Cu(I)-amido complexes in the ullmann reaction: Reactions of Cu(I)-amido complexes with iodoarenes with and without autocatalysis by CuI

Article abstract of DOI:10.1021/ja105695s

A series of Cu(I)-amido complexes both lacking ancillary ligands and containing 1,10-phenanthroline (phen) as ancillary ligand have been prepared. These complexes react with iodoarenes to form arylamine products, and this reactivity is consistent with the intermediacy of such complexes in catalytic Ullmann amination reactions. The stoichiometric reactions of the Cu(I)-amido complexes with iodoarenes are autocatalytic, with the free CuI generated during the reaction serving as the catalyst. Such autocatalytic behavior was not observed for reactions of iodoarenes with copper(I) amidates, imidates, or phenoxides. The selectivity of these complexes for two sterically distinct aryl halides under various conditions imply that the autocatalytic reaction proceeds by forming highly reactive [CuNPh₂]_n lacking phen. Reactions with radical probes imply that the reactions of phen-ligated Cu(I)-amido complexes with iodoarenes occur without the intermediacy of aryl radicals. Density functional theory calculations on the oxidative addition of iodoarenes to Cu(I) species are consistent with faster reactions of iodoarenes with CuNPh₂ species lacking phen in DMSO than reactions of iodoarenes with LCuNPh₂ in which L = phen. The free-energy barrier computed for the reaction of PhI with (DMSO)CuNPh₂ was 21.8 kcal/mol, while that for the reaction of PhI with (phen)CuNPh₂ was 33.4 kcal/mol.

Full text of DOI:10.1021/ja105695s

Published on Web 10/26/2010
Cu(I)-Amido Complexes in the Ullmann Reaction: Reactions of Cu(I)-Amido
Complexes with Iodoarenes with and without Autocatalysis by CuI
Ramesh Giri and John F. Hartwig*
Department of Chemistry, UniVersity of Illinois, 600 South Mathews AVenue, Urbana, Illinois 61801, United States
Received June 28, 2010; E-mail: jhartwig@illinois.edu
cuprates from the reaction of lithium amides with copper halides
Abstract: A series of Cu(I)-amido complexes both lacking ancillary
ligands and containing 1,10-phenanthroline (phen) as ancillary ligand
have been prepared. These complexes react with iodoarenes to form
arylamine products, and this reactivity is consistent with the inter-
mediacy of such complexes in catalytic Ullmann amination reactions.
The stoichiometric reactions of the Cu(I)-amido complexes with
iodoarenes are autocatalytic, with the free CuI generated during the
reaction serving as the catalyst. Such autocatalytic behavior was
not observed for reactions of iodoarenes with copper(I) amidates,
imidates, or phenoxides. The selectivity of these complexes for two
sterically distinct aryl halides under various conditions imply that the
autocatalytic reaction proceeds by forming highly reactive [CuNPh2]n
lacking phen. Reactions with radical probes imply that the reactions
of phen-ligated Cu(I)-amido complexes with iodoarenes occur
without the intermediacy of aryl radicals. Density functional theory
calculations on the oxidative addition of iodoarenes to Cu(I) species
when the ratio of LiNR2 to CuX is greater than 1 (a condition that
exists in the catalytic Ullmann reaction) has been proposed.14
However, amidocuprate complexes of the type MCu(NR2)2 have
not been isolated, characterized, or assessed as potential intermedi-
ates in Ullmann aminations.
