Highly active well-defined palladium precatalysts for the efficient amination of aryl chlorides

Article abstract of DOI:10.1021/om2005222

The efficient preparation of [Pd(Amphos)(cinnamyl)Cl)] and [Pd(Amphos)(TFA)(κ²-N,C-C₆H₄-CH ₂NMe₂)] (Amphos = 4-(di-tert-butylphosphino)-N,N- dimethylaniline and TFA = trifluoroacetate), two new well-defined palladium precatalysts, is reported. These complexes prove highly active in the Buchwald-Hartwig amination reaction, allowing the coupling of a wide range of (hetero)aryl chlorides, including unactivated, neutral, and sterically hindered substrates, with a wide range of amines, including primary and secondary amines. Finally, the catalytic systems have proven efficient at low catalyst loadings ranging from 0.1 to 0.3 mol %.

Full text of DOI:10.1021/om2005222

ARTICLE
pubs.acs.org/Organometallics
Highly Active Well-Defined Palladium Precatalysts for the Efficient
Amination of Aryl Chlorides
Anthony Chartoire, Mathieu Lesieur, Alexandra M. Z. Slawin, Steven P. Nolan,* and Catherine S. J. Cazin*
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, U.K.
S Supporting Information
b
ABSTRACT: The efficient preparation of [Pd(Amphos)
(cinnamyl)Cl)] and [Pd(Amphos)(TFA)(k2-N,C-C6H4-CH2-
NMe2)] (Amphos = 4-(di-tert-butylphosphino)-N,N-dimethylani-
line and TFA = trifluoroacetate), two new well-defined palladium
precatalysts, is reported. These complexes prove highly active in
the BuchwaldꢀHartwig amination reaction, allowing the coupling of a wide range of (hetero)aryl chlorides, including unactivated,
neutral, and sterically hindered substrates, with a wide range of amines, including primary and secondary amines. Finally, the
catalytic systems have proven efficient at low catalyst loadings ranging from 0.1 to 0.3 mol %.
’ INTRODUCTION
phosphine ligands, the 4-(di-tert-butylphosphino)-N,N-dimethy-
laniline (Amphos) has recently demonstrated good efficiency in
SuzukiꢀMiyaura12 coupling and moderate reactivity in amina-
tion reactions.13 We thus report here the preparation of two new
well-defined Pd-based precatalysts by combining the Amphos
ligand with a palladium cinnamyl and a palladacycle moiety
(Figure 1). The reactivity of these systems in amination reactions
was then examined.
Since its discovery in 1983,1 the palladium-catalyzed aryl
amination reaction, most commonly known as the Buch-
waldꢀHartwig reaction, has emerged as one of the most power-
ful methods for the formation of CꢀN bonds.2,3 During the past
decades, in order to increase the versatility and the potential of
amination reactions, most efforts have been devoted to the
development of new Pd-based precatalysts. The nature of the
ligand in these systems appears crucial since its ligation to the
metal center dictates the catalytic properties. In this context, a
wide range of ligands has been studied, including bulky electron-
rich trialkylphosphines,4 biaryldialkylphosphines,5 bidentate
diphosphines,6 and N-heterocyclic carbenes (NHCs).7 The
stability of palladium complexes bearing such ligands comes
from the strong σ-donating effect of the ligand. The high catalytic
activity of these Pd/L systems can be explained by the formation
of a highly reactive monoligated [Pd0L] species,8 and the facile
delivery of such a reactive species can be modulated by ancillary
ligand (non L ligands) selection. Most often, the active species is
generated in situ by mixing a palladium source (oxidation state 0
or +2) with an excess of the ligand L. Nevertheless, in order to
better understand the mechanism of the catalytic process and
most often increase catalytic performance, the use of a well-
defined precatalyst is preferred.
