Charge and spin confinement to the amine site in 3-connected triarylamine vinyl ruthenium conjugates

Article abstract of DOI:10.1021/om4007455

The triarylamine vinyl ruthenium conjugate (4-OMeC₆H ₄)₂N{C₆H₄-3-CHi - -CH-RuCl(CO)(PⁱPr₃)₂} (m-1) has been prepared and investigated in its neutral and one-electron-oxidized states. Comparison with tris(4-anisylamine), An₃N, and the related 4-methoxystyryl complex 4-OMeC₆H₄-CHi - -CH-RuCl(CO)(P ⁱPr₃)₂, 2, shows that the intrinsic formal potentials of the two nonidentical redox-active subunits of complex m-1 (triarylamine and vinyl ruthenium) are very similar. Complex m-1 is oxidized in two consecutive one-electron waves with a half-wave potential splitting of 320 mV. Detailed investigations of the one-electron-oxidized radical cation m-1 ^?+ by IR and EPR spectroscopy and by quantum chemical calculations as well as comparison to An₃N^?+ and 2^?+ indicate that the charge and the unpaired spin of m-1 ^?+ are dominantly located on the triarylamine site. This is in stark contrast to the previously published para isomer p-1^?+, which, despite the nonidentical redox sites, is a fully delocalized mixed-valent system of Class III. As a consequence of partial charge localization, the low-energy absorption bands in the near-infrared assume the character of ruthenium or styryl ruthenium to triarylamine intervalence charge-transfer (IVCT) transitions with significantly diminished absorptivities compared to the highly intense charge resonance bands of p-1^?+. Hush analysis of the IVCT bands indicates that m-1^?+ is a significantly coupled mixed-valent system of Class II. The crystallographically determined structures of complexes m-1 and 2 and of the amine precursor (4-OMeC₆H ₄)₂N(C₆H₄Br-3) (An₂N-Br) are also reported.

Full text of DOI:10.1021/om4007455

Article
pubs.acs.org/Organometallics
Charge and Spin Confinement to the Amine Site in 3‑Connected
Triarylamine Vinyl Ruthenium Conjugates
†
†
†
‡
,†
Walther Polit, Philipp Mu
̈
cke, Evelyn Wuttke, Thomas Exner, and Rainer F. Winter*
†
Fachbereich Chemie, Universitat
̈
Konstanz, Universitat
Pharmazeutisches Institut, Eberhard-Karls Universitat Tu
S Supporting Information
̈
sstraße 10, D-78457 Konstanz, Germany
‡
̈
̈
bingen, Auf der Morgenstelle 8, D-72076 Tu
̈
bingen, Germany
*
ABSTRACT: The triarylamine vinyl ruthenium conjugate (4-OMeC H ) N-
6
4 2
i
{
C H -3-CHCH-RuCl(CO)(P Pr ) } (m-1) has been prepared and
6
4
3 2
investigated in its neutral and one-electron-oxidized states. Comparison with
tris(4-anisylamine), An N, and the related 4-methoxystyryl complex 4-
3
i
OMeC H -CHCH-RuCl(CO)(P Pr ) , 2, shows that the intrinsic formal
6
4
3 2
potentials of the two nonidentical redox-active subunits of complex m-1
(
triarylamine and vinyl ruthenium) are very similar. Complex m-1 is oxidized in
two consecutive one-electron waves with a half-wave potential splitting of 320
mV. Detailed investigations of the one-electron-oxidized radical cation m-1• by
IR and EPR spectroscopy and by quantum chemical calculations as well as
+
•
+
•+
comparison to An N and 2 indicate that the charge and the unpaired spin of
3
•
+
m-1 are dominantly located on the triarylamine site. This is in stark contrast
to the previously published para isomer p-1 , which, despite the nonidentical
•+
redox sites, is a fully delocalized mixed-valent system of Class III. As a consequence of partial charge localization, the low-energy
absorption bands in the near-infrared assume the character of ruthenium or styryl ruthenium to triarylamine intervalence charge-
transfer (IVCT) transitions with significantly diminished absorptivities compared to the highly intense charge resonance bands of
•
+
•+
p-1 . Hush analysis of the IVCT bands indicates that m-1 is a significantly coupled mixed-valent system of Class II. The
crystallographically determined structures of complexes m-1 and 2 and of the amine precursor (4-OMeC H ) N(C H Br-3)
6
4 2
6
4
(
An N-Br) are also reported.
2
INTRODUCTION
of triarylamines, as is shown by the very similar properties of
bis(triarylamine)- and bis(vinylruthenium)-appended styre-
■
Triarylamines combine a convenient synthesis from cheap
commercial starting materials with very favorable electro-
chemical properties. They usually undergo reversible oxidations
at well-accessible formal potentials that are easily tuned by the
substituents on the aryl rings. Their associated radical cations
are generally stable if para substituents on the arenes prevent
benzidine-type rearrangements. Owing to these favorable
properties, triarylamines have found extensive use as selective
6
d,8
9
10
2
nes, squaraines, and [2.2]paracyclophanes. We and others
have just demonstrated that alkynyl or alkenyl ruthenium
triarylamine conjugates N(C H ) {−CC−C H -RuCl-
6
5
n
6
4
1
1
3
(dppe) }
(n = 1 or 3) and N(C H -4-OMe) {(C H -4-
2
3−n 6 4 n 6 4
i
CHCH−)RuCl(CO)(P Pr ) }
(n = 1−3) constitute
3
2 3−n
highly electrochromic compounds with as many accessible
redox states as electroactive NAr and alkynyl or vinyl metal
3
3
a,c,4
moieties are present. In particular the vinyl systems show
massive NIR absorptions (ε of up to 90.000 and oscillator
strengths f of up to 1.0) for the higher oxidized forms (n = 2:
one-electron oxidants and electrocatalysts
or as hole-
conducting materials in electrooptical devices or in
5
xerography. Moreover, their radical cations display intense
2
+, n = 3: 2+ and 3+). The mixed-valent radical cation of the
absorptions at low energies whose positions can again be tuned
by the aryl substituents. These absorptions are shifted well
into the near-infrared (NIR) for the mixed-valent radical
cations of bis(triarylamine)s [Ar N(μ-arylene)NAr ] and
move to higher energies into the vis/NIR borderline region
upon further oxidation to their dications. Mono- and
bis(triarylamine)s hence constitute two- or three-state poly-
electrochromic materials whose absorption profiles change
reversibly upon the application of a suitable potential, which
3d
monoruthenium complex (4-OMeC H ) N{C H -4-CH
6
4
2
6
4
i
CH-RuCl(CO)(P Pr ) } (p-1 in Chart 1) exhibits full charge
3
2
•
+
and spin delocalization over the electroactive NAr and vinyl
3
2
2
ruthenium subunits, as is indicated by the Ru(CO) band shift
of about half the magnitude of that observed in the related
6
i
12
styryl complex (C H -4-CHCH−)RuCl(CO)(P Pr ) .
6
5
3 2
Moreover, hyperfine splittings of the unpaired spin with the
amine nitrogen atom of one site and the phosphorus and
ruthenium nuclei of the other are half those in the
7
makes them good candidates for the construction of “smart
windows”.
