New Cu(I)-ethylene complexes based on tridentate imine ligands: Synthesis and structure

Article abstract of DOI:10.1021/ic302325u

A new bulky facially coordinating N₃-donor tach-based ligand (tach: cis,cis-1,3,5-triaminocyclohexane) [1: cis,cis-1,3,5-tris(2-fluoro-6- (trifluoromethyl)benzylideneamino)cyclohexane] has been obtained from the condensation of tach with 3 equiv of the appropriate benzaldehyde. Reaction of 1 with [Cu(NCMe)₄][PF₆] gave the complex [(1)Cu(NCMe)][PF₆]. Displacement of the acetonitrile ligand is possible with CO and C₂H₄ (3-5 bar). Cu(I)-ethylene complexes of ligands 1 and 2 [2: cis,cis-1,3,5-(mesitylideneamino)cyclohexane] were prepared successfully by treatment of the ligands with CuBr and AgSbF ₆ in the presence of ethylene. These complexes display reversible complexation of the ethylene molecule under mild changes to pressure, suggesting possible application in olefin separation and extraction.

Full text of DOI:10.1021/ic302325u

Article
pubs.acs.org/IC
New Cu(I)-Ethylene Complexes Based on Tridentate Imine Ligands:
Synthesis and Structure
Parisa Ebrahimpour, Mairi F. Haddow, and Duncan F. Wass*
School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
S
* Supporting Information
ABSTRACT: A new bulky facially coordinating N3-donor tach-based ligand (tach: cis,cis-
1,3,5-triaminocyclohexane) [1: cis,cis-1,3,5-tris(2-fluoro-6-(trifluoromethyl)-
benzylideneamino)cyclohexane] has been obtained from the condensation of tach with
3 equiv of the appropriate benzaldehyde. Reaction of 1 with [Cu(NCMe)4][PF6] gave
the complex [(1)Cu(NCMe)][PF6]. Displacement of the acetonitrile ligand is possible
with CO and C2H4 (3−5 bar). Cu(I)-ethylene complexes of ligands 1 and 2 [2: cis,cis-
1,3,5-(mesitylideneamino)cyclohexane] were prepared successfully by treatment of the
ligands with CuBr and AgSbF6 in the presence of ethylene. These complexes display
reversible complexation of the ethylene molecule under mild changes to pressure,
suggesting possible application in olefin separation and extraction.
complexes supported by cis,cis-1,3,5-tris(arylamino)cyclohexane
ligands have proved unsuccesful.
In this paper, we report the synthesis of copper complexes
supported by a new fluorinated face-capping N3 donor ligand,
and copper ethylene complexes supported by a range of related
ligands. The reversible nature of olefin binding augers well for
application in olefin separation.
INTRODUCTION
■
Ligands based on a cis,cis-1,3,5-tris(arylamino)cyclohexane
framework have attracted attention as they provide a face-
capping N3-coordination environment around a metal center
which is a versitile mimic for metalloenzyme active sites.2,3
More generally, these ligands form a protected cavity around
the metal center which has been exploited in biomimetic and
catalysis research.4 Our interest in such ligands stems from the
potential of their group 11 complexes to separate simple
substrates (such as CO and ethylene) from the mixture of
waste gases that are common in petrochemical plants and
refining, by weakly binding to such molecules.5,6
We have previously communicated the synthesis and
preliminary study of one derivative of these ligands, namely,
cis,cis-1,3,5-tris(mesitylideneamino)cyclohexane, its copper(I)
complex and substrate binding selectivity of this complex,7,1
together with a broader study of novel nonfluorinated and
fluorinated N3-donor ligands, their Cu(I) complexes and the
propensity of such complexes to bind CO.
The ability of Cu(I) to coordinate ethylene has important
ramifications in biochemistry (e.g., in fruit ripening),8 in
synthetic methodlogy (e.g., copper-catalyzed aziridination),8f,9
and in industrial applications (e.g., epoxidation, paraffin
separation).10 As model intermediates for these processes,
and in general as novel coordination compounds, a number of
Cu(I)-ethylene complexes have been isolated and in many
cases structurally characterized. Supporting ligands are almost
exclusively based on nitrogen donors, with bidentate imines
including α-diimines or β-diketimines, and particularly
tridentate pyrazolylborate derivatives pre-eminent.11,8d,e Stabil-
ity is a function of the supporting ligands used and in some
cases sensitivity toward heat, light, and ethylene-loss is
reported. To date, and perhaps surprisingly given the success
of other tridentate N-donor ligands, efforts to isolate olefin
RESULTS AND DISCUSSION
■
Synthesis and Structural Study of cis,cis-1,3,5-Tris(2-
fluoro-6-(trifluoromethyl)benzylideneamino)-
cyclohexane (1). cis,cis-1,3,5-Tris(2-fluoro-6-
(trifluoromethyl)benzylideneamino)cyclohexane (1) was pre-
pared using the same method as used to obtain previous cis,cis-
1,3,5-tri(arylamino)cyclohexane ligands.7,1 Treatment of cis,cis-
1,3,5-triaminocyclohexane (tach) with 3 equiv of 2-fluoro-6-
(trifluoromethyl)benzaldehyde in toluene and removal of water
by azeotropic distillation over an 18 h period gives 1 in 86%
yield (Scheme 1). The 1H NMR spectrum of the ligand
exhibited a characteristic quartet at 8.64 ppm and a broad
triplet of triplets around 3.72 ppm, corresponding to the imine
protons (-NCH-, Hb in Scheme 1) and cyclohexane protons
(=N−CtachH-, Ha in Scheme 1) respectively. Ligand 1 is stable
under ambient conditions.