We report the synthesis and characterization of a series of
Cu(I)-amido complexes, some lacking additional ligands and some
ligated by phen. These complexes are chemically and kinetically
competent to be intermediates in the Ullmann amination or to lead to
such intermediates. Under some conditions, these complexes react with
iodoarenes by an autocatalytic process in which CuI serves as the
catalyst. Our data imply that the autocatalysis occurs by generation of
a highly reactive [CuNPh2]n species lacking a phen ligand. Experi-
mental and theoretical studies imply that these complexes react with
iodoarenes without the intermediacy of aryl radicals, and this result
implies the involvement of Cu(III) intermediates.15,16
are consistent with faster reactions of iodoarenes with CuNPh2
species lacking phen in DMSO than reactions of iodoarenes with
LCuNPh2 in which L ) phen. The free-energy barrier computed for
the reaction of PhI with (DMSO)CuNPh2 was 21.8 kcal/mol, while
Our synthesis of Cu(I)-amido complexes is outlined in Scheme
1. Phen-ligated complex 1 and cuprates 2-4 in which phen and a
crown ether are ligated to K+ or Li+ were prepared by the reaction
of CuOtBu with HNPh2 or a mixture of HNPh2 and either LiNPh2
or KNPh2 in the presence of phen or 18-crown-6 in THF. Cuprates
that for the reaction of PhI with (phen)CuNPh2 was 33.4 kcal/mol.
2 and 3 were also prepared from phen, LiNPh2 or KNPh2, and
double-salt 1 in THF. Finally, ligandless cuprate 5 was prepared
A century has passed since the discovery of Ullmann reactions,
in which arylamines couple with aryl halides through mediation
by copper.1 The synthetic scope of this process remained limited
for many decades and often required stoichiometric amounts of
copper and high reaction temperatures (typically 200 °C) to obtain
satisfactory yields. More recently, copper catalysts containing
ancillary ligands have been used, and these systems react with
broader scope and at lower temperatures.2 In 1999, Goodbrand and
Hu3 reported the coupling of arylamines with aryl iodides catalyzed
by a combination of 1,10-phenanthroline (phen) and CuCl under
mild conditions. Thereafter, a variety of ligands, such as 1,2-
diamines,4 1,3-diketones,5 and others6 have been used with copper
to promote the Ullmann amination reaction.
from HNPh2, KNPh2, and CuOtBu in the absence of any dative
ligand. These complexes were characterized by elemental analysis
and NMR spectroscopy. Solid-state structures of complexes 1 and
3 were determined by single-crystal X-ray diffraction.
Scheme 1
Despite significant improvements in the scope and conditions
for the copper-catalyzed arylation of amines, little direct information
on the mechanism of this reaction is available. Ligandless “CuNPh2”
was proposed by Paine7 in 1987 to be an intermediate in Ullmann
reactions catalyzed by CuI,8 and tetramers of similar species,
[CuNR2]4 (R ) alkyl), have been isolated.9 Ligated copper(I)
phenoxides, amidates, and imidates have recently been characterized
and shown to be likely intermediates in the Cu-catalyzed formation
of biaryl ethers and N-arylamides.10,11 However, Cu(I)-amido
complexes (LCuNR2) containing a ligand that generates syntheti-
cally useful catalysts have not been characterized.12
The solid-state structure of complex 1 (Figure 1) is an ion pair
consisting of a tetrahedral, cationic copper ligated by phen and a
linear, anionic copper ligated by two amides. In DMSO, the molar
conductivity of a 1.0 mM solution of 1 was high (16.9 Ω-1 cm2
mol-1) relative to that of a 1.0 mM solution of neutral ferrocene
(0.3 Ω-1 cm2 mol-1) and similar to that of a 1.0 mM solution of
[Bu4N][BPh4] (23.5 Ω-1 cm2 mol-1). In THF, the conductivity of
a 1.0 mM solution of 1 was 13.7 µΩ-1 cm-1 (13.7 Ω-1 cm2 mol-1),
whereas the conductivity of a 65.5 mM solution of [(n-octyl)4N][Br]
was 65.1 µΩ-1 cm-1 (0.99 Ω-1 cm2 mol-1) and that of a 65.5 mM
Anionic copper(I) amides also could be intermediates in Ullmann
reactions. Organocuprates (MCuR2) are among the most reactive
nucleophiles in organic chemistry,13 and the formation of similar
9
15860 J. AM. CHEM. SOC. 2010, 132, 15860–15863
10.1021/ja105695s  2010 American Chemical Society

C O M M U N I C A T I O N S
solution of ferrocene was 0.0 µΩ-1 cm-1 (0.0 Ω-1 cm2 mol-1).
