Phosphine ligands stabilized Cu(I) catalysts for carbene insertion into the N-H bond

Article abstract of DOI:10.1016/j.jorganchem.2016.01.016

Phosphine ligands have been successfully used along with Cu(I) for several catalytic reactions, nevertheless these ligands were less explored relatively for carbene involved reactions owing to the formation of carbene-phosphine ylides. In this report we successfully used three different phosphine stabilized Cu(I) complexes (1-3) as catalysts for chemoselective carbene insertion into the N-H bond of different aromatic amines over the formation of olefin (carbene dimerized product). In order to understand the substrate scope, different α-diazo esters have been reacted with large number of amines and all the reactions produced reasonably good yields under normal experimental conditions (38 examples). All the carbene inserted products have been isolated by column chromatography and fully characterized using standard spectroscopic techniques without any ambiguities. Several control reactions have been conducted in order to understand the importance of the type of phosphine ligands used in the catalysts 1-3 and found that without these catalysts we observed less selectivity (more of olefin as the product over N-H inserted product) and low yield. From this present study, it can be noted that the rigid framework phosphine ligands would be the better choice for carbene chemistry. The results obtained from the current studies would inspire chemists to develop more novel Cu(I)-phosphine catalysts for carbene related reactions including asymmetric versions in the near future.

Full text of DOI:10.1016/j.jorganchem.2016.01.016

Accepted Manuscript
Phosphine ligands stabilized Cu(I) catalysts for carbene insertion into the N-H bond
Kankanala Ramakrishna, Chinnappan Sivasankar
PII:
S0022-328X(16)30016-X
10.1016/j.jorganchem.2016.01.016
JOM 19367
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 21 October 2015
Revised Date: 11 January 2016
Accepted Date: 12 January 2016
Please cite this article as: K. Ramakrishna, C. Sivasankar, Phosphine ligands stabilized Cu(I) catalysts
for carbene insertion into the N-H bond, Journal of Organometallic Chemistry (2016), doi: 10.1016/
j.jorganchem.2016.01.016.
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ACCEPTED MANUSCRIPT
Phosphine ligands stabilized Cu(I) catalysts for carbene insertion
into the N-H bond
Kankanala Ramakrishna and Chinnappan Sivasankar*
Catalysis and Energy Laboratory, Department of Chemistry,
Pondicherry University, Puducherry 605014, INDIA
E-Mail: siva.che@pondiuni.edu.in
Graphical abstract
Graphical synopsis
Cu(I)-phosphine complexes as catalysts for carbene insertion into the N-H bond of different
anilines
Keywords: Cu(I) catalyst, phosphine ligands, carbene, insertion reaction, C-N bond formation.
*Corresponding author. Tel.: +91-413-2654709, Fax: +91-413-2655987
E-mail address: siva.che@pondiuni.edu.in (Dr. C. Sivasankar)
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Abstract
Phosphine ligands have been successfully used along with Cu(I) for several catalytic reactions,
nevertheless these ligands were less explored relatively for carbene involved reactions owing to
the formation of carbene-phosphine ylides. In this report we successfully used three different
phosphine stabilized Cu(I) complexes (1-3) as catalysts for chemoselective carbene insertion into
the N-H bond of different aromatic amines over the formation of olefin (carbene dimerized
product). In order to understand the substrate scope, different α-diazo esters have been reacted
with large number of amines and all the reactions produced reasonably good yields under normal
experimental conditions (38 examples). All the carbene inserted products have been isolated by
column chromatography and fully characterized using standard spectroscopic techniques without
any ambiguities. Several control reactions have been conducted in order to understand the
importance of the type of phosphine ligands used in the catalysts 1-3 and found that without
these catalysts we observed less selectivity (more of olefin as the product over N-H inserted
product) and low yield. From this present study, it can be noted that the rigid framework
phosphine ligands would be the better choice for carbene chemistry. The results obtained from
the current studies would inspire chemists to develop more novel Cu(I)-phosphine catalysts for
carbene related reactions including asymmetric versions in the near future.
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1. INTRODUCTION
The C-N bond has the significant place in both synthetic and nature made molecules. There are
many methods known in the literature to form C-N bonds,[1–3] however the most studied
methods are simple nucleophilic substitution and coupling reactions. Apart from these
widespread methods, carbene insertion into the N-H bond catalyzed by metals or metal salts is
also found to be a useful method.[4–6] Nevertheless from the commercial point of view, catalytic
methods are more economic than the simple stoichiometric nucleophilic substitution methods.
