Ruthenium complexes containing the hemilabile ligand PPh 2(CH2)P(O)PPh2 (dppmO): Reactivity towards CO and X-ray molecular structures of tcc-RuCl2(η2-dppmO) 2 and mer-RuCl3(η<sup

Article abstract of DOI:10.1016/j.poly.2005.02.026

Ruthenium (II) complexes with the hemilabile ligand Ph₂PCH ₂P(O)Ph₂ (dppmO) were obtained and characterized by ³¹P{¹H} NMR, IR and cyclic voltammetry. The reaction of the compound tcc-[RuCl₂

Full text of DOI:10.1016/j.poly.2005.02.026

Polyhedron 24 (2005) 1063–1070
www.elsevier.com/locate/poly
Ruthenium complexes containing the hemilabile ligand
PPh2(CH2)P(O)PPh2 (dppmO): reactivity towards CO and
X-ray molecular structures of tcc-RuCl2(g2-dppmO)2 and
mer-RuCl3(g1,g2-dppmO)2
a,
a,
a
Marcella P. Felicissimo *, Alzir A. Batista *, Antonio G. Ferreira ,
b
Javier Ellena , Eduardo E. Castellano
b
a
´
Departamento de Quımica, Universidade Federal de Sa˜o Carlos, Av. Trabalhador Sao-carlense 400, CEP 13565-905, Sa˜o Carlos (SP), Brazil
b
´
Instituto de Fısica de Sa˜o Carlos, Universidade de Sa˜o Paulo, CEP 13560-970, Sa˜o Carlos (SP), Brazil
Received 21 June 2004; accepted 25 February 2005
Available online 4 May 2005
Abstract
Ruthenium (II) complexes with the hemilabile ligand Ph2PCH2P(O)Ph2 (dppmO) were obtained and characterized by 31P{1H}
NMR, IR and cyclic voltammetry. The reaction of the compound tcc-[RuCl2(g2-dppmO)2] with carbon monoxide yielded the com-
plexes [RuCl2(CO)(g1,g2-dppmO)2] and [RuCl(CO)(g2-dppmO)2]PF6. For the tcc-[RuCl2(g2-dppmO)2] and [RuCl2(CO)(g1,g2-
1
dppmO)2] species, two dimensional NMR analyses 31P–31P gCOSY, 13C–1H HSQC, H–31P HMBC were performed. Based on
the resulting chemical shifts, coupling constants and correlations between 1H, 13C and 31P spectra it was possible to reveal the struc-
tures of these complexes in solution. The structure of the tcc-[RuCl2(g2-dppmO)2] complex was determined by X-ray diffraction,
confirming the NMR results. The mer-[RuCl3(g1,g2-dppmO)2] complex was characterized by EPR and its crystal structure was also
established by X-ray diffraction. The isomerization of tcc-[RuCl2(g2-dppmO)2] into cct-[RuCl2(g2-dppmO)2] was followed by UV–
Vis spectroscopy and 31P{1H} NMR.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Hemilabile ligands; Ruthenium; Biphosphine oxide; NMR; X-ray structures
1. Introduction
complex, and a monodentate ligand providing a free
coordination site for an incoming substrate (through
the labilization of the weakly bonded oxygen atom) [5].
The combination of a soft phosphino group with a hard
phosphoryl one in the same molecule enables biphosphine
monoxide ligands (BPMOs) to have different coordina-
tion modes depending on the transition metal involved.
In a recent study by Grushin, BPMOs were described as
an interesting species for the synthesis of model homoge-
neous catalysts allowing transformations at the metal
center, such as ligand exchange, isomerization, oxidative
addition, migratory insertion, reductive elimination,
among others [6]. The synthesis of complexes containing
Great interest has been devoted to transition metal
complexes containing the so-called hemilabile ligands,
due to their potential application as homogeneous cata-
lysts [1–5]. Phosphorus–oxygen hemilabile ligands react
with various metals of catalytic relevance due to their
ability to act as both a chelate ligand, stabilizing the metal
*
Corresponding authors. Tel.: +55 16 33739957; fax: +55 16 260
8350/33739976.
