Heteroleptic Ni(II) Complexes Bearing a Bulky Yet Flexible IBiox-6 Ligand: Improved Selectivity in Cross-Electrophile Coupling of Benzyl Chlorides with Aryl Chlorides/Fluorides

Article abstract of DOI:10.1021/acs.organomet.0c00515

A bisoxazoline-derived NHC known as IBiox-6 reacted smoothly with Ni[P(OEt)3]2Br2 and Ni(PPh3)2Br2 to give the respective heteroleptic Ni(II) complexes Ni(IBiox-6)[P(OEt)3]Br2 (1) and Ni(IBiox-6)(PPh3)Br2 (2) in yields of 60% and 71%. Their crystal structures were characterized to reveal a rare cis disposition of the IBiox-6 ligand to the phosphite ligand in 1, while 2 possessed the more common trans configuration. Both complexes catalyzed the cross-electrophile coupling of benzyl chlorides with aryl chlorides and fluorides in the presence of Mg turnings at 50 °C via a "real one-pot"procedure, featuring no requirement for temperature variation or portionwise addition of any coupling partner. In particular, complex 1 showed a better balance between the catalytic activity and selectivity. The scope of the procedure catalyzed by 1 and Mg turnings was investigated, providing a highly selective, simple, and practical approach to the synthesis of diarylmethanes with high steric hindrance and various functional groups, including oligo-diarylmethane with asymmetric structures.

Full text of DOI:10.1021/acs.organomet.0c00515

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Article
Heteroleptic Ni(II) Complexes Bearing a Bulky Yet Flexible IBiox‑6
Ligand: Improved Selectivity in Cross-Electrophile Coupling of
Benzyl Chlorides with Aryl Chlorides/Fluorides
Zheng-Wang Shen, Die-Die Meng, Sajid Imran, Chun-Hui Yan, and Hong-Mei Sun*
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ABSTRACT: A bisoxazoline-derived NHC known as IBiox-6 reacted smoothly with
Ni[P(OEt)3]2Br2 and Ni(PPh3)2Br2 to give the respective heteroleptic Ni(II)
complexes Ni(IBiox-6)[P(OEt)3]Br2 (1) and Ni(IBiox-6)(PPh3)Br2 (2) in yields of
60% and 71%. Their crystal structures were characterized to reveal a rare cis disposition
of the IBiox-6 ligand to the phosphite ligand in 1, while 2 possessed the more common
trans configuration. Both complexes catalyzed the cross-electrophile coupling of benzyl
chlorides with aryl chlorides and fluorides in the presence of Mg turnings at 50 °C via a
“real one-pot” procedure, featuring no requirement for temperature variation or
portionwise addition of any coupling partner. In particular, complex 1 showed a better
balance between the catalytic activity and selectivity. The scope of the procedure
catalyzed by 1 and Mg turnings was investigated, providing a highly selective, simple, and practical approach to the synthesis of
diarylmethanes with high steric hindrance and various functional groups, including oligo-diarylmethane with asymmetric structures.
Scheme 1. Typical Bulky Yet Flexible NHCs
INTRODUCTION
■
Over the past decade interest in the development of nickel
catalysts for various cross-coupling reactions has continued to
grow rapidly. This research has been inspired by the recent
push for the development of non-precious-metal catalysts and
the potential of nickel catalysts in many valuable and difficult
transformations.1 So far, N-heterocyclic carbenes (NHCs)
have been found to be especially valuable ligands2 to design
active nickel catalysts, and they can be more efficient than
palladium-based systems for certain cross-coupling reactions.3
On the basis of mechanistic studies, sterically hindered NHCs
have been intensively investigated because they promote the
reductive elimination step and coordinatively stabilize
unsaturated low-valent catalytic species. However, such steric
hindrance around the metal center can disfavor the approach
of the coupling substrate, which might inhibit the oxidative
addition step and then the transmetalation step. This inherent
limitation may be partially addressed by a new generation of
sterically hindered NHCs endowed with some flexibility (so-
called bulky yet flexible NHCs), which could adjust their steric
bulk toward incoming substrates while fulfilling the require-
ments of a defined catalytic transformation.4
coordinate Ni(0) cmplex Ni(IPr*)(η6-C7H8) with exceptional
reactivity.6 Since then, a variety of well-defined nickel
complexes bearing a bulky yet flexible NHC ligand have
been reported by Nolan,7 Nakao, Hartwig,8 Schomaker,9
Chetcuti, Ritleng,10 Montgomery,11 and our group,12d,e in
some cases affording improved catalytic performances for
Buchwald−Hartwig arylamination and related sulfination,
carboxylation of organoboronates with CO2, and cross-
coupling of methyl esters with amines. Nevertheless, the
study of their application in nickel catalysis is still in its infancy.
