Titanium hydrocarbyl complexes with a linked cyclopentadienyl-alkoxide ancillary ligand; participation of the ligand in an unusual activation of a (trimethylsilyl)methyl group

Article abstract of DOI:10.1021/om970867e

The titanium complexes [η⁵:η¹-C₅Me₄(CH ₂)₃O]-TiR₂ (R = Cl, Me, CH₂Ph, CH₂CMe₃, CH₂SiMe₃), with a linked Cp-alkoxide ancillary ligand, have been prepared in good yield. Cationic [C₅Me₄CH₂)₃O]Ti(η ²-CH₂-Ph)⁺ catalyzes the polymerization of propene to atactic polypropene. B(C₆F₅)₃ reacts with [C₅Me₄(CH₂)₃O]Ti(CH ₂-SiMe₃)₂ by Me abstraction from one of the CH₂SiMe₃ groups accompanied by an attack of the ligand alkoxide functionality on the Si atom of this group.

Full text of DOI:10.1021/om970867e

1652
Organometallics 1998, 17, 1652-1654
Tita n iu m Hyd r oca r byl Com p lexes w ith a Lin k ed
Cyclop en ta d ien yl-Alk oxid e An cilla r y Liga n d ;
P a r ticip a tion of th e Liga n d in a n Un u su a l Activa tion of
a (Tr im eth ylsilyl)m eth yl Gr ou p †
Esther E. C. G. Gielens, J ohan Y. Tiesnitsch, Bart Hessen,* and J an H. Teuben
Center for Catalytic Olefin Polymerization, Department of Chemistry, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, The Netherlands
Received October 6, 1997
Summary: The titanium complexes [η5:η1-C5Me4(CH2)3O]-
TiR2 (R ) Cl, Me, CH2Ph, CH2CMe3, CH2SiMe3), with
a linked Cp-alkoxide ancillary ligand, have been pre-
pared in good yield. Cationic [C5Me4(CH2)3O]Ti(η2-CH2-
Ph)+ catalyzes the polymerization of propene to atactic
polypropene. B(C6F5)3 reacts with [C5Me4(CH2)3O]Ti(CH2-
SiMe3)2 by Me abstraction from one of the CH2SiMe3
groups accompanied by an attack of the ligand alkoxide
functionality on the Si atom of this group.
Sch em e 1
There is considerable interest in early-transition-
metal organometallic species with η5:η1-ancillary ligands
that consist of a Cp group covalently linked to another
anionic moiety. Usually this anionic moiety is an alkyl/
aryl-amido group, and these so-called “constrained
geometry” complexes (of the group 4 metals) have been
highly successful as catalysts for the copolymerization
of ethene with R-olefins,1 especially using the C5Me4-
SiMe2Nt-Bu ligand.2,3 These ligands are considered to
be inert ancillary ligands, but they have more reactive
possibilities than, e.g., the ansa-metallocene framework.
For example, Herrmann et al. reported photochemical
cleavage of the Si-N bond in η5:η1-C5H4SiMe2NPh
complexes of Nb and Ta.4 Here, we report the synthesis
and reactivity of neutral and cationic organotitanium
complexes with a linked Cp-alkoxide ancillary ligand.
In this system we observed that the alkoxide functional-
ity of the Cp-alkoxide ligand participates in an unex-
pected Lewis-acid-induced fragmentation of a (trimeth-
ylsilyl)methyl group bound to titanium.
