Zinc Complexes with an Ethylene-Bridged Bis(β-diketiminate) Ligand: Syntheses, Structures, and Applications as Catalysts in the Borylation of Aryl Iodides

Article abstract of DOI:10.1021/acs.organomet.0c00733

A dinucleating bis(β-diketiminate) ligand with a flexible bridge has been employed to synthesize zinc complexes. The ligand, abbreviated H2L (H2L = N-(4-((2-((4-((2,6-diisopropylphenyl)imino)pent-2-en-2-yl)amino)ethyl)imino)pent-2-en-2-yl)-2,6-diisopropylaniline), was deprotonated with ZnEt2 to afford [LZn2Et2] (1). Reactions of 1 with 2 equiv of BnOH and nBuOH, respectively, gave access to [LZn2(OBn)2]·C6H14 (2·C6H14) and [LZn2(OnBu)2] (3). Treatment of 1 with 2 equiv of I2 in THF produced [LZn2I2(THF)2]·2THF (4·2THF). X-ray single-crystal diffraction analyses revealed that they are all heteroleptic bimetallic compounds with two metal centers being chelated by one ligand set. The structurally similar compounds 1 and 4·2THF possess approximate C2 symmetry, with two β-diketiminate units being arrayed in head-to-tail antiparallel mode. Thus, the molecular structures of 1 and 4·2THF exhibit a seesaw-like topology. The structures of 2·C6H14 and 3 are almost identical, in which two zinc atoms are shared by two ZnN2C3 six-membered rings, two Zn2ON2C2 seven-membered rings, and one Zn2O2 four-membered ring. Therefore, the metal cores of 2·C6H14 and 3 display a crownlike topology. All complexes are catalytically active for the borylation of aryl iodides with B2Pin2 (B2Pin2 = 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bis(1,3,2-dioxaborolane). Complex 1 shows higher activity in comparison to 2, 3, and 4·2THF. The borylation reactions catalyzed by 1 could proceed under mild conditions and can be applied to a series of substrates with high functional group generality. This methodology thus represents a novel use of β-diketiminate zinc complexes for C-I borylation.

Full text of DOI:10.1021/acs.organomet.0c00733

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Article
Zinc Complexes with an Ethylene-Bridged Bis(β-diketiminate)
Ligand: Syntheses, Structures, and Applications as Catalysts in the
Borylation of Aryl Iodides
Yafei Li, Yan Dang, Dawei Li, Huifen Pan, Liang Zhang, Li Wang, Zhu Cao, and Yahong Li*
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ABSTRACT: A dinucleating bis(β-diketiminate) ligand with a
flexible bridge has been employed to synthesize zinc complexes.
The ligand, abbreviated H2L (H2L = N-(4-((2-((4-((2,6-
diisopropylphenyl)imino)pent-2-en-2-yl)amino)ethyl)imino)pent-2-
en-2-yl)-2,6-diisopropylaniline), was deprotonated with ZnEt2 to
afford [LZn2Et2] (1). Reactions of 1 with 2 equiv of BnOH and
nBuOH, respectively, gave access to [LZn2(OBn)2]·C6H14 (2·
C6H14) and [LZn2(OnBu)2] (3). Treatment of 1 with 2 equiv of
I2 in THF produced [LZn2I2(THF)2]·2THF (4·2THF). X-ray
single-crystal diffraction analyses revealed that they are all
heteroleptic bimetallic compounds with two metal centers being
chelated by one ligand set. The structurally similar compounds 1 and
4·2THF possess approximate C2 symmetry, with two β-diketiminate units being arrayed in head-to-tail antiparallel mode. Thus, the
molecular structures of 1 and 4·2THF exhibit a seesaw-like topology. The structures of 2·C6H14 and 3 are almost identical, in which
two zinc atoms are shared by two ZnN2C3 six-membered rings, two Zn2ON2C2 seven-membered rings, and one Zn2O2 four-
membered ring. Therefore, the metal cores of 2·C6H14 and 3 display a crownlike topology. All complexes are catalytically active for
the borylation of aryl iodides with B2Pin2 (B2Pin2 = 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bis(1,3,2-dioxaborolane). Complex 1 shows
higher activity in comparison to 2, 3, and 4·2THF. The borylation reactions catalyzed by 1 could proceed under mild conditions and
can be applied to a series of substrates with high functional group generality. This methodology thus represents a novel use of β-
diketiminate zinc complexes for C−I borylation.
