The effect of titanium alkoxides in the synthesis of heterobimetallic complexes by titanocene(III) alkoxide-induced metal-metal bond cleavage of metal carbonyl dimers

Article abstract of DOI:10.1016/j.jorganchem.2004.09.075

A series of titanocene(III) alkoxides L₂Ti(III)OR where L = Cp, R = Et(1b), ^tBu(1a), 2,6-Me₂C₆H ₃(1c), 2,6-^tBu₂-4-Me-C₆H ₂(1d), or L = Cp*, R = Me(2e), ^tBu(2a), Ph(2f) was synthesized and subjected to reaction with [CpM(CO)₃]₂ [M = Mo, W], [CpRu(CO)₂]₂, and Co₂(CO) ₈. The Ti(III) precursors 1a, 1c, 2a, 2e, and 2f reacted with [CpM(CO)₃]₂ [M = Mo, W] to form heterobimetallic complexes L₂Ti(OR)(μ-OC)(CO)₂MCp [M = Mo, W], of which Ti and M are linked by an isocarbonyl bridge. Reactions of these Ti(III) complexes with Co₂(CO)₈ resulted in formation of Ti-Co₁ heterobimetallic complexes, Cp₂*Ti(O_tBu)(μ-OC) Co(CO)₃ from 2a, 2e, or 2f, or Ti-Co₃ tetrametallic complexes, Cp₂Ti(O^tBu)(μ-OC)Co₃(CO) ₉ from 1a, 1b, or 1c. The products were characterized by NMR, IR, and X-ray crystallography. Reaction mechanisms were proposed from these results, in particular, from steric/electronic effects of titanium alkoxides.

Full text of DOI:10.1016/j.jorganchem.2004.09.075

Journal of Organometallic Chemistry 690 (2005) 276–285
www.elsevier.com/locate/jorganchem
The effect of titanium alkoxides in the synthesis of heterobimetallic
complexes by titanocene(III) alkoxide-induced metal–metal bond
cleavage of metal carbonyl dimers
*
Shota Niibayashi, Kaoru Mitsui, Yukihiro Motoyama, Hideo Nagashima
Institute for Materials Chemistry and Engineering, Graduate School of Engineering Sciences, Kyushu University, Kasugakouen 6-1, Kasuga,
Fukuoka 816-8580, Japan
Received 8 July 2004; accepted 14 September 2004
Abstract
A series of titanocene(III) alkoxides L2Ti(III)OR where L = Cp, R = Et(1b), tBu(1a), 2,6-Me2C6H3(1c), 2,6-tBu2-4-Me–C6H2(1d),
or L = Cp*, R = Me(2e), tBu(2a), Ph(2f) was synthesized and subjected to reaction with [CpM(CO)3]2 [M = Mo, W], [CpRu(CO)2]2,
and Co2(CO)8. The Ti(III) precursors 1a, 1c, 2a, 2e, and 2f reacted with [CpM(CO)3]2 [M = Mo, W] to form heterobimetallic com-
plexes L2Ti(OR)(l-OC)(CO)2MCp [M = Mo, W], of which Ti and M are linked by an isocarbonyl bridge. Reactions of these Ti(III)
complexes with Co2(CO)8 resulted in formation of Ti–Co1 heterobimetallic complexes, Cpꢀ2TiðOtBuÞðl-OCÞCoðCOÞ from 2a, 2e, or
3
2f, or Ti–Co3 tetrametallic complexes, Cp2Ti(OtBu)(l-OC)Co3(CO)9 from 1a, 1b, or 1c. The products were characterized by NMR,
IR, and X-ray crystallography. Reaction mechanisms were proposed from these results, in particular, from steric/electronic effects of
titanium alkoxides.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Heterobimetallic complexes; Ti(III) alkoxides; Ti(III) complex; Dinuclear metal carbonyls
1. Introduction
t-butoxides, Cp2Ti(OtBu) (Cp = g5-C5H5; 1a) and
Cpꢀ2TiðOtBuÞ (Cp* = g5-C5Me5; 2a), with certain metal
carbonyl dimers, [CpM(CO)3]2 [M = Mo, W], [CpRu
(CO)2]2, and Co2(CO)8 [15]. Heterobimetallic com-
plexes, in which two organometallic units are linked
by an isocarbonyl bridge, Cp2Ti(OtBu)(l-OC)-
(CO)2MCp [M = Mo (3a-Mo), W (3a-W)] and their
Cpꢀ2Ti-homologues [M = Mo (4a-Mo), W (4a-W)], were
prepared from 1a or 2a with [CpM(CO)3]2, whereas a
Ti–Ru complex having a Ti–Ru direct bond, Cp2Ti
(OtBu)Ru(CO)2Cp (5a), was formed by photo-assisted
reaction of 1a with [Cp2Ru(CO)2]2 [15a]. Two Ti–Co
complexes, Cp2Ti(OtBu)(l-OC)Co(CO)3 (6a) and
Heterobimetallic complexes have received considera-
ble attention from organometallic chemists in terms of
potential cooperative effects by two metals in the com-
plex leading to activation of organic molecules in homo-
geneous catalysis [1]. In typical examples, their catalysis
has been investigated in hydroformylation [2–5], car-
bonylation [6], hydrogenation/isomerization [7], asym-
metric synthesis [8–11], olefin methathesis [12], enol
ester formation [13], and olefin polymerization [14]. In
our previous papers, we have reported unique access
to heterobimetallic complexes by reactions of titanocene
Cpꢀ2TiðOtBuÞðl-OCÞCoðCOÞ ð7aÞ were obtained by
3
treatment of 1a or 1b with Co2(CO)8; 6a readily reacted
with Co2(CO)8 existing in the reaction medium to result
in formation of Cp2Ti(OtBu)(l-OC)Co3(CO)9 (8a) [15b].
