Intermolecular Alkene Aziridination: An Original and Efficient Cu I···CuI Dinuclear Catalyst Deriving from a Phospha-Amidinate Ligand

Article abstract of DOI:10.1002/ejoc.201201478

Mononuclear and dinuclear Cu^I complexes 1 and 2 derived from the phospha-amidinate ligands [tBu₂P(NSiMe₃) ₂]^- and [Ph₂P(NSiMe₃) ₂]^-, respectively, have been

Full text of DOI:10.1002/ejoc.201201478

FULL PAPER
DOI: 10.1002/ejoc.201201478
Intermolecular Alkene Aziridination: An Original and Efficient CuI···CuI
Dinuclear Catalyst Deriving from a Phospha-Amidinate Ligand
Noel Nebra,[a] Camille Lescot,[b] Philippe Dauban,[b] Sonia Mallet-Ladeira,[c]
Blanca Martin-Vaca,*[a] and Didier Bourissou*[a]
Keywords: Homogeneous catalysis / Copper / Ligand design / Small ring systems / Nitrogen heterocycles / Metal–metal
interactions
Mononuclear and dinuclear CuI complexes 1 and 2 derived
from the phospha-amidinate ligands [tBu2P(NSiMe3)2]– and
[Ph2P(NSiMe3)2]–, respectively, have been evaluated in the
catalytic aziridination of olefins using PhI=NTs (Ts = p-tolyl-
alkenes within 12 h at room temperature using 5 mol-% Cu
and 1.2 to 2.4 equiv. PhINTs with respect to the alkene. Com-
plex 2 performed best with styrenes and methyl acrylate. The
presence of weak Cu···Cu interactions in 2 is uncommon in
sulfonyl) as the nitrene source. Dinuclear complex 2 featur- catalytic aziridination reactions, and some interesting paral-
ing bridging NPN ligands and weak Cu···Cu interactions
proved to be a robust and efficient catalyst. Aziridines could
be obtained in good to excellent yields for a broad range of
lels with the widespread dinuclear Rh(II) catalysts can be
drawn.
ficient nitrene precursors and transition metal catalysts to
generate the key metallanitrene intermediates. Nowadays,
the most commonly used nitrene source is certainly the
iminoiodinane PhI=NTs (Ts = p-tolylsulfonyl),[5] although
various alternative functional groups have been shown to
also be competent.[6] In terms of catalysts, most studies
are performed with dirhodium(II) tetracarboxylates
[Rh2(O2CR)]2 and related systems.[7] But copper complexes
also occupy a prominent position, and are becoming more
and more frequently used in natural product synthesis, me-
dicinal chemistry and materials science.[8]
Following the pioneering discovery of D. A. Evans et al.
in the early 1990s that simple and inexpensive CuI and CuII
salts catalyze alkene aziridination under relatively mild con-
ditions,[9] a broad range of copper complexes have been
studied.[10,11] The structure of the copper catalyst was
shown to have a great influence, and the use of ancillary
ligands has allowed the catalytic performance to be modu-
lated in terms of both activity and selectivity. Mostly, N-
based polydentate ligands have been used in such catalytic
aziridination reactions, and Scheme 1 shows representative
examples of the ligands that have been investigated. These
studies have resulted in significant progress being made, and
some very efficient catalytic systems have been de-
scribed.[10b,10d,10f,10h,11c–11e] However, most of the reported
systems use relatively high catalytic loadings (up to 10 mol-
%) and/or large excess of alkenes (often 5 to 10 equiv.).
These remain significant drawbacks of Cu-catalyzed azirid-
ination with iminoiodanes, and further studies seeking to
develop new efficient catalysts are thus warranted. As for
ourselves, we became interested in Cu complexes derived
from [R2P(NRЈ)2]– ligands.
