Intramolecular pyridine-based frustrated Lewis-pairs

Article abstract of DOI:10.1039/c5dt01068c

Deprotonation of the methylpyridines 2,6-lutidine, 2-picoline, 4-dimethylamino-2,6-dimethylpyridine as well as 2,6-dimethyl-4-(piperidine-1-yl)pyridine with n-butyllithium or n-butyllithium/KO-t-Bu at the methyl positions led to the corresponding organoli

Full text of DOI:10.1039/c5dt01068c

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ARTICLE
Intramolecular pyridine-based frustrated Lewis-pairs
a
a
a
a
Cite this: DOI: 10.1039/x0xx00000x
Leif A. Körte, Robin Warner, Yury V. Vishnevskiy, Beate Neumann, Hansꢀ
a
a
Georg Stammler and Norbert W. Mitzel*
Deprotonation of the methylpyridines 2,6ꢀlutidine, 2ꢀpicoline, 4ꢀdimethylaminoꢀ2,6ꢀdimethylꢀ
pyridine as well as 2,6ꢀdimethylꢀ4ꢀ(piperidineꢀ1ꢀyl)pyridine with ꢀbutyllithium or ꢀbutylꢀ
lithium/KOꢀ ꢀBu at the methyl positions led to the corresponding organolithium or ꢀpotassium
compounds. Treatment with ClB(C F ) resulted in formation of the 2ꢀborylmethylpyridines
Received 00th January 2012,
Accepted 00th January 2012
n
n
t
DOI: 10.1039/x0xx00000x
6 5 2
pyꢀCH ꢀB(C F ) . They are monomeric and form intramolecular B–N bonds and fourꢀmembeꢀ
red rings. A short intramolecular B–N distance was observed in the crystal structure of the
dimethylaminoꢀfunctionalized derivative and proposed to be responsible for the low reactivity
2
6 5 2
www.rsc.org/
of the products towards hydrogen, thf, acetonitrile and CO . Hydroboration of 6ꢀtertꢀbutylꢀ2ꢀ
2
butꢀ4’ꢀenylpyridine with HB(C F ) led to the corresponding hydroboration product
t
ꢀBuꢀpyꢀ
6
5 2
(
CH ) ꢀB(C F ) which shows no intramolecular B–N bond formation due to steric crowding.
2
4
6 5 2
H/Dꢀscrambling experiments with a H /D mixture revealed its reactivity towards hydrogen.
2
2
1
3
14
Introduction
gen cleavage. Bourissou and coꢀworkers as well as Son and
1
5
Hoefelmeyer have reported the synthesis of a series of
Frustrated Lewis pairs (FLPs) are systems for which the 2ꢀ(picolyl)boranes, 2ꢀ(picolyl)ꢀBR [R = Cy, Et, Ph, BR =
2
2
conventional adduct formation between a Lewis acid and base 9ꢀborafluorenyl, 9ꢀborabicyclononane (9ꢀBBN)]. The dimeric
is precluded by either steric demands or ring strain. This former compounds show nucleophilic 1,2ꢀaddition (carboboration) to
textbook phenomenon began to attract enormous interest after nitriles, aldehydes, ketones and amides. Son and Hoefelmeyer
Stephan and coꢀworkers discovered the extraordinary reactivity have proposed a Lewis base induced formation of a
Nꢀboroꢀ
of such systems. They have shown that combinations of stericaꢀ nium stabilized 2ꢀpicolyl anion by a dissociation of the B–
lly encumbered phosphanes and electronꢀpoor boranes are able C(benzylic) bond as the initial step of the reaction. The reaction
1,2
to activate hydrogen and other small molecules. Furthermore, rate of the 1,2ꢀaddition has been calculated to be faster with less
hydrogen can be cleaved reversibly, bound and liberated at electronꢀwithdrawing ability of the organic groups attached to
elevated temperatures and used for catalytic reductions of steriꢀ boron. Strongly electronꢀwithdrawing groups at the boron atom
3
cally demanding imines. Since then, a variety of frustrated might therefore prevent the 1,2ꢀaddition reaction and make
Lewis pairs has been discovered. Besides the initially reported these systems bifunctional catalysts in the activation of polar
1
,3,4
2
intraꢀ
and intermolecular boronꢀphosphorus frustrated unsaturated bonds. Hence, we synthesized intramolecular
5
Lewis pairs, such based on boron/NHC, aluminium/phosphoꢀ pyridineꢀboron Lewis pairs by deprotonating 2ꢀmethylpyridines
rus and some zincꢀbased FLP systems (including combinations followed by borylation with bis(pentafluorophenyl)chloroboraꢀ
Zn/P, Zn/NHC, and Zn/R P=C=PR ) as well as siliceniumꢀ ne. Furthermore, the basicity and acidity of the reacting Lewis
based ones have been studied. Shortly after the discovery of functions, as well as the common steric demand have a strong
frustrated Lewis pairs, the concept was applied to nitrogen influence on the reactivity of frustrated Lewis pairs towards
6
7
2
2
8
9
2,11,16
Lewis bases and it has been shown that inter ꢀ and intramoleꢀ hydrogen and other small molecules.
For this reason, we
boronꢀnitrogen FLPs are capable of hydrogen studied the effect of a varied basicity of the pyridine nitrogen
1
0–12
cular
cleavage in a heterolytic manner and can be used in catalytic by introducing +M substituents in paraꢀposition of the aromatic
reductions of sterically less demanding imines and enamines. backbone.
2
sp ꢀHybridised nitrogen has been used in intermolecular frusꢀ
trated Lewis pairs in a combination of 2,6ꢀlutidine and trisꢀ
(
pentafluorophenyl)borane. This is capable of reversible hydroꢀ
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Jou5DrnT0al Name
Results and discussion
pair
diffraction experiments were obtained.
were preꢀ Treatment of Lewis pair
with hydrogen, acetonitrile as well as
pared in 98% and 63% yield by deprotonation of 2,6ꢀlutidine or carbon dioxide resulted in no observable reactions. Furthermore
ꢀpicoline with KOꢀtꢀBu and ꢀbutyllithium neat or in ꢀhexane Lewis pair
did also not show reactivity in H/Dꢀscrambling
experiments when exposing a solution in CD Cl to a H /D
5 was synthesized, but so far no suitable crystals for Xꢀray
Metallated lutidine
1
as well as metallated picoline
2
4
2
n
n
4
1
7
(
Scheme 1).
2
2
2
2
1
9
mixture revealing the absence of typical FLP activity. A 1,2ꢀ
carboboration reaction, as it was found for the less electronꢀ
poor picolylꢀboranes, was also not observed; this agrees with
1
5
earlier theoretical descripttions.
In order to achieve FLP activity, we tried to enhance the
reactivity of the system by introducing +M substituents in para
ꢀ
position of the aromatic ring to afford a higher basicity of the
pyridine nitrogen site. Repo and coꢀworkers showed that the
introduction of a more basic dimethylamino group in the
1
1
system R NꢀC H ꢀB(C F ) leads to FLP activity. By contrast,
2
6
4
6 5 2
the less basic diphenylamino derivative is not capable of
2
0
heterolytic hydrogen splitting. Moreover, the steric demand at
Scheme 1: Synthesis of four-membered ring boron-pyridine Lewis pairs. the pyridine nitrogen atom was enhanced by introducing tertꢀ
Deprotonation of methyl pyridines followed by the reaction with chloroborane
yields the Lewis pairs and
ClB(C , −30 °C, toluene; iii) KO-t-Bu, n-BuLi, n-hexane.
3
butyl groups in orthoꢀposition. The required aminolutidines
and 10 were synthesized by nucleophilic substitution of the
chlorine functions of 4ꢀchloroꢀ2,6ꢀdimethylpyridine ( ) with
7
4
5 selectively. Conditions: i) KO-t-Bu, n-BuLi, neat; ii)
6 5 2
F )
6
aqueous dimethyl amine solution or, alternatively, in a solventꢀ
free transformation with piperidine at 160 °C (Scheme 2).
The resulting solids, yellow
1
and orange
2
, were characterized
by solution NMR spectroscopy. The corresponding lithium
compounds were synthesised as well and show different chemiꢀ
cal shifts of the CH2 groups attached to the alkali metal.
