Decisive steps of the hydrodefluorination of fluoroaromatics using [Ni(NHC)2]

Article abstract of DOI:10.1021/om2009815

The hydrodefluorination reaction of perfluorinated arenes using [Ni ₂(ⁱPr₂Im)₄(COD)] (1; ⁱPr₂Im = 1,3-bis(isopropyl)imidazolin-2-ylidene) as a catalyst as well as stoichiometric transformations to elucidate the decisive steps for this reaction are reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of 5 mol % of 1 affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et ₃SiH for 4 days at 80 °C results in the selective formation of 1-(CF₃)-2,3,5,6-C₆F₄H. Stoichiometric transformations of the complexes cis-[Ni(ⁱPr₂Im) ₂(H)(SiPh₃)] and cis-[Ni(ⁱPr ₂Im)₂(H)(SiMePh₂)] with hexafluorobenzene at room temperature lead to the formation of trans-[Ni(ⁱPr ₂Im)₂(F)(C₆F₅)] (2) and trans-[Ni(ⁱPr₂Im)₂(H)(C₆F ₅)] (4) with elimination of the corresponding silane or fluorosilane. The reactions of the C-F activation products trans-[Ni(ⁱPr ₂Im)₂(F)(C₆F₅)] (2) and trans-[Ni(ⁱPr₂Im)₂(F)(4-(CF₃)C ₆F₄)] (3) with PhSiH₃ and Ph ₂SiH₂ afford the hydride complexes trans-[Ni( ⁱPr₂Im)₂(H)(C₆F₅)] (4) and trans-[Ni(ⁱPr₂Im)₂(H)(4-(CF ₃)C₆F₄)] (5), which convert into the compounds trans-[Ni(ⁱPr₂Im)₂(F)(2,3,5,6-C ₆F₄H)] (7), trans-[Ni(ⁱPr₂Im) ₂(F)(3-(CF₃)-2,4,5-C₆F₃H)] (9a), and trans-[Ni(ⁱPr₂Im)₂(F)(2-(CF ₃)-3,4,6-C₆F₃H)] (9b), respectively. In the case of the rearrangement of trans-[Ni(ⁱPr₂Im) ₂(H)(4-(CF₃)C₆F₄)] (5) the intermediate [Ni(ⁱPr₂Im)₂(η²-C, C-(CF₃)C₆F₄H)] (8) was detected. Reaction of 8 with perfluorotoluene gave the C-F activation product trans-[Ni( ⁱPr₂Im)₂(F)(4-(CF₃)C ₆F₄)] (3). All these experimental findings point to a mechanism for the HDF by [Ni(ⁱPr₂Im)₂] via the "fluoride route" involving C-F activation of the polyfluoroarene, H/F exchange of the resulting nickel fluoride, reductive elimination of the polyfluoroaryl nickel hydride to an intermediate with a η²-C,C- coordinated arene ligand, subsequent ligand exchange with the higher fluorinated polyfluoroarene, and renewed C-F activation of the polyfluoroarene. Without additional reagents, [Ni(ⁱPr₂Im)₂(η ²-C,C-(CF₃)C₆F₄H)] (8) rearranges to the isomers trans-[Ni(ⁱPr₂Im)₂(F)(3-(CF ₃)-2,4,5-C₆F₃H)] (9a; major) and trans-[Ni(ⁱPr₂Im)₂(F)(2-(CF₃)-3,4,6- C₆F₃H)] (9b; minor) in a ratio of 80:20. DFT calculations performed on conversion of trans-[Ni(ⁱPr₂Im) ₂(H)(4-(CF₃)C₆F₄)] 5 into the two products trans-[Ni(ⁱPr₂Im)₂(F)(3-(CF ₃)-2,4,5-C₆F₃H)] 9a and trans-[Ni( ⁱPr₂Im)₂(F)(2-(CF₃)-3,4,6-C ₆F₃H)] (9b) using the commonly accepted intramolecular concerted pathway via η²-C,F-σ-bound transition states predict 9b to be the major product. We thus propose that this reaction mechanism is not valid for the [Ni(NHC)₂]-mediated C-F activation of partially fluorinated arenes with special substitution patterns.

Full text of DOI:10.1021/om2009815

Article
pubs.acs.org/Organometallics
Decisive Steps of the Hydrodefluorination of Fluoroaromatics using
[
Ni(NHC)2]
̈
Peter Fischer, Kathrin Gotz, Antonius Eichhorn, and Udo Radius*
̈ ̈ ̈
̈
Institut fur Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, D-97074 Wurzburg, Germany
*
S Supporting Information
ABSTRACT: The hydrodefluorination reaction of perfluorinated arenes using
i
i
[
Ni ( Pr Im) (COD)] (1; Pr Im = 1,3-bis(isopropyl)imidazolin-2-ylidene) as a catalyst as
2 2 4 2
well as stoichiometric transformations to elucidate the decisive steps for this reaction are
reported. The reaction of hexafluorobenzene with 5 equiv of triphenylsilane in the presence of
5
mol % of 1 affords 1,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-difluorobenzene
after 96 h at 80 °C; the reaction of perfluorotoluene and 5 equiv of Et SiH for 4 days at 80 °C
results in the selective formation of 1-(CF )-2,3,5,6-C F H. Stoichiometric transformations of
the complexes cis-[Ni( Pr Im) (H)(SiPh )] and cis-[Ni( Pr Im) (H)(SiMePh )] with
hexafluorobenzene at room temperature lead to the formation of trans-[Ni( Pr Im) (F)-
3
3
6 4
i
i
2
2
3
2
2
2
i
2
2
i
(
C F )] (2) and trans-[Ni( Pr Im) (H)(C F )] (4) with elimination of the corresponding
6 5 2 2 6 5
i
silane or fluorosilane. The reactions of the C−F activation products trans-[Ni( Pr Im) (F)-
(
2
2
i
C F )] (2) and trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3) with PhSiH and Ph SiH afford
6 5 2 2 3 6 4 3 2 2
i
i
the hydride complexes trans-[Ni( Pr Im) (H)(C F )] (4) and trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5), which convert into the
2
2
6
5
2
2
3
6 4
i
i
compounds trans-[Ni( Pr Im) (F)(2,3,5,6-C F H)] (7), trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a), and trans-[Ni-
2
2
6
4
2
2
3
6 3
i
i
(
(
Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b), respectively. In the case of the rearrangement of trans-[Ni( Pr Im) (H)(4-
2
2
3
6
3
2
2
i
2
CF )C F )] (5) the intermediate [Ni( Pr Im) (η -C,C-(CF )C F H)] (8) was detected. Reaction of 8 with perfluorotoluene
3
6
4
2
2
3
6 4
i
gave the C−F activation product trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3). All these experimental findings point to a
2
2
3
6 4
i
mechanism for the HDF by [Ni( Pr Im) ] via the “fluoride route” involving C−F activation of the polyfluoroarene, H/F
2
2
exchange of the resulting nickel fluoride, reductive elimination of the polyfluoroaryl nickel hydride to an intermediate with a
2
η -C,C-coordinated arene ligand, subsequent ligand exchange with the higher fluorinated polyfluoroarene, and renewed C−F
activation of the polyfluoroarene. Without additional reagents, [Ni( Pr Im) (η -C,C-(CF )C F H)] (8) rearranges to the isomers
trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a; major) and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b; minor) in a
ratio of 80:20. DFT calculations performed on conversion of trans-[Ni( Pr Im) (H)(4-(CF )C F )] 5 into the two products
trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] 9a and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b) using the commonly
accepted intramolecular concerted pathway via η -C,F-σ-bound transition states predict 9b to be the major product. We thus
i
2
2
2
3
6 4
i
i
2
2
3
6
3
2
2
3
6 3
i
2
2
3
6 4
i
i
2
2
3
6
3
2
2
3
6 3
2
propose that this reaction mechanism is not valid for the [Ni(NHC) ]-mediated C−F activation of partially fluorinated arenes
2
with special substitution patterns.
INTRODUCTION
and octafluorotoluene with silanes R SiH (R = OEt, Et, Ph)
3
■
using β-diketiminate iron(II) fluoride complexes as catalysts.
For this system high catalyst loadings up to 20 mol % were
needed and the turnover numbers observed were low due to
catalyst degradation at the temperatures used. Another
interesting example was reported recently by Whittlesey and
The selective synthesis of fluoroarene compounds has become
a subject of growing interest due to the prominent role such
species play in many modern pharmaceuticals, agrochemicals,
and other industrially important products. An attractive route
for the selective substitution of fluoroarenes is based on the
1
4h,l
co-workers. The HDF of C F and C F H using a NHC-
6
6
6 5
functionalization of activated aromatic C−F bonds derived
from readily available perfluoroarenes. The simplest example
2
stabilized ruthenium dihydride complex resulted in the
formation of C F H and 1,2,3,4-C F H . The most unusual
6
5
6
4
2
for this process is the hydrodefluorination reaction (HDF), in
which fluorine is substituted for hydrogen. Catalytic HDF of
C F and C F H to C F H and 1,2,4,5-C F H has been
feature of this system is the high ortho regioselectivity, which is
in complete contrast to the reaction products observed for the
systems of Milstein and Holland. Initially, the involvement of a
tetrafluorobenzyne intermediate was postulated to account for
this unusual regioselectivity, but later an alternative pathway
6
6
6
5
6
5
6
4
2
reported by Milstein and Aizenberg using a silylrhodium
3
complex. Since their seminal work on the F/H exchange
between hydrosilanes and fluoroarenes under mild conditions,
the work on hydrodehalogenation reactions of fluorocarbons
using silanes has grown consistently. Holland et al. reported
in 2005 on the catalytic HDF of perfluorinated aromatic
compounds such as hexafluorobenzene, pentafluoropyridine,
4
4c
Special Issue: Fluorine in Organometallic Chemistry
Received: October 14, 2011
Published: January 18, 2012
©
2012 American Chemical Society
1374
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
based on nucleophilic attack of a coordinated hydride ligand at
case of the formation of 1,2,4,5-tetrafluorobenzene we detected
pentafluorobenzene as an intermediate of the reaction. Thus,
the regioselectivities observed are in accordance with earlier
work reported by Milstein et al. and Holland et al. for the
rhodium and iron systems mentioned above, where the HDF of
pentafluorobenzene leads to the 1,2,4,5-isomer.