catalysts for the ring-opening polymerization (ROMP) of
lactides.24−33 Particularly, Harder and co-workers reported a
series of dinuclear zinc complexes supported by bridged β-
diketiminate ligands.34 In studies of the copolymerization of
epoxides and CO2, they found that there existed an equilibrium
between the active dimer and inactive monomer (both are
adducts of a catalyst, CO2, and epoxide), and the coexistence
of the dimer and monomer decreased the efficiency of
polymerization reactions. They solved this problem by using
zinc complexes with bridged β-diketiminate ligands. The rigid
p-phenylene, m-phenylene, and 2,6-pyridylene were employed
as bridges. Inspired by the works of Harder, we anticipated that
the rigid bridges may be replaced by flexible ones, affording a
INTRODUCTION
■
The chemistry of zinc complexes has undergone a remarkable
renaissance in the past decade.1−5 The renewed interest toward
these compounds has mainly arisen from their attractive
reactivities6−9 and potential applications in a broad range of
reactions,10 including the hydroboration of alkynes,11,12 the
Strecker reaction,13 the Barbier reaction,14 the aminophenol
oxidation reaction,15 the C−S cross-coupling reaction,16 the
hydrosilylation of N-heterocycles,17 the copolymerization of
epoxides and CO2,18−20 and so forth.21,22 Zinc is an
inexpensive, biocompatible, less toxic and earth-abundant
metal, which makes it particularly appealing to replace toxic
and/or noble-metal complexes in catalytic transformations.
Thus, the synthesis of zinc complexes with high catalytic
activity is of great importance.
One fertile route for the preparation of zinc complexes is to
employ β-diketiminate ligands.23 These ligands could be easily
synthesized, and their steric demands can be readily tuned by
varying the organic substituents attached to the imine groups.
Consequently, a number of zinc complexes have been
synthesized by the utilization of a large variety of β-
diketiminate ligands.24−33 They behaved as highly active
Received: November 17, 2020
Published: February 9, 2021
https://dx.doi.org/10.1021/acs.organomet.0c00733
© 2021 American Chemical Society
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plethora of zinc complexes with interesting structures and
properties.
In this work, we employed an ethylene-bridged β-
diketiminate N-(4-((2-((4-((2,6-diisopropylphenyl)imino)-
pent-2-en-2-yl)amino)ethyl)imino)pent-2-en-2-yl)-2,6-diiso-
propylaniline (H2L) as a ligand to synthesize zinc complexes.
Four complexes of the compositions [LZn2Et2] (1),
[LZn2(OBn)2]·C6H14 (2·C6H14), [LZn2(OnBu)2] (3), and
[LZn2I2(THF)2]·2THF (4·2THF) were prepared. They are
catalytically active for the borylation of aryl iodides with
bis(pinacolato)diboron. Complex 1 shows higher activity in
comparison to 2, 3, and 4·2THF, giving a series of arylboronic
acid derivatives.
Figure 1. Molecular structure of 1 from X-ray diffraction. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are drawn at the 30%
probability level.
Arylboronic acid derivatives are highly valuable synthetic
precursors that are widely used as intriguing building blocks in
organic synthesis, particularly as substrates for transition-metal-
catalyzed C−C, C−O, and C−N bond-forming reactions.35
Recent advances in the preparation of arylboronic acid
derivatives revealed that these compounds can be generated
by the borylation of aryl halides with diborons.36−39 Several
metal complexes, including Pd,40−43 Rh,44 Fe,45 W,46 Zn,47−50
Co,51,52 Cu,53−56 and Ni,57−60 have been proven to be able to
catalyze the borylation of aryl halides. It is found that visible
light61,62 and free radicals63,64 are also effective in this
transformation. However, there has beeh no report about
this borylation reaction catalyzed by β-diketiminate complexes.
