Olefin coordination in copper(I) complexes of bis(2-pyridyl)amine

Article abstract of DOI:10.1039/b814829e

Complexes of the type [Cu(H-dpa)(olefin)]BF₄ for ethylene (1), propylene (2), 1-butene (3), 1-hexene (4), 1-octene (5), cis-2-octene (6), trans-2-octene (7), cis-3-octene (8), trans-3-octene (9), 2-norbornylene (10), 1,5-cyclooctadiene (11), st

Full text of DOI:10.1039/b814829e

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PAPER
www.rsc.org/dalton | Dalton Transactions
Olefin coordination in copper(I) complexes of bis(2-pyridyl)amine†
John J. Allen and Andrew R. Barron*
Received 26th August 2008, Accepted 18th November 2008
First published as an Advance Article on the web 3rd December 2008
DOI: 10.1039/b814829e
Complexes of the type [Cu(H-dpa)(olefin)]BF4 for ethylene (1), propylene (2), 1-butene (3), 1-hexene
(4), 1-octene (5), cis-2-octene (6), trans-2-octene (7), cis-3-octene (8), trans-3-octene (9), 2-norbornylene
=
(10), 1,5-cyclooctadiene (11), styrene (12), cis-stilbene (13), trans-stilbene (14), and Ph2C CH2 (15) have
been prepared and characterized by 1H and 13C NMR, FTIR, and TGA. The crystal structures have
been determined for compounds 5, 6, 8, and 10–13. With the exception of compound 11, copper atoms
in each complex are coordinated to the two pyridine nitrogen atoms and the appropriate olefin;
consistent with a pseudo three-coordinate Cu(I) cation. Compound 11 has a second weaker
p-interaction resulting in a distorted tetrahedral geometry. 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. The shifts in the nN-H IR spectral band for H-dpa ligand are consistent with
the formation of N–H ◊ ◊ ◊ F hydrogen bonded interactions observed in the crystal structures. 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 terminal olefins shows that the similarity of
=
binding for H2C CHR (R = CnH2n+1, n = 1–6) mitigates any preferential complexation of various
terminal olefins using the H-dpa ligand. For octenes there is a significant difference in binding between
a terminal and internal olefin, but there is little preference between binding for different internal olefins
and only a modest difference between the cis and trans isomers of the same olefin. A good correlation
exists between the 1H NMR Dd values and the TGA data, confirming that the shift of the olefin NMR
resonances upon coordination is associated with the binding strength of the complex. Ab initio
calculations using four different method/basis set combinations on the structure of
[Cu(H-dpa)(1-octene)]+ were compared with the crystal structure.
recent years. Since there is little that can be done to control the price
Introduction
of natural gas in the current market, the large volume of olefins
produced and the requisite purity for most applications provide
strong incentives for novel alternative separation approaches. The
use of chemically specific separation reagents is a potentially
inexpensive and efficient approach for separation.3
With respect to complex formation, various complexing
reagents have been described,4 but in all cases the function of the
complexing agent is to coordinate the olefin under one condition,
and liberate it under another (Eq. 1).5
Olefins are the largest volume feedstock in the chemical and
petrochemical industry, and are widely used in the production
of polymers, acids, alcohols, esters, and ethers. The lightest olefin,
ethylene, is the largest volume organic chemical. While demand
is increasing, production is lagging, primarily because the cost of
producing olefins has escalated dramatically in the past several
years. One part of this is due to the fact that olefin production
is extremely energy intensive, generally requiring the separation
of these molecules from their alkane counterparts (olefin/paraffin
separation) via cryogenic distillation. Over a decade ago it was
estimated that these two separations accounted for 6.3% (about
0.15 quadrillion BTUs) of the energy used by the chemical and
petrochemical industries,1 leading to the suggestion that less
energy-intensive separations would be useful for the petroleum
refining industry.2 Another reason for increased production costs
is the fact that feedstock (natural gas liquids) prices have soared in
(1)
Thus, the olefin coordination must be easily reversible upon
change in ambient conditions (heat or reduced pressure) in order
to release the olefin when desired. It follows that the solvent and
the metal complex must be of sufficiently high boiling points that
the olefin is removed upon heating without loss of complexing
agent. The latter can be accomplished through the use of a salt
rather than a neutral complex.
In designing a suitable coordination system for olefins, we
are interested in a metal ◊ ◊ ◊ olefin interaction that is sufficiently
strong to allow for isolation, but will allow for recovery of the
olefin after extraction. Although redox-active metal salts such as
copper6,7 have been reported to reversibly coordinate olefins they
do not allow for selectivity. Unfortunately, in general, Cu ◊ ◊ ◊ olefin
complexes are not strong and dissociation occurs under ambient
Energy and Environmental Systems Institute and Department of Chem-
istry, Rice University, 6100 Main Street, Houston, Texas 77005, USA.
E-mail: arb@rice.edu
† Electronic supplementary information (ESI) available: Structural disor-
der for compounds 6, 8, and 11, calculated structure of [Cu(H-dpa)(1-
octene)]+, and comparison of calculated bond lengths and angles with
experimentally determined values. CCDC reference numbers 692443 (5),
692444 (6), 693280 (8), 692446 (10), 698583 (11), 692447 (12) and 692445
(13). For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/b814829e
878 | Dalton Trans., 2009, 878–890
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) determined for [Cu(H-dpa)(olefin)]BF4
Olefin
1-octene (5)
cis-2-octene (6)
cis-3-octene (8)
2-norbornylene (10)
1,5-cyclooctadiene (11)
styrene (12)
cis-stilbene (13)
Cu–C
Cu–C¢
Cu–N
1.997(6)
2.024(6)
1.963(5)
1.965(5)
1.374(8)
97.0(2)
39.9(2)
112.3(4)
5.4(5)
2.024(6)
2.034(6)
1.959(4)
1.979(4)
1.373(9)
96.5(1)
39.5(2)
114.0(5)
2.5(4)
2.026(4)
2.038(4)
1.974(3)
1.978(3)
1.363(6)
96.2(1)
39.2(1)
116.2(3)
2.1(3)
2.030(6)
2.026(6)
1.962(5)
1.957(5)
1.388(7)
97.7(2)
40.0(2)
113.1(4)
1.6(3)
2.087(4)c
—
1.990(6)
2.044(5)
1.959(5)
1.967(5)
1.387(8)
96.7(2)
40.2(2)
108.6(4)
6.8(4)
2.011(6)
2.013(5)
1.959(5)
1.964(4)
1.380(7)
96.9(2)
40.1(2)
117.9(4)
2.6(4)
1.996(3)
—
Cu–N¢
C–Colefin
N–Cu–N
C–Cu–C
Cu–C–C
twista
1.35(1)d
95.3(1)
38.0(3)
112.9(3)
0
foldb
10.3(3)
4.4(3)
7.7(2)
7.2(4)
23.1(2)
12.3(3)
6.5(3)
a
Dihedral angle between the olefin C C bond and the plane of the H-dpa ligand, i.e., N(3)–N(2)–C(11)–C(12). b Fold angle between the mean planes for
=
c
d
˚
˚
each pyridine ring, i.e., MPLNpy(1)–MPLNpy(2)
.
Cu(1)–C(9) = 2.560(5) A. C(9)–C(9A) = 1.33(1) A.
conditions; however, interest in the copper(I) ◊ ◊ ◊ ethylene interac-
tion present in biological systems has resulted in the synthesis
of several potential ligand systems. Ethylene plays a variety of
roles in plant development, ranging from germination and growth
to sex expression and fruit ripening.8,9 Considering all of the
metals present in biological systems, copper is the only metal
known to interact with ethylene. This assortment of naturally
occurring processes has inspired a great deal of work, which
has found applications in catalysis10 and industrial processing
of hydrocarbon feedstocks.11 These studies have also demon-
strated that enhanced stability of the Cu ◊ ◊ ◊ olefin interaction can
be achieved incorporating multidentate, electron rich N-donor
ligands. The tridentate ligand, pentamethyldiethylenetriamine,
has been used to prepare copper(I) complexes of several olefin
monomers.12 Stable complexes have also been prepared using
anionic ligands,8,13,14 but the class of ligands more commonly
used is the neutral N-donor heterocyclic compounds, including
bis(pyrazolyl)methanes,15 dipyridylamine,16,17 phenanthroline,18
and bipyridines.15,19 Of all these studies, it is the report by
Thompson and Whitney that stable complexes with ethylene are
formed when stabilized with the chelate ligand bis(2-pyridyl)amine
(H-dpa), that has formed the basis for the present study.
Compounds 1–15 are soluble in alcohols and show instability
in air. All the compounds have been characterized by 1H and 13
NMR, FT-IR, and TG/DTA. The crystal structures have been
determined for compounds 5, 6, 8, and 10–13.