Carbene insertion into the N-H bond is one of the fast growing research areas in the last decade.
Thus far only Cu,[7–22] Rh[23–27] and Fe[28–36] based catalysts have been widely used with
nitrogen and carbene type ligands respectively.
Scheme 1. Some known catalysts for carbene insertion into the N-H bond.
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Apart from these metal based catalysts, Ru,[33,37–40] Pd,[41] Ir,[42] Au,[43,44] Re[45] and
Ag[10] have also been developed for carbene insertion into the N-H bond. Thus far mostly N, O
and C based ligands have been used to stabilize the desired oxidation states of the above
mentioned transition metal ions (Scheme 1). However, phosphine based ligands have been
neglected for carbene chemistry mainly owing to the formation of carbene-phosphine ylides
when the phosphine ligands are not tightly linked with the metal ions.[11,41] Therefore only few
Cu(I) phosphine complexes are known for this carbene chemistry (Scheme 2).
Ph
B
O
PPh2
NH HN
N
PR2
Ph2P
PPh2
Cu
L
PPh2
+ CuPF6
Ph2P
+ CuPF6
L = PPh3 or THF
R = Ph or tolyl or 2,4-dimethylphenyl
Scheme 2. Widely used phosphine ligands stabilized Cu(I) catalysts for carbene insertion
reaction.
On the other hand phosphine ligands based catalysts have been used successfully for the C-C
coupling reactions, C-H activation and many other organic reactions.[46–50] Nevertheless if the
phosphine ligands exist only in the complex form during the course of the reaction, one can
avoid the formation of carbene-phosphine ylides. Prudently by choosing the right substituents
and scaffold, one can develop catalysts with phosphine ligands for carbene chemistry. In this
regard, continuation of our research upon carbene insertion reaction,[21] we herein report three
phosphine based copper catalysts (Scheme 3) for carbene insertion reactions and demonstrate the
substrate scope (38 examples). These results perhaps useful to develop large number of
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phosphine stabilized cooper catalysts for similar chemistry including for asymmetric version in
the near future.
Scheme 3. Cu(I) catalysts used in the present study.
2. RESULTS AND DISCUSSION
We started our investigation with simple aniline and α-phenyl diazoacetate using 2 mol % of
catalyst 1 in DCM (Scheme 4). The reaction was completed within 4 hours and furnished an
excellent yield 97%. This result prompted us to optimize the reaction conditions.
Scheme 4. Carbene insertion into the N-H bond using catalyst 1.
For optimizing the reaction conditions, we screened commonly used organic solvents and
catalyst load as well. First of all we screened the catalyst load, we observed the best yield with 2
mol % of catalyst. In case of solvents, we observed excellent yields with DCM solvent. In case
of coordinating solvent THF (Table 1, entry 2), the reaction was found to be slow and given 76%
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yield in 10 h. In acetonitrile solvent (Table 1, entry 3), the rate of the reaction was very slow and
given only 67% yield in 36 h, however we have not observed carbene dimerized product but
recovered unreacted diazo and aniline. This could be owing to the difference in the rate of
carbene formation versus acetonitrile binding. In water (Table 1, entry 6), we have isolated 32%
yield in 48 h, although in toluene the reaction mixture was happened to be heterogeneous,
surprisingly this carbene insertion reaction furnished 92% yield (Table 1, entry 7) (catalyst 1 is
insoluble in toluene, throughout the reaction we observed solid particles). After completion of
the reaction in toluene, we reused the catalyst 1 for two more runs and observed that the yield
was reduced for second and third runs (74% and 49% respectively).
Table 1. Optimization of reaction conditions.
Entrya
Solvent
DCM
THF
MeCN
DMF
MeOH
Water
Toluene
t [h]b
4
10
36
48
6
Yield [%]c
1
2
97
76
67
45
93
32
92
3d
4
5
6
7
48
5
aAll the reactions are carried out with 0.5 mmol (with respect to aniline) in 5 mL of solvent with 2 mol % of catalyst
b
and 0.55 mmol of diazo compound in a 25 mL Schlenk flask under nitrogen atmosphere. Diazo compound (1.1
equiv.) added at 0°C followed by warming to rt. cIsolated product yield. dWe have not observed any homo coupling
product of diazo compound.
