Synthesis and characterization of neutral luminescent diphosphine pyrrole- and indole-aldimine copper(I) complexes

Article abstract of DOI:10.1021/ic2007588

Heteroleptic copper(I) complexes of the types [Cu(N,N)(P,P)] and [Cu(N,O)(P,P)], where (P,P) = phosphine (PPh₃) or diphosphine (dppb, DPEPHOS, XANTPHOS), (N,N) = pyrrole-2-phenylcarbaldimine, 2PyN: [Cu(2PyN)(PPh₃)₂] (1), [Cu(2PyN) (dppb)] (2), [Cu(2PyN)(DPEPHOS)] (3), and [Cu(2PyN)(XANTPHOS)] (4), (N,N) = indole-2-phenylcarbaldimine, 2IndN: [Cu(2IndN)(DPEPHOS)] (8), and (N,O) = pyrrole-2-carboxaldehyde, 2PyO: [Cu(2PyO)(DPEPHOS)] (5), [Cu(2PyO)(XANTPHOS)] (6), or (N,O) = indole-2-carboxaldehyde, 2IndO: [Cu(2IndO)(DPEPHOS)] (7), were synthesized and characterized by multinuclear NMR spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, and X-ray crystallography (1-3, 5-8). The complexes with aldimine ligands are thermally stable, and sublimation of 2-4 was possible at T = 230-250 °C under vacuum. All complexes exhibit long-lived emission in solution, in the solid state, and in frozen glasses. The excited states have been assigned as mixed intraligand and metal-to-ligand charge transfer ³(MLCT + π-π*) transitions through analysis of the photophysical properties and DFT calculations on representative examples.

Full text of DOI:10.1021/ic2007588

ARTICLE
pubs.acs.org/IC
Synthesis and Characterization of Neutral Luminescent
Diphosphine Pyrrole- and Indole-Aldimine Copper(I) Complexes
Marco G. Crestani, Gerald F. Manbeck, William W. Brennessel, Theresa M. McCormick, and
Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
S Supporting Information
b
ABSTRACT: Heteroleptic copper(I) complexes of the types
[Cu(N,N)(P,P)] and [Cu(N,O)(P,P)], where (P,P) = phos-
phine (PPh3) or diphosphine (dppb, DPEPHOS, XANTPHOS),
(N,N) = pyrrole-2-phenylcarbaldimine, 2PyN:[Cu(2PyN)(PPh3)2]
(1), [Cu(2PyN) (dppb)] (2), [Cu(2PyN)(DPEPHOS)] (3),
and [Cu(2PyN)(XANTPHOS)] (4), (N,N) = indole-2-phenyl-
carbaldimine, 2IndN:[Cu(2IndN)(DPEPHOS)] (8),and(N,O) =
pyrrole-2-carboxaldehyde, 2PyO: [Cu(2PyO)(DPEPHOS)] (5),
[Cu(2PyO)(XANTPHOS)] (6), or (N,O) = indole-2-carboxaldehyde, 2IndO: [Cu(2IndO)(DPEPHOS)] (7), were synthesized and
characterized by multinuclear NMR spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, and X-ray crystal-
lography (1ꢀ3, 5ꢀ8). The complexes with aldimine ligands are thermally stable, and sublimation of 2ꢀ4 was possible at T =
230ꢀ250 ꢀC under vacuum. All complexes exhibit long-lived emission in solution, in the solid state, and in frozen glasses. The excited
states have been assigned as mixed intraligand and metal-to-ligand charge transfer 3(MLCT + πꢀπ*) transitions through analysis of the
photophysical properties and DFT calculations on representative examples.
’ INTRODUCTION
[Cu(NN)(PP)]+ (NN = diimine and PP = diphosphine),6cꢀf,iꢀl
following the seminal advances made by McMillin and co-workers
in the design of such complexes for higher photoluminescence
quantum yields.7 The cationic nature of these complexes usually
would preclude device fabrication by vapor deposition, but none-
theless several cases of vapor-deposited OLEDs have been
reported.6c,d,i A few studies of vapor-deposited OLEDs have
appeared using neutral, sublimable Cu(I) complexes,6a,b,h includ-
ing the highly emissive dinuclear Cu(I) complex, [Cu(PNP)]2
(PNP = bis(2-diisobutylphosphinophenyl)amide).6b A novel de-
vice fabrication method involving codeposition of Cu(I) with
coordinating ligands to form emissive complexes in situ has also
been reported.6a Previous work in our laboratory has focused on
neutral Cu(I) complexes supported by diphosphine and amido-
triazole ligands, but their thermal instability prevented practical
device application.8
In the current work, we have prepared heteroleptic neutral
copper(I) compounds of the types [Cu(N,N)(P,P)] and [Cu(N,
O)(P,P)] ((P,P) = 2 PPh3 or a diphosphine (see Scheme 1),
(N,N) = pyrrole-2-phenylcarbaldimine, 2PyN, or indole-2-phe-
nylcarbaldimine, 2IndN, and (N,O) = pyrrole-2-carboxaldehyde,
2PyO, or indole-2-carboxaldehyde, 2IndO) that could be em-
ployed for the construction of OLED devices by vacuum
deposition. Our choice of using pyrrole-aldimine derivatives as
ligands was motivated by the use of thermally stable homoleptic
The search for low-cost, highly efficient emitters for the
manufacture of organic light-emitting diodes (OLEDs) is con-
sidered of great importance given the potential that OLEDs have
for flat panel displays and solid-state lighting.1 OLEDs are current-
driven devices and in their simplest form are comprised of an
anode (hole injection), a cathode (electron injection), and an
organic medium that is sandwiched between the two electrodes to
support charge recombination that yields emission of light.2 To
improve the power efficiency of the device, phosphorescent
emitters are doped into a polymer matrix of the OLED, thereby
allowing access to emissive triplet excitons which would otherwise
be lost as heat in organic emitters.3 OLED fabrication may be done
by solution processing or vapor deposition. Solution processing is
attractive for its low cost, whereas vapor deposition generally offers
more options in multilayer device fabrication by eliminating
problems, such as dissolution of underlying layers during solution
processing of succeeding layers. Thus, in addition to high lumines-
cence quantum efficiency, thermal stability and sublimability are
required properties of emitters for vapor-deposited OLEDs.
Cyclometalated d6 and d8 complexes of the third row transition
series, especially iridium(III), have been employed with the most
success in OLEDs because of their high phosphorescence quan-
tum yield, wavelength tunability, and thermal stability.4 However,
because of the high cost and limited availability of these precious
metals, extensive efforts have been directed toward the discovery
of less expensive alternatives,5 especially copper(I) complexes.6
Many of the complexes employed have been of the type
Received: April 12, 2011
Published: June 29, 2011
r
2011 American Chemical Society
7172
dx.doi.org/10.1021/ic2007588 Inorg. Chem. 2011, 50, 7172–7188
|

Inorganic Chemistry
ARTICLE
Scheme 1. Phosphine (PPh3) and Diphosphines (P,P) Used
in This Work: PPh3 = Triphenylphosphine, dppb = 1,2-
Bis(diphenylphosphino)benzene, DPEPHOS = (Oxydi-2,1-
phenylene)bis-diphenylphosphine, XANTPHOS = 9,9-Di-
methyl-4,5-bis(diphenylphosphino)xanthene
fluorimetry. Quartz cells(Starna Cells, Inc., Atascadero, CA) were usedfor
recording room temperature absorption and emission spectra of fluid
solutions.
1H (400, 500 MHz), 13C{1H} (100, 125 MHz), and 31P{1H} (162,
202 MHz) NMR spectra were recorded on Bruker Avance 400 and
Avance 500 spectrometers. 1H and 13C{1H} chemical shifts (δ, ppm) are
reported relative to the residual proton or carbon resonances of the
deuterated solvent. 31P{1H} NMR spectra are reported in ppm relative to
external 85% H3PO4. UV/visible absorption spectra were recorded using
quartz cuvettes in a Hitachi U2000 scanning spectrophotometer
(200ꢀ1100 nm), at 298 K. Excitation and emission spectra of fluid
solutions (298 K), solid-state samples, and frozen glasses (77 K) were
recorded using a Spex Fluoromax-P fluorimeter. All fluid-solution spectra
were measured using freshly prepared samples, deoxygenated by FPT.
Emission spectra were corrected for the spectral sensitivity of the
photomultiplier tube and the spectral output of the lamp. Extinction
coefficients (ε, Mꢀ1 cmꢀ1) of all the copper compounds and their
deprotonated ligands were determined from their corresponding Beer’s
plots at three different concentrations (5, 3, and 1 ꢁ 10ꢀ5 M; see
copper(II) bis-pyrrole-2-phenylcarbaldimine compounds for Cu
metal deposition via a CVD/ALD (CVD = chemical vapor
deposition; ALD = atomic layer deposition) process.9 The
pyrrole-aldehyde congeners were prepared for comparison of
their photophysical properties to those of pyrrole-aldimine com-
plexes. The indole derivatives (both with aldimine and aldehyde
functions) were studied to determine the effect of extended
conjugation on photoluminescence. In addition, the use of
pyrrole-aldimine ligands for the synthesis of the copper(I)
compounds was encouraged by literature precedents that showed
that this type of ligand is a useful scaffold for the preparation of
luminescent Zn(II) compounds and other coordination
complexes,10,11 although the short-lived singlet emission in these
complexes makes them unsuited for triplet harvesting in OLED
devices.10b To our knowledge, emissive indole-based copper(I)
complexes have not been described in the literature.
Supporting Information). The relative emission quantum yields (Φem
)
were determined in fluid dichloromethane solution (refractive index, η =
1.4242), following the method of Demas and Crosby for optically dilute
2
solutions,15 according to the formula Φem = Φf = ΦR(IR/If)(ηf2/ηR )-
(Df/DR)(AR/Af), where I is the excitation intensity ((IR/If) ∼ 1), η is the
refractive index of the solution, D = integrated emission intensity, and A is
the absorption at the excitation wavelength for the standard reference (R)
and the sample (f), respectively.16 An aerated aqueous solution of
tris(2,20-bipyridyl)ruthenium(II) ion, [Ru(bipy)3]+, (η = 1.333, Φ =
0.028) was used as the standard.17 The emission spectra of each sample
and of the reference were recorded at the same excitation wavelength
(λex nm) under identical instrument configurations for all Φem determi-
nations. Concentrations of both the sample and the reference were then
adjusted to match an absorbance of 0.1 at the excitation wavelength, and
the resulting emission spectra were integrated. At least three independent
measurements were performed for each determination. Closed-cap NMR
tubes charged with Me-THFsolutions ofthecopper(I) compoundsunder
nitrogen were used to record low-temperature emission and excitation
spectra. Flame-sealedcapillaries were usedfor solid state samples. Lifetime
data were collected using the Spex Fluoromax-P fluorimeter in phos-
phorimeter mode. Spectra were obtained after a 10 ms flashlamp delay,
and decay curves were collected as the average of 5 runs. Data were fit to
appropriate exponential or biexponential decay equations.
