Nucleophilic Addition and α-C-H Substitution Reactions of an Imine Mediated by Dibutylmagnesium and Organolithium Reagents

Article abstract of DOI:10.1021/acs.organomet.0c00815

A series of nucleophilic addition reactions and α-C-H substitution reactions of an imine-containing ligand 2-(2-((((1H-pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine (HL1) were reported. The reactions of HL1 with 0.5 and 2 equiv ofⁿBu₂Mg, respectively, gave two complexes of compositions [Mg(L1)₂] (1) and [Mg₂(L2)₂] (2) (H₂L2 =N-((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-yl)pentan-1-amine). The nucleophilic addition ofⁿBu₂Mg to the C═N bond of the HL1 ligand occurred in the process for the formation of2. Treatment of HL1 with 2 and 1 equiv ofⁿBuLi generated [Li₂(L3)₂] (3) (HL3 = 2-(2-(((1-(1H-pyrrol-2-yl)pentylidene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine) and [Li₂(L1)₂] (4). An α-C-H substitution of the HC═NR moiety of the HL1 ligand triggered byⁿBuLi was discovered in the preparation of3. The formation of3demonstrates a new concept for the C-C coupling that involved inert C-H bond activation of HC═NR skeleton. The reactions of HL1 with MeLi,sec-BuLi, and tert-BuLi, respectively, were also examined. The products for both the nucleophilic addition of organolithium reagents to the C═N bond and α-C-H substitution of the HC═NR moiety of the HL1 ligand were determined. The mechanisms for the formations of2and3were rationalized by DFT calculations. The hydroboration reactions catalyzed by2were investigated, and these reactions characterize ample substrate scope, very good yields, and high selectivity.

Full text of DOI:10.1021/acs.organomet.0c00815

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Nucleophilic Addition and α‑C−H Substitution Reactions of an Imine
Mediated by Dibutylmagnesium and Organolithium Reagents
Yan Dang,§ Yalan Wang,§ Yafei Li, Man Xu, Chaohong Jia, Yanhua Lu, Liang Zhang, Yahong Li,*
and Yuanzhi Xia*
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ABSTRACT: A series of nucleophilic addition reactions and α-C−
H substitution reactions of an imine-containing ligand 2-(2-((((1H-
pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dime-
thylethan-1-amine (HL1) were reported. The reactions of HL1 with
n
0.5 and 2 equiv of Bu2Mg, respectively, gave two complexes of
compositions [Mg(L1)2] (1) and [Mg2(L2)2] (2) (H2L2 = N-((1-
(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-
n
yl)pentan-1-amine). The nucleophilic addition of Bu2Mg to the
CN bond of the HL1 ligand occurred in the process for the
n
formation of 2. Treatment of HL1 with 2 and 1 equiv of BuLi
generated [Li2(L3)2] (3) (HL3 = 2-(2-(((1-(1H-pyrrol-2-yl)-
pentylidene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-
amine) and [Li2(L1)2] (4). An α-C−H substitution of the HC
n
NR moiety of the HL1 ligand triggered by BuLi was discovered in
the preparation of 3. The formation of 3 demonstrates a new concept for the C−C coupling that involved inert C−H bond
activation of HCNR skeleton. The reactions of HL1 with MeLi, sec-BuLi, and tert-BuLi, respectively, were also examined. The
products for both the nucleophilic addition of organolithium reagents to the CN bond and α-C−H substitution of the HCNR
moiety of the HL1 ligand were determined. The mechanisms for the formations of 2 and 3 were rationalized by DFT calculations.
The hydroboration reactions catalyzed by 2 were investigated, and these reactions characterize ample substrate scope, very good
yields, and high selectivity.
approaches to amines, generating target amines in deep
eutectic solvents and water. In contrast to the facile
nucleophilic additions of organolithium reagents to imines,
the additions to imines by dialkylmagnesium reagents are less
common.13 It was found that the dialkylmagnesium reagents
could only be added to the activated CN bonds.13a Recent
work of Capriati and co-workers showed that the addition of
organomagnesium reagents to imines is a facile protocol to
produce amine compounds.13b Owing to the commercial
availability and cheapness of dialkylmagnesium reagents, the
preparation of amines by the addition of organomagnesium
reagents to unactivated CN bond is of practical importance.
