Reactivity of mixed organozinc and mixed organocopper reagents: 14. Phosphine-nickel catalyzed aryl-allyl coupling of (n-butyl)(aryl)zincs. Ligand and substrate control on the group selectivity and regioselectivity

Article abstract of DOI:10.1016/j.jorganchem.2016.05.014

The group selectivity and regioselectivity in the allylation of mixed (n-butyl)(aryl)zinc reagents in THF depends on the nickel catalyst type and also on nature of the allylic substrate. Allylation of (n-butyl)(phenyl)zinc reagent with alkyl substituted primary allylic chlorides and acetates in the presence of NiCl₂(dppf) catalysis affords the phenyl coupling product with γ-selectivity. However, allylation with aryl substituted primary allylic substrates results in both phenyl- and alkyl-coupling products with medium α-selectivity in the presence of NiCl₂(dppf) catalysis whereas phenyl coupling product is formed with α-selectivity in the presence of NiCl₂(Ph₃P)₂ catalysis. This new NiCl₂(dppf) catalyzed protocol for γ-selective aryl allylation of (n-butyl)(aryl)zinc reagents with alkyl substituted primary allylic chlorides in THF at room temperature provides an atom economic alternative to allylation of (aryl)₂Zn reagents. A mechanism for the dependence of group selectivity and regioselectivity of Ni catalyzed allylation of (n-butyl)(aryl)zinc reagents on the catalyst ligand and the substrate was proposed.

Full text of DOI:10.1016/j.jorganchem.2016.05.014

Journal of Organometallic Chemistry 818 (2016) 28e36
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactivity of mixed organozinc and mixed organocopper reagents: 14.
Phosphine-nickel catalyzed aryl-allyl coupling of (n-butyl)(aryl)zincs.
Ligand and substrate control on the group selectivity and
regioselectivity
Melike Kalkan, Ender Erdik*
Ankara University, Science Faculty, Bes¸evler, Ankara 06100, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The group selectivity and regioselectivity in the allylation of mixed (n-butyl)(aryl)zinc reagents in THF
depends on the nickel catalyst type and also on nature of the allylic substrate. Allylation of (n-butyl)(-
phenyl)zinc reagent with alkyl substituted primary allylic chlorides and acetates in the presence of
Received 25 December 2015
Received in revised form
12 May 2016
Accepted 18 May 2016
Available online 24 May 2016
NiCl2(dppf) catalysis affords the phenyl coupling product with
substituted primary allylic substrates results in both phenyl- and alkyl-coupling products with medium
-selectivity in the presence of NiCl2(dppf) catalysis whereas phenyl coupling product is formed with
selectivity in the presence of NiCl2(Ph3P)2 catalysis. This new NiCl2(dppf) catalyzed protocol for -se-
g-selectivity. However, allylation with aryl
a
a-
g
Keywords:
lective aryl allylation of (n-butyl)(aryl)zinc reagents with alkyl substituted primary allylic chlorides in
THF at room temperature provides an atom economic alternative to allylation of (aryl)2Zn reagents. A
mechanism for the dependence of group selectivity and regioselectivity of Ni catalyzed allylation of (n-
butyl)(aryl)zinc reagents on the catalyst ligand and the substrate was proposed.
© 2016 Elsevier B.V. All rights reserved.
(Alkyl)(aryl)zincs
Mixed diorganozincs
Allylation
Ni catalyst
Regioselectivity
Group selectivity
1. Introduction
also developed to use instead of homo diorganocuprates [28,29].
For the group selectivity of mixed cuprates, R1R2CuLi the widely
Transition metal catalyzed coupling of organozinc reagents with
carbon electrophiles are among the most valuable methodologies
in organic synthesis [1e3]. Organozinc reagents RZnX and R2Zn
have proved to be intensively useful due to their easy preparation,
high reactivity and functional group tolerance. Diorganozincs, R2Zn
are more reactive than monoorganozincs, RZnX. However, the use
of R2Zn reagents are not atom-economic, since only one of the R
groups can be transferred to the electrophile. The problem has been
solved by developing mixed diorganozincs, R1R2Zn type, in which
one of the R groups has a lower transfer rate than the other [4e18],
and recently RRRTZn type, composed of one transferable group, RT
together with the residual group, RR with almost no transfer
[19,20]. RRRTZn reagents have been mostly used in 1,2-addition
[19e22] and 1,4-addition reactions [23e26], but their CeC
coupling reactions are quite limited [27].
accepted hypothesis is that the group with a stronger CeCu bond
acts as the group of lower selectivity, i.e. better residual group
[28e31]. Theoretical studies on the control of group selectivity have
been reported by Nakamura [32,33] and experimental studies on
the effects of organyl groups on the reactivity and selectivity of
mixed cuprates have been reported by Bertz [34] and Nakamura
[35].
Our group carried out a series of synthetic and mechanistic work
[36e40] on the reactivity and group selectivity of mixed dio-
rganozincs, R1R2Zn [36]; mixed diorganocuprates, R1R2CuM
(M
¼
MgBr [37], ZnCl [38]) and Cu catalyzed mixed tri-
organozincates, R1(R2)2ZnMgBr [38] in their CeC [36], C-COR [39],
C-COOR [38] and CeN coupling [40] reactions. We showed that the
group selectivity of both mixed diorganocuprates and dio-
rganozincs can be controlled by changing reaction parameters, i.e.
the solvent and the temperature as well as the transition metal
catalyst and the organocatalyst.
