Synthesis and characterization of the series of d° arene complexes [Cp*MMe2(η6-arene)] [MeB(C6F5)3] (M = Ti, Zr, Hf)

Article abstract of DOI:10.1021/om960174i

Treatment of the neutral trimethyl compounds Cp*MMe₃ (M = Ti, Zr, Hf) with the highly electrophilic borane B(C₆F₅)₃ in methylene chloride in the presence of various arenes results in methyl carbanion abstraction and coordination of the arene to form complexes of the type [Cp*MMe₂(η⁶-arene)][MeB(C₆F ₅)₃] (M = Ti, Zr, Hf; arene = benzene, toluene, m- and p-xylene, anisole, styre7ne, mesitylene). Indications of relative metal-arene affinities have been gleaned from a variety of low-temperature ¹H NMR experiments, and it seems that both steric and electronic factors play significant roles in determining stabilities. The crystal and molecular structures of [Cp*HfMe₂(η⁶-toluene)][MeB(C₆F ₅)₃] have been determined; as anticipated, there are no significant contacts between anion and cation, and the latter assumes a bent-metallocene type of structure.

Full text of DOI:10.1021/om960174i

3600
Organometallics 1996, 15, 3600-3605
Syn th esis a n d Ch a r a cter iza tion of th e Ser ies of d 0 Ar en e
Com p lexes [Cp *MMe2(η6-a r en e)][MeB(C6F 5)3]
(M ) Ti, Zr , Hf)
Daniel J . Gillis, Ruhksana Quyoum, Marie-J o Tudoret, Qinyan Wang,
Dusan J eremic, Aleksander W. Roszak,† and Michael C. Baird*
Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6
Received March 5, 1996X
Treatment of the neutral trimethyl compounds Cp*MMe3 (M ) Ti, Zr, Hf) with the highly
electrophilic borane B(C6F5)3 in methylene chloride in the presence of various arenes results
in methyl carbanion abstraction and coordination of the arene to form complexes of the type
[Cp*MMe2(η6-arene)][MeB(C6F5)3] (M ) Ti, Zr, Hf; arene ) benzene, toluene, m- and p-xylene,
anisole, styrene, mesitylene). Indications of relative metal-arene affinities have been
1
gleaned from a variety of low-temperature H NMR experiments, and it seems that both
steric and electronic factors play significant roles in determining stabilities. The crystal
and molecular structures of [Cp*HfMe2(η6-toluene)][MeB(C6F5)3] have been determined; as
anticipated, there are no significant contacts between anion and cation, and the latter
assumes a bent-metallocene type of structure.
In earlier papers,1 we have discussed the structure
oxidation states are known,4a relatively few such com-
plexes of these metals in the +4 oxidation state (d0) have
been reported.4a Typical examples are Zr(CH2Ph)3{η6-
PhBPh3}4b and Zr(CH2Ph)3{η6-PhCH2B(C6F5)3},4c con-
taining anionic arene ligands, and cationic complexes
of electron-rich arenes such as [(η6-C6Me6)TiCl3]+, formed
by dissolving TiCl4 in hexamethylbenzene.4d,e
and chemistry of Cp*TiMe2(µ-Me)B(C6F5)3, in which the
borate anion appears to coordinate in an η2 fashion,
analogous to metallocene compounds with bridging
methyl groups linking this same borate anion to transi-
tion-metal ions.2 Similar, as yet poorly characterized,
species are formed by treating the zirconium and
hafnium compounds Cp*MMe3 (M ) Zr, Hf) with the
highly electrophilic borane B(C6F5)3.1a The cationic
dimethyl complexes of all three metals are of interest
because they and similar species are extremely active
olefin polymerization initiators.1b,3
Aspects of this work have appeared previously as a
communication.1a Since then, the properties and the
X-ray crystal structure of the similar complex [{η5-1,3-
C5H3(SiMe3)2}HfMe2(η6-toluene)][MeB(C6F5)3] have also
been reported.5
In this paper we discuss reactions of Cp*TiMe2(µ-
Me)B(C6F5)3 and its zirconium and hafnium analogues
with aromatic solvents to form [Cp*MMe2(η6-arene)]-
[MeB(C6F5)3] (M ) Ti, Zr, Hf), complexes of a type
which, aside from their catalytic activities, are of
significant interest in their own right. Thus, while a
number of arene complexes of these metals in lower
Exp er im en ta l Section
All experiments were carried out under nitrogen using
standard Schlenk line techniques, a Vacuum Atmospheres
glovebox, and dried, thoroughly deoxygenated solvents. 1H,
13C, and 19F NMR spectra were run using a Bruker AM 400
spectrometer operating at 400.14, 100.6, and 376.5 MHz,
respectively; 1H and 13C{1H} NMR spectra are referenced with
respect to internal TMS, using residual proton or carbon
resonances, respectively, of the solvents; 19F spectra are
referenced to external CFCl3. 1H and 13C{1H} NMR data are
listed in Tables 1 and 2. The 13C{1H} NMR spectra of all
compounds containing a free [MeB(C6F5)3]- anion exhibited
C6F5 resonances at δ ∼150 (d, J CF ∼240 Hz, o-CF), ∼138 (d,
J CF ∼230 Hz, m-CF), ∼136 (d, J CF ∼250 Hz, p-CF), and ∼125
(br, ipso-C), while the 19F spectra exhibited resonances at δ
∼-123 (m, 2F, o-F), ∼-126.1 (t, 2F, m-F) and ∼-157 (t, 1F,
p-F). Since these parameters are essentially independent of
temperature, solvent, etc., they vary little and are not useful
for purposes of characterization and are therefore omitted from
† Present address: Protein Crystallography Group, Department of
Chemistry, University of Glasgow, Glasgow G12 8QQ, U.K.
X Abstract published in Advance ACS Abstracts, August 1, 1996.
(1) (a) Gillis, D. J .; Tudoret, M.-J .; Baird, M. C. J . Am. Chem. Soc.
1993, 115, 2543. (b) Wang, Q.; Quyoum, R.; Gillis, D. J .; Tudoret, M.-
J .; J eremic, D.; Hunter, B. K.; Baird, M. C. Organometallics 1996, 15,
693. (c) Wang, Q.; Quyoum, R.; Gillis, D. J .; J eremic, D.; Baird, M. C.
J . Organomet. Chem., in press.
