Photoluminescent copper(I) complexes with amido-triazolato ligands

Article abstract of DOI:10.1021/ic102338g

A series of heteroleptic copper(I) complexes incorporating amido-triazole and diphosphine ligands, [Cu^I(N-phenyl-2-(1-phenyl-1H- 1,2,3-triazol-4-yl)aniline)(dppb)] (1), [Cu^I(N-(4-methylphenyl)-2-(1- phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (2), [Cu^I(N-(4- methoxyphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (3), [Cu ^I(N-(4-chlorophenyl)-2-(1-phenyl-1H-1,2,3-triazol-4- yl)aniline)(dppb)] (4), [Cu^I(2,6-dimethyl-N-[2-(1-phenyl-1H-1,2,3- triazol-4-yl)phenyl]aniline)(dppb)] (5), [Cu^I(2,6-dimethyl- N-[2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl]aniline)(dppb)] (6), (dppb = 1,2-bis(diphenylphosphino)benzene), have been prepared. The complexes adopt a distorted tetrahedral geometry in the solid statewith the amido-triazole ligand forming a six-member ring with the Cu(I) ion. The complexes exhibit long-lived photoluminescence with colors ranging from yellow to red-orange in the solid state, in frozen glass at 77 K, and in fluid solution withmodest quantum yields of up to 0.022. Electrochemically, complexes 1-4 show irreversible oxidation waves while 5 and 6 are characterized by quasi-reversible oxidations as determined by cyclic voltammetry. For 1-4, the emission energy and oxidation potential are found to vary linearly with the Hammett parameter σ_p of the substituent in thepara position of the amido ligand, while in 5 and 6, large differences in emission are observed because of the nature ofN3 substitution in the triazole ring. Density functional theory calculations have been performed on the singlet ground states (S₀) of all complexes at the BP86/6-31G(d) level to assist in assignment of the excited states.On the basis of both experimental and computational results, we have assigned the excited states as intraligand+ metal-to-ligand charge transfer ³(ILCT+MLCT) or ligand-to-ligand charge transfer mixed with MLCT ³(MLCT +LLCT) in these complexes.

Full text of DOI:10.1021/ic102338g

ARTICLE
pubs.acs.org/IC
Photoluminescent Copper(I) Complexes with
Amido-Triazolato Ligands
Gerald F. Manbeck, William W. Brennessel, and Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
S Supporting Information
b
ABSTRACT:
A series of heteroleptic copper(I) complexes incorporating amido-triazole and diphosphine ligands, [CuI(N-phenyl-2-(1-phenyl-1H-
1,2,3-triazol-4-yl)aniline)(dppb)] (1), [CuI(N-(4-methylphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (2), [CuI(N-(4-
methoxyphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (3), [CuI(N-(4-chlorophenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-
yl)aniline)(dppb)] (4), [CuI(2,6-dimethyl-N-[2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl]aniline)(dppb)] (5), [CuI(2,6-dimethyl-
N-[2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl]aniline)(dppb)] (6), (dppb = 1,2-bis(diphenylphosphino)benzene), have been pre-
pared. The complexes adopt a distorted tetrahedralgeometry in thesolidstate with theamido-triazole ligand forminga six-member ring
with the Cu(I) ion. The complexes exhibit long-lived photoluminescence with colors ranging from yellow to red-orange in the solid
state, in frozen glass at 77 K, and in fluid solution with modest quantum yields of up to 0.022. Electrochemically, complexes 1-4 show
irreversible oxidation waves while 5 and 6 are characterized by quasi-reversible oxidations as determined by cyclic voltammetry. For
1-4, the emission energy and oxidation potential are found to vary linearly with the Hammett parameter σp of the substituent in the
para position of the amido ligand, while in 5 and 6, large differences in emission are observed because of the nature of N3 substitution in
the triazole ring. Density functional theory calculations have been performed on the singlet ground states (So) of all complexes at the
BP86/6-31G(d) level to assist in assignment of the excited states. On the basis of both experimental and computational results, we have
assigned the excited states as intraligand þ metal-to-ligand charge transfer 3(ILCTþMLCT) or ligand-to-ligand charge transfer mixed
with MLCT 3(MLCT þLLCT) in these complexes.
’ INTRODUCTION
a constraint that ideal dopants should be thermally stable and
sublimable.
Organic light emitting diodes (OLEDs) are becoming the
preeminent technology in flat panel displays because of their
superior viewing quality, efficiency, and durability. OLEDs work
on the principle of light emission upon charge recombination.
Upon application of an external potential, electrons and holes
migrate from the cathode and anode, respectively, to form light-
emitting excitons at a luminescent compound. Since spin statistics
dictate that 75% of the excitons are triplet states, heavy metal
dopant emitters are desirable because they induce rapid inter-
system crossing and triplet emission, thereby enhancing device
efficiency.1 Conversely, for organic emitters, only singlet excitons
lead to emission while the triplet excitons are wasted. For device
fabrication, spin coating and vapor deposition methods are used
although the latter is generally preferred. This preference imposes
While iridium(III) and platinum(II) complexes have found
extensive application in OLED’s, there is also considerable
interest in the use of luminescent copper(I) complexes as dopant
emitters.2-11 Although luminescence in Cu(I) complexes is well-
known, many of these complexes suffer from poor emission
efficiency or are cationic and thus unsuitable for device fabrication
by vapor deposition methods. One notable exception is a di-
nuclear complex reported by Peters and co-workers in 2005. The
complex, which is supported by a PNP ligand set exhibited an
unusually high quantum yield and long-lived excited state.12 It was
Received: November 22, 2010
Published: March 21, 2011
r
2011 American Chemical Society
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ARTICLE
Chart 1. 1,2,3-Triazole Ligands and Relevant Copper
Complexesa
Scheme 1a
a Conditions: (a) PdCl2(PPh3)2 (1%), CuI (3.5%), trimethylsilyl-acet-
ylene, iPr2NH, 25 ꢀC, 6 h. (b) K2CO3, phenyl azide or benzylbromide/
NaN3, sodium ascorbate (6-10%), CuSO4 (3-5%, 0.5 M in H2O), t-
BuOH/H2O 1:1, 60 ꢀC, 12 h. (c) Pd(OAc)2 (5%), dppf (7.5%),
NaOtBu (1.3 equiv), Ar(-2,6-R3-4-R1)NH2, toluene, 100 ꢀC, 48 h.
species coordinated by triazole and pyridyl groups has been
described for biphasic catalysis.38
Photophysicalproperties ofCu(I) complexeswith 1,2,3-triazole
ligands (Chart 1) have been examined by us39 and others40-42
(IV-V). Depending on the organic ligand, cuprous iodide com-
plexes containingtriazoles withpendantpyridyl or pyrazolegroups
(V) form luminescent polymeric metal organic frameworks.40 We
have recently shown that symmetric chelating triazoles linked by a
phenylene backbone react with CuI in a 1:2 ratio to provide
discrete tetranuclear clusters which are brightly luminescent in the
solid state (IV).39 However, the high molecular weight of these
compounds rendered them unsuitable for sublimation and vapor
deposition processing. Encouraged by the bright emission, we
hypothesized that neutral mononuclear complexes with amido-
triazole and diphosphine chelating ligands may exhibit similar
bright luminescence and thermal stability. Related work on mono-
nuclear Cu(I) complexes with amido-phosphine supporting li-
gands (VII) has in fact led to complexes with highly efficient
solution photoluminescence.43 Herein, we report the synthesis
and photophysical properties of neutral, mononuclear copper(I)
complexes supported by chelating amido-triazole ligands and
1,2-bis(diphenylphosphino)benzene (dppb).
a(I) Ref 35. (II, III) Ref 36. (IV) Ref 39. (V) Ligands used in ref 40. (VI)
Ref 41. (VII) Ref 43.
also thermally stable and has been incorporated in an OLED
device with a 16% external quantum efficiency.13,14
The performance of Peters’ neutral complex in a device has
stimulated the synthesis of other new copper(I) complexes
exhibiting the properties desirable for device performance
and fabrication, specifically sublimability, thermal stability, and
bright photoluminescence. While modification of commonly
used ligands such as phenanthroline or bipyridine represents
a reasonable approach for the development of new complexes, a
second option involves the use of previously unemployed
ligands.