E-mail addresses: mafelici@iqsc.usp.br (M.P. Felicissimo), daab@
power.ufscar.br (A.A. Batista).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.02.026

1064
M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
biphosphine monoxide of metals such as nickel, palla-
dium, rhenium, rhodium and platinum has been exten-
sively described and some species have been found to be
efficient catalysts in oligomerization reactions [7,8]. On
the other hand various ruthenium complexes with O,
P ligands such as keto-phosphine, ether-phosphine,
ester-phosphine and o-phenylenobis(methyl(phenyl)-
phosphine) have been reported, showing the coordination
modes P ꢀ O: g1-P and P \ O: g2-O,P [9]. Some of these
compounds are regarded as holding interesting properties
in catalytic reactions [10].
The present study reports on the synthesis of Ru(II)
complexes with the hemilabile biphosphine monoxide li-
gand PPh2(CH)2P(O)Ph2 (dppmO). The behavior of the
tcc-[RuCl2(g2-dppmO)2] complex – chlorine ions in
trans positions, phosphorus and oxygen atoms in cis
positions – towards carbon monoxide was also investi-
gated and proved to be consistent with the predicted
hemilabile character of the ligand.
The dppmO ligand presents two chemically different
phosphorus atoms and the characterization of the syn-
thesized species through 1H and 31P NMR, reported
here, was a very effective tool in disclosing the phospho-
rus–phosphorus spin coupling systems. The reaction of
the biphosphine monoxide ligand with a Ru(III) precur-
sor yielded the mer-RuCl3(g1,g2-dppmO)2 complex. The
crystallographic structure of the latter was determined
by X-ray analysis, identifying a species analogous to
the mer-RuCl3(g1,g2-Ph2PCH2C(O)Oet)2 complex de-
scribed in the literature [9d].
Braun MB Series model spectrometer in the 4000–200
cmꢁ1 region. The elemental analysis was performed in
a Fison EA 1108 model.
The electrochemical experiments were performed at
room temperature in freshly distilled dichloromethane
containing 0.1 mol/L TBAP under argon atmosphere
(1 atm), using EG/PARC 273A electrochemical equip-
ment. A three-electrode system was used. The working
and auxiliary electrodes were a stationary platinum foil
and the reference electrode was Ag/AgCl 0.1 mol/L TBAP
in CH2Cl2, a medium in which ferrocene is oxidized at
0.43 V, with all potentials referred to this electrode.
2.1. tcc-[RuCl2(g2-dppmO)2] (t = Cl) (1)
RuCl2(PPh3)3 (0.050 g, 0.050 mmol) and
PPh2CH2P(O)Ph2 (0.042 g, 0.10 mmol) were dissolved
in acetone (10 mL) and the mixture was stirred for 1 h
at room temperature. During this time the color of the
solution changed from dark brown to light pink and
precipitation of a small amount of solid with the same
color occurred. To increase the precipitation ethyl ether
was added. The solid was then filtered and washed with
ethyl ether. Yield: 0.045 g (94%). Anal. Calc. for
C50H44P4O2Cl2Ru: C, 61.74; H, 4.56. Found: C, 61.69;
H, 4.57%. IR (CsI) (RuCl) 317 cmꢁ1; m(P@O) 1140
cmꢁ1. See Scheme 1.
2.2. cct-[RuCl2(g2-dppmO)2] (t = O) (2)
PPh2CH2P(O)Ph2 (0.23 g, 0.60 mmol) and [RuCl2-
(COD)]2 (0.10 g, 0.30 mmol) were added to a solution
of dichloromethane/methanol 1:3 (15 mL). The mixture
was stirred for 18 h. At the end of this period the sol-
vents were evaporated until only around 3 mL were left
and then ethyl ether was added. A light brown solid was
obtained, which was then filtered and dried under vac-
2. Experimental
All manipulations were performed under an inert
atmosphere of purified argon using Schlenk techniques.
The solvents were purified according to standard proce-
dures. The RuCl2(PPh3)3 [11] and [RuCl2(COD)]2 [12]
complexes as well as the PPh2(CH)2P(O)Ph2 [7d] ligand
were prepared according to the procedures described in
the literature. CO was generated from HCO2H with
H2SO4. All the NMR spectra were obtained in a 9.4 T
BRUKER DRX400 spectrometer at 298 K, using
TMS and H3PO4 85% as internal and external references
uum. Yield: 0.205
C50H44P4O2Cl2Ru: C, 61.74; H, 4.56. Found: C, 60.85;
g
(70%). Anal. Calc. for
H, 4.85%. IR (CsI). m(P@O) 1132 cmꢁ1
.
