Intra- and intermolecular NMR studies on the activation of arylcyclometallated hafnium pyridyl-amido olefin polymerization precatalysts

Article abstract of DOI:10.1021/ja802072n

Pyridyl-amido catalysts have emerged recently with great promise for olefin polymerization. Insights into the activation chemistry are presented in an initial attempt to understand the polymerization mechanisms of these important catalysts. The activation of C₁-symmetric arylcyclometallated hafnium pyridylamido precatalysts, denoted Me₂Hf{N^-,N,C ^-} (1, aryl = naphthyl; 2, aryl = phenyl), with both Lewis (B(C ₆F₅)₃ and [CPh₃][B(C ₆F₅)₄]) and Bronsted ([HNR ₃][B(C₆F₅)₄]) acids is investigated. Reactions of 1 with B(C₆F₅)₃ lead to abstraction of a methyl group and formation of a single inner-sphere diastereoisomeric ion pair [MeHf{N^-,N,C^-}][MeB(C ₆F₅)₃] (3). A 1:1 mixture of the two possible outer-sphere diastereoisomeric ion pairs [MeHf{N^-,N,C ^-}][B(C₆F₅)₄] (4) is obtained when [CPh₃][B(C₆F₅)₄] is used. [HNR ₃][B(C₆F₅)₄] selectively protonates the aryl arm of the tridentate ligand in both precatalysts 1 and 2. A remarkably stable [Me₂Hf{N^-,N,C₂}][B(C₆F ₅)₄] (5) outer-sphere ion pair is formed when the naphthyl substituent is present. The stability is attributed to a hafnium/η ²-naphthyl interaction and the release of an eclipsing H-H interaction between naphthyl and pyridine moieties, as evidenced through extensive NMR studies, X-ray single crystal investigation and DFT calculations. When the aryl substituent is phenyl, [Me₂Hf{N^-,N,C ₂}][B(C₆F₅)₄] (10) is originally obtained from protonation of 2, but this species rapidly undergoes remetalation, methane evolution, and amine coordination, giving a diastereomeric mixture of [MeHf{N^-,N,C^-}NR₃][B(C₆F ₅)₄] (11). This species transforms over time into the trianionic-ligated [Hf{N^-,C^-,N,C^-}NR ₃][B(C₆F₅)₄] (12) through activation of a C-H bond of an amido-isopropyl group. In contrast, ion pair 5 does not spontaneously undergo remetalation of the naphthyl moiety; it reacts with NMe₂Ph leading to [MeHf{N^-,N}NMe₂C ₆H₄][B(C₆F₅)₄] (7) through orthometalation of the aniline. Ion pair 7 successively undergoes a complex transformation ultimately leading to [Hf{N^-,C ^-,N,C^-}NMe₂Ph][B(C₆F ₅)₄] (8), strictly analogous to 12. The reaction of 5 with aliphatic amines leads to the formation of a single diastereomeric ion pair [MeHf{N^-,N,C^-}NR₃][B(C₆F ₅)₄] (9). These differences in activation chemistry are manifested in the polymerization characteristics of these different precatalyst/cocatalyst combinations. Relatively long induction times are observed for propene polymerizations with the naphthyl precatalyst 1 activated with [HNMe₃Ph][B(C₆F₅)₄]. However, no induction time is present when 1 is activated with Lewis acids. Similarly, precatalyst 2 shows no induction period with either Lewis or Bransted acids. Correlation of the solution behavior of these ion pairs and the polymerization characteristics of these various species provides a basis for an initial picture of the polymerization mechanism of these important catalyst systems.

Full text of DOI:10.1021/ja802072n

Published on Web 07/10/2008
Intra- and Intermolecular NMR Studies on the Activation of
Arylcyclometallated Hafnium Pyridyl-Amido Olefin
Polymerization Precatalysts
Cristiano Zuccaccia,† Alceo Macchioni,*,† Vincenzo Busico,‡ Roberta Cipullo,‡
Giovanni Talarico,‡ Francesca Alfano,‡ Harold W. Boone,§ Kevin A. Frazier,|
Phillip D. Hustad,§ James C. Stevens,§ Paul C. Vosejpka,| and Khalil A. Abboud
Department of Chemistry, UniVersity of Perugia, Via Elce di Sotto, 8, 06123 Perugia, Italy,
Department of Chemistry, UniVersity of Napoli, Via Cintia, 80126 Napoli, Italy, The Dow
Chemical Company, 2301 North Brazosport BouleVard, B-1814, Freeport, Texas 77541, The
Dow Chemical Company, 1776 Building, Midland, Michigan 48674, and Department of
Chemistry, UniVersity of Florida, GainesVille, Florida 32611
Received March 25, 2008; E-mail: alceo@unipg.it
Abstract: Pyridyl-amido catalysts have emerged recently with great promise for olefin polymerization.
Insights into the activation chemistry are presented in an initial attempt to understand the polymerization
mechanisms of these important catalysts. The activation of C1-symmetric arylcyclometallated hafnium pyridyl-
amido precatalysts, denoted Me2Hf{N-,N,C-} (1, aryl ) naphthyl; 2, aryl ) phenyl), with both Lewis (B(C6F5)3
and [CPh3][B(C6F5)4]) and Brønsted ([HNR3][B(C6F5)4]) acids is investigated. Reactions of 1 with B(C6F5)3
lead to abstraction of a methyl group and formation of a single inner-sphere diastereoisomeric ion pair
[MeHf{N-,N,C-}][MeB(C6F5)3] (3). A 1:1 mixture of the two possible outer-sphere diastereoisomeric ion
pairs [MeHf{N-,N,C-}][B(C6F5)4] (4) is obtained when [CPh3][B(C6F5)4] is used. [HNR3][B(C6F5)4] selectively
protonates the aryl arm of the tridentate ligand in both precatalysts 1 and 2. A remarkably stable
[Me2Hf{N-,N,C2}][B(C6F5)4] (5) outer-sphere ion pair is formed when the naphthyl substituent is present.
The stability is attributed to a hafnium/η2-naphthyl interaction and the release of an eclipsing H-H interaction
between naphthyl and pyridine moieties, as evidenced through extensive NMR studies, X-ray single crystal
investigation and DFT calculations. When the aryl substituent is phenyl, [Me2Hf{N-,N,C2}][B(C6F5)4] (10) is
originally obtained from protonation of 2, but this species rapidly undergoes remetalation, methane evolution,
and amine coordination, giving a diastereomeric mixture of [MeHf{N-,N,C-}NR3][B(C6F5)4] (11). This species
transforms over time into the trianionic-ligated [Hf{N-,C-,N,C-}NR3][B(C6F5)4] (12) through activation of a
C-H bond of an amido-isopropyl group. In contrast, ion pair 5 does not spontaneously undergo remetalation
of the naphthyl moiety; it reacts with NMe2Ph leading to [MeHf{N-,N}NMe2C6H4][B(C6F5)4] (7) through ortho-
metalation of the aniline. Ion pair 7 successively undergoes a complex transformation ultimately leading to
[Hf{N-,C-,N,C-}NMe2Ph][B(C6F5)4] (8), strictly analogous to 12. The reaction of 5 with aliphatic amines
leads to the formation of a single diastereomeric ion pair [MeHf{N-,N,C-}NR3][B(C6F5)4] (9). These
differences in activation chemistry are manifested in the polymerization characteristics of these different
precatalyst/cocatalyst combinations. Relatively long induction times are observed for propene polymerizations
with the naphthyl precatalyst 1 activated with [HNMe3Ph][B(C6F5)4]. However, no induction time is present
when 1 is activated with Lewis acids. Similarly, precatalyst 2 shows no induction period with either Lewis
or Brønsted acids. Correlation of the solution behavior of these ion pairs and the polymerization
characteristics of these various species provides a basis for an initial picture of the polymerization mechanism
of these important catalyst systems.
Introduction
1. Performance of these catalysts is unique and truly remarkable.
In particular, highly isotactic high molecular weight propene
An important class of C1-symmetric (pyridyl-amido)Hf(IV)-
based olefin polymerization catalysts was recently discovered
by means of high throughput screening technologies.1–3 The
general structure of the neutral precatalysts is shown in Chart
homopolymers and copolymers can be produced at very high
reaction temperatures, enabling their production in solution
process technologies.4 In ethylene/1-alkene copolymerizations,
higher 1-alkenes (such as 1-hexene or 1-octene) are effectively
incorporated. Last but not least, under proper conditions, the
active species are amenable to fast and reversible trans-alkylation
with main group metal-alkyls (such as ZnR2); this can be used
advantageously in the preparation of olefin block copolymers
via “chain shuttling”.5
† University of Perugia.
‡ University of Napoli.
§ The Dow Chemical Company, Texas.
| The Dow Chemical Company, Michigan.
University of Florida.
9
10354 J. AM. CHEM. SOC. 2008, 130, 10354–10368
10.1021/ja802072n CCC: $40.75
2008 American Chemical Society

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
Chart 1
From the structural point of view, precatalysts shown in Chart
1 are unconventional and peculiar in several respects. A most
notable feature is the ortho-metalation of the aryl substituent
on the pyridine ring, resulting in tridentate ligation of the
pyridyl-amido moiety and a slightly distorted trigonal bipy-
ramidal Hf coordination.3 A second important structural element
is a stereogenic carbon linking the pyridyl and the amido
fragments; albeit remote from the active site, this chiral center
appears to influence enantioselectivity in the insertion of
prochiral 1-alkenes.3 A third feature is the high Lewis acidity
of the 5-coordinate 12e- Hf(IV) center, which is further
enhanced upon activation with cocatalysts.
Scheme 1. Hafnium Pyridyl-Amido Dimethyl Complexesa
Despite the well-defined nature of the precatalysts (Chart 1),
catalysts derived from them exhibit polymerization character-
istics indicative of multiple catalytic species. For example,
ethylene copolymers from these precatalysts normally display
multimodal molecular weight and composition distributions.6
To gain understanding of the mechanism of these important and
intriguing systems, we undertook a comprehensive experimental
and computational investigation of their reactivity. Integrated
results of intra- and intermolecular solution NMR studies, X-ray
crystallography, density functional theory (DFT) calculations,
and ad hoc (poly-)-insertion experiments revealed a complex
and in some respects surprising picture. In this manuscript, we
describe interactions of precatalyst with various cocatalysts. A
subsequent report will focus on chain initiation reactions. While
the activation of precatalysts shown in Chart 1 with Lewis acids
is in line with the normal observations described for other
precatalysts for olefin polymerization,7–9 an additional layer of
complexity appears when the activation is carried out with
a The stereoisomer with (R)-Configuration at C* is shown although
racemic mixtures were used.
Scheme 2. Activation Chemistry of 1 with B(C6F5)3 to Give
Inner-Sphere Ion Pairs 3
Brønsted acids. This is substantially due to the presence of the
cyclometalated aryl moiety that provides an alternative site for
protonation with respect to other dimethyl precatalysts.
(1) (a) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe,
A. M.; Leclerc, M. K.; Lund, C.; Murphy, V. U.S. Patent Appl.
0135722 A1, 2006. (b) Boussie, T. R.; Diamond, G. M.; Goh, C.;
Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Lund, C.; Murphy, V.
U.S. Patent 7,018,949, 2006. (c) Boussie, T. R.; Diamond, G. M.;
Goh, C.; LaPointe, A. M.; Leclerc, M. K.; Lund, C.; Murphy, V. U.S.
Patent 6,750,345, 2004. (d) Boussie, T. R.; Diamond, G. M.; Goh,
C.; Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Lund, C.; Murphy,
V. U.S. Patent 6,713,577, 2004. (e) Boussie, T. R.; Diamond, G. M.;
Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Lund, C.;
Murphy, V. U.S. Patent 6,706,829, 2004. (f) Boussie, T. R.; Diamond,
G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Lund,
C.; Murphy, V. PCT Int. Appl. WO 046249, 2002. (g) Boussie, T. R.;
Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc,
M. K.; Lund, C.; Murphy, V. PCT Pat. Appl. WO 038628, 2002.
(2) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.;
Leclerc, M. K.; Lund, C.; Murphy, V.; Shoemaker, J. A. W.; Tracht,
U.; Turner, H.; Zhang, J.; Uno, T.; Rosen, R. K.; Stevens, J. C. J. Am.
Chem. Soc. 2003, 125, 4306.
Results and Discussion
In an attempt to understand the complex polymerization
characteristics exhibited by these catalyst systems, we initially
set out to characterize the ion pairs resulting from reaction of
the dimethyl derivatives 1 and 2 (Scheme 1 and Figure S1 of
the Supporting Information) with typical cocatalysts. We decided
not to explore methylalumoxane (MAO) because of its complex
solution NMR spectra and instead focused on two well-known
Lewis acids, B(C6F5)3 and [CPh3][B(C6F5)4], and the Brønsted
acid [HNMe2Ph][B(C6F5)4]. Characterization of the resulting ion
pairs in solution was performed using an array of NMR
techniques and is described in detail as follows. For the
discussion, the structure of the ligand is abbreviated as
{N-,N,C-} to indicate a tridentate species with a neutral Hf-
pyridyl bond (N) and anionic Hf-amide (N-) and Hf-carbon
(C-) bonds. Similarly, the ligand in a dimethyl complex where
the aryl has been protonated would be designated {N-,N,C2}.