Herein, we report the synthesis and structures of complexes 1,
2·C6H14, 3, and 4·2THF and the first efficient borylation of
aryl iodides with bis(pinacolato)diboron catalyzed by zinc β-
diketiminate complexes.
and one C atom of the ethyl group. Thus, compound 1 shows
a trigonal geometry (Figure 1). The C1−Zn1−N2, C1−Zn1−
N1, and N1−Zn1−N2 angles are 132.44, 132.69, and 96.7°,
respectively. The sum of these angles is 361.86°, indicating that
these four atoms are perfectly planar. The two N2C3Zn
chelating rings for the bidentate ligands are arranged in a head-
to-tail antiparallel fashion. The two N-phenyl substituents of
two β-diketiminate groups are also arrayed in an antiparallel
mode and are vertical to the planes formed by N2C3Zn
chelating rings. Thus, compound 1 displays a seesaw-like
topology.
Syntheses and Structures of [LZn2(OBn)2]·C6H14 (2·
C6H14) and [LZn2(OnBu)2] (3). Intrigued by the successful
preparation of zinc alkyl complex 1, we next attempted to
study the reactivity of 1 with alcoholic reagents. Two
metathesis reactions with the zinc alkyl starting material 1
were explored. The reaction of 1 with 2 equiv of BnOH in
THF gives a crude product. The recrystallization of the crude
product in hexane generated the zinc alkoxide complex
[LZn2(OBn)2]·C6H14 (2·C6H14). Treatment of 1 with 2
RESULTS AND DISCUSSION
■
n
Dinucleating Ligand H2L. The ethylene-bridged β-
diketiminate ligand H2L (H2L = N-(−4-((2-((4-((2,6-
diisopropylphenyl)imino)pent-2-en-2-yl)amino)ethyl)imino)-
pent-2-en-2-yl)-2,6-diiso-propylaniline) has been synthesized
according to the literature procedure.65−68 The H2L ligand was
equiv s of BuOH afforded another zinc alkoxide compound,
[LZn2(OnBu)2] (3) (Scheme 2). The structures of 2·C6H14
and 3 were determined by X-ray single-crystal diffraction, and
ORTEP drawings of the molecular structures of 2·C6H14 and 3
are given in Figures 2 and 3, respectively. The structures of 2·
C6H14 and 3 are quite similar; therefore, only the structure of
2·C6H14 is discussed in detail. As expected, the ethyl groups
binding to Zn atoms are replaced by two OBn groups. The
1
characterized by H/13C NMR spectroscopy and X-ray single
crystal diffraction. An ORTEP drawing of the molecular
1
structure of the H2L ligand is shown in Figure S1. The H
NMR spectrum of the H2L ligand in CDCl3 is fully consistent
with its structure (Figure S6).