4l
C F H was established by means of DFT calculations.
6
5
Although much work has been done in the field of nickel-
5
mediated C−F bond activation, reports on applications of
nickel complexes in hydrodefluorination reactions are rather
6
0
scarce. It is now well established that Ni complexes, stabilized
by phosphine, carbene, and certain nitrogen ligands, undergo
C−F activation with hexafluorobenzene to yield complexes of
the type trans-[Ni(L) (F)(C F )]. Over the past few years we
Whereas Ph SiH is the silane of choice for a controlled HDF
3
reaction of C F , we have found that Et SiH gives the best
6
6
3
2
6
5
results for a controlled HDF of C F . The HDF reaction of
7 8
have reported the facile and clean oxidative addition of
hexafluorobenzene and perfluorotoluene to the NHC-stabilized
perfluorinated toluene is noticeably slower compared to the
HDF of perfluorobenzene. Heating C F and 5 equiv of Et SiH
i
7
i
7
8
3
complex fragment [Ni( Pr Im) ] ( Pr Im = 1,3-bis(isopropyl)-
2
2
2
for 4 days at 80 °C leads to the selective formation of 1-(CF )-
i
8
3
imidazolin-2-ylidene), as provided by [Ni (Pr Im) (COD)] (1).
2
2
4
2
,3,5,6-C F H (see Scheme 2). All the reaction products were
6 4
Those were the first C−F activation reactions of polyfluoroarenes
at nickel performed at room temperature on a time scale
reasonable for practical catalysis. The C−F activation re-
actions have been applied in Suzuki−Miyaura-type cross-
coupling reactions of perfluorinated aromatics with boronic
Scheme 2. Catalytic HDF of C F to 1-(CF )-2,3,5,6-C F H
7
8
3
6 4
i
(
L = Pr Im)
2
i
7b
acids using [Ni ( Pr Im) (COD)] (1) as a catalyst. In
2
2
4
stoichiometric reactions we have shown that the fluorine atom
i
in complexes of the type trans-[Ni( Pr Im) (F)(Ar )] can
2
2
F
7
d
be substituted easily. As an example, we reported the
preparation of trans-[Ni( Pr Im) (R)(Ar )] via salt metathesis
i
2
2
F
using organolithium compounds and the silaphilicity of the Ni−
verified by comparison of the analytical data with commercial
samples.
i
F bond in trans-[Ni( Pr Im) (F)(Ar )]. The reaction of X-
2
2
F
i
SiMe with trans-[Ni( Pr Im) (F)(Ar )] leads in many cases to
3
2
2
F
In light of these results we were interested in the essential
steps of the nickel-catalyzed HDF reaction. In the NMR spectra
of the reaction mixtures we observe resonances for nickel
fluoride and nickel hydride species. We reported earlier the
i
the substitution product trans-[Ni( Pr Im) (X)(Ar )] with
2
2
F
elimination of F−SiMe , making these fluoride complexes
3
attractive synthetic precursors for new molecules with a variety
7
d
i
of ligands. We recognized already at that time that the
reaction of [Ni ( Pr Im) (COD)] (1) with silanes such as
2
2
4
i
reaction of trans-[Ni( Pr Im) (F)(C F )] with phenylsilanes
2
2
6
5
Ph SiH and Ph MeSiH, which affords nickel silyl hydride
3 2
8i
i
affords the highly sensitive nickel hydride complex trans-
complexes of the type cis-[Ni( Pr Im) (H)(SiR )]. Although
2
2
3
i
[
Ni( Pr Im) (H)(C F )]. We wish to report here initial
2 2 6 5
formation of such species is likely in the reaction mixture of
investigations into catalytic HDF reactions of polyfluoroar-
omatics using hydrosilanes as well as results concerning the
isolation and characterization of intermediates of this reaction.
HDF catalysis, we observe in stoichiometric reactions of cis-
i
i
[
Ni( Pr Im) (H)(SiPh )] and cis-[Ni( Pr Im) (H)(SiMePh )]
2 2 3 2 2 2
with hexafluorobenzene at room temperature the formation of
i
i
trans-[Ni( Pr Im) (F)(C F )] (2) and trans-[Ni( Pr Im) (H)-
2
2
6
5
2
2
RESULTS AND DISCUSSION
In preliminary experiments we realized that catalytic HDF re-
actions with silanes as the hydride source and [Ni -
■
(C F )] (4) with elimination of the corresponding silane or
6 5
fluorosilane, respectively (vide infra). This is a clear indication
i
2
that complexes of the type trans-[Ni( Pr Im) (F)(Ar )] and
2
2
F
i
i
(
Pr Im) (COD)] (1) as a catalyst lead to complex reaction
trans-[Ni( Pr Im) (H)(Ar )] are more likely intermediates than
complexes of the type cis-[Ni( Pr Im) (H)(SiR )].
2 2 3
2
4
2 2 F
i
mixtures. Using different silanes and reaction conditions, we
usually obtain mixtures of fluoroaromatics, depending on the
reaction time, the temperature, and the silane employed. In
some cases, however, we can also optimize the reaction con-
ditions in a way to obtain specifically one product. The reaction
of hexafluorobenzene with 5 equiv of triphenylsilane in the
presence of 5 mol % of the nickel catalyst affords exclusively
Therefore, we were interested in the reactivity of complexes
i
of the type trans-[Ni( Pr Im) (F)(Ar )] with silanes and the
2
2
F
reactivity of the reaction products. The reaction of
i
[Ni ( Pr Im) (COD)] (1) with stoichiometric amounts of the
2
2
4
perfluorinated arenes C6F6 and (CF )C F in toluene or
3
6 5
tetrahydrofuran proceeds quickly and cleanly at room temper-
ature. As reported previously, oxidative addition of one of the
C−F bonds takes placein the case of perfluorotoluene
1
,2,4,5-tetrafluorobenzene after 48 h at 60 °C and 1,4-
difluorobenzene after 96 h at 80 °C (see Scheme 1). In the
regioselectively in a position para to the CF groupand leads
3
i
Scheme 1. Catalytic HDF of C F to 1,2,4,5-C F H (a) and
to the C−F activation products trans-[Ni( Pr Im) (F)(C F )]
6
6
6
4
2
2
2
6 5
i
i
1
,4-C F H (b) (L = Pr Im)
(2) and trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3) (fluoroaryl
6
2
4
2
2 2 3 6 4
ligands are numbered with the nickel atom in the position 1).
These can be isolated in good yields.
The reactions of these C−F activation compounds with
silanes such as PhSiH and Ph SiH lead to the formation of the
3
2
2
i
corresponding hydride complexes trans-[Ni( Pr Im) (H)-
C F )] (4) and trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5)
6 5 2 2 3 6 4
2
2
i
(
(
see Scheme 3). After addition of the silane at room
temperature to 2 and 3 in thf or toluene the suspension
cleared up rapidly but was stirred for another 2 h before
workup. These reactions are quantitative if performed on an
1
375
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
i
i
Scheme 3. Synthesis of the Hydride Complexes trans-[Ni( Pr Im) (H)(C F )] (4) and trans-[Ni( Pr Im) (H)(4-(CF )C F )]
2
2
6
5
2
2
3
6 4
i
(
[
5) and the Rearrangement of These Compounds to the Fluoride Complexes trans-[Ni( Pr Im) (F)(2,3,5,6-C F H)] (7), trans-
Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a), and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b)
2
2
6 4
i
i
a
2
2
3
6
3
2
2
3
6 3
a
Intermediate 6 was not observed.
NMR scale, but isolation of the pure compound was hampered
by an ineffective crystallization step. Both complexes were
isolated in analytically pure form in rather low yields of
approximately 20%. In the proton NMR spectra of both
complexes the characteristic hydride resonances were detected
at −13.99 ppm (4) and −13.68 ppm (5) as irregular septets
due to the coupling of the hydride ligand with the fluorine
nuclei of the perfluoroaryl ligand. In contrast to the C−F
activation products 2 and 3, for which we observe broadened
7c
signals for the carbene isopropyl methyl hydrogen atoms,
these resonances appear in the case of the hydride compounds
as sharp doublets at 1.21 (4) and 1.20 ppm (5) at room
Figure 1. ORTEP diagram of the molecular structure of trans-
1
9
i
temperature. The set of F NMR resonances for the
perfluoroaryl ligand of 4 and 5 are almost identical with the
resonances observed for the C−F activation products 2 and 3.
Crystals of 5 suitable for X-ray diffraction were grown from a
hexane solution at −40 °C. The crystals obtained are very
sensitive toward air and moisture and decompose in ethereal
and halogenated solvents, but they are stable and can be stored
for a longer period of time in the solid state under an inert gas
atmosphere. In toluene and thf solutions, however, the hydride
complexes show rearrangement within a few days at room
temperature (vide infra). Compound 5 crystallizes in the
monoclinic space group C2/m with half of the molecule in the
[
Ni( Pr Im) (H)(4-(CF )C F )] (5) in the solid state. With the
2 2 3 6 4
exception of the hydride ligand H(1), all other H atoms have been
omitted for clarity (thermal ellipsoids shown at the 50% probability
level). Selected bond lengths (Å) and angles (deg): Ni−C(1) =
1
.877(3), Ni−C(10) = 1.945(5), Ni−H(1) = 1.54(5); C(1)−Ni−
C(1)′ = 163.2(2); C(1)−Ni−C(10) = 98.32(10); C(1)−Ni−H(1) =
8
1.69(10); C(10)−Ni−H(1) = 179.2(16).
i
the corresponding nickel fluoride trans-[Ni( Pr Im) (F)(4-
2
2
7b
(
CF )C F )] (3).
