Zirconium and Hafnium Complexes that Contain the Electron-Withdrawing Diamido/Donor Ligands [(2,6-X2C6H3NCH 2)2C(2-C5H4N)(CH3)] 2- (X = Cl or F). An Evaluation of the Role of Ortho Halides in 1-Hexene Polymerization

Article abstract of DOI:10.1021/om0305364

The preparation of zirconium and hafnium complexes containing pyridyldiamine ligands, through Pd catalyzed coupling was discussed. Activation of dimethyl species in bromobenzene led to the formation of dimeric monocations, which are inactive for polymerization of 1-hexene. The results show that the introduction of ortho fluorides and chlorides decreases the rate of polymerization. The introduction also led to the formation of shorter polymer chains and β hydride elimination.

Full text of DOI:10.1021/om0305364

Organometallics 2003, 22, 5079-5091
5079
Zir con iu m a n d Ha fn iu m Com p lexes th a t Con ta in th e
Electr on -With d r a w in g Dia m id o/Don or Liga n d s
[(2,6-X2C6H3NCH2)2C(2-C5H4N)(CH3)]2- (X ) Cl or F ).
An Eva lu a tion of th e Role of Or th o Ha lid es in 1-Hexen e
P olym er iza tion
Richard R. Schrock,* J ennifer Adamchuk, Klaus Ruhland, and L. Pia H. Lopez
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,
Cambridge, Massachusetts 02139
Received J uly 11, 2003
The pyridyldiamines [(2,6-X2C6H3NHCH2)2C(CH3)(2-C5H4N)] (X ) Cl or F) can be prepared
in good yield through the Pd-catalyzed coupling between 2,6-dihalobromobenzene and (H2-
NCH2)2C(CH3)(2-C5H4N). Zirconium and hafnium complexes that contain these ligands were
prepared through traditional routes; they include [ArCl2Npy]M(NMe2)2 (M ) Zr or Hf), [ArCl2
-
Npy]MCl2, [ArCl2Npy]MMe2, [ArCl2Npy]Hf(i-Bu)2, [ArF2Npy]Hf(i-Bu)2, and [ArF2Npy]HfMe2.
Attempts to prepare [ArF2Npy]Hf(NMe2)2 in a reaction between Hf(NMe2)4 and free ligand
led to compounds in which one or two dimethylamino groups had been exchanged with one
or two ortho fluorides on the 2,6-difluorophenyl rings. Compounds whose structures were
determined in X-ray studies include [ArCl2Npy]Hf(i-Bu)2, [ArF2Npy]Hf(i-Bu)2, and [Ar(FNMe2)2
-
Npy]Hf(F)Cl, a compound that contains 2-fluoro-6-dimethylaminophenyl rings. In the first
compound one chloride is weakly bonded to the metal, in the second two fluorides are weakly
bonded to the metal, and in the third two dimethylamino groups are strongly bonded to the
metal. Activation of dimethyl species with [Ph3C][B(C6F5)4] in bromobenzene led initially to
the formation of dimeric monocations such as {[ArX2Npy]2M2Me3}[B(C6F5)4], which are
inactive for polymerization of 1-hexene. The {[ArX2Npy]2M2Me3}[B(C6F5)4] compounds react
further with [Ph3C][B(C6F5)4] to give {[ArX2Npy]MMe}[B(C6F5)4] species, which are active
for polymerization of 1-hexene. Activation of [ArX2Npy]Hf(i-Bu)2 complexes with [Ph3C]-
[B(C6F5)4] in bromobenzene led to the formation of {[ArX2Npy]Hf(i-Bu)}[B(C6F5)4] species
that are also active for the polymerization of 1-hexene. The rate of consumption of 1-hexene
followed a first-order dependence on 1-hexene (and hafnium), although the rates were
substantially slower compared to those for the known catalyst with mesityl substituents on
the amido nitrogens and slower when X ) F than when X ) Cl. The ease of preparation of
the cations also followed the order aryl ) mesityl > 2,6-Cl2C6H3 > 2,6-F2C6H3. Finally, the
quality of the polymerization, in terms of its living characteristics, deteriorated markedly
when the aryl was 2,6-F2C6H3. We conclude that the introduction of ortho chlorides or
fluorides decreases the rate of polymerization and also encourages â hydride elimination
and formation of shorter polymer chains, therefore compromising the living characteristics
of the polymerization.
In tr od u ction
diamido/donor ligands that can be activated to yield
cationic initiators for the living polymerization of ordi-
nary olefins.3,11-15 We have recently explored catalysts
Recent activity in the area of Ziegler-Natta catalysis
has centered on the development of well-behaved,
nonmetallocene systems for the polymerization of ordi-
nary R-olefins.1-12 Our attention recently has focused
on zirconium and hafnium dialkyl complexes containing
(7) Tshuva, E. Y.; Goldberg, I.; Kol, M. J . Am. Chem. Soc. 2000,
122, 10706.
(8) Tshuva, E. Y.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Chem.
Commun. 2001, 2120.
(9) Tshuva, E. Y.; Groysman, S.; Goldberg, I.; Kol, M.; Goldschmidt,
Z. Organometallics 2002, 21, 662.
(10) Baumann, R.; Schrock, R. R. J . Organomet. Chem. 1998, 557,
69.
(1) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int.
Ed. 2002, 41, 2236.
(2) J eon, Y.-M.; Park, S. J .; Heo, J .; Kim, K. Organometallics 1998,
17, 3161.
(11) Schrock, R. R.; Baumann, R.; Reid, S. M.; Goodman, J . T.;
Stumpf, R.; Davis, W. M. Organometallics 1999, 18, 3649.
(12) Goodman, J . T.; Schrock, R. R. Organometallics 2001, 20, 5205.
(13) Flores, M. A.; Manzoni, M.; Baumann, R.; Davis, W. M.;
Schrock, R. R. Organometallics 1999, 18, 3220.
(14) Schrock, R. R.; Casado, A. L.; Goodman, J . T.; Liang, L.-C.;
Bonitatebus, P. J ., J r.; Davis, W. M. Organometallics 2000, 19, 5325.
(15) Mehrkhodavandi, P.; Bonitatebus, P. J ., J r.; Schrock, R. R. J .
Am. Chem. Soc. 2000, 122, 7841.
(3) Mehrkhodavandi, P.; Schrock, R. R. J . Am. Chem. Soc. 2001,
123, 10746.
(4) Schrock, R. R.; Bonitatebus, P. J ., J r.; Schrodi, Y. Organometal-
lics 2001, 20, 1056.
(5) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996, 118,
10008.
(6) Tian, J .; Hustad, P. D.; Coates, G. W. J . Am. Chem. Soc. 2001,
123, 5134.
10.1021/om0305364 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/31/2003

5080 Organometallics, Vol. 22, No. 24, 2003
Schrock et al.
containing [(ArNCH2)2C(CH3)(2-C5H4N)]2- ([ArNpy]2-
;
see structure B below),3,15,16 which is an arylated version
of the trimethylsilyl-substituted ligand developed by
Gade.17 Cationic zirconium and hafnium complexes
formed from complexes of type B (Ar ) mesityl) are
relatively stable toward CH activation during the po-
lymerization of up to 600 equiv of 1-hexene at 0 °C in
bromobenzene or chlorobenzene.3,15 In contrast, cationic
zirconium complexes formed from complexes of type A
(Ar ) mesityl)4,18 are deactivated via aryl ortho-methyl
CH activation. Since we found that 2,6-Cl2C6H3 sub-
stituents were viable alternatives to mesityl groups in
catalysts derived from complexes of type A,4 we became
interested in the possibility of preparing catalysts of
type B that contain 2,6-X2C6H3 groups (X ) Cl or F).
We hoped to compare the catalytic activity of complexes
that contain 2,6-X2C6H3 aryl groups on the amido
nitrogens with those that contain 2,4,6-Me3C6H2 (mesi-
tyl) groups on the amido nitrogens. The results of this
study are reported here.
F igu r e 1. Thermal ellipsoid drawing of [ArCl2Npy]Hf(i-
Bu)2.
The X-ray structure of [ArCl2Npy]Hf(i-Bu)2 (Figure 1,
Table 1) features a distorted octahedral species in which
one ortho chloride (Cl(1)) interacts weakly with the
metal (Hf-Cl(1) ) 2.760(3) Å). (Selected bond distances
and angles can be found in Table 2.) The Hf-C and
Hf-N distances are not unusual for a complex of this
type, and the magnitudes of the Hf-C-C angles (125.7-
(9)° and 116.4(9)°) do not suggest any agostic interac-
tion21 between the â alkyl protons and the metal. It is
interesting to note that the Hf-N(2)-C(24) and Hf-
N(3)-C(18) angles are essentially identical (131.0(7)°
and 128.9(7)°, respectively). Therefore the interaction
between Cl(1) and the metal must take place simply by
rotation of the aryl ring into the Hf-N(2)-C(24) plane.
The Hf-Cl interaction apparently is not strong enough
to permit the formation of a sterically congested seven-
coordinate complex with two coordinating aryl ortho
chlorides.
Resu lts
P r ep a r a t ion of [(2,6-Cl2C6H 3NCH 2)2C(CH 3)(2-
C5H4N)]2- ([Ar Cl2Np y]2-) Com p lexes. The palladium-
catalyzed coupling reaction19,20 between 2,6-dichloro-
bromobenzene and (H2NCH2)2C(CH3)(2-C5H4N) produces
H2[ArCl2Npy] in good yield (65%, eq 1). Impurities
arising from what is believed to be competitive coupling
at the 2 and 6 positions of 2,6-dichlorobromobenzene
Room-temperature NMR spectra of [ArCl2Npy]Hf-
(i-Bu)2 feature separate resonances for axial and equa-
torial alkyl groups and mirror symmetry consistent with
a TBP structure rather than an octahedral structure.
Therefore the Hf-Cl interaction does not persist in
solution at room temperature. 1H-NOESY experiments
exhibited a cross-peak between the equatorial bound
alkyl methylene and the pyridyl ortho proton (Ho),
showing that the methylene resonance for the equatorial
alkyl group is found at lower field than the methylene
resonance for the axial alkyl group. In the zirconium
(5%) cannot be eliminated, however, and impure H2[ArCl2
-
Npy] must be employed to prepare zirconium and
hafnium complexes. As shown in eq 2, [ArCl2Npy]MCl2
is synthesized via a method analogous to that employed
to prepare zirconium and hafnium complexes bearing
[MesNpy]2- ligands.3,15,16 Alkylation of the [ArCl2Npy]-
MCl2 complexes with Grignard reagents proceeds
smoothly to yield [ArCl2Npy]MR2 complexes, where M
) Zr and R ) Me, or M ) Hf and R ) Me or i-Bu. [ArCl2
-
Npy]Zr(i-Bu)2 is unstable at room temperature and
therefore could not be isolated. Impurities formed as a
consequence of competitive coupling in the ligand
synthesis are removed by recrystallization of either the
[ArCl2Npy]M(NMe2)2 or [ArCl2Npy]MR2 complexes.
1
dimethyl species, the H NMR methyl resonances ap-
pear as two broadened singlets, characteristic of ex-
change of axial and equatorial methyl groups on the
NMR time scale. Upon mixing [ArCl2Npy]Hf 13Me2 and
[ArCl2Npy]ZrMe2 in benzene at 22 °C, the methyl groups
scrambled between the two metals within seconds.
Therefore we believe that the broad methyl resonances
can be ascribed to rapid intermolecular exchange.16 In
contrast, the i-Bu resonances are sharp because inter-
molecular exchange is relatively slow on the NMR time
scale due to steric constraints.
A second dynamic process that can be observed in
these compounds is restricted rotation of the aryl
(16) Mehrkhodavandi, P.; Schrock, R. R.; Bonitatebus, P. J . J .
Organometallics 2002, 21, 5785.
(17) Gade, L. H.; Mountford, P. Coord. Chem. Rev. 2001, 216, 65.
(18) Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M.
Organometallics 1999, 18, 428.
(19) Wolfe, J . P.; Wagaw, S.; Marcoux, J .-F.; Buchwald, S. L. Acc.
Chem. Res. 1998, 31, 805.
(20) Hartwig, J . F. Angew. Chem., Int. Ed. 1998, 37, 2046.
(21) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem.
1988, 36, 1.

