Nickel fluoro complexes as intermediates in catalytic cross-coupling reactions

Article abstract of DOI:10.1016/j.jfluchem.2012.06.025

The C-F activation of pentafluoropyridine or 2,3,5,6-tetrafluoropyridine at [Ni(COD)₂] (COD = 1,5-cyclooctadiene) in the presence of ⁱPr₂PCH₂CH₂OMe resulted in the formation of the nickel(II) fluoro bisphosphine complexes trans-[Ni(F)(2-C ₅NF₄){κ¹-(P)-(ⁱPr ₂PCH₂CH₂OMe)₂}] (1), trans-[Ni(F)(4-C₅NF₄){κ¹-(P)-( ⁱPr₂PCH₂CH₂OMe)₂}] (2) and trans-[Ni(F)(2-C₅NHF₃){κ¹-(P)-( ⁱPr₂PCH₂CH₂OMe)₂}] (3). The employment of ⁱPr₂PCH₂CH ₂NMe₂ gave the nickel(II) fluoro monophosphine complexes [Ni(F)(2-C₅NF₄){κ²-(P,N)- ⁱPr₂PCH₂CH₂NMe₂}] (4), [Ni(F)(4-C₅NF₄){κ²-(P,N)- ⁱPr₂PCH₂CH₂NMe₂}] (5) and [Ni(F)(2-C₅NHF₃){κ²-(P,N)- ⁱPr₂PCH₂CH₂NMe₂}] (6) instead, in which the amino moiety coordinates at the metal center. In catalytic experiments pentafluoropyridine could be converted into 3,5,6- trifluorodiphenylpyridine (7) and 3,5-difluoro-2,4,6-triphenylpyridine (8) in the presence of PhB(OH)₂ and 5 mol% of a mixture of 1 and 2 (ratio 8:1) or 5 and 4 (ratio 2:1) as catalysts. Additionally 2,3,5,6- tetrafluoropyridine could be converted catalytically into 3,5-difluoro-2,6- diarylpyridines (9: aryl = Ph; 10: aryl = Tol; 11: aryl = 4-(F ₃C)C₆H₅; 12: aryl = 4-MeOC₆H ₅) in the presence of boronic acids when 5 mol% of 3 was employed as catalyst.

Full text of DOI:10.1016/j.jfluchem.2012.06.025

Journal of Fluorine Chemistry 143 (2012) 263–271
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Nickel fluoro complexes as intermediates in catalytic cross-coupling reactions
*
David Breyer, Josefine Berger, Thomas Braun , Stefan Mebs
Humboldt-Universita¨t zu Berlin, Department of Chemistry, Brook-Taylor-Str. 2, 12489 Berlin, Germany
A R T I C L E I N F O
A B S T R A C T
Article history:
The C–F activation of pentafluoropyridine or 2,3,5,6-tetrafluoropyridine at [Ni(COD)2] (COD = 1,5-
i
Received 16 April 2012
Received in revised form 23 June 2012
Accepted 27 June 2012
Available online 11 July 2012
cyclooctadiene) in the presence of Pr2PCH2CH2OMe resulted in the formation of the nickel(II) fluoro
bisphosphine complexes trans-[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (1), trans-[Ni(F)(4-
C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (2) and trans-[Ni(F)(2-C5NHF3){k1-(P)-(iPr2PCH2CH2OMe)2}] (3).
i
The employment of Pr2PCH2CH2NMe2 gave the nickel(II) fluoro monophosphine complexes [Ni(F)(2-
C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (4), [Ni(F)(4-C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (5) and [Ni(F)(2-
C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (6) instead, in which the amino moiety coordinates at the metal
center. In catalytic experiments pentafluoropyridine could be converted into 3,5,6-trifluorodiphenyl-
pyridine (7) and 3,5-difluoro-2,4,6-triphenylpyridine (8) in the presence of PhB(OH)2 and 5 mol% of a
mixture of 1 and 2 (ratio 8:1) or 5 and 4 (ratio 2:1) as catalysts. Additionally 2,3,5,6-tetrafluoropyridine
could be converted catalytically into 3,5-difluoro-2,6-diarylpyridines (9: aryl = Ph; 10: aryl = Tol; 11:
aryl = 4-(F3C)C6H5; 12: aryl = 4-MeOC6H5) in the presence of boronic acids when 5 mol% of 3 was
employed as catalyst.
This article is dedicated to David O’Hagan in
honor of his receipt of the 2012 ACS Award
for Creative Work in Fluorine Chemistry.
Keywords:
C–F activation
Nickel fluoro complexes
Cross coupling reactions
Fluorinated building blocks
ß 2012 Elsevier B.V. All rights reserved.
1. Introduction
There is some precedent in the literature which suggests that
complexes bearing hemilabile coordinating ligands can catalyse
Fluorinated building blocks are of considerable significance for
a variety of functional compounds such as for example pharma-
ceuticals, agrochemicals or advanced materials [1]. A possible
strategy to access unique fluorinated moieties is represented by a
transition-metal mediated derivatization of easily available highly
fluorinated precursors. Such reaction pathways can involve C–F
activation steps, e.g. at palladium, nickel or rhodium [2–17]. Thus,
hydrodefluorination or cross coupling reactions can provide
fluorinated building blocks, which are often not accessible
otherwise [3–31]. However, catalytic C–F bond functionalization
reactions of highly fluorinated aromatic precursors via cross
coupling reactions are still rare [4,14,17,23–25,32–47]. Radius
et al. reported an initial and exceptional example of a nickel-
mediated Suzuki–Miyaura cross coupling reaction of perfluoroto-
luene with aryl boronic acids on using a nickel(II) carbene complex
as catalyst [25]. Sandford et al. demonstrated that [Pd(PPh3)4]
catalyses the derivatization of the electron-poor polyfluoronitro-
benzene with aryl boronic acids and esters [17]. In a recent
cross-coupling reactions in a more efficient way than related
monodentate counterparts [48]. Thus, Milstein et al. compared the
ligand properties of the hemilabile coordinating phosphine di-tert-
butyl(2,6-dimethoxybenzyl)phosphine (dmobp) with these of di-
tert-butyl-(2,4,6-trimethylbenzyl)phosphine (tmbp) [49]. They
studied the catalytic activity of [Pd(dmobp)2] and [Pd(tmbp)2]
in Suzuki–Miyaura coupling reactions of arylchlorides and found
that [Pd(dmobp)2] is much more effective than [Pd(tmbp)2]. Also
Stradiotto et al. demonstrated that [Pd(cinnamyl)Cl]2/2-(di-tert-
butylphosphino)-N,N-dimethylaniline represents a highly versa-
tile catalytic system for the coupling of aryl chlorides with amines.