(2) (a) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,
113, 3623. (b) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.;
Abdul Malik, K. M. Organometallics 1994, 13, 2235. (c) Bochmann,
M.; Lancaster, S. J . Angew. Chem., Int. Ed. Engl. 1994, 33, 1634. (d)
Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10015.
(3) For recent examples, see: (a) Quyoum, R.; Wang, Q.; Tudoret,
M.-J .; Baird, M. C.; Gillis, D. J . J . Am. Chem. Soc. 1994, 116, 6435.
(b) Barsan, F.; Baird, M. C. J . Chem. Soc., Chem. Commun. 1995, 1065.
(c) J eremic, D.; Wang, Q.; Quyoum, R.; Baird, M. C. J . Organomet.
Chem. 1995, 497, 143. (d) Wang, Q.; Baird, M. C. Macromolecules 1995,
28, 8021. (e) Pellecchia, C.; Longo, P.; Proto, A.; Zambelli, A. Makromol.
Chem., Rapid Commun. 1992, 13, 265. (f) Pellecchia, C.; Longo, P.;
Proto, A.; Zambelli, A. Makromol. Chem., Rapid Commun. 1992, 13,
277. (g) Chien, J . C. W.; Salajka, Z.; Dong, S. Macromolecules 1992,
25, 3199. (h) Kucht, A.; Kucht, H.; Barry, S.; Chien, J . C. W.; Rausch,
M. D. Organometallics 1993, 12, 3075. (i) Ready, T. E.; Day, R. O.;
Chien, J . C. W.; Rausch, M. D. Macromolecules 1993, 26, 5822. (j)
Grassi, A.; Pellecchia, C.; Oliva, L. Macromol. Chem. Phys. 1995, 196,
1093. (k) Kucht, H.; Kucht, A.; Chien, J . C. W.; Rausch, M. D. Appl.
Organomet. Chem. 1993, 12, 3075. (l) Pellecchia, C.; Immirzi, A.;
Grassi, A.; Zambelli, A. Organometallics 1993, 12, 4473.
(4) (a) Troyanov, S. J . Organomet. Chem. 1994, 475, 139 and
references therein. (b) Bochmann, M.; Karger, G.; J aggar, A. J . J .
Chem. Soc., Chem. Commun. 1990, 1038. (c) Pellecchia, C.; Grassi, A.;
Immirzi, A. J . Am. Chem. Soc. 1993, 115, 1160. (d) Solari, E.; Musso,
F.; Ferguson, R.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 1510. (e) Solari, E.; Floriani, C.; Schenk, K.;
Chiesi-Villa, A.; Rizzoli, C.; Rosi, M.; Sgamellotti, A. Inorg. Chem. 1994,
33, 2018.
(5) Lancaster, S. J .; Robinson, O. B.; Bochmann, M.; Coles, S. J .;
Hursthouse, M. B. Organometallics 1995, 14, 2456.
S0276-7333(96)00174-4 CCC: $12.00 © 1996 American Chemical Society

d0 Arene Complexes of Ti, Zr, and Hf
Organometallics, Vol. 15, No. 16, 1996 3601
Ta ble 1. 1H NMR Da ta for th e Com p lexes [Cp *MMe2(η6-a r en e)][MeB(C6)3] (CD2Cl2)
arene
δ(M-Me)
δ(Cp*Me)
δ(arene) (J , Hz)
M ) Ti
toluenea
0.11
0.09
1.90
1.93
7.74 (d, o-H), 7.2 (t, m-H), 6.70 (t, p-H), 2.78 (s, Me)
mesitylenea
7.34 (s, Ph H), 2.52 (s, Me)
M ) Zr
benzenea
tolueneb
-0.15
-0.11
-0.10
-0.29
-0.15
-0.23
1.89
1.96
1.94
1.89
1.96
1.89
7.64 (s, PhH) (free benzene at 7.39)
7.78 (d, m-H), 7.38 (t, m-H), 7.04 (t, p-H), 2.71 (s, Me)
7.48 (s, Ph H), 2.42 (s, Me)
8.26 (s, 1 H, H-2), 7.10 (d, 2H, H-4,6), 6.97 (t, 1H, H-5), 2.54 (s, Me)
7.29 (s, Ph H), 2.47 (s, Me)
7.95 (d, o-H), 7.41 (t, m-H), 7.11 (t, p-H), 6.82 (dd, CHdCH2),
6.34 (d, J ) 17.2, CHdCH2), 6.04 (d, J ) 10.9, CHdCH2)
p-xylened
m-xylened
mesitylenec
styrenea
M ) Hf
tolueneb
p-xylened
m-xylened
styrened
-0.28
-0.46
-0.41
-0.37
2.10
1.93
2.02
2.02
7.55 (d, m-H), 7.32 (t, m-H), 7.28 (t, p-H), 2.76 (s, Me)
7.44 (s, PhH), 2.35 (s, Me)
7.81 (s, 1 H, H-2), 7.13 (d, 2H, H-4,6), 6.97 (t, 1H, H-5), 2.58 (s, Me)
7.94 (d, o-H), 7.47 (t, m-H), 7.21 (t, p-H), 6.80 (dd, CHdCH2),
6.33 (d, J ) 17.5, CHdCH2), 6.08 (d, J ) 10.9, CHdCH2)
7.47 (t, m-H), 7.15 (d, o-H), 6.74 (t, p-H), 4.05 (s, OMe)
7.28 (s, Ph H), 2.44 (s, Me)
anisoled
-0.49
-0.47
1.95
1.95
mesitylened
a
b
c
d
T ) 223 K. T ) 298 K. T ) 273 K. T ) 213 K.