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5081
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for [Ar Cl2Np y]Hf(i-Bu )2, [Ar (F NMe2)2Np y]Hf(F )Cl, a n d
[Ar F 2Np y]Hf(i-Bu )2
[ArCl2Npy]Hf(i-Bu)
[Ar(FNMe2)2Npy]Hf(F)Cl
[ArF2Npy]Hf(i-Bu)2
empirical formula
fw
C
29H35Cl4HfN
C25H29ClF3HfN5
670.47
C29H35F4HfN3
680.09
745.92
temperature (K
cryst syst, space group
unit cell dimens
293(2)
293(2)
273(2)
monoclinic, P2(1)/n
a ) 15.562(3) Å
b ) 12.314(3) Å
c ) 16.897(5) Å
R ) 90°
â ) 109.925(15)°
γ ) 90°
3044.0(13)
monoclinic, P2(1)
a ) 8.4334(14) Å
b ) 17.106(3) Å
c ) 9.2935(16) Å
R ) 90°
â ) 111.336(3)°
γ ) 90°
1248.8(4)
monoclinic, C2/c
a ) 15.2329(9) Å
b ) 12.1484(7) Å
c ) 29.4719(17) Å
R ) 90°
â ) 96.2770(10)°
γ ) 90°
5421.2(5)
volume (Å3)
Z, calcd density (Mg/m3)
4, 1.628
3.801
2, 1.78
4.330
8, 1.667
3.899
abs coeff (mm-1
)
F(000)
148
660
2704
θ range for data collection (deg)
2.19 to 23.34
-17 e h e 11, -10 e k e 6,
-12 e l e 18
5603
3585 [R(int) ) 0.0431]
81.2%
2.35 to 20.98
-8 e h e 8, -14 e k e 17,
-9 e l e 9
2.48 to 28.31
-18 e h e 18, -16 e k e 7,
-39 e l e 37
14 787
6180 [R(int) ) 0.0735]
91.8%
limiting indices
no. of reflns collected/unique
no. of indep reflns
completeness to θ max
no. of data/restraints/params
goodness-of-fit on F2
4017
1398 [R(int) ) 0.0536]
99.8%
1398/0/178
1.263
3585/0/33
1.056
6180/0/340
1.020
final R indices [I>2σ(I)]
R1 ) 0.0645, wR2 ) 0.150
R1 ) 0.0770, wR2 ) 0.159
2.149 and -3.583
R1 ) 0.0540, wR2 ) 0.1152
R1 ) 0.0574, wR2 ) 0.1166
1.533 and -2.586
R1 ) 0.0367, wR2 ) 0.0898
R1 ) 0.0498, wR2 ) 0.0945
2.496 and -1.215
R indices (all data)
largest diff peak and hole (e Å-3
)
a
In each case the wavelength was 0.71073 Å and the refinement method was full-matrix least-squares on F2. No absorption correction
was applied.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) in [Ar Cl2Np y]Hf(i-Bu )2
H2[ArF2Npy] reacted readily with Hf(NMe2)4; how-
ever, the primary product was [ArF2;FNMe2Npy]HfF-
(NMe2) (3, Scheme 1), with [ArF2Npy]Hf(NMe2)2 (1,
Scheme 1) formed only in trace quantities (e5%). In 3
one of the four ortho fluorides has been replaced by a
dimethylamido group, and the fluoride transferred to
Hf-N(1)
2.416(9)
2.112(9)
2.048(8
2.261(11)
2.222(12)
2.760(3
75.2(3)
83.2(4
86.7(4)
170.4(4)
79.8(2
99.1(3)
N(2)-Hf-C(5)
N(2)-Hf-Cl(1)
N(3)-Hf-C(1)
N(3)-Hf-C(5
N(3)-Hf-Cl(1)
C(1)-Hf-Cl(1)
C(1)-Hf-C(5
C(5)-Hf-Cl(1)
C(24)-N(2)-Hf
C(18)-N(3)-Hf
C(6)-C(5)-Hf
C(2)-C(1)-H
97.4(4)
70.2(3)
106.6(4)
104.2(4)
161.8(3)
79.1(3)
96.8(5)
92.0(3)
131.0(7)
128.9(7)
125.7(9)
116.4(9)
Hf-N(2)
Hf-N(3
Hf-C(1)
Hf-C(5
1
the metal. The H NMR and 19F NMR spectra at 22 °C
Hf-Cl(1
N(1)-Hf-N(2)
N(1)-Hf-N(3)
N(1)-Hf-C(1)
N(1)-Hf-C(5
N(1)-Hf-Cl(1)
N(2)-Hf-N(3)
N(2)-Hf-C(1)
are indicative of an asymmetric complex with the aryl
NMe2 moiety coordinating strongly to the metal and the
2,6-difluoro aryl ring rotating freely. Two separate
singlets, each representing three hydrogens, are ob-
served for the donor NMe2 group, while a singlet
representing six hydrogens is observed for the covalently
bound NMe2 ligand. This type of exchange of a dim-
ethylamido group for an ortho aryl fluoride has been
documented in a related molybdenum system.22
The 19F NMR spectrum of 3 consists of three reso-
nances representing a total of four fluorides. Two
resonances at -128.6 and -122.0 ppm show fine
structure as a consequence of coupling with aryl hydro-
gens (J FH ) 6 Hz). The resonance at -122.0 ppm
(representing two fluorides) is further split into a
doublet by the fluoride covalently bound to the metal
(J FF ) 32.9 Hz). Conversely, the Hf-F resonance
appears as a triplet (J FF ) 32.9 Hz) at 28.5 ppm, which
is in the expected range for a metal-bound fluoride.23-27
Observation of only one doublet for the two fluorides in
the 2,6-F2C6H3 ring confirms that the 2,6-F2C6H3 ring
146.5(4)
groups, as indicated by the inequivalence of the meta
protons in the 2,6-dichlorophenyl ring. The barrier
toward aryl ring rotation is slightly larger in [ArCl2Npy]-
Hf(i-Bu)2 than in [ArCl2Npy]HfMe2; that is, the barrier
is higher in the more crowded complexes. The coales-
cence temperatures (at 400 mHz), respectively, are -67
and -90 °C, with activation energies at the coalescence
temperature of ∼40 and ∼35 kJ mol-1, respectively. A
higher barrier toward ring rotation in more crowded
circumstances would be expected as a consequence of a
straightforward steric effect.
P r ep a r a tion of [(2,6-F 2C6H3NCH2)2C(CH3)(2-
C5H4N)]2- ([Ar F 2Np y]2-) Com p lexes. The coupling
reaction between 1-bromo-2,6-difluorobenzene and (H2-
NCH2)2C(Me)(2-py) proceeded at a much slower rate
than the coupling reaction to give H2[ArCl2Npy], afford-
ing H2[ArF2Npy] in only 37% yield. In contrast to the
24 h reaction time required to prepare H2[ArCl2Npy],
temperatures up to 120 °C for 4 to 5 days still failed to
convert all of the monoarylated intermediate to the
desired H2[ArF2Npy]. Ultimately H2[ArF2Npy] was ob-
tained free from impurities by column chromatography,
in contrast to H2[ArCl2Npy], which could not be sepa-
rated from impurities in this manner.
(22) Cochran, F. V.; Bonitatebus, P. J ., J r.; Schrock, R. R. Organo-
metallics 2000, 19, 2414.
(23) Shah, S. A. A.; Dorn, H.; Voigt, A.; Roesky, H. W.; Paraisini,
E.; Schmidt, H.-G.; Noltemeyer, M. Organometallics 1996, 15, 3176.
(24) Turculet, L.; Tilley, T. D. Organometallics 2002, 21, 3961.
(25) Edelbach, B. L.; Rahman, A. K. F.; Lachicotte, R. J .; J ones, W.
D. Organometallics 1999, 18, 3170.
(26) Kraft, B. M.; Lachicotte, R. J .; J ones, W. D. J . Am. Chem. Soc.
2000, 122, 8559.
(27) Murphy, E. F.; Murugavel, M. R.; Roesky, H. W. Chem. Rev.
1997, 97, 3425.

5082 Organometallics, Vol. 22, No. 24, 2003
Sch em e 1. Rea ction s Lea d in g to P r od u cts 1-7
Schrock et al.
rotates freely on the NMR time scale, as noted in proton
NMR spectra.
a typical reaction, several products remained in solution
in addition to 7. One was [ArF2Npy]HfCl2 (2), the
presence of which confirmed that [ArF2Npy]Hf(NMe2)2
was present in the sample of crude 3. Another compound
The presence of [ArF2Npy]Hf(NMe2)2 (1) as a product
of the reaction between Hf(NMe2)4 and H2[ArF2Npy] was
overlooked initially. Compound 1 can be identified by a
pyridyl Ho resonance at 8.42 ppm. (The Ho resonance
in free ligand is found at 8.35 ppm.) [ArF2Npy]Hf(NMe2)2
is more soluble in both ether and pentane than 3, and
therefore is removed easily upon recrystallization of the
crude product from ether, and identified more easily in
the residue obtained from the mother liquor. The 19F
NMR spectrum of 1 gives rise to one singlet at -125.1
ppm with fine structure (J FH ) 6.8 Hz) characteristic
of aryl fluorides in a mirror symmetric species with two
2,6-F2C6H3 rings that rotate freely on the NMR time
scale at 22 °C. Subsequent reaction of the crude product
that was identified in the toluene solution was [Ar(FNMe2)2
-
Npy]Hf(F)Cl (6), a species with mirror symmetry in
which a second ortho fluoride has been exchanged with
an amido group to give a compound in which two aryl
NMe2 groups are coordinating to hafnium. Compound
6 could be derived directly from 4 as a result of
dimethylamido/fluoride exchange.
Recrystallization of a sample of 7 from ether led to a
product that we initially assumed to be a purer sample
of 7. Three successive recrystallizations were required
to obtain X-ray quality yellow-orange, single crystals.
In fact the recrystallization process had succeeded in
concentrating and purifying the least soluble component
of the crude reaction, which turned out to be 6 (Scheme
1). The 19F NMR spectrum of 6 contains a resonance at
-127.5 ppm for two equivalent ortho aryl fluorides (J FH
) 6.3 Hz) and a resonance at 45.8 ppm for a single
fluoride on the metal (J FH ) 6.3 Hz).
with Me3SiCl led to formation of small amounts of [ArF2
-
Npy]HfCl2 (2). NMR spectra of 2 are also consistent with
the presence of a plane of symmetry on the NMR time
scale and freely rotating aryl rings.
The reaction of pure 3 with excess Me3SiCl afforded
[ArF2;FNMe2Npy]HfCl2 (7, Scheme 1) in good yield; that
is, both the Hf-F and Hf-NMe2 groups are replaced
by chlorides upon reaction with excess Me3SiCl. Addi-
tion of 1 equiv of Me3SiCl to 3 yields [ArF2;FNMe2Npy]-
HfCl(NMe2) (4) according to NMR experiments. This
result suggests that 4 is a more likely intermediate than
[ArF2;FNMe2Npy]Hf(F)Cl (5); that is, the fluoride bound
to hafnium is replaced more readily than the dimethy-
lamido group. The 19F spectrum of 7 contained a
resonance for two fluorides at -120.9 ppm and a
resonance for one fluoride at -129.7 ppm. No resonance
was observed downfield characteristic of a fluoride on
the metal. Compound 7 is relatively insoluble in toluene
and therefore could be isolated cleanly by filtration. In
The X-ray structure of [Ar(FNMe2)2Npy]Hf(F)Cl (6) is
shown in Figure 2. (See also Tables 1 and 3.) In this
seven-coordinate species the aryl NMe2 donors are
coordinated to the metal at a distance of 2.459(11) Å,
while the pyridine donor is bound at a distance of 2.355-
(14) Å. The Hf-Ndonor bond length (2.459(11) Å) is
significantly longer than the covalent Hf-N bond
lengths (2.136(10) Å). Also notable is the Hf-N(2)-C(8)
bond angle of 119.6(7)°, which is smaller than in [ArCl2
-
Npy]Hf(i-Bu)2 as a consequence of strong coordination
of the o-NMe2 group. In a closely related molybdenum
difluoride complex in which the substituents on the
amido nitrogens are o-dimethylamidotetrafluorophenyls