Scheme 2. Syntheses and Structures of [LZn2(OBn)2] (2)
and [LZn2(OnBu)2] (3)
Synthesis and Structure of [LZn2Et2] (1). Compound 1
was obtained by reacting the dinucleating ligand H2L with 2
equiv of diethylzinc in hexane through an alkyl elimination
reaction (Scheme 1), generating the corresponding zinc ethyl
complex 1 in 81% yield. The structure of 1 was determined by
X-ray single-crystal diffraction. In the solid state, compound 1
exhibits an approximate C2 symmetry (Figure 1). Two zinc
atoms are chelated by one ligand set. Each zinc atom is
tricoordinated by two N atoms of one β-diketiminate moiety
Scheme 1. Synthesis of [LZn2Et2] (1)
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attract intense attention because they are necessary precursors
for the synthesis of complexes with low-valence metal centers
by reducing iodine-coordinated metal complexes utilizing alkali
metals.69 With the successful preparation of zinc alkoxide
complexes by employing the zinc alkyl compound 1 as the
starting material, we endeavored to prepare iodine-coordinated
metal complexes by using 1 as the reagent as well. Addition of
2 equiv of I2 to a THF solution of 1 gave [LZn2I2(THF)2]·
2THF (4·2THF) in moderate yield (Scheme 3). An X-ray
Scheme 3. Synthesis of [LZn2I2(THF)2]·2THF (4·2THF)
single-crystal diffraction analysis reveals that complex 4·2THF
crystallizes in the monoclinic space group P21/c. As can be
seen in Figure 4, complex 4·2THF is a bimetallic compound,
Figure 2. (a) Molecular structure of 2 from X-ray diffraction.
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn
at the 30% probability level. (b) The crownlike topology of the core
structure of 2.
Figure 4. Molecular structure of 4 from X-ray diffraction. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are drawn at the 30%
probability level.
and each β-diketiminate unit chelates one ZnII ion. The ethyl
group of 1 is replaced by an iodine atom to form a zinc−iodide
bond. In addition, there is one tetrahydrofuran molecule
coordinating to the ZnII center. Each four-coordinated zinc
center exhibits a tetrahedral geometry.
Borylation of Aryl Iodides. Inspired by the discoveries
50
that the ZnX2-dtbpy,47 ZnCl2-NHC,48,49 and ZnEt2 systems
could effectively catalyze the borylation of aryl halides with
diboron reagents, we envisioned that the synthesized
complexes 1−3 and 4·2THF may be also feasible catalysts
for the borylation of aryl halides in the presence of strong
alkaline alkoxide bases. To examine this proposal, the possible
borylation of 1-iodo-4-methoxybenzene (5a) by B2Pin2, using
1−3 and 4·2THF, respectively, as catalysts was tested (Table
1). The reactions were initially conducted by employing KOEt
as the base, in THF solution at 75 °C. To our delight, all four
complexes could catalyze this borylation transformation. It was
found that the yield was the highest by employing 1 as the
catalyst, affording 6a in 81% yield (entry 1). The employment
of 2, 3, and 4·2THF as catalysts under the same conditions as
those of 1 produced 6a in 45%, 55%, and 50% yields,
respectively (entries 2−4). To compare the catalytic activities
of the dinuclear compound 1 with its mononuclear analogue,
the mononuclear complex L2ZnEt (HL2 = N-(4-((2,6-
diisopropylphenyl)imino)pent-2-en-2-yl)-2,6-diisopropylani-
line) was prepared (Figure S16).70 To our surprise, the
Figure 3. Molecular structure of 3 from X-ray diffraction. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are drawn at the 30%
probability level.
oxygen atom of the OBn moiety coordinates with metal
centers in a η2 mode. As a consequence, the two zinc atoms are
doubly bridged by two oxygen atoms of two OBn groups,
forming a four-membered Zn2O2 core. Each zinc atom is four-
coordinated by two nitrogen atoms and two oxygen atoms to
give a tetrahedral geometry. Two zinc atoms are shared by two
ZnN2C3 six-membered rings, two Zn2ON2C2 seven-membered
rings, and one Zn2O2 four-membered ring to form a crownlike
topology (Figure 2b).