Scheme 1. Synthesis of tach-Based Ligand 1
Received: October 24, 2012
Published: March 15, 2013
© 2013 American Chemical Society
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Crystals of 1 suitable for X-ray structure determination were
obtained by slow evaporation of a CH2Cl2 solution of the
complex. . Crystals of 1 form in the space group P21/c. The
molecular structure shows that the three fluorinated benzyl
imino arms inherit the cis,cis-stereochemistry, the cyclohexane
backbone is in the chair conformation, and each imine moiety
adopts the sterically favorable position (see Figure 1 and Table
1 for selected bond lengths and angles).
Scheme 2. Synthesis of [(1)Cu(NCMe)][PF6]
Figure 1. Molecular structure of 1. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms have been omitted for
clarity.
Figure 2. Molecular structure of [(1)Cu(NCMe)][PF6]. Thermal
ellipsoids are drawn at the 50% probability level. All hydrogen atoms
and [PF6]¯ counterion have been omitted for clarity.
To compare this new ligand with the derivatives we have
previously reported, its complexation chemistry with copper
was explored. Reaction of 1 with [Cu(NCMe)4][PF6] in
CH2Cl2 gives [(1)Cu(NCMe)][PF6] in 85% yield as an intense
yellow solid (Scheme 2).
Scheme 3. Reaction of [(1)Cu(NCMe)][PF6] with Carbon
Monoxide
Crystals of [(1)Cu(NCMe)][PF6] were grown by slow
diffusion of n-hexane into a saturated CH2Cl2 solution of
[(1)Cu(NCMe)][PF6] at room temperature. Crystals of
[(1)Cu(NCMe)][PF6] form in a P213 space group (see Figure
2 and Table 1 for selected bond lengths and angles). The
fluorinated phenyl rings are arranged facially around the copper
center, producing a cavity in which one molecule of acetonitrile
is accommodated. A slight shortening of the CNCMe−NNCMe
bond length (1.137 Å) in comparison with free acetonitrile
(1.155 Å) is observed as expected upon coordination to a metal
center. The Cu(I) center adopts a pseudotetrahedral geometry
with Ntach−Cu−Ntach bond angles of 94.10°, and NNCMe−Cu−
Ntach bond angles of 122.31°.
Bubbling CO through the intensely yellow CH2Cl2 solution
of [(1)Cu(NCMe)][PF6] resulted in decolorization and
spectroscopic data consitent with CO coordination (Scheme
3).
The IR spectrum of [(1)Cu(CO)][PF6] exhibited ν(CO) at
2091 cm−1 indicative of only a moderate degree of π-back-
bonding. As previously reported, copper can cause fast
relaxation of proximal nuclei, and it was not possible to
observe the 13C{1H} NMR resonance for the coordinated
carbon monoxide ligand in this case.1,7
Crystals of [(1)Cu(CO)][PF6] suitable for X-ray structure
determination were grown by slow diffusion of n-hexane into a
CH2Cl2 solution of the complex. Crystals of [(1)Cu(CO)]-
[PF6] form in the space group P213 (see Figure 3 and Table 1
for selected bond lengths and angles). The fluorine atoms on
the −CF3 group and [PF6]¯ counterion in the molecular
structure of [(1)Cu(CO)][PF6] were disordered, requiring the
use of some restraints to ensure a smooth refinement. The
copper carbonyl complex adopts a pseudo-tetrahedral geometry
very similar to the related Cu-NCMe complex.
