Controlled benzylation of α-diimine ligands bound to zirconium and hafnium: An alternative method for preparing mono- and bis(amido)M(CH 2Ph)n (n = 2, 3) complexes as catalyst precursors for isospecific polymerization of α-olefins

Article abstract of DOI:10.1021/om800880n

Reactions of M(CH₂Ph)₄ (M = Zr, Hf) with various α-diimine ligands afforded amido-imino or diamido complexes through intramolecular benzylation of the C=N bonds of the ligands. Selective benzylation of a-diimine ligands, i.e., single

Full text of DOI:10.1021/om800880n

680
Organometallics 2009, 28, 680–687
Controlled Benzylation of r-Diimine Ligands Bound to Zirconium
and Hafnium: An Alternative Method for Preparing Mono- and
Bis(amido)M(CH2Ph)n (n ) 2, 3) Complexes as Catalyst Precursors
for Isospecific Polymerization of r-Olefins
Hayato Tsurugi, Ryuji Ohnishi, Hiroshi Kaneko, Tarun K. Panda, and Kazushi Mashima*
Department of Chemistry, Graduate School of Engineering Science, Osaka UniVersity,
Toyonaka, Osaka 560-8531, Japan
ReceiVed September 10, 2008
Reactions of M(CH2Ph)4 (M ) Zr, Hf) with various R-diimine ligands afforded amido-imino or diamido
complexes through intramolecular benzylation of the CdN bonds of the ligands. Selective benzylation
of R-diimine ligands, i.e., single- and double-benzylation, was accomplished by varying the substituent
on the nitrogen atom of the imine moiety or the ligand backbone. Kinetic analysis of the second benzylation
step indicated that the benzyl group migrated from the metal center to the CdN moiety via an ordered
four-center transition state (∆Sq ) -3(4) eu for 3a; -5(9) eu for 5b). Upon activation with B(C6F5)3 or
[Ph3C][B(C6F5)4], amido-imino (3, 6) and diamido (2, 4) complexes became active catalysts for 1-hexene
polymerization, and the resulting poly(1-hexene)s had moderate isotacticity ([mmmm], up to 90%).
Polymerization of vinylcyclohexane was also catalyzed with moderate activity to give highly isotactic
poly(vinylcyclohexane) ([mmmm] > 95%) via a chain-end control mechanism.
ising methodology for convenient synthesis of the catalysts is
an alkylation reaction of the CdN bond of ligand precursors,
such as commercially available carbodiimides or imine-based
compounds easily designed by the condensation of amines and
aldehydes. The alkylation approach is controlled by selective
alkylation of the CdN bond of the ligands to give amido-metal
or imino-metal species. Sita et al. demonstrated one-pot
syntheses of Cp(amidinate)MR2 (M ) group 4 metal) complexes
by treating CpMR3 with appropriate carbodiimides via the
insertion of metal-alkyl into the CdN bond of carbodiimides.4
We investigated a selective alkylation reaction of the CdN bond
in a pyrrole-imine ligand motif and found that benzylation of
the CdN bond of the ligand could be controlled by varying the
scaffold of the pyrrole-imine ligand (bidentate or tridentate) or
the steric bulkiness on the nitrogen atom of the imine moiety.
This method allowed us to isolate a variety of group 4 metal
dibenzyl complexes having pyrrolyl-imine, pyrrolyl-amido, and
pyrrolyl-amido-imine ligands in a one-pot procedure.5,6 Con-
trolled alkylation of the CdN bond in a ligand motif by
alkylmetal complexes is one rational method to access a variety
of catalyst precursors supported by amido or imine moieties,
and such a controlled alkylation was reported for pyridine-
bis(imine), tetradentate phenol-imine, and bi/terpyridine ligand
systems of early transition metals, lanthanides, and main group
metals.7
Introduction
Recent progress in homogeneous R-olefin polymerization
catalysts has been focused on the development of nonmetal-
locene-type catalysts with flexibly tunable multidentate ligands.1
Because the catalytic activity as well as the regio- and
stereoselectivity of the polymerization reaction can be controlled
by modifying the ligand architecture, the simple preparation of
various precatalysts is desirable. Among the wide variety of
ligand types, amido- or imine-based ligands have attracted much
interest because precise steric and electronic control is possible
by changing the substituents at the nitrogen atoms of the
ligands.2 The high-throughput screening method developed by
Dow and Symyx for screening polymerization precatalysts uses
mainly an amine elimination reaction: the reaction of group 4
metal-amide complexes with various amine ligands, which
produce amido metal complexes, has been applied to finely
optimize pyridyl-amide-based group 4 metal catalysts with
unprecedented unique polymerization behavior.3 Another prom-
* Corresponding author. E-mail: mashima@chem.es.osaka-u.ac.jp. Fax:
81-6-6850-6245.
(1) (a) Brintzinger, H. H.; Fischer, D.; Muelhaupt, R.; Rieger, B.;
Waymouth, R. M. Angew. Chem., Int. Ed. 1995, 34, 1143. (b) Britovsek,
G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428.
(c) Ittel, S. D.; Johnson, L. K.; Brookhard, M. Chem. ReV. 2000, 100, 1169.
(d) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002,
41, 2237. (e) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103,
283.
(2) (a) Rieger, B.; Baugh, L. S.; Kracker, S.; Striegler, S. Late Transition
Metal Polymerization Catalysis: Wiley-VCH Verlag GmbH & Co. KGaA:
Weinheim, 2003. (b) Mitani, M.; Saito, J.; Ishii, S.; Nakayama, Y.; Makio,
H.; Matsukawa, N.; Matsui, S.; Mohri, J.; Furuyama, R.; Terao, H.; Bando,
H.; Tanaka, H.; Fujita, T. Chem. Rec. 2004, 4, 137.
Recently, we and the group at Dow Chemical independently
reported that the reaction of M(CH2Ph)4 (M ) Zr, Hf) with
neutral R-diimine ligands produces various tribenzyl complexes
supported by monoanionic amido-imino ligands (types A and
B in Chart 1), in which one CdN bond of the R-diimine ligand
(3) (a) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.;
Wenzel, T. T. Science 2006, 312, 714. (b) 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.
(c) Froese, R. D. J.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. J. Am.
Chem. Soc. 2007, 129, 7831.
(4) (a) Sita, L. R.; Babcock, J. R. Organometallics 1998, 17, 5228. (b)
Jayarante, K. C.; Sita, L. R. J. Am. Chem. Soc. 2000, 122, 958.
(5) Tsurugi, H.; Matsuo, Y.; Yamagata, T.; Mashima, K. Organome-
tallics 2004, 23, 2797.
(6) Tsurugi, H.; Yamagata, T.; Tani, K.; Mashima, K. Chem. Lett. 2003,
32, 756.
10.1021/om800880n CCC: $40.75
2009 American Chemical Society
Publication on Web 01/13/2009

Benzylation of R-Diimine Ligands Bound to Zr and Hf
Organometallics, Vol. 28, No. 3, 2009 681
Chart 1
is selectively benzylated.8,9 The research group at Dow Chemical
also reported that thermolysis of the tribenzyl complexes having
2,6-disubstituted aromatic substituents on the nitrogen atom
results in the formation of dibenzyl complexes with ene-diamido
dianionic ligands (type D),8 which is a typical coordination mode
of R-diimine ligands to early transition metals.10 Although
several transformations of neutral R-diimine ligands to monoan-
ionic amido-imino or dianionic ene-diamido ligands were
accomplished, double alkylation of both CdN bonds to form a
diamido ligand (type C) has not been reported. In the course of
our studies on controlling alkylation of the CdN bond of
R-diimine ligands, leading to various R-olefin polymerization
catalyst precursors, we found that a rational modification of
substituents on the nitrogen atom of R-diimine ligands led to
the selective formation of monobenzylated products A and B,
as well as double-benzylated product C. In this contribution,
we report the selective transformation of various R-diimine
ligands and M(CH2Ph)4 (M ) Zr and Hf) to give amido-imino
and bis(amido) complexes of zirconium and hafnium, and a
kinetic study for estimating thermodynamic parameters in the
second benzylation step of the double-benzylation reaction. The
mono- and double-benzylated complexes are capable of cata-
lyzing isospecific polymerization of 1-hexene and vinylcyclo-
hexane and copolymerization of ethylene and 1-hexene.
Figure 1. ORTEP drawing of the molecular structure of 2a. All
hydrogen atoms are omitted for clarity.