Somewhat to our surprise, the family of bis-oxazoline-derived
Following significant success in palladium-catalyzed cross-
coupling reactions,5 several kinds of bulky yet flexible NHCs,
such as IPr*-type ligands (Scheme 1, A),4c ITent-type ligands
(Scheme 1, B),4d and cyclic alkylaminocarbenes (CAACs,
Scheme 1, C),4b have been used to develop nickel catalysts. In
this context, the initial publication in 2011 by Hillhouse and
co-workers showed that 1,3-bis(2,6-bis(diphenylmethyl)-4-
methylphenyl)imidazol-2-ylidene (IPr*) could form the two-
Received: July 30, 2020
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NHCs (IBiox-type ligands, i.e. IBiox-6, Scheme 1, D), in which
the concept of “bulky yet flexible NHCs” was first proposed by
Glorius in 2003,4a still remains unexplored in the design of
well-defined catalytic nickel complexes. In fact, IBiox-type
ligands have been intensively investigated in palladium-
catalyzed cross-coupling reactions5 because their flexibility
can be easily achieved by rapid conformational conversion of
cycloalkyl rings while their steric rigidity comes from the
tricyclic backbone.4a
In recent years, nickel-catalyzed cross-electrophile couplings
between two electrophiles have evolved to be an interesting
method to forge C(sp2)−C(sp3) bonds, in which nickel
catalysts display significantly better catalytic performances in
comparison to palladium-based systems.13 Whereas good to
excellent selectivity has been achieved when two organic
bromides and/or iodides were used as coupling partners, the
cross-electrophile coupling between two organic chlorides
remains challenging, and it has not been reported until
recently.14 In this context, the difficulty in the cross-
electrophile coupling of aryl chlorides with alkyl chlorides
lies in meeting the dual reactivity−selectivity requirements;
that is, the nickel catalyst should be capable of oxidative
addition of aryl chlorides, while it inhibits the homocoupling or
dehalogenation of any coupling partner.14b Therefore, we
hypothesized that the use of an IBiox-type ligand (i.e., IBiox-6)
might provide a promising alternative to overcome this
difficulty, because its adaptability could tune the coordination
environment of the metal center to afford nickel catalysts with
high activity and selectivity.
The complex containing P(OEt)3 was more stable, with
coloration still observed after exposure to air for 1 day.
