Triphenylsilanolato complexes of Group 4 metals: Syntheses, X-ray crystal structures and catalytic cyclization reaction of 1,5-hexadiene

Article abstract of DOI:10.1016/S0020-1693(98)00371-5

Complexes of the type [(Ph₃SiO)₂MCl₂(thf)₂](toluene) ₂ (M=Zr (1), Ti (2), Hf (3)) were prepared from MCl₄(thf)₂ and two equivalents Ph₃SiOLi in thf. In the presence of additional ligands L the compounds [(Ph₃SiO)₂ZrCl₂(L)](tol)_n (L=tmen (5), diphos (6), bpy (7)) were isolated. The X-ray structures of 1-3 show in all cases a distorted octahedral coordination around the metals containing the silanolate ligands in cis-positions and the chloride ligands in axial positions. Reaction of solvent-free [(Ph₃SiO)₂ZrCl₂]_n (4) with CH₃Li in the presence of 2,2′-bipyridine yielded the organometallic compound [(Ph₃SiO)₂Zr(CH₃) ₂(bpy)](toluene)₂ (8) whose molecular structure has been determined by X-ray crystallography. With an excess of methylalumoxane (MAO) the complexes form Ziegler-Natta catalysts, which convert 1,5-hexadiene into methylenecyclopentane and several dimers depending on the nature of the pre-catalyst and the reaction conditions. The highest rate and selectivity of the catalytic cyclization has been observed when compound 8 acts as the starting complex.

Full text of DOI:10.1016/S0020-1693(98)00371-5

Inorganica Chimica Acta 286 (1999) 14–23
Triphenylsilanolato complexes of Group 4 metals: syntheses,
X-ray crystal structures and catalytic cyclization reaction of
1,5-hexadiene
Bernd Schweder, Helmar Go¨rls, Dirk Walther *
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-Uni6ersita¨t Jena, August-Bebel-Straße 2, D-07743 Jena, Germany
Received 4 June 1998; accepted 31 August 1998
Abstract
Complexes of the type [(Ph3SiO)2MCl2(thf)2](toluene)2 (M=Zr (1), Ti (2), Hf (3)) were prepared from MCl4(thf)2 and two
equivalents Ph3SiOLi in thf. In the presence of additional ligands L the compounds [(Ph3SiO)2ZrCl2(L)](tol)n (L=tmen (5),
diphos (6), bpy (7)) were isolated. The X-ray structures of 1–3 show in all cases a distorted octahedral coordination around the
metals containing the silanolate ligands in cis-positions and the chloride ligands in axial positions. Reaction of solvent-free
[(Ph3SiO)2ZrCl2]n (4) with CH3Li in the presence of 2,2%-bipyridine yielded the organometallic compound [(Ph3SiO)2Zr(CH3)2-
(bpy)](toluene)2 (8) whose molecular structure has been determined by X-ray crystallography. With an excess of methylalumoxane
(MAO) the complexes form Ziegler–Natta catalysts, which convert 1,5-hexadiene into methylenecyclopentane and several dimers
depending on the nature of the pre-catalyst and the reaction conditions. The highest rate and selectivity of the catalytic cyclization
has been observed when compound 8 acts as the starting complex. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Catalytic cyclization; Group 4 metal complexes; Silanolato complexes
1. Introduction
selectivity and rate of the catalytic oligomerization of
this diolefinic substrate.
Cyclopentadienyl-free complexes of Group 4 metals
containing anionic silyloxy-type ligands R3SiO− are of
great interest in the synthetic chemistry not only as a
pendant to the well-known cp complexes which form
active Ziegler–Natta catalysts with methylalumoxane
(MAO) [1] but also as molecular models for catalyti-
cally-active metals at silica surfaces [2], as starting
compounds for sol–gel processes and as precursors for
aggregation reactions to give oligomeric oxo- and hy-
droxo complexes which model the first steps of hy-
drolytic reactions.
We report here the syntheses of new complexes con-
taining metals of the Group 4b and triphenylsilyloxo
ligands, the X-ray structures of key compounds and
their catalytic reactions with 1,5-hexadiene. One goal
was to compare the influence of different ligands on the
Despite the fact that silica-supported compounds of
Group 4 elements act as catalysts in several reactions,
e.g. C–H activation [3], alkene polymerization [4] or
oxidation reactions [5], and silyloxy ligands, besides
alkyl, alkoxy and halogen, are used as components of
Ziegler–Natta systems [6], detailed knowledge about
structures and the catalytic reactivity of defined silyloxy
complexes is not available to a great extent.
A number of (R3SiO)nM compounds including some
mono-, di- and trihalogen silyloxy compounds of tita-
nium were reported [7,8].
The chemistry of metallasiloxanes from silanols with
more than one hydroxy function was recently reviewed
[9]. Complexes containing cyclopentadienyl-type ligands
as well as silyloxy ligands are also known [10]. A
number of metallocene complexes involving a,v-silox-
anediolate ligands have been found as components in
active Ziegler–Natta catalysts [11]. Some cyclopentadi-
enyl-free complexes derived from disiloxanediolate lig-
* Corresponding author. Tel.: +49-3641-948110; fax: +49-3641-
948102; e-mail: cdw@rz.uni-jena.de.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00371-5

B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
15
ands yielding eight-membered metallasiloxane rings are
also known [12].
Organosesquisiloxanes containing up to three hy-
droxy groups form metallasesquisiloxanes have been
structurally elucidated by X-ray analysis and employed
in catalytic reactions [13].
Triorganosilyloxy complexes of Group 3 and some
lanthanide elements have been structurally character-
ized [14]. Some molecular structure determinations
have been reported for complexes of Group 4 metals
containing further ligands besides triorganosilyloxy
[15], cyclopentadienyl-bound silyloxy ligands and com-
plexes of the type Cp2MCl(OSiPh3), M=Ti, Zr
[16,17]. (tBu3SiO)3Ti and other Group 4 derivatives are
reactive in R–X bond cleavages [18], as precursors to
zirconia- and hafnia-silica materials [19] and in C–H
activation [20]. The compounds (Ph3SiO)TiCl3 and
(Ph3SiO)2ZrCl2(dimethoxyethane) are the only exam-
ples of complexes related to our studies [21,22].
ference Fourier synthesis and refined isotropically. The
hydrogen atoms for the thf and the toluene molecule
of 2 and of the other compounds were included at
calculated positions with fixed thermal parameters. All
non-hydrogen atoms were refined anisotropically. XP
(Siemens Analytical X-ray Instruments, Inc.) was used
for structure presentations.