Activation with Lewis Acids. a. B(C6F5)3. The reaction of
B(C6F5)3 with complexes 1a and 1b leads to the selective
abstraction of the methyl group Me-37, which lies in the pseudo-
cis position with respect to H-17, and formation of inner-sphere
ion pairs (ISIPs) 3a and 3b, as shown in Scheme 2. The broad
B-Me resonance observed around 3 ppm in the 1H NMR
spectrum provides evidence of methide abstraction; this reso-
nance is typical of a MeB(C6F5)3- counterion partially coordi-
nated to the metal.10 Consistent with this partial coordination,
(3) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.;
Leclerc, M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen,
R. K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G.
Angew. Chem., Int. Ed. 2006, 45, 3278.
(4) (a) Arriola, D. J.; Bokota, M.; Timmers, F. J. PCT Int. Appl. WO
026925 A1, 2004. (b) Frazier, K. A.; Boone, H.; Vosejpka, P. C.;
Stevens, J. C. U.S. Patent Appl. 0220050 A1, 2004. (c) Tau, L.-M.;
Cheung, Y. W.; Diehl, C. F.; Hazlitt, L. G. U.S. Patent Appl. 0087751
A1, 2004. (d) Tau, L.-M.; Cheung, Y. W.; Diehl, C. F.; Hazlitt, L. G.
U.S. Patent Appl. 0242784 A1, 2004. (e) Coalter, J. N., III; Van
Egmond, J. W.; Fouts, L. J., Jr.; Painter, R. B.; Vosejpka, P. C. PCT
Int. Appl. WO 040195 A1, 2003. (f) Stevens, J. C.; Vanderlende, D. D.
PCT Int. Appl. WO 040201 A1, 2003.
(5) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel,
T. T. Science 2006, 312, 714.
(6) Froese, R. D. J.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. J. Am.
Chem. Soc. 2007, 129, 7831.
(7) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391.
(8) Britovsek, G. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
1999, 38, 428.
(9) (a) Macchioni, A. Chem. ReV. 2005, 105, 2039. (b) Bochmann, M. J.
Organomet. Chem. 2004, 689, 3982.
(10) Axenov, K. V.; Martti, K.; Markku, L.; Repo, T. Organometallics
2005, 24, 1336.
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10355

A R T I C L E S
Zuccaccia et al.
Figure 1. Full QM-optimized structures of the ion pairs 3a with the coordination of the anion in a pseudo-cis position with respect to H17 (3a) and in
pseudo-trans position (3a′). For the sake of visibility, some H atoms are omitted and the [MeB(C6F5)3]- anion is reported with the methyl group in scale and
B(C6F5)3 moiety as a ball. Distances are in Å.
Scheme 3. Activation Chemistry of 1b with [CPh3][B(C6F5)4],
a ∆δ(m-F, p-F) of 4.7 ppm is observed in the 19F NMR
spectrum.11 The selectivity of the Me-abstraction is indicated
by the observation of intense NOEs between the remaining Hf-
Me38 group and H2, H19, and H31, while no interaction is
observed with H35. The anion coordination in a pseudo-cis
position with respect to H17 is supported by the 19F,1H HOESY
NMR experiment;12 the o-F shows strong interionic interactions
with H2, H34, H32, and H35, while none is observed with H31.
In addition, very weak interionic contacts are present between
cationic H32 and H35 resonances and the m-F, in agreement
with an orientation in which the anion steadily points Me-37
toward the Hf atom.13,14 An exchange NOE cross peak between
the broad B-Me resonance and Me38 is also observed in a
phase-sensitive 1H-nuclear Overhauser effect spectroscopy
(NOESY) experiment. This suggests that the other diastereoi-
someric ion pair, with MeB(C6F5)3- in a pseudo-trans position
with respect to H17, is accessible, but its abundance is under
the threshold of detection of the NMR spectroscopy. As a
consequence, 3a,b are thermodynamically favored with respect
to the other possible diastereoisomers.
The activation reaction of 1a (Scheme 2) was also evaluated
theoretically using full quantum mechanical (QM) calculations
(see Supporting Information for details). The calculated enthalpy
for the methide abstraction reaction is -17 kcal/mol. As
expected, correcting for solvation effects with the COSMO
model15 does not change the ∆H value significantly (-16.6 kcal/
mol), as there is no net charge separation on either side of the
reaction. The calculated value is in line with the few experi-
mental values reported for metallocene systems (e.g., Cp2ZrMe2
precatalyst, where a ∆H value of -23.1 kcal/mol was measured
by titration calorimetry)16 and with similar computations done
by Ziegler et al.17 In agreement with NOE NMR results, the
ion pair with the anion in the pseudo-cis position with respect
Including Significant Chemical 13C Shift Values
to H17 (Figure 1, 3a) is more stable compared to the one in the
pseudo-trans position (Figure 1, 3a′) by 0.7 kcal/mol.18
Ion pairs 3a and 3b have limited stability at room temperature
in benzene or toluene solution under an inert atmosphere. After
a few hours, they begin to decompose through a process
involving both single and double C6F5-transfers19 forming
MeB(C6F5)2 and Me2B(C6F5).20,21
b. [CPh3][B(C6F5)4]. The reaction of complex 1b with 1 equiv
of [CPh3][B(C6F5)4] in toluene-d8 proceeds quantitatively, giving
two diastereoisomeric ion pairs 4b and 4b′ in approximately a
1:1 ratio (Scheme 3). Although the complete assignment of the
NMR resonances of 4b and 4b′ is hampered by extensive
overlapping and the 1:1 abundance ratio, a partial assignment
1
can be performed upon inspection of the low temperature H
rotating frame Overhauser effect spectroscopy (ROESY) spec-
trum (Supporting Information).
(18) This value does not take into account the entropic effect. In fact, for
the structure 3a we found two stable species with the same energy
which differs for the relative configuration of the B(C6F5)3 moiety.
This is not true for 3a′.
(19) For some examples of C6F5-transfer to the metal see:(a) Phomphrai,
K.; Fenwick, A. E.; Sharma, S.; Fanwick, P. E.; Caruthers, J. M.;
Delgass, W. N.; Abu-Omar, M. M.; Rothwell, J. P. Organometallics
2006, 25, 214. (b) Metcalfe, R. A.; Kreller, D. I.; Tian, J.; Kim, H.;
Taylor, N. J.; Corrigan, J. F.; Collins, S. Organometallics 2002, 21,
1719. (c) Woodman, T. J.; Thornton-Pett, M.; Hughes, D. L.;
Bochmann, M. Organometallics 2001, 20, 4080. (d) Guerin, F.;
Stewart, J. C.; Beddie, C.; Stephan, D. W. Organometallics 2000, 19,
2994–3000. (e) Scollard, J. D.; McConville, D. H.; Rettig, S. J.
Organometallics 1997, 16, 1810. (f) Yang, X. M.; Stern, C. L.; Marks,
T. J. J. Am. Chem. Soc. 1994, 116, 10015. For a recent theroretical
work see: (g) Wondimagegn, T.; Xu, Z.; Vanka, K.; Ziegler, T.
Organometallics 2004, 23, 3847, and references therein.
(11) The value of ∆d(m,p-F) (19F NMR) is a good probe of coordination
-
of MeB(C6F5)3 to cationic d0 metals (values of 3-6 ppm indicate
coordination; <3 ppm indicates non-coordination). See : Horton, A. D.;
de With, J. Organometallics 1997, 16, 5424, and references therein.
(12) Macchioni, A. Eur. J. Inorg. Chem. 2003, 195, and references therein.
(13) Correa, A.; Cavallo, L. J. Am. Chem. Soc. 2006, 128, 10952.
(14) Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M.-C.; Roberts,
J. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448.
(20) Krempner, C.; Ko1ckerling, M.; Reinke, H.; Weichert, K. Inorg. Chem.
2006, 45, 3203.
(15) Pye, C. C.; Ziegler, T. Theor. Chim. Acta 1999, 101, 396.
(16) (a) Deck, P. A.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 6128. (b)
Deck, P. A.; Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 1998,
120, 1772.
(21) Although structures of the hafnium-containing decomposition products
were difficult to assign, the appearance of high frequency resonances
in the 19F NMR spectrum (around-120 ppm) suggests the formation
of Hf-C6F5 fragments : Tonzetich, Z. J.; Schrock, R. R. Polyhedron
2006, 25, 469.
(17) Xu, Z.; Vanka, K.; Firman, T.; Michalak, A.; Zurek, E.; Zhu, C.;
Ziegler, T. Organometallics 2002, 21, 2444.
9
10356 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
Scheme 4. Activation Chemistry of 1a,b with [HNMe2Ph][B(C6F5)4]
Exchange cross peaks are observed in the 1H NOESY
spectrum recorded at room temperature between resonances of
4b and 4b′, indicating that, as for 3a,b, the observed abundance
ratio is dictated by thermodynamics. The observation of a 1:1
ratio for 4b and 4b′ suggests that the vacant coordination site,
derived from the abstraction of the methyl group, remains
substantially unoccupied and can be “kinetically” stabilized by
the bulky 2,6-diisopropylphenyl moiety or involved in weak
interactions with solvent or counterion. In all cases, 4b and 4b′
have to be considered outer-sphere ion pairs (OSIPs).22
The results of theoretical investigations (see section 1.1 and
Figure S2 of the Supporting Information) are again consistent
with these observations. In fact, the energy of the two diaste-
reoisomeric ion pairs is substantially the same (∆E < 0.2 kcal/
mol), indicating no diastereoselectivity for the activation pro-
cess.23
In contrast to 3a and 3b, the mixture 4b/4b′ is stable in
toluene-d8 solution for days at room temperature in the absence
of light. Exposure to sunlight or the use of more polar and
coordinating solvents, such as C6D5Cl, causes rapid decomposi-
tion to a complex mixtures of species.
Activation with Brønsted Acids. a. Naphthyl Precatalysts,
1a,b. As mentioned above, the activation of 1 and 2 with Lewis
acids is not unusual compared to that of other dialkyl precata-
lysts. However, the chemistry observed in combination with
Brønsted acids is strikingly different and makes this catalyst
family unique. The reaction of 1a and 1b with
[HNMe2Ph][B(C6F5)4] proceeds with selective protonation of
the Hf-napthyl bond and formation of 5a and 5b OSIPs
(Scheme 4) rather than liberation of methane as is typical of
other dimethyl precatalysts.
Figure 2. Two sections of the 1H NOESY NMR spectrum of complex 5b
(C6D5Cl, 298 K). The upper section shows the selective interactions of H37
with H7, H6, H5, and H8 and those of H38 with H19, H1, H2, and H3,
while, in the lower section, the selective and strong interaction between
H34 and H8 is illustrated.
Table 1. 13C NMR Chemical Shifts for the Naphthyl Protons of
Complexes 1 and 5-9
1a
1b
5a
5b
6a
7b
8b
9b
C1
C2
C3
C4
C5
C6
C7
C8
C9
206.7 206.8 133.6 132.9 122.7 127.6
134.8 134.8 131.9 131.3 130.2 127.7
206.1 202.2
132.1 131.5
130.6 130.5 134.0 133.3 136.8 134.1 ∼128.5 131.2
136.4 136.4 138.7 137.9 136.8
135.4 135.8
129.9 130.0
127.0 127.6
130.6 130.6 137.9 137.2 131.2 130.5
126.2 126.2 131.7 131.0 133.4 130.1
127.6 127.6 143.9 143.0 133.0 130.1 ∼128.5 128.9
127.3 124.9 114.1 113.3 124.6 124.1
131.3 131.4 128.6 127.7 129.3
123.7 123.7
130.8 129.8
142.3 144.5
Protonation of the Hf-naphthyl bond is demonstrated by the
disappearance of the high-frequency 13C NMR resonance
(around 200 ppm), and the appearance of an additional aromatic
C-H moiety. The naphthyl orientation in solution after de-
metalation is deduced by analyzing the 1H NOESY NMR
spectrum (Figure 2). The following selective contacts are
present: H37 with H7 (strong), H6 (strong), H8 (medium), and
H5 (medium); H38 with H1 (medium), H2 (medium), and H3
(weak); H1 with H12; H8 with H34. The average distance in
solution between H34 and H8, estimated by semiquantitative
analysis of NOESY data, is 2.94 Å.24 These observations
C10 144.7 144.7 130.7 129.9 133.4
indicate that the C6H4 moiety of the napthyl group is oriented
toward H34 as shown in Figure 2. In agreement, both resonances
of the terminal Hf-Me groups appear at lower frequency
compared to the neutral precatalysts (H37, δH ) -0.50 ppm in
5a and -0.49 ppm in 5b; H38, δH ) -0.29 ppm in 5a and
-0.25 ppm in 5b), due to the shielding effect exerted by the
naphthyl group. In addition, variations in the 13C NMR shifts
of naphthyl carbons of 1a,b and 5a,b suggest an electronic
interaction between the naphthyl unit and the metal center (Table
1).
