Bonding and electron delocalization in ruthenium(III) σ-arylacetylide radicals [trnsCl(η2-dppe)2Rue≡C(4-C 6H4X)]+ (X = NO2, C(O)H, C(O)Me, F, H, OMe, NMe2): Misleading aspects of

Article abstract of DOI:10.1021/om801138q

The bonding within the series of [trans-Cl(η²-dppe) ₂RuC≡C(4-C₆H₄X)]ⁿ⁺ complexes (1-Xⁿ⁺; n = 1, 0 and X = NO₂, C(O)H, C(O)Me, F, H, OMe, NMe₂) has been examined by IR,

Full text of DOI:10.1021/om801138q

Organometallics 2009, 28, 2253–2266
2253
Bonding and Electron Delocalization in Ruthenium(III)
σ-Arylacetylide Radicals [trans-Cl(η2-dppe)2RuCtC(4-C6H4X)]+
(X ) NO2, C(O)H, C(O)Me, F, H, OMe, NMe2): Misleading Aspects
of the ESR Anisotropy
Nicolas Gauthier,† Noureddine Tchouar,†,‡ Fre´de´ric Justaud,† Gilles Argouarch,†
Marie P. Cifuentes,§ Loic Toupet, Daniel Touchard,† Jean-Franc¸ois Halet,†
Ste´phane Rigaut,† Mark G. Humphrey,§ Karine Costuas,*,† and Fre´de´ric Paul*,†
Sciences Chimiques de Rennes, UniVersite´ de Rennes 1, CNRS (UMR 6226), Campus de Beaulieu,
35042 Rennes Cedex, France, Department of Chemistry, Australian National UniVersity, Canberra,
ACT 0200, Australia, and Institut de Physique de Rennes, UniVersite´ de Rennes 1, CNRS (UMR 6251),
35042 Rennes Cedex, Campus de Beaulieu, France
ReceiVed NoVember 28, 2008
The bonding within the series of [trans-Cl(η2-dppe)2RuCtC(4-C6H4X)]n+ complexes (1-Xn+; n ) 1,
0 and X ) NO2, C(O)H, C(O)Me, F, H, OMe, NMe2) has been examined by IR, ESR, and UV-vis-near-
IR spectroscopy together with computational modeling. A strong substituent effect is evidenced for radical
delocalization from the metal to the functional arylacetylide fragment. This effect is also apparent in the
large anisotropy change of their ESR signatures. DFT calculations substantiate these experimental
observations and permit discussion of the influence of the X substituent on spin delocalization in compounds
containing isolobal metal fragments. Evidence is given that the ESR anisotropy alone cannot reliably be
used to compare the metallic character of the unpaired electrons in closely related families of pseudo-
octahedral cationic Ru(III) functional arylacetylides with rhombic symmetry when the complexes possess
different coordination spheres. ESR anisotropy constitutes nevertheless a useful benchmark for this purpose
within the presently investigated 1-X+ family.
previously shown that the electron-releasing capability of “trans-
Cl(η2-dppe)2RuCtC-” is larger than that of “(η2-dppe)(η5-
C5Me5)FeCtC-” and somewhat lower than that of the ruthe-
nium analogue of the latter, “(η2-dppe)(η5-C5Me5)RuCtC-.7
On the basis of its electronic substituent parameter (ESP), this
Ru(II) fragment is comparable to an amino substituent.9 It has
Introduction
Over the past few years, electron-rich electroactive group 8
metal acetylide complexes have attracted particular attention
as redox-switchable building blocks for the realization of
molecular-based devices, in a similar fashion to the ubiquitous
ferrocenyl group.1,2 For instance, it has been shown on several
occasions that electron-rich acetylide fragments of d6-transition
metals such as “trans-Cl(η2-dppe)2RuCtC-” or “(η2-dppe)(η5-
C5Me5)FeCtC-” permit the efficient redox control of linear
and nonlinear optical activities, when incorporated in suitable
molecular architectures.3-5 This particular property rests on the
fact that these organometallic units behave as strongly electron-
releasing groups in their neutral (d6) closed-shell state but not
in their mono-oxidized (d5) cationic state. This has been
evidenced in several investigations on functional mononuclear
Fe(II) and Ru(II) model compounds such as 1-X, 2-X, and 3-X
(Chart 1), in which the X substituent was varied from strongly
electron-withdrawing to strongly electron-releasing.6-8 How-
ever, we think that in order to utilize such metal-containing
fragments in new functional architectures, a better knowledge
of their electronic characteristics is needed.
7,10
also been shown that d5 paramagnetic cations such as 2-X+
or 3-X+ 11,12 possess one electronic hole (or unpaired electron)
that is significantly delocalized over the arylacetylide ligand.
(1) (a) Akita, M.; Koike, T. J. Chem. Soc., Dalton Trans. 2008, 3523–
3530. (b) Ren, T. Organometallics 2005, 24, 4854–4870. (c) Blum, A. S.;
Ren, T.; Parish, D. A.; Trammell, S. A.; Moore, M. H.; Kushmerick, J. G.;
Xu, G.-L.; Deschamps, J. R.; Polack, S. K.; Shashidar, R. J. Am. Chem.
Soc. 2005, 127, 10010–10011. (d) Fillaut, J.-L.; Perruchon, J.; Blanchard,
P.; Roncali, J.; Gohlen, S.; Allain, M.; Migalska-Zalas, A.; Kityk, I. V.;
Sahraoui, B. Organometallics 2005, 24, 687–695. (e) Qi, H.; Sharma, S.;
Li, Z.; Snider, G. L.; Orlov, A. O.; Lent, C. S.; Fehlner, T. P. J. Am. Chem.
Soc. 2003, 125, 15250–15259. (f) Wong, K. M.-C.; Lam, S. C.-F.; Ko,
C.-C.; Zhu, N.; Yam, V. W.-W.; Roue´, S.; Lapinte, C.; Fathallah, S.;
Costuas, K.; Kahlal, S.; Halet, J.-F. Inorg. Chem. 2003, 42, 7086–7097.
(g) Morrall, J. P.; Dalton, G. T.; Humphrey, M. G.; Samoc, M. AdV.
Organomet. Chem. 2008, 55, 61–136. (h) Liu, Y.; Lagrost, C.; Costuas,
K.; Tchouar, N.; Le Bozec, H.; Rigaut, S. Chem. Commun. 2008, 6117–
6119. (i) Rigaut, S.; Touchard, D.; Dixneuf, P. H. In Redox Systems Under
Nano-space Control; Hirao, T., Ed.; Springer Verlag: Heidelberg, 2006.
(j) Venkatesan, K.; Blacque, O.; Fox, T.; Alfonso, M.; Schmalle, H. W.;
Berke, H. Organometallics 2004, 23, 1183–1186. (k) Fernandez, F. J.;
Venkatesan, K.; Blacque, O.; Alfonso, M.; Schmalle, H.; Berke, H. Chem.-
Eur. J. 2003, 9, 6192–6209. (l) Yam, V. W.-W. Acc. Chem. Res. 2002, 35,
555–563. (m) Ibn Ghazala, S.; Paul, F.; Toupet, L.; Roisnel, T.; Hapiot, P.;
Lapinte, C. J. Am. Chem. Soc. 2006, 128, 2463–2476. (n) Paul, F.; Lapinte,
C. Coord. Chem. ReV. 1998, 178/180, 427–505. (o) Bruce, M. I.; Low,
P. J. AdV. Organomet. Chem. 2004, 50, 179–444.
By deriving the electronic substituent parameters of the
organometallic end groups in 1-X, 2-X, and 3-X, we have
* Corresponding author. E-mail: frederic.paul@univ-rennes1.fr.
† Sciences Chimiques de Rennes, Universite´ de Rennes 1.
‡ Permanent address: De´partement de Chimie, Faculte´ des Sciences,
Universite´ des Sciences et de Technologie d’Oran Mohamed Boudiaf, Oran,
Alge´rie.
(2) Kim, B.; Beebe, J. M.; Olivier, C.; Rigaut, S.; Touchard, D.;
Kushmerick, J. G.; Zhu, X.-Y.; Frisbie, C. D. J. Phys. Chem. C 2007, 111,
7521–7526.
§ Australian National University.
Institut de Physique de Rennes, Universite´ de Rennes 1.
10.1021/om801138q CCC: $40.75
2009 American Chemical Society
Publication on Web 03/16/2009