Sublimation Experiments. Laboratory-scale sublimations were
performed using a cylindrical glass microsublimator. Samples (0.050 g)
of three copper(I) compounds (2, 3, 4) were tested in separate runs. The
sublimator was charged in a glovebox and further heated under vacuum
on a Schlenk line. Heating was maintained using a mantle until
sublimation of the material was observed. For compounds 2 and 3,
sublimation occurred at 230 ꢀC. In the case of 4, sublimation took place
at 250 ꢀC. The typical yield of sublimation was 40% (0.020 g).
’ EXPERIMENTAL SECTION
General Considerations. Unless otherwise noted, all manipula-
tions in this work were performed using standard Schlenk and glovebox
techniques under a nitrogen atmosphere. A double VAC inert-atmo-
sphere glovebox was used. Glassware was oven- or flame-dried and
cooled to room temperature under dynamic vacuum.
Materials and Methods. All of the solvents used were reagent
grade. Dichloromethane (CH2Cl2), tetrahydrofuran (THF), hexanes, and
diethyl ether were dried and purified by filtration through activated-
alumina columns using a solvent purifier.12 Acetonitrile (MeCN) was
driedovercalciumhydride(CaH2). Ethanolandmethanolweredriedover
calcium sulfate (CaSO4). Toluene was distilled over sodium. 2-Methylfur-
an (2-Me-THF, 99% stabilized with ca. 150ꢀ400 ppm of BHT) was
distilled from sodium/benzophenone ketyl.13 All of the water used was
deionized. Isopropyl alcohol was used as received. d2-Dichloromethane
(CD2Cl2) and d1-chloroform (CDCl3) were purchased from Cambridge
Isotope Laboratories (CIL, Andover, MA), degassed by freezeꢀ
pumpꢀthaw (FPT), and stored over activated 3 Å molecular sieves. CuCl
(Aldrich, 98%), pyrrole-2-carboxaldehyde (2PyO-H; Aldrich, 98%),
indole-2-carboxaldehyde (2IndO-H; TCI America, 97%), aniline
(PhNH2; Aldrich, 97%), triphenylphosphine (PPh3; Aldrich, 99%), 1,2-
bis(diphenylphosphino)benzene (dppb; Aldrich, 97%), (oxidi-2,1-pheny-
lene)bis-diphenylphosphine (DPEPHOS; 98%, Aldrich), 9,9-dimethyl-
4,5-bis(diphenylphosphino)xanthene (XANTPHOS; ACROS organics,
98%), andpotassiumtert-butoxide(KOtBu; Aldrich, 95%) werepurchased
in high purity grade and used as received. [Cu(NO3)(PPh3)2] was
prepared following the literature procedure.14 Purities of all products were
confirmed bymicroanalyses carried outbyQuantitativeTechnologies, Inc.
(QTI, Whitehouse, NJ). Thin-wall (0.38 mm) WILMAD screw-capped
NMR tubes were used for both NMR spectroscopy and low-temperature
Preparation of [N,N] Ligand Precursors. Pyrrole-2-phenylcar-
baldimine (2PyN-H). This compound was prepared according to the
literature18 in 98%yieldandrecrystallizedfromethanol/hexanes (1:5 v/v).
Indole-2-phenylcarbaldimine (2IndN-H). A mixture of 2-indoleal-
dehyde (0.2496 g, 1.7 mmol) and aniline (0.16 mL, 1.7 mmol) in water
(15 mL) was refluxed for 12 h. The mixture was cooled and partitioned
between CH2Cl2 and water. The aqueous layer was washed 3 times with
CH2Cl2. The organic portions were combined and dried over MgSO4,
filtered, and concentrated. The resulting dark red solid was recrystallized
from ethanol/hexanes (1:5% v/v). The yield of 2IndN-H was 0.3517 g
1
(1.6 mmol, 94.1%) of dark red-brown microcrystals. H NMR (500
MHz, CD2Cl2): δ/ppm 9.63 (br s, 1H, NꢀH), 8.59 (s, 1H, CH=N),
7.75 (dd, J1 = 8 Hz, J2 = 1 Hz, 1H, indole CꢀH), 7.52ꢀ7.45 (m, 3H, m-
aryl, and indole CꢀH), 7.38ꢀ7.32 (m, 4H, o-, p-aryl, and indole CꢀH),
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Inorganic Chemistry
ARTICLE
7.198 (m, 1H, indole CꢀH), 7.08 (dd, J1 = 2 Hz, J2 = 0.5 Hz, 1H, indole
CꢀH). 13C{1H} NMR (125 MHz, CD2Cl2): δ/ppm 151.53 (s, indole
C), 150.78 (s, CHdN), 137.99 (s, indole C), 136.14 (s, indole C), 129.82
(s, m-aryl), 128.78 (s, ipso-aryl), 126.76 (s, indole CꢀH), 125.61 (s, p-
aryl), 122.45 (s, indole CꢀH), 121.53 (s, o-aryl), 120.91 (s, indole
CꢀH), 112.11 (s, indole CꢀH), 110.47 (s, indole CꢀH). Anal. Calcd
(%) for C15H12N2: C, 81.79; H, 5.49; N, 12.72. Found: C, 80.94; H,
5.56; N, 12.52.
Deprotonation of [N,O] and [N,N] Ligand Precursors. K-
(2PyO). In the glovebox, a CH2Cl2 solution (∼10 mL) of 2PyO-H (0.1 g,
1.05 mmol) was added to a vial containing KOtBu (0.1178 g, 1.05 mmol),
and the mixture was stirred overnight. The slurry produced was then
filtered through a frit charged with Celite, and the filtrate was evaporated
to dryness under vacuum. A white oily residue remained which was
recrystallized from a cold (ꢀ35 ꢀC) mixture of THF/diethyl ether
(1:1% v/v), filtered, and dried. The yield of K(2PyO) was 0.1009 g
(0.75 mmol, 71.4%) of gray-white solid. λmax (CH2Cl2, 298 K) =
285 nm (ε = 12800 Mꢀ1 cmꢀ1).
K(2PyN). The compound was prepared following the procedure for
K(2PyO), using 2PyN-H (0.5 g, 3 mmol) and KOtBu (0.3360 g,
3 mmol). The product was recrystallized from a cold (ꢀ35 ꢀC) mixture
of CH2Cl2/n-hexanes (1:1% v/v) to give a pale brown solid. The yield of
K(2PyN) was 0.5626 g (2.7 mmol, 93.1%). 1H NMR (400 MHz,
CD2Cl2): δ/ppm 8.28 (s, 1H, CH=N), 7.38 (t, JHH = 8.8 Hz, 2H, o-aryl),
7.22ꢀ7.17 (m, 3H, m-, p-aryl), 6.94 (pseudo t, JHH = 1 Hz, 1H, pyrrole
CꢀH), 6.69 (dd, J1 = 3.6 Hz, J2 = 1.6 Hz, 1H, pyrrole CꢀH), 6.29 (dd, J1
= 3.6 Hz, J2 = 2.4 Hz, 1H, pyrrole CꢀH). 13C{1H} NMR (100 MHz,
CD2Cl2): δ/ppm 151.79 (s, ipso-aryl), 149.71 (s, CHdN), 130.87 (s,
pyrrole C), 129.15 (s, m-aryl), 125.36 (s, p-aryl), 123.01 (s, pyrrole
CꢀH), 120.84 (s, o-aryl), 116.37 (s, pyrrole CꢀH), 110.3 (s, pyrrole
CꢀH). λmax (CH2Cl2, 298 K) = 326 nm (ε = 26650 Mꢀ1 cmꢀ1). λex
(CH2Cl2, 298 K) = 359 nm. λem (CH2Cl2, 298 K) = 404 nm.
Φem = 0.09%.
PPh3), 124.04 (s, pyrrole CꢀH), 122.19 (s, m-aryl of 2PyN), 118.2
(s, pyrrole CꢀH), 112.51 (s, pyrrole CꢀH). 31P{1H} NMR (202 MHz,
CD2Cl2): δ/ppm ꢀ0.96 (br s). Anal. Calcd (%) for [(Ph3P)2-
Cu(2PyN)] CH2Cl2 = C48H41Cl2CuN2P2: C, 68.45; H, 4.91; N,
3
3.33. Found: C, 68.29; H, 4.79; N, 3.12.
[Cu(2PyN)(dppb)] (2). CuCl (0.1003 g, 1 mmol) was dissolved in
MeCN (2 mL), and dppb (0.4466 g, 1 mmol) in CH2Cl2 (∼10 mL)
solution was added to it. An immediate color change from pale green to
yellow took place, followed by precipitation of a green yellow solid
attributed to [(dppb)Cu(μ-Cl)]2. The mixture was stirred for 1 h, after
which time K(2PyN) (0.2085 g, 1 mmol) was also added. A bright
yellow solution was obtained that gradually darkened to a brown slurry.
The mixture was stirred for 12 h and then filtered through a frit charged
with Celite. Evaporation of the solvent in vacuo yielded an orange solid
residue (0.5725 g) which was recrystallized from cold (ꢀ35 ꢀC) CH2Cl2
and hexanes to give yellow-brown crystals. The yield of 2 was 0.5706 g
(0.84 mmol, 84%). 1H NMR (500 MHz, CD2Cl2): δ/ppm 8.40 (pseudo
d, J1 = 0.5 Hz, 1H, CH=N), 7.60ꢀ7.54 (m, 4H, o-, m-aryl of 2PyN),
7.38ꢀ7.25 (m, 21H, p-aryl of 2PyN and phenyl protons of ArPPh2),
6.99ꢀ6.96 (m, 3H, pyrrole CꢀH and backbone C-H), 6.93ꢀ6.90 (m,
3H, pyrrole CꢀH and backbone C-H), 6.45 (dd, J1 = 3.5 Hz, J2 = 1.5 Hz,
1H, pyrrole CꢀH). 13C{1H} NMR (125 MHz, CD2Cl2): δ/ppm
1
153.53 (s, CHdN), 151.27 (s, pyrrole C), 143.48 (t, JCꢀP = 33 Hz,
backbone CꢀP), 141.29 (s, ipso-aryl of 2PyN), 137.6 (s, p-aryl of 2PyN),
134.76 (t, 2JCꢀP = 4 Hz, o-aryl of ArPPh2), 134.53 (t, 1JCꢀP = 15.5 Hz,
ipso-aryl of ArPPh2), 133.76 (br s, backbone CꢀH), 130.79 (s, m-aryl of
2PyN), 129.85 (br s, backbone CꢀH), 129.12 (s, p-aryl of ArPPh2),
128.96 (t, 3JCꢀP = 4.5 Hz, m-aryl of ArPPh2), 124.18 (s, pyrrole CꢀH),
122.09 (s, o-aryl of 2PyN), 117.74 (s, pyrrole CꢀH), 112.84 (s, pyrrole
CꢀH). 31P{1H} NMR (202 MHz, CD2Cl2): δ/ppm ꢀ8.43 (br s). Anal.
Calcd (%) for [(dppb)Cu(2PyN)] 1/2(CH2Cl2) = C42H34ClCuN2P2:
3
C, 69.32; H, 4.71; N, 3.85. Found: C, 68.50; H, 4.52; N, 3.80.