Differences in the 13C chemical shift of C7-C10 are
comparable or even higher than those observed for benzene or
toluene coordination to a group 4 d0 metal25 and for unsym-
metrical (η1-fashion) olefin coordination in metallocene-based
(22) Schrock, R. R.; Casado, A. L.; Goodman, J. T.; Liang, L-C.;
Bonitatebus, P. J. J.; Davis, W. M. Organometallics 2000, 19, 5325.
(23) The heterolytic separation of the [MeHf{N-,N,C-}][B(C6F5)4] ion pair
with the solvent inclusion is calculated lower than the one for
[MeHf{N-,N,C-}][MeB(C6F5)3] ion pair (see Supporting Information).
(24) Integration of NOESY cross peaks in the initial rate approximation
(see Neuhaus, D.; Williamson, M. The Nuclear OVerhauser Effect in
Structural and Conformational Analysis, Wiley-VCH: New York,
2000; Chapter 4) gave the following relative values: AH7/H8 ) 1;
AH34/H17 ) 1.06; AH34/H8 ) 0.35. The distance between H7 and H8,
2.47 Å, (Zuccaccia, C.; Bellachioma, G.; Cardaci, G.; Macchioni, A.
J. Am. Chem. Soc. 2001, 123, 11020. was used as reference distance,
affording 2.44 and 2.94 Å for H34/H17 and H34/H8 distances,
respectively.
(25) (a) Deckers, P. J. W.; van der Linden, A. J.; Meetsma, A.; Hessen, B.
Eur. J. Inorg. Chem. 2000, 929. (b) Lancaster, S. J.; Robinson, O. B.;
Bochmann, M.; Coles, S. J.; Hursthouse, M. B. Organometallics 1995,
14, 2456.
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10357

A R T I C L E S
Zuccaccia et al.
Figure 3. X-ray crystallographic characterization of 5b, displaying (a) an ORTEP drawing of the cationic portion of the ion pair and (b) a CPK representation
of the ion pair in almost the same orientation, displaying the shortest Hf-B distance (7.230 Å) in the solid state. Some hydrogen atoms are omitted in both
drawings for the sake of clarity.
systems.26 It appears clear that C8, which shows the largest
decrease in chemical shift, is involved in naphthyl coordination
(Table 1). Both the Hf-naphthyl interaction and the release of
the strong H-H eclipsing interaction between H8 and H12,
originally present in the neutral precatalyst (vide infra), impart
stability to 5a and 5b ion pairs, which do not show any sign of
decomposition in toluene after 10 days at room temperature.
As far as cation-anion interactions are concerned, there are
six anions surrounding each cation in the solid state. The one
displaying the shortest Hf-B distance (7.230 Å, Figure 3b) is
located close to the backbone of the pyridyl-amido ligand, on
the side of H17, in good agreement with the average solution
interionic OSIP structure determined by 19F,1H HOESY
experiments.
A
19F,1H HOESY experiment allows location of the anion
To determine whether and under what conditions the remeta-
lation of 5 takes place, the reactivities of ion-pairs 5a and 5b
were investigated under conditions similar to those employed
in typical polymerizations. These experiments included inves-
tigations at higher reaction temperatures and combinations with
other reagents that can be present during polymerizations, such
as Lewis and Brønsted acids and other nucleophiles. This
chemistry is described below and summarized in Scheme 5.
Increasing the temperature of solutions of 5a,b in different
solvents leads to evolution of CH4 and decomposition both in
the absence and presence of an excess of AlMe3. Addition of a
stoichiometric amount of B(C6F5)3 to a benzene-d6 solution of
5a does not produce any immediate detectable reaction, but
extensive decomposition is observed after two days.27 No
indication of naphthyl remetalation is observed in either case.
The reaction of 5a with a stoichiometric amount of
[HNMe2Ph][B(C6F5)4] leads to selective protonation of Me37,
evolution of CH4, and occupation of the generated coordination
site by NMe2Ph to afford ion pair 6a (Scheme 5, pathway A).
Consistently, the remaining Hf-Me38 methyl group shows
intense NOEs with H31 and H32, indirectly demonstrating the
selective protonation of Me37. The NOE contacts of H8 with
H12 and H38 with H1 and H2 indicate that the naphthyl moiety
is now almost perpendicularly oriented to the pyridyl ring and
is no longer coordinated to the Hf center. This decoordination
is also supported by the chemical shift values of C7-C10, which
are similar to those of 1a,b (Table 1). Interestingly, the
coordinated NMe2Ph shows seven 1H resonances, five aromatic
and two aliphatic, indicating a restricted rotation around the
with respect to the cation. In this case, both the o-F and m-F
interact with selected cationic resonances in a fashion typical
of OSIPs;14 the o-F and m-F correlate with H14 (strong), H8
(strong), H13 (medium), H12 (medium), H7 (weak), H3 (weak),
H5 (weak), H1 (weak), H34 (weak), H36 (weak), H35 (weak),
and H17 (very weak). These results indicate that, in solution,
the anion is positioned close to the pyridyl-amido ligand, partly
shifted on the side of H17, and far away from the two terminal
methyl groups.
The solid state and theoretical structures of 5b are consistent
with the solution structure determined by NMR investigations.
An ORTEP drawing of the cationic portion of the species is
shown in Figure 3a. The naphthyl group is oriented toward H34,
as deduced in solution through NOE experiments, and has a
H8/H34 distance equal to 2.93 Å, in excellent agreement with
NOE results (2.94 Å). The closest distances from naphthyl
carbons to the hafnium center are observed for C8 (2.612 Å)
and C9 (2.737 Å), while the C8-C9 centroid is closer (2.576
Å), suggesting an η2-coordination of the naphthyl group. The
overall geometry around the metal center can be considered a
markedly distorted trigonal bipyramid having the pyridine
nitrogen N1 and C37 in apical positions, approaching a square
pyramid having C38 in the vertex.
The results of theoretical calculations are consistent with the
NOE results and the solid state structure 5b. In fact, the lowest
minima structure corresponds to 5b; however, a structure with
similar energy (<0.3 kcal/mol) showing a short C1-Hf distance
was also found, indicating an accessible restricted rotation of
the naphthyl group along the C10-C11 bond (see Figure S3 of
Supporting Information).
1
(27) The H NMR spectrum allows us to individuate some resonances of
MeB(C6F5)2 and Me2B(C6F5) (dH ) 0.96 and 1.33 ppm, respectively),
while the appearance of high frequency (around-120 ppm) resonances
in the 19F NMR spectrum suggests the formation of Hf-C6F5 fragments.
(26) (a) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 8638.
(b) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126, 11170.
9
10358 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
Scheme 5. Reactions of 5a,b with Possible Species Present in Polymerization Reactions
N-Cipso bond. The o-H/H39 and o-H′/H40 NOEs are of
comparable intensity (Figure 4) and are in agreement with an
almost perpendicular orientation of the aniline ring with respect
to the plane containing the Cipso-N bond that bisects the
Me-N-Me angle. The presence of Overhauser contacts of o-H
with H38, H3 and H2, m-H with H2, H3, and H1, o-H′ with
H35, and, most notably, p-H with H8 and H34 (Figure 4) shows
that the phenyl ring of the aniline is oriented toward the
backbone of the ligand. This orientation may be due to a partial
electronic interaction of the aniline arene ring with Hf, similar
to that observed in complex 5a and 5b for the naphthyl unit.
13C NMR data shows evidence of this through a high frequency
shift for m-C and Cipso (ca. 6 and ca. 2 ppm, respectively) and
a significant low frequency shift for the p-C (ca. 8 ppm).
Moreover, despite its bicationic nature, complex 6a is rather
stable in aromatic nonchlorinated solvents such as a benzene/
1,2-F2C6H4 mixture, but it slowly decomposes in CD2Cl2 at
room temperature.28 The 19F NMR spectrum of 6a displays the
typical resonances for uncoordinated [B(C6F5)4]- anions, while
the 19F,1H HOESY spectrum displays rather unselective inte-
rionic contacts as expected for a bicationic species.
reaction of 5b with NMe2Ph was investigated by an in situ
activation of 1b with [HNMe2Ph][B(C6F5)4] in C6D5Cl at room
temperature. As hypothesized, decoordination of the naphthyl
moiety and metalation does occur, but the latter does not involve
the naphthyl moiety. Instead, a C-H activation occurs at the
o-carbon of aniline,29,30 leading to the formation of 7b (Scheme
5, pathway B). The release of a terminal methyl group is
indicated by CH4 evolution and the final presence of a single
Hf-Me resonance (δH ) 1.40; δC ) 66.7 ppm). The metalation
of an o-carbon of aniline is evidenced by the observation of
two NMe2 resonances (δH ) 2.20 and 0.86 ppm; δC ) 46.4
and 41.1 ppm) that show strong NOEs, of similar intensities,
with the doublet at 6.70 ppm, assigned to the only ortho-proton
of the aniline present in the 1H NMR spectrum. The 1H COSY
spectrum (Supporting Information) undoubtedly indicates that
this o-H resonance is part of a scalarly coupled four-spin system
lacking one proton in the aniline ring. Aniline ortho metalation
is further supported by a high frequency resonance in the 13C
NMR spectrum (δC ) 192.9 ppm) that also has long-range
1
correlations with m-H′, p-H, and o-H in the H, 13C, HMBC
spectrum.
Another species that is surely present in solution when 1a,b
are activated with [HNMe2Ph][B(C6F5)4] is NMe2Ph. To
determine if the presence of this aniline may facilitate the η2-
decoordination and metalation of the naphthyl moiety, the
The three-dimensional structure of the cationic portion of 7b
1
1
can be inferred by analyzing the H NOESY and H ROESY
spectra. The Hf-Me moiety remains in a pseudo-trans position
with respect to H17 (NOEs with H1, H2, H19, and H31). The
carbon and nitrogen arms of the cyclometallated aniline are in
pseudo-trans31 and pseudo-cis32 positions with respect to the
pyridine nitrogen, respectively. The NOE interaction between
(28) The decomposition product could not be completely characterized;
1H NMR data are consistent with formation of a mixed-methyl-chloride
hafnium species having a structure similar to 5a, together with
[ClCD2NMe2Ph][B(C6F5)4]. 1H NMR for the Hf species (CD2Cl2, 298
3
3
K, J values in Hz): d 8.71 (d, JHH ) 8.4, H5), 8.67 (td, JHH ) 7.4,
(29) For examples of amine activation, see: (a) Krut’ko, D. P.; Borzov,
M. V.; Kirsanov, R. S.; Churakov, A. V.; Kuz’mina, L. G. J.
Organomet. Chem. 2005, 690, 3243. (b) Pflug, J.; Bertuleit, A.; Kehr,
G.; Fro¨hlich, R.; Erker, G. Organometallics 1999, 18, 3818.
(30) For examples of N,N-bis-alkyl-aniline ortho-metallation see: (a) Sole´,
D.; Vallverdu`, L.; Solans, X.; Font-Bard`ıa, M.; Bonjock, J. J. Am.
Chem. Soc. 2003, 125, 1587. (b) Drost, C.; Hitchcock, P. B.; Lappert,
M. F. Angew. Chem., Int. Ed. 1999, 38, 1113. (c) Edema, J. J. H.;
Gambarotta, S.; Meetsma, A.; Speks, A. L. Organometallics 1992,
11, 2452.
4JHH ) 1.1, H7), 8.58 (d, 3JHH ) 8.4, H3), 8.42 (t, 3JHH ) 8.0, H13),
8.33 (dd, JHH ) 8.4, 4JHH ) 7.3, H2), 8.21 (dd, JHH ) 7.3, 4JHH
)
3
3
1.1, H1), 8.14 (d, 3JHH ) 8.0, H12), 8.12 (td, 3JHH ) 7.3, 4JHH ) 1.1,
3
3
H6), 8.05 (d, JHH ) 7.8, H8), 7.45 (d, JHH ) 8.0, H14), 7.32 (m,
H28 and H29), 7.20 (m, H20 and H21), 7.10 (dd, 3JHH ) 7.2, 4JHH
)
)
3
4
3
1.7, H22), 7.00 (dd, JHH ) 7.3, JHH ) 2.0, H27), 6.87 (dd, JHH
4
3
7.2, JHH ) 1.6, H19), 6.51 (s, H17), 3.14 (sept, JHH ) 6.8, H34),
2.85 (sept, 3JHH ) 6.8, H31), 1.78 (s, H24), 1.57 (d, 3JHH ) 6.8, H36),
3
3
1.55 (d, JHH ) 6.8, H35), 0.90 (d, JHH ) 6.8, H32), 0.08 (s, H38),
0.04 (d, JHH ) 6.8, H33). 1H NMR for [ClCD2NMe2Ph][B(C6F5)4]
(31) H39 shows NOE peaks with H1, H2, and H3 while H40 shows an
NOE with H8.
