Reactivities of mixed organozinc and mixed organocopper reagents: 9. Solvent dependence of group transfer selectivity in sp3C coupling and acylation of mixed diorganocuprates and diorganozincs

Article abstract of DOI:10.1016/j.jorganchem.2013.07.037

The selectivity and/or reactivity of organyl group transfer of mixed diorganocuprates in their alkyl coupling in THF depends on N- or O-donor solvents as cosolvents. Selective n-Bu group transfer is observed in room temperature alkylation of Grignard reagent derived stoichiometric n-BuPhCuMgBr reagent in THF:cosolvent and solvation effects do not change the group transfer ability. However, in the alkylation of catalytic mixed cuprates derived from CuI catalyzed n-BuPh₂ZnMgBr and n-Bu₂PhZnMgBr, group transfer ability depends on the solvation effect and it can be controlled by using N- or O-donor solvents. In alkylation of CuI catalyzed mixed zincate n-BuPh ₂ZnMgBr and also n-Bu₂PhZnMgBr in THF at reflux temperature Ph group transfer takes place (n-Bu/Ph transfer ratio is 1:9 and 4:6, respectively) whereas n-Bu transfer increases in THF:NMP (1:1) resulting n-Bu/Ph transfer ratio of 4:6 and 8:2, respectively. Group transfer ability in allylation of n-BuPhZn seems not to be solvent dependent. The solvent effect on the group transfer ability has been found to be dependent also on the R ¹ and R² partnership in room temperature benzoylation of catalytic mixed cuprates, R¹R²CuZnI, derived from CuI catalyzed R¹R²Zn. These results are briefly discussed in terms of solvation of mixed diorganocuprate and diorganozinc reagents and provide useful information in their atom-economic alkyl, allyl and acyl coupling reactions.

Full text of DOI:10.1016/j.jorganchem.2013.07.037

Journal of Organometallic Chemistry 745-746 (2013) 235e241
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Reactivities of mixed organozinc and mixed organocopper reagents: 9.
Solvent dependence of group transfer selectivity in sp3C coupling and
acylation of mixed diorganocuprates and diorganozincs
,
a
a
a
a
Ender Erdik a , Fatma Eroglu , Melike Kalkan , Özgen Ömür Pekel , Duygu Özkan ,
*
ꢀ
Ebru Z. Serdar b
a Ankara University, Science Faculty, Bes¸evler, Ankara 06100, Turkey
b
_
Dermikaya Center, Kadıköy, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The selectivity and/or reactivity of organyl group transfer of mixed diorganocuprates in their alkyl coupling
in THF depends on N- or O-donor solvents as cosolvents. Selective n-Bu group transfer is observed in room
temperature alkylation of Grignard reagent derived stoichiometric n-BuPhCuMgBr reagent in THF:co-
solvent and solvation effects do not change the group transfer ability. However, in the alkylation of catalytic
mixed cuprates derived from CuI catalyzed n-BuPh2ZnMgBr and n-Bu2PhZnMgBr, group transfer ability
depends on the solvation effect and it can be controlled by using N- or O-donor solvents. In alkylation of
CuI catalyzed mixed zincate n-BuPh2ZnMgBr and also n-Bu2PhZnMgBr in THF at reflux temperature Ph
group transfer takes place (n-Bu/Ph transfer ratio is 1:9 and 4:6, respectively) whereas n-Bu transfer in-
creases in THF:NMP (1:1) resulting n-Bu/Ph transfer ratio of 4:6 and 8:2, respectively. Group transfer ability
in allylation of n-BuPhZn seems not to be solvent dependent. The solvent effect on the group transfer
ability has been found to be dependent also on the R1 and R2 partnership in room temperature benzoy-
lation of catalytic mixed cuprates, R1R2CuZnI, derived from CuI catalyzed R1R2Zn. These results are briefly
discussed in terms of solvation of mixed diorganocuprate and diorganozinc reagents and provide useful
information in their atom-economic alkyl, allyl and acyl coupling reactions.
