Chemoselectivity diversity in the reaction of LiNC6F 5SiMe3 with nitriles and the synthesis, structure, and reactivity of zirconium mono-and tris[2-(2-pyridyl)tetrafluorobenzimidazolate] complexes

Article abstract of DOI:10.1021/ic100696r

Unlike the reaction of LiNTMS₂· TMEDA (TMS = SiMe ₃; TMEDA = tetramethylethylenediamine) with 2-cyanopyridine, which results in the nearly exclusive formation of the amidinate, (Me ₃SiNC₆F₅)Li · TMEDA (1) reacts with 2-cyanopyridine in toluene to yield quantitatively the lithium pyridyltetrafluorobenzimidazolate complex [C₆F₄N ₂C(2-C₅H₄N)]Li · TMEDA (3). In this work, the reactivity of complex 1 toward aromatic nitriles Ar-CN (Ar = Ph, o-OMeC₆H₄, C₆F₅, 2-pyridyl) was examined. Whereas complex 1 fails to react with o-methoxybenzonitrile, its reaction with benzonitrile or pentafluorobenzonitrile gives triphenyl-1,3,5- triazine (4) or the hexacoordinate lithium polymer [LiN(4-NCC₆F ₄)(C₆F₅) · THF · TMEDA] _n (7), respectively. When 1 is reacted with 2-cyanopyridine in tetrahydrofuran (THF), the benzimidazolate coordination polymer {[C ₆F₄N₂C(2-C₅H₄N)]Li · THF}_n (5) is obtained. Herein we discuss how this diverse chemoselectivity in the reaction of the examined lithium N-silylated amides LiNRTMS · TMEDA (R = TMS, C₆F₅) with nitriles is influenced by the electronic properties of the nitrile or amide substituents and by the ability of these substituents to interact with the lithium or silicon atoms. Further, we present the syntheses and structures of zirconium tris(pyridyltetrafluorobenzimidazolate) chloride (10) and zirconium bis(dimethylamido)(pyridyltetrafluorobenzimidazolate) chloride · THF (11) complexes. These complexes, the first prepared zirconium mono-and tris(benzimidazolate)s, were crystallographically characterized and examined in the polymerization of propylene with methyl aluminoxane (1:1000 Zr/Al molar ratio).

Full text of DOI:10.1021/ic100696r

Inorg. Chem. 2010, 49, 9217–9229 9217
DOI: 10.1021/ic100696r
Chemoselectivity Diversity in the Reaction of LiNC6F5SiMe3 with
Nitriles and the Synthesis, Structure, and Reactivity of Zirconium
Mono- and Tris[2-(2-pyridyl)tetrafluorobenzimidazolate] Complexes
Sinai Aharonovich,† Mark Botoshansky,† Robert M. Waymouth,‡ and Moris S. Eisen*,†
†Schulich Faculty of Chemistry and Institute of Catalysis Science and Technology, Kyriat Hatechnion,
Technion;Israel Institute of Technology, Haifa 32000, Israel, and ‡Department of Chemistry,
Stanford University, Stanford, California 94305-5080
Received April 12, 2010
Unlike the reaction of LiNTMS2 TMEDA (TMS = SiMe3; TMEDA = tetramethylethylenediamine) with 2-cyanopyridine,
which results in the nearly exclusive formation of the amidinate, (Me3SiNC6F5)Li TMEDA (1) reacts with
2-cyanopyridine in toluene to yield quantitatively the lithium pyridyltetrafluorobenzimidazolate complex
3
3
[C6F4N2C(2-C5H4N)]Li TMEDA (3). In this work, the reactivity of complex 1 toward aromatic nitriles Ar-CN
3
(Ar = Ph, o-OMeC6H4, C6F5, 2-pyridyl) was examined. Whereas complex 1 fails to react with o-methoxyben-
zonitrile, its reaction with benzonitrile or pentafluorobenzonitrile gives triphenyl-1,3,5-triazine (4) or the
hexacoordinate lithium polymer [LiN(4-NCC6F4)(C6F5) THF TMEDA]n (7), respectively. When 1 is reacted
3
3
with 2-cyanopyridine in tetrahydrofuran (THF), the benzimidazolate coordination polymer {[C6F4N2C(2-
C5H4N)]Li THF}n (5) is obtained. Herein we discuss how this diverse chemoselectivity in the reaction of the
examined lithium N-silylated amides LiNRTMS TMEDA (R = TMS, C6F5) with nitriles is influenced by the
3
3
electronic properties of the nitrile or amide substituents and by the ability of these substituents to interact with the
lithium or silicon atoms. Further, we present the syntheses and structures of zirconium tris(pyridyl-
tetrafluorobenzimidazolate) chloride (10) and zirconium bis(dimethylamido)(pyridyltetrafluorobenzimidazolate)
chloride THF (11) complexes. These complexes, the first prepared zirconium mono- and tris(benzimidazolate)s,
were crystallographically characterized and examined in the polymerization of propylene with methyl aluminoxane
(1:1000 Zr/Al molar ratio).
3
Introduction
substantial studies of the structural chemistry of these lithium
complexes.
Utilization of the amidinates [N(R1)C(R2)NR3]- as ancil-
lary ligands in the synthesis of coordination compounds1,2 is
partially due to their ability to form stable complexes of
metals or metalloids from the s, p, d, and f blocks, which can
support unusual bonding motifs and reactivities.1-9 Lithium
amidinates are widely used as ligand-transfer reagents in the
preparation of the aforementioned amidinate complexes
and as synthons in the preparation of various aza hetero-
cycles10-13 and other valuable organonitrogen compounds.9,14,15
These applications have motivated, in the last 2 decades,
The structure of an amidinate complex, in general, can be
influenced by three main structural factors: (i) the tautomeric
form of the amidinate (Figure 1), (ii) the amidinate coordina-
tion mode (chelating or bridging; Figure 2a-d), and (iii) the
degree and manner of participation of the amidinate π system
in the bonding (compare part b with parts c and d in
Figure 2). These structural factors can be influenced by the
properties of other ligands in the coordination sphere,2,11,15-22
by the electronic or steric properties of the amidinate backbone
substituents,2,7,11,13,16,20,21,23 or by the presence of pendant
coordinating groups.5,8,18,22
*To whom correspondence should be addressed. E-mail: chmoris@
tx.technion.ac.il.
Benzimidazolates, along with the free base benzimidazoles,
are an important class of compounds with diverse pharma-
ceutical applications25 and coordination chemistry.11,26-29
The benzimidazolates, which can be regarded as amidinates
“frozen” at the Z-syn tautomer, are different from the latter
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ligand type in their exclusive preference for the κ coordi-
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r
2010 American Chemical Society
Published on Web 09/21/2010
pubs.acs.org/IC

9218 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
neighboring metal center, thus creating the fairly common
ortho C-F bond to yield quantitatively lithium pyridyltetra-
1
κ :κ1 bimetallic bridging coordination mode (Figure 2f),31
fluorobenzimidazolate [C6F4N2C(2-C5H4N)]Li TMEDA (3)
3
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and TMSF. In general, the lithium amino-imide intermedi-
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As a part of our efforts toward the tailoring of the steric
and electronic properties of diazaallyl ligands and, in parti-
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3
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Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9219
In the second part of the presentation, we disclose the
syntheses, reactivity, structure, and propylene polymeriza-
tion behavior of the zirconium mono- and tris[tetrafluoro-
2-(2-pyridyl)benzimidazolate] complexes, which are, to the
best of our knowledge, the first synthesized zirconium mono-
and tris(benzimidazolate)s.
Results and Discussion
Figure 1. Structures and accepted nomenclatures of the amidinate
tautomeric forms.24
Reactivity of 1 toward Nitriles. Reaction of Complex 1
with Benzonitrile and o-Methoxybenzonitrile. When ben-
zonitrile is added to a cold toluene solution (0 °C) of
complex 1, the color of the solution changes from yellow
to dark purple-blue after the reaction mixture is brought
to room temperature. From this solution, crystals of
triphenyl-1,3,5-triazine (4), which was characterized using
1H NMR and X-ray analysis, can be obtained in an isolated
yield of 67% (Scheme 1). Because the trimerization of
nitriles by metal amides involves amino-imide and 1,3,5-
triazahexatriene intermediates12 (Scheme 2), it seems that,
while the nucleophilic addition of complex 1 to benzonitrile
is operative, the second nucleophilic attacks on silicon or on
the perfluorinated ring are slower than an attack on
another nitrile molecule, unlike the situation in the reaction
of complex 1 and 2-cyanopyridine11 or in the reaction
Figure 2. Examples of common coordination modes of the E-anti
of LiNTMS2 TMEDA and 2-cyanopyridine16a or benzo-
2
amidinate (a-d) and benzimidazolate (e and f) ligands: (a) κ and (b)
3
κ 1:κ 1 bimetallicbridging;(c) κ2:κ1 bimetallic bridgingand monochelating;
nitrile.36
2
1
1
(d) κ 2:κ bimetallic bridging and bischelating; (e) κ and (f) κ 1:κ
bimetallic bridging.