(32) m-H′, p-H and o-H interact with H35.
3
(CD2Cl2, 298 K): 7.72 (m, 3 protons), 7.42 (m, 2 protons), 3.48 (s, 6
protons).
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10359

A R T I C L E S
Zuccaccia et al.
Figure 5. Full QM optimized structures of complexes 7b. For the sake of
visibility, H atoms are omitted with the exception of the ones discussed in
the text. The arrows display some important NOEs observed in solution.
The stereogenic carbon center linking the pyridyl and the amido fragment
is indentified with a star.
5, pathway B). This transformation formally involves the
decyclometalation of the aniline, metalation of both the naphthyl
and an isopropyl group,33 and methane evolution. Methane is
clearly visible in 1H NMR spectrum. As an indication of
isopropyl metalation, only five isopropyl doublets were present
1
in the aliphatic region of the H NMR spectrum. Two new
multiplets, each integrating for one proton, appeared at δH
)
1.40 ppm (H32a) and δH ) 0.78 ppm (H32b). These resonances
showed a scalar correlation with H31 in the 1H-COSY spectrum,
and H32a and H32b correlated with the same carbon resonance
1
(δC ) 81.2 ppm) in the H,13C HMQC spectrum (Figure 6A).
Naphthyl metalation is verified by the observation of a two spin
1
system in the aromatic region of the H NMR spectrum and a
long-range correlation with the carbon resonance at δC ) 206.1
1
ppm in the H,13C HMBC spectrum (Figure 6B). Finally, the
demetalation of aniline is supported by the observation of
magnetically equivalent ortho and meta resonances and the
integration consistent with five aromatic protons. As far as the
stereochemistry of 8b is concerned, the observation of selective
and relatively strong dipolar interactions between H17 and H34
and H36 indicate that the unaltered isopropyl group resides in
the relative pseudo-cis position with respect to H17, while,
consequently, C32 remains in the pseudo-trans relative position.
DFT calculations on the stereochemistry of 8b confirmed that
structure 8b is 1.5 kcal/mol more stable than 8b′, the structure
with the isopropyl group in the relative pseudo-trans position
with respect to H17 (see Figure S5 of the Supporting Informa-
tion).
Figure 4. Three sections of the 1H ROESY NMR spectrum of complex
6a (CD2Cl2 217 K), showing Overhauser contacts between the aniline
aromatic protons (o-H, o-H′, and p-H) and protons of the pyridyl-amido
ligand. The contact between p-H and H34 (middle section) is of particular
interest.
Because activation of aromatic amines competes with cyclo-
metalation of the naphthyl moiety, we decided to test the
reactivity of 5 with aliphatic amines. According to Scheme 5,
pathway C, when 1 equiv of CH3N(C18H37)2 is added to a
C6D5Cl solution of 5b, a release of CH4 and formation of
complex 9b is observed. The reaction proceeds cleanly at room
temperature and is complete in one hour. Evidence of naphthyl
metalation is provided by the appearance of a carbon resonance
at δC ) 202 ppm having long-range correlations with both H2
H12 and H8 and the chemical shift values of C7 and C8 indicate
that the naphthyl moiety points away from the Hf center (Table
1). The structure obtained by DFT calculations, with its distorted
square pyramid geometry, is in agreement with 1H NOESY and
1H ROESY results (Figure 5).
In C6D5Cl at room temperature, 7b slowly undergoes a
remarkably complex but clean transformation into 8b (Scheme
1
and H3 in the H,13C HMBC spectrum. The selective NOE
interaction between the Hf-Me group and H31 again indicates
that the protonation occurs stereoselectively at C37 of the
starting ion pair 5b. Finally, coordination of the amine is
demonstrated by the presence of two separate resonances for
the diastereotopic R-CH2 carbons (δC ) 54.4 and 53.9 ppm)
and the presence of a strong NOE cross peak between the
(33) (a) For similar isopropyl C-H activation reactions, see for example: Otten,
E.; Dijkstra, P.; Visser, C.; Meetsma, A.; Hessen, B. Organometallics
2005, 24, 4374. (b) Volkis, V.; Nelkenbaum, E.; Lisovskii, A.; Hasson,
G.; Semiat, R.; Kapon, M.; Botoshansky, M.; Eishen, M.; Eisen, M. S.
J. Am. Chem. Soc. 2003, 125, 2179. (c) Tempel, D. J.; Johnson, L. K.;
Huff, R. L.; White, P. S.; Brookhart, M. J. Am. Chem. Soc. 2000,
122, 6686.
9
10360 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
Scheme 6. Activation Chemistry of 2 with [HNMe2Ph][B(C6F5)4]
at the aromatic ring may be kinetically and/or thermodynami-
cally stabilized by a Hf-η2-naphthyl interaction. With the aim
of better understanding the impact of the naphthyl functionality,
we investigated the stoichiometric reaction of the corresponding
precatalyst 2, bearing a phenyl instead of a naphthyl substituent,
with [HNMe2Ph][B(C6F5)4] in C6D5Cl at room temperature. We
also explored the thermodynamics of the reaction with com-
putational calculations.
The reaction of 2 with [HNMe2Ph][B(C6F5)4] is much faster
than that of 1b, proceeding to completion in 20 min instead of
56 h. As with precatalysts 1a,b, the phenyl group is initially
protonated to give monocationic species 10 (Scheme 6).
However, before it is completely formed, 10 begins to transform
through phenyl metalation with methane evolution and aniline
coordination (Supporting Information). The reaction gives a
mixture of the diastereoisomeric monomethyl ion pairs 11 and
11′ in a 72:28 molar ratio. When the reaction is carried out at
low temperature, an almost complete conversion of 2 into 10 is
observed, suggesting that protonation proceeds regioselectively
at the Hf-phenyl bond. In a few hours at room temperature,
the 11/11′ mixture leads to complex 12 as a consequence of
C-H activation of the isopropyl moiety with concurrent
methane evolution (Scheme 6).
Complex 12 is analogous to 8b, and similar rationale can be
followed to obtain the complete resonance assignments and
determine its three-dimensional structure through NOE studies.
The 19F NMR spectrum is typical of an uncoordinated
B(C6F5)4-, while several cross peaks with both aliphatic and
aromatic resonances are present in the 19F,1H HOESY spectrum
(Figure 7). The absence of fluorine interactions with H32a,
H32b, H31, and H33 suggests that the anion approaches the
cation from the side occupied by the coordinated aniline.
Figure 6. Correlation spectra for complex 8b (C6D5Cl, 298 K), including
(A) a section of the 1H,13C HMQC NMR spectrum showing the connection
between the methylene carbon C32 and the two diasterotopic hydrogens
1
(H32a and H32b) and (B) a section of the H,13C HMBC NMR spectrum
showing the long-range correlation between the metallated carbon (C1) and
aromatic H2 and H3 protons.
N-Me group and H2. The 19F NMR spectrum shows resonances
corresponding to an uncoordinated anion, while the 19F,1H
HOESY experiment shows that the anion prefers to pair with
the cation from the side of the coordinated amine. Both the o-F
and m-F resonances of the anion show interactions with the
N-Me and the -(CH2)n- resonances of the aliphatic chains.
b. Phenyl Precatalyst, 2. From the results reported above, it
is clear that the naphthyl unit plays a crucial role in determining
the reactivity of complexes 1a and 1b with Brønsted acids.
Structural information, both in solution (NMR) and solid state
(X-ray diffraction), consistently indicates that the initially formed
cationic species (5a and 5b) arising from selective protonation
The main difference in the reactivity of dimethyl precatalysts
1 and 2 toward the Brønsted acid [HNMe2Ph][B(C6F5)4] is a
consequence of the higher stability of the protonated naphthyl
complex (5) with respect to the analogous phenyl one (10). The
latter is the kinetic product of the protonation process that readily
undergoes phenyl metalation with methane evolution to give a
monomethyl cation stabilized by the coordination of aniline (11
and 11′). On the contrary, the η2-naphthyl interaction with
hafnium stabilizes species 5 such that it first undergoes binding
of the aniline followed by (probably fast) cyclometalation with
methane evolution to give 7b. Both 11/11′ and 7b evolve to
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10361

A R T I C L E S
Zuccaccia et al.
Figure 8. Lateral view of the full QM optimized 8 and 12 structures. For
the sake of visibility, H atoms are omitted and the ligands have been reduced
to the pyridine and naphthyl and phenyl rings. Distortion of the naphthyl
ring compared to the phenyl one is evidenced.
Table 2. Polymerization of 1-Octene at Room Temperature Using
Precatalysts 1b and 2a
b
c
run precatalyst precatalyst (µmol)
activator
Tmax (°C) tmax (min)
1
2
3
4
5
6
1b
1b
1b
1b
2
10
10
5
2
10
10
[CPh3][B(C6F5)4]
[HNMe2Ph][B(C6F5)4] 126.5
[HNMe2Ph][B(C6F5)4] 122.2
[HNMe2Ph][B(C6F5)4]
[CPh3][B(C6F5)4]
[HNMe2Ph][B(C6F5)4] 107.6
117.3
0.87
9.80
15.30
81.90
5.97
91.7
110.3
2
8.23
a General reaction conditions: [1-octene] ) 3.2 M, 1 equiv activator.
c
b Tmax ) maximum temperature observed during reaction. tmax ) time
required to reach the maximum reaction temperature.
Correlations with the Catalytic Behavior in r-Olefin Poly-
merization. In principle, ortho-aryl-metallated [{N-,N,C-}-
HfMe]+ and nonmetallated [{N-,N}HfMe2]+ cations can both
represent active species in catalytic olefin polymerization. These
species both have at least one Hf-C σ-bond and one coordina-
tion vacancy on Hf for the incoming monomer. The factual
observation of Mw/Mn values >2.0 (Schulz-Flory distribution)
for ethene/1-alkene copolymers obtained with a number of
(pyridyl-amido)Hf-based catalysts is indeed an indication of a
nonsingle-center catalyst nature. This may (also) be traced to
the fact that [{N-,N,C-}HfMe]+ cations undergo monomer
insertion into the Hf-aryl σ-bond with a corresponding in situ
ligand modification and diversification.6 To explore these
possibilities, we carried out a number of polymerization
experiments in the presence of catalyst systems obtained by
reacting precatalysts 1b and 2 with stoichiometric amounts of
[CPh3][B(C6F5)4] and [HNMe2Ph][B(C6F5)4]. In particular, we
conducted polymerizations of 1-octene at room temperature,
monitoring the exotherm produced by polymerization as an
indication of the catalytic activity. We also performed poly-
merizations of propene at 50 °C under more controlled condi-
tions to measure kinetic profiles from monomer uptake.
Polymerizations of 1-octene (Table 2) provide insight into
the differences in activation chemistry of these complexes.
Reactions with 1b and 2 demonstrate large differences in the
kinetic profiles generated with different types of cocatalysts
(Figure 9). For both precatalysts, activation with [CPh3]-
[B(C6F5)4] results in an immediate increase in reaction temper-
ature. The Brønsted acid [HNMe2Ph][B(C6F5)4], however,
produces a different response; the profiles from both 1b and 2
show induction times consistent with slow activation processes.
Precatalyst 2 has a shorter induction period than 1b, consistent
with the NMR observations that show the aryl metalation is
much faster for phenyl derivatives. The duration of the induction
period is also highly dependent on catalyst concentration. The
time required (tmax) to reach the maximum reaction temperature
(Tmax) was extended from 9.8 to 81.9 min with a 5-fold decrease
in concentration of 1b. These results are all consistent with
the activation processes observed by NMR.
Figure 7. A section of the 19F,1H HOESY NMR spectrum (C6D5Cl, 298
K) of ion pairs 12. No interaction between the m-F and H31, H32a, H32b,
and H33 is observed.
thermodynamically stable complexes (8b and 12)34 derived from
the activation of a C-H bond of the isopropyl group. This
process is more complex in the case of 7b since aniline
decyclometalation and naphthyl metalation must both occur. 7b
may initially undergo an exchange of a proton between the
naphthyl and aniline moieties leading to an intermediate
analogous to 11/11′ that successively transforms into 8b. An
additional explanation for the different reactivity of dimethyl
precatalysts 1 and 2 toward the Brønsted acid was offered by
DFT calculations on the thermodynamic cycle for the reactions
going from 5 to 8b (system 1) and from 10 to 12 (system 2,
see Figure S6 of Supporting Information for the relative
structures). In fact, computations show gains in the energy of
18.4 and 26.7 kcal/mol for 1 and 2, respectively, for these
processes. This difference of about 9 kcal/mol is attributed to
the steric hindrance between the naphthyl and pyridine rings in
the ortho-metallated species, which forces the naphthyl to have
an orientation out of the Hf-pyridine plane (Figure 8); this
constraint is not present for the system bearing the phenyl group
(Figure 8). A comparable distortion is surely present in
metallated precatalysts 1a and 1b, and the release of the steric
congestion after protonation/demetalation of the naphthyl
functionality may substantially contribute to the overall stability
of ion pairs 5a and 5b.
