Intramolecular π-stacking in copper(i) diketiminate phenanthroline complexes

Article abstract of DOI:10.1039/c0dt00240b

Diketimines N,N′-dibenzyl-2-amino-4-imino-pent-2-ene (1), S,S-N,N′-di(phenylethyl)-2-amino-4-imino-pent-2-ene (2), N,N′-bis(3,4,5-trimethoxyphenylmethyl)-2-amino-4-imino-pent-2-ene (3), N,N′-bis(pentafluorophenylmethyl)-2-amino-4-imino-pent-2-ene (4) and

Full text of DOI:10.1039/c0dt00240b

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www.rsc.org/dalton | Dalton Transactions
Intramolecular p-stacking in copper(I) diketiminate phenanthroline
complexes†
Paul O. Oguadinma, Alexandre Rodrigue-Witchel, Christian Reber and Frank Schaper*
Received 31st March 2010, Accepted 8th June 2010
DOI: 10.1039/c0dt00240b
Diketimines N,N¢-dibenzyl-2-amino-4-imino-pent-2-ene (1),
S,S-N,N¢-di(phenylethyl)-2-amino-4-imino-pent-2-ene (2),
N,N¢-bis(3,4,5-trimethoxyphenylmethyl)-2-amino-4-imino-pent-2-ene (3),
N,N¢-bis(pentafluorophenylmethyl)-2-amino-4-imino-pent-2-ene (4) and
N,N¢-diisobutyl-2-amino-4-imino-pent-2-ene (5) react with CuOtBu in the presence of
2,9-R2-1,10-phenanthroline to give the respective neutral, tetracoordinated diketiminate copper(I)
phenanthroline complexes 1a+2a (R = H), 1b, 3b–5b (R = Me) and 1c+3c (R = Ph). Crystal structures
were obtained for all complexes except 5b and intramolecular p-stacking between the phenanthroline
ligand and one or two N-benzyl substituents were observed in 1a, 2a, 1b and 1c, or 3b and 4b,
respectively. UV/vis absorption spectra show two transitions in the visible region, a diketiminate-based
transition at 373–386 nm and a transition at 600–666 nm, tentatively assigned as an MLCT to
phenanthroline. All complexes were weakly luminescent in the solid state at room temperature with
lifetimes of less than 60 ns. Weak luminescence was also observed in solution with lmax = 720–830 nm
for 1b, 1c, 3b, 4b and 5b and short luminescence lifetimes. Intramolecular p-stacking interactions, which
prevent flattening distortions in the solid state, appear to have advantageous effects on luminescence
intensities.
Introduction
Luminescent metal complexes find application in solar light
harvesting and conversion, and complexes of second and third
row metals, in particular Ru(II) polypyridines, have been among
the most prominent examples.1,2 Their widespread use is, however,
limited by a notable toxicity and, in particular, high costs. There
Chart 1
is thus interest in cheaper and more environmentally benign metal
sources as alternatives.3 Complexes with a d10 electron config-
uration, in particular Cu(I), have been considered as potential
candidates, since their closed shell structure prevents the non-
radiative deactivation through low-lying MC transitions, which
are prevalent with other first-row transition metals.4 Copper(I)
phenanthroline complexes are among the most studied copper
complexes in this regard,4–8 following the pioneering work of
McMillin and coworkers.9,10 However, these complexes do deacti-
vate non-radiatively after irradiation by means other than thermal
equilibration of the MC and the MLCT levels. Bisphenanthroline
copper(I) complexes, for example, undergo a flattening distortion
in the excited state rendering them prone to nucleophilic attack
by solvent molecules or counter ions to form a penta-coordinated
exciplex, which deactivates via non-radiative relaxation (Chart 1).
Substitution of the 2,9-positions of the phenanthroline ligand,
avoiding coordinating solvents and excited state equilibration with
organic auxiliaries have been used as strategies to avoid excited
state quenching.4–8
We have previously reported the syntheses of copper(I) com-
plexes with N-alkyl substituted diketiminate ligands (nacnacR),11–13
in particular nacnacBn,12 in which p-stacking interactions are
present in most of its complexes. We envisaged that this ligand
would allow a “sandwiched” p-stacking arrangement of the
phenanthroline ligand between the N-benzyl substituents, thus
minimising excited state distortion (Chart 1). Due to the neutral
nature of diketiminate copper complexes, exciplex quenching
by the counter ion might be prevented as well. Not counting
Cu(I) halogen compounds14 and polynuclear complexes,15 we
are aware of only one report on neutral copper phenanthroline
complexes,16 although luminescent neutral copper complexes have
been reported with other ligands.17–20
Results and discussion
NacnacBn and nacnacCH(Me)Ph complexes
Reaction of diketimines 1 and 2 with CuOtBu21 in the presence
of the appropriate phenanthroline afforded the four-coordinated
copper(I) complexes 1a–d and 2a (Scheme 1). Complexes 1a–
d could also be obtained by displacement of styrene from
nacnacBnCu(styrene) with phenanthroline if liberated styrene
was removed under vacuum. Analogously, phenanthroline re-
placed acetonitrile in nacnacCH(Me)PhCuNCMe to yield 2a. Only
De´partement de chimie, Universite´ de Montre´al, 2900 Boul. E.-Montpetit,
Montre´al, QC, H3T 1J4, Canada. E-mail: Frank.Schaper@umontreal.ca
† Electronic supplementary information (ESI) available: Details of emis-
sion in the solid state. Additional solution spectra. CCDC reference
numbers 771783–771791. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00240b
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Solid-state structures of 1a–d and 2a are displayed in Fig. 1. Cu–
N bond distances and N–Cu–N bond angles f◦or the diketiminate
˚
ligand (1.959(2)–1.981(2) A, 98.3(2)–100.8(1) , Table 1) and for
◦
˚
the phenanthroline ligand (1.998(2)–2.194(1) A, 79.3(1)–83.4(4) )
˚
are in the usual range expected for these ligands (nacnac : 1.94(2) A,
◦
◦
99(1) ; phenanthroline: 2.05(4) A, 82(1) ).25 All structures show a
common motif, with one phenyl ring of the benzyl (or phenylethyl)
substituent in a parallel p-stacking arrangement with phenanthro-
line (angles and distances between least-square planes: 5–15◦, 3.0–
˚
˚
3.8 A), while the other is rotated out of a parallel arrangement.
Scheme 1 Preparation of complexes 1a-1d and 2a.