2.3. [RuCl2(CO)(g1,g2-dppmO)2] (3)
tcc-[RuCl2(g2-dppmO)2], complex (1), was dissolved
in 15 mL of dichloromethane and stirred under an atmo-
sphere of CO at room temperature. After 10 min the
1
for H and 31P (161 MHz), respectively. The IR spectra
were recorded as CsI pellets in a Bomen Hartmann and
RuCl2(PPh3)3
dppmO
∆
∆
2-dppmO)2]
CO
cct-[RuCl2(η
2-dppmO)2]
[RuCl2(COD)]2
tcc-[RuCl2(
η
dppmO
hν
CO + NH4PF6
[RuCl(CO)(η
2-dppmO)2]PF6
[RuCl2(CO)(η1
, η
2-dppmO)2]
Scheme 1. Summary of the reactions for Ru(II) complexes with the dppmO ligand.

M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
1065
light pink color of the solution turned to light yellow.
After the removal of around 10 mL of the solvent under
vacuum, ethyl ether was added, observing the formation
of a pale yellow solid which was then filtered and dried
under vacuum. This complex had its structure deter-
mined by 1H and 31P NMR. IR (CsI) m(RuCl) 320
mixture was evaporated until a volume of approximately
5 mL remained. A light orange precipitate was obtained
with the addition of 15 mL of ether. The compound ob-
tained was then filtered and dried under vacuum. Recrys-
tallization was obtained in a mixture of ethanol/
dichloromethane. Yield: 0.083 g (55%). Anal. Calc. for
C50H44P4O2Cl3Ru: C, 58.57; H, 4.33. Found: C, 59.23;
H, 4.34%. EPR (experimental) gy 2.347 and gz 1.833.
EPR (simulated) gx 2.415, gy 2.359 and gz 1.833.
cmꢁ1; m(PB@O) 1097 cmꢁ1; m(PD@O) 1166 cmꢁ1
m(CO) 1975 cmꢁ1
;
.
2.4. [RuCl(CO)(g2-dppmO)2]PF6 (4)
2.6. X-ray crystallographic analyses of complexes 1 and 5
tcc-[RuCl2(g2-dppmO)2] (0.015 g, 0.015 mmol) and
NH4PF6 (0.0244 g, 0.154 mmol) were dissolved in 1:1
methanol/dichloromethane and stirred under a CO
atmosphere at room temperature. After 12 h, precipita-
tion of a bright yellow solid occurred. The solid was
then washed several times with methanol, filtered and
dried under vacuum. Yield: (60%). Anal. Calc. for
C51H44P5O3F6ClRu: C, 55.17; H, 3.99%. Found: C,
54.99; H, 4.19. IR (CsI) m(RuCl) 320 cmꢁ1; m(P@O)
1131 cmꢁ1; m(CO) 1946 cm1.