These data indicate that unlike ligated copper(I) amidates, imidates,
and phenoxides, which vary in structure with the polarity of the
solvent,10 ligated Cu(I)-amido complexes are predominantly double
salts in both polar and less polar solvents.
are complex. Figure 2 shows the profile of the decay of 1 from its
reaction with 4-iodotoluene. This sigmoidal behavior is character-
istic of an autocatalytic process. When normalized for the concen-
tration of iodoarene, the plots of iodoarene concentration versus
time for reactions with a two-fold difference in [ArI] overlapped.
This result indicates that the reaction is first-order in iodoarene.
Further experiments showed that the autocatalysis results from the
generation of CuI. The reaction of 1 with p-iodotoluene conducted
with 0.5 equiv of added CuI was faster and formed triarylamine 6
with a first-order decay of 1 (Figure 2a). In contrast, this reaction was
unaffected by added ligated copper iodide [phenCuI]2. In the presence
of 1 equiv of CuI, the reaction occurred at 30 °C with a first-order
decay and a half-life (t1/2) of 37 min (kobs ) 3.1 × 10-4 s-1); no reaction
of complex 1 with p-iodotoluene occurred at this temperature in the
absence of added CuI. The reaction of 1 with p-iodotoluene in the
presence of CuI was first-order in added CuI and in iodoarene.
The effect of added phen on the reaction of complex 1 with
p-iodotoluene was not straightforward. The reaction of complex 1 with
p-iodotoluene in the presence of added phen was slower than that in
the absence of added phen, but the reactions with 0.010 and 0.020 M
added phen occurred with identical rates (Figure 2b). The reaction at
80 °C with 0.010 M added phen was first-order in 1 with t1/2 ) 32
min (kobs ) 3.6 × 10-4 s-1). Thus, the lower rate with added phen did
not result from reversible dissociation of phen to generate the active
species, as is often concluded when a reduction in rate is observed
with added ligand. Instead, these data imply that the added phen
consumes the free CuI generated in the absence of added phen that is
responsible for the autocatalysis and that the reaction occurs through
a pathway lacking the autocatalysis in the presence of added phen.
Reactions of 1 with various concentrations of iodoarene and added
phen showed that the reaction is first-order in iodoarene.
Figure 1. (a) ORTEP drawings of (a) 1 and (b) 3 with 50% ellipsoids.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å)
and angles (deg) for 1: Cu2-N5, 1.8659(15); N5-Cu2-N5, 180.0. For 3:
Cu1-N1, 1.860(2); Cu1-N2, 1.879(2); N1-Cu1-N2, 176.45(10).
The solid-state structure of complex 3 contains two K+ ions
ligated by six phens and two bisamidocopper anions (Figure 1).
Two of the six phen ligands in the dimer are shared by two K+
ions with each nitrogen of the bridging ligand coordinated to two
K+ ions, making each K+ ions eight-coordinate.
The reactions of these Cu(I)-amido complexes with iodoarenes are
summarized in Table 1. Phen-ligated complex 1 reacted with p-
iodotoluene in DMSO at 80 °C to afford triarylamine 6 in 95% yield
after 1.5 h. Cuprates 2 and 3, in which Li+ and K+ ions are ligated
with phen, reacted similarly with p-iodotoluene in DMSO at 110 and
80 °C in 1 and 3 h, respectively, to give 1 equiv of 6 per copper in 84
and 90% yield. The second amido group in 2 and 3 forms dipheny-
lamine, presumably by abstracting a proton from DMSO. Cuprates 4
and 5, which do not contain ancillary ligands to bind copper, did not
react with p-iodotoluene when heated at 80 °C for 3 h; at 110 °C,
they formed 6 in modest yields (54 and 44%, respectively). The
combination of phen and complex 4 containing the crown ether and
complex 5 containing no added ligand reacted with p-iodotoluene at
80 °C to give 6 in >95 and 56% yield, respectively. These results
indicate that dative ligands such as phen can convert less reactive
cuprates to a more reactive species, possibly by substitution of the
phen for one of the two amido ligands to form a ligated copper amide.