Nevertheless, the stabilities of 1 and 2 were slightly lower than
12d
those of the previously reported Ni(IPr*OMe)[P(OEt)3]Br2
and Ni(IPr*)(PPh3)Br2.12e
The structures of 1 and 2 were initially characterized by
1
elemental analysis and NMR spectroscopy. H NMR spectra
showed characteristic signals similar to those of the free IBiox-
6 ligand, indicating the presence of the carbene ligand in 1 and
2. The coordination of the carbene ligand to nickel was further
supported by the 13C NMR spectra, wherein the carbene
carbon was observed as a doublet at δ 156.5 (JC−P = 203.5 Hz)
for 1 and δ 161.7 (JC−P = 457.3 Hz)15 for 2. Moreover, a
downfield shift of ca. Δδ 5.2 observed for the carbene carbon
in 1 with respect to that of 2 reflects the lower electron density
on the carbene carbon, which is possibly related to the stronger
π-electron acceptance of the P(OEt)3 ligand in comparison
with the PPh3 ligand.15 In this regard, the room-temperature
31P NMR signal of P(OEt)3 ligand in 1, which appeared as a
sharp singlet at δ 99.1, was shifted upfield in comparison with
the corresponding free phosphite ligand (δ 138.7). For the
phosphine ligand, the 31P NMR signal of PPh3 in 2 was shifted
downfield relative to the free phosphine ligand (δ −6.0) and
was observed at δ 17.1 as a sharp singlet. When the recording
temperature was lowered to −30 °C, an additional small singlet
appeared in each 31P NMR spectrum, with chemical shifts of δ
94.0 for 1 and δ 20.7 for 2, which indicated that 1 and 2 are
probably the trans and cis isomers in solution, wherein the
rotation of the Ni−P bond seemed to be hindered as the
temperature was decreased.16
On the basis of our studies on the design and catalytic
applications of well-defined heteroleptic Ni(II) complexes of
NHCs,12 we herein report the preparation and molecular
structure of the first heteroleptic Ni(II) complexes containing
an IBiox-type ligand (1 and 2). The preliminary investigation
of their catalytic performances for the cross-electrophile
coupling of benzyl chlorides with aryl chlorides or less reactive
aryl fluorides in the presence of Mg turnings are also described.
Structural Description. The molecular structures of
complexes 1 and 2 were unambiguously established by X-ray
crystallography (Figure 1). Notably, the crystal structures of 1
RESULTS AND DISCUSSION
■
Synthesis and Characterization. To date, well-defined
metal complexes containing an IBiox-type ligand remain less
developed in comparison to their direct use as added ligands in
transition-metal-based catalysis.5
Figure 1. Molecular structures of 1 (left) and 2 (right) with thermal
ellipsoids at the 30% probability level. Hydrogen atoms are omitted
for clarity.
At the outset of the present work, we wondered if previously
reported substitution reactions12b,d would be suitable for the
synthesis of the target Ni(II) complexes 1 and 2. Fortunately,
as shown in Scheme 2, when a THF solution of in situ
and 2 were significantly different from each other, with an
unexpected cis configuration observed in 1, while 2 featured a
common trans configuration.9,12b,e,16 To the best of our
knowledge, complex 1 is the first example of a heteroleptic
NHC Ni(II) complex adopting a cis configuration stabilized by
monodentate ligands, whereas previously reported Ni(II)
analogues such as Ni(IMes)[P(OEt)3]Br2 (IMes = 1,3-
bis(mesityl)imidazol-2-ylidene) and Ni(IPr*OMe)[P(OEt)3]Br2
still exhibited a trans configuration of the two kinds of
ligands.12d As shown in Figure 1, the molecular structures of 1
and 2 show the nickel centers supported by an IBiox ligand, a
phosphorus-based ligand, and two bromide atoms with a
slightly distorted square-planar geometry. The nickel atom in 1
features the IBiox-6 ligand in a cis configuration to the P(OEt)3
ligand (C(1)−Ni(1)−P(1) = 92.0(2)°), while 2 shows a trans
C(1)−Ni−P(1) angle equal to 175.9(2)°. The Ni−Ccarbene
Scheme 2. Synthesis of Complexes 1 and 2
generated IBiox-6 was added to a THF solution of readily
available Ni[P(OEt)3]2Br2 at room temperature, a gradual
color change from dark purple to orange was observed, and the
desired Ni(II) complex Ni(IBiox-6)[P(OEt)3]Br2 (1) was
isolated as an orange solid in 60% yield. A similar reaction with
Ni(PPh3)2Br2 gave rise to Ni(IBiox-6)(PPh3)Br2 (2) as a pink
solid in 71% yield. Both complexes are heat- and air-stable in
the solid state. However, their solutions are still sensitive to air.
