Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a Promising Class of Electroneutral, Amidinate-Type Ligands

Article abstract of DOI:10.1021/acs.inorgchem.5b02141

The first complexes containing imidazolium-2-amidinates as ligands (betaine-type adducts of imidazolium-based carbenes and carbodiimides, NHC-CDI) are reported. Interaction of the sterically hindered betaines ICyCDI^DiPP and IMeCDI^DiPP [both bearing 2,6-diisopropylphenyl (DiPP) substituents on the terminal N atoms] with Cu(I) acetate affords mononuclear, electroneutral complexes 1a and 1b, which contain NHC-CDI and acetate ligands terminally bound to linear Cu(I) centers. In contrast, the less encumbered ligand ICyCDI^p-Tol, with p-tolyl substituents on the nitrogen donor atoms, affords a dicationic trigonal paddlewheel complex, [Cu₂(μ-ICyCDI^p-Tol)₃]²⁺[OAc^-]₂ (2-OAc). The nuclear magnetic resonance (NMR) resonances of this compound are broad and indicate that in solution the acetate anion and the betaine ligands compete for binding the Cu atom. Replacing the external acetate with the less coordinating tetraphenylborate anion provides the corresponding derivative 2-BPh₄ that, in contrast with 2-OAc, gives rise to sharp and well-defined NMR spectra. The short Cu-Cu distance in the binuclear dication [Cu₂(μ-ICyCDI^p-Tol)₃]²⁺ observed in the X-ray structures of 2-BPh₄ and 2-OAc, ca. 2.42 ?, points to a relatively strong "cuprophilic" interaction. Attempts to force the bridging coordination mode of IMeCDI^DiPP displacing the acetate anion with BPh₄^- led to the isolation of the cationic mononuclear derivative [Cu(IMeCDI^DiPP)₂]⁺[BPh₄]^- (3b) that contains two terminally bound betaine ligands. Compound 3b readily decomposes upon being heated, cleanly affording the bis-carbene complex [Cu(IMe)₂]⁺[BPh₄^-] (4) and releasing the corresponding carbodiimide (C(=N-DiPP)₂).

Full text of DOI:10.1021/acs.inorgchem.5b02141

Article
pubs.acs.org/IC
Copper(I) Complexes of Zwitterionic Imidazolium-2-Amidinates, a
Promising Class of Electroneutral, Amidinate-Type Ligands
́ ́
Astrid Marquez, Elena Avila, Carmen Urbaneja, Eleuterio Alvarez, Pilar Palma, and Juan Campora*
́ ́
́
Instituto de Investigaciones Químicas, CSIC-Universidad de Sevilla, C/Americo Vespucio, 49, 41092 Sevilla, Spain
*
S Supporting Information
ABSTRACT: The first complexes containing imidazolium-2-
amidinates as ligands (betaine-type adducts of imidazolium-
based carbenes and carbodiimides, NHC-CDI) are reported.
DiPP
Interaction of the sterically hindered betaines ICyCDI
IMeCDI
and
DiPP
[both bearing 2,6-diisopropylphenyl (DiPP)
substituents on the terminal N atoms] with Cu(I) acetate
affords mononuclear, electroneutral complexes 1a and 1b,
which contain NHC-CDI and acetate ligands terminally bound
to linear Cu(I) centers. In contrast, the less encumbered ligand
p‑Tol
ICyCDI , with p-tolyl substituents on the nitrogen donor
atoms, affords a dicationic trigonal paddlewheel complex,
p‑Tol
2+
−
[
Cu (μ-ICyCDI ) ] [OAc ] (2-OAc). The nuclear mag-
2 3 2
netic resonance (NMR) resonances of this compound are broad and indicate that in solution the acetate anion and the betaine
ligands compete for binding the Cu atom. Replacing the external acetate with the less coordinating tetraphenylborate anion
provides the corresponding derivative 2-BPh that, in contrast with 2-OAc, gives rise to sharp and well-defined NMR spectra.
4
p‑Tol
2+
The short Cu−Cu distance in the binuclear dication [Cu (μ-ICyCDI ) ] observed in the X-ray structures of 2-BPh and 2-
OAc, ca. 2.42 Å, points to a relatively strong “cuprophilic” interaction. Attempts to force the bridging coordination mode of
displacing the acetate anion with BPh led to the isolation of the cationic mononuclear derivative
Cu(IMeCDI ) ] [BPh ] (3b) that contains two terminally bound betaine ligands. Compound 3b readily decomposes
2
3
4
DiPP
−
IMeCDI
[
4
DiPP
+
−
2
4
+
−
upon being heated, cleanly affording the bis-carbene complex [Cu(IMe) ] [BPh ] (4) and releasing the corresponding
2
4
carbodiimide (C(N-DiPP)2).
INTRODUCTION
■
Amidinates make up an important class of ligands, characterized
by the proximity of two potentially binding and electronically
conjugated nitrogen atoms. They can be seen as the nitrogen
1
analogues of carboxylates; accordingly, they have in common
with these many aspects of their rich coordination chemistry.
For example, carboxylates and amidinates usually coordinate in
the monodentate (A), bidentate (B), or bridge (C) modes,
shown in the top part of Figure 1. In the bridging coordination
mode, they give rise to a series of appealing multibridged
binuclear “paddlewheel” complexes (D and E, Figure 1,
1
,2
down). These types of compounds are also formed by
1
,3
related ligands bearing vicinal N donors, such as guanidinates.
A significant difference between carboxylates and their
nitrogen analogues is the presence of additional organic
substituents (R′) on the terminal N donor atoms of the latter,
which allow for a more precise tuning of steric and electronic
properties. This has prompted the intensive application of
amidinates and guanidinates in homogeneous catalysis,
Figure 1. (A−C) Main coordination modes of amidinate (R = H,
alkyl, or aryl) or guanidinate (R = NR ) ligands. (D and E) Tetragonal
2
and trigonal paddlewheel complexes (R′ omitted for the sake of
clarity).
4
particularly in olefin polymerization, and spurred the develop-
ment of their coordination chemistry. The design of new
catalyst architectures based on amidinate ligands has often been
guided by analogies. Thus, when considering early transition or
f-block elements, amidinates are regarded as “steric equivalents”
Received: September 16, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b02141
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1
a,5
of the ubiquitous cyclopentadienyl ligands.
Although this
through the steric and electronic properties of their
substituents. Surprisingly enough, no complexes of carbene-
carbodiimide betaines with either transition or main group
metals appear to have ever been described. As a preliminary
step before pursuing the development of transition metal-based
catalysts for olefin polymerization based on NHC-CDI adducts,
or other catalytic reactions, we decided to explore their
coordination to a diamagnetic Cu(I) center. Herein, we report
the results of this study.
concept loses usefulness upon moving to catalysts based on late
transition elements, whose design is often inspired by the
highly successful Ni and Pd α-diimine complexes, analogy
reasoning remains useful because both α-diimine and amidinate
chelates are built on trigonal sp nitrogen centers that can be
similarly substituted with bulky organic groups, such as 2,6-
dialkylaryls. The main difference between the α-diimine and
amidinate families of ligands is the electric charge, which results
in very different chemistries. In this context, we decided that
the analogy between α-diimines and amidinates could be
strengthened if the latter ligands could be modified somehow to
render them electrically neutral. Seeking examples of neutral
5
,6
2
RESULTS AND DISCUSSION
■
As shown in Scheme 1, this work focuses on three NHC-CDI
adducts that are combinations of imidazolium-based hetero-
2
ligands bearing two sp nitrogen donor centers adjacent to a
single carbon atom, we realized that very few molecules that
fulfill such requirements exist. A rather unique example of such
ligands would be 1,8-naphtyridines, naphthalene derivatives in
which the vicinal CH groups at positions 1 and 8 are replaced
by N atoms. The coordination chemistry of these ligands has
Scheme 1
7
been extensively developed, but without the possibility of
attaching additional organic substituents to the nitrogen atoms,
their coordination chemistry is peculiar and usually quite
different from that of α-diimines.