We have prepared and structurally characterized two
magnesium complexes [Mg(L1)2] (1) and [Mg2(L2)2] (2)
(HL1 = 2-(2-((((1H-pyrrol-2-yl)methylene)amino)methyl)-
INTRODUCTION
■
Imines, due to the reactivity of the CN bond, are valuable
building blocks for the synthesis of various compounds with
fundamental important functionalities. Molecules with the C
N bond are utilized as the ligands for the coordination
complexes1 and applied as key intermediates in the preparation
of pharmaceutical-based compounds.2 Particularly, imines have
enjoyed an outstanding place in the synthesis of amine
scaffolds, owing to the prevalence of amines as feedstock
chemicals, building blocks for biologically active compounds,
and valuable species in the agrochemical and polymer
industries.3 Consequently, the rapid and efficient synthesis of
amines from imines is an energetically pursued area.
Several methodologies are developed for these trans-
formations.4 The important strategies include: (i) photo-
catalytic alkylation of imines enabled by organic photo-
catalysts5 or metal catalysts;6 (ii) nucleophilic additions of
the CN bond of imines by dialkylzinc,7 Grignard reagents,8
and organolithium complexes.9 Several review articles have
been published on this topic.10 Reports of Hevia11 and
Capriati12 have demonstrated that the additions of organo-
lithium reagents to imines are efficient and sustainable
Received: December 30, 2020
Published: June 18, 2021
https://doi.org/10.1021/acs.organomet.0c00815
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n
1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine; H2L2 = N-((1-
(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-(1H-pyr-
rol-2-yl)pentan-1-amine). Two lithium compounds [Li2(L3)2]
(3) (HL3 = 2-(2-(((1-(1H-pyrrol-2-yl)pentylidene)amino)-
methyl)-1H-pyrrol-1-yl)-N,N-dimethyl-ethan-1-amine) and
[Li2(L1)2] (4) were also isolated. The α-C−H substitution
of the HCN unit of the HL1 ligand occurred in the process
for preparing 3. Due to the increased electrophilicity of
azomethine carbon of imines compared with that of
aldehydes,7a the α-C−H substitution of HCN moiety of
aldimines is a formidable challenge. As can be seen in Scheme
1, the atomic charge of the azomethine carbon of imines,
recrystallized in toluene. When the ratio of HL1 to Bu2Mg
was increased to 1:2, a dinuclear compound [Mg2(L2)2] (2)
was afforded (Scheme 2).
Single-crystal diffraction analysis revealed that complex 1
crystallizes in monoclinic crystal system of the P21/n space
group. The structure of 1 is composed of one Mg(II) ion and
two [L1]− ligands. The central Mg(II) ion is hexa-coordinated
by six nitrogen atoms from two tridentate [L1]− ligands and
displays an octahedron geometry (Figure 1a). Three pairs of
coordinated nitrogen atoms originated from pyrrole, imine,
and N,N-dimethylamine are trans-arranged. Thus, compound 1
shows approximate Ci symmetry.
Scheme 1. Atomic Charges of the Central Carbon Atoms of
Imines and Carbonyls Obtained by the DFT Calculations7a
obtained by the DFT calculations, is 0.17, which is much lower
than that of the carbon atom of carbonyls of 0.51. The
activation of the α-C−H atom of HCN unit of aldimines by
organometallic reagents has never been reported. Herein, we
describe the detailed study of our findings, including
mechanistic investigations of the formations of 2 and 3 via
DFT calculations, as well as the hydroboration reactions of
aldehydes and ketones by pinacolborane (HBpin) catalyzed by
2.