B
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bond length of 1.880(6) Å in 1 is slightly shorter than that in 2
(1.882(5) Å), while the Ni−P bond in 1 is obviously shorter
Table 1. Nickel-Catalyzed Cross-Electrophile Coupling of
C6H5X with 4-CH3C6H5CH2Cl
a
than that in 2 (2.133(2) Å vs 2.257(2) Å). These data fall
12d
between the values found for Ni(NHC)[P(OR)3]Br2
and
Ni(NHC)(PR3)Br2.9,12b,e,16 Similarly, Cazin found that the
Pd(II) analogue Pd(NHC)[P(OR)3]Cl2 had a shorter Pd−P
bond length in the presence of the phosphite ligand with better
π acidity.15 In addition, the presence of the phosphite ligand
led to longer Ni−Br bond lengths (2.334(1) and 2.348(1) Å in
1 vs 2.3177(9) and 2.3072(9) Å in 2). On the other hand, data
obtained with a percent buried volume (%VBur) model17
disclosed the smaller steric hindrance of IBiox-6 in comparison
to IMes and IPr*OMe (33.5% VBur for 1 vs 34.9%VBur for
Ni(IMes)[P(OEt)3]Br2 and 40.2%VBur for Ni(IPr*OMe)[P-
(OEt)3]Br212d). Therefore, the rare cis configuration of
complex 1 may be the result of the interaction between the
flexibility of the IBiox-6 ligand and the π acidity of the
phosphite ligand.
Catalytic Behaviors. Our previous work on Ni(II)-
catalyzed cross-electrophile coupling has shown that hetero-
leptic Ni(II) complexes (i.e., Ni(IPr)(PPh3)Br2 (IPr = 1,3-
bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and Ni(IPr*)-
(PPh3)Br2) efficiently catalyzed the Mg-mediated cross-
electrophile coupling of benzyl chlorides with aryl chlorides
in a one-pot procedure, wherein the reaction needs to be
conducted step by step at two different temperatures to avoid
the formation of bibenzyl byproducts.12c,d To compare the
catalytic performances of 1 and 2 directly with those of
reported Ni(II) analogues, we selected the cross-electrophile
coupling of 3a and 4a as the benchmark reaction. Under the
conditions that were employed previously, initial experiments
showed that both 1 and 2 could afford the desired product 5aa
in almost quantitative yield, and the homocoupling byproduct
6aa was observed in only 3% yield (Table 1, runs 1 and 2).
Inspired by this result, we decided to test whether 1 and 2 have
better selectivity so that the benchmark reaction could proceed
smoothly without temperature variation when both chlorides
were added in one portion: that is, to achieve cross-electrophile
coupling via a “real one-pot” process.
Interestingly, high selectivity was still achieved with
complexes 1 and 2 after optimizing the conditions, wherein
the desired product 5aa was obtained in 99% and 98% yields,
respectively, at 50 °C with a 1 mol % loading (Table 1, runs 3
and 4). Between them, complex 1 showed a better catalytic
performance in comparison to complex 2 (Table 1, runs 5 and
6). Under the optimized conditions, the previously reported
Ni(II) analogues exhibited relatively poor selectivity, affording
5aa in yields ranging from 58% to 65%, accompanied by the
formation of considerable yields of bibenzyl byproduct 6aa
(Table 1, runs 7−9). In comparison, the heteroleptic Ni(II)-
based system showed catalytic performance superior to that of
the corresponding homoleptic system (Table 1, runs 10−12),
which indicates a significant synergic effect between the IBiox-
6 ligand and the phosphite ligand in the catalytic process.