Ta ble 2. 13C{1H} NMR Da ta for th e Com p lexes [Cp *MMe2(η6-a r en e)][MeB(C6F 5)3] (CD2Cl2)
arene
δ(M-Me)
δ(Cp* ring)
δ(Cp* Me)
δ(arene)
M ) Ti
12.9
toluened
65.2
138.1
M ) Zr
11.6
12.0
11.9
11.6
benzenea
tolueneb
45.3
45.5
45.2
45.6
40.7
44.6
123.1
123.6
123.6
122.5
122.4
122.9
131.6 (free benzene 128.2)
147.0, 134.8, 130.9, 129.2 (ring), 22.4 (Me)
141.6, 134.8 (ring), 21.4 (Me)
146.6, 136.9, 138.1 (ring), 22.0 (Me)
141.1, 132.4 (ring), 21.3 (Me)
140.8, 126.5 (CdC), 130.7, 129.6, 126.8, 126.5 (ring)
p-xylened
m-xylened
mesitylenec
styrenea
11.7
11.7
M ) Hf
11.6
11.4
tolueneb
46.5
47.2
50.3
121.7
121.0
122.3
146.8, 134.7, 130.5, 124.7 (ring), 31.8 (Me)
140.6, 132.4 (ring), 21.2 (Me)
147.6, 138.9, 138.1, 128.9 (ring), 22.5 (Me)
p-xylened
m-xylened
11.9
a
b
c
d
T ) 223 K. T ) 298 K. T ) 273 K. T ) 213 K.
the data compilations appearing below. Elemental analyses
were performed by Canadian Microanalytical Services or at
E. I. DuPont de Nemours, Central Research and Development,
Wilmington, DE.
TiMe). The 1H NMR spectra for similar experiments with
benzene, p-xylene, hexamethylbenzene, and chlorobenzene
exhibited only the resonances of Cp*TiMe2(µ-Me)B(C6F5)3 and
free arene; no [Cp*TiMe2(η6-arene)][MeB(C6F5)3] appeared to
have been formed. Similar experiments with styrene, even
at 173 K, resulted in very rapid polymerization to atactic
polystyrene.1b
The following compounds were prepared as described
previously: Cp*MMe3 (M ) Ti,6a Zr,6b Hf6c), B(C6F5)3.6d
Syn th esis of [Cp *TiMe2(η6-tolu en e)][MeB(C6F 5)3] a n d
[Cp *TiMe2(η6-1,3,5-C6H 3Me3)][MeB(C6F 5)3]. At t em p t ed
Syn th eses of [Cp *TiMe2(η6-a r en e)][MeB(C6F 5)3] (a r en e )
Ben zen e, H exa m et h ylb en zen e, p -Xylen e, Ch lor ob en -
zen e, Styr en e). To a solution of Cp*TiMe2(µ-Me)B(C6F5)3
(0.04 mmol in 0.6 mL of CD2Cl2) prepared as before,1 at 195
K, was added 21.0 µL of toluene (0.2 mmol). The sample was
then placed in the NMR spectrometer probe at 223 K.
Resonances of Cp*TiMe2(µ-Me)B(C6F5)3 and of free toluene
were observed, as well as a new set of resonances, attributable
to [Cp*TiMe2(η6-toluene)][MeB(C6F5)3] by comparison with
spectra of the more stable zirconium and hafnium analogues
(see below). Conversion to [Cp*TiMe2(η6-toluene)][MeB(C6)3]
was ∼30%. 1H NMR (CD2Cl2 at 223 K): δ 7.74, ∼7.2, 6.70
(all Ph), 2.78 (s, 3H, toluene Me), 1.90 (s, 15H, Cp*), 0.38 (br
s, 3H, BMe), 0.11 (s, 6H, TiMe).
Syn th esis of [Cp*Ti(13CH3)2(η6-tolu en e)][13CH3B(C6F5)3].
To a solution of Cp*Ti(13CH3)2(µ-13CH3)B(C6F5)31b,c (0.042 mmol
in 0.4 mL of CD2Cl2) at 195 K was added 27.0 µL of toluene
(0.26 mmol). The sample was then placed in the NMR
spectrometer probe at 223 K. Resonances of Cp*Ti(13CH3)2(µ-
13CH3)B(C6F5)31c and of free toluene were observed, as well as
a new set of resonances, attributed to [Cp*Ti(13CH3)2(η6-
toluene)][13CH3B(C6F5)3] (see above). 1H NMR (CD2Cl2 at 223
K): δ 7.74, ∼7.2, 6.70 (Ph), 2.78 (s, 3H, toluene Me), 1.90 (s,
15H, Cp*), 0.44 (br d, 3H, J HC 112.6 Hz, BMe), 0.167 (d, 6H,
J
HC 120.1 Hz, TiMe). 13C{1H} NMR (CD2Cl2 at 223 K): δ 138.1
(w, Cp* ring C), 65.2 (vs, Ti-Me), 12.9 (w, Cp* Me).
Syn th esis of [Cp *Zr Me2(η6-tolu en e)][MeB(C6F 5)3].
A
solution of 0.511 g of B(C6F5)3 (1.0 mmol) in 200 mL of hexanes,
cooled to 273 K, was added dropwise over 45 min to a well-
stirred solution of 0.272 g of Cp*ZrMe3 (1.0 mmol) in 20 mL
of toluene cooled to 273 K. The resulting yellow suspension
was stirred for a further few minutes, and the product was
collected by filtration, washed five times with cold hexanes,
and dried in vacuo for 30 min at room temperature. Yield:
0.82 g (94% yield). Anal. Calcd for C38H32BF15Zr: C, 52.12;
H, 3.68. Found: C, 52.40; H, 3.75. 1H NMR (CD2Cl2 at 298
K): δ 7.78 (d, 2H, o-Ph), 7.38 (t, 2H, m-Ph), 7.04 (t, 1H, p-Ph),
2.71 (s, 3H, toluene Me), 1.96 (s, 15H, Cp*), 0.48 (br s, 3H,
A similar experiment with mesitylene showed ∼50% conver-
sion to [Cp*TiMe2(η6-1,3,5-C6H3Me3)][MeB(C6F5)3]. 1H NMR
(CD2Cl2 at 223 K): δ 7.34 (s, 3H, ring CH), 2.52 (s, 9H, ring
Me), 1.93 (s, 15H, Cp*), 0.39 (br s, 3H, BMe), 0.09 (s, 6H,
(6) (a) Mena, M.; Royo, P.; Serrano, R.; Pellinghelli, M. A.; Tiripic-
chio, A. Organometallics 1989, 8, 476. (b) Wolczanski, P. T.; Bercaw,
J . E. Organometallics 1982, 1, 793. (c) Schock, L. E.; Marks, T. J . J .
Am. Chem. Soc. 1988, 110, 7701. (d) Massey, A. G.; Park, A. J . J .
Organomet. Chem. 1964, 2, 245.

3602 Organometallics, Vol. 15, No. 16, 1996
Gillis et al.