the appropriate alkyllithium or Grignard reagents
produces the corresponding bis(hydrocarbyl) derivatives
[η5:η1-C5Me4(CH2)3O]TiR2 (R ) Me, 2; CH2Ph, 3; CH2-
SiMe3, 4; CH2CMe3, 5) that are readily obtained as
crystalline solids in 60-80% yield (Scheme 1). These
compounds show the expected NMR spectroscopic fea-
tures for Cs-symmetric dialkyls, such as diastereotopic
alkyl methylene protons for 3-5.7 For the benzyl
complex 3, the downfield shift of the benzyl ipso carbon
1
(δ 149.60) and the J CH of 121.3 Hz for the methylene
group is normal for an η1-benzyl group attached to an
electropositive metal center.8
Reaction of the cyclopentadienyl-alkoxide titanium
dichloride complex [η5:η1-C5Me4(CH2)3O]TiCl2 (1)5,6 with
The dibenzyl complex 3 reacts cleanly with the Lewis-
acidic borane B(C6F5)3 in bromobenzene solvent to give
† This contribution is dedicated to Prof. P. Royo on the occasion of
his 60th birthday.
* Author to whom correspondence should be addressed. E-mail:
hessen@chem.rug.nl.
(6) An improved preparation of 1 over that in ref 5 involves the
elimination of MeCl from [C5Me4(CH2)3OMe]TiCl3 under thermolysis
conditions. A solution of [C5Me4(CH2)3OMe]TiCl3 (3.00 g, 8.63 mmol)5
in 60 mL of toluene was heated to 225 °C for 16 h in a 250 mL stainless
steel autoclave, during which the pressure increased to 15 bar. After
the autoclave was cooled to room temperature, it was vented and the
solvent removed in vacuo. The residual solid was sublimed at 112 °C
and 0.005 mmHg. After the solid was rinsed with cold pentane and
dried, 2.19 g (7.37 mmol, 86%) of orange crystalline 1 was obtained,
with satisfactory elemental analysis.
(1) (a) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.;
Nickias, P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. Eur. Pat. Appl. EP
416815, 1991. (b) Canich, J . M. Eur. Pat. Appl. EP 420436, 1991.
Canich, J . M. U.S. Pat. Appl. 5026798, 1991. Canich, J . M.; Hlatky,
G. G.; Turner, H. W. PCT Appl. WO92-00333, 1992.
(2) (a) Shapiro, P. J .; Bunel, E. E.; Schaefer, W. P.; Bercaw, J . E.
Organometallics 1990, 9, 867. (b) Piers, W. E.; Shapiro, P. J .; Bunel,
E. E.; Bercaw, J . E. Synlett 1990, 2, 74.
(3) Other recent papers dealing with Cp-amide titanium alkyl
species: (a) Okuda, J .; Eberle, T.; Spaniol, T. P. Chem. Ber./ Recl. 1997,
130, 209. (b) Chen, Y.-X.; Marks, T. J . Organometallics 1997, 16, 3649.
(c) Sinnema, P.-J .; van der Veen, L.; Spek, A. L.; Veldman, N.; Teuben,
J . H. Organometallics 1997, 16, 4245.
(7) Selected NMR data (C6D5Br, 25 °C). 1H NMR: 2 δ 0.27 (s,
2
TiCH3); 3 δ 2.22, 1.92 (d, J HH ) 10.3 Hz, TiCH2); 4 δ 0.81, -0.06 (d,
2
2J HH ) 11.7 Hz, TiCH2); 5 δ 1.36, 0.29 (d, J HH ) 12.2 Hz, TiCH2). 13C
NMR: 2 δ 47.63 (q, J CH ) 112.0 Hz, TiCH3); 3 δ 78.35 (t, J CH ) 121.2
Hz, TiCH2), 149.60 (s, Ph ipso C); 4 63.74 (dd, J CH ) 104.5, 113.8 Hz,
TiCH2); 5 90.05 (t, J CH ) 111.9 Hz, TiCH2).
(8) For some recent examples of η1- and η2-benzyl groups, see: (a)
Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg, H.
Organometallics 1996, 15, 2672. (b) Bochmann, M.; Lancaster, S. J .;
Hursthouse, M. B.; Malik, K. M. A. Organometallics 1994, 13, 2235
and references therein.
(4) Herrmann, W. A.; Baratta, W. J . Organomet. Chem. 1996, 506,
357.
