Polynuclear copper(I) complexes with chelating bis- and tris-N-heterocyclic carbene ligands: Catalytic activity in nitrene and carbene transfer reactions

Article abstract of DOI:10.1002/ejoc.201101480

Di- and trinuclear complexes of copper(I) bearing bis- or tris-N-heterocyclic carbene ligands have been prepared and evaluated as catalysts in nitrene transfer reactions from PhI=NTs to unsaturated and saturated substrates (olefin aziridination and C-H bond amidation) and carbene transfer reactions from diazo compounds to olefins. The complexes exhibited moderate-to-high catalytic activity in both processes. The tosylamidation of C-H bonds, previously unreported with a NHC-containing copper catalyst, was promoted by the dinuclear complexes. Polynuclear oligo-NHC-copper complexes catalyse the transfer of carbene or nitrene fragments to unsaturated and saturated substrates. The first example of the tosylamidation of C-H bonds with a catalyst containing the NHCCu core is described. Copyright

Full text of DOI:10.1002/ejoc.201101480

FULL PAPER
DOI: 10.1002/ejoc.201101480
Polynuclear Copper(I) Complexes with Chelating Bis- and Tris-N-Heterocyclic
Carbene Ligands: Catalytic Activity in Nitrene and Carbene Transfer
Reactions
Cristina Tubaro,[a] Andrea Biffis,*[a] Riccardo Gava,[a] Elena Scattolin,[a] Andrea Volpe,[a]
Marino Basato,[a] M. Mar Díaz-Requejo,[b] and Pedro J. Perez[b]
Keywords: Copper / Carbenes / Nitrenes / Nitrogen heterocycles / Aziridination / Cyclopropanation
Di- and trinuclear complexes of copper(I) bearing bis- or tris-
N-heterocyclic carbene ligands have been prepared and
evaluated as catalysts in nitrene transfer reactions from
PhI=NTs to unsaturated and saturated substrates (olefin azir-
idination and C–H bond amidation) and carbene transfer re-
actions from diazo compounds to olefins. The complexes ex-
hibited moderate-to-high catalytic activity in both processes.
The tosylamidation of C–H bonds, previously unreported
with a NHC-containing copper catalyst, was promoted by the
dinuclear complexes.
Introduction
Research into copper(I) complexes with N-heterocyclic
carbenes (NHC)[1] as ligands has attracted considerable at-
tention in recent years. In particular, copper(I) complexes
containing an NHC ligand have been reported as catalysts
for a number of synthetically useful reactions such as selec-
tive reductions, cyclopropanations, aziridinations, 1,3-di-
polar cycloadditions, and hydrosilylations.[2] Encouraged by
these results, further research efforts focused on the synthe-
sis and characterisation of this type of complex has led to
the development of a wide variety of synthetic strategies
and complex structures.[3,4] Thus, copper(I) complexes con-
taining polycarbene ligands, that is, multidentate ligands
with two or more NHC units, have been widely studied,[4,5]
affording mono- or polynuclear complexes by virtue of the
different chelating[6,7] or bridging[8–14] modes that such li-
gands can adopt when interacting with a metal centre. De-
spite the wide variety of (NHC)CuI complexes available, the
majority of catalytic studies have been carried out with mo-
nonuclear compounds, in particular, with complex
[IPrCuCl] [Scheme 1, left; IPr = 1,3-bis(2,6-diisoprop-
ylphenyl)imidazol-2-ylidene], first described by Buchwald
and co-workers[15] and further extensively studied by Diez-
Gonzalez and Nolan.[2b,2c]
Scheme 1. Mono- and trinuclear NHC–copper(I) complexes.
We have described the first example of a catalytic system
based on the trinuclear tricarbene–copper(I) complexes 1
and 2 (Scheme 1, right) for C–N and C–C coupling reac-
tions.[10] Encouraged by these results, we have now extended
our investigation on the catalytic efficiency of such com-
pounds to nitrene and carbene transfer reactions. Copper
complexes have been reported to catalyse these transforma-
tions in which a carbene group from a diazo compound
(Scheme 2) or a nitrene group from an iodine hypervalent
compound can be transferred to unsaturated or saturated
acceptors.[16c,16e] The former route leads to the formation of
cyclopropanes or aziridines, whereas the second leads to the
functionalisation of C–H bonds. Of the catalysts employed
in these transformations, mononuclear copper(I)–NHC
complexes[16,17] have successfully been used in carbene trans-
fer as well as in olefin aziridination reactions. However, the
use of the NHCCu core to promote the functionalisation of
C–H bonds by nitrene insertion is, to the best of our knowl-
edge, hitherto unknown. Thus, we have prepared a series of
dinuclear copper complexes bearing bidentate NHC ligands
(Scheme 3) and tested them, along with the complexes 1 and
2 with a tris-carbene ligand (Scheme 1), in the above trans-
formations; the first example of C–H amidation induced by
a NHCCu-based catalyst was observed.
