Iron and ruthenium σ-polyynyls of the general formula [{M(dppe)Cp*}-(C≡C)n-R]0/+ (M = Fe, Ru): An experimental and theoretical investigation

Article abstract of DOI:10.1021/om300584u

Two series of metal-polyynyl complexes of iron and ruthenium of general formula [{M(dppe)Cp*}-(C≡C)_n-R]^0/+ (M = Fe, Ru; R = H, Ph, SiMe₃, Au(PPh₃); n = 1-3), have been synthesized, characterized, and theoretically analyzed. The results provide a comprehensive description of the effect of the length of the conjugated carbon chain and the role of the nature of the metal atom and the terminal substituent on their neutral and oxidized states. For the latter, the spin density found on the carbon chain is a source of instability; e.g., for R = Au(PPh₃), the oxidized compounds are much more accessible electrochemically than the rest of the series but are susceptible to radical attack. Of particular interest is the use of joint experimental and theoretical EPR studies, which allow elucidation of the differences of behavior within the two series. It reveals that the atomic spin density on the metal is not a sufficient criterion to evaluate EPR anisotropy but that the specific nodal properties of the frontier spin-orbitals highly influence the EPR components. The localization of the spin density on specific carbon atoms of the conjugated chain (even numbered) opens up the possibility of building extended systems by targeted radical reactions.

Full text of DOI:10.1021/om300584u

Article
pubs.acs.org/Organometallics
Iron and Ruthenium σ‑Polyynyls of the General Formula
[{M(dppe)Cp*}−(CC)n−R]0/+ (M = Fe, Ru): An Experimental and
Theoretical Investigation
Frederic Gendron,† Alexandre Burgun,†,‡ Brian W. Skelton,§,∥ Allan H. White,§ Thierry Roisnel,†
́
́
Michael I. Bruce,‡ Jean-Francois Halet,† Claude Lapinte,*,† and Karine Costuas*,†
̧
†Institut des Sciences chimiques de Rennes, UMR 6226 CNRS-Universite
France
́
de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex,
‡School of Chemistry and Physics, University of Adelaide, South Australia 5005, Australia
§School of Chemistry and Biochemistry M313, University of Western Australia, Crawley, Western Australia 6009, Australia
S
* Supporting Information
ABSTRACT: Two series of metal-polyynyl complexes of iron and ruthenium of
general formula [{M(dppe)Cp*}−(CC)n−R]0/+ (M = Fe, Ru; R = H, Ph, SiMe3,
Au(PPh3); n = 1−3), have been synthesized, characterized, and theoretically analyzed.
The results provide a comprehensive description of the effect of the length of the
conjugated carbon chain and the role of the nature of the metal atom and the terminal
substituent on their neutral and oxidized states. For the latter, the spin density found
on the carbon chain is a source of instability; e.g., for R = Au(PPh3), the oxidized
compounds are much more accessible electrochemically than the rest of the series but
are susceptible to radical attack. Of particular interest is the use of joint experimental
and theoretical EPR studies, which allow elucidation of the differences of behavior
within the two series. It reveals that the atomic spin density on the metal is not a sufficient criterion to evaluate EPR anisotropy
but that the specific nodal properties of the frontier spin−orbitals highly influence the EPR components. The localization of the
spin density on specific carbon atoms of the conjugated chain (even numbered) opens up the possibility of building extended
systems by targeted radical reactions.
Chart 1
INTRODUCTION
■
Due to the high reactivity of long all-carbon chains, the
development of the chemistry of conjugated polyynes has been
facilitated by stabilizing the chain with bulky end groups, often
with metal fragments, or with protecting side ligands.1
Nevertheless, synthesis of the oxidized parents, sufficiently
stable to be characterized, remains difficult to access.1 Such
open-shell systems have high potential as conducting molecular
wires or as building blocks toward larger functional molecules.
In order to achieve this, the redox properties of the electron-
rich Fe(dppe)Cp* and Ru(dppe)Cp* moieties have been used
to stabilize different polyyne chains. Here, for the first time, a
series of substituted metal polyynyls containing diynyl to triynyl
carbon chains have been characterized in their neutral and
oxidized states (see Chart 1).
The iron complex {Fe(dppe)Cp*}−(CC)2−Ph (Fe-2-Ph)
was produced by treatment of FeCl(dppe)Cp* with 1 equiv of
phenylbutadiyne in the presence of NaBPh4 in triethylamine.2
Before the solvent was removed under reduced pressure, an
excess of KOBut was added to prevent the formation of the
butatrienylidene intermediate and thus subsequent decom-
position. After extraction, Fe-2-Ph was isolated as an orange
powder in 85% yield. When applied similarly to the ruthenium
analogues, this described synthetic route did not give Ru-2-Ph
This comprehensive study was carried out with particular
attention to the rationalization of the spin delocalization by a
combined EPR and quantum chemical approach. The question
of instability of the oxidized compounds was also studied
experimentally and theoretically.
EXPERIMENTAL RESULTS
■
Syntheses and Characterization of Fe-2-Ph and Ru-2-
Ph. As illustrated in Scheme 1, the iron and ruthenium
derivatives were obtained by following different procedures.
Received: June 26, 2012
Published: September 13, 2012
© 2012 American Chemical Society
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Scheme 1
Scheme 2
Scheme 3
(see Scheme 1). However, Ru-2-Ph can be obtained from the
reaction between RuCl(dppe)Cp* and PhCCCCSiMe3 in
methanol containing 1 equiv of KF, 1% of water, and a small
amount of DBU.3 The complex Ru-2-Ph was isolated as a
bright yellow powder in 87% yield. Satisfactory elemental
analyses were obtained for these new complexes, which were
also characterized by the usual spectroscopic methods and their
structures confirmed by single-crystal X-ray studies (see below).
The IR spectrum of the new iron diynyl complex Fe-2-Ph
shows three ν(CC) bands at 2150, 2007, and 1987 cm−1, the
lowest energy band being assigned to a Fermi resonance
resulting from a coupling between a ν(CC) mode with
another vibration mode of the molecule, as previously observed
for the alkynyl−iron derivatives.4 In accord with our assign-
ment, the IR spectrum of Ru-2-Ph contains only two ν(CC)
(PPh3) (Fe-2-Au(PPh3)) has been prepared by following a
procedure similar to that previously developed for the
ruthenium analogue {Ru(dppe)Cp*}−(CC)2−Au(PPh3)
(Ru-2-Au(PPh3)).5 Treatment of Fe-2-SiMe3 with sodium
methoxide in a 1/1 THF/methanol mixture was followed by
addition of 1 equiv of AuCl(PPh3) to the solution (Scheme 2).
After 4 h of stirring, the precipitate was collected and washed
with cold methanol to afford Fe-2-Au(PPh3) as an orange
solid.
The identity of the complex Fe-2-Au(PPh3) was confirmed
by an X-ray structure and by full spectroscopic characterization,
including the four 13C resonances of the carbon atoms of the
chain, which were found at δ 88.84, 94.18, 104.06, and 123.26
2
ppm (t, JCP = 40 Hz). The solution IR spectrum of Fe-2-
Au(PPh3) contains two ν(CC) bands at 2069 and 1969
cm−1, consistent with the asymmetry of the carbon bridge, as
previously observed with other related heterobinuclear
butadiynyl complexes.6,7
1
bands at 2153 and 2016 cm−1. The H, 13C, and 31P NMR
spectra of the two complexes are very similar. However, while
for Fe-2-Ph the α-carbons of the diynyl ligand are found as a
triplet at δ 144.74 ppm (2JCP = = 38 Hz), for Ru-2-Ph this
resonance lies among the aromatic carbon resonances and
cannot be assigned.
Synthesis and Characterization of Fe-2-Au(PPh3). The
heterobinuclear complex {Fe(dppe)Cp*}−(CC)2−Au-
Synthesis and Characterization of Fe-3-SiMe3. The
binuclear complexes {Fe(dppe)Cp*}−(CC)3−{Fe(dppe)-
Cp*} (isolated as a mixture with its higher homologue
{Fe(dppe)Cp*}−(CC)4−{Fe(dppe)Cp*}) and {Fe(dppe)-
Cp*}−(CC)3−{Re(NO)(PPh3)Cp*} constitute the only
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Figure 1. Molecular structures of the isomorphous systems Fe-2-Ph (top left) and Ru-2-Ph (top right), of Fe-3-SiMe3 (middle left) and Ru-3-SiMe3
(middle right), and of Fe-2-Au(PPh3) (bottom left) and Ru-3-Au(PPh3) (bottom right), (mol. 1 in each case) showing thermal ellipsoids at the
50% probability level. Hydrogen atoms have been removed for clarity.
compounds of this iron series bearing a hexatriynediyl
moiety.8,9 Mononuclear iron complexes containing the Fe-
(dppe)Cp* fragment and a hexatriynyl ligand have never been
synthesized before. The Bruce group has developed a useful
methodology for preparing ruthenium complexes with long all-
carbon chains with diverse groups on the opposite termini.10
Following the synthesis of the ruthenium analogue Ru-3-
SiMe3,10 the iron derivative was successfully prepared. The
diynyl−gold complex Fe-2-Au(PPh3) was treated with an
excess of iodo(trimethylsilyl)ethyne in a 1/1 THF/triethyl-
amine mixture in the presence of Pd(PPh3)4 and CuI as
catalysts (Scheme 3). After workup, the compound Fe-3-SiMe3
was obtained as an orange powder in 55% yield.