One underutilized ligand set is composed of chelating agents
containing 1,4-disubstituted-1,2,3-triazoles that are readily made
via Cu(I)-catalyzed Huisgen dipolar cycloaddition.15-17 Due in
part to the simplicity of synthesis as well as the broad potential for
variation in design, numerous reports on the coordination
chemistry of triazoles and chelating ligands containing them have
appeared recently in the literature.18-34 Among these reports are
a number of new copper(I) triazolato complexes. In 2004, tris-
(benzyltriazolylmethyl)amine (TBTA) (I) was used as an effec-
tive ligand for Cu(I) in cycloaddition reactions, presumably
stabilizing the catalyst through chelation.35 Later, evidence re-
garding the coordination modes of this ligand was obtained
through structural characterization of [CuIICl(TBTA)]þ (II) and
’ RESULTS AND DISCUSSION
Synthesis of the Ligands. Ligand precursors HL1-HL6
were prepared in three steps as outlined in Scheme 1. Briefly,
the Sonogoshira coupling reaction of commercially available
1-bromo-2-iodobenzene (A) with trimethylsilyl acetylene pro-
vided compound B. TMS-protected B was then subjected to one-
pot deprotection and Cu(I)-catalyzed Huisgen cycloaddition
with phenyl azide or benzyl azide generated in situ from benzyl
bromide and NaN3. This convenient single pot sequence has
been used before by us39 and others.30 Finally, aryl amination of
C using Pd(OAc)2/dppf as the catalyst44 proceeded in good
yield to provide the ligand precursors HL1-HL6 after
an air-sensitive dinuclear complex, [CuI2(TBTA)2]2þ (III).36
A
related complex, [CuICl(tris(triazolyl)methanol)], was prepared as
an air-stable complex that exhibited high catalytic activity, but its
structure was inferred indirectly.37 A polymer-supported Cu(I)
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Inorganic Chemistry
ARTICLE
chromatographic purification. The ligand precursors were
1
characterized by mass spectrometry and 13C and H NMR
spectroscopy. For HL1-HL4, the NH proton resonance in
CDCl3 was broadened into the baseline. In HL5 and HL6,
the NH resonance appeared significantly downfield at 8.86
and 8.94 ppm respectively. The observed chemical shift was
interpreted as an effect of hydrogen bonding with the triazole
ring that was later confirmed by an X-ray structure analysis of
HL5.
Synthesis of the Complexes and X-ray Crystallography.
Complexes 1-6 were prepared by treating a tetrahydrofuran
(THF) slurry of Cu2(μ2-Cl)2(dppb)2 (dppb = 1,2-bis-
(diphenylphosphino)benzene) with a mixture of potassium
tert-butoxide and the ligand precursor in THF. During the
addition, a rapid color change from yellow to orange occurs with
concurrent dissolution of the Cu2(μ2-Cl)2(dppb)2 suspension.
Gentle heating (5 min at 40 ꢀC) is required for full consumption
of the starting material. After removal of KCl by filtration, the
desired compounds are precipitated with hexanes as yellow or
orange solids. The complexes are highly soluble in THF, margin-
ally soluble in benzene and ether, virtually insoluble in hexanes,
and unstable in chlorinated solvents. The complexes oxidize
slowly when exposed to air in the solid state, but decompose
Single crystals of complexes 4-6 were grown from THF/
hexanes mixtures. Additionally, the structure of HL5 was solved
for comparison of the free and coordinated ligand geometries.
Unit cell, data collection, and structure refinement details are
provided in Table 1, and selected bond lengths and angles are
shown in Table 2. Full metrical parameters are provided in the
Supporting Information as a cif file. Figure 1 is a perspective view
of complex 5. ORTEP diagrams of 4, 6, and HL5 are shown in the
Supporting Information, Figures S1-S4.
Complexes 4-6 each adopt a distorted tetrahedral geo-
metry around the Cu(I) center as judged by the bond
angles at the metal and the dihedral angles between planes
containing chelating ligand donor atoms and copper(I) ions
(Table 2). Regarding the latter, angles between chelating atoms
(P2-Cu1-P1) and (N1-Cu1-N4) are near 90ꢀ, while
1
rapidly when exposed to oxygen in solution. H NMR spectra
recorded in C6D6 show characteristic amido-triazole ligand
resonances which in many cases overlap with aromatic signals
from the dppb ligand while 31P NMR spectra exhibit a broad
singlet for each complex. Parent ions with the correct isotope
patterns were seen by mass spectrometry under atmospheric
pressure ionization (APCI), and all complexes provided satisfac-
tory combustion analyses.
Table 1. Summary of Crystallographic Data
4 1/4 THF
5
6 2 THF
HL5
3
3
formula
fw
C
51H40CuN4O0.25P2
C52H43CuN4P2
849.38
C61H61CuN4O2P2
1007.62
100.0(1)
triclinic
P1
C22H20N4
340.42
100.0(1)
monoclinic
P21/c
873.80
100.0(1)
triclinic
P1
T (K)
cryst syst
space group
a (Å)
100.0(1)
triclinic
P1
13.006(4)
16.949(6
19.756(8)
87.334(8)
70.893(6)
82.130(6)
4076(2)
4
10.7576(9)
11.0452(9)
20.440(2)
80.040(2)
79.368(2)
60.986(1)
2077.5(3)
2
11.252(3)
13.518(3)
16.918(4)
82.476(4)
79.651(4)
86.882(4)
2508(1)
2
8.8824(9)
13.883(1)
14.824(2)
90
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
Z
100.077(2)
90
1799.7(3)
4
F
calcd (g cm-3
μ (mm-1
)
1.424
1.358
1.334
1.256
)
0.724
0.645
0.549
0.076
no. reflns collected
no. unique reflns
44205
48129
19070
43136
9575
14414
19741
8801
a
Rint
0.2963
5353
0.0389
0.0983
0.0356
7235
no. of obsd reflns
no. of params
GOFb on F2
14440
4900
1078
534
633
315
0.930
1.021
0.970
1.027
R1 [I > 2σ(I)]c
0.0856
0.0423
0.0512
0.0514
wR2d
0.1162
0.1027
0.0812
0.1350
2
2
a Rint = |Fo2 - ÆFo æ|/|Fo |. b GOF = S = [∑[w(Fo2 - Fc2)2]/(m - n)]1/2, where m = number of reflections and n = number of parameters. c R1 = ∑||Fo| -
|Fc||/∑|Fo|. d wR2 = [∑w(Fo2 - Fc2)2/∑w(Fo2)2]1/2 where w = 1/[2(Fo ) þ (aP)2 þ bP] and P = 1/3 max (0, Fo ) þ 2/3 Fc2.
2
2
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N-Cu-P bond angles are all greater than 109ꢀ. Six-
membered amido-triazole chelate rings are nearly planar,
but the 5-membered diphosphine chelate rings are slightly
buckled. The geometry of uncoordinated L5, where hydro-
gen-bonding exists between the diaryl amine and N1 of the
triazole ring, is nearly identical to that of the coordinated
ligand in 5. In the free ligand, as well as in 4-6, the
phenylene and triazole rings deviate slightly from planarity
(∼14ꢀ).
are significantly longer than in the two-coordinate anilido com-
plex [Cu(IPr)(NHPh)] (IPr = 1,3-bis(2,6-diisopropylphe-
45
ꢀ
nyl)imidazol-2-ylidene) (1.841(2) Å).
