Synthesis and (spectro)electrochemical behavior of 2,5-diferrocenyl-1- phenyl-1 H-phosphole

Article abstract of DOI:10.1021/om400201b

2,5-Diferrocenyl-1-phenyl-1H-phosphole (3) has successfully been prepared by a cyclization reaction of phenylphosphine with 1,4-diferrocenyl butadiyne. Subsequent reaction with elemental sulfur and selenium, respectively, leads to the formation of the appropriate phosphole sulfide (4) or selenide (5). Molecules 4 and 5 have structurally been characterized by single-crystal X-ray diffraction. Despite the tetrahedral environment at the phosphorus atom, the ^cC₄P ring itself is planar and coplanar with the cyclopentadienyl rings of the ferrocenyl termini. Electrochemical measurements revealed that the two ferrocenyl groups could be oxidized at discrete potentials, with separation of the individual redox waves of 280 (3), 240 (4), and 235 mV (5), respectively. These values agree with other examples of heterocyclic-bridged diferrocenyl compounds such as diferrocenylthiophene (260 mV) and diferrocenylfuran (290 mV). Compounds [3]⁺-[5]⁺ exhibit IVCT absorptions of weak to moderate strength, which conforms well to the predictions of the Hush two-state model for weakly coupled mixed-valence systems. These conclusions are supported by DFT and TD-DFT results, which satisfactorily model the observed structural and spectroscopic parameters. The computational work assists in assigning the various low-energy (LF, IVCT) electronic transitions and also highlights the key role of the unsaturated cis-diene-like C₄H₂ building block of the heterocycle in promoting the Fc → Fc⁺ electron-transfer transition.

Full text of DOI:10.1021/om400201b

Article
pubs.acs.org/Organometallics
Synthesis and (Spectro)electrochemical Behavior of 2,5-Diferrocenyl-
1-phenyl‑1H‑phosphole
Dominique Miesel,† Alexander Hildebrandt,† Marcus Korb,† Paul J. Low,‡,§ and Heinrich Lang*,†
†Technische Universitat Chemnitz, Faculty of Natural Sciences, Institute of Chemistry, Inorganic Chemistry, Straße der Nationen 62,
̈
09111 Chemnitz, Germany
‡Durham University, Department of Chemistry, South Road, Durham DH1 3LE, U.K.
S
* Supporting Information
ABSTRACT: 2,5-Diferrocenyl-1-phenyl-1H-phosphole (3) has
successfully been prepared by a cyclization reaction of phenyl-
phosphine with 1,4-diferrocenyl butadiyne. Subsequent reaction
with elemental sulfur and selenium, respectively, leads to the
formation of the appropriate phosphole sulfide (4) or selenide (5).
Molecules 4 and 5 have structurally been characterized by single-
crystal X-ray diffraction. Despite the tetrahedral environment at the
c
phosphorus atom, the C4P ring itself is planar and coplanar with
the cyclopentadienyl rings of the ferrocenyl termini. Electrochemical
measurements revealed that the two ferrocenyl groups could be
oxidized at discrete potentials, with separation of the individual
redox waves of 280 (3), 240 (4), and 235 mV (5), respectively. These values agree with other examples of heterocyclic-bridged
diferrocenyl compounds such as diferrocenylthiophene (260 mV) and diferrocenylfuran (290 mV). Compounds [3]+−[5]+
exhibit IVCT absorptions of weak to moderate strength, which conforms well to the predictions of the Hush two-state model for
weakly coupled mixed-valence systems. These conclusions are supported by DFT and TD-DFT results, which satisfactorily
model the observed structural and spectroscopic parameters. The computational work assists in assigning the various low-energy
(LF, IVCT) electronic transitions and also highlights the key role of the unsaturated cis-diene-like C4H2 building block of the
heterocycle in promoting the Fc → Fc+ electron-transfer transition.
Within recent studies of our research group it could be
demonstrated by the example of di-, tri-, and tetraferrocenyl
heterocycles (thiophenes, furans, and pyrroles)22,24 and metal-
lacycles featuring a Cp*2M (M = Ti, Zr)17,18 moiety that the
electronic characteristics (conjugation and distribution of
electron density) greatly influence the intermetallic communi-
cation between the mixed-valent termini. In continuation of this
work we herein present the synthesis and characterization of
diferrocenyl phosphole as well as its chalcogenides. While
neglected for decades, phospholes have gained increasing levels
of interest during the last few years.26−31 Their successful
application in metal-containing organic light-emitting devices
(OLEDs) accelerated the research on this topic.32,33 The
phosphole ring shows a degree of aromaticity depending on the
substituents in 1-, 2-, and 5-positions, as bulky substituents
force the phosphorus to adopt a planar environment. However,
blocking the phosphorus lone pair by coordination or oxidation
reactions, for example, prevents the extended conjugation
around the ring system and removes the aromaticity. Hence,
the phosphole motif may offer a tool to fine tune the electronic
nature of the π-conjugated connector unit and hence the
electronic effects that may be transmitted across it. This
INTRODUCTION
■
Compounds with two redox-active transition-metal fragments
connected via a π-conjugated spacer unit are of considerable
interest, as they can be regarded as model compounds for
molecular wires.1−14 In the last years huge efforts in the
development of molecules in which the two redox-active metal
centers exhibit a pronounced electronic communication across
the spacer unit have been made. During the course of these
investigations, a wide variety of π-conjugated spacers have been
explored, including systems based on all-carbon chains,
vinylogous moieties, aromatic hydrocarbons, metallacycles,
and heteroatom-containing groups.15−24 An equally wide
variety of metal fragments have been used as redox-active
termini, including half-sandwich, five- and six-coordinate metal
centers, metallocenyl groups, bimetallic complexes, and clusters,
with the degree of electronic interaction between them in the
mixed-valence state assessed by drawing on electrochemical and
spectroscopic (UV−vis/near-IR, IR, EPR) data, often sup-
ported by quantum chemical calculations.2,11,12,25 While it is
well-known that the electronic structure of such linear arrays,
and hence the “intermetallic communication” or coupling in the
mixed-valence state, depends on the nature of both the metal
termini and the spacer unit, predicting these a priori is not
always a simple task.