The structures for the complex cations in compounds 5, 6, 8, and
10–13 are shown in Fig. 1–7, respectively. Selected bond lengths
and angles are given in Table 1. It is interesting to note that
complexes 6, 8, and 13 represent, to the best of our knowledge,
the first structurally characterized complexes of these olefins with
any metal, while 5 is only the second 1-octene complex with
any metal.12 The copper atoms in compounds 5, 6, 8, 10, 12,
and 13 are each coordinated to two pyridine nitrogen atoms
and the appropriate olefin; consistent with three-coordinate Cu(I)
C
˚
cation. The Cu-N distances [1.957(5)–1.996(3) A] are within
experimental error of the analogous ethylene and cyclohexene
complexes [1.963(2)–1.973(3) A].16,17 In a similar manner the Cu-C
˚
˚
distances [1.990(6)–2.087(4) A] overlap the range for the previously
16,17
˚
reported derivatives [2.019(3)–2.032(4) A].
We are interested in using bis(2-pyridyl)amine-type ligands to
effect the binding propensity of various olefins. But prior to this
work we desire to have a detailed understanding of the structural
trends observed with terminal versus internal olefin’s coordination,
as well as using spectroscopic and computational methods as a
tool in ligand design. Herein we report the first part of this study:
a structural, spectroscopic, and computational study of olefin
coordination in copper(I) complexes of bis(2-pyridyl)amine.
Results and discussion
The reaction of [Cu(MeCN)4]BF4 with H-dpa in the presence
of the appropriate olefin results in the formation of the olefin
complex, [Cu(H-dpa)(olefin)]BF4 (Eq. 2) where olefin = ethylene
(1), propylene (2), 1-butene (3), 1-hexene (4), 1-octene (5), cis-
2-octene (6), trans-2-octene (7), cis-3-octene (8), trans-3-octene
(9), 2-norbornylene (10), 1,5-cyclooctadiene (11), styrene (12), cis-
Fig. 1 The structure of the [Cu(H-dpa)(1-octene)]+ cation in compound
5. Thermal ellipsoids are shown at the 30% level and hydrogen atoms
attached to carbon are omitted for clarity.
=
stilbene (13), trans-stilbene (14), and Ph2C CH2 (15).
The copper atom in compound 11 is situated on a crystallo-
graphic mirror plane, and is coordinated to two pyridine nitrogen
atoms and the 1,5-cyclooctadiene via two distinct interactions. As
[Cu(MeCN)4]BF4 + H-dpa + olefin →
[Cu(H-dpa)(olefin)]BF4 + 4 MeCN
(2)
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Fig. 4 The structure of the [Cu(H-dpa)(2-norbornylene)]+ cation in
compound 10. Thermal ellipsoids are shown at the 30% level and hydrogen
atoms attached to carbon are omitted for clarity.
Fig. 2 The structure of the [Cu(H-dpa)(cis-2-octene)]+ cation in com-
pound 6. Thermal ellipsoids are shown at the 30% level and hydrogen
atoms attached to carbon are omitted for clarity.
Fig. 5 The structure of the [Cu(H-dpa)(1,5-cyclooctadiene)]+ cation in
compound 11. Thermal ellipsoids are shown at the 30% level and hydrogen
atoms attached to carbon are omitted for clarity.
Fig. 3 The structure of the [Cu(H-dpa)(cis-3-octene)]+ cation in com-
pound 8. Thermal ellipsoids are shown at the 30% level and hydrogen
atoms attached to carbon are omitted for clarity.
˚
significantly longer distance [2.560(5) A]. It should be noted that
has been observed for the 2,2¢-bipyridine analog20 and the neutral
hexafluoroacetylacetonato derivative,21 the geometry about the
Cu atom, which is coordinated to the two pyridine nitrogen
atoms and two olefinic moieties of the 1,5-cyclooctadiene, is that
of a very distorted tetrahedron. The angle between the Cu(1)–
C(6)–C(6a) plane, and the Cu(1)–N(2)–N(2a) plane is 158.7(2)◦,
which is close to the 2,2¢-bipyridine derivative (154.3◦). In a
similar manner, the angle between the plane Cu(1)–C(9)–C(9a)
plane, ◦and the Cu(1)–N(2)–N(2a) plane is 118.7(2)◦ compared
to 118 in the 2,2¢-bipyridine analog.20 The primary Cu ◊ ◊ ◊ olefin
in compound 11 the stronger Cu ◊ ◊ ◊ olefin interaction is shorter,
and the weaker interaction is longer as compared to [Cu(bipy)(1,5-
˚
cyclooctadiene)]PF6 [2.113(8) and 2.105(9) A, and 2.47(1) and
20
˚
2.40(1) A, respectively].
˚
=
The C C bond and C–Cu–C angle determined for 5 [1.374(8) A
and 39.9(2)◦, respectively] are slightly larger than those for the
pentamethyldiethylenetriamine (PMDETA) derivative reported
◦
by Braunecker et al. [1.35(1) A and 38.3(3) ],12 suggesting a weaker
Cu–olefin interaction in the latter; however, the PMDETA acts
as a tridentate ligand giving a pseudotetrahedral coordination
geometry around Cu(I) which may account for the variation. The
˚
˚
interaction [2.087(4) A] is slightly weaker than those observed for
˚
=
our other structures, while the secondary interaction involves a
C C bond determined for compound 10 [1.388(7) A] is lengthened
880 | Dalton Trans., 2009, 878–890
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styrene [1.325(2) A],25 as well as compared to the PMDETA, bipy,
˚
12,13,26
˚
and neutral b-diketiminato complexes [1.35(1)–1.373(6) A].
It is worth noting that, the C C bond lengthening as compared
to the free olefin (0.06 A), as well as the shift in the H and 13C
=
1
˚
NMR signal upon complexation (see below) for 10 are amongst
the largest for any olefin examined. This is consistent with the
stabilization of the olefin complex, especially in comparison
with the cis-2-octene and cis-3-octene homologues. As a result
of the rigid nature of the uncomplexed cyclic nornornylene
molecule, the alkene C–C–C angles (106.5◦)21 are constrained
to less than ideal for sp2 hybridization. Partial rehybridization
to sp3 upon coordination results in a relief of this angle strain,
thereby accounting for a stronger interaction than observed for
unconstrained cis-olefins.
=
Even assuming a coplanar structure (i.e., the H-dpa and C C
bond of the olefin being coplanar) there will be steric hindrance
between the ligands for any olefin above ethylene. The structural
consequence of such a steric interaction would be to expect
twisting of the olefin out of the plane of the H-dpa ligand (Table 1).
Quantifying this twist by the dihedral angle between the olefin
Fig. 6 The structure of the [Cu(H-dpa)(styrene)]+ cation in compound
12. Thermal ellipsoids are shown at the 30% level and hydrogen atoms
attached to carbon are omitted for clarity.
=
C C bond and the plane of the H-dpa ligand [i.e., N(3)–N(2)–
C(11)–C(12)] allows for comparison with different steric bulks
of the olefin substituents. As may be seen from Table 1, this
twist is largest for terminal olefins and smallest for constrained
olefins, including the previously reported cyclohexene derivative
(0.81◦).16 Associated with the twisting of the olefin out of the CuN2
plane, is a folding of the H-dpa ligand (Table 1), such that the
pyridyl groups are no longer co-planar (Fig. 8). As may be seen
from Fig. 9, these effects are related for substituted olefins. We
note that the twist angle observed for [Cu(H-dpa)(ethylene)]ClO4
(9.91◦)15 is significantly larger than other examples, while the fold
observed in compound 11 is large [23.1(2)◦] the twist is 0◦ due
to the crystallographic mirror plane and the secondary olefin
interaction. We propose that the combination of a folding of the
H-dpa ligand and a rotation of the olefin out of the CuN2 plane
(as measured by the twist) provide the relief of inter-ligand/intra-
molecular steric strain for terminal and cis-olefins. It should be
noted that while we have been unable to structurally characterize
any of the trans-isomers, the folding of the H-dpa ligand would
not provide relief of steric strain. We propose that this may be a
method for differentiating the binding of cis- and trans-olefins.
Fig. 7 The structure of the [Cu(H-dpa)(cis-stilbene)]+ cation in com-
pound 13. Thermal ellipsoids are shown at the 30% level and hydrogen
atoms attached to carbon are omitted for clarity.
22
˚
compared to free norbornylene [1.334(1) A], and is slightly
longer than those observed in the neutral iminophosphanamide-
norbornylene and diethylenetriamine (detn) complexes [1.37(2)
14,23
˚
and 1.38(2) A, respectively].
The C(6)–C(6a) distance of
Fig. 8 Partial coordination sphere of [Cu(H-dpa)(styrene)]+ cation in
compound 12 showing the twisting of the olefin out of the CuN2 plane,
and the folding of the H-dpa ligand.
