Triarylphosphine ligands with pendant electron-rich [Fe(κ 2-dppe)(η5-C5Me5)(Ci -c)]- substituents

Article abstract of DOI:10.1021/ic4011828

The synthesis of four triaylphosphine ligands featuring electron-rich Fe(II) Fe(κ²-dppe)(η⁵-C₅Me ₅)Ci -C- pendant substituents in para and meta position(s) (1-4) is reported along with that of their corresponding radical cations (1-2[PF₆] or 3-4[PF₆]₃). These triarylphosphines possessing redox-active organometallic substituents constitute a new class of phosphorus-based metallo-ligands. In contrast to many related ferrocenylphosphines, these metallo-ligands are stable and isolable in two redox-states. Their steric and electronic properties are also briefly discussed.

Full text of DOI:10.1021/ic4011828

Article
pubs.acs.org/IC
Triarylphosphine Ligands with Pendant Electron-Rich
“[Fe(κ2‑dppe)(η5‑C5Me5)(CC)]−” Substituents
Ayham Tohme,† Guillaume Grelaud,† Gilles Argouarch,† Thierry Roisnel,† Arnaud Bondon,‡
́
and Frederic Paul*,†
́
́
†Institut des Sciences Chimiques de Rennes-UMR CNRS 6226, Universite
France
́
de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex,
‡SIM-UMR CNRS 6290, Universite
́
de Rennes 1, PRISM-Biosit-CS 34317, Campus de Villejean, 35043 Rennes Cedex, France
S
* Supporting Information
ABSTRACT: The synthesis of four triaylphosphine ligands
featuring electron-rich Fe(II) “Fe(κ2-dppe)(η5-C5Me5)CC−”
pendant substituents in para and meta position(s) (1−4) is
reported along with that of their corresponding radical cations (1−
2[PF6] or 3−4[PF6]3). These triarylphosphines possessing redox-
active organometallic substituents constitute a new class of
phosphorus-based metallo-ligands. In contrast to many related
ferrocenylphosphines, these metallo-ligands are stable and isolable in two redox-states. Their steric and electronic properties are
also briefly discussed.
only triarylphosphine representative reported to date, exhibits a
chemically irreversible Ru(II/III) oxidation in cyclic voltam-
metry (CV).26,29 In this respect, 1−4 appear quite promising
for redox-controlling chemical transformations, since 1−4 are
reversibly oxidized at much lower potentials than 5, but also
than most of the known metallo-phosphines. Considering the
fair kinetic stability reported for almost all arylalkynyl Fe(III)
complexes such as 8-X (Scheme 1),30,31 a comparably better
kinetic stability can be expected for the cationic species 1+−
43+.32 Moreover, the recent demonstration that the neutral
precursors 1−4 can behave as active ligands in a given catalytic
transformation certainly warrants further interest for these
derivatives.12
Accordingly, we now report here (i) a full account of the
synthesis and characterization of the new metallo-ligands 1−
4[PF6]n in their neutral (n = 0) and cationic (n = 1 or 3) redox
states, (ii) the study of the electronic effect induced by the
Fe(II)-based oxidations on Rh(I) carbonyl complexes of 1 and
2 to quantify the effect of the perturbation induced by oxidation
on the terminal phosphorus atom, and (iii) a brief discussion of
their electronic and steric parameters in relation to these
reported for related metallo-phosphines.
INTRODUCTION
■
Judicious spatial or topologic arrangements of redox-active end
groups can lead to molecular architectures presenting unique
properties for information storage or processing at the
molecular level.1 Accordingly, ferrocene-containing ligands
have attracted a strong attention in the organometallic scientific
community very early for the realization of molecular-based
devices.2,3 Likewise, we4−7 and others8 became interested in
introducing the redox-active “Fe(κ2-dppe)(η5-C5Me5)(C
C−)” fragment in several classes of ubiquitous ligands.9
When appended to an (hetero)aromatic ring, this organoiron
fragment usually presents a chemically reversible oxidation at
rather accessible potentials (around −0.1 V vs SCE)10 and,
depending on its redox state, was shown to interact more or
less strongly with this unit,5 opening access to various devices
such as self-assembled molecular wires.7,11
In the continuation of our studies aimed at developing
organoiron-based metallo-ligands, we have recently turned our
attention toward triarylphosphines such as 1−4 and briefly
communicated on their use in catalysis (Scheme 1).12 Indeed,
given the strong implication of triarylphosphines in many
catalytic transformations,13 the possibility of using the redox
state of “Fe(κ2-dppe)(η5-C5Me5)(CC−)” substituents of 1−
4 to switch/modulate one of these transformations constitutes
an additional incentive to study such derivatives.14 However,
the redox-control of a catalytic transformation represents a
challenging goal only seldom met with redox-active phosphine-
based ligands.15 Although several phosphine ligands function-
alized with electron-rich organometallics have been designed for
catalysis,16−22 only few among these ligands have been studied
in their oxidized states.18−21,23−25 In spite of these develop-
ments, phosphines functionalized with redox-active metal-
alkynyl substituents (5−7) remain scarce,26−28 and 5, the
RESULTS
■
Synthesis and Characterization of the Fe(II) Metal-
lophosphines. The organometallic ligands 1−4 were
synthesized from the corresponding organic phosphine
precursors presenting peripheral alkyne groups 9−1233 and
from the Fe(II) chloride complex Fe(κ2-dppe)(η5-C5Me5)Cl
(13) in two steps, following a classic activation-deprotonation
Received: May 13, 2013
Published: July 19, 2013
© 2013 American Chemical Society
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Scheme 1. New Fe(II) Metallo-Ligands 1−4 and Related Metallo-Phosphines and Metal-Alkynyl Complexes (Inset).
reaction which has ample precedence in our group (Scheme
2).34,35 While the mono- or tris-cationic vinylidene complexes
Table 1. Characteristic Spectroscopic and Redox Signatures
of the Fe(II) Metalloligands 1−4, Their Rh(I) Complexes 15
and 16, and 8-H
Scheme 2. Synthesis of the Fe(II) Metallophosphines 1−4
δ
δP
(ppm)
E° [ΔE ]
dppe a
a
bc
,
dep
,
entry
(ppm)
νCCFe (cm−1
)
(V)
PPh3
1
−5.5
−5.4
−5.9
−5.3
−3.8
100.1
100.1
100.3
100.1
101.7
100.0
100.0
2048 (vs), 2018 (m)
2068 (m), 2034 (vs)
2048 (vs), 2015 (sh)
2068 (sh), 2035 (vs)
2053 (s)
−0.14 [0.08]
−0.15 [0.08]
−0.12 [0.12]
−0.13 [0.18]
−0.15 [0.08]
−0.10 [0.13]
−0.13 [0.11]
2
3
4
8-H
15
16
fg
28.7 ,
fg
29.5 ,
2043 (s), 2022 (sh)
2039 (s)
a
b
31P{1H} NMR in C6D6 ( 0.2 ppm). IR in KBr pellets ( 2 cm−1).
c
In most cases two νCC modes are reported. These are presumably
due to Fermi coupling.38 Values in V ( 5 mV) vs SCE. Conditions:
d
CH2Cl2 solvent, 0.1 M [nBu4N][PF6] supporting electrolyte, 20 °C, Pt
e
electrodes, sweep rate 0.100 V s−1. ΔEp represents the peak-to-peak
f
g
separation in V. JPRh = 127 Hz. A 31P NMR signal is observed at δP
1
1
= 29.0 ppm (d, JPRh = 127 Hz) for the reference compound
[Rh(Ph3P)2(CO)Cl] (17) under similar conditions.
