Synthesis of new copper(i) complexes with tris(2-pyridyl) ligands. Applications to carbene and nitrene transfer reactions

Article abstract of DOI:10.1039/b812604f

New copper(i) complexes with tris(2-pyridyl)methane (TPC), tris(2-pyridyl)methoxymethane (TPM) and tris(2-pyridyl)amine (TPN) ligands have been synthesized and characterized, including structural determinations by X-ray diffraction of some examples. Their activity as catalysts in carbene and nitrene transfer reactions was studied.

Full text of DOI:10.1039/b812604f

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Synthesis of new copper(I) complexes with tris(2-pyridyl) ligands. Applications
to carbene and nitrene transfer reactions†
Julio Pe´rez,*a Dolores Morales,*a Luis A. Garc´ıa-Escudero,‡a He´ctor Mart´ınez-Garc´ıa,a Daniel Miguelb and
Pablo Bernada
Received 23rd July 2008, Accepted 2nd October 2008
First published as an Advance Article on the web 14th November 2008
DOI: 10.1039/b812604f
New copper(I) complexes with tris(2-pyridyl)methane (TPC), tris(2-pyridyl)methoxymethane (TPM)
and tris(2-pyridyl)amine (TPN) ligands have been synthesized and characterized, including structural
determinations by X-ray diffraction of some examples. Their activity as catalysts in carbene and nitrene
transfer reactions was studied.
Introduction
Results and discussion
Copper complexes of tridentate tris(pyrazolyl)borates (CuTp)
are some of the most useful catalysts for carbene and nitrene
transfer (CNT) reactions.1 Therefore, there is an obvious interest
in the exploration of other copper complexes of nitrogen-donor
ligands as catalysts for these reactions. Ligands with pyridyl donor
groups have been extensively employed in copper coordination
chemistry,2 including the catalysis of CNT reactions.3 However,
tridentate tris(2-pyridyl) ligands (TPy), widely used for complexes
of other metals,4 received little attention in copper chemistry, and
their copper complexes were never used as catalysts for CNT
reactions.5
Copper(I) complexes of the ligands tris(2-pyridyl)methane (TPC),
tris(2-pyridyl)methoxymethane (TPM) and tris(2-pyridyl)amine
(TPN) (Chart 1) were chosen for this study.
In CuTp complexes, a correlation was found between catalytic
activity and metal center electron deficiency.6 In turn, the latter
can be estimated by the position of the infrared nCO band of
the TpCu–CO complex, electron-poor metal centers giving rise
to high nCO values. Some of the CuTp complexes that have been
found to display a high activity in CNT reactions and the nCO
values of their carbonyl adducts are: [(TpBr3)CuCO] (2110 cm-1)6
and [(TpCF3,CF3)CuCO] (2137 cm-1).7 Very recently, Fujii and
co-workers8 reported that nCO values for [(TPOH)CuCO]ClO4
(TPOH= tris(2-pyridyl)carbinol), [(TPM)CuCO]ClO4 (TPM=
tris(2-pyridyl)metoxymethane) and [(TPC)CuCO]ClO4 (TPC =
tris(2-pyridyl)methane) are 2106, 2101 and 2091 cm-1 respectively.
The comparison between these values suggests that CuTPy
complexes could be good catalysts for CNT reactions. Here we
report our studies in this area.
Chart 1
The reaction of equimolar amounts of CuOTf and TPC in a
THF/MeCN mixture afforded a high yield of a white powder.
The 1H and 13C NMR spectra of its CD2Cl2 solution were
consistent with a [Cu(TPC)(NCMe)]OTf (1) formulation, and
indicate the equivalence at room temperature of the three 2-
pyridyl groups. Attempts to isolate a related THF (instead of
MeCN) complex, either as a triflate salt or as a salt of the low
coordinating BAr¢4 anion (Ar¢ = 3,5-bis(trifluoromethyl)phenyl)
(see below), afforded a material insoluble in dichloromethane
or chloroform. Compound 1 was employed as the catalyst for
the reaction of ethyldiazoacetate (EDA) and styrene in non-
coordinating solvents. The results are displayed in Table 1.