Compounds
7 and 10 were characterized by NMR spectroscoꢀ
py, high resolution mass spectrometry as well as CHN elemenꢀ
tal analyses. Deprotonation with
afforded organolithium compounds
yield, respectively. Their reactions with chloroborane
n
8
ꢀbutyllithium in
and 11 in 72% and 87%
in toluꢀ
ene at −30 °C proceeded with high selectivity. The previously
described deprotonation of the methyl pyridines and 10 with
nꢀhexane
Further, the absence of lithium was confirmed by the absence
7
of resonances in the Li NMR spectra of
1
and
with bis(pentafluorophenyl)ꢀ
) in toluene at −30 °C yielded the Lewis pair
as a slightly yellow, as well as as an orange solid. The
2. The reactions
3
of potassium compounds
chloroborane (
1 and 2
3
4
7
5
KOꢀtꢀBu and nꢀbutyllithium was also tried, but the obtained
organopotassium compounds turned out to be less selective in
products were identified by NMR spectroscopy, high resolution
mass spectrometry as well as by CHN elemental analyses. The
1
1
the reaction with chloroborane
where characterized by multinuclear NMR spectroscopy, the
Lewis pairs and 12 by NMR spectroscopy as well as high
resolution mass spectrometry. The NMR spectra again reveal a
3. The lithium compounds
B NMR spectra indicate fourꢀcoordinate boron atoms with a
B NMR chemical shift of −0.75 ppm for and −0.77 ppm for
1
1
4
1
9
9
5
, respectively. The small difference between the F NMR
chemical shifts of the paraꢀ and metaꢀfluorine atoms confirms
boron to be fourꢀcoordinate. The F NMR spectrum shows
only one set of signals for the two C F rings and the H NMR
spectrum contains one signal for the bridging CH group, which
indicates a monomeric structure in solution. Comparable 2ꢀpiꢀ
colylboranes, with organic groups of comparable size attached
to the boron, e.g. phenyl groups, are found to adopt a dimeric 8ꢀ
membered ring structure in solution. This was demonstrated by
the detection of diastereotopic protons of the bridging CH
groups as well as of the organic groups attached to boron. An
attempt to determine the crystal structure of was hampered by
1
1
1
8
19
fourfoldꢀcoordinate boron atom. The B NMR chemical shifts
of (−2.27 ppm) and 12 (−2.43 ppm) indicate stronger boronꢀ
1
9
6
5
nitrogen bonds due to higher Lewis basicity of the nitrogen
atom caused by the amino +M substituents in paraꢀposition of
2
the aromatic ring. The crystal structure of Lewis pair
9 was
determined and is depicted in Figure 1. The structure reveals a
strong and thereby short boronꢀnitrogen bond [1.607(2) Å].
This strong bond causes small angles about the aromatic carbon
2
1
5
atom C(1) with
methylene group C(7)
Compared to the literatureꢀknown intramolecular frustrated
∢
[N(1)–C(1)–C(7)] = 98.6(1)° and about the
∢
[C(1)–C(7)–B(1)] 85.2(1)°.
=
4
structural disorder within the crystals. The limited quality of the
resulting structure determination does not allow discussing
structural parameters. Anyhow,
1
1
12
Lewis pairs with aromatic and aliphatic backbones with B–
N distances of 1.719(3) Å and 1.771(3) Å, respectively, Lewis
4 has a fourꢀcoordinated boron
pair
right). The B–N distance in Lewis pair
adduct of 4ꢀ(dimethylamino)pyridine with tris(pentafluoropheꢀ
nyl)borane. In contrast to , the latter contains the stronger
9
shows an extremely short boronꢀnitrogen bond (Figure 1,
atom in the solid state, with intramolecular coordination of
nitrogen to boron. The monomeric structures in the solid state
as well as in solution are therefore in contrast to the dimeric
9
is as long as that in the
1
5
9
structures observed. To prevent disorder in the crystal, Lewis
Lewis acid and does not have to overcome ring strain during
formation. Intramolecular bonding is obviously favoured over
2
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Scheme 2: Synthesis of the four-membered ring boron-pyridine Lewis pairs with +M-substituent in para-position.
Figure 1: Left: Crystal structure of dimethylamino substituted Lewis pairs
nitrogen distances in the crystal structures of literature-known active frustrated Lewis pairs
.607(2), N(1)–C(1) 1.360(2), C(1)–C(7) 1.507(2), C(7)–B(1) 1.679(2), N(1)–C(1)–C(7) 98.6(1), C(1)–C(7)–B(1) 85.2(1), C(7)–B(1)–N(1) 82.9(1), B(1)–N(1)–C(1) 93.1(1).
9 (displacement ellipsoids drawn at 50% probability level). Right: Comparison of the boron-
1
1,12,21
and Lewis pair 9. Selected bond length [Å] and angles [°]: N(1)–B(1)
1
an intermolecular B–N bonding, e.g. with either the terminal Treatment of Lewis pairs
9 and 12 with an atmosphere of
dimethylamino group or in a possible dimeric or polymeric hydrogen as well as that of 12 with acetonitrile, tetrahydrofuran
form, all without necessity to overcome ring strain. The and carbon dioxide did not result in reactions typical for frustraꢀ
introduction of a sterically more demanding
orthoꢀposition did not yield the desired product. Deprotonation reactivity in H/Dꢀscrambling experiments. This characteristic
of 2ꢀtertꢀbutylꢀ6ꢀmethylpyridine (14) either with ꢀbutyllithium is attributed to the short and consequently strong boronꢀ
in ꢀhexane or in combination with KOꢀtꢀBu and the following nitrogen bond found in the crystal structure of the
reaction of the organolithium and ꢀpotassium compounds with dimethylamino functionalized Lewis pairs . The typical reactiꢀ
chloroborane afforded product mixtures that could not be vity of frustrated Lewis pairs would require a weaker coordinaꢀ
tꢀbutyl group in ted Lewis pairs. Furthermore Lewis pair 9 did also not show
1
9
n
n
9
3
separated (Scheme 2).
tion between the acid and the base.
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Jou5DrnT0al Name
–
1
Table 1: Calculated relative energies
ꢁ
E
(open – closed) in kcal mol and boration of the terminal olefin functions with Piers’ borane
3
in
toluene at 120 °C selectively yielded the hydroboration proꢀ
ducts 19 20 and 21. The products where characterized by
B–N distances (in Å) of the closed form of several pyridines with spacerꢀ
bound B(C
and 4.
6 5 2
F ) groups in position 2 and further substituents in positions 6
,
multinuclear NMR spectroscopy, high resolution mass spectroꢀ
pyridine substituents
ꢁ
E
e
r (B–N)
metry as well as CHN elemental analyses. Both compounds 19
6ꢀMe
15.0
17.8
17.3
32.5
36.7
19.9
23.1
10.9
11.4
–2.8
1.623
1.610
1.611
1.622
1.608
1.665
1.635
1.674
1.654
1.694
19
and 20 show a small separation of the F resonances of para
ꢀ
2
ꢀCH
2
6 5
ꢀB(C F )
2
6ꢀMeꢀ4ꢀNMe
2
1
1
and metaꢀfluorine atoms. This and B resonances at 0.11 and
−2.16 ppm indicate the boron atoms to be fourꢀcoordinate. The
molecular structure of 19 in the crystal was determined and is
depicted in Figure 3. It shows a structural disorder of N(1) and
C(1) to C(10) over two positions in a ratio of 55:45. Structure
19a (Figure 3, ellipsoid model) shows a chair conformation of
the sevenꢀmembered ring, structure 19b (Figure 3, wireꢀmodel)
shows a twist conformation. The B–N distances (19a: 1.66(1)
6
ꢀMeꢀ4ꢀPip
ꢀMe
6ꢀMeꢀ4ꢀNMe
Bu
ꢀMe
Bu
ꢀMe
Bu
6
2
ꢀ(CH
2
)
2
ꢀB(C
6
F
5
)
2
2
6ꢀtꢀ
6
6ꢀtꢀ
6
2
ꢀ(CH
2
)
3
ꢀB(C
6
F
F
5
)
2
2
2
ꢀ(CH
2
)
4
ꢀB(C
6
5
)
6ꢀtꢀ
Considering what is necessary to weaken the strong bond of the Å, 19b: 1.65(2) Å) are within the range of pyridine perfluoroꢀ
pyridine nitrogen to the Lewis acid we undertook DFT calculaꢀ arylboron adducts with comparable steric demand.13,22
tions [PBE0ꢀD3/6ꢀ31G(d,p)]. The elongation of the alkyl spacer The reaction of the
in Pyꢀ(CH ) ꢀB(C F ) (Py = 6ꢀR,4ꢀR’ꢀpyridinꢀ2ꢀyl, with R = borane yielded the hydroboration product 21 as colourless oil
tꢀbutyl substituted pyridine 18 with Piers’
2
n
6 5 2
1
1
Me, tꢀBu, R’ = H, NMe , Pip) in combination with the introꢀ (Scheme 3). Its B NMR spectrum shows a typical resonance
2
duction of a sterically demanding group in pyridineꢀposition 6 for a threefoldꢀcoordinate boron atom at 74.8 ppm, in agreeꢀ
next to the Lewis base site was expected to result in a frustrated ment with the quantumꢀchemical calculations discussed above.
Lewis pair. Starting from
n = 1 in the substituent (CH ) ꢀ Therefore, the B–N bond formation could be precluded by the
2 n
B(C F ) both conformers, B–N bonded (closed form) and B–N combination of more steric demand of the tꢀbutyl group and the
6
5 2
nonꢀbonded (open form) were found and optimised. In most elongation of the alkyl spacer. The frustrated Lewis pair 21 was
cases the closed form was predicted to be more stable than the again treated with an atmosphere of hydrogen and carbon dioxiꢀ
open form. First, from
closed form reaches a maximum (see Table 1). With further test the reactivity against molecular hydrogen, degassed soluꢀ
increasing the relative stability of the closed form became tions of Lewis pairs 19 and 20 as well as of FLP 21 in CD Cl
lower while the B–N bond lengthened. Introduction of a
n = 1 to n = 2, the relative stability of the de, but under these conditions showed no reaction. In order to
n
2
2
tꢀBu were exposed to an atmosphere of a 1:1 mixture of hydrogen
instead of a Me group in position 6 significantly decreases the and deuterium. For compound 19 and 20, with fourfold
stability of the closed form and forces further elongation of the coordinate boron, no reaction was observed. However, for FLP
B–N bond. In comparison to this effect the influence of 21 the formation of deuterium hydride, HD, was observed by
1
substituents in position 4 is negligible. Finally, at
with a
n
= 4 and the characteristic 1:1:1 triplet at 4.57 ppm with a JD,H = 42.6
1
t
ꢀBu group in position 6 the open form becomes 2.8 kcal Hz coupling constant in the H NMR spectrum. Due to steric
mol more stable than the closed one. Taking entropy into demand of the tertꢀButyl group the BꢀN bond formation was
account makes it even more stable with ꢁ °298.15 = 8.3 kcal precluded successfully and FLPꢀreactivity was achieved by
ꢀ
1
G
–
1
mol . An additional stabilising effect in this open form arises rational design.
probably from πꢀπ stacking, which was geometrically identified
in the optimised structure (Figure 2).