[Cu(2PyN)(DPEPHOS)] (3). The compound was prepared following
the procedure for 2, using CuCl (0.5 g, 0.5 mmol), DPEPHOS (0.2693
g, 0.5 mmol), and K(2PyN) (0.1047 g, 0.5 mmol). A crude yellow solid
(0.3378 g) was obtained from this reaction. Recrystallization from cold
(ꢀ35 ꢀC) CH2Cl2 and n-hexanes resulted in formation of yellow-brown
crystals. The yield of 3 was 0.2757 g (0.36 mmol, 72%). 1H NMR (500
MHz, CD2Cl2): δ/ppm 8.40 (pseudo d, J1 = 1 Hz, 1H, CH=N),
7.4ꢀ7.19 (m, 25H, p-aryl of 2PyN, backbone CꢀH and phenyl protons
of ArPPh2), 7.1 (d, J = 7 Hz, 2H, o-aryl of 2PyN), 7.05 (d, J = 7 Hz, 2H,
m-aryl of 2PyN), 6.96 (dt, J1 = 13.5 Hz, J2 = 7.5 Hz, 4H, backbone
CꢀH), 6.89 (pseudo t, J = 7.5 Hz, 1H, pyrrole CꢀH), 6.85 (d, J = 3 Hz,
1H, pyrrole CꢀH), 6.73ꢀ6.7 (m, 2H, backbone CꢀH), 6.28 (dd, J1 =
3.5 Hz, J2 = 1 Hz, 1H, pyrrole CꢀH). 13C{1H} NMR (125 MHz,
CD2Cl2): δ/ppm 159.1 (t, 2JCꢀP = 6.4 Hz, backbone CꢀO), 153.1 (s,
CHdN), 151.42 (s, pyrrole C), 141.16 (s, ipso-aryl of 2PyN), 137.3 (s, p-
aryl of 2PyN), 134.81 (s, backbone CꢀH), 134.24 (t, 2JCꢀP = 7.6 Hz, o-
aryl of ArPPh2), 133.62 (t, 1JCꢀP = 14.8 Hz, backbone CꢀP), 131.33 (s,
m-aryl of 2PyN), 129.7 (s, backbone CꢀH), 128.85 (s, p-aryl of ArPPh2),
128.62 (t, 3JCꢀP = 4.5 Hz, m-aryl of ArPPh2), 126.54 (t, 1JCꢀP = 11.4 Hz,
ipso-aryl of ArPPh2), 124.73 (s, backbone CꢀH), 123.75 (s, pyrrole
CꢀH), 122.12 (s, o-aryl of 2PyN), 120.7 (s, backbone CꢀH), 117.55 (s,
pyrrole CꢀH), 112.2 (s, pyrrole CꢀH). 31P{1H} NMR (202 MHz,
CD2Cl2): δ/ppm ꢀ15.22 (br s), ꢀ16.6 (br s). Anal. Calcd (%) for
K(2IndO). The compound was prepared and recrystallized following
the procedures for K(2PyN), using 2IndO-H (0.1006 g, 0.69 mmol)
and KOtBu (0.076 g, 0.68 mmol). The yield of K(2IndO) was 0.126 g
(0.68 mmol, 98.5%) of a dark red solid. λmax (CH2Cl2, 298 K) = 276 nm
(ε = 9225 Mꢀ1 cmꢀ1), 306 (ε = 8000 Mꢀ1 cmꢀ1), 321 (ε = 6175
M
ꢀ1 cmꢀ1), 336 (ε = 5850 Mꢀ1 cmꢀ1), 370 (ε = 1650 Mꢀ1 cmꢀ1), 408
(ε= 850 Mꢀ1 cmꢀ1). λex (CH2Cl2, 298 K) = 336 nm. λem (CH2Cl2, 298 K)
= 421 nm. Φem = 28%.
K(2IndN). The compound was prepared and recrystallized following
the procedure for K(2PyN), using 2IndN-H (0.0502 g, 0.23 mmol) and
KOtBu (0.0262 g, 0.23 mmol). The yield of K(2IndN) was 0.0138 g
(0.053 mmol, 23%) of a brown solid. λmax (CH2Cl2, 298 K) = 338 nm
(ε = 34000 Mꢀ1 cmꢀ1). λex (CH2Cl2, 298 K) = 365 nm. λem (CH2Cl2,
298 K) = 423 nm. Φem = 0.19%.
Preparation of Copper(I) Compounds. [Cu(2PyN)(Ph3P)2]
(1). In the glovebox, a pale yellow-orange solution of K(2PyN) (0.031 g,
0.15 mmol) in CH2Cl2 (15 mL) was added to [Cu(NO3)(Ph3P)2]
(0.100 g, 0.15 mmol). The solution turned bright orange and then turbid
as a result of the precipitation of KNO3. The mixture was stirred for 12 h,
filtered through Celite, and evaporated to dryness under a vacuum. A
light yellow solid residue (0.0912 g) was obtained, which was recrys-
tallized from cold (ꢀ35 ꢀC) CH2Cl2 and hexanes to give orange crystals.
1
The yield of 1 was 0.0895 g (0.12 mmol, 80%). H NMR (500 MHz,
[(DPEPHOS)Cu(2PyN)] 2(CH2Cl2) = C49H41Cl4CuN2OP2: C,
3
CD2Cl2): δ/ppm 8.31 (s, 1H, CH=N), 7.42ꢀ7.39 (m, 5H, phenyl
protons of 2PyN), 7.28ꢀ7.24 (m, 30H, phenyl protons of PPh3), 7.10
(m, 1H, pyrrole CꢀH), 6.94 (m, 1H, pyrrole CꢀH), 6.34 (dd, J1 = 3.5
Hz, J2 = 1.5 Hz, 1H, pyrrole CꢀH). 13C{1H} NMR (125 MHz,
CD2Cl2): δ/ppm 153.99 (s, CHdN), 152.1 (s, pyrrole C), 141.14 (s,
ipso-aryl of 2PyN), 137.46 (s, p-aryl of 2PyN), 134.14 (d, 2JCꢀP = 15.5
Hz, o-aryl of PPh3), 133.85 (s, o-aryl of 2PyN), 132.45 (s, m, ipso-aryl of
PPh3), 130.23 (br s, p-aryl of PPh3), 129.11 (d, 3JCꢀP = 8.7 Hz, m-aryl of
62.53; H, 4.39; N, 2.98. Found: C, 63.24; H, 4.31; N, 3.11.
[Cu(2PyN)(XANTPHOS)] (4). The compound was prepared following
the procedure for 2, using CuCl (0.0505 g, 0.5 mmol), XANTPHOS
(0.2896 g, 0.5 mmol), and K(2PyN) (0.1048 g, 0.5 mmol), which
resulted in formation of a yellow solid (0.3479 g). Slow diffusion of a
CH2Cl2 solution of 4 into hexanes (20 mL) at ꢀ30 ꢀC yielded two
crops of purified product. The yield of 4 was 0.2966 g (0.36 mmol,
1
70.6%). H NMR (400 MHz, CD2Cl2): δ/ppm 8.43 (s, 1H, CH=N),
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7.56 (dd, J1 = 7.8 Hz, J2 = 1.4 Hz, 2H, backbone CꢀH), 7.28ꢀ7.08 (m,
21H, phenyl protons of ArPPh2), 7.02 (partially resolved t, J = 7.6 Hz,
2H, backbone CꢀH), 6.87ꢀ6.85 (m, 2H, o-aryl of 2PyN), 6.84ꢀ6.78
(m, 2H, m-aryl of 2PyN), 6.77ꢀ6.74 (m, 2H, pyrrole CꢀH), 6.44ꢀ6.39
(m, 2H, backbone CꢀH), 6.19 (dd, J1 = 3.4 Hz, J2 = 1.4 Hz, 1H, pyrrole
CꢀH), 1.85 (s, 3H, Me), 1.63 (s, 3H, Me). 13C{1H} NMR (100 MHz,
CD2Cl2): δ/ppm 155.96 (t, 2JCꢀP = 5 Hz, backbone CꢀO), 152.45 (s,
CHdN), 150.98 (s, pyrrole C), 141.33 (s, ipso-aryl of 2PyN), 137.19 (s,
CꢀH), 134.46 (s, backbone CꢀC(Me)2), 134.19 (t, 2JCꢀP = 6.2 Hz, o-
aryl of ArPPh2), 133.59 (t, 1JCꢀP = 12.3 Hz, backbone CꢀP), 131.81 (s,
backbone CꢀH), 129.94 (s, p-aryl of ArPPh2), 128.86 (br s, m-aryl of
ArPPh2), 126.87 (s, backbone CꢀH), 124.98 (s, backbone CꢀH),
1
122.02 (t, JCꢀP = 10 Hz, ipso-aryl of ArPPh2), 121.44 (s, pyrrole
CꢀH), 113.43 (s, pyrrole CꢀH), 35.26 (s, C(Me)2), 32.2 (s, Me).
31P{1H} NMR (162 MHz, CD2Cl2): δ/ppm ꢀ16.65 (br s). Anal. Calcd
(%) for [(XANTPHOS)Cu(2PyO)] = C44H36CuNO2P2: C, 71.78; H,
4.93; N, 1.90. Found: C, 71.05; H, 5.70; N, 1.43.
2
p-aryl of 2PyN), 134.5 (t, JCꢀP = 8.5 Hz, o-aryl of ArPPh2),
2
[Cu(2IndO)(DPEPHOS)] (7). The compound was prepared following
the procedure indicated for 5, using CuCl (0.1007 g, 1 mmol),
DPEPHOS (0.539 g, 1 mmol), 2IndO-H (0.1447 g, 1 mmol), and
KOtBu (0.1121 g, 1 mmol). A green yellow solid (0.7912 g) crashed out
after the mixing of the reactants and required several washings with
CH2Cl2 (5 ꢁ 20 mL), to extract and separate it from produced KCl
during filtration. Recrystallization from CH2Cl2 and hexanes at low
temperature (ꢀ30 ꢀC) yielded two crops of pure product. The yield of 7
was 0.6538 g (0.79 mmol, 79%) of green yellow crystals. 1H NMR (500
MHz, CD2Cl2): δ/ppm 9.64 (s, 1H, CH=O), 7.58 (dd, J1 = 7 Hz, J2 = 1
Hz, 1H, indole CꢀH), 7.55 (br q, J = 5.5 Hz, 2H, indole CꢀH),
7.46ꢀ7.23 (m, 22H, o-, m-, and p-aryl of ArPPh2, indole CꢀH), 7.14 (dd,
J1 = 8 Hz, J2 = 1 Hz, 1H, backbone CꢀH), 7.06 (d, J = 7.5 Hz, 1H,
backbone CꢀH), 7.02 (t, J = 7.5 Hz, 1H, backbone CꢀH), 6.96 (t, J =
7.5 Hz, 2H, backbone CꢀH), 6.91 (m, 2H, backbone CꢀH), 6.74 (m,
1H, backbone CꢀH). 13C{1H} NMR (125 MHz, CD2Cl2): δ/ppm
186.36 (s, CHdO), 159.03 (t, 2JCꢀP = 6.3 Hz, backbone CꢀO), 158.36
(t, 2JCꢀP = 6.3 Hz, backbone CꢀO), 148.53 (s, indole CꢀCHO), 146.96
134.37ꢀ134.21 (m, backbone CꢀP), 133.35 (t, JCꢀP = 8 Hz, o-aryl
of ArPPh2), 131.41 (s, m-aryl of 2PyN), 130.41 (s, backbone CꢀC-
(Me)2), 129.89 (s, backbone CHꢀCP), 129.43 (s, backbone CHꢀCP),
128.89 (s, p-aryl of ArPPh2), 128.76 (t, 3JCꢀP = 5 Hz, m-aryl of ArPPh2),
128.64 (t, 3JCꢀP = 5 Hz, m-aryl of ArPPh2), 126.41 (s, backbone CꢀH),
124.79 (s, backbone CꢀH), 123.73 (s, pyrrole CꢀH), 122.63 (t, 1JCꢀP
=
13 Hz, ipso-aryl of ArPPh2), 121.45 (s, o-aryl of 2PyN), 117.97 (s, pyrrole
CꢀH), 112.34 (s, pyrrole CꢀH), 36.6 (s, C(Me)2), 30.24 (s, Me), 26.33
(s, Me). 31P{1H} NMR (162 MHz, CD2Cl2): δ/ppm ꢀ14.5 (br s),
ꢀ17.7 (br s). Anal. Calcd (%) for [(XANTPHOS)Cu(2PyN)] =
C50H41CuN2OP2: C, 74.02; H, 5.09; N, 3.45. Found: C, 72.99; H,
4.79; N, 3.48.
