Ruthenium complexes with vinyl, styryl, and vinylpyrenyl ligands: A case of non-innocence in organometallic chemistry

Article abstract of DOI:10.1021/ja075547t

We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-CH=CH-R where the phosphine ligands at the (PR′ ₃)₂Ru(CO)Cl={Ru} moiety, the coordination number at the metal (L = 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R = ⁿbutyl, phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh₃)₂(η ¹:η²-ⁿBuHC=CHC≡CⁿBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule of 1-hexyne, of the hexenyl complexes (ⁿBuCH=CH)Ru(CO) Cl(PⁱPr₃)₂ (1c) and (ⁿBUCH=CH)RU(CO) Cl(PPh₃)₂(NC₅H₄COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CH=CH)Ru(CO)Cl(PⁱPr₃) ₂ (3c) and (1-Pyr-CH=CH)Ru(CO)Cl(PPh₃)₃ (3a-P) have been established by X-ray crystallography. All vinyl complexes undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as π-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are significantly smaller than is expected of a metal-centered oxidation process and are further diminished as the vinyl CH=CH entity is incorporated into a more extended π-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the average g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation processes. This renders them a class of truly non-innocent ligands in organometallic ruthenium chemistry. Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes from ⁿbutyl to 1-pyrenyl.

Full text of DOI:10.1021/ja075547t

Published on Web 12/12/2007
Ruthenium Complexes with Vinyl, Styryl, and Vinylpyrenyl
Ligands: A Case of Non-innocence in Organometallic
Chemistry
Jo¨rg Maurer,†,‡ Michael Linseis,† Biprajit Sarkar,‡ Brigitte Schwederski,‡
Mark Niemeyer,‡ Wolfgang Kaim,‡ Stanislav Za´lisˇ,*,§ Chris Anson,
Manfred Zabel,† and Rainer F. Winter*,†
Contribution from the Institut fu¨r Anorganische Chemie der UniVersita¨t Regensburg,
D-93040 Regensburg, Germany, Institut fu¨r Anorganische Chemie der UniVersita¨t Stuttgart,
D-70563 Stuttgart, Germany, J. HeyroVsky´ Institute of Physical Chemistry V.V.i., Academy of
Sciences of the Czech Republic, Czech Republic, Institut fu¨r Anorganische Chemie der
UniVersita¨t Karlsruhe, D-76131 Karlsruhe, Germany
Received August 8, 2007; E-mail: rainer.winter@chemie.uni-regensburg.de; stanislav.zalis@jh-inst.cas.cz
Abstract: We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-
CHdCH-R where the phosphine ligands at the (PR′3)2Ru(CO)Cld{Ru} moiety, the coordination number
at the metal (L ) 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R ) nbutyl,
phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh3)2(η1:η2-nBuHCd
CHCtCnBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule
of 1-hexyne, of the hexenyl complexes (nBuCHdCH)Ru(CO)Cl(PiPr3)2 (1c) and (nBuCHdCH)Ru(CO)Cl-
(PPh3)2(NC5H4COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CHdCH)Ru(CO)Cl(PiPr3)2 (3c) and
(1-Pyr-CHdCH)Ru(CO)Cl(PPh3)3 (3a-P) have been established by X-ray crystallography. All vinyl complexes
undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials.
Anodic half-wave or peak potentials show a progressive shift to lower values as π-conjugation within the
vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are
significantly smaller than is expected of a metal-centered oxidation process and are further diminished as
the vinyl CHdCH entity is incorporated into a more extended π-system. ESR spectra of the electrogenerated
radical cations display negligible g-value anisotropies and small deviations of the average g-value from
that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation
processes. This renders them a class of truly “non-innocent” ligands in organometallic ruthenium chemistry.
Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl
ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes
n
from butyl to 1-pyrenyl.
Introduction
unusual (formal) oxidation states at the metal as, for example,
in compound I of cytochrome P-450.6 If, on the other hand, the
Redox active ligands that actively participate in electron-
transfer processes, in conjunction with appropriate redox active
transition metal entities, render an assignment of redox states
ambiguous.1 Such behavior has been denoted as “non-in-
nocent”.2 When the energy barrier for intramolecular electron
transfer is low, charge and unpaired spin are delocalized over
the metal ion and the “non-innocent” ligand(s). This may either
result in metal stabilized radicals3-5 or in the stabilization of
energy barrier of intramolecular electron transfer is sufficiently
high, “non-innocent” behavior gives rise to the phenomenon of
valence tautomerism.7-10 The charge distribution within valence
tautomers can be controlled by exterior physical stimuli such
as pressure, light, or applied magnetic field.11,12 Such behavior
sets the ground for the development of molecule based,
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331-442.
† Universita¨t Regensburg.
‡ Universita¨t Stuttgart.
§ J. Heyrovsky´ Institute.
Universita¨t Karlsruhe.
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9
10.1021/ja075547t CCC: $40.75 © 2008 American Chemical Society
J. AM. CHEM. SOC. 2008, 130, 259-268
259

A R T I C L E S
Maurer et al.
Chart 1. The Complexes Employed in This Study
switchable materials with possible applications, inter alia, for
data storage.
Set against this background there is a continued need to
prepare and identify redox-active, potentially non-innocent
ligands and to study their interaction with various transition-
metal moieties. Important sets of redox-active ligands are based
on tetracyanoethene (TCNE), 7,7,8,8-tetracyano-p-quinodimethane
(TCNQ),13 or dithiolenes,14,15 dioxolenes,9,16 diimines,15 and
ligands with mixed donor atoms. While most of the work in
this area has concentrated on inorganic coordination compounds,
ligands like TCNE and TCNQ may equally well coordinate
organometallic entities.17-22 Potentially redox-active ligands that
form metal-carbon bonds for use in organometallic chemistry
are, however, much less well precedented. Examples are
paramagnetic alkene complexes of rhodium and iridium,4 and
manganese complexes containing π-coordinated quinones (or
semiquinonates or catecholates, respectively).23-25 While indi-
vidual building blocks are organometallic in nature, the quinone
complexes still rely on the traditional metal-dioxolene chelate
linkage for their interesting electronic properties. The radical
derived from a triphenylmethyl substituted vinylferrocene
constitutes a rare example of a genuine organometallic valence
tautomeric system with a temperature-dependent equilibrium
Thus, butadienediyl-bridged diruthenium complexes constitute
completely delocalized organometallic π-chromophores that defy
any assignment of the redox processes as metal or ligand
based.29 To further develop this chemistry toward true organo-
metallic valence tautomers and to extended chainlike arrays with
high electron mobility along the main chain, it is mandatory to
understand and to quantify the principal factors that govern the
electron distribution within the ruthenium vinyl entities. Di-
nuclear systems present the added complexity of possible
metal-metal interactions across the bridging ligands. We
therefore turned to the mononuclear complexes shown in Chart
1. These were designed such as to allow us to study how (i)
extending the π-system of the vinyl ligand, (ii) manipulating
the electron density at the metal atom, and (iii) varying the
degree of coordinative saturation at the metal atom affect the
bonding, the anodic behavior, and metal versus ligand contribu-
tion to the redox-orbitals.
betweenFc-CHdCH-CPh3 andFc+-CHdCH-CPh3--states.26
•
We have recently investigated the anodic electrochemistry
of divinylphenylene-bridged diruthenium complexes {(PR3)2-
(CO)Cl(L′)Ru}2{µ-C6H4(CHdCH)2-1,3 or -1,4) (R ) Ph, L′
i
) 4-substituted pyridine; R ) Pr, L′ ) none)27,28 and studied
their radical cations and dications by UV-vis-NIR, IR, and
ESR spectroscopy. These studies indicated bridge-dominated
oxidation processes although the oxidation potentials of ruthe-
nium complexes are intrinsically lower than those of comparable
donor substituted phenylene vinylenes. The metal Versus vinyl
ligand contribution to the frontier molecular orbitals (FMOs)
depends on the energy gap between the appropriate metal d
levels and the π orbitals of the vinyl ligand. Raising the energy
of the ruthenium d manifold or decreasing the energy of the
ligand π orbitals enhances the metal character of the FMOs.