When EDA was added in one portion to a dichloromethane
solution of styrene (styrene : EDA ratio = 5 : 1) containing
1
1% of the [Cu(TPC)(NCMe)]OTf (1) complex as catalyst, a H
NMR spectrum taken after two hours showed full conversion
of EDA to a mixture of the two diasteromers of 2-phenyl-
ethoxycarbonylcyclopropane (82%), ethyl fumarate and ethyl
maleate (Scheme 1). When the experiment was repeated using a
1 : 1 mixture of 1 and NaBAr¢4 as catalyst, the yield obtained
was the same. This lack of an activating effect of NaBAr¢4
supports our assumption that the triflate anion is not copper-
bonded in 1 (see below). When EDA was slowly added over
10 hours to minimize the formation of the olefins formally
resulting from carbene dimerization, the cyclopropanation was
virtually quantitative (entry 1). Applying the same procedure
to other olefins also afforded the corresponding cyclopropanes
aDepartamento de Qu´ımica Orga´nica e Inorga´nica-IUQOEM, Facultad de
Qu´ımica, C/Julia´n Claver´ıa, n◦8, Universidad de Oviedo-CSIC, 33006
Oviedo, Spain. E-mail: japm@uniovi.es, moralesdolores.uo@uniovi.es;
Fax: +33 (0) 985103446; Tel: +33 (0) 985103465
bIU CINQUIMA/Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad
de Valladolid, Campus Miguel Delibes, 47011 Valladolid, Spain
† Electronic supplementary information (ESI) available: Tables of crystal
data of 4 and 5 and references giving the spectroscopic data of the products.
CCDC reference numbers 695439 and 695440. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b812604f
‡ Present address: IU CINQUIMA/Qu´ımica Inorga´nica, Facultad de
Ciencias, Universidad de Valladolid, 47071 Valladolid, Spain
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Table 1 Yields of cyclopropanes and aziridines in the Cu-catalyzed
reactions of EDA with the listed olefins
entry
1
2b
3
4
Scheme 3
Cyclopropanationa
Styrene
1-Hexene
Cyclooctene
Cis-stilbene
Trans-stilbene
1
2
3
4
5
6
97 (77,20) 84(62,22)
—
—
—
—
—
—
98 (67, 31)
32
94
64
38
17
95
41
32
76
21
98
84
50
96
=
In this case, addition of the PhI NTs caused an immediate
development of a green color, suggestive of a Cu(II) species as the
catalyst resting state.
Next, the known complex [Cu(TPM)(NCMe)]OTf (2a) was
prepared by reaction of CuOTf and TPM in THF/MeCN, using a
slight modification of the method reported by Jonas and Stack.10
In agreement with these authors, 2a was found to be quite sensitive
to aerobic oxidation. Using 2a as catalyst in the cyclopropanation
of styrene and 1-hexene afforded 57% and 7% respectively of the
corresponding cyclopropanes.
Unlike when the tris(pyridyl) methane complex 1 was used
as catalyst, now the addition of NaBAr¢4 led to a significant
increase of the yield. Such an activation effect has been noted
for copper complexes used as catalysts for aziridination reac-
tions by Vedernikov and co-workers.11 These authors found that
chloro complexes are poor catalysts for olefin aziridination, and
that they can be effectively activated by replacing the chloro
1,1-Diphenylethylene 83
Aziridinationb
7
8
9
10
11
12
Styrene
1-Hexene
Cyclooctene
Cis-stilbene
Trans-stilbene
70
18
77
28
15
55
16
63
15
11
26
100
20
80
26
13
45
—
—
—
—
—
—
1,1-Diphenylethylene 33
a 5 mmol of substrate, 1 mmol EDA (added over 11 h), 1 mol% cat, CH2Cl2
(25 mL), in parentheses, ratio of trans/cis products. Yield based on EDA
and determined by 1H-NMR spectroscopy, average of two runs. Mass
balance was accounted for by dimethyl maleate and fumarate formation.
reactions run for 5h with 5 mmol substrate, 1 mmol PhI NTs, 2 mol% cat,
b
=
1
=
CH2Cl2 (15 mL). Yield based on PhI NTs and determined by H-NMR
spectroscopy, average of two runs.
-
ligand by the non-coordinating BAr¢4 anion, because more
unsaturated catalysts are so generated. The authors suggest that
such species could be tri-coordinated copper(I) complexes. In
our case, we have found that the reaction of 2a with NaBAr¢4
afforded [Cu(TPM)(NCMe)]BAr¢4 (2b) which was employed in
the cyclopropenation and aziridination reactions (Table 1). In the
preparation of 2b from 2a, addition of NaBAr¢4 to a CH2Cl2
solution of 2a causes precipitation of triflate as its sodium
salt, insoluble in CH2Cl2, leaving the triflate-free, more active
catalyst 2b.
Interestingly, compound 2b is more active than 2a, in spite
of the fact that both are tetra-coordinate nitrile-bonded species.
The higher activity of 2b suggests that, although in the case
of the tris(pyridyl)methoxymethane compound 2a the isolated
copper complexes feature a nitrile ligand and the triflate is a
non-bonded couteranion, in solution, the triflate anion effec-
tively competes with acetonitrile for the copper center, which
is rendered more unsaturated in the absence of triflate, that is,
in 2b.
Scheme 1
(entries 2–6), the different yields reflecting the relative reactivity
of the olefins.
When furan was used as substrate (Table 2), the reaction
afforded not only the cyclopropane, ethyl fumarate and ethyl
maleate, but also the two diasteromeric ring-opened dienes
(Scheme 2).