In order to understand the role of catalyst 1, we screened various copper sources as catalysts,
when we used Cu(I) complex of commercially available bis-phosphine ligands such as xantphos
(xantphos = 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene) and dppf (dppf = 1,1′-
Ferrocenediyl-bis(diphenylphosphine)) (Table 2, entry 2 and 3), we observed good yields 91%
and 90%. In case of PPh3-Cu(I) complex (Table 2, entry 6), we observed only 38% yield and in
case of dppe (Table 2, entry 7), we observed 69% yield in 8 h, with simple [Cu(CH3CN)4]ClO4
salt (Table 2, entry 4), we observed 76% yield in 5 h. In the presence of nitrogen based donor
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ligand (1, 10-Phenanthroline) (Table 2, entry 5), we observed 71% yield in 4 h. In order to gain
more insight to understand the importance of Cu(I) ion in dppf-Cu(I) complex, we screened
simple ferrocene and FeCl2.4H2O (Table 2, entry 8 and 9) as catalysts for carbene insertion into
the N-H bond and we observed less than 10% yield in 48 h.
Table 2. Carbene insertion into the N-H bond using various copper sources as catalysts.
Entrya
Solvent
DCM
DCM
DCM
DCM
DCM
Catalyst
1
t [h]
4
5
5
5
Yield [%]b
1
2
3
97
91
90
76
71
2
3
4
(CH3CN)4CuClO4
CH3CN)4CuClO4
+ 1, 10-Phenanthroline
(CH3CN)4CuClO4 + 2PPh3
(CH3CN)4CuClO4 + dppe
Ferrocene
5c
4
6
7
8
9
10
DCM
DCM
DCM
DCM
DCM
8
8
48
48
6
38
69
<10
<10
89
FeCl2.4H2O
1 (1 mol %)
aAll the reactions are carried out with 0.5 mmol (with respect to aniline) in 5 mL dichloromethane with 2 mol % of
b
catalyst and 0.55 mmol of diazo compound in a 25 mL Schlenk flask under nitrogen atmosphere. Isolated product
yield. cWe observed 8% of unidentified product.
From the above observation we found that the complex 1 is the best choice catalyst for
carbene insertion into the N-H bond of aniline. After optimizing the reaction conditions, we
focused our investigation on the scope of different diazo compounds. We have screened reaction
of various diazo derivatives with simple aniline using catalyst 1 (2 mol %) in DCM solvent. All
the diazo compounds smoothly reacted with the aniline and given good to excellent yields. We
observed highest yield in case of simple α-phenyl diazoacetates 97% (Table 3, entry 1) and we
observed lowest yield (82%) with o-Cl-phenyl diazoacetates (Table 3, entry 4). These results
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prompted us to study the electronic effects of various substituents on aryl part of diazo
compounds and observed good correlations with yields and reaction times. In case of electronic
withdrawing groups, we observed lower yields and less reaction time. On the other hand
insertion reaction has taken more time to complete the reaction when the electronic donating
groups were used, nevertheless given more yields. Changing of ester groups also affected the
yields, isopropylate and benzylate (Table 3, entry 2 and 3) were given 94% and 89% yields in 4
hours respectively. These results prompted us to examine the substrate scope with various
anilines.
Table 3. Substrate scope of aryl diazoesters.
Entrya
Ar
Ph
Ph
R
Et
iPr
Bn
Et
Et
Et
Et
Et
Et
Et
t [h]
4
4
5
a
b
c
d
e
f
g
h
i
Yield [%]b
97
94
89
82
91
86
85
92
89
93
1
2
3
4
5
6
7
8
9
4
Ph
3
o-ClC6H4
m-ClC6H4
p-ClC6H4
p-BrC6H4
o-OMeC6H4
p-OMeC6H4
o-OMe, p-OMeC6H3
4
3
3
5
4
6
10
j
aAll the reactions are carried out with 0.5 mmol (with respect to aniline) in 5 mL dichloromethane with 2 mol % of
b
catalyst and 0.55 mmol of diazo compound in a 25 mL Schlenk flask under nitrogen atmosphere. Isolated product
yield.