In addition to the usual spectroscopic characterization, the
molecular structure of Fe-3-SiMe3 was established by an X-ray
crystal structure. The IR spectrum of Fe-3-SiMe3 displays only
two ν(CC) bands at 2092 and 1952 cm−1. In the 13C NMR
spectrum, the α-carbon resonates as a triplet at δ 151.07, while
the other five carbon atoms of the hexatriynyl ligand appeared
as singlets at δ 47.06, 69.29, 77.18, 94.34, and 100.95.
Molecular Structures of Fe-2-Ph, Ru-2-Ph, Fe-2-Au-
(PPh3), Fe-3-SiMe3, Ru-3-SiMe3, and Ru-3-Au(PPh3). Plots
of single molecules of these complexes are shown in Figure 1;
the main bond lengths and angles are summarized in Table S1
(see the Supporting Information), and crystal data and
refinement details are summarized in the Experimental Section
(Table 10). The crystallographic investigation confirms the
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typical pseudo-octahedral geometry of the iron and ruthenium
centers.4,8,11 All bond distances and bond angles are usual for
these types of organo-iron and -ruthenium compounds. The C4
and C6 chains are quasi-linear with angles ranging between 174
and 180°. Alternation of short and long carbon−carbon bond
lengths confirms the diynyl or triynyl nature of the chains.
Electrochemical Properties. The redox properties of the
polyynyl complexes Fe-2-Ph, Ru-2-Ph, Fe-2-Au(PPh3), and
Fe-3-SiMe3 have been investigated, and the data are compared
with those previously obtained for the Fe-n-R and Ru-n-R
series (n = 1−3; R = H, Ph, SiMe3, Au(PPh3)).4,12,13 The cyclic
voltammograms of the polyynyl Fe(II) and Ru(II) complexes
were recorded in the ranges −0.4 to +0.5 and −0.4 to +0.9 V vs
the standard calomel electrode (SCE), respectively. Interest-
ingly, the degree of chemical reversibility depends not only on
the nature of the metal center but also on the carbon chain
length and the nature of the terminal R groups. In the iron
series, when the carbon chain bears a phenyl ring or a
trimethylsilyl group, the heterogeneous electron transfer is fully
reversible on the platinum electrode regardless of the number
of carbon atoms of the chain. In contrast, for R = H, only partial
chemical reversibility is found at a scan rate of 0.100 V/s, and
the ipc/ipa current ratio decreases with the number of carbon−
carbon triple bonds in the carbon chain (see Table 1),
2 nicely illustrates the difference in chemical reversibility for the
one-electron oxidations of the iron and ruthenium diynyls Fe-
Figure 2. Cyclic voltammograms of Fe-2-Ph (solid line, in red) and
Ru-2-Ph (dotted line, in blue). Experimental conditions are given in
Table 1.
2-Ph and Ru-2-Ph. In the ruthenium series, the electron
transfer is quasi-irreversible on the platinum electrode and
replacement of the phenyl group by H, SiMe3, and Au(PPh3)
makes the electron transfer fully irreversible. For the higher
homologues Ru-3-SiMe3, the oxidation is also fully irreversible.
In both series, the redox center senses the electronic effect of
the terminal R group. The E° values range from −0.16 to +0.08
V and from +0.15 to +0.44 V in the iron and ruthenium series,
respectively. The Au(PPh3) and phenyl termini are apparently
electron-releasing groups to the electroactive center, while the
trimethylsilyl and hydrogen substituents show weak electron-
withdrawing properties. It is noteworthy that the gold fragment
shows unexpected behavior. While its presence renders the
complex easier to oxidize, it does not contribute to the
stabilization of the resulting radical cation.
In Situ Glass EPR Spectroscopy of [Fe-n-R](PF6) and
[Ru-n-R](PF6). The compounds Fe-n-R and Ru-n-R were
reacted with less than 1 equiv of [FeCp2](PF6) in CH2Cl2 at
−80 °C directly in the quartz EPR tube, and the resulting
mixtures were immediately cooled to liquid nitrogen temper-
ature. The X-band EPR spectra of the radical cations generated
in situ at 66 K display three well-resolved features
corresponding to the components of the g-tensors character-
istic of d5 low-spin Fe(III) and Ru(III) in a pseudo-octahedral
environment. The g-tensor values extracted from the spectra
are collected in Table 2.
Table 1. Electrochemical and IR Data for Fe-n-R and Ru-n-R
Complexes (n = 1−3; R = H, Ph, SiMe3, Au(PPh3))
E° (V/
a
compd
Fe-1-H
SCE)
ipc/ipa
νCC (cm−1
)
ref
b
−0.12
−0.15
−0.02
0.00
0.80
1.0
1.0
0.48
1.0
0.61
1.0
0.8
0.8
0.02
0
1910
14
15
b
d
Fe-1-Ph
2049 (2053 )
c
Fe-2-Ph
2150, 2007, 1987
this work
b
Fe-2-H
2099, 1958
6
b
Fe-2-SiMe3
Fe-2-Au(PPh3)
Fe-3-SiMe3
Ru-1-H
0.00
2165, 2090, 1980
6
d
−0.16
0.08
2069, 1969
this work
d
2092, 1952
this work
d
0.31
1930
3
d
Ru-1-Ph
0.23
2071
13
d
Ru-2-Ph
0.44
2153, 2016
this work
b
Ru-2-H
0.44
2109, 1971
5
b
b
Ru-2-SiMe3
Ru-2-Au(PPh3)
Ru-3-SiMe3
Ru-3-Au(PPh3)
0.43
0
2171, 2095, 1990
2119, 2072, 1981
5
0.15
0
5
b
0.41
0
2110, 1971
10
10
b
2121, 2088, 1965
a
n
Conditions: in CH2Cl2, 0.1 M [NBu4 ]PF6, scan rate 0.1 V/s, Pt
electrodes, V vs SCE (FeCp2/[FeCp2]+ = 0.46 V vs SCE used as
internal reference for potential measurements).16 Nujol/KBr
b
c
d
windows. KBr pellet. CH2Cl2/KBr windows.
Solutions of these radical cations are all stable at low
temperature when they are kept as a glass. As the temperature
is allowed to increase, the glass melts and rapid decomposition
of the organometallic materials takes place, except for the
Fe(III) radical cations [{Fe(dppe)Cp*}−(CC)−Ph)](PF6)
([Fe-1-Ph](PF6)) and [{Fe(dppe)Cp*}−(CC)−SiMe3]-
(PF6) ([Fe-1-SiMe3](PF6)), which are stable in solution at
−20 °C. Replacing iron by ruthenium or increasing the number
of carbon atoms in the polyynyl ligand decreases the kinetic
stability of the radical cations. In the case of R = Ph and n = 2,
the disappearance of the radical is associated with a decrease in
intensity of the EPR signal, suggesting that a radical coupling
process occurs. In the other cases, the appearance of several
new signals in the spectra indicates that the radicals decompose
to give several byproducts, some of them being paramagnetic.
indicating that the kinetic stability of the Fe(III) complexes on
the platinum electrode decreases in the same order. For any
carbon chain length, the stability of the Fe(III) complexes
decreases with R according to the sequence Ph > SiMe3 >
Au(PPh3) > H.
Previous work has shown that the kinetic stabilities and the
reactivities of the monoalkynyl radicals [{M(dppe)Cp*}−(C
C)−H)]+ (M = Fe, Ru) are very similar. Both radical cations
slowly dimerize in solution to produce bis(vinylidene)
complexes.3,14 While both the iron and ruthenium cations
[M-1-Ph]+ are stable in the solid state and in solution,12,15 they
have significantly different electronic structures,13 which results
in the rich reactivity recently reported for [Ru-1-Ph]+.17 Figure
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a
order to understand how the nature of the metal, the length of
the carbon chain, and the nature of the R substituent affect their
electronic properties. All systems considered were fully
optimized without symmetry constraints (see Computational
Details).
Table 2. Experimental EPR Data for Selected
[{M(dppe)Cp*}−(CC)n−R](PF6) Complexes
f
f
compd
g1
g2 (a2 )
2.033
g3 (a3 )
1.975
Δg
giso
b
[Fe-1-Ph]+
[Fe-2-Ph]+
2.464
2.335
2.488
2.476
2.475
2.401
0.489
0.454
0.513
0.505
0.504
0.407
2.157
2.051
2.164
2.160
2.159
2.160
b
1.937
2.030
2.032
2.030
2.084
1.881
1.975
1.971
1.971
1.994
Effect of the Length of the Carbon Chain. The effect of
lengthening the carbon chain on the electronic and physical
properties was investigated going from alkynyl to triynyl chains
in the iron and ruthenium series. This study, which also
includes the effect of oxidation, is limited to R = H, Ph.
Pertinent computed metric data are reported in Tables 3 and 4
for iron and ruthenium complexes, respectively. They are
compared to the experimental data where available. The
optimized geometries of Fe-n-R (n = 1−3) compare rather well
with those obtained by X-ray diffraction. The largest bond
distance deviations between calculated and experimental results
are found for Fe−Cp*(centroid) and Fe−P(dppe) distances,
which are computationally overestimated by 0.06 and 0.04 Å,
respectively. The rest of the bond lengths are reproduced well,
the CC triple bonds being computed as only 0.02 Å too long.
Such deviations between theory and experiment are typical for
this kind of organometallic system at this level of theory.17−19
The lengthening of the carbon chain from Fe-1-H to Fe-3-H
hardly changes the metal−ligand (Cp*, dppe) distances. In
contrast, the metal−carbon backbone is more affected. The
Fe−C1 bond length shortens from 1.905 to 1.858 Å, while the
CC triple bonds slightly lengthen (+0.02 Å for C1C2) and
the C−C single bonds shorten (−0.02 Å for C2−C3) upon
chain lengthening. For the {Cp(PH3)2Ru}−(CC)n−Ph (n =
1−6) analogues, the same trend was observed.20 The
geometrical analyses of Fe-n-Ph and Ru-n-R (n = 1−3)
compounds lead to exactly the same conclusions. in agreement
with the experimental trends.