In our search for new types of ligands that could match our
concept of “neutral amidinates”, we considered the possibility
of building betaine-type zwitterions in which a positively
charged fragment would counterbalance the negative charge of
the amidinate donor group. While developing this idea, we
came across betaine adducts of heterocyclic carbenes (NHC)
cyclic carbenes (NHCs) containing either cyclohexyl (ICy) or
methyl (IMe) substituents at the nitrogen atoms with di-p-tolyl
p‑Tol
DiPP
or di-2,6-diisopropylphenylcarbodiimide (CDI
or CDI
,
8
with carbodiimides (CDI). By analogy with the well-known
respectively). The heterocyclic carbenes were generated in a
THF solution by deprotonation of the corresponding
imidazolium salts with KOtBu and then reacted in situ with
the suitable carbodiimide. It must be mentioned that, in
contrast with the thermally robust ICy carbene, IMe is relatively
unstable, and to obtain satisfactory results, its solution should
not be allowed to warm to room temperature, until it is reacted
with the carbodiimide. The corresponding NHC-CDI adducts
were easily isolated in high yields as yellow solids, stable in the
open atmosphere (although in the long term they are best
stored under nitrogen), very soluble in CH Cl , and only
9
NHC-CO adducts, or imidazolium-2-carboxylates, NHC-CDI
2
adducts could be termed “imidazolium-2-amidinates” (Figure
iPr
2
). The first example of such a compound was Me IMeCDI ,
2
2
2
Figure 2. Imidazolium-2-carboxylate (NHC-CO , left) and imidazo-
lium-2-amidinate (NHC-CDI, right).
slightly soluble in toluene or hydrocarbon solvents. Surpris-
ingly, their solubility in THF is only moderate. The yellow
color of these compounds is due to the lowest-frequency
absorption of a series of overlapping intense UV bands, which
2
prepared in 1999 by Kuhn and co-workers by addition of the
imidazole-based carbene 1,2,3,4-tetramethylimidazol-2-ylidene
occurs at ∼350 nm and tails into the visible zone. The fact that
iPr 10
iPr
(
Me IMe) to diisopropylcarbodiimide (CDI ). They
the alkyl-substituted betaine adduct Me IMeCDI reported by
2
2
1
0
reported the crystal structure and some chemical properties
of this compound, which confirm that this has a true dipolar
Kuhn is colorless indicates that the color-responsible
transition involves the π-orbitals of the aryl rings bound to
the amidinate N atoms. A TD-DFT calculation (see the
Supporting Information) shows that the lowest-energy band
corresponds to an electronic transition from the HOMO, a π-
orbital centered mainly on the anionic amidinate group, to the
LUMO, which pertains mainly to the cationic heterocyclic
fragment. The energy of this transition is lowered because the
HOMO is destabilized by a nonbonding interaction with filled
π-orbitals of the aryl substituents. The color-responsible
absorption is most intense in the bright yellow derivative
̈
structure. As such, it exhibits a strong Bronsted basicity on the
terminal “amidinate” nitrogen atoms. Very recently, Johnson
Ar
and co-workers reported that similar betaines, SIArCDI , are
spontaneously formed in the thermal decomposition of 2,3-
diarylimidazolidin-2-ylidenes (SIAr). They also prepared a
series of new NHC-CDI adducts starting from carbodiimides
11
by Kuhn’s method. Simultaneously, we showed that the
p‑Tol
adduct ICyCDI
acts as a stabilizing ligand for Ru
nanoparticles, allowing control over their size and selectivity
12
p‑Tol
DiPP
DiPP
in styrene hydrogenation. We believe that these betaines bind
adjacent metal centers on the surface of the nanoparticles
ICyCDI , but neither this, ICyCDI , nor IMeCDI
exhibits fluorescence, as reported by Johnson for betaines
11
(
coordination type C in Figure 1). Furthermore, we expected
carrying aryl substituents in all four nitrogen atoms. The IR
spectra of our three betaines display a medium-intensity band at
that, analogously to amidinate ligands, NHC-CDI betaines
could also coordinate in the terminal (A) or bidentate (B)
modes, and that their binding preferences could be controlled
−
1
∼1600 cm and a complex superposition of intense bands in
the 1550−1510 cm− region. DFT analysis of a simplified
1
B
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molecular model suggests that the former absorption
corresponds to the asymmetric NCN stretch of the terminal
Table 1. Selected Bond Distances (angstroms) and Angles
(degrees) for NHC-CDI Adducts
a
“amidinate” fragment, and the latter arise from a combination
ICy-CDIDiPP
Distances
IMe-CDIDiPP
ICy-CDIp‑Tol
of CN stretches (from the amidinate and the imidazolium
units) and C−H flexion modes.
CCDI−NC
CCDI−Nt
1.315(3)
1.313(3)
1.502(3)
1.349(3)
1.339(4)
1.312(5)
1.319(5)
1.505(6)
1.347(5)
1.340(5)
1.3302(16)
1.3202(16)
1.5044(18)
1.3415(16)
1.3448(17)
The solution NMR spectra of the betaines are relatively
simple, for both imidazolium (R) or amidinate (Ar) substituent
groups are chemically equivalent, each of them giving rise to
CCDI−Cimz
DiPP
Cimz−N1imz
Cimz−N2im
single set of signals. For ICyCDI , the signals of the
diastereotopic Me groups of the DiPP unit (DiPP = 2,6-
1
13
1
Angles
diisopropylphenyl) are well-resolved in the H and C{ H}
N −CCDI−N
126.5(2)
107.5(2)
54.6
127.5(4)
106.7(4)
50.2
130.12(12)
107.52(11)
54.9
NMR spectra at room temperature. In contrast, the DiPP
t
c
DiPP
N1imz−C −N2imz
methyls of the less bulky derivative IMeCDI
give rise to a
imz
b
1
13
CDI∠imz
single resonance in the H spectrum, and to two broad
C
DiPP
a
NMR resonances. This indicates that for ICyCDI , rotation
of the DiPP groups is locked on the NMR time scale, whereas
For ORTEP views and full numbering schemes, see the Supporting
b
Information. Torsion angles between the mean planes defined by
atoms N , N , CCDI, and C
DiPP
and N1imz, N2imz, Cimz, and CCDI
.
they undergo restricted rotation for IMeCDI . Because of
c
t
imz
the symmetrical substitution pattern of the CDI-NHC adducts,
their NMR spectra provide no indication as to whether the
imidazolyl ring and amidinate moieties rotate one with regard
to the other; therefore, they give no direct evidence of the
existence of some π-delocalization over the central C−C bond
that connects them. Charge separation has seemingly little
influence in the position of the C NMR resonances of the
corresponding quaternary carbon atoms of the imidazole ring
and the amidinate fragment, as they appear in very close
positions, between 145 and 150 ppm.
the C−N bonds is labile, and they rapidly exchange their
configuration in solution.
The main metric parameters in the three compounds are
almost identical to those of the previously reported NHC-CDI
10,11
betaines.
the amidinate C−N bond lengths are within a narrow range,
.31−1.33 Å, and those of the imidazolyl fragments are only
In a manner independent of their configuration,
1
3
1
slightly longer, 1.34−1.35 Å. These distances can be regarded as
typical for delocalized, partially double bonds. Conversely, the
C−C bonds between both moieties, close to 1.505 Å, are
consistent with pure σ-character. The imidazolium rings are
always rotated by nearly 60° with regard to the corresponding
amidinate fragment. Curiously, the amidinate N −C−N angles
The crystal structures of the three NHC-CDI adducts have
been determined. As they are very similar, only the ORTEP
DiPP
view of ICyCDI
with an indication of key atoms is shown in
DiPP
p‑Tol
Figure 3. Plots of IMeCDI
and ICyCDI
can be found in
t
c
DiPP
are somewhat narrower in ICyCDI
(126.5°) and
(130.1°), in spite
DiPP
p‑Tol
IMeCDI
(127.5°) than in IMeCDI
of the considerable steric bulk of the DiPP substituent.
To investigate the coordination chemistry of the NHC-CDI
adducts, we chose to study their interaction with Cu(I) acetate.
In addition to the known ability of Cu(I) to bind many
different types of ligands and its diamagnetic character, we
selected this starting material because the potentially bridging
acetate ligand might be complementary to the electroneutral
NHC-CDI unit, giving rise to multinuclear assemblies
simultaneously bridged by both ligands, as observed in a
13
number of acetate-amidinate complexes. Copper(I) acetate
forms itself infinite planar chains composed of Cu (μ-OAc)
2
2
dimers enchained through secondary bridging Cu···O inter-
Figure 3. ORTEP view (50% probability ellipsoids) of ICyCDIDiPP
.
14
actions. However, we never observed simultaneous acetate/
betaine coordination in our complexes. Scheme 2 summarizes
the reactivity of Cu(I) acetate with these betaine-type ligands.
1
the Supporting Information (Figures S2 and S3), and selected
bond distances and angles for the three compounds are listed in
Table 1. The three structures show identical conformations.
The C−N bonds of the amidinate moiety adopt different
configurations, one cisoid and the other transoid with regard to
The different products were fully characterized by NMR ( H,
13
C, and a range of binuclear homo- and heterocorrelation
spectra) IR, UV−vis, and elemental analysis, and their X-ray
structures were determined in all cases.