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5083
F igu r e 2. Thermal ellipsoid drawing of [Ar(FNMe2)2Npy]-
Hf(F)Cl (6).
Ta ble 3. Bon d Len gth s (Å) a n d An gles (d eg) for
[Ar (F NMe2)2Np y]Hf(F )Cl.
F igu r e 3. Thermal ellipsoid drawing of [ArF2Npy]Hf(i-
Bu)2.
Hf-F(1)
1.989(9
2.440(4)
2.355(14) Hf-N(2)-C(8)
108.0(4)
79.8(5)
132.1(3)
72.8(3)
Hf-N(2)
Hf-N(3)
2.136(10)
2.459(11)
119.6(7)
81.5(3)
79.9(3)
101.2(3)
154.0(4)
85.5(5)
Ta ble 4. Bon d Len gth s (Å) a n d An gles (d eg) for
[Ar F 2Np y]Hf(i-Bu )2.
Hf-Cl(1
Hf-N(1)
F(1)-Hf-Cl(1)
F(1)-Hf-N(1)
F(1)-Hf-N(2)
F(1)-Hf-N(3)
Cl(1)-Hf-N(3)
N(1)-Hf-N(2)
N(1)-Hf-N(3)
N(2)-Hf-N(3)
N(2)-Hf-N(2A)
Hf-N(2
2.103(3)
2.117(4)
2.261(5)
2.277(4)
2.442(4)
N(1)-Hf-F(3)
N(1)-Hf-N(2)
F(1)-Hf-C(5)
F(1)-Hf-C(1)
F(1)-Hf-F(3)
F(1)-Hf-N(2)
C(5)-Hf-C(1)
C(5)-Hf-F(3)
C(5)-Hf-N(2)
C(1)-Hf-N(2)
C(1)-Hf-F(3)
N(2)-Hf-F(3)
C(18)-N(1)-Hf
C(24)-N(2)-Hf
C(2)-C(1)-Hf
C(6)-C(5)-Hf
162.34(13)
96.38(14)
67.16(13)
78.37(15)
130.41(9)
161.59(12)
99.06(16)
71.33(14)
129.16(15)
104.23(16)
82.65(16)
67.76(13)
125.2(3)
Hf-N(1
Hf-C(1)
Hf-C(5
Cl(1)-Hf-N(1) 172.2(4)
Cl(1)-Hf-N(2) 94.4(3)
Hf-N(3)
N(3)-Hf-N(3A) 134.3(5)
Hf-F(3
2.443(3)
2.674(3)
Hf-F(1)
N(3)-Hf-N(1)
N(3)-Hf-F(1)
N(3)-Hf-C(5)
N(3)-Hf-C(1)
N(3)-Hf-F(3)
N(3)-Hf-N(2)
N(1)-Hf-F(1)
N(1)-Hf-C(5)
76.36(13)
96.09(11)
85.48(14)
170.66(15)
106.59(12)
78.67(13)
65.22(11)
126.28(15)
(Ar′ in [(Ar′NCH2CH2)2NMe]HfF2)22 the NMe2 donors
are coordinated to the metal at distances of 2.482(5) and
2.440(5) Å, the amine donor is bound at a distance of
2.330(5) Å, and the covalent Mo-N bond lengths are
2.008(5) and 2.013(5) Å. The M-F bond lengths in the
two compounds are 1.989(9) Å (Hf) and 1.968(3) Å (Mo).
The reaction between 7 and 2.1 equiv of i-BuMgCl
resulted in formation of [ArF2;FNMe2Npy]HfCl(i-Bu). As
expected, no metal-bound fluoride could be found in the
19F NMR spectrum. Further substitution of the chloride
to give [ArF2;FNMe2Npy]Hf(i-Bu)2 did not occur, most
likely because [ArF2;FNMe2Npy]HfCl(i-Bu) is much more
crowded than 7 and the metal is not as electrophilic.
However, 7 reacted with 2 equiv of MeMgBr in 1 h at
room temperature to give [ArF2;FNMe2Npy]HfMe2 accord-
ing to NMR spectra. Activation of [ArF2;FNMe2Npy]HfMe2
with [Ph3C][B(C6F5)4] yielded a monomethyl cationic
species that did not react readily with 1-hexene under
the conditions used in similar experiments described
later.
Because Hf(NMe2)4 could not be employed in the
synthesis of [ArF2Npy]HfR2 complexes, the synthesis of
[ArF2Npy]Hf(i-Bu)2 was attempted “directly” from HfCl4
by forming a complex between HfCl4 and the ligand
prior to the addition of 4.1 equiv of i-BuMgCl. After
several experiments in ether and toluene, we found that
dichloromethane was a suitable solvent for forming the
initial adduct. In order for the reaction to succeed,
complete dissolution of HfCl4 in the presence of ligand
is essential. After 36 h, the solvent was removed in
vacuo to afford the adduct between H2[ArF2Npy] and
HfCl4 as a yellow powder. Isobutylmagnesium chloride
(4.1 equiv) was then added to a suspension of this
adduct in ether that had been cooled to -30 °C. After
filtering the mixture through Celite, the ether-soluble
portion was concentrated in vacuo and the product
124.8(3)
129.3(4)
120.4(3)
recrystallized from a mixture of ether and pentane (1:
4) to give [ArF2Npy]Hf(i-Bu)2 in 52% yield. When
equivalent amounts of H2[ArF2Npy] and HfCl4 were
used, free ligand (<5%) was present as an impurity and
could not be removed easily. When a slight excess of
HfCl4 was employed, however, clean [ArF2Npy]Hf(i-Bu)2
was obtained without successive recrystallization. Al-
though this is not a high-yield route to [ArF2Npy]Hf-
(i-Bu)2, it is the only one available thus far.
The X-ray structure of [ArF2Npy]Hf(i-Bu)2 is shown
in Figure 3. (See also Table 1 for crystal and structure
refinement data and Table 4 for selected bond lengths
and angles.) Two ortho fluorides in the 2,6-difluorophe-
nyl rings are interacting weakly with the metal at
distances of 2.443(3) and 2.674(3) Å to form a sterically
congested seven-coordinate complex. The pyridine donor
is bound at a distance of 2.442(4) Å, and the covalent
Hf-N bond lengths are 2.103(3) and 2.117(4) Å, which
are similar to those found in the analogous compound
that contains 2,6-dichlorophenyl substituents. The Hf-
N(2)-C(24) and Hf-N(3)-C(18) angles are smaller than
those in [ArCl2Npy]Hf(i-Bu)2 (124.8° and 125.2°, respec-
tively, compared to 131.0° and 128.9°, respectively), but
larger than those in 6 (119.6°). We propose that two
fluorides are interacting in this complex (versus only
one chloride in [ArCl2Npy]Hf(i-Bu)2) as a consequence
of the more electron-poor nature of the metal and the
smaller size of a fluoride versus a chloride.

5084 Organometallics, Vol. 22, No. 24, 2003
Schrock et al.
The synthesis of [ArF2Npy]HfMe2 was also successful
through the direct route. The initial yield was much
higher (89%); however, the reaction was not as clean
as in the case of [ArF2Npy]Hf(i-Bu)2, with an unidentifi-
able impurity being formed (∼10%). This impurity could
be removed through recrystallization, leading to pure
[ArF2Npy]HfMe2 in a yield of 43%.
Attempts to prepare [ArCl2Npy]Hf(i-Bu)2 in a similar
direct manner failed. Only trace amounts of [ArCl2Npy]-
Hf(i-Bu)2 were observed. The synthesis of [ArCl2Npy]-
HfMe2 in this manner was more promising, although
clean [ArCl2Npy]HfMe2 could be obtained in a yield of
only about 10%.
Activa tion
of [(2,6-Cl2C6H3NCH2)2C(CH3)(2-
Figu r e 4. Decomposition of {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4}
(formed by trityl activation of [ArCl2Npy]Hf(i-Bu)2) at 0 °C
by following the disappearance of the isobutyl methyl
C5H4N)]2- ([Ar Cl2Np y]2-) Com p lexes. Addition of
[Ph3C][B(C6F5)4] to the [ArCl2Npy]MMe2 complexes (M
) Zr or Hf) resulted in formation of dimeric monoca-
tions, {[ArCl2Npy]2M2Me3}+; that is, {[ArCl2Npy]MMe}+
is formed and captured rapidly by [ArCl2Npy]HfMe2, as
shown in eq 3. Therefore only 0.5 equiv of [Ph3C]-
1
resonances in the H NMR spectrum.
{[ArCl2Npy]MMe}+ and the (unobservable) dimethyl
species [ArCl2Npy]MMe2. Trityl then reacts with the
dimethyl species in competition with recombination of
[ArCl2Npy]MMe2 with {[ArCl2Npy]MMe}+; we do not
believe that [Ph3C][B(C6F5)4] reacts with the dimeric
monocation itself. In contrast, in the mesityl system
{[MesNpy]2Zr2Me3}+ dissociates into {[MesNpy]ZrMe}+
and [MesNpy]ZrMe2 significantly more slowly,28 and
therefore pure {[MesNpy]ZrMe}[B(C6F5)4] species could
not be prepared. We propose that the ortho chlorides
assist in breaking up the {[ArCl2Npy]2M2Me3}+ cation
by coordinating weakly to the metal and perhaps also
[B(C6F5)4] is consumed. Proton and carbon NMR spectra
of this hafnium species show a broad resonance for the
methyl group at ∼1.3 ppm in the proton NMR spectrum
and ∼42.9 ppm in the carbon NMR spectrum. In the
zirconium species these resonances are found at 1.13
and 44.64 ppm (1J CH ) 109.5 Hz), respectively, and are
not as broad as in the hafnium case. Variable-temper-
ature 13C NMR studies of the hafnium species showed
that the broad methyl resonance splits into two at 52.2
(3 protons) and 38.0 (6 protons) at -60 °C, consistent
with two types of methyl groups being present in the
dimer. These observations are similar to those made for
{[ArNpy]2Zr2Me3}+ (Ar ) mesityl or 2,4,6-i-Pr3C6H2)
species.28 A dimeric monocation of this general type,
but with the [(MesNCH2CH2)2NMe]2- ligand, was shown
in an X-ray study to contain one bridging methyl
group.14 In the analogous {[MesNpy]2M2Me3}+ species,
it was proposed that three bridging methyl groups are
present in the ratio of 2:1 by virtue of the mirror plane
of symmetry. The same is proposed to be the case in
{[ArCl2Npy]2M2Me3}+, as shown in eq 3. The mechanism
by which the three methyl groups average intramolecu-
larly is not known. We cannot discount the possibility
that the pyridyl donor dissociates from the metal at one
or both metal centers, thereby leading to a five-
coordinate metal center that can rearrange by a pseu-
dorotation or turnstile mechanism.
by stabilizing {[ArCl2Npy]MMe}+, thereby making [ArCl2
-
Npy]MMe2 available in a high enough concentration to
react with [Ph3C][B(C6F5)4] at a practical rate. The
methyl resonances in the {[ArCl2Npy]MMe}+ species are
found in the proton NMR spectra at 0.88 ppm (Zr) and
0.63 ppm (Hf) in bromobenzene at room temperature,
while the carbon resonances in the 13C-labeled com-
pounds are found at 60.32 ppm (J CH ) 115 Hz) in the
hafnium complex. It is clear on the basis of proton NMR
spectra that these cations are not formed quantitatively
and/or that they decompose slowly at 22 °C in bro-
mobenzene over a period of hours. The decomposition
products have not been identified.
Addition of 1.0 equiv of [Ph3C][B(C6F5)4] to [ArCl2Npy]-
Hf(i-Bu)2 in bromobenzene yielded {[ArCl2Npy]Hf(i-Bu)}-
{B(C6F5)4}, triphenylmethane, and isobutene quantita-
tively in seconds (eq 4). The decomposition of {[ArCl2Npy]-
The {[ArCl2Npy]2M2Me3}+ cations are slowly con-
verted into monomeric monocations in the presence of
[Ph3C][B(C6F5)4]. In the zirconium system the conver-
sion requires a few minutes at 20 °C at the concentra-
tions employed (12-17 mM), while more than 2 h is
required in the hafnium system under similar condi-
tions. We propose that the dimeric monocation dissoci-
ates to a small extent to give the monomethyl cation
Hf(i-Bu)}{B(C6F5)4} at 0 °C has been monitored by
observing the disappearance of the isobutyl methyl
resonance (0.77 ppm) in the proton NMR spectrum
compared to the Ph3CH standard as a function of time
for varying concentrations of catalyst (Figure 4). In the
0.0075 M sample (and in many other similar runs) the
catalyst initially displayed first-order decomposition
with a kdecomp ≈ 0.0005 min-1. The rate of decomposition
then accelerated to a rate approximately 6 times faster
(28) Mehrkhodavandi, P.; Pryor, L. L.; Schrock, R. R. Organome-
tallics 2003, 22, 4569.
than that for {[MesNpy]Hf(i-Bu)}{B(C6F5)4} (kdecomp
≈