(vin-1[PF6]/vin-2[PF6]/vin-3[PF6]3/vin-4[PF6]3), isolated as
intermediates during the synthesis, were only briefly charac-
terized (NMR), the final alkynyl complexes were fully
characterized. For the latter, NMR and IR are plainly diagnostic
of the presence of Fe(II) metal-alkynyl substituents on the aryl
groups of the phosphines (Table 1). The compounds 1−3 were
also characterized by X-ray diffraction (Figure 1).
These orange complexes are redox-active and present a
chemically reversible Fe(III)/Fe(II) metal-centered oxidation
near −0.15 V vs SCE (Table 1).34 The PPh2 substituent in the
monometallic derivatives 1 and 2 plays the role of a weakly
electron-attracting substituent, as evidenced by the higher
oxidation potential and the slightly lower νCC values
compared to Fe(κ2-dppe)(η5-C5Me5)(CCPh) (8-H).36
Expectedly, this effect is slightly stronger for the para- than
for the meta-substituted Fe(II) complex. The corresponding
trimetallic complexes 3 and 4 also exhibit a single and broader
redox wave, corresponding to the simultaneous oxidation of the
three organoiron end groups at slightly higher redox potentials
values than for the monometallic derivatives 1 and 2. The
observation of a single oxidation wave for the three redox-active
units in the trinuclear structures is indicative of virtually no
electronic coupling between these units. Also, a single but
broader absorption band is observed by IR spectroscopy for the
overlapping E and A1 νCC modes of 1 and 2 which are both in
principle infrared active.37 This absorption is observed at
roughly the same energy than for the corresponding
monometallic complexes, in line with a weak (or null) vibronic
coupling between the alkynyl stretching motions.
Synthesis and Characterization of the Fe(III) Metal-
lophosphines. The Fe(III) complexes were synthesized by
chemical oxidation using one equivalent of ferrocenium
hexafluorophosphate per organoiron end-group, and readily
isolated in good to excellent yields by reprecipitation of the
crude solid from dichloromethane/n-pentane (Scheme 3). The
CVs of 1[PF6]−4[PF6]3 remained identical to those of the
starting Fe(II) complexes with the sign of the initial current
changing from anodic to cathodic, indicating the absence of
decomposition and/or the formation of new electroactive side-
products, while observation of characteristic spectroscopic
signatures evidences that the targeted Fe(III) complexes have
indeed been isolated (Table 2). For instance, the IR showed the
characteristic shift toward lower wave numbers of the νCCFe
stretching mode(s) (Table 2).31,38 The compound 2[PF6]
could also be characterized by its solid state structure (Figure
2).
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Figure 1. ORTEP representations of the complexes 1 (a), 2 (b), and 3 (c) with displacement ellipsoids at the 50% probability level. Selected
distances (Å) and angles (deg): (a) Fe1−(Cp*)centroid 1.740, Fe1−P1 2.1705(5), Fe1−P2 2.1750(5), Fe1−C37 1.8893(17), C37−C38 1.222(2),
C38−C39 1.437(2), C42−P3 1.8315(18), P1−Fe1−P2 85.638(19), Fe1−C37−C38 176.96(16), C37−C38−C39 177.37(19), C40−C39−Fe1−
(Cp*)centroid −52.3; (b) Fe1−(Cp*)centroid 1.736, Fe1−P1 2.1893(7), Fe1−P2 2.1821(7), Fe1−C37 1.906(2), C37−C38 1.221(3), C38−C39
1.440(3), C44−P3 1.838 (3), P1−Fe1−P2 86.20(2), Fe1−C37−C38 178.0(2), C37−C38−C39 176.7(2), C40−C39−Fe1−(Cp*)centroid −77.6; (c)
Fe1−(Cp*)centroid 1.741, Fe1−P1 2.1794(6), Fe1−P2 2.1832(6), Fe1−C37 1.882(2), C37−C38 1.220(3), C38−C39 1.432(3), C42−P3 1.8241(19),
P1−Fe1−P2 84.99(2), Fe1−C37−C38 176.56(19), C37−C38−C39 169.2(2), C42−P3−C42 103.00(7), C40−C39−Fe1−(Cp*)centroid −24.9.
when placed in para-position on the ring.31 In comparison, the
Scheme 3. Synthesis of the Fe(III) Metallophosphines
trications give much broader and apparently more isotropic
signals at about the same g values, a feature likely attributable to
their tri-radical nature inducing a faster spin relaxation, possibly
because of intramolecular spin−spin interactions.39,40
1[PF6]−4[PF6]3
The νCCFe shifts observed for 1[PF6] and 2[PF6] and for
the corresponding trications 3[PF6]3 and 4[PF6]3 are
comparable to these previously observed for closely related
Fe(III) complexes (Table 2).38 They suggest a weakening of
the alkynyl bond order upon oxidation because of some
delocalization of the electronic vacancy on the nearby phenyl
ring and perhaps even on the phosphorus lone pair, based on π-
conjugation effects.31 Indeed, in line with VB considerations,
the observed bond weakening is larger in the para- than in the
meta-substituted triarylphosphines. Finally, a weak signal in the
near-IR range corresponding to a forbidden LF transition can
be detected for all these compounds,31 with roughly a 3-fold
As evidenced by rhombic electron spin resonance (ESR)
signatures in solvent glasses at about 77 K, the monocations
1[PF6] and 2[PF6] are typical Fe(III) metallo-centered radicals
(Table 2).10 The slight change in anisotropy (Δg) and mean g
value (⟨g⟩) observed between them being attributable to the
higher electron-withdrawing capability of the PPh2 substituent
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Table 2. Characteristic Spectroscopic Signatures of the Fe(III) Metallo-Ligands 1[PF6]−4[PF6]3
a
d
e
e
e
entry
νCC (cm−1
1993
)
λLF (nm)
g1
g2
g3
Δg
0.526
⟨g⟩
1[PF6]
1879 (0.08)
1857 (0.11)
1846 (0.09)
1884 (0.21)
1861 (0.14)
1.969
1.972
1.975
1.978
1.976
2.027
2.027
2.033
2.033
2.032
2.495
2.470
2.464
2.474
2.472
2.164
2.156
2.157
2.162
2.160
2[PF6]
2000
0.498
0.489
0.496
0.496
b
8-H[PF6]
15[PF6]2
16[PF6]2
2021/1988
2025/2007
2022/2010
bc
,
bc
,
e
f
g
ΔHpp (Hz)
3[PF6]3
4[PF6]3
1988
1863 (0.34)
1863 (0.32)
2.116
445
2000
2.137
377
a
b
c
IR in KBr pellets (2 cm−1). Two bands were observed for the Fe(III) parent, presumably due to Fermi coupling.38 Determined by Raman
d
e
spectroscopy because of their weak intensity in the IR range. UV−vis−near-IR in CH2Cl2 (10−3 × ε in M−1 cm−1). ESR of Fe(III) complex at ca.
77 K in CH2Cl2/1,2-C2H4Cl2 (1:1) glass. Peak-to-peak separation.
f
are certainly dominated by the so-called contact contribution
which reflects the changes in spin polarization along the
backbone of the unsaturated carbon-rich ligand.30,41 Thus,
given that the signals corresponding to H1, H1′, and H1″ (Chart
1) accidentally overlap for 2[PF6] and come close together for
4[PF6]3, the changes in the bridging phenylene group when
proceeding from 1[PF6] to 2[PF6] essentially translate in a
change in intensity of the most shifted signals of the spectrum
at high and low fields (Figure 3). The most notable difference
between these two Fe(III) complexes originate from the phenyl
protons of the terminal PPh2 groups, absent on the trications
3[PF6]3 and 4[PF6]3, but readily identified for 1[PF6] and
2[PF6] by polarization transfer experiments (See Supporting
Information). The spin polarization being of opposite sign
depending on whether the PPh2 substituent is positioned in
meta- or para- position relative to the Fe(III)-CC- arm on
Figure 2. ORTEP representation of the complex 2[PF6] with
displacement ellipsoids at the 50% probability level. Selected distances
the ring,42 the ortho/para and meta sets of protons of the
(Å) and angles (deg): Fe1−(Cp*)centroid 1.780, Fe1−P1 2.2780(9),
Fe1−P2 2.2545(9), Fe1−C37 1.879(3), C37−C38 1.221(4), C38−
C39 1.430(4), C44−P3 1.848(3), P1−Fe1−P2 84.71(3), Fe1−C37−
C38 167.1(3), C37−C38−C39 169.3(3), C40−C39−Fe1−
(Cp*)centroid 20.3.
terminal phenyl rings are thus shifted in opposite directions
from their position in the diamagnetic Fe(II) complex (near 7.5
ppm). This shift, albeit weak, results in a characteristic inversion
of these sets of signals in 1[PF6] and 2[PF6].
