Addition of C-H Bonds of Pyridine Derivatives to Alkenes Catalyzed by Zirconium Complexes Bearing Amine-Bridged Bis(phenolato) Ligands

Article abstract of DOI:10.1021/acs.inorgchem.8b01959

Cationic zirconium complexes in situ generated from zirconium dibenzyl complexes bearing amine-bridged bis(phenolato) ligands have been developed to catalyze addition of C(sp²)-H and C(sp³)-H bonds of pyridine derivatives to alkenes.

Full text of DOI:10.1021/acs.inorgchem.8b01959

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Addition of C−H Bonds of Pyridine Derivatives to Alkenes Catalyzed
by Zirconium Complexes Bearing Amine-Bridged Bis(phenolato)
Ligands
Qiu Sun,†,‡ Ping Chen,† Yaorong Wang,† Yunjie Luo,*,§ Dan Yuan,*,† and Yingming Yao*,†
†Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science,
Soochow University, Dushu Lake Campus, Suzhou 215123, People’s Republic of China
‡School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, People’s Republic of China
§School of Material Science and Chemical Engineering, Ningbo University, Ningbo 315211, People’s Republic of China
S
* Supporting Information
ABSTRACT: Cationic zirconium complexes in situ generated
from zirconium dibenzyl complexes bearing amine-bridged
bis(phenolato) ligands have been developed to catalyze addition
of C(sp2)−H and C(sp3)−H bonds of pyridine derivatives to
alkenes. A series of zirconium complexes bearing different
ligands have been synthesized, and their activities in catalyzing
addition of C(sp3)−H bonds of pyridine derivatives to alkenes
have been studied and compared. Both reaction activity and
regioselectivity are influenced by electronic and steric properties
of ligand backbones. In addition, a cationic zirconium complex
has been isolated and structurally characterized to shed some
light on reaction mechanism.
and Jordan reported the stoichiometric activation of C(sp3)−H
INTRODUCTION
■
bonds by group 3 and 4 metal complexes.10,11 Hou and co-
Pyridine skeletons find wide application in natural products,
workers reported the first example of catalytic reactions of
medicinal agents, ligands, and functional materials.1 Recent
benzylic C(sp3)−H bonds of α-alkyl pyridines with simple
development of transition-metal-catalyzed C−H bond func-
alkenes in the presence of cationic half-sandwich yttrium alkyl
tionalization allows the most atom- and step-economical way
complexes.12 We have recently communicated cationic
to introduce functional groups onto pyridine skeletons.2 Direct
zirconium complexes-catalyzed addition of C(sp3)−H bonds
addition of C−H bonds of pyridines to C−C unsaturated
of alkylpyridines to alkenes.13 A preliminary study revealed the
bonds has been intensively studied for alkylated pyridine
influence of ligand backbones on reaction regioselectivity. As a
derivative synthesis. In the literature, late transition metal
continuation of this study, we investigated the structure−
activity relationship of a range of zirconium complexes
stabilized by different amine-bridged bis(phenolato) ligands.
Herein, we report highly efficient, ortho-selective addition of
C(sp2)−H and benzylic C(sp3)−H bonds of pyridine
derivatives to alkenes catalyzed by cationic zirconium alkyl
complexes.
complexes, typically Rh,3 Ni,4 Co,5 Cr,6 and Ru7 complexes,
are developed as versatile catalysts. For early transition metal
catalysts, pioneering work on cationic zirconocene alkyl
complexes-catalyzed addition of C−H bonds of pyridine
derivatives was reported by Jordan and co-workers in 1989.8a
Co-catalyst H2 was essential to generate Zr−H compounds as
active species.8c Teuben and co-workers reported a group 3
metal complex Cp*2Y(η2-pyridyl) which catalyzed ethylation
of pyridine.9a Hou and co-workers reported cationic half-
metallocene complexes of yttrium and scandium, which
catalyzed the addition of ortho-C−H bonds of pyridine
derivatives to various alkenes.9b−e Overall, examples of early
transition metal catalysts are rare, and development of group 4
metal catalysts that are active in the absence of H2 is highly
desirable.
RESULTS AND DISCUSSION
■
Synthesis of Complexes. Amine-bridged bis(phenol)s
L1H2−L9H2 with different phenyl and N-substituents were
synthesized (Figure 1)14 to introduce different coordinating
environments for metal center.
Metathesis reactions of ZrBn4 and bis(phenol)s at room
temperature provide an easy access to zirconium dialkyl
complexes.13,15,16 Complexes 1−9 were isolated in 90−95%
Comparing to C(sp2)−H bond functionalization, reactions
of more inert C(sp3)−H bonds are generally more challenging.
Reports on reactions of simple alkenes with benzylic C−H
bonds of alkyl pyridines remain scarce. Teuben, Rieger, Wang,
Received: July 13, 2018
© XXXX American Chemical Society
A
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(Table 1, entries 4−7). Reactions in different solvents (i.e.,
PhCl, toluene, THF) were conducted, and the best yield was
obtained in PhCl, possibly due to good solubility of cationic
complexes in PhCl (Table 1, entries 4, 8, 9). Overall, reaction
with 2 equiv of 11a at 100 °C in PhCl gave the best yield of
94% (Table 1, entry 4). Reducing the catalyst loading to 5 mol
% gave equally good yield (Table 1, entries 10 and 11).
Controlled experiments with TB or neutral complexes only
were inactive (Table 1, entries 12 and 13). Apparently, a
cationic zirconium complex is essential to achieve good
transformations, due to accessible coordination site and a
more Lewis acidic metal center comparing to neutral
counterparts. Under each condition, almost exclusive for-
mation of linear products was observed (vide infra), which is
consistent with literature reports of Ni-, Ru-, Zr-, and Y-
catalyzed reactions,4a,7,8,9 but different from those of Co- and
Cr-catalyzed reactions.5,6
Figure 1. Ligand precursors.
1
yields (Scheme 1). All complexes were characterized by H
and 13C NMR spectroscopy, elemental analysis, and single-
crystal X-ray diffraction analysis (in the case of complex 3 as
communicated earlier).13
Catalytic Studies. In a preliminary study, a mixture of
[Ph3C][B(C6F5)4] and complex 1 stabilized by an [ONNO]-
type tetradentate ligand, which in situ generated cationic
species, showed no activity in catalyzing the reaction of α-
picoline with styrene (Table 1, entry 1). In comparison,
complexes 2 and 3 bearing [ONO]-type tridentate ligand and
[Ph3C][B(C6F5)4] proved active in catalyzing addition of the
ortho-C(sp2)−H bond, which gave rise to linear product 12a
almost exclusively in 53% and 65% yields, respectively (Table
1, entries 2 and 3). Reducing coordination sites in
bis(phenolato) ligands led to complexes of enhanced catalytic
activity, which is consistent with previous findings on Zr-
catalyzed hydroamination reactions.16 It is noteworthy that this
reaction worked in the absence of H2, which is of more
practical use compared to zirconium catalysts reported by
Jordan et al.8
Detailed optimization of reaction conditions includes
changing substrate ratios, temperatures, solvents, cationic
reagents, and catalysts loadings (Table 1, entries 3−9).
Screening of different substrate ratios revealed that a higher
yield of 94% was obtained in the presence of excess alkene
(Table 1, entries 3−4). Raising the reaction temperature from
80 to 110 °C led to the increase of yield from 37% to 94%
Reactions of α-picoline with various alkenes were studied
under optimized conditions, and results are summarized in
Table 2.
Aromatic alkenes bearing either electron-donating (Me, tBu,
OMe) or electron-withdrawing (F, Cl) substituents reacted
smoothly under established conditions, and afforded linear
ortho-C(sp2)−H addition products 12a−f in 81−99% yields.