Therefore, the calculations predicted the hydroboration of a 6ꢀ
butꢀ3’ꢀenylꢀ2ꢀtertꢀbutylpyridine (18) to yield the frustrated
Lewis pair 21, where the steric repulsion between the B(C F5)2
6
groups and the tꢀbutyl group in 21 inhibits the coordination of
the Lewis base to boron. The corresponding methyl pyridines,
with less steric crowding next to the pyridine nitrogen atom,
were predicted to form the closed sevenꢀmembered ring structuꢀ
res and were synthesised for comparison (Scheme 3).
Deprotonation of 2,6ꢀlutidine as well as methyl pyridines
with ꢀbutyllithium in diethyl ether and treatment with allyl
bromide yielded the butꢀ4’ꢀenylpyridines 16 17 and 18. The
7 and
1
4
n
,
products were purified by either distillation or column chromaꢀ
tography and characterized by NMR spectroscopy, high resoluꢀ
tion mass spectrometry and CHN elemental analyses. Hydroꢀ
Figure 2: Optimized structure [PBE0-D3/6-31G(d,p)] of the open form of 21 [2-
(
CH
2
)
4
-B(C
6
5
F )
2
,6-tBu-pyridine]. Hydrogen atoms are omitted for clarity.
4
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Scheme 3: Syntheses of intramolecular Lewis pairs 19 and 20 as well as the frustrated Lewis pair 21 by hydroboration of the respective olefins 16, 17 and 18.
acetonitrile as well as towards H /D mixtures in scrambling
2
2
experiments.
Attempts to weaken the B–N coordination by placing sterically
demanding tertꢀbutyl groups next to the pyridine nitrogen were
unsuccessful; reactions of the corresponding metallated pyridiꢀ
nes with ClB(C F ) were unselective. Quantumꢀchemical calꢀ
6
5 2
culations predicted longer alkylꢀspacers between pyridine and
boron function to afford frustrated Lewis pairs with no B–N
bond if such bulky pyridineꢀsubstituents in orthoꢀposition were
present. Indeed, the
nalized derivatives 19 show intramolecular B–N bonds, whereꢀ
as the tertꢀbutyl derivative 21 does not. The obtained
oꢀmethyl 18 and pꢀdimethylamino functioꢀ
o
ꢀ
frustrated Lewisꢀpair 21 showed no quantitative addition of
hydrogen or carbon dioxide, however H/Dꢀscrambling was
observed upon treatment with an atmosphere of a 1:1 mixture
of H and D (formation of HD)
2
2
Figure 3: Molecular structure of Lewis pair 19 in the crystal. Hydrogen atoms are In essence, this demonstrates the complex interplay of steric,
omitted for clarity. Due to structural disorder two different conformers where
found in a ratio of 55:45. The structure presented as an ellipsoid model (drawn
ring strain and electronic factors in the formation of intramoleꢀ
cular Lewis acidꢀbase adducts – one of the aspects needed for
at 50% probability level) for the majority chair conformation 19a (site occupation
5
5%), the part represented as a wire-model the minority twist conformation 19b the rational design of new frustrated Lewisꢀpairs.
site occupation 45%). Selected bond length [Å] and angles [°] for the majority
(
chair conformation 19a: N(1)–B(1) 1.66(1), N(1)–C(5) 1.38(1), N(1)–C(1) 1.363(8),
Experimental
C(5)–C(6) 1.517(5), C(9)–B(1) 1.68(2), B(1)–N(1)–C(1) 122.2(8), B(1)–N(1)–C(5)
1
21.4(7), N(1)–C(5)–C(6) 120.5(9), C(9)–B(1)–N(1) 108.7(8).
All operations with air and moisture sensitive compounds were
performed under conventional Schlenk technique or in a gloveꢀ
box. Volatile compounds were handled in a vacuum line. Toluꢀ
Conclusion
ene and tetrahydrofuran were dried over potassium,
ꢀpentane and diethyl ether over LiAlH and distilled prior to
and thfꢀd8 were dried over Na/K alloy, CDCl and
. Workup and column chromatography were
nꢀhexane,
Reactions of metallated methylpyridines (
1
,
2
,
8
and 11) with
n
4
bis(pentafluorophenyl)chloroborane afforded intramolecular use. C
D
6
6
3
1
9
fourꢀmembered ring B/N Lewis pairs (
4
,
5
,
9
and 12). F and CD
2
Cl
2
over CaH
2
1
1
B NMR confirm the presence of monomeric structures in performed with technical grade solvents. 2,6ꢀLutidine was purꢀ
solution, and a crystal structure determination of ꢀMe Nꢀ
chased from Merck, 2ꢀpicoline from SigmaꢀAldrich, allyl broꢀ
Meꢀ
ꢀ[CH B(C F ) ]ꢀC H N) reveals a monomeric structure in mide from Acros Organics, piperidine from SigmaꢀAldrich and
the solid state. This is in contrast to previously observed dimeꢀ dimethylamine solution from BASF. Chlorobis(pentafluoropheꢀ
9
(
p
oꢀ
2
o
2
6
5 2
6
2
2
3
24
ric borylꢀ2ꢀmethylpyridines with boronꢀsubstituents of compaꢀ nyl)borane (
3), bis(pentafluorophenyl)borane (22), 4ꢀchloroꢀ
2
5
rable size (solution and solid). Despite the obvious presence of 2,6ꢀdimethylpyridine (
6
)
and 2ꢀbromoꢀ6ꢀtertꢀbutylpyridine
were prepared as described in literature. Column chromaꢀ
is 1.602 Å). These are the tography was performed on silica gel 60 (0.04 – 0.063 mm
likely reason for the absence of typical frustrated Lewisꢀpairꢀ mesh). NMR spectra were recorded using BRUKER AV 300,
type reactivity: Lewis pairs and 12 proofed to be unreactive
RUKER DRX 500, BRUKER Avance III 500 and BRUKER AV
towards hydrogen and
2
6
ring strain the new compounds form strong intramolecular B–N
bonds (the B–N bond length in
(13)
9
4
,
9
B
4
and 12 towards carbon dioxide, 600 spectrometers at ambient temperature. NMR spectroscopic
chemical shifts were referenced to the residual peaks of the
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

Dalton Transactions
Page 6 of 12
View Article Online
ARTICLE
DOI: 10.1039
J
/
o
C
u
5DrnT0
a
1
l
0
N
68
a
C
me
2
7
1
13
7
13
1
2
protons of the used solvents ( H, C) or externally ( Li: LiCl
C{ H} NMR (126 MHz, C D ):
δ [ppm] = 166.9 (C ), 154.2
6
6
1
1
19
6
1
4
in D O; B: BF ·OEt ; F: CFCl ). Elemental analyses were (C ), 148.2 (dm, JF,C = 238 Hz, oꢀCꢀF), 141.3 (C ), 140.3 (dm,
2
3
2
3
1
1
carried out using a EuroEA Elemental Analyser. ESI mass
JF,C = 252 Hz,
p
ꢀCꢀF), 137.6 (dm, JF,C = 248 Hz,
m
ꢀCꢀF),
ꢀC), 24.3 (broad, CH2),
spectrometer (Bruker Daltonik GmbH, Bremen, Germany) 17.9 (CH3). F NMR (470 MHz, C D ): [ppm] = −135.1 (m,
ꢀF), −163.6 (m, 4F, ꢀF). ESIꢀMS
5
3
spectra were recorded using an Esquire 3000 ion trap mass 122.9 (C ), 121.2 (C ), 117.8 (broad,
i
1
9
δ
6
6
equipped with a standard ESI source. Samples were introduced 4F,
o
ꢀF), −157.4 (m, 2F,
p
m
+
by direct infusion with a syringe pump. Nitrogen served both as (positive ions, acetonitrile): m/z = 452.0 ([M + H] ). HRꢀMS
the nebulizer gas and the dry gas. EI mass spectra were recorꢀ (ESI, positive ions, acetonitrile): calcd for C H BF N
+
1
9
8
10
ded using an Autospec X magnetic sector mass spectrometer 452.06521, found 452.06629. Analysis: calcd for C H BF N
1
9
9
10
with EBE geometry (Vacuum Generators, Manchester, UK) C 50.7, H 1.8, N 3.1%; found C 51.0, H 2.0, N 3.0%.
equipped with a standard EI source. Samples were introduced
2
-{[Bis(pentafluorophenyl)boryl]methyl}pyridine (5)
by push rod in aluminium crucibles. Ions were accelerated by 8
kV in EI mode.
