Demonstration of remote steric differentiation of cis/trans alkene coordination in copper(i) complexes of aryl-substituted bis(2-pyridyl)amine

Article abstract of DOI:10.1039/c0dt01301c

Complexes of the type [Cu(R-dpa)(η²-olefin)]BF₄ (R = Mes and 2-ⁱPrC₆H₄) for cis- and trans- isomers of 3-octene, as well as those for cis- and trans-4-octene (R = 2- ⁱPrC₆H₄) have been prepared and characterized by ¹H and ¹³C NMR, FTIR, and TGA. The crystal structure of [Cu(Mes-dpa)(η²-trans-3-octene)]BF₄ (2) has been determined via X-ray crystallography. The asymmetric unit in the crystal lattice of 2 contains two unique conformations of the complex cation related by a pseudo center of symmetry, which differ primarily in the orientation of the olefin with respect to the rest of the molecule. The ¹H and ¹³C NMR spectra of [Cu(Ar-dpa)(η²-olefin)]BF ₄ exhibit olefin resonances shifted upfield with respect to free olefin. The difference in Δδ(¹³C) relative magnitudes between cis- and trans- complexes, i.e., the binding, correlates with the degree of substitution at the amine nitrogen. The identity of the remote ligand substituent (Ar) controls the differentiation of binding between cis and trans isomers as a consequence of increased folding of the Ar-dpa ligand along the Cu...N axis.

Full text of DOI:10.1039/c0dt01301c

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PAPER
Demonstration of remote steric differentiation of cis/trans alkene
coordination in copper(I) complexes of aryl-substituted bis(2-pyridyl)amine†
John J. Allen and Andrew R. Barron*
Received 28th September 2010, Accepted 26th November 2010
DOI: 10.1039/c0dt01301c
2
Complexes of the type [Cu(R-dpa)(h -olefin)]BF4 (R = Mes and 2-iPrC6H4) for cis- and trans- isomers
of 3-octene, as well as those for cis- and trans-4-octene (R = 2-iPrC6H4) have been prepared and
characterized by 1H and 13C NMR, FTIR, and TGA. The crystal structure of
2
[Cu(Mes-dpa)(h -trans-3-octene)]BF4 (2) has been determined via X-ray crystallography. The
asymmetric unit in the crystal lattice of 2 contains two unique conformations of the complex cation
related by a pseudo center of symmetry, which differ primarily in the orientation of the olefin with
2
respect to the rest of the molecule. The 1H and 13C NMR spectra of [Cu(Ar-dpa)(h -olefin)]BF4 exhibit
olefin resonances shifted upfield with respect to free olefin. The difference in Dd(13C) relative
magnitudes between cis- and trans- complexes, i.e., the binding, correlates with the degree of
substitution at the amine nitrogen. The identity of the remote ligand substituent (Ar) controls the
differentiation of binding between cis and trans isomers as a consequence of increased folding of the
Ar-dpa ligand along the Cu ◊ ◊ ◊ N axis.
olefins to a metal center in processes such as reactive extractive
Introduction
distillation and reactive absorption to a supported medium offer
As the largest volume feedstock in the chemical and petrochemical
potential alternatives in overcoming the issues inherent with their
separation.5
industry, olefins are used in the production of polymers, acids,
alcohols, esters, and ethers. Unfortunately, olefin production is
extremely energy intensive, generally requiring separation from
their alkane counterparts (olefin/paraffin separation).1 More
problematic is the separation of particular olefins from a mixture,
considering the range of phase-transition temperatures for a
given set of isomers is usually small. For instance, the◦seven n-
octene isomers have a boiling range of 121.3–125.6 C.2 The
large volumes of olefins produced and the required purity for
most applications provides strong incentives for novel purification
approaches. The use of chemically specific separation reagents is a
potentially inexpensive and efficient approach for separation.3 The
development of metal complexes incorporating sterically directive
ancillary ligands tailored to the selective removal of olefins from
their isomeric counterparts is currently of great interest in the
petroleum/petrochemical industries.
