Highly efficient copper-mediated atom-transfer radical addition (ATRA) in the presence of reducing agent

Article abstract of DOI:10.1002/ejic.200701144

The synthesis, characterization and exceptional activity of Cu ^I(TPMA)Br [TPMA = tris(2-pyridylmethyl)amine] and [Cu ^II(TPMA)Br][Br] complexes in ATRA reactions of polybrominated compounds to alkenes in the presence of reducing agent

Full text of DOI:10.1002/ejic.200701144

FULL PAPER
DOI: 10.1002/ejic.200701144
Highly Efficient Copper-Mediated Atom-Transfer Radical Addition (ATRA) in
the Presence of Reducing Agent
[a]
[a]
[a]
William T. Eckenhoff, Sean T. Garrity, and Tomislav Pintauer*
Keywords: Catalysis / Copper / ATRA / Reducing agent
I
+
The synthesis, characterization and exceptional activity of
mide anion to the [Cu (TPMA)] cation resulted in a forma-
I
I
Cu (TPMA)Br [TPMA
=
tris(2-pyridylmethyl)amine] and
tion of much more reducing Cu (TPMA)Br complex (E1/2
–720 mV vs. Fc/Fc ) than the corresponding ClO
–422 mV vs. Fc/Fc ) and PF
logues. In [Cu (TPMA)Br][Br], the Cu atom was coordinated
by four nitrogen atoms [Cu –Neq 2.073(2) Å and Cu –Nax
2.040(3) Å] from TPMA ligand and a bromine atom [Cu –Br
2.3836(6) Å]. The overall geometry of the complex was dis-
torted trigonal bipyramidal. Cu (TPMA)Br and [Cu (TPMA)-
Br][Br] complexes showed similar structural features from the
point of view of TPMA coordination. The only more pro-
nounced difference in the TPMA coordination to the copper
center was observed in the shortening of Cu–Nax bond length
=
=
II
+
–
[Cu (TPMA)Br][Br] complexes in ATRA reactions of polybro-
4
(E1/2
+
–
+
minated compounds to alkenes in the presence of reducing
6
(E1/2 = –421 mV vs. Fc/Fc ) ana-
II
II
II
agent (AIBN) was reported. [Cu (TPMA)Br][Br], in conjunc-
II
II
tion with AIBN, effectively catalyzed ATRA reactions of CBr
and CHBr to alkenes with concentrations between 5 and
00 ppm, which is the lowest number achieved in copper-
4
II
3
1
I
I
II
mediated ATRA. The molecular structure of Cu (TPMA)Br
indicated that the complex was pseudo-pentacoordinate in
the solid state due to the coordination of TPMA [Cu –N:
I
2
.1024(15), 2.0753(15), 2.0709(15) and 2.4397(14) Å] and bro-
I
mide anion to the copper(I) center [Cu –Br 2.5088(3) Å]. Vari-
able temperature H NMR and cyclic voltammetry studies
1
I
by approximately 0.400 Å on going from Cu (TPMA)Br to
I
I
II
confirmed the equilibrium between Cu (TPMA)Br and [Cu -
TPMA)(CH CN)][Br], indicating some degree of halide
[Cu (TPMA)Br][Br].
(
3
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
anion dissociation in solution. The coordination of the bro-
Introduction
which are continuously reduced to copper(I) complexes in
the presence of phenols, glucose, ascorbic acid, hydrazine,
tin(II) 2-ethylhexanoate and radical initiators. With ICAR
ATRP, controlled synthesis of poly(styrene) and poly-
The addition of halogenated compounds to carbon–car-
bon double (or triple) bonds through a radical process is
one of the fundamental reactions in organic chemistry.
It was first reported in the early 1940s in which halogenated
methanes were directly added to olefinic bonds in the pres-
ence of radical initiators or light.[ Today, this reaction is
known as the Kharasch addition or atom-transfer radical
[
1,2]
(
methyl methacrylate) can be implemented with catalyst
[
22]
concentrations between 10 and 50 ppm.
This technique
for catalyst regeneration has recently been utilized with
3,4]
III
great success in ATRA reactions catalyzed by [Cp*Ru -
[
25,26]
Cl (PPh )] complex.
In the case of ATRA of CCl to
[
5]
2
3
4
addition (ATRA), and it is typically catalyzed by transi-
tion metal complexes of Ru, Fe, Ni and Cu.
olefins in the presence of AIBN, TONs as high as 44500
[6–9]
Although
[
25]
were obtained.
copper mediated ATRA utilizing Cu (TPMA)Cl and [Cu -
TPMA)Cl][Cl] complexes [TPMA = tris(2-pyridylmethyl)-
We have also applied this technique in
transition metal catalyzed ATRA can be applied to a vari-
ety of halogenated substrates and alkenes, the principal
drawback of this useful synthetic tool until recently re-
mained the large amount of catalyst required to achieve the
high selectivity towards monoadduct. The solution to this
problem has been found for atom transfer radical polymeri-
I
II
(
[
27]
amine]. TPMA ligand was chosen for the study because
its complexation to Cu X (X = Cl or Br) results in a forma-
I
tion of one of the most active catalysts in copper mediated
[
28–30]
ATRP.
to alkenes was achieved with the catalyst to olefin ratio of
:10,000, resulting in TONs of 7,200 for 1-hexene and 6,700
The maximum activity in the addition of CCl4
[
10–21]
zation (ATRP),
new processes termed initiators for continuous activator re-
which originated from ATRA. These
1
[
22]
generation (ICAR)
and activators regenerated by elec-
for 1-octene.
tron transfer (ARGET)[
23,24]
utilize copper(II) complexes
The underlying principle of catalyst regeneration in the
presence of reducing agent in ATRA is shown in Scheme 1.
The mechanism is modified from the well established free
radical mechanism operating in metal-catalyzed ATRA re-
[
a] Department of Chemistry and Biochemistry, Duquesne Univer-
sity,
6
00 Forbes Avenue, 308 Mellon Hall, Pittsburgh, PA 15282,
USA
[
7,31–34]
actions.
In order to increase the chemoselectivity
Fax: +1-412-396-5683
E-mail: pintauert@duq.edu
towards the monoadduct, the following general guidelines
Eur. J. Inorg. Chem. 2008, 563–571
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
563

W. T. Eckenhoff, S. T. Garrity, T. Pintauer
FULL PAPER
need to be met: (a) radical concentration must be low in Results and Discussion
order to suppress radical termination reactions [activation
rate constant (ka,1 and ka,2) ϽϽ deactivation rate constant ATRA of CHBr and CBr to Alkenes
3 4
(
kd,1 and kd,2)], (b) further activation of the monoadduct
The addition of CBr to simple olefins (1-hexene, 1-oc-
4
should be avoided (ka,1 ϾϾka,2) and (c) the formation of
oligomers/polymers should be suppressed {rate of transfer
tene and 1-decene) in the presence of the reducing agent
I
AIBN, but without the Cu (TPMA)Br complex, proceeded
II
[
kd,2(Cu L X)] ϾϾ rate of propagation [k (alkene)]}. If a
m
p
very efficiently at 60 °C and the desired monoadduct was
formed in quantitative yields (Table 1). These results are not
large excess of alkyl halide is used relative to copper(I) com-
plex, the equilibrium K = ka,1/kd,1 will be shifted towards
1
surprising because of the known ability of CBr to function
4
the right hand side and, as a result of irreversible radical
coupling reactions, all of the copper(I) complex will be con-
verted into the corresponding copper(II) complex. To com-
pensate for this unavoidable side reaction in ATRA, a re-
ducing agent such as the radical initiator 2,2Ј-azobis(2-
methylpropionitrile) (AIBN) is added to the reaction mix-
ture. The slow decomposition of AIBN provides a constant
source of radicals, which continuously reduce copper(II) to
copper(I) complex. Copper(I) complex is needed for the ac-
tivation of alkyl halide (R–X). Furthermore, the efficient
regeneration of the copper(I) complex by reducing agent
[
38,39]
as a very efficient chain-transfer agent.
