Synthesis and characterization of aryl substituted bis(2-pyridyl)amines and their copper olefin complexes: Investigation of remote steric control over olefin binding

Article abstract of DOI:10.1039/c0dt00608d

The aryl-functionalized pyridylamine 2-ⁱPrC₆H ₄N(H)py (1) and bis(2-pyridyl)amines of the type ArN(py)₂ for Ar = Mes (2), 2,6-Et₂C₆H₃ (3), 2- ⁱPrC₆H₄

Full text of DOI:10.1039/c0dt00608d

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Synthesis and characterization of aryl substituted bis(2-pyridyl)amines and
their copper olefin complexes: Investigation of remote steric control over olefin
binding†
John J. Allen, Christopher E. Hamilton and
Andrew R. Barron*
Received 5th June 2010, Accepted 14th July 2010
DOI: 10.1039/c0dt00608d
The aryl-functionalized pyridylamine 2-iPrC6H4N(H)py (1) and bis(2-pyridyl)amines of the type
ArN(py)2 for Ar = Mes (2), 2,6-Et2C6H3 (3), 2-iPrC6H4 (4), 2,6-iPr2C6H3 (5), and 1-naph (6), have been
prepared by the palladium-catalyzed cross-coupling of substituted anilines with 2-bromopyridine, and
have been characterized by 1H and 13C NMR NMR, FTIR, MS, and TGA. Complexes of these new
N-aryl bis(2-pyridyl)amines have been prepared for the acid salts [H{ArN(py)2}]BF4 where Ar = Mes
(7) and 2-iPrC6H4 (8), and the dimeric bridged complexes [Cu{ArN(py)2}(m-X)(Y)]2 where X/Y = Cl-
and Ar = Ph (9), 2-iPrC6H4 (10), and 1-naph (11), in addition to X = OH-, Y = H2O and Ar = Mes (12).
The olefin complexes [Cu(Ar-dpa)(styrene)]BF4 for Ar = Ph (13), Mes (14), 2-iPrC6H4 (15), and 1-naph
(16), in addition to the norborylene complexes of Ar = Mes (17) and 2-iPrC6H4 (18) have been prepared
and characterized by 1H and 13C NMR, FTIR, and TGA. The crystal structures have been determined
for compounds 1–17. Secondary amine 1 crystallizes in hydrogen-bonded head-to-tail dimers, while the
N-aryl bis(2-pyridyl)amines 2–6 crystallize in a three-bladed propellar conformation, having nearly
planar geometries about the amine nitrogen. The geometry about copper centers in the dimeric
complexes 9–12 is distorted trigonal bypyramidal, with the axial positions occupied by one of the two
pyridyl nitrogens and one of the bridging ligands (i.e., Cl or OH). The copper atoms in each of the
olefin complexes 13–17 are coordinated to the two pyridine nitrogen atoms and the appropriate olefin;
consistent with a pseudo three-coordinate Cu(I) cation. Distortion of pyridyl ring geometries about the
copper centers, and concomitant bending of the aryl groups away from the Cu ◊ ◊ ◊ N(amine) vectors
were found to correlate with the steric bulk of the aryl group present in both dimeric and olefin
complexes. Such distortion is also observed to a lesser extent in the acid salts as well. The 1H and 13
C
NMR spectra of [Cu(Ar-dpa)(olefin)]BF4 exhibit an upfield shift in the olefin signal as compared to free
olefin. A good correlation exists between the 1H and 13C NMR Dd values and olefin dissociation
temperatures, confirming that the shift of the olefin NMR resonances upon coordination is associated
with the binding strength of the complex.
Introduction
(1)
The control over the selective binding of olefins to a metal center
In designing a suitable coordination system for olefins, sev-
eral groups have based the system on a biological model for
ethylene complexation.5,6 These studies have also demonstrated
that stable Cu ◊ ◊ ◊ olefin interactions can be achieved using mul-
tidentate, electron rich N-donor ligands.7,8,9 The class of ligand
most commonly used is the neutral N-donor heterocyclic com-
pounds, including bis(pyrazolyl)methanes,10 dipyridylamine,11,12
phenanthroline,13 and bipyridines.14 Of all these studies, it is the
report by Thompson and Whitney that has formed the basis for our
studies. They showed that stable copper complexes with ethylene
are formed with the chelate ligand bis(2-pyridyl)amine (Hdpa).
We have shown that the bis(2-pyridyl)amine ligand (I, where
Ar = H) allows for the isolation and structural characterization of a
wide range of ionic copper ◊ ◊ ◊ olefin complexes.15 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 cis-olefins.
has the potential as a simple route to overcoming the inherent
difficulty in the separation of different olefins with near identical
boiling points.1,2 To this end, various complexing reagents have
been described,3 where the function of the complexing agent is to
coordinate the olefin under one condition, and liberate it under
another (eqn (1)).4
Department of Chemistry, Rice University, Houston, Texas, 77005, USA.
E-mail: arb@rice.edu
† Electronic supplementary information (ESI) available: IR and 13C NMR
spectral data. Thermal ellipsoid plots of the second unique molecule
present in the asymmetric unit 3–5, 14, and 16 (including structural
disorder for 4), as well as comparisons between conformers for 3–5, and 14.
Structural disorders for BF4- in 7, 8, and 12–15, and PF6- in 17. Highlighted
intermolecular interactions present in 9, 11–13, and 17. CCDC reference
numbers 720342 (1), 720335 (2), 720338 (3), 720340 (4), 720339 (5), 720337
(6), 720347 (7), 735399 (8), 720344 (9), 733833 (10), 720343 (11), 720346
(12), 724010 (13), 724009 (14), 740151 (15), 743482 (16), and 728875 (17).
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c0dt00608d
1
Using H and 13C NMR we showed that there is a significant
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difference in binding between a terminal and internal olefin, but
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 results suggested that while
differential complexation of cis and trans isomers is possible using
a H-dpa type ligand, separation of different internal olefins by
their C C position will not be possible. However, the use of pre-
folded bis(2-pyridyl)amine ligands should allow for differentiation
in coordination of olefin isomers.
Herein we report the synthesis and structural characterization
of a range of aryl substituted bis(2-pyridyl)amines (I), along with
their copper complexes in order to determine how the steric bulk of
the aryl substituent effects the geometry of the ligand. In addition,
we report the affect of remote steric substitution on the binding of
an olefin to copper.
Results and discussion
The direct reaction of an aniline with 2-bromopyridine yields the
appropriate mono-pyridyl amine derivatives, i.e., ArN(H)py, see
Scheme 1. We have found that in order to prepare the associated
dipyridyl amine derivatives, ArN(py)2 (hereafter referred to as Ar-
dpa), it is better to isolate the mono-pyridyl amine and react
with additional 2-bromopyridine in the presence of a catalyst,
see Scheme 1 and Experimental. Using these methods we have
prepared the new pyridyl amine compounds, (2-iPrC6H5)N(H)py
(1), and Ar-dpa, where Ar = Mes (2), 2,6-Et2C6H3 (3), 2-iPrC6H5
(4), 2,6-iPr2C6H3 (5), and naphthyl (6).
During a study of the consequences of increased steric effects
of quinolyl instead of pyridyl (i.e., II16 and III17) we have
observed that the presence of a sterically hindered aryl group
on the amine nitrogen results in a distortion about the amine
nitrogen. Furthermore, molecular mechanics calculations on
aryl substituted bis(2-pyridyl)amine ligands (I) suggest that the
presence of the aryl substituent results in a folding of the bis(2-
pyridyl)amine unit. Based upon this initial data we have proposed
that steric substitution remotely from the metal could have an
effect on the binding of an olefin to copper.