Vinyl ruthenium complexes of the type (RCHCH−)-
Received: July 26, 2013
Published: September 20, 2013
i
RuCl(CO)(P Pr ) can be viewed as metal−organic analogues
3
2
©
2013 American Chemical Society
5461
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Organometallics
Article
Chart 1
Scheme 1
•
+
trianisylaminium radical cation [N(C H -4-OMe) ]
shira coupling of the resulting 3-bromo-N,N-di(4-
6
4
3
•
+
13
(
(
An N )
and in [(C H -4-CHCH−)RuCl(CO)-
methoxyphenyl)aniline An N-Br with trimethylsilyl acetylene
3
6
5
2
i
•+ 12
P Pr ) ] , but very similar to those in the related arylene-
(70%) followed by deprotection (KF, MeOH, 97%), and the
3
2
6
f,8b,14
bridged bis(triarylamine) radical cations
and in [1,4-
subsequent insertion of the ethynyl function of the free alkyne
i
•+ 15
i
C H {−CHCH-RuCl(CO)(P Pr ) } ] . The strong elec-
into the Ru−H bond of HRuCl(CO)(P Pr ) (97%). The first
6
4
3 2
2
3 2
tronic coupling in these conjugates and their radical cations is a
consequence of significant aryl contributions to the occupied
frontier levels (FMOs) of triarylamines and of styryl ruthenium
complexes and their close FMO energies. Similar properties
have already been reported for neutral triarylamine tris-
reaction provides a more straightforward access to the
brominated precursor than the original three-step synthesis of
Bushby et al. A comparison of the H NMR data of
17
1
precursors An N-Br, An N-CCTMS, and An N-CCH with
2
2
2
those of m-1 reveals a continuous downfield shift of the
resonance signals of the four unique protons at the 3-
substituted phenyl ring and, to a smaller degree, of the arene
protons at the anisyl groups as the 3-substituent becomes more
electron releasing (see Experimental Section). As a point of
comparison for the electrochemical and spectroscopic proper-
ties of m-1 we also investigated the 4-methoxystyryl ruthenium
complex 2 (Chart 1), which was analogously prepared from 4-
(
perchlorophenyl)methyl radicals, which likewise constitute
rare cases of strongly or completely delocalized mixed-valent
16
systems with two dissimilar redox sites.
In all these systems the two redox-active subunits are in
direct conjugation through 1,4-disubstituted (oligo)phenylene
bridges, often with additional alkynyl or alkenyl spacers. We
herein disclose that changing the 1,4- into the 1,3-disubstitution
pattern has a dramatic influence on the formal potentials and
the degree of electronic coupling in a triarylamine vinyl
ruthenium conjugate and leads to charge and spin localization
18
methoxyphenylacetylene (98%). The NMR spectra of styryl
complexes m-1 and 2 display all the characteristic features of
this class of compounds such as the signals of the vinyl protons
and carbon atoms at 8.35 and 151.3 or 8.25 and 146.5 ppm
on the NAr unit and only weak NIR electrochromism.
3
(
Ru-CH) and at 5.86 and 134.7 or 5.90 and 133.8 ppm (Ru-
RESULTS AND DISCUSSION
CHCH) for complexes m-1 and 2, respectively, with the
■
3
2
4
The synthesis of complex m-1 was accomplished in the overall
four-step procedure of Scheme 1 involving Ullman coupling of
-bromoaniline with 2 equiv of 4-iodoanisol (49%), Sonoga-
JH,H coupling of 12.8 or 13.4 Hz and resolved JP,C and JP,H
couplings in the usual range of 11 or 2 Hz, respectively. Other
characteristic resonance signals include the Ru(CO) at 203.5 or
3
5
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Article
2
2
09.4 ppm ( J
ca. 13 Hz), the proton and carbon signals of
P−C
i
31
the P Pr protons, and the singlet resonance in the P NMR
3
spectrum at 38.2 or 38.3 ppm. Further details can be found in
the Experimental Section.
Suitable crystals for an X-ray analysis of An N-Br and
2
complexes m-1 and 2 could be grown from CH Cl by layering
2
2
with n-hexane (An N-Br, m-1) or MeOH (2). Amine An N-Br
2
2
crystallizes in the monoclinic space group P2 /c with four
1
identical molecules in the unit cell. Details of the data collection
and refinement are compiled in Table 1 of the Supporting
Information. The three arene rings show the usual propeller-
like arrangement but with a notably high degree of coplanarity
of the acceptor-substituted 3-bromophenyl ring and the plane
through the central nitrogen atom and the ipso carbon atoms of
the attached aryl rings (see Figure 1) with an interplanar angle
Figure 2. ORTEP of a molecule of complex m-1 with ellipsoids shown
at the 30% probability level. Hydrogen atoms are omitted for reasons
of clarity. Important bond lengths (in Å) and angles (in deg): Ru(1)−
Cl(1) 2.4326(11), Ru(1)−P(1) 2.3987(11), Ru(1)−P(2) 2.4066(11),
Ru(1)−C(41) 1.817(4), Ru(1)−C(1) 1.999(4), C(1)−C(2) 1.336(5),
C(2)−C(3) 1.472(5), C(7)−N 1.419(4), C(9)−N 1.423(5), C(15)−
N 1.423(5), Cl(1)−Ru(1)−C(1) 100.47(11), C(41)−Ru(1)−C(1)
89.18(16), P(1)−Ru(1)−C(1) 93.44(11), P(2)−Ru(1)−P(1)
97.24(11), P(1)−Ru(1)−P(2) 169.27(2), Cl(1)−Ru(1)−C(41)
170.21(12), Ru(1)−C(1)−C(2) 133.4(3), C(1)−C(2)−C(3)
124.2(3), C(7)−N(1)−C(9) 119.8(3), C(7)−N(1)−C(15)
120.0(3), C(9)−N(1)−C(15) 119.5(3).
error margins. The vinyl ligand shows an unusual high deviation
from coplanarity with the Ru(CO)Cl plane and the attached
phenyl ring, as is indicated by torsional angles Cl(1)−Ru(1)−
C(1)−C(2) of 167.3(4)°, C(41)−Ru(1)−C(1)-C(2) of
Figure 1. ORTEP of a molecule of An N-Br with ellipsoids shown at
2
the 30% probability level. Hydrogen atoms are omitted for clarity
reasons. Important bond lengths (in Å) and angles (in deg): N(1)−
C(1) 1.436(3), N(1)−C(7) 1.437(4), N(1)−C(13) 1.404(3), C(17)−
Br(1) 1.905(3), C(1)−N(1)−C(7) 117.0(2), C(1)−N(1)−C(13)
−
16.1(4)°, Ru(1)−C(1)−C(2)−C(3) of 172.2(3)°, C(1)−
C(2)−C(3)−C(4) of −36.2(6)°, and C(1)−C(2)−C(3)−
C(8) of 143.5(4)°. Such rotation limits π-conjugation between
the redox-active triarylamine and vinyl ruthenium entities.
Hydrogen bonding between hydrogen atom H(14) next to the
vinyl substituent and O(1) of a neighboring molecule (2.568 Å,
0.152 Å shorter than the sum of the van der Waals radii) might
also contribute to the observed torsion in the crystalline state
(see Figure 2 of the Supporting Information). We note here
that the quantum chemically optimized structure of the slightly
truncated PMe model complex m-1 has an almost perfectly
120.4(2), C(7)−N(1)−C(13) 118.9(2).
of 20.2°. The latter contrasts with the interplanar angles of
4.6° and 61.5° for the two anisyl rings. Preferred conjugation
5
with the nitrogen lone pair is also indicated by the short N(1)−
C(13) bond of 1.404(3) Å when compared to the N(1)−C(1)
and N(1)−C(7) bonds of 1.436(3) and 1.437(4) Å. Similar
trends are observed for other triarylamines bearing two 4-anisyl
and a third, acceptor-substituted aryl ring such as (4-
3
Me
coplanar arrangement of the vinyl ruthenium fragment and the
aryl ring, as is indicated by torsional angles Ru(1)−C(1)−
C(2)−C(3) of 178.3° and C(1)−C(2)−C(3)−C(4) of −1.5°.
This suggests that the observed deviations might indeed
originate from “packing effects”. A comparison of the
experimental and computed values of relevant structural
parameters may be found in Table 3 of the Supporting
Information.
