Reactivity of 2-benzylpyridyl lithium toward benzonitrile derivatives: Addition versus elimination

Article abstract of DOI:10.1016/j.jorganchem.2017.10.042

This work investigated the reactivity of 2-benzylpyridyl lithium (2-Pyr)C(Ph)(R)Li (R = SiMe₃, Li1; R = H, Li2) toward benzonitrile derivatives. Based on the different products, the reaction between lithium salts and nitriles might involve in addition, elimination and bimolecular coupling pathways, respectively. Treatment of Li1 with ArCN (Ar = Ph, p-Tolyl, o-Tolyl, p-OMePh) yielded an addition intermediate pyridyl-1-aza-allyl-lithium [{(2-Pyr)C(Ph)C(Ar)N(SiMe₃)}Li]₂ (1, Ar = Ph) and its corresponding hydrolysis product 2-benzylpyridyl-ketone 2–5, respectively, in which the reaction involved in a 1,3-shift of -SiMe₃ group to form a dimeric pyridyl-1-aza-allyl-lithium then followed by acidic hydrolysis. The MeOLi elimination reaction between Li2 and p-MeO(C₆H₄)CN resulted in formation of 4-(2-benzylpyridyl)benzonitrile 6. The reaction of Li2 with p-Me(C₆H₄)CN in the presence of TMEDA generated a 1:2 hydrolysis adduct 2-benzylpyridyl-enaminone 7, however, in the absence of TMEDA it afforded a coupling product of bimolecular nitriles, 1-(4-methylphenyl)-2-cyanophenyl-ethanone 8. We speculated the reaction mechanisms in sequence. The crystal structures of 1 and 5–8 were analyzed.

Full text of DOI:10.1016/j.jorganchem.2017.10.042

Accepted Manuscript
Reactivity of 2-benzylpyridyl lithium toward benzonitrile derivatives: Addition versus
elimination
Xiaomin Hao, Lu Qin, Mali Xu, Xia Chen
PII:
S0022-328X(17)30629-0
10.1016/j.jorganchem.2017.10.042
JOM 20162
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 7 September 2017
Revised Date: 24 October 2017
Accepted Date: 30 October 2017
Please cite this article as: X. Hao, L. Qin, M. Xu, X. Chen, Reactivity of 2-benzylpyridyl lithium toward
benzonitrile derivatives: Addition versus elimination, Journal of Organometallic Chemistry (2017), doi:
10.1016/j.jorganchem.2017.10.042.
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ACCEPTED MANUSCRIPT
Reactivity of 2-benzylpyridyl lithium toward benzonitrile derivatives:
addition versus elimination
Xiaomin Hao,†a Lu Qin,†a Mali Xua, Xia Chen*a,b
aSchool of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China
bState Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, China
Corresponding author. E-mail address: chenxia@sxu.edu.cn (Xia Chen).
†These authors contributed equally to this work
Abstract
This work investigated the reactivity of 2-benzylpyridyl lithium (2-Pyr)C(Ph)(R)Li (R =
SiMe3, Li1; R = H, Li2) toward benzonitrile derivatives. Based on the different products, the
reaction between lithium salts and nitriles might involve in addition, elimination and bimolecular
coupling pathways, respectively. Treatment of Li1 with ArCN (Ar = Ph, p-Tolyl, o-Tolyl,
p-OMePh)
yielded
an
addition
intermediate
pyridyl-1-aza-allyl-lithium
[{(2-Pyr)C(Ph)C(Ar)N(SiMe3)}Li]2 (1, Ar = Ph) and its corresponding hydrolysis product
2-benzylpyridyl-ketone 2-5, respectively, in which the reaction involved in a 1,3-shift of -SiMe3
group to form a dimeric pyridyl-1-aza-allyl-lithium then followed by acidic hydrolysis. The
MeOLi elimination reaction between Li2 and p-MeO(C6H4)CN resulted in formation of
4-(2-benzylpyridyl)benzonitrile 6. The reaction of Li2 with p-Me(C6H4)CN in the presence of
TMEDA generated a 1:2 hydrolysis adduct 2-benzylpyridyl-enaminone 7, however, in the absence
of
TMEDA
it
afforded
a
coupling
product
of
bimolecular
nitriles,
1-(4-methylphenyl)-2-cyanophenyl-ethanone 8. We speculated the reaction mechanisms in
sequence. The crystal structures of 1 and 5-8 were analyzed.
Keywords: 2-benzylpyridyl lithium; nitriles; addition; elimination; bimolecular coupling; silyl
group migration.
1. Introduction