2254 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Chart 1. Selected Mononuclear Acetylide d6 Complexes
Scheme 1. Synthesis of 1-NMe2 ([Ru] ) trans-(dppe)2Ru)
These studies have also evidenced that this hole is somewhat
more delocalized in 2-X+ than in 3-X+.7 With these results in
mind, it is of particular interest to investigate more closely how
the “trans-Cl(η2-dppe)2RuCtC-” fragment, in a given redox
state, influences the electronic properties of selected functional
complexes such as 1-X and 1-X+ and to carefully compare these
data with those of the corresponding 2-X and 2-X+ relatives,
in order to gain a deeper understanding of the similarities and
differences between these isolobal and isoelectronic organo-
metallic end groups.
We therefore report in the following (i) the synthesis and
characterization of a new 1-X complex featuring the strongly
electron-releasing dimethylamino substituent (1-NMe2), (ii) an
investigation of the electronic substituent effects in a series of
Ru(II) complexes composed of this new compound comple-
mented by previously reported analogues functionalized with
less electron-releasing substituents (X ) NO2, C(O)H, C(O)Me,
F, H, and OMe), (iii) the characterization of these compounds
in their mono-oxidized Ru(III) state along with a study of
electronic substituent effects in this state, (iv) an extensive
theoretical study using density functional theory (DFT) calcula-
tions of selected Ru(II) and Ru(III) model compounds, and (v)
a comparative discussion of the bonding within the “Ru-CtC-
1,4-C6H4-” core between 1-X/1-X+ and 2-X/2-X+, with
particular emphasis placed on spin delocalization in the Ru(III)
radicals in relation to their ESR signatures.
investigations on these compounds,13,14,18 the metal-centered
pseudoreversible Ru(II)/Ru(III) oxidation was detected close to
the ferrocene redox potential (the use of 3-NO2 as internal
calibrant allowed accurate evaluation of the E° values for these
(3) (a) Powell, C. E.; Humphrey, M. G. Coord. Chem. ReV. 2004, 248,
725–756. (b) Whittall, I. R.; Mac Donagh, A. M.; Humphrey, M. G.; Samoc,
M. AdV. Organomet. Chem. 1998, 42, 291–362. (c) Whittall, I. R.; Mac
Donagh, A. M.; Humphrey, M. G.; Samoc, M. AdV. Organomet. Chem.
1999, 43, 349–405. (d) Cifuentes, M. P.; Humphrey, M. G.; Morrall, J. P.;
Samoc, M.; Paul, F.; Roisnel, T.; Lapinte, C. Organometallics 2005, 24,
4280–4288. (e) Paul, F.; Costuas, K.; Ledoux, I.; Deveau, S.; Zyss, J.; Halet,
J.-F.; Lapinte, C. Organometallics 2002, 21, 5229–5235. (f) Weyland, T.;
Ledoux, I.; Brasselet, S.; Zyss, J.; Lapinte, C. Organometallics 2000, 19,
5235–5237. (g) Powell, C. E.; Humphrey, M. G.; Cifuentes, M. P.; Morrall,
J. P.; Samoc, M.; Luther-Davies, B. J. Phys. Chem. A 2003, 107, 11264–
11266. (h) Cifuentes, M. P.; Powell, C. E.; Humphrey, M. G.; Heath, G. A.;
Samoc, M.; Luther-Davies, B. J. Phys. Chem. A 2001, 105, 9625–9627.
(4) Powell, C. E.; Cifuentes, M. P.; Morrall, J. P.; Stranger, R.;
Humphrey, M. G.; Samoc, M.; Luther-Davies, B.; Heath, G. A. J. Am. Chem.
Soc. 2003, 125, 602–610.
(5) See also for the tetra-amino analogues: Wong, W.-Y.; Che, C.-M.;
Chan, M. C. W.; Han, J.; Leung, K.-H.; Phillips, D. L.; Wong, K.-Y.; Zhu,
N. J. Am. Chem. Soc. 2005, 127, 13997–14007.
(6) Costuas, K.; Paul, F.; Toupet, L.; Halet, J.-F.; Lapinte, C. Organo-
metallics 2004, 23, 2053–2068.
(7) Paul, F.; Ellis, B. J.; Bruce, M. I.; Toupet, L.; Roisnel, T.; Costuas,
K.; Halet, J.-F.; Lapinte, C. Organometallics 2006, 25, 649–665.
(8) Mc Grady, J. E.; Lovell, T.; Stranger, R.; Humphrey, M. G.
Organometallics 1997, 16, 4004–4011.
(9) Gauthier, N.; Olivier, C.; Rigaut, S.; Touchard, D.; Roisnel, T.;
Humphrey, M. G.; Paul, F. Organometallics 2008, 26, 1063–1072.
(10) Fox, M. A.; Roberts, R. L.; Khairul, W. M.; Hartl, F.; Low, P. J.
J. Organomet. Chem. 2007, 692, 3277–3290.
(11) Paul, F.; da Costa, G.; Bondon, A.; Gauthier, N.; Sinbandhit, S.;
Toupet, L.; Costuas, K.; Halet, J.-F.; Lapinte, C. Organometallics 2007,
26, 874–896.
(12) Paul, F.; Toupet, L.; The´pot, J.-Y.; Costuas, K.; Halet, J.-F.; Lapinte,
C. Organometallics 2005, 24, 5464–5478.
(13) Touchard, D.; Haquette, P.; Guesmi, S.; Le Pichon, L.; Daridor,
A.; Toupet, L.; Dixneuf, P. H. Organometallics 1997, 16, 3640–3648.
(14) (a) Hurst, S. K.; Cifuentes, M. P.; Morrall, J. P. L.; Lucas, N. T.;
Whittall, I. R.; Humphrey, M. G.; Asselberghs, I.; Persoons, A.; Samoc,
M.; Luther-Davies, B.; Willis, A. C. Organometallics 2001, 20, 4664–4675.
(b) Morrall, J. P.; Cifuentes, M. P.; Humphrey, M. G.; Kellens, R.; Robijns,
E.; Asselberghs, I.; Clays, K.; Persoons, A.; Samoc, M.; Willis, A. C. Inorg.
Chim. Acta 2006, 359, 998–1005.
(15) Rigaut, S.; Touchard, D.; Dixneuf, P. H. Coord. Chem. ReV. 2004,
248, 1585–1601.
(16) Chatt, J.; Hayter, R. G. J. Chem. Soc. 1961, 896–904.
(17) Polam, J. R.; Porter, L. C. J. Coord. Chem. 1993, 29, 109–119.
(18) Younus, M.; Long, N. J.; Raithby, P. R.; Lewis, J.; Page, N. A.;
White, A. J. P.; Williams, D. J.; Colbert, M. C. B.; Hodge, A. J.; Khan,
M. S.; Parker, D. G. J. Organomet. Chem. 1999, 578, 198–209.
Results
Synthesis and Characterization of the Ru(II) Com-
plexes. To date, several Ru(II) complexes of type 1-X featuring
strongly electron-withdrawing to moderately electron-releasing
substituents have been reported.13,14 The compounds required
for the present study (X ) NO2, C(O)H, C(O)Me, F, H, and
OMe) were therefore obtained according to these procedures.
However, a complex possessing a strongly electron-releasing
group, e.g. the dimethylamino group, was also needed for
comparison. The synthesis of this complex was undertaken
according to an original procedure inspired from the Ru(II)
allenylidene synthesis recently reported by Touchard and co-
workers.15 Instead of starting from the known cis-(η2-
dppe)2RuCl2 precursor complex,16 this synthetic approach starts
from the triflate Ru(II) precursor2,17 and allows isolation of the
corresponding vinylidene salt under mild conditions from para-
dimethylaminophenylacetylene (Scheme 1). The latter complex
was not characterized, but rather was deprotonated using tBuOK
to yield the desired Ru(II) acetylide complex (1-NMe2) in
modest yield (37%) after chromatographic separation. This new
complex was completely characterized by elemental analysis,
mass spectrometry, and routine spectroscopies (Supporting
Information).
The cyclic voltammetry (CV) of the previous Ru(II) com-
pounds along with their IR and 13C NMR spectra in solution
were systematically recorded. As expected from previous

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2255
Scheme 2. Oxidation of the Ru(II) Complexes 1-X ([Ru] )
trans-(dppe)2Ru)
Table 1. IR Data and Ru(III/II) Oxidation Potentials for
[trans-Cl(η2-dppe)2Ru(CtC-C6H4X)]0/+ Complexes in CH2Cl2
Solution (cm-1
)
cmpd
X
Ru(II)
νCtC
Ru(III)
νCtC
Ru(III/II)
a
∆νCtC
E°c
NO2
2051 2023(sh)
2069(sh) 2049
2062 2036(sh)
2074
2068
2076
1928
1909
1906
1910
1908
1922
1890
-123b
-140b
-156b
-164
-160
-154
-186
0.63
0.55
0.54
0.46
0.44
0.36
0.14
C(O)H
C(O)Me
F
H
OMe
NMe2
Figure 1. ORTEP diagram of 1-C(O)Me. Thermal ellipsoids are
at the 50% probability level. Hydrogen atoms have been omitted
for clarity. Selected distances (Å) and angles (deg): Ru1-P1
2.3800(12), Ru1-P2 2.3701(11), Ru1-P3 2.3480(11), Ru1-P4
2.3761(12), Ru-Cl1 2.4831(11), Ru1-C1 1.989(4), C1-C2
1.212(6), C2-C3 1.434(6), C3-C4 1.410(6), C4-C5 1.392(7),
C5-C6 1.399(7), C6-C7 1.388(7), C7-C8 1.371(6), C8-C3
1.398(6), C6-C9 1.476(7), C9-C10 1.482(8), C9-O1 1.237(6),
P1-Ru1-P2 80.80(4), P3-Ru1-P4 82.46(4), P1-Ru1-C1
84.39(4), Cl1-Ru1-C1 178.60(13), P2-Ru1-C1 84.80(4),
Ru1-C1-C2 178.0(4), C1-C2-C3 169.4(5), C2-C3-C4
121.1(4),C4-C5-C6121.4(5),C6-C7-C8118.0(4),C7-C6-C9
119.5(5), C6-C9-O1 120.3(5), C10-C9-O1 120.9(4), P1-Ru1/
C3-C4 -131.9, P4-Ru1/C3-C4 48.8, C6-C7/C9-O1 5.3.
2076
a Neutral vs oxidized νCtC difference. b ∆νCtC value with the most
intense peak. c All E° values in V vs SCE. Conditions: CH2Cl2 solvent,
0.1 M (NnBu4)(PF6) supporting electrolyte, 20 °C, Pt electrode, sweep
rate 0.100 V s-1. The ferrocene/ferricinium (Fc/Fc+) couple was used as
an internal reference for potential measurements.
electrochemical processes). Note that another irreversible oxida-
tion above 1.2 V vs SCE can also be detected for all compounds.
In addition, in the case of the nitro-substituted complex 1-NO2,
the nitro reduction is observed at -1.26 V vs SCE, while for
the dimethylamino-substituted complex 1-NMe2 a second pseu-
doreversible event, corresponding to the amine oxidation, is
detected at ca. 0.64 V vs SCE. In the 13C NMR spectra, the
characteristic quintuplet signal corresponding to the R-acetylide
carbon atom was detected in most cases, exhibiting coupling
with the four equivalent equatorial phosphorus nuclei of ca. 15
Hz. A high-field 500 MHz NMR spectrometer was required to
identify this weak signal for 1-F, 1-OMe, and 1-NMe2. IR
spectra recorded in dichloromethane solutions reveal intense
νCtC bands in the 2050-2075 cm-1 spectral range (Table 1).
The shoulder apparent on this absorption band when electron-
withdrawing substituents are present possibly arises from Fermi
coupling.19
Ru(III) cations generated this way were stable in dichlo-
romethane over more than 10 min and that their lifetime
increased somewhat with electron-releasing substituents. In the
case of the complex 1-NMe2, the dimethylamino substituent can
also be oxidized if acetylferricinium tetrafluoroborate is present
in excess. Thus, when overstoichiometric concentration of
oxidant was used for IR monitoring, ferricinium hexafluoro-
phosphate ([(η5-C5H5)2Fe][PF6]) was preferred as an oxidant,
to ensure that only 1-NMe2[PF6] is initially generated.
The reaction is evidenced by a color change to purple-brown,
except in the case of the dimethylamino-substituted complex
1-NMe2, for which the reaction medium turns green. For all
compounds, new νCtC absorptions are detected in the 1930-1890
cm-1 spectral range (Table 1) concomitantly with the disap-
pearance of the νCtC band of the reactant. This absorption is
rather weak for the complexes with the most electron-withdraw-
ing substituents but becomes more and more intense when the
substituent becomes increasingly electron-releasing (Supporting
Information).
We followed a similar workup in an ESR probe, but varied
the procedure by quenching the reaction medium in liquid
nitrogen immediately after admixture of the ferricinium salt.
After transferring the tube to the cavity of the ESR spectrometer,
a rhombic signal was detected at 80 K (Figure 2 and Table 2).
For most compounds, this signal weakens and becomes isotropic
after melting of the solvent glass, eventually disappearing when
the temperature of the sample returns to ambient. For the Ru(III)
complexes with the most electron-releasing substituents such
In the process of characterizing the Ru(II) complexes we
obtained yellow crystals of 1-C(O)Me by slow evaporation of
the solvent from a dichloromethane solution of this complex.
Figure 1 discloses the resulting solid-state structure. The
j
complex crystallizes in the triclinic P1 space group with one
molecule of complex in the asymmetric unit and one-half of a
dichloromethane molecule as solvate (see Experimental Section
for details). The bond lengths and angles of this complex are
not unusual in comparison with available X-ray data for related
mononuclear bis-dppe Ru(II) acetylide complexes and warrant
no further comments.14,18
In Situ Generation of the Ru(III) Complexes and IR/
ESR Characterization. The corresponding Ru(III) complexes
1-F[BF4], 1-H[BF4], 1-OMe[BF4], and 1-NMe2[BF4] were
generated in situ by oxidizing these compounds with acetyl-
ferricinium tetrafluoroborate. An excess of this oxidant was
necessary to push the reaction to completion in the case of
1-NO2[BF4], 1-C(O)H[BF4], and 1-C(O)Me[BF4]. Monitoring
solutions of 1-NO2[BF4] and 1-OMe[BF4] evidenced that the
(19) Paul, F.; Mevellec, J.-Y.; Lapinte, C. J. Chem. Soc., Dalton Trans.
2002, 1783–1790.