Electronic structures of these polyynyl complexes were
investigated. Overall, they are similar (see Figure S1 in the
Supporting Information). Using the Fe-n-H series as an
example, we see that the highest occupied molecular orbital
(HOMO) and HOMO-1 are dπ/π type in character,
antibonding between the Fe and C1 atoms and the carbon
atoms of the chain involved in a single bond, and bonding
between the carbon atoms of the triple bonds (Figure 3). Their
spatial extensions are in two distinct perpendicular planes, the
HOMO lying in the π network orthogonal to the polyynyl
ligand, whereas the HOMO-1 sits in the parallel plane. The
lowest unoccupied molecular orbital (LUMO) is metal−ligand
(Cp*, dppe) antibonding in character in all cases, and the
LUMO+1 is π* dppe centered.22
bc
,
[Fe-1-SiMe3]+
[Fe-2-SiMe3]+
[Fe-3-SiMe3]+
cd
,
d
[Fe-2-
de
,
Au(PPh3)]+
b
[Ru-1-Ph]+
[Ru-2-Ph]+
2.227
2.418
2.345
2.057
1.988
0.239
0.420
0.371
2.091
2.167
2.129
d
2.086 (35)
2.069
1.998 (55)
1.974
[Ru-1-
cd
,
SiMe3]+
[Ru-2-
SiMe3]+
2.273
2.299
2.275
2.100
2.048
1.988
0.285
0.324
0.289
0.096
2.103
2.105
2.104
2.046
c e
−
[Ru-3-
SiMe3]+
2.040 (41)
2.051
1.975 (40)
1.986
c e
−
[Ru-2-
Au(PPh3)]+
c e
−
[Ru-3-
Au(PPh3)]+
2.034 (40)
2.004 (25)
c e
−
a
At 66 K in CH2Cl2 glass; [FeCp2]PF6 was used as the oxidizing
reagent. The M(III) radical cation is thermally stable at 20 °C for at
least a few minutes in the EPR tube. Complexes prepared using
methods cited in Table 1. The M(III) radical cation is not thermally
stable above −20 °C. The EPR spectrum contains significant amounts
b
c
d
e
f
of paramagnetic impurities. In gauss.
For the iron complexes of this series, the g-tensor
anisotropies (Δg) are large, ranging from 0.513 to 0.407;
they are not very sensitive to the number of carbon atoms in
the polyynyl ligand and the nature of R. In contrast, for the
ruthenium analogues, the Δg parameters range from 0.420 to
0.096, showing that the localization of spin density is strongly
dependent both on the number of carbon atoms in the polyynyl
fragment and on the nature of the terminal substituents. When
the Fe and Ru analogues are compared (same chain length and
same substituent), the Δg parameters are smaller overall in the
ruthenium series. These observations are in line with previous
experimental and theoretical results which concluded that the
spin density is mainly localized on the metal center in the iron
series but largely distributed between the metal and the
unsaturated ligand in the case of the ruthenium complexes.13
In the ruthenium series, the data should be considered with
caution, due to the high instability of the Ru(III) compounds,
and we cannot exclude the possibility that the active EPR
species observed in the spectra is not the original oxidized
species but a radical resulting from its thermal evolution.
Assuming that the [Ru-n-R]•+ radicals were effectively
quenched in the glass, the Δg values decrease when the
number of carbon atoms increases for R = SiMe3, Ph,
Au(PPh3), but this correlation is far from being linear. In
addition, for a given value of n, the Δg tensors are generally
smaller for R = SiMe3, Au(PPh3), which have spherical
symmetry, than for the planar phenyl substituent. Serious
doubts arise concerning the almost identical EPR results
obtained for [Ru-2-SiMe3]+ and [Ru-2-Au(PPh3)]+, suggesting
that the same decomposition product was measured.
Although the energies and nodal properties of the MOs are
somewhat modified, the lengthening of the carbon chain hardly
affects the HOMO−LUMO energy gap within the series, which
is roughly 1.7 eV, because of an overall stabilization of the
energy levels. Indeed, replacement of the (CC)−H fragment
by a (CC)3−H fragment stabilizes the first HOMOs by only
0.30 eV. This is associated with a diminishing of the iron
contribution to the first HOMOs, from 63% for the Fe-1-H
complex to 44% for the Fe-3-H complex, and with a
consequent increase of the carbon chain character from 20%
to 42% (see Table S2 in the Supporting Information). The
shortening of the metal−carbon distance upon lengthening of
the chain is thus due to a smaller antibonding π interaction and
also to a reinforced σ bond (deeper MOs). The first LUMOs
are also stabilized by 0.33 eV on going from Fe-1-H to Fe-3-H,
mainly because of the electrostatic contributions. This analysis
COMPUTATIONAL RESULTS AND DISCUSSION
■
DFT calculations (BP86/TZP) were performed on the series of
mononuclear complexes [Fe-n-R]0/+ and [Ru-n-R]0/+, for n =
1−3 and R = H, Ph and for n = 2 and R = SiMe3, Au(PPh)3, in
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bonding. The geometry relaxations of the fragments do not
modify these observations (see Tables S7−S10 in the
Supporting Information). The main difference in M−C
interaction arises from the electrostatic attraction and the
Pauli repulsion. Overall, the latter is more important in Ru-1-
Ph and explains the weaker Ru−carbon bond. Electrostatic and
Pauli interactions cannot be deduced from orbital properties.
This prevents drawing any conclusions about the difference
between Fe- and Ru-containing systems from orbital analysis
alone.
The oxidized open-shell systems [M-n-R]+ were also
considered. As expected, the metal−ligand (Cp*, dppe) bond
lengths are elongated upon oxidation, but to a lesser extent with
increasing chain length. The computed elongations for the Fe-
Cp* bond lengths are 0.03 and 0.03 Å for [Fe-1-H]+ and [Fe-
3-H]+, respectively, and the computed lengthening for the Fe−
P(dppe) distances are 0.09 and 0.06 Å for [Fe-1-H]+ and [Fe-
3-H]+, respectively. The Fe−C and C−C distances are also
affected upon oxidation. The Fe−C1 bond is diminished by
roughly 0.03 Å, while the C−C single bonds and CC triple
bonds alternately shorten and lengthen to a lesser extent. These
changes are consistent with the nodal properties of the
HOMOs (see above), considering that the oxidation process
corresponds formally to removal of an electron from one of the
two highest occupied MOs. This illustrates the fact that the
oxidation takes place not only on the metal atom but also on
the carbon chain. This is particularly the case for the ruthenium
series, for which the HOMOs are more localized on the carbon
chain. The ruthenium−ligand bond lengths are thus less
affected upon oxidation than in the iron series. Similar trends
were previously found for related arylvinyl ruthenium
compounds, where the first HOMOs are fully delocalized
along the ruthenium−arylvinyl unit.24
Atomic spin densities were computed by means of the
Mulliken population analysis technique for monocationic
species in order to describe the delocalization of the unpaired
electron. The results are summarized in Scheme 4 for [Fe-n-
H]+ and [Ru-n-H]+ complexes, and the spatial distributions of
the computed spin density for [Fe-3-H]+ and [Ru-3-H]+ are
shown in Figure 4. The largest part of the positive spin density
is located on the metal center for both series of complexes. The
rest is distributed over the even-numbered carbon atoms. The
atomic spin density on the metal decreases with lengthening of
the carbon chain, from 0.96 electron (e) to 0.74 e, and from
0.53 to 0.36 e for [Fe-n-H]+ and for [Ru-n-H]+ respectively, on
going from n = 1 to 3. Consequently, the spin density is more
localized on the organic chain but divided on more atoms.
The adiabatic ionization potentials (IPs) were computed for
several carbon chain lengths and are given in Tables 3 and 4 for
iron and ruthenium complexes, respectively. For the Fe-n-H
series, the oxidation is found to become more difficult with
increasing n (5.35, 5.42, and 5.46 eV for n = 1−3, respectively),
in agreement with the experimental redox potentials (E°). For
Ru-n-H, the calculated IPs are unchanged for n = 1 to n = 3
(5.67 eV), whereas a noticeable increase is measured in the
oxidation potentials (0.23 and 0.44 V for n = 1, 2, respectively).
In the type of systems studied here, solvation energies of
neutral and oxidized compounds are different, due to the fact
that the unprotected carbon chain is affected upon oxidation.
They do not compensate and thus cannot be neglected. The
IPsolv values, including solvation corrections, were thus
calculated (see Tables 3 and 4 and Computational Details).
For Fe-n-H, Ru-n-H, and Fe-n-Ph, oxidation in a solvent is
Figure 3. Contour plots, energies, and Fe/Cn percentages of the
HOMO (left) and HOMO-1 (right) of (a) Fe-1-H, (b) Fe-2-H, and
(c) Fe-3-H. Contour values are 0.045 (e/bohr3)1/2
.
of the changes in the electronic structure upon carbon chain
lengthening is also relevant to the phenyl-substituted series Fe-
n-Ph (n = 1−3), even though the first HOMOs can possess
additionally also a subsequent phenyl character. The analysis
done above is qualitatively the same for the closely related Ru-
n-R (n = 1−3; R = H, Ph) series. However, the two first
HOMOs of the ruthenium compounds are less metal-centered
than the corresponding ones in the iron series, with a Ru
percentage ranging from 25 to 49% (44−63% for Fe).