Among the large number of palladium precatalysts described
in the literature, [Pd(NHC)(cinnamyl)Cl]7d,e derivatives
(NHC: IPr = N,N0-bis(2,6-diisopropylphenyl)imidazol-2-yli-
dene, SIPr = N,N0-bis(2,6-diisopropylphenyl)-4,5-dihydroimida-
zol-2-ylidene) and [Pd(PR3)(X)(k2-N,C-C6H4-CH2NMe2)]
palladacycles9 (X = TFA, OTf, Cl, Br, and I) have proven to
be excellent precatalysts in aryl amination reactions, allowing the
coupling of unactivated aryl chlorides with catalyst loadings as
low as 100 and 1000 ppm, respectively. These two architectures
were selected for the present study in view of the ease with which
the palladium sheds them to generate the putative [Pd0L]
species.10,11 Additionally, among the large number of possible
’ RESULTS AND DISCUSSION
The preparation of two new precatalysts, [Pd(Amphos)
(cinnamyl)Cl)] (1) and [Pd(Amphos)(TFA)(k2-N,CꢀC6H4-
CH2NMe2)] (2), is straightforward and makes use of a simple
fragmentation of the corresponding palladium dimer14,15using
the Amphos ligand (Scheme 1). In the case of 1, the process
requires a stoichiometric amount of phosphine and is complete
in 1.5 h in THF at room temperature. This synthesis affords the
desired complex with an excellent 95% isolated yield after
recrystallization. In the case of 2, a slight excess of phosphine
was used (2.1 equiv), and the complex is obtained at room
temperature in CH2Cl2 with a very good 82% yield in 1 h. Finally,
it is noteworthy that both Pd complexes are air- and moisture-
stable.
For 1 and 2, crystals suitable for X-ray diffraction were grown
by slow diffusion of hexane into a saturated CDCl3 solution of
the complex.16 In both cases, the bond lengths between palla-
dium and the phosphine are similar (2.3291(15) and 2.3110(13)
Å for 1 and 2, respectively). These values are also comparable to
those found for complexes described in the literature.17 We can
note that in the case of 1 the distance between the palladium and
the cinnamyl group is comparable to [Pd(NHC)(cinnamyl)Cl]
complexes.7d The structure of 2 adopts a slightly distorted
square-planar geometry, and the bond lengths are similar to
Received: June 17, 2011
Published: July 28, 2011
r
2011 American Chemical Society
4432
dx.doi.org/10.1021/om2005222 Organometallics 2011, 30, 4432–4436
|

Organometallics
ARTICLE
literature values (within 0.05 Å).14b Finally, the percent buried
volume of Amphos in both systems was calculated using the web
application SambVca.18 Similar results were obtained for both
complexes (1: %Vbur = 34.7; 2: %Vbur = 34.3), showing that the
Amphos ligand is quite bulky in comparison to reported tertiary
phosphine congeners.19
One of the current challenges in amination reactions is to
achieve the coupling of unactivated chlorides at low catalyst
loadings. In order to perform a rapid optimization of reaction
conditions using a challenging aryl halide, the reactivity of
4-chloroanisole with morpholine was examined. At first, 0.1 mol
% of the palladacycle 2 was used, using conditions previously
described by Bedford and Cazin,9 using sodium tert-butoxide
(NaOtBu) as the base in toluene for 17 h at 110 °C (Table 1,
entry 1). Under these conditions, the desired product 3 is
obtained in 50% conversion of the starting 4-chloroanisole. In
order to favor the formation of 3, several bases and solvents
were next screened. It was found that weaker bases such as
NaOH, KOH, K3PO4, or carbonate bases (Table 1, entries
3ꢀ8) did not prove as efficient as the stronger NaOtBu.
Surprisingly, under these conditions, it was shown that KOtBu
as base led to poor conversion (10%, Table 1, entry 2) in
comparison to reactions conducted using NaOtBu. Several
Figure 1. Design of the new palladium/Amphos precatalysts.
Scheme 1. Synthesis of the Two New Well-Defined Palladium
Precatalysts 1 and 2a,b
Figure 3. Graphical representation of 2. Hydrogens have been omitted
for clarity. Selected bond lengths (Å) and angles (deg): Pd1ꢀC17,
2.015(5); Pd1ꢀO27, 2.141(3); Pd1ꢀN24, 2.181(4); Pd1ꢀP1,
2.3110(13); C17ꢀPd1ꢀN24 81.32(18), O27ꢀPd1ꢀN24 87.56(15),
C17ꢀPd1ꢀP1 95.36(15), O27ꢀPd1ꢀP1 96.16(10).
a Reagents and conditions: (i) [Pd(cinnamyl)(μ-Cl)]2 (1 equiv),
Amphos (2 equiv), THF, rt, 1.5 h; (ii) [{Pd(μ-TFA)-(k2-N,C-C6H4-
CH2NMe2)}2] (1 equiv), Amphos (2.1 equiv), CH2Cl2, rt, 1 h.
b Isolated yields.