In contrast the use of di-tert-butyl-(2-isopropylphenyl)phosphine,
which does not bear any hemilabile coordinating moiety, resulted
in much lower yields [50]. We recently reported that trans-
[Pd(F)(4-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] catalyses the hydro-
defluorination and cross-coupling reaction of pentafluoropyridine
to give 2,3,5,6-tetrafluoropyridine or 4-phenyltetrafluoropyridine,
respectively [51].
example, Love et al. described the application of [(Me)2Pt(
SMe2)2]2 or [Ni(COD)2]/PPh3 as precatalysts for the functionaliza-
tion of polyfluorinated arylimines on using boronic acids [39,47].
m
-
In this work we present studies on the C–F oxidative addition
of pentafluoropyridine and 2,3,5,6-tetrafluoropyridine at
[Ni(COD)2] in the presence of the phosphines Pr2PCH2CH2OMe
i
and iPr2PCH2CH2NMe2. Furthermore, we studied the catalytic
activity of the resulting nickel(II) fluoro complexes towards
cross coupling reactions of the fluorinated heterocycles with
boronic acids.
* Corresponding author.
E-mail address: thomas.braun@chemie.hu-berlin.de (T. Braun).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.06.025

264
D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
2. Results
2.1. C–F activation at [Ni(COD)2] in the presence of iPr2PCH2CH2OMe
A reaction of [Ni(COD)2] with an excess of iPr2PCH2CH2OMe and
pentafluoropyridine at room temperature in n-hexane led to a C–F
activation at the 2- and 4-position to yield the nickel fluoro
complexes trans-[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (1)
and trans-[Ni(F)(4-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (2) in a
ratio of 8:1 (Scheme 1). The use of THF instead of n-hexane as a
solvent has no influence of the observed ratio of the products [26].
i
Treatment of [Ni(COD)2] with one equivalent Pr2PCH2CH2OMe
and pentafluoropyridine gives nearly the same ratio of products,
but in considerable lower yields.
The structure which is proposed for 1 is supported by the
31P{1H}, 19F and 1H NMR data. The 31P{1H} NMR spectrum exhibits
2
a doublet at
d
21.7 with a coupling of JPF = 44 Hz between the
phosphorus atoms and the metal-bound fluorine. The 19F NMR
spectrum shows five signals. The signal at
d
À376.2 (2JPF = 44 Hz,
JFF = 8 Hz) is characteristic for the fluoro ligand at the metal center
[6,23,27,28,52–57]. The assignment of 1 as a 2-tetrafluoropyridyl
nickel derivative is based on the presence of four signals of equal
Fig. 1. An ORTEP diagram of 3; ellipsoids are drawn at the 50% probability level;
hydrogen atoms, with the exception of H(3), are omitted for clarity; only one of two
crystallographically independent molecules is shown.
integration at
d
À86.0, À130.6, À151.8 and À174.0 in the 19F NMR
spectrum. The 1H NMR spectrum shows the expected signals for
the metal-bonded phosphines. Complex 2 was identified by its
Compound 3 crystallizes in the space group P 212121. Selected
bond lengths and angles are summarized in Table 1. Complex 3
reveals a distorted square-planar structure at the Ni center, with a
trans configuration of the phosphines as well as of the trifluor-
opyridyl and the fluoro ligands. The angles at Ni vary from
86.34(11)8 to 94.42(15)8. The nickel-fluorine distance in 3 is
31P{1H}, 19F NMR data. The 31P NMR spectrum displays a doublet at
2
d
21.1 with a coupling constant of JPF = 44 Hz. The 19F NMR
spectrum reveals two signals at
d
À91.6 and À109 for the fluorine
atoms bound at the tetrafluoropyridyl ligand and a triplet of
doublets at
fluorine.
d
À372.2 (2JPF = 44 Hz, JFF = 6 Hz) for the metal-bond
˚
1.862(3) A. For comparison, the Ni–F length in trans-[Ni(F)(2-
Addition of iPr2PCH2CH2OMe and 2,3,5,6-tetrafluoropyridine to
[Ni(COD)2] in n-hexane gave the C–F activation product trans-
[Ni(F)(2-C5NHF3){k1-(P)-(iPr2PCH2CH2OMe)2}] (3) after 4 h. Com-
plex 3 was characterized by its 31P{1H} and 19F NMR data. The
presence of four signals in the 19F NMR spectrum is indicative for
C5NHF3)(PEt3)2] is 1.856(2) A, and the one in trans-[Ni(F)(C6F5)(-
˚
˚
PEt3)2] is 1.836(5) A [52].
2.2. C–F activation at [Ni(COD)2] in the presence of
iPr2PCH2CH2NMe2.
the trifluoropyridyl ligand (
d
À91.6, À109.3, À151.9) with the
i
nickel at the ortho position as well as for the metal-bond fluorine (
d
Treatment of [Ni(COD)2] with Pr2PCH2CH2NMe2 and subse-
À372.4). The 31P{1H} NMR spectrum of complex 3 shows a doublet
quent addition of pentafluoropyridine resulted in the formation
2
at
d
21.1 with a coupling constant of JPF = 44 Hz. The molecular
of a yellow precipitate, which consisted of [Ni(F)(2-C5NF4){k2
-
structure of 3 was also confirmed by X-ray crystallography.
Complex 3 was crystallized from n-hexane at 0 8C and the
molecular structure of one of the two crystallographically
independent molecules is depicted in Fig. 1.
(P,N)-iPr2PCH2CH2NMe2}] (4) and [Ni(F)(4-C5NF4){k2-(P,N)-
iPr2PCH2CH2NMe2}] (5) in a ratio of 1:2 (Scheme 2). The two
complexes were identified as nickel fluoro monophosphine
complexes on the basis of doublets (2JPF = 117 Hz) in the 19F
F
F
F
N
F
F
F
F
F
F
F
N
F
F
N
MeO
OMe
MeO
OMe
F
iPr2P Ni PiPr2
+
iPr2P Ni PiPr2
n-hexane
F
1
F
2
- COD
8 : 1
[Ni(COD)2]
+
iPr2PC2H4OMe
F
F
N
H
F
F
H
F
F
F
N
MeO
OMe
iPr2P Ni PiPr2
n-hexane
F
3
- COD
Scheme 1. C–F activation of fluorinated pyridines at [Ni(COD)2]/iPr2PCH2CH2OMe.