Results and Discussion
Syntheses and Characterization of the Vinyl Complexes.
Ruthenium vinyl complexes (RCHdCH)Ru(CO)Cl(PR3)2 are
easily prepared from hydride complexes HRu(CO)Cl(PR3)n (PR3
) PPh3, n ) 3; PR3 ) PiPr3, PCy3, n ) 2) via hydroruthenation
of terminal alkynes. Metal hydride insertion into the CtC bond
occurs in a regio- and stereospecific manner and results in the
anti-Markovnikov product where the metal atom is connected
to the terminal carbon atom and the remaining substituent is in
a trans position at the vinyl group. Depending on the reaction
conditions HRu(CO)Cl(PPh3)3 either gives coordinatively satu-
rated six-coordinated tris(phosphine) derivatives or coordina-
tively unsaturated five-coordinated square pyramidal bis-
(phosphine) complexes with a vacant coordination site trans to
the apical vinyl ligand.30-32 Irrespective of five- or six-
(13) Miller, J. S. Inorg. Chem. 2000, 39, 4392-4408.
(14) Kirk, M. L.; McNaughton, R. L.; Helton, M. E. Electronic and Spectroscopic
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111-212.
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2005, 9, 738-749.
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2004, 1900-1901.
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9
260 J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008

Ru Complexes with Vinyl, Styryl, and Vinylpyrenyl
A R T I C L E S
coordination, PPh3 substituted vinyl complexes readily react with
sterically less demanding two electron ligands such as CO,
isonitriles, amines, or pyridines to give octahedral 18 valence
electron complexes with the newly introduced donor opposite
to the vinyl ligand. The 16 valence electron complexes (RCHd
CH)Ru(CO)Cl(PiPr3)2, on the other hand, are less prone to
addition of a pyridine ligand but may still add CO, isonitriles,
or, under simultaneous chloride substitution, a bidentate monoan-
ionic ligand such as acetate.33,34
The reaction of HRu(CO)Cl(PPh3)3 with 1-hexyne gave an
equilibrium mixture of the five- and six-coordinated bis- and
tris(phosphine) hexenyl complexes. Variable temperature NMR
spectroscopy in CD2Cl2 indicates that the equilibrium lies
completely on the side of the red 16 valence electron complex
and free phosphine at room temperature, while only six-
coordinated (nBuCHdCH)(PPh3)3(CO)ClRu is present at or
below 203 K or in the solid. Similar findings were just reported
for the styryl complex 2a.32
Figure 1. ORTEP representation of complex 3c‚CHCl3 at a 50%
probability level.
doublets for the vinyl protons. The signal of the vinyl proton at
the metal-bonded carbon atom CR resonates at lower field with
δ values ranging from 9.26 to 6.90 ppm. It is less sensitive to
the ligand environment than the one at the neighboring carbon
atom Câ where the shift ranges from 8.79 to 4.76 ppm. The
vinyl carbon atoms resonate at 156.4-138.4 ppm (CR) and
139.6-130.7 ppm (Câ), respectively. Addition of the substituted
pyridine ligand to complexes 1a, 2a, and 3a shifts the resonance
signals of the vinylic protons and those of the RuCHdCH and
the RuCH)CH carbon atom to lower field and that of the 31P
resonance to higher field. In their IR spectra the vinyl complexes
show an intense band of the CO stretch. The position of this
band is more sensitive to the number and nature of the phosphine
ligands than to that of the vinyl substituent. Thus, in every series
1a-c, 2a-c, and 3a-c the CO band shifts follow the sequence
1a, 2a, 3a > 1b, 2b, 3b > 1c, 2c, 3c such that the
five-coordinated PiPr3 substituted complexes feature the most
electron-rich metal centers.
X-ray Structures of 1b, 1c, 3c‚CHCl3, 3a-P‚2CH2Cl2, and
of Ru(CO)Cl(PPh3)2(η1:η2-nBuHCdCHCtCnBu). Crystals
of the five-coordinated vinyl complex 1c were grown from
methanol, while 3c crystallizes from chloroform as a monosol-
vate. Figure 1 provides a plot of the complex molecule of 3c‚
CHCl3 along with the atomic numbering scheme. A similar plot
of 1c is given as Figure S2 of the Supporting Information. In
each of the two structures the ruthenium atom adopts the
distorted square pyramidal coordination with the strongly trans
influencing vinyl ligand in the apical position that is familiar
of M(CO)Cl(PR3)2X (X ) H, vinyl, alkyl, aryl) complexes.33,39-42
Distortions arise from a compression of the P-Ru-P angle
toward the vacant coordination site to 168.63(4)° (1c) or 173.72-
(1)° (3c) and a slight displacement of the metal atom by 0.152-
(1) Å (3c) or 0.198 (1) Å (1c) out of the best plane defined by
the four donor atoms at the pyramid base. The vinyl ligand
resides in the plane defined by the Ru, Cl, and C(1) atoms as
it is shown by the torsional angles Cl(1)-Ru-C(2)-C(3) of
-177.5(5) or 177.7(1)° for 1c or 3c, respectively. The angles
Ru-C2-C3-C4 of 176.2(5) (1c) and Ru-C2-C3-C31 of
178.6(1)° (3c) signal hardly any twisting of the vinyl double
bond.
When this equilibrium mixture was reacted with isonicotinate,
a mixture of the desired complex 1b, unreacted 1a, and the
disubstitution product [(PPh3)2(CO)(NC5H4COOEt)2(nBuCHd
CH)Ru]+ Cl- was formed from which no pure compound could
be isolated. Complex 1b was finally prepared from HRu(CO)-
Cl(PPh3)2(NC5H4COOEt). Like in the case of HRu(PiPr2Ph)2-
(CO)Cl(py)35 this latter hydride was obtained as a 78:22 mixture
of two mutually interconverting isomers that differ with respect
to the arrangement of the four different ligands in the equatorial
plane. According to 1H ROESY the major isomer has the
isonicotinate cis to the hydride. For the major isomer slow
rotation of the substituted pyridine at room temperature is
evident from the four different pyridine resonance signals.
Cooling to 193 K is required for the minor isomer where the
isonicotinate ligand is trans to the hydride in order to freeze
pyridine rotation (Tc ≈ 208 K). This large difference in rotational
barriers may arise from hydrogen bonding between the ortho
proton of the pyridine and the hydride ligand. The inequivalence
of the 2,6- and 3,5-hydrogen atoms in both isomers points to
static structures where the pyridine planes avoid eclipsing the
PRuP axis. Similar observations have been made for pyridine
adducts of HRu(CO)X(PtBu2Me)2 (X ) monoanionic ligand)
where the pyridine ligand is in a trans position to the hydride.36,37
Treating this isomeric mixture with 1-hexyne results in the
exclusive formation of 1b. Under gentle warming HRu(CO)-
Cl(PPh3)3 reacted with excess 1-hexyne to give the dodec-5-
en-7-ynyl complex Ru(CO)Cl(PPh3)2(η1:η2-nBuHCdCH-Ct
CnBu), which was studied by X-ray crystallography (vide infra).