*
Corresponding author. Tel.: +81925837819; fax: +81925837819.
E-mail address: niba@cm.kyushu-u.ac.jp (S. Niibayashi).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.075

S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
277
A unique feature of these reactions is that the titano-
2. Results and discussion
cene(III) t-butoxides are good reagents to cleave the
metal–metal bond of metal carbonyl dimers, presumably
via electron transfer from Ti(III) to the metal dimer, and
the metal–metal bond cleavage leads to change of the
oxidation state of titanium from III to IV and formation
of heterobimetallic complexes. Although formation of
anionic organometallic compounds is often seen in reac-
tions of metal-carbonyl dimers with alkali metals or
mercury by way of the metal–metal bond fission [16],
it is rare that titanium(III) complexes act as reducing
reagents. On the other hand, a number of heterobimetal-
lic complexes which have an organotitanium moiety and
a metal carbonyl fragment in the molecule have been
synthesized and characterized; however, they are com-
monly synthesized from Ti(IV) precursors [1e,17–21].
In typical examples, treatment of Cp2TiCl2 with Li
[Co3(CO)10] gives Cp2Ti[(l-OC)Co3(CO)9]2 and LiCl
[17], whereas reaction of Cp2TiMe2 with CpMo(CO)3H
affords Cp2TiMe(l-OC)(CO)2MoCp via methane elimi-
nation [18]. The closest example to the Cp2Ti(OtBu)-in-
duced heterobimetalic formation is a brief comment
from a research group of Mo¨ıse, in which reaction of
Cp2TiCl with Co2(CO)8 slowly produced Cp2TiCl
(l-OC)Co3(CO)9 [22]. We reexamined the reaction of
Cp2TiCl with Co2(CO)8 and compared its reaction rate
with the reaction of 1a with Co2(CO)8 under similar
conditions; The reaction of Cp2TiCl was approximately
150 times slower than that of 1a. This clearly demon-
strates the special reactivity of titanocene t-butoxides
for the heterobimetallic formation, and prompted us
to compare their reactivity with other titanocene(III)
alkoxides. In this paper, we wish to report our studies
and findings on this t-butoxide effect, in which a series
of titanocene(III) alkoxides shown in Fig. 1 were synthe-
sized and systematically reacted with metal carbonyl di-
mers as shown in Scheme 1. The results showed that two
factors, steric circumstance around the titanium center
and monomeric or dimeric structure of the titano-
cene(III) alkoxides, proved to be important.
2.1. Preparation and characterization of titanocene(III)
alkoxides
It is known that Cp2TiCl exists as a chloro-bridged
dimer, Cp2Ti(l-Cl)2TiCp2 [23]. In sharp contrast, the
molecular structure of Cp2TiOtBu (1a) revealed a mono-
meric structure as reported previously [15a]. In several
other titanocene(III) alkoxides synthesized and charac-
terized, whether the complex is monomeric or dimeric
depends on the steric bulkiness of the ligands around
the titanium center [24,25]. In fact, a titanocene(III)
complex with a small alkoxide ligand such as Cp2TiOEt
(1b) is dimeric [24], whereas a sterically bulky titanium
alkoxide like Cp2Ti[O(2,6-tBu2-4-MeC6H2)] (1d) exists
as a monomer [25]. Since the bulky pentamethylcyclo-
pentadienyl group prevents the dimerization of
Cpꢀ2TiðORÞ, 2a, 2e, and 2f are monomeric regardless
of the steric bulkiness of the alkoxide [26].
We are interested in a new complex, Cp2Ti[O(2,6-
Me2C6H3)] (1c) which has a phenoxide of medium size,
and possibly has both monomeric and dimeric struc-
tures. Preparation of 1c was made by treatment of
Cp2TiCl with Li[O(2,6-Me2C6H3)] in THF at room tem-
perature for 12 h. Purification of the reaction mixture by
sublimation gave 1c as red violet crystals in 67% yield;
these were paramagnetic and showed an ESR signal at
g = 1.98 in a 1 · 10ꢁ5 M toluene solution. The molecular
structure of 1c was determined by crystallography, and
the ORTEP view is illustrated in Fig. 2. Similar to the
structure of 1a, 1c is monomeric, and two Cp and one
alkoxide are bound to the titanium center. There are
interesting differences in the Ti–O–C bond angle and
the bond distances of the Ti–O and O–C bonds in 1c
from those in 1a: the Ti–O–C angle of 1c [144.2 (2)ꢁ]
is smaller than that of 1a [175 (1)ꢁ]. The Ti–O bond of
˚
˚
1c [1.895 (2) A] is longer than that of 1a [1.810 (3) A],
˚
whereas the O–C bond of 1c [1.343 (4) A] is shorter than
˚
that of 1a [1.411 (5) A]. The reason for these significant
2a R = tBu
2e R = Me
1a R = tBu
1b R = Et
Ti OR
Me
Ti OR
2f R =
1c R =
(Cp*2TiOR)
(Cp2TiOR)
Me
tBu
1d R =
Me
tBu
Fig. 1. Titanocene(III) alkoxides.