3 6 4
As mentioned above, the hydride complexes 4 and 5
rearrange within a few days in solution at room temperature,
but the reaction time is significantly reduced to several hours if
solutions are heated to 60 °C. The product of the rearrange-
asymmetric unit (Figure 1). The hydride hydrogen atom of
i
the complex has been refined isotropically. trans-[Ni( Pr Im) -
2
2
i
ment of trans-[Ni( Pr Im) (H)(C F )] (4) is the tetrafluo-
2
2
6 5
(
H)(4-(CF )C F )] (5) adopts a square-planar geometry,
3 6 4
i
rophenyl fluoride complex trans-[Ni( Pr Im) (F)(2,3,5,6-
which is significantly distorted in comparison to other
2
2
i
7,8
C F H)] (7), which was prepared before from the reaction of
complexes of the type trans-[Ni( Pr Im) (X)(Ar )]. Both
6 4
2
2
F
i
7c
[
Ni ( Pr Im) (COD)] (1) and pentafluorobenzene. For the
carbene ligands are bent away from the pentafluorophenyl
2 2 4
i
perfluorotolyl complex trans-[Ni( Pr Im) (H)(4-(CF )C F )]
ligand toward the hydride ligand. The angle C(1)−Ni−C(1)′ of
2
2
3
6 4
(
5) we observe the formation of two isomers, trans-
163.2(2)° differs significantly from an ideal value of 180°, and
i
[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a) and trans-[Ni-
the angle C(1)−Ni−H(1) of 81.69(10)° clearly reveals the
2 2 3 6 3
i
(
Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b), in a ratio of
distortion toward the hydride. The Ni−H(1) distance of
2
2
3
6 3
1.54(5) Å observed by X-ray diffraction is close to the recently
approximately 80:20 (see Scheme 3).
2
published value of 1.4919 Å calculated for trans-[Ni-
Intermediates with an η -C,C-coordinated perfluoroarene ligand,
i
i
2
i
2
(
Pr Im) (H)(C F )] by means of DFT (TURBOMOLE,
i.e. [Ni( Pr Im) (η -C,C-C F )] and [Ni(Pr Im) (η -C,C-C10F )],
2 2 6 6 2 2 8
2
2
6 5
7d
RIDFT, BP86, TZVPP). This distance is considerably shorter
have been detected in solution for the C−F activation of hexafluoro-
i
compared to the Ni−F distance of 1.856(4) Å determined for
benzene and octafluoronaphthalene with [Ni (Pr Im) (COD)] (1)
2
2
4
1
376
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
or the ethylene complex [Ni( Pr Im) (η -C H )]. For the
Article
i
2
7c
start to develop after approximately 60 min. This is a clear in-
dication that in the meantime an intermediate without Ni−H or
Ni−F ligands is formed in solution. These findings are
corroborated by the F NMR spectra recorded for the aryl
fluoride region, shown in Figure 3b. No signals of the hydride com-
2
2
2
4
rearrangement observed here, we anticipated a reductive elimi-
nation/oxidative addition mechanism leading to the formation of
2
i
2
19
η -bound intermediates [Ni( Pr Im) (η -C,C-C F H)] (6) and
2
2
6 5
i
2
[
Ni( Pr Im) (η -C,C-(CF )C F H)] (8).
2
2
3
6 4
Figure 2 displays the time-dependent 19F NMR spectra for
plex trans-[Ni( Pr Im) (H)(4-(CF )C F )] 5 at −55.2, −114.1, or
i
2
2
3
6 4
i
the conversion of trans- [Ni( Pr Im) (H)(C F )] (4) to trans-
Ni( Pr Im) (F)(2,3,5,6-C F H)] (7) at 60 °C. The signals of
−145.8 ppm (marked with a green asterisk in Figure 3) can be
2
2
6 5
i
2
[
detected after 1 h, and a set of resonances attributed to the η -
2
2
6 4
i
2
the perfluorophenyl ligand of the hydride complex trans-
coordinated intermediate [Ni( Pr Im) (η -C,C-(CF )C F H)] (8)
2 2 3 6 4
i
[
Ni( Pr Im) (H)(C F )] (4) at −114.2 and −164.8 ppm
(marked in Figure 3b with a blue asterisk) develop rapidly after the
reaction starts. This intermediate is the predominant species after
approximately 1 h. The 19F NMR spectrum shows a sharp triplet
2
2
6 5
decrease with time and are completely absent after 90 min.
On the other side, a new set of signals starts to develop after a
few minutes at −117.7 and −143.5 ppm for the tetrafluoro-
phenyl ligand and at −374.2 ppm for the fluoride ligand of
at −49.6 ppm for the CF group and two broad singlets at −142.8
3
19
and −155.5 ppm for the F nuclei of the aromatic system,
i
1
1
trans-[Ni( Pr Im) (F)(2,3,5,6-C F H)] (7). The H NMR
which are typical for this kind of coordination mode. The H
2
2
6 4
spectrum of 7 (not shown in Figure 2) reveals a broad singlet
at 1.30 ppm for the isopropyl methyl hydrogen atoms, a septet
for the isopropyl methane hydrogen atoms at 6.56 ppm, a
singlet at 6.31 ppm for the carbene olefinic protons, and a
multiplet between 6.23 and 6.29 ppm for the hydrogen atom
located in a position para to the activated C−F bond. These
resonances are in accordance with those of trans-[Ni-
NMR spectrum of 8 reveals a broad resonance at 1.07 ppm for
the isopropyl methyl hydrogen atoms at room temperature,
a broad signal for the isopropyl methine hydrogen atoms at
5.06 ppm, a singlet at 6.38 ppm for the NHC backbone
protons, and, most significantly, a multiplet at 5.56 ppm for the
hydrogen atom located in a position para to the CF group in
3
an integration ratio of 24:4:4:1. Similar broadened resonances
i
7c
1
(
Pr Im) (F)(2,3,5,6-C F H)] reported earlier. According to
F NMR tiny amounts of two minor products were observed
of the isopropyl ligands have been found in the H NMR
2
2
6 4
1
9
i
spectrum of the structurally characterized complex [Ni(Pr Im) -
2
2
2
7c
in 3.6% and 0.2% yields, as judged from the integration of the
nickel fluoride resonances. These are presumably the products
of an activation at the ortho and para positions (relative to H),
(η -C,C-C F )]. Compound 8 was synthesized and charac-
10 8
terized independently from the reaction of 1 with 1-(CF )-2,3,
3
5,6-C F H at room temperature (with minor impurities of 9a
6
4
i
trans-[Ni( Pr Im) (F)(2,3,4,6-C F H)] and trans-[Ni-
and 9b) to substantiate the assignment. Despite several attempts,
2
2
6 4
i
(
Pr Im) (F)(2,3,4,5-C F H)]. However, these compounds
we were unsuccessful in growing crystals of this complex suitable
2
2
6 4
19
i
2
could not be characterized properlynot even by F NMR
for X-ray diffraction. However, having [Ni(Pr Im) (η -C,C-
2 2
spectroscopy.
(CF )C F H)] (8) in hand, we reacted this complex with per-
3
6 4
Time-dependent NMR spectra for the conversion of trans-
fluorotoluene to simulate the conditions of the HDF reaction
(perfluorotoluene present in solution). Experimentally, we
found the formation of the C−F activation product trans-
i
i
[
(
3
Ni( Pr Im) (H)(4-(CF )C F )] (5) to trans-[Ni( Pr Im) (F)(3-
2 2 3 6 4 2 2
i
CF )-2,4,5-C F H)] (9a) and trans-[Ni( Pr Im) (F)(2-(CF )-
3
6
3
2
2
3
i
,4,6-C F H)] (9b) at 60 °C are given in Figure 3. Aside from the
[Ni( Pr Im) (F)(4-(CF )-C F )] (3) from the reaction of 8
6
3
2
2
3
6 4
i
signals of 5, 9a, and 9b, we observe in the intermediate time
with perfluorotoluene at 80 °C, presumably via [Ni( Pr Im) -
2 2
2
intervals resonances of an intermediate, presumably [Ni-
(η -C,C-(CF )C F )] as an intermediate (see Scheme 4).
3 6 5
i
2
2
(
Pr Im) (η -C,C-(CF )C F H)] (8). Figure 3a displays the
DFT calculations predicted the η -C,C-bound intermediate
of perfluorotoluene [Ni( Pr Im) (η -C,C-(CF )C F )] to be
2
2
3
6 4
i
2
proton and fluorine NMR spectra in the region relevant for the
nickel hydride and nickel fluoride ligands discussed here. The
2 2 3 6 5
energetically more stable by at least 7 kJ/mol compared to
i
i
2
hydride resonance of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5)
[Ni( Pr Im) (η -C,C-(CF )C F H)] (8). This experiment
2
2
3
6
4
2 2 3 6 4
i
at −13.68 ppm, still apparent at the beginning of the measure-
ment, is absent after 35 min. The resonances of the fluoride
ligands at −368.0 (9a) and −378.8 ppm (9b), on the other hand,
reveals that hopping of the [Ni( Pr Im) ] moiety between
2 2
(CF )C F and 1-(CF )-2,3,5,6-C F H rings is more rapid than
3
6
5
3
6 4
C−F bond activation. Furthermore, the introduction of C−H
Figure 2. Time-dependent 19F NMR spectra for the conversion of trans-[Ni( Pr Im) (H)(C F )] (4) to trans-[Ni( Pr Im) (F)(2,3,5,6-C F H)] (7)
i
i
2
2
6
5
2
2
6 4
at 60 °C. Resonances of different complexes are marked with colored asterisks: 4, green, 7, red.
