Synthesis and crystal structure of oxo-bridged binuclear titanium complex [{Ti(acac)2Cl}{TiCp2(Cl)}(μ-O)] and its catalytic reactions toward silation of aldehyde

Article abstract of DOI:10.1016/S0022-328X(01)01021-X

Reaction of [Cp₂TiCl₂] with two equivalents of 2,4-pentanedione in the presence of one equivalent of NEt₃ in CH₃CN at room temperature yielded oxo-bridged binuclear titanium complex [{Ti(acac)₂Cl}{TiC

Full text of DOI:10.1016/S0022-328X(01)01021-X

Journal of Organometallic Chemistry 631 (2001) 16–18
www.elsevier.com/locate/jorganchem
Synthesis and crystal structure of oxo-bridged binuclear titanium
complex [{Ti(acac)2Cl}{TiCp2(Cl)}(m-O)] and its catalytic reactions
toward silation of aldehyde
Sock-Sung Yun a,*, IL-Hwan Suh a, Eun Hee Kim a, Byong-Jin Choi a,
Samkeun Lee b,*
a Department of Chemistry and Department of Physics, Chungnam National Uni6ersity, Taejon 305-764, Republic of Korea
b Department of Chemistry, Taejon Uni6ersity, Taejon 300-716, Republic of Korea
Received 13 November 2000; received in revised form 10 May 2001; accepted 15 May 2001
Abstract
Reaction of [Cp2TiCl2] with two equivalents of 2,4-pentanedione in the presence of one equivalent of NEt3 in CH3CN at room
temperature yielded oxo-bridged binuclear titanium complex [{Ti(acac)2Cl}{TiCp2(Cl)}(m-O)], which was characterized crystallo-
graphically and spectroscopically. Reaction mixture of oxo-bridged binuclear titanium complex and 2nBuLi catalytically activate
the mixture of phenylsilane and aldehyde to yield O-silation products at room temperature. © 2001 Elsevier Science B.V. All
rights reserved.
Keywords: Oxo-bridged binuclear titanium; Diffraction studies; O-Silation; Aldehyde
1. Introduction
2. Results and discussion
Organometallic compounds of early transition ele-
ments have an important role in the development of
both synthetic organometallic and catalytic chemistry
[1,2]. Dialkyl metallocenes of Group 4 elements could
be utilized as the catalysts for the hydrosilation of
olefins and aldehydes, and dehydrogenative silation of
alcohols [3]. During studies of the reactivity of
‘Cp2Ti(II)’ [4] generated from [Cp2TiCl2] and 2nBuLi
toward diketones, we have reported the easy method
for the preparation of [Ti(III)(acac)3] complex [5] and
titanocene(III) b-diketonate complexes [6], and their
X-ray crystal structures [5,6]. We have also reported the
alternative formation of [CpZr(acac)2Cl], and its cata-
lytic reaction toward various aldehydes [7].
Reaction of [Cp2TiCl2] with two equivalents of 2,4-
pentanedione and one equivalent of NEt3 in CH3CN at
room temperature resulted in the formation of a
brownish red solution in 2 h (Eq. (1)). Layering of ether
to the toluene extracts afforded red cubes of 1 in 40%
1
yield. Complexities of the chemical shifts in H-NMR
spectrum of 1 in CDCl3 prompted us to examine the
diffraction studies of 1. Fig. 1 shows a perspective view
of 1 along with selected bond distances and angles.
In this report we wish to report the synthesis of
oxygen-bridged titanium(IV) complex, [{Ti(acac)2Cl}-
{TiCp2(Cl)}(m-O)] (1), and its catalytic reactions toward
silation of aldehyde.
(1)
A molecule consists of two titanium atoms, two chlo-
rine atoms, two cyclopentadienyl, two acetylacetonate
and an oxygen atom connecting the two titanium
,
atoms. The distance of Ti(1)ꢀO(5) in 1 is 1.914(3) A
and is 0.184(3)
Ti(2)ꢀO(5). The distance between Ti(2) and oxygen
* Corresponding authors. Tel.: +82-42-8215478; fax: +82-42-
8228632.
E-mail address: ssyun@cnu.ac.kr (S.-S. Yun).
,
A longer than the distance of
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01021-X