Introduction
Aziridines are highly reactive and versatile synthons for
the preparation of nitrogen-containing compounds.[1] Simi-
larly to epoxides, they readily undergo ring-opening reac-
tions with a wide range of nucleophiles, and this has led
to numerous applications in natural product synthesis and
medicinal chemistry.[2] Besides their transformation into
1,2-difunctionalized scaffolds, aziridines have also shown
rich reactivity in ring-expansion reactions, giving straight-
forward access to various five- and six-membered rings.[1,3]
Although aziridines can be classically prepared by func-
tional group manipulations starting from epoxides, amino
alcohols, or azido alcohols,[1,2] most modern methods rely
on two types of transition-metal-catalyzed group-transfer
reactions: (i) the addition of carbenes or ylids to imines;
and (ii) the transfer of nitrenes to alkenes.[4] The latter ap-
proach, referred to as catalytic aziridination, has attracted
considerable interest over the last two decades. In particu-
lar, significant efforts have been made to develop new ef-
[a] Université de Toulouse, UPS, LHFA, CNRS, LHFA UMR
5069,
118 route de Narbonne, 31062 Toulouse, France
Fax: +33-5-61558204
E-mail: bmv@chimie.ups-tlse.fr; dbouriss@chimie.ups-tlse.fr
Homepage: http://hfa.ups-tlse.fr/LBPB/index_lbpb.htm
[b] Centre de Recherche de Gif-sur-Yvette, Institut de Chimie des
Substances Naturelles, UPR 2301 CNRS,
Avenue de la Terrasse, 91198 Gif-sur-Yvette, France
[c] Université de Toulouse, UPS, Institut de Chimie de Toulouse,
FR2599,
118 Route de Narbonne, 31062 Toulouse, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201478.
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Intermolecular Alkene Aziridination
Me3)(NHSiMe3) pro-ligand, obtained by a double Staud-
inger reaction between tBu2PH and N3SiMe3,[14b] was lithi-
ated with nBuLi. After reaction with CuBr(SMe2) in pent-
ane followed by ethylene bubbling, complex 1 was obtained
as white crystals upon crystallization at –30 °C (65% yield;
Scheme 2). The structure of 1 was confirmed by complete
NMR analysis, all data being consistent with those reported
previously.[16]
Scheme 1. Representative N-based polydentate ligands that have
been investigated in Cu-catalyzed aziridination.
These NPN ligands are phosphorus analogs of the exten-
sively used amidinates [RC(NRЈ)2]–,[12] and can thus be re-
ferred to as phospha-amidinates.[13] They are readily access-
ible[14] and show versatile coordination properties[15] includ-
ing to Cu.[16,17] Most remarkably, Hofmann[16] prepared the
ethylene-CuI complex {Cu[tBu2P(NSiMe3)2](H2C=CH2)}
(1) and used it to identify for the first time a Cu carbene
complex relevant to catalytic cyclopropanation.[18] But to
the best of our knowledge, NPN Cu complexes have not
been investigated in aziridination to date. It is noteworthy
that bridging rather than chelate coordination has also been
observed with such NPN ligands. Despite differing from 1
only in the nature of the substituents at phosphorus, the
{Cu[Ph2P(NSiMe3)2]}2 complex 2 described by Müller[17]
adopts a dinuclear structure with weak Cu···Cu interactions
in the solid state. Phospha-amidinate ligands thus offer the
opportunity to evaluate both mononuclear and dinuclear
NPN CuI complexes. To date, only a few polynuclear Cu
complexes have been investigated in catalytic aziridination.
Morales and Pérez[19] have studied a dinuclear CuI complex
deriving from tris(thiocyanatomethyl)mesitylene, while
Biffis and co-workers[20] have investigated di- and trinuclear
CuI complexes bridged by bis- and tris-NHC (N-heterocy-
clic carbene) ligands.
In this paper, we report the first study of phospha-amid-
inate Cu complexes in catalytic aziridination. The mononu-
clear vs. dinuclear structure of complexes 1 and 2 has been
analyzed in detail, and their catalytic performance has been
evaluated. The dinuclear species 2 proved to be a robust
and efficient catalyst. It performed best with styrenes and
methyl acrylate, giving very good yields of the correspond-
ing aziridines. The presence of weak Cu···Cu interactions is
uncommon in catalytic aziridination, and some interesting
parallels with the widespread dinuclear Rh(II) catalysts can
be drawn.
Scheme 2. Synthesis of the NPN-CuI complexes 1 and 2.
A similar procedure was then used to prepare a related
complex featuring Ph instead of tBu groups at phosphorus.