1
377
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
i
i
Figure 3. Time-dependent NMR spectra for the conversion of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5) to trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-
2
2
3
6
4
2
2
3
i
1
19
C F H)] (9a) and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b) at 60 °C: (a) time-dependent H (left) and F (right) NMR spectra in the
nickel hydride and nickel fluoride region; (b) time-dependent F NMR spectra in the aryl fluoride region. Resonances of different complexes are
6
3
2
2
3
6 3
19
marked with colored asterisks: 5, green; 8, blue; 9a, red; 9b, magenta.
i
2
Scheme 4. Reaction of [Ni( Pr Im) (η -C,C-(CF )C F H)] (8) with Perfluorotoluene
2
2
3
6 4
i
2
bonds into substrates usually slows the reaction rates of C−F
activation and generates competition between the two
substrates perfluorotoluene and 1-(CF )-2,3,5,6-C F H, with a
ligand with perfluorotoluene occurs to give [Ni( Pr Im) (η -
2 2
C,C-(CF )C F )], a step which can also be considered as
3
6 5
i
intermolecular, exothermic ring hopping of [Ni( Pr Im) ] from
3
6
4
2
2
much faster reaction rate for perfluorotoluene. Overall, our
results presented here are in agreement with the crucial steps
1-(CF )-2,3,5,6-C F H to perfluorotoluene. This compound is
3 6 4
the precursor complex for oxidative addition of the C−F bond
i
i
for the [Ni( Pr Im) ] catalyzed HDF of perfluorotoluene as
to yield trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3), and thus the
2
2
2
2
3
6 4
depicted in Scheme 5.
catalytic cycle is closed.
The mixture of perfluorotoluene, silane, and nickel complex
Without additional perfluorotoluene, complex 8 rearranges
to the products of C−F activation of 1-(CF )-2,3,5,6-C F H, as
1
(
reacts to give the C−F activation product trans-[Ni-
3
6 4
i
Pr Im) (F)(4-(CF )C F )] (3). C−F activation takes place
depicted in Figure 3. After approximately 1 h two sets of
2
2
3
6 4
regioselectively at the position para to the CF group. Complex
resonances start to develop for the C−F activation products
3
i
3
reacts readily with the silane R Si−H with H/F exchange to
trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a) (marked
3
2
2
3
6 3
i
afford the fluorosilane R Si−F and the hydrido complex trans-
with a red asterisk in Figure 3) and trans-[Ni( Pr Im) (F)(2-
3
2 2
i
[
Ni( Pr Im) (H)(4-(CF )C F )] (5). This compound elimi-
(CF )-3,4,6-C F H)] (9b) (marked with a magenta asterisk in
3 6 3
2
2
3
6
4
2
nates 1-(CF )-2,3,5,6-C F H with formation of the η -C,C-
Figure 3) in a ratio of approximately 80:20, on the basis of the
3
6 4
i
2
19
coordinated intermediate [Ni( Pr Im) (η -C,C-(CF )C F H)]
integration of the F NMR signals of the fluoride ligands. In
2
2
3
6 4
(
8). At this stage substitution of the 1-(CF )-2,3,5,6-C F H
other words, the product of an oxidative addition of the C−F
3
6 4
1
378
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Scheme 5. Key Intermediates of the [Ni( Pr Im) ] Catalyzed
Article
i
The 19F NMR spectrum of 9a reveals a doublet of doublets
at −56.3 ppm for the CF group with two J coupling
2
2
4
HDF of Perfluorotoluene
3
FF
constants of 21.4 and 24.7 Hz to the fluorine atoms in ortho
and para positions (with respect to the Ni atom) as well
as resonances in the aryl fluoride region at −92.5, −146.0,
and −147.7 ppm. For the minor product 9b we observe a doublet
4
at −56.3 ppm with a J coupling constant of 18.8 Hz to the
FF
fluorine ligand in a meta position (with respect to the Ni atom)
and resonances at −79.7, −144.5, and −145.8 ppm for the
fluorophenyl ligand. The resonances of the fluoride ligands
were detected in the region typically observed for Ni−F
at −368.0 (9a) and −378.8 ppm (9b). The assignment of the
two products is based on resonance positioning and coupling
constant arguments observed for the signals in the polyfluoro-
aryl region of the 19F NMR spectra. Our earlier work on
partially fluorinated benzenes revealed that o-fluoride substit-
uents of polyfluoroaryl ligands are detected in a range between
−
80 and −100 ppm in the absence of fluoride substituents in
meta postions. If m-fluoride substituents are present, these
resonances are usually detected in a range between −110
bond next to the hydrogen atom prevails over the product of an
and −120 ppm. Furthermore, the signal of the main product
4
oxidative addition of the C−F bond next to the CF group.
at −92.5 ppm reveals a J coupling constant of 21.4 Hz to an
3
FF
This experimental result was corroborated by the reaction of
adjacent CF group and was therefore assigned to the signal
3
i
i
[
Ni (Pr Im) (COD)] (1) with 1-(CF )-2,3,5,6-C F H at 60 °C,
set of trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a). The
2
2
4
3
6
4
2
2
3
6 3
which leads to the same product ratio. Within experimental
error, this distribution is not affected by factors such as
substrate concentration and nickel complex concentration. As a
general trend, transition-metal complexes often react with
polyfluoroaromatics in nucleophilic replacement reactions with
similar selectivity as simple nucleophiles, such as methoxide.
resonance at −79.7 ppm, on the other hand, reveals coupling with
5
the two fluorine ligands of the aromatic system ( J = 15.6 Hz,
FF
4
4
JFF = 3.6 Hz), but no J coupling to a CF group is observed.
FF
3
DFT calculations have been performed to gain more information
i
about the energetics of the conversion of trans-[Ni( Pr Im) (H)
2
2
i
(4-(CF )C F )] (5) into the two products trans-[Ni( Pr Im) (F)
3
6
4
2
2
i
For the methoxydefluorination reaction of 1-(CF )-2,3,5,6-
(3-(CF )-2,4,5-C F H)] (9a) and trans-[Ni( Pr Im) (F)(2-(CF )-
3
3 6 3 2 2 3
C F H it has been found that nucleophilic replacement occurs
3,4,6-C F H)] (9b). The calculations of this process along a
6 3
reductive elimination/oxidative addition pathway are summarized in
Figure 4 and were calibrated on the basis of the isolated hydride
6
4
9
at the position ortho to the CF substituent and thus a pure
3
nucleophilic reaction pathway is unlikely in our case.
i
Figure 4. Calculated energetics (electronic energies) for likely intermediates and transition states of the conversion of trans-[Ni( Pr Im) (H)
2
2
i
i
(
4-(CF )C F )] (5) into the products trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a) and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b).
3 6 4 2 2 3 6 3 2 2 3 6 3
1
379
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
complex 5. The reductive elimination reaction starting from the
p-perfluorotolyl nickel hydride complex to a compound with an
evidence that the reaction mechanisms differ individually in the
dependence of the metal atom and the ligand environment
employed. For the nickel phosphine system, for example, a
phosphine-assisted mechanism was recently established for C−F
2
2
η -coordinated arene ligand via an η -C,H-σ complex as a transition
state TS1 requires only 28.2 kJ/mol. The transition state features an
2
5
o
η -C,H-σ-coordinated ligand in which the C−H bond length of
activation reactions of pentafluoropyridine. The Johnson
group has shown lately that the introduction of C−H bonds
into substrates often changes reaction mechanisms and
1
.619 Å is significantly elongated in comparison to C −H distances.
ar
This energetically low lying transition state is a consequence of the
relatively weak Ni−H bond in comparison with Ni−F bonds in
generates competition between C−F and C−H activation at
i
5l,n,q
complexes such as trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3). For a
nickel.
In the case of C F H, 1,2,4,5-C F H , and 1,2,3,5-
2
2
3
6
4
6 5 6 4 2
similar transformation of the latter complex to a transition state with
C F H C−H activated species are formed reversibly as kinetic
6
4
2
2
5n,q
the η -C,F-σ-coordinated ligand in a position para to the CF
products of their reaction with [Ni(PEt ) ].
Moreover,
3
3 2
i
2
substituent, i.e. [Ni( Pr Im) {η -C,F-4-(CF )C F )], we calculated a
barrier of 216.3 kJ/mol. Lower in energy in comparison to TS1
are all of the possible η -C,C-bound intermediates, denoted as I1−
I3 in Figure 4. A closer inspection of these η -C,C-bound inter-
Johnson et al. have isolated the dinuclear complexes
2
2
3
6 5
7
c
2
2
[{(Et P) Ni} (μ-η :η -C,C-C F X)] (X = H, F), in which a
3 2 2 6 5
2
hexafluoro- or pentafluorobenzene ligand bridges two [Ni-
2
(PEt ) ] complex fragments. In the case of [{(Et P) Ni} -
3
2
3
2
2
2
i
2
2
mediates reveal that η -C,C binding of the [Ni(Pr Im) ] complex
(μ-η :η -C,C-C F H)] it was shown that the addition of C F H
2
2
6
5
6
5
fragment is actually preferred at the 1,2-C−C position (I1): i.e. the
to solutions of this dinuclear complex provided equilibrium
2
bond of the ipso carbon atom at the CF substituent to the ortho
amounts of the mononuclear compound [Ni(PEt ) (η -C,C-
3
3 2
carbon atom. Coordination at the 3,4-C−C bond (I2) is disfavored
by 19.7 kJ/mol with respect to I1 and coordination at the 2,3-C−C
bond by 30.6 kJ/mol. If we presume that these isomers are in
C F H)] and the C−H activation product trans-[Ni-
6
5
(PEt ) (H)(C F )] as intermediates. Solutions of
3
2
6
5
2
2
[{(PEt ) Ni} (μ-η :η -C,C-C F H)] with added C F H, how-
3
2
2
6
5
6 5
2
equilibrium with each other, the different energies of the η -C,C
ever, convert with high selectivity to the o-C−F activated
intermediates will, according to the Curtin−Hammett principle,
have no influence on the selectivity of the product formation.
However, the calculations also predict that the metal atom of the
energetically favored intermediate I1 is already in the correct
position to reach the energetically lowest lying transition state for
C−F activation. The transition states leading to cleavage of the C−F
bond are much higher in energy in comparison to the transition
state for C−H activation, and C−F cleavage leads to products 9a,b
which are thermodynamically much more stable compared to 5.