In the case of
methyl acrylate (Entry 4) and styrene (Entry 5), quantitative
conversions were also observed, however, the decreased
yield of the monoadduct was mostly due to the formation
of oligomers/polymers as a result of the presence of free
radical initiator. Similar reactions in the presence of CHBr3
yielded very low amounts of the monoadduct in the case of
-hexene (8%, Entry 6), 1-octene (9%, Entry 7) and 1-de-
cene (8%, Entry 8) or none in the case of methyl acrylate
Entry 9) and styrene (Entry 10). For the latter two alkenes,
1
(
the major products were oligomers/polymers. In the absence
enables ATRA reactions to be conducted starting with the
I
of AIBN, ATRA of CBr and CHBr with the Cu (TPMA)-
air-stable copper(II) complex.[27] Similar observations were
4
3
Br to alkene ratios between 1:500 and 1:10000 did not yield
the desired monoadduct, despite the high activity of the
III
[25,26]
also made in the case of [Cp*Ru Cl (PPh )] complex.
2
3
The outlined methodology to decrease the amount of metal
catalyst in ATRA reactions could have a significant impact
in radical syntheses of natural products, pharmaceutical
drugs and other complex molecules, which are currently
[
28–30]
complex in ATRP.
The principle reason was the com-
plete deactivation of the copper(I) complex to the corre-
sponding copper(II) complex, consistent with the proposed
mechanism shown in Scheme 1.
predominantly conducted utilizing stoichiometric amounts
of organotin and organosilane reagents.[
35–37]
In conjunc-
Table 1. Addition of polybrominated compounds to alkenes in the
presence of AIBN.
tion with the reduced amount of metal catalyst, the other
potential advantage of transition-metal-catalyzed ATRA is
that the resulting product contains a halide group, which
can be easily reduced, eliminated, displaced or converted to
a Grignard reagent.
Entry[a] Alkene
RBr
% Conversion % Yield
1
2
3
4
5
6
7
8
9
1
1-hexene
1-octene
1-decene
methyl acrylate CBr
styrene
1-hexene
1-octene
1-decene
methyl acrylate CHBr
styrene CHBr
CBr
CBr
CBr
4
≈100
≈100
≈100
≈100
99
10
9.5
11
99
41
≈100
≈100
≈100
32
72
8
4
4
4
4
CBr
CHBr
CHBr
CHBr
3
3
3
3
3
9
8
0
0
0
[
[
a] All reactions were performed in CH
3
CN at 60 °C for 24 h with
R–Br] :[alkene] :[AIBN] = 4:1:0.05. The yield is based on the for-
0
0
0
1
mation of monoadduct and was determined by H NMR using
anisole or toluene as internal standard.
ATRA of CHBr and CBr to Alkenes Catalyzed by
3
4
II
[
Cu (TPMA)Br][Br] in the Presence of AIBN
Table 2 shows the results for the ATRA of polybromin-
II
ated compounds to alkenes catalyzed by [Cu (TPMA)-
Br][Br] complex in the presence of a reducing agent AIBN.
The reaction conditions were optimized in such a way as to
Scheme 1. Proposed mechanism for copper(I) regeneration in the
presence of reducing agent (AIBN) during ATRA process.
In this article, we report on the synthesis, characteriza- achieve maximum conversion of the alkene and high yield
I
II
tion and exceptional activity of Cu (TPMA)Br and [Cu - of the monoadduct. For methyl acrylate, a significant im-
TPMA)Br][Br] complexes in ATRA reactions of polybro- provement in the yield of the monoadduct was achieved
(
II
minated compounds to alkenes in the presence of a reduc- using [Cu (TPMA)Br][Br] to methyl acrylate ratios of
ing agent (AIBN). 1:200000 (81%, Entry 1) and 1:100000 (94%, Entry 2).
564
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 563–571

Copper-Mediated Atom ATRA in the Presence of Reducing Agent
Furthermore, using identical reaction conditions, the com- and the yield of the monoadduct, is approximately 10 times
II
plete conversion of styrene was also achieved with the main higher than the activity of previously reported [Cu -
product being the desired monoadduct (95% Entry 3 and (TPMA)Cl]Cl in the ATRA of polychlorinated compounds
9
9% Entry 4). These results clearly indicate that the slow to alkenes. Also, for comparable monomers and alkyl ha-
III
decomposition of AIBN provides a constant source of radi- lides, its activity is very close to the activity of [Cp*Ru -
cals, which continuously reduce [Cu (TPMA)Br][Br] com- Cl (PPh )] complex. [Cu (TPMA)Br][Br], in conjunction
plex to Cu (TPMA)Br, which is needed to homolytically with AIBN, effectively catalyzes ATRA reactions of poly-
II
[25]
II
2
3
I
cleave the R–Br bond.
brominated compounds to alkenes with concentrations be-
tween 5 and 100 ppm, which is by far the lowest number
achieved in copper mediated ATRA.
Table 2. ATRA of polybrominated compounds to alkenes catalyzed
[9,27,40,41]
II
by [Cu (TPMA)Br][Br] in the presence of AIBN.
Entry[a] Alkene
RBr
methyl acrylate CBr
[Alk.]
/[CuII]
% Conv. % Yield[b]
0
0
1
2
3
4
5
6
7
8
9
4
200000:1
100000:1
200000:1
100000:1
10000:1
5000:1
1000:1
500:1
10000:1
5000:1
1000:1
≈100
≈100
≈100
99
≈100
≈100
≈100
≈100
≈100
≈100
≈100
67
81 (76)[c]
94
I
Synthesis and Characterization of Cu (TPMA)Br
95 (86)[
c]
styrene
CBr
4
99
I
II
The high activity of [Cu (TPMA)Br] and [Cu (TPMA)-
Br][Br] complexes in ATRA can be explained in terms of
11 (11)[
c]
methyl acrylate CHBr
3
23
57
66
70
increased values of the activation rate constant (ka,1
Scheme 1) and the equilibrium constant for atom transfer
K = ka,1/kd,1, Scheme 1), when compared to other cop-
,
styrene
CHBr
3
(
1
1
0
77
per(I) complexes with bidentate and tridentate nitrogen-
1
1
92
[
42–45]
[
c]
based ligands and different counterions.