[a] Dipartimento di Scienze Chimiche, Università di Padova,
Via Marzolo 1, 35131 Padova, Italy
Fax: +39-049-8275223
E-mail: andrea.biffis@unipd.it
[b] Laboratorio de Catálisis Homogénea, Departamento de
Química y Ciencias de los Materiales, Unidad Asociada al
CSIC, Centro de Investigación en Química Sostenible (CIQSO),
Universidad de Huelva,
Campus de El Carmen s/n, 21007 Huelva, Spain
Fax: +34-959219942
E-mail: perez@dqcm.uhu.es
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A. Biffis et al.
FULL PAPER
clear bis-carbene complexes are visible (see the Exptl.
Sect.). Interestingly, a signal related to a dioxygen adduct
of the dinuclear complex is sometimes detected in the ESI-
MS spectrum and in the case of complex 5b it is the major
signal. We are currently investigating the preparative syn-
thesis of such adducts and their detailed characterisation.
Compounds 3b–6b are somewhat unstable in solution
and, in some cases, attempts to obtain pure analytical sam-
ples failed. Complex 3b, which has a methylene bridge be-
tween the two carbene ligands and methyl groups on the N
atoms, is the most stable complex. It seems that elongation
of the bridge between the carbene units or an increase in
the steric bulk of the N substituents, that is, the cases of 4–
6, negatively affected the stability of the complexes, which
Scheme 2. Carbene and nitrene transfer reactions catalysed with
copper complexes.
1
invariably showed decomposition in their H NMR spectra
after 1–2 d in solution. In contrast, the complexes were
stable in the solid state without special precautions, al-
though upon prolonged storage in air they invariably
showed a light-blueish tinge, which indicates slow oxidation
of the metal by atmospheric oxygen. In this context, the
instability of copper(I)–NHC complexes towards air oxi-
dation has very recently been reported.[13,21]
Scheme 3. Dinuclear copper(I) complexes employed in this work.
Catalytic Activity: Nitrene Transfer Reactions
We first screened the potential of these copper complexes
in nitrene transfer reactions. As a test reaction, we focused
on the aziridination of styrene and employed 3b as the
catalyst precursor and N-tosylimino(phenyl)iodinane
(PhI=NTs) as the nitrene source. The results are shown in
Results and Discussion
Synthesis of Bis-carbene–Silver and –Copper Complexes
We have previously described the syntheses of the trinu- Table 1. The reaction was found to proceed at room tem-
clear tris-carbene–copper(I) complexes
1
and
2
perature with only 1 mol-% catalyst, although the yield
(Scheme 1).[10] We were also interested in preparing related greatly depended on the excess of olefin employed (Table 1,
dinuclear bis-carbene–copper(I) complexes such as 3b entries 1–5). Addition of molecular sieves to the reaction
(Scheme 3), the preparation of which has just recently been mixture did not significantly alter the results (Table 1, en-
reported.[12,13] Following the same methodology, we have tries 4 and 6). The in situ generation of PhI=NTs by mixing
synthesised the complexes 4b–6b (Scheme 3).
PhI(OAc)2 and TsNH2 gave a poor yield of the product.
The reactions of the bis-imidazolium precursors 3–6 with The use of acetonitrile as solvent led to a decrease in the
Ag2O[18] and subsequent anion exchange afforded the corre- aziridination yield at room temperature, which significantly
sponding dinuclear bis-carbene–silver complexes 3a–6a. Al- increased at 50 °C (Table 1, entry 10); furthermore, in this
though complexes 3a[12,13] and 4a[19] have previously been solvent, in situ generated PhI=NTs gave higher yields than
reported in the literature (4a with a different counter-ion), in dichloromethane (Table 2, entry 11).
the related complexes 5a and 6a are hitherto unreported.
The use of alternative nitrene sources gave mixed results.