We have screened various aniline derivatives containing electron donating groups on the
aryl part (Scheme 5). All the anilines reacted smoothly with α-aryl diazoesters and given very
good yields, we observed highest yield with p-toludine (90%). We observed lowest yield with o-
methoxyaniline (77%) in 16 h, this might be owing to the formation of Cu(I) complex with the
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subtrate in a ɳ2 fashion and reducing the possibility of forming carbene complex. In case of
electron donating groups substituted anilines, the steric factor not reflected on the yields and
reaction times. For an instant, sterically bulky 2, 6-diisopropyl aniline also given good yield 85%
in 6 h.
N2
Ar2
HN
O
NH2
R'
Ar2
O
+
1
catalyst (2 mol %)
R'
O
DCM, rt
O
O
O
HN
O
HN
HN
O
O
O
O
O
6c, 81%, 5 h
6a, 90%, 5 h
6b, 86%, 5 h
O
O
HN
O
HN
O
HN
O
O
6d, 77%, 16 h
iPr
O
O
6f, 88%, 5 h
6e, 86%, 6 h
HN
iPr
HN
O
HN
O
O
O
O
O
6h, 87%, 6 h
6g, 85%,6 h
6i, 85%, 6 h
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Scheme 5. Scope of anilines with electron donating groups.
N2
Ar3
catalyst 1 (2 mol %)
HN
O
NH2
O
Ar3
+
DCM, rt
O
O
NO2
Cl
O
NO2
Cl
O2N
HN
F
HN
HN
HN
HN
O
O
O
O
O
O
O
O
O
7e, 87%, 3 h
7a, 94%, 4 h
7d, 39%, 5 h
7b, 92%, 4 h
7c, 57%, 6 h
Cl
Cl
NO2
F
I
Br
Cl
Cl
HN
O
HN
O
HN
HN
O
HN
O
Cl
O
O
O
O
O
O
7f, 95%, 3 h
7g, 71%, 5 h
7j, 97%, 5 h
7h, 99 %, 4 h
7i, 87%, 3 h
Br
CN
F3C
NC
Br
F
HN
O
HN
HN
F
HN
O
HN
O
Br
O
O
O
O
O
O
O
7k, 78%, 3 h
7m, 91%, 2 h
7l, 83%, 3 h
7n, 76%, 6 h
7o, 72%, 8 h
O
Cl
O
Br
Br
HN
HN
HN
HN
O
O
O
O
O
O
O
7p, 89%, 3 h
7s, 91 %, 4 h
7q, 89%, 4 h
7r, 85%, 4 h
Scheme 6. Scope of anilines with electron withdrawing groups.
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Furthere we have also screnned various anilines with electron withdrawing groups on the aryl
group (Scheme 6). All the anilines smoothly reacted with α-phenyl diazoacetates and given good
to excellent yields. We also observed faster reaction rates when compared to the electron
donating anilines. We observed highest yield when the modarate electron withdrawing groups
present on the aryl part of aniline, observed hightest yield 99% and 97% with 4-iodoaniline and
4-bromoaniline respectively. In case of 2-aminonitrile, we observed 72% yield in 8 h, it has
taken reasonably longer time when compared to other subtrates and this might be owing to the
complexation of nitrile group with copper and diminshed the rate of carbene formation. We
observed lowest yields 39% and 47% with 4-nitroaniline and 2,4-dinitro aniline respectively.
Sterically bulky anilines have also given good to excellent yields, in case 2,4,6-tribromoaniline
given 78% in 3 h. In order to gain more evidence for carbene insertion into the N−H bond, two
of the products 5a and 7q (Figure 1) were subjected to the single-crystal XRD studies, and the
molecular solid-state structure clearly revealed that the carbene is inserted into the N−H bond of
aninlines.
Figure 1. Molecular structure of ethyl 2-phenyl-2-(phenylamino)acetate (5a) and ethyl 2-((2-
bromo-4-methylphenyl)amino)-2-phenylacetate (7q); thermal ellipsoids are set at 50%
probability. Hydrogen atoms are omitted for clarity.
In order to understand how the electronic factors of aniline affecting the yields, we have
screened series of para substituted anilines towards carbene insertion into the N-H bond using
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catalysts 1, 2 and 3. We ploted the isolated yields versus para substitued groups (Figure 2), in
case of catalyst 1, we observed lowering the yields while increasing or decreasing the electron
density. We observed best yields with moderate electron withdrawing group 4-iodo aniline. In
case of catalysts 2 and 3, we have not observed any particular trends in yeilds while increasing or
decreasing the electron density. In case of catalyst 2 we observed best yields with simple aniline
and 4-nitroaniline, whereas with catalyst 1, we observed 39% yield with 4-nitroaniline. In case of
4-acetylaniline we observed lowest yield 26%, however in this case we observed 32% of
unidentified product. In case of catalyst 3, we observed best yield 97% with 4-iodoaniline and
lowest yield 69% with 4-chloroaniline.