Complex 2 was prepared by Müller et al.[17] in 2000 using
a different strategy, and its structure was confirmed by X-
ray crystallography. Here, we treated the lithium salt of
Ph2P(NSiMe3)(NHSiMe3)[15b,15c] with CuBr(SMe2) in pent-
ane, and proceeded with NMR characterization. The ap-
pearance of a unique set of 31P and 29Si NMR signals [31P:
δ = 23.2 (s) ppm; 29Si: δ = –6.5 (d, J = 8.0 Hz) ppm] indi-
cated the clean formation of a symmetrical compound. In
this case, bubbling ethylene induced no change in the NMR
spectra, and complex 2 was isolated as white crystals (75%
yield) after filtration and cooling to –30 °C for 3 d. Its mo-
lecular structure was unambiguously confirmed by X-ray
diffraction analysis.
According to X-ray diffraction data, complexes 1 and 2
adopt mononuclear and dinuclear structures, respectively,
in the solid-state. This difference clearly has to do with
whether or not ethylene is present in the coordination
sphere of Cu, and it also reveals the subtle influence of the
substituents at phosphorus on the coordination properties
of the NPN ligands. The sterically demanding tBu groups
induce wide C–P–C and acute N–P–N bond angles
(Thorpe–Ingold effect), and thereby favor chelate coordina-
tion in complex 1 [C–P–C: 111.89(13)° and N–P–N:
104.33(12)°].[16] In contrast, the Ph groups are less bulky,
and lead to more acute CPC and wider NPN bond angles,
so that bridging coordination is preferred in complex 2 [C–
P–C: 105.1(2)° and N–P–N: 115.8(2)°].[17] Remarkably, the
distance between the two copper atoms in the dinuclear
complex 2 [2.621(1) Å] is much shorter than that found by
Morales and Pérez in the complex derived from tris(thiocy-
anatomethyl)mesitylene [2.936(2) Å],[19] and actually falls
Results and Discussion
Synthesis and Structure of CuI Complexes {Cu[tBu2P-
(NSiMe3)2](H2C=CH2)} (1) and {Cu[Ph2P(NSiMe3)2]}2 (2)
CuI complex 1 was prepared following the procedure de- within the typical range associated with weak d10···d10, so-
scribed by Hofmann et al.[16] in 1999. The tBu2P(NSi- called metallophilic interactions.[21,22]
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The two related NPN CuI complexes show markedly dif- ane (actually 1.2 equiv. of PhI=NTs with respect to styr-
ferent chemical behavior. Complex 1 proved to be extremely ene). The use of apolar solvents such as benzene gave good
sensitive, and decomposed rapidly both in solution and in results with both catalysts (Table 1, entries 1 and 2). Azirid-
the crystalline state in the absence of an ethylene atmo- ine 5a was obtained in high yields within a few hours. Mo-
sphere. In contrast, solution and solid-state samples of nonuclear complex 1 was clearly more efficient than dinu-
complex 2 showed no sign of decomposition over several clear complex 2 under these conditions (97 vs. 82% yield
days at room temperature. The lack of reaction with ethyl- after 12 h). This difference probably stems from solubility
ene suggests that 2 is not prone to dissociation, and actually issues. Indeed, complex 1 is very soluble in benzene,[25]
retains its dimeric structure in solution. To confirm this hy- whereas 2 forms suspensions even at dilute concentrations.
pothesis, 1H DOSY NMR experiments were carried out on In contrast, complex 2 out-performed 1 in chlorinated sol-
both complexes 1 and 2.[23] For mononuclear ethylene com- vents (Table 1, entries 3–5). With 2, aziridine 5a was ob-
plex 1, a diffusion coefficient of D = 7.6ϫ10–11 m2 s–1 was tained in quantitative yield in dichloromethane or chloro-
found in CDCl3 solution at 22 °C. Complex 2 gave a signifi- form, whereas 1 was not able to achieve conversions higher
cantly lower value, D = 4.7ϫ10–11 m2 s–1, under the same than 70%, probably due to catalyst degradation. The use
conditions. The corresponding hydrodynamic radii RH of coordinating solvents proved detrimental in our case:[26]
(8.37 Å for 2 vs. 5.30 Å for 1), as estimated from the Stokes– acetonitrile significantly lowered the catalytic activity of
Einstein equation,[24] unambiguously indicate that the dif- complex 2, and tetrahydrofuran completely shut down the
ference in nuclearity between complexes 1 and 2 is main- process (Table 1, entries 6 and 7).
tained in solution.