2256 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Figure 3. UV-vis-near-IR spectra of CH2Cl2 solutions of (a)
1-NO2 and (b) 1-NMe2 on application of potentials of ca. 0.9 and
0.2 V, respectively, vs SCE (Fc/Fc+ ) 0.46 V) at 298 K in an
OTTLE cell.
protons, were the only ones detected, the more informative and
presumably more shifted signals of the functional aryl group
remaining undetected.11
Figure 2. ESR spectra in CH2Cl2/1,2-C2H4Cl2 (1:1) glasses between
+
295 and 70 K for 1-NMe2
.
Spectroelectrochemical Characterization of the Ru(III)
Complexes. In order to obtain additional data on these Ru(III)
complexes, the electrochemical oxidation of a Ru(II) compound
possessing a strongly electron-withdrawing substituent (1-NO2)
and of compounds with strongly electron-releasing substituents
(1-OMe and 1-NMe2) were monitored in an OTTLE cell in the
UV-vis-near-IR range (Figures 3a,b). Note that the spectro-
electrochemical data for the phenyl complex 1-H have been
previously reported by one of us.4
Table 2. ESR Spectroscopic Dataa for
[trans-Cl(η2-dppe)2Ru(CtC-C6H4X)][BF4] Complexes
X
g1
g2
g3
g
∆g
NO2
1.766
1.818
1.835
1.901
1.896
1.958
1.994
1.993
1.955
1.988
1.997
2.046
2.039
2.061
2.040
2.037
2.777
2.683
2.650
2.489
2.519
2.309
2.102
2.100
2.166
2.163
2.161
2.145
2.151
2.109
2.045
2.043
1.011
0.865
0.815
0.588
0.623
0.351
0.108
0.107
C(O)H
C(O)Me
F
H
OMe
NMe2
Conversion to the corresponding oxidized species 1-X+ was
observed, the latter being characterized by a completely different
set of absorptions; in the case of compounds with electron-
releasing substituents, new intense absorptions appear in the
visible and near-IR range, leading to a darker color for the
oxidized species. In the OTTLE cell, the oxidations seem to be
reversible (in the chemical sense) only for compounds possess-
ing electron-releasing substituents. In contrast, for 1-NO2+, clean
isosbestic points could not be obtained. The spectrum of the
sample obtained after reducing back the in situ-generated
oxidized species was similar to that of the starting 1-NO2
complex, albeit of smaller intensity in the spectral window
b
NMe2
a At 77 or 80 K in CH2Cl2/C2H4Cl2 (1:1) glass. b Values for the
[PF6-] salt generated in situ using [(η5-C5H5)2Fe][PF6].
as 1-OMe+ or 1-NMe2 , an isotropic signal can still be observed
+
at room temperature, as shown in Figure 2 in the latter case.20
Attempts to characterize these radicals by 1H NMR analysis
were unrewarding, since only the most electron-rich Ru(III)
complexes gave rise to sufficiently stable paramagnetic species
in solution.21 Thus, after oxidation of 1-OMe or 1-NMe2 with
acetyl ferricinium tetrafluoroborate, the resulting solutions
exhibited very broadened signals in the diamagnetic range. These
signals, which certainly correspond to the dppe and methyl
+
scanned. In line with the high reactivity observed for 1-NO2
(21) For instance, a ca. 80% conversion to the carbonyl adduct [trans-
Cl(η2-dppe)2Ru(CO)]+ was evidenced in the case of 1-NO2 when this Ru(II)
complex was oxidized using NOPF6. This known cationic complex22 was
characterized by mass spectrometry, NMR and IR. MS (ESI): m/z 961.1
(M+•), calc for C53H48O1P4Ru1+ 961.1 (M+•). FT-IR (ν, KBr, cm-1): 1954
(RuCdO). 31P NMR (81 MHz, CDCl3, δ in ppm): 42.9 (s, 4P, dppe). 1H
NMR (200 MHz, CDCl3, δ in ppm): 7.45-6.70 (m, 80H, HAr), 3.19 (m,
8H, CH2). 31P NMR reveals that the formation of this compound is
apparently accompanied by the formation of a vinylidene-like Ru(II)
complex. For a closely related reference see ref 23.
(22) Szczecpura, L. F.; Giambra, J.; See, R. F.; Lawson, H.; Janik, T. S.;
Jircitano, A. J.; Churchill, M. R.; Takeuchi, K. J. Inorg. Chim. Acta 1995,
239, 77–85.
(23) Rigaut, S.; Monier, F.; Mousset, F.; Touchard, D.; Dixneuf, P. H.
Organometallics 2002, 21, 2654–2661.
(20) A noticeable feature in this variable-temperature (VT) study is the
occurrence of signals for the three tensors around 160 K narrower than at
70 K. We have currently no firm explanation for that phenomenon. We
tentatively relate it to the presence of conformers with quasi-similar ESR
signatures. These are possibly different dppe-based conformers but not
arylacetylide rotamers, as discussed later. Upon heating beyond the
coalescence temperature (presumably around 135 K), the initial inhomo-
geneously broadened tensors further broaden before eventually sharpening,
the latter because of the rapid interconversion taking place between
conformers to give the isotropic signal upon melting of the solvent glass.
Note also that the increasingly faster relaxation of the electronic spin with
temperature should also result in an overall broadening, which explains
the overall loss of intensity of the ESR signal upon heating.