Note, the use of a bis-imidazolium salt similar to 5 but with Anhydrous chloramine T was unsuitable as a reagent in
chloride counter-ions has been reported to afford a silver dichloromethane, whereas moderate yields of aziridine were
complex with a different dinuclear structure, with only one achieved in acetonitrile. The presence of water was found
bridging dicarbene ligand and one chloride coordinated to to be highly detrimental in this case; the reaction yield im-
each silver atom.[20]
proved upon the addition of molecular sieves and decreased
Complexes 3a–6a were employed as starting materials in drastically when using commercial chloramine T trihydrate
the transmetallation reaction in which the NHC ligands (Table 1, entries 12–17). In contrast, very high yields were
were transferred from silver to copper to yield the com- obtained with the system PhI=O + H2NTs at 50 °C in
plexes 3b–6b. Their spectroscopic data compare well with acetonitrile (Table 1, entry 18).
those of the previously reported, structurally characterised
Following these preliminary investigations, complexes 1,
complex 3b[12,13] and also suggest for the novel complexes 2 and 3b–6b were tested in the styrene aziridination reaction
a dinuclear structure with two bridging dicarbene ligands. under the optimised conditions. Table 2 shows the results,
Support for the dinuclear structures is also provided by allowing the catalytic capabilities of the series of catalysts
ESI-MS analyses in which only signals attributable to dinu- in this reaction to be assessed. Although all the complexes
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Catalysed Nitrene and Carbene Transfer Reactions
Table 1. Styrene aziridination catalysed by complex 3b.[a]
copper catalysts in our series (Table 2), but also with
[IPrCuCl], and the reason appears to be the higher stability
of 3b under the reaction conditions.
Entry Nitrene source
T
Styrene/ Solvent Yield[b]
[°C] nitrene
[%]
1
2
3
4
5
6
7
8
PhI=NTs
PhI=NTs
PhI=NTs
PhI=NTs
PhI=NTs
PhI=NTs
PhI(OAc)2 + H2NTs
PhI=NTs
PhI(OAc)2 + H2NTs
PhI=NTs
PhI(OAc)2 + H2NTs
chloramine T
chloramine T
chloramine T
chloramine T
chloramine T commercial (·3H2O)
chloramine T
PhI=O + H2NTs
25
25
25
25
25
25
25
25
25
50
50
25
25
25
25
25
50
50
5:1
CH2Cl2 14
CH2Cl2 25
CH2Cl2 44
CH2Cl2 76
CH2Cl2 80
CH2Cl2 78[c]
CH2Cl2 14
CH3CN 26
CH3CN 25
CH3CN 82
CH3CN 91
10:1
20:1
30:1
50:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
30:1
9
10
11
12
13
14
15
16
17
18
CH2Cl2
4
CH2Cl2 6[c]
CH3CN 26
CH3CN 37[c]
Figure 1. Conversion curves for the aziridination of styrene with in
situ formed PhI=NTs catalysed by 3b (ᮀ) and [IPrCuCl] (᭛). Reac-
tion conditions: 0.263 mmol PhI(OAc)2 + H2NTs, 30 equiv. styrene,
4 mL acetonitrile, 2 mol-% [Cu], 50 °C.
CH3CN
8
CH3CN 43
CH3CN 95[c]
To complete the aziridination screening, a series of ole-
fins bearing aromatic and aliphatic substituents as well as
electron-withdrawing and -donating groups were employed
as substrates using 3b as catalyst. The results are reported
in Table 3. p-Substituted styrenes showed moderate azirid-
ination yields (Table 3, entries 1–7), which were quite unaf-
fected by the nature of the group located at the para posi-
tion, but they were affected by the use of in situ generated
PhI=NTs (Table 3, entries 3 and 4). Geminal-disubstituted
olefins also gave moderate yields, provided the substituents
were not too bulky (entries 8 and 9). On the other hand,
vicinal-disubstituted olefins and cyclic olefins gave rather
low aziridination yields (entries 10–12). Interestingly, when
cis-propenylbenzene was used as the substrate, most of the
aziridination product was found to be in the trans configu-
ration (entry 11). This inversion of stereochemistry can be
interpreted to be a result of the existence of a radical path-
way for the aziridination reaction.[22]
[a] Reaction conditions: 0.263 mmol nitrene source, 4 mL solvent,
2 mol-% [Cu], 17 h. [b] Yields were determined by NMR spec-
troscopy. [c] With addition of 100 mg of molecular sieves (4 Å).