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The insertion reaction of α-H-free aromatic nitriles into Li-C has been reported for its
superiority of forming 1-azaallyls [1,2] and β-diketiminates [3,4]. Pyridyl-substituted azaallyls and
β-diketiminates have attracted much more attention for the rigidity of N-heterocycle [5,6,7].
Berth-Jan Deelman and his co-workers have obtained trimethylsilyl-substituted [N,N] bidentate
pyridyl-azaallyl ligands [7] and their zirconium complexes [8], which have good π-donating
properties than the β-diketiminates [7]. In further studies, they synthesized a series of [N,N]
bidentate chelating lithium complexes by the reaction of –SiMe3 substituted pyridyl-alkyl lithium
with different α-H free nitriles [6,7], the product existed as a dimeric structure. Zsuzsa Majer and
co-workers have prepared a range of [N,O] bidentate nitrogen ligands, and further synthesized
β-diketiminates [9]. Thomas C.W. Mak has afforded several group 14 metal-pyridyl-1-azaallyls as
dimmers
[Li{N(SiMe3)C(Ph)C(R)(C5H4N-2)}]2 [R = SiMe3 or H] with group 14 metal halides, such as
[Ge{C(C5H4N-2)C(Ph)N(SiMe3)}Cl2]2, [Sn{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}2],
by
the
reaction
of
lithium
pyridyl-1-azaallyl
complex
[Pb{N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}2] and [{(C5H4N-2)C(SiMe3)C(Ph)N}(µ-SiHCl)]2 [5].
As mentioned above, –SiMe3 substituted pyridyl-alkyl lithium (Chart 1, A) is often as the
preferred reactant to produce pyridyl-azaallyls. We have also reported the addition of
2-(trimethylsilyl)pyridylmethyl lithium and nitriles to form pyridyl-1-azaallyllithium complexes
[{2-(6-Me-Pyr)C(H)C(tBu)N(SiMe3)}Li]2,
[{2-(6-Me-Pyr)C(H)C(Ph)N(SiMe3)}Li]2
and
[{(2-Pyr)C(H)C(Ph)N(SiMe3)}Li]2 [10]. It implies that pyridyl-alkyl lithiums containing -SiMe3
substituent may take nucleophilic addition reaction with nitriles more easily than those of lithium
compounds without -SiMe3 substituent, probably due to the -SiMe3 group migrating easier than
other alkyl or H atom.
Very recently, we investigated the reactions of 2-ethylpyridyl or 2-methylpyridyl lithium
(Chart 1, B and C) without –SiMe3 substituent reacts with nitriles, in situ, followed by acid
hydrolysis
to
give
β-pyridyl
ketones
1-(2-pyridinyl)-2-propanone,
1-phenyl-2-(2-pyridinyl)-1-propanone and 1-(2-methylphenyl)-2-(2-pyridinyl)-1-propanone, etc
[11], in which the reaction pathway involves in the intermediate adducts
pyridyl-1-aza-allyl-lithiums.

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Chart 1. Different substituted pyridyl lithiums.
Now, we are interested in 2-benzylpyridyl lithiums (Chart 1, D) and their reactivity with
nitriles. According to reports in the literature, 2-benzylpyridine has been widely studied due to the
activity of C(sp3)-H bonds between the two aromatic rings, such as α-methylenation of
benzylpyridines [12], Oxidative Carbonylation [13], N,C-metallization [14], nucleophilic addition
of 2-benzylpyridyl lithium and ketones [15]. Nevertheless, influenced by different properties of
substituents and external conditions, the reaction of 2-benzylpyridyl lithium and ArCN usually
exerts various mechanisms except addition. The diverse substituents of nitriles and less optimum
conditions may give rise to elimination or bimolecular coupling outcomes [16] instead of addition
products, especially when the electron-donating group is absent in the benzylpyridyl lithium.
Herein, the present work complements the previous 2-(2-Pyr)C(R)2Li/nitrile insertion
investigations by extending the system to include reactions of the carbon anion prepared by the in
situ lithiation of the hitherto unknown 2-benzylpyridyl ligand, (2-Pyr)C(Ph)(R)Li (R = SiMe3, Li1;
R = H, Li2) (Chart 1, D), with ArCN (Ar = Ph, p-Tolyl, o-Tolyl, p-OMePh). Full details on the
synthesis and characterization of insertion, elimination and bimolecular coupling compounds are
provided.
2. Results and discussion
2.1. Reactions of (2-Pyr)C(Ph)(R)(Li) with ArCN
The general synthesis route for compounds 1-8 are illustrated in Scheme 1. The starting
lithium compounds (2-Pyr)C(Ph)(R)(Li) (R = SiMe3, Li1; R = H, Li2) were prepared by lithiation
n
of 2-[(2-trimethylsilyl)-benzyl]pyridine [17] and 2-benzylpyridine with BuLi, respectively. The
dimeric pyridyl-1-aza-allyllithiums were prepared by the addition of Li1 with ArCN (Ar = Ph,
p-Tolyl, o-Tolyl, p-OMePh), respectively, but only [{(2-Pyr)C(Ph)C(Ph)N(SiMe3)}Li]2 (1) was

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isolated. However, their corresponding hydrolysis products 2-benzylpyridyl-ketones
(2-Pyr)C(H)(Ph)(CO)Ph (2), (2-Pyr)C(H)(Ph)(CO)(4-Me-Ph) (3), (2-Pyr)C(H)(Ph)(CO)(2-Me-Ph)
(4) and (2-Pyr)C(H)(Ph)(CO)(4-OMe-Ph) (5) were obtained in high yields. The elimination
product (2-Pyr)C(H)(Ph)(4-CNPh) (6) was synthesized by the reaction of Li2 with ArCN (Ar =
p-OMePh)
via
the
intermolecular
elimination
of
MeOLi.
(2-Pyr)-
C(Ph)C(4-Me-Ph)N(H)(CO)(4-Me-Ph) (7) was given by 1:2 addition of Li2 with ArCN (Ar =
p-Tolyl). Bimolecular coupling of p-MePhCN generated (4-Me-Ph)(CO)C(H)(H)(4-CN-Ph) (8).
Scheme 1. Synthesis of the compounds 1-8.
2.2. Synthesis and reaction pathways of compounds 1-5
Li1 reacts with an equiv. of ArCN to yield the adduct compounds 1-5. Dimeric
pyridyl-1-aza-allyl-lithiums 1 was prepared by insertion reaction of Li1 with PhCN in a 1:1 molar
ratio in Et2O for 48 h, and was isolated as orange red crystalline solids 1·toluene in a high yield of
96% at room temperature, then followed by acidic hydrolysis to give 2-benzylpyridyl-ketone 2 in
83.6% yield (Scheme 1). Similarly, 2-benzylpyridyl-ketones 3-5 were derived from Li1 and
p-(Me)PhCN, o-(Me)PhCN and p-(OMe)PhCN as yellow solids in 82.4%, 66.6% and 29.1% yield,
respectively. Such a reaction involved a 1,2-insertion of the ArCN into the Li-C bond to generate

