Ti-Ru bimetallic complexes: Catalysts for ring-closing metathesis

Article abstract of DOI:10.1016/S0022-328X(01)01248-7

The reaction of the titanocene monophosphanes (1-4) with the dimer [(p-cymene)RuCl₂]₂ gives the heterobimetallic compounds here. A preliminary assessment of the performance of these complexes in ring-closing metathesis (RCM) revealed an excellent Ti-Ru-allenylidene pre-catalyst 12.

Full text of DOI:10.1016/S0022-328X(01)01248-7

Journal of Organometallic Chemistry 643–644 (2002) 231–236
www.elsevier.com/locate/jorganchem
Ti–Ru bimetallic complexes: catalysts for ring-closing metathesis
Pierre Le Gendre, Michel Picquet, Philippe Richard, Claude Mo¨ıse *
Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, LSEO-UMR 5632, Faculte´ des Sciences Gabriel, Uni6ersite´ de Bourgogne,
6 Boule6ard Gabriel, 21000 Dijon, France
Received 29 June 2001; accepted 11 September 2001
Dedicated to Professor Franc¸ois Mathey on the occasion of his 60th birthday
Abstract
The reaction of the titanocene monophosphanes (1–4) with the dimer [(p-cymene)RuCl2]2 gives the heterobimetallic compounds
(p-cymene)[(h5-C5H5)(m-h5:h1-C5H4(CR2)nPR2%)TiCl2]RuCl2 (5–8). The structure of 8, determined by X-ray diffraction, is reported
here. A preliminary assessment of the performance of these complexes in ring-closing metathesis (RCM) revealed an excellent
Ti–Ru–allenylidene pre-catalyst 12. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Titanocene; Ruthenium; Heterobimetallic complexes; Metathesis; Allenylidenes
catalysts has recently been upgraded by the addition of
a substoichiometric amount of titanium complexes [3].
1. Introduction
The catalytic behavior of early–late heterobimetallic
compounds remains almost unexplored [1]. However,
the combination of two metal centers with different
properties in the same molecule may show enhanced
cooperative effect. In an attempt to examine such type
of activity, we focused our attention on the synthesis
and study of heterobimetallic complexes in which both
metal fragments are already well known in the field of
catalysis. Our goal was achieved via the reaction be-
tween the bent-titanocene phosphanes 1 and 3 with the
dimer [(p-cymene)RuCl2]2 (Scheme 1) [2]. Herein, we
report the synthesis of two new Ti–Ru bimetallic com-
plexes (6 and 8) with complementary features by using
the same strategy. The complex 6 contains a C1 spacer
between the Cp and PPh2 functionalities and the com-
plex 8 has a highly basic and bulky phosphane group.
Work was then focused on RCM as a representative
reaction for comparing the activity of the bimetallic
complexes (5–8) with the monometallic species (p-
cymene)RuCl2(PCy3). At this point, we should mention
that the performance of ruthenium-based metathesis
2. Results and discussion
The monophosphanes 2 and 4 were prepared accord-
ing to similar procedures as 1 and 3, i.e. synthesis of the
lithium [1-methyl-1-(diphenylphosphino)ethyl] or [(dicy-
clohexylphosphino)ethyl] cyclopentadienides by means
of the fulvene [4] or the spiro[2,4]hepta-4,6-diene [5]
routes, followed by treatment with CpTiCl3. As ex-
pected, the 31P{1H}-NMR spectrum of 2 appears as a
singlet but with a very unusual chemical shift at 30.1
ppm. This value, when compared with the other phos-
phanes, corresponds to a downfield shift of about 50
ppm. This result, closely similar to those reported by G.
Erker and co-workers [4,6] for the analogue zir-
canocene series, is probably due to the presence of the
alkyl substituents on the spacer carbon between the Cp
and PPh2 groups. It is worth mentioning that both
lithium cyclopentadienide and its cyclopentadiene
derivative formed by hydrolysis show 31P-chemical
shifts in the 20 ppm range. This suggests that the
titanium atom is not responsible for this unexpected
1
deshielding. The H-NMR spectrum shows a doublet
* Corresponding author. Tel.: +33-3-8039-6081; fax: +33-3-8039-
6076.