˚
1.35(1) A for the strongest interaction in compound 11 is shorter
=
than the C C distance observed for the other compounds reported
here, consistent with the longer Cu–C distance. Furthermore,
C(9)–C(9a) distance associated with the secondary Cu ◊ ◊ ◊ olefin
interaction [1.33(1) A] is within experimental error to that reported
˚
A common feature of the crystal packing is that the counter
ion, BF4 , interacts with the amine hydrogen of the H-dpa
-
˚
for free 1,5-cyclooctadiene (1.34 A), consistent with a very weak
Cu ◊ ◊ ◊ olefin interaction and little or no p-back donation.24 The
ligand (Fig. 10). The N ◊ ◊ ◊ F distances (2.80–3.00 A) are within
˚
27
˚
˚
=
C C bond in compound 12 [1.387(8) A] is longer than in free
the range previously observed (2.77–3.31 A), and hence
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Table 2 Change in 1H and 13C NMR chemical shift (ppm) for olefins
upon coordination to copper in [Cu(H-dpa)(olefin)][BF4]a,b
Complex
DdHa
DdHb
DdHc
DdCx
DdCy
1
0.91
0.67
0.68
0.64
0.59
0.29
0.32
0.29
0.32
0.93
0.03
0.68
0.34
0.29
0.10
—
—
39.4
34.2
34.1
33.9
32.7
27.7
23.2
27.8
24.8
33.9
7.2
—
2
0.64
0.62
0.66
0.64
—
—
—
—
—
—
0.82
—
0.53
0.50
0.50
0.47
—
—
—
—
—
—
0.55
—
33.3
33.1
33.0
32.2
27.0
22.9
27.4
25.0
—
—
36.1
—
—
7.7
3
4
5
6
7
8
9
10
11
12
13
14
15
32.9
22.8
7.7
Fig. 9 Plot of folding of the H-dpa ligand as measured by the
angle between the mean planes for each pyridine ring [fold angle =
MPLNpy(1)–MPLNpy(2)] as a function of the diahedral angle between the
—
—
—
—
6.1
=
olefin C C bond and the plane of the H-dpa ligand (twist angle =
a NMR collected at 298 K in CD3OD. b Ha, Hb, Hc, Cx, and Cy are defined
as shown in Fig. 11.
N–N–C–C) for [Cu(H-dpa)(olefin)]BF4 (R2 = 0.764).
The aromatic (3260–3120 cm-1) and alkene (3080–3000 cm-1)
C–H stretching bands in the IR spectra yielded relatively weak
bands in each case, while aliphatic C–H stretching (2980–
2850 cm-1) in 1, 2, and 7 gave medium strength bands. Bands
caused by N–H bending in complexes (1640–1650 cm-1) are
shifted to higher wavenumber than in the free ligand (1592 cm-1).
=
Assignment of the olefin C C stretch was obscured by the presence
=
=
of several strong bands caused by aromatic C C and C N
stretching (1580–1440 cm-1) from the H-dpa ligand. As a result,
=
no conclusions can be drawn concerning the shift in C C stretch.
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.18 We have previously
1
used similar methods for Lewis acid–base complexes.28 The H
NMR spectra of [Cu(H-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 (Table 2).
Fig. 10 Crystal packing diagram of [Cu(H-dpa)(cis-stilbene)]BF4 (13)
showing the cation ◊ ◊ ◊ anion hydrogen bonded interaction. Hydrogen
atoms attached to carbon are omitted for clarity.
consistent with N–H ◊ ◊ ◊ F hydrogen bonding. This cation ◊ ◊ ◊ anion
interaction is in contrast to the perchlorate derivatives [Cu(H-
15
16
Fig. 11 Schematic representation of [Cu(H-dpa)(olefin)]+ showing the
atom labels used in Tables 2 and 3.
dpa)(ethylene)]ClO4 and [Cu(H-dpa)(cyclohexene)]ClO4 that
show clear separation of the cation and anion in the solid state.
The presence of N–H ◊ ◊ ◊ F hydrogen bonding is confirmed by
the infrared spectra of compounds 1–15 by the observation of
a medium strength bands for each complex (3340–3353 cm-1).
These bands are shifted to a higher wavenumber than the
corresponding band in the free ligand (3263 cm-1) in which there is
strong intermolecular N–H ◊ ◊ ◊ N hydrogen bonding; however, the
observed shifts in N–H stretching and bending bands are indicative
of association of the amine hydrogen.
Given the ionic nature of the complex, the solvent must
be solvating enough to allow formation of a non-coordinating
cation ◊ ◊ ◊ anion pair, but not coordinating enough to inhibit olefin
binding. The relative shift of the olefin protons is dependant on
the donor ability of the solvent used (Fig. 12). The difference
in shifts with respect to changes in solvent is a measure of the
competition between the olefin and the solvent, i.e., Eq. 3. Thus,
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Fig. 12 Comparison of 1H NMR spectra shifts for the olefin region
for [Cu(H-dpa)(1-octene)]BF4 as a function of solvent in (a) CD3OD, (b)
d6-acetone, and (c) CD3CN. Ha, Hb, and Hc are defined as shown in Fig. 11.
Solvent peak is designated by “S”.
from Fig. 12 it may be seen that MeCN competes strongly (Eq. 3
is shifted to the right) while MeOH shows little competition (Eq.
3 is shifted to the left). As a consequence we used CD3OD for
all subsequent measurements. We note, however, that the use of
MeOH is also a model for the choice of the solvent for suitable for
olefin separation.
[Cu(H-dpa)(olefin)]+ + solvent ꢀ [Cu(H-dpa)(solvent)]+
Fig. 13 Plots of difference in chemical sift (Dd) for the olefin (a) 1H and
(b) 13C NMR spectra between the free olefin and [Cu(H-dpa)(olefin)]BF4
for terminal olefins.
+ olefin
(3)
A consideration of the data in Table 2 shows that the change
1
in both H and 13C NMR shifts upon coordination is greatest
for sterically unhindered and constrained olefins (i.e., ethylene
and 2-norbornylene) and least for internal olefins. This trend is
consistent with the expected binding stability of the olefin complex
(cf., Eq. 3). A comparison of the Dd values (and hence binding
ability) for terminal olefins shows that ethylene binds significantly
better than substituted olefins, but there is little effect of increasing
chain length (Fig. 13). This result suggests that while the H-dpa
parent complex may allow for differentiation of ethylene from
other terminal olefins, the preferential complexation of various
terminal olefins is not possible with the H-dpa ligand.
13
=
Using the alteration in the C NMR shift of the C C unit
upon coordination, it is possible to compare the binding efficiency
=
as a function of the position of the C C group. For example, a
comparison of the 13C Dd values for 1-octene, 2-octene and 3-
octene. Fig. 14 shows that while there is a significant difference
in binding between a terminal and internal olefin (irrespective of
cis or trans isomer), there is much less preference between binding
for different internal olefin, i.e., there is only a small difference
between cis-2-octene versus cis-3-octene or trans-2-octene versus
trans-3-octene. There is, however, a modest difference between the
cis and trans isomers of the same olefin (i.e., cis-2-octene versus
trans-2-octene). This suggests that while differential complexation
of cis and trans isomers is possible for the H-dpa ligand, the parent
ligand will not allow for separation of different internal olefins by
Fig. 14 13C NMR Dd for Cx (black) and Cy (grey) as a function of octane
double bond position in [Cu(H-dpa)(olefin)]BF4 for compounds 5–9.
are not indicative of a comparison with the solvent complex,
i.e., [Cu(H-dpa)(solvent)]BF4, they can be used to compare the
effective changes with different olefins. As may be seen from
Table 3, changes in the olefin result in the largest range of shifts for
H
3,3¢ > H4,4¢ = H5,5¢ > H6,6¢. This is consistent with the binding of the
H-dpa to the copper and breaking of the strong inter-molecular
dimer in free H-dpa. A comparison of the difference in chemical
shift for the H-dpa protons between the ethylene complex (1) and
the sterically more demanding olefins (compounds 2–15) provides
a measure of the electronic and potentially steric effects of the
olefin on the H-dpa ligand. We have previously demonstrated that
1H and 13C NMR may be used as a measure of changes in structure
as a consequence of ligand binding.29,30 Unfortunately, as may be
=
their C C position.