Compounds 1–6 have been characterized by NMR and IR
spectroscopy, as well as mass spectrometry. The molecular struc-
tures for compounds 1–6 have been determined by single crystal
X-ray diffraction. Selected bond lengths and angles can be found
Scheme 1 Synthesis routes to Ar–dpa. (a) neat, reflux 2 h, (b) NaOtBu, Pd cat., toluene 90 ◦C, and (c) neat, 180 ◦C, 2 h.
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◦
a
˚
Table 1 Selected bond lengths (A) and angles ( ) for compound 1
N(1)–C(1)
N(1) ◊ ◊ ◊ N(2¢)
1.363(2)
2.995(2)
N(1)–C(6)
1.419(2)
N(1)–H(1a ◊ ◊ ◊ N(2¢)
cAr
173(2)
85.4(2)
qAr
fAr
125.5(1)
66.07(9)
a
q-bond angle Cpy–N–Ci; c-torsion Npy–Cpy–Ci–(C N-1)I; f-mean-
plane angle from py ring.
in Tables 1 and 2. Details of data collection and structure solution
and refinement are outlined in the Experimental section.
The molecular structure of the secondary aromatic amine
compound 1 is shown in Fig. 1, selected bond lengths and
angles are given in Table 1. Bond distances and angles measured
between the amine nitrogen, N(1), and its substituent carbon
atoms are within the ranges of those reported for ArN(H)py
(Ar = Mes, 2,6-Et2C6H3, 2,6-iPr2C6H3, and napthyl) [N–Cpy =
˚
˚
1.355(3)–1.370(6) A; N◦–CAr = 1.415(6)–1.435(3) A; Cpy–N–
CAr = 122.4(1)–126.6(4) ].18-24 As is typical for compounds of the
type ArN(H)py, compound 1 crystallizes in the hydrogen-bonded
head-to tail dimer, and the N–H ◊ ◊ ◊ N interaction [N(1) ◊ ◊ ◊ N(2¢) =
Fig. 1 Molecular structure of compound 1. Thermal ellipsoids are shown
at the 30% level, and hydrogen atoms attached to carbon are omitted for
clarity.
˚
2.995(2) A] is comparable to those previously reported for anal-
˚
ogous compounds [2.929(6) – 3.041(2) A]. However, the presence
of the bulky isopropyl group prevents any p–p stacking similar to
that seen in homologous compounds.
˚
The N–C bond lengths [1.438(5)–1.454(3) A] and the angles
The molecular structures for compounds 2–6 are shown in
Fig. 2–6, while selected bond lengths and angles can be found
in Table 2. Compounds 3–5 crystallize with two independent
molecules in the asymmetric unit, and the atom numbering
schemes for the second molecule of each are given in Fig. S1,
S3, and S5.† The most significant differences observed between
the two conformers are the orientation of alkyl substituents on the
phenyl rings, the degree of pitch between the planes of the rings,
and C–N–C bond angles between rings (Table 2 and Fig. S2, S4,
and S6†).
between the tertiary amine nitrogen and the aryl substituent
[116.4(3)–120.4(3)◦] also seem to match well with similar com-
◦
˚
pounds [1.415(3)–1.463(4) A and 117.2(1)–121.3(2) , respectively].
The geometry about N(1) in compounds 2–6 is essentially planar
ꢀ
(
C–N–C = 359.3 – 360◦); consequently the pyridyl and aryl
rings are forced to twist out of plane due to the steric bulk of
the ortho-substituents. Thus, as proposed, the presence of the
aryl’s substituents forces the pyridyl rings out of plane from
the NC3 core. Interestingly, the trend is the opposite of what
may be expected, i.e., the greater the steric bulk of the ortho-
substituents the more co-planar the pyridyl rings. This may be
seen from a consideration of either the N(2)–C(1) ◊ ◊ ◊ C(6)–N(3)
torsion angle or the angle between the mean plane of each pyridyl
ring (MPLN[py–py¢]) for compounds 2 (R = Me), 3 (R = Et), and
The N–C bond lengths and the bond angles between the amine
nitrogen and the heterocycles in the compounds 2–6 [1.398(3)–
◦
˚
1.416(4) A and 123.2(3)–124.6(1) , respectively] are within the
ranges to previously reported aryl-substituted dipyridylamines
◦
25,26
i
˚
[1.400(2)–1.435(3) A, 118.8(1)–123.8(1) ],
as well as N-alkyl
˚
5 (R = Pr), see Table 2. In part, this may be explained by a greater
◦
27,28
pyridyl- and quinolyl-amines [1.378(4)–1.415(4) A, 123.7(3) ].
twisting of the aryl ring with respect to the amines’s NC3 core with
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for Ar–dpa
Compound
2
3a
4a
5a
6
N(1)–C(1)
N(1)–C(6)
N(1)–C(11)
C(1)–N(1)–(6)
C(1)–N(1)–C(11)
C(6)–N(1)–C(11)
N(2)–C(1)–C(6)–N(3)
N(2)–C(1)–N(1)–C(11)
N(3)–C(6)–N(1)–C(11)
MPLN[py–py¢]
MPLN[py–Ar]
MPLN[py¢–Ar]
1.398(3)
1.411(3)
1.439(3)
124.0(2)
118.3(2)
117.6(1)
119.1(3)
151.4(2)
24.1(4)
1.402(5), 1.402(5)
1.403(5), 1.413(5)
1.442(5), 1.438(5)
123.4(3), 123.2(3)
117.8(3), 120.4(3)
118.6(3), 116.4(3)
119.1(4), 126.9(5)
21.8(5), 15.3(6)
1.403(4), 1.395(4)
1.411(4), 1.416(4)
1.445(5), 1.453(4)
123.7(3), 124.6(3)
118.2(3), 118.7(3)
117.8(3), 116.6(3)
124.1(5), 127.8(5)
156.1(4), 159.3(4)
22.0(5), 24.3(4)
1.405(3), 1.405(3)
1.387(3), 1.400(3)
1.454(3), 1.451(3)
124.0(1), 124.5(2)
117.5(2), 117.3(1)
117.8(1), 118.0(1)
120.3(3), 128.9(3)
22.3(3), 23.6(3)
1.411(1)
1.410(1)
1.442(1)
124.6(1)
117.0(1)
117.9(1)
137.2(1)
155.7(1)
17.5(1)
149.5(5), 145.6(4)
47.5(2), 46.5(2)
87.3(2), 82.1(2)
153.8(2), 162.0(2)
46.4(1), 40.7(1)
88.9(1), 85.1(1)
48.7(1)
82.0(1)
81.1(1)
43.3(2), 41.8(2)
85.8(2), 84.9(2)
88.8(2), 85.4(2)
42.17(7)
84.02(7)
69.49(7)
87.3(2), 86.5(2)
81.7(1), 79.7(1)
a Two crystallographically independent molecules in the asymmetric unit. The atom numbering scheme for the second molecule is given in Fig. S1, S3,
and S5.†
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Fig. 4 Molecular structure of one of the two crystallographically
independent molecules of compound 4. Thermal ellipsoids are shown at
the 30% level, and all hydrogen atoms are omitted for clarity.
Fig. 2 Molecular structure of compound 2. Thermal ellipsoids are shown
at the 30% level, and all hydrogen atoms are omitted for clarity.
Fig. 5 Molecular structure of one of the two crystallographically
independent molecules of compound 5. Thermal ellipsoids are shown at
the 30% level, and all hydrogen atoms are omitted for clarity.
Fig. 3 Molecular structure of one of the two crystallographically
independent molecules of 3. Thermal ellipsoids are shown at the 30%
level, and all hydrogen atoms are omitted for clarity.