To
a solution of chlorobis(pentafluorophenyl)borane (3)
(
0.581 g, 1.53 mmol) in toluene (7 mL) was added organoꢀ
potassium compound at −30 °C and the orange suspension
To a suspension of KOꢀtꢀBu (2.24 g, 20.0 mmol) in 2,6ꢀlutidine was slowly warmed to ambient temperature and stirred for three
21.4 g, 0.20 mol), purified by distillation over CaH , was days at ambient temperature. The resulting lithium salts were
[
(6-Methylpyridin-2-yl)methyl]potassium (1)
2
(
2
added
0 mmol) within 20 min and the orange suspension was stirred solid was suspended in
for 2 h at ambient temperature. The yellow precipitate was product was dissolved at boiling heat. The clear supernatant
filtered off, washed with ꢀpentane (10 mL) and dried in vacuo liquid was transferred to another flask via a syringe and the
2.83 g, 98%). H NMR (500 MHz, thfꢀd ): [ppm] = 5.99 (dd, product was precipitated at −30 °C. The supernatant liquid was
n
ꢀbutyllithium solution in
n
ꢀhexane (12.5 mL, 1.6 M, filtered off and the solvent was removed in vacuo. The resulting
2
n
ꢀhexane (20 mL) and a main part of the
1
n
1
(
δ
8
3
3
4
3
JH,H = 8.3 Hz,
J
= 6.2 Hz, 1H, H ), 5.43 (d, JH,H = 8.3 Hz, removed by a syringe and the yellowish solid dried in vacuo to
H, H ), 4.68 (d, JH,H = 6.3 Hz, 1H, H ), 2.58 (d, JH,H = 1.8 yield
H,H
3
3
5
2
1
1
5
(0.20 g, 29%). H NMR (500 MHz, C D ):
δ
[ppm] =
6
6
3
4
3
5/6
Hz, 1H, CH ), 2.53 (d, JH,H = 1.8 Hz, 1H, CH ), 1.76 (s, 3H, 8.08 (m, 1H, H ), 6.75 (m, 1H, H ), 6.30 (m, 2H, H ), 2.50 (s,
CH3). C{ H} NMR (126 MHz, thfꢀd ):
1
(
2
2
1
3
1
2
11
δ
[ppm] = 163.5 (C ), 2H, CH2). B NMR (160 MHz, C D ):
δ
[ppm] = −0.77 (s,
8
6
6
6
4
3
5
13
1
56.6 (C ), 132.4 (C ), 121.3 (C ), 94.7 (C ), 58.9 (CH ), 25.1 τ1/2 = 120 Hz). C{ H} NMR (126 MHz, C D ): [ppm] =
δ
2
6
6
2
1
4
CH3).
167.5 (C ), 147.7 (dm, JF,C = 240 Hz, oꢀCꢀF), 143.6 (C ), 140.3
1
1
(
1
dm, JF,C = 250 Hz, pꢀCꢀF), 137.6 (dm, JF,C = 247 Hz, mꢀCꢀF),
(Pyridin-2-yl-methyl)potassium (2)
5/6
19
23.8 and 122.2 (C ), 117.8 (br., iꢀC), 23.1 (br., CH2).
[ppm] = −133.7 (m, 4F, ꢀF), −157.5
ꢀF), −163.5 (m, 4F, ꢀF). ESIꢀMS (positive ions,
ꢀhexane (19.0 mL, 1.6 M, 30 mmol) dropꢀ acetonitrile): m/z = 438.1 ([M + H] ). HRꢀMS (ESI, positive
F
To a suspension of 2ꢀpicoline (2.8 g, 20 mmol) and KOꢀtꢀBu NMR (470 MHz, C D ):
δ
o
6
6
(
3.41 g, 30.4 mmol) in
lithium solution in
wise at ambient temperature and the orange suspension was ions, acetonitrile): calcd for C H BF N 438.05064, found
n
ꢀhexane (15 mL) was added
n
ꢀbutylꢀ (m, 2F,
p
m
+
n
+
1
8
6
10
stirred for 1 h. The orange solid was filtered off, washed with
n
ꢀ
438.04841.
1
hexane (15 mL) and dried in vacuo to yield
2 (2.53 g, 63%). H
3
2,6-Dimethyl-4-dimethylaminopyridine (7)
NMR (500 MHz, thfꢀd ):
δ [ppm] = 6.96 (d, JH,H = 4.4 Hz, 1H,
8
5
6
3
3
H ), 5.98 (m, 1H, H ), 5.53 (d, JH,H = 9.0 Hz, 1H, H ), 4.73 (t, A glass ampoule was filled with 4ꢀchloroꢀ2,6ꢀdimethylpyridine
3
4
13
1
JH,H = 5.9 Hz, 1H, H ), 2.51 (s, 2H, CH ). C{ H} NMR (126
(
6
) (1.00 g, 7.98 mmol) and aqueous dimethylamine solution
2
2
5
6
MHz, thfꢀd ):
δ [ppm] = 162.1 (C ), 148.9 (C ), 130.6 (C ), (10 mL, 79 mmol, 40 wt%) and the colourless suspension was
8
3
4
1
13.0 (C ), 94.5 (C ), 57.9 (CH ).
stirred at 160 °C for 3 days. Water (30 mL) was added at room
temperature and the aqueous phase extracted three times with
dichloromethane (30 mL). The combined organic extracts were
washed with brine (30 mL), dried over Na SO and the solvent
2
2
-{[Bis(pentafluorophenyl)boryl]methyl}-6-methylpyridine (4)
solution of chlorobis(pentafluorophenyl)borane (3)
To
a
2
4
(
0.570 g, 1.50 mmol) in toluene (10 mL) was added organoꢀ was removed under reduced pressure to yield
7
as a colourless
[ppm] =
1
potassium compound
1
(0.220 g, 1.52 mmol) at −30 °C. The solid (1.04 g, 87%). H NMR (300 MHz, CDCl ):
δ
3
orange suspension was slowly warmed to ambient temperature 6.22 (s, 2H, ArꢀH), 2.97 (m, 6H, NCH3), 2.43 (s, 6H, CH ).
3
1
3
1
2
and stirred at ambient temperature for 1 h. The yellow suspenꢀ
C{ H} NMR (76 MHz, CDCl ):
δ
[ppm] = 157.6 (C ), 155.5
H ), 24.9 (CH ). EIꢀMS (70 eV):
3
4
3
sion was filtered, the toluene was evaporated to dryness and the (C ), 103.4 (C ), 39.3 (N–
C
3
3
+
ꢂ
+
resulting oil was washed three times with
yield as a yellowish solid (0.45 g, 66%). Analytically pure CH ] , 30%). HRꢀMS (EI, 70 eV): calcd for C H N
crystals were obtained from a concentrated toluene solution at 150.11515, found: 150.11517. Analysis: calcd for C H N C
nꢀpentane (5 mL) to m/z = 150.0 ([M] , 100%), 149.0 ([M − H] , 99%), 135.0 ([M −
+
+ꢂ
4
3
9
14
14
2
9
2
1
3
−
7
=
80 °C. H NMR (500 MHz, C D ):
δ
[ppm] = 6.76 (t,
J
=
72.0, H 9.4, N 18.7%; found C 71.5, H 9.7, N 18.4%.
6
6
H,H
4
3
3
3
.9 Hz, 1H, H ), 6.33 (d, JH,H = 7.8 Hz, 1H, H ), 6.11 (d,
8.0 Hz, 1H, H ), 2.43 (s, 2H, CH ), 1.78 (s, 3H, CH ).
J
H,H
5
11
B
2
3
NMR (160 MHz, C D ):
δ [ppm] = −0.75 (s, τ1/2 = 109 Hz).
6
6
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 7 of 12
Journal Name
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT01068C
ART LE
IC
{
[4-(Dimethylamino)-6-methylpyridine-2-yl]methyl}lithium (8)
To a solution of aminolutidine (0.64 g, 4.3 mmol) in ꢀhexane
10 mL) was added ꢀbutyllithium solution in ꢀhexane (2.8
149.1 (14%), 134.1 (24%). ESIꢀMS (positive ions, acetonitrile):
+
ꢂ
m/z = 191.1 ([M + H] ). HRꢀMS (EI, 70 eV): calcd for
7
n
+
2
ꢂ
C H N : 190.14645, found: 190.14694. Analysis: calcd for
1
2
18
(
n
n
C H N C 75.7, H 9.5, N 14.7%; found C 75.5, H 10.0, N
1
2
18
2
mL, 1.6 M, 4.5 mmol) within 15 minutes at 0 °C and the resulꢀ
ting yellow suspension was stirred at ambient temperature for 3
1
4.8%.
h. The yellow solid was filtered off, washed with
n
ꢀhexane (5
{
[6-Methyl-4(piperidin-1’-yl)pyridine-2-yl]methyl}lithium (11)
To a solution of aminolutidine 10 (2.51 g, 13.2 mmol) in ꢀhexꢀ
ane (30 mL) was added ꢀbutyllithium solution in ꢀhexane
1
mL) and dried in vacuo to yield
MHz, thfꢀd ): δ [ppm] = 5.02 (s, 1H, H ), 4.88 (s, 1H, H ), 2.67
8 (0.48 g, 72%). H NMR (500
3
5
n
8
7
n
n
(
m, 6H, NꢀCH ), 2.26 (s, 2H, CH Li), 1.81 (s, 3H, CH ). Li
3 2 3
1
3
1
(9.0 mL, 1.6 M, 14 mmol) within 10 min at 0 °C and the resulꢀ
ting yellow suspension was stirred at ambient temperature for 2
h. The yellow solid was filtered off, washed with nꢀhexane
NMR (194 MHz, thfꢀd ):
MHz, thfꢀd ): δ [ppm] = 168.5 (C ), 155.9 (C ), 154.8 (C ), 91.4
(
δ [ppm] = 0.40. C{ H} NMR (126
8
4
6
2
8
3
5
1
C ), 90.2 (C ), 50.0 (CH Li), 39.8 (NꢀCH ), 25.1 (C ).