These first catalytic runs showed that mononuclear and
dinuclear NPN CuI complexes both catalyze the aziridina-
tion of styrene at room temperature. Dinuclear complex 2
clearly gives the best compromise: it is much more stable
than mononuclear complex 1, and it performs very ef-
ficiently in chlorinated solvents (quantitative conversion of
styrene within 12 h). Compound 2 is a rare example of a
dinuclear Cu complex that shows activity in this transfor-
mation;[19,20] the presence of weak Cu···Cu interactions is
very uncommon in catalytic aziridination reactions. We
were thus very interested in further evaluating the catalytic
performance of 2.
Styrene Aziridination Promoted by NPN CuI Complexes 1
and 2
Having synthesized NPN CuI complexes 1 and 2, we
were eager to evaluate their catalytic properties in olefin
aziridination. For this study, iminophenyliodinane
PhI=NTs 4 was chosen as the nitrene source.[5] First, we
focused on styrene (3a) as a model substrate, and tested
various solvents (Table 1). The reactions were performed at
25 °C, and the catalyst loading was set at 5 mol-% in Cu to
enable a comparison between the mononuclear and dinu-
clear complexes. Large excesses of olefins (5 to 10 equiv.
with respect to the nitrene source) are often used in catalytic
aziridination reactions to achieve high yields. This is a real
limitation on a preparative scale, and so we decided to use
nearly equimolar quantities of styrene and the iminoiodin-
Scope of the Intermolecular Aziridination Catalyzed by
NPN Dinuclear CuI Complex 2
The catalytic activity of complex 2 towards a broad range
of styrenic substrates was evaluated (Table 2). Aziridination
of para-substituted styrenes 3b–d (p-Me, Cl, MeO) pro-
ceeded in 68–75% yield (Table 2, entries 2–4) under the op-
timal conditions identified for styrene (5 mol-% Cu, CDCl3,
25 °C, 12 h, 1.2 equiv. PhI=NTs). These rather modest
yields can be explained by the formation of p-toluenesulfon-
amide TsNH2 (as confirmed by 1H NMR spectroscopy and
GC-MS), as the result of undesirable hydrolysis of the
nitrene source in solution. To improve the efficiency of the
catalytic process, the amount of iminoiodinane was in-
creased to 2.4 equiv. Gratifyingly, para-substituted styrenes
3b–d were then converted into the corresponding aziridines
(i.e., 5b–d) in much higher yields (88–92%).
Table 1. Cu-catalyzed aziridination of styrene (3a).
Under these conditions, complex 2 was successfully used
in the aziridination of a wide variety of substrates, including
functionalized ones. As shown in Table 2, entries 5–7, 2 ef-
ficiently promotes the aziridination of para-substituted styr-
enes bearing fluorinated (p-F, F3C) and ester (p-AcO) moie-
ties. It is noteworthy that the aziridines were obtained in
very high yields (84–95%), regardless of the electron-donat-
ing or accepting nature of the para-substituent of the styr-
enic substrates. The catalytic system was also compatible
[a] All experiments were performed under an argon atmosphere
starting from 0.2 mmol styrene (0.1 m solution). [b] Yields were de-
termined by 1H NMR spectroscopy. [c] Yields after 3 h given in
parentheses.
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Intermolecular Alkene Aziridination
Table 2. Aziridination of styrenic olefins 3a–p catalyzed by the di- and proceeded efficiently with ortho- and meta-substituted
nuclear Cu complex 2.[a]
substrates. Chloro-substituted styrenes 3h and 3i were con-
verted into the corresponding aziridines (i.e., 5h and 5i) in
72 and 89% yields, respectively (Table 2, entries 8 and 9).
Very good results were also obtained with 1- and 2-vinyl-
naphthalenes (3j and 3k; Table 2, entries 10 and 11; 88 and
99% yields of the respective aziridines).