In designing a suitable coordination system for olefins, several
groups have based the system on a biological model for ethylene
complexation.6,7 These studies have also demonstrated that stable
Cu ◊ ◊ ◊ olefin interactions can be achieved using multidentate, elec-
tron rich N-donor ligands.8–10 The class of ligand most commonly
used for robust, yet reversibly bound olefin complexes, is the
neutral N-donor heterocyclic compounds.11–15 Of these, it was the
report by Thompson and Whitney that has formed the basis for
our studies.16,17 They showed that stable copper complexes with
ethylene are formed with the chelate ligand bis(2-pyridyl)amine
(H-dpa, I where R = H).
The control over the selective binding of olefins to a metal
center has the potential as a simple route to overcoming the
inherent difficulty in the separation of different olefins with near
identical boiling points. To this end, various complexing reagents
have been described,4 where the function of the complexing
agent is to coordinate one particular isomer of an olefin in
preference to another.5 The control over the selective binding of
Our previous studies16,18 have shown that steric hindrance
between the olefin and H-dpa manifests as both a twisting of
the olefin out of the plane of the H-dpa ligand and a concomitant
folding of the H-dpa ligand. During a study of the consequences of
increased steric effects in quinolyl analogs we have observed that
Department of Chemistry, Rice University, Houston, Texas, 77005, USA.
E-mail: arb@rice.edu
† CCDC reference numbers 733204 (2). For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c0dt01301c
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the presence of a sterically hindered aryl group on the amine ni-
trogen results in a further distortion about the amine nitrogen.19,20
Subsequently we have prepared a range of N-substituted bis(2-
pyridyl)amines, and studied the effects of aryl steric bulk with
regard to olefin binding. For a range of olefin complexes, [Cu(Ar-
dpa)(olefin)]+, it was found that the distortion of pyridyl ring
geometries about the copper centers, and concomitant bending
of the aryl groups away from the Cu ◊ ◊ ◊ N(amine) vectors, resulted
in a folding of the R-dpa ligand. Furthermore, as may be seen
from Fig. 1, there is a clear steric consequence of the butterfly
conformation of the Ar-dpa ligand on the olefin ligand. Based
upon this observation we proposed that the complexation of a
mono-substituted or cis-substituted olefin should be favored over
complexation of a trans-substituted olefin in complexes where the
Ar-dpa ligand has the most distortion due to a sterically large aryl
substituent (Ar). Thus, for the trans-olefin (II) there will be inter-
ligand interactions irrespective of the olefin conformation, while
for a cis-olefin (III) the substituents could adopt a conformation
that limits steric interactions.
Results and discussion
The reaction of [Cu(MeCN)4]BF4 with either cis or trans 3-octene
in the presence of the appropriate Ar-dpa results in the formation
of the olefin complex, [Cu(Ar-dpa)(h -olefin)]BF4 (eqn (1)) where
2
Ar = H for cis-3-octene and trans-3-octene;16 Ar = Mes for cis-3-
octene (1) and trans-3-octene (2); Ar = 2-iPrC6H4 for cis-3-octene
(3) and trans-3-octene (4). In addition the 4-octene derivatives were
prepared, where Ar = 2-iPrC6H4 for cis-4-octene (5) and trans-4-
octene (6). New compounds 1–6 are soluble in alcohols and show
instability in air and have been characterized by 1H and 13C NMR,
FT-IR, and TG/DTA. The crystal structure of compound 2 has
been determined.†
[Cu(MeCN)4]BF4 + Ar-dpa + olefin →
(1)
2
[Cu(Ar-dpa)(h -olefin)]BF4 + 4 MeCN
The structures of the two unique conformations of the complex
2
cation, [Cu(Mes-dpa)(h -trans-3-octene)]+, in compound 2 are
shown in Fig. 2. The two conformations are related by a pseudo
center of symmetry, i.e., a non-crystallographic inversion center,
but are shown to be unique in other structural aspects. Selected
bond lengths and angles are compared in Table 1. Both conformers
exhibit a pseudo-trigonal planar geometry about copper centers,
with coordination sites occupied by the two pyridine nitrogen
atoms and the midpoint of the olefin C C bond. The copper
atoms are each coordinated to two pyridine nitrogen atoms and
the olefin; consistent with three-coordinate Cu(I) cation. The
Cu–N distances are within experimental error of the analogous
17
˚
ethylene and cyclohexene complexes [1.949(3)–1.973(3) A]. In
a similar manner the Cu–C distances overlap the range for
17
˚
the previously reported derivatives [1.972(5)–2.064(2) A]. The
structure of compound 2 fits in with the other olefin complexes
we have structurally characterized. As may be seen from Fig. 3,
there is a correlation between the Cpy–N–Cpy¢ bond angle and both
the fold of the Ar-dpa ligand (i.e., the mean-plane angle difference
between pyridyl rings), as well as the out of plane bend of the aryl
substituent (i.e., the angle resulting from Cu ◊ ◊ ◊ Namine–CAr).