The similarity
between the Cu-N1 and Cu-N4 bond lengths confirms the
single bond character of the amido ligand as the filled Cu d
orbitals and filled nitrogen π orbital preclude a π-bonding
interaction.
Absorption Spectroscopy. The electronic spectra of com-
plexes 1-6 were recorded in benzene as shown in Figure 2 and in
THF as given in the Supporting Information. In both benzene
and THF, the spectra of 1-5 are similar with three prominent
features: an intense band from 280 to 300 nm with a molar
For N3-phenyl complexes 4 and 5, the phenyl rings and
triazole heterocycles are nearly coplanar. In contrast, 4-chloro
or 2,6-dimethyl substituted aryl rings are twisted approximately
90ꢀ out of plane of the central phenylene ring in each complex.
The Cu-N1 distances are comparable to those observed in
copper(I) halide clusters with triazole ligands,39 but Cu-N4
distances are somewhat shorter than those reported in similar
mononuclear Cu(I) compounds with chelating amido ligands
extinction coefficient (ε) in the range of 18,000-24,000 M-1 cm-1
,
a strong band appearing as a shoulder ranging from 325 to
440 nm, and a broad, low energy band with maxima from 415 to
430 nm and ε of 4,000-10,000 M-1 cm-1. Consistent with
the pale yellow solution color at dilute concentrations, the low
energy bands of each complex extend into the visible region of
(2.086(1) Å).43 However, the Cu-N4 distances observed here
ꢀ
Table 2. Selected Bond Lengths (Angstroms) and Angles
(Degrees)
4a
5
6
Cu1-N1 (Cu2-N5)
Cu1-N4 (Cu2-N8)
Cu1-P2 (Cu2-P4)
Cu1-P1 (Cu2-P3)
1.981(7), 2.003(7) 1.996(1) 2.031(3)
1.989(7), 1.978(7) 1.964(1) 1.981(3)
2.253(3), 2.271(3) 2.2618(4) 2.273(1)
2.269(3), 2.236(3) 2.2180(4) 2.276(1)
N1-Cu1-N4 (N5-Cu2-N8) 92.3(3), 92.7(3)
92.05(4) 93.2(1)
N1-Cu1-P2 (N5-Cu2-P4) 115.0(2), 105.3(2) 104.34(3) 109.8(1)
N4-Cu1-P2 (N8-Cu2-P4) 126.5(2), 123.0(2) 125.70(3) 128.9(1)
N1-Cu1-P1 (N5-Cu2-P3) 111.1(2), 120.2(2) 112.10(3) 109.1(1)
N4-Cu1-P1 (N8-Cu2-P3) 123.7(2), 125.2(2) 130.55(3) 130.9(1)
P2-Cu1-P1 (P3-Cu2-P4) 89.5(1), 91.2(1)
P1, P2, Cu1 and N1, N4, Cu1 89
(P3, P4, Cu2 and N5, N8, Cu2) 82
90.47(1) 84.51(4)
87 89
a There are two independent molecules in the asymmetric unit of
complex 4. Measurements refer first to the molecule containing Cu1
and the second measurement as well as parenthetical atom labels refer to
the molecule containing Cu2.
Figure 2. Absorption spectra for 1-6 in benzene (c = 2.5 ꢀ 10-5 M).
Inset: Hammett plots of absorption energy versus σp of the substituent
para to the amido donor (1 = H, 2 = Me, 3 = OMe, 4 = Cl).
Figure 1. ORTEP diagrams of complex 4 (left) and complex 6 (right) (50% probability ellipsoids). Hydrogen atoms and cocrystallized solvent
molecules have been omitted for clarity.
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In 2-methyl-tetrahydrofuran frozen glass at 77 K, the emission
maxima are significantly blue-shifted from the solid state and lie
in the range of 555-585 nm with lower energy shoulders evident
in 1-5 (Table 3, Supporting Information, Figures S7-S8).
Decay profiles in frozen glass samples were fit to single expo-
nential functions with lifetimes ranging from 330 μs for 1 to 1400
μs for 5.
The solid state emission of N-benzyl substituted complex 6 is
blue-shifted relative to 1-5 at room temperature while the
luminescence lifetime of 1.7 μs is similar to those of the other
complexes. Upon cooling the solid state sample of 6 to 77 K, a red
shift from 575 to 589 nm is observed. The excited state lifetime of
6 at 77 K in the solid state (270 μs) is considerably longer than
that of the other complexes. In frozen 2-methyl-tetrahydrofuran,
the emission at 567 nm is similar to 1-5, with a lifetime of 70
microseconds that is notably shorter than those of 1-5.
At 298 K, the solid state emission energy in 1-4 varies linearly
with Hammett σp parameter of the aryl amido substituent
(Supporting Information, Figure S12). The same trend (4 > 1 >
2 > 3) is observed in frozen glass samples (Supporting Informa-
tion, Figure S9). Hammett plots of emission energy versus σp have
a positive slope in which complex 3 with an electron-donating
methoxy group exhibits the lowest energy emission. The same
trend was found in the lowest energy absorption bands of these
complexes and is consistent with electronic perturbation of the
HOMO by the amido ligand substituent.
Figure 3. Solid state emission spectra for 1-4 at 298 K. λexc = 400 nm.
Inset: Hammett plot of emission maximum versus σp values of the
substituent para to the amido donor (1 = H, 2 = Me, 3 = OMe, 4 = Cl).
the spectrum. The spectrum of complex 6 (Figure 2, solid purple
line) is similar to those of 1-5 with the exception that the lowest
energy band displays an additional feature with a maximum at
423 nm and a shoulder at 445 nm.
The energy of the strong absorption near 300 nm varies only
slightly between complexes, suggesting little perturbation of the
involved molecular orbitals by differences in the amide part of the
anionic ligand. This band may be assigned as π-π* transitions of
the numerous aromatic groups in the ligand set. The homoleptic
Complexes 1 and 5 both have H atoms in the R1 position, yet
the emission of 5 isred-shifted relative to thatof 1 in the solid state
and frozen glass by 16 and 10 nm, respectively. This observation
may be explained in inductive electronic or stereoelectronic terms
regarding the dimethyl substitution of 5. Since the emission of 2 is
red-shifted relative to 1 by 3-7 nm, a purely electronic argument
suggests that a second methyl group might perturb the emission
by a similar amount more. A stereoelectronic argument is that
absence of free rotation around the N-aryl bond because of 2,6-
dimethyl substitution results in electronic isolation of the aryl ring
from the π system of the amide donor, the central phenylene ring,
and the copper ion. Presumably, disrupted conjugation raises the
energy of the involved molecular orbitals.
Comparison of the emission in complexes 5 and 6 provides
some insight into the nature of the lowest unoccupied molecular
orbital (LUMO). Complex 6 shows higher energy emission in
frozen glass and in the solid state. Since absorption and emission
data for complexes 1-4 have already established that substitu-
tion of the aryl ring in the amido part of the ligand affects the
HOMO, the higher energy emission in 6 must arise from a higher
triazole-based LUMO relative to 5 since the aryl amido part of
the ligands are the same in both complexes.