Table 1. Selected Bond Distances (Å) and Angles (deg) of 2a
Zr-N1
2.044(2)
2.275(3)
2.289(3)
1.488(3)
88.43(8)
109.48(10)
113.64(9)
84.76(16)
Zr-N2
2.037(2)
2.585(3)
1.498(3)
1.516(4)
109.20(9)
105.53(10)
124.58(9)
108.00(16)
Zr-C45
Zr-C46
Zr-C52
N2-C2
N1-Zr-N2
N1-Zr-C52
N2-Zr-C52
Zr-C45-C46
N1-C1
C1-C2
N1-Zr-C45
N2-Zr-C45
C45-Zr-C52
Zr-C52-C53
at δ 2.26 and 2.35 with a coupling constant of 10.2 Hz, and the
other was displayed as mutually coupled methylene protons at
δ 2.99 and 3.14 due to the benzyl groups that migrated into the
two imine moieties of 1a. A doublet of doublets centered at δ
4.47, coupled with the methylene protons of the benzyl group,
was assigned to the methine proton adjacent to the nitrogen
atom.6,7 The 1JC-H value (129 Hz) of ZrCH2Ph of 2a indicated
that the benzyl group coordinated to the zirconium atom of 2a
in an η2-configuration in solution.11
The molecular structure of 2a was clarified by X-ray
crystallographic analysis (Figure 1), confirming the formation
of a dianionic bis(amido) ligand by the double benzylation of
both imine moieties of 1a with an anti-stereochemistry. The
zirconium atom adopted a pseudo-tetrahedral geometry. Al-
though the two benzyl groups bound to zirconium are magneti-
cally equal on the NMR time scale, an interaction between the
ipso carbon of one benzyl group and the zirconium atom
(Zr-C46, 2.585(3) Å; Zr-C45-C46, 84.76(16)°) was observed
in the solid state.5,6,12 The N1-C1 (1.498(3) Å) and N2-C2
(1.488(3) Å) bonds were in the normal range for a single bond,
and the Zr-N(amido) bonds Zr-N1 (2.044(2) Å) and Zr-N2
Results and Discussion
Synthesis and Characterization of Zirconium and
Hafnium Complexes. Treatment of the R-di(aldimine) ligand
1a with Zr(CH2Ph)4 produced the double-benzylated bis(amido)
1
complex 2a in moderate isolated yield (eq 1). The H NMR
spectrum of 2a in benzene-d6 had a symmetric pattern with two
sets of benzyl methylene protons: one was observed as an AB-
type resonance due to the benzyl groups bound to the zirconium
(7) An alkylation of the CdN bond of a ligand backbone was reported
in several cases. The use of pyridine-bis(imine) ligands: (a) Bruce, M.;
Gibson, V. C.; Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J.
Chem. Commun. 1998, 2523. The use of tetradentate phenol-imine
ligands: (b) Woodman, P. R.; Alcock, N. W.; Munslow, I. J.; Sanders, C. J.;
Scott, P. J. Chem. Soc., Dalton Trans. 2000, 3340. (c) Knight, P. D.; Clarke,
A. J.; Kimberley, B. S.; Jackson, R. A.; Scott, P. Chem. Commun. 2002,
352. (d) Knight, P. D.; O’Shaughnessy, P. N.; Munslow, I. J.; Kimberley,
B. S.; Scott, P. J. Organomet. Chem. 2003, 683, 103. (e) Knight, P. D.;
Clarkson, G.; Hammond, M. L.; Kimberley, B. S.; Scott, P. J. Organomet.
Chem. 2005, 690, 5125. The use of bi-/terpyridine ligands: (f) Jantunen,
K. C.; Scott, B. L.; Hay, P. J.; Gordon, J. C.; Kiplinger, J. L. J. Am. Chem.
Soc. 2006, 128, 6322. (g) Masuda, J. D.; Jantunen, K. C.; Scott, B. L.;
Kiplinger, J. L. Organometallics 2008, 27, 803. (h) Masuda, J. D.; Jantunen,
K. C.; Scott, B. L.; Kiplinger, J. L. Organometallics 2008, 27, 1299.
(8) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi, H. Chem. Lett.
2007, 36, 1420.
(10) (a) Galindo, A.; Ienco, A.; Mealli, C. New J. Chem. 2000, 24, 73,
and references therein. (b) van Koten, G.; Vrieze, K. AdV. Organomet. Chem.
1982, 21, 151. (c) Vrieze, K. J. Organomet. Chem. 1986, 300, 307. (d)
Mashima, K.; Matsuo, Y.; Tani, K. Chem. Lett. 1997, 767. (e) Pindado,
G. J.; Thornton-Pett, M.; Bochmann, M. J. Chem. Soc., Dalton Trans. 1998,
393. (f) Kawaguchi, H.; Yamamoto, Y.; Asaoka, K.; Tatsumi, K. Orga-
nometallics 1998, 17, 4380. (g) Mashima, K.; Matsuo, Y.; Tani, K.
Organometallics 1999, 18, 1471. (h) Tsurugi, H.; Ohno, T.; Yamagata, T.;
Mashima, K. Organometallics 2006, 25, 3179.
(11) Bochmann, M.; Lancaster, S. J. Organometallics 1993, 12, 633.
(12) (a) Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse,
M. B. J. Chem. Soc., Dalton Trans. 1984, 2789. (b) Latesky, S. L.;
McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P.; Huffman, J. C.
Organometallics 1985, 4, 902. (c) Pellecchia, C.; Immirzi, A.; Grassi, A.;
Zambelli, A. Organometallics 1993, 12, 4473.
(9) De Waele, P.; Jazdzewski, B. A.; Klosin, J.; Murray, R. E.; Theriault,
C. N.; Vosejpka, P. C.; Petersen, J. L. Organometallics 2007, 26, 3896.

682 Organometallics, Vol. 28, No. 3, 2009
Tsurugi et al.
(2.037(2) Å) were within the range observed for zirconium-
nitrogen single bonds.13 Both amido nitrogen atoms (the sum
of angles around the amido nitrogen atoms ) 359.91° and
359.93°) were planar, thus resulting in the formation of a planar
five-membered metallacyclic ring.
In contrast to the reaction of Zr(CH2Ph)4, Hf(CH2Ph)4 reacted
with the same ligand 1a in toluene at -78 °C to give the
corresponding monobenzylated complex 3a, which was a
product of the monobenzylation of one of two CdN bonds
followed by intramolecular hydrogen transfer, the same as that
observed for the reactions of M(CH2Ph)4 (M ) Zr, Hf) with
R-di(aldimine) ligands having a 2,6-disubstituted aryl ring.8,9
Complex 3a was thermally stable at room temperature, and no
further benzylation reaction proceeded under mild conditions.
Complex 3a was characterized on the basis of its spectral data
Figure 2. First-order thermal decomposition of 3a at 333, 343, 353,
and 363 K.
1
and combustion analysis. The H NMR spectrum of 3a in
benzene-d6 displayed rather simple singlet signals due to two
benzyl methylene protons at δ 2.46 and 3.12, respectively,
assignable to the benzyl groups bound to the hafnium atom and
the benzyl group bound to the ligand in a 3:1 integral ratio.
The resonance of methylene protons between the amido nitrogen
and imine moiety was observed as a singlet at δ 4.52 with two-
proton intensity.
Figure 3. Eyring plot of the first-order thermal decomposition of
3a.
Scheme 1
When the hexane solution of 3a was heated to 110 °C for
5 h in a sealed tube, further benzylation of the other imine
moiety of the ligand proceeded to afford bis(amido)hafnium
1
complex 4a. In the H NMR spectrum, the resonances due to
methylene protons bound to hafnium were observed at δ 2.08
and 2.18 as a typical ABq signal, whereas the methylene protons
of the two benzyl groups inserted into the imine moiety were
observed as a doublet of doublets centered at δ 2.87 (2JH-H
)
14.0 Hz and 3JH-H ) 10.7 Hz) and 3.15 (2JH-H ) 14.0 Hz and
3JH-H ) 3.6 Hz). The similarity of the 1H NMR spectrum of 4a
to that of 2a suggested that 4a was a doubly benzylated
bis(amido) complex. This result is in sharp contrast to that
reported by Dow Chemical Company: thermolysis of a similar
hafnium tribenzyl complex bearing 2,6-diisopropylphenyl groups
at the nitrogen atoms afforded an ene-diamido complex (type
D in Chart 1) via the elimination of two benzyl groups.10 The
mechanism for the conversion of 3a to 4a might involve pre-
equilibrium of the 1,2-hydrogen shift before the second ben-
zylation (Scheme 1). The differences between the two reaction
patterns observed by us and the Dow Chemical group may be
due to the steric bulkiness around the imine moiety; the less
bulky aromatic ring of 1a allowed for the second benzylation
of the imine group of 3a.