Crystals were obtained through slow evaporation of
methanol solvent containing the dissolved complexes,
at room temperature. A single crystal of approximate
dimensions of 0.25 · 0.2 · 0.16 mm3 for tcc-[RuCl2-
(g2-dppmO)2] (1) and 0.30 · 0.27 · 0.20 mm3 for
mer-[RuCl3(g1,g2-dppmO)2] (5) were used for the data
collections and unit cell determinations in an Enraf Non-
ius CAD-4 diffractometer at room temperature. The data
collections were made using the CAD-4 [13] program and
the data reductions were performed with the XCAD4 [14]
program. The data were corrected for Lorentz, polariza-
tion and absorption. The structures were solved using di-
rect methods with SHELXS-97 [15]. The models were
refined by full-matrix least-squares procedures on F2
using SHELXL-97 [16]. The WINGX [17] program was used
to analyze and prepare the data for publication. Crystal
data, data collection procedures, structure determination
2.5. mer-RuCl3(g1,g2-dppmO)2 (5)
PPh2CH2P(O)Ph2 (0.13 g, 0.325 mmol) was added to a
solution (15 mL) of methanol/dichloromethane (1:3)
containing RuCl3 Æ 3H2O (0.04 g, 0.15 mmol). The proce-
dure was conducted under an inert atmosphere to pre-
vent ligand oxidation. After being stirred for 2 h, the
Table 1
Crystallographic data for tcc-RuCl2(g2-dppmO)2 and mer-RuCl3(g1,g2-dppmO)2
Complex
tcc-RuCl2(g2-dppmO)2
mer-RuCl3(g1,g2-dppmO)2
Empirical formula
Formula weight
˚
Wavelength (A)
[C50H44O2Cl2P4Ru] Æ 1/2H2O
981.71
[C50H44O2Cl3P4Ru] Æ 3/4H2O
1021.66
1.54184
monoclinic
Cc
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
˚
a (A)
11.030(1)
17.500(2)
13.913(1)
18.092(2)
˚
b (A)
˚
c (A)
23.113(2)
97.797(9)
4419.8(7)
21.307(2)
92.384(8)
5358.6(9)
b (ꢁ)
Volume (A )
3
˚
Z
4
1.475
4
1.266
Dcalc (Mg mꢁ3
)
Absorption coefficient (mmꢁ1
F(000)
Ranges
)
0.663
2012
5.158
2090
0 6 h 6 13; 0 6 k 6 20; ꢁ27 6 l 6 27
0 6 h 6 16; 0 6 k 6 22; ꢁ25 6 l 6 25
Reflections collected
8196
10516
Independent reflections [Rint
h Maximum (ꢁ)
Completeness to theta maximum (%)
]
7760 [0.0390]
25
100.0
5244 [0.0309]
70.0
99.3
Absorption correction
empirical (DIFABS) [20]
0.8524/0.5280
7760/541
analytical [19]
0.472/0.3101
5244/2/551
Maximum/minimum transmission
Data/restraints/parameters
Goodness-of-fit on F2
1.008
1.024
Final R indexes [I > 2r(I)]
R indexes (all data)
Largest difference in peak and hole (e A
R1 = 0.0390, wR2 = 0.0853
R1 = 0.1164, wR2 = 0.1057
0.380 and ꢁ0.492
R1 = 0.0371, wR2 = 0.0996
R1 = 0.0372, wR2 = 0.0999
0.721 and ꢁ0.813
ꢁ3
˚
)

1066
M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
Table 2
Selected bond lengths (A) and angles (ꢁ)
a
˚
tcc-RuCl2(g2-dppmO)2
mer-RuCl3(g1,g2-dppmO)2
Ru–O(2)
Ru–O(4)
Ru–Cl(1)
Ru–Cl(2)
Ru–P(1)
Ru–P(3)
P(2)–O(2)
P(4)–O(4)
2.214(3)
2.193(3)
2.407(1)
2.421(1)
2.239(1)
2.236(1)
1.502(3)
1.493(3)
Ru–O(2)
Ru–Cl(1)
Ru–Cl(1)
Ru–Cl(3)
Ru–P(1)
Ru–P(3)
P(2)–O(2)
P(4)–O(4)
2.076(4)
2.337(1)
2.333(2)
2.373(1)
2.372(1)
2.396(1)
1.505(4)
1.495(5)
O(2)–Ru–Cl(1)
O(2)–Ru–Cl(2)
O(2)–Ru–P(1)
85.67(8)
83.84(8)
85.59(8)
O(2)–Ru–Cl(1)
O(2)–Ru–Cl(2)
O(2)–Ru–Cl(3)
O(2)–Ru–P(1)
O(2)–Ru–P(3)
Cl(1)–Ru–Cl(3)
Cl(1)–Ru–P(1)
Cl(1)–Ru–P(3)
Cl(2)–Ru–Cl(1)
Cl(2)–Ru–Cl(3)
Cl(2)–Ru–P(2)
Cl(2)–Ru–P(3)
Cl(3)–Ru–P(3)
P(1)–Ru–Cl(3)
P(1)–Ru–P(3)
86.9(1)
177.8(1)
85.4(1)
O(2)–Ru–P(3)
O(4)–Ru–O(2)
O(4)–Ru–Cl(1)
O(4)–Ru–Cl(2)
O(4)–Ru–P(1)
O(4)–Ru–P(3)
Cl(1)–Ru–Cl(2)
P(1)–Ru–Cl(1)
P(1)–Ru–Cl(2)
P(3)–Ru–Cl(1)
P(3)–Ru–Cl(2)
P(3)–Ru–P(1)
a
171.00(8)
86.8(1)
85.6(1)
89.9(1)
82.14(9)
84.89(9)
171.79(9)
87.90(9)
163.73(5)
100.35(5)
91.22(5)
86.40(5)
102.93(5)
100.04(5)
171.99(6)
92.71(5)
88.27(5)
94.89(6)
92.88(5)
93.09(5)
91.38(5)
89.62(4)
88.79(5)
175.33(5)
Fig. 1. ORTEP18 type view of mer-RuCl3(g1,g2-dppmO)2.