Solution Emission. Emission spectra were measured in THF
and benzene at room temperature. All complexes exhibit orange
emission in fluid solution and relevant photophysical data are
summarized in Table 3. When the complexes are excited in their
lowest energy absorptions (420 nm), the emission profiles are
broad with maxima ranging from about 630 to 660 nm and lower
energy shoulders separated by about 25 nm from the maxima
(Supporting Information, Figures S13-S24). For each complex,
notably higher quantum yields were found in benzene than in
THF with 4 exhibiting the highest emission quantum yield (Φ =
0.022) measured relative to Ru(bpy)32þ in air-equilibrated water
(Φ = 0.028).47 The emission bands do not overlap with the
absorption bands. With the exception of 3 and 6 in THF, lifetimes
range from several hundred nanoseconds to a few microseconds,
þ
cationic complex Cu(dppb)2 exhibits a similar feature in its
absorption spectrum.46 On the other hand, the absorption
energies of the bands near 340 and 420 nm vary noticeably
between the complexes. In the series 1-4, the maximum
absorption wavelengths of both bands in benzene vary linearly
with the Hammett σp constant of the substituent at the 4-posi-
tion of the aryl amido group (Figure 2, inset). While the slope is
negative for the shoulder near 340 nm, it is positive for the lower
energy absorption. In THF, the data were not modeled as well by
linear fits as in benzene, but the trends are similar (Supporting
Information, Figures S5-S6). At the two extremes of the lower
energy band in benzene, electron donating methoxy-substituted
complex 3 exhibits the lowest energy maximum while electron
withdrawing chloro-substituted 4 exhibits the highest energy
maximum. This trend is consistent with increasing the highest
occupied molecular orbital (HOMO) energy with greater elec-
tron donating properties of the substituent para to the amido
donor. The absorption shoulder near 340 nm is affected in the
opposite way, implying that electronic differences in the ligand
influence the energy of the electron accepting orbital in this
electronic transition.
Solid State and Frozen Glass Emission. Solid state emission
spectra (Figure 3) were obtained for complexes 1-6 in KBr
matrixes at 298 K and 77 K. Emission profiles are broad with
maxima at 575-615 nm and shoulders for 1-5 in the 645-
655 nm range (Table 3). Upon cooling to 77 K, only subtle
changes in the emission maxima are observed (ca. 2 nm). Solid
state emission decay curves were fitted to single exponential
functions with lifetimes at 298 K ranging from 0.30 to 1.9 μs. At
77 K, there is a modest increase in the lifetime of 1-5 by about
one order of magnitude.
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Table 3. Summary of Photophysical Data
complex
1
media
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
THFa
benzenea
glass 77 K
solid 298 K
solid 77 K
absorptions λ/nm (ε/M-1 cm-1)>
λem/nm (τ /μs)c
Φd
286 (31,680), 325 (24,800), 362 (18,480), 416 (9,480)
295 (24,200), 337 (31,000), 420 (9,800)
632, 658 (0.57)
629, 651 (1.7)
567 (330)
0.0058
0.016
608 (1.9)
610 (13)
2
3
4
5
6
288 (23,360), 330 (17,600), 425 (6,810)
295 (23,800), 336 (18,700), 426 (6700)
633, 662 (0.35)
632, 653 (1.0)
575 (310)
0.0033
0.011
612 (2.1)
615 (6.1)
287 (21,440), 328 (16,440), 436 (4,560)
296 (18,500), 335 (14,100), 430 (4,100)
633, 667 (0.07)
634, 659 (0.20)
583 (450)
0.00040
0.0019
615 (0.59)
613 (3.4)
289 (20,640), 321 (15,640), 378 (15,640), 419 (5,160)
298 (21,000), 340 (17,000), 415 (6,800)
631, 649 (0.75)
622, 647 (2.4)
555 (490)
0.010
0.026
602 (1.5)
604 (11)
284 (33,160), 330 (16,200), 416 (1,000)
290 (27,000), 327 (17,000), 416 (8700)
631, 649 (2.0)
628, 653 (2.8)
577 (1400)
623 (0.30)
0.013
0.019
626 (2.1)
290 (22,320), 328 (11,720), 419 (8,400), 440 (6,480)
295 (18,500), 326 (13,400), 423 (7,000), 445 (5,600)
632, 658 (0.06)
631, 653 (0.11)
567 (70)
0.0015
0.0048
575 (1.7)
589 (270)
a c = 2.5 ꢀ 10-5 M, (b) In 2-methyltetrahydrofuran (c) λexc = 420 nm. (d) Measured as a relative quantum yield using Ru(bpy)32þ in water (Φ = 0.28).47
As was observed for emission in the solid state and frozen glass,
the order of emission energy in the series 1-4 (Figure 4) varies
linearly with σp with the Hammett plot having a negative slope
(Supporting Information, Figures S10-S11). This relationship
supports the notion that substitution of the aryl amido group in
the 4 position affects the energy of the highest occupied
molecular orbital. Its energy level increases with the electron
donating ability of the R1 substituent.
In comparing the emission data in THF and benzene, emission
energy, luminescence lifetime, and quantum yields are all lower in
THF. These results suggest that the emissive excited state
possesses charge transfer character which is stabilized better by
the morepolar solvent. Therelationship between emission energy
and lifetimes in the same solvent for 1-4 is possibly a manifesta-
tion of the “energy gap law” in which nonradiative decay pathways
are more accessible to lower energy excited states.
In solution, the emission of 5 is slightly higher in energy than
that of 6. This differs from solid state and frozen glass measure-
ments in which 6 exhibits higher energy emission. While the solid
Figure 4. Absorption and emission spectra of 4 in THF (red) and
benzene (blue).
and in each case, they are shorter in THF. In the series 1- 4,
luminescence lifetimes decrease with decreasing emission energy.
Lifetime values and the large Stokes’ shifts suggest an excited state
of triplet multiplicity. In benzene, the emission of each complex is
slightly blue-shifted relative to that in THF.
state and 77 K glass emission data suggest that the LUMO may be
triazole-based, a higher energy LUMO in 6 is not supported in
solution. A possible explanation is that conjugation of the triazole
and phenyl ring in 5 differs between the fluid solution orientation
and its average conformer in the solid state and frozen glass.48
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Table 4. Electrochemical Potentialsa (V versus NHE)b,c
complex
oxidation potential
1 Cu(L1)dppb
2 Cu(L2)dppb
3 Cu(L3)dppb
4 Cu(L4)dppb
5 Cu(L5)dppb
6 Cu(L6)dppb
0.37d
0.32d
0.26d
0.47d
0.41 (0.15)e
0.38 (0.16)e
a Measured in degassed THF with 0.1 M n-Bu4NPF6 as the supporting
electrolyte using a glassy carbon working electrode with a Pt wire
auxiliary electrode and Ag wire reference electrode. b Oxidation poten-
tials obtained using ferrocene as an internal standard (Fcþ/0 = 0.56 V
versus SCE in THF, SCE = 0.24 V versus NHE).52 c The peak-to-peak
difference for the ferrocene/ferroceniumþ couple under these experi-
mental conditions was 0.14 to 0.16 V. d Irreversible anodic wave. e Quasi-
reversible oxidation with E0 reported as (Eanodic - Ecathodic)/2. Peak-to-
peak difference value in parentheses.
Electrochemistry. Complexes 1-6 were studied by cyclic
voltammetry in THF, and the results are shown in Table 4.
Complexes 5 and 6 exhibit quasi-reversible oxidations at 0.41 and
0.38 V versus NHE, respectively. Conversely, 1-4 show irrever-
sible oxidations at potentials ranging from 0.25 to 0.47 V versus
NHE. No reduction waves were found within the solvent
window. Facile oxidations are not surprising in view of the high
oxygen sensitivity of the complexes in solution.
Figure 5. Frontier molecular orbitals for complexes 4-6 calculated at
BP86/6-31G(d) level of theory.
Table 5. Frontier Orbital Energies for the Ground State of
Oxidation potentials are an effective measure of the relative
HOMO energies in a series of compounds. For 1-4, the
irreversible oxidation peak potential varies linearly with the σp
parameter (Supporting Information, Figure S25), supporting the
inferences made previously regarding the effect of R1 on the
photophysical properties. Complex 3, with an electron-donating
OMe group, is the most easily oxidized, while chloro-substituted
4 is the most difficult to oxidize. The nearly identical oxidation
potentials determined for complexes 5 and 6 suggest that the N3
substituted triazole ring is not involved in the HOMO. Thus, the
electrochemical data are consistent with an oxidation involving a
portion of the molecule electronically coupled to the 4 position
of the aryl amido ligand. The HOMO must be amido ligand-
based or Cu(I)-based.