Mixed diorganocuprates, RRRTCuM (M ¼ Li, MgBr) have been
Recently, we have studied on the allylation of mixed (n-alky-
l)(aryl)zinc reagents with the aim of controlling not only the group
selectivity, but also the regioselectivity by changing the reaction
* Corresponding author.
E-mail address: erdik@science.ankara.edu.tr (E. Erdik).
http://dx.doi.org/10.1016/j.jorganchem.2016.05.014
0022-328X/© 2016 Elsevier B.V. All rights reserved.

M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
29
parameters [36]. Transition metal catalyzed allylic coupling of
Grignard, organolithium and organozinc reagents are very useful
reactions in organic synthesis [41]. Over the past decade, investi-
gation of their regiochemistry and stereochemistry have attracted
In the Ni catalyzed allylation of diorganozincs, we selected (n-
alkyl)(aryl)zincs for the following reasons: (i) To control the group
selectivity and the regioselectivity in the allylic coupling of n-alkyl
and aryl groups on the same reagent, (ii) To find atom-economic
routes for regioselective synthesis of n-alkyl or aryl selective
allylic coupling products, and (iii) To present new reagent/catalyst
systems for catalyst controled regioselective n-alkyl or aryl
coupling of substituted primary allylic substrates.
much attention [42]. Cu catalysis favors
g-selective allylation of
alkylzinc reagents whereas -selective allylation takes place in the
a
presence of Ni or Pd catalysis [43]. However, regioselectivity of
allylation of arylzinc reagents has not been well documented.
Our previous work on the allylic coupling of (n-butyl)(phenyl)
zinc reagent with E-crotyl chloride in the presence of Cu, Pd or Ni
catalysis at room temperature (Scheme 1) has revealed the
following points:
In this paper, we wish to report our succesful results on the
group selective and regioselective Ni catalyzed allylation of (n-
alkyl)(aryl)zinc reagents and an atom economic synthetic proce-
dure for g-selective aryl-allyl coupling with alkyl substituted pri-
mary allylic chlorides.
(i) The allylation in THF in the presence of CuI or CuCN gives
almost quantitative total yield, but does not give a satisfac-
tory group selectivity, i.e. n-Bu: Ph transfer ratio is about
2:3 and 3:2 with CuI and CuCN catalysis respectively. n-Bu
2. Results and discussion
In order to draw conclusions about the effect of Ni catalysis on
the group selectivity and regioselectivity of the allylation of (n-
alkyl)(aryl)zinc reagents, we planned firstly to investigate the ally-
lation in the presence of Ni catalysts and also in the presence of
nickel-copper dual metal catalysis (Scheme 2). Secondly, we were
transfer takes place with g-selectivity.
(ii) The allylation in the presence of CuI in THF:HMPA (4:1 v/v)
results in n-Bu transfer: Ph transfer ratio of about 4:1 (and
total n-Bu transfer takes place in the presence of CuCN and
MgCl2).
interested in using different g-mono- and g,g-disubstituted allylic
(iii) The allylation in the presence of CuI catalyst and n-Bu3P
(5 mol%) in THF takes place with quantitative yield with a n-
Bu transfer: Ph transfer ratio of about 1:3. Ph transfer results
substrates in the presence of CuI, NiCl2(Ph3P)2 and NiCl2(dppf) to
make a comparison for the effects of catalyst, structure of electro-
phile and leaving group on the group selectivity and regioselectivity.
On the basis of our previous studies [36], allylation of (n-
butyl)(phenyl)zinc 1ab with E-crotyl chloride 2 in THF was chosen
as the model reaction. We used magnesium-based organozinc re-
agents in THF [36]. For the preparation of n-BuPhZn 1ab, n-butyl-
magnesium bromide was added to phenylzinc chloride prepared by
transmetallation of phenylmagnesium bromide with ZnCl2/THF at
ꢀ15 ꢁC. Allylation was carried out by adding allylic substrate 2 to
the mixed diorganozinc reagent 1ab in THF in the presence of a
transition metal catalyst and if necessary, organic catalyst. Group
selectivity of 1ab, i.e. n-Bu group transfer: Ph group transfer ratio
in moderate
a
-selectivity (
a
:
g
¼ 3:1).
(iv) The allylation takes place with complete Ph transfer in the
presence of NiCl2(Ph3P)2 in THF with a yield of 76% (NiCl2
catalysis yields 45% yield). a:g ratio is about 3:2.
(v) The allylation in the presence of Pd(OAc)2 in THF results in
complete Ph transfer, however with a quite low yield of 24%.
As seen, in the allylation of n-BuPhZn 1ab, group selectivity can
be controlled by transition metal catalysis, i.e. CuI catalysis leads to
n-Bu group and Ph group transfer whereas NiCl2(Ph3P)2 catalysis
leads to Ph group transfer. It is quite interesting that organic
catalysis can also change the group selectivity. The use of HMPA or
n-Bu3P in the presence of CuI catalysis results in an important in-
crease or decrease respectively in n-Bu transfer.
and regioselectivity, i.e. a-coupling: g-coupling ratio for each group
were determined by finding the GC yields of coupled products 3a,
4a, 3b and 4b.
As expected, CuI catalyzed n-Bu group transfer gave predomi-
2.1. Nickel catalysis with phosphine ligands
nantly g-product, whereas NiCl2(Ph3P)2 catalyzed Ph group transfer
did not take place with complete regioselectivity due to our all
efforts. So, we were interested in a study to find new Ni catalysts
and/or organic catalysts to control both group selectivity and
regioselectivity allylation of mixed (n-alkyl)(aryl)zinc reagents.