1
Munakata et al. have previously demonstrated that H NMR
can be used to assess the binding efficacy of various ligand/olefin
combinations in Cu(I) olefin complexes,15 while we have previously
used similar methods for Lewis acid–base complexes.21 We have
Fig.
1
An example of the folding of the Ar-dpa ligand in the
◦
[Cu(Mes-dpa)(h -styrene)]+ cation as viewed along the Cu ◊ ◊ ◊ N vector.
Adapted from J. J. Allen, C. E. Hamilton, and A. R. Barron, Dalton
Trans., 2010, DOI: 10.1039/c0dt00608d.
2
˚
Table 1 Selected bond lengths (A) and angles ( ) in the unique conform-
ers of compound 2
Molecule 1
Molecule 2
Cu–C
Cu–C¢
Cu–N
2.038(7)
2.014(7)
1.967(5)
1.936(5)
1.36(1)
1.435(9)
1.429(8)
1.423(8)
92.9(2)
2.016(8)
2.059(6)
1.980(5)
1.991(6)
1.39(1)
1.416(9)
1.439(9)
1.487(8)
92.5(2)
In our previous work we have shown that the 1H and 13C
NMR spectra of [Cu(H-dpa)(olefin)]BF4 exhibit an upfield shift
in the olefin signal as compared to free olefin. A comparison of
the Dd values for olefins with olefin dissociation temperatures
(as determined by TG/DTA) confirms that the shift of the
olefin NMR resonances upon coordination is associated with the
binding strength of the complex, making this a simple method for
comparing the binding of isomers.
The results reported herein are aimed at determining the
differentiation in binding between cis and trans olefins by N-
substituted bis(2-pyridyl)amine copper complexes. In particular
the effect of the aryl substituent on the binding of cis versus trans
isomers of 3- and 4-octene.
Cu–N¢
C–C¢
N–CAr
N–Cpy
N–Cpy¢
N–Cu–N¢
C–Cu–C¢
Cpy–N–Cpy¢
Cpy–N–C
39.3(3)
40.0(3)
125.2(6)
119.3(5)
115.5(5)
156.0(5)
11.2(6)
122.5(6)
121.8(5)
115.1(6)
159.0(5)
2.5(7)
C
py¢–N–C
Cu ◊ ◊ ◊ N–CAr
Twist
DMPLN(py-py¢)
32.2(4)
34.5(4)
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Fig. 3 Correlation between aspects of structural geometries in copper
complexes of aryl-functionalized dipyridylamines.
Fig. 4 Change in 13C NMR olefin chemical shifts (Dd) upon coordination
2
in complexes [Cu(Ar-dpa)(h -olefin)]BF4 as a function of decomposition
temperature.
Table 2 Olefin dissociation temperatures and change in 13C NMR
chemical shift for olefin signals upon coordination in complexes [Cu(Ar-
2
dpa)(h -olefin)]BF4
Fig. 2 Molecular structures of the two unique cation conformers in 2.
Thermal ellipsoids are shown at the 30% level, and hydrogen atoms are
omitted for clarity.