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an intermediate I as well as a 1,3-trimethylsilyl migration to form a tautomeric azaallyls II and II',
Ⅲ was obtained by dimerization of II', followed by acidic hydrolysis to afford 2-5 (Scheme 2).
This method was related to that previously employed in synthesis of other pyridyl azaalyl
complexes, e.g. pyridyl-1-azaallyllithium complexes [{2-(6-Me-Pyr)C(H)C(R)N(SiMe3)}Li]2 [R =
tBu or Ph] or [{(2-Pyr)C(H)C(Ph)N(SiMe3)}Li]2 [10], 2,6-pyridyl-linked bis(1-azaallyl) and
2,3-pyrazyl-linked bis(1-azaallyl)alkalimetal compounds [18,19]. Furthermore, a series of derived
pyridyl-1-azaallyl low-valent group 14 compounds were described [5,20,21].
Scheme 2. Proposed pathway for the formation of 2-5.
Compound 1 is extremely air- and moisture-sensitive. It is soluble in THF and Et2O, but poor
solubility in toluene and hexane. It was isolated as an orange crystalline suitable for X-ray
diffraction study in toluene at – 30 ºC for three days. Compounds 2-5 were obtained as yellow
solids after purification by a flash chromatography, and 5 was crystallized as yellow crystals from
mixture of Et2O and hexane at room temperature. Compounds 2-5 are slightly air-sensitive or
stable. Most commonly, these compounds exist in two tautomers: enol and ketone, depending on
1
the substituent in the molecule [11]. However, the H NMR spectra of 2-5 show no resonance
signals of enol protons OH appearing in the range of 14-15 ppm, which confirmed they exist as
the ketone form alone.
2.3. Synthesis and reaction pathways of compounds 6-8
In contrast, Li2 reacts with ArCN to provide a variety of products 6-8, depending on the
reaction substrates and the presence or absence of TMEDA (Scheme 1). An elimination product 6

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towards the reaction of Li2 with p-(OMe)PhCN was synthesized accidentally. When an equiv. of
p-(OMe)PhCN was added to the solution of Li2 in THF, in situ the mixture was suffered to acid
hydrolysis and purified by column chromatography, a white solid 6 was obtained in 33.5% yield.
The possible mechanism for the formation of 6 was shown in Scheme 3. It depicts that Li atom
was more electropositive while -OMe group was to the contrary, the carbanion on benzylpyridyl
lithium attacked electropositive aromatic-C and an intermolecular elimination reaction between
Li2 and p-(OMe)PhCN was apt to come up to form 6 via elimination of LiOMe, which may be
due to the –OMe group more likely to leave when existence of a electron-withdrawing group. This
is consistent with the reaction of ortho-methoxy group in 1- and 2- naphthoic acids with
organolithium to produce a substitution product concomitantly with elimination of methoxyl
lithium [22].
Scheme 3. Possible mechanism for the formation of 6.
When the reaction of Li2 with p-(Me)PhCN was carried out in the presence of TMEDA,
followed by acid hydrolysis, adduct compound 7 was given as a yellow solid in 26% yield; but the
same reaction in the absent of TMEDA, coupling product 8 was obtained as a white solid in 64.2%
yield. Crystals of 7 and 8 suitable for X-ray diffraction study were grown from a concentrated
CH2Cl2 solution at room temperature for 3 days, respectively.
By analyzing the structure of 7, it is a 1:2 adduct which bearing a large conjugated structure
instead of the 1-azaallyllithiums as anticipated. As it reported in the literature, TMEDA as an
amine component reagent [23] can effectively preclude secondary oligomerizing interactions and
produce monomeric or dimeric lithium complex, which increases the carbanionic reactivity
distinctly. Therefore, nucleophilic carbanion of 2-benzylpyridyl-lithium is an attack on ArCN to
yield an intermediate 1-azaallyl lithium, a second attack ArCN to give another intermidiate
1,3-diazaallyl lithium, undergoing hydrolysis to afford a conjugated product which exists as three
tautomers: pyridyl-imino ketone, 1,2-(dihydropyridyl)-imino ketone and pyridyl-enaminone
1
(Scheme 4). X-ray crystallography and the H NMR spectra (resonance signal of NH proton
appearing at δ 14.54 ppm) demonstrated that compound 7 presented in the form of

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pyridyl-enaminone. The pathway is comparable to the previousely reported reaction of
LiCH(SiMe3)2 with PhCN in a 1:2 M ratio to yield the 1,3-diazaallyl lithium [24,25].
Scheme 4. Reaction pathways for the formation of 7.
Unexpectedly, compound 8 is the hydrolyzate of bimolecular ArCN coupling product. We
suggest the formation of 8 as shown in Scheme 5. i) Lithiation of p-(Me)PhCN occurred by Li2
firstly to yield [(4-cyanophenyl)methyl]-lithium, ii) a C-centered nucleophile adds to ArCN
proceeding C-C coupling to give an intermediate lithioimine, followed by acidic hydrolysis to
yield 8. It illustrates that with the nonparticipation of TMEDA, the insertion reaction of Li2 with
ArCN (Ar = p-Tolyl) was difficult to occur. It may be owing to Li2 existence as an oligomer,
which reduced its nucleophilic reactivity, by contrast, the lithiation of alkyl-substituted arenes is
come up quickly [23]. Meanwhile, it may be that α-hydrogen of alkyl-substituted arenes is active
enough to react with organolithium under the strong electron-withdrawing effect of –CN, and
form the constitutionally stable carbanion which is effective to couple another p-tolunitrile
molecular.
Scheme 5. Possible mechanism for the formation of 8.
2.4. Crystal structures of compounds 1, 5, 6, 7 and 8

