Synthesis and structural characterisation of (aryl-BIAN)copper(i) complexes and their application as catalysts for the cycloaddition of azides and alkynes

Article abstract of DOI:10.1039/c2dt11854h

A series of Ar-BIAN-based copper(i) complexes (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine) were synthesised and characterised by ¹H and ¹³C NMR spectroscopies, FT-IR spectroscopy, MALDI-TOF-MS spectrometry, cyclic voltammetr

Full text of DOI:10.1039/c2dt11854h

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PAPER
Synthesis and structural characterisation of (aryl-BIAN)copper(I) complexes
and their application as catalysts for the cycloaddition of azides and alkynes†
Lidong Li,a Patrícia S. Lopes,a Vitor Rosa,b Cláudia A. Figueira,a M. Amélia N. D. A. Lemos,c
M. Teresa Duarte,a Teresa Avilés*b and Pedro T. Gomes*a
Received 1st October 2011, Accepted 16th January 2012
DOI: 10.1039/c2dt11854h
A series of Ar-BIAN-based copper(I) complexes (where Ar-BIAN = bis(aryl)
acenaphthenequinonediimine) were synthesised and characterised by 1H and 13C NMR spectroscopies,
FT-IR spectroscopy, MALDI-TOF-MS spectrometry, cyclic voltammetry and single crystal X-ray
diffraction. The bis-chelated complexes of general formula [Cu(Ar-BIAN)2]BF4 (where Ar = C6H5 (1),
4-iPrC6H4 (3), 2-iPrC6H4 (4)) were prepared by reaction of [Cu(NCMe)4]BF4 with two equivalents of the
corresponding Ar-BIAN ligands, in dichloromethane, while the mono-chelated complexes of the type
[Cu(Ar-BIAN)L2]BF4 (where Ar = 2,6-iPr2C6H3, L = PhCN (6); Ar = 4-iPrC6H4, L = PPh3 (7)) were
readily accessible by treatment of [Cu(NCR)4]BF4 (R = Me, Ph) with one equivalent of the corresponding
Ar-BIAN ligands in the absence or presence of two equivalents of PPh3, in the same solvent. The
structures of complexes 3, 4, 6 and 7 were obtained by single crystal X-ray diffraction, showing distorted
tetrahedral geometries around the copper centres in all cases. The electrochemical studies of these
complexes and of the already reported [Cu(2,4,6-Me3C6H2-BIAN)2]BF4 (2) and [Cu(2,6-iPr2C6H3-
BIAN)(NCMe)2] (5), demonstrated that the bis-chelated complexes 1–4 undergo a reversible one-electron
reduction or oxidation processes on copper, while the mono-chelated complexes 5–7 show a partially
reversible oxidation and an irreversible reduction feature. Both kinds of (Ar-BIAN)copper(I) complexes
are active catalysts for the copper(I)-catalysed azide–alkyne cycloaddition reaction (CuAAC). Complex 7,
bearing PPh3 ligands, exhibits the highest catalytic activity, which is comparable with that of the typical
CuSO4–sodium ascorbate catalyst system.
been extensively used in organic synthesis,3 polymer science,4
Introduction
biological systems,5 medicinal chemistry,6,7 and material
science.3c,4a
Copper(I) compounds have many applications in homogeneous
catalysis.1 Among these applications is their use as catalysts
The CuAAC reaction is generally promoted by a multiple
component catalyst system, e.g., CuSO4–sodium ascorbate2a and
for the Huisgen 1,3-dipolar cycloaddition reaction of azides
CuI/DIPEA (DIPEA = diisopropylethylamine).8 In the former
and alkynes (CuAAC), which can be regarded as the most
efficient “click” reaction known to date.2 This reaction has
case, an excess of reducing agent is necessary to stabilise the in
situ formed copper(I) species, while in the latter case, the pres-
ence of ancillary ligands is essential to promote the reaction and
aCentro de Química Estrutural, Departamento de Engenharia Química,
to avoid formation of undesired by-products such as diacetylenes
Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco
and bistriazoles. Heterogeneous copper(0) and copper(I) species
Pais, 1049-001 Lisboa, Portugal. E-mail: pedro.t.gomes@ist.utl.pt;
such as copper(0) turnings/clusters,9 copper(0)–cuprous oxide
Fax: +351 218419612Tel: +351 218419612
bREQUIMTE, Departamento de Química, Faculdade de Ciências e
Tecnologia, Universidade Nova de Lisboa, Caparica 2829-516,
Portugal. E-mail: tap@dq.fct.unl.pt; Fax: +351 212948550;
Tel: +351 212948559
nanoparticles10 and charcoal-immobilised copper nanoparticles11
provide alternative catalysts for the production of triazoles.
However, although numerous nitrogen-containing ligands that
may coordinate or ligate to copper(I) to form copper(I) com-
plexes, such as bipyridines, Schiff bases, phenanthrolines, pyri-
dine-containing compounds and polytriazoles, have been
extensively used in situ and screened for high activities,12 only a
scarce number of well-defined nitrogen-containing ligand-co-
ordinated copper(I) complexes have been directly employed to
promote the CuAAC reaction.13
cInstituto de Biotecnologia e Bioengenharia, Centro de Engenharia
Biológica e Química, Instituto Superior Técnico, Universidade Técnica
de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
†Electronic supplementary information (ESI) available: tables contain-
ing: electrochemical data for the ligands L1–L5 (Table S1), energies of
the HOMO and LUMO of ligands L1–L5 (Table S2), and crystal data
and structure refinements for complexes 3, 4, 6 and 7 (Table S3); figures
containing: the cyclic voltammograms of ligand L4 (Fig. S1), and the
plot of Epox(I) versus E(HOMO) of the ligands L1–L5 (Fig. S2). CCDC
830550–830553. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt11854h
The bis(aryl)acenaphthenequinonediimine compounds (Ar-
BIAN),14 proved to be very efficient bidentate nitrogen ligands
5144 | Dalton Trans., 2012, 41, 5144–5154
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for the formation of a wide range of robust homogeneous cata-
lysts.14a,15 In this context, we have been interested in the chem-
istry of these ligands and their corresponding metal complexes.16
Recently, we and other authors reported the synthesis and charac-
terisation of a limited number of Ar-BIAN copper(I) com-
plexes.17,18 In the present work, we describe a further set of
cationic Ar-BIAN copper(I) complexes of the type [Cu(Ar-
BIAN)L2]BF4, where L = PhCN, PPh3 and L2 = Ar-BIAN and,
along with the complexes already reported,17 investigate their
catalytic performances in the copper(I)-catalysed azide–alkyne
cycloaddition reaction (CuAAC).
Results and discussion
Syntheses and characterisation of (Ar-BIAN)copper(I)
complexes
Treatment of a suspension of [Cu(NCMe)4]BF4, in dichloro-
methane, with a solution of Ar-BIAN in the same solvent gives
rise to mono- or bis-chelated copper(I) complexes, [Cu-
(Ar-BIAN)(NCMe)2]BF4 and [Cu(Ar-BIAN)2]BF4, respectively,
the selectivity of the reaction substantially depending on the
steric bulk of the aryl groups and on the molar ratio of ligand to
metal used, as confirmed experimentally and theoretically in our
previous work for compounds 2 and 5 (Scheme 1).17
Reaction of [Cu(NCMe)4]BF4 with the less bulky Ar-BIANs,
where Ar = C6H5 (L1), 2,4,6-Me3C6H2 (L2), 4-iPrC6H4 (L3),
and 2-iPrC6H4 (L4), in a 1 : 2 stoichiometry, favours the for-
mation of the homoleptic bis-chelated complexes [Cu(Ar-
BIAN)2]BF4 (Ar = C6H5 (1), 2,4,6-Me3C6H2 (2), 4-iPrC6H4 (3)
and 2-iPrC6H4 (4)) in high yields (72–84%), as represented in
Scheme 1. This can be ascribed to the “chelating effect” in
which the bidentate Ar-BIAN ligand exhibits an enhanced
affinity for the cationic copper(I) compared to the monodentate
acetonitrile. Similar trends were observed in the reaction of [Ag
(NCMe)4]BF4 with the ligand 2,4,6-Me3C6H2-BIAN.17 The
reaction of [Cu(NCMe)4]BF4 with the bulkier ligand 2,6-
iPr2C6H3-BIAN (L5) exclusively leads to the mono-chelated
complex [Cu(2,6-iPr2C6H3-BIAN)(NCMe)2]BF4 (5) (Scheme 1),
regardless of the stoichiometry of ligand to metal used (e.g., 1 : 1
and 2 : 1).17 The heteroleptic mono-chelated complex [Cu(2,6-
iPr2C6H3-BIAN)(NCPh)2]BF4 (6) is readily accessible by the
reaction of [Cu(NCPh)4]BF4 with an equimolar amount of 2,6-
iPr2C6H3-BIAN, in moderate yield (67%) (Scheme 1). Addition-
ally, the mono-chelated complex [Cu(4-iPrC6H4-BIAN)(PPh3)2]
BF4 (7) can be prepared in good yield (92%) by reaction of [Cu
(NCMe)4]BF4 with an equimolar amount of 4-iPrC6H4-BIAN, in
the presence of two equivalents of PPh3. Its analogue [Cu(C6H5-
BIAN)(PPh3)2]PF6 was recently synthesised by Knör and co-
workers using the same procedure.18e
Scheme 1 The Ar-BIAN-based copper(I) complexes synthesised.
anticipated shifts of 1H NMR resonances due to enhanced aniso-
tropic shielding, the 31P NMR resonances were still absent. As
five equivalents of free PPh3 were added into the CD2Cl2 sol-
ution of complex 7, at 20 °C, except the appearance of the corre-
sponding additional aromatic hydrogen resonances in the 1H
NMR spectra, neither coordinated nor free PPh3 were observed
in the 31P NMR spectrum. On cooling this solution to −80 °C,
the 31P NMR remained invariant with no visible resonances.