Crystal data for 1: C44H46Cl2O4Si2Zr · 2C7H8, Mr=
1041.38 g mol−1, colorless prism, size 0.38×0.36×
0.32 mm3, monoclinic, space group I2/a, a=21.925(2),
˚
b=10.671(1), c=23.591(2) A, i=100.85(1)°, V=
3
˚
5420.6(8) A , T= −90°C, Z=4, zcalc. =1.276
g
cm−3, v (Mo Ka)=3.9 cm−1, F(000)=2176, 5174
reflections in +h, −k, 9l, measured in the range
2.135q525.67°, 5026 independent reflections, Rint
0.023, 3843 reflections with Fo\4|(Fo), 312 parame-
ters, ten restraints,
obs=0.048, wR2obs=0.127,
GOF=1.132, largest difference peak and hole: 0.65
=
R
−3
˚
and −0.55 e A
.
Crystal data for 2: C44H46Cl2O4Si2Ti · 2C7H8, Mr=
998.06 g mol−1, colorless prism, size 0.40×0.38×
0.36 mm3, monoclinic, space group I2/a, a=21.563(2),
2. Experimental
˚
b=10.707(1), c=23.400(4) A, i=100.47(1)°, V=
3
5312(1) A , T= −90°C, Z=4, zcalc. =1.248 g cm−3
v (Mo Ka)=3.52 cm−1, F(000)=2104, 6175 reflec-
tions in 9h, −k, 9l, measured in the range 2.365
q527.43°, 6057 independent reflections, Rint=0.021,
4286 reflections with Fo\4|(Fo), 351 parameters,
,
˚
2.1. General procedures
All operations were carried out under argon using
Schlenk techniques. Solvents were dried by usual
methods and distilled under argon prior to use. NMR
spectra were recorded on a Bruker AC 200 F (200 and
50.3 MHz for 1H and 13C, respectively). IR spectra
were measured as Nujol mulls on a Perkin-Elmer FT
spectrometer ‘System 2000’. A Chrompack CP 9000
(with methylsilicone CP-SIL-5CB) was used for GC
and a Finnigan MAT SSQ 710 for GC–MS. For
GC–IR measurements a Perkin-Elmer AutoSystem
XL was used. Elemental analyses were carried out in
the Institut fu¨r Organische Chemie und Makromoleku-
lare Chemie (Friedrich-Schiller-Universita¨t Jena).
Some analyses for carbon were found to be lower than
calculated. We assume that silicium carbide was ob-
tained during the analytical procedure. MAO was pur-
chased from Witko GmbH, Bergkamen, Germany, as
a 30% solution in toluene.
R
obs=0.049, wR2obs=0.131, GOF=1.109, largest dif-
ference peak and hole: 0.64 and −0.55 e A
−3
˚
.
Crystal data for 3: C44H46Cl2O4Si2Hf · 2C7H8, Mr=
1128.65 g mol−1, colorless prism, size 0.40×0.38×
0.36
mm3,
monoclinic,
space
group
C2/c,
˚
a=29.005(4), b=10.651(1), c=21.904(3) A, i=
126.96(1)°, V=5407(1) A , T= −90°C, Z=4,
3
˚
zcalc. =1.386 g cm−3, v (Mo Ka)=21.17 cm−1, psi-
scan, transmission min.: 0.64, transmission max.: 0.99,
F(000)=2304, 6286 reflections in +h, −k, 9l, mea-
sured in the range 2.335q527.46°, 6168 independent
reflections, Rint=0.020, 5319 reflections with Fo\
4|(Fo), 339 parameters, ten restraints, Robs=0.030,
wR2obs=0.073, GOF=1.032, largest difference peak
−3
˚
and hole: 1.096 and −0.698 e A
.
Crystal data for 8: C48H44N2O2Si2Zr · 2C7H8, Mr=
1012.52 g mol−1, colorless prism, size 0.40×0.36×
0.20 mm3, monoclinic, space group I2/a, a=21.871(3),
2.2. X-ray crystallography
The crystals were mounted in a cold nitrogen stream
at −90°C. For the data collection a CAD4 diffrac-
tometer using graphite-monochromated Mo Ka radia-
tion was used. Data were corrected for Lorentz and
polarization effects [23]. An absorption correction was
made for 3 and 11 [23]. The structures were solved by
direct methods (SHELXS [24]) and refined by full-ma-
trix least-squares techniques against Fo
[25]). For 2 the hydrogen atoms were located by dif-
˚
b=11.778(1), c=22.138(3) A, i=104.40(1)°, V=
3
5523(1) A , T= −90°C, Z=4, zcalc. =1.218 g cm−3
,
˚
v (Mo Ka)=2.86 cm−1, F(000)=2120, 5897 reflec-
tions in 9h, −k, 9l, measured in the range 2.345
q527.42°, 5780 independent reflections, Rint=0.041,
3319 reflections with Fo\4|(Fo), 300 parameters,
obs=0.056, wR2obs=0.129, GOF=1.089, largest dif-
2
R
(SHELXL-93
−3
˚
ference peak and hole: 0.423 and −0.330 e A
.

16
B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
Crystal data for 10: C80H76Cl4O6Si4Zr2, Mr=1570.01
2.3.2. Bis(triphenylsilyloxo)-titanium(IV)-chloride-bis-
tetrahydrofurane-bis-toluene (2)
g mol−1, colorless prism, size 0.35×0.32×0.32 mm3,
monoclinic, space group P21/c, a=15.255(1), b=
Analogous to 1, starting from TiCl4(thf)2. Yield
1
˚
18.899(1), c=13.691(1) A, i=102.194(4)°, V=
(65%) colorless crystals. H NMR (CD2Cl2): l 1.80 (m,
3858.1(4) A , T= −90°C, Z=2, zcalc. =1.351 g cm−3
,
8H, thf), 2.35 (s, 6H, Me), 3.92 (m, 8H, thf), 7.15–7.85
(m, 40H, aryl-H) ppm. 13C NMR (CD2Cl2): l 21.54
(Me), 25.85 (thf), 71.00 (thf), 128.33, 130.60, 135.33,
136.23 (Ph) and 125.65, 128.58, 129.39, 140.50 (toluene)
ppm. IR: w 3046, 1588, 1262, 1188, 1118, 1016, 990,
919, 869, 747, 731, 712, 515 cm−1. Anal. calc. for
C58H62Cl2O4Si2Ti (998.0 g mol−1): C, 69.79; H, 6.26;
Cl, 7.10; found: C, 69.18; H, 6.05; Cl, 6.91%.
