Metal-free hydrogenation of N -based heterocycles

Article abstract of DOI:10.1021/om4000727

Metal-free hydrogenation of substituted pyridines, quinolines, and several other N-heterocycles is achieved upon treatment of the nitrogen-based Lewis base with an equivalent of the Lewis acid B(C₆F₅)₃ and H₂ (4

Full text of DOI:10.1021/om4000727

Article
pubs.acs.org/Organometallics
Metal-Free Hydrogenation of N‑Based Heterocycles
Tayseer Mahdi, Jon Nathaniel del Castillo, and Douglas W. Stephan*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
S
* Supporting Information
ABSTRACT: Metal-free hydrogenation of substituted pyr-
idines, quinolines, and several other N-heterocycles is achieved
upon treatment of the nitrogen-based Lewis base with an
equivalent of the Lewis acid B(C6F5)3 and H2 (4 atm) at 115
°C, to afford the ammonium-[HB(C6F5)3] salts of the reduced
N-heterocycles.
series of substituted pyridines, quinolines, and several other N-
INTRODUCTION
■
based heterocycles targeting more fully reduced products.
Historically, partial homogeneous hydrogenation of quino-
lines using H2 was first reported using a Ru catalyst by Fish and
co-workers in 1982.29 Since then, Rh, Ir, and Os catalysts have
been developed.30 The reported homogeneous catalysts do not
effect the complete reduction of the N-heterocycle quinoline,
although Fache et al.31,32 found that substituted quinolines
were fully reduced to decahydroquinolines using colloidal Rh
on Al2O3 at room temperature and 50 atm of H2. In a recent
intriguing finding, Glorius et al. communicated that alteration
of the catalysts allowed for unprecedented selectivity, allowing
the reduction of substituted quinolines diastereoselectively to
5,6,7,8-tetrahydroquinolines or hydrogenation to decahydro-
quinolines.33 Furthermore, Glorius and co-workers have also
developed a homogeneous catalyst for the regioselective
asymmetric hydrogenation of the carbocyclic ring of substituted
quinoxalines.34
FLPs derived from boranes and N-based heterocycles such as
sterically hindered pyridines or quinolines are known to effect
the heterolytic cleavage of H2 under mild conditions,27,35,36 and
as mentioned above, partial catalytic reduction of the N-
heterocycle has been achieved. In this report, we explore the
hydrogenation of a variety of N-based heterocycles employing a
stoichiometric amount of B(C6F5)3 and 4 atm of H2. These
reductions are shown to selectively reduce aromatic pyridyl-
and aniline-type rings, leaving other aromatic rings untouched,
thus providing a unique and metal-free route to polycarbocyclic
amines.
Homogeneous hydrogenation of unsaturated substrates began
in the 1960s with the discovery of Rh1 and Ru2,3 catalysts by
Wilkinson and co-workers. Since this seminal work, a variety of
other systems have been developed.4−10 Although unprece-
dented levels of activity and selectivity have been achieved
through these metal systems, alternative hydrogenation
strategies using non-transition-metal catalysts are being ex-
plored. For example, an initial report by Berkessel et al.
described the reduction of benzophenone using KOtBu and H2
under forcing conditions.11 Subsequently, main group systems
were shown to react with H2 under mild conditions by
Power.12,13 In 2006, we uncovered the ability of frustrated
Lewis pairs (FLPs), that is, combinations of sterically
encumbered Lewis acids and bases, to heterolytically split
H2.14 Shortly thereafter we described the application of FLPs as
metal-free catalysts for the hydrogenation of imines, aziridines,
and nitriles.15 The research groups of Erker,16,17 Repo,18−20 and
Berke21 have further broadened the scope of substrates to
include enamines and silylenol ethers but perhaps more
importantly have broadened the range of FLP catalysts to
include a variety of P/B and N/B systems. In addition,
Klankermayer and co-workers have cleverly unveiled related
metal-free systems capable of asymmetric hydrogenations.22,23
More recently, we demonstrated the utilization of weak Lewis
bases in combination with B(C6F5)3 to permit the catalytic
hydrogenation of 1,1-disubstituted olefins24 and extended such
catalytic reductions to polycyclic aromatic hydrocarbons.25 In
an exciting extension of the study of these metal-free
reductions, we demonstrated that stoichiometric combinations
of sterically hindered anilines and B(C6F5)3 under 4 atm of H2
pressure effected reduction of the aromatic ring, affording
cyclohexylammonium salt derivatives.26 We have also pre-
viously communicated the partial reduction of N-heterocycles
using catalytic conditions,27 while Soos and co-workers28
extended the scope of such catalytic reductions using
specifically designed Lewis acids. Employing stoichiometric
conditions, we sought to extend the scope of aromatic
reductions beyond anilines and focused our attention on a
RESULTS AND DISCUSSION
■
Hydrogenation of Substituted Pyridines. The combi-
nation of the Lewis base 2,6-diphenylpyridine and the Lewis
acid B(C6F5)3 does not show evidence of a donor−acceptor
interaction by multinuclear NMR spectroscopy, in contrast to
the observation of a reversible adduct formation for 2,6-
lutidine.35 Exposure of either the combination of 2,6-lutidine or
Received: January 28, 2013
© XXXX American Chemical Society
A
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2,6-diphenylpyridine with B(C6F5)3 has been previously
reported to result in the activation of H2 at room temperature
over 16 h, affording the corresponding pyridinium−hydrido-
borate salt.36 However, on heating a mixture of 2,6-
diphenylpyridine and B(C6F5)3 under H2 (4 atm) at 115 °C
for 16 h, a new product, 1, was isolated in 92% yield (Table 1,
Table 1. Hydrogenation of Substituted Pyridines
Figure 1. POV-ray depiction of the molecular structure of (a) 1 and
(b) 2. Hydrogen atoms, except for BH and NH2 atoms, are omitted for
clarity.
amine−borane adduct formation in which rotation about the
B−N bond was inhibited. The 1H, 13C{1H}, 11B, and 19F NMR
of 3 displayed the presence of two diastereomers in a 1:1 ratio.
Most obvious were the 13C{1H} resonances at 167.4 and 171.2
ppm attributable to the CO2-ester carbons and the correspond-
a
The isolated product mixture consisted of 4 and 5 in a 4:1 ratio.
1
Reactions were carried out at 4 atm of H2.
ing H signals at 4.18 and 4.24 ppm arising from the methine
1
protons adjacent to the ester. Furthermore, H{1H} NOESY
experiments confirmed the assignment of these peaks to the
respective RS/SR and RR/SS diastereomers (see SI).
Interestingly, independent reaction of B(C6F5)3 with optically
pure S-2-(EtCO2)C5H9NH at low temperature (−35 °C) in
CD2Cl2 afforded the preferential formation of the SS-
diastereomer of 3. However, on warming to room temperature
over 18 h, racemization at nitrogen afforded a 1:1 mixture of
the SS and SR diastereomers of 3.
entry 1). The NMR data for 1 in CD2Cl2 displayed a doublet in
the 11B NMR at −24.6 ppm and three resonances in the 19F
NMR at −134.0 (o), −163.4 (m), and −166.6 (p) ppm,
1
confirming the presence of the HB(C6F5)3 anion. The H
NMR data showed a broad singlet at 5.90 ppm attributed to the
NH2 group, multiplets at 4.53, 2.26, 2.12, and 1.89 ppm, and
the signals assignable to the phenyl and HB(C6F5)3 groups.
These data were consistent with the formulation of 1 as the
diphenylpiperidium−hydridoborate salt [2,6-Ph2C51H8NH2]-
[HB(C6F5)3] (Table 1, entry 1). Furthermore, the H NMR
data revealed a diastereomeric excess (de) of 91% favoring the
meso-diastereomer of 1, an assignment that was confirmed via
NMR spectroscopy and isolation of crystals of meso-[2,6-
Ph2C5H8NH2][HB(C6F5)3] (see Supporting Information (SI)).
The structure of the major product 1 was confirmed via a
crystallographic study (Figure 1a). In a similar fashion, the
reaction of 2,6-lutidine with B(C6F5)3 under H2 at 115 °C for
60 h afforded the corresponding salt [2,6-Me2C5H8NH2][HB-
(C6F5)3] (2) in 84% yield with a de of 80%, favoring the meso-
diastereomer (Figure 1b). It should be noted that we have
previously demonstrated the ability of B(C6F5)3 to effect the
epimerization of chiral carbons adjacent to nitrogen by a
process involving hydride-abstraction and redelivery.37 Such
reactivity may account for the observed diastereoselectivity.
Ethyl 2-picolinate was also reduced under analogous
conditions. In this case, the adduct of the reduced pyridine,
(2-(EtCO2)C5H9NH)B(C6F5)3 (3), was isolated in 74% yield
after 36 h (Table 1, entry 2). The 11B NMR spectrum in
CD2Cl2 showed a broadened singlet at −4.86 ppm and
inequivalent 19F NMR resonances that were consistent with
In the case of 2-phenylpyridine and B(C6F5)3, a mixture of
two products of reduction was obtained after 48 h under H2 (4
atm). The mixture was isolated in 54% overall yield. A broad
11B NMR signal was seen at −3.91 ppm, together with a
doublet at −24.0 ppm, in a 4:1 ratio, consistent with the
presence of B−N adduct (2-PhC5H9NH)B(C6F5)3 (4) and [2-
PhC5H9NH2][HB(C6F5)3] (5), respectively (Table 1, entry 3).