Given that the broadened ESR spectra of the tricationic
species 3[PF6]3 and 4[PF6]3 were suggestive of some spin−spin
interactions, we wondered if any sizable intramolecular
exchange interactions was taking place between the unpaired
spins in these triradical species, as was the case with the related
triarylamine compound 14 recently studied by some of us
(Scheme 5).43 However, the fact that the protons H1 and H2
(Chart 1) appear nearly as shifted in 3[PF6]3 than in 1[PF6]
suggests that the electronic environment of the unpaired spins
in the para-substituted trication and in the corresponding
monocation are not so different in solution at room
temperature, in line with a weak to negligible exchange
coupling between them in the trications.42 A simple means to
confirm the existence of significant antiferromagnetic inter-
actions is to monitor the temperature dependence of the most
shifted protons of these Fe(III) derivatives.42 The clear Curie
dependence of these shifts with temperature for both 3[PF6]3
and 4[PF6]3 (Supporting Information) in the range accessible
for dichloromethane (20 to −90 °C) reveals that if any such
exchange interaction is taking place, the latter must be quite
weak, and is anyway not significantly larger than that taking
place in the related arylamine complexes previously mentioned
(mean JFeFe ∼ 14 cm−1).
intensity for the trinuclear derivatives corresponding to the
increased number of Fe(III) chromophores in 3[PF6]3 and
4[PF6]3. In full accordance with the available ESR data (Table
2), the energies of these transitions in 1[PF6] and 2[PF6], as
well as those of their first LMCT bands relative to the
corresponding bands in 8-H[PF6] are indicative of the weakly
electron-withdrawing nature of the PPh2 substituent.31
1H NMR of the Fe(III) Metallophosphines. These
paramagnetic species were also characterized in solution by
NMR.30,40 They give well-resolved spectra in which the shift of
all their protons can be identified by analogy with those of
related complexes, supplemented by integration and, whenever
possible, by polarization transfer experiments. Such an
approach leads to an unambiguous assignment of all the
observed signals of 1[PF6]−4[PF6]3. Regardless of their mono-
(1[PF6]−2[PF6]) or trinuclear (3[PF6]3−4[PF6]3) nature, the
1H NMR shifts of the “Fe(κ2-dppe)(η5-C5Me5)” end-groups are
quasi-unchanged from one Fe(III) complex to the other, with
the various proton signals coming out at classical shift values.30
Thus, while the spectra of the trications are fairly similar (see
Supporting Information), they differ from these of the
monocations, which are also different from each other (Figure
3). These changes mostly originate from the protons of the
three phenyl groups bound to the phosphorus atom. The
isotropic shifts of these nuclei remote from the Fe(III) center
Synthesis of Rhodium(I) Carbonyl Complexes. Rho-
dium carbonyl complexes of 1 and 2 were synthesized by
reacting these ligands with the dimeric Rh(I) precursor
[Rh(CO)2Cl]2 (Scheme 4).44,45 The square planar carbonyl
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Figure 3. 1H NMR spectra of 1[PF6] (a) and 2[PF6] (b) in CD2Cl2 at 25 °C with proposed assignment according to Chart 1 for selected protons.
Specific assignment of protons in the diamagnetic range are given on scaled up spectra. Unlabeled signals correspond to residual solvent peaks.
and 16 with two equivalents of ferrocenium hexafluorophos-
phate in dichloromethane. IR, UV−vis and 1H NMR
spectroscopies, combined with cyclic voltammetry of the
isolated species 15[PF6]2 and 16[PF6]2 indicate that no
dissociation of the oxidized ligands takes place subsequent to
oxidation (Table 2). The characterization of all these Rh(I)
complexes was then complemented by Raman spectroscopy to
firmly identify the carbonyl stretching frequencies (Table 3).
Indeed, we have found that the stretching motion of the
strongly polarized carbonyl bond was not active in Raman,
allowing for a clear identification of the latter mode in infrared
where both the νCC and νCO modes proved to be active. The
νCO mode in 15[PF6]n−16[PF6]n (n = 0, 2) is always observed
at marginally higher values than that of the reference
compound [Rh(Ph3P)2(CO)Cl] (17).46
Chart 1. Labeling of Selected Protons of 1[PF6], 2[PF6],
3[PF6]3, and 4[PF6]3 ([Fe] = Fe(κ2-dppe)(η5-C5Me5))
Crystallography. We report the solid-state structures of the
Fe(II) complexes 1, 2, and 3 (Figure 1), along with that of the
Fe(III) complex 2[PF6] (Figure 2) and of the Rh(I) complex
15 (Figure 4). As often observed, the mononuclear complexes
1, 2, and 2[PF6] crystallize in mono- or triclinic systems, in
centrosymmetric space groups. In this respect, the trinuclar
Fe(II) complex is more original since it crystallizes in a trigonal
Rh(I) trans-complexes 15 and 16 were readily obtained in
nearly quantitative yields and were characterized by NMR (1H
and 31P), cyclic voltammetry, land by UV−visible spectroscopy.
The crystal structure of 15 could also be solved (Figure 4).
Complexation is clearly evidenced by a characteristic shift to
higher wavelengths of the metallo-ligand-based MLCT
transition, in the 420−450 nm range (Supporting Information),
and by an increase in its Fe(II/III) oxidation potential because
of the coordination of the Lewis acidic Rh(I) carbonyl fragment
to the lone pair of the terminal phosphorus atom. The
corresponding complexes with the Fe(III) phosphine ligands
15[PF6]2 and 16[PF6]2 were then generated by oxidation of 15
system, in the R3 space group (Table 4). Both distances and
̅
angles values are classical for Fe(II)6,31,34,36,39,43,55,56 and
Fe(III)30,31,42 piano-stool alkynyl complexes (Supporting
Information, Table S2); a slight but characteristic lengthening
of the Fe−Cp and Fe−P bonds and a shortening of the Fe−
C37 bond being observed for the Fe(III) complex 2[PF6]
relative to its Fe(II) parent 2. Also, in all these compounds, the
P−C bonds of the uncoordinated phosphorus atom are close to
the average value expected for purely organic triarylphosphines
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Scheme 4. Synthesis of the Rh(I) Carbonyl Complexes of the Fe(II) and Fe(III) Metallophosphines 1[PF6]n and 2[PF6]n (n = 0,
1)
Table 3. Evaluation of the Steric (θT) and Electronic
Parameters for 1−4 and 1−2[PF6]
ΔνCO
d
a
b
c
phosphine
θT (deg)
1JPSe (Hz)
νCO (cm−1
)
(cm−1
)
1
151
747
1975
1979
1977
1979
1 [PF6]
2
+4
+2
136
144
186
752
2[PF6]
3
729
744
4
e
f
g
PPh3
18a
18b
19a
19b
145
730
1978
h
h
168
746
i
175
j
k
l
155−173
731−3
1970
m
1773
a
b
1
Cone angle determined from available X-ray data (see text). JPSe for
c
the corresponding selenophosphine derivatives in C6D6 ( 1 Hz). IR
in CH2Cl2 solution ( 2 cm−1) of the bis(phosphine)chloro(carbonyl)
d
rhodium(I) complex. Fe(II) vs Fe(III) νCO difference of the
corresponding Rh(I) complexes (previous column). See ref 52. See
ref 54a. Same value found in CHCl3. See ref 20. See ref 18. See refs
21, 22, 45, and 53. See refs 21 and 54. See refs 45 and 49. See ref
e
f
g
h
i
j
k
l
m
Figure 4. ORTEP representations of one of the conformations of the
complex 15 present in the asymmetric unit with displacement
ellipsoids at the 50% probability level. Selected distances (Å) and
angles (deg): Fe1−(Cp*)centroid 1.737, Fe1−P1 2.1821(13), Fe1−P2
2.1735(15), Fe1−C37 1.886(4), C37−C38 1.218(6), C38−C39
1.431(5), Fe2−(Cp*)centroid 1.734, Fe2−P11 2.1884(13), Fe2−P12
2.1671(14), Fe2−C137 1.874(5), C137−C138 1.225(6), C138−C139
1.433(6), Rh1−C201 1.831(6), Rh1−Cl2 2.3683(13), Rh1−P3
2.3143(9), Rh1−P13 2.3170(10), C201−O202 1.069(5), Fe1−C37−
C38 174.0(4), C37−C38−C39 179.6(5), Fe2−C137−C138 176.0(4),
C137−C138−C139 174.5(5), Rh1−C201-O202 177.9(4), P3−Rh1−
C201 92.2, P3−Rh1−Cl1 88.0, C40−C39−Fe1−(Cp*)centroid −144.9,
C40−C39−Fe1−(Cp*)centroid −103.2.