E-mail address: claude.moise@u-bourgogne.fr (C. Mo¨ıse).
for the methyl groups bound to the spacer carbon with
phosphorus coupling of 15.3 Hz. The 1H- and 31P-
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01248-7

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P. Le Gendre et al. / Journal of Organometallic Chemistry 643–644 (2002) 231–236
Scheme 1.
NMR chemical shifts of the phosphane 4 are consistent
with the free ligand not coordinated to a metal atom.
However, it is noteworthy that its NMR characteriza-
tion has been done in a nonprotic solvent like C6D6 and
often shows slightly broadened signals.
The molecular structures of the bimetallic complexes
7 and 8 with a diphenyl or a dicyclohexylphosphane
group are very similar. Surprisingly, although the dicy-
clohexylphosphane group is known to be bulkier than
its diphenyl analogue, the only structural change, ob-
served in the arene–ruthenium moiety, consists in a
Preliminary complexation studies have shown that
the titanocene monophosphanes 1 and 3 are able to
cleave the chloride bridges of the dimer [(p-
cymene)RuCl2]2 to lead to the bimetallic complexes 6
and 8 [2]. Therefore, we carried out experiments by
using the metalloligands 2 and 4 to obtain the targeted
heterobimetallic complexes 6 and 8. Except for the
single 1H resonances of the cyclopentadienyl and p-
cymene hydrogens, which are apparently degenerate, all
other 31P and 1H resonances are in accordance with
their structural features. A single crystal of 8, suitable
for X-ray diffraction, was obtained by slow evaporation
of a CHCl3 solution of the compound. An ORTEP view
of 8 is given in Fig. 1.
,
slight elongation of the RuꢀP bond distance (2.350(2) A
for 7 [2]) (Table 1).
Recently, it has been demonstrated that the complex
(p-cymene)RuCl2(PCy3) converts into an efficient
metathesis catalyst upon photochemical irradiation
(light emitted by neon tube) [7]. We, therefore, carried
out experiments by refluxing a solution of N,N-diallyl-
tosylamide (10) and a catalytic amount of the bimetallic
complex 8 in CH2Cl2 under neon light (Scheme 2). In
this reaction, only 3% of the cyclization product 11
could be detected by GC and NMR analysis of the
crude mixture. Other bimetallic complexes (5–7)
showed no catalytic activity under the same conditions.
Fig. 1. An ORTEP view of compound 8 with thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms and the chloroform solvate
molecules are omitted for clarity. Only disordered fragments with s.o.f.\0.5 are shown.

P. Le Gendre et al. / Journal of Organometallic Chemistry 643–644 (2002) 231–236
233
Table 1
Although in case of the monometallic complex, the
precise nature of the active species is still unknown, it
seems that the photochemical irradiation induces a
decomplexation of the arene ligand and so liberates a
14-electron RuII entity, which triggers the catalytic pro-
cess [8]. It is worth noting that both monometallic and
bimetallic species show absorption maxima at 360 nm
attributed to the coordinated arene; therefore, a similar
dissociation should occur with the bimetallic com-
plexes. One can then propose that both chlorides on the
titanium atom work as a chelate on the ruthenium
center and so inhibit the desired catalytic reaction.
These results clearly show a totally different behavior
between mono and bimetallic complexes.