The symmetric NMR spectra obtained for all complexes indicate
that p-stacked and non-p-stacked rings interchange easily or that
in solution a C2v-symmetric arrangement of both substituents is
preferred. There are no evident structural reasons which would
prevent the p-stacking of the second N-substituent. In 1a and
1d, slight intermolecular p-stacking between two phenanthroline
ligands is observed, but it seems to be a minor structural motif
and is absent in the other structures. With the exception of 1c,
N–CH2–CPh angles of 114–116◦ (Table 1) for the non-p-stacked
substituent (e.g. N1–C12–C6 in 1a) are comparable to◦ those
observed in other nacnacBn metal complexes (Cu:12 114–116 , Zr:26
115◦, Zn:27 112–113◦). Corresponding angles for the p-stacked
substituent (e.g. N2–C19–C13 in 1a) are 3–5◦ smaller, indicating
a bending of the phenyl substituent towards the phenanthroline
ligand. Analogously, the phenanthroline ligand is either placed
on the bisector of the diketiminate ligand (1d and 2a, Fig. 2)
or angled slightly towards the p-stacked N-substituent in 1a–c
(Fig. 2). p-Stacking between the benzyl and the phenanthroline
substituent seems thus to require a slight deformation of the
decomposition products were observed with either method
when sterically bulky 2,9-di(tert-butyl)phenanthroline or 2,9-
dimesitylphenanthroline was employed. This mirrors common re-
activity patterns of phenanthroline copper complexes: [Cu(tbp)2]+
was only synthesized indirectly by oxidation of elemental cop-
per in the presence of tbp22 after conventional methods had
failed,23 while copper complexes of 2,9-dimesitylphenanthroline
have not been reported. The corresponding monosubstituted 2-
mesitylphenanthroline, on the other hand, cleanly yielded the
respective copper complex 1d. All complexes are dark-blue in
colour and sensitive to air and moisture. The complexes are soluble
in dichloromethane, toluene and THF and moderately soluble in
ether.24 1H NMR spectra of 1a–c display a singlet for the benzylic
protons, indicating a C2v-symmetric structure or fast rotation
around the N–CBn bond. In 1d, the benzylic protons split into
two doublets due to the non-symmetric mesitylphenanthroline
ligand.
Fig. 1 X-Ray structures of 1a–d and 2a. Thermal ellipsoids are drawn at the 50% probability level (30% for 2a). Hydrogen atoms were omitted for clarity.
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◦
˚
Table 1 Selected bond distances [A] and angles [ ] for 1a–d and 2a
1a
1b
1c
1d
2a
Cu–N1/2
Cu–N3/4
1.959(2)/1.981(2)
2.148(2)/2.071(2)
99.3(1)
78.7(1)
111.0(3)
115.6(2)
5
3.2–3.5
1.963(4)/1.975(4)
2.085(4)/2.092(4)
98.3(2)
79.8(2)
111.7(4)
115.1(4)
14
3.3–3.9
1.961(2)/1.964(2)
2.058(2)/2.110(2)
100.7(1)
81.3(1)
113.3(2)
110.9(2)
7
3.1–3.5
1.958(2)/1.965(2)
2.194(1)/1.998(2)
101.4(1)
82.5(1)
111.0(2)
113.8(2)
10
3.1–3.6
1.962(2)/1.963(2)
2.006(6)–2.204(6)
100.8(1)
N1–Cu–N2
N3–Cu–N4
N–CH2–Cp-Ph
N–CH2–CPh
∠ Ph–phen b
d Ph–phenc
83.4(4)d
a
110.0(2)
114.8(3)
15
3.0–3.8
a N–C–C angle of the p-stacked Bn substituent. b Angle between least-square planes of the p-stacked phenyl ring and the phenanthroline ligand. c Distances
of the carbon atoms of the p-stacked phenyl ring to the least-square plane of the phenanthroline ligand.
Fig. 2 Rocking (top) and flattening (bottom) distortions in 1a–d and 2a. Numbers indicate Dqx, Dqy, and Dqz.
N–C–CPh angle from its equilibrium position, but appears to be a
stabilizing interaction.
Copper dmp complexes with different diketiminate ligands
In an attempt to stabilize the planar, p-stacked arrangement
of the phenanthroline ligand with both N-benzyl substituents
depicted in Chart 1, we prepared diketimines 3 and 4 with
trimethoxybenzyl or pentafluorobenzyl N-substituents, following
the protocol established elsewhere (Scheme 2).12,30 Ligand 3 could
be further characterized by an X-ray diffraction study (Fig. 3,
ESI†). Ligand 4 was obtained only in purities of 85–90%, which
were however sufficient for subsequent reactions.
Distortions from an ideal geometry can be described using the
qx, qy, and qz angles, introduced by White and coworkers.28 Perfect
C2v symmetry yields qx = qy = qz = 90◦. A rocking distortion of
the phenanthroline ligand causes a deviation in qx and can be
expressed in the form of Dqx = |90◦ - qx| (Fig. 2). Analogously, a
flattening of the complex can be expressed by qz and Dqz = |90◦ -
qz|, where qz is roughly equivalent to the angle between the mean
planes of the ligands. Of the investigated complexes, sterically least
encumbered 1a and 2a display the most symmetrical coordination.
Symmetrical substitution of the phenanthroline ligand in 1b and
1c resulted in small rocking distortions, but significant complex
flattening of 13◦ and 20◦, respectively. Complex 1d shows the
highest rocking deformation (13◦), probably due to attractive
p-stacking between the mesityl substituent and the diketiminate
ligand. Despite the high flexibility of the benzyl substituents and
the unsymmetrical conformation with one p-stacked phenyl ring,
the complexes do not deviate significantly from ideal geometry.