Somewhat to our surprise, the replacement of Mg turnings
with Mn powder or Zn dust resulted in almost no formation of
5aa (Table 1, runs 13 and 14). Notably, 1 also showed high
activity toward less reactive aryl fluorides, i.e. benzene fluoride,
to afford the desired product in 96% yield with a longer
reaction time of 12 h (Table 1, run 15), while the same trend
in catalytic activity, i.e. 1 > 2, was observed in turn (Table 1,
run 16). Therefore, these results showed that the use of IBiox-
6 can improve the selectivity, achieving a significant advance in
T (°C)/
run
1
X
[Ni]/(mol %)
t (h)
5aa/6aa (%)
b
Cl 1/1.0
0/0.2;
50/1.0
0/0.2;
50/1.0
99 (94 )/3
2
Cl 2/1.0
99/3
3
4
5
6
7
8
9
10
Cl 1/1.0
Cl 1/0.5
Cl 2/1.0
Cl 2/0.5
Cl Ni(IPr)(PPh3)Br2/1.0
Cl Ni(IPr*)(PPh3)Br2/1.0
Cl Ni(IPr*OMe)(PPh3)Br2/1.0
50/1.0
99/3
90/8
98/3
46/23
64/32
65/29
58/23
89/4
50/1.0
50/1.0
50/1.0
50/1.0
50/1.0
50/1.0
50/1.0
Cl Ni(DME)Br2/IBiox-6/P(OEt)3
(1.0/1.0/1.0)
11
12
Cl Ni(DME)Br2/IBiox-6 (1.0/2.0) 50/1.0
Cl Ni(DME)Br2/P(OEt)3 (1.0/2.0) 50/1.0
51/16
8/35
∼0/0
∼0/2
96/3
66/5
c
13
d
Cl 1/1.0
Cl 1/1.0
F
F
50/1.0
50/1.0
50/12
50/12
14
15
16
1/2.0
2/2.0
a
Reaction conditions unless stated otherwise: 3a (0.5 mmol), 4a (0.6
mmol), Mg turnings (0.6 mmol), THF (1 mL), under Ar, GC yields
using n-dodecane as an internal standard. Isolated yield. Mn powder
b
c
d
in place of Mg turnings. Zn dust in place of Mg turnings.
the balance between catalytic activity and selectivity. Complex
1 and Mg turnings is a simple yet efficient combination in
catalyzing the coupling of benzyl chloride with benzene
chloride via a “real one-pot” process.
Next, the process scope of 1 with a variety of coupling
partners was investigated in the presence of Mg turnings. As
shown in Scheme 3, both electron-rich and electron-poor
coupling partners were compatible, furnishing diarylmethanes
5ba−ga in yields ranging from 53 to 97%, wherein fluorinated
diarylmethanes (5ca,da,db,fa,ga) could be obtained via
selective activation of the C(sp2)−Cl bond. An remarkable
feature of the action of complex 1 was its high tolerance of
steric hindrance, even when it was exhibited by both coupling
partners, providing an efficient approach to forming di-ortho-
substituted (5ha,ia,bd,dd,de,je), tri-ortho-substituted (5ke),
and even tetra-ortho-substituted (5hd,id) diarylmethanes,
which have seldom been reported elsewhere.14b In comparison
with Ni(IPr*)(PPh3)Br2 reported previously, complex 1
showed a better tolerance of steric hindrance by producing
the sterically demanding product 5id in 58% yield under the
enhanced conditions, whereas no desired product was obtained
with Ni(IPr*)(PPh3)Br2. Sterically bulky 2-chloronaphthalene,
its fluoro analogue, and 9-chloroanthracene were also suitable
reactants (5la,ld,ma). This outstanding tolerance to steric
hindrance of complex 1 is likely caused by its higher flexibility
in comparison to that found in other NHC ligands, such as
IPr*.7 Notably, a variety of functional groups such as ester
(5na), ketone (5oa), amine (5pa), ketal (5qa,ra), and several
heterocyclic rings (5sa−aaa) on the coupling partners were
preserved. Moreover, the effective structural unit in antineo-
plastic agents (5abb) and the precursor of naturally occurring
polyphenols (5acb) were obtained in yields of 89% and 83%,
C
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respectively. A gram-scale reaction between 3d and 4b still
afforded the desired product 5db in 92% yield.
