, 8H, Hortho).
31P-NMR (CDCl3): l 35.0 (1J W=238.6 Hz). 1H-
183
P
NMR (CD2Cl2): l 7.40 (bs, 12H, Hmeta, Hpara), 7.49–
7.57 (m, 8H, Hortho). 13C-NMR (CD2Cl2): l 13.5 (s,
CH3), 114.3 (s, S2CꢁCS2), 114.6 (s, S2CꢁCS2), 123.3 (s,
CH3Cꢁ), 129.2 (d, 3JCP=10.1 Hz, Cmeta), 131.1 (s,
Cpara), 132.6 (d, 2JCP=13.0 Hz, Cortho), 134.4 (dd,
4.2.2. Tetrakis(diphenylphosphino)tetrathiaful6alenebis-
[rheniumtricarbonylchloride)], [P4][Re(CO)3Cl]2
1JCP=42.6 Hz, JCP=2.2 Hz, Cipso), 152.5 (dd, JCP
=
4
1
2
2
39.5 Hz, JCP=20.2 Hz, PCꢁCP), 201.0 (t, JCP=6.4
Hz, COax), 206.5 (dd, JCP(trans)=25.7 Hz, JCP(cis)=5.9
Hz, COeq).
P4 (280 mg, 0.3 mmol) and Re(CO)5Cl (310 mg, 0.8
mmol) were heated under reflux in toluene (50 ml) for
4 h. Cooling the solution at −18 °C afforded a micro-
crystalline orange solid (205 mg, 44%) representing a
mixture of two diasteroisomers in a ratio A/B of 1:1.6,
according to 31P-NMR spectrum. Anal. Calc. for
C60H40Cl2O6P4S4Re2: C, 46.42; H, 2.60; Cl, 4.57.
Found: C, 45.69; H, 2.52; Cl, 5.82%. IR (KBr, cm−1):
wCO 1905, 1931, 1974, 2033. 31P-NMR (CD2Cl2): l 23.5
(B), 24.6 (A). 1H-NMR (CD2Cl2): l 7.37–7.53 (m, 24H,
Hmeta, Hpara), 7.77–7.91 (m, 16H, Hortho).
2
2
4.2.6. [Tetrakis(diphenylphosphino)tetrathiaful6alene]-
bis[tetracarbonyl(tungsten)], [P4][W(CO)4]2
A solution of W(CO)4(piperidine)2 (200 mg, 0.43
mmol) and P4 (200 mg, 0.21 mmol) in CH2Cl2 is heated
under reflux for 2.5 h. The product is precipitated by
addition of MeOH, filtered and recrystallized from
toluene to afford burgundy red crystal (205 mg, 53%).
Anal. Calc. for C62H40O8P4S4W2·(C7H8)3: C, 55.10; H,
3.57; S, 7.09. Found: C, 55.17; H, 3.59; S, 9.69%. IR
(KBr, cm−1): wCO 1877, 1903, 1925, 2019. 31P-NMR
4.2.3. [3,4-Bis(diphenylphosphino)-3%,4%-dimethyl-
tetrathiaful6alene][tetracarbonyl)]molybdenum,
[P2][Mo(CO)4)]
(CD2Cl2):
l
35.9 (1JP W=238.4 Hz). 1H-NMR
183
(CD2Cl2): l 7.43 (bs, 24H, Hmeta, Hpara), 7.48–7.55 (m,
Mo(CO)4(piperidine)2 (120 mg, 0.32 mmol) and P2
(200 mg, 0.33 mmol) were dissolved in CH2Cl2 (30 ml)
and the solution heated to reflux for 1.5 h. The orange
solution turned dark red. After concentration and lay-
ering with MeOH, dark red crystals of [P2][Mo(CO)4)]
were obtained (175 mg, 64%). Anal. Calc. for
C36H26O4P2S4Mo: C, 53.46; H, 3.24; S, 15.86. Found:
C, 53.27; H, 3.13; S, 16.17%. IR (KBr, cm−1): wCO
1891, 1908, 1934, 2024. 31P-NMR (CDCl3): l 51.9.
1H-NMR (CD2Cl2): l 7.42 (bs, 12H, Hmeta, Hpara),
7.51–7.59 (m, 8H, Hortho).