When a similar reaction between complex 1 and
o-methoxybenzonitrile is attempted, no significant color
change was noted, and the starting materials could be
identified (via 1H NMR) as the major components of the
mixture even after prolonged reaction times (Scheme 1).
This result implies that in the case of o-methoxybenzoni-
trile even the first nucleophilic addition is hindered, which
again is in a sharp contrast to the situation for the reaction
electrophilic aromatic ring may induce competing deprotona-
tion or nucleophilic aromatic substitution reactions with
either the amino-imide moiety or the parent lithium amide.35
The many possible reaction paths raise fundamental ques-
tions regarding the effect of the electronic properties of the
nitrile and amide and the coordination mode of the lithium
metal in the reaction between nitriles and N-silylated amides.
In the first part of the current presentation, we compare the
of this nitrile and LiNTMS2 TMEDA, which provides
3
bis(trimethylsilyl)amidinate in good yields.16a
Reaction of Complex 1 with 2-Cyanopyridine in THF.
When the addition-elimination reaction of 2-cyanopyr-
idine with complex 1 is performed in THF, transparent
reactions of complex 1 and LiNTMS2 TMEDA with several
3
substituted aromatic nitriles of similar steric properties and
we demonstrate how the electronic properties of the nitrile
and amide and the presence of pendant groups that can
participate in the coordination of lithium or silicon influence
the chemoselectivity of the reaction. In addition, we present
the synthesis and structure of a lithium coordination polymer
of the pyridyltetrafluorobenzimidazolate ligand and also the
synthesis and structure of a unique hexacoordinate lithium
coordination polymer with TMEDA, tetrahydrofuran
(THF), and nonafluoro-p-benzonitrilephenylamide ligands.
crystals of the polymeric lithium benzimidazolate THF
3
complex 5 can be obtained in 78% isolated yield by the
slow evaporation of the solvent (Scheme 3). As was
mentioned in the Introduction, when a similar reaction
is carried out in toluene, the benzamidinate 2 and its
cyclization product, the benzimidazolate 3, are produced
(Scheme 3).11 The solubility of 5 in THF suggests that
upon polymer solvation fragments of smaller lithium
benzimidazolate monomers, such as a 2THF complex
(6, Scheme 3), are obtained. Polymer 5 was also obtained
when a THF solution of complex 3 was vacuum-concen-
trated. We have recently reported the formation of
coordination polymers of 3- and 4-pyridylamidinates,
which resulted from the coordination of lithium centers
to the pendant nitrogen atoms at the expense of TMEDA.18
The displacement of TMEDA with THF in complex 3 is
also supported by the almost identical 1H and 19F NMR
spectra (pyridyl and tetrafluorophenylene regions,
respectively) of 3 and 5 in THF-d8.
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D. Inorg. Chem. 2008, 47, 6692–6700. (b) Cui, D.; Nishimura, M.; Hou, Z.
Angew. Chem., Int. Ed. 2005, 44, 959–962.
(34) (a) Guo, J.-P.; Wong, W.-K.; Wong, W.-Y. Eur. J. Inorg. Chem.
2006, 3634–3640. (b) Guo, J.; Wong, W.-K.; Wong, W.-Y. Eur. J. Inorg. Chem.
2004, 267–275.
Unlike the four signals in the room-temperature 19F
NMR spectrum of 3 in toluene-d8, which support the
(35) (a) Divald, S.; Chun, M. C.; Joullie, M. M. J. Org. Chem. 1976, 41,
2835–2846. (b) Bures, E.; Nieman, J.; Yu, A. S.; Spinazze, P. G.; Bontront, J.-L. J.;
Hunt, I. R.; Rauk, A.; Keay, B. A. J. Org. Chem. 1997, 62, 8750–8759.
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U. J. Organomet. Chem. 1990, 388, 21–45.

9220 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
Scheme 1. Reactivity of the Lithium N-(Trimethylsilyl)pentafluoro-
anilide Complex 1 with Benzonitrile and o-Methoxybenzonitrile
Scheme 3. Reactivity of the Lithium N-(Trimethylsilyl)pentafluoro-
anilide Complex 1 with 2-Cyanopyridine in THF and Toluene
Scheme 2. Plausible Mechanism for the Trimerization of Nitriles by
Lithium Amides
retention of its solid-state structure in solution at these
conditions, there are only two fluorine signals in the 19F
NMR spectrum of 3 in THF-d8.11 This higher symmetry
about the tetrafluorinated ring (AB pattern) implies
that a rapid rotation of the pyridine ring and Li-
N(imidazolate) bond breaking and formation are operative.
Crystallographic data and structure refinement details
for complex 5 and selected bond lengths and angles are
presented in Tables 1 and 2, respectively. In the crystalline
lattice of complex 5 (Figure 3a), each lithium atom has a
distorted tetrahedral environment with two coordina-
tion sites occupied by the κ2-chelating NCCN unit of
the 2-(2-pyridyl)tetrafluorobenzimidazolate ligand. The
two other coordination sites are taken by a THF oxygen
atom and a second nitrogen atom of an adjacent benzi-
midazolate fragment (κ 1:κ 1 bimetallic bridging benzimi-
dazolate coordination mode). The lithium benzimi-
and tetrafluoeophenylene ring of neighboring chains
(Figure 3b), which create a two-dimensional supramo-
lecular structure (the pyridyl-tetrafluorophenylene cen-
˚
troid distance is 3.906 A).
Reaction of Complex 1 with Pentafluorobenzonitrile. In
an attempt to synthesize the perfluorinated 2-phenylben-
zimidazolate ligand, we have examined the reaction of
complex 1 with pentafluorobenzonitrile. When a similar
reaction is performed with LiNTMS2, the chemoselec-
tivity of the nucleophilic attack (on the nitrile carbon or
para position of the perfluorinated ring) is dependent on
the solvent. Thus, when the reaction is carried out in
ether,21 the pentafluoroamidinate is formed, whereas the
reaction of the same starting materials in THF37 gives a
mixture of two para substitution products (see eqs 1 and
2, respectively). These substitution products, p-N,N-bis-
(trimethylsilyl)aminotetrafluorobenzonitrile and the
coordination polymer {lithium [bis(4-cyano-2,3,5,6-
˚
dazolate Li-N3 bond [2.083(4) A] is slightly longer than
˚
the Li-N2 bond [2.028(4) A].
The long distance (3.033 A) between the lithium atom
˚
and the o-fluorine F1 atom implies that only a weak
Coulombic attraction may exist between these atoms.
The crystal lattice is composed of infinite chains made
by the bridging benzimidazolate ligands and lithium
atoms, whereas the THF ligands are disposed in a quasi-
syndiotactic arrangement. Counterintuitively, the tetra-
fluoro and pyridyl rings of the 2-(2-pyridyl)tetra-
fluorobenzimidazolate ligand point to the same direction
of the chain rather than adopting an alternating stereoar-
rangement, which is expected to provide less steric and
Coulombic repulsion between adjacent rings. This orienta-
tion probably results from π stacking between the pyridyl
tetrafluorophenyl)amide] 2THF}n, result from LiF
3
or Me3SiF elimination, respectively.
LiNTMS2 þ C6F5CN
½C F CðNTMSÞ Li Et Oꢀ
3
f
6
5
2
2
2
ether
ð1Þ
(37) Shmulinson, M.; Pilz, A.; Eisen, M. S. J. Chem. Soc., Dalton Trans.