S.-S. Yun et al. / Journal of Organometallic Chemistry 631 (2001) 16–18
17
troscopically. Other aldehydes and phenylsilanes were
similarly reacted with the catalytic amount of 1 and
2nBuLi in THF (Eq. (2)), and the products were charac-
terized by GC–MS. Results are summarized in Table 1.
n
1+2 BuLi
Aldehyde+PhSiH3 ꢀꢀꢀꢀꢀꢁ O-silation products
(2)
THF
For propionaldehyde and butyraldehyde, tris(alkoxy)-
phenylsilane was catalytically formed, respectively.
However, a mixture of 1 and 2nBuLi did not activate
the acetaldehyde and the benzaldehyde. The reason for
the failure of O-silation reaction was unclear, and
efforts to elucidate the reasons and the pathway for
n
O-silation reaction by 1 and BuLi are being under-
taken.
,
Fig. 1. ORTEP drawing of 1. Selected bond distances (A) and angles
(°): Ti(1)ꢀO(5) 1.914(3), Ti(2)ꢀO(5) 1.730(3), Ti(2)ꢀO(1) 1.980(4),
Ti(2)ꢀO(2) 2.105(4), Ti(2)ꢀO(3) 2.010(4), Ti(2)ꢀO(4) 1.982(4),
Ti(1)ꢀCent(1) 2.052(3), Ti(1)ꢀCent(2) 2.058(3), Ti(1)ꢀCl(1) 2.3632(19),
Ti(2)ꢀCl(2) 2.3405(19), Cl(1)ꢀTi(1)ꢀO(5) 94.68(13), Cent(1)ꢀTi(1)ꢀ
Cent(2) 131.63(14), Cl(2)ꢀTi(2)ꢀO(5) 94.90(14). *Cent1: C(11), C(12),
C(13), C(14), C(15). *Cent2: C(16), C(17), C(18), C(19), C(20).
3. Experimental
3.1. General procedures
All manipulations were carried out using standard
Schlenk techniques under an inert atmosphere of nitro-
gen. Acetonitrile was distilled from P2O5, and toluene
and ether were distilled from potassium/benzophenone
ketyl under nitrogen, respectively. All solvents were
deoxygenated immediately prior to use. [Cp2TiCl2], 2,4-
pentanedione, NEt3, acetaldehyde, benzaldehyde, pro-
pionaldehyde, and butyraldehyde were purchased from
Aldrich and used without purification. 1H- and 13C-
NMR spectra were recorded at 25 °C on a Bruker AM
300 (1H-NMR 300 MHz, 13C-NMR 75.5 MHz) spec-
trometer and infrared spectra were obtained on a Shi-
madzu FTIR-8300. GC-MS were taken on a JEOL
JES-DX 303 mass spectrometer equipped with JMA-
DA 500 data system. X-ray diffraction studies were on
crystals mounted on a fine glass rod. A minimum
amount of epoxy resin was used to affix the crystal.
X-ray data were collected on a Siemens R3m/V.
,
ranges from 2.105(4) to 1.980(4) A, with an average of
,
,
2.019(4) A and is 0.05–0.06 A longer than that of TiꢀO
in titanocene(III) b-diketonate complexes [5,6,8]. The
five oxygen atoms and a chlorine Cl(2) atom coordi-
nated Ti(2) atom form a slightly distorted octahedron.
The O(5) atom bridges two titanium atoms almost
linearly with an angle of 171.96(15)°.
It has been reported that [CpTi(acac)2Cl] is prepared
from the same reaction as Eq. (1), characterized spec-
troscopically, and 1H-NMR spectrum of [CpTi(a-
cac)2Cl] reveals the co-existence of several isomers in
solution state [9]. To find the source of the bridged
1
oxygen, we examined the H-NMR spectra of the crude
products generated from the reaction of Eq. (1) in the
presence of a stoichiometric amount of oxygen or wa-
1
ter. H-NMR spectrum of the crude materials reacted
without oxygen or water was very similar to that of the
products reacted in the presence of stoichiometric water
or oxygen, respectively. Based on the results and New-
ton’s work [9], the possibility of the formation of 1
from recombination of [CpTi(acac)2Cl] during recrys-
tallization could not be excluded. To identify the source
of bridging oxygen, several experiments are now being
undertaken.
Reaction of 1 with methyllithium, phenyllithium or a
reducing reagent such as Na/Hg, K/Na or potassium
naphthalenide resulted in the formation of intractable
materials. However, a mixture of 1 and 2nBuLi catalyt-
ically activated the mixture of phenylsilane and alde-
hyde to yield O-silation products at room temperature.
When a mixture of propionaldehyde and phenylsilane
was treated with a catalytic amount of 1 and 2nBuLi in
THF, tripropoxyphenylsilane was obtained as a yellow
oil after flash chromatography, and characterized spec-
3.2. Preparation of [{Ti(acac)2Cl}{TiCp2(Cl)}(v-O)] (1)
To a stirred solution of [Cp2TiCl2] (1.00 g, 4.0 mmol)
in CH3CN (ca. 60 ml) under nitrogen was added a
solution of 2,4-pentanedione (0.83 ml, 8.0 mmol) and
Table 1
O-Silation products of aldehydes with phenylsilane catalyzed by 1
and 2nBuLi
Aldehyde
Products
GC yield (%)
Acetaldehyde
Benzaldehyde
Propionaldehyde
Butyraldehyde
–
–
No silation
No silation
53 a
(CH3CH2CH2O)3SiPh
(CH3CH2CH2CH2O)3SiPh
59 b
a Yield calculated after separation by flash chromatography.
b Yield calculated by GC–MS based on [aldehyde].