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The molecular structure of 1 (the molecule of toluene has been omitted) is illustrated in Fig.
1, the selected bond distances and bond angles are shown in Table 1.
The lithium compound 1 exists as the centrosymmetric dimer. Each Li atom is
three-coordinated with N [2.029(3) Å, 2.068(4) Å, 1.993(3) Å (Li1-N1i, Li1-N2i, Li1-N2)]. The
diatance of Li1-N2 is shorter than that of Li1-N1i and Li1-N2i, and is also shorter than that found
in the pyridyl-substituted 1-azaallyl [{2-(6-Me-Pyr)C(H)C(tBu)N(SiMe3)}Li]2 [Li-N=2.207(4) Å]
[10]. The distance of Li1 atom to pyridine nitrogen N1i[Li1-N1i =2.029(3) Å] is slight longer than
that found in the lithium β-diketiminate [Li{N(SiMe3)C(But)C(H)C(Ph)N(SiMe3)}]2[1.970(2) Å]
[26]. The distance of Li1 atom to enamine nitrogen N2i[Li1-N2i =2.068(4) Å] is longer than that
found
in
the
1,3-diazaallyllithium
complexes
[Li{N(R)C(Ph)NC(Ph)=C(H)R}(thf)]2[Li-N=1.990(1)] [26]. The atoms of Li1, N2i, Li1i, N2 form
a four-membered ring and they are coplanar. Steric-hindrance effect results from the aryl groups of
1 generates a distorted six-membered ring Li1iN1C5C6C13N2, which is similar to the structure of
pyridyl-1-azaallyllithium [{2-(6-Me-Pyr)C(H)C(tBu)N(SiMe3)}Li]2 [10]. Li1iN2C13 is planar,
and forming a dihedral angle of 62.83(0.12)° to the planar Li1iN1C5C13. The distance of C6 to
the planar Li1iN1C5C13 is 0.3600 (0.0028) Å.
Fig. 1. Molecular structure of compound 1.
Table 1

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Selected bond lengths (Å) and angles (°) for complex 1.
Li(1)-N(2)
1.993(3)
Li(1) i -N(2)i
1.993(3)
Li(1)-N(1)i
2.029(3)
Li(1) i -N(1)
2.029(3)
Li(1)-N(2)i
2.068(4)
Li(1) i -N(2)
2.068(4)
N(1)-C(5)
1.355(2)
N(2) -Si(1)
1.7071(15)
1.388(2)
N(1)-C(1)
1.347(2)
N(2)-C(13)
C(5)-C(6)
1.485(2)
C(6)-C(13)
1.374(2)
N(2)-Li(1)-N(2) i
N(2)-Li(1)-N(1) i
N(1)-C(5)-C(6)
C(13)-C(6)-C(5)
C(13)-N(2)-Si(1)
C(13)-N(2)-Li(1) i
Si(1)-N(2)-Li(1)
Li(1)-N(2)-Li(1) i
100.91(14)
160.74 (19)
118.17(14)
122.45(15)
124.40(12)
92.64(13)
121.73(12)
79.09(14)
N(1) i -Li(1)-N(2) i
C(6)-C(13)-N(2)
C(5)-N(1)-Li(1) i
N(2)-C(13)-C(14)
C(13)-N(2)-Li(1)
C(1)-N(1)-Li(1) i
Si(1)-N(2)-Li(1) i
96.67(14)
125.91(15)
111.99(14)
113.80(14)
108.88(14)
127.29(16)
116.85(12)
The molecular structure of 5 is illustrated in Fig. 2, the selected bond distances and bond
angles are shown in Table 2.
Compound 5 consists of three six-membered rings. The bond length of C13-O2 [1.219(3) Å]
is confirmed as C=O bond. The distance of C17-O1[1.361(3) Å] is shorter than that of
C20-O1[1.442(4) Å], it may due to the p-π conjugation between O1 and benzene. The angle of
C17-O1-C20 is 117.3(2)°. The atoms of C20, O1, C13, O2 and benzene with C14, C17 in it are
coplanar, and respectively, forming a dihedral angle of 58.29(0.07)°, 78.57(0.08)° with the
benzene contains C6 in it and the pyridine ring.

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Fig. 2. Molecular structure of compound 5.
Table 2
Selected bond lengths (Å) and angles (°) for complex 5.
N(1)-C(1)
1.330(3)
1.523(3)
1.538(3)
1.219(3)
1.442(4)
118.0(2)
113.54(19)
120.4(2)
117.3(2)
C(12)-C(1)
C(6)-C(7)
1.523(3)
1.382(3)
1.488(3)
1.361(3)
C(12)-C(6)
C(13)-C(12)
C(14)-C(13)
O(1)-C(17)
O(2)-C(13)
O(1)-C(20)
N(1)-C(1)-C(12)
C(6)-C(12)-C(13)
O(2)-C(13)-C(14)
C(17)-O(1)-C(20)
C(6)-C(12)-C(1)
O(2)-C(13)-C(12)
C(14)-C(13)-C(12)
110.15(19)
120.8(2)
118.8(2)
The molecular structure of 6 is illustrated in Fig. 3, the selected bond distances and bond
angles are shown in Table 3.
Compound 6 consists of three six-membered rings. The bond angle of C16-C19-N2 is almost
close to linear [179.1(3)°]. The cyclobenzene with C16 in it and the atoms of C6, C19, N2 are in

