Novel phosphinite and phosphonite copper(I) complexes: Efficient catalysts for click azide-alkyne cycloaddition reactions

Article abstract of DOI:10.1021/om200791u

The preparation of novel phosphinite- and phosphonite-bearing copper(I) complexes of the general formula [CuX(L)] is reported. These compounds, which remain scarce in the literature, could be prepared using readily available starting materials and were spectroscopically and structurally characterized. These complexes, together with their known phosphine and phosphite analogues, were then applied to the 1,3-dipolar cycloaddition of azides and alkynes, to find that the new complexes displayed the best activities. Full optimization of the reaction conditions resulted in a noteworthy Click catalytic system, active under very mild reaction conditions in the absence of any additive and using low metal loadings.

Full text of DOI:10.1021/om200791u

Article
pubs.acs.org/Organometallics
Novel Phosphinite and Phosphonite Copper(I) Complexes: Efficient
Catalysts for Click Azide−Alkyne Cycloaddition Reactions
́
Steven Lal, Jayne McNally, Andrew J. P. White, and Silvia Dıez-Gonzalez*
́
Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, U.K.
S
* Supporting Information
ABSTRACT: The preparation of novel phosphinite- and phosphonite-bearing
copper(I) complexes of the general formula [CuX(L)] is reported. These
compounds, which remain scarce in the literature, could be prepared using readily
available starting materials and were spectroscopically and structurally characterized.
These complexes, together with their known phosphine and phosphite analogues,
were then applied to the 1,3-dipolar cycloaddition of azides and alkynes, to find that
the new complexes displayed the best activities. Full optimization of the reaction conditions resulted in a noteworthy Click
catalytic system, active under very mild reaction conditions in the absence of any additive and using low metal loadings.
the reaction mixture. Furthermore, ligands in this trans-
formation are key to both protecting and activating copper(I)
centers, allowing for milder reaction conditions and broader
scopes.9 Hence, the use of ligands/additives in this cyclo-
addition reaction has definitely helped to increase its impact,
but still, this cycloaddition process remains a victim of its own
success and only few efforts have been focused on developing
efficient catalytic systems, particularly in comparison with the
reports on the diverse applications of this process.
Phosphorus-based ligands were among the first ones applied
to the cycloaddition of azides and alkynes. In 2003, the
previously reported [CuBr(PPh3)3] and {CuI[P(OEt)3]}
complexes were applied to the preparation of various glyco-
derived triazoles in good yields.10 We recently reported the
optimized conditions for using such catalytic systems under
strict Click conditions.11
Despite the popularity of these ligands in modern chemistry,
only three other methodology studies have been available so far
in this context. The related [Cu(NO3)(PPh3)2] was reported as
an efficient catalyst at room temperature under neat
conditions.12 Alternatively, Elsinga and Feringa screened a
number of phosphoramidite ligands for this reaction, although
they generated the active copper(I) species in situ from
CuSO4·5H2O and sodium ascorbate.13 Soon after, triphenyl-
phosphine was shown to greatly improve the catalytic activity of
various copper carboxylates, much better than the more
expensive PCy3, BINAP, and dppe ligands.14 However, in all
these studies the reaction products had to be purified on silica
gel, a technique precluded by Click postulates.
1. INTRODUCTION
Phosphorus(III) compounds, and phosphines and phosphites
in particular, are ubiquitous ligands in modern organometallic
chemistry. The related phosphinite and phosphonite deriva-
tives, however, are far less popular and their applications in
catalysis remain limited. Accordingly, copper(I) halogen
complexes bearing tertiary phosphines are widely known in
the literature and compounds with 1:3, 2:3, 1:2, and 1:1 Cu/L
ratios can be prepared under different reaction conditions.1
Phosphite-containing complexes are also relatively common;
known since the beginning of the 20th century, both 1:1 and
1:2 Cu/L adducts can be easily prepared. In contrast, only a few
reports concerning the preparation of phosphinite-2 or
phosphonite-containing3 CuI complexes can be found in the
literature.
Similarly, only a few applications of these ligands can be
found in the literature for copper(I)-mediated transformations.