The influence of substitution at the reactive C=C double
bond was then investigated. Methylstyrene was chosen as
substrate since its gem, trans, and cis isomers are all com-
mercially available. In addition, β-methylstyrenes offer the
opportunity to probe the stereoselectivity of aziridination,
and thereby to gain some mechanistic insight. A mixture of
diastereomers is usually obtained starting from either the E
or Z alkene, with ratios depending on the catalytic system
used.[9b,10b,10e,10i,11b,11f] A modest yield of 33% was ob-
tained in the aziridination of α-methylstyrene 3l (Table 2,
entry 12), indicating a strong deleterious effect of geminal
substitution. Steric factors probably impede the formation
of the quaternary center in the corresponding aziridine. β-
E-Methylstyrene 3m gave a slightly higher but still modest
yield of 52% (Table 2, entry 13). Remarkably, the reaction
proceeded with complete stereoselectively to give the corre-
sponding trans aziridine (i.e., 5m) exclusively.[27] Under the
same conditions, β-Z-methylstyrene 3n also provided a sin-
gle aziridine in 52% yield (Table 2, entry 14), but surpris-
ingly, this was again identified as trans aziridine 5m. 1H
NMR spectroscopic analysis of the crude reaction mixture
indicated that the formation of 5m was accompanied by a
complete isomerization of the unreacted substrate. Accord-
ing to control experiments, the isomerization of 3n into its
more thermodynamically stable E isomer 3m did not occur
in the presence of dinuclear Cu complex 2 alone, but re-
quired the presence of PhI=NTs. Under these conditions,
ZǞE isomerization of β-methylstyrene took place very
easily and much more quickly than aziridination. From a
mechanistic viewpoint, metal-catalyzed alkene aziridination
reactions typically involve metallanitrene intermediates, and
proceed by concerted or radical stepwise pathways.[28]
Based on the complete retention of stereochemistry ob-
served upon aziridination of β-E-methylstyrene 3m, we sur-
mise that a concerted pathway operates in our case.
The aziridination of cyclic β-substituted styrenes was
then investigated. With 3,4-dihydronaphthalene 3o and in-
dene 3p (Table 2, entries 15 and 16), Z Ǟ E isomerization is
inherently prevented, and the corresponding aziridines (i.e.,
5o,p) were obtained in relatively good yields (62 and 74%,
respectively). The complete chemoselectivity observed in
these reactions is worth mentioning. Despite the presence
of activated C–H bonds (in allylic and/or benzylic posi-
tions), no products arising from C–H amination were de-
tected.[29]
Finally, the encouraging results obtained with styrenic
substrates prompted to us to assess the efficiency of com-
plex 2 towards unactivated alkenes (Table 3). Modest yields
in the range of 20–43% were obtained with 1-hexene (3q),
cyclohexene (3r), and cyclooctene (3s) (Table 3, entries 1–
3), indicating that linear and cyclic aliphatic olefins are rela-
[a] Experiments were performed at room temperature under an ar-
gon atmosphere starting from 0.2 mmol olefin (0.1 m in CDCl3).
1
[b] Yields were determined by H NMR spectroscopy. [c] Isolated
yield from a reaction carried out with 1 mmol olefin.
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D. Bourissou et al.
FULL PAPER
tively poor substrates. But once again, it is remarkable that interesting parallels with the widely used dinuclear Rh(II)
complete chemoselectivity in favor of aziridination over C– catalysts, in which the central Rh–Rh bond clearly plays a
H amination was observed, particularly for 3r. This stands major role.[31] It is conceivable that the dinuclear, weakly
in stark contrast with the fact that mixtures of aziridines bonded Cu···Cu structure of 2 behaves somewhat similarly,
and allylic amines are typically obtained with Cu[10b,10e] as and enables some cooperativity between the two metal cen-
well as Rh[7] complexes. Finally, complex 2 showed very ters.[32] The participation of mononuclear copper species
good reactivity towards methyl acrylate (3t), giving the cor- cannot be excluded, but the dinuclear species seems to be
responding aziridine 5t in 89% yield (Table 3, entry 4). This highly favored with the phospha-amidinate ligand
transformation holds particular synthetic interest as func- [Ph2P(NSiMe3)2]–. At this stage, it is clearly not possible to
tionalized aziridine 5t gives ready access to α- and β-amino give a detailed mechanistic picture for these aziridination
acids.[2,30]
reactions, and the precise structure of the key metalla-
nitrene intermediate remains unclear. Based on the few
nitrene/carbene dinuclear complexes proposed or eventually
even characterized with copper and rhodium,[18b,33,34] sev-
eral structures can be envisioned, with terminal or bridging
coordination of the nitrene moiety (Scheme 3).