1
9
OMeC H ) N(C H -C(O)Me-4) and (4-OMeC H ) N-
6
4
2
6
4
6
4 2
20
{
C H -(COOH) -3,5}. In the crystal individual molecules
6 3 2
of An N-Br associate through C−Br···CC interactions of
2
3
.322 (Br(1), C(10)), 3.461 Å (Br(1), C(9)) and several CH···
O hydrogen bonds involving arene protons with CH···O
contacts of 2.503 and 2.684 Å (for a packing diagram see Figure
1
of the Supporting Information).
Figure 2 displays the crystallographic structure of complex
The 4-methoxystyryl ruthenium complex 2 crystallizes in the
m-1, which also crystallizes in the P2 /c space group (for a
monoclinic space group P2 /n (for relevant data see Table 4 of
1
1
listing of the data collection and structure refinement
parameters see Table 2 of the Supporting Information). With
interplanar angles of 36.1°, 37.1°, and 43.5°, all three donor-
substituted aryl rings of complex m-1 are similarly rotated out
the Supporting Information). As for m-1, the immediate
environment of the ruthenium atom shows all the characteristic
features of styryl ruthenium complexes with this particular
ligand set including the distorted square pyramidal geometry
with trans angles of the basal ligands of ca. 170° and the
displacement of the ruthenium atom out of the pyramid base
of the NC plane of the nitrogen and the three ipso carbon
3
atoms. All three N−C(ipso) bond lengths are equal within the
5
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Article
toward the apical alkenyl ligand (see Figures 2 and 3) and
ruthenium ligand bond lengths in the usual range of ca. 2.43 Å
the half-wave potential anodically by 186 mV and to basically
the same value as observed in N(C H OMe-4) (C H Cl-4)
6
4
2
6
4
3d
(
E1/2 = 0.290 V). Under the same conditions complex 2
shows a fully reversible first oxidation at 0.135 V. As for other
styryl ruthenium complexes of this type, a second one-electron
oxidation is observed at higher potential, here at 0.725 V. The
electron-donating methoxy substituent has the effect of shifting
the potentials of these oxidations cathodically by 145 and 125
mV, respectively, when compared to the parent styryl complex
and of slowing down detrimental chemical processes following
the second oxidation to a degree that allows for the observation
of the associated cathodic return peak, particularly at higher
sweep rates (see Figure 5 of the Supporting Information).
Complex m-1 features two interlinked, well-behaved electro-
active subunits and is hence oxidized in two consecutive,
chemically reversible one-electron waves at formal potentials of
0
.170 and 0.490 V against the ferrocene/ferrocenium couple
Figure 3. ORTEP of a molecule of complex 2 with ellipsoids shown at
the 30% probability level. Hydrogen atoms are omitted for reasons of
clarity. Important bond lengths (in Å) and angles (in deg): Ru(1)−
Cl(1) 2.4289(5), Ru(1)−P(1) 2.4102(5), Ru(1)−P(2) 2.4116(5),
Ru(1)−C(1) 1.808(2), Ru(1)−C(2) 1.992(2), C(1)−O(1) 1.160(3),
C(2)−C(3) 1.337(3), C(3)−C(4) 1.473(3), Cl(1)−Ru(1)−C(2)
(
Figure 4). The 320 mV splitting between these processes
101.17(7), C(1)−Ru(1)−C(2) 89.57(10), P(1)−Ru(1)−C(2)
93.92(6), P(2)−Ru(1)−C(2) 91.77(6), P(1)−Ru(1)−P(2)
174.26(2), Cl(1)−Ru(1)−C(1) 168.78(7), Ru(1)−C(1)−C(2)
135.2(2), C(2)−C(3)−C(4) 126.2(2).
for Ru−Cl, 2.40 Å for Ru−P, 2.00 Å for Ru−C(alkenyl), and
1
,8c,12,21
1
.81 Å for Ru−C(CO).
As in the vast majority of such
structures, the alkenyl ligand is oriented toward the CO ligand,
which has been attributed to secondary bonding interactions
between the occupied alkenyl π and unoccupied CO π*
orbitals. There are no particular intermolecular interactions in
the packing of 2 apart from very weak CH···π contacts just
below the sum of the van der Waals radii, which involve
2
2
i
Figure 4. Cyclic voltammogram of complex m-1 in CH Cl /NBu PF
2 2 4
protons of the Pr substituents on the phosphine ligands.
6
at rt and v = 0.1 V/s.
The electrochemical properties of the triarylamine precursor
An N-CCTMS and of complexes 2 and m-1 were investigated
2
5
translates into a comproportionation constant (K ) of 2.6 × 10
by cyclic voltammetry in the CH Cl /NBu PF supporting
c
2
2
4
6
and indicates that the radical cation is chemically stable with
respect to disproportionation. The comparison of the formal
potentials of m-1 to those of An N-CCTMS, An N, complex 2,
and the para-substituted analogue, complex p-1 (Chart 1), in
Table 1 reveals some interesting details. First, substitution of
electrolyte. Relevant data are collected in Table 1 along with
those of complex p-1 and An N. An N-CCTMS displays a
3
2
Nernstian oxidation wave at a formal potential of 0.295 V
against the internal ferrocene/ferrocenium standard (see Figure
2
3
4
of the Supporting Information for a representative CV).
Substitution of one 4-anisyl substituent of N(C H OMe-4)
3
the mildly electron withdrawing trimethylsilyl-protected
6
4
i
ethynyl function by the powerful CHCH-RuCl(CO)(P Pr )
(
An N, E = 0.109 V) by the 3-CCSiMe one thus shifts
3 2
3
1/2
3
donor shifts the formal potential of the first oxidation to a value
that is negative of that of An N-CCTMS but slightly positive of
that of complex 2 and that of An N. Second, placement of the
vinyl ruthenium moiety in the 3- (m-1) instead of the 4-
position (p-1) of the attached phenyl ring, i.e., out of the path
of direct π-conjugation with the bis(4-anisyl)phenylaniline
Table 1. Cyclic Voltammetry Data of An N-Br and
2
2
Complexes m-1 and 2 along with Those of the Reference
3
a
Compounds of Chart 1
E1/20/+ [V]
E1/20/+ [V]
ΔE
1/2
b
(
ΔE [mV])
(ΔE [mV])
[mV]
Kc
17
p
p
moiety into a “coextensive” location, increases the oxidation
potentials of the first and the second oxidations by ca. 290
An N-
0.295 (62)
2
CCTMS
(E1/20 ) and 225 mV (E1/2 ), respectively.
/+
+/2+
3d
An N
0.109
0.860
751
590
320
384
62
1.7 × 1017
3
c
9.5 × 109
N,N,N′,N′-Tetra-4-anisyl-3,4′-diaminobiphenyl (TADP, see
Chart 1) provides another interesting point of comparison with
m-1. Here, a small splitting of half-wave potentials ΔE of 62
2
0.135 (63)
0.170 (64)
−0.118 (68)
0.245
0.725 (84)
m-1
p-1
0.490 (67)
0.266 (71)
0.307
2.6 × 105
6
1
1
/2
3.1 × 10
11
d
17
mV and formal potentials of 0.245 and 0.307 V have been
TADP
17
observed under comparable conditions. TADP, m-1, and p-1
all feature inequivalent redox sites such that the difference in
half-wave potentials also includes the intrinsic energy difference
between the two hypothetical valence tautomers resulting from
the primary oxidation of one site or the other. This factor adds
a
Data in CH Cl /NBu PF (0.1 M) at rt and v = 0.1 V/s; potentials
2
2
4
6
0/+
are provided against the internal Cp Fe standard (E1/2 = 0.000 V).
2
b
K is the comproportionation constant given by the equation K =
c
c
c
d
exp[nFΔE1/2/(RT)]. At v = 1.0 V/s. Data in PhCN, 0.1 M NBu PF .