Closely related butenynyl complexes have already been re-
ported.38
All complexes of this study (Chart 1) were investigated and
characterized by the usual spectroscopic and analytical methods
including multinuclear NMR, IR, and electronic spectroscopy.
1
Characteristic features in their H NMR spectra are the two
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Chem. Soc., Chem. Commun. 1995, 369-370.
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9
J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008 261

A R T I C L E S
Maurer et al.
Figure 2. ORTEP representation of one of the two independent molecules
of 3a-P at a 50% probability level.
The pyrenyl part of 3c, while strictly planar, is rotated out of
the Ru-C2-C3 plane by about 25° such that the vinylpyrenyl
plane intersects the P-Ru-P axis at an angle of about 67°.
The Ru-C2, C2-C3, and C3-C31 bonds of 1.9866(18), 1.350-
(2), and of 1.473(2) Å are typical of a Ru-C(sp2) single bond,
a CdC double bond and a C(sp2)-C(sp2) single bond, respec-
tively. Similar bond lengths for Ru-C2 (1.984(5)) and C2-
C3 (1.346(9)) are found for 1c and related five-coordinated vinyl
complexes.33,39-42 Structural features of the vinylpyrenyl part
of 3c show essentially the same bond-length pattern as that
observed in styryl43 or alkynyl substituted pyrenes.44,45 The
chloroform solvate molecule forms an almost linear CH‚‚‚Cl-
Ru array with a H‚‚‚Cl distance of 2.56 Å, a C‚‚‚Cl distance of
3.551 Å, and a CH‚‚‚Cl angle of 169°.
All attempts to crystallize the PPh3 substituted counterpart
3a only led to the formation of few small crystals of a distinctly
lighter, yellow color as that of the bulk sample. These were
subjected to X-ray analysis and turned out as the PPh3 adduct
3a-P. The structure of 3a-P, as depicted in Figure 2 (only one
of two independent molecules is shown), bears clear witness to
the distortion of the coordination sphere around ruthenium
induced by the strong trans influence of the vinyl ligand and
the steric hindrance of three meridionally displaced PPh3 ligands.
Thus, the distances between the ruthenium atom and the
mutually trans disposed P atoms P1, P2 (molecule A) or P4,
P5 (molecule B) of 2.4221(13) and 2.4024(13) Å or 2.4397-
(13) and 2.4446(13) Å are distinctly smaller than those of
2.5850(13) or 2.5638(14) Å involving the PPh3 ligand trans to
the pyrenylvinyl group. Steric congestion at the metal center is
also evident from the strongly compressed P1-Ru-P2 (P4-
Ru-P5) angle of 161.74(4)° (163.83(5))° and from the bending
of the phosphines toward the pyrenylvinyl ligand as opposed
to the five-coordinated complexes 1c and 3c. This distortion
surpasses that observed in similar vinyl complexes bearing PEt3
or PMe3 coligands46-49 and also that observed in the closely
Figure 3. ORTEP representation of complex 1b at a 50% probability level.
related osmium complex (PPh3)3(CO)ClOs(CHdCHPh)47 but
resembles that in the recently reported divinyl phenylene bridged
diruthenium complex {(PPh3)3(CO)ClRu}2(µ-CHdCH-C6H4-
CHdCH-1,4).32 The long Ru1-P3 (Ru2-P6) bond also pro-
vides a good rationale for the facile loss and selective
replacement of the phosphine ligand trans to the vinyl group.
The pyrenylvinyl ligand is nearly coplanar with the Cl1-
Ru-C1 axis and forms a torsional angle of 178.15(4)° (Cl1-
Ru1-C2-C3) or -165.95(5)° (Cl101-Ru2-C102-C103).
Again, the organic π-system and the ruthenium atoms are in
direct conjugation as it is inferred from the torsional angles
Ru1-C2-C3-C4 (-178.7(4)°) and Ru2-C102-C103-C104
(175.6(3)°). In contrast to 3c the pyrenyl entities display some
twist around the central C-C bonds. Thus, the vinyl-substituted
and the opposing, outermost six-membered rings of the con-
densed π perimeter form angles of 5.9(2)° or 3.9(3)°.
Complex 1b, the other crystallographically characterized six-
coordinated derivative of this study, features a much less
distorted coordination environment. A view of the molecular
structure of this complex is provided as Figure 3. Angles
between trans ligands span a range of 176.46(3)° to 179.46(8)°
while cis angles range from 86.40(6)° to 93.45(1)°. The acute
angle N1-Ru-Cl1 of 86.40(6)° is enforced by a hydrogen bond
between an isonicotinate ortho CH proton and the adjacent
chloride ligand with a C12‚‚‚Cl1 distance of 3.153(3) Å. Such
an interaction may contribute to the rotational barrier of the
two isomers of HRu(CO)Cl(PPh3)2(isonicotinate) (vide supra).
Further C‚‚‚Cl contacts of 3.301(3) and 3.347(4) Å are observed
to one ortho CH of a phenyl ring on each PPh3 ligand. While
longer, these contacts are still well below the sum of the Van
der Waals radii (3.45 Å).50 The substituted pyridine ligand is
rotated by about 21° out of the plane of the equatorial donors
but resides in the same plane as the vinylic double bond.
The structure of the dodecenynyl complex Ru(CO)Cl(PPh3)2-
(η1:η2-nBuHCdCHCtCnBu) in its crystalline state is shown
as Figure S3 of the Supporting Information. σ,π-Coordination
of the enynyl ligand leads to a rather long Ru-C(vinyl) σ-bond
of 2.081(4) Å as compared to those in vinyl complexes like 1c,
3c, and 3a-P of ca. 1.98 Å. The Ru-C bonds of 2.300(3) and
2.558(4) Å observed for the η2-coordinated alkyne part of that
(43) Natarajan, A.; Mague, J. T.; Venkatesan, K.; Arai, T.; Ramamurthy, V. J.
Org. Chem. 2006, 71, 1055-1059.
(44) Ziessel, R.; Goze, C.; Ulrich, G.; Ce´sario, M.; Retailleau, P.; Harriman,
A.; Rostron, J. P. Chem. Eur. J. 2005, 11, 7366-7378.
(45) Pohl, R.; Anzenbacher, Jr., P. Org. Lett. 2003, 5, 2769-2772.
(46) Xia, H. P.; Yeung, R. C. Y.; Jia, G. Organometallics 1998, 17, 4762-
4768.
(47) Xia, H.; Wen, T. B.; Hu, Q. Y.; Wang, X.; Chen, X.; Shek, L. Y.; Williams,
I. D.; Wong, K. S.; Wong, G. K. L.; Jia, G. Organometallics 2005, 24,
562-569.