Electron-deficient substrates (11e and 11f) required longer
reaction time and/or higher catalyst loading. Notably, with the
introduction of a coordinating O atom in 4-methoxystyrene
(11d), the catalytic activity remained, and the desired product
12d formed in a good yield of 88%.
The cationic zirconium catalyst showed higher activity for
reactions of aliphatic alkenes. The addition of the o-C(sp2)−H
bond of α-picoline with norbornene (11g), 1-octene (11h), 1-
hexene (11i), and dicyclopentadiene (11j) gave desired
products 12g−j quantitatively within 6 h. It is noteworthy
that branched products (12h−i) formed exclusively, which is
different from results of styrene derivatives (vide supra). The
cationic zirconium catalyst is also applicable for addition of the
C−H bond of α-picoline to conjugated dienes, e.g., 1,3-
Scheme 1. Synthesis of Zirconium Complexes
B
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a
Table 1. Catalytic Addition of ortho-C(sp2)−H Bond of α-Picoline 10a to Styrene 11a
b
c
entry
cat.
10a:11a
T (°C)
cat. (mol %)
solvent
time (h)
yield (%)
12a:12a′
1
2
3
4
5
6
7
8
9
10
11
12
13
1/TB
2/TB
3/TB
3/TB
3/TB
3/TB
3/TB
3/TB
3/TB
3/TB
3/TB
3
1:1
1:1
1:1
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:1
1:2
100
100
100
100
80
10
10
10
10
10
10
10
10
10
5
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
Tol
THF
PhCl
PhCl
PhCl
PhCl
12
12
12
12
12
12
12
24
24
12
24
12
24
trace
53
65
94
37
82
94
83
trace
94
95:5
98:2
90
110
100
100
100
100
100
100
98:2
2.5
10
10
61
trace
trace
TB
a
Conditions: 10a (0.099 mL, 1 mmol), 11a (amount stated in each entry), complex (amount stated in each entry), [Ph3C][B(C6F5)4] (TB) (46
b
c
1
mg, 0.05 mmol) if necessary, solvent (2 mL). Isolated yield based on 10a. The product ratio was determined by H NMR spectroscopy.
a b
,
Table 2. Catalytic Addition of ortho-C(sp2)−H Bond of α-Picoline to Various Alkenes
a
Conditions: 10a (0.099 mL, 1 mmol), 11 (2 mmol), 3 (0.040 g, 0.05 mmol), [Ph3C][B(C6F5)4] (TB) (46 mg, 0.05 mmol) in PhCl (2 mL) for 12
b
c
d
e
f
h at 100 °C. Isolated yield. 4 mol % catalyst loading. 24 h reaction time. 10 mol % catalyst loading. 6 h reaction time.
cyclohexadiene (11k) and isoprene (11l), which generated
1,4-addition products in yields of 85% and 17%, respectively.
This catalytic system showed limited activities when catalyzing
the reaction of cyclohexene (11m) and methyl acrylate (11n).
Different pyridine derivatives were also studied in reactions
with 1-hexene to further investigate the scope of the cationic
zirconium complex-catalyzed addition of ortho-C(sp2)−H
bonds, and results are summarized in Table 3.
Substrates bearing an ethyl (10b), isopropyl (10c), or
phenyl (10d) substituent reacted smoothly with 1-hexene
under the afore-optimized conditions, and yielded selectively
branched addition products 13b−d in 97−99% yields. It is
noteworthy that 2-phenylpyridine (10d) was alkylated
selectively in the pyridine ring in 97% yield, instead of the
phenyl group, which is different from late transition-metal-
catalyzed reactions.17 Bicyclo-compounds 10e−g reacted
selectively at the ortho-position of pyridine rings, and generated
addition products 13e−g in 91−95% yields. In contrast with
cationic scandium-catalyzed reactions reported by Hou et al.,9b
reactions of electron-deficient pyridine derivatives proceeded
sluggishly, and gave neglectable yields (13h−j). Poor
coordination of these pyridine derivatives to the zirconium
center may account for their low reactivity.
C
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a b
,
Table 3. Catalytic Addition of ortho-C(sp2)−H Bonds of Pyridine Derivatives to 1-Hexene
a
Conditions: 10 (1 mmol), 11i (0.248 mL, 2 mmol), 3 (0.040 g, 0.05 mmol), [Ph3C][B(C6F5)4] (TB) (46 mg, 0.05 mmol) in PhCl (2 mL) at 100
b
c
d
e
°C. Isolated yield. 6 h reaction time. 24 h reaction time. 48 h reaction time.
Table 4. Addition of Benzylic C(sp3)−H Bonds to Styrene Catalyzed by Zirconium Complexes Bearing Different [ONO]-Type
a
Ligands
b
c
entry
cat.
T (°C)
solvent
time (h)
yield (%)
15a:15a′
1
2
3
4
5
6
7
8
9
1+TB
2+TB
3+TB
4+TB
5+TB
6+TB
7+TB
8+TB
9+TB
100
100
100
100
100
100
100
100
100
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
24
24
24
24
36
48
24
24
24
trace
75
81
80
62
trace
77
82
1:5
10:1
10:1
10:1
5:1
3:1
1:1
81
a
Conditions: 11a (0.45 mL, 4 mmol), 14a (0.116 mL, 1 mmol), complex (0.1 mmol), [Ph3C][B(C6F5)4] (TB) (92 mg, 0.1 mmol), PhCl (2 mL).
b
c
1
Isolated yield. The product ratio was determined by H NMR spectroscopy.
Successful addition of C(sp2)−H bonds of pyridines to
observed (Table 4, entry 2). Similar to addition of the C(sp2)−
H bond of α-picoline, complex 1 carrying a tetradentate ligand
did not show any activity (Table 4, entry 1) (vide supra). This
is the first example of group 4 metal-based catalysts capable of
catalyzing addition of benzylic C(sp3)−H bonds of alkylpyr-
idines to alkenes.13
alkenes encouraged us to explore the application of cationic
zirconium complexes in catalyzing more challenging addition
of C(sp3)−H bonds. For α-picoline bearing both C(sp2)−H
and C(sp3)−H bonds, reactions occurred selectively at the
ortho-C(sp2)−H bond (vide supra), while the addition of
excess alkene or elevation of reaction temperature did not
result in C(sp3)−H activation. This finding is different from
that of KHMDS-catalyzed reactions, which preferred C(sp3)−
H over the C(sp2)−H bond.18
Study to further tune the reaction regioselectivity was
performed by changing the bridges and substituents of
tridentate phenolato ligands. Different substituents, including
i
F (4 and 6), CF3 (5), OMe (7), and Pr (8) groups, were
To achieve the addition of benzylic C(sp3)−H bonds,
reactions of 2,6-lutidine (14a) with 4 equiv of styrene were
studied in the presence of complex 3 and TB, which generated
the benzylic C(sp3)−H addition product 15a in 81% yield
(Table 4, entry 3). Branched and linear products formed in the
ratio of 10:1, which is different from results catalyzed by half-
metallocene yttrium and scandium complexes reported by Hou
et al.12 Further screening of cationic zirconium complexes
bearing different [ONO]-type ligands revealed significant
differences. A lower yield (75%) was obtained in the presence
of n-butylamine bridged bis(phenolato) zirconium bis(benzyl)
complex 2 and [Ph3C][B(C6F5)4]. More importantly, reversed
regioselectivity of 1:5 in preference of the linear product was
introduced to N-phenyl groups. para-Fluoroaniline-bridged
complex 4 showed similar activity and regioselectivity with that
of complex 3 (Table 4, entry 4). Introduction of a CF3 group
in complex 5 resulted in a low yield of 62% while the
regioselectivity maintained (Table 4, entry 5). Pentafluoroani-
line-bridged complex 6 and TB showed no activity (Table 4,
entry 6). It is thus conclusive that the presence of electron-
withdrawing groups led to reduced activity and maintained
regioselectivity. On the other hand, the presence of electron-
donating groups in complexes 7 and 8 did not influence
catalytic activity, but resulted in poor regioselectivity (Table 4,
entries 7 and 8). Overall, mildly electron-deficient bridges
result in good activity as well as regioselectivity, while changing
D
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a
Table 5. Addition of Benzylic C(sp3)−H Bonds of Pyridine Derivatives to Various Alkenes
a
Conditions: 14 (0.116 mL, 1 mmol), alkene (4 mmol), 3 (0.080 g, 0.1 mmol), [Ph3C][B(C6F5)4] (TB) (92 mg, 0.1 mmol) in PhCl (2 mL) for 24
b
c
d
e
f
g
h at 100 °C. Isolated yield. 36 h reaction time. 12 mol % catalyst loading. 48 h reaction time. 8 mol % catalyst loading. 16 h reaction time. 6
equiv norbornene. 12 h at 100 °C.