This closely resembles the experimental data. The calculated
transition states for C−F activation lie 59.7 kJ/mol (TS2) and
compound trans-[Ni(PEt ) (F)(2,3,4,5-C F H)]. The mecha-
3
2
6 4
nism of this conversion is not yet clear, but all the complexes
2
2
2
[{(PEt ) Ni} (μ-η :η -C,C-C F H)], [Ni(PEt ) (η -C,C-
3
2
2
6
5
3 2
C F H)], and trans-[Ni(PEt ) (H)(C F )] are likely interme-
6
5
3 2
6 5
5n,q
diates.
In the case presented here we could not observe
dinuclear intermediates in solution (judged by the integration
of the proton NMR spectrum). Similar to the work of Johnson
et al. mentioned above, we demonstrated that conversion of
i
2
[Ni( Pr Im) (η -C,C-(CF )C F H)] (8) to the C−F activation
2
2
3
6 4
product 9a occurs with an ortho selectivity (ortho to the
hydrogen substituent) much higher than predicted using a
concerted reaction model. This is also in line with results
obtained earlier for the C−F activation of 1,2,3-trifluoroben-
8
3.5 kJ/mol (TS3) above the transition state TS1 for C−H
activation and 116.0 kJ/mol (TS2) and 139.8 kJ/mol (TS3) above
the energetically lowest lying intermediate I1. Assuming a concerted
reaction pathway for the oxidative addition, the transition states TS2
i
7c
zene by [Ni( Pr Im) ]. We reported that the reaction of
2
2
i
[Ni ( Pr Im) (COD)] (1) with 1,2,3-trifluorobenzene leads to
a mixture of the isomers trans-[Ni( Pr Im) (F)(2,3-C F H )]
and trans-[Ni( Pr Im) (F)(2,6-C F H )]. The activation prod-
2 2 6 2 3
2
2
4
2
i
and TS3 feature η -C,F-σ-coordinated arene ligands, in which the
2 2 6 2 3
i
C−F bond lengths of 1.493 Å (TS2) and 1.494 Å (TS3) are
elongated compared to C −F distances. Both transition states are
uct of the statistically more favored C−F bonds at position 1
ar
19
closely related to the geometries obtained for similar transition states
leads to the major isomer (approximately 90% judged by
F
2
5g,7c
with η -C,F-σ-coordinated arene ligands calculated previously.
NMR spectroscopy) and minor amounts (approximately 10%)
of the second isomer resulting from an activation of the 2-
position. This distribution closely resembles the product
distribution obtained for the nucleophilic replacement with
methoxide reacted with a 4:1 preference for the 1-site with
For a concerted oxidative addition, the relative energies of TS2 and
TS3 reveal a kinetic preference for the formation of trans-
i
[
Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b), because the transi-
2
2
3
6 3
tion state corresponding to this complex is favored by 23.8 kJ/mol
1
0
2
with respect to the transition state for the formation of trans-
1,2,3-trifluorobenzene. However, DFT calculations of the η -
i
i
2
[
Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a). From a thermody-
C,F-transition states clearly render [Ni( Pr Im) (η -C,F-2-1,2,3-
2
2
3
6
3
2 2
namic point of view the products 9a,b lie at almost the same energy;
thus, a clear kinetic resolution is predicted by theory. However, in
this case we calculate an energetically much lower lying transition
C F H )], i.e. the transition state leading to the minor isomer
6 3 3
i
trans-[Ni( Pr Im) (F)(2,6-C F H )], as energetically more
2
2
6
2
3
favorable by approximately 12 kJ/mol compared to [Ni-
i
2
state (red path in Figure 4) for the formation of trans-
( Pr Im) (η -C,F-1-1,2,3-C F H )] (unpublished results). Fur-
2 2 6 3 3
i
[
Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b), the isomer we
thermore, the DFT calculations predict the minor isomer trans-
2
2
3
6 3
i
experimentally observe as a minor product.
[Ni( Pr Im) (F)(2,6-C F H )] to be the thermodynamically
2
2
6
2
3
The most interesting feature of the calculations presented
here is the mismatch between experiment and theory. The
mechanism of C−F oxidative addition of hexafluorobenzene at
more stable complex. Thus, a mechanism for the activation of
1,2,3-trifluorobenzene via a concerted reaction mechanism
seems to be either unlikely or is at least superimposed by other
pathways. All these findings lead to the conclusion that for C−F
0
Ni is usually thought to involve precoordination of the fluoro-
0
arene followed by concerted oxidative cleavage of the C−F
activation of partially fluorinated aromatics at Ni reaction
2
bond. The η -C,C-fluoroarene intermediates were isolated,
mechanisms different from the commonly accepted intra-
molecular (concerted) pathways are likely to predominate for
certain cases, depending on the substrate employed. These
include a mechanism via nucleophilic attack of the metal base,
and the conversion to nickel fluoride was followed directly in
2
g,5e,n,q,7c
some cases.
Computational studies of the reaction
pathways also support this mechanism, but there is compelling
1
380
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
radical pathways, or pathways that include NHC assistance.
reaction of 1-(CF )-2,3,5,6-C F H takes place exclusively at the
3
6 4
9
Future work will focus on mechanistic studies of the C−F
position ortho to the CF3 substituent, and thus a pure
nucleophilic reaction pathway is unlikely here. High selectivity
for o-C−F activation has been previously reported for specific
examples: e.g., for the nickel phosphine system by Johnson et
i
activation of partially fluorinated aromatics using [Ni( Pr Im) ].
2
2
CONCLUSIONS
■
5n,q
7c
i
al. and for our nickel carbene system. We assume therefore
[
Ni ( Pr Im) (COD)] (1) is an active catalyst for the
2
2
4
that in certain cases of the [NiL ]-mediated C−F activation of
hydrodefluorination (HDF) of polyfluorinated arenes using
hydrosilanes as the hydrogen source. The reaction of hexa-
fluorobenzene with 5 equiv of triphenylsilane in the presence
of 5 mol % of 1 affords 1,2,4,5-tetrafluorobenzene after 48 h at
2
partially fluorinated arenes neither the commonly accepted
intramolecular concerted pathway nor a mechanism via
nucleophilic attack of the metal base are valid.
6
0 °C and 1,4-difluorobenzene after 96 h at 80 °C. Similarly,
the reaction of perfluorotoluene and 5 equiv of Et SiH for
EXPERIMENTAL SECTION
3
■
4
days at 80 °C in the presence of 5 mol % of 1 leads to the
General Considerations. All reactions and subsequent manipu-
lations involving organometallic reagents were performed under a
nitrogen or argon atmosphere using standard Schlenk techniques as
selective formation of 1-(CF )-2,3,5,6-C F H. Conceivable
3
6 4
reaction sequences for the HDF at nickel are (i) the activation
of the silyl hydride and subsequent reaction with the
fluoroarene (“silane route”) and (ii) C−F activation of the
fluoroarene and subsequent reaction of the resulting nickel
fluoride with the silane (“fluoride route”). Stoichiometric transfor-
1
1
reported previously. Elemental analyses were performed in the
microanalytical laboratory of the authors' department. EI mass spectra
were recorded on a Varian MAT 3830 instrument (70 eV). NMR
spectra were recorded on a Bruker AV 400 at 333 K or a Bruker
1
3
i
Avance 200 at 296 K unless otherwise stated. C NMR spectra are
mations of the complexes cis-[Ni( Pr Im) (H)(SiPh )] and cis-
2
2
3
13
1
i
broad-band proton-decoupled C{ H}. NMR data are listed in parts
[
Ni( Pr Im) (H)(SiMePh )] with hexafluorobenzene at room
2 2 2
1
per million (ppm) and are reported relative to tetramethylsilane ( H
i
temperature lead to the formation of trans-[Ni( Pr Im) (F)-
13
19
2
2
and C) and CFCl ( F). Coupling constants are quoted in hertz
i
3
(
C F )] (2) and trans-[Ni( Pr Im) (H)(C F )] (4) with
6 5 2 2 6 5
(Hz). Spectra are referenced internally to residual protio solvent
1
elimination of the corresponding silane or fluorosilane. The re-
resonances ( H, C D H 7.16 ppm) or natural-abundance carbon
6
5
i
13
19
actions of C−F activation products trans-[Ni( Pr Im) (F)(C F )]
resonances ( C, C D , 128.02 ppm). The F NMR spectra were
2
2
6
5
6 6
i
(
2) and trans-[Ni( Pr Im) (F)(4-(CF )C F )] (3) with PhSiH
referenced to external C F at δ −162.9 ppm. Infrared spectra were
2
2
3
6
4
3
6 6
and Ph SiH result in the formation of the hydride complexes
recorded as KBr pellets on a Bruker IFS 28 instrument and are
2
2
−
1
i
7a
i
i
i
reported in cm . [Ni( Pr Im) (F)(C F )] and [Ni( Pr Im) (F)(4-
trans-[Ni( Pr Im) (H)(C F )] (4) and trans-[Ni( Pr Im) (H)-
2
2
6
5
2
2
2
2
6
5
2
2
7
b
(
CF )C F )] were prepared according to literature procedures.
3
6
4
(
4-(CF )C F )] (5), which convert into the compounds trans-
3 6 4
i
i
PhSiH
3
and C F were purchased from ABCR and used without
6 6
[Ni( Pr Im) (F)(2,3,5,6-C F H)] (7), trans-[Ni( Pr Im) (F)(3-
2 2 6 4 2 2
further purification.
General Procedure for the HDF Reactions. A 1.25 mmol
i
(
3
CF )-2,4,5-C F H)] (9a), and trans-[Ni( Pr Im) (F)(2-(CF )-
,4,6-C F H)] (9b), respectively. In the case of the rearrangement
3
6
3
2
2
3
6 3
amount of the silane (Et SiH, 199 μL; Ph SiH, 326 mg) was added to
3
3
i
of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5) the intermediate
i
2
2
3
6
4
a suspension of 10 mg (0.013 mmol) of [Ni ( Pr Im) (COD)] (1)
and 0.25 mmol of perfluoroarene (C F , 29 μL; C F , 35 μL) in 3 mL
6 6 7 8
2 2 4
i
2
[Ni( Pr Im) (η -C,C-(CF )C F H)] (8) was detected in solution.