We could only find one example with D-xylose-derived
phosphinite ligands for the asymmetric conjugate addition of
organometallic fragments onto enones.4 Likewise, taddol- or
biphenol-based phosphonite ligands have almost exclusively
been applied to conjugate additions,5 but also have been used
for the dehydrogenative coupling of hydrosilanes and alcohols.6
It is important to note that in all examples the active species
were generated in situ upon mixing of a copper source and the
phosphi(o)nite ligand and that, to the best of our knowledge,
no well-defined copper system with these ligands has been
applied to catalysis to date.
Consequently, we were interested in the preparation of novel
copper(I) complexes bearing simple phosphinite and phos-
phonite ligands and in their application in catalysis. Among the
plethora of existing copper-catalyzed reactions, the [3 + 2]
cycloaddition of organic azides and terminal alkynes has
recently attracted enormous interest due to its status of best
“Click” reaction to date.7 In this extremely efficient preparation
of 1,4-disubstituted [1,2,3]-triazoles,8 the use of pre-formed
copper(I) complexes avoids the need for any reducing agent in
This prompted us to closely examine the potential of a
related series of phosphorus-containing ligands in the copper-
catalyzed cycloaddition of azides and alkynes. Herein, we report
the preparation of phosphine, phosphinite, phosphonite, and
Received: August 24, 2011
Published: November 2, 2011
© 2011 American Chemical Society
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phosphite-bearing copper complexes and their application in
cycloaddition reactions under Click-suitable conditions.
Scheme 2. Preparation of Phosphinite and Phosphonite
Copper(I) Complexes
RESULTS AND DISCUSSION
■
Preparation of Copper(I) Complexes. In order to carry
out a thorough methodological study, we synthesized four
series of copper(I) complexes bearing phosphine, phosphinite,
phosphonite, and phosphite ligands. Thus, different phosphin-
ite and phosphonite ligands were prepared from the
corresponding phenols and chlorophosphines (Scheme 1).15
Scheme 1. Preparation and 31P NMR Signals for Phosphinite
and Phosphonite Ligands
a
b
Conditions: toluene, reflux, 2 h. Conditions: toluene, room
temperature, 3 days.
It is important to note that, regardless of the stoichiometry of
the reactions, only the Cu/L 1:1 complexes were obtained.20
This is in great contrast with the more usual phosphine and
phosphite copper(I) complexes.
Crystallographic Studies. In an effort to establish the
stoichiometry of the newly prepared complexes, mass
spectrometry studies were carried out, but unfortunately in
each case the results were inconclusive. However, material
suitable for single-crystal X-ray analysis was obtained for
complexes 13, 14, 17, 18, and 20 by slow diffusion of hexane in
warm toluene solutions. Ball and stick representations are given
in Figures 1 and 2, and selected bond lengths are provided in
Table 1 and in the captions of these figures.
All five structures have a cubane-like [Cu4X4] core, with each
copper center having a tetrahedral environment comprised of
three bridging halogens and a neutral phosphine ligand. This
confirmed the originally assumed stoichiometry for these
complexes. As expected for a complex containing a smaller
halogen atom, the copper core is less distorted in 14 (X = Cl)
than in 13, 17, 18, or 20 (X = Br), as shown by the X−Cu−X
angles. These range between 93.56(4) and 98.12(4)° for the
chloro species 14, while for the bromo species 13, 17, 18, and
20 they lie in the ranges 93.256(10)−105.903(12),
98.656(13)−107.119(15), 94.835(18)−101.760(18), and
98.544(12)−103.409(12)°, respectively.21 This same effect is
seen for the Cu−X bond lengths (Table 1), which vary between
2.3534(11) and 2.4430(11) Å for the chloro species 14 and in
the ranges 2.4773(4)−2.5822(4), 2.4572(5)−2.6096(6),
2.4683(4)−2.6102(4), and 2.4945(3)−2.5584(4) Å for the
bromo species 13, 17, 18, and 20, respectively.21 The shortest
intracube Cu···Cu distances are 3.0295(4), 3.1760(9),
3.0039(7), 3.1643(6), and 3.0979(6) Å in 13, 14, 17, 18, and
20, respectively. All of these distances are significantly longer
than the sum of the van der Waals radii (2.80 Å).