Scheme 3. Substrate Scope of Cross-Electrophile Coupling
Catalyzed by 1
a
In view of the significant difference of complex 1 in the
activation of C(sp2)−Cl and C(sp2)−F bonds, oligo-diaryl-
methanes with asymmetric structures in the para (7a), meta
(7b), and ortho (7c) positions were constructed via selective
activation of the C(sp2)−Cl bond and the C(sp2)−F bond
(Scheme 4), further demonstrating the utility potential of the
IBiox-6 ligand in the design of Ni(II)-based catalysts with high
selectivity.
Scheme 4. Selective Activation of Aryl Chlorides or
Fluorides by 1
a
Reaction conditions unless stated otherwise: THF (1 mL), 50 °C, 1
b
h, under Ar, isolated yield. 60 °C.
On the basis of others’13 and our own proposed mechanism
reported previously,12b,e and experiments presented in the
Supporting Information, we suggest that the current reaction
proceeds via an initial in situ generation of a benzyl Grignard
reagent, which then couples with an aryl chloride catalyzed by
1 through a catalytic cycle involving oxidative addition of an
aryl chloride, transmetalation of the benzyl Grignard reagent,
reductive elimination to form the desired product, and
regeneration of the low-valent nickel species. Relevant
comparative experiments showed the presence of a strong
synergistic effect between the IBiox-6 ligand and a phosphite
ligand on the catalytic nickel species. In addition, a free-radical
chain mechanism is also possible because the reaction did not
proceed when TEMPO was added (see the Supporting
Information).
CONCLUSION
■
This work provides the first example of heteroleptic Ni(II)
complexes containing an IBiox-type ligand. It has been
demonstrated that well-defined heteroleptic Ni(II) complexes
1 and 2 can be used as robust precatalysts for the cross-
electrophile coupling of benzyl chlorides with aryl chlorides/
fluorides in the presence of stoichiometric amounts of Mg
turnings. This method provides a “real one-pot” route for the
synthesis of a variety of diarylmethanes. The present study
shows that IBiox-type ligands, such as IBiox-6, can significantly
improve the selectivity of catalytic Ni(II) complexes and thus
have great potential for the development of nickel catalysts
with a promising balance between catalytic activity and
selectivity. Further studies currently underway in our
laboratory are directed toward fine-tuning the catalytic
performances of well-defined heteroleptic Ni(II) complexes
by surveying other NHC-based pairs and a detailed
mechanistic investigation.
a
Reaction conditions unless stated otherwise: 3 (0.5 mmol), 4 (0.6
mmol), 1 (1 mol %), Mg turnings (0.6 mol), THF (1 mL), 50 °C, 1
h, under Ar, isolated yield. 1 (2 mol %), 12 h. Four hours. 1 (2 mol
%). 60 °C. Eight hours. Twenty hours. 1 (5 mol %), 24 h. 4 (0.7
mmol), Mg turnings (0.75 mmol), ZnCl2 (0.7 mmol), LiCl (0.8
mmol), THF (2.5 mL), 60 °C, 24 h. 4 (1.2 mmol), Mg turnings (1.2
mmol), THF (2 mL). Six hours.
b
c
d
e
f
g
h
i
k
j
D
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acetate/petroleum ether (0/100 to 1/5) as eluent to give the target
product.