Scheme 2
Finally, we explored the activity of the complex [Cu(OTf)(TPN)]
(3), previously reported by Marks and Ibers.12 The presence
of acetonitrile in the medium used for the preparation of the
tris(pyridyl) amine complex 3 was found to be beneficial, leading
to a shorter reaction time and to a more pure compound, free
of Cu(II) contamination. However, unlike 1 and 2a, for 3, the
isolated product was found to contain no acetonitrile. Therefore,
the role of this solvent must be to stabilize and solubilize
copper(I) as the cationic tetrakis(acetonitrile) complex, preventing
its decomposition in solution before the final TPN complex is
formed.
The reaction of styrene with EDA employing 3 (1 mol%) as a
catalyst yielded cyclopropane in 49% (ratio trans : cis 28 : 21).
A significant activation was observed upon addition of NaBAr¢4
(98%, ratio trans : cis 67 : 31), in agreement with the proposal
of Marks and Ibers that a copper-bonded triflate is formed. In
In these cyclopropanation reactions, no green or blue color,
indicative of an oxidation to a Cu(II) species, was observed.
Therefore, we propose that the catalyst resting state is a Cu(I)
species. Accordingly, no broadening was observed in the NMR
lines in the spectra of the reaction crudes. The same can be said of
all the reactions in which EDA serves as carbene source discussed
below.
Compound 1 was also active in olefin aziridination9 employing
=
PhI NTs as nitrene source (Scheme 3, Table 1, entries 7–12).
Table 2 Yields of cyclopropane and ring-opened dienes in the Cu-
catalyzed reactions of furan and EDA
Cat
Addition time
%Cyclopr
ZZ%, ZE%
1
4
12h
15h
58
60
2, 14
12, 12
=
contrast, in the aziridination of styrene with PhI NTs as the
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nitrene source, a quantitative conversion resulted when 3 was used
as catalyst (Table 1, entry 7).
NMR spectrum, an obvious possibility is the operation of a
dynamic process that exchanges the three pyridyl arms. Such
dynamic processes are frequent in Cu(I) chemistry. However, the
1H spectrum of 4 in CD2Cl2 did not change when the temperature
was lowered to 183 K.
A comparison between the catalytic results of the three families
of complexes (TPM, TPC and TPN) shows that, in general, once
the Cu–OTf precatalyst was activated by NaBAr¢4, the latter are
the more active. This, and the fact that no previous copper(I) TPN
complexes have been structurally characterized, prompted us to
isolate and characterize cationic, triflate-free Cu–TPN complexes
as BAr¢4 salts. Thus, equimolar amounts of 3 and NaBAr¢4 were
allowed to react in THF. After THF evaporation, extraction of the
residue in CH2Cl2 and filtration (to eliminate NaOTf) followed by
addition of hexane precipitated a white solid. Its 1H and 13C NMR
spectra were consistent with a formulation [Cu(TPN)(THF)]BAr¢4
(4), and indicated the equivalence of the three pyridyl groups at
room temperature. The chemical shifts of the THF signals in 4 were
indistinguishable from those of free THF; however, their intensity,
consistent with the presence of one THF molecule per copper
atom, did not decrease when 4 was maintained under vacuum
several hours. Slow diffusion of hexane into a CH2Cl2 solution
of 4 afforded crystals, one of which was used for the structural
determination by X-ray crystallography. The results, graphically
displayed in Fig. 1, indicate that 4 exists in the solid state as
the [{Cu(TPN)(THF)}2][BAr¢4]2 salt. The dicationic complex is
a centrosymmetric dimer, in which each TPN ligand acts as
a bidentate chelate towards one of the copper atoms, binding
the other in a monodentate manner through the third pyridyl
group. Therefore, the TPN ligand acts simultaneously as a chelate
and a bridge. A THF molecule completes the pseudotetrahedral
coordination environment of each copper atom. Metrical data are
unremarkable.
While this does not rule out the possibility of a dynamic
process with a very low kinetic barrier, we rather postulate
3
a C3-symmetric, monomeric [Cu(k -TPN)(THF)]+ complex as
the species in solution for three reasons: (a) its instantaneous
structure would be in agreement with the 1H NMR spectrum, (b)
pseudotetrahedral complexes of this type are the ones most often
encountered in Cu(I) complexes of tridentate tripodal ligands, and
(c) such a complex would be entropically favored over the X-ray
characterized dimer. Formation of the latter upon crystallization
would be driven by its lower solubility resulting from its higher
molecular weight. As a matter of fact, the mononuclear complex
3
[Cu(k -TPN)(THF)]+ was found to be the predominant species
in CH2Cl2 by ESI-MS (m/z 383). Moreover, in the presence of
five equivalents of styrene (the conditions used in catalysis), ESI-
3
MS showed that the monomer [Cu(k -TPN)(styrene)]+ (ESI-MS
m/z 415) was the most abundant species in CH2Cl2 solution. The
relative intensity of the lines and the separation between them in
the signals are consistent with monomeric, monocationic copper
complexes.