Received 18 May 2013
Received in revised form
4 July 2013
Accepted 16 July 2013
Keywords:
Mixed diorganocuprates
Mixed diorganozincs
Group transfer selectivity
Solvent effect
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
copper reagents of RRRTCuM [9,12], RRRTZn [10,13] and (RR)2RTZnM
type [11,14] composedof one transferable group RT together with the
Diorganocuprates R2CuM (M ¼ Li, MgX) have provided one of the
most consistently popular organometallic reagents for CeC bond
formation [1e3]. However, the synthetic problem associated with
the use of copper nucleophile, R2CuƟ is that only one of the R groups
can be transferred to the electrophile. Organozinc reagents are the
other most used organometallic reagents due to their compatibility
of many functional groups. However, in the reactions of dio-
rganozincs, R2Zn [4e7], and triorganozincates, R3ZnM (M ¼ Li, Na,
MgX) [7,8], which are more reactive than organozinc halides, RZnX
[4e7], the problem of one R group transfer is again a serious limi-
tation to the atom-economic use of diorganozincs and tri-
organozincates. The problem has been solved by (i) preparing mixed
organozinc and copper reagents of R1R2CuM [9], R1R2Zn [10], and
R1R22ZnM type [11], in which the R2 group has a lower transfer rate
than R1 group and also by (ii) preparing mixed organozinc and
residual group, RR. A variety of mixed diorganocuprates and mixed
diorganozincs have found extensive application in organometallic
synthesis. Mixed triorganozincates have not been used extensively.
However, recently (iii) catalytic mixed triorganozincates have been
prepared using R1MgBr and catalytic amounts of ZnCl2 [7,15aed]
and R22Zn containing residual R2 groups, respectively [15a,e,f].
We are currently working on the mechanisms and controlling
factors of group transfer selectivity in the reactions of mixed dio-
rganocuprates [16,17], diorganozincs [18e22], and triorganozincates
[23] and their synthetic applicability [19e21].
So far, we observed that the group transfer selectivity in mixed
diorganocuprates and diorganozincs depend not only on the reac-
tion mechanism, but also (i) on the counter ion of the cuprates
R1R2CuM (M ¼ MgX, ZnX) and (ii) on the reaction parameters, i.e.
solvent, temperature and reaction time. We recently reported that
the transfer ability of organyl groups in n-BuPhZn in their Cu(I)
catalyzed reaction with benzoyl chloride in THF can be controlled
using N- or O-donor solvents [18]. n-Bu group:Ph group transfer
ratio is 6:4 in THF and 9:1 in THF:NMP (2:1), but 1:9 in THF:TMEDA
* Corresponding author. Ankara Üniversitesi, Fen Fakültesi, Kimya Bölümü, Bes¸ evler,
Ankara 06100, Turkey. Tel.: þ90 312 212 67 20x1039; fax: þ90 312 223 23 95.
E-mail address: erdik@science.ankara.edu.tr (E. Erdik).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.07.037

236
E. Erdik et al. / Journal of Organometallic Chemistry 745-746 (2013) 235e241
(2:1). Then, we carried out a brief study to gain some qualitative
insight for the solvent effect on the group transfer ability of mixed
diorganocuprates and also mixed diorganozincs in their sp3C
coupling reactions. In this paper, we wish to report the perfor-
mance of donor solvents with the aim of finding the best solvent
(2ab2) and n-Bu2PhZnMgBr (2a2b) in the presence of CuI catalyst,
i.e. catalytic n-BuPhCuMgBr reagents (Scheme 1b) with n-pentyl
bromide 3 as alkyl halide. For diorganozincs, which do not couple
with alkyl halides, we investigated (iii) coupling of n-BuPhZn (6ab)
with allyl bromide (Scheme 1c). As cosolvents, we used N-donor
and O-donor solvents and also toluene as a noncoordinating sol-
vent for comparison and we found the coupling yield and relative
transfer ability n-Bu and Ph groups in THF:cosolvent in competi-
tion with the outcome of the reaction in THF alone. (iv) For acyl-
ation reactions, catalytic mixed diorganocuprates containing alkyl,
benzyl, aryl and alkenyl groups were prepared in situ using mixed
diorganozincs and CuI catalysis and they were allowed to react
with benzoyl chloride in THF and in THF:TMEDA (1:2) (Scheme 1d).
(i) in the alkylation of stoichiometric mixed diorganocuprate, n-
BuPhCuMgBr,
(ii) in the alkylation of catalytic mixed diorganocuprate, n-BuPh-
CuMgBr derived from zincates n-BuxPh3ꢀxZnMgBr (x ¼ 1 and
2) in the presence of CuI catalysis and
(iii) in the allylation of mixed diorganozinc, n-BuPhZn,
and we give a short explanation for the solvent effect on their group
transfer ability.
2.1. Coupling of n-BuPhCuMgBr with n-pentyl bromide
We already gave a brief explanation for the solvent effect in acyl-
ation of catalytic n-BuPhCuZnI, derived from n-BuPhZn in the pres-
ence of CuI catalysis [18]. However, from these results, we raised the
question of how the solvent affects the group selectivity in the acyl-
ationofothercatalytic mixed diorganocuprates. So, wealsoexamined
Optimized yields and 4:5 product ratios for the alkylation of n-
BuPhCuMgBr in THF and in THF:cosolvent at room temperature
(Scheme 1a) are summarized in Table 1. Coupling yields in
THF:cosolvent (1:1) mixtures and background yields for alkylation
of homocuprates in THF were already found [16].