D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
265
Table 1
˚
Selected bond lengths (A) and angles (8) in 3 with the estimated standard deviations
in parentheses.
Bond
Length
Bond
Length
Ni(1)–C(1)
Ni(1)–F(1)
Ni(1)–P(1)
Ni(1)–P(2)
N(1)–C(1)
N(1)–C(5)
C(1)–C(2)
1.875 (5)
1.862 (3)
2.2120 (15)
2.2123 (14)
1.352 (6)
1.323 (7)
1.391 (7)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–F(4)
C(2)–F(2)
C(4)–F(3)
1.384 (7)
1.379 (8)
1.374 (8)
1.337 (6)
1.358 (6)
1.352 (6)
Bonds
Angle
Bonds
Angle
C(1)–Ni(1)–P(1)
F(1)–Ni(1)–P(2)
C(1)–Ni(1)–F(1)
P(1)–Ni(1)–P(2)
N(1)–C(1)–Ni(1)
C(2)–C(1)–Ni(1)
94.42 (15)
86.34 (11)
176.3 (2)
171.04 (6)
120.3 (4)
121.8 (4)
C(5)–N(1)–C(1)
N(1)–C(1)–C(2)
C(3)–C(2)–C(1)
C(4)–C(3)–C(2)
C(5)–C(4)–C(3)
N(1)–C(5)–C(4)
119.4 (5)
117.8 (5)
123.9 (5)
115.4 (5)
119.6 (5)
123.9 (5)
NMR spectrum at
indicate a trans position of the fluoro ligands and the phosphine
d
À294.7 and
d
À313.4. The coupling constants
moieties.
(P,N)-iPr2PCH2CH2NMe2}] (5) exhibits two multiplets in the 19F
NMR spectrum at
À99.9 and À123.1 for the tetrafluoropyridyl
ligand with the nickel at the 4-position. The 31P{1H} NMR
spectrum shows a doublet at
61.0 (2JP,F = 117 Hz). The 2-pyridyl
complex 4 was also characterized by its 19F, 31P{1H} NMR data. The
31P{1H} NMR spectrum of 4 exhibits a doublet at
61.0
(2JPF = 117 Hz), whereas the 19F NMR spectrum shows four
The
4-pyridyl
isomer
[Ni(F)(4-C5NF4){k2
-
Fig. 2. An ORTEP diagram of 5; ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity.
d
˚
d
1.892(3) A are in a similar range as the corresponding separations
˚
in [Ni(F)(2-C5NF4)(Cy2PCH2CH2PCy2)] (Ni–F = 1.8473(12) A, Ni–
˚
d
C = 1.917(2) A) [26].
The activation of a fluorinated pyridine at the 2-position was also
found when iPr2PCH2CH2NMe2 and 2,3,5,6-tetrafluoropyridine
were added to a solution of [Ni(COD)2] in n-hexane at room
temperature. After 1 h the formation of the fluoro complex [Ni(F)(2-
C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (6) was observed (Scheme
resonances for the tetrafluoropyridyl ligand at
À150.8 and À172.5.
d
À88.6, À132.6,
The molecular structure of 5 was also confirmed by X-ray
crystallography (Fig. 2 and Table 2). Complex 5 was crystallized by
gas phase diffusion of n-hexane into a saturated THF solution. The
unit cell contains two crystallographically independent molecules.
However, oneof the moieties isa superposition of4 and 5, which will
not be discussed further. The molecular structure of 5 confirms the
expected trans disposition of the fluoro ligand and the phosphorus
atom and reveals a distorted square-planar coordination geometry
at the metal center. The angles about the nickel atom vary from
2), which was characterized by its NMR spectroscopic data. The 19
NMR spectrum shows three signals at
À93.3, À109.8 and À149.9,
which indicate the presence of the trifluoropyridyl ligand with the
F
d
nickel center at the 2-position of the heterocycle. The doublet at
d
À292.2 (2JPF = 120 Hz) results from the metal-bonded fluorine in the
trans position to the phosphorus atom. The 31P{1H} NMR spectrum
exhibits a doublet at
d
À61.4 (2JPF = 120 Hz).
˚
87.53(9)8 to 94.69(8)8. The Ni(1)–F(1) distance of 1.8383(14) A and
Complex 6 was crystallized from gas phase diffusion of n-
the Ni(1)–C(11) distance to the tetrafluoropyridyl ligand of
hexane into a solution of wet THF. The yellow crystals were
F
F
F
N
F
F
F
N
F
F
F
F
N
F
F
F
iPr2P Ni F
NMe2
+
iPr2P Ni F
NMe2
n-hexane
- COD
4
5
1 : 2
[Ni(COD)2]
+
iPr2PC2H4NMe2
F
F
F
N
H
F
F
H
F
F
N
iPr2P Ni F
NMe2
n-hexane
- COD
6
Scheme 2. C–F activation of fluorinated pyridines at [Ni(COD)2]/iPr2PCH2CH2NMe2.

266
D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
Table 2
Table 3
˚
˚
Selected bond lengths (A) and angles (8) in 5 with the estimated standard deviations
Selected bond lengths (A) and angles (8) in 6 with the estimated standard deviations
in parentheses.
in parentheses.
Bond
Length
Bond
Length
Bond
Length
Bond
Length
Ni(1)–C(11)
Ni(1)–F(1)
Ni(1)–N(1)
Ni(1)–P(1)
1.892 (3)
C(12)–F(2)
C(13)–F(3)
C(14)–F(4)
C(15)–F(5)
1.346 (3)
1.347 (4)
1.349 (4)
1.322 (4)
Ni(1)–C(1)
Ni(1)–F(1)
Ni(1)–P(1)
Ni(1)–N(2)
1.348 (6)
1.876 (3)
2.1122 (12)
1.999 (4)
C(2)–F(2)
1.364 (5)
1.8383 (14)
1.992 (2)
C(5)–F(4)
1.353 (5)
F(1)–H(102i)
F(1)–O(1i)
1.7236 (36)
2.6740 (62)
2.1251 (7)
Bonds
Angle
Bonds
Angle
Bonds
Angle
Bonds
Angle
C(11)–Ni(1)–N(1)
F(1)–Ni(1)–P(1)
C(11)–Ni(1)–P(1)
C(11)–Ni(1)–F(1)
N(1)–C(1)–C(2)
C(1)–C(2)–P(1)
176.71 (9)
177.06 (6)
94.69 (8)
87.53 (9)
111.5 (2)
107.76 (17)
C(15)–C(11)–C(12)
C(13)–C(12)–C(11)
N(33)–C(13)–C(12)
N(33)–C(14)–C(15)
C(11)–C(15)–C(14)
C(13)–N(33)–C(14)
113.1 (3)
121.7 (3)
124.7 (3)
124.7 (3)
120.5 (3)
115.2 (3)
C(1)–Ni(1)–P(1)
F(1)–Ni(1)–P(1)
F(1)–Ni(1)–N(2)
C(1)–Ni(1)–N(2)
90.85 (13)
C(4)–C(3)–C(2)
C(3)–C(2)–C(1)
N(1)–C(1)–C(2)
C(5)–N(1)–C(1)
114.9 (4)
124.5 (4)
117.9 (4)
118.7 (4)
91.62 (15)
89.48 (15)
172.1 (2)
formation of 8 was observed (Scheme 3). We did not observe any
reaction of PhB(OH)2 with pentafluoropyridine without adding a
nickel fluoro complex, even in the presence of NEt3. To the best of
our knowledge only 8 is known in the literature [59]. The pyridines
7 and 9 were identified by their mass spectra and 19F NMR
spectroscopic data (Table 5).