,
Selected bond distances (A) and bond angles (°) for the Ru moiety of
8
Bond distances
RuꢀCt(1)
RuꢀP
RuꢀCl(3)
RuꢀCl(4)
1.70(1)
2.3869(7)
2.4253(7)
2.4205(7)
Bond angles
Ct(1)ꢀRuꢀP
Ct(1)ꢀRuꢀCl(3)
Ct(1)ꢀRuꢀCl(4)
PꢀRuꢀCl(3)
PꢀRuꢀCl(4)
Cl(3)ꢀRuꢀCl(4)
131.9(10)
122.1(9)
128.1(9)
87.93(3)
86.32(3)
86.19(3)
Cationic allenylidene ruthenium complexes of the
type (p-cymene)RuCl(PR3)(ꢁCꢁCꢁCPh2)+TfO− pre-
pared in situ or not, by successive addition of silver
triflate and diphenylpropynol to (p-cymene)RuCl2-
(PR3), have proved to be excellent catalysts for RCM
[9]. We, therefore, studied the RCM of N,N-diallyltosy-
lamide (10) by using a mixture of the bimetallic com-
plexes 5–8, silver triflate and diphenylpropynol as in
situ catalysts. Table 2 summarizes both the conversions
in dihydropyrrole 11 and the rates of formation of the
cumulene species according to the bimetallic complex
used. The catalytic system obtained from 8, allows the
cyclization of N,N-diallyltosylamide (10) with complete
conversion after 1 h at 80 °C in toluene.
Scheme 2.
Table 2
Screening of the catalytic activity of the Ti–Ru–allenylidene com-
plexes
This result comparable to those obtained with (p-
cymene)RuCl(PCy3)(ꢁCꢁCꢁCPh2)+TfO− suggests that
a similar structure is obtained with the bimetallic com-
plex 8. In order to check this hypothesis, we isolated
the cationic Ti–Ru–allenylidene complex 12 (Scheme
3). The reaction of 8 with AgOTf in CH2Cl2 yields the
isolable cationic 16-electron ruthenium compound.
Subsequent treatment with diphenylpropynol at room
temperature affords the dark-violet complex 12. The
most significant spectroscopic data for 12 is a strong IR
absorption at 1964 cm−1 which corresponds to the
asymmetric CꢁCꢁC stretch of an allene system [10].
Other bimetallic complexes (5–7) tested in similar
conditions led to very low conversions (Table 2). In line
with previous observations, these results can be corre-
lated with the nature of the phosphane. Indeed, a
Bimetallic complex
Yield
(%)
Formation of the
allenylidene a
TiꢀCH2CH2PCy2/Ru (8)
TiꢀCH2CH2PPh2/Ru (7)
TiꢀCMe2PPh2/Ru (6)
TiꢀPPh2/Ru (5)
98
B10 min
30 min
1.5 h
1 b
2 b
1 b
nonobserved
Conditions: Complex Ti/Ru (0.025 mmol), AgOTf (0.026 mmol),
CH2Cl2 (1 ml), 30 min–1 h; diphenylpropynol (0.0275 mmol), CH2Cl2
(1 ml), 30 min–1.5 h; N,N-diallyltosylamide (251 mg, 1 mmol),
toluene (3 ml), 80 °C, 1 h.
a A dark-violet color characteristic of the allenylidene fragment is
observed after a lapse of time.
b Determined by 1H-NMR of the crude reaction mixture.
Scheme 3.

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P. Le Gendre et al. / Journal of Organometallic Chemistry 643–644 (2002) 231–236
3.1. Complex 2
A 0.71 g (2.4 mmol) sample of Li[C5H4(CMe2)PPh2]
in 10 ml of THF was added to 0.52 g of CpTiCl3 (2.4
mmol) in 15 ml of THF. After stirring for 4 h at room
temperature (r.t.), the solvent was removed in vacuo.
The red residue was extracted with CH2Cl2, filtered
through celite, and precipitated by the addition of
hexane. The solution was then placed in a freezer
(−20 °C) overnight. The solvent was removed by
filtration and the red residue was dried under vacuum
(70% yield). 31P{1H}-NMR (81.004 MHz, CDCl3): l
30.70 (s, PPh2). 1H-NMR (200.135 MHz, CDCl3): l
1.62 (d, J=15.3 Hz, 6H, CH3), 6.46 (s, 5H, Cp),
6.32–6.66 (m, 4H, Cp%), 7.17–7.50 (m, 10H, Ph). Anal.