(5) Fandos, R.; Meetsma, A.; Teuben, J . H. Organometallics 1991,
10, 59.
S0276-7333(97)00867-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/08/1998

Communications
Organometallics, Vol. 17, No. 9, 1998 1653
Sch em e 2
a deep red solution of the ionic complex {[η5:η1-C5-
Me4(CH2)3O]Ti(η2-CH2Ph)}[PhCH2B(C6F5)3] (6, Scheme
1).9 Various NMR spectroscopic features of the anion
trast, the bis(trimethylsilylmethyl) complex 4 reacts
readily with B(C6F5)3 in bromobenzene, but the product
is not a simple [η5:η1-C5Me4(CH2)3O]Ti(alkyl) cation.
Instead, in a clean reaction an ionic complex is pro-
duced, which we formulate as {[η5:η1:η1-C5Me4(CH2)3-
OSiMe2CH2]Ti(CH2SiMe3)}[MeB(C6F5)3] (7, Scheme 2).
In the formation of this complex, one methyl group has
been removed from one of the (trimethylsilyl)methyl
groups and the ligand alkoxide oxygen is now bound to
both Ti and Si. One could consider this as a silyl ether
moiety attached to the Cp ligand via the (CH2)3 bridge
and coordinated to the electrophilic Ti center. The
compound could not be crystallized, and the identifica-
tion of 7 was performed through 1H, 13C, 19F, and 29Si
NMR. The NMR characteristics12 of the four-membered
Ti-CH2-Si-O ring in 7 show strong resemblance with
those of related M-CH2-Si-N rings obtained by cy-
clometalation of trimethylsilyl amide ligands.13 The
metallacycle methylene group in 7 has characteristically
(19F NMR ∆δ(p-m) ) 2.77 ppm; 13C NMR BCH2Cipso
δ
148.47 ppm) show that it is not coordinated to the metal
center.10 The bonding of the benzyl ligand in 6 is
1
fluxional. At 50 °C, H NMR shows a symmetrically
averaged spectrum, but at -35 °C, an asymmetric
structure is evident. The strong upfield shift of the
1
2
benzyl o-H nucleus and the large J CH and small J HH
coupling constants for the benzylic methylene group are
indicative of a significant amount of η2-character in the
bonding of this fragment.8 In C6D5Br solution, 6 is
stable at ambient temperature for days. Complex 6 is
active in the catalytic polymerization of olefins and
polymerizes propene (4 bar, ambient temperature,
benzene solvent, 18 min run time) with a productivity
of 263 kg of PP (mol of Ti)-1 h-1
. The polypropene
formed is atactic with a noticeable amount of 2,1-
misinsertions,11 Mw ) 41 000, and Mn ) 19 600
(Mw/Mn ) 2.1, indicative of a single active species).
The bis(neopentyl) complex 5 does not react with
B(C6F5)3 in bromobenzene solvent at ambient temper-
ature. This is likely to be due to the steric bulk of the
neopentyl groups that prevents attack of the borane on
the nucleophilic neopentyl methylene carbons. In con-
1
large 2J HH (14.2 Hz) and J CH (136.2, 124.9 Hz) coupling
constants, and in the 13C NMR spectrum, its chemical
shift of δ 80.58 ppm is considerably upfield from that
(12) 7. 1H NMR (500 MHz, C6D5Br, -20 °C): δ 3.69, 3.35 (m, OCH2),
2.84, 2.20 (d, J ) 11.2 Hz, TiCH2SiMe3), 2.05, 1.76 (d, J ) 14.2 Hz,
TiCH2SiMe2O), 2.11, 1.74, 1.69, 1.60 (s, CpMe), 1.96, 1.7 (m, CpCH2),
1.56, 0.81 (m, bridge CH2), 1.14 (br, BMe), 0.35, 0.14 (s, OSiMe2), -0.08
(s, SiMe3). 13C NMR (126 MHz, C6D5Br, -20 °C): δ 137.22, 135.71,
132.76, 130.35, 123.93 (s, CpC), 110.22 (dd, J ) 106.3, 111.9 Hz, TiCH2-
SiMe3), 80.58 (dd, J ) 124.9, 136.2 Hz, TiCH2SiMe2O), 70.06 (t, J )
148.3 Hz, OCH2), 30.01 (t, J ) 128.7 Hz, bridge CH2), 21.85 (t, J )
130.6 Hz, CpCH2), 13.26, 12.95 (2×), 12.89 (q, J ) 128-129 Hz, CpMe),
11.08 (br, BMe), 1.79 (q, J ) 118.5 Hz, SiMe3), -0.06 (q, J ) 121.2 Hz,
SiMeMe), -4.03 (q, J ) 125.0 Hz, SiMeMe) (C6F5 resonances omitted).