The intramolecular benzylation process from 3a to 4a obeyed
first-order kinetics at 333, 343, 353, and 363 K (Figure 2), as
determined by 1H NMR spectroscopy. The corresponding Eyring
plot afforded the thermodynamic parameters ∆Hq ) 26(2) kcal
mol-1 and ∆Sq ) -3(4) eu (Figure 3). Scott et al. investigated
the kinetics of thermolysis of dibenzylzirconium complexes
containing a tetradentate phenoxyimine ligand, revealing that a
simple insertion reaction of a benzyl group bound to zirconium
into the imino moiety obeyed first-order kinetics with a negative
∆Sq value (Figure 4).7d,14 A radical mechanism was accordingly
(13) (a) Scollard, J. D.; McConville, D. H.; Vittal, J. J. Organometallics
1997, 16, 4415. (b) Gibson, V. C.; Kimberley, B. S.; White, A. J. P.;
Williams, D. J.; Howard, P. Chem. Commun. 1998, 313. (c) Jeon, Y. M.;
Park, S. J.; Heo, J.; Kim, K. Organometallics 1998, 17, 3161. (d) Jeon,
Y. M.; Heo, J.; Lee, W. M.; Chang, T. H.; Kim, K. Organometallics 1999,
18, 4107. (e) Gauvin, R. M.; Lorber, C.; Choukroun, R.; Donnadieu, B.;
Kress, J. Eur. J. Inorg. Chem. 2001, 2337. (f) Daniele, S.; Hitchcock, P. B.;
Lappert, M. F.; Merle, P. G. J. Chem. Soc., Dalton Trans. 2001, 13.
(14) Rice, F. O.; Herzfeld, K. F. J. Am. Chem. Soc. 1934, 56, 284.

Benzylation of R-Diimine Ligands Bound to Zr and Hf
Organometallics, Vol. 28, No. 3, 2009 683
r-Olefin Polymerization Behavior of Zirconium and
Hafnium Complexes. Zirconium and hafnium dibenzyl com-
plexes 2 and 4 having C2-symmetric chiral diamido ligands may
act as isospecific catalyst precursors. This hypothesis was tested
using these complexes as catalyst precursors for 1-hexene
polymerization and combining them with B(C6F5)3 or
[Ph3C][B(C6F5)4] as cocatalysts (Table 2). It is noteworthy that
these dibenzyl complexes activated by cocatalysts catalyzed the
polymerization of 1-hexene to afford isotactic-rich poly(1-
hexene) (up to [mmmm] ) 70% as determined by the 13C NMR
spectra of the polymers).17 In the 1H NMR spectra of the
resulting polymer having a bimodal distribution, signals char-
acteristic of the disubstituted vinylidene (around δ 4.7; arising
from a ꢀ-hydrogen elimination after a 1,2-insertion) and the
vinylene (around δ 5.4; arising from a ꢀ-hydrogen elimination
after a 2,1-insertion) end groups were observed as main
Figure 4. Thermal decomposition of dibenzylzirconium complexes
having a tetradentate phenoxyimine ligand (from refs 7b-e).
Scheme 2
unsaturated end groups (Table 2, entry 5).18 The H NMR
1
spectra of poly(1-hexene)s with a unimolecular weight distribu-
tion displayed the resonance (around δ 5.4) corresponding to
the vinylene end groups (see the Supporting Information for
ruled out because it had a positive ∆Sq value together with less
selective formation of many products. Thus, the negative
activation entropy observed in our case suggested that a
concerted four-membered cyclic transition state occurred during
the second benzylation of the nascent product 3a′.
1
the H NMR spectrum of poly(1-hexene)s). The broadened
polydispersity and the higher molecular weight compared to the
calculated value based on the ratio of the catalyst and 1-hexene
implied the polymerization occurred in an uncontrolled manner,
which was presumably due to the rapid decomposition of the
catalytically active cationic species or slow initiation compared
to the propagation. Selection of the cocatalyst remarkably
affected the polymerization activity of this catalyst system. The
combination of dibenzyl complexes 2a and 4a-c with B(C6F5)3
resulted in very low yield (up to 4% yield of poly(1-hexene),
entries 1-5), whereas the combination of [Ph3C][B(C6F5)4] with
4a and 4b afforded poly(1-hexene)s in moderate to good yields
(entries 10-12). The tendency of the benzyl[tris(pentafluo-
rophenyl)]borate anion to bind to a naked cationic metal center
through η6-coordination of the benzyl group12c dramatically
retards the catalytic activity. When dibenzyl complexes were
treated with [Ph3C][B(C6F5)4] in the absence of 1-hexene, the
cationic species was thermally sensitive and rapidly decom-
posed. In contrast, treatment of 2a or 4a with B(C6F5)3 resulted
in the formation of rather stable zwitterionic benzyl complexes
in which coordination of the benzylborate anion to the metal
center was confirmed by the ∆(m,p-F) in the 19F NMR spectra
(eq 4).19
We previously reported that alkyl-substituted R-di(aldimine)
ligands such as 1b and 1c react with Hf(CH2Ph)4 at -78 °C to
give the corresponding monobenzylated complexes 5b and 5c.8
We anticipated that the remaining CdN bond of 5b and 5c could
react further with Hf-CH2Ph. In fact, this reaction occurred under
a high reaction temperature or a prolonged reaction time to give
the corresponding double-benzylated complexes 4b and 4c
(Scheme 2), which were spectroscopically characterized to have
the same ligand backbone and benzyl groups as 2a and 4a,
respectively. Kinetic analysis of the transformation from 5b to
4b was perfomed at 358, 363, 368, and 373 K, and similar to
3a, the first-order rate constant was obtained for each temper-
ature (Figure S1 in the Supporting Information), giving the
activation parameters ∆Hq ) 26(3) kcal/mol and ∆Sq ) -5(9)
eu (Figure S2 in the Supporting Information). Thus, benzyl
migration from 5b to 4b also proceeded through an ordered
cyclic transition state.
When the R-di(ketimine) ligands 1d-g were used, monoben-
zylation proceeded smoothly to give the corresponding com-
plexes 6d-g in moderate to excellent yield (eq 3). In contrast
to the reaction of R-di(aldimine) ligands, neither methyl
migration nor double benzylation occur even upon heating the
solution of 6f at 100 °C overnight, being consistent with the
fact that ꢀ-methyl elimination rarely proceeds via a C-C bond
cleavage in early transition metal complexes.15,16
(16) (a) Eshuis, J. J. W.; Tan, Y. Y.; Meetsma, A.; Teuben, J. H.;
Renkema, J.; Evans, G. G. Organometallics 1992, 11, 362. (b) Suzuki, Y.;
Yasumoto, T.; Mashima, K.; Okuda, J. J. Am. Chem. Soc. 2006, 128, 13017.,
and references therein.
(17) Asakura, T.; Demura, M.; Nishiyama, Y. Macromolecules 1991,
24, 2334.
(18) Liu, Z.; Somsook, E.; White, C. B.; Rosaaen, K. A.; Landis, C. R.
J. Am. Chem. Soc. 2001, 123, 11193.
(19) (a) Horton, A. D.; de With, J.; van der Linden, A. J.; van de Weg,
H. Organometallics 1996, 15, 2672. (b) Horton, A. D.; de With, J.
Organometallics 1997, 16, 5424.
(15) Riollet, V.; Cope´ret, C.; Basset, J.-M.; Rousset, L.; Bouchu, D.;
Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41, 3025.

684 Organometallics, Vol. 28, No. 3, 2009
Tsurugi et al.