(iv) the performance of THF and THF:TMEDA (1:2) as solvents in
the acylation of a number of catalytic mixed diorganocuprates,
R1R2CuZnI derived from mixed diorganozincs, R1R2Zn in the
presence of CuI catalysis.
As seen, the total yield and 4:5 product ratio (98:2e90:10) did
not change much in THF:NMP (1:1), in THF:DMPU (1:1) and in
THF:diglyme (1:1) (entries 2, 4 and 6) compared to the reaction in
THF (entry 1). Using THF:HMPA (1:1) as solvent decreased the yield
(entry 7) and THF:TMEDA (1:1) resulted in a much lower yield
(entry 9). However, selective n-Bu group transfer takes place in the
presence of coordinating solvents. Using toluene as a cosolvent
decreased the yield to 23%, but the product ratio remained the
same. Carrying out the coupling in THF:cosolvent (1:2) (entries 5, 8
and 10) resulted in about 30% decrease in the yield in all cases,
however did not make a remarkable change in the product ratio.
We can see that the use of a R1R2CuMgBr (R1 ¼ n-alkyl, R2 ¼ aryl)
instead of R12CuMgBr for alkyl coupling in THF increases n-alkyl
transfer (in the case of n-BuPhCuMgBr, from 71% to 90%); however
using a N- or O-donor solvent in 1:1 molar ratio or less does not
change either the yield or the relative group transfer ability.
The results may provide useful information when mixed dio-
rganocuprates and diorganozincs are used for atom-economic
synthesis.
2. Results and discussion
For the solvent effect on the group transfer ability of mixed
diorganocuprate and diorganozinc reagents in their sp3C coupling
reactions, we firstly focused on the sp3C alkyl coupling reactions of
mixed bromomagnesium diorganocuprates and secondly allyl
coupling reactions of mixed diorganozincs planning to see also the
dependence of solvent effect on the reaction mechanism. In acyl-
ation reactions, we screened the solvent effect on the group transfer
ability on a number of mixed cuprates using THF and THF:TMEDA
(1:2) as selectivity controlling solvents and/or solvent mixtures.
As model reactions, we chose (i) coupling of stoichiometric n-
BuPhCuMgBr (1ab) reagent (Scheme 1a) and (ii) coupling of cat-
alytic n-BuPhCuMgBr reagents formed in situ from n-BuPh2ZnMgBr
2.2. Coupling of CuI catalyzed n-BuPh2ZnMgBr and n-
Bu2PhZnMgBr with n-pentyl bromide
As we already observed that CuI catalyzed alkylation of n-
BuPh2ZnMgBr (2ab2) and n-Bu2PhZnMgBr (2a2b) in THF lead to
higher yields at reflux temperature [23], we investigated the group
Scheme 1.

E. Erdik et al. / Journal of Organometallic Chemistry 745-746 (2013) 235e241
237
Table 1
In the coupling of n-Bu2PhZnMgBr/“CuI”, the results are similar
to those obtained with n-Bu2PhZnMgBr/“CuI”. Transfer of mostly Ph
group takes place in THF (4:5 ratio is 38:62) (entry 1) and selective
n-Bu group transfer takes place in THF:NMP (1:1) (4:5 ratio is 98:2)
(entry 2) and in THF:DMPU (1:1) (4:5 ratio is 98:2) (entry 3).
Coupling in THF:TMEDA (1:1) also resulted in selective n-Bu group
transfer (4:5 ratio is 81:19) (entry 5). We were delighted to see that
organic group transfer in CuI catalyzed n-alkyl coupling
R12R2ZnMgBr (R1 ¼ n-alkyl, R2 ¼ aryl) reagents can be controlled by
using N- or O-donor cosolvents in THF.