A number of Ni catalysts were screened to find the group selec-
tivity and regioselectivity in the allylation of (n-butyl)(phenyl)zinc
1ab with E-crotyl chloride 2a. For ligands in NiCl2.L2 complexes, we
used bidentate phosphine ligands dppp(1,2-bis(diphenylphosphino)
Group selectivity
n-Bu coupling: Ph coupling
Regiochemistry
Coupling yield, %
3a:4a
5:95
7:93
5:95
-
3b:4b
(i)
(ii)
(iii)
(iv)
98
95
100
76
42:58
82:18
23:77
0:100
53:47
63:37
76:24
59:41
Scheme 1. Group selective and regioselective allylation of (n-butyl)(phenyl)zinc 1ab with E-crotyl chloride 2 in THF in the presence of transition metal and organic catalysis.

30
M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
Scheme 2. Group selective and regioselective coupling of (n-butyl)(phenyl)zinc 1ab with allylic substrates 2 in the presence of transition metal and organic catalyst.
propane), dppen (1,2-bis(diphenylphosphino)pentane), and dppf
(1,2-bis(difenilphosphino)ferrocene) and also monodentate phos-
phine ligand (c-Hex)3P (Table 1). Catalytic reactivity of Ni(COD) and
nano NiO were also examined in the presence of Ph3P and dppf.
noting that using dppf as an additive (entry 2) did not make a
change on the -selective Ph transfer outcome of the allylation,
g
except gave somewhat lower yield. The optimized conditions in
allylation of 1ab with NiCl2/L2 were applied to a series of phosphine
ligands (entries 3e6). However, NiCl2 catalyzed allylation did not
take place in the presence of dppp (entry 3). NiCl2 catalyzed ally-
lation in the presence of dpppen led to a moderate yield and poor
As NiCl2(Ph3P)2 catalysis gives Ph transfer with
¼ 59:41) (Scheme 1), we expected to observe Ph transfer
possibly with a higher -selectivity in the presence of bidentate
phosphine ligands. Surprisingly and gratifyingly, allylation of 1ab in
the presence of NiCl2(dppf) resulted in -selective Ph transfer with
ratio of 16:84. We also carried out the allylation using the ligand
a-selectivity
(a:g
a
regioselectivity (
a
:
g
¼ 26:74) for Ph transfer (entry 4) compared to
g
NiCl2 catalyzed allylation in the presence of dppf. Using NiCl2(dppf)
with Ph3P ligand (entry 5) did not lead to a change in the yield and
a:g
dppf as an organic catalyst in the presence of NiCl2. It is worth
a:g ratio of Ph transfer compared to dppf catalyzed allylation
Table 1
Screening of ligands with Ni(II) and Ni(0) catalysts and Ni(II) and Cu(I) dual catalysis for the group selectivity and regioselectivity in the allylation of n-butylphenylzinc 1ab with
E-crotyl chloride 2a in THF.a
Entry
Catalystsb
Coupling yieldc,%
Group selectivityd
Regioselectivity
n-Bu coupling: Ph coupling
3a: 4ae
3b: 4bf
1
2
3
NiCl2(dppf)
NiCl2/dppf
NiCl2/dppp
99
84
e
0:100
0:100
e
e
16:84
11:89
e
e
e
4
5
6
7
8
9
NiCl2/dppen
NiCl2(dppf)/Ph3P
NiCl2/dppf/Ph3P
NiCl2[(c-Hex)3P]2
NiCl2/t-Bu-P4 base
Nano NiO
42
94
84
59
40
e
0:100
0:100
0:100
0:100
0:100
e
e
26:74
16:84
14:86
47:53
60:40
e
e
e
e
e
e
10
11
12
13
14
Ni(COD)2
47
80
74
79
96
0:100
0:100
0:100
30:70
21:79
e
62:38
73:27
41:59
64:36
72:28
Ni(COD)2/Ph3P
Ni(COD)2/dppf
NiCl2/CuI
e
e
12:88
5:95
NiCl2/CuI/Ph3P
a
All the data are the average of at least two experiments. The reactions were carried out on a 2 mmol scale according to the conditions indicated by the above equation,
unless otherwise specified. Molar ratio of 1ab:2 was optimized to be 1.1:1.
b
Catalytic amounts of all Ni(II) and Ni(0) catalysts and ligands were optimized to 2.5 mol %. 5 mol % CuI was used.
The sum of GC yields of n-Bu coupling products (3a and 4a) and Ph coupling products (3b and 4b).
c
d
The ratio of GC yields of (3aþ 4a) and (3bþ 4b).
e
The ratio of GC yields of 3a and 4a.
f
The ratio of GC yields of 3b and 4b.