The interaction of Cu(I) acetate with equimolar amounts of
DiPP
DiPP
the imidazolyl and aryl groups. This is the same observed by
ICyCDI
and IMeCDI
leads to the formation of pale
iPr 10
Kuhn for Me IMeCDI , but different from that of Johnson’s
yellow-green 1:1 (CuOAc)(L) complexes, 1a and 1b,
respectively. Their crystal structures are shown in Figure 4,
and selected bond lengths and angles are listed in Table 2. Both
structures show a single Cu atom with terminally coordinated
NHC-CDI and acetate ligands in a linear arrangement. In these
compounds, the betaine ligands have the same configuration
observed in the crystal structures of the free ligands. The
copper atom coordinates the amidinate nitrogen atom of the
2
betaines (recall that these bear bulky aryl rings both in the
heterocycle and in the amidinate N atoms), in which both
nitrogen substituents are trans with regard to the imidazole
1
1
ring. As mentioned before, solution NMR spectra show a
single set of signals for the aryl substituents of the amidinate
fragment, but in the solid state, the preferred cis−trans
configuration of the amidine renders the aryl substituents
chemically nonequivalent. This indicates that the geometry of
“transoid” CN bond (N ), leaving free the one in the
t
C
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Scheme 2
Figure 4. ORTEP view (50% probability ellipsoids) of compounds 1a (left) and 1b (right). For a list of selected bond distances and angles, see
Table 2.
“
cisoid”-configured bond (N ). The mean planes defined by the
contrast, those of the acetate are very broad and hardly
identifiable (in particular in the 13C{ H} spectrum), presum-
ably because in both 1a and 1b this ligand undergoes
intermolecular exchange. The room-temperature NMR spectra
c
1
imidazole and the amidinate groups are rotated by similar
amounts in the complexes and in the free ligands, ∼60°. The
coordinated trans C−N amidinate bond is significantly longer
(
∼1.35 Å) than the free cis C−N bond (∼1.29 Å). A similar
of 1a and 1b in CD Cl2 suggest that the monodentate
2
difference is noted between the coordinated and free C−O
bonds of the monohapto acetate ligand. This effect can be
attributed to the localization of the π-bonding upon
coordination to the metal center.
The NMR signals of the betaine ligands are easily recognized
and have been precisely assigned with the aid of a full range of
two-dimensional (2D) homocorrelation (COSY and NOESY)
and heterocorrelation (HSQC and HMBC) spectra. In
coordination of the amidinate ligands is maintained in solution,
1
at least in noncoordinating solvents (the H spectrum of 1a is
shown in Figure S7). This is readily deduced from the fact that
they display single sets of signals for the imidazolium H and R
substituents (R = Cy and Me in 1a and 1b, respectively), but
two sets of signals for the aryl substituents of the amidinate,
indicating that these become nonequivalent. For both 1a and
1b, the signals of one of the DiPP groups appear to be perfectly
D
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Table 2. Selected Bond Distances (angstroms) and Angles
map, although on the basis of its diamagnetic character and its
(
degrees) for Compounds 1a, 1b, and 3b
elemental analysis, the formula of 2·OAc must be [Cu (μ-
2
p‑Tol
2+
−
ICyCDI ) ] [AcO ] . Likely, a disorder problem prevented
3
2
1
a
1b
3b
the location of the missing acetate anion. Accordingly, the same
Distances
1.870(2)
p‑Tol
compound was obtained when the reaction of ICyCDI
and
Cu−Nt
1.8498(11)
1.8460(11)
1.2596(17)
1.3390(16)
1.4493(18)
1.3363(19)
1.3470(16)
1.2555(17)
1.2077(18)
1.855(2)
CuOAc was conducted in the correct 3:2 stoichiometric ratio.
Complex 2-OAc appears to be the only species formed in this
system, regardless of whether the reagent ratio was 3:2 or 1:1.
The spontaneous assembly of this binuclear structure provides
Cu−O2Ac
1.843(2)
a
CCDI−Nc
CCDI−Nt
1.286(3)
1.292(4)
1.348(4)
1.503(4)
1.334(4)
1.340(4)
1.354(3)
CCDI−Cimz
Cimz−N1imz
Cimz−N2im
O2Ac−CAc
O1Ac−CAc
1.503(3)
p‑Tol
some support to our previous suggestion that ICyCDI
1.347(3)
stabilizes small Ru nanoparticles by bridging adjacent metal
1.344(3)
12
atoms on their surface.
1.277(4)
To definitively clarify the identity of 2-OAc, we decided to
1.228(4)
exchange the acetate anions with NaBPh . Thus, mixing
4
Angles
p‑Tol
ICyCDI , CuOAc, and NaBPh in a 3:2:2 ratio in CH Cl
4
2
2
N −Cu−(O or N ′)
N −CCDI−Nt
c
178.97(10)
122.9(2)
171.24(5)
175.67(11)
123.1(3)
107.1(3)
t
t
containing a small amount of THF to improve the solubility of
the reagents afforded the corresponding ionic complex 2·BPh4,
which was isolated as brick-red crystals in excellent yield. The
123.11(12)
N1imz−Cimz−N2imz
107.3(2)
107.16(11)
b
Angles between Planes
61.2
p‑Tol
2+
presence of the [Cu (μ-ICyCDI ) ] dication was con-
2
3
CDI∠imz
63.9
60.6
24.8
firmed by ESI-MS. When the spectrum of 2·BPh was recorded
4
CDI∠L (L = OAc or CDI′)
71.4
61.3
from a CH Cl solution, the main species observed in the gas
2
2
a
DiPP
b
Averaged values from both IMeCDI
ligands. Angle between
p‑Tol
+
phase was a monocation of composition [Cu(ICyCDI ) ]
2
mean planes containing amidinate CCN or acetate CCO atoms
2
2
(
m/z 971.6); however, a weak signal for the dication [Cu (μ-
2
(
CDI or OAc, respectively), or the imidazolium ring (imz).
p‑Tol
2+
ICyCDI ) ] was also observed at the expected m/z of 744
3
with the correct isotope distribution and a spacing of half mass
units between consecutive isotope peaks. The dication is
probably destabilized in the gas phase because of the
intramolecular Coulombic repulsions, but optimal conditions
for its observation were developed using different solvents. Best
conditions for the observation of this signal were found using
relatively noncoordinating dichloromethane or anisole as the
solvent.
sharp, but those of the other are very broad, particularly in the
H spectra, which shows the diastereotopic iPr methyl signals
1
close to the coalescence (1a) or already forming a single broad
hump (1b). This selective line broadening indicates that the
DiPP group responsible for the broad signals is undergoing
restricted rotation on the NMR time scale, whereas the other is
fixed in its position, presumably because of the steric bulk of the
coordinated Cu(OAc) fragment. Monodimensional spectra
provide no evidence of any further dynamic effects, but
phase-sensitive 2D NOESY/EXSY for both 1a and 1b clearly
shows exchange cross-peaks linking the signals of the two types
of DiPP groups, implying that the Cu(OAc) fragment is
actually jumping from one amidinate nitrogen atom to the
other. In the case of 1a, this movement must involve
simultaneous cis/trans isomerization of the C−N bonds
because the exchange of the Cu atom does not lead to the
appearance of any isomeric forms of the complex. However,
Two types of crystals of 2·BPh were grown using different
4
methods. Cooling a saturated solution in a dichloromethane/
toluene mixture in the freezer (−20 °C) afforded solvent-free
crystals, whereas layering a dichloromethane solution with
toluene at room temperature produced a mixed solvate
containing three molecules of toluene and five dichloro-
methanes per unit cell. The structural data from both structures
are fully consistent (for details, see Figure S5 and Table S2),
but the latter produced a slightly better quality X-ray structure;
therefore, the discussion will be referred to this data set. An
1
13
1
both the H and the C{ H} spectra of 1b show the presence
of a minor species that is invariably in ∼1:6 intensity ratio with
regard to the main complex. This is presumably a geometric
isomer resulting from the migration of the Cu atom to the
nitrogen atom of the cisoid C−N bond. The observation of two
independent DiPP sets also in this minor isomer is consistent
with this assignment, as it indicates that the increased level of
steric crowding hinders the rotation of not just one but both
DiPP rings.