Received: March 13, 2013
© XXXX American Chemical Society
A
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a
Scheme 1. Synthesis of Phospholes 3−5
a
Legend: (i) benzene/thf (1/1, v/v), 0 °C, 1 h; (ii) thf, 25 °C, 12 h; Fc = Fe(η5-C5H5)(η5-C5H4).
the 1J Se values allow a quantification of the donor abilities of
31P77
potential electronic flexibility prompted us to study the mixed-
valence behavior of diferrocenyl phospholes as a function of the
chemical nature of the phosphorus atom.
phosphines PR3.35−38 An electron-withdrawing group results in
increased values for the coupling constants, indicating an
increased s character for the phosphorus orbital involved in the
31
1
phosphorus−selenium bond. P{1H} NMR data and J
RESULTS AND DISCUSSION
31P77Se
■
coupling constants for several phosphine selenides are
summarized in Table 1. A comparison with other P(III)
species showed that phosphole 3 can be characterized as a weak
donor.36−38
Synthesis and Characterization. 2,5-Diferrocenyl-1-phe-
nyl-1H-phosphole (3) was synthesized by cyclization of
phenylphosphine with diferrocenyl butadiyne according to a
reaction procedure first described by Markl and Potthast.34
̈
Phenylphosphine (1) was reacted with 0.8 equiv of n-
butyllithium, and the resulting solution was added slowly to
1,4-diferrocenyl butadiyne (2), giving 2,5-diferrocenyl-1-
phenyl-1H-phosphole (3) (Scheme 1). Treatment of 3 with
elemental sulfur or selenium resulted in the formation of the
corresponding phosphole chalcogenides 4 and 5 (Scheme 1).
Compounds 3−5 are stable toward air and moisture both in
the solid state and in solution. They have been characterized by
elemental analysis, IR and NMR (1H, 13C{1H}, 31P{1H})
spectroscopy, and ESI-TOF mass spectrometry. The electro-
chemical and spectroelectrochemical behavior was investigated
by cyclic voltammetry (CV) and square wave voltammetry
(SWV) as well as in situ UV−vis/near-IR and IR spectroelec-
trochemistry.
Table 1. 31P NMR Chemical Shifts and 31P−77Se Coupling
Constants for 5 and Several Phosphine Selenides
compd
δ (ppm)
1J
31P−77Se
(Hz)
5
33.2
35.9
745
35
SePPh3
732
753
703
683
39
SeP(4-Cl-C6H4)3
2.2
35
SeP(2,4,6-(MeO)3-C6H2)3
−16.8
41.6
40
SeP(4-NMe2-C6H4)3
The molecular structures of 4 and 5 in the solid state have
been determined by single-crystal X-ray diffraction analysis.
Suitable crystals were obtained by diffusion of n-hexane into a
dichloromethane solution of either 4 or 5 at ambient
temperature. The ORTEP diagrams with selected bond lengths,
bond angles, and torsion angles are shown in Figures 1 and 2.
Compounds 4 and 5 both crystallize in the orthorhombic
space group P212121. The ferrocenyl groups are antiparallel
oriented and are almost coplanar with the heterocyclic core
(torsion of the plane of the C5H4 unit to the plane of the
phosphole core: 4, −4.4(18)° for Fe1, 3.0(19)° for Fe2; 5,
3.3(12)° for Fe1, −1.7(11)° for Fe2). The conformation of the
cyclopentadienyl ligands in individual ferrocenyl units is almost
eclipsed (4, −8.73(81)° for Fe1, 5.33(75)° for Fe2; 5,
2.79(53)° for Fe1, −4.00(47)° for Fe2). The P1−C1−C2−
C3−C4 arrangement is planar (4, rms deviation 0.0025 Å,
highest deviation from planarity observed for P1 with
−0.0302(158) Å; 5, rms deviation 0.0078 Å, highest deviation
from planarity observed for P1 with 0.0280(101) Å). The
phosphorus atom possesses, as expected, a tetrahedral environ-
ment (Figure 1). The structural features found in phosphole
chalcogenides 4 and 5 resemble those typically found in other
examples of this family of molecules.41,42
For the 1H NMR spectra of all three diferrocenyl phospholes
3−5 one singlet for the C5H5 rings and four multiplets for the
C5H4 protons of the ferrocenyl substituents appear as the α-
and β-protons are diastereotopic, which is due to the prochiral
nature of the phosphorus atom. The signals of the CH
phosphole protons appear almost at the same chemical shift (3,
3
6.87 ppm; 4, 6.87 ppm; 5, 6.90 ppm) as doublets with JPH
=
3
3
11.4 Hz (3), JPH = 36.5 Hz (4), and JPH = 35.9 Hz (5). The
respective carbon atoms in the 13C{1H} NMR spectra of these
species are observed at ca. 130.5 ppm, which indicates that the
electronic character of the carbons (and attached protons) in 3-
and 4-positions of the heterocycle remain unchanged upon
oxidation of the phosphorus atom, while the JPH coupling
V
IIIH
constants change upon oxidation (JP < JP H). The signals of
the meta and para protons of the phenyl group in 3 appear as
an unresolved multiplet at 7.4 ppm (Experimental Section). For
the respective ortho protons a multiplet at 7.6 ppm could be
observed. In contrast, the ortho protons in 4 and 5 appear as
doublet of doublets of doublets at 8.02 ppm (4) and 8.04 ppm
(5) with 4JHH = 1.6 Hz, 3JHH = 7.9 Hz, and 3JHP = 14.0 Hz for 4
4
3
3
and JHH = 1.7 Hz, JHH = 7.8 Hz, and JHP = 14.3 Hz for 5.
After oxidation of P(III) in 3 to P(V) in 4 and 5 the signals of
the ferrocenyl and phenyl protons in 4 and 5 are shifted to
lower field. In the 31P{1H} NMR spectrum of phosphole 3 a
singlet at 5.1 ppm is characteristic. After oxidation with sulfur
and selenium, respectively, a shift to lower field (46.6 ppm (4),
33.2 ppm (5)) occurred.