Based upon the forgoing, the presence of ortho-substitution
in the uncomplexed Ar-dpa compounds results in a significant
distortion of the coordination around the amine nitrogen and
twisting of the two pyridyl rings with respect to each other.
larger substituents. As may be seen from Table 2, the pyridyl rings
appear more coplanar for asymmetrically substituted aryl groups.
A plot of N(1)–C(11) bond distance (also an indirect measure of
the twist of the aryl ring) versus the angle between the mean plane
of each pyridyl ring (MPLN[py–py¢]) for compounds 2–6, as well
as the previously reported analogs shows a distinct trend (Fig. 7a).
The inter-pyridyl angle [C(1)–N(1)–C(6)] is also dependent on the
N(1)–C(11) distance (Fig. 7b). However, a closer consideration of
the ortho-versus para-substitution suggests that electronic factors
also come into play. Specifically, ortho-substituents result in longer
bond lengths and larger bond angles.
Acid confinement of the conformation of the pyridyl rings in Ar-dpa
Based upon the structural trends of compounds 2–6, it is clear
that the steric bulk of the aryl substituents has a controlling
influence on the orientation of the pyridyl rings. In the free
compounds this influence results in the twisting of the pyridyl rings
with regard to each other, and their splaying out [i.e., increased
C(1)–N(1)–C(6) angle] to relieve the steric strain imposed by the
aryl’s ortho-substituents. However, in a coordination complex the
pyridyl nitrogen atoms are held by the geometry of the complex,
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˚
Table 3 Selected bond lengths (A) and angles ( ) for compounds 7 and 8
7
8
N(1)–C(1)
N(1)–C(6)
N(1)–C(11)
1.394(3)
1.417(3)
1.453(3)
1.04(3)
1.61(3)
2.40(3)
124.6(1)
117.1(1)
118.1(1)
120(2)
1.382(3)
1.403(3)
1.449(3)
1.18(3)
1.51(3)
2.28(3)
125.4(2)
116.9(2)
117.7(2)
114(2)
N(2) ◊ ◊ ◊ H
N(3) ◊ ◊ ◊ H
F ◊ ◊ ◊ H
C(1)–N(1)–C(6)
C(1)–N(1)–C(11)
C(6)–N(1)–C(11)
N(2)–H ◊ ◊ ◊ F
MPLN[py–py¢]
MPLN[py–Ar]
MPLN[py¢–Ar]
5.0(1)
83.3(1)
81.3(1)
1.7(1)
89.5(1)
89.4(1)
in confinement in the orientation of the pyridyl and quinolyl
rings in the isolated complex, [PhN(py)(H-quin)]BF4.17 In order
to ascertain the geometric effects of the aryl substituents in a
simple complex we have structurally characterized the protonated
derivatives. Protonation of ArN(py)2 can be accomplished by the
reaction of KBF4 dissolved in dilute HCl (Experimental).17 The
molecular structures of 7 and 8, which are the HBF4 salts of
compound 2 and 4, respectively, are shown in Fig. 8 and Fig. 9.
Selected bond lengths and angles are given in Table 3.
Fig. 6 Molecular structure of compound 6. Thermal ellipsoids are shown
at the 30% level, and all hydrogen atoms are omitted for clarity.
Fig. 8 Molecular structure of [(Mes–dpa)H]BF4 (7). Thermal ellipsoids
are shown at the 30% level, and hydrogen atoms attached to carbon are
omitted for clarity.
The pyridyl nitrogens in compounds 7 and 8 are found to
coordinate the proton in an asymmetric fashion (Table 3). This
degree of asymmetry is not observed in the structurally similar
Fig. 7 Plot of the N–CAr bond lengths versus (a) the mean-plane-differ-
ence between pyridyl rings (R2 = 0.793) and (b) Cpy–N–Cpy¢ bond angle
(R = 0.828) for compounds 2–6, as well as previously reported Ar–dpa
derivatives.
29
˚
˚
HClO4 and HBr salts [1.362(6) and 1.362(6) A; 1.33 and 1.40 A],
30
˚
or the [(H-dpa)H]CoCl4 complex [1.33(3) and 1.36(3) A]. The
asymmetry is more pronounced for the mesityl derivative (7) than
the 2-iPrC6H4 compound (8).
and thus a different distortion will be required to release the
steric strain. We have previously reported that the protonation
of the N-(2-pyridyl)-N-(2-quinolyl)amine, PhN(py)quin, results
The N–C distances about the amine nitrogen in compounds 7
and 8 are similar to those observed in the free ligands. Considera-
tion of the fold angle, i.e., the mean-plane-angle difference between
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Fig. 9 Molecular structure of [(2-iPr–C6H4–dpa)H]BF4 (8). Thermal
ellipsoids are shown at the 30% level, and hydrogen atoms attached to
carbon are omitted for clarity.
Fig. 10 Molecular structure of the [Cu(Ph–dpa)(Cl)(m-Cl)]2 (9) dimer.
Thermal ellipsoids are shown at the 30% level, and all hydrogen atoms are
omitted for clarity.
pyridyl rings [5.0(1) and 1.7(1)◦, respectively], and the N–C–C–N
torsion angle across the amine-bound carbons [4.9(2) and 1.3(2)◦,
respectively], reveals that, in contrast to the free ligands, the two
heterocycles are almost coplanar in the complexes. However, as a
result of the forcible co-planarity of the two pyridyl rings, there
is a bending-up of the aryl group out of the di-pyridyl plane. The
observed bending of the aryl group is found to be slightly greater
for the mesityl derivative [8.0(8)◦ versus 4.9(6)◦].
The presence of ortho-substitution in the complexed Ar-dpa
compounds, in which the two pyridyl rings are constrained
by a complexed atom, results in the bending-up of the aryl
ring substituent out of the di-pyridyl plane with consequential
folding of the two pyridyl into a “butterfly” conformation. In
order to ascertain whether these distortions translate to metal
derivatives we have structurally characterized simple dimeric
copper complexes of Ar-dpa.
Copper(II) complexes of Ar–dpa
The copper complexes [Cu(Ph–dpa)(Cl)(m-Cl)]2 (9), [Cu(2-
iPrC6H4–dpa)(Cl)(m-Cl)]2 (10), and [Cu(Nap–dpa)(Cl)(m-
Cl)]2·(MeOH)2 (11) are prepared by the reaction of
[Cu(MeCN)4]BF4 with the appropriate Ar–dpa in tetraethylelene
glycol in the presence of dilute HCl. If the reaction is
carried out using Mes–dpa (2) in the presence of water, the
structurally related hydroxy derivative, [Cu(Mes–dpa)(H2O)(m-
OH)]2[BF4]2·(MeOH)2, (12) is isolated. Despite the difference in
ligation and charge, compound 12 is isolobal with compounds
9–11.
Fig. 11 Molecular structure of the [Cu(2-iPrC6H4–dpa)(Cl)(m-Cl)]2 (10)
dimer. Thermal ellipsoids are shown at the 30% level, and all hydrogen
atoms are omitted for clarity.
the second half of the molecule is symmetry related through an
inversion center.
The coordination geometry about the copper centers in
compounds 9–12 is a distorted trigonal bipyramid, with the
axial positions occupied by one of the two pyridyl nitrogens
and one of the bridging ligands (i.e., Cl or OH), with the
trans-angle ranging from 171.8(1)–178.2(1)◦ (Tables 4 and 5).
The trigonal bipyramidal coordination spheres observed in
these bridged dimers is common in other structurally related
The molecular structures of compounds 9–11 are shown in
Fig. 10–12; selected bond lengths and angles are given in Table 4.