Complex 5 differs from 1 primarily by the 2,6-dimethyl
substitution of the amido ligand. In the X-ray structure, the aryl
substituent bound to the amido donor is twisted perpendicular to
the triazole ring so that the methyl groups are located above and
below the copper(I) ion. It is well-known that metal-to-ligand
charge transfer in copper(I) complexes entails a formal oxidation
from Cu(I) to Cu(II) and a possible geometrical change from
tetrahedral toward square planar in the excited state.49,50 As a
result, addition of a ligand (solvent) is more likely to occur in the
excited state, and oxidations may be irreversible during the
electrochemical measurement. Complexes with bulky substituents
near the Cu(I) ion are less prone to solvent coordination in the
excited state.51 In complexes 5 and 6, the methyl groups of the
amido ligand likely shield the metal center from coordination by
THF upon electrochemical oxidation and allow some reversibility.
Electronic Structure Calculations. Density functional theory
(DFT) calculations were performed on the singlet ground states
(S0) of complexes 1-6 to further probe the nature of the excited
states and to clarify the discrepancies between emission energies
in 5 and 6. While the optimized geometry around the Cu(I) ions
remains similar to that determined from the X-ray structure
1-6 in eV
complex
1
2
3
4
5
6
LUMOþ1
LUMO
-1.71
-2.13
-3.15
-1.73
-2.09
-3.11
-1.71
-2.12
-3.05
-1.81
-2.17
-3.26
-1.78
-1.90
-3.14
-1.56
-1.73
-3.11
HOMO
determinations, significant differences are noted in the pheny-
lene-N-(4-X aryl) torsion angles. The calculated torsion angles
are 60.6ꢀ for 1, 58.6ꢀ for 2, 66.2ꢀ for 3, and 56.4ꢀ for 4. For 2,6-
dimethyl substituted 5 and 6, the substituted ring remains
perpendicular to the phenylene ring. Dihedral angles between
the triazole heterocycle and the N3 phenyl rings deviate slightly
from planarity in the optimized geometry and lie in the range of
24.71ꢀ to 27.75ꢀ.
Diagrams of the HOMO, LUMO, and LUMOþ1 for the
ground states of 4-6 are shown in Figure 5, and energies of these
orbitals for all complexes are provided in Table 5. Orbitals for
complex 4 were chosen as a representative example for the series
1-4. Complete diagrams for all complexes are provided in the
Supporting Information. In all complexes, the HOMO is com-
posed primarily of π-functions on the aryl amido ligand and d
orbitals of the Cu(I) ion. In 1-4, where the 4-substituted ring is
not perpendicular to the phenylene ring, there are small con-
tributions from π orbitals on the substituted ring to the HOMO.
On the other hand, the perpendicularly oriented dimethyl
substituted rings in 5 and 6 show negligible contributions to
the HOMO. The electronic effect of the 4-substituted groups in
1-4 is evident in the energy level diagram. Complex 3 (σp = -
0.28) has the highest HOMO level, while 4, with the most
electron-withdrawing substituent (σp = 0.24), possesses the
lowest energy HOMO.
For complexes 1-5 with N3-phenyl triazole rings, the LUMO
is delocalized over both rings. For 1-4, there are only minor
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Inorganic Chemistry
ARTICLE
deviations in the LUMO energies. The LUMOþ1 level in 1-5 is
composed of π-functions on the diphosphine ligand with the
greatest contribution from the central dppb phenylene ring. In 6,
the LUMO is located on the dppb ligand and is nearly identical in
character and energy to the LUMOþ1 of 1-5 while the
LUMOþ1 level of 6 is composed of triazole and benzyl π
functions despite the nonconjugating methylene group separat-
ing the two rings. In the absence of conjugation, the energy of this
orbital (-1.56 eV) is greater than that of the corresponding
conjugated triazole orbital in 5 (-1.90 eV).
Analyzed in the context of emission and electrochemical data,
the electronic structure calculations provide valuable insight into
the excited states. First, the optimized geometries suggest that
free rotation of the 4-substituted N-aryl rings in 1-4 is possible,
but rotation in 5 and 6 is hindered by the methyl groups.
Rotation allows for conjugation between the amido donor and
the phenylene backbone, and prevents electronic isolation of the
para substituent. This is evident in the calculated HOMO
energies, and experimentally in the oxidation potential, electronic
spectra, and emission spectra which all vary according to the
electronic influence of the para substituent.
While spectroscopy and electrochemistry shed light on the
identity of the HOMO, the nature of the LUMO is not as easily
ascertained experimentally. In the solid state and frozen glass
samples, N-phenyl substituted 5 exhibited lower energy emission
than N-benzyl substituted 6, suggesting a triazole-based LUMO.
Conversely, in solution the emission of 5 is higher energy than in
6. DFT calculations provided insight into this discrepancy,
showing that the LUMO of 5 is triazole-based, whereas the
LUMO of 6 is actually diphosphine-based. In the absence of
triazole conjugation for complex 6, the triazole-based orbital
energy is raised to the LUMOþ1 level. The dissimilar nature of
excited states in 5 and 6 helps to explain the additional low energy
absorption feature in 6 as well as differences in lifetime data
among 1-5 compared with 6.
modification of the ligands, sublimation and device fabrication
may be possible. Such efforts are currently underway.
’ EXPERIMENTAL SECTION
Chemicals. Trimethylsilylacetylene and 1-bromo-2-iodobenzene
were purchased from Oakwood Chemicals. Substituted anilines, benzyl
bromide, sodium azide, sodium tert-butoxide, and potassium tert-butoxide
were purchased from Aldrich Chemical Co. and used as received.
Palladium(II) acetate was purchased from Strem Chemicals. 1,10-Bis-
(diphenylphosphino)ferrocene was purchased from VWR. Toluene, THF,
hexanes, and benzene were dried using a Grubbs-type solvent system and
stored in a nitrogen-filled glovebox. 2-Methyltetrahydrofuran was distilled
from sodium/benzophenone. Phenyl azide was prepared from aniline.
Characterization. 1H, 13C{1H}, and 31P{1H} NMR spectra were
recorded using a Bruker Avance 500 MHz spectrometer with 1H and 13
C
chemical shifts referenced to the residual solvent peaks in CDCl3 or
C6D6 and 31P chemical shifts referenced to external 85% H3PO4. Mass
spectra of the ligands and complexes were measured on a Shimadzu 2010
series liquid chromatography mass spectrometer (LCMS) under atmo-
spheric pressure chemical ionization (APCI). Absorptions spectra were
measured on a Hitachi U2000 UV-vis spectrometer. Steady-state
excitation and emission spectra were obtained using a Spex Fluoro-
max-P fluorometer with excitation and emission slits set for a 2 nm band-
pass. Solution phase samples were prepared using dry, deoxygenated
benzene in a nitrogen-filled glovebox. Frozen glass samples were
prepared in 5 mm NMR tubes in the glovebox and sealed with a septum.
Solid state emission samples were measured as a finally ground mixture
of the emissive complex and KBr (1:9 w/w) in a flame-sealed capillary
tube. For low temperature measurements, the capillary was held in a
vacuum dewar filled with liquid nitrogen. Lifetime measurements were
performed using a model LN203C nitrogen laser (Laser Photonics Inc.)
with λ = 337.1 nm and a 0.1 nm spectral width pulsed at 1 pulse/second.
Signals were detected by a silicon photodiode and photomultiplier tube
(1P28 type) with a 2 ns rise time and viewed with a Hewlett-Packard
54510-B oscilloscope connected to a computer via a GPIB interface. No
less than five decay curves were averaged for data fitting. Elemental
analyses were performed on a PerkinElmer 2400 Series II analyzer
operated by the Center for Enabling New Technologies through
Catalysis elemental analysis facility at the University of Rochester.
