Exploring CH-activation pathways in bifunctional zirconocene/borane systems

Article abstract of DOI:10.1021/ja048447l

The dimethylsilanediyl-bridged ansa-zirconocene dichloride 1, that contains a pendent allyl substituent at a Cp-ring, adds HB(C₆F ₅)₂ to the vinyl group to yield the bifunctional zirconocene/borane complex 2. Substituted benzimidazoles were added to the strongly electrophilic borane moiety as protective groups, which allowed subsequent chloride versus -CH₂SiMe₃ exchange at zirconium to take place by treatment with the respective alkyllithium reagent. Alternatively, the introduction of active σ-ligands at zirconium is carried out first, followed by the hydroboration reaction. This route was followed for the synthesis of the diphenyl-ansa-zirconocene/borane complex 12. Complex 12 reacts slowly in solution by intramolecular electrophilic attack of the borane at its adjacent Cp-ring, followed by deprotonation using a [Zr]-Ph group to yield the zwitterionic complex 14 featuring a borata-tetrahydroindenyl moiety as part of the ansametallocene framework. Complex 14 was characterized by X-ray diffraction. It adds PMe₃ at zirconium to yield 15. Thermolysis of 12 with excess PMe₃ leads to the formation of the (aryne)zirconocene complex 18, which is stabilized by PMe₃ coordination to zirconium and PMe₃ addition to boron. N-Methylbenzimidazole adds to the -B(C₆F₅)₂ unit of 12 to give the 1:1 adduct 19. Thermolysis of 19 at 80 °C in benzene solution in the presence of one additional equivalent of N-methylbenzimidazole results in deprotonation of the substrate to yield the σ-N- methylbenzimidazolyl zirconium complex 20 (as a mixture of two diastereoisomers). An additional N-methylbenzimidazole ligand is bonded to the B(C₆F₅)₂ unit in this product.

Full text of DOI:10.1021/ja048447l

Published on Web 08/14/2004
Exploring CH-Activation Pathways in Bifunctional
Zirconocene/Borane Systems
Michael Hill, Gerhard Erker,* Gerald Kehr, Roland Fro¨hlich,† and Olga Kataeva†
Contribution from the Organisch-Chemisches Institut UniVersita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received March 18, 2004; E-mail: erker@uni-muenster.de
Abstract: The dimethylsilanediyl-bridged ansa-zirconocene dichloride 1, that contains a pendent allyl
substituent at a Cp-ring, adds HB(C6F5)2 to the vinyl group to yield the bifunctional zirconocene/borane
complex 2. Substituted benzimidazoles were added to the strongly electrophilic borane moiety as protective
groups, which allowed subsequent chloride versus -CH2SiMe3 exchange at zirconium to take place by
treatment with the respective alkyllithium reagent. Alternatively, the introduction of active σ-ligands at
zirconium is carried out first, followed by the hydroboration reaction. This route was followed for the synthesis
of the diphenyl-ansa-zirconocene/borane complex 12. Complex 12 reacts slowly in solution by intramolecular
electrophilic attack of the borane at its adjacent Cp-ring, followed by deprotonation using a [Zr]-Ph group
to yield the zwitterionic complex 14 featuring a borata-tetrahydroindenyl moiety as part of the ansa-
metallocene framework. Complex 14 was characterized by X-ray diffraction. It adds PMe3 at zirconium to
yield 15. Thermolysis of 12 with excess PMe3 leads to the formation of the (aryne)zirconocene complex
18, which is stabilized by PMe3 coordination to zirconium and PMe3 addition to boron. N-Methylbenzimidazole
adds to the -B(C6F5)2 unit of 12 to give the 1:1 adduct 19. Thermolysis of 19 at 80 °C in benzene solution
in the presence of one additional equivalent of N-methylbenzimidazole results in deprotonation of the
substrate to yield the σ-N-methylbenzimidazolyl zirconium complex 20 (as a mixture of two diastereoisomers).
An additional N-methylbenzimidazole ligand is bonded to the B(C6F5)2 unit in this product.
Scheme 1
Introduction
Enzymatic functionalization (or oxidation) of carbon-
hydrogen bonds often follows pathways different from those
established and used in organic synthesis.1 In nature’s catalysts,
substrate orientation and substrate/active site proximity are often
more important than an intrinsic intramolecular activation of
CH bonds by adjacent functional groups in the substrate. Thus,
selective transformations at seemingly “unactivated” positions
are often achieved in enzymatic processes with apparent ease.
The search for artificial catalysts that exhibit a similar behavior
has led to the discovery of a variety of metal catalyst systems
that can selectively attack C-H bonds (and sometimes C-C
bonds) in hydrocarbon substrates.2 Their selectivity features,
however, often rely on thermodynamic preference or selectivity
being effected by specific kinetic control.3-6 Proximity control
has, of course, often been observed in selective metal-mediated
attack on C-H bonds,7 but most such systems involve hydro-
carbon core systems with pendent nucleophilic (e.g., alkylphos-
phino) groups to which the active metal systems were attached.8,9
Much of the knowledge assembled about spatial effects in metal-
induced C-H (and C-C) activation was derived from studying
such systems, but their actual C-H activation processes are
usually limited to functionalization of the ligand systems
themselves (see example 1 in Scheme 1).10
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† To whom correspondence should be addressed regarding X-ray crystal
structure analyses.
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11046
J. AM. CHEM. SOC. 2004, 126, 11046-11057
10.1021/ja048447l CCC: $27.50 © 2004 American Chemical Society

CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
Scheme 2
As an attractive alternative, one might envision the synthesis
of a metal complex system that itself contains a pendent
functionality that is able to bind an incoming substrate and orient
it in the proximity of the active metal site as required for a
selective activation process. Using an electrophilic “anchoring”
group would be attractive because this would allow for
(reversible) binding of a great variety of organic substrates
through a number of nucleophilic donor functionalities. We have
begun to design and synthesize such systems (see example 2 in
Scheme 1) that are complementary to many such approaches
described in the literature. We have not arrived at a catalytic
system so far, but made a number of interesting observations
on this route that will be described below.
The problem that we faced next was to achieve a selective
functionalization at the transition metal center without affecting
the electrophilicity of the pendent borane group. Because
chloride versus alkyl anion exchange at the stage of the
bifunctional electrophilic system 2 was to be effected by
treatment with, for example, an alkyllithium or a Grignard
reagent, we needed to develop a protective group scheme, which
is, of course, a common feature in organic synthesis, but almost
completely unexplored in organometallic chemistry.
For this purpose, we reacted the bifunctional complex 2 with
N-methylbenzimidazole (3a). Treatment of 2 with the hetero-
cycle 3a in toluene at ambient temperature gave the adduct 4a
in almost quantitative yield.16 The 11B NMR spectrum of the
product indicated that the benzimidazole nucleophile had cleanly
added to the boron atom. Complex 4a features a broad 11B NMR
Results and Discussion
Initial Experiments. Our synthetic aproach was based on
an ansa-zirconocene system that contained a pendent very
electrophilic -B(C6F5)2 borane group that was connected by a
trimethylene linker to one of its cyclopentadienide ligands. As
we had previously described,11 the respective zirconocene
dichloride complex (2) was prepared by treatment of the Cp-
allyl-containing ansa-zirconocene dichloride precursor (1)12 with
“Piers’ borane” [HB(C6F5)2].13 This resulted in a clean hy-
droboration reaction to yield the bifunctional complex 2 (see
Scheme 2).14,15
resonance at δ -5.56 (ν
) 324 Hz) that is very typical of
1/2
tetravalent boron adduct formation17 [cf. 2: 11B NMR: δ +75.6
(ν 1/2 ) 1085 Hz)]. Also, the pair of C6F5 substituents at boron
in 4a has become diastereotopic [19F NMR signals at: δ -132.2/
133.1 (o), δ -164.0/-164.1 (m), δ -158.8/-159.1 (p)] due to
the element of planar chirality of the adjacent metallocene [in
contrast to the single set of C6F5 resonances at the planar-
tricoordinate boron atom of 2: δ -130.2 (o), -160.8 (m),
-148.6 (p)], and the typical upfield shift of the p-C6F5 19F NMR
was observed upon borane adduct formation16 to yield 4a.
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9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11047

A R T I C L E S
Hill et al.
Figure 1. Two views of the molecular structure of complex 4a in the crystal. Selected bond lengths (Å) and angles (deg): Zr-Cl1 2.438(1), Zr-Cl2
2.426(1), Si1-C1 1.876(3), Si-C6 1.842(3), Si-C7 1.850(3), Si-C8 1.873(3), C11-C13 1.493(4), C13-C14 1.547(4), C14-C15 1.528(4), C15-B1
1.624(4), B1-N16 1.607(4), B1-C26 1.653(4), B1-C32 1.658(4), N16-C17 1.319(3), N16-C24 1.409(3), C17-N18 1.337(3), N18-C19 1.382(3), N18-
C25 1.462(4), C19-C24 1.391(4); Cl1-Zr-Cl2 98.93(3), C1-Si1-C8 93.7(1), C1-Si1-C6 112.6(2), C1-Si1-C7 110.7(2), C8-Si1-C6 112.8(1), C8-
Si1-C7 112.0(2), C6-Si1-C7 113.5(2), C11-C13-C14 117.1(2), C13-C14-C15 111.4(2), C14-C15-B1 118.9(2), C15-B1-N16 110.0(2), C15-
B1-C26 108.4(2), C15-B1-C32 111.4(2), N16-B1-C26 109.7(2), N16-B1-C32 103.0(2), C26-B1-C32 114.2(2), B1-N16-C17 126.3(2), B1-
N16-C24 127.6(2), C24-N16-C17 106.0(2), N16-C17-N18 112.5(2), C17-N18-C19 107.4(2).
Similarly, treatment of 2 with 1,2-dimethylbenzimidazole (3b)
gave the corresponding 1:1 adduct 4b (97% isolated, for details
see the Experimental Section).
The C13-C14-C15-B orientation is close to antiperiplanar
(θ ) -176.7(2)°), but the torsion angles C14-C15-B-N16
and C15-B1-N16-C17 amount to -71.3(3)° and 3.8(4)°,
respectively. The Zr‚‚‚B distance in complex 4a is 6.228 Å. In
this conformational arrangement, the imidazole N-C(H)dN
methine unit (C17-H in Figure 1) is even closer to zirconium
(Zr‚‚‚C17: 4.877 Å) and the adjacent Zr-bound chloride ligands
(Zr-Cl1: 2.438(1) Å, Zr-Cl2: 2.426(1) Å), featuring distances
of 3.492 Å [(Zr)Cl1‚‚C17] and 4.173 Å [(Zr)Cl2‚‚C17],
respectively.
Complex 4a was characterized by X-ray diffraction. It features
a typical ansa-metallocene core. To one of its Cp-rings is the
-(CH2)3-B(C6F5)2 moiety attached. The N-methylbenzimida-
zole unit18 has added to the electrophilic boron center by means
of its “imine-type” nitrogen center. The resulting boron-
nitrogen linkage is strong. The B-N16 bond length (1.607(4)
Å) is shorter than the adjacent B-C linkages (e.g., B-C15:
1.624(4) Å). The topology of the system positions the -(CH2)3-
[B] unit at the front of the bent metallocene wedge. Nevertheless,
it is remarkable that the observed conformational arrangement
of the -(CH2)3-B(N-methylbenzimidazole)(C6F5)2 unit in the
crystal is such that it brings the functionalized end of the
benzimidazole ligand into a direct spatial opposition with the
open ZrCl2 side of the group 4 bent metallocene (see Figure
1).14 This is achieved by an appropriate rotation of the C-C
bonds of the trimethylene linker (dihedral angles C10-C11-
C13-C14: -34.3(4)° and C11-C13-C14-C15: -147.5(2)°).