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5085
0.003 min-1 for Ar ) ArCl2, kdecomp ≈ 0.00055 min-1 for
Ar ) Mes28) before decreasing again after 2 h to a value
roughly comparable to the initial value. We have not
been able to determine the origin of this strange
behavior, although it appears to be linked in some way
to the polymerization of any isobutene that is present
and possibly also to the presence of traces of [Ph3C]-
[B(C6F5)4]. Isobutene is polymerized in the presence of
traces of Ph3C+, not by the cationic hafnium complex
itself, as found in the parent system that contains the
mesityl-substituted ligand.28 Purification of the reac-
tants through recrystallization did not alter the results.
Similar observations have been made for the decompo-
sition of {[MesNpy]Hf(i-Bu)}{B(C6F5)4} at 22 °C, al-
though at 0 °C the decomposition followed first-order
kinetics.28
Ta ble 5. Kin etic Da ta for P olym er iza tion of
1-Hexen e by {[Ar Cl2Np y]Hf(i-Bu )}{B(C6F 5)4} a n d
{[Ar F 2Np y]Hf(i-Bu )}{B(C6F 5)4}
equiv
initiator temp (°C) [Hf] (M) 1-hexene
kp (M-1 s-1
0.12, 0.15
0.080
0.088
0.032
0.049, 0.050, 0.052
0.047, 0.056, 0.039
0.055
0.023
0.018
0.028
0.016
)
ArCl2
ArCl2
ArCl2
ArCl2
ArCl2
ArCl2
ArCl2
ArCl2
ArCl2
ArF2
ArF2
ArF2
ArF2
20
10
10
0
0
0
0.012
0.012
0.006
0.015
0.012
0.012
0.012
0.015
0.015
0.012
0.012
0.012
0.012
100
100
100
50
100
300
400
50
0
-5
-10
20
10
0
50
100
100
50
0.0007
0.0007
0
100
Activa tion
of
[(2,6-F 2C6H3NCH2)2C(CH3)(2-
catalyst concentration of 15 mM, or kp ) 0.027 M-1 s-1
.
C5H4N)]2- ([Ar F2Np y]2-) Com p lexes. [ArF2Npy]HfMe2
may be activated with trityl to yield {[ArF2Npy]HfMe}-
{B(C6F5)4} (∼70% pure) and Ph3CCH3. The dissociation
of the {[ArX2Npy]2M2Me3}+ dimer required only 15 min
at room temperature when X ) F compared to 2.5 h
when X ) Cl. This lends further evidence that the
halides assist in breaking up the dimer by coordinating
to hafnium, with X ) F being more efficient than X )
Cl.
A second run produced a value of kp ) 0.031 M-1 s-1. If
the initiator is prepared at 30 °C, only 45 min is
required in order to produce a maximum yield. In a
polymerization with the initiator prepared in this man-
ner, kp ) 0.034 M-1 s-1. These values for kp are ∼60%
of those obtained with the analogous isobutyl initiator
(see below), suggesting that ∼40% of the metal that is
present is not available to polymerize 1-hexene. The
problem is that although {[ArCl2Npy]2Hf2Me3}{B(C6F5)4}
Activation of [ArF2Npy]Hf(i-Bu)2 with [Ph3C][B(C6F5)4]
at 0 °C in bromobenzene-d5 did not produce {[ArF2Npy]-
Hf(i-Bu)}{B(C6F5)4} as cleanly as {[ArCl2Npy]Hf(i-Bu)}-
{B(C6F5)4}. Several very small resonances for impurities
were observed, none of them amounting to more than
8% of the initial dialkyl; however, in combination they
comprised nearly 20% of the monocationic initiator.
Decomposition of {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4} is also
more rapid than the decomposition of {[ArCl2Npy]Hf(i-
Bu)}{B(C6F5)4}, a trend that was most apparent at room
temperature. After 20 min at room temperature, nearly
65% of the initial {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4} de-
composed, whereas only ∼20% of the initial {[ArCl2Npy]-
Hf(i-Bu)}{B(C6F5)4} decomposed. At 0 °C approximately
38% of {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4} decomposed in
loses [ArCl2Npy]HfMe2 slowly and therefore {[ArCl2
Npy]2Hf2Me3}{B(C6F5)4} can be converted into {[ArCl2
Npy]HfMe}{B(C6F5)4}, {[ArCl2Npy]HfMe}{B(C6F5)4} be-
gins to decompose slowly to unknown products before
{[ArCl2Npy]2Hf2Me3}{B(C6F5)4} is completely consumed.
-
-
As reported previously, addition of 1.0 equiv of trityl
to [ArCl2Npy]Hf(i-Bu)2 at -40 °C followed by warming
to 0 °C afforded {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4}, triph-
enylmethane, and isobutene. Addition of 1-hexene then
led to a smooth consumption of 1-hexene at 0 °C at a
rate that was first order in 1-hexene and first order in
hafnium. The polymerization of 1-hexene was followed
until consumption of 1-hexene was essentially complete
(>98%), and kp values were obtained from plots of ln-
([1-hexene]/[standard]) versus time. At 0 °C (see Table
5), the average kp value was 0.049 M-1 s-1, demonstrat-
ing that the {[ArCl2Npy]Hf(CH2R)}{B(C6F5)4} catalyst
system polymerizes 1-hexene at half the rate of the
{[MesNpy]Hf(CH2R)}{B(C6F5)4} system, for which kp
was found to be 0.10 M-1 s-1 at 0 °C.28 Plots of ln[1-
hexene] versus time at 10 and 20 °C also were linear
(Figure 5). An Eyring plot of the rate constants between
0 and 20 °C gave ∆Hq ) 7.23 kcal/mol and ∆Sq ) -37.9
cal/mol K (at [Hf] ) 1 M). This should be compared with
polymerization of 1-hexene by {[MesNpy]Hf(i-Bu)}-
[B(C6F5)4] in C6D5Br, where ∆Hq ) 10.82 kcal and ∆Sq
) -23.0 cal mol-1 K-1 (at [Hf] ) 1 M).
270 min, which is about 1.5 times faster than {[ArCl2
-
Npy]Hf(i-Bu)}{B(C6F5)4} in the same time. For com-
parison, after 270 min at 0 °C only ∼5% of the
{[MesNpy]Hf(i-Bu)}{B(C6F5)4} initiator had decom-
posed. It is clear that the stabilities of the {[ArNpy]Hf-
(i-Bu)}{B(C6F5)4} species follow the order Ar ) mesityl
> ArCl2 > ArF2, even though the decompositions are not
smooth and the rates are not reproducible.
P olym er iza tion of 1-Hexen e by [Ar Cl2Np y]2- Ca t-
ion ic Alk yls. It is possible to prepare {[ArCl2Npy]-
HfMe}{B(C6F5)4} and use it as an initiator in 1-hexene
polymerization, although 2.5 h is required to form it at
room temperature, and some impurities are present. A
plot of ln([1-hexene]/[standard]) versus time at 0 °C is
curved before becoming linear after 10 min, a trend that
suggests a slower initiation than propagation. We
ascribe the slower initiation rate to either a tighter
binding of the anion to the methyl cation than to the
propagating cation formed upon 1,2-insertion and/or to
an interaction of an ortho chloride in the aryl substitu-
ent that is stronger in the methyl cation than the
propagating cation. At 0 °C the observed rate constant
for propagation was found to be 0.024 min-1 at a
Despite the linearity of the plots of ln([1-hexene]/
[standard]) versus time over more than 5 half-lives,
significant â-H elimination was observed to occur by 1H
NMR. A broad vinylidene resonance corresponding to
the olefinic product of 1,2 â-H elimination in bromoben-
zene-d5 grew in at 4.86 ppm28,29 in the 1H NMR
spectrum as 1-hexene was consumed at 0 °C (to ap-
proximately 15% of [Hfcat]i after ∼98% consumption of
(29) Liu, Z.; Somsook, E.; White, C. B.; Rosaaen, K. A.; Landis, C.
R. J . Am. Chem. Soc. 2001, 123, 11193.