Electrochemistry. Cyclic voltammograms were measured using an
EG&G PAR 263A potentiostat/galvanostat equipped with a single com-
partment cell using a glassy carbon working electrode, Ag wire pseudor-
eference electrode, and Pt wire auxiliary electrode. In all cases, a solution of
tetrabutylammonium hexafluorophosphate (Fluka) in dry THF was
purged with N2 for 8 min, and a blank scan was obtained to verify the
purity of the solvent. During purge, portions of solid copper(I) complex
and ferrocene were added to the solution for measurements to obtain a
’ CONCLUSIONS
In pursuit of new photoluminescent Cu(I) compounds for
application in OLEDs, we have prepared a series of mononuclear
copper(I) complexes supported by 1,2-bis(diphenylphosphino)
benzene and anionic amido-triazole ligands and investigated their
structural, electrochemical, and photophysical properties. The
complexes exhibit modest solution emission and bright solid state
emission. Modification of the electronic properties of the amido
ligand has led to elucidation of the HOMO as a mixture of Cu-d
orbitals and biaryl amido π-functions. The LUMO, on the other
hand, depends on the nature of the triazole ligand. For 1-5 in
which the triazole is N3-phenyl substituted, the LUMO is located
on the triazole and the emission is assigned as mixed metal-to-
ligandþ intraligandcharge transfer3(MLCTþILCT). A variation
in ligand as simple as changing the N3-phenyl group to a benzyl
group (complex 6) results in a phosphine based LUMO and
changes the assignment of the excited state to metal-to-ligand þ
concentration of about 1 mM complex. The scan rate was 100 mV s-1
.
Crystal Structure Determination. Each crystal was placed onto
the tip of a glass fiber and mounted on a Bruker SMART Platform
diffractometer equipped with an APEX II CCD area detector. All data
were collected at 100.0(1) K using MoKR radiation (graphite
monochromator.)53 For each sample a preliminary set of cell constants
and an orientation matrix were determined from reflections harvested
from three orthogonal wedges of reciprocal space. Full data collections
were carried out with frame exposure times of 45-60 s at detector
distances of 4 cm. Randomly oriented regions of reciprocal space were
surveyed for each sample: four major sections of frames were collected
with 0.50ꢀ steps in ω at four different j settings and a detector position of
-38ꢀ in 2θ. The intensity data were corrected for absorption,54 and final
cell constants were calculated from the xyz centroids of approximately
4000 strong reflections from the actual data collection after integration.53
Structures were solved using SIR9755 and refined using SHELXL-97.56
3
ligand-to-ligand charge transfer (MLCTþLLCT). While these
complexes exhibit the desired photoluminescence and quasi-
reversible electrochemistry desired for OLED devices, thermal
decomposition remains a problem and sublimation is not feasible
for vapor phase deposition processing. Nevertheless, these com-
plexes are an important addition to the rapidly expanding litera-
ture on triazole coordination chemistry, and with judicious
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Inorganic Chemistry
ARTICLE
Space groups were determined based on systematic absences, intensity
statistics, and Cambridge Structural Database frequencies.57 Direct-
methods solutions were calculated which provided most non-hydrogen
atoms from the difference Fourier map. Remaining non-hydrogen atoms
were located through full-matrix least-squares (on F2)/difference Fourier
cycles. Non-hydrogen atoms were refined with anisotropic displacement
parameters and hydrogen atoms were placed in ideal positions and
refined as riding atoms with relative isotropic displacement parameters.
All refinements were run to mathematical convergence.
After cooling the reaction, water was added. The aqueous layer was
extracted with CH2Cl2, and the combined organic layers were washed
with brine. After evaporation of the solvent, the crude products were
adsorbed onto silica gel and the ligands were purified by column
chromatography (hexanes:ethyl acetate 5:1).
N-Phenyl-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline (HL1).
The general method was followed using bromo-phenyl triazole, C
(1.00 g, 3.3 mmol), aniline (0.34 g, 3.7 mmol), Pd(OAc)2 (37 mg),
dppf (138 mg), and NaOtBu (0.416 g). After chromatography, the
residue was triturated with pentane, filtered, and recrystallized from hot
ethanol to provide white crystals. (0.85 g, 82%). 1H NMR (CDCl3, 500
MHz): δ 8.23 (s, 1H, triazole CH), 7.81-7.78 (m, 2H), 7.59-7.55 (m,
4H), 7.48 (tt, 2H, J = 1.2, 8.1), 7.32-7.22 (m, 5H), 6.98 (tt, 1H, J = 1.2,
7.1) 6.92 (dt, 1H, J = 1.1, 7.5). 13C{1H} NMR (CDCl3, 125 MHz):
δ 148.6 (q), 142.6 (q), 142.0 (q), 137.0 (q), 129.9, 129.4, 129.2, 129.1,
128.5, 121.9, 120.8, 119.7, 118.6, 116.9, 116.6 (q). MS (APCIþ) m/z
calcd. 312.14. Found: 313.05 (MþH)þ.
DFT Calculations. The geometries obtained from X-ray crystal-
lography were used as a starting point for geometry optimization in
complexes 4, 5, and 6. For 1-3, the starting geometry of 4 was used.
Ground state optimizations were first carried out at the HF/6-31G level
in Gaussian 03. The resultant coordinates were input for optimization
and single point calculations using the BP86 method which incorporates
Becke’s 1988 exchange functional58 and Perdew’s gradient corrections
and correlation function59 with the 6-31G(d) basis set on all atoms.
1-(Trimethylsilyl-ethynyl)-2-bromo-benzene. A solution of
1-iodo-2-bromobenzene (13.8 g) in diisopropyl amine (250 mL) was
purged with a rapid flow of N2 for 20 min. In one portion, CuI (0.33 g,
3.5%) and Pd(PPh3)2Cl2 (0.34 g, 1%) were added. After stirring for 10
min, trimethylsilyl-acetylene (8.23 mL, 1.2 equiv) was added via syringe. A
heavy precipitate formed immediately, and the mixture was stirred rapidly
at room temperature for 5 h. The precipitate was removed via filtration,
and the volatiles were evaporated leaving a black residue which was
purified via flash chromatography on silica gel using hexanes as the eluent
to provide 11.76 g of the title compound as a pale yellow oil (95% yield).
N-(4-Methylphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)-
aniline (HL2). The general method was followed using bromo-
phenyl triazole, C (1.00 g, 3.3 mmol), 4-toluidine (0.393 g, 3.7 mmol),
Pd(OAc)2 (37 mg), dppf (138 mg), and NaOtBu (0.416 g). After
chromatography, the residue was triturated with hexanes, filtered, and
recrystallized from hot ethanol to provide the title compound as white
1
crystals (0.62 g, 57%). H NMR (CDCl3, 500 MHz): δ 8.23 (s, 1H,
triazole CH), 7.80-7.79 (m, 2H), 7.58-7.55 (m, 3H), 7.48 (tt, 1H, J =
1.4, 7.4), 7.38 (dd, 1H, J = 0.8, 8.4), 7.23-7.12 (m, 5H), 6.88 (dt, 1H, J =
1.1, 7.4), 2.32 (s, 3H, CH3). 13C{1H} NMR (CDCl3, 125 MHz) δ 148.8
(q), 142.8 (q), 139.8 (q), 137.0 (q), 131.9 (q), 129.95, 129.94, 129.3,
129.1, 128.4, 121.1, 120.8, 119.0, 118.5, 116.0, 115.8 (q), 20.9 (-CH3).
MS (APCIþ) m/z calcd. 326.15. Found: 327.30 (MþH)þ.