BMe), -0.11 (s, 6H, ZrMe). 13C{1H} NMR (CD2Cl2 at 298 K):
δ 147.0, 134.8, 130.9, 129.2 (ipso-, o-, m-, p-Ph, respectively),
123.6 (Cp* ring C), 45.5 (ZrMe), 22.4 (toluene Me), 11.5 (Cp*
Me), 10.2 (br, BMe).
Syn th esis of [Cp*Zr Me2(η6-1,3,5-C6H3Me3)][MeB(C6F5)3].
This compound was prepared as above, with mesitylene
substituted for toluene, and the orange product was obtained
in 89% yield. Anal. Calcd for C40H36BF15Zr: C, 53.16; H, 4.01.
Found: C, 53.28; H, 4.12. 1H NMR (CD2Cl2 at 273 K): δ 7.29
(s, 3H, ring CH), 2.47 (s, 9H, ring Me), 1.96 (s, 15H, Cp*), 0.50
(br s, 3H, BMe), -0.15 (s, 6H, ZrMe). 13C{1H} NMR (CD2Cl2
at 278 K): δ 141.1, 132.4 (mesitylene ring), 122.4 (Cp* ring
C), 40.7 (ZrMe), 21.3 (mesitylene Me), 11.7 (Cp* Me), 10.2 (br,
BMe).
Syn th esis of [Cp*Zr Me2(η6-ben zen e)][MeB(C6F5)3]. This
compound was prepared as above, with benzene substituted
for toluene. Although a yellow, solid product could be obtained
in 88% yield at 273 K, it readily decomposed at room temper-
ature and was therefore characterized spectroscopically at low
temperature. 1H NMR (CD2Cl2 at 223 K): δ 7.64 (s, 6H,
benzene), 1.89 (s, 15H, Cp*), 0.53 (br s, 3H, BMe), -0.15 (s,
6H, ZrMe). 13C{1H} NMR (CD2Cl2 at 278 K): δ 131.6 (ben-
zene), 123.1 (Cp* ring C), 45.3 (ZrMe), 11.6 (Cp* Me), 9.2 (br,
BMe).
Syn th esis of [Cp *Zr Me2(η6-styr en e)][MeB(C6F 5)3]. This
compound could not be prepared as above because of thermal
instability. It was therefore generated in an NMR tube and
characterized spectroscopically at low temperature. 1H NMR
(CD2Cl2 at 223 K): δ 7.95, 7.41, 7.11 (Ph), 6.82 (dd, 1H,
PhCHd), 6.34 (d, 1H, J HH 10.9 Hz, cis dCH2), 6.04 (d, 1H, J HH
17.2 Hz, trans dCH2), 1.89 (s, 15H, Cp*), 0.41 (br s, 3H, BMe),
-0.23 (s, 6H, ZrMe). 13C{1H} NMR (CD2Cl2 at 223 K): δ 152.1
(PhCd), 140.8 (dCH2), 130.7, 129.6, 126.8, 126.5 (Ph), 122.9
(Cp* ring C), 44.6 (ZrMe), 11.7 (Cp* Me), 9.8 (br, BMe). When
the product stood at 223 K for 2 h, polymerization of styrene
was observed. When a freshly prepared sample was warmed
to 273 K, complete polymerization of styrene was observed and
several resonances appeared in the Cp* region.
Syn th esis of [Cp*Zr Me2(η6-p-xylen e)][MeB(C6F5)3]. This
compound could not be isolated analytically pure as above
because of thermal instability, and it was therefore generated
in an NMR tube and characterized spectroscopically at low
temperature. 1H NMR (CD2Cl2 at 213 K): δ 7.48 (s, 4H, ring
H), 2.42 (s, 6H, ring Me), 1.94 (s, 15H, Cp*), 0.46 (br s, 3H,
BMe), -0.10 (s, 6H, ZrMe). 13C{1H} NMR (CD2Cl2 at 298 K):
δ 141.6, 134.8 (xylene ring C), 123.6 (Cp* ring C), 45.2 (ZrMe),
21.4 (xylene Me), 11.9 (Cp* Me), 10.5 (br, BMe).
Syn th esis of [Cp*Zr Me2(η6-m-xylen e)][MeB(C6F5)3]. This
compound could not be isolated analytically pure as above
because of thermal instability, and it was therefore generated
in an NMR tube and characterized spectroscopically at low
temperature. 1H NMR (CD2Cl2 at 213 K): δ 8.26 (s, 1H, xylene
ring H-2), 7.10 (d, 2H, xylene ring H-4,6), 6.97 (t, 1H, xylene
ring H-5), 2.54 (s, 6H, xylene ring Me), 1.89 (s, 15H, Cp*), 0.41
(br s, 3H, BMe), -0.29 (s, 6H, ZrMe). 13C{1H} NMR (CD2Cl2
at 213 K): δ 146.6, 139.6, 138.1, 126.4 (xylene ring C), 122.5
(Cp* ring C), 45.6 (ZrMe), 22.0 (xylene Me), 11.6 (Cp* Me),
10.5 (br, BMe).
Syn th esis of [Cp*HfMe2(η6-p-xylen e)][MeB(C6F5)3]. This
compound was prepared as above. Anal. Calcd for C39H34
-
BF15Hf: C, 47.95; H, 3.51. Found: C, 46.62; H, 3.59. 1H NMR
(CD2Cl2 at 213 K): δ 7.44 (s, 4H, ring H), 2.35 (s, 6H, ring
Me), 1.93 (s, 15H, Cp*), 0.41 (br s, 3H, BMe), -0.46 (s, 6H,
HfMe). 13C{1H} NMR (CD2Cl2 at 298 K): δ 140.6, 132.4
(xylene ring C), 121.0 (Cp* ring C), 47.2 (HfMe), 21.2 (xylene
Me), 11.4 (Cp* Me), 10.5 (br, BMe).
Syn th esis of [Cp*HfMe2(η6-m-xylen e)][MeB(C6F5)3]. This
compound was prepared as above; although apparently ther-
mally stable at room temperature, it could not be obtained
analytically pure and was characterized spectroscopically. 1H
NMR (CD2Cl2 at 213 K): δ 7.81 (s, 1H, xylene ring H-2), 7.13
(d, 2H, xylene ring H-4,6), 6.97 (t, 1H, xylene ring H-5), 2.58
(s, 6H, xylene ring Me), 2.02 (s, 15H, Cp*), 0.52 (br s, 3H, BMe),
-0.41 (s, 6H, HfMe). 13C{1H} NMR (CD2Cl2 at 213 K): δ 147.6,
138.9, 138.1, 128.9 (xylene ring C), 122.3 (Cp* ring C), 50.3
(HfMe), 22.5 (xylene Me), 11.9 (Cp* Me), 10.5 (br, BMe).