+
The structure of the cation, [Cu(Mes–dpa)(H2O)(m-OH)]2 , is
shown in Fig. 13, with selected bond lengths and angles given
in Table 5. Compounds 9, 11, and 12 crystallize with only half of
the molecule in the asymmetric unit of the unit cell. In each case,
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◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for compounds 9–11
Compound
9a
10
11a
Cu(1)–Cl(1)
Cu(1)–Cl(1A)
Cu(2)–Cl(1)
Cu(2)–Cl(2)
Cu(1)–Cl(2)
Cu(2)–Cl(4)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(2)–N(5)
Cu(2)–N(6)
N(1)–C(1)
N(4)–C(17)
N(1)–C(6)
N(4)–C(22)
N(1)–C(11)
N(4)–C(27)
Cu(1) ◊ ◊ ◊ Cu(1A)
Cl(1)–Cu(1)–Cl(1A)
Cl(1)–Cu(2)–Cl(2)
Cl(1)–Cu(1)–Cl(2)
Cl(2)–Cu(2)–Cl(4)
Cl(1)–Cu(1)–N(2)
Cl(1)–Cu(1)–N(3)
Cl(2)–Cu(2)–N(6)
Cl(1)–Cu(2)–N(5)
Cl(2)–Cu(1)–N(2)
Cl(2)–Cu(1)–N(3)
N(2)–Cu(1)–N(3)
N(5)–Cu(2)–N(6)
Cu(1)–Cl(1)–Cu(1A)
C(1)–N(1)–C(6)
C(17)–N(4)–C(22)
C(1)–N(1)–C(11)
C(17)–N(4)–C(27)
C(22)–N(4)–C(27)
2.2755(6)
2.7299(7)
2.261(1)
2.698(1)b
2.264(1)
2.683(1)
2.286(1)c
2.285(1)
2.013(4)
2.018(4)
2.016(4)
2.028(4)
1.399(6)
1.417(6)
1.412(7)
1.403(6)
1.450(7)
1.454(6)
3.594(1)d
87.64(5)e
88.03(5)
92.85(6)f
93.39(6)
177.8(1)
93.4(1)
2.296(2)
2.596(2)
2.2547(9)
2.285(2)
2.025(1)
2.030(1)
2.020(6)
1.998(6)
1.421(2)
1.421(3)
1.416(3)
1.415(9)
1.404(8)
1.466(8)
3.6728(8)
86.03(2)
3.513(1)
88.41(7)
93.45(3)
91.92(9)
92.01(5)
176.18(5)
92.4(1)
177.2(1)
178.2(1)
99.0(1)
Fig. 12 Molecular structure of the [Cu(Naph–dpa)(Cl)(m-Cl)]2 (11)
dimer. Thermal ellipsoids are shown at the 30% level, and all hydrogen
atoms are omitted for clarity.
156.14(5)
89.30(5)
86.52(6)
90.5(1)g
97.5(1)h
86.7(1)
148.7(1)
88.6(1)
85.7(2)
85.6(1)
93.97(2)
115.6(1)
92.30(5)i
122.4(4)
122.1(4)
119.3(4)
118.6(4)
118.1(4)
119.2(4)
91.59(7)
123.1(6)
121.1(1)
123.1(1)
118.4(5)
118.0(6)
a Centrosymmetric structures. b Cu(1)–Cl(2). c Cu(1)–Cl(3). d Cu(1)–Cu(2).
e Cl(1)–Cu(1)–Cl(2). f Cl(1)–Cu(1)–Cl(3). g Cl(3)–Cu(1)–N(2). h Cl(3)–
Cu(1)–N(3). i Cu(1)–Cl(1)–Cu(2).
◦
˚
Table 5 Selected bond lengths (A) and angles ( ) for compound 12
Cu(1)–N(2)
Cu(1)–O(1)
Cu(1)–O(2)
N(1)–C(6)
Cu(1) ◊ ◊ ◊ Cu(1a)
N(2)–Cu(1)–N(3)
N(2)–Cu(1)–O(1A)
N(3)–Cu(1)–O(1)
N(3)–Cu(1)–O(2)
O(1)–Cu(1)–O(2)
C(1)–N(1)–C(6)
C(6)–N(1)–C(11)
1.977(2)
1.960(2)
2.223(3)
1.407(3)
2.9666(9)
86.6(1)
171.8(1)
162.4(1)
101.3(1)
96.0(1)
Cu(1)–N(3)
Cu(1)–O(1a)
N(1)–C(1)
1.987(2)
1.953(2)
1.404(3)
1.453(4)
N(1)–C(11)
N(2)–Cu(1)–O(1)
N(2)–Cu(1)–O(2)
N(3)–Cu(1)–O(1A)
O(1)–Cu(1)–O(1A)
Cu(1)–O(1)–Cu(1a)
C(1)–N(1)–C(11)
94.73(9)
95.6(1)
94.9(1)
81.39(9)
98.61(9)
116.6(2)
Fig. 13 Molecular structure of the [Cu(Mes-dpa)(H2O)(m-OH)]22+ cation
(12). Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
attached to carbon are omitted for clarity.
125.4(2)
116.8(2)
36
compounds [Cu{CH2(py)2}(Cl)(m-Cl)]2,31 [Cu(o-phen)(Cl)(m-
Cl)]2,32 [Cu(bipy)(Cl)(m-Cl)]2,33 and [Cu(o-phen)(H2O)(m-
OH)]2NO3.34
the bipy/PhNHpy complex [1.94(1) and 1.96(1) A], and the
˚
37
˚
bis(imidazolin-2-imine) complex [1.932(2) and 1.930(2) A]. The
Cu–O distance for the aquo ligand [2.223(3)] is also similar to those
38,39
˚
The Cu–Cl distances between bridging and non-bridging chlo-
previously reported [2.035(4)–2.518(1) A].
The observed Cu–
˚
rine atoms in 9–11 are with the ranges [2.255(3)–2.722(3) A
(m-O)–Cu(1A) angle in 12 is slightly larger than the corresponding
angles in the chloride analogs, but much longer distances between
bridging atoms in the latter result in significantly longer [3.513(1)–
˚
and 2.256(1)–2.272(3) A] previously reported for similar
compounds.31–33 The Cu–O distances for the bridging hydroxo
˚
˚
˚
ligands [1.960(2) and 1.953(2) A] are similar to those reported
3.6728(8) A] Cu ◊ ◊ ◊ Cu distances than in 12 [2.9666(9) A].
Overall, the [Cu(X)(m-X)2Cu(X)] core in compounds 9–12 is
rigid and appears to be unaffected by the nature of the Ar–dpa
˚
for the aforementioned ortho-phen complex [1.944(3) A], the
35
˚
neutral b-diketiminato complex [1.914(1) and 1.923(1) A],
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ligand. It is therefore useful to look at the distortions in the Ar-
dpa ligands as a function of the steric bulk of the aryl substituents.
As may be seen from Fig. 14, the bend of the N–CAr out of the
plane of the two pyridyl rings is proportional to the folding along
the Cu ◊ ◊ ◊ N vector (i.e., formation of a butterfly conformation).
It is interesting to note that of the ligands studied, it is the phenyl
derivative (compound 9) that appears to have the greatest steric
differentiation about the copper due to the remotely substituted
aryl. Observation of Fig. 10–13, suggests that this is because of
the almost eclipsed orientation of the phenyl with respect to the
two pyridyl rings. Clearly, in solution this will be averaged due to
free rotation about the N(1)–C(11) bond.
Fig. 14 Plot of the bend of the N–CAr out of the plane of the two pyridyl
rings versus folding along the Cu ◊ ◊ ◊ N vector for compounds 9–12 (R2 =
0.928).