(48) Liu, S. H.; Chen, Y.; Wan, K. L.; Wen, T. B.; Zhou, Z.; Lo, M. F.; Williams,
I. D.; Jia, G. Organometallics 2002, 21, 4984-4992.
(49) Yuan, P.; Liu, S. H.; Xiong, W.; Yin, J.; Yu, G.-a.; Sung, H. Y.; Williams,
I. D.; Jia, G. Organometallics 2005, 24, 1452-1457.
(50) Lide, D. R.; Frederikse, H. P. CRC Handbook of Chemistry and Physics,
76 ed.; CRC Press: Boca Raton, FL, 1995.
9
262 J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008

Ru Complexes with Vinyl, Styryl, and Vinylpyrenyl
A R T I C L E S
Table 1. Electrochemical Data of the Vinyl Complexesa
E1 /+ in V
E1
/2
+ in V
+/2
0
/
2
1a
1b
1c
2a
2b
2c
3a
0.470c
0.440d
0.270
0.330
0.360
0.280
0.195c
0.19d
n.a.
1.42b
1.35b
0.795b
1.05b
0.850b
0.54b
0.495c,d
0.620c
0.670d
0.660
3b
3c
0.180c
0.220d
0.155
a Data in CH2Cl2/0.2 M NBu4PF6 at room temperature unless stated
otherwise. Potentials are calibrated against the internal Cp2Fe0/+ couple
which is set as 0.00 V. b Peak potential of an irreversible process at V )
0.1 V/s. c Half-wave potential of a partially reversible wave. d At 195 K.
for the first oxidation were achieved and half-wave potentials
of the second oxidation process could be determined. For the
1-pyrenylvinyl complexes 3a-c the two consecutive one-
electron oxidations are more closely spaced than for the hexenyl
and styryl complexes with ∆E1/2 ) E1/2+/2+ - E1/20/+ values of
350 to 500 mV. The lowering of especially the second oxidation
potential renders the radical cation of 3a and even the dication
of 3c stable, at least on the voltammetric time scale of about
10 s.
Figure 4. Cyclic voltammograms of (a) complex 1c, (c and d) complex
2c and (e) complex 3c in CH2Cl2/NBu4PF6 (0.2 M) at V ) 0.1 V/s. (b)
Square wave voltammogram of complex 1c at 10 mV/s. Potentials are given
relative to the ferrocene/ferrocenium standard.
A comparison of the data in Table 1 reveals the following
trends: (i) Extending the vinyl ligand’s π-system from hexenyl
to styryl and to 1-pyrenylvinyl shifts the oxidation potentials
of both processes to more cathodic values. (ii) The effect of
extending the vinyl ligand’s π-system is much larger for the
second oxidation. (iii) Within each series of compounds 1a-c,
2a-c, and 3a-c the first oxidation potentials follow the order
ligand are unusually long for this type of complexes,51 which
points to steric crowding at the metal atom. The occupation of
two cis positioned coordination sites by the enynyl ligand
induces significant angular distortions in the equatorial plane.
These are most evident by the acute angle C6-Ru-C8 of 66.38-
(14)° spanned by the outermost carbon atoms of the enynyl
ligand and the ruthenium atom and the concomitant opening of
the angles C1-Ru-Cl and C1-Ru-C8 (105.68(10)° and 102.58-
(15)°, respectively). These and other structural features such as
the bond lengths within the enynyl part of the organic ligand
(C6-C7 ) 1.243(5) Å, C7-C8 ) 1.418 Å, C8-C9 ) 1.319-
(5) Å) closely resemble those of other ruthenium enynyl
complexes.51
Electrochemistry. The vinyl complexes were studied by
cyclic voltammetry in CH2Cl2/NBu4PF6 (0.2 M) as the sup-
porting electrolyte. Representative voltammograms of complexes
1c, 2c, and 3c are shown in Figure 4; pertinent data are compiled
in Table 1. A more complete set of voltammograms recorded
for the studied vinyl complexes at room temperature and in a
dry ice/isopropanol slush bath are provided as Figures S7-S15
of the Supporting Information. The PiPr3-substituted five
coordinated complexes 1c, 2c, and 3c undergo a reversible one-
electron oxidation at moderately positive potential. The radical
cations of the five coordinated PPh3 substituted complexes 1a,
2a, and 3a are less stable as follows from ip,c/ip,a peak current
ratios of 0.37, 0.63, or 0.68 at V ) 0.1 V/s at room temperature.
A second one-electron oxidation occurs at substantially higher
potential. This process is completely irreversible at slow sweep
rates and at room temperature. For 2b,c the chemical follow
processes underlying degradation of the mono- and dications
are slowed down at faster sweep rates or upon cooling the cell
in a dry ice/iPrOH slush bath such that ip,c/ip,a ratios of unity
i
five-coordinate Pr3 (1c, 2c, 3c) < five-coordinate PPh3 (1a,
2a, 3a) ≈ six-coordinate isonicotinate adducts (1b, 2b, 3b). This
matches the trends for the CO band shifts and the electron
densities at the metal center. Similar observations have been
reported for divinylphenylene-bridged diruthenium complexes
{(PR3)2(CO)Cl(L′)Ru}2{µ-C6H4-(CHdCH)2-1,3 or -1,4) (R )
i
Ph, L′ ) 4-substituted pyridine; R ) Pr, L′ ) none).27,28 On
the other hand, the observed cathodic shift of 40-50 mV
between related complexes of series a and c is notably smaller
than expected on the basis of Levers EL parameters for PPh3
(0.39 V) and trialkylphosphines (e.g., PnPr3 ) 0.29).52 In Lever’s
approach, the anodic oxidation potential of the metal centered
RuII/III couple is expressed by eq 1, where ΣEL denotes the sum
of the EL parameters of each ligand. Substituting two PPh3 by
two PiPr3 ligands should thus decrease the oxidation potential
by about 200 mV.53
E(RuII/III) ) 0.97 E + 0.04 V
(1)
∑
L
There are two possible explanations for these trends: On one
hand, the vinyl ligand becomes more electron rich as π-conjuga-
tion increases, thus decreasing its EL parameter. This renders
oxidation more facile. Support for this idea comes from a
(52) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271-1285.
(53) Similar parameter sets have been proposed by Leigh, Pickett, and Pombeiro.
These are linearly related to the more extensive ones of Lever. See for
example: (a) Chatt, J.; Kan, C. T.; Leigh, G. L.; Pickett, C. J.; Stanley, D.
L. J. Chem. Soc., Dalton Trans.1980, 2032-2038. (b) Zhang, L.; Guedes
da Silva, M. F. C.; Kuznetsov, M. L.; Gamasa, M. P.; Gimeno, J.; Frausto
da Silva, J. J. R.; Pombeiro, A. J. L. Organometallics, 2001, 20, 2782-
2793.
(51) Yang, S.-M.; Chan, M. C.-W.; Cheung, K.-K.; Che, C.-M.; Peng, S.-M.
Organometallics 1997, 16, 2819-2826.
9
J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008 263

A R T I C L E S
Maurer et al.
comparison of the calculated HOMO energies of 1-hexene
(-9.97 eV),54 propene (-9.73 eV),55 styrene (-7.87 eV),55 and
of the 1-propylpyrenyl localized HOMO (-7.64 eV) of a
pyrenyl donor/perylene-3,4,9,10-bis(dicarboximide) dyad.56 In
this view the oxidation would still be a metal-centered process.