The reaction of the adduct 4a with 2 mol equiv of LiCH2-
SiMe3 in ether (-20 °C to room temperature) proceeded cleanly
with metathetical exchange of both chloride ligands at zirco-
nium. The benzimidazole-protected -B(C6F5)2 Lewis acid was
left untouched under these conditions. The product 5 (94%
isolated) showed typical AB quartetts of the two -CH2SiMe3
1
pairs of hydrogens in the H NMR spectrum (δ 0.05/-0.10, δ
-0.04/-0.29; corresponding 13C NMR signals at δ 35.0 and δ
38.4). The 11B NMR resonance was found at δ -5.16. Complex
5 proved rather stable. Even heating to ca. 90 °C did not result
in an intramolecular attack of the bulky σ-ligands at the adjacent
benzimidazole system.
(16) For related B(C6F5)3 adduct formation, see, for example: Ishihara, K.;
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We tried to mimick such a reaction by treatment of 4a with
LDA. When the reaction was carried out in tetrahydrofuran,
we observed the formation of the product 7 (see Scheme 2).
This indicated that the coordinated benzimidazole system was
deprotonated under these conditions, and the resulting carbanion
(6) did not react intramolecularly with the [Zr]Cl2 unit but rather
underwent a nucleophilic aromatic substitution reaction at one
of the adjacent C6F5 ring systems. A similar reaction had
previously been observed with a benzimidazole/B(C6F5)3 adduct
to occur under similar reaction conditions.19,20
In this reaction, a chirality center at boron is introduced in
addition to the persistent planar chirality element of the bent
(17) Wrackmeyer, B.; Ko¨ster, R. In Houben-Weyl, Methoden der Organischen
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Thieme Verlag: Stuttgart, 1984; Vol. 13/3a-c. Wrackmeyer, B. Nuclear
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9
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CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
Scheme 3
metallocene. Therefore, two diastereoisomers 7/7′ were formed
in a ca. 1:1 ratio. These gave rise to the observation of doubled
sets of a number of signals in the NMR spectra [e.g., N-CH3:
δ 4.34/4.32, both showing a long-range JHF coupling of 3.4 Hz
that is typical for this general framework19,21); C6F5 (19F
NMR): δ -133.5/-134.2 (o), δ -160.2/-161.1 (p), δ -165.5/-
165.9 (m)], while others were isochronous for the two diaster-
eomers [e.g., C6F4 (19F NMR): δ -132.6, -135.8, -151.7,
-159.3; 11B NMR: δ -4.0].
Preparation and Reactions of Bifunctional Diphenylzir-
conocene/Borane Complexes. Diphenylzirconocenes allow for
several pathways of activation.22 Among them, thermally
induced (aryne)zirconocene formation23-25 gives reactive in-
termediates that had previously been used in CH-activation
reactions.22,26 For the synthesis of a bifunctional diphenylzir-
conocene/borane system, we first reacted the alkyl-Cp-contain-
ing ansa-metallocene complex 1 with phenyllithium to yield 8.
At 80 °C, complex 8 loses 1 equiv of benzene. The NMR spectra
of the resulting solution indicate that the (aryne)zirconocene
(9) had probably been formed as a reactive intermediate that
was rapidly trapped by the internal Cp-bonded olefin27 to form
10. Complex 10 was generated on a preparative scale in the
Scheme 4
24
presence of excess PMe3 to avoid side reactions and then
directly quenched28 by treatment with the anilinium Brønsted
acid [PhNMe2H]+Cl- to yield 11, as expected as a single
diastereoisomer (Scheme 3).
Complex 8 was then reacted with HB(C6F5)2. In principle,
this strongly Lewis acidic borane might have been able to
abstract a phenyl anion equivalent from zirconium.29 However,
this is not observed, but a clean hydroboration of the pendent
CdC double bond takes place to give 12 (Scheme 4). Complex
12 shows a 11B NMR resonance at δ +79.2, which is
characteristic for a free tricoordinate borane, and three typical
19F NMR signals corresponding to the pair of symmetry
equivalent C6F5 substituents at boron [δ -129.7 (o), -147.5
(p), -160.9 (m)]. The 1H/13C NMR spectra show the presence
of two nonequivalent phenyl substituents at the zirconium center.
Complex 12 is not stable for prolonged time at ambient
temperature in solution. During ca. 3 d, it loses 1 equiv of
(21) Hilton, J.; Sutcliffe, L. H. Prog. Nucl. Magn. Reson. Spectrosc. 1975, 10,
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1975, 97, 4770. Berger, S.; Braun, S.; Kalinowski, H.-O. NMR-Spek-
troskopie Von Nichtmetallen, 19F NMR-Spektroskopie; Georg Thieme
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benzene with the formation of 14.30 The dipolar product 14
contains a strongly electrophilic zirconium center, to which
PMe3 could be added. We isolated the addition product 15 as a
single isomer in 89% overall yield, starting from 8.
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Soc. 1991, 113, 4685-4686. Aoki, K.; Peat, A. J.; Buchwald, S. L. J. Am.
Chem. Soc. 1998, 120, 3068-3073. Frid, M.; Pe´rez, D.; Peat, A. J.;
Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 9469-9470. Kraft, B. M.;
Lachicotte, R. J.; Jones, W. D. Organometallics 2002, 21, 727-731.
(25) Erker, G.; Dorf, U.; Mynott, R.; Tsay, Y.-H.; Kru¨ger, C. Angew. Chem.
1985, 97, 572-574; Angew. Chem., Int. Ed. Engl. 1985, 24, 584-585.
Erker, G.; Albrecht, M.; Kru¨ger, C.; Werner, S.; Binger, P.; Langhauser,
F. Organometallics 1992, 11, 3517-3525.
Complex 12 contains a pair of σ-ligands at zirconium and a
strongly electrophilic -B(C6F5)2 Lewis acid in close vicinity.
It is remarkable that even in this situation σ-ligand transfer from
zirconium to boron does not take place. Instead, complex 12
utilizes the strongly electrophilic pendent -B(C6F5)2 moiety to
enter into a different reaction pathway. It is apparently initiated
by -B(C6F5)2 addition to the adjacent Cp-ring from the
“outside” to generate the intermediate 13. This has the ipso-
hydrogen atom pointing toward the “inside” of the former
metallocene system, which brings an acidified hydrogen into
close proximity of zirconium bound σ-phenyl ligand. Its kinetic
basicity is apparently sufficient to abstract the proton with
(26) Erker, G.; Czisch, P.; Mynott, R.; Tsay, Y.-H.; Kru¨ger, C. Organometallics
1985, 4, 1310-1312.
(27) Erker, G.; Kropp, K. J. Am. Chem. Soc. 1979, 101, 3659-3660. Kropp,
K.; Erker, G. Organometallics 1982, 1, 1246-1247. Erker, G.; Kropp, K.
J. Organomet. Chem. 1980, 194, 45-60.
(28) Warren, T. H.; Erker, G.; Fro¨hlich, R.; Wibbeling, B. Organometallics 2000,
19, 127-134. Hora´_cek, M.; ?St_epni_cka, P.; Gyeped, R.; C`ısa_rova´, I.;
T_islerova´, I.; Zema´nek, J.; Kub_ista, J.; Mach, K. Chem.-Eur. J. 2000, 6,
2397-2408.
(29) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10015-
10031. Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434.
(30) Preliminary communication: Hill, M.; Kehr, G.; Erker, G.; Kataeva, O.;
Fro¨hlich, R. Chem. Commun. 2004, 1020-1021.
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11049

A R T I C L E S
Hill et al.
Figure 2. A view of the molecular structure of complex 14. Selected bond
lengths (Å) and angles (deg): Zr-F23 2.250(1), Zr-C14 2.203(2), Si1-
C1 1.871(2), Si-C20 1.849(2), Si-C21 1.855(2), Si-C9 1.872(2), C3-B
1.627(3), C8-B 1.649(3), B-C22 1.663(3), B-C28 1.665(3), C23-F23
1.410(2); F23-Zr-C14 113.03(7), C1-Si-C9 93.8(1), C1-Si-C20 113.5-
(1), C1-Si-C21 110.9(1), C9-Si-C20 110.8(1), C9-Si-C21 112.8(1),
C20-Si-C21 113.5(1), C2-C3-B 130.5(2), C7-C8-B 111.4(2), C3-
B-C8 106.7(2), C3-B-C22 115.3(2), C3-B-C28 106.2(2), C8-B-C22
105.6(2), C8-B-C28 111.6(2), C22-B-C28 111.5(2), Zr-F23-C23
142.8(1).
Figure 3. A projection of the molecular geometry of complex 14 showing
the half-chair-like conformational arrangement of the tetrahydroboratain-
denyl part of the ligand system (parts of the molecule were omitted for
clarity).
Complex 14 features dynamic NMR spectra, which arise from
a conformational equilibration of the boratatetrahydroindenyl
part of the system. This is best illustrated by the temperature-
dependent 19F NMR spectra of 14. At ambient temperature, three
pairs of signals are observed, corresponding to the ortho (δ
-116.6/-130.0)-, para (δ -156.0/-153.2)-, and meta (δ
-161.3/-162.7)-F-substituents of the cis- and trans-C6F5 groups
of the rapidly equilibrating system. Lowering the temperature
leads to decoalescence and the appearance of two separate sets
of 19F NMR signals that originate from two nonidentical
conformers. The major conformer (14A) exhibits a total of 10
separate 19F NMR resonances (see Figure 4). This indicates that
under these conditions (233 K, 564 MHz) the rotation of both
C6F5 rings around the B-C(sp2) bonds is frozen on the NMR
time scale. Most remarkable is the observation of one ortho-
C6F5 signal at a very negative δ-value of -175.433 [remaining
signals of this C6F5 ring at δ -126.2 (o), δ -156.8 (p), δ
-155.6 and δ -164.2 (m); resonances of the second C6F5
substituent at δ -131.2, -132.1 (o), δ -160.0 (p), δ -162.8,
-164.6 (m)]. We assume that the conformer 14A corresponds
to the structure observed in the solid state (see above). From
the coalescence of the 19F NMR resonances of the pair of o-F
substituents [Tc ≈ 283 K, ∆ν (213 K) ) 27 800 Hz], we
estimated an activation energy of this exchange process of ∆Gq-
(Tc) ≈ 10.5 ( 1.0 kcal/mol. This value must be regarded to be
close to the Zr‚‚‚F(C) bond dissociation energy of 14A. The
other conformational (14B) isomer shows five 19F NMR signals
of a static C6F5 substituent [δ -108.6/-111.2 (o), δ -154.7
formation of benzene and the observed product 14.31 Complex
12 represents a rare example where electrophilic borane addition
to the adjacent cyclopentadienyl ring is favored over σ-ligand
abstraction.
Complex 14 was characterized by X-ray diffraction (see
Figure 2). It shows that the -B(C6F5)2 electrophile has attacked
the adjacent Cp-ring to close a six-membered heterocycle (C3-
B: 1.627(3) Å). This has created a dipolar structural framework.
One of the phenyl groups has remained at zirconium (Zr-C14:
2.203(2) Å). The anellated six-membered ring of the borate
tetrahydroindenyl moiety of complex 14 attains a slightly
distorted half-chair conformation. As is illustrated by the
projection of 14 as depicted in Figure 3, this has led to a
differentiation of the C6F5 substituents at boron. The equatorial
C6F5 ring [dihedral angle C2-C3-B-C28: -41.8(3)°] becomes
oriented away from the core of the complex, whereas this
specific conformational arrangement brings the axial C6F5 ring
(θ C2-C3-B-C22: 82.2(2)°) close toward the inside of the
metallocene. This has allowed one of the (aryl)C-F ortho
fluorine atoms to bind to the electrophilic zirconium center. The
resulting (aryl)C-F-Zr linkage is rather strong (Zr-F23 2.250-
(1) Å, C23-F23-Zr: 142.8(1)°).32,33 Consequently, the C23-
F23 bond (1.410(2) Å) is markedly elongated as compared to
the average bond length of the remaining ortho-(aryl)-C-F
bonds in 14 (1.353(2) Å).