In a similar manner to the shift of the olefin signals in the
1H NMR spectrum of [Cu(H-dpa)(olefin)]BF4 versus free olefin,
the chemical shifts of the ligand protons (Table 3) are shifted
in comparison with free H-dpa. While the shifts in this case
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Table 3 Changes in 1H NMR chemical shifts of the H-dpa ligand in [Cu(H-dpa)(olefin)]BF4 as compared to the free ligand and compound 1a,b
Ddfree (ppm)
Dd1 (ppm)
Compound
H3,3¢
H4,4¢
H5,5¢
H6,6¢
H3,3¢
H4,4¢
H5,5¢
—
0.01
0.01
-0.01
-0.02
-0.01
0.02
0.00
0.02
-0.03
0.09
H6,6¢
—
1
0.33
0.38
0.38
0.36
0.35
0.39
0.39
0.38
0.39
0.36
0.42
0.43
0.52
0.47
0.34
-0.27
-0.24
-0.23
-0.25
-0.26
-0.24
-0.23
-0.23
-0.23
-0.26
-0.19
-0.14
-0.12
-0.15
-0.27
-0.23
-0.22
-0.22
-0.24
-0.25
-0.24
-0.21
-0.23
-0.21
-0.26
-0.14
0.01
-0.05
-0.03
-0.02
-0.03
-0.04
-0.02
-0.03
-0.01
-0.04
-0.16
0.12
—
—
2
0.05
0.05
0.03
0.02
0.06
0.06
0.05
0.06
0.03
0.09
0.10
0.19
0.14
0.01
0.03
0.04
0.02
0.01
0.03
0.04
0.04
0.04
0.01
0.08
0.13
0.15
0.12
0.00
0.02
0.03
0.02
0.01
0.03
0.02
0.04
0.01
-0.11
0.17
0.32
0.18
0.15
0.09
3
4
5
6
7
8
9
10
11
12
13
14
15
0.27
0.13
0.10
0.04
0.24
0.15
0.12
-0.05
-0.08
-0.11
-0.28
a NMR collected at 298 K in CD3OD. b Hn,n¢ (n = 3–5) are defined as shown in Fig. 11.
seen from Table 3, there are only small differences (except for the
aromatic substituted olefins where ring current effects are possibly
in force) between different olefins. This suggests that the electronic
effects of different olefins on the H-dpa ligand are minimal.
We have previously found that thermogravimetric/differential
thermal analysis (TG/DTA) of Lewis acid–base complexes pro-
vides information as to the relative strength of the M ◊ ◊ ◊ L
interaction.30,31 The TG/DTA of compounds 1–15 is consistent
with their decomposition resulting via the loss of the olefin. It
should be noted that in all cases the boiling point of the olefin
is lower than the temperature of decomposition of the respective
[Cu(H-dpa)(olefin)][BF4] derivative, thus any mass loss is related
to the strength Cu ◊ ◊ ◊ olefin interaction rather than the boiling
point of the olefin. This is also confirmed by the DTA that shows
decomposition to be exothermic rather than the endothermic
process of boiling/evaporation. As with the 1H and 13C NMR Dd
measurements the temperature associated with olefin dissociation
(see Experimental) indicates a significant difference in binding
of ethylene versus substituted olefins. Importantly, Fig. 15 shows
NMR resonances uponcoordination is associated withthebinding
strength of the complex (see above). Also following the NMR
data, the similarity of the Tdec for cis-2-octene (146 C) and cis-
◦
3-octene (143 ◦C), as well as that for cis-3-octene and trans-3-
octene (144 ◦C) suggest that separation of various olefin isomers
through differentiation of binding to the Cu(I) H-dpa complex is
not possible and that alternative ligands must be explored.
As part of our efforts to determine the viability of modeling
for comparing how various olefins interact with the copper
H-dpa unit, we have calculated the structure of the [Cu(H-
dpa)(1-octene)]+ cation using four different method/basis set
combinations. A comparison with the experimentally determined
structure will indicate which method most faithfully replicates
observed structural trends; in particular, we are interested in
choosing an appropriate computational method for predicting the
conformational interactions between the olefin and the H-dpa
ligand. A summary of the relevant lengths and angles is given in
Table 4.
As may be seen from Table 4 none of the method/basis set
combinations replicate all of the parameters exactly. They all over-
estimate the Cu–X distances; however, the highest-level calculation
studied (RMP2-FC LANL2DZ/6-311++G*) is consistently the
closest (Fig. S1†). Interestingly, despite significantly overestimat-
1
the good correlation between the H NMR Dd values and the
TGA data, validating the assumption that the shift of the olefin
=
ing the olefin C C distance this does replicate the C–Cu–C angle
=
associated with the olefin. The C C distance is faithfully predicted
(within 3s) using RB3LYP at the LANL2DZ/6-311++G* level,
as is the chelate angle of the H-dpa ligand. It is interesting that
the lowest level calculations (MOPAC and RHF STO-3G) are
clearly sufficient to predict the extent of distortion from planar of
the olefin substituents, since this out-of-plane distortion is usually
used as a measure of the extent of p-back bonding from a metal
to an olefin.
Unfortunately, the most difficult structural features to replicate
(and therefore use reliably in future predictions) is the twist angle
between the H-dpa ligand and the olefin [N(3)–N(2)–C(11)–C(12)]
and the folding of the H-dpa ligand [MPLNpy(1)–MPLNpy(2)]. This is
in part a function of inter-molecular crystal packing forces on the
organic tail of the 1-octene that may overshadow intra-molecular
Fig. 15 Plot of the change in chemical shift of Ha as compared to the free
olefin (ppm) versus the temperature of terminal olefins dissociation for in
[Cu(H-dpa)(olefin)][BF4] as determined from TGA (R2 = 0.965).
884 | Dalton Trans., 2009, 878–890
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◦
+
˚
Table 4 Selected bond lengths (A) and angles ( ) calculated for [Cu(H-dpa)(1-octene)] in comparison with values determined experimentally by X-ray
crystallographya
Calculation method and basis set
RB3LYP LANL2DZ/
6-311++G*
RMP2-FC LANL2DZ/
6-311++G*
Parameter
MOPAC
RHF STO-3G
Experimental
Cu(1)–C(11)
Cu(1)–C(12)
Cu(1)–N(2)
Cu(1)–N(3)
2.078
2.119
2.044
2.029
1.406
90.49
39.14
112.20
3.52
2.080
2.115
2.043
2.029
1.406
90.49
39.14
112.21
3.52
2.096
2.161
2.012
2.004
1.391
97.70
38.11
111.81
7.48
2.062
2.060
1.982
1.982
1.427
97.92
40.49
110.72
4.70
1.997(6)
2.024(6)
1.963(5)
1.965(5)
1.374(8)
97.0(2)
39.9(2)
112.3(4)
5.4(5)
C(11)–C(12)
N(2)–Cu(1)–N(3)
C(11)–Cu(1)–C(12)
Cu(1)–C(12)–C(13)
Twist angleb
Fold anglec
6.18
6.18
3.91
16.27
10.3(3)
a Values in bold are within 3s of experimental values, while those in italic are the closest to experimental but outside 3s. b Dihedral angle between the
olefin C C bond and the plane of the H-dpa ligand, i.e., N(3)–N(2)–C(11)–C(12). c Fold angle between the mean planes for each pyridine ring, i.e.,
MPLNpy(1)–MPLNpy(2)
=
.
interactions. As may be seen from Fig. 16, MOPAC and RHF
STO-3G equally underestimate both values. In contrast, RB3LYP
(LANL2DZ/6-311++G*) overestimates the twisting between the
ligands, but underestimates the folding of the H-dpa. The converse
is true for RMP2-FC using the same basis set. For any individual
olefin the greater the twist angle (the further away from ideal
planar geometry around the copper) the less the steric interactions
between the olefin and the pyridine rings of the H-dpa ligand, and
consequently the more planar the H-dpa ligand will be. Fig. 17
shows a plot of twist angle [N(3)–N(2)–C(11)–C(12)] as a function
of the folding of the H-dpa ligand [MPLNpy(1)–MPLNpy(2)]. The
linear relationship between the crystal structural determined value
and the values calculated using RB3LYP and RMP2-FC suggest
that while neither of the latter provide exact replication of the
crystal structure, they do replicate the steric relationship between
intra-molecular inter-ligand interactions.
Fig. 17 Plot of calculated and experimental twist angle
[N(3)–N(2)–C(11)–C(12)] as a function of the folding of the H-dpa
ligand [MPLNpy(1)–MPLNpy(2)
]
for [Cu(H-dpa)(1-octene)]+ (ꢀ) using
RB3LYP LANL2DZ/6-311++G*, RMP2-FC LANL2DZ/6-311++G*,
and X-ray crystallography (R2 = 0.934). The values calculated using
MOPAC and RHF STO-3G are shown for comparison (ꢁ).
of ionic copper ◊ ◊ ◊ olefin complexes. Interestingly we have been
unable to crystallographically characterize any of the trans isomer
complexes. Unfortunately, there appears to be no correlation of
=
the binding strength of the olefin with Cu–C or C C bond lengths.
We have observed that a twisting of the olefin out of the plane of
the H-dpa ligand and a related folding of the H-dpa ligand provide
relief of inter-ligand/intra-molecular steric strain for terminal and
1
cis-olefins. The difference in the H and 13C NMR shift values
between free and complexed olefins can be used to compare
binding interactions. While there is a significant difference in
binding between a terminal and internal olefin, there is much less
preference between binding for different internal olefins. There is
also a modest difference between the cis and trans isomers of the
same olefin. These trends are also mimicked by the temperature of
dissociation of the olefin in the solid state as determined by TGA.