The catalytic activity of 4 in the reactions mentioned above was
the same when the compound was isolated or generated in situ by
NaBAr¢4 addition to a solution of 3 in THF. When the catalyst
was prepared directly by mixing CuOTf, TPN and NaBAr¢4, the
employment of higher than equimolar amounts of TPN led to a
decrease in the yields of cyclopropanes. This fact was attributed to
the blocking of labile positions in the copper complex by the excess
of ligand, generating a [Cu(TPN)2]+ species. Thus, [Cu(TPN)2]OTf
was obtained by reaction of [Cu(OTf)]2·toluene with the equimolar
1
amount of TPN (see Experimental). In the H and 13C NMR
of the product at room temperature, the only signals observable
were those of the equivalent pyridyl groups (upon lowering the
temperature to 183 K, the signals broadened somewhat but did
not split). A structural determination by X-ray diffraction showed
that the copper atom was in a tetrahedral geometry (Fig. 2), where
each TPN ligand acts as bidentate to the metal center, and the third
pyridyl arm remained uncoordinated. This mode of coordination
for the TPN was known in some Cu(II) complexes,13 however, 5
is the first example of a Cu(I) complex. As expected, the Cu–
˚
˚
N distances in 5 (2.057(3)A) are longer than in the mentioned
2+
˚
Cu(II) complexes (2.020(3)A in [Cu(TPN)2(NCMe)2] , 1.999(3)A
in [Cu(OClO3)2(TPN)2]).
The reaction of styrene with EDA (added over 15 hours)
employing 5 as catalyst (1 mol%) yielded cyclopropanes in 72%
(ratio trans : cis 45 : 27), a yield lower than that obtained with 4.
Compound 4 was also found to be effective in the cyclo-
propanation of furan (Table 2), affording, in addition, the two
diasteromeric ring-opened dienes.
The addition of a carbene fragment to alkynes affords cyclo-
propenes, a reaction less studied than cyclopropanation. The first
catalysts, based on metallic copper or simple Cu(I) or Cu(II) salts,
gave low yields, even at high temperatures.14 Recently, the group of
Pe´rez (no relation to the present author) reported excellent results
with copper(trispyrazolylborate) systems at room temperature.15
We carried out the catalytic reaction of EDA with alkynes using the
Fig. 1 Thermal ellipsoid plot (30%) of the cation of 4. Selected bond
lengths (A) and angles ( ): Cu(1)–N(1) 1.944(8), Cu(1)–N(2) 1.994(9),
Cu(1)–N(3) 2.022(8, Cu(1)–O(1) 2.439(9), N(1)–Cu(1)–N(2) 129.4(4),
N(1)–Cu(1)–N(3) 131.3(4), N(2)–Cu(1)–N(3) 91.9(4), N(1)–Cu(1)–O(1)
96.0(4), N(2)–Cu(1)–O(1) 97.3(4), N(3)–Cu(1)–O(1) 103.8(4).
◦
˚
Since the three pyridyl groups are inequivalent in the solid state
structure of 4, but appear equivalent in the room temperature
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those of the best copper systems, with a lower charge of catalyst
in our case.17
The O–H bonds of alcohols are generally activated preferen-
tially over C–H bonds and insertion is usually preferred over
other reactions. Recently Fu18 and Pe´rez19 have reported effective
copper-based catalysts. Catalyst 4 was found to be highly active for
this reaction, and a low catalyst loading (0.5 mol%) was required.
EDA was added in one portion and the alkoxyesters are obtained
almost quantitatively (Table 5). To the best of our knowledge,
these yields are the highest ever reported.
In the activation of N–H bonds of amines, a problem usually
found is the poisoning of the catalyst by amine coordination.20
We studied the carbene insertion into N–H bonds of primary and
secondary amines with 4 as a catalyst (1 mol%) (Table 6). Even
when EDA and amine were added in one portion, diethyl fumarate
and maleate were not detected. The yields are close to the highest
published results.21 Deactivation of the catalysts due to amine
coordination is often a concern in this type of catalysis; in our
case, high yields were obtained even for aniline, a primary amine,
for which the highest coordinating ability would be expected.
As mentioned above, the position of the nCO bands of LnCu–
CO complexes has been used to gauge the electronic proper-
ties of the L ligands. For TPC and TPM ligands, the LCu–
carbonyl complexes have already been synthetized.8 The com-
pound [Cu(TPN)(CO)]BAr¢4 (6) was prepared by bubbling CO
through a solution of 4 (see Experimental). The nCO band appeared
at 2108 cm-1 in KBr, indicating that the copper center in 6 is
more electron-deficient than those in the compounds with TPM
(2101 cm-1 in KBr) and TPC (2091 cm-1 in KBr) ligands. Moreover,
the comparison of the nCO values indicates that these cationic
compounds with tris(pyridyl) ligands are more electron rich
than the neutral complexes with halogenated trispyrazolylborates,
probably due to the high electron withdrawing effect of the
halogenated substituents in the latter.
