Stille coupling involving bulky groups feasible with gold cocatalyst

Article abstract of DOI:10.1002/anie.201209262

Gold shuttle: Bulky groups, which will not (or only very sluggishly) undergo Stille coupling with stannanes and inexpensive ligands, can be efficiently coupled using bimetallic catalysis. A gold cocatalyst serves as an efficient shuttle to convey the bulky group from tin to palladium by reducing the steric crowding in the transition-states (see scheme). Copyright

Full text of DOI:10.1002/anie.201209262

Angewandte
Chemie
DOI: 10.1002/anie.201209262
Cross-Coupling
Stille Coupling Involving Bulky Groups Feasible with Gold
Cocatalyst**
Juan delPozo, Desirꢀe Carrasco, Mꢁnica H. Pꢀrez-Temprano, Max Garcꢂa-Melchor,
Rosana ꢃlvarez, Juan A. Casares,* and Pablo Espinet*
There is a growing interest in bimetallic catalysis, a synthetic
approach combining two or more non-main-group-metal
result of the copper(I) mediating the aryl transfer from
[
11]
organotin to palladium. However, it has also been shown
that in some cases the kinetic effect observed is simply
because of the ability of copper(I) to sequestrate the excess
[1]
catalysts working in tandem. A main-group metal is often
involved as the nucleophilic reagent. The aim of bimetallic
catalysis is to take advantage of the specific behavior of each
catalyst in new one-pot synthetic routes. For the Au/Pd couple
it is known that the Au/Pd transmetalation, a step which is
hoped to connect the palladium and the gold catalytic cycles,
[
12]
ligand in solution.
Blum and co-workers have recently
succeeded in using gold as a vinyl carrier from tin to
[
1b,6a]
palladium in the carbostannylation of alkynes.
We speculated that using AuXL complexes as the trans-
[
2,3]
[4]
1
is kinetically feasible,
even for fairly bulky groups.
metalation cocatalyst to [PdR L ] intermediates (L is identi-
2
However, so far only a few Au/Pd bimetallic catalyzed
processes have been reported, including the Sonogashira-like
cal in both species), instead of CuX salts, we might produce
a Stille reaction cocatalyzed by gold(I) instead of copper(I).
Moreover, should this cocatalysis occur, we could avoid the L
sequestration or any ligand scrambling (for different ligands
on palladium and gold) and thus observe a nonperturbed
effect of the gold catalyst on the transmetalation. Further-
more, this reaction might be a good model to check the
compatibility of palladium and gold as cocatalysts, and to
explore the thermodynamic and kinetic parameters control-
ling this bimetallic system. In fact the results show that the
intermediacy of gold can be critical to making Stille reactions
involving bulky stannanes feasible.
[5]
[6]
cross-coupling, the carbometallation of alkynes, and
[
7,8]
processes combining cyclization with cross-coupling steps.
Herein we examine the potential of the Au/Pd pair in a Stille
reaction, where tin is the third metal involved in the system,
thus providing the nucleophile.
The classic palladium-catalyzed Stille reaction (Scheme 1)
[9,10]
is a well-known, efficient, and deeply studied process.
The
reaction is sometimes cocatalyzed by addition of CuX salts.
The so-called copper effect is frequently deemed to be the
The thermodynamics of the Au/Sn transmetalation equi-
libria are important. There are only very few reports of
isolated transmetalations from tin to gold and vice versa. The
transmetalation of Ar groups from SnArMe3 (Ar= Ph,
naphtyl, or 8-iodonaphtyl) to [AuCl(EPh )] (E = P, As)
3
complexes has been reported, whereas the same reaction
[
13]
fails with SnPh(nBu)3. Attempts at performing Ar trans-
metalations with SnAr4 or SnClAr (Ar= C F , C F Cl ,
3
6
5
6
3
2
[
14]
Scheme 1. Classical Stille reaction.
C Cl ) were also unsuccessful. These results suggest that
6
5
the thermodynamics of the Sn/Au transmetalation might be
shifted in either direction, depending on the specific groups
involved.