Table 1. Reactivity of Complexes 1-5 with p-Iodotoluene
Figure 2. (a) Decay of complex 1 from reactions with p-iodotoluene alone
(red), with added CuI (blue), and with added [phenCuI]2 (green) at 60 °C.
(b) Decay of complex 1 from reactions with p-iodotoluene alone (red) and
with the addition of 0.010 M (blue) or 0.020 M (green) phen at 80 °C.
entry complex
additive
temp (°C) time (h) % yield of 6a 7/1-5b
Similar autocatalysis was observed for reactions of other copper
amides. The reactions of cuprates 2 and 3 with p-iodotoluene
occurred with sigmoidal reaction profiles (see the Supporting
Information), and the same reactions with added CuI were faster
and occurred with an exponential decay. The reaction of 2 with 1
1
2
3
4
5
6
7
1
2
3
4
4
5
5
none
none
none
none
phen (1 equiv)
none
phen (3 equiv)
80
110
80
110
80
1.5
1
3
3
2.5
3
95
84
90
54
>95
-
1.14c
0.62
1.24c
0.80
equiv of CuI occurred with t1/2 ) 9.1 min (kobs ) 1.3 × 10-3 s-1
)
110
80
44
56
1.48c
1.24c
3
at 100 °C, and the reaction of 3 with 2 equiv of CuI occurred with
t1/2 ) 20.6 min (kobs ) 5.6 × 10-4 s-1) at 80 °C.
a Yield by GC with an internal standard. b Molar ratio of amine 7
formed relative to the starting complex 1-5. The balanced equation for the
reaction of 2-5 requires a proton from a solvent molecule or adventitious
water. c Each of complexes 1-5 contains two amido groups. In the
balanced equation, one amido group forms the triarylamine and the other
forms the diarylamine. Some diarylamine is apparently formed in
competition with the process that forms triarylamine, leading to a ratio that
is greater than 1.
To assess the relationship between complexes 1-5 and intermediates
in Ullmann reactions catalyzed by Cu(I)-phen species and to
determine whether the intermediates in the autocatalytic reactions are
the same as those in reactions in which free CuI is sequestered by
added phen, we studied the selectivity of these complexes toward the
sterically distinct aryl iodides o- and p-iodotoluene. We then compared
the distribution of products from these stoichiometric reactions in the
presence and absence of phen to those of the catalytic reactions.
Results from these competitive reactions are provided in eq 1-2
and Table 2. The reaction of HNPh2 with o- and p-iodotoluene
Although phen-ligated double salt 1 and cuprates 2 and 3 react
with aryl halides to form triarylamines, monitoring of these reactions
by 1H NMR spectroscopy showed that the events during this process
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C O M M U N I C A T I O N S
Table 2. Selectivity of Complexes 1-5 for o- and p-iodotoluene
Scheme 2
entry
complex
additive
temp (°C)
yield (%)a
product ratio (8/6)
1
2
3
4
5
6
7
8
9
1
1
1
1
2
3
2
3
4
5
none
CuI (1 equiv)
none
phen (1 equiv)
none
none
CuI (4 equiv)
CuI (4 equiv)
CuI (1 equiv)
CuI (1 equiv)
80
30
80
80
100
80
80
80
80
80
11b
72
85
72c
82
92
77
84
89
80
14:86b
49:51
34:66
20:80
15:85
10:90
43:57
43:57
47:53
47:53
p-iodotoluene in the presence of CuI were equally unselective (eq
7-10). Thus, the reactions of these cuprates in the presence of CuI
generate the same species, which we propose to be [CuNPh2]n.18,19
To probe the potential intermediacy of free aryl radicals during these
reactions, we conducted the reaction of complex 1 with o-(allyloxy)-
iodobenzene (9) in the presence and absence of phen. The aryl radical
from this iodoarene is known to undergo cyclization to form the methyl
radical 11 with kobs ) 9.6 × 109 s-1 in DMSO, with subsequent
formation of 12.20 Reaction of complex 1 with this arene (eq 3) formed
amine 10 in 16% yield with added phen and 60% yield without added
phen, and no detectable amount of cyclized 12 was observed by
GC-MS in either reaction mixture.