2
Fig. 15 Structure of the [Cu(Ph-dpa)(h -styrene)]+ cation in compound
13. Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
attached to carbon are omitted for clarity.
Based upon the forgoing, the presence of ortho-substitution
in the uncomplexed Ar–dpa compounds results in a significant
distortion of the coordination around the amine nitrogen and
twisting of the two pyridyl rings with respect top each other. What
this result does show is that the steric bulk of the substituents
on the aryl ring in Ar–dpa does have a significant effect on the
orientation and configuration of the two pyridyl rings, even when
the pyridyl nitrogens are rigidly coordinated to a copper center.
Effect on olefin binding by the remote steric bulk of the Ar–dpa
ligands
The reaction of [Cu(MeCN)4]BF4 with styrene in the presence
of the appropriate Ar–dpa results in the formation of the olefin
2
complex, [Cu(Ar–dpa)(h -styrene)]BF4 (eqn (2)) where Ar – Ph
(13), Mes (14), (2-iPr)Ph (15), and naph (16). The analogous nor-
2
bornylene derivatives, [Cu(Ar–dpa)(h -norbornylene)]X, where
Ar = Mes with X = PF6 (17) and (2-iPr)Ph with X = BF4 (18),
were also prepared using Mes–dpa (2) and iPr2-dpa (4) as ligands,
respectively.
2
Fig. 16 Structure of the [Cu(Mes-dpa)(h -styrene)]+ cation in compound
[Cu(MeCN)4]BF4 + Ar–dpa + styrene →
(2)
14. Thermal ellipsoids are shown at the 30% level, and hydrogen atoms
attached to carbon are omitted for clarity.
2
[Cu(Ar–dpa)(h -styrene)]BF4 + 4 MeCN
Compounds 13–18 are soluble in alcohols and show instability
1
2
in air and have been characterized by H and 13C NMR, FT-IR,
[Cu(H-dpa)(h -styrene)]+ that we have previously reported.15 Two
and TG/DTA. The crystal structures of compounds 13–17 have
independent molecules of compounds 14 and 16 are present in
the asymmetric unit, and the numbering schemes for the second
molecules are given in Fig. S15 and Fig. S19.† As with the
been determined.
2
The structure of the complex cation, [Cu(Ar–dpa)(h -styrene)]+,
-
in compounds 13–16 are shown in Fig. 15–18. Selected bond
other BF4 salts, the anion is disordered in the solid state for
lengths and angles are compared in Table 6 with those of
compounds 13–15 (see Experimental and Fig. S13, S17, and S18†).
11458 | Dalton Trans., 2010, 39, 11451–11468
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2
Fig. 17 Structure of the [Cu(2-iPrC6H4-dpa)(h -styrene)]+ cation in
compound 15. Thermal ellipsoids are shown at the 30% level, and hydrogen
atoms attached to carbon are omitted for clarity.
2
Fig. 19 Structure of the [Cu(Mes-dpa)(h -norbornylene)]+ cation in
compound 17. Thermal ellipsoids are shown at the 30% level, and hydrogen
atoms attached to carbon are omitted for clarity.
overlap the range for the previously reported derivatives [2.019(3)–
15,16,17
˚
˚
2.032(4) A].
The C C bond determined for compound 17
[1.361(5) A] is somewhat lengthened compared to free norborny-
40
˚
lene [1.334(1) A], and is slightly shorter than those observed in
the neutral iminophosphanamide-norbornylene and diethylenetri-
14,41
˚
amine (detn) complexes [1.37(2) and 1.38(2) A, respectively],
as well as the H–dpa complex [Cu(H–dpa)(h -norbornylene)]+
2
15
˚
[1.388(7) A].
As we noted above, the presence of ortho-substitution in the
uncomplexed Ar–dpa compounds results in a significant distor-
tion of the coordination around the amine nitrogen. Additional
distortions, resulting in the ligand to fold along the Cu ◊ ◊ ◊ N
vector, occur when the ligand is bound to a copper. In the olefin
complexes (13–16), both of these deformations are observed.
Importantly, however, the folding along the Cu ◊ ◊ ◊ N vector (i.e.,
formation of a butterfly conformation) is related to the size of
the ligand’s aryl group (Fig. 20). This is amply demonstrated by a
comparison of the ligand dpa and styrene conformations for the
two crystallographically unique conformers of the [Cu(1-naph-
2
Fig. 18 Structure of the [Cu(1-naph-dpa)(h -styrene)]+ cation in com-
pound 16. Thermal ellipsoids are shown at the 30% level, and hydrogen
atoms attached to carbon are omitted for clarity.
2
dpa)(h -styrene)]+ cation present in compound 16, Fig. 21.
-
The PF6 anion in 17 also exhibits a site-occupancy disorder for
four of the six fluorine atoms (Fig. S20†). The structure of the
complex cation, [Cu(Ar–dpa)(h -norbornylene)]+, in compound
The increased folding of the Ar–dpa ligand can be seen from
2
the [Cu(Ar–dpa)(h -styrene)]+ cations viewed down the Cu ◊ ◊ ◊ N
2
vector (Fig. 22). Furthermore, as may be seen from Fig. 22, there
is a clear steric consequence of the butterfly conformation of the
Ar–dpa ligand on the olefin ligand. Based upon this observation
we propose 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 (IV) there will be inter-ligand interactions
irrespective of the olefin conformation, while for a cis-olefin (V)
the substituents could adopt a conformation that limits steric
17 is shown in Fig. 19. Selected bond lengths and angles are
compared in Table 7 with those of [Cu(H-dpa)(h -norbornylene)]+
2
that we have previously reported.15
The copper atoms in compounds 13–17 are each coordinated to
two pyridine nitrogen atoms and the appropriate olefin; consistent
with three-coordinate Cu(I) cation. The Cu–N distances [1.949(3)–
1.973(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 [1.972(5)–2.064(2) A]
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◦
2
˚
Table 6 Selected bond lengths (A) and angles ( ) for [Cu(Ar–dpa)(h -styrene)]BF4
Compound
H–dpa
H
13
14a
15
16a
R
Ph
Mes
(2-iPr)Ph
naph
Cu(1)–C
Cu(1)–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)
1.984(2)
2.064(2)
1.965(2)
1.956(2)
1.381(3)
1.462(2)
95.20(7)
39.82(9)
114.9(1)
1.972(5), 1.981(6)
2.042(5), 2.032(6)
1.968(4), 1.951(4)
1.951(4), 1.965(4)
1.372(7), 1.381(8)
1.455(5), 1.449(5)
91.9(2), 92.3(2)
1.992(5)
2.022(5)
1.958(3)
1.973(3)
1.395(6)
1.461(5)
92.3(2)
1.978(4), 1.997(4)
2.021(4), 2.027(4)
1.949(3), 1.956(3)
1.968(3), 1.959(3)
1.371(6), 1.393(6)
1.463(5), 1.437(4)
94.0(1), 95.8(1)
Cu(1)–N(2)
Cu(1)–N(3)
C–C¢
N–CAr
N(2)–Cu(1)–N(3)
C–Cu(1)–C¢
Cu(1)–C–CPh
39.9(2), 40.2(2)
113.1(4), 109.1(4)
40.7(2)
109.8(3)
40.1(2), 40.5(2)
110.3(3), 108.5(3)
a Two crystallographically independent molecules in the asymmetric unit. Atom numbering scheme for the second molecule given in Fig. S15 and S19.†
◦
2
˚
Table 7 Selected bond lengths (A) and angles ( ) for [Cu(Ar–dpa)(h -
norbornylene)]+
R
H
Mes (17)
Cu(1)–C
Cu(1)–C¢
2.026(6)
2.030(6)
1.957(5)
1.962(5)
1.388(7)
—
2.46
97.7(2)
40.0(2)
2.027(3)
2.007(4)
1.957(3)
1.961(3)
1.361(5)
1.466(4)
2.46(4)
Cu(1)–N(2)
Cu(1)–N(3)
C–C¢
N–CAr
Cu ◊ ◊ ◊ H
N(2)–Cu(1)–N(3)
C–Cu(1)–C¢
94.0(1)
39.5(2)
Fig. 21 Comparison of the two crystallographically unique conformers
2
of the [Cu(1-naph-dpa)(h -styrene)]+ cation present in compound 16.