278
S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
OR
L
L
L
L
Ti+
+
[CpM(CO)3]2
M = Mo, W
Ti OR
O C M-(CO)2Cp
L = Cp; 3-Mo, 3-W
L = Cp*; 4-Mo, 4-W
L = Cp, Cp*
hν
OR
L
L
L
Ti OR
L
Ti
+
[CpRu(CO)2]2
[Co(CO)4]2
∆
Ru(CO)2Cp
L = Cp; 5
L = Cp
OR
Ti+
L
L
L
+
Ti OR
L
O C Co(CO)3
L = Cp; 6
L = Cp*; 7
Co2(CO)8
L = Cp, Cp*
OR
-
L
L
(CO)3
Co
Ti+
O C
Co(CO)3
Co
L = Cp; 8
(CO)3
Scheme 1. The reactions of titanocene(III) alkoxides with metal carbonyl dimers leading to synthesis of heterometallic complexes.
˚
Fig. 2. The ORTEP drawing of 1c. Thermal ellipsoids are drawn at the 50% probability level. Representative bond distances (A) and angles (ꢁ):
Ti(1)–O(1) 1.895(2), O(1)–C(11) 1.343(4), Ti(1)-center of Cp (average) 2.349(1), Ti(1)–O(1)–C(11) 144.2(2), O(1)–Ti(1)-center of Cp (average) 107.4ꢁ.
differences in the bond distances and angles can be
attributed to the lower electron donating property of
the aryl group than the t-butyl group. In fact, the angle
and bond distances of 1c are similar to those of another
titanocene aryloxide 1d [25]. As shown in Fig. 3, two
lone pairs of the oxygen atom in 1a have strong interac-
tion with a Lewis acidic titanium center; this makes the
Ti–O bond shorter and the Ti–O–C angle larger. The
aryl group less electron-donating than alkyl groups
causes a reduction in the electron density of the oxygen
atom in 1c, contributing to elongation of the Ti–O bond
and shortening of the O–C bond.
Cp2Ti O CMe3
Cp2Ti O CMe3
Me
Me
Cp2Ti
O
Cp2Ti
O
Me
Me
Fig. 3. Two resonance structures for titanocene(III) alkoxides.

S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
279
We thus obtained the seven titanium(III) alkoxides
summarized in Fig. 1, one being dimeric and the other
six monomeric, and four the Cp-derivatives, the other
three their Cp* analogues. Using these, we next carried
out the reactions with metal carbonyl dimers.
OC bond of these complexes were observed by NMR in
solution. In the cases of Cpꢀ2TiðORÞ as starting materi-
als, the reactions were essentially reversible as described
later, but the equilibrium was favored for the products.
Thus, the products were able to be isolated and com-
pletely characterized by spectroscopy as shown in Table
1 and by elemental analysis. Interesting spectral features
of these Cpꢀ2Ti derivatives of heterobimetallic complexes
are three IR absorptions and two 13C resonances due to
the CO ligands. This clearly indicates that three CO lig-
ands exist, and two of them are terminal CO and
exchangeable in the NMR time scale. The remaining
CO ligand is an isocarbonyl bridge, and its Ti–O bond
is tight and difficult to dissociate in a C6D6 solution.
The reactions of Co2(CO)8 took place with all of the
titanocene alkoxides except 1d. Similar to the reactions
of 1a, 1b and 1c gave the corresponding Ti–Co3 prod-
ucts, 8b and 8c. The reactions of 2e and 2f with
Co2(CO)8 are analogous to that of 2a in affording the
corresponding Ti–Co complexes, 7e and 7f. All of these
new compounds are characterized from spectroscopy
(Table 2) in comparison with those of 6a, 7a, and 8a re-
ported previously, and the assignments were supported
by crystallographic analysis of two of the compounds.