The dmp-coordinated complex 1b, for example, shows deviations
of Dqx,y,z = 4◦, 9◦ and 13◦, while values of Dqx,y,z = 0–12◦, 1–16◦,
and 2–18◦ were found for the symmetric [Cu(dmp)2]+ cation with
different anions.28,29
Scheme 2 Preparation of complexes 1b, 3c and 4b.
Reaction of 3 or 4 with CuOtBu in the presence of the corre-
sponding phenanthroline yielded the respective copper complexes
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Fig. 3 Crystal structures of 3b, 3c and 4b. Hydrogen atoms were omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level.
◦
˚
Table 2 Selected bond distances [A] and angles [ ] for 3b, 3c and 4b
3b
3c
4b
Cu–N1/2
Cu–N3/4
1.948(1)
1.961(1)
1.985(1)
2.136(1)
100.3(1)
111.2(1)
111.6(1)
113.0(1)
13, 20
1.959(1)
1.959(1)
2.060(1)
2.060(1)
101.4(1)
82.5(1)
1.984(2)
1.982(2)
2.148(2)
2.052(2)
99.3(1)
79.6(1)
110.6(2)
109.9(2)
5, 4
N1–Cu–N2
N3–Cu–N4
N–CH2–CPh
112.5(1)
∠ Ph–phena
d (Ph–phen)b
40
3.4–5.0
3.4–4.0,
3.0–3.8
3.0–3.3,
3.0 –3.3
a Angle between least-square planes of p-stacked phenyl rings and the
phenanthroline ligand. b Distances of the carbon atoms of p-stacked phenyl
rings to the least-square plane of the phenanthroline ligand.
Fig. 4 Rocking (top) and flattening (bottom) distortions in 3b, 3c and 4b.
Numbers indicate Dqx, Dqy, and Dqz.
3b, 3c and 4b (Scheme 2). Their crystal structures showed indeed
more symmetrical conformations (Fig. 3 and 4, Table 2). In 3c,
p-stacking between both benzyl substituents and the dpp ligand
is lost. In 3b, on the other hand, the second phenyl ring is now
found in a more planar arrangement with the dmp ligand (Ph–
dmp angle: 3b: 20◦, 1b: 79◦). Complex 4b, carrying perfluorinated
benzyl substituents, shows the targeted sandwich-like p-stacking
of both phenyl rings, characterized by small angles between the
phenyl and phenanthroline planes (4◦ and 5◦) and small distance
UV/vis spectroscopy
For the sake of comparison, we prepared nacnaciBuCu(dmp),
5b, where the benzyl substituents were replaced by sterically
comparable isobutyl groups, which, however, cannot undergo p-
stacking interactions. UV/vis absorption and emission spectra
were recorded in toluene and, for selected complexes, in diethyl
ether at room temperature (Table 3). UV/vis absorption spectra
of all compounds show two distinct peaks above 350 nm with e =
variations (0.3 A). Both N–C–CPh angles are now reduced to
1200–12000 M-1cm-1 (Fig. 5). One transition is located at lmax
=
˚
109.9(2)◦ and 110.6(2)◦, respectively, a deformation apparently
required for a planar arrangement. The more planar conformation
of the second phenyl ring in 3b compared to 1b is mirrored by
a decrease of Dqz (13◦ in 1b, 9◦ in 3b) and the close planar
arrangement of all aromatic rings in 4b resulted in a very small
Dqz of 3◦. Increased p-stacking thus seems to reduce the flattening
distortion in the ground state, while slightly increasing rocking
distortions (Fig. 4). Complex 3c, which is the only compound
not showing any intramolecular p-stacking interactions in the
solid state, displayed the highest flattening distortion observed
for all complexes (25◦). Since 3c crystallized on a crystallographic
C2 axis, rocking and wagging distortions are consequently absent
(Fig. 4).
373–386 nm and appears as a shoulder on more intense p–p*
transitions for several complexes (Table 3). A second transition of
lower intensity, showing a distinctively asymmetric peak profile, is
found at lmax = 600–667 nm. Both transitions are weaker than p–p*
transitions located below 350 nm in these compounds and might
be associated with charge-transfer transitions. The transition at
lmax = 373–386 nm is found at shorter wavelengths than the
MLCT in [CuL2]+ complexes (L = phen,31,32 dmp,32–35 dpp:31–33,36,37
l
max(CH2Cl2) = 440–460 nm, with occasional shoulders at longer
wavelengths around 540–580 nm). Replacing an electron-poor
phenanthroline ligand with an anionic, electron-rich diketiminate
would not be expected to result in a hypsochromic shift of the
metal-phenanthroline CT. N-substituent effects also argue against
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Table 3 Longest wavelength absorption and luminescence maxima for nacnacRCu(L)
Toluene, lmax/nm (e·M cm)
Absorption
Diethyl ether, lmax/nm (e·M cm)
R
L
Dqz
p-stacking
Emission
Absorption
Emission
1a
2a
1b
3b
4b
5b
1c
3c
1d
Bn
CH(Me)Ph
Bn
CH2C6H2(OMe)3
CH2C6F5
iBu
Bn
phen
phen
dmp
dmp
dmp
dmp
dpp
3◦
Moderate
Moderate
Moderate
Strong
Very strong
None
Moderate
None
Moderate
382 (4448), 666 (2070)
377sh, 665 (1870)
375sh, 662 (2460)
None
None
820
801
735
822
805
None
None
2◦
13◦
9◦
386 (6247), 646 (3017)
385 (7721), 645 (3652)
384 (13469), 600 (7458)
370 (2836), 661 (1407)
785
825
722
814
376sh, 656 (1720)
3◦
386 (9560), 605 (5270)
373 (7163), 667 (1830)
376 (3786), 646 (1429)
377sh, 661 (1670)
n.d.
20◦
25◦
12◦
CH2C6H2(OMe)3
Bn
dpp
phenMes
378sh, 661 (1340)
Emission wavelengths are given for excitation at lmax of the longest wavelength transition.