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the same plane, and respectively, forming a dihedral angle of 76.82(0.09)°, 77.53(0.10)° with the
benzene contains C7 in it and the pyridine ring. The distance between C19 and N2 is 1.136(3) Å,
which is demonstrated as C≡N bond.
Fig. 3. Molecular structure of compound 6.
Table 3
Selected bond lengths (Å) and angles (°) for complex 6.
N(1)-C(1)
1.335(3)
1.529(4)
1.449(4)
110.4(2)
179.1(3)
C(6)-C(1)
1.525(4)
1.524(3)
1.136(3)
113.8(2)
C(6)-C(7)
C(13)-C(6)
N(2)-C(19)
C(13)-C(6)-C(7)
C(19)-C(16)
C(1)-C(6)-C(7)
N(2)-C(19)-C(16)
The molecular structure of 7 is illustrated in Fig. 4, the selected bond distances and bond
angles are shown in Table 4.
Compound 7 contains four six-membered rings. Respectively, the bond lengths of C21-O1
[1.218(2) Å], N(2)-C(21) [1.366(2) Å], C21-C22 [1.496(2) Å], C7-N2 [1.395(2) Å], C6-C7
[1.368(2) Å], C1-C6 [1.485(2) Å], C1-N1 [1.345(2) Å], indicating that a p,π-electron conjugation
among the structure framework N1=C1-C6=C7-N2-(C21=O1)-C22. The pyridine ring and C6,
C7, N2 are coplanar. The atom of C21 is with a deviation of 0.5061 (0.0033) Å to the planar. The

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structure of 7 is distorted because of the steric hinerance from four six-membered rings. The
dihedral angle of pyridine ring and cyclobenzene with C8 in it is 73.21(0.08)°.
Fig. 4. Molecular structure of compound 7.
Table 4
Selected bond lengths (Å) and angles (°) for complex 7.
N(1)-C(1)
1.345(2)
C(1)-C(6)
C(6)-C(7)
N(2)-C(21)
C(21)-C(22)
1.485(2)
1.368(2)
1.366(2)
1.496(2)
C(6)-C(8)
1.495(2)
N(2)-C(7)
1.395(2)
O(1)-C(21)
1.218(2)
C(14)-C(7)
1.485(2)
N(1)-C(1)-C(6)
C(7)-C(6)-C(1)
C(21)-N(2)-C(7)
N(2)-C(21)-C(22)
118.78(14)
124.94(15)
129.29(15)
114.11(15)
C(1)-C(6)-C(8)
N(2)-C(7)-C(14)
O(1)-C(21)-N(2)
O(1)-C(21)-C(22)
116.01(13)
116.44(13)
123.80(17)
122.08(16)
The molecular structure of 8 is illustrated in Fig. 5, the selected bond distances and bond
angles are shown in Table 5.

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Compound 8 is composed of two cyclobenzenes. The distance of C9-O1 is 1.214(2) Å, which
is comparable to the bond lengths of C=O bond. C9-O1 and the cyclobenzene which contain C10
in it are in the same plane, it is suggested that they are conjugated. The bond length of
C1-N1[1.141(2) Å] is confirmed as C≡N bond. The dihedral angle of two cyclobenzenes is 58.66
(0.05)°.
Fig. 5. Molecular structure of compound 8.
Table 5
Selected bond lengths (Å) and angles (°) for complex 8.
N(1)-C(1)
1.141(2)
1.500(3)
1.483(3)
177.8(2)
120.64(18)
C(1)-C(2)
1.442(3)
C(5)-C(8)
C(9)-C(8)
1.510(3)
C(10)-C(9)
C(9)-O(1)
1.214(2)
N(1)-C(1)-C(2)
O(1)-C(9)-C(8)
C(5)-C(8)-C(9)
O(1)-C(9)-C(10)
115.37(16)
120.81(17)
3. Conclusions
To summarize, reactivity of 2-benzylpyridyl lithium toward benzonitrile derivatives have
been investigated and discussed. Very different from the 2-alkylpyridyl lithiums, when
2-benzylpyridyl lithium reacts with nitriles, it could give addition, elimination and bimolecular
coupling products based on the substituent of carbanion. The reaction of
2-[(2-trimethylsilyl)-benzyl]pyridyl-lithiums and ArCN gave the addition products. Reaction
between 2-benzylpyridyl-lithiums and ArCN may give rise to three different kinds of products:
when TMEDA was added into the system, a 1:2 adduct was generated, but in the absence of
TMEDA, a coupling product of bimolecular nitriles was obtained, and an elimination product was
came up when methoxyl nitrile p-MeO(C6H4)CN reacts with 2-benzylpyridyl-lithium.