3
˚
v (Mo Ka)=5.21 cm−1, F(000)=1616, 10269 reflec-
tions in 9h, 9k, −l, measured in the range 3.125
q523.34°, 5533 independent reflections, Rint=0.073,
3521 reflections with Fo\4|(Fo), 433 parameters,
R
obs=0.052, wR2obs=0.133, GOF=0.916, largest dif-
−3
˚
ference peak and hole: 0.322 and −0.518 e A
.
Crystal data for 11: C8H16Cl8O2Zr2, Mr=610.24 g
mol−1, colorless prism, size 0.40×0.40×0.20 mm3,
monoclinic, space group P21/c, a=9.823(1), b=
2.3.3. Bis(triphenylsilyloxo)-hafnium(IV)-chloride-bis-
tetrahydrofurane-bis-toluene (3)
˚
8.796(1), c=12.262(1) A, i=113.46(1)°, V=972.0(2)
A , T= −90°C, Z=2, zcalc. =2.085 g cm−3, v (Mo
To a suspension of 0.89 g (2.78 mmol) HfCl4 in 40 ml
toluene 10 ml diethylether were added at 0°C. After
stirring for several minutes at 50°C an almost clear
solution was formed. This solution was treated at 25°C
with a suspension of Ph3SiOLi, prepared in a mixture
of 15 ml diethylether and 20 ml toluene from 1.54 g
(5.55 mmol) Ph3SiOH and 3.47 ml (5.55 mmol) of a 1.6
M n-BuLi solution in hexane at −40°C. After stirring
at 25°C for 15 min followed by addition of 0.9 ml (11.1
mmol) thf the mixture was filtered and the solvent
partially distilled off. From the warm toluene solution
the crystalline product precipitates upon standing at
25°C.
3
˚
Ka)=21.67 cm−1, psi-scan, transmission min.: 0.75,
transmission max.: 0.99, F(000)=592, 1458 reflections
in +h, −k, 9l, measured in the range 2.265q5
23.70°, 1358 independent reflections, Rint=0.0326, 1270
reflections with Fo\4|(Fo), 91 parameters, Robs
=
0.024, wR2obs=0.064, GOF=1.142, largest difference
−3
˚
peak and hole: 0.471 and −0.549 e A
.
2.3. Syntheses
2.3.1. Bis(triphenylsilyloxo)-zirconium(IV)-chloride-bis-
tetrahydrofurane-bis-toluene (1)
A solution of 1.70 g (4.5 mmol) ZrCl4(thf)2 in 30 ml
thf was treated at 25°C with a solution of Ph3SiOLi,
prepared from 2.49 g (9.0 mmol) Ph3SiOH in 25 ml thf
and 5.63 ml (9.0 mmol) of a 1.6 M n-BuLi solution in
hexane at −40°C. The nearly clear mixture was stirred
at 25°C for 30 min and the solvent was distilled off.
The residue was then suspended in 20 ml CH2Cl2 and
filtered; after removing the solvent from the filtrate and
drying under vacuum, the complex (Ph3SiO)2ZrCl2(thf)2
was obtained as a colorless solid.
Yield 1.95 g (62%) colorless crystals. 1H NMR
(CD2Cl2): l 1.58 (m, 8H, thf), 2.35 (s, 6H, Me), 4.07
(m, 8H, thf), 7.16–7.72 (m, 40H, aryl-H) ppm. 13C
NMR (CD2Cl2): l 21.56 (Me), 25.64 (thf), 75.00 (thf),
127.98, 129.80, 135.74, 137.64 (Ph) and 125.68, 128.60,
129.42, 138.42 (toluene) ppm. IR: w 3066, 1588, 1116,
1031, 1013, 997, 938, 853, 748, 733, 710, 518 cm−1
.
Anal. calc. for C58H62Cl2O4Si2Hf (1128.6 g mol−1): C,
61.72; H, 5.54; Cl, 6.28; found: C, 61.92; H, 5.65; Cl,
6.18%.
The crude product or the isolated toluene-free com-
pound was warmed up to 80°C in 42 ml toluene.
Cooling to 25°C resulted in a crystalline precipitate,
which was filtered off and dried under vacuum. Crystals
suitable for X-ray structure determination were ob-
tained by further crystallization from toluene.
2.3.4. Bis(triphenylsilyloxo)-zirconium(IV)-chloride (4)
To a solution of 2.84 g (10.3 mmol) Ph3SiOH in 50
ml toluene 6.43 ml (10.3 mmol) of a 1.6 M n-BuLi
solution in hexane at −40°C were added slowly. The
resulting suspension was warmed up to 25°C and added
slowly to a suspension of 1.20 g (5.15 mmol) ZrCl4 in
60 ml toluene. The mixture was stirred for 1 h and the
LiCl was filtered off.
Yield 3.42 g (73%) colorless crystals. 1H NMR
(CD2Cl2): l 1.61 (m, 8H, thf), 2.38 (s, 6H, Me), 4.06
(m, 8H, thf), 7.14–7.76 (m, 40H, aryl-H) ppm. 13C
NMR (CD2Cl2): l 21.59 (Me), 25.58 (thf), 74.09 (thf),
128.04, 129.92, 135.74, 137.17 (Ph) and 125.70, 128.62,
129.42, 138.39 (toluene) ppm. IR: w 3066, 1588, 1116,
This solution can be used for the syntheses of the
complexes 5–7 by addition of the appropriate ligands
(5: tmen, 6: diphos, 7: bpy). To isolate 4, 20 ml of this
solution were concentrated to 5–10 ml. Addition of
hexane resulted in precipitation of a colorless solid,
which was filtered, washed with hexane and dried under
vacuum.
1029, 1006, 993, 916, 853, 748, 732, 710, 518 cm−1
.
Anal. calc. for C58H62Cl2O4Si2Zr (1041.4 g mol−1): C,
66.89; H, 6.00; Cl, 6.81; found: C, 65.19; H, 5.85; Cl,
6.21%.
1
An analogous preparation as described for 3, starting
with ZrCl4, is also possible.
Yield 0.24 g (38%). H NMR (C6D6): l 7.15–7.68
(m, aryl-H) ppm. 13C NMR (C6D6): l 128.11, 130.08,

B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
17
134.90, 135.55 (Ph) ppm. IR: w 3068, 3046, 1590, 1117,
997, 983, 913, 741, 712, 697, 515 cm−1. Anal. calc. for
C36H30Cl2O2Si2Zr (712.9 g mol−1): C, 60.65; H, 4.24;
Cl, 9.95; found: C, 58.40; H, 4.34; Cl, 11.81%.
cm−1. Anal. calc. for C60H54N2O2Si2Zr (1053.3 g
mol−1): C, 68.41; H, 5.16; N, 2.66; Cl, 6.74; found: C,
66.78; H, 5.22; N, 2.95; Cl, 6.73%.