48.
Rh(Ph3P)2(CO)Cl (17).50 The key bond lengths and angles
within each metallo-ligand are classic, albeit several phenyl rings
appear disordered in the solid state.
DISCUSSION
■
Electronic Structures of the New Metallo-Phosphines
1−4. The Fe(II) metallo-ligands 1−4 have now been fully
characterized. In line with the electron-rich nature of the Fe(κ2-
dppe)(η5-C5Me5) end group(s), the corresponding Fe(III)
congeners 1[PF6]−4[PF6]3 are thermodynamically stable
species that can be simply isolated by chemical oxidation
(Scheme 3), the oxidation taking place at significantly lower
potentials than ferrocene (around −0.12 V vs SCE). Both
neutral and oxidized derivatives present diagnostic spectro-
scopic signatures of Fe(κ2-dppe)(η5-C5Me5) alkynyl complexes
(Tables 1−2), the latter species corresponding mainly to metal-
centered Fe(III) radicals. Comparison of the data obtained for
1[PF6]n (n = 0, 1) with data previously gathered for the model
compounds 8-X[PF6]n (n = 0, 1)30,31,34,36 plainly reveals that
(1.837 Å), and a nearly tetrahedral geometry is observed
around the phosphorus atom.57 Comparison between 2 and
2[PF6] suggests that these structural features are not
significantly altered by oxidation, at least for the mononuclear
derivatives.
Regarding the Rh(I) carbonyl complex 15, the rhodium
center exhibits a classic square planar coordination geome-
try,45,58 with typical Rh−Cl (2.369 Å), Rh−P (2.314 Å), and
Rh−C(O) (1.847 Å) bonds,59 resembling these observed in
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Table 4. Crystal Data, Data Collection, and Refinement Parameters for 1, 2, 2[PF6], 3, and 15
1
2
2[PF6]
3
15
formula
Mr (g)
T (K)
cryst. syst.
space group
a /Å
C56H53Fe1P3
874.74
C56H53Fe1P3
874.74
100(2)
monoclinic
P21/n
C56H53F6Fe1P4
1019.71
100(2)
monoclinic
Pn
C132H129Fe3P7
2099.69
C113H106Cl1Fe2O1P6Rh1
1915.86
150(2)
100(2)
150(2)
triclinic
trigonal
monoclinic
P21/n
P1
̅
R3
̅
10.9204(5)
11.1057(4)
20.2650 (7)
102.848(2)
94.335(2)
107.709(2)
2255.33(15)
2
12.2780(4)
21.9742(10)
16.8487(7)
90.0
12.3940(6)
11.9823(6)
16.4380(9)
90.0
24.5857(9)
24.5857(0)
34.7513(13)
90.0
11.4178(2)
28.7416(7)
30.8356(7)
90.0
b /Å
c /Å
α /deg
β /deg
γ /deg
V/Å3
103.994(2)
90.0
93.027(3)
90.0
90.0
99.0520(10)
90.0
120.0
4410.9(3)
4
2437.8(2)
2
18191.4(8)
6
9993.2(4)
Z
dcalc (g cm−3
)
1.288
1.317
1.389
1.15
1.273
3984
F000
920
1840
1058
6624
number unique refl.
number obs. refl. [I > 2σ(I)]
Rint
10236
10013
10348
9269
22666
14041
0.0554
0.069
0.184
0.114
0.201
1.127
8458
7719
9370
7935
0.0350
0.0875
0.050
0.0386
0.045
0.0397
0.044
final R
0.038
Rw
0.094
0.094
0.102
0.109
R indices (all data)
Rw (all data)
GOF on F2 (Sw)
0.049
0.130
0.050
0.055
0.099
0.072
0.109
0.114
1.079
1.031
1.030
1.074
PPh2 behaves as a moderately electron-withdrawing group in 1/
1[PF6], but also certainly in the metallo-phosphines 2/2[PF6],
in line with the Hammett electron substituent parameters
about their steric and electronic parameters and also about the
changes undergone by these features upon oxidation.
The steric parameters of phosphine ligands are often
discussed in terms of their Tolman cone-angle values (θT).52
Indeed, compared to alternative measures often used to
evaluate the steric requirements of ligands, such as solid angles
(Ω) or repulsive energies (ER), θT values can be readily derived
and give usually a consistent picture with Ω and ER.61 Assuming
a correspondence between cone angles in the solid state and in
solution, we have derived θT values from the available
crystallographic data for 1−3 and 2[PF6] (see Supporting
Information).62 A cone angle of 186° was found for the
symmetric phosphine 3 (Table 3) while cone angles of 151°
and 136° and 144° were similarly derived for the unsym-
metrical phosphines 1, 2, and 2[PF6], respectively. Alter-
natively, an effective θT value closer to 164° was found for 1
from the structural data of 15. Also, based on the θT value
found for 3 and on that reported for PPh3 (145°), a value of
about 159° can be derived for 1 using the procedure of Tolman
allowing to estimate the cone of mixed phosphines from the
cone angle of the corresponding symmetric phosphines.52
Remarkably, by reason of the quite folded conformation
adopted by this ligand, the θT value found for 2 is lower than
that of PPh3. Notably, a quite similar conformation is adopted
by its oxidized counterpart 2[PF6], it seems therefore that
oxidation will only have a minimum impact on the cone angles
of the monometallic derivatives. Because of the possibility of
such a “folding”, the cone angle of 4 can hardly be estimated
from molecular models. In the absence of crystallographic
evidence, we would thus tentatively propose that its cone angle
is larger than or at least equal to that of 3.
