Neutron and X-ray diffraction and spectroscopic investigations of intramolecular [C-H...F-C] contacts in post-metallocene polyolefin catalysts: Modeling weak attractive polymer-ligand interactions

Article abstract of DOI:10.1002/chem.200501054

A family of Group 4 post-metallocene catalysts, supported by fluorine-functionalized tridentate ligands with the fluorine substituent in the locality of the metal center, is described. For the first time, the contentious C-H...F-C interaction has been cha

Full text of DOI:10.1002/chem.200501054

FULL PAPER
DOI: 10.1002/chem.200501054
Neutron and X-ray Diffraction and Spectroscopic Investigations of
ꢀ
ꢀ
Intramolecular [C H···F C] Contacts in Post-Metallocene Polyolefin
Catalysts: Modeling Weak Attractive Polymer–Ligand Interactions
Michael C. W. Chan,*[a] Steven C. F. Kui,[b] Jacqueline M. Cole,*[c] Garry J. McIntyre,[d]
Shigekazu Matsui,[e] Nianyong Zhu,[b] and Ka-Ho Tam[b]
ꢀ
ꢀ
Abstract: A family of Group 4 post-
metallocene catalysts, supported by flu-
orine-functionalized tridentate ligands
with the fluorine substituent in the lo-
cality of the metal center, is described.
neutron and X-ray crystallography.
Evidence is presented to demonstrate
C H···F C interactions are important
with regards to potential applications
in polyolefin catalysis because they
substantiate the proposed ortho-
F···H(b) ligand–(polymer chain) con-
tacts derived from DFT calculations
ꢀ
ꢀ
that the spectroscopic C H···F C cou-
pling occurs “through-space” rather
than “through-bond” or by M···F coor-
dination. The titanium catalysts exhibit
excellent activities and high co-mono-
mer incorporation in olefin polymeri-
zation. The observed intramolecular
ꢀ
For the first time, the contentious C
ꢀ
H···F C interaction has been character-
for
the
remarkable
fluorinated
ized by a neutron diffraction study,
which has allowed the position of the
hydrogen atoms to be accurately deter-
mined. The nature of the weak intra-
phenoxyimine Group 4 catalysts. Com-
pared with agostic and co-catalyst···me-
tal contacts, weak attractive noncova-
lent interactions between a polymer
chain and
“active” ligand is a new concept in
polyolefin catalysis.
Keywords: fluorinated ligands · hy-
drogen bonds · neutron diffraction ·
ꢀ
ꢀ
molecular C H···F C contacts in these
complexes in solution and the solid
state was probed by using multinuclear
NMR spectroscopy in tandem with
a
judiciously designed
noncovalent interactions
metallocenes
· post-
Introduction
tic interactions between the a-(plus b- and g-)hydrogen
atoms of the polymer chain and the metal center during the
polymerization process, which influences the rate of olefin
insertion and migration, is well-established.[1,2] The weak
The consideration of weak transient attractive interactions
has been instrumental in the development of metal-cata-
lyzed olefin polymerization reactions. The existence of agos-
ꢀ
metal-coordinating capabilities (C F···M) of putative “non-
[d] Dr. G. J. McIntyre
[a] Dr. M. C. W. Chan
Institut Laue-Langevin, B.P. 156, 38042 Grenoble Cedex 9 (France)
Department of Biology and Chemistry
City University of Hong Kong
Tat Chee Avenue, Kowloon, Hong Kong (China)
Fax : (+852)2788-7406
[e] Dr. S. Matsui
R&D Center, Mitsui Chemicals, Inc., 580–32 Nagaura
Sodegaura, Chiba 299–0265 (Japan)
E-mail: mcwchan@cityu.edu.hk
Supporting information (experimental details and characterization
data, perspective views of 4, 7, and 12, NMR spectra of 10 showing
effects of 19F decoupling, details of DFT calculations, results from a
[b] S. C. F. Kui, Dr. N. Zhu, K.-H. Tam
Department of Chemistry and HKU-CAS Joint Laboratory on New
Materials
The University of Hong Kong, Pokfulam Road, Hong Kong (China)
ꢀ
ꢀ
CSD search for neutron structures containing C H and F C bonds)
for this article is available on the WWW under http://www.chemeur-
j.org/ or from the author.
[c] Dr. J. M. Cole
Department of Chemistry, University of Cambridge
Lensfield Road, Cambridge, CB2 1EW (UK)
Office Mailing Address: St. Catharineꢀs College
Cambridge, CB2 1RL (UK)
Fax : (+44)1223-338-340
E-mail: jmc61@cam.ac.uk
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interacting” perfluorinated anion co-catalysts (for example,
B(C6F5)3) have become apparent and can cause catalyst de-
activation,[3] but these initiators have also been utilized to
stabilize extremely electron-deficient and coordinatively un-
saturated catalytic centers, especially when integrated into
the spectator ligand.[4] This approach is conceptually related
to the development of polydentate “hemilabile” ligands[5] in
olefin polymerization and other catalytic processes,[6] where-
by a substitutionally labile moiety can be displaced from
and yet remain available for recoordination to the reactive
metal species in a reversible manner. Conversely, repulsive
nonbonding interactions (and steric effects) between bulky
ancillary ligands and the incoming prochiral olefin form the
basis for controlling the stereoselectivity of metallocene-cat-
alyzed a-olefin polymerization reactions.[2c,7]
Weak noncovalent interactions between a functionalized
ligand and the polymer chain offer intriguing possibilities,
but there is no precedent for their exploration. In contrast
to steric repulsion, fragile attractive forces are inherently
tunable in a rational fashion. Like agostic and co-catalyst···
metal contacts, the development of ligand–polymer interac-
tions is feasible only if the interaction is dynamic and the
polymerization process (e.g. chain propagation) is not inter-
rupted. Significantly, a remarkably active and versatile class
of fluorinated phenoxyimine Group 4 polyolefin catalysts
was recently described. The abilities of these titanium “FI”
catalysts, pioneered by Fujita and co-workers,[8] to mediate
living polyethylene formation at high temperatures (up to
708C) and syndiotactic living propylene polymerization with
exceedingly rare 2,1-insertions have been reported, while
the robust living nature of these catalysts has been exploited
for the fabrication of new multiblock copolymers and chain-
end functionalized polyolefin materials. Coates and co-
workers observed exclusive 2,1-regiochemistry for propylene
insertion in homo-, co-, and cyclopolymerization reactions
using these catalysts, and very recently achieved isotacticity
and living behavior for propylene polymerization using fluo-
rine-rich phenoxyketimine titanium catalysts.[9,10] Theoretical
investigations aimed at rationalizing these impressive results,
and in particular the unusual stereoselectivity, have been
carried out.[11]
The C H···F C interaction is one of the weakest hydro-
gen bonds to be scrutinized. Indeed, the existence, nature,
and relevance (in a crystallographic context) of this interac-
tion are all highly contentious issues that have been dis-
cussed in numerous critical reviews over the last decade.[12]
Nevertheless, the body of structural evidence from X-ray
ꢀ
ꢀ
crystallography in support of C H···F C contacts, with H···F
separations less than the sum of their van der Waals radii
(2.5–2.7 Š),[13] plus their impact in the realm of crystal engi-
neering, is conspicuous.[14] Advanced rotational spectroscop-
ꢀ
ic techniques have been employed to probe the weak C
ꢀ
H···F C bridges between bimolecular fluoromethane species
in the gas phase[15] and these investigations have been com-
plemented by systematic theoretical calculations.[16] In mate-
ꢀ
ꢀ
rials science, C H···F C contacts have been invoked to ex-
plain the solid-state organization and physical and molecular
characteristics of fluorinated conjugated organic materials
with emerging applications in optoelectronics.[17] With re-
gards to biological recognition, the exploitation of fluorinat-
ꢀ
ꢀ
ed substituents and the accompanying C H···F C interac-
tions to enhance the affinity and selectivity at enzyme active
sites and in RNA and DNA bases has recently been advo-
cated,[18] while close C H···F C contacts in the crystal struc-
tures of fluorine-rich molecular sensors and receptors have
also been observed.[19]
ꢀ
ꢀ
A key focus of our studies in post-metallocene polyolefin
catalyst design is the development of nonsymmetric triden-
tate ancillary ligands.[20] We began to explore the possibility
of using aryl s-carbanion moieties as a chelating group since
the resultant M C(sp ) bond should be relatively covalent
(affording a highly electrophilic catalytic center) and its in-
ertness is, crucially, expected to be greater than those of its
aliphatic M C(sp ) counterparts. Our preliminary report
2
ꢀ
3
[21]
ꢀ
described the first direct spectroscopic and X-ray crystallo-
ꢀ
ꢀ
graphic evidence for the presence of weak C H···F C inter-
actions in fluorinated Group 4 polyolefin catalysts, which
are reminiscent of the ortho-F···H(b) contacts proposed by
Fujita and co-workers.[8] The use of X-ray crystal structures
to validate hydrogen-bonding interactions is nevertheless
questionable because the positions of hydrogen atoms
cannot be determined accurately; this can only be achieved
by employing neutron crystallography. We now present the
neutron structure of a fluorinated zirconium catalyst and, to
the best of our knowledge, this is the first time that the con-
To elucidate the role the fluorine groups have in living
polymerization reactions, Fujita and co-workers performed
computational analysis on several active species derived
from these catalysts.[8e–g] The DFT calculations indicated the
existence of a weak CꢀH···FꢀC interaction between the flu-
orine atom ortho to the imine nitrogen and a b-hydrogen
atom of the polymer chain, which would inhibit b-hydrogen
transfer to the metal and/or a reacting monomer, resulting
in chain termination. This clearly emphasizes the potential
importance of noncovalent attractive ligand–polymer inter-
actions for stabilizing b-hydrogen atoms and achieving living
polymerization processes. Furthermore, it is envisaged that
such weak contacts may allow manipulation of the reactivity
at the polymer chain and offer new opportunities to create
novel polymeric microstructures and materials.