1997, 2483–2486.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9221
Table 1. Crystallographic Data for Complexes 5, 7, 10, and 11
5
7
10
11
empirical formula
fw [g/mol]
T [K]
λ [A]
cryst syst
C16H12F4LiN3O
345.23
240(2)
0.710 73
orthorhombic
Pbca
15.886(3)
11.780(2)
16.277(3)
90
3046.0(3)
8
1.506
C23H24F9LiN4O
550.40
240(2)
C43H20ZrN9F12Cl
1017.35
240.0(2)
0.710 73
monoclinic
P21/c
12.048(2)
23.408(5)
15.806(3)
116.72(3)
3981(1)
4
1.697
0.447
C20H24ZrN5F4ClO
553.11
293(2)
0.710 73
monoclinic
C2/c
11.225(2)
15.239(3)
27.853(6)
98.972(3)
4706.2(16)
8
˚
0.710 73
monoclinic
P21
8.807(2)
16.647(3)
9.424(2)
114.82(3)
1254.0(5)
2
1.468
0.140
space group
˚
a [A]
˚
b [A]
˚
c [A]
β [deg]
3
V [A ]
˚
Z
F [g/cm3]
1.561
0.634
μ(Mo KR) [mm-1
]
0.129
R1, wR2 [I >2σ(I)]
R1, wR2 (all data)
GOF on F2
0.0418, 0.0935
0.0783, 0.1039
0.929
0.0411, 0.1107
0.0576, 0.1186
1.031
0.0571, 0.1445
0.1100, 0.1683
1.032
0.0674, 0.1770
0.1624, 0.2031
1.051
F(000)
θ range for data collection [deg]
limiting indices
1408
256
2024
2240
2.49-25.02
-16 e h e 18
-13 e k e 14
-17 e l e 19
15 200/2679
0.0869
2.38-25.41
0 e h e 10
0 e k e 20
-11 e l e 10
8173/2390
0.0430
1.89-25.63
0 e h e 14
-28 e k e 0
-19 e l e 16
26 405/7378
0.0690
2.27-25.01
0 e h e 13
0 e k e 17
-33 e l e 32
27 004/4010
0.0970
reflns collected/unique
R(int)
completeness to θmax [%]
data/restraints/parameters
largest diff peak and hole [e/A ]
100.0
2679/0/226
0.165 and 0.191
99.6
2390/1/347
0.210 and -0.183
98.1
7378/0/567
0.675 and -0.568
96.7
4010/0/274
0.579 and -0.731
3
˚
˚
Table 2. Selected Bond Lengths [A] and Angles [deg] for Complex 5
and implies that, under the examined reaction conditions,
the aromatic para position of pentafluorobenzonitrile is
more susceptible to nucleophilic attack than the nitrile
carbon. Concerning the heavier halogens, the rate-deter-
mining step of the nucleophilic aromatic substitution is
usually the σ-complex formation;38a however, influoroaro-
matic substrates, the rate-determining step can often be the
fluoride elimination38b because of the exceptionally high
enthalpy of the C-F bond.38c This involvement of the
fluoride elimination step in the kinetics of the rate-deter-
mining step was, e.g., observed in the reaction of 2,4-
dinitrofluorobenzene (Sanger’s reagent) with N-methyl-
aniline.38d Therefore, C-F bond activation by coordina-
tion of the fluorine atom is expected to accelerate the
reaction in such cases. Because the Si-F bond enthalpy
is more than 100 kJ greater than that of the Li-F bond,37
the formation of a Si-F interaction isexpectedtoprovide a
more significant activation of the C-F bond in the transi-
tion state than that of a Li-F interaction, and thus silicon
is expected to lower the relevant activation barrier more
efficiently than lithium. This difference in activation bar-
riers, which translates to the observed selectivity, is more
noticeable with the less reactive, weaker nucleophile 1.
Crystallographic data and structure refinement details
for complex 7 and selected bond lengths and angles are
presented in Tables 1 and 3, respectively. In the solid state
(Figure 4), complex 7 is a linear coordination polymer.
The repeating units of 7 consist of a distorted octahedral
Bond Lengths
N1-Li1
N2-Li1
N3-Li1
2.140(4)
2.028(4)
2.083(4)
O1-Li1
N2-C1
N3-C1
1.962(3)
1.344(2)
1.359(2)
N2-C2
N3-C3
C1-C8
1.367(3)
1.387(3)
1.475(3)
Bond and Torsion Angles
N2-C1-N3
O1-Li1-N2
O1-Li1-N3
N2-Li1-N3
O1-Li1-N1
116.83(18)
102.35(15)
104.12(16)
137.13(19)
120.13(18)
N2-Li1-N1
N3-Li1-N1
N2-C1-C8-N1
Li1-N2-C1-C8
Li1-N3-C1-C8
80.04(13)
113.56(16)
0.06
1.23
10.69
LiNTMS2 þ C6F5CN
p-TMS NC F CN
2 6 4
f
THF
þ ½ðp-NCC6F4Þ2NLi 2THFꢀn
ð2Þ
3
Hence, when pentafluorobenzonitrile is added to a chilled
THF solution of complex 1, the bright-yellow color of the
reaction mixture is changed to mustard-yellow, and the
coordination polymer {lithium [(4-cyano-2,3,5,6-tetrafluoro-
phenyl)(pentafluorophenyl)amide] THF TMEDA}n (7)
3
3
can be isolated from the solution in 87% yield as faint-
yellow crystals (Scheme 4).
Contrarily to the reaction with LiNTMS2, this Me3SiF
elimination product, which results from a silicon-assisted
SNAR reaction, is not accompanied by N-(trimethylsilyl)-
N-(4-cyano-2,3,5,6-tetrafluorophenyl)pentafluoroaniline
(8), the expected product from LiF elimination. When
lithium (pentafluorophenyl)(trimethylsilyl)amide (9)11 in
ether was used, no benzamidinate product was obtained;21
however, when THF and TMEDA (1 equiv) were added to
the reaction mixture, polymer 7 was produced. The high
chemoselectivity of complex 1 toward the production of
polymer 7 is plausibly due to its lower reactivity toward
nucleophilic attack reactions in comparison to LiNTMS2
(38) (a) Smith, M. B.; March, J. March’s advanced organic chemistry:
reactions, mechanism and structure, 5th ed.; Wiley-Interscience: New York,
2007; pp 854-857. (b) Nudelman, N. S. In The Chemistry of Amino, Nitroso,
Nitro and Related Groups; Patai, S., Ed.; Wiley: Chichester, U.K., 1996;
pp 1215-1300. (c) O'Hagan, D. Chem. Soc. Rev. 2008, 37, 308–319. (d) De La
Mare, P. B. D.; Swedlund, B. E. Heterolytic Mechanisms of Substitution
Involving Carbon-Halogen Bonds. In The Chemistry of the Carbon-Halogen
Bond; Patai, S., Ed.; Wiley: New York, 1973; pp 472-475 and references cited
therein.

9222 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
bonds of similar ligands to lithium in less saturated
complexes, as suggested by a search of the Cambridge
Crystallographic Data Centre (CCDC).41
Interestingly, the Li-NCN bond length in complex 7
˚
[2.142(8) A] is even shorter than the Li-amide bond
length [2.209(7) A], suggesting an extensive delocalization
˚
of the negative charge from the amide to the nitrile, which
is supported by the partly quinonical 4-cyano-2,3,5,6-
tetrafluorophenylamide ring (Table 3). The hexacoordi-
nation of the lithium atom is probably facilitated by the
soft nature of the 4-cyano-2,3,5,6-tetrafluorophenyl-
(pentafluorophenyl)amide ligand, whereas the polymeri-
zation is aided by the “two-faced” 1,4 distribution of the
negative charge in this ligand.
Insights into the Reactions of Complex 1 or LiNTMS2
TMEDA with Nitriles. When LiNTMS2 TMEDA is
3
3
added to 2-cyanopyridine or benzonitrile (route i or ii,
respectively, Scheme 5), the imido nitrogen atom of the
generated bis-silylated amino-imide (A or E, respectively,
Scheme 5) can attack either a silicon atom (rendering the
1,3 silyl shift) or another nitrile molecule (toward the nitrile
trimerization; Scheme 2). The production of the bis-sily-
lated amidinates (D and H) in high yields from these two
nitriles and also from o-methoxybenzonitrile16 suggests
that the 1,3-shift reaction is faster in these cases, as implied
by the production of triazine when dialkylamides are
used.16b
Because the silyl shift proceeds through a concerted
four-membered transition state (C and G, Scheme 5),43,44
we propose that a preliminary condition to its occurrence
is the coordination of the lithium trans to the amino
nitrogen atom about the imido CdN bond (as presented
in species B and F). This κ1 amino-imide coordination
mode is expected to be less favored enthalpically than the
κ2 mode, if no significant pendant donors are present. The
2-pyridyl substituent can, therefore, provide a better
stabilization of this κ1 amino-imide in comparison to
the weaker Li-aryl π interactions provided by the phenyl
ring (compare B to F). Similar preference for the forma-
tion of such NCCN chelates in the 2-pyridylamidinate
ligand is given in the structure of complex 3,11 in the
catalytic propylene polymerization by the titanium bis-
(2-pyridyl)amidinate complex,45 and in the precise cyclo-
oligomerization of ε-caprolactone by the thorium bis-
(2-pyridyl) complex.8 This lithium chelation, besides
clearing the way for the silyl shift,44 is also expected to
increase the nucleophilicity of the imide.