2
2
3
6
4
This intermediate is prone to substitution of the arene ligand with
perfluorotoluene under the conditions of HDF catalysis to give the
of benzene. The reaction mixtures were stirred for several days at 60 or
19
80 °C. The products were analyzed by F NMR spectroscopy. The
identification of the compounds was confirmed by comparison of the
data with those of commercial samples.
i
C−F activation product trans-[Ni(Pr Im) (F)(4-(CF )C F )] (3),
2
2
3
6 4
2
presumably via another intermediate with η -C,C-coordinated
i
i
2
Synthesis of trans-[Ni( Pr Im) (H)(C F )] (4). PhSiH (65.0 μL,
2
2
6
5
3
perfluorotoluene: i.e., [Ni( Pr Im) (η -C,C-(CF )C F )]. All these
2
2
3
6
5
i
0
.50 mmol) was added to a solution of trans-[Ni( Pr Im) (F)(C F )]
2 2 6 5
experimental findings point to a mechanism for the catalytic HDF
(
2; 275 mg, 0.50 mmol) in 10 mL of toluene, and the mixture was
i
by [Ni( Pr Im) ] along the “fluoride route”, which involves C−F
2
2
stirred at room temperature for 2 h. The solution was filtered over a
pad of Celite, all volatiles of the filtrate were removed in vacuo, and
the remaining solid was dissolved in 15 mL of pentane. The product
was crystallized at −40 °C, filtered off, and dried in vacuo to give
60.0 mg (0.11 mmol, 22%) of pale yellow crystals. Anal. Calcd (found)
for C H F N Ni [530.20 g/mol]: C, 54.26 (54.34); H, 6.26 (6.21);
activation of the polyfluoroarene, H/F exchange of the resulting
nickel fluoride ligand, reductive elimination of the polyfluoroaryl
nickel hydride to an intermediate with an η -C,C-coordinated
2
arene ligand, and subsequent ligand exchange with the higher
fluorinated polyfluoroarene, which is the precursor for the C−F
activation step to close the catalytic cycle (see Scheme 5).
Furthermore, DFT calculations performed on the conversion
24 33
5
4
+
N, 10.55 (10.47). EI/MS m/z (%): 530 (85) [M] , 510 (93) [M −
HF] , 361 (90) [Ni( Pr Im) ] . IR (KBr [cm ]): 527 (w), 577 (w),
+
i
+
−1
2
2
i
611 (vw), 628 (vw), 673 (m), 692 (s), 706 (m), 749 (m), 809 (vw),
of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5) into the two
2
2
3
6 4
8
1
81 (w), 939 (s), 999 (m), 1037 (s), 1056 (m), 1081 (w), 1134 (m),
170 (vw), 1214 (s), 1280 (vw), 1302 (s), 1368 (s), 1431 (vs), 1488
i
products trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a)
and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b) along
a reductive elimination/oxidative addition pathway via η -C,H-
and η -C,F-σ-complexes as transition states are in disagreement
2
2
3
6 3
i
2
2
3
6
3
(s), 1601 (w), 1627 (w), 1808 (s, br, νNi−H), 2875 (m), 2939 (m),
2
2
1
979 (s), 3145 (w), 3181 (w). H NMR (400 MHz, C D , 333 K):
6 6
2
3
δ −13.99 (m, 1 H, Ni−H), 1.21 (d, 24 H, J = 6.8 Hz, CH ), 5.87
HH
3
3 i 13 1
with the data obtained experimentally. The rate and product
(sept, 4H, JHH = 6.8 Hz, PrCH), 6.37 (s, 4H, NCHCHN). C{ H}
NMR (100 MHz, C , 333 K): δ 23.49 (CH ), 52.55 (iPr CH),
116.32 (NCCN), 187.41 (NCN). F NMR (376.4 MHz, C D , 333 K):
contribution determining transition states are those of the C−F
6
D
6
3
19
2
activation step. Starting from the η -C,C intermediate [Ni-
6
6
i
2
δ −114.2 (m, 2 F, aryl F ), −164.8 (m, 3 F, aryl Fm+p).
o
(
Pr Im) (η -C,C-(CF )C F H)] (8), we calculate a low-lying
2 2 3 6 4
i
2
Synthesis of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5). PhSiH
65.0 μL, 0.50 mmol) was added to a solution of trans-[Ni-
2 2 3 6 4 3
η -C,F transition state which leads to the minor isomer trans-
(
(
i
[
Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b), if we assume a
i
2
2
3
6 3
Pr Im) (F)(4-(CF )C F )] (3; 300 mg, 0.50 mmol) in 10 mL of
2
2
3
6 4
concerted mechanism. The major isomer observed experimen-
toluene and stirred at room temperature for 2 h. All volatiles were
removed in vacuo, and the remaining solid was dissolved in 15 mL of
pentane and filtered over a pad of Celite. The product was crystallized at
−40 °C, filtered off, and dried in vacuo to give 50.0 mg (0.09 mmol, 18%)
i
tally is trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a), the
2
2
3
6 3
product in which C−F activation takes place at the position
ortho to the hydrogen substituent. The methoxydefluorination
1
381
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
i
of pale yellow crystals. Anal. Calcd (found) for C H F N Ni [580.19
was added to a solution of [Ni (Pr Im) (COD)] (1; 210 mg, 0.25 mmol)
2 2 4
25
33
7
4
g/mol]: C, 51.66 (51.96); H, 5.72 (6.02); N, 9.64 (8.70). EI/MS m/z
in 15 mL of toluene and stirred at 60 °C for 64 h. All volatiles were re-
moved in vacuo, and the remaining solid was suspended in 15 mL of
hexane. The product was filtered off and dried in vacuo to give 120 mg
+
+
i
+
(
%): 580 (25) [M] , 560 (34) [M − HF] , 361 (93) [Ni( Pr Im) ] .
2
2
1
H NMR (400 MHz, C D , 333 K): δ −13,68 (m, 1 H, Ni-H), 1.20 (d,
2
6
6
3
3
i
4 H, J = 6.8 Hz, CH ), 5.84 (sept, 4H, J = 6.8 Hz, PrCH),
.35 (s, 4H, NCHCHN). C NMR (100 MHz, C D , 333 K): δ 23.5
Pr CH ), 52.6 ( Pr CH), 116.5 (NCCN), 186.3 (NCN). F NMR
(0.21 mmol, 42%) of a yellow powder.
HH
3
HH
1
3
i
H)] (9a). 1H NMR (200
), 6.21 (s, 4 H, NCH-
6
trans-[Ni( Pr
2
Im)
2
(F)(3-(CF
3
)-2,4,5-C
6
F
3
6
6
i
i
19
(
MHz, C
6
D
6
, 296 K): δ 1.24 (bs, 24 H, CH
3
3
4
3
i
(
−
376.4 MHz, C D , 333 K): δ −55.2 (t, 3 F, J = 21.2 Hz, CF3),
CHN), 6.40 (sept, 4 H, JHH = 6.8 Hz, PrCH), 7.49 (bt, 1 H, aryl H).
6
6
FF
19
4
114.1 (m, 2 F, aryl F ), −145.8 (m, 2 F, aryl F ).
F NMR (188.3 MHz, C
6
D
6
, 296 K): δ −56.2 (dd, 3 F, JFF
=
=
o
m
i
4
5
4
Rearrangement of trans-[Ni( Pr Im) (H)(C F )] (4) to trans-
21.6 Hz, J = 24.6 Hz, CF ), −92.7 (ddq, 1 F, J = 16.9 Hz, J
2
2
6
5
FF
3
FF
FF
i
4
3
[
Ni( Pr Im) (F)(2,3,5,6-C F H)] (7). A 5.00 mg amount (0.01 mmol)
4.5 Hz, J = 21.6 Hz, aryl F ), −145.6 (dd, 1 F, J = 20.3 Hz,
2
2
6
4
FF
o
FF
i
5
4
3
of the hydride complex trans-[Ni( Pr Im) (H)(C F )] (4) was
JFF = 16.1 Hz, aryl F ), −147.7 (ddq, 1 F, J = 4.0 Hz, J
=
FF
2
2
6
5
m
FF
4
dissolved in 0.70 mL of C D , heated to 60 °C. The reaction, which
6
6
20.7 Hz, J = 24.7 Hz, aryl F ), −364.8 (s, 1 F, Ni−F).
FF
p
1
19
i
1
was completed after 90 min, was monitored using H and F NMR
spectroscopy. H NMR (400 MHz, C D , 333 K): δ 1.30 (bs, 24 H,
trans-[Ni(Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b). H NMR (200
2
2
3
6 3
1
6
6
MHz, C D , 296 K): δ 1.24 (bs, 24 H, CH ), 6.17 (s, 4H, NCHCHN),
6
6
3
3
i
19
CH ), 6.23−6.29 (m, 1 H, aryl H), 6.31 (s, 4H, NCHCHN), 6.56
3
6.46 (sept, 4H, J = 6.8 Hz, PrCH), 6.67 (m, 1 H, aryl H).
F
HH
3
i
19
4
(
sept, 4H, J = 6.8 Hz, PrCH). F NMR (376.4 MHz, C D , 333
H
H
6
6
NMR (188.3 MHz, C D , 296 K): δ −55.7 (d, 3 F, J = 18.8 Hz,
6
6
FF
3
5
3 4
K): δ −117.8 (m, 2 F, aryl F ), −143.5 (dd, 2 F, J = 16.0 Hz, J
=
o
FF
FF
CF ), −79.7 (m, 1 F, aryl F ), −144.3 (dd, 1 F, J = 20.1 Hz, J
=
3
o
FF
FF
3
5
1
4.0 Hz, aryl F ), −374.2 (s, 1 F, Ni−F).
m
3.2 Hz, aryl F ), −146.1 (ddq, 1 F, J = 19.7 Hz, J = 15.6 Hz,
p
FF
FF
i
4
Rearrangement of trans-[Ni( Pr Im) (H)(4-(CF )C F )] (5) to
2
2
3
6
4
J
= 18.2 Hz, aryl F ), −372.1 (s, 1 F, Ni-F).