4
6
5
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to the statistical, inductive, Coulombic, and resonance
contributions that are operative in compounds with two
2
3
interlinked and potentially interacting redox sites. Only the
resonance contribution, however, relates to the strength of the
electronic coupling between the interlinked redox sites.
Experimental and quantum chemical investigations on p-1
and its mono- and dioxidized forms have shown that the
positive charge (hole) and the unpaired spin in the radical
cation are equally shared between the vinyl ruthenium and the
triarylamine moieties. This extensive conjugation also gives rise
1
•+
to intense absorption in the NIR. TAPD , with the same
topological placement of the redox sites as in m-1, has its spin
17
localized on just one triarylamine subunit. This raises
questions about the extent to which the hole and the unpaired
•+
spin in m-1 are delocalized over both subunits or whether
they are confined to just one of these sites (and, if so, to which)
and how this affects the NIR (poly)electrochromism of m-1.
These questions can be addressed by monitoring the
spectroscopic changes on one-electron oxidation in IR and
UV/vis/NIR spectroscopies as well as by analysis of the
hyperfine splitting patterns in the EPR spectrum of m-1 . IR
spectroelectrochemistry of complexes m-1 and 2 was therefore
conducted, and the results are collected in Table 2 along with
Figure 5. Spectroscopic changes during the first oxidation of complex
m-1 in a transparent thin-layer electrolysis cell at rt in the 1,2-
C H Cl /NBu PF (0.2 M) supporting electrolyte. The asterisk marks
2
4
2
4
6
a region of strong supporting electrolyte background absorption.
•+
band at 2025 cm− (see Figure 7 of the Supporting
1
2
+
Information). This behavior suggests that dication m-1 and
the species giving rise to the band at 1952 cm− are related by a
chemical process. All attempts to identify this electrogenerated
product and to clarify the nature of the underlying chemical
process were so far in vain. We also note that the second
oxidation is accompanied by a decrease of the intensity of the
low-energy electronic band. This latter transition is therefore
specific to the radical cation.
1
Table 2. IR Data of Complexes m-1, p-1, and 2 in Their
a
Various Oxidation States
complex ν(CO) [cm−1]
ν(CC , CC ) [cm−1
]
vinyl
aryl
m-1
m-1
p-1
1910(s)
1922(m)
1910(s)
1944(vs)
1985(s)
1909(s)
1966(s)
1592(w), 1583(w), 1576(w), 1555(m), 1507(s)
1603(m), 1577(m), 1560(m), 1507(s)
1503(s)
•
+
•+
The spin distribution in the m-1 radical cation is
conveniently probed by EPR spectroscopy. Radical cations of
•
+
p-1
p-1
2
1608(s), 1503(vs)
ruthenium styryl complexes [(4-R-C H )CHCH-RuCl-
6
4
2
+
1605(m), 1591(m), 1503(w)
1604(w), 1582(w), 1554(w), 1506(m)
1585(vs), 1506(w)
i
•+
(
CO)(P Pr ) ] usually show an isotropic signal in fluid
3 2
solution at g = 2.04 to 2.05, often with resolved hyperfine
•
+
2
31
splittings to the P nuclei of the phosphine coligands of ca. 22
a
10c,12
Data in 1,2-C H Cl , 0.2 M NBu PF at rt.
2
4
2
4
6
G.
This is a token of the large contribution of the styryl
ligand to the HOMO of the neutral complexes and the SOMO
of their associated radical cations. Oxidized 2 is no exception
and shows a resolved triplet signal at g = 2.033 with hyperfine
−
1
those of p-1. The 12 cm blue shift of the Ru(CO) tag from
−1
1
910 to 1922 cm during the first oxidation of m-1 is much
smaller than that of 34 cm observed for the p-1 process
−1
0/+
31
99/101
couplings of 26.5 G to P and of 15.4 G to the
Ru nuclei
−1
and that of 57 cm that accompanies the first oxidation of
complex 2 (see Figure 6 of the Supporting Information).
Radical cation 2•+ may be seen as a model of m-1 with
hypothetical charge confinement to just the styryl ruthenium
site. Overall, our observations indicate that the vinyl ruthenium
subunit is rather little affected by the first oxidation of m-1 and
that the hole is largely confined to the triarylamine entity. Also
of note is the parallel growth of a broad absorption band of
electronic origin at ca. 5800 cm (1720 nm) (see inset of
Figure 5). While a more detailed discussion of this band is
deferred to a later section of this paper, we note here that its
position and shape already suggest that it originates from an
intervalence charge-transfer (IVCT) transition within an
asymmetric mixed-valent system.
as well as additional hyperfine splittings to the alkenyl protons
of 11.5 and 3.2 G (see Table 3 and Figure 8 of the Supporting
24
•+
Information). Triarylaminium ions, on the other hand, are
characterized by a nonbinomial triplet with hyperfine coupling
14
to the N nucleus (I = 1) of ca. 7−10 G at a g-value even closer
3
c,10b,17
to the free-electron one (g
= 2.0023).
Consistent with
e
•
+
complete spin delocalization in p-1 , hyperfine splittings to
Ru are half those in simple triarylaminium
ions and the radical cations of aryl-substituted vinyl
ruthenium complexes, but very similar to those in the related
arylene-bridged bis(triarylamine) radical cations
14
31
99/101
N, P, and
−1
13
12
6
f,8b,14
and in
i
•+ 15
[1,4-C H {−CHCH-RuCl(CO)(P Pr ) } ] . Chemically
6
4
3 2 2
•
+
generated m-1 (oxidation with acetylferrocenium hexafluor-
ophosphate) displays a structured EPR signal at g = 2.0048
(Figure 6, Table 3). By simulation of the experimental
•
+
Further oxidation of m-1 at an applied potential sufficiently
anodic of the half-wave potential of the m-1+ couple resulted
/2+
spectrum, hyperfine coupling constants A( N) of 10.0 G,
14
−1
31
99/101
24
in the initial growth of a new Ru(CO) band at 1965 cm and
then the parallel growth of a new band at 1952 cm− that was
not present during the initial stages of this process. The
assignment of the 1965 cm band to m-1 is therefore only
tentative. Despite this coupled chemical process, an isosbestic
point was maintained until the final stages when the intensity of
the 1965 cm− band decreased at the expense of an additional
A( P) of 3.9 G, and A(
Ru) of 4.3 G were extracted. We
1
have to concede, though, that the rather low resolution of the
experimental spectrum induces a higher level of uncertainty
−1
2+
14
than usual, but the trend, in particular the N hyperfine
splitting, is nevertheless clear. The EPR signature is thus fully
consistent with the results of IR spectroelectrochemistry in
indicating an only moderate delocalization of the SOMO with
1
5
465
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Organometallics
Article
Figure 6. Comparison of the simulated (top) and experimental
5
(
bottom) EPR spectrum of chemically generated (oxidation with [(η -
5
+
−
•+
C H C(O)Me)(η -C H )Fe] PF ) m1 (CH Cl ) at rt.
5
4
5
5
6
2
2
Figure 7. Calculated spin densities of the radical cation of model
•+
•
+
•+
•+
complex m-1Me
.
Table 3. EPR Data of Radical Cations m-1 , p-1 , and 2
and of Some Triarylaminium Ions
confinement has rather dramatic consequences for the
g
hyperfine splittings
•+
electronic absorption spectrum of m-1 .