5086 Organometallics, Vol. 22, No. 24, 2003
Schrock et al.
F igu r e 5. Polymerization of 100 equiv of 1-hexene by
0.012 M {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4} (formed by trityl
activation of [ArCl2Npy]Hf(i-Bu)2).
F igu r e 6. Molecular weight measurements for poly(1-
hexene) obtained with {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4} as
the initiator at 0 °C in C6D5Br.
Ta ble 6. â-Hyd r id e Elim in a tion Associa ted w ith
th e P olym er iza tion of 1-Hexen e Ca ta lyzed by
{[Ar X2Np y]Hf(i-Bu )}{B(C6F 5)4} in C6D5Br
hydride) reacts with 1-hexene to generate a new poly-
mer chain or whether the product of â hydride elimina-
tion is inactive even in the presence of 1-hexene.
However, the linearity of the plots of ln([1-hexene]/
[standard]) versus time over more than 5 half-lives
would suggest that the Hf hydride byproduct of 1,2 or
2,1 â-H elimination may still be active for polymeriza-
tion in the presence of a high enough concentration of
1-hexene. A plot of the expected molecular weight versus
equivalents of 1-hexene added for a series of experi-
equiv
â-H1,2
(48 h)
T (°C) 1-hexene % complete â-H1,2
â-H2,1
Cl
Cl
Cl
Cl
F
F
F
F
F
0
10
20
0
0
0
100
100
100
300
50
100
100
100
100
93
77
77
77
98
0.1-0.2 ∼0.05
0.7
0.8
1.1
1.0
0.6
0.8
0.9
0.5-0.8 ∼0.05
1.0-1.1 ∼0.05
0.1-0.2
0.2
0.1-0.3
0.2
0.2
0.2
0.4
0.6
1.5
50
0.2
0.4
0
100
100
100
100
10
10
20
0.6
1.3
ments run at 0 °C in bromobenzene with the {[ArCl2
-
F
77
1.4
1.9
Npy]Hf(i-Bu)}{B(C6F5)4} initiator yielded linear plots,
with molecular weight values being ∼90% of the ex-
pected molecular weight values for a perfect living
system (Figure 6). Polydispersities (Mw/Mn) also were
quite low, ranging from 1.01 to 1.05. We believe that
these data accurately show that a small amount of 1,2
â-H elimination takes place during the polymerization
reaction and that the product of that decomposition
reacts with more 1-hexene to form polymer. However,
the amount of 1,2 â-H elimination apparently is not
great enough to affect the polydispersity values to any
significant degree.
P olym er iza tion of 1-Hexen e by [Ar F 2Np y]2- Ca t-
ion ic Alk yls. Although the reaction of [ArF2Npy]HfMe2
with trityl to give {[ArF2Npy]HfMe}{B(C6F5)4} at 0 °C
was the most rapid as a consequence of the greater ease
of dissociation of intermediate {[ArF2Npy]2Hf2Me3}-
1-hexene) and continued to grow after the polymeriza-
tion was complete (to about 70% [Hfcat]i after 48 h).
(Landis found vinylidene resonances due to 1,2 â-H
elimination at 4.68 and 4.76 ppm in toluene.29) The ratio
of the 1,2 â-H elimination product to the initial hafnium
concentration was obtained by comparing the integra-
tion of the olefinic product peak to a known Ph2CH2
standard concentration. (Integrations are not highly
accurate under these conditions, and the product of â
elimination from a 1,2 insertion product, like isobutene,
may be polymerized itself in the presence of trityl under
these conditions.) These details are listed in Table 6 for
reference. Under the conditions of 1-hexene polymeri-
zation employed here the half-life for the consumption
of 1-hexene is ∼40 min (for [Hf] ) 0.012 M), so
consumption is complete in ∼200 min. During this time
10-20% of chain termination by â elimination from a
1,2 insertion product has taken place.
When 300 equiv of 1-hexene was polymerized at 0 °C,
vinylene resonances due to â-H elimination after a 2,1
insertion grew between 5.36 and 5.40 ppm and inte-
grated to about 0.1-0.2 equiv of [Hfcat]i. (Landis re-
ported the shifts of the vinylene resonances due to 2,1
â-H elimination to be at 5.3 ppm in toluene.29) In runs
where 100 equiv of 1-hexene was employed at 0 °C,
however, only 0.05 equiv of â-2,1 elimination was
observed. Since the resonance due to the â-2,1 elimina-
tion product was not observed to grow after all of the
1-hexene had been consumed, it appears that a â-2,1
elimination product forms only when 1-hexene is present
in high enough concentrations.
{B(C6F5)4} into {[ArF2Npy]HfMe}{B(C6F5)4} and [ArF2
-
Npy]HfMe2, {[ArF2Npy]HfMe}{B(C6F5)4} was not formed
quantitatively before {[ArF2Npy]2Hf2Me3}{B(C6F5)4} was
consumed due to concomitant decomposition of {[ArF2
-
Npy]HfMe}{B(C6F5)4} and perhaps also formation of
side products during the activation process. At 0 °C, kp
was found to be 0.002(1) M-1 s-1 for {[ArF2Npy]HfMe}-
{B(C6F5)4} prepared in this manner. This value was
lower than that for {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4} (see
below) as a consequence of formation of inactive side
products during polymerization and perhaps also as a
consequence of a slower initiation relative to propaga-
tion. Approximately 50% of the {[ArF2Npy]HfMe}-
{B(C6F5)4} initiator remained in solution after the
consumption of 50 equiv of 1-hexene.
On the basis of olefinic peak integration alone we
cannot say in this case whether the metal-containing
product of â hydride elimination (assumed to be a
Polymerization of 1-hexene by {[ArF2Npy]Hf(i-Bu)}-
{B(C6F5)4} led to plots of ln([1-hexene]/[standard]) ver-
sus time that were linear throughout the reaction for

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5087
F igu r e 7. Plots of ln([1-hexene]/[Ph2CH2]) versus time for
the consumption of 1-hexene by {[ArF2Npy]Hf(i-Bu)}-
{B(C6F5)4}: (a) [Hfcat] ) 0.012 M, 0 °C, 50 equiv 1-hexene,
kp ) 0.0070 M-1 s-1; (b) [Hfcat] ) 0.015 M, 0 °C, 100 equiv
1-hexene, kp ) 0.0073 M-1 s-1; (c) [Hfcat] ) 0.012 M, 10 °C,
100 equiv 1-hexene, kp ) 0.0155 M-1 s-1; (d) [Hfcat] ) 0.012
F igu r e 8. Molecular weight measurements for poly(1-
hexene) obtained with {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4} as
the initiator at 0 °C in C6D5Br.
1.1 and 1.4, consistent with less than perfect charac-
teristics for a living polymerization reaction.
M, 20 °C, 100 equiv 1-hexene, kp ) 0.028 M-1 s-1
.
temperatures ranging from 0 to 20 °C (Figure 7). At 0
°C for 50 and 100 equiv of 1-hexene, kp was found to be
0.007 M-1 s-1. This should be compared with kp ) 0.10
M-1 s-1 for {[MesNpy]Hf(i-Bu)}{B(C6F5)4} and 0.049
M-1 s-1 for {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4}. Both 1,2
and 2,1 â-H elimination also were more prominent in
the {[ArF2Npy]Hf(CH2R)}{B(C6F5)4} catalyst system
than in the {[ArCl2Npy]Hf(CH2R)}{B(C6F5)4} catalyst
system. The vinylidene resonance corresponding to the
1,2 â-H elimination product was again found at 4.86
ppm, and the vinylene resonances corresponding to the
2,1 â-H elimination products were found between 5.36
and 5.40 ppm and also at 5.48 ppm. For the polymeri-
zation of 50 equiv of 1-hexene at 0 °C, the 1,2 â-H
elimination product peak (representing 2 protons) in-
tegrated to 0.2 equiv of [Hfcat]i after approximately 77%
consumption of 1-hexene was observed (the polymeri-
zation was stopped after 77% polymerization due to time
restraints). At 20 °C, the 1,2 â-H elimination product
peak (representing 2 protons) integrated to 1.4 equiv of
the [Hfcat]i after 77% of the 1-hexene was consumed and
grew to 1.9 equiv after a period of 48 h. 2,1 â-H
elimination was also more prominent in this system,
with the 2,1 â-H elimination product peaks growing to
a total of 1.5 equiv at 20 °C.
Virtually all of the propagating catalyst decomposed
after a period of 48 h at 0 °C to give one or more
unidentifiable metal complexes. If the metal-containing
product of â hydride elimination (assumed to be a
hydride) decomposes before it can react with 1-hexene,
then the amount of â hydride elimination product from
1,2 insertion cannot be greater than the amount of
initiator initially present unless the hydride is able to
react with 1-hexene to start a new polymer chain. Since
the total equivalents of â-H elimination product was
significantly greater than the amount of catalyst present
initially at 20 °C, it seems probable that new polymer
chains can be generated at this temperature when
1-hexene is present. Molecular weights for polymeriza-
tion reactions run at 0 °C were much lower than
expected (∼50% of theory; Figure 8), suggesting that the
decomposition product may indeed react with 1-hexene
to re-form poly(1-hexene), thus leading to the observed
first-order kinetics. The polydispersities varied between
Discu ssion
The main goal of this work was to determine the
behavior of {[2,6-X2C6H3Npy]Hf(i-Bu)}{B(C6F5)4} (X )
Cl or F) initiators in 1-hexene polymerization and to
compare their behavior with the system in which 2,4,6-
Me3C6H2 (mesityl) groups are present on the amido
nitrogens. We found that the catalytic activity steadily
decreases in the order aryl ) mesityl > 2,6-Cl2C6H3 >
2,6-F2C6H3. Three explanations for this effect are plau-
sible. First, the electron-withdrawing effect of the
halides increases the strength of anion binding to the
cationic metal center. The resulting stronger interaction
between cation and anion lowers the metal’s electro-
philicity and hinders olefin binding to the metal and
insertion into the M-carbon bond. The second possibil-
ity is that Cl or F coordinates to the cationic metal
center, again competing with olefin binding. Metal-
halide binding is not strong enough to observe readily
by NMR methods, in contrast to binding of an ortho
dimethylamino group, but it may be detected in terms
of a decrease in polymerization rate. A third possibility
is some hydrogen bonding between the ortho chloride,
or especially the ortho fluoride, and R or â protons in
the alkyl in cationic monoalkyl species. There is some
evidence gathering in the literature that interactions
between fluorides and R30 or â protons31 can signifi-
cantly alter olefin polymerization pathways. However,
we believe there is considerably more evidence that
ortho fluorides in aryl rings can coordinate to early
transition metals such as Zr24,32 or Ta33 (in addition to
the structure reported here) and therefore favor one of
the first two explanations. We can think of no way to
differentiate between these explanations in the actual
cationic intermediates in 1-hexene polymerization.
Initially we had entertained the possibility that a
halide in the ortho position would coordinate to the
(30) Kui, S. C. F.; Zhu, N.; Chan, M. c. W. Angew. Chem., Int. Ed.
2003, 42, 1628.
(31) Mitani, M.; Mohri, J .; Yoshida, Y.; Saito, J .; Ishii, S.; Tsuru,
K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.;
Matsugi, T.; Kashiwa, N.; Fujita, T. J . Am. Chem. Soc. 2002, 124, 3327.
(32) Plenio, H. Chem. Rev. 1997, 97, 3363.
(33) Schrock, R. R.; Lee, J .; Liang, L.-C.; Davis, W. M. Inorg. Chim.
Acta 1998, 270, 353.