To quantify the differences between ruthenium- and iron-
containing systems, an analysis of the different terms of the
metal−carbon chain bond energy was performed (see Table
5).23 This approach decomposes the bond dissociation energy
(ΔEBDE) between the metal fragment and the carbon chain as a
sum of orbital interactions (ΔEorb), electrostatic contributions
(ΔEel), and Pauli repulsion interactions (ΔEPauli). Interestingly,
the orbital interactions are largely similar for both metals,
probably with compensation between σ bonding and d/π
Table 5. Heterolytic Bond Dissociation Energies (BDEs) of
the M−C1 Bond for Fe-1-Ph and Ru-1-Ph (in eV)
compd
Fe-1-Ph
Ru-1-Ph
ΔEPauli
ΔEorb
ΔEel
+9.27
−4.67
−10.86
−6.26
−6.18
+9.92
−4.63
−11.41
−6.12
−6.05
a
ΔEBDE
ΔEBDE
b
a
b
Without basis set superposition error (BSSE) correction. With BSSE
correction.
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Scheme 4. Calculated Atomic Spin Densities for [Fe-n-H]+ and [Ru-n-H]+ Complexes
Figure 4. Spatial distributions of computed spin density of [Fe-3-H]+ (left) and [Ru-3-H]+ (right). Isocontour value: 0.005 e/bohr3.
Table 6. Pertinent Optimized Bond Lengths (Å) and Ionization Potentials (IP, eV) for [Fe-2-R]0/+ (R = H, Ph, SiMe3,
Au(PPh3)), in Comparison with the Corresponding Experimental Data Given in Parentheses Where Available
compd
Fe-2-H
charge
Fe−P
Fe−Cp*
1.800
Fe−C1
1.875
C1C2
1.247
C2−C3
1.357
C3C4
1.228
1.225
1.234 (1.211) 1.416 (1.434)
C4−R
1.067
1.069
IP
0
2.221/2.213
2.297/2.286
5.42
1+
0
1.829
1.847
1.251
1.349
a
Fe-2-Ph
2.224/2.214
(2.181/2.196)
1.799 (1.746)
1.870 (1.873)
1.249 (1.230)
1.351 (1.372)
5.26
5.35
4.80
1+
0
2.282/2.268
1.825
1.829
1.255
1.339
1.236
1.411
Fe-2-SiMe3
2.215/2.218
(2.180/2.188)
1.801 (1.742)
1.868 (1.874)
1.248 (1.227)
1.351 (1.374)
1.241 (1.220) 1.823 (1.822)
bc
,
1+
0
2.280/2.297
1.831
1.842
1.253
1.341
1.241
1.856
a
Fe-2-
Au(PPh3)
2.206/2.212
(2.181/2.180)
1.797 (1.741)
1.882 (1.875)
1.249 (1.237)
1.356 (1.371)
1.243 (1.217) 1.980 (1.986)
d
1+
2.262/2.275
1.824
1.837
1.257
1.343
1.247 1.990
a
b
c
d
This work. See ref 5. See ref 6. Relativistic effects included; see Computational Details. Cp* = centroid.
Table 7. Pertinent Optimized Bond Lengths (Å) and Ionization Potentials (IP, eV) for [Ru-2-R]0/+ (R = H, Ph, SiMe3,
Au(PPh3)), in Comparison with the Corresponding Experimental Data Given in Parentheses Where Available
compd
Ru-2-H
charge
0
Ru−P
Ru−Cp*
Ru−C1
C1C2
C2−C3
C3C4
C4−R
1.066
IP
a
2.313/2.325
(2.256/2.279)
2.005 (1.883)
2.009 (2.015)
1.245 (1.186)
1.356 (1.387) 1.227 (1.193)
5.67
1+
0
2.364/2.377
2.027
1.957
1.257
1.344
1.228
1.068
b
a
a
Ru-2-Ph
2.317/2.329
(2.261/2.277)
1.996 (1.896)
2.008 (1.997)
1.247 (1.202)
1.350 (1.377) 1.235 (1.211)
1.417 (1.429)
5.47
5.58
5.02
1+
0
2.359/2.372
2.021
1.953
1.262
1.334
1.240
1.409
Ru-2-SiMe3
2.321/2.326
(2.261/2.278)
2.007 (1.903)
2.004 (1.983)
1.248 (1.231)
1.353 (1.371) 1.241 (1.222)
1.818 (1.822)
1+
0
2.361/2.374
2.024
1.951
1.261
1.339
1.244
1.849
Ru-2-
Au(PPh3)
2.283/2.290
(2.262/2.278)
1.949 (1.897)
1.992 (1.992)
1.248 (1.221)
1.357 (1.378) 1.243 (1.205)
1.976 (1.992)
c
1+
2.336/2.350
1.999
1.938
1.266
1.339
1.248
1.985
a
b
c
See ref 5. This work. Relativistic effects included; see Computational Details. Cp* = centroid.
calculated to become more difficult with increasing n. This
agrees with the available experimental data. For Ru-n-Ph,
similar IPsolv values are calculated for n = 1, 2. This can be
explained by the geometry fluctuation detailed below.
Effects of the R Substituents. To analyze the effects of
end groups R on the electronic properties, DFT calculations
were carried out on two representative examples: namely, [Fe-
2-R]0/+ and [Ru-2-R]0/+ (R = H, Ph, SiMe3, Au(PPh3)). The
main optimized bond lengths obtained for the different R
groups (R = H, Ph, SiMe3, Au(PPh3)) in the neutral and
monocationic species are reported in Tables 6 and 7 for [Fe-2-
R]0/+ and [Ru-2-R]0/+, respectively, and are compared to
experimental bond lengths where available. The analysis of the
optimized structures reveals that the computed bond lengths in
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the chain are not significantly affected by the substitution
ligand. In the ruthenium series, the main differences between
experimental and calculated structures are found for Ru−
P(dppe) and Ru−Cp* bond lengths which are computed to be
longer by 0.05 and 0.10 Å, respectively. These discrepancies in
the M−P(dppe) and M−Cp* centroid lengths are the same as
those found previously, except in the case of R = Au(PPh3), for
which the agreement is much better, with computed
elongations of 0.02 and 0.04 Å for Ru−P(dppe) and Ru−
Cp*, respectively.19
The calculated Ru−C1 separation deviates by up to 0.02 Å
from the experimental X-ray results, whereas the maximum
deviation in the C−C distances within the chain is 0.04 Å.
Nevertheless, in all cases, the total lengths of the metal−carbon
chains (Ru−Cn) are in good agreement with the experimental
data, with a discrepancy of less than 0.06 Å for the sum of the
four bond distances for the triynyl complexes. In fact, the
homogeneous delocalization of the electron density along the
metal−carbon chain often leads to imprecise experimental
positioning of the atoms.
Au(PPh3)-containing complex, for which it is calculated to be
1.2 eV. In the latter case, the two first LUMOs are mainly
Au(PPh3)-centered, in contrast with the other complexes of the
series, where the first LUMOs are Ru−ligand (Cp*, dppe)
antibonding molecular orbitals or π* on the phenyl groups of
the dppe. For R = Au(PPh3), the antibonding MOs centered on
the metal atom are the LUMO+2 and LUMO+5, lying roughly
1.7 eV above the HOMO found in the other complexes (see
Figure S2 in the Supporting Information). In all cases, as found
for R = H, Ph, the first HOMOs are fully delocalized on the
metal−carbon chain and have an important antibonding
character between the metal center and atom C1. For the
Au(PPh3)-containing complex, the carbon chain character is
roughly 50%, in comparison to 40% for the other complexes,
whereas the metal character is unchanged.
The IPs were computed for the different end groups and
compared to the corresponding experimental redox potentials.
The computed IPs values slightly diminish from 5.7 to 5.6 and
5.5 eV when H is replaced by SiMe3 and phenyl groups,
respectively, suggesting that these compounds have similar
oxidative properties. Experimentally, this trend is confirmed by
the measured redox potentials, which show similar values (0.44
and 0.43 V for R = Ph, SiMe3, respectively). The computed
HOMO energies stay approximately constant for these
substituents and confirm this trend theoretically. The easiest
complex to oxidize is found both theoretically (IP = 5.0 eV)
and experimentally (E° = 0.15 V) for R = Au(PPh3).5
Energies and isosurfaces of the HOMOs and LUMOs for
Ru-2-R complexes are shown in Figure 5. All HOMO−LUMO
energy gaps are computed to be roughly 1.9 eV, except for the
The spin density distributions computed for [Ru-2-R]+
cations are given in Scheme 5. The largest positive atomic
spin density is found associated with the metal atom, but as
expected, our calculations also reveal that the unpaired electron
is partly delocalized on the even-numbered carbon atoms of the
chain. The atomic spin density on the C4 atom is strongly
influenced by the nature of the substituent. The smallest value
is found for the phenyl substituent (0.21 e), since a part of the
unpaired electron density is also delocalized on the phenyl end
group (following the HOMOs spatial properties, see above).
The atomic spin densities computed on the C4 atom for the H,
SiMe3, and Au(PPh3) substituents are 0.25, 0.28, and 0.30 e,
respectively. This increase has to be correlated with the donor
character of the substituent (H < SiMe3 < Au(PPh3)). The
same trend is observed with the iron complexes but with a
more important localization of the unpaired electron on the
metal atom and less on the carbon chain, in comparison with
the ruthenium analogues, as expected. Indeed, the oxidation of
the [Ru-2-R]+ compounds is partly or fully irreversible, whereas
[Fe-2-R]+ are more stable.