ꢀ
ꢀ
troversial C H···F C interaction has been characterized by
neutron diffraction.
Herein we describe the synthesis of a series of fluorine-
substituted Group 4 catalysts and their characterization by a
variety of NMR spectroscopic and X-ray and neutron crys-
tallographic techniques. The abilities of these complexes to
mediate homo- and copolymerization processes in conjunc-
tion with different co-catalysts have been evaluated and of
particular interest are the high activities and excellent de-
grees of co-monomer incorporation observed. It is envisaged
ꢀ
ꢀ
that a greater insight into the nature of the C H···F C con-
tacts apparent in these catalysts can be derived and a possi-
ble correlation between the magnitude of the spectroscopic
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Intramolecular Contacts in Post-Metallocene Catalysts
FULL PAPER
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ꢀ
ꢀ
C H···F C coupling and the associated structural parame-
ters is examined.
favorable thermodynamically than C F activation. The de-
rivatives are thus designed with a CF3 (1, 2, 9, and 10) or F
substituent (6, 8, and 12) at the ortho (R1) position of the
aryl s-carbanion moiety, which is in close proximity to, but
not interacting with, the metal core. In place of the fluorinat-
ed group, complexes bearing a methyl substituent (3 and 11)
or only a hydrogen atom (4, 5, and 7) at R1 have been pre-
pared for comparison purposes. We note that attempts to
synthesize titanium and zirconium derivatives with tert-butyl
groups as the R1 and R2 substituents yielded intractable mix-
tures, characterization of which (1H NMR) signified non-cy-
clometalation.
Results and Discussion
Synthesis of Group 4 complexes bearing a fluorinated aryl
s-carbanion moiety: Tremendous progress has been ach-
ieved recently in the design of new-generation non-metallo-
cene olefin polymerization catalysts.[22] In the context of this
work, it is notable that non-cyclopentadienyl carbon-based
anionic ligand sets are rarely investigated and the resultant
complexes typically exhibit poor-to-moderate catalytic per-
formances.[23] With respect to aromatic s-carbanions, zirconi-
um complexes with bis(s-aryl)amine dianionic tridentate li-
gands have been reported as catalysts for propylene poly-
merization, but low activities were observed.[24] Further-
more, descriptions of the use of fluorine-rich supporting li-
gands in post-metallocene polyolefin catalysts are sparse in
Neutron diffraction study of complex 1: An exhaustive
search[26] of the Cambridge Structural Database for neutron
ꢀ
ꢀ
structures that contain both C H and F C bonds in any ca-
pacity afforded eight structures (see the Supporting Infor-
mation), but none of the associated papers report any C
ꢀ
ꢀ
ꢀ
ꢀ
H···F C contacts. Therefore the controversial C H···F C in-
teraction has been characterized by neutron diffraction for
the first time in this study. A perspective view of complex 1,
determined from a neutron diffraction experiment carried
out at 20 K to minimize disorder of the tBu and CF3 moiet-
ies, is shown in Figure 1. As listed in Table 1, there is gener-
ally good correlation between the structural parameters de-
rived from the neutron and X-ray[21] analyses. The zirconium
center resides in a distorted trigonal bipyramidal environ-
ment and is chelated by the phenolate-pyridine carbanion
[O,N,C] ligand with axial O and C(aryl) and equatorial N
and C(benzyl) atoms. Upon initial inspection, the most un-
usual feature of the structure is the “anti,anti” orientation of
the benzyl groups (see below). The short Zr···Cipso(benzyl)
the literature.[25] To model the weak C H···F C contacts
proposed by Fujita and co-workers,[8] our synthetic approach
targeted the generation of complexes containing fluorine-
functionalized ancillary ligands. Specifically, we endeavored
to position a fluorinated substituent in the vicinity of the
metal (e.g. ortho to the C(carbanion) atom; see below) so
that weak noncovalent interactions with metal-bound alkyl/
polymer chains become feasible.
ꢀ
ꢀ
A versatile procedure for the preparation of nonsymmet-
ric 2-(2’-hydroxyphenyl)-6-arylpyridine substrates has been
devised,[20] which in essence entails the sequential coupling
of two substituted acetophenone molecules. Metalation of
these substrates, which possess acidic protons, proceeds
upon reaction with the basic [M(CH2Ph)4] (M=Zr, Ti) or
[Zr(CH2Ph)2Cl2(OEt2)2] precursors and is accompanied by
the elimination of toluene to afford complexes 1–12 as
yellow-orange (Zr) to red (Ti) crystalline solids (Scheme 1).
For 7 and 8, the presence of THF as a donor facilitates com-
plex isolation. The cyclometalation process readily takes
place at 258C and is observed to be highly regioselective.
Hence, for substrates in which two potential cyclometalation
sites exist (i.e. R1 ¼R2, R3 =H), only the pictured compound
(4, 6, 8, and 12; in which R1 is less sterically demanding than
ꢀ ꢀ
separations and acute Zr C Cipso(benzyl) angles are indica-
tive of h2-coordination to the metal.
Saliently, the neutron diffraction study of 1 enables the lo-
cation of hydrogen atoms to be accurately determined. Of
special concern is the methylene hydrogen atoms H28B and
H35A, which point towards the CF3 unit and particularly
ꢀ
F1. The observed H···F distances and C H···F angles
ꢀ
ꢀ
(Table 1) are entirely consistent with C H···F C interactions
as proposed in previously reported X-ray crystal struc-
tures.[14] Stronger C H···F C contacts have been observed in
ꢀ
ꢀ
R2) has been isolated or detected by H NMR spectroscopy.
Generation of 2 and 10 by C H activation is clearly more
the X-ray crystal structures of 4-fluoroethynylbenzene[14c]
1
[14k]
ꢀ
and an amine adduct of B(C6F5)3
(H···F 2.26 and 2.20 Š;
ꢀ
C H···F 140 and 1518, respec-
tively). For the methylene
groups, apparent elongation of
ꢀ
the C H bonds which interact
with
F1
(1.109(10)
and
ꢀ
1.102(7) Š for C28 H28B and
ꢀ
C35 H35A, respectively; cf.
ꢀ
1.094(5) Š for both C28
H28A and C35 H35B) is very
minor and firm conclusions
should not be drawn, while the
ꢀ
ꢀ ꢀ
H C H angles (109.5(5) and
110.4(5)8) are normal. This
Scheme 1. [a] Zr(CH2Ph)2 replaced by ZrCl2(thf) (conditions: [Zr(CH2Ph)2Cl2(Et2O)2] in toluene/THF).
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2609

M. C. W. Chan, J. M. Cole et al.
ꢀ
ꢀ
rameters associated with the C H···F C fragment. This neu-
tron diffraction study may therefore be regarded as a struc-
ꢀ
ꢀ
tural reference for intramolecular C H···F C interactions
that are detectable in solution with potential relevance to
polymer–ligand interactions in polyolefin catalysis.
The position of the ortho-hydrogen atom H41relative to
ꢀ
F2 is also noteworthy (H41···F2 2.774(7) Š; C41 H41···F2
148.7(4)8). This would be equivalent to the interaction of a
g-hydrogen atom of the polymer chain with the fluorinated
ligand and may be compared with a g-agostic interaction in
metallocene catalysts.[28] We previously remarked upon the
curious inclination of the benzyl groups towards the CF3
ꢀ
ꢀ ꢀ
group; namely, the N Zr C Cipso(benzyl) dihedral angles
are 4.3 and 30.18 (8.4 and 26.58 by X-ray analysis[21]). Apart
from crystal packing effects, we now propose that it is more
appropriate to describe the benzyl ligands as leaning away
from the adjacent tert-butyl unit because the neutron struc-
ture has revealed that the methylene hydrogen atoms H28A
and H35B are only separated from the H21A and H23C
atoms of the tert-butyl substituent by 2.148(7) and
2.206(7) Š, respectively. The shortest Zr···F distance of
2.959(4) Š far exceeds the range expected for a significant
[29]
ꢀ
Zr···F C interaction.
Figure 1. Top: Perspective view of 1 from the neutron diffraction study
(50% probability ellipsoids), showing selected hydrogen atoms. Bottom:
Comparisons with X-ray crystal structures: The X-ray crys-
tal structures of several complexes, including those anticipat-
ꢀ
View along the Zr1 N1vector.