(ESPs) reported for this substituent (σp = 0.19 and σm
=
0.11).60 This constitutes a significant difference with nitrogen
analogues of 1/1[PF6] or 3/3[PF6]3 such as 8-NPh2/8-
NPh2[PF6] (X = NPh2) or 14/14[PF6]3 (Scheme 5),43 for
Scheme 5. Nitrogen Analogues of Fe(II) Alkynyl Complexes
1 and 3
which the pnictogen substituent presents a significant electron-
releasing character (σp = −0.22, σm = 0.00).60 Such a difference
can be primarily ascribed to the difference in group
electronegativity between PPh2 and NPh2, also resulting in
the different geometry adopted by these substituents in the
solid state. Thus, a better overlap between the pnictogen lone
pair and the bridging phenyl ring is achieved in 8-NPh2
compared to 1, as revealed by the X-ray structures of these
complexes (CPh−N−C(4‑C6H4) angles of about 120 2° in 8-
NPh243 vs CPh−P−C(4‑C6H4) angles of about 101 1° in 1). In
1
line with the available H NMR data, the relatively weaker π-
donicity of phosphorus compared to nitrogen and its nearly
tetrahedral geometry in 3[PF6]3 make it certainly less prone to
convey electronic exchange coupling interactions between
unpaired spins in this trication than in 14[PF6]3.43
Steric and Electronic Parameters of the Metallo-
Phosphine Ligands. Before further evaluation of these new
metallo-phosphines as redox-switchable ligands, we wondered
Various spectroscopic markers have been used to empirically
access the electronic parameters of a given phosphine ligand.
One way is to use phosphorus−selenium coupling constants
(1JPSe) that can be considered as a marker of the s character of
the lone pair.54,63 Thus, the smaller the coupling is, the more
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nucleophilic (basic) the phosphine is and the more electron-
releasing the peripheral substituents on the aromatic ring must
be. In parallel to this work, we have therefore synthesized the
CONCLUSIONS
■
We have reported here the synthesis and characterization of
four new Fe(II) triphenylphosphine ligands (1−4) function-
alized with electron-rich [Fe(κ2-dppe)(η5-C5Me5)(CC)]
substituents at their periphery, along with the evaluation of
their electronic and steric parameters (θT). Based on these
estimates, these new metallo-phosphine ligands appear to be
only slightly more electron-donating than PPh3. Among these,
the para derivatives appear comparable to related ferrocenyle-
thynyl-phosphine ligands, but less electron-donating than
ferrocenylphosphine analogues. On steric grounds, they
certainly compare to their ferrocenyl or ferrocenylethynyl
analogues, and are clearly bulkier than PPh3, except perhaps for
2. An interesting advantage over the ferrocenyl-based ligands is
that 1−4 are oxidized at significantly lower potentials and give
rise to remarkably more stable cationic species, a feature
certainly in part attributable to the largely metal-centered
nature of the electronic vacancy generated by oxidation.32
Regarding their charge distribution, all the Fe(II) metallo-
phosphines present a dipolar or multipolar structure charac-
terized by electron-rich site(s) located on the iron center(s)
and an electron-poorer site located on the terminal/central
phosphorus atom. This structure is significantly altered by
oxidation; however, the electronic changes induced by
oxidation appear to be only moderately sensed at the metal
center to which these metallo-ligands are coordinated. Actually,
these changes resemble those that would be induced by
replacing the electron-releasing Fe(II) organometallic end
group(s) on the phenyl ring(s) by a very weakly electron-
withdrawing substituent. While these purely inductive/meso-
meric changes induced on the phosphorus atom by oxidation of
the [Fe(κ2-dppe)(η5-C5Me5)(CC)] substituent(s) may seem
too weak to strongly influence the reactivity of a remote metal
center, it should however be remembered that they are
accompanied by the creation of electronic vacancies localized
on the substituents of the phosphine ligand, along with the
creation of positive charge(s). Depending on the actual nature
of the metal center coordinated to it and of the surrounding
medium, both of these features might also be able to influence
profoundly its reactivity, either by intramolecular electron-
transfer or by purely through-space electrostatic interactions.
Moreover, we would like to stress here that redox-switchable
metalloligands such as 1−4 might lead to interesting
applications in fields more related to material sciences, and
different from catalysis, especially those for which a large
electronic interaction between the redox-active iron center and
the terminal phosphine group that binds to a given metal center
is less crucial in the ground state.3,66
1
corresponding selenium derivatives and measured their JPSe
values (Table 3). Based on these, the following order can be
proposed for the electron-richness of the phosphine ligand: 3 >
4 ≥ 1 > 2. However, according to the values found, it would
also seem that the metallo-phosphines 1−2 and 4 are less
electron-rich than PPh3, an observation which stands against
the well-known electron-releasing character of the [Fe(κ2-
dppe)(η5-C5Me5)(CC)]− end-group.55,64 Actually, as will be
discussed more thoroughly elsewhere, it appears that the
ordering found for the metallo-ligands is basically correct, but
1
that the JPSe data obtained for metallo-phosphines cannot be
compared to those obtained for purely “organic” phosphines
such as PPh3 for instance.
A more classic approach to obtain the electronic parameters
of a given phosphine ligand is to look at a CO stretching energy
of a carbonyl complex to which the ligand is coordinated; νCO
values being shifted to lower values when the phosphine
donicity increases. While [Ni(CO)3(PR3)] complexes were
initially used for such studies,52 [Rh(PR3)2(CO)Cl] complexes
have recently been proposed as an interesting alternative,
because of their lower toxicity and increased shift range.45,48 We
have therefore synthesized the latter complexes with the
mononuclear ligands 1−2[PF6]n in their two (n = 0, 1) redox
states, and measured the νCO values in dichloromethane
solution (Table 3). The previous trend (1 > 2) can be
retrieved from our data, but the differences between νCO wave
numbers remain within experimental uncertainties, evidencing
that the electronic changes between them are poorly sensed at a
metal center to which they are coordinated. Regarding the
Fe(III) metallo-ligands 1−2[PF6], a consistent (but very slight)
weakening of the ligand donicity is observed compared to their
Fe(II) parents. Obviously, considering the range spanned by
the data along with its experimental uncertainty,45 the νCO
1
wavenumbers are presently less accurate markers than JPSe
values to compare Fe(II) metalloligands between themselves
when only slight changes in donicity take place.
1
Comparison of the θT, JPSe and νCO determined for 1−4
with the scant data available for the known ferrocenyl
phosphines 18a−b or 19a−b (Scheme 6 and Table
Scheme 6. Related Ferrocenyl Phosphines24,65
EXPERIMENTAL SECTION
■
General Procedures. All reactions and workup procedures were
carried out under dry, high purity argon using standard Schlenk
techniques.67 All solvents were freshly distilled and purged with argon
before use. Infrared spectra were obtained on a Bruker IFS28 FT-IR
spectrometer (400−4000 cm−1). Raman spectra of the solid samples
were obtained by diffuse scattering on the same apparatus and
recorded in the 100−3300 cm−1 range (Stokes emission) with a laser
excitation source at 1064 nm (25 mW) and a quartz separator with a
FRA 106 detector. NMR spectra were acquired at 298 K on a Bruker
DPX200 and Bruker AV300P (300 MHz) or on a Bruker AVANCE
500, equipped with a 5 mm broadband observe probe and a z-gradient
coil. Chemical shifts are given in parts per million (ppm) and
3),20−22,48,49,53,54 reveals that 1−2 (resp. 3−4) will present
lower cone angles than 18a−19a (resp. 18b−19b), but that the
donor properties of the para-substituted derivatives 1 and 3
should be comparable to those of 18a−b, and lower than those
of 19a−b. Note however that from the point of view of redox-
switching, 18a−b or 19a−b are less attractive ligands than 1−4.
Indeed, oxidation of 18a−b20,24 and 19a−b21,23e,j,i takes place
at significantly higher redox potentials (usually above 0.5 V vs
SCE). Moreover, electrochemical oxidations were reported to
be chemically irreversible for 19a21,23i,j or 19b,23e and to yield
organometallic radicals of lower kinetic stability at the electrode
for 18a−b than for 1−4.20
referenced to the residual nondeuterated solvent signal68 for H and
1
13C and external H3PO4 (0.0 ppm) for 31P NMR spectra. Experimental
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details regarding measurements on paramagnetic Fe(III) complexes
can be found in previous contributions.5,30,42 Cyclic voltammograms
were recorded in dry CH2Cl2 solutions (containing 0.10 M
[nBu4N][PF6], purged with argon and maintained under argon
atmosphere) using a EG&G-PAR model 263 potentiostat/galvanostat.