The atomic spin density on the carbon chain can also be
correlated to the instability within the [M-2-R]+ series. A non-
negligible spin density is found for the C2 atom, but it is less
than that for the analogous [M-1-R]+. The latter dimerizes for
R = H, for which the C2 atomic spin density is the highest. For
n = 2, spin density is more concentrated on the C4 atoms with
the largest value calculated for R = SiMe3, Au(PPh3) (see
Scheme 5). This is particularly the case for [Ru-2-R]+, for
which 0.28 and 0.30 e are calculated, respectively. This favors
radical−radical reactions, with traces of O2 for example.25 On
this basis, the stability would be Ph > H > SiMe3 > Au(PPh3),
with ruthenium systems less stable in any case. Nevertheless,
the bulkiness of SiMe3 and Au(PPh3) can slow down the
process and would explain the Ph > SiMe3 > Au(PPh3) > H
found experimentally by electrochemical studies.
Figure 5. Contour plots, energies, and Ru/C4 percentages of the
HOMO (left) and of the LUMO (right) for (a) Ru-2-H, (b), Ru-2-
Ph, (c) Ru-2-SiMe3, and (d) Ru-2-Au(PPh3). Contour values: 0.045
(e/bohr3)1/2
.
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Scheme 5. Calculated Atomic Spin Densities for [Fe-2-R]+ and [Ru-2-R]+
Table 8. g-Tensor Components and Anisotropies for the [Fe-n-R]+ and [Ru-n-R]+ Complexes, with Experimental Values Given
in Parentheses Where Available
compd
g1
g2
g3
Δg
[Fe-1-H]+
2.601
2.480
2.402
2.001
2.023
2.034
1.900
1.930
1.948
0.701
0.550
0.454
[Fe-2-H]+
[Fe-3-H]+
[Fe-1-Ph]+
2.499 (2.464)
2.225 (2.335)
2.263
1.989 (2.033)
2.037 (1.937)
2.032
1.917 (1.975)
1.984 (1.881)
1.977
0.582 (0.489)
0.241 (0.454)
0.286
[Fe-2-Ph]+
[Fe-3-Ph]+
[Fe-2-SiMe3]+
[Fe-2-Au(PPh3)]+
[Ru-1-H]+
2.386 (2.476)
2.556 (2.401)
2.331
2.039 (2.032)
2.007 (2.084)
2.046
1.950 (1.971)
1.898 (1.994)
1.946
0.436 (0.505)
0.658 (0.407)
0.385
[Ru-2-H]+
2.321
2.039
1.949
0.372
[Ru-3-H]+
2.319
2.032
1.954
0.365
[Ru-1-Ph]+
[Ru-2-Ph]+
[Ru-3-Ph]+
[Ru-2-SiMe3]+
[Ru-2-Au(PPh3)]+
2.283 (2.227)
2.190 (2.418)
2.542
2.033 (2.057)
2.049 (2.086)
1.929
1.956 (1.988)
1.982 (1.998)
1.860
0.327 (0.239)
0.208 (0.420)
0.682
2.305 (2.273)
2.521 (2.275)
2.037 (2.048)
1.986 (2.051)
1.952 (1.988)
1.899 (1.986)
0.353 (0.285)
0.622 (0.289)
EPR Properties. EPR properties of the optimized [Fe-n-R]+
and [Ru-n-R]+ complexes were computed (mPBE/TZP). The
resulting g-tensor components are given in Table 8. The
agreement between the computed and experimental aniso-
tropies Δg is moderately satisfactory. The largest deviation is
found for [Ru-2-Au(PPh3)]+, but its low stability suggests that
decomposition products are present (see below).
the metal atom. For example, in the [Ru-n-H]+ series, the
ruthenium spin density goes from 0.53 to 0.36 e for n = 1−3
(see Scheme 4), while Δg is calculated to be almost constant
(0.38 to 0.36). The same is found for the phenyl-substituted
series. A more detailed study is needed to understand this
apparent discrepancy.
For R = Au(PPh3), the computed Δg values are the largest
ones, but they are probably overestimated. Indeed, for high
atomic number atom containing systems, spin−orbit coupling
is known to contribute importantly.27 The ESR module in
quantum chemistry code we use does not allow including full
spin−orbit coupling but only first-order perturbation correc-
tions (see Computational Details). Nevertheless, one would
expect a noticeable change between systems substituted by
SiMe3 and by Au(PPh3), as measured experimentally for M =
Fe. For M = Ru, the g-tensor components and the anisotropies
are measured to be almost identical (Δg= 0.29 for both; cf.
Table 8). In this case, it is highly probable that some
decomposition may have occurred in both cases, as mentioned
in the Experimental Section, leading to the measurement of the
same decomposition product, as already observed for analogous
systems.13,25 C4−R bond breaking can be proposed. Homolytic
C4−R bond dissociation energies (Tables S7−S10 in the
Supporting Information) have been calculated to evaluate this
possibility. They are effectively much weaker for SiMe3 and
Au(PPh3) than for H and Ph substituents (4.65−4.88 vs 5.31−
5.66 eV), but these bonds are stronger for ruthenium
compounds than for the more stable iron systems. The
instabilities of [Ru-2-SiMe3]+ and [Ru-2-Au(PPh3)]+ are thus
Looking at the computed g-tensor components of the [Fe-n-
R]+ and [Ru-n-R]+ complexes, some general trends appear.
First, the influence of the R group on the main g-tensor
components is important and is clearly evidenced by computed
Δg anisotropies computed to follow the order H > SiMe3 ≫
Ph. The presence of a conjugated R group strongly diminishes
Δg. Second, the lengthening of the carbon chain in some cases
affects the g-tensor components; the computed Δg values
overall diminish as the carbon chain becomes longer, but for R
= Ph and [Ru-n-H]+ this is not the case. Third, the computed
anisotropies Δg in the iron series are always much larger than
those in the ruthenium series, except for R = Ph. These results
are roughly understood if one considers, as currently accepted
in the literature, that EPR parameters of organometallic
compounds are related to the metal spin density distribution.26
As mentioned previously, the computed atomic spin density on
the metal center (i) decreases when the hydrogen substituent is
replaced by SiMe3 and by phenyl groups, (ii) decreases as the
carbon chain lengthens, and (iii) is always computed to be
much larger in the iron series than in ruthenium. In contrast to
what is commonly admitted, the calculated Δg values have a
different evolution that the calculated atomic spin density on
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Figure 6. Calculated variation of the anisotropy Δg (in blue, dotted line) and the relative energy ΔEθ (in red, solid line) as a function of the rotation
angle θ of the phenyl end group for [Fe-1-Ph]+ (left) and [Ru-1-Ph]+ (right).
not due to cleavage of the C4−Si or C4−Au bonds but, as
detailed in the previous section, can be attributed to the large
atomic spin density on the C4 atom favoring radical instability.
For R = Ph, the computed anisotropies do not vary linearly
as a function of the metallic spin density, and no clear tendency
can be established. In fact, calculations were performed on the
most stable optimized structures and do not take into account
possible geometrical changes which can occur in solution: i.e.,
rotation of the phenyl end group (θ = Cp* centroid−M−
Cipso−Cortho).28 It has already been shown, particularly by Paul
and co-workers on substituted arylacetylide complexes, that the
geometries of the molecules strongly influence the g-tensor
values.29,30 They showed that the phenyl orientation plays an
important role in the EPR values. In order to evaluate the effect
of rotation of the phenyl end groups, 14 different geometrical
arrangements of [Fe-1-Ph]+ with dihedral angles θ ranging
from 22° to 179° were investigated (see Computational
Details). The EPR properties were computed in each case
and are reported in Table S11 (Supporting Information) and
plotted in Figure 6. A sizable change in the computed
anisotropies is found upon rotation of the phenyl ring. Indeed,
the computed anisotropies Δg evolve in a Gaussian way with θ
going from 22 to 179° (see left of Figure 6), with a minimum
value of 0.27 corresponding to the rotamers θ = 22° and θ =
179° (labeled [Fe-1-Ph-⊥]+),31 and a maximum value of 1.88
found at θ = 100°. These results can be correlated
approximately with changes in the positive atomic spin
densities distribution along the arylalkynyl ligand (Table
S11). For the most stable system, [Fe-1-Ph]+ (θ = 165°), the
spin density is spread all along the carbon chain and the phenyl
group, whereas for the θ = 89° rotamer (labeled [Fe-1-Ph-∥]+),
it is concentrated heavily on the metal atom and the carbon
chain and hardly on the phenyl ring. The computed anisotropy
Δg increases when the atomic spin density is more localized on
the metal center. The relative energy ΔEθ of the different
conformers, which corresponds to the difference in total energy
between the most stable conformation and the conformer of a
given θ value, is also plotted in Figure 6 as a red curve. Even
though the shape of this curve is similar to that when Δg is
plotted against θ, the maxima are not at the same θ values,
allowing us to conclude that both Δg and ΔEθ have to be taken
into account to simulate the experimental measurements.
Indeed, ionization potentials are thus correlated to the angle θ.
This conformational study was extended for each phenyl-
ended system, and the resulting curves of the anisotropy and of
the energy as a function of the dihedral angle θ are shown in
Figure 6 (right) for [Ru-1-Ph]+ and in Figure S3 of the
Supporting Information for [Fe-2-Ph]+ and [Ru-2-Ph]+. As
previously observed, the minima of anisotropy and energy are
found for a value of θ close to 0° or 180° for both compounds.
For the [Ru-1-Ph]+ complex, some fluctuations of the energy
and the anisotropy are computed for θ close to 90° (see Figure
6). Guided by these energetic and anisotropic fluctuations of
phenyl-containing systems, we can reconsider the computed
anisotropy Δg values, taking into account the probability that a
molecule exists in a certain conformation in the frozen solution.