ꢀ
ꢀ
ed to display C H···F C interactions, have been determined
(perspective views of 9, 10, and 5 are shown in Figure 2; see
the Supporting Information for 4, 7, and 12) and their most
informative features are given in Table 2, together with the
neutron structural parameters for 1. All the bis(benzyl) de-
rivatives exhibit trigonal bipyramidal geometry around the
metal core, but only complexes 9, 10, and 12, together with
1, show the two benzyl ligands pointing outwards in a strik-
ing “anti,anti” configuration; this differs from the normal
“syn,anti” arrangement observed for 4 and 5 and analogous
post-metallocene complexes.[30] The h2-coordination mode of
the two benzyl moieties at the titanium center is evident,
with the strength of the interaction ranging from strong to
Table 1. Comparison of selected bond lengths [Š] and angles [8] from
neutron and X-ray crystallographic analyses of complex 1.
Neutron
X-ray[a]
ꢀ
Zr1 C12.338(3)
2.330(3)
2.391
ꢀ
Zr1 N12.426((32))
ꢀ
Zr1 O1
1.963(3)
2.343(3)
2.722(2)
2.327(3)
2.821(3)
2.572(6)
3.026(4)
2.607(5)
3.132(3)
147.3(2)
1.952(2)
2.276(3)
2.729(3)
2.267(3)
2.765(3)
2.471
2.996(3)
2.592
3.115(3)
147.3(2)
ꢀ
Zr1 C28
Zr1···C29
ꢀ
Zr1 C35
Zr1···C36
F1···H28B
F1···C28
F1···H35A
F1···C35
C13-O1-Zr1
C29-C28-Zr187.8(2)
C36-C35-Zr192.0(2)
F1···H28B C28
F1···H35A C35
ꢀ
rather weak in 9 and 10 (Ti···Cipso 2.592(4) to 2.843(2) Š; M
ꢀ
C Cipso 90.0(3) to 102.7(2)8), respectively. Although crystal
90.7(2)
92.8(2)
103.3(4)
108.2(3)
packing effects cannot be disregarded, we ascribe the recur-
ring yet atypical “anti,anti” bis(benzyl) conformation to the
highly congested nature of the space at the equatorial plane
between the tert-butyl and fluorinated substituents such that
a metal–(h2-benzyl) interaction cannot be accommodated.
The shortest M···F distances are also listed in Table 2. Sig-
nificant Zr···F contacts have been reported for a “hemila-
bile” or “active” ligand,[4,29] and Gade and co-workers have
structurally characterized zirconium derivatives supported
by 2-fluorophenyl-substituted tripodal trisilyl-amido ligands
which display noncovalent Zr···F coordination (2.511(2) and
2.535(5) Š).[31] Undoubtedly, the M···F separations observed
in this work, especially for titanium (>3.15 Š), are exces-
sively long to be considered even as weak interactions. This
ꢀ
113.8
114.0
ꢀ
[a] The positions of hydrogen atoms were calculated based on a riding
model.
lack of obvious geometric distortion, compared with that ob-
served in neutron structures for agostic interactions,[27] is
perhaps not surprising for very weak hydrogen bonds like
ꢀ
ꢀ
C H···F C. Along this vein of thought, the importance and
applicability of such weak interactions has been debated.[12]
In the context of this work, since “through-space” coupling
ꢀ
ꢀ
within the C H···F C moiety has unequivocally been dem-
onstrated by NMR spectroscopy (see below), our objective
was to elucidate by neutron diffraction the geometric pa-
ꢀ
ꢀ
supports our view that the C H···F C coupling detected by
NMR spectroscopy is not a consequence of M···F contacts.
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Intramolecular Contacts in Post-Metallocene Catalysts
FULL PAPER
spectively) appear to be slightly stronger than in 1. It is ap-
propriate to remark that a H···F separation of 2.55 Š is ap-
parent in 12 between a methylene hydrogen and the ortho-
fluorine atom of the aryl carbanion moiety. However, H···F
NMR coupling is not observed in solution and we contend
that a C···F distance of 3.281(11) Š is excessively long to
ꢀ
constitute a significant C H···F interaction. In contrast to a
single fluorine atom, rotation of a CF3 unit in solution can
enable a closer approach and improved alignment between
the methylene hydrogen and fluorine atoms to afford stron-
ꢀ
ꢀ
ger and spectroscopically recognizable C H···F C interac-
ꢀ
tions. Finally, the existence of a strong intraligand C H···F
ꢀ
contact (H(8)···F(4) 2.19 Š; C(8) H(8)···F(4) 1208) between
a pyridyl hydrogen atom and the distal fluorine atom in the
structure of 10, observable in solution by NMR spectrosco-
py, is noted.
Characterization by NMR spectroscopy: Our preliminary
report[21] presented direct evidence for the existence in solu-
ꢀ
ꢀ
tion of weak intramolecular C H···F C interactions in 1
(plus its benzyl cation) and 9, obtained by using a variety of
multinuclear NMR spectroscopic methods, including decou-
1
1
pling, H–19F 2D correlation and H/19F NOE difference ex-
periments. In this work, detailed spectroscopic characteriza-
tion of the related complexes 2 and 10 also signify compara-
ꢀ
ꢀ
ble C H···F C coupling phenomena between one of the dia-
stereotopic methylene hydrogen atoms and the CF3 substitu-
ent proximal to the metal. For example, complex
2
(Figure 3; see the Supporting Information for 10) displays
an overlapping doublet of quartets at 3.09 ppm (2JH,H =9.5,
1
1hJH,F =3.6 Hz) in the H NMR spectrum for one of the dia-
stereotopic methylene hydrogen atoms, which collapses to a
normal doublet upon 19F decoupling. Furthermore, a quartet
at 70.6 ppm (2hJC,F =6.5 Hz) in the 13C{1H} NMR spectrum
for the CH2 group, plus characteristic sharpening of the
downfield 19F NMR signal at ꢀ56.3 ppm only, relative to the
1H-coupled version, are observed. In addition, strong intrali-
gand H···F coupling (11.3 Hz for 2 and 10; assignable as
1h
5
J
H,F
rather than JH,F) between a pyridyl hydrogen and the
distal fluorine atom is apparent.
5
ꢀ
ꢀ
As expected, C H···F C coupling (formally JH,F) is unde-
tected for 12 bearing a single fluorine atom at the ortho-s-
carbanion position because the H···F separation is excessive-
ly long, although the 13C NMR signal for the methylene
carbon atoms at 96.3 ppm exhibits 19F coupling (formally
4JC,F =3.3 Hz) by a through-bond mechanism [a through-
space process is discounted because the Ti···F separation of
3.469(7) Š is excessively long]. The implication of this is im-
portant: if the JC,F and JH,F couplings in 9 and 10 occur by
similar through-bond processes, the corresponding 5JC,F (and
6JH,F) values should be smaller. However, the actual coupling
constants are larger, which provides further support for the
Figure 2. Perspective views of 9 (top, 50% probability ellipsoids), 10, and
5 (middle and bottom, respectively, 30% probability ellipsoids), showing
selected hydrogen atoms as white spheres (positions were calculated
based on the riding model).
ꢀ
We wish to emphasize that the following discussion on C
ꢀ
H···F C interactions is based on calculated hydrogen posi-
tions and should be treated cautiously, except when refer-
ring to the neutron structural data of 1. Allowing for this
2h
1h
ꢀ
caveat, the H···F (and C···F) distances and C H···F angles in
9 and 10 between two of the methylene hydrogen atoms and
“through-space” interpretation (i.e.
J
and
J
). Inciden-
H,F
C,F
tally, through-space coupling between the methylene hydro-
a fluorine atom of the CF3 group are consistent with the
gen atoms and the ortho-methyl group in 3 and 11 is not
ꢀ
ꢀ
ꢀ
presence of C H···F C interactions and in fact these con-
perceived; while C F bonds are longer, such interactions
would also lack an electrostatic basis. As manifested in the
ꢀ
tacts (e.g. H···F 2.39 and 2.43 Š; C H···F 125 and 1238, re-
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M. C. W. Chan, J. M. Cole et al.