1
Since the solution colour (deep red) and the H chemical shifts
of complex 7 in CD2Cl2 did not change with time and tempera-
ture, except for the anisotropic shielding shifts, we exclude the
possibility of complex decomposition or other side reactions
upon the addition of an excess of PPh3. This absence of reson-
ances in the 31P NMR spectrum seems to be consistent with the
fact that an extensive dissociation of complex 7 and a fast
exchange of free and coordinated PPh3 occur in solution (eqn (1)).
All the mono- and bis-chelated copper(I) complexes 1–7 were
1
characterised by H and 13C{1H} NMR spectroscopies, IR spec-
troscopy, elemental analysis, and MALDI-TOF-MS spec-
trometry. From the 1H NMR data, it can be seen that the
resonances of the Ar-BIAN ligands have shifted to lower field
upon coordination, being consistent with donation of electron
density from the Ar-BIAN ligand to the metal centre. The 31P
NMR resonances of complex 7 were not observed, in CD2Cl2, at
room temperature. Upon cooling down to −80 °C, except the
ꢁnPPh3
þ
½CuðAr-BIANÞðPPh3Þ2ꢀþ
ðn ¼ 1 or 2Þ
½CuðAr-BIANÞðPPh Þ2ꢁnꢀ
Q
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
R
3
þnPPh3
ð1Þ
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Analogous behaviours have also been observed for phos-
phorus-coordinated nickel(0) complexes of the type [Ni(PR3)4],
where PR3 = PEt3, PMePh2, or PPh3.19
The IR spectra of the complexes were recorded as Nujol
mulls. Their characteristic absorption bands in the region ν
1651–1614 cm−1 of the IR spectra, which are ascribed to the
stretching vibration absorption of the iminic CvN bonds, are
markedly shifted to lower frequencies compared to those of the
free Ar-BIAN (ν 1674–1637 cm−1) due to coordination of these
ligands to the copper(I) ions. Complex 6 shows a strong absorp-
tion around ν 2246.7 cm−1, being assigned to the stretching
vibration of the CuN bonds of the PhCN ligands. The absorp-
tion bands assigned to the BF4− anion are displayed in the range
of ν 1058–1047 cm−1. In the MALDI-TOF-MS spectra of com-
plexes 1–7, the [Cu(Ar-BIAN)2]+ parent ions of the bis-chelated
complexes were observed at m/z 727.2 (100%) for 1, 895.2
(100%) for 3 and 895.2 (20%) for 4, and their corresponding
[Cu(Ar-BIAN)]+ fragments at m/z 395.1 (27%), 479.7 (20%)
and 479.1 (100%), respectively. In the case of the mono-chelated
complexes, the parent ions are not observed, but [Cu(Ar-
BIAN)]+ fragments appear at m/z 563.2 (47%) for 6 and 479.1
(22%) for 7. In the case of 7, it is worth noting that the most
intense peak, at m/z 895.1 (100%), is assigned to the fragment
[Cu(4-iPrC6H4-BIAN)2]+, which is originated by the gas phase
rearrangement of the parent molecule.
Fig. 1 An ORTEP diagram of molecule B of complex 3 with 50%
probability ellipsoid displacement. A methyl carbon of one of the four
isopropyl groups is disordered over two positions (50 : 50% occupancy
for each carbon), one of them being represented by a no octant-shading
white sphere with a dashed bond. The counteranion (BF4−) and calcu-
lated hydrogen atoms were omitted for clarity. The inset exhibits the
dihedral angle ω. Selected bond distances (Å) and angles (°): Cu1B–
N1B 1.988(4), Cu1B–N2B 2.028(3), Cu1B–N3B 1.989(4), Cu1B–N4B
2.028(4), N1B–C1B 1.293(6), N2B–C12B 1.280(6), N3B–C31B 1.281
(6), N4B–C42B 1.288(6), N1B–Cu1B–N2B 82.40(14), N3B–Cu1B–
N4B 82.12(15).
X-ray diffraction
Crystals of complexes 3, 4, 6 and 7 suitable for single crystal
X-ray diffraction were obtained by slow diffusion of pentane
into their dilute dichloromethane solution, at −20 °C. Complexes
4 and 7 crystallised in the orthorhombic system, space group
Fddd and Pbca, respectively, while complexes 3 and 6 crystal-
lised in the monoclinic system, space group P21/c and P21/n,
respectively. Each of the complexes has an ionic nature, being
complexes 3 and 4 indicates that ω varies with the volume of the
aryl substituents, the less bulky ones favouring high values of ω.
Another feature of the bis-chelated complexes is that the relative
orientation of the aryl and acenaphthene rings, which is charac-
terised by the dihedral angle τ between the aryl and ace-
naphthene ring planes, also varies with the bulkiness of the aryl
substituents. In the molecule of complex 3 represented in Fig. 1,
the four para-isopropyl substituted aryl groups are diversely
oriented with respect to the corresponding acenaphthene plane,
displaying angles of τ = 56.2(3), 65.9(2), 77.9(3) and 43.6(3)°,
while in complex 4 (containing 2-isopropyl substituted phenyl
rings) an angle τ = 75.65(12)° is determined. A comparison of
these values with a τ value of 89.79(11)° for complex 217 (con-
taining 2,4,6-trimethyl substituted phenyl rings) shows that this
dihedral angle is sensitive to the bulkiness and, mainly, to the
number of substituents at the ortho aryl group positions, the 2,6-
disubstitued case leading to a higher value of τ.
In the case of the heteroleptic mono-chelated complexes 6 and
7, distorted tetrahedral geometries around the copper centres are
also adopted, with dihedral angles ω = 87.99(9), 85.75(12)
(complex 6 has two independent molecules in the asymmetric
unit) and 78.88(5), respectively (see Figs 3 and 4), this angle
now being defined between the copper(I)-diimine five-membered
ring plane and the plane bearing the copper, the two nitrile nitro-
gen and the two nitrile carbon atoms, for complex 6, or the plane
−
composed of a chelated copper(I) cation and a BF4 anion. For
the homoleptic bis-chelated complexes 3 and 4, the copper(I)
centres are coordinated by the four iminic nitrogens, adopting
distorted tetrahedral geometries. Their ORTEP diagrams and the
most relevant bond distances and angles are displayed in Figs 1
and 2. Their corresponding bond distances are comparable,
being consistent with those of complex 2,17 whereas the bond
angles remarkably vary with the aryl substituents and the relative
orientation of the aryl and acenaphthene groups (vide infra).
Their deviation from an ideal tetrahedral geometry can be
defined by the dihedral angle (ω) between the two copper(I)-
diimine five-membered ring planes, their corresponding atoms
being practically coplanar. For an ideal tetrahedral geometry, ω is
equal to 90°, while for a square planar one, ω should be 0°. In
complex 3, as four independent molecules are present in the
asymmetric unit, the corresponding dihedral angles ω are 84.73
(18), 89.39(18), 88.52(18) and 80.99(19)°, one of them being
represented in the inset of Fig. 1, while in complex 4 a single
dihedral angle of ω = 55.29(8)° is observed (see the inset in
Fig. 2). It is evident that complex 4 deviates significantly more
from the ideal tetrahedral geometry than complex 3, the latter
being close to the ideal case. The comparison of the dihedral
angle of ω = 62.17(10)° for complex 217 with those of
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Fig. 3 An ORTEP diagram of molecule B of complex 6 with 50%
probability ellipsoid displacement. The counteranion (BF4−) and calcu-
lated hydrogen atoms were omitted for clarity. The inset exhibits the
dihedral angle ω. Selected bond distances (Å) and angles (°): Cu1B–
N1B 2.108(4), Cu1B–N2B 2.080(4), Cu1B–N3B 1.958(5), Cu1B–N4B
1.929(5), N1B–C1B 1.272(6), N2B–C12B 1.286(6), N3B–C37B 1.165
(7), N4B–C44B 1.144(7), N1B–Cu1B–N2B 80.51(14), N3B–Cu1B–
N4B 112.17(19).