Propene uptake curves from polymerizations conducted at
50 °C in toluene solution (Table 3 and Figure 10) are consistent
with the above observations. For precatalyst 1b, activation with
(34) Reactions of 8b and 12 with molecular hydrogen at room temperature
did not afford any reaction after several hours.
9
10362 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
Figure 9. Temperature profiles from 1-octene polymerizations, including (a) 1b and 2 activated with different cocatalysts (TB ) [CPh3][B(C6F5)4], DMAB
) [HNMe2Ph][B(C6F5)4]), and (b) concentration effects with 1b/DMAB.
Table 3. Polymerization of Propene at 50°C using Precatalysts 1b
and 2a
subsequent rearrangements of the formed ion pairs. These
reactions proceed initially with selective protonation of the aryl
moiety, not the methyl moiety as typically observed for other
dialkyl precatalysts (Scheme 7). In the case of naphthyl
precatalysts 1, protonation leads to an ion pair stabilized by an
Hf-η2-naphthyl interaction that slowly undergoes remetalation
of the naphthyl moiety with methane evolution to form a single
diastereoisomeric ion pair (Scheme 7). A nucleophile appears
to be necessary to release the Hf-η2-naphthyl interaction,
allowing naphyl rotation and remetalation. The structural
impossibility of stabilizing the protonated species, the lack of
an eclipsing H-H interaction, and the statistically doubled
possibility of activating an o-C-H bond makes the aryl
remetalation much faster in the case of the phenyl precatalyst
2 (Scheme 7). Again, one diastereosomeric ion pair prevalently
forms in these C1-symmetric chiral complexes.
The parallelism between the ease of aryl-CH-activation of
the dimethyl aryl-protonated species and the induction time
observed in R-olefin polymerizations is consistent with previous
conclusions that these species are more distant from the
catalytically active species (if not altogether inactive) than the
monomethyl aryl-metallated species generated by reaction with
Lewis acids. It would be reasonable to conclude that the latter
complexes were representative of the catalytically active species.
While this work demonstrates the indispensability of the
Hf-aryl carbon bond to the catalysis, it does not necessarily
indicate that the aryl-metallated species are active polymerization
catalysts. As if the mechanisms described above were not
complex enough, it has been recently proposed that the first
olefin insertion is more likely to occur into the Hf-aryl carbon
bond instead of the Hf-methyl bond.6 This mechanism, based
on theoretical and experimental evidence, involves a very
unusual modification of the ligand structure by monomer to give
the highly active polymerization catalyst. Recent observations
by Domski and Coates35 and Hustad and co-workers,36 who
independently discovered that related achiral species give
prevalently isotactic poly-(R-olefins) in spite of the Cs-symmetry
of the precatalysts, also supports this mechanism. To understand
the importance of this hypothesis of ligand modification by
precatalyst
(µmol)
yield
t (min) (mg) [mmmm]b
run precatalyst
activator
1
2
3
4
1b
1b
2
0.010
0.050
0.010
0.050
[Ph3C][B(C6F5)4]
29
149 0.975
150 0.970
90 0.885
90 0.885
[HNMe2Ph][B(C6F5)4] 50
[Ph3C][B(C6F5)4] 22
[HNMe2Ph][B(C6F5)4] 36
2
a General reaction conditions: p(propene) ) 2.0 bar, 1.2 equiv. acti-
vator, 1.0 mM Al(iBu)3 as a scavenger. b Fraction of isotactic pentad in
the polymer, measured by 13C NMR.
[CPh3][B(C6F5)4] resulted into practically immediate polymer-
ization activity, whereas a long (ca. 20 min) induction period
was observed upon activation with [HNMe2Ph][B(C6F5)4]. On
the other hand, catalyst systems based on 2 behaved similarly
with both [CPh3][B(C6F5)4] and [HNMe2Ph][B(C6F5)4] activa-
tion, with no appreciable induction. For each catalyst, a different
choice of activator resulted in a different productivity at
stationary state (ca. 5-10 times higher with [CPh3][B(C6F5)4]
than with [HNMe2Ph][B(C6F5)4], possibly due to the coordinat-
ing ability of dimethylaniline), but had no measurable effects
on the selectivity as identical polymer microstructures were
observed by 13C NMR.
On the basis of these polymerization results and on the
precatalyst activation studies reported in the previous sections,
we conclude that nonmetallated [{N-,N}HfMe2]+ species 5a,b
and 10 are polymerization-inactive (or poorly active at most),
and that the ortho-aryl-metalation is essential for (high) poly-
merization activity.
Conclusions and Perspectives
Because of the wealth of interesting polymerization charac-
teristics displayed by hafnium pyridyl-amido complexes, we
sought to gain a fundamental understanding of their activation
and polymerization mechanisms. These studies have revealed
that the unique catalytic properties displayed by these species
are perhaps rivaled by the peculiarities observed in the activation
chemistry. Treatment of these procatalysts with Lewis acids
B(C6F5)3 and [CPh3][B(C6F5)4] reveals typical chemistry for
such reactions, forming the expected ion pairs. However,
activation of these precatalysts with Brønsted acids proceeds
in a rather unusual way leading to complex, and aryl-dependent,
(35) Domski, G. J.; Lobkovsky, E. B.; Coates, G. W. Macromolecules 2007,
40, 3510–3513.
(36) Hustad, P. D.; Froese, R. D. J.; Zuccaccia, C.; Macchioni, A.; Busico,
V.; Cipullo, R.; Talarico, G. Unpublished results.
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10363

A R T I C L E S
Zuccaccia et al.
Figure 10. Results of propene polymerization at 50 °C in toluene for catalyst systems derived from precatalyst 1b (left) and 2 (right): (a) activation with
[CPh3][B(C6F5)4] and (b) activation with [HNMe2Ph][B(C6F5)4].
Scheme 7. Differences in Activation Chemistry of Naphthyl and
Phenyl Precatalysts with Brønsted Acids
performed on a Bruker Avance DRX 400 instrument. Referencing
by residual solvent signals is relative to TMS. Typical mixing time
for the Overhauser experiments were in the range 120-800 ms.
General Synthesis of Hafnium Dimethyl Complexes. The
desired precatalysts 1 and 2 were synthesized by reaction of the
ligand with tetrakis(dimethylamido)hafnium (IV) followed by
treatment with trimethylaluminum, as described previously.1,4b
A
representative procedure for 1a is given below.
Synthesis of [N-[2,6-Diisopropylphenyl]-r-[2-methylphenyl]-
6-(1-naphthalenyl)-2-pyridinemethanaminato] Hafnium Di-
methyl (1a). A 27.5 g portion of N-[2,6-diisopropylphenyl]-R-[2-
methylphenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine (56.7
mmol) was dissolved in 100 mL of toluene, and a solution of
tetrakis(dimethylamido) hafnium(IV) (20 g, 56.4 mmol) in toluene
(50 mL) was slowly added to this solution dropwise over a period
of 30 min. The reaction vessel was equipped with a condenser filled
with activated acidic alumina to remove the liberated dimethyl-
amine. The reaction was heated under reflux conditions for 1.5 h,
and then stirred at room temperature for 16 h. Subsequently, the
solution was subjected to a dynamic vacuum which reduced the
volume of the solvent to ∼40 mL. To this solution, ∼35 mL of
hexane were added and the mixture was stirred for 1 h before the
precipitate was isolated by filtration on a glass frit. The precipitate
was washed 3 times with ∼20 mL of pentane and then dried under
dynamic vacuum. Another 50 mL of hexane were added to the
filtrate, and it was stirred for another 2 h. This again led to the
formation of a precipitate that was filtered off using a glass frit
and, after washing 3 times with ∼20 mL of pentane, was dried
under dynamic vacuum. The two precipitate fractions were com-
bined, giving 30.5 g of the desired diamido complex (72.2% yield).
monomer, we are currently working to determine the selectivity
of the first monomer insertion. These results, including detailed
NMR characterization and computational studies, will be
reported in the near future.
Experimental Section
All manipulations were performed in flamed Schlenk-type
glassware interfaced to a high-vacuum line (<10-5 Torr), or in a
nitrogen-filled Vac-Atmosphere glovebox (<1 ppm O2). Molecular
sieves (MS) were activated for 24 h at 200-230 °C under dynamic
vacuum.Allthesolventsandliquidreagentswerefreeze-pump-thaw
degassed on the high-vacuum line, dried over the appropriate drying
agent, vacuum-transferred to a dry storage-tube with a PTFE valve,
and stored over activated MS. Benzene-d6, toluene-d8, pentane,
hexane, and toluene were dried over Na/K alloy; 1,2-F2C6H4 was
refluxed for three days over P2O5, and finally dried over CaH2,
chlorobenzene-d5 and methylene chloride-d2 were dried over CaH2.
[HNMe2Ph][B(C6F5)4] and [CPh3][B(C6F5)4] were obtained from
Boulder Scientific Company and were used as received. B(C6F5)3
was obtained from Boulder Scientific Company and was purified
by sublimation (40-60 °C, 10-5 Torr). NMe(C18H37)2 (Aldrich)
and AlMe3 (22% in hexane, Akzo Nobel) were used as received.
The pyridylamine ligands N-[2,6-diisopropylphenyl]-R-[2-meth-
ylphenyl]-6-(1-naphthalenyl)-2-pyridinemethanamine,1 N-[2,6-di-
isopropylphenyl]-R-[2-isopropylphenyl]-6-(1-naphthalenyl)-2-
pyridinemethanamine,4b and N-[2,6-diisopropylphenyl]-R-phenyl-
6-(1-phenyl)-2-pyridinemethan-amine1 were prepared as described
previously.
The diamido complex (20.0 g, 26.7 mmol) was dissolved in ∼80
mL of toluene, and 113 mL (226 mmol, 8.5 equiv.) of a solution
of trimethylaluminum (2.0 M in hexane) was added over a period
of 30 min. After 2.5 h of stirring at room temperature, the solvent
volume was reduced under dynamic vacuum to ∼100 mL. The
resulting precipitate was isolated by filtration and was washed 3
times with ∼20 mL of hexane before being dried under vacuum.
The filtrate was reduced in volume to ∼30 mL, forming further
precipitate which was again isolated on a frit, washed 3 times with
∼20 mL of hexane, and dried under vacuum. The two precipitate
1
fractions were combined, giving 15.6 g of 1a (85.1% yield). H
3
NMR (C6D6, 298 K, J values in Hz): δ 8.58 (d, JHH ) 7.6, H2),
8.26 (m, H8), 7.81 (d, 3JHH ) 7.5, H3), 7.72 (m, H5), 7.50 (d, 3JHH
) 7.8, H12), 7.29 (m, H6, H7 and H19), 7.17 (m, H28), 7.16 (m,
NMR samples were prepared in oven-dried J-Young NMR tubes.
1H, 13C{1H}, 1H COSY, 1H NOESY, 1H ROESY, 1H,13C HMQC,
1H,13C HMBC, 19F, and 19F,1H HOESY NMR experiments were
3
3
H29), 7.09 (m, H27), 6.98 (d, JHH ) 7.5, H20), 6.91 (td, JHH
)
)
7.3, 4JHH ) 1.4, H21), 6.85 (d, 3JHH ) 7.2, H22), 6.82 (d, 3JHH
9
10364 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
3
7.8, H13), 6.39 (s, H17), 6.36 (d, JHH ) 7.8, H14), 3.80 (sept,
(s, C11), 148.1 (s, C26), 147.9 (s, C25), 147.2 (s, C30), 145.6 (s,
C10) 144.7 (s, C18), 141.9 (s, C13), 139.2 (s, C2), 131.5 (s, C3),
129.7, 129.6 (s, C19, C20, C22, C23), 129.3 (s, C4), 128.6 (s, C21),
126.7 (s, C28), 125.8 (s, C29), 125.1 (s, C27), 124.0 (s, C9), 120.7
(s, C14), 116.4 (s, C12), 84.8 (s, C16), 67.7 (s, C37), 63.8 (s, C38),
29.3 (s, C34), 28.7 (s, C31), 27.7 (s, C32), 27.6 (s, C36), 25.5 (s,
C35), 25.0 (s, C33). Anal. Calcd. (found) for C32H36HfN2: H, 5.79
(5.81); C, 61.29 (61.29); N, 4.47 (4.45).