In controllingthe background yields, weobserved lowercoupling
yield for CuI catalyzed homozincate n-Bu3ZnMgBr in the presence of
diglyme and TMEDA as cosolvents (entries 4 and 5, respectively) and
for CuI catalyzed homozincate Ph3ZnMgBr in the presence of DMPU
and diglyme as cosolvents (entries 3 and 4, respectively) compared
to the yields obtained in THF. Then we expected to see a similar
decrease for n-Bu group transfer in the presence of diglyme and/or
TMEDA and a decrease for Ph grouptransfer in the presence of DMPU
and/or diglyme in the CuI catalyzed coupling yields of both mixed
zincates. As expected, we observed that the presence of diglyme and
TMEDA in coupling of n-buPh2ZnMgBr/“CuI” and diglyme in
coupling of n-Bu2PhZnMgBr/“CuI” lead to minimum n-Bu group
transfer. A decrease in Ph group transfer was also observed in CuI
coupling of both zincates, but only in the presence of DMPU. From a
comparison of CuI catalyzed coupling yields of homozincates and
mixed zincates, the use of NMP, DMPU or especially TMEDA as a
cosolvent in THF appears promising in atom-economic n-alkylen-
alkyl coupling using R12R2ZnMgBr (R1 ¼ n-alkyl, R2 ¼ aryl) reagents
and n-alkyl bromides (entries 2, 3 and 5). It is also apparent that
coupling of R1R22ZnMgBr (R1 ¼ n-alkyl, R2 ¼ aryl) reagents in THF
rather than homozincates, R23ZnMgBr seems to be the best choice
for aryl-n-alkyl coupling (entry 1).
Effect of cosolvents on the organic group transfer ability in the reaction of bromo-
magnesium n-butylphenylcuprate 1ab with n-pentyl bromide in THF at room
temperature.a,b
Entry
Solvent
Total yield, %c (4:5)d
1
2
3
4
5
6
7
8
THF
93 (98:2)
98 (90:10)
65 (89:11)
92 (91:9)
63 (84:16)
84 (95:5)
73 (95:5)
46 (98:2)
21 (90:10)
6 (83:17)
23 (95:5)
9 (95:5)
THF:NMP (1:1)
THF:NMP (1:2)
THF:DMPU (1:1)
THF:DMPU (1:2)
THF:diglyme (1:1)
THF:HMPA (1:1)
THF:HMPA (1:2)
THF:TMEDA (1:1)
THF:TMEDA (1:2)
THF:toluene (1:1)
THF:toluene (1:2)
9
10
11
12
a
Molar ratio of 1ab:3 was used to be 3:1.
GC yields for alkylation of n-Bu2CuMgBr 1a2 and Ph2CuMgBr 1b2 are 71% and 8%,
b
respectively [16].
c
The sum of GC yields of 4 and 5.
The ratio of GC yields of 4 and 5.
d
transfer ability of organic groups in THF:cosolvent at this temper-
ature. Optimized yields and 4:5 product ratios are given in Table 2.
To see the effect of solvent on the performance of n-BuPh2ZnMgBr
(2ab2)/“CuI” and n-Bu2PhZnMgBr (2a2b)/“CuI” we carried out
studies in parallel with homozincates n-Bu3ZnMgBr (2a3)/“CuI” and
Ph3ZnMgBr (2b3)/“CuI”.
As seen in the coupling of n-BuPh2ZnMgBr/“CuI”, transfer of
only Ph group takes place in THF (4:5 ratio is 8:92) (entry 1).
However, transfer ability of n-Bu group appreciably increases in
THF:NMP (1:1) (4:5 ratio is 44:56) (entry 2) and in THF:DMPU (1:1)
(4:5 ratio is 43:57) (entry 3). In THF:diglyme (1:1) (entry 4) and in
THF:TMEDA (entry 5), the coupling again results in selective Ph
group transfer (4:5 ratios are 14:86 and 20:80, respectively). So, it
seems that NMP and DMPU as a cosolvent have an effect to increase
the relative transfer ability of alkyl groups in the CuI catalyzed
alkylation of R1R22ZnMgBr (R1 ¼ n-alkyl, R2 ¼ aryl) reagents.
In order to propose a brief convincing explanation for the sol-
vent dependence of the relative transfer ability of n-Bu and Ph
groups in the alkylation of stoichiometric mixed cuprate n-BuPh-
CuMgBr (1ab), we assumed a contact ion pair (CIP) such as a dimer
A or a hetero aggregate B in equilibrium with solvent-separated ion
pair (SSIP) (Scheme 2) [16,17,23]. The structure of similar to lithium
homo and mixed diorganocuprates [2,3,9j,24e29] and Grignard
reagent derived homocuprates [24,26e30] were determined by
crystallographical and NMR spectral studies. These findings
Table 2
Effect of cosolvents on the organic group transfer ability in the reaction of CuI catalyzed alkylation of bromomagnesium n-butyldiphenylzincate 2ab2, di(n-butyl) phenylzincate
2a2b, tri-n-butylzincate 2a3 and triphenylzincate 2b3 with n-pentyl bromide in THF at reflux temperature.a
Entry
Solvent
Yield, %b
Total yield, %c (4:5)d
With 2ab2
With 2a3
With 2b3
With 2a2b
1
2
3
4
5
6
THF
78
65
70
39
24
41
58
48
34
35
53
60
59 (8:92)
55 (44:56)
58 (43:57)
35 (14:86)
61 (20:80)
46 (9:91)
61 (38:62)
70 (80:20)
54 (98:2)
30 (28:72)
77 (81:19)
38 (40:60)
NMP (1:1)
DMPU (1:1)
Diglyme (1:1)
TMEDA (1:1)
Toluene (1:1)
a
Molar ratio of 2:3 was used to be 1.5:1.