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2257
free electron g-value (ge ) 2.0023) and concomitantly reduce
the anisotropy ∆g of the signal. This means that the organo-
metallic radicals 1-X+ resemble organic radicals more and more
as the X substituent becomes more and more electron-releasing.
The best fits for g were obtained with σ+ ESPs, while the
best fits for ∆g were obtained with the regular Hammett ESPs.
The equations of the linear fits for g and ∆g are given in
equations 2a and 2b.
g ) 0.047σ+p + 2.138
∆g ) 0.591σp + 0.577
(2a)
(2b)
Figure 4. Plot of the Ru(III)/Ru(II) oxidation potentials (V) vs
Hammett ESPs (σ) for 1-X complexes in CH2Cl2. The data for the
previously reported meta-fluoro9 complex have been added for
comparison.
DFT Calculations on Model Compounds. Theoretical
computations were performed on model Ru(II/III) complexes
4-NO2/4-NO2 , 4-H/4-H+, 4-OMe/4-OMe+, 4-NMe2/4-NMe2
+
+
in solution,20 this suggests that some decomposition occurred
for this radical during the measurement.
and the precursor complex trans-5, in which the chelating dppe
ligands have been replaced by 1,2-diphosphinoethane (dpe)
ligands. Two conformations were considered for 4-X0/+ com-
plexes, one where the aryl plane and the ethane bridges of the
Linear Free Energy Relationships (LFERs) with
Electronic Substituent Parameters (ESPs). To assess the
possibility of sizable electronic substituent effects, we have
investigated if any correlation could be found between electronic
substituent parameters (ESPs) and characteristic redox or
spectral signatures of the Ru(II) compounds 1-X. A very good
(R2 ) 0.98) LFER is obtained between the σ Hammett ESPs24
and the redox potentials corresponding to the Ru(II)/Ru(III)
oxidation of 1-X (eq 1 and Figure 4). In line with related LFERs
previously obtained for 2-X and 3-X,6,7 the positive slope reflects
the fact that an electron-releasing substituent renders the
ruthenium-centered oxidation more facile, and the almost perfect
linear fit suggests an essentially electronic origin for this
phenomenon.
dpe ligands are roughly parallel (4|)0/+ and a second one (4 )0/+
,
where the plane of the functional aryl ring roughly bisects the
dpe ligands (Chart 2). For comparison purposes, DFT computa-
tions were also performed on 6-NO2+, 6-H+, 6-OMe+, and
6-NMe2 in two similar conformations (i.e., with the plane of
the functional aryl ring bisecting the dpe and cyclopentadienyl
+
ligands).
The structures of the 4-X model compounds were optimized
without symmetry constraints. The largest energetic differences
between the two conformations are found with electron-releasing
groups, with a maximum of ca. 0.02 eV between the two
conformations examined. The most stable configuration is that
in which the functional aryl ring is roughly parallel to the dpe
ethylene bridge, consistent with the available X-ray data for
several 1-X representatives.14,18,25 As a check for the compu-
tational accuracy, we have verified that the bond lengths found
for 4|-NO2 after optimization matched quite well those reported
for 1-NO2 by Long et al. (Supporting Information).18 Energies
of the frontier molecular orbitals (MOs) for Ru(II) complexes
are shown in Figure 6. The computations reveal that the rotation
of the Cl(dpe)2Ru fragment around the acetylide axis slightly
affects the HOMO-LUMO gap (up to 0.12 eV), as well as the
MO ordering. Nevertheless, the global description of the
electronic structure remains very similar, whatever orientation
of the ruthenium moiety is retained for the neutral systems. The
two closely lying highest occupied MOs (HOMO and HO-
MO-1) are mainly metal and acetylide in character (ca.
E0(V) ) 0.305σ + 0.422
(1)
Fair to excellent fits were also obtained with the energy (in
cm-1) of the lowest-lying electronic (MLCT) transition (R2 )
0.99), with the 13C NMR shifts of the R- and ꢀ-carbon atoms
(R2 ) 0.98 and 0.92, respectively) of the acetylide ligand, or
with νCtC expressed in cm-1 (R2 ) 0.87) against the σ- ESPs
(Supporting Information).
In the case of the corresponding Ru(III) parents 1-X+,
electron-releasing substituents seem to decrease the Ru(III)
acetylide stretching frequency according to the poor correlation
obtained. Much more significant LFERs could be evidenced with
ESR data (Figures 5a,b). These trends reveal that electron-
releasing substituents shift the mean g-value g closer to the
Figure 5. (a) Plot of the ESR mean g-value and (b) of the g-tensor anisotropy vs Hammett ESPs for [trans-Cl(η2-dppe)2RuCtC(4-
C6H4X)][BF4] complexes 1-X+ (X ) NO2, C(O)H, C(O)Me, F, H, OMe, NMe2).

2258 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Figure 6. Molecular orbital diagram of the Ru(II) complexes 4|-NO2, 4|-H, 4|-OMe, and 4|-NMe2. Frontier MOs having a sizable metallic
character are indicated on the left-hand side.
Chart 2. Mononuclear Model Complexes Used in the DFT Calculations and Numbering Scheme Used
46-13% and 30-39%, respectively). These MOs roughly
correspond to the perpendicular π-manifolds on the acetylide
ligand. The HOMO corresponds to the π-manifold conjugated
with the X substituent except in the complex 4|-NO2, where
the order is inverted. The phenylacetylide character of these
two MOs increases slightly concomitantly with the decrease
of the Ru character, when going from 4-NO2 to 4-OMe. For
all the compounds, the LUMOs are Ru-P antibonding, except
for 4-NO2, where the LUMO is an MO essentially localized on
the NO2 fragment. Accordingly, this complex shows a markedly
smaller HOMO-LUMO gap than the other 4-X complexes.
Without this specific difference, the HOMO-LUMO gap
slightly decreases when going from the most electron-withdraw-
ing substituent to the most electron-releasing one (from 2.72 to
2.22 eV).
spin-MOs (R and ꢀ) possessing a strong metal character (two
unoccupied and four occupied) are shown in Figure 7 for these
complexes in the perpendicular conformation (4 -X)+. Calcula-
tions reveal that the metal contribution to the higher lying spin-
MOs is dominated by one type of d atomic orbital. Actually,
the SOMO and the two lower lying MOs correspond to the “t2g”
set of the Ru(III) ion (pseudo-Oh symmetry). However, both
the R-SOMO and R-SOMO-1 contain an important acetylide
+
character (Supporting Information). In the case of 4-NO2 , aryl-
and nitro-based MOs (SOMO-3, SOMO-6, and SOMO-7)
are found between these filled d-based spin-orbitals. In 4-X+
radicals, the filled frontier π-spin-orbital of dominant dxz
character is more strongly stabilized by electron-withdrawing
substituents than is that of dyz character, resulting in a crossing
+
between these spin-orbitals for 4-NO2
.
7,12 The rotation of the
The computed ionization potentials for 4-X correlate linearly
with the first oxidation potentials measured for the corresponding
1-X complexes by cyclic voltammetry (Supporting Information).
Upon oxidation, one electron is removed from the HOMO or
HOMO-1 depending on the substituent and on the conforma-
tion of the functional aryl ring. Regardless of the nature of the
substituent, the most stable conformation of 4-X+ radicals is
the perpendicular one (Table 3). The energies of the six frontier
(24) (a) March, J. AdVanced Organic Chemistry Reactions, Mechanisms
and Structures, 4th ed.; J. Wiley & Sons: New York, 1992. (b) Hansch, C.;
Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165–195.
(25) Note that in the Ru(II) complexes, the stability of the parallel
conformation is possibly also enforced by the steric hindrance of the phenyl
groups of the dppe ligands and by packing forces in the crystal. In solution
at ambient temperature, however, the rotation of the functional aryl group
around the acetylide axis is facile for these compounds.

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2259
Table 3. Calculated Mulliken Spin Densities (in electrons) for Selected Atoms in [trans-Cl(η2-dpe)2RuCtC(4-C6H4X)]+ (4-X+) and
[trans-(η2-dpe)2RuCl2]+ (trans-5+) Complexes (see Chart 2 for atom numbering)
4-X+
X
a
b
Cl
Ru
Pa
CR
Cꢀ
C1
C2
C3
C4
X
∆Eb
c
NO2
|
|
|
|
0.110
0.105
0.082
0.081
0.060
0.057
0.039
0.043
0.366
0.398
0.313
0.300
0.255
0.294
0.195
0.235
0.004
-0.003
0.000
-0.001
0.001
-0.001
0.001
-0.001
0.067
0.048
0.112
0.087
0.146
0.124
0.164
0.142
0.275
0.265
0.250
0.251
0.193
0.201
0.140
0.148
-0.026
-0.032
-0.006
-0.010
0.038
0.031
0.074
0.065
0.090
0.095
0.102
0.099
0.072
0.072
0.038
0.040
-0.040
-0.043
-0.044
-0.043
-0.004
-0.005
0.035
0.111
0.116
0.160
0.152
0.116
0.111
0.067
0.065
0.018
0.020
0.000
0.000
0.068
0.069
0.183
0.173
742
0
645
0
532
0
387
0
d
c
H
d
c
OMe
NMe2
d
c
d
0.032
trans-5+
0.190a
0.654
-0.007
b
a Mean value. Relative energy between the two conformations (cm-1). c Parallel conformation. d Perpendicular conformation.
Figure 7. Molecular orbital diagram of the Ru(III) complexes (4 -NO2)+, (4 -H)+, (4 -OMe)+, and (4 -NMe2)+. Frontier MOs having a
sizable metallic character are indicated on the left-hand side.
functional aryl ring also significantly affects the energies of the
frontier orbitals, albeit not their ordering (Supporting Informa-
tion). The energetic gap between the ꢀ-SOMO and ꢀ-SOMO-1
is maximized in the most stable 4 -X+ conformation.
The spin distributions computed for 4-NO2 , 4-H+, 4-OMe+,
+
and 4-NMe2+ are given in Table 3 for two different orientations
of the aryl ring. While the spin density is spread over the
π-conjugated arylacetylide ligand, it is strongly influenced by
the X substituent. Indeed, the atomic spin densities on Ru and
Cꢀ increase from 0.23 and 0.15 to 0.40 and 0.26 electron,
respectively, while that on CR slightly decreases from 0.14 to
0.05 electron, when going from the most electron-releasing to
the most electron-withdrawing substituents, in line with a lesser
delocalization of the electronic hole on the X substituent. The
spin remains mainly located on the metal and to a lesser extent
on the chlorine atom or on the CR or Cꢀ carbon atoms. In terms
of overall density, these calculations indicate that more spin
density is present on the arylacetylide ligand than on the metallic
end group (Table 3). In terms of MO location, the unpaired
Figure 8. Comparison of the spatial distribution of spin densities
spin density shows up in the π-manifold conjugated with the
aryl ring regardless of the nature of the X substituent and seems
to be only marginally affected by rotation (Table 3), in contrast
to what happens for 6-X+ radicals (Figure 8).
The g-tensor components were computed for 4-X+, trans-5+
(Table 4), and 6-X+ (Supporting Information). These computa-
tions reveal a rhombic tensor for all these radicals, as experi-
mentally observed for 1-X+ and 2-X+.7 Then, for 4-X+ radicals,
computed for both conformations of [trans-Cl(η2-dpe)2RuCtC(4-
C6H4X)]+ (X ) NO2 and NMe2) model complexes (4-X+) and the
corresponding [(dpe)(η5-C5H5)RuCtC(C6H5)]+ analogues (6-X+).
The Mulliken spin density on the ruthenium atom (SpinRu) is also
indicated.
sizable substituent effects on the mean g-value are clearly
evidenced. These complexes exhibit a reduced asymmetry with
increasing electron-releasing capability of the X substituent. The