The ORTEP drawings of two new compounds, 7e and
8b, as well as the representative bond distances and an-
gles are shown in Fig. 4. The heterobimetallic complex
7e bearing sterically bulky Cp*-ligands has an analo-
gous structure to 7a. Two metal fragments are linked
by an isocarbonyl bridge, and the Ti–O–C–Co moiety
is almost linear. Crystallographic disorder problems pre-
vent a detailed comparison in bond distances and angles
between 7a and 7e, but similarities apparently exist. In
contrast, the complex 8b is a Ti–Co3 compound analo-
gous to 8a; the bond length of Ti-O(CCo3) in 8b is
2.2. Reactions of titanocene alkoxides with metal
carbonyl dimers
First, the titanocene alkoxides synthesized were sub-
jected to the reactions with [CpMo(CO)3]2 or
[CpW(CO)3]2. As reported previously, 1a and 2a reacted
with [CpMo(CO)3]2 or [CpW(CO)3]2 to form the corre-
sponding heterobimetallic complex, Cp2Ti(OtBu)
(l-OC)(CO)2MCp [M = Mo (3a-Mo), W (3a-W)] and
Cpꢀ2TiðOtBuÞðl-OCÞðCOÞ MCp [M = Mo (4a-Mo), W
2
(4a-W)] [15]. Among the Cp-substituted titanocene alk-
oxides, 1b and 1d did not react with [CpM(CO)3]2, but
the reaction with 1c reversibly formed the corresponding
heterobimetallic complexes, 3c-Mo and 3c-W; a toluene-
d8 solution of a 1:1 mixture of 1c and [CpM(CO)3]2 gave
a 40:60 equilibrium mixture of the heterobimetallic
product and the starting materials. Isolation of the com-
plexes was difficult to achieve due to the reversibility of
3c-Mo or 3c-W to a mixture of 1c and [CpM(CO)3]2;
however, the structures homologous to the t-butoxy
derivatives can be assigned from the spectroscopic simi-
larities between 3a-Mo and 3c-Mo and those between
3a-W and 3c-W as summarized in Table 1. In these com-
plexes, 1H and 13C resonances due to the CpTi and CpM
(M = Mo, W) moieties are seen in the region of dH
(CpTi) 5.88–5.94, dC (CpTi) 117.19–118.98, and dH
(CpM) 5.19–5.33, dC (CpM) 87.81–89.93. Only one 13C
signal due to the three CO ligands was visible because
of their rapid scrambling in the NMR time scale; how-
ever, they can be differentiated by their IR spectra,
which showed two terminal (1813–1837 and 1909–1923
cmꢁ1) and one isocarbonyl bridging CO (around 1590
cmꢁ1) absorptions. In other words, the one CO peak ob-
served reflects that cleavage and reformation of the Ti–
˚
apparently shorter than 8a [1.98(1) and 2.026(5) A,
respectively], whereas the C–O bond distance of the iso-
carbonyl bridge in 8b is longer than 8a [1.297(15) and
˚
1.231(7) A, respectively]. Since the OEt group in 8b is
less bulky than the OtBu moiety in 8a, the steric repulsion
Table 1
Spectral data of Ti–Mo or Ti–W heterobimetallic complexes
Spectroscopy
Assignment
3a-Mo
3c-Mo
3a-W
3c-W
4a-Mo
4e-Mo
4f-Mo
4a-W
4e-W
4f-W
1H NMRad, ppm
Cp or Cp*Ti
CpM
5.91(s)
5.29(s)
5.88(s)
5.33(s)
5.94(s)
5.19(s)
5.90(s)
5.20(s)
1.78(s)
5.40(s)
1.73(s)
5.38(s)
1.74(s)
5.43(s)
1.80(s)
5.31(s)
1.74(s)
5.28(s)
1.76(s)
5.33(s)
13C NMRa d, ppm
Cp or Cp*Ti
117.19
118.98
117.08
118.97
13.00
127.50
89.16
11.83
126.67
89.39
12.26
128.87
89.64
13.08
127.35
87.60
12.10
126.69
88.02
12.27
128.66
88.06
CpM
CO
89.35
226.90
248.10
89.93
226.99
87.81
214.25
242.47
88.39
214.33
233.50
241.34
233.34
242.47
223.29
241.26
223.84
234.47
223.90
232.50
223.52
234.57
IR (KBr) cmꢁ1
mCO
1920(s)
1833(s)
1648(m)
1612(m)
1923(s)
1837(s)
1587(s)
1909(s)
1813(s)
1601(s)
1920(s)
1826(s)
1587(s)
1923(s)
1833(s)
1653(s)
1911(s)
1829(s)
1618(s)
1926(s)
1833(s)
1639(s)
1911(s)
1824(s)
1619(s)
1910(s)
1824(s)
1814(s)
1620(s)
1922(s)
1829(s)
1642(s)
a
Measured in toluene-d8 (for 3) or benzene-d6 (for 4).

280
S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
Table 2
Spectral data of Ti–Co or Ti–Co3 heterometallic complexes
Spectroscopy
Assignment
Cp or Cp*Ti
Cp or Cp*Ti
8a
8b
8c
7a
7e
7f
1HNMR,a d, ppm
13C NMR, d, ppm
5.93(s)
115.50
6.13(s)
117.67
5.96(s)
117.35
1.65(s)
1.61(s)
1.62(s)
12.80
128.44
201.20
11.68
125.57
202.76
12.26
c
–
204.57
b
CO
203.30
–
203.03
IR (KBr) cmꢁ1
m co
2077(w)
2028(sh)
2015(s)
1988(s)
1980(s)
1405(s)
1999(s)
1965(s)
1441(s)
2019(s)
1921(s)
1766(s)
2019(s)
1933(sh)
1919(s)
1767(s)
1750(s)
2021(s)
1936(s)
1920(s)
1753(s)
2001(s)
1989(sh)
1972 (m)
1472(s)
a
Measured in toluene-d8 (for 8a and 8c) or benzene-d6 (for 8b, 7a, 7e and 7f).
The signal was not detected because of rapid CO ligand exchange.
The peak was overlapped with the solvent signal.
b
c
Fig. 4. The ORTEP drawings of (a) 7e and (b) 8b. Thermal ellipsoids are drawn at the 50% probability level. Two chemically equivalent but
crystallographically independent molecules are included in a unit cell of 8b, and one of them is illustrated in this figure. Representative bond distances
˚
(A) and angles (ꢁ): 7e Ti(1)–O(2) 2.23(1); O(2)–C(23) 1.26(1); Ti(1)–O(1) 1.813(9); O(1)–C(22) 1.42(2); C(23)–Co(1) 1.686(5); 8b Ti(1)–O(1) 1.79(1);
O(1)–C(11) 1.33(2); Ti(1)–O(2) 1.98(1); O(2)–C(13) 1.29(2); Ti(1)–O(1)–C(11) 151.1(8); Ti(1)–O(2)–C(13) 162.9(10); O(1)–Ti(1)–O(2) 98.2(5).
t
between the Cp* ring and the alkoxy group is likely to
be reduced. We also confirmed the structural analogy
of 8c to 8a or 8b by crystallography of 8c, though the
R value (R1 = 0.11) was not satisfactory (see Supporting
information). The reactions of [CpRu(CO)2]2 with all of
the titanocene alkoxides other than 1a did not occur
either thermally or photochemically (see Table 4).