Electrochemistry and Spectroelectrochemistry. The
redox properties of heterocycles 3−5 were investigated by
cyclic voltammetry, square wave voltammetry, and spectroelec-
trochemistry (UV−vis/near-IR, IR). As supporting electrolyte a
dry dichloromethane solution containing 0.1 mol L−1 of
[NnBu4][B(C6F5)4] or [NnBu4][PF6] was used, allowing effects
of ion pairing on the stability of the redox products to be
assessed in a qualitative fashion.43−45 The cyclic voltammetry
measurements were performed at 20 °C at a scan rate of 100
For selenide 5 the characteristic selenium satellites with a
1J
coupling constant of 745 Hz could be found. Typically,
31P77Se
B
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Figure 1. ORTEP diagram (50% probability level) of the molecular structure of 4 with the atom-numbering scheme. All hydrogen atoms have been
omitted for clarity. Selected bond distances (Å), angles (deg), and torsion angles (deg): D1−Fe1 = 1.6417(15), D2−Fe1 = 1.6542(15), D3−Fe2 =
1.6487(16), D4−Fe2 = 1.6504(16), P1−C1 = 1.815(12), C1−C2 = 1.363(15), C2−C3 = 1.450(14), C3−C4 = 1.337(14), C4−P1 = 1.851(10),
C1−C5 = 1.431(15), C4−C15 = 1.411(15), P1−C25 = 1.834(11), P1−S1 = 1.951(4); C2−C1−P1 = 106.6(8), C1−P1−C4 = 93.8(5), C3−C4−P1
= 105.6(8), C2−C1−C5 = 128.0(11), C3−C4−C15 = 130.2(9), D1−Fe1−D2 = 177.88(11), D3−Fe2−D4 = 179.78(12), C1−P1−C25 = 104.1(5),
C25−P1−C4 = 106.2(5), C1−P1−S1 = 116.9(4), C25−P1−S1 = 114.7(4), C4−P1−S1 = 118.4(4); C3−C4−C15−C16 = 3.0(19), C2−C1−C5−
C9 = −4.4(18), C2−C3−C4−P1 = 1.5(11), P1−C1−C2−C3 = −0.5(12), C5−D1−D2−C10 = −8.73(81), C15−D3−D4−C20 = 5.33(75). D
denotes the centroid of C5H4 or C5H5.
Figure 2. ORTEP diagram (50% probability level) of the molecular structure of 5 with the atom-numbering scheme. All hydrogen atoms have been
omitted for clarity. Selected bond distances (Å), angles (deg), and torsion angles (deg): D1−Fe1 = 1.6420(10), D2−Fe1 = 1.6496(10), D3−Fe2 =
1.6406(10), D4−Fe2 = 1.6411(10), P1−C1 = 1.827(7), C1−C2 = 1.349(9), C2−C3 = 1.443(9), C3−C4 = 1.358(9), C4−P1 = 1.819(8), C1−C5 =
1.415(10), C4−C15 = 1.439(10), P1−C25 = 1.807(7), P1−Se1 = 2.1047(15); C2−C1−P1 = 106.4(6), C4−P1−C1 = 93.8(4), C3−C4−P1 =
106.3(6), C2−C1−C5 = 128.2(7), C3−C4−C15 = 127.8(7), D1−Fe1−D2 = 177.45(8), D3−Fe2−D4 = 179.97(10), C25−P1−C1 = 104.5(3),
C25−P1−C4 = 106.8(3), C1−P1−Se1 = 116.3(2), C25−P1−Se1 = 115.0(2), C4−P1−Se1 = 117.8(2); C3−C4−C15−C16 = −1.7(11), C2−C1−
C5−C9 = 3.3(12), C2−C3−C4−P1 = −2.5(7), P1−C1−C2−C3 = −0.6(8), C5−D1−D2−C10 = 2.79(53), C15−D3−D4−C20 = −4.00(47). D
denotes the centroid of C5H4 or C5H5.
mV s−1. All potentials are referenced to the FcH/FcH+ redox
couple.46 The data of the cyclic voltammetry experiments are
summarized in Table 2. The voltammograms of 3−5 measured
in the presence of [NnBu4][B(C6F5)4] are shown in Figure 3,
and those measured using [NnBu4][PF6] as supporting
electrolyte are depicted in Figure SI1 (Supporting Informa-
tion).
The ferrocenyl groups of compounds 3−5 could be oxidized
separately, showing two reversible redox events in each
electrolyte system with differences between the cathodic peak
potential and the anodic peak potential (ΔEp) falling between
68 and 80 mV (Table 2), and peak currents proportional to ν1/2
being observed confirming the essentially reversible character of
these ferrocenyl-based oxidation events. The electron-with-
drawing character of the P(V) center in 4 and 5 leads to a shift
of the E°1′ values to more positive potentials relative to the
P(III) species 3. The more electron-rich P(III) center also leads
to an enhanced thermodynamic stability of the mono-oxidized
complex [3]+, evidenced by the greater comproportionation
constant (KC) (Table 2). Due to the higher ion-pairing
C
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a
were performed in an OTTLE (optically transparent thin-layer
electrochemical) cell.48 The compounds were oxidized by
stepwise increase in the applied potential (step width 25, 50, or
100 mV). During the measurements, oxidation of the neutral
compounds to mixed-valence monocationic [3]+−[5]+ and
finally to the dicationic species [3]2+−[5]2+ could be observed.
To prove the reversibility after full oxidation, each compound
was reduced and the resulting UV−vis/near-IR spectra are
identical with those of the starting compound. The UV−vis/
near-IR spectra of phospholes 3−5 measured in dichloro-
methane are depicted in Figures 4 (3), SI2 (4), and SI3 (5),
and the spectra measured in acetonitrile are shown in Figures
SI4 (3), SI5 (4) and SI6 (5) (Figure SI2-SI6 are given in the
Supporting Information). Phospholes 3−5 show, as expected,
no absorptions in the near-IR region (1000−3000 nm). Upon
oxidation of these molecules mixed-valence [3]+−[5]+ are
formed, resulting in the appearance of a broad band enveloping
between 1500 and 2500 nm (Figure 4 and Figure SI2)). A
further potential increase above 500 mV vs Ag/AgCl leads to
the disappearance of these absorptions, a behavior typically
observed for intervalence charge transfer (IVCT) excitations.
The observed spectra can be deconvoluted into three Gaussian-
shaped bands, which are assumed to represent the IVCT
transition, a LF (ligand field) transition associated with the
ferrocenium moiety, and a third band simulating the edge to
the higher energy absorptions. The sum of these three Gaussian
functions allows an almost exact overlay with the experimental
spectra. Therefore, the intensity εmax, the full width at half-
height Δν1/2, and the νmax values associated with the IVCT
component could be determined.
The data derived from deconvoluted IVCT absorption bands
from [3]+−[5]+ are summarized in Table 3, although the
assignment and interpretation of absorption profiles taken from
deconvolution should always be treated with caution, as the
underlying band shapes are sensitive to the degree of coupling.
To help confirm the IVCT assignment, the spectroelectro-
chemical UV−vis/near-IR experiments were also carried out in
acetonitrile as a solvent, as the IVCT band of a class II
compound should display solvatochromic behavior.3,13,50
Changing the polarity of the solvent from P = 3.1 (dichloro-
methane) to P = 5.8 (acetonitrile) resulted in hypsochromic
shifts of 1500 cm−1 (3+) and 2000 cm−1 (4+, 5+) (Table 3).51
This solvatochromic behavior is entirely consistent with the
IVCT assignment.