The struc-
1
2
1-hexene
1-octene
1-decene
CHBr
CHBr
CHBr
3
10000:1
10000:1
10000:1
61 (59)
69 (54)[
c]
1
3
3
75
tural features of highly ATRP and now ATRA active
14
3
74
63 (64)[
c]
I
Cu X/TPMA (X = Cl and Br) complexes are still not fully
a] All reactions were performed in bulk at 60 °C for 24 h with [R– understood.[46] TPMA typically coordinates to the cop-
[
Br]
0 0 0
/[alkene] /[AIBN] = 4:1:0.05, except reactions for Entries 1–4 per(I) complex in a tetradentate fashion, similarly to struc-
which were performed in CH
3
CN. [b] The yield is based on the
turally
related
tris[2-(N,N-dimethylamino)ethyl]amine
However, the role of the counterion in
1
formation of monoadduct and was determined by H NMR using
anisole or toluene as internal standard. [c] Isolated yield after col-
umn chromatography.
[
47,48]
(
Me TREN).
6
these complexes is also very unclear. For example, in the
I
[48]
crystal structure of [Cu (Me TREN)][ClO ],
the cop-
6
4
As indicated in Table 2, the methodology for the cop- per(I) atom was found to be distorted trigonal bipyramidal
per(I) regeneration in ATRA in the presence of the reducing and it was coordinated by 4 nitrogen atoms from the
I
I
agent AIBN worked very well for the less active bromo- Me TREN ligand [Cu –N
2.122(7) A and Cu –N
6
eq
ax
–
form. Relatively high yields of the monoadduct were ob- 2.200(14) A] and an oxygen atom from the ClO anion
tained in ATRA of CHBr to methyl acrylate (Entry 7 and [Cu –O 3.53(1) A]. In the case of Cu Br/Me TREN com-
4
I
I
3
6
8
) and styrene (Entry 10 and 11), but with much higher plex, EXAFS studies have indicated several possible struc-
I
catalyst loadings. Further decrease in the amount of cata- tures in solution which included [Cu (Me TREN)][Br],
lyst for both monomers resulted in a decrease in the yield [Cu (Me TREN)][Cu Br ] and [Cu (Me TRENЈ)Br] (Me -
of the monoadduct. The decrease in the yield of monoad- TRENЈ denotes a tricoordinate Me TREN).
6
I
I
I
6
2
6
6
[
46,49–51]
These
6
duct was mostly due to the formation of oligomers/poly- structures were based on the validated assumption that the
mers, which can be attributed to (a) insufficient trapping of maximum coordination number of copper(I) should not ex-
[
52]
I
radicals generated from AIBN by the copper(II) complex ceed four.
and (b) further activation of the monoadduct by the cop- (TPMA)Cl complex, which was surprisingly pseudo-penta-
Recently, we have isolated a neutral Cu -
[
27]
per(I) complex (more pronounced in the case of methyl ac- coordinate.
The copper(I) ion was coordinated by four
rylate). In the ATRA of CHBr to 1-hexene (Entry 12), 1- nitrogen atoms with bond lengths of 2.0704(11), 2.0833(11)
3
octene (Entry 13) and 1-decene (Entry 14), moderate yields and 2.0888(11) Å for the equatorial Cu–N and 2.4366(11) Å
of the monoadduct can be attributed to incomplete alkene for the axial Cu–N bonds and a chlorine atom with a bond
conversions. Furthermore, the conversions of the alkene for length of 2.3976(4) Å.
I
Entries 12–14 were relatively independent on the copper-
The molecular structure of the Cu (TPMA)Br complex
I
(II):alkene ratios between 1:500 and 1:10000, indicating that (Figure 1) was obtained by slow crystallization of Cu Br/
the rate of addition of CHBr ·radicals to alkenes is slow. TPMA from THF/EtOH at –35 °C. The copper(I) center is
2
ATRA of CHBr to alkenes (Entries 5–14, Table 2) yielded also pseudo-pentacoordinate and the geometry of the com-
3
similar results in acetonitrile, indicating that an increase in plex is distorted trigonal bipyramidal. The copper(I) atom
solvent polarity did not significantly alter the catalytic per- is coordinated by four nitrogen atoms with bond lengths of
II
formance of [Cu (TPMA)Br][Br].
2.1014(15), 2.0753(15), and 2.0709(15) Å for the equatorial
II
The activity of [Cu (TPMA)Br][Br] complex in ATRA Cu–N and 2.4397(14) Å for the axial Cu–N bonds and a
of polybrominated compounds to alkenes in the presence Cu–Br bond length of 2.5088(3) Å. Furthermore, the cop-
of AIBN, based on catalyst loading, conversion of alkene per(I) atom lies 0.538(6) Å below the least-squares plane
Eur. J. Inorg. Chem. 2008, 563–571
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
565

W. T. Eckenhoff, S. T. Garrity, T. Pintauer
FULL PAPER
derived from N2, N3 and N4, towards the bromide ion.
The molecule possesses near (noncrystallographic) three-
fold symmetry with respect to the Cu–Br1 or Cu–N1 vector.
I
Figure 1. Molecular structure of Cu (TPMA)Br, shown with 30%
thermal probability ellipsoids. H atoms have been omitted for clar-
ity. Selected distances [Å] and angles [°]: Cu1–N1 2.4397(14), Cu1–
N2 2.1024(15), Cu1–N3 2.0753(15), Cu1–N4 2.0709(15), Cu1–Br1
2
.5088(3), N4–Cu1–N3 120.51(6), N4–Cu1–N2 112.40(6), N3–
Cu1–N2 107.61(6), N4–Cu1–N1 75.37(5), N3–Cu1–N1 74.86(5),
N2–Cu1–N1 74.80(5), N1–Cu1–Br1 179.14(3).
1
The proton resonances in the H NMR spectrum of the
Cu (TPMA)Br complex in (CD ) CO at room temperature Figure 2. Variable-temperature 1H NMR spectra [400 MHz,
(
I
3
2
I
(
3 2
CD ) CO] of the Cu (TPMA)Br complex.
Figure 2) are very broad, indicating a fluxional system.