Table 2. Comparison of selected bond lengths [Š] and angles [8] for molecular structures of bis(benzyl) complexes.[a]
1 (o-CF3)
9 (o-CF3)
10 (o-CF3)
12 (o-F)[b]
5 (o-H)
ꢀ
M C(carbanion)
2.338(3)
2.207(4)
2.210(2)
2.174(9)
2.275(4)
ꢀ
M CH2
2.343(3), 2.327(3)
2.722(2), 2.821(3)
87.8(2), 92.0(2)
2.959(4)
2.572(6), 2.607(5)
3.026(4), 3.132(3)
103.3(4), 108.2(3)
2.128(4), 2.135(4)
2.592(4), 2.765(4)
90.0(3), 98.5(3)
3.231(3)
2.385, 2.595
3.064(5), 3.194(5)
125.1, 119.0
2.118(2), 2.121(2)
2.696(2), 2.843(2)
95.6(2), 102.7(2)
3.153(4)
2.069(10), 2.093(10)
2.669(11), 2.732(11)
96.3(6), 98.6(6)
3.469(7)
2.551, 2.887
3.281(11), 3.516(11)
2.276(4), 2.286(4)
2.808(4), 2.587(4)
94.4(2), 84.4(2)
M···Cipso(benzyl)
ꢀ ꢀ
M C Cipso(benzyl)
M···F
H···F
2.427, 2.494, 2.189[d]
3.069(3), 3.072(3), 2.770(3)[d]
123.3, 118.0, 119.7[d]
C···F[c]
[c]
ꢀ
C H···F
[a] Determined by X-ray crystallography (positions of hydrogen atoms were calculated based on the riding model) except 1 (neutron diffraction); the R1
group ortho to the C(carbanion) atom is given in parentheses. [b] Only the titanium atom was refined anisotropically. [c] The parameters are listed in se-
ꢀ
quence with respect to the above cell. [d] Intraligand C H···F interaction.
correlate the spectroscopic and
structural data and make rele-
vant comparisons with previ-
ous investigations (Table 3).
2h
While
J
values appear
C,F
comparable (5.3–6.5 Hz), the
1h
J
values indicate that the
H,F
ꢀ
ꢀ
C H···F C contacts in the tita-
nium derivatives (1.2 and
1.6 Hz) are weaker than those
in the zirconium congeners
(3.3 and 3.6 Hz). Overall, the
anticipated spectroscopy–struc-
ture relationship is not appar-
ent, for example, the H···F dis-
tances
are
unpredictably
longer for zirconium, although
it is apt to consider the relative
inaccuracies of the X-ray struc-
tural data for the titanium
Figure 3. 1H NMR spectra (400 MHz, C6D6) of 2, demonstrating the effects of 19F decoupling upon the diaster-
eotopic methylene and aromatic hydrogen resonances (* and # refer to decoupling from CF3 and F groups, re-
spectively).
complexes.
Notwithstanding
this, a very tentative correla-
molecular structures, the h2-coordination modes of the
tion may exist between 9 and 10, for which slightly stronger
coupling in 9 is accompanied by marginally shorter H···F
and C···F separations.
benzyl groups are indicated for all complexes by diminished
1
2JH,H (<10 Hz) and large JC,H (>125 Hz) values, plus the
high-field shift of the ortho-phenyl resonances (e.g. for 9 in
We note two literature reports that have proposed related
C6D6: 8.3 and 138.9 Hz; 6.44 ppm respectively).[32]
intramolecular C H···F coupling in solution in organometal-
ꢀ
lic complexes (Table 3). Van Eldik, Goldberg, and co-work-
Evaluation of spectroscopic and structural parameters for
ers[14g] have studied the spectroscopic and structural proper-
ꢀ
ꢀ
C H···F C interactions: To acquire a greater insight into
ties of [Tp(CF3)2PtMe3] and tentatively suggested the pres-
1h
ꢀ
ꢀ
ꢀ
ꢀ
the nature of C H···F C interactions, we have attempted to
ence of weak through-space C H···F C coupling ( JH,F =1.8
[b]
Table 3. Comparison of selected NMR spectroscopic data[a] showing intramolecular C H···F C coupling and associated structural parameters.
ꢀ
ꢀ
1h
2h
1H: dq
[ppm]
J
[Hz]
13C{1H}: q
[ppm]
J
[Hz]
C,F
19F
[ppm]
Mean H···F
[Š]
Mean C···F
[Š]
Mean C H···F
ꢀ
H,F
[8]
1
2
9
10
3.09
3.09[c]
4.00
4.04
3.3
3.6
1.2
1.6
1.8
70.5
5.9
6.5
5.3
5.9
3.9
ꢀ58.12.589(6)
ꢀ56.3
3.079(4)
05.81(4)
70.6[d]
96.2
ꢀ56.5
ꢀ55.0
2.49
2.46
3.13
3.07
3.14
122
121
95.5
[Tp(CF3)2PtMe3][e,f] 1.58[g]
ꢀ4.9[g]
47.3
ꢀ57.0[g] 2.63
ꢀ121.3
[(F-N3)ZrMe][e,h]
0.65: q
8.4: JH,F (via
Zr···F)
17.6: 2JC,F (via
3
Zr···F)
[a] At 400 (1H), 126 (13C), and 376 (19F) MHz in C6D6 unless otherwise stated. [b] From X-ray crystallography (the positions of hydrogen atoms were cal-
culated based on the riding model), except 1 (neutron diffraction). [c] 500 MHz. [d] 151 MHz. [e] At 200 (1H), 63 (13C), and 188 (19F) MHz. [f] See
ref. [14g]; Tp(CF3)2 =HB[3,5-bis(trifluoromethyl)pyrazolyl]3; in [D6]acetone. [g] Septet resonance. [h] See reference [31a]; (F-N3)=HC[SiMe2N(2-
FC6H4)]3.
2612
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Chem. Eur. J. 2006, 12, 2607 – 2619

Intramolecular Contacts in Post-Metallocene Catalysts
FULL PAPER
and 2hJC,F =3.9 Hz in [D6]acetone; c.f. 9 and 10) between the
methyl groups and the attendant CF3 substituents which
point towards them. In contrast, Gade and co-workers have
described the tripodal amido-ligated methylzirconium deriv-
ative [(F-N3)ZrMe];[31a] the larger coupling constants are
proposed to occur through Zr···F coordination and are as-
feed, 5 mmol catalyst, 1000 equiv MAO, 20 mL toluene) indi-
cated that catalysts bearing fluorinated substituents adjacent
to the metal cleft display superior activities (units: g-
(polymer)mmol(catalyst)ꢀ1 hꢀ1). For zirconium derivatives,
the activity of complex 1 (260 gmmolꢀ1 hꢀ1) is incomparably
higher than those of 4 and 5 (11 and 4 gmmolꢀ1 hꢀ1, respec-
tively) with non-fluorinated substituents, while for the THF
adducts, 8 is noticeably more active than 7 (595 and
150 gmmolꢀ1 hꢀ1, respectively). The large discrepancies in
activities cannot solely be rationalized by steric arguments,
since complex 3 bearing a methyl substituent in place of a
3
2
ꢀ ꢀ
ꢀ
signed to J(H C Zr···F) and J(C Zr···F) (8.4 and 17.6 Hz,
respectively), as evidenced by the short Zr···F contact
(2.535(5) Š) in the crystal structure of the chloro-bridged
analogue.[31b] In addition, there is an extended history of in-
ꢀ
ꢀ
vestigations into “long-range”/through-space C H···F C
coupling in fluorinated organic molecules.[33]
CF3/F
moiety
only
exhibits
moderate
activity
Density functional theory (DFT) calculations have been
successfully utilized by Fujita and co-workers to analyze the
structures of FI catalysts and active species.[8e–g] We have
performed DFT calculations using the Gaussian program to
investigate the complexes reported in this work and to make
comparisons with the FI catalysts (see the Supporting Infor-
mation for details).[34] First, the structure calculated for 1
was observed to match excellently the neutron and X-ray
crystallographic analyses. The calculated distances between
the a-hydrogen atoms of each benzyl group and the nearest
fluorine atom of the CF3 group are 2.447 and 2.549 Š, which
equate to estimated electrostatic energies (ES) of ꢀ29.4 and
ꢀ28.7 kJmolꢀ1, respectively. Second, DFT calculations on
the alkyl cationic complex derived from 1 (alkyl=n-propyl
(70 gmmolꢀ1 hꢀ1). Hence the difference in activities may be
attributed to other factors, including the electron-withdraw-
ing effect of multiple CF3/F groups, which would increase
the electrophilicity of the catalytic center. Our initial studies
also revealed that for a given ancillary ligand, the titanium
catalysts (9 and 12: 1060 and 855 gmmolꢀ1 hꢀ1, respectively)
are appreciably more active than the zirconium congeners
(1 and 8: 260 and 595 gmmolꢀ1 hꢀ1, respectively).
Complexes 9 and 12, together with 1, were selected as
promising candidates for detailed ethylene polymerization
and copolymerization studies with propylene and norbor-
nene (Table 4). In addition to MAO, the tests were conduct-
ed by using iBu3Al/Ph3CB(C6F5)4 as the co-catalyst. For eth-
ylene polymerization, excellent activities were observed
as a model for the polymer
chain), which is widely regard-
ed as the catalytically active
species, have been undertaken.