Fig. 2 An ORTEP diagram of complex 4 with 50% probability ellip-
soid displacement. The counteranion (BF4−) and calculated hydrogen
atoms were omitted for clarity. The inset exhibits the dihedral angle ω.
Selected bond distances (Å) and angles (°): Cu1–N1 2.0256(19), N1–C1
1.287(3), N1–Cu1–N1f 83.00(7). Cu is sitting in a crystallographically-
imposed 222 symmetry. (Symmetry operations: d) −x + 1/4, −y + 1/4, z;
e) x, −y + 1/4, −z + 1/4; f) −x + 1/4, y, −z + 1/4).
defined by the copper and the two phosphorus atoms, for
complex 7, respectively. These two complexes display approxi-
mately ideal tetrahedral geometries around their copper atoms.
Their corresponding bond distances are comparable, but the
bond angles are evidently different due to the variable orien-
tation of the aryl and acenaphthene planes. For instance, in
complex 6, the latter are almost perpendicular (τ = 88.8(3) and
87.4(3)°), giving rise to angles C(imine)–N(imine)–C(aryl) of
117.2(4) and 117.6(4)° (see Fig. 3), whereas in complex 7, these
two planes substantially deviate from perpendicularity (τ = 61.07
(12) and 70.34(11)°), leading to angles C(imine)–N(imine)–C
(aryl) of 122.7(2) and 120.9(2)° (see Fig. 4).
Electrochemical studies
Fig. 4 An ORTEP diagram of complex 7 with 50% probability ellip-
soid displacement. The counteranion (BF4−), a dichloromethane solvate
molecule and calculated hydrogen atoms were omitted for clarity. The
inset exhibits the dihedral angle ω. Selected bond distances (Å) and
angles (°): Cu1–N1 2.119(2), Cu1–N2 2.112(2), Cu1–P1 2.2640(8),
Cu1–P2 2.2841(8), N1–C1 1.285(3), N2–C12 1.283(3), N1–Cu1–N2
78.95(8), P1–Cu1–P2 124.36(3).
It is well-known that only a two electron reduction peak in cyclic
voltammetry, corresponding to the process Cu(II) + 2e− → Cu
(0), is commonly observed for the electroreduction of Cu(II) in
water, in the absence of ligands that stabilise Cu(I). The
reduction of Cu(II) to Cu(I) is a slow step, followed by a fast
reduction of [Cu(H2O)y]+ to Cu(0), whereas, in the presence of
stronger bases such as Cl−, CN− or NH3 in water, this electro-
reduction occurs at two well-separated stages, corresponding to
the processes Cu(II) + e− → Cu(I) and Cu(I) + e− → Cu(0),
respectively.20 The Cu(I) species is remarkably stabilised by the
presence of the bases. This might be the reason why the formed
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Table 1 Electrochemical data for the complexes 1–7a
Anodic scan
Cathodic scan
Complex
Epox(I)b
Epred(I)b
E1/2ox(I)c
Epox(II)b
Epred(III)b
Epox(III)b
E1/2red(III)c
Epred(IV)b
Epred (V)b
1
2
3
4
5
6
7
0.45
0.49
0.30
0.51
0.67
0.69
0.77
0.28
0.39
0.16
0.38
0.30
0.32
0.28
0.37
0.44
0.23
0.45
1.26
1.45
0.57
1.46
1.86
−1.30
−1.42
−1.36
−1.35
−1.21
−1.13
−1.36
−1.18
−1.34
−1.25
−1.25
−1.24
−1.38
−1.31
−1.30
−0.98
−1.94
−1.77
−1.91
−1.80
−1.45
−1.86
−1.64
−2.15
−2.01
−2.07
−2.15
1.10
a General conditions: [NBu4][BF4]–CH2Cl2 electrolyte solution, Pt-disk working electrode, scan rate: 200 mV s−1; all potentials are given in V versus
ox
red
c
ox
red
Fc–Fc+ redox couple. b Ep and Ep stand for oxidation and reduction peak potentials, respectively. E1/2 and E1/2 are the half-wave oxidation
and reduction potentials, respectively.
triazole products and additional ligands or bases have a rate-
accelerating effect on the CuAAC reaction. To investigate this
effect amongst the present copper(I) complexes, we studied the
electrochemical behaviours of complexes 1–7, in dichloro-
methane, using cyclic voltammetry, and also of the correspond-
ing free Ar-BIAN ligands (Ar = C6H5 (L1), 2,4,6-Me3C6H2
(L2), 4-iPrC6H4 (L3), 2-iPrC6H4 (L4) and 2,6-iPr2C6H3 (L5))
for comparison. The results are presented in Tables 1 and S1 (the
latter in ESI†), respectively. All the potential values are given
relative to the Fc–Fc+ (ferrocene–ferrocenium ion redox couple)
reference electrode.
In the cyclic voltammograms of all the ligands L1–L5, a
reduction peak IIIred, at ca. −2.0 V, was observed, as shown in
Table S1,† and exemplified in Fig. S1b (in ESI†) for L4. After
reduction of the ligand at IIIred, and upon reversal of the potential
scan, an oxidation peak IVox appeared in the range of −1.4 to
−1.7 V, depending on the ligands (Fig. S1b†). Upon oxidation
of ligands L1–L5, two irreversible oxidation peaks were
observed in the ranges of 0.6–0.9 V (Fig. S1a†) and 1.1–1.5 V,
respectively (Table S1†). The latter is likely to originate from the
oxidised product of the ligands. Upon reversal of the potential
scan after peak Iox, two reduction waves 1red and 2red appear,
corresponding to the reduction of the products formed during the
oxidation process occurring in peak Iox; the reduction wave 2red
corresponds to a quasi-reversible process (see Table S1†), as rep-
resented in Fig. S1a†. As expected, the potential of the Iox peak
(Epox(I)) varies consistently with the energy of the highest occu-
pied molecular orbital (HOMO) of the ligands (see Fig. S2 in
ESI†), the latter being calculated using the HF/DFT B3LYP/6-
31G* model (see Table S2 in ESI†).
In the cyclic voltammograms of complexes 1–7, two oxidation
peaks Iox and IIox were observed for each case, as shown in
Table 1 and exemplified in Fig. 5. For the bis-chelated com-
plexes 1–4, Iox is a reversible process, varying with the nature of
ox
the complexes in the range of 0.30–0.50 V (E1/2 = 0.23–0.44
V), and IIox is an irreversible one, located at ca. 0.57–1.46 V
(Fig. 5a), while in the case of mono-chelated complexes 5–7, Iox
is a partially reversible process, lying at ca. 0.70 V, and IIox is
also an irreversible one (Fig. 5b). It is likely that, for complexes
1–4, the first oxidation process could be described by eqn (2).
þ
2þ
½CuðiÞðAr-BIANÞ2ꢀ ꢁ 1eꢁ
½CuðiiÞðAr-BIANÞ ꢀ
ð2Þ
Q
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
R
2
In the case of the oxidation of the mono-chelated complexes
5–7, although it appears partially reversible, the difference in the
oxidation and reduction waves is quite large, indicating that
Fig. 5 Cyclic voltammograms of (a) complex 3 and (b) complex 7, obtained at a scan rate of 200 mV s−1
.
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Table 2 Catalytic activities of complexes 1–7 in the CuAAC reactiona
some rearrangement or chemical process is likely occurring upon
the oxidation represented in eqn (3).