The formulation of 4 is further supported by the observation of
19F signals and 1H NMR resonances resulting from the
B(C6F5)3 adduct of 2-phenylpiperidine. These NMR data,
together with the two distinctively broad NH singlets in the 1H
NMR at 5.55 and 5.81 ppm, were attributable to a 7:1 ratio of
the two diastereomers of 4. The RS/SR diastereomer 4 was the
more abundant form, as evidenced by NMR and X-ray
crystallographic data (Figure 2). Presumably, the favored RS/
SR diastereomer results from intramolecular π−π stacking
interactions of the C6H5 and C6F5 groups in addition to the
interactions between the C−H···Fortho and N−H···Fortho, which
are evidenced by 1H{19F} HOESY NMR spectroscopy (see SI).
Hydrogenation of Substituted N-Heterocycles. Expo-
sure of a stoichiometric mixture of 2-methylquinoline and
B(C6F5)3 to H2 (4 atm) at 115 °C for 48 h was found to effect
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Figure 3. POV-ray depiction of the molecular structures of the cations
(a) 6, (b) 7, (c) 8, and (d) 9. Selected hydrogen atoms are shown.
Figure 2. POV-ray depiction of the molecular structure of 4.
Hydrogen atoms are omitted for clarity. B−N: 1.66(5) Å.
1
[HB(C6F5)3] (8) in 76% yield (Table 2, entry 1). H and
the hydrogenation of the N-hetero- and carbocyclic rings to
yield [2-MeC9H15NH2][HB(C6F5)3] (6) in 67% yield (Table 2,
13C{1H} NMR data showed only the presence of the RRR/SSS
diastereomers (Figure 3c). The corresponding reduction of
acridine results in the isolation of the fully reduced tricyclic
species in 76% yield (Table 2, entry 2). The isolated product is
obtained as a mixture of two isomers, one of which was
characterized crystallographically as the salt [C13H22NH2][HB-
(C6F5)3] (9), in which the ring junctions in the cation are all
equatorially positioned (Figure 3d) and thus the SRSR/RSRS
diastereomers. Interestingly, a second product, 10, was isolated
from the pentane wash. Crystallographic data demonstrated it
to be the Lewis acid−base adduct (C13H22NH)B(C6F5)3
(Figure 4); however in this case the stereochemistry of the
a
Table 2. Hydrogenation of Substituted N-Heterocycles
Figure 4. POV-ray depiction of the molecular structure of 10.
Hydrogen atoms except for NH are omitted for clarity. B−N: 1.66(6)
Å.
a
Two equivalents of B(C6F5)3. Reactions were carried out at 4 atm of
ring junctions alpha to nitrogen are inverted, affording the
RRSS/SSRR diastereomers of the reduced acridine heterocycle.
Compound 10 was also independently synthesized in 73% yield
from a mixture of isomers of the neutral amine, C13H22NH, and
B(C6F5)3.
Reductions of the additional substrates 2,3-dimethyl- and 2,3-
diphenylquinoxaline yielded the piperazinium derivatives
[ ( C 4 H 6 M e ) 2 N H N H 2 ] [ H B ( C 6 F 5 ) 3 ] ( 1 1 ) a n d
[(C4H6Ph)2NHNH2][HB(C6F5)3] (12) in 59% and 55%
yield, respectively (Table 2, entry 3). In the case of 11, a
single set of diastereomers was observed and the NMR data
were consistent with ring junctions and methyl groups adopting
equatorial dispositions. In contrast, the isolated product 12 was
comprised of two diastereomers. One of these was crystallo-
graphically characterized (Figure 5) and shown to be the
diastereomer in which the phenyl rings adopt equatorial
H2.
entry 1). In a similar fashion, 2-phenylquinoline was reduced
after 48 h to give [2-PhC9H15NH2][HB(C6F5)3] (7) in 95%
yield. 1H NMR spectroscopy for 6 and 7 exhibits characteristic
chemical shifts corresponding to the NH2, methine, and
methylene groups. Both compounds 6 and 7 were produced
as mixtures of diastereomers, although in both cases the major
isomer was crystallized and found to comprise 60% and 73% of
the isolated products, respectively. X-ray methods (Figure 3a,b)
showed that the isolated diastereomers of 6 and 7 exhibited
SSS/RRR stereochemistries, in which one of the ring junctions
adopts an equatorial disposition, while the other is axially
disposed. Analogous treatment of 8-methylquinoline with H2
and B(C6F5)3 in toluene for 48 h yielded [8-MeC9H15NH2]-
C
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positions, while the ring junctions are axial and equatorially
disposed (Figure 5a).
Figure 6. POV-ray depiction of the cation of 14. Selected hydrogen
atoms are shown. Selected bond distances (Å) and angles (deg):
B(1)−N(1) 1.61(6), B(1)−N(2) 1.59(8), N(1)−B(1)−N(2) 96.6(3).
(NB: N(1) in heterocyclic amine, N(2) in pyridyl ring.)
number of N-heterocycles. It is clear that the products arise
from reduction of pyridyl- and/or aniline-type rings. In some
cases, the observation of a preferred set of diastereomers is
consistent with the known ability of B(C6F5)3 to effect
epimerization of chiral centers alpha to nitrogen.37 Efforts to
monitor several of the mixtures over the course of the reactions
failed to provide unambiguous mechanistic insight. Nonethe-
less, it is known that N-heterocycles in combination with
B(C6F5)3 effect the heterolytic cleavage of H2 under mild
conditions. By analogy with previous computational studies for
aniline hydrogenations, the need for elevated temperatures
presumably reflects the fact that hydride delivery from
[HB(C6F5)3] to the heterocycle is energetically uphill; however
once this is achieved, there is an exothermic route to the
saturated amine.26 Subsequent activation of H2 by the product
amine and borane affords the corresponding ammonium salt,
which is irreversible under the reaction conditions. This latter
reaction sequesters the borane and thus precludes further
catalytic reduction. While the reactions are nominally
stoichiometric in N and B, multiple turnovers of H2 delivery
are achieved in these reductions. For example, eight equivalents
of H2 are taken up by acridine in the formation of 9. The
reaction stoichiometry also facilitates product isolation and
purification, as the product salts readily crystallize from
solution.
Figure 5. POV-ray depiction of the molecular structures of the cations
(a) 12, (b) 13a, and (c) 13b. Selected hydrogen atoms are shown.
It is noteworthy that while the aromatic ring of the
quinoxaline fragment is fully reduced, the phenyl substituents
remain intact. In a similar situation reduction of 7,8-
benzoquinoline resulted in the formation of [(C6H4)-
C7H12NH2][HB(C6F5)3] (13) in 55% yield (Table 2, entry
4). The product was comprised of a 4:1 mixture of two
1
diastereomers, as evidenced by H NMR spectroscopy. X-ray
crystallography was used to unambiguously confirm that in
both isomers reduction of the pyridine and adjacent ring was
achieved while aromaticity of the ring remote from the N atom
was retained. The dominant diastereomer 13a was found to be
the SR/RS diastereomers (Figure 5b), while the less abundant
diastereomer 13b showed SS/RR stereochemistry (Figure 5c).
Finally, efforts to reduce the heterocycle 1,10-phenanthroline
were undertaken employing two equivalents of B(C6F5)3. This
resulted in the isolation of product 14 in 73% yield after 96 h at
115 °C (Table 2, entry 5). The 11B NMR spectrum revealed
the presence of two four-coordinate boron centers with
resonances at 3.91 and −25.4 ppm. The latter 11B NMR signal
together with the three corresponding 19F resonances arises
from the [HB(C6F5)3] anion. The second boron species
exhibited six inequivalent fluorine atoms, as evidenced by the
19F NMR spectrum, inferring the presence of two inequivalent
fluoroarene rings. X-ray crystallography confirmed the for-
mulation of 14 as the SRS/RSR diastereomer of [(C5H3N)-
(CH2)2(C5H8NH)B(C6F5)2][HB(C6F5)3]. The reported major
diastereomer was present as 65% of the isolated reaction
mixture. In the cationic fragment of compound 14, the boron
center is bound to two perfluoroarene rings and is chelated by a
pyridine and amine nitrogen atoms of a partially reduced 1,10-
phenanthroline (Figure 6). The B−N distances in the cation
were found to be 1.61(6) Å for B(1)−N(1)amine and 1.59(8) Å
for B(1)−N(2)py. In this unique case, presumably as the
reduction of the heterocycle proceeds, the relative disposition
of the two nitrogen atoms results in the preferential loss of
C6F5H from B(C6F5)3 and chelation of the partially reduced
phenanthroline to boron, thus affording the cation of 14.