According to the Maxwell−Boltzmann distribution, this
probability φθ is given by eq 1, where ΔEθ is the difference
solv(θ)
e−ΔE /(kT+ΔE
θ
φ =
θ
∑θ e−ΔE /(kT+ΔE
solv(θ)
θ
(1)
in energy between the most stable conformation and the
conformer θ and ΔEsolv(θ) is a solvation term specific for each
complex (see Computational Details), which takes into account
the energetic stabilization due to the solvent effects.
From this probability, the averaged values of the anisotropies
⟨Δg⟩ are calculated using eq 2 and are reported in Table 9. The
Δg
=
Δg × φ
θ
θ
∑
(2)
θ
Table 9. Experimental Δg and Computed ⟨Δg⟩ Values for
[Fe-n-Ph]+ and [Ru-n-Ph]+ for n = 1, 2
a
compd
exptl Δg
computed ⟨Δg⟩
[Fe-1-Ph]+
[Fe-2-Ph]+
[Ru-1-Ph]+
[Ru-2-Ph]+
0.489
0.454
0.229
0.420
0.483
0.445
0.273
0.333
a
See eqs 1 and 2.
computed anisotropies ⟨Δg⟩ are much closer to the
experimental values than the values reported in Table 8. The
weakening of the anisotropy found in the R = H series is also
found for the [Fe-n-Ph]+ systems, in accord with the decrease
of the atomic spin density on the metal center. For the related
ruthenium complexes, the lengthening of the carbon chain
leads, both experimentally and theoretically, to an increase in
Δg. This is due to the probabilities φθ of the conformations,
with θ close to 90° for [Ru-1-Ph]+ being much smaller than
similar conformations of the other systems, resulting in a
smaller Δg value (see Figure 6). A larger Δg value is calculated
for [Ru-2-Ph]+, for which this phenomenon does not occur.
The anisotropy tends to follow the metallic spin density, but
some structures show the same spin density with a different
computed anisotropy. Obviously, the atomic spin density is an
average value that does not contain the information to
understand this difference. The g-tensor values and anisotropies
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Figure 7. MO diagrams for the (⊥) and (∥) conformers of the [Fe-1-Ph]+ complex. The numerical values of the Λgp,occ‑vir contributions are given in
ppm.
Δg depend on the environment of the unpaired electron.
Ziegler and co-workers proposed a specific formalism to
highlight this fact and thus to better understand the EPR
properties.32 In this treatment, interest is focused on the
deviation (Λg) of the computed g-tensor components from the
free electron value ge (ge = 2.002319). Each g-tensor
component (g1, g2, g3, and giso) is described as the sum of the
free electron value plus several contributions.33 For the
complexes [Fe-n-Ph]+ and [Ru-n-Ph]+, the main contribution
of the deviation of g-tensor components (Λg) from the free
electron value is the paramagnetic term Λgp. This contribution
can also be decomposed into several terms, which are the
frozen core component (Λgp,core) and the magnetic field
induced couplings between occupied orbitals (Λgp,occ‑occ) and
between occupied and virtual orbitals (Λgp,occ‑vir). We will focus
on the Λgp,occ‑vir contribution, which dominates the Λg value
(deviation from the ge value).34
only 2° in the angle θ. In fact, other geometrical changes are
associated with those small variations of the angle θ when close
to 90°, mainly found in bending of the metal−carbon chain.
The systems are unstable when linearity is imposed: geometry
optimizations always lead to various distorted chains that
induce better overlaps between the π-type phenyl and alkynyl
networks and weaker overlaps between the metal and alkynyl
parts. Most probably, this is due to the fact the ruthenium
center is electronically saturated for θ far from 90° for this short
chain. For θ close to 90°, due to the nonequivalence of the dπ⊥
and dπ∥ fragment orbitals of [Ru(dppe)Cp*]2+, additional
electron density would be transferred to the metal because of
better orbital interactions. The ligand-to-metal back-bonding is
reduced by geometrical distortions to avoid this excess of
density. This is peculiar to [Ru-1-Ph]+; for n = 2, 3, the
electron density is more distributed over the chain and this
phenomenon does not occur.
Molecular orbital diagrams of [Fe-1-Ph-⊥]+ and [Fe-1-Ph-
∥]+ are shown in Figure 7 together with the principal
contributions of the paramagnetic term Λgp,occ‑vir. These
contributions are either positive or negative. The negative
values are equivalent for both conformers. In contrast, a sizable
change in intensities is found for the positive paramagnetic
contributions corresponding to the coupling between the β-
SOMO and β-SOMO-1 with the β-LUSO. Indeed, the two
computed occupied-virtual mixing 122β ↔ 123β and 121β ↔
123β increase from 29 466 and 28 490 ppm to 32 011 and 41
685 ppm, for the [Fe-1-Ph-⊥]+ and [Fe-1-Ph-∥]+ conformers,
respectively. These values, which can be described as the
magnetic coupling between spin−orbitals, include a term which
is inversely proportional to their energy differences. Indeed, a
large reduction of the β-SOMO−β-LUSO energy gap occurs
upon rotation of the phenyl end group from θ = 179 to 89°.
For [Ru-1-Ph]+, important fluctuations of Δg are calculated
for θ close to 90°, but the atomic spin densities are only weakly
affected. As previously highlighted, these variations can be
explained by some modification of the electronic structures in
the SOMO−LUSO region. Indeed, the β-SOMO−β-LUSO
energy gap varies between 0.26 and 0.34 eV for a change of
CONCLUSION
■
New organo-iron and -ruthenium complexes {M(dppe)Cp*}−
(CC)n−R containing C2, C4, and C6 chains with different R
end groups have been synthesized and characterized and their
molecular structures determined. From the electrochemical
investigations, some clear conclusions can be drawn: As
expected, the iron complexes are easier to oxidize than their
ruthenium analogues. Oxidation potentials are very sensitive to
the chain length: the shorter the carbon chain, the easier the
oxidation of the organometallic complex. Additionally,
conclusions from the EPR investigations can be given: As
expected, the anisotropy parameters in the iron complexes are
larger overall than those in the ruthenium complexes. However,
the effect of the carbon chain length seems to be negligible in
some cases, as observed in the [M-n-SiMe3](PF6) (n = 1−3)
series, where the g values are almost identical. This behavior is
also computed for the [Ru-n-H]+ series, even though the
ruthenium spin density changes drastically. By studying more
particularly the [M-n-Ph]+ series, we are able to show
theoretically that g and Δg depend on the environment of
the unpaired electron and that magnetic coupling between
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Organometallics
Article
Synthesis of Fe(CCCCPh)(dppe)Cp* (Fe-2-Ph). To a
suspension of FeCl(dppe)Cp* (100 mg, 0.16 mmol) and NaBPh4
(66 mg, 0.19 mmol) in triethylamine (15 mL) was added a solution of
HCCCCPh35 (24 mg, 0.19 mmol) in THF (1 mL). The mixture
turned slowly from dark green to orange. After one night at room
temperature, tBuOK (excess) was added to the solution before
removal of the solvent under reduced pressure. The solid residue was
then extracted with toluene (3 × 10 mL), and the solvent was removed
under reduced pressure. The residue was extracted a second time with
diethyl ether (3 × 10 mL), and after removal of the solvent under
reduced pressure, the resulting orange powder was dried under
vacuum to afford Fe(CCCCPh)(dppe)Cp* (Fe-2-Ph; 97 mg,
85%). Anal. Calcd for C46H44FeP2: C, 77.31; H, 6.21. Found: C, 76.59;
H, 6.18. IR (KBr): ν(CC) 2150, 2007, 1987 cm−1. 1H NMR (C6D6,
300 MHz): δ 1.45 (s, 15H, Cp*), 1.77, 2.58 (2 × m, 4H, PCH2),
6.87−8.02 (m, 25H, Ph). 13C NMR (C6D6, 75 MHz, ppm): δ 8.89 (s,
C5Me5), 28.79−29.91 (m, dppe), 59.70 (s, CCCCPh), 80.98 (s,
CCCCPh), 87.26 (s, C5Me5), 100.06 (s, CCCCPh),
occupied and virtual spin−orbitals provides the correct
description of the evolution found within a series. EPR
anisotropies do not correlate with metal spin density if the
changes in the electronic structure are important.
Finally, with the more electron-rich R end groups, such as
Au(PPh3), the oxidation is easier. Analysis of the calculated
atomic spin density of the oxidized system together with bond
dissociation energies shows that radical reactions can occur on
the even carbon atoms, labeled C2, C4, and C6. This is tuned by
the importance of the spin density and the steric hindrance of
the considered carbon atom. Indeed, in the iron series, the
stability of the iron(III) radical bearing ligands with four and six
sp carbon atoms is in marked contrast with that of their alkynyl
homologues. While the latter are stable in solution and in the
solid state at 20 °C, the former decompose above −20 °C. This
different behavior could be steric in origin, the two carbon
atoms close to the metal center being more protected by the
ancillary ligands. It can be also anticipated that the 17 e radical
can change via a clean chemical process, since the ESR signal
disappeared cleanly, no traces of other radicals being detected,
except in the particular case of R = Au(PPh3). Guided by these
stimulating results, we are currently investigating the reactivities
of these radical cations.
2
124.42−137.88 (m, Ph), 144.74 (t, JCP = 38 Hz, CCCCPh).
31P NMR (C6D6, 121 MHz): δ 100.2 (s). ES-MS (m/z): calcd for
C46H44FeP2 714.2268, found 714.2275 [M]+.