The working electrode was a Pt disk, the counter electrode a Pt wire
and the reference electrode a saturated calomel electrode. The
C5(CH3)5). UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] = 261 (sh)
[49.4], 328 [12.8], 365 [13.2], 398 (sh) [11.1].
Synthesis of the Trinuclear Fe(II) Metallophosphines (3−4).
In a Schlenk tube, the complex [Fe(κ2-dppe)(η5-C5Me5)Cl] (13; 656
mg, 1.05 mmol), KPF6 (193 mg, 1.05 mmol) and 11/12 (100 mg, 0.3
mmol) were dissolved in THF (15 mL) and MeOH (15 mL) and
stirred for 2 days at 40 °C. After removal of the solvents, the dark
brown residue was extracted with dichloromethane and concentrated
in vacuo (ca. 5 mL). Precipitation by addition of n-pentane and
filtration gave the corresponding tris-vinylidene complexes (vin-
3[PF6]3/vin-4[PF6]3), isolated as brown powders.
a
FeCp20/1+ couple (E1/2: 0.46 V, ΔEp = 0.08 V; Ip /Ipc = 1) was used as
an internal calibrant for the potential measurements.69 Near-IR and
UV−visible spectra were recorded as CH2Cl2 solutions, using a 1 cm
long quartz cell on a Cary 5000 spectrometer. Electron paramagnetic
resonance (EPR) spectra were recorded on a Bruker EMX-8/2.7 (X-
band) spectrometer, at 77 K (liquid nitrogen). Elemental analysis and
high resolution mass spectra (ESI on Micromass MS/MS ZABSpec
TOF spectrometer) were performed at the “Centre Regional de
[{Fe(κ2-dppe)(η5-C5Me5)CCH(p-C6H4)}3P][PF6]3 (vin-3[PF6]3).
Yield: 89%. 31P{1H} NMR (81 MHz, CDCl3): δ = 87.8 (s, 6P,
Pdppe), −4.2 (broad s, 1P, PAr3), −143.1 (sept, 3P, JPF = 713 Hz, PF6).
1H NMR (200 MHz, CDCl3): δ = 7.64−7.19 (m, 60H, Haryl), 6.83 (m,
6H, Haryl), 6.38 (m, 6H, Haryl), 5.11 (broad s, 3H, Hvinylidene), 3.14 (m,
6H, CH2/dppe), 2.55 (m, 6H, CH2/dppe), 1.62 (s, 45H, C5(CH3)5).
[{Fe(κ2-dppe)(η5-C5Me5)CCH(m-C6H4)}3P][PF6]3 (vin-4[PF6]3).
Yield: 85%. 31P{1H} NMR (81 MHz, CDCl3): δ = 88.2 (s, 6P, Pdppe),
−143.1 (sept, 3P, JPF = 713 Hz, PF6), the signal corresponding to the
́
Mesures Physiques de l’Ouest” (CRMPO), Universite de Rennes 1.
The complex [Fe(κ2-dppe)(η5-C5Me5)Cl] (13),70 the organic
phosphines 9−12,33 and [(η5-C5H5)2Fe][PF6]69 were prepared as
described in the literature. Other chemicals were purchased from
commercial suppliers and used as received. Whenever needed, silica
(Merck Kieselgel 60; 0.063−0.200 mm) was deactivated by stirring in
a mixture of n-hexane and triethylamine (10:1), then packed in a
column and washed with pure CH2Cl2. The plug of silica was dried in
vacuo for 2 h and used under argon.
1
(C6H4)3P was not detected (presumably too broad). H NMR (200
MHz, CDCl3): δ = 7.58−6.89 (m, 72H, Haryl), 4.93 (broad s, 3H,
Hvinylidene), 2.92 (m, 6H, CH2/dppe), 2.39 (m, 6H, CH2/dppe), 1.52 (s,
45H, C5(CH3)5).
Synthesis of the Mononuclear Fe(II) Metallophosphines (1−
2). In a Schlenk tube, the complex [Fe(κ2-dppe)(η5-C5Me5)Cl] (13;
625 mg, 1 mmol), KPF6 (221 mg, 1.2 mmol) and 9/10 (344 mg, 1.2
mmol) were dissolved in tetrahydrofuran (THF, 15 mL) and MeOH
(15 mL) and stirred 12 h at 25 °C. After removal of the solvents, the
dark brown residue was extracted with dichloromethane and
concentrated in vacuo (ca. 5 mL). Precipitation by addition of n-
pentane and filtration gave the corresponding vinylidene complexes
(vin-1[PF6]/vin-2[PF6]), isolated as brown powders.
These tris-vinylidene salts (vin-3[PF6]3/vin-4[PF6]3) were stirred
for 1 h in THF in the presence of excess DBU (0.22 mL, 1.5 mmol).
The solvent was then removed in vacuo, and the residue was purified
by column chromatography under argon atmosphere (deactivated
silica gel, toluene). Removal of toluene in vacuo and washing of the
resulting solid with n-pentane afforded the tris-alkynyl complexes as
orange powders.
[Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4)]3P (3). Total yield: 71%. X-
ray quality crystals were grown from slow diffusion of Et2O in a
dichloromethane solution of the complex. Anal. Calc for
C132H129P7Fe3: C, 75.50; H, 6.19; Found: C, 75.66; H, 6.42. HRMS:
calc: 2098.63059 [M+.], found: 2098.6357. 1H NMR (300 MHz,
C6D6): δ = 7.98 (m, 12H, Haryl), 7.49−7.44 (m, 6H, Haryl), 7.14−6.99
(m, 54H, Haryl), 2.62 (m, 6H, CH2/dppe), 1.83 (m, 6H, CH2/dppe), 1.52
(s, 45H, C5(CH3)5). UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] =
265 (sh) [80.8], 328 (sh) [29.3], 392 [37.4], 424 (sh) [32.9].
[Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4)]3P (4). Total yield 74%.
Anal. Calc for C132H129P7Fe3: C, 75.50; H, 6.19; Found: C, 75.55;
[Fe(κ2-dppe)(η5-C5Me5)CCH(p-C6H4PPh2)][PF6] (vin-1[PF6]).
Yield: 96%. 31P{1H} NMR (121 MHz, CDCl3): δ = 86.5 (s, 2P,
1
Pdppe), −5.2 (s, 1P, PPh2), −144.3 (sept, 1P, JPF = 713 Hz, PF6). H
NMR (300 MHz, CDCl3): δ = 7.60−7.11 (m, 30H, Haryl), 6.68 (m,
2H, Haryl), 6.22 (m, 2H, Haryl), 5.10 (m, 1H, Hvinylidene), 3.05 (m, 2H,
CH2/dppe), 2.48 (m, 2H, CH2/dppe), 1.57 (s, 15H, C5(CH3)5).
[Fe(κ2-dppe)(η5-C5Me5)CCH(m-C6H4PPh2)][PF6] (vin-2[PF6]).
Yield: 93%. 31P{1H} NMR (121 MHz, CDCl3): δ = 87.3 (s, 2P,
1
Pdppe), −5.2 (s, 1P, PPh2), −144.3 (sept, 1P, JPF = 713 Hz, PF6). H
1
H, 6.14. HRMS: calc: 2098.6306 [M+.], found: 2098.6315. H NMR
NMR (300 MHz, CDCl3): δ = 7.57−7.13 (m, 30H, Haryl), 6.92−6.80
(m, 2H, Haryl), 6.50 (m, 1H, Haryl), 6.30 (m, 1H, Haryl), 4.98 (m, 1H,
Hvinylidene), 3.02 (m, 2H, CH2/dppe), 2.48 (m, 2H, CH2/dppe), 1.50 (s,
15H, C5(CH3)5).