EXPERIMENTAL SECTION
■
General Experimental Procedures. Unless mentioned other-
wise, all manipulations were performed using standard Schlenk
techniques or in an N2-filled glovebox. Solvents were distilled from
Na/benzophenone under pure argon prior to use. Ni[P(OEt)3]2Br,18
General Procedure for Cross-Electrophile Coupling Reac-
tions of Benzyl Chlorides with Aryl Fluorides. In a typical
example, a 10 mL oven-dried Schlenk tube with a stir bar was charged
with complex 1 (0.01 mmol), magnesium turnings (0.6 mmol), aryl
fluorides (0.5 mmol), and THF (1.0 mL) in the glovebox. To this
stirred mixture were added benzyl chlorides (0.6 mmol) by syringe at
50 °C. The mixture was stirred for 12 h at 50 °C. After the mixture
was cooled to room temperature, the reaction was quenched by the
addition of saturated NH4Cl(aq) and then the resulting mixture was
extracted with ethyl acetate (3 × 5 mL), dried over anhydrous
Na2SO4, filtered, and concentrated. The GC yields of the target
product and byproduct were determined using GC analysis, with n-
dodecane as an internal standard. The crude mixture was purified by
column chromatography on silica gel (300−400 mesh) using ethyl
acetate/petroleum ether (0/100 to 1/5) as eluent to give the target
product.
Ni(PPh3)2Br2,19 IBiox-6,4a Ni(IPr)(PPh3)Br2,12b Ni(IPr*)(PPh3)-
Br2,12e and Ni(IPr*OMe)[P(OEt)3]Br2
were prepared according
12d
to published methods. Other commercially available reagents were
purchased from Acros, Sigma-Aldrich, and Alfa Aesar Chemical
Company. NMR spectra were measured on a Bruker AVANCE III
HD spectrometer at 25 °C. Carbon, hydrogen, and nitrogen analysis
was performed by direct combustion on a Carlo-Erba EA-1110
instrument. The melting points of complexes 1 and 2 were
determined on SDT 2960 simultaneous DSC-TGA (TA Instruments,
USA) using powder samples under an N2 atmosphere (50 mL/min).
Melting points of diarylmethanes products were measured using
INESA WRR, and values are uncorrected. Gas chromatographic (GC)
analysis was performed on a Thermo Fisher Trace 1300 instrument.
High-resolution mass spectra were obtained using GCT-TOF
instrument with CI source. Electron spin resonance (ESR) spectros-
copy was measured on a JEOL JES-X320 electron spin resonance
spectrometer at 50 °C.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00515.
Ni(IBiox-6)[P(OEt)3]Br2 (1). A Schlenk flask was charged with
Ni[P(OEt)3]2Br2 (0.6600 g, 1.2 mmol), dry THF (15 mL), and a stir
bar. To this solution was added IBiox-6 (0.3456 g, 1.2 mmol) in dry
THF (15 mL) at room temperature. The mixture turned orange
immediately. The solution was then stirred for 3 h at room
temperature. Volatiles were removed in vacuo. The residue was
washed with hexane (3 × 10 mL), extracted with toluene (3 × 10
mL), and crystallized from a concentrated toluene/hexane solution at
0 °C. The product precipitated as orange crystals in a yield of 60%
Supplementary characterization data for 1 and 2,
detailed experimental procedures for the mechanism
study, and details pertaining to the characterization of
the products (PDF)
Accession Codes
CCDC 2015126 and 2015129 contain 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
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
(0.4844 g). Mp: 188−189 °C dec. H NMR (400 MHz, C6D6): δ
4.20 (s, 4H), 4.09−3.82 (m, 6H), 3.04 (s, 1H), 2.21 (s, 3H), 1.90−
0.50 (m, 25H). 13C NMR (101 MHz, C6D6): δ 156.5 (d, J = 203.5
Hz), 124.6, 114.4, 85.4, 83.5, 67.0, 65.4, 63.5, 35.4, 34.2, 24.6, 23.9,
23.4, 22.9, 15.9. 31P NMR (162 MHz, C6D6): δ 99.1. Anal. Calcd for
C23H39N2O5PNiBr2: C, 41.06; H, 5.84; N, 4.16. Found: C, 41.44; H,
6.21; N, 4.01.
AUTHOR INFORMATION
Corresponding Author
■
Ni(IBiox-6)(PPh3)Br2 (2). A Schlenk flask was charged with
Ni(PPh3)2Br2 (0.8916 g, 1.2 mmol), dry THF (15 mL), and a stir bar.