Table 2. Aziridination of styrene with PhI=NTs catalysed by poly-
nuclear copper(I)–NHC complexes.[a]
Entry
Catalyst
Yield [%][b]
1
2
3
4
5
6
1
34
64
82
67
41
35
2
3b
4b
5b
6b
[a] Reaction conditions: 0.263 mmol PhI=NTs, 30 equiv. styrene,
4 mL acetonitrile, 2 mol-% [Cu], 50 °C, 17 h. [b] Yields were deter-
mined by NMR spectroscopy.
Having demonstrated the catalytic capabilities of these
catalysed the aziridination reaction, significant differences compounds, and particularly that of complex 3b, to catalyse
in catalytic activity were found. In the case of the tris- the nitrene transfer reactions, we decided to investigate its
carbene derivatives, complex 1 is less active than the related potential in the functionalisation of the C–H bond given
2. With the bis-carbene series, the activity follows the trend that, as mentioned before, there are no examples of the use
3bϾ4bϾ5bϾ6b. In fact, this trend correlates to a certain of a NHCCu-based catalyst for this reaction. The selection
extent with the stability of the complexes in solution men- of the model substrate was somewhat limited by the poor
tioned above.
solubility of 3b in non-polar solvents. Because of this we
To compare the catalytic efficiency of complex 3b with first targeted 1,4-dioxane as a suitable substrate. Thus, the
that of the standard complex [IPrCuCl], we determined the reaction of several nitrene sources in 1,4-dioxane as solvent
conversion curves for the aziridination of styrene for both in the presence of catalytic amounts of 3b led to the product
catalysts with in situ formed PhI=NTs (Figure 1). It is ap- derived from the formal insertion of an NTs group into the
parent that the initial activity is very similar for the two α-C–H bond of the cyclic ether (Scheme 4 and Table 4).
catalysts, but [IPrCuCl] is deactivated faster and the reac-
Although negligible reactivity was observed at 50 °C,
tion stops after about 5 h and 60% yield whereas 3b retains moderate yields of the insertion product were obtained
its activity for a longer period of time allowing a much upon raising the reaction temperature to 70 °C (Table 4, en-
higher yield to be obtained. Thus, the catalytic efficiency of tries 1–4). Under these conditions, anhydrous chloramine T
3b compares favourably not only with the other polynuclear was found to be a significantly better nitrene source than
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A. Biffis et al.
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Table 3. Aziridination of olefins with PhI=NTs catalysed by com- ligand on the complex is displaced by a non-coordinating
plex 3b.[a]
anion or a donor ligand. We investigated the same reaction
Entry Nitrene source
Olefin
Yield[b] [%]
with complexes 1 and 3b under comparable reaction condi-
tions (1–4 mol-% catalyst, dichloromethane, room tempera-
ture) and found that, in contrast to [IPrCuCl], the decom-
position reaction was catalysed by both complexes. The re-
action was faster with 3b, reaching completion with 1 mol-
% catalyst after only 2 h and yielding a 60:40 fumarate/
maleate ratio, whereas in the case of 1 the reaction was
slower, reaching a conversion of 90% with a 77:23 fumar-
ate/maleate ratio after 24 h with 4 mol-% catalyst. Appar-
ently, the inherent cationic nature and consequent electro-
philicity of our polynuclear complexes is high enough to
trigger EDA decomposition in spite of the presence of two
strongly coordinated ligands such as the two NHC moieties
in the coordination sphere of the copper(I) centres.
The olefin cyclopropanation reaction also proved to be
effective with these di- and trinuclear copper(I) complexes.
Ethyl diazoacetate and methyl phenyldiazoacetate (PhDA)
were employed along with an excess of the olefin acceptor
(10 equiv. with respect to the diazo compound) and 1 mol-
% of the copper catalyst. The results are reported in Table 5.