Interestingly, the predicted
structure exhibits a weak inter-
Table 4. Homo- and copolymerization results.[a]
Reaction
Time
[min]
Yield
[g]
Activity[b]
Co-monomer
Tm
[8C]
content [mol%][c]
12/MAO
PE
EPR
COC
5
5
10
1.86
1.03
0.98
4460
136.5
no Tm observed
134.9
2480
40
19.4
1180[d]
action with
a
distance of
12/iBu3Al/Ph3CB(C6F5)4
9/MAO
PE
EPR
COC
5
5
10
0.84
0.17
0.37
2010
410
2.606 Š between one of the
fluorine atoms and a b-hydro-
gen atom of the alkyl chain
(see the Supporting Informa-
tion). The ES associated with
this interaction is estimated to
be ꢀ31.6 kJmolꢀ1, which is
comparable to the predicted
<10
20.0
450[d]
no Tm observed
135.5
PE
EPR
COC
5
5
10
0.74
0.46
0.81
1770
1120[e]
970[e]
16.8
11.1
5.2
(106.3)[f]
134.5
9/iBu3Al/Ph3CB(C6F5)4
1/MAO
PE
EPR
COC
5
5
10
0.58
0.31750
0.48
1400
[e]
590[e]
(111.0)[f]
134.7
ES
of
approximately
ꢀ30 kJmolꢀ1 for the corre-
sponding ortho-F···H(b) con-
tacts in alkyl cationic FI cata-
lysts.[8e]
PE
EPR
COC
10
30
10
0.32
0.62
0.12
390
250
140
131.0
1/iBu3Al/Ph3CB(C6F5)4
PE
EPR
COC
10
30
10
0.69
1.39
0.20
830
550
240
133.3
17.5
Ethylene polymerization and
copolymerization studies: The
complexes described in this
work have been evaluated as
catalysts for the polymerization
of ethylene. Importantly, our
preliminary investigations in
conjunction with methyl alu-
moxane (MAO) (conditions:
258C, 5 min, 1atm ethylene
129.0
[a] Conditions: 258C, 1atm olefin feed, toluene (250 mL), catalyst (5 mmol), co-cat. MAO (1.25 mmol) or
iBu3Al (0.25 mmol)/Ph3CB(C6F5)4 (1.2 equiv vs. cat.), PE (ethylene polymerization): C2=100 Lhꢀ1, EPR (eth-
ylene/propylene copolymerization): C2/C3=100/100 Lhꢀ1
, COC (ethylene/norbornene copolymerization):
C2=50 Lhꢀ1; NB=1g. [b] g(polymer)mmol(catalyst) ꢀ1 hꢀ1. [c] C3 and NB contents were determined by 1H
(except for 12: IR) and 13C NMR analysis, respectively. [d] Mw and Mw/Mn values with MAO (1.51”107 and
2.66, respectively) and borate (2.00”107 and 1.52, respectively) co-catalysts were determined by GPC. [e] Mv
values were determined from the intrinsic viscosity [h] of the polymer in decalin at 1358C and calculated using
0.7
[h]=6.2”10ꢀ4Mv to be (1.34, 2.33, 1.73, and 1.37)”106, respectively, upon descending the column; all other
polymers were insoluble under the analysis conditions, presumably as a result of their very high molecular
weights. [f] Very small peaks.
Chem. Eur. J. 2006, 12, 2607 – 2619
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2613

M. C. W. Chan, J. M. Cole et al.
with the titanium catalysts, up to 4460 gmmolꢀ1 hꢀ1 for 12/
MAO (considering the Al/Ti ratio is only 250). Like many
of the experiments, the resultant polymer is insoluble under
the conditions used for intrinsic viscosity analysis (1358C in
decalin), presumably due to its very high molecular weight
degree of NB incorporation for 12, with a sterically accessi-
ble (relative to 9) and highly electrophilic catalytic center,
surpasses the performance of the metallocene rac-[Et-
(Ind)2ZrCl2] (Ind=indenyl) and begins to approach that of
the bis(pyrrolide-imine) titanium catalyst system developed
by Fujita and co-workers (8.3 and 26.5 mol% NB, respec-
tively under similar conditions[37]). In contrast, the zirconium
catalyst 1 exhibits poor NB incorporation, as implied by the
high PE-like Tm values.
The narrow molecular weight distributions (low Mw/Mn
values) for 12/MAO and 12/iBu3Al/Ph3CB(C6F5)4 (2.66 and
1.52, respectively) are entirely consistent with active-site
uniformity. In contrast, under small-scale polymerization
conditions accompanied by the appearance of an exotherm,
9 produces PE samples with broad molecular weight distri-
butions (Mw/Mn >10). We note that a ligand-transfer degra-
dation pathway involving the FI catalyst [L2TiMe]+ (L=N-
(3-tert-butylsalicyclidene)pentafluoroanilinato) and AlMe3,
resulting in the formation of LAlMe2 and an unidentified ti-
tanium species that is less active, has been elucidated.[38] We
suggest that in this system, similar transmetalation reactions
6
(Mv >3”10 ).
Interesting results were obtained for these catalysts in eth-
ylene/propylene copolymerization reactions. The 12/MAO
system displays impressive activities that are superior to 9/
MAO and the molecular weight of the poly(ethylene-co-pro-
pylene) (EPR) produced is also higher such that the poly-
1
mer is insoluble and unsuitable for H NMR determination
of propylene (C3) content. Hence IR analysis was employed
to show that 40 mol% of propylene is incorporated into the
EPR prepared using 12/MAO, compared with 17 mol%
1
(from H NMR) incorporated using 9/MAO. The ability of
the 12/MAO system, with a single fluorine atom adjacent to
the metal rather than a CF3 substituent, to incorporate high
C3 content into the copolymer (FI catalysts can incorporate
up to about 20 mol%[8e,g,35]) is striking and may be ascribed
to the increased availability of space around the active site
which facilitates the coordination/insertion of sterically de-
manding monomers.
ꢀ
ꢀ
between the Al C(alkyl) and Ti C(aryl s-carbanion) bonds
of the co-catalyst and catalytic center, respectively, may
transpire at elevated temperatures. The development of
these catalysts may therefore be hampered by the fragile
The 12/iBu3Al/Ph3CB(C6F5)4 system yielded lower activi-
ties and decreased C3 content for EPR, the latter indicated
by IR analysis (<10 mol%) and the appearance of Tm
(114.68C) for the resultant polymer. In general, the use of
the iBu3Al/Ph3CB(C6F5)4 co-catalyst resulted in inferior ac-
tivities and suppressed co-monomer incorporation. Fujita
and co-workers have investigated the contrasting effects of
the MAO and iBu3Al/Ph3CB(C6F5)4 co-catalysts upon the
performance of FI catalysts,[8j,35] and concluded that the
imine moiety is readily reduced by iBu3Al to the amine and
that the reduced catalytic species is typically less active than
the MAO-activated analogue but tends to produce extreme-
ly high molecular weight polymers. In this work, while the
pyridine group should be more resistant to electrophilic
attack by iBu3Al, we note that reduction of the titanium
center is possible (see below) and there is a precedence for
such transformations in related ligand systems.[36] Intriguing-
ly, this trend is reversed for the zirconium catalyst; the 1/
iBu3Al/Ph3CB(C6F5)4 system displays improved activities as
well as greater C3 incorporation (17.5 versus 5.2 mol%)
compared with 1/MAO. The zirconium active sites are evi-
dently less susceptible to reduction processes, although rea-
sons for the superior performance are unclear.
ꢀ
nature of the [O,N,C] chelation and particularly the Ti C-
(aryl) linkage.
The catalytic capabilities of Group 4 alkyl complexes sup-
ported by fluorine- and chlorine-functionalized multi-amido/
donor ligands, recently developed by Schrock and co-work-
ers, are of relevance to the issues in this work and warrant
discussion. The impressive ability of the diamidoamine-
bound cation [{2,6-Cl2C6H3NCH2CH2)2NMe}ZrMe]+ to me-
diate the living polymerization of 1-hexene has been report-
ed[39] and it is interesting to note that the possibility of stabi-
lizing catalytic centers ’via “light” (or transiently dative) co-
ordination of the chloride to the metal’ was proposed. In a
related system, the impact of ortho-fluorine and -chlorine
substituents in alkylhafnium cations containing the diamido-
pyridine
ligands
[(2,6-X2C6H3NCH2)2C(2-py)Me]2ꢀ
([ArX2Npy]2ꢀ; X=F, Cl) upon their 1-hexene polymeri-
zation performance has been examined.[40] Compared with
mesityl, the introduction of the 2,6-Cl2- and especially 2,6-
F2C6H3 group resulted in detrimental activities and acceler-
ated the rate of b-hydride elimination. These observations
are seemingly contradictory to the beneficial effects of weak
ꢀ
ꢀ
The abilities of these catalysts to mediate ethylene/nor-
bornene (C2/NB) copolymerizations are also noteworthy.
The activity of 12/MAO (1180 gmmolꢀ1 hꢀ1) remains very re-
spectable and is greater than that for 9/MAO with higher
molecular weights. Significantly, both 12 and 9 with MAO or
iBu3Al/Ph3CB(C6F5)4 can produce very high molecular
weight C2/NB copolymers (COC: cyclic olefin copolymers),
as shown by lower Tm values relative to those of the PE
samples. Furthermore, 12/MAO and 12/iBu3Al/Ph3CB(C6F5)4
afford C2/NB elastomers with no Tm value and excellent NB
content (19.4 and 20.0 mol% NB, respectively). The elevated
C H···F C ligand–polymer interactions espoused by Fujita
and co-workers[8h] and the present work. However, it is rea-
sonable to point out that there are clear chemical and struc-
tural distinctions between the catalytic systems mentioned.