However, on cooling to 220 K, the resonances due to the
coordinated TMPA ligand become very well resolved. Only
one set of resonances for the protons in the TPMA ligands
The broadened resonances in the solution 1H NMR
I
were observed which is consistent with near threefold sym- spectra of Cu (TPMA)Br (260–298 K) in (CD ) CO could
3
2
I
metry observed in the solid-state structure of Cu (TPMA)- be induced by the occurrence of the fluxional processes
Br complex. Because TPMA coordinates to the copper(I) such as the ligand dissociation, which are well known in
center through four nitrogen atoms, hydrogen atoms that copper(I) complexes with nitrogen-containing ligands.[
are close to the coordinated nitrogen atoms should be sig- In the case of the tetradentate TPMA ligand, the dissoci-
nificantly deshielded relative to the free ligand. This was ation and association of the pyridine nitrogen atoms has
indeed observed. The chemical shift of the hydrogen atom been proposed in the previous studies, as well as the pos-
57–59]
1
next to the nitrogen atom in the pyridine ring (H , Figure 2) sibility for the formation of dimers in which each copper(I)
at 220 K moves approximately 0.60 ppm downfield relative ion is ligated with two pyridine nitrogen atoms and one
to free TPMA. Such downfield shift in proton resonances tertiary amine nitrogen atom of a single TPMA and one
between 0.50 and 0.70 ppm is typically observed in cop- pyridine nitrogen atom of the second adjacent TPMA li-
per(I) complexes with nitrogen-based ligands.[
53–56]
Simi- gand.
larly, the downfield shift of the methylene protons in TPMA ure 2 are not consistent with the dimer formation because
[60,61]
The H NMR spectra of Cu (TPMA)Br in Fig-
1
I
5
(
H , Figure 2) by 0.10 ppm also indicates coordination. such coordination environment would result in two chemi-
Much smaller downfield shift for methylene protons (H ) cally inequivalent methylene groups. Furthermore, the asso-
5
1
when compared to H in coordinated TPMA is also consis- ciation/dissociation of the pyridine atoms in TPMA ligand
I
tent with the solid-state structure of the Cu (TPMA)Br (Scheme 2) appears to be the minor dynamic process be-
I
complex. In Cu (TPMA)Br, the distance between the cen- cause significant deshielding effects would have been ob-
tral nitrogen atom and the copper(I) center is on average served in the variable temperature H NMR studies. For
1
0.360 Å longer than the distance between the copper(I) cen- example, the chemical shift of the hydrogen atom next to
ter and the nitrogen atom from the pyridine ring. Conse- the nitrogen atom in the pyridine ring of the TPMA ligand
1
quently, the deshielding effect for the methylene protons (H , Figure 2) becomes deshielded by approximately
5
1
(
H ) should be less than for the pyridine proton (H ), which 0.10 ppm in the temperature range 298–188 K. In order to
was observed. The resonances for H and H protons in test the possibility for Br– dissociation from the Cu -
2
3
I
I
Cu (TPMA)Br are only slightly shielded upon coordination (TPMA)Br complex, NMR experiments were performed in
–
(
∆δ = 0.12 and 0.05 ppm, respectively). Furthermore, the the presence of externally added source of Br anions, such
resonance for the H proton moves approximately 0.32 ppm as tetrabutylammonium bromide (TBABr). In the presence
upfield upon TPMA coordination to the copper(I) center.
4
1
of 1.0 equiv. of TBABr, the room temperature H NMR
566
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 563–571

Copper-Mediated Atom ATRA in the Presence of Reducing Agent
I
spectrum of Cu (TPMA)Br appeared sharper and re-
I
sembled the spectrum of Cu (TPMA)Br at 260 K in the ab-
sence of TBABr. This indicates that the broadening in the
1
I
H NMR spectra of Cu (TPMA)Br (260–298 K) is induced
–
I
by the dissociation of the Br anions to generate [Cu -
+
–
(TPMA)] [Br] . Furthermore, variable temperature experi-
ments performed in CD CN (230–298 K) also indicated ha-
3
I
lide anion dissociation. Additionally, in the case of Cu -
(
TPMA)Br complex in CD CN (99% D), we were able to
3
observe the proton resonance for the coordinated CD CN,
3
which progressively shifted from 2.13 ppm (298 K) to
2.35 ppm (230 K). At 230 K, only four resonances for the
coordinated TPMA ligand were observed, indicating the
I
formation of [Cu (TPMA)(CH CN)][Br] complex in solu-
3
tion (Scheme 2). Copper(I) complexes with the TPMA li-
gand and its derivatives containing acetonitrile as the fifth
ligand have been previously observed and structurally char-
[
60]
acterized.
Quantifying the temperature and solvent de-
pendence on the equilibrium constant for the bromide
I
anion dissociation from Cu (TPMA)Br complex is the sub-
ject to future investigation in our laboratories. The study
could provide much needed information in an ongoing de-
bate on the nature of the atom transfer radical addition and
polymerization from the point of view of concerted inner-
sphere electron transfer process (ISET) or a two step pro-
[
11,62,63]
cess with an outer-sphere electron transfer (OSET).
I
–,
and Br ) in the presence of different supporting electrolytes
in CH CN at room temperature. Spectra are presented with respect
Figure 3. Cyclic voltammograms of [Cu (TPMA)][A] (A = ClO
4
–
–
PF
6
3
+
to Fc/Fc couple.
Table 3. Cyclic voltammetry data for copper(I) complexes in
CH CN.
3
Complex[a]
Supp. Elect.
E
1/2 [mV] ∆E
[mV]
ipa/ipc
I
p
Scheme 2. Proposed equilibria for Cu (TPMA)Br involving (a) ha-
lide anion and (b) pyridine nitrogen association/dissociation.
I
[Cu (TPMA)][ClO ] TBAClO4
4
–422
–706
–421
–711
–720
94
97
88
88
93
0.95
0.92
0.94
0.91
1.08
TBABr
I
[
Cu (TPMA)][PF
6
]
TBAPF
TBABr
TBABr
6
I
Cu (TPMA)Br
In order to further examine the coordination of the bro-
mide anion to the Cu (TPMA)Br complex, cyclic voltam-
metry experiments were performed. Cyclic voltammetry has
been extensively used in probing the catalytic activity of
copper(I) complexes in ATRP/ATRA because the redox po-
+
I
[a] Potentials are reported vs. Fc/Fc and were measured under the
same electrochemical cell conditions.
Peak separations were all less than 100 mV at a scan rate
tential can be correlated with the equilibrium constant for of 100 mV/s. The Cu /Cu reduction potentials measured
Fig- for the copper(I) complexes are reported relative to the fer-
ure 3 shows cyclic voltammograms of [Cu (TPMA)][A] (A rocene-ferrocenium couple which was used as an external
II
I
[44,46,50,64]
atom transfer (KATRA or KATRP, Scheme 1).
I
–
–
–
I
=
ClO , PF and Br ) complexes in the presence of dif- reference. The redox potentials for [Cu (TPMA)][ClO ]/
4 6 4
I
ferent supporting electrolytes in CH CN at room tempera- TBAClO (supporting electrolyte) and [Cu (TPMA)][PF ]/
3
4
6
ture. The electrochemical data are given in Table 3. The TBAPF were determined to be E = –422 mV (∆E =
6
1/2
p
copper(I) complexes display single quasireversible redox be- 94 mV) and E1/2 = –421 mV (∆E = 88 mV) in CH CN,
p
3
havior with ipa/ipc varying from 0.91 to 1.08.
respectively. Changing the supporting electrolyte to TBABr
Eur. J. Inorg. Chem. 2008, 563–571
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
567

W. T. Eckenhoff, S. T. Garrity, T. Pintauer
FULL PAPER
resulted in the shifting of cyclic voltammograms for both
complexes by approximately 300 mV [E = –706 mV (∆Ep
1
/2
–
=
97 mV) for ClO and E1/2 = –711 mV (∆E = 88 mV) for
4
p
–
PF6 complex, respectively]. Furthermore, as indicated in
Figure 3, both voltammograms were nearly identical to the
cyclic voltammogram of Cu (TPMA)Br complex using
I
TBABr as the supporting electrolyte [E1/2 = –720 mV (∆Ep
=
93 mV)]. Therefore, for both complexes, it is apparent
I
that the bromide anion has coordinated to the [Cu -
+
I
(TPMA)] cation forming the Cu (TPMA)Br complex, con-
firming the reverse of the equilibrium shown in Scheme 2.