M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
31
possibly due to strong binding of dppf as a ligand to Ni. Also, using
NiCl2 with dppf and Ph3P together (entry 6) just resulted in
somewhat lower yield. A drastic decrease in the yield and a:g ratio
(47:53) of Ph transfer was observed when NiCl2[(c-Hex)3P]2 was
used as a catalyst (entry 7). Phosphazene base (t-Bu-P4 base) as a
ligand to NiCl2 gave low yield and poor regioselectivity
allylation with 2b. Compared to E-crotyl chloride 2a, 2-hexenyl
acetate 2c provided somewhat higher and lower yield in
NiCl2(Ph3P)2 and NiCl2(dppf) catalyzed allylation, respectively. CuI
catalyzed allylation was not succesful (entry 3). Diethyl crotyl
phosphonate 2d was not found reactive under the same conditions
(entry 4). This screening of leaving groups on
g-alkyl substituted
(
a
:
g
¼ 60:40) (entry 8). Allylation in the presence of nano NiO was
allyl chlorides showed that chloride was the best for their
unsuccessful (entry 9). We also tried Ni(COD)2 and Ni(COD)2/L as a
catalyst in the allylation (entries 10e12). Ni(COD)2 afforded a
NiCl2(dppf) catalyzed
zinc reagents.
g-selective arylation using (n-butyl)(aryl)
moderate yield of Ph transfer, however with a poor
¼ 62:38) (entry 10). Ni(COD)2/Ph3P resulted in a high yield, but
did not make an appreciable change in the regioselectivity
¼ 73:27) (entry 11). Catalysis with Ni(COD)2/dppf resulted in a
lower ratio (41:59) (entry 12). As expected, Ni(COD)2 catalysis
in the presence of Ph3P and dppf increased -selectivity and
selectivity, respectively due to a possible ligand exchange.
The allylation of (n-butyl)(phenyl)zinc 1ab with 2a was also
carried out in the presence of copper and nickel dual metal catalysis
with the aim of finding different chemoselectivity and/or regiose-
lectivity (entries13 and 14). As summarized in Scheme 1 catalysis
by CuI and NiCl2 resulted in 98% and 76% total yield, respectively. n-
Bu transfer: Ph transfer ratio is 42:58 in the presence of CuI and
total Ph transfer takes place in the presence of NiCl2. Using CuI and
NiCl2 together led to 79% yield with n-Bu transfer: Ph transfer ratio
of 30:70 possibly due to the higher catalyst reactivity of Cu (entry
a
-selectivity
Allylation of 1ab with cinnamyl substrates, 2e (entry 5) and 2f
(entry 6) in the presence of NiCl2(Ph3P)2 catalysis provided mostly
-selective phenyl transfer, as expected. Reactivity of cinnamyl
chloride 2e was found slightly better than that of cinnamyl acetate
2f. However, in cinnamyl substrates, NiCl2(dppf) catalysis did not
(
a
:
g
a
(a
:g
a:g
a
g-
lead to Ph selective allylation of 1ab with
n-Bu transfer: Ph transfer ratios) are 55% (37:63) and 34% (47:53) in
the allylation of 2e and 2f, respectively. ratios in Ph transfer
g-selectivity. Yields (and
a:g
with NiCl2(Ph3P)2 catalysis were not different than those found
with NiCl2(dppf) catalysis.
Among g,g-disubstituted allylic substrates tested (entries 7e9),
only prenyl chloride (1-chloro-3-methyl-2-butene) 2g was found
reactive in allylation of 1ab (entry 7). NiCl2(Ph3P)2 and NiCl2(dppf)
catalysis provided Ph selective allylation with medium and high
yields and with low a- and g-selectivity, respectively. Prenyl acetate
2h led to very low yields in Cu and Ni catalyzed reactions and
geranyl acetate 2ı did not show reactivity.
13). As a result, a:g ratio for n-Bu and Ph transfer did not change
appreciably in the presence of Cu and Ni dual catalysis compared to
that in the presence of Cu catalysis. As expected, addition of Ph3P to
CuI and NiCl2 resulted in low n-Bu transfer and high Ph transfer
with a higher a:g ratio of selectivity (entry 14).
In the NiCl2(dppf) catalyzed Ph selective allylation of 1ab, donor
solvents and LiCl as a Lewis acid were also used to see if a further
We further investigated Cu and Ni catalyzed allylation of
homodiorganozincs, n-Bu2Zn 1a2 and Ph2Zn 1b2 with some of the
allylic substrates 2a-ı (Table 3) to find support for group selective
and regioselective allylation of mixed n-BuPh. In Ni catalyzed
allylation with crotyl substrates 2a and 2b, 1a2 gave quite low yield
in the presence of NiCl2(dppf) and showed no reactivity in the
presence of NiCl2(Ph3P)2, however 1b2 gave high and quantitative
yields (Table 3, entries 1 and 5). These are expected results since Ni
catalysis furnished Ph selective allylation of 1ab. The regiose-
lectivity of Ph transfer in the allylation of 1b2 also appeared in the
Ph transfer in the allylation of 1ab. It is interesting to observe that
improvement could be obtained in the yield and
However, HMPA, DMF and DMSO as cosolvents all decreased the
yield (78, 72 and 83%, respectively) and -selectivity
ratio ¼ 22:78, 54:46 and 32:68, respectively). The use of LiCl also
g-selectivity.
g
(a:g
did not give a better result with a yield of 74% and a:g ratio of 24:76.
Carrying out the allylation of 1ab in THF at 60 ꢁC did not an
appreciable change in the chemoselectivity and regioselectivity of
the coupling.
g-selectivity of Ph transfer in NiCl2(dppf) allylation of 1ab (Table 2,
entry 1) was higher than that obtained in the allylation of 1b2
(Table 3, entry 5).
As seen, the yield and regioselectivity of Ph transfer in the
allylation of (n-butyl)(phenyl)zinc 1ab with 2a catalyzed by Ni(II)
complexes with mono- and bidentate ligands strongly depends on
the ligand.