3
(300 MHz, C6D6): δ = 8.01−7.97 (m, 12H, Haryl), 7.53 (d, JHH = 9
Hz, 3H, Haryl), 7.33−7.02 (m, 57H, Haryl), 2.57 (m, 6H, CH2/dppe),
1.78 (m, 6H, CH2/dppe), 1.51 (s, 45H, C5(CH3)5). UV−vis (CH2Cl2):
λmax/nm [ε/103 M−1·cm−1] = 261 (sh) [51.8], 306 (sh) [18.2], 365
[21.5], 404 (sh) [16.5].
These vinylidene salts (vin-1[PF6]/vin-2[PF6]) were stirred for 1h
in THF in the presence of excess DBU (0.22 mL, 1.5 mmol). The
solvent was then removed in vacuo, and the residue was purified by
column chromatography under argon atmosphere (deactivated silica
gel, toluene). Removal of toluene in vacuo and washing of the resulting
solid with n-pentane afforded the desired alkynyl complexes as orange
powders.
Synthesis of the Mononuclear Fe(III) Metallophosphines
(1[PF6]−2[PF6]). In a Schlenk tube, the Fe(II) complexes 1/2 (219
mg, 0.25 mmol) and [FcH][PF6] (83 mg, 0.25 mmol) were dissolved
in THF (15 mL) and stirred for 1 h at room temperature. After
removal of the solvent, the residue was dissolved in dichloromethane
(5 mL) and precipitated by addition of n-pentane. Filtration and
drying in vacuo gave the corresponding Fe(III) complexes 1[PF6]/
2[PF6] as black powders.
Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4PPh2) (1). Total yield: 72%. X-
ray quality crystals could be grown by slow diffusion of either n-
pentane or methanol in a dichloromethane solution of the complex.
Anal. Calc for C56H53P3Fe: C, 76.89; H, 6.11; Found: C, 76.62; H,
6.27. HRMS: calc: 874.2709 [M+.], found: 874.2711. Raman (neat,
[Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4PPh2)][PF6] (1[PF6]). Yield:
94%. 31P{1H} NMR (121 MHz, CD2Cl2): δ = 252.8 (broad s,
ArPPh2), Pdppe and PF6− not detected. 1H NMR (500 MHz, CD2Cl2):
δ = 28.9 (broad s, H2), 8.0 (s, HPh), 7.9 (s, HPh/dppe), 7.5−7.3 (s,
H3+H5), 6.8 (s, HPh/dppe), 6.6 (broad s, CH2/dppe), 6.2 (s, HPh/dppe), 3.7
(s, HPh/dppe), 1.7 (s, HPh/dppe), −2.7 (broad s, CH2/dppe), −10.4 (broad
s, C5(CH3)5), −39.0 (very broad s, H1) [See Chart 1 for labeling].
UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] = 261 [37.2], 320
[20.9], 495 (sh) [3.2], 568 [1.8], 653 [1.8].
1
cm−1): ν = 2054 (vs, CC), 2019 (w, CC). H NMR (300 MHz,
C6D6): δ = 7.98−7.93 (m, 4H, Haryl), 7.47−7.02 (m, 30H, Haryl), 2.58
(m, 2H, CH2/dppe), 1.80 (m, 2H, CH2/dppe), 1.50 (s, 15H, C5(CH3)5).
UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] = 273 (sh) [45.9], 328
[15.2], 387 [18.0], 424 (sh) [14.8].
Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4PPh2) (2). Total yield: 73%. X-
ray quality crystals were grown from slow diffusion of n-pentane in a
chloroform solution of the complex. HRMS: calc: 874.2709 [M+.],
found: 874.2705. Raman (neat, cm−1): ν = 2072 (vw, CC), 2063
(w, CC), 2036 (vs, CC). 1H NMR (300 MHz, C6D6): δ = 7.97−
7.92 (m, 4H, Haryl), 7.48−7.42 (m, 4H, Haryl), 7.30−7.04 (m, 26H,
Haryl), 2.53 (m, 2H, CH2/dppe), 1.77 (m, 2H, CH2/dppe), 1.48 (s, 15H,
[Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4PPh2)][PF6] (2[PF6]). Yield
96%. X-ray quality crystals were grown from slow diffusion of n-
pentane in a dichloromethane solution of the complex. 31P{1H} NMR
−
(121 MHz, CD2Cl2): δ = −29.2 (s, ArPPh2), Pdppe and PF6 not
1
detected. H NMR (500 MHz, CD2Cl2): δ = 29.1 (broad s, 1H, H2),
9001
dx.doi.org/10.1021/ic4011828 | Inorg. Chem. 2013, 52, 8993−9004

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7.9 (s, HPh/dppe), 7.6−7.5 (2s, H3+H5), 7.3 (s, H4), 6.7 (s, HPh/dppe), 6.7
(broad s, CH2/dppe), 6.2 (s, HPh/dppe), 3.6 (s, HPh/dppe), 1.5 (s, HPh/dppe),
−2.8 (broad s, CH2/dppe), −10.4 (broad s, C5(CH3)5), −41.5 (very
broad s, 3H, H1+ H1′+H1″) [See Chart 1 for labeling]. UV−vis
(CH2Cl2) λmax/nm [ε/103 M−1·cm−1] = 259 [51.1], 281 (sh) [44.1],
306 (sh) [25.5], 393 (sh) [3.9], 583 [2.8], 670 [3.9].
Synthesis of the Trinuclear Fe(III) Metallophosphines (3-
[PF6]3−4[PF6]3). In a Schlenk tube, Fe(II) complexes 3/4 (210 mg,
0.1 mmol) and [FcH][PF6] (99 mg, 0.3 mmol) were dissolved in THF
(15 mL) and stirred for 1 h at room temperature. After removal of the
solvent, the residue was dissolved in dichloromethane (5 mL) and
precipitated by addition of n-pentane. Filtration and drying in vacuo
gave the corresponding Fe(III) complexes 3[PF6]3/4[PF6]3 as black
powders.
M−1·cm−1] = 262 [87.6], 324 [53.6], 396 (sh) [12.0], 582 [5.0], 678
[6.4].
[{Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4PPh2)}2Rh(CO)Cl][PF6]2 (16-
[PF6]2). Yield: 97%. IR (KBr, cm−1): ν = 1973 (s, CO). Raman
(neat, cm−1): ν = 2010 (w, CC). 31P{1H} NMR (121 MHz,
1
−
CD2Cl2): δ = 63.8 (d, JP−Rh ∼ 124 Hz, ArPPh2), Pdppe and PF6 not
detected. 1H NMR (300 MHz, CD2Cl2): δ = 27.9 (broad s, H2), 8.0 (s,
HPh), 7.9 (s, HPh/dppe), 7.6 (s, HPh), 7.4 (s, HPh), 6.7 (s, HPh/dppe), 6.5
(very broad s, CH2/dppe), 6.1 (s, HPh/dppe), 3.8 (s, HPh/dppe), 1.8 (s,
HPh/dppe), −2.6 (broad s, CH2/dppe), −9.9 (broad s, C5(CH3)5), −38.1
(very broad s, 3H, H1+H1′+H1″) [See Chart 1 for labeling]. UV−vis
(CH2Cl2) λmax/nm [ε/103 M−1·cm−1] = 254 [88.3], 286 (sh) [65.7],
307 (sh) [47.3], 349 (sh) [15.6], 575 [4.0], 663 [5.0].