Figure 3. (a) ORTEP diagram of the molecular structure of a repeating
unit of polymer 5 (50% thermal ellipsoids), showing the mutual arrange-
ment of the fluorinated 2-(2-pyridyl)benzimidazolate ligands and the
quasi-syndiotactic stereochemistry of the THF ligands at the lithium
centers. Hydrogen atoms are omitted for clarity. (b) Illustration of the
segments of two neighboring chains of polymer 5 (50% thermal ellipsoids),
showing the π-stacking interactions. Hydrogen and fluorine atoms are
omitted for clarity (the tetrafluorophenylene ring is marked with an “F”).
lithium atom, which is cis-bischelated by an NCCF frag-
ment from a 4-cyano-2,3,5,6-tetrafluorophenyl ring, and
a TMEDA ligand.
The LiNCCF metallacycle is virtually planar, and
contrarily to complex 1, no C-F bond elongation is
noted, as shown by the similarity of the C2-F1 and
The different reactivities of amide 1 with 2-cyanopyr-
idine or benzonitrile (routes iii or iv, respectively) are
particularly obvious when compared to the exclusive
˚
C6-F4 bond lengths [1.358(4) and 1.362(4) A, respecti-
vely]. The two remaining coordination sites are taken by a
THF molecule and a nitrile nitrogen atom from an
adjacent repeating unit. Whereas coordination poly-
mers39 of hexacoordinate lithium are extremely rare by
their own right,40 complex 7 is, to the best of our knowl-
edge, the first hexacoordinate lithium coordination poly-
mer with both TMEDA and THF ligands.
amidinate formation with LiNTMS2 TMEDA. The
3
(41) For the Cambridge Crystallographic Data Centre (CCDC), see
http://www.ccdc.cam.ac.uk/
(42) Hansch, C.; Leo, A.; Hoekman, D. Exploring QSAR: Hydrophobic,
Electronic, and Steric Constants; American Chemical Society: Washington, DC,
1995; pp 254 and 270.
(43) (a) Takahashi, M.; Kira, M. J. Am. Chem. Soc. 1999, 121, 8597–8603.
(b) Jia, Z.; Feng, S.; Song, E.; Sun, W.; Cong, L. Int. J. Quantum Chem. 2008,
109, 342–348.
(44) Lim, C.; Lee, H. S.; Kwak, Y.-W.; Choi, C. H. J. Comput. Chem.
2006, 27, 228–237.
The bond lengths of all of the ligands in polymer 7 to
the lithium atom are markedly longer in comparison to
(45) Aharonovich, S.; Kapon, M.; Botoshanski, M.; Eisen, M. S. Sub-
stituent Effects in Propylene Polymerization Promoted by Titanium(IV)
Amidinates. Proceedings of the 38th International Conference on Coordina-
tion Chemistry, Kenes International, Jerusalem, Israel, July 20-25, 2008; p 369.
(39) Fromm, K. M. Coord. Chem. Rev. 2008, 252, 856–885.
(40) (a) Henderson, W. A.; Brooks, N. R.; Young, V. G., Jr. J. Am. Chem.
Soc. 2003, 125, 12098–12099. (b) Liu, X.; Guo, G.-C.; Wu, A. Q.; Huang, J.-S.
Inorg. Chem. Commun. 2004, 7, 1261–1263.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9223
Scheme 4. Reactivity of the Lithium N-(Trimethylsilyl)pentafluoroanilide TMEDA Complex 1 or the Unsolvated Lithium N-(Trimethylsilyl)-
3
pentafluoroanilide 9 with Pentafluorobenzonitrile in THF and Ether, Respectively
˚
Table 3. Selected Bond Lengths [A] and Angles [deg] for Complex 7
ring results in the formation of the amidinate 2 or the
benzimidazolate 3, respectively. The triazine formation
Bond Lengths
(4) by the reaction of 1 with benzonitrile suggests, there-
fore, that the isomerization, or more probably, the attack
F1-C2
F1-Li1
F4-C6
O1-Li1
N1-C1
N1-C7
1.358(4)
2.309(7)
1.362(4)
2.232(8)
1.336(5)
1.395(5)
N1-Li1
N2-C23
N2-Li1
N3-Li1
N4-Li1
C1-C6
2.209(7)
1.146(5)
2.142(8)
2.310(7)
2.357(8)
1.417(5)
C1-C2
C2-C3
C3-C4
C4-C5
C4-C23
C5-C6
1.417(5)
1.358(5)
1.402(6)
1.403(5)
1.416(5)
1.354(5)
of the imide is effectively suppressed in this system, allowing
the slower nitrile trimerization to prevail (route iv,
Scheme 5). Therefore, the lack of reactivity of amide 1 with
o-methoxybenzonitrile hints that the amino-imide inter-
mediate is not formed in this case.
Bond and Torsion Angles
These observations indicate that the N-pentafluoro
substituent has an inhibiting effect on the TMS shift
whereas the 2-pyridyl carbon substituent has an acceler-
ating effect and that the effect of the latter is stronger. The
major causes for these effects are not simply the steric
bulk of the substituents, due to the similar steric proper-
ties of the phenyl and pyridyl rings, the TMS and C6F5
moieties, and the OMe and F substituents.42 Except for
the latter case, the expected electronic effects of these
substituents on the reaction rates are opposite to the
experimental observations: Replacement of the phenyl
ring by the more electron-withdrawing pyridyl ring on the
amino-imide carbon is expected to have a stronger
negative inductive affect on the β-imido nitrogen (decrease
of its nucleophilicity) than on the γ-silicon (increase of its
electrophilicity), which would generate a net deceleration of
the silyl shift for route iii as compared to route iv. Similarly,
replacement of a TMS group by the more electron-
withdrawing C6F5 ring is expected to accelerate the rate
of the silyl shift of the remaining TMS for route iv as
compared to route ii because of the increase of its
electrophilicity.
C1-N1-C7
119.6(3)
118.4(3)
119.6(3)
168.9(4)
114.3(3)
177.3(4)
98.5(3)
93.4(3)
91.1(3)
98.3(3)
163.1(4)
96.1(3)
N1-Li1-N4
98.2(3)
165.6(4)
78.7(2)
85.3(2)
89.2(3)
170.7(4)
72.2(2)
87.1(3)
91.0(3)
3.78
C1-N1-Li1
C7-N1-Li1
C23-N2-Li1
C2-F1-Li1
N2-C23-C4
N2-Li1-N1
N2-Li1-O1
N1-Li1-O1
N2-Li1-N3
N1-Li1-N3
N2-Li1-N4
O1-Li1-N4
N3-Li1-N4
F1-Li1-N4
O1-Li1-N3
N2-Li1-F1
N1-Li1-F1
O1-Li1-F1
N3-Li1-F1
Li-N1-C1-C2
N1-C1-C2-F1
4.42
The TMS shift observed for the 2-pyridyl substituent is
therefore a plausible result of its assistance in chelation of
the lithium atom in the trans coordination mode. The
inhibiting effect of the pentafluorophenyl group on the
TMS shift can be explained by two cooperating factors:
i
Chelation of the silicon in an NCCF moiety, due to
the Si-F strong interactions with the o-fluorine of
the C6F5 ring (routes iii and iv). This interaction
reduces the electrophilicity of the silicon atom and
also provides some kinetic stability to the silylated
amino-imide motif. Similar intramolecular inter-
actions of silicon with various anionic or neutral
pendant donors,6,11,46,47 including organic
fluorine,11,48 are known. Support for this interac-
tion also comes from the room-temperature, silicon-
assisted C-F activation in complex 311 and from
Figure 4. ORTEP diagram of the molecular structure of the repeating
unit of polymer 7 (50% thermal ellipsoids). Hydrogen atoms are omitted
for clarity.