Table 3. Cu-catalyzed aziridination of aliphatic alkenes 3q–s and
methyl acrylate (3t).[a]
Scheme 3. Conceivable structures for the key metallanitrene inter-
mediate involved in aziridination reactions catalyzed by 2.
Future work will seek to gain some mechanistic insight
and further explore the catalytic properties of such NPN
copper complexes in aziridination and related nitrene-trans-
fer reactions.
[a] Experiments were performed at room temperature under an ar-
gon atmosphere starting from 0.2 mmol olefin (0.1 m in CDCl3).
1
[b] Yields were determined by H NMR spectroscopy.
Conclusions
Experimental Section
In conclusion, the first evaluation of NPN Cu complexes
in catalytic aziridination is reported. Phospha-amidinates
[R2P(NRЈ)2]– readily form CuI complexes such as
General Methods: All reactions were performed using standard
Schlenk techniques under an argon atmosphere. Solvents were
dried and distilled prior to use (Et2O and THF over sodium, pent-
ane and dichloromethane over CaH2). All organic reagents were
obtained from commercial sources and used as received. [CuBr-
(SMe2)] was purchased from Sigma–Aldrich. {Cu[tBu2P(NSiMe3)2]-
(CH2=CH2)} (1)[16] and {Li[Ph2P(NSiMe3)2]}[15b,15c] were prepared
{Cu[tBu2P(NSiMe3)2](H2C=CH2)}
1
and {Cu[Ph2P-
(NSiMe3)2]}2 2. The bulky tBu groups favor chelate coordi-
nation of the NPN ligand in 1 (mononuclear complex),
whereas the less sterically demanding Ph groups lead to
bridging coordination in 2 (dinuclear complex). Both com-
plexes have been shown to be competent catalysts for the
according to literature procedures. 31P, H, and 13C NMR spectra
1
were recorded with Bruker Avance 300, 400, and 500 spectrometers.
aziridination of styrene with iminoiodinane PhI=NTs as ni- 31P, 28Si, H, and 13C chemical shifts are expressed with a positive
1
sign, in parts per million, relative to external 85% H3PO4 and
Me4Si. H DOSY NMR experiments were recorded with a Bruker
trene source. Dinuclear complex 2 clearly gives the best
compromise. It is a robust and efficient catalyst for the azir-
idination of a broad range of substrates, in particular styr-
ene derivatives and methyl acrylate.
From this work, phospha-amidinates appear to be a
promising yet relatively underexplored class of N-based li-
gands.[15b–15d,15f] The presence of weak Cu···Cu interactions
in the dinuclear complex 2 is also remarkable. To date, es-
sentially only mononuclear Cu complexes have been used
1
Avance 500 spectrometer equipped with a 5 mm triple resonance
inverse Z-gradient probe. All chemical shifts are relative to TMS
and samples were prepared in CDCl3. All diffusion measurements
were made using the stimulated echo pulse sequence with bipolar
gradient pulses. The shape of the gradients was square. The dif-
fusion delay (Δ) was fixed at 100 ms, and the gradient pulse dura-
tion (δ) at 2 ms. The recycle delay was adjusted to 3 s, and the
strength of the gradient was varied in 16 increments (from 5 to
in catalytic aziridination reactions. These results draw some 95%) in a linear ramp.