Estimated standard deviations are given in parentheses.
constraints caused by the chelate ring formed between
the phosphine ligand and the metal center. Braunstein
and coworkers described the X-ray structure of the
mer-[RuCl3(g1,g2-(PPh2CH2C(O)OEt)2] complex, anal-
ogous to the one synthesized here [9d]. In their study
˚
the Ru(III)–O distance [2.143(5) A] is reported to be
the shortest one encountered in similar complexes, being
just slightly longer than the sum of the two covalent ra-
dii. For the mer-[RuCl3(g1,g2-dppmO)2] species an even
Fig. 2. ORTEP18 type view of tcc-RuCl2(g2-dppmO)2.
shorter Ru(III)–O distance was found [2.076(4) A]. This
˚
fact may be attributed to the greater hard acid character
of the oxygen atom, which is directly connected to a
phosphorus atom through a double bond system.
methods and refinement results are summarized in
Table 1. Figs. 1 and 2 were prepared using ORTEP-3
for Windows [18]. All non-H atoms were refined aniso-
tropically. Hydrogen atoms were stereochemically posi-
tioned and refined using the riding model [21]. The
aromatic and methylene H atoms were assigned a ther-
mal parameter 20% greater than that of the equivalent
isotropic thermal parameter of the associated C atom.
Selected bond lengths and angles are shown in Table 2.
The EPR spectrum of mer-RuCl3(g1,g2-dppmO)2 in
a dichloromethane frozen solution (at ꢁ160 ꢁC) showed
a well resolved g^ signal of 1.833. The other two g values
are very close to each other, with gi = 2.388 and 2.347.
This fact indicates the presence of an octahedral config-
uration with slightly rhombic distortions, consistent
with the crystallographic structure shown in Fig. 1.
The structure of the tcc-[RuCl2(g2-dppmO)2] com-
plex was also determined by single crystal X-ray diffrac-
tion, showing both chlorine atoms in trans positions and
the phosphorus and oxygen atoms of the two ligands in
cis positions, respectively (Fig. 2). The configuration ob-
served at the metal center is also a distorted octahedron
in which the angle between the axial chlorines is smaller
than 180ꢁ, and the chelate rings show O–Ru–P angles
3. Results and discussion
The metal coordination of the mer-[RuCl3(g1,g2-
dppmO)2] species (Fig. 1) may be described as a
distorted octahedron with three chlorine atoms in a
meridional arrangement, two phosphorus atoms in trans
positions and the oxygen atom from one of the two
phosphine moieties occupying the sixth coordination
site. The distortion observed is mainly due to the steric
˚
close to 85ꢁ. The Ru–Cl distances of ca. 2.4 A are typical
of ruthenium (II) complexes, but the Ru–P bonds are
comparatively shorter than those found in simple

M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
1067
Table 3
31P {1H} NMR of the tcc-RuCl2(g2-dppmO)2 and cct-RuCl2(g2-
dppmO)2 isomers
biphosphine ligands probably due to the presence of
the oxygen atom, which makes the phosphorus atoms
harder [22–29].
The IR spectra of the tcc-RuCl2(g2-dppmO)2 and cct-
RuCl2(g2-dppmO)2 isomers revealed a P@O band dislo-
cated 40–50 cmꢁ1 to a region of lower energy, compared
to the free ligand [30]. This is indicative of the coordina-
tion, through the oxygen atom, of the mono-oxidated li-
gand to the metal. The Ru–Cl stretching band appears
in the region of 310–340 cmꢁ1 for these isomeric
complexes.