Table 2. Cyclic Voltammetry Data of Compounds 3−5
E°1′, mV (ΔEp, E°2′, mV (ΔEp,
ΔE°′,
KC/
compd (electrolyte)
mV)
mV)
mV
104
3 ([NnBu4][PF6])
4 ([NnBu4][PF6])
5 ([NnBu4][PF6])
−135 (76)
−65 (76)
−60 (80)
−110 (72)
50 (62)
100 (76)
100 (78)
170 (80)
185
165
160
280
0.14
0.05
0.05
5.4
3 ([NnBu4]
[B(C6F5)4])
4 ([NnBu4]
−15 (68)
−15 (74)
225 (74)
220 (80)
240
235
1.1
0.9
[B(C6F5)4])
5 ([NnBu4]
[B(C6F5)4])
a
Potentials vs FcH/FcH+, scan rate 100 mV s−1 at glassy-carbon
electrode of 1.0 mmol L−1 solutions of 3−5 in dry dichloromethane;
0.1 mol L−1 [NnBu4][B(C6F5)4] or [NnBu4][PF6] as supporting
electrolyte at 20 °C.
capability (spherical diameter [PF6]−, 3.3 Å; [B(C6F5)4]−, 10
Å), the use of dichloromethane and [NnBu4][PF6] as solvent/
supporting electrolyte results in a lower redox splitting (ΔE°′)
(Table 2).47 The difference between ΔE°′[PF ] to ΔE°′[B(C F ) ]
−
−
6
6 5 4
of about 75−100 mV mostly reflects the electrostatic
contribution to the stability of mixed-valent monocationic
molecules [3]+−[5]+. A comparison of phospholes 3−5 with
analogous bis(ferrocenes) featuring thiophene-, furan-, and
pyrrole-derived bridges reveals similar trends in the first
oxidation potential, E°1′, and ΔE°′ under identical conditions,
with the more readily oxidized complexes bearing the more
electron donating heteroatoms giving rise to the larger ΔE°′
values and hence larger KC values. For example, ΔE°′ for 3−5
and other 2,5-diferrocenyl-substituted heterocycles fall in the
sequence NPh (450 mV) > NMe (410 mV) > O (290 mV) ≈ 3
(280 mV) > S (260 mV) > 4 (240 mV) = 5 (235 mV).22 The
ΔE°′ values (Table 2) indicate sufficient stability of the
monocations with respect to disproportionation to the neutral
and dicationic forms. Assuming that the oxidation processes are
ferrocene-based, which seems reasonable given the chemical
composition, and given the robustness of the ferrocene/
ferrocenium redox couple, the mixed-valence species [3]+−[5]+
could be characterized by in situ spectroelectrochemical
methods to address the underlying electronic structures and
influence of the bridging ligand on the electronic properties.
The UV−vis/near-IR spectroelectrochemical measurements
of dichloromethane solutions containing 3−5 (2.0 mmol L−1)
and [NnBu4][B(C6F5)4] (0.1 mol L−1) as supporting electrolyte
Figure 3. (left) Cyclic voltammograms of 3−5; scan rate 100 mV s−1. (right) Square wave voltammograms of 3−5 in dichloromethane solutions (1.0
mmol L−1) at 20 °C; supporting electrolyte 0.1 mol L−1 [NnBu4][B(C6F5)4], glassy carbon working electrode (surface area 0.031 cm2).
D
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Figure 4. (left) UV−vis/near-IR spectra of 3 at 20 °C in dichloromethane (2.0 mmol L−1) at rising potentials (bottom, −200 to 560 mV; top, 560 to
800 mV vs Ag/AgCl); supporting electrolyte [NnBu4][B(C6F5)4]. (right) Deconvolution of the near-IR absorptions of [3]+ using three Gaussian-
shaped bands determined by spectroelectrochemistry in an OTTLE cell.
IVCT absorptions of sulfide 4 and selenide 5 show smaller
intensities (4, 1300 L mol−1 cm−1; 5, 1100 L mol−1 cm−1)
(Table 3). This indicates that the involvement of the
phosphorus lone pair in bonding to the chalcogenide element
Table 3. Near-IR Data of the IVCT Absorptions of
a
Phospholes [3]+−[5]+
b
νmax, cm−1 (εmax
,
Δν1/2
,
(Δν1/2
)
,
theor
solvent
compd
L mol−1 cm−1
)
cm−1
cm−1
c
slightly decreases the interaction among the C4P ring and
dichloromethane
[3]+
[4]+
[5]+
[3]+
[4]+
[5]+
5000 (1750)
4900 (1300)
4850 (1100)
6500 (1600)
3050
4200
4200
3200
3100
3400
3400
3360
3350
3870
3990
3990
characterizes those two molecules as weak class II compounds.
In general, the characteristics of the IVCT absorptions resemble
those found for 1,4-diferrocenyl butadiene (νmax 5290 cm−1,
εmax = 2280 L mol−1 cm−1, Δν1/2 = 3900 cm−1).55 One may
conclude that the C4 backbone mainly promotes the electron
transfer between the ferrocenyl termini.
acetonitrile
c
6900
c
6900
a
In dry dichloromethane or acetonitrile containing 0.1 mol L−1 of
b
[NnBu4][B(C6F5)4] as supporting electrolyte at 20 °C. Values
Computational Studies. To help characterize the redox
products and better understand the nature of the electronic
transitions, electronic structure calculations were carried out.
The computational systems are designated [3′]n+, [4′]n+, and
[5′]n+ (n = 0−2) to distinguish them from the experimental
complexes. All geometry optimizations and TD-DFT calcu-
lations were undertaken using the B3LYP functional and 3-
21G* basis set combination. In the case of the dications, the
triplet states were found to be considerably more stable than
the analogous singlet states (ΔET‑S = −134.27 kJ/mol ([3′]2+),
−81.21 kJ/mol ([4′]2+), −76.74 kJ/mol ([5′]2+)), and the
latter were not considered further. Selected bond lengths (Å)
and angles (deg) (Table SI1), orbital energy and composition
(Table SI2), calculated and spectroelectrochemically observed
IR data (Table 4) and TD-DFT results (Table SI3) are given in
the indicated tables (Tables SI1−SI3 are given in the
Supporting Information).
The optimized geometries are in excellent agreement with
the available experimentally determined structures of 4 and 5,
with individual bond lengths being overestimated by less than
0.03 Å. Within the neutral members of the series 3′−5′
oxidation of the PPh center from P(III) to P(V) leads to a
modest increase in the localization of the double bonds in the
heterocyclic ring and a small contraction of the Fc−C4H2 bond
lengths, probably due to increased electrostatic attraction.
However, these variations are small and in all cases the
phosphole ring system presents a clear alternation in bond
lengths consistent with a description in terms of a cyclic diene.