suitable for X-ray diffraction analysis (Fig. 3 and Table 3). The unit
cell contains two crystallographically independent molecules that
exhibit only minor structural differences, but both exhibit a
hydrogen bridge to the same water molecule. However, only one
molecule will be discussed. Complex 6 crystallized in the space
group P 21. It exhibits a square-planar structure at Ni with the
fluoro ligand coordinated in the trans position to the phosphorus
atom. The angles about the nickel atom are distorted from an ideal
square-planar geometry and vary from 89.48(15)8 to 91.62(15)8.
Note that the use of Cs2CO3 as base instead of NEt3 afforded the
same products in lower yields for the use of 1 and 2 (ratio 8:1) and
5 and 4 (ratio 2:1) as catalysts. In addition the formation of second
product was observed which we tentatively assign as Cs[(4-
OC5NF4)]. The same compound was formed in an NMR experiment
in a reaction of Cs2CO3 with pentafluoropyridine at 60 8C and was
˚
The nickel fluoro bond in 6 of 1.876(3) A is similar to the
corresponding distances in 3 and 4. The F–O separation F(1)–O(1i)
˚
of 2.6740(62) A indicates that the additional water molecule in the
identified by its 19F NMR spectroscopic data [
(m, 2F), À172.0 (m, 2F)] and its mass spectrum.
d
(THF-d8): À102.6
cell is bound to 6 via a hydrogen bond to the fluoro ligand.
Comparable hydrogen–fluoro interactions have been observed
before for other metal fluoro complexes [20,26,28,53,58].
2.4. Catalytic cross-coupling reactions of 2,3,5,6-tetrafluoropyridine
2.3. Catalytic cross-coupling reactions of pentafluoropyridine
Treatment of 2,3,5,6-tetrafluoropyridine with boronic acids in
the presence of 5 mol% trans-[Ni(F)(2-C5NHF3){k1-(P)-(iPr2PCH2-
CH2OMe)2}] (3) as a catalyst and a base afforded at 60 8C with high
regioselectively 3,5-difluoro-2,6-di(aryl)pyridines (9: aryl = Ph;
10: aryl = Tol; 11: aryl = 4-(F3C)C6H5; 12: aryl = 4-MeOC6H5) in
95–99% yield. Representative results are summarized in Scheme 4
and Table 6.
The influence of several bases such as KF, Et3N or Cs2CO3 was
tested for the formation of 9. We found that Cs2CO3 led to the
highest yield and the other reactions were, therefore, performed in
the presence of Cs2CO3 (Table 6). The compounds 9–12 have not
been described before and were characterized by their 19F NMR
spectroscopic data (Table 5) and ESI-MS. Employment of [Ni(F)(2-
C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (6) as catalyst also yielded
with phenyl boronic acid the diaryl pyridine 9, but in lower yields.
We did not observe any reaction of PhB(OH)2 with 2,3,5,6-
tetrafluoropyridine without adding a nickel fluoro complex, even
in the presence of Cs2CO3.
Treatment of pentafluoropyridine with phenyl boronic acid in
the presence of 5 mol% of a mixture of trans-[Ni(F)(2-C5NF4){k1
-
(P)-(iPr2PCH2CH2OMe)2}] (1) and trans-[Ni(F)(4-C5NF4){k1-(P)-
(iPr2PCH2CH2OMe)2}] (2) (ratio: 8:1) and NEt3 as base gave the
C–C coupling products 3,4,5-trifluoro-2,6-biphenylpyridine (7)
and 3,5-difluoro-2,4,6-triphenylpyridine (8) with yields of 20% and
10% after 17 h at 60 8C (Scheme 3 and Table 4). In addition, the
formation of traces of 3,5-difluoro-2,6-biphenylpyridine (9) and
2,3,5,6-tetrafluoropyridine was observed.
A mixture of the
complexes 5 and 4 (ratio: 2:1) also shows catalytic activity in
cross coupling reactions. In contrast to the reaction above only the
3. Discussion
The syntheses of the isomeric nickel fluoro complexes trans-
[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (1) and trans-
[Ni(F)(4-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (2) are shown in
Scheme 1. Comparable oxidative addition reactions at nickel
bisphosphine moieties are known in the literature [6,26,27,52–
54,56]. Note that for the C–F activation step several mechanism
have been discussed [3,6,26]. A phosphine-assisted mechanism
has been suggested, and comparable reaction pathways were
found at rhodium, iridium and platinum [16,19,60,61]. However,
Johnson et al. suggested a concerted oxidative addition for the
activation of 2,3,5,6-tetrafluoropyridine at [Ni(h2-C14H10)(PEt3)2]
[62]. For the C–F activation of pentafluoropyridine they discussed a
radical mechanism.
Fig. 3. An ORTEP diagram of 6; ellipsoids are drawn at the 50% probability level;
hydrogen atoms at the nickel complex, with the exception of H(3), are omitted for
clarity.

D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
267
Scheme 3. Catalytic cross-coupling reactions of pentafluoropyridine.