To this solution was added IBiox-6 (0.3456 g, 1.2 mmol) in dry THF
(15 mL) at room temperature. The mixture turned dark red
immediately. The solution was then stirred for 2 h at room
temperature. Volatiles were removed in vacuo. The residue was
washed with hexane (2 × 5 mL), extracted with toluene (3 × 10 mL),
and crystallized from concentrated toluene solution at 0 °C. The
product was as pink crystals in a yield of 71% (0.6550 g). Mp: 141−
Hong-Mei Sun − The Key Laboratory of Organic Synthesis of
Jiangsu Province, College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou, Jiangsu
215123, People’s Republic of China; orcid.org/0000-0003-
3400-7991; Email: sunhm@suda.edu.cn
Authors
1
Zheng-Wang Shen − The Key Laboratory of Organic Synthesis
of Jiangsu Province, College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou, Jiangsu
215123, People’s Republic of China
Die-Die Meng − The Key Laboratory of Organic Synthesis of
Jiangsu Province, College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou, Jiangsu
215123, People’s Republic of China
Sajid Imran − The Key Laboratory of Organic Synthesis of
Jiangsu Province, College of Chemistry, Chemical Engineering
and Materials Science, Soochow University, Suzhou, Jiangsu
215123, People’s Republic of China
142 °C dec. H NMR (400 MHz, CDCl3): δ 7.82 (s, 6H), 7.40 (s,
9H), 4.59 (s, 4H), 3.69 (s, 4H), 2.08 (s, 8H), 1.95−1.78 (m, 2H),
1.69−1.48 (m, 2H), 1.43−1.20 (m, 4H). 13C NMR (101 MHz,
CDCl3): δ 161.7 (d, J = 457.3 Hz), 134.7 (d, J = 9.4 Hz), 131.6 (d, J
= 42.2 Hz), 129.8, 128.0, 127.9, 83.8, 65.4, 35.4, 25.1, 24.1. 31P NMR
(162 MHz, CDCl3): δ 17.1. Anal. Calcd for C35H39N2O2PNiBr2: C,
54.65; H, 5.11; N, 3.64. Found: C, 54.84; H, 5.42; N, 3.59.
General Procedure for Cross-Electrophile Coupling Reac-
tions of Benzyl Chlorides with Aryl Chlorides. In a typical
example, a 10 mL oven-dried Schlenk tube with a stir bar was charged
with complex 1 (0.005 mmol), magnesium turnings (0.6 mmol), aryl
chlorides (0.5 mmol), and THF (1.0 mL) in the glovebox. To this
stirred mixture was added benzyl chlorides (0.6 mmol) by syringe at
50 °C. The mixture was stirred for 1 h at 50 °C. After the mixture was
cooled to room temperature, the reaction was quenched by the
addition of saturated NH4Cl(aq) and then the resulting mixture was
extracted with ethyl acetate (3 × 5 mL), dried over anhydrous
Na2SO4, filtered, and concentrated. The GC yields of the target
product and byproduct were determined using GC analysis, with n-
dodecane as an internal standard. The crude mixture was purified by
column chromatography on silica gel (300−400 mesh) using ethyl
Chun-Hui Yan − Analysis and Testing Center, Soochow
University, Suzhou, Jiangsu 215123, People’s Republic of China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00515
Notes
The authors declare no competing financial interest.
E
https://dx.doi.org/10.1021/acs.organomet.0c00515
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Markovnikov-Selective Hydroboration of Styrenes. Organometallics
2016, 35, 3436−3439.
ACKNOWLEDGMENTS
■
We are grateful to the National Natural Science Foundation of
China (Grants 21971183), the Natural Science Foundation of
the Jiangsu Higher Education Institutions of China
(19KJA610001), and the Key Laboratory of Organic
Chemistry of Jiangsu Province for financial support.
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Defined Nickel(0) Catalysts for Catalytic C−-C and C−N Bond
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Organometallics XXXX, XXX, XXX−XXX