Synthesis of Cu(I)-C2H4 Complexes of cis,cis-1,3,5-
Tri(arylideneamino)cyclohexanes: [(1)Cu(C2H4)][X], (X =
PF6 or SbF6) and [(2)Cu(C2H4)][SbF6]. In a preliminary
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1, [(1)Cu(NCMe)][PF6], and [(1)Cu(CO)][PF6]
1
[(1)Cu(NCMe)][PF6]
Cu1−N2
N2−C11
Cu1−N1
N1−C3
[(1)Cu(CO)][PF6]
N1−C7
N2−C15
N3−C24
N1−C7−C8−C9
N2−C15−C16−C17
N3−C23−C24−C25
1.269(3)
1.256(3)
1.265(3)
45.5(4)
1.897(6)
1.137(9)
2.050(3)
1.257(5)
180.0
C9−O1
Cu1−C9
N1−C8
1.134(6)
1.810(4)
1.271(3)
180.0
Cu1−C9−O1
N1−Cu1−C9
N1−C8−C1−C6
118.6(3)
−46.4(4)
N2−C11−C12
N1−Cu1−N2
N1−Cu1−N1
C3−C4−C9−F4
123.25(6)
65.3(4)
122.1(1)
94.32(13)
2.2(6)
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that, because of the highly labile nature of the copper-olefin
bonding interaction, 13C{1H} NMR chemical shifts cannot
always be reported.11b,d,f,12
Following the successful synthesis and characterization of an
ethylene-Cu(I) complex with this fluorinated tach-based ligand,
a nonfluorinated tach-based ligand 2 (previously reported)7 was
subjected to the same protocol. Upon coordination of ethylene
1
to the copper center in [(2)Cu(C2H4)][SbF6], the H NMR
signal corresponding to ethylene moved upfield from 5.27 ppm
1
to 3.09 ppm. The H NMR upfield shift of the coordinated
ethylene proton has been attributed to increased shielding
caused bycopper-to-ethylene π-back-donation.11b,c,13 However,
́
Walton et al. and Perez et al. suggested that such an upfield
shift may also be caused by an anisotropic effect generated by
the π-system of the aromatic rings.14 Certainly, the coordinated
ethylene is sandwiched between three aromatic rings, such that
the effects of the aromatic ring currents on the chemical shifts
of the ethylene protons cannot be discounted. Similar shifts
were reported by Vitagliano et al. for Cu(I)-ethylene complexes
with a chiral diamine ligand.14d,15 The 13C{1H} NMR spectrum
of [(2)Cu(C2H4)][SbF6] displayed a peak at 85.8 ppm which
was assigned to the carbon atoms of coordinated ethylene (free
ethylene: 123.5 ppm).11a−c,12a,14a
Compounds [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)]-
[SbF6] are stable if kept under an atmosphere of ethylene,
both in solution and in the solid state. In weakly or
noncoordinating solvents (e.g., CH2Cl2), these complexes are
observed to lose ethylene under a stream of dinitrogen or under
reduced pressure, illustrating reversible complexation of
ethylene.
Figure 3. Molecular structure of [(1)Cu(CO)][PF6]. Thermal
ellipsoids are drawn at the 50% probability level. All hydrogen
atoms and [PF6]¯ counterion have been omitted for clarity.
experiment, bubbling ethylene through a CH2Cl2 solution of
[(1)Cu(NCMe)][PF6] did not result in the desired sub-
stitution at the copper center. This result is in line with our
previous unsuccesful attempts to isolate such species with a
range of tach ligand derivatives.1,7 However, upon subjecting
the solution of [(1)Cu(NCMe)][PF6] to a slightly higher
pressure of ethylene (3−5 bar), a signal corresponding to
1
coordinated ethylene was observed by H NMR spectroscopy.
Compound [(1)Cu(C2H4)][PF6] was only stable under a
pressure of ethylene (3−5 bar), suggesting a rapid displacement
of ethylene from the Cu(I) center by recoordination of the
liberated acetonitrile ligand (see Scheme 4). An ethylene
saturated CD2Cl2 solution of [(1)Cu(NCMe)][PF6] exhibited
1H NMR signals for both free and coordinated ethylene (and
acetonitrile), suggesting a mixture of olefin and nitrile
complexes.
The selective coordination of ethylene over higher olefins
was examined to test the applicability of complexes [Cu(1)-
(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6] as mass-separation
agents. Reactions between the labile copper-ethylene complexes
and 2-butene (1:1 cis and trans), 1-pentene, 1-hexene, 1-octene,
To avoid this exchange between ethylene and the acetonitrile
liberated from [(1)Cu(NCMe)][PF6], a route to a Lewis base-
free Cu(I)-tach precursor was sought. This was achieved by the
one pot reaction of ligand 1 with CuBr and AgSbF6 under a
pressure of ethylene (5−10 bar). Following passage through a
short plug of Celite, a colorless solution of [(1)Cu(C2H4)]-
[SbF6] was concentrated while under a stream of ethylene to
prevent further loss of the potentially labile olefin ligand (see
Scheme 5). Compound [(1)Cu(C2H4)][SbF6] was character-
1
and norbornene were monitored by H NMR spectroscopy.
However, no signals due to replacement of coordinated
ethylene were observed, the signals for [Cu(1)(C2H4)][SbF6]
or [(2)Cu(C2H4)][SbF6] remaining unchanged. Using the
same protocol for the synthesis of the ethylene complexes with
these other olefins also resulted in no reaction, as did attempted
substitution reactions from the acetonitrile complexes. We
speculated that the cavity imposed by the tridentate ligand is
too small to accommodate these larger olefins.
