Reactivity of the bis(allyl)-ruthenium(IV) dimer towards dppf and dppfO.

Article abstract of DOI:10.1016/S0022-328X(01)00914-7

The bis(allyl)-ruthenium(IV) derivative [{Ru(η³:η³-C₁₀H₁₆)(μ-Cl)Cl}₂] reacts with dppf and dppfO to yield complexes [{Ru(η³:η³-C₁₀H₁₆)Cl₂}_2<

Full text of DOI:10.1016/S0022-328X(01)00914-7

Journal of Organometallic Chemistry 637–639 (2001) 767–771
www.elsevier.com/locate/jorganchem
Note
Reactivity of the bis(allyl)-ruthenium(IV) dimer
[{Ru(h3:h3-C10H16)(m-Cl)Cl}2]
(C10H16=2,7-dimethylocta-2,6-diene-1,8-diyl) towards dppf
(dppf=[Fe(h5-C5H4PPh2)2]) and dppfO
(dppfO=[Fe(h5-C5H4PPh2)(h5-C5H4P(ꢀO)Ph2)])
Victorio Cadierno, Sergio E. Garc´ıa-Garrido, Jose´ Gimeno *
Departamento de Qu´ımica Orga´nica e Inorga´nica, Facultad de Qu´ımica, Instituto Uni6ersitario de Qu´ımica Organometa´lica ‘Enrique Moles’
(Unidad Asociada al CSIC), Uni6ersidad de O6iedo, E-33071 O6iedo, Spain
Received 2 January 2001; received in revised form 22 February 2001; accepted 22 February 2001
Abstract
The bis(allyl)-ruthenium(IV) derivative [{Ru(h3:h3-C10H16)(m-Cl)Cl}2] reacts with dppf and dppfO to yield complexes
[{Ru(h3:h3-C10H16)Cl2}2(m-dppf)] and [Ru(h3:h3-C10H16)Cl2(k1-P-dppfO)], respectively. The electrochemical data of these com-
plexes are reported. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: 1,1%-Bis(diphenylphosphino)ferrocene; h3:h3-Octadienediyl complexes; Bis(allyl) complexes; Ruthenium(IV) complexes
ene, respectively. Moreover, the unusual properties ex-
hibited by the dimeric complex [{Ru(h3:h3-C10-
H16)Cl(m-Cl)}2] (1) and some of its derivatives, namely,
remarkable stability, water solubility [5], and catalytic
activity in ROMP of cycloolefins [5b,6] and butadiene
polymerization [7], make 1 a source of considerable
interest. Although the molecular structure of 1 in the
solid state shows an overall Ci symmetry (see Fig. 1)
[3b], in solution it exists as an approximately equimolar
mixture of two diastereoisomers, referred to as the Ci
(meso) and C2 (rac) forms (Fig. 1), arising as a conse-
1. Introduction
Bis(allyl)-ruthenium(II) derivatives [Ru(h3-2-RC3-
H4)2L2] (R=H, Me; L2=chiral or achiral diphosphine)
have attracted a great deal of attention in recent years
due to their useful applications in catalytic organic
synthesis [1]. In contrast, much less attention has been
devoted to the preparation of mononuclear bis(allyl)-
ruthenium(IV) complexes containing chelating diphos-
phines [2]. This is rather surprising given that
h3:h3-octadienediyl-ruthenium(IV) derivatives such as
the chloro-bridged dimer [{Ru(h3:h3-C10H16)Cl(m-Cl)}2]
(C10H16=2,7-dimethylocta-2,6-diene-1,8-diyl) [3] or the
mononuclear complex [Ru(h3:h2:h3-C12H18)Cl2] (C12-
H18=dodeca-2,6,10-triene-1,12-diyl) [4], known since
the 1960s, are readily available from the reaction of
ethanolic ruthenium trichloride and isoprene or butadi-
* Corresponding author. Tel.: +34-985-103-461; fax: +34-985-
103-446.
E-mail address: jgh@sauron.quimica.uniovi.es (J. Gimeno).