Table 4
metal complexes [20,33,51,64,65]. For instance, at palladium the
generation of trans-[Pd(F)(4-C5NF4)(PR3)2] (PR3 = PCy3, PiPr3,
iPr2PCH2CH2OMe) was observed [20,51]. Other examples involve
the formation of [Ru(ICy)(dppp)(CO)(4-C5NF4)(H)] [dppp = 1,4-
bis(diphenylphosphanyl)propane], [Rh(4-C5NF4)(PEt3)3] or [Pt(4-
C5NF4)(iPr)(PiPr3)(PFiPr2)] [20,33,64]. Activation reactions at the 2-
position involve reactions at nickel to yield trans-[Ni(F)(2-
C5NF4)(L)2] (L = PEt3, iPr2Im), at rhodium to give [Rh(2-
C5NF4)(PEt3)3], but also conversions at titanium and zirconium
[16,19,26,28,29,52,62,66].
Cross-coupling reactions of pentafluoropyridine with phenyl boronic acid.
Entry
Cat.
Product
Yield (%)
TON
Product
Yield (%)
TON
1
2
1 + 2a
5 + 4b
7
7
20
–
8
–
8
8
10
13
6
8
5 mol% of catalyst (aratio of 8:1; bratio of 2:1); Et3N, THF, 60 8C, 17 h; yields are based
on the amounts of pentafluoropyridine and have been determined by 19F NMR
spectroscopy on using
a capillary which contained a,a,a-trifluorotoluene as
external standard; TON, turn-over number.
Table 5
The activation of 2,3,5,6-tetrafluoropyridine at [Ni(COD)2]
19F NMR data of fluorinated pyridines at 25 8C (ppm).
i
proceeds in the presence of both phosphines, Pr2PCH2CH2OMe
i
Compound
d (
19F) (THF-d8)
or Pr2PCH2CH2NMe2, at the 2-position (Schemes 1 and 2) and
yielded trans-[Ni(F)(2-C5NHF3){k1-(P)-(iPr2PCH2CH2OMe)2}] (3)
and [Ni(F)(2-C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (6). In both
cases the C–F activation is favored over the C–H activation. The
activation of a C–F bond in the presence of a C–H bond was
observed before at nickel bisphosphine complexes [6,52,54,67].
The formation of the nickel fluoro complexes is presumably
thermodynamically favored whereas the formation of the C–H
activation products seem to be kinetically preferred [57,62,67,68].
Recently Johnson et al. reported an experimental study of the C–F
activation of 2,3,5,6-tetrafluoropyridin at a Ni(PEt3)2 synthon to
yield trans-[Ni(F)(2-C5NHF3)(PEt3)2]. At low temperature they
observed the formation of the kinetically favored nickel hydrido
complex trans-[Ni(H)(4-C5NF4)(PEt3)2] [62].
The C–F activation reactions are key-steps for the development
of catalytic processes such as C–C coupling reactions access new
fluoropyridines. The nickel fluoro complexes which have been
synthesized can be considered as essential intermediates of a
putative catalytic cycle. Note that it has been shown before that
fluoro complexes often exhibit a higher reactivity than their chloro
or bromo counterparts [18,19,21–29,31,51,69]. Representative
results of the cross coupling reactions of pentafluoropyridine
7
À146.5 (d, 2F, JFF = 19.1 Hz), À148.8
(t, 1F, JFF = 19.1 Hz) [59]
À126.5 (s, 2F)
8
9
À121.5 (s, 2F)
10
11
12
À122.1 (s, 2F)
À123.0 (s, 2F)
À119.4 (s, 2F)
In contrast, the C–F activation of pentafluoropyridine at
[Ni(COD)2]/iPr2PCH2CH2NMe2 (Scheme3)yieldsthemonophosphine
4-pyridyl complex [Ni(F)(4-C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (5)
as the main product and the 2-pyridyl complex [Ni(F)(2-C5NF4){k2
-
(P,N)-iPr2PCH2CH2NMe2}] (4) as the minor product. In these cases the
phosphine coordinates with both donor atoms (P,N) at the nickel
center. Treatment of 5 with an excess of iPr2PCH2CH2NMe2 does not
afford the formation of a bisphosphine complex. Note that the
formation of [Ni(F)(2-C5NF4)(Cy2PCH2CH2PCy2)] and [Ni(F)(2-
C5NF4)(tBu2PCH2CH2PtBu2)] has been observed, which also exhibit
a cis configuration of a fluoro- and a fluoroaryl ligand [26,63].
In general, there is
pentafluoropyridine at the 4-position at a variety of transition
a preference for the activation of
Scheme 4. Catalytic cross-coupling reactions of 2,3,5,6-tetrafluoropyridine.

268
D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
5.2. Synthesis of trans-[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}]
(1) and trans-[Ni(F)(4-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}] (2).
Table 6
Cross-coupling reactions of 2,3,5,6-tetrafluoropyridine with boronic acids.
Entry
Boronic acid
Product
Base
Yield (%)
TON
A solution of [Ni(COD)2] (391 mg, 1.43 mmol) in THF (5 mL) was
treated with iPr2PCH2CH2OMe (1.20 mL, 6.42 mmol). After stirring
the reaction mixture for 30 min, pentafluoropyridine (0.19 mL,
1.85 mmol) was added. The reaction mixture was stirred for
another 3.5 h and the volatiles were removed under vacuum. The
remaining dark red oil was washed with n-hexane (4Â 5 mL) at
À85 8C. The residue was then extracted with n-hexane (5 mL) at
room temperature. Evaporation of the solvent from the extract
under vacuum yielded a yellow solid. Yield: 593 mg (72%, with a
ratio of 8:1 for 2:1). Anal. Calcd. for C23H42NF5O2P2Ni: C, 47.61; H,
1
2
3
4
5
6
7
PhB(OH)2
PhB(OH)2
PhB(OH)2
PhB(OH)2
TolB(OH)2
4-(F3C)C6H5
4-(MeO)C6H5
9
9
NEt3
62a
47a
99a
17b
98a
95a
97a
25
19
40
7
KF
9
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
9
10
11
12
39
38
39
Yields are based on the amounts of 2,3,5,6-tetrafluoropyridine and have been
determined by 19F NMR spectroscopy on using
a
capillary which contained
fluorobenzenea or
a,a,a
-trifluorotolueneb as external standard; TON, turn-over
number.
a
5 mol% of 3, THF, 60 8C, 3 h.
5 mol% of 6, THF, 60 8C, 3 d.