A summary of these reactions is shown in Table 3.
In the reactions of Cp2TiOR with [CpMo(CO)3]2
or [CpW(CO)3]2, it is of interest that two of the
titanocene(III) alkoxides did not react at all: one is a
dimer, [Cp2Ti(OEt)]2 (1b), whereas the other is
Cp2Ti[O(2,6-tBu2-4-MeC6H2)] (1d) having a sterically
bulky phonoxide. A monomeric form of 1b could be
generated reversibly in solution; however, its reaction
with [CpM(CO)3]2 would be less favorable than the re-
verse formation of the dimer. Two Bu groups in the
O(2,6-tBu2-4-MeC6H2) group in 1d, of which the molec-
ular structure was determined by Cetinkaya et al. [25],
completely protected the metal center, and prohibited
access of the CpM(CO)3 species to the titanium atom.
The heterobimetallic formation proceeded when OR =
OtBu and O(2,6-Me2C6H3); the reaction rates are signif-
icantly different [OR = OtBu ꢂ O(2,6-Me2C6H3)]. The
electron-donating tBuO group may contribute to the ra-
pid reaction. Three complexes, 2a, 2e, and 2f having
electron-rich Cp* ligands also react with [CpM(CO)3]2
almost instantly regardless of the alkoxy group (OtBu,
OMe, and OPh) attached to the titanium atom. As re-
ported previously, the Ti–Mo and Ti–W heterobimetal-
lic complex formation is essentially reversible [15a].
Introduction of electron-donating substituents is likely

S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
281
Table 3
Reactions of L2TiOR with [CpM(CO)3]2 (M = Mo, W) or Co2(CO)8
L2TiOR
Reaction with [CpMo(CO)3]2
Reaction with [CpW(CO)3]2
Reaction with Co2(CO)8
b
Timea
Product (% yield)
Eq.b
Timea
Product (% yield)
Eq.b
Timea
Product (% yield)
Eq.
1a
1b
1c
1d
2a
2e
2f
a
<5 min
No reaction
48 h
3a-Mo (ꢁ)
26:74
<5 min
No reaction
48 h
3a-W (ꢁ)
30:70
<5 min
48 h
48 h
8a (60)
8b (65)
8c (40)
0:100
0:100
0:100
3c-Mo (ꢁ)
60:40
3c-W (ꢁ)
60:40
No reaction
<5 min
<5 min
No reaction
<5 min
<5 min
No reaction
<5 min
<5 min
<5 min
4a-Mo (70)
4e-Mo (42)
4f-Mo (70)
0:100
0:100
0:100
4a-W (61)
4e-W (20)
4f-W (72)
0:100
0:100
0:100
7a (66)
7e (67)
7f (68)
0:100
0:100
0:100
<5 min
<5 min
The reaction time to reach the equilibrium.
The equilibrium ratio of the starting materials to the bimetallic product.
b
Table 4
Crystallographic tables of 1c, 7e, and 8b
1c
7e
8bd
Empirical formula
Formula weight
Crystal system
Space group
C18H19OTi
299.25
C25H33O5TiCo
520.34
Triclinic
C22H15O11TiCo3
680.05
Orthorhombic
P212121
Triclinic
P1
ꢀ
P1
˚
a (A)
7.945(3)
13.831(7)
10.6577(12)
13.0602(16)
9.9219(13)
95.247(6)
107.642(4)
92.517(6)
1306.8(3)
2
8.250(3)
12.481(5)
13.372(5)
93.55(3)
87.47(3)
112.52(3)
1269.1(8)
2
˚
b (A)
˚
c (A)
13.889(6)
90
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
3
˚
V (A )
1526(1)
4
1.302
Z
Dcalcd (Mg/m3)
1.322
0.970
544
1.779
2.288
Absorption coefficient (l, mmꢁ1
F(000)
Crystal size (mm)
)
0.554
628
676
0.10 · 0.10 · 0.10
9328
0.50 · 0.20 · 0.15
3496
0.45 · 0.35 · 0.05
5578
Number of reflections measured
Number of independent reflections (Rint
Number of reflections observed (>2r)
Refinement method
GOFa
)
3496 (0.00)
3254
5578 (0.00)
3324
9328 (0.00)
7268
Full-matrix least-squares on F2
1.068
Full-matrix least-squares on F2
1.023
Full-matrix least-squares on F2
1.03
R1 [I > 2r(I)]b
0.0505
0.0568
0.0711
0.1272
0.0414
0.0967
wR2 [I > 2r(I)]c
R1 (all data)b
0.1085
0.1109
0.1577
0.1943
0.0618
0.1063
wR2 (all daꢁta3)c
˚
Dqmax (e A
)
0.466 and ꢁ0.608
0.351 and ꢁ0.520
0.455 and ꢁ0.765
P
2
1=2
a
GOF ¼ ½ wðF 2o ꢁ F 2c Þ =ðN ꢁ PÞꢃ
.