h
Scheme 2. One-Pot, Two-Step Synthesis of 16
to an electron-donating alkyl bridge (in the case of 2) gives rise
to inversed regioselectivity, which is consistent with the
computational finding that electronic effects play crucial roles
in product distribution (vide infra).13 Aniline-bridged complex
9 with bulkier substituents at phenolate groups led to poor
regioselectivity of 1:1 with activity maintained, demonstrating
the steric influence of ligands (Table 4, entry 9).
Aniline-bridged complex 3 showed overall the best activity
and regioselectivity, and the substrate scope has been
communicated.13 A variety of substituted aromatic and
aliphatic alkenes reacted with 2,6-lutidine, and generated
branched C(sp3)-H addition products in 41−98% yields, while
pyridine derivatives were restricted to electron-rich α-methyl
pyridines (Table 5).
with excess norbornene, which generated double-addition
product 16 in near quantitative yield (Scheme 2).
Characterization of Cationic Species. Attempts to
isolate and characterize cationic compounds from reaction of
3 and [Ph3C][B(C6F5)4] failed, due to coordination
unsaturation of possible cationic species. Instead, reaction of
complex 3 and [PhMe2NH][B(C6F5)4] was conducted, which
generated N,N-dimethyl aniline as one coordinating ligand to
1
stabilize the zirconium center. The H NMR spectrum shows
clearly the disappearance of one benzyl group, and the
presence of N,N-dimethyl aniline (Figure 2), proving the
formation of cationic complex 3a (Scheme 3). The 19F NMR
spectrum shows identical signals as those of [PhMe2NH][B-
(C6F5)4], suggesting that there is no interaction between the
cation and anion (Supporting Information).
Using the methodology developed for C−H bond
functionalization, a successive addition of C(sp2) and
C(sp3)−H bonds was performed by reacting 2-methylpyridine
The structure of ion-pair complex 3a was also characterized
by single-crystal X-ray diffraction analysis (Figure 3).
E
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1
Figure 2. H NMR spectra of complexes 3 and 3a.
Scheme 3. Synthesis of Complex 3a
Comparing with neutral complex 3, shorter Zr−O1 (1.971(2)
vs 1.998(2) Å), Zr−O2 (1.978(6) vs 1.997(2) Å), and Zr−N1
(2.361(7) vs 2.512(3) Å) bonds are observed, while the Zr−
C37 bond is found to be longer (2.284(7) vs 2.250(4) Å), due
to the coordinating bulky N,N-dimethyl aniline.13 This
colorless crystalloid of 3a also catalyzed the addition of 2,6-
lutidine to styrene, which gave 77% yield in a 10:1 ratio of
branched to linear products under conditions stated in Table 4.
This result is comparable with that of complex 3 and TB (81%
yield in 10:1 ratio, Table 4, entry 3), further corroborating that
cationic species formed during the catalytic process.
Mechanistic Proposal. A mechanism is proposed for Zr-
catalyzed addition of C(sp2)−H bonds to alkenes (Scheme 4).
Cationic zirconium alkyl species A was generated through
reactions of neutral complexes with [Ph3C][B(C6F5)4].19
Coordination of pyridine to the zirconium center in A assisted
C(sp2)−H activation to give three-membered zirconacycles
B.8,20 Regioselectivity of this reaction is determined by
substrate structures: migratory insertion of styrene into the
Zr−C bond of B occurred in 1,2-mode, while insertion of
aliphatic alkenes occurred in 2,1-mode.9b Hydrolysis of
insertion products C or D with pyridine substrates gave linear
(in the former) or branched (in the latter) products, as well as
zirconacycles B for the next cycle.
The mechanism of Zr-catalyzed addition of a C(sp3)−H
bond follows a similar pathway (Scheme 5).13 It is noteworthy
that regioselectivity of addition of C(sp3)−H bonds is both
substrate- and ligand-controlled: reactions of aliphatic alkenes
gave branched products regardless of catalyst structures;
reactions of aromatic alkenes formed branched products
when catalyzed by complexes of aryl-bridged ligands, while
they formed linear products when catalyzed by complexes of
alkyl-bridged ligands. As suggested by computational study
(Scheme 6),13 the ligand backbone influences the insertion of
styrene into the Zr−C bond; i.e., 1,2-insertion is preferred in
the case of the aniline bridged ligand, while 2,1-insertion is
preferred in the case of the n-butyl amine bridged ligand.
The difference between C(sp2)-H and C(sp3)-H reactions
may lie in the fact that the former has a lower barrier which
does not differentiate the subtle differences between two types
of ligands.
F
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alkenes. Regioselectivity of the addition of benzylic C(sp3)−H
bonds was significantly influenced by ligand backbones. For
reactions of styrene derivatives, branched products formed as
the majority in the presence of N-aryl amine-bridged
bis(phenolato) Zr complexes, while linear addition products
were preferred in the presence of N-alkyl amine-bridged
bis(phenolato) Zr complexes. Development of group 4 metal-
catalyzed C(sp2/sp3)−H functionalization reactions is ongoing
in our laboratory.
EXPERIMENTAL SECTION
General Considerations. All manipulations of air- and/or
moisture-sensitive compounds were performed under a nitrogen
atmosphere using standard Schlenk or glovebox techniques. H and
■
1
13C NMR spectra were recorded on a Varian XL 400 MHz
spectrometer. In a glovebox, a properly dried sample for elemental
analysis was ground in a mortar, weighed into tin foil cups, and sealed
in Schlenk tubes. Carbon, hydrogen, and nitrogen analyses were
performed by direct combustion with a Carlo-Erba EA-1110
instrument. X-ray crystallographic data were collected using a Bruker
AXS D8 X-ray diffractometer. Toluene and hexane were freshly
distilled by refluxing over sodium/benzophenone ketyl and distilled
prior to use. C6H5Cl, C6D6, and C6D5Cl were degassed and distilled
over CaH2. [Ph3C][B(C6F5)4] purchased from Strem Chemicals, Inc.,
was used without purification. ZrBn4, ligand precursors L3H2−L9H2,
and complexes 1−3 were prepared according to reported
procedures.13,15 Pyridines and olefins were distilled over CaH2,
flushed with argon, and stored over molecular sieves (4 Å).
Figure 3. Molecular structure of 3a·2C6H5Cl showing 30%
probability ellipsoids; hydrogen atoms and solvent molecules are
omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
Zr1−O1 1.971(6), Zr1−O2 1.978(6), Zr1−N1 2.361(7), Zr1−N2
2.362(6), Zr1−C37 2.284(7); O1−Zr1−O2 159.9(2), O1−Zr1−C37
95.2(3), O2−Zr1−C37 94.2(3), O1−Zr1−N1 80.5(2), O2−Zr1−N1
79.5(2), C37−Zr1−N1 123.1(2), O1−Zr1−N2 95.9(2), O2−Zr1−
N2 93.8(2), C37−Zr1−N2 122.7(3), N1−Zr1−N2 114.2(2).