Alternatively, extending the vinyl ligand’s π-system increases
its contribution to the occupied FMOs that govern the oxidation
processes (orbital mixing). The lower energy of the oxidized
forms then mainly relies on more extensive delocalization of
the positive charge(s) across the organic π-system. We will show
that this is indeed the case and that replacing the hexenyl by
the styryl and pyrenylvinyl ligands alters the character of the
first oxidation from a metal/ligand delocalized to a ligand
dominated process. The even stronger effect of vinyl ligand
substitution on the second oxidation potential suggests that the
alteration of relative metal/ligand contributions is even more
pronounced for the second oxidation process. We also note that
the first oxidation potentials of the vinyl complexes are much
lower than those of comparable alkenes, styrenes, and pyrenes
(cf. E1/2 ) 1.11 V for R-methylstyrene and 1.20 V for styrene,54
E1/2 ) ca. 0.9 V for pyrene57 and 2-ethynylpyrene derivatives44),
but also than those of related ruthenium complexes such as
Figure 5. IR spectroelectrochemistry: spectroscopic changes during
oxidation of complex 2b (NBu4PF6/DCE).
RuCl2(CO)(PPh3)2(py-R) (R ) substituted pyridine, E1/2
)
0.66-0.76 V),58 or HRu(CO)Cl(PiPr3)2 (Ep ) 0.505 V) and
RuCl2(CO)(PiPr3)2 (E1/2 ) 0.625 V) as determined by us.
Cathodic shifts of ca. 400 mV for the pyrene-based oxidation
have been observed in pyrenyl phenylene vinylene conjugates.59
The low oxidation potentials observed for the vinyl complexes
thus provide further evidence for an efficient conjugation within
the organometallic chromophore.
Figure 6. IR spectroelectrochemistry: spectroscopic changes during the
first oxidation of complex 3c (NBu4PF6/DCE).
IR-Spectroelectrochemistry. Owing to the synergistic nature
of the metal carbonyl bond the oxidation induced shift of ν˜ (CO)
provides an ideal tool for gauging the metal contribution to the
oxidation process. A metal-centered one-electron oxidation is
expected to increase the energy of the CO stretch by 100-150
cm-1 as less electron density is transferred from the metal atom
to the π* orbitals of the carbonyl ligand. Representative
0/+
examplesinrutheniumchemistryareprovidedbyRu(PR3)2(CO)3
pairs of complexes, where blue-shifts of 120-130 cm-1 upon
oxidation have been reported.60
With this in mind, complexes 1b-c, 2a-c and 3a-c were
oxidized inside an optically transparent thin layer electrolysis
(OTTLE) cell61 under IR monitoring. Results of this study are
displayed as Figures 5-7 and as Figures S16-S22 of the
Supporting Information. Table 2 summarizes the ν˜ (CO), ν˜ (Cd
C), and, if applicable, the ν˜ (COOEt) data for the complexes in
their various oxidation states.
Figure 7. IR spectroelectrochemistry: spectroscopic changes during the
second oxidation of complex 3c (NBu4PF6/DCE).
to spectroscopically characterize their corresponding dications
by IR spectroelectrochemistry. The second oxidation induces a
further, yet even smaller blue shift of the CO band than was
observed for the first oxidation. Pertinent data are provided in
Table 2 (see also Figures 7 and S22 of the Supporting
Information).
The chemical reversibility of the second oxidations of
1-pyrenylvinyl complexes 3b,c even allowed us to generate and
Comparison of the data in Table 2 reveals the following: (i)
For each series a-c the overall CO band shift upon oxidation
consistently decreases with increasing π conjugation of the
substituent at the vinyl ligand. (ii) Oxidation induced CO band
shifts are larger for the five-coordinate complexes and are
seemingly independent of the nature of the phosphine ligands.
The distinctly lower CO band shifts in the 18 VE isonicotinate
adducts show that the weak π acceptor pyridine coligands serve
as electron buffers to ruthenium as is indicated by the
concomitant blue-shift of the isonicotinate ester band. (iii) Even
for the hexenyl complexes 1b,c the CO band shifts are
considerably smaller than is expected of a metal centered
(54) Engels, R.; Scha¨fer, H. J.; Steckhan, E. Liebigs Ann. Chem. 1977, 204-
224.
(55) Zhan, G.-G.; Nichols, J. A.; Dixon, D. A. J. Phys. Chem. A 2003, 107,
4184-4195.
(56) Shumate, W. J.; Mattern, D. L.; Jaiswal, A.; Dixon, D. A.; White, T. R.;
Burgess, J.; Honciuc, A.; Metzger, R. M. J. Phys. Chem. B 2006, 110,
11146-11159.
(57) Daub, J.; Engl, R.; Kurzawa, J.; Miller, S. E.; Schneider, S.; Stockmann,
A.; Wasiliewski, M. R. J. Phys. Chem. A 2001, 105, 5655-5665.
(58) Wohnrath, K.; Batista, A. A.; Ferreira, A. G.; Zukerman-Schpector, J.; de
Oliveira, L. A. A.; Castellano, A. E. Polyhedron 1998, 17, 2013-2020.
(59) Mizutani, M. AdV. Colloid Interface Sci. 1997, 71-72, 111-124.
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1991, 20, 3626-3632.
(61) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. 1991, 317, 179-
187.
9
264 J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008

Ru Complexes with Vinyl, Styryl, and Vinylpyrenyl
A R T I C L E S
Table 2. IR Data for Complexes 1a-c, 2a-c, and 3a-c in Their
Various Oxidation States
ν˜ (CO) ∆ν˜ (CO)
ν˜ (CdC)
1a
1931
1923
1968
1906
1983
1912
1927
1967
1911
1976
1935
1983
1927
1962
1587(w)
1726b
1b
1b+
1c
45
77
1731b
1586(m)
1580(m)
1c+
2a
1595(w), 1585(m), 1562(m), 1553(m)
1726(s),b 1594(w), 1578(m), 1548(m)
1730(s),b 1613(w), 1580(m), 1556(m), 1519(w)
1595(w), 1579(m), 1554(m)
2b
2b+
2c
40
65
48
2c+
3a
1595(w), 1579(m), 1576(m), 1554(m)
1600(w), 1584(w), 1556(m), 1531(m)
1600(sh), 1588(m)
3a+
3b
1727,b 1599(w), 1550(m), 1527(m)
1730,b 1601(m), 1587(m),
3b+
35
22
3b2+ 1984
1741,b 1612(m), 1559(m), 1521(w)
1599(w), 1552(s), 1529(s)
Figure 8. UV-vis-NIR spectroelectrochemistry: spectroscopic changes
upon the first oxidation of complex 3b (NBu4PF6/DCE).
3c
1911
1959
3c+
48
34
1605(s), 1586(s), 1569(s)
1610(s), 1574(w), 1564(m), 1529(w)
3c2+ 1993
.
a Energies are given for 1,2-C2H4Cl2 solutions in cm-1 b Isonicotinate
ester band.
Table 3. Electronic Spectra of the Vinyl Complexes in Their
Various Oxidation States
λmax (
ꢀmax [M-1 cm-1])
1b
400 (2200)
1c
290(sh, 3700), 328(1120), 383(1600), 512(320)
296(8600), 340(sh), 508(1800), 980(200)
310(14300), 376(2750), 490(820)
1c+
2a
2b
308(23000), 406(3700), 522 (300)
2b+
2c
397(3600), 686(6500), 967(595), 1020(545)
272(sh, 1750), 306(3200), 381(580), 510(290)
272(1800), 301(2270), 388(2640), 633(1145), 875(280)
296(sh, 13700), 386(12200), 486(1600), 584(1200)
350(sh, 8400), 363(9000), 385(9200), 465(3800),
603(2300), 1150(1700)
2c+
3a
Figure 9. UV-vis-NIR spectroelectrochemistry: spectroscopic changes
upon the first oxidation of complex 2c (NBu4PF6/DCE).