Syn th esis of [Cp *HfMe2(η6-a n isole)][MeB(C6F 5)3]. This
compound could not be prepared analytically pure because of
thermal instability but was generated in an NMR tube and
characterized spectroscopically at low temperature. 1H NMR
(CD2Cl2 at 213 K): δ 7.47 (t, 2H, m-H), 7.15 (d, 2H, o-H), 6.74
(t, 1H, p-H), 4.05 (s, 3H, OMe), 1.95 (s, 15H, Cp*), 0.39 (br s,
3H, BMe), -0.49 (s, 6H, HfMe). 13C{1H} NMR (CD2Cl2 at 213
K): δ 163.8, 133.5, 121.2, 115.5 (Ph), 116.9 (Cp* ring C), 44.6
(HfMe), 11.4 (Cp* Me), 10.2 (br, BMe). When the compound
was warmed to 295 K in the presence of free anisole,
coalescence of the phenyl 1H resonances of free and coordinated
anisole to broad bands at δ ∼7.37 (2H) and δ ∼6.95 (3H) and
of the OMe resonances of free and coordinated anisole to a
broad band at δ ∼3.9 was observed. The Hf-Me resonance of
the anisole complex (δ -0.38) was also noticeably broadened.
X-r a y St r u ct u r e Det er m in a t ion of [Cp *H fMe2(η6-
tolu en e)][MeB(C6F 5)3]. Crystals of this complex were grown
by slow diffusion of hexanes into an o-dichlorobenzene solution
at 243 K over several weeks, and a platelike sample was
mounted on a glass fiber with epoxy cement and sealed under
an argon atmosphere in a thin glass capillary. Table 3
presents the crystal data, details of the experimental measure-
ments, and a summary of refinement parameters. The cell
constants were obtained from least-squares refinement of 25
reflections with 34° e 2θ e 36°. Intensity data were collected
by ω-2θ scans. Three standard reflections monitored through-
out the data collection showed significant degradation of the
compound (30% at the end of data collection), and a correction
based on the variation of the standards’ intensities was
applied.7 The data were corrected for absorption using the
program DIFABS.8 The structure was solved by heavy-atom
methods (Patterson and Fourier maps) using the program
SHELXS86.9 Full-matrix least-squares refinement on F2 data
with the anisotropic displacement parameters for all non-H
atoms was performed using the program SHELXL9210 (the
neutral atom scattering factors and anomalous dispersion
corrections used are those from ref 11). The structure has
shown the presence of one solvent molecule of toluene per two
pairs of complex cations. It was found disordered around the
inversion center at 1/2, 0, 1/2 and was refined originally as a
rigid group (as an ideal hexagon with ring C-C bonds of 1.390
Å and a single C-C bond of 1.51 Å) with common isotropic
displacement parameters. In the last cycles, the restrained
anisotropic refinement was used and the Cphenyl-Cmethyl bond
Attem p ted Syn th eses of [Cp *Zr Me2(η6-a r en e)][MeB-
(C6F 5)3] (a r en e ) P h Cl, C6Me6). Low-temperature (223 K)
NMR experiments designed to detect these complexes revealed
no resonances which could be attributed to arene species.
Syn th esis of [Cp *HfMe2(η6-tolu en e)][MeB(C6F 5)3]. This
compound was prepared as above for the zirconium analogue.
Anal. Calcd for C38H32BF15Hf: C, 47.38; H, 3.32. Found: C,
46.62; H, 3.41. 1H NMR (CD2Cl2 at 293 K): δ 7.55 (d, 2H,
o-Ph), 7.32 (t, 2H, m-Ph), 7.28 (t, 1H, p-Ph), 2.76 (s, 3H, toluene
Me), 2.10 (s, 15H, Cp*), 0.56 (br s, 3H, BMe), -0.28 (s, 6H,
HfMe). 13C{1H} NMR (CD2Cl2 at 298 K): δ 146.8, 134.7, 130.5,
124.7 (ipso-, o-, m-, p-Ph, respectively), 121.7 (Cp* ring C), 46.5
(ZrMe), 31.8 (toluene Me), 11.6 (Cp* Me), 10.2 (br, BMe).
(7) Hall, S. R.; Stewart, J . M. Xtal 3.0 Reference Manual; Universi-
ties of Western Australia and Maryland, 1990.
(8) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(9) Sheldrick, G. M. SHELXS86. Program for the Solution of Crystal
Structures; University of Go¨ttingen, Go¨ttingen, Germany, 1985.
(10) Sheldrick, G. M. SHELXL92. Program for the Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1992.
(11) International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C, Tables 6.1.1.4 and 4.2.6.8, pp 500-502, 219-222.