We also used 1a2 and 1b2 in the allylation with cinnamyl sub-
strate 2f to check the a-selectivity of Ph transfer in the allylation of
1ab with CuI, NiCl2(Ph3P)2 and with NiCl2(dppf) catalysis (Table 2,
entry 6). 1a2 was not reactive in CuI catalyzed allylation with 2f,
however allylation yields in the presence of NiCl2(Ph3P)2 and
2.2. Allylic substrate scope in copper and nickel catalyzed allylation
NiCl2(dppf) catalysis were quantitative with a-selectivity (Table 3,
entry 3). Allylation of 1b2 afforded 47%, 66% and 91% yields in the
presence of CuI, NiCl2(Ph3P)2 and NiCl2(dppf) catalysis. Thus, 1ab
could be readily allylated with 2f giving a mixture of n-Bu transfer
and Ph transfer products in the presence of Ni catalysis. As ex-
pected, in allylation of 1ab, NiCl2(dppf) catalysis led to both n-Bu
and Ph transfer, however NiCl2(Ph3P)2 catalysis resulted in only Ph
transfer (Table 2, entry 6). a-selectivity in both n-Bu transfer and Ph
transfer in the allylation of 1a2 and 1b2 remained in the allylation of
1ab with 2f.
In order to examine the compatibility of the optimized condi-
tions for NiCl2(dppf) catalyzed
butyl)(phenyl)zinc 1ab with E-crotyl chloride 2a, we screened a
series of -mono and -disubstituted allylic electrophiles with
g-selective phenyl allylation of (n-
g
g,g
different leaving groups and observed the dependence of both
group selectivity and regioselectivity on the allylic electrophile and
also leaving group. The results are given in Table 2. For comparison,
allylation of 1ab were examined not only in the presence of
NiCl2(dppf), but also in the presence of CuI, NiCl2(Ph3P)2 and
NiCl2[(c-Hex)3P]2 catalysis.
Using activated g,g-disubstituted allylic chloride 2g in the ally-
lation of 1a2 was not succesful in the presence of NiCl2(Ph3P)2 and
NiCl2(dppf) catalysis (entry 4), however 1b2 reacted with 81% and
100% yields (entry 8), respectively. This result supported the
As outlined in Scheme 1, CuI catalyzed allylation of 1ab with E-
crotyl chloride 2a is not group selective. NiCl2(Ph3P)2 catalysis leads
to Ph selective allylation with an
we observed that NiCl2(dppf) afforded Ph transfer with
tivity (entry 1). E-crotyl bromide 2b showed the same -selective
Ph transfer in NiCl2(dppf) catalyzed allylation. NiCl2(Ph3P)2 catal-
ysis provided Ph selective allylation with an ratio of about 3:2
(entry 2). CuI catalysis increased ratio of Ph transfer in the
a
:
g
ratio of about 3:2. In this study,
observed Ph transfer in the allylation of 1ab. However, 1:1
selectivity in Ph transfer in allylation of 1b2 turned to g-selectivity
in the presence of NiCl2(dppf) catalysis.
At this stage, it is worth noting that the outcome of the allylation
of (n-butyl)(phenyl)zinc reagent 1ab in the presence of Cu and Ni
catalysts seemed consistent with those obtained for the allylation
a
-to
g-
g-selec-
g
a:g
a:g

32
M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
Table 2
Group selectivity and regioselectivity in CuI and NiCl2.L2 (L ¼ Ph3P, (c-Hex)3P, dppf) catalyzed reaction of n-butylphenylzinc 1ab with allylic substrates 2.a
Entry
1
Allylic substrate
Catalystb
Coupling yield,%c
Group selectivityd
Regioselectivity
n-Bu coupling: Ph coupling
3a: 4ae
3b: 4bf
2a
CuI
97g
53:47
0:100
0:100
0:100
2:98
0:100
0:100
0:100
0:100
0:100
0:100
4:96
e
43:57
59:41
47:53
16:84
62:38
65:35
18:82
88:12
49:51
39:61
16:84
e
NiCl2(Ph3P)2
NiCl2[(c-Hex)3P]2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2[(c-Hex)3P]2
NiCl2(dppf)
NiCl2(dppf)
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2[(c-Hex)3P]2
NiCl2(dppf)
CuI
76g
59h
e
99h
e
2
3
2b
2c
99
88
90
16
86
33
70
0:100
e
e
e
e
e
e
4
5
2d
2e
No reactioni
e
69j
55
0:100
37:63
0:100
0:100
61:39
47:53
32:68
0:100
0:100
0:100
0:100
0:100
0:100
e
86:14
62:38
90:10
76:24
45:55
76:24
78:22
65:35
75:25
e
6
2f
20
55j
e
28
0:100
67:33
100:0
e
34k,l
7
8
2g
2h
100
54
99
6
18
10
12
No reaction
No reaction
No reaction
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2[(c-Hex)3P]2
NiCl2(dppf)
CuI
e
38:62
e
Not determined
Not determined
Not determined
Not determined
e
e
e
9
2i
NiCl2(Ph3P)2
NiCl2(dppf)
a
All the data are the average of at least two experiments. The reactions were carried out on a 2 mmol scale according to the conditions indicated by the above equation,
unless otherwise specified. Molar ratio of 1ab:2 was optimized to be 1.1:1.
b
5 mol % CuI and/or 2.5 mol % Ni catalyst was used.