2 3
1
(
10 mL) and dried in vacuo to yield 11 (2.25 g, 87%). H NMR
3
5
2
-{[Bis(pentafluorophenyl)boryl]methyl}-4-dimethylamino-6-
(500 MHz, thfꢀd ):
2.91 (m, 4H, H ), 2.32 (s, 2H, CH Li), 1.79 (s, 3H, CH ), 1.52
δ
[ppm] = 5.12 (s, 1H, H ), 4.83 (s. 1H, H ),
8
’
2
methylpyridine (9)
To solution of chlorobis(pentafluorophenyl)borane
0.731 g, 1.92 mmol) in toluene (8 mL) was added organolithiꢀ
um compound (0.300 g, 1.92 mmol) at −30 °C. The yellow
2
3
3
’/4’
7
(
1
m, 6H, H ). Li NMR (194 MHz, thfꢀd ):
3
δ
[ppm] = 0.33.
8
a
(3)
1
4
C{ H} NMR (126 MHz, thfꢀd ):
δ
5
[ppm] = 167.8 (C ), 155.8
8
(
6
2
3
2’
(
C ), 155.5 (C ), 94.1 (C ), 91.8 (C ), 52.0 (CH –Li), 49.9 (C ),
2
8
3
’
4’
2
7.0 (C ), 25.0 (C ).
solution was slowly warmed to ambient temperature and stirred
overnight. The brown suspension was filtered, the solvent was
evaporated and the brown residue washed with
2
1
-{[Bis(pentafluorphenyl)boryl]methyl}-6-methyl-4-(piperidin-
’-yl)pyridine (12)
nꢀpentane
(
5 mL). The brown solid was suspended in ꢀhexane (20 mL), a
n
To
a solution of chlorobis(pentafluorophenyl)borane (3)
main part of the product was dissolved and the supernatant
solution transferred to a separate flask by syringe. The product
(
0.612 g, 1.60 mmol) in toluene (8 mL) was added organoꢀ
lithium compound 11 (0.299 g, 1.60 mmol) at −30 °C. The
yellow suspension was slowly warmed to ambient temperature
and stirred for three days. The brown suspension was filtered,
the solvent was evaporated and the resulting residue washed
9
was crystallized at −30 °C, the supernatant was removed by
syringe and the slightly yellow solid dried in vacuo (0.16 g,
7%). Crystals suitable for Xꢀray diffraction were obtained
1
1
from a concentrated solution in benzene at r.t. H NMR (500
MHz, C D ):
3
5
with
n
ꢀpentane (5 mL) three times and dried in vacuo. The
ꢀhexane (50 mL) and
δ [ppm] = 5.69 (s, 1H, H ), 5.52 (s. 1H, H ), 2.53
6
6
1
1
resulting brown solid was suspended in n
(
(
s, 2H CH ), 2.00 (s, 6H, NꢀCH ), 1.93 (s, 3H, CH ). B NMR
160 MHz, C D ):
2
3
3
1
3
1
most of the product was dissolved. The supernatant liquid was
transferred to a separate flask, concentrated and 12 precipitated
at −30 °C. The supernatant liquid was removed by a syringe
and the remaining solid dried in vacuo to yield 12 (0.28 g,
δ [ppm] = −2.27 (s, τ1/2 = 172 Hz). C{ H}
6
6
2
4
NMR (126 MHz, C D ):
δ
[ppm] = 164.7 (C ), 157.0 (C ),
52.0 (C ), 148.1 (dm, JF,C = 239 Hz, ꢀCꢀF), 139.7 (dm,
JF,C = 249 Hz, pꢀCꢀF), 137.3 (dm, JF,C = 252 Hz, ꢀCꢀF),
ꢀC), 104.7 (C ), 102.1 (C ), 38.3 (NCH ), 23.3 (br.,
6
6
6
1
1
o
1
1
m
1
3
3
5
32%). H NMR (500 MHz, C
6
D
6
):
δ
[ppm] = 5.84 (s, 1H, H ),
and CH –B), 1.93 (s, 3H,
1
19.7 (br., i
3
5
1
9
5.70 (s, 1H, H ), 2.55 (m, 6H, N–CH
CH ), 1.10 (m, 2H, C ), 0.99 (m, 4H, C ). B NMR (160
2
2
CH B), 17.9 (CH ). F NMR (470 MHz, C D ):
−
ESIꢀMS (positive ions, acetonitrile): m/z = 495.2 ([M + H] ).
HRꢀMS (ESI, positive ions, acetonitrile): calcd for
δ
[ppm] =
2
3
6
6
4
’
3’
11
3
135.0 (m, 4F,
o
ꢀF), −158.5 (m, 2F,
p
ꢀF), −164.1 (m, 4F, ꢀF).
m
1
3
1
+
ꢂ
MHz, C
6
D
):
6
δ
[ppm] = −2.43 (s,
τ1/2 = 197 Hz). C{ H} NMR
2
4
6
(
126 MHz, C D ):
148.1 (dm,
pꢀCꢀF), 137.6 (dm,
105.9 (C ), 103.3 (C ), 46.8 (N–CH ), 25.1 (C ), 24.0 (C ),
2
δ
[ppm] = 165.5 (C ), 157.4 (C ), 152.9 (C ),
6
6
1
1
+
2
J
F,C = 227 Hz,
o
ꢀCꢀF), 140.0 (dm,
J
F,C = 249 Hz,
ꢀC),
C H BF N 495.10849, found 495.10693.
2
1
14
10
1
J
= 252 Hz, ꢀCꢀF), 119.9 (broad, i
m
F,C
5
3
3’
4’
2
,6-Dimethyl-4-(piperidine-1-yl)pyridine (10)
A glass ampoule was filled with 4ꢀchloroꢀ2,6ꢀdimethylpyridine
) (2.14 g, 7.63 mmol) and piperidine (12.9 g, 151 mmol),
sealed and stirred for 3 days at 160 °C. The colourless preciꢀ
pitate was filtered off, washed two times with ꢀhexane (5 mL).
1
9
2
3.7 (br., CH ꢀB), 18.3 (CH ). F NMR (470 MHz, C D ):
δ
2
3
6
6
[
4
ppm] = −135.0 (m, 4F,
F,
HRꢀMS (ESI, pos. acetonitrile): calcd for C H BF N
2
o
ꢀF), −158.4 (m, 2F, pꢀF), −164.1 (m,
(
6
+
mꢀF). ESIꢀMS (pos., acetonitrile): m/z = 535.2 ([M + H] ).
+
2
3
18
10
n
5
35.13979, found 535.13851.
The solvent and the residual piperidine were removed in vacuo
and 2,6ꢀdimethylꢀ4ꢀ(piperidinꢀ1’ꢀyl)pyridine (10) was obtained
as a colourless solid (2.51 g, 93%). H NMR (500 MHz,
CDCl3):
2
NMR (126 MHz, CDCl ):
1
C
1
2
-tert-Butyl-6-methylpyridine (14)
1
To a solution of 2ꢀbromoꢀ6ꢀtertꢀbutylpyridine (13) (6.46 g,
30.2 mmol) in thf (150 mL) was added ꢀbutyllithium solution
in ꢀhexane (19.0 mL, 1.6 M, 30 mmol) within 20 min at
δ
[ppm] = 6.38 (s, 2H, ArꢀH), 3.30 (m, 4H, N–C
H
2),
1
3
1
n
.41 (s, 6H, CH ), 1.63 (m, 6H, N–CH –CH2–CH2). C{ H}
3
2
2,6
4
n
δ
[ppm] = 158.1 (C ), 156.3 (C ),
3
3,5
−78 °C and the yellow solution stirred at this temperature for
another 40 min. Methyl iodide (4.40 g, 31.0 mmol) was added
and the solution warmed to ambient temperature and stirred
overnight. An excess of methyl iodide was quenched with aqueꢀ
05.2 (C ), 47.6 (N–
CH ), 25.3 and 25.0 (s, N–CH –CH2–
2 2
+
ꢂ
H ), 24.6 (CH ). EIꢀMS (70 eV): m/z = 190.2 ([M] , 67%),
89.2 ([M − H] , 100%), 175.2 ([M − CH ] , 6%), 161.1 (8%),
3
2
3
+
+
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

Dalton Transactions
Page 8 of 12
View Article Online
ARTICLE
DOI: 10.1039/C 1068C
Jou5DrnT0al Name
ous ammonia (5 mL, 25 wt%), water was added (200 mL) and (6.25 mL, 1.6 M, 10 mmol) within 10 min and the yellow susꢀ
the aqueous phase was extracted three times with dichloroꢀ pension was stirred at ambient temperature for 2 h. Allyl broꢀ
methane (200 mL). The combined organic extracts were mide (1.46 g, 12.2 mmol) in diethyl ether (10 mL) was added
washed with brine (50 mL), dried over Na SO and the solvents dropwise and the resulting colourless suspension stirred at
2
4
removed under reduced pressure. Pyridine derivative 14 was ambient temperature overnight. Water (20 mL) was added, the
obtained after vacuum distillation (b.p. 80 °C, 3 Torr) as a aqueous phase was extracted three times with dichloromethane
1
colourless liquid (2.75 g, 61%). H NMR (500 MHz, CDCl ):
δ
(20 mL) and the combined organic extracts were washed with
3
3
4
3
[
1
1
ppm] = 7.47 (t,
H, H ), 6.92 (d,
J
= 7.8 Hz, 1H, H ), 7.12 (d, JH,H = 7.9 Hz, brine (20 mL). After drying over Na SO , all volatile comꢀ
= 7.6 Hz, 1H, H ), 2.53 (s, 3H, CH ), pounds were removed in vacuo
ꢀBu). C{ H} NMR (126 MHz, CDCl ):
168.7 (C ), 157.1 (C ), 136.2 (C ), 120.0 (C ), 115.7 (C ), (20 mL). The aqueous phase was separated, basified with
H,H
2
4
3
3
5
J
.