•
+
a
14
31
99/101
m-1
2.0048 A( N) = 10.0 G, A( P) = 3.9 G, A(
Ru) = 4.3 G
The UV/vis spectrum of neutral m-1 is dominated by an
•+
a
14
31
99/101
1
p-1
2.015
2.0342 A( P) = 26.5 G, A(
1.5, 3.2 G
A( N) = 5.1 G, A( P) = 6.6 G, A(
Ru) = 5.1 G
intense, asymmetric, and structured band with a main peak at
2•
+
a
31
99/101
Ru) = 15.4 G, A( Halkenyl) =
1
−1
−1
305 nm (ε = 44 400 M
cm , Figure 8, Table 4), which can
1
14
NAn •
+
A( N) = 9.05 G
13
3
TAPD•
+
A( N) = 9.1 G
14
17
a
+
−
Data for chemically oxidized compounds (p-1: [Cp Fe] PF ; m-1,
2
6
5
5
+
−
2
: [(η -C H C(O)Me)(η -C H )Fe] PF in CH Cl at rt).
5
4
5
5
6
2
2
major contributions from the triarylamine entity and smaller
ones from the vinyl ruthenium one.
Our experimental results are nicely backed by quantum
chemical calculations on the slightly truncated model complex
i
m-1Me with the P Pr ligands of the real complex replaced by
3
PMe . The HOMO of m-1 is delocalized over the nitrogen
3
Me
atom and the three appended aryl rings and represents an
antibonding interaction between the nitrogen lone pair and the
π2 orbitals of the three phenyl rings with one nodal plane on
each ring and one additional nodal plane between the arenes
and their 4- or 3-substituents. There is only little contribution
from the alkenyl substituent and practically none from the
ruthenium atom and the other coligands (see Figure 9 of the
Supporting Information). The HOMO−1, on the other hand,
is delocalized over the styryl ruthenium moiety with little
contribution from the amine lone pair and practically none
from the anisyl rings. This level ordering is also maintained in
the associated radical cation, as shown by the calculated spin
density distribution in Figure 7. The trends in the experimental
EPR parameters are also reproduced by our calculations, which
Figure 8. Spectroscopic changes during the first oxidation of complex
m-1 in a transparent thin-layer electrolysis cell at rt in the 1,2-
C H Cl /NBu PF (0.2 M) supporting electrolyte.
2
4
2
4
6
be assigned to π → π* transitions within the extended metal−
organic chromophore. A splitting of the NAr π → π* band is
3
the expected result of lowering the ideal C symmetry due to
3
the different substitution patterns and torsions of the appended
3d
aryl rings. TD-DFT calculations on m-1Me provide several
intense transitions at close energies (see Table 5). All
transitions that originate from the HOMO are due to
1
4
gave a larger g-value and a smaller A( N) value of 2.013 and
•+
•+
6
.9 G for p-1Me compared to those of m-1Me (g = 2.0030
excitations that are confined within the NAr subunit. The
3
and 9.6 G), in satisfactory agreement with the experimental
values (Table 3). We also note that our calculations predict
only minor structural changes at the vinyl ruthenium site on
one-electron oxidation, in internal consistency with all other
results (see Table 3 of the Supporting Information).
most intense band, however, involves a transition from the
styryl ruthenium-based HOMO−1 to the LUMO+1. The latter
orbital is centered on the triarylamine subunit and has major
contributions from the phenyl ring that is common to both.
Some transfer of charge density from the styryl ruthenium to
the triarylamine site may hence accompany this excitation. We
note that the more intense bands are markedly blue-shifted
with respect to the ones of p-1 at 322 and 343 nm. This is
another token of the lower degree of conjugation within the
meta isomer m-1. Like for p-1, the additional, weaker band at
511 nm (ε = 565) is due to a weakly allowed excitation from
Shifting the site of vinyl ruthenium attachment from direct
conjugation with the amine nitrogen at the 4-position of p-1 to
the less well coupled 3-position of m-1 thus has the effect of
partially decoupling the unlike redox sites and shifting the hole
•
+
and the unpaired spin of one-electron-oxidized m-1 toward
the triarylamine unit. As it will be shown in brief, such hole
5
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Table 4. UV/Vis/NIR Data of Complexes m-1, p-1, and 2 and of An N-CCTMS in Their Various Oxidation States
2
λmax (εmax
)
m-1
m-1
p-1
305 (44 400), 387 (sh, 3200), 512 (565)
•
+
298 (28 700), 360 (26 750), 584 (9600), 739 (20 900), 1075 (3100), 1666 (2300)
322 (sh, 26 000), 343 (30 000), 553 (300)
•+
p-1
2
365 (7500), 487 (27 000), 516 (sh, 20 000), 575 (sh, 3000), 870 (sh, 10 000), 1030 (19 600), 1160 (22 000)
301 (11 800), 379 (835), 519 (250)
•
+
2
298 (4200), 333 (2800), 433 (10 400), 692 (5900)
+
An N-CCTMS
2
300 (20 000), 360 (sh, 1900)
•
+
An N-CCTMS
2
304 (10 000), 322 (9300), 356 (sh, 7500), 368 (7700), 568 (3450), 776 (20 200)
Table 5. Calculated Electronic Transitions of m-1Me•+ with Oscillator Strengths f and Major Contributions and Comparison
with the Experimental Data
calculated data for m-1Me•
λmax [nm] (ν
[in cm−1])
694 (5902)
+
experimental data for m-1•+
[in cm−1]) εmax [M−1 cm−1] (f)a
1666 (6000)
075 (9300)
̃
f
λmax [nm] (ν
̃
major contributors
1
0.031
2350 (0.030)
3000 (0.039)
20 900 (0.152)
5600 (0.071)
β-HOMO → β-LUMO
1
679 (14 733)
553 (18 100)
489 (20 460)
472 (21 202)
0.3105
0.1805
0.0099
0.0078
739 (13 475)
587 (17 020)
β-HOMO−3 → β-LUMO
β-HOMO−5 → β-LUMO
β-HOMO−8 → β-LUMO
α-HOMO → α-LUMO;
β-HOMO → β-LUMO+1
α-HOMO → α-LUMO+1;
β-HOMO → β-LUMO+2
β-HOMO−6 → β-LUMO;
β-HOMO−9 → β-LUMO
5
40 (18 500)
4700 (0.137)
4
63 (21 595)
45 (22 472)
0.0318
0.0097
4
a
−9
Oscillator strength calculated by the equation f = (4.6 × 10 )εmaxΔν1/2, where Δν1/2 is the bandwidth at half-height.
the mixed d(Ru)/π(arylamine) HOMO−1 to the largely metal-
based LUMO that points toward the vacant coordination site.
On oxidation in an optically transparent thin-layer
electrolysis (OTTLE) cell, the electronic spectrum of m-1
changes to a pattern of two intense absorptions in the UV at
λmax = 298 and 360 nm, two moderately intense visible bands at
apparent on inspection of the frontier molecular orbitals (see
Figure 9 of the Supporting Information), which are localized on
either the styryl ruthenium moiety (HOMO−1, HOMO−3),
the metal atom (LUMO), or the triarylamine (HOMO−2,
HOMO, LUMO+1, LUMO+2, LUMO+4 to LUMO+6).
TD-DFT calculations on m-1Me were conducted with the
aim of determining the origins of the low-energy transitions and
of the two more intense transitions in the visible. Despite the
problems associated with performing such calculations on
open-shell systems, they reproduce most features of the
experimental spectrum rather well, most notably the weak
low-energy band, which is calculated at 1694 nm, and the series
of three neighboring absorptions in the visible at 679, 553, and
25
•
+
5
84 and 739 nm, the former with a distinct tail to higher
−1
energies, and two weak NIR bands at 1075 (ε = 3000 M
−1
−1
−1
cm ) and 1666 nm (ε = 2350 M cm , see Figure 8 and
Table 4). The latter band matches with the NIR band that was
already observed in the IR spectroelectrochemical experiment.
The band pattern of m-1 is clearly different from that of p-
1
•+
•
+
, which showed two much more intense absorptions at 1003
−1
and 1169 nm with extinction coefficients of ca. 20 000 M
cm and just one major absorption in the visible at 485 nm.