16H, Hortho). 13C-NMR (CD2Cl2): l 119.2 (s, S2CꢁCS2),
3
129.1 (d, JCP=10.2 Hz, Cmeta), 131.2 (s, Cpara), 132.5
2
1
(d, JCP=13.1 Hz, Cortho), 134.5 (dd, JCP=42.8 Hz,
4JCP=2.1 Hz, Cipso), 152.3 (dd, JCP=39.4 Hz, JCP
=
1
2
2
20.3 Hz, PCꢁCP), 201.1 (t, JCP=6.5 Hz, COax), 206.7
(dd, JCP(trans)=25.5 Hz, JCP(cis)=5.8 Hz, COeq).
2
2
4.2.7. [3,4-Bis(diphenylphosphino)-3%,4%-dimethyl-
tetrathiaful6alene][tricarbonyl]iron, [P2][Fe(CO)3]
P2 (300 mg, 0.50 mmol) and Fe2(CO)9 (250 mg, 0.68
mmol) were weighted in the glove-box in a Schlenk

N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
299
tube, then toluene (15 ml) was added. The mixture was
4.2.8. [Tetrakis(diphenylphosphino)tetrathiaful6alene]-
bis[tricarbonyl(iron)], [P4][Fe(CO)3]2
heated over night, at 70 °C, under magnetic stirring.
The completeness of the reaction was checked by 31P-
NMR spectroscopy. After cooling down to r.t., the red
solution was filtered through celite on a glass frit and
then almost all the solvent was removed under vacuum.
The remaining solution was deposited onto the top of a
short silica-gel column eluted with toluene. An orange
fraction was recuperated and after removing the solvent
on a rota-evaporator, precipitation with pentane and
drying under vacuum, a red solid was recovered. Re-
crystallization in hexane yielded bright red crystals of
complex (200 mg, 54%). Anal. Calc. for
C35H26O3P2S4Fe·(C6H14)1/4: C, 57.52; H, 3.90. Found:
C, 57.61; H, 3.95%. IR (KBr, cm−1): wCO 1901, 1925,
1991. 31P-NMR (C6D6): l 86.7. 1H-NMR (C6D6): l
1.24 (s, 6H, CH3), 7.02 (bs, 12H, Hmeta, Hpara), 7.74 (bs,
8H, Hortho). 13C-NMR (C6D6): l 13.2 (s, CH3), 114.2 (s,
S2CꢁCS2), 114.4 (s, S2CꢁCS2), 123.0 (s, CH3Cꢁ), 129.0
(vt, X part of an ABX system, ꢀJCP=10.2 Hz, Cmeta),
130.8 (s, Cpara), 132.8 (vt, X part of an ABX system,
ꢀJCP=11.5 Hz, Cortho), 135.4 (vt, X part of an ABX
To a mixture of P4 (300 mg, 0.32 mmol) and
Fe2(CO)9 (300 mg, 0.82 mmol), weighted in the glove-
box in a Schlenk tube, toluene (20 ml) was added. The
resulting suspension is stirred over night at 70 °C.
After this period the reaction was complete and the
deep red solution was filtered over celite. Chromato-
graphic separation through a short silica-gel column
eluted with toluene, followed by evaporation of solvent
under vacuum and precipitation with pentane allowed
the obtention of the complex as an orange solid (220
mg, 56%). Suitable crystals for X-ray analysis have
been obtained by recrystallization in acetonitrile or in
toluene. In the second case the crystals contain toluene.
Anal. Calc. for C60H40O6P4S4Fe2·(C7H8)3: C, 64.98; H,
4.31. Found: C, 64.94; H, 4.34%. IR (KBr, cm−1): wCO
1
1905, 1923, 1987. 31P-NMR (C6D6): l 87.2. H-NMR
(C6D6): l 7.04 (bs, 24H, Hmeta, Hpara), 7.76 (bs, 16H,
Hortho). 13C-NMR (CD2Cl2): l 119.1 (s, S2CꢁCS2), 129.0
(vt, X part of an ABX system, ꢀJCP=10.3 Hz, Cmeta),
131.1 (s, Cpara), 132.5 (vt, X part of an ABX system,
ꢀJCP=11.6 Hz, Cortho), 134.5 (vt, X part of an ABX
system, ꢀJCP=46.8 Hz, Cipso), 151.9 (vt, X part of an
2
ABX system, ꢀJCP=77.6 Hz, PCꢁCP), 219.3 (t, JCP
=
system, ꢀJCP=47.0 Hz, Cipso), 151.2 (vt, X part of an
2
6.6 Hz, CO). EIMS; m/z (ion, rel. intensity): 740 (M, 1),
712 (M−CO, 11), 684 (M−2CO, 27), 656 (M−3CO,
93), 600 (M−Fe(CO)3, 44).