Complexes
d
M
N
L
tcc-RuCl2(g2-dppmO)2
PA 52.1
PB 53.8
PA 48.5
PB 59.2
43.8
17.1
3.6
cct-RuCl2(g2-dppmO)2
n.o.
16.0
4.9
n.o., not observable; N = [2J(PAPB) + 4J(PAPB )], in Hz; M =
0
4
2
3
[2J(PAPA ) + J(PBPB )], in Hz; L = [ J(PAPB) + J(PAPB )]; d ppm, in
relation to H3PO4 85%.
0
0
0
The Ru(II) complexes studied had their structures
investigated by NMR, resulting in a very interesting
set of data. For this reason, two-dimensional NMR
techniques were also applied in order to obtain a deeper
mer coupling constants J, where N ¼ ½2JðPAPBÞþ
4
2
4
0
0
0
JðPAPB Þꢂ, and M ¼ ½ JðPAPA Þ þ JðPBPB Þꢂ. Abraham
4
0
[31] and Harris [32] consider the JðPBPB Þ coupling con-
stant to be equal to zero in the simple AA0XX0 systems,
which makes the value of the constant M basically the
1
understanding of the complexes. The H NMR multi-
plicity spectral analysis became difficult due to the cou-
1
pling between H and 31P. In order to eliminate this
coupling between PA and PA corresponding, in our case,
to the coupling between the two phosphorus atoms in the
cis position.
0
1
interaction a H{31P} spectrum was run, enabling the
assignment of the methylene hydrogens between the
two phosphorus of the dppmO ligand and the ortho
hydrogens of the two kinds of aromatic rings (A and
B, see Scheme 2). From the integral values it was possi-
ble to identify all the other hydrogen chemical shifts. To
The reaction of tcc-RuCl2(g2-dppmO)2 with CO gen-
erates the RuCl2(CO)(g1,g2-dppmO)2 species, which
shows a weak band at 320 cmꢁ1 related to mRu–Cl, sug-
gesting a trans position chlorides, and two strong bands
(at 1097 and at 1166 cmꢁ1) attributed to stretching P@O
bonds. A very intense band at 1975 cmꢁ1 for mC„O is
also observed.
1
confirm this assignment a H–31P HMBC was also run
using 2 and 8 Hz. In these spectra, it was possible to ob-
serve the correlation between the phosphorus and the
hydrogen atoms positioned at 2, 3 and 4 bonds, corre-
sponding to ortho, meta and para hydrogens of the phe-
For RuCl2(CO)(g1,g2-dppmO)2 (3) the 31P{1H}
NMR spectrum shows four different phosphorus atoms.
From 31P–31P COSY (Fig. 3) the deshielded chemical
shift was attributed to phosphorus PB (see Scheme 2)
based on the fact that it is coordinated to the metal
through oxygen, having a similar chemical environment
to the PB phosphorus in complex 1. For complex 3, it
was possible to attribute unequivocally all the phospho-
rus atoms of the molecule (see Table 4). The PA and PC
signals, with d 40.8 and 27.2, respectively, are double
double doublets due to three possible couplings. Thus,
PA couples with PC with a coupling constant about 10
times the value of a cis coupling, in the 30–40 Hz range
[33]. This is characteristic of trans position phosphorus
nylic rings A and B. In the 13C{1H} spectrum, all the 13
C
chemical shifts were identified and most of the 13C–31P
coupling constants were observed. A 1H–13C HMCB
spectrum enabled the correlation between all the hydro-
gens and the respective carbons of the phenylic rings.
1
Based on the H–31P HETCOR NMR spectrum, it is
possible to conclude that the most deshielded hydrogens
pertaining to the phenylic ring correlate to the more
shielded phosphorus type (PA) and not the opposite,
as one could expect. These data are presented in the sup-
plemental section.
The 31P chemical shifts and coupling constants of the
tcc-RuCl2(g2-dppmO)2 and cct-RuCl2(g2-dppmO)2 iso-
mers are summarised in Table 3 and the phosphorus nu-
clei are considered as an AA0XX0 spin system. The values
for N and M are actually the sum or difference of the for-
2
atoms and J(PCPA) = 375.8 Hz.