Colorless crystals of [(1)Cu(C2H4)][SbF6] and [(2)Cu-
(C2H4)][SbF6] suitable for X-ray analysis were obtained from
concentrated CH2Cl2 solutions of these compounds under 1
bar of ethylene at −18 °C. Crystals of [(1)Cu(C2H4)][SbF6]
and [(2)Cu(C2H4)][SbF6] belong to the triclinic space group
1
ized by H, 13C{1H}, and 19F NMR spectroscopy, Elemental
Analysis and electrospray ionization (ESI) mass spectrometry
(and also structurally characterized vide infra).
The 1H NMR spectrum of [(1)Cu(C2H4)][SbF6] in
ethylene-saturated CD2Cl2 displayed a resonance at 3.12 ppm
corresponding to the ethylene coordinated to the copper
center. The 13C{1H} NMR resonance for the coordinated
ethylene was observed at 85.3 ppm, an upfield shift of 38 ppm
relative to free ethylene (123.5 ppm).1,11a−c,e It is noteworthy
P1 (see Figure 4 and Table 2 for selected bond lengths and
̅
angles).
Scheme 4. Reaction of Compound [(1)Cu(C2H4)][PF6] with C2H4 (3−5 bar)
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Scheme 5. Synthesis of [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]
Figure 4. Molecular structures of [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]. Thermal ellipsoids are drawn at the 50% probability level. All
hydrogen atoms and the [SbF6]¯ counterions have been omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]
[(1)Cu(C2H4)][SbF6]
[(2)Cu(C2H4)][SbF6]
C1−C2
N1−C9
Cu1−N1
Cu1−N2
1.352(3)
1.267(3)
2.3085(19)
2.036(2)
2.0611(18)
91.09(7)
89.01(7)
95.85(8)
−1.5(3)
1.6(3)
C1−C2
N1−C9
N2−C19
N3−C29
Cu1−N1
Cu1−N2
Cu1−N3
N1−Cu1−N2
N1−Cu1−N3
N2−Cu1−N3
C9−C10−C11−C16
C19−C20−C21−C26
C29−C30−C31−C36
1.347(6)
1.282(5)
1.268(5)
1.273(5)
2.030(3)
2.083(3)
2.128(3)
94.47(12)
91.46(12)
92.30(12)
−0.7(6)
−1.7(6)
0.3(6)
Cu1−N3
N1−Cu1−N2
N1−Cu1−N3
N2−Cu1−N3
C9−C10−C15-F1
C17−C18−C23−F5
C25−C26−C31−F9
1.1(3)
In both [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]
one molecule of ethylene is coordinated to Cu(I) in the typical
η2-fashion.11b−e,12a The ethylene protons were located on the
difference map and were refined isotropically. The C−C
distance of coordinated ethylene is 1.325(3) Å and 1.347(6) Å
in [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6], respec-
tively, which does not differ significantly from the correspond-
ing distance in free ethylene [1.3369(16) Å],11b,f,16 consistent
with the weak nature of the Cu−C2H4 interaction. This
observation supports the hypothesis that the upfield chemical
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shifts observed in the 1H and 13C{1H} NMR spectra are largely
due to anisotropic ring effects originating from the aromatic
arms rather than back-donation from the metal center.
The X-ray structure of [(1)Cu(C2H4)][SbF6] reveals a
sterically constrained pocket around the fourth coordination
site of the Cu(I) center, in which the arms adopt the expected
trans imine geometry. By contrast, the structure of [(2)Cu-
(C2H4)][SbF6] shows two imine arms with the expected trans
geometry, and the third imine arm with a cis geometry.
To investigate the origins of the geometry differences in
structures [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6],
the complexes were modeled computationally. Crystal structure
geometries were used to generate input files, modifying
substituents as required to access a range of different
conformers for the trans,trans,trans- and trans,trans,cis- geo-
metric isomers of the [(1)Cu(C2H4)][SbF6] and [(2)Cu-
(C2H4)][SbF6] respectively (see Table 3 and Figure 5).
Geometry optimizations were carried out on isolated molecules
using Jaguar18 and the standard B3LYP density functional19
with a 6-31G* basis set on all atoms apart from copper, where
the LACV3P basis set was implemented. Since the main aim
was to compare the different possible conformers, frequency
calculations were not performed. It was deemed unlikely that
these large complexes of low symmetry would optimize to a
saddle point. Dispersion corrections were calculated in
ORCA20 for the B3LYP-D21 approach and added to the Jaguar
energies; geometries were not reoptimized in this case.
The calculated energy differences are within computational
error, and it may be concluded that all conformers are likely to
be accessible in solution, the different structures observed
crystallographically due not to significant energy differences
between conformers but to more subtle effects such as crystal
packing.
CONCLUSION
■
A new bulky facially coordinating N3-donor tach-based ligand
cis,cis-1,3,5-tris(2-fluoro-6-(trifluoromethyl)benzylideneamino)-
cyclohexane 1 has been obtained. Reaction of 1 with
[Cu(NCMe)4][PF6] gave the complex [(1)Cu(NCMe)][PF6]
In which displacement of the acetonitrile ligand is possible with
CO and C2H4 (3−5 bar). Cu(I)-ethylene complexes of ligands
1 and cis,cis-1,3,5-(mesitylideneamino)cyclohexane 2 were
prepared by treatment of the ligands with CuBr and AgSbF6
in the presence of ethylene, the absence of other potentially
coordinating ligands such as acetonitrile being essential for
clean reactions. These complexes display reversible complex-
ation of the ethylene molecule under mild changes to pressure,
suggesting possible application in olefin separation and
extraction.