n
ꢀPentane (20 mL) was added
H,H
3
1
3
1
.36 (s, 9H,
t
δ
[ppm] and the pyridine acidified with 2 mL conc. HCl in water
3
2
6
4
5
3
=
3
m
7.4 [ (CH ) ], 30.4 [C( H ) ], 24.9 (CH ). EIꢀMS (70 eV): NaOH and extracted three times with dichloromethane
C
C
3 3
3
3
3
+
ꢂ
+
/z = 149.1 (([M] , 17%), 148.1 ([M − H] , 28%), 134.0 ([M − (30 mL). The combined organic extracts were dried over
+
CH ] , 100%), 107.0 (43%).
Na SO and all volatile compounds removed in vacuo. After
2 4
3
column chromatography (
nꢀpentane/dichloromethane 5:1 +
{
[6-(tert-Butyl)pyridine-2-yl]methyl}lithium (15)
To a solution of methyl pyridine 14 (1.34 g, 8.98 mmol) in
hexane (6 mL) was added ꢀbutyllithium solution in ꢀhexane H ), 5.89 (m, 1H, CH=CH ), 5.07 (d, JH,H = 17.2 Hz, 1H,
7.0 mL, 1.6 M, 11 mmol) at 0 °C within 10 min and stirred at CH=CH2,trans), 4.97 (d, JH,H = 10.2 Hz, 1H, CH=CH2,cis), 2.97
1
.5% Et N) 17 was obtained as a slightly yellow liquid (0.79 g,
3
1
n
ꢀ
45%). H NMR (500 MHz, CDCl ): δ [ppm] = 6.23 (s, 2H,
3
3/5
3
n
n
2
3
(
3
ambient temperature for 3 h. The precipitated yellow solid was (s, 6H, N(CH ) ), 2.74 (t, JH,H = 7.8 Hz, 2H, CH2–CH2–
3
2
filtered off, washed with
nꢀhexane (3 mL), dried in vacuo and CH=CH ), 2.43 (m, 5H, CH –CH2–CH=CH2 and ArꢀCH ).
2 2 3
1
13
1
2
1
5
was obtained as a yellow solid (0.77 g, 55%). H NMR (300
C{ H} NMR (126 MHz, CDCl ): δ [ppm] = 161.1 (C ), 157.9
3
3
3
6
4
MHz, thfꢀd ):
δ
[ppm] = 6.21 (dd, JH,H = 6.7 Hz, JH,H = 8.6 (C ), 155.5 (C ), 138.6 (CH –CH –
C
H=CH ), 114.7 (CH –
8
2
2
2
2
4
3
3
5
3
Hz, 1H, H ), 5.62 (d, JH,H = 8.7 Hz, 1H, H ), 5.11 (d, CH –CH=
C
H ), 103.7 (C ), 102.9 (C ), 37.3 (N(
C
H ) ), 38.4
3 2
2
2
3
5
J
= 6.7 Hz, 1H, H ), 2.25 (s, 2H, CH ), 1.10 (s, 9H,
t
ꢀBu).
(
C
H –CH –CH=CH ), 34.4 (CH –CH –CH=CH ), 25.2 (Arꢀ
H,H
2
2
2
2
2 2 2
1
3
1
6
+ꢂ
C{ H}ꢀNMR (76 MHz, thfꢀd ):
δ
[ppm] = 166.1 (C ), 163.7 CH ). EIꢀMS (70 eV): m/z = 190.2 ([M] , 82%), 189.1 ([M −
8
3
2
4
3
5
+
+
(
[
C ), 132.0 (C ), 111.9 (C ), 92.2 (C ), 50.3 (CH –Li), 35.7 H] , 100%), 176.0 ([M − CH ] , 30%), 163.1 (30%), 150.1 (M
2 3
C
+
ꢂ
(CH )], 29.6 [C(
C
H )].
− allyl). HRꢀMS (EI, 70eV): calcd for C H N 190.14645,
12 18 2
3
3
found: 190.14682. Analysis: calcd for C H N C 75.7, H 9.5,
1
2
18
2
2
-But-3’-enyl-6-methylpyridine (16)
To a solution of 2,6ꢀlutidine (5.69 g, 53.1 mmol) in diethyl
ether (100 mL) was added ꢀbutyllithium solution in ꢀhexane
34 mL, 1.6 M, 54.4 mmol) within 15 min and the deep red To a solution of methyl pyridine 17 (1.22 g, 8.18 mmol) in
solution was stirred at ambient temperature for 1.5 h. A solution diethyl ether (20 mL) was added ꢀbutyllithium solution in nꢀ
N 14.7%; found C 75.2, H 9.7, N 14.2%.
6
-But-3’-enyl-2-tert-butylpyridine (18)
n
n
(
n
of allyl bromide (7.18 g, 59.3 mmol) in diethyl ether (15 mL) hexane (5.6 mL, 1.6 M, 9.0 mmol) dropwise and the orange
was added dropwise and the resulting yellow solution stirred at solution stirred at ambient temperature for 3 h. Allyl bromide
ambient temperature overnight. Water (100 mL) was added, the (1.21 g, 10.0 mmol) in diethyl ether (10 mL) was added within
phases separated and the aqueous phase extracted three times 20 min and the mixture stirred overnight. Water (40 mL) was
with dichloromethane (50 mL). The combined organic extracts added and the aqueous phase extracted three times with
were dried over Na SO4 and the solvents removed under dichloromethane (30 mL). The combined organic extracts were
2
reduced pressure to yield 16 after vacuum distillation (b.p. washed with brine (20 mL), dried over Na SO and all volatile
2
4
6
0 °C, 4 torr) as a colourless liquid (3.15 g, 40%). The NMR compounds were removed in vacuo. The product 18 was
2
8 1
data are in good agreement with the literature. H NMR (500 obtained after column chromatography (dichloromethane/nꢀ
MHz, CDCl ):
3
4
1
δ [ppm] = 7.45 (t, JH,H = 7.6 Hz, 1H, H ), 6.93 hexane 1:3) as a colourless liquid (0.96 g, 62%). H NMR (300
3
3
3/5
3
4
(
3
t, JH,H = 7.6 Hz, 2H, H ), 5.86 (m, 1H, CH=CH ), 5.03 (d, MHz, CDCl ): δ [ppm] = 7.48 (t, JH,H = 7.8 Hz, 1H, H ), 7.11
2 3
JH,H = 17.0 Hz, 1H, CH=C
3
3
3
3
5
H
3
2,trans), 4.95 (d, JH,H = 10.4 Hz, (d, JH,H = 7.8 Hz, 1H, H ), 6.90 (d,
J
= 7.8 Hz, 1H, H ),
H,H
3
1
H, CH=CH2,cis) 2.83 (t, JH,H = 7.6 Hz, 2H, CH2–CH2– 5.89 (m, 1H,
C
H
=CH ), 5.05 (d, JH,H = 17.3 Hz, 1H,
2
3
3
CH=CH ), 2.50 (s, 3H, CH ), 2.45 (q, JH,H = 7.5 Hz, 2H, CH2– CH=CH2,trans), 4.95 (d, JH,H = 10.3 Hz, 1H, CH=CH2,cis), 2.86
C
1
1
2
3
1
3
1
3
3
H2–CH=CH ). C{ H} NMR (126 MHz, CDCl ):
δ
[ppm] = (t, JH,H = 7.0 Hz, 2H, CH2–CH –CH=CH ), 2.51 (q,
J
=
2
3
2
2
H,H
1
2
6
4
13
60.9 (C ), 157.8 (C ), 138.0 (CH –CH –
20.6 and 119.6 (C ), 115.0 (CH –CH –CH=
H –CH –CH=CH ), 34.1 (CH –
C
H=CH ), 136.4 (C ), 7.0 Hz, 2H, CH –CH2–CH=CH ), 1.34 (s, 9H,
t
2
ꢀBu). C{ H}
2
2
2
2
2
3/5
6
C
H ), 37.9 NMR (76 MHz, CDCl3):
δ
[ppm] = 168.5 (C ), 159.9 (C ),
2
2
2
4
5
3
(
C
C
H –CH=CH ), 24.6 (CH ).