˚
Fig. 2 Thermal ellipsoid plot (30%) of 5. Selected bond lengths (A) and
angles (◦):Cu(1)–N(5) 2.022(3), Cu(1)–N(1) 2.039(3), Cu(1)–N(2) 2.072(3),
Cu(1)–N(6) 2.097(3), N(4)–C(11) 1.393(4), N(4)–C(6) 1.420(4), N(4)–C(5)
1.429(4), N(8)–C(31) 1.406(4), N(8)–C(26) 1.429(4), N(8)–C(25) 1.434(4),
N(5)–Cu(1)–N(1) 122.31(11), N(5)–Cu(1)–N(2) 122.19(12), N(1)–Cu(1)–
N(2) 92.65(11), N(5)–Cu(1)–N(6) 93.60(12), N(1)–Cu(1)–N(6) 117.41(11),
N(2)–Cu(1)–N(6) 110.16(11), C(11)–N(4)–C(6) 122.8(3), C(11)–N(4)–
C(5) 120.0(3), C(6)–N(4)–C(5) 117.2(3), C(31)–N(8)–C(26) 119.4(2),
C(31)–N(8)–C(25) 117.9(3), C(26)–N(8)–C(25) 117.8(3).
same methodology than in cyclopropanation, i.e. 1 mol% catalyst,
room temperature, ratio alkyne : EDA= 5 : 1 in CH2Cl2, and EDA
added over 10 hours. The yields are summarized in Table 3.
The performance of 4 in cyclopropanation, aziridination and
cyclopropenation reactions prompted us to study its activity for
the insertion of carbenes into C–H, O–H and N–H bonds.16
We explored the C–H insertion reactions of alkanes and ethers
(Table 4). Reactions were typically run in neat substrate, except
for cyclohexane, hexane and pentane, which required the use of
CH2Cl2 as a co-solvent in order to solubilize the catalyst. For linear
alkanes, secondary C–H bonds were exclusively functionalized
with yields similar to those obtained by Pe´rez.6 For the aromatic
substrates benzene, toluene, and mesitylene, ring-expansion to
7-membered rings (Bu¨chner reaction) occurred exclusively (no
insertion took place in the methyl C–H bonds),17 and mixtures
of the different isomers were yielded. For ethylbenzene, carbene
insertion at the secondary C–H aliphatic bond was also observed.
The yields and distribution of the products are in the range of
Conclusions
Copper(I) complexes with tris(2-pyridyl)methane, tris(2-pyridyl)-
methoxymethane and tris(2-pyridyl)amine are efficient catalysts
for carbene and nitrene transfer reactions, with activities compara-
ble to those shown by the extensively studied tris(pyrazolyl)borate
ligands. Tris(2-pyridyl) amine complexes are the best catalysts,
due to a combination of ease of preparation, stability and their
susceptibly to activation by OTf/BAr¢4 exchange.
Experimental
Table 3 Yields of cyclopropenes in the Cu-catalyzed reactions of listed
acetylenes with EDA
General considerations
Substrate
Yielda
All experiments were carried out at room temperature under a
dinitrogen atmosphere employing Schlenk techniques. The amines
and solvents were freshly distilled prior to use. CH2Cl2 was dried
over CaH2. THF and diethyl ether and were dried over Na–
Phenylacetylene
Diphenylacetylene
1-Hexyne
3-Hexyne
1-Phenyl-1-propyne
27
31
36
43
26
benzophenone, and hexane, pentane and toluene were dried over
i
˚
sodium. MeOH, EtOH and PrOH were stored over 4 A molecular
a Standard conditions: 5 mmol of substrate,1 mmol EDA (added over 11 h),
1 mol% 4, CH2Cl2 (25 mL), a) Yield based on EDA and determined by
1H-NMR spectroscopy, average of two runs. Mass balance was accounted
for by dimethyl maleate and fumarate formation.
sieves for several hours prior for use as substrates. EDA and the
=
remaining reagents were used as received. PhI NTs was prepared
according to a literature procedure22 and stored in a Schlenk
flask under nitrogen at -20 ◦C. For slow addition of EDA, a
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Table 4 Results of the 4-catalyzed insertion of the carbene from EDA into C–H bonds of the listed substrates
Substratea
Products
tb
Yield
85%
5
11
11
45%, 11%
28%, 34%
20
20
25%
27%, 14%, 8%
20
20
27%, 10%, 12%
93%
5
5
79%
93%
a Standard conditions: 20 mL substrate, 1 mol% 4. Yield based on EDA and determined by 1H-NMR spectroscopy, average of two runs. Mass balance
was accounted for by dimethyl maleate and fumarate formation. b Time of addition of EDA (hours).
gas-tight syringe mounted on an automatic syringe pump was
employed. 1H NMR spectra were recorded in CDCl3 on a Bruker
AV-400 spectrometer. An internal standard (hexamethylbenzene
or 1,3,5-tribromobenzene) was added to each reaction mixture
immediately before taking an aliquot. The NMR spectra of all
products were consistent with those reported in the literature.