The reductions described above demonstrate the ability of
B(C6F5)3 to mediate the complete aromatic reduction of a
CONCLUSIONS
■
The reduction of a variety of pyridyl- and aniline-type rings in
N-containing compounds is readily achieved upon heating a
mixture of the substrate precursor with an equivalent of
B(C6F5)3 under H2 (4 atm) at 115 °C. We are continuing to
develop FLP systems capable of such reductions and to explore
their utility in synthetic applications.
EXPERIMENTAL SECTION
■
General Considerations. All preparations were performed under
an atmosphere of dry, oxygen-free N2 by means of both standard
Schlenk line and glovebox techniques (MBraun glovebox equipped
with a −40 °C freezer). Pentane and toluene (Aldrich) were dried
employing a Grubbs-type column system (Innovative Technology),
degassed, and stored over molecular sieves (4 Å) in the glovebox.
Molecular sieves (4 Å) were purchased from Aldrich Chemical Co.
and dried at 140 °C under vacuum for 24 h prior to use.
Dichloromethane-d2 and bromobenzene-d5 were purchased from
Cambridge Isotope Laboratories, dried over CaH2, and distilled
under N2 prior to use. Tetrahydrofuran-d8 was purchased from
Cambridge Isotope Laboratories and distilled under N2 from Na/
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benzophenone. All substituted quinolines, pyridines, and other N-
heterocycles were purchased from Sigma-Aldrich or Alfa Aesar. The
oils were distilled over CaH2, and solids were sublimed under high
vacuum prior to use. B(C6F5)3 was purchased from Boulder Scientific
and sublimed at 80 °C under high vacuum before use. Nuclear
magnetic resonance (NMR) spectroscopy spectra were recorded on a
Bruker Avance III 400 MHz or a Varian 400 MHz spectrometer
equipped with an HFX AutoX triple resonance indirect probe (used
for 13C{1H, 19F} experiments), and spectra were referenced to residual
solvent of C6D5Br (1H = 7.28 ppm for meta-proton; 13C = 122.4 ppm
for ipso-carbon), CD2Cl2 (1H = 5.32 ppm; 13C = 53.84 ppm), THF-d8
(1H = 1.72 ppm for CH2(3,4); 13C = 25.31 ppm for CH2(3,4)), or
externally (11B: (Et2O)BF3, 19F: CFCl3). Chemical shifts (δ) are
reported in ppm, and the absolute values of the coupling constants (J)
are in Hz. NMR assignments are supported by additional 2D and
DEPT-135 experiments. Elemental analyses (C, H, N) were
performed in-house employing a Perkin-Elmer 2400 Series II CHNS
analyzer. H2 (grade 5.0) was purchased from Linde and dried through
a Nanochem Weldassure purifier column prior to use.
Reduction Procedure. These compounds were prepared in a
similar fashion; thus only one preparation is detailed and only specific
variations are presented below. In the glovebox, a 50 mL Teflon screw
cap glass bomb equipped with a stirbar was charged with a solution of
B(C6F5)3 (0.379 g, 0.740 mmol) and the respective N-heterocycle in
toluene (5 mL). The reaction tube was degassed three times through a
freeze−pump−thaw cycle on the vacuum/H2 line and filled with H2 (4
atm) at −196 °C. After the addition of H2 the reaction tube was placed
in a 115 °C oil bath for the indicated reaction time. The solvent was
then removed under reduced pressure, and the crude product was
washed with pentane to yield the product as a solid.
precipitate was washed with pentane (3 × 5 mL) and placed under
vacuum in a Schlenk flask at 50 °C for 2 h to give meso-2,6-
Me2C5H8NH·HCl in 98% yield.
Synthesis of [meso-2,6-Me2C5H8NH2][HB(C6F5)3]. A 4 dram vial
with a magnetic stirbar was charged with a slurry of NaHB(C6F5)3
(341 mg, 0.64 mmol) in dicholormethane (10 mL) and meso-2,6-
Me2C5H8NH·HCl (95 mg, 0.64 mmol) in dichloromethane (5 mL).
The mixture was stirred for 16 h at room temperature and filtered
through a pad of Celite. The solvent was removed under vacuum to
yield 74% of the product as a white solid.
Synthesis of [2-(CO2Et)C5H9NHB(C6F5)3] (3). Ethyl 2-picolinate
(112 mg, 0.740 mmol), reaction time 36 h, white solid, 74% isolated
yield. The isolated product consisted of a 1:1 ratio of both isomers.
Anal. Calcd (%) for C26H15BF15NO2: C 46.67; H 2.26; N 2.09. Found:
C 46.60; H 2.47; N 2.11.
[RS/SR-2-(CO2Et)C5H9NHB(C6F5)3] (3a). 1H NMR (400 MHz,
CD2Cl2): δ 5.90 (m, 1H, NH), 4.30 (m, 1H, CH(H)NH), 4.18 (br
2
3
m, 1H, CHCO2Et), 3.93 (dq, 1H, JHH = 10.8 Hz, JHH = 7.1 Hz,
2
3
OCH2), 3.73 (dq, 1H, JHH = 10.8 Hz, JHH = 7.1 Hz, OCH2), 3.20
(dm, 1H, 2JHH = 12.6 Hz, CH(H)NH), 2.17 (m, 2H, CH2), 2.04 (dm,
2
1H, JHH = 13.4 Hz, CH2), 1.84 (m, 1H, CH2), 1.75 (m, 1H, CH2),
1.19 (t, 3H, JHH = 7.2 Hz, Me), 1.03 (m, 1H, CH2). 13C{1H} NMR
3
(101 MHz, CD2Cl2): δ 167.4 (CO2), 63.6 (OCH2), 56.8 (CHCO2Et),
44.5 (CH(H)NH), 30.5 (CH2), 20.8 (CH2), 18.1 (CH2), 13.4 (Me).
19F NMR (377 MHz, CD2Cl2): δ −126.4 (m, 1F, o-C6F5), −128.0 (m,
1F, o-C6F5), −129.5 (m, 1F, o-C6F5), −129.7 (m, 1F, o-C6F5), −140.4
(m, 1F, o-C6F5), −143.3 (m, 1F, o-C6F5), −155.5 (t, 1F, 3JFF = 21 Hz,
p-C6F5), −157.3 (t, 1F, 3JFF = 21 Hz, p-C6F5), −157.5 (t, 1F, 3JFF = 21
Hz, p-C6F5), −161.6 (m, 1F, m-C6F5), −162.1 (m, 1F, m-C6F5),
−162.8 (m, 1F, m-C6F5), −163.1 (m, 1F, m-C6F5), −164.0 (m, 1F, m-
C6F5), −164.9 (m, 1F, m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ
−4.86 (s, BNH).
Synthesis of [2,6-Ph2C5H8NH2][HB(C6F5)3] (1). 2,6-Diphenylpyr-
idine (171 mg, 0.740 mmol), reaction time 16 h, white solid, 92%
isolated yield. Crystals suitable for X-ray diffraction were grown from a
layered solution of dichloromethane/pentane at −40 °C over 36 h.
Isomer ratio meso 91%, rac 9%.
[RR/SS-2-(CO2Et)C5H9NHB(C6F5)3] (3b). 1H NMR (400 MHz,
2
CD2Cl2): δ 7.43 (br m, 1H, NH), 4.40 (dq, 1H, JHH = 10.7 Hz,
2
3
3JHH = 7.1 Hz, OCH2), 4.38 (dq, 1H, JHH = 9.1 Hz, JHH = 7.1 Hz,
[meso-2,6-Ph2C5H8NH2][HB(C6F5)3]. 1H NMR (400 MHz,
2
OCH2), 4.24 (br m, 1H, CHCO2Et), 3.50 (ddd, 1H, JHH = 13.4 Hz,
3
4
3JHH = 8.9 Hz, JHH = 4.9 Hz, CH(H)NH), 3.33 (dm, 1H, JHH = 13.3
3
CD2Cl2): δ 7.34 (tt, 2H, JHH = 7.0 Hz, JHH = 2.4 Hz, p-Ph), 7.26
3
(m, 8H, o,m-Ph), 5.90 (br, 2H, NH2), 4.53 (m, 2H, JHH = 12.2 Hz,
Hz, CH(H)NH), 2.18 (m, 1H, CH2), 2.08 (m, 1H, CH2), 1.85 (m,
3JHH = 2.4 Hz, C(H)(Ph), 3.39 (br q, 1H, 1JHB = 90 Hz, BH), 2.26 (br
1H, CH2), 1.54 (m, 1H, CH2), 1.51 (m, 1H, CH2), 1.35 (t, 3H, 3JHH
=
m, 3H, B,ACH2), 2.12 (m, 2H, CH2), 1.89 (m, 1H, CH2). 13C{1H}
B
A
7.1 Hz, Me), 1.24 (m, 1H, CH2). 13C{1H} NMR (101 MHz,
CD2Cl2,): δ 171.2 (CO2), 61.6 (OCH2), 58.1 (CHCO2Et), 45.7
(CH(H)NH), 25.9 (CH2), 23.5 (CH2), 17.1 (CH2), 13.9 (Me). 19F
NMR (377 MHz, CD2Cl2): δ −127.6 (m, 1F, o-C6F5), −128.5 (m, 2F,
o-C6F5), −129.1 (m, 1F, o-C6F5), −137.1 (m, 1F, o-C6F5), −142.1 (m,
NMR (101 MHz, CD2Cl2): δ 148.3 (dm, 1JCF = 237 Hz, C6F5), 138.0
1
1
(dm, JCF = 244 Hz, C6F5), 136.7 (dm, JCF = 246 Hz, C6F5), 133.8
(ipso-Ph), 131.3 (p-Ph), 127.1 (Ph), 126.4 (Ph), 124.1 (ipso-C6F5),
65.7 (C(H)(Ph)), 29.7 (BCH2), 23.3 (ACH2). 19F NMR (377 MHz,
3
1F, o-C6F5), −154.9 (t, 1F, 3JFF = 21 Hz, p-C6F5), −157.2 (t, 1F, 3JFF
=
CD2Cl2): δ −134.0 (m, 2F, o-C6F5), −163.4 (t, 1F, JFF = 20 Hz, p-
C6F5), −166.6 (m, 2F, m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ
21 Hz, p-C6F5), −157.8 (t, 1F, 3JFF = 21 Hz, p-C6F5), −161.8 (m, 1F,
m-C6F5), −162.6 (m, 1F, m-C6F5), −162.8 to −163.2 (m, 3F, m-
C6F5),), −163.3 (m, 1F, m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ
−4.86 (s, BNH).