GC yield.
The sum of GC yields of 4 and 5.
The ratio of GC yields of 4 and 5.
b
c
d

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E. Erdik et al. / Journal of Organometallic Chemistry 745-746 (2013) 235e241
Mixed zincate n-BuPh2ZnMgBr (2ab2) has the possibility of
forming Ph2CuMgBr (1b2) and n-BuPhCuMgBr (1ab) more than n-
Bu2CuMgBr (1a2) in in situ Zn / Cu transmetallation. Similarly,
formation of n-Bu2CuMgBr (1a2) and n-BuPhCuMgBr (1ab) is ex-
pected to be more than Ph2CuMgBr (1b2) in in situ Zn / Cu
transmetallation of mixed zincate n-Bu2PhZnMgBr (2a2b). These
assumptions seem to be in accordance with the group transfer
selectivity in the coupling of n-BuPh2ZnMgBr (2ab2) and n-
Bu2PhZnMgBr (2a2b) derived catalytic mixed cuprates (Table 2,
entry 1).
Our brief study suggests that using a N- or O-donor solvent as a
cosolvent does not change n-Bu group transfer ability in the
alkylation of n-BuPhCuMgBr (1ab) in THF. However, the group
transfer abilities of mixed zincate derived catalytic cuprates in alkyl
coupling are solvent dependent. These findings support the dif-
ference in the reactivity of Grignard reagent derived and zincate
derived diorganocuprate reagents. So, further comments on the
group selectivity of mixed zincate derived catalytic cuprates must
await more information concerning structure of these reagents.
Scheme 2.
indicated the equilibrium between CIP and SSIP structures which
are in accordance with reactivities [9j,24,30].
2.3. Coupling of n-BuPhZn with allyl bromide
In general, CIP is dominant in weakly solvating solvents and SSIP
is preferred in solvents with strong coordination ability [3,24,31,32].
However, it is known that it is essentially only CIP structures of a
cuprate which undergoes the reaction and the reactions proceed
with a small equilibrium concentration of CIP in solution and SSIP is
the much less or even unreactive species [3,9j,26,30,32e37].
Coupling of stoichiometric n-BuPhCuMgBr (1ab) in THF and in
We also investigated uncatalyzed coupling of n-BuPhZn with
allyl bromide at room temperature (Scheme 1c) to see the effect of
the reaction mechanism and also N-donor solvent as a cosolvent on
the group transfer ability.
Coupling of n-BuPhZn takes place by reaction of n-Bu group and/
or Ph group as nucleophiles with allyl bromide in THF quantita-
tively without Cu(I) catalysis. Optimized yields and 8:9 product
ratios for Relative transfer of n-Bu and Ph groups are shown in
Table 3.
THF:cosolvent
(1:1)
affords
almost
the
same
yield
(cosolvent ¼ NMP, DMPU, HMPA and diglyme). However, the yields
in THF:cosolvent (1:2) compared to those in THF:cosolvent (1:1) are
quite low. These results provide support for the equilibrium in
favour of SSIP in strongly coordinating solvents resulting in the
predominance of the unreactive SSIP in these solvents.
Background yields for coupling of n-Bu2Zn (6a2) and Ph2Zn (6b2)
in THF were found to be 92% and 98%, respectively. The yield
remained same in the presence of NMP and HMPA as N-donor
cosolvents; NMP as a cosolvent noticeably increased 8:9 product
ratio (entry 2), but HMPA did not result in a much change (entry 3).
It is interesting that the yield decreased much in the presence of
TMEDA and selective Ph group transfer took place (entry 4).