Yields were estimated by integration of the 1H NMR signals of the
products relative to the internal standard. TPC,23 TPM,10 TPN24
with graphite monochromatized Mo–Ka X-radiation and a CCD
area detector. Due to the poor quality of the crystals, data
collection was taken only to 2q = 46◦, since the intensity of the
reflections was very poor from 40◦ upwards. Raw frame data
were integrated with the SAINT26 program. A semi-empirical
absorption correction was applied with the program SADABS27
The structure was solved by direct methods and refined against
F2 with SHELXTL.28 All non-hydrogen atoms were refined
anisotropically, except for N(1), N(2) and N(4) in the structure
of 4, which had to be kept isotropic since otherwise their ellipsoids
went to non-positive-definite during the refinement. An incipient
disorder was found to affect some atoms of 4, which show large
25
and NaBAr¢4 were prepared according to literature procedures.
Crystallographic details. Crystallographic data for 4 and 5
were collected with a Bruker AXS SMART 1000 diffractometer
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Table 5 Results of the 4-catalyzed insertion of the carbene from EDA
into O–H bonds of the listed alcohols
of a white microcrystalline solid, which was washed with hexane
(3 ¥ 10 mL) and dried under vacuum. Yield: 0.092 g (93%) H
1
NMR(CD2Cl2): 8.36 [d(4.7) 3H, Hpy], 7.78 [dt (7.7, 1.7), 3H,
Hpy], 7.56 [dt (4.7, 1.7), 3H, Hpy], 7.31 [d(7.7), 3H, Hpy], 6.99 [s,
1H, CH] 2.23 [s, 3H, CH3CN]. 13C{1H} NMR(CD2Cl2): 156.8,
148.8, 146.9, 130.3, 129.2 [s, py], 118.1 [s, CN], 58.6 [s, CH], 2.7
[s, CH3CN]. Anal. Calcd. for C19H16CuF3N4O3S: Calcd.: C, 45.60;
H, 3.22; N, 11.20. Found: C, 45.62; H, 3.31; N, 11.23.
Substratea
MeOH
Product
Yieldb
95%
EtOH
iPrOH
95%
88%
Synthesis of [Cu(TPM)(NCMe)]BAr¢4 (2b). To a solution of
[Cu(OTf)]2·toluene (0.050 g, 0.097 mmol) in THF (20 mL) tris(2-
pyridyl)metoxymethane10 (TPM, 0.053 g, 0.193 mmol) and MeCN
(0.5 mL) were added and the mixture was stirred for 30 min. After
solvent concentration to ca. 2 mL, addition of hexane (10 mL)
caused the precipitation of [Cu(TPM)(NCMe)]OTf10 (2a) as a
white solid. 2a was redissolved in CH2Cl2 (10 mL), NaBAr¢4
(0.171 g, 0.193 mmol) was added, the mixture was stirred for 1 hour
and filtered through diatomaceous earth. In vacuo concentration
to a volume of 2 mL and addition of hexane (10 mL) caused the
precipitation of 2b as a white microcrystalline solid, which was
washed with hexane (2x 20 mL) and dried under vacuum. Yield:
0.202 g (87%). 1H NMR(CD2Cl2): 8.65 [s br, 3H, Hpy], 8.10 [s br,
14H, Ho of Ar¢4 and Hpy], 7.47 [m, 7H, Hp of Ar¢4 and Hpy], 3.63
[s, 3H, OCH3], 2.23 [s, 3H, CH3CN].
Phenol
95%c
a standard conditions: 1.1 mmol substrate, 1 mmol EDA added in one
portion, 0.5 mmol% 4, CH2Cl2 (10 mL). b Yield based on EDA, and
determined by 1H-NMR spectroscopy, average of two runs. Mass balance
was accounted for by dimethyl maleate and fumarate formation. c EDA
added over 30 min.