Figure 2. Graphical representation of 1. Hydrogens have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Pd1ꢀC17, 2.115(6);
Pd1ꢀC18, 2.154(6); Pd1ꢀC19, 2.273(6); Pd1ꢀP1, 2.3291(15); Pd1ꢀCl1, 2.3672(15); C17ꢀPd1ꢀC19, 67.0(2); C17ꢀPd1ꢀP1, 97.29(18);
C19ꢀPd1ꢀCl1, 93.56(16); P1ꢀPd1ꢀCl1, 102.68(5).
4433
dx.doi.org/10.1021/om2005222 |Organometallics 2011, 30, 4432–4436

Organometallics
ARTICLE
Table 1. Optimization of the Reaction Conditionsa
the coupling partner reaction site, such as in the case of
2-chlorotoluene, the amount of palladium necessary to reach
completion had to be slightly increased (0.3 mol %). The case of
the more challenging N-methylaniline (Table 2, entries 4 and 5)
was next explored, and using 0.3 mol % of 1, the expected aniline
derivatives were obtained in very good yields (84ꢀ89%). The
reactivity of some primary amines with some sterically hindered
aryl chlorides was next studied. Excellent results were obtained in
these instances, and the corresponding secondary amines were
isolated in high yields (Table 2, entries 6ꢀ9, 86ꢀ98%). It is
noteworthy here that the necessary amount of palladium to reach
completion appears dependent on the bulkiness of the amine.
However, the reaction requires only 0.2 mol % of 1 to allow the
coupling of 2,6-dimethylchlorobenzene with the bulkiest 2,
6-diisopropylaniline (Table 2, entry 9). 1-Chloronaphthalene
could be successfully coupled to piperidine (Table 2, entry 10).
Despite the fact that a significant amount of the dehydrohaloge-
nated product (naphthalene) was detected by GC (<10%), the
formation of the desired product was obtained with a good, 71%
isolated yield. Finally, the compatibility of the catalytic system
with heterocycles was demonstrated, and very good results
were obtained for the coupling of 2-chloropyridine, but also
for the more challenging deactivated 3-chloropyridine (Table 2,
entries 11ꢀ13, 77ꢀ85%).
entry precatalyst (mol %)
solvent
toluene
base
GC conversion (%)b
1
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
2 (0.1)
1 (0.1)
1 (0.15)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.05)
2 (0.05)
NaOtBu
KOtBu
NaOH
KOH
50
2
toluene
toluene
toluene
toluene
toluene
toluene
toluene
10
3
2
4
4
5
K3PO4
Na2CO3
K2CO3
Cs2CO3
6
6
0
7
0
8
4
9
1,4-dioxane NaOtBu
90
10
11
12
13
14
15
16
17
18
19
20
DME
NaOtBu
NaOtBu
12
THF
2
1,4-dioxane NaOtBu
1,4-dioxane NaOtBu
1,4-dioxane KOtBu
1,4-dioxane NaOH
1,4-dioxane KOH
1,4-dioxane K3PO4
1,4-dioxane Cs2CO3
1,4-dioxane NaOtBu
1,4-dioxane NaOtBu
95
99 (85)c
16d
0
2
0
0
’ CONCLUSION
82
65
In summary, we have disclosed a facile and efficient access to
two new, well-defined palladium precatalysts containing the
Amphos ligand. These complexes have shown excellent catalytic
activities in the BuchwaldꢀHartwig reaction, allowing for cou-
pling of various (hetero)aryl chlorides with a wide range of
amines in very good yields (71ꢀ98%) and using low catalyst
loadings (0.1ꢀ0.3 mol %). The use of these systems in flow
chemistry is presently being examined in our laboratories.
a Reagents and conditions: 4-chloroanisole (1 equiv), morpholine (1.26
equiv), Pd precatalyst 1 or 2 (mol %), solvent, base (1.40 equiv),
reflux, 17 h. b Conversion to coupling product based on 4-chloroanisole
c
determined by GC. Isolated yield after chromatography on silica gel,
average of two runs. d The formation of 3 and another unidentified
product is observed by GC.
solvents were next screened. While 1,2-dimethoxyethane
(DME) and tetrahydrofuran (THF) gave poor conversions
(Table 1, entries 10 and 11), 1,4-dioxane gave the best result,
affording the desired product with conversions up to 90%
(Table 1, entry 9). This result can probably be explained by
the stabilization of the [Pd0-L] active species by the high-
boiling and donating 1,4-dioxane.