Ar
Olefin
Dd CY (ppm) Dd Cz (ppm)
Td (◦C)
H
H
Mes
Mes
cis-3-octene
trans-3-octene
cis-3-octene
trans-3-octene
27.80
24.80
24.01
20.06
26.07
16.46
24.20
17.85
27.40
25.00
23.68
19.95
25.78
16.35
—
143–146
144–146
135–137
123–125
134–136
122–124
136–138
121–123
previously shown that the change in NMR shift correlates with the
decomposition temperature (Tdec) of the complex that is associated
with the dissociation of the olefin. Thus, the change in chemical
shift is a direct measure of the relative bonding energy of an
olefin to the copper complex. However, for the present class of
compounds (i.e., internal olefins) the shift in the 13C NMR provides
a better comparison (Fig. 4).
The 13C NMR spectra of [Cu(Ar-dpa)(olefin)]BF4 exhibits
an upfield shift in the olefin signal as compared to free olefin
(consistent with the difference between complexed and free olefin).
In simple terms, the further upfield (lower d) peaks are, the
more complexed the olefin. Consideration of the data in Table 2
shows that the change in the 13C NMR shifts upon coordination
is greater for the cis isomers than the trans isomers. Thus, the
binding of the cis isomer of both 3-octene and 4-octene is stronger
to the copper than the trans isomers. As such this is consistent
2-iPrC6H4 cis-3-octene
2-iPrC6H4 trans-3-octene
2-iPrC6H4 cis-4-octene
2-iPrC6H4 trans-4-octene
—
with the concept that the folded Ar-dpa ligand provides steric
differentiation between trans and cis olefins (i.e., II versus III).
Using the alteration in the 13C NMR shift of the C C unit upon
coordination (Dd), it is possible to compare the differentiation in
binding efficiency as a function of the Ar group. Fig. 5 shows that
while there is a small difference between cis-3-octene versus trans-
3-octene for the parent H-dpa complex, this difference increases
with increased steric bulk, i.e., H < Mes ꢀ 2-iPrC6H4. Again
this result is consistent with our view of steric differentiation as a
consequence of the folding of the Ar-dpa ligand, since we have
previously shown that the folding is increased with increasing
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to the flask containing the ligand, which was stirred to dissolve
i
the solid. cis-3-octene (ca. 4 mL) in PrOH (25 mL) was added
via cannula to the flask containing the copper precursor. After
stirring for one hour, the ligand solution was added to the copper–
olefin mixture, and the combined solutions were stirred under
an argon atmosphere overnight. The solution volume was then
reduced by approximately half under vacuum, warmed gently with
a water bath to redissolve the product, and then filtered through a
medium porosity glass frit to remove insoluble impurities. Argon
was vigorously bubbled through the resulting pale green solution
to further reduce its volume to ca. 15 mL. The solution was
gently warmed to dissolve any precipitate, and upon cooling to
-12 ◦C for several days, afforded 0.292 g colorless semi-crystalline
powder. Yield: 53%. MP (TGA; decomp.) 137–139 ◦C. FTIR (neat,
ATR, cm-1): 3100 (w, aromatic nC–H), 3039 (w, alkene nC–H), 2964
(m, alkyl nC–H), 2929 (m, alkyl nC–H), 2872 (w, alkyl nC–H), 2859
(w, alkyl nC–H), 1600 (s), 1581–1429 (s, aromatic dC C), 1327 (s,
aromatic nC–N), 1233 (m), 1168 (m), 1025 (br vs, nB–F), 930 (w), 909
(w), 856 (w), 777 (s). 1H NMR (298 K; CD3OD): d 8.32 (2H, br s,
6-py), 7.78 (2H, br t, 4-py), 7.20 (2H, s, CH, m-mes), 7.19 (2H, br s,
5-py), 6.57 (2H, br d, 3-py), 5.04 (2H, m, HC CH), 2.38 (3H, s,
p-CH3), 2.02 (6H, s, o-CH3), 1.96 (4H, m, CHCH2), 1.36 (4H,
m, CH2CH2CH3), 1.01 [3H, t, J(H–H) = 7.5 Hz, CHCH2CH3],
0.89 [3H, t, J(H–H) = 7.1 Hz, CH2CH2CH3]. 13C NMR (298 K;
CD3OD): d 156.19, 149.93, 141.98, 141.66, 138.12, 137.59, 132.40,
119.88, 116.48, 108.54 (CHEt), 106.57 (CHCH2), 33.80, 28.84,
23.59, 22.46, 21.32, 17.99, 15.18, 14.36.