[
*] J. delPozo, D. Carrasco, Dr. M. H. Pꢀrez-Temprano,
Prof. J. A. Casares, Prof. P. Espinet
Quꢁmica Inorgꢂnica, I. U. CINQUIMA, Facultad de Ciencias
Universidad de Valladolid, 47071 Valladolid (Spain)
E-mail: casares@qi.uva.es
We have studied the equilibrium for different combina-
tions of reagents (X = Cl, I; R = vinyl, aryl, alkynyl) and
ligands (L = PPh , AsPh ), and the K values are shown in
3
3
eq
espinet@qi.uva.es
Homepage: http://gircatalisishomogenea.blogs.uva.es/
Table 1. For L = AsPh3 the equilibria were measured in
MeCN, and for L = PPh the equilibria were measured in THF
3
Prof. R. ꢃlvarez
Dpto. Quꢁmica Orgꢂnica, Facultad de Quꢁmica
Universidade de Vigo
(the complexes are only sparingly soluble in MeCN) in the
presence of added L (L/Au = 2:1) to stabilize the gold
complexes. Most equilibria were achieved within 5 minutes
Lagoas-Marcosende s/n, 36310 Vigo (Spain)
(
for L = AsPh ) or 24 hours (for L = PPh ) at room temper-
3
3
Dr. M. Garcꢁa-Melchor
Quꢁmica Fꢁsica, Edifici C.n. Universitat Autꢄnoma de Barcelona
ature. More time was needed for systems with bulky aryl
groups. Numerical values were obtained for a few cases with
08193 Bellaterra, Catalonia (Spain)
L = PPh , by integration of the peaks for the two gold
3
[
**] We thank the Spanish Ministerio de Ciencia e Innovaciꢅn
3
1
complexes at equilibrium as observed in the P NMR
spectrum. For the rest, only reagents or only products were
observed, thus restricting us to fix a minimum or maximum
(
(
CTQ2010-18901/BQU) and the Junta de Castilla y Leꢅn
VA281A11-2 and VA373A11-2) for financial support.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201209262.
3
1
1
value for K , assuming that a 1% (for P) or 0.1% (for H
eq
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2189

.
Angewandte
Communications
1
2
[a]
Table 1: Keq for Sn/Au transmetalation (L =PPh ; L =AsPh ).
So, AsPh was chosen for this study, and was complemented
3
3
3
with some experiments with PPh . Stille coupling reactions,
3
with and without a gold cocatalyst, and with or without added
2
Entry
1
R
Keq (X=I)
Keq (X=Cl)
LiCl, were tested using p-CF C H I (1), which allows for easy
3
6
4
1
9
À5
1
À5
1
quantification of the products by F NMR spectroscopy. All
our results in this study show that transmetalation is the rate-
determining step.
vinyl
<10 (L )
<10 (L )
À5
1
À5
1
<
<
10 (L )
<10 (L )
2
3
À4
2
À2
2
10 (L )
2ꢆ10 (L )
The cross-coupling results with AsPh3 are shown in
Table 2. The percentages of untransformed 1 and the main
side-products p-CF C H ÀC H CF -p (2) and CF C H (3) are
À5
1
4
1
<
<
10 (L )
2ꢆ10 (L )
À4
2
6
2
10 (L )
>10 (L )
3
6
4
6
4
3
3
6
5
À5
1
1
<
<
10 (L )
39 (L )
4
5
Table 2: Palladium-catalyzed cross-coupling of p-CF C H I (1) with
3 6 4
À4
2
6
2
10 (L )
>10 (L )
various ArSn(nBu) compounds using L=AsPh , and added LiCl in both
3
3
[
a]
the absence and presence of a gold cocatalyst.
1
1
Entry
Au cat.
Product
t
[h]
Yield
[%]
Other products
(Yield [%])
0
>
.02 (L )
0.30 (L )
6
2
6
2
10 (L )
>10 (L )
1
2
yes
–
5
5
83
68
2(7), 3(10)
1(22), 2(5), 3(5)
1
1
6
7
0.12 (L )
0.50 (L )
1
1
3
4
yes
–
6
6
89
4
2(8), 3(3)
1(80), 2(3), 3(12)
0.15 (L )
0.20 (L )
[
a] The same results shown for p-CF C H are obtained for C H , or
3
6
4
6
5
1
p-MeOC H and L .