The reaction of EDA with the trinuclear catalyst 1 was very
slow, yielding a negligible amount of the cyclopropane even
after 24 h. The catalytic performances of the dinuclear cata-
lysts 3b, 4b and 6b were somewhat better, but the yields
of cyclopropane were still only moderate after 24 h. The
diastereoselectivity of the reaction with EDA was also mod-
erate (ca. 70:30), whereas the use of the phenyl-containing
diazo compound induced a much higher diastereoselectiv-
ity, although the yields remained only moderate (entries 5–
7).[23]
1
PhI=NTs
styrene
styrene
82
91
39
78
36
45
38
36
15
2
3
PhI(OAc)2 + H2NTs
PhI=NTs
4-chlorostyrene
4-chlorostyrene
4-fluorostyrene
4-methylstyrene
4-methoxystyrene
α-methylstyrene
1,1-diphenylethylene
cis-propenylbenzene
trans-propenylbenzene
cis-cyclooctene
4
5
PhI(OAc)2 + H2NTs
PhI=NTs
6
PhI=NTs
7
PhI=NTs
8
PhI=NTs
9
PhI=NTs
10
11
12
PhI=NTs
PhI=NTs
PhI=NTs
7(11[c])
28
11
[a] Reaction conditions: 0.263 mmol nitrene source, 30 equiv. ole-
fin, 4 mL acetonitrile, 2 mol-% [Cu], 50 °C, 17 h. [b] Yields were
determined by NMR spectroscopy. [c] Yield of the trans-aziridine
product.
Scheme 4. C–H bond functionalisation by nitrene insertion cata-
lysed by 3b.
Table 4. C–H bond functionalisation of 1,4-dioxane catalysed by
complex 3b.[a]
Entry Substrate
Nitrene source
T [°C] Yield[b] [%]
1
2
3
4
5
6
7
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
PhI=NTs
50
50
70
70
70
70
70
0
0
20
PhI(OAc)2 + H2NTs
PhI(OAc)2 + H2NTs
PhI(OAc)2 + H2NTs
chloramine T
Table 5. Cyclopropanation of styrene catalysed by polynuclear cop-
per(I)–NHC complexes.[a]
38[c]
51[c]
48[c]
32[c]
tetrahydrofuran chloramine T
1,4-dioxane [d]
chloramine T
[a] Reaction conditions: 0.263 mmol nitrene source, 4 mL substrate,
20 mol-% [Cu], 17 h. [b] Yields were determined by NMR spec-
troscopy. [c] With addition of 100 mg of 4 Å molecular sieves. [d]
The reaction was performed with 1 mmol 1,4-dioxane and
1.3 mmol chloramine T in 6 mL acetonitrile.
Entry
Catalyst
Diazo compound
Yield[b] [%]
dr[c]
PhI=NTs (Table 4, entries 5 and 7); the reaction could be
performed in acetonitrile as solvent with nearly stoichio-
metric amounts of reagents. Under similar reaction condi-
tions, tetrahydrofuran was also functionalised in moderate
yields (Table 4, entry 6).
1
2
3
4
5
6
7
1
EDA
EDA
EDA
3
38:62
73:27
71:29
71:29
Ͼ95:5
Ͼ95:5
Ͼ95:5
3b
4b
6b
3b
4b
6b
45
21
41
25
33
45
EDA
PhDA
PhDA
PhDA
Catalytic Activity: Carbene Transfer Reactions
[a] Reaction conditions: see the Exp. Sect. [b] Yields were deter-
mined by NMR spectroscopy. [c] Diastereomeric ratio (E/Z).
We also tested the polynuclear copper complexes in carb-
ene transfer reactions using ethyl diazoacetate (EDA) as the
carbene source. An interesting feature of the mononuclear
[IPrCuCl] complex is that it suppresses the diazo coupling
reaction that leads to the formation of diethyl maleate and
fumarate, an unwanted side-reaction in carbene transfer
Conclusions
We have found that polynuclear poly-NHC copper com-
processes.[16a] Catalysis only takes place if the chloride plexes catalyse the transfer of carbene (from diazo com-
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Catalysed Nitrene and Carbene Transfer Reactions
sphere and the filtrate was concentrated to about 1–2 mL under
reduced pressure and finally treated with diethyl ether (ca. 20 mL).
The resulting white precipitate was filtered off under an inert atmo-
sphere, washed diethyl ether (2ϫ 5 mL) and dried under reduced
pressure.
pounds) or nitrene (from iodine hypervalent compounds)
fragments to unsaturated and saturated substrates in mod-
erate-to-high yields. In particular, this system has provided
the first example of the tosylamidation of C–H bonds with
a catalyst containing the NHCCu core, which was known
to induce other transformations (olefin cyclopropanation,
aziridination and C–H bond functionalisation by carbene
insertion).
1
Complex 4b: Yield 52%. H NMR ([D6]DMSO): δ = 7.33 (s, 4 H,
CH), 7.28 (s, 4 H, CH), 4.66 (s, 8 H, CH2), 3.73 (s, 12 H, CH3) ppm.