[Cu(2PyO)(DPEPHOS)] (5). Similarly to the previous procedures, the
compound was prepared from CuCl (0.0501 g, 0.5 mmol) and
DPEPHOS (0.270 g, 0.5 mmol) in MeCN solution. K(2PyO) was
prepared fresh from 2PyO-H (0.0471 g, 0.5 mmol) and KOtBu (0.0563
g, 0.5 mmol) and then added to the copper(I) slurry. A yellow-brown
solution was produced, accompanied by extensive precipitation of KCl.
The mixture was stirred for 12 h. Standard workup and recrystallization
from CH2Cl2 and hexanes yielded pale yellow crystals. The yield of 5 was
0.1608 g (0.23 mmol, 46%). An alternative preparation of this com-
pound in refluxing ethanol/CH2Cl2 (1:1% v/v, ∼40 mL) for 12 h, using
the same amounts of starting materials, resulted in extensive formation
of the large pale-yellow single crystals of 5 (40% yield). 1H NMR (400
MHz, CD2Cl2): δ/ppm 9.02 (pseudo d, J1 = 1 Hz, 1H, CH=O),
7.35ꢀ7.23 (m, 21H, o-, m-, and p-aryl of ArPPh2 and pyrrole CꢀH),
7.19 (partially resolved td, J1 = 2 Hz, J1 = 0.4 Hz, 2H, backbone CꢀH),
6.97 (dd, J1 = 0.9 Hz, J1 = 0.2 Hz, 1H, pyrrole CꢀH), 6.92ꢀ6.87 (m, 4H,
backbone CꢀH), 6.64 (m, 2H, backbone CꢀH), 6.36 (dd, J1 = 0.9 Hz, J2 =
0.3 Hz, 1H, pyrrole CꢀH). 13C{1H} NMR (100 MHz, CD2Cl2): δ/
2
(s, indole C), 134.77 (t, JCꢀP = 7.5 Hz, backbone CꢀH), 134.64 (t,
2JCꢀP = 7.5 Hz, backbone CꢀH), 134.49 (t, 2JCꢀP = 7.5 Hz, o-aryl of
1
ArPPh2), 132.75 (t, JCꢀP = 16.1 Hz, backbone CꢀP), 132.01 (s,
backbone CꢀH), 131.64 (s, backbone CꢀH), 131.33 (s, indole C),
130.75 (s, indole CꢀH), 130.18 (br s, p-aryl of ArPPh2), 129.29 (pseudo
3
t, J = 5 Hz, ipso-aryl of ArPPh2), 128.98 (t, JCꢀP = 4.5 Hz, m-aryl of
1
ArPPh2), 125.96 (t, JCꢀP = 12.6 Hz, backbone CꢀP), 125.19 (s,
backbone CꢀH), 124.99 (s, backbone CꢀH), 123.25 (d, 1JCꢀP = 16.6
Hz, indole CꢀH, endo), 120.72 (s, backbone CꢀH), 120.37 (s, back-
bone CꢀH), 119.64 (s, indole CꢀH), 118.4 (s, indole CꢀH), 112.26 (s,
indole CꢀH). 31P{1H} NMR (162 MHz, CD2Cl2): δ/ppm ꢀ17.52 (br
s), ꢀ19.37 (br s). Anal. Calcd (%) for [(DPEPHOS)Cu(2IndO)]
1.5(CH2Cl2) = C47H37Cl3CuNO2P2: C, 64.17; H, 4.24; N, 1.59. Found:
C, 63.89; H, 4.08; N, 1.62.
2
ppm 179.49 (s, CHdO), 158.58 (t, JCꢀP = 6 Hz, backbone CꢀO),
143.75 (s, pyrrole C), 139 (s, pyrrole CꢀH), 134.67 (s, backbone CꢀH),
1
134.47 (t, 2JCꢀP = 9 Hz, o-aryl of ArPPh2), 132.88 (t, JCꢀP = 16 Hz,
[Cu(2IndN)(DPEPHOS)] (8). The compound was prepared following
the procedure indicated for 5, using CuCl (0.0999 g, 1 mmol),
DPEPHOS (0.5398 g, 1 mmol), 2IndN-H (0.2209 g, 1 mmol), and
KOtBu (0.1130 g, 1 mmol). As with 7, a yellow solid (0.7513 g) crashed
out from solution and several washings with CH2Cl2 (3 ꢁ 20 mL) were
required to filter it through a frit in the first stage of the workup.
Recrystallization from CH2Cl2 and hexanes at low temperature
(ꢀ30 ꢀC) also yielded two crops of pure product. The yield of 8 was
backbone CꢀP), 131.42 (s, backbone CꢀH), 130.1 (s, p-aryl of ArPPh2),
3
1
128.91 (t, JCꢀP = 4.5 Hz, m-aryl of ArPPh2), 125.98 (t, JCꢀP
=
10 Hz, ipso-aryl of ArPPh2), 124.80 (s, backbone CꢀH), 121.23 (s,
pyrrole CꢀH), 120.54 (s, backbone CꢀH), 113.43 (s, pyrrole CꢀH).
31P{1H} NMR (162 MHz, CD2Cl2): δ/ppm ꢀ17.48 (br s). Anal. Calcd
(%) for [(DPEPHOS)Cu(2PyO)] 1.5(CH2Cl2) = C43H35Cl3Cu-
NO2P2: C, 62.25; H, 4.25; N, 1.69. Found: C, 62.06; H, 4.95; N, 1.95.
[Cu(2PyO)(XANTPHOS)] (6). The compound was prepared following
the procedure indicated for 5, using CuCl (0.05 g, 0.5 mmol),
XANTPHOS (0.2903 g, 0.5 mmol), and K(2PyO), prepared in situ
from 2PyO-H (0.0475 g, 0.5 mmol) and KOtBu (0.0566 g, 0.5 mmol) in
a mixture of CH2Cl2/MeCN (10:1% v/v, ∼10 mL). The latter was
refluxed at 80 ꢀC for 24 h. The workup of this mixture and recrystalliza-
tion from CH2Cl2 and hexanes yielded pale yellow crystals. The yield of
1
0.7589 g (0.92 mmol, 92%) of yellow-brown crystals. H NMR (500
MHz, CD2Cl2): δ/ppm 8.43 (s, 1H, CH=N), 7.65ꢀ7.63 (m, 1H, indole
CꢀH), 7.54 (br q, J = 5.5 Hz, 1H, indole CꢀH), 7.46ꢀ7.4 (m, 2H,
indole CꢀH), 7.37ꢀ7.27 (m, 5H, o-, m-, and p-aryl of IndN), 7.25 (ddd,
J1 = 8 Hz, J2 = 1.5 Hz, 1H, indole CꢀH), 7.23ꢀ7.07 (m, 20H, o-, m-, and
p-aryl of ArPPh2), 7.03 (br d, J1 = 7.5 Hz, 2H, backbone CꢀH), 6.95 (t,
J = 7.5 Hz, 2H, backbone CꢀH), 6.84ꢀ6.77 (m, 4H, backbone CꢀH),
6.74 (m, 2H, backbone CꢀH). 13C{1H} NMR (125 MHz, CD2Cl2): δ/
1
6 was 0.2803 g (0.38 mmol, 76%). H NMR (400 MHz, CD2Cl2):
2
δ/ppm 9.13 (s, 1H, CH=O), 7.58 (dd, J1 = 7.6 Hz, J2 = 1.6 Hz, 2H,
backbone CꢀH), 7.28ꢀ7.13 (m, 21H, o-, m-, and p-aryl of ArPPh2,
pyrrole CꢀH), 7.09 (partially resolved t, J = 7.6 Hz, 2H, backbone
CꢀH), 7.02 (d, J = 7.6 Hz, 1H, pyrrole CꢀH), 6.51 (m, 2H, backbone
CꢀH), 6.34 (dd, J1 = 3.6 Hz, J2 = 1.2 Hz, 1H, pyrrole CꢀH), 1.68 (s, 6H,
Me). 13C{1H} NMR (125 MHz, CD2Cl2): δ/ppm 179.83 (s, CHdO),
155.99 (br, backbone CꢀO), 143.9 (s, pyrrole C), 138.89 (s, pyrrole
ppm 159.2 (t, JCꢀP = 6.4 Hz, backbone CꢀO), 157.91 (s, CHdN),
152.1 (s, indole CꢀCH=N), 148.63 (s, indole C), 146.03 (s, indole C),
134.31 (s, backbone CꢀH), 134.31 (br s, o-aryl of ArPPh2), 133.43 (t,
1JCꢀP = 14.8 Hz, backbone CꢀP), 132.26 (s, ipso-aryl of 2IndN), 131.42
(s, backbone CꢀH), 129.72 (br s, p-aryl of ArPPh2), 129.24 (pseudo t,
J = 5 Hz, ipso-aryl of ArPPh2), 129.08 (s, m-aryl of 2IndN), 128.68
1
(pseudo t, J = 4.4 Hz, m-aryl of ArPPh2), 126.78 (t, JCꢀP = 14.8 Hz,
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backbone CꢀP), 125.18 (s, p-aryl of 2IndN), 124.78 (s, backbone
CꢀH), 122.41 (s, o-aryl of 2IndN), 121.7 (s, indole CꢀH), 121.33 (s,
indole CꢀH), 120.81 (s, backbone CꢀH), 118.47 (s, indole CꢀH),
117.07 (s, indole CꢀH), 107.91 (s, indole CꢀH). 31P{1H} NMR (202
MHz, CD2Cl2): δ/ppm ꢀ15.17 (br s), ꢀ19.47 (br s). Anal. Calcd (%)
independent solvent channels were found parallel to the a-axis. One of
them contained well-ordered cocrystallized dichloromethane solvent
molecules, whereas the second one contained highly disordered solvent.