Table 3. Comparison of Relative Energies of the
trans,trans,cis- and trans,trans,trans-Geometry of Complexes
a
[(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]
relative energy (/kcalmol−1) of
isolated molecules
DFT DFT-D
trans,trans,cis-[(2)Cu(C2H4)][SbF6]:
0.00
0.22
1.01
0.35
0.00
0.27
2.21
0.00
0.00
0.95
1.64
1.44
from crystal
structure
2A
trans,trans,trans-[(2)Cu(C2H4)]
[SbF6]: 2B
trans,trans,trans-[(1)Cu(C2H4)]
[SbF6]: 1A
from crystal
structure
trans,trans,cis-[(1)Cu(C2H4)][SbF6]:
1B
trans,trans,cis-[(1)Cu(C2H4)][SbF6]:
1C
EXPERIMENTAL DETAILS
■
trans,trans,cis-[(1)Cu(C2H4)][SbF6]:
1D
General Considerations. All operations were carried out under an
inert atmosphere of Ar or N2 using standard Schlenk line techniques
or an MBraun glovebox MB-BL-01. Dry N2-saturated solvents were
purified using an anhydrous engineering Grubbs-type solvent system.
A Parr Instrument Company Autoclave (0.3L) was used for reactions
a
Because of the asymmetry of the aryl substituents in complex
[(1)Cu(C2H4)][SbF6], there are three possible conformations, for
trans,trans,cis- geometry, the energies of which are listed in the table.
Figure 5. Imine geometric isomers of [(1)Cu(C2H4)][SbF6] and [(2)Cu(C2H4)][SbF6]. Input files for 2A (trans,trans,cis-) and 1A
(trans,trans,trans-) were generated directly from crystallographic data; 2B (trans,trans,trans-) was modeled by modification of crystallographic data
for [(1)Cu(C2H4)][SbF6]. Because of the asymmetry of the aryl substituents in [(1)Cu(C2H4)][SbF6], three conformers of the (trans,trans,cis-)
geometry were considered (1B, 1C, and 1D), modeled from crystallographic data for [(2)Cu(C2H4)][SbF6].
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under high pressure (5−10 bar). NMR spectra of complexes under a
pressure of ethylene were recorded in a 5 mm Heavy Wall (Pressure/
Vacuum) Value NMR Sample tube (7″ L) 522-PV-7 (Wilmad).
Chemicals were obtained from Sigma-Aldrich and used without further
purification unless otherwise stated. Ethylene (99.92%) was obtained
from BOC UK.
CF3), −73.19 (d, 6F, 1JPF 708.76 Hz, PF6), and −110.54 (s, 3F, Ar-F).
ESI mass spectrometry: calculated exact mass for C32H24CuF12N3·PF6:
900.07. Found: m/z 714.09 [M-(-NCCH3, PF6)]+. ESI HR mass
spectrum: m/z 714.0834 [M-(-NCCH3, PF6)]+ (calcd 714.0838).
Elemental analysis: calcd (%) for C32H24CuF12N4·PF6: C, 42.65. H,
2.68, N, 6.22. Found: C, 41.42. H, 2.83. N, 6.40.
All the X-ray diffraction experiments were carried out at 100 K on a
Bruker Apex II Kappa CCD diffractometer using Mo Kα radiation (λ =
0.71073 Å). Intensities were integrated from several series of exposures
measuring 0.5° in ω or φ using the Apex II or proteum programs.
Absorption corrections were based on equivalent reflections using
Synthesis of [(1)Cu(CO)][PF6]. Carbon monoxide was bubbled
through a CH2Cl2 solution (5 mL) of [(1)Cu(NCCH3)][PF6] (0.05 g,
0.06 mmol) for 30 min to give a light yellow solution. The product was
precipitated by addition of n-hexane (10 mL), collected and dried
under stream of carbon monoxide to afford [(1)Cu(CO)][PF6]
(0.047 g, 95%) as a pale yellow solid. 1H NMR (399.77 MHz,
2
SADABS, and structures were refined against all Fo data with
3
CD2Cl2): δ 8.67 (s, 3H, HCN), 7.61 (t, 3H, JHH 7.91 Hz, H4-Ar),
hydrogen atoms (on carbon atoms) riding in positions calculated using
SHELXL.22
7.59 (m, 3H, H3-Ar), 7.26 (m, 3H, H5-Ar), 4.39 (s, 3H, −CH-N=),
2
2.58 (dt, 3H, JHH 15.15 Hz, 3JHH 3.79 Hz, trans-CHH-), and 2.16 (d,
Microanalyses were carried out by the Microanalytical Laboratory of
the School of Chemistry at the University of Bristol. Mass spectra were
recorded on a VG Analytical Quattro spectroscope (ESI) by the Mass
Spectrometry Service at the University of Bristol. 19F, 13C{1H}, and 1H
NMR spectra were recorded at 25 °C in deuterated solvents to provide
the field/frequency lock. 13C{1H} and 1H NMR spectra were
referenced to residual NMR solvent peaks; chemical shifts are
reported in parts per million (ppm) relative to tetramethylsilane
standard. 19F NMR spectra are reported in ppm relative to BF3·OEt2
standard.