1
−24.6 (d, JHB = 90 Hz, BH). Anal. Calcd (%) for C35H21BF15N: C
55.95; H 2.82; N 1.86. Found: C 55.47; H 3.03; N 1.86.
Synthesis of [2,6-Me2C5H8NH2][HB(C6F5)3] (2). 2,6-Dimethyl-
pyridine (79.3 mg, 0.740 mmol), reaction time 60 h, white solid, 84%
isolated yield. Crystals suitable for X-ray diffraction were grown from a
layered solution of bromobenzene/pentane at −40 °C over 48 h.
Isomer ratio meso 80%, rac 20%.
Independent Synthesis of [SS-2-(CO2Et)C5H9NHB(C6F5)3]
(3b). Synthesis of (S)-Piperidine-2-carboxylic Acid Ethyl Ester. A 4
dram vial with a magnetic stirbar was charged with (S)-piperidine-2-
carboxylic acid ethyl ester hydrochloride (491 mg, 2.53 mmol) and
dichloromethane (3 mL). To the slurry was added in portions
potassium tert-butoxide (296 mg, 264 mmol) over 5 min and allowed
to mix for 8 h. The mixture was filtered through a pad of Celite, and
the solvent was removed under vacuum to give a yellow oil in 65%
yield.
Synthesis of [SS-2-(CO2Et)C5H9NHB(C6F5)3] (3b). In a vial, (S)-
piperidine-2-carboxylic acid ethyl ester (11.6 mg, 0.074 mmol) and d2-
dichloromethane (0.25 mL) were cooled to −35 °C. To the vial was
added a cooled (−35 °C) solution of B(C6F5)3 (37.9 mg, 0.074 mmol)
in d2-dichloromethane (0.25 mL), and the multinuclear NMR of 3b
was obtained within 10 min of the reaction.
[meso-2,6-Me2C5H8NH2][HB(C6F5)3]. 1H NMR (400 MHz,
1
C6D5Br): δ 5.08 (br, 2H, NH2), 3.45 (br q, JHB = 83 Hz, BH),
3
2.68 (m, 2H, NCH), 1.37 (m, 4H, CH2), 0.86 (d, 6H, JHH = 6.4 Hz,
Me), 0.77 (m, 2H, CH2). 13C{1H} NMR (101 MHz, C6D5Br): δ 148.5
(dm, 1JCF = 235 Hz, CF), 138.5 (dm, 1JCF = 246 Hz, CF), 137.0 (dm,
1JCF = 249 Hz, CF), 123.6 (ipso-C6F5), 56.7 (NCH), 30.3 (CH2), 22.0
(CH2), 19.3 (Me). 19F NMR (377 MHz, C6D5Br): δ −134.1 (m, 2F,
3
o-C6F5), −161.7 (t, 1F, JFF = 20 Hz, p-C6F5), −165.5 (m, 2F, m-
C6F5). 11B NMR (128 MHz, C6D5Br): δ −23.8 (d, 1JHB = 83 Hz, BH).
Anal. Calcd (%) for C25H17BF15N: C 47.87; H 2.73; N 2.23. Found: C
47.64; H 2.90; N 2.22.
Independent Synthesis of [meso-2,6-Me2C5H8NH2][HB-
(C6F5)3]. Synthesis of meso-2,6-Me2C5H8NH·HCl. A 4 dram vial
with a magnetic stirbar was charged with 2,6-lupetidine (500 mg, 4.4
mmol) in pentane (ca. 3 mL) followed by the dropwise addition of
HCl (1.4 mL, 4 M in 1,4-dioxane, 5.7 mmol, 1.3 equiv). The formation
of a white precipitate was gradually observed in the vial. The
Synthesis of [2-(Ph)C5H9NHB(C6F5)3] (4) and [2-(Ph)-
C5H9NH2][HB(C6F5)3] (5). 2-Phenylpyridine (115 mg, 0.740 mmol),
reaction time 48 h, white solid, 54% isolated yield. Crystals suitable for
X-ray diffraction were grown from a layered solution of dichloro-
methane/pentane at −40 °C over 1 week. The isolated product
consisted of 4a (70%), 4b (10%), and 5 (20%) Anal. Calcd (%) for
E
dx.doi.org/10.1021/om4000727 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
C29H17BF15N: C 51.58; H 2.54; N 2.09. Found: C 52.09; H 2.58; N
2.10.
NH2), 5.01 (br t, 1H, NH2), 4.33 (dm, 1H, 3JHH = 10.5 Hz, 3JHH = 3.3
Hz, C(H)Ph), 3.80 (br m, 1H, CH2C(H)NH2), 3.20 (br q, 1H, 1JBH
=
[RS/SR-2-(Ph)C5H9NHB(C6F5)3] (4a). 1H NMR (400 MHz,
CD2Cl2): δ 7.27 (m, 2H, Ph), 7.14 (m, 3H, Ph), 5.55 (br s, 1H,
87 Hz, BH), 2.18−1.08 (m, 13H, CH2C(H)CH2 and CH2). 13C{1H}
NMR (101 MHz, CD2Cl2): δ 134.2 (ipso-Ph), 131.2 (p-Ph), 130.1 (m-
Ph), 126.9 (o-Ph), 64.7 (CH2C(H)NH2), 60.1 (C(H)Ph), 34.5
(CH2C(H)CH2), 29.1 (CH2), 28.5 (CH2), 25.1 (CH2), 24.9 (CH2),
24.8 (CH2), 19.7 (CH2). 19F NMR (377 MHz, C6D5Br): δ −133.4 (m,
3
3
3
NH), 4.15 (ddd, 1H, JHH = 11.1 Hz, JHH = 9.38 Hz, JHH = 3.6 Hz,
2
CHPh), 3.56 (dm, 1H, JHH = 13.2 Hz, CH(H)NH), 2.57 (ddd, 1H,
2JHH = 13.2 Hz, JHH = 10.3 Hz, JHH = 3.1 Hz, CH(H)NH), 1.99−
1.35 (m, 6H, CH2). 13C{1H} NMR (101 MHz, CD2Cl2): δ 138.5
(ipso-Ph), 129.7 (p-Ph), 129.1 (Ph), 128.5 (Ph), 64.6 (CHPh), 52.1
(NCH2), 35.5 (CH2), 24.8 (CH2), 21.9 (CH2). 19F NMR (377 MHz,
C6D5Br): δ −121.6 (m, 1F, o-C6F5), −123.6 (m, 1F, o-C6F5), −127.4
(m, 1F, o-C6F5), −128.6 (m, 1F, o-C6F5), −131.2 (m, 1F, o-C6F5),
−142.6 (m, 1F, o-C6F5), −153.4 (t, 1F, 3JHH = 22 Hz, p-C6F5), −156.6
3
3
3
2F, o-C6F5), −161.2 (t, 1F, JFF = 21 Hz, p-C6F5), −164.7 (m, 2F, m-
C6F5). 11B NMR (128 MHz, C6D5Br): δ −24.2 (d, 1JBH = 87 Hz, BH).
Anal. Calcd (%) for C33H23BF15N: C 54.34; H 3.18; N 1.92. Found: C
54.31; H 3.31; N 1.92.
Synthesis of [8-MeC9H15NH2][HB(C6F5)3] (8). 8-Methylquinoline
(106 mg, 0.740 mmol), reaction time 48 h, white solid, 76% isolated
yield. Crystals suitable for X-ray diffraction were grown from a layered
solution of dichloromethane/pentane at −40 °C over 48 h. Only the
reported SSS/RRR diastereomer was observed.