5
6
yes
–
24
24
84
<1
1(<1), 2(8), 3(6)
1(85), 2(3), 3(10)
6
4
7
8
yes
–
24
24
90
0
2(4), 3(6)
1(81), 2(5), 3(11)
1
9
and F) concentration or higher should be observable by
NMR spectroscopy.
9
yes
–
48
48
64
0
1(1), 2(19), 3(1)
1(19), 2(38), 3(29)
As suspected, the picture obtained is more complex than
known so far. Table 1 shows that for X = I all the equilibria
studied are shifted to the left, that is, the desired trans-
metalation from tin to gold is counter-thermodynamic. This
shift is very pronounced for vinyl and most aryls groups
10
1
1
1
2
yes
–
48
48
0
1(22), 2(36), 4(42)
1(90), 2(2), 4(2)
(
entries 1–4), and less so for alkynyl groups (entries 6 and 7)
[a] Reaction conditions: MeCN, 808C, [p-CF
3
C
6
H
4
I]=0.10m, [ArSn-
À3
(
nBu) ]=0.11m, [AsPh ]=4.07ꢆ10 m, [LiCl]=saturated solution. Pd
and for mesityl (entry 5). Importantly, electronic and steric
factors can tune or modify this observed trend. Thus, all the
equilibria are shifted less to the left for L = AsPh than for
L = PPh , probably because the hard-base PPh (compared to
the softer AsPh ) interacts better with the hard AuXL. The
3
3
À3
catalyst: [PdCl (AsPh ) ]=2ꢆ10 m, Au catalyst: [AuCl(AsPh )]=
2
2
3
2
3
À3
ꢆ10 m. The reactions were monitored until total conversion of the
3
starting p-CF C H I was observed, or for the time indicated. Yields were
3
6
4
3
3
19
determined by peak integration of the F NMR spectra, and are average
of two runs.
3
halide is very influential, and these equilibria shift more to the
right for X = Cl. This effect is more clearly observed in
entries 3–5, and is mostly a result of the energetic balance of
the markedly different Sn-X bond energies (Sn-Cl =
given in the column labeled other products. In experiments
with nonbulky aryltributyltin derivatives (entries 1 and 2), the
effect of using a gold cocatalyst is small. But as the bulkiness
of the aryl group substituents increases, a large beneficial
effect is observed for the gold cocatalyst, as compared to the
classic reaction (entries 3 versus 4, 5 versus 6, 7 versus 8, and 9
versus 10): the yields are negligible without the gold
cocatalyst, and very satisfactory with the gold cocatalyst,
although the bulkiest aryl groups still require longer reaction
times. Overall, the presence of a gold cocatalyst clearly
provides a more efficient pathway for the coupling with bulky
stannylated groups.
À1
À1
3
50 kJmol ; Sn-I = 235 kJmol ) compared to the similar
À1
AuÀX bond energies (Au-Cl = 280 kJmol ; Au-I =
À1 [15]
2
76 kJmol ). Steric features of the transmetalated group
2
are also influential: for bulky R groups (entries 4 and 5) the
equilibrium is more shifted to the right than for electronically
similar but smaller R groups. This trend probably results
2
from some steric constraint at the tetrahedral tin center is
released upon transmetalation of the bulky group to a linear
gold(I) complex.
The thermodynamic results suggest that, as far as the
reaction rate might depend on a higher concentration of the
expected organogold intermediate, addition of LiCl should
produce better results. Preliminary tests showed that in the
presence of added LiCl, [PdCl (AsPh ) ] was a faster catalyst
The fluoromesityl group (Table 2, entries 11 and 12) could
not be coupled by using a gold cocatalyst, even after a long
reaction time. Interestingly, under the reaction conditions for
the cocatalyzed reaction (entry 11), considerable amounts of
the homocoupling product 2 and the hydrolysis product
(CF ) C H (4) were formed, both of which were are almost
2
3 2
than [PdCl (PPh ) ]. This is a well-known effect in Stille
2
3 2
reactions when transmetalation is the rate-determining state,
3
3
6
3
[
9,16]
and results from the easier displacement of arsane ligands.
absent in the reaction attempted without the gold cocatalyst
2
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(
entry 12). Homocoupling by-products such as 2 are typically
product 2 is formed initially but does not increase with
formed in the classical Stille reactions where a slow coupling
a prolonged reaction time. With added LiCl the homocou-
[
11h,12,17]
results in undesired transmetalations.