(32) Siedle, A. R.; Newmark, R. A.; Lamanna, W. M. Organometallics 1993,
12, 1491-1492; Zr‚‚‚F 2.346(3) Å. Sun, Y.; Spence, R. E. v. H.; Piers,
W. E.; Parvez, M.; Yap, G. P. A. J. Am. Chem. Soc. 1997, 119, 5132-
5143; Zr‚‚‚F 2.267(5) Å. Burlakov, V. V.; Troyanov, S. I.; Letov, A. V.;
Strunkina, L. I.; Minacheva, M. K.; Furin, C. G.; Rosenthal, U.; Shur, V.
B. J. Organomet. Chem. 2000, 598, 243-247; Ti‚‚‚F 2.248(2), 2.223(3)
Å.
(33) Temme, B.; Erker, G.; Karl, J.; Luftmann, H.; Fro¨hlich, R.; Kotila, S. Angew.
Chem. 1995, 107, 1867-1869; Angew. Chem., Int. Ed. Engl. 1995, 34,
1755-1757; Zr‚‚‚F 2.423(3) Å. Karl, K.; Erker, G.; Fro¨hlich, R. J. Am.
Chem. Soc. 1997, 119, 11165-11173; Zr‚‚‚F 2.408(3), 2.402(1) Å.
Dahlmann, M.; Erker, G.; Fro¨hlich, R.; Meyer, O. Organometallics 2000,
19, 2956-2967; Zr‚‚‚F 2.385(3), 2.403(1) Å. Kleigrewe, N.; Brackemeyer,
T.; Kehr, G.; Fro¨hlich, R.; Erker, G. Organometallics 2001, 20, 1952-
1955; Zr‚‚‚F 2.310(3) Å.
(31) See for a comparison: Ruwwe, J.; Erker, G.; Fro¨hlich, R. Angew. Chem.
1996, 108, 108-110; Angew. Chem., Int. Ed. Engl. 1996, 35, 80-82. Sun,
Y.; Piers, W. E.; Rettig, S. J. Organometallics 1996, 15, 4110-4112.
Pindado, G. J.; Thornton-Pett, M.; Bochmann, M. Chem. Commun. 1997,
609-610. Pindado, G. J.; Thornton-Pett, M.; Bouwkamp, M.; Meetsma,
A.; Hessen, B.; Bochmann, M. Angew. Chem. 1997, 109, 2457-2460;
Angew. Chem., Int. Ed. Engl. 1997, 36, 2358-2361. Pindado, G. J.;
Thornton-Pett, M.; Bochmann, M. J. Chem. Soc., Dalton Trans. 1997,
3115-3127. Pindado, G. J.; Thornton-Pett, M.; Hursthouse, M. B.; Coles,
S. J.; Bochmann, M. J. Chem. Soc., Dalton Trans. 1999, 1663-1668. Arndt,
P.; Baumann, W.; Spannenberg, A.; Rosenthal, U.; Burlakov, V. V.; Shur,
V. B. Angew. Chem. 2003, 114, 1455-1458; Angew. Chem., Int. Ed. 2003,
42, 1414-1418.
9
11050 J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004

CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
Scheme 6
NMR: δ -18.5), and the other is inserted into a Zr-Ph moiety
to give a single isomer of a (η2-iminoacyl)zirconium com-
plex.34,35 The product 16 shows a typical 13C NMR resonance
of the iminoacyl carbon atom at δ 240.1. The single remaining
σ-phenyl group at the zirconium metal shows very typical 13C
NMR features at δ 179.1 (ipso), 141.8 (o), 126.7 (m), and 123.9
(p).
Figure 4. Dynamic 19F NMR spectra (564 MHz) of complex 14. The
numbers 1 and 2 denote the resonances of the cis- and trans-C6F5 ring
systems at high temperature. The letters A and B mark C6F5 resonances of
the two conformational isomers 14A and 14B at low temperature.
Treatment of 12 with PMe3 at room temperature in toluene
gave the 1:1 adduct (17, 97% isolated). The phosphine was
Scheme 5. Equilibration of the Dipolar Metallocene Conformers
14b / 14B (Only the Inversion of the Boratatetrahydroindenyl Part
of the Molecule Is Depicted)
added to the -B(C6F5)2 moiety [11B NMR: δ -14.1 (ν1/2
)
258 Hz), 31P NMR: δ -10.2 (ν1/2 ) 115 Hz)]. Attachment of
the additional PMe3 ligand at boron made the pair of C6F5
groups diastereotopic. This became just experimentally observ-
able by the splitting of the ortho-C6F5 resonances [δ -130.7/-
130.8], while the pair of para (δ -158.3)- and meta-C6F5 signals
(δ -163.6) was not resolved. Complex 17 features the 1H NMR
signals of two σ-phenyl ligands at zirconium [δ 7.52, 7.23, 7.13
(o, m, p) and δ 7.31, 7.20, 7.08].
When complex 12 was kept for 3 h at 80 °C in benzene in
the presence of a ca. 10-fold excess of PMe3, the formation of
the PMe3-stabilized (aryne)zirconocene complex 18 was ob-
served.24 A single isomer was obtained (92% isolated). Again,
1 equiv of PMe3 was also added to the B(C6F5)2 group [11B
NMR: δ -14.0; 19F NMR: δ -129.9/-130.3 (o), -158.4/-
157.9 (p), -163.2/-163.1 (p)]. Consequently, complex 17
features two PMe3 31P NMR resonances [δ -7.9 (ν1/2 ) 7 Hz,
[Zr]-PMe3) and δ -10.0 (ν1/2 ) 120 Hz, [B]-PMe3)]. The
benzyne ligand shows typical 13C NMR signals of the coordi-
nated carbon centers at δ 178.5 and 157.8.
(p), δ -160.0/-161.5 (m)] and three 19F NMR resonances [δ
-129.6 (o), δ -150.0 (p), δ -161.1 (m)] of a freely rotating
C6F5 group at 203 K. The 14A / 14B equilibrium is slightly
temperature dependent. The amount of the minor isomer 14B
decreases with decreasing temperature. We assume that we have
here observed the ring inversion process of the boratatetrahy-
droindenyl unit (see Scheme 5). The 14A to 14B rearrangement
brings both C6F5 substituents in positions that do not enable
them to build up a slightly stabilizing (aryl)C-F-metal
interaction.
In-situ-generated 12 also reacts cleanly with N-methylbenz-
imidazole or 1,2-dimethylbenzimidazole. Selective addition to
the -B(C6F5)2 functional group is observed to give the
corresponding 1:1 addition products 19a and 19b, respectively,
in almost quantitative yield (see Scheme 7). The presence of a
pair of inequivalent σ-phenyl ligands at zirconium is revealed
by their very characteristic 13C NMR resonances [19a: δ 186.1
(ipso), 134.4 (o), 126.5 (m), 125.7 (p) and δ 181.7, 136.3, 126.5,
126.1]. The formation of a tetravalent boron compound is
apparent from the typical 11B NMR feature (δ -4.5) of 19a
The intramolecular electrophilic aromatic substitution reaction
at the Cp-ring of 12 to give 14 is sufficiently slow to allow for
a successful competition of a variety of other reactions starting
from the bifunctional complex 12. Thus, it rapidly reacts with
n-butylisonitrile in toluene at room temperature.34 Two molar
equivalents of the RNtC reagent are consumed to yield 16
(Scheme 6). One butylisonitrile is added to the borane (11B
(34) Berg, F. C.; Petersen, J. L. Organometallics 1989, 8, 2461-2470. Berg, F.
C.; Petersen, J. L. Organometallics 1991, 10, 1599-1607. Valero, C.; Grehl,
M.; Wingbermu¨hle, D.; Kloppenburg, L.; Carpenetti, D.; Erker, G.; Petersen,
J. L. Organometallics 1994, 13, 415-417. Kloppenburg, L.; Petersen, J.
L. Organometallics 1997, 16, 3548-3556. Antinolo, A.; Fernandez-Galan,
R.; Orive, I.; Otero, A.; Prashar, S. Eur. J. Inorg. Chem. 2002, 2470-
2476.
(35) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729-1742.
Erker, G.; Rosenfeldt, F. J. Organomet. Chem. 1980, 188, C1-C4.
Review: Erker, G. Acc. Chem. Res. 1984, 17, 103-109.
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11051

A R T I C L E S
Hill et al.
Scheme 7
and the observation of the 19F NMR signals of a pair of
diastereotopic C6F5 groups at the boron atom. The 13C NMR
resonance of the NCHN imidazole carbon center (C10 in
Scheme 7) occurs at δ 141.2. Complex 19b features similar
NMR spectra [13C NMR: δ 151.8 (C10), 11B: δ -3.3.].
Heating complex 19a to 80 °C initially resulted in the
formation of a pair of new compounds (with formation of
benzene). However, the reaction was not clean enough under
these conditions, especially with increasing conversion, to allow
us to isolate and identify the newly formed products. We tried
to potentially stabilize the products by carrying out the reaction
in the presence of trimethylphosphine, but this resulted only in
the rapid replacement of the weaker benzimidazole donor by
the phosphine. Eventually, only the PMe3-stabilized complex
18 was formed in these experiments.
The reaction system became sufficiently clean when we
thermolyzed complex 19a at 80 °C in benzene in the presence
of 1 mol equiv of N-methylbenzimidazole. After 3 h, the reaction
was complete, and we isolated a 3:2 mixture of the diastereo-
isomeric products 20A and 20B in a combined yield of ca. 90%.
The complexes 20 were formed from 19a by liberation of 1
equiv of benzene, and the five-membered ring of a N-
methylbenzimidazole was deprotonated and has become attached
to the zirconium center. The remaining σ-phenyl ligand is readily
identified by its typical 13C NMR resonances (20A: δ 181.4
(ipso), 142.0 (o), 127.0 (m), 124.1 (p)]. The newly formed σ-N-
methylbenzimidazole ligand shows a very characteristic 13C
NMR feature of the Zr-C(N2) carbon atom (C10′ in Scheme
7) at δ 202.9.36,37 In addition, there is one intact N-methyl-
benzimidazole coordinated to the boron center of complex 20A
[11B NMR: δ -5.1; benzimidazole C10: δ 141.2 (13C), 10-H:
δ 7.32 (1H)]. The 19F NMR spectra show the presence of two
diastereotopic C6F5 groups present in 20A.
20A and 20B are apparently diastereoisomers that differ by their
relative configuration of the metal chirality center and the
element of planar chirality of the substituted ansa-metallocene
backbone.38
Conclusions
Our study has shown that bifunctional zirconocene complexes
with a pendent strongly Lewis acidic -B(C6F5)2 functional
group that contain active σ-ligands at zirconium can be obtained
by either of two ways. Some active ligands (e.g., σ-phenyl) can
actually be introduced at an early stage of the synthesis, because
they have been shown to be resistant to abstraction by both the
HB(C6F5)2 reagent and the attached -B(C6F5)2 Lewis acid.
Alternatively, the borane is introduced first at the stage of the
respective zirconocene dichloride precursor, but then a protective
group must be introduced at the boron Lewis acid before
σ-ligand exchange at the transition metal center can be carried
out. We have described such an example and have shown
independently that the protective donor ligand can be removed
or exchanged subsequently at the boron center.
The N-methylbenzimidazole model substrate is CH-activated
by the bifunctional Zr/B system. Unfortunately, direct mecha-
nistic evidence is hard to achieve from such a rapidly ligand
exchanging system, but it is well conceivable that the in-situ-
generated reactive (aryne)zirconocene intermediate has attacked
the CH bond of the adjacent benzimidazole whose kinetic acidity
has probably been increased considerably by coordination
through its “imino” nitrogen atom to boron.39,40 So it seems
that bifunctional transition metal/boron-Lewis acid systems that
show some potential for increased CH (or maybe even CC)
activation can be easily available by the principal synthetic
routes as outlined in this paper. We will try to adapt these
successful synthetic entries for the preparation of related systems
using other metal/electrophile combinations and additional
Complex 20B shows very similar spectra [σ-phenyl: δ 177.2
(13C, ipso); Zr-benzimidazolide: δ 202.7 (13C, C10′); B-benz-
imidazole: δ 141.2 (13C, C10), δ 7.19 (1H, 10-H)]. Complexes
(38) For a comparison, in an NMR experiment, the unfunctionalized parent
system [Me2Si(C5H4)2]ZrPh2 was treated with a 6-fold excess of N-
methylbenzimidazole in d6-benzene at 80 °C to yield the corresponding
(36) Wacker, A.; Pritzkow, H.; Siebert, W. Eur. J. Inorg. Chem. 1998, 843-
849.
reaction product [Me2Si(C5H4)2]Zr(Ph)(N-methyl-2-benzimidazolyl) [13
C
(37) Herrmann, W. A.; O¨ fele, K.; Elison, M.; Ku¨hn, F. E.; Roesky, P. W. J.