þ
2þ
½CuðiÞðAr-BIANÞL2ꢀ ꢁ 1eꢁ
½CuðiiÞðAr-BIANÞL ꢀ ð3Þ
Q
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
R
2
The oxidation of the mono-chelated complexes 5–7 (eqn (3))
has a partially reversible nature, probably due to the presence of
the additional ligand L (e.g., MeCN, PhCN or PPh3). Wang
et al. observed a similar reversible oxidation peak in the CuSO4–
TCEP catalyst system, being ascribed to the TCEP coordinated
copper(I) species, which values are comparable with those
obtained for our complexes.21 The cathodic peaks patterns of
complexes 1–7 vary substantially with their nature. For the bis-
Catalyst
(mol%)
Time
(h)
Temperature
(°C)
Yield
(%)
TOF
(h−1
Entry
)
1
2
3
4
5
6
7
8
1 (5)
2 (5)
3 (5)
4 (5)
5 (5)
6 (5)
7 (5)
1 (5)
2 (5)
3 (5)
4 (5)
5 (1)
6 (1)
7 (1)
36
36
36
36
36
36
36
24
24
24
24
24
24
24
20
20
20
20
20
20
20
50
50
50
50
50
50
50
11.0
4.2
14.3
8.7
26.4
25.6
100.0
63.7
63.1
81.8
48.3
44.4
47.6
100.0
0.061
0.023
0.079
0.048
0.147
0.142
≥0.556b
0.531
0.526
0.682
0.403
1.850
1.983
≥4.167b
chelated complexes 1–4, a reversible peak IIIred (E1/2 = −1.24
red
to −1.38 V, Table 1) was observed (Fig. 5a), while for the mono-
chelated complexes 5–7, two irreversible peaks IIIred and IVred
appeared (Fig. 5b). The reversible reduction of the bis-chelated
complexes 1–4 at IIIred can be tentatively assigned to a one-elec-
tron reduction of copper(I):
9
10
11
12
13
14
þ
½CuðiÞðAr-BIANÞ2ꢀ þ 1eꢁ
½Cuð0ÞðAr-BIANÞ ꢀ ð4Þ
a General reaction conditions: phenylacetylene, 2.0 mmol; benzyl azide,
2.0 mmol; THF, 10 mL. b Value corresponding to a lower limit.
Q
ꢁꢁꢁꢁ
ꢁꢁꢁꢁ
R
2
However, it is noteworthy that in the case of the reduction
of [Pd(II)Cl2(C6H5-BIAN)], in tetrahydrofuran, the authors
observed the formation of a radical anion on the ligand C6H5-
BIAN, the oxidation state of the palladium centre remaining con-
stant.22 In the case of the mono-chelated complexes 5–7, their
reduction pattern is complicated due to the irreversibility in the
reduction of both ligands and complexes.
In summary, the electrochemical studies demonstrate that the
bis-chelated complexes 1–4 can undergo a reversible one elec-
tron oxidation or reduction, while the mono-chelated complexes
5–7 have a partially reversible oxidation and an irreversible
reduction pattern, indicating that complexes 1–4 are chemically
more stable upon oxidation–reduction than 5–7.
to lower activities. The combined di-o- and p-substitution effects
render complex 2, with a 2,4,6-Me3C6H2 group, less active than
the mono-o-substituted complex 4, with a 2-iPrC6H4 group, at
20 °C, but more active, at 50 °C. In the case of the mono-che-
lated complexes 5–7, the ancillary monodentate ligands show a
dramatic effect on the catalytic activity. The P-donor ligand PPh3
gives rise to a remarkably high catalytic activity, much higher
than the N-donor ligands MeCN and PhCN, the latter two
showing comparable catalytic activities, at both 20 and 50 °C.
A search for more favourable reaction conditions was carried
out in the case of the reaction of phenylacetylene and ethyl 2-azi-
doacetate, using complexes 5 and 7 as catalysts, although using
different reaction times (24 and 2 h for reactions with 5 and 7,
respectively) due to their large difference in catalytic activities.
The results are listed in Table 3.
The reaction temperature has a remarkable effect on the
activity of complex 5. At 25 °C, the activity is very low
(0.17 h−1), but a significant increase is observed at 50 °C
(0.72 h−1). A further increase to 70 °C does not lead to a signifi-
cant improvement (0.73 h−1). Therefore, a temperature of 50 °C
was chosen for further studies. A decrease of the complex
loading from 5 to 1 mol% leads to a marked increase of the
activity of catalyst 5 from 0.72 to 2.62 h−1, despite it correspond-
ing to a decrease in the conversion of the reactants from 86.1 to
62.9%. The same loading decrease also leads to an increase of
more than an order of magnitude, from 2.67 to 32.5 h−1, in the
activity of complex 7, at 50 °C. A similar tendency can be
observed when the complex loading is further reduced to
0.1 mol%, indicating that complexes 5 (15.3 h−1) and 7
(141.0 h−1) have high efficiencies even if a very small loading is
used. Based on these results, and following a criterion of conver-
sion optimisation (and not activity), the use of a catalyst loading
of 1 mol% was chosen to be used in the solvent studies. In fact,
complexes 5 and 7 are active catalysts not only in non-aqueous
solvents, such as THF and CH2Cl2, but also in the aqueous
solvent mixture tBuOH–H2O (1 : 1), which is commonly used in
Catalytic cycloaddition reactions
All the synthesised copper(I) complexes 1–7 are active catalysts
for the copper(I)-catalysed azide–alkyne cycloaddition reaction
(CuAAC) without the need of any additional ligands or bases.
The catalytic results are summarised in Table 2, for the reaction
of phenylacetylene with benzyl azide, in THF.
The complexes exhibit low catalytic activities at 20 °C
(0.023–0.147 h−1), and moderate ones at 50 °C
(0.403–1.983 h−1), except complex 7, which is revealed to be an
efficient catalyst (>0.556 h−1 at 20 °C and >4.167 h−1 at 50 °C,
respectively), comparable to the typical CuSO4–sodium ascor-
bate catalytic system (3.42–7.83 h−1).2a The structures of the
copper(I) complexes and the reaction conditions have substantial
effects on the catalytic activities. An increase of the reaction
temperature leads to a significant increase in the activities. For
instance, when the reaction temperature rises from 20 to 50 °C,
there is an increase of 8–23 times in the catalytic activities.
The bis-chelated complexes 1–4 are much less active than the
mono-chelated ones 5–7 (Table 2). The catalytic activity of 1–4
depends on the substituents at the aryl rings of the ligand. Com-
plexes 1 and 3 with the less bulky o-substituents (H atoms) lead
to higher activities, at both 20 and 50 °C, while complexes 2 and
4 with bulkier o-substituents (Me and iPr, respectively) give rise
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Table 3 The influence of the reaction conditions on the cycloaddition
Table 4 Syntheses of 1,4-disubstituted 1,2,3-triazoles (8) catalysed by
complexes 5 and 7a
of ethyl 2-azidoacetate to phenylacetylene catalysed by complexes 5 and
7a
Entry Product
Catalyst t (h) Yield (%) TOF (h−1
)
Catalyst
(mol%)
T
t
Yield TOF
(h−1
)
1
2
5
7
24
2
44.4
71.2
1.85
35.6
Entry Solvent
(°C) (h) (%)
1
2
3
4
5
6
7
8
THF
THF
THF
THF
THF
THF
THF
THF
5 (5)
7 (5)
5 (5)
5 (5)
5 (1)
7 (1)
5 (0.1)
7 (0.1)
5 (1)
7 (1)
25
25
50
70
50
50
50
50
50
50
50
50
24
2
24
24
24
2
24
2
24
2
20.5
26.7
86.1
87.4
62.9
84.5
36.6
28.2
6.0
0.17
2.67
0.72
0.73
2.62
32.5
15.3
3
4
5
7
24
2
62.9
84.5
2.62
42.2
5
6
5
7
24
2
96.3
88.9
4.01
44.5
141.0
7
8
5
7
24
2
53.1
49.3
2.21
24.7
9
CH2Cl2
CH2Cl2
tBuOH–H2O (1 : 1) 5 (1)
tBuOH–H2O (1 : 1) 7 (1)
0.25
35.7
2.50
16.8
10
11
12
71.3
60.1
33.5
24
2
9
10
5
7
24
2
40.1
64.4
1.67
32.2
a General reaction conditions: phenylacetylene, 2.0 mmol; ethyl 2-
azidoacetate, 2.0 mmol; solvent, 10 mL.
11
12
5
7
24
2
38.7
82.5
1.61
41.3
aqueous CuAAC reactions. The catalytic activity of 5 in CH2Cl2
(0.25 h−1) is significantly lower than those observed in THF and
tBuOH–H2O (2.62 and 2.50 h−1, respectively), the latter ones
being comparable. Conversely, the activity of complex 7 is
a General reaction conditions: phenylacetylene, 2.0 mmol; azide,
2.0 mmol; solvent, THF, 10 mL; catalyst, 1.0 mol%; T = 50 °C.
slightly higher in CH2Cl2 than in THF (32.5 and 35.7 h−1
,
respectively), whereas in tBuOH–H2O it is ca. half of the value
of the one in THF (16.8 and 32.5 h−1, respectively). Therefore,
THF and tBuOH–H2O are preferential solvents for the catalytic
reactions involving complex 5, while THF or CH2Cl2 are pre-
ferred for catalyst 7.
complexes, such as [CuBr(PPh3)3]23a or [Cu(OOCC3H7)
(PPh3)2],23b it shows lower activities.