Apart from ligand characteristics/geometry and metal envi-
ronments, the salient difference is the propensity for the
ortho-fluorine (or chlorine) atoms of the [ArX2Npy]2ꢀ li-
gands to coordinate to the hafnium center, as illustrated in
the respective crystal structures[40] (Hf···F 2.443(3) and
2.674(3) Š; Hf···Cl 2.760(3) Š); the fluorine groups in the
catalysts reported here and by Fujita and co-workers do not
2614
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Chem. Eur. J. 2006, 12, 2607 – 2619

Intramolecular Contacts in Post-Metallocene Catalysts
FULL PAPER
were appropriately dried, distilled, and then degassed prior to use. 1H
and 13C NMR spectra were recorded at 300 K on a Bruker Avance 600,
500 DRX, 400, or 300 FT-NMR spectrometer (referenced to residual sol-
vent protons). Peak assignments were based on combinations of DEPT-
135, 2-D 1H–1H and 13C–1H correlations, and NOE NMR experiments.
19F NMR spectra were recorded at 300 K on a Bruker Avance 400 spec-
trometer (with trifluoroacetic acid as external reference). Elemental anal-
yses were performed by Medac Ltd., UK.
The complexes [M(CH2Ph)4] (M=Ti, Zr)[42] and [Zr(CH2Ph)2Cl2-
(OEt2)n][43] were prepared according to published procedures. The 2-(2’-
methoxyaryl)-6-arylpyridines were prepared by modification of a litera-
ture method[44] and subsequent demethylation using molten pyridinium
chloride[45] gave the 2-(2’-hydroxyphenyl)-6-arylpyridine substrates (see
the Supporting Information for details).
interact with the titanium/zirconium core. It is well-estab-
lished that such Hf···F/Cl contacts can increase the steric
demand at the active site leading to the suppression of cata-
lytic activity.[3] In general, we anticipate that catalytically ap-
ꢀ
ꢀ
plicable C H···F C polymer–ligand interactions may be
ꢀ
pre-empted if the C F unit(s) can approach the metal (due
to a flexible ligand framework) and stronger M···F metal–
ligand coordination could occur.
Conclusion
A family of Group 4 post-metallocene catalysts, supported
by fluorine-functionalized tridentate ligands that impose the
fluorine group in proximity to the active site, has been de-
signed and synthesized. By employing multinuclear NMR
spectroscopy in tandem with neutron and X-ray crystallogra-
phy, attempts have been made to: 1) elucidate the nature of
General synthetic procedure for the preparation of bis(benzyl) com-
plexes: 2-(2’-Hydroxyphenyl)-6-arylpyridine substrate in pentane/diethyl
ether (5:1) was slowly added to a stirred solution of [M(CH2Ph)4] in pen-
tane/diethyl ether (5:1) at ꢀ788C. The reaction mixture was allowed to
warm to 258C and stirred for 12h. The resultant solution was filtered,
concentrated to about 10 mL, and stored at ꢀ158C to afford a crystalline
solid. Analytically pure products were obtained by recrystallization from
pentane (detailed procedures and characterization data for all complexes
are provided in the Supporting Information).
ꢀ
ꢀ
the intramolecular C H···F C interactions in these com-
plexes in solution and in the solid state, and 2) gather evi-
ꢀ
ꢀ
dence to explicitly show that the C H···F C coupling occurs
“through-space” rather than “through-bond” or by M···F co-
ordination. The performances of the titanium catalysts ap-
pended with fluorine substituents are intriguing, with excel-
lent activities, high co-monomer incorporation and consider-
able effects due to the choice of co-catalyst.
Importantly, a neutron diffraction study of complex 1 has
been completed and this constitutes the first time that the
ꢀ
ꢀ
structural parameters of weak C H···F C interactions have
been accurately determined. The observed H···F distances
1: Orange-red crystals; yield 62%. Elemental analysis calcd (%) for
ꢀ
(2.572(6) and 2.607(5) Š) and C H···F angles (103.3(4) and
C41H39F6NOZr (766.98): C 64.21, H 5.13, N 1.83; found: C 63.99, H 5.57,
108.2(3)8) indicate a moderate-to-weak interaction when
compared with previous X-ray crystallographic reports.
Indeed, the former are fractionally longer than the sum of
the van der Waals radii (2.54 Š) as defined by Rowland and
Taylor,[13] which is routinely described as a cut-off distance
for nonbonded interatomic contacts.[41] However weak they
1
N 1.89. H NMR (400 MHz, C6D6): d=1.36 (s, 9H; 5-tBu), 1.72 (s, 9H; 3-
tBu), 3.09 (dq, J=9.6, 1hJH,F =3.3 Hz, 2H; 20’-H and 21’-H), 3.26 (d, J=
9.4 Hz, 2H; 20-H and 21-H), 6.18 (t, J=7.3 Hz, 2H; p-Ph), 6.25 (t, J=
7.7 Hz, 4H; m-Ph), 6.54 (d, J=7.4 Hz, 4H; o-Ph), 6.57 (d, J=7.9 Hz,
1H; 10-H), 6.77 (t, J=8.0 Hz, 1H; 9-H), 7.25 (d, J=8.0 Hz, 1H; 8-H),
7.40 (d, J=2.3 Hz, 1H; 6-H), 7.60 (s, 1H; 13-H), 7.69 (d, J=2.4 Hz, 1H;
4-H), 7.81ppm (s, 1H; 15-H); 13C NMR (126 MHz, C6D6): d=31.3 (3-
CMe3), 32.1(5-C Me3), 35.0 and 36.1( CMe3), 70.5 (q, 2hJC,F =5.9 Hz
(JC,H =133.3 Hz), C-20 and C-21), 118.1 (C-10), 127.6 (C-4), 122.1 (br, C-
15), 123.2 (br, C-13), 123.8 (p-Ph), 124.4 (C-8), 125.4 (C-6), 129.1 (o-Ph),
129.9 (m-Ph), 130.8 and 138.5 (q, JC,F =31.1 Hz, C-18 and C-19), 136.9 (i-
Ph), 139.3 (C-9), 189.9 ppm (C-17); 4o carbons: 126.7, 138.1, 142.8, 145.1,
155.3, 159.3, 161.6 ppm; 19F NMR (376 MHz, C6D6): d=ꢀ58.1(91-F),
ꢀ62.6 ppm (18-F).
ꢀ
ꢀ
may be perceived, we regard the C H···F C interactions in
ꢀ
ꢀ
this work to be genuine (because the C H···F C coupling in
solution is tangible) and of relevance with respect to poten-
tial applications in olefin polymerization reactions. Namely,
these results corroborate Fujitaꢀs proposed ortho-F···H(b)
contacts and demonstrate that such interactions are experi-
mentally feasible. In essence, we have an authenticated ex-
ample of a neutron structure containing weak intramolecu-
ꢀ
ꢀ
lar C H···F C interactions, the geometric parameters of
which are (or approach the outer limit of being) translated
ꢀ
ꢀ
into NMR-discernible C H···F C coupling in solution and
which may be consequential for the new concept and devel-
opment of weak attractive polymer–ligand interactions in
polyolefin catalysis.
Experimental Section
2: Orange crystalline solid; yield 75%. Elemental analysis calcd (%) for
C40H39F4NOZr (716.97): C 67.01, H 5.48, N 1.95; found: C 66.93, H 5.57,
General considerations: All reactions were performed under nitrogen
using standard Schlenk techniques or in a Braun dry-box. All solvents
1
N 2.18. H NMR (400 MHz, C6D6): d=1.36 (s, 9H; 5-tBu), 1.75 (s, 9H; 3-
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2615

M. C. W. Chan, J. M. Cole et al.
tBu), 3.09 (dq, J=9.5, 1hJH,F =3.6 Hz, 2H; 19’-H and 20’-H), 3.26 (d, J=
9.5 Hz, 2H; 19-H and 20-H), 6.25 (t, J=7.3 Hz, 2H; p-Ph), 6.35 (t, J=
7.4 Hz, 4H; m-Ph), 6.58–6.62 (m, 5H; o-Ph and 14-H), 6.85 (t, J=8.0 Hz,
1H; 9-H), 7.19–7.21 (m, 2H; 10-H and 15-H), 7.36 (d, J=2.4 Hz, 1H; 6-
H), 7.58 (d, J=8.1Hz, 1H; 8-H), 7.70 ppm (d, J=2.4 Hz, 1H; 4-H); 13C
NMR (151 MHz, C6D6): d=31.4 (3-CMe3), 32.2 (5-CMe3), 35.0 and 36.1
(CMe3), 70.6 (q, 2hJC,F =6.5 Hz, C-19 and C-20), 116.9 (d, 2JC,F =27.6 Hz,
C-14), 122.5 (d, 2hJC,F =22.6 Hz, C-10), 123.6 (p-Ph), 124.3 (C-8), 125.6
(C-6), 127.4 (C-4), 127.9 (C-15, obscured by residual solvent peak), 128.9
(m-Ph), 129.9 (o-Ph), 132.7 (q, JC,F =33.0 Hz, CF3), 137.4 (i-Ph), 139.2 (C-
9), 159.9 (d, 2JC,F =7.3 Hz, C-12), 162.4 (d, 1JC,F =265.0 Hz, C-13),
190.5 ppm (m, C-17); 48 carbons: d=127.1, 137.8, 142.6, 155.3,
159.8 ppm; 19F NMR (376 MHz, C6D6): d=ꢀ56.3 (CF3), ꢀ108.6 ppm (d,
1hJF,H =11.3 Hz, 13-F).