In all cases the expected compounds were isolated as pure
products after filtration on alumina/Celite in air. However,
ligand 5 was particularly unstable and had to be used promptly
after isolation to avoid its decomposition.
The introduction of other functional groups on the phenyl
rings of these ligands, such as nitro, cyano, and amino groups,
was also attempted. However, either the formation of complex
mixtures of products or the fast decomposition of the expected
compounds was observed, even when alternative procedures
were used.16 Actually, these compounds are known to be
sensitive to hydrolysis,17 which has certainly hampered their
more widespread use in catalysis.
Following procedures described in the literature, we prepared
the phosphine-based complexes [CuX(PPh3)] (X = Cl, 7; X =
Br, 8; X = I, 9), and phosphite-containing compounds
{CuX[P(OPh)3]} (X = Cl, 10; X = Br, 11). All attempts to
synthesize the iodo analogue from triphenyl phosphite were
unsuccessful, resulting instead in the related {CuI[P(OPh)3]2}
(12).18
On the other hand, [CuX(L)] complexes bearing ligands 1−
5 were generally prepared in refluxing anhydrous toluene in fair
to excellent yields after recrystallization (Scheme 2).
Commercially available methyl diphenylphosphinite and
dimethyl phenylphosphonite were also employed. Reactions
in DCM, DCE, and MeCN led to the isolation of the
corresponding hydrolyzed ligands, with only traces (at the
most) of the expected coordination complexes. Also, reactions
with the thioether derivative 6 led to complex mixtures
insoluble in all solvents tested. Furthermore, the in situ
reduction of CuBr2 salts by phosphinite 1 in boiling methanol
also did not produce any copper(I) complex.19
These cubane-like solid structures are well-known for
copper(I) complexes. For the related complexes [CuX(PR3)],
it has been unambiguously shown that their structure in the
solid state depends not only on the complex itself but also on
the solvent used for growing the crystal.22 In particular, the use
of polar solvents has been reported to favor step-like rather
than cubane-like structures in the solid state. In our case, all
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Figure 1. Ball and stick representations of {CuBr[PPh2(OPh)]} 13, {CuCl[PPh(OPh)2]} 14, and the S4-symmetric {CuBr[PPh(OMe)2]} 17.
Hydrogen atoms have been omitted for clarity. Selected bond lengths for 17 (Å): Cu(1)−Br(1) = 2.5396(4), Cu(1)−Br(1B) = 2.4683(4), Cu(1)−
Br(1C) = 2.6102(4), Cu(1)−P(1) = 2.1835(6), Br(1)−Cu(1B) = 2.6102(4), Br(1)−Cu(1C) = 2.4683(4).
attempts to grow suitable crystals from chloroform or
dichloromethane failed.
observed on comparison of chloro analogues 7 and 10 or
bromo derivatives 8 and 11. The observed differences in
reactivity could not be linked to the relative stability of the
complexes, and actually these catalysts were still active after 48
h of stirring under ambient conditions.23
It is important to note that we did not observe any bright
yellow color in the reaction mixtures with any of these
complexes. This color has previously been related to the
formation of copper acetylide derivatives24 and also to the use
of related tris-phosphine copper complexes,11 but not with a
1:1 Cu/L ratio. In addition, it is important to note that no
green-blue colorindicating metal oxidation to copper(II)
was observed during the complex screening, nor did the
disproportionation of any of the catalysts result in copper(0)
precipitation. These results clearly show the good potential of
Catalytic Studies: [3 + 2] Cycloaddition of Azides and
Alkynes. We screened all the prepared copper complexes for
the preparation of [1,2,3]-triazoles in air. The obtained results
for the cycloaddition of benzyl azide with phenylacetylene
under standard cycloaddition conditions are shown in Table 2.