ORTEP view of the binuclear dication in 2·BPh is shown in
4
Figure 5. This is essentially the same found in 2·OAc, with
minimal differences of no chemical significance. As mentioned
before, three betaine units act as bridging ligands between both
Cu centers. The lengths of Cu−N bonds involving the ligand
termed “C” are nominally longer than those of ligands “A” and
“B”. The difference, although statistically significant, is very
minor and is not observed in the solvent-free structure of 2·
BPh or in the cationic fragment of 2·OAc; therefore, it can be
4
In contrast with the well-defined and informative NMR
safely neglected. However, the lengths of Cu−N bonds in the
spectra of compounds 1a and 1b, those of the orange product
binuclear dication (average of 2.00 Å in 2·BPh ) are
4
p‑Tol
2
·OAc, isolated from the reaction of CuOAc with ICyCDI 1
,
significantly longer than those in complexes with monodentate
show very broad lines at room temperature. However, the H
spectrum shows two readily recognizable signals in a 3:1
intensity ratio, one at δ 2.23 for the tolyl p-Me group and the
other at δ 4.39 for the 1-CH of the Cy groups, which suggest a
symmetrical structure. The X-ray structure of this compound
betaine ligands (1a, 1.869 Å; 1b, 1.850 Å). Both CuN units are
3
very nearly flat, each Cu atom coming outside of the plane
defined by the three nitrogen atoms by only 0.07 Å. The
average dihedral angles formed by each bridging betaine ligand
and the copper atoms are small (average N−Cu−Cu−N angle
(
see Figure S4) reveals a trigonal paddlewheel Cu complex,
of 8.5°); therefore, the CuN units are close to an eclipsed
3
p‑Tol
[
Cu (ICyCDI )3], containing two Cu atoms bridged by
configuration. The Cu···Cu distance, 2.4213(4) Å, is rather
2
1
0
10
betaine ligands, and free-standing acetate anions. Only one
short and clearly points to a closed shell (d −d ) or
15
acetate per Cu unit could be located in the electron density
“cuprophilic” interaction. Interestingly, this distance is shorter
2
E
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Figure 6. H NMR spectra (CD Cl , 400 MHz, 298 K) of complexes
2
2
p‑Tol
2
·BPh and 2·OAc and the ligand ICy·CDI . The solvent residual
peak is marked with an asterisk.
4
Figure 5. ORTEP view (50% probability ellipsoids) of the cationic
fragment of 2·BPh . For the sake of clarity, only the atoms located in
4
competition with the acetate anion for binding the Cu(I)
center. Acetate does not displace the betaine fully, as the signals
of the free ligand are not observed in the NMR spectra of 2·
the Cu N core are represented as ellipsoids, and those in the Cy and
2
6
p-tolyl groups are dimmed. Selected bond distances (angstroms) and
angles (degrees): Cu1−Cu2, 2.4213(4); Cu1−N , 1.965(2); Cu1−
1A
1
OAc, either at room temperature or below it. A VT-NMR H
N , 1.975(2); Cu1−N , 2.066(2); Cu2−N , 1.976(2); Cu2−N ,
1B
1C
2A
2B
study of 2·OAc conducted between room temperature and −80
°C showed that this compound exists in solution as a mixture of
species, but static spectra were not observed even at the lowest
temperature. Below −10 °C, the spectrum resolves partially,
showing at least three sets of signals, each of them showing a
characteristic cyclohexyl methyne resonance. One of these Cy
1−CH signals appears at δ 3.61; hence, it probably corresponds
1
.970(2); Cu2−N , 2.070(2); C −C (ave.), 1.505(2); N −
2C
CDI
imz
1A
Cu1−N , 115.17(9); N −Cu1−N , 108.38(9); N −Cu1−N ,
1B
1B
1C
1C
1A
1
5
36.10(10); N −Cu1−Cu2−N , 9.53(9); N −Cu1−Cu2−N ,
1
A
2A
1B
2B
.91(9); N −Cu1−Cu2−N , 10.16(9). The angle between imida-
1B
2B
zolyl and amidinate mean planes (ave.) is 58.15°.
2
+
than those in related [Cu (μ-L )] complexes bridged by
2
n
p‑Tol
2+
comparable electroneutral ligands such as the closely related N
to the [Cu (μ-ICyCDI ) ] dication, while the higher field
2
2 3
16
donor 1,8-naphtyridyne (2.534 Å) or bridging diphosphino-
shifts of the other (δ 4.15 and 4.36, respectively) suggest that
they arise from terminally bound betaine ligands. The presence
of betaine-bridged species in the solutions of 2·OAc is also
supported by their distinctive reddish-orange color, similar to
1
5c,17
methanes (∼2.73 Å),
and ranges among the shortest Cu−
Cu interactions observed in binuclear Cu(I) complexes bridged
18
by anionic amidinate or guanidinate anions (2.40−2.54 Å).
This observation suggests that, although electrically neutral, the
electronic influence of the betaine on the Cu atoms is more
similar to that of related anionic ligands.
that of the solid material or 2·BPh (either in solution or in the
4
solid state) but contrasts with the very pale mononuclear
complexes 1a and 1b. The color of 2·OAc or 2·BPh is
4
Although the solid-state structures of 2·OAc and 2·BPh
probably due to the presence of Cu···Cu interactions. For
example, [Cu (μ-dcpm) ]X complexes give rise to absorption
4
p‑Tol
2+
contain the same [Cu (ICyCDI ) ] subunit, their NMR
2
3
2
2
2
spectra look very different, suggesting that the counterion has a
strong effect on their solution behavior. Figure 6 shows a
bands at 307−311 nm that have been assigned to metal−metal
15c
3d → 4p transitions. The UV−vis spectra of both types of
1
comparison of the H NMR spectra of both compounds with
Cu(I) complexes, 1 and 2, are monotonous curves with λ
max
p‑Tol
that of the free ICyCDI
ligand. As one can see, the sharp
values of <200 nm tailing into the visible region, doubtless
because of the overlapping of a number of individual bands, as
previously mentioned for the free ligands. However, the
extinction in the visible region below 400 nm is considerably
and well-defined signals in the spectrum of 2·BPh contrast
4
with the broad spectrum of 2·OAc. In agreement with the high
symmetry of the dicationic unit, both complexes give rise to a
single set of signals for the betaine ligand, but their positions
are quite different. For example, the resonance of the cyclohexyl
higher for 2·OAc and 2·BPh , the spectrum of the latter
4
showing two shoulders whose frequencies (∼310 nm, ε ≈ 6000
−
1
−1
−1
−1
1
-methyne signal (marked B in Figure 6) in 2·OAc is 4.39 ppm,
mol L cm , and 370 nm, ε ≈ 3000 mol L cm ) are similar
to those in the aforementioned diphosphine-bridged com-
plexes.
which is definitely closer to that of the free ligand (4.57 ppm)
than to that of the analogous resonance in 2·BPh , 3.59 ppm.
4
In general, the signals of 2·BPh exhibit stronger shifts relative
Next, we conducted the reaction of IMeCDIDiPP with CuOAc
4
to those of the free ligand than those of 2·OAc. Noteworthy is
the fact that the chemical shifts of the cyclohexyl or the
imidazolium signals in the spectrum of 2·OAc resemble more
in the presence of NaBPh , reasoning that the removal of the
4
acetate ligand would allow the bulky betaine to act as a bridge,
giving rise to a binuclear product analogous to 2·BPh . When
4
those observed in the spectrum of mononuclear 1a (see Figure
we conducted the reaction at a 1:1:1 or 2:3:2 CuOAc:ligand:-
DiPP
S7), in which the ICyCDI
ligand coordinates in terminal
NaBPh ratio, yellow-orange materials whose NMR spectra
4
mode, than those of 2·BPh . This suggests that the broad
indicated the formation of a mixture containing two main
species were obtained. However, upon recrystallization from a
CH Cl /hexane mixture, pale yellow crystals containing a single
4
appearance of the NMR spectra of 2·OAc could be due to the
dynamic shift of the betaine ligand between the bridging and
terminal coordination modes, presumably caused by the
2
2
product, 3b, were obtained. The X-ray diffraction structure of
F
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
this compound, shown in Figure 7, shows a mononuclear
CuL2 cation with two terminally bound betaine ligands. Main
Scheme 3
+
long-term instability in solution; therefore, we pursued no
further its isolation in crystalline form. A similar compound of
+
−
composition [Cu(IMe) ] [OTf] has been reported in the
2
1
19
literature, whose H NMR data closely match those of 4.
The reaction shown in Scheme 3 is analogous to the
decarboxylation of 2-imidazoliumcarboxylates in the coordina-
tion sphere of metals, a facile process that is often used as a
8
,9
mild and effective route to heterocyclic carbene complexes.
Figure 7. ORTEP view (50% probability ellipsoids) of compound 3b.