FF
m
i
trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a) and trans-[Ni-
i
2
2
3
6
3
Crystal Structure Determination of trans-[Ni( Pr Im) (H)(4-
2 2
i
(
Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b). A 5.00 mg amount (0.01
−1
2
2
3
6
3
(CF )C F )] (5). Crystal data: C H F N Ni, M = 583.26 g mol ,
3 6 4 25 35 7 4 r
3
i
mmol) of the hydride complex trans-[Ni( Pr Im) (H)(4-(CF )C F )]
2
2
3
6
4
yellow prism, size 0.30 × 0.20 × 0.15 mm , monoclinic, space group
C2/m, a = 20.229(3) Å, b = 14.609(2) Å, c = 11.919(2) Å, β =
(
5) was dissolved in 0.70 mL of C D , heated to 60 °C. The reaction,
6 6
1 19
which was completed after 24 h, was monitored using H and
F
3
−3
1
19.72(3)°, V = 3059.0(12) Å , T = 203 K, Z = 4, ρ
= 1.266 g cm ,
calcd
NMR spectroscopy. After 24 h we obtained two sets of signals in a
−1
μ (Mo Kα) = 0.695 cm , F(000) = 1216, 12 366 reflections in h (−25
ratio of approximately 80:20, as judged by 19F NMR spectroscopy. The
to +16), k (−18 to +16), l (−13 to +14), measured in the range
isomer with the hydrogen atom adjacent to the activated C−F bond
3
.44° < θ < 27.77°, completeness θ = 98.2%, 3688 independent
max
i
and the CF group at the 5-position, trans-[Ni( Pr Im) (F)(3-(CF )-
3
2
2
3
reflections, Rint = 0.1004, 2624 reflections with F > 2σ(F ), 208
o o
2
,4,5-C F H)] (9a), is the major reaction product.
6 3
parameters, 0 restraints, R1obs = 0.0706, wR2obs = 0.1642, R1all =
trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a). 1H NMR (400
i
2
2
3
6
3
0.1056, wR2 = 0.1861, GOF = 1.097, largest difference peak and hole
all
MHz, C D , 333 K): δ 1.26 (bd, 24 H, CH ), 6.29 (s, 4 H,
−3
6
6
3
0.403/−0.417 e Å .
3
i
NCHCHN), 6.38 (sept, 4 H, J = 6.8 Hz, PrCH), 7.43 (bt, 1 H, aryl
HH
Crystals were immersed in a film of perfluorpolyether oil on a glass
fiber and transferred to a STOE-IPDS 1 image plate diffractometer
(Mo Kα radiation) equipped with a FT AirJet low-temperature device.
Data were collected at 200 K; equivalent reflections were merged, and
the images were processed with the STOE IPDS software package.
Corrections for Lorentz−polarization effects and adsorption were
performed, and the structures were solved by direct methods.
Subsequent difference Fourier syntheses revealed the positions of all
non-hydrogen atoms, and hydrogen atoms were included in all
calculated positions. Extinction corrections were applied as required.
Crystallographic calculations were performed using SHELXS-97 and
H). 19F NMR (376.4 MHz, C D , 333 K): δ −56.3 (dd, 3 F, J
4
=
=
=
6
6
FF
4
5
4
2
3
1.4 Hz, J = 24.7 Hz, CF ), −92.5 (ddq, 1 F, J = 16.6 Hz, J
FF
3
FF
FF
4
3
5
.4 Hz, J = 21.4 Hz, aryl F ), −146.0 (dd, 1 F, J = 20.3 Hz, J
FF
o
FF
FF
4
3
1
6.1 Hz, aryl F ), −147.7 (ddq, 1 F, J = 3.6 Hz, J = 20.4 Hz,
m
FF
FF
4
J
= 24.4 Hz, aryl F ), −368.0 (s, 1 F, Ni−F).
FF
p
i
trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b). Byproduct with the
2
2
3
6 3
1
CF group at the 2-position and the hydrogen at the 5-position. H
3
NMR (400 MHz, C D , 333 K): δ 1.20 (bd, 24 H, CH ), 6.34 (s, 4H,
6
6
3
3
i
NCHCHN), 6.45 (sept, 4H, J = 6.8 Hz, PrCH), 6.65 (m, 1 H, aryl
HH
H). 19F NMR (376.4 MHz, C D , 333 K): δ −56.3 (d, 3 F, J = 18.8
4
6
6
FF
5
4
1
2
Hz, CF ), −79.7 (dd, 1 F, J = 15.6 Hz, J = 3.6 Hz, aryl F ), −144.5
3
FF
FF
o
SHELXL-97.
3
4
3
(
2
dd, 1 F, J = 19.9 Hz, J = 3.5 Hz, aryl F ), −145.8 (ddq, 1 F, J
=
FF
FF
p
FF
Computational Details. All calculations were carried out with the
5
4
0.0 Hz, J = 15.3 Hz, J = 18.8 Hz, aryl F ), −378.8 (s, 1 F, Ni-F).
FF
FF
m
DFT implementation of the TURBOMOLE program package, Version
i 2
1
3
14
[
Ni( Pr Im) (η -C,C-(CF )C F H)] (8). After approximately 1 h of
2 2 3 6 4
5.7. For the DFT calculations we used the BP86 functional, SV(P)
1
5−17
the reaction the following resonances were detected. These are attri-
basis sets, and the RI-J approximation.
The equilibrium structures
i
2
1
buted to the intermediate [Ni( Pr Im) (η -C,C-(CF )C F H)] (8). H
2
2
3
6
4
and transition states of the complexes were optimized at the RIDFT
level using a SV(P) basis. Analytic second derivatives were calculated
with the program AOFORCE using the RI-J approximation. All
energies given are ZPE corrected.
NMR (400 MHz, C D , 333 K): δ 1.07 (bs, 24 H, CH ), 5.06 (bsept,
6
6
3
3
i
4
H, J = 6.4 Hz, PrCH), 5.56 (m, 1H, aryl H) 6.38 (bs, 4H,
HH
1
9
4
NCHCHN). F NMR (376.4 MHz, C D , 333 K): δ −49.6 (t, 3 F, J
6
6
FF
=
12.3 Hz, CF ), −142.8 (bs, 2 F, aryl F ), −155.5 (bs, 2 F, aryl F ).
3
o
m
The method employed here for the calculations has been chosen to
give a qualitative understanding of the system. Truncation of the
i 2
Synthesis of [Ni( Pr Im) (η -C,C-(CF )C F H)] (8). 1-(Trifluoro-
2
2
3
6 4
i
methyl)-2,3,5,6-tetrafluorobenzene (68.0 μL, 0.50 mmol) was added
complexes under consideration, i.e. substitution of the NHC Pr
i
to a solution of [Ni ( Pr Im) (COD)] (1; 210 mg, 0.25 mmol) in
2
2
4
groups by hydrogen atoms, led to unreliable results, since hydrogen
bonds between the N−H groups and the fluorine substituents override
the steric and electronic effects in the complexes. Although the SV(P)
basis set is possibly a little inflexible and the BP86 functional tends to
underestimates barriers, a recent benchmark study by Bickelhaupt et
15 mL of toluene and stirred at room temperature for 75 min. All
volatiles were removed in vacuo, and the remaining solid was
suspended in 10 mL of hexane. The product was filtered off and dried
in vacuo to give 140 mg (0.24 mmol, 48%) of a yellow, pyrophoric
powder. Anal. Calcd (found) for C H F N Ni [580.19 g/mol]: C,
1
8
2
5
33
7
4
al. on C−F activation at Pd(0) shows that BP86 correctly reproduces
1
5
1.66 (51.72); H, 5.72 (6.11); N, 9.64 (9.51). H NMR (200 MHz,
all qualitative trends for the oxidative addition of C−F to Pd(0).
i
C D , 296 K): δ 1.04 (bs, 24 H, CH ), 5.04 (bsept, 4H, PrCH), 5.62
6
6
3
1
9
(
m, 1H, aryl H), 6.31 (s, 4H, NCHCHN). F NMR (188.3 MHz,
C D , 296 K): δ −49.3 (t, 3 F, J = 11.9 Hz, CF ), −142.6 (bs, 2 F,
4
ASSOCIATED CONTENT
6
6
FF
3
■
aryl F ), −155.6 (bs, 2 F, aryl F ).
o
m
S
*
Supporting Information
i
Synthesis of trans-[Ni( Pr Im) (F)(3-(CF )-2,4,5-C F H)] (9a)
2
2
3
6 3
i
A CIF file giving X-ray crystal data and tables giving compu-
tational details. This material is available free of charge via the
Internet at http://pubs.acs.org.
and trans-[Ni( Pr Im) (F)(2-(CF )-3,4,6-C F H)] (9b) Start-
2
2
3
6 3
i
ing from [Ni ( Pr Im) (COD)] (1) and 1-(CF )-2,3,5,6-C F H.
2
2
4
3
6 4
1-(Trifluoromethyl)-2,3,5,6-tetrafluorobenzene (68.0 μL, 0.50 mmol)
1
382
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383

Organometallics
Article
Mendeleev Commun. 2008, 18, 211. (d) Prikhod’ko, S. A.; Adonin, N. Y.;
Parmon, V. N. Russ. Chem. Bull. 2009, 58, 2304.
AUTHOR INFORMATION
■
Corresponding Author
E-mail: u.radius@uni-wuerzburg.de. Tel: (Int) +49-931-31-
0302.
(7) (a) Schaub, T.; Radius, U. Chem. Eur. J. 2005, 11, 5024.
*
(b) Schaub, T.; Backes, M.; Radius, U. J. Am. Chem. Soc. 2006, 128,
8
15964. (c) Schaub, T.; Fischer, P.; Steffen, A.; Braun, T.; Radius, U.;
Mix, A. J. Am. Chem. Soc. 2008, 130, 9304. (d) Schaub, T.; Backes, M.;
Radius, U. Eur. J. Inorg. Chem. 2008, 2680. (e) Schaub, T.; Fischer, P.;
Meins, T.; Radius, U. Eur. J. Inorg. Chem. 2011, 3122.