olefins can be used to compare binding interactions and compare
well with the temperature of dissociation of the olefin in the solid
state as determined by TGA. Fig. 24 shows that the change in the
1H and 13C NMR chemical shifts for the styrene ligand in [Cu(Ar–
2
dpa)(h -styrene)]+ as compared to uncomplexed styrene (i.e., Dd)
is indeed related to the stability of the Cu ◊ ◊ ◊ styrene interaction as
determined by the compounds decomposition temperature. Thus,
the binding efficiency of an olefin to the copper is affected by the
identity of the remote aryl substituent.
In the case of the aryl substituted ligands (i.e., Ar–dpa), the
binding efficiency follows the order: Ph ꢀ 1-naph < 2-iPrC6H4 <
Mes. In fact, the complex stability is directly related to the steric
bulk (cone angle) of the aryl, see Fig. 25. However, what is
interesting is that the complex of the parent ligand (H–dpa) shows
a complex stability almost equal to that of the Mes–dpa complex,
despite the difference in steric bulk, and hence folding of the ligand.
We conclude that the stability of the Cu ◊ ◊ ◊ olefin interaction is
controlled by both electronic and remote steric effects. A strong
Cu ◊ ◊ ◊ olefin interaction is enabled by either an electron donating
substituent at the central nitrogen of the dpa ligand or a sterically
large substituent at the central nitrogen of the dpa ligand. The
first effect is presumably due to the increased electron density
on copper and thence increased p back-donation to the olefin. We
propose that the second effect is due to the increased folding of the
dpa ligand (Fig. 20), resulting in a decrease in intra-complex inter-
ligand steric hindrance, and thus allowing for a tighter binding of
the olefin to the copper.
Fig. 20 Plot of the folding of the Ar–dpa ligand as a function of the
◦
2
substituent¢s cone angle ( ) for [Cu(Ar–dpa)(h -styrene)]+.
interactions. The alternative view of the norbornylene complex
2
cation [Cu(Ar-dpa)(h -norbornylene)]+ in compound 17 shown
in Fig. 23 shows the preferred orientation of a cis-substituted
olefin with its substituents away from the Ar–dpa ligand. We are
currently investigating the selectivity of olefin coordination as a
function of the Ar–dpa ligand.
We have previously shown15 that the bond distances around
2
copper in [Cu(H–dpa)(h -olefin)]+ do not correlate with changes
in binding constant. Instead we have shown that the difference
in the 1H and 13C NMR shift values between free and complexed
11460 | Dalton Trans., 2010, 39, 11451–11468
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2
Fig. 23 Alternative view of the [Cu(Mes-dpa)(h - norbornylene)]+ cation
showing the preferred orientation of the cis-substituted olefin and the
Mes-dpa ligand.
Fig. 24 Plots of the difference in chemical shift (Dd) for styrene
(a) 1H and (b) 13C NMR spectra between free styrene and
2
[Cu(Ar–dpa)(h -styrene)]BF4 versus the temperature for dissociation of
the styrene. R2 values are as follows: (a) ꢀ = 0.922, ꢁ = 0.897, ᭹ = 0.906
(b) ꢁ = 0.967, ꢀ = 0.932.
of the coordination around the amine nitrogen (in the solid state)
and twisting of the two pyridyl rings with respect to each other.
Thus, the steric bulk of the aryl substituents have a controlling
influence on the orientation of the pyridyl rings. The presence
of ortho-substitution in the complexed Ar-dpa compounds, in
which the two pyridyl rings are constrained by a complexed
atom, results in the bending-up of the aryl ring substituent out
of the pyridyl plane with consequential folding of the two pyridyls
into a “butterfly” conformation. For olefin complexes of the type
2
Fig. 22 The folding of the Ar–dpa ligand in the [Cu(Ar–dpa)(h -
styrene)]+ cations as viewed along the Cu ◊ ◊ ◊ N vector, for Ar – H (a),
Ph (b), 1-naph (c), and Mes (d).
Conclusions
2
[Cu(Ar–dpa)(h -styrene)]BF4, the increased steric bulk of the aryl
We have shown that for a range of aryl-substituted bis(2-
pyridyl)amine ligands the presence of ortho-substitution in the un-
complexed Ar–dpa compounds results in a significant distortion
group results in the folding of the dpa ligand and the subsequent
facial differentiation of the complex so as to favor cis- or mono-
substituted olefins. In addition, binding interaction of the olefin
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1.9 Hz,J(H–H) = 0.7 Hz, 6-CH, py], 7.44 [1H, ddd, J(H–H) =
8.5 Hz, J(H–H) = 7.2 Hz, J(H–H) = 1.9 Hz, 4-CH, py], 7.37–
7.35 (2H, m, CH, Ph), 7.23–7.20 (2H, m, CH, Ph), 6.69 [1H, ddd,
J(H–H) = 7.2 Hz, J(H–H) = 5.1 Hz, J(H–H) = 0.8 Hz, CH, 5-py],
6.67 (1H, br s, NH), 6.57 [1H, ddd, J(H–H) = 8.5 Hz, J(H–H) =
0.8 Hz,J(H–H) = 0.7 Hz, CH, 3-py], 3.23 [1H, sept, J(H–H) =
6.8 Hz, CH(CH3)2], 1.23 [6H, d, J(H–H) = 6.8 Hz, CH(CH3)2].
Mes–dpa (2)
N-(2,4,6-trimethyl)phenyl-N-(2-pyridyl)amine
(21.23
g,
100 mmol), sodium tert-butoxide (11.53 g, 120 mmol), Pd2(dba)3
(2.289 g, 2.5 mmol), and DPPF (2.772 g, 5.0 mmol) were added to
a Schlenk flask in a drybox. The flask was capped with a septum,
removed from the drybox, and toluene (ca. 15 mL) was added via
cannula. The mixture was stirred, and 2-bromopyridine (19.02 g,
120 mmol) was injected via syringe into the reaction vessel. The
reaction was stirred under nitrogen at 90 ◦C for 120 h. After
cooling, CHCl3 (50 mL) was added, the mixture was filtered, and
the solvent was removed under vacuum. The crude product was
purified by column chromatography on silica gel (eluent: 5% ethyl
acetate in hexanes). The purified product was recrystallized by
cooling a saturated solution in hexanes to -12 ◦C for several days,
giving co◦lorless crystals. Yield: 20.58 g (71%). Mp (TGA; sublim.):
141–143 C. MS (EI,%): m/z 289 (M+, 13.2), 274 (M+ - Me, 100).
1H-NMR (CD3OD): d 8.17 [2H, ddd, J(H–H) = 5.0 Hz, J(H–H) =
1.9 Hz, J(H–H) = 0.7 Hz, CH, 6,6¢-py], 7.65 [2H, ddd, J(H–H) =
8.6 Hz, J(H–H) = 7.2 Hz, J(H–H) = 1.9 Hz, CH, 4,4¢-py], 7.01
(2H, s, C6H2), 6.98 [2H, ddd, J(H–H) = 7.2 Hz, J(H–H) = 5.0 Hz,
J(H–H) = 0.9 Hz, CH, 5,5¢-py], 6.88 [2H, ddd, J(H–H) = 8.6 Hz,
J(H–H) = 0.9 Hz, J(H–H) = 0.7 Hz, CH, 3,3¢-py], 2.33 (3H, s,
p-CH3), 1.96 (6H, s, o-CH3).