Table 2. 1-Hexene Polymerization Behavior of C2-Symmetric
Zirconium and Hafnium Complexes Activated with B(C6F5)3 or
[Ph3C][B(C6F5)4]a
Table 3. 1-Hexene Polymerization Behavior of Hafnium Tribenzyl
Complexes Activated with B(C6F5)3 or [Ph3C][B(C6F5)4]a
cat./
temp
(°C)
yield
(%)
[mmmm]
c
cat./
temp
(°C)
yield
(%)
Mw
Mw/
Mn
[mmmm]
entry
cocat.b
Mw (103)c
Mw/Mn
(%)d
c
entry
cocat.b
(× 103)c
(%)d
1
6d/B
6d/B
6e/B
6e/B
6f/B
6f/B
6g/B
6d/TB
6d/TB
6e/TB
6e/TB
6f/TB
6f/TB
6g/TB
rt
-20
rt
-20
rt
-20
rt
rt
-20
rt
-20
rt
-20
rt
88
86
91
86
91
86
tr
88
90
91
90
92
92
3
45
375
46
187
24
138
nd
102
385
100
225
30
2.3
1.7
2.1
6.5
2.3
2.3
nd
4.0
2.3
5.6
7.2
2.4
1.7
5.5
65
75
60
80
60
90
nd
30
80
40
80
60
90
40
1
2
3
2a/B
4a/B
4b/B
rt
rt
rt
3
4
tr
bimodal
190
nd
1.5
nd
nd
55
nd
2e
3
nd
4e
5
4
4c/B
rt
tr
nd
nd
nd
5
2a/TB
2a/TB
4a/TB
4a/TB
4b/TB
4b/TB
4c/TB
4c/TB
rt
-10
rt
-10
rt
-10
rt
28
11
37
54
89
6
bimodal
314
365
451
239
nd
245
361
nd
nd
70
45
55
atactic
atactic
55
6e
7
6e
7
1.5
1.5
1.5
1.9
nd
8
8e
9
9e
10
11e
12
13e
14
10e
11
12e
20
23
1.6
1.3
-10
50
179
318
a Conditions: [cat.]:[cocat.]:[1-hexene] ) 0.01:0.01:5.0 (in mmol) in
C6H5Cl for 6 h. Total volume is 2 mL. b B ) B(C6F5)3, TB )
[Ph3C][B(C6F5)4]. c Determined by GPC. d Determined by 13C NMR (ref
17). e Polymerization for 24 h.
a Conditions: [cat.]:[cocat.]:[1-hexene] ) 0.01:0.01:5.0 (in mmol) in
C6H5Cl for 6 h. Total volume is 2 mL. b B ) B(C6F5)3, TB )
[Ph3C][B(C6F5)4]. c Determined by GPC. d Determined by 13C NMR (ref
17). e Polymerization for 24 h.
Table 4. Vinylcyclohexane Polymerization Behavior of Zirconium
and Hafnium Complexes Activated with [Ph3C][B(C6F5)4]a
entry
cat.
temp (°C)
yield (%)
Tm (°C)c
[mmmm] (%)d
1
2
3
4
2a
3a
4a
6f
rt
rt
rt
rt
8
64
20
87
>95
>95
>95
>95
339
347
a Conditions: [cat.]:[cocat.]:[1-hexene] ) 0.01:0.01:5.0 (in mmol) in
6 h. Total volume is 2
mL. b Determined by GPC.
d
Unexpectedly, Cs-symmetric hafnium tribenzyl complexes
6e-h were much better precatalysts for the polymerization of
1-hexene (Table 3). The polymers obtained by 6/B(C6F5)3 or
6/[Ph3C][B(C6F5)4] had moderate to excellent isotacticity (up
to [mmmm] ) 90%), despite the broad molecular weight
distribution. In the 13C NMR of the poly(1-hexene), the signal
of the C3 carbon derived from [mrrm]-pentad was not observed,
and lowering the polymerization temperature to -20 °C
increased the isotacticity, suggesting that stereoregularity re-
sulted from the chain-end control. In contrast to the dibenzyl
complexes 2a and 4a, both B(C6F5)3 and [Ph3C][B(C6F5)4]
effectively activated complexes 6, except for 6g, to give poly(1-
hexene) in excellent yield. As described in eq 5, the reactions
of 6f with these cocatalysts gave the corresponding ionic pairs
9f and 10f. In this case, the benzylborate anion of 9f was
separated from the metal center as confirmed by its 19F NMR
spectrum.
C6H5Cl for
c Determined by DSC. Determined by 13C NMR (ref 22).
Table 4, the activity of tribenzyl complexes 3a and 6f was
relatively high to give polymerized VCH (PVCH) in good yield.
Measuring 13C{1H} NMR spectra of PVCHs, only six sharp
peaks due to six different carbons of the highly isotactic polymer
were observed (Figure S14 in the Supporting Information).22
Recently, Sita et al. demonstrated living isospecific polymeri-
zation of VCH by half-sandwich zirconium acetamidinate
catalysts, and Kol disclosed that the non-Cp-type zirconium
complexes with amine-bis(phenolate) ligands catalyzed isospe-
cific VCH polymerization with ultrahigh activity.23 In all cases,
the achiral Cs-symmetric precatalysts afford highly isotactic
PVCHs, but the stereochemistry control mechanism is still not
clear due to the absence of the peaks corresponding to the
stereoerrors. Hafnium complexes 3a and 6f/[Ph3C][B(C6F5)4]
were found to be active catalysts for the copolymerization of
ethylene/1-hexene (Table S1 in the Supporting Information),
and there was relatively high 1-hexene incorporation (39%,
24
1
determined by H NMR ) in the catalyst system using 3a.
Conclusion
We demonstrated that the substituents on the nitrogen atoms
of the R-diimine ligands significantly affected the following
reaction pattern: (1) single benzylation of diaryl or dialkyl
R-di(aldimine) ligands or diaryl R-di(ketimine) ligands, giving
amido-imino complexes 3a, 5, and 6, and (2) double benzylation
The molecular structure of 2a suggested that the coordination
environment around the metal atoms in complexes 2-6 was
spacious enough to polymerize bulky monomers. We thus
studied the polymerization of vinylcyclohexane (VCH), which
is a monomer that is difficult to polymerize by homogeneous20
and heterogeneous21 catalysts due to the bulky cyclohexyl
substituent next to the vinyl moiety. Among the runs shown in
(22) (a) Ammendola, P.; Tancredi, T.; Zambelli, A. Macromolecules
1986, 19, 307. (b) Soga, K.; Nakatani, H.; Shiono, T. Macromolecules 1989,
22, 1499. (c) Endo, K.; Otsu, T. J. Polym. Sci., Part A: Polym. Chem. 1992,
30, 679.
(23) (a) Keaton, R. J.; Jayaratne, K. C.; Henningsen, D. A.; Koterwas,
L. A.; Sita, L. R. J. Am. Chem. Soc. 2001, 123, 6197. (b) Segal, S.; Yeori,
A.; Shuster, M.; Rosenberg, Y.; Kol, M. Macromolecule 2008, 41, 1612.
(24) Cho, D. J.; Wu, C. J.; Han, W.-S.; Kang, S. O.; Lee, B. Y.
Organometallics 2006, 25, 2133.
(20) Grisi, F.; Pragliola, S.; Costabile, C.; Longo, P. Polymer 2006, 47,
1930.
(21) (a) Kissin, Y. V. AdV. Polym. Sci. 1974, 15, 91. (b) Endo, K.; Fujii,
K.; Otsu, T. J. Polym. Sci., Part A 1991, 29, 1991.

Benzylation of R-Diimine Ligands Bound to Zr and Hf
Organometallics, Vol. 28, No. 3, 2009 685
129 Hz, ZrCH2Ph), 65.5 (d, 1JC-H ) 136 Hz, NCH), 111.0, 116.4,
123.0, 126.2, 126.4, 128.5, 129.6, 131.2, 139.9, 143.2, 149.6, 153.1.
Anal. Calcd for C58H72N2Zr: C, 78.41; H, 8.17; N, 3.15. Found: C,
78.07; H, 7.90; N, 3.25.
of the bis(3,5-di(tert-butyl)phenyl)-R-di(aldimine) or dialkyl-
R-di(aldimine) ligands, giving bis(amido) complexes 2 and 4.
Some of these complexes serve as catalyst precursors for
isospecific polymerizations of 1-hexene and VCH and copo-
lymerization of ethylene and 1-hexene polymerization upon
activation by the appropriate cocatalysts. Thus, in addition to
salt-, amine-, and alkane-eliminations, alkylation of the CdN
bonds of neutral ligands by starting alkyl complexes is a
convenient alternative method for preparing a wide variety of
early transition metal complexes, due to the easy alkylation of
polarized unsaturated CdN bonds bound to early transition
metals.
Preparation of (3,5-tBu2Ph-DAB-CH2Ph)Hf(CH2Ph)3 (3a). In
a Schlenk tube, Hf(CH2Ph)4 (1.10 g, 2.02 mmol) was dissolved in
toluene (10 mL) at room temperature. The solution was cooled to
-78 °C, and a solution of ligand 1a (873 mg, 2.02 mmol) in toluene
(5 mL) was added. The reaction mixture was allowed to warm to
room temperature and then stirred overnight. The color of the
solution turned orange. After removal of insoluble products by
centrifugation, all volatiles were removed in vacuo. The resulting
orange oil was dissolved in hexane (3 mL) and stored in a freezer
(-30 °C). Yellow microcrystals were formed and dried under
vacuum to give 3a (1.16 g, 1.19 mmol, 59% yield), mp 133-140
Experimental Section
1
°C. H NMR (300 MHz, C6D6, 35 °C): δ 1.31 (s, 18H, C(CH3)3),
General Procedures. All manipulations involving air- and
moisture-sensitive organometallic compounds were carried out
under argon using the standard Schlenk technique or an argon-
filled glovebox. B(C6F5)3 was purchased and used as received.