The activity of the second palladium cinnamyl precatalyst 1
was next studied under similar conditions to those optimized for 2.
The reaction proved very efficient when using the NaOtBu/1,
4-dioxane combination, permitting a 95% conversion of the
starting 4-chloroanisole (Table 1, entry 12). Other bases gave
no or poor conversions (Table 1, entries 14ꢀ18). Finally,
complete conversion can be obtained by using 1.4 equivalents
of NaOtBu, refluxing the 1,4-dioxane during 17 h with 0.15 mol %
1 (99%, Table 1, entry 13). To compare the efficiency of both 1
and 2, the catalyst loading was further decreased. The reaction
was then performed using 0.05 mol % Pd, showing that 1
provided an improved conversion over that obtained with 2
(82% vs 65%, Table 1, entry 19 vs entry 20). For this reason, the
scope of the reaction was next explored using 1 as precatalyst in
the presence of 1,4-dioxane and NaOtBu.
’ EXPERIMENTAL SECTION
Synthesis of [Pd(Amphos)(cinnamyl)Cl)], 1. In a glovebox, in
a 100 mL round-bottom flask equipped with a magnetic bar,
[Pd(cinnamyl)(μ-Cl)]2 (1.04 g, 2 mmol) and Amphos (1.06 g, 4 mmol)
were added to THF (30 mL). The reaction mixture was stirred at room
temperature during 1.5 h. After this time, outside the glovebox, THF was
concentrated, and the complex was precipitated with pentane and
collected by filtration. The complex was recrystallized from DCM and
pentane, yielding the title compound as a yellow powder, 2.0 g (95%).
1H NMR (400 MHz, CDCl3): δ 7.56ꢀ7.51 (m, 4H, HAr), 7.37ꢀ7.27
(m, 3H, HAr), 6.67 (dd, JHH = 9.0 Hz, J0HH = 1.1 Hz, 2H, HAr),
5.90ꢀ5.82 (m, 1H, HCin), 5.21ꢀ5.15 (m, 1H, HCin), 3.30 (dd, JHH = 6.5
Hz, J0HH = 1.5 Hz, 1H, HCin), 3.01 (s, 6H, NCH3), 2.71 (d, JHH = 11.6
Hz, 1H, HCin), 1.47 (d, JHP = 14 Hz, 9H, CCH3), 1.38 (d, JHP = 13.9 Hz,
9H, CCH3). 13C{1H} NMR (100 MHz, CDCl3): δ 151.0 (d, JCP = 1.5
Hz, CAr), 137.0 (d, JCP = 5.9 Hz, CAr), 136.7 (d, JCP = 12.5 Hz, CAr),
128.8 (d, JCP = 1.0 Hz, CAr), 128.1 (d, JCP = 2.9 Hz, CAr), 127.9 (d, JCP
=
2.2 Hz, CAr), 117.1 (d, JCP = 36.0 Hz, CAr), 110.5 (d, JCP = 10.3 Hz, CAr),
108.9 (d, JCP = 5.9 Hz, CCin), 99.7 (d, JCP = 26.4 Hz, CCin), 55.2 (CCin),
40.1 (NCH3), 36.3 (d, JCP = 13.9 Hz, CMe3), 36.2 (d, JCP = 13.2 Hz,
CMe3), 30.7 (d, JCP = 5.9 Hz, C(CH3)3), 30.2 (d, JCP = 5.1 Hz,
C(CH3)3). 31P{1H} NMR (162 MHz, CDCl3): δ 67.0 (s) Anal. Calcd
for C25H37ClNPPd: C, 57.26; H, 7.11; N, 2.67. Found: C, 57.36; H,
6.93; N, 2.79.
The results are summarized in Table 2. The system displays
good efficiency for the coupling of nonactivated (Table 2, entries
1 and 2) and deactivated chlorides (Table 2, entry 3) with cyclic
dialkylamines, yielding the expected compounds in excellent
isolated yields (82ꢀ93%). If steric hindrance is increased about
Synthesis of [Pd(Amphos)(TFA)(j2N,C-C6H4-CH2NMe2)], 2.