CONCLUSION
■
In summary, we demonstrate that cationic zirconium
complexes derived from zirconium dibenzyl complexes bearing
a tridentate [ONO]-type amine-bridged bis(phenolato) ligand
and [Ph3C][B(C6F5)4] are active catalysts for ortho-selective
addition of C(sp2)−H bonds of pyridines to a variety of
alkenes, which gave rise to alkylated pyridine derivatives in
100% atom-economy. This is the first example of group 4
metal-based catalysts capable of catalyzing ortho-selective C−H
addition of pyridines in the absence of H2. Meanwhile, these
cationic zirconium complexes also catalyzed the ortho-selective
addition of benzylic C−H bonds of various dialkylpyridines to
General Procedure for Zirconium Complexes Synthesis. To
a solution of ZrBn4 (3 mmol) in toluene (10 mL) was added dropwise
LnH2 (3 mmol) in toluene (5 mL) at room temperature over 15 min.
After stirring for 12 h at room temperature, toluene was removed
under reduced pressure and the residue was washed with hexane (2 ×
5 mL). Complexes 4−10 were obtained as colorless solids after
recrystallization from toluene solution.
1
ZrBn2L4 (4). Complex 4 was isolated in 2.22 g (91% yield). H
NMR (400 MHz, C6D6): δ 7.87 (m, 2H, Ar), 7.42 (s, 2H, Ar), 7.36
(m, 2H, Ar), 7.22 (m, 1H, Ar), 6.91 (m, 2H, Ar), 6.79 (m, 2H, Ar),
6.72 (s, 2H, Ar), 6.66 (m, 1H, Ar), 6.60 (m, 2H, Ar), 6.20 (m, 2H,
Scheme 4. Possible Reaction Mechanism of Addition of C(sp2)−H Bond to Alkenes
G
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Scheme 5. Possible Reaction Mechanism of Addition of C(sp3)−H Bonds to Styrene
a
Scheme 6. Computational Study on Regioselectivity
a
Relative free energies are in kcal/mol.
Ar), 3.81 (br d, J = 13.52 Hz, 2H, ArCH2), 3.26 (br d, J = 13.68 Hz,
2H, ArCH2), 3.23 (s, 2H, PhCH2), 1.86 (s, 2H, PhCH2), 1.76 (s,
18H, C(CH3)3), 1.22 (s, 18H, C(CH3)3). 13C{1H} NMR (100 MHz,
C6D6): 157.0, 149.3, 140.5, 135.1, 134.3, 130.7, 130.3, 127.9, 125.4,
124.4, 124.1, 123.9, 123.8, 123.4, 121.0, 115.1, 114.0 (Ar-C), 64.1
(ArCH2N), 59.6 (PhCH2), 34.5 (C(CH3)3), 33.4 (C(CH3)3), 30.9
(C(CH3)3), 29.5 (C(CH3)3). Anal. Calcd for C50H62FNO2Zr: C,
80.95; H, 7.00; N, 1.22. Found: C, 81.01; H, 6.97; N, 1.23.
6.92−6.86 (m, 4H, Ar-H), 6.81−6.73 (m, 4H, Ar-H), 6.69−6.64 (m,
3H, Ar-H), 3.81 (br d, J = 18.04 Hz, 2H, ArCH2), 3.26 (br d, J =
18.32 Hz, 2H, ArCH2), 3.23 (s, 2H, PhCH2), 1.85 (s, 2H, PhCH2),
1.73 (s, 18H, C(CH3)3), 1.21 (s, 18H, C(CH3)3). 13C{1H} NMR
(100 MHz, C6D6): 157.5, 149.6, 146.9, 141.2, 135.8, 134.4, 131.2,
130.8, 128.5, 126.1, 125.6, 124.0, 124.3, 124.1, 123.5 (Ar-C), 64.4
(ArCH2N), 60.1 (PhCH2), 35.0 (C(CH3)3), 33.9 (C(CH3)3), 31.3
(C(CH3)3), 30.0 (C(CH3)3). Anal. Calcd for C51H62F3NO2Zr: C,
70.41; H, 7.10; N, 1.62. Found: C, 70.47; H, 7.19; N, 1.61.
1
ZrBn2L5 (5). Complex 5 was isolated in 2.30 g (88% yield). H
1
NMR (400 MHz, C6D6): δ 7.87−7.84 (m, 2H, Ar-H), 7.40−7.39 (m,
2H, Ar-H), 7.38−7.33 (m, 2H, Ar-H), 7.25−7.23 (m, 1H, Ar-H),
ZrBn2L6 (6). Complex 6 was isolated in 2.41 g (90% yield). H
NMR (400 MHz, C6D6): δ 7.83 (m, 2H, J = 7.44 Hz, Ar-H), 7.42 (s,
H
DOI: 10.1021/acs.inorgchem.8b01959
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2H, Ar-H), 7.32 (m, 2H, Ar-H), 7.22 (m, 1H, Ar-H), 7.16 (m, 1H, Ar-
H), 6.84 (m, 6H, Ar-H), 6.65 (m, 1H, Ar-H), 4.07 (br d, J = 13.12 Hz,
2H, ArCH2), 3.86 (br d, J = 13.28 Hz, 2H, ArCH2), 3.48 (s, 2H,
PhCH2), 1.99 (s, 2H, PhCH2), 1.76 (s, 18H, C(CH3)3), 1.14 (s, 18H,
C(CH3)3). 13C{1H} NMR (100 MHz, C6D6): 157.5, 150.4, 141.7,
138.7, 136.5, 130.6, 130.4, 128.4, 126.9, 125.5, 125.0, 124.3, 123.8,
121.2 (Ar-C), 65.5 (ArCH2N), 64.9 (PhCH2), 60.7 (PhCH2), 35.1
(C(CH3)3), 33.8 (C(CH3)3), 31.2 (C(CH3)3), 29.8 (C(CH3)3). Anal.
Calcd for C50H58F5NO2Zr: C, 67.36; H, 6.58; N, 1.55. Found: C,
67.38; H, 6.56; N, 1.57.
Calcd for C75H67BF20N2O2Zr: C, 59.68; H, 4.39; N, 1.86. Found: C,
59.64; H, 4.47; N, 1.85.
General Procedure for Addition of ortho-C(sp2)−H Bond of
Pyridines to Various Olefins Catalyzed by 3 and [Ph3C][B-
(C6F5)4]. In a glovebox filled with nitrogen, a PhCl solution (1 mL) of
[Ph3C][B(C6F5)4] (92 mg, 0.01 mmol) was added to a PhCl solution
(2 mL) of 3 (80 mg, 0.01 mmol) under stirring. A color change from
orange to colorless was observed immediately. After 5 min, alkene 10
(1 mmol) and pyridine derivative 11 (2 mmol) were added to the
mixture successively. The resulting solution was stirred at 100 °C for
the desired time. After the mixture was cooled to room temperature,
the crude product obtained after removal of solvent was isolated by
column chromatography (petroleum ether, silica gel, 0.5% NEt3) as a
viscous colorless oil and characterized by 1H and 13C NMR
spectroscopy.