Synthesis and Structure of [LZn2I2(THF)2]·2THF (4·
2THF). The iodine-coordinated metal complexes continue to
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Table 1. Optimization of the Conditions for Borylation of 1-
Iodo-4-methoxybenzene (5a) with B2pin2
Table 2. Scope of Cross-Coupling of B2Pin2 with Aryl
a
a
Iodides
b
entry cat. (10 mol %)
base
time (h)
solvent
yield (%)
1
2
3
4
5
6
7
8
1
2
3
KOEt
KOEt
KOEt
KOEt
12
12
12
12
12
12
12
12
12
12
12
24
12
12
12
12
12
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
MTBE
toluene
THF
81
d
45
d
55
d
4·2THF
L2ZnEt
50
KOEt
0
57
0
1
1
1
1
1
1
1
1
NaOEt
NaOAc
NaOtBu
KOtBu
KOMe
NaOMe
KOEt
trace
trace
9
d
10
11
12
13
14
15
16
17
74
d
41
d
>99
0
trace
>99
KOEt
KOEt
KOEt
KOEt
d
1
1
1
trace
c
64
a
Reaction conditions unless specified otherwise: 1 (0.025 mmol, 10
mol %), B2Pin2 (0.375 mmol, 1.5 equiv), base (0.0375 mmol, 1.5
equiv), and 5a (0.25 mmol, 1 equiv) in 1 mL of solvent, 75 °C, 12 h.
b
c
Isolated yield. 1 (0.0125 mmol, 5 mol %) and B2Pin2 (0.375 mmol,
d
1
1.5 equiv). Yield determined by H NMR using 1,2-dichloroethane
as the internal standard.
mononuclear compound L2ZnEt did not catalyze the
borylation reaction of 5a by B2Pin2 (entry 5, Figure S35).
We reasoned that the steric hindrance of the mononuclear
complex L2ZnEt is greater than that of the dinuclear
compound 1. It is easier for the substrates to combine with
the more open zinc centers of 1. Next, the reaction conditions
catalyzed by 1 were optimized. The borylation product 6a was
not obtained by using NaOAc as a base (entry 6). Trace
amounts of products were obtained by employing NaOtBu
(entry 7) and KOtBu (entry 8) as bases, although 57% (entry
5), 41% (entry 10), and 74% (entry 9) yields were obtained by
utilizing NaOEt, NaOMe, and KOMe as bases, respectively.
Heating of 5a and B2pin2 in THF at 75 °C without base did
not give any product (entry 13). Similarly, a trace amount of
product (entry 14) was detected without adding 1 as the
catalyst. When the solvent was switched to MTBE, we
obtained a yield similar to that of in tetrahydrofuran (entry
15). However, when the solvent was changed to toluene (entry
16), a trace amount of the desired product was afforded.
Decreasing the amount of catalyst from 10 mol % to 5 mol %
caused a marked drop in the yield, generating 6a in 64% yield
(entry 17).
a
Reaction conditions unless specified otherwise: 1 (0.025 mmol, 10
mol %), B2Pin2 (0.375 mmol, 1.5 equiv), base (0.0375 mmol, 1.5
equiv), and aryl iodides (0.25 mmol, 1 equiv). in 1 mL of solvent, 75
b
c
°C, 12 h. Isolated yield unless otherwise noticed. Yield determined
d
by 1H NMR using 1,2-dichloroethane as internal standard. 75 °C, 15
e
f
min. 75 °C, 3 h. 75 °C, 24 h.
Having the optimized conditions in hand, we investigated
the scope of this transformation, and the results are
summarized in Table 2. Aryl iodides with different electronic
properties as well as different steric hindrances were examined.
It was found that iodobenzene (5d) and its derivatives with
electron-donating groups underwent borylation smoothly to
afford the corresponding arylboronates in high yields (Table 2,
entries 1−8). Remarkably, the substituent position of the
methyl and methoxy groups had no remarkable effect on the
present borylation reactions, giving the corresponding products
in 73% to 84% yields (Table 2, entries 1−3 and 5−7).
Electron-withdrawing substituents, including Br, F, CF3, and
CN groups, are well tolerated (Table 2, entries 14−17).