3a+
respect to pyrene,62 1-phenylpyrene derivatives,57 and 1-ethy-
nylpyrene,62 whose optical absorptions peak at 330-350 nm.
This, and the loss of the characteristic vibrational fine structure
of the pyrene chromophore signal efficient electronic conjuga-
tion between the pyrenyl and the vinylruthenium entities.57,63
The five-coordinated derivatives 1a,c, 2a,c and 3a,c also display
a weak absorption (ꢀ < 1000 M-1 cm-1) in the 500-600 nm
range that are typical of d-d type transitions of d6 ML5
complexes of ruthenium.64-66
Oxidation of the vinyl complexes in an OTTLE cell under
UV-vis-NIR monitoring induces the collapse of the LMCT
or LLCT/MLCT bands and the simultaneous growth of intense
absorptions at lower energies in the visible and the near-infrared
(NIR, see Figures 8, 9 and Figures S23-S25 of the Supporting
Information). With clearly discernible vibrational splittings of
1500-1570 cm-1 the overall appearance of the individual bands
is highly reminiscent of that of alkene and arene radical cations,
including that of styrene and various pyrene derivatives.67-69
3b
265(sh, 39000), 285(sh, 25000), 300(23000),
414(29000), 603(420)
278(37000), 348(18000), 608(10000), 1139(4100)
264(sh, 15700), 309(11000), 414(17000), 510(1200)
277(13000), 346(8800), 376 (8900), 395(8400),
415(7700), 509(3900), 551(8100),
3b+
3c
3c+
594(11900), 704(1100), 1086(5650)
0/+
oxidation. Taking the redox pairs Ru(PR3)2(CO)3 as bench-
mark systems and assuming a CO band shift of 130 cm-1 for a
ruthenium centered process, the metal contribution to oxidation
of the PiPr3 complexes can be estimated as ca. 60% (1c), 50%
(2c), and as ca. 35% (3c) of that in the benchmark systems.
For complexes 3b,c, the second oxidation is even more centered
on the 1-pyrenylvinyl ligand than the first one. IR-spectroelec-
trochemistry thus provides clear evidence for “non-innocent”
behavior of even simple alkyl substituted vinyl ligands in these
ruthenium complexes.
Vis-NIR Spectroelectrochemistry. Electronic spectra of the
parent hexenyl and styryl complexes in the visible region are
dominated by an only moderately intense absorption band of
mainly vinyl ligand to metal charge transfer (LMCT) for the
five-coordinated complexes of series a and c or mixed vinyl to
pyridine ligand/metal-to-pyridine ligand (LLCT/MLCT) char-
acter for complexes of series b. For complexes 3a-c the
pyrenyl-based absorption appears as an intense band near 410
nm without resolved vibrational structure (see Table 3 and
Figure 8). We note a substantial red shift of this band with
(62) Marsh, N. D.; Mikolajczak, C. J.; Wornat, M. J. Spectrochim. Acta 2000,
A 56, 1499-1511.
(63) Harriman, A.; Hissler, M.; Ziessel, R. Phys. Chem. Chem. Phys. 1999, 1,
4203-4211.
(64) Briggs, J. C.; McAuliffe, C. A.; Dyer, G. J. Chem. Soc., Dalton Trans.
1984, 423-427.
(65) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Pahor, R. B. J. Chem. Soc., Dalton
Trans. 1989, 1045-1052.
(66) Winter, R. F.; Hornung, F. M. Inorg. Chem. 1997, 36, 6197-6204.
(67) Shida, T. Electronic Absorption Spectra of Radical Ions; Elsevier: Am-
sterdam, The Netherlands, 1988.
(68) Tsuchida, A.; Ikawa, T.; Yamamoto, M.; Ishida, A.; Takamuku, S. J. Phys.
Chem. 1995, 99, 14793-14797.
(69) Shafirovich, V. Y.; Levin, P. P.; Kuzmin, V. A.; Thorgeirsson, T. E.; Kliger,
D. S.; Geacintov, N. S. J. Am. Chem. Soc. 1994, 116, 63-72.
9
J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008 265

A R T I C L E S
Maurer et al.
Figure 10. X-band ESR spectra of the radical cation of complex 2c (NBu4-
PF6/DCE) at 110 K (left) and at room temperature (right).
Table 4. Experimental and Calculated ESR Data of Oxidized
Mononuclear Ru-Vinyl Complexesa
Figure 11. Contour plots of the frontier orbitals of complexes 1cMe, 2cMe
and 3cMe
,
b
c
.
giso
gav
g1
g2
g3
∆g
1c+
2.023
2.0473
2.050
2.0653
2.018
2.0382
2.001
0.049
0.0271
Chart 2. Vinyl Model Complexes Employed in This Study and
2b+
2.010
Their Designation
2c+
2.0448d
2.0243
2.0032e
3b+
2.0242
2.0132
2.0248
2.0186
2.0116
2.0221
2.0159
2.039
2.0225
2.0066
2.0553
2.0513
2.0560
2.0382
2.0271
2.011
0.0280
0.0197
0.0506
0.0434
0.0326
0.0286
0.0123
3c+
2.0263
2.0958
2.0894
2.0829
2.0606
2.0389
1cMe+
1c+
2.0452
2.0460
2.0503
2.0320
2.0266
2bMe+
2cMe+
3cMe+
a Radical cations were electrogenerated (CH2Cl2/NBu4PF6) inside an ESR
tube. b Isotropic g-value in fluid solution. c Average g-value at 77 K. d A(31P)
) 21.5 G. e A(31P) ) 17.2 G.
There is again a notable red-shift of the bands in the oxidized
vinyl complexes when compared to the oxidized forms of their
purely organic counterparts. As an example, the absorption
bands of the parent styryl radical cation at 344 and 614 nm67
are shifted to 388 and 633 nm in 2c+. Photoionized trans-1-
styrylpyrene absorbs at 580 nm.70 The corresponding radical
cation band of 3b,c+ is observed at 608 and 594 nm,
respectively. The results of UV-vis-NIR spectroelectrochem-
istry thus confirm the dominant organic character of the vinyl
complex radical cations and extensive electron delocalization
within the metalloorganic chromophore.
investigated radical cations display intense isotropic spectra in
fluid solution at room temperature (see Figure 10 and Figures
S26 to S29 of the Supporting Information and Table 4). This
bears clear witness to their dominant organic character. Some
metal contribution to the SOMO is evidenced by the line
broadening, which in most cases conceals hyperfine splittings
to the vinyl protons and the P-atoms of the phosphine ligands.
Excemptions are the radical cations 2c+ and 3c+ where resolved
hyperfine couplings to the 31P nuclei of 21.5 and 17.2 G,
respectively, were observed in fluid solution. Further manifesta-
tions of metal contribution to the SOMO orbital are the deviation
of the measured g-values from ge and some discernible axial or
rhombic splitting of the g-tensor in frozen matrices (110 K).