Scheme 7. Carbene insertion into para-substituted anilines using catalysts 1-3.
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Figure 2. Electronic effects upon yields for catalyst 1-3.
It is important to mention here that the rigid ligand fromwork is seems to be one of the
important creaters for observed reactivity pattern over the formation of phophine-carbene ylide.
The rigid frmaework is one of the general features that present in the catalysts 1-3, when
compared to other phosphine lingands which are used in the current study (Table 2, entry 6 and
7). It is well known in the litarature that depending upon the solvent medium, the Cu(I)
complexes of PPh3 and dppe are in equilibrium with more than one complex form as described
by A.G.Samuelson et. al.[51,52] And therefore perhaps rigid framework is more imporatnt for
the stability of catalysts 1-3 in the solution during the course of the reaction.
Plausible mechanism for carbene insertion into N-H bond of different anilines by Cu(I)
catalysts is given in Scheme 8, two acetonitrile molecules can be replaced by aniline and
carbene to give four coordinate Cu(I) complexes II and III respectively as key intermediates,
subsequently these intermediates can form ylide IV by the attack of nitrogen lone pair of
electrons as proposed and proved by the DFT calculations.in the literature.[53] Eventually the
ylide (IV) can undergo subsequent proton transfer to offer the final product. Nevertheless more
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specific experiments are to be conducted to gain more insights to understand the reaction
mechanism in the near future.
3. CONCLUSSIONS
In this report, we successfully demonstrated three different Cu(I)-phosphine complexes
as catalysts for carbene insertion into the N-H bond of different anilines under normal
experimental conditions. Unlike previously reported Cu(I) catalysts, the catalysts 1 and 3 are air
stable while catalyst 2 is relatively less stable. All the carbene inserted products were fully
characterized using standard spectroscopic techniques without any ambiguities. We have also
studied the effects of electronic factor upon yield and reaction time while using catalysts 1-3.
From the observed results, it can be noted that the rigid scaffold phosphine ligands are important
to stabilize the Cu(I) ion in solution during the course of the reaction which prevents the
formation of phosphine-carbene ylide. These results would inspire chemists to develop more
phosphine based Cu(I) catalysts for carbene related reactions. The mechanistic studies and other
related work is underway in our laboratory.
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Scheme 8. Plausible mechanism for carbene insertion into the N-H bond promoted by catalysts
1-3.
Appendix A. Supplementary material
Contains analytical data, NMR spectra. X-ray crystallographic data CCDC 1420257 (5a) and
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CCDC 1420258 (7q). These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
ACKNOWLEDGMENT
C. S gratefully acknowledges the Council of Scientific and Industrial Research (CSIR), New
Delhi, India for the financial support (No. 01(2535)/11/EMR-II). K. R gratefully acknowledges
the University Grants commission (UGC) for a Junior Research Fellowship. We thank Ms.
Apeksha for helping in the speration techniques for few componds. We also thank the Central
Instrumentation Facility, Pondicherry University, for NMR spectra and DST-FIST for the single-
crystal X-ray diffraction and ESI-MS facility.
4. EXPERIMENTAL SECTION
4.1. General information
Unless otherwise stated all the reactions were performed under dry nitrogen or argon atmosphere
using oven dried glassware and standard Schlenk techniques. All the solvents were distilled prior
to use and stored in solvent storage flasks under nitrogen atmosphere. THF and Et2O were
distilled from sodium and benzophenone, all other solvents were distilled from the CaH2 and
used. Commercially available chemicals were obtained from Sigma-Aldrich and Loba Chemie,
and used as received, unless otherwise mentioned. Ligand (L1)[54], complex 1[21] and all diazo
compounds were prepared by following the standard literature procedures.[55,56] The
[Cu(CH3CN)4]ClO4 is explosive in nature therefore minimum quantity was prepared and used
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whenever is needed by following adequate safety measures. TLC was performed on pre coated
silica gel 60 GF254 on aluminum plates and UV light (254 nm). Column chromatography was
1
performed on silica gel 100-200 mesh size. H, 13C and 31P NMR recorded on Bruker Avance II
400 MHz (1H), 100 MHz (13C) and 162 MHz (31P), Chemical shifts (δ) are given in ppm. The
residual solvent signals were used as references for 1H and 13C, 31P NMR spectra recorded using
85% H3PO4 as an external standard, ESI-MS was recorded on Agilent 6540 UHD Q-TOF mass
spectrometer.