Organomet. Chem. 1994, 480, C7-C9. Kuhn, N.; Kratz, T.; Bla¨ser, D.;
Boese, R. Inorg. Chim. Acta 1995, 238, 179-181. Niehues, M.; Kehr, G.;
Erker, G.; Wibbeling, B.; Fro¨hlich, R.; Blaque, O.; Berke, H. J. Organomet.
Chem. 2002, 663, 192-203. Vagedes, D.; Erker, G.; Kehr, G.; Fro¨hlich,
R.; Grimme, S.; Mu¨ck-Lichtenfeld, C. Z. Naturforsch. 2003, 58b, 305-
310.
NMR δ 202.5 (C10′)] plus benzene. Under these conditions, this reaction
took ca. 7 h to go to completion, which makes it ca. 5-7 times slower
than the corresponding 19a to 20 transformation.
(39) Ro¨ttger, D.; Erker, G.; Fro¨hlich, R.; Kotila, S. J. Organomet. Chem. 1996,
518, 17-19.
(40) Ren, J.; Workman, D. B.; Squires, R. R. Angew. Chem. 1997, 109, 2330-
2332; Angew. Chem., Int. Ed. Engl. 1997, 36, 2230-2232.
9
11052 J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004

CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
correction (0.848 e T e 0.871), Z ) 8, monoclinic, space group C2/c
(No. 15), λ ) 0.71073 Å, T ) 198 K, ω and æ scans, 23 838 reflections
collected ((h, (k, (l), [(sin θ)/λ] ) 0.68 Å-1, 8969 independent (Rint
) 0.042) and 5488 observed reflections [I g 2 σ(I)], 472 refined
parameters, R ) 0.043, wR2 ) 0.092, max. residual electron density
0.32 (-0.45) e Å-3, hydrogens calculated and refined as riding atoms.
activation/protection protocols to hopefully arrive eventually at
some synthetically useful CH (or CC)-activating systems that
utilize such specific proximity effects.
Experimental Section
All reactions with organometallic compounds were carried out under
argon using Schlenk-type glassware or in a glovebox. Solvents were
dried and distilled prior to use. The following instruments were used
for physical characterization of the compounds: Melting points, DSC
2010 TA-Instruments; elemental analyses, Foss-Heraeus CHNO-Rapid
and Vario El III Mikro elemental analyzer; IR, Nicolet 5 DXC FT IR
spectrometer; NMR, Bruker AC 200 P (1H: 200.13 MHz, 13C: 50.32
MHz, 11B: 64.21 MHz) or Varian UNITY plus NMR spectrometer
(1H: 599.8 MHz, 13C: 150.8 MHz, 19F: 564.3 MHz).
Reaction of Complex 2 with 1,2-Dimethylbenzimidazole; Prepa-
ration of 4b. A solution of 1,2-dimethylbenzimidazole (0.24 g, 1.64
mmol) in 10 mL of toluene was added to a solution of 1.20 g (1.63
mmol) of 2 in 20 mL of toluene at ambient temperature. After 2 h at
room temp, the solvent was removed in vacuo to yield 1.38 g (96%)
of complex 4b as a pale yellow solid, mp 207 °C. Anal. Calcd for
C36H29N2BF10Cl2SiZr (880.6): C, 49.10; H, 3.32; N, 3.18. Found: C,
1
49.25; H, 3.09; N, 3.05. H NMR (d8-toluene, 600 MHz, 300 K): δ
7.43 (m, 1H, 13-H), 6.88 (m, 1H, 15-H), 6.85 (m, 1H, 14-H), 6.65 (m,
1H, 3-H′), 6.62 (m, 1H, 4-H′), 6.60 (m, 2H, 16-H), 6.20 (m, 1H, 4-H),
5.36 (m, 1H, 5-H′), 5.25 (m, 2H, 5-H, 2-H′), 5.01 (m, 1H, 2-H), 2.73
(m, 2H, 6-H), 2.52 (s, 3H, 9-H), 2.09 (s, 3H, 10-Me), 1.95/1.62 (each
m, each 1H, 8-H, 8-H′), 1.48/1.12 (each m, each 1H, 7-H, 7-H′), 0.09/
0.04 (each s, each 3H, Si(CH3)2). 13C{1H} NMR (d8-toluene, 150 MHz,
300 K): δ 152.4 (C10), 148.8 (1JCF ) 241.3 Hz, o-C of C6F5), 148.5
(1JCF ) 240.0 Hz, o-C of C6F5), 139.9 (1JCF ) 241.5 Hz, p-C of C6F5),
139.6 (1JCF ) 242.9 Hz, p-C of C6F5), 137.7 (1JCF ) 246.9 Hz, m-C of
C6F5), 136.6 (C12), 143.6 (C3), 132.6 (C17), 127.9 (C4′), 127.7 (C4),
126.3 (C3′), 124.1 (C14), 124.0 (C15), 116.9 (C13), 114.3 (C5), 114.2
(C2), 114.1 (C2′), 112.6 (C5′), 110.4 (C16), 107.8 (C1′), 107.5 (C1),
33.1 (C6), 29.2 (C9), 26.9 (C7), 23.4 (C8), 12.7 (Me-10), -6.0/-6.9
(Si(CH3)2), ipso-C of C6F5 not observed. 11B{1H} NMR (d8-toluene,
64 MHz, 298 K): δ -3.35 (ν1/2 ) 491 Hz). 19F NMR (d8-toluene, 564
MHz, 300 K): δ ) -131.6 (m, 2F, o-F of C6F5), -131.7 (m, 2F, o-F′
of C6F5), -158.3 (t, 3JFF ) 20.6 Hz, 1F, p-F′ of C6F5), -159.0 (t, 3JFF
) 20.8 Hz, 1F, p-F of C6F5), -163.5 (m, 2F, m-F′ of C6F5), -163.8
(m, 2F, m-F of C6F5).
X-ray crystal structure analyses: Data sets were collected with a
Nonius KappaCCD diffractometer, equipped with a rotating anode
generator Nonius FR591. Programs used: data collection COLLECT
(Nonius, B. V., 1998), data reduction Denzo-SMN (Otwinowski, Z.;
Minor, W. Methods Enzymol. 1997, 276, 307-326), absorption
correction SORTAV (Blessing, R. H. Acta Crystallogr. 1995, A51, 33-
37. Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421-426), structure
solution SHELXS-97 (Sheldrick, G. M. Acta Crystallogr. 1990, A46,
467-473), structure refinement SHELXL-97 (Sheldrick, G. M. Uni-
versita¨t Go¨ttingen, 1997), graphics SCHAKAL (Keller, E. Universita¨t
Freiburg, 1997).
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications CCDC
232735 (4a) and 229733 (14a). Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union Road,
CambridgeCB2 1EZ, UK [fax: int. code +44(1223)336-033, e-mail:
deposit@ccdc.cam.ac.uk].
Complexes 111 and 214 were prepared as we have previously
described in the literature. HB(C6F5)2 was synthesized as described by
Piers et al.13 For atom numbering, see Scheme 2.
Treatment of Adduct 4a with (Trimethylsilyl)methyl Lithium:
Synthesis of Complex 5. A Schlenk flask was charged with complex
4a (80.6 mg, 93 µmol) and 17.5 mg (186 µmol) of solid Me3SiCH2Li.
The mixture was suspended in ether (30 mL) at -20 °C, and then it
was allowed to warm to room temperature. After being stirred for 1 h,
the solvent was removed in vacuo and the residue was suspended in
toluene. It was filtered through Celite, and the clear filtrate was
evaporated to dryness to yield 84.8 mg (94%) of complex 5 as a yellow
solid, mp 119 °C. Anal. Calcd for C43H49N2BF10Si3Zr (970.1): C, 53.24;
Reaction of Complex 2 with N-Methylbenzimidazole; Prepara-
tion of Adduct 4a. Complex 2 (1.10 g, 1.50 mmol) and 1-methylbenz-
imidazole (0.20 g, 1.50 mmol) were dissolved together in 50 mL of
toluene at ambient temperature. After 2 h, the solvent was removed in
vacuo to give 4a as a yellow solid (1.24 g, 95%). Single crystals for
the X-ray crystal structure analysis of 4a were obtained from a
concentrated toluene solution, mp 194 °C. Anal. Calcd for C35H27N2-
BF10Cl2SiZr (866.6): C, 48.51; H, 3.14; N, 3.23. Found: C, 48.92; H,
3.32; N, 3.06. 1H NMR (d8-toluene, 600 MHz, 300 K): δ 8.27 (s, 1H,
10-H), 7.66 (m, 1H, 13-H), 6.81 (m, 2H, 14-H, 15-H), 6.72 (m, 1H,
3-H′), 6.67 (m, 1H, 4-H′), 6.47 (m, 1H, 16-H), 6.42 (m, 1H, 4-H),
5.40 (m, 1H, 5-H′), 5.33 (m, 1H, 2-H′), 5.30 (m, 1H, 5-H), 5.11 (m,
1H, 2-H), 2.89/2.78 (each m, each 1H, 6-H, 6-H′), 2.76 (s, 3H, 9-H),
1.83/1.76 (each m, each 1H, 8-H, 8-H′), 1.55 (m, 2H, 7-H), 0.13/0.07
(each s, each 3H, Si(CH3)2). 13C{1H} NMR (d8-toluene, 150 MHz, 300
K): δ 148.8 (1JCF ) 238.1 Hz, o-C of C6F5), 143.1 (C3), 141.8 (C10),
139.5 (1JCF ) 250.9 Hz, p-C of C6F5), 137.5 (1JCF ) 249.8 Hz, m-C of
C6F5), 136.6 (C12), 132.9 (C17), 128.7 (C4′), 128.3 (C4), 125.7 (C3′),
125.3 (C14), 125.2 (C15), 121.8 (broad, ipso-C of C6F5), 116.5 (C13),
114.4 (C2′), 114.3 (C2), 114.1 (C5), 112.8 (C5′), 111.0 (C16), 107.9
(C1′), 107.6 (C1), 33.0 (C6), 31.9 (C9), 26.2 (C7), 23.8 (C8), -5.7/-
6.5 (Si(CH3)2). 11B{1H} NMR (d8-toluene, 64 MHz, 298 K): δ -5.56
(ν1/2 ) 324 Hz). 19F NMR (d8-toluene, 564 MHz, 300 K): δ -132.2
1
H, 5.09; N, 2.89. Found: C, 53.21; H, 4.71; N, 2.55. H NMR (d2-
dichloromethane, 600 MHz, 300 K): δ 8.00 (s, 1H, 10-H), 7.62 (d,
3JHH ) 8.4 Hz, 1H, 13-H), 7.55 (d, 3JHH ) 8.2 Hz, 1H, 16-H), 7.48 (m,
1H, 15-H), 7.36 (m, 1H, 14-H), 6.92 (m, 1H, 3-H′), 6.91 (m, 1H, 4-H′),
6.69 (m, 1H, 4-H), 5.80 (m, 1H, 2-H′), 5.79 (m, 1H, 5-H′), 5.68 (m,
1H, 5-H), 5.60 (m, 1H, 2-H), 3.95 (s, 3H, 9-H), 2.69/2.66 (each m,
each 1H, 6-H, 6-H′), 1.54 (m, 2H, 8-H), 1.37/1.31 (each m, each 1H,
a
7-H, 7-H′), 0.53/0.47 (each s, each 3H, Si(CH3)2), 0.01 (s, 9H, Si-
b
2
(CH3)3), -0.02 (s, 9H, Si(CH3)3), 0.05/-0.10 (AB, JHH ) 5.8 Hz,
b
2
a
each 1H, Si(CH2)), -0.04/-0.29 (AB, JHH ) 5.8 Hz, each 1H, Si-
(CH2)). 13C{1H} NMR (d2-dichloromethane, 150 MHz, 300 K): δ 138.2
(1JCF ) 238.8 Hz, o-C of C6F5), 131.4 (C10), 129.1 (1JCF ) 251.5 Hz,
p-C of C6F5), 127.1 (1JCF ) 249.7 Hz, m-C of C6F5), 126.3 (C12), 125.3
(C3), 123.5 (C17), 115.5 (C14, C15), 111.4 (C4), 110.0 (C3′), 106.6
(C13), 107.1 (C4′), 102.9 (C2), 102.6 (C2′), 101.5 (C16), 100.8 (C5′),
100.7 (C5), 91.9 (C1′), 91.4 (C1), 38.4 (aSi(CH2)), 35.0 (bSi(CH2)),
23.7 (C9), 22.4 (C6), 18.5 (C7), 11.3 (C8), -4.6/-5.8 (Si(CH3)2), -6.9
(aSi(CH3)3), -7.1 (bSi(CH3)3), ipso-C of C6F5 not observed. 11B{1H}
NMR (d2-dichloromethane, 64 MHz, 298 K): δ ) -5.16 (ν1/2 ) 346
Hz). 19F NMR (d2-dichloromethane, 564 MHz, 300 K): δ ) -133.3
(m, 2F, o-F of C6F5), -133.1 (m, 2F, o-F′ of C6F5), -158.8 (t, 3JFF
)
20.7 Hz, 1F, p-F of C6F5), -159.1 (t, 3JFF ) 20.8 Hz, 1F, p-F′ of C6F5),
-164.0 (m, 2F, m-F of C6F5), -164.1 (m, 2F, m-F′ of C6F5). X-ray
crystal structure analysis of complex 4a: formula C35H27BCl2F10N2-
SiZr, M ) 866.61, colorless crystal 0.30 × 0.30 × 0.25 mm, a )
20.170(1), b ) 14.898(1), c ) 23.905(1) Å, â ) 92.44(1)°, V ) 7176.8-
(7) Å3, Fcalc ) 1.604 g cm-3, µ ) 5.70 cm-1, empirical absorption
3
(m, 4F, o-F of C6F5), -160.4 (t, JFF ) 20.2 Hz, 2F, p-F of C6F5),
-165.1 (m, 4F, m-F of C6F5).