In a glovebox, a 50 mL Schlenk flask equipped with a magnetic bar
4434
dx.doi.org/10.1021/om2005222 |Organometallics 2011, 30, 4432–4436

Organometallics
ARTICLE
Table 2. Scope of the Amination Reactiona
a Reagents and conditions: (Het)ArCl (1 equiv), amine (1.2ꢀ1.3 equiv), 1 (mol %), base (1.4 equiv), 1,4-dioxane, reflux, 17 h. b Isolated yield after
chromatography on silica gel, average of two runs. c Hydrodehalogenation side-product observed by GC (<10%).
was charged with [Pd(TFA)(k2-N,C-C6H4-CH2NMe2)]2 (0.283 mmol,
0.200 g), Amphos (0.595 mmol, 0.157 g), and 1,2-dichloromethane
(DCM) (11 mL). The reaction mixture was stirred at room temperature
during 1 h. After this time, outside the glovebox, the solvent was concentrated
to ca. 1 mL in vacuo, and ethanol (10 mL) was added. The solution was
concentrated, leading to the precipitation of a yellow solid. The supernatant
was removed, and the solvents were evaporated in vacuo, yielding the title
amine (1.2 ꢀ1.3 mmol), and finally the precatalyst solution were added. The
reaction mixture was stirred at reflux during 17 h. The reaction mixture was
cooled, quenched with HCl(aq) (5 mL, 2.3 M), and neutralized with NaOH(aq)
(5 mL, 5 M), and the aqueous layer was extracted with DCM (3 ꢁ 10 mL).
The combined organic layers were dried over MgSO4, and the solvents were
evaporated in vacuo. The crude product was finally purified by flash chroma-
tography on silica gel. The reported yields are the average of two reactions.
1
compound as a yellow powder, 0.286 g (82%). H NMR (400 0MHz,
CD2Cl2): δ 7.47ꢀ7.41 (m, 2H, HAr), 6.87 (dd, JHH = 7.3 Hz, J HH
=
’ ASSOCIATED CONTENT
1.4 Hz, 1H, HAr), 6.74 (td, JHH = 7.3 Hz, J0HH = 1.4 Hz, 1H, HAr), 6.47
(dd, JHH = 9.0 Hz, J0HH = 1.4 Hz, 2H, HAr), 6.40ꢀ6.29 (m, 2H, HAr), 3.94
(s, 2H, CH2), 2.93 (s, 6H, NCH3), 2.62 (s, 6H, NCH3), 1.47 (d, JCP = 13.8
S
Supporting Information. Crystallographic data for 1 and
b
2, procedure for the amination reactions, and NMR spectra for all
complexes and cross coupling products. This material is available
free of charge via the Internet at http://pubs.acs.org.
Hz, 18H, CCH3). 13C {1H} NMR (100 MHz, CDCl3): δ 151.1 (d, JCP
=
2.1 Hz, CdO),147.5(d,JCP =2.1Hz,CAr), 146.0 (d, JCP =2.1Hz,CAr), 139.3
(d,JCP =6.9Hz,CAr), 137.1 (d, JCP = 9.7 Hz, CAr), 124.5 (d, JCP =4.2Hz,CAr),
123.5 (CAr), 122.2 (CAr), 113.9 (CAr), 113.4 (CAr), 110.4 (d, JCP = 10.4 Hz,
CAr),72.4(d,JCP =2.8Hz,CH2),49.7(d,JCP =2.1Hz,NCH3), 40.1 (NCH3),
37.4 (CMe3), 37.1 (CMe3), 30.8 (d, JCP = 4.2 Hz, C(CH3)3). 31P{1H} NMR
(162 MHz, CD2Cl2): δ 67.2 (s). Anal. Calcd for C27H40F3N2O2PPd: C,
52.39; H, 6.51; N, 4.53. Found: C, 52.51; H, 6.60; N, 4.47.
BuchwaldꢀHartwig Cross-Coupling of Aryl Halides with
Primary and Secondary Amines: General Procedure. In a
glovebox, a vial equipped with a stirring bar and sealed with a screw
cap fitted with a septum was charged with NaOtBu (0.136 g, 1.4 mmol)
and the necessary amount of 1,4-dioxane to bring the total solvent
volume to 3 mL. Outside the glovebox, the aryl chloride (1.0 mmol), the
’ AUTHOR INFORMATION
Corresponding Author
*Fax: +44 (0) 1334 463 808. E-mail: cc111@st-andrews.ac.uk;
snolan@st-andrews.ac.uk.