Fig. 5 Comparison of averaged Dd C values for olefin resonances in cis-
(ꢀ) and trans- ( ) 3-octene complexes with [Cu(Ar-dpa)(3-octene)]BF4 as
the substituent, Ar is varied.
steric bulk and more importantly steric asymmetry (2-iPrC6H4
versus 2,6-iPr2C6H3). This result suggests that differentiation of
complexation of cis and trans isomers is possible for the 2-
iPrC6H4-dpa ligand complex. It is finally interesting to note that
the difference in binding between cis and trans is greater for the
asymmetrical 3-octene than the symmetrical 4-octene.
Conclusions
We have shown that the complexation of cis and trans olefins to
a copper coordination center can be differentiated by changes of
a remote substituent rather than the coordination pocket per se.
Thus, remote alteration of steric bulk (i.e., the Ar substituent)
results in the folding of the Ar-dpa ligand with a consequential
change in the orientation of the pyridine groups with regard to
the substituents on the olefin. The resulting asymmetry results in
preferential binding of cis olefins (III) over a trans olefin (II).
[Cu(Mes-dpa)(g2-trans-3-octene)]BF4 (2)
This compound was prepared in an analogous manner to that
of (1), using the olefin trans-3-octene. Yield: 45%. MP (TGA;
decomp.) 123–125 ◦C. FTIR (neat, ATR, cm-1): 3123 (w, aromatic
n
n
C–H), 3097 (w, aromatic nC–H), 3043 (w, alkene nC–H), 2960 (w, alkyl
C–H), 2930 (w, alkyl nC–H), 2871 (w, alkyl nC–H), 1599 (s), 1581–1426
(s, aromatic dC C), 1383 (w), 1327 (s, aromatic nC–N), 1234 (m),
1171 (m), 1034 (br vs, nB–F), 931 (w), 908 (w), 881 (w), 777 (s). 1H
NMR (298 K; CD3OD): d 8.30 (2H, br s, py, 6-CH), 7.77 (2H,
br t, py, 4-CH), 7.18 (2H, br s, C6H2), 7.16 (2H, br t, py, 5-CH),
6.55 (2H, br d, py, 3-CH), 5.05 (2H, m, HC CH), 2.37 (3H, s,
p-CH3), 2.00 (4H, m, CHCH2), 1.96 (6H, s, o-CH3), 1.37 (4H,
m, CH2CH2CH3), 1.02 [3H, t, J(H–H) = 7.4 Hz, CHCH2CH3],
0.90 [3H, t, J(H–H) = 7.1 Hz, CH2CH2CH3]. 13C NMR (298 K;
CD3OD): d 156.29, 149.84, 141.98, 141.69, 141.06, 138.04, 132.47,
119.84, 116.49, 113.19, 110.51, 34.05, 33.87, 27.38, 23.24, 21.33,
17.95, 15.48, 14.36.
Experimental
All reagents in this study were used as received from commercial
suppliers and were stored under an argon atmosphere in a drybox.
Precursor complex [Cu(MeCN)4]BF4 was prepared according to
Hathaway et al.22 Aryl-functionalized di-(2-pyridyl)amines (Mes-
dpa and 2-iPrC6H4-dpa) were prepared according to established
methods.17 All solvents were distilled and degassed via freeze–
pump–thaw immediately prior to use. Glassware was thoroughly
cleaned and dried prior to use. All manipulations were performed
under an argon atmosphere using standard Schlenk line tech-
1
niques. H and 13C NMR spectra were obtained at room tem-
[Cu(2-iPrC6H4-dpa)(g2-cis-3-octene)]BF4 (3)
perature using Bruker Avance 400 and 500 MHz spectrometers.