B: A product of less purity was obtained when a
solution of 4 was treated with bipyridine. Evaporating
the solvent and drying under vacuum yielded a color-
less solid.
2.3.5. Bis(triphenylsilyloxo)-zirconium(IV)-chloride-
tetramethylethylenediamine (5)
A: To a solution of 0.74 g (0.71 mmol) 1 in 20 ml thf
0.12 ml (0.78 mmol) tetramethylethylenediamine were
added under stirring at 25°C. The solvent was removed
and the resulting colorless solid was dried under
vacuum.
2.3.8. Bis(triphenylsilyloxo)-zirconium(IV)-dimethyl-
bipyridine-bis-toluene (8)
A: To a solution of 1.92 g (6.94 mmol) Ph3SiOH in
40 ml toluene 4.34 ml (6.94 mmol) of a 1.6 M n-BuLi
solution in hexane were added slowly at −40°C. The
resulting suspension was warmed up to 25°C and slowly
added to a suspension of 0.81 g (3.47 mmol) ZrCl4 in 20
ml toluene. After stirring at 25°C for 1 h the mixture
was cooled to −70°C and 4.34 ml (6.94 mmol) of a 1.6
M methyl lithium solution in diethylether was added
slowly. The suspension was allowed to warm up to
−40°C and 0.54 g (3.47 mmol) bipyridine, dissolved in
10 ml toluene, were added. The mixture was allowed to
warm up to 25°C over a period of 1 h while stirring and
then filtered. The filtrate was layered with 30 ml hex-
ane. Standing at 25°C resulted in the formation of a
crystalline product, which was filtered off and dried
under vacuum. Yield 1.12 g (32%) orange crystals.
B: To a suspension of 0.90 g (3.86 mmol) ZrCl4 in 25
ml toluene 15 ml diethylether were added at 0°C and
the mixture was stirred at 50°C for several minutes. The
almost clear solution was cooled to −78°C and slowly
treated with 9.70 ml (15.5 mmol) of a 1.6 M methyl
lithium solution in diethylether. Over a 4 h period the
suspension was allowed to warm up to −40°C. After
cooling to −70°C a solution of 2.13 g (7.7 mmol)
Ph3SiOH in 10 ml diethylether were added very slowly,
resulting in the evolution of methane. The mixture was
then heated to −40°C. A solution of 0.6 g (3.86 mmol)
bipyridine in 5 ml toluene was added and, after the
suspension reached 25°C, filtration was carried out.
Well shaped crystals, beside decomposition products,
were formed upon standing at 25°C. The product was
filtered through a wide-pored filter tube and washed
several times with toluene.
1
Yield 90%. H NMR (CD2Cl2): l 2.3 (broad s, 12H,
Me), 2.57 (m, 4H, CH2), 6.70–7.80 (m, 30H, aryl-H)
ppm. 13C NMR (CD2Cl2): l 49.9 and 51.19 (Me), 61.5
(CH2), 127.80, 129.63, 135.43, 137.66 (Ph) ppm. IR: w
3070, 1588, 1113, 947, 908, 741, 709, 516 cm−1. Anal.
calc. for C42H58Cl2N2O2Si2Zr (841.2 g mol−1): C,
59.96; H, 6.95; N, 3.33; Cl, 8.43; found: C, 60.92; H,
6.65; N, 2.98; Cl, 8.08%.
B: A product of less purity was obtained when a
solution of 4 was treated with a slight excess of tetra-
methylethylenediamine. Evaporating the solvent and
drying under vacuum leads to a colorless solid.
2.3.6. Bis(triphenylsilyloxo)-zirconium(IV)-chloride-
(1,2-bis(diphenylphosphino)ethane)-bis-toluene (6)
A 0.99 g (0.95 mmol) sample of 1 and 0.4 g (1.0
mmol) 1,2-bis(diphenylphosphino)ethane were stirred in
20 ml toluene at 60°C for 1 h. After cooling to 25°C
and addition of 20 ml hexane a small amount of
amorphous precipitate was formed. The mixture was
filtered and the solvent was removed from the filtrate to
yield a colorless solid.
1
Yield 90%. H NMR (CD2Cl2): l 2.30 (m, 4H, CH2),
2.43 (s, 6H, Me), 7.12–7.85 (m, 60H, aryl-H) ppm. 13C
NMR (CD2Cl2): l 21.62 (Me), 25.44 (CH2), 128.08,
129.97, 135.73, 137.21 (Ph); 129.2, 131.9, 132.2, 137.8
(Ph-P) and 125.72, 128.64, 129.44, 138.39 (toluene)
ppm. 31P NMR (CD2Cl2): l −12.06 ppm. IR: w 3130,
3043, 1587, 1114, 986, 926, 740, 697, 516 cm−1. Anal.
calc. for C76H70Cl2O2P2Si2Zr (1295.6 g mol−1): C,
70.45; H, 5.45; Cl, 5.47; found: C, 67.88; H, 5.44; Cl,
5.00%.
Yield 0.43 g (11%) red–orange crystals. 1H NMR
(CD2Cl2): l −0.59 (s, 6H, Me), 2.35 (s, 6H, Me), 6.90
(m, 2H, H5-bpy), 7.18–7.75 (m, 40H, aryl-H), 7.85 (m,
2H, H4-bpy), 8.11 (m, 2H, H3-bpy), 8.50 (m, 2H,
H6-bpy) ppm. 13C NMR (CD2Cl2): l −9.59 (Me),
21.54 (Me), 128.06, 129.69, 135.72, 133.38 (Ph) and
125.68, 128.60, 129.41, 137.81 (toluene) and 122.24,
124.52, 135.41, 149.39, 150.09 (bpy) ppm. IR: w 3044,
1597, 1570, 1115, 1004, 992, 936, 764, 736, 710, 514
cm−1. Anal. calc. for C62H60N2O2Si2Zr (1012.5 g
mol−1): C, 73.54; H, 5.98; N, 2.76; found: C, 73.86; H,
5.88; N, 3.15%.