According to the literature data, the relative Ph > n-Bu transfer
in allyl coupling may not be surprising. Since in the Ni catalyzed
reaction of mixed diorganozincs with anhydrides, the relative
transfer ability of organyl groups was reported to be
Ph > Me > Et >> i-Pr [39] and theoretical study also supported the
higher reactivity of Ph compared to Et group for the reaction of
diphenylzinc/diethylzinc with aldehydes [10j]. Increased n-Bu
coupling in the presence of NMP and HMPA is also in accordance
with the smooth allylation of dialkylzincs in the presence of N-
donor solvents [40]. Chelating diamines, such as TMEDA were also
reported as the key for successful aryl transfer from mixed alky-
larylzincs in their reactions with aldehydes [10m]. In the allylation
of n-BuPhZn, similarly, selective Ph coupling takes place in
THF:TMEDA compared to THF alone, but with a quite low yield
(entry 4). We also wanted to see how the yield and 8:9 product ratio
would change using chelating diamines as additives. In the pres-
ence of 1 mol equiv of bipyridyl and urotropine, the yield decreased
to 85% and 65%, respectively, but 8:9 product ratio was found not
much different than that in THF alone (entries 5 and 6). Using
THF:toluene (1:1) as solvent just decreased the yield as excepted,
but did not change 8:9 product ratio (entry 7). So, it seems that
On the contrary, TMEDA as a cosolvent gave unexpectedly low yield
even using THF:TMEDA (1:1) as solvent. We think that TMEDA can
afford strong complexationwith two MgBr4 counter ions as a bridging
ligand [26]. In this case, the equilibrium lying completely on the side of
SSIP can prevent the presence of CIP structure in a small equilibrium
concentration to react. However, quite a low yield for the coupling in
THF:toluene (1:1) is not an unexpected behaviour. Since, in this case,
cosolvent has no coordination ability, but diminished nucleophilic
character of CIP structure will possibly prevent formation of coupled
products although the equilibrium is far beyond the CIP structures.
The selective n-Bu group transfer in the coupling of n-BuPh-
CuMgBr with 90% yield in THF compared with coupling yields of
homocuprates, i.e. 71% yield of n-Bu2CuMgBr (1a2) and 8% yield of
Ph2CuMgBr (1b2) simply shows that the residual group Ph facili-
tates the transfer of n-Bu group [9a].
As active catalytic intermediates in the copper catalyzed re-
actions of mixed zincates, n-BuPh2ZnMgBr (2ab2) and n-
Bu2PhZnMgBr (2a2b), we may assume transmetallation of n-butyl
and phenyl carbanions which are known to be in equilibrium in
small amounts with zincate as Grignard reagents and diorganozincs
(1) [8j,23,36e38]. Transmetallation of Grignard reagents possibly
result in formation of n-BuCu and PhCu and then formation of homo
and mixed cuprates. As zinc cuprates do not couple with n-pentyl
bromide, transmetallation of diorganozincs are omitted.
nꢀBuPh2ZnMgBr
nꢀBuPh ZnMgBr%n ꢀ BuMgBr þ Ph Zn and=or PhMgBr þ n ꢀ BuPhZnCuIn ꢀ BuCu and=or PhCu
!
2
2
n ꢀBu2CuMgBr þ Ph2CuMgBr þn ꢀ BuPhCuMgBr
(1)
1a2
1b2
1ab

E. Erdik et al. / Journal of Organometallic Chemistry 745-746 (2013) 235e241
239
Table 3
Effect of cosolvents on the organic group transfer ability in the reaction of n-butylphenylzinc 6ab with allyl bromide 7 in THF at room temperature.a,b
Entry
Solvent
Total yield, %c (8:9)d
1
2
3
4
5
6
7
THF
99 (17:83)
100 (40:60)
98 (26:74)
20 (0:100)
85 (27:63)
67 (31:69)
72 (21:79)
THF:NMP (1:1)
THF:HMPA (1:1)
THF:TMEDA (1:1)
Bipyridyle
Urotropinee
THF:toluene (1:1)
a
Molar ratio of 6ab:7 was used to be 1.5:1.
GC yields for allylation of n-Bu2Zn 6a2 and Ph2Zn 6b2 are 92% and 98%, respectively.
The sum of GC yields of 8 and 9.
The ratio of GC yields of 8 and 9.
1 mol equiv of additive was used.
b
c
d
e
using THF alone as a solvent is the best choice for atom-economic
aryl-allyl coupling using n-alkylarylzincs and allylic bromides.