138.5 (CH ꢀCH ꢀCH=CH ), 136.0 (C ), 119.4 (C ), 115.8 (C ),
2 2 2
2
2
2
2
2
2
3
1
14.6 (CH ꢀCH ꢀCH=
C
C
H ), 37.8 (
C
H –CH –CH=CH ), 37.4
2
2
2
2
2
2
2
-But-3’-enyl-4-dimethylamino-6-methyl-pyridine (17)
(
C
(CH ) ), 33.4 (CH –
H –CH=CH ), 30.2 (C(
C
H ) ). EIꢀMS
3
3
2
2
2
3 3
+
ꢂ
+
To a solution of aminolutidine
ether (30 mL) was added ꢀbutyllithium solution in
7
(1.45 g, 9.65 mmol) in diethyl (70 eV): m/z = 189.1 ([M] , 21%), 188.1 ([M − H] , 49%),
+
n
n
ꢀhexane 174.1 ([M − CH ] ,100%), 147.1 (M – H − C H ), 133.1. HRꢀ
3
3
5
8
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

Page 9 of 12
Journal Name
Dalton Transactions
View Article Online
ARTICLE
DOI: 10.1039/C5DT01068C
+
ꢂ
MS (EI, 70eV): calcd for C H N 189.15120, found C H BF N C 53.8, H 3.6, N 5.2%; found C 53.8, H not deꢀ
1
3
19
24 19
10
2
1
7
89.15158. Analysis: calcd for C H N C 82.5; H 10.1; N tectable due to HF formation, N 4.9%.
13 19
.4%; found C 82.2; H 10; N 7.4%.
6
-{4’-[Bis(perfluorophenyl)boranyl]butyl}-2-tert-butylpyridine
2
-{4’-[(Bis(perfluorophenyl)boranyl]butyl}-6-methylpyridine
(21)
(19)
Bis(pentafluorophenyl)borane (22) (365 mg, 1.05 mmol) was
A reaction flask was filled with bis(pentafluorophenyl)borane filled into a glass ampoule and toluene (5 mL) was condensed
22) (471 mg, 1.36 mmol) and toluene (10 mL) and olefin 16 onto it. Olefine 18 (200 mg, 1.05 mmol) was added via syringe
(
was added to the colourless suspension by syringe. The flask at ambient temperature and the colourless solution was heated
was closed and the colourless solution heated to 100 °C overꢀ to 120 °C for 3 d. Toluene was evaporated to dryness, the
night. The solvent was condensed off, the remaining solid remaining colourless solid was washed with
washed two times with ꢀpentane (2 mL) and dried in vacuo dried in high vacuum and the hydroboration product 21 was
Toluene (4 mL) was added and 19 was precipitated at −80 °C as obtained (0.54 g, 96%). H NMR (500 MHz, C D ):
nꢀpentane (5 mL),
n
.
1
δ
[ppm] =
6
6
1
3
3
3
a colourless solid (290 mg, 43%). H NMR (500 MHz, C D ):
δ
7.15 (overlap with C D H, H ), 6.90 (d. JH,H = 7.9 Hz, 1H, H ),
6 5
6
6
3
4
3
3
5
3
[
1
1
ppm] = 6.59 (t,
J
3
= 7.7 Hz, 1H, H ), 6.23 (d. JH,H = 7.8 Hz, 6.65 (d, JH,H = 7.7 Hz, 1H, H ), 2.75 (t, JH,H = 7.4 Hz, 2H, Ar–
H,H
5
3
3
H, H ), 6.05 (d, JH,H = 7.7 Hz, 1H, H ), 2.54 (s, 2H, CH –B),
.78 (s, 3H, CH ), 1.48 and 1.43 (m, 6H, Ar–CH2–CH2–CH2
CH –B). BꢀNMR (160 MHz, C D ):
CH2–CH –CH –CH ꢀB), 1.92 (t, JH,H = 7.7 Hz, 2H, Ar–CH2ꢀ
2 2 2
2
3
–
CH –CH –CH2–B), 1.86 (quin, JH,H = 7.5 Hz, 2H, Ar–CH2–
2 2
3
1
1
3
δ
[ppm] = 0.11 (s,
CH2–CH –CH –B), 1.56 (quin, JH,H = 7.5 Hz, 2H, Ar–CH2–
2 2
δ [ppm] = CH –CH2–CH –B). B NMR (160 MHz, C D ): δ [ppm] =
2 2 6 6
ꢀCꢀF), 139.6 74.8 (s, τ1/2 = ~1100 Hz). C{ H} NMR (126 MHz, C D ):
[ppm] = 168.9 (C ), 160.5 (C ), 147.0 (dm, JF,C = 248 Hz,
iꢀC), 36.2 F), 143.5 (dm, JF,C = 258 Hz, pꢀCꢀF), 139.2 (C ), 137.6 (dm,
2
6
6
1
3
1
11
τ1/2 = 140 Hz). C{ H} NMR (126 MHz, C D ):
6
6
2
6
1
13
1
1
(
2
65.3 (C ), 160.4 (C ), 148.2 (dm, JF,C = 240 Hz,
o
δ
6
6
1
4
1
2
6
1
dm, JF,C = 250 Hz, pꢀCꢀF), 139.2 (C ), 137.6 (dm, JF,C
=
o
ꢀCꢀ
5
3
1
4
43 Hz,
m
ꢀCꢀF), 125.7 (C ), 125.6 (C ), 123.4 (br.,
1
4
5
3
(
C
C
H2–
H –B), 25.6 (
C
H –CH –CH –CH –B), 24.2 (CH and CH –
JF,C = 251 Hz,
[ppm] = 114.3 (br., ꢀC), 38.2 (
ꢀF), −163.9 32.8 (CH2– H –CH –CH –B), 32.4 (CH –
ꢀF). ESIꢀMS (positive ions, acetonitrile): m/z 32.2 (br, H –B) 30.3 (C(
m
ꢀCꢀF), 136.4 (C ), 119.6 (C ), 116.2 (C ),
2
2
2
2
2
3
2
1
9
C
H –CH –B). F NMR (470 MHz, C D ):
δ
i
C
C
C
(CH ) ), 37.6 ( H –CH –CH –CH –B),
C
2
2
2
6
6
3 3
2
2
2
−
130 – −135 (very broad,
o
ꢀF), −158.3 (broad, 2F,
p
C
H –CH –CH –B),
2
2
2
2
2
2
2
(
4
broad, 4F,
m
=
CH ) ), 24.8 (CH –
C
H2–
CH –CH –
2
3 3
2
2
2
+
19
94.1 ([M + H] ). HRꢀMS (ESI, positive ions, acetonitrile): B). F NMR (470 MHz, C D ):
calcd for (C H BF N) H : 987.21920, found: 987.21676. −147.3 (m, 2F,
δ
[ppm] = −130.4 (m, 4F,
ꢀF), −160.8 (m, 4F,
Analysis: calcd for C H BF N C 53.6, H 2.9, N 2.8%; found ions, acetonitrile): m/z = 536.3 ([M + H] ). HRꢀMS (ESI,
o
ꢀF),
6
6
+
p
mꢀF). ESIꢀMS (positive
2
2
14
10
2
+
2
2
14
10
+
C 53.2, H 3.1, N 2.8%.
positive ions, acetonitrile): calcd for C H BF N 536.16019,
25 21 10
found: 536.16088. Analysis: calcd for C H BF N C 56.1, H
2
5
20
10
2
-{4’-[Bis(perfluorophenyl)boranyl]butyl}-4-dimethylamino-6-
3
.8, N 2.6%; found C 55.9, H 4.1, N 2.7%.
methyl-pyridine (20)
H/D-scrambling experiments
Bis(pentafluorophenyl)borane (22) (183 mg, 0.96 mmol) was
filled in a glass ampoule and toluene (5 mL) was condensed A Young valve NMR tube was filled with 15–25 mg of the
onto it. Olefine 17 (100 mg, 0.53 mmol) was added via syringe sample and 0.4 mL CD Cl . The solution was degassed by two
2
2
at ambient temperature and the colourless solution was heated freeze pump thaw cycles and backfilled with one atmosphere of
to 120 °C overnight. Toluene was evaporated to dryness, the a 50:50 mixture of hydrogen and deuterium, premixed in a
remaining colourless solid was washed with
nꢀpentane 60 mL glass tube. The formation of HD by compound 21 was
1
(
2
[
4
1.5 mL), dried in high vacuum and the hydroboration product detectable by NMR spectroscopy within 5 hours. HD: H NMR
1
1
0
was obtained (0.28 g, 98%). H NMR (500 MHz, C D ):
δ
(300 MHz, CD Cl ): δ [ppm] = 4.57 (t 1:1:1, JD,H = 42.6 Hz).