13C NMR ([D6]DMSO): δ = 176.7 (NCN), 123.2 (CH), 122.4 (CH),
51.2 (CH2), 39.2 (CH3) ppm. MS (ESI, CH3CN): m/z (%) = 253.22
(74) [Cu2L2]2+, 269.19 (100) [Cu2L2·O2]2+; the simulated isotopic
pattern of the ions matches the experimental pattern.
Experimental Section
1
Complex 5b: Yield 48%. H NMR ([D6]DMSO): δ = 7.67 (s, 4 H,
General Methods: All manipulations were carried out by using stan-
dard Schlenk techniques under dry argon or dinitrogen. The rea-
gents were purchased by Aldrich or Merck as high-purity products
and generally used as received. All solvents were dried by standard
procedures and distilled under dinitrogen immediately prior to use.
N-Tosylimino(phenyl)iodinane (PhI=NTs),[24] complexes 1,[10a]
CH), 7.55 (s, 4 H, CH), 4.12 (m, 8 H, CH2), 3.37 (s, 12 H, CH3),
2.50 (m, 4 H, CH2) ppm. 13C NMR ([D6]DMSO): δ = 177.2
(NCN), 125.7 (CH), 122.5 (CH), 47.5 (CH2), 39.0 (CH3), 31.3
(CH2) ppm. MS (ESI, CH3CN): m/z = 283.21 (100) [Cu2L2·O2]2+
;
the simulated isotopic pattern of the ion matches the experimental
pattern. C22H32Cu2F12N8P2 (825.56): calcd. C 31.99, H 3.91, N
13.57; found C 32.04, H 4.06, N 13.34.
2,[10b] 3a[25] and 3b[12] and ligand precursors 4,[19] [26] and 6[27] were
5
prepared according to literature procedures. NMR spectra were re-
corded with a Bruker Avance 300 MHz spectrometer (300.1 MHz
1
Complex 6b: Yield 45%. H NMR ([D6]DMSO): δ = 7.75 (s, 4 H,
CH), 7.66 (s, 4 H, CH), 6.56 (br. s, 4 H, CH2), 4.26 (m, 4 H, CH),
1.00–2.00 (m, 40 H, CH2) ppm. 13C NMR ([D6]DMSO): δ = 176.7
(NCN), 123.7 (CH), 121.3 (CH), 62.2 (CH2), 64.2 (CH), 25–41 (CH
and CH2) ppm. MS (ESI, CH3CN): m/z (%) = 375.43 (100)
[Cu2L2]2+, 749.33 (56) [Cu2L2]+, 769.34 (56) [Cu2L2·HF]+, 895.16
(57) [Cu2L2PF6]+; the simulated isotopic pattern of the ions
matches the experimental pattern.
1
for H and 75.5 MHz for 13C). Chemical shifts (δ) are reported in
units of ppm relative to the residual solvent signals.
General Procedure for the Synthesis of the Silver Complexes 4a–6a:
The bis-imidazolium ligand precursor (1 mmol) and Ag2O
(2.5 mmol) were placed in a 100 mL two-necked round-bottomed
flask equipped with a magnetic stirring bar under an inert atmo-
sphere under light exclusion. Deionised water (50 mL) was sub-
sequently added and the reaction mixture was maintained at room
temperature whilst stirring for 24 h. Subsequently, the reaction mix-
ture was filtered through Celite under an inert atmosphere and the
filtrate was treated with NH4PF6 (2.1 mmol). The resulting white
precipitate was filtered off under an inert atmosphere and dried
under reduced pressure under light exclusion.
Decomposition of Ethyl Diazoacetate: The copper(I) complex
(10 μmol) was placed in a 50 mL three-necked round-bottomed
flask under an inert atmosphere. Dichloromethane (20 mL for com-
plex 1, 5 mL for complex 3b) was subsequently added and the mix-
ture was stirred until dissolution of the catalyst was complete. Ethyl
diazoacetate (EDA, 0.25 mmol for complex 1, 1 mmol for complex
3b) was then added and the mixture was stirred at room tempera-
ture for 24 h. Aliquots (0.2 mL) of the reaction mixture were re-
moved after 2, 5 and 24 h, evaporated to dryness and analysed by
1H NMR spectroscopy in CDCl3 using 4-bis(trimethylsilyl)benzene
as internal standard.