In our experi-
pling disappears (entry 6)and the reaction with PPh is as
3
ence the hydrolysis by-products like 4 are also observed in
efficient as that with AsPh , although noticeably slower
3
processes frustrated at the coupling step (e.g. [Pd(C F ) L ]
(entry 2 versus 6 and 1 versus 7). The reactions with PPh still
6
5
2
2
3
hardly undergoes reductive elimination to C F -C F and
continued slowly after 110 hours. This effect is well known in
the classic Stille process, and results from the facile displace-
ment of weaker ligands during the associative transmetalation
6
5
6
5
formation of C F H is observed). Thus, it appears that the
6
5
unsuccessful cocatalysis in entry 11 of Table 2 is due to the
difficulty with the final reductive elimination, rather than at
any of the two successive transmetalation steps.
Furthermore, experiments were carried out to check the
influence of the added LiCl, the ligand L, and other effects
[
10a]
to palladium.
Other positive effects of a large excess of
LiCl are that it exchanges I for Cl in the metal complexes. This
reduces the energetic barrier of the tin to palladium trans-
[
10a,20]
metalation step.
Also, excess LiCl helps to keep the gold
[
21]
(
Table 3). The reactions can be carried out with similarly good
cocatalyst in the [AuCl(AsPh )] form, which, as shown in
3
yields using either [PdCl (AsPh ) ] or the intermediate
Table 1, shifts the tin to gold transmetalation equilibrium
towards the gold arylated compound. Furthermore, LiCl
improves the overall thermodynamic balance of the coupling
(whether it be the classical or the gold cocatalyzed) because of
the higher stability of SnCl(nBu)3.
2
3 2
Table 3: Results of the cross-coupling experiments between p-CF C H I
3
6
4
[
a]
and mesityltributyltin under other reaction conditions.
Entry
1
Pd catalyst
cocatalyst, LiCl)
t
[h]
Yield
[%]
Finally, it is interesting that under similar experimental
conditions, [AuCl(AsPh )] and [AuCl(PPh )] were much
(
3
3
[PdCl (AsPh ) ]
24
84
2
3
2
more efficient cocatalysts than CuCl (Table 3, entries 1, 2, 6,
and 7 versus 8), as shown by the yields achieved for entries 2
and 8 (84% for the gold complex versus 13% for CuCl).
The ability of gold to promote the cross-coupling of
sterically encumbered aryltin derivatives is remarkable. Thus
far, these cross-coupling processes required the use of bulky
and strong s-donor phosphanes to facilitate the reaction going
[
AuCl(AsPh )], LiCl
3
2
3
4
5
6
7
8
[Pd(C H CF )I(AsPh ) ]
24
84
6
4
3
3 2
[
AuCl(AsPh )], LiCl
3
[Pd(C H CF )I(AsPh ) ]
24
<1
33
6
4
3
3 2
[
AuI(AsPh )], no LiCl
3
[
22]
through tricoordinated palladium intermediates.
Appa-
[PdCl (AsPh ) ]
24
2
3 2
rently, when gold (and expectedly when Cu) complexes act
as intermediates in the transmetalation, the steric hindrance
for direct transmetalation with tetracoordinated tin and
palladium compounds is circumvented via the less sterically
demanding linear gold complexes. Moreover, in the direct Sn/
[
AuCl(AsPh ), no LiCl
3
[Pd(C H CF )I(PPh ) ]
110
110
84
58(+5)
75
6
4
3
3 2
[
AuI(PPh )], no LiCl
3
[Pd(C H CF )I(PPh ) ]
6
4
3
3
2
Pd transmetalation the bulky group (Sn(nBu) ) is directly
3
[
AuI(PPh )], LiCl
3
involved in the bridging system, producing a very encumbered
high-energy transition state, whereas with gold the bulky
substituent on gold (the ancillary ligand) is one bond away
from the bridging system , further relaxing the steric
encumbrance and reducing the energy of the corresponding
transmetalation transition state (see below and Figure 1). This
improvement allows the process to occur using palladium and
gold complexes with inexpensive common ligands.