amino-imide complex generated by 1 (complexes I and
N) can participate in an additional reaction: the intramo-
lecular attack of the ortho position of the N-pentafluo-
roaryl ring. Similarly to the silyl shift, this reaction is also
expected to proceed in a κ1-bonded amino-imide
(complexes K and O). Therefore, the formation of both
amidinate and benzimidazolate in the reaction of 1 with
2-cyanopyridine suggests that the amino-imide I can
isomerizes to either species J or L, in which attack on
the silicon or on the ortho position of the perfluorinated
the solid-state structure of complex 1, in which the
˚
o-F Si distance is 2.956 A, which is shorter by
3 3 3
˚
0.494 A than the sum of the van der Waals radii
of these atoms. In a toluene solution, at room

9224 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
Scheme 5. Plausible Mechanism for the Reaction of Complex 1 or LiNTMS2 TMEDA with Benzonitrile or 2-Cyanopyridine
3
temperature, the hydrogen and carbon signals in
N-(trimethylsilyl)pentafluoroaniline are split,11,49
as a result of coupling of the o-fluorine rings with
the 1H and 13C NMR spectra of both 1 and
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(47) Kalikhman, I.; Gostevskii, B.; Kingston, V.; Krivonos, S.; Stalke, D.;
Walfort, B.; Kottke, T.; Kocher, N.; Kost, D. Organometallics 2004, 23,
4828–4835.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9225
carbon or hydrogen from the TMS methyl. Similar
splitting of the signals γ and δ to the perfluorinated
phenyl ring are absent from the spectrum of carbon-
substituted pentafluoroanilides,50 whereas four-
Scheme 6. Syntheses of the Zirconium Benzimidazolate Complexes 10
and 11
4
bond coupling constants, JFH (H-C-NfSi-F),
were observed in fluorosilicon complexes with intra-
molecular dative Si-N interactions.47
ii Strengthening of the Si-N bond β to the C6F5 ring.
The strengthening of C-C, C-H, and particularly
the more polar metal-carbon bonds, mainly due
to the negative inductive effect of fluorine, are
well documented in both experiment and theory.51
Because the silicon shift occurs through a concerted
rate-determining transition state, the stronger
Si-N bond translates to a higher activation barrier
for the reaction.
Synthesis, Structure, and Reactivity of the Zirconium
Mono- and Tris[tetrafluoro-2-(2-pyridyl)benzimidazolate]
Complexes. Synthesis of the Zirconium Benzimidazolate
Complexes. Because of our long-standing interest in the
study of new group 4 complexes with heteroazaallyl
ligands with unique pendant groups, we aimed to synthe-
size the zirconium and titanium tetrafluoro-2-(2-pyri-
dyl)benzimidazolate complexes. When a solution of 2
equiv of complex 3 is added to a toluene solution of TiCl4,
Isolation of complex 11, which results from the formal
substitution of a chloride and a THF ligand in Zr-
(NMe2)2Cl2 2THF with a benzimidazolate ligand, even
in the presence of an additional 1 equiv of complex 3,
3
hints that the salt metathesis stops after replacement of
the first chloride with
a benzimidazolate ligand
(Scheme 6). It is worth mentioning that, unlike the lithium
benzimidazolate 5, the external nitrogen atom, which
does not participate in the zirconium NCCN chelation,
does not displace a THF ligand or coordinate to the
zirconium metal while increasing its coordination number.
Solid-State Structure of the Zirconium Tris(benzimida-
zolate) Complex 10. Crystallographic data and structure
refinement details for complex 10 and selected bond
lengths and angles are collected in Tables 1 and 4, res-
pectively. In the solid state, the heptacoordinated zirco-
nium atom in complex 10 adopts a distorted capped-
octahedral environment, coordinated to a chlorine atom
and to three κ2-chelating pyridylbenzimidazolate ligands
(Figure 5). The Zr-Cl bond makes the “shaft” of “pro-
peller”-shaped, three chelating benzimidazolate ligands,
one of which forms a close contact with a toluene solvent
molecule through its tetrafluorobenzene ring. The similar
distance between the centroids of the toluene and the
perfluorocarbon rings in complex 10, as compared to the
centroid-centroid distance found in the C6F6/C6H6
a bright-orange solid precipitates after 30 min. 1H and 19
F
NMR spectroscopy of a THF-d8 solution of this solid,
which has a negligible solubility in toluene or ether,
indicates that it contains a mixture of compounds. These
compounds are most likely titanium benzimidazolate
complexes, as suggested by the disappearance of the
1
respective lithium benzimidazolate signals from the H
and 19F NMR spectra. When 2 equiv of complex 3 is
added to a toluene suspension of ZrCl4, in an attempt to
prepare the zirconium bis(benzimidazolate) complex, the
nearly white mixture turns faint bright yellow after 1 h.
From this mixture, the tris(benzimidazolate) complex 10
was obtained in an isolated yield of 65% (calculated on
the basis of complex 3), which was slightly improved (to
78%) when stoichiometric amounts of complex 3 and
ZrCl4 (3:1) were used (Scheme 6). In an attempt to gain
some kinetic control over the ligand substitution process,
2 equiv of complex 3 was reacted with Zr(NMe2)2Cl2
3
molecular complex52 (3.72 and 3.77 A, respectively),
˚
2THF. However, instead of the expected zirconium bis-
(benzimidazolate)diamide complex, the mono(benzimi-
dazolate) complex 11 was obtained in an isolated yield
suggests that complex 10 may be considered as a 1:1
molecular complex of toluene and a molecule of zirco-
nium tris(tetrafluorobenzimidazolate) chloride. Interest-
ingly, despite the many conceivable structural isomers,
the asymmetric pyridyltetrafluorobenzimidazolate ligands
adopt a single mutual arrangement about the zirconium
atom.
of 74% [on the basis of Zr(NMe2)2Cl2 2THF; Scheme 6].
3
(49) Oliver, A. J.; Graham, W. A. G. J. Organomet. Chem. 1969, 19, 17–
27.
(50) (a) Bezombes, J. P.; Hitchcock, P. B.; Lappert, M. F.; Merle, P. G.
J. Chem. Soc., Dalton Trans. 2001, 816–821. (b) Panda, A.; Stender, M.; Wright,
R. J.; Olmstead, M. M.; Klavins, P.; Power, P. P. Inorg. Chem. 2002, 41, 3909–
3916. (c) Vidovic, D.; Findlater, M.; Cowley, A. H. J. Am. Chem. Soc. 2007, 129,
8436–8437. (d) Wright, R. J.; Steiner, J.; Beaini, S.; Power, P. P. Inorg. Chim.
Acta 2006, 359, 1939–1946.
(51) (a) Clot, E.; Besora, M.; Maseras, F.; Megret, C.; Eisenstein, O.;
Oelckers, B.; Perutz, R. N. Chem. Commun. 2003, 490–491. (b) Clot, E.;
Megret, C.; Eisenstein, O.; Perutz, R. N. J. Am. Chem. Soc. 2009, 131, 7817–
7827. (c) Evans, M. E.; Burke, C. L.; Yaibuathes, S.; Clot, E.; Eisenstein, O.;
Jones, W. D. J. Am. Chem. Soc. 2009, 131, 13464–13473. (d) Perutz, R. N.;
Braun, T. Transition metal-mediated C-F bond activation. In Comprehensive
Organometallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier:
Oxford, U.K., 2007; pp 725-758.
Whereas all of the three benzimidazolate ligands have
similar intramolecular bond lengths and angles, the
ligand that interacts with the toluene molecule is differ-
entiated from the other two by its recognizable ligand
π-system interaction with the zirconium metal. This differ-
ence is evident from comparisons of the degree to which
the zirconium atom is displaced from the NCCN plane
˚
of the benzimidazole ligands (0.719 A from the N4-
C13-C20-N6 plane, while for the other two ligands,
(52) Williams, J. H. Acc. Chem. Res. 1993, 26, 593–598.