d0 Arene Complexes of Ti, Zr, and Hf
Organometallics, Vol. 15, No. 16, 1996 3603
Ta ble 3. Cr ysta llogr a p h ic Da ta for
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
[Cp *HfMe2(η6-tolu en e)][MeB(C6F 5)3]
(a) Crystal Parameters
Hf-C1
2.219(9)
2.204(9)
2.172(4)
2.334(6)
2.487(8)
2.480(7)
2.481(8)
2.487(7)
2.480(8)
2.805(9)
2.666(9)
2.623(11)
2.62(2)
C5-C6
1.424(11)
1.408(12)
1.499(13)
1.488(12)
1.478(12)
1.490(12)
1.477(12)
1.387(14)
1.42(2)
1.48(2)
1.31(2)
1.36(3)
1.33(3)
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
41.5H36BF15Hf
Hf-C2
C6-C7
1009.00
triclinic
Hf-Cg(1)a
Hf-Cg(2)b
Hf-C3
C3-C8
C4-C9
P1h(No. 2)
9.380(3)
17.639(3)
12.335(2)
82.37(1)
101.14(2)
96.32(2)
1977.2(8)
2
C5-C10
C6-C11
C7-C12
C13-C14
C13-C18
C13-C19
C14-C15
C15-C16
C16-C17
C17-C18
B-C20
Hf-C4
Hf-C5
Hf-C6
Hf-C7
Hf-C13
Hf-C14
Hf-C15
Hf-C16
Hf-C17
Hf-C18
C3-C4
C3-C7
C4-C5
Z
D
calcd, g/cm3
1.695
27.39
2.710(14)
2.768(10)
1.397(11)
1.421(12)
1.420(11)
1.34(2)
µ(Mo KR), cm-1
cryst dimens, mm
cryst color
1.665(11)
1.668(10)
1.647(11)
1.628(10)
0.18 × 0.50 × 0.70
B-C30
yellow-brown
B-C40
B-C50
(b) Data Collection
diffractometer
radiation
monochromator
temp, K
Enraf-Nonius CAD-4
Mo KR (γ ) 0.710 69 Å)
graphite
C1-Hf-C2
93.6(5)
C20-B-C30
C20-B-C40
C20-B-C50
C30-B-C40
C30-B-C50
C40-B-C50
103.7(6)
112.2(5)
113.0(6)
113.6(6)
109.7(6)
104.9(6)
C1-Hf-Cg(1)a
C1-Hf-Cg(2)b
C2-Hf-Cg(1)a
C2-Hf-Cg(2)b
Cg(1)a-Hf-Cg(2)b
108.5(3)
102.1(3)
108.4(3)
103.2(3)
133.8(2)
298
data collected
-11 e h e 10, -20 e k e 20,
0 e l e 14
1.2-25.00
7176
6921 (Rint ) 0.031)
4598
θ scan range, deg
no. of rflns collected
no. of indep rflns
no. of indep obsd reflns
(I > 2σ(I))
C50-B-C20-C21
3.2(10) C50-B-C30-C35 -128.4(8)
C50-B-C40-C41 -111.6(8)
55.2(9) C50-B-C40-C45 61.2(8)
C50-B-C20-C25 -173.3(6)
C50-B-C30-C31
a
Cg(1): center of gravity of the C3-C7 five-membered ring.
Cg(2): center of gravity of the C13-C18 six-membered ring.
abs cor
empirical (transmissn factors
0.587-1.249)
b
(c) Structure Solution and Refinement
solution method
refinement method
Patterson and Fourier methods
full-matrix least squares on F2
(for all indep data)
no. of variables
no. of restraints
554
60
data/variables ratio
function minimized
weighting scheme
12.5
2
2 2
∑w(Fo - Fc
)
w ) 1/[σ2(Fo2) + (0.0602P)2],
where P ) (Fo + 2Fc2)/3
2
R,a wR2,b indep obsd rflns
R,a wR2,b all indep rflns
goodness-of-fit indicatorc
max shift/error, final cycle
0.0448, 0.1222
0.0729, 0.1436
1.094 (all indep data)
0.008
max resid electron dens, e/Å3 1.379
min resid electron dens, e/Å3
-1.484
a
b
R ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {[∑w(Fo2 - Fc2)2]/[∑w(Fo2)2]}1/2
.
Goodness of fit on F2: S ) {[∑w(Fo - Fc2)2]/(Nobs - Nvar)}1/2
.
c
2
F igu r e 1. Molecular structure of [Cp*HfMe2(η6-toluene)]-
[BMe(C6F5)3] showing 30% probability displacement el-
lipsoids. The toluene solvent molecule is shown in one of
two positions related by a center of symmetry; H atoms
were omitted for clarity.
length was allowed to vary. All atoms of the solvent toluene
were refined with site occupancy factor of 50%. The
a
hydrogen atoms of the structure were placed in calculated
positions (for toluene methyl groups in two positions rotated
by 60° with half-occupancy each; for other methyl groups, the
torsion angle was determined on the basis of the electron
density map features). In the refinement, all H atoms were
riding on the carbon atoms to which they are attached; their
isotropic thermal displacement parameters were kept as
Uiso(H) ) 1.2Ueq(C) (for aromatic H) or Uiso(H) ) 1.5Ueq(C) (for
methyl H). The refinement converged at the final R value
(conventional, based on F) of 0.0448. Selected bond lengths,
bond angles, and torsion angles are listed in Table 4. Tables
of all bond lengths and angles, positional parameters for non-H
atoms, anisotropic displacement parameters for non-H atoms,
hydrogen atom positional and thermal parameters, and least-
squares planes data, as well as a diagram showing the disorder
of the solvent molecule of toluene, are available as Supporting
Information. The geometrical analysis of the structure was
done with the programs SHELXL9210 and PLATON.12 An
ORTEP13 drawing of the complex ions and the solvent toluene
molecule with the atom-numbering scheme is given in Figure
1. Figure 2 shows the arrangement of two pairs of the complex
ions around the disordered solvent molecule of toluene, drawn
with the program PLUTON.14
Resu lts a n d Discu ssion
Syn th esis of Ar en e Com p lexes of Zir con iu m a n d
Ha fn iu m . In general, addition of the highly electro-
philic borane B(C6F5)3 to solutions of Cp*MMe3 (M )
Zr, Hf) in CD2Cl2 in the presence of excess arene (arene
) benzene, toluene, styrene, m-xylene, p-xylene, anisole,
mesitylene) at low temperatures results in the disap-
1
pearance of the H resonances of Cp*MMe3, in weaken-
(13) J ohnson, C. K. ORTEPII; Report ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
(14) Spek, A. L. PLUTON: Molecular Graphics Program; University
of Utrecht, Utrecht, The Netherlands, 1991.
(12) Spek, A. L. Acta Crystallogr. 1990, A46 (Suppl.), C34.

3604 Organometallics, Vol. 15, No. 16, 1996
Gillis et al.
In the 1H NMR spectra of the complexes, all arene
resonances except for the 1H resonances of the p-H
atoms of the monosubstituted ligands toluene, styrene
and anisole were found to be significantly deshielded
relative to the chemical shifts of the free ligands. The
p-H resonances were all found to be slightly shielded
relative to the chemical shifts of the free ligands. We
presume that the anisole ligand coordinates preferen-
tially in an η6 fashion because of these similarities in
1
coordination shifts and because integrations of the H
NMR spectra of the hafnium anisole complex indicate
quite clearly that only one arene ligand coordinates, not
two. As shown previously, an analogous bis-THF
complex, [Cp*ZrMe2(THF)2][BPh4], is known.15 How-
ever, coordination via the oxygen is also possible and
probably occurs to some extent (see below).