2
3H, JHH 14.90 Hz, cis-CHH-). 13C{1H} NMR (100.63 MHz,
1
CD2Cl2): δ 159.4 (d, JCF 252.90 Hz, Ar-C2), 159.3 (s, CN),
2
2
133.0 (d, JCF 9.23 Hz, Ar-C3), 130.0 (q, JCF 32.29 Hz, Ar-C6), 127.2
4
1
(d, JCF 9.23 Hz, Ar-C5), 123.5 (q, JCF 274.00 Hz, Ar-CF3), 122.4 (s
br, Ar-C1), 120.2 (d, 3JCF 22.50 Hz, Ar-C4), 66.2 (s, Cy-CH), and 36.2
(s, Cy-CH2). 19F NMR (282.78 MHz, CD2Cl2): −58.69 (s, 9F, Ar−
CF3), −73.26 (d, 6F, 1JPF 708.76 Hz, PF6) and −110.81 (s, 3F, Ar-F).
IR/cm−1 (CD2Cl2): ν coordinated (CO) 2094 s, ν free (CO) 2143 m.
ESI mass spectrometry: calcd exact mass for C31H21CuF12N3O·PF6:
887.04. Found: m/z 714.09 [M-(−CO, PF6)]+, 742.08 [M-(PF6)]+.
ESI HR mass spectrum: m/z 714.0834 [M-(−CO, PF6)]+ (calcd
714.0836), 742.0783 [M-(−CO, PF6)]+ (calcd 742.0762).
Synthesis of cis,cis-1,3,5-Tris(2-fluoro-6-(trifluoromethyl)-
benzylideneamino)cyclohexane 1. cis,cis-1,3,5-Triaminocyclohex-
ane·3HBr (0.5 g, 1.3 mmol) was dissolved in a solution of 3 equiv of
sodium hydroxide (0.16 g, 3.9 mmol) in water (10 mL), followed by
addition of toluene (30 mL) and 3 equiv of 2-fluoro-6-
(trifluoromethyl)benzaldehyde (0.41 mL, 3.9 mmol). The reaction
was heated to 150 °C in an oil bath for 18 h, during which time water
was removed via azeotropic distillation with a Dean−Stark trap. The
solution was allowed to cool, passed through a short Celite plug, and
concentrated under reduced pressure to leave a pale yellow solid. The
crude material was recrystallized from a minimum volume of hot
diethyl ether and dried in vacuo. 1 (0.73 g, 86% yield) was obtained as
Synthesis of [(1)Cu(C2H4)][PF6]. A high pressure NMR tube,
charged with CD2Cl2 (0.3 mL) and [(1)Cu(NCCH3)][PF6] (0.05 g,
0.06 mmol), was pressurized with ethylene (3−5 bar). 1H NMR
3
(299.90 MHz, CD2Cl2): δ 8.43 (s, 3H, HCN), 7.53 (t br, 3H, JHH
7.57 Hz, H4-Ar), 7.44 (d br, 3H, 3JHH 7.40 Hz, H5-Ar), 7.20 (m br, 3H,
H3-Ar), 5.27 (s, free C2H4), 4.20 (s, 3H, −CH-N=), 3.11 (s br,
2
3
coordinated C2H4), 2.44 (dt, 3H, JHH 14.27 Hz, JHH 3.70 Hz, trans-
2
CHH-), 2.07 (d br, 3H, JHH 14.27 Hz, cis-CHH-), and 1.19 (s,
-NCCH3).