In a first stage, we tested the ligands bearing only phenyl/
phenoxy groups in order to determine the most promising
series. Phosphinite- and phosphonite-bearing complexes, and
15 in particular, clearly displayed the best catalytic activities,
with complete conversions after 5−8 h of stirring. In contrast,
only modest conversions were obtained with known
phosphine- or phosphite-containing catalysts 7−9 and 10 and
11. Interestingly, for the latter series no ligand effect was
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Figure 2. Ball and stick representations of {CuBr[PPh2(OPh-2-OMe)]} (18) and the C2-symmetric {CuBr[PPh2(OPh-4-OMe)]} 20. Hydrogen
atoms have been omitted for clarity. Selected bond lengths for 20 (Å): Cu(1)−Br(1) = 2.4737(7), Cu(1)−Br(2) = 2.5162(11), Cu(1)−Br(1A) =
2.692(3), Cu(1)−P(1) = 2.1955(8), Cu(2)−Br(1) = 2.5584(4), Cu(2)−Br(2) = 2.5407(3), Cu(2)−Br(2A) = 2.4945(3), Cu(2)−P(31) =
2.1796(6).
phosphinite and phosphonite derivatives as ancillary ligands for
this cycloaddition reaction.
Table 1. Selected Bond Lengths (Å) for Complexes (13),
(14), and (18)
Among these series, phosphite ligands are probably the least
promising (Table 2). In particular, complex 12, bearing two
phosphite ligands, led to even more disappointing conversions
after 24 h of stirring than the monophosphite complexes 10
and 11. This is not, however, a general trend, and significant
increases in the reaction rate were observed when 5 mol % of
free ligand was added to the reaction mixtures containing 5 mol
% of 7 or 13 (Table 3). Further enhancements were observed
with 10 mol % of ligand, but not with higher loadings. Of note,
the preformed tris-phosphine complex [CuCl(PPh3)3] pro-
vided the best catalytic results in that series, showing the
advantage of using preformed catalysts over in situ generated
species.25,26 It is worth mentioning that, in these reactions, the
addition of extra phosphorus ligand led to bright yellow
reaction mixtures.
13 (X = Br)
14 (X = Cl)
18 (X = Br)
Cu(1)−X(1)
Cu(1)−X(2)
Cu(1)−X(3)
Cu(1)−P(1)
Cu(2)−X(1)
Cu(2)−X(2)
Cu(2)−X(4)
Cu(2)−P(2)
Cu(3)−X(2)
Cu(3)−X(3)
Cu(3)−X(4)
Cu(3)−P(3)
Cu(4)−X(1)
Cu(4)−X(3)
Cu(4)−X(4)
Cu(4)−P(4)
2.5043(3)
2.5159(3)
2.5822(4)
2.1934(7)
2.5051(3)
2.4926(3)
2.5692(4)
2.1866(6)
2.4773(4)
2.5483(3)
2.5745(3)
2.1829(6)
2.5289(3)
2.5265(3)
2.5439(3)
2.1818(6)
2.4500(10)
2.3534(11)
2.4083(13)
2.1320(11)
2.3657(10)
2.4304(11)
2.4037(11)
2.1522(10)
2.4158(13)
2.4086(14)
2.4430(11)
2.211(3)
2.5709(6)
2.4572(5)
2.5371(5)
2.1745(10)
2.4873(5)
2.6096(6)
2.5302(5)
2.1848(10)
2.6070(5)
2.5439(5)
2.4723(6)
2.1859(9)
2.4686(5)
2.5644(6)
2.5588(5)
2.1758(10)
2.4029(11)
2.3649(12)
2.4304(13)
2.1453(13)
Following our optimization studies, we next screened
different solvents using {CuBr[PPh(OPh)2]} 15 as catalyst to
Table 2. Catalyst Screening for the Preparation of [1,2,3]-Triazoles
a
a
[CuX(L)]
time (h)
conversn (%)
[CuX(L)]
time (h)
conversn (%)
[CuCl(PPh3)] 7
24
24
24
24
24
47
42
14
56
36
{CuI[P(OPh)3]2} 12
24
8
∼5
>95
>95
>95
[CuBr(PPh3)] 8
{CuBr[PPh2(OPh)]} 13
{CuCl[PPh(OPh)2]} 14
{CuBr[PPh(OPh)2]} 15
[CuI(PPh3)] 9
8
{CuCl[P(OPh)3]} 10
5
{CuBr[P(OPh)3]} 11
a
1H NMR conversions are the average of at least two independent runs.