Synthesis of Ru(CCCCPh)(dppe)Cp* (Ru-2-Ph). A meth-
anolic (7 mL, containing 1% of distilled H2O) suspension of
RuCl(dppe)Cp* (100 mg, 0.15 mmol), Me3SiCCCCPh36 (33
mg, 0.16 mmol), KF (10 mg, 0.16 mmol), and DBU (2 drops) was
heated under reflux. After 1 h, the mixture was cooled and the yellow-
green precipitate filtered off and washed with cold MeOH. The
resulting powder was then dissolved in DCM (containing 5% of NEt3)
and the solution passed through a basic alumina column with the same
solvent as eluent. The yellow band was collected and the solvent
removed to give Ru(CCCCPh)(dppe)Cp* (Ru-2-Ph; 99 mg,
87%) as a bright yellow powder. Anal. Calcd for C46H44P2Ru: C,
72.71; H, 5.84. Found: C, 72.59; H, 6.00. IR (CH2Cl2): ν(CC)
EXPERIMENTAL SECTION
■
General Procedures. Manipulations of air-sensitive compounds
were performed under an argon atmosphere using standard Schlenk
techniques or in an argon-filled Jacomex 532 drybox. Tetrahydrofuran
(THF), diethyl ether, toluene, and pentane were dried and
deoxygenated by distillation from sodium/benzophenone ketyl.
Acetone was distilled from P2O5. Dichloromethane and dichloroethane
were distilled under argon from P2O5 and then from Na2CO3.
Methanol was distilled from dried magnesium turnings. The following
compounds were prepared following published procedures: ferroce-
nium hexafluorophosphate (Fe(η5-C5H5)2(PF6)),16 FeCl(dppe)Cp*,2
and RuCl(dppe)Cp*.3 The complexes Fe-2-SiMe3,6 Ru-2-SiMe3,5 Ru-
2-Au(PPh3),5 Ru-3-SiMe3,10 and Ru-3-Au(PPh3)10 were prepared
following the cited procedures. Potassium tert-butoxide (ACROS) was
used without further purification. Infrared spectra were obtained in
KBr disks with a Bruker IFS28 FTIR infrared spectrophotometer
(4000−400 cm−1). UV−visible spectra were recorded on a Varian
CARY 5000 spectrometer. 1H, 13C, and 31P NMR spectra were
recorded on Bruker DPX200, Avance 300, and Avance 500 NMR
multinuclear spectrometers at ambient temperature, unless otherwise
noted. Chemical shifts are reported in ppm (δ) relative to
tetramethylsilane (TMS), using the residual solvent resonances as
internal references. Coupling constants (J) are reported in hertz (Hz),
and integrations are reported as numbers of protons. The following
abbreviations are used to describe peak patterns: br = broad, s =
singlet, d = doublet, dd = doublet of doublets, t = triplet, q = quartet,
1
2153, 2016 cm−1. H NMR (C6D6, 600 MHz): δ 1.59 (s, 15H, Cp*),
1.84, 2.60 (2 × m, 4H, PCH2), 6.87−7.89 (m, 25H, Ph). 13C NMR
(C6D6, 150 MHz, ppm): δ 9.88 (s, C5Me5), 29.23−29.54 (m, dppe),
62.98, 82.34, 92.19 (s, CC), 93.10 (s, C5Me5), 125.47−138.55 (m,
Ph and Cα). 31P NMR (C6D6, 121 MHz): δ 80.3 (s). ES-MS (m/z):
calcd for C46H45P2Ru 761.2040, found 761.2065 [M + H]+.
Synthesis of Fe{CCCCAu(PPh3)}(dppe)Cp* (Fe-2-Au-
(PPh3)). To a suspension of Fe(CCCCSiMe3)(dppe)Cp* (7)
(400 mg, 0.56 mmol) in THF (10 mL) was added a solution of
NaOMe (from Na (65 mg, 2.81 mmol) in methanol (10 mL)). After
the mixture was stirred for 20 min at room temperature, AuCl(PPh3)
(278 mg, 0.56 mmol) was added, upon which the solution turned dark
red. After 4 h, the orange precipitate was filtered off and washed with
cold MeOH (3 × 10 mL) to afford Fe{CCCCAu(PPh3)}-
(dppe)Cp* as an orange powder ([Fe-2-Au(PPh3)]; 452 mg, 74%).
Anal. Calcd for C58H54AuFeP3: C, 63.52; H, 4.96. Found: C, 63.10; H,
1
5.23. IR (CH2Cl2): ν(CC) 2069, 1969 cm−1. H NMR (C6D6, 300
MHz): δ 1.53 (s, 15H, Cp*), 1.83, 2.73 (2 × m, 4H, PCH2), 6.88−
8.19 (m, 35H, Ph). 13C NMR (C6D6, 150 MHz, ppm): δ 10.45 (s,
C5Me5), 30.22−31.39 (m, dppe), 88.25 (s, C5Me5), 88.84 (s), 94.18
2
(s), 104.06 (s), 123.26 [t, JCP = 40 Hz, CCCCAu(PPh3)],
1
m = multiplet. H and 13C NMR peak assignments are supported by
126.30−140.40 (m, Ph). 31P NMR (C6D6, 121 MHz): δ 100.0 (s,
dppe), 42.0 (s, PPh3). ES-MS (m/z): calcd for C58H54AuFeP3
1096.2453, found 1096.2525 [M]+.
the use of COSY, HMQC, and HMBC experiments. High-resolution
mass spectra (HRMS) were recorded with a high-resolution ZabSpec
TOF VG analytical spectrometer operating in the ESI+ mode, at the
Synthesis of Fe(CCCCCCSiMe3)(dppe)Cp* (Fe-3-
SiMe3). To a stirred solution of Fe{CCCCAu(PPh3)}(dppe)Cp*
(Fe-2-Au(PPh3); 250 mg, 0.23 mmol) in a 1/1 mixture of THF and
triethylamine (24 mL) was added ICCSiMe3 (128 mg, 0.57 mmol)
followed immediately by Pd(PPh3)4 (26 mg, 0.023 mmol) and CuI (8
mg, 0.041 mmol). The solution was stirred in the dark at room
temperature overnight before solvent was removed under reduced
pressure. The residue was extracted with triethylamine and directly
loaded onto a basic alumina column which was eluted with
triethylamine/hexane (1/1); the orange band was collected to afford
Fe(CCCCCCSiMe3)(dppe)Cp* (Fe-3-SiMe3; 93 mg, 55%)
as an orange powder. Anal. Calcd for C45H48FeP2Si: C, 73.56; H, 6.58.
Found: C, 73.80; H, 7.47. IR (CH2Cl2): ν(CC) 2092, 1952 cm−1.
́
Centre Regional de Mesures Physiques de l’Ouest (CRMPO), Rennes,
France, or with a Bruker MicroTOF spectrometer at the University of
Waikato, Waikato, New Zealand. Poly(ethylene glycol) (PEG) was
used as an internal reference, and dichloromethane was used as
solvent. All mass measurements refer to peaks for the most abundant
isotopic combination (1H, 12C, 31P, 56Fe, 102Ru). EPR spectra were
recorded on a Bruker EMX-8/2.7 (X-band) spectrometer. Elemental
analyses of the iron compounds were conducted on a Thermo-
FINNIGAN Flash EA 1112 CHNS/O analyzer by the Microanalytical
Service of the CRMPO at the University of Rennes 1, Rennes, France,
and those of the ruthenium complexes at Campbell Microanalytical
Laboratory, Dunedin, New Zealand.
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Table 10. Crystal Data and Refinement Details for Fe-2-Ph, Ru-2-Ph, Fe-2-Au(PPh3), Fe-3-SiMe3, Ru-3-SiMe3, and Ru-3-
Au(PPh3)
Fe-2-Ph
Ru-2-Ph
Fe-2-Au(PPh3)
Fe-3-SiMe3
Ru-3-SiMe3
Ru-3-Au(PPh3)
formula
mol wt
T (K)
C46H44FeP2
714.60
C46H44P2Ru
759.82
C58H54AuFeP3.3CH2Cl2 C45H48FeP2Si
C45H48RuP2Si.0.25C6H14 C60H54AuP3Ru
1349.82
100(2)
triclinic
734.71
801.48
1165.98
150(2)
triclinic
100(2)
110(2)
100(2)
150(2)
cryst syst
space group
a (Å)
monoclinic
P21/c
monoclinic
P21/c
monoclinic
C2/c
monoclinic
C2/c
P1
P1
̅
̅
10.6050(3)
35.2980(11)
10.3375(4)
10.6501(4)
35.7310(13)
10.2532(3)
12.6624(5)
14.5461(6)
16.4850(7)
93.418(4)
102.305(4)
99.647(4)
2910.3(2)
2
47.893(3)
17.882(2)
20.3130(10)
90.00
48.476(14)
18.052(6)
20.193(6)
90.00
10.523(1)
11.313(1)
23.935(3)
96.928(3)
97.902(3)
110.162(3)
2605.8(5)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
107.578(1)
107.285(3)
102.660(10)
90.00
102.174(5)
90.00
3689.0(2)
4
3725.5(2)
4
16974(2)
16
17273(9)
16
ρcalcd (g cm−3
)
1.287
1.355
1.540
1.150
1.233
1.486
cryst size (mm)
0.36 × 0.27 ×
0.24
0.51 × 0.17 × 0.04 0.33 × 0.24 × 0.15
0.55 × 0.04 × 0.03 0.35 × 0.07 × 0.05
0.26 × 0.14 × 0.13
F(000)
1504
1576
1354
6208
6696
1164
radiation
Mo Kα
Mo Kα
Mo Kα
Cu Kα
Mo Kα
Mo Kα
abs coeff (mm−1
θ range (deg)
hkl range
)
0.528
0.538
3.16
4.04
0.494
3.23
3.46−27.47
−13 to +13
−45 to +45
−13 to +6
54 427
2.63−32.63
−15 to +16
−53 to +53
−15 to +15
58 066
3.56−30.00
−17 to +17
−20 to +20
−15 to +23
35 043
3.32−67.18
−56 to +55
−20 to +20
−23 to +15
43 988
1.21−27.59
−63 to 61
−23 to 23
−26 to 26
68 019
1.75−31.00
−15 to +15
−16 to +16
−34 to +34
30 112
Ntot
N (Rint)
No
8379 (0.032)
7641
13 019 (0.048)
9594
16 932 (0.051)
11 588
14 952 (0.129)
7101
19 746 (0.072)
13 480
15 458 (0.035)
11 359
no. of restraints/params 0/447
0/447
0/678
114/960
0.062
16/925
0/591
R1 (I > 2σ(I))
wR2 (all data)
goodness of fit/F2
0.029
0.074
1.036
0.037
0.047
0.060
0.047
0.081
0.105
0.174
0.157
0.124
0.94
0.977
0.945
1.019
1.107
largest diff peak, hole (e 0.421, −0.334
1.327, −0.384
3.499, −2.764
0.763, −0.792
1.501, −0.74
2.65, −0.654
Å−3
)
1H NMR (C6D6, 300 MHz): δ 0.13 (s, 9H, SiMe3), 1.37 (s, 15H,
Cp*), 1.69, 2.42 (2 × m, 4H, PCH2), 6.98−7.85 (m, 20H, Ph). 13C
NMR (C6D6, 150 MHz, ppm): δ 0.35 (s, SiMe3), 10.12 (s, C5Me5),
30.23−31.08 (m, dppe), 47.06, 69.29, 77.18, 94.34, 100.95 (s, CC),
was used for the geometry optimizations of [Fe-n-R]0/+ and [Ru-n-
R]0/+, with n = 1−3 and R = H, Ph and with n = 2 and R = SiMe3.