5088 Organometallics, Vol. 22, No. 24, 2003
Schrock et al.
described in the literature.34 Bromobenzene and deuterated
solvents were stirred over CaH2 for 48 h, vacuum-transferred,
and stored over 4 Å molecular sieves. Commercial reagents
were used without further purification. The parent pyridyl
diamine (NH2CH2)2C(CH3)(2-C5H4N)),35,36 Hf(NMe2)4, and Zr-
metal and in fact stabilize a cationic alkyl against â-H1,2
(â hydride elimination from a 1,2 insertion product),
while reactivity toward insertion would be maintained
or possibly increased as a consequence of the electron-
withdrawing ability of the halide. Instead we find that
the isobutyl initiators decompose more readily by â
hydride elimination, and the propagating species in
37
(NMe2)4 were synthesized according to reported methods.
Ordinary Grignard reagents were bought from Aldrich and
titrated prior to use with 4-cumylphenol or 1-propanol using
1,10-phenanthroline as an indicator. 13CH3MgI was prepared
from 13CH3I (purchased from Cambridge Isotopes) and Mg as
an etheral solution. NMR data were recorded using Varian
Inova-500, Bruker AVANCE-400, Varian Unity-300, or Varian
Mercury-300 spectrometers. Chemical shifts are reported in
parts per million (ppm), and coupling constants are reported
in hertz. The residual protons or 13C atoms of the deuterated
solvents were used as internal references. 19F NMR chemical
shifts were referenced to the external standard C6F6. Elemen-
tal analyses (C, H, N, Cl) were done by Kolbe Mikroanalytis-
ches Laboratorium, Mu¨lheim an der Ruhr, Germany.
1-hexene polymerization are less stable toward â-H1,2
.
Again there appear to be three possible explanations.
The first is that the metal is more electrophilic as a
consequence of the electron-withdrawing ability of the
halides, and â hydride elimination is faster if the metal
center is more electrophilic. The second possible expla-
nation is that interaction of the halide with the metal
accelerates the rate of â hydride elimination. The third
is that any hydrogen-bonding interactions between
ortho halides and R or â protons in the alkyl in cationic
monoalkyl species promotes more rapid â-H1,2 processes.
This last explanation would be in contrast with recent
evidence that such a hydrogen-bonding interaction
between a fluoride and a â proton in the alkyl stabilizes
a Ti system against â-H1,2 processes and therefore
allows a polymerization at room temperature to be
living.31 Again it is difficult to differentiate between
these possible explanations.
GPC analyses were conducted using a system equipped with
two J ordi-Gel DVB mixed bed columns (250 mm length × 10
mm inner diameter) in series and a Wyatt Technology mini
Dawn light scattering detector coupled with a Knauer dif-
ferential refractometer. A Knauer 64 HPLC pump was used
to supply HPLC grade THF at a flow rate of 1.0 mL/min. The
auxiliary constant of the apparatus (5.9 × 10-4) was calibrated
using a polystyrene standard (Mn ) 2.2 × 105), and Mn and
Mw values for poly(1-hexene) were obtained using dn/dc )
0.076 mL/gr (Wyatt Technology). Data analysis was carried
out using Astrette 1.2 software (Wyatt Technology).
The third intriguing result is that more â-H2,1 is
observed in the order aryl ) mesityl < 2,6-Cl2C6H3
<
2,6-F2C6H3, assuming that â-H2,1 gives rise to the
hexene-dependent resonances at 5.36-5.40 ppm. The
fact that â-H2,1 appears only in the presence of 1-hexene
can be explained if â-H2,1 takes place a significant
percentage of the time that there is a 2,1 “misinser-
tion”.29 Much more work is needed in order to elucidate
the origin of an increase in the amount of â-H2,1 and to
quantitate it. Unfortunately, the precise reason may be
difficult to pin down, for reasons that we have already
alluded to above.
We conclude that substitution of chlorides or fluorides
(especially the latter) in the ortho positions of the aryl
groups attached to the amido nitrogens in [ArylNpy]2-
complexes in place of methyl groups is detrimental to
the development of living olefin polymerization catalysts
of this general type. Not only do 1-hexene polymeriza-
tion reactions slow down, but during polymerization
more â hydride elimination from both 1,2 and 2,1
insertion products is observed. Even without detailed
knowledge about the stability of the putative “hydride”
that is formed as a consequence of a â hydride elimina-
tion, it is clear that the living nature of the polymeri-
zation is compromised. We plan to explore the behavior
of catalysts with other groups in the 2 and 6 positions
of the aryl rings (e.g., isopropyl groups16) or with
electron-withdrawing or electron-donating groups in
positions other than ortho positions in the aryl substit-
uents on the amido nitrogens.
[(2,6-Cl2C6H3NHCH2)2C(CH3)(2-C5H4N)] (H2[Ar Cl2Np y]).
BINAP (566 mg, 0.91 mmol) was added to 30 mL of toluene,
and the mixture was heated until the BINAP dissolved. To
this solution was added 416 mg (0.45 mmol) of Pd2(DBA)3. The
reaction was stirred for 15 min and filtered through a glass
frit. The parent diamine (5.00 g, 30.3 mmol) was dissolved in
30 mL of toluene. To this solution were added NaO-t-Bu 6.7 g
(70 mmol) and 1-bromo-2,6-dichlorobenzene (13.69 g, 60.6
mmol), and the total volume was brought to 200 mL. The
sealed Schlenk flask was then heated for 1 day at 95 °C. The
hot mixture was filtered, and the toluene was removed from
the filtrate in vacuo. The residue was extracted with 300 mL
of ether, and the ether solution was washed with water (400
mL total) and saturated NaCl solution (200 mL). The combined
water extracts were then washed with ether (200 mL total).
The combined ether extracts were concentrated to about 30
mL, and pentane (10 mL) was added. A solid precipitated and
was filtered off and discarded. The solvent was removed from
the filtrate to yield a brown oil; yield 8.9 g (19.7 mmol, 65%).
1H NMR (CDCl3): δ 1.5 (3H, s, CH3), 3.65 (2H, dd, J ) 12.2
and 7.3, CHH), 3.79 (2H, dd, J ) 12.2 and 7.3, CHH), 4.68
(2H, t, J ) 7.3, NH), 6.62 (2H, t, J ) 8.4, arom. p-H), 7.05
(4H, d, J ) 8.4, arom. m-H), 7.06 (1H, t, J ) 4.2, py-H), 7.35
(1H, t, J ) 8.4, py-H), 7.57 (1H, t, J ) 8.4, py-H), 8.55 (1H, d,
J ) 4.2, py-Ho). HRMS (ESI): calcd for C21H19N3Cl4 [M]+
453.0328, found [M]+ 453.0328. The product was estimated to
be ∼95% pure according to its 1H NMR spectrum.
[Ar Cl2Np y]Zr (NMe2)2. To a solution of Zr(NMe2)4 (1.5 g,
7.48 mmol) in 60 mL of pentane was added 2.55 g (7.48 mmol)
of H2[ArCl2Npy]. The mixture was stirred at room temperature
for 16 h. The solvent was removed in vacuo, and the resulting
orange solid was washed with 20 mL of pentane; yield 3.05 g
1
Exp er im en ta l P r oced u r es
(86%). H NMR (toluene-d8): δ 1.22 (3H, s, CH3), 3.18 (6H, s,
Gen er a l Deta ils. All reactions were conducted under an
atmosphere of dinitrogen in a Vaccum Atmospheres drybox
or using standard Schlenk techniques, and catalyst activation
was performed in an inert atmosphere (dinitrogen) box free
of ether, THF, or other coordinating solvents. Nondeuterated
solvents were sparged with nitrogen for 45 min followed by
passage through a 1 gallon column of activated alumina as
(34) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(35) Friedrich, S.; Schubart, M.; Gade, L. H.; Scowen, I. J .; Edwards,
A. J .; McPartlin, M. Chem. Ber. Rec. 1997, 130, 1751.
(36) Blake, A. J .; Collier, P. E.; Gade, L. H.; McPartlin, M.;
Mountford, P.; Schubart, M.; Scowen, I. J . Chem. Commun. 1997, 1555.
(37) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. Organometallics
1996, 15, 4030.