This description is entirely consistent with the distribution and
nodal properties of the HOMOs, which are derived from the
cis-butadiene-like π system of the C4H2 fragment mixed with
the ferrocenyl moieties, with vanishingly small contributions
1/2
calculated as (Δν1/2
)
= (2310νmax
)
according to the Hush
theor
relationships for weakly coupled systems.49 Due to the lack of
solubility of compounds 4 and 5 in acetonitrile, the extinction
coefficients were not determined.
c
Analysis of the IVCT absorption allows classification of 3 as a
moderately coupled class II system within the scheme proposed
by Robin and Day.5 A comparison of the IVCT absorption of
phosphole 3 (εmax = 1750 L mol−1 cm−1, Δν1/2 = 3050 cm−1)
with those of analogous 2,5-diferrocenyl substituted hetero-
cycles shows that the molar extinction coefficient can be placed
between those of 2,5-diferrocenyl furan (εmax = 1496 L mol−1
cm−1) and 2,5-diferrocenyl-1-methyl-1H-pyrrole (εmax = 3145 L
mol−1 cm−1).22 Nevertheless, the full width at half height of the
IVCT band in 3 exceeds those found in all other molecules of
the thus mentioned series, indicating a weaker interaction. It
should be noted that the Hush two-state model is only valid in
the weak class II regime, while stronger coupling includes
partial delocalization and therefore a more narrow bandwidth is
observed.49,52 Brunschwig, Creutz, and Sutin stated that the
quotient between the observed bandwidth and the theoretical
bandwidth according to Hush can be taken as a measure for the
strength of this coupling.50 Nevertheless, solvent broadening as
observed for [4]+ and [5]+ in dichloromethane (Table 3) also
contributes to the bandwidth and therefore hinders the direct
comparability. A good comparison to other diferrocenyl
heterocycles is complicated, because phosphole 3 possesses a
c
somewhat different geometry at the C4P backbone, as in
contrast to other heterocycles the phosphorus lone pair is only
c
involved to some extent in the delocalization of the C4E
ring.53,54 Thus, the phosphole behaves similarly to a cis-diene
system rather than an aromatic five-membered heterocycle. The
E
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Table 4. Selected Calculated (and Observed) IR-Active
ν(CC) Vibrations (cm−1) for [3′]n+, [4′]n+, and [5′]n+ (n =
a
0−2)
n = 0
n = 1
n = 2
b
[3′]n+ ([3]n+) 1595 w (−)
1421 s (1471 m)
1505 m (1556 w)
1398 m (1413 m) 1430 m (1455 w)
1363 s (1407 m)
[4′]n+ ([4]n+) 1548 m (1587 w) 1423 s (1486 m)
1403 s (1415 w)
b
1543 m (−)
1404 m (1434 m) 1455 m (1434 w)
1378 s (1421 m)
1409 s (1419 w)
b
[5′]n+ ([5]n+) 1546 m (1585 w) 1423 s (1481 m)
1541 m (−)
1402 m (1434 m) 1452 m (1463 w)
1376 m (1419 m) 1409 s (1434 w)
b
1374 m (−)
1390 s (1417)
a
b
Correction factor of 0.95 applied to all calculated frequencies. Signal
to noise ratio too low.
from the phosphorus atom and its substituents (Figure SI9 and
Table SI2, Supporting Information).
The optimized structures of the radical cations [3′]+−[5′]+
reflect the depopulation of the parent HOMO, with a subtle
(≤0.03 Å) contraction of the Fc-C4H2 and C(3)−C(4) bond
lengths and concomitant elongation in the C(3)−C(4) bond
(Table SI2, Scheme 2). Interestingly, while the C(1)−C(2) and
Scheme 2. Numbering Scheme for the Calculation of
Phospholes 3−5
Figure 5. Plots of the β-LUMO (top) and β-HOMO (bottom) of
[3′]+ (isosurface 0.04 (e bohr−3)1/2).
C(5)−C(6) bond lengths are arguably different in [3′]+
(C(1)−C(2) = 1.4315; C(5)−C(6) = 1.4199 Å), and there is
little difference in the C(2)−P and C(5)−P bond lengths
(1.8337, 1.8255 Å), the opposite is true of the P(V) complexes
[4′]+ and [5′]+ (Table SI2). However, while only small
structural distortions in the phosphole ring fragment hint at a
localized electronic structure, plots of the critical frontier
molecular orbitals (Figure 5, Table SI2) and the spin density
distributions (Figure 6) are more compelling. Again, the
phosphorus group makes little if any contribution to the
electronic description, and [3′]+−[5′]+ can each be accurately
described in terms of a localized oxidation on the ferrocenyl
moiety anti to the phosphole phenyl ring.
Figure 6. Plot of the spin density for the cation radical [3′]+
(isosurface 0.04 (e bohr−3)1/2).
trochemical methods were employed to obtain experimental IR
data, with measurements carried out on solutions of 3−5 in
dichloromethane (10 mmol L−1) containing 0.1 mol L−1
[NnBu4][PF6] as supporting electrolyte in an OTTLE cell
with CaF2 windows (Figure 7 and Figures SI7 and SI8
(Supporting Information)). The IR spectra of the neutral
complexes 3−5 are each characterized by a weak band near
1590 cm−1, which is replicated by calculated frequencies
between 1550 and 1600 cm−1 for the computational models
3′−5′ (Table 4). Analysis of the atomic displacements confirms
this feature to be an asymmetric ν(CC−CC) stretch
associated with the cis-butadiene fragment of the phosphole
moiety.
The triplet dications [3′]2+−[5′]2+ are also well described in
terms of ferrocene-based oxidation processes, and interestingly
the structural parameters of the phosphole ring are almost
indistinguishable from those of the parent neutral analogues.
The β-LUMO and β-LUMO+1 are each largely localized on a
ferrocenyl moiety, with the β-LUMO+1 in [4′]2+ and [5′]2+
also containing a small contribution from the C4H2 fragment
(Figure SI10, Supporting Information).