’ ACKNOWLEDGMENT
We gratefully acknowledge the EC for funding through the
seventh framework program SYNFLOW and the EaStCHEM
4435
dx.doi.org/10.1021/om2005222 |Organometallics 2011, 30, 4432–4436

Organometallics
ARTICLE
School of Chemistry. Johnson Matthey (Dr. C. Barnard) and
Umicore (Dr. R. Karch) are thanked for their generous gifts of
materials. S.P.N. is a Royal SocietyꢀWolfson Research Merit
Award holder.
(14) [Pd(cinnamyl)(μ-Cl)]2 is commercially available from Umi-
core. [{Pd(μ-TFA)-(k2-N,C-C6H4CH2NMe2)}2] is prepared in a two-
step literature procedure.9
(15) For recent use of [Pd(cinnamyl)(μ-Cl)]2 as a palladium source
in catalysis, see: (a) Watson, D. A.; Su, M.; Teverovskiy, G.; Zhang, Y.;
Garcia-Fortanet, J.; Kinzel, T.; Buchwald, S. L. Science 2009, 325, 1661.
(b) Dumrath, A.; Wu, X.-F.; Neumann, H.; Spannenberg, A.; Jackstell,
R.; Beller, M. Angew. Chem., Int. Ed. 2010, 49, 8988. (c) Wu, X.-F.;
Sundararaju, B.; Neumann, H.; Dixneuf, P. H.; Beller, M. Chem.ꢀEur.
J. 2011, 17, 106.
(16) CCDC-830310 (1) and CCDC-830311 (2) contain the sup-
plementary crystallographic data for this contribution. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
(17) (a) As a comparison for 1 see for example the case of [Pd
(η3-allyl)(PNSO)]: Achard, T.; Benet-Buchholz, J.; Escudero-Adan,
E. C.; Riera, A.; Verdaguer, X. Organometallics 2011, 30, 3119. (b) As
a comparison for 2 see for example the cases of [Pd(PR3)(X)(k2-N,
C-C6H4-CH2NMe2)] palladacycles: Bedford, R. B.; Cazin, C. S. J.;
Coles, S. J.; Gelbrich, T.; Horton, P. N.; Hursthouse, M. B.; Light, M. E.
Organometallics 2003, 22, 987.
’ REFERENCES
(1) Kosugi, M.; Kameyama, M.; Migita, T. Chem. Lett. 1983, 927.
(2) For early references on amination reactions see: (a) Guram,
A. S.; Rennels, R. A.; Buchwald, S. L. Angew. Chem., Int. Ed. Engl. 1995,
34, 1348. (b) Louie, J.; Hartwig, J. F. Tetrahedron Lett. 1995, 36, 3609.
(3) For reviews on amination reactions see: (a) Hartwig, J. F.
Handbook of Organopalladium Chemistry for Organic Synthesis; 2002;
Vol. 1, p 1051. (b) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002,
219, 131. (c) Bedford, R. B.; Cazin, C. S. J.; Holder, D. Coord. Chem. Rev.
2004, 248, 2283.(d) Jiang, L.; Buchwald, S. L. Metal-Catalyzed Cross-
Coupling Reactions, 2nd Ed.; 2004; Vol. 2, p 699. (e) Hartwig, J. F. Acc.
Chem. Res. 2008, 41, 1534.
(4) (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000,
122, 4020. (b) Hill, L. L.; Smith, J. M.; Brown, W. S.; Moore, L. R.;
Guevera, P.; Pair, E. S.; Porter, J.; Chou, J.; Wolterman, C. J.; Craciun, R.;
Dixon, D. A.; Shaughnessy, K. H. Tetrahedron 2008, 64, 6920.
(c) Fleckenstein, C. A.; Plenio, H. Chem. Soc. Rev. 2010, 39, 694.
(5) (a) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008,
47, 6338. (b) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2011, 2, 27.
(6) (a) Wolfe, J. P.; Wagaw, S.; Buchwald, S. L. J. Am. Chem. Soc.
1996, 118, 7215. (b) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1996,
118, 7217. (c) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1144.
(d) Shen, Q.; Shekhar, S.; Stambuli, J. P.; Hartwig, J. F. Angew. Chem., Int.
Ed. 2005, 44, 1371. (e) Shen, Q.; Ogata, T.; Hartwig, J. F. J. Am. Chem.
Soc. 2008, 130, 6586.
(18) (a)
https://www.molnac.unisa.it/OMtools/sambvca.php.