1.45 (s, 18H, C(CH3)3), 2.46 (s, 6H, HfCH2Ph), 3.12 (s, 2H, CH2Ph),
4.52 (s, 2H, NCH2), 6.58-6.63 (m, 2H, aromatics), 6.67 (d, 2H, 4J
t
) 1.6 Hz, NC6H3 Bu2-o), 6.86-7.01 (m, 11H, aromatics), 7.14 (m,
t
9H, aromatics), 7.29 (br t, 1H, NC6H3 Bu2-p), 7.39 (br t, 1H,
26,27
Compounds [Ph3C][B(C6F5)4],25 Zr(CH2Ph)4, and Hf(CH2Ph)4
NC6H3 Bu2-p). 13C NMR (75 MHz, C6D6, 35 °C): δ 31.6 (CH3),
t
and 1,4-diaza-1,3-butadiene ligands28 were prepared according to
the literature. Hexane and toluene were dried and deoxygenated
by distillation over sodium benzophenone ketyl under argon.
1-Hexene and vinylcyclohexane were distilled from sodium ben-
zophenone ketyl and then distilled over CaH2 by trap-to-trap
distillation, stored in glovebox. Chlorobenzene was distilled over
CaH2 by trap-to-trap distillation, stored in glovebox. Benzene-d6,
bromobenzene-d5, and toluene-d8 were distilled from P2O5 and
thoroughly degassed by trap-to-trap distillation before use.
1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
measured on a Varian-Unity-Inova-300 spectrometer. Assignments
32.0 (CH3), 35.4 (C(CH3)3), 35.5 (C(CH3)3), 39.0 (CH2Ph), 64.3
(NCH2), 84.7 (HfCH2Ph), 112.0, 114.9, 122.1, 127.4, 127.9, 128.1,
128.2, 128.5, 128.6, 128.7, 128.9, 129.0, 143.1, 145.1, 151.5, 152.5,
189.8 (NdC). Anal. Calcd for C58H72N2Hf: C, 71.40; H, 7.44; N,
2.87. Found: C, 71.49; H, 7.38; N, 2.95.
Preparation of (3,5-tBu2Ph-DAB-(CH2Ph)2)Hf(CH2Ph)2
(4a). In a sealed Schlenk tube, 3a (100 mg, 0.102 mmol) was
dissolved in hexane (3 mL) at room temperature. The solution was
stirred for 5 h at 110 °C. The color of the solution turned orange.
After removal of insoluble products by centrifugation, all volatiles
were removed in vacuo to give 4a as a yellow-orange powder (89.5
mg, 91.7 µmol, 90% yield), mp 148-150 °C. 1H NMR (300 MHz,
1
for H and 13C NMR peaks for all complexes were aided by 2D
1H-1H COSY and 2D 1H-13C HETCOR spectra, respectively. The
gel permeation chromatographic analyses were carried out at 40
°C by using a Shimadzu LC-10A liquid chromatograph system and
a RID 10A refractive index detector, equipped with a Shodex KF-
806 L column, which was calibrated versus commercially available
polystyrene standards (Showa Denko). Thermal analyses of the
polymers were made on a Seiko DSC 6200 under an N2 atmosphere.
The samples were heated to 400 °C. The DSC curves were recorded
2
C6D6, 35 °C): δ 1.46 (s, 36H, C(CH3)3), 2.08 (d, 2H, J ) 11.5
2
Hz, HfCHHPh), 2.18 (d, 2H, J ) 11.5 Hz, HfCHHPh), 2.87 (dd,
2H, 2J ) 14.0 Hz, 3J ) 10.7 Hz, CHHPh), 3.15 (dd, 2H, 2J ) 14.0
3
3
Hz, J ) 3.6, CHHPh), 4.55 (dd, 2H, J ) 3.6, 10.7 Hz, NCH),
6.80-7.24 (m, 26H, aromatics). 13C NMR (75 MHz, C6D6, 35 °C):
δ 31.8 (CH3), 35.3 (C(CH3)3), 42.7 (CH2Ph), 60.8 (d, 1JC-H ) 138
Hz, NCH), 72.0 (t, 1JC-H ) 126 Hz, HfCH2Ph), 111.0, 115.9, 123.7,
126.2, 127.2, 127.8, 128.6, 129.4, 130.8, 139.9, 150.2, 152.6.
at a heating rate of 10 °C min-1
.
Preparation of (3,5-tBu2Ph-DAB-(CH2Ph)2)Zr(CH2Ph)2
(2a). To a solution of Zr(Ch2Ph)4 (542 mg, 1.19 mmol) in toluene
(10 mL) cooled to - 78 °C was added a solution of ligand 1a (514
mg, 1.19 mmol) in toluene (10 mL). The reaction mixture was
allowed to warm to room temperature and then stirred overnight.
The color of the solution turned to red-orange. After removal of
insoluble products by centrifugation, all volatiles were removed in
vacuo. The resulting red-orange solid was dissolved in hexane (7
mL) and stored in a freezer (-30 °C). Orange microcrystals were
formed and dried under vacuum to give 2a (614 mg, 0.691 mmol,
Compounds 5b and 5c were prepared as described in the
procedure for 3a.
Preparation of (Cy-DAB-CH2Ph)Hf(CH2Ph)3 (5b). Yield:
76%, mp 162-164 °C (dec). 1H NMR (300 MHz, C6D6, 35 °C): δ
0.43-1.97 (m, 20H, cyclohexyl), 2.01 (d, 3H, 2J ) 12.1 Hz,
HfCHHPh), 2.06 (d, 3H, 2J ) 12.1 Hz, HfCHHPh), 2.54 (dd, 1H,
2J ) 13.5 Hz, 3J ) 7.4 Hz, CHHPh), 2.85 (dd, 1H, 2J ) 13.5 Hz,
3J ) 3.8 Hz, CHHPh), 3.45 (m, 1H, cyclohexyl), 3.82 (m, 1H,
cyclohexyl), 4.43 (ddd, 1H, 3J ) 1.7, 3.8, 7.4 Hz, NCH), 6.90-6.97
(m, 5H, aromatics), 7.05 (d, 6H, J ) 7.1 Hz, o-Ph of HfCH2Ph),
3
1
7.11-7.22 (m, 3H, aromatics), 7.28 (t, 6H, J ) 7.7 Hz, m-Ph of
58% yield), mp 125-130 °C. H NMR (300 MHz, C6D6, 35 °C):
HfCH2Ph), 7.71 (d, 1H, J ) 1.7 Hz, NdCH). 13C NMR (75 MHz,
C6D6, 35 °C): δ 25.5 (CH2), 25.6 (CH2), 26.0 (CH2), 26.3 (CH2),
27.1 (CH2), 27.2 (CH2), 33.3 (CH2), 34.3 (CH2), 35.0 (CH2), 35.8
(CH2), 43.7 (CH2Ph), 56.2, 61.8, 68.3 (NCH), 82.5 (Hf(CH2Ph)),
121.7, 127.3, 127.4, 128.6, 128.8, 130.5, 137.1, 147.9, 178.2
(NdCH). Anal. Calcd for C42H52N2Hf: C, 66.08; H, 6.87; N, 3.67.
Found: C, 65.99; H, 7.15; N, 3.74.
2
δ 1.26 (s, 36H, C(CH3)3), 2.26 (d, 2H, J ) 10.2 Hz, ZrCHHPh),
2
2
2.35 (d, 2H, J ) 10.2 Hz, ZrCHHPh), 2.99 (dd, 2H, J ) 13.7
Hz, 3J ) 10.2 Hz, CHHPh), 3.14 (dd, 2H, 2J ) 13.7 Hz, 3J ) 4.1
Hz, CHHPh), 4.47 (dd, 2H, 3J ) 4.1, 10.2 Hz, NCH), 6.80 (d, 4H,
4J ) 1.6 Hz, NC6H3 Bu2-m), 6.81-7.18 (m, 20H, aromatics), 7.24
t
(t, 2H, J ) 1.6 Hz, NC6H3 Bu2-p). 13C NMR (75 MHz, C6D6, 35
4
t
°C): δ 31.8 (CH3), 35.3 (C(CH3)3), 42.9 (CH2Ph), 63.7 (t, 1JC-H
)
Preparation of (tBu-DAB-CH2Ph)Hf(CH2Ph)3 (5c). Yield:
1
41%, mp 90-92 °C (dec). H NMR (300 MHz, C6D6, 35 °C): δ
(25) Chien, J. C. W.; Tsai, W. M.; Rausch, M. D. J. Am. Chem. Soc.