4
50 nm with decreasing oscillator strengths, but fail to
−1
1
reproduce the experimental band at 1075 nm (see Figure 12
of the Supporting Information). Based on our TD-DFT results,
We note that the radical cations of amine precursor An N-
2
CCTMS and of complex 2 both present strong absorptions in
the visible, as shown in Figures 10 and 11 in the Supporting
Information. These transitions are located at 433 and at 692 nm
•
+
the low-energy NIR band of m-1 can be assigned as the β-
HOMO → β-LUMO transition. The two more prominent
transitions in the visible are due to excitations from the lower-
lying β-HOMO−3 and β-HOMO−5 to the same acceptor
orbital, while the unresolved shoulder at higher energy involves
several weak transitions that are highly mixed in character. We
note that the level ordering of closed-shell m-1 carries over to
that of the β-manifold of its radical cation; that is, the former
HOMO resembles the β-LUMO, the former HOMO−1 the β-
HOMO, and so forth, while for the α-manifold the ordering of
the HOMO and the HOMO−1 are inverted with respect to the
neutral state. The stronger visible bands hence emanate from
MOs that are delocalized over the triarylamine subunit and can
thus be assigned as π → π* transitions within that moiety. We
also note that these bands closely resemble those observed for
•+
•+
for 2 or at 568 and 776 nm for An N-CCTMS . None of
2
these absorption bands, however, extend deeper into the NIR.
The low-energy transitions in p-1•+ and m-1•+ are thus a
consequence of extending the conjugated π-system through
coupling of the vinyl ruthenium and the triarylamine entities. In
•
+
p-1 , this coupling is so strong that a very weakly polarized,
highly delocalized chromophore results. As a consequence, the
NIR bands are best described as π → π* transitions within an
extended, open-shell, metal−organic π-system with no net
transfer of charge from one component to the other, i.e., as
charge resonance bands. In m-1 and its associated radical
cation, however, the two chromophoric and electroactive
subunits are only weakly coupled to one another such that a
less delocalized metal−organic π-system results. This is already
•
+
An N-CCTMS (see Figure 9 of the Supporting Information),
2
5
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Figure 9. Level ordering of m-1Me•+ and graphical representations of relevant spin orbitals.
Table 6. Data Pertaining to Hush Analysis of the NIR Bands of m-1•+
λ [cm−1]
Δν
̃1/2,theo
3655
4580
[cm−1
]
Δν
̃1/2,exp
2650
2900
[cm−1
]
Γ
Hab [cm−1
]
α
band 1
band 2
5790
9090
0.28
0.35
1003
1485
0.17
0.16
−
1
but are shifted by 37 and 16 nm (645 and 482 cm ),
respectively.
nonidentical redox sites, the relation between the reorganiza-
tion energy λ, the energy at the IVCT band maximum νmax, and
the energy difference ΔG between the two possible valence
̃
0
The low-energy band hence involves a transition from the β-
HOMO to the β-LUMO. The donor orbital is delocalized over
the styryl ruthenium part of this molecule, whereas the acceptor
orbital is delocalized over the triarylamine subunit with larger
contributions of the anisyl rings. This band hence qualifies as an
intervalence charge-transfer transition within a molecule that
encompasses two different redox systems. The same may also
apply to the band at 1070 nm, which our TD-DFT calculations
failed to reproduce. The level ordering of Figure 9 strongly
suggests that this transition is due to (an) excitation(s) from
the β-HOMO−1 and/or the β-HOMO−2 to the β-LUMO.
Both these suspect donor orbitals are localized on the
ruthenium bis(phosphine) moiety. We therefore assume that
this transition is also of IVCT origin. We note here that the
observation of multiple IVCT bands is not wholly uncommon
and may originate from spin−orbit coupling of the d-levels at a
30
tautomers in their vibrational ground states is given by eq 1.
•
+
In the case of m-1 , these valence tautomers can be identified
•
+
i
as An N -C H CHCH-RuCl(CO)(P Pr ) with an oxidized
2
6
4
3 2
i
•+
amine site and An N-C H CHCH-RuCl(CO)(P Pr ) with
2
6
4
3 2
0
the styryl ruthenium site as the primary oxidation center. ΔG
can be approximated by the half-wave potential difference
0
/+
i
between the An N
and the (P Pr ) (CO)ClRu-CH
3
3 2
0/+
CHC H OMe-4 couples, which both contain the 4-anisyl
6
4
ring as an integral part of the redox system. It amounts to only
−1
0.026 V (210 cm ). The theoretical half-widths of an IVCT
band, Δν1/2,theo, is given by eq 2. Comparison of these values to
the experimental ones derived from spectral deconvolution of
̃
•
+
the NIR part of the electronic spectrum of m-1 (see Table 6)
shows that the experimental half-widths are consistently smaller
than those calculated for the limiting case of a weakly coupled
Class II system. Brunschwig, Creutz, and Sutin have introduced
26
metal-based donor site, low symmetry of the metal-bridge
array, or the heavy involvement of the nominal bridge in
2
7
29c
the parameter Γ as defined by eq 3, which allows one to
6
b,c,10a,28
some but not all of the IVCT bands.
This latter
discriminate between weakly coupled (0 ≤ Γ ≤ 0.1),
moderately coupled (0.1 ≤ Γ ≤ 0.5), Class II/III borderline
(Γ ≈ 0.5), or strongly coupled, delocalized Class III systems (Γ
situation is somewhat similar to that encountered for the β-
HOMO to β-LUMO transition if one regards the common
phenylene ring as the bridge that is common to both individual
redox sites.
The IVCT bands can be analyzed within the theoretical
framework of Hush’s theory. In a mixed-valent system with
31
> 0.5) according to the Robin-and-Day classification scheme.
The Γ values of 0.28 and 0.35 obtained for the two NIR bands
indicate that the electronic coupling between the individual
29
•+
redox sites of m-1 is appreciable, but certainly lower than for
5
468
dx.doi.org/10.1021/om4007455 | Organometallics 2013, 32, 5461−5472

Organometallics
Article
•
+
its para-isomer p-1 , which is a completely delocalized Class
III system.
conjugate as a (multi)electrochromic dye require therefore an
intimate electronic coupling between these nonidentical, but
similar, redox-active subunits and high degrees of charge
delocalization of their oxidized forms. This concept should also
carry over to other systems where two potentially interacting
and per se electrochromic entities are combined into one
compound.
1
0
λ = v
̃
− ΔG
(1)
max
1
/2
1/2
Δv1̃ /2,theo = [16(ln 2)RTλ] = [2310λ] at rt
̃ /2,exp
Γ = 1 − θ, where θ = Δv1 /Δv
H = 0.0206(v Δv
(2)
(3)
̃
1/2,theo
EXPERIMENTAL SECTION
General Methods. All operations were performed under an
atmosphere of purified nitrogen using standard Schlenk techniques.
Solvents were dried over and distilled from CaH2 (CH Cl , 1,2-
)1/2 /rab
■
̃
ε
̃
ab
max max
1/2,exp
(4)
(5)
α = H /v
̃
ab max
2
2
C H Cl ), LiAlH (n-hexane), or sodium (THF, toluene) and
2
4
2
4
Hush’s theory also allows one to derive the electronic
coupling parameter H from the IVCT band parameters via eq
, where r denotes the effective charge-transfer distance of the
degassed by saturation with nitrogen or argon prior to use. The
ab
yields refer to analytically pure compounds and were not optimized.