Fig. 1. The two diastereomeric forms of [{Ru(h3:h3-C10H16)Cl(m-
Cl)}2] (1).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00914-7

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V. Cadierno et al. / Journal of Organometallic Chemistry 637–639 (2001) 767–771
Scheme 1.
quence of the three ways of joining together the two
chiral (h3:h3-C10H16)Ru units [8].
nificantly, the 31P{1H}-NMR spectrum displays two
singlet signals in ca. 1:1 ratio (18.31 and 18.55 ppm).
This fact seems to indicate the presence of two different
isomers in solution. Although we have not carried out
detailed variable-temperature NMR experiments, we
note that when a solution of 2 in CD2Cl2 is cooled
below 293 K the 31P{1H}-NMR spectra show only one
broad signal indicating that an interconversion process
between conformational isomers is taken place. The
presence of an equimolar mixture of two energetically
favoured conformational isomers with overall Ci sym-
metry (confirmed by X-ray diffraction analysis) has
been reported previously for the related dinuclear
complex [{Ru(h3:h3-C10H16)Cl2}2(m-dppm)] (dppm=
Dimer 1 shows a versatile chemistry with preserva-
tion of the bis(allyl) unit. Thus, chloride bridging cleav-
age using neutral and anionic ligands is the starting
point for the preparation of wide series of: (a) mononu-
clear [Ru(h3:h3-C10H16)Cl2L] (L=phosphines, phos-
phites, CO, nitriles, amines, thiols, etc.) [8,9] and
[Ru(h3:h3-C10H16)Cl(k2-L–L)]
(L–L=dithiocarba-
mates, semicarbazides, acetates, pyridine-2-thiolate, ni-
trate, etc.) [5a,10] derivatives, and (b) dinuclear
ligand-bridged [{Ru(h3:h3-C10H16)Cl2}2(m-L–L)] (L–
L=diamines, dppm) [9d,11] and [{Ru(h3:h3-C10-
H16)Cl(m-L)}2] (L=thiolates, thiocyanate, seleno-
cyanate, etc.) [9e,12] complexes. In addition, cationic
species [Ru(h3:h3-C10H16)ClL2]+ (L=isocyanides, tri-
methylphosphite, acetone, acetonitrile; L2=chelating
diamines) and [Ru(h3:h3-C10H16)L3]2+ (L=acetone,
acetonitrile, L3=2,2%:6,2%%-terpyridine) have been also
prepared by treatment of 1 with the appropriate two-
electron ligands in the presence of AgBF4 [6d,9c,
9d,10f,11b].
bis(diphenylphosphino)methane)
[11a].
1H-
and
13C{1H}-NMR spectra of 2 display only one set of
resonances for the h3:h3-C10H16 moiety with their two
halves in apparent equivalent environments (i.e. only
five resonances are observed in the 13C{1H}-NMR spec-
trum). This is rather surprising since a doubling of
signals should be expected as a consequence of the
presence of two different isomers in solution [11a].
It is noteworthy that compound 2 is also obtained by
treatment of 1 with an excess of dppf. This result
contrasts with that shown by the diphosphine ligand
dppm for which the mononuclear adduct [Ru(h3:h3-
C10H16)Cl2(k1-P-dppm)] is isolated [11a]. The different
behaviour observed for dppm and dppf is most likely
due to the steric requirements of the bulky h3:h3-octa-
dienediyl-Ru(IV) fragment. It seems that the steric hin-
drance between the two [Ru(h3:h3-C10H16)Cl2] units,
which increases when the bridged diphosphine dppf is
replaced by the smaller dppm ligand, leads to the
isolation of the mononuclear derivative [Ru(h3:h3-
C10H16)Cl2(k1-P-dppm)]. All attempts to prepare the
cationic species [Ru(h3:h3-C10H16)Cl(k2-P,P-dppf)]-
[BF4] by treatment of dimer 1 with two equivalents of
dppf and AgBF4 in dichloromethane, acetone or aceto-
nitrile have been unsuccessful obtaining instead mix-
tures of uncharacterized products. Apparently, the
tendency of dppf to act as a bridging ligand in 2 also
prevents the formation of the desired chelated complex.