Our results suggest that while differential complexation of cis and
trans isomers is possible using a H-dpa type ligand, separation of
Fig. 16 Plot of torsion angles for calculated structure of [Cu(H-dpa)-
(1-octene)]+, using MOPAC (red), RHF STO-3G (yellow), RB3LYP
LANL2DZ/6-311++G* (green), and RMP2-FC LANL2DZ/
6-311++G* (blue) in comparison with experimentally determined
values (white).
Conclusions
=
We have shown that the bis(2-pyridyl)amine ligand allows for
different internal olefins by their C C position will not be possible.
the isolation and structural characterization of a wide range
However, the use of pre-folded bis(2-pyridyl)amine ligands should
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allow for differentiation of coordination of olefin isomers. We are
presently investigating the synthesis and complexation of alkyl
substituted bis(2-pyridyl)amine ligands.
J(H-H) = 6.1 Hz, CHCH3]. 13C NMR: d 154.19 (2,2¢-py), 149.74
(6,6¢-py), 141.66 (4,4¢-py), 118.97 (5,5¢-py), 116.10 (3,3¢-py), 100.59
(CHCH2), 82.87 (CHCH2), 19.69 (CHCH3).
Experimental
[Cu(H-dpa)(1-butene)]BF4 (3)
All reagents in this study were used as received from commercial
suppliers and were stored under an argon atmosphere in a drybox.
The precursor complex [Cu(MeCN)4]BF4 was prepared according
to the literature.32 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
This compound was prepared in an analogous manner to that of
compound 1. Yield: 32%. Mp: 146–148 ◦C (dec.). IR (ATR, cm-1):
3346 (m, nN-H), 3261 (w, aromatic nC-H), 3224 (w, aromatic nC-H),
3157 (w, aromatic nC-H), 3122 (w, aromatic nC-H), 3081 (w, alkene
n
n
C-H), 3049 (w, alkene nC-H), 2969 (w, alkyl nC-H), 2934 (w, alkyl
C-H), 2871 (w, alkyl nC-H), 1637 (s, dN-H), 1584 (s), 1531 (s), 1477–
line techniques. H NMR and 13C NMR spectra were obtained
1
1379 (s, aromatic dC C), 1231 (s, aromatic dC N), 1063–986 (br vs).
=
=
1H NMR: d 8.21 (2H, br d, 6,6¢-py), 7.89 (2H, br t, 4,4¢-py), 7.20
(2H, br d, 3,3¢-py), 7.11 (2H, br t, 5,5¢-py), 5.36 [1H, ddt, J(H-
H) = 15.2 Hz, J(H-H) = 9.0 Hz. J(H-H) = 7.3 Hz, H2CCH],
4.31 [1H, d, J(H-H) = 9.0 Hz, trans-CH], 4.27 [1H, dd, J(H-
H) = 15.2 Hz, cis-CH], 2.09 (2H, br quint, CHCH2), 1.08 [3H,
t, J(H-H) = 7.3 Hz, CH2CH3]. 13C NMR: d 154.22 (2,2¢-py),
149.72 (6,6¢-py), 141.67 (4,4¢-py), 118.88 (5,5¢-py), 116.11 (3,3¢-
py), 107.63 (CHCH2), 80.73 (CHCH2), 27.97 (CH2CHCH2), 14.98
(CH2CH3).
at room temperature using Bruker Avance 400 and 500 MHz
spectrometers. Spectra were collected at 298 K in CD3OD unless
otherwise stated. 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 10–15 mL min-1. Elemental analysis was
attempted on the compounds; however, TGA indicated the slow
loss of olefin over the times used for transportation of samples.
[Cu(H-dpa)(ethylene)]BF4 (1)
[Cu(H-dpa)(1-hexene)]BF4 (4)
[Cu(MeCN)4]BF4 (1.0 mmol) and H-dpa (1.0 mmol) were charged
to separate 100 mL schlenk flasks in a dry box. MeOH (10 mL)
was added to the flask containing the H-dpa, which was stirred to
dissolve solids. To the flask containing the copper precursor was
added ethylene saturated MeOH (20 mL), which was stirred for
two hours at room temperature before adding the H-dpa solution.
The mixture was allowed to stir under an atmosphere of ethylene
for two hours, after which, ethylene was bubbled through the
solution on a medium porosity glass frit until the volume had
reduced by half. The solution was then filtered, and n-pentane
(10 mL) was added to precipitate ◦the complex. Filtration afforded
3.76 g (60% yield). Mp: 196–199 C (dec.). IR (ATR, cm-1): 3347
(m, nN-H), 3261 (w, aromatic nC-H), 3225 (w, aromatic nC-H), 3158
(w, aromatic nC-H), 3115 (w, aromatic nC-H), 3082 (w, alkene nC-H),
3052 (w, alkene nC-H), 1640 (s, dN-H), 1584 (s), 1530 (s), 1478–1380
(s, aromatic dC C), 1233 (s, aromatic dC N), 1006 (br vs). 1H NMR:
[Cu(MeCN)4]BF4 (0.314 g, 1.00 mmol) and H-dpa (0.172 g,
1.0 mmol) were charged to separate 100 mL Schlenk flasks in
a dry box. MeOH (10 mL) was added to the flask containing
the H-dpa, which was stirred to dissolve solids. To the flask
containing the copper complex was added 1-hexene (5 mL, ca.
5 x excess) in MeOH (20 mL). The mixture was allowed to stir
for 1 hr at room temperature before adding the H-dpa/methanol
solution. After, the combined solutions were stirred another three
hours at room temperature; the solution volume was reduced
under vacuum by approximately half. The solution was gently
warmed 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. 10 mL. The
solution was gently warmed to dissolve any precipitate, and upon
cooling to -12 ◦C for several days, the solution yielded 0.231 g
(57%) colorless needles. Mp: 131–134 ◦C (dec.). IR (ATR, cm-1):
3339 (m, nN-H), 3260 (w, aromatic nC-H), 3225 (w, aromatic nC-H),
3158 (w, aromatic nC-H), 3122 (w, aromatic nC-H), 3087 (w, alkene
=
=
d 8.24 (2H, br d, 6,6¢-py), 7.93 (2H, br t, 4,4¢-py), 7.25 (2H, br d,
3,3¢-py), 7.12 (2H, br t, 5,5¢-py), 4.48 (4H, br s, CH2). 13C NMR: d
154.04 (2,2¢-py), 150.27 (6,6¢-py), 141.94 (4,4¢-py), 118.83 (5,5¢-py),
116.28 (3,3¢-py), 84.22 (CH2).
n
n
C-H), 3051 (w, alkene nC-H), 2954 (w, alkyl nC-H), 2925 (w, alkyl
C-H), 2862 (w, alkyl nC-H), 1641 (s, dN-H), 1583 (s), 1532 (s), 1478–
[Cu(H-dpa)(propylene)]BF4 (2)
This compound was prepared in an analogous manner to that of
compound 1. Yield: 64%. Mp: 152–154 ◦C (dec.). IR (ATR, cm-1):
3342 (m, nN-H), 3258 (w, aromatic nC-H), 3223 (w, aromatic nC-H),
3156 (w, aromatic nC-H), 3122 (w, aromatic nC-H), 3084 (w, alkene
1340 (s, aromatic dC C), 1231 (s, aromatic dC N), 1070–985 (br vs).