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4. Experimental
4.1. General
All manipulations were performed under nitrogen atmosphere by standard Schlenk
techniques. Solvents were dried with sodium, and distilled from sodium, and stored over
molecular sieves (4 Å). Deuterated solvents were dried with sodium/potassium alloy (C6D6) and
molecular sieves (4 Å) (CDCl3). All chemicals were purified by distillation. 2-Benzylpyridine,
trimethylchlorosilane, benzonitrile, o-tolunitrile, p-tolunitrile, 4-methoxybenzonitrile and
n-butyllithium in hexane (2.5 M) were purchased from energy chemical. 1H and 13C NMR spectra
were performed with a Bruker DRX-300 MHz spectrometer. Elemental analyses were performed
with a Vario EL-III instrument.
4.2. Synthesis of 1
nBuLi (4.02 mL, 2.5 M, 10.00 mmol) was added to the solution of
2-[(2-trimethylsilyl)-benzyl]pyridine (2.48 mL, 10.00 mmol) in Et2O (30 mL) at 0 ℃, the
orange-red solution was restored upto room temperature and stirred for 24 h. Benzonitrile (1.02
mL, 10.00 mmol) was added to the mixture at 0 ℃, warmed to room temperature gradually, and
stirred for 48 h to give a dark red solution mixture. The solvents of residue were removed in vacuo
to give a dark red solid, and recrystallized as orange crystals in toluene at -30℃ for three days.
1
Yield: 3.36 g (96%). H NMR (C6D6, TMS, 300MHz): δ(ppm) 8.63(d, 2H, Py-H), 7.83(d, 4H,
Ar-H), 7.41-7.57(m, 18H, Py-H and Ar-H), 7.24-7.30(m, 4H, Py-H and Ar-H), 0.08[s, 9H,
Si(CH3)3]. 13C NMR(C6D6, TMS, 75MHz): δ(ppm) 155.7, 149.6, 137.0, 122.7, 120.9 (Py-C),
140.0, 134.2, 128.6, 128.3, 127.9 (Ar-C), 140.5, 112.8 (C=C), 17.7 (-CH3). Anal. Calcd for
C44H46Li2N4Si2·C7H8: C, 77.24; H, 6.86; N, 7.06. Found: C, 77.21; H, 6.88; N, 7.03.
4.3. Synthesis of 2
Enough distilled water was added to the solution of 1 (2.12 g, 3.02 mmol) in Et2O (30 mL) at
0 ℃ and stirred for 24 h, followed by extraction with dichloromethane (50 mL×3). The yellow
subnatant was collected and dried with anhydrous MgSO4, the volatile solvent was removed in
vacuo, a yellow solid was purified by column chromatography. Yield: 1.38 g (83.6%). M.p.

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1
132 ℃. H NMR (CDCl3, TMS, 300MHz): δ(ppm) 8.44 (d, 1H, Py-H), 8.00(d, 2H, Ar-H),
7.55-7.68(m, 4H, Py-H and Ar-H), 7.37-7.38 (m, 4H, Py-H and Ar-H), 7.11(t, 1H, Py-H), 7.21
(m, 2H, Ar-H), 5.56 (s, 1H, -CH-). 13C NMR (CDCl3, TMS, 75MHz): δ(ppm) 162.25 (C=O),
150.12, 147.41, 137.21, 136.23, 133.11, 130.38, 128.33, 128.12, 126.29, 125.57, 122.28, 118.09
(Ar-C and Py-C), 54.32 (-CH-). Anal. Calcd for C19H15NO: C, 83.49; H, 5.53; N, 5.12. Found: C,
83.45; H, 5.62; N, 5.09.
4.4. Synthesis of 3
nBuLi (4.25 mL, 2.5 M, 10.48 mmol) was added to the solution of
2-[(2-trimethylsilyl)-benzyl]pyridine (2.60 mL, 10.48 mmol) in Et2O (30 mL) at 0 ℃, the
orange-red solution was restored upto room temperature and stirred for 24 h. p-Tolunitrile (2.38 g,
10.48 mmol) was added to the mixture at 0 ℃, warmed to room temperature gradually, and
stirred for 48 h to give a dark red solution mixture. Just enough distilled water was added to
hydrolyze the above product, followed by extraction with dichloromethane (50 mL×3). The
yellow subnatant was collected and dried with anhydrous MgSO4, the volatile solvent was
removed in vacuo, a yellow solid was purified by column chromatography. Yield: 2.48 g (82.4%).
M.p. 162.6 ℃. 1H NMR (CDCl3, TMS, 300MHz): δ(ppm) 8.45 (d, 1H, Py-H), 7.17-7.33 (m, 2H,
Py-H), 7.07-6.89 (m, 9H, Py-H and Ar-H), 6.78-6.82 (t, 1H, Ar-H), 6.59 (d, 1H, -CH-), 2.24 (s,
13
3H, Ar-CH3). C NMR (CDCl3, TMS, 75MHz): δ(ppm) 162.29 (C=O), 150.09, 147.45, 137.15,
136.27, 133.03, 130.42, 128.38, 128.16, 126.33, 125.63, 122.31, 118.12 (Ar-C and Py-C), 30.38
(-CH-), 20.16 (-CH3). Anal. Calcd for C20H17NO: C, 83.59; H, 5.96; N, 4.87. Found: C, 83.55; H,
5.98; N, 4.91.
4.5. Synthesis of 4
nBuLi (4.01 mL, 2.5 M, 10.00 mmol) was added to the solution of
2-[(2-trimethylsilyl)-benzyl]pyridine (2.48 mL, 10.00 mmol) in Et2O (30 mL) at 0 ℃, the
orange-red solution was restored upto room temperature and stirred for 24 h. o-Tolunitrile (1.18
mL, 10.00 mmol) was added to the mixture at 0 ℃, warmed to room temperature gradually, and
stirred for 48 h to give a dark red solution mixture. Just enough distilled water was added to
hydrolyze the above product, followed by extraction with dichloromethane (50 mL×3). The