Fig. 25 Plot of relationship between the temperature for dissociation
2
of the styrene in and [Cu(Ar–dpa)(h -styrene)]BF4 as a function of the
Toleman cone angle (◦) of the aryl substituent (R2 = 0.988). The value for
2
the parent [Cu(Ar–dpa)(h -styrene)]BF4 is shown for comparison (ꢀ).
with the copper is controlled by the steric bulk of the remote
aryl group. We are presently investigating the use of substituted
bis(2-pyridyl)amine copper complexes for the separation of olefins.
These results will be reported elsewhere.
Experimental
All reagents in this study were used as received from commercial
suppliers and were stored under an argon atmosphere in a drybox.
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 techniques.
Precursor complex [Cu(MeCN)4]BF4 was prepared according to
Hathaway, et al.42 Precursors for the ligands, ArN(H)py (Ar =
Ph, 2,4,6-Me3Ph, 2,6-Et2Ph, 2,6-iPr2Ph, and 1-naphthyl), were
prepared according to previously reported methods.20,23 N-phenyl-
N,N-(2,2¢-dipyridyl)amine (Ph–dpa) was prepared according to
the literature methods.25 1H and 13C NMR spectra were obtained
at room temperature 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 an ATR accessory. Thermo-
gravimetric analyses were performed on a Seiko I TG/DTA 200
under an argon gas flow of 10–15 mL min-1. GC-MS analyses
were performed using Agilent Technologies 5973 network mass
selective detector, equipped with 6890 N network GC system.
2,6-Et2C6H3–dpa (3)
Prepared in an analogous manner to that of compound 2, using
N-(2,6-diethyl)phenyl-N-(2-pyridyl)amine (2.26 g, 10 mmol), 2-
bromopyridine (1.89 g, 12 mmol), sodium tert-butoxide (1.53 g,
16 mmol), Pd2(dba)3 (137 mg, 0.15 mmol), DPPF (166 mg,
0.30 mmol), and toluene (15 mL). The purified product was
recrystallized by cooling a saturated solution in CHCl3 to -12 ◦C
for several days to give colorless crystals. Yield: 0.77 g (25%). Mp
◦
(TGA; sublim.): 86–88 C. MS (EI, %): m/z 303 (M+, 2.2), (M+
- Et, 100). 1H-NMR (298 K; CDCl3): d 8.28 [2H, ddd, J(H–H) =
5.0 Hz, J(H–H) = 2.0 Hz, J(H–H) = 0.8 Hz, CH, CH, 6,6¢-py],
7.49 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) = 7.2 Hz, J(H–H) =
2.0 Hz, CH, 4,4¢-py], 7.34 [1H, dd, J(H–H) = 7.7 Hz, J(H–H) =
7.7 Hz, p- CH, Ph], 7.23 [2H, d, J(H–H) = 7.7 Hz, m- CH, Ph],
6.94 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) = 0.9 Hz, J(H–H) =
0.8 Hz, CH, 3,3¢-py], 6.83 [2H, ddd, J(H–H) = 7.2 Hz, J(H–H) =
5.0 Hz, J(H–H) = 0.9 Hz, CH, 5,5¢-py], 2.44 [4H, q, J(H–H) =
7.6 Hz, CH2CH3], 0.96 [6H, t, J(H–H) = 7.6 Hz, CH2CH3].
2-iPrC6H4N(H)(C5H4N) (1)
2-isopropylaniline (49.86 g, 0.369 mol) and 2-bromopyridine
(29.13 g, 0.184 mol) were refluxed under an argon atmosphere for
12 h. The reaction mixture was then made alkaline with a saturated
solution of Na2CO3, followed by steam distillation to remove
excess reactants. Extraction with Et2O, followed by removal of the
solvent in vacuum gave an off-white powder. The crude product
was recrystallized by the slow evaporation of methanol solution to
afford colorless crystals. Yield: 32.24 g (82%). Mp (TGA; sublim.):
2-iPrC6H4–dpa (4)
Prepared in an analogous manner to that of compound 2, using N-
(2-isopropyl)phenyl-N-(2-pyridyl)amine (10.645 g, 50 mmol), 2-
bromopyridine (9.980 g, 60 mmol), sodium tert-butoxide (5.765 g,
60 mmol), Pd2(dba)3 (1.373 g, 1.25 mmol), DPPF (1.663 g,
2.5 mmol), and toluene (200 mL). The crude product was purified
◦
i
120–122 C. MS (EI, %): m/z 212 (M+, 8.7), 169 (M+ - Pr, 100).
1H-NMR (CDCl3): d 8.14 [1H, ddd, J(H–H) = 5.1 Hz, J(H–H) =
11462 | Dalton Trans., 2010, 39, 11451–11468
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by column chromatography on silica gel (eluent: 5% ethyl acetate
in hexanes). The purified product was recrystallized by a slow
evaporation of a 4 : 1 hexanes : CH2Cl2 solution to give colorless
crystals. Yield 5.311 g (38%). Mp (TGA; sublim.): 101–103 ◦C. MS
[(Mes-dpa)H]BF4 (7)
In a 25 mL round bottom flask, compound 2 (0.289 g, 1.0 mmol)
was dissolved in MeOH (5 mL). With stirring, KBF4 (0.130 g,
1.0 mmol) dissolved in dilute HCl (5 mL). The mixture was
allowed to stir for 30 min, followed by extraction with CH2Cl2 (2 ¥
5 mL) The solvent was removed under vacuum, and the solid was
dissolved in methanol, followed by filtration through a medium
porosity sintered-glass frit. Slow evaporation of the filtrate yielded
0.156 g (41%) colorless crystals. Mp (TGA; decomp.): 228–229 ◦C.
1H-NMR (CD3OD): d 8.60 [2H, ddd, J(H–H) = 5.7 Hz, J(H–H) =
1.9 Hz, J(H–H) = 0.7 Hz, CH, 6,6¢-py], 8.05 [2H, ddd, J(H–H) =
8.9 Hz, J(H–H) = 7.3 Hz, J(H–H) = 1.9 Hz, CH, 4,4¢-py], 7.42
[2H, ddd, J(H–H) = 7.3 Hz, J(H–H) = 5.7 Hz, J(H–H) = 0.8 Hz,
CH, 5,5¢-py], 7.28 (2H, s, C6H2), 6.63 [2H, ddd, J(H–H) = 8.9 Hz,
J(H–H) = 0.8 Hz, J(H–H) = 0.7 Hz, CH, 3,3¢-py], 2.45 (3H, s,
p-CH3), 2.02 (6H, s, o-CH3).