Explicitly, this basis set is a triple-ξ STO basis set for the valence shells
augmented with a 2p polarization function for H, a 3d polarization
function for C, P, and Si, a 4p polarization function for Fe, and a 5p
polarization function for Ru, respectively. Orbitals up to 1s, 2p, 3p, and
4p were kept frozen for C, P, Si, Fe, and Ru, respectively. For [Fe-2-
Au(PPh3)]0/+ and [Ru-2-Au(PPh3)]0/+, a relativistic zeroth-order
regular approximation (ZORA) was applied using the ZORA/TZP
adapted basis set (frozen core: Au 1s−4f).42 The geometries were fully
optimized without constraints (C1 symmetry), and convergence
criteria used were more drastic than default criteria (energy change
<0.0005 hartree, atomic position displacement <0.005 Å). The
bonding energies and Cartesian coordinates of each structure are
given in Table S12 (Supporting Information). In order to evaluate the
effect of rotation of the phenyl end groups in the [Fe-n-Ph]+ and [Ru-
n-Ph]+ series (n = 1, 2), a sequence of constrained-geometry
optimizations were carried out. The dihedral θ (θ = Cp* centroid−
M−Cipso−Cortho) cannot be fixed directly, since one of the geometrical
points which defines it is the centroid of five atoms. A combination of
dihedral angles between atoms (P(dppe), M, C(Ph)) was used to
obtain θ values that can diverge from 1° from the expected value.
Computed EPR properties given in Table 8 and Tables S4−S6 and 11
(Supporting Information) were performed using the ESR procedure
developed by van Lenthe and co-workers.27a,43 The g-tensor
components were obtained from self-consistent spin-restricted DFT
calculations after incorporating the relativistic spin−orbit coupling by
first-order perturbation theory from a ZORA Hamiltonian. Calcu-
lations did not take spin-polarization effects into account. For these
calculations, the nonlocal correction of Adamo−Barone and of
2
89.31 (s, C5Me5), 127.53−138.60 (m, Ph), 151.07 (t, JPC = 38 Hz,
Cα). 31P NMR (C6D6, 121 MHz): δ 97.9 (s). ES-MS (m/z): calcd for
C45H48FeP2Si 734.2350, found 734.2388 [M]+.
X-ray Crystallography. Single crystals suitable for X-ray structure
determination were obtained as follows: (i) Fe-2-Ph, slow diffusion of
pentane in a toluene solution of the complex; (ii) Ru-2-Ph, slow
diffusion of hexane into dichloromethane solution of the complex; (iii)
Fe-2-Au(PPh3) and Ru-3-Au(PPh3), slow evaporation of a dichloro-
methane solution of the complex; (iv) Fe-3-SiMe3 and Ru-3-SiMe3,
slow diffusion of hexane into triethylamine solutions of the complexes.
Crystal data and data collection and refinement parameters are given
in Table 10. Full spheres of diffraction data were measured using CCD
area-detector instrumentation equipped with monochromatic Mo or
Cu Kα radiation (λ = 0.710 73 or 1.54178 Å). Anisotropic
displacement parameter forms were refined for the non-hydrogen
atoms. All H atoms were added at calculated positions and refined by
use of a riding model with isotropic displacement parameters based on
those of the parent atom. Neutral atom complex scattering factors
were used; computation used the SHELXL 97 program.37
Computational Details. Calculations were performed with the
ADF2010.02 package.38 Electron correlation was treated within the
local density approximation (LDA) in the Vosko−Wilk−Nusair
parametrization.39 The nonlocal corrections (GGA) of Becke and
Perdew were added to the exchange and correlation energies,
respectively.40 The analytical gradient method implemented by
Versluis and Ziegler was used.41 The standard ADF TZP basis set
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Organometallics
Article
Perdew−Burke−Ernzerhof (mPBE) were added to the exchange and
correlation energies, respectively,44 and the basis set was expanded for
Fe and Ru, where orbitals up to 2p and 3d were kept frozen,
respectively. Deviations (Λg) of the computed g-tensor components
from the free electron value ge, shown in Figure 7, were computed
using the EPR module developed by Ziegler and co-workers.32 Scalar
relativistic effects were included employing relativistic frozen core
potentials in conjunction with the first-order Pauli Hamiltonian.45
Evaluation of the g-tensors was obtained with spin-unrestricted
calculations using the gradient-corrected BP86 functional,40 and the
basis set was expanded for Fe and Ru, where orbitals up to 2p and 3d
were kept frozen, respectively.
ΔEθ is the energetic difference between the most stable
conformation and a conformer θ. The ΔEsolv(θ) term, used in eq 1,
reports the energetic stabilization due to the solvent. To address
solvation effects, the conductor-like screening model (COSMO)46 was
used with a dielectric constant simulating dichloromethane solvent.
The geometries were not relaxed because of the prohibitive
computational cost. To evaluate the degree of this approximation,
we have performed full COSMO geometry optimizations of the two
conformers of [Fe-1-Ph]+ with θ equal to 75 and 180°. The difference
in energy between the two compounds is 0.096 eV when 0.138 eV is
calculated between the two conformers relaxed under vacuum. The
difference of solvation calculated by COSMO is thus 0.043, and it was
estimated to be 0.068 eV on the basis of nonrelaxed structures. The
geometries are slightly different with optimized angles θ of 74.3 and
178.1° in comparison to 74.2 and 178.7° under vacuum. The Δg
values are thus also slightly modified with 0.695 instead of 0.683 for θ
≈ 75° and 0.298 instead of 0.266 for θ ≈ 180°. Overall, these changes
will marginally affect our results, since they will most probably be on
the same order of magnitude for all of the rotamers.
ACKNOWLEDGMENTS
■
The MNERT (Ph.D. grants to A.B. and F.G.) and UEB (travel
grant to A.B.) are acknowledged for financial support. We thank
the Centre National de la Recherche Scientifique and the
́
Australian Research Council for support of this work. Frederic
Justaud is warmly acknowledged for EPR assistance. We thank
Johnson Matthey plc, Reading, U.K., for a generous loan of
RuCl3·nH2O. This work was performed using HPC resources
from GENCI-CINES and GENCI-IDRIS (Grant 2011-80649).
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ASSOCIATED CONTENT
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́
(12) Paul, F.; Toupet, L.; Thepot, J.-Y.; Costuas, K.; Halet, J.-F.;
S
* Supporting Information
Lapinte, C. Organometallics 2005, 24, 5464−5478.
CIF files, figures, and tables giving all crystallographic data and
selected bond distances and bond angles for Fe-2-Ph, Ru-2-Ph,
Fe-2-Au(PPh3), Fe-3-SiMe3, Ru-3-SiMe3, and Ru-3-Au-
(PPh3), selected X-ray structural parameters, energies and
Mulliken decomposition of Ru-2-R MOs, calculated EPR data,
atomic spin densities, and dipole moments for [Ru-n-Ph]+ and
[Fe-n-Ph]+ (n = 1, 2), DFT MO diagrams of Fe-n-H (n = 1−3)
and Ru-2-R, bond dissociation energy decomposition of C4-R
for [M-2-R]+, and Cartesian coordinates of all calculated
geometries. This material is available free of charge via the
Internet at http://pubs.acs.org. Full details of the structure
determinations have also been deposited with the Cambridge
Crystallographic Data Centre as CCDC 887627, 804391,
885401, 881307, 885402, and 830957. Copies of this
information may be obtained free of charge from The Director,
CCDC, 12 Union Street, Cambridge CB2 1EZ, U.K. (fax, +44-
1223-336-033; e-mail, deposit@ccdc.cam.ac.uk; web, http://
www.ccdc.cam.ac.uk).
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: claude.lapinte@univ-rennes1.fr (C.L.); kcostuas@
univ-rennes1.fr (K.C.).
Present Address
∥CMCA, University of Western Australia, Crawley, Western
Australia 6009, Australia.
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Notes
The authors declare no competing financial interest.
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