2.3.7. Bis(triphenylsilyloxo)-zirconium(IV)-chloride-
bipyridine-bis-toluene (7)
A: An analogous reaction to 6 following the addition
1
of bipyridine. Yield 90%. H NMR (CD2Cl2): l 2.36 (s,
6H, Me), 6.90 (m, 2H, H5-bpy), 7.14–7.90 (m, 40H,
aryl-H), 8.03 (m, 2H, H4-bpy), 8.16 (m, 2H, H3-bpy),
8.42 (m, 2H, H6-bpy) ppm. 13C NMR (CD2Cl2): l
21.56 (Me), 128.35, 130.03, 135.81, 138.40 (Ph) and
125.68, 128.60, 129.42, 136.92 (toluene) and 122.41,
126.45, 140.92, 150.67, 151.72 (bpy) ppm. IR: w 3066,
1599, 1574, 1116, 1002, 986, 918, 765, 736, 711, 518

18
B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
2.4. Catalytic reactions
2.3.9. Tris(triphenylsilyloxo)-zirconium(IV)-chloride-
tetrahydrofuran-0.5-toluene (9)
The catalytic system was formed from 5×10−5
mol complex and 5×10−3 mol MAO (or 25×10−3
mol for 500 equivalents, respectively) in 5 ml toluene.
At ambient temperature 0.696 g (8.5 mmol) of 1,5-
hexadiene was added and the mixture was stirred.
Probes were taken from the mixture in regular inter-
vals and hydrolyzed under cooling with half concen-
trated hydrochloric acid. The organic layer was
treated with sodium carbonate and investigated using
GC, GC–MS and GC–IR. Methylenecyclopentane
was further identified by NMR and comparison with
an authentic sample.
A solution of 0.87 g (2.3 mmol) ZrCl4(thf)2 in 20
ml thf was treated at 25°C with a solution of
Ph3SiOLi, prepared from 1.91
g
(6.91 mmol)
Ph3SiOH in 25 ml thf and 4.32 ml (6.91 mmol) of a
1.6 M n-BuLi solution in hexane at −40°C. The
mixture was stirred at 25°C for 30 min and the sol-
vent was distilled off. The crude product was warmed
up to 80°C in 40 ml toluene. Cooling down to 25°C
resulted in a clear solution. After partial removal of
the solvent and addition of hexane a colorless solid
was filtered off, washed with hexane and dried under
vacuum.
Yield 0.55 g (22%) colorless powder. 1H NMR
(CD2Cl2): l 1.61 (m, 4H, thf), 2.35 (s, 1.5H, Me),
4.00 (m, 4H, thf), 7.15–7.80 (m, 47.5H, aryl-H) ppm.
13C NMR (CD2Cl2): l 21.60 (Me), 25.55 (thf), 73.92
(thf), 128.06, 129.92, 135.70, 137.10 (Ph) and 125.70,
128.63, 129.38, 138.36 (toluene) ppm. IR: w 3066,
Quantitative determination was carried out under
the assumption that GC-correction factors of all
products were very similar. The ratio of peak areas
therefore correlate with the ratio of the masses of the
appropriate products. Thus the turnover number
(ton—mmol product per mmol catalyst) of a product
is defined as:
1588, 1115, 1027, 997, 923, 869, 741, 700, 517 cm−1
.
Anal. calc. for C61.5H57ClO4Si3Zr (1071.0 g mol−1):
C, 68.96; H, 5.36; Cl, 3.30; found: C, 70.93; H, 5.49;
Cl, 3.25%.
ton=mass of 1,5-hexadiene
×peak area of the product/S peak areas
×molar mass of the product
×molar amount of the catalyst.
Methylenecyclopentane A
2.3.10. Bis-{bis(triphenylsilyloxo)-zirconium(IV)-
chloride-tetrahydrofurane} (10)
A 1.16 g (1.11 mmol) sample of 1 was refluxed in
20 ml toluene for 48 h. The cold solution was layered
with 20 ml hexane. On standing at 25°C a colorless
product precipitated, which contained the educt. Fil-
tration and layering the filtrate with further hexane
resulted in the formation of crystals, which were
filtered off and dried under vacuum.
GC–MS (m+/e): 82 (M+), 67 (base), 54, 39. GC–
IR: w 3071 (w ꢀCH); 2965 and 2892 (w CH2), 1660 (w
1
CꢀC), 1446 (l CH2), 880 (l ꢀCH2) cm−1. H NMR
(CDCl3): l 1.64 (m, 4H, CH2), 2.25 (m, 4H, CH2),
4.82 (m, 2H, ꢀCH2) ppm. 13C NMR (CDCl3): l 26.29
and 32.97 (CH2), 104.46 (ꢀCH2), 153.33 (ꢀC) ppm.
Yield 0.34 g (38%) colorless crystals. 1H NMR
(CD2Cl2): l 1.57 (m, 8H, thf), 4.02 (m, 8H, thf),
7.20–7.66 (m, 60H, aryl-H) ppm. 13C NMR
(CD2Cl2): l 25.51 (thf), 74.50 (thf), 128.07, 130.15,
135.56, 137.21 (Ph) ppm. IR: w 3068, 1588, 1115,
1000, 977, 905, 845, 742, 711, 514 cm−1. Anal. calc.
for C80H76Cl4O6Si4Zr2 (1570.0 g mol−1): C, 60.05; H,
4.79; Cl, 8.86; found: C, 60.37; H, 5.05; Cl, 8.63%.
3-(Cyclopentylmethyl)-methylenecyclopentane B
GC–MS (m+/e): 164 (M+), 149, 135, 108, 95,
81 (base), 67, 55, 41. GC–IR: w 3078 (w ꢀCH), 2955
and 2873 (w CH2), 1662 (w CꢀC), 1479 and 1442 (l
CH2), 880 (l ꢀCH2) cm−1
.
Methylcyclopentane
GC–MS (m+/e): 84 (M+), 69, 56 (base), 41. GC–
IR: w 2961 and 2881 (w CH2/CH3), 1466 (l CH2), 1366
2.3.11. Dimeric zirconium(IV)-chloride-tetrahydrofuran
(11)
(l CH3) cm−1
.
1,3-Dimethyl-cyclopentane (cis/trans mixture)
To a suspension of 0.27 g (1.15 mmol) ZrCl4 in 5
ml CH2Cl2 0.08 ml (0.9 mmol) thf were added. After
stirring for 48 h at 25°C the suspension was filtered.
A small amount of crystalline product precipitated
from the filtrate.
GC–MS (m+/e): 98 (M+), 83, 70 (base), 56, 55,
41. GC–IR: w 2957 and 2879 (w CH2/CH3), 1463 (l
CH2), 1378 (l CH3) cm−1
.