F igu r e 2. Packing diagram of [Cp*HfMe2(η6-toluene)]-
[BMe(C6F5)3], showing two pairs of the complex ions and
two overlapped molecules of solvent toluene (50% occupa-
The general trends seem reasonable, since the arenes
are in each case coordinated to cationic complexes in
which the metals are in the +4 oxidation state. Bonding
of the arenes to the d0 metal ions must involve es-
sentially no metal-ligand back-bonding but rather
significant net flow of electron density from arene to
metal, a bonding model seemingly confirmed by the
coordination shifts exhibited in the NMR spectra. The
fact that chlorobenzene does not coordinate to either
[Cp*TiMe2]+ or [Cp*HfMe2]+ seems to confirm this
hypothesis.16 The 13C{1H} resonances of the coordi-
nated arenes also generally occur to low field relative
to the corresponding resonances of the free arenes. The
1H NMR spectra of most of the complexes of both metals
are essentially unchanged on warming from 223 to 273
K, indicating reasonable thermal stabilities.
1
tion each) around the inversion center at 1/2, 0, /2.
ing of the resonances of the free arene, and in the
appearance of new resonances attributable to free borate
ion, [MeB(C6F5)3]- (δ ∼0.5),1 and the new species
[Cp*MMe2(η6-arene)]+ (Table 1). In some cases, e.g.
[Cp*ZrMe2(η6-toluene)][MeB(C6F5)3], [Cp*ZrMe2(η6-1,3,5-
C6H3Me3)][MeB(C6F5)3], [Cp*HfMe2(η6-toluene)][MeB-
(C6F5)3], and [Cp*HfMe2(η6-p-xylene)][MeB(C6F5)3], ana-
lytically pure compounds could be obtained as yellow
solids by precipitation from CH2Cl2 with hexanes.
However, many of the new compounds could not be
obtained pure in this way but were instead character-
1
ized unambiguously by H and 13C{1H} NMR spectros-
An exception is the anisole complex [Cp*HfMe2(η6-
PhOMe)][MeB(C6F5)3], for which all of the 1H reso-
nances except the Cp* resonance broaden on warming.
We note, however, that the toluene of [Cp*ZrMe2(η6-
toluene)][MeB(C6F5)3] is readily displaced from the
metal by amines and phosphines,1b and we suggest that
the η6-anisole ligand is displaced also, to some extent,
from the highly oxophilic hafnium by the ether group
of free anisole. Other exceptions are the styrene
complexes [Cp*MMe2(η6-styrene)][MeB(C6F5)3], in the
copy (Tables 1 and 2). NMR spectra of experiments
involving the zirconium complex with hexamethyl-
benzene and the hafnium complex with chlorobenzene
at 223 K resulted in the appearance of no 1H resonances
attributable to new arene complexes. In the case of
zirconium, there appeared a number of new Cp* methyl
resonances and a resonance at δ ∼0.5 attributable to
free borate but no resonances attributable to coordi-
nated arene. In the case of hafnium, new Cp* and Hf-
Me singlet resonances appeared at δ 2.09 and 0.09,
respectively, as well as a broad singlet at δ ∼0.9 but
not at δ ∼0.5. The broad resonance at δ ∼0.9 is
reminiscent of the boron-broadened (µ-Me resonance of
Cp*TiMe2(µ-Me)B(C6F5)3, at δ ∼1.1,1 and it is possible
that the compound formed is Cp*HfMe2(µ-Me)B(C6F5)3.
The 1H NMR spectra of all the arene complexes
exhibit Cp* methyl resonances at δ ∼1.9-2.1 and
metal-methyl resonances at δ ∼0.1 (Ti), δ -0.1 to -0.2
(Zr), and δ -0.3 to -0.5 (Hf). The 13C{1H} NMR spectra
of the zirconium and hafnium complexes exhibit metal-
methyl, Cp* methyl, and Cp* ring resonances at δ 41-
54, ∼12, and ∼122, respectively, and thus the chemical
shifts vary little within these series of complexes,
lending confidence to the assignments where pure
compounds could not be obtained. In contrast, the
13C{1H} NMR spectrum of [Cp*TiMe2(η6-toluene)][MeB-
(C6F5)3] exhibits metal-methyl and Cp* ring resonances
at considerably lower field: δ 65.2 and 138.1, respec-
tively. However, this complex was 13C-enriched at the
Ti-Me site and thus, even though no 13C{1H} NMR
spectra of other (arene)titanium complexes were ob-
tained, the Ti-Me resonance of this compound is
assigned quite unambiguously.
1
presence of free styrene. The H NMR spectra of these
change quite drastically on warming to 273 K; atactic
polystyrene is formed, and many new Cp* peaks appear.
Interestingly, spin saturation transfer experiments at
223 K with mixtures of free arenes and [Cp*ZrMe2(η6-
arene)][MeB(C6F5)3] (arene ) benzene, toluene) suggest
that exchange between free and coordinated arenes is
not facile in these cases. Irradiation of the resonances
of the coordinated arenes had no effect on the intensities
of the resonances of the free arenes, and vice versa. Spin
saturation was also not observed with the toluene
compound on warming to 273 K but was observed with
the benzene compound, consistent with exchange in the
latter case. The lower reactivity of the toluene complex
is consistent with the stronger arene-metal bonding
anticipated on substitution of hydrogen by a more
electron-releasing methyl group.
As indicated above, the pattern of coordination shifts
of the aromatic hydrogen and carbon atoms in the
(15) Crowther, D. J .; J ordan, R. F.; Baenziger, N. C.; Verma, A.
Organometallics 1990, 9, 2574.
(16) While hexamethylbenzene would therefore be expected to
coordinate strongly, steric factors might well weaken arene-metal
interactions in the case of this potential ligand.

d0 Arene Complexes of Ti, Zr, and Hf
Organometallics, Vol. 15, No. 16, 1996 3605
styrene complexes [Cp*MMe2(η6-styrene)][MeB(C6F5)3]
(M ) Zr, Hf) implies a coordination mode similar to that
of the toluene complexes, i.e. an η6-arene rather than
an η2-olefin mode of bonding. While this result seems
surprising in view of the high activities exhibited by
these complexes, and their titanium analogue, as sty-
rene polymerization initiators,1 a detailed examination
of the vinyl hydrogen atom spin-spin coupling con-
stants supports the conclusion. A number of styrene
complexes of both types, η2- and η6-, are known, and
while the vinyl H-H coupling constants of (η6-styrene)-
were obtained by slow diffusion of hexanes into an
o-dichlorobenzene solution at 243 K over several weeks.