Taking into account the lower ability of diphosphine-
monoxides to act as bridging ligands [15], we became
interested in studying the reactivity of dimer 1 towards
dppfO [16] in order to prepare the chelated derivative
With all these precedents in mind we wondered about
the possibility of using the dimeric complex 1 as a
suitable starting material for the preparation of bis(al-
lyl)-ruthenium(IV) complexes containing chelating
diphosphines. Thus, we present herein our studies on
the reactivity of 1 towards the versatile diphosphine
ligand 1,1%-bis(diphenylphosphino)ferrocene (dppf) and
its monoxide dppfO [13].
2. Results and discussion
The dimeric bis(allyl)-ruthenium(IV) complex [{Ru-
(h3:h3-C10H16)Cl(m-Cl)}2] (1) reacts with one equivalent
of dppf [14], in dichloromethane at room temperature,
to afford the trinuclear derivative [{Ru(h3:h3-C10-
H16)Cl2}2(m-dppf)] (2; 91% yield) (Scheme 1).
Compound 2 is an air-stable solid soluble in polar
solvents (e.g. dichloromethane or acetone). It has been
characterized by elemental analyses and IR and NMR
1
(31P{1H}, H and 13C{1H}) spectroscopy (for details see
Section 4) being its dimeric nature confirmed clearly by
the relative intensities of the octadienediyl and diphos-
1
phine resonances (2:1) in the H-NMR spectrum. Sig-

V. Cadierno et al. / Journal of Organometallic Chemistry 637–639 (2001) 767–771
769
[Ru(h3:h3-C10H16)Cl(k2-P,O-dppfO)]+. Thus, we have
found that complex 1 reacts with a twofold excess of
dppfO to generate the neutral dinuclear adduct
[Ru(h3:h3-C10H16)Cl2(k1-P-dppfO)] (3; 67% yield) as
the result of the selective coordination of the
diphenylphosphino group on the Ru(IV) center
(Scheme 2). As expected, no dinuclear bridged products
were detected even when the reaction was carried out
with only one equivalent of dppfO obtaining instead an
equimolar mixture of 3 and the precursor complex 1.
Characterization of 3 was achieved unequivocally by
means of spectroscopic techniques (IR and 31P{1H}-,
1H- and 13C{1H}-NMR) as well as elemental analyses
(see Section 4). Remarkably, while the 1H spectrum
displays a single set of signals for the two allylic
moieties of the 2,7-dimethylocta-2,6-diene-1,8-diyl lig-
and, as expected for the formation of simple equatorial
adduct [Ru(h3:h3-C10H16)Cl2L] [8,9], the 13C{1H}-
NMR spectrum shows two different resonances for the
C1/C8 (69.03 (d, JCP=4.9 Hz) and 70.26 (s) ppm) and
C3/C6 (107.50 (d, JCP=6.6 Hz) and 107.71 (d, JCP=6.6
Hz) ppm) atoms of the octadienediyl skeleton (for
numbering see Section 4) suggesting that the two halves
of the ligand are in inequivalent environments. This
inequivalence, which should be also observed for the
trinuclear complex 2, can be explained assuming that
the molecule is locked in a given conformation due to a
restricted rotation about the Ru–P bond which could
arise from the steric requirements of the octadienediyl
and ferrocenyl bulky groups. Significantly, all attempts
to form the cationic derivative [Ru(h3:h3-C10H16)Cl(k2-
P,O-dppfO)][BF4] by treatment of 3 with AgBF4 or
starting directly from 1 have been unsuccessful obtain-
ing instead mixtures of uncharacterized products. Once
again, this behaviour can be attributed to the steric
hindrance between the metallic fragment and the bulky
ferrocenyl ligand which prevents its chelation.
containing coordinated dppf normally show irreversible
ferrocene-based oxidations due to the high lability of
the oxidized ligand [13,17]. In contrast, cyclic voltam-
metry (CV) studies on dichloromethane solutions of
[{Ru(h3:h3-C10H16)Cl2}2(m-dppf)] (2) and [Ru(h3:h3-
C10H16)Cl2(k1-P-dppfO)] (3) show that these complexes
undergo one-electron oxidation (E°%=0.27 (2) and 0.38
(3) V), which is chemically reversible under the experi-
mental conditions (scan rate: 100 mV s−1). Reversible
oxidations of coordinated dppf are also known for the
complexes [MCl2(dppf)] (M=Pd, Pt) [17b].