P
P
b
c
R(F) = jjFoj ꢁ jFcjj/ jFoj.
P
P
2
2 1=2
wRðF 2Þ ¼ ½ wðF 2o ꢁ F c2Þ = wðF 2oÞ ꢃ
.
Two chemically equivalent but crystallographically independent molecules are included in a unit cell.
d
to take part in favorable formation of the product; the
equilibrium ratios between the starting materials,
L2Ti(OR) and [CpM(CO)3]2, and the product,
L2Ti(OR)(l-OC)(CO)2MCp, were altered in the order
of electron donating nature of the auxiliary ligands,
i.e., 60:40 [L = Cp, OR = O(2,6-Me2C6H3)], 26: 74–
30:70 [L = Cp, OR = OtBu], and 0:100 (L = Cp* regard-
less of OR). Although the reaction of Cp*2Ti(OR) with
[CpM(CO)3]2 looked irreversible, the following NMR
experiments offering evidence for the scrambling of the
metal fragments as shown in Scheme 2 unequivocally
mixture of 4e-Mo and 4f-W at room temperature gave
peaks due to a mixture of 4e-Mo, 4e-W, 4f-Mo, and
4f-W. Similarly, reaction of 4a-W with 4f-Mo took place
instantly to afford a mixture of 4a-Mo, 4a-W, 4f-Mo,
and 4f-W.
The titanocene(III) alkoxides reacted with Co2(CO)8
to result in formation of the Ti–Co products. Exception
is 1d which is sterically crowded around the titanium
atom. Similar to the reactions of the titanocene(III)-t-
butoxides, 1a and 2a, those of Cp2Ti(OR), 1b and 1c,
gave the corresponding clusters containing one Ti and
three Co atoms, whereas Cpꢀ2TiðORÞ complexes, 2e
1
proved the reversibility. Thus, H NMR spectrum of a

282
S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
OR1
Cp*
Cp*
Cp*2Ti(OR1)
Ti+
OR2
Cp*
Cp*
Ti+
+
O C Mo-(CO)2Cp
O C Mo-(CO)2Cp
Cp*2Ti(OR2)
+
+
+
OR2
OR1
Cp*
Cp*
Cp*
Ti+
Ti+
[CpMo(CO)3]2
+
O C W-(CO)2Cp
O C W-(CO)2Cp
Cp*
[CpW(CO)3]2
Scheme 2. Scrambling of metal fragments suggesting the reversibility of the reaction of CpꢀTiðORÞ with [CpM(CO)3]2 (M = Mo, W).
2
and 2f, formed the Ti–Co heterobimetallic products.
The reason why Ti–Co3 clusters formed in the reactions
of the Cp-substituted titanocene alkoxides can be attrib-
uted to the fact that the Ti–Co bimetallic complexes are
generally not very stable unless the bulky and electron-
donating Cp* ligands stabilize them, as discussed in
our previous paper [15]. Among the monomeric titano-
cene alkoxides, 1a, 1c, 2a, 2e, and 2f, 1c reacted
Co2(CO)8 more slowly than others; this is attributed to
the electron-withdrawing nature of the aryloxy ligand
as discussed in the reactions with [CpM(CO)3]2. Of par-
ticular importance is that Co2(CO)8 can react with a
monomer, Cp2Ti(OEt), which is reversibly formed the
dimer, [Cp2Ti(l-OEt)]2 (1b), in solution. Since regenera-
tion of the dimer of Cp2Ti(OEt) from the monomer pre-
dominantly occurs, the reaction of 1b with [CpM(CO)3]2
does not take place. In contrast, Co2(CO)8 is more reac-
tive than [CpM(CO)3]2, being reactive with generated
monomer to form 8b. Since this process is somewhat
complicated and produces an amount of unknown by-
products, detailed analysis of the reaction mechanisms
including equilibrium formation of the monomeric form
of 1b is difficult at present. Proposed mechanisms for
titanocene(III)-induced reactions with Co2(CO)8 or
[CpM(CO)3]2 are summarized in Scheme 3.
Photo-assisted reaction of titanocene(III) alkoxides
with [CpRu(CO)2]2 was only observed when 1a was
used as the organotitanium source. The mechanism
must be different from that of the thermal processes
shown in Scheme 3, in which electron transfer from
the Ti(III) species to the metal carbonyl dimer induces
the Ti–O bond formation and the metal–metal bond
R
O
L2Ti
TiL2
O
R
cases that
L and
R are not
bulky
"OC-M-M-CO"
from Co2(CO)8
and [CpM(CO)3]2
(M = Mo, W)
OR
L2Ti
O
C
OR
L2Ti-OR
monomeric form
L2Ti
2
M M
O C M
C
O
TiL2
RO
cases that L is small and M = Co
OR
L2Ti
O C Co
(OC)4Co-Co(CO)4
- 2CO
OR
L2Ti
OR
L2Ti
(OC)3Co Co(CO)3
O
OR
C
O C Co
Co Co
Co
Co
L2Ti
O C Co
Co
Scheme 3. Proposed mechanisms for the titanocene(III) alkoxides-induced formation of heterobimetallic complexes.