These results also indicate that the coordination of the bro-
I
+
mide anion to the [Cu (TPMA)] cation results in a forma-
I
tion of much more reducing Cu (TPMA)Br complex, when
–
–
compared to ClO4 and PF6 analogues. Because previous
studies by Matyjaszewski et al.[
44,46,50,64]
have indicated that
II
the KATRP or KATRA equilibrium constants correlate lin- Figure 4. Molecular structure of the [Cu (TPMA)Br][Br], shown
with 30% probability displacement ellipsoids. H atoms have been
omitted for clarity. Symmetry codes: (i) –y + 1/2, –z + 1, x + 1/2
and (ii) z – 1/2, –x + 1/2, –y + 1. Selected distances (Å) and angles
early with the E1/2 values of the copper complexes [provided
that copper(II) complexes have similar “halidophilicities”
(
KHP) or the equilibrium constants for the heterolytic disso-
[°]: Cu1–N1 2.040(3), Cu1–N2 2.073(2), Cu1–Br1 2.3836(6), N1–
I
i
ciation of the halide anion], one can assume that the Cu - Cu1–N2 80.86(5), N2–Cu1–N2 117.53(3), N1–Cu1–Br1 180.00(5).
TPMA)Br complex should be a better catalyst for ATRA/
(
I
I
ATRP, then [Cu (TPMA)][ClO ] or [Cu (TPMA)][PF ].
I
II
4
6
were also made in the case of Cu (TPMA)Cl and [Cu -
TPMA)Cl][Cl] complexes, in which the shortening of Cu–
However, in the ATRA of CHBr and CBr to alkenes cata-
3
4
(
I
–
–
–
lyzed by [Cu (TPMA)][A] (A = ClO , PF and Br ) sim-
4
6
Nax bond length on going from copper(I) to copper(II)
ilar catalytic activities were obtained. Therefore, apart from
the redox potentials, additional factors must also contribute
towards the equilibrium constant for atom transfer.
[27]
complex was determined to be 0.389 Å. From the struc-
I
tural point of view, the high activity of Cu (TPMA)Br and
II
[
Cu (TPMA)Br][Br] complexes in ATRA, can be explained
by the fact that minimum entropic rearrangement is re-
I
quired when Cu (TPMA)Br complex homolytically cleaves
II
II
Synthesis and Characterization of [Cu (TPMA)Br][Br]
R–Br bond to generate [Cu (TPMA)Br][Br]. At the present
–
moment, it is the unclear what is the role of Br coordina-
II
The corresponding deactivator, [Cu (TPMA)Br][Br] was
I
+
I
tion to the [Cu (TPMA)] cation [Cu –Br = 2.5088(3) Å].
The most reasonable explanation is that the activation in
ATRA/ATRP process proceeds with either prior dissoci-
II
synthesized by reacting Cu Br with the stoichiometric
amount of TPMA. The same complex can be alternatively
prepared by reacting Cu (TPMA)Br with excess alkyl halide
CBr or CHBr ). Figure 4 shows the molecular structure
of the [Cu (TPMA)Br][Br] complex. In {Cu (TPMA)-
Br(Br), the Cu atom is coordinated by four nitrogen atoms
Cu –N 2.073(2) Å and Cu –N 2.040(3) Å]} from the
TPMA ligand and a bromine atom [Cu –Br 2.3836(6) Å].
The overall geometry of the complex is distorted trigonal
bipyramidal and the copper(II) atom is positioned
2
I
–
I
ation of Br from Cu (TPMA)Br complex or dissociation
(
–
II
4
3
of Br from the corresponding Cu (TPMA)Br to generate
the deactivator [Cu (TPMA)Br][Br]. As a part of an ongo-
2
II
II
II
II
ing investigation in our laboratories, detailed kinetic mea-
surements and cyclic voltammetry studies are being con-
ducted in order to further investigate the equilibrium for
II
II
[
eq ax
II
–
I
+
I
Br coordination to the [Cu (TPMA)] cation in Cu -
TPMA)Br complex and its effect on catalytic activity and
(
0
.329(3) Å below the least-squares plane derived from the
reaction mechanism.
equatorial nitrogen atoms in TPMA. The N1, Cu1 and Br1
atoms lie on the crystallographic threefold rotation axis.
From the point of view of TPMA coordination, the
Conclusions
I
II
structures of Cu (TPMA)Br and [Cu (TPMA)Br][Br] are
I
I
very similar. In Cu (TPMA)Br complex, the average Cu –
In summary, the synthesis, characterization and high ac-
II
I
II
Neq bond length is 0.0100 Å longer than in [Cu (TPMA)- tivity of Cu Br and Cu Br complexes with TPMA in
2
Br][Br]. The N –Cu–N angles are very similar in both ATRA of polybrominated compounds to alkenes was re-
ax
eq
complexes, while the average angle in the plane N –Cu– ported. The methodology utilized AIBN, which provided
ax
II
Nax is slightly larger in [Cu (TPMA)Br][Br] [117.53(3)°] external source of radicals for continuous regeneration of
than in Cu (TPMA)Br [113.51(10)°]. The only more pro- the copper(I) complex. [Cu (TPMA)Br][Br], in conjunction
I
II
nounced difference in the TPMA coordination to the cop- with AIBN, effectively catalyzed ATRA reactions of CBr4
per center can be seen in the shortening of Cu–Nax bond and CHBr to alkenes with concentrations between 5 and
3
I
length by approximately 0.400 Å on going from Cu - 100 ppm, which is the lowest number achieved in copper-
II
I
(
TPMA)Br to [Cu (TPMA)Br][Br]. Similar observations mediated ATRA. Molecular structure of Cu (TPMA)Br
568
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 563–571

Copper-Mediated Atom ATRA in the Presence of Reducing Agent
indicated that the complex was pseudo-pentacoordinate in der was washed with 2ϫ10 mL of n-pentane and dried under vac-
II
uum to yield 1.93 g (96%) of [Cu (TPMA)Br][Br]. C18
H18Br
2
CuN
4
the solid state due to the coordination of the bromide anion
I
(513.72): calcd. C 42.08, H 3.53, N 10.91; found C 42.06, H 3.55,
N 10.72. FT-IR (solid): ν˜ = 3048 (w), 2932, (w), 2864 (w), 1602
m), 1470 (m), 1434 (m), 1299 (m), 1155 (w), 1091 (m), 1016 (m),
92 (s), 648 (m) cm . Crystals suitable for X-ray analysis were
obtained by slow diffusion of diethyl ether into an acetonitrile solu-
tion of the complex at room temperature.