(b) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano,
V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 1759. (c) Clavier, H.; Correa, A.;
Cavallo, L.; Escudero-Adan, E. C.; Benet-Buchholz, J.; Slawin, A. M. Z.;
Nolan, S. P. Eur. J. Inorg. Chem. 2009, 1767.
(19) Among 13 tertiary phosphines, only P(C6F5)3, P(o-Tol)3, and
P(Mes)3 have a bigger buried volume than Amphos for a MꢀP length of
2.28 Å: Clavier, H.; Nolan, S. P. Chem. Commun. 2010, 46, 841.
(7) (a) Viciu, M. S.; Kissling, R. M.; Stevens, E. D.; Nolan, S. P. Org.
Lett. 2002, 4, 2229. (b) Navarro, O.; Marion, N.; Scott, N. M.; Gonzalez,
J.; Amoroso, D.; Bell, A.; Nolan, S. P. Tetrahedron 2005, 61, 9716.
(c) Marion, N.; Ecarnot, E. C.; Navarro, O.; Amoroso, D.; Bell, A.;
Nolan, S. P. J. Org. Chem. 2006, 71, 3816. (d) Marion, N.; Navarro, O.;
Mei, J.; Stevens, E. D.; Scott, N. M.; Nolan, S. P. J. Am. Chem. Soc. 2006,
128, 4101. (e) Navarro, O.; Marion, N.; Mei, J.; Nolan, S. P. Chem.ꢀEur.
J. 2006, 12, 5142. (f) Esposito, O.; Gois, P. M. P.; Lewis, A. K. d. K.;
Caddick, S.; Cloke, F. G. N.; Hitchcock, P. B. Organometallics 2008,
27, 6411. (g) Organ, M. G.; Abdel-Hadi, M.; Avola, S.; Dubovyk, I.;
Hadei, N.; Kantchev, E. A. B.; O’Brien, C. J.; Sayah, M.; Valente, C.
Chem.ꢀEur. J. 2008, 14, 2443. (h) Jin, Z.; Guo, S.-X.; Gu, X.-P.; Qiu,
L.-L.; Song, H.-B.; Fang, J.-X. Adv. Synth. Catal. 2009, 351, 1575.
(i) Fortman, G. C.; Nolan, S. P. Chem. Soc. Rev. 2011, DOI: 10.1039/
C1CS15088J.
(8) Christmann, U.; Vilar, R. Angew. Chem., Int. Ed. 2005, 44, 366.
(9) Bedford, R. B.; Cazin, C. S. J.; Coles, S. J.; Gelbrich, T.; Horton,
P. N.; Hursthouse, M. B.; Light, M. E. Organometallics 2003, 22, 987.
(10) (a) For the first mechanistic details involving imines: Bedford,
R. B.; Cazin, C. S. J.; Hursthouse, M. B.; Light, M. E.; Pike, K. J.;
Wimperis, S. J. Organomet. Chem. 2001, 633, 173. (b) For the first use of
dmba to such an end see: Bedford, R. B.; Cazin, C. S. J. Chem. Commun.
2001, 1540.
(11) (a) Viciu, M. S.; Germaneau, R. F.; Nolan, S. P. Org. Lett. 2002,
4, 4053. (b) Viciu, M. S.; Germaneau, R. F.; Navarro, O.; Stevens, E. D.;
Nolan, S. P. Organometallics 2002, 21, 5470. (c) Viciu, M. S.; Kelly, R. A.,
III; Stevens, E. D.; Naud, F.; Studer, M.; Nolan, S. P. Org. Lett. 2003,
5, 1479. (d) C€ammerer, S.; Viciu, M. S.; Stevens, E. D.; Nolan, S. P.
Synlett 2003, 1871. (e) Viciu, M. S.; Navarro, O.; Germaneau, R. F.;
Kelly, R. A., III; Sommer, W.; Marion, N.; Stevens, E. D.; Cavallo, L.;
Nolan, S. P. Organometallics 2004, 23, 1629.
(12) Guram, A. S.; King, A. O.; Allen, J. G.; Wang, X.; Schenkel, L. B.;
Chan, J.; Bunel, E. E.; Faul, M. M.; Larsen, R. D.; Martinelli, M. J.; Reider,
P. J. Org. Lett. 2006, 8, 1787.
(13) Lundgren, R. J.; Sappong-Kumankumah, A.; Stradiotto, M.
Chem.ꢀEur. J. 2010, 16, 1983.
4436
dx.doi.org/10.1021/om2005222 |Organometallics 2011, 30, 4432–4436