1
Complex 4a: Yield 49%. H NMR ([D6]DMSO): δ = 7.56 (s, 4 H,
CH), 7.34 (s, 4 H, CH), 4.67 (s, 8 H, CH2), 3.76 (s, 12 H, CH3) ppm.
13C NMR (CD3CN): δ = 124.0 (CH), 123.0 (CH), 52.3 (CH2), 39.4
(CH3) ppm, carbene carbon not detected. C20H28Ag2F12N8P2
(886.15): calcd. C 27.09, H 3.19, N 12.65; found C 26.46, H 3.37,
N 12.25.
General Procedure for the Cyclopropanation Reactions: The cop-
per(I) complex (10 μmol) was placed in a 50 mL three-necked
round-bottomed flask under an inert atmosphere. Styrene
(1.25 mmol for complex 1, 10 mmol for the others) and dichloro-
methane (20 mL for complex 1, 5 mL for the others) were sub-
sequently added and the mixture was stirred until dissolution of
the catalyst was complete. The diazo compound was then added
(0.25 mmol in one portion for complex 1, 1 mmol in 1 mL dichloro-
methane over 1 h with a syringe pump for the others) and the mix-
ture was stirred at room temperature for 24 h. After this time the
reaction mixture was evaporated to dryness and analysed by 1H
NMR spectroscopy in CDCl3 using 4-bis(trimethylsilyl)benzene as
internal standard. The products were identified by comparison of
1
Complex 5a: Yield 45%. H NMR ([D6]DMSO): δ = 7.68 (s, 4 H,
CH), 7.57 (s, 4 H, CH), 4.07 (m, 8 H, CH2), 3.49 (s, 12 H, CH3),
2.50 (m, 4 H, CH2) ppm. 13C NMR (CD3CN): δ = 124.8 (CH),
121.9 (CH), 48.4 (CH2), 38.7 (CH3), 30.6 (CH2) ppm, carbene
carbon not detected. C22H32Ag2F12N8P2 (914.21): calcd. C 28.89,
H 3.53, N 12.26; found C 28.67, H 3.67, N 11.95.
1
Complex 6a: Yield 41%. H NMR ([D6]DMSO): δ = 7.84 (s, 4 H,
CH), 7.72 (s, 4 H, CH), 6.89 and 6.37 (AB system, 4 H, CH2), 4.25
(m, 4 H, CH), 0.90–2.10 (m, 40 H, CH2) ppm. 13C NMR ([D6]-
DMSO): δ = 123.3 (CH), 121.9 (CH), 65.2 (CH2), 62.2 (CH), 35.1
(CH2), 26.4 (CH2), 25.9 (CH2) ppm, carbene carbon not detected.
C38H56Ag2F12N8P2 + 3H2O (1184.16): calcd. C 38.51, H 5.28, N
9.46; found C 38.59, H 4.78, N 9.55.
1
the H NMR spectra with literature data.[28]
General Procedure for the Aziridination Reactions: The nitrene
source (0.263 mmol), the copper(I) complex (2.63 μmol for the di-
nuclear complexes and 1.75 μmol for the trinuclear complexes,
2 mol-% [Cu]), the olefin, if solid (5–50 equiv. with respect to the
nitrene source), and, if appropriate, 4 Å molecular sieves (100 mg)
were placed in a 50 mL two-necked round-bottomed flask under
an inert atmosphere. The flask was thermostatted at the desired
temperature (25 or 50 °C) and solvent (4 mL) and olefin, if liquid
(5–50 equiv. with respect to the nitrene source), were then added.
General Procedure for the Synthesis of the Copper(I) Complexes 4b–
6b: The dinuclear dicarbene silver complex was placed in a 50 mL
two-necked round-bottomed flask equipped with a magnetic stir-
ring bar under an inert atmosphere. Acetonitrile (3–5 mL) was sub-
sequently added followed by CuI (2 equiv. with respect to the intro-
duced silver complex). The reaction mixture was maintained at
room temperature whilst stirring for 30 min. Subsequently, the re-
action mixture was filtered through Celite under an inert atmo-
Eur. J. Org. Chem. 2012, 1367–1372
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1371

A. Biffis et al.
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Acknowledgments
We thank the Junta de Andalucía (grant number P07-02870) and
the Ministerio de Ciencia e Innovación (MICINN) (grant number
CTQ2008-00042) for funding.
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Received: October 11, 2011
Published Online: January 18, 2012
1372
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 1367–1372