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yellow subnatant was collected and dried with anhydrous MgSO4, the volatile solvent was
removed in vacuo, a light yellow solid was purified by column chromatography. Yield: 1.91 g
(66.6%). M.p. 145~149 ℃. 1H NMR (CDCl3, TMS, 300 MHz): δ(ppm) 8.52 (d, 1H, Py–H), 7.35
(t, 1H, Pyr-H), 7.24 (s, 1H, Py–H), 7.01 (m, 9H, Pyr-H and Ar-H), 6.86 (t, 1H, Ar-H), 6.66 (d,
1H, -CH-), 2.31 (s, 3H, Ar-CH3). 13C NMR (CDCl3, TMS, 75 MHz): δ(ppm) 162.27 (C=O),
150.11, 147.44, 141.35, 140.50, 136.24, 133.02, 130.40, 128.38, 126.34, 125.65, 122.32, 118.14,
108.04 (Ph-C and Py-C), 30.39 (-CH-), 20.21 (-CH3). Anal. Calcd for C20H17NO: C, 83.59; H,
5.96; N, 4.87. Found: C, 83.56; H, 5.93; N, 4.93.
4.6. Synthesis of 5
nBuLi (7.01 mL, 2.5 M, 15.75 mmol) was added to the solution of
2-[(2-trimethylsilyl)-benzyl]pyridine (3.80 mL, 15.75 mmol) in Et2O (30 mL) at 0 ℃, the
orange-red solution was restored upto room temperature and stirred for 24 h.
4-Methoxybenzonitrile (3.83 g, 15.75 mmol) was added to the mixture at 0 ℃, warmed to room
temperature gradually, and stirred for 48 h to give a dark red solution mixture. Just enough
distilled water was added to hydrolyze the above solution, followed by extraction with
dichloromethane (50 mL×3). The yellow subnatant was collected and dried with anhydrous
MgSO4, the volatile solvent was removed in vacuo, a yellow solid was purified by column
chromatography. The product was crystallized as yellow crystals from mixture of Et2O and
n-hexane at room temperature. Yield: 1.38 g (29.1%). M.p. 195.4 ℃. 1H NMR (CDCl3, TMS, 300
MHz): δ(ppm) 8.42 (d, 1H, Py-H), 7.12-7.25 (m, 2H, Py-H), 7.02-6.78 (m, 9H, Py-H and Ar-H),
13
6.65-6.74 (t, 1H, Ar-H), 6.56(d, 1H, -CH-), 2.21 (s, 3H, Ar-CH3). C NMR (CDCl3, TMS, 75
MHz): δ(ppm) 162.22 (C=O), 150.03, 147.42, 137.11, 136.23, 133.01, 130.38, 128.35, 128.13,
126.32, 125.61, 122.29, 118.11 (Ar-C and Py-C), 30.32 (-CH-), 20.12 (-CH3). Anal. Calcd for
C20H17NO2: C, 79.19; H, 5.65; N, 4.62. Found: C, 79.22; H, 5.66; N, 4.57.
4.7. Synthesis of 6
nBuLi (23.95 mL, 2.5 M, 59.87 mmol) was added to the solution of 2-benzylpyridine (4.00
mL, 24.95 mmol) in THF (100 mL) at 0 ℃, the red suspension was restored upto room
temperature and stirred for 24 h. 4-Methoxybenzonitrile (3.32 g, 24.95 mmol) was added to the

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mixture at 0 ℃, warmed to room temperature gradually, and stirred for 48 h to give a dark red
clear solution mixture. After the acid hydrolysis of 60% H2SO4 solution under the condition of ice
bath until pH=1, neutralized with saturated NaOH until pH=7, amount of solid arised in the
process and dissolved by just enough distilled water, followed by extraction with dichloromethane
(100 mL×3). The mixture was dried with anhydrous MgSO4, the volatile solvent was removed in
vacuo, a white solid was purified by column chromatography. The product was crystallized as
colorless crystals from mixture of EtOAc and n-hexane at room temperature. Yield: 2.26 g
(33.5%). M.p. 87 ℃. 1HNMR (CDCl3, TMS, 300 MHz): δ(ppm) 8.57 (s, 1H, Py-H), 7.54 (m, 3H,
Ar-H), 7.05 (m, 9H, Py-H and Ar-H), 6.86 (t, 1H, Ar-H), 5.69 (s, 1H, CH). 13C NMR (CDCl3,
TMS, 75 MHz): δ(ppm) 162.67, 150.59, 149.32, 142.34, 138.20, 133.33, 131.30, 130.37, 129.90,
128.28, 125.08, 123.14, 120.00 (Ar-C and Py-C), 111.62 (-CN), 60.08 (-CH-). Anal. Calcd for
C19H14N2: C, 84.42; H, 5.22; N, 10.36. Found: C, 84.46; H, 5.20; N, 10.34.
4.8. Synthesis of 7
nBuLi (24.00 mL, 2.5 M, 60.00 mmol) was added to the solution of 2-benzylpyridine (4.85
mL, 30.00 mmol) in THF (100 mL) at 0 ℃, then TMEDA (9.00 mL, 60.00 mmol) was added, the
red suspension was restored upto room temperature and stirred for 24 h. p-Tolunitrile (3.51 g,
30.00 mmol) was added to the mixture at 0 ℃, warmed to room temperature gradually, and
stirred for 48 h to give a dark red clear solution mixture. After the acid hydrolysis of 60% H2SO4
solution under the condition of ice bath until pH=1, neutralized with saturated NaOH until pH=7,
amount of solid arised in the process and dissolved by just enough distilled water, followed by
extraction with dichloromethane (100 mL×3). The mixture was dried with anhydrous MgSO4, the
volatile solvent was removed in vacuo, a yellow solid was purified by column chromatography.
The product was crystallized as yellow crystals from CH2Cl2 at room temperature. Yield: 3.15 g
(26%). M.p. 233.5 ℃. 1H NMR (CDCl3, TMS, 300 MHz): δ(ppm) 14.54 (s, 1H, NH), 8.64 (d, 1H,
Py-H), 8.01 (d, 2H, Py-H), 7.32 (d, 1H, Ar-H), 6.95-7.28 (m, 14H, Py-H and Ar-H), 2.46 (s, 3H,
-CH3), 2.24 (s, 3H, -CH3). 13C NMR (CDCl3, TMS, 75 MHz): δ(ppm) 174.4 (C=O), 164.6 (C=N),
144.2, 132.5, 132.3, 129.8, 129.5, 129.4, 129.1, 128.9, 128.6, 127.9 (Ar-C), 134.1, 125.9, 122.8,
101.5 (Py-C), 93.9 (C=C), 21.3 (-CH3). Anal. Calcd for C28H24N2O: C, 83.14; H, 5.98; N, 6.93.
Found: C, 83.11; H, 5.92; N, 6.96.