[PdCl (PPh ) ]
83
2
3 2
[
AuCl(PPh )], LiCl
3
[Pd(C H CF )I(AsPh ) ]
24
13
6
4
3
3 2
CuCl, LiCl
[a] General reaction conditions as in Table 2, except for the catalysts used
and for the addition or not of LiCl, as indicated.
Our hypothesis was confirmed by DFT calculations, which
estimated the energy of the transmetalation transition states
from tin to palladium (involved in the direct Stille reaction),
or from tin to gold and from gold to palladium (involved in
the gold cocatalyzed pathway). The calculations were per-
formed for the formation of (2-methyl-1-(4-(trifluoromethyl)-
phenyl)naphthalene (Table 2, entry 7) with the real mole-
formed after the first oxidative addition to Pd, [Pd-
[18]
(
C H CF )I(AsPh ) ], prepared independently,
as far as
6
4
3
3 2
excess LiCl is used (entries 1 and 2; also entries 6 and 7). The
suppression of added LiCl is very detrimental to the gold
cocatalyzed reaction with AsPh . The reaction still works
3
albeit poorly when chloride is introduced in the catalytic
system because it is part of the Pd and Au catalysts (entry 4),
but it fails completely when the catalysts are iodide complexes
and there is no other chloride source in the system (entry 3).
This chloride effect is clearly related to the fact that the
cules, except for the Sn(nBu) group, which was simplified to
3
SnMe . The transmetalation mechanisms from tin to palla-
3
dium and from gold to palladium have been studied before for
[
3,23]
sterically nondemanding groups.
The transmetalation
mechanism from tin to gold has not been studied so far, and
is depicted in Scheme 2. The structures of the three rate-
determining transition states and their free energies in
0
oxidative addition step to Pd complexes with weak ligands
such as arsanes does not take place without the addition of
[
9,10a,19]
[24]
chloride.
runs perfectly in the absence of chloride, although very slowly
entry 5). In this case a 5% of undesired homocoupling
In fact, a similar reaction using PPh catalysts
vacuum and in MeCN are shown in Figure 1.
3
The transition energies very clearly show that there is
a considerable difference in favor of the bimetallic pathway,
(
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2191

.
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Fortunately this transmetalation, which involves the replace-
ment of aryl-Sn for X-Sn bonds, is favored in the presence of
LiCl because of the high SnÀCl bond energy, and is also more
favorable for hindered aryl groups on the stannane, when the
mediation of gold is more necessary. Thus the combination of
a gold cocatalyst and LiCl provides an interesting modifica-
tion of the Stille process for its application to bulky reagents
that were not accessible so far in the classic way.
DFT calculations for the classic Stille and for the two
successive transmetalations in the bimetallic processes
(including the first study of a tin to gold transmetalation)
show that, for a fairly bulky aryl group, the intermediacy of
gold drives the reaction through transition states (Scheme 3)
Scheme 2. DFT calculated pathway for the tin to gold transmetalation.
Scheme 3. Pathways for a) the classical Stille and b) the gold cocata-
lyzed processes, including the transition-state energies for the rate-
2
determing step when X=Cl and R =2-methyl-1-(4-(trifluoromethyl)-
phenyl)naphthalene.
much lower in energy than the classic direct Stille processes.
This reduction of the energetic barrier is associated with
a lower crowding that additionally allows formation of
metallophilic Au-Pd and Au-Sn stabilizing interactions,
which are non-existent in the Sn-Pd transition state of the
classic process. Obviously the effect of gold is expected to be
very important for crowded systems, and less so for conven-
tional aryls where the classic process is still sufficiently fast, as
observed.
°
Figure 1. Transition states and DG for the transmetalations.
Received: November 19, 2012
Published online: January 22, 2013
thus predicting that, for this case, the direct Stille trans-
metalation should not take place, and the bimetallic process
should be facile, as observed. Interestingly the two transition
states involving gold show intermetallic distances much
shorter than the sum of the van der Waals radii (in fact not
far from the sum of covalent radii) for Sn-Au (2.904 versus
Keywords: density functional calculations · gold ·
.
homogeneous catalysis · palladium · tin
3
.83 ꢀ) and for Pd-Au (2.995 versus 3.29 ꢀ), thus suggesting
[
1] Recent reviews: a) M. H. Pꢁrez-Temprano, J. A. Casares, P.