4-(2-Bromophenyl)-1-phenyl-1-H-1,2,3-triazole (C, R2
=
Ph). To a solution of 1 (4.24 g, 16.7 mmol) in 1:1 tBuOH/H2O
(50 mL) was added K2CO3 (5.6 g, 2 equiv). After stirring for 10 min,
phenyl azide (2.00 g) and sodium ascorbate (0.20 g, 6%) were added. The
mixture was purged with N2 for 15 min then CuSO4 (1.00 mL of a 0.5 M
aqueous solution, 3%) was added dropwise with vigorous stirring. The
reaction was stirred at room temperature for 1 h then at 60 ꢀC for 24 h.
Upon cooling, 50 mL of a dilute aqueous ammonia solution was added to
provide a fine suspension which was extracted with diethyl ether. The
ether layer was washed with brine, dried over MgSO4 and evaporated. The
residue was purified via flash column chromatography (silica gel, hexanes:
ethyl acetate 10:1) to provide 2.97 g (59%) of the title compound a white
powder. 1H NMR (CDCl3) δ 8.67 (s, 1H, triazole C-H), 8.20 (d, J = 7.7
Hz, 1H), 7.81 (d, J = 8.0 Hz, 2H), 7.69 (d, J = 8.0 Hz, 1H), 7.56 (t, J = 7.7
Hz, 2H), 7.45 (m, 2H), 7.24 (t, J = 7.7 Hz, 1H). MS (APCIþ) m/z calcd.
299.01, 301.00. Found: 300.05, 302.05 (MþH)þ.
N-(4-Methoxyphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)-
aniline (HL3). The general method was followed using bromo-
phenyl triazole C (1.00 g, 3.3 mmol), 4-anisidine (0.452 g, 3.7 mmol),
Pd(OAc)2 (37 mg), dppf (138 mg), and NaOtBu (0.416 g). After
chromatography, the residue was triturated with pentane, filtered, and
recrystallized from hot ethanol to provide the title compound as white
1
crystals (0.97 g, 85%). H NMR (CDCl3, 500 MHz): δ 8.25 (s, 1H,
triazole CH), 7.81-7.80 (m, 2H), 7.57-7.47 (m, 4H), 7.49 (tt, 1H, J =
1.5, 7.5), 7.26-7.18 (m, 4H), 6.90 (d, 1H, J = 8.9), 6.85 (t, 1H, J = 7.2),
3.82 (s, 3H, CH3). 13C{1H} NMR (CDCl3, 125 MHz): δ 155.9 (q),
149.0 (q), 143.9 (q), 137.0 (q), 135.1 (q), 129.9, 129.3, 129.1, 128.3,
124.2, 120.8, 118.4, 118.3, 115.0, 114.8 (q), 114.7, 55.65 (-OCH3). MS
(APCIþ) m/z calcd. 342.15. Found: 343.10 (MþH)þ.
1-Benzyl-4-(2-bromophenyl)-1-H-1,2,3-triazole (C, R2
=
N-(4-Chlorophenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)ani-
line (HL4). The general method was followed using bromo-phenyl
triazole C (1.00 g, 3.3 mmol), 4-chloroaniline (0.467 g, 3.7 mmol),
Pd(OAc)2 (37 mg), dppf (138 mg), and NaOtBu (0.416 g). After
chromatography, the residue was triturated with hexanes, filtered, and
recrystallized from hot ethanol to provide the product as white crystals
Bn). To a solution of 1 (1.00 g, 4 mmol) in 1:1 tBuOH/H2O (15 mL)
were added consecutively K2CO3 (1.1 g, 8 mmol), NaN3 (0.28 g, 4.4
mmol), benzyl bromide (0.47 mL, 4 mmol), and sodium ascorbate (0.078
g, 0.4 mmol). The mixture was purged with N2, and CuSO4 (5%, 0.4 mL
of a 0.5 M solution in water) was added via syringe. The reaction was
heated at 65 ꢀC for 24 h. Upon cooling, the mixture was diluted with
aqueous ammonia and extracted with several portions of diethyl ether.
The combined organic phase was washed with brine, dried (MgSO4), and
evaporated to give provide 0.90 g (73%) of the title compound as a pale
yellow powder. 1H NMR (CDCl3, 500 MHz) δ 8.15 (s, 1H), 8.12 (d, J =
7.8 Hz, 1H), 7.63 (d, J = 8.0 Hz, 1H), 7.41-7.31 (m, 6H), 7.32-7.31 (m,
2H), 7.19 (dt, J = 7.7 Hz, 0.8 Hz, 1H), 5.61 (s, 2H). MS (APCIþ) m/z
calcd. 313.02, 315.02. Found: 313.95, 315.95 (MþH)þ.
1
(0.95 g, 85%). H NMR (CDCl3, 500 MHz): δ 8.23 (s, 1H, triazole
CH), 7.80-7.79 (m, 2H), 7.59-7.56 (m, 3H), 7.49 (tt, 1H, J = 1.1, 7.5),
7.26-7.23 (m, 4H), 7.19-7.16 (m, 2H). 13C{1H} NMR (CDCl3, 125
MHz): δ 148.6 (q), 141.7 (q), 141.3 (q), 136.9 (q), 130.0, 129.33,
129.29, 129.21, 128.5, 126.4 (q), 121.1, 120.8, 119.9, 118.6, 116.7, 116.6
(q). MS (APCIþ) m/z calcd. 346.10 Found: 347.05 (MþH)þ.
2,6-Dimethyl-N-[2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl]-
aniline (HL5). The general procedure for aryl amination was fol-
lowed using C (0.500 g, 1.6 mmol), Pd(OAc)2 (11 mg), dppf (41 mg),
NaOtBu (0.19 g), and 2,6-dimethylaniline (0.25 mL) in 10 mL of toluene.
After chromatography, the residue was crystallized from a 1:5 mixture of
acetonitrile/ethanol to provide HL5 as white blocks upon standing
Aryl Amination General Procedure. In a drybox, a Schlenk tube
was charged with bromophenyl-triazole C, Pd(OAc)2 (5%), 1,10-
bis-(diphenylphosphino)-ferrocene (dppf, 7.5%), sodium tert-butoxide
(1.3 equiv.), and toluene (∼3 mL/mmol). After stirring for 5 min, the
appropriate aniline was added as a solid or as a solution in toluene. The
flask was sealed with a Teflon stopper and heated at 100 ꢀC for 48 h.
Unless specified otherwise, the following workup procedure was used.
1
at room temperature (244 mg, 43%). H NMR (CDCl3, 400 MHz):
δ 8.86 (s, 1H, NH), 8.23 (s, 1H, triazole CH), 7.83 (d, 2H, J = 7.6),
7.60-7.47 (m, 4H), 7.16-7.07 (m, 4H), 6.74 (t, 1H, J = 7.4), 6.31 (d, 1H,
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ARTICLE
J = 8.4), 2.27 (s, 6H, -CH3). 13C{1H} NMR (CDCl3, 125MHz):δ149.6
(q), 144.9 (q), 138.6 (q), 137.1 (q), 136.7 (q), 130.0, 129.6, 129.1, 128.5,
128.0, 126.0, 120.8, 118.0, 116.8, 113.0 (q), 112.9, 18.6 (-CH3). MS
(APCIþ) m/z calcd. 370.17 Found: 341.15 (MþH)þ.
Found: 855.10 (MþH)þ Anal. Calcd. for C50H39ClCuN4P2: C, 70.17;
H, 4.48; N, 6.55. Found: C, 69.79; H, 4.70; N, 6.40
Cu(L5)(dppb) (5). The general procedure was followed using 0.164
g of HL5, 0.065 g of tBuOK, and 0.263 g of [dppbCuCl]2 to provide
0.390 g of 5 as an orange powder (95%). X-ray quality crystals were
obtained from a mixture of precipitate and filtrate which was left to stand
prior to filtration. 1H NMR (C6D6, 500 MHz): δ 7.46-7.41 (m, 4H),
7.34 (s, 1H), 7.33-7.32 (m, 2H), 7.28-7.27 (m, 2H), 7.12-7.09 (m,
3H), 7.04-6.95 (m, 3H), 6.97-6.82 (m, 20H), 6.70 (dd, J = 1.1, 6.7,
1H), 6.49 (m, 1H), 2.44 (s, 6H, CH3). 31P{1H} NMR (C6D6, 202
MHz): δ -10.4. MS (APCIþ) m/z calcd. 848.23. Found: 849.40
(MþH)þ Anal. Calcd. for C52H43CuN4P2: C, 73.53; H, 5.10; N, 6.60.