4
i
21a
ab
HRuCl(CO)(P Pr )
was prepared according to a modified
3
2
mixed-valent system. This parameter is traditionally approxi-
mated by the geometrical distance between the centers of the
nominal redox sites. Even in clear-cut cases such as cyanide-
bridged dimetal complexes or analogues of the Creutz−Taube
ion where the redox sites are readily identified as the metal
atoms, the effective charge-transfer distance is significantly
literature procedure with addition of K CO to neutralize the HCl
2
3
formed in the reaction. Acetylferrocenium hexafluorophosphate was
−
prepared according to the literature procedure for the BF salt by
4
4
using AgPF instead of AgBF . All other chemicals were commercial
6
4
1
13
19
31
products and used as supplied. Instrumentation: H, C, F, and
P
NMR spectra were recorded on either a Bruker Avance 400 MHz, a
Bruker Avance III Kryo-Platform 600 MHz, or a Varian Inova 400
MHz spectrometer in C D , CD Cl , or CDCl at ambient
3
2
smaller than the metal···metal distance. A particularly
instructive example is the 4,4′-bipyridine-bridged, “elongated”
version of the Creutz−Taube ion, [(NH ) Ru-(μ-4,4′-bipy)-
6
6
2
2
3
temperature. Chemical shifts are relative to the residual solvent
3
5
1
13
31
peaks ( H, C) or 100% H PO ( P). Infrared spectra were obtained
5+
3
4
Ru(NH ) ] . Although this system is a weakly coupled mixed-
3
5
on a Nicolet iS10 instrument (Thermo Fischer Scientific Inc.). UV/vis
spectra were obtained on an Omega 10 spectrometer from Bruins
Instruments or a TIDAS fiberoptic diode array spectrometer
(combined MCS UV/NIR and PGS NIR instrumentation) from
j&m Analytik AG in HELLMA quartz cuvettes with 1 cm optical path
lengths. Elemental analysis (C, H, N) were performed with a Heraeus
Elementar Vario MICRO Cube. The equipment for voltammetric and
spectroelectrochemical studies and the conditions employed were
valent system of Class II with 95% charge localization on one
ruthenium site, the difference dipole moment between the
adiabatic charge-transfer states and, consequently, the charge-
transfer distance r are less than 50% of the value expected for
ab
the transfer of a full charge between the individual ruthenium
3
2a
atoms. Even larger discrepancies are found in systems where
the effective redox system extends onto the nominal bridge or
when the ground state of the mixed-valent system is more
34
described elsewhere. Electron paramagnetic resonance (EPR) studies
were performed on a MiniScope MS 400 table-top X-band
6
d,16a,32c,33
strongly delocalized.
spectrometer from Magnettec. Simulation of the experimental spectra
2
4
Given these results, half the ruthenium−nitrogen distance of
was performed with the EasySpin software. X-ray diffraction
measurements were performed at 100(2) K on a Stoe IPDS II
diffractometer (graphite monochromator, Mo Kα radiation, λ =
0.71073 Å) on crystals mounted on a glass fiber. The structures were
solved by direct methods using the SHELX-97 and the SIR program
•
+
m-1 (d(Ru···N = 7.80 Å based on the experimental structure
of m-1 and 7.96 Å based on the optimized structure of m-
•
+
1Me ) may be a realistic estimate of r . This would give H
ab
ab
−1
values on the order of 1000 and 1500 cm for the IVCT bands
at the lower and the higher energies, respectively (see Table 6).
Finally, the ground-state delocalization parameter α, which
measures the percentage of charge shifted from one redox site
to the other, is given by the ratio of Hab to the energy at the
IVCT band maximum (eq 5). In internal consistency with the
assignment of both NIR bands as IVCT transitions, their α
parameters are practically identical. In further agreement with
3
5
packages. The positions of the hydrogen atoms were calculated by
assuming an ideal geometry, and their coordinates were refined
together with those of the attached carbon atoms applying the riding
model. All other atoms were refined anisotropically.
Quantum Chemical Calculations. The ground-state electronic
structures were calculated by density functional theory (DFT)
3
6
methods using the Gaussian 09 program package. In order to
i
reduce computational time to a reasonable limit, P Pr ligands were
3
•
+
the values of their Γ parameters, they place m-1 in the reg
of a moderately coupled mixed-valent system of Class II.
́
ime
replaced by PMe . Open-shell systems were calculated by the
3
unrestricted Kohn−Sham approach. Geometry optimization followed
by vibrational analysis was made either under vacuum or in solvent
media. The quasirelativistic Wood−Boring small-core pseudopoten-
In conclusion, shifting the site of vinyl ruthenium attachment
to the bis(4-anisyl)-(phenyl)amine core of vinyl triarylamine
conjugates from the para position of p-1 to the meta position in
m-1 has the effect of increasing the oxidation potentials by
37
38
tials and the corresponding optimized set of basis functions for Ru
39
and 6-31G(d) polarized double-ζ basis sets for the remaining atoms
were employed together with the Perdew, Burke, and Ernzerhof
4
0
>
200 mV for each consecutive redox step and localizing the
exchange and correlation functional (PBE0). Hyperfine coupling
•+
•+
hole and the unpaired spin of its associated radical cation on
mainly the triarylamine entity, although the intrinsic redox
potentials of the likewise electroactive triarylamine and vinyl
constants of the radical cations m-1Me and p-1Me were calculated
for the geometry-optimized radical cations with the same basis
functions. Solvent effects were described by the polarizable conductor
42
4
1
continuum model with standard parameters for 1,2-dichloroethane.
ruthenium sites are very similar. Partial charge localization in
the ground state of mixed-valent m-1•+ changes the character of
Synthesis and Characterization. N,N-Bis(4-methoxyphenyl)-N-
3
-bromophenylamine, An N-Br. An 8.60 g (50 mmol) amount of 3-
2
the low-energy transitions in the near-infrared from charge-
bromoaniline, 25.74 g (110 mmol) of 4-iodoanisole, and 1.80 g of
,10-phenanthroline (5 mmol) were dissolved in 60 mL of toluene,
•
+
resonance absorptions in p-1 to styryl ruthenium to
triarylaminium IVCT transitions in m-1• and significantly
decreases their absorptivities. Strong electrochromism and
good performance of an alkenyl ruthenium triarylamine
1
+
and the solution was heated to 110 °C. KOH (112 mmol) and CuCl
(2.8 mmol) were added to the boiling solution, which was stirred
under reflux conditions for 72 h. After cooling to room temperature,
5
469
dx.doi.org/10.1021/om4007455 | Organometallics 2013, 32, 5461−5472

Organometallics
Article
1
i
5
00 mL of toluene, 500 mL of water, and 10 mL of acetic acid were
114.9 (C11), 55.3 (OCH ), 24.3 (t, J
= 9.6 Hz, CH( Pr)), 19.5
3
P−C
i
31
added. The layers were separated, and the aqueous layer was extracted
several times with CH Cl . The combined organic layers were dried
over MgSO , and the solvent was removed in vacuo. Purification by
column chromatography (petrol ether/ethyl acetate, 9:1) gave the
pure product. Yield = 9.50 g, 24.7 mmol (49%).
and 19.4 (each s, CH
38.2 ppm. Anal. Calcd for C41
g/mol): C, 60.39; H, 7.66; N, 1.72. Found: C, 60.21; H, 7.46; N, 1.75.
3
( Pr)) ppm. P NMR (161.9 MHz, CD
Cl ): δ
2 2
H
62ClNO Ru × 0.5CH Cl (1295.42
P
2
2
3
2
2
2
4
i
4
-OMe-C H -CHCH-RuCl(CO)(P Pr ) , 2. To a solution of
6
4
3 2
i
HRuCl(CO)(P Pr ) (120 mg, 0.240 mmol) in 6 mL of CH Cl was
3
2
2
2
1
3
added a solution of 32 mg (0.24 mmol) of 4-ethynylanisole, which
resulted in an immediate color change from red-orange to purple. The
solution was stirred under gentle warming to 45 °C for 30 min, and
the solvent removed under vacuum. The resulting solid was dissolved
in the minimum amount of CH Cl and precipitated by addition to 30
mL of rapidly stirred methanol, and the solvent was removed by
filtration. After repeating this procedure two more times, the resulting
purple solid was dried under vacuum to yield 145 mg (0.235 mmol,
8%) of spectroscopically pure complex 2.