The ready decomposition of 3b may suggest that similar
For selected bond distances and angles, see Table 2.
carbodiimide elimination could also take place from other
copper NHC-CDI complexes. Indeed, H NMR monitoring of
1
bond lengths and angles for this compound are listed in Table
solutions of complex 1a, 1b, or 2·BPh
4
at 90 °C provided
2
, where they can be compared with those of 1a and 1b.
evidence of the release of the corresponding carbodiimide
DiPP
p‑Tol
Although not affected by the crystal symmetry, each molecule
has an effective center of symmetry in the Cu atom; therefore,
the configuration and metric parameters of both ligands are
virtually the same. These are almost coplanar [the dihedral
angle formed by the symmetrical CCDI(N )(N )(C ) units is
(CDI
or CDI
) and formation of a mixture of
unidentified NHC complexes. These processes are significantly
slower than the decomposition of 3b: after 2 h at the
mentioned temperature; 2·BPh decomposes only partially,
4
while the neutral complexes 1a and 1b remain essentially
unaltered. However, decomposition of the latter was noticeable
after longer periods of time. The estimated half-life of 1a at this
c
t
imz
2
4.8°]. In spite of the cationic character of 3b, its Cu−N bond
distances are nearly identical to those of the neutral 1b (1.855
and 1.850 Å, respectively). Other internal measurements are
also very nearly the same in both compounds.
temperature is 8.3 h. The decomposition reactions of 2·BPh ,
1a, and 1b are not completely selective, as H NMR monitoring
4
1
The room-temperature NMR spectra of complex 3b are well-
defined and informative. They indicate that both IMeCDI
indicates the formation of more than one carbene-containing
product.
DiPP
ligands are chemically equivalent, but they originate independ-
ent sets of signals for the coordinated and noncoordinated N-
DiPP groups. Different from those of 1a or 1b, the room-
temperature NMR spectra of 3b are purely static and show no
signs of rotation of the DiPP groups, each of them giving rise to
a pair of doublets for the diastereotopic iPr methyls. The phase-
CONCLUSIONS
■
Adducts formed by heterocyclic carbenes and carbodiimides
(NHC-CDI or imidazolium-2-amidinates) pose interesting
analogies with some key ligands used in catalysis, such as
amidinates or α-diimines, but surprisingly, their coordination
chemistry has remained hitherto unexplored. We have prepared
a series of three such NHC-CDI adducts in a simple, single-pot
procedure from imidazolium salts and carbodiimides and
prepared several Cu(I) complexes that are the very first
examples of their kind.
1
sensitive H NOESY/EXSY homocorrelation displays no
exchange cross-peaks, indicating that the Cu atom does not
exchange its position between both potentially binding sites of
each ligand. To detect this type of exchange, we recorded the
1
H spectrum of 3b above the ambient temperature in PhCl-d5.
The first visible effect of warming, detected above 40 °C, was
the broadening of one set of iPr methyls caused by the onset of
slow rotation of the noncoordinated N-DiPP group. Heating at
higher temperatures had no further effects on the spectrum of
Depending on the steric hindrance of the NHC-CDI ligands,
these can coordinate the Cu(I) center in terminal or bridging
DiPP
DiPP
mode. Thus, reaction of ICyCDI
or IMeCDI
with
copper(I) acetate affords terminally bound complexes with the
composition of 1a and 1b, in which the Cu(I) has a
coordination number of 2 and linear geometry. In contrast,
the bridging coordination mode becomes more favorable for
3b than the expected acceleration of the rotation movement of
the pending aryl group. However, as the temperature was
increased, the intensity of the spectrum of 3b decreased in favor
of a new set of signals. At 90 °C, the transformation proceeds
cleanly and quantitatively within 2 h. The final spectrum shows
signals that were identified as belonging to the free
p‑Tol
ICyCDI , which gives rise the ionic complex 2·OAc. In the
solid state, this complex contains the trigonal binuclear
p‑Tol
2+
paddlewheel dication [Cu (ICyCDI ) ] , but in solution,
the acetate ligands and ICyCDI
2
3
p‑Tol
carbodiimide C(N-DiPP) as well as to a new species
compete for binding the
2
containing IMe. Analysis of the resulting solution by ESI-MS
Cu(I) center, giving rise to broad NMR spectra. However, the
binuclear paddlewheel structure is stabilized in solution when
showed a cluster of signals at m/z 255 with the isotope pattern
+
expected for the cation [Cu(IMe) ] (Scheme 3). The ionic
acetate ligands are exchanged by the poorly coordinating anion
2
+
−
−
product [Cu(IMe) ] [BPh ] , 4, can be separated from the
BPh , which allows informative NMR spectra of the dication
2
4
4
DiPP
carbodiimide by washing with diethyl ether the solid residue left
after solvent removal, but its crystallization was prevented by its
to be recorded. Attempts to induce the bulkier IMeCDI
−
−
ligand to coordinate in bridging mode by a similar OAc /BPh
4
G
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
exchange reaction led to a mononuclear derivative containing
two terminally bound ligands, 3b. In general, Cu(I) NHC-CDI
the solid, until the extracts became colorless. The solvent was
evaporated to dryness, and the residue was washed with hexane and
dried under vacuum, leaving a yellow solid of a hue paler than that of
the ICy betaine derivatives (yield, 1.744 g, 95%). X-ray quality crystals
complexes are quite stable in solution at room temperature, but
DiPP
3b cleanly eliminates carbodiimide CDI
when heated in
1
were obtained by slow evaporation of a CH Cl solution: H NMR
2
2
solution at 90 °C, affording the corresponding cationic bis-
carbene complex 4.
3
(
3
400 MHz, CD Cl , 25 °C) δ 1.06 (d, 24H, J = 6.8 Hz, CHMe2),
2 2 HH
3
.38 (h, 4H, J = 6.8 Hz, CHMe ), 3.75 (s, 6H, N-Me), 6.78 (t, 2H,
HH 2
3
JHH = 7.5 Hz, p-CHarom), 6.81 (s, 2H, Imidz), 6.95 (d, 4H, m-CHarom);
EXPERIMENTAL SECTION
All operations were conducted under a dry nitrogen atmosphere using
standard Schlenk techniques. Solvents were rigorously dried and
degassed before use. Microanalyses were performed by the Analytical
13
1
■
C{ H} (100 MHz, CD Cl , 25 °C) δ 23.4 (br, CHMeMe), 24.5 (br,
2 2
CHMeMe), 28.6 (CHMe ), 36.6 (N-Me), 120.4 (p-CHarom), 121.2
2
(
1
CH Imidz), 122.6 (m-CHarom), 140.5 (o-Carom), 142.3 (ipso-Carom),
−1
48.7 (C(NAr) ), 148.8 (C Imdz); IR (Nujol, cm ) 3164 (sh, w,
2 q
Service of the Instituto de Investigaciones Quim
were recorded on a Bruker Avance III 400/R spectrometer. H and
́
icas. NMR spectra
νs+as C−H Imidz), 1594 (m, ν NCN carbodiim), 1542 (br, st,
as
1
ν
and δ CH); UV−vis (CH Cl ) intense absorption λ < 200
NCN
2
2
max
1
3
1
C{ H} resonances of the solvent were used as internal standards, but
6
6
nm, λ = 254 nm (ε = 1.61 × 10 ), 291 nm (ε = 1.11 x10 ), shoulder
at 357 nm (ε = 4.54 × 10 ); ESI-MS (MeOH) m/z 459.4 (HM ).
max
5
+
the chemical shifts are reported with respect to TMS. Resonance
assignments were routinely aided by using gated 13C, 2D homonuclear
Elemental Analysis Calcd for C H N : C, 78.56; H, 9.23; N, 12.21.
30
42
4
13
1
H−H COSY and phase-sensitive NOESY, and heteronuclear C− H
HSQC and HMBC heterocorrelations. IR and UV−vis spectra were
recorded on Bruker Tensor 27 and PerkinElmer Lambda 750
spectrophotometers, respectively. Mass spectra were recorded on a
Bruker Esquire 6000 instrument with an ESI ion source and ion trap
Found: C, 78.49; H, 9.23; N, 12.21.
Syntheses of ICyCDIp‑Tol. Four milliliters of a 1 M stock solution
of KOtBu in THF was diluted to 30 mL in the same solvent; 1.281 g
(
4 mmol) of N,N′-dicyclohexylimidazolium tetrafluoborate (HI-
+
−
Cy BF ) was dissolved in 20 mL of THF, and the resulting solution
20
4
analyzer. N,N′-Bis(2,6-diisopropylphenyl)carbodiimide, 1,3-dimethy-
was stirred at −78 °C. The KOtBu solution was added dropwise. Once
the addition was finished, the cooling bath was removed and the
stirring was continued for ∼30 min while the mixture warmed to room
temperature. The flask was cooled again, and N,N′-bis-di-p-
tolylcarbodiimide (0.889 g, 4 mmol) dissolved in 10 mL of THF
was added dropwise while the mixture was being stirred. A bright
yellow color developed as the carbodiimide solution was added. The
mixture was allowed to warm to room temperature and dried, and the
residue was extracted several times with 15 mL portions of CH Cl ,
21
limidazolium iodide, and 1,3-dicyclohexylimazolium tetrafluoorbo-
22
rate were obtained according to literature procedures.