3JHH ) 6.7, H31), 3.35 (sept, JHH ) 6.7, H34), 1.85 (s, H24),
3
1.37 (d, 3JHH ) 6.7, H32), 1.36 (d, 3JHH ) 6.7, H36), 1.14 (d, 3JHH
3
) 6.7, H35), 0.94 (s, H38), 0.70 (s, H37), 0.44 (d, JHH ) 6.7,
H33). 13C{1H} NMR (C6D6, 298K): δ 206.8 (s, C1), 170.9 (s, C15),
165.0 (s, C11), 148.0 (s, C26), 147.0 (s, C30), 146.5 (s, C25), 144.7
(s, C10 or C4) 143.3 (s, C18), 141.5 (s, C13), 136.7 (s, C23), 136.4
(s, C4 or C10), 134.8 (s, C2), 131.3 (s, C9), 130.63 (s, C5), 130.56
(s, C3), 130.4 (s, C19), 128.4 (s, buried under C6D6, C21), 127.9
(s, C20), 127.6 (s, C7), 127.3 (s, C9), 126.7 (s, C28), 126.2 (s,
C6), 125.8 (s, C29), 125.0 (s, C27), 124.8 (s, C8), 121.1 (s, C12),
120.0 (s, C14), 78.7 (s, C16), 67.6 (s, C37), 63.3 (s, C38), 29.4 (s,
C34), 28.8 (s, C31), 28.1 (s, C32), 26.6 (s, C36), 26.0 (s, C35),
24.6 (s, C33), 20.5 (s, C24). Anal. Calcd (found) for C37H40HfN2:
H, 5.83 (5.86); C, 64.29 (64.35); N, 4.05 (4.08).
Synthesis of 3a. Complex 1a (50 mg, 0.072 mmol) and
B(C6F5)3 (40 mg, 0.078 mmol) were loaded in the glovebox into
the two separate vessels of a flip-frit reaction apparatus. The
flip-frit was then interfaced to the high-vacuum line and
evacuated to 10-5 Torr. Approximately 30 mL of dry pentane
was condensed under vacuum at -196 °C into the vessel
containing 1a. The reaction vessel was then warmed to room
temperature while stirring. After approximately 1/2 h, the yellow
solution was filtered into the second vessel containing B(C6F5)3.
A yellow solid precipitate formed almost instantaneously. Stirring
[N-[2,6-Diisopropylphenyl]-r-[2-isopropylphenyl]-6-(1-naph-
thalenyl)-2-pyridinemethanaminato] Hafnium Dimethyl (1b). 1H
3
NMR (C6D6, 298 K, J values in Hz): δ 8.60 (d, JHH ) 7.6, H2),
8.25 (m, H8), 7.82 (d, 3JHH ) 7.6, H3), 7.72 (m, H5), 7.50 (d, 3JHH
1
was continued for an additional /2 h and then the yellow solid
) 7.9, H12), 7.31 (m, H6, H7 and H19), 7.16 (m, H28 and H29),
was collected by filtration, rinsed once with a small amount of
pentane, and dried under vacuum overnight. Yield: 50 mg (55%).
3
7.08 (m, H27 and H22), 7.00 (m, H20 and H21), 6.83 (d, JHH
)
3
3
7.9, H13), 6.58 (s, H17), 6.55 (d, JHH ) 7.9, H14), 3.83 (sept,
H NMR(C6D6, 298 K, J values in Hz): δ 8.11 (d, JHH ) 8.3,
3JHH ) 6.7, H31), 3.38 (sept, 3JHH ) 6.7, H34), 2.90 (sept, 3JHH
)
3
3
H8), 7.99 (d, JHH ) 7.9, H2), 7.55 (d, JHH ) 7.9, H3), 7.48
3
3
(d, 3JHH ) 7.9, H5), 7.32 (d, 3JHH ) 8.0, H12), 7.28 (td, 3JHH
)
6.7, H24), 1.39 (d, JHH ) 6.7, H36), 1.38 (d, JHH ) 6.7, H32),
3
3
4
1.17 (d, JHH ) 6.7, H24a), 1.16 (d, JHH ) 6.7, H35), 0.96 (s,
6.8, JHH ) 1.5, H7), 7.18 (m, H6, H19, H28, and H20), 6.95
3
3
3
4
3
H38), 0.71 (s, H37), 0.70 (d, JHH ) 6.7, H24b), 0.39 (d, JHH
)
(dd, JHH ) 7.7, JHH ) 1.1, H27), 6.90 (t, JHH ) 6.9, H21),
6.7, H33). 13C{1H} NMR (C6D6, 298 K): δ 206.7 (s, C1), 171.2
(s, C15), 165.0 (s, C11), 148.0 (s, C26), 147.4 (s, C23), 147.0 (s,
C30), 146.2 (s, C25), 144.7 (s, C10) 141.5 (s, C18), 141.4 (s, C13),
136.4 (s, C4), 134.8 (s, C2), 131.4 (s, C9), 130.8 (s, C19), 130.6
(s, C5), 130.5 (s, C3), 128.8 (s, buried under C6D6, C21), 127.6 (s,
C7), 127.5 (s, C20), 126.6 (s, C28), 126.2 (s, C6), 126.1 (C22),
125.8 (s, C29), 125.1 (s, C27), 124.9 (s, C8), 121.1 (s, C12), 120.1
(s, C14), 77.5 (s, C16), 67.6 (s, C37), 63.5 (s, C38), 29.4 (s, C34),
29.3 (s, C24), 28.8 (s, C31), 28.1 (s, C32), 26.5 (s, C36), 26.1 (s,
C35), 25.8 (s, C24a), 24.4 (s, C33), 23.7 (s, C24b). Anal. Calcd
(found) for C39H44HfN2: H, 6.17 (6.23); C, 65.12 (65.15); N, 3.89
(3.85).
3
4
3
6.80 (dd, JHH ) 7.7, JHH ) 1.1, H29), 6.75 (d, JHH ) 8.6,
H22), 6.73 (t, 3JHH ) 7.9, H13), 6.15 (d, 3JHH ) 7.9, H14), 6.09
(s, H17), 3.22 (sept, 3JHH ) 6.8, H31), 3.03 (br, Hf-Me-B), 2.70
3
(sept, JHH ) 6.8, H34), 1.61 (s, H24), 1.12 (s, H38), 1.07 (d,
3JHH ) 6.8, H36), 1.03 (d, JHH ) 6.8, H32), 0.79 (d, JHH
)
3
3
6.8, H35), 0.13 (d, JHH ) 6.8, H33). 19F NMR (C6D6, 298 K):
δ -132.8 (br o-F), -159.2 (br, p-F), -163.9 (br, m-F). Anal.
Calcd. (found) for C55H40BF15HfN2: H, 3.35 (3.40); C, 54.90
(54.97); N, 2.33 (2.27).
3
[N-[2,6-Diisopropylphenyl]-r-[phenyl]-6-(1-phenyl)-2-py-
ridinemethanaminato] Hafnium Dimethyl (2). H NMR (C6D6,
Synthesis of 3b. Complex 1b (200 mg, 0.277 mmol) and
B(C6F5)3 (142.2 mg, 0.277 mmol) were loaded into one vessel
of a flip-frit reaction apparatus within the glovebox. The flip-
frit was interfaced to the high-vacuum line and evacuated up to
10-5 Torr. Approximately 25 mL of pentane was condensed
under vacuum at -196 °C into the vessel containing the
reactants. The reaction vessel was warmed up to approximately
-20 °C and stirred for approximately 1 h at this temperature.
The bright yellow solid that formed was collected by filtration,
washed with a small amount of pentane, and dried under vacuum
overnight. Yield: 240 mg (70%). 1H NMR (C6D5Cl, 244 K, J
3
3
298 K, J values in Hz): δ 8.41 (d, JHH ) 6.9, H2), 7.44 (d, JHH
) 7.6, H9), 7.43 (dt, 3JHH ) 7.4, 4JHH ) 0.7, H3), 7.20 (dt, 3JHH
)
4
7.6, JHH ) 1.2, H4), 7.16 (m, buried under solvent signal H29,),
7.14 (t, 3JHH ) 7.6, H28), 7.08 (dd, 3JHH ) 7.4, 4JHH ) 2.2, H27),
3
6.98 (m, H19, H20, H21; H22, H23) 6.89 (d, JHH ) 7.8, H12),
6.79 (d, 3JHH ) 7.8, H13), 6.36 (d, 3JHH ) 7.8, H14), 5.90 (s, H17),
3
3
3.79 (sept, JHH ) 6.7, H31), 3.21 (sept, JHH ) 6.7, H34), 1.39
3
3
3
(d, JHH ) 6.7, H32), 1.37 (d, JHH ) 6.7, H36), 1.13 (d, JHH
)
6.7, H35), 0.94 (s, H38), 0.62 (s, H37), 0.38 (d, 3JHH ) 6.7, H33).
13C{1H} NMR (C6D6, 298K): δ 202.9 (s, C1), 170.1 (s, C15), 164.6
3
values in Hz): δ 8.12 (m, H8), 7.84 (d, JHH ) 7.8, H2), 7.56
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10365

A R T I C L E S
Zuccaccia et al.
3
3
(d, JHH ) 7.8, H3), 7.51 (m, H5), 7.39 (d, JHH ) 8.1, H12),
7.32 (m, H19, H6 and H7), 7.13 (m, H13 and H28), 7.06 (m,
H20, H21 and H22), 6.92 (buried under residual solvent signals,
H27), 6.82 (d, 3JHH ) 7.6, H29), 6.61 (d, JHH ) 8.1, H14), 6.28
(s, H17), 3.28 (sept, 3JHH ) 6.7, H31), 3.04 (br, Hf-Me-B), 2.86
(t, 3JHH ) 21.0, p-F), -167.13 (brt, 3JHH ) 17.2, m-F). Anal. Calcd.
(found) for C61H41BF20HfN2: H, 3.01 (3.12); C, 53.43 (53.55); N,
2.04 (2.12).
3
3
(sept, JHH ) 6.7, H34), 2.52 (sept, JHH ) 6.7, H24), 1.19 (d,
3JHH ) 6.7, H36), 1.14 (s, H38), 1.08 (d, JHH ) 6.7, H24a),
3
3
3
0.99 (d, JHH ) 6.7, H32), 0.76 (d, JHH ) 6.7, H35), 0.47 (d,
3JHH ) 6.7, H24b), 0.03 (d, 3JHH ) 6.7, H33). Selected 13C{1H}
NMR (C6D5Cl, 244 K): δ ) 207.3 (s, C1), 170.4 (s, C15), 165.0
(s, C11), 142.3 (s, C13), 132.1 (s, C2), 130.1 (s, C3), 129.9 (s,
C5), 124.4 (s, C8), 121.7 (s, C12), 120.8 (s, C14), 75.7 (s, C16),
65.8 (s, C38), 40.7 (s, Hf-Me-B), 26.4 (s, C32), 25.6 (s, C36),
25.4 (s, C24a), 25.0 (s, C35), 23.6 (s, C33), 22.3 (s, C24b). 19F
Synthesis of 5b. Complex 1b (100 mg, 0.139 mmol) and
[HNMe2Ph][B(C6F5)4] (111.4 mg, 0.139 mmol) were loaded into
a vessel of a flip-frit reaction apparatus within the glovebox. The
flip-frit was then interfaced to the high-vacuum line and evacuated
to 10-5 Torr. Approximately 20 mL of toluene were condensed
under vacuum at -196 °C into the vessel. The reaction mixture
was warmed up to room temperature and stirred approximately for
10 min. After that, toluene was removed under vacuum and
approximately 30 mL of pentane were condensed into the vessel.
The initially formed yellow oil was handled until a light yellow
solid was obtained. It was washed with a small amount of pentane
and dried under vacuum overnight. Yield: 150 mg (76%). Single
crystals suitable for X-ray analysis were grown by slow diffusion
of n-hexane into a concentrated solution of ion pair 5b in C6D5Cl.
NMR (C6D5Cl, 244 K, J values in Hz): δ -132.70 (brd,3JFF
)
3
3
23.7, o-F), -158.90 (t, JFF ) 21.3, p-F), -163.60 (brt, JFF
)
23.3, m-F). 19F NMR (C6D5Cl, 244 K, J values in Hz): δ
3
3
-132.70 (brd, JFF ) 23.7, o-F), -158.90 (t, JFF ) 21.3, p-F),
3
-163.60 (brt, JFF ) 23.3, m-F). Anal. Calcd (found) for
C57H44BF15HfN2: H, 3.60 (3.62); C, 55.60 (55.64); N, 2.28 (2.25).
j
The crystals belong to the P1 space group with two ion pairs in
1
each unit cell. H NMR (C6D5Cl, 298 K, J values in Hz): δ 8.06
(td, 3JHH ) 7.1, 4JHH ) 1.3, H7), 7.95 (d, 3JHH ) 8.5, H5), 7.90 (d,
3
3
3JHH ) 8.4, H3), 7.81 (d, JHH ) 8.1, H8), 7.63 (dd, JHH ) 8.3,
3
3
4JHH ) 7.3, H2), 7.59 (t, JHH ) 8.0, H13), 7.46 (d, JHH ) 8.0,
3
4
3
H12), 7.44 (dd, JHH ) 7.3, JHH)1.1, H1), 7.39 (td, JHH ) 7.2,
3
4
4JHH ) 1.1, H6), 7.14 (dd, JHH ) 7.7, JHH ) 1.6, H29), 7.07 (t,
3JHH ) 7.8, H28), 7,06 (m, H22), 7.00 (m, H21 and H20), 6.92 (d,
3JHH ) 8.0, H14), 6.85 (dd, 3JHH ) 7.4, 4JHH ) 1.9, H27), 6.67 (d,
Synthesis of 5a. Complex 1a (70 mg, 0.101 mmol) and
[HNMe2Ph][B(C6F5)4] (81 mg, 0.101 mmol) were loaded into a
vessel of a flip-frit reaction apparatus within the glovebox. The
flip-frit was then interfaced to the high-vacuum line and evacuated
to 10-5 Torr. Approximately 20 mL of dry toluene were condensed
under vacuum at -196 °C into the vessel. The reaction mixture
was warmed up to room temperature and stirred approximately for
10 min. After that toluene was removed under vacuum and
approximately 30 mL of dry pentane were condensed into the vessel.