Figure 1 illustrates the structure of the complex cation,
and Figure 2 gives a packing diagram showing two pairs
each of both complex ions and two overlapped molecules
of solvent toluene (50% occupation each) about the
1
inversion center at 1/2, 0, /2. Crystal data, details of
the experimental measurements, and a summary of
refinement parameters are presented in Table 3 and
important bond lengths and angles in Table 4.
As anticipated, the [Cp*HfMe2(η6-toluene)]+ cation
and the [BMe(C6F5)3]- anion are well separated in the
crystal lattice, and the former forms a bent-sandwich
structure, analogous to the structures of [{η5-1,3-C5H3-
(SiMe3)2}HfMe2(η6-toluene)][MeB(C6F5)3]5 and Cp2-
HfMe2.18 The Hf-Me bond lengths of [Cp*HfMe2(η6-
toluene)]+ (2.219(9), 2.204(9) Å) are shorter than those
of [{η5-1,3-C5H3(SiMe3)2}HfMe2(η6-toluene)]+ (2.245(7),
2.244(7) Å at 120 K)5 and Cp2HfMe2 (2.318(8), 2.382(7)
Å),18 but the averages of the Hf-Cp* and Hf-toluene
bond lengths (2.483, 2.669 Å, respectively) are very
similar to those of [{η5-1,3-C5H3(SiMe3)2}HfMe2((η6-
toluene)]+ (2.487, 2.689 Å, respectively).5 The Me-Hf-
Me and Cp* ring centroid-Hf-toluene ring centroid
bond angles of [Cp*HfMe2(η6-toluene)]+ are 93.6(5) and
133.8(2)°, respectively, very similar to those of [{η5-1,3-
C5H3(SiMe3)2}HfMe2(η6-toluene)]+ (93.5(3), 134.2(2)°,5
respectively). The corresponding angles in Cp2HfMe2
are 94.8(3) and 132.1°, respectively.18
17a
Cr(CO)3 and [Cp*Ru(η6-styrene)]+ 17b are very similar
to those of free styrene, the vinyl H-H coupling
constants of [CpFe(CO)2(η2-styrene)]+ 17c and PtCl2(η2-
17d
styrene)2 are quite different, in accord with changes
in hybridization on coordination. In the case of the
complexes [Cp*MMe2(η6-styrene)][MeB(C6F5)3], the vi-
nyl H-H coupling constants are essentially identical
with those of free styrene, consistent only with the η6
mode of bonding.
Syn th esis of Ar en e Com p lexes of Tita n iu m . Ad-
dition of borane to a solution of Cp*TiMe3 in CD2Cl2 in
the presence of excess toluene results in disappearance
of the 1H resonances of Cp*TiMe3, weakening of the
peaks of the free arene, and the appearance of new
resonances attributable to the species [Cp*TiMe2(η6-
toluene)]+. The 1H NMR spectrum also exhibits a
resonance at δ ∼0.5, attributable to free borate, and the
Cp* and BMe resonances of the complex Cp*TiMe2(µ-
Me)B(C6F5)3.1 Thus, in contrast to the zirconium and
hafnium systems, described above, an equilibrium is
established between the neutral borate complex and the
cationic arene complex, formed to the extent of ∼30%
(eq 1). Similar results were obtained with mesitylene,
The packing diagram of [Cp*HfMe2(η6-toluene)][BMe-
(C6F5)3] (Figure 2) shows that there are two pairs of each
of the complex ions and two disordered molecules of
solvent toluene around the inversion center. The di-
hedral angle between the plane of the toluene solvent
molecule and the Cp* least-squares plane is 11(2)°,
while the Cp*-toluene stacking distance is 3.6(2) Å;
thus, the structure may be stabilized by π-π stacking19
in the solid state.
Cp*TiMe2(µ-Me)B(C6F5)3 + toluene a
[Cp*TiMe2(η6-toluene)]+ + [BMe(C6F5)3]- (1)
Ack n ow led gm en t. We are indebted to the Natural
Sciences and Engineering Research Council of Canada
for financial support of this research (Research, Col-
laborative Research and Development, and Strategic
Grants to M.C.B., Graduate Fellowship to D.J .G.), to
the Government of Ontario for a graduate fellowship
to D.J .G., and to DuPont Canada Inc. for both generous
financial support and for a leave of absence to D.J .G.
but no reaction was observed with benzene or p-xylene
at 213 K. Only the resonances of the free arene and
Cp*TiMe2(µ-Me)B(C6F5)3 were present. The lack of
coordination of benzene must reflect the lowered elec-
tron density on the ring of this ligand relative to the
case with toluene, and we note the spin-saturation
transfer experiments with [Cp*ZrMe2(η6-arene)][BMe-
(C6F5)3] (arene ) benzene, toluene), described above,
which showed that the (benzene)zirconium complex is
more labile than the toluene analogue. The reason for
the lack of reactivity with p-xylene is less clear; possibly
steric effects are important.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, bond lengths and angles, anisotropic displacement
parameters for non-H atoms, hydrogen atom positional and
thermal parameters, and least-squares planes data and a
diagram showing disorder of the solvent molecule of toluene
(14 pages). Ordering information is given on any current
masthead page.
Str u ctu r e of [Cp*HfMe2(η6-tolu en e)][BMe(C6F5)3].
Usable crystals of [Cp*HfMe2(η6-toluene)][BMe(C6F5)3]
(17) (a) Knox, G. R.; Leppard, D. G.; Pauson, P. L.; Watt, W. E. J .
Organomet. Chem. 1972, 34, 347. (b) Fagan, P. J .; Ward, M. D.;
Calabrese, J . C. J . Am. Chem. Soc. 1989, 111, 1689. (c) Laycock, D.
E.; Hartgerink, J .; Baird, M. C. J . Org. Chem. 1980, 45, 291. (d)
Albinati, A.; Caseri, W. R.; Pregosin, P. S. Organometallics 1987, 6,
788.
OM960174I
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