RESULTS AND DISCUSSION
■
Synthesis and Structure of HL1. Initially, we conducted
experiments for the synthesis of the ligand. The ligand 2-(2-
((((1H-pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-
yl)-N,N-dimethylethan-1-amine (HL1, Scheme S1) was
generated by the condensation reaction between 2-(2-(amino-
methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine14 and
1H-pyrrole-2-carbaldehyde. The structure of the HL1 ligand
was characterized by X-ray single-crystal diffraction (Figure
S1) and NMR spectroscopy (Figures S6 and S7).
Figure 1. Solid-state structures of 1 (a) and 2 (b) with ORTEP
diagram of 30% probability ellipsoid. Hydrogen atoms are omitted for
clarity.
Syntheses and Structures of [Mg(L1)2] (1) and
[Mg2(L2)2] (2). Treatment of HL1 with 0.5 equiv of Bu2Mg
n
produced a mononuclear magnesium complex [Mg(L1)2] (1)
(Scheme 2), which was isolated as a colorless solid after being
The crystal structure of 2 was determined by X-ray single-
crystal diffraction analysis. An ORTEP representation of the
structure of 2 is shown in Figure 1b. Complex 2 exhibits
approximately Ci symmetry and consists of two Mg(II) ions
and two newly formed [L2]2− ligands. Undoubtedly, the
[L2]2− ligand was afforded by the nucleophilic addition of
nBu2Mg to the imine scaffold of the HL1 ligand. The geometry
around each magnesium atom can be described as a distorted
tetrahedron. Two magnesium atoms are doubly bridged by two
amine nitrogen atoms of [L2]2− ligands, forming a rhombus-
like configuration. The nucleophilic addition of nBu2Mg to the
CN bond of the HL1 ligand was also confirmed by NMR
spectroscopy (Figure S10).
Scheme 2. Syntheses of [Mg(L1)2] (1) and [Mg2(L2)2] (2)
Syntheses and Structures of [Li2(L3)2] (3) and
[Li2(L1)2] (4). Intrigued by the expected observation of the
nucleophilic addition of nBu2Mg to the imine skeleton, we next
n
endeavored to achieve this addition mediated by BuLi. The
1:2 reaction between the HL1 ligand and nBuLi in toluene gave
a new lithium compound [Li2(L3)2] (3) (HL3 = 2-(2-(((1-
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(1H-pyrrol-2-yl)pentylidene)amino)methyl)-1H-pyrrol-1-yl)-
N,N-dimethyl ethan-1-amine) and an unknown compound.
Another new complex [Li2(L1)2] (4) was afforded by the 1:1
aldehydes,7a it is not easy to abstract the hydrogen atom from
the HCN unit. The preparation of compound 3
demonstrates a new strategy for C−C coupling involving C−
H bond activation of HCN moiety.
n
reaction between the HL1 ligand and BuLi (Scheme 3).
Instructed by the work of Capriati and co-workers that the
addition of nBuLi to imines could give amines,13b we suspected
that the unknown compound found in the process for
preparing 3 is an amine compound. Thus, we reconducted
the reaction between HL1 and 2 equiv of nBuLi and
hydrolyzed the reaction mixture directly. An amine compound
N-((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-
(1H-pyrrol-2-yl)pentan-1-amine (H2L3′, Scheme 4) was
isolated, which was characterized by NMR spectroscopy and
HRMS.
Scheme 3. Syntheses of [Li2(L3)2] (3) and [Li2(L1)2] (4)
Scheme 4. Syntheses of HL3−H2L6′
Single-crystal X-ray diffraction analysis revealed that
̅
complex 3 crystallizes in the triclinic space group P1 with Z
= 1. Complex 3 is composed of two newly formed [L3]−
ligands and two Li(I) ions (Figure 2a). The two symmetry-
To expand the scope of the nucleophilic addition and α-C−
H substitution reactions of the HL1 ligand, we conducted the
1:2 reactions of the HL1 ligand with MeLi, sec-BuLi, and tert-
BuLi, respectively, and hydrolyzed the reaction mixtures
directly. A series of imines HL4−HL6 and amines H2L4′−
H2L6′ (Scheme 4) were afforded. They were characterized by
NMR spectroscopy and HRMS. It was found that the amines
were the major products.