IR spectroscopy and calculated molecular vibrational
frequencies provide a useful link between experimentally
observable and calculated parameters, allowing the accuracy
of the optimized geometries to be assessed. IR spectroelec-
The cation radicals [3]+−[5]+ generated by one-electron
oxidation in the spectroelectrochemical cell display new
vibrational band envelopes between 1400 and 1500 cm−1. In
addition, a degree of decomposition of [3]+ is also evident by
appearance of a new feature near 1700 cm−1 in the spectrum
that is not sensitive to further changes in redox state (vide
F
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Figure 7. IR spectra of 4 at 20 °C in dichloromethane (10 mmol L−1) at rising potentials: (left) −200 to 600 mV (4 → [4]+); (right) 600 to 1300
mV ([4]+ → [4]2+). All potentials vs Ag/AgCl; supporting electrolyte [NnBu4][PF6].
infra). The lower frequency feature ([3]+, 1407 cm−1; [4]+,
1421 cm−1; [5]+, 1419 cm−1) can be assigned to the butadiene-
like ν(CC−CC) stretch ([3′]+, 1363 cm−1; [4′]+, 1378
cm−1; [5′]+, 1376, 1374 cm−1). The shift of this band to lower
frequency in the cation radicals in comparison with the neutral
species is consistent with the structure of the HOMO (3′−5′)
and β-LUMO ([3′]+,−[5′]+). The calculations also reveal a
relatively strong ν(C−C) stretch for the Fc+-C4H2 moiety
([3′]+, 1421 cm−1; [4′]+, 1423 cm−1; [5′]+, 1423 cm−1) and a
weaker ν(C−C) stretch for the Fc-C4H2 fragment ([3′]+, 1398
cm−1; [4′]+, 1404 cm−1; [5′]+, 1402 cm−1). These calculated
bands are consistent with the observed features at 1471, 1413
cm−1 ([3]+); 1486, 1434 cm−1 ([4]+), and 1481, 1434 cm−1
([5]+).
calculations with the cation radicals [3′]+−[5′]+ reveal two
low-energy (near-IR) excitations arising from the β-HOMO →
β-LUMO transition (i.e., IVCT character; Figure 5 and Table
SI3 (Supporting Information)) and a lower lying filled
ferrocenium orbital transition (β-HOMO-11, [3′]+ ; β-
HOMO-12, [4′]+ and [5′]+) to the β-LUMO, hence offering
more intraligand ferrocenium character. It is noteworthy that
the calculated oscillator strength of the transition with IVCT
character for [3′]+ is higher in comparison with that of [4′]+
and [5′]+, consistent with the trends in absorptivity observed in
the experimental spectra (Table SI3), which may be taken as an
indication of increased electronic interaction in the nonoxidized
phosphole. Although the relative energies of the IVCT and
ferrocenium-based LF transitions in the model cation radicals
[3′]+−[5′]+ are reversed relative to experiment, the results
support the general conclusions drawn from initial inspection of
the UV−vis/near-IR spectroelectrochemical results. The TD-
DFT calculations of [3′]+−[5′]+ also contain two higher energy
excitations near 11000 and 12000 cm−1, with FcC4H2 → Fc+
and Fc → C4H2Fc+ charge transfer character, which together
account for the absorption features observed in the
experimental spectra of the radical cations between 1000 and
650 nm (10000−15380 cm−1). In the case of the triplet
dications test calculations with [3′]2+ confirm the absence of
transitions with any oscillator strength below 16500 cm−1. The
most significant excitation is calculated at 19493 cm−1 with
considerable C4H2 → Fc+ character, consistent with the intense
absorption feature near 500 nm in the experimental spectra.
The IR spectra of the dications [3]2+−[5]2+ are characterized
by a complicated series of bands between 1415 and 1556 cm−1.
These complicated band patterns are consistent with the
calculated vibrational frequencies (Table 4); the strongest IR-
active modes have ν(CC−CC) and ν(C−C) Fc+-C4H2
character similar to that noted for the monocations, admixed
with additional aromatic ν(C−C) modes from both the
ferrocenium moieties and the phosphole phenyl ring.
TD-DFT calculations can provide a very useful link between
the calculated electronic structure and experimentally observ-
able electronic absorption spectra. While pure DFT functionals
perform poorly for excitations with considerable charge transfer
character, hybrid functionals with increasingly sophisticated
treatments of direct exchange can result in a much better
match, especially when calculations are augmented by a suitable
solvent model. In the present case, TD-DFT calculations with
even the relatively simple B3LYP functional and small basis set
(3-21G*) performed surprisingly well. The UV−vis/near-IR
spectra of 3−5 feature two absorption bands near 500 and 400
nm (20000 and 25000 cm−1). TD-DFT calculations with 3′
contain two excitations with significant oscillator strength at
18975 cm−1, which has largely ferrocene-based LF character
admixed with ferrocene to C4H2 charge transfer character, and
25445 cm−1, which has more clearly defined Fc → C4H2
character. For both 4′ and 5′ TD-DFT calculations reveal
two excitations of similar energy and character that are likely
responsible for the lower energy absorption band observed in
the experimental spectra (4′, 17921, 18050 cm−1; 5′, 17986,
18166 cm−1) and a higher energy transition with Fc → C4H2
character (4′, 23255 cm−1; 5′, 23584 cm−1). TD-DFT
CONCLUSION
■
2,5-Diferrocenyl-1-phenyl-1H-phosphole (3) and its chalcoge-
nides 4 (PS) and 5 (PSe) have been successfully prepared
by a cyclization reaction of phenylphosphine with 1,4-
diferrocenyl butadiyne and subsequent reaction with sulfur
and selenium, respectively. NMR spectroscopic studies revealed
a tetrahedral environment at phosphorus in 3−5. Therefore,
the interaction of the phosphorus’ lone pair with the dienic π
system is hindered. Oxidation to P(V) with sulfur or selenium
blocks any involvement in the delocalization of the C4
backbone. Nevertheless, the electronic character at the carbon
atoms at the 3- and 4-positions seems to remain unchanged.
Molecules 4 and 5 have been structurally characterized by
single-crystal X-ray diffraction, showing that they exhibit, as
expected, a planar geometry of the heterocyclic core. The
G
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Excel worksheet to set the formal reduction potentials of the FcH/
FcH+ couple to 0.0 V. Under our conditions the Fc*/Fc*+ couple was
at −619 mV vs FcH/FcH+, ΔEp = 60 mV, while the FcH/FcH+ couple
itself was at 220 mV vs Ag/Ag+, ΔEp = 61 mV.56
ferrocenyl groups are antiparallel oriented and are almost
coplanar with the C4P group. Electrochemical measurements
c
revealed that the two ferrocenyl groups in 3−5 undergo two
sequential one-electron-oxidation processes, with a significant
separation of the two waves (280 mV (3), 240 mV (4), and 235
mV (5)), due to a combination of environmental and inherent
electronic effects. As observed in spectroelectrochemical
investigations, all three compounds 3−5 exhibit IVCT
absorptions of weak to moderate strength. Upon oxidation of
phosphorus the intensity of the IVCT absorption decreases
from εmax = 1750 L mol−1 cm−1 (3) to εmax = 1300 L mol−1
cm−1 (4) and εmax = 1100 L mol−1 cm−1 (5), while the band
broadens (Δν1/2 = 3050 cm−1 (3), Δν1/2 = 4200 cm−1 (4, 5)).