Reaction of Complex 4a with LDA; Formation of the Products
7 and 7′. d8-Tetrahydrofuran was added at -78 °C to a mixture of 4a
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11053

A R T I C L E S
Hill et al.
(73.4 mg, 85 µmol) and LDA (9.1 mg, 85 µmol). The mixture was
slowly warmed to room temperature. The formation of the diastereo-
isomeric products 7 and 7′ (1:1) was monitored by NMR, and these
products were characterized spectroscopically from the mixture without
6.89 (m, 1H, 4-H′), 6.83 (m, 1H, 12-H), 6.82 (m, 1H, 11-H), 6.74 (m,
1H, 14-H), 6.72 (m, 1H, 13-H), 6.20 (m, 1H, 4-H), 5.69 (m, 1H, 5-H′),
5.64 (m, 1H, 2-H′), 5.60 (m, 1H, 5-H), 5.19 (m, 1H, 2-H), 3.68 (m,
1H, 7-H), 2.97/2.83 (each m, each 1H, 6-H, 6-H′), 1.19/0.60 (each m,
each 1H, 8-H, 8-H′), 0.56/ 0.40 (each s, each 3H, Si(CH3)2). 13C{1H}-
NMR (d12-cyclohexane, 150 MHz, 300 K): δ 181.2 (C10), 156.0 (C9),
134.9 (C11), 130.4 (C3), 127.2 (C12), 126.8 (C14), 124.6 (C13), 124.5
(C4), 120.2 (C3′), 117.6 (C4′), 116.5 (C2), 113.7 (C2′), 112.2 (C5′),
110.2 (C5), 102.1 (C1′), 98.0 (C1), 57.8 (C8), 45.5 (C7), 38.6 (C6),
-4.4/-6.4 (Si(CH3)2).
1
isolating them. Diastereoisomer 7, H NMR (d8-tetrahydrofuran, 600
MHz, 300 K): δ 7.83 (m, 1H, 16-H), 7.48 (m, 2H, 13-H, 15-H), 7.40
(m, 1H, 14-H), 6.80 (m, 1H, 3-H′), 6.79 (m, 1H, 4-H′), 6.28 (m, 1H,
4-H), 6.04 (m, 1H, 5-H′), 5.89 (m, 1H, 5-H), 5.81 (m, 1H, 2-H′), 5.43
(m, 1H, 2-H), 2.42 (m, 2H, 6-H), 1.56/1.37 (each m, each 1H, 8-H,
8-H′), 0.98/0.72 (each m, each 1H, 7-H, 7-H′), 0.69/0.60 (each s, each
3H, Si(CH3)2). 13C{1H} NMR (d8-tetrahydrofuran, 150 MHz, 300 K):
δ 152.5 (C10), 143.3 (C3), 138.1 (C17), 133.6 (C12), 128.7 (C4′), 128.6
(C4), 126.8 (C3′), 126.1 (C14), 125.7 (C15), 115.2 (C2), 115.1 (C13),
115.0 (C5), 114.9 (C2′), 113.9 (C5′), 113.3 (C16), 108.7 (C1′), 108.1
(C1), 33.8 (C6), 33.0 (C9), 27.3 (C7), 21.3 (C8), -5.5/-5.7 (Si(CH3)2).
Formation of 11 on a Preparative Scale. A solution containing
67.8 mg (144 µmol) of the diphenylzirconocene complex 8 and 10
mol equiv of PMe3 in benzene was kept for 3 h at 80 °C. A suspension
of 46.1 mg (294 µmol) of N,N-dimethylanilinium chloride in benzene
was added at room temperature. The mixture was stirred for 24 h and
then filtered through Celite. Removal of the solvent from the clear
filtrate gave 59.8 mg (89%) of 11, mp 132 °C. Anal. Calcd for C21H24-
Cl2SiZr (466.6): C, 54.05; H, 5.18. Found: C, 53.74; H, 5.05. 1H NMR
(d6-benzene, 600 MHz, 300 K): δ 7.08 (m, 2H, 11-H), 7.02 (m, 1H,
12-H), 6.92 (m, 2H, 10-H), 6.85 (m, 1H, 3-H′), 6.75 (m, 1H, 4-H′),
6.26 (m, 1H, 4-H), 5.49 (m, 1H, 5-H′), 5.40 (m, 1H, 2-H′), 5.39 (m,
1H, 5-H), 5.18 (m, 1H, 2-H), 3.06/3.00 (each m, each 1H, 6-H, 6-H′),
1
Diastereoisomer 7′, H NMR (d8-tetrahydrofuran, 600 MHz, 300 K):
δ 7.83 (m, 1H, 16-H), 7.48 (m, 2H, 13-H, 15-H), 7.40 (m, 1H, 14-H),
6.85 (m, 1H, 3-H′), 6.79 (m, 1H, 4-H′), 6.21 (m, 1H, 4-H), 6.04 (m,
1H, 5-H′), 5.86 (m, 1H, 5-H), 5.84 (m, 1H, 2-H′), 5.47 (m, 1H, 2-H),
4.34/4.32 (each d, each nJHF ) 3.4 Hz, each 3H, 9-H), 2.47/2.38 (each
m, each 1H, 6-H, 6-H′), 1.45 (m, 2H, 8-H), 0.93/0.83 (each m, each
1H, 7-H, 7-H′), 0.69/0.62 (each s, each 3H, Si(CH3)2). 13C{1H} NMR
(d8-tetrahydrofuran, 150 MHz, 300 K): δ 152.5 (C10), 143.3 (C3),
138.1 (C17), 133.6 (C12), 128.7 (C4′), 128.5 (C4), 127.0 (C3′), 126.1
(C14), 125.7 (C15), 115.2 (C5), 115.1 (C2), 115.1 (C13), 114.8 (C2′),
113.9 (C5′), 113.3 (C16), 108.7 (C1′), 108.0 (C1), 33.8 (C6), 33.0 (C9),
3
2.76 (m, 1H, 7-H), 1.17 (d, JHH ) 7.0 Hz, 3H, 8-H), 0.10/0.06 (each
s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-benzene, 150 MHz, 300 K):
δ 146.2 (C9), 140.7 (C3), 128.9 (C4), 128.5 (C11), 127.7 (C4′), 127.4
(C3′), 127.3 (C10), 126.2 (C12), 115.7 (C2′), 114.8 (C5), 114.2 (C2),
113.7 (C5′), 107.7 (C1), 107.1 (C1′), 41.8 (C7), 39.4 (C6), 22.1 (C8),
-5.8/-6.1 (Si(CH3)2).
27.1 (C7), 21.1 (C8), -5.5/-5.7 (Si(CH3)2). The 1H NMR of 9-H, 13
C
NMR of B(C6F5)2, 11B NMR, and 19F NMR resonances could not be
assigned specifically to the single isomers. 1H NMR (d8-tetrahydrofuran,
600 MHz, 300 K): δ 4.34/4.32 (each d, each nJHF ) 3.4 Hz, each 3H,
9-H). 13C{1H} NMR (d8-tetrahydrofuran, 150 MHz, 300 K): δ 149.9
(1JCF ) 243.7 Hz, o-C of C6F5), 140.2 (1JCF ) 246.8 Hz, p-C of C6F5),
137.8 (1JCF ) 243.7 Hz, m-C of C6F5) (ipso-C of C6F5 was not observed;
no assignment of the anellated C6F4-ring). 11B{1H} NMR (d8-tetrahy-
drofuran, 64 MHz, 298 K): δ ) -4.40 (ν1/2 ) 274 Hz). 19F NMR
(d8-tetrahydrofuran, 564 MHz, 300 K): δ -132.6, -135.8, -151.7,
-159.3 (each m, each 1F, 2-, 5-, 4-, 3-F of C6F4), -133.5 (m, 2F, o-F
of C6F5), -134.2 (m, 2F, o-F′ of C6F5), -160.2 (t, 3JFF ) 20.1 Hz, 1F,
p-F of C6F5), -161.1 (t, 3JFF ) 20.0 Hz, 1F, p-F′ of C6F5), -165.5 (m,
2F, m-F of C6F5), -165.9 (m, 2F, m-F′ of C6F5).
Addition of HB(C6F5)2 to Complex 8; Generation of 12. The
diphenylzirconocene complex 8 (27.8 mg, 59 µmol) and HB(C6F5)2
(20.4 mg, 59 µmol) were dissolved in d8-toluene. The hydroboration
reaction is instantaneous. The product 12 was immediately characterized
spectroscopically using this solution. 1H NMR (d8-toluene, 600 MHz,
b
300 K): δ 7.41, 7.15, 7.06 (each m, 5H, o-, m-, p-H of Ph), 7.20,
a
7.14, 7.02 (each m, 5H, o-, m-, p-H of Ph), 6.46 (m, 1H, 3-H′), 6.34
(m, 1H, 4-H′), 6.31 (m, 1H, 4-H), 5.55 (m, 1H, 5-H), 5.54 (m, 1H,
2-H′), 5.48 (m, 1H, 5-H′), 5.29 (m, 1H, 2-H), 1.88/1.70 (each m, each
1H, 6-H, 6-H′), 1.62 (m, 2H, 8-H), 1.40 (m, 2H, 7-H), 0.23 (s, 6H,
Si(CH3)2). 13C{1H} NMR (d8-toluene, 150 MHz, 300 K): δ 186.0,
a
134.6, 127.3, 125.8 (ipso-, o-, m-, p-C of Ph), 181.6, 136.0, 126.6,
126.2 (ipso-, o-, m-, p-C of bPh), 147.0 (1JCF ) 250.1 Hz, o-C of C6F5),
143.4 (1JCF ) 253.2 Hz, p-C of C6F5), 137.6 (1JCF ) 250.1 Hz, m-C of
C6F5), 136.9 (C3), 123.9 (C4′), 122.6 (C4), 121.5 (C3′), 114.3 (C2′),
114.2 (C2), 113.8 (C5), 112.7 (C5′), 101.1 (C1), 100.3 (C1′), 32.3 (C6),
31.8 (C8), 26.9 (C7), -5.8 (Si(CH3)2), (ipso-C of C6F5 was not
observed). 11B{1H} NMR (d8-toluene, 64 MHz, 298 K): δ 79.2. 19F
NMR (d8-toluene, 564 MHz, 300 K): δ -129.7 (m, 4F, o-F of C6F5),
Reaction of Complex 1 with Phenyllithium; Synthesis of 8.