Generally, a stepwise cycloaddition mechanism via a copper(I)
acetylide intermediate, generated from the reaction of copper(I)
and a terminal alkyne, has been supported for the CuAAC reac-
tion, both experimentally and theoretically.2a,24 In the present
case, the copper(I) ions are coordinated and stabilised by Ar-
BIAN ligands with varied steric bulkinesses, or by the latter and
other ancillary ligands (MeCN, PhCN and PPh3). The electro-
chemical results presented above have demonstrated that both
bis- and mono-chelated Ar-BIAN copper(I) complexes are stable
upon either oxidation or reduction, the former species being
more stable than the latter ones. The very low catalytic activities
exhibited by complexes 1–4 can be related to the high energy
barrier required to dissociate one of their Ar-BIAN ligands,
which will be much higher than the one necessary to dissociate
the monodentate PPh3 or N-donor ligands (MeCN and PhCN) in
the monochelated catalysts 5–7 (Scheme 2). In particular, the
PPh3 ligands in complex 7 tend to dissociate much more exten-
sively (see above) than the nitrile ligands (MeCN and PhCN) in
5 and 6, a fact that may be in the origin of the significant differ-
ence in catalytic activities observed for 7 in comparison with
those of 5 or 6.
We selected several typical alkyl-, aryl- and functional group-
containing azides to test the efficiency of complexes 5 and 7,
using again different reaction times (24 and 2 h for reactions
with 5 and 7, respectively). The results are given in Table 4.
Apparently, these complexes behave efficiently with the various
substrates. Under the most favourable reaction conditions
defined above, i.e., 50 °C, 1 mol% of copper(I) complex and
THF as solvent, moderate (catalyst 5) to high (catalyst 7) conver-
sions are obtained in the reaction of phenylacetylene with alkyl
azides, including primary and secondary ones, which seem to be
slightly conditioned by their bulkiness in the case of 5, but not
in that of 7. In the reaction with phenyl azide a slightly higher
conversion in relation to the alkyl azides seem to occur in the
case of catalyst 5, whereas a significant decrease is observed in
the case of catalyst 7. The presence of functional substituents,
such as ester and hydroxyl groups, does not interfere in the reac-
tions, but rather enhances the activities and conversions (see
entries 3 and 5 or 4 and 6, respectively, in Table 4).
The activities obtained for the catalysts described in the
present work (Tables 2–4) vary from very low, in the case of the
bis-chelated complexes 1–4, to high, in the case of complex 7,
and depend on the reaction conditions used. In the best con-
ditions, catalyst 7 shows activities comparable to or higher
than other well-defined nitrogen-containing ligand-coordinated
copper(I) complexes,13b–e,g but lower than others.13f When
compared with well-defined phosphine-coordinated copper(I)
Conclusions
A series of mono- or bis-chelated (Ar-BIAN)copper(I) com-
1
plexes 1–7 have been synthesised and fully characterised by H
and 13C NMR spectroscopies, FT-IR spectroscopy, MALDI-
TOF-MS spectrometry, cyclic voltammetry and single crystal
5150 | Dalton Trans., 2012, 41, 5144–5154
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Scheme 2 The proposed dissociation of ancillary ligands in the catalytic CuAAC reactions involving complexes 1–7.
X-ray diffraction. X-ray diffraction shows that all the complexes
adopt a distorted tetrahedral geometry around the metal centre,
with degrees of distortion increasing with the bulkiness of the
ligands. The electrochemical studies suggested that the Ar-BIAN
ligands effectively stabilise the copper(I) ions, and that the bis-
chelated complexes 1–4 are chemically more stable upon oxi-
dation–reduction than the mono-chelated 5–7, the former dis-
playing a reversible one electron oxidation or reduction
behaviour and the latter showing a partially reversible oxidation
and an irreversible reduction feature. All the complexes 1–7 are
active catalysts for the copper(I)-catalysed azide–alkyne cyclo-
addition reaction (CuAAC). The bis-chelated complexes 1–4 are
substantially less active than the mono-chelated ones 5–7, pre-
sumably due to a much lower extent of dissociation of one of the
Ar-BIAN ligands in comparison to that of the nitrile or PPh3
monodentate ancillary ligands, which is believed to be the first
step to enable the coordination of the substrates to copper.
Complex 7 is a very active catalyst for the CuAAC reaction
because the ligand PPh3 presents a highly exchanging and disso-
ciative behaviour, as proved by 31P NMR spectroscopy. The
influence of the reaction conditions, such as temperature, amount
of catalyst, time and solvents, were investigated, revealing that a
temperature of 50 °C and the use of coordinating/protic solvents,
such as THF or tBuOH–H2O, favour this catalytic reaction.
4 Å molecular sieves and degassed by the freeze–pump–thaw
method. The ligands Ar-BIAN (Ar = C6H5 (L1), 2,4,6-Me3C6H2
(L2), 4-iPrC6H4 (L3), 2-iPrC6H4 (L4) and 2,6-iPr2C6H3 (L5))
were prepared according to the literature,14c and the complexes
[Cu(2,4,6-Me3C6H2-BIAN)2]BF4 (2) and [Cu(2,6-iPr2C6H3-
BIAN)(NCMe)2]BF4 (5) were prepared according to the
literature.17
Nuclear magnetic resonance (NMR) spectra were recorded on
Bruker Avance II 400 (UNL) or Bruker Avance III 400 (IST)
(1H, 400.132 MHz; 13C, 100.623 MHz; 31P, 161.923 MHz) spec-
trometers. Spectra were referenced internally using the residual
protio solvent resonance relative to tetramethylsilane (δ = 0). IR
spectra were recorded as Nujol mulls on NaCl plates using a
Bruker Tensor 27 FTIR spectrometer. MALDI-TOF-MS (Matrix
Assisted Laser Desorption-Ionisation Time-of-Flight Mass Spec-
trometry) analyses were obtained in the REQUIMTE-MALDI-
TOF-MS Service Laboratory, and were performed in
a
MALDI-TOF-MS Voyager DE-PRO Biospectrometry Work-
station equipped with a nitrogen laser radiating at 337 nm from
Applied Biosystems (Foster City, United States). Elemental ana-
lyses were obtained from the elemental analysis service of Insti-
tuto Superior Técnico (IST) or Universidade Nova de Lisboa
(UNL), on a Fisons Instrument Mod EA-1108, or a Thermo
Finnigan-CE Flash-EA 1112-CHNS instrument, respectively.
Syntheses of bis-chelated complexes 1, 3 and 4. A typical pro-
cedure is described as follows: a suspension of [Cu(NCMe)4]
BF4 (0.36 mmol) in CH2Cl2 (10 mL) was treated with a solution
of Ar-BIAN (Ar = C6H5 (L1) or 4-iPrC6H4 (L3) or 2-iPrC6H4
(L4)) (0.72 mmol) in CH2Cl2 (20 mL), at room temperature. The
colour of the mixture turned quickly to blue (1 and 3) or red (4),
and was left stirring overnight until all the solids dissolved. After
filtration, the solution was concentrated under vacuum and
double-layered with pentane. The mixture was placed in a
refrigerator (−20 °C) to crystallise. Blue (1), purple (3) or brown
(4) crystalline solids were isolated by filtration, washed with
pentane (2 × 20 mL), and dried under vacuum. Yield: 72% (1),
84% (3) and 76% (4).
Experimental
General
All manipulations dealing with air- or moisture-sensitive
materials were carried out under inert atmosphere using a dual
vacuum–nitrogen line and standard Schlenk techniques. Unless
otherwise stated, all reagents were purchased from commercial
suppliers and used as received. All solvents were used under
inert atmosphere and purified prior to use. Pentane and tetra-
hydrofuran were purified by refluxing over sodium or sodium–
benzophenone ketyl respectively, and distilled prior to use.
Dichloromethane and acetonitrile were purified over calcium
hydride and phosphorus pentoxide, respectively, and distilled
prior to use. Deuterated solvents (chloroform-d1, dichloro-
methane-d2, and tetrahydrofuran-d8) were dried by storage over
Data for 1. 1H NMR (300 MHz, CD2Cl2): δ 8.12 (d, J = 8.3
Hz, 4H), 7.57–7.42 (m, 16 H), 7.26–7.18 (m, 12 H). 13C{1H}
(75 MHz, CD2Cl2): δ 164.3 (CvN), 147.7 (CvN–C), 143.1,
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138.2, 131.5, 130.4, 129.2, 128.8, 128.4, 127.8, 126.5, 125.5,
125.0, 120.8 (aromatic CHs and other quaternary carbons). IR
(nujol): ν (cm−1) 1644 and 1635 (CvN), 1047 (BF4−). Anal.