This indicates that the occupation of the lone pair slightly
Spectroelectrochemistry. Spectroelectrochemical UV−vis/near-
IR measurements of 2.0 mmol L−1 solutions of 3−5 in dry
dichloromethane containing 0.1 mol L−1 of [NnBu4][B(C6F5)4] as
the supporting electrolyte were performed in an OTTLE (optically
transparent thin-layer electrochemical)48 cell with a Varian Cary 5000
spectrophotometer at 20 °C. Spectroelectrochemical IR measurements
of 10 mmol L−1 solutions of 3−5 in dry dichloromethane containing
0.1 mol L−1 [NnBu4][PF6] as supporting electrolyte were performed in
an OTTLE cell with CaF2 windows. The values obtained by
deconvolution could be reproduced within εmax = 100 L mol−1
cm−1: νmax 50 cm−1; Δν1/2 50 cm−1.
Single-Crystal X-ray Diffraction Analysis. Suitable single
crystals of 4 and 5 for X-ray diffraction analysis were obtained by
diffusion of n-hexane into a dichloromethane solution containing 4 or
5 at ambient temperature. Data were collected with an Oxford Gemini
S diffractometer at 100 K with graphite-monochromated Cu Kα
radiation (λ = 1.54184 Å) (4) or Mo Kα radiation (λ = 0.71073 Å)
(5). The structures were solved by direct methods and refined by full-
matrix least-squares procedures on F2.57,58 All non-hydrogen atoms
were refined anisotropically, and a riding model was employed in the
treatment of the hydrogen atom positions.
c
decreases the interaction among the C4P ring. However, the
electronic characteristics of this series of molecules resemble
those of a cis-diene structure more than those of an aromatic
system and the changes upon oxidation of the phosphorus are
therefore small. DFT and TD-DFT calculations in combination
with in situ IR spectroscopy support the general interpretation
of the electrochemical and in situ UV−vis/near-IR data,
allocating the main contribution of the electron transfer to
the C4H2 part of the bridging unit.
Reagents. All starting materials were obtained from commercial
suppliers and used without further purification. Phenylphosphine59
and 1,4-diferrocenyl butadiyne60 were prepared according to published
procedures.
EXPERIMENTAL SECTION
■
General Data. All reactions were carried out under an argon or
nitrogen atmosphere using standard Schlenk techniques. Tetrahy-
drofuran and benzene were purified by distillation from sodium/
benzophenone ketyl; dichloromethane was purified by distillation from
calcium hydride. For column chromatography silica was used with a
particle size of 40−60 μm (230−400 mesh (ASTM), Fa. Macherey-
Nagel).
Synthesis of 2,5-Diferrocenyl-1-phenyl-1H-phosphole (3).
To 0.25 g (2.3 mmol) of 1 in 30 mL of a 1/1 (v/v) tetrahydrofuran/
benzene mixture at 0 °C 0.7 mL (1.8 mmol) of n-butyllithium was
added dropwise. The resulting yellow solution was stirred for 10 min
at 0 °C and was then added dropwise to a solution of 0.95 g (2.3
mmol) of 1,4-diferrocenyl butadiyne (2) in 20 mL of tetrahydrofuran.
The deep red solution was stirred overnight at ambient temperature,
and then all volatiles were removed under vacuum. The remaining
solid was purified under argon by column chromatography (column
size 4 × 20 cm) on silica using a 5/1 (v/v) n-hexane/dichloromethane
mixture as eluent to give 3 as a red solid. Yield: 0.61 mg (1.2 mmol,
52% based on 1). Anal. Calcd for C30H25Fe2P (528.04 g/mol): C,
68.22; H, 4.77. Found: C, 68.15; H, 4.73. Mp: 207 °C. IR data (KBr,
ν/cm−1): 3086 m, 3037 m, 2954 m, 2920 w, 2847 w, 1714 w, 1635 w,
1562 m, 1477 m, 1433 m, 1408 m. 1H NMR (CDCl3, δ): 3.92 (s, 10H,
C5H5), 4.17 (m, 2H, C5H4), 4.18 (m, 2H, C5H4), 4.25 (m, 2H, C5H4),
Instruments. FT IR spectra were recorded with a Nicolet IR 200
spectrometer (Fa. Thermo). NMR spectra were recorded with a
1
Bruker Avance III 500 spectrometer (500.3 MHz for H, 125.7 MHz
for 13C{1H}, and 202.5 MHz for 31P{1H} spectra). Chemical shifts are
reported in δ (parts per million) downfield from tetramethylsilane
with the solvent as reference signal (1H NMR, CHCl3 δ 7.26; 13C{1H}
NMR, CDCl3 δ 77.16, CD2Cl2 δ 53.8; 31P{1H} NMR, standard
external relative to 85% H3PO4 δ 0.0, P(OMe)3 δ 139.0). The melting
points were determined using a Gallenkamp MFB 595 010 M melting
point apparatus. Elemental analyses were measured with a Thermo
FlashAE 1112 instrument. High-resolution mass spectra were recorded
on a Bruker Daltonik micrOTOF-QII spectrometer.
3
4.39 (m, 2H, C5H4), 6.87 (d, JHP = 11.4 Hz, 2H, C4H2P), 7.38−7.40
(m, 3H, Hm,Hp/C6H5), 7.58−7.62 (m, 2H, Ho/C6H5). 13C{1H} NMR
(CDCl3, δ): 65.83 (d, JCP = 3.9 Hz, C5H4), 67.18 (d, JCP = 6.8 Hz,
C5H4), 68.64 (d, JCP = 12.0 Hz, C5H4), 69.84 (s, C5H5), 82.39 (d, 2JCP
Electrochemistry. Electrochemical measurements on 1.0 mmol
L
−1 solutions of compounds 3−5 in dichloromethane were performed
= 20.0 Hz, Ci/C5H4), 128.92 (d, JCP = 8.7 Hz, C6H5), 130.07 (d, 2JCP
=
in a dried, argon-purged cell at 20 °C with a Radiometer Voltalab PGZ
100 electrochemical workstation interfaced with a personal computer.
[NnBu4][B(C6F5)4] or [NnBu4][PF6] (0.1 mol L−1) was used as
supporting electrolyte. For the measurements a three-electrode cell
containing a Pt auxiliary electrode, a glassy-carbon working electrode
(surface area 0.031 cm2), and an Ag/Ag+ (0.01 mmol L−1 [AgNO3])
reference electrode fixed on a Luggin capillary was used. The working
electrode was pretreated by polishing on a Buehler microcloth first
1.7 Hz, CH/C4H2P), 130.57 (d, JCP = 9.3 Hz, C6H5), 133.05 (d, JCP
=
4
11.7 Hz, Ci/C6H5), 134.98 (d, JCP = 21.1 Hz, Co/C6H5), 147.96 (d,
JCP = 1.5 Hz, Ci/C4H2P). 31P{1H} NMR (CDCl3, δ): 5.10 (s). HRMS
(ESI-TOF, m/z): calcd for C30H25Fe2P 528.0388, found 528.0384
[M]+.