3. Conclusions
It is well-known that the bidentate ligand 1,1%-bis-
(diphenylphosphino)ferrocene (dppf) shows a versatile
coordination chemistry adapting its bite angle to the
geometric requirements of the metal fragment through
the appropriate ring twisting or tilting [13]. Although
the chelating coordination mode is the predominant
character of dppf in most metal centers to which it is
attached, a large number of homo- and heteropolinu-
clear complexes containing bridging dppf are known. In
this paper, a clear example of the ability of dppf to act
as a bridging ligand, i.e. [{Ru(h3:h3-C10H16)Cl2}2(m-
dppf)], has been presented and rationalized as the result
of the steric hindrance between the bulky ferrocenyl
and bis(allyl)-ruthenium(IV) fragments. Steric require-
ments seem also to be responsible of the non chelation
of dppfO from the neutral adduct [Ru(h3:h3-
C10H16)Cl2(k1-P-dppfO)]. These results contrast with
those observed using bis(diphenylphosphino)methane,
1,2-bis(diphenylphosphino)ethane and their diphos-
phine-monoxide counterparts which are able to coordi-
nate in a chelating fashion on the sterically demanding
Ru(h3:h3-C10H16) moiety [18].
Complexes incorporating ferrocenyl units are ex-
pected to exhibit a ferrocene-centered oxidative process.
The redox behaviour of free dppf has been studied by
several groups [17], being accepted that undergoes an
initial ferrocene-based reversible oxidation followed by
a fast chemical reaction involving the phosphorus sub-
stituents on the cyclopentadienyl rings [17e]. Electro-
chemical studies on transition-metal complexes
4. Experimental
The manipulations were performed under an atmo-
sphere of dry nitrogen using vacuum-line and standard
Schlenk techniques. Solvents were dried by standard
methods and distilled under nitrogen before use. Com-
Scheme 2.

770
V. Cadierno et al. / Journal of Organometallic Chemistry 637–639 (2001) 767–771
pounds [{Ru(h3:h3-C10H16)Cl(m-Cl)}2] (1) [10a], dppf
[14] and dppfO [16] were prepared by following the
methods reported in the literature. Infrared spectra
were recorded on a Perkin–Elmer 1720-XFT spectrom-
eter. The C and H analyses were carried out with a
Perkin–Elmer 240-B microanalyzer. Cyclic voltamme-
try (CV) measurements (25 °C) were carried out with a
three-electrode system. The working electrode was a
platinum disk electrode, the counter electrode was a
platinum spiral, and the reference electrode was an
aqueous saturated calomel electrode (SCE) separated
from the solution by a porous septum. Current and
voltage parameters were controlled using a PAR system
M273. In a typical experiment, 1.5×10−2 mmol of the
complex was dissolved under a nitrogen atmosphere in
10 ml of freshly distilled and deoxygenated dichloro-
methane containing 1.15 g of pure [NBu4][PF6] (0.3
mmol) as electrolyte. Formal CV potentials (E°%) are
referenced relative to potential of the [Cp2Fe]/[Cp2Fe]+
couple (E°=0.22 V) run under identical conditions
(E°% = E°(Complex+/Complex) − E°([Cp2Fe]+/[Cp2-
Fe])) [19]. NMR spectra were recorded on a Bruker
AC300 instrument at 300 MHz (1H), 121.5 MHz (31P)
or 75.4 MHz (13C) using SiMe4 or 85% H3PO4 as
standards. DEPT experiments have been carried out for
all the compounds reported.
C5H4), 5.07 (m, 4H, H3 and H8), 7.30–7.90 (m, 20H,
Ph) ppm; 13C{1H}-NMR (CDCl3) l 20.85 (s, CH3),
36.77 (s, C4 and C5), 69.15 (s, C1 and C8), 72.60, 72.63,
73.00 and 73.05 (d, JCP=7.6 Hz, CH of C5H4), 75.62,
76.06, 76.44 and 76.81 (d, JCP=9.5 Hz, CH of C5H4),
83.08 and 83.13 (d, JCP=41.4 Hz, C of C5H4), 107.54
(d, JCP=10.2 Hz, C3 and C6), 125.82 (s, C2 and C7),
127.00–136.00 (m, Ph) ppm.