1991, 113, 8570.
(26) Zucchini, U.; Albizzati, E.; Giannini, U. J. Organomet. Chem. 1971,
26, 357.
(27) Felten, J. J.; Anderson, W. P. J. Organomet. Chem. 1972, 36, 87.
(28) (a) Kliegman, J. M.; Barnes, R. K. Tetrahedron 1970, 26, 2555.
(b) Kliegman, J. M.; Barnes, R. K. J. Org. Chem. 1970, 35, 3140. (c) Zhong,
H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2002, 124, 1378.
1.01 (s, 9H, C(CH3)3), 1.13 (s, 9H, C(CH3)3), 2.39 (br, 6H,
2
3
HfCH2Ph), 2.67 (dd, 1H, J ) 13.2 Hz, J ) 11.3 Hz, CHHPh),
3.09 (dd, 1H, 2J ) 13.2 Hz, 3J ) 5.5 Hz, CHHPh), 3.93 (ddd, 1H,
3J ) 2.7, 5.5, 11.3 Hz, NCH), 6.88-7.23 (m, 14H, aromatics), 7.28
3
(t, 6H, J ) 7.4 Hz, HfCH2C6H5-m), 7.83 (d, 1H, J ) 2.7 Hz,
NdCH). 13C NMR (75 MHz, C6D6, 35 °C): δ 30.0 (C(CH3)3), 31.0

686 Organometallics, Vol. 28, No. 3, 2009
Tsurugi et al.
(C(CH3)3), 46.6 (CH2Ph), 57.7 (C(CH3)3), 59.9 (C(CH3)3), 63.9
(Hf(CH2Ph)), 121.9, 122.0, 127.0, 127.7, 128.4, 129.0, 129.1, 138.9,
176.4 (NdC). Anal. Calcd for C38H48N2Hf: C, 64.17; H, 6.80; N,
3.94. Found: C, 64.46; H, 7.11; N, 4.60.
Preparation of (3,5-Me2C6H3-MeDAB-CH2Ph)Hf(CH2Ph)3
(6e). Yield: 75%, mp 108 °C (dec). 1H NMR (300 MHz, C6D6, 35
°C): δ 1.08 (s, 3H, NdCCH3), 1.39 (s, 3H, NCCH3), 1.96 (d, 3H,
2
2J ) 11.8 Hz, HfCHHPh), 2.06 (s, 6H, CH3), 2.12 (d, 3H, J )
2
11.8 Hz, HfCHHPh), 2.27 (s, 6H, CH3), 2.43 (d, 1H, J ) 14.0
Preparation of (Cy-DAB-(CH2Ph)2)Hf(CH2Ph)2 (4b). In a
Schlenk tube, Hf(Ch2Ph)4 (309 mg, 0.551 mmol) was dissolved in
toluene (5 mL) at room temperature. The solution was cooled to -
78 °C, and a solution of Cy-DAB (125 mg, 0.551 mmol) in toluene
(7 mL) was added. The reaction mixture was allowed to warm to
room temperature and stirred overnight. Then the mixture was
stirred for 4 h at 100 °C. After removal of insoluble products by
centrifugation, all volatiles were evaporated to give 4b as an orange
2
Hz, CHHPh), 3.45 (d, 1H, J ) 14.0 Hz, CHHPh), 5.80 (br, 2H,
aromatics), 6.63 (d, 6H, 3J ) 7.1 Hz, o-Ph of HfCH2Ph), 6.63 (2H,
aromatics overlapped with other resonance), 6.88 (s, 1H, NC6H3Me2-
3
p), 6.90 (t, 3H, J ) 7.1 Hz, p-Ph of HfCH2Ph), 7.01 (s, 2H,
NC6H3Me2-o), 7.18 (t, 6H, 3J ) 7.1 Hz, m-Ph of HfCH2Ph),
7.23-7.43 (m, 4H, aromatics). 13C NMR (75 MHz, C6D6, 35 °C):
δ 19.7 (CH3), 21.1 (CH3), 21.6 (CH3), 25.5 (CH3), 44.6 (CH2Ph),
79.0 (NC), 85.1 (Hf(CH2Ph)), 121.7, 127.9, 128.3, 129.0, 129.3,
129.5, 137.8, 139.3, 147.5, 147.7, 148.1, 193.6 (NdC). Anal. Calcd
for C48H52N2Hf: C, 69.01; H, 6.27; N, 3.35. Found: C, 68.64; H,
6.64; N, 3.39.
1
powder (162 mg, 0.212 mmol, 39% yield), mp 162 °C (dec). H
NMR (300 MHz, C6D6, 35 °C): δ 0.76-2.09 (m, 20H, cyclohexyl),
2.06 (br, 4H, HfCH2Ph), 2.82 (m, 2H, cyclohexyl), 2.91 (dd, 2H,
2J ) 13.7 Hz, 3J ) 9.9 Hz, CHHPh), 3.01 (dd, 2H, 2J ) 13.7 Hz,
Preparation of (3,5-tBu2C6H3-MeDAB-CH2Ph)Hf(CH2Ph)3
(6f). Yield: 97%, mp 193 °C (dec). 1H NMR (300 MHz, C6D6, 35
°C): δ 1.17 (s, 3H, NdCCH3), 1.26 (s, 18H, C(CH3)3), 1.42 (s,
3
3J ) 3.8 Hz, CHHPh), 3.66 (dd, 2H, J ) 3.8, 9.9 Hz, NCH),
6.77-7.34 (m, 20H, aromatics). 13C NMR (75 MHz, C6D6, 35 °C):
δ 25.3 (CH2), 26.0 (CH2), 26.2 (CH2), 33.7 (CH2), 34.7 (CH2), 43.7
(CH2Ph), 60.0, 60.7 (NCH), 69.8 (HfCH2Ph), 109.7, 122.3, 126.0,
127.7, 128.5, 129.2, 129.5, 140.5, 145.2. Anal. Calcd for
C42H52N2Hf: C, 66.08; H, 6.87; N, 3.67. Found: C, 66.54; H, 7.01;
N, 3.25.
2
18H, C(CH3)3), 1.56 (s, 3H, NCCH3), 2.01 (d, 3H, J ) 12.4 Hz,
2
HfCHHPh), 2.10 (d, 3H, J ) 12.4 Hz, HfCHHPh), 2.51 (d, 1H,
2J ) 14.5 Hz, CHHPh), 3.52 (d, 1H, 2J ) 14.5 Hz, CHHPh), 6.57
(d, 6H, 3J ) 7.4 Hz, o-Ph of HfCH2Ph), 6.90 (t, 3H, 3J ) 7.4 Hz,
p-Ph of HfCH2Ph), 7.14-7.58 (m, 11H, aromatics), 7.17 (t, 6H, 3J
) 7.4 Hz, m-Ph of HfCH2Ph). 13C NMR (75 MHz, C6D6, 35 °C):
δ 19.8 (CH3), 26.0 (CH3), 31.4 (C(CH3)3), 31.7 (C(CH3)3), 35.1
(C(CH3)3), 35.2 (C(CH3)3), 44.2 (CH2Ph), 79.1 (NC), 85.2
(Hf(CH2Ph)), 119.7, 120.0, 121.8, 126.3, 127.4, 127.8, 127.9, 128.4,
129.4, 129.5, 137.9, 147.2, 147.5, 147.7, 152.1, 152.8, 193.0 (NdC).
Anal. Calcd for C60H76N2Hf: C, 71.80; H, 7.63; N, 2.79. Found:
C, 71.27; H, 8.18; N, 2.78.