Luminescence in solution was generally very weak (an exception
seems to be 4b) and again short-lived (t < 60 ns). While other
reasons cannot be excluded, a contributing factor to the low
luminescence intensities is certainly the low energy of the emission,
which makes non-radiative deactivation pathways more probable.
Complexes 1a, 2a, 1c and 1d were not luminescent in solution.
Qualitative luminescence intensity did not seem to correlate
with the observed distortions in the solid state: undistorted
complexes 1a and 2a, carrying an unsubstituted phenanthroline
ligand, did not show any luminescence in solution. Analogous
to [Cu(phenR)2]+, lack of luminescence in 1a and 2a might be
related to distortions in the excited state rather than to ground-
state distortions:4–8,40 despite their symmetrical structures, both
1a and 2a show evidence for easy thermal motions following a
rocking distortion mode in their crystal structures.
Luminescence spectra in toluene or diethyl ether solution
showed the same general features for all luminescent complexes,
which will be discussed in detail for 3b in diethyl ether. Excitation
at different wavelengths across the longest-wavelength transition
in 3b yielded a weak emission peak at 825 nm (Fig. 6). Excitation
of the higher-energy transition at 385 nm did not lead to any
observable luminescence (Fig. 7), in agreement with its assignment
as a diketiminate-based transition, not involving a phenanthroline
acceptor orbital.
Fig. 5 UV/vis absorption spectra of 1b and 3b–5b in diethyl ether at
room temperature.
an assignment of the transition around 380 nm as a charge
transfer transition towards phenanthroline: in the series 1b–5b,
isobutyl-substituted 5b displays the highest-energy transition (373
and 370 nm in toluene and diethyl ether, respectively), while
4b, carrying pentafluorobenzyl substituents, is found at the low-
energy end of the observed range (386 and 384 nm). We assign
transitions around 380 nm thus to diketiminate-based transitions,
not involving a phenanthroline acceptor orbital. In agreement with
this, nacnacBnCu(styrene) and (nacnacBn)2Zn show comparable
transitions at 349 nm (e = 2.2 ¥ 104 M-1cm-1) and 362 nm
(e = 2.1 ¥ 104 M-1cm-1, ESI†). Intense transitions in copper
diketiminate complexes around 350 nm have been previously
assigned to diketiminate p–p* transitions,38,39 but relatively low
molar absorption coefficients (2800–15000 M-1cm-1), line widths
of ª80 nm at half maximum, and the effect on the N-substituent
on lmax for 2b–5b would also be in agreement with a metal to
diketiminate CT, normally hidden below p–p* transitions in this
region.
Room temperature luminescence in the solid state (lexc = 514.5
nm) was observed for all complexes, with emission wavelengths
of 715–740 nm. Luminescence was weak and short-lived (t <
60 ns). Overlapping emission peaks from decomposition of the
air-sensitive compounds on the surface caused high errors in the
determination of lmax and we refrain from reporting lmax values
for solid state emission (ESI†).
Fig. 6 Emission spectra of 3b in diethyl ether with lexc = 600 nm (above)
and 660 nm (below).
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luminescence in solution is observed for the dpp complex 3c,
where p-stacking was lost in the crystal structure, while complexes
1c or 3b, which show moderate p-stacking interactions, are both
luminescent in solution. Complex 4b, which displays the targeted
sandwich-like arrangement of all aryl rings, shows the highest
luminescence intensity. However, even for 4b luminescence is weak
and short-lived, and the increased intensity might simply be a
result of its high absorption coefficient.
While p-stacking was only shown in the solid state, observed
changes in lmax values of absorption spectra of 1b and 3b, when the
solvent was changed from toluene to diethyl ether, are in agreement
with an increase of intramolecular p-stacking in the non-aromatic
solvent: the MLCT/LLCT is displaced slightly hypsochromi-
cally, the diketiminate-based transition around 380 nm slightly
bathochromically, and p–p* transitions of the benzyl substituent,
which were present above 350 nm in toluene, are now found below
350 nm. On the other hand, complexes 4b and 5b with very strong
or no possible p-stacking interactions, respectively, show only
minor changes in their absorption maxima between toluene and
diethyl ether solution. In comparison to 5b, 13C NMR spectra of
1b–4b in benzene-d6 show a high-field shift of C10A/C10B (C30
and C31 in the crystal structure of 4b, Fig. 3), which qualitatively
correlates with the observed p-stacking and might be attributed
to the ring current effect of the p-stacked benzyl substituent. The
effect is however minor (Dd < 2 ppm) and could not be reliably
reproduced in diethyl ether/acetone-d6 mixtures.
Fig. 7 Absorption spectrum (dashed line) and excitation spectrum (lem
=
825 nm, solid line) of 3b in diethyl ether. The increase of intensity in the
excitation spectrum around 390 nm is due to stray light from the 2l fraction
in the excitation beam.
Based on the results above, the lower-energy transition in the
obtained absorption spectra is most likely an MLCT transition
to the phenanthroline ligand or a mixture of LLCT and MLCT
transitions. Stokes shifts of 129–159 nm in toluene and 122–
166 nm in diethyl ether solution are intermediate between those of
[CuL2]+ (250–260 nm in CH2Cl2, L = dmp, dpp)31–37 and those ob-
served in neutral amidophosphine copper complexes (65–110 nm
in C6H6), for which LLCT transitions have been proposed.18
Substitution of a phenanthroline in cationic diphenanthroline
copper complexes [CuL2]+ (L = phen, dmp, dpp),22 which show
maxima of the longest wavelength absorption at lmax = 440–
460 nm (in CH2Cl2),31–37 with a diketiminate ligand thus led to
a significant bathochromic shift of approx. 200 nm. Although
reduction of complex symmetry from D2d to D2 is considered
to be responsible for the formation of shoulders around 540–
580 nm for bisphenanthroline copper complexes,41–43 reduction to
Conclusions
Heteroleptic diketiminate copper phenanthroline complexes can
be prepared readily through protonation of CuOtBu by dike-
timines in the presence of the desired phenanthroline ligand. The
complexes are stable and show no evidence of undergoing ligand
redistribution reactions. Intramolecular p-stacking interactions
between the N-benzyl substituents and the phenanthroline ligand
suppress complex flattening in the ground state and reduced
Stokes shifts in solution (compared to copper bisphenanthroline
complexes) are indicative of reduced distortions in the excited
states. Comparatively sharp luminescence peaks with full-width-
at-half-maximum (FWHM) values well below 100 nm (Fig. 6)
also support the notion that the investigated complexes do not
undergo extensive exited state distortions. For comparison, typical
FWHM values for [Cu(dmp2]+ complexes in solution range from
120–240 nm.29,32,34
Luminescence intensities, however, were low and lifetimes were
shorter than 60 ns for all complexes, which might be partly due
to the low energies of the emission (up to 830 nm). We are
currently investigating if luminescence properties can be improved
by shifting the emission to shorter wavelengths or by further
increasing p-stacking interactions between N-substituents and
phenanthroline.