1
ZrBn2L7 (7). Complex 7 was isolated in 2.26 g (91% yield). H
NMR (400 MHz, C6D6): δ 7.94 (m, 2H, Ar-H), 7.42 (s, 2H, Ar-H),
7.38 (m, 2H, Ar-H), 7.24 (m, 1H, Ar-H), 6.94 (m, 2H, Ar-H), 6.80
(m, 4H, Ar-H), 6.74 (m, 2H, Ar-H), 6.67 (m, 1H, Ar-H), 6.22 (m,
2H, Ar-H), 3.84 (br d, J = 13.60 Hz, 2H, ArCH2), 3.37 (br d, J =
13.64 Hz, 2H, ArCH2), 3.35 (s, 2H, PhCH2), 2.65 (s, 3H, OCH3),
1.92 (s, 2H, PhCH2), 1.80 (s, 18H, C(CH3)3), 1.23 (s, 18H,
C(CH3)3). 13C{1H} NMR (100 MHz, C6D6): 158.0, 157.5, 149.8,
140.8, 135.4, 135.1, 131.2, 130.7, 129.0, 128.4, 128.2, 125.3, 125.0,
123.7, 123.4, 121.4, 113.9 (Ar-C), 64.7 (ArCH2N), 60.0 (PhCH2),
53.9 (OCH3), 35.0 (C(CH3)3), 33.9 (C(CH3)3), 31.4 (C(CH3)3),
30.1 (C(CH3)3). Anal. Calcd for C51H65NO3Zr: C, 63.66; H, 7.91; N,
1.66. Found: C, 63.69; H, 7.88; N, 1.68.
1
6-Methyl-2-phenethyl-3,4-dihydropyridine (12a). H NMR (400
MHz, CDCl3): δ 7.48−7.44 (m, 1H, γ-Py-H), 7.31−7.27 (m, 2H, o-
Ar-H), 7.24−7.18 (m, 3H, m, p-Ar-H), 6.98 (d, 1H, J = 7.6 Hz, β-Py-
H), 6.89 (d, 2H, J = 7. 64 Hz, β′-Py-H), 3.12−3.02 (m, 4H, CH2),
2.58 (s, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 160.7 (α-
Py-C), 157.8 (α′-Py-C), 141.7 (CH2Ar-C), 136.6 (γ-Py-C), 128.5 (m-
Ar-C), 128.4 (o-Ar-C), 125.9 (p-Ar-C), 120.7 (β′-Py-C), 119.8 (β-Py-
C), 40.3, 36.3 (CH2), 24.6 (CH3). HR MS (ESI+): Found 198.1288
[M + H]+, calcd. for C14H16N+: 198.1283.
1
ZrBn2L8 (8). Complex 8 was isolated in 2.02 g (80% yield). H
NMR (400 MHz, C6D6): δ 7.92 (m, 2H, Ar-H), 7.50 (m, 1H, Ar-H),
7.38 (m, 4H, Ar-H), 7.22 (m, 1H, Ar-H), 7.03 (m, 2H, Ar-H), 6.94
(m, 3H, Ar-H), 6.80 (m, 3H, Ar-H), 6.58 (m, 2H, Ar-H), 3.83 (br d, J
= 18.00 Hz, 2H, ArCH2), 3.38 (br d, J = 18.16 Hz, 2H, ArCH2), 3.32
(s, 2H, PhCH2), 3.18 (m, 1H, CH(CH3)2), 1.92 (s, 2H, PhCH2), 1.76
(s, 18H, C(CH3)3), 1.24 (s, 18H, C(CH3)3), 0.65 (d, J = 9.24 Hz, 6H,
CH(CH3)2). 13C{1H} NMR (100 MHz, C6D6): 157.6, 149.8, 147.6,
147.1, 140.8, 140.7, 135.4, 135.2, 131.1, 130.6, 129.0, 128.4, 128.2,
127.9, 126.6, 125.9, 125.7, 125.4, 125.3, 125.0, 124.9, 123.6, 122.4,
121.4 (Ar-C), 64.6 (ArCH2N), 60.1 (PhCH2), 37.8 (CH(CH3)2),
35.0 (C(CH3)3), 33.9 (C(CH3)3), 31.4 (C(CH3)3), 30.1 (C(CH3)3),
22.9 (CH(CH3)2). Anal. Calcd for C53H69NO2Zr: C, 75.44; H, 8.27;
N, 1.66. Found: C, 75.48; H, 8.25; N, 1.66.
2-Methyl-6-(4-methylphenethyl)pyridine (12b). 1H NMR (400
MHz, CDCl3): δ 7.45−7.42 (m, 1H, γ-Py-H), 7.11−7.06 (m, 4H, o,m-
Ar-H), 6.95 (d, 1H, J = 7.6 Hz, β-Py-H), 6.88 (d, 2H, J = 7. 64 Hz, β′-
Py-H), 3.06−3.95 (m, 4H, CH2), 2.54 (s, 3H, CH3), 2.30 (s, 3H,
CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 160.8 (α-Py-C), 157.8
(α′-Py-C), 138.6 (CH2Ar-C), 136.5 (γ-Py-C), 135.3 (p-Ar-C), 129.0
(m-Ar-C), 128.4 (o-Ar-C), 120.6 (β′-Py-C), 119.8 (β-Py-C), 40.4,
35.8 (CH2), 24.6, 21.0 (CH3). HR MS (ESI+): Found 212.1433 [M +
H]+, calcd. for C15H28N+: 212.1439.
1
ZrBn2L9 (9). Complex 9 was isolated in 3.11 g (91% yield). H
2-(4-(tert-Butyl)phenethyl)-6-methylpyridine (12c). 1H NMR
(400 MHz, CDCl3): δ 7.47−7.43 (m, 1H, γ-Py-H), 7.32−7.30 (m,
2H, o-Ar-H), 7.19−7.17 (m, 2H, m-Ar-H), 6.96 (d, 1H, J = 7. 60 Hz,
β-Py-H), 6.92 (d, 2H, J = 7. 64 Hz, β′-Py-H), 3.10−2.98 (m, 4H,
CH2), 2.56 (s, 3H, CH3), 1.32 (s, 9H, C(CH3)3). 13C{1H} NMR (100
MHz, CDCl3): δ 160.9 (α-Py-C), 157.8 (α′-Py-C), 149.7 (CH2Ar-C),
138.7 (γ-Py-C), 136.6 (p-Ar-C), 128.2 (m-Ar-C), 125.2 (o-Ar-C),
120.6 (β′-Py-C), 119.8 (β-Py-C), 40.3, 35.8 (CH2), 34.9 (CH3). 31.5
(C(CH3)3), 24.6 (C(CH3)3). HR MS (ESI+): Found 254.1905 [M +
H]+, calcd. for C18H24N+: 254.1909.
NMR (400 MHz, C6D6): δ 7.37 (s, 2H, Ar), 7.17−7.10 (m, 18H, Ar),
7.05−6.97 (m, 12H, Ar), 6.92−6.86 (m, 3H, Ar), 6.83−6.79 (m, 2H,
Ar), 6.70−6.68 (m, 2H, Ar), 6.64−6.60 (m, 1H, Ar), 6.49 (s, 2H, Ar),
6.23 (m, 2H, Ar), 3.66 (br d, J = 13.36 Hz, 2H, ArCH2), 2.95 (br d, J
= 13.60 Hz, 2H, ArCH2), 2.11 (s, 3H, PhCH3), 2.08 (s, 6H,
C(CH3)2Ph), 1.57 (s, 6H, C(CH3)2Ph), 1.54 (s, 6H, C(CH3)2Ph),
1.51 (s, 6H, C(CH3)2Ph), 1.28 (s, 2H, PhCH2), 0.84 (s, 2H, PhCH2).