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Table 3. Phosphine and Phosphinite Effects in the Model Reaction
a
a
7 + PPh3 (mol %)
time (h)
conversn (%)
13 + PPh2(OPh) (mol %)
time (h)
conversn (%)
0
24
6
47
>95
>95
>95
0
8
>95
74
5
5
5.5
4.5
10, 15, or 20
5
10, 15, or 20
>95
b
5
2.5
a
b
1H NMR conversions are the average of at least two independent runs. [CuCl(PPh3)3] was used in this instance.
find that pure water was the best-performing media. It is
important to note that only sluggish reactions were observed in
the absence of solvent, and 2 days of reaction was required in
order to obtain high conversion into triazole 21a even with 5
mol % of 15. Taking into consideration the high activity
displayed by copper(I) species in this cycloaddition reaction,
one might think that any catalyst could provide shorter reaction
times when used neat. However, these results clearly show that
not all copper complexes are suitable to be used neat.27 Under
Figure 3. Postulated interactions in catalysts 18 and 19.
aqueous conditions, the catalyst loading could be lowered to 0.5
mol % while keeping convenient reaction times (under 6 h for
the model reaction). Next, we screened all the other
phosphi(o)nite complexes 16−20 under these optimized
conditions (Table 4).
in Scheme 3. In most cases, the triazole products precipitated
out of the reaction mixture and could be isolated in excellent
yields by simple filtration and washing with water and pentane.
Oily triazoles were isolated from the reaction mixture by
extraction with ethyl acetate, and in no case was purification on
silica gel necessary. Different functional groups were well
tolerated, such as esters, alcohols, amines, halogen atoms, and
alkenes. Interestingly, when a propargylamine was used as
starting material (21c,i), the reaction mixtures turned blue-grey,
probably due to nitrogen binding to the copper center.
Gratifyingly, this had no negative effect on the catalytic ability
and good conversions into triazoles were observed in both
cases.28
We also attempted some reactions using the phosphinite−
copper complex 16. Even if this catalyst did not display the best
catalytic activity during the optimization studies (see Table 4),
it has the advantage of being prepared from commercially
available starting materials in very high yields. As shown in
Scheme 3, {CuBr[PPh2(OMe)]} 16 displayed a remarkable
activity in the reactions tested, providing a new convenient
Click catalyst for this cycloaddition reaction.
Table 4. Phosphi(o)nite-Based Catalyst Screening for the
Preparation of [1,2,3]-Triazoles
a
[CuX(L)]
time (h)
conv (%)
{CuBr[PPh(OPh)2]} 15
5.5
5
>95
>95
>95
>95
>95
>95
{CuBr[PPh2(OMe)]} 16
{CuBr[PPh(OMe)2]} 17
5
{CuBr[PPh2(OPh-2-OMe)]} 18
{CuBr[PPh(OPh-2-OMe)2]} 19
{CuBr[PPh2(OPh-4-OMe)]} 20
3
6
5
a
1H NMR conversions are the average of at least two independent
runs.
No significant differences between related phosphinite and
phosphonite complexes were observed. Furthermore, inde-
pendently of the ligand on the copper center, all these catalysts
showed remarkably similar activities under such conditions,
with complete conversions in 5−6 h. The only exception was
observed with phosphinite complex 18, which reduced the
required reaction time by half. We think this might be due to
the beneficial effect of the oxygen coordination to the copper
center (Figure 3). Even though such an interaction was not
observed in the solid state (see Figure 2), the tetrameric
structure of 18 is unlikely to be kept in solution, which would
enable the postulated interaction. A similar interaction in
phosphonite complex 19, now bearing two o-methoxy groups
per copper center, might be deleterious for the catalytic activity,
since no enhancement of the reaction rate was observed with
this catalyst.
CONCLUSIONS
■
Four series of copper complexes bearing phosphine,
phosphinite, phosphonite, and phosphite ligands have been
investigated in the present study. In particular, we have
synthesized and fully characterized eight novel phosphinite- and
phosphonite-bearing complexes with copper(I) halogen pre-
cursors, species that are surprisingly scarce in the literature.