Crystallography. Data collection of the various crystals was
performed on a KappaCCD diffractometer, at 120(2) K, with graphite
monochromatized MoKα radiation (λ = 0.71073 Å). The structure was
solved by direct methods using the SIR97 program,71 and then refined
with full-matrix least-squares methods based on F2 (SHELX-97)72 with
the aid of the WINGX73 program. For 3 and 15, the contribution of
the disordered and unidentified residual electronic densities to the
calculated structure factors was estimated following the BYPASS
[{Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4)}3P][PF6]3 (3[PF6]3). Yield:
91%. 31P{1H} NMR (202 MHz, CD2Cl): δ = 520.6 (broad s,
ArPPh2), Pdppe and PF6− not detected. 1H NMR (500 MHz, CD2Cl2):
δ = 28.4 (broad s, H2), 7.9 (s, HPh/ArPPh2), 6.9 (s, HPh/dppe), 6.4 (broad
s, CH2/dppe), 6.2 (s, HPh/dppe), 3.6 (s, HPh/dppe), 1.6 (s, HPh/dppe), −2.7
(broad s, CH2/dppe), −10.4 (broad s, C5(CH3)5), −36.6 (very broad s,
H1) [See Chart 1 for labeling]. UV−vis (CH2Cl2): λmax/nm [ε/103
M−1·cm−1] = 267 [142.61], 325 [95.2], 403 (sh) [21.2], 587 [8.2], 695
[11.9].
algorithm,74 implemented as the SQUEEZE option in PLATON.75
A
new data set, free of solvent contribution, was then used in the final
refinement. The complete structures were refined with SHELXL9772
by the full-matrix least-squares technique. All non-hydrogen atoms
were refined with anisotropic atomic displacement parameters. H
atoms were finally included in their calculated positions. A final
refinement on F2 converged to the ωR(F2) values indicated (Table 4).
Bruker AXS BV diffractometer atomic scattering factors were taken
from the literature.76
Crystallographic Derivation of Cone Angles. Cif files for 1, 2,
3, and 2[PF6] containing a dummy atom at 2.28 Å along a line linking
the barycenter of the three ipso carbon atoms and the phosphorus
atom. Based on these cif files, the cone angles at the phosphorus can
be derived following the procedure proposed by Mingos et al. and
considering a van der Waals radius of 1.09 Å for hydrogen.62
[{Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4)}3P][PF6]3 (4[PF6]3). Yield:
89%. 31P{1H} NMR (202 MHz, CD2Cl2): δ = −40.9 (s, ArPPh2),
−
1
Pdppe and PF6 not detected. H NMR (500 MHz, CD2Cl2): δ = 27.3
(broad s, 1H, H2), 7.9 (s, HPh/dppe), 6.8 (s, HPh/dppe), 6.4 (broad s,
CH2/dppe), 6.1 (s, HPh/dppe), 3.7 (s, HPh/dppe), 1.6 (s, HPh/dppe), −2.8
(broad s, CH2/dppe), −10.4 (broad s, C5(CH3)5), −33.7 and −35.4
(very broad s, 1H and 2H, H1+H1′+H1″) [See Chart 1 for labeling].
UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] = 258 [114.3], 281
(sh) [44.1], 310 (sh) [65.5], 390 (sh) [11.1], 574 [7.3], 662 [8.4].
Synthesis of Rh(I) Carbonyl Complexes of the Fe(II)
Metallophosphines. In a dry Schlenk tube, [Rh(CO)2Cl]2 (21.5
mg, 55.3 μmol) and the corresponding phosphines 1 or 2 (194 mg,
221.2 μmol) were dissolved in dichloromethane (5 mL) and stirred
overnight at room temperature. Addition of either n-pentane or
methanol and filtration gave the desired Rh(I) carbonyl complexes as
orange powders.
ASSOCIATED CONTENT
■
[Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4PPh2)]2Rh(CO)Cl (15). Yield:
94%. X-ray quality crystals were grown from slow diffusion of
methanol in a dichloromethane solution of the complex. HRMS: calc:
1914.4106 [M+.], found: 1914.4133. IR (KBr, cm−1): ν = 1969 (s,
CO). Raman (neat, cm−1): ν = 2044 (w, CC). 1H NMR (300 MHz,
C6D6): δ = 8.02−7.89 (m, 20H, Haryl), 7.30−7.02 (m, 48H, Haryl), 2.57
(m, 4H, CH2 dppe), 1.79 (m, 4H, CH2 dppe), 1.50 (s, 30H,
C5(CH3)5). UV−vis (CH2Cl2): λmax/nm [ε/103 M−1·cm−1] = 274
[60.0], 378 (sh) [28.7], 422 [34.3].
* Supporting Information
S
UV−vis spectra and cyclic voltammograms for all compounds.
1
ESR spectra for all Fe(III) compounds. H NMR spectra,
assignment, and temperature dependence of selected protons of
1−2[PF6] and 3−4[PF6]3. Crystallographic (CIF) file for 1, 2,
2[PF6], 3, and 15. This material is available free of charge via
the Internet at http://pubs.acs.org. Final atomic positional
coordinates, with estimated standard deviations, bond lengths
and angles, and anisotropic thermal parameters have been
deposited at the Cambridge Crystallographic Data Centre and
were allocated the deposition numbers CCDC 925017, CCDC
755887, CCDC 925015, CCDC 925016, and CCDC 925018,
respectively.
[Fe(κ2-dppe)(η5-C5Me5)CC(m-C6H4PPh2)]2Rh(CO)Cl (16). Yield:
97%. HRMS: calc: 1914.4106 [M+.], found: 1914.4106. IR (KBr,
cm−1): ν = 1973 (s, CO). Raman (neat, cm−1): ν = 2039 (m, CC).
1H NMR (300 MHz, C6D6): δ = 8.06−7.88 (m, 16H, Haryl), 7.30−7.02
(m, 52H, Haryl), 2.52 (m, 4H, CH2 dppe), 1.76 (m, 4H, CH2 dppe),
1.46 (s, 30H, C5(CH3)5). UV−vis (CH2Cl2): λmax/nm [ε/103
M−1·cm−1] = 286 (sh) [41.5], 365 [25.5], 409 (sh) [18.6].
AUTHOR INFORMATION
Synthesis of Rh(I) Carbonyl Complexes of the Fe(III)
Metallophosphines. In a dry Schlenk tube, Rh(I) complexes 15 or
16 (200 mg, 0.1 mmol) and [FcH][PF6] (70 mg, 0.2 mmol) were
dissolved in dichloromethane (10 mL) and stirred for 1 h at room
temperature. Addition of n-pentane and filtration gave the Fe(III)
complexes 15[PF6]2/16[PF6]2 as black solids.
■
Corresponding Author
*E-mail: frederic.paul@univ-rennes1.fr.
Notes
The authors declare no competing financial interest.
[{Fe(κ2-dppe)(η5-C5Me5)CC(p-C6H4PPh2)}2Rh(CO)Cl][PF6]2 (15-
[PF6]2). Yield: 95%. IR (KBr, ν in cm−1): 1973 (s, CO). Raman
(neat, cm−1): ν = 2007 (m, CC). 31P{1H} NMR (121 MHz,
ACKNOWLEDGMENTS
■
−
CD2Cl2): δ = −17.8 (broad s, ArPPh2), Pdppe and PF6 not detected.
1H NMR (300 MHz, CD2Cl2): δ = 28.4 (broad s, H2), 7.8 (s, HPh
+
The ANR Blanc program is acknowledged for financial support
(ANR 2010 BLAN 719). G.G. thanks Region Bretagne for
partial support of a PhD scholarship. S. Sinbandhit (CRMPO -
UMR 6226) is kindly acknowledged for his assistance during
the VT-NMR studies.
HPh/dppe), 7.6−7.5 (s, HPh), 6.9 (s, HPh/dppe), 6.3 (very broad s,
CH2/dppe), 6.2 (s, HPh/dppe), 3.6 (s, HPh/dppe), 1.5 (s, HPh/dppe), −2.7
(broad s, CH2/dppe), −10.6 (broad s, C5(CH3)5), −33.9 (very broad s,
H1) [See Chart 1 for labeling]. UV−vis (CH2Cl2): λmax/nm [ε/103
9002
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