Mechanistic Insights from DFT Calculations. DFT
calculations were carried out to better understand the
divergent results in reactions of nBuLi and nBu2Mg with
HL1, and methyllithium and dimethylmagnesium were used as
model organometallic reagents. When the lithium reagent is
involved (Figure 3), the formation of (L1)Li by deprotonation
of HL1 with methyllithium should be formed first.
Incorporation of another methyllithium with (L1)Li forms a
more stable complex 9-Li, in which the two lithium atoms are
bridged by the methyl group. The addition of LiCH3 to the
imino functionality occurs via TS1-Li, which is 26.1 kcal/mol
above that of 9-Li and exergonically forms complex 10-Li.
From the latter intermediate, the regeneration of the imino
functionality could possibly occur by elimination of LiH via
Figure 2. Solid-state structure of 3 (a) and 4 (b) with ORTEP
diagram of 30% probability ellipsoid. Hydrogen atoms are omitted for
clarity.
related Li(I) ions are doubly bridged by nitrogen atoms of
pyrroles of two [L3]− ligands. The structure of 4 (Figure 2b) is
similar to that of 3, except that the hydrogen atom of the imine
moiety of the HL1 ligand in 4 was not replaced by butyl group.
A remarkable structural feature of 3 is the presence of a
(nBu)CNR skeleton derived from the replacement of the
hydrogen atom of the HCN moiety by an n-butyl group. As
mentioned above, due to the increased electrophilicity of the
azomethine carbon of imines in comparison with that of
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Figure 3. DFT results for the reaction of LiCH3 with HL1. Solvation free energies (in kcal/mol) are relative to free LiCH3 with HL1.
Figure 4. DFT results for the reaction of Mg(CH3)2 with HL1. Solvation free energies (in kcal/mol) are relative to free Mg(CH3)2 with HL1.
TS2-Li, which requires an activation barrier of 23.0 kcal/mol
and leads to intermediate 11-Li. After releasing of LiH from
11-Li, 12-Li could be formed before its final dimerization to
complex 3.
In reaction of dimethylmagnesium with HL1 (Figure 4),
upon the formation of complex (L1)MgMe, the direct addition
of the Mg(CH3)2 moiety to the imino functionality via TS1′-
Mg is very difficult as a high barrier of 48.0 kcal/mol was
predicted, which could be attributed to the fact that the Mg
chelates tightly with three nitrogen atoms in (L1)MgMe
making difficult the approach of the Mg(CH3)2 moiety to the π
orbital of the CN unit. Instead, the incorporation of another
Mg(CH3)2 forms first a bridged complex, 13-Mg, from which
the addition of Mg and methyl to the CN functionality
could be realized via TS1-Mg with a barrier of 21.7 kcal/mol.
After the formation of intermediate 14-Mg, it was found that
the regeneration of the CN functionality by a similar β-H
elimination as described in reaction of lithium reagent is more
difficult, as the TS2′-Mg is 28.2 kcal/mol higher than 14-Mg.
However, the deprotonation of another HL1 ligand by one of
the remaining methyl groups in the complex is much more
facile via TS2-Mg with a lower barrier of 16.4 kcal/mol and
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exergonically forms intermediate 15-Mg highly, from which
complex 2 could be finally expected by further transformations.
The energy profile explains well that no CN contained in
reaction with magnesium reagent is attributed to the difficult β-
H elimination of 14-Mg as in competition with the facile NH
deprotonation of pyrrole in HL1.
Table 1. Hydroboration of Aldehydes Catalyzed by
Complex 2
a
Hydroboration of Aldehydes and Ketones. Motivated
by the successful preparation of 1−4 with 2 and 3 displaying
intriguing structural features, we endeavored to employ 2 as
catalyst for the hydroboration of carbonyl compounds.15,16
Several lithium and magnesium complexes were reported to
affect the hydroboration of carbonyl compounds.17−24
Encouraged by these examples, we screened 2 for catalytic
activity. 4-Chlorobenzaldehyde (0.25 mmol), pinacolborane
(0.25 mmol), and 0.0025 mol of 2 in CDCl3 (0.5 mL) were
1
loaded in a J. Young’s NMR tube, and the H NMR spectrum
was determined at room temperature. It was found that the
hydroboration underwent promptly, affording corresponding
borate ester in 99% yield within 30 min (Table 1, entry 1).