3-Methyl-methylenecyclopentane
Yield 0.01 g. 1H NMR (CD2Cl2): l 1.67 (m, 8H,
thf), 4.05 (m, 8H, thf) ppm. 13C NMR (CD2Cl2): l
25.53 (thf), 74.52 (thf) ppm. Anal. calc. for
C8H16Cl8O2Zr2 (610.2 g mol−1): C, 15.74; H, 2.64;
Cl, 46.47; found: C, 14.99; H, 2.56; Cl, 46.83%.
GC–MS (m+/e): 96 (M+), 81 (base), 70, 67, 55,
39. GC–IR: w 3074 (w ꢀCH), 2958 and 2888 (w CH2/
CH3), 1656 (w CꢀC), 1449 (l CH2), 1366 (l CH3), 879
(l ꢀCH2) cm−1
.

B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
19
3-(Cyclopentylmethyl)-methylcyclopentane
GC–MS (m+/e): 166 (M+), 151, 137, 109, 96, 81
(base), 80, 67, 55, 41. GC–IR: w 2956 and 2877 (w
CH2/CH3), 1455 (l CH2) cm−1
.
3-(3-Methyl-cyclopentylmethyl)-methylcyclopentane
GC–MS (m+/e): 180 (M+), 165, 151, 123, 109, 96,
83, 81 (base), 67, 55, 41. GC–IR: w 2955 and 2875 (w
CH2/CH3), 1458 (l CH2) cm−1
.
3-(3-Methyl-cyclopentylmethyl)-methylenecyclopentane
GC–MS (m+/e): 178 (M+), 163, 149, 122, 107, 95,
81 (base), 67, 55, 41. GC–IR: w 3079 (w ꢀCH), 2954 and
2875 (w CH2/CH3), 1657 (w CꢀC), 1446 (l CH2), 880 (l
ꢀCH2) cm−1
.
Fig. 1. ORTEP drawing of the molecular structure of bis(triphenylsilyl-
oxo)-titanium(IV)-chloride-bis-tetrahydrofurane-bis-toluene (2) with
50% probability ellipsoids.
3-(3-Cyclopentylmethyl-cyclopentylmethyl)-methylene-
cyclopentane
GC–MS (m+/e): 246 (M+), 165, 163, 137, 123, 109,
97, 83, 81 (base), 67, 55, 41. GC–IR: w 3071 (w ꢀCH),
2951, 2908 and 2873 (w CH2/CH3), 1653 (w CꢀC), 1456
silyloxy groups is also demonstrated by the coordina-
tion of thf in a trans-position to the silyloxy groups,
forcing the chloro ligands in a trans-arrangement. The
same structural motif has been observed in bis-pheno-
lato complexes of Group 4 metals [26].
and 1442 (l CH2), 882 (l ꢀCH2) cm−1
.
If ZrCl4 is reacted with two equivalents Ph3SiOLi in
3. Results and discussion
toluene,
the
highly
toluene-soluble
complex
[(Ph3SiO)2ZrCl2]n (4) is obtained (Eq. (2)), probably
According to Eq. (1) ZrCl4(thf)2 reacts with two
equivalents Ph3SiOLi in thf to give (Ph3SiO)2ZrCl2(thf)2
as a colorless solid. Recrystallization from toluene leads
to the crystalline complex [(Ph3SiO)2ZrCl2(thf)2](tolu-
ene)2 (1), which could also be obtained from ZrCl4 and
Ph3SiOLi in toluene/diethylether followed by addition
of thf. Reacting TiCl4(thf)2 or HfCl4 results in the
formation of the analogous complexes [(Ph3SiO)2
TiCl2(thf)2](toluene)2 (2) or [(Ph3SiO)2HfCl2(thf)2](tolu-
ene)2 (3), respectively. Attempted reactions of MCl4
with triphenylsilanol in toluene failed even when thf
was present, because of the decomposition of silanol.
containing chloro bridges.
2Ph SiOLi
3
ZrCl4 ꢁꢁꢁꢁꢁꢁꢂ [(Ph3SiO)2ZrCl2]n
(2)
toluene
(4)
The substitution of both thf ligands in 1 by the
chelate ligands N,N,N%,N%-tetramethylethylenediamine
(tmen), 1,2-bis(diphenylphosphino)ethane (diphos) or
Table 1
˚
Selected bond lengths (A) and angles (°) for 1–3
M=Zr (1)a
M=Ti (2)b
M=Hf (3)c
2Ph SiOLi
3
M–O(1)
M–O(2)
M–Cl
1.928(2)
2.276(3)
2.4683(9)
1.634(2)
1.782(2)
2.179(2)
2.3565(7)
1.642(2)
1.929(2)
2.255(2)
2.4499(8)
1.623(2)
MCl4(thf)2 or MCl4 ꢁꢁꢁꢁꢁꢁꢂ (Ph3SiO)2MCl2(thf)2(tol)2
thf/toluene
(1)
Si–O(1)
where M=Zr (1), Ti (2), Hf (3).
O(1)–M–O(1)i
O(1)–M–O(2)i
O(1)–M–O(2)
O(2)i–M–O(2)
O(1)–M–Cli
O(2)–M–Cli
O(1)–M–Cl
O(2)–M–Cl
Cl–M–Cli
99.90(14)
170.22(10)
89.29(10)
81.8(2)
96.93(7)
82.64(8)
92.84(7)
85.87(7)
164.79(5)
170.3(2)
100.65(11)
170.37(8)
88.73(7)
81.97(11)
93.46(5)
85.13(5)
96.32(6)
83.30(5)
164.65(4)
167.81(11)
99.80(13)
170.41(9)
89.27(10)
81.86(14)
96.53(7)
86.05(7)
92.80(6)
83.00(7)
165.50(5)
169.76(14)
The X-ray structures of the isostructural compounds
1–3 (Fig. 1 shows the titanium complex 2 as an exam-
ple) exhibit a distorted octahedral environment around
the central metal. Both the silanolate groups and the thf
ligands occupy cis-positions of the equatorial plane,
whereas the chlorides coordinate at the axial positions
leading to trans-chloro complexes. In all compounds
toluene is included in the crystals without any coordi-
nation to the complexes. Selected bond length and
angles are given in Table 1.
Almost linear Si–O–M bond angles indicate the
partial multiple bond character of the Si–O–M bond,
which is typical for silyloxy compounds with electron
deficient metal centers. The p-acceptor character of the
Si–O(1)–M
a Symmetry transformations used to generate equivalent atoms for
i
1: −x+3/2, y, −z+1.
b Symmetry transformations used to generate equivalent atoms for
i
2: −x+1/2, y, −z.
c Symmetry transformations used to generate equivalent atoms for
i
3: −x, y, −z+1/2.