19F NMR (282 MHz, C6D5Br, 25 °C): δ -133.56 (o-F), -165.75 (p-F),
-168.28 (m-F), ∆δ(m-p) ) 2.53 ppm. For 29Si NMR see ref 14.
(13) (a) Horton, A. D.; de With, J . J . Chem. Soc., Chem. Commun.
1996, 1375. (b) Bennett, C. R.; Bradley, D. C. J . Chem. Soc., Chem.
Commun. 1974, 29. (c) Planalp, R. P.; Andersen, R. A.; Zalkin, A.
Organometallics 1983, 2, 16.
(9) 6. Selected NMR data. 1H NMR (500 MHz, C6D5Br, -35 °C): δ
2
3
2.43, 2.90 (d, J HH ) 5.4 Hz, TiCH2), 5.65 (d, J HH ) 6.4 Hz, TiCH2Ph
o-H, 1H, other o-H obscured around δ 6.9 ppm). 13C NMR (126 MHz,
C6D5Br, -35 °C): δ 76.14 (t, J ) 151.1 Hz, TiCH2). An upfield-shifted
MCH2Ph ipso-C resonance is also indicative of an η2-benzyl group, but
for 6 this resonance was not unambiguously assigned.
(10) For representative examples of coordinated and noncoordinated
PhCH2B(C6F5)3 anion, see: Pellecchia, C.; Immirzi, A.; Grassi, A.;
Zambelli, A. Organometallics 1993, 12, 4473 and ref 13b.
(11) (a) Cheng, H. N.; Ewen, J . A. Makromol. Chem. 1989, 190, 1931.
(b) McKnight, A. L.; Masood, Md. A.; Waymouth, R. M.; Straus, D. A.
Organometallics 1997, 16, 2879.

1654 Organometallics, Vol. 17, No. 9, 1998
Communications
of the remaining (trimethylsilyl)methyl methylene group
(δ 110.22 ppm, dd, 1J CH ) 106.3, 111.9 Hz). 29Si NMR14
shows a considerable downfield shift of one of the two
Si atoms to δ 9.96 ppm. The NMR data of the anion
are consistent with those of a noncoordinating MeB-
(C6F5)3 anion.15
A possible route of formation for 7 could involve
nucleophilic attack of the alkoxide functionality on the
Si atom, with the borane acting as an acceptor for the
methyl anion. This would be similar to the alkoxide-
induced cleavage of Si-C bonds observed for alkyl-
silanes (e.g., with t-BuOK/DMSO18 or NaOH/MeOH19).
An alternative pathway involving â-Me elimination and
formation of a silaethene intermediate, as suggested for
the thermolysis of cis-(R3P)2Pt(CH2SiMe3)2 yielding
(R3P)2Pt(Me)(CH2SiMe2CH2SiMe3),20 would probably
have too high an activation barrier, even if the borane
would initially interact with the alkoxide moiety (cer-
tainly considering that the neopentyl derivative 5 is
unreactive under the same conditions). Experiments on
NMR-tube scale show that 7 is still able to effect the
catalytic polymerization of olefins, and the reactivity of
this species is currently the subject of further study.