13C{1H} NMR (100 MHz, C6D6): 156.9, 150.9, 150.8, 149.8, 143.0,
139.6, 137.0, 134.8, 133.2, 131.1, 129.9, 128.5, 127.8, 127.7, 127.6,
127.4, 127.2, 127.0, 126.8, 126.3, 125.5, 125.4, 125.2, 124.9, 124.7,
124.5, 123.2, 120.4 (Ar-C), 64.0 (ArCH2N) 62.4, 60.8, 57.5 (ArCH2),
42.1 (PhCH3), 41.9 (C(CH3)2Ph), 33.0 (C(CH3)2Ph), 31.1
(C(CH3)2Ph), 30.6 (C(CH3)2Ph), 30.1 (C(CH3)2Ph), 27.2, 20.6
(PhCH2). Anal. Calcd for C77H77NO2Zr: C, 80.90; H, 7.00; N, 1.22.
Found: C, 81.01; H, 6.97; N, 1.23.
1
2-(4-Methoxyphenethyl)-6-methylpyridine (12d). H NMR (400
MHz, CDCl3): δ 7.44−7.41 (m, 1H, γ-Py-H), 7.10−7.08 (m, 2H, o-
Ar-H), 6.95 (d, 1H, J = 7.6 Hz, β-Py-H), 6.85 (d, 2H, J = 7. 64 Hz, β′-
Py-H), 6.80−6.78 (m, 2H, m-Ar-H), 3.76 (s, 3H, OCH3), 3.03−2.90
(m, 4H, CH2), 2.56 (s, 3H, CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 160.8 (α-Py-C), 157.8 (α′-Py-C, p-Ar-C), 136.5 (γ-Py-C),
133.8 (CH2Ar-C), 129.4 (o-Ar-C), 120.6 (β′-Py-C), 119.8 (β-Py-C),
113.7 (m-Ar-C), 55.2 (OCH3), 40.5, 35.4 (CH2), 24.6 (CH3). HR MS
(ESI+): Found 228.1379 [M + H]+, calcd. for C15H18NO +: 228.1388.
2-(4-Fluorophenethyl)-6-methylpyridine (12e). 1H NMR (400
MHz, CDCl3): δ 7.44−7.40 (m, 1H, γ-Py-H), 7.13−7.09 (m, 2H, o-
Ar-H), 6.96−6.90 (m, 3H, m-Ar-H and β-Py-H), 6.84 (d, 1H, J = 7.6
Hz, β′-Py-H), 3.04−2.96 (m, 4H, CH2), 2.58 (s, 3H, CH3). 13C{1H}
NMR (100 MHz, CDCl3): δ 162.5 (p-Ar-C), 160.3 (α-Py-C), 160.1
(α-Py-C), 157.9 (α′-Py-C), 137.3 (CH2Ar-C), 136.5 (γ-Py-C), 129.8
(o-Ar-C), 120.7 (β′-Py-C), 119.8 (β-Py-C), 115.1, 114.9 (m-Ar-C),
40.3, 36.5 (CH2), 24.6 (CH3). HR MS (ESI+): Found 216.1188 [M +
H]+, calcd. for C14H15FN+: 216.1189.
Synthesis of Cationic Zirconium Complex 3a. To a solution of
complex 3 (0.160 g, 0.2 mmol) in PhCl (2 mL) was added dropwise
[PhNMe2H][B(C6F5)4] (0.160 g, 0.2 mmol) in PhCl (2 mL) at room
temperature over 15 min. After stirring for 15 min at room
temperature, PhCl was removed under reduced pressure and the
residue was washed with hexane (2 × 5 mL). Complexes 3a were
obtained as colorless solids after recrystallization from chlorobenzene
and hexane solution.
1
Complex 3a was isolated in 0.287 g (95% yield). H NMR (400
MHz, C6D6): δ 7.77 (m, 2H, Ar-H); 7.40 (m, 4H, Ar-H); 7.08 (m,
2H, Ar-H); 6.81 (m, 6H, Ar-H); 6.69 (m, 2H, Ar-H); 6.55 (m, 1H,
Ar-H); 6.46 (m, 2H, Ar-H); 3.43 (d, J = 14.40 Hz, 2H, ArCH2); 3.18
(s, 2H, PhCH2); 2.71 (d, J = 14.32 Hz, 2H, ArCH2); 2.62 (m, 2H,
PhCH2); 2.41 (s, 6H, N(CH3)2); 1.58 (s, 18H, C(CH3)3); 1.16 (s,
18H, C(CH3)3). 19F{1H} NMR (282 MHz, C6D6): δ −131.74 (d, J =
8.28 Hz), −162.5 (t, J = 17.72 Hz), −166.3 (t, J = 15.28 Hz). Anal.
2-(4-Chlorophenethyl)-6-methylpyridine (12f). 1H NMR (400
MHz, CDCl3): δ 7.45−7.41 (m, 1H, γ-Py-H), 7.21−7.19 (m, 2H, o-
Ar-H), 6.10−6.08 (m, 2H, m-Ar-H), 6.96 (d, 1H, J = 7.6 Hz, β-Py-H),
6.83 (d, 1H, J = 7.6 Hz, β′-Py-H), 3.04−2.95 (m, 4H, CH2), 2.53 (s,
I
DOI: 10.1021/acs.inorgchem.8b01959
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3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 160.2 (α-Py-C),
157.9 (α′-Py-C), 140.1(CH2Ar-C), 136.6 (γ-Py-C), 131.6 (p-Ar-C),
129.9 (o-Ar-C), 128.4 (m-Ar-C), 120.8 (β′-Py-C), 119.8 (β-Py-C),
40.0, 35.5 (CH2), 24.5 (CH3). HR MS (ESI+): Found 232.0892 [M +
H]+, calcd. for C14H15ClN+: 232.0893.
2-(Hexan-2-yl)-6-isopropylpyridine (13c). 1H NMR (400 MHz,
CDCl3): δ 7.49−7.45 (m, 1H, γ-Py-H), 6.94−6.88 (m, 2H, β,β′-Py-
H), 3.05−2.96 (m, 1H, CH), 2.87−2.78 (m, 1H, CH), 1.78−1.67 (m,
1H, CH), 1.58−1.49 (m, 1H, CH), 1.31−1.23 (m, 12H, alkyl-H),
1.17−1.10 (m, 1H, CH), 0.85−0.82 (m, 3H, CH3). 13C{1H} NMR
(100 MHz, CDCl3): δ 166.0 (α′-Py-C), 165.4 (α-Py-C), 135.8 (γ-Py-
C), 117.6 (β′-Py-C), 116.6 (β-Py-C), 41.5, 36.4, 35.9 (alkyl-C), 29.3
(CH), 22.3 (CH3), 22.2, 22.1, 20.4, 13.6 (alkyl-C). HR MS (ESI+):
Found 206.1901 [M + H]+, calcd. for C14H24N+: 206.1909.
2-(Hexan-2-yl)-6-phenylpyridine (13d). 1H NMR (400 MHz,
CDCl3): δ 8.07−8.05 (m, 2H, o-Ar-H), 7.66−7.62 (m, 1H, γ-Py-H),
7.54−7.53 (m, 1H, β-Py-H), 7.49−7.45 (m, 2H, m-Ar-H), 7.42−7.38
(m, 1H, p-Ar-H), 7.07−7.05 (m, 1H, β′-Py-H), 3.00−2.92 (m, 1H,
CH), 1.89−1.80 (m, 1H, CH), 1.36−1.29 (m, 6H, alkyl-H), 1.26−
1.18 (m, 1H, CH), 0.91−0.87 (m, 3H, CH3). 13C{1H} NMR (100
MHz, CDCl3): δ 166.1 (α′-Py-C), 155.9 (α-Py-C), 139.5 (γ-Py-C),
136.3 (Py-Ar-C), 128.2 (m,p-Ar-C), 126.5 (o-Ar-C), 119.3 (β′-Py-C),
117.1 (β-Py-C), 41.6, 36.4, 29.4 (alkyl-C), 22.4 (CH3) 20.4, 13.6
(alkyl-C). HR MS (ESI+): Found 240.1755 [M + H]+, calcd. for
C17H22N+: 240.1752.