is 79:21) and PhCH2 group transfer ability decreases in THF:TMEDA
(PhCH2/Ph transfer ratio is 42:58). These results are similar to those
obtained in the acylation of n-BuPhZn 6ab (entry 5). In the CuI
catalyzed acylation of n-Bu(PhCH2)Zn 6ac, the higher transfer
ability of PhCH2 group than that of n-Bu group both in THF and also
in THF:TMEDA seems surprising (entry 6). However, in the acyla-
tion of catalytic cuprate derived from Ph(MeCH]CH)Zn 6bd (entry
9), MeCH]CH group results in a high decrease in the yield of Ph
group transfer in THF:TMEDA and Ph group transfer seems not to
take place in THF compared to the background yields of Ph2Zn 6b2
(entry 2). A similar result was obtained in the acylation of catalytic
cuprate derived from (PhCH2)(MeCH]CH)Zn 6cd and quite a low
total yield was obtained (entry 10). However, some MeCH]CH
group transfer in THF:TMEDA (1:2) seemed interesting implying
that in the presence of aryl group as a partner, alkenyl group may be
reactive in acylation whereas in the presence of benzyl group it
appears inactive. As we could not pre(PhCH2)2Zn and (MeCH]
2.4. Acyl coupling of CuI catalyzed R1R2Zn with benzoyl chloride
We already found that the group transfer ability in the CuI
catalyzed benzoylation of n-BuPhZn inTHFat room temperature can
be controlled using N- and O-donor cosolvents [18]. For n-Bu group
selective and Ph group selective acylation in THF and THF:TMEDA
(1:2), respectively, we offered an explanation depending on the
acylation mechanism of solvent coordinated cuprates.
In order to observe if the group selectivity control of THF and
THF:TMEDA (1:2) works for other mixed diorganozincs, R1R2Zn, 6
in their CuI catalyzed acylation, we determined the optimized
yields and 11:12 product ratios (Table 4).
As seen, CuI catalyzed acylation of Ph(PhCH2)Zn 6bc (entry 8)
results in PhCH2 selective reaction in THF (PhCH2/Ph transfer ratio
Table 4
The yield of homo diorganozincs and group transfer ability in mixed diorganozincs in their CuI catalyzed acylation with benzoyl chloride 10 in THF and THF:TMEDA (1:2) at
room temperature.a
Entry
R1
R2
Total yield, %b,c (11:12)d
In THF
In THF:TMEDA (1:2)
1
2
3
4
5
6
7
8
9
6a2
6b2
6c2
6d2
6ab
6ac
6ad
6bc
6bd
6cd
n-Bu
Ph
n-Bu
Ph
PhCH2
MeCH]CH
Ph
PhCH2
MeCH]CH
PhCH2
MeCH]CH
MeCH]CH
90
64
59
66
PhCH2
MeCH]CH
n-Bu
n-Bu
n-Bu
Ph
ee
e
ee
e
78 (60:40)
91 (27:73)
e
67 (7:93)
54 (22:78)
e
61 (21:79)
4 (100:0)
20 (100:0)
60 (58:42)
32 (100:0)
16 (81:19)
Ph
PhCH2
10
a
Molar ratio of 6:10 was used to be 2:1.
GC yield for homo diorganozincs 6a2ed2.
The sum of GC yields of 11 and 12 for mixed diorganozincs.
The ratio of GC yields of 11 and 12.
b
c
d
e
6c2 and 6d2 could not be prepared in THF at room temperature.

240
E. Erdik et al. / Journal of Organometallic Chemistry 745-746 (2013) 235e241
CH)2Zn, we did not compare the CuI catalyzed acylation yields of
mixed benzyl and alkynyl zincs with their background yields. The
group selectivity order of PhCH2 > n-Bu > Ph > MeCH]CH in the
acylation of catalytic iodozinc diorganocuprates, R1R2CuZnI in THF
appears similar to the reported order for substitution of lithium
diorganocuprates [9a,f,g]. However, further investigation will be
necessary for the interpretation of the solvent effect in the group
transfer ability of R1 group depending on R2 groups in the reactions
of diorganocuprates, R1R2CuM (M ¼ Li, MgX, ZnX).
a stirring bar, CuI catalyst (0.2 mmol, 0.0381 g) was added and the
mixture was stirred at that temperature for 15 min. n-Pentyl bro-
mide (2) (1 mmol, 0.12 ml) was added dropwise with a syringe. The
mixture was allowed to warm to room temperature and stirred at
required temperature for an appropriate time. After addition of an
internal standard, the mixture was hydrolyzed with aqueous NH3/
NH4Cl solution. The aqueous phase was extracted with ether and
aliquots were analyzed by GC.
4. Conclusions
3. Experimental
We carried out this work to show the dependence of group
selectivity on the solvent in the reactions of diorganocuprates,
either stoichiometric or catalytic and diorganozincs.
All reactions were carried out under a nitrogen atmosphere in
oven dried glassware using standard syringe-septum cap tech-
niques [41]. Quantitative GC analysis were performed on a Thermo-
Finnigan gas chromatograph equipped with a ZB-5 capillary col-
umn packed with phenylsiloxane using standard technique. THF
was distilled from sodium benzophenonedianion; alkyl bromides
and bromobenzene were obtained commercially and purified 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 [42].