2260 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Table 4. Computed ESR g-Values for the Model Complexes
[trans-Cl(η2-dpe)2RuCtC(4-C6H4X)]+ (4-X+) and
[trans-(η2-dpe)2RuCl2]+ (trans-5+)
For the cationic Ru(III) congeners, calculations also indicate the
occurrence of several intense transitions. Their composition needs
to be carefully considered due to the possible occurrence of spin
contamination.28 The present TD-DFT data can nevertheless be
used as a rough guide to assign the observed transitions for 1-X+
(Table 5) taking place at the vis/near-IR edge. The intense
transitions calculated around 11 000 cm-1 for 4-X+ radicals have
a dominant LMCT character and mostly originate from MOs on
the chlorine atom. Consistent with the measurements on 1-X+
radicals, their oscillator strength is computed to increase with the
electron-releasing character of the X substituents, while their
energies are only marginally affected. The intense transitions found
in the 16 000-23 000 cm-1 spectral region have no true LMCT
character, since no marked charge transfer takes place along the
acetylide axis; they are more appropriately described as πfdRu
transitions distributed over the chlorine-metal-arylacetylide axis.
Transitions with a marked MLCT character are computed at higher
energies, around 30 000 cm-1.
4-X+
X
conformer
g1
g2
g3
giso
∆g
NO2
1.833
0.632
1.233
1.931
1.257
1.594
1.975
1.819
1.897
1.986
1.951
1.968
1.925
0.725
1.325
2.009
1.330
1.669
2.034
1.872
1.953
2.032
1.988
2.010
2.645
3.513
3.079
2.404
3.219
2.812
2.218
2.596
2.407
2.139
2.282
2.211
2.134
1.623
1.879
2.115
1.935
2.025
2.075
2.096
2.086
2.052
2.074
2.063
0.812
2.881
1.846
0.473
1.962
1.218
0.243
0.777
0.510
0.153
0.331
0.243
|
mean
H
|
mean
OMe
NMe2
|
mean
|
mean
trans-5+
1.499
1.542
1.752
1.597
0.253
calculations reveal a significantly larger effect of the rotation
of the functional phenylacetylide ligand on the mean values and
on the anisotropy than that induced by a change of the X
substituent (Table 4). The values computed for the perpendicular
conformation (4 -X+), the most stable for the oxidized com-
pounds 4-X+, correspond much better with the experimental
ESR data determined for 1-X+. Both the anisotropy and the
mean g-value computed for 4 -X+ are quite close (within 3%)
to the experimental values and follow the observed substituent-
dependent trends (Table 2). The slight discrepancies are
attributed to the simplification of some ligands coordinated to
the ruthenium in the model compounds and to the neglect of
the surrounding medium (solvent and counterions).
In order to assign the shoulder at ca. 12 160 cm-1 for
1-NMe2+ (Figure 3), we examined more closely the computed
excitations possessing a dominant ligand field (LF) character.
For each 4-X+ complexes, two d-d forbidden transitions
corresponding to SOMO-1/SOMO and SOMO-2/SOMO
excitations were found. While the former LF excitation always
constitutes the lowest energetic transition (2930-5460 cm-1
,
f< 2 × 10-4), the second is computed to occur at higher energy
and appears to be slightly more intense (13 200-16 000 cm-1
,
f < 3 × 10-3).29 However, for 4-NMe2+, the match with the
+
shoulder experimentally observed at 12 160 cm-1 for 1-NMe2
remains poor.30 More likely, this shoulder corresponds to a
vibronic transition involving the acetylide stretch in the LMCT
excited state, since an energetic difference of 1940 cm-1 is found
with the absorption attributed to this state (Table 1).
Finally, the first excitation energies were computed for the
complexes 4-X/4-X+ (Table 5) and for 6-H/6-H+ using the TD-
DFT approach.26 The match between the computed values
gathered for the most stable 4-Xn+ conformer (n ) 0, 1) under
vacuum and the experimental data obtained in dichloromethane
solutions for 1-Xn+ compounds (n ) 0, 1), where the molecules
can thermally rotate, can be considered as satisfying.27 The most
intense transitions (f > 0.05) computed for the most stable
conformations of the 4-Xn+ (n ) 0, 1) complexes are given in
Table 5, along with the available experimental data for 1-X
complexes.
For the neutral Ru(II) parents (4|-X), only a few transitions
below 30 000 cm-1 have a significant oscillator strength (f g
0.05). These appear to be multiconfigurational MLCT excitations
from metal- and chloride-based MOs toward aryl-based π*
MOs, except for the methoxy complex 1-OMe. For this
compound, the most intense transition involves a dominant
charge transfer contribution from metal-centered MOs toward
π* MOs located on the phosphorus. Corresponding absorption
bands were experimentally detected (within 2000 cm-1 error
margin) for 1-X complexes. Computations also reproduce rather
well the shift to higher energy of these transitions for 4|-X
complexes as the substituent becomes more electron-releasing.
Discussion
This work has afforded evidence for the existence of sizable
electronic substituent effects for 1-X and 1-X+ complexes. These
are immediately apparent in the linear dependence of the redox
potentials (Figure 4) corresponding to the first oxidation of these
complexes on the Hammett ESPs,31 but also on other charac-
teristic signatures for the Ru(II) and Ru(III) complexes (Figure
5 and Supporting Information).
Substituent Effects on the Bonding in the Ru(II) Com-
plexes. In a similar manner to these of 2-X, electron-releasing
substituents facilitate the oxidation of the neutral 1-X
complexes. Comparison with data previously reported for 2-X
reveals that for a given substituent the ruthenium-centered
oxidation of 1-X takes place at slightly higher potentials
(210-230 mV) than for the corresponding 2-X analogues.7
This was expected on the basis of the slightly lower electron-
releasing capability of the “trans-Cl(η2-dppe)2RuCtC-”
(28) Casida, M. E.; Ipatov, A.; Cordova, F. In Time-dependent Density-
functional Theory; Marques, M. A. L., Ullrich, C., Nogueira, F., Rubio,
A., Gross, E. K. U., Eds.; Springer: Berlin, 2006.
(26) Because of the simplified structure considered for these model
compounds, any transitions involving the π or π* MOs of phenyl rings of
the dppe ligand in 1-X and 1-X+ are overlooked. Since πfπ* transitions
of this kind are expected above 35 000 cm-1 (ca. 4.3 eV), excitations were
not computed above this value.
(27) To a have a perfect fit with the experimental data, a systematic
study of all the conformers should have been done (dynamical study).
However, results for 4|-X and 4 -X or 4|-X+ and 4 -X+ indicate that
rotation of the functional aryl ring induces an energetic shift up to 5000
cm-1, which largely overwhelms the solvent effect without actually changing
the nature of the transitions. Under such circumstances, calculations
including the solvent effect were not systematically undertaken.
(29) Even when located in the spectral range investigated, the oscillator
strengths of these forbidden LF transitions are however seemingly insuf-
ficient to permit their detection under the spectro-electrochemical conditions
used to generate the 1-X+ radicals.
(30) Alternatively these SOMO-1/SOMO LF transitions could cor-
respond (within 3300 cm-1) with the lowest intensity transitions detected
in the near-IR range which were attributed to “πfd” transitions. However,
on the basis of calculations, such an assignment is poorly supported by the
substituent effect on their energies. Indeed, according to the present
computations, all these forbidden LF transitions should be shifted toward
higher energies (∆E ≈ 2020 cm-1) when the X substituent becomes more
electron-releasing.12

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2261
Table 5. Energy (cm-1) and Composition of the First Excitation Energies (oscillator strength f g 0.05, transition percentage g7%) below 35 000
cm-1, Computed for [trans-Cl(η2-dpe)2Ru(CtC-C6H4X)]n+ (4|-X/4 -X+;; n ) 0, 1; X ) NO2, H, OMe, NMe2) Model Complexes vs
Experimental Values (cm-1) for the Corresponding [trans-Cl(η2-dppe)2Ru(CtC-C6H4X)]n+ Complexes (1-X/1-X+; n ) 0, 1; X ) NO2, H, OMe,
NMe2)
X
calculateda νmax (f b)
composition
major assignment
observeda νmax (ꢀc)
n ) 0
NO2
18 670 (0.36)
23 915 (0.17)
32 125 (0.07)
33 730 (0.14)
86% 59af61a
12% 58af61a
80% 58af61a
10% 59af61a
69% 51af61a
10% 50af61a
28% 59af68a
23% 59af67a
16% 59af69a
10% 59af70a
Ru f C6H4NO2
20 750 (13.1)
Cl f C6H4NO2
ndd
ClRuCtC f C6H4NO2
Ru f P + C6H4NO2
30 300-34 000 (sh, 5.8-11.9)
38 460 (34.7)
ndd e
,
H
27 100 (0.07)
30 835 (0.28)
61% 52af55a
33% 52af57a
49% 52af57a
23% 52af55a
10% 50af55a
7% 52af61a
Ru f C6H5
Ru f C6H5
31 350e (23.0)e
38 480e (50.0)e
ndd
OMe
25 830 (0.06)
31 700 (0.39)
82% 58af61a
7% 58af64a
36% 58af65a
25% 58af64a
11% 56af61a
10% 58af61a
65% 56af61a
14% 57af68a
Ru f C6H4OMe
Ru/Cl f P/C6H4OMe
33 560 (sh, 21.0)
34 420 (0.08)
Cl/Ru f C6H4OMe/P
Ru f P/C6H4NMe2
Ru f P/C6H4NMe2
ndd
38 760 (sh, 41.4)
24 000 (sh, 4.0-6.0)
32 470 (26.0)
NMe2
23 695 (0.06)
31 250(0.48)
92% 61af64a
53% 61af69a
31% 59af64a
63% 59af64a
19% 61af69a
8% 59af69a
32 430 (0.27)
ndd
40 000 (46.7)
n ) 1
NO2
11 070 (0.11)
17 540 (0.06)
92% 58af60a (ꢀ)
82% 52af60a (ꢀ)
14% 59af61a (R)
71% 59af61a (R)
11% 52af60a (ꢀ)
39% 57af61a (R)
17% 58af61a (ꢀ)
13% 46af60a (ꢀ)
77% 59af65a (R)
Cl f Ru
Cl/P f Ru
11 600 (5.0)
16 500 (2.4)
21 910 (0.28)
27 590 (0.12)
Ru f NO2
Cl f NO2
22 220 (sh,4.6)
25 510 (5.2)
33 800 (0.11)
11 500 (0.09)
18 150 (0.12)
29 030 (0.28)
35 570 (0.10)
Ru f CtCC6H4NO2
Cl f Ru
30 300 (sh, 10.2)
37 000 (32.1)
H
86% 50af52a (ꢀ)
10% 49af52a (ꢀ)
90% 46af52a (ꢀ)
12 040e (10.0)e
ClRuCtCC6H5 f Ru
Ru/Cl f CtCC6H5
ClRu f CtCC6H5
16 980e (1.0)e
27 290e (7.0)e
29 830e (13.0)e
75% 52af55a (R)
10% 50af55a (ꢀ)
44% 50af55a (ꢀ)
29% 50af55a (R)
35 710e (52.9)e
36 510e (53.0)e
11 960 (11.9)
17 120 (2.6)
OMe
11 460 (0.14)
16 360 (0.10)
91% 56af58a (ꢀ)
77% 54af58a (ꢀ)
14% 52af58a (ꢀ)
72% 58af61a (R)
8% 58af62a (R)
82% 58af62a (R)
58% 57af64a (R)
11% 56af61a (ꢀ)
10% 58af66a (R)
Cl f Ru
ClRuCtCC6H4OMe f Ru
27 630 (0.30)
Ru f CtCC6H4OMe
26 180 (13.8)
28 640 (0.08)
34 720 (0.06)
Ru f C6H4
Ru f P
28 700 (sh, 7.8)
35 900 (sh, 41.0)
37 590 (45.9)
10 220 (14.7)
12 160 (sh, 4.8)
16 950 (0.8)
24 150 (15.3)
32 680 (15.8)
NMe2
11 300 (0.20)
90% 59af61a (ꢀ)
Cl f Ru
15 560 (0.13)
26 920 (0.52)
33 680 (0.12)
86% 57af61a (ꢀ)
86% 61af64a (R)
48% 60af67a (R)
19% 59af64a (ꢀ)
16% 59af64a (R)
ClRuCtCf Ru
Ru f CtCC6H4NMe2
Ru/Cl f P/CtC-C6H4NMe2
39 060 (41.6)
c
a The calculated excited states are 1A. b Computed transition moment under vaccum. Experimental absorption coefficients (ꢀ) in 103 M-1 cm-1
.
d Not detected. e Taken from ref 4.
fragment relative to the “(η2-dppe)(η5-C5Me5)RuCtC-”
fragment previously evidenced.32 As indicated by the slopes
of the linear fits, this substituent effect on the redox potential
is slightly more pronounced than it was for 2-X complexes
(eq 1; 0.305 vs 0.235 for 1-X vs 2-X, respectively).
Otherwise, the substituent effect on spectroscopic signatures
is quite similar within experimental error for both series
(Supporting Information). These data also resemble those
reported for the 3-X iron analogues.6 Again, the best fits are
obtained with σ- ESPs rather than with regular Hammett

2262 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Scheme 3. Valence Bond-Based Representation of the Substituent-Dependent Delocalization of the Unpaired Electron in 1-X
and 1-X+ Complexes ([Ru] ) trans-(dppe)2Ru)
Chart 3. Selected Mononuclear Acetylide d6 Model
complemented by a new mesomeric form (E) proposed to
rationalize the concomitant decrease in spin density observed
on the chloro ligand.
Complexes Previously Used in DFT Computations
A closer examination reveals that while the atomic spin
density computed for the most stable conformations of 4 -X+
and 6 -X+ are quite similar for most X substituents (Table 6),
more significant differences exist for the parallel conformers.
While the spatial localization of the spin density is not markedly
affected by rotation of the aryl ring in octahedral complexes
4-X+, significant differences are evidenced in the case of piano-
stool radical cations 6-X+, especially when strongly electron-
attracting X substituents are appended to the aromatic ring
(Table 3 and Figure 8).11,12
ESPs in LFER correlations involving spectroscopic data,
which tends to indicate the prevalence of mesomeric effects
on the bonding.6,7 A similar valence bond (VB) scheme can
thus be proposed to rationalize the observed substituent
effects (a in Scheme 3).
As previously stated for 2-X/2-X+ complexes, a bond
weakening of the acetylide linkage takes place upon oxidation
of 1-X complexes (Table 1). This effect, which has already been
rationalized on the basis of MO considerations,6,7,12 is slightly
larger for the 1-X/1-X+ complexes regardless of the substituent.
Considering the rather similar spin distributions for both series
of compounds in the oxidized state (b in Scheme 3), the larger
bond weakening taking place upon oxidation for 1-X relative
to 2-X might be ascribed to a lesser delocalization according
to the VB (Scheme 3a) in the neutral state.
Low-Energy Electronic Transitions for 1-X and 1-X+
Complexes. The assignment previously proposed by Stranger
and Humphrey for the first intense electronic excitation in 1-H
is confirmed here by our TD-DFT computations. As shown by
the LFER with the UV data of the 1-X complexes (Supporting
Information), the energy of this transition is decreased for
electron-withdrawing X substituents, in line with its ruthenium-
to-aryl MLCT character along the metal-acetylide axis. This
substituent effect, reminiscent of that previously reported for
2-X,7 is also qualitatively reproduced by our computations.
In contrast to the similarity existing between the low lying
excited states of the Ru(II) complexes 1-X and 2-X, significant
differences are evidenced for the corresponding Ru(III) radicals
1-X+ and 2-X+. Thus, 1-X+ radicals exhibit much more intense
electronic absorptions in the near-IR range, as revealed by the
available spectral data (Figure 3).7,10 Still in line with the
assignment of the electronic transitions proposed for 1-H+ by
Stranger and Humphrey and in spite of the different theoretical
approach presently used (TD-DFT instead of ∆SCF),4 the most
intense near-IR transitions of 1-X+ are computed to be
dominantly LMCT transitions originating from chloride-based
MOs. This contrasts with the situation prevailing for 2-X+
analogues, for which only very weak transitions with a strong
In support of such a proposal, DFT calculations performed
on the model complexes 4-X and 6-X reveal that the electronic
structure of 1-X strongly resembles that of 2-X or 3-X in terms
of energy ordering of the frontier MOs. This statement is also
in line with previous theoretical studies carried out on the related
model compounds 7-X lacking the chelating dpe ligand,4,5,8,33
but also on previous studies involving piano-stool model
complexes such as 8-X and 9-X, related to 2-X and 3-X (Chart
3).6,7,10-12 In this connection, a detailed comparison between
the frontier MOs of 4-X and 6-X in the two redox states is given
in Figure 9.
Substituent Effects on the Bonding in the Ru(III)
Complexes. The spin delocalization on the arylacetylide frag-
ment also seems to not differ significantly between the two
families of Ru(III) cations 1-X+ and 2-X+, in spite of their
different coordination spheres. Calculations on 4-X+ and 6-X+
show that delocalization of the spin density on the arylacetylide
ligand is strongly favored by electron-releasing substituents,
which efficiently compete with the trans-chloride ligand for
delocalizing the spin density. Thus, a qualitatively similar VB
scheme to that for 2-X+ can also be proposed for 1-X+ to
rationalize the observed substituent effect (b in Scheme 3),6,7
(31) For related works on acetylide complexes evidencing LFERs on
redox potentials, see for instance: (a) Ying, J.-W.; Cordova, A.; Ren, T. Y.;
Xu, G.-L.; Ren, T. Chem.-Eur. J. 2007, 13, 6874–6882. (b) Kuo, C.-K.;
Chang, J.-C.; Yeh, C.-Y.; Lee, G.-H.; Wang, C.-C.; Peng, S.-M. J. Chem.
Soc., Dalton Trans. 2005, 3696–3701. (c) Hurst, S. K.; Xu, G.-L.; Ren, T.
Organometallics 2003, 22, 4118–4123.
(32) Slightly lower σm and σp ESPs were found for 1-X relative to 2-X
(-0.33 vs -0.47 and -0.39 vs -0.52, respectively).7,9
(33) (a) Delfs, C. D.; Stranger, R.; Humphrey, M. G.; Mac Donagh,
A. M. J. Organomet. Chem. 2000, 607, 208–212. (b) Powell, C. E.;
Cifuentes, M. P.; McDonagh, A. M.; Hurst, S. K.; Lucas, N. T.; Delfs,
C. A.; Stranger, R.; Humphrey, M. G.; Houbrechts, S.; Asselberghs, I.;
Persoons, A.; Hockless, D. C. Inorg. Chim. Acta 2003, 352, 9–18.

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2263
Figure 9. Comparison of the energy (eV) of the frontier MOs of the [trans-(η2-dpe)2ClRuCtC(4-C6H5)]n+ model complexes (n ) 0,1;
4-H/4-H+) and the corresponding [(η2-dpe)(η5-C5H5)Ru(CtCC6H5)]n+ analogues (n ) 0,1; 6-H/6-H+). The spin-MOs are shown for the
cationic species. The most intense (allowed) transitions of these compounds are also drawn.
Table 6. Comparison of the Calculated Mulliken Spin Densities for
[trans-Cl(η2-dpe)2RuCtC(4-C6H4X)]+ Complexes (4 -X+) and
[(η2-dpe)(η5-C5H5)RuCtC(4-C6H4X)]+ (6 -X+) Complexes (X )
NO2, H, OMe, NMe2)
ESR Anisotropy and Spin Delocalization in Ru(III)
Radicals. Another noticeable difference between 1-X+ and 2-X+
radicals is manifested in their ESR signature. Indeed, while the
substituent effect on the mean g-value is rather similar in
amplitude for both series, the effect on the anisotropy of the
signal is markedly larger for 1-X+ (Figure 10). Thus, solely on
the basis of the ∆g values, a much larger change in the spin
delocalization seems to take place for 1-X+ relative to 2-X+
along the series.
However, the computed spin densities for 4-X+ and 6-X+
clearly indicate that this is not the case (Table 6). In spite of
the similar spin distribution, much larger changes in the ESR
anisotropies are found for 4-X+ (Table 4) relative to the
corresponding 6-X+ cations (Supporting Information). Actually,
the anisotropies computed for 4-X+ and 6-X+ are in good
accordance with those experimentally derived for 1-X+ and
2-X+. This evidences that the change in anisotropy from one
family of compounds to the other cannot be reliably used to
compare the relative magnitudes of spin present at the metal
center. However, within a given family, a fair correspondence
is apparent between the spin density on the metal center and
the computed anisotropies (Figure 10b), especially for 6-X+,
where a good linear correlation can be evidenced (R2 ) 0.99).
Thus, in spite of the inherent difficulties in studying such Ru(III)
radicals by NMR, the changes in spin delocalization in Ru(III)
radicals and closely related arylacetylide analogues can be
conveniently characterized experimentally by means of ESR.
This proves especially true for 1-X+ radicals, considering the
large changes in anisotropy presently evidenced along the
substituent series.
4 -X+
6 -X+
X
NO2
H
OMe NMe2 NO2
H OMe NMe2
Cl
0.105 0.081 0.057 0.043
Ru
CR
Cꢀ
0.398 0.360 0.294 0.235 0.377
0.048 0.087 0.124 0.142 0.026
0.265 0.251 0.201 0.148 0.282
0.343 0.291 0.231
0.066 0.101 0.124
0.265 0.211 0.155
0.252 0.269 0.271
C1-4 0.188 0.253 0.274 0.274 0.191
X
0.020 0.000 0.069 0.173 0.022 -0.011 0.057 0.154
d-d LF character have been found in the near-IR range, while
the more intense LMCT transitions show up below 1000
nm.7,10,12,34 TD-DFT calculations indicate that similar (forbid-
den) LF transitions take also place in the near-IR range for 1-X+
radicals. However, given the relatively low oscillator strengths,
they are presumably not detected under the spectroelectrochemi-
cal conditions employed. The shoulder at 12 160 cm-1 for
+
1-NMe2 is therefore tentatively assigned as resulting from a
νCtC vibronic progression (1940 cm-1),4 similar progressions
having often been observed for related organic or organometallic
radicals.35-37 Thus, the notable change in optical properties
between 1-X+ and 2-X+ can be ascribed to the presence of
chloride-based p-type AOs, which strongly mix with the metal-
based d AOs in the frontier MOs of 1-X+ radicals, and also to
the higher symmetry of the coordination sphere of 1-X+. As
previously emphasized,4 this makes the former type of com-
plexes uniquely suited to exploit third-order NLO redox
switching based on multiphotonic absorption properties.
DFT computations shed light on the origin of the rhombic
anisotropy observed for the ESR signals of 1-X+ complexes. A
priori, the latter might have originated from the nonequivalence
of the two π-manifolds of the alkynyl ligand induced by the
presence of the aryl ring, but also from the presence of two
chelating diphosphines, which lower the C4V symmetry around
the ruthenium center. The rhombic signal computed for trans-
[(η2-dpe)2RuCl2]+ suggests that the diphosphine ligands con-
stitute a determining factor in this respect, since the ESR
(34) These were alternatively termed ꢀ-HOSOfꢀ-LUSO-1 and
ꢀ-HOSO-1fꢀ-LUSO-1 in a less “localized” description.10
(35) Maurer, J.; Linseis, M.; Sarkar, B.; Schwederski, B.; Niemeyer,
M.; Kaim, W.; Zalis, S.; Anson, C.; Zabel, M.; Winter, R. F. J. Am. Chem.
Soc. 2008, 130, 259–268.
(36) (a) Klein, A.; Lavastre, O.; Fiedler, J. Organometallics 2006, 25,
635–643. (b) Adams, C. J.; Pope, S. J. A. Inorg. Chem. 2004, 43, 3492–
3499.
(37) Choi, M.-Y.; Chan, M. C.-W.; Zhang, S.; Cheug, K.-K.; Che, C.-
M.; Wong, K.-Y. Organometallics 1999, 2074–2080.

2264 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
Figure 10. (a) Comparative plot of the g-tensor anisotropy vs Hammett ESPs for [trans-Cl(η2-dppe)2RuCtC(4-C6H4X)][BF4] complexes
1-X+ ((: X ) NO2, C(O)H, F, H, OMe, NMe2) and [(η2-dppe)(η5-C5Me5)RuCtC(4-C6H4X)][OTf] complexes 2-X+ (9: X ) NO2, CN, F,
H, OMe, NH2). (b) Computed ESR anisotropy values against computed spin densities on the metal center for 4-X+ (b) and 6-X+ (2) model
compounds.
signature computed for trans-5+ should be axial if a pseudo-
C
4V symmetry is preserved around the ruthenium. A posteriori,
this emphasizes the need to use 4-X+ model compounds instead
of 7-X+ models to accurately derive ESR parameters by DFT.
Then, the good match obtained between ESR tensors calculated
for the most stable conformer 4 -X+ (Table 4) and the ESR
data available for 1-X+ radicals (Table 2) strongly suggests that
it is largely this particular conformer that is trapped in the
solvent-glass at low temperatures.
ˆ
ˆ
[gij ) geδij + 2ꢁ ∑m*0( 0|Ii|m m|Ij|0 )/(E0-Em)] (3)
gxx ) ge + 2ꢁ(c0c2)2/(∆2)
gyy ) ge - 2ꢁ(c0c3)2/(∆3) - 6ꢁ(c0c4)2/(∆4)
gzz ) ge - 2ꢁ(c0c1)2/(∆1)
(4a)
(4b)
(4c)
Figure 11. Schematic spin-restricted representation of the frontier
MOs and dominant metal character for d5 rhombic radicals such
as [trans-Cl(η2-dppe)2RuCtC(4-C6H4X)]+ (1-X+).
in the metal-centered spin density, or they reflect the substituent-
induced changes in the SOMO/SOMO-1 gaps (∆1). Given that
similar spin distributions were computed for 4 -X+ and 6 -X+
for a specific substituent, the increased g-anisotropy stated for
4 -X+ (Figure 8) must originate from larger relative changes
in ∆1 along the series, in line with the lower SOMO/SOMO-1
gaps computed for 4 -X+ relative to 6 -X+.
In order to understand further the origin of the observed
anisotropy differences between both series of compounds, we
decided to use the ligand field approach to derive the value of
the anisotropy by following the classic second-order perturba-
tional treatment based on the ruthenium d-orbital contribution,
as we did previously with the organoiron radicals 3-X+ (eq 3).12
Taking the z axis along the acetylide ligand, the expressions of
the gii values are quite simple given the pseudo-Oh symmetry
of these compounds (eqs 4a-c), since the g-tensor is diagonal
in this reference system (Figure 11).38 These equations have
been given for a SOMO with dxz character (i.e., perpendicular
conformation), but rigorously similar expressions result for a
SOMO of dyz character (i.e., parallel conformation) with the
gxx expression exchanged for gyy. Because gzz dominates the
anisotropy of the ESR signal, the main component of
the g-tensor anisotropy (g3) is along the z direction, similar to
the situation prevailing in the case of 2-X+ radicals and for
which similar gzz expressions have been proposed.7 Thus, the
changes in ∆g for these compounds have essentially two origins;
either they reflect the substituent-induced changes in c0 and c1
(eq 4c), which are themselves mostly determined by the changes
While the ligand field approach constitutes a wonderful tool
to qualitatively interpret the origin of the changes in ESR
anisotropy, a word of caution is needed here, given that this
approach was originally derived for metal-centered radicals. It
therefore becomes increasingly more approximate for delocal-
ized radicals such as 4 -X+ and 6 -X+ because of the decreasing
metal character of the frontier MOs. Thus, while the trends
deduced from eqs 4a-c are certainly qualitatively correct when
comparing 4 -X+ and 6 -X+, a quantitative agreement with ∆g
cannot be expected. Accordingly, when SOMO/SOMO-1 gaps
and d AO coefficients extracted from the present DFT calcula-
tions are used in eq 4c, much smaller anisotropies are found
than those actually computed for these radicals using the ESR
routine implemented in the ADF program. Also, according to
eqs 4a-c, two of the principal g-tensors values should be above
ge and one below (g1 < ge e g2 < g3). This condition is however
neither fulfilled by the principal g-tensor components computed
by DFT for 4 -X+ radicals featuring electron-withdrawing
substituents nor by these experimentally measured for 1-X+
radicals. This is certainly because the SOMO is close in energy
(38) In these equations, ge stands for the free electron g-value, ꢁ for the
spin-orbit coupling constant, cn for coefficients of the d AOs in the frontier
MOs, according to Figure 11, and ∆n for the absolute values of the
corresponding transition energies.

Ru(III) σ-Arylacetylide Radicals
Organometallics, Vol. 28, No. 7, 2009 2265
Chart 4. Selected Mononuclear d5 Alkenyl Radicals
electronic substituent effects on their various spectral and redox
signatures along the series. These effects on the bonding of these
compounds are comparable to those previously reported for
the related family of ruthenium analogues [(η2-dppe)(η5-
C5Me5)RuCtC(4-C6H4X)]n+ (2-Xn+). They can be similarly
rationalized by resonance with different cumulene-like VB
mesomers, depending on the redox state of the complex (Scheme
3). ESR measurements on 1-X+ radicals and DFT calculations
on corresponding Ru(III) model complexes reveal an important
influence of the substituent on the electronic spin delocalization
along the functional arylacetylide ligand. In spite of a much
more pronounced change in anisotropy of the ESR spectra along
the 1-X+ series compared to 2-X+, a comparable electronic
delocalization is computed to take place. This finding can be
rationalized on the basis of simple ligand field considerations.
It evidences that ESR anisotropy does not constitute a reliable
(and absolute) reporter permitting comparison of the metal-
centered spin densities of different families of functional
arylacetylide Ru(III) radicals, even when isolobal metal-
containing fragments are considered. However, the large sub-
stituent sensitivity of the ESR anisotropy presently evidenced
for 1-X+ radicals suggests that this technique constitutes a very
accurate method to experimentally gauge the metal-centered spin
density for analogous Ru(III) arylacetylides in which the
coordination sphere has been preserved. More generally, we
believe that the set of data presently gathered on 1-X and 1-X+
will prove very useful for future studies concerned with mono-
or polynuclear architectures containing [trans-Cl(dppe)2Ru]n+
fragments (n ) 0, 1).
n
Recently Characterized by ESR (R ) Bu, Ph, pyrenyl)
Table 7. Crystal Data, Data Collection, and Refinement Parameters
for 1-C(O)Me · 1/2CH2Cl2
formula
fw
cryst syst
space group
a (Å)
C62H55Cl1O1P4Ru1, 1/2CH2Cl2
1118.92
triclinic
j
P1
12.9876(5)
13.3094(7)
17.4046(7)
74.848(4)
75.788(3)
64.045(4)
2581.1(2)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
Dcalcd (g cm-3
)
1.440
cryst size (mm)
F(000)
0.32 × 0.32 × 0.20
1154
abs coeff (mm-1
)
0.575
number total/unique refns
no. of variables
final R
18 621/10 745
634
0.0523
Rw
0.1424
1.055
goodness of fit/F2 (Sw)
to the SOMO-1 in these particular cases, rendering the
perturbative treatment at second order used to derive these
equations no longer valid. In accord with that statement, the
proportionality between the metal-centered spin density and ∆g
computed for 6 -X+ radicals is lost for 4 -X+ radicals with
strongly electron-withdrawing substituents (Figure 10b).
Rhombic ESR spectra have recently been reported for closely
related octahedral Ru(III) acetylide cations.36,39 For instance,
Maurer and co-workers have reported ESR data for the
complexes 10-R, 11-R, and 12-R (Chart 4).35 Similar to our
most electron-rich compounds 1-NMe2+, the observation of a
pseudoisotropic signal at ambient temperatures, along with very
weak anisotropy at low temperature (∆g < 0.03 for several
representatives), was taken as diagnostic of dominantly organic-
based radicals.35 The lower anisotropy of their ESR spectra
compared to that of the 1-X+ radicals would suggest a larger
electronic delocalization of the unpaired electron on the organic
framework for these organometallic radicals. However, subse-
quent to this investigation, which points out the decisive
influence of geometrical and electronic features on the ESR
anisotropy for a constant spin distribution, the relative electronic
delocalization between 1-X+, 10-R, 11-R, and 12-R radicals
cannot be reliably inferred from their ∆g-values alone, especially
when considering the changes taking place in the coordination
sphere of these radicals.
Experimental Section
Computational Details. DFT calculations were carried out using
the Amsterdam Density Functional (ADF) program.40 The model
compounds [trans-Cl(η2-dpe)2RuCtC(4-C6H4X)]n+ and [(η2-dpe)(η5-
C5H5)Ru-CtC(4-C6H4X)]n+ (X ) NO2, H, OMe, NMe2; n ) 0,
1) were used in order to reduce computational effort. Electron
correlation was treated within the local density approximation
(LDA) in the Vosko-Wilk-Nusair parametrization.41 The nonlocal
corrections of Becke42 and of Perdew43 were added to the exchange
and correlation energies, respectively. The numerical integration
procedure applied for the calculations was developed by te Velde
et al.44 The standard ADF TZP basis set was used, i.e., a triple-ꢁ
Slater-type orbital (STO) basis for Ru 4d and 5s, and a single-ꢁ
function for 5p of Ru. A triple-ꢁ STO basis set was employed for
H 1s and for 2s and 2p of C, N, and O, extended with a single-ꢁ
polarization function (2p for H; 3d for C, N and O). Orbitals up to
1s, 2p, and 4p were kept frozen for C, O and N, P, and Ru,
respectively. Full geometry optimizations (assuming C1 symmetry)
were carried out on each complex, using the analytical gradient
method implemented by Versluis and Ziegler.45 Geometry optimi-
zation convergence criteria were more drastic than default ones
(energy change < 0.0005 hartree, atomic position displacement
< 0.005 Å). Harmonic vibrational frequency calculations were
performed to check that the geometries are stationary points. Spin-
unrestricted calculations were performed for all the open-shell
Conclusion
(40) (a) SCM; ADF 2007.01; Theoretical Chemistry, Vrije Universiteit:
Amsterdam, The Netherlands, 2007. (b) te Velde, G.; Bickelhaupt, F. M.;
Fonseca Guerra, C.; van Gisbergen, S. J. A.; Baerends, E. J.; Snijders, J.;
Ziegler, T. Theor. Chem. Acc. 2001, 22, 931–967.
(41) Vosko, S. D.; Wilk, L.; Nusair, M. Can. J. Chem. 1990, 58, 1200–
1211.
We have shown here that the family of [trans-Cl(η2-
dppe)2RuCtC(4-C6H4X)]n+ complexes (1-Xn+; n ) 0, 1; X )
NO2, C(O)H, C(O)Me, F, H, OMe, NMe2) exhibits sizable
(42) (a) Becke, A. D. J. Chem. Phys. 1986, 84, 4524–4529. (b) Becke,
A. D. Phys. ReV. A 1988, 38, 3098–3100.
(43) Perdew, J. P. Phys. ReV. B 1986, 33, 8822–8824.
(44) te Velde, G.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84–98.
(45) Versluis, L.; Ziegler, T. J. Chem. Phys. 1988, 88, 322–328.
(39) (a) Maurer, J.; Sarkar, B.; Kaim, W.; Winter, R. F.; Zalis, S. Chem.-
Eur. J. 2007, 13, 10257–10272. (b) Adams, C. J.; Bowen, L. E.; Humphrey,
M. G.; Morrall, J. P. L.; Samoc, M.; Yellowlees, L. J. J. Chem. Soc., Dalton
Trans. 2004, 4130–4138.

2266 Organometallics, Vol. 28, No. 7, 2009
Gauthier et al.
systems considered. The Cartesian coordinates of the optimized
geometries are given as Supporting Information.
with anisotropic thermal parameters. H atoms were included in their
calculated positions. A final refinement on F2 with 12775 unique
intensities and 658 parameters converged at wR(F2) ) 0.1883 (R(F)
) 0.0846) for 8075 observed reflections with I > 2σ(I). Selected
bond lengths and angles are given in Figure 1.
Time-dependent density functional theory (TD-DFT) calculations
were performed on the optimized structures. The excitation energies
and oscillator strengths were calculated following the procedure
described by van Gisbergen and co-workers.46 In this case, the
functional PBE was used.47 The EPR g-tensor calculations were
calculated as implemented in ADF.48 In this case, relativistic
corrections were taken into account using the ZORA (zeroth order
regular approximation) spin-orbit Hamiltonian with the appropriate
basis set.49
Crystallography. Data collection of crystals of 1-C(O)Me ·
1/2CH2Cl2 was performed on an APEXII Bruker-AXS diffracto-
meter (Table 7) at 110 K. The structure was solved by direct
methods using the SIR97 program,50 and then refined with full-
matrix least-squares methods based on F2 (SHELX-97)51 with the
aid of the WINGX program.52 All non-hydrogen atoms were refined
Acknowledgment. These studies were facilitated by travel
support (ARC, Australia, and CNRS, France). F.P. and N.G.
thank the CNRS for financial support and Region Bretagne
for a Ph.D. grant. K.C. and J.-F.H. thank the CINES and
the IDRIS-CNRS for computing facilities. N.T. thanks the
AUF for a postdoctoral grant. M.G.H. is an ARC Australian
Professorial Fellow.
Supporting Information Available: Experimental part for the
synthesis and characterization of 1-X complexes. Solution IR and
UV-vis-near-IR spectra for selected 1-Xn+ (n ) 0,1) complexes.
LFERs obtained for 1-X. Fitting data (slopes and R2 indices).
Composition of the frontier MOs computed for 4-X/4-X+, com-
parison of bonding parameters, correlations between computed IPs
and measured E0 values, dipole moments, low-lying excitations
computed for 4-X/4-X+ and low-lying excitations computed for
6-H/6-H+. Spin densities and ESR parameters computed for 6-X+.
CIF files for 1-C(O)Me · 1/2CH2Cl2. Final atomic positional
coordinates, with estimated standard deviations, bond lengths and
angles and anisotropic thermal parameters have been deposited at
the Cambridge Crystallographic Data Centre and allocated the
deposition number CCDC 668173. This material is available free
of charge via the Internet at http://pubs.acs.org.
(46) van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J. Comput.
Phys. Commun. 1999, 118, 119–138.
(47) (a) Hammer, B.; Hansen, L. B.; Norskov, J. K. Phys. ReV. B 1999,
59, 7413–7421. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV.
Lett. 1996, 77, 3865–3868.
(48) (a) Schreckenbach, G.; Ziegler, T. J. Phys. Chem. A 1997, 101,
3388–3399. (b) van Lenthe, E.; van der Avoird, A.; Wormer, P. E. S.
J. Chem. Phys. 1997, 107, 2488–2498.
(49) (a) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys.
1993, 99, 4597–4610. (b) van Lenthe, E.; Baerends, E. J.; Snijders, J. G.
J. Chem. Phys. 1994, 101, 9783–9792. (c) van Lenthe, E.; Ehlers, A. E.;
Baerends, E. J. J. Chem. Phys. 1999, 110, 8943–8953.
(50) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
J. Appl. Crystallogr. 1999, 32, 115–119.
(51) Sheldrick, G. M. SHELX97-2. Program for the refinement of crystal
structures; Univ. of Go¨ttingen: Germany, 1997.
(52) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
OM801138Q