To explore the generality of the hydroboration protocol, a
range of aldehydes were subjected to hydroboration with
pinacolborane using 2 as catalyst. The results are summarized
in Table 1. In virtually all cases, hydroboration of aldehydes
proceeded smoothly, generating corresponding borate ester in
almost quantitative yield. Benzaldehydes bearing electron-
withdrawing (5a and 5b) and electron-releasing groups (5d
and 5e) were well-tolerated. Pyridine-2-aldehyde (5f) was
selectively hydroborated on the aldehyde, leaving the imine
group unattacked. Furthermore, the aldehyde group of pyrrole-
2-aldehyde (5g) was chemoselectively hydroborated, leaving
the NH moiety unaffected. Similarly, when two aldehyde
groups are attached to pyrrole or benzene ring (5h and 5i), we
obtained the dihydroborated products exclusively (>99%
yield) by adding 2 equiv of pinacolborane.
In light of the successful results of aldehydes, we next
examined the potentials of 2 for the hydroboration of ketones
(Table 2). The studies of other groups revealed that the
hydroboration of ketones was slower than that of aldehydes.
To our delight, results of several different ketones demonstrate
a broad scope of this protocol. In all cases, the desired borate
ester products were exclusively obtained (97−99%) within 30
min at room temperature under the catalyst loading of 1 mol
%. Alkyl ketones are compatible with this system; acetone (7a)
and cyclohexanone (7f) were cleanly converted to the
corresponding borate ester in >99% yields within 30 min.
Acetophenone bearing electron-donating (7e) and electron-
withdrawing groups (7c and 7d) proceeded well. Diary
ketones (7h−7k) were completely converted to the corre-
sponding borate esters. Remarkably, the steric hindered
ketones also underwent hydroboration smoothly within 30
min in good to excellent yield (7k). In addition, extraordinary
chemoselectivity was observed for 1-(pyridin-2-yl)ethan-1-one
(7g); the carbonyl group was hydroborated, leaving the imine
moiety nonreduced.
Inspired by the successful results for the hydroboration of
aldehydes and ketones, we sought to further explore the
catalyst selectivity between aldehydes and ketones. To this end,
the stoichiometric amount of benzaldehyde and acetophenone
were subjected to hydroboration by using 2 (1 mol %) as
catalyst. It is found that 97% hydroboration of aldehydes
occurred for 2. Similar results were observed when 4-
chlorobenzaldehyde and 4-chloroacetophone were reacted
with HBPin in a 1:1:1 molar ratio. Meanwhile, the 1:1:1
a
Conditions: aldehydes (0.25 mmol), HBpin (0.25 mmol), and
b
catalyst (0.0025 mmol) in CDCl3(0.5 mL), 30 min. Yields of the
borate esters based on H NMR analysis.
1
reaction of pyridine-2-aldehyde, 1-(pyridin-2-yl)ethan-1-one
and HBpin were examined, and exclusive hydroboration of
pyridine-2-aldehyde was achieved. Analogous results were
found for the reaction of 4-methylbenzaldehyde, 4-methyl-
acetonphone and HBpin (1:1:1). The intramolecular selectiv-
ity of the aldehyde over ketone was also realized for the 1:1 4-
acetyl benzaldehyde and HBpin, and the aldehyde group was
hydroborated in 99% yield. Naturally, the ketone functionality
of 4-acetyl benzaldehyde was also reduced, when the molar
ratio of 4-acetyl benzaldehyde and HBPin was changed to 1:2
(Scheme 5).