Calc. for C25H25TiCl2P (475.2578): C, 63.18; H, 5.30.
Found: C, 62.10; H, 5.25%. The relatively low percent-
age of carbon can be attributed to the presence of
LiCl.
Scheme 4.
highly basic and bulky phosphane ligand on the ruthe-
nium center is required for the catalytic reaction to
turn over. Finally, these results highlight the tremen-
dous influence of the spacer between both metals on
the easiness of access to the allenylidene complex. In-
deed, the shorter the alkyl arm, the slower the appear-
ance of the dark-violet color of the cumulene complex.
Thus, when the PPh2 group is directly bonded to the
cyclopentadienyl ring, which corresponds to the worst
case, no change in the coloration of the reaction mix-
ture has been observed. This aspect is subjected to
further studies in our laboratory.
3.2. Complex 4
We also employed catalyst 12 in RCM of a,v-di-
enes. As can be seen in Scheme 4, this catalytic system
performs the cyclization of the dimethyl diallyl-
malonate well and gives the RCM product 13 with
63% yield [11]. In the macrocyclic series, the 16-mem-
bered cycloalkene 14 has been efficiently obtained in
high dilution conditions [12].
These preliminary results which are comparable to
those obtained with the monometallic species illustrate
the compatibility of both metallic fragments with func-
tional groups such as esters or sulfonamides. Current
work in our laboratory is aiming at exploring the
catalytic activity of the Ti–Ru–allenylidene complex
12 with other diene substrates including other func-
tional groups (ether, amide, silyl ether, …) as well as
replacing the chloride atoms on the titanium center in
order to implicate it more in the catalytic reaction.
Further applications of these Ti–Ru bimetallic com-
plexes in catalysis are also under study.
This compound was obtained by following the
above procedure but with Li[C5H4CH2CH2PCy2] (80%
yield). 31P{1H}-NMR (81.004 MHz, C6D6): l −7.03
(s, PCy2). 1H-NMR (200.135 MHz, C6D6): l 1.08–
2.05 (m, 24H, Cy+CH2), 3.16 (pseudoquadruplet,
J=8.5 Hz, 2H, CH2), 5.74 (pseudotriplet, J=2.6 Hz,
2H, Cp%), 6.08 (s, 5H, Cp), 6.17 (pseudotriplet, J=2.6
Hz, 2H, Cp%). Anal. Calc. for C24H35TiCl2P (473.3263):
C, 60.90; H, 7.45. Found: C, 60.10; H, 7.30%. The
relatively low percentage of carbon can be attributed
to the presence of LiCl.
3.3. Complex 6
A 25 ml Schlenk flask was charged under argon
with 2 (0.13 g, 0.28 mmol), [(p-cymene)RuCl2]2 (0.086
g, 0.14 mmol) and degassed benzene. The mixture was
stirred at r.t. for 4 h during which time a brick-red
precipitate slowly formed. The solvent was removed
by filtration and the red residue was dried under vac-
uum (85% yield). 31P{1H}-NMR (81.004 MHz,
CDCl3): l 25.37 (s, PPh2). 1H-NMR (200.135 MHz,
CDCl3): l 1.04 (d, J=7.0 Hz, 6H, isopropyl CH3),
1.48 (s, 3H, CH3 p-cymene), 1.72 (d, J=15.9 Hz, 6H,
CH3), 2.50 (hept, J=7.0 Hz, 1H, CH isopropyl), 4.99
(d, J=5.6 Hz, 2H, ꢁCH p-cymene), 5.04 (d, J=5.6
Hz, 2H, ꢁCH p-cymene), 6.19 (pseudotriplet, J=2.6
Hz, 2H, Cp%), 6.46 (s, 5H, Cp), 6.57 (pseudotriplet,
J=2.6 Hz, 2H, Cp%), 7.34–7.54 (m, 6H, m,p-Ph),
7.84–7.92 (m, 4H, o-Ph). Anal. Calc. for
C35H39TiRuCl4P (781.4291): C, 53.80; H, 5.03. Found:
C, 54.13; H, 5.13%.