The g-value anisotropies are, however, much smaller than those
usually associated with Ru(III) species.74
Smaller g-tensor anisotropies ∆g and smaller deviations of
the average g-value from ge are observed as the covalency of
the Ru-ligand bond increases and more spin density is shifted
to the ligand. Recent examples of Ru(III) alkynyl complexes
document close correlations between (calculated) metal contri-
butions to the SOMO and the ∆g parameter.75,76 In none of
these cases, however, g-value anisotropies as small as those in
mono- and dinuclear27,28 vinyl complexes have been observed.
Quantum Chemistry. Quantum chemical calculations on
models of the mononuclear ruthenium vinyl complexes were
carried out in order to (i) assess metal versus ligand contributions
to the frontier molecular orbitals (fmos) that are involved in
the redox chemistry and in the low-energy optical transitions,
(ii) investigate how extending π-conjugation within the vinyl
ligand affects the fmo composition, (iii) rationalize the electronic
spectra of the complexes, (iv) establish how oxidation changes
ESR Spectroscopy. Metal-centered paramagnetic species
display fundamentally different properties in their ESR spectra
than organic-based radicals. This is particularly true for Ru-
(III) complexes, which are mostly ESR silent at room-temper-
ature owing to rapid relaxation processes.60 Spectra recorded
at low temperatures, usually in frozen matrices, display axial
or rhombic g-tensors with large g-anisotropies, that is, large
differences between the individual components of the g-tensor,
and average g-values distinctly different than the free electron
value ge of 2.0023.71-73 Organic radicals, on the other hand,
typically display richly structured isotropic signals at room
temperature, g-values close to that of the free electron, and
g-value anisotropies which are too small to be resolved in the
X-band. ESR spectroscopy is thus ideally suited to probe the
character of the vinyl complex radical cations.
Oxidized samples of most vinyl complexes were electrogen-
erated inside an ESR tube. With the exception of 1c+ and 2b+,
which became ESR active only upon cooling, all other
(70) Ellsei, F.; Aloisi, G. G.; Latterini, L.; Galiazzo, G.; Go¨rner, H. J. Chem.
Soc.; Faraday Trans. 1995, 91, 3117-3121.
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1920.
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9
266 J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008

Ru Complexes with Vinyl, Styryl, and Vinylpyrenyl
A R T I C L E S
Table 5. Calculated FMO Compositions of Mononuclear Ru-Vinyl Model Complexes.
model
MO
E (eV)
prevailing character
Ru
vinyl
R
CO
Cl
PR3
1cMe
LUMO+1
LUMO
HOMO
HOMO-1
LUMO+1
LUMO
-0.21
-1.62
-5.30
-6.15
-0.16
-1.39
-5.38
-6.33
-0.44
-1.55
-5.38
-6.55
-0.17
-0.20
-0.40
-0.98
-5.15
-6.25
-1.54
-1.59
-5.08
-6.14
dRu
dRu
dRu + πvinyl
dRu
60
60
46
61
56
59
40
63
8
60
28
60
58
8
1
13
43
4
0
1
4
0
0
1
5
0
58
1
30
0
0
61
0
0
29
0
87
1
63
63
6
11
0
17
7
9
0
17
0
11
0
17
18
0
0
0
0
32
0
12
0
0
3
3
1
16
5
3
0
14
0
3
0
17
5
0
0
0
0
12
0
3
0
30
11
2
2
1c
dRu
0
32
15
13
1
1
11
4
1
14
1
1
0
2
0
0
12
2
dRu + PR3
dRu + πvinyl
dRu + Cl
πvinyl + πPh
dRu
dRu + πvinyl + πPh
dRu
dRu
π*vinyl + π*Ph
π*py
π*py
dRu + πvinyl + πPh
dRu
πpyr + πvinyl
dRu
13
41
4
32
13
37
5
2
28
0
0
39
4
10
12
21
13
HOMO
HOMO-1
LUMO+1
LUMO
2cMe
HOMO
HOMO - 1
LUMO + 3
LUMO + 2
LUMO + 1
LUMO
2bMe
3
4
HOMO
29
50
3
60
14
21
HOMO - 1
LUMO + 1
LUMO
HOMO
HOMO - 1
3cMe
πpyr + πvinyl + dRu
πpyr + πvinyl + dRu
1
2
Table 6. TDDFT (G03/PBE0/CPM (CH2Cl2)) Singlet Excitation Energies (eV) for 1c, 2bMe, 2cMe (G03/PBE0/CPCM (CH2Cl2)), and 3cMe
(G03/PBE1PBE/CPCM (CH2Cl2)) with Oscillator Strengths Larger than 0.001
transition energy
[eV (nm)]
expt trans
[nm]
ext coeff
1
model
state
main components (%)
osc str
[M-1 cm-
]
1c
a1A
b1A
f1A
h1A
i1A
91 (HOMO f LUMO)
2.28 (544)
3.18 (390)
3.60 (344)
4.14 (299)
4.35 (285)
2.34 (529)
3.16 (392)
4.05 (306)
4.23 (293)
3.50 (354)
4.08 (304)
4.19 (296)
4.26 (291)
2.18 (569)
2.98 (416)
3.45 (359)
3.92 (316)
0.05
512
383
328
290
320
1600
1120
3700
88 (HOMO-2 f LUMO)
82 (HOMO f LUMO+1)
37 (HOMO-3 f LUMO)
30 (HOMO-1 f LUMO+1)
90 (HOMO f LUMO)
98 (HOMO-1 f LUMO)
70 (HOMO -3 f LUMO)
98 (HOMO f LUMO+1)
98 (HOMO f LUMO)
97 (HOMO f LUMO+1)
78 (HOMO -1 f LUMO+3)
87 (HOMO f LUMO+2)
92 (HOMO f LUMO)
92 (HOMO f LUMO+1) (π π*)
80 (HOMO f LUMO+2)
37 (HOMO-1 f LUMO+1)
40 (HOMO f LUMO+4)
30 (HOMO-1 f LUMO+1)
42 (HOMO f LUMO+4)
0.027
0.024
0.029
0.065
0.005
0.025
0.025
0.634
0.133
0.017
0.181
0.464
0.003
0.938
0.042
0.077
2bMe a
b1A
c1A
f1A
g1A
b1A
e1A
f1A
g1A
a1A
b1A
f1A
h1A
521
394
308
300
3700
23000
2cMe
383
306
580
3200
3cMe
510
414
n.d.
309
1200
17000
n.d.
11000
i1A
4.01 (309)
0.124
a Contributions missing to 100% correspond to py ligand-based orbitals.
the bonding within the organometallic Ru-vinyl chromophore,
and (v) compare the experimentally observed CO and CdC
frequencies for the accessible oxidation states and the g-
parameters of the radical cations to those predicted by theory.
The phosphine ligands were modeled as PMe3 for most
calculations. To probe for the effect of such simplification, the
model complex Cl(CO)(PMe3)2Ru(CHdCHMe) (1cMe) was
compared to fully optimized 1c. The effect of six versus five
coordination was finally addressed by comparing Cl(CO)-
(PMe3)2Ru(CHdCHPh) (2cMe) and (py)Cl(CO)(PMe3)2Ru(CHd
CHPh) (2bMe) as models of complexes 2a,c and 2b. The model
complexes employed in the computational study and their
designation are summarized in Chart 2.