to the copper(I) center [Cu –Br 2.5088(3) Å]. Variable tem-
1
perature H NMR and cyclic voltammetry studies con-
(
7
I
I
firmed the equilibrium between Cu (TPMA)Br and [Cu -
TPMA)(S)][Br] (S = solvent) complexes, indicating halide
–
1
(
anion dissociation in solution. The extent of dissociation
was dependent on the solvent polarity and temperature. In
II
II
Catalyst Solutions: Two catalyst solutions were made using dilution
flasks to accommodate the various catalyst loadings. Catalyst solu-
tion A was made by dissolving 25.7 mg of [Cu(TPMA)Br][Br] in
.00 mL of acetonitrile to give a 0.01  solution. Catalyst solution
B was made in two steps by first dissolving 25.7 mg of [Cu(TPMA)-
[
Cu (TPMA)Br[Br], the Cu atom was coordinated by four
II
II
nitrogen atoms [Cu –N
.040(3) Å]] from TPMA ligand and a bromine atom [Cu –
2.073(2) Å and Cu –N
eq
ax
II
2
5
Br 2.3836(6) Å]. The overall geometry of the complex was
I
II
distorted trigonal bipyramidal. Cu (TPMA)Br and [Cu -
TPMA)Br][Br] complexes showed similar structural fea-
Br][Br] in 10.00 mL of acetonitrile to give a 0.005  solution.
.00 mL of this 0.005  solution was then diluted to 10.00 mL of
(
1
tures for the point of view of TPMA coordination. The only acetonitrile to yield a 0.0005  catalyst solution.
more pronounced difference in the TPMA coordination to
3
ATRA of CHBr to Alkenes: To a 5-mL Schlenk flask was added
the copper center was observed in the shortening of Cu–
bond length by approximately 0.400 Å on going from
bromoform (282.0 µL, 3.22 mmol), which was dissolved in 500 µL
of acetonitrile. To this solution was added alkene (0.805 mmol),
AIBN (6.6 mg, 40.3 µmol), and toluene (15.0 µL) in the case of 1-
N
ax
I
II
Cu (TPMA)Br to [Cu (TPMA)Br][Br]. Apart from the de-
tailed structural and mechanistic studies of this interesting hexene, 1-octene, and 1-decene or anisole in the case of styrene and
catalytic system, we are presently utilizing the outlined pro- methyl acrylate. The catalyst solution A was then added at the de-
cedure to decrease the amount of copper catalyst in syn- sired alkene/catalyst ratio between 500:1 and 10000:1. The flask
was then sealed under argon and stirred at 60 °C for 24 h. The
thetically more attractive atom transfer radical cyclization
conversion of the alkene and the yield of the monoadduct was de-
(ATRC) reactions.
1
termined by H NMR using internal standard. Column chromatog-
raphy was used to determine isolated yields (10% ethyl acetate in
hexanes for styrene and methyl acrylate and hexane for 1-hexene,
Experimental Section
1-octene, and 1-decene).
General Procedures: All chemicals were purchased from commer-
ATRA of CBr to Alkenes: Carbon tetrabromide (1.067 g,
3.22 mmol) was placed in a 5-mL Schlenk flask and dissolved in
4
cial sources and used as received. Tris(2-pyridylmethyl)amine
TPMA) was synthesized according to literature procedures.[ Sol-
65]
(
5
4
00.0 µL of acetonitrile. Alkene (0.805 mmol), AIBN (6.6 mg,
0.3 µmol), and toluene (15.0 µL) was added to this solution in the
vents (dichloromethane, pentane, acetonitrile and toluene) were de-
gassed and deoxygenated using Innovative Technology solvent pu-
rifier. All monomers were degassed by bubbling argon for 30 min
and stored in the dry box. Methanol was distilled and deoxy-
genated by bubbling argon for 30 min prior to use. All manipula-
case of 1-hexene, 1-octene, and 1-decene or anisole in the case of
styrene and methyl acrylate. The catalyst solution B was then added
at the desired alkene/catalyst ratio between 100000:1 and 200000:1.
The flask was then sealed under argon and stirred at 60 °C for 24 h.
tions were performed under argon in a dry box (Ͻ1.0 ppm of O
and Ͻ0.5 ppm of H O) or using standard Schlenk line techniques.
H NMR spectra were obtained with Bruker Avance 300 and
00 MHz spectrometers and chemical shifts are given in ppm rela-
tive to residual solvent peaks [C , 7.16 ppm; CDCl , 7.26 ppm;
CD CO, 2.05 ppm]. IR spectra were recorded in the solid state
or in solution with a Nicolet Smart Orbit 380 FT-IR spectrometer
Thermo Electron Corporation). Elemental analyses for C, H and
N were obtained from Midwest Microlab, LLC.
2
The conversion of the alkene and the yield of the monoadduct was
2
1
1
determined by
H NMR using internal standard. Column
chromatography was used to determine isolated yields (10% ethyl
acetate in hexanes for styrene and methyl acrylate and hexane for
4
6
D
6
3
1-hexene, 1-octene, and 1-decene).
(
3 2
)
X-ray Crystal Structure Determination: The X-ray intensity data
(
were collected at 150 K using graphite-monochromated Mo-K ra-
α
diation (λ = 0.71073 Å) with a Bruker Smart Apex II CCD dif-
fractometer. Data reduction included absorption corrections by the
multiscan method using SADABS.[ Crystal data and experimen-
tal conditions are given in Table 4. Structures were solved by direct
I
I
Synthesis of Cu (TPMA)Br: Cu Br (25.0 mg, 0.174 mmol) and
TPMA (50.0 mg, 0.174 mmol) were dissolved in 2 mL of EtOH/
THF (50%/50% vol.) and slow crystallization at –35 °C afforded
orange crystals. The supernatant liquid was decanted and the crys-
tals washed with 2ϫ10 mL n-pentane and dried under vacuum to
66]
methods and refined by full-matrix least-squares using SHELXTL
67]
6
.1 bundled software package.[ The H atoms were positioned ge-
I
1
ometrically (aromatic C–H 0.93 Å, methylene C–H 0.97 Å and
methyl C–H 0.96 Å) and treated as riding atoms during subsequent
refinement, with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C). The
methyl groups were allowed to rotate about their local threefold
axes. ORTEP-3 for Windows and Crystal Maker 7.2 were used to
generate molecular graphics.[
yield 47 mg (63%) of Cu (TPMA)Br. H NMR [(CD
3
)
2
CO,
= 7.7,
= 1.8 Hz, 3 H), 7.36 (d, J = 7.8 Hz, 3 H), 7.32 (m, 3 H), 3.94 (s,
H) ppm. C18 18BrCuN (433.81): calcd. C 49.84, H 4.18, N
3
J
6
1
00 MHz, 220 K]: δ = 9.10 (d, J = 4.2 Hz, 3 H), 7.81 (dt, J
1
2
H
4
2.91; found C 49.55, H 4.09, N 12.65.