ABX system, ꢀJCP=77.5 Hz, PCꢁCP), 218.9 (t, JCP
=
6.8 Hz, CO). EIMS; m/z (ion, rel. intensity): 600 (M−
2Fe(CO)3−PPh2−2Ph, 44).
Table 6
Crystallographic data
[P4][W(CO)4]2
[P2][Re(CO)3Cl]
[P2][Fe(CO)3]
[P4][Fe(CO)3]2
Empirical formula
Formula mass
C83H64O8P4S4W2
1809.16
C42H34ClO3P2ReS4
998.52
C36.5H29.5O3P2S4Fe
762.13
C60H40O6P4S4Fe2
1220.74
Crystal dimensions (mm)
Crystal system
Space group
Temperature (K)
Unit cell dimensions
0.51×0.06×0.06
Monoclinic
P21/c
0.36×0.06×0.03
Orthorhombic
Pna21
0.30×0.15×0.10
Orthorhombic
Pbca
0.58×0.20×0.04
Triclinic
(
P1
150
293
293
250
,
a (A)
11.7651(8)
19.4854(11)
16.9667(12)
90.
106.377(8)
90.
3731.8(4)
2
1.610
37.4504(18)
11.2345(5)
20.3263(9)
90.
90.
90.
8552.0(7)
8
1.551
19.653(4)
21.216(4)
34.820(7)
90.
90.
90.
14519(5)
16
1.395
8.6014(17)
11.491(2)
15.417(3)
77.93(3)
86.00(3)
71.07(3)
1409.5(5)
1
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
1.438
0.827
v (mm−1
)
3.335
3.211
0.768
Data collected
Independent data
Rint
28 992
7204
0.0428
5682
47 739
16 263
0.1589
8031
86 225
14 150
0.1452
5443
5096
5096
0.0570
3168
343
0.0348
0.0543
0.728
Observed data
Parameters refined
R(F)
470
857
838
0.0219
0.0416
0.876
0.0578
0.0972
0.807
0.0456
0.0857
0.751
wR(F2)
Goodness-of-fit (obs.)
−3
,
Residual d (e A
)
0.54 and −0.73
1.34 and −0.78
0.245 and −0.194
0.289 and −0.278

300
N. A6ar6ari et al. / Journal of Organometallic Chemistry 643–644 (2002) 292–300
[4] (a) M. Fourmigue´, P. Batail, J. Chem. Soc. Chem. Commun.
4.3. Crystallography
(1991) 1370;
(b) M. Fourmigue´, Y.-S. Huang, Organometallics 12 (1993) 797;
(c) F. Gerson, A. Lamprecht, M. Fourmigue´, J. Chem. Soc.
Perkin Trans. 2 (1996) 1409.
Data were collected on a Stoe IPDS diffraction sys-
tem at r.t. unless otherwise specified. Details about data
collection and solution refinement are given in Table 6.
Structures were solved by direct methods (SHELXS) and
refined by full-matrix least-squares procedures. All
atoms were refined anisotropically except those of the
disordered toluene molecules found in the structures of
[P4][W(CO)4]2[toluene]3 and [P2][Re(CO)3Cl][toluene].
Hydrogen atoms were introduced at calculated posi-
tions (except on the disordered toluene molecules) in-
troduced in structure factor calculations and not refined
(riding model).
[5] M. Fourmigue´, P. Batail, Bull. Soc. Chim. Fr. 129 (1992) 29.
[6] M. Fourmigue´, C.E. Uzelmeier, K. Boubekeur, S.L. Bartley,
K.R. Dunbar, J. Organomet. Chem. 529 (1997) 343.
[7] P. Pellon, E. Brule, N. Bellec, K. Chamontin, D. Lorcy, J.
Chem. Soc. Perkin Trans. 1 (2000) 4409.
[8] J. Chatt, H.R. Watson, J. Chem. Soc. London (1961) 4980.
[9] P.E. Garrou, Inorg. Chem. 14 (1975) 1435.