128.9 (m, C-15), 130.2 (o-Ph), 131.4 (q, JC,F =30.0 Hz, CF3), 136.4 (i-Ph),
139.2 (C-9), 159.6 (d, 2JC,F =7.6 Hz, C-12), 161.5 (d, 1JC,F =265.4 Hz, C-
13), 193.7 ppm (m, C-17); 48 carbons: d=137.9, 142.7, 156.6, 156.9 ppm;
19F NMR (376 MHz, C6D6): d=ꢀ55.0 (CF3), ꢀ108.6 (d, 1hJF,H =11.3 Hz,
13-F).
12: Dark red crystals; yield 78%. Elemental analysis calcd (%) for
C40H39F4NOTi (673.64): C 71.32, H 5.84, N 2.08; found: C 71.40, H 6.01,
1
N 2.12. H NMR (600 MHz, C6D6): d=1.34 (s, 9H; 5-tBu), 1.80 (s, 9H; 3-
tBu), 4.13 (d, J=8.5 Hz, 2H; CH2), 4.39 (d, J=8.5 Hz, 2H; CH2), 6.31(t,
J=7.3 Hz, 2H; p-Ph), 6.42–6.44 (m, 5H; m-Ph and 10-H), 6.64 (t, J=
7.9 Hz, 1H; 9-H), 6.66 (d, J=7.3 Hz, 4H; o-Ph), 7.12 (d, J=8.0 Hz, 1H;
8-H), 7.33 (s, 1H; 13-H), 7.35 (d, 3JH,F =4.7 Hz, 1H; 15-H), 7.39 (d, J=
2.3 Hz, 1H; 6-H), 7.71ppm (d, J=2.3 Hz, 1H; 4-H); 13C NMR
(150.9 MHz, C6D6): d=30.7 (3-CMe3), 31.5 (5-CMe3), 34.4 and 35.5
(CMe3), 96.3 (d, 4JC,F =3.3 Hz, CH2), 112.6 (dq, 2JC,F =36.2, 3JC,F =3.6 Hz,
C-15), 115.4 (m, C-13), 116.0 (C-10), 122.8 (C-8), 123.9 (p-Ph), 124.2 (C-
6), 127.0 (C-4), 127.8 (m-Ph, obscured by residual solvent peak), 131.0
(o-Ph), 131.9 (q, 1JC,F =32.5 Hz, CF3), 135.8 (i-Ph), 139.1 (C-9), 145.4 (d,
3JC,F =20.8 Hz, C-12), 166.1 (d, 1JC,F =233.9 Hz, C-16), 181.1 ppm (d,
2JC,F =59.4 Hz, C-17); 48 carbons: 127.1, 136.8, 142.7, 156.6, 156.9,
161.5 ppm; 19F NMR (376 MHz, C6D6): d=ꢀ62.1(CF 3), ꢀ98.5 ppm (16-
F).
Neutron diffraction study: A 1.5”1.3”1.0 mm3 single crystal, suspended
between two quartz wool plugs in a glass capillary flushed with nitrogen,
was mounted on the Very-Intense Vertical-Axis Laue Diffractometer
(VIVALDI) at the Institut Laue-Langevin (ILL), Grenoble, France in a
helium-flow cryostat and cooled to T=20.0(5) K (Table 5). Laue diffrac-
tion patterns were obtained using a polychromatic thermal-neutron beam
with a large solid-angle (8 sterad) cylindrical image-plate detector[46] to
increase the detected diffracted intensity by one-to-two orders of magni-
tude compared with a conventional monochromatic experiment. Fifteen
Laue diffraction patterns, successive patterns separated by 5–20 8 in f ro-
tation of the crystal perpendicular to the incident neutron beam, were
collected over a 1708 range at T=20.0(5) K, each pattern requiring a
6 hour acquisition time with blue Fuji image plates.
9: Dark red crystals; yield 57%. Elemental analysis calcd (%) for
C41H39F6NOTi (723.66): C 68.05, H 5.43, N 1.93; found: C 68.08, H 5.58,
1
N 2.09. H NMR (400 MHz, C6D6): d=1.34 (s, 9H; 5-tBu), 1.77 (s, 9H; 3-
tBu), 4.00 (brdq, J=8.4, 1hJH,F =1.2 Hz, 2H; 20’-H and 21’-H), 4.04 (d,
J=8.3 Hz, 2H; 20-H and 21-H), 6.25 (t, J=7.2 Hz, 2H; p-Ph), 6.32 (t,
J=7.1Hz, 4H; m-Ph), 6.42 (d, J=8.3 Hz, 1H; 10-H), 6.44 (d, J=7.3 Hz,
4H; o-Ph), 6.66 (t, J=8.0 Hz, 1H; 9-H), 7.21 (d, J=8.0 Hz, 1H; 8-H),
7.40 (d, J=2.1Hz, 1H; 6-H), 7.60 (s, 1H; 13-H), 7.70 (d, J=2.3 Hz, 1H;
4-H), 8.12 ppm (s, 1H; 15-H); 13C NMR (126 MHz, C6D6): d=31.1 (3-
CMe3), 31.7 (5-CMe3), 34.7 and 35.7 (CMe3), 96.2 (q, 2hJC,F =5.3 Hz
(JC,H =138.9 Hz), C-20 and C-21), 116.6 (C-10), 122.8 (br, C-13), 123.2
(br, C-15), 123.4 (C-8), 124.1 (p-Ph), 124.4 (C-6), 127.5 (C-4), 127.6 (m-
Ph), 131.1 and 137.2 (q, JC,F =32.5 and 30.2 Hz resp., C-18 and C-19),
130.5 (o-Ph), 137.6 (i-Ph), 139.3 (C-9), 193.4 ppm (C-17); 4o carbons:
127.3, 137.0, 143.1, 144.9, 156.8, 156.9, 161.4 ppm; 19F NMR (376 MHz,
C6D6): d=ꢀ56.5 (19-F), ꢀ62.6 ppm (18-F).
The images were indexed by using the LAUEGEN program of the
Daresbury Laboratory Laue Suite[47] and the reflections were integrated
using the local INTEGRATE+ program which uses a two-dimensional
version of the minimum s(I)/I algorithm.[48] The individual reflections
were corrected for absorption using the calculated (wavelength-depen-
dent) absorption coefficient, 0.08437l+0.08936 mmꢀ1 (transmission
range: 0.717–0.869). The reflections were normalized to a common wave-
length using a curve derived by comparing equivalent reflections and
multiple observations with the LAUENORM program.[49] Only reflec-
tions in the wavelength range of 0.9–2.2 Š were retained to yield a total
of 23578 single and 6641unique reflections. Fourier difference analysis
allowed unambiguous identification and location of the hydrogen atoms.
The model was refined by full-matrix least-squares refinement using
SHELXL-97.[50] Positional and anisotropic displacement parameters were
refined for all atoms except the phenyl carbon atoms for which only the
positional and isotropic displacement parameters were refined. This
atom-selective difference in the treatment of displacement parameters
was applied in order to optimize the refinement data/parameter ratio to
obtain the most accurate parameters for the most scientifically important
10: Dark red crystalline solid; yield 74%. Elemental analysis calcd (%)
for C40H39F4NOTi (673.64): C 71.32, H 5.84, N 2.08; found: C 71.05, H
5.91, N 2.23; 1H NMR (400 MHz, C6D6): d=1.35 (s, 9H; 5-tBu), 1.79 (s,
9H; 3-tBu), 4.02 (d, J=8.4 Hz, 2H; 19-H and 20-H), 4.04 (dq, J=8.5,
1hJH,F =1.6 Hz, 2H; 19’-H and 20’-H), 6.29 (t, J=7.5 Hz, 2H; p-Ph), 6.38
(t, J=7.5 Hz, 4H; m-Ph), 6.49 (d, J=7.2 Hz, 4H; o-Ph), 6.66–6.74 (m,
2H; 14-H and 9-H), 7.16 (1H; 8-H, fused with residual solvent peak),
7.33 (d, J=2.2 Hz, 1H; 6-H), 7.46–7.51 (m, 2H; 10-H and 15-H),
7.68 ppm (d, J=2.3 Hz, 1H; 4-H); 13C NMR (126 MHz, C6D6): d=30.9
(3-CMe3), 31.5 (5-CMe3), 34.4 and 35.4 (CMe3), 95.5 (q, 2hJC,F =5.9 Hz, C-
19 and C-20), 116.3 (d, 2JC,F =27.2 Hz, C-14), 120.8 (d, 2hJC,F =24.1Hz, C-
10), 123.0 (C-8), 123.7 (p-Ph), 124.4 (C-6), 127.0 (C-4), 127.3 (m-Ph),
2616
www.chemeurj.org
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 2607 – 2619

Intramolecular Contacts in Post-Metallocene Catalysts
FULL PAPER
Table 5. Crystal data and structure refinement for 1.