Espinet, Chem. Eur. J. 2012, 18, 1864 – 1884; b) S. A. Blum, J. J.
Hirner, Y. Shi, Acc. Chem. Res. 2011, 44, 603 – 613.
2] A. L. Casado, P. Espinet, Organometallics 1998, 17, 3677 – 3683.
3] M. Pꢁrez-Temprano, J. A. Casares, A. R. de Lera, R. ꢂlvarez, P.
Espinet, Angew. Chem. 2012, 124, 5001 – 5004; Angew. Chem.
Int. Ed. 2012, 51, 4917 – 4920.
metallophilic interactions in the transition states. In contrast,
the sum of the van der Waals radii is found for Sn-Pd (3.714
versus 3.80 ꢀ), thereby suggesting no interaction.
[
[
This study shows that gold(I) complexes in the presence of
LiCl efficiently catalyze the transmetalation step of bulky
groups from tin to palladium, thus making possible some
cross-couplings that would not proceed under the classical
Stille reaction conditions. The effect of gold in the reaction
might be limited by the unfavorable thermodynamics of the
transmetalation equilibrium from organotin to gold if the
concentrations of the arylgold intermediate were kinetically
insufficient for the process to go on to the next step.
[
4] a) A. S. K. Hashmi, C. Lothschꢃtz, R. Dçpp, M. Rudolph, T. D.
Ramamurthi, F. Rominger, Angew. Chem. 2009, 121, 8392 –
8395; Angew. Chem. Int. Ed. 2009, 48, 8243 – 8246; b) A. S. K.
Hashmi, R. Dçpp, C. Lothschꢃtz, M. Rudolph, D. Riedel, F.
Rominger, Adv. Synth. Catal. 2010, 352, 1307 – 1314.
[
5] For Sonogashira-like cross-coupling employing palladium/gold
instead of palladium/copper systems, see: a) L. A. Jones, S. Sanz,
2
192
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Angewandte
Chemie
M. Laguna, Catal. Today 2007, 122, 403 – 406; b) B. Panda, T. K.
Sarkar, Tetrahedron Lett. 2010, 51, 301 – 305.
6] a) Y. Shi, S. M. Peterson, W. W. Haberaecker III, S. A. Blum, J.
Am. Chem. Soc. 2008, 130, 2168 – 2169; b) Y. Shi, S. D. Ramgren,
S. A. Blum, Organometallics 2009, 28, 1275 – 1277.
[14] R. V. Bojan, J. M. Lꢄpez-de-Luzuriaga, M. Monge, M. E. Olmos,
J. Organomet. Chem. 2010, 695, 2385 – 2393.
[15] CRC Handbook of Chemistry and Physics, Internet Version 2005
(Ed.: D. R. Lide), CRC, Boca Raton, FL, 2005; http://www.
hbcpnetbase.com.
[
[
[
[
7] a) Y. Shi, K. E. Roth, S. D. Ramgren, S. A. Blum, J. Am. Chem.
Soc. 2009, 131, 18022 – 18023; b) Y. Shi, S. D. Ramgren, S. A.
Blum, Organometallics 2011, 30, 4811 – 4813.
8] A. S. K. Hashmi, C. Lothschꢃtz, R. Dçpp, M. Ackermann,
J. D. B. Becker, M. Rudolph, C. Scholz, F. Rominger, Adv. Synth.
Catal. 2012, 354, 133 – 147.
[16] M. H. Pꢁrez-Temprano, A. Nova, J. A. Casares, P. Espinet, J.
Am. Chem. Soc. 2008, 130, 10518 – 10520.
[
[
17] D. Milstein, J. K. Stille, J. Am. Chem. Soc. 1979, 101, 4992 – 4998.
18] For the isomers arising from the oxidative addition and their
isomerization, see the following paper and references therein:
M. H. Pꢁrez-Temprano, A. M. Gallego, J. A. Casares, P. Espinet,
Organometallics 2011, 30, 611 – 617.