18
S.-S. Yun et al. / Journal of Organometallic Chemistry 631 (2001) 16–18
triethylamine (0.56 ml, 4.0 mmol) in CH3CN (50 ml).
The reaction mixture became brownish red, and stirring
continued for 2 h at room temperature (r.t.). Volatile
materials were removed under reduced pressure. The
residues was taken up in toluene, 30 ml, and filtered,
and the volume was reduced to ca. 10 ml. Layering of
ether (40 ml) to a toluene solution gave 1 as rectangular
cubes (0.82 g, 1.6 mmol, 40%); IR (Nujol mull) 3002
(w), 1600 (w), 1574 (w), 1525 (m), 1463 (vs), 1377 (m),
1352 (m), 1286 (w), 1269 (m), 1016 (vs), 930 (m), 826
(m), 798 (s), 785 (sh), 723(m), 665 (vs), 599 (m), 544
mixture was stirred for 24 h at r.t. The resulting mix-
ture was subjected to the GC–MS analysis after remov-
ing metal moieties by passing through Florisil, and the
yield of (CH3CH2CH2CH2O)3SiPh was 59%, calculated
by GC–MS based on the concentration of butyralde-
hyde. GC–MS (EI) Anal. Found: 324. Calc. for
C18H32O3Si+: 324.
4. Supplementary material
(m), 453 (s), 410 (w) cm−1
;
1H-NMR (300 MHz,
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 151984 for compound 1.
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).
CDCl3) l 6.57–6.50 (m, 10H), 5.58 (m, 2H), 2.28–1.90
(m, 12H); 13C-NMR (75.5 MHz, CDCl3) l 194.90,
191.67, 190.10, 185.24 (s, CO), 120.82, 119.62, 119.48,
119.03 (s, C5H5), l 105.50, 105.00 (s, CH), l 28.15,
27.02, 26.48, 25.84 (s, CH3). Crystal data: monoclinic
(P21/c) with a=13.4146(19), b=11.999(2), c=
3
,
,
14.0801(16) A, i=91.139(7)°, V=2266.0(6) A ,
D
calc=1.320 Mg m−3, Z=4, T=22 °C, R1=0.0508
and wR2=0.1085. Details are available in the supple-
mentary material.
Acknowledgements
3.3. O-Silation reaction of aldehyde with phenylsilane
catalyzed by 1 and BuLi (aldehyde; propionaldehyde,
butyraldehyde)
Financial support from the Korea Science and Engi-
neering Foundation (971-0306-049-2) and Korea Re-
search Foundation (2000–2001) are gratefully
acknowledged.
n
3.3.1. O-Silation reaction of propionaldehyde with
phenylsilane catalyzed by 1
n
A solution of BuLi (235 ml, 0.38 mmol, 1.6 M) in
References
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stirred for 10 min, and a solution of phenylsilane (2.51
ml, 20.3 mmol) and propionaldehyde (1.46 ml, 20.3
mmol) in THF (10 ml) was then added at 0 °C. The
resultant mixture was stirred for 24 h at r.t. Flash
chromatography (5% EtOAc in hexane) furnished
[(CH3CH2CH2O)3SiPh] (1.02 g, 3.61 mmol, 53% yield)
as a yellow liquid: IR (neat) 3072 (m), 3051 (m), 2936
(vs), 2876 (vs), 2735 (w), 1593 (w), 1464 (s), 1431 (s),
1391 (s), 1381 (m), 1304 (w), 1261 (m), 1084 (vs), 1016
(vs), 920 (m), 899 (m), 845 (vs), 797 (m), 735 (vs), 700
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n
A solution of BuLi (235 ml, 0.38 mmol, 1.6 M) in
hexane was added to a solution of 1 (0.096 g, 0.19
mmol) in THF (5 ml) at −78 °C. The mixture was
stirred for 10 min, and a solution of phenylsilane (2.51
ml, 20.3 mmol) and butyraldehyde (1.83 ml, 20.3 mmol)
in THF (10 ml) was then added at 0 °C. The resultant