Table 6 Results of the 4-catalyzed insertion of the carbene from EDA
into N–H bonds of the listed amines
Substratea
Product
treac(h)
1c
Yieldb
95%
Synthesis of [Cu(TPN)(OTf)] (3). A mixture of [Cu(OTf)]2·
toluene (0.050 g, 0.097 mmol) and tris(2-pyridyl)amine24 (TPN,
0.048 g, 0.193 mmol) in THF/MeCN (20/0.5 mL) was stirred
until precipitation of a white solid (15 min.), which was washed
with hexane and dried in vacuo.29 Yield: 0.077 g (87%). 1H NMR
(CDCl3): 8.25 [d(4.9), 3H], 8.10 [dt (8.0, 1.5), 3H], 7.49 [dt (4.9,
1
4
42%d
1.5), 3H], 7.05 [d (8), 3H]. 13C{ H} NMR(CDCl3): 156.8 [s], 153.1
[s], 144.9 [s], 125.4 [s], 123.5 [s]. 19F NMR (CDCl3): -77.19. Anal.
Calcd. for C16H12CuF3N4O3S: Calcd.: C, 41.70; H, 2.62; N, 12.16.
Found: C, 41.94; H, 2.78; N, 12.25.
24
14
79%
95%
Synthesis of [Cu(TPN)(THF)]2(BAr¢4)2 (4). A mixture of 3
(0.090 g, 0.193 mmol) and NaBAr¢4 (0.170 g, 0.193 mmol) in
THF (20 mL) was stirred for 2 hours and the solvent was removed
under vacuum. The residue was extracted with CH2Cl2, filtered
through diatomaceous earth and concentrated to 2 mL. Addition
of hexane caused the precipitation of 4 as a white microcrystalline
solid. By slow diffusion of hexane into a concentrated solution of
4 in CH2Cl2 at -20 ◦C white crystals were obtained, one of which
was employed for an X-ray structure determination. Yield: 0.198 g
11e
46%
a Standard conditions:1 mmol substrate, 1 mmol EDA added in one
portion, 0.5 mol% 4, CH2Cl2 (10 mL). b Yield determined by 1H-NMR
spectroscopy, average of two runs. Mass balance was accounted for by
dimethylmaleate and fumarate formation. c EDA added over 30 min.
d 1 mol% 4. e Time of addition of EDA 11 hours.
1
(83%). H NMR (CDCl3): 8.30–8.05 [m, 3H, Hpy], 7.80–7.70 [m,
8H, Ho of Ar¢4], 7.54–7.39 [m, 7H, Hp of Ar¢4 and Hpy], 7.25–
7.10 [m, 3H, Hpy], 6.85–6.60 [m, 3H, Hpy], 3.77 [m, 4H, CH2 of
1
THF], 1.87 [m, 4H, CH2 of THF]. 13C{ H} NMR(CDCl3): 162.1
[c (1JCB= 49.9 Hz), Ci of Ar¢4], 156.8 [s, Cpy], 149.1 [s, Cpy], 135.9
[s, Cpy], 135.1 [s, Co of Ar¢4], 129.4 [s, Cpy], 129 [c (2JCF= 31.7 Hz),
Cm of Ar¢4], 126.7 [s, Cpy], 123.1 [c (1JCF= 272.4 Hz), CF3 of Ar¢4],
117.8 [s, Cp of Ar¢4], 68.1 [s, CTHF], 25.9 [s, CTHF]. Anal. Calcd. for
C51H32BCuF24N4O: Calcd.: C, 49.12; H, 2.59; N, 4.49. Found: C,
49.24; H, 2.78; N, 4.71.
ellipsoids. Despite of some attempts of modelling these atoms in
split positions, the quality of the results did not improve. This,
and the resulting low C–C bond precision, can attributed to the
poor quality of the crystal. Hydrogen atoms were set in calculated
positions and refined as riding atoms, with a common thermal
parameter.
B) To a solution of [Cu(OTf)]2·toluene (0.050 g, 0.097 mmol) in
THF (20 mL), TPN (0.048 g, 0.193 mmol) and NaBAr¢4 (0.171 g,
0.193 mmol) were added and the mixture was stirred for 30 min.
After removing the solvent, the residue was extracted in CH2Cl2,
filtered through a diatomaceous earth, concentrated to a volume
Synthesis of [Cu(TPC)(NCMe)]OTf (1). Tris(2-pyridyl)-
methane23 (TPC, 0.047 g, 0.193 mmol) was added to a solution
of [Cu(OTf)]2·toluene (0.050 g, 0.097 mmol) in a mixture of
THF/MeCN (20/0.5 mL) causing immediately the precipitation
380 | Dalton Trans., 2009, 375–382
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of 2 mL and addition of hexane (10 mL) caused the precipitation
of 4 as a white solid. The spectroscopic data matched with that
reported above for 4.
transferred to an NMR tube. Yields were estimated using 1H NMR
spectroscopy by integration of product resonances relative to the
internal standard.
Carbene insertion into C–H bonds. A solution of EDA
(1 mmol, 0.105 mL) in substrate (10 mL) was added using a syringe
pump over the specified period of time to a Schlenk flask charged
with 4 (0.012 g, 0.005 mmol), 10 mL of the substrate and CH2Cl2
(10 mL, only for cyclohexane, pentane, and hexane substrates).