With the data obtained from 1H–31P HMBC, using 8
and then 2 Hz for the coupling constants in the NMR
experiment, it was possible to finally see the connection
4
5
4
3
5
A
3
6
A
6
2
Cl
2
Cl
1
1
PA
X
PA
O
CO
PC
O
CO
PA '
O
Ru
Cl
Ru
Cl
PB
PB
PB'
B
Y
PD
O
D
B
C
Scheme 2. Structures of tcc-RuCl2(g2-dppmO)2 and RuCl2(CO)(g1,g2-dppmO)2.

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M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
P@O group coordinated to the metalꢁcenter. A band at
840 cmꢁ1 due to the presence of PF6 as a counter ion
was also observed.
The 31P{1H} NMR spectrum of [RuCl(CO)(g2-
dppmO)2]PF6 is very similar to the spectrum of RuCl2-
(CO)(g1,g2-dppmO)2, except that in this case both
phosphorus atoms bonded to the oxygen atoms have
chemical shifts in the low field region, at 71.3 and 64.1
ppm, respectively (see Table 4). These facts suggest that
for this molecule the two P@O groups of the phosphine
ligand are coordinated to the metal. The two double
double doublets with d 40.3 and 25.7 were assigned to
PA and PC, respectively. These two phosphorus atoms
are trans to one another, therefore they have a coupling
constant of ca. 300 Hz.
Cyclic voltammetric measurements of the tcc-RuCl2-
(g2-dppmO)2 and cct-RuCl2(g2-dppmO)2 isomers
showed reversible processes, attributed to the redox pair
RuIII/II. The E1/2 value for the cct species (Cl atoms in
the cis position) is more anodic than the value found for
the tcc complex (Table 5). This fact is due to the trans
cooperative effect, which describes a rise in the magni-
tude of the retrodonation metal ! ligand in cis isomers
of MCl2(dppm)2 (M = Ru and Os) complexes [34,35]. As
expected, the carbonyl complexes RuCl2(CO)(g1,g2-
dppmO)2 and [RuCl(CO)(g2-dppmO)2]PF6 presented
much more anodic E1/2 values, even for a reversible
1eꢁ process, as determined by differential pulse voltam-
metry. It is interesting to observe that when the CO mol-
ecule displaces a Cl instead of an O atom of the O,P
ligand, as in the case of the cationic species [RuCl(CO)-
(g2-dppmO)2]PF6, the redox potential is appreciably
increased, as compared to the case in the RuCl2(CO)-
(g1,g2-dppmO)2 complex.
Fig. 3. 31P–31P COSY NMR spectrum in CDCl3 of RuCl2(CO)
(g1,g2-dppmO)2.
between the ortho hydrogen from the phenylic ring, as
well as the methylene hydrogen atoms of the ligand, to
the corresponding phosphorus atoms (data reported in
the supplemental section). In the spectrum where 2 Hz
was used, the correlation with hydrogens in meta and
para positions with the respective phosphorus was estab-
lished. In addition 1H–13C gHSQC and 31C{1H} spectra
were also acquired enabling the assignment of all carbon
chemical shifts related to the hydrogens of rings A, B, C
and D and most of the J13C–31P coupling constants.
A new mono-carbonyl cationic complex was obtained
through the reaction of tcc-RuCl2(g2-dppmO)2 with
NH4PF6 in the presence of CO. The [RuCl(CO)(g2-
dppmO)2]PF6 complex was also characterized by IR
and NMR spectroscopy. The IR spectrum of this new
species displays an intense band at 1946 cmꢁ1 attributed
to mC„O and a broad band at 1131 cmꢁ1 related to the
We find that the tcc-RuCl2(g2-dppmO)2 isomer can
be easily and quantitatively converted into the cct-
RuCl2(g2-dppmO)2 isomer by thermolysis (heating at
reflux in CH2Cl2) and the opposite conversion is reached
by photolysis of cct-RuCl2(g2-dppmO)2 in CH2Cl2
Table 4
31P NMR Chemical Shifts (d) and J coupling constants (Hz) for RuCl2(CO)(g1,g2-dppmO)2 and [RuCl(CO)(g2-dppmO)2]PF6 complexes
da
Jb
RuCl2 (CO)(g1,g2-dppmO)2
PA
PB
PC
PD
40.8ddd
60.1dd
27.2ddd
24.2dd
JAC = 375.80; JAB = 35,00; JAD = 8.90
JAB = 35.00; JBC = 20.80
JCA = 375.80; JCD = 27.60; JBC = 20.80
JDC = 27.60; JDA = 8.90
[RuCl(CO)(g2-dppmO)2]PF6
PA
PB
PC
PD
40.3ddd
64.1dd
JAC = 354.2; JAB = 33.3; JAD = 16.6
JBA = 33.3; JBC = 21.5
25.7ddd
71.3dd
JCA = 354.2; JCD = 31.3; JCB = 21.5
JDC = 31.3; JDA = 16.6
J31P–19F = 712.8
ꢁ
PF6
ꢁ143.4q
a
d ppm, in relation to H3PO4.