C
2v symmetry does not seem to be the cause for the displacement of
the MLCT here. Related C2v-symmetric complexes (acac)Cu(dmp)
(acac = acetylacetonate or derivatives), for example, display
longest wavelength absorption maxima around 460 nm,44 very
comparable to those of cationic bisphenanthroline complexes.
Copper dmp complexes with neutral or anionic diphosphinesulfide
ligands also display absorption maxima between 420–460 nm,
which were again accompanied by shoulders at longer wavelengths
(500–550 nm).16 The bathochromic shift of the longest wavelength
transition is thus most likely due to the electron-donating na-
ture of the N-alkyl substituted diketiminate ligand. The high
electron-donor characteristics of b-diketiminate ligands have been
described previously.21,45–52 In particular for copper complexes,
p back-bonding to ancillary ligands is significantly increased in
the presence of N-alkyl substituted diketiminate ligands.12,53,54
A
hypsochromic shift in lmax of 60 nm when the isobutyl substituent
in 5b is replaced with pentafluorobenzyl (4b) further supports a
strong influence of the diketiminate ligand on the position of the
absorption maximum.
Complexes 1a–d and 2a do not display any correlation of flat-
tening or rocking distortions with lmax in their absorption spectra.
The difference in p-stacking interactions observed in the crystal
structures of 1b/c, 3b/c, and 4b and its correlation with Dqz make
it interesting to compare the presence of these interactions with
photophysical properties. Some qualitative indications argue that
p-stacking of the N-benzyl substituent and the phenanthroline
ligand might indeed increase luminescence intensity. Thus no
Experimental section
All operations, except ligand synthesis, were carried out under
nitrogen atmosphere using Schlenk or glove box techniques.
Solvents were dried by passage through activated aluminium
oxide (MBraun SPS) and de-oxygenated by repeated extraction
with nitrogen. C6D6 was distilled from Na and de-oxygenated
8764 | Dalton Trans., 2010, 39, 8759–8768
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©

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by three freeze-pump-thaw cycles. CuOtBu,55 dpp,56 monomesityl
phenanthroline,57 1,12,30 2,11,30 nacnaciBuH,30 nacnacBnCu(styrene),12
and nacnacCH(Me)PhCu(NCMe)11 were synthesized according liter-
ature procedures. Dmp was purchased as the hemihydrate and
dried by allowing a solution in dry toluene to stand overnight
˚
over activated molecular sieves (4 A), followed by decantation and
evaporation of the solvent. All other chemicals were obtained from
commercial suppliers and used as received. Elemental analyses
were performed by the Laboratoire d’Analyse Ele´mentaire (Uni-
versite´ de Montre´al). NMR spectra were recorded on a Bruker
ARX 400 MHz spectrometer and referenced to residual solvent
(C6D5H: d 7.15, C6D6: d 128.02, CHCl3: d 7.26, CDCl3: d 77.0).
NMR coupling constants are provided in Hz. UV/vis spectra
were recorded on a Cary 500i UV/vis/NIR spectrometer in dry
and oxygen-free diethyl ether or toluene using a sealable UV
cell. Emission and excitation spectra in solution were obtained
on a Cary Eclipse Fluorescence spectrometer. The luminescence
spectra of the solid state samples were measured using a Ren-
ishaw 3000 imaging microscope system equipped with a CCD
detector. The excitation source was the 514.5 nm line of an
Argon ion laser. All measurements were undertaken at ambient
temperature.
NacnacBnCu(phen), 1a
A flask was charged with 1 (100 mg, 0.36 mmol), CuOtBu
(44 mg, 0.33 mmol) and 1,10-phenanthroline (58 mg, 0.33 mmol).
Toluene (15 mL) was added and the mixture was stirred for
1 h to give a dark-blue suspension. The suspension was filtered
and the resulting dark blue solution was evaporated to dryness.
The residue was washed twice with hexane (6 mL). Residual
solvent was removed under vacuum to obtain dark-blue powder
1
(104 mg, 60%). H NMR (C6D6, 400 MHz, 298 K): d 8.84 (d,
J = 4 Hz, 2H, phen), 7.36 (d, J = 8, 2H, phen), 7.05 (s, 2H,
phen), 6.91 (d, J = 6, 4H, Bn), 6.85 (dd, J = 4, 8, 2H, phen),
=
6.73–6.76 (m, 6H, Bn), 4.83 (s, 1H, CH(C N)2), 4.53 (s, 4H,
13
=
Bn CH2), 2.16 (s, 6H, C( N)Me). C NMR (C6D6, 101 MHz,
=
298 K): d 162.5 (C N), 146.7, 144.1, 142.9, 131.4, 128.6, 128.3,
127.0, 125.8, 125.0, 124.0, 94.3 (CH(C N)2), 57.5 (Bn CH2), 22.4
(C( N)Me). Anal. Calcd for C31H29N4Cu: C, 71.45; H, 5.61; N,
10.75. Found: C, 70.80; H, 5.74; N, 10.43. X-Ray quality crystals
were obtained by slow evaporation of a diethyl ether solution
(20 mg, 1 mL).