7.30; N, 2.41. Found: C, 47.89; H, 7.55; N, 2.12.
b
3
1: 1H NMR (300.1 MHz, C6D6)
d
1.04 (6 H, dd, JPH = 13.2 Hz,
3JHH = 7.2 Hz, PCHCH3), 1.13 (6H, dd, JPH = 14.0 Hz, JHH = 7.1 Hz,
PCHCH3), 1.33 (6H, dd, 3JPH = 15.6 Hz, 3JHH = 7.1 Hz, PCHCH3), 1.38
(6H, dd, 3JPH = 16.1 Hz, 3JHH = 7.2 Hz, PCHCH3), 1.50 (4H, m, t in the
3
3
and 2,3,5,6-tetrafluoropyridine as substrates are summarized in
Schemes 3 and 4. For the former 2,6-diaryl- as well as 2,4,6-
triarylpyridines were generated. For the latter substrate the
bisphosphine complex trans-[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2-
CH2OMe)2}] (3) is superior as a catalyst in comparison to the
1H{31P} NMR spectrum, JHH = 7.4 Hz, PCH2), 1.80 (2H, m, sept in
the 1H{31P} NMR spectrum, 3JHH = 7.1 Hz, PCH), 1.91 (2H, m, sept in
the 1H{31P} NMR spectrum, 3JHH = 7.1 Hz, PCH), 3.09 (6H, s, OCH3),
3
3
nickel fluoro monophosphine complex [Ni(F)(2-C5NHF3){k2
-
3.48 (4H, m, CH2OCH3); the JHH coupling constants were
(P,N)-iPr2PCH2CH2NMe2}] (6). Some rare examples for cross-
coupling reactions that involve the cleavage of a C–F bond at
highly fluorinated aromatics have been reported [4,14,17,21,23–
25,32–47,51,70]. Chambers and Sandford described palladium
catalysed Suzuki cross-coupling reactions via C–Br activation of
2,4,6-tribromo-3,5-difluoropyridine and aromatic boronic acids.
They also observed a threefold or twofold substitution at the
pyridine, in this case by CÀBr activation [59].
confirmed from a 1H{31P} NMR spectrum. 19F NMR (282.4 MHz,
C6D6):
d
= À86.0 (1F, td, J = 29, J = 15 Hz), À130.6 (1F, tm, J = 28 Hz),
2
À151.8 (1F, m), À174.0 (1F, m), À376.2 (1F, td, JPF = 44 Hz,
JFF = 8 Hz). 31P{1H} (121.5 MHz, C6D6)
2: 19F NMR (282.4 MHz, C6D6):
À109.3 (2F, dm, J = 31 Hz), À372.2 (1F, td, JPF = 44 Hz, JFF = 6 Hz).
d
21.7 (d, JPF = 44 Hz).
2
d
= À91.6 (2F, tm, J = 31 Hz),
2
31P{1H} (121.5 MHz, C6D6)
d 21.1 (d, JPF = 44 Hz).
2
5.3. Synthesis of trans-[Ni(F)(2-C5NHF3){k1-(P)-
(iPr2PCH2CH2OMe)2}] (3)
4. Summary
A solution of [Ni(COD)2] (203 mg, 0.741 mmol) in THF (5 mL)
Inconclusion,wepresentedstudiesonthesynthesisandcatalytic
activity of the nickel fluoro complexes trans-[Ni(F)(2-C5NF4){k1-(P)-
(iPr2PCH2CH2OMe)2}] (1), trans-[Ni(F)(4-C5NF4){k1-(P)-(iPr2PCH2-
CH2OMe)2}] (2), trans-[Ni(F)(2-C5NF4){k1-(P)-(iPr2PCH2CH2OMe)2}]
(3), [Ni(F)(2-C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (4), [Ni(F)(4-
was treated with iPr2PCH2CH2OMe (623
m
L, 3.33 mmol). After
stirring the reaction mixture for 30 min, 2,3,5,6-tetrafluoropyr-
idine (102 L, 1.85 mmol) was added. The reaction mixture was
m
stirred for another 3.5 h and the volatiles were removed under
vacuum. The remaining dark red oil was washed with n-hexane
(4Â 5 mL) at À85 8C. The residue was then extracted with n-hexane
at room temperature. Evaporation of the solvent from the extract
under vacuum yielded a yellow solid. Yield: 235 mg (56%). Anal.
Calcd. for C23H43NF4O2P2Ni: C, 49.13; H, 7.71; N, 2.49. Found: C,
C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (5) and [Ni(F)(2-C5NF4){k2
-
(P,N)-iPr2PCH2CH2NMe2}] (6). All complexes can be synthesized by
carbon-fluorine-bond activation of pentafluoropyridine or 2,3,5,6-
tetrafluoropyridine. Via catalytic cross-coupling reactions with
pentafluoropyridine several new fluorinated building blocks have
been accessed by C–F activation. Complex 3 catalyses a twofold C–F
activation at 2,3,5,6-tetrafluoropyridine to yield the new 3,5-
difluoro-2,6-di(aryl)-pyridines (9: aryl = Ph; 10: aryl = Tol; 11:
aryl = 4-(F3C)C6H5; 12: aryl = 4-MeOC6H5).
49.28; H, 7.58; N, 2.37. 1H NMR (300.1 MHz, C6D6)
d 1.08 (6H, dd,
3
3JPH = 13.8 Hz, 3JHH = 7.1 Hz, PCHCH3), 1.15 (6H, dd, JPH = 14.0 Hz,
3
3
3JHH = 7.0 Hz, PCHCH3), 1.35 (6H, dd, JPH = 14.8 Hz, JHH = 7.1 Hz,
PCHCH3), 1.42 (6H, dd, 3JPH = 15.1 Hz, 3JHH = 7.1 Hz, PCHCH3), 1.55
(4H, m, PCH2), 1.83 (2H, m, sept in the 1H{31P} NMR spectrum,
3JHH = 7.1 Hz, PCH), 1.95 (2H, m, sept in the 1H{31P} NMR spectrum,
3JHH = 7.0 Hz, PCH), 3.10 (s, 6H, OCH3), 3.52 (4H, m, CH2OCH3), 6.21
5. Experimental
3
(1H, m, CH); the JHH coupling constants were confirmed from a
5.1. General
1H{31P} NMR spectrum. 19F NMR (282.4 MHz, C6D6)
d
À91.6 (1F, t,
J = 31 Hz), À109.3 (1F, dm, J = 32 Hz), À151.9 (1F, dt, J = 30,
2
The synthetic work was carried out on a Schlenk line under Ar.
All solvents were purified and dried by conventional methods and
distilled under argon before use. Benzene-d6 and THF-d8 were
J = 4 Hz), À372.4 (1F, tm, JPF = 44 Hz). 31P{1H} (121.5 MHz,
2
C6D6)
d
21.1 (d, JPF = 44 Hz).
i
dried over Na/K prior to use. [Ni(COD)2], Pr2PCH2CH2OMe and
5.4. Synthesis of [Ni(F)(2-C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (4)
and [Ni(F)(4-C5NF4){k2-(P,N)-iPr2PCH2CH2NMe2}] (5)
iPr2PCH2CH2NMe2 were prepared according to the literature [71].