3
3
(t, 2F, JHH = 21 Hz, p-C6F5), −156.7 (t, 1F, JHH = 21 Hz, p-C6F5),
−161.5 (m, 2F, m-C6F5), −162.0 (m, 3F, m-C6F5), −162.4 (m, 1F, m-
C6F5). 11B NMR (128 MHz, CD2Cl2): δ −3.91 (s, BN).
[SS/RR-2-(Ph)C5H9NHB(C6F5)3] (4b). 1H NMR (400 MHz,
C6D5Br): δ 7.10−6.81 (m, 5H, Ph), 5.81 (br s, 1H, NH), 4.49 (m,
1H, CHPh), 3.47 (dm, 1H, 2JHH = 12.5 Hz, CH(H)NH), 3.21 (m, 1H,
2JHH = 12.5 Hz, CH(H)NH), 1.85 (m, 2H, CH2), 1.76 (m, 2H, CH2),
1.28 (m, 2H, CH2). 13C{1H} NMR (101 MHz, CD2Cl2): δ 136.5
(ipso-Ph),129.4 (p-Ph), 128.3 (Ph), 125.6 (Ph), 62.9 (CHPh), 45.4
(NCH2), 35.0 (CH2), 29.7 (CH2), 26.0 (CH2). 19F NMR (377 MHz,
C6D5Br): δ −124.9 (m, 1F, o-C6F5), −126.3 (m, 1F, o-C6F5), −126.8
(m, 1F, o-C6F5), −128.7 (m, 1F, o-C6F5), −139.0 (m, 1F, o-C6F5),
−143.1 (m, 1F, o-C6F5), −155.5 (t, 1F, 3JHH = 21 Hz, p-C6F5), −155.9
[SSS/RRR-8-MeC9H15NH2][HB(C6F5)3]. 1H NMR (400 MHz,
C6D5Br): δ 5.55 (br, 1H, NH2), 4.97 (br, 1H, NH2), 3.52 (br q,
1
2
1H, JBH = 80 Hz, BH), 3.27 (dm, 1H, JHH = 12.1 Hz, NH2CH(H)),
2.63 (dm, 1H, JHH = 11.2 Hz coupling to NH2 is observed in 1H,1H-
3
2
3
COSY, CHN) 2.52 (qt, 1H, JHH = 12.1 Hz, JHH = 2.7 Hz,
NH2CH(H), 1.41−1.33 (br m, 2H, CH2), 1.34 (m, 1H, CH2CHCH2),
1.25−1.14 (br m, 4H, CH2), 1.22 (m, 1H, CHMe), 1.02 (m, 1H), 0.89
(m, 2H), 0.63 (d, 3H, JHH = 7.5 Hz, Me), 0.58 (m, 1H). 13C{1H}
3
1
NMR (101 MHz, C6D5Br): δ 148.4 (dm, JCF = 234 Hz, CF), 138.3
1
1
(dm, JCF = 246 Hz, CF), 136.8 (dm, JCF = 249 Hz, CF), 123.7 (br,
ipso-C6F5), 63.2 (CHN), 47.8 (NH2CH(H)), 33.9 (CH2CHCH2),
33.7 (CHMe), 27.1 (CH2), 26.8 (CH2), 24.3 (CH2), 23.1 (CH2), 17.8
(CH2), 16.3 (Me). 19F NMR (377 MHz, C6D5Br): δ −134.3 (m, 2F,
3
3
(t, 1F, JHH = 21 Hz, p-C6F5), −156.2 (t, 1F, JHH = 21 Hz, p-C6F5),
−159.8 (m, 1F, m-C6F5), −161.0 (m, 1F, m-C6F5), −161.7 (m, 1F, m-
C6F5), −162.0 (m, 1F, m-C6F5), −162.2 (m, 1F, m-C6F5), −164.3 (m,
1F, m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ −3.9 (s, BN).
3
o-C6F5), −161.8 (t, 1F, JFF = 21 Hz, p-C6F5), −165.6 (m, 2F, m-
1
C6F5). 11B NMR (128 MHz, C6D5Br): δ −24.2 (d, 1JBH = 80 Hz, BH).
Anal. Calcd (%) for C28H21BF15N: C 50.40; H 3.17; N 2.10. Found: C
50.26; H 3.30; N 2.09.
[2-(Ph)C5H9NH2][HB(C6F5)3] (5). H NMR (400 MHz, CD2Cl2): δ
3
7.10 − 6.81 (m, 5H, Ph), 5.57 (br s, 2H, NH2), 3.55 (dd, 1H, JHH
=
3
1
11.7 Hz, JHH = 2.8 Hz, CHPh), 3.30 (br q, 1H, JHB = 86 Hz, BH),
2.95 (dm, 1H, JHH = 12.4 Hz, CH(H)NH2), 2.44 (td, 1H, JHH = 12.4
Hz, 3JHH = 3.0 Hz, CH(H)NH2), 1.86 (m, 2H, B,CCH2), 1.65 (m, 1H,
ACH2), 1.57 (m, 1H, CCH2), 1.41 (m, 1H, BCH2), 1.37 (m, 1H,
ACH2);. 13C{1H} NMR (101 MHz, CD2Cl2): δ 139.9 (ipso-Ph), 129.7
(Ph), 129.5 (p-Ph), 126.7 (Ph), 62.5 (CHPh), 47.1 (NCH2), 32.7
(CCH2), 24.2 (BCH2), 24.0 (ACH2). 19F NMR (377 MHz, CD2Cl2): δ
Synthesis of [C13H22NH2][HB(C6F5)3] (9). Acridine (132 mg,
0.740 mmol), reaction time 36 h, white solid, 76% isolated yield.
Crystals suitable for X-ray diffraction were grown from a layered
solution of bromobenzene/pentane at 25 °C over 16 h. The isolated
product is a mixture of the SRSR/RSRS and RRSS/SSRR isomers in a
1:1 ratio. The SRSR/RSRS diastereomer was separated by crystal-
lization.
−134.4 (m, 2F, o-C6F5), −161.0 (t, 1F, 3JHH = 20 Hz, p-C6F5), −166.7
[SRSR/RSRS-C13H22NH2][HB(C6F5)3]. 1H NMR (400 MHz, CD2Cl2):
1
(m, 2F, m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ −24.8 (d, JHB
=
δ 6.26 (br m, 1H, NH2), 5.13 (br m, 1H, NH2), 3.27 (br q, 1H, 1JBH
=
86 Hz, BH).
86 Hz, BH), 2.85 (ddt, 2H, 3JHH = 11.1 Hz, 3JHH = 11.1 Hz, 3JHH = 4.0
Hz, CHN), 1.82 (m, 2H, NH2CHCH2), 1.76 (m, 2H, CyCH2), 1.75
(m, 1H, CHCH2CH), 1.71 (m, 2H, CyCH2), 1.67 (m, 2H, CyCH2),
Synthesis of [2-MeC9H15NH2][HB(C6F5)3] (6). 2-Methylquinoline
(106 mg, 0.740 mmol), reaction time 48 h, white solid, 67% isolated
yield. Crystals suitable for X-ray diffraction were grown from a layered
solution of dichloromethane/pentane at −40 °C over 36 h. Sixty
percent of the isolated reaction product consisted of the SSS/RRR
diastereomer.
3
3
1.44 (qt, 2H, JHH = 11.1 Hz, JHH = 4.0 Hz, CH2CHCH2), 1.23 (m,
2H, CyCH2), 1.22 (m, 2H, NH2CHCH2), 1.18 (m, 2H, CyCH2), 1.01
(m, 2H, CyCH2), 1.00 (m, 1H, CHCH2CH). 13C{1H} NMR (101
MHz, CD2Cl2) partial: δ 63.9 (CHN), 40.6 (CH2CHCH2), 37.1
(CHCH2CH), 31.8 (CyCH2), 30.7 (NH2CHCH2), 24.9 (CyCH2), 24.8
(CyCH2). 19F NMR (377 MHz, CD2Cl2): δ −134.5 (m, 2F, o-C6F5),
[SSS/RRR-2-MeC9H15NH2][HB(C6F5)3]. 1H NMR (400 MHz,
C6D5Br): δ 6.02 (br, 1H, NH2), 4.60 (br d, 1H, NH2), 3.36 (br q,
1
3
3
1H, JBH = 83 Hz, BH), 3.15 (dt, 1H, JHH = 10.0 Hz, JHH = 5.2 Hz,
NCH), 2.76 (m, 1H, CHMe), 1.45−0.96 (m, 8H, CH2), 1.10 (m, 1H,
CHCHN), 0.93−0.67 (m, 4H, CH2), 0.81 (d, 3H, 3JHH = 6.4 Hz, Me).