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5089
N(CH3)2), 3.28 (2H, d, J ) 9.6, CHH), 3.33 (6H, s, N(CH3)2),
4.63 (2H, d, J ) 9.6, CHH), 6.35 (2H, t, J ) 8.6, arom. p-H),
6.68 (1H, t, J ) 5.2, py-H), 6.92 (1H, d, J ) 8.6, py-H), 7.05
(1H, t, J ) 8.6, py-H), 7.12 (4H, d, J ) 8.6, arom. m-H), 8.75
(1H, d, J ) 5.2, o-py-Ho). The product was estimated to be
∼95% pure according to its 1H NMR spectrum.
43.95; H, 3.37; N, 6.11; Cl, 20.62. Found: C, 44.08; H, 3.31;
N, 6.11; Cl, 20.49.
[Ar Cl2Np y]Hf(i-Bu )2. [ArCl2Npy]HfCl2 (460 mg, 0.655 mmol)
was suspended in 20 mL of ether, and the mixture was cooled
to -30 °C. A solution of i-BuMgBr (0.69 mL, 1.375 mmol, 2 M
in ether) was then added. The reaction mixture was stirred
for 1 h at room temperature. The mixture was filtered, and
the solvent was removed from the filtrate in vacuo. The
resulting light yellow powder is about 95% pure. Pure product
was obtained by recrystallization from a mixture of benzene
[Ar Cl2Np y]Zr Cl2. To a solution of 1.69 g (2.67 mmol) of
[ArCl2Npy]Zr(NMe2)2 in 30 mL of ether was added 1.16 g (10.67
mmol) of Me3SiCl. After 6 h the resulting pale yellow solid
was filtered off, washed with pentane, and dried in vacuo; yield
1
1
1.15 g (70%). H NMR (toluene-d8): δ 0.89 (3H, s, CH3), 2.95
and pentane (1:1); yield 283 mg (58%). H NMR (toluene-d8):
(2H, d, J ) 12.0, CHH), 4.35 (2H, d, J ) 12.0, CHH), 6.1 (2H,
t, J ) 7.2, arom. p-H), 6.35 (1H, t, J ) 2.4, py-H), 6.54 (1H, d,
J ) 4.8, py-H), 6.75 (4H, d, J ) 7.2, arom. m-H), 6.75 (1H, t,
py-H), 9.4 (1H, d, J ) 2.4, py-Ho). The product was estimated
to be ∼95% pure according to its 1H NMR spectrum.
δ 0.80 (2H, d, ax CH2CH(CH3)2), 0.85 (3H, s, CH3), 0.95 (6H,
d, ax CH2CH(CH3)2), 0.98 (2H, d, eq CH2CH(CH3)2), 1.15 (6H,
d, eq CH2CH(CH3)2), 2.34 (1H, m, CH2CH(CH3)2), 2.45 (1H,
m, CH2CH(CH3)2), 3.1 (2H, d, ligand CHH), 4.23 (2H, d, ligand
CHH), 6.11 (2H, t, arom. p-H), 6.38 (1H, t, meta py-H), 6.50
(1H, d, meta py-H), 6.75 (1H, t, para py-H), 6.8 (4H, d, arom.
m-H), 8.65 (1H, d, py-Ho). Anal. Calcd for C29H35N3Cl4Hf: C,
46.70; H, 4.73; N, 5.63; Cl, 19.01. Found: C, 46.58; H, 4.65;
N, 5.56; Cl, 19.10.
[Ar Cl2Np y]Zr Me2. [ArCl2Npy]ZrCl2 (0.3 g, 0.488 mmol) was
suspended in 10 mL of diethyl ether. The mixture was cooled
to -30 °C, and MeMgCl (0.34 mL, 3 M in THF) was added.
The reaction mixture was stirred for 1 h at room temperature.
Dioxane (0.090 g) was then added, and after 5 min the reaction
mixture was filtered through Celite. The filtrate’s volume was
reduced to 3 mL, and the solution was stored at -30 °C for
one week. White microcrystals were filtered off and dried in
[(2,6-F 2C6H3NHCH2)2C(CH3)(2-C5H4N)] (H2[Ar F 2Np y]).
BINAP (0.113 g, 0.181 mmol) was added to 25 mL of toluene,
and the resulting suspension was heated until the BINAP
dissolved. Pd(DBA)3 (0.083 g, 0.091 mmol) was added, and the
solution was heated until the reaction turned orange. The
solution was filtered through Celite and combined with the
parent diamine (1.00 g, 6.05 mmol), 1-bromo-2,6-difluoroben-
zene (2.34 g, 12.1 mmol), and NaO-t-Bu (1.34 g, 0.0139 mmol)
in 40 mL of toluene. The reaction was heated at 95 °C for 5
days under N2 in a sealed Schlenk flask. The hot reaction
mixture was filtered, and toluene was removed in vacuo. The
product was extracted into ether, and the solution was treated
as described above for H2[ArCl2Npy]. The volume of the
combined ether extracts was reduced to 6 mL, and pentane
(10 mL) was added. A brown precipitate was filtered off
through a bed of packed Celite. The filtrate was collected, and
the solvent was removed in vacuo to yield a brown oil, which
was purified via column chromatography (silica gel, ethyl
acetate solvent) to give a red-brown oil; yield 1.20 g (37%). 1H
NMR (CDCl3): δ 1.43 (3H, s, CH3), 3.79 (4H, m, CHH), 4.60
(2H, s, NH), 6.63 (2H, m, arom. p-H), 6.77 (4H, m, arom. m-H),
7.16 (1H, dd, py-H), 7.42 (1H, d, py-H), 7.67 (1H, t, py-H), 8.62
1
vacuo; yield 158 mg (56%). H NMR (toluene-d8): δ 0.88 (3H,
s, HfCH3), 3.1 (2H, d, J ) 11.7, CHH), 4.24 (2H, d, J ) 11.7,
CHH), 6.1 (2H, t, J ) 8.3, arom. p-H), 6.3 (1H, t, J ) 5.0, py-
H), 6.5 (1H, d, J ) 8.3, py-H), 6.68 (1H, t, J ) 8.3, py-H), 6.84
(4H, d, J ) 8.3, arom. m-H), 8.51 (1H, d, J ) 5.0, py-Ho). Anal.
Calcd for C23H23N3Cl4Zr: C, 48.09; H, 4.04; N, 7.31; Cl, 24.68.
Found: C, 47.88; H, 3.92; N, 7.24; Cl, 24.63.
[Ar Cl2Np y]Hf(NMe2)2. Hf(NMe2)4 (2 g, 5.64 mmol) was
suspended in 60 mL of pentane, and 2.57 g (5.64 mmol) of
H2[ArCl2Npy] was added. The reaction mixture was stirred at
room temperature for 16 h. The solvent was removed in vacuo,
and the resulting orange solid was washed with 20 mL of
pentane and dried in vacuo; yield 3.52 g (87%). 1H NMR
(toluene-d8): δ 1.15 (3H, s, CH3), 3.3 (6H, s, N(CH3)2), 3.35
(6H, s, N(CH3)2), 3.42 (2H, d, J ) 10.6, CHH), 4.6 (2H, d, J )
10.6, CHH), 6.32 (2H, t, J ) 7.8, arom. p-H), 6.7 (1H, t, J )
7.0, py-H), 6.85 (1H, d, J ) 7.8, py-H), 7.05 (1H, t, J ) 7.8,
py-H), 7.15 (4H, d, J ) 7.8, arom. m-H), 8.75 (1H, d, J ) 7.0,
py-Ho). The product was estimated to be ∼95% pure according
to its 1H NMR spectrum.
[Ar Cl2Np y]HfCl2. [ArCl2Npy]Hf(NMe2)2 (1.763 g, 2.45 mmol)
was dissolved in 25 mL of toluene, and 1.064 g (9.8 mmol) of
Me3SiCl was added. The Schlenk flask was then sealed and
heated at 85 °C for 16 h. The mixture was cooled to room
temperature, and the volatile compounds were removed in
vacuo. The pale yellow-brown solid was washed with pentane
(2 times 10 mL) and dried in vacuo; yield 1.5 g (87%). 1H NMR
(toluene-d8): δ 1.57 (3H, s, CH3), 3.34 (2H, d, J ) 11.8, CHH),
4.55 (2H, d, J ) 11.8, CHH), 6.8 (2H, t, J ) 8.5, arom. p-H),
7.18 (4H, d, J ) 8.5, arom. m-H), 7.47 (1H, t, J ) 6.8, py-H),
7.53 (1H, d, J ) 8.5, py-H), 7.97 (1H, t, J ) 8.5, py-H), 9.36
(1H, d, J ) 6.8, py-Ho). The product was estimated to be ∼95%
pure according to its 1H NMR spectrum.
[Ar Cl2Np y]HfMe2. [ArCl2Npy]HfCl2 (200 mg, 0.285 mmol)
was suspended in 10 mL of ether, and the mixture was stored
at -30 °C for 1 h. MeMgBr (0.2 mL, 0.598 mmol, 3 M in ether)
was added, and the mixture was stirred for 1 h while it
warmed to room temperature. The mixture was filtered, and
the solvent was removed from the filtrate in vacuo. The
resulting residue was triturated with pentane until a powder
was obtained. This crude material was then recrystallized from
a mixture of benzene and pentane (1:2); yield 116 mg (62%).
1H NMR (toluene-d8): δ 0.33 (3H, s, Hf-CH3), 0.45 (3H, s, Hf-
CH3), 0.85 (3H, s, ligand CH3), 3.1 (2H, d, CHH), 4.23 (2H, d,
CHH), 6.11 (2H, t, arom. p-H), 6.38 (1H, t, meta py-H), 6.50
(1H, d, meta py-H), 6.75 (1H, t, para py-H), 6.8 (4H, d, arom.
m-H), 8.65 (1H, d, py-Ho). Anal. Calcd for C23H23N3Cl4Hf: C,
1
(1H, d, py-H). H NMR (C6D6): δ 1.42 (3H, s, CH3), 3.78 (4H,
m, CHH), 4.98 (2H, s, NH), 6.22, 6.98, 6.55 (9H total, 3 py H,
6 arom. H), 8.35 (1H, d, py-Ho). 19F NMR (C6D6): δ -130.0
(4F, s, arom. o-F). HRMS (ESI): calcd for C21H19N3F4 [M +
Na] 412.1407, found [M + Na] 412.1402.
[Ar F 2;F NMe2Np y]Hf(F )(NMe2) (3). H2[ArF2Npy] (0.852 g,
2.19 mmol) and Hf(NMe2)4 (0.739 g, 2.08 mmol) were dissolved
in a mixture of pentane (30 mL) and benzene (5 mL). After 20
h the solvent was removed in vacuo to yield a brown powder
that was recrystallized from ether at -30 °C to yield yellow
crystals; yield 1.189 g (87%), 1H NMR (C6D6): δ 1.15 (3H, s,
CH3), 2.07 (3H, s, ArNCH3), 2.82(3H, s, ArNCH3), 2.94 (6H, s,
HfNCH3), 3.20 (1H, d, CHH), 3.55 (1H, dd, CHH), 4.58 (1H, d,
CHH), 4.91 (1H, dd, CHH), 6.2-7.0 (9H, complex, 3 py-H, 6
arom. H), 9.19 (1H, d, py-Ho). 19F NMR (C6D6): δ -128.6 (1F,
s, arom. uncoord. o-F, J FH ) 5.9), -122.0 (2F, d, J FF ) 32.9,
arom. o-F, J FH ) 6.5), 28.5 (1F, t, J FF ) 32.9, Hf-F). Anal. Calcd
for C25H29N5F4Hf: C, 45.91; H, 4.47; N, 10.71. Found: C, 46.08;
H, 4.41; N, 10.64.
[Ar F 2Np y]Hf(NMe2)2 (1). This compound is the byproduct
of the synthesis of 3, identified in solution only; yield e5%.
1H NMR (C6D6): δ 1.18 (3H, s, CH3), 2.89 (6H, s, N(CH3)2),
3.07 (6H, s, N(CH3)2), 3.39 (2H, d, CHH), 4.35 (2H, d, J ) 10.6,
CHH), 6.1-7.0 (6H, arom. protons), 8.42 (1H, d, py-Ho). 19F
NMR (C6D6): δ -125.1 (4F, s, arom. o-F, J FH ) 6.84).
[Ar F 2;F NMe2Np y]Hf(Cl)(NMe2) (4). [ArF2;FNMe2Npy]Hf(F)-
NMe2 (3, 0.300 g, 0.465 mmol) and Me3SiCl (0.050 g, 0.465
mmol) were dissolved in toluene (7 mL), and the solution was
stirred for 30 h. The reaction was filtered through Celite and