The catalytic activity of 1 toward the hydroboration reaction
of carbonyl compounds were also examined. It is found that
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Table 2. Hydroboration of Ketones Catalyzed by Complex
2
Scheme 5. Chemoselective Hydroboration of Aldehydes and
Ketones Catalyzed by Complex 2
a
a
a
Conditions: aldehyde (0.25 mmol), ketones (0.25 mmol), HBpin
b
(0.25 mmol) and catalyst (0.0025 mmol) in CDCl3 (0.5 mL). Yields
of the products based on H NMR analysis.
1
CONCLUSIONS
■
In conclusion, the α-C−H substitution of the HCNR
skeleton of the Schiff base ligand HL1 mediated by a series of
organolithium reagents were realized, giving C−C coupling
products that involving inert C−H bond activation of the
HCNR moiety. In addition, the successful conversion of
imine into amine was achieved through nucleophilic addition
n
of Bu2Mg and organolithium reagents to the CN bond of
the HL1 ligand. The mechanisms for the formations of 2 and 3
were rationalized by DFT calculations. Complex 2 demon-
strated its competence as a catalyst toward the hydroboration
of aldehydes and ketones. The key advantages of this protocol
are mild reaction conditions, extremely high yields, wide
functional group tolerance, and high selectivity for aldehyde
over ketone. The very good economy, great earth abundance,
and nontoxic natures of lithium and magnesium render them
as ideal alternatives to replace precious metal catalysts in some
organic reactions.
EXPERIMENTAL SECTION
■
General Methods. All the reactions were performed in a N2-filled
Vigor glovebox. THF, hexane, and toluene were dried over purple
sodium benzophenone ketyl and stored with 4 Å molecular sieves.
n
nBu2Mg, BuLi, MeLi, sec-BuLi, and tert-BuLi were purchased from
J&K and Macklin chemical and directly used as received.
Deuterochloroform was dried over CaH2 before distilled under
vacuum and stored with 4 Å molecular sieves. H NMR spectra were
a
Conditions: ketones (0.25 mmol), HBpin (0.25 mmol) and catalysts
1
b
(0.0025 mmol) in CDCl3 (0.5 mL), 30 min. Yields of the products
based on H NMR analysis.
recorded at the ambient temperature on Bruker Avance-III 400 MHz
and Aglient 400 and 300 MHz instruments and the spectra were
referenced to the TMS signal (0 ppm). 13C NMR spectra were
recorded at the ambient temperature on Bruker Avance-III 600 MHz
NMR spectrometer. Elemental analyses for C, H, and N were carried
out on a PerkinElmer 2400 analyzer. Crystal determination was
performed with a Bruker SMART APEX II CCDC diffractometer
equipped with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). HRMS spectrum was obtained by TOF-MS. The detailed
1
compound 1 shows very high catalytic activity for the
hydroboration of benzaldehyde (5c, Figure S46) and cyclo-
hexanone (7f, Figure S47).
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procedure for the synthesis of the HL1 ligand was provided in the
Supporting Information.
Accession Codes
CCDC 2052855−2052858 and 2080621 contain the supple-
mentary 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 Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Synthesis of [Mg(L1)2] (1). At −35 °C, HL1 (0.2444 g, 1.0
mmol) was dissolved in THF (2 mL). Then nBu2Mg (0.5 mL, l.0 M in
hexane, 0.5 mmol) was added dropwise. The reaction mixture was
stirred at room temperature overnight. Volatiles were removed under
vacuum, and the resulting crude product was washed with n-hexane to
give a white powder. Yield: 0.21 g (83%). Colorless crystals were
obtained in toluene at room temperature. The structure of 1 was
determined by X-ray single-crystal diffraction. Anal. Calcd for
C28H38MgN8: C, 65.82; H, 7.50; N, 21.93. Found: C, 65.50; H,
7.58; N, 21.38.