DiPP
Syntheses of ICyCDI . Four milliliters of a 1 M stock solution
of KOtBu in THF was diluted to 30 mL in the same solvent; 1.281 g
(
(
4 mmol) of N,N′-dicyclohexylimidazolium tetrafluoroborate
+ −
HICy BF ) was dissolved in 20 mL of THF. The imidazolium salt
4
solution was magnetically stirred in a cooling bath at −78 °C, and the
KOtBu solution was added dropwise. Once the addition was finished,
the cooling bath was removed, the stirring was continued for ∼30 min,
and the mixture was warmed to room temperature. Then, it was
cooled again to −78 °C, and N,N′-bis(2,6-diisopropylphenyl)-
carbodiimide (1.449 g, 4 mmol) dissolved in 10 mL of THF was
added dropwise while the mixture was being stirred. A yellow color
developed as the carbodiimide solution was added. The mixture was
allowed to warm to room temperature and dried, and the residue was
extracted several times with 15 mL portions of CH Cl , until the
2
2
until the filtered extracts were very pale or colorless. The combined
extracts were dried, leaving a bright yellow solid that was washed with
hexane (3 × 10 mL) and dried under vacuum (yield, 1.507 g, 83%).
The solid can be recrystallized from a hexane/dichloromethane
1
mixture: H NMR (400 MHz, CD Cl , 25 °C) δ 1.17 (m, 2H, Cy),
2
2
1
2
.40 (m, 8H, Cy), 1.70 (m, 2H, Cy), 1.81 (m, 6H, Cy), 1.86 (br m,
H, Cy), 2.21 (s, 6H, p-Me), 4.57 (m, 2H, 1-CH Cy), 6.89 (br s, 8H,
2
2
13
1
p-Tol), 6.95 (s, 2H, Imdz); C{ H} (100 MHz, CD Cl , 25 °C) δ
2
2
filtered extracts are very pale or colorless. The combined extracts were
evaporated to dryness, leaving a yellow solid that was washed with
hexane (3 × 10 mL) and dried under vacuum (yield, 2.140 g, 90%). X-
2
0.8 (p-CH ), 25.4 (4-CH Cy), 25.7 (3,3′-CH Cy), 33.5 (2,2′-CH
3
2
2
2
Cy), 58.5 (CH, Cy), 116.4 (CH Imdz), 123.0 (br s, o-CH p-Tol),
28.7 (p-C p-Tol), 129.2 (m-CH p-Tol), 145.1 (ipso-C p-Tol), 146.8
1
ray quality crystals were obtained by slow evaporation of a CH Cl
2
2
−1
1
3
(C Imidz), 150.7 (C(NAr) ); IR (Nujol, cm ) 3149 (sh, m, νs+as C−
q
2
solution: H NMR (400 MHz, CD Cl , 25 °C) δ 0.99 (d, 12H, J
=
2
2
HH
3
H Imidz), 1609 (m, νas NCN carbodiim), 1530 (br, st, ν N
CN + δ C−H); UV−vis (CH Cl ) intense absorption λ < 200
6
1
1
.1 Hz, CHMeMe), 1.00 (d, 12H, J = 6.5 Hz, CHMeMe), 1.06−
HH
2
2
max
.47 (m, 8H, Cy), 1.24 (d, 2H, J = 6.9 Hz, Cy), 1.67 (m, 2H, Cy),
6
5
3
nm, shoulders at 230 nm (ε ≈ 1.03 × 10 ), 308 nm (ε ≈ 9.06 × 10 ),
.73−1.84 (m, 8H, Cy), 3.13 (h, 4H, J = 6.8 Hz, CHMe ), 4.78 (m,
HH
2
5
+
3
358 nm (ε ≈ 7.96 × 10 ); ESI-MS (MeOH) m/z 455.3 (HM ).
Elemental Analysis Calcd for C30 : C, 79.25; H, 8.42; N, 12.32.
2
H, 1-CH Cy), 6.68 (t, 2H, J = 7.5 Hz, p-CH ), 6.89 (d, 4H,
HH arom
3
13
1
H N
38 4
JHH = 7.5 Hz, m-CHarom), 7.03 (s, 2H, Imidz); C{ H} (100 MHz,
Found: C, 79.66; H, 8.65; N, 12.25.
CD Cl , 25 °C) δ 23.5 (CHMeMe), 23.8 (CHMeMe), 25.4 (4-CH
2
2
2
Syntheses of [Cu(OAc) (ICyCDIDiPP)] (1a). A solution of
Cy), 26.7 (3-CH Cy), 29.3 (CHMe ), 33.8 (2-CH Cy), 58.6 (1-CH
2
2
2
DiPP
ICyCDI
(0.594 g, 1 mmol) in 15 mL of dichloromethane was
added dropwise to a stirred suspension of Cu(I) acetate (0.123 mg, 1
mmol) in the same solvent. The mixture was stirred for 3 h at the
room temperature and filtered and the solution dried. The residue was
washed with 20 mL of hexane and dried under vacuum to afford the
product as a pale yellow solid (yield, 0.705 g, 98.3%). X-ray quality
crystals were obtained by recrystallization from a dichloromethane/
Cy), 116.9 (CH Imidz), 119.4 (p-CHarom), 122.4 (m-CHarom), 139.7
(
(
o-Carom), 140.2 (ipso-C ), 146.3 (C Imidz), 149.1 (C(NAr) ); IR
arom q 2
−1
Nujol, cm ) 3184 (sh, w, ν C−H Imidz), 1593 (m, ν NCN
s+as
as
carbodiim), 1541 (br, st, ν
δ CH); UV−vis (CH Cl ) intense
NCN
2 2
5
absorption λmax < 200 nm, λ = 298 nm (ε ≈ 9.73 × 10 ), shoulders
max
6
5
at 237 nm (ε ≈ 1.12 × 10 ), 354 nm (ε ≈ 4.37 × 10 ); ESI-MS
+
(
MeOH) m/z 595.7 (HM ). Elemental Analysis Calcd for C H N :
40 58 4
1
diethyl ether mixture: H NMR (400 MHz, CD Cl , 25 °C) δ 0.77 (br
2
2
C, 80.76; H, 9.83; N, 9.42. Found: C, 80.48; H, 9.68; N, 9.34.
DiPP
s, 12 H, CHMe , free DiPP-N), 1.00−1.60 (m, 12H, Cy), 1.29 (d, 6H,
Syntheses of IMeCDI . A 1 M solution of KOtBu in THF (4
2
3
3
+
−
J
= 6.7 Hz, CHMeMe, coord DiPP-N), 1.36 (d, 6H, J = 6.7 Hz,
HH HH
mL, 4 mmol) was added dropwise to a stirred solution of HIMe I
2
CHMeMe, coord DiPP-N), 1.69 (br s, 3H, OAc, overlapping with Cy
(
0.892 g, 4 mmol) in 20 mL of the same solvent, cooled at −78 °C.
2
2
signals), 1.71 (d, 2H, J = 12.4 Hz, Cy), 1.79 (d, 2H, J = 12.4 Hz,
Once the addition was complete, the cooling bath was removed and
the stirring continued for 10 min, without allowing the mixture to
warm to room temperature. Then, the mixture was placed again in the
HH
HH
2
3
Cy), 1.92 (d, 2H, J = 12.4 Hz, Cy), 2.71 (h, 2H, J = 6.6 Hz,
HH
HH
2
CHMe , free DiPP-N), 2.79 (d, 2H, J = 12.4 Hz, Cy), 3.52 (h, 2H,
HH = 6.8 Hz, CHMe
6.74 (t, 1H, JHH = 7.5 Hz, p-CHarom coord DiPP-N), 6.86 (d, 2H, JHH
= 7.5 Hz, m-CHarom coord DiPP-N), 7.05 (t, 1H, J = 7.1 Hz, p-
CHarom free DiPP-N), 7.11 (d, 2H, J = 7.1 Hz, m-CHarom free DiPP-
N), 7.18 (s, 2H, CH Imidz); C{ H} (100 MHz, CD Cl , 25 °C) δ
2
HH
3
−
78 °C cooling bath, and a solution of N,N′-bis(2,6-
J
2
, coord DiPP-N), 4.50 (m, 2H, N−CH Cy),
3
3
diisopropylphenyl)carbodiimide (1.449 g, 4 mmol) in 15 mL of
THF was added while the mixture was being stirred. The mixture was
allowed to warm at room temperature, dried, and extracted repeatedly
with 10 mL portions of CH Cl , filtering off the liquid fractions from
3
HH
3
HH
13
1
2
2
2
2
H
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2
2
2
2.3 (br, CHMeMe, free DiPP-N), 23.4 (CHMeMe, coord DiPP-N),
3.7 (br, CHMeMe, free DiPP-N), 25.2 (CHMeMe, coord DiPP-N),
5.7 (3-CH Cy), 25.9 (3′-CH Cy), 26.4 (4-CH Cy), 29.3 (two
(CH Cl ) m/z 971.5 (Cu(ICyNCNp ‑ T o l )2 + ), 744. 4
2
2
p‑Tol
2+
([Cu (ICyCDI
)3] ). Elemental Analysis Calcd for
2
C H Cu N O : C, 70.16; H, 7.52; N, 10.45. Found: C, 70.39; H,
2
2
2
94 120
2
12
4
overlapping signals, CHMe ), 32.2 (2-CH Cy), 35.53 (2′-CH Cy),
7.67; N, 10.59.