In Hz.
b

M.P. Felicissimo et al. / Polyhedron 24 (2005) 1063–1070
1069
Table 5
E1/2 (RuIII/II) potentials for complexes 1–4
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Complexes
E1/2 (RuIII/II)a
tcc-RuCl2(g2-dppmO)2
0.40
0.53
1.10
1.51
cct-RuCl2(g2-dppmO)2
RuCl2(CO)(g1,g2-dppmO)2
[RuCl(CO)(g2-dppmO)2]PF6
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Suranna, R. Wang, Inorg. Chim. Acta 280 (1998) 150;
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solution with white light, resulting in a quantitative con-
version to tcc-RuCl2(g2-dppmO)2. These processes were
followed by cyclic voltammetric and 31P{1H} measure-
ments. Similar conversions were observed for the cis-
and trans-M(dppm)2Cl2 (M = OsII, RuII) complexes
[35]. Since the 31P{1H} NMR experiments during the
isomerization process show free dppmO it is possible
to infer that a dissociative mechanism is involved.
As mentioned in the experimental section, the cct-
RuCl2(g2-dppmO)2 isomer is light brown while the tcc-
RuCl2(g2-dppmO)2 isomer is pink. Our hypotheses is
that the pink color of tcc-RuCl2(g2-dppmO)2 is due to
the MLTC transition at 502 nm of the ruthenium metal
to the oxygen atoms of the P@O groups trans to phos-
phorus atoms. In this case, this transition could easily
occur (at low energy) since the phosphorus atoms are
good p acceptors and could make the oxygen atoms
harder and better electron acceptors. It is worth men-
tioning that complexes such as RuCl2(dppm)2 (with the
absence of an oxygen atom in the ligand) are yellow or
light brown and show MLTC transitions below 400 nm
[35]. cct-RuCl2(g2-dppmO)2 shows a MLTC transition
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Nobile, G.P. Suranna, J. Mol. Catal. 157 (2000) 41.
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Fawzi, M. Steimann, Inorg. Chem 32 (1993) 1266;
(c) E. Lindner, M. Haustein, H.A. Mayer, H. Kuhbauch, K.
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Urieze, B. Klerk-Engels, Inorg. Chim. Acta 215 (1994) 165;
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945.
[12] J.P. Geneˆt, C. Pinel, Tetrahedron: Asymmetry 5 (1994) 665.
[13] Enraf–Nonius CAD-4, Enraf–Nonius, Delft, The Netherlands,
1993.
[14] K. Harms, S. Wocadlo, XCAD-4, Program for Processing CAD-4
Diffractometer Data, University of Marburg, Marburg, Germany,
1995.
at 340 nm (e ꢃ 103
M
ꢁ1 cmꢁ1). On the other hand
tcc-RuCl2(g2-dppmO)2 presents two shoulders (at about
340 and 400 nm) and a well defined band at 502 nm
[15] G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Reso-
lution, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[16] G.M. Sheldrick, SHELXL-97, Program for Crystal Structures Anal-
ysis, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[17] L.J. Farrugia, WinGX, J. Appl. Cryst. 32 (1999) 837.
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565.
(e ꢃ 102
M
ꢁ1 cmꢁ1). Thus the isomerization process
can be followed by UV–Vis spectroscopy in CH2Cl2.
Acknowledgments
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(1965) 3175.
The authors acknowledge the Brazilian agencies
CAPES, CNPq and FAPESP for the financial support
given to this research.
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Appendix A. Supplementary data
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Supplementary data associated with this article can
be found in the online version at doi:10.1016/
j.poly.2005.02.026.
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