Diethyl ether was added at -40 °C to a mixture of the zirconocene
dichloride complex 1 (1.01 g, 2.60 mmol) and phenyllithium (0.44 g,
5.20 mmol). The mixture was warmed to 0 °C and stirred for 2 h. The
solvent was removed in vacuo, and the residue was taken up in toluene
and filtered through Celite. The solvent was removed from the clear
filtrate in vacuo to yield 1.18 g (96%) of complex 8 as a slightly yellow
solid, mp 114 °C. Anal. Calcd for C27H28SiZr (471.8): C, 68.73; H,
3
-147.5 (t, JFF ) 21.7 Hz, 2F, p-F of C6F5), -160.9 (m, 4F, m-F of
C6F5).
1
5.98. Found: C, 67.69; H, 5.81%. H NMR (d8-toluene, 600 MHz,
b
300 K): δ 7.44, 7.15, 7.06 (each m, 5H, o-, m-, p-H of Ph), 7.20,
Reaction of Complex 8 with HB(C6F5)2; Formation of 14 and
Preparation of 15. A solution containing 125 mg (265 µmol) of the
diphenylzirconocene complex 8 and 91.8 mg (265 µmol) of HB(C6F5)2
in toluene was stirred for 3 d at room temperature. The solvent was
removed in vacuo to give 14 (174 mg, 89%) as a yellow solid, which
a
7.12, 6.99 (each m, 5H, o-, m-, p-H of Ph), 6.48 (m, 1H, 3-H′), 6.37
(m, 1H, 4-H′), 6.34 (m, 1H, 4-H), 5.51 (m, 1H, 5-H′), 5.56 (m, 1H,
5-H), 5.54 (m, 1H, 2-H′), 5.50 (m, 1H, 7-H), 5.32 (m, 1H, 2-H), 4.72
(dm, 3JHH ) 10.1 Hz, 1H, 8-H), 4.64 (dm, 3JHH ) 17.0 Hz, 1H, 8-H′),
2
1
2.56/2.44 (each ABX, JHH ) 16.2 Hz, each 1H, 6-H, 6-H′), 0.22 (s,
was characterized spectroscopically. H NMR (d8-toluene, 600 MHz,
6H, Si(CH3)2). 13C{1H} NMR (d8-toluene, 150 MHz, 300 K): δ 186.0,
300 K): δ 7.21, 7.20, 7.04 (each m, 5H, o-, m-, p-H of Ph), 6.44 (m,
2H, 4-H′, 5-H), 6.35 (m, 1H, 5-H′), 5.95 (m, 1H, 3-H′), 5.80 (m, 1H,
2-H), 5.79 (m, 1H, 2-H′), 2.32/1.68 (each m, each 1H, 6-H, 6-H′), 1.56/
1.23 (each m, each 1H, 8-H, 8-H′), 1.46/1.30 (each m, each 1H, 7-H,
7-H′), 0.65/0.61 (each s, each 3H, Si(CH3)2). 13C{1H} NMR (d8-toluene,
150 MHz, 300 K): δ 189.3, 128.6, 128.3, 127.6 (ipso-, o-, m-, p-C of
Ph), 151.9 (C3), 125.0 (C5′), 121.6 (C4′), 119.8 (C5), 118.8 (C2), 115.2
(C2′), 112.4 (C3′), 105.0 (C1), 99.9 (C1′), 27.8 (C6), 24.3 (C8), 22.8
(C7), -5.5/-5.6 (Si(CH3)2) (C4 and C of C6F5 were not observed).
19F NMR (d8-toluene, 564 MHz, 300 K): δ -130.3 (br, 4F, o-F of
C6F5), -156.1 (br, 2F, p-F of C6F5), -162.6 (br, 4F, m-F of C6F5).
a
134.6, 127.2, 125.8 (ipso-, o-, m-, p-C of Ph), 181.7, 136.9, 126.5,
126.0 (ipso-, o-, m-, p-C of bPh), 137.5 (C7), 135.7 (C3), 123.6 (C4′),
123.1 (C4), 121.4 (C3′), 115.2 (C8), 114.8 (C2), 114.1 (C2′), 113.7
(C5), 112.7 (C5′), 100.6 (C1), 100.2 (C1′), 34.1 (C6), -5.8 (Si(CH3)2).
Thermolysis of Complex 8; Formation of the Products 10 and
11. NMR Experiment. A solution of 15.0 mg (3.18 µmol) of the
diphenylzirconocene complex 8 in d12-cyclohexane (or alternatively in
d6-benzene with ca. 10 mol equiv of PMe3 added) was kept for 3 h at
80 °C. The obtained product (10) was characterized spectroscopically.
1H NMR (d12-cyclohexane, 600 MHz, 300 K): δ 7.12 (m, 1H, 3-H′),
9
11054 J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004

CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
The temperature-dependent 19F NMR spectra revealed a conformational
equilibration between 14A and 14B. Conformer 14A, 19F NMR (d8-
toluene, 564 MHz, 203 K): δ -126.2, -175.4 (each br, each 1F, o-F
of C6F5), -131.2, -132.1 (br, 2F, o-F′ of C6F5), -155.6, -164.2 (each
m, each 1F, m-F of C6F5), -156.8 (br, 1F, p-F of C6F5), -160.0 (br,
1F, p-F′ of C6F5), -162.8, -164.6 (each m, each 1F, m-F′ of C6F5).
19F/19F GCOSY (d8-toluene, 564/564 MHz, 203 K): δ (19F)/δ (19F)
-126.2/-164.2 (o-F/m-F), -131.2/-164.6 (o-F′/m-F′), -132.1/-162.8
(o-F′/m-F′), -155.6/-175.4, -156.8 (m-F/o-F, p-F), -156.8/-155.6,
-164.2 (p-F/m-F), -160.0/-162.8, -164.6 (p-F′/m-F′), -162.8/-
132.1, -160.0 (m-F′/o-F′, p-F′), -164.2/-126.2, -156.8 (m-F/o-F,
p-F), -164.6/-131.2, -160.0 (m-F′/o-F′, p-F′), -175.4/-155.6 (o-F/
m-F). Conformer B, 19F NMR (d8-toluene, 564 MHz, 203 K): δ -108.6,
-111.2 (each br, each 1F, o-F of C6F5), -129.6, (br, 2F, o-F′ of C6F5),
-150.0 (br, 1F, p-F′ of C6F5), -154.7 (br, 1F, p-F of C6F5), -160.0,
-161.5 (each m, each 1F, m-F of C6F5), -161.1 (each br, each 1F,
m-F′ of C6F5). 19F/19F GCOSY (d8-toluene 564/564 MHz, 203 K): δ
(19F)/δ (19F) -108.6/-160.0 (o-F/m-F), -111.2/-161.5 (o-F/m-F),
-129.6/-161.1 (o-F′/m-F′), -150.0/-161.1 (p-F′/m-F′), -154.7/-
160.0, -161.5 (p-F/m-F), -160.0/-108.6, -154.7 (m-F/o-F, p-F),
-161.1/-129.6, -150.0 (m-F′/o-F′, p-F′), -161.5/-111.2, -154.7 (m-
F/o-F, p-F). X-ray crystal structure analysis of complex 14A: single
crystals were obtained from a concentrated toluene solution at -20
°C, formula C33H23BF10SiZr‚C7H8, M ) 831.77, yellow crystal 0.50 ×
0.50 × 0.20 mm, a ) 9.766(1), b ) 10.662(1), c ) 18.675(1) Å, R )
2.68. 1H NMR (d6-benzene, 600 MHz, 300 K): δ 7.97, 7.44, 7.28 (each
a
m, 5H, o-, m-, p-H of Ph), 6.96, 7.23, 7.07 (each m, 5H, o-, m-, p-H
b
of Ph), 6.52 (m, 1H, 3-H′), 6.03 (m, 1H, 5-H), 5.99 (m, 1H, 5-H′),
5.75 (m, 1H, 2-H′), 5.43 (m, 1H, 2-H), 5.25 (m, 1H, 4-H′), 5.19 (m,
1H, 4-H), 3.58 (m, 2H, 13-H), 2.21 (m, 2H, 9-H), 2.04 (m, 2H, 6-H),
1.51/1.30 (each m, each 1H, 14-H, 14-H′), 1.44/1.35 (m, 2H, 7-H, 7-H′),
1.44/1.33 (m, 2H, 8-H, 8-H′), 1.03 (m, 2H, 15-H), 0.78 (m, 2H, 10-H),
0.75 (m, 2H, 11-H), 0.68 (t, 3JHH ) 7.3 Hz, 3H, 16-H), 0.43 (t, 3JHH
)
7.2 Hz, 3H, 12-H), 0.40/0.26 (each s, each 3H, Si(CH3)2). 13C{1H}
NMR (d6-benzene, 150 MHz, 300 K): δ 240.1 (Zr-CdN), 179.1,
a
141.8, 126.7, 123.9 (ipso-, o-, m-, p-C of Ph), 148.2 (1JCF ) 245.7
Hz, o-C of C6F5), 142.6, 129.8, 127.4, 123.1 (ipso-, m-, p-, o-C of
bPh), 139.9 (1JCF ) 250.1 Hz, p-C of C6F5), 138.8 (C3), 137.6 (1JCF
)
261.0 Hz, m-C of C6F5), 117.7 (ipso-C of C6F5), 121.9 (C3′), 112.1
(C4′), 111.9 (C4), 108.1 (C5), 107.6 (C5′), 105.6 (C2′), 105.4 (C2),
102.3 (C1), 102.0 (C1′), 48.6 (C13), 43.0 (C9), 33.6 (C6), 31.2 (C14),
30.9 (C7), 29.2 (C10), 20.7 (C8), 20.5 (C15), 19.1 (C11), 13.5 (C16),
12.6 (C12), -4.4/-6.3 (Si(CH3)2) (B-CN not observed). 11B{1H} NMR
(d6-benzene, 64 MHz, 298 K): δ ) -18.5 (ν1/2 ) 232 Hz). 19F NMR
(d6-benzene, 564 MHz, 300 K): δ ) -132.8 (m, 4F, o-F of C6F5),
3
-157.4 (t, JFF ) 20.7 Hz, 2F, p-F of C6F5), -163.2 (m, 4F, m-F of
C6F5).
Addition of PMe3 to Complex 12; Preparation of 17. Trimeth-
ylphosphine (24 mg, 315 µmol) was added to a freshly prepared solution
of the diphenylzirconocene/borane complex 12 (49 mg, 60 µmol) in
toluene at room temperature. The mixture was stirred for 1 h, and then
all volatiles were removed in vacuo to yield 52 mg (97%) of 17 as a
light yellow solid, mp 227 °C (decomp.). Anal. Calcd for C42H38BF10-
PSiZr (893.8): C, 56.44; H, 4.29. Found: C, 56.10; H, 4.41%. 1H NMR
(d6-benzene, 600 MHz, 300 K): δ ) 7.52, 7.23, 7.13 (each m, 5H, o-,
104.46(1), â ) 96.15(1), γ ) 109.47(1)°, V ) 1736.2(3) Å3, Fcalc
)
1.591 g cm-3, µ ) 4.36 cm-1, empirical absorption correction (0.812
e T e 0.918), Z ) 2, triclinic, space group P?1 (No. 2), λ ) 0.71073
Å, T ) 198 K, ω and æ scans, 16 169 reflections collected ((h, (k,
(l), [(sin θ)/λ] ) 0.67 Å-1, 8376 independent (Rint ) 0.037) and 7283
observed reflections [I g 2σ(I)], 480 refined parameters, R ) 0.035,
b
a
m-, p-H of Ph), 7.31, 7.20, 7.08 (each m, 5H, o-, m-, p-H of Ph),
6.52 (m, 1H, 3-H′), 6.45 (m, 1H, 4-H′), 6.45 (m, 1H, 4-H), 5.63 (m,
1H, 5-H), 5.62 (m, 1H, 2-H′), 5.58 (m, 1H, 5-H′), 5.41 (m, 1H, 2-H),
2.01/1.89 (each m, each 1H, 6-H, 6-H′), 1.22/1.09 (each m, each 1H,
wR2 ) 0.086, max. residual electron density 0.74 (-0.59) e Å-3
,
hydrogens calculated and refined as riding atoms.