1
a white microcrystalline solid. H NMR (399.77 MHz, CD2Cl2): δ
Synthesis of [(1)Cu(C2H4)][SbF6]. Dry, degassed CH2Cl2 (10
mL) was added to CuBr (0.15 g, 1.0 mmol), AgSbF6 (0.37 g, 1.0
mmol), and 1 (0.65 g, 1.0 mmol) in an autoclave. The mixture was
stirred under positive pressure of ethylene (5−10 bar) for 8 h. The
mixture was passed through a plug of Celite. The resulting colorless
solution was reduced to 3 mL under a stream ethylene and layered
with n-hexane to give colorless crystals of [(1)Cu(C2H4)][SbF6] (0.85
g, 80%) after 20 h at −18 °C. 1H NMR (399.77 MHz, CD2Cl2): δ 8.66
(s, 3H, HCN), 7.58 (t br, 3H, 3JHH 8.36 Hz, H4-Ar), 7.51 (d br, 3H,
3JHH 8.36 Hz, H5-Ar), 7.35 (m br, 3H, H3-Ar), 5.33 (s, free C2H4), 4.30
4
8.64 (q, 3H, JHF 2.69, HCN), 7.49 (m, 6H, Hmeta-Ar), 7.33 (m br,
3
3
3H, Hpara-Ar), 3.72 (tt, 3H, JHH 11.39 Hz, JHH 3.91 Hz, −CH-N=),
2.16 (q, 3H, 2JHH 11.97 Hz, trans-CHH-), and 2.02 (m, 3H, 2JHH 11.97,
3JHH 3.67 Hz, cis-CHH-). 13C{1H} NMR (100.63 MHz, CD2Cl2): δ
160.9 (d, 1JCF 253.29 Hz, Ar-C2), 152.2 (s, CN), 130.7 (d, 2JCF 9.23
2
4
Hz, Ar-C3), 130.3 (q, JCF 32.85 Hz, Ar-C6), 123.9 (d, JCF 13.80 Hz,
1
Ar-C5), 123.5 (q, JCF 274.00 Hz, Ar-CF3), 121.9 (s br, Ar-C1), 120.2
(d, 3JCF 22.50 Hz, Ar-C4), 67.4 (s, Cy-CH), and 39.9 (s, Cy-CH2). 19
F
NMR (282.78 MHz, CD2Cl2): δ −57.75 (s, 9F, Ar−CF3) and −112.81
(s, 3F, Ar-F). ESI mass spectrometry: calculated exact mass for
C30H21F12N3: 651.15. Found: m/z 674.14 [M+Na]+, 652.16 [M+H]+.
ESI HR mass spectrum: m/z 674.1436 [M+Na]+ (calcd 674.1449),
652.1635 [M+H]+ (calcd 652.1616). Elemental analysis: calcd (%) For
C30H21F12N3: C, 55.31. H, 3.25. N, 6.45. Found: C, 55.38. H, 3.59. N,
6.14.
2
(s br, 3H, −CH-N=), 3.12 (s, coordinated C2H4), 2.55 (dt, 3H, JHH
3
2
15.37 Hz, JHH 4.15 Hz, trans-CHH-), and 2.18 (d br, 3H, JHH 15.40
Hz, cis-CHH-). 13C{1H} NMR (125.71 MHz, CD2Cl2): δ 160.2 (d,
1JCF 252.93 Hz, Ar-C2), 157.8 (s, CN), 132.0 (d, JCF 9.24 Hz, Ar-
2
2
4
C3), 129.9 (q, JCF 32.19 Hz, Ar-C6), 127.0 (d, JCF 9.23 Hz, Ar-C5),
1
3
123.5 (q, JCF 272.80 Hz, Ar-CF3), 122.3 (s, Ar-C1), 120.2 (d, JCF
22.26 Hz, Ar-C4), 85.3 (s, coordinated C2H4), 66.4 (s, Cy-CH), and
35.5 (s, Cy-CH2). 19F NMR (282.78 MHz, CD2Cl2): δ −59.19 (s, 9F,
-CF3) and −112.19 (s, 3F, CF). ESI mass spectrometry: calcd exact
mass for C32H25CuF12N3.SbF6: 977.00. Found: m/z 742.10 [M-
(SbF6)]+, 714.09 [M-(−C2H4, SbF6)]+. ESI HR mass spectrum: m/z
742.1147 [M-(SbF6)]+ (calcd 742.1147). Elemental analysis: calcd (%)
for C32H25CuF12N3.SbF6: C, 39.27. H, 2.57. N, 4.29. Found: C, 39.08.
H, 2.43. N, 4.25.