=
=
1H NMR: d 8.22 (2H, br d, 6,6¢-py), 7.91 (2H, br t, 4,4¢-py), 7.22
(2H, br d, 3,3¢-py), 7.13 (2H, br t, 5,5¢-py), 5.30 [1H, ddt, J(H-
H) = 15.2 Hz, J(H-H) = 9.0 Hz. J(H-H) = 7.2 Hz, H2CCH],
4.34 [1H, d, J(H-H) = 9.0 Hz, trans-CH], 4.25 [1H, d, J(H-
H) = 15.2 Hz, cis-CH], 2.06 (2H, br q, CHCH2), 1.47 (2H, br
mult, CH2CH2CH3), 1.38 (2H, br mult, CH2CH2CH3), 0.90 [3H,
t, J(H-H) = 7.2 Hz, CH2CH3]. 13C NMR: d 154.08 (2,2¢-py),
149.75 (6,6¢-py), 141.78 (4,4¢-py), 118.96 (5,5¢-py), 116.17 (3,3¢-
py), 106.30 (CHCH2), 81.87 (CHCH2), 34.65 (CH2CHCH2), 33.79
(CH2CH2CH2), 23.27 (CH2CH3), 14.31 (CH2CH3).
nC-H), 3048 (w, alkene nC-H), 2968 (w, alkyl nC-H), 2929 (w, alkyl nC-H),
1637 (s, dN-H), 1585 (s), 1531 (s), 1475–1375 (s, aromatic dC C), 1230
=
1
(s, aromatic dC N), 1067–993 (br vs). H NMR: d 8.22 (2H, br d,
=
6,6¢-py), 7.90 (2H, br t, 4,4¢-py), 7.20 (2H, br d, 3,3¢-py), 7.11
(2H, br t, 5,5¢-py), 5.29 [1H, ddq, J(H-H) = 15.0 Hz, J(H-H) =
8.9 Hz. J(H-H) = 6.1 Hz, H2CCH], 4.34 [1H, d, J(H-H) = 8.9 Hz,
trans-CH], 4.27 [1H, d, J(H-H) = 15.0 Hz, cis-CH], 1.76 [3H, d,
886 | Dalton Trans., 2009, 878–890
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[Cu(H-dpa)(1-octene)]BF4 (5)
[Cu(H-dpa)(cis-3-octene)]BF4 (8)
This compound was prepared in an analogous manner to that of
compound 4. Yield: 56%. Mp: 123–125 ◦C (dec.). IR (ATR, cm-1):
3333 (m, nN-H), 3259 (w, aromatic nC-H), 3224 (w, aromatic nC-H),
3127 (w, aromatic nC-H), 3083 (w, alkene nC-H), 3053 (w, alkene
This compound was prepared in an analogous manner to that of
compound 4. Yield: 47%. Mp: 142–145 ◦C (dec.). IR (ATR, cm-1):
3344 (m, nN-H), 3257 (w, aromatic nC-H), 3224 (w, aromatic nC-H),
3154 (w, aromatic nC-H), 3123 (w, aromatic nC-H), 3077 (w, alkene
n
C-H), 2922 (w, alkyl nC-H), 2853 (w, alkyl nC-H), 1643 (m, dN-H),
n
n
C-H), 3047 (w, alkene nC-H), 2955 (w, alkyl nC-H), 2927 (w, alkyl
C-H), 2871 (w, alkyl nC-H), 1639 (s, dN-H), 1583 (s), 1531 (m),
1581 (s), 1479–1396 (s, aromatic dC C), 1256 (m, aromatic dC N),
=
=
1056–1006 (br vs). 1H NMR: d 8.23 (2H, br d, 6,6¢-py), 7.92 (2H,
br t, 4,4¢-py), 7.23 (2H, br d, 3,3¢-py), 7.14 (2H, br t, 5,5¢-py),
5.32 [1H, ddt, J(H-H) = 15.0 Hz, J(H-H) = 9.0 Hz, J(H-H) =
1478–1377 (s, aromatic dC C), 1233 (m, aromatic dC N), 1060–992
=
=
1
(br vs). H NMR: d 8.20 (2H, br d, 6,6¢-py), 7.89 (2H, br d,
4,4¢-py), 7.20 (2H, br d, 3,3¢-py), 7.12 (2H, br d, 5,5¢-py), 5.04
=
=
6.8 Hz, H2C CH], 4.36 [1H, d, J(H-H) = 9.0 Hz, trans-CH], 4.26
(2H, m, HC CH), 2.05 (4H, m, CHCH2), 1.49–1.34 (4H, m,
[1H, d, J(H-H) = 15.0 Hz, cis-CH], 2.05 (2H, br q, CHCH2),
1.49 (2H, br quint, CHCH2CH2), 1.35 (2H, br m, CH2Pr),
1.28 (4H, br m, CH2CH2CH3) 0.88 [3H, t, J(H-H) = 6.8 Hz,
CH2CH3]. 13C NMR: d 154.11 (2,2¢-py), 149.78 (6,6¢-py), 141.85
(4,4¢-py), 118.96 (5,5¢-py), 116.23 (3,3¢-py), 107.40 (CHCH2),
82.77 (CHCH2), 34.89 (CH2CHCH2), 32.89 (CH2CH2CH2), 31.38
(CH2CH2CH2), 29.94 (CH2CH2CH2), 23.74 (CH2CH2CH2), 14.51
(CH2CH3).
CH2CH2CH3), 1.07 [2H, t, J(H-H) = 7.5 Hz, CHCH2CH3], 0.93
[3H, t, J(H-H) = 7.2 Hz, CH2CH2CH3]. 13C NMR: d 154.41 (2,2¢-
py), 149.35 (6,6¢-py), 141.54 (4,4¢-py), 119.01 (5,5¢-py), 116.04
(3,3¢-py), 104.80 (CH), 102.89 (CHCH2), 34.14 (CH2Et), 28.84
(CHCH2CH2), 23.66 (CH2CH2CH3), 22.43 (CHCH2CH3), 15.47
(CHCH2CH3), 14.41 (CH2CH2CH3).
[Cu(H-dpa)(trans-3-octene)]BF4 (9)
This compound was prepared in an analogous manner to that of
compound 4. Yield: 46%. Mp: 143–145 ◦C (dec.). IR (ATR, cm-1):
3349 (m, nN-H), 3265 (w, aromatic nC-H), 3230 (w, aromatic nC-H),
3164 (w, aromatic nC-H), 3086 (w, alkene nC-H), 3051 (w, alkene
[Cu(H-dpa)(cis-2-octene)]BF4 (6)
This compound was prepared in an analogous manner to that
of compound 4. Yield: 47%. MP (TGA; decomp.) 145–147 ◦C.
IR (ATR, cm-1): 3352 (m, nN-H), 3261 (w, aromatic nC-H), 3226
(w, aromatic nC-H), 3160 (w, aromatic nC-H), 3123 (w, aromatic
n
C-H), 2961 (w, alkyl nC-H), 2923 (w, alkyl nC-H), 2869 (w, alkyl nC-H),
1646 (s, dN-H), 1586 (s), 1534 (s), 1481–1383 (s, aromatic dC C), 1231
(m, aromatic dC N), 1054–996 (br vs). H NMR: d 8.23 (2H, br
=
1
=
n
n
C-H), 3083 (w, alkene nC-H), 3048 (w, alkene nC-H), 2937 (w, alkyl
C-H), 2857 (w, alkyl nC-H), 1640 (s, dN-H), 1583 (s), 1531 (m), 1479–
d, 6,6¢-py), 7.89 (2H, br t, 4,4¢-py), 7.19 (2H, br d, 3,3¢-py), 7.10
=
(2H, br t, 5,5¢-py), 5.08 (2H, br m, HC CH), 2.04 (4H, br m,
1381 (s, aromatic dC C), 1234 (m, aromatic dC N), 1090–997 (br
=
=
CH2CHCHCH2), 1.49–1.32 (4H, br m, CH2CH2CH3), 1.07 [3H,
t, J(H-H) = 7.3 Hz, CHCH3], 0.91 [3H, t, J(H-H) = 7.2 Hz,
CH2CH3]. 13C NMR: d 154.33 (2,2¢-py), 149.43 (6,6¢-py), 141.66
(4,4¢-py), 118.94 (5,5¢-py), 116.16 (3,3¢-py), 108.14 (CHCH2CH3),
105.73 (CHCH2CH2), 34.37 (CHCH2CH2), 33.74 (CH2CH2CH3),
27.33 (CHCH2CH3), 23.23 (CH2CH2CH3), 15.76 (CHCH2CH3),
14.35 (CH2CH2CH3).
1
vs). H NMR: d 8.21 (2H, br d, 6,6¢-py), 7.90 (2H, br d, 4,4¢-
py), 7.19 (2H, br d, 3,3¢-py), 7.13 (2H, br d, 5,5¢-py), 5.10 (2H,
=
m, HC CH), 2.07 (2H, br q, CHCH2), 1.66 [3H, d, J(H-H) =
5.4 Hz, CHCH3], 1.47 (2H, br quin, CHCH2CH2), 1.34 (4H, br m,
CH2CH2CH3), 0.91 [3H, t, J(H-H) = 7.0 Hz, CH2CH3]. 13C NMR:
d 154.34 (2,2¢-py), 149.39 (6,6¢-py), 141.56 (4,4¢-py), 118.98 (5,5¢-
py), 116.08 (3,3¢-py), 104.10 (CHCHCH2), 97.54 (CHCH3), 32.75
(CH2Et), 30.81 (CH2CH2CH), 28.94 (CH2CH), 23.73 (CH2CH3),
14.48 (CH2CH3), 13.59 (CHCH3).