The latter channel appeared to contain both CH2Cl2 and n-hexane (or
perhaps diethyl ether). Figure S30 in the Supporting Information shows a
view of the packing with empty channels. In the case of 6, only highly
disordered solvent molecules were found in channels parallel to the c-axis
(four per unit cell), which could not be modeled. The reflection
contributions from the highly disordered solvent in both 3 and 6 were
removed using the program PLATON and the function SQUEEZE,24
which determined there to be 152 electrons in 416 Å3 and 380 electrons in
1584 Å3 removed per unit cell for the structures of these two systems,
respectively. In either case, because the exact identities of the solvent
molecules removed are unknown, these were not included in the
molecular formulas or atom lists of 3 and 6. As a result, all calculated
fields that derive from these (e.g., F(000), density, formula weight, etc.)
are known to be incorrect.
for [(DPEPHOS)Cu(2IndN)] 1/2(CH2Cl2) = C52H40ClCuN2OP2:
3
C, 71.8; H, 4.64; N, 3.22. Found: C, 71.11; H, 4.87; N, 3.03.
X-ray Structural Determinations. Data Collections. Crystals
were placed in separate runs onto the tip of a 0.1 mm diameter glass
capillary tube or fiber and mounted on a Bruker SMART APEX II CCD
Platform diffractometer for a data collection at 100.0(1) K.19
A
preliminary set of cell constants and an orientation matrix were
calculated for each crystal from reflections harvested from three
orthogonal wedges of reciprocal space. The full data collections were
carried out at a detector distance of 4 cm using Mo KR radiation
(graphite monochromator) with the following frame times: 2PyN-H,
5 s; 1, 60 s; 2, 45 s; 3, 90 s; 5, 5 s; 6, 20 s; 7, 90 s; 8, 45 s; 9, 45 s. Randomly
oriented regions of reciprocal space were surveyed: (i) 2PyN-H, 1, 2, 5,
6, and 8, four major sections of frames were collected with 0.50ꢀ steps in
ω at four different ϕ settings and a detector position of ꢀ38ꢀ in 2θ. (ii)
Compound 3, four major sections with 0.75ꢀ steps in ω at four different
ϕ settings and a detector position of ꢀ38ꢀ in 2θ. (iii) Compound 7,
three major sections of frames with 0.75ꢀ steps in ω at three different ϕ
settings and a detector position of ꢀ38ꢀ in 2θ. (iv) Compound 9, three
major sections of frames with 0.50ꢀ steps in ω at three different ϕ
settings and a detector position of ꢀ38ꢀ in 2θ. The intensity data were
corrected for absorption.20 The final cell constants were calculated from
the xyz centroids resulting from approximately 4000 strong reflections
from the actual data collection after integration.21 Tables 4and 5 in the
main text summarize crystal data and refinement information for
compounds 1ꢀ8. Table S-1 in the Supporting Information summarizes
the data for compound 9.
’ RESULTS AND DISCUSSION
Syntheses of [N,N] Ligand Precursors. Pyrrole-2-phenylcar-
baldimine (2PyN-H) and indole-2-phenylcarbaldimine (2IndN-H)
were prepared on the basis of the method by Grushin and
Marshall for the syntheses of pyrrole-aldimines, which consists of
the condensation of pyrrole-2-carboxaldehyde (2PyO-H) with
alkyl- or aryl-amines (aniline) in aqueous media.18 The choice of
employing phenyl substituted ligands was made on the basis of
the stability that the phenyl ring confers.25 To our knowledge
2IndN-H has not been prepared previously.11 The condensation
reactions were performed by refluxing the precursor aldehyde in
the presence of water and aniline for 12 h. The products were
obtained in good yields as air-stable dark red solids (eqs 1 and 2).
Structure Solutions and Refinements. All of the structures were
solved using SIR9722 and refined using SHELXL-97.23 Space groups for
compounds 2PyN-H (Pbca), 2 (P21/c), 6 (P42/n), 7 (P21/n), and 9
(C2/c) were determined on the basis of systematic absences. In the case
of compounds 1, 3, 5, and 8, the space group P1 was determined on the
basis of the intensity statistics alone. A direct-methods solution was
calculated for each system, which provided most non-hydrogen atoms
from the E-map. Full-matrix least-squares (on F2) /difference Fourier
cycles were performed, which located the remaining non-hydrogen
atoms. All non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All hydrogen atoms were placed in ideal positions and
refined as riding atoms with relative isotropic displacement parameters
except for the structure of 2PyN, for which the hydrogen atoms were
found from the difference Fourier map and refined independently from
their bonded heavier atoms with individual isotropic displacement
parameters. A summary of the final full matrix least-squares refinements
is listed as follows: 2PyN, converged to R1 = 0.0502 (F2, I > 2σ(I)) and
wR2 = 0.1499 (F2, all data); 1 converged to R1 = 0.0563 (F2, I > 2σ(I))
and wR2 = 0.1407 (F2, all data); 2 converged to R1 = 0.0541 (F2, I >
2σ(I)) and wR2 = 0.1479 (F2, all data); 3 converged to R1 = 0.0613 (F2,
I > 2σ(I)) and wR2 = 0.1654 (F2, all data); 5 converged to R1 = 0.0390
(F2, I > 2σ(I)) and wR2 = 0.1050 (F2, all data); 6 converged to R1 =
0.0552 (F2, I > 2σ(I)) and wR2 = 0.1660 (F2, all data); 7 converged to
R1 = 0.0791 (F2, I > 2σ(I)) and wR2 = 0.2553 (F2, all data); 8 converged
to R1 = 0.0446 (F2, I > 2σ(I)) and wR2 = 0.1209 (F2, all data); 9
converged to R1 = 0.0571 (F2, I > 2σ(I)) and wR2 = 0.1327 (F2, all data).
For compounds 2 and 3, two independent molecules cocrystallized in the
asymmetric unit (Figures S28 and S29 in the Supporting Information).
The pyrrole-aldehyde ligand in complex 6 is modeled as disordered over
two positions (61:39), each of which is essentially the inversion of the
other within the same plane. In the case of 3 and 6, highly disordered
solvent channels in their structures were found. In compound 3, two
In the 1H NMR spectra (CD2Cl2), the two types of aldimines
exhibit a singlet (s) characteristic of the CHdN moiety at ca. 8.5
ppm that is clearly different from that of the CHdO resonance in
the starting materials at ca. 9.5 ppm. The same trend is
reproduced in the 13C{1H} NMR spectra where the CHdN
signal appears at about 150 ppm, while the CHdO peak appears
at 179 ppm. The integrated 1H and the 13C{1H} NMR spectra of
the two [N,N] ligand precursors are included in the Supporting
Information. Crystals of 2PyN-H suitable for X-ray diffraction
(XRD) were obtained from the slow evaporation of a concen-
trated dichloromethane solution of this compound. The ligand
2PyN-H crystallizes in the orthorhombic space group Pbca with
two independent molecules in the asymmetric unit (Figure 1)
linked pairwise by intermolecular hydrogen bonding. The mol-
ecules are not oriented coplanar to each other, and although
dimerization takes place, this does not result in stacking (see
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Supporting Information).26 The complete crystallographic data
for 2PyN-H is summarized in Table 2.
compounds of the type [Cu(L2)(P,P)] (P,P = mono- or dipho-
sphine; L2 = bidentate ligand = 2PyOꢀ, 2PyNꢀ, 2IndOꢀ, or
2IndNꢀ), otherwise denoted in this work as [Cu(N,N)-
(diphosphine)] ((N,N) = 2PyN for compounds 1ꢀ4 and 2IndN
for 8) or [Cu(N,O)(diphosphine)] ((N,O) = 2PyO for com-
pounds 5ꢀ6 and 2IndO for 7), were prepared by salt metathesis
using the deprotonated ligands and a neutral source of copper(I).
In the preparation of [Cu(2PyN)(Ph3P)2] (1), [Cu(NO3)-
(Ph3P)2]14 was used as the starting material. The rest of the
[Cu(L2)(diphosphine)] compounds (2ꢀ8) were synthesized
from their diphosphine dimers, [Cu(μ-Cl)(P,P)]2 (P,P = dppb,
DPEPHOS, XANTPHOS), which were prepared in one
step from CuCl and the respective diphosphine in CH2Cl2
(Scheme 2).27
Within each molecule in the asymmetric unit, the N-phenyl ring
is twisted out of plane with respect to the pyrrole-aldimine moiety,
with torsion angles of 46.59(3)ꢀ and 44.13(3)ꢀ. The imine CdN
distances of 1.287(1)Å and 1.285(1)Å are within the range for this
group.10a,c The pyrrole-to-aldimine CꢀC single bond lengths
(1.428(1) Å and 1.425(1) Å) are shorter than normal and are
consistent with the conjugation of the pyrrole rings with the
coplanar CdN bond, a feature that has also been highlighted by
Gomes’s group with a closely related iminopyrrole.10b
Syntheses of Copper(I) Compounds. The carboxaldehyde
starting materials and their carbaldimine derivatives were depro-
tonated in CH2Cl2 using potassium tert-butoxide (KOtBu) to
provide the potassium salts of the (N,N)ꢀ or (N,O)ꢀ bidentate
ligands, K(L2), where (L2)ꢀ = (2PyO)ꢀ, (2PyN)ꢀ, (2IndO)ꢀ,
or (2IndN)ꢀ (eqs 3 and 4). Neutral heteroleptic copper(I)
The colors of the product complexes varied from blue-green
(7) to pale yellow (5 and 6) to yellow-brown (1ꢀ4 and 8),
depending on the nature of the (N,N)ꢀ or (N,O)ꢀ bidentate
ligand. The identities of the complexes were confirmed by
multinuclear NMR spectroscopy and by elemental analyses.
For compounds 1ꢀ3 and 5ꢀ8, the slow diffusion of concen-
trated CH2Cl2 solutions into hexanes resulted in the
formation of single crystals from which the structures in the
Figure 1. ORTEP representation of the asymmetric unit of 2PyN-H,
showing thermal displacement ellipsoids at the 50% probability level.
Hydrogen bond distances (Å): N(1)ꢀH(1N) N(4) = 2.078(13),
3 3 3
N(3)ꢀH(3N) N(2) = 2.098(14).
3 3 3
Scheme 2
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Inorganic Chemistry
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solid state were established by X-ray crystallography. The
structure of an additional, unexpected compound, namely
{[Cu(XANTPHOS)]2(μ-Cl)(μ-ClCuCl)} (9), was also estab-
lished by the examination of crystals from a batch of
[Cu(2PyO)(XANTPHOS)] (6), the latter of which represented
the majority of the material present in the particular batch.
Crystals of 9 were present as trace impurities that were initially
thought to be polymorphs of 6. The finding is interesting because
it shows a linear CuCl unit inserted as a bridge onto [Cu(μ-
Cl)(XANTPHOS)]2, the precursor of 6. Additional details along
with ORTEP representations of this compound are included in
the Supporting Information.
1
The H and 13C{1H} NMR spectra of the Cu(I) complexes
were compared to those of their free (N,N) or (N,O) ligand
precursors, with particular emphasis on the diagnostic reso-
nances of the aldehyde or aldimine moieties (Table 1). In
general, only small changes were found for these signals, suggest-
ing that the electronic environments of the ligands remain
relatively unperturbed upon coordination. For the [Cu(N,N)-
(diphosphine)] complexes with pyrrole-aldimine (1ꢀ4) or
indole-aldimine (8) ligands, a 0.1ꢀ0.2 ppm to high field shift
was seen for the proton resonance of the coordinated imine.