ACKNOWLEDGMENTS
■
This work was supported by the University Karlsruhe (TH),
the Julius-Maximilians-Universitat Wurzburg, and the Deutsche
Forschungsgemeinschaft (DFG).
(
8) (a) Schaub, T.; Backes, M.; Radius, U. Organometallics 2006, 25,
196. (b) Schaub, T.; Radius, U. Z. Anorg. Allg. Chem. 2006, 632, 981.
(c) Schaub, T.; Radius, U. Z. Anorg. Allg. Chem. 2007, 633, 2168.
̈
̈
4
(
(
(
(
(
̈
d) Schaub, T.; Doring, C.; Radius, U. Dalton Trans. 2007, 1993.
e) Schaub, T.; Backes, M.; Radius, U. Chem. Commun. 2007, 2037.
f) Radius, U.; Bickelhaupt, F. M. Organometallics 2008, 27, 3410.
g) Radius, U.; Bickelhaupt, F. M. Coord. Chem. Rev. 2009, 253, 678.
h) Schaub, T.; Backes, M.; Plietzsch, O.; Radius, U. Dalton Trans.
REFERENCES
■
(
1) (a) Mu
̈
ller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881.
(
b) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc.
Rev. 2008, 37, 320. (c) O’Hagan, D. J. Fluorine Chem. 2010, 131, 1071.
2) For recent reviews see: (a) Perutz, R. N.; Braun, T. In
2
009, 7071. (i) Zell, T.; Schaub, T.; Radacki, K.; Radius, U. Dalton
(
Trans. 2011, 40, 1852. (j) Zell, T.; Feierabend, M.; Halfter, B.; Radius,
U. J. Organomet. Chem. 2011, 696, 1380.
Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos,
M. P., Eds.; Elsevier, Oxford, U.K., 2007; Vol. 1, p 725. (b) Amii, H.;
Uneyama, K. Chem. Rev. 2009, 109, 2119. (c) Meier, G.; Braun, T.
Angew. Chem., Int. Ed. 2009, 48, 1546. (d) Hughes, R. P. Eur. J. Inorg.
Chem. 2009, 4591. (e) Sun, A. D.; Love, J. A. Dalton Trans. 2010, 39,
(
(
(
(
9) Atwal, R. K.; Bolton, R. Aust. J. Chem. 1987, 40, 241.
10) Bolton, R.; Dandall, J. P. B J. Fluorine Chem. 1982, 21, 459.
11) Attner, J.; Radius, U. Chem. Eur. J. 2001, 7, 783.
12) (a) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
1
(
0362. (f) Braun, T.; Wehmeier, F. Eur. J. Inorg. Chem. 2011, 613.
g) Clot, E.; Eisenstein, O.; Jasim, N.; MacGregor, S. A.; McGrady,
J. E.; Perutz, R. N. Acc. Chem. Res. 2011, 44, 333.
3) (a) Aizenberg, M.; Milstein, D. Science 1994, 265, 359.
b) Aizenberg, M.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 8674.
4) (a) Kiplinger, J. L.; Richmond, T. G. Chem. Commun. 1996, 1115.
b) Kiplinger, J. L.; Richmond, T. G. J. Am. Chem. Soc. 1996, 118,
805. (c) Vela, J.; Smith, J. M.; Yu, Y.; Ketterer, N. A.; Flaschenriem,
C. J.; Lachicotte, R. J.; Holland, P. L. J. Am. Chem. Soc. 2005, 127,
857. (d) Jager-Fiedler, U.; Klahn, M.; Arndt, P.; Baumann, W.;
Spannenberg, A.; Burlakov, V. V.; Rosenthal, U. J. Mol. Catal. A 2007,
61, 184. (e) Fuchibe, K.; Ohshima, Y.; Mitomi, K.; Akiyama, T.
Solution; Universitat
G. M. SHELXL-97, Program for Crystal Structure Refinement; Universitat
̈
Go
̈
̈
ttingen, Germany, 1997. (b) Sheldrick,
̈
Go
13) (a) Ahlrichs, R.; Bar
Phys. Lett. 1989, 162, 165. (b) Has
̈
̈
ttingen, Germany, 1997.
(
(
̈
, M.; Haser, M.; Horn, H.; Ko
̈
̈
lmel, C. Chem.
(
(
̈
er, M.; Ahlrichs, R. J. Comput. Chem.
989, 10, 104. (c) von Arnim, M.; Ahlrichs, R. J. Comput. Chem. 1998,
9, 1746.
14) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Perdew, J. P.
Phys. Rev. B 1986, 33, 8822. (c) Erratum: Perdew, J. P. Phys. Rev. B
986, 34, 7406.
15) (a) Treutler, O.; Ahlrichs, R. J. Chem. Phys. 1995, 102, 346.
(
1
1
1
(
7
̈
1
(
2
̈
̈
b) Eichkorn, K.; Treutler, O.; Ohm, O.; Haser, M.; Ahlrichs, R. Chem.
(
J. Fluorine Chem. 2007, 128, 1158. (f) Braun, T.; Noveski, D.; Ahijado,
M.; Wehmeier, F. Dalton Trans. 2010, 39, 7513. (g) Douvris, C.;
Ozerov, O. V. Science 2008, 321, 1188. (h) Reade, S. P.; Mahon, M. F.;
Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 1847. (j) Douvris, C.;
Nagaraja, C. M.; Chen, C.-H.; Foxman, B. M.; Ozerov, O. V. J. Am.
Chem. Soc. 2010, 132, 4946. (k) Kuhnel, M. F.; Lentz, D. Angew.
̈
Chem., Int. Ed. 2010, 49, 2933. (k) Breyer, D.; Braun, T.; Penner, A.
Dalton Trans. 2010, 39, 7513. (l) Panetier, J. A.; MacGregor, S. A.;
Whittlesey, M. K. Angew. Chem., Int. Ed. 2011, 50, 2783.
Phys. Lett. 1995, 240, 283. (c) Eichkorn, K.; Weigend, F.; Treutler, O.;
Ahlrichs, R. Theor. Chem. Acc. 1997, 97, 119.
̈
(
16) (a) Eichkorn, K.; Treutler, O.; Ohm, H.; Has
Chem. Phys. Lett. 1995, 242, 652. (b) Haase, F.; Ahlrichs, R. J. Comput.
Chem. 1993, 14, 907. (c) Weigand, F.; Haser, M. Theor. Chem. Acc.
997, 97, 331. (d) Weigand, F.; Haser, M.; Patzelt, H.; Ahlrichs, R.
Chem. Phys. Lett. 1998, 294, 143.
̈
er, M.; Ahlrichs, R.
̈
1
̈
(
(
17) Schaf
̈
er, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571.
18) de Jong, G. T.; Bickelhaupt, F. M. J. Phys. Chem. A 2005, 109,
(
(
1
5) (a) Fahey, D. R.; Mahan, J. E. J. Am. Chem. Soc. 1977, 99, 2501.
b) Cronin, L.; Higgitt, C. L.; Karch, R.; Perutz, R. N. Organometallics
997, 16, 4920. (c) Braun, T.; Parsons, S.; Perutz, R. N.; Voith, M.
9
685.
Organometallics 1999, 18, 1710. (d) Braun, T.; Foxon, S. P.; Perutz, R. N.;
Walton, P. H. Angew. Chem., Int. Ed. 1999, 38, 3326. (e) Braun, T.;
Cronin, L.; Higgitt, C. L.; McGrady, J. E.; Perutz, R. N.; Reinhold, M.
New J. Chem. 2001, 25, 19. (f) Sladek, M. I.; Braun, T.; Neumann, B.;
Stammler, H.-G. J. Chem. Soc., Dalton Trans. 2002, 297. (g) Reinhold,
M.; McGrady, J. E.; Perutz, R. N. J. Am. Chem. Soc. 2004, 126, 5268.
(
h) Steffen, A.; Sladek, M. I.; Braun, T.; Neumann, B.; Stammler,
H.-G. Organometallics 2005, 24, 4057. (i) Burling, S.; Elliott, P. I. P.;
Jasim, N. A.; Lindup, R. J.; McKenna, J.; Perutz, R. N.; Archibald, S. J.;
Whitwood, A. C. Dalton Trans. 2005, 3686. (j) Yoshikai, N.; Mashima,
H.; Nakamura, E. J. Am. Chem. Soc. 2005, 127, 17978. (k) Saeki, T.;
Takashima, Y.; Tamao, K. Synlett 2005, 1771. (l) Johnson, S. A.; Huff,
C. W.; Mustafa, F.; Saliba, M. J. Am. Chem. Soc. 2008, 130, 17278.
(
m) Doster, M. E.; Johnson, S. A. Angew. Chem., Int. Ed. 2009, 48,
2185. (n) Johnson, S. A.; Taylor, E. T.; Cruise, S. J. Organometallics
2
009, 28, 3842. (o) Nova, A.; Reinhold, M.; Perutz, R. N.; Macgregor,
S. A.; McGrady, J. E. Organometallics 2010, 29, 1824. (p) Doster, M.
E.; Hatnean, J. A.; Jeftic, T.; Modi, S.; Johnson, S. A. J. Am. Chem. Soc.
2
010, 132, 11923. (q) Johnson, S. A.; Mroz, N. M.; Valdizon, R.;
Murray, S. Organometallics 2011, 30, 441.
6) (a) Adonin, N. Y.; Starichenko, V. F. J. Fluorine Chem. 2000, 101,
(
65. (b) Adonin, N. Y.; Starichenko, V. F. J. Fluorine Chem. 2000, 101,
65. (c) Prikhod’ko, S. A.; Adonin, N. Y.; Babushkin, D. E.; Parmon, V. N.
1
383
dx.doi.org/10.1021/om2009815 | Organometallics 2012, 31, 1374−1383