Synthesis of [Cu (μ-ICyCDI ) ] (BPh ) (2-BPh ). NaBPh
2
2
2
p‑Tol 2+
−
5
1
1
9.9 (1-CH Cy), 118.7 (CH Imidz), 121.8 (p-CH , coord DiPP-N),
22.9 (m-CHarom coord DiPP-N), 123.4 (m-CHarom free DiPP-N),
24.6 (p-CHarom, free DiPP-N), 139.3 (o-Carom coord DiPP-N), 142.3
arom
2
3
4
2
4
4
2
(0.342 g, 0.66 mmol) was dissolved in a mixture of 20 mL of CH Cl
2
and 2 mL of THF. Copper(I) acetate (0.123 g, 0.66 mmol) and
p‑Tol
(ipso-Carom), 143.0 (C ), 143.3 (o-C
free DiPP-N), 143.9 (two
ICyCDI
20 mL of CH Cl was added. The mixture was stirred and the NaBPh
4
(0.455 g, 1 mmol) were loaded into a Schlenk tube, and
q
arom
−
1
overlapping signals, C ); IR (Nujol, cm ) 3165, 3163 (w, ν C−H
q
s+as
2
2
Imidz), 1567 (br, ν CO OAc, ν CN); UV−vis (CH Cl ) intense
solution added. Stirring was continued for 2 h at the room
temperature, the mixture filtered, and the filtrate dried. The red
solid residue was extracted with approximately 30 mL of CH Cl and
2
2
3
absorption λ < 200 nm, shoulders at 270 nm (ε = 3.13 × 10 ), 287
max
3
nm (ε = 2.75 × 10 ). Elemental Analysis Calcd for C H CuN O : C,
42
61
4
2
2
2
70.31; H, 8.57; N, 7.81. Found: C, 70.37; H, 8.85; N, 7.75.