Similarly, the coordination of the ligand is evident in the 13C{1H}
NMR spectra as the chemical shift of the CHdN peak is
increased by approximately 3 ppm for the [Cu(2PyN)-
(diphosphine)] compounds (1ꢀ4) and by approximately
8 ppm for the indole-aldimine analogue (8). Similar analyses apply
to the [Cu(N,O)(diphosphine)] ((N,O) = pyrrole-aldehyde
(5, 6) or indole-aldehyde (7)) compounds, for which the aldehyde
proton is more shielded by ca. 0.5 ppm while the carbonyl is more
deshielded upon coordination. The CHdO resonances of the
[Cu(2PyO)(diphosphine)] compounds 5 and 6 in the respective
13C{1H} spectra exhibit a much smaller change (e0.3 ppm)
than the one for CHdN of the [Cu(2PyN)(diphosphine)]
analogues, 1ꢀ4 (ca. 2ꢀ3 ppm), which is consistent with weaker
coordination of the aldehyde relative to the imine. Similar trends
are observed when comparing [Cu(2IndO)(DPEPHOS)] (7)
with [Cu(2IndN)(DPEPHOS)] (8).
Table 1. Comparison of Distinctive NMR Signals of Free
Ligands and Their Corresponding Copper(I) Compounds
1H NMR
13C{1H} NMR
31P{1H} NMR
compound CHdO CHdN CHdO CHdN
δ1
δ2
2PyO
9.5
9
179.5
179.5
179.8
5
ꢀ17.5
ꢀ16.6
6
9.1
2PyN
8.5
8.3
8.4
8.4
8.4
150.9
153.9
153.5
153.1
152.5
1
ꢀ0.9
ꢀ8.4
ꢀ15.2
ꢀ14.5
2
3
ꢀ16.6
ꢀ17.7
4
2IndO
9.9
9.6
182.7
186.4
7
ꢀ17.5
ꢀ15.2
ꢀ19.4
ꢀ19.5
The presence of coordinated PPh3 on compound 1, or
coordinated diphosphines for the other copper compounds,
was confirmed by 31P{1H} NMR, which typically exhibited
2IndN
8
8.6
8.4
150.8
157.9
Table 2. Selected Bond Distances (Å) and Angles (deg) for Compounds 1ꢀ3 and 5ꢀ8 a
compound
2PyN-H
1
2b
3b
5
6
7
8
bond
distance (Å)
Cu1ꢀN1
2.042(2)
2.115(2)
2.008(1)
2.070(1)
2.023(2)
2.106(2)
1.995(1)
2.001(3)
1.973(6)
2.015(1)
2.144(1)
Cu1ꢀN2
Cu1ꢀO1
Cu1ꢀP1
Cu1ꢀP2
C4ꢀC5
N2ꢀC5
O1ꢀC5
2.279(1)
2.2267(4)
2.2784(4)
1.411(2)
2.254(3)
2.352(6)
2.266(2)
2.228(2)
1.43(1)
2.2303(6)
2.2363(6)
1.406(3)
1.291(3)
2.2385(5)
2.2418(5)
1.414(2)
1.308(2)
2.2660(8)
2.2170(8)
1.415(4)
1.292(4)
2.2475(4)
2.2236(4)
1.319(12)
2.283(4)
2.2395(4)
1.432(2)
1.293(2)
1.428(1)
1.287(1)
1.2487(2)
1.289(6)
1.25(1)
angle
angle (deg)
N1ꢀCu1ꢀN2
N1ꢀCu1ꢀO1
P1ꢀCu1ꢀP2
N2ꢀC5ꢀC4
O1ꢀC5ꢀC4
81.48(7)
82.76(6)
81.9(1)
81.10(5)
80.71(4)
80.55(14)
115.84(1)
78.2(2)
122.57(2)
120.1(2)
87.30(2)
110.25(3)
119.7(3)
114.86(1)
115.84(8)
113.24(1)
119.2(1)
123.85(7)
119.78(14)
123.1(1)
123.5(5)
122.3(8)
84.9(2)
dihedral angle
angle (deg)
PꢀCuꢀP^NꢀCuꢀN
82.56(2)
44.97(8)
86.02(4)
30.53(9)
82.73(6)
88.72(3)
PꢀCuꢀP^OꢀCuꢀN
83.47(3)
87.39(7)
ligand tilt
angle (deg)
{Pyrrole-C(5)ꢀN(2)}^{Ph}
46.59(3)
32.4(2)
{Indole-C(5)ꢀN(2)}^{Ph}
19.85(4)
a Selected data for 2PyN-H is included for additional comparison purposes. b Refers to one of the independent molecules cocrystallized in the
asymmetric unit (Figures S28 and S29 in the Supporting Information).
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Figure 3. Molecular structure of one independent molecule of 2.
Hydrogen atoms have been omitted for clarity.
Figure 2. Molecular structure of 1. Hydrogen atoms have been omitted
for clarity.
broad signals. The spectra of [Cu(2PyN)(DPEPHOS)] (3),
[Cu(2PyN)(XANTPHOS)] (4), [Cu(2IndO)(DPEPHOS)]
(7), and [Cu(2IndN)(DPEPHOS)] (8) exhibited two broad
peaks of unequal intensity, which were interpreted as resulting
from coordination isomers as a result of the arrangement of the
(N,N) or (N,O) ligand with respect to the puckered diphosphine
ligands (Table 1). Analysis of the solid state structure for
compound 6 provides evidence for this assumption. There is a
disorder in the (N,O) ligand in which each position is essentially
the inverse of the other within the same plane. While the
phosphorus atoms within each isomer are equivalent via a mirror
plane, they are inequivalent between isomers. The isomers can
interconvert by dissociation and recoordination of the anionic
ligand or by the twisting of the diphosphine. Although only a
single 31P resonance was observed for compound 6, the presence
of such coordination isomers in 3ꢀ4 and 7ꢀ8 in solution is
possible especially if the additional steric bulk provided by the
N-phenyl aldimine or indole rings prevents rapid isomerization
via twisting of the diphosphine ligand.
Figure 4. Molecular structure of one independent molecule of 3.
Hydrogen atoms have been omitted for clarity.
refinement details are summarized in Tables 3 and 4. Unless
otherwise noted, all structural diagrams containing thermal dis-
placement ellipsoids are drawn at the 50% probability level.
Both the (N,N) and (N,O) bidentate ligands, structures form
five-membered chelate rings with copper(I). For the [Cu(N,N)
(diphosphine)] series, 1ꢀ3 and 8, the pending phenyl substi-
tuent is tilted out of plane from the pyrrole- or indole-aldimine
unit, with dihedral angles varying from 19.85(4)ꢀ in 8 to
46.59(3)ꢀ in 1 (Table 2). For 1ꢀ3, the comparison of the
C4ꢀC5 and N2ꢀC5 bond lengths with the corresponding ones
of the ligand precursor, 2PyN-H, shows that the CꢀC bond
distance is slightly shorter, whereas the CꢀN bond is longer, in
the complexes. The N2ꢀC5ꢀC4 angle of the copper(I) com-
pounds (mean ∼119.86ꢀ) is slightly more acute than that of
2PyN-H (123.85ꢀ). In 8, both CꢀC and NꢀC bond distances
are slightly elongated compared to the case of the free ligand.
The NꢀCuꢀN bond angles are very similar among the
[Cu(N,N)(diphosphine)] compounds, but the PꢀCuꢀP angle
varies more so, ranging from 87.296(19)ꢀ for 2 to 113.239(14)ꢀ
in 8. For the [Cu(N,O)(diphosphine)] complexes, neither the
NꢀCuꢀO nor the PꢀCuꢀP bond angles exhibit a great
variation. The dihedral angle between the PꢀCuꢀP and
NꢀCuꢀN planes for the [Cu(pyrrole-aldimine)(diphosphine)]
Because thermal stability and sublimability are critical proper-
ties for successful OLED device preparation by vapor deposition,
small scale sublimations were attempted for complexes 2ꢀ4.
Successful sublimation occurred at 230ꢀ250 ꢀC under vacuum
(ca. 2 ꢁ 10ꢀ3 Torr) with approximately 40% recovery.
Molecular Structures of Copper(I) Compounds. The struc-
tures of compounds 1ꢀ3 and 5ꢀ8 were established by the X-ray
diffraction of single crystals (Figures 2ꢀ8). Table 2 summarizes
the relevant bond distances and angles for these compounds, and
all other data are available in the Supporting Information in cif
format. The complete crystallographic data and structure
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Inorganic Chemistry
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Figure 7. Molecular structure of 7. Hydrogen atoms have been omitted
Figure 5. Molecular structure of 5. Hydrogen atoms have been omitted
for clarity.
for clarity.
Figure 6. Molecular structure of 6. Hydrogen atoms have been omitted
for clarity.
Figure 8. Molecular structure of 8. Hydrogen atoms have been omitted
for clarity.
compounds 1ꢀ3 (mean ∼83.77ꢀ) and the [Cu(indole-
aldimine)(diphosphine)] compound (8) (88.72ꢀ) reveals a
distorted tetrahedral geometry around the copper(I) ion for all
of the structures and is consistent with previously reported
structures of heteroleptic phosphine- or diphosphine-based
copper(I) complexes containing (N,N) donors.6j,k,7 The same
observation holds true for the indole-aldehyde complexes 5 and 6
(mean ∼85.43ꢀ) and the indole-aldehyde complex 7 (84.93ꢀ),
even though the aldehyde functional group encounters much less
steric congestion than the substituted imine does.
Spectroscopic Properties in Fluid Solution. The absorption
and emission spectra of the potassium salts of the deprotonated
ligands (Figure S34 in the Supporting Information) and their
respective copper(I) compounds (Figures 9ꢀ12) were mea-
sured in CH2Cl2, at room temperature (298 K). All data are
summarized in Table 5.
single broad bands at ca. 420 nm. All of the emission spectra
overlap strongly with the absorption bands of these ligands with
Stokes shifts in the range 45ꢀ85 nm (3100ꢀ6010 cmꢀ1),
suggesting singlet 1(πꢀπ*) emission.
The absorption spectra of the copper(I) complexes are each
characterized by intense absorptions in the UV region. The
highest energy bands in 1ꢀ4 are not apparent in the free ligands
and are assigned as πꢀπ* transitions of the ancillary phosphine
ligands.28 The lowest energy bands in complexes 1ꢀ4 have
maxima at ca. 390 nm and show limited dependence on the
identity of the phosphine or diphosphine ligand. Complexes 5
and 6 have maxima at ca. 285 nm with the spectrum of each
complex exhibiting an additional low energy shoulder. In 5, this
shoulder is well-pronounced while, in 6, it appears as a tail
extending to 350 nm. Complex 7 displays a strong band at
337 nm and a low-energy, broad absorption at 432 nm. This
low energy absorption is notably weaker with a molar
extinction coefficient (ε) of 3400 Mꢀ1 cmꢀ1. The spectrum of
8 exhibits strong transitions at 261 and 370 nm with a shoulder at
about 336 nm.