H NMR (300.1 MHz, CD Cl ): δ 8.25 (d, 1H, J = 13.44 Hz,
= 8.78 Hz, H4), 6.73 (d, 2H, J
= 13.44 Hz, J
CH), 3.73 (s, 3H, OMe), 2.81−2.67 (m, 6H, PCHCH ), 1.35−1.21
m, 36H, PCHCH ). C NMR (150.9 MHz, CD Cl ): 209.4 (t,
H NMR (400 MHz, acetone-d ): δ 7.61 (d, J
= 8.8 Hz, 1H,
H−H
6
3
H2), 7.11 (d, J
= 8.9 Hz, 4H, H6), 7.10 (m, 1H, H3), 6.95 (d,
H−H
3
3
JH−H = 8.8 Hz, 4H, H5), 6.80 (d, J
= 8.8 Hz, 1H, H4), 6.76 (s,
H−H
1
H, H1), 3.80 (s, 6H, OMe) ppm.
N,N-Bis(4-methoxyphenyl)-N-(3-trimethylsilylethynylphenyl)-
2
2
amine, An N-CCTMS. N,N-Bis(4-methoxyphenyl)-N-3-bromo-
2
phenylamine (1.0 g, 2.6 mmol) and trimethylsilylacetylene (5
mmol) were dissolved in a mixture of triethylamine (15 mL) and
THF (15 mL). The solution was freeze−pump−thaw degassed (three
cycles), and then CuI (10 mol %) and PdCl (PPh ) (5 mol %) were
added. The reaction mixture was stirred for 48 h at 60 °C in a closed
vessel. The completeness of the reaction was controlled by TLC. After
full conversion, the mixture was filtered over a Celite pad and eluted
with THF. The solvent was removed in vacuo. Purification by column
chromatography (petrol ether/ethyl acetate, 6:1) gave the product as a
yellow oil. Yield = 731 mg, 1.82 mmol (70%).
9
1
3
2
2
H−H
2
3 2
3
3
Ru-CH), 6.95 (d, 2H, J
= 8.78
H−H
= 2.19 Hz, Ru-CH
H−H
3
4
Hz, H5), 5.90 (dt, 1H, J
H−H
H−P
3
13
43
(
3
2
2
2
2
JC−P = 13.14 Hz, Ru(CO)), 157.0 (s, C6), 146.5 (t, J
Ru-CH), 133.8 (s, RuCH-CH), 132.8 (s, C3), 125.1 (s, C4), 114.0 (s,
= 10.9 Hz,
C−P
1
i
C5), 55.5 (s, OCH ), 24.8 (t, J
= 9.9 Hz, CH( Pr)), 20.0 and 19.9
3
P−C
1
3
H NMR (400 MHz, acetone-d ): δ 7.15 (d, J
= 8.0Hz, 1H,
i
31
1
6
H−H
(each s, CH ( Pr)). P{ H} NMR (121.5 MHz, CD Cl ): 38.3 (s).
3
2
2
3
H2), 7.06 (d, J
= 8.7 Hz, 4H, H6), 7.10 (m, 1H, H3), 6.92 (d,
H−H
Anal. Calcd for C H ClO P Ru (618.15 g/mol): C, 54.40; H, 8.32.
28 51 2 2
3
3
JH−H = 8.7 Hz, 4H, H5), 6.90 (d, J
= 8.6 Hz, 1H, H4), 6.76 (s,
H−H
Found: C, 54.80; H, 8.41.
1
H H1), 3.80 (s, 6H, OMe) ppm, 0.18 (s, 9H, TMS).
N,N-Bis(4-methoxyphenyl)-N-(3-ethynylphenyl)amine, N An-
2
ASSOCIATED CONTENT
Supporting Information
X-ray crystallographic data for An N-Br and complexes m-1
■
CCH. N,N-Bis(4-methoxyphenyl)-N-(3-trimethylsilylethynylphenyl)-
amine (140 mg, 0.35 mmol) was dissolved in methanol, and a small
amount of KOH was added. The mixture was stirred for 3 h until the
completeness of the deprotection was shown by TLC and then
quenched with water. The aqueous layer was neutralized with 1 N
hydrochloric acid and extracted several times with CH Cl . The
*
S
2
and 2, representative voltammetric scans of An N-CCTMS and
2
of complex 2, and IR spectroelectrochemistry of complex m-1
(second oxidation) and UV/vis/NIR spectroelectrochemistry
of complex 2, EPR spectra of complex 2, plots of the crucial
frontier molecular orbitals of complex m-1, as well as results of
TD-DFT calculations on m-1 and its associated radical cation.
This material is available free of charge via the Internet at
http://pubs.acs.org. Crystallographic data have been deposited
with the Cambridge Structural Data Base as CCDC 928205
2
2
combined organic layers were dried over MgSO , and the solvent was
4
removed in vacuo to provide the product as a yellow-brown solid. Yield
=
112 mg, 0.34 mmol (97%).
1
3
H NMR (400 MHz, acetone-d ): δ 7.15 (d, J
= 8.0 Hz, 1H,
H−H
6
3
H4), 7.06 (d, J
= 8.7 Hz, 4H, H6), 7.10 (m, 1H, H3), 6.92 (d,
H−H
3
3
JH−H = 8.7 Hz, 4H, H5), 6.90 (d, J
= 8.6 Hz, 1H, H2), 6.76 (s,
H−H
1
H, H1), 3.80 (s, 6H, OMe) ppm, 3.11 (s, 1H, CCH).
(
9
An N-CCTMS), CCDC 928206 (complex m-1), and CCDC
i
2
(
4-OMeC H ) N(C H -3-CHCH-RuCl(CO)(P Pr ) , m-1. N,N-Bis-
6
4 2
6
4
3 2
50385 (complex 2). They can be obtained free of charge at
(
4-methoxyphenyl)-N-(3-ethynylphenyl)amine (34 mg, 0.1 mmol)
was dissolved in CH Cl , and a solution of HRuCl(CO)(P Pr ) (48
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ; fax (+44) 1223-336-033 or at deposit@ccdc.
cam.ac.uk.
i
2
2
3 2
mg, 0.099 mmol) in CH Cl was added dropwise. The color rapidly
2
2
changed from orange-red to deep red. The solution was stirred for 30
min, and the solvent was removed in vacuo. The crude product was
washed with hexane and then dried in vacuo to give the product as a
red solid. Yield: 80 mg, 0.097 mmol (97%).
AUTHOR INFORMATION
Corresponding Author
*E-mail: rainer.winter@uni-konstanz.de.
Notes
■
Chart 2. Numbering Scheme for Signal Assignment for
Complex m-1
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support of this work by the Deutsche Forschungsge-
meinschaft (DFG) through grant Wi1262/9-1 is gratefully
■
̈
acknowledged. We also thank the state of Baden-Wurttemberg
1
3
for providing us access to the bwGrid computational facilities at
the University of Ulm.
H NMR (400 MHz, CD Cl , Chart 2): δ 8.35 (td, J = 12.8 Hz,
H−H
2
2
3J
3
= 1.1 Hz, 1H, H1), 6.98 (d, J
= 8.4 Hz, 4H, H11), 6.96 (m,
= 8.4 Hz, 4H, H10), 6.59 (s, 1H, H8), 6.55 (d,
P−H
H−H
3
1
H, H5), 6.79 (d, J
JH−H = 7.9 Hz, 1H, H6), 6.50 (d, 1H, J
H−H
3
3
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