The NMR spectra were recorded at 300 K at a Bruker DPX 300
spectrometer. The 1H NMR chemical shifts were referenced to
residual C6D5H at 7.15 ppm, THF-d7 at 1.72 ppm or at 3.58 ppm. The
19F NMR spectra were referenced to external C6F6 at À162.9 ppm.
The 31P{1H} NMR spectra were referenced externally to H3PO4 at
0.0 ppm. Microanalyses were carried out using a HEKAtech EURO EA
3000 elemental analyzer. Mass spectra (ESI) were recorded on an
Agilent 6210 Time-of-Fight LC–MS instrument.
To a suspension of [Ni(COD)2] (147 mg, 0.53 mmol) in n-hexane
(12 mL) iPr2PCH2CH2NMe2 (113
mL, 0.53 mmol) was added and
the mixture was and stirred for 20 min at room temperature.
Within 1 min the yellow solution turned orange. After addition of
an excess pentafluoropyridine (71
mL, 0.69 mmol) a yellow solid
starts to precipitate. The reaction mixture was stirred for 1 h and
filtered. The yellow residue was washed with n-hexane (3Â 2 mL)

D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
269
Table 7
Crystallographic data for 3, 5 and 6.
Compound
3
5
6
Empirical formula
Formula weight
Crystal dimensions (mm3)
Crystal system
C23H43NF4O2P2Ni
562.23
C15H24N2F5PNi
417.04
C30H52N4F8P2Ni2 H2O
417.09
0.09 Â 0.05 Â 0.01
Orthorhombic
P 212121
0.40 Â 0.23 Â 0.15
Monoclinic
P 21/c
0.90 Â 0.43 Â 0.19
Monoclinic
P 21
Space group
˚
a (A)
8.4409(4)
19.0669(3)
9.0499(2)
21.9130(3)
101.4790(10)
3705.53(11)
8
12.2685(5)
10.5179(3)
14.3884(6)
103.109(3)
1808.28(12)
2
˚
b (A)
16.8825(5)
19.5388(6)
˚
c (A)
(8)
b
3
˚
V (A )
2784.35(18)
4
Z
Density (calcd.) (Mg mÀ3
)
1.341
1.495
1.499
m
(Mo-K
a
) (mmÀ1
)
0.858
1.180
1.201
u
range (8)
2.08–29.50
18478
2.18–29.50
70894
3.39 to 29.61
26966
Reflections collected
Independent reflections
Rint
Goodness-of-fit on F2
7743
10325
9640
0.0983
0.0622
0.0883
0.996
0.839
1.076
Completeness to max.
u
99.8
100.0
99.2
R1, wR2 on all data
0.0938, 0.1682
0.0626, 0.1477
5551
0.0670, 0.1042
0.0422, 0.0990
6809
0.0674, 0.1431
0.0674, 0.1431
8877
R1, wR2 [Io > 2s(Io)]
Reflect. with [Io > 2
s
(IoÀ)]3
˚
Max diff peak, hole e A
CCDC
0.763 and À1.199
876294
1.186 and À0.459
876295
1.571 and À1.082
876296
at 0 8C and dried under vacuum. Yield: 177 mg (80%, with a ratio of
1:2 for 4:5). Anal. Calcd. for C15H24F5N2PNi: C, 43.20; H, 5.80; N,
6.72. Found: C, 43.24; H, 5.50; N, 6.97.
yields of 3,4,5-trifluoro-2,6-diphenylpyridine
difluoro-2,4,6-triphenylpyridine 8 were determined on using
an external standard of -trifluorotoluene and are 20%
7 and 3,5-
a,a,a
4: 19F NMR (282.4 MHz, C6D6)
d
À88.6 (1F, m), À132.6 (1F, t,
(TON = 8) and 10% (TON = 6), respectively.
J = 27 Hz), À150.8 (1F, m), À172.5 (1F, m), À294.7 (1F, d, br,
(b) In an NMR tube phenyl boronic acid (50 mg, 0.41 mmol) was
2JPF = 117 Hz). 31P{1H} (121.5 MHz, C6D6)
d
61.8 (d, JPF = 117 Hz).
added to a
mixture of [Ni(F)(4-C5NF4){k2-(P,N)-iPr2PCH2
2
5: 1H NMR (300.1 MHz, C6D6)
d
= 0.43–0.58 (2H, m, PCH2), 0.65–
CH2NMe2}]
(5)
and
[Ni(F)(2-C5NF4){k2-(P,N)-iPr2PCH2
0.87 (6H, m, PCHCH3), 1.38–1.49 (4H, m, CH2N(CH3)2, PCHCH3),
CH2NMe2}] (4) (ratio 2:1; 5 mg, 0.014 mmol), pentafluoropyr-
idine (15 L, 0.14 mmol) and NEt3 (56 L, 0.41 mmol) in THF-
d8 (0.6 mL). The reaction mixture was then heated for 17 h to
60 8C. The yield of 8 was determined on using an external
2.13 (6H, s, NCH3). 19F NMR (282.4 MHz, C6D6)
d
À99.9 (2F, m),
m
m
2
À123.1 (2F, m), À313.4 (1F, d, br, JPF = 117 Hz). 31P{1H}
2
(121.5 MHz, C6D6)
d
61.0 (d, JPF = 117 Hz).
standard of
a,a,a-trifluorotoluene and is 13% (TON = 8).
5.5. Synthesis of [Ni(F)(2-C5NHF3){k2-(P,N)-iPr2PCH2CH2NMe2}] (6)
5.7. Catalytic formation of 3,5-difluoro-2,6-diphenylpyridine (9)
To a suspension of [Ni(COD)2] (60 mg, 0.22 mmol) in n-hexane
(a) In an NMR tube phenyl boronic acid (34 mg, 0.28 mmol) was
(12 mL) iPr2PCH2CH2NMe2 (46
mixture was stirred for 20 min at room temperature. Within 1 min
the yellow solution turned orange. After addition of 2,3,5,6-
mL, 0.22 mmol) was added and the
added to
CH2OMe)2] (3) (4 mg, 0.007 mmol), 2,3,5,6-tetrafluoropyridine
(8 L, 0.14 mmol) and Cs2CO3 (102 mg, 031 mmol) in THF-d8
a
mixture of trans-[Ni(F)(2-C5NHF3)(iPr2PCH2-
m
tetrafluoropyridin (22
mL, 0.22 mmol) a yellow precipitate formed.