20
B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
Table 2
2,2%-bipyridine (bpy) in thf leads to the formation of the
complexes [(Ph3SiO)2ZrCl2(tmen)] (5), [(Ph3SiO)2ZrCl2-
(diphos)](toluene)2 (6) and [(Ph3SiO)2ZrCl2(bpy)](tolu-
ene)2 (7), which could also be isolated in situ, generated
4 as colorless solids (Eq. (3)).
a
˚
Selected bond lengths (A) and angles (°) for 8
Zr–O
Zr–C(1)
1.959(3)
2.307(5)
Zr–N
Si–O
2.377(4)
1.626(3)
Ni–Zr–N
O–Zr–C(1)
Oi–Zr–O
O–Zr–Ni
O–Zr–N
67.8(2)
100.8(2)
105.4(2)
161.05(13)
93.43(13)
O–Zr–C(1)i
C(1)–Zr–Ni
C(1)–Zr–N
97.4(2)
78.3(2)
76.7(2)
149.8(3)
172.0(2)
C(1)–Zr–C(1)i
Si–O–Zr
a Symmetry transformations used to generate equivalent atoms:
−x+3/2, y, −z+1.
i
(3)
The reaction of 4 with methyl lithium leads to ther-
mally unstable compounds, which could not be isolated
as pure compounds, but in the presence of 2,2%-
bipyridine the reaction results in the formation of the
stable complex [(Ph3SiO)2ZrMe2(bpy)](toluene)2 (8).
This compound is also available if in situ generated
ZrMe4 is reacted with triphenylsilanol/bpy at −40°C;
however the product yielded by the first and more
convenient method is of higher purity (Eq. (4)).
leading to a trans-arrangement. In comparison to the
chloro derivatives, the Me–Zr–Me angle is distinctively
smaller (Fig. 2). Selected bond length and angles are
listed in Table 2.
In order to obtain complexes with one or three
triphenylsilyloxy groups, respectively, ZrCl4(thf)2 was
reacted with Ph3SiOLi in molar ratios 1:1 or 1:3, but
attempts to isolate the mono-silyloxo complex, thus far,
have failed. Instead of the monosubstituted product a
mixture of complex 1 and ZrCl4(thf)2 was obtained, in
contrast to both the Ti analog [21] and the monophe-
noxo complex of Zr [26].
However, the reaction of three equivalents of
Ph3SiOLi with ZrCl4(thf)2 in thf/toluene results in the
desired colorless complex [(Ph3SiO)3ZrCl(thf)](tolu-
ene)0.5 (9) (Eq. (5)).
(4)
3Ph SiOLi
3
ZrCl4(thf)2 ꢁꢁꢁꢁꢁꢁꢂ (Ph3SiO)3Zr C l(thf)(tol)0.5
(5)
(6)
thf/toluene
(9)
The X-ray structure of 8 shows that the Zr(IV) atom
is surrounded by six ligands yielding a distorted octahe-
dron. Analogous to 1–3 the silanolato groups and the
bipyridine ligand form an equatorial plane, whereas
both of the methyl groups occupy the axial positions
2Ph SiOLi
3
ZrCl4(thf)2 ꢁꢁꢁꢁꢁꢁꢁꢁꢂ [(Ph3SiO)2 Z rCl2(thf)]2
toluene/110°C
(10)
Because complex 10, obtained by heating compound
1 in toluene solution under the elimination of thf (Eq.
(6)), is a dimeric compound containing two chloro
bridges, we assume a similar dimeric structure for com-
plex 9 too. Fig. 3 shows the molecular structure of 10,
determined by X-ray analysis.
Two octahedral Zr centers are bridged by two chloro
ligands with the triphenylsilyloxy groups in trans-posi-
tion to the bridging chlorides. Related to this plane, thf
molecules occupy opposite sides.
A similar arrangement of the thf donors was found in
the simple complex [ZrCl4(thf)]2 (11), which can be
obtained by reacting ZrCl4 in methylenechloride con-
taining less than one equivalent of thf per Zr. Fig. 4
shows the X-ray crystal structure of 11.
4. Catalytic reactions
In order to determine the ability of the synthesized
complexes to catalyze C–C coupling reactions depend-
ing on their structure, the number of coordinated silyl-
oxo groups and the nature of the further ligands, we
Fig. 2. ORTEP drawing of the molecular structure of bis(triphenylsilyl-
oxo)-zirconium(IV)-dimethyl-bipyridine-bis-toluene (8) with 50%
probability ellipsoids.

B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
21
cyclic product, dimers, oligomers or polymers accord-
ing to Eq. (7).
(7)
With zirconocene/MAO systems cyclopolymerization
of 1,5-hexadiene to form C occurs [27]. Cyclization
products are obtained only if further termination pro-
cesses occur [28] or if less reactive systems are used and
reaction conditions are optimized carefully [29].
Ziegler–Natta catalysts based on the complexes 1–10
with MAO are able to convert 1,5-hexadiene into
methylenecyclopentane A as the main product; a side
product is the cyclodimer B.
Table 3 shows that the selectivity and the rate of this
rather slow catalytic reaction depend on the nature of
the coordinating ligands and the ratio between the Zr
complex and MAO.
Fig. 3. ORTEP drawing of the molecular structure of bis-
{bis(triphenylsilyloxo)-zirconium(IV)-chloride-tetrahydrofurane} (10)
˚
with 50% probability ellipsoids. Selected bond lengths (A) and angles
First investigating 1 as a key compound, the reaction
conditions were found to be optimal for the cyclization
reaction, when 100 equivalents MAO were used at
25°C. The catalytic system formed is deactivated with
increasing temperature. Higher amounts of MAO result
in carboalumination reactions, especially at higher tem-
perature, as proved by increased formation of methy-
lated and saturated products (see Table 3, runs 5 and
6). No activation occurs if Me3Al is used as co-catalyst.
It is noteworthy that, when 1 acts as starting com-
plex, the activity of the catalytic system formed with
MAO also depends on the fraction used. This observa-
tion indicates that the way to the catalytic system
probably is not a simple methylation reaction of the Zr
followed by the formation of a cationic methyl complex
as observed in the case of zirconocene/MAO systems.
The Ti complex 2 forms with MAO a catalytic
system which is very selective for methylenecyclopen-
tane formation (Table 3, run 7). Its activity can be
compared with those of 1/MAO. The Hf analog 3 is
inactive in agreement with the well-known low catalytic
activity of other Hf complexes.