1
2-((1S,4R)-Bicyclo[2.2.1]heptan-2-yl)-6-methylpyridine (12g). H
NMR (400 MHz, CDCl3): δ 7.44−7.40 (m, 1H, γ-Py-H), 6.95 (d,
1H, J = 7.6 Hz, β-Py-H), 6.88 (d, 1H, J = 7. Six Hz, β′-Py-H), 2.85−
2.81 (m, 1H, CH), 2.49 (s, 3H, CH3), 2.41 (s, 1H, CH), 2.33 (s, 1H,
CH), 1.88−1.84 (m, 1H, CH), 1.74−1.69 (m, 1H, CH), 1.61−1.56
(m, 1H, CH), 1.41−1.38 (m, 1H, CH), 1.28−1.24 (m, 1H, CH),
1.15−1.12 (m, 1H, CH). 13C{1H} NMR (100 MHz, CDCl3): δ 165.5
(α-Py-C), 157.4 (α′-Py-C), 136.2 (γ-Py-C), 120.0 (β-Py-C), 117.8
(β′-Py-C), 49.6, 42.8, 37.4, 36.9, 36.0, 30.4, 29.0 (alkyl-C), 24.7
(CH3). HR MS (ESI+): Found 188.1439 [M + H]+, calcd. for
C14H18N+: 188.1439.
2-Methyl-6-(octan-2-yl)pyridine (12h). 1H NMR (400 MHz,
CDCl3): δ 7.43−7.39 (m, 1H, γ-Py-H), 6.88−6.86 (m, 2H, β,β′-Py-
H), 2.84−2.75 (m, 1H, CH), 2.47 (s, 3H, CH3), 1.71−1.62 (m, 1H,
CH), 1.54−1.46 (m, 1H, CH), 1.27−1.10 (m, 11H, alkyl-H), 0.82−
0.79 (m, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 166.4 (α-
Py-C), 157.4 (α′-Py-C), 136.4 (γ-Py-C), 120.4 (β-Py-C), 117.6 (β′-
Py-C), 42.2, 37.2, 31.8, 29.4, 27.6 (alkyl-C), 24.6 (CH3), 22.6, 20.9,
14.0 (alkyl-C). HR MS (ESI+): Found 206.1910 [M + H]+, calcd. for
C14H24N+: 206.1909.
1
2-(Hexan-2-yl)-5,6,7,8-tetrahydroquinoline (13e). H NMR (400
MHz, CDCl3): δ 7.26 (d, J = 7.8 Hz, 1H, γ-Py-H), 6.87 (d, J = 7.9 Hz,
1H, β-Py-H), 2.89 (m, 2H, CH2), 2.86−2.76 (m, 1H, CH), 2.72 (m,
2H, CH2), 1.93−1.84 (m, 2H, CH2), 1.83−1.75 (m, 2H, CH2), 1.69
(m, 1H, CH), 1.54 (m, 1H, CH), 1.35−1.22 (m, 6H, alkyl-H), 1.21−
1.11 (m, 1H, CH), 0.90−0.80 (m, 3H, CH3). 13C{1H} NMR (100
MHz, CDCl3): δ 163.4 (α′-Py-C), 155.7 (α-Py-C), 136.6 (γ-Py-C),
128.6 (β-Py-C), 117.3 (β′-Py-C), 41.4, 36.5, 32.1, 29.4, 28.0, 22.8,
22.4, 20.5, 13.6 (alkyl-C). HR MS (ESI+): Found 218.1904 [M +
H]+, calcd. for C15H24N+: 218.1909.
2-(Hexan-2-yl)-6-methylpyridine (12i). 1H NMR (400 MHz,
CDCl3): δ 7.41 (m, 1H, γ-Py-H), 6.86 (m, 2H, β,β′-Py-H), 2.83−
2.74 (m, 1H, CH), 2.47 (s, 3H, CH3), 1.71−1.62 (m, 1H, CH), 1.53−
1.46 (m, 1H, CH), 1.27−1.19 (m, 6H, alkyl-H), 1.15−1.05 (m, 1H,
CH), 0.82−0.78 (m, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ
165.9 (α-Py-C), 156.9 (α′-Py-C), 135.9 (γ-Py-C), 119.9 (β-Py-C),
117.2 (β′-Py-C), 41.7, 36.4, 29.4 (alkyl-C), 24.1 (CH3), 22.3, 20.4,
13.5 (alkyl-C). HR MS (ESI+): Found 178.1599 [M + H]+, calcd. for
C12H20N+: 178.1596.
2-(Hexan-2-yl)-6,7-dihydro-5H-cyclopenta[b]pyridine (13f). 1H
NMR (400 MHz, CDCl3): δ 7.36 (d, J = 7.36 Hz, 1H, γ-Py-H),
6.83 (d, J = 7.8 Hz, 1H, β-Py-H), 3.07−2.91 (m, 2H, CH2), 2.80 (m,
3H, alkyl-H), 2.16−1.95 (m, 2H, CH2), 1.74−1.62 (m, 1H, CH),
1.58−1.43 (m, 1H, CH), 1.32−1.19 (m, 6H, alkyl-H), 1.19−1.01 (m,
1H, CH), 0.87−0.73 (m, 3H, CH3). 13C{1H} NMR (100 MHz,
CDCl3): δ 164.4 (α′-Py-C), 164.3 (α-Py-C), 133.4 (γ-Py-C), 131.7
(β-Py-C), 117.7 (β′-Py-C), 41.4, 36.6, 33.9, 29.9, 29.45, 22.7, 22.3,
20.6, 13.6 (alkyl-C). HR MS (ESI+): Found 204.1757 [M + H]+,
calcd. for C14H22N+: 204.1752.
2-((3aR,4R,7R,7aR)-3a,4,5,6,7,7a-Hexahydro-1H-4,7-methano-
inden-6-yl)-6-methylpyridine + 2-((3aS,4R,7R,7aS)-3a,4,5,6,7,7a-
Hexahydro-1H-4,7-methanoinden-5-yl)-6-methylpyridine (12j:12j′
1
= 1:0.44). H NMR (400 MHz, CDCl3): δ 7.41−7.37 (m, 1H, γ-Py-
H), 6.92 (d, 1H, J = 7.6 Hz, β-Py-H), 6.85 (d, 2H, J = 7. 64 Hz, β′-Py-
H), 5.73−5.67 (m, 1H, CHCH), 5.66−5.58 (m, 1H, CHCH),
3.17−3.04 (m, 1H, CH), 2.93−2.81 (m, 1H, CH), 2.55 (m, 3H,
CH3), 2.48 (s, 3H, CH3), 2.41−2.36 (m, 1H, CH), 2.34−2.30 (m,
1H, CH), 2.26−2.21 (m, 2H, CH), 1.82−1.62 (m, 3H, CH), 1.40−
1.36 (m, 1H, CH). 13C{1H} NMR (100 MHz, CDCl3): δ 165.9 (α-
Py-C), 165.7 (α-Py-C), 157.3 (α′-Py-C), 136.1 (γ-Py-C), 136.0 (γ-Py-
C), 132.6 (CHCH), 132.4 (CHCH), 131.7 (CHCH), 130.8
(CHCH), 119.8 (β-Py-C), 119.8 (β-Py-C), 118.2 (β′-Py-C), 118.0
(β′-Py-C), 53.74, 52.55, 47.21, 45.56, 44.14, 42.79, 42.10, 41.35,
41.29, 40.21, 39.12, 38.83, 33.06, 32.56, 32.28, 29.04, 24.74. (alkyl-C).