10
a Combined GC yield of 6 and 8; reactions of 2-5 also form Ph2NH
(see Table 1). b After 2 min of reaction. c Reaction time was 4 h.
catalyzed by a 1:1 ratio of CuI to phen in the presence of K3PO4
formed a 19:81 ratio of 8 to 6 (eq 1), and that of KNPh2 with o-
and p-iodotoluene in the presence of stoichiometric amounts of a
1:1 ratio of CuI to phen formed an indistinguishable 20:80 ratio of
these products (eq 2):
Because our detection limit for 12 was 0.1% of the amount of 10,
recombination would need to be >103 faster than cyclization. Thus,
any free aryl radical must react with the copper(II) amide21 to form
the arylamine with a pseudo-first-order rate constant greater than 1013
s-1,22 which is the lifetime of a transition state.23 Clearly, bimolecular
trapping of two reactive intermediates present in low concentrations
is unlikely to occur on this time scale. Thus, the arylation of
diarylamines catalyzed by Cu(I) and phen is unlikely to involve free
aryl radicals.
A similar selectivity (14:86) was also observed at the early stage
of the reaction of complex 1 with o- and p-iodotoluene (2 min,
11% yield) when the concentration of free CuI was low and the
autocatalytic pathway was not yet dominant (Table 2, entry 1). In
contrast, the reaction of 1 with o- and p-iodotoluene in the presence
of CuI formed nearly equal amounts of the two amine products (49:
51) (entry 2). This selectivity is similar to that of the reaction of KNPh2
with stoichiometric CuI and no added phen (47:53) (eq 2).
The ratio of products from reaction of complex 1 with o- and
p-iodotoluene and no added phen (34:66) (Table 2, entry 3) was
between that of the reaction of HNPh2 with o- and p-iodotoluene
catalyzed by a 1:1 ratio of CuI to phen in the presence of K3PO4 base
and the reaction of 1 and added CuI with the iodoarenes. However,
the ratio of products from the reaction of 1 with o- and p-iodotoluene
in the presence of 1 equiv of phen to sequester the free CuI formed a
ratio of the two products (20:80) (entry 4) that was similar to that of
catalytic reactions with added phen and the reaction of complex 1
before autocatalysis. Thus, we conclude that the reaction of 1 in the
presence of phen occurs through complex 1, most likely in its neutral
form [Cu(phen)(NPh2)], but that the portion of the reaction between 1
and aryl iodide without added phen that is autocatalytic in CuI likely
proceeds by the transfer of an amido group from the Cu(NPh2)2- unit
to CuI to form a [CuNPh2]n species lacking phen (Scheme 2).17 This
species likely is less selective than 1 because it contains a more open
coordination sphere.
Finally, to assess whether a copper amide lacking the phen ligand
would be expected to add iodoarenes faster or slower than
[(phen)Cu(I)(NPh2)], we used density functional theory (DFT) to
calculate the barriers for oxidative addition of iodobenzene to
[(phen)Cu(NPh2)] and [(DMSO)Cu(NPh2)].24,25 The Cu(III) species
[(DMSO)Cu(NPh2)(Ph)(I)] lacking a dative nitrogen ligand is
computed to lie uphill of the combination of (DMSO)Cu(NPh2)
and PhI by 17.1 kcal/mol and to be formed with a free energy of
activation (∆Gq) of 21.8 kcal/mol at 25 °C.26 This barrier is much
lower than that for formation of [(phen)Cu(NPh2)(Ar)(I)], which
was computed to be 33.4 kcal/mol (see the Supporting Information
for details). These calculated barriers for oxidative addition are
consistent with our proposal that the CuNPh2 species lacking phen
in DMSO is more reactive than LCuNPh2, in which L ) phen, and
that the species lacking phen reacts with aryl halides when CuI is
added.