(0.6 mL). The reaction mixture was heated for 3 h to 60 8C. The
yield of 9 was determined on using an external standard of
fluorobenzene and is 99% (TON = 40).
The reaction mixture was stirred for 1 h and filtered. The yellow
residue was washed with n-hexane (3Â 2 mL) at 0 8C and dried
under vacuum. Yield: 56 mg (64%). Anal. Calcd. for C15H25F4N2PNi:
C, 45.15; H, 6.31; N, 7.02. Found: C, 45.19; H, 6.39; N, 7.05. 1H NMR
(b) In an NMR tube phenyl boronic acid (46 mg, 0.38 mmol) was
added
(P,N)-iPr2PCH2CH2NMe2}] (6) (5 mg, 0.013 mmol), 2,3,5,6-
tetrafluoropyridine (13 L, 0.13 mmol) and Cs2CO3 (122 mg,
to
a
solution
of
[Ni(F)(4-C5NHF3){k2
-
(300.1 MHz, C6D6)
d = 0.52–0.62 (2H, m, PCH2), 0.81 (6H, dd,
3
3
3JPH = 16 Hz, JHH = 7 Hz, PCHCH3), 0.89 (6H, dd, JPH = 16 Hz,
3JHH = 7 Hz, PCHCH3), 1.43–1.54 (4H, m, CH2N(CH3)2, PCHCH3),
2.18 (6H, s, NCH3), 6.23–6.31 (1H, m, CH); the JHH coupling
m
3
0.38 mmol) in THF-d8 (0.6 mL). The reaction mixture was
heated for 3d to 60 8C. The yield of 9 was determined on using
constants were confirmed from a 1H{31P} NMR spectrum. 19F NMR
an external standard of
(TON = 7).
a,a,a-trifluorotoluene and is 17%
(282.4 MHz, C6D6)
d
À93.3 (1F, t, J = 30 Hz), À109.8 (1F, d,
2
J = 31 Hz), À149.9 (1F, d, J = 29 Hz), À292.2 (1F, d, JPF = 120 Hz).
31P{1H} (121.5 MHz, C6D6)
d 61.4 (d, JPF = 120 Hz).
2
ESI-MS (9) calc. for C17H11NF2+: m/z 268.0932; found: 268.0938.
5.6. Catalytic activity of 1 and 5 in Suzuki type cross-coupling
reactions
5.8. Catalytic formation of 3,5-difluoro-2,6-di(4-
methylphenyl)pyridine (10)
(a) In an NMR tube phenyl boronic acid (33 mg, 0.27 mmol) was
added to
CH2OMe)2] (1) and trans-[Ni(F)(4-C5NF4)(iPr2PCH2CH2OMe)2]
(2) (ratio 2:1; 5 mg, 0.009 mmol), pentafluoropyridine (10 L,
0.18 mmol) and NEt3 (36 L, 0.26 mmol) in THF-d8 (0.6 mL).
The reaction mixture was then heated for 17 h to 60 8C. The
a
mixture of trans-[Ni(F)(2-C5NF4)(iPr2PCH2-
In an NMR tube tolyl boronic acid (38 mg, 0.28 mmol) was
added to a mixture of trans-[Ni(F)(2-C5NHF3)(iPr2PCH2CH2OMe)2]
m
(3) (4 mg, 0.007 mmol), 2,3,5,6-tetrafluoropyridine (8
mL,
m
0.14 mmol) and Cs2CO3 (101 mg, 0.31 mmol) in THF-d8 (0.6 mL).
The reaction mixture was heated for 3 h to 60 8C. The yield of 11

270
D. Breyer et al. / Journal of Fluorine Chemistry 143 (2012) 263–271
(p) S.M. Ametamey, M. Honer, P.A. Schubiger, Chemical Reviews 108 (2008)
1501–1516;
(q) M.H.G. Prechtl, M. Teltewskoi, A. Dimitrov, E. Kemnitz, T. Braun, Chemis-
try: A European Journal 17 (2011) 14385–14388.
was determined on using an external standard of fluorobenzene
and is 98% (TON = 39). ESI-MS calc. for C19H15NF2+: m/z 296.1251;
found: 296.1239.
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5.9. Catalytic formation of 3,5-difluoro-2,6-di(4-
trifluormethylphenyl)pyridine (11)
In an NMR tube 4-trifluormethylphenyl boronic acid (53 mg,
0.28 mmol) was added to
C5NHF3)(iPr2PCH2CH2OMe)2] (3) (4 mg, 0.007 mmol), 2,3,5,6-
tetrafluoropyridine (8 L, 0.14 mmol) and Cs2CO3 (97 mg,
a
mixture of trans-[Ni(F)(2-
m
0.30 mmol) in THF-d8 (0.6 mL). The reaction mixture was heated
for 3 h to 60 8C. The yield of 12 was determined on using an
external standard of fluorobenzene and is 95% (TON = 38). ESI-MS
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In an NMR tube 4-methoxyphenyl boronic acid (55 mg,
0.36 mmol) was added to
C5NHF3)(iPr2PCH2CH2OMe)2] (3) (5 mg, 0.009 mmol), 2,3,5,6-
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a
mixture of trans-[Ni(F)(2-
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0.37 mmol) in THF-d8 (0.6 mL). The reaction mixture was heated
for 3 h to 60 8C. The yield of 13 was determined on using an
external standard of fluorobenzene and is 97% (TON = 39). ESI-MS
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5.11. Structure determination for the complexes 3, 5 and 6
Yellow crystals of 3 were obtained from n-hexane at 0 8C. 5 and
6 were crystallized via gas phase diffusion of n-hexane in a THF
solution. The diffraction data were collected on a STOE IPDS 2
diffractometer at À173 8C. Crystallographic data are depicted in
Table 7. The structures were solved by direct methods and refined
with the full matrix least squares method on F2 (SHELX-97).
u
Acknowledgments
[29] R.J. Lindup, T.B. Marder, R.N. Perutz, A.C. Whitwood, Chemical Communications
(2007) 3664–3666.
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We acknowledge the research training group GRK ‘‘Fluorine as a
Key Element’’ funded by the Deutsche Forschungsgemeinschaft for
financial support. We thank Dr. B. Braun and R. Herrmann for help
with the X-ray crystallography and P. Haack for recording the Mass
spectra (ESI).
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