Preparation of (tBu-DAB-(CH2Ph)2)Hf(CH2Ph)2 (4c). To a
suspension of Hf(Ch2Ph)4 (581 mg, 1.07 mmol) in hexane (20 mL)
cooled to -78 °C was added a solution of tBu-DAB (180 mg, 1.07
mmol) in hexane (5 mL). The reaction mixture was allowed to warm
to room temperature and then stirred for 67 h. The color of the
solution turned yellow. After removal of insoluble products by
centrifugation, all volatiles were removed under vacuum to give
4c as a yellow powder (717 mg, 1.01 mmol, 94% yield), mp 82 °C
(dec). 1H NMR (300 MHz, C6D6, 35 °C): δ 1.13 (s, 18H, C(CH3)3),
1.89 (d, 2H, 2J ) 11.5 Hz, HfCHHPh), 2.17 (d, 2H, 2J ) 11.5 Hz,
Preparation of (Cy-MeDAB-CH2Ph)Hf(CH2Ph)3 (6g). Yield:
1
54%, mp 200 °C (dec). H NMR (300 MHz, C6D6, 35 °C): δ
0.80-2.13 (m, 20H, cyclohexyl), 1.03 (s, 3H, NdCCH3), 1.36 (s,
2
3
3H, NCCH3), 2.21 (d, 3H, 2J ) 11.8 Hz, HfCHHPh), 2.28 (d, 3H,
HfCHHPh), 2.92 (dd, 2H, J ) 14.8 Hz, J ) 10.4 Hz, CHHPh),
2
3
2
2J ) 11.8 Hz, HfCHHPh), 2.61 (d, 1H, J ) 14.3 Hz, CHHPh),
3.00 (dd, 2H, J ) 14.8 Hz, J ) 3.3 Hz, CHHPh), 3.58 (dd, 2H,
3J ) 3.3, 10.4 Hz, NCH), 6.87-7.31 (m, 20H, aromatics). 13C NMR
(75 MHz, C6D6, 35 °C): δ 29.8 (CH3), 45.3 (CH2Ph), 56.7 (NCH),
58.6 (C(CH3)3), 69.9 (HfCH2Ph), 122.2, 126.0, 127.6, 128.5, 129.0,
129.3, 140.5, 145.2. Anal. Calcd for C38H48N2Hf: C, 64.17; H, 6.80;
N, 3.94. Found: C, 64.18; H, 7.14; N, 4.48.
2
2.82 (d, 1H, J ) 14.3 Hz, CHHPh), 3.28-3.46 (m, 2H, cyclo-
3
hexyl), 6.91 (t, 3H, J ) 7.4 Hz, p-Ph of HfCH2Ph), 7.02-7.22
3
(m, 5H, aromatics), 7.09 (d, 6H, J ) 7.4 Hz, o-Ph of HfCH2Ph),
7.26 (t, 6H, 3J ) 7.4 Hz, m-Ph of HfCH2Ph). 13C NMR (75 MHz,
C6D6, 35 °C): δ 19.7 (CH3), 20.7 (CH3), 20.9 (CH3), 25.5 (CH3),
44.5 (CH2Ph), 79.1 (NC), 85.2 (Hf(CH2Ph)), 121.7, 122.7, 127.7,
127.9, 128.4, 129.3, 129.5, 130.1, 130.5, 131.4, 135.3, 136.0, 137.7,
144.8, 145.6, 147.5, 194.0 (NdC). Anal. Calcd for C44H56N2Hf:
C, 66.78; H, 7.13; N, 3.54. Found: C, 66.64; H, 7.38; N, 3.56.
Preparation of (4-MeC6H4-MeDAB-CH2Ph)Hf(CH2Ph)3
(6d). In a Schlenk tube, Hf(Ch2Ph)4 (292 mg, 0.537 mmol) was
dissolved in toluene (5 mL) at room temperature. The solution was
cooled to -78 °C, and a solution of 4-MeC6H4-MeDAB (299 mg,
0.649 mmol) in toluene (5 mL) was added. The reaction mixture
was allowed to warm to room temperature and then stirred
overnight. After removal of insoluble products by centrifugation,
all volatiles were removed in vacuo. The resulting orange solid
was washed with hexane to give 6e as pale yellow microcrystals
(397 mg, 0.492 mmol, 92% yield), mp 95 °C (dec). 1H NMR (300
MHz, C6D6, 35 °C): δ 1.00 (s, 3H, NdCCH3), 1.35 (s, 3H, NCCH3),
1.92 (d, 3H, 2J ) 11.8 Hz, HfCHHPh), 2.05 (s, 3H, CH3), 2.06 (d,
Observation of [(3,5-tBu2Ph-DAB-(CH2Ph)2)Zr(CH2Ph)]-
[PhCH2B(C6F5)3] (7a). In a glovebox, to a solid mixture of 2a (10
mg, 11 µmol) and B(C6F5)3 (5.7 mg, 11 µmol) was added C6D5Br
(0.60 mL) at -30 °C, and the solution was transferred to a J-Young
NMR tube. The color of the solution gradually turned orange. The
1H and 19F NMR spectra of the solution at 25 °C revealed the
quantitative
formation
of
[(3,5-tBu2Ph-DAB-(CH2Ph)2)-
1
Zr(CH2Ph)][PhCH2B(C6F5)3] (7a). H NMR (300 MHz, C6D5Br,
25 °C): δ 1.29 (s, 18H, C(CH3)3), 1.30 (s, 18H, C(CH3)3), 2.35 (d,
1H, 2J ) 11.6 Hz, ZrCHHPh), 2.57 (d, 1H, 2J ) 11.6 Hz,
ZrCHHPh), 2.73-2.90 (m, 2H, CH2Ph), 2.95-3.15 (m, 2H,
CH2Ph), 3.57 (br, 2H, BCH2Ph), 4.33-4.43 (m, 2H, NCH),
6.39-7.24 (aromatic protons). 19F NMR (282 MHz, C6D5Br, 25
°C): δ -130.5 (d, 6F, J ) 21.1 Hz, ortho), -160.7 (t, 3F, J )
21.1 Hz, para), -164.6 (m, 6F, meta).
2
2
3H, J ) 11.8 Hz, HfCHHPh), 2.27 (s, 3H, CH3), 2.40 (d, 1H, J
) 14.3 Hz, CHHPh), 3.27 (d, 1H, 2J ) 14.3 Hz, CHHPh), 6.00 (d,
3
3
2H, J ) 8.0 Hz, NC6H4CH3), 6.60 (d, 6H, J ) 7.1 Hz, o-Ph of
3
3
HfCH2Ph), 6.82 (d, 2H, J ) 8.0 Hz, NC6H4CH3), 6.92 (t, 3H, J
) 7.1 Hz, p-Ph of HfCH2Ph), 6.99-7.36 (m, 9H, aromatics), 7.19
(t, 6H, 3J ) 7.1 Hz, m-Ph of HfCH2Ph). 13C NMR (75 MHz, C6D6,
35 °C): δ 19.7 (CH3), 20.7 (CH3), 20.9 (CH3), 25.5 (CH3), 44.5
(CH2Ph), 79.1 (NC), 85.2 (Hf(CH2Ph)), 121.7, 122.7, 127.7, 127.9,
128.4, 129.3, 129.5, 130.1, 130.5, 131.4, 135.3, 136.0, 137.7, 144.8,
145.6, 147.5, 194.0 (NdC). Anal. Calcd for C46H48N2Hf: C, 68.43;
H, 5.99; N, 3.47. Found: C, 67.98; H, 6.25; N, 3.51.
Observation of [(3,5-tBu2Ph-DAB-(CH2Ph)2)Hf(CH2Ph)]-
[PhCH2B(C6F5)3] (8a). In a glovebox, to a solid mixture of 4a (10
mg, 11 µmol) and B(C6F5)3 (5.7 mg, 11 µmol) was added C6D5Br
(0.60 mL) at -30 °C, and the solution was transferred to a J-Young
NMR tube. The color of the solution gradually turned orange. The
1H and 19F NMR spectra of the solution at 25 °C revealed the
quantitative formation of [(3,5-tBu2Ph-DAB-(CH2Ph)2)Hf-
Compounds 6e-g were prepared as described in the procedure
for 6d.

Benzylation of R-Diimine Ligands Bound to Zr and Hf
Organometallics, Vol. 28, No. 3, 2009 687
1
(CH2Ph)][PhCH2B(C6F5)3] (8a). H NMR (300 MHz, C6D5Br, 25
reaction was quenched by adding MeOH. The polymer was
extracted with hexane, and the extract was purified by passing
through silica gel. Polymer was obtained by evaporating hexane
and dried at 60 °C. The isotacticity of the poly(1-hexene) was
determined by the 13C NMR measurement.17
Polymerization of Vinylcyclohexane. In a glovebox, a solution
of precatalyst (10 µmol) in C6H5Cl (0.50 mL) was added to a
solution of [Ph3C][B(C6F5)4] (10 mmol) and vinylcyclohexane (0.68
mL) in C6H5Cl (0.82 mL). The reaction mixture was stirred for the
appropriate temperature and time outside of a glovebox. The
reaction was quenched by adding MeOH. After filtering and
removal of the volatiles in vacuo, the crude product was dissolved
in toluene. The solution was poured into a large excess of MeOH,
and then white precipitates were collected by filtration and dried
at 60 °C. The isotacticity of the poly(vinylcyclohexane) was
determined by the 13C NMR measurement.22
°C): δ 1.31 (s, 18H, C(CH3)3), 1.32 (s, 18H, C(CH3)3), 2.26 (d,
1H, 2J ) 12.6 Hz, HfCHHPh), 2.45 (d, 1H, 2J ) 12.6 Hz,
ZrCHHPh), 2.54-2.75 (m, 2H, CH2Ph), 2.85-3.20 (m, 2H,
CH2Ph), 3.65 (br, 2H, BCH2Ph), 4.39-4.51 (dd, 1H, 3J ) 3.8, 11.0
Hz, NCH), 6.31-7.24 (aromatic protons). 19F NMR (282 MHz,
C6D5Br, 25 °C): δ -131.8 (d, 6F, J ) 22.0 Hz, ortho), -161.8 (t,
3F, J ) 21.4 Hz, para), -165.7 (m, 6F, meta).