[Cu(H-dpa)(2-norbornene)]BF4 (10)
This compound was prepared in an analogous manner to that
◦
of compound 4. Yield: 77%. Mp: 169–172 C. IR (ATR, cm-1):
3341 (m, nN-H), 3262 (w, aromatic nC-H), 3224 (w, aromatic nC-H),
3159 (w, aromatic nC-H), 3121 (w, aromatic nC-H), 3055 (w, alkene
[Cu(H-dpa)(trans-2-octene)]BF4 (7)
This compound was prepared in an analogous manner to that of
compound 4. Yield: 53%. Mp: 126–129 ◦C (dec.). IR (ATR, cm-1):
3347 (m, nN-H), 3257 (w, aromatic nC-H), 3223 (w, aromatic nC-H),
3158 (w, aromatic nC-H), 3091 (w, alkene nC-H), 3047 (w, alkene
n
n
C-H), 2982 (w, alkyl nC-H), 2944 (w, alkyl nC-H), 2878 (w, alkyl
C-H), 2853 (w, alkyl nC-H), 1643 (s, dN-H), 1582 (s), 1530 (m), 1478–
1379 (s, aromatic dC C), 1232 (s, aromatic dC N), 1087–965 (br vs).
=
=
1H NMR: d 8.35 (2H, br d, 6,6¢-py), 7.92 (2H, br t, 4,4¢-py),
7.22 (2H, br d, 3,3¢-py), 7.15 (2H, br t, 5,5¢-py), 5.05 (2H, br s,
CH=CH), 3.17 (2H, s, CHCH2CH), 1.65 (2H, m, CH2), 1.27 (1H,
m, CHCH2CH), 1.12 (2H, m, CH2), 0.99 (1H, m, CHCH2CH). 13C
NMR: d 153.87 (2,2¢-py), 150.07 (6,6¢-py), 141.88 (4,4¢-py), 118.95
(5,5¢-py), 116.18 (3,3¢-py), 102.44 (CH=CH), 44.45 (CHCH2CH),
44.41 (CHCH2CH), 25.62 (CH2CH2).
n
C-H), 2940 (w, alkyl nC-H), 2867 (w, alkyl nC-H), 1635 (s, dN-H),
1584 (s), 1532 (s), 1474–1377 (s, aromatic dC C), 1231 (m, aromatic
dC N), 1058–1000 (br vs). H NMR: d 8.22 (2H, br s, 6,6¢-py),
=
1
=
7.89 (2H, br s, 4,4¢-py), 7.19 (2H, br d, 3,3¢-py), 7.10 (2H, br s,
=
5,5¢-py), 5.09 (2H, br m, HC CH), 2.01 (2H, br q, CHCH2),
1.73 (3H, br d, CHCH3), 1.45 (2H, br quin, CHCH2CH2),
1.31 (4H, br m, CH2CH2CH3), 0.89 (3H, br t, CH2CH3). 13C
NMR: d 154.41 (2,2¢-py), 149.31 (6,6¢-py), 141.58 (4,4¢-py),
119.02 (5,5¢-py), 116.08 (3,3¢-py), 109.59 (CHCHCH2), 102.79
(CHCHCH2), 34.07 (CHCHCH2), 32.56 (CH2CH2CH3), 31.50
(CHCH2CH2), 23.65 (CH2CH2CH3), 18.67 (CH2CH2CH3), 14.47
(CH3CH).
[Cu(H-dpa)(1,5-cyclooctadiene)]BF4 (11)
This compound was prepared in an analogous manner to that of
compound 4. Yield: 79%. Mp: 182–185 ◦C (dec.). IR (ATR, cm-1):
3339 (m, nN-H), 3256 (w, aromatic nC-H), 3220 (w, aromatic nC-H),
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Dalton Trans., 2009, 878–890 | 887
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=
[Cu(H-dpa)(Ph2C CH2)]BF4 (15)
3156 (w, aromatic nC-H), 3125 (w, aromatic nC-H), 3086 (w, alkene
C-H), 3013(w, alkene nC-H), 2982 (w, alkyl nC-H), 2949 (w, alkyl nC-H),
n
This compound was prepared in an analogous manner to that of
compound 4. Yield: 25%. Mp: 131–133 ◦C (dec.). IR (ATR, cm-1):
3348 (m, nN-H), 3257 (w, aromatic nC-H), 3225 (w, aromatic nC-H),
3157 (w, aromatic nC-H), 3128 (w, aromatic nC-H), 3084 (w, alkene
2886 (w, alkyl nC-H), 2849 (w, alkyl nC-H), 1634 (s, dN-H), 1582 (s),
1523 (s), 1469–1361 (s, aromatic dC C), 1229 (s, aromatic dC N),
=
=
1076–979 (br vs). 1H NMR: d 8.23 (2H, br d, 6,6¢-py), 7.93 (2H,
br t, 4,4¢-py), 7.24 (2H, br d, 3,3¢-py), 7.17 (2H, br t, 5,5¢-py),
5.50 (4H, br m, CH), 2.40 (8H, br m, CH2). 13C NMR: d 154.40
(2,2¢-py), 149.42 (6,6¢-py), 141.94 (4,4¢-py), 122.46 (CH), 119.45
(5,5¢-py), 116.22 (3,3¢-py), 29.18 (CH2).
n
C-H), 3047 (w, alkene nC-H), 1635 (s, dN-H), 1583 (s), 1532 (s), 1472–
1377 (s, aromatic dC C), 1231 (s, aromatic dC N), 1055–998 (br vs).
=
=
1H NMR: d 8.09 (2H, br d, 6,6¢-py), 7.81 (2H, br t, 4,4¢-py),
7.32 (10H, m, CH Ph), 7.11 (2H, br d, 3,3¢-py), 7.00 (2H, br t,
5,5¢-py), 5.29 (2H, s, CH2). 13C NMR: d 154.83 (2,2¢-py), 149.14
(6,6¢-py), 145.82 (CCH2), 142.64 (1,1¢-Ph), 140.99 (4,4¢-py), 129.50
(o-CH, Ph), 129.36 (m-CH, Ph), 129.09 (p-CH, Ph), 118.50 (5,5¢-
py), 115.85 (3,3¢-py), 106.92 (CH2).
[Cu(H-dpa)(styrene)]BF4 (12)
This compound was prepared in an analogous manner to that of
compound 4. Yield: 82%. Mp: 173–176 ◦C (dec.). IR (ATR, cm-1):
n 3346 (m, nN-H), 3265 (w, aromatic nC-H), 3228 (w, aromatic nC-H),
3162 (w, aromatic nC-H), 3083 (w, alkene nC-H), 3056 (w, alkene nC-H),
Crystallographic studies
1641 (s, dN-H), 1584 (s), 1530 (s), 1477–1378 (s, aromatic dC C), 1231
=
X-Ray data for compounds 5, 6, 8, and 10–13 were collected at
room temperature on a Bruker SMART 1000 CCD diffractometer
equipped with graphite monochromated Mo-Ka radiation (l =
(s, aromatic dC N), 1076–988 (br vs). 1H NMR: d 8.07, (2H, br d,
=
6,6¢-py), 7.85 (2H, br t, 4,4¢-py), 7.54 (2H, d, o-CH, Ph), 7.30, (2H,
t, m-CH, Ph), 7.24 (1H, t, p-CH, Ph), 7.16 (2H, br d, 3,3¢-py), 7.03
(2H, br t, 5,5¢-py), 6.11 [1H, dd, J(H-H) = 15.6 Hz, J(H-H) =
9.7 Hz, CHPh], 4.88 [1H, d, J(H-H) = 15.6 Hz, cis-CH], 4.48
[1H, d, J(H-H) = 9.7 Hz, trans-CH]. 13C NMR: d 153.99 (2,2¢-
py), 149.65 (6,6¢-py), 141.70 (4,4¢-py), 138.79 (1-Ph), 130.20 (m-
CH, Ph), 129.40 (p-CH, Ph), 127.28 (o-CH, Ph), 118.80 (5,5¢-py),
116.03 (3,3¢-py), 105.20 (H2C=CH), 77.97 (H2C=CH).
˚
0.71073 A) and corrected for Lorentz and polarization effects.
Samples were prepared for single crystal X-ray diffraction by
suspending crystal samples in mineral oil under an inert atmo-
sphere, followed by sealing in a thin layer of epoxy resin and
securing to the end of a glass fiber. Fibers were fastened onto brass
pins and mounted onto a fixed-c 4-axis goniometer head. Data
collection and unit cell refinement were carried out according to
established methods33 using the program SMART.34 The program
SAINT35 was used for data reduction, and absorption correction
was applied using SADABS.36 Pertinent details are given in
Table 5. Heavy atom sites were located by Patterson methods
for complexes 8 and 11; all other structures were solved by direct
methods, and models were refined using full-matrix least squares
techniques.37 Refinement was performed with anisotropic thermal
parameters for all non-hydrogen atoms: shift/error less than 0.01.