4.2. Typical procedures of Cu(I) catalyzed carbene insertion into N-H bond
Oven dried 25 mL Schlenk flask was charged with aniline (0.5 mmol.) and catalyst (2 mol %),
then 4 mL of solvent was added, the diazo compound (0.55 mmol.) was dissolved in 1 mL of
solvent and added to the reaction flask at 0oC, then allowed to room temperature and stirred for
required time. The progress of the reactions were monitored by TLC experiment using
appropriate mixture of hexane and ethyl acetate as an eluent. After completion of reaction, the
solvent was evaporated under reduced pressure and the crude residue was purified using column
chromatography on silica gel using hexane/ethyl acetate to give analytically pure compound.
4.3. Experimental procedure for preparation (P-P)CU(I) complexes
The catalyst 1 was reported recently by our group. [17] Catalysts 2 and 3 were prepared by
following standard literature procedures.[57–59] Catalysts 1-3 were prepared from an equimolar
mixture of respective ligands and [Cu(CH3CN)4]ClO4 in acetonitrile.
4.3a. Preparation of xantphos-Cu(I) complex (catalyst 2):
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A 50 mL Schlenk flask was loaded with ligand (L2) (4,5-bis(diphenylphosphino)-9,9-
dimethylxanthene) (xantphos) (1 mmol, 0.57 g) and [Cu(CH3CN)4]ClO4 (1 mmol, 0.32 g), and
acetonitrile. The reaction mixture was stirred for 3 h at room temperature. Then filtered through
the pad of celite, the filtrate was concentrated under reduced pressure and diethyl ether was
added to yield complex 2 as a white solid. Yield: 91%. Complex 2 was further purified by
1
crystallization (DCM/diethyl ether) to yield analytically pure compound. H NMR (400 MHz,
CDCl3) δ 7.51 (d, J = 6.8 Hz, 2 H, Ar-H), 7.30 – 7.05 (m, 22 H, Ar-H), 6.54 (d, J = 3.6 Hz, 2 H,
Ar-H), 2.06 (s, 6 H, CH3CN), 1.60 (s, 6 H, -CH(CH3)2). 31P (162 MHz, CDCl3) δ -14.65.
4.3b. Preparation of dppf-Cu(I) complex (catalyst 3):
A 50 mL Schlenk flask was loaded with ligand (L3) (1,1′-ferrocenediyl-bis(diphenylphosphine
(dppf) (1 mmol, 0.55 g), [Cu(CH3CN)4]ClO4 (1 mmol, 0.32 g) and acetonitrile. The reaction
mixture was stirred for 3 h at room temperature. Then filtered through the pad of celite, the
filtrate was concentrated under reduced pressure and diethyl ether was added to yield complex 3
as a white solid. Yield: 83%. Complex 3 was further purified by crystallization (CH3CN/diethyl
ether) to yield analytically pure compound. 1H NMR (400 MHz, CDCl3) δ 7.35 (m, 20 H, Ar-H),
4.28 (s, 4 H, HCp), 4.08 (s, 4 H, HCp), 2.0 (s, 6 H, CH3CN); 31P (162 MHz, CDCl3) δ -13.91.
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Phosphine ligands stabilized Cu(I) catalysts for carbene insertion
into the N-H bond
Kankanala Ramakrishna and Chinnappan Sivasankar*
Catalysis and Energy Laboratory, Department of Chemistry,
Pondicherry University, Puducherry 605014, INDIA
Corresponding author. Tel.: +91-413-2654709, Fax: +91-413-2655987,
E-mail address: siva.che@pondiuni.edu.in
Highlights
• Have been used phosphine stabilized Cu(I) complexes for carbene reactions
• Carbene inserted into the N-H bond of anilines under mild experimental conditions
• Wide scope of diazo and aniline derivatives
• Studied electronic effects on yields of carbene inserted products
• Wide range α-aryl amino esters were synthesized and characterized
1