(EI,%): m/z 289 (M+, 0.7), 246 (M+
-
iPr, 100). 1H-NMR
(CD3OD): d 8.18 [2H, ddd, J(H–H) = 5.0 Hz, J(H–H) = 2.0 Hz,
J(H–H) = 0.8 Hz, CH, 6,6¢-py], 7.65 [2H, ddd, J(H–H) = 8.4 Hz,
J(H–H) = 7.3 Hz, J(H–H) = 2.0 Hz, CH, 4,4¢-py], 7.47 [1H, dd,
J(H–H) = 7.9 Hz, J(H–H) = 1.5 Hz, CH, Ph], 7.39 [1H, ddd, J(H–
H) = 7.9 Hz, J(H–H) = 7.2 Hz, J(H–H) = 1.3 Hz, CH, Ph], 7.29
[1H, ddd, J(H–H) = 7.9 Hz, J(H–H) = 7.2 Hz, J(H–H) = 1.5 Hz,
CH, Ph], 7.15 [1H, dd, J(H–H) = 7.9 Hz, J(H–H) = 1.3 Hz, CH,
Ph], 6.99 [2H, ddd, J(H–H) = 7.3 Hz, J(H–H) = 5.0 Hz, J(H–H) =
1.0 Hz, CH, 5,5¢-py], 6.88 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) =
1.0 Hz, J(H–H) = 0.8 Hz, CH, 3,3¢-py], 3.05 [1H, sept, J(H–H) =
6.8 Hz, CH(CH3)2], 0.99 [6H, d, J(H–H) = 6.8 Hz, CH(CH3)2].
2,6-iPr2C6H3–dpa (5)
[(2-iPrC6H4-dpa)H]BF4 (8)
Prepared in an analogous manner to that of compound 2,
using 2,6-diisopropylaniline (0.355 g, 2.0 mmol), 2-bromopyridine
(0.700 g, 4.4 mmol), sodium tert-butoxide (0.550 g, 5.7 mmol),
Pd2(dba)3 (0.055 g, 0.06 mmol), DPPF (0.083 g, 0.15 mmol),
and toluene (10 mL). The crude product was purified by flash
chromatography on silica gel (eluent: 2% MeOH in CH2Cl2)
followed by recrystallization by vapor diffusion of pentane into
a saturated CHCl3 solution yielding colorless crystals Yield: yield
0.331 g (50%). Mp (TGA; sublim.): 95–97 ◦C. MS (EI, %): m/z 331
This compound was prepared in an analogous manner to that of
compound (7), using 0.289 g (1.0 mmol) of compound 4. Crystals
suitable for X-ray diffraction were obtained cooling a saturated
solution in iPrOH to -12 ◦C f◦or several days. Yield = X g (78%).
Mp (TGA; decomp.): 222–224 C. 1H-NMR (CD3OD): d 8.58 [2H,
ddd, J(H–H) = 5.7 Hz, J(H–H) = 1.9 Hz,J(H–H) = 0.7 Hz, CH,
6,6¢-py], 8.02 [2H, ddd, J(H–H) = 8.9 Hz, J(H–H) = 7.3 Hz,J(H–
H) = 1.9 Hz, CH, 4,4¢-py], 7.78 (1H, CH), 7.75 (1H, CH), 7.60 (1H,
CH),7.45 (1H, CH), 7.41 [2H, ddd, J(H–H) = 7.3 Hz, J(H–H) =
5.7 Hz,J(H–H) = 0.8 Hz, CH, 5,5¢-py], 6.65 [2H, ddd, J(H–H) =
8.9 Hz, J(H–H) = 0.8 Hz,J(H–H) = 0.7 Hz, CH, 3,3¢-py], 2.80 [1H,
sept, J(H–H) = 8.9 Hz, CH(CH3)2], 1.08 [6H, d, J(H–H) = 8.9 Hz,
CH(CH3)2].
i
(M+, 0.8), 288 (M+ - Pr, 100). 1H-NMR (CDCl3): d 8.27 [2H, ddd,
J(H–H) = 5.0 Hz, J(H–H) = 1.9 Hz, J(H–H) = 0.8 Hz, CH, 6,6¢-
py], 7.50 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) = 7.2 Hz, J(H–H) =
1.9 Hz, CH, 4,4¢-py], 7.42 [1H, dd, J(H–H) = 7.7 Hz, J(H–H) =
7.7 Hz, p- CH, Ph], 7.27 [2H, d, J(H–H) = 7.7 Hz, m- CH, Ph],
6.96 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) = 0.9 Hz, J(H–H) =
0.8 Hz, CH, 3,3¢-py], 6.82 [2H, ddd, J(H–H) = 7.2 Hz, J(H–H) =
5.0 Hz, J(H–H) = 0.9 Hz, CH, 5,5¢-py], 3.09 [2H, sept, J(H–H) =
6.9 Hz, CH(CH3)2], 0.95 [12H, d, J(H–H) = 6.9 Hz, CH(CH3)2].
[Cu(Ph-dpa)(Cl)(l-Cl)]2 (9)
[Cu(MeCN)4]BF4 (0.157 g, 0.5 mmol) and Ph-dpa (0.124 g,
0.5 mmol) were stirred together in tetraethylene glycol (2 mL) in a
conical vial open to the atmosphere, until all solids had dissolved.
Dilute HCl (2 mL) was then added to the mixture, turning the dark
blue/green solution milky white. The mixture was then extracted
with CH2Cl2 (2 ¥ 5 mL), and the combined organic layers were
allowed to evaporate. The resulting brown residue was taken up
in MeOH (5 mL), which was filtered and cooled to -12 ◦C for
several days, yielding dark green plates. Yield: 0.114 g (60%). Mp
(TGA; decomp.) 265–267 ◦C.
1-Naph–dpa (6)
Prepared in an analogous manner to that of compound 2,
using N-(1-naphthyl)-N-(2-pyridyl)amine (2.20 g, 10 mmol), 2-
bromopyridine (1.89 g, 12 mmol), sodium tert-butoxide (1.53 g,
16 mmol), Pd2(dba)3 (137 mg, 0.15 mmol), DPPF (166 mg,
0.30 mmol), and toluene (15 mL). The purified product was
recrystallized by a slow evaporation of a 1 : 1 hexanes : CH2Cl2
solution to yield ◦1.37 g (46%) colorless crystals. Mp (TGA;
sublim.): 166–168 C. MS (EI,%): m/z 297 (M+, 41.9), 296 (M+ -
[Cu(2-iPrC6H4-dpa)(Cl)(l-Cl)]2 (10)
1
H, 100). H-NMR (CDCl3): d 8.34 [2H, ddd, J(H–H) = 5.0 Hz,
This compound was prepared in an analogous manner to that of
compound 9, using compound 4 (0.149 g, 0.5 mmol) for the ligand.
Recrystallization by slow evaporation of MeOH solution. Yield:
48%. Mp (TGA; decomp.) 231–233 ◦C.
J(H–H) = 2.0 Hz, J(H–H) = 0.8 Hz, CH, 6,6¢-py], 7.91 [1H, d,
J(H–H) = 8.2 Hz, CH, naph], 7.88 [1H, d, J(H–H) = 8.2 Hz, CH,
naph], 7.84 [1H, ddd, J(H–H) = 8.5 Hz, J(H–H) = 1.8 Hz, J(H–
H) = 0.9 Hz, CH, naph], 7.55 [1H, dd, J(H–H) = 8.2 Hz, J(H–H) =
7.2 Hz, CH, naph], 7.49 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) =
7.3 Hz, J(H–H) = 2.0 Hz, CH, 4,4¢-py], 7.47 (2H, m, CH, naph),
7.37 [1H, ddd, J(H–H) = 8.3 Hz, J(H–H) = 6.9 Hz, J(H–H) =
1.2 Hz, CH, naph], 6.90 [2H, ddd, J(H–H) = 8.4 Hz, J(H–H) =
1.0 Hz, J(H–H) = 0.8 Hz, CH, 3,3¢-py], 6.89 [2H, ddd, J(H–H) =
7.3 Hz, J(H–H) = 5.0 Hz, J(H–H) = 1.0 Hz, CH, 5,5¢-py].
[Cu(1-naph-dpa)(Cl)(l-Cl)]2 (11)
This compound was prepared in an analogous manner to that
of compound 9, using compