Dissecting out the effect of Ru-OAr bonding in a five-coordinate complex of ruthenium (II)

Article abstract of DOI:10.1139/V08-147

Blue Ru(o-cat)(PPh₃)₃ (5; o-cat = ortho-catecholate), obtained in 94% yield by reaction of RuCl₂(PPh₃) ₃ (4) with dithallium catecholate, was characterized by NMR, MALDI-MS, IR, and single crystal X-r

Full text of DOI:10.1139/V08-147

361
Dissecting out the effect of Ru-OAr bonding in a
five-coordinate complex of ruthenium (II)1
Sebastien Monfette, João A. Duarte Silva, Serge I. Gorelsky, Scott J. Dalgarno,
Eduardo N. dos Santos, Maria H. Araujo, and Deryn E. Fogg
Abstract: Blue Ru(o-cat)(PPh3)3 (5; o-cat = ortho-catecholate), obtained in 94% yield by reaction of RuCl2(PPh3)3 (4)
with dithallium catecholate, was characterized by NMR, MALDI-MS, IR, and single crystal X-ray analysis, and by a
combined electronic spectroscopy and time-dependent density functional theory (TD-DFT) study. The frontier orbitals
in 5 participate in a low-energy charge transfer excitation involving donation from the Ru-catecholate π bond (largely
localized on catecholate) to a low-lying σ* orbital on Ru-PPh3(apical). The energy of this transition increases on binding
a pyridine ligand in the sixth site.
Key words: ruthenium aryloxide, catecholate, phosphine, electronic spectroscopy, time-dependent DFT.
Résumé : Le Ru(o-cat)(PPh3) bleu (5; o-cat = ortho-catécholate) qui est obtenu avec un rendement de 94% par réac-
tion du RuCl2(PPh3)3 (4) avec le catécholate de dithallium a été caractérisé par RMN, spectrométrie de masse
“MALDI”, spectroscopie IR et par diffraction des rayons X par un cristal unique ainsi que par une combinaison de
spectroscopie électronique et d’une étude de théorie de la fonctionnelle de densité en fonction du temps. Les orbitales
frontières du produit 5 participent dans une excitation par transfert de charge de basse énergie impliquant le don
d’électron à partir de la liaison π du catécholate de ruthénium (principalement localisée sur le catécholate) vers une or-
bitale σ* de basse énergie du Ru-PPh3(apical). L’énergie de cette transition augmente lors de la fixation d’un ligand pyri-
dine sur le sixième site.
Mots-clés : aryloxyde de ruthénium, catécholate, phosphine, spectroscopie électronique, théorie de la fonctionnelle de
densité en fonction du temps.
[Traduit par la Rédaction] Monfette et al. 367
Introduction
gaged in a program of study focusing on the largely ne-
glected (2) potential of the anionic sites to expand the modu-
larity, tunability, and lifetime of the Ru-NHC catalysts (3)
(NHC = N-heterocyclic carbene). Particular success has
emerged for derivatives containing monodentate or κ2-
chelating aryloxide ligands (Fig. 1). These exhibit, inter alia,
increased lifetime (for 1), enhanced efficiency (2 and 3), and
a high kinetic selectivity for cyclic vs. oligomeric products
in macrocycle RCM (2, 3; RCM = ring-closing metathesis)
(3).
Emerging findings from our laboratory have focused our
attention on the importance of the Ru-aryloxide electronic
interactions in determining not merely catalyst activity, but
also the kinetic bias toward RCM products. In the present
work, we wished to evaluate the electronic interactions spe-
cific to the basal Ru-aryloxide moiety within the square py-
ramidal coordination geometry, unperturbed by the variety
of additional bonding interactions present in the alkylidene
complexes of Fig. 1. While five-coordinate Ru complexes
containing monodentate phosphine and phenoxide ligands
(e.g., RuX(OPh)(PPh3)3) would be suitable candidates for
study, such species are unstable with respect to isomeri-
zation to piano-stool structures (Scheme 1) (4), unless the
aryloxide ligand is stabilized by electron-withdrawing sub-
stituents that add to the complexity of our intended elec-
tronic analysis.
Olefin metathesis is now one of the most powerful meth-
ods in use for the construction of C=C bonds (1). Of the
many well-defined catalysts developed for this versatile re-
action, the Grubbs-class catalysts, RuCl2LL′(=CHPh), have
had the greatest impact in organic synthesis owing to their
relative robustness and ease of handling. We have been en-
Received 3 June 2008. Accepted 31 July 2008. Published on
the NRC Research Press Web site at canjchem.nrc.ca on
25 November 2008.
This paper is dedicated to Professor Dick Puddephatt, in
honour of his many contributions to chemistry and the
Canadian chemistry community.
S. Monfette, S.I. Gorelsky, and D.E. Fogg.2 Department of
Chemistry, Center for Catalysis Research & Innovation,
University of Ottawa, Ottawa ON K1N 6N5, Canada.
S.J. Dalgarno.3 School of EPS-Chemistry, Heriot-Watt
University, Edinburgh EH14 4AS Scotland.
J.A. Duarte Silva, E.N. dos Santos, and M.H. Araujo.
Departamento de Química– ICEx, Universidade Federal de
Minas Gerais, 31270–901 Belo Horizonte, Brazil.
1This article is part of a Special Issue dedicated to Professor
R. Puddephatt.
2Corresponding author (e-mail: dfogg@uottawa.ca).
3Present address: Department of Chemistry, University of
Missouri, 601 S. College Ave, Columbia, MO 65211, USA.
In earlier work, we established that σ–π isomerization of
aryloxide donors in these labile, coordinatively unsaturated
Can. J. Chem. 87: 361–367 (2009)
doi:10.1139/V08-147
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Can. J. Chem. Vol. 87, 2009
Fig. 1. Key Ru-aryloxide catalysts (3); one isomer shown for 2.
IMes = N,N′-bis(mesityl)imidazol-2-ylidene, py = pyridine.
Scheme 2.
Scheme 3.
Scheme 1.
coordination geometry represents the energetic minimum by
DFT optimization. The steric constraints in 5 may thus cause
averaging of the 31P environments in solution, via a series of
equilibria such as those depicted in Scheme 3. Notably, no
loss of PPh3 in solution is evident by NMR analysis, despite
this steric pressure, and in contrast to the behaviour of the
corresponding dichloride complex 4 (6). This point is exam-
ined in more detail below.
species is not inhibited by chelation within large (seven-
membered) chelate rings (4a). The stability of the
catecholate ligand in 3, however, suggested that a smaller
chelate might stabilize our target systems. We therefore
sought to examine an alternative model complex, Ru(o-
cat)(PPh3)3 (5, o-cat = ortho-catecholate). Here we describe
the synthesis and structural characterization of 5 and an
analysis of its frontier orbital interactions by electronic
spectroscopy and time-dependent density functional theory
(TD-DFT) calculations.
Blocky blue crystals of 5 suitable for X-ray analysis were
obtained by slow evaporation of a benzene solution. An
ORTEP diagram is shown in Fig. 2 with crystal data in
Table 1. Only one five-coordinate Ru-catecholate complex,
Ru(o-cat)2(ϵN) 6 (7), has previously been structurally char-
acterized. In contrast with the slightly distorted square py-
ramidal geometry of 6, in which the nitrido ligand is only
0.6 Å above the basal plane, the structure of 5 exhibits sig-
nificant deviations, though it remains closer to square py-
ramidal than trigonal bipyramidal at Ru. Two “basal” PPh3
ligands lie trans to the catecholate oxygen donors (P(1)-
Ru(1)-O(1) = 144.61(4)°; P(2)-Ru(1)-O(2) = 158.53(4)°),
with the third phosphine approximately apical (P(3)-Ru(1)-
P(1) = 97.766(17)°; P(3)-Ru(1)-P(2) = 99.561(17)°;
P(3)-Ru(1)-O(1) = 116.13(4)°; P(3)-Ru(1)-O(2) = 98.45(4)°),
trans to the vacant site. The extent of distortion is also evi-
dent from the 0.05 Å difference in length between the two
Ru–P bonds in the basal plane (Ru(1)–P(1) 2.2954(5) Å;
Ru(1)–P(2) 2.3496(5) Å). The apical Ru–P bond (Ru(1)–
P(3) 2.2527(5) Å) is shorter by 0.04–0.09 Å. This is not due
to population of the Ru-P(3) σ*-orbital (LUFO+1 of
[Ru(PPh3)3]2+): while there is indeed a 19% population of
this orbital, the basal Ru–P bonds are likewise populated and
to a greater extent (22% for LUFO; 11% for LUFO+2). In-
stead, the decreased bond length is due to the apical position
of the phosphine ligand involved, and the consequent ab-
sence of a trans ligand that would give rise to a competing
donor–acceptor interaction. A similar effect was found for
the apical Ru–P bond in the dichloride analogue 4 (6).
The distorted geometry of 5 is unsurprising, given the ri-
gidity and small bite angle of the catecholate ligand and the
unfavourable steric interaction between the three cis-PPh3
ligands. In comparison, the crystal structure of 4, containing
a meridional arrangement of these ligands, shows little dis-
tortion in the bond angles about ruthenium (6). Similarly,
Results and discussion
Synthesis of Ru(o-cat)(PPh3)3 (5)
The addition of solid thallium catecholate to a homoge-
neous solution of RuCl2(PPh3)3 4 in THF caused a colour
change from brown to deep blue within 1 h at room temper-
ature, accompanied by precipitation of TlCl. 31P NMR anal-
ysis of the crude reaction mixture indicated clean formation
of a single Ru product, without liberation of PPh3. The sus-
pension was filtered through Celite, and the Ru product was
isolated in 94% yield by precipitation from THF–hexanes. It
was identified as Ru(κ2-O2C6H4)(PPh3)3 5 (Scheme 2) on the
basis of spectroscopic, crystallographic, and combustion
analysis. This complex exhibits high air-sensitivity even in
the solid state (possibly a function of the high-lying HOMO
in this system; vide infra).
The anaerobic MALDI-TOF mass spectrum (5) of 5 re-
vealed a well-defined isotope pattern for [M–PPh3]+· at m/z
734.4 Da. The facile elimination of one triphenylphosphine
group in the gas phase probably reflects the steric pressure
within the three approximately facial PPh3 ligands. Reten-
tion of all three of these ligands in the solid state is con-
firmed by X-ray analysis, as discussed below; their retention
1
in solution can be inferred from the H NMR integration
values as well as the absence of a signal for free PPh3 in the
31P NMR spectrum of the crude reaction mixture. Unex-
pectedly, however, a sharp 31P{1H} NMR singlet was ob-
served at 55.1 ppm, rather than the A2X pattern predicted on
the basis of the square pyramidal geometry of Scheme 2.
This singlet undergoes no change in multiplicity even on
cooling to –90 °C. We confirmed that the square pyramidal
© 2008 NRC Canada

Monfette et al.
363
Fig. 2. ORTEP diagram for Ru(o-cat)(PPh3)3 5·C6H6. Thermal el-
Fig. 3. Experimental and calculated electronic spectra for 5
lipsoids at 50% probability; hydrogen atoms omitted for clarity.
(solid black and red lines, respectively) and calculated spectrum
for 7 (dashed red line).
lengths within 5 (1.350(2) and 1.345(2) Å for C(1)–O(1) and
C(6)–O(2), respectively) are within the range of 1.34–1.47 Å
usual for Ru-catecholate complexes; benzoquinone com-
plexes exhibit shorter C–O bond lengths (1.27–1.31 Å (10)).
The magnitude and uniformity of C–C bond lengths within
Table 1. Crystal data and structure refinement for 5·C6H6
Formula
C66H55O2P3Ru
Formula mass
1074.08
2–
the O2C6H4 ligand (1.372(4)–1.407(4) Å) likewise support
Size (mm)
Colour, crystal morphology
Temperature (K)
0.6 × 0.44 × 0.42
Blue, block
173(2) K
formulation of 5 as a Ru-catecholate complex, as does the
presence of an IR band for νC-O at 1270 cm–1, which is not
observed for starting 4, but is present in the IR spectra of the
catecholate salts.
Wavelength (Å)
0.710 73
Crystal system, space group
Monoclinic, P21/c
The electronic structure of 5 was analyzed experimentally
by UV–vis spectroscopy and theoretically by use of TD-
DFT calculations (11–13) to establish the key metal-ligand
bonding contributions. Our interest was stimulated further
by the unusual blue color of 5, rare in Ru(II) complexes (for
examples see refs. 14–21), which could provide added in-
sight into its properties. A fragment molecular orbital
(FMO) analysis enabled the quantification of charge dona-
tion. Orbital interactions were considered in terms of dative
bonds between the lowest unoccupied fragment orbitals
(LUFOs) of the metal fragment [Ru(PPh3)3]2+ and the high-
a (Å)
b (Å)
c (Å)
13.3727(13)
17.1572(18)
23.022(2)
90
94.653(3)
90
5264.7(9)
4, 1.355
0.435
α (°)
β (°)
γ (°)
Volume (Å3)
Z, calcd. density (mg/m3)
Absorption coefficient (mm–1)
F(000)
2224
Data collection range
Index ranges
1.48° ≤ θ ≤ 27.07°
–17 ≤ h ≤ 12,
–17 ≤ k ≤ 21,
–22 ≤ l ≤ 28
21 831
10 952 [R(int) = 0.0224]
9287 [I > 2σ(I)]
Multi-scan
0.8383 and 0.7802
Full
10 952, 0, 649
1.032
R1 = 0.0286,
wR2 = 0.0716
2–
est occupied fragment orbitals (HOFOs) of the O2C6H4
ligand.
The calculated electronic spectrum is in very good agree-
ment with the experimental spectrum (Fig. 3). The latter,
measured in THF, is comprised of three absorption maxima of
near-identical intensity (16 000, 18 400, and 23 500 cm–1),
whereas TD-DFT predicts three principal bands (16 500,
19 700, and 23 200 cm–1), of which the latter two overlap
with two weaker bands at 18 000 and 23 600 cm–1. The band
energies thus correspond within ca. 500 cm–1 vs. the more
typical agreement of 2 000 cm–1 (11–13, 22); a minor differ-
ence in intensity is also evident. The level of theory was
therefore deemed appropriate for the analysis of the elec-
tronic transitions. Electron excitations contributing to each
band are summarized in Table 2.
The FMO analysis indicates that the formation of 5 in-
volves a significant (>2%) change in the electronic popula-
tion for only three orbitals on the Ru fragment. We therefore
confine our discussion of the metal-based orbital interactions
to these three acceptor orbitals. Contributions from Ru are
cited as the composite of s, p, and d contributions; those
from PPh3 are largely p in character (for individual constitu-
Reflections collected
Independent reflections
Observed reflections
Absorption correction
Max. and min. transmission
Refinement method
Data, restraints, parameters
Goodness of fit
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0375,
wR2 = 0.075
Largest diff. peak and hole (e Å–3)
0.558 and –0.279
six-coordinate Ru(II)-catecholate complexes containing
smaller neutral ligands such as PMe3 (8) or pyridine (9) form
reasonably regular octahedral complexes. The C–O bond
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Can. J. Chem. Vol. 87, 2009
Table 2. Electron excitations contributing to bands in the visible region for 5.
(TD-DFT (B3LYP/DZVP))
Exptl. energya
Calcd. energya
f b
Assignmentc
16.0
18.4
16.5
18.0
19.7
0.0370
0.0190
0.0338
H→L (44%), H-2→L (29%), H-1→L (10%)
H-1→L (57%), H→L (17%)
H-2→L (45%), H-3→L (24%)
H→L (15%)
H-3→L (31%), H-4→L (20%)
H→L+1 (15%)
H→L+1 (47%)
23.5
23.2
0.0272
0.0166
23.6
aBand locations in 103 cm–1.
bOscillator strength.
cH = HOMO; L = LUMO. Only major (> 10%) parent one-electron excitations shown; percentage contributions to
wavefunctions of excited states in parentheses.
Fig. 4. Lowest unoccupied fragment orbitals (LUFOs) of
[Ru(PPh3)3]2+ and their compositions (excluding phenyl
ontributions). Isosurface contour value for orbital images 0.03 au.
Table 3. Molecular orbital energies (E) and atomic contributions
for 4 and 5.
Orbital
–E (eV)
Ru (%)
PPh3 (%) X-ligand (%)
5.1
38.5
1.5
12.4
78.7
57.8
41.7
29.8
27.8
4, LUMO
4, HOMO
5, LUMO +1
5, LUMO
5, HOMO
5, HOMO –1
5, HOMO –2
5, HOMO –3
5, HOMO –4
2.03
5.10
1.07
1.81
4.62
5.26
5.43
5.80
6.13
47.3
55.6
7.0
38.5
12.8
34.3
46.5
53.3
59.3
47.6
5.9
91.5
49.1
8.5
7.9
11.8
16.9
12.9
Note: Atomic contributions evaluated by Mulliken population analysis.
ents see Fig. 4). The LUFO is 62% Ru and 38% PPh3 (of
which 21% is contributed from the P atoms) in character; cf.
relative contributions of 58% Ru + 42% PPh3 for LUFO+1,
and 59% Ru + 40% PPh3 for LUFO+2. The population of
each of these orbitals increases from its null value in the
non-interacting fragment to 22%, 19%, and 11%, respec-
tively, in 5. LUFO and LUFO+2 participate in forming the
two σ bonds with the ligand, while LUFO+1 forms a π bond
(19% × 2 = 0.38 e–). For the catecholate FMOs, turning on
the bonding interaction with Ru results in a significant
change in population for six occupied and one unoccupied
orbital. These are the HOFO (–21%, i.e., 21% depopula-
tion), HOFO–1 (–14%), HOFO–2 (–7%), HOFO–3 (–3%),
HOFO–6 (–5%), HOFO–7 (–4%), and LUFO (+5% popula-
tion). Thus, in addition to strong ligand-to-metal charge
donation (0.94 e–), formation of the complex involves signif-
icant polarization of the electron density on the catecholate
ligand through 5% population of the LUFO. This charge dis-
tribution description is consistent with the Mulliken popula-
tion analysis (23–26) and the NPA-derived charges assessed
for the catecholate ligand in the complex (–1.06 and –
1.20 au, respectively; NPA = natural population analysis).
The molecular orbitals that contribute to the visible spec-
trum of 5 are summarized in Table 3; visual depictions of all
of these are given in the supporting information.4 The
LUMO is a σ* orbital for the apical Ru-PPh3 bond (Fig. 5),
while LUMO+1 consists principally of the aromatic π*
orbitals of PPh3 with a 7% contribution from the Ru 4d
orbitals. The low energy of the LUMO of 5 derives from the
contribution of a single (apical) phosphine ligand to this σ*
orbital (pz(P)–dz2(Ru)); the other σ* orbital involves both
basal PPh3 ligands. The HOMO is a π bonding orbital
between the catecholate and Ru. HOMO-1, HOMO-2, and
HOMO-3 are also dominated by Ru-catecholate contribu-
tions: these are a largely non-bonding π orbital, a largely σ
nonbonding orbital, and a σ–π hybrid, respectively. Finally,
HOMO-4 is nonbonding, being composed of a Ru d orbital
and the catecholate π orbital.
For four of the five visible bands calculated for 5, the
LUMO (σ* orbital of the apical Ru-PPh3 bond) participates
4 Supplementary data contains molecular orbitals implicated in the visible spectrum of 5; tables of crystal data collection and refinement pa-
rameters, atomic coordinates, bond lengths, and angles, anisotropic displacement parameters and hydrogen coordinates, and NMR spectra
for 5. Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository
of Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3854. For more
information on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml. CCDC 689209 contains the crystallographic data for
this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2008 NRC Canada

Monfette et al.
365
Fig. 5. Frontier orbitals for (a) 4 and (b) 5. Isosurface contour
value for orbital images = 0.03 au.
rich coordination chemistry of this classic ruthenium precur-
sor (28)). The low lability of the PPh3 ligand in 5, evident
by NMR analysis, is further supported by the unreactivity of
the complex toward terminal alkynes, a facile, high-yield
route to cumulenylidene products for 4 (29). The difference
in behaviour lies in the stronger donation and back-donation
involving the basal PPh3 ligands in 5, which result in a
larger binding energy for Ru-P(basal) (–16.0 kcal mol–1 in
5 and –10.6 kcal mol–1 in 4) (1 cal = 4.184 J). The weaker
donation from the catechol ligand, relative to chloride, is an-
ticipated on the basis of the higher electronegativity of oxy-
gen vs. chlorine, reinforced by the capacity of the
catecholate phenyl ring to delocalize negative charge. Con-
sistent with this view, the NPA-derived charge for the
catecholate ligand is –1.20 au, while for the chloride ligands
the corresponding sum charge is –1.11 au.
Summary
The foregoing demonstrates that replacing chloride by
catecholate in the simple model system RuCl2(PPh3)3 raises
the energy of the X-based HOMO. By analogy, replacing
chloride by catecholate in Ru metathesis catalysts is ex-
pected to raise the energy of the corresponding Ru-X occu-
pied molecular orbital(s). While the nature and energy of the
frontier molecular orbitals in Ru metathesis catalysts has
been surprisingly little examined (30), it is clear that the
higher energy of the Ru-OAr HOMO will facilitate interac-
tion with any LUMOs of appropriate symmetry present
(which may include those for the alkylidene and bound ole-
fin as well as the neutral donor that serves as a proxy for in-
coming olefin). These amplified interactions enhance the
potential for modulating reactivity and selectivity by tuning
the electronic properties of the anionic donors. Important
steps in the catalytic cycle for olefin metathesis that may be
affected range from dissociation of the neutral donor (in 3,
the pyridine ligand), to olefin binding and activation, and po-
tentially, the key 2+2 cycloaddition step. Of additional inter-
est is the extent to which the energy of the Ru-X
(catecholate) HOMO is affected by the constrained bond ge-
ometry of the catecholate ligand. Future work will explore
the specifics of these interactions, and their impact on the
energy profile for metathesis in the RuX2(IMes)(py)(=CH2)
family of catalysts (X = Cl, o-cat, OC6F5).
in the electronic excitations. However, the LUMO+1, com-
posed of the π* orbitals of the aromatic rings of the PPh3
ligands (Table 3), is also implicated in the absorption bands
at 23 200 and 23 600 cm–1. To determine whether this or-
bital plays a significant role in the electronic spectrum, we
calculated the electronic spectrum of Ru(o-cat)(PMe3)3 (7),
which contains no π*(Ph) orbitals. The calculated spectra for
5 and 7 are very similar, as shown in Fig. 3 (7: three
absorption maxima at 16 300, 20 400, and 23 800 cm–1; cf.
the values for 5 noted above). We conclude that the LUMO
is more critical to the spectroscopic features in the visible
region than is LUMO+1. The intense blue colour of 5
(ε 3000 L mol–1cm–1) is thus due to charge transfer from the
Ru-catecholate π bond (localized mostly on catecholate) to
the low-lying σ* orbital on the apical Ru-PPh3 bond.
Replacing the two chloride ligands in 4 by catecholate
reduces the magnitude of the HOMO–LUMO gap, as evi-
denced by the change in colour from brown to blue. Consis-
tent with this, the calculated values drop from –3.06 eV for
4 to –2.81 eV for 5. The coordination number also affects
the energy of the relevant electronic transitions, as noted
above; Ru(o-cat)(PMe3)4 (8) and Ru(o-cat)(py)4 (9), for ex-
ample, are yellow in colour. While crystallographic analysis
has demonstrated that a phenyl ring blocks the sixth coordi-
nation site in the solid state for 4, the Ru–H distance
(2.82 Å, corresponding to a bond order of 0.03) precludes
the presence of an agostic C–H bond (27). We therefore ex-
clude octahedral coordination as a potential explanation for
the higher-energy visible transition for 4. The smaller
HOMO–LUMO gap in 5 is thus due principally to the higher
energy of the HOMO, the Ru-Papical σ* LUMO interaction
being less affected, as shown in Fig. 5 and Table 3.
Experimental
General procedures
Synthesis of 5 was carried out at room temperature (RT)
(23 °C) under N2 using standard drybox techniques. Dry,
oxygen-free solvents, obtained using a Glass Contour
solvent purification system, were stored over Linde 4 Å mo-
lecular sieves. Thallium catecholate (3d) and RuCl2(PPh3)3
(31) were prepared by the methods reported.
1H NMR (500 MHz), 13C (125 MHz), and 31P (121 MHz)
spectra were recorded on a Bruker Avance-500 spectrometer.
Chemical shifts are reported relative to TMS (1H, 13C) or
85% H3PO4 (31P) at 0 ppm. X-ray data were collected on a
Bruker SMART 1000 CCD diffractometer. IR spectra were
measured on a Bomem MB100 IR spectrometer. Inert-
atmosphere MALDI-MS analyses were carried out using a
While the smaller HOMO–LUMO gap present in 5 might
be expected to heighten reactivity, the resistance of this com-
plex to loss of PPh3 is in striking contrast to the behaviour of
4 (phosphine dissociation being the stepping-stone to the
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Can. J. Chem. Vol. 87, 2009
Bruker OmniFlex MALDI-TOF mass spectrometer equipped
with an N2 laser (337 nm), interfaced to an MBraun
glovebox (5). Data were collected in positive reflectron
mode, with the accelerating voltage held at 20 kV. Matrix
(pyrene) and analyte solutions were prepared in CH2Cl2 at
concentrations of 20 and 1 mg/mL, respectively. Samples
were mixed in a matrix/analyte ratio of 20:1. UV–vis spectra
were measured on a Varian Cary-50 spectrophotometer at a
scan rate of 600 nm/min. Samples were prepared under N2
by filling a Hellma screw-top optical glass cell with 2 mL of
a 0.24 mmol/L solution of 5 in THF and sealing prior to
analysis. Microanalyses were carried out by Guelph Chemi-
cal Laboratories Ltd., Guelph, Ontario, Canada.
Note: The toxicity of thallium (particularly in the +1 oxi-
dation state) is well-established (32). Care must be taken to
prevent introduction into the body by inhalation, ingestion,
or through the skin. All thallium reagents and wastes, in-
cluding contaminated solvents, were handled using double-
glove and secondary containment procedures, with separate
disposal of all wastes in accordance with government regula-
tions.
Structural determination
Blue, blocky crystals of 5 were grown by slow evapora-
tion of a saturated benzene solution. Data were collected on
a Bruker SMART 1000 CCD diffractometer with Mo Ka ra-
diation using the ω-scan mode. A single crystal (0.6 mm ×
0.44 mm × 0.42 mm) was mounted on a thin glass fiber us-
ing paraffin oil and cooled to the data collection temperature
(173 K). Data were corrected using the SADABS program
(Bruker). Structure solution in the space group P21/c was
performed with Patterson methods, completed with differ-
ence Fourier syntheses, and refined by full-matrix least-
squares procedures based on F2 using the SHELX-97 soft-
ware package. All non-hydrogen atoms were refined
anisotropically; hydrogen atoms were placed at geometri-
cally calculated positions and allowed to ride on their parent
atoms. Although the crystals were weakly diffracting, a sat-
isfactory structural solution was obtained.
Computational details
DFT calculations were carried out using the Gaussian 03
package (33). The X-ray structures of 4 (27b) and 5 were
used for these calculations, after adjusting all C–H distances
to 1.08 Å, as only aromatic C–H bonds are present in the
structure. All other interatomic distances were left unper-
turbed. That the square pyramidal structure represents a true
energy minimum for 5 was confirmed by geometry optimi-
zation. DFT calculations utilized the B3LYP (34) exchange-
correlation functional with the DZVP basis set (35) for all
atoms. Tight SCF convergence criteria (10–8 au) were used
for all calculations. The converged wave functions were
tested to confirm that they correspond to the ground-state
surface. Bond orders and the compositions and populations
of molecular orbitals were calculated using the AOMix pro-
gram (36). The energies and intensities of the lowest 30 sin-
glet-singlet transitions were calculated by TD-DFT.
Absorption profiles were calculated from TD-DFT bands by
the method reported (22), assuming for all electronic transi-
tions a bandwidth at half-height of 2500 cm–1 (a typical
value for complexes of the type described). Pseudo-Voigt
functions with 50% weights for contributing Gaussian and
Lorentzian functions were used to simulate the absorption
bands.
Synthesis of Ru(␬2-O,O′-O2C6H4)(PPh3)3 5
Solid thallium catecholate (296 mg, 0.573 mmol) was
added to a stirred solution of 4 (500 mg, 0.521 mmol) in
10 mL THF at RT. A colour change from brown to blue took
place over 1 h, and the solution became cloudy. The suspen-
sion was filtered through Celite to remove TlCl, and the fil-
trate stripped to dryness. Precipitation from THF–hexanes
and washing with hexanes (3 × 5 mL) afforded deep blue 5.
Yield 486 mg (94%). 1H NMR (C6D6, 500 MHz) δ: 7.39 (m,
2H, catechol CO-CH), 7.30 (m, 18H, o-CH of PPh3), 7.02
(m, 2H, catechol CH), 6.90 (m, 9H, p-CH of PPh3), 6.74 (m,
18H, m-CH of PPh3). 13C{1H} NMR (C6D6, 125 MHz) δ:
163.3 (s, catechol C-O), 137.4–137.1 (m, i-C of PPh3),
135.3–135.2 (m, o-CH of PPh3), 128.9 (s, p-CH of PPh3),
127.5–127.4 (m, m-CH of PPh3), 117.6 (s, catechol CH),
117.5 (s, catechol CH). 31P{1H} NMR (C6D6, 121 MHz) δ:
55.1 ppm (s); multiplicity unchanged down to –90 °C. IR
(Nujol, cm–1): νC-O 1270. Anal. calcd. for C60H49O2P3Ru: C
72.35, H 4.96%; found C 72.08, H 4.85%. MALDI-MS, m/z
(pyrene matrix): calcd. for [M-PPh3]+.: 734.1; found, 734.4.
Representative reaction of 5 and 3,3-dimethylbutyne
To a blue solution of 5 (14 mg, 0.014 mmol) in C6D6
(1 mL) was added 3,3-dimethylbutyne (10 µL, 0.084 mmol,
6 equiv). The reaction vessel was sealed and heated to 60 °C
in an aluminum block for up to 72 h, after which NMR anal-
ysis showed only unreacted 5.
Acknowledgements
This work was supported by Natural Sciences and Engi-
neering Research Council of Canada (NSERC) of Canada,
the Canada Foundation for Innovation, and the Ontario Inno-
vation Trust. NSERC and Coordenação de Aperfeiçoamento
de Pessoal de Nível Superior (CAPES) and Conselho
Nacional de Desenvolvimento Científico e Tecnológico
(CNPq) of Brazil are acknowledged for fellowships to SM
and JDS.
Representative reaction of 5 with 1,1-diphenylprop-2-
yn-1-ol
To a blue solution of 5 (25 mg, 0.025 mmol) in THF
(2 mL) was added solid 1,1-diphenylprop-2-yn-1-ol (6 mg,
0.029 mmol, 1.2 equiv). No reaction was evident by NMR
analysis at RT over a period of 24 h. Only the 31P NMR sig-
nal for 5 was present after heating for 1 h in an oil bath set
at 70 °C. Complex 5 remains a major species after heating
for 17 h, but it is accompanied by multiple products, sug-
gesting sample decomposition. Similar results were found on
use of up to 5 equiv of the alkyne.
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