For the preparation of 15, a solution containing 162 mg (343 µmol)
of complex 8 and 119 mg (344 µmol) of HB(C6F5)2 in toluene was
stirred for 3 d at room temperature. A slight excess of PMe3 was added,
and then all volatiles were removed in vacuo to yield 250 mg (89%)
of the product 15 as a yellow solid, mp 168 °C. Anal. Calcd for C36H32-
2
7-H, 7-H′), 0.74 (m, 2H, 8-H), 0.38 (d, JPH ) 10.7 Hz, 9H, PMe3),
0.27/0.26 (each s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-benzene, 150
MHz, 300 K): δ 186.2, 134.4, 126.8, 125.5 (ipso-, o-, m-, p-C of aPh),
181.7, 136.2, 126.4, 125.9 (ipso-, o-, m-, p-C of Ph), 148.1 (1JCF
)
b
1
BF10PSiZr (815.7): C, 53.01; H, 3.95. Found: C, 52.53; H, 3.69. H
236.4 Hz, o-C of C6F5), 139.4 (1JCF ) 251.3 Hz, p-C of C6F5), 138.4
(C3), 137.4 (1JCF ) 253.6 Hz, m-C of C6F5), 123.2 (C4′), 123.2 (C4),
121.5 (C3′), 119.7 (ipso-C of C6F5), 114.7 (C2), 114.3 (C2′), 113.2
(C5), 112.1 (C5′), 100.4 (C1), 100.3 (C1′), 33.2 (C6), 29.4 (C7), 20.0
NMR (d8-toluene, 600 MHz, 300 K): δ ) 7.15, 7.12, 7.00 (each m,
5H, m-, o-, p-H of Ph), 6.71 (m, 1H, 4-H′), 6.09 (m, 1H, 5-H), 5.97
(m, 1H, 3-H′), 5.79 (m, 1H, 2-H), 5.74 (m, 1H, 5-H′), 5.53 (m, 1H,
2-H′), 2.30/1.96 (each m, each 1H, 6-H, 6-H′), 1.66/0.96 (each m, each
1H, 7-H, 7-H′), 1.31/0.85 (each m, each 1H, 8-H, 8-H′), 0.35/0.31 (each
(C8), 8.9 (d, JCP ) 37.2 Hz, PMe3), -5.5/-5.8 (Si(CH3)2). 11B{1H}
1
NMR (d6-benzene, 64 MHz, 298 K): δ -14.1 (ν1/2 ) 258 Hz). 31P-
{1H} NMR (d6-benzene, 81 MHz, 300 K): δ -10.2 (ν1/2 ) 115 Hz).
19F NMR (d6-benzene, 564 MHz, 300 K): δ -130.7 (m, 2F, o-F of
2
s, each 3H, Si(CH3)2), 0.22 (d, JPH ) 10.1 Hz, 9H, PMe3). 13C{1H}
NMR (d8-toluene, 150 MHz, 300 K): δ ) 186.7, 131.4, 127.0, 126.0
(ipso-, o-, m-, p-C of Ph), 149.0 (1JCF ) 238.3 Hz, o-C of C6F5), 144.3
(C3), 139.5 (1JCF ) 261.6 Hz, p-C of C6F5), 137.7 (1JCF ) 263.0 Hz,
m-C of C6F5), 125.0 (C3′), 120.2 (C4′), 119.4 (C2), 116.3 (C5), 115.4
(C2′), 109.6 (C5′), 99.7 (C1), 97.4 (C1′), 28.5 (C6), 24.3 (C7), 16.2
3
C6F5), -130.8 (m, 2F, o-F′ of C6F5), -158.3 (t, JFF ) 20.8 Hz, 2F,
p-F of C6F5), -163.6 (m, 4F, m-F of C6F5).
Thermolysis of Complex 12 in the Presence of Excess PMe3;
Preparation of the (Aryne)zirconocene Complex 18. A 10-fold excess
of PMe3 was added to a solution of 49 mg (60 µmol) of freshly
generated 12 in toluene at room temperature. The reaction mixture was
then kept for 3 h at 80 °C. Volatiles were removed in vacuo at ambient
temperature to yield 49 mg (92%) of complex 18 as a pale yellow
solid, mp 224 °C (decomp.). Anal. Calcd for C39H41BF10P2SiZr
1
(C8), 8.9 (d, JCP ) 30.2 Hz, PMe3), -4.9/-5.8 (Si(CH3)2) (C4 and
ipso-C of C6F5 were not observed). 11B{1H} NMR (d8-toluene, 64 MHz,
300 K): δ ) -13.0 (ν1/2 ) 224 Hz). 31P{1H} NMR (d8-toluene, 81
MHz, 300 K): δ ) -9.4 (ν1/2 ) 0.3 Hz). 19F NMR (d8-toluene, 564
MHz, 300 K): δ ) -106.3, -109.5 (each br, each 1F, o-F of C6F5),
-124.9 (br, 2F, o-F of C6F5), -156.9, -157.8 (each t, 3JFF ) 20.1 Hz,
each 1F, p-F of C6F5), -161.9, -162.2 (each m, each 1F, m-F of C6F5),
-163.1 (m, 2F, m-F of C6F5).
1
(891.8): C, 52.53; H, 4.63. Found: C, 52.53; H, 3.69. H NMR (d6-
benzene, 600 MHz, 300 K): δ 8.09 (m, 1H, 11-H), 7.66 (m, 1H, 14-
H), 7.33 (m, 2H, 12-H, 13-H), 6.28 (m, 1H, 2-H′), 6.02 (m, 1H, 2-H),
5.26 (m, 2H, 4-H, 5-H′), 5.25 (m, 1H, 4-H′), 5.19 (m, 1H, 5-H), 5.16
Reaction of Complex 12 with n-Butylisocyanide; Preparation of
the Insertion Product 16. At room temperature, a solution of 73 mg
(0.88 mmol) of n-butylisocyanide was added dropwise with stirring to
a solution of freshly generated complex 12 (347 mg, 0.42 mmol) in
toluene. The mixture was stirred for 2 h, and then all volatiles were
removed in vacuo to give complex 16 (385 mg, 92%) as a pale yellow
solid, mp 147 °C (decomp.). Anal. Calcd for C49H47N2BF10SiZr
(984.9): C, 59.81; H, 4.81; N, 2.85. Found: C, 58.87; H, 4.63; N,
(m, 1H, 3-H′), 1.53/1.29 (each m, each 1H, 6-H, 6-H′), 1.08 (d, 2JPH
)
6.1 Hz, 9H, Zr-PMe3), 1.07/0.74 (each m, each 1H, 7-H, 7-H′), 0.54
(m, 2H, 8-H), 0.38 (d, 2JPH ) 11.4 Hz, 9H, B-PMe3), 0.48/0.37 (each
s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-benzene, 150 MHz, 300 K):
δ 178.5 (C10), 157.8 (C9), 148.1 (1JCF ) 241.3 Hz, o-C of C6F5), 139.4
(1JCF ) 252.4 Hz, p-C of C6F5), 137.5 (1JCF ) 257.8 Hz, m-C of C6F5),
134.1 (C14), 132.3 (C3), 131.6 (C11), 127.4 (C12, C13), 119.9 (ipso-C
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11055

A R T I C L E S
Hill et al.
of C6F5), 114.2 (C3′), 109.6 (C4), 108.5 (C4′), 106.9 (C2), 106.2 (C2′),
101.5 (C1′), 100.5 (C5′), 100.2 (C1), 99.8 (C5), 33.0 (C6), 28.0 (C7),
20.4 (C8), 18.2 (d, 1JCP ) 17.4 Hz, Zr-PMe3), 8.8 (d, 1JCP ) 36.6 Hz,
B-PMe3), -4.8/-5.1 (Si(CH3)2). 11B{1H} NMR (d6-benzene, 64 MHz,
298 K): δ -14.0 (ν1/2 ) 258 Hz). 31P{1H} NMR (d6-benzene, 81 MHz,
300 K): δ -7.9 (Zr-PMe3, ν1/2 ) 7 Hz), -10.0 (B-PMe3, ν1/2 ) 120
Hz). 19F NMR (d6-benzene, 564 MHz, 300 K): δ -129.9 (m, 2F, o-F
of C6F5), -130.3 (m, 2F, o-F′ of C6F5), -157.9 (t, 3JFF ) 20.7 Hz, 1F,
p-F′ of C6F5), -158.4 (t, 3JFF ) 20.8 Hz, 1F, p-F of C6F5), -163.1 (m,
2F, m-F′ of C6F5), -163.2 (m, 2F, m-F of C6F5). 19F/19F GCOSY (d6-
benzene, 564/564 MHz, 300 K): δ (19F)/δ (19F) -129.9/-163.2 (o-
F/m-F), -130.3/-163.1 (o-F′/m-F′), -158.4/-163.2 (p-F/m-F), -157.9/-
163.1 (p-F′/m-F′), -163.1/-157.9, -130.3 (m-F/p-F, o-F), -163.2/-
158.4, -129.9 (m-F/p-F, o-F).
33.2 (C6), 28.9 (C7), 28.8 (C9), 22.9 (C8), 11.8 (Me10), -5.3/-5.6
(Si(CH3)2). 11B{1H} NMR (d6-benzene, 64 MHz, 298 K): δ -3.30
(ν1/2 ) 416 Hz). 19F NMR (d6-benzene, 564 MHz, 300 K): δ -132.1
3
(m, 4F, o-F of C6F5), -158.5 (t, JFF ) 22.0 Hz, 1F, p-F of C6F5),
3
-158.6 (t, JFF ) 22.0 Hz, 1F, p-F′ of C6F5), -163.7 (m, 4F, m-F of
C6F5).
Thermolysis of 19a in the Presence of N-Methylbenzimidazole;
Formation of 20. A solution of 50 mg (53 µmol) of complex 19a and
7 mg (53 µmol) of 1-methylbenzimidazole in benzene was kept for 3
h at 80 °C. The solvent was then removed in vacuo at room temperature,
and the product was dried in vacuo, to yield complex 20 (48 mg, 90%),
a yellow solid, as a mixture of two diastereoisomers (20A:20B ) 3:2),
mp 283 °C (decomp.). Anal. Calcd for C49H39N4BF10SiZr (1004.0):
C, 58.62; H, 3.92; N, 5.58. Found: C, 58.54; H, 4.06; N, 5.10.