Contour plots of crucial fmos of the complexes 1cMe, 2cMe
,
and 3cMe are provided as Figure 11, while Table 5 lists their
compositions as obtained by Mulliken analysis. These data fully
conform to our experimental observation that metal contribution
to the occupied frontier levels decreases as the π-conjugation
of the vinyl ligand increases. For the propenyl and hexenyl
systems 1cMe and 1c the HOMO is fully delocalized over the
Ru-vinyl entity. Vinyl ligand contributions to the HOMO
become more and more important as the organic π-system
extends. It increases from 47% in 1cMe or 46% in fully optimized
1c to 67% in 2cMe and 84% in 3cMe. This clearly justifies
denoting them as “non-innocent”. A comparison of model
complex 1cMe and the accurate model of 1c shows, that
approximating PiPr3 by PMe3 coligands underestimates the
phosphine contribution to the HOMO and LUMO orbitals. The
LUMO of all five coordinated complexes is essentially a
ruthenium d-orbital with contributions from the phosphine and
carbonyl ligands such that the electronic transition at the lowest
The optimized structures of the model complexes agree well
with the experimental ones (see Tables S11 to S14 of the
Supporting Information). Deviations between experimental and
calculated structures are restricted to the immediate vicinity of
the vinyl bond.
9
J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008 267

A R T I C L E S
Maurer et al.
andprincipalconstituentsoforganometallic“molecularwires”.77-81
There, the occupied frontier levels are metal centered and the
metal atoms interact through direct orbital overlap with the
π-conjugated bridge. In our case, delocalization of the ligand
centered HOMO onto the metal atoms suggests another possible
way to construct extended electron conducting systems from
vinyl ruthenium building blocks by employing the metal atoms
as the conduit between two redox active ligands. Such a
possibility has already been realized in a mononuclear bis-
(alkynyl) platinum complex.82 Our results add to a growing body
of redox-active organometallic compounds where the organic
π-ligandheavilyparticipatesinelectron-transferprocesses.79,80,83-85
Five-coordinated mononuclear ruthenium complexes as they
were investigated herein offer an additional vacant coordination
site trans to the vinyl ligand. This allows for the easy assembly
of di- and oligonuclear systems with possibly high conductivity
along the vinyl-metal-bridge chain by interconnecting them
through appropriate bridging ligands or by employing alkynes
with an additional coordinating functionality in the hydroruth-
enation reaction. This is the subject of ongoing research in our
laboratories.
Table 7. Calculated IR Parameters of Vinyl Complexes in Their
Various Oxidation States.
n
)
0
n
)
1
n ) 2
1cMe n+
1cn+
ν˜ (CO)
ν˜ (CO)
ν˜ (CO)
ν˜ (CC)
ν˜ (CO)
ν˜ (CC)
ν˜ (CO)
ν˜ 1(CC)
ν˜ 2(CC)
1926.9
1924.5
1916.0
1554.2
1927.6
1549.9
1926.9
1550.2
1526.6
1988.5
1986.0
1961.0
1597.0
1978.9
1595.7
1967.2
1606.7
1584.0
2045.0
2037.5
2001.5
1607.4
2024.9
1607.9
2002.5
1608.4
1576.8
2bMe n+
2cMe n+
3cMe n+
energy is assigned as a mixed ligand-to-metal/ligand-to-ligand
charge-transfer band (LMCT/LLCT). This is also borne out by
TDDFT calculations which account for CH2Cl2 solvation. As
is seen from the comparison in Table 6, the calculated spectra
reproduce the experimental ones well. On the basis of these
calculations, the lowest energy band at ca. 510 nm is assigned
as the HOMO-LUMO transition. Higher energy transitions
within the styryl and pyrenyl complexes have dominant πfπ*
character owing to sizable contributions of the vinyl ligand to
the LUMO + n and the HOMO - n orbitals, particularly for
the pyrenyl complex. For six-coordinated 2bMe, however, two
π* orbitals of the pyridine coligands are interspersed between
the HOMO and the appropriate unoccupied metal d orbital such
that the two lowest electron transitions assume mixed arylvinyl-
to-pyridine (LLCT) and metal-to-pyridine charge transfer
(MLCT) character.
Acknowledgment. Financial support of this work by Deut-
sche Forschungsgemeinschaft (R.F.W., projects Wi 1262/7-1
and 436 TSE 113/45/0-1), by the Grant Agency of the Academy
of Sciences of the Czech Republic (S.Z., Grant 1ET400400413),
and the Ministry of Education of the Czech Republic (S.Z. Grant
OC 139) are gratefully acknowledged.
Supporting Information Available: Synthetic procedures and
characterization of compounds, Figures displaying the crystal-
lographically determined structures of the complexes 1b,c, Ru-
(CO)Cl(PPh3)2(η1:η2-nBuHCdCHCtCnBu), 3a-P‚2CH2Cl2 and
3c‚CHCl3 (Figures S1-S5); tables detailing the crystal data and
structure refinement (Tables S1-S8); voltammograms of com-
plexes 1a-c, 2a-c and 3a-c at room temperature and in an
isopropanol/dry ice slush bath (Figures S6-S14); IR-spectro-
scopic changes upon the first oxidation of complexes 1b, 1c,
2b, 3a, and 3b (S15-S20), and upon the second oxidation of
complex 3b (S21); Changes in the UV-vis-NIR spectrum of
1b (S22), 2b (S23), and 3b (S24); ESR spectra of the radical
cations of complexes 1c, 3a,b, and 3b,c (S25-S28); tables of
the G03/B3LYP and ADF/BP calculated bond parameters for
the fully optimized complexes 1c and 3cMe (Tables S9, S10)
and contour plots of all orbitals involved in the electronic
transitions of Table 6. This material is available free of charge
via the Internet at http://pubs.acs.org.
To trace the effect of successive charge removal from the
occupied frontier levels diagnostic IR parameters such as ν˜ (CO)
and ν˜ (CdC) of the model complexes were calculated for the
neutral compounds and the oxidized mono- and dications. The
compilation in Table 7 shows the expected decrease of oxida-
tion-induced CO band shifts with decreasing HOMO metal
character, paralleling our experimental results. Thus, for the first
oxidation, ∆ν˜ (CO) diminishes from 61 cm-1 in the propenyl
complex 1cMe to 51 in 2cMe and 40 cm-1 for 3cMe. The
calculations slightly underestimate ∆ν˜ (CO), which is mostly
due to somewhat high ν˜ (CO) values for the neutral complexes.
For the styryl and pyrenylvinyl complexes the energies of the
vinyl and substituent CdC bands are predicted to increase with
the overall oxidation state. We note again good agreement with
the experimental data, particularly for the pyrenylvinyl com-
plexes where these vibrations are rather intense. Computed ESR
parameters as they are given in Table 4 fully reproduce the
experimentally observed small g-anisotropies ∆g, the systematic
decrease of ∆g with increasing π-conjugation and lower metal
character of the SOMO as well as the small deviations of the
average g-values from ge.
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that even simple alkenyls behave as “non-innocent” ligands
when coordinated to Ru(CO)Cl(PR3)2(L) (L ) electron donating
or weakly π-accepting coligand) entities. Extending the conju-
gation within the vinyl ligand gradually alters the nature of the
HOMO and, accordingly, of the anodic redox processes from
fully delocalized across the metal-vinyl entity to ligand
dominated with smaller, yet still discernible metal contributions.
Such a situation is opposite to that encountered in most
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268 J. AM. CHEM. SOC. VOL. 130, NO. 1, 2008