Synthesis of [Mg2(L2)2] (2). At −35 °C, HL1 (0.2444 g, 1.0
mmol) was dissolved in THF (2 mL). Then nBu2Mg (2 mL, l.0 M in
hexane, 2 mmol) was added dropwise. The reaction mixture was
stirred at room temperature overnight. Volatiles were removed under
vacuum, and the resulting crude product was washed with n-hexane to
give a white powder. Yield: 0.28 g (85%). Colorless crystals were
obtained in toluene at room temperature. The structure of 2 was
determined by X-ray single-crystal diffraction. Anal. Calcd for
C36H56Mg2N8: C, 66.57; H, 8.69; N, 17.25. Found: C, 66.18; H,
8.53; N, 16.92.
AUTHOR INFORMATION
Corresponding Authors
■
Yahong Li − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, PR
China; orcid.org/0000-0002-6467-0607;
Email: liyahong@suda.edu.cn
Yuanzhi Xia − College of Chemistry and Materials
Engineering, Wenzhou University, Wenzhou 325035, PR
China; orcid.org/0000-0003-2459-3296; Email: xyz@
wzu.edu.cn
Authors
Synthesis of [Li2(L3)2] (3) and Characterization of HL3. At
−35 °C, HL1 (0.2444 g, 1.0 mmol) was dissolved in toluene (2 mL).
Then nBuLi (1.0 mL, 2.4 M in hexane, 2.4 mmol) was added
dropwise. The reaction mixture was stirred at room temperature
overnight. Volatiles were removed under vacuum, and the resulting
crude product was washed with n-hexane to give 0.224 g of a red
powder. Colorless crystals were obtained in toluene at room
temperature. The structure of 3 was obtained by X-ray single-crystal
diffraction. 1H and 13C NMR spectra of 3 are very complicated. Thus,
the compound was characterized by being hydrolyzed to HL3.
Complex 3 was hydrolyzed with water (3 mL) and extracted with
DCM (3 × 10 mL). The organic layer was dried over anhydrous
MgSO4 and filtered. The solvent was removed under vacuum to give a
yellow oil. HRMS (EI) Calcd for: C18H28N4 [HL3] 300.2314. Found:
300.2312.
Yan Dang − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, PR
China
Yalan Wang − College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou 215123,
PR China
Yafei Li − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, PR
China
Man Xu − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou 325035, PR China
Chaohong Jia − College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou 215123,
PR China
Yanhua Lu − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, PR
China
Liang Zhang − College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou 215123,
PR China
Synthesis of [Li2(L1)2] (4). At −35 °C, HL1 (0.1222 g, 0.5 mmol)
n
was dissolved in toluene (2 mL). Then BuLi (0.32 mL, l.6 M in
hexane, 0.5 mmol) was added dropwise. The reaction mixture was
stirred at room temperature overnight, produced a pink powder.
Volatiles were removed under vacuum, and the resulting crude
product was washed with toluene/hexane to give a light pink powder.
Yield: 0.083 g (66%). Colorless crystals were obtained in toluene at
room temperature. The structure of 4 was determined by X-ray single-
crystal diffraction. Anal. Calcd for C28H38Li2N8: C, 67.19; H, 7.65; N,
22.39. Found: C, 66.76; H, 7.73; N, 22.32.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00815
General Procedure for the Hydroboration Reaction. In a
nitrogen-filled dry box, pinacol borane (HBpin, 0.032 g, 0.25 mmol),
aldehyde or ketone substrate (0.25 mmol), catalyst (0.0025 mmol),
and CDCl3 (0.5 mL) were added to a J. Young NMR tube. The tube
was taken out from the glovebox and was shaken for 30 min. Then the
1H NMR spectrum of the mixture was recorded. The yield of the
product was calculated by comparing the area of the Bpin of the
product with that of the unreacted HBpin.
Author Contributions
§Y.D. and Y.W. contributed equally to this paper.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors appreciate the financial support from Natural
Science Foundation of China (21772140 and 21873074),
Natural Science Foundation of Jiangsu Province of China
(BK20171213), a Project Funded by the Priority Academic
Program Development of Jiangsu Higher Education Institu-
tion, and the project of scientific and technologic infrastructure
of Suzhou (SZS201905).
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00815.
Crystal data and data collection details for the HL1
ligand, newly formed HL3−H2L6′ ligands and com-
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