=
=
NacnacBnCu(dmp), 1b
Preparation analogous to 1a from 1 (100 mg, 0.36 mmol), CuOtBu
(49 mg, 0.36 mmol), 2,9-dimethyl-1,10-phenanthroline (84 mg,
0.36 mmol) and ether (10 mL) gave a crude product, which was
recrystallised from diethyl ether (5 mL) at -30 ◦C. Dark-blue plates
formed after 1 day (72 mg, 35%). 1H NMR (C6D6, 400 MHz, 298
K): d 7.48 (d, J = 8 Hz, 2H, dmp 4/7), 7.18 (s, 2H, dmp 5/6),
6.94 (d, J = 8 Hz, 2H, dmp 3/8), 6.65 (d, J = 6 Hz, 4H, Bn),
=
6.36–6.37 (m, 6H, Bn), 4.78 (s, 1H, CH(C N)2), 4.38 (s, 4H, Bn
13
=
CH2), 2.79 (s, 6H, dmp Me), 2.16 (s, 6H, C( N)Me). C NMR
=
(C6D6, 101 MHz, 298 K): d 161.7 (C N), 155.5 (dmp 2/9), 143.5
(ipso Bn), 142.6 (dmp 10A/10B), 132.1 (dmp 4/7), 128.2 (meta
Bn), 126.8 (dmp 4A/6A), 126.7 (ortho Bn), 124.9 (para Bn), 124.7
=
(dmp 5/6), 124.2 (dmp 3/8), 94.0 (CH(C N)2), 57.8 (Bn CH2),
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=
25.7 (dmp Me), 22.4 (C( N)Me). Anal. Calcd for C33H33N4Cu: C,
71.45; H, 5.61; N, 10.75. Found: C, 70.80; H, 5.74; N, 10.43.
N,N¢-Bis(3,4,5-trimethoxyphenylmethyl)-2-amino-4-imino-pent-2-
ene, 3
Acetylacetone (0.4 mL, 4 mmol), p-toluenesulfonic acid monohy-
drate (0.7 g, 4 mmol) and 3,4,5-trimethoxybenzylamine (1.5 g, 7.6
mmol) were suspended in toluene (175 mL) and refluxed under
azeotropic removal of water (Dean–Stark apparatus). A white
suspension formed immediately, which turned yellow after 6 h
and finally became orange after 5 days. The reaction mixture was
cooled to room temperature and then transferred to a solution of
KOH (0.4 g in 150 mL H2O). The organic layer was separated and
the aqueous phase was extracted with 2 ¥ 100 mL of toluene. The
combined organic phases were dried over Na2SO4, filtered and
evaporated to give a yellow solid. Washing of the yellow solid with
MeOH (15 mL) afforded 900 mg (65%) of a white solid. 1H NMR
(CDCl3, 400 MHz, 298 K) d 6.50 (s, 4H, C6H2(OMe)3), 4.68 (s, 1H,
NacnacBnCu(dpp), 1c
Preparation analogous to 1a from 1 (100 mg, 0.36 mmol), CuOtBu
(49 mg, 0.36 mmol), 2,9-diphenyl-1,10-phenanthroline (128 mg,
0.36 mmol) and ether (10 mL) afforded a dark-blue solid (143 mg,
1
59%). H NMR (C6D6, 400 MHz, 298 K): d 8.68 (d, J = 8, 2H,
phen Ph), 7.22–7.65 (m, 16H), 6.45 (d, J = 4, 2H), 6.20–6.22 (m,
=
6H), 4.66 (s, 1H, CH(C N)2), 3.84 (s, 4H, Bn CH2), 1.91 (s, 6H,
13
=
=
C( N)Me). C NMR (C6D6, 101 MHz, 298 K): d 161.5 (C N),
142.9, 140.3, 133.0, 129.9, 129.1, 129.0, 128.6, 128.5, 128.4, 127.8,
=
127.5, 126.4, 124.6, 124.1, 94.0 (CH(C N)2), 56.8 (Bn CH2), 22.9
=
(C( N)Me). Anal. Calcd for C43H37N4Cu: C, 76.70; H, 5.54; N,
8.32. Found: C, 77.17; H, 5.44; N, 8.24. Crystals suitable for an
X-ray diffraction study were obtained by slow evaporation of a
diethyl ether solution (20 mg, 1 mL).
=
HC(C N)2), 4.43 (s, 4H, CH2Ar), 3.80 (s, 6H, p-C6H2(OMe)3),
3.68 (s, 6H, m-C6H2(OMe)3), 1.96 (s, 6H, Me(C N)2). 13C NMR
=
=
(CDCl3, 101 MHz): d 161.3 (C N), 153.1, 138.8, 136.3, 103.6 (o-
=
C6H2(OMe)3), 95.7 (HC(C N)2), 60.7 (p-C6H2(OMe)3), 55.7 (m-
C6H2(OMe)3), 50.8 (CH2Ar), 19.6 (Me(C N)2). Anal. Calcd. for
C25H34N2O6: C, 65.48; H, 7.47; N, 6.11. Found C, 65.20; H, 7.48;
N, 6.14. X-Ray quality crystals were obtained by slow evaporation
of a CH2Cl2 solution.
NacnacBnCu(monomesityl phenanthroline), 1d
=
Diketimine 1 (44 mg, 0.16 mmol) and CuOtBu (24 mg, 0.18 mmol)
were dissolved in toluene (2 mL) to afford a yellow solution. A
solution of 2-mesityl-1,10-phenanthroline (47 mg, 0.16 mmol)
in toluene (2 mL) was added drop-wise to give a dark-blue
suspension. After stirring for 1 h, the suspension was filtered and
the resulting dark blue–green solution was evaporated to dryness.
The crude product was dissolved in diethyl ether (3 mL) and kept
at -30 ◦C. Dark-blue crystals (20 mg, 20%) formed after 2 months.