In conclusion, we have found that the use of a mixed cuprate
R1R2CuMgBr (R1 ¼ n-alkyl, R2 ¼ aryl) instead of a homocuprate
R12CuMgBr for alkyl coupling in THF increases n-alkyl transfer and
using a N- or O-donor cosolvent in 1:1 molar ratio or less does not
change either the yield or the relative group transfer ability. How-
ever, in the alkylation of catalytic mixed cuprates derived from CuI
catalyzed mixed zincates R12R2ZnMgBr and R12R2ZnMgBr (R1 ¼ n-
alkyl, R2 ¼ aryl), group transfer ability depends on the solvation ef-
fect of N- and O-donor solvents and it can be controlled by using N-
donor cosolvents. In the CuI catalyzed alkylation of n-Bu2PhZnMgBr,
mostly Ph group transfer takes place in THF whereas n-Bu group
transfer takes place in the presence of NMP, DMPU or TMEDA. In the
CuI catalyzed alkylation of n-BuPh2ZnMgBr, the presence of NMP or
DMPU increases n-butyl group transfer. It seems that the use of
TMEDA as a cosolvent in THF appears promising in atom-economic
HMPA, NMP, DMPU, diglyme and TMEDA were distilled under
reduced pressure and kept over molecular sieves under nitrogen.
Toluene was distilled and kept over Na under nitrogen.
Grignard reagents, RMgBr (R ¼ n-Bu, Ph, PhCH2, MeCH]
CH) were prepared in THF by standard methods and their con-
centrations were found by titration before use [43]. n-Bu2CuMgBr
1a2 and Ph2CuMgBr 1b2 were prepared by addition of 2 mol equiv
of n-BuMgBr or PhMgBr, respectively to a suspension of 1 mol equiv
of CuI in THF at ꢀ20 ꢁC and stirring at that temperature for 15e
30 min. For the preparation of n-BuPhCuMgBr 1ab, first n-BuCu was
prepared by addition of 1 mol equiv of n-BuMgBr to 1 mol equiv of
CuI in THF at ꢀ20 ꢁC and then by addition of 1 mol equiv of PhMgBr
to freshly prepared n-BuCu at ꢀ20 ꢁC and the solution was stirred at
that temperature for 15e30 min.
n-Bu3ZnMgBr 1a3 and Ph3ZnMgBr 1b3 were prepared by drop-
wise addition of 3 mol equiv of n-BuMgBr or PhMgBr, respectively
in THF to a solution of 1 mol equiv of ZnCl2 in THF at ꢀ15 ꢁC and
stirring at that temperature for 15 min. For the preparation of n-
BuPh2ZnMgBr 1ab2 and n-Bu2PhZnMgBr 1a2b, freshly prepared
Ph2Zn and PhZnCl respectively were used. Ph2Zn and PhZnCl were
prepared in THF by dropwise addition of 2 mol equiv and 1 mol
equiv of PhMgBr, respectively in THF, respectively to a solution of
1 mol equiv of ZnCl2 in THF at ꢀ15 ꢁC and stirring at that temper-
ature for 5 min. n-BuPh2ZnMgBr 1ab2 was prepared by dropwise
addition of 1 mol equiv of n-BuMgBr in THF to 1 mol equiv of Ph2Zn
in THF at ꢀ15 ꢁC and stirring at that temperature for 15 min. n-
Bu2PhZnMgBr 1a2b was prepared by dropwise addition of 2 mol
equiv of n-BuMgBr in THF to 1 mol equiv PhZnCl in THF at ꢀ15 ꢁC
and stirring at that temperature for 15 min.
n-alkylen-alkyl coupling using R12R2ZnMgBr (R1
¼
n-alkyl,
R2
¼
aryl) reagents and n-alkyl bromides and coupling of
R12R2ZnMgBr reagents inTHFrather than homozincates, R23ZnMgBr
seems to be the best choice for aryl-n-alkyl coupling.
In the allylation of n-BuPhZn, selective Ph group transfer takes
place without solvent effect. The results are briefly discussed in
terms of solvation of the mixed diorganocuprates and use of
coordinating solvents in atom-economic alkylation of n-alkyl(aryl)
cuprates and allylation of (n-alkyl)arylzincs. Solvent effect on the
group transfer ability in the acylation of catalytic mixed cuprates
derived from R1R2Zn in the presence of CuI catalysis has been found
to be dependent also on the R1 and R2 partnership. Further studies
on the synthetic use of solvent control of group transfer selectivity
in the reactions of mixed diorganocuprates and diorganozincs are
underway.
Acknowledgements
We thank the Turkish Scientific and Technical Research Council,
Grant No. TBAG106T644 and Ankara University Research Project,
Grant No. BAP 09B424004 for financial support.
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