9226 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
˚
Table 4. Selected Bond Lengths [A] and Angles [deg] for Complex 10
Bond Lengths
Zr1-N1
Zr1-N4
Zr1-N8
Zr1-N3
Zr1-N9
Zr1-Cl1
Zr1-N6
N1-C1
2.191(4)
2.230(4)
2.237(4)
2.363(4)
2.363(4)
2.4113(16)
2.434(4)
1.374(6)
N1-C2
N2-C1
N2-C7
N4-C13
N4-C14
N5-C13
N5-C19
N7-C25
1.392(6)
1.321(6)
1.399(6)
1.372(6)
1.374(6)
1.320(6)
1.382(6)
1.326(6)
N7-C26
N8-C25
N8-C31
C1-C8
C13-C20
C25-C32
1.387(7)
1.359(6)
1.385(6)
1.443(6)
1.464(7)
1.456(7)
Bond and Torsion Angles
N1-Zr1-N4
N1-Zr1-N8
N4-Zr1-N8
N1-Zr1-N3
N4-Zr1-N3
N8-Zr1-N3
N1-Zr1-N9
N4-Zr1-N9
N8-Zr1-N9
N3-Zr1-N9
N1-Zr1-Cl1
N4-Zr1-Cl1
N8-Zr1-Cl1
N3-Zr1-Cl1
N9-Zr1-Cl1
134.04(14)
79.53(14)
143.87(15)
69.72(14)
78.45(14)
109.46(14)
129.91(14)
89.22(14)
70.79(14)
158.31(14)
81.76(12)
85.28(12)
117.65(11)
118.28(11)
77.79(11)
N1-Zr1-N6
136.85(15)
68.65(14)
76.86(14)
84.89(14)
73.96(14)
141.34(10)
15.72
20.26
2.61
4.66
2.86
N4-Zr1-N6
N8-Zr1-N6
N3-Zr1-N6
N9-Zr1-N6
Cl1-Zr1-N6
Zr1-N4-C13-N5
Zr1-N6-C20-C21
N4-C13-C20-N6
Zr1-N1-C1-N2
Zr1-N3-C8-C9
N1-C1-C8-N3
Zr1-N8-C25-N7
Zr1-N9-C32-C33
N8-C25-C32-N9
0.45
6.83
3.34
1.60
independent structural isomers (11A and 11B in 23% and
77% occupancy, respectively; Figure 6). These two over-
lapping molecules are predominantly distinguished by the
different extent of the slippage of the central octahedral
zirconium atom from the plane of the chelating tetra-
fluoro-2-(2-pyridyl)benzimidazolate ligand. The dimethyl-
amido, THF, and chloride ligands in complex 11 retain
their relative positions as in the structure of Zr(NMe2)2-
Cl2 2THF,53 i.e., two cis-NMe2 ligands and THF and
3
chloride ligands, which are trans and cis, respectively, to
one of the NMe2 ligands. The κ2-tetrafluoro-2-(2-pyri-
dyl)benzimidazolateligandisbondedtothe positions trans
to the chloride and second NMe2 ligands with the benzi-
midazolate and pyridyl moieties, which replaces the Zr-Cl
and “dative” Zr-O bonds, respectively, in Zr(NMe2)2Cl2
3
2THF. The two occupation sites of the zirconium atom in
˚
the overlapping complexes 11A and 11B are ca. 1 A apart
Figure 5. ORTEP diagram of the molecular structure of complex 10
(50% thermal ellipsoids). Hydrogen and fluorine atoms are omitted for
clarity (the tetrafluorophenylene ring is marked with an “F”).
and roughly inline with respect to the O1-N2 axis [the
O1-Zr1A-N2 and N2-Zr1B-O1 angles are 165.4(3)°
and 165.6(3)°, respectively]. In both of the structures,
a noticeable slippage of the zirconium metal from the
pyridylbenzimidazolate ligand is observed (the deviations
from the NCCN plane by Zr1A and Zr1B are 0.671 and
˚
this distance is 0.192 and 0.151 A). Additionally, there is a
notable bending of the C-C bond of the N4 benzimida-
zolate ligand, as evidenced by a dihedral angle of 11.49°
between the pyridyl and benzimidazolyl rings. Interest-
ingly, in the benzimidazolate ligand forming the motif
Zr-N6-C20-N4, both nitrogen atoms are partially
π-bonded. However, when the Zr-N6 and Zr-N4 bond
˚
0.348 A, respectively).
It is worth noting that, in both complexes 10 and 11, the
first structurally characterized zirconium benzimidazo-
lates, particularly in the latter, a noticeable tendency of
the zirconium metal toward an interaction with the ligand
π system was observed (probably in both cases because of
packing forces), a common bonding mode for the closely
related amidinates.
Behavior of the Zirconium Mono- and Tris[tetrafluoro-
2-(2-pyridyl)benzimidazolate] Complexes 10 and 11 in the
Polymerization of Propylene. The addition of methyl
˚
lengths are compared, the former is longer by 0.08 A,
whereas the Zr-N4 bond is similar to those of the other
benzimidazolate ligands. This difference in bond lengths
can be rationalized by the involvement of the electron-
rich azaallyl moiety N4-C13-N5 as compared to that of
the pyridyl system.
Solid-State Structure of the Zirconium Mono(benzimi-
dazolate) Complex 11. Crystallographic data and struc-
ture refinement details for complex 11 and selected bond
lengths and angles are collected in Tables 1 and 5, res-
pectively. In the solid state, complex 11 crystallizes as two
(53) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem. 1995, 621,
2121–2124.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9227
˚
Table 5. Selected Bond Lengths [A] and Angles [deg] and for Complex 11
Bond Lengths
Zr1A Zr1B
1.022(6)
1.391(13)
2.199(9)
2.900(13)
2.391(6)
2.473(6)
Zr1A-Cl1
2.474(3)
2.402(10)
2.036(6)
1.890(9)
2.297(5)
2.452(5)
Zr1B-Cl1
N3-C11
N5-C11
C11-C12
2.496(2)
1.370(7)
1.312(7)
1.465(8)
3 3 3
Zr1A-O1
Zr1A-N1
Zr1A-N2
Zr1A-N3
Zr1A-N4
Zr1B-O1
Zr1B-N1
Zr1B-N2
Zr1B-N3
Zr1B-N4
Bond and Torsion Angles
O1-Zr1A-N1
O1-Zr1A-N2
O1-Zr1A-N3
N1-Zr1A-N3
O1-Zr1A-N4
N1-Zr1A-N4
N3-Zr1A-N4
O1-Zr1A-Cl1
N1-Zr1A-Cl1
N3-Zr1A-Cl1
N4-Zr1A-Cl1
N2-Zr1B-N1
N2-Zr1B-N3
N1-Zr1B-N3
N2-Zr1B-O1
116.4(4)
165.4(3)
96.9(3)
93.9(3)
97.6(3)
143.5(5)
67.89(19)
109.9(3)
94.7(2)
144.4(3)
85.20(17)
106.4(4)
96.7(3)
N3-Zr1B-O1
76.4(2)
89.7(3)
162.7(3)
69.69(17)
76.1(2)
99.1(2)
98.3(2)
150.16(17)
82.32(15)
85.17(13)
117.5(5)
3.45
N2-Zr1B-N4
N1-Zr1B-N4
N3-Zr1B-N4
O1-Zr1B-N4
N2-Zr1B-Cl1
N1-Zr1B-Cl1
N3-Zr1B-Cl1
O1-Zr1B-Cl1
N4-Zr1B-Cl1
N5-C11-N3
N3-C11-C12-N4
Zr1A-N4-C13-N5
Zr1A-N4-C12-C16
Zr1B-N4-C13-N5
Zr1B-N4-C12-C16
17.03
20.18
11.32
6.71
101.3(2)
165.6(3)
aluminoxane (MAO; 1:1000 Zr/Al molar ratio) to a
toluene solution of complex 10 or 11 results in no
significant color change. Whereas the solution of complex
10 showed only negligible activity in the polymerization
of liquefied propylene, complex 11 gave a sticky polymer
the electrophilicity of the nitrile, by the availability of
adequate pendant group for the chelation of the lithium
metal during the reaction, and by three unique effects of the
pentafluorophenyl ring: strengthening of the Si-N bond,
decreasing of the nitrogen nucleophilicity, and interaction of
the o-fluorine and silicon atoms. In addition, zirconium
mono- or tris[tetrafluoro-2-(2-pyridyl)benzimidazolate] were
in a modest activity of 6.99 ꢁ 104 [g/mol h]. This hexane-
3
soluble polymer has a low tacticity and molecular weight
(mmmm % = 9.5 and Mn = 3000, respectively) and a high
polydispersity (Mw/Mn = 4.4). Theseresults imply thatthe
tris- and mono(benzimidazolate) complexes are not con-
verted during the polymerization process to common
active species, as was observed for the titanium bis- and
mono(benzamidinate)s.54 Further, the pendant 3- and
6-fluorine atoms do not participate in the termination-
hindering interaction with the growing polymer chain and
the polymerization is neither single-site nor living.55
prepared from the reaction of complex 3 and Zr(NMe2)2Cl2
3
2THF or ZrCl4, respectively. In these complexes, the first
synthesized zirconium mono- and tris(benzimidazolate)s, the
benzimidazolate ligand has a distinct tendency toward π
bonding with the zirconium metal. When activated by
MAO, only the mono(benzimidazolate) complex showed
modest activity in the polymerization of propylene. Synthetic
attempts to produce the bis(perfluorinated benzimidazolate)
complexes are in progress toward their study in the stereo-
regular polymerization and copolymerization of R-olefins.