68]
II
Synthesis of [Cu (TPMA)Br][Br]: Dichloromethane (2 mL) was
II
CCDC-649993 [for Cu (TPMA)Br] and -649992 {for [CuII-
I
2
added to a round-bottomed flask containing Cu Br (0.878 g,
3
3
.93 mmol) and tris(2-pyridylmethyl)amine (TPMA) (1.141 g, (TPMA)Br][Br]} contain the supplementary crystallographic data
.93 mmol). The reaction mixture was stirred at room temperature
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
for 30 min and the product precipitated by the slow addition of n-
pentane. The supernatant liquid was decanted and the green pow-
Eur. J. Inorg. Chem. 2008, 563–571
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
569

W. T. Eckenhoff, S. T. Garrity, T. Pintauer
Table 4. Crystallographic data and experimental details for Cu (TPMA)Br and [Cu (TPMA)Br][Br].
FULL PAPER
I
II
I
II
Cu (TPMA)Br
[Cu (TPMA)Br][Br]
Empirical formula
Color/shape
Formula weight
Crystal system
Space group
Temperature [K]
Cell constants
a [Å]
C
18
H
18BrCuN
4
C
18
H
18Br
2
CuN
4
orange/needles
433.81
monoclinic
P 21/c
green/rhomboids
513.72
cubic
P21 3
150(2)
150(2)
10.3042(9)
14.2256(12)
12.6335(3)
12.6335(3)
b [Å]
c [Å]
α [°]
12.5491(11)
90
12.6335(3)
90
β [°]
105.5800(10)
90
1771.9(3)
90
90
γ [°] 3
V (Å )
2016.37(8)
Formula units/unit cell
4
4
–3
ρcalcd. [gcm ]
1.626
3.494
1.692
5.054
–1
Absorption coefficient [mm ]
Diffractometer
Bruker Smart Apex II
Bruker Smart Apex II
Radiation, graphite-monochromated
Crystal size [mm]
θ range [°]
Range of h,k,l
Reflections collected/unique
Mo-K
α
(λ = 0.71073 Å)
α
Mo-K (λ = 0.71073 Å)
0.26ϫ0.14ϫ0.09
2.28 to 32.81
Ϯ18, –18Ǟ19, –19Ǟ18
26426/2460
0.41ϫ0.14ϫ0.03
2.05 to 32.25
Ϯ15, –21Ǟ20, Ϯ18
23037/6166
R
int
0.0390
0.1665
2
2
Refinement method
full-matrix least-squares on F
6166/0/217
1.015
full-matrix least-squares on F
2460/0/76
1.030
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
R
R
1
= 0.0304, wR
= 0.0511, wR
2
= 0.0621
= 0.0680
R
R
1
= 0.0271, wR
= 0.0343, wR
2
= 0.0637
= 0.0649
1
2
1
2
–
3
Max. resid. peaks [eÅ ]
0.450 and –0.357
0.566 and –0.544
Cyclic Voltammetry: Electrochemical measurements were carried
out using Bioanalytical Systems (BAS) model CV-50W in a dry
box. Cyclic voltammograms were recorded with a standard three-
electrode system consisting of a Pt-wire working electrode, a stan-
dard calomel reference electrode, and a Pt-wire auxiliary electrode.
[8] R. A. Gossage, L. A. Van De Kuil, G. Van Koten, Acc. Chem.
Res. 1998, 31, 423–431.
[
[
9] A. J. Clark, J. Chem. Soc. Rev. 2002, 31, 1–11.
10] J. S. Wang, K. Matyjaszewski, J. Am. Chem. Soc. 1995, 117,
5614–5615.
[11] K. Matyjaszewski, J. Xia, Chem. Rev. 2001, 101, 2921–2990.
4
Tetrabutyammonium perchlorate (TBAClO ), tetrabutylammo-
[
12] K. Matyjaszewski (Ed.), Controlled Radical Polymerization
nium hexafluorophosphate (TBAPF ) and tetrabutylammonium
6
(ACS Symp. Ser. 685), ACS, Washington, DC, 1998.
bromide (TBABr) were used as the supporting electrolyte, and all
voltammograms were externally referenced to ferrocene. As such,
the potentials are reported with respect to Fc/Fc+ couple, without
junction correction. All cyclic voltammograms were simulated digi-
tally to obtain the half-wave potentials.
[
13] K. Matyjaszewski (Ed.), Controlled/Living Radical Polymeriza-
tion. Progress in ATPR, NMP and RAFT (ACS Symp. Ser.
768), ACS, Washington, DC, 2000.
[14] V. Coessens, T. Pintauer, K. Matyjaszewski, Prog. Polym. Sci.
2001, 26, 337.
[15] K. Matyjaszewski, T. P. Davis (Eds.), Handbook of Radical Po-
lymerization, Wiley, Hoboken, 2002.
[16] K. Matyjaszewski (Ed.), Advances in Controlled/Living Radical
Polymerization (ACS Symp. Ser. 854), ACS, Washington, DC,
Acknowledgments
2
003.
Financial support from Duquesne University (start-up grant and
faculty development grant), National Science Foundation X-ray fa-
cility grant (NSF CRIF 0234872), and National Science Founda-
tion NMR grant (NSF CHE 0614785) is gratefully acknowledged.
[
[
[
17] K. Matyjaszewski, Macromol. Symp. 2003, 195, 25–31.
18] K. Matyjaszewski, Prog. Polym. Sci. 2005, 30, 858–875.
19] K. Matyjaszewski (Ed.), Controlled Radical Polymerization.
From Synthesis to Materials (ACS Symp. Ser. 944), ACS,
Washington, DC, 2006.
[
20] T. E. Patten, K. Matyjaszewski, Acc. Chem. Res. 1999, 32, 895–
[
[
[
1] D. P. Curran, Synthesis 1988, 6, 417–439.
903.
2] D. P. Curran, Synthesis 1988, 7, 489–513.
3] M. S. Kharasch, E. V. Jensen, W. H. Urry, Science 1945, 102,
[21] M. Kamigaito, T. Ando, M. Sawamoto, Chem. Rev. 2001, 101,
128.
3689–3745.
[
[
[
[
4] M. S. Kharasch, E. V. Jensen, W. H. Urry, J. Am. Chem. Soc.
[22] K. Matyjaszewski, W. Jakubowski, K. Min, W. Tang, J. Huang,
W. A. Braunecker, N. V. Tsarevsky, Proc. Natl. Acad. Sci. USA
2006, 103, 15309–15314.
[23] W. Jakubowski, K. Matyjaszewski, Angew. Chem. Int. Ed.
2006, 45, 4482–4486.
[24] W. Jakubowski, K. Min, K. Matyjaszewski, Macromolecules
2006, 39, 39–45.
1945, 67, 1626.
5] D. P. Curran, Comprehensive Organic Synthesis, Pergamon,
New York, 1992.
6] J. Iqbal, B. Bhatia, N. K. Nayyar, Chem. Rev. 1994, 94, 519–
564.