[Cu(dpa)(cis-stilbene)]BF4 (13)
This compound was prepared in an analogous manner to that
of compound 4. Yield: 33%. Mp: 157–159 ◦C (dec.). Analysis
(calc.,%): C, 57.0 (57.4); H, 4.25 (4.22). IR (ATR, cm-1): 3341 (m,
n
N-H), 3263 (w, aromatic nC-H), 3224 (w, aromatic nC-H), 3161 (w,
aromatic nC-H), 3093 (w, alkene nC-H), 3051 (w, alkene nC-H), 1640
(s, dN-H), 1585 (s), 1531 (s), 1477–1379 (s, aromatic dC C), 1232 (s,
=
All hydrogen atoms were placed in calculated positions [C–Halkene
=
1
aromatic dC N), 1053–1014 (br vs). H NMR: d 7.92 (2H, br s,
=
˚
˚
˚
˚
0.98 A, C–Halkyl = 0.97 A, C–Hmethyl = 0.96 A, C–Haryl = 0.93 A,
6,6¢-py), 7.80 (2H, br s, 4,4¢-py), 7.27 (4H, m, o-CH), 7.14 (8H, br
m + s, m-CH, p-CH + 3,3¢-py), 6.88 (2H, br s, 5,5¢-py), 6.25 (2H,
s, CHPh). 13C NMR: d 154.32 (2,2¢-py), 149.32 (6,6¢-py), 141.47
(1,1¢-Ph), 138.25 (4,4¢-py), 130.44 (o-CH, Ph), 129.47 (m-CH, Ph),
128.71 (p-CH, Ph), 118.80 (5,5¢-py), 115.99 (3,3¢-py), 108.50 (CH).
˚
N–H = 0.86 A] for refinement. Neutral-atom scattering factors
were taken from the usual source.38 Refinement of positional and
anisotropic displacement parameters led to convergence for all
data. The program used for structure solution and refinement was
SHELXTL Version 5.10.39 The program PLATON was employed
for structure validation.40 Selected bond lengths and angles are
given in Table 1.
[Cu(H-dpa)(trans-stilbene)]BF4 (14)
Refinement of compound 6 indicated that the C5H11 groups
[C(14)–C(18)] showed a site occupancy disorder. While the first
methylene carbon [C(14)] has a fixed position, the remainder of
the alkyl chain exhibits a reversal of the conformation of the
substituent with a 60:40 site occupancy (Fig. S2†). Disordered
atoms C(15) through C(18) were refined with site occupancies
of 60:40 [C(15a)–C(18a):C(15b)–C(18b)], with adjacent C–C dis-
This compound was prepared in an analogous manner to that
of compound 4. Yield: 25%. Mp: 126–128 ◦C (dec.). Analysis
(calc.,%): C, 57.6 (57.4); H, 4.19 (4.22). IR (ATR, cm-1): 3348 (m,
n
N-H), 3263 (w, aromatic nC-H), 3227 (w, aromatic nC-H), 3163 (w,
aromatic nC-H), 3078 (w, alkene nC-H), 3059 (w, alkene nC-H), 3021
(w, alkene nC-H), 1642 (s, dN-H), 1583 (m), 1532 (m), 1478–1423 (s,
aromatic dC C), 1234 (m, aromatic dC N), 1073–1014 (br vs). H
1
˚
tances restrained to 1.54(0.025) A and alternating C–C distances,
=
=
˚
NMR: d 8.06 (2H, br d, 6,6¢-py), 7.78 (2H, br t, 4,4¢-py), 7.57
(4H, br d, o-CH Ph), 7.32 (4H, br t, m-CH Ph), 7.23 (2H, br t,
p-CH, Ph), 7.06 (2H, br d, 3,3¢-py), 6.97 (2H, br t, 5,5¢-py), 6.88
(2H, s, CHPh). 13C NMR (298 K; CD3OD): d 154.58 (2,2¢-py),
149.50 (6,6¢-py), 141.32 (4,4¢-py), 138.80 (1,1¢-Ph), 129.98 (m-CH,
Ph), 128.87 (p-CH, Ph), 127.64 (o-CH, Ph), 122.19 (CH), 118.73
(5,5¢-py), 115.88 (3,3¢-py).
i.e. C(15a)–C(17a), restrained to 2.60(0.05) A. H atoms for C(18a)
and C(18b) were placed in idealized positions for a disordered
methyl group. This form of static disorder is sometimes observed
for “floppy” ligands.41,42 Such disorder is seen to a lesser extent
in the other two complexes having long alkyl chains (5 and 8), as
shown by their relatively large thermal ellipsoids. These disorders
are likely a result of room temperature data collection. Refinement
888 | Dalton Trans., 2009, 878–890
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©

View Article Online
Table 5 Summary of X-ray diffraction data
Compound
5
6
8
10
11
12
13
Empir. formula
MW
CuC18H25N3BF4 CuC18H25N3BF4 CuC18H25N3BF4 CuC17H19N3BF4 CuC18H17N3BF4 CuC18H17N3BF4 CuC24H21N3BF4
433.76
Monoclinic
C2/c
433.76
Monoclinic
P21/n
433.76
Triclinic
¯
P1
415.70
Monoclinic
C2/c
425.70
Monoclinic
P21/m
425.70
Monoclinic
P21/n
501.79
Monoclinic
P21/n
Cryst. system
Space group
˚
a/A
17.770(4)
10.399(2)
23.290(5)
8.885(1)
10.554(2)
21.729(4)
9.652(1)
10.106(1)
11.396(1)
69.020(2)
77.699(2)
80.746(2)
1009.7(2)
2
21.438(4)
14.935(3)
14.510(3)
7.217(1)
11.797(2)
10.771(2)
12.503(3)
10.368(2)
13.827(3)
10.324(2)
22.671(5)
10.923(2)
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
108.98(3)
92.36(3)
130.56(3)
95.30(3)
92.70(3)
116.92(3)
3
˚
V/A
4069(1)
8
2035.9(7)
4
3529(1)
8
913.0(3)
2
1790.5(6)
4
2279.8(8)
4
Z
D
calc/g cm-3
1.416
1.115
1.415
1.115
1.427
1.124
1.565
1.283
1.563
1.242
1.579
1.266
1.462
1.007
m/mm-1
2q range/◦
No. collected
3.70–56.50
24172
3.76–56.62
24020
3.88–56.64
12398
3.70–56.86
20570
3.80–56.58
7472
4.30–56.86
21029
3.60–56.68
27790
No. ind. (Rint
No. obsd. (|Fo| >
4.0 |Fo|)
)
4921 (0.1494)
1475
4942 (0.0551)
1921
4798 (0.0419)
1900
4279 (0.0860)
2401
2289 (0.0258)
1699
4329 (0.1717)
1505
5568 (0.1147)
2098
R
0.0702
0.1501
0.413, -0.340
0.0556
0.1536
0.549, -0.343
0.0495
0.1258
0.269, -0.229
0.0883
0.2193
1.523, -0.623
0.0656
0.1796
1.456, -0.955
0.0656
0.1529
0.696, -0.843
0.0713
0.1584
0.629, -0.310
Rw
Largest difference
peak and hole/e A
-3
˚
Weights
CCDC Deposit No. 692443
0.0671, 0
0.1113, 0.9024
692444
0.0825, 0
693280
0.0575, 0
692446
0.0977, 1.5308
698583
0.0920, 0
692447
0.0820, 0.7302
692445
of 5 and 8 as having site occupancy disorder in the alkyl chains did
not result in better agreement of data, so refinement was performed
without the disorder.
University. We acknowledge Dr Robert C. Schucker and Michael
F. Lynch for useful discussion.
The BF4- anion in compounds 8 and 11 show a 50:50 positional
disorder (Fig. S3 and S4, respectively). For compound 8 the
disordered atoms F(1) through F(4) were refined with 50:50
site occupancies [F(1)–F(4):F(1a)–F(4a)]. In compound 11 only
fluorine atoms F(1) through F(4) are present in the asymmetric
unit of the complex. Disordered atoms F(1a)–F(4a) were refined
with 50% site occupancies, as B(1) lies on a mirror plane. For
initial refinement cycles, similar distance restraints (SADI) were
placed on all B–F and F–F distances, in addition to similar ADP
restraints (SIMU) and rigid bond restraints (DELU) for all F
atoms. Restraints were lifted for final refinement cycles.
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were prepared using MOPAC44 semi-empirical energy minimiza-
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3G level.45,46 Subsequent modeling was performed using effective
electron core potentials for Cu at the B3LYP/LanL2DZ basis
set level.47,48 The 6-311++G* basis set49 was used for N, C, and
H atoms. Final calculations were then performed at the RMP2-
FC/LanL2DZ level.50 Gaussian 03 Package was used for all
calculations.51
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Financial support for this work is provided by Trans Ionics
Corporation. The Robert A. Welch Foundation is acknowledged
for funding of the Texas Center for Crystallography at Rice
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 878–890 | 889
©

View Article Online
18 J. Zhang, R.-G. Xiong, J.-L. Zuo and X.-Z. You, Chem. Commun.,
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