5090 Organometallics, Vol. 22, No. 24, 2003
Schrock et al.
the solvent removed in vacuo from the filtrate to afford a yellow
powder. The product was recrystallized from ether in order to
remove unreacted [ArF2;FNMe2Npy]Hf(F)(NMe2); yield ) 0.126
g (41%). 1H NMR (C6D6): δ 1.07 (3H, s, CH3), 2.05 (3H, s,
ArNCH3), 2.85 (3H, s, ArNCH3), 2.91 (6H, s, HfNCH3), 3.43
(1H, d, CHH), 3.57 (1H, dd, CHH), 3.70 (1H, d, CHH), 4.95
(1H, dd, CHH), 6.2-7.0 (9H, multiplets, 3 py-H, 6 arom. H),
9.19 (1H, d, py-Ho). 19F NMR (C6D6): δ -127.9 (1F, s, arom.
uncoord. o-F, J FH ) 5.9), -119.3 (2F, d, J FF ) 32.9, arom. o-F,
J FH ) 6.5).
mL). The mixture was cooled to -30 °C, i-BuMgCl (0.631 g,
5.40 mmol) was added, and the reaction was stirred at room
temperature for 1 h. A white precipitate was filtered off
through Celite, and the solution was concentrated in vacuo to
afford an orange residue, which was washed with pentane (25
mL). The resulting yellow powder was recrystallized in a 1:4
mixture of ether and pentane; yield 0.488 g (52%). 1H NMR
(C6D6): δ 0.09 (2H, m, CH2CH(CH3)2), 0.96 (3H, s, CH3), 1.05
(6H, d, CH2CH(CH3)2), 1.12 (2H, m, CH2CH(CH3)2), 1.48 (6H,
d, CH2CH(CH3)2), 2.31 (1H, p, CH2CH(CH3)2), 2.93 (1H, p,
CH2CH(CH3)2), 3.56 (2H, d, ligand CHH), 4.47 (2H, d, ligand
CHH), 6.12 (2H, m, ArF2 p-H), 6.37 (1H, t, py-H), 6.68 (4H,
m, ArF2 m-H), 6.69 (1H, d, py-H), 6.83 (1H, t, py-H), 8.69 (1H,
d, py-Ho). 19F NMR (C6D6): δ -117.4 (4F, s, arom. o-F). Anal.
Calcd for C29H35N3F4Hf: C, 51.22; H, 5.19; N, 6.18. Found: C,
51.31; H, 5.14; N, 6.06.
[Ar F 2;F NMe2Np y]HfCl2 (7). [ArF2;FNMe2Npy]Hf(F)NMe2 (3,
0.771 g, 1.18 mmol) and Me3SiCl (0.767 g, 7.07 mmol) were
dissolved in toluene (25 mL), and the solution was stirred for
30 h. The yellow precipitate was filtered off and washed with
ether (10 mL) and pentane (10 mL); yield 0.634 g (83%). 1H
NMR (C6D6): δ 0.93 (3H, s, CH3), 2.32 (3H, s, ArNCH3), 3.03
(1H, d, CHH), 3.07, (3H, s, ArNCH3), 3.63 (1H, dd, CHH), 4.05
(1H, d, CHH), 4.55 (1H, dd, CHH), 6.3-6.9 (9H, ms, 3 py-H, 6
arom. H), 9.44 (1H, d, py-Ho). 19F NMR (C6D6): δ -129.7 (1F,
s, arom. uncoord. o-F, J FH ) 6.3), -120.9 (2F, s, arom. o-F,
J FH ) 6.3). Anal. Calcd for C23H23N4F3HfCl2: C, 41.74; H, 3.5;
N, 8.47; Cl, 10.71. Found: C, 41.50; H, 3.43; N, 8.43; Cl, 10.71.
[Ar F2;FNMe2Np y]HfCl(i-Bu ). A suspension of [ArF2;FNMe2Npy]-
HfCl2 (0.600 g, 0.907 mmol) in ether (25 mL) was cooled to
-30 °C, and i-BuMgCl (0.228 g, 1.952 mmol, 2.7 M in ether)
was added. The mixture was stirred at room temperature for
24 h and filtered off through Celite. The solvent was removed
in vacuo from the filtrate, and the resulting residue was
triturated thoroughly with pentane to give a yellow powder;
[Ar F 2Np y]HfMe2. HfCl4 (0.229 g, 0.715 mmol) and H2[ArF2
-
Npy] (0.265 g, 0.681 mmol) were dissolved in dichloromethane
(150 mL), and the reaction was stirred at room temperature
for 36 h. Dichloromethane was removed in vacuo to give a
yellow powder, which was suspended in ether (150 mL). The
mixture was cooled to -30 °C, MeMgBr (0.337 g, 2.83 mmol)
was added, and the reaction mixture was stirred at room
temperature for 1 h. A white precipitate was filtered off
through Celite, and the resulting solution was concentrated
in vacuo to afford a brown residue. This residue was triturated
with pentane (20 mL) to afford a brown powder. The resulting
brown powder was dissolved in pentane. The solution was
filtered and cooled to -30 °C to afford yellow crystals; yield
0.172 g (43%). 1H NMR (C6D6Br): δ 0.08 (3H, m, HfCH3), 0.68
(3H, m, HfCH3), 1.23 (3H, s, CH3), 3.55 (2H, d, CHH), 4.38
(2H, d, CHH), 6.26 (2H, m, arom. p-H), 6.76 (4H, m, arom.
m-H), 6.80 (1H, t, py-H), 7.09 (1H, d, py-H), 7.36 (1H, t, py-
H), 8.67 (1H, d, py-Ho). 19F NMR (C6D6Br): δ -114.6 (4F, s,
arom. o-F). Anal. Calcd for C23H23N3F4Hf: C, 46.36; H, 3.89;
N, 7.05. Found: C, 46.42; H, 3.95; N, 6.88.
Gen er a l P r oced u r e for Kin etic Stu d ies of 1-Hexen e
P olym er iza tion . Suspensions of [Ph3C][B(C6F5)4] (0.0036-
0.0139 g; 0.004-0.015 mmol) and an equimolar amount of
[ArX2Npy]HfR2 in equal volumes of bromobenzene-d5 (total
solution volume, including 1-hexene ) 1 mL) were cooled to
-40 °C and mixed along with the internal standard Ph2CH2
(∼0.005 g, 0.030 mmol, R ) i-Bu) or hexamethylbenzene
(∼0.005 g, 0.031 mmol, R ) Me). The dimethyl complexes were
stirred at room temperature for 10 min with M ) Zr and 3 h
with M ) Hf, or at 30 °C with M ) Hf for 45 min. Activation
of the diisobutyl complexes occurred immediately for both M
) Zr and M ) Hf and was marked by a change in color from
an orange to a yellow solution. The activated complex was
transferred to a J -Young NMR tube and cooled to -40 °C. To
this solution was added the appropriate volume of 1-hexene.
The NMR tube was shaken immediately, brought out of the
glovebox, and frozen in liquid nitrogen. The frozen sample was
brought to the NMR machine, which was precooled to a defined
temperature. The sample was warmed until it was liquid again
and then placed into the NMR machine, and the reaction was
monitored by standard NMR measurement. Disappearance of
the olefinic signals of the 1-hexene was measured against the
internal standard.
1
yield 0.203 g (33%). H NMR (C6D6): δ 0.72 (1H dd, CHHCH-
(CH3)2), 0.90 (3H, d, CH2CH(CH3)2), 0.94 (3H, s, CH3), 1.06
(3H, dd, CHHCH(CH3)2), 1.17 (3H, d, CH2CH(CH3)2), 2.02 (3H,
s, ArNCH3), 2.24 (1H, sept, CH2CH(CH3)2), 3.02 (3H, s,
ArNCH3), 3.05 (1H, d, CHH), 3.45 (1H, dd, CHH), 4.12 (1H, d,
CHH), 4.93 (1H, dd, CHH), 6.3-7.0 (9H, ms, 3 py-H, 6 arom.
H), 9.29 (1H, d, py-Ho). 19F NMR (C6D6): δ -127.3 (1F, s, arom.
uncoord. o-F, J FH ) 6.12), -119.2 (2F, s, arom. o-F, J FH ) 6.10).
Anal. Calcd for C27H32N4F3Cl1Hf: C, 47.48; H, 4.65; N, 8.12;
Cl, 5.25. Found: C, 47.45; H, 4.72; N, 8.2; Cl, 5.19.
[Ar F 2;F NMe2Np y]HfMe2. A suspension of [ArF2;FNMe2Npy]-
HfCl2 (0.100 g, 0.151 mmol) in ether (5 mL) was cooled to -30
°C, and MeMgBr (0.038 g, 0.317 mmol, 3.45 M in ether) was
added. The mixture was stirred at room temperature for 1 h,
and the mixture was filtered through a bed of Celite. The
solvent was removed in vacuo from the filtrate, and the
resulting residue was triturated thoroughly with pentane to
yield a pale yellow powder; yield 0.043 g (46%). 1H NMR
(C6D6): δ 0.28 (3H, m, HfCH3), 0.57 (3H, m, HfCH3), 1.04 (3H,
s, CH3), 2.14 (3H, s, ArNCH3), 2.75 (3H, s, ArNCH3), 3.27 (1H,
d, CHH), 3.59 (1H, dd, CHH), 4.17 (1H, d, CHH), 4.77 (1H,
dd, CHH), 6.2-7.0 (9H, ms, 3 py-H, 6 arom. H), 8.66 (1H, d,
py-Ho).
[Ar (F NMe2)2Np y]Hf(F )Cl (6). This compound was a byprod-
uct of the synthesis of [ArF2;FNMe2Npy]HfCl2 (e5%). It was
1
identified only by its NMR spectrum. H NMR (C6D6): δ 1.10
(3H, s, CH3), 2.22 (3H, s, ArNCH3), 3.10, (3H, s, ArNCH3), 3.39
(2H, dd, CHH), 4.90 (2H, dd, CHH), 6.2-7.0 (9H, complex, 3
py-H, 6 arom. H), 9.11 (1H, d, py-Ho). 19F NMR (C6D6):
δ
-127.5 (2F, s, arom. uncoord. o-F, J FH ) 6.28), 45.8 (1F, s,
Hf-F, J FH ) 6.26).
Gen er a l P r oced u r e for th e P r ep a r a tive P olym er iza -
tion of 1-Hexen e a t 0 °C. Suspensions of [Ph3C][B(C6F5)4]
(0.0221 g, 0.024 mmol) and an equimolar amount of [ArCl2]Hf-
(i-Bu)2 in equal volumes of bromobenzene (total solution
volume, including 1-hexene ) 3 mL) were cooled to -40 °C
and mixed. The activated complex was again cooled to -40 °C
and transferred to a reaction bomb to which 1-hexene was
added. The reaction bomb was sealed with a Teflon screw cap,
shaken, removed from the glovebox, and cooled in an ice bath
for the length of the polymerization. Methanol was added to
the reaction after 6 h for the {[ArCl2Npy]Hf(i-Bu)}{B(C6F5)4}
system and after 9 h for the {[ArF2Npy]Hf(i-Bu)}{B(C6F5)4}
[Ar F2Np y]HfCl2. This compound was the byproduct of failed
1
direct method reaction. H NMR (C6D6): δ 0.84 (3H, s, CH3),
3.26 (2H, d, CHH), 4.39 (2H, d, CHH), 6.18 (2H, m, ArF2 p-H),
6.36 (1H, t, py-H), 6.52 (4H, m, ArF2 m-H), 6.61 (1H, d, py-H),
6.80 (1H, t, py-H), 9.52 (1H, d, py-Ho). 19F NMR (C6D6): δ
-118.7 (4F, s, arom. o-F, J FH ) 6.03).
[Ar F 2Np y]Hf(i-Bu )2. HfCl4 (0.428 g, 1.34 mmol) and H2-
[ArF2 Npy] (0.496 g, 1.27 mmol) were dissolved in dichlo-
romethane (150 mL), and the reaction was stirred at room
temperature for 36 h. Dichloromethane was removed in vacuo
to afford a yellow powder, which was suspended in ether (100

Ortho Halides in 1-Hexene Polymerization
Organometallics, Vol. 22, No. 24, 2003 5091
system. After stirring the solution at room temperature for 1
min, all volatiles were removed in vacuo and the polymer was
extracted into pentane. The pentane solution was filtered
through silica gel and Celite, and the pentane was then
removed in vacuo to afford a colorless viscous oil, which was
used for further NMR and GPC studies.
(v) To Give {[Ar F 2Np y]HfMe}{B(C6F 5)4} a n d P h 3CCH3.
1H NMR (C6D6Br): δ 0.44 (3H, s, Hf-CH3), 1.23 (3H, s, ligand
CH3), 2.09 (3H, s, Ph3CCH3), 3.78 (2H, d, CHH), 3.94 (2H, d,
CHH), 6.40-7.80 (aromatics), 8.26 (1H, d, o-py-H). 19F NMR
(C6D6): δ -116.1 (4F, s, arom. o-F).
(vi) To Give {[Ar F 2;F NMe2Np y]H fMe}{B(C6F 5)4} a n d
P h 3CCH3. 1H NMR (C6D6Br): δ 0.38 (3H, s, Hf-CH3), 1.25 (3H,
s, CH3), 2.09 (3H, s, Ph3CCH3), 2.13 (3H, s, ArNCH3), 2.78 (3H,
s, ArNCH3), 3.35 (1H, d, CHH), 3.39 (1H, dd, CHH), 3.97 (1H,
d, CHH), 4.23 (1H, dd, CHH), 6.3-7.6 (aromatics), 8.20 (1H,
d, py-Ho).
Activa tion of [Ar X2Np y]HfR2 w ith [P h 3C][B(C6F 5)4]. (i)
To Give {[Ar Cl2Np y]H f(i-Bu )}{B(C6F 5)4}, P h 3CH , a n d
1
Isobu ten e. H NMR (C6D5Br): δ 0.77 (6H, d, CH2CH(CH3)2),
1.03 (2H, d, CH2CH(CH3)2), 1.26 (3H, s, CH3), 1.62 (6H, s,
isobutene), 2.09 (1H, p, CH2CHMe2), 3.64 (2H, d, CHH), 4.13
(2H, d, CHH), 4.70 (2H, s, isobutene), 5.45 (1H, s, Ph3CH)
6.61-7.59 (aromatics), 8.29 (1H, d, py-Ho).
(ii) To Give {[Ar Cl2Np y]Zr Me}{B(C6F 5)4} a n d P h 3CCH3.
1H NMR (C6D5Br): δ 0.88 (3H, s, Zr-CH3), 1.30 (3H, s, CH3),
2.09 (3H, s, Ph3CCH3), 3.06 (2H, d, CHH), 4.54 (2H, d, CHH),
6.69 (2H, arom. p-H), 7.25 (1H, d, m-py-H), 7.63 (1H, t, p-py-
H), 8.25 (1H, d, py-Ho).
Ack n ow led gm en t. We thank the Department of
Energy (DE-FG02-86ER13564) for supporting this re-
search, and Dr. William M. Davis for assistance with
X-ray studies. K.R. thanks the Deutsche Forschungs-
gemeinschaft for partial support in the form of a
postdoctoral fellowship.
(iii) To Give {[Ar Cl2Npy]HfMe}{B(C6F5)4}} an d P h 3CCH3.
1H NMR (C6D5Br): δ 0.63 (3H, s, Hf-CH3), 1.33 (3H, s, CH3),
2.09 (3H, s, Ph3CCH3), 3.45 (2H, d, CHH), 4.45 (2H, d, CHH),
6.64 (2H, t, arom. p-H), 7.27 (1H, d, m-py-H), 7.64 (1H, t, p-py-
H), 8.25 (1H, d, py-Ho). 13C NMR: δ 60.32 (s, Hf-CH3).
(iv) To Give {[Ar F 2Np y]Hf(i-Bu )}{B(C6F 5)4}, P h 3CH,
a n d Isobu ten e. 1H NMR (C6D5Br): δ 0.97 (6H, d, CH2CH-
(CH3)2), 1.09 (2H, q, CH2CH(CH3)2), 1.22 (3H, s, CH3), 1.62
(6H, s, isobutene), 2.31 (1H, p, CH2CHMe2), 3.67 (2H, d, ligand
CHH), 4.02 (2H, d, ligand CHH), 4.70 (2H, s, isobutene), 5.45
Su p p or tin g In for m a tion Ava ila ble: Fully labeled ther-
mal ellipsoid drawing, crystal data and structure refinement,
atomic coordinates, bond lengths and angles, anisotropic
displacement parameters, and hydrogen coordinates for [ArCl2
-
Npy]Hf(i-Bu)2, [Ar(FNMe2)2Npy]Hf(F)Cl, and [ArF2Npy]Hf(i-Bu)2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(1H, s, Ph3CH), 6.48-7.66 (aromatics), 8.35 (1H, d, py-Ho). 19
NMR (C6D6): δ -117.2 (4F, s, arom. o-F).
F
OM0305364