13C{1H} NMR (101 MHz, C6D5Br): δ 148.4 (dm, 1JCF = 234 Hz, CF),
138.4 (dm, 1JCF = 246 Hz, CF), 136.9 (dm, 1JCF = 249 Hz, CF), 123.3
(ipso-C6F5), 57.7 (NCH), 49.3 (CHMe), 32.2 (CHCHN), 28.1
(CH2), 27.2 (CH2), 25.5 (CH2), 24.0 (CH2), 23.6 (CH2), 21.1 (CH2),
18.9 (Me). 19F NMR (377 MHz, C6D5Br): δ −133.5 (m, 2F, o-C6F5),
3
−162.7 (t, 1F, JFF = 20 Hz, p-C6F5), −166.3 (m, 2F, m-C6F5). 11B
1
NMR (128 MHz, CD2Cl2): δ −24.4 (d, JBH = 86 Hz, BH). Anal.
Calcd (%) for C31H25BF15N: C 52.64; H 3.56; N 1.98. Found: C
52.14; H 3.58; N 1.96.
Synthesis of RRSS/SSRR and SRSR/RSRS Tetradecahydroa-
cridine. In a 4 dram vial, compound 9 (278 mg, 0.393 mmol) was
dissolved in toluene (5 mL), and potassium bis(trimethylsilyl)amide
(78.4 mg, 0.393 mmol) was added in small portions over 5 min. The
reaction was allowed to mix for 1 h at room temperature, and the
solvent was removed. The reaction mixture was washed with pentane
(3 × 5 mL) and filtered through a pad of Celite. The filtrate was
collected, and pentane was removed under vacuum to yield a white
solid, which was collected and sublimed under dynamic vacuum at 40
°C for 5 h to give the product in 91% yield.
3
−160.7 (t, 1F, JFF = 22 Hz, p-C6F5), −164.6 (m, 2F, m-C6F5). 11B
1
NMR (128 MHz, C6D5Br): δ −24.1 (d, JBH = 83 Hz, BH). Anal.
Calcd (%) for C28H21BF15N: C 50.40; H 3.17; N 2.10. Found: C
50.21; H 3.31; N 2.12.
Synthesis of [2-PhC9H15NH2][HB(C6F5)3] (7). B(C6F5)3 (289 mg,
0.564 mmol), 2-phenylquinoline (116 mg, 0.564 mmol), reaction time
48 h, white solid, 95% isolated yield. Seventy-three percent of the
reaction mixture consisted of the reported SSS/RRR diastereomer.
[SSS/RRR-2-PhC9H15NH2][HB(C6F5)3]. 1H NMR (400 MHz,
RRSS/SSRR-Tetradecahydroacridine. 1H NMR (400 MHz,
3
3
CD2Cl2) partial: δ 2.79 (ddd, 2H, JHH = 7.0 Hz, JHH = 3.4 Hz,
3JHH = 3.1 Hz, NCH), 1.73 (ddm, 2H, JHH = 13.0 Hz, JHH = 3.8 Hz,
3
3
3
CD2Cl2): δ 7.33 (tm, 1H, JHH = 7.3 Hz, p-Ph), 7.26 (tm, 2H, JHH
3
= 7.3 Hz, m-Ph), 7.20 (dm, 2H, JHH = 7.3 Hz, o-Ph), 6.46 (br, 1H,
NH2CHCH2), 1.45 (m, 2H, CH2CHCH2), 1.20 (m, 2H,
F
dx.doi.org/10.1021/om4000727 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
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NH2CHCH2). 13C{1H} NMR (101 MHz, CD2Cl2) partial: δ 55.8
(NCH), 37.0 (CH2CHCH2), 26.7 (NH2CHCH2).
0.86 (m, 1H, CH2). 13C{1H} NMR (101 MHz, C6D5Br): δ 148.3 (dm,
1JCF = 235 Hz, CF), 138.5 (dm, 1JCF = 246 Hz, CF), 136.7 (dm, 1JCF
=
SRSR/RSRS-Tetradecahydroacridine. 1H NMR (400 MHz,
248 Hz, CF), 136.2 (ipso-Ph), 131.3 (Ph), 130.1 (Ph), 126.7 (Ph),
63.7 (CHPh), 61.9 (CHPh), 59.7 (CH2CHN), 56.1 (CH2CHN), 31.4
(CH2), 28.2 (CH2), 24.2 (CH2), 23.3 (CH2). 19F NMR (377 MHz,
3
3
CD2Cl2): partial: δ 2.02 (ddd, 2H, JHH = 10.8 Hz, JHH = 9.2 Hz,
3JHH = 3.6, NCH), 1.43 (m, 2H, NH2CHCH2), 1.11 (m, 2H,
3
CH2CHCH2), 1.06 (m, 2H, NH2CHCH2). 13C{1H} NMR (101 MHz,
CD2Cl2) partial: δ 63.5 (NCH), 37.6 (CH2CHCH2), 33.5
(NH2CHCH2).
C6D5Br): δ −133.1 (m, 2F, o-C6F5), −160.6 (t, 1F, JFF = 21 Hz, p-
C6F5), −164.3 (m, 2F, m-C6F5). 11B NMR (128 MHz, C6D5Br): δ
1
−23.8 (d, JBH = 82 Hz, BH).
1
(RRRS/SSSR) (12b). H NMR (500 MHz, CD2Cl2): δ 7.29−7.08
Synthesis of [RRSS/SSRR and SRSR/RSRS-(C13H22NH)B(C6F5)3]
(10). In a 4 dram vial, tetradecahydroacridine (36.6 mg, 0.189 mmol)
was dissolved in pentane (5 mL) at room temperature. To the vial was
added B(C6F5)3 (96.5 mg, 0.189 mmol) at once and allowed to mix for
2 min. The solution was filtered through a bed of Celite to yield a
colorless solution. The vial was placed in a −35 °C freezer for 3 h, and
colorless crystals were collected in 73% yield.
3
(m, 10H, Ph), 6.57 (br, 2H, NH2), 4.51 (dm, 1H, JHH = 10.2 Hz,
CHPh), 4.29 (dm, 1H, 3JHH = 10.2 Hz, CHPh), 3.86 (dm, 1H, 3JHH
=
10.7 Hz, CH2CHN), 3.66 (br, 1H, NH), 3.28 (br q, 1H, 1JBH = 82 Hz,
3
BH), 2.68 (dm, 1H, JHH = 10.7 Hz CH2CHN), 2.05 (m, 1H, CH2),
1.88 (m, 2H, CH2), 1.78 (m, 2H, CH2), 1.57 (m, 1H, CH2), 1.45 (m,
1H, CH2), 1.30 (m, 1H, CH2). 13C{1H} NMR (125 MHz, CD2Cl2): δ
147.9 (dm, 1JCF = 235 Hz, CF), 138.2 (dm, 1JCF = 246 Hz, CF), 136.6
(dm, 1JCF = 248 Hz, CF), 131.4 (ipso-Ph), 130.4 (Ph), 130.1 (ipso-Ph),
129.3 (Ph), 129.0 (Ph), 128.6 (Ph), 127.7 (Ph), 127.4 (Ph), 122.6
(ipso-C6F5), 65.5 (CHPh), 62.1 (CHPh), 58.1 (CH2CHN), 52.6
(CH2CHN), 30.8 (CH2), 24.5 (CH2), 22.9 (CH2), 18.8 (CH2). 19F
NMR (377 MHz, C6D5Br): δ −133.1 (m, 2F, o-C6F5), −160.6 (t, 1F,
3JFF = 21 Hz, p-C6F5), −164.3 (m, 2F, m-C6F5). 11B NMR (128 MHz,
The isolated mixture of compound 10 consisted of a 1:1 mixture of
RRSS/SSRR and SRSR/RSRS (C13H22NH)B(C6F5)3, and only the
diagnostic resonances of RRSS/SSRR-(C13H22NH)B(C6F5)3 have been
reported.
[RRSS/SSRR-(C13H22NH)B(C6F5)3]. 1H NMR (400 MHz, CD2Cl2): δ
3
5.03 (br, 1H, NH), 3.53 (dm, 2H, JHH = 12.3 Hz, NCH), 2.14 (dm,
2H, JHH = 12.3 Hz, NH2CHCH2), 1.96−1.60 (m, 6H, CH2), 1.88 (m,
2H, CH2CHCH2), 1.77 (m, 4H, NH2CHCH2 and CHCH2CH),
1.49−1.11 (m, 6H, CH2). 13C{1H} NMR (101 MHz, CD2Cl2) partial:
δ 63.0 (NCH), 35.9 (CHCH2CH), 35.6 (CH2CHCH2), 29.9
(NH2CHCH2). 19F NMR (377 MHz, CD2Cl2): δ −127.0 (m, 1F, o-
C6F5), −127.7 (m, 1F, o-C6F5), −128.1 (m, 1F, o-C6F5), −129.1 (m,
1
C6D5Br): δ −23.8 (d, JBH = 82 Hz, BH).