Conclusions
Experimental Section
There are marked differences between the reactivity of
LiNTMS2 TMEDA or 1 toward aromatic nitriles. Whereas
amidinates are the major products of the reaction of
General Procedures. All manipulations of air-sensitive mate-
rials were carried out with the rigorous exclusion of oxygen and
moisture in an oven-dried or flamed Schlenk-type glassware on
a dual-manifold Schlenk line or interfaced to a high-vacuum
(10-5 Torr) line or in a nitrogen-filled glovebox (M. Braun) with
a medium-capacity recirculator (1-2 ppm O2). Argon and
nitrogen were purified by passage through a MnO oxygen-
3
LiNTMS2 TMEDA with all of the examined nitriles except
3
for C6F5CN in THF, complex 1 showed a diverse chemos-
electivity in its reactions: no reaction with o-OMeC6H4CN,
trimerization of benzonitrile to triazine, nucleophilic aro-
matic attack with C6F5CN in both ether or THF, and
production of amidinate and subsequently benzimidazolate
(3) with 2-cyanopyridine. From the reaction of complex 1
and C6F5CN, a unique, hexacoordinate lithium coordination
polymer was obtained. This lesser activity and different
reaction paths taken by complex 1 in its reactions with nitriles
˚
removal column and a Davison 4 A molecular sieve column.
Analytically pure solvents were distilled under nitrogen from
potassium benzophenone ketyl (THF), sodium (toluene and
TMEDA), and Na/K alloy (ether, hexane, toluene-d8, and
THF-d8). Complexes 1, 3, and 911 and Zr(NMe2)2Cl2 2THF53
3
were synthesized according to literature procedures. Nitriles
(Aldrich) were degassed, and ZrCl4 (Aldrich) was sublimed
under reduced pressure prior to use.
as compared to LiNTMS2 TMEDA seems to be affected by
3
NMR spectra were recorded on Bruker Avance 300 and 500
spectrometers. 1H and 13C chemical shifts are referenced to
internal solvent resonances and reported relative to TMS. 19F
(54) Volkis, V.; Lisovskii, A.; Tumanskii, B.; Shuster, M.; Eisen, M. S.
Organometallics 2006, 25, 2656–2666.
(55) (a) Sakuma, A.; Weiser, M.-S.; Fujita, T. Polym. J. 2007, 39, 193–207.
(b) Makio, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2005, 78, 52–66. (c) Furuyama,
R.; Saito, J.; Ishii, S.; Makio, H.; Mitani, M.; Tanaka, H.; Fujita, T. J. Organomet.
Chem. 2005, 690, 4398–4413.
7
and Li chemical shifts were referenced according to IUPAC
recommendations.56 The experiments were conducted in Tef-
lon-sealed NMR tubes (J. Young) after the preparation of the

9228 Inorganic Chemistry, Vol. 49, No. 20, 2010
Aharonovich et al.
methods59 and refined by the SHELXL-97 program package.60
The atoms were refined anisotropically. Hydrogen atoms were
included using the riding mode. Software used for molecular
graphics: ORTEP, TEXSAN Structure Analysis Package.61 The
cell parameters and refinement data are presented in Table 1.
Syntheses. General Procedure for the Reaction of (Me3-
SiNC6F5)Li TMEDA (1) with Nitriles. A certain amount of
3
complex 1 was charged in the glovebox into a swivel frit
equipped with two 100 mL flasks. After the frit was connected
to a high-vacuum line, 30 mL of toluene or THF was added, the
resulting solution was cooled to 0 °C, and an equimolar amount
of the corresponding nitrile was added dropwise using a syringe.
The cooling bath was removed, the resulting solution was stirred
at room temperature for 2 h and then filtered, and the volatiles
were evaporated from the filtrate until turbidity was noted. The
concentrated filtrate was cooled to -50 °C, and the formed
solids were separated from the mother liquor by fast filtration or
decantation, washed with small amounts of cold hexane, and
dried with a stream of argon.
Synthesis of Triphenyl-1,3,5-triazine (4). A total of 1.888 g
(4.85 mmol) of complex 1 and 0.500 g (4.85 mmol) of benzoni-
trile gave 0.336 g (67% yield) of 4. This previously published
compound13 was identified by 1H NMR and X-ray analysis. It is
important to add that catalytic amounts of complex 1 with
benzonitrile will also produce the same trimer but in a less
efficient manner.
Synthesis of {[C6F4N2C(2-C5H4N)]Li THF}n (5). A total of
3
1.869 g (4.8 mmol) of complex 1 and 0.500 g (4.8 mmol) of
2-cyanopyridine gave 1.342 g (78% yield) of 5. H NMR (300
1
MHz, THF-d8): δ 8.522 (br m, 1H, py-H6), 8.465 (td, J1=7.9 Hz,
J2 = 1.2 Hz, 1H, py-H3), 7.887 (dt, J1 = 8.0 Hz, J2=1.4 Hz, 1H,
py-H5), 7.351 (t, 3J=7.9 Hz, 1H, py-H4), 3.614 (m, OCH2), 3.577
(s, OCHD), 1.771 (m, OCH2CH2), 1.725 (s, OCD2CHD). 19F
NMR (188 MHz, THF-d8): δ -160.685 (br s, 2F, o-F), -175.710
(br s, 2F, m-F). 7Li NMR (194.4 MHz, THF-d8): δ -1.7975. 13
C
NMR (76.5 MHz, THF-d8): δ 162.92 (s, 1C, NCN), 155.71 (s,
1C, py-C2), 149.13 (s, 1C, py-C6), 138.11 (s, 1C, py-C4), 138.17
(m, 1JCF = 243.2 Hz, 2C, o-C-F), 135.38 (m, 1JCF = 239.8 Hz,
2C, m-C-F), 133.09 (m, 2C, C-N), 122.84 (s, 1C, py-C5),
122.54 (s, 1C, py-C3), 67.31 (q, OCD2), 66.33 (s, OCH2), 26.38
(s, OCH2CH2), 25.32 (q, OCD2CD2). Anal. Calcd for C16H12-
F4LiN3O (345.22): C, 55.67; H, 3.50; F, 22.01; N, 12.17. Found:
C, 47.68; H, 3.43; F, 24.31; N, 11.09.
Figure 6. ORTEP diagram of the molecular structure of complexes 11A
(a) and 11B (b) (50% thermal ellipsoids). Hydrogen atoms are omitted for
clarity.
Synthesis of [LiN(4-CN-2,3,5,6 tetrafluorophenyl)(C6F5)
THF TMEDA]n (7). A total of 2.017 g (5.2 mmol) of complex
3
3
1 and 1.000 g (5.2 mmol) of pentafluorobenzonitrile gave 2.548 g
(87% yield) of 5. H NMR (300 MHz, THF-d8): δ 3.576 (s,
sample under anaerobic conditions, with dried toluene-d8 or
THF-d8. The molecular weights and polydispersities of the
polymers were determined by the gel permeation chromatogra-
phy (GPC) method on a Varian PL-GPC 220 instrument using
1,2,4-trichlorobenzene as the mobile phase at 160 °C. Polystyr-
ene standards were used for the standard calibration curve
of GPC.