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4.9. Synthesis of 8
nBuLi (23.95 mL, 2.5 M, 59.87 mmol) was added to the solution of 2-benzylpyridine (4.8 mL,
29.93 mmol) in THF (100 mL) at 0 ℃, the red suspension was restored upto room temperature
and stirred for 24 h. p-Tolunitrile (3.51 g, 29.93 mmol) was added to the mixture at 0 ℃, warmed
to room temperature gradually, and stirred for 48 h to give a dark red clear solution mixture. After
the acid hydrolysis of 60% H2SO4 solution under the condition of ice bath until pH=1, neutralized
with saturated NaOH until pH=7, amount of solid arised in the process and dissolved by just
enough distilled water, followed by extraction with dichloromethane (100 mL×3). The mixture
was dried with anhydrous MgSO4, the volatile solvent was removed in vacuo, a white solid was
purified by column chromatography. The product was crystallized as colorless crystals from
1
CH2Cl2 at room temperature. Yield: 2.26 g (64.2%). M.p. 106 ℃. H NMR (CDCl3, TMS, 300
MHz): δ(ppm) 7.81-7.84 (d, 1H, Ar-H), 7.53-7.56 (d, 2H, Ar-H), 7.28-7.31 (d, 2H, Ar-H),
7.20-7.22 (d, 2H, Ar-H), 4.26 (s, 2H, -CH2-), 2.35 (s, 3H, -CH3). 13C NMR(CDCl3, TMS, 75
MHz): δ(ppm) 170.37 (-CN), 145.56, 141.20, 133.24, 131.44, 130.48, 129.55 (Ar-C), 46.05
(-CH2-), 22.60 (-CH3). Anal. Calcd for C16H13NO: C, 81.68; H, 5.57; N, 5.95. Found: C, 81.62;
H, 5.53; N, 6.01.
Table 6. Details of the X-ray structure determination of complexes 1, 5, 6, 7, 8
Complex
Formula
1·toluene
C44H46Li2N4Si2·
C7H8
5
6
7
8
C20H17NO2
C19H14N2
C28H24N2O
C16H13NO
Mw(g mol−1)
T (K)
793.04
303.35
276(2)K
Monoclinic
P21/n
270.32
297(2)K
Monoclinic
P21/c
404.49
235.27
200(2)K
Monoclinic
P21/n
279(2)K
Triclinic
P-1
298(2)K
Triclinic
P-1
Crystal system
Space group
a (Å)
13.8654(5)
9.7373(3)
17.6892(6)
90
17.2353(14)
5.7560(4)
32.539(3)
90
10.910(5)
11.857(5)
12.016(5)
90
8.6482(4)
9.4014(4)
14.6248(7)
87.128(2)
82.705(2)
69.5480(10)
1105.08(9)
2
5.6225(8)
8.7441(13)
14.160(2)
83.361(5)
79.706(5)
71.791(5)
649.32(17)
2
b (Å)
c (Å)
α (°)
β (°)
100.0860(10)
90
99.676(2)
90
106.596(13)
90
γ (°)
V (Å3)
2351.34(14)
2
3182.1(4)
8
1489.6(11)
4
Z
Dcalcd (g cm-3)
µ (mm-1)
F (000)
1.120
1.266
1.205
1.216
1.203
0.113
0.082
0.072
0.074
0.075
844
1280
568
428
248

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Reflections collected
17066
16590
7996
12273
8194
Independent (Rint) reflections
Goodness of fit on F2
4154 (0.0319)
1.045
5453 (0.0388)
1.055
1732 (0.0543)
1.067
3910 (0.0243)
1.027
2290 (0.0225)
1.015
Final R indices [I＞2σ(I)]
R1
0.0446
0.1095
0.0587
0.1497
0.0479
0.0978
0.0450
0.1148
0.0532
0.1305
wR2
R indices (all data)
R1
0.0579
0.1186
0.0959
0.1740
0.0849
0.1113
0.0710
0.1309
0.0806
0.1551
wR2
4.10. X-ray crystallography
Data collection of 1, 5, 6, 7 and 8 was performed with Mo Kα radiation (λ = 0.71073 Å) on
a Bruker Smart Apex CCD diffractometer. Crystals were coated in oil and then directly mounted
on the diffractometer under a stream of cold nitrogen gas. The structures were solved by direct
methods (SHELXS-2014) and refined against F2 by full-matrix least squares using SHELXL-2014.
All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms
were placed in calculated positions. In the checkCIF report of complex 1·toluene, calculated
moiety formula (C44H46Li2N4Si2, C7H7) was caused by the absence of a hydrogen atom, the lack of
a hydrogen atom resulted from a unordered carbon atom (C26) of –CH3 in toluene. Resolution of
data collection of compound 6 was not good enough, which resulted the less value of sine
(theta_max)/wavelength (0.5195). Crystal data and experimental details of the structure
determinations are listed in Table 6.
Supplementary materials
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Centre CCDC no.1571792 for 1, no.1571793-1571796 for 5-8, Copies of
this information may be obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc. cam.ac.uk).
Acknowledgments
We thank the National Natural Science Foundation of China (grant No. 21072120), the
Shanxi Patent Promotion Implementation Project (20161001), and Key Research and

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Development (R&D) Projects of Shanxi Province (201703D321008), and Open Research Fund of
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences (2017-10). We also acknowledge the support of the
Scientific Instrument Center of Shanxi University.
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Highlights
ò Insertion reaction of 2-benzylpydidyl lithium with nitriles has been investigated
ò C-C coupling is proceed via a carbanion attack
ò Possible mechanism for the formation of different products is been speculated