An internal standard, 1,3,5-tribromobenzene (0.030 mmol, 10 mg)
was added, an aliquot (1 mL) was filtered through diatomaceous
earth, and the solution was concentrated to ~0.5 mL. CDCl3
(0.5 mL) was added and the sample was transferred to an NMR
tube. Yields were estimated using 1H NMR spectroscopy by
integration of product resonances relative to the internal standard.
Synthesis of [Cu(TPN)2]OTf (5). A mixture of [Cu(OTf)]2·
toluene (0.050 g, 0.097 mmol) and tris(2-pyridyl)amine (TPN,
0.096 g, 0.386 mmol) in THF (20 mL) was stirred for 15 min. In
vacuo concentration to a volume of 5 mL and addition of hexane
caused the precipitation of 5 as a yellow solid. Slow diffusion
of hexane into a solution of 5 in CH2Cl2 at -20 ◦C afforded
yellow crystals, one of which was employed for an X-ray structure
determination. Yield: 0.121 g (89%). 1H NMR (CDCl3): 8.61–8.11
1
[m, 3H], 7.90–7.55 [m, 3H], 7.45–6.85 [m, 6H]. 13C{ H} NMR
(CDCl3): 154.2 [s br], 148.7 [s br], 139.1 [s br], 121.6 [s br], 120.2 [s
br]. Anal. Calcd. for C31H24CuF3N8O3S: Calcd.: C, 52.54; H, 3.42;
N, 15.80. Found: C, 51.23; H, 3.74; N, 16.09.
Carbene insertion into O–H bonds. EDA (1 mmol, 0.105 mL)
was added in one portion to a solution of 4 (0.006 g, 0.0025 mmol)
and the alcohol (1.1 mmol) in CH2Cl2 (10 mL). After 4 hours, an
aliquot (0.5 mL) was taken and analyzed as described above, using
C6Me6 (0.055 mmol, 9 mg) as an internal standard. For phenol,
best results were obtained when EDA was added over 30 min.
Synthesis of [Cu(TPN)(CO)]BAr¢4 (6). CO was bubbled
through a solution of 4 (0.09 mmol) in CH2Cl2 (10 mL) for
30 min. By addition of hexane (20 mL) into this solution, a
white microcrystalline solid was obtained, which was washed with
hexane and dried under vacuum. This compound decomposed
after few hours in CH2Cl2 solution. IR(KBr) nCO(cm-1):2108.
IR(CH2Cl2) nCO(cm-1): 2103. 1H NMR (CD2Cl2): 8.10 [d(4.5), 3H],
7.98 [t(7.5), 3H], 7.73 [m, 8H, Ho of Ar¢4], 7.56 [m, 4H, Hp of Ar¢4],
7.42 [d(8,2), 3H], 7.26 [t(6.2), 3H].
Carbene insertion into N–H bonds. EDA (1 mmol, 0.105 mL)
was added in one portion to a solution of 4 (0.012 g, 0.005 mmol)
and the amine (1 mmol) in CH2Cl2 (10 mL).The mixture was
stirred for the specified amount of time, then an aliquot was taken
and analyzed as described above using C6Me6 (0.055 mmol, 9 mg)
as the internal standard for aniline, and 1,3,5-tribromobenzene
(0.030 mmol, 10 mg) as the internal standard for the others amines.
Cyclopropanation. A solution of EDA (1 mmol, 0.105 mL) in
CH2Cl2 (10 mL) was added over 10 h using a syringe pump to a
solution of the corresponding catalyst (0.01 mmol) and the olefin
(5 mmol) dissolved in CH2Cl2 (15 mL). The solution was stirred for
two hours after complete addition of EDA. An internal standard,
C6Me6 (0.055 mmol, 9 mg) was added, an aliquot (1 mL) was
then filtered through silica gel, and the solution was concentrated
to ~0.5 mL. CDCl3 (0.5 mL) was added and the sample was
transferred to an NMR tube. Yields were estimated using 1H NMR
spectroscopy by integration of product resonances relative to the
internal standard. Only for the cyclopropane from styrene the
signals due to the different diastereomers appeared at sufficiently
different chemical shifts so that their integration could be used to
obtain an estimation of the trans/cis ratio.
Acknowledgements
We thank Principado de Asturias (Grant IB05-069 administered
by FICYT), Ministerio de Ciencia y Tecnolog´ıa (CTQ2006-
07036/BQU and CTQ-2006-08924) and Junta de Castilla y Leo´n
(VA017B08 and VA070A08) for support. D. M. thanks Ministerio
de Educacio´n y Ciencia for a Ramo´n y Cajal contract.
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382 | Dalton Trans., 2009, 375–382
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©