Ligand emission spectra are characterized by maxima in the
UV or blue region of the visible spectrum. Vibronic structure is
present in the spectra of both pyrrole-based ligands K(2PyO)
and K(2PyN) with spacings of 4325 and 1278 cmꢀ1, respec-
tively. The indole-aldehyde and indole-aldimine ligands show
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Table 3. Crystal Data and Structure Refinement for 2PyN-H and Compounds 1ꢀ3
compound
2PyN-H
1
2
3
formula
C
11H10N2
C48H41Cl2CuN2P2
842.21
C41H34CuN2O0.5P2
688.18
100.0(1)
monoclinic
P21/c
C48H39Cl2CuN2OP2
856.19
fw
170.21
100.0(1)
orthorhombic
Pbca
T (K)
100.0(1)
triclinic
P1
100.0(1)
triclinic
P1
crystal system
space group
a (Å)
9.3869(9)
18.119(2)
21.187(2)
90
10.0778(9)
11.001(1)
19.326(2)
103.585(2)
91.243(2)
103.576(2)
2017.8(3)
2
16.631(3)
26.069(4)
17.111(3)
90
10.229(1)
16.583(2)
25.942(3)
91.109(2)
94.510(2)
96.686(2)
4355.3(8)
4
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
Z
90
115.337(3)
90
90
3603.5(6)
16
6705(2)
8
F
calcd (mg mꢀ3
μ (mmꢀ1
)
1.255
1.386
1.363
1.306
)
0.076
0.790
0.781
0.735
no. reflections collected
no. unique reflections
84197
9638
45236
165018
35726
67641
18316
24376
a
Rint
0.0589
6602
0.0676
0.0833
21785
0.0593
no. observed reflections
11178
14846
no. parameters
315
496
866
1052
GOFb on F2
1.042
1.011
1.052
1.021
R1c [I > 2σ(I)]
0.0502
0.0563
0.0541
0.1273
0.0613
wR2d
0.1293
2
0.1188
0.1510
2
2
a Rint = |Fo ꢀ ÆFc2æ|/|Fo |. b GOF = S = [[w(Fo ꢀ Fc2)2]/(m ꢀ n)]1/2, where m = number of reflections and n = number of parameters. c R1 = ||Fo| ꢀ
|Fc||/|Fo|. d wR2 = [[w(Fo ꢀ Fc2)2]/[w(Fo ) ]]1/2, where w = 1/[2(Fo ) + (aP)2 + bP] and P = 1/3 max(0, Fo ) + 2/3Fc2.
2
2 2
2
2
Table 4. Crystal Data and Structure Refinement for Compounds 5ꢀ8
compound
formula
5
6
7
8
C
42H34Cl2CuNO2P2
C44H36CuNO2P2
736.22
100.0(1)
tetragonal
P42/n
C47H38Cl4CuNO2P2
916.06
100.0(1)
monoclinic
P21/n
C51H39CuN2OP2
821.32
fw
781.08
100.0(1)
triclinic
P1
T (K)
100.0(1)
triclinic
P1
crystal system
space group
a (Å)
9.657(1)
14.258(2)
14.593(2)
88.946(2)
74.641(2)
71.779(2)
1836.0(4)
2
26.407(2)
26.407(2)
11.966(1)
90
9.483(1)
27.440(4)
16.305(3)
90
9.5399(7)
10.8501(8)
19.801(1)
96.277(1)
94.581(1)
99.023(1)
2002.2(3)
2
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
Z
90
100.859(3)
90
90
8344.7(13)
8
4166.7(11)
4
F
calcd (mg mꢀ3
μ (mmꢀ1
)
1.413
1.172
1.460
1.362
)
0.865
0.634
0.899
0.668
no. reflections collected
no. unique reflections
39666
200283
22366
33657
44929
15924
7426
18176
a
Rint
0.0329
12515
0.0547
14350
0.1709
4058
0.0385
no. observed reflections
no. parameters
GOFb on F2
13432
461
493
514
514
1.041
1.064
1.015
1.025
R1c [I > 2σ(I)]
wR2d
0.0390
0.0552
0.0791
0.0446
0.0975
0.1523
0.2077
0.1095
a Rint = |Fo ꢀ ÆFo æ|/|Fo |. b GOF = S = [[w(Fo ꢀ Fc2)2]/(m ꢀ n)]1/2, where m = number of reflections and n = number of parameters. c R1 = ||Fo| ꢀ
2
2
2
2
|Fc||/|Fo|. d wR2 = [[w(Fo ꢀ Fc2)2]/[w(Fo ) ]]1/2, where w = 1/[2(Fo ) + (aP)2 + bP] and P = 1/3 max(0, Fo ) + 2/3Fc2.
2
2 2
2
2
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Figure 9. (a) Absorption and (b) emission spectra of K(2PyN) and the [Cu(2PyN)(diphosphine)] compounds 1ꢀ4 in fluid CH2Cl2 (1 ꢁ 10ꢀ5 M).
Figure 10. (a) Absorption and (b) emission spectra of K(2PyO) and the [Cu(2PyO)(diphosphine)] compounds 5ꢀ6 in fluid CH2Cl2 (1 ꢁ 10ꢀ5 M).
Figure 11. (a) Absorption and (b) emission spectra of K(2IndO) and [Cu(2IndO)(DPEPHOS)] (7) in fluid CH2Cl2 (1 ꢁ 10ꢀ5 M).
The solution emission spectra of complexes 1ꢀ4, which all
contain the 2PyN ligand, are similar, with maxima near 590 and
shoulders at 630 nm. Complexes 1 and 3 lack the vibronic structure
observed in the free ligand. The spacing between peaks for complex
4 is 1080 cmꢀ1. With the exception of 4, lifetimes are on
the order of 70ꢀ2400 μs. The solution emission spectrum of
complex 8, which also possesses a (N,N), (P,P) donor set, exhibits
dual emission with maxima at 560 and 680 nm with a lifetime of
65 μs for the low energy emission and a lifetime shorter than the
limit of the phosphorimeter (∼2 μs) for the high energy band.
Excitation spectra were obtained while monitoring emission at
both emission peaks. Both excitation spectra are characterized
by strong maxima at 405 nm and weaker shoulders at 290 nm. The
(N,O), (P,P) complexes 5 and 6 exhibit identical emission at
370 nm with lifetimes of <2 μs, while complex 7exhibits a structured
emission with a maximum at 403 nm and a lifetime of 10 μs.
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Figure 12. (a) Absorption and (b) emission spectra of K(2IndN) and [Cu(2IndN)(DPEPHOS)] (8) in fluid CH2Cl2 (1 ꢁ 10ꢀ5 M).
The excited states in 1ꢀ8 may be assigned by comparison of
the complex and free ligand emission spectra in conjunction with
lifetime data. For 4 the similar vibronic spacing between K-
(2PyN) and the complex is suggestive of strong contributions
from ligand-based excited states in the complex. The large
Stokes’ shift and long lifetimes in each complex are consistent
with triplet emissions. The emission maxima are marginally
affected by the identity of the phosphine ligand, suggesting little
participation of phosphine in the charge transfer state. Instead,
we propose that the Cu(I) ion primarily helps to promote
energy band could not be measured, but the 680 nm emission
lifetime is 9 μs. A possible assignment for the two bands is
separate emission from 3(MLCT) and 3(πꢀπ*).
Spectroscopic Properties in Frozen Glass. The excitation
and emission of the copper(I) compounds 1ꢀ8 were measured
in frozen Me-THF at low temperature (77 K). Table 5 includes
the emission data obtained from these measurements, and the
spectra are shown in Figures 13 and 14.
The excitation bands of all the compounds at 77 K
are approximate mirror images of their emission bands (see
Figures 14 and 15). The emission spectra of 2PyN derivatives are
structured with maxima at 569 nm for 1 and 577 nm for 2ꢀ4. The
peaks are better defined than in solution, and the vibronic spacings
are 1420 cmꢀ1 and 1185 cmꢀ1 for 1, and 1458 cmꢀ1 and
1253 cmꢀ1 for 2ꢀ4. Lifetimes in the frozen glass range from
2500 to 3600 μs. The emission of complex 8 is similar in vibronic
progression to those of 1ꢀ4, with spacings of 1328 cmꢀ1 and
1144 cmꢀ1. The emission maximum at 622 nm is significantly red-
shifted from those of the other complexes with N,N ligands by ca.
45 nm, which is attributed to the delocalization of the frontier
orbitals onto the conjugated indole ring. For 1ꢀ4 and 8, the similar
structure in solution and frozen glass and the long luminescence
lifetimes support an assignment of ligand-based triplet emission,
3(πꢀπ*).
3
intersystem crossing (ISC) to the ligand-based (πꢀπ*) emis-
sive state although the absence of vibronic structure in 1 and 3
suggests some MLCT component. This assignment of 3(πꢀπ*)
contrasts with that made for zinc bis(pyrrole-aldimine) com-
plexes, in which the radiative lifetimes are consistent with singlet
fluorescence rather than triplet phosphorescence.10b
The absorption maxima of the pyrrole-aldehyde complexes 5
and 6 are identical to those of K(2PyO), indicating little perturba-
tion of the pyrrole-aldehyde ILCT absorption upon coordination
to Cu, although the additional low energy shoulders may be
indicative of a MLCT component. Emission spectra of 5 and 6 are
red-shifted from that of the free K(2PyO) ligand and lack the
vibronic structure present in the ligand emission, indicating some
modification of the emissive state upon coordination to copper.
The UV region in the absorption spectrum of 7 is similar to that
of K(2IndO) and is thus assigned as mainly a ligand-based
1(πꢀπ*). However, a lowenergy bandat 432nm may be assigned
as a metal-to-ligand charge transfer (MLCT) on the basis of its
extinctioncoefficient (ε = 3400 Mꢀ1 cmꢀ1) and by comparisonto
copper complexes in the literature.6j,k The maximum in the
excitation spectrum of 7 of 336 nm is congruent with the
maximum absorption, and excitation into this band results in
emission that is slightly blue-shifted from that of K(2IndO). This
result may be due to slight differences in the indole-aldehyde π-
orbital energies in the presence of K+ or in the copper(I) complex.
The absorption at 261 nm in 8 is similar to those of 7 and 3 and
is logically phosphine-based while the broad band at 370 nm has a
high energy shoulder which overlaps with K(2IndN). The
shoulder can be assigned as 2IndN 1(πꢀπ*) while the maximum
at 370 nm may contain some MLCT character. The emission of 8
is unique among complexes studied here insomuch as two
emission bands with different lifetimes are observed, which is
consistent with dual emission. The excitation spectra obtained
while monitoring emission at both emission maxima are iden-
tical, with maxima at 405 and 290 nm. The lifetime of the higher
In the frozen glass, the emission spectra of 5 and 6 are nearly
identical, with maxima at 502ꢀ504 nm and shoulders at
472ꢀ473 nm. The luminescence lifetimes of both complexes
are 1800 μs. The spectrum of 7 is broad with λmax = 436 nm and a
lifetime of 730 μs. Complexes 5 and 6 differ only in the identity of
the diphosphine, and their identical emission at 77 K corrobo-
rates conclusions made in the solution phase regarding the
emission assignment as 3(MLCT + πꢀπ*).
Spectroscopic Properties in Solid State. The emission
spectra of 1ꢀ8 were measured in the solid state at 298 K
(Figure 15) and at 77 K (Figure 16). Powder samples were
packed in glass capillary tubes.