1H NMR (C6D6, 400 MHz, 298 K): d 8.20 (d, J = 4, 1H), 7.64
(d, J = 8, 1H), 7.32 (d, J = 8, 1H), 7.28 (d, J = 8, 1H), 6.89–
7.19 (m, 12H), 6.59 (dd, J = 4, 8, 1H), 4.55 (d, J = 15, 2H, Bn
N,N¢-Bis(C6H2(OMe)3)-nacnacCu(dmp), 3b
Diketimine 3 (70 mg, 0.15 mmol) and 2,9-dimethyl-1,10-
phenanthroline (45 mg, 0.15 mmol) were dissolved in toluene (5
mL) to give a colourless solution. A solution of CuOtBu (26 mg,
0.15 mmol) in toluene 2 (mL) was added, affording a dark-green
solution, which was stirred for 1 h, filtered and evaporated to
1
dryness (109 mg, 98%). H NMR (C6D6, 400 MHz, 298 K): d
=
CH2), 4.27 (s, 1H, HC(C N)2), 3.93 (d, 2H, J = 15, Bn CH2),
7.54 (d, J = 8, 2H, dmp), 7.20 (s, 2H, dmp 5/6), 7.01 (d, J = 8,
=
2.36 (s, 3H, Mes p-CH3), 2.17 (s, 6H, Mes o-CH3), 1.86 (s, 6H,
2H, dmp), 5.88 (s, 4H, C6H2(OMe)3), 4.78 (s, 1H, CH(C N)2),
13
=
=
Me(C N)2). C NMR (C6D6, 101 MHz, 298 K): d 161.8 (C N),
158.8, 146.1, 145.0, 144.2, 142.3, 138.4, 137.3, 135.8, 129.9, 129.4,
128.6, 127.4 126.9, 126.8, 125.9, 125.8, 125.6, 125.4, 124.6, 105.4,
4.36 (s, 4H, NCH2), 3.54 (s, 6H, para OMe), 2.96 (s, 12H, meta
13
=
OMe), 2.85 (s, 6H, dmp Me), 2.23 (s, 6H, C( N)Me). C NMR
=
(C6D6, 101 MHz, 298 K): d 161.3 (C N), 155.3 (dmp 2/9), 152.7
(meta Ar), 142.4 (dmp 10A/10B), 139.1 (Ar), 136.6 (Ar), 132.4
=
94.3 (HC(C N)2), 57.1 (Bn CH2), 22.0 (Mes o-CH3), 21.3 (Mes
=
p-CH3), 20.6 (Me(C N)2). Anal. Calcd for C40H39N4Cu: C, 75.15;
(dmp 4/7), 126.8 (dmp 4A/6A), 125.0 (dmp), 124.3 (dmp), 105.6
=
H, 6.15; N, 8.76. Found: C, 74.82; H, 6.12; N, 8.67.
(ortho Ar), 93.9 (CH(C N)2), 60.1 (para OMe), 58.2 (NCH2), 55.0
=
(meta OMe), 25.8 (dmp Me), 22.5 (C( N)Me). Anal. Calcd for
SS-nacnacCH(Me)PhCu(phen), 2a
C39H45N4O6Cu: C, 64.22; H, 6.22; N, 7.68. Found: C, 64.22; H,
6.17; N, 7.56. X-ray quality crystals were obtained by layering a
toluene solution (20 mg, 1 mL) with an equal amount of hexane
and keeping the mixture at -30 ◦C for 3 days.
A flask was charged with SS-2 (100 mg, 330 mmol), CuOtBu
(45 mg, 0.33 mmol) and 1,10-phenanthroline (60 mg, 0.33 mmol).
Toluene (15 mL) was added and the mixture was stirred to give
a dark-blue solution. After stirring for 1 h, the solution was
concentrated to 1/5th of its volume and layered with hexane (3
N,N¢-Bis(C6H2(OMe)3)-nacnacCu(dpp), 3c
1
Preparation analogous to 3b afforded 118 mg (90%) of 3c,
mL). Dark-blue crystals (80 mg, 44%) formed after 3 days. H
which contained approximately 15% of dpp. Recrystallisation
from toluene–hexane at -30 C yielded crystalline material, still
contaminated however with dpp and elemental analyses were not
NMR (C6D6, 400 MHz, 298 K): d 8.70 (d, J = 4, 2H, phen),
7.36 (d, J = 8, 2H, phen), 7.03 (s, 1H, phen), 6.91 (d, J = 6,
4H, Ph), 6.85 (dd, J = 4, 8, 2H, phen), 6.55–6.57 (m, 6H, Ph),
◦
satisfactory. Hand picking of a suitable crystal allowed an X-ray
=
4.98 (q, J = 6, 2H, CH(Me)Ph), 4.73 (s, 1H, CH(C N)2), 2.17
1
13
diffraction study. H NMR (C6D6, 400 MHz, 298 K): d 8.86 (d,
=
(s, 6H, C( N)Me), 1.03 (d, J = 6, 6H, CH(Me)Ph). C NMR
J = 8, 2H, dpp), 7.29–7.75 (m, 12H, dpp), 7.28 (s, 2H, dpp),
=
(C6D6, 101 MHz, 298 K): d 161.5 (C N), 149.0, 147.5, 142.6,
132.0, 129.1, 127.3, 127.1, 126.1, 125.1, 124.2, 94.6 (CH(C N)2),
59.0 (CHMePh), 24.0 (C( N)Me), 23.2 (CHMePh). Anal. Calcd
=
5.71 (s, 4H, C6H2(OMe)3), 4.69 (s, 1H, CH(C N)2), 3.77 (s, 4H,
=
NCH2), 3.34 (s, 6H, para OMe), 2.89 (s, 12H, meta OMe), 2.85 (s,
=
13
=
6H, dmp Me), 1.98 (s, 6H, C( N)Me). C NMR (C6D6, 101 MHz,
for C33H33N4Cu: C, 72.17; H, 6.06; N, 10.20. Found: C, 71.75; H,
6.19; N, 10.24.
=
298 K): d 161.4 (C N), 154.2 (meta Ar), 152.3, 143.4, 139.9, 138.4,
8766 | Dalton Trans., 2010, 39, 8759–8768
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136.4, 133.5, 129.9, 128.6, 128.2, 127.9, 127.5, 126.0, 123.7, 119.8,
142.6 (dmp 10A/10B), 132.4 (dmp 4/7), 127.8 (dmp 4A/6A),
=
=
111.3 (o-C6H2(OMe)3), 93.9 (CH(C N)2), 60.0 (para OMe), 57.2
125.2 (dmp), 124.7(dmp), 93.8 (CH(C N)2), 61.7 (NCH2), 30.8
=
=
(NCH2), 54.9 (meta OMe), 23.0 (C( N)Me).