Calcd for C48H32CuBF4N4: C 70.73, H 3.96, N 6.87; found: C
71.11, H 4.18, N 6.54. MALDI-TOF-MS: m/z 727.2 (100%) [Cu
(C6H5-BIAN)2]+, 395.1 (27%) [Cu(C6H5-BIAN)]+, 331.2 (3%)
[C6H5-BIAN-H]+.
Data for 3. 1H NMR (400 MHz, CD2Cl2): δ 8.11 (d, J = 8.3
Hz, 4H), 7.52 (t, J = 7.8 Hz, 4H), 7.35–7.33 (m, 12H), 7.07 (d, J
= 8.0 Hz, 8H), 3.03 (m, 4H), 1.35 (d, J = 6.9 Hz, 24H). 13C{1H}
(100 MHz, CD2Cl2): δ 163.3 (CvN), 148.8 (CvN–C), 145.0,
142.5, 131.3, 131.0, 128.5, 127.9, 126.6, 124.4, 120.9 (aromatic
CHs and other quaternary carbons), 33.9 (CH(CH3)2), 23.8 (CH
(CH3)2). IR (nujol): ν (cm−1) 1633 (CvN), 1047 (BF4−). Anal.
Calcd for C60H56CuBF4N4: C 73.28, H 5.74, N 5.70; found: C
72.88, H 5.66, N 5.65. MALDI-TOF-MS: m/z 895.2 (100%) [Cu
(4-iPrC6H4-BIAN)2]+, 479.7 (20%) [Cu(4-iPrC6H4-BIAN)]+,
415.2 (4%) [4-iPrC6H4-BIAN-H]+.
treated with an orange solution of 4-iPrC6H4-BIAN (0.26 g,
0.64 mmol) in CH2Cl2 (20 mL). The mixture turned quickly to
red, and was left stirring for another 2 h. After filtration, the sol-
ution was concentrated under vacuum and double-layered with
pentane. The mixture was placed in a refrigerator (−20 °C) to
crystallise. A bright red microcrystalline solid was isolated by fil-
tration, washed with pentane (2 × 10 mL), and dried under
vacuum. Yield: 92%. 1H NMR (400 MHz, CD2Cl2): δ 8.24 (d, J
= 8.3 Hz, 2H), 7.60 (t, J = 7.8 Hz, 2H), 7.38–7.29 (m, 8H),
7.11–7.03 (m, 16H), 6.88 (br, 12H), 6.36–6.35 (d, J = 7.9 Hz,
4H), 3.00 (m, 2H), 1.35–1.34 (d, J = 6.8 Hz, 12H). 13C{1H}
(100 MHz, CD2Cl2): δ 162.9 (CvN), 148.8 (CvN–C), 144.7,
133.3, 133.2, 133.1, 131.7, 131.5, 131.4, 130.4, 128.9, 128.4,
127.6, 126.1, 124.9, 120.6 (aromatic CHs and other quaternary
carbons), 33.8 (CH(CH3)2), 23.9 (CH(CH3)2). IR (nujol): ν
(cm−1
)
1644 (CvN), 1051 (BF4−). Anal. Calcd for
C66H58CuBF4N2P2·0.5CH2Cl2: C 70.44, H 5.24, N 2.47; found:
C 70.34, H 5.27, N 2.40. MALDI-TOF-MS: m/z 895.1 (100%)
[Cu(4-iPrC6H4-BIAN)2]+, 741.1 (17%) [Cu(4-iPrC6H4-BIAN)
(PPh3)]+, 479.1 (22%) [Cu(4-iPrC6H4-BIAN)]+, 415.1 (12%)
[4-iPrC6H4-BIAN-H]+.
Data for 4. 1H NMR (400 MHz, CD2Cl2): δ 8.10 (d, J = 8.4
Hz, 4H), 7.47–7.43 (m, 10H), 7.32 (t, 4H), 6.80–6.74 (m, 4H),
6.18 (d, 4H), 3.53 (s, 4H), 1.35 (d, 12H), 1.10 (d, 12H). 13C
{1H} (100 MHz, CD2Cl2): δ 164.4 (CvN), 145.1 (CvN–C),
142.6, 140.4, 131.1, 131.0, 128.7, 128.0, 127.7, 126.8, 126.3,
124.9, 120.4 (aromatic CHs and other quaternary carbons), 28.9
(CH(CH3)2), 25.0 (CH(CH3)2), 22.9 (CH(CH3)2). IR (nujol): ν
General procedure for the copper(I)-catalysed azide–alkyne
cycloaddition reaction (CuAAC). The desired amount of azides
(2.0 mmol), phenylacetylene (2.0 mmol) and copper(I) com-
plexes (0.1, 1.0, or 5.0 mol%) were weighed in the glovebox,
and mixed in a 100 mL Schlenk tube. 10 mL of THF were
added and the resulting mixture was stirred for 2, 24 or 36 h, at a
certain temperature (20, 50 or 70 °C). The solvent and the
remaining reagents were removed under vacuum. Crude products
with trace remaining copper(I) complexes were obtained, and
characterised by 1H NMR spectroscopy in CDCl3. The yield was
calculated by the subtraction of the amount of the residual
(cm−1
)
1632 (CvN), 1058 (BF4−). Anal. Calcd for
C60H56CuBF4N4·0.5CH2Cl2: C 70.83, H 5.60, N 5.46; found: C
70.61, H 5.78, N 5.48. MALDI-TOF-MS: m/z 895.2 (20%) [Cu
(2-iPrC6H4-BIAN)2]+, 479.1 (100%) [Cu(2-iPr2C6H4-BIAN)]+,
415.1 (29%) [2-iPrC6H4-BIAN-H]+, 373.1 (6%) [2-iPrC6H4-
BIAN - iPr]+.
Synthesis of complex 6. A suspension of [Cu(NCPh)4]BF4
(0.23 g, 0.40 mmol) in CH2Cl2 (10 mL) was treated with an
orange solution of 2,6-iPr2C6H3-BIAN (0.20 g, 0.40 mmol) in
CH2Cl2 (30 mL) at room temperature. The mixture turned
quickly to green, and was left stirring overnight. After filtration,
the solution was concentrated under vacuum and double-layered
with pentane. The mixture was placed in a refrigerator (−20 °C)
to crystallise. A green microcrystalline solid was isolated by fil-
tration, washed with pentane (2 × 10 mL), and dried under
vacuum. Yield: 67%. 1H NMR (400 MHz, CD2Cl2): δ 8.20 (d, J
= 8.0 Hz, 2H), 7.72–7.41 (m, 18H), 6.77 (d, J = 6.9 Hz, 2H),
3.07 (m, 4H), 1.33 (d, J = 6.4 Hz, 12H), 1.02 (d, J = 6.5 Hz,
12H). 13C{1H} (100 MHz, CD2Cl2): δ 164.4 (CvN), 145.1
(CvN–C), 142.6, 140.4, 131.1, 131.0, 128.7, 128.0, 127.7,
126.8, 126.3, 124.9, 120.4 (aromatic CHs and other quaternary
carbons), 28.9 (CH(CH3)2), 25.0 (CH(CH3)2), 22.9 (CH(CH3)2).
IR (nujol): ν (cm−1) 2246.7 (CuN), 1651 and 1614 (CvN),
1047 (BF4−). Anal. Calcd for C50H50CuBF4N4: C 70.05,
H 5.88, N 6.54; found: C 69.69, H 5.84, N 6.48. MALDI-
TOF-MS: m/z 726.9 (5%) [Cu(2,6-iPr2C6H3-BIAN)(NCPh)2-
iPr]+, 563.2 (47%) [Cu(2,6-iPr2C6H3-BIAN)]+, 499.6 (30%)
[2,6-iPr2C6H3-BIAN-H]+, 457.1 (5%) [2,6-iPr2C6H3-BIAN-
iPr]+.
1
copper(I) complexes, which was estimated using the H NMR
spectra of the crude reaction products. The triazole products
1
8a,25 8b,26 8c,27 8d,28 8e29 and 8f30 were identified by their H
NMR spectra, which are consistent with the data reported in the
corresponding literature.
X-ray diffraction. Crystallographic and experimental details
of crystal structure determinations are given in Table S3.† In
each case, a specimen crystal was selected under an inert atmos-
phere, covered with polyfluoroether, and mounted on the end of
a nylon loop. All crystal data were collected, at 150 K, in a
Bruker AXS-KAPPA APEX II diffractometer equipped with an
Oxford Cryosystems open-flow nitrogen cryostat, using graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å). Cell par-
ameters were retrieved using Bruker SMART31 software and
refined using Bruker SAINT32 on all observed reflections.