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Intermolecular Alkene Aziridination
Synthesis of Homo-Bimetallic Complex {Cu[Ph2P(NSiMe3)2]}2 (2):
A mixture of {Li[Ph2P(NSiMe3)2]} (192 mg, 0.80 mmol) and
[CuBr(SMe2)] (115 mg, 1.04 mmol, 1.3 equiv.) was stirred in dried
pentane (30 mL) under an argon atmosphere at room temperature
for 4 h. Then the solution was filtered to remove the lithium salts
and the excess of the Cu-precursor. The solution was concentrated
to 10 mL and kept at –30 °C for 72 h. The white crystals formed
were isolated by simple filtration, and product 2 (201 mg, 75%)
was isolated as a white powder. 31P{1H} NMR (121.5 MHz, C6D6,
0 °C): δ = 23.1 (s) ppm. 29Si{1H} NMR (59.6 MHz, C6D6, 0 °C):
δ = –5.5 (d, JSi,P = 8.0 Hz) ppm. 1H NMR (300 MHz, C6D6, 0 °C):
δ = 7.63 (ddd, J = 9.5, 3.4, and 1.7 Hz, 4 H, HPh2P), 7.10 (br., 1
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H, HPh2P), 7.03–6.96 (m, 5 H, HPh2P), 0.02 (s, 18 H, SiMe3) ppm.
1
13C{1H} NMR (75.5 MHz, C6D6, 0 °C): δ = 139.4 [d, JC,P
=
3
113.7 Hz, CipsoPh2P], 132.3 (d, JC,P = 10.1 Hz, CmetaPh2P), 130.4
4
2
(d, JC,P
=
2.8 Hz, CparaPh2P), 127.9 (d, JC,P
=
12.2 Hz,
[3]
[4]
3
CorthoPh2P), 4.6 (d, JC,P = 3.6 Hz, SiMe3) ppm.
Crystal-Structure Determination of Complex 2: Data were collected
using an oil-coated shock-cooled crystal with a Bruker-AXS Kappa
APEXII Quazar diffractometer with Mo-Kα radiation (λ
=
0.7103 Å). Phi and omega scans were used. Semi-empirical absorp-
tion corrections were used.[35] The structure was solved by direct
methods (SHELXS97)[36] and refined using the least-squares
method on F2 with SHELXL97.[37] All non-H atoms were refined
with anisotropic displacement parameters. The H atoms were re-
fined isotropically at calculated positions using a riding model with
their isotropic displacement parameters constrained to be equal to
1.5 times the equivalent isotropic displacement parameters of their
pivot atoms for terminal sp3 atoms and 1.2 times for all other car-
bon atoms. The new set of X-ray data has been deposited to the
Cambridge Crystallographic Data Centre (improved resolution
quality): CCDC-901290. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Crystal Data for 2: C36H56Cu2N4P2Si4, Mr = 846.25, monoclinic,
space group C2/c, a = 18.4120(8), b = 12.5009(5), c = 19.6122(8) Å,
β = 106.200(2)°, V = 4334.8(3) Å3, Z = 4, ρcalcd. = 1.297 gcm–3,
F(000) = 1776, T = 193(2) K, crystal size 0.60ϫ0.16ϫ0.12 mm3,
46915 reflections collected (6629 independent, Rint = 0.0207), θ Յ
30.55°, 223 parameters, R1 [IϾ2σ(I)] = 0.0247, wR2 (all data) =
0.0770, largest diff. peak and hole: 0.307 and –0.329 eÅ–3.
Typical Procedure for the Intermolecular Alkene Aziridination: In-
side the glove-box under an argon atmosphere, a Schlenk tube was
charged with the catalyst (5 mol-%), the alkene (0.2 mmol), and the
solvent (2 mL). After stirring for 1 min, PhI=NTs (1.2 or 2.4 equiv.)
was added in one portion. The mixture was stirred at room tem-
perature for 12 h under an argon atmosphere. The reaction mixture
[7]
[8]
1
was then directly analyzed by H NMR spectroscopy.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures and NMR spectra of complex 2 and
compound 5c.
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Acknowledgments
The authors are grateful to the Centre National de la Recherche
Scientifique (CNRS), Université Paul Sabatier (UPS), and the Ag-
ence Nationale de la Recherche (ANR) (grant number ANR-08-
BLAN-013, NitCH) for their financial support for this work. N. N.
thanks the European Commission for a Marie Curie Intra-Euro-
pean Postdoctoral Fellowship (grant number PIEF-GA-2009-
253112, INDEN).
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Published Online: December 19, 2012
990
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 984–990