Gratifyingly, all complexes prepared could be handled in air
without any particular precautions.
Catalytic studies on the [3 + 2] cycloaddition of azides and
alkynes showed that, for a 1:1 Cu/L ratio, these phosphinite
and phosphonite complexes were the most efficient ones.
Careful optimization of the reaction conditions allowed for the
use of {CuBr[PPh2(OPh-2-OMe)] 18 in the preparation of
diverse 1,2,3-triazoles under very mild reaction conditions and
low catalytic loadings.29
With an optimized catalytic system in hand, we next
investigated the scope of the reaction. The results are presented
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a
Scheme 3. Preparation of 1,2,3-Triazoles
a
b
c
Isolated yields are the average of at least two independent runs. Reactions run with 1 mol % [Cu]. Reactions run with 0.5 mol % of 16.
154.5 (CAr), 135.9 (d, J = 33.4 Hz, CAr), 131.7 (d, J = 17.5 Hz, CHAr),
These results also highlight the fact that, despite the sudden
and huge popularity of this transformation, most efforts have
mainly been concentrated on its applications rather than in the
development of better performing catalytic systems, therefore
130.8 (CHAr), 129.3 (CHAr), 128.5 (d, J = 10.2, CHAr), 123.6 (CHAr),
120.3 (CHAr). 31P NMR (162 MHz, CDCl3): δ 89.4 (s, broad). Anal.
Calcd for C18H15OPBrCu (419.94): C, 51.26; H, 3.58. Found: C,
51.21; H, 3.67.
overlooking the true potential of well-defined copper species.
{CuCl[PPh(OPh)2]} 14. Phenylphosphonite 2 (0.294 g, 1 mmol)
was added to a stirred suspension of CuCl (0.099 g, 1 mmol) in dry
EXPERIMENTAL SECTION
toluene (20 mL) under a nitrogen atmosphere. The reaction mixture
was then refluxed overnight to give a clear solution, which yielded a
viscous yellow oil upon concentration. Methanol addition resulted in
the formation of a white precipitate, which was filtered, washed with
methanol, and dried under vacuum (0.27 g, 69%). 1H NMR (400
MHz, CDCl3): δ 8.04−7.87 (m, 2H), 7.56−7.45 (m, 1H), 7.45−7.33
(m, 2H), 7.22−7.12 (m, 4H), 7.11−7.05 (m, 2H), 7.04−6.97 (m, 2H).
13C NMR (100 MHz, DMSO-d6): δ 152.6 (CAr), 132.2 (CHAr), 130.5
(d, J = 20.4 Hz, CAr), 129.9 (CHAr), 129.7 (CHAr), 128.5 (d, J = 10.3
Hz, CHAr), 124.5 (CHAr), 120.5 (d, J = 6.3 Hz, CHAr). 31P NMR (162
MHz, CDCl3): δ 127.2 (s, broad). Anal. Calcd for C18H15O2ClPCu
(393.28): C, 54.97; H, 3.84. Found: C, 55.06; H, 3.76.
■
General Considerations. All reagents were used as received.
Unless otherwise stated, all reactions were carried out in air and using
technical solvents without any particular precautions to exclude
moisture or oxygen. Anhydrous solvents were dried by passing them
through columns of molecular sieves in a solvent purification system.
1H NMR and 13C NMR spectra were recorded on a 400 MHz
spectrometer at room temperature. Chemical shifts (δ) are reported in
ppm with respect to tetramethylsilane (1H NMR) or H3PO4 (31P
NMR) as internal standard. Mass spectra (MS) were recorded on a
Micromass Autospec Premier, Micromass LCT Premier, or VG
Platform II spectometer using EI or ESI techniques at the Mass
Spectroscopy Service of Imperial College London. Elemental analyses
were performed at London Metropolitan University (U.K.). All
reported yields are isolated yields and in the catalytic studies are the
average of at least two independent runs.