The initially formed deep yellow-brown oil was handled until a
yellow solid was obtained. It was washed with a small amount of
pentane and dried under high-vacuum overnight. Yield: 95 mg
(68%). 1H NMR (C6D6/1,2-C6H4F2, 298 K, J values in Hz): δ 7.92
(td, 3JHH ) 7.5, 4JHH ) 1.3, H7), 7.75 (d, 3JHH ) 7.9, H5), 7.72 (d,
3JHH ) 7.8, H19), 6.57 (s, H17), 3.11 (sept, JHH ) 6.8, H34),
3
3
3
3.00 (sept, JHH ) 6.8, H31), 2.59 (sept, JHH ) 6.8, H24), 1.47
3
3
3
(d, JHH ) 6.8, H36), 1.36 (d, JHH ) 6.8, H35), 1.15 (d, JHH
)
3
3
6.8, H24a), 0.88 (d, JHH ) 6.8, H32), 0.5 (d, JHH ) 6.8, H35),
0.08 (d, 3JHH ) 6.8, H33), -0.25 (s, H38), -0.49 (s, H37). Cation
13C{1H} NMR ((C6D5Cl, 298 K, 298 K): δ 168.3 (s, C15), 152.2
(s, C11), 148.0 (s, C26), 146.4 (s, C30), 144.6 (s, C25), 144.4 (s,
C13), 143.0 (s, C7), 139.2 (s, C23 or C18), 137.9 (s, C4), 137.2 (s,
C5), 136.9 (s, C18 or C23), 133.3 (s, C3), 132.9 (s, C1), 131.3 (s,
C2), 131.0 (s, C6), 129.9 (s, C10), 129.7 (s, C19), 129.5 (s, C21 or
C22), 128.8 (s, C28), 127.7 (s, C9), 126.9 (s, C20), 126.3 (s, C22
or C21), 125.4 (s, C29), 125.2 (s, C27), 124.4 (s, C14), 122.3 (s,
C12), 113.3 (s, C8), 73.0 (s, C16), 72.9 (s, C37), 61.8 (s, C38),
29.3 (s, C34), 28.7 (s, C24), 28.2 (s, C31), 25.82 (s, C32), 25.78
(s, C35), 25.1 (s, C24a), 25.0 (s, C36), 23.2 (s, C33), 22.3 (s, C24b).
19F NMR (C6D6Cl, 298 K, J values in Hz): δ -132.2 (br, o-F),
-162.6 (t, 3JFF ) 21.0, p-F), -166.6 (brt, 3JFF ) 19.0, m-F). Anal.
Calcd. (found) for C63H45BF20HfN2: H, 3.24 (3.30); C, 54.07
(54.15); N, 2.00 (2.06).
3
3
3JHH ) 7.8, H3), 7.61 (d, JHH ) 7.6, H8), 7.50 (dd, JHH ) 8.2,
3
3
4JHH ) 7.2, H2), 7.49 (t, JHH ) 7.8, H13), 7.32 (d, JHH ) 7.6,
H12), 7.23 (dd, 3JHH ) 7.3, 4JHH ) 1.0, H1), 7.18 (td, 3JHH ) 7.3,
3
4
4JHH ) 1.1, H6), 7.12 (dd, JHH ) 7.8, JHH ) 1.9, H29), 7.08 (t,
3JHH ) 7.6, H28), 6.93 (m, H20 and H21), 6.84 (dd, JHH ) 7.4,
3
4JHH ) 1.9, H27), 6.79 (m, buried under 1,2-C6H4F2, H22), 6.65
(d, 3JHH ) 7.8, H14), 6.61 (d, 3JHH ) 7.6, buried under 1,2-C6H4F2,
H19), 6.38 (s, buried under 1,2-C6H4F2 side bands, H17), 3.08 (sept,
3JHH ) 6.8, H34), 3.00 (sept, JHH ) 6.8, H31), 1.71 (s, H24),
3
1.45 (d, 3JHH ) 6.8, H36), 1.36 (d, 3JHH ) 6.8, H35), 0.88 (d, 3JHH
) 6.8, H32), 0.08 (d, 3JHH ) 6.8, H33), -0.29 (s, H38), -0.50 (s,
H37). Cation 13C{1H} NMR (C6D6/1,2-C6H4F2, 298 K): δ 168.6
(s, C15), 153.1 (s, C11), 147.1 (s, C26), 145.5 (s, C30), 145.4 (s,
C13), 143.9 (s, C7), 140.8 (s, C25), 139.7 (s, C23 or C18), 138.7
(s, C4), 138.1 (s, C18 or C23), 137.9 (s, C5), 134.0 (s, C3), 133.6
(s, C1), 132.1 (s, C22), 131.9 (s, C2), 131.7 (s, C6), 130.7 (s, C10),
130.1 (s, C19), 129.8 (s, C20 or C21), 128.6 (s, C9), 128.0 (s, C21
or C20), 126.1 (s, C29), 125.8 (s, C27), 125.4 (s, C14), 125.0 (s,
C28), 123.1 (s, C12), 114.1 (s, C8), 75.1 (s, C16), 73.4 (s, C37),
61.8 (s, C38), 30.1 (s, C34), 29.0 (s, C31), 26.4 (s, C32), 26.2 (s,
C35), 25.9 (s, C36), 24.0 (s, C33), 19.9 (s, C24). 19F NMR (C6D6/
1,2-C6H4F2, 298 K, J values in Hz): δ -132.40 (br, o-F), -163.24
Generation of complex 6a. Complex 5a (7.5 mg, 0.0055 mmol)
and [HNMe2Ph][B(C6F5)4] (4.4 mg, 0.0055 mmol) were loaded into
a 2 mL vial within the glovebox. One milliliter of C6D6 was added.
The vial was closed with a screw cap, shaken several times during
the first two hours, and left overnight at room temperature. A deep
9
10366 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008

Activation of Hafnium Olefin Precatalysts
A R T I C L E S
yellow-brown oil separated from the solution. The supernatant
solution was removed, and the residual oil was washed with C6D6
(2 × 0.3 mL). The same procedure was repeated starting directly
from 1a and using 2 equiv of [HNMe2Ph][B(C6F5)4]. NMR analysis
indicated that the final product was the same but of lower purity.
3
1H NMR (CD2Cl2, 217 K, J values in Hz): δ 8.66 (d, JHH ) 8.3,
3
3
H3), 8.48 (t, JHH ) 7.9, H13), 8.41 (d, JHH ) 7.7, H5), 8.37 (d,
3JHH ) 7.8, H8), 8.21 (d, 3JHH ) 7.8, H12), 8.10 (m, H6 and H7),
7.99 (dd, 3JHH ) 8.2, 4JHH ) 6.3, H2), 7.60 (d, 3JHH ) 8.0, H14),
3
3
7.48 (d, JHH ) 6.3, H1), 7.42 (d, JHH ) 7.6, H29), from 7.40 to
7.10 series of multiplets in the following order H28, H21, H20,
H19, H22, H27, and m-H, 6.61 (dd, 3JHH ) 8.3, 4JHH ) 2.3, o-H),
8b. 1H NMR (C6D5Cl, 298 K, J values in Hz): δ 8.34 (d, 3JHH ) 8.5,
H8), 7.83 (d, 3JHH ) 7.3, H12), 7.81 (d, 3JHH ) 7.9, H5), 7.63 (d, 3JHH
)
6.17 (s, H17), 5.75 (brd, o-H′), 5.72 (t, 3JHH ) 7.1, p-H), 5.03 (td,
7.7, H3), 7.58 (td, 3JHH ) 8.5, 4JHH ) 1.0, H7), 7.496 (d, 3JHH ) 7.7,
H2), 7.492 (m, H6), 7.46 (d, 3JHH ) 7.9, H13), 7.30 (d, 3JHH ) 7.1, H29),
7.22 (m, H28), 7.13-7.04 (m, H22, H21 and H27), 7.03 (s, H17), 6.93
(d, 3JHH ) 8.3, H14), 6.90 (t, 3JHH ) 7.4, H20), 6.71 (m, H19 and m-H),
6.13 (d, 3JHH)7.9, o-H), 6.11 (t, 3JHH)7.7, p-H), 3.23 (sept, 3JHH)6.6,
H34), 3.13 (sept, 3JHH ) 6.6, H24), 2.96 (m, H31), 2.37 (s, H39 or H40),
1.96 (s, H40 or H39), 1.68 (d, 3JHH ) 6.6, H36), 1.38 (m, H32a), 1.32 (d,
3JHH ) 6.6, H35), 1.24 (d, 3JHH ) 6.6, H24a), 1.01 (d, 3JHH ) 6.6, H33),
3
3JHH ) 8.3,4JHH ) 1.5, m-H′), 3.23 (s, H39), 2.81 (sept, JHH
)
6.5, H34), 2.72 (sept, 3JHH ) 6.5, H31), 2.60 (s, H40), 2.81 (sept,
3JHH ) 6.5, H34), 1.87 (s, H24), 1.51 (d, JHH ) 6.5, H36), 1.50
3
3
3
(s, H38), 1.32 (d, JHH ) 6.5, H35), 0.97 (d, JHH ) 6.5, H32),
0.02 (d, JHH ) 6.5, H33). Cation 13C{1H} NMR (CD2Cl2, 217
3
K): δ 167.9 (s, C15), 153.3 (s, C11), 152.8 (s, Cipso) 147.4 (s, C13),
147.0 (s, C26), 142.7 (s, C25), 142.3 (s, C30), 138.2 (s, C18), 136.8
(s, C3), 136.79 (s, C4), 135.7 (s, C23), 135.4 (s, m-C′), 134.7 (m-
C), 133.4 (s, C6 and C10), 133.0 (s, C7), 132.9 (s, C22), 131.2 (s,
C5), 130.2 (s, C2 and C20), 130.0 (s, C28), 129.6 (s, C19), 129.3
(s, C9), 128.2 (s, C21), 127.6 (s, C29), 127.2 (s, C12), 126.7 (s,
C27), 125.0 (s, C14) 124.6 (s, C8), 122.7 (s, C1), 114.8 (s, o-C),
111.6 (s, o-C′), 107.9 (s, p-C), 73.7 (s, C16), 56.9 (S, C38), 41.4
(s, C39), 40.9 (s, C40), 28.8 (s, C34), 28.6 (s, C31), 27.3 (s, C36),
26.3 (s, C32), 25.2 (s, C35), 23.9 (s, C33), 20.8 (s, C24). 19F NMR
(CD2Cl2, 217 K, J values in Hz): δ -133.70 (brd, o-F), -163.00
3
0.78 (m, H32b), 0.63 (d, JHH ) 6.6, H24b). Selected cation 13C{1H}
NMR signals (C6D5Cl, 298 K): δ 206.1 (s, C1), 170.8 (s, C15), 162.4 (s,
C11), 150.3 (s, C26), 147.9 (s, C23), 146.6 (s, Cipso), 146.2 (s, C30), 142.6
(s, C13), 142.3 (s, C10) 141.1 (s, C25), 139.4 (s, C18), 135.4 (s, C4),
132.3 (s, m-C) 132.1 (s, C2), 130.8 (s, C9), 129.9 (s, C5), 128.6-128.1
(buried under solvent signal, C3, C7, C19 and C21), 127.7 (s, C28), 127.0
(s, C6), 126.7 (s, C20), 126.1 (buried under solvent signal, C22 and C29),
124.0 (s, C27), 123.7 (C8), 121.0 (s, C12), 119.7 (s, C14), 116.9 (s, p-C),
113.8 (s, o-C), 81.2 (s, C32), 75.8 (s, C16), 41.3 (s, C39 or C40), 40.4 (s,
C40 or C39), 36.2 (s, C31), 28.8 (s, C24), 28.0 (s, C34), 26.1 (s, C35),
26.0 (s, C33), 25.5 (s, C24a), 25.0 (s, C36), 22.3 (s, C24b). 19F NMR
3
3
(t, JFF ) 21.0, p-F), -167.09 (brt, JFF ) 17.8, m-F).