[10] (a) A.M. Bond, R. Colton, M.E. McDonald, Inorg. Chem. 17
(1978) 2842;
(b) P.J. Giordano, M.S. Wrighton, J. Am. Chem. Soc. 101 (1979)
2888.
[11] (a) R.S. Berry, J. Chem. Phys. 32 (1960) 933;
(b) I. Ugi, D. Marquarding, H. Klusacek, P. Gillespie, F.
Ramirez, Acc. Chem. Res. 4 (1971) 288;
(c) F.A. Cotton, K.I. Hardcastle, G.A. Rusholme, J. Coord.
Chem. 2 (1973) 217.
5. Supplementary material
[12] G.R. Langford, M. Akhtar, P.D. Ellis, A.G. MacDiarmid, J.D.
Odom, Inorg. Chem. 14 (1975) 2937.
[13] G. Hogarth, T. Norman, Inorg. Chim. Acta 248 (1996) 167.
[14] C.-H. Ueng, L.-C. Leu, Acta Crystallogr. C 47 (1991) 725.
[15] K. Maitra, V.J. Catalano, J.H. Nelson, J. Organomet. Chem.
529 (1997) 409.
[16] T.M. Miller, K.J. Ahmed, M.S. Wrighton, Inorg. Chem. 28
(1989) 2347.
[17] C.E. Uzelmeier, S.L. Bartley, M. Fourmigue´, R. Rogers, G.
Grandinetti, K.R. Dunbar, Inorg. Chem. 37 (1998) 6706.
[18] (a) F.W.B. Einstein, C.-H. Huang, Acta Crystallogr. B 34 (1978)
1486;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 166271–166274 for com-
pounds P4[W(CO)4]2, P2Re(CO)3Cl, P4[Fe(CO)3]2, and
P2Fe(CO)3, respectively. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
(b) L.P. Battaglia, D. Delledonne, M. Nardelli, C. Pelizzi, G.
Predieri, G.P. Chiusoli, J. Organomet. Chem. 330 (1987) 101;
(c) L.-S. Luh, L.-K. Liu, Inorg. Chim. Acta 206 (1993) 89.
[19] (a) A.W. Addition, R.T. Nageswara, J. Reedjik, J. van Rijn,
G.C. Verschoor, J. Chem. Soc. Dalton Trans. (1984) 1349;
(b) D.K. Mills, Y.M. Hsiao, P.J. Farmer, E.V. Atnip, J.H.
Reibenspies, M.Y. Darensbourg, J. Am. Chem. Soc. 113 (1991)
1421.
[20] G. Hogarth, J. Organomet. Chem. 406 (1991) 391.
[21] A.M. Bond, D.J. Darensbourg, E. Moccelin, B.J. Stewart, J.
Am. Chem. Soc. 103 (1981) 6827.
[22] P.K. Baker, N.G. Connelly, B.M.R. Jones, J.P. Maher, K.R.
Somers, J. Chem. Soc. Dalton Trans. (1980) 579.
[23] J.H. MacNeil, A.C. Chiverton, S. Fortier, M.C. Baird, R.C.
Hynes, A.J. Williams, K.F. Preston, T. Ziegler, J. Am. Chem.
Soc. 113 (1991) 9834.
References
[1] (a) P.F. Crossing, M.R. Snow, J. Chem. Soc. A (1971) 610;
(b) L.F. Warren, M.A. Bennet, Inorg. Chem. 15 (1976) 3126;
(c) F.L. Wimmer, M.R. Snow, A.M. Bond, Inorg. Chem. 13
(1974) 1617.
[2] (a) A.M. Bond, R. Colton, J.J. Jackowski, Inorg. Chem. 14
(1975) 274 (see also p. 2526);
(b) A.M. Bond, R. Colton, F. Daniels, D.R. Fernando, F.
Marken, Y. Nagaosa, R.F.M. Van Steveninck, J.N. Walter, J.
Am. Chem. Soc. 115 (1993) 9556.
[3] (a) J.C. Kotz, C.L. Nivert, J. Organomet. Chem. 52 (1973) 387;
(b) J.C. Kotz, C.L. Nivert, J.M. Lieber, R.C. Reed, J.
Organomet. Chem. 91 (1975) 87.
[24] D.J. Darensbourg, M.A. Murphy, J. Am. Chem. Soc. 100 (1978)
463.