Absorption corrections were applied using SADABS.33 Structure
solution and refinement were performed using direct methods
with the programs SIR92,34 SIR200435 and SHELXL,36 all
included in the WINGX-Version 1.70.01 package of programs.37
Crystal structures were refined to convergence, even though
some of the crystals were of poorer quality, such as compounds
3 and 6 that presented high Rint (0.1300 and 0.1835 respectively)
and a relatively low ratio of observed/unique reflections (respect-
ively 48 and 40%). Crystal 3 presented some disordered carbon
atoms in the isopropyl groups of the four molecules of the
Synthesis of complex 7. A suspension of [Cu(NCPh)4]BF4
(0.20 g, 0.64 mmol) and PPh3 (0.33 g, 1.28 mmol) in CH2Cl2
(30 mL) was stirred for 2 h, at room temperature, and then
5152 | Dalton Trans., 2012, 41, 5144–5154
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1302–1315; (e) K. D. Hänni and D. A. Leigh, Chem. Soc. Rev., 2010, 39,
1240–1251.
asymmetric unit. The disorders have been modeled with a
50 : 50 occupancy in the corresponding carbon atoms that were
refined isotropically. Compounds 4 and 6 showed the presence
of disordered solvent molecules, and the PLATON/SQUEEZE38
routine was applied as no good disorder model was possible to
attain, showing different potential solvent area volumes of 635.3
and 613.1 Å3 and different electron density (160 and 95 e−
respectively). Half and 0.3 dichloromethane molecules were
found in the asymmetric units for compounds 4 and 6, respect-
ively. In compound 4 the Cu atom is sitting in a crystallographi-
cally-imposed 222 symmetry site, with x = y = z = 0.125
fractional parameters. Non-hydrogen atoms were refined with
anisotropic thermal parameters. All hydrogens were inserted in
idealised positions and allowed to refine riding in the parent C
atoms, with C–H distances of 0.93, 0.96 and 0.98 Å for aro-
matic, methyl and methine H atoms, respectively, and with
4 (a) J.-F. Lutz, Angew. Chem., Int. Ed., 2007, 46, 1018–1025;
(b) D. Fournier, R. Hoogenboom and U. S. Schubert, Chem. Soc. Rev.,
2007, 36, 1369–1380; (c) R. K. Iha, K. L. Wooley, A. M. Nyström, D.
J. Burke, M. J. Kade and C. J. Hawker, Chem. Rev., 2009, 109, 5620–
5686; (d) P. L. Golas and K. Matyjaszewski, Chem. Soc. Rev., 2010, 39,
1338–1354; (e) B. S. Sumerlin and A. P. Vogt, Macromolecules, 2010,
43, 1–13; (f) A. Qin, J. W. Y. Lam and B. Z. Tang, Macromolecules,
2010, 43, 8693–8702.
5 N. Uhlig and C.-J. Li, Chem. Sci., 2011, 2, 1241–1249.
6 G. C. Tron, T. Pirali, R. A. Billington, P. L. Canonico, G. Sorba and A.
A. Genazzani, Med. Res. Rev., 2008, 28, 278–308.
7 (a) H. C. Kolb and K. B. Sharpless, Drug Discovery Today, 2003, 8,
1128–1137; (b) J. E. Moses and A. D. Moorhouse, Chem. Soc. Rev.,
2007, 36, 1249–1262; (c) Y. L. Angell and K. Burgess, Chem. Soc. Rev.,
2007, 36, 1674–1689; (d) J.-F. Lutz and Z. Zarafshani, Adv. Drug Deliv-
ery Rev., 2008, 60, 958–970; (e) J. M. Holub and K. Kirshenbaum,
Chem. Soc. Rev., 2010, 39, 1325–1337; (f) A. H. El-Sagheer and
T. Brown, Chem. Soc. Rev., 2010, 39, 1388–1405.
8 F. Fazio, M. C. Bryan, O. Blixt, J. C. Paulson and C.-H. Wong, J. Am.
Chem. Soc., 2002, 124, 14397–14402.
9 L. D. Pachón, J. H. van Maarseveen and G. Rothenberg, Adv. Synth.
Catal., 2005, 347, 811–815.
10 (a) H. A. Orgueira, D. Fokas, Y. Isome, P. C.-M. Chan and C.
M. Baldino, Tetrahedron Lett., 2005, 46, 2911–2914; (b) G. Molteni, C.
L. Bianchi, G. Marinoni, N. Santo and A. Ponti, New J. Chem., 2006, 30,
1137–1139.
11 B. H. Lipshutz and B. R. Taft, Angew. Chem., Int. Ed., 2006, 45, 8235–8238.
12 (a) W. G. Lewis, F. G. Magallon, V. V. Fokin and M. G. Finn, J. Am.
Chem. Soc., 2004, 126, 9152–9153; (b) B. Gerard, J. Ryan, A. B. Beeler
and J. A. Porco Jr., Tetrahedron, 2006, 62, 6405–6411.
13 (a) S. Díez-González, Catal. Sci. Technol., 2011, 1, 166–178; (b) F. Li
and T. S. A. Hor, Chem.–Eur. J., 2009, 15, 10585–10592;
(c) N. Candelon, D. Lastécouères, A. K. Diallo, J. R. Aranzaes, D. Astruc
and J. M. Vincent, Chem. Commun., 2008, 741–743; (d) P. S. Donnelly,
S. D. Zanatta, S. C. Zammit, J. M. White and S. J. Williams, Chem.
Commun., 2008, 2459–2461; (e) S. Özçubukçu, E. Ozkal, C. Jimeno and
M. A. Pericàs, Org. Lett., 2009, 11, 4680–4683; (f) J. García-Álvarez,
J. Díez and J. Gimeno, Green Chem., 2010, 12, 2127–2130; (g) S.-
Q. Bai, L. Koh and T. S. A. Hor, Inorg. Chem., 2009, 48, 1207–1213;
(h) I. Cano, M. C. Nicasio and P. J. Pérez, Org. Biomol. Chem., 2010, 8,
536–538.
14 (a) R. van Asselt and C. J. Elsevier, Organometallics, 1992, 11, 1999–
2001; (b) R. van Asselt, E. E. C. G. Gielens, R. E. Riilke, K. Vrieze and
C. J. Elsevier, J. Am. Chem. Soc., 1994, 116, 977–985; (c) R. van Asselt,
C. J. Elsevier, W. J. J. Smeets, A. L. Spek and R. Benedix, Recl. Trav.
Chim. Pays-Bas, 1994, 113, 88–98; (d) M. Gasperini, F. Ragaini and
S. Cenini, Organometallics, 2002, 21, 2950–2957; (e) M. Gasperini and
F. Ragaini, Organometallics, 2004, 23, 995–1001; (f) M. Gasperini,
F. Ragaini, E. Gazzola, A. Caselli and P. Macchi, Dalton Trans., 2004,
3376–3382.
U
iso(H) = 1.2Ueq(C). Graphic presentations were prepared with
ORTEP-III.39 Data was deposited in CCDC under the deposit
numbers 830550 for 3, 830551 for 4, 830552 for 6 and 830553
for 7.†
Cyclic voltammetry. Cyclic voltammetry experiments were
carried out in a gastight three-electrode cell, equipped with Pt-
disc working (1 mm radius), Pt-wire auxiliary and Ag-wire
pseudo-reference electrodes, under the protection of a nitrogen
atmosphere, at 25 °C. The Ag-wire pseudo-reference electrode
was separated from the main compartment by a Luggin capillary.
A 0.2 M [NBu4][BF4] solution in CH2Cl2 was used as an elec-
trolyte solution, and the concentrations used for complexes 1–7
and ligands L1–L5 were around 1.2 × 10−3 M. The solution was
bubbled with dry nitrogen gas before each scan. All the cyclic
voltammograms were recorded using a Radiometer DEA 101
Digital Electrochemical Analyser interfaced with an IMT 102
Electrochemical Interface. All potentials were reported against
the ferrocene–ferrocenium (Fc–Fc+) redox couple, which was
used as an internal standard, according to the IUPAC
recommendations.40
Acknowledgements
We thank the Fundação para Ciência e Tecnologia for financial
support (grants PEst-OE/QUI/UI0100/2011 and PEst-C/EQB/
LA0006/2011; Projects PTDC/QUI/65474/2006, PTDC/
EQU-EQU/110313/2009 and PTDC/QUI-QUI/099873/2008, co-
financed by FEDER) and fellowships to L.L., V.R. and C.A.F.
(SFRH/BPD/30733/2006, SFRH/BPD/44262/2008 and SFRH/
BD/47730/2008, respectively).