Some authors have proposed that the mechanism of Cu(I)-
catalyzed C-N and C-O coupling reactions of haloarenes occur
by radical pathways,7,27 and others have proposed that they occur
by nonradical pathways28 involving oxidative addition to form a
Cu(III) intermediate (Scheme 3).8b,25,29 The radical mechanism has
been proposed to be triggered by electron transfer from copper to
the haloarene to form a haloarene radical anion, which eliminates
the halide to form a neutral aryl radical. The aryl radical would
then combine with the copper(II) amide21 to afford the arylated
amine and regenerate the Cu(I) catalyst.
The reactions of cuprates 2 and 3, which contain phen-ligated
alkali-metal cations, and the reactions of cuprates 4 and 5, which
lack ancillary ligands capable of binding Cu(I), with o- and
Previous theoretical studies and reactions of radical probes with
isolated copper(I) amidate, imidate, and phenoxide complexes
9
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C O M M U N I C A T I O N S
Scheme 3
Acknowledgment. We thank the NIH NIGMS (GM-55382) for
support of this work.
Supporting Information Available: Experimental procedures,
computational details, characterization of complexes, and crystal-
lographic data (CIF) for 1 and 3. This material is available free of charge
via the Internet at http://pubs.acs.org.
provided evidence against the involvement of aryl radicals in
Ullmann-type reactions.10 This work provided some evidence for
arylcopper(III) intermediates, and arylcopper(III) species have now
been isolated.15 However, the barriers predicted from Marcus theory
using energies of reactants and products calculated by DFT led to
the conclusion that the copper-catalyzed coupling of iodobenzene
with methylamine as a representative alkylamine occurs by a radical
path22 and that the Cu(III) species [LCu(III)(NHMe)(Ph)(I)] lies
at too high an energy to be an intermediate. Our results from the
reactions of isolated amidocopper(I) intermediates with radical probe
9 suggest that the Cu(I)-catalyzed Ullmann reactions of diarylamines
with iodoarenes do not proceed through free radical intermediates.30
We propose that the Ullmann reaction catalyzed by phen-ligated
Cu(I) occurs by the pathway in Scheme 4. By this mechanism, phen-
ligated CuI (13) is converted to alkali-metal cuprate 2 or 3 in the
presence of excess amine and base. This cuprate then equilibrates
with the neutral, monomeric form of 1, which undergoes oxidative
addition of the iodoarene to form Cu(III) species 14. This Cu(III)
species then reductively eliminates the amine product and regener-
ates 13. The autocatalysis by free CuI observed in the reactions of
complexes 1-3 with iodoarenes would not be expected to occur
as part of this cycle because the excess amine and base would
convert free CuI to the corresponding amidocuprate 2 or 3.
References
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Hartwig, J. F. Angew. Chem., Int. Ed. 2010, 49, 2185.
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(12) Blue, E. D.; Davis, A.; Conner, D.; Gunnoe, T. B.; Boyle, P. D.; White,
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(13) Krause, N.; Gerold, A. Angew. Chem., Int. Ed. Engl. 1997, 36, 186.
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Scheme 4. Proposed Catalytic Cycle without Autocatalysis
(17) A referee asked whether [CuNAr2]n could be directly observed in this
system. The 19F NMR spectrum of the reaction of a p-fluoro analogue of
complex 1 with CuI in DMF-d7 at -50 °C contained a new signal, but the
identity of the new species could not be determined unambigously.
(18) This complex likely contains a DMSO ligand. Reactions in tBuS(O)Me
occurred in lower yield than those in DMSO, suggesting that coordination
of DMSO controls the reactivity of the unsaturated copper amide.
(19) Tetrameric CuNR2 complexes in which R ) alkyl are known (see ref 9),
and we found that they do not react with iodoarenes. The CuNPh2 species
generated in situ would have weaker bridging ligands and would be
generated initially as a lower-coordinate species.