The spectra of 1ꢀ4 and 8 exhibit the same type of vibronic
structure seen in solution and frozen glass samples. At 298 K, the
emission maxima of the 2PyN- and 2IndN-supported complexes
are similar to those of solution samples, with slight variations
between complexes (Figure 16a). Upon cooling to 77 K, the
emission of 1 blue shifts, while 2ꢀ4 exhibit slightly red-shifted
spectra. Lifetimes on the order of 100ꢀ1400 μs at room
temperature are somewhat longer at 77 K. The similarities
between solid state and dilute solution emission data suggest
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Table 5. Absorption and Emission Data of K(L2) Ligands and Compounds 1ꢀ8
absorptionsa, λmax/nm
emission, λem/nm
Stokes’ shiftb/nm
(cmꢀ1
compound
media
CH2Cl2
(ε/Mꢀ1 cmꢀ1
)
excitation, λex/nm
(τ/μs)d
)
Φemc , %
K(2PyO)
K(2PyN)
K(2IndO)
285 (12800)
326 (26650)
262
359
336
310
404
421
48 (5910)
0.54
0.09
28
CH2Cl2
CH2Cl2
45 (3103)
85 (6009)
276 (9225), 306 (8000), 321 (6175),
336 (5850), 370 (1650), 408 (850)
338 (34000)
K(2IndN)
1
CH2Cl2
365
366
423
58 (3757)
0.19
0.02
CH2Cl2
258 (25750), 379 (8550)
556 (2400)
569 (3600)
589 (1400)
597 (3100)
564
190 (9337)
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
CH2Cl2
2
3
289 (19550), 343 (21500),
379 (27225)
328
366
236 (12757)
190 (9337)
0.12
0.02
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
577 (2600)
591 (520)
601 (1500)
556 (210)
CH2Cl2
284 (18875), 327 (14975),
386 (16450)
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
577 (2600)
586 (900)
595 (2300)
589 (70)
4
5
6
CH2Cl2
288 (25050), 392 (23250)
287 (19250), 312 (21825)
287 (23625)
399
314
312
190 (8085)
56 (4820)
56 (4877)
0.26
2.9
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
577 (2500)
593 (190)
615 (1100)
370e
CH2Cl2
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
502 (1800)
587 (3000)
577 (2700)
368e
CH2Cl2
2.8
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
504 (2500)
560 (10)
425 (250)
524 (530, 50)f
403 (10)
7
8
CH2Cl2
337 (23425), 432 (3400)
336
405
67 (4948)
1.6
2-Me-THF, 77 K
solid, 298 K
solid, 77 K
CH2Cl2
436 (730)
370e
457 (480)
560, 680 (65)
261 (36625), 336 (20975),
370 (27750)
155 (6834), 275 (985)
0.06
2-Me-THF, 77 K
solid, 298 K
622 (470)
611 (85)
615 (470)
solid, 77 K
c
a Solution concentration ∼ 10ꢀ5 M. b Measured as the difference between maxima of excitation and emission. Measured in CH2Cl2 relative to
[Ru(bpy)3]+ in air-equilibrated water (ΦR = 0.028).17 d Fluorescence-decay curves are included in Figures S35ꢀS38 of the Supporting Information.
e Lifetime less than 2 μs. f Fit to a biexponential decay.
that the emission is insensitive to aggregation and that molecular
emission is observed in the solid state. Structured emission is
observed for 8 with λmax = 611 nm at 298 K and 615 nm at 77 K.
At 298 K, the spectra of 5 and 6 are similar, with maxima at 587
and 560 nm, respectively. Upon cooling, two bands at 425 and
524 nm are evident in 6 while the band in 5 is only slightly blue-
shifted. The two emission bands in 6 have unique excitation
spectra and different lifetimes, suggesting possible emission from
aggregation states in the solid state at low temperature. The large
blue shift of the maximum in 6 may indicate emission from a
higher energy TN state as a result of slow relaxation to T1 at 77 K.
Complex 7 emits at 370 nm at 298 K and 457 nm at 77 K.
Molecular Orbital Calculations. To further examine the
excited states in these complexes, DFT calculations at the
B3LYP/6-31+G level of theory as implemented in Gaussian
0929 were performed on the singlet ground states (S0) of
complexes 3, 5, 7, and 8 as representative examples that vary in
the (N,N) or (N,O) ligands and are consistent in the diphosphine
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Figure 13. (a) Excitation and (b) emission spectra of compounds 1ꢀ4 and 8 in frozen Me-THF at 77 K.
Figure 14. (a) Excitation and (b) emission spectra of compounds 5, 6, and 7 in frozen Me-THF at 77 K.
Figure 15. Emission spectra of compounds (a) 1ꢀ4 and 8 and (b) 5ꢀ7 in solid-state at 298 K.
Figure 16. Phosphorescence emission spectra of compounds (a) 1ꢀ4 and 8 and (b) 5ꢀ7 in solid-state at 77 K. Spectra were obtained after a 0.01 ms
delay and are the average of five consecutive scans.
(DPEPHOS). The optimized geometries of 3 and 8 are similar to
the X-ray structures, but the calculated geometries of 5 and 7
differ somewhat from experimentally determined structures. The
main difference is an elongation of the CuꢀO bond length, with a
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Table 6. Lowest Energy Electronic Transitions for 5 and 7
Calculated by TD-DFT
transition
energy wavelength oscillator
major
complex
(cmꢀ1
)
(nm)
strength
contributions
5
T1
S1
21820
27395
458.3
365.0
0
Hꢀ1 f L+2 (95%)
0.0265 HOMO f LUMO (45%)
Hꢀ2 f L+2 (30%)
HOMO f L+2 (10%)
S2
27548
363.0
0.0131 HOMO f LUMO (34%)
Hꢀ2 f L+2 (47%)
7
T1
S1
15004
21740
666.5
460.0
0
HOMO f LUMO (100%)
0.0687 HOMO f LUMO (86%)
indole-aldehyde complex 7 is not as straightforward. Complex 7
emits lower energy in solution but emits higher energy in the
solid state or frozen glass, and simple indole delocalization
arguments are not sufficient. Close examination of the molecular
orbitals for the emissive states reveals that the HOMO f LUMO
transition of 7 contains significant Cu-d character (MLCT +
πꢀπ*) and no participation of aldehyde lone pairs in the
HOMO. Conversely, the HOMOꢀ1 f LUMO+1 triplet state
in complex 5 has minimal Cu-character and extensive oxygen
lone pair contribution. Thus, emission in 5 and 6 is more
appropriately described as 3(nꢀπ* + πꢀπ*).
Figure 17. Diagrams and energies (eV) of the HOMO and LUMO for
complexes 3, 8, 5, and 7. Isovalue = 0.05.
consequential flattening of the tetrahedral geometry toward
pyramidal coordination. Coordinates for the calculated geometry
in xyz format are provided in the Supporting Information.
Diagrams of the HOMO and LUMO for each complex are
shown in Figure 17. Additional frontier orbital diagrams are
included in the Supporting Information.
In each complex, the HOMO is comprised primarily of pyrrole
or indole π functions mixed to varying degrees with Cu-d
character. For complexes 3, 8, and 7, the LUMO is delocalized
over π* orbitals of the anionic ligand while the LUMO of 5 is
localized on the aryl moieties of the DPEPHOS backbone. The
different nature of the LUMO calculated for 5 was viewed with
some concern; therefore, time-dependent calculations were
performed for 5 and 7 to better model the electronic transitions
in these complexes. Complete results of these calculations are
included in the Supporting Information, and the lowest energy
singlet and triplet transitions, along with energies, oscillator
strengths, and major orbital contributions, are given in Table 6.
In 7, the T1 and S1 absorptions are exclusively HOMO f
LUMO excited states (πꢀπ*). The two lowest singlet absorptions
in complex 5 were found to be transitions from mixed HOMO and
HOMOꢀ2 orbitals to mixed LUMO and LUMO+2 orbitals. The
HOMOꢀ2 level is largely copper-localized while LUMO+2 is the
lowest π* level of the pyrrole-aldehyde (Supporting Information).
The lowest triplet absorption, which would correspond in char-
acter to an emissive triplet state, is a HOMOꢀ1 f LUMO+2
Conclusions. A series of neutral luminescent copper(I) com-
plexes of the types [Cu(N,N)(P,P)] and [Cu(N,O)(P,P)],
containing phosphine or diphosphines and coordinated pyrrole-
or indole-aldimine or aldehyde ligands, was prepared and struc-
turally characterized, and the photophysical properties of the
complexes were established in solution, the solid state, and frozen
glasses. The complexes are all thermally stable and exhibit long-
lived emission, the excited states of which have been assigned as
mixed intraligand and metal-to-ligand charge transfer 3(MLCT +
πꢀπ*) transitions. The experimental results are consistent with
the conclusions drawn from quantum chemical calculations, the
latter of which demonstrate a large dependence of the photo-
physical properties of these complexes on the identity of the (N,N)
or (N,O) anionic ligands. In the case of the aldimine-derived
compounds, 1ꢀ4 and 8, the experimental results show that
the emission is insensitive to aggregation and, thus, molecular
emission—a desired property for OLED emitters—is obser-
ved. Furthermore, compounds 2ꢀ4 can be sublimed at T =
230ꢀ250 ꢀC under vacuum and, in turn, give proof for this
class of (N,N) compounds as potential candidates for chemical
vapor deposition (CVD) processes.
3
transition. The latter is identified as pyrrole-aldehyde (πꢀπ*)
and is consistent with 3, 8, and 7. Apparently the relative energies
of phosphine and pyrrole π* orbitals in these complexes are highly
sensitive to subtle modifications of the anionic ligand. In related
work, we have observed that the electronic modification of a
triazole ring changes the emissive state from predominately
intraligand to interligand charge transfer.8
’ ASSOCIATED CONTENT
S
Supporting Information. Selected NMR spectra, addi-
b
tional structural information, fluorescence decay plots, frontier
orbital diagrams, calculated electronic transition energies, rele-
vant orbitals for the four lowest singlet and triplet states in
compounds 3, 5, 7, and 8, and xyz coordinates for calculated
geometries. This material is available free of charge via the
Internet at http://pubs.acs.org.
Analyzed in the context of experimental data, the molecular
orbital calculations reinforce the unifying theme that the photo-
physical properties of these complexes depend largely on the
identity of the anionic ligands and less upon differences in the
supporting diphosphine. Complexes 1ꢀ4 and 8 with (N,N)
pyrrole or indole ligands form a congruent series with similar
behavior in solution, in frozen glass, or in the solid state. The
lower energy emission in 8 is interpreted as a result of charge
delocalization in the LUMO and was modeled well by DFT. A
similar comparison of pyrrole-aldehyde complexes 5 and 6 vs
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: eisenberg@chem.rochester.edu.
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ARTICLE
’ ACKNOWLEDGMENT
2007, 280, 69–115. (g) Moudam, O.; Kaeser, A.; Delavaux-Nicot, B.;
Duhayon, C.; Holler, M.; Accorsi, G.; Armaroli, N.; Sꢀeguy, I.; Navarro, J.;
Destruel, P.; Nierengarten, J.-F. Chem. Commun. 2007, 3077–3079.
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The authors thank the National Science Foundation (NSF-
GOALI, Grant CHE-0616782) for the financial support to this
work. We thank Dr. Joseph Deaton (Dept. of Chemistry,
Bowling Green State University), Dr. Henry J. Gysling, and Prof.
David R. McMillin (Dept. of Chemistry, Purdue University) for
very helpful discussions.
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