Synthesis of [(C6H4)C7H12NH2][HB(C6F5)3] (13). 7,8-Benzoqui-
noline (133 mg, 0.740 mmol), reaction time 48 h, white solid, 55%
isolated yield. Crystals of the SR/RS isomer suitable for X-ray
diffraction were grown from a layered solution of bromobenzene/
pentane at −40 °C over 16 h. Crystals of the SS/RR isomer suitable for
X-ray diffraction were grown from a layered solution of dichloro-
methane/pentane at −40 °C over 1 week. Isomer ratio SR/RS 80%
(pale orange crystals), SS/RR 20% (colorless crystals).
3
2F, o-C6F5), −130.2 (m, 1F, o-C6F5), −155.8 (t, 1F, JHH = 20 Hz, p-
C6F5), −157.9 (t, 1F, 3JHH = 21 Hz, p-C6F5), −158.9 (t, 1F, 3JHH = 21
Hz, p-C6F5), −162.4 (m, 1F, m-C6F5), −163.6 to −163.8 (m, 3F, m-
C6F5), −164.1 8 (m, 1F, m-C6F5), −164.4 8 (m, 1F, m-C6F5). 11B
NMR (128 MHz, CD2Cl2): δ −3.18 (s, BN). Anal. Calcd (%) for
C31H23BF15N: C 52.79; H 3.29; N 1.99. Found: C 52.66; H 3.28; N
1.96.
[SR/RS-(C6H4)C7H12NH2][HB(C6F5)3] (13a). 1H NMR (400 MHz,
CD2Cl2): δ 7.25 (td, 1H, 3JHH = 7.7 Hz, 4JHH = 1.4 Hz, C6H4), 7.15 (d,
1H, 3JHH = 7.7 Hz, C6H4), 7.07 (d, 1H, 3JHH = 7.7 Hz, C6H4), 7.00 (t,
1H, 3JHH = 7.7 Hz, C6H4), 5.97 (br, 2H, NH2), 4.40 (d, 1H, 3JHH = 3.8
Synthesis of [SRSS/RSRR-(C4H6Me)2NHNH2][HB(C6F5)3] (11).
2,3-Dimethylquinoxaline (0.117 g, 0.740 mmol), reaction time 96 h,
white solid, 59% isolated yield. Only the reported diastereomer was
3
Hz, NCH), 3.61 (dt, 1H, JHH = 13.1 Hz, JHH = 3.5 Hz, NCH(H)),
3.28 (m, 1H, NCH(H)), 3.14 (br q, 1H, 1JBH = 80 Hz, BH), 2.94 (dm,
1
2
2
observed. H NMR (400 MHz, CD2Cl2): δ 6.43 (br, 1H, NH2), 5.92
1H, JHH = 17.2 Hz, C6H4-CH(H)), 2.85 (dm, 1H, JHH = 17.2 Hz,
C6H4-CH(H)), 2.39 (m, 1H, CH2CHCH2), 2.00−1.88 (br m, 6H,
Piperidine,CyCH2). 13C{1H} NMR (101 MHz, CD2Cl2): δ 148.3 (dm, 1JCF
(br, 1H, NH2), 3.49 (dm, 1H, 3JHH = 12.8 Hz, CH2CHN), 3.34 (br q,
1
1H, JBH = 94 Hz, BH), 3.26 (br m, 2H, NCHMe, CH2CHN), 2.81
(dq, 1H, 3JHH = 12.3 Hz, 3JHH = 6.4 Hz, NCHMe), 2.23 (dm, 1H, JHH
= 12.8 Hz, CH2), 1.89 (dm, 1H, JHH = 13.4 Hz, CH2), 1.79 (dm, 1H,
JHH = 13.4 Hz, CH2), 1.62 (dm, 2H, JHH = 13.4 Hz, CH2), 1.47 (m,
1H, CH2), 1.31 (m, 1H, CH2), 1.28 (d, 3H, 3JHH = 6.4 Hz, Me), 1.21
1
= 235 Hz, CF), 138.3 (dm, JCF = 246 Hz, CF), 137.8 (quaternary C
for C6H4-CHN), 136.8 (dm, JCF = 248, CF), 131.1 (C6H4), 130.7
1
(C6H4), 129.2 (C6H4), 128.8 (quaternary C for C6H4-CH2), 127.7
(C6H4), 123.4 (ipso-C6F5), 60.5 (NCH), 47.9 (NCH2), 32.0
(CH2CHCH2), 28.6 (C6H4-CH(H)), 27.4 (PiperidineCH2), 22.5
(CyCH2), 18.4 (PiperidineCH2). 19F NMR (377 MHz, C6D5Br): δ
3
(d, 3H, JHH = 6.2 Hz, Me), 1.20 (m, 1H, CH2). 13C{1H} NMR (101
MHz, C6D5Br): δ 148.1 (dm, 1JC−F = 234 Hz, C6F5), 138.4 (dm, 1JC−F
= 246 Hz, C6F5), 136.8 (dm, 1JC−F = 247 Hz, C6F5), 123.2 (ipso-C6F5),
57.6 (CH2CHN), 56.3 (NCHMe), 54.1 (NCHMe), 51.9 (CH2CHN),
30.4 (CH2), 24.2 (CH2), 22.4 (CH2), 18.5 (CH2), 17.8 (Me), 15.1
(Me). 19F NMR (377 MHz, C6D5Br): δ −133.6 (m, 2F, o-C6F5),
−134.5 (m, 2F, o-C6F5), −162.1 (t, 1F, 3JFF = 21 Hz, p-C6F5), −165.7
1
(m, 2F, m-C6F5). 11B NMR (128 MHz, C6D5Br): δ −24.1 (d, JBH
=
80 Hz, BH). Anal. Calcd (%) for C31H21BF15N: C 52.94; H 3.01; N
1.99. Found: C 53.47; H 2.91; N 2.09.
3
−160.7 (t, 1F, JFF = 21 Hz, p-C6F5), −164.6 (m, 2F, m-C6F5). 11B
[SS/RR-(C6H4)C7H12NH2][HB(C6F5)3] (13b). 1H NMR (400 MHz,
C6D5Br) partial: δ 7.01 (m, 1H, C6H4), 6.99 (m, 1H, C6H4), 6.85 (m,
1
NMR (128 MHz, C6D5Br): δ −24.1 (d, JBH = 94 Hz, BH). Anal.
3
3
Calcd (%) for C28H22BF15N: C 49.29; H 3.25; N 4.11. Found: C
49.09; H 3.33; N 4.21.
1H, C6H4), 6.75 (d, 1H, JHH = 7.7 Hz, C6H4), 3.50 (d, 1H, JHH
=
10.4 Hz, NCH), 3.24 (br dm, 1H, JHH = 12.4 Hz, NCH(H)), 2.79 (m,
1H, NCH(H)), 2.54 (m, 1H, C6H4-CH(H)), 2.42 (m, 1H, C6H4-
CH(H)), 1.42 (m, 2H, CH2), 1.28 (m, 2H, CH2), 1.05 (m, 1H,
CH2CHCH2), 0.83 (m, 2H, CH2); (not observed NH2). 13C{1H}
NMR (101 MHz, C6D5Br): δ 137.0 (quaternary C for C6H4-CHN),
130.4 (C6H4), 129.1 (C6H4), 128.4 (quaternary C for C6H4-CH2),
126.4 (C6H4), 122.6 (C6H4), 62.9 (NCH), 47.4 (NCH2), 37.8
(CH2CHCH2), 29.1 (CH2), 28.8 (C6H4-CH(H)), 27.6 (CH2), 22.9
(CH2).
Synthesis of [2,3-Ph2C8H12NHNH2][HB(C6F5)3] (12). 2,3-Dime-
thylquinoxaline (117 mg, 0.740 mmol), reaction time 96 h, white solid,
59% isolated yield. Crystals suitable for X-ray diffraction were grown
from a layered solution of dichloromethane/pentane at ambient
temperature over 1 week. Diastereomers 12a and 12b are present in
equal ratios. The obtained structures were supported with the through-
space distances derived from 1H,1H NOESY NMR spectra. Anal.
Calcd (%) for C28H22BF15N: C 49.29; H 3.25; N 4.11. Found: C
49.09; H 3.33; N 4.21.
Synthesis of [(C5H3N)(CH2)2(C5H8NH)B(C6F5)2][HB(C6F5)3] (14).