Found: C, 73.50; H, 5.13; N, 6.42.
2,6-Dimethyl-N-[2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl]-
aniline (HL6). The general procedure was followed using C (2.00 g,
6.4 mmol), Pd(OAc)2 (43 mg), sodium tert-butoxide (0.73 g), dppf
(0.159 g), toluene (15 mL), and 2,6-dimethylaniline (0.87 mL). Upon
completion, the reaction was cooled, and 50 mL of water was added. The
aqueous layer was extracted with diethyl ether (3 ꢀ 100 mL). Ether was
removed under reduced pressure, and the residue was triturated with a
small amount of ethanol which was then decanted from the tan solid.
Crystallization of the solid from hot EtOH provided the title compound as
white needles (1.36 g, 60.3%).1H NMR(CDCl3, 400MHz) δ8.94 (s, 1H,
N-H), 7.76 (s, 1H), 7.42-7.34 (m, 6H), 7.15-7.09 (m, 3H), 7.03 (t, J =
7.2 Hz, 1H), 6.66 (t, J = 7.4 Hz, 1H), 6.27 (d, J = 8.2 Hz, 1H), 5.61 (s, 2H,
CH2), 2.24 (s, 6H, CH3). 13C{H} NMR (CDCl3, 125 MHz): δ 149.4 (q),
144.7 (q), 138.6 (q), 136.7 (q), 134.6 (q), 129.3, 129.2, 129.0, 128.5,
128.3, 127.8, 125.9, 119.8, 116.5, 113.1 (q), 112.8, 54.6 (-CH2-), 18.6
(-CH3). MS (APCIþ) m/z calcd. 354.18. Found: 355.15 (MþH)þ.
General Procedure for Cu(amido-triazole)dppb Complex
Synthesis. To a solution of ligand precursor in THF was added
solid potassium tert-butoxide. After agitation, this solution was dropwise
added to a stirred slurry of [CuCl(dppb)]2 in THF. The reaction was
stirred with moderate warming (<40 ꢀC) until nearly clear and then
filtered through celite to remove KCl. The solution was concentrated to
1-2 mL, and hexanes were added slowly to precipitate the product which
was collected by filtration, washed with hexanes, and dried under vacuum.
Cu(L1)(dppb) (1). The general procedure was followed using 0.050
g of HL1, 0.020 g of tBuOK, and 0.080 g of [dppbCuCl]2 to provide
Cu(L6)(dppb) (6). The general procedure was followed using 0.244
g of HL6, 0.077 g of tBuOK, and 0.333 g of [dppbCuCl]2 to provide
0.486 g of 6 as a yellow powder (92%). X-ray quality crystals were
obtained from slow evaporation of the filtrate after filtration of the bulk
product or by vapor diffusion of hexanes into THF. 1H NMR (C6D6, 500
MHz): δ 7.46-7.41 (m, 3H), 7.28-7.26 (m, 3H), 7.16-7.12 (m, 2H),
7.07-6.80 (m, 25H), 6.69-6.65 (m, 3H), 6.39-6.36 (m, 1H), 4.48 (s,
2H, CH2), 2.43 (s, 6H, CH3). 31P{1H} NMR(C6D6, 202 MHz): δ -
12.4. MS (APCIþ) m/z calcd. 862.24 Found: 862.95 (MþH)þ Anal.
Calcd. for C53H45CuN4P2 THF (THF by 1H NMR): C, 73.18; H, 5.71;
3
N, 5.99. Found: C, 73.49; H, 5.94; N, 6.04.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data in CIF
b
format. Further details are given in Figures S1-S27 and Tables
S1-S6. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
0.102 g of 1 as a yellow powder (76% yield). H NMR (C6D6, 500
MHz): 7.72 (dd, J = 2.3, 7.7 1H), 7.48-7.42 (m, 10H), 7.38-7.36 (m,
3H), 7.35 (s, 1H), 7.28 (dd, J = 1.8, 7.3, 1H), 7.24-7.21 (m, 2H), 7.03-
6.90 (m, 20H), 6.77 (tt, J = 1.1 7.2, 1H), 6.24-6.59 (m, 1H), 6.90-6.82
(m, 2H), 6.61-6.58 (m, 1H), 2.23 (s, 3H). 31P{1H} NMR (C6D6, 202
MHz): δ -12.4. MS (APCIþ) m/z calcd 820.19. Found: 821.50
(MþH)þ Anal. Calcd. for C50H39CuN4P2: C, 73.11; H, 4.79; N, 6.82.
Found: C, 73.06; H, 5.17; N, 6.31.
Cu(L2)(dppb) (2). The general procedure was followed using 0.053
g of HL2, 0.020 g of tBuOK, and 0.080 g of [dppbCuCl]2 to provide
0.101 g of complex 2 as an orange powder (75%). 1H NMR (C6D6, 500
MHz): 7.66 (dd, J = 1.0, 7.7 1H), 7.48-7.40 (m, 10H), 7.37 (s, 1H),
7.30 (dd, J = 1.7, 7.3, 1H), 7.25-7.22 (m, 3H), 7.02-6.91 (m, 19H),
6.90-6.82 (m, 2H), 6.61-6.58 (m, 1H), 2.23 (s, 3H). 31P{1H} NMR-
(C6D6, 202 MHz): δ -12.4. MS (APCIþ) m/z calcd 834.21. Found:
835.30 (MþH)þ Anal. Calcd. for C51H41CuN4P2: C, 73.33; H, 4.95; N,
6.71. Found: C, 73.88; H, 5.00; N, 6.32.
Cu(L3)(dppb) (3). The general procedure was followed using 0.052
g of L3, 0.020 g of tBuOK, and 0.080 g of [dppbCuCl]2 to provide 0.112
g of 3 as an orange powder (84%). 1H NMR (C6D6, 500 MHz): 7.54-
7.53 (d, J = 8.6, 1H), 7.47-7.38 (m, 10H), 7.33 (s, 1H), 7.32-7.30 (m,
2H), 7.27-7.24 (m, 1H), 7.02-6.84 (m, 20H), 6.65-6.64 (m, 2H),
6.60-6.57 (m, 1H), 3.44 (s, 3H). 31P{1H} NMR(C6D6, 202 MHz): δ -
12.1. MS (APCIþ) m/z calcd 850.21. Found: 851.40 (MþH)þ Anal.
Calcd. for C51H41CuN4OP2: C, 71.95; H, 4.85; N, 6.58. Found: C,
71.80; H, 4.89; N, 6.34.
Cu(L4)(dppb) (4). The general procedure was followed using 0.056
g of HL4, 0.020 g of tBuOK, and 0.180 g of [dppbCuCl]2 to provide
0.096 g of complex 4 as an orange powder (70%). X-ray quality crystals
were obtained from a mixture of precipitate and filtrate which was left to
stand prior to filtration. 1H NMR (C6D6, 500 MHz): 7.61-7.59
(m, 1H), 7.56-7.41 (m, 10H), 7.31 (s, 1H), 7.24-7.18 (m, 4H),
7.07-7.01 (m, 2H), 7.01-6.86 (m, 19H), 6.61 (t, 1H, J = 7.3). 31P{1H}
NMR(C6D6, 202 MHz): δ -10.7. MS (APCIþ) m/z calcd. 854.16.
’ ACKNOWLEDGMENT
We thank the National Science Foundation GOALI program
(Grant CHE-0616782) for support of this research.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: eisenberg@chem.rochester.edu.
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