S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
283
cleavage. One explanation for the photoreaction is gen-
4.2. Preparation of Cp2Ti[O(2,6-Me2C6H3)] (1c)
eration of Cp(OC)2Ruꢀ, which is trapped by the metal-
centered radical of 1a. The trapping is presumably very
sensitive towards a small change of the electronic prop-
erties and steric circumstances of the titanium atom,
and other titanocene(III) alkoxides shown in this paper
are unlikely to be suitable for the Ti–Ru bond
formation.
Preparation of lithium 2,6-dimethylphenoxide was
done by treatment of 2,6-dimethylphenol with n-BuLi
in THF. In a 100 ml flask were placed [Cp2TiCl]2 (213
mg, 0.5 mmol), Li[O(2,6-Me2C6H3)] (128 mg, 1 mmol),
and THF (30 ml), and the mixture was stirred overnight
at room temperature. The resulting red-violet solution
was concentrated, and the residue was extracted with
toluene (30 ml). After removal of toluene from the ex-
tracts, the solid materials were purified with sublimation
(2 · 10ꢁ2 Torr, 90 ꢁC) to afford the desired product. The
solid was recrystallized from THF/pentane to afford
purple needle-like crystals of 1c in 67% yield (200 mg);
m.p. 116–117 ꢁC. Anal. Calcd. for C18H9OTi: C,
3. Conclusion
The titanocene(III)-induced reactions of metal carbo-
nyl dimers are unique methods for synthesis of heterobi-
metallic complexes, by which complexes containing one
organotitanium moiety and either organomolybdenum,
tungsten, ruthenium, or cobalt species are readily ob-
tained. Our previous papers reported special reactivity
of titanocene t-butoxides, 1a and 2a, for these reactions,
whereas the present studies changing the alkoxides in
L2Ti(OR) (L = Cp or Cp*) clearly demonstrated how
electronic and steric factors of the L and OR groups af-
fect the reactions. On the basis of these findings, one can
predict the results of the reactions, e.g., the reaction rate,
reversibility in the cases using [CpM(CO)3]2, and
nuclearity of the product in the reaction with Co2(CO)8.
These results contribute to understanding of the hetero-
bimetallic chemistry, and further synthetic as well as
mechanistic studies [27] or these reactions and applica-
tion of these new complexes to homogeneous catalysis
are being undertaken.
1
72.19; H, 6.39. Found: C, 71.92; H, 6.40%. H NMR
(C6D6) broad peaks appeared at d 4.13, 4.74, 8.00. MS
(m/z) 299. ESR (toluene, 1 · 10ꢁ5 M) g = 1.98.
4.3. Reversible reactions of Cp2Ti(OR) with
[CpM(CO)3]2
In a typical example, 1c (6.0 mg, 0.02 mmol) and
[CpMo(CO)3]2 (4.9 mg, 0.01 mmol) were dissolved in
toluene-d8 in a 5 mm i.d. NMR tube. The reaction
was achieved instantly, and produced an equilibrium
mixture of the product (3c-Mo) and the starting materi-
als (1c and [CpMo(CO)3]2) in a ratio of 40:60. In a sim-
ilar fashion, an equilibrium mixture of 3c-W, 1c, and
[CpW(CO)3]2 was obtained (the product: the starting
materials = 40:60). The products were assigned from
the spectroscopic similarity to 3a-Mo or 3a-W as sum-
marized in Table 1.
4. Experimental
4.4. Reactions of Cpꢀ2Ti(OR) with [CpM(CO)3]2
4.1. General
In a typical example, Cpꢀ2TiOMe ð2eÞ (35 mg, 0.10
mmol) and [CpMo(CO)3]2 (25 mg, 0.051 mmol) were
dissolved in toluene (4 ml) in a 20 ml Schlenk tube.
The resulting dark red solution was stirred for 5 min
at room temperature. After removal of the solvent in va-
cuo, the residue was recrystallized from a mixture of
THF and pentane to give the desired product, 4e-Mo,
as brown microcrystals (25 mg). NMR observation of
the crude product revealed the complete conversion of
the starting materials to the product; however, signifi-
cant loss of the materials in the recrystallization process
lowered the isolated yields of the products. 4e-Mo: 42%
isolated yields; m.p. 183 ꢁC (dec). Anal. Calcd. for
C29H38O4TiMo: C, 58.59; H, 6.44. Found: C, 58.55;
H, 6.39%. 4e-W: 20% isolated yields; m.p. 168 ꢁC
(dec). Although the equilibrium inhibited the prepara-
tion of samples suitable for elemental analysis, its spec-
tropic similarity to 4e-Mo is enough to assign the
structure of 4e-W. 4f-Mo: 70% isolated yields; m.p.
195 ꢁC (dec). Anal. Calcd. for C34H40O4TiMo: C,
All reactions were carried out with the Schlenk tech-
nique associated with experiments using a glove box
filled with dry nitrogen gas containing less than 1
ppm of O2 and H2O. Toluene-d8 was dried over so-
dium and distilled just before use. Other solvents
(THF, benzene, toluene, pentane, benzene-d6) were dis-
tilled from sodium benzophenone ketyl, and other rea-
gents were used as received. [Cp2TiCl]2 [28] and
titanocene(III) alkoxides, 1a [15a], 1b [24], 1d [25], 2a,
2e, and 2f [26], were prepared according to the meth-
ods reported in the literature. NMR spectroscopy was
carried out with JEOL Lambda 400 and 600 spectrom-
eters. Chemical shifts (d, ppm) were recorded from
residual peaks of the deuterated solvents. ESR spectra
were taken with a JEOL JES FE-3X. IR spectra were
measured with a JASCO FT/IR-550 spectrometer and
the absorptions were recorded in cmꢁ1. The spectral
data of the heterobimetallic complexes are summarized
in Tables 1 and 2.