50.48, 4573 independent reflections (Rint =0.0454), 376 variable parame-
ters, R1 =0.047 [I>2s(I)], wR2 =0.121, GOF(F2)=0.930, largest diff.
peak/hole=0.50/ꢀ0.30 eŠꢀ3. For 9: C41H39F6NOTi, Mw =723.66, mono-
clinic, P21/n, a=10.6069(3), b=10.7982(3), c=31.4667(8) Š, b=
empirical form.
form. wt.
C41H39F6NOZr
766.98
T [K]
20.0(5)
94.7610(10)8, V=3591.62(17) Š3, Z=4, 1calcd =1.338 gcmꢀ3
, m(MoKa)=
accepted wavelength [Š]
0.9–2.2
0.303 mmꢀ1, F(000)=1504, T=150(2) K, 2qmax =518, 6676 independent
crystal system
space group
triclinic
P1
reflections (Rint =0.0708), 452 variable parameters, R1 =0.065 [I>2s(I)],
¯
ꢀ3
wR2 =0.166, GOF(F2)=1.051, largest diff. peak/hole=1.02/ꢀ1.06 eŠ
.
unit cell dimensions
For 10: C40H39F4NOTi, Mw =673.64, monoclinic, P21/n, a=13.790(3), b=
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š3]
Z
9.613(2)
11.860(2)
16.928(3)
109.37(3)
90.88(3)
97.88(3)
1799.7(6)
2
1.412
0.08437l+0.08936
366
1.50”1.30”1.00
3.77–45.81
15.478(3), c=16.345(3) Š, b=102.04(3)8, V=3412.0(12) Š3, Z=4, 1calcd
1.311 gcmꢀ3, m(MoKa)=0.305 mmꢀ1, F(000)=1408, T=253(2) K, 2qmax
=
=
50.88, 5825 independent reflections (Rint =0.0388), 424 variable parame-
ters, R1 =0.041[ I>2s(I)], wR2 =0.116, GOF(F2)=1.047, largest diff.
peak/hole=0.51/ꢀ0.30 eŠꢀ3. For 12: C40H39F4NOTi, Mw =673.64, ortho-
rhombic, P212121, a=10.182(2), b=15.879(3), c=21.376(4) Š, V=
3456.1(12) Š3, Z=4, 1calcd =1.295 gcmꢀ3, m(MoKa)=0.301mm ꢀ1, F(000)=
1408, T=253(2) K, 2qmax =47.38, 3056 independent reflections (Rint
=
1calcd [gcmꢀ3
]
0.0678), 206 variable parameters, R1 =0.066 [I>2s(I)], wR2 =0.162,
absorption coefficient [mmꢀ1
F(000)
]
ꢀ3
GOF(F2)=0.908, largest diff. peak/hole=0.44ꢀ0.38 eŠ
.
CCDC-281869 (1; neutron diffraction), CCDC-190343[21] (4), CCDC-
281867 (9), and CCDC-280315–280318 (7, 5, 12, and 10, respectively)
contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data request/cif.
crystal size [mm3]
q range for data collection [8]
index range
ꢀ11ꢁhꢁ11, ꢀ18ꢁkꢁ18,
ꢀ26ꢁlꢁ20
23493
reflections collected
independent reflections
completeness to q=45.818 [%]
absorption correction
max. and min. transmission
refinement method
6641[ Rint =0.1899]
43.5
Gaussian integration
0.869 and 0.717
full-matrix least-squares on F2
6641/0/667
Polymerization procedures: Ethylene polymerization was carried out
under atmospheric pressure in toluene in a 500-mL glass reactor equip-
ped with a propeller-like stirrer. Toluene (250 mL) was introduced into
the nitrogen-purged reactor and stirred (600 rpm). The toluene was ther-
mostated at 258C, and the ethylene gas feed (100 Lhꢀ1) was then started.
After 15 min, polymerization was initiated by adding toluene solutions of
the co-catalyst and then catalyst to the reactor whilst vigorously stirring
(600 rpm) the mixture. After the prescribed time, isobutyl alcohol
(10 mL) was added to terminate the polymerization and the ethylene gas
feed was stopped. Methanol (1000 mL) and concentrated HCl (2 mL)
were added to the resulting mixture. The polymer was collected by filtra-
tion, washed with methanol (200 mL), and dried in vacuo at 808C for
1 0 h.
data/restraints/parameters
GOF on F2
1.117
final R indices [I>2s(I)]
R indices (all data)
R1 =0.0642, wR2 =0.1037
R1 =0.1511, wR2 =0.1175
1.070 and ꢀ0.978
largest diff. peak and hole
ꢀ3
[fmŠ
]
atoms in this study; the phenyl carbon atoms did not merit special atten-
tion and, in any event, their displacement parameters are naturally con-
strained by the geometry of the ring.
Ethylene/propylene copolymerization was performed by using a similar
procedure to that for ethylene polymerization, except ethylene
(100 Lhꢀ1) and propylene (100 Lhꢀ1) were used. After the prescribed
time, isobutyl alcohol (10 mL) was added to terminate the polymerization
and the olefin gas feed was stopped. Concentrated HCl (2 mL) was
added to the resulting mixture and the mixture was washed with water
(3”250 mL) and concentrated in vacuo. The resultant polymer was dried
in vacuo at 1308C for 10 h.
The vertical detector axis is nearly parallel to the real-space direction
[210]. The bonds of interest (H28B···F1, H35 A···F1) are approximately
perpendicular to [210] and are thus least affected by the inherent paucity
of data near the detector axis for only one mounting of the (triclinic)
crystal in this instrument geometry. The same remark applies to the com-
ponents of the thermal-displacement tensors and may lead to them be-
coming nonpositive definite. However, refinement of all the components
of the tensors was still needed to correctly model the displacements in
the horizontal plane. Other data collections on VIVALDI, for which
monochromatic data for the same compound are also available, indicate
that the bond distances from anisotropic refinements are more accurate
than the values from isotropic refinements provided that the data permits
sensible refinement of the horizontal plane components. These conclu-
sions were borne out in a series of refinements in which various numbers
of atoms were refined anisotropically; the H···F distances differed insig-
nificantly and the estimated standard deviations were smaller than, for
Ethylene/NB copolymerization was performed using a similar procedure
to that for ethylene polymerization, except the prescribed amount of NB
(1g) was added to the toluene before the ethylene gas feed (50 Lh ꢀ1
)
was started. The polymerization was quenched after the prescribed time
by the addition of methanol (5 mL) and the ethylene gas feed was stop-
ped. The resulting mixture was added to a stirred solution of acidic meth-
anol (500 mL including 5 mL of conc. HCl) and acetone (500 mL). The
polymer was collected by filtration, washed with methanol (3”200 mL),
and dried in vacuo at 1308C for 10 h.
ꢀ
example, the C28 H28B bond which is more and nearly parallel to the
vertical axis. The final structural refinement yielded R1 =0.0642 for
4132Fo >4s(Fo) data, and wR2 =0.1175 and GOF=1.117 for all data.
Acknowledgements
X-ray crystallography: For 5: C39H41NOZr, Mw =630.98, monoclinic, P21/
n, a=10.592(2), b=21.642(4), c=14.410(3) Š, b=92.86(3)8, V=
3299.1(11) Š3, Z=4, 1calcd =1.270 gcmꢀ3, m(MoKa)=0.363 mmꢀ1, F(000)=
M.C.W.C. is grateful to the Research Grants Council of the Hong Kong
SAR, China [HKU 7095/00P], the City University of Hong Kong, and
The University of Hong Kong for financial support, Dr. Haruyuki Makio
for helpful discussions, Dr. Glenna S. M. Tong for assistance with DFT
calculations, and Prof. Chi-Ming Che for supporting this work. J.M.C.
wishes to thank the Royal Society for a University Research Fellowship,
St. Catharineꢀs College, Cambridge for a Senior Research Fellowship, the
Institut Laue-Langevin, Grenoble, France for financial support and facili-
ty access during the commissioning of VIVALDI, and the University of
1320, T=301(2) K, 2qmax =50.78, 4725 independent reflections (Rint
=
0.0336), 379 variable parameters, R1 =0.036 [I>2s(I)], wR2 =0.083,
ꢀ3
GOF(F2)=0.881, largest diff. peak/hole=0.41/ꢀ0.40 eŠ
.
For 7:
C36H43Cl2NO2Zr, Mw =683.87, monoclinic, P21/c, a=14.160(3), b=
12.883(3), c=19.260(4) Š, b=97.21(3)8, V=3485.7(13) Š3, Z=4, 1calcd
1.303 gcmꢀ3, m(MoKa)=0.499 mmꢀ1, F(000)=1424, T=293(2) K, 2qmax
=
=
Chem. Eur. J. 2006, 12, 2607 – 2619
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2617

M. C. W. Chan, J. M. Cole et al.
Durham for provision of X-ray diffraction facilities through a Long Term
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Received: August 28, 2005
Published online: December 19, 2005
Chem. Eur. J. 2006, 12, 2607 – 2619
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