7] K. Severin, Curr. Org. Chem. 2006, 10, 217–224.
570
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 563–571

Copper-Mediated Atom ATRA in the Presence of Reducing Agent
[
[
[
[
[
[
25] L. Quebatte, K. Thommes, K. Severin, J. Am. Chem. Soc. 2006,
28, 7440–7441.
26] K. Thommes, B. Icli, R. Scopelliti, K. Severin, Chem. Eur. J.
007, 13, 6899–6907.
27] W. T. Eckenhoff, T. Pintauer, Inorg. Chem. 2007, 46, 5844–
846.
28] J. Xia, S. G. Gaynor, K. Matyjaszewski, Macromolecules 1998,
1, 5958–5959.
29] J. Xia, K. Matyjaszewski, Macromolecules 1999, 32, 2434–
437.
[47] K. D. Karlin, J. Zubieta, Copper Coordination Chemistry: Bio-
chemical and Inorganic Perspectives, Adenine Press, New York,
1983.
1
2
[48] M. Becker, F. W. Heinemann, S. Schindler, Chem. Eur. J. 1999,
5
, 3124–3129.
[
[
[
[
[
[
49] G. Kickelbick, T. Pintauer, K. Matyjaszewski, New J. Chem.
002, 26, 462–468.
50] T. Pintauer, B. McKenzie, K. Matyjaszewski, ACS. Symp. Ser.
003, 854, 130–147.
5
2
3
2
51] T. Pintauer, U. Reinohl, M. Feth, H. Bertagnolli, K. Ma-
tyjaszewski, Eur. J. Inorg. Chem. 2003, 2082–2094.
52] G. Wilkinson, Comprehensive Coordination Chemistry, Vol. 5,
Pergamon Press, New York, 1987.
2
30] H. Tang, N. Arulsamy, M. Radosz, Y. Shen, N. V. Tsarevsky,
W. A. Braunecker, W. Tang, K. Matyjaszewski, J. Am. Chem.
Soc. 2006, 128, 16277–16285.
53] M. Munakata, S. Kitagawa, S. Kosome, A. Asahara, Inorg.
Chem. 1986, 25, 2622–2627.
[
[
[
31] F. Minisci, Acc. Chem. Res. 1975, 8, 165–171.
32] M. Asscher, D. Vofsi, J. Chem. Soc. 1961, 2261–2264.
33] L. Delaude, A. Demonceau, A. F. Noels, in Topics in Organo-
metallic Chemistry, vol. 11 (Eds.: C. Bruneau, P. H. Dixneuf),
Springer, Berlin, 2004, pp. 155–171.
54] J. S. Thompson, R. M. Swiatek, Inorg. Chem. 1985, 24, 110–
1
13.
[
[
55] S. Kitagawa, M. Munakata, Inorg. Chem. 1981, 20, 2261–2267.
56] S. Kitagawa, M. Munakata, N. Miyaji, Inorg. Chem. 1982, 21,
[
34] H. Nagashima, in Ruthenium in Organic Synthesis (Ed.: S.-I.
Murahashi), Wiley-VCH, Weinheim, 2004, pp. 333–343.
35] C. P. Jasperse, D. P. Curran, T. L. Fevig, Chem. Rev. 1991, 91,
3842–3843.
[57] C. Mealli, C. A. Arcus, J. L. Wilkinson, T. J. Marks, J. A. Ibers,
J. Am. Chem. Soc. 1976, 98, 711–718.
[58] D. K. Coggin, J. A. Gonzalez, A. M. Kook, D. M. Stanbury,
L. J. Wilson, Inorg. Chem. 1991, 30, 1115–1125.
[59] S. M. Carrier, C. E. Ruggiero, R. P. Houser, W. B. Tolman, In-
org. Chem. 1993, 32, 4889–4899.
[60] C. X. Zhang, S. Kaderli, M. Costas, E.-I. Kim, Y.-M. Neuhold,
K. D. Karlin, A. D. Zuberbuhler, Inorg. Chem. 2003, 42, 1807–
1824.
[
1237–1286.
[
[
36] B. Giese, Angew. Chem. 1985, 97, 555.
37] D. P. Curran, M.-H. Chen, E. Spletzer, C. M. Seong, C.-T.
Chang, J. Am. Chem. Soc. 1986, 108, 6384.
38] J. Brandrup, E. H. Immergut, E. A. Gulke, Polymer Handbook,
Wiley Interscience, New York, 1999.
39] G. C. Eastmond, in Comphrehensive Chemical Kinetics, vol. 14A
[
[
(
Eds.: C. H. Bamford, C. F. H. Tipper), American Elsevier,
[61] Z. Tyeklar, R. R. Jacobson, N. Wei, N. N. Murthy, J. Zubieta,
K. D. Karlin, J. Am. Chem. Soc. 1993, 115, 2677–2689.
[62] N. V. Tsarevsky, K. Matyjaszewski, Chem. Rev. 2007, 107,
2270–2299.
New York, 1976.
[
[
40] F. De Campo, D. Lastecoueres, J.-B. Verlhac, J. Chem. Soc.
Perkin Trans. 1 2000, 575–580.
41] J. M. Munoz-Molina, A. Caballero, M. M. Diaz-Requejo, S. [63] W. A. Braunecker, K. Matyjaszewski, Prog. Polym. Sci. 2007,
Trofimenko, T. R. Belderrain, P. J. Perez, Inorg. Chem. 2007,
6, 7725–7730.
42] W. Tang, N. V. Tsarevsky, K. Matyjaszewski, J. Am. Chem. Soc.
006, 128, 1598–1604.
32, 93–146.
4
[64] J. Qiu, K. Matyjaszewski, L. Thounin, C. Amatore, Macromol.
Chem. Phys. 2000, 201, 1625–1631.
[65] Z. Tyeklar, R. R. Jacobson, N. Wei, N. N. Murthy, J. Zubieta,
K. D. Karlin, J. Am. Chem. Soc. 1993, 115, 2677–2689.
[66] G. M. Sheldrick, SADABS Version 2.03, University of
Göttingen, Germany, 2002.
[67] G. M. Sheldrick, SHELXTL 6.1, Crystallographic Computing
System, Bruker Analytical X-ray System, Madison, WI, 2000.
[68] L. J. Faruggia, J. Appl. Crystallogr. 1997, 30, 565.
Received: October 22, 2007
[
[
[
[
[
2
43] K. Matyjaszewski, H.-j. Paik, P. Zhou, S. J. Diamanti, Macro-
molecules 2001, 34, 5125–5131.
44] K. Matyjaszewski, B. Gobelt, H.-j. Paik, C. P. Horwitz, Macro-
molecules 2001, 34, 430–440.
45] M. A. J. Schellekens, F. de Wit, B. Klumperman, Macromole-
cules 2001, 34, 7961–7966.
46] T. Pintauer, K. Matyjaszewski, Coord. Chem. Rev. 2005, 249,
1
155–1184.
Published Online: December 3, 2007
Eur. J. Inorg. Chem. 2008, 563–571
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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