284
S. Niibayashi et al. / Journal of Organometallic Chemistry 690 (2005) 276–285
62.20; H, 6.14. Found: C, 62.12; H, 6.11%. 4f-W: 72%
isolated yields; m.p. 217 ꢁC (dec). Anal. Calcd. for
C34H40O4TiW: C, 54.86; H, 5.42. Found: C, 54.88; H,
5.46%. 4a-W: 61% isolated yields; m.p. 145 ꢁC (dec).
Anal. Calcd. for C32H44O4TiW: C, 53.06; H, 6.12.
Found: C, 52.86; H, 6.15%.
tube was flame-sealed under reduced pressure, then irra-
diated for 4 h by 500 W Xe lamp at ꢁ10 ꢁC. The reac-
1
tion was monitored by H NMR spectroscopy.
4.8. X-ray data collection and reduction
Single crystals of 1c, 7e, and 8b were grown from
THF/pentane. X-ray crystallography was performed
on a Rigaku RAXIS RAPID imaging plate diffractom-
eter with graphite monochromated Mo Ka radiation
4.5. Reactions of Cp2Ti(OR) with Co2(CO)8
In a typical example, 1c (60 mg, 0.20 mmol) and
Co2(CO)8 (137 mg, 0.40 mmol) were dissolved in toluene
(5 ml) in a 20 ml Schlenk tube. The mixture was stirred
in a glove box for two days at room temperature. After
removal of the solvent in vacuo, excess amounts of
Co2(CO)8 were removed by sublimation (1 · 10ꢁ3 Torr,
at room temperature, for 1 day). Recrystallization of the
resulting black solids from toluene at ꢁ35 ꢁC gave the
desired Ti–Co3 compound, 8c as black crystals. NMR
observation of the crude product revealed the complete
conversion of the starting materials to the product; how-
ever, significant loss of the materials in the recrystalliza-
tion process lowered the isolated yields of the products.
8c: 40% isolated yields; m.p. 128 ꢁC. Anal. Calcd. for
C28H19O11TiCo3: C, 44.48; H, 2.53. Found: C, 44.29;
H, 2.63%. Treatment of 1b with Co2(CO)8 afforded 8b
(65% isolated yield), and some unidentified by-products.
Although a single crystal suitable for X-ray analysis was
obtained, difficulty in removing small amounts of the
by-products prevented preparation of pure samples suit-
able for elemental analysis.
˚
(k = 0.71070 A). The data were collected at 123(2) K
(1c and 8b) and 173(2) K (7e) using x scan in the h range
of 3.28 6 h 6 27.48ꢁ (1c) and 2.46 6 h 6 27.48ꢁ (7e),
3.05 6 h 6 27.48ꢁ (8b). Data collection and cell refine-
ment were done using ÔMSC/AFC Diffractometer Con-
trol’’ on a Pentium computer. The structures were
solved by direct method (SIR92) [29a] and were refined
using full-matrix least squares (SHELXL97) [29b] based
on F2 of all independent reflections measured. The occu-
pancies of each disordered fragment of 7e were refined
with constraints that their sum is 1 (0.52:0.48). All H
atoms were located at ideal positions. They were in-
cluded in the refinement, but restricted to riding on
the atom to which they were bonded. Isotropic thermal
factors of H atoms were held to 1.2–1.5 times (for
methyl groups) Ueq of the riding atoms.
Appendix A. Supplementary data
1H NMR charts showing the metal fragment scram-
bling in the reactions of 4e-Mo and 4f-W (Fig. S-5-1)
and that of 4a-W with 4f-Mo (Fig. S-6-1). Crystallo-
graphic data for the structural analyses have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 243161, 243162, 243163 for com-
pounds 1c, 7e and 8b, respectively. Copies of the data
can be obtained, free of charge, from The Director
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44 1223 336033 or e-mail: deposit@ccdc.cam.
ac.uk). A preliminary X-ray structure of 8c is described
as a supporting information. Supplementary data asso-
ciated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2004.09.075.
4.6. Reactions of Cpꢀ2Ti(OR) with Co2(CO)8
In a typical example, a mixture of 2e (50 mg, 0.14
mmol) and Co2(CO)8 (25 mg, 0.07 mmol) was dissolved
in THF (5 ml) in a 20 ml Schlenk tube. The resulting
dark red solution was stirred for 5 min at room temper-
ature. After the solvent was removed in vacuo, the resi-
due was recrystallized from a mixture of pentane and
THF at ꢁ30 ꢁC to form 7e as brown crystals. NMR
observation of the crude product revealed the complete
conversion of the starting materials to the product; how-
ever, significant loss of the materials in the recrystalliza-
tion process lowered the isolated yields of the products.
7e: 67% yields; m.p. 120 ꢁC (dec). Anal. Calcd. for
C25H33O5TiCo: C, 57.31; H, 6.39. Found: C, 57.23; H,
6.37%. 7f: 68% yield; m.p. 117 ꢁC (dec). Anal. Calcd.
for C30H35O5TiCo: C, 61.87; H, 6.06. Found: C, 61.88;
H, 6.03%.
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