1,10-Phenanthroline (66.7 mg, 0.370 mmol), reaction time 96 h, white
solid, 73% isolated yield. Crystals suitable for X-ray diffraction were
grown from a layered solution of tetrahydrofuran/pentane at −40 °C
over 1 week. Sixty-five percent of the reaction mixture consisted of the
(SRSS/RSRR) (12a). 1H NMR (400 MHz, C6D5Br): δ 7.63 (m, 2H,
Ph), 6.99−6.84 (m, 3H, Ph), 5.72 (br, 2H, NH2), 4.76 (d, 1H, 3JHH
=
3
3.4 Hz, CHPh), 4.41 (d, 1H, JHH = 3.4 Hz, CHPh), 4.07 (br, 1H,
NH), 3.56 (br q, 1H, 1JBH = 82 Hz, BH), 3.14 (td, 1H, 3JHH = 10.2 Hz,
3JHH = 3.4 Hz, CH2CHN), 2.60 (m, 1H, 3JHH = 10.2 Hz, 3JHH = 3.4 Hz,
CH2CHN), 1.67 (m, 1H, CH2), 1.59 (m, 1H, CH2), 1.53 (m, 1H,
CH2), 1.29 (m, 1H, CH2), 1.22 (m, 2H, CH2), 1.21 (m, 1H, CH2),
1
SRS/RSR diastereomer. H NMR (400 MHz, CD2Cl2): δ 9.44 (br s,
1H, NH), 8.50 (dd, 1H, JHH = 4.7 Hz, JHH = 1.5 Hz, C5H3N), 7.44
(dd, 1H, JHH = 7.8 Hz, JHH = 1.5 Hz, C5H3N), 7.22 (dd, 1H, JHH = 7.8
G
dx.doi.org/10.1021/om4000727 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Hz, JHH = 4.7 Hz, C5H3N), 4.42 (d, 1H, 3JHH = 4.3 Hz, CyNCH), 3.42
(8) Monfette, S.; Turner, Z. R.; Semproni, S. P.; Chirik, P. J. J. Am.
Chem. Soc. 2012, 134, 4561.
(9) Dobereiner, G. E.; Nova, A.; Schley, N. D.; Hazari, N.; Miller, S.
J.; Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 2011, 133, 7547.
(10) Yamaguchi, R.; Ikeda, C.; Takahashi, Y.; Fujita, K.-i. J. Am.
Chem. Soc. 2009, 131, 8410.
(11) Berkessel, A.; Schubert, T. J. S.; Mueller, T. N. J. Am. Chem. Soc.
2002, 124, 8693.
(12) Peng, Y.; Ellis, B. D.; Wang, X.; Power, P. P. J. Am. Chem. Soc.
2008, 130, 12268.
(13) Spikes, G. H.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc.
2005, 127, 12232.
(14) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124.
(15) Chase, P. A.; Welch, G. C.; Jurca, T.; Stephan, D. W. Angew.
Chem., Int. Ed. 2007, 46, 8050.
2
(br, 1H BH), 3.22 (dm, 1H, JHH = 13.8 Hz, NC(H)H), 2.91 (ddd,
2
3
3
1H, JHH = 13.8 Hz, JHH = 8.7 Hz, JHH = 5.3 Hz, NC(H)H), 2.76−
2.72 (m, 2H, C6H4-CH(H)), 2.12 (dp, 1H, 3JHH = 12.1 Hz, 3JHH = 3.8
Hz, CH2CHCH2), 1.96 (m, 1H, CH2), 1.88 (m, 1H, CH2), 1.73 (m,
2
3
1H, CH2), 1.32 (dt, 1H, JHH = 14.0 Hz, JHH = 3.2 Hz, CH2), 0.91
(qd, 1H, JHH = 13.1 Hz, 3JHH = 3.8 Hz, CH2), 0.71 (qt, 1H, JHH = 13.7
Hz, 3JHH = 4.0 Hz, CH2). 13C{1H} NMR (101 MHz, CD2Cl2): δ 148.4
(quaternary C for C5H3N), 146.6 (quaternary C for C5H3N), 144.8
(C5H3N), 135.4 (C5H3N), 126.0 (C5H3N), 58.1 (CyNCH), 45.1
(NC(H)H), 29.6 (CH2C(H)CH2), 24.1 (CH2), 21.8 (CH2), 21.0
(CH2), 20.6 (CH2). 19F NMR (377 MHz, CD2Cl2): δ −128.9 (m, 2F,
B(C6F5)2o-C6F5), −134.3 (m, 6F, HB(C6F5)3o-C6F5), −134.8 (m, 2F,
B(C6F5)2o-C6F5), −149.1 (t, 1F, 3JFF = 20 Hz, B(C6F5)2p-C6F5), −151.1 (t,
3
1F, JFF = 20 Hz, B(C6F5)2p-C6F5), −159.6 (m, 4F, B(C6F5)2m-C6F5),
3
−164.5 (t, 3F, JFF = 20 Hz, HB(C6F5)3p-C6F5), −167.6 (m, 6F,
HB(C6F5)3m-C6F5). 11B NMR (128 MHz, CD2Cl2): δ 3.43 (br s, BN).
̈
(16) Wang, H. D.; Frohlich, R.; Kehr, G.; Erker, G. Chem. Commun.
1
11B NMR (128 MHz, CD2Cl2): δ 3.91 (s, BN), −25.4 (d, JBH = 93
2008, 5966.
(17) Spies, P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.;
̈
Hz, BH). Anal. Calcd (%) for C42H17B2F25N2: C 48.22; H 1.64; N
2.68. Found: C 47.83; H 1.97; N 2.69.
Erker, G. Angew. Chem., Int. Ed. 2008, 47, 7543.
(18) Sumerin, V.; Chernichenko, K.; Nieger, M.; Leskela, M.; Rieger,
̈
X-ray Data Collection, Reduction, Solution, and Refinement.
Single crystals were coated in Paratone-N oil in the glovebox, mounted
on a MiTegen Micromount, and placed under an N2 stream. The data
were collected on a Bruker Apex II diffractometer. The data were
collected at 150( 2) or 293( 2) K for all crystals. Data reduction was
performed using the SAINT software package, and an absorption
correction applied using SADABS. The structures were solved by
direct methods using XS and refined by full-matrix least-squares on F2
using XL as implemented in the SHELXTL suite of programs.38 All
non-hydrogen atoms were refined anisotropically. Carbon-bound
hydrogen atoms were placed in calculated positions using an
appropriate riding model and coupled isotropic temperature factors
(see Supporting Information).
B.; Repo, T. Adv. Synth. Catal. 2011, 353, 2093.
(19) Sumerin, V.; Schulz, F.; Nieger, M.; Atsumi, M.; Wang, C.;
Leskela, M.; Pyykko, P.; Repo, T.; Rieger, B. J. Organomet. Chem.
̈
̈
2009, 694, 2654.
(20) Sumerin, V.; Schulz, F.; Atsumi, M.; Wang, C.; Nieger, M.;
Leskela, M.; Repo, T.; Pyykko, P.; Rieger, B. J. Am. Chem. Soc. 2008,
̈
̈
130, 14117.
(21) Jiang, C.; Blacque, O.; Berke, H. Chem. Commun. 2009, 5518.
(22) Chen, D.; Wang, Y.; Klankermayer, J. Angew. Chem., Int. Ed.
2010, 49, 9475.
(23) Chen, D.; Klankermayer, J. Chem. Commun. 2008, 2130.
(24) Greb, L.; Ono-Burgos, P.; Schirmer, B.; Breher, F.; Grimme, S.;
Stephan, D. W.; Paradies, J. Angew. Chem., Int. Ed. 2012, 51, 10164.
(25) Segawa, Y.; Stephan, D. W. Chem. Commun. 2012, 48, 11963.
(26) Mahdi, T.; Heiden, Z. M.; Grimme, S.; Stephan, D. W. J. Am.
Chem. Soc. 2012, 134, 4088.
(27) Geier, S. J.; Chase, P. A.; Stephan, D. W. Chem. Commun. 2010,
46, 4884.
(28) Eros, G.; Nagy, K.; Mehdi, H.; Papai, I.; Nagy, P.; Kiraly, P.;
Tarkanyi, G.; Soos, T. Chem.Eur. J. 2012, 18, 574.
(29) Fish, R. H.; Thormodsen, A. D.; Cremer, G. A. J. Am. Chem. Soc.
1982, 104, 5234.
ASSOCIATED CONTENT
■
S
* Supporting Information
Synthetic, spectroscopic, and crystallographic data are depos-
ited. See CCDC 917790−917798. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
(30) Wang, D.-S.; Chen, Q.-A.; Lu, S.-M.; Zhou, Y.-G. Chem. Rev.
2011, 112, 2557.
(31) Fache, F. Synlett 2004, 2827.
(32) Fache, F.; Piva, O. Synlett 2004, 1294.
Corresponding Author
*E-mail: dstephan@chem.utoronto.ca.
Notes
The authors declare no competing financial interest.
(33) Heitbaum, M.; Frohlich, R.; Glorius, F. Adv. Synth. Catal. 2010,
̈
352, 357.
(34) Urban, S.; Ortega, N.; Glorius, F. Angew. Chem., Int. Ed. 2011,
50, 3803.
(35) Geier, S. J.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 3476.
(36) Geier, S. J.; Gille, A. L.; Gilbert, T. M.; Stephan, D. W. Inorg.
Chem. 2009, 48, 10466.
ACKNOWLEDGMENTS
■
D.W.S. gratefully acknowledges the financial support of the
NSERC of Canada and the award of a Canada Research Chair.
T.M. is grateful for the award of a Norman Stuart Robertson
Fellowship from the University of Toronto.
(37) Heiden, Z. M.; Stephan, D. W. Chem. Commun. 2011, 47, 5729.
(38) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
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dx.doi.org/10.1021/om4000727 | Organometallics XXXX, XXX, XXX−XXX