3. Experimental
All manipulations were carried out under argon at-
mosphere using vacuum line techniques. Solvents were
dried and distilled under argon before use. NMR spec-
tra were recorded in a BRUKER AC200 (200.135
MHz for 1H, 81.004 MHz for 31P) spectrometer. IR
spectra were obtained in a Bruker IFS 66v; abbrevia-
tions: vs (very strong). Elemental analyses were per-
formed on a FISON EA 1108 within the laboratory.
CpTiCl3 [13] and the cyclopentadienyl phosphane lig-
ands Li[C5H4(CR2)nPR%] [4,5] were prepared according
2
to the literature method.

P. Le Gendre et al. / Journal of Organometallic Chemistry 643–644 (2002) 231–236
235
Table 3
Ka radiation under a cold nitrogen flux (110 K) and
15886 reflections (10726 unique) were collected up to
Crystal data and structure refinement parameters for complex 8
sin(q)/u=0.65 A−1. Absorption corrections were ap-
,
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C34H49Cl4PRuTi·3(CHCl3)
1137.58
110(2)
0.71073
Triclinic
plied to the data during integration by the
SCALEPACK [14] algorithm. The structure was solved
via a Patterson search program [15] and refined (space
,
(
group P1) with full-matrix least-squares methods [15]
(
P1
based on ꢁF2ꢁ. During refinement, one cyclopentadienyl
ring, the p-cymene ligand and one CHCl3 solvate were
found to be disordered. The former two occupy two
positions while the solvate molecule is disordered over
three positions. The occupation factors converged to
Unit cell dimensions
,
a (A)
9.9486(1)
15.4455(2)
17.3907(3)
68.604(1)
76.978(1)
77.069(1)
2394.42(6)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
m1=0.623 and m% =1−m1 for the Cp rings (restrained
1
3
to regular pentagons, AFIX 59), to m2=0.571 and
,
V (A )
Z
m% =1−m2 for the p-cymene and to the three indepen-
2
Dcalc (g cm−3
)
1.578
1.268
1152
dent values m3=0.425, m% =0.425 and m¦=0.144
3
3
Absorption coefficient (mm−1
F(000)
)
(leading to ꢀm=0.994) for the CHCl3 molecule. Fur-
thermore, the CꢀCl distances and ClꢀCꢀCl angles in the
disordered CHCl3 molecule were restrained (DFIX
card). The atoms belonging to the disordered groups
were left isotropic during the refinement while other
atoms were anisotropically refined. Hydrogen atoms
were included in their calculated positions and refined
with a riding model. Crystal data and final agreement
indices are reported in Table 3.
Crystal size (mm)
Diffractometer
Scan type
0.20×0.15×0.10
Enraf–Nonius Kappa-CCD
Mixture of f rotations and v
scans
−1
,
Sin(q)/u max (A
Index ranges
)
0.65
−125h59, −195k520,
−225l521
SCALEPACK
Absorption correction
RC=reflections collected
IRC=independent RC
IRCGT=IRC and [I\2|(I)]
Refinement method
Data/restraints/parameters
R for IRCGT
15886
10726 [Rint=0.021]
9526
3.5. Complex 12
Full-matrix least-squares on F2
10726/18/466
R1 a=0.0438, wR2 b=0.0987
R1 a=0.0512, wR2 b=0.1029
1.055
A 0.03 g (0.17 mmol) sample of silver triflate was
added to a solution of 8 (0.091 g, 0.17 mmol) in CH2Cl2
(5 ml). The mixture was stirred for 3 h at r.t. The
solution was filtered, evaporated to dryness and washed
with 5 ml of ether. The residue was dissolved in CH2Cl2
(5 ml) and 1,1-diphenylpropynol (0.029 g, 0.2 mmol)
was added. After stirring for 1 h, the solvent was
evaporated and the crude product washed with 5 ml of
ether to afford the dark-violet powder 12 (85% yield).