Chemical shifts are reported relative to internal solvent resonances.
IR spectra were obtained using a Nicolet FTIR spectrometer
equipped with ATR accessory. Thermogravimetric analyses were
performed on a Seiko I TG/DTA 200 under an argon gas flow of
15–20 mL min-1.
This compound was prepared in an analogous manner to that
of (1), using the ligand 2-iPrC6H4-dpa. Yield: 49%. MP (TGA;
decomp.) 133–135 ◦C. FTIR (neat, ATR, cm-1): 3120 (w, aromatic
n
C–H), 3073 (w, aromatic nC–H), 3027 (w, alkene nC–H), 2963 (w,
alkene nC–H), 2931 (w, alkyl nC–H), 2870 (w, alkyl nC–H), 1598 (m),
1582–1430 (s, aromatic dC C), 1328 (s, aromatic nC–N), 1282 (w),
1243 (m), 1168 (m), 1050 (br vs, nB–F), 931 (w), 764 (s). 1H NMR
(298 K; CD3OD): d 8.21 (2H, br s, py, 6-CH), 7.82 (2H, br t,
py, 4-CH), 7.62 (1H, m, C6H4), 7.59 (1H, m, C6H4), 7.45 (1H,
br s, C6H4), 7.43 (1H, br s, C6H4), 7.21 (2H, br t, py, 5-CH), 6.87
[Cu(Mes-dpa)(g2-cis-3-octene)]BF4 (1)
In a drybox, [Cu(MeCN)4]BF4 (0.314 g, 1.0 mmol) and Mes-dpa
(0.291 g, 1.0 mmol) were charged to separate Schlenk flasks. After
removal from the drybox, EtOH (20 mL) was added via cannula
1192 | Dalton Trans., 2011, 40, 1189–1194
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(2H, br d, py, 3-CH), 5.02 (2H, m, HC CH), 2.92 [1H, br sept,
CH(CH3)2], 1.95 (4H, m, CHCH2), 1.36 (4H, m, CH2CH2CH3),
1.01 [3H, t, J(H–H) = 7.5 Hz, CHCH2CH3], 0.96 [6H, br d,
CH(CH3)2], 0.89 [3H, t, J(H–H) = 7.1 Hz, CH2CH2CH3]. 13C
NMR (298 K; CD3OD): d 157.66, 149.88, 148.38, 141.66, 140.05,
132.25, 131.76, 130.52, 129.57, 120.68, 118.94, 106.49, 104.47,
33.79, 29.53, 29.05, 23.89, 23.66, 22.61, 15.19, 14.35.
5.06 (2H, m, HC CH), 2.92 [1H, br s, CH(CH3)2], 1.96 (4H,
m, CHCH2), 1.44 [4H, sext, J(H–H) = 7.4 Hz, CH2CH3], 0.98
[6H, br s, CH(CH3)2], 0.93 [6H, t, J(H–H) = 7.4 Hz, CH2CH3].
13C NMR (298 K; CD3OD): d 157.80, 149.67, 148.42, 141.54,
140.26, 132.01, 131.75, 130.54, 129.73, 120.55, 118.73, 113.75,
36.38, 29.47, 24.96, 23.88, 14.04.
Crystallographic studies
[Cu(2-iPrC6H4-dpa)(g2-trans-3-octene)]BF4 (4)
X-ray data for compound 2 was collected at room temperature
on a Bruker SMART 1000 CCD diffractometer equipped with
This compound was prepared in an analogous manner to that
of (1), using the ligand 2-iPrC6H4-dpa and olefin trans-3-octene.