The non commercially available ligands were prepared by following
the reported procedure by Mukaiyama.15a It is important to note that
in all cases we needed to use DMAP as additive in order to achieve full
conversions. Monophosphine complexes 7 and 830 were prepared
from the corresponding CuX2 salts following the literature procedures,
whereas the iodo analogue 931 was prepared from CuI. Phosphite
complexes 10−12 were prepared by following the conditions reported
by Nishizawa using toluene instead of benzene as solvent.18
{CuBr[PPh(OPh)2]} 15. Copper(I) bromide (0.143 g, 1 mmol) was
added to a stirred solution of phenylphosphonite 2 (0.294 g, 1 mmol)
in toluene (1 mL) in air. The reaction mixture was stirred for 3 days at
room temperature and then concentrated under reduced pressure to
give an off-white precipitate, which was washed with methanol to give
1
the title complex as an off-white solid (0.279 g, 64%). H NMR (400
MHz, CDCl3): δ 7.97−7.87 (m, 2H), 7.51−7.42 (m, 1H), 7.39−7.30
(m, 2H), 7.17−7.02 (m, 8H), 7.02−6.94 (m, 2H). 13C NMR (100
MHz, DMSO-d6): δ 152.7 (d, J = 2.2 Hz, CAr), 135.6 (d, J = 39.9 Hz,
(CHAr), 132.3 (CHAr), 130.6 (d, J = 20.3 Hz, CHAr), 129.8 (CHAr),
128.6 (d, J = 10.4 Hz, CHAr), 124.6 (CHAr), 120.7 (d, J = 6.3 Hz,
CHAr). 31P NMR (162 MHz, CDCl3): δ 122.8 (s, broad). HRMS:
calcd for C20H18NO2PCu 398.0371, found 398.0241 ([M − Cl +
MeCN]+). Anal. Calcd for C18H15O2BrPCu (435.93): C, 49.39; H,
3.45. Found: C, 49.61; H, 3.29.
{CuBr[PPh2(OMe)]} 16. Methyl diphenylphosphinite (0.40 mL, 2
mmol) was added to CuBr (0.28 g, 2 mmol) in dry toluene (20 mL)
under a nitrogen atmosphere. The reaction mixture was then refluxed
for 18 h before being concentrated under reduced pressure. The
resulting residue was recrystallized from toluene/hexane to give the
title complex as an off-white solid (0.79 g, 90%). 1H NMR (400 MHz,
CDCl3): δ 7.86−7.66 (m, 4H, HAr), 7.43−7.28 (m, 6H, HAr), 3.75 (d,
J = 14.6 Hz, 3H, OCH3). 13C NMR (100 MHz, CDCl3): δ 136.5 (d, J
Synthesis of [CuX(L)] Complexes. {CuBr[PPh2(OPh)]} 13.
Copper(I) bromide (0.143 g, 1 mmol) was added to a solution of
phosphinite 1 (0.326 g, 1 mmol) in dry toluene (20 mL) under a
nitrogen atmosphere. The reaction mixture was then heated at reflux
for 2 h and filtered over a sintered glass while still hot. The obtained
filtrate was concentrated to yield an off-white viscous oil. Methanol
addition resulted in the formation of a white solid, which was
recrystallized from a toluene/hexane mixture and dried under vacuum
1
(0.23 g, 56%). H NMR (400 MHz, CDCl3): δ 7.87−7.72 (m, 4H),
7.45−7.35 (m, 2H), 7.34−7.26 (m, 4H), 7.14−7.06 (m, 2H), 7.03−
6.93 (m, 2H), 6.87−6.78 (m, 1H). 13C NMR (100 MHz, CDCl3): δ
6230
dx.doi.org/10.1021/om200791u|Organometallics 2011, 30, 6225−6232

Organometallics
Article
= 33.0 Hz, CAr), 131.3 (d, J = 92.6 Hz, CHAr), 130.5 (CHAr), 128.4 (d,
J = 9.9 Hz, CHAr), 56.4 (d, J = 6.9 Hz, CH3). 31P NMR (162 MHz,
DMSO-d6): δ 94.9 (s, broad). HRMS (ESI): calcd for C15H16NOPCu
320.0266, found 320.0265 ([M − Br + MeCN]+). Anal. Calcd for
C13H13OPBrCu (357.9183): C, 43.41; H, 3.64. Found: C, 43.59; H,
3.79.