However, the yields are lower than those of the substrates with
electron-donating groups. Naphthyl iodides with the iodide in
the 1- or 2-position are effective in the borylation reactions,
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giving naphthyl borates in high yields of 91% and 75%,
respectively (Table 2, entries 10 and 11). Substrates with larger
sterically congested substituents, such as 1-iodo-2,4-dimethyl-
benzene (5h) and 2-iodo-1,3,5-trimethyl-benzene (5i), are
compatible with this borylation transformation, whereas the
yields were decreased from 88% to 43% with an increase in
steric hindrance. The heterocycle-containing substrate 5-
iodobenzo[d][1,3]dioxole (5r) gives a very good yield. To
the best of our knowledge, this is the first time that the β-
diketiminate compounds have been used as catalysts for the
borylation of aryl iodides.
On consideration that the borylation of 1-iodo-4-phenyl-
benzene (5l) could give a 93% yield, the borylation reaction of
5l with B2Pin2 was then conducted on a large scale (Scheme
4). The borylation of 5 mmol of 5l afforded 1.19 g (85%) of 6l,
revealing that high efficiency was maintained even in the large-
scale reaction.
challenging substrates are well tolerated. Thus, this method
provides a cost-effective alternative to the widely utilized
palladium catalysts. As far as the substrate scope and activities
of the simple Zn system of Marder and co-workers48 and our
system are concerned, the activity of their system is higher than
ours and the substrate scope of their system is broader than
that of this work. In comparison with the pyrophoric ZnEt2,
complex 1 is much easier to handle. The successful preparation
of arylborate on a large scale makes such a paradigm much
more attractive.
EXPERIMENTAL SECTION
■
General Methods. All of 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. ZnEt2 was purchased from J&K and Macklin Chemical and
directly used as received. Deuterochloroform was dried over CaH2
before it was distilled under vacuum and stored with 4 Å molecular
1
sieves. H NMR spectra were recorded at ambient temperature on
Scheme 4. Gram-Scale Reaction
Bruker Avance-III 400 MHz and Aglient 400 MHz instruments and
the spectra were referenced to the TMS signal (0 ppm). 13C NMR
spectra were recorded at ambient temperature on a 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).
Synthesis of [LZn2Et2] (1). H2L (0.542 g, 1 mmol) was dissolved
in hexane (2 mL), and then a solution of ZnEt2 (3 mL, 1 M in hexane,
3 mmol) was added. The mixture was stirred at room temperature for
15 h. Volatiles were removed under vacuum to give a white powder.
Yield: 0.589 g (80.7%). Block-shaped colorless crystals were obtained
in toluene at −35 °C after 1 day. Anal. Calcd for C40H62N4Zn2 (1): C,
65.84; H, 8.56; N, 7.68. Found: C, 66.03; H, 8.73; N, 7.71.
Synthesis of [LZn2(OBn)2]·C6H14 (2·C6H14). Compound 1
(0.589 g, 0.81 mmol) was dissolved in THF (2 mL), and then
BnOH (0.18 g 1.66 mmol) was added. The mixture was stirred at
room temperature for 12 h. Volatiles were removed under vacuum to
give a white powder. Yield: 0.687 g (96.0%). Block-shaped colorless
crystals were obtained in hexane at −35 °C overnight. Anal. Calcd for
C50H66N4O2Zn2 (2): C, 67.79; H, 7.51; N, 6.32. Found: C, 67.74; H,
7.58; N, 6.23.
Mechanistic studies on the borylation of aryl iodides
catalyzed by zinc β-diketiminate complexes are ongoing. On
consideration that the borylation of 1-iodo-4-methoxybenzene
(5a) by B2Pin2 proceeded extremely quickly, affording 6a in
82% yield within 15 min, and the reaction was completed in 3
h (>99% NMR yield; Table 2, entry 1), we speculated that the
radical mechanism is plausible for this transformation.47 Thus,
we conducted several reactions by adding radical scavengers.
For the borylation reaction of 5a, under the conditions given
in Table 2, entry 1, the yield of 6a decreased from 82% to 50%
when ethene-1,1-diyldibenzene (2 equiv) was added as a
radical scavenger (Figure S36). The products 6a,f,l were not
afforded (0% yields) when TEMPO (2 equiv) was added to
the borylation reaction systems of 5a,f,l (Figures S37−S39),
respectively. These results revealed the involvement of the
radicals in the borylation transformation.