In conclusion, we have shown that a stable cationic
[(Cp-alkoxide)Ti(CH2Ph)]+ species can be prepared and
that this species is active in catalytic olefin polymeri-
zation. However, it is clear that the Cp-alkoxide
ancillary ligand is not always innocent and that the
alkoxide moiety can engage in nucleophilic reactivity.
Presently, we are investigating the extent in which this
functionality can be involved in reactivity with other
Lewis-acidic reagents.
The Si atom in the Ti-O-Si-C moiety of 7 is prone
to nucleophilic attack, in which the O atom, which in 7
is shared between Ti and Si, is restored to the Ti center.
For example, when a solution of 7 is reacted with
gaseous anhydrous HCl, Me3SiCl and Me4Si are formed
in equimolar amounts and 1 is regenerated (Scheme
2).16 In this case, nucleophilic attack by the chloride
anion on the Si atom in the cationic complex 7 occurs.
In contrast, reaction of 7 with the Lewis base THF takes
place on the most Lewis-acidic center (Ti), which induces
an intramolecular nucleophilic attack of the Me3SiCH2
group on the Si atom to yield {[η5:η1:η1-C5Me4(CH2)3O]-
Ti(CH2SiMe2CH2SiMe3)(THF)}[MeB(C6F5)3] (8, Scheme
1
2). This compound was identified by H, 13C, and 29Si
NMR17 and by its reaction with DCl, which yields 1 and
Me3SiCH2SiMe2(CH2D) (NMR, GC/MS).
(14) 29Si-DEPT NMR data (99.3 MHz, C6D5Br, -20 °C): 4 δ 0.18; 7
δ 9.96 (OSiMe2) and 2.50 (TiCH2SiMe3); 8 δ 3.24 (TiCH2SiMe2C) and
0.25 (CH2SiMe3). For comparison, SiMe4 δ 0.00; Me3SiOSiMe3 δ 6.7.
(15) For data on coordinating and noncoordinating MeB(C6F5)3
anions, see, e.g.: (a) Horton, A. D. Organometallics 1996, 15, 2675.
(b) Beck, S.; Prosenc, M.-H.; Brintzinger, H.-H.; Goretzki, R.; Herfert,
N.; Fink, G. J . Mol. Catal. A 1996, 111, 67. (c) Yang, X.; Stern, C. L.;
Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10015.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and characterization data for the reported compounds
(8 pages). Ordering information is given on any current
masthead page.
(16) Use of DCl instead of HCl yields SiMe4-d1 and SiMe3Cl-d1,
consistent with bonding of both fragments to Ti.
(17) 8. Selected NMR data. 1H NMR (500 MHz, C6D5Br, -20 °C): δ
1.96, -0.10 (d, J ) 13.2 Hz, TiCH2Si), 0.08 (s, SiMe3), 0.01, -0.09 (s,
SiMe2), -0.36, -0.44 (d, J ) 13.2 Hz, SiCH2Si). 13C NMR (126 MHz,
C6D5Br, -20 °C): δ 87.60 (dd, J ) 105.8, 113.3 Hz, TiCH2), 5.73 (t, J
) 110.1 Hz, SiCH2Si), 2.32 (q, J ) 118.8 Hz, SiMe2), 2.05 (q, J ) 118.8
Hz, SiMe3), 1.34 (q, J ) 118.1 Hz, SiMe2). For 29Si NMR data, see ref
14.
OM970867E
(18) Price, C. C.; Sowa, J . R. J . Org. Chem. 1967, 32, 4126.
(19) Bott, R. W.; Eaborn, C.; Swaddle, T. W. J . Chem. Soc. 1963,
2342.
(20) Ankianiec, B. C.; Christou, V.; Hardy, D. T.; Thomson, S. K.;
Young, G. B. J . Am. Chem. Soc. 1994, 116, 9963.