solvent was evaporated, water (0.5 mL), azide (0.5 mmol), and alkyne
(0.5 mmol) were added. The reaction was allowed to proceed at room
temperature and monitored by H NMR analysis of aliquots. After
total consumption of the starting azide or no further conversion, the
reaction product was extracted with EtOAc (oily triazoles) or,
alternatively, collected by filtration and washed with pentane (solid
triazoles). In all examples, the crude products were estimated to be
greater than 95% pure by 1H NMR. Reported yields are isolated yields
and are the average of at least two independent runs.
1
{CuBr[PPh(OMe)2]} 17. From dimethyl phenylphosphonite (0.32
mL, 2 mmol), following the procedure described for the preparation of
16, the title complex was isolated as an off-white solid (0.49 g, 1.6
1
mmol, 78%). H NMR (400 MHz, CDCl3): δ 7.82−7.74 (m, 2H,
HAr), 7.47−7.40 (m, 1H, HAr), 7.40−7.34 (m, 2H, HAr), 3.73 (d, J =
13.0 Hz, 6H, CH3). 13C NMR (100 MHz, CDCl3): δ 135.8 (d, J =
42.1 Hz, CAr), 131.2 (CHAr), 130.5 (d, J = 18.0 Hz, CHAr), 128.2 (d, J
= 9.8 Hz, CHAr), 54.6 (CH3). 31P NMR (162 MHz, DMSO-d6): δ
135.3 (s, broad). HRMS (ESI): calcd for C10H14NO2PCu 274.0058,
found 273.9976 ([M − Br + MeCN]+). Anal. Calcd for
C8H11BrO2PCu (311.8976): C, 30.64; H, 3.54. Found: C, 30.66; H,
3.53.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, and figures giving experimental procedures,
product characterization, crystallographic data and CIF files
giving crystallographic data for 13, 14, 17, 18, and 20. This
material is available free of charge via the Internet at http://
pubs.acs.org.
{CuBr[PPh2(OPh-2-OMe)]} 18. From phosphinite 3 (0.308 g, 1
mmol), following the procedure described for the preparation of 16,
the title complex was isolated as an off-white solid (0.31 g, 0.67 mmol,
67%). 1H NMR (400 MHz, CDCl3): δ 7.89−7.73 (m, 4H, HAr), 7.46−
7.33 (m, 6H, HAr), 7.04−6.97 (m, 1H, HAr), 6.97−6.88 (m, 1H, HAr),
6.83−6.74 (m, 1H, HAr), 6.73−6.64 (m, 1H, HAr), 3.68 (s, 3H, CH3).
13C NMR (100 MHz, CDCl3): δ 150.5 (CAr), 143.4 (CHAr), 136.6 (d,
J = 33.0 Hz, CHAr), 130.8 (d, J = 17.8 Hz, CHAr), 128.5 (d, J = 10.1
Hz, CHAr), 124.3 (CHAr), 120.2 CHAr), 112.7 (CHAr), 55.5 (CH3).
31P NMR (162 MHz, DMSO-d6): δ 95.2 (s, broad). HRMS (ESI):
calcd for C21H20NO2PCu 412.0528, found 412.0533 ([M − Br +
MeCN]+). Anal. Calcd for C19H17O2BrPCu (449.94): C, 50.51; H,
3.79. Found: C, 50.70; H, 3.83.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: s.diez-gonzalez@imperial.ac.uk.
ACKNOWLEDGMENTS
■
Imperial College London and the EPSRC are gratefully
acknowledged for financial support of this work. We sincerely
thank Dr. King Kuok (Mimi) Hii for her generous sponsorship
over the last year.
{CuBr[PPh(OPh-2-OMe)2]} 19. From phosphonite 4 (1.00 g, 2
mmol), following the procedure described for the preparation of 16,
the title complex was isolated as an off-white solid (0.21 g, 0.86 mmol,
REFERENCES
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43%). H NMR (400 MHz, DMSO-d6): δ 7.85−7.70 (m, 2H, HAr),
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