Observation of [(3,5-tBu2Ph-MeDAB-CH2Ph)Hf(CH2Ph)2]-
[PhCH2B(C6F5)3] (9f). In a glovebox, to a solid mixture of 6f (10
mg, 10 µmol) and B(C6F5)3 (5.1 mg, 10 µmol) was added C6D5Br
(0.60 mL) at -30 °C, and the solution was transferred to a J-Young
NMR tube. The color of the solution gradually turned red. The 1H
and 19F NMR spectra of the solution at 25 °C revealed the
quantitative formation of [(3,5-tBu2Ph-MeDAB-CH2Ph)Hf-
1
(CH2Ph)2][PhCH2B(C6F5)3] (9f). H NMR (300 MHz, C6D5Br, 25
°C): δ 1.29 (s, 18H, C(CH3)3), 1.32 (s, 18H, C(CH3)3), 1.40 (br,
Copolymerization of Ethylene/1-Hexene. Under ethylene at-
mosphere (1 atm), a solution of precatalyst (10 µmol) in toluene
(0.88 mL) was added to a solution of [Ph3C][B(C6F5)4] and 1-hexene
(0.62 mL) in toluene (8.5 mL). The reaction was quenched by
adding MeOH, and then white precipitates were collected by
filtration and dried at 60 °C. The 1-hexene content of the copolymer
2
1H, HfCHHPh), 1.54 (s, 3H, NCCH3), 1.66 (br d, 1H, J ) 11.1
Hz, HfCHHPh), 1.77 (br d, 1H, 2J ) 9.0 Hz, HfCHHPh), 1.99 (s,
2
3H, NCCH3), 2.35 (br d, 1H, J ) 9.0 Hz, HfCHHPh), 2.81 (d,
2
2
1H, J ) 15.0 Hz, CHHPh), 2.93 (d, 1H, J ) 15.0 Hz, CHHPh),
3
3.36 (br, 2H, BCH2Ph), 5.73 (br d, 2H, J ) 4.9 Hz, o-Ph of
HfCH2Ph), 5.89 (br d, 2H, 3J ) 6.5 Hz, o-Ph of HfCH2Ph),
6.46-7.50 (aromatic protons). 19F NMR (282 MHz, C6D5Br, 25
°C): δ -130.4 (d, 6F, J ) 22.4 Hz, ortho), -164.3 (t, 3F, J )
21.2 Hz, para), -166.9 (m, 6F, meta).
24
1
was determined by H NMR measurement.
X-ray Crystallographic Analysis. Single crystals were grown
from a solution of hexane under argon atmosphere at ambient
temperature. A yellow platelet crystal of C58H72N2Zr having
approximate dimensions of 0.60 × 0.25 × 0.20 mm was mounted
on a CryoLoop (Hampton Research Corp.) with a layer of light
mineral oil and placed in a nitrogen stream at 120(1) K. All
measurements were made on a Rigaku RAXIS RAPID imaging
plate area detector with graphite-monochromated Mo KR (0.71075
Å) radiation. Crystal data and structure refinement parameters are
summarized in Table S2 (see Supporting Information).
Observation of [(3,5-tBu2Ph-MeDAB-CH2Ph)Hf(CH2Ph)2]-
[B(C6F5)4] (10f). In glovebox, to a solid mixture of 6f (10 mg, 10
µmol) and [Ph3C][B(C6F5)4] (9.2 mg, 10 µmol) was added C6D5Br
(0.60 mL) at - 30 °C, and the solution was transferred to a J-Young
NMR tube. The color of the solution gradually turned yellow. The
1H and 19F NMR spectra of the solution at 25 °C revealed the
quantitative formation of [(3,5-tBu2Ph-MeDAB-CH2Ph)Hf-
1
The structure was solved by direct methods (SIR2004)29 and
refined on F2 by full-matrix least-squares methods, using SHELXL-
97.30 Non-hydrogen atoms of C58H72N2Zr were anisotropically
refined. H-atoms were included in the refinement on calculated
positions riding on their carrier atoms. The function minimized was
(CH2Ph)2][B(C6F5)4] (10f) and Ph3CCH2Ph. H NMR (300 MHz,
C6D5Br, 25 °C): δ 1.40 (s, 18H, C(CH3)3), 1.43 (s, 18H, C(CH3)3),
2
1.54 (d, 1H, J ) 11.2 Hz, HfCHHPh), 1.66 (s, 3H, NdCCH3),
1.80 (d, 1H, 2J ) 11.2 Hz, HfCHHPh), 1.89 (d, 1H, 2J ) 10.2 Hz,
2
HfCHHPh), 2.12 (s, 3H, NCCH3), 2.45 (d, 1H, J ) 10.2 Hz,
2
2
HfCHHPh), 2.94 (d, 1H, J ) 14.9 Hz, CHHPh), 3.06 (d, 1H, J
) 14.9 Hz, CHHPh), 5.57 (br d, 2H, 2J ) 7.0 Hz, o-Ph of
HfCH2Ph), 6.01 (br d, 2H, 2J ) 5.7 Hz, o-Ph of HfCH2Ph),
6.72-7.00 (aromatic protons). 19F NMR (282 MHz, C6D5Br, 25
°C): δ -132.1 (d, 6F, J ) 22.4 Hz, ortho), -162.8 (t, 3F, J )
21.2 Hz, para), -166.5 (m, 6F, meta).
[∑w(Fo2 - Fc2)2] (w ) 1/[σ2(Fo ) + (0.0548P)2 + 0.0000P]), where
2
P ) (Max(Fo2,0) + 2Fc2)/3 with σ2(Fo ) from counting statistics.
2
2
The functions R1 and wR2 were (∑|Fo| - |Fc|)/∑|Fo| and [∑w(Fo
- Fc2)2/∑(wFo4)]1/2, respectively. The ORTEP-3 program31 was used
to draw the molecule.
Kinetic Study for the Thermal Decomposition. Complex 3a
(20.0 mg, 20.5 µmol) and Cp2Fe (1.7 mg as an internal standard)
were placed in a J-Young NMR tube, and toluene-d8 (ca. 0.6 mL)
was added. The tube was heated in an oil-bath at appropriate
temperature (temperature regulated in the range of 1 K), and the
1H NMR spectra were measured at 308 K. The initial concentrations
were calculated with respect to the internal standard, and the
disappearance of 3a was monitored over 1-2 half-lives. Kinetic
experiments were conducted at four different temperatures (333,
343, 353, and 363 K) to obtain separate reaction rates. First-order
kinetics plots were generated by ploting time versus -ln(relative
concentration). An Eyring plot was generated by plotting ln(rate
constant/T) versus (1000/T). The activation energy and transition-
state thermodynamic values were determined in the standard
fashion. Observation of the thermal decomposition of 5b was carried
out at 358, 363, 368, and 373 K as described in the procedure for
3a.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas “Advanced
Molecular Transformations of Carbon Resources” from the
Ministry of Education, Culture, Sports, Science, and Tech-
nology, Japan. We appreciate Dr. T. Yamagata for his
contribution to the X-ray analysis of 2a.
Supporting Information Available: Kinetic profile for 5b, 1H and
19F NMR spectra of cationic species, 13C NMR spectra of poly(1-hexene)
and poly(vinylcyclohexane), table of ethylene/1-hexene copolymerization,
1H NMR spectra of copolymer, and X-ray crystallographic file for 2a in
CIF format are included. These materials are available free of charge via
the Internet at http://pubs.acs.org.
OM800880N
(29) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano,
G. L.; De Caro, L.; Giacovazzo, C.; Polidoria, G.; Spagna, R. J. Appl.
Crystallogr. 2005, 38, 381.
(30) Sheldrick, G. M. Programs for Crystal Structure Analysis (Release
97-2); University of Go¨ttingen: Germany.
Polymerization of 1-Hexene. In a glovebox, a solution of
precatalyst (10 µmol) in C6H5Cl (0.50 mL) was added to a solution
of B(C6F5)3 or [Ph3C][B(C6F5)4] (10 mmol) and 1-hexene (0.62 mL)
in C6H5Cl (0.88 mL). The reaction mixture was stirred for the
appropriate temperature and time outside of a glovebox. The
(31) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.