9] P. Espinet, A. M. Echavarren, Angew. Chem. 2004, 116, 4808 –
[
19] R. ꢂlvarez, M. Pꢁrez, O. Nieto-Faza, A. R. de Lera, Organo-
metallics 2008, 27, 3378 – 3389.
4839; Angew. Chem. Int. Ed. 2004, 43, 4704 – 4734.
[
[
10] a) A. L. Casado, P. Espinet, J. Am. Chem. Soc. 1998, 120, 8978 –
[
20] A. Ariafard, Z. Lin, I. J. S. Fairlamb, Organometallics 2006, 25,
8
1
985; b) A. L. Casado, P. Espinet, J. Am. Chem. Soc. 2000, 122,
1771 – 11782.
5788 – 5794. Probably the effect on the tin to gold transmetala-
tion should be similar, as this barrier is related to the electro-
philicity of the metal center.
11] a) J. P. Marino, J. F. Long, J. Am. Chem. Soc. 1988, 110, 7916 –
7917; b) L. S. Liebeskind, R. W. Fengl, J. Org. Chem. 1990, 55,
5359 – 5364; c) L. S. Liebeskind, J. Wand, Tetrahedron Lett. 1990,
31, 4293 – 4296; d) L. S. Liebeskind, M. S. Yu, R. H. Yu, J. Wang,
[
[
3
21] The coupling reaction is continuously producing ISn(nBu) .
Should no other source of Cl be available, this ISn(nBu) would
3
react with [AuCl(AsPh )] to give ClSn(nBu) and [AuI(AsPh )],
3
3
3
K. S. Hagen, J. Am. Chem. Soc. 1993, 115, 9048 – 9055; e) L. S.
Liebeskind, S. W. Riesinger, J. Org. Chem. 1993, 58, 408 – 413;
f) J. R. Falck, R. K. Bhatt, J. Ye, J. Am. Chem. Soc. 1995, 117,
which is undesired.
22] a) G. C. Fu, Acc. Chem. Res. 2008, 41, 1555 – 1564; b) J. R.
Naber, S. L. Buchwald, Adv. Synth. Catal. 2008, 350, 957 – 961;
c) M. Dowlut, D. Mallik, M. G. Organ, Chem. Eur. J. 2010, 16,
5973 – 5982; g) G. D. Allred, L. S. Liebeskind, J. Am. Chem. Soc.
1996, 118, 2748 – 2749; h) X. Han, B. M. Stoltz, E. J. Corey, J.
4279 – 4283; d) R. D. Mazzola, S. Giese, C. L. Benson, F. G. West,
Am. Chem. Soc. 1999, 121, 7600 – 7605; i) R. D. Mazzola, S.
Giese, C. L. Benson, F. G. West, J. Org. Chem. 2004, 69, 220 –
J. Org. Chem. 2004, 69, 220 – 223; e) M. Garcꢅa-Melchor, G.
Ujaque, F. Maseras, A. Lledꢄs in Phosphorus Compounds:
Advanced Tools in Catalysis and Material Sciences, Vol. 37 (Eds.:
M. Peruzzini, L. Gonsalvi), Springer, Berlin, 2011, chap. 3,
pp. 57 – 84.
223; j) E. Flçistrup, P. Goede, R. Strçmberg, J. Malm, Tetrahe-
dron Lett. 2011, 52, 209 – 211.
[
[
12] a) A. L. Casado, P. Espinet, Organometallics 2003, 22, 1305 –
1309; b) V. Farina, S. Kapadia, B. Krishnan, C. Wang, L. S.
[
23] A. Nova, G. Ujaque, F. Maseras, A. Lledꢄs, P. Espinet, J. Am.
Chem. Soc. 2006, 128, 14571 – 14578.
Liebeskind, J. Org. Chem. 1994, 59, 5905 – 5911.
13] N. Meyer, S. Sivanathan, F. Mohr, J. Organomet. Chem. 2011,
[24] Calculated using Gaussian09 and the wB97X-D hybrid func-
696, 1244 – 1247.
tional.
Angew. Chem. Int. Ed. 2013, 52, 2189 –2193
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2193