15 For example: (a) R. van Asselt, C. J. Elsevier, W. J. J. Smeets and A.
L. Spek, Inorg. Chem., 1994, 33, 1521–1531; (b) R. van Asselt and C.
J. Elsevier, Tetrahedron, 1994, 50, 323–334; (c) L. K. Johnson, C.
M. Killian and M. Brookhart, J. Am. Chem. Soc., 1995, 117, 6414–6415;
(d) L. K. Johnson, S. Mecking and M. Brookhart, J. Am. Chem. Soc.,
1996, 118, 267–268; (e) C. M. Killian, D. J. Tempel, L. K. Johnson and
M. Brookhart, J. Am. Chem. Soc., 1996, 118, 11664–11665;
(f) A. Scarel, M. Rosa Axet, F. Amoroso, F. Ragaini, C. J. Elsevier,
A. Holuigue, C. Carfagna, L. Mosca and B. Milani, Organometallics,
2008, 27, 1486–1494; (g) F. Ragaini, S. Cenini, S. Tollari,
G. Tummolillo and R. Beltrami, Organometallics, 1999, 18, 928–942;
(h) F. Ragaini, S. Cenini, E. Borsani, M. Dompé, E. Gallo and M. Moret,
Organometallics, 2001, 20, 3390–3398; (i) J. W. Sprengers, M. Greef, M.
A. Duin and C. J. Elsevier, Eur. J. Inorg. Chem., 2003, 3811–3819.
16 (a) S. G. Correia, M. M. Marques, J. R. Ascenso, A. F. G. Ribeiro, P.
T. Gomes, A. R. Dias, M. Blais, M. D. Rausch and J. C. W. Chien, J.
Polym. Sci., Part A: Polym. Chem., 1999, 37, 2471–2480; (b) H.-R. Liu,
S. I. Costa, P. T. Gomes, M. T. Duarte, R. Branquinho, A. C. Fernandes,
J. C. W. Chien and M. M. Marques, J. Organomet. Chem., 2005, 690,
1314–1323; (c) J.-C. Yuan, L. C. Silva, P. T. Gomes, P. Valerga, J.
M. Campos, M. R. Ribeiro, J. C. W. Chien and M. M. Marques, Polymer,
2005, 46, 2122–2132; (d) V. Rosa, P. J. Gonzalez, T. Avilés, P. T. Gomes,
R. Welter, A. C. Rizzi, M. C. G. Passeggi and C. D. Brondino,
References
1 P. J. Pérez and M. M. Díaz-Requejo, in Comprehensive Organometallic
Chemistry III, ed. R. H. Crabtree and D. M. P. Mingos, Elsevier,
New York, 2007, vol. 2, pp. 153–195.
2 (a) V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless,
Angew. Chem., Int. Ed., 2002, 41, 2596–2599; (b) C. W. Tornøe,
C. Christensen and M. Meldal, J. Org. Chem., 2002, 67, 3057–3064.
3 (a) D. B. Ramachary and C. F. Barbas III, Chem.–Eur. J., 2004, 10,
5323–5331; (b) W. H. Binder and C. Kluger, Curr. Org. Chem., 2006, 10,
1791–1815; (c) Y. Hua and A. H. Flood, Chem. Soc. Rev., 2010, 39,
1262–1271; (d) J. E. Hein and V. V. Fokin, Chem. Soc. Rev., 2010, 39,
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5144–5154 | 5153

View Article Online
Eur. J. Inorg. Chem., 2006, 23, 4761–4769; (e) V. Rosa, S.
A. Carabineiro, T. Avilés, P. T. Gomes, R. Welter, J. M. Campos and M.
R. Ribeiro, J. Organomet. Chem., 2008, 693, 769–775; (f) L.-D. Li,
C. S. B. Gomes, P. T. Gomes and M. T. Duarte, Synth. Commun., 2008,
38, 4415–4425; (g) L.-D. Li, C. S. B. Gomes, P. T. Gomes, M. T. Duarte
and Z. Fan, Dalton Trans., 2011, 40, 3365–3380; (h) L. Li, P. T. Gomes,
M. A. N. D. A. Lemos, F. Lemos and Z. Fan, Macromol. Chem. Phys.,
2011, 212, 367–374; (i) L. Li, C. S. B. Gomes, P. S. Lopes, P. T. Gomes,
H. P. Diogo and J. R. Ascenso, Eur. Polym. J., 2011, 47, 1636–1645;
( j) D. M. Antonelli, P. T. Gomes, M. L. H. Green, A. M. Martins and
P. Mountford, J. Chem. Soc., Dalton Trans., 1997, 2435–2444;
(k) P. Frémont, H. Clavier, V. Rosa, T. Avilés and P. Braunstein, Organo-
metallics, 2011, 30, 2241–2251.
24 F. Himo, T. Lovell, R. Hilgraf, V. V. Rostovtsev, L. Noodleman,
K. B. Sharpless and V. V. Fokin, J. Am. Chem. Soc., 2005, 127, 210–216.
25 V. O. Rodionov, V. V. Fokin and M. G. Finn, Angew. Chem., Int. Ed.,
2005, 44, 2210–2215.
26 L. S. Campbell-Verduyn, L. Mirfeizi, R. A. Dierckx, P. H. Elsinga and B.
L. Feringa, Chem. Commun., 2009, 2139–2141.
27 I. Jlalia, F. Meganem, J. Herscovici and C. Girard, Molecules, 2009, 14,
528–539.
28 S. Díez-González, A. Correa, L. Cavallo and S. P. Nolan, Chem.–Eur. J.,
2006, 12, 7558–7564.
29 J.-C. Meng, V. V. Fokin and M. G. Finn, Tetrahedron Lett., 2005, 46,
4543–4546.
30 B. Sreedhar, P. S. Reddy and V. R. Krishna, Tetrahedron Lett., 2007, 48,
5831–5843.
31 SMART Software for the CCD detector System Version 5.625, Bruker
AXS Inc., Madison, WI, USA, 2001.
32 SAINT Software for the CCD detector System, Version 7.03, Bruker
AXS Inc., Madison, WI, USA, 2004.
17 V. Rosa, C. I. M. Santos, R. Welter, G. Aullón, C. Lodeiro and T. Avilés,
Inorg. Chem., 2010, 49, 8699–8708.
18 (a) A. Paulovicova, U. El-Ayaan, K. Shibayama, T. Morita and
Y. Fukuda, Eur. J. Inorg. Chem., 2001, 2641–2646; (b) U. El-Ayaan,
A. Paulovicova and Y. Fukuda, J. Mol. Struct., 2003, 645, 205–212;
(c) U. El-Ayaan, F. Murata, S. El-Derby and Y. Fukuda, J. Mol. Struct.,
2004, 692, 209–216; (d) K. V. Vasudevan, M. Findlater and A.
H. Cowley, Chem. Commun., 2008, 1918–1919; (e) T. Kern,
U. Monkowius, M. Zabel and G. Knör, Eur. J. Inorg. Chem., 2010,
4148–4156.
33 G. M. Sheldrick, SADABS, Program for Empirical Absorption Correc-
tion, University of Göttingen, Göttingen, 1996.
34 A. Altomare, G. L. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl.
Crystallogr., 1993, 26, 343–350.
35 M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G. L. Cascarano,
L. De Caro, C. Giacovazzo, G. Polidori and R. Spagna, J. Appl. Crystal-
logr., 2005, 38, 381–388.
19 C. A. Tolman, W. C. Seidel and L. W. Gosser, J. Am. Chem. Soc., 1974,
96, 53–60.
20 I. D. Macleod, A. J. Parker and P. Singh, J. Solution Chem., 1981, 10,
757–774.
21 Q. Wang, T. R. Chan, R. Hilgraf, V. V. Fokin, K. B. Sharpless and M.
G. Finn, J. Am. Chem. Soc., 2003, 125, 3192–3193.
22 R. van Asselt, C. J. Elsevier, C. Amatore and A. Jutand, Organometallics,
1997, 16, 317–328.
23 (a) S. Lal and S. Diéz-González, J. Org. Chem., 2011, 76, 2367–2373;
(b) Z. Gonda and Z. Novák, Dalton Trans., 2010, 39, 726–729.
36 G. M. Sheldrick, Shelxl-97-A Computer Program for Refinement of
Crystal Structure, University of Göttigen, Göttigen, 1997.
37 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
38 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
39 M. N. Burnett and C. K. Johnson, ORTEP-III: Oak Ridge Thermal Ellip-
soid Plot Program for Crystal Structure Illustration, Oak Ridge National
Laboratory Report ORNL-6895, 1996.
40 G. Gritzner and J. Kůta, Electrochim. Acta, 1984, 29, 869–873.
5154 | Dalton Trans., 2012, 41, 5144–5154
This journal is © The Royal Society of Chemistry 2012