Yield: 39%. MP (TGA; decomp.) 123–125 ◦C. FTIR (neat,
ATR, cm-1): 3123 (w, aromatic nC–H), 3094 (w, aromatic nC–H),
3071 (w, aromatic nC–H), 3037 (w, alkene nC–H), 2961 (w, alkene
˚
graphite monochromated Mo-Ka radiation (l = 0.71073 A) and
a fixed-c 3-circle GGCS configuration, and corrected for Lorentz
and polarization effects. The sample was prepared by suspension
in mineral oil under an inert atmosphere (facilitating separation
and selection of a single crystal), followed by sealing in a thin
layer of epoxy resin and securing to the end of a glass fiber.
The fiber was fastened to a brass pin and mounted onto the
goniometer head. Data collection and unit cell refinement were
carried out according to established methods23 using the program
SMART.24 The program SAINT25 was used for data reduction,
and absorption correction was applied using SADABS.26 Pertinent
details are given in Table 3. The structure was solved by direct
methods, and the model was refined using full-matrix least squares
techniques.27 All non-hydrogen atoms were first refined as having
isotropic thermal parameters, followed by having anisotropic
thermal parameters: shift/error less than 0.01. Refinement of
the noncentrosymmetric structure (space group P21) was per-
formed according to established methods, using TWIN/BASF
instructions.28,29 This treatment (refinement of the structure as
having an inversion twin) refined the absolute structure with a
fractional presence, i.e. Flack ¥ parameter, of 0.45(2), with 6210
(79.9%) measured Friedel pairs. All hydrogen atoms were placed in
n
C–H), 2927 (w, alkyl nC–H), 2870 (w, alkyl nC–H), 1598 (m), 1582–
1431 (s, aromatic dC C), 1324 (s, aromatic nC–N), 1281 (w), 1242
(m), 1170 (m), 1052 (br vs, nB–F), 930 (w), 783 (m), 772 (m), 764
(m). 1H NMR (298 K; CD3OD): d 8.22 (2H, br s, py, 6-CH), 7.80
(2H, br t, py, 4-CH), 7.63 (1H, m, C6H4), 7.60 (1H, m, C6H4), 7.42
(2H, br m, C6H4), 7.18 (2H, br t, py, 5-CH), 6.78 (2H, br d, py, 3-
CH), 5.09 (2H, m, HC CH), 2.91 [1H, br sept, CH(CH3)2], 1.99
(4H, m, CHCH2), 1.36 (4H, m, CH2CH2CH3), 1.02 [3H, t, J(H–
H) = 7.3 Hz, CHCH2CH3], 0.97 [6H, br d, CH(CH3)2], 0.91 [3H,
t, J(H–H) = 7.2 Hz, CH2CH2CH3]. 13C NMR (298 K; CD3OD):
d 157.73, 149.64, 148.44, 141.54, 140.18, 132.04, 131.80, 130.55,
129.80, 120.37, 118.55, 116.59, 114.03, 33.93, 33.85, 29.45, 27.32,
23.88, 23.28, 15.31, 14.38.
[Cu(2-iPrC6H4-dpa)(g2-cis-4-octene)]BF4 (5)
This compound was prepared in an analogous manner to that of
(1), using the ligand 2-iPrC6H4-dpa and olefin cis-4-octene. Yield:
65%. MP (TGA; decomp.) 132–134 ◦C. FTIR (neat, ATR, cm-1):
3127 (w, aromatic nC–H), 3068 (w, aromatic nC–H), 2959 (m, alkyl
˚
calculated positions [C–H (alkene) = 0.98 A, C–H (methylene) =
˚
˚
˚
0.97 A, C–H (methyl) = 0.96 A, and C–H (aromatic) = 0.93 A]
and refined using a riding model with fixed isotropic displacement
parameters. Neutral-atom scattering factors were taken from the
usual source.30 Refinement of positional and anisotropic displace-
ment parameters led to convergence for all data. The program
n
C–H), 2930 (w, alkyl nC–H), 2869 (w, alkyl nC–H), 1599 (m), 1582–
1431 (s, aromatic dC C), 1327 (s, amine nC–N), 1242 (m), 1167 (w),
1057 (br vs, nB–F), 1025 (br vs), 783 (s). 1H NMR (298 K; CD3OD):
d 8.28 (2H, br s, py, 6-CH), 7.82 (2H, br t, py, 4-CH), 7.64 (1H,
m, C6H4), 7.60 (1H, m, C6H4), 7.53 (1H, br s, C6H4), 7.49 (1H,
br s, C6H4), 7.23 (2H, br t, py, 5-CH), 6.88 (2H, br d, py, 3-CH),
5.08 (2H, m, HC CH), 2.97 [1H, br s, CH(CH3)2], 1.93 (4H,
m, CHCH2), 1.42 [4H, sext, J(H–H) = 7.4 Hz, CH2CH3], 0.97
[6H, br s, CH(CH3)2], 0.92 [6H, t, J(H–H) = 7.4 Hz, CH2CH3].