4.2. Synthesis of [Ru(p3:p3-C10H16)Cl2(s1-P-dppfO)]
(3)
A solution of 1.078 g (1.75 mmol) of [{Ru(h3:h3-
C10H16)(m-Cl)Cl}2] (1) in 20 ml of dichloromethane was
treated at r.t. with 1.996 g (3.5 mmol) of dppfO. After
stirring for 5 min, the solvent was removed under
vacuum and the resulting orange solid residue washed
with diethyl ether (3×20 ml) and dried in vacuo. Yield:
2.06 g (67%). Anal. Calc. for FeRuC44H44Cl2P2O
(878.61): C, 60.15; H, 5.04. Found: C, 59.75; H, 5.17%;
IR (KBr, cm−1): 1435 (s), 1261 (vs), 1209 (s), 1169 (s),
1098 (vs), 1024 (vs), 800 (vs), 697 (s), 567 (s); 31P{1H}-
NMR (CDCl3) l 18.73 (s, Ph2P), 28.97 (s, Ph2PꢀO)
1
ppm; H-NMR (CDCl3) l 2.09 (s, 6H, CH3), 2.54 (m,
2H, H4 and H6), 2.97 (d, 2H, JHP=3.7 Hz, H2 and
H10), 3.34 (m, 2H, H5 and H7), 3.98 (d, 2H, JHP=9.1
Hz, H1 and H9), 3.88–4.62 (m, 8H, CH of C5H4), 5.07
(m, 2H, H3 and H8), 7.35–7.90 (m, 20H, Ph) ppm;
13C{1H}-NMR (CDCl3) l 20.88 (s, CH3), 36.81 (s, C4
and C5), 69.03 (d, JCP=4.9 Hz, C1 or C8), 70.26 (s, C1
or C8), 71.89 and 72.10 (d, JCP=7.8 Hz, CH of C5H4),
73.46 and 73.81 (d, JCP=12.4 Hz, CH of C5H4), 74.38
(d, JCP=114.6 Hz, C of C5H4), 74.75 and 75.01 (d,
The numbering for protons and carbons of the octa-
dienediyl skeleton are as follows:
JCP=10.3 Hz, CH of C5H4), 75.75 and 77.19 (d, JCP=
9.2 Hz, CH of C5H4), 83.09 (d, JCP=41.6 Hz, C of
C5H4), 107.50 and 107.71 (d, JCP=6.6 Hz, C3 and C6),
125.75 (d, JCP=1.2 Hz, C2 and C7), 127.00–137.00 (m,
Ph) ppm.
4.1. Synthesis of [{Ru(p3:p3-C10H16)Cl2}2(v-dppf )] (2)
Acknowledgements
A solution of 0.300 g (0.487 mmol) of [{Ru(h3:h3-
C10H16)(m-Cl)Cl}2] (1) in 30 ml of dichloromethane was
treated at room temperature (r.t.) with 0.270 g (0.487
mmol) of dppf. After stirring for 5 min, the solvent was
removed under vacuum and the resulting orange solid
residue washed with hexanes (3×20 ml) and dried in
This work was supported by the Direccio´n General
de Investigacio´n Cient´ıfica y Te´cnica of Spain (DGI-
CYT, project PB96-0558).
vacuo. Yield: 0.518
g
(91%). Anal. Calc. for
References
FeRu2C54H60Cl4P2 (1170.82): C, 55.39; H, 5.16. Found:
C, 54.67; H, 4.98%; IR (KBr, cm−1): 1431 (s), 1155 (s),
1089 (s), 1040 (s), 1021 (s), 746 (s), 693 (vs), 512 (s), 470
(s); 31P{1H}-NMR (CDCl3) l 18.31 (s), 18.55 (s) ppm;
1H-NMR (CDCl3) l 2.07 (s, 12H, CH3), 2.54 (m, 4H,
H4 and H6), 2.93 (m, 4H, H2 and H10), 3.33 (m, 4H, H5
and H7), 3.83 (m, 4H, H1 and H9), 3.86–3.90 (m, 6H
CH of C5H4), 4.26 and 4.35 (br, 1H each one, CH of
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