Synthesis of [LZn2(OnBu)2] (3). Compound 1 (0.124 g, 0.17
n
mmol) was dissolved in THF (2 mL), and then BuOH (0.0375 g,
0.51 mmol) was added. The mixture was stirred at room temperature
for 12 h. Volatiles were removed under vacuum to give a white
powder. Yield: 0.133 (97%). Block-shaped colorless crystals were
obtained in hexane at −35 °C overnight. Anal. Calcd for
C44H70N4O2Zn2 (3): C, 64.62; H, 8.63; N, 6.85. Found: C, 64.58;
H, 8.81; N, 6.85.
Another pathway is that the metathesis between borylzincate
and aryl iodides50 might occur independently. We have
endeavored to synthesize a borylzincate by the stoichiometric
reaction of complex 1, KOEt, and B2Pin2. A mixture with black
precipitates was obtained. Unfortunately, our many attempts to
characterize the black precipitates failed, due to their poor
solubility or the instability of a Zn−B bond.50 Studies on this
pathway are underway.
Synthesis of [LZn2I2(THF)2]·2THF (4·2THF). Compound 1
(0.125 g, 0.17 mmol) was dissolved in THF (2 mL), and then a
solution of I2 (0.104 g, 0.41 mmol) in THF was added. The mixture
was stirred at room temperature for 15 h. The solvent and excess
iodine were removed under vacuum to give an orange powder.
Orange crystals were obtained in THF at −35 °C overnight. Yield:
0.117 g (63.9%). Anal. Calcd for C44H68N4O2I2Zn2 (4): C, 49.41; H,
6.41; N, 5.24. Found: C, 49.28; H, 6.38; N, 5.21.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00733.
■
CONCLUSIONS
■
sı
The use of a flexible dinucleating bis(β-diketiminate) ligand
with an ethylene bridge allowed the synthesis of the series of
zinc diketiminate complexes [LZn2Et2] (1), [LZn2(OBn)2]·
C6H14 (2·C6H14), [LZn2(OnBu)2] (3), and [LZn2I2(THF)2]·
2THF (4·2THF), which were facile catalysts for the borylation
of aryl iodides with B2Pin2. Borylation reactions catalyzed by 1
were thoroughly investigated. Electronically and sterically
Crystal data and data collection details for compounds 1,
2·C6H14, 3, and 4·2THF, details of experimental
procedures, and 1H and 13C NMR spectra of the
compounds and products (PDF)
486
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Organometallics 2021, 40, 482−489

Organometallics
pubs.acs.org/Organometallics
Article
Polymerization of O-Carboxyanhydrides. Nat. Commun. 2018, 9, 1−
10.
Accession Codes
CCDC 2009130−2009131, 2009146, and 2042443−2042444
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.ca-
m.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.
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Carbene Complexes: Synthesis, Structural Diversity, Intramolecular
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AUTHOR INFORMATION
■
̈
(7) Schulz, S.; Eisenmann, T.; Schmidt, S.; Blaser, D.; Westphal, U.;
Corresponding Author
Boese, R. Reactions of a β-diketiminate Zinc Hydride Complex with
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Yahong Li − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China; orcid.org/0000-0002-6467-
0607; Email: liyahong@suda.edu.cn
Authors
Yafei Li − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Yan Dang − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Dawei Li − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Huifen Pan − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Liang Zhang − College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Li Wang − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
Zhu Cao − College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
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Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00733
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors appreciate financial support from the Natural
Science Foundation of China (21772140), the Natural Science
Foundation of Jiangsu Province of China (BK20171213), a
Project Funded by the Priority Academic Program Develop-
ment of Jiangsu Higher Education Institution, and the project
of scientific and technologic infrastructure of Suzhou
(SZS201708).
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