2 2
6
6
4
3
ppm]
=
5.65 (d, JH,H = 3.1 Hz, 1H, H ), 5.53 (d,
5
Crystallographic data
JH,H = 3.1 Hz, 1H, H ), 2.62 (broad, 1H, Ar–CH –CH –CH –
2
2
2
C
H2ꢀB), 1.93 (s, 6H, N(CH ) ), 1.90 (s, 3H, CH ), 1.62 (m, 6H, Crystal structures were determined by Xꢀray diffraction on a
3 2
3
1
1
Ar–CH2–CH2–CH2–CH –B). BꢀNMR (160 MHz, C D ):
δ
SuperNova, single source at offset, Eos diffractometer. Using
2
6
6
1
3
1
29
30
[
ppm] = −2.16 (s, τ1/2 = 210 Hz). C{ H} NMR (126 MHz, Olex2, the structure was solved with the ShelXS structure
2
6
4
C D ):
δ [ppm] = 163.1 (C ), 158.0 (C ), 154.0 (C ), 148.1 (dm, solution program using Direct Methods and refined with the
6
6
1
1
30
JF,C = 238 Hz,
o
ꢀCꢀF), 139.1 (dm, JF,C = 225 Hz, pꢀCꢀF), ShelXL refinement package using Least Squares minimisaꢀ
37.2 (dm, JF,C = 235 Hz, ꢀCꢀF), 125.1 (br., ꢀC), 106.9 tion. Data are listed in Table 2.
C ), 37.6 (N(CH ) ), 36.2 (ArꢀCH –CH –CH –CH2–B), 26.8
1
1
(
m
i
3
/5
3
2
2
2
2
1
9
Quantum-chemical calculations
and 24.8 and 23.0 (Ar–
NMR (470 MHz, C D ):
F), −159.5 (br., 2F,
C
H2–
[ppm] = −130 – −135 (very broad,
ꢀF), −164.3 (br., 4F, ꢀF). ESIꢀMS onal with D3 correction for dispersion interactions paired with
CH2ꢀCH –CH –B), 24.1 (CH ). F
2 2 3
3
1
32
δ
o
ꢀ
Density functional theory calculations with the PBE0 functiꢀ
6
6
3
3
p
m
+
(
positive ions, acetonitrile): m/z = 537.3 ([M + H] ). HRꢀMS builtꢀin 6ꢀ31G(d,p) basis set were carried out using the Gaussiꢀ
+
34
(
ESI, positive ions, acetonitrile): calcd for C H BF N : an 09 program package. Frequencies calculations were done
25 21 10 2
5
37.15544, found: 537.15633. Analysis: calcd for for all optimized structures to prove their equilibrium nature.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 9

Dalton Transactions
Page 10 of 12
View Article Online
ARTICLE
DOI: 10.1039/C 1068C
Jou5DrnT0al Name
Acknowledgements
6
7
a) G. Ménard, J. A. Hatnean, H. J. Cowley, A. J. Lough, J. M.
Rawson and D. W. Stephan, J. Am. Chem. Soc. 2013, 135, 6446–
We thank KlausꢀPeter Mester, Gerd Lipinski and Dr. Andreas
Mix for recording the NMR spectra, Brigitte Michel for perforꢀ
ming the elemental analyses as well as Dr. Jens Spross, Heinzꢀ
Werner Patruck and Sandra Heitkamp for recording the mass
spectra.
6
449; b) C. Appelt, J. C. Slootweg, K. Lammertsma and W. Uhl,
Angew. Chem Int. Ed. 2013, 52, 4256–4259.
a) P. Jochmann and D. W. Stephan, Angew. Chem. Int. Ed. 2013 ,
.
,
52
9
831–9835; b) R. Dobrovetsky and D. W. Stephan, Angew. Chem.
Int. Ed. 2013
,
52, 2516–2519; c) R. Dobrovetsky and D. W. Stephan,
55, 206–209.
M. Reißmann, A. Schäfer, S. Jung and T. Müller, Organometallics
013, 32, 6736−6744; b) A. Schäfer, M. Reißmann, A. Schäfer, M.
Israel J. Chem. 2015
,
8
9
Table 2: Crystallographic data of compounds 9 and 19.
2
9
19
Schmidtmann and T. Müller, Chem. Eur. J. 2014, 20, 9381–9386.
Empirical formula
C
21
H
13BF10
494.14
0.71073
94.98(13)
992
N
2
C
22
H
14BF10N
493.15
0.71073
99.99(10)
992
V. Sumerin, F. Schulz, M. Nieger, M. Leskelä, T. Repo and B.
M
r
Rieger, Angew. Chem
10 V. Sumerin, F. Schulz, M. Atsumi, C. Wang, M. Nieger, M. Leskelä,
. Int. Ed. 2008, 47 , 6001–6003.
λ [Å]
T [K]
F(000)
T. Repo, P. Pyykkö and B. Rieger, J. Am. Chem. Soc. 2008, 130
4117–14119.
11 K. Chernichenko, M. Nieger, M. Leskelä and T. Repo, Dalton Trans
012, 41, 9029–9032.
2 S. Schwendemann, R. Fröhlich, G. Kehr and G. Erker, Chem. Sci
2011, , 1842.
,
.
.
Crystal system
Space group
a [Å]
monoclinic
P2 /n
monoclinic
P2 /n
1
1
1
12.0013(3)
11.1213(2)
14.8617(3)
93.860(2)
1979.09(8)
4
1.658
0.164
60.06
−16 ≤ h ≤ 16
−15 ≤ k ≤ 15
−20 ≤ l ≤20
61610
5765
0.0325
5034
359
0.0392
0.1036
11.2973(2)
13.7505(2)
12.6885(2)
96.5752(17)
1958.11(6)
4
b [Å]
c [Å]
2
1
1
1
β [°]
3
V [Å ]
2
Z
3 S. J. Geier and D. W. Stephan, J. Am. Chem. Soc. 2009, 131, 3476–
3477.
–
3
ρ
calcd. [g cm ]
[mm ]
1.673
0.164
59.99
–
1
ꢁ
4 J. Vergnaud, T. Ayed, K. Hussein, L. Vendier, M. Grellier, G.
Bouhadir, J.ꢀC. Barthelat, S. SaboꢀEtienne and D. Bourissou, Dalton
Trans. 2007, 2370.
2
θmax [°]
Index range h
Index range k
Index range l
Refl. collect.
Indep. refl.
−15 ≤ h ≤ 14
−19 ≤ k ≤ 19
−17 ≤ l ≤ 17
55604
5687
0.0257
4928
343
0.0387
0.0920
0.0468
0.0960
1.084
0.35/–0.23
1042620
1
1
5 J.ꢀH. Son and J. D. Hoefelmeyer, Org. Biomol. Chem. 2012, 10
,
6656.
R
int
6 T. A. Rokob, A. Hamza, I. Pápai, J. Am. Chem. Soc. 2009, 131
,
Observed refl., I>2σ(I)
1
0701–10710.
17 Y. H. Kim, T. H. Kim, N. Y. Kim, E. S. Cho, B. Y. Lee, D. M. Shin
and Y. K. Chung, Organometallics 2003, 22 1503.
Parameters
R
1
, I>2σ(I)
wR , I>2σ(I)
(all data)
2
,
R
1
0.0459
0.1084
1.061
0.50/–0.22
1042619
1
8 a) T. Beringhelli, D. Donghi, D. Maggioni and G. D’Alfonso, Coord.
Chem. Rev. 2008, 252, 2292–2313; b) H. Nöth and B. Wrackmeyer,
wR
2
(all data)
GoF
max/min [e Å ]
−
3
ρ
Nuclear Magnetic Resonance Spectroscopy of Boron Compounds
,
,
CCDCꢀNo.
Springer, Berlin, 1978, vol. 14; c) W. E. Piers, Adv. Orgmet. Chem
2
004, 52, 1–76;
1
2
2
9 L. J. Hounjet, C. Bannwarth, C. N. Garon, C. B. Caputo, S. Grimme
Notes and references
and D. W. Stephan, Angew. Chem. Int. Ed. 2013, 52, 7492–7495.
0 R. Roesler, W. E. Piers and M. Parvez, Organomet. Chem. 2003, 680
,
a
Bielefeld University, Faculty of Chemistry, Chair of Inorganic and
2
18ꢀ222.
Structural Chemistry, Centre for Molecular Materials CM
straße 25, 33615 Bielefeld, Germany.
2
, Universitätsꢀ
1 M. J. G. Lesley, A. Woodward, N. J. Taylor, T. B. Marder, I.
Cazenobe, I. Ledoux, J. Zyss, A. Thornton, D. W. Bruce and A. K.
Kakkar, Chem. Mater. 1998, 10, 1355–1365.
1
2
3
4
G. C. Welch, Juan, R. R. San, J. D. Masuda, and D. W. Stephan,
2
2
2
2
2
2 S. J. Geier, A. L. Gille, T. M. Gilbert and D. W. Stephan, Inorg.
Chem. 2009, 48, 10466–10474.
Science 2006, 314, 1124–1126.
G. C. Welch and D. W. Stephan, J. Am. Chem. Soc. 2007, 129, 1880–
3 D. J. Parks, W. E. Piers and G. P. A. Yap, Organometallics, 1998, 17
,
1
881.
P. A. Chase, G. C. Welch, T. Jurca and D. W. Stephan, Angew.
Chem Int. Ed. 2007, 46, 8050–8053.
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TOC entry
Intramolecular pyridine-based frustrated Lewis-
pairs
L. A. Körte, R. Warner, Yu. V. Vishnevskiy, B. Neumann, H.-
G. Stammler and N. W. Mitzel*
Besides a series of pyridine-based Lewis pairs with B(C F )
6
5 2
groups with varying electronic and steric situations and strong
intramolecular B–N bonds, 2-[(CH ) B(C F ) ]-6- Bu-pyridine
t
2
4
6 5 2
was found to behave as a frustrated Lewis pair.
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