The sum of GC yields of n-Bu coupling products (3a and 4a) and Ph coupling products (3b and 4b).
c
d
The ratio of GC yields of (3aþ 4a) and (3bþ 4b).
e
The ratio of GC yields of 3a and 4a.
f
The ratio of GC yields of 3b and 4b.
Taken from Scheme 1.
Taken from Table 1.
No activity even after 24 h reaction.
g
h
i
j
Taken from Ref. [46].
k
In a 2 h reaction, the coupling yield increased to 60%, the group selectivity did not change appreciably (40:60), 3a:4a ¼ 96:4 and 3b: 4b ¼ 81:19.
l
In the presence of 5 mol % of catalyst in a 1 h and 2 h reaction, the coupling yields are 61% and 96%, respectively. Group selectivity is 44:56 in 1 h reaction and 42:58 in 2 h
reaction. In 1 h reaction, regioselectivities are 3a:4a ¼ 96:4 and 3b: 4b ¼ 74:26. In 2 h reaction, regioselectivities are 3a:4a ¼ 90:10 and 3b: 4b ¼ 66:34.

M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
33
Table 3
Regioselectivity in the reaction of n-Bu2Zn 1a2 and Ph2Zn 1b2 with allylic substrates 2 in the presence of CuI and NiCl2.L (L ¼ Ph3P, dppf).a
Entry
R2Zn
Allylic substrate
Catalystb
Coupling yield,%c
82f
Regioselectivity
A: A′d
B: B′e
1
2
3
4
5
6
7
8
1a2
2a
2b
2f
CuI
7:93
f
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
CuI
NiCl2(Ph3P)2
NiCl2(dppf)
-
26
76
4
28
e
6:94
16:84
Not determined
15:85
100
96
63
e
95:5
99:1
100:0
2g
2a
2b
2f
e
1b2
100f
100f
100
98
99
88
47
66
91
100
81
100
60:40
56:44
37:63
56:44
65:35
32:68
81:19
73:27
70:30
80:20
77:23
53:47
2g
a
Molar ratio of 1a2:2 and 1b2:2 was optimized to be 1.1:1.
b
c
d
e
f
5 mol % CuI and/or 2.5 mol % Ni catalyst was used.
The sum of GC yields of n-Bu coupling products (A and A′) or Ph coupling products (B and B′).
The ratio of GC yields of A and A′.
The ratio of GC yields of B and B′.
Taken from Ref. [46].
of the homo diorganozinc reagents, di n-butylzinc 1a2 and diphe-
nylzinc 1b2.
alkyl substituted allylic chlorides provides a new protocol for the
selective aryl transfer. This protocol seems complementary to
g
a
-
-
selective aryl transfer using NiCl2(Ph3P)2 catalyzed coupling of (n-
butyl)(aryl)zinc reagents [36].
2.3.
g-Selective aryl-allyl coupling of (n-butyl)(aryl)zinc reagents. A
synthetic procedure
2.4. Mechanism
This study showed that NiCl2(dppf) catalyzed allylation of (n-
butyl)(aryl)zinc reagents with
allylic chlorides and acetates yields
products. Thus, we have been interested in developing a new atom
economic method for -selective aryl allylation using mixed (n-
butyl)(aryl)zinc reagents. The reaction was performed with various
(n-butyl)(substituted phenyl)zinc reagents and E-crotyl chloride in
the presence of NiCl2(dppf) catalysis (Table 4). The data are aver-
g
-alkyl and
g
,
g
-dialkyl substituted
With these results in hand, group selectivity and regioselectivity
of Ni catalyzed allylation of (alkyl)(aryl)zinc reagents proved to be a
function of catalyst ligand and the nature of allylic substrate as well
as solvent. The dependence of allylic regioselectivity on the steric
and electronic effects of allylic substrate [44e46] and catalyst
[44e47] was already reported in detail for Pd [45] and Ni catalyzed
[44,46,47] allylation of Grignard reagents.
g-selective aryl-allyl coupling
g
ages of at least two independent experiments. Best
g
-selective aryl
We proposed the catalytic cycle shown in Scheme 3 for Ni
catalyzed allylic coupling of (n-butyl)(phenyl)zinc reagent. This
mechanism is analogous to that proposed for Ni catalyzed allylic
coupling of Grignard reagents [44,47]. For the sake of clarity, the
catalytic cycle was drawn for allylation of diphenylzinc 1b2 with
allylic reagent, R1CH ¼ CH2CH2X in the presence of a Ni catalyst
coupling yields were obtained in the allylation of methyl, tert-butyl
and methoxy substituted phenyl and biphenyl containing mixed
reagents. Yield and regioselectivity decreased in the allylation of
bromo substituted phenyl containing zinc reagents. However,
NiCl2(dppf) catalyzed coupling of (n-butyl)(aryl)zinc reagents with

34
M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
Table 4
NiCl2(dppf) catalyzed coupling of (n-butyl)(aryl)zinc reagents with E-crotyl chloride 2a in THFa
Entry.
R
Coupling yield, %b
Regoselectivity
3: 4c
1
2
3
4
5
6
7
8
9
Ph
99
79
77
96
100
54
26
100
92
16:84
37:63
19:81
22:78
21:79
50:50
65:35
16:84
17:83
4-MeOC6H4
3-MeOC6H4
4-MeC6H4
3-MeC6H4
4-BrC6H4
3-BrC6H4
4-t-BuC6H4
C6H5eC6H5
a
Reactions were run with 2:1 molar ratio of 1:2a. General reaction conditions: n-BuArZn reagent (2.2 mmol) in THF, E-crotyl chloride (2 mmol), NiCl2(dppf) (0.05 mol) at
room temperature for 1 h. For a representative coupling procedure see Experimental Section.
b
Yields of product mixture of 3 and 4 were determined by GC.
The a:g ratio was determined by GC.
c
Scheme 3. Proposed catalytic cycle for NiCl2L2 catalyzed allylation of diorganozinc reagents.
with two monodentate phosphine ligands or a bidentate diphos-
phine ligand, i.e. NiCl2L2 (L2 ¼ 2Ph3P and dppf, respectively). In the
catalytic process, after the generation and coordination of stable
NiCl2L2 complex to the alkene, oxidative addition takes place to
with mono- and diphosphine ligands, MCl2L2 (L2 ¼ 2Ph3P, dppe,
dppp, dppp, dppb, dpppen (diphenylphosphinoethane, -propane,-
butane and epentane) and metallo-ligand dppf) [44,49e51]. The
activity and selectivity of the complexes with bidentate phosphines
are known to be strongly dependent upon the P-M-P angle (bite
angle) in the complex ML2Cl2 [49e51]. In other words, the smaller
angle of Cl-M-Cl is important and must be favorable for the easier
give (p
-allyl)NiL2 complex, A1 and/or A2 (Scheme 3). It was re-
ported that in the presence of phosphine ligands, an equilibrium
between neutral A1 and cationic A2 complexes appears and cationic
complexes are favored using diphosphine ligands [48]. Diphe-
nylzinc reagent 1b2 attacks the Ni atom in A1 or A2 to form the
coupling of p-allyl and R groups in the intermediate (p-allyl)MRL2
B in the reductive elimination step. Our findings on the higher
allylation yields of (n-butyl)(phenyl)zinc 1ab with NiCl2(dppf) or
NiCl2/dppf compared to NiCl2/dpppen or NiCl2/dppp (no coupling)
(Table 1, entries 1e4) are in accordance with the PeNieP bite angle.
In the case of monophosphine ligand, Ph3P, two molecules are free
arround the M atom and they may have smaller P-M-P angle than
that of dppf ligand [51]. In addition, just a few of the conformations
of the free ligands contain the P atoms with the correct orientation
to allow bidentate coordination to M. This lower stability of Ph3P as
a ligand compared to dppf can lead to somewhat lower yield ally-
lation of 1ab with 2a and also can ensure the turning of regiose-
intermediate
(p-allyl)NiRL2 B. In reductive elimination,
regioisomers of allylic coupling product are released with the
regeneration of catalyst NiCl2.
Depending on this mechanism, we tried to explain the results on
the outcome of the allylation of (n-butyl)(phenyl)zinc 1ab and
diphenylzinc 1b2 with E-crotyl chloride 2a in the presence of
NiCl2L2 catalysts and also the results on the outcome of the Ni
catalyzed allylation of 1ab and 1b2 with
g-alkyl or g-phenyl
substituted allylic substrates.
(i) Effect of catalyst on the yield and regioselectivity in the
lectivity from
g-to a-in the NiCl2(Ph3P)2 catalysis compared to
coupling of 1ab and 1b2 with 2a:
NiCl2(dppf) catalysis.
It is known that reductive elimination step is favored with
coupling partners carrying opposite electronic properties [52].
However, electronic and steric effects are opposing in this step
[51,52]. In the catalysis with NiCl2(dppf), due to the stability of
For the CeC coupling of a variety organometallic reagents (Mg,
Zn, B, Sn), MCl2(dppf) (M ¼ Pd, Ni) was already reported to be the
most active and selective catalysts among the Pd and Ni catalysts

M. Kalkan, E. Erdik / Journal of Organometallic Chemistry 818 (2016) 28e36
35
bidentate coordination with a larger PeNieP angle, electronic ef-
fect may be the main factor. Thus, þI, þM effect of -Me group in E-
crotyl chloride 2a is expected to lead the transfer of Ph group
-C in
allylation (Table 2 entry 1, Table 3 entry 5). In the catalysis with
NiCl2(Ph3P)2, possibly, occupation of more space by two molecules
of ligand compared to NiCl2(dppf) in the coordination sphere of Ni
regioselectivity and also group selectivity in the allylation of (n-
butyl)(aryl)zinc reagents. A mechanism was also proposed for the
dependence of group selectivity and regioselectivity of Ni catalyzed
allylation of (n-butyl)(aryl)zinc reagents on the catalyst ligand and
the substrate.
g
(ꢀI, þM effect) of diorganozinc reagents 1ab and 1b2 to
g
4. Experimental
in the intermediate B will cause the transfer of R ¼ Ph group to
a
-C
much more than to
Table 3 entry 5).
g-C due to the steric effects (Table 2 entry 1,
4.1. General
It was reported that in the Ni catalyzed allylation of phenyl-
magnesium bromide with crotyl ethers the coupling takes place
with higher yield and regioselectivity in the presence of NiCl2(dppf)
catalysis compared to NiCl2(Ph3P)2 catalysis [44]. The use of
All reactions were carried out in oven-dried glassware under a
positive pressure of nitrogen using standard syringe-septum cap
techniques [53]. GC analyses were performed on a Thermo Finnigan
gas chromatograph equipped with a ZB-5 capillary column packed
with phenylpolysiloxane using the internal standard technique.
THF was distilled from sodium benzophenonedianion; alkyl bro-
mides and bromobenzene were obtained commercially and puri-
fied using literature procedures. Mg turnings for Grignard reagents
was used without further purification. ZnCl2 (Aldrich) was dried
under reduced pressure at 100 ꢁC for 2 h and used as a THF solution.
CuI was purified according to the literature procedure, dried under
reduced pressure at 60e90 ꢁC for at least 1 h and kept under ni-
trogen [54]. Ni catalysts and phosphine ligands were used without
further purification.
Grignard reagents, RMgBr (R ¼ n-Bu, C6H5, FG-C6H4 (FG ¼ 3-
MeO-, 4-MeO-, 3-Me-, 4-Me-, 3-Br-, 4-Br-, 4-t-Bu-, C6H5-)) were
prepared in THF by standard methods and their concentrations
were found by titration before use [55]. For the preparation of (n-
Bu)(aryl)zinc reagents, (n-Bu)(Ar)Zn (Ar ¼ C6H5, FG-C6H4, arylzinc
chlorides, ArZnCl were reacted with n-BuMgBr. ArZnCl were pre-
pared by addition of arylmagnesium bromide (1 mol equiv.) to
ZnCl2 (1 mol equiv.) in THF (1.1 ml) at ꢀ20 ꢁC and stirring at that
temperature for 15 min. To freshly prepared ArZnCl reagent
(1 mol equiv.), n-BuMgBr (1 mol equiv.) in THF was added dropwise
and the mixture was stirred at that temperature for another 15 min.
NiCl2(dppf) was found to give rise to coupling at
g-C whereas the
use of NiCl2(Ph3P)2 resulted in mostly at
a-C. These results are
accordance with our findings.
(ii) Effect of allylic substrate (g-C substitution of primary allylic
chloride and leaving group) on the yield and regioselectivity of Ph
transfer in (n-butyl)(phenyl)zinc 1ab and diphenylzinc 1b2 and
group selectivity of 1ab:
Changing the substituent on g-C of allylic chloride from Me to
Ph, i.e. using cinnamyl chloride 2e instead of E-crotyl chloride 2a,
and using cinnamyl acetate 2f instead of 2-hexenyl acetate 2c led to
change in the regioselectivity of Ph transfer in 1ab and 1b2 and also
group selectivity of 1ab in NiCl2(dppf) catalyzed allylation. Ac-
cording to our suggestions for the regioselectivity of 1ab and 1b2 in
NiCl2(Ph3P)2 and NiCl2(dppf) catalyzed allylation with E-crotyl
chloride 2a, we find it reasonable to think that eI, þM effect of
g-Ph
group may prevent transfer of Ph group to -C in allylation with
g
cinnamyl chloride 2e and with cinnamyl acetate 2f. Thus, electronic
effect will be an important factor as well as steric factor resulting in
mainly a-selectivity in NiCl2(Ph3P)2 catalyzed allylations (Table 2
entries 1 and 5; entries 3 and 6). Similarly, in NiCl2(dppf) cata-
lyzed allylations, electronic effect seems to be a dominant factor
and mainly g-selectivity is observed (Table 2 entries 1 and 5; en-
tries 3 and 6). In addition, coupling yield was observed to decrease
in the allylation of 1ab with cinnamyl chloride 2e compared to
crotyl chloride 2a and also with cinnamyl acetate 2f compared to 2-
hexenyl acetate 2c. Substitution of Ph group instead of Me group at
4.2. Typical procedure for NiCl2(dppf) catalyzed g-aryl-allyl
coupling of (n-butyl)(aryl)zincs with alkyl substituted linear allylic
chlorides in THF
g
-C also resulted in n-Bu transfer to a-C in NiCl2(dppf) catalyzed
To the prepared (n-Bu)(Ar)Zn reagent (2.2 mmol), NiCl2(dppf)
(0.05 mmol, 0.0341 g) was added at ꢀ20 ꢁC and stirred at that
temperature for 15 min. Allylic chloride (2 mmol) was added
dropwise at ꢀ20 ꢁC. The mixture was stirred at room temperature
for 1 h. After addition of internal standard (nonane), the mixture
was hydrolyzed with saturated NH4Cl solution. The aqueous phase
was extracted with ether and aliquots were analyzed with GC to
allylations as expected (Table 2 entries 3 and 6).
Changing the leaving group from eCl or eBr to eOAc in crotyl
substrate, i.e. allylation with 2b and 2c instead of 2a and also
changing the leaving group from eCl to eOAc in cinnamyl sub-
strate, i.e. allylation with 2f instead of 2e did not lead to important
changes in the regioselectivity of Ph transfer of 1ab. Just, the yield
of Ph transfer somewhat decreased in allylation with cinnamyl
acetate 2f instead of cinnamyl chloride 2e (Table 2 entries 5 and 6).
However, allylation with crotyl phosphonate 2d was not succesful.
determine the coupling yield and
coupling product.
a-product: g-product ratio of aryl
Acknowledgement
3. Conclusions
We thank Turkish Scientific and Technical Research Council
(Grant No. TBAG 112T886) for the financial support.
In conclusion, we have demonstrated that (n-butyl)(aryl)zinc
reagents react with
THF in the presence of NiCl2(dppf) catalysis to afford linear alkene
with high -regioselectivity. This new protocol provides an atom
g-alkyl substituted primary allylic chlorides in
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