(°) for 10: Zr–O(1) 1.926(4), Zr–O(2) 1.930(4), Zr–O(3) 2.204(4),
Zr–Cl(1) 2.419(2), Zr–Cl(2) 2.639(2), Zr–Cl(2)i 2.652(2), Si(1)–O(1)
1.640(4), Si(2)–O(2) 1.636(4), O(1)–Zr–O(2) 102.7(2), O(1)–Zr–O(3)
88.4(2), O(2)–Zr–O(3) 90.8(2), O(1)–Zr–Cl(1) 98.10(12), O(2)–Zr–
Cl(1) 96.82(12), O(3)–Zr–Cl(1) 168.66(11), O(1)–Zr–Cl(2) 89.49(12),
O(2)–Zr–Cl(2) 166.20(13), O(3)–Zr–Cl(2) 83.09(11), Cl(1)–Zr–Cl(2)
87.66(6), O(1)–Zr–Cl(2)i 166.15(12), O(2)–Zr–Cl(2)i 88.16(12),
O(3)–Zr–Cl(2)i 82.85(11), Cl(1)–Zr–Cl(2)i 88.95(5), Cl(2)–Zr–Cl(2)i
88.85(5), Zr–Cl(2)–Zri 101.15(5), Si(1)–O(1)–Zr 166.8(2), Si(2)–
O(2)–Zr 170.3(3). Symmetry transformations used to generate equiv-
i
alent atoms: −x, −y, −z.
investigated them as pre-catalysts in Ziegler–Natta sys-
tems employing MAO as a co-catalyst. We used 1,5-
hexadiene as model substrate, which can be
catalytically converted to form either a monomeric
The stable coordination of three anionic Ph3SiO−
groups around the Zr in compound 9 may explain the
catalytic inactivity of the system 9/MAO, because ac-
tive (may be cationic) centers containing CH3–Zr
bonds and free position for the coordination of the
diolefinic substrate cannot be formed.
In this context the observed activities of the trans-
chloro complexes appear to be unusual. A possible
explanation for this behavior could be that, in the
course of the reaction with MAO, the coordinated
neutral donors change their positions forming monoca-
tionic CH3–Zr compounds with a free or weakly occu-
pied cis-position which is able to bind the substrate as
the starting step of the catalytic cycle.
Fig. 4. ORTEP drawing of the molecular structure of dimeric zircon-
ium(IV)-chloride-tetrahydrofuran (11) with 50% probability ellip-
˚
soids. Selected bond lengths (A) and angles (°) for 11: Zr–O 2.206(2),
Zr–Cl(3) 2.3511(8), Zr–Cl(4) 2.3604(9), Zr–Cl(1) 2.3691(8), Zr–Cl(2)
2.5751(8), Zr–Cl(2)i 2.6228(7), O–Zr–Cl(3) 89.17(5), O–Zr–Cl(4)
89.34(6), Cl(3)–Zr–Cl(4) 99.78(3), O–Zr–Cl(1) 170.00(6), Cl(3)–Zr–
Cl(1) 96.15(3), Cl(4)–Zr–Cl(1) 98.06(3), O–Zr–Cl(2) 82.74(6), Cl(3)–
Zr–Cl(2) 92.74(3), Cl(4)–Zr–Cl(2) 165.09(3), Cl(1)–Zr–Cl(2)
88.53(3), O–Zr–Cl(2)i 84.06(5), Cl(3)–Zr–Cl(2)i 170.22(3), Cl(4)–
Zr–Cl(2)i 87.22(3), Cl(1)–Zr–Cl(2)i 89.56(3), Cl(2)–Zr–Cl(2)i
79.43(2), Zr–Cl(2)–Zri 100.57(2). Symmetry transformations used to
i
generate equivalent atoms: −x+2, −y+2, −z.

22
B. Schweder et al. / Inorganica Chimica Acta 286 (1999) 14–23
Table 3
Cyclization of 1,5-hexadiene with systems complex/MAO
Run
Complex
MAO equivalents
Temp. (°C)
Time
Aa
Ba
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1
1
1
1
1
1
2
2
4
5
6
7
8
100
100
100
500
500
500
100
500
100
100
100
100
100
100
−20
25
25
25
25
60
25
25
25
25
25
25
25
25
10 days
10 days
20 days
10 days
20 daysb
8 hc
25
14
0–1
1–2
8
12
3
0
3
0
48
2
2
traces
traces
6–15
8–22
66
92
53
15
3
10 days
3 days
10 days
20 daysd
10 days
10 days
10 days
5 days
4
71
17
13
61–72
50
10
a Catalyst: 5×10−5 mol complex/5×10−3 mol MAO (or 25×10−3 mol for 500 equivalents, respectively) in 5 ml toluene, substrate
1,5-hexadiene: 8.5×10−3 mol; turnover number (ton)=mmol product per mmol complex.
b Complete consumption of the educt, further products (ton): methylcyclopentane (19), 1,3-dimethylcyclopentane (13), 3-methyl-methylenecy-
clopentane (12), 3-(cyclopentylmethyl)-methylcyclopentane (7), 3-(3-methyl-cyclopentylmethyl)-methylcyclopentane (7), 3-(3-methyl-cyclopentyl-
methyl)-methylenecyclopentane (4).
c Complete consumption of the educt, further products (ton): methylcyclopentane (26), 1,3-dimethylcyclopentane (21), 3-methyl-methylenecy-
clopentane (17), 3-(cyclopentylmethyl)-methylcyclopentane (6), 3-(3-methyl-cyclopentylmethyl)-methylcyclopentane (4), 3-(3-methyl-cyclopentyl-
methyl)-methylenecyclopentane (8) and others.
d The cyclotrimer 3-(3-cyclopentylmethyl-cyclopentylmethyl)-methylenecyclopentane (13).
Surprisingly, the solvent-free complex 4 is nearly
inactive. The dimeric [(Ph3SiO)2ZrCl2(thf)]2 10 reaches
distinctively higher activity than 1, retaining a high
selectivity. Showing a similar activity, the tmen adduct
5 is much less selective. Although complexes 6 and 7
possess different p-acceptor ligands, they behave similar
to 1 (Table 3).
The most active system in the cyclization of 1,5-hexa-
diene is formed from the dimethyl complex
[(Ph3SiO)2ZrMe2(bpy)(toluene)2] (8) with MAO. In ad-
dition, it is very selective and shows a high stability for
a prolonged period too. It is remarkable that the
analogous chloro complex 7 does not at all reach these
turnover numbers, selectivity and stability. The above
stated points indicate that the formation and activity of
the catalysts are influenced by subtle variations in the
system.
Acknowledgements
This work was supported by the Bundesministerium
fu¨r Bildung und Forschung and the Fonds der Chemis-
chen Industrie.
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