(C6D5Cl, 298 K, J values in Hz): δ -131.9 (br, o-F), -163.1 (t, 3JHH
19.9, p-F), -166.90 (brt, 3JHH ) 18.1, m-F).
)
Generation of Complexes 7b and 8b. Complex 1b (25 mg, 0.035
mmol) and [HNMe2Ph][B(C6F5)4] (27.8 mg, 0.035 mmol) were loaded
into a J-Young NMR tube within the glovebox and approximately 0.6
mL of C6D5Cl were added. After 56 h at room temp the solution changed
color from light-yellow to deep-yellow, while a mixture containing 7b
(ca. 80%), 1b, and other minor species was obtained.
Generation of Complex 9b. Complex 5b (20 mg, 0.0143 mmol)
and CH3N(C18H37)2 (7.7 mg, 0.0144 mmol) were weighted inside
a J-Young NMR tube and approximately 0.7 mL of C6D5Cl were
added at room temperature inside the glovebox. The reaction was
followed by NMR as described in the text, affording complex 9b
quantitatively after 1 h at room temperature. 1H NMR(C6D5Cl, 298
7b. 1H NMR (C6D5Cl, 251 K, J values in Hz): δ 8.11 (m, H8), 7.98
(d, 3JHH ) 8.3, H3), 7.94 (m, H5), 7.73 (d, 3JHH ) 6.9, H1), 7.68 (m, H6
and H7), 7.56 (dd, 3JHH ) 8.3, 3JHH ) 6.9, H2), 7.46 (m, H19, H12 and
H13), 7.28 (m, H20, H21 and H22), 7.17 (m, H27, H28 and H14), 6.98
(m, H29 and m-H), 6.77 (t, 3JHH ) 7.3, p-H), 6.70 (d, 3JHH ) 8.1, o-H),
6.60 (s, H17), 6.21 (dd, 3JHH ) 7.3, 4JHH ) 1.3, m-H′), 3.88 (sept, 3JHH
) 6.8, H31), 2.89 (sept, 3JHH ) 6.8, H24), 2.57 (sept, 3JHH ) 6.8, H34),
2.13 (s, H40), 1.48 (d, 3JHH ) 6.8, H32), 1.41 (d, 3JHH ) 6.8, H36), 1.40
(s, H38), 1.32 (d, 3JHH ) 6.8, H24a), 0.86 (s, H39), 0.64 (d, 3JHH ) 6.8,
H24b), 0.40 (d, 3JHH ) 6.8, H33), -0.09 (d, 3JHH ) 6.8, H35). Selected
13C{1H} NMR signals (C6D5Cl, 251 K): δ 192.9 (s, o-C′), 170.5 (s, C15),
155.8 (s, C11), 153.2 (s, Cipso), 141.8 (s, C13), 134.8 (s, mC′), 134.1 (s,
C3), 132.8 (s, mC), 130.5 (s, C5), 130.1 (buried under solvent signal, C6
and C7), 128.9 (s, pC), 127.7 (s, C2), 127.6 (s, C1), 124.5 (s, C14), 124.1
(s, C8), 117.2 (s, oC), 73.7 (s, C17), 66.7 (s, C38), 46.5 (s, C40), 44.1 (s,
C39), 29.3 (s, C34), 29.2 (s, C24), 28.8 (s, C31), 26.8 (s, C32), 26.0 (s,
C36), 24.9 (s, C24a), 24.0 (s, C33), 23.2 (s, C24b), 22.6 (s, C35). 19F
NMR (C6D5Cl, 251 K, J values in Hz): δ -132.10 (br, o-F), -162.7 (t,
3JHH ) 20.6, p-F), -166.60 (brt, 3JHH ) 17.9, m-F). After seven days at
room temperature, the solution changed its color from deep-yellow to light-
orange. The complete consumption of ion pair 7b was observed, while
mixture containing approximately 75% of 8b was obtained.
3
3
K, J values in Hz): δ 8.30 (d, JHH ) 8.5, H8), 8.16 (d, JHH
)
3
3
7.9, H2), 7.90 (d, JHH ) 7.9, H3), 7.79 (d, JHH ) 8.3, H5), 7.72
3
(d, 3JHH ) 8.0, H12), 7.53 (m, H7), 7.43 (m, H6), 7.35 (t, JHH
)
7.9, H13), 7.20-7.00 (m, H19, H20, H21, H22, H27, H28, H29),
3
3
6.74 (d, JHH ) 7.8, H14), 6.64 (s, H17), 3.37 (sept, JHH ) 6.6,
3
H31), 2.88 (sept, JHH ) 6.6, H34), 2.59 (m, H24 and NCH2-),
2.35 (m, NCH2-), 2.33 (s, NCH3), 2.21 (m, NCH2-), 1.48 (s, H38),
1.44 (d, 3JHH ) 6.6, H36), 1.35-1.20 (m, (-CH2-)n), 1.14 (m, H24a,
3
3
H33, H35), 0.88 (t, JHH ) 7.0, CH2CH3), 0.57 (d, JHH ) 6.6,
H24b), 0.14 (d, 3JHH ) 6.6, H32). Selected 13C{1H} NMR (C6D5Cl,
298 K): δ 202.2 (s, C1), 170.3 (s, C15), 163.8 (s, C11), 147.4 (s,
C26), 147.1 (s, C23), 145.2 (s, C25), 144.5 (s, C10), 144.3 (s, C30),
143.5 (s, C13), 138.9 (s, C18), 135.8 (s, C4), 131.5 (s, C2), 131.2
(s, C3), 130.0 (s, C5), 129.8 (s, C9), 128.9 (s, C7), 127.6 (s, C6),
123.7 (s, C8), 121.1 (s, C12), 120.4 (s, C14), 77.1 (s, C16), 71.7
(s, C38), 54.4 (s, NCH2-), 53.9 (s, NCH2-), 40.3 (s, NCH3),
32.0-24.0 (several signals corresponding to the (-CH2-)n, the main
signal is centered at 30.1 ppm), 28.7 (s, C24), 28.11 (s, C34) 28.07
(s, C31), 27.0, 26.0, 25.1 (C24a, C33, C35), 26.6 (S, C36), 24.0
9
J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008 10367

A R T I C L E S
Zuccaccia et al.
(s, C32), 22.6 (s, C24b), 14.3 (s, CH2CH3). 19F NMR (C6D5Cl,
ambient heat loss. The vial was loaded with 1-octene (10 mL),
catalyst, precatalyst, and enough toluene to give a final total volume
of 20 mL. The vial was fitted with a septum cap and a thermocouple
connected to a datalogging thermometer was introduced to record
the temperature of the reaction medium. The polymerization was
initiated by addition of the desired cocatalyst (1 equiv), and the
temperature was recorded until it began to decrease. Further details
of the specific polymerization experiments are given in the
Supporting Information.
3
298 K, J values in Hz): δ -132.24 (br, o-F), -162.95 (t, JHH
)
3
20.8, p-F), -166.75 (brt, JHH ) 18.5, m-F).
General Procedure for Propene Polymerization. Polymeriza-
tion experiments were carried out with a high throughput parallel
reactor setup (PPR24 available from Symyx Technologies, Inc.),
with three reactor modules each containing eight reaction cells (6
mL working volume per cell). The whole system is housed in a
triple MBraun LabMaster glovebox maintaining a pure nitrogen
atmosphere (oxygen and water levels <1 ppmv). The monomer gas
and quench gas lines are plumbed directly into the reactors and
controlled by automatic valves. Liquid reagents are robotically
added to individual cells by syringes. For the purpose of this work,
one eight-cell reactor was used (four experiments in duplicate)
according to the following procedure. The cells are fitted with a
preweighed glass vial insert and a disposable stirring paddle. The
reactor is then closed, and 0.25 mL of a 0.020 M solution of iBu3Al
in toluene and 3.95 mL of toluene are injected into each cell through
a valve. The reactor temperature is set to 50 °C, and stirring is
started at a speed of 800 rpm. The reactor is pressurized at 2.0 bar
(30 psi) with nitrogen and then an overpressure of 2.0 bar (30 psi)
of propene is applied. In an array of 8 × 1.2 mL glass vials
positioned on a vortexer, precatalyst, and activator are premixed
immediately prior to addition to the cells. To each vial, 0.890 mL
of toluene, 0.050 mL of a 4.0 mM precatalyst solution in toluene,
and 0.060 mL of a 4.0 mM activator solution in toluene are added.
Aliquots of the resultant solutions are then injected into the cells
(50 µL for activation with [CPh3][B(C6F5)4], 250 µL for activation
with [HNMe2Ph][B(C6F5)4]). In each cell the polymerization is run
at constant temperature and propene partial pressure until a
predetermined propene uptake is reached (typically, 100-150 mg),
at which point the reaction is quenched with air at 3.4 bar (50 psi)
overpressure. The reactor is opened, and the glass inserts are
unloaded from the cells, transferred to a centrifuge/vacuum drying
unit (Genevac EZ-2 Plus), and dried to constant weight, after which
the polymer samples are recovered and weighed. Reproducility of
polymer yield for experiments run is duplicate is typically better
than (20%.
Generation of Complex 12. Complex 2 (20 mg, 0.032 mmol) and
[HNMe2Ph][B(C6F5)4] (25.5 mg, 0.032 mmol) were loaded in two separate
vials inside the glovebox. C6D5Cl was added to both vials; the solutions
were mixed and then transferred into a J-Young NMR tube. Evolution of
gas was instantaneously observed inside the NMR tube. After 40 min a
mixture of 11 and 11′ was obtained as described in the text. Leaving the
NMR tube at room temperature for approximately 6 h or, alternatively,
gently warming it for 2-4 min caused the quantitative formation of 12.
1
H NMR(C6D5Cl, 298 K, J values in Hz): δ 7.60 (d, 3JHH ) 7.5, H9),
7.44 (t, 3JHH ) 7.3, H13), 7.40 (d, 3JHH ) 7.4, H12), 7.25 (m, H3, H4,
H29, H2), 7.12 (t, 3JHH ) 7.7, H28), 6.99 (t, 3JHH ) 7.2, H21), 6.91 (m,
H20 and H27), 6.82 (m, H14, H19 and m-H), 6.57 (s, H17), 6.10 (d, 3JHH
) 8.7, o-H), 6.01 (t, 3JHH ) 7.1, p-H), 3.26 (m, H31), 3.10 (sept, 3JHH
6.7, H34), 2.37 (s, H39 or H40), 2.11 (s, H40 or H39), 1.68 (d, 3JHH
)
)
6.7, H36), 1.33 (d, 3JHH ) 6.7, H35), 1.26 (dd, 2JHH ) 14.4,3JHH ) 13.2,
3
2
H32b), 0.97 (d, JHH ) 6.6, H33), 0.37 (dd, JHH ) 14.4,3JHH ) 4.7,
H32b). Cation 13C{1H} NMR (C6D5Cl, 298 K): δ 197.0 (s, C1), 169.9
(s, C15), 163.1 (s, C11), 151.0 (s, C26), 148.8 (s, Cipso), 146.8 (s, C10),
146.4 (s, C30), 143.3 (s, C13), 142.0 (s, C18) 141.1 (s, C25), 138.0 (s,
C2), 132.5 (s, m-C) 130.2 (s, C3), 129.9 (s, C4), 129.0 (s, C20, C22),
128.8 (s, C21), 128.4 (s, C19, C23), 127.5 (s, C28), 126.1 (s, C29), 125.0
(s, C9), 123.9 (s, C27), 121.1 (s, C14), 117.0 (s, C12), 114.5 (s, p-C),
113.3 (s, o-C), 82.5 (s, C32), 80.5 (s, C16), 40.5 (s, C39 or C40), 40.4 (s,
C40 or C39), 36.8 (s, C31), 28.6 (s, C34), 26.34 (s, C36), 26.30 (s, C33),
25.1 (s, C35). 19F NMR (C6D5Cl, 298 K, J values in Hz): δ -132.2 (br,
o-F), -162.7 (t, 3JHH ) 21.0, p-F), -166.6 (brt, 3JHH ) 18.5, m-F).
Acknowledgment. We thank the Ministero dell’Universita` e
della Ricerca (MUR, Rome, Italy) and The Dow Chemical
Company for support.
Supporting Information Available: Computational details,
additional NMR data, and X-ray crystallographic characteriza-
tion of complex 5b. This material is available free of charge
via the Internet at http://pubs.acs.org.
X-ray Crystallographic Analysis. Details of the analysis are
included in the Supporting Information.
General Procedure for 1-Octene Polymerization. In a glove-
box under inert atmosphere, a 40 mL vial was loaded with a
magnetic stir bar and was placed into a foam block to minimize
JA802072N
9
10368 J. AM. CHEM. SOC. VOL. 130, NO. 31, 2008