31P{1H}-NMR (81.004 MHz, CDCl3): l 49.54 (s,
R for IRC
Goodness-of-fit c
Largest difference peak and hole 1.60 and −0.93
−3
,
(e A
)
a R1=ꢀ(ꢁꢁFoꢁ−ꢁFcꢁꢁ)/ꢀꢁFoꢁ.
b wR2=[ꢀw(F2o−Fc2)2/ꢀ[w(Fo2)2]1/2 where w=1/[|2(F2o)+7.73P+
(2.63P)2] where P=(Max(Fo2, 0)+2Fc2)/3.
c Goodness-of-fit=[ꢀw(F2o−F2c)2/(No−Nv)]1/2
.
1
3.4. Complex 8
PCy2). H-NMR (200.135 MHz, CDCl3): l 1.05–2.50
(m, 24H, Cy+CH2), 1.25 (d, J=7.0 Hz, 3H, isopropyl
CH3), 1.27 (d, J=7.0 Hz, 3H, isopropyl CH3), 2.30 (s,
3H, CH3 p-cymene), 2.60–3.10 (m, 3H, CH2+CH
isopropyl), 5.92–6.00 (m, 1H, Cp%), 6.10 (d, J=6.0 Hz,
1H, ꢁCH p-cymene), 6.47–6.83 (m, 6H, ꢁCH p-
cymene+Cp%), 6.55 (s, 5H, Cp), 7.47 (pseudotriplet,
J=7.4 Hz, 4H, o-Ph), 7.76 (triplet, J=7.4 Hz, 2H,
p-Ph), 7.88 (d, J=7.4 Hz, 4H, m-Ph). IR (KBr): 1964,
Under the above experimental conditions, 90% of 8
was isolated as a brick-red powder. 31P{1H}-NMR
(81.004 MHz, CDCl3): l 23.61 (s, PCy2). 1H-NMR
(200.135 MHz, CDCl3): l 1.15–2.41 (m, 24H, Cy+
CH2), 1.28 (d, J=7.0 Hz, 6H, isopropyl CH3), 2.09 (s,
3H, CH3 p-cymene), 2.72–2.98 (m, 3H, CH2+CH
isopropyl), 5.57 (pseudosinglet, 4H, ꢁCH p-cymene),
6.42 (pseudosinglet, 4H, Cp%), 6.56 (s, 5H, Cp). Anal.
Calc. for C34H49TiRuCl4P (779.5254): C, 52.39; H, 6.34.
Found: C, 52.92; H, 6.33%.
cm−1
.
3.6. General procedure for the RCM of
N,N-diallyltosylamide (10) promoted by the in situ
Ti–Ru–allenylidene complex 12
3.4.1. Crystal structure determination of complex 8
A red crystal of 8 (0.20×0.15×0.10 mm) suitable
for an X-ray analysis was obtained from a slow evapo-
ration of a CHCl3 solution of 8. The crystal was
mounted on an Enraf–Nonius Kappa-CCD using Mo–
A 0.0067 g (0.026 mmol) sample of silver triflate was
added to a solution of 8 (0.0195 g, 0.025 mmol) in
CH2Cl2 (1 ml). The mixture was stirred for 1 h at r.t.;

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P. Le Gendre et al. / Journal of Organometallic Chemistry 643–644 (2002) 231–236
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then 1,1-diphenylprop-2-yn-1-ol (0.0057 g, 0.027 mmol)
was added and the solution stirred for 30 min more at
r.t. The solution was then evaporated to dryness and a
deep-violet solid was thus obtained. To this solid, were
added toluene (5 ml) and N,N-diallyltosylamide (10)
(0.251 g, 1 mmol). The mixture was heated to 80 °C for
1 h. After evaporation of the solvent, N-tosyl-2,5-dihy-
dropyrrole (11) was purified by flash chromatography
on silica gel using diethyl ether–pentane (1:4) as eluent
and obtained as a white solid for which analytical data
are in full agreement with those reported in the litera-
ture [9b].
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 166284 for compound 8.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
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