Synthesis of 2,5-Diferrocenyl-1-phenyl-1H-phosphole Sul-
fide (4). To 0.10 g (0.19 mmol) of 3 in dichloromethane (20 mL) was
added 0.07 g (0.27 mmol) of elemental sulfur in a single portion. The
deep purple solution was stirred overnight at ambient temperature. All
volatiles were removed under vacuum, and the remaining solid was
purified by column chromatography (column size 3 × 15 cm) on silica
using a 3/1 (v/v) n-hexane/dichloromethane mixture. Compound 4
was obtained as a purple solid. Yield: 0.097 mg (0.17 mmol, 89% based
on 3). Anal. Calcd for C30H25Fe2PS·0.5CH2Cl2 (601.99 g/mol): C,
60.78; H, 4.35. Found: C, 60.57; H, 4.33. Mp: 248 °C. IR data (KBr,
ν/cm−1): 3081 w, 3039 w, 2960 m, 2923 m, 2853 w, 1727 w, 1646 w,
1585 m, 1464 m, 1433 m, 1405 m. 1H NMR (CDCl3, δ): 3.98 (s, 10H,
C5H5), 4.27 (m, 2H, C5H4), 4.29 (m, 2H, C5H4), 4.47 (m, 2H, C5H4),
1
with 1 μm and then /4 μm diamond paste. The reference electrode
was constructed from a silver wire inserted in a 0.01 mmol L−1
[AgNO3] and 0.1 mol L−1 [NnBu4][B(C6F5)4] or [NnBu4][PF6]
acetonitrile solution in a Luggin capillary with a Vycor tip. This Luggin
capillary was inserted in a second Luggin capillary containing a 0.1 mol
L−1 [NnBu4][B(C6F5)4] or [NnBu4][PF6] dichloromethane solution
and a Vycor tip. Experiments under the same conditions showed that
all reduction and oxidation potentials were reproducible within 5 mV.
Experimental potentials were referenced against an Ag/Ag+ reference
electrode, but the presented results are referenced against ferrocene as
an internal standard, as required by IUPAC.46 To achieve this, each
experiment was repeated in the presence of 1 mmol L−1
decamethylferrocene (Fc*). Data were processed on a Microsoft
3
4.62 (m, 2H, C5H4), 5.30 (s, CH2Cl2), 6.87 (d, JHP = 36.5 Hz, 2H,
3
C4H2P), 7.48−7.52 (m, 3H, Hm,Hp/C6H5), 8.02 (ddd, JHH = 7.9 Hz,
H
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Article
3
4JHH = 1.6 Hz, JHP = 14.0 Hz, 2H, Ho/C6H5). 13C{1H} NMR
financial support. PJL thanks the EPSRC for financial support
(CD2Cl2, δ): 53.52 (s, CH2Cl2), 66.45 (d, JCP = 6.3 Hz, C5H4), 67.53
(d, JCP = 5.8 Hz, C5H4), 69.84 (d, JCP = 12.5 Hz, C5H4), 70.58 (s,
C5H5), 77.65 (d, 2JCP = 22.5 Hz, Ci/C5H4), 129.26 (d, JCP = 12.4 Hz,
and the award of a Leadership Fellowship.
REFERENCES
■
C6H5), 129.68 (d, 1JCP = 12.8 Hz, Ci/C6H5), 130.61 (d, 2JCP = 24.1 Hz,
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1
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3 was reacted with 0.02 g (0.25 mmol) of selenium to give 5 as a
purple solid. Yield: 0.109 mg (0.18 mmol, 86% based on 3). Anal.
Calcd for C30H25Fe2PSe (607.96 g/mol): C, 59.35; H, 4.15. Found: C,
59.15; H, 4.49. Mp: 263 °C. IR data (KBr, ν/cm−1): 3074 w, 3048 w,
2958 m, 2923 m, 2853 w, 1738 m, 1653 w, 1582 m, 1461 m, 1433 m,
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1
1407 m. H NMR (CDCl3, δ): 3.97 (s, 10H, C5H5), 4.27 (m, 2H,
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3
6.90 (d, JHP = 35.9 Hz, 2H, C44H2P), 7.47−7.52 (m, 3H, Hm,Hp/
3
3
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C6H5), 8.04 (ddd, JHH = 7.8 Hz, JHH = 1.7 Hz, JHP = 14.3 Hz, 2H,
Ho/C6H5). 13C{1H} NMR (CD2Cl2, δ): 66.80 (d, JCP = 6.2 Hz, C5H4),
67.42 (d, JCP = 6.0 Hz, C5H4), 69.81 (d, JCP = 9.3 Hz, C5H4), 70.67 (s,
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2
CH/C4H2P), 131.64 (d, JCP = 11.9 Hz, Co/C6H5), 132.59 (d, JCP
=
3.1 Hz, C6H5), 141.57 (d, JCP = 74.4 Hz, Ci/C4H2P). 31P{1H} NMR
1
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9898 reflections collected, 4283 independent reflections (Rint
=
Ruffer, T.; Spannenberg, A.; Lang, H.; Rosenthal, U. Chem. Eur. J.
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ASSOCIATED CONTENT
■
S
* Supporting Information
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Chem. 2011, 50, 10623−10632.
Figures, tables, and CIF files giving further (spectro)-
electrochemical spectra, computational data, and crystallo-
graphic data for 4 and 5. This material is available free of charge
via the Internet at http://pubs.acs.org. Crystallographic data of
4 and 5 are also available from the Cambridge Crystallographic
Database as file numbers CCDC 928309 (4) and 928310 (5).
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AUTHOR INFORMATION
■
(27) Dienes, Y.; Durben, S.; Kar
́ ́
pati, T.; Neumann, T.; Englert, U.;
Corresponding Author
Nyulas
́
zi, L.; Baumgartner, T. Chem. Eur. J. 2007, 13, 7487−500.
*H.L.: e-mail, heinrich.lang@chemie.tu-chemnitz.de; tel, +49
(0)371-531-21210; fax, +49 (0)371-531-21219.
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should be directed.
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The authors declare no competing financial interest.
́
u,
ACKNOWLEDGMENTS
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We are grateful to the Fonds der Chemischen Industrie (FCI)
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