Reaction of Complex 12 with N-Methylbenzimidazole; Prepara-
tion of 19a. A solution of 41 mg (313 µmol) of 1-methylbenzimidazole
in 10 mL of toluene was added to a solution of 256 mg (313 µmol) of
freshly generated 12 in 50 mL of toluene at room temperature. The
solvent was removed after 1 h to yield 294 mg (99%) of the product
19a as a yellow solid, mp 181 °C (decomp.). Anal. Calcd for C47H37N2-
BF10SiZr (949.9): C, 59.43; H, 3.93; N, 2.95. Found: C, 59.34; H,
1
Diastereoisomer 20A, H NMR (d6-benzene, 600 MHz, 300 K): δ
8.29, 7.52, 7.33 (each m, 5H, o-, m-, p-H of Ph), 8.01 (m, 1H, 13-H′),
7.69 (m, 1H, 13-H), 7.32 (s, 1H, 10-H), 7.14 (m, 1H, 15-H′), 7.12 (m,
1H, 14-H′), 6.97 (m, 1H, 16-H′), 6.83 (m, 2H, 14-H, 15-H), 6.57 (m,
1H, 3-H′), 6.46 (m, 1H, 16-H), 6.16 (m, 1H, 5-H), 6.08 (m, 1H, 5-H′),
5.84 (m, 1H, 2-H′), 5.55 (m, 1H, 2-H), 5.13 (m, 1H, 4-H′), 5.09 (m,
1H, 4-H), 3.37 (s, 3H, 9-H′), 2.31 (s, 3H, 9-H), 1.97/1.94 (each m,
each 1H, 6-H, 6-H′), 1.45 (m, 2H, 8-H), 1.14 (m, 2H, 7-H), 0.46/0.44
(each s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-benzene, 150 MHz,
300 K): δ 181.4, 142.0, 127.0, 124.1 (ipso-, o-, m-, p-C of Ph), 202.9
(C10′), 148.5 (1JCF ) 238.4 Hz, o-C of C6F5), 143.6 (C17′), 141.2 (C10),
140.8 (C12′), 140.6 (C3), 139.4 (1JCF ) 251.5 Hz, p-C of C6F5), 137.5
(1JCF ) 249.6 Hz, m-C of C6F5), 136.4 (C12), 132.7 (C17), 127.3 (C14′),
125.4 (C14), 125.1 (C15), 122.9 (C3′), 122.7 (C15′), 121.7 (ipso-C of
C6F5), 118.4 (C13′), 116.7 (C13), 114.4 (C4), 114.0 (C4′), 110.9 (C16),
109.8 (C16′), 108.9 (C5), 108.8 (C2), 108.5 (C5′), 108.4 (C2′), 102.9
(C1), 102.8 (C1′), 33.3 (C6), 32.6 (C9′), 30.8 (C9), 28.7 (C7), 21.6
(C8), -4.2/-5.9 (Si(CH3)2). 11B{1H} NMR (d6-benzene, 64 MHz, 298
K): δ -5.10 (ν1/2 ) 341 Hz). 19F NMR (d6-benzene, 564 MHz, 300
K): δ -132.9 (m, 2F, o-F of C6F5), -133.2 (m, 2F, o-F′ of C6F5),
-158.7 (t, JFF ) 20.8 Hz, 1F, p-F of C6F5), -158.8 (t, JFF ) 20.8
Hz, 1F, p-F′ of C6F5), -164.0 (m, 2F, m-F of C6F5), -164.1 (m, 2F,
m-F′ of C6F5). 19F-19F GCOSY (d6-benzene, 564/564 MHz, 300 K):
δ (19F)/δ (19F) -132.9/-164.0 (o-F/m-F), -133.2/-164.1 (o-F′/m-F′),
-158.7/-164.0 (p-F/m-F), -158.8/-164.1 (p-F′/m-F′), -164.0/-132.9,
-158.7 (m-F/o-F, p-F), -164.1/-133.2, -158.8 (m-F′/o-F′, p-F′).
Diastereoisomer 20B, 1H NMR (d6-benzene, 600 MHz, 300 K): δ 8.30,
7.52, 7.33 (each m, 5H, o-, m-, p-H of Ph), 8.01 (m, 1H, 13-H′), 7.63
(m, 1H, 13-H), 7.19 (s, 1H, 10-H), 7.14 (m, 1H, 15-H′), 7.12 (m, 1H,
14-H′), 6.97 (m, 1H, 16-H′), 6.83 (m, 2H, 14-H, 15-H), 6.48 (m, 1H,
4-H′), 6.46 (m, 1H, 16-H), 6.35 (m, 1H, 4-H), 6.14 (m, 1H, 2-H′),
6.09 (m, 1H, 2-H), 5.83 (m, 1H, 5-H′), 5.74 (m, 1H, 5-H), 5.17 (m,
1H, 3-H′), 3.43 (s, 3H, 9-H′), 2.29 (s, 3H, 9-H), 1.55/1.15 (each m,
each 1H, 6-H, 6-H′), 1.40/1.28 (each m, each 1H, 8-H, 8-H′), 0.90 (m,
2H, 7-H), 0.44/0.42 (each s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-
benzene, 150 MHz, 300 K): δ 177.2, 141.7, 126.8, 124.1 (ipso-, o-,
m-, p-C of Ph), 202.7 (C10′), 148.5 (1JCF ) 238.4 Hz, o-C of C6F5),
143.6 (C17′), 141.2 (C10), 140.8 (C12′), 139.4 (1JCF ) 251.5 Hz, p-C
of C6F5), 137.5 (1JCF ) 249.6 Hz, m-C of C6F5), 136.4 (C12), 132.7
(C17), 132.0 (C3), 127.3 (C14′), 125.4 (C14), 125.1 (C15), 124.5 (C4′),
124.4 (C4), 122.7 (C15′), 121.7 (ipso-C of C6F5), 118.4 (C13′), 116.5
(C13), 112.9 (C3′), 110.9 (C16), 110.8 (C2), 109.8 (C16′), 109.1 (C2′),
107.0 (C5′), 106.9 (C5), 103.5 (C1′), 102.6 (C1), 32.6 (C9′), 31.6 (C6),
30.8 (C9), 28.1 (C7), 20.9 (C8), -4.2/-6.1 (Si(CH3)2). 11B{1H} NMR
(d6-benzene, 64 MHz, 298 K): δ -5.1 (ν1/2 ) 341 Hz). 19F NMR
(benzene-d6, 564 MHz, 300 K): δ -132.9 (m, 2F, o-F of C6F5), -133.4
1
4.19; N, 3.11. H NMR (d6-benzene, 600 MHz, 300 K): δ 7.72 (m,
b
1H, 13-H), 7.56, 7.26, 7.15 (each m, 5H, o-, m-, p-H of Ph), 7.36 (s,
1H, 10-H), 7.35, 7.26, 7.12 (each m, 5H, o-, m-, p-H of aPh), 6.85 (m,
1H, 14-H), 6.83 (m, 1H, 15-H), 6.58 (m, 1H, 3-H′), 6.52 (m, 1H, 4-H),
6.47 (m, 1H, 4-H′), 6.43 (m, 1H, 16-H), 5.66 (m, 1H, 5-H), 5.64 (m,
1H, 2-H′), 5.60 (m, 1H, 5-H′), 5.48 (m, 1H, 2-H), 2.21 (s, 3H, 9-H),
2.12/1.94 (each m, each 1H, 6-H, 6-H′), 1.49 (m, 2H, 8-H), 1.23/1.19
(each m, each 1H, 7-H, 7-H′), 0.28/0.25 (each s, each 3H, Si(CH3)2).
13C{1H} NMR (d6-benzene, 150 MHz, 300 K): δ 186.1, 134.4, 126.5,
125.7 (ipso-, o-, m-, p-C of aPh), 181.7, 136.3, 126.5, 126.1 (ipso-, o-,
b
m-, p-C of Ph), 148.6 (1JCF ) 241.7 Hz, o-C of C6F5), 141.2 (C10),
139.6 (1JCF ) 256.8 Hz, p-C of C6F5), 138.9 (C3), 137.5 (1JCF ) 253.0
Hz, m-C of C6F5), 136.3 (C12), 132.7 (C17), 125.4 (C14), 125.1 (C15),
123.5 (C4′), 123.1 (C4), 121.8 (C3′), 116.7 (C13), 114.9 (C2), 114.3
(C2′), 113.5 (C5), 112.4 (C5′), 110.7 (C16), 100.5 (C1), 100.1 (C1′),
33.4 (C6), 30.6 (C9), 28.5 (C7), 21.7 (C8), -5.8/-6.2 (Si(CH3)2)
(ipso-C of C6F5 not observed). 11B{1H} NMR (d6-benzene, 64 MHz,
298 K): δ -4.54 (ν1/2 ) 383 Hz). 19F NMR (d6-benzene, 564 MHz,
3
3
3
300 K): δ -132.7 (m, 4F, o-F of C6F5), -158.5 (t, JFF ) 21.1 Hz,
1F, p-F of C6F5), -158.6 (t, 3JFF ) 21.1 Hz, 1F, p-F′ of C6F5), -164.2
(m, 4F, m-F of C6F5).
Reaction of Complex 12 with 1,2-Dimethylbenzimidazole; Prepa-
ration of 19b. A solution containing 29 mg (195 µmol) of 1,2-
dimethylbenzimidazole in 10 mL of toluene was added to a freshly
prepared solution of 159 mg (195 µmol) of 12 in 30 mL of toluene.
The solvent was removed in vacuo after 1 h, and the product was dried
in vacuo, to yield 189 mg (99%) of 19b as a yellow powder, mp 170
°C (decomp.). Anal. Calcd for C48H39N2BF10SiZr (964.0): C, 59.81;
1
H, 4.08; N, 2.91. Found: C, 59.69; H, 4.27; N, 2.79. H NMR (d6-
benzene, 600 MHz, 300 K): δ 7.67 (m, 1H, 13-H), 7.53, 7.22, 7.14
(each m, 5H, o-, m-, p-H of bPh), 7.33, 7.21, 7.07 (each m, 5H, o-, m-,
a
p-H of Ph), 6.92 (m, 1H, 14-H), 6.90 (m, 1H, 15-H), 6.54 (m, 1H,
3-H′), 6.46 (m, 1H, 16-H), 6.45 (m, 1H, 4-H′), 6.43 (m, 1H, 4-H),
5.63 (m, 1H, 2-H′), 5.61 (m, 1H, 5-H), 5.55 (m, 1H, 5-H′), 5.43 (m,
1H, 2-H), 2.09/1.99 (each m, each 1H, 6-H, 6-H′), 2.08 (s, 3H, 9-H),
1.75 (s, 3H, Me-10), 1.59 (m, 2H, 8-H), 1.23/1.15 (each m, each 1H,
7-H, 7-H′), 0.25/0.23 (each s, each 3H, Si(CH3)2). 13C{1H} NMR (d6-
benzene, 150 MHz, 300 K): δ 186.2, 134.3, 126.8, 125.6 (ipso-, o-,
m-, p-C of aPh), 181.7, 136.4, 126.3, 125.8 (ipso-, o-, m-, p-C of bPh),
151.8 (C10), 148.5 (1JCF ) 240.4 Hz, o-C of C6F5), 139.5 (1JCF ) 248.3
Hz, p-C of C6F5), 138.5 (C3), 137.5 (1JCF ) 251.1 Hz, m-C of C6F5),
136.2 (C12), 132.1 (C17), 124.5 (C14), 124.2 (C15), 123.6 (C4′), 123.2
(C4), 122.7 (ipso-C of C6F5), 121.1 (C3′), 117.7 (C13), 114.8 (C2),
114.3 (C2′), 113.2 (C5), 112.1 (C5′), 110.0 (C16), 100.3 (C1, C1′),
3
(m, 2F, o-F′ of C6F5), -158.6 (t, JFF ) 20.8 Hz, 1F, p-F of C6F5),
3
-158.9 (t, JFF ) 20.8 Hz, 1F, p-F′ of C6F5), -163.9 (m, 2F, m-F of
C6F5), -164.0 (m, 2F, m-F′ of C6F5). 19F/19F GCOSY (d6-benzene, 564/
564 MHz, 300 K): δ (19F)/δ (19F) -132.9/-163.9 (o-F/m-F), -133.4/
9
11056 J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004

CH-Activation Pathways in Zirconocene/Borane Systems
A R T I C L E S
-164.0 (o-F′/m-F′), -158.6/-163.9 (p-F/m-F), -158.9/-164.0 (p-F′/
m-F′), -163.9/-132.9, -158.6 (m-F/o-F, p-F), -164.0/-133.4, -158.9
(m-F′/o-F′, p-F′).
Supporting Information Available: Additional spectroscopic
data of the metallocene complexes 4-20 (PDF and CIF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen Indus-
trie is gratefully acknowledged.
JA048447L
9
J. AM. CHEM. SOC. VOL. 126, NO. 35, 2004 11057