HR MS (ESI+): Found 226.1599 [M + H]+, calcd. for C16H20N+:
226.1596.
1
2-(Hexan-2-yl)quinoline (13g). H NMR (400 MHz, CDCl3): δ
8.06−8.03 (m, 2H, 4,8-Ar-H), 7.75−7.73 (m, 1H, 5-Ar-H), 7.67−7.63
(m, 1H, 7-Ar-H), 7.46−7.43 (m, 1H, 6-Ar-H), 7.27 (d, J = 7.27 Hz,
1H, 3-Ar-H), 3.12−3.03 (m, 1H, CH), 1.84−1.76 (m, 1H, CH2),
1.71−1.62 (m, 1H, CH), 1.58−1.43 (m, 1H, CH), 1.36−1.26 (m, 6H,
alkyl-H), 1.20−1.12 (m, 1H, CH), 0.85−0.81 (m, 3H, CH3). 13C{1H}
NMR (100 MHz, CDCl3): 166.8 (2-Ar-C), 147.3 (9-Ar-C), 135.8 (4-
Ar-C), 128.7 (7-Ar-C), 128.6 (8-Ar-C), 127.0 (5-Ar-C), 126.5 (10-
Ar-C), 125.1 (6-Ar-C), 119.1 (3-Ar-C), 42.5, 36.4, 29.5, 22.3, 20.4,
13.6 (alkyl-C). HR MS (ESI+): Found 214.1599 [M + H]+, calcd. for
C15H20N+: 214.1596.
General Procedure for Benzylic C(sp3)−H Addition of
Pyridine Derivatives to Various Olefins Catalyzed by 3 and
[Ph3C][B(C6F5)4]. In a glovebox filled with nitrogen, a PhCl solution
(1 mL) of [Ph3C][B(C6F5)4] (92 mg, 0.01 mmol) was added to a
PhCl solution (2 mL) of 3 (80 mg, 0.01 mmol) under stirring. A color
change from orange to colorless was observed immediately. After 5
min, 14 (1 mmol) and 11 (4 mmol) were added to the mixture
successively. The resulting solution was stirred at 100 °C for the
desired time. After the mixture was cooled to room temperature, the
crude product obtained after removal of solvent was isolated by
column chromatography (petroleum ether, silica gel, 0.5% NEt3) as a
viscous colorless oil and characterized by 1H and 13C NMR
spectroscopy.
2-(Cyclohex-2-en-1-yl)-6-methylpyridine (12k). 1H NMR (400
MHz, CDCl3): δ 7.47 (m, 1H, γ-Py-H), 6.94 (m, 2H, β,β′-Py-H),
5.78−5.70 (m, 2H CHCH), 2.97−2.89 (m, 1H, CH), 2.51 (s, 3H,
CH3), 2.35−2.07 (m, 4H, alkyl-H), 1.99−1.94 (m, 1H, CH), 1.82−
1.72 (m, 1H, CH). 13C{1H} NMR (100 MHz, CDCl3): δ 165.4 (α-
Py-C), 157.4 (α′-Py-C), 136.6 (γ-Py-C), 126.9 (CHCH), 126.5
(CHCH), 120.6 (β-Py-C), 117.6 (β′-Py-C), 42.3 (CH3), 31.7, 28.7
25.6, 24.6 (alkyl-C). HR MS (ESI+): Found 174.1280 [M + H]+,
calcd. for C12H16N+: 174.1283.
2-Ethyl-6-(hexan-2-yl)pyridine (13b). 1H NMR (400 MHz,
CDCl3): δ 7.48−7.44 (m, 1H, γ-Py-H), 6.92−6.89 (m, 2H, β,β′-Py-
H), 2.86−2.73 (m, 3H, Alkyl-H), 1.74−1.65 (m, 1H, CH), 1.57−1.48
(m, 1H, CH), 1.27−1.22 (m, 9H, alkyl-H), 1.16−1.09 (m, 1H, CH),
0.88−0.80 (m, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ
165.8 (α-Py-C), 162.2 (α′-Py-C), 135.9 (γ-Py-C), 118.4 (β-Py-C),
117.4 (β′-Py-C), 41.6, 36.4, 31.0 (alkyl-C), 29.3 (CH2), 22.1 (CH3),
20.4, 13.6, 13.5 (alkyl-C). HR MS (ESI+): Found 192.1750 [M +
H]+, calcd. for C13H22N+: 192.1752.
Successive C(sp2)−H and C(sp3)−H Addition of α-Picoline to
Norbornene. In a glovebox filled with nitrogen, a PhCl solution (1
mL) of [Ph3C][B(C6F5)4] (92 mg, 0.01 mmol) was added to a PhCl
solution (2 mL) of 3 (80 mg, 0.01 mmol) under stirring. A color
change from orange to colorless was observed immediately. After 5
min, α-picoline (10a) (1 mmol) and norbornene (11g) (2 mmol)
J
DOI: 10.1021/acs.inorgchem.8b01959
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
were added to the mixture successively. The resulting solution was
stirred at 100 °C for 12 h. After the mixture was cooled to room
temperature, another portion of norbornene (4 mmol) was added.
The resulting mixture was heated at 100 °C for another 12 h. The
product 16 was isolated by column chromatography (petroleum
ether, silica gel, 0.5% NEt3) as a viscous colorless oil (276 mg, 0.98
mmol, 98%). Compound 16: 1H NMR (400 MHz, CDCl3): δ 7.44 (t,
1H, J = 7.6 Hz, γ-Py-H), 6.95 (d, 1H, J = 7.6 Hz, β-Py-H), 6.86 (d,
1H, J = 7.6 Hz, β′-Py-H), 2.87−2.84 (m, 1H, CH), 2.74−2.68 (m,
1H, CH), 2.60−2.54 (m, 1H, CH), 2.42 (s, 1H, CH), 2.36 (s, 1H,
CH), 2.22 (s, 1H, CH), 2.01−1.93 (m, 3H, CH), 1.74−1.66 (m, 2H,
CH), 1.60−1.56 (m, 2H, CH), 1.48−1.36 (m, 5H, CH), 1.30−1.29
(m, 1H, CH), 1.20−1.09 (m, 5H, CH). 13C{1H} NMR (100 MHz,
CDCl3): δ 165.4 (α′-Py-C), 160.4 (α-Py-C), 135.7 (γ-Py-C), 119.8
(β′-Py-C), 118.2 (β′-Py-C), 49.6, 45.2, 43.0, 42.3, 40.8, 37.9, 37.3,
37.2, 36.9, 36.8, 36.0, 35.3, 30.4, 30.1, 29.1, 28.9 (alkyl-C).
X-ray Crystallographic Structure Determination. Suitable
single crystals of complex 3a were sealed in a thin-walled glass
capillary for determination of the single-crystal structures. Intensity
data were collected with a Rigaku Mercury CCD area detector in ω
scan mode using Mo−Kα radiation (λ = 0.71070 Å). The diffracted
intensities were corrected for Lorentz/polarization effects and
empirical absorption corrections.
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01959.
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CCDC 1855756 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: luoyunjie@nbu.edu.cn (Y.L.).
*E-mail: yuandan@suda.edu.cn (D.Y.).
*E-mail: yaoym@suda.edu.cn (Y.Y.).
■
ORCID
Yunjie Luo: 0000-0002-2480-1385
Yingming Yao: 0000-0001-9841-3169
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the National Natural Science
Foundation of China (21402135, 21572205, and 21674070),
the project of scientific and technologic infrastructure of
Suzhou (SZS201708), China Postdoctoral Science Foundation
(No. 2017M621831), and PAPD is gratefully acknowledged.
K
DOI: 10.1021/acs.inorgchem.8b01959
Inorg. Chem. XXXX, XXX, XXX−XXX

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