filtered. Toluene (15 mL) was added and the mixture stored at −20
°C overnight to afford a first crop of crystals. The solution was
separated, concentrated, and cooled again, to yield a second crop. The
crystals were collected by filtration and dried under vacuum. The
DiPP
Syntheses of [Cu(OAc) (IMeCDI )] (1b). A Schlenk tube was
DiPP
charged with an equimolar mixture of solid ligand IMeCDI
(0.227
g, 0.5 mmol) and Cu(I) acetate (0.061 g, 0.5 mmol). After 20 mL of
dichloromethane had been added, the mixture was stirred for 2 h at
room temperature, filtered, and dried. The oily residue was stirred with
1
combined yield was 303 mg or 41%: H NMR (400 MHz, CD Cl , 25
2
2
3
2
°C) δ 0.55 (q, 12H, J ≈ J = 12.9 Hz, 3-CHH Cy), 0.81 (br s,
12H, 2-CHH Cy), 1.02 (m, 18H, 2-CHH + 4-CHH Cy), 1.43 (br d,
HH
HH
15 mL of diethyl ether to afford a pale green solid that was
2
3
recrystallized from a dichloromethane/toluene mixture to afford the
title complex as a pale green crystalline solid (yield, 74.1 mg, 25%): H
NMR (400 MHz, CD Cl , 25 °C) two isomers in a 6:1 ratio, major
isomer, δ 0.82 (br s, 6 H, CHMeMe, free DiPP-N), 0.82 (br s, 6 H,
CHMeMe, free DiPP-N), 1.32 (d, 6H, J = 6.9 Hz, CHMeMe, coord
DiPP-N), 1.37 (d, 6H, J = 6.8 Hz, CHMeMe, coord DiPP-N), 1.69
6H, J = 12.9 Hz, 4-CHH Cy), 1.53 (br d, 12H, J = 13.2 Hz, 3-
HH HH
1
3
CHH Cy), 2.23 (s, 18H, p-Me), 3.59 (tt, 6H, J = 11.8, 2.7 Hz, 1-
CH Cy), 6.56 (s, 6H, CH imidz), 6.61 (d, 12H, J = 7.8 Hz, m-
CHarom), 6.85 (t, 8H, J = 7.1 Hz, p-CH BPh ), 6.99 (t, 16H, J
HH
3
2
2
HH
3
3
=
HH
4
HH
3
3
HH
7.1 Hz, m-CH BPh ), 7.00 (d, 12H, J = 7.8 Hz, o-CHarom), 7.28 (br
4 HH
3
13
1
HH
m, 16H, o-CH BPh ); C{ H} (100 MHz, CD Cl , 25 °C) δ 20.7 (p-
4 2 2
3
(
3
br s, 3H, OAc), 2.98 (h, 2H, J = 6.8 Hz, CHMe , free DiPP-N),
.49 (h, 2H, J = 6.9 Hz, CHMe , coord DiPP-N), 3.91 (s, 6H, N-
Me), 25.0 (4-CH Cy), 25.3 (3-CH Cy), 33.4 (2-CH Cy), 59.4 (1-
HH
2
2 2 2
3
HH
2
CH Cy), 119.7 (CH imidz), 122.1 (m-CHarom), 122.2 (p-CH BPh4),
3
Me), 6.79 (t, 1H, J = 7.5 Hz, p-CHarom coord DiPP-N), 6.87 (d, 2H,
126.0 (m, m-CH BPh ), 130.4 (o-CHarom), 133.0 (p-Carom), 136.3 (o-
HH
4
3
JHH = 7.5 Hz, m-CHarom coord DiPP-N), 7.02 (s, 2H, CH Imidz),
CH BPh ), 140.9 (CN Imidz), 142.9 (C(N−Ar) ), 146.6 (ipso-Carom),
4
2
2
−1
7
J
.08−7.18 (m, 3H, CH . freeDiPP-N); minor isomer, δ 1.12 (d, 6H,
164.4 (m, ipso-C, BPh ); IR (nujol mull, cm ) 3180 (w, νC−H
arom
4
3
3
= 7.0 Hz, CHMeMe), 1.15 (d, 6H, J = 7.0 Hz, CHMeMe),
imidz); 1580 (m, ν C−C ring, BPh ), 1514, 1461 (br, st, ν NCN), 730,
HH
HH
4
3
1
2
3
.47 (d, 6H, J = 7.0 Hz, CHMeMe), 1.58 (br s, 3H, OAc), 3.18 (h,
H, J = 7.0 Hz, CHMe ), 3.39 (h, 2H, J = 7.0 Hz, CHMe2),
.81 (s, 6H, N-Me); C{ H} (100 MHz, CD Cl , 25 °C) major
703 (st, δ C−H arom BPh
4
); UV−vis (CH Cl ) intense absorption
2 2
HH
3
3
−1
−1
λmax < 200 nm, shoulders at 310 nm, ε ≈ 6000 mol L cm , and 370
HH
2
HH
13
1
−1 −1
nm ε ≈ 3000 mol L cm ; ESI-MS (anisole) m/z 971.6
p‑Tol + p‑Tol 2+
2
2
isomer, δ 21.6 (br, CHMeMe, free DiPP-N), 23.0 (CHMeMe, coord
DiPP-N), 23.9 (br, confirmed in the HSQC spectrum, OAc), 24.8 (br,
CHMeMe, free DiPP-N), 25.7 (CHMeMe, coord DiPP-N), 28.8
(Cu(ICyNCN
Analysis Calcd for C138
7.59. Found: C, 75.18; H, 6.93; N, 7.19.
)
2
), 744.4 ([Cu
2
(ICyCDI
) ] ). Elemental
3
H
155Cu
N12·CH
Cl
2
: C, 75.39; H, 7.10; N,
2
2
DiPP
+
−] (3b). A solution of
(
1
1
CHMe , free DiPP-N), 29.2 (CHMe , coord DiPP-N), 37.0 (N-Me),
22.3 (p-CHarom, coord DiPP-N), 122.5 (m-CHarom coord DiPP-N),
22.8 (CH Imidz), 123.2 (m-CHarom free DiPP-N), 124.8 (p-CHarom
Synthesis of [Cu(IMeCDI
NaBPh
was added to a stirred solution of copper(I) acetate (0.049 g, 0.38
)
2
] [BPh
4
2
2
(0.128 g, 0.38 mmol) in 20 mL of a 9:1 CH Cl /THF mixture
4
2
2
,
DiPP
free DiPP-N), 139.5 (o-Carom coord DiPP-N), 143.3 (o-Carom free
DiPP-N), 143.6 (ipso-Carom free DiPP-N), 144.2, 144.5 (ipso-Carom
coord DiPP-N and C(N-Ar) ), 145.9 (C Imidz), 177.6 (MeCO );
mmol) and ligand IMeCDI
CH Cl . The mixture was stirred for 2 h, filtered, and dried. The oily
residue solidified on stirring with 20 mL of diethyl ether. The solid was
filtered out, dried under vacuum, and recrystallized from a CH Cl
Et O mixture to afford the product as pale yellow microcrystalline
(0.344 g, 0.75 mmol) in 20 mL of
2
2
2
q
2
minor isomer, 21.77 (CHMeMe), 24.8 (CHMeMe), 28.7 (CHMe2),
9.5 (CHMe ), 37.1 (N-Me), 139.5 (m-CHarom), 142.7 (m-CHarom); IR
2
/
2
2
2
2
−
1
(
Nujol, cm ) 3110 (w, ν C−H Imidz), 1596, 1560 (br, ν CO
material (yield, 0.352 g, 72%). X-ray quality crystals were obtained by
layering benzene over a concentrated solution of the product in
s+as
OAc, ν CN); UV−vis (CH Cl ) featureless spectrum, intense
2
2
1
3
absorption λ
< 200 nm. Elemental Analysis Calcd for
CH
2
Cl
2
: H NMR (400 MHz, CD
2
Cl
2
, 25 °C) δ 0.72 (d, 6H, JHH
=
max
3
C H CuN O : C, 66.12; H, 7.80; N, 9.64. Found: C, 66.48; H,
6.5 Hz, CHMeMe, free DiPP-N), 0.86 (d, 6H,
CHMeMe, free DiPP-N), 1.08 (d, 6H, JHH = 6.8 Hz, CHMeMe, coord
DiPP-N), 1.24 (d, 6H, JHH = 6.9 Hz, CHMeMe, coord DiPP-N), 2.65
J
HH = 7.0 Hz,
32
45
4
2
3
7
.18; N, 9.53.
p‑Tol 2+
−
3
Synthesis of [Cu (μ-ICyCDI ) ] (OAc ) (2-OAc). A solution
2
3
2
p‑Tol
3
3
of the ligand ICyCDI
dichloromethane was added dropwise to a suspension of Cu(I) acetate
0.228 g, 0.50 mmol) in the same amount of solvent. As the ligand was
(0.465 g, 0.75 mmol) in 10 mL of
(h, 2H, JHH = 6.8 Hz, CHMe
Hz, CHMe , coord DiPP-N), 3.30 (s, 12H, N-Me), 6.35 (s, 4H, CH
Imidz), 6.81−6.91 (m, 6H, CHarom free DiPP-N), 6.85 (t, 4H, JHH
2
, free DiPP-N), 3.16 (h, 2H, JHH = 7.0
2
3
(
=
3
added, an orange color developed. The mixture was stirred for 2 h at
room temperature, filtered, and dried. The oily residue was stirred with
diethyl ether to afford a red solid, which was filtered out and dried
under vacuum. The solid was recrystallized from CH Cl /toluene
7.1 Hz, p-CH BPh ), 7.02 (t, 8H, JHH = 7.4 Hz, m-CH BPh ), 7.16 (d,
4
4
3
3
4H, JHH = 6.7 Hz, m-CHarom coord DiPP-N), 7.24 (t, 2H, JHH = 6.7
Hz, p-CHarom coord DiPP-N), 7.32 (m, 8H, o-CH BPh
(100 MHz, CD Cl , 25 °C) δ 21.6 (CHMeMe, free DiPP-N), 23.9
1
3
1
); C{ H}
4
2
2
2
2
solvent and obtained as red crystals, which were left under vacuum for
4 h to remove crystallization solvent. The yield after recrystallization
(CHMeMe, coord DiPP-N), 24.4 (CHMeMe, coord DiPP-N), 25.0
(CHMeMe, free DiPP-N), 28.8 (CHMe , free DiPP-N), 29.2 (CHMe ,
2
2
2
1
was 0.306 g or 38%: H NMR (400 MHz, CD Cl , 25 °C) δ 1.22 (m,
coord DiPP-N), 36.3 (N-Me), 122.2 (p-CH BPh ), 122.9 (m-CH
2
2
4
arom
1
2H, 3-CHH Cy), 1.31−1.59 (m, 30 H, 2-CH + 4-CHH Cy), 1.73
free DiPP-N), 123.0 (CH imidz), 123.2 (p-CHarom free DiPP-N), 124.1
(m-CHarom coord DiPP-N), 125.3 (p-CHarom coord DiPP-N), 126.1
2
2
3
(
br d, 6H, J = 11.4 Hz, 4-CHH Cy), 1.87 (br d, 12H, J = 9.1
HH HH
Hz, 3-CHH Cy), 2.23 (br s, 9H, p-Me), 4.39 (br s, 6H, 1-CH, Cy),
(m, m-CH BPh ), 136.3 (o-CH, BPh ), 139.0 (o-C
free DiPP-N),
4
4
arom
.20−7.8 (br m, 24H, CH ), 7.15 (br s, 6H, CH Imidz); 13C{ H}
1
142.8 (C ), 143.1 (C ), 143.2 (o-C
coord DiPP-N), 143.2 (Cq),
6
arom
q
q
arom
−1
(
100 MHz, CD Cl , 25 °C) δ 20.8 (p-Me), 25.2 (4-CH Cy), 25.7 (3-
144.2 (CN Imidz); IR (nujol mull, cm ) 3125 (w, ν(C−H) imidz),
2
2
2
CH, Cy), 33.1 (br, 2-CH Cy), 34.4 (br, OAc), 59.4 (1-CH, Cy), 118.0
1553 (m), 1556 (br, st), 1511 (m) (ν(CN)); UV−vis (CH Cl )
2
2
(
CH, Imidz), 120−140 (br, CH ), 144.4 (br, C ), 147.5 (br, C ); IR
featureless spectrum, intense absorption λ < 200 nm. Elemental
arom
q
q
max
−1
(
cm ), 1600, 1550 (st, νCO (OAc), ν (CN)); UV−vis (CH Cl )
Analysis Calcd for C H BCuN : C, 77.60; H, 8.06; N, 8.62. Found:
2
2
84 104
8
featureless spectrum, intense absorption λ
< 200 nm; ESI-MS
C, 77.77; H, 7.76; N, 9.00.
max
I
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Thermal Decomposition of 3. A solution of 3 (20 mg, 15 μmol)
in C D Cl (0.6 mL) was heated at 90 °C for 2 h in an airtight NMR
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5
3
Me), 6.15 (s, 4H, CH ), 6.94 (t, 4H, J = 7.7 Hz, p-CH BPh4),
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(
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28
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The Supporting Information is available free of charge on the
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chem.5b02141.
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Crystallographic data (CIF)
Details of the TD-DFT calculation of the UV−vis
spectrum of a model betaine molecule, supplementary
crystallographic data and ORTEP views for compounds
(
́
pora, J.;
DiPP
p‑Tol
IMeCDI , ICyCDI , 2·OAc, and 2·BPh (solvent-
4
(
free crystals), and a list of selected bond lengths and
angles for the dication [Cu (μ-ICyCDI ) ] in 2·OAc
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p‑Tol
2+
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AUTHOR INFORMATION
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■
M.; Murillo, C. A.; Schooler, P. J. Chem. Soc., Dalton Trans. 2000,
Corresponding Author
E-mail: campora@iiq.csic.es.
Notes
2
(
8
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ACKNOWLEDGMENTS
This work was supported by the Government of Spain (Project
CTQ2012-30962), Junta de Andalucia (Project FQM6276),
■
(
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́
2
(
and the European Union (FEDER funds). We thank Dr. Gloria
́ ́
Gutierrez-Alcala (Mass Spectrometry Service, Instituto de
́
Investigaciones Quimicas) for her assistance in the ESI-MS
characterization of Cu complexes.
J
DOI: 10.1021/acs.inorgchem.5b02141
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
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DOI: 10.1021/acs.inorgchem.5b02141
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