13C NMR (298 K; CD3OD): d 157.40, 149.75, 148.42, 141.62,
139.92, 132.66, 131.83, 130.53, 129.53, 120.57, 118.60, 107.40,
31.46, 29.52, 24.69, 23.94, 14.35.
Table 3 Summary of X-ray diffraction data for compound 2
Empirical formula
MW
CuC27H35N3BF4
551.93
Monoclinic
P21
9.943(2)
21.275(4)
13.874(3)
107.19(3)
2804(1)
4
1.308
0.825
3.08–58.34
68486
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
b/◦
[Cu(2-iPrC6H4-dpa)(g2-trans-4-octene)]BF4 (6)
3
˚
V/A
Z
This compound was prepared in an analogous manner to that
of (1), using the ligand 2-iPrC6H4-dpa and olefin trans-4-octene.
Yield: 59%. MP (TGA; decomp.) 124–125 ◦C. FTIR (neat,
ATR, cm-1): 3121 (w, aromatic nC–H), 3069 (w, aromatic nC–H),
2960 (m, alkyl nC–H), 2928 (w, alkyl nC–H), 2868 (w, alkyl nC–H),
1596 (m), 1580–1429 (s, aromatic dC C), 1325 (s, amine nC–N), 1243
D
calc/g cm-3
m/mm-1
2q range/◦
No. collected
No. ind. (Rint
)
13982 (0.0885)
6381
0.0937
No. obsd. (|F0| > 4.0s |F0|)
R
Rw
1
(m), 1168 (w), 1052 (br vs), 1025 (br vs, nB–F), 783 (s). H NMR
0.2139
-3
˚
Largest difference peak and hole/eA
Weights
CCDC no.
2.449, -0.624
0.0926, 0
733204
(298 K; CD3OD): d 8.18 (2H, br s, py, 6-CH), 7.81 (2H, br t,
py, 4-CH), 7.64 (1H, m, C6H4), 7.59 (1H, m, C6H4), 7.42 (2H, br
m, C6H4), 7.19 (2H, br t, py, 5-CH), 6.81 (2H, br s, py, 3-CH),
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used for structure solution and refinement was SHELXTL Version
6.14.31 Selected bond lengths and angles are given in Table 1.
The program PLATON was employed for structure
validation,32,33 which revealed solvent accessible voids in the crystal
lattice (see .cif file in ESI† for platon squeeze details). The
CALC SQUEEZE instruction was used to correct data of residual
electron density in these voids, and all subsequent refinement was
performed using the corrected data set. Some disorder is apparent
in C(23) of conformer 1, which required treatment of the atom as
having approximately isotropic behavior (ISOR), with rigid bond
restraints (DELU) for carbon atoms C(21)–C(24), as well as a fixed
distance restraint for the Cu(1)–C(23) bond distance (DFIX =
2.010). BUMP and DAMP restraints were used in preliminary
refinement, but lifted for the final cycles.
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Acknowledgements
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Financial support for this work is provided by Trans Ionics
Corporation and the Robert A. Welch Foundation (C-0002).
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2010, 2, 137.
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25 Bruker, SAINT v6.45, 2003, Bruker AXS Inc., Madison, WI.
26 G. M. Sheldrick, SADABS, 2008, H, Germany.
27 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2007,
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1194 | Dalton Trans., 2011, 40, 1189–1194
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