Synthesis of [(1)Cu(NCCH3)][PF6]. 1 (0.10 g, 0.15 mmol) was
dissolved in CH2Cl2 (5 mL), and an equivalent amount of
[Cu(NCMe)4][PF6] (0.06g, 0.15 mmol) in CH2Cl2 (5 mL) was
added dropwise. An instantaneous color change from pale to intense
yellow was observed. The reaction was stirred for 30 min under an
inert atmosphere at room temperature. The product was precipitated
by addition of n-hexane, collected by filtration, and dried in vacuo to
obtain [(1)Cu(NCCH3)][PF6] (0.13 g, 97%) as a bright yellow
1
powder. H NMR (399.77 MHz, CD2Cl2): δ 8.47 (s, 3H, HCN),
Synthesis of [(2)Cu(C2H4)][SbF6]. Dry, degassed CH2Cl2 (10
mL) was added to CuBr (0.15 g, 1.0 mmol), AgSbF6 (0.38 g, 1.0
mmol), and 2 (0.52 g, 1.0 mmol) in an autoclave. The mixture was
stirred under positive pressure of ethylene (5−10 bar) for 10 h. The
mixture was passed through a plug of Celite. The resulting colorless
solution was reduced to 3 mL under a stream of ethylene and layered
with n-hexane to give colorless crystals of [(2)Cu(C2H4)][SbF6] (0.70
g, 83%) after 20 h at −18 °C. 1H NMR (399.77 MHz, CD2Cl2): δ 8.53
(s, 3H, HCN), 6.73 (s, 6H, Hmeta-Ar), 5.28 (s, free C2H4), 4.13 (s br,
7.57 (m br, 3H, H4-Ar), 7.50 (m, 3H, H4-Ar), 7.24 (m, 3H, H5-Ar),
4.24 (s br, 3H, −CH-N=), 2.47 (dt, 3H, 2JHH 15.15 Hz, 3JHH 4.00 Hz,
2
trans-CHH-), 2.12 (d br, 3H, JHH 14.66 Hz, cis-CHH-), and 1.24 (s,
3H, -NCCH3). 13C{1H} NMR (100.63 MHz, CD2Cl2): δ 159.9 (d,
2
1JCF 253.29 Hz, Ar-C2), 155.5 (s, CN), 131.9 (d, JCF 9.23 Hz, Ar-
2
4
C3), 130.1 (q, JCF 32.85 Hz, Ar-C6), 124.5 (d, JCF 13.80 Hz, Ar-C5),
1
2
123.5 (q, JCF 274.00 Hz, Ar-CF3), 121.6 (s br, Ar-C1), 119.8 (d, JCF
22.50 Hz, Ar-C4), 67.4 (s, Cy-CH), 39.9 (s, Cy-CH2) and 1.1 (s,
-NCCH3). 19F NMR (282.78 MHz, CD2Cl2): δ −58.83 (s, 9F, Ar−
2
3H, −CH-N=), 3.09 (s, 3H, coordinated C2H4), 2.50 (dt, 3H, JHH
3770
dx.doi.org/10.1021/ic302325u | Inorg. Chem. 2013, 52, 3765−3771

Inorganic Chemistry
Article
15.19 Hz, 3JHH 4.47 Hz, trans-CHH-), 2.13 (s, 9H, para-ArCH3), 2.01
(s, 18H, ortho-ArCH3), and 1.95 (d, 3H, JHH 14.85 Hz, cis-CHH).
Barteau, M. A. Angew. Chem., Int. Ed. 2004, 43, 2918−2921. (d) Torres,
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509−522. Bidentate ligands: (c) Adiraju, V. A. K.; Flores, J. A.;
Yousufuddin, M.; Dias, H. V. R. Organometallics 2012, 31, 7926−7932.
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2009, 28, 6721−6731. (f) Dai, X.; Warren, T. H. Chem. Commun.
2001, 1998−1999. (g) Stamp, L.; tom Dieck, H. Inorg. Chim. Acta
1987, 129, 107−114. (h) Munakata, M.; Kitagawa, S.; Kosome, S.;
Asahara, A. Inorg. Chem. 1986, 25, 2622−2627. (i) Strauß, B. F.;
Eisentrager, F.; Hofmann, P. Chem. Commun. 1999, 2507−2508.
Tridentate ligands: (j) Thompson, J. S.; Whitney, J. F. Inorg. Chem.
1984, 23, 2813−2819. (k) Dias, H. V. R.; Lu, H.; Kim, H.; Polach, S.
A.; Goh, T. K. H. H.; Browning, R. G.; Lovely, C. J. Organometallics
2002, 21, 1466−1473. (l) Dias, H. V. R.; Singh, S. Inorg. Chem. 2004,
43, 5786−5788. (m) Dias, H. V. R.; Wang, X. Dalton Trans. 2005,
2985−2987. (n) Dias, H. V. R.; Wu, J. Eur. J. Inorg. Chem. 2008, 509−
522. (o) Masuda, H.; Yamamoto, N.; Taga, T.; Machida, K.; Kitagawa,
S.; Munakata, M. J. Organomet. Chem. 1987, 322, 121−129. (p) Kou,
X.; Dias, H. V. R. Dalton Trans. 2009, 7529−7536. (q) Martin, C.;
Munoz-Molina, J. M.; Locati, A.; Alvarez, E.; Maseras, F.; Belderrain,
T. R.; Perez, P. J. Organometallics 2010, 29, 3481−3489.
2
13C{1H} NMR (100.63 MHz, CD2Cl2): δ 166.1 (s, CN), 139.5 (s,
Ar-Cpara), 135.1 (s, Ar-Cortho), 132.3 (s, Ar-Cipso), 128.5 (s, Ar-Cmeta),
85.8 (s, coordinated C2H4), 65.7 (s, Cy-CH), 32.8 (s, Cy-CHH), 20.7
(s, ortho-ArCH3), and 19.4 (s, para-ArCH3). ESI mass spectrometry:
calcd exact mass for C38H49CuN3.SbF6: 845.22. Found: m/z 582.29
[M-(C2H4, SbF6)]+. ESI HR mass spectrum: m/z 582.2904 [M-(C2H4,
SbF6)]+ (calcd 582.2909).
ASSOCIATED CONTENT
* Supporting Information
Crystallographic details and cif files. This material is available
■
S
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: Duncan.Wass@bristol.ac.uk.
■
Notes
The authors declare no competing financial interest.
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