In summary, we have prepared and characterized a series of
amidocuprates, some having phen-ligated Cu(I) countercations, some
with phen-ligated alkali-metal cations, and some with alkali-metal
cations lacking bound phen. Free CuI accelerates the reactions of each
of these complexes. Double salt 1 was more reactive with iodoarenes
than were the alkali-metal cuprates 2-5. The relative reactivities in
the presence of added CuI were 1 . 3 > 2. These rates relate to
reactions of amines with aryl halides, base, and stoichiometric copper
during which CuI would be generated. In the absence of added CuI,
the relative rates for the reactions of the cuprates with iodotoluene
were complicated by autocatalysis but followed the rough trend 1 > 3
> 1 + phen > 2 > 4 ≈ 5. The low reactivity of cuprates 4 and 5,
which lack phen, implies that the reactions of 2 and 3 occur through
a phen-ligated Cu(I) species, such as [Cu(phen)(NPh2)]. The inherent
reactivity of [Cu(phen)(NPh2)] with aryl iodides was assessed by
conducting the reactions in the presence of added phen to sequester
CuI, and these reactions occurred in high yields at 80 °C. The reaction
of 1 with a radical probe implies that the reactions occur without Ph ·
intermediates, most likely through Cu(III) intermediates from oxidative
addition of the iodoarene. DFT calculations further support a mech-
anism proceeding through Cu(III) intermediates, as the formation of
such Cu(III) species is predicted to occur with a low energy barrier.
(20) Annunziata, A.; Galli, C.; Marinelli, M.; Pau, T. Eur. J. Org. Chem. 2001,
1323.
(21) (a) Melzer, M.; Mossin, S.; Dai, X.; Bartell, A.; Kapoor, P.; Meyer, K.;
Warren, T. Angew. Chem., Int. Ed. 2010, 49, 904. (b) Mankad, N. P.;
Antholine, W. E.; Szilagyi, R. K.; Peters, J. C. J. Am. Chem. Soc. 2009,
131, 3878.
(22) Jones, G. O.; Liu, P.; Houk, K. N.; Buchwald, S. L. J. Am. Chem. Soc.
2010, 132, 6205.
(23) Newcomb, M.; Le Tadic, M.-H.; Putt, D. A.; Hollenberg, P. F. J. Am. Chem.
Soc. 1995, 117, 3312.
(24) Previous DFT calculations have shown that the barriers for oxidative
addition of ArI to complexes [Cu(Nphth)2]- and [Cu(NHAc)2]- are higher
than those for oxidative addition of ArI to three-coordinate L2Cu(Nphth)
and L2Cu(NHAc). See refs 10a and 25.
(25) Zhang, S.-L.; Liu, L.; Fu, Y.; Guo, Q.-X. Organometallics 2007, 26, 4546.
(26) DFT calculations suggested that both Cu(I) and Cu(III) species, [Cu(I)-
(NPh2)] and [Cu(III)(NPh2)(Ph)(I)], bind a single DMSO though oxygen.
(27) (a) Aalten, H. L.; Vankoten, G.; Grove, D. M.; Kuilman, T.; Piekstra, O. G.;
Hulshof, L. A.; Sheldon, R. A. Tetrahedron 1989, 45, 5565. (b) Couture,
C.; Paine, A. J. Can. J. Chem. 1985, 63, 111. (c) Arai, S.; Hida, M.;
Yamagishi, T. Bull. Chem. Soc. Jpn. 1978, 51, 277.
(28) (a) Weingarten, H. J. Org. Chem. 1964, 29, 3624. (b) Lindley, J.
Tetrahedron 1984, 40, 1433.
(29) Cohen, T.; Cristea, I. J. Am. Chem. Soc. 1976, 98, 748.
(30) Because LCuNHMe is more electron-rich than LCuNPh2, LCuNHMe could
be more prone to engage in single electron transfer processes.
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