(CHMe2), 25.8 (dmp Me), 22.9 (C( N)Me), 20.6 (CHMe2). Anal.
Calcd for C27H37N4Cu: C, 67.40; H, 7.75; N, 11.64. Found: C,
67.70; H, 7.96; N, 11.32.
N,N¢-Bis(pentafluorophenylmethyl)-2-amino-4-imino-pent-2-ene,
4
X-Ray diffraction studies
To a flask containing pentafluorobenzylamine (310 mg, 1.6 mmol)
in toluene (5 mL) were added acetylacetone (80 mL, 0.8 mmol)
and HCl (196 mL, 12 M, 2.4 mmol) to give white precipitate. The
mixture was refluxed under azeotropic removal of water for 5 days
during which the reaction mixture turned yellow. By cooling to
room temperature, yellow precipitate formed. The solvent was
decanted and KOH solution (1.5 g in 5 mL of water) was added
to the solid, followed by toluene (5 mL). After stirring for 15 min,
the mixture was separated and the aqueous phase was extracted
with toluene (5 mL). The combined organic phases were dried
over Na2SO4, filtered and evaporated to afford 40 mg (6%) of
a beige solid in 85–90% purity. 1H NMR (CDCl3, 400 MHz,
All data sets were recorded on a Bruker SMART 6000 with
Montel 200 monochromator, except that of compound 1b which
was collected on a Bruker Microstar-Proteum with Helios optics,
both equipped with a rotating anode source for Cu-Ka radiation
(l = 1.54178 nm). Cell refinement and data reduction were
performed using APEX2.58 Absorption corrections were applied
using SADABS.59 Structures were solved by direct methods using
SHELXS97 and refined on F2 by full-matrix least squares using
SHELXL97.60 All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were refined on calculated positions using
a riding model. Additional details are provided in Table 4.
=
298 K) d 11.08 (bs, 1H, NH), 4.58 (s, 1H, HC(C N)2), 4.44 (s,
4H, CH2C6F5), 1.98 (s, 6H, Me(C N)2). 13CNMR (CDCl3, 101
=
Acknowledgements
1
=
MHz): d 161.2 (C N), 145.1 (dm, JCF = 250, ortho), 140.5 (dm,
1JCF = 250), 137.5 (dm, 1JCF = 250), 113.7 (t, 2JCF = 2, ipso), 95.9
We thank Prof. Garry Hanan for access to his spectrometers, and
Mr Daniel Chartrand and Ms Vale´rie Baslon for assistance with
UV/vis spectroscopy.
=
=
(HC(C N)2), 37.9 (CH2C6F5), 19.3 (Me(C N)2). Three aromatic
peaks are missing. 19F NMR (CDCl3, 377 MHz, 298 K) d -144.9
(dd, J = 9, 22), -156.5 (t, J = 22), -162.9 (td, J = 9, 22). Anal.
Calcd for C19H12N2F10: C, 49.79; H, 2.64; N, 6.11. Found: C, 50.58;
H, 2.76; N, 6.13. MS ESI-HRMS (hexane) (m/z): [M+H]+ for
C19H12N2F10 calcd. 459.0919; found 459.0915.
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◦
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7.22 (s, 2H, dmp 5/6), 7.04 (d, J = 8, 2H, dmp), 4.73 (s, 1H,
=
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19
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=
6H, C( N)Me). F NMR (C6D6, 377 MHz, 298 K) d -144.6 (dd,
J = 9, 22), -160.5 (t, J = 22), -165.7 (td, J = 9, 22). 13C NMR
=
(C6D6, 101 MHz, 298 K): d 162.7 (C N), 156.5 (dmp 2/9), 145.0
1
(dm, JCF = 240, ortho C6F5), 141.2 (dmp 10A/10B), 140.4 (dm,
1JCF = 180, para C6F5), 135.9 (dm, 1JCF = 240, meta C6F5), 133.6
(dmp 4/7), 126.3 (dmp 4A/6A), 125.2 (dmp), 124.4 (dmp), 116.0
(t, 2JCF = 2, ipso C6F5), 94.5 (CH(C N)2), 43.7 (CH2), 25.4 (dmp
=
=
Me), 22.8 (C( N)Me). Anal. Calcd for C33H23N4F10Cu: C, 54.36;
H, 3.18; N, 7.68. Found: C, 54.73; H, 3.53; N, 7.65.
NacnaciBuCu(dmp), 5b
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7244–7246.
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and 2,9-dimethyl-1,10-phenanthroline (66 mg, 0.29 mmol) were
dissolved in diethyl ether (4 mL) to give a dark-green solution.
After stirring for 10 min, the solvent was evaporated and the
residue was washed with hexane (2 ¥ 2 mL) and dried under
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phenanthroline.
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24 In contrast to other solvents, an apparently reversible colour change to
brown is observed in dichloromethane, which was not investigated in
detail.
1
vacuum to yield 109 mg (84%) of a dark-blue solid. H NMR
(C6D6, 400 MHz, 298 K): d 7.55 (d, J = 8, 2H, dmp), 7.17 (s, 2H,
=
dmp 5/6), 7.07 (d, J = 8, 2H, dmp), 4.67 (s, 1H, CH(C N)2), 3.12
=
(m, 4H, NCH2) 3.08 (s, 6H, dmp Me), 2.16 (s, 6H, C( N)Me),
1.24 (sp, J = 7, 2H, CHMe2), 0.58 (d, J = 7, 12H, CHMe2). 13
C
25 Based on the structures of 34 nacnacCu(I) and 144 tetracoordinated
=
NMR (C6D6, 101 MHz, 298 K): d 161.1 (C N), 155.8 (dmp 2/9),
Cu(I) phenanthroline complexes in the Cambridge Structural Database.
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Dalton Trans., 2010, 39, 8759–8768 | 8767
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