1
OCHD), 2.300 (s, 4H, CH2N), 2.146 (s, 12H, CH3N), 1.725 (s,
OCD2CHD). 19F NMR (282.4 MHz, THF-d8): δ -147.115 (m,
3JFF=14.7 Hz, 2F, N-CCF), -158.316 (m, 3JFF=20.8 Hz, 2F,
o-F), -166.491 (m, 3JFF=14.7 Hz, 2F, NC-CCF), -172.417 (t,
3
3JFF = 20.8 Hz, 2F, m-F), -177.763 (m, JFF =20.8 Hz, 1F,
p-F). 13C NMR (75.4 MHz, THF-d8): δ 148.74, (m, 1JCF=242.3
1
X-ray Crystallographic Measurements. The single-crystalline
material was immersed in parathone-N oil and was quickly
fished with a glass rod and mounted on a Kappa CCD diffract-
ometer under a cold stream of nitrogen. Data collection was
performed using monochromatized Mo KR radiation using j
and ω scans to cover the Ewald sphere.57 Accurate cell para-
meters were obtained with the amount of indicated reflections
(Table 1).58 The structure was solved by SHELXS-97 direct
Hz, 2C, N-CCF), 142.59 (m, JCF =225.7 Hz, 2C, o-C-F),
141.42, (m, 1JCF = 221.5 Hz, 2C, NC-CCF), 139.54 (m, 1JCF
=
=
234.1 Hz, 2C, m-C-F), 136.67 (m, 1C, C-N), 134.64 (m, 1JCF
3
240.2 Hz, 1C, p-C-F), 112.15 (t, JCF =3.5 Hz, 1C, C-CN),
67.45 (q, OCD2), 58.85 (CH2N), 46.23 (CH3N), 25.32 (q, OCD2-
CD2). Anal. Calcd for C23H24F9LiN4O (550.39): C, 50.19; H,
4.40; F, 31.07; N, 10.18. Found: C, 49.13; H, 3.56; F, 24.10; N,
8.86.
Synthesis of [C6F4N2C(2-C5H4N)]3ZrCl C7H8 (10). To a
3
(56) Harris, R. K.; Becker, E. D.; Cabral De Menezes, S. M.; Goodfellow,
R.; Granger, P. Pure Appl. Chem. 2001, 73, 1795–1818.
(57) Kappa CCD Server Software; Nonius BV: Delft, The Netherlands, 1997.
(58) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(59) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990,
A46, 467.
swivel frit equipped with 100 mL flasks was added inside the
glovebox 0.400 g (1.71 mmol) of ZrCl4. The frit was connected to
a high-vacuum line, and the solids were suspended in 25 mL of
toluene, which was cooled to 0 °C. A total of 2.000 g (5.14 mmol)
(60) ORTEP, TEXSAN Structure Analysis Package; Molecular Structure
Corp., MSC: The Woodlands, TX, 1999.
(61) Sheldrick, G. M. SHELXL97, Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1997.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9229
of complex 3 was dissolved in 20 mL of toluene, and the solution
was injected dropwise to the frit. The faint-yellow suspension
that resulted was stirred for 3 h, after which the reaction mixture
was evaporated and TMEDA was removed by low-pressure
azeotrope distillations with toluene. The resulting solids were
extracted with hot toluene (ca. 50 °C, 3 ꢁ 25 mL), and the extract
was filtered. The volume of the filtrate was reduced to half, and
the concentrated solution was cooled gradually to -4 °C for 72 h
to yield bright-yellow crystals of the product. The crystals were
separated from the mother liquor by decantation, washed twice
with a small amount of cold hexane, and dried with a gentle
stream of argon (1.359 g, 78% yield). 1H NMR (300 MHz, THF-
(dt, 3J = 8.1 Hz, 4J = 1.5 Hz, 1H, py-H4), 7.294 (ddd, 3J = 7.4
and 4.9 Hz, 4J = 1.3 Hz, 1H, py-H5), 3.626 (m, OCH2), 3.575 (s,
OCHD), 3.055 (s, 6H, NMe2), 3.047 (s, 6H, NMe2), 1.775 (m,
OCH2CH2), 1.725 (s, OCD2CHD). 19F NMR (188 MHz, THF-
d8): δ -160.494 (br s, 2F, o-F), -175.671 (dd, 3JFF = 14.0 and
11.5 Hz, 2F, m-F). 13C NMR (75.5 MHz, THF-d8): δ 163.80 (s,
1C, NCN), 147.18 (s, 1C, py-C2), 145.19 (s, 1C, py-C6), 139.81 (s,
1C, py-C4), 122.97 (s, 1C, py-C5), 122.89 (s, 1C, py-C3), 67.38 (q,
OCD2), 66.31 (s, OCH2), 45.85 (s, 2C, NMe2), 45.61 (s, 2C,
NMe2), 26.33 (s, OCH2CH2), 25.32 (q, OCD2CD2). Anal. Calcd
for C20H24ClF4N5OZr (553.11): C, 43.43; H, 4.37; N, 12.66.
Found: C, 46.36; H, 3.17; N, 11.79.
3
d8): δ 8.675 (ddd, J = 4.8 Hz, 4J = 1.7 Hz, 5J = 1.0 Hz,1H,
Propylene Polymerization Experiments with Complexes 10
and 11. In a glovebox, a 3 mL toluene solution of 46.5 μmol of
the catalyst (47.4 or 32.4 mg of complexes 10 or 11, respectively)
was added to a solution of 2.700 g of MAO in 15 mL of toluene,
followed by stirring with a glass rod. The resulting solution was
equally divided into three parts, each of which was transferred to
a 100 mL beaker equipped with a stir bar. The beakers were
placed in steel reactors that were then connected to a high-
vacuum line, cooled to liquid-nitrogen temperature, and
pumped down. A total of 35 mL of liquid propylene was vacuum
transferred to each of the reactors. The temperature was then
raised to 25 °C using a thermostatted bath, and the stirring
began. After 3 h, the unreacted propylene was exhausted in a
hood and the reaction mixture was quenched by the addition of
30 mL of acetylacetone (acac). The polymer was separated from
the organic phase, cut down to small pieces, extracted for 2 days
with methanol and then acetone to remove traces of Al(acac)3,
acac, and toluene, and dried under vacuum at 50 °C. No soluble
polymeric fractions were found in the organic washing solvents.
py-H6), 8.425 (td, 3J = 7.9 Hz, 4J = 5J = 1.0 Hz, 1H, py-H3),
3
4
7.939 (dt, J = 7.7 Hz, J = 1.8 Hz, 1H, py-H4), 7.456 (ddd,
3J = 7.6 and 4.8 Hz, 4J = 1.2 Hz, 1H, py-H5), 3.577 (s, OCHD),
1.725 (s, OCD2CHD). 19F NMR (188 MHz, THF-d8): δ
-162.763 (br s, 2F, o-F), -164.554 (br s, 2F, m-F). 13C NMR
(76.5 MHz, THF-d8): δ 159.91 (s, 1C, NCN), 151.13 (s, 1C, py-
C2), 147.66 (s, 1C, py-C6), 136.94 (s, 1C, py-C4), 122.45 (s, 1C,
py-C5), 122.04 (s, 1C, py-C3), 67.35 (q, OCD2), 25.32 (q,
OCD2CD2). Anal. Calcd for C43H20ClF12N9Zr (1017.34): C,
50.77; H, 1.98; N, 12.39. Found: C, 49.53; H, 2.29; N, 11.86.
Synthesis of [C6F4N2C(2-C5H4N)](NMe2)2ZrCl THF (11).
To a swivel frit equipped with 100 mL flasks was added inside
the glovebox 1.013 g (2.57 mmol) of Zr(NMe2)2Cl2 2THF. The
3
3
frit was connected to a high-vacuum line, and the solids were
dissolved in 20 mL of THF, which was cooled to 0 °C. A total of
1.000 g (2.57 mmol) of complex 3 was dissolved in 15 mL of
THF, and the solution was injected dropwise to the frit. The off-
white suspension that resulted was stirred for 3 h, after which the
reaction mixture was evaporated and TMEDA was removed by
low-pressure azeotrope distillations with toluene. The resulting
solids were extracted with toluene (2 ꢁ 25 mL), and the extract
was filtered. The filtrate was evaporated until saturation, and
the concentrated solution was cooled gradually to -35 °C for
96 h to yield faint-yellow crystals of the product. The crystals
were separated from the mother liquor by filtration, washed
twice with a small amount of cold hexane, and dried carefully
under vacuum (1.052 g, 74% yield). 1H NMR (200 MHz, THF-
d8): δ 8.494 (br m, 1H, py-H6), 8.462 (m, 1H, py-H3), 7.853
Acknowledgment. This research was supported by the
USA-Israel Binational Science Foundation under Contract
2008283. S.A. thanks Raymond Rosen for his fellowship.
Supporting Information Available: Figures of the extended
structures of polymers 5 and 7 and X-ray crystallographic data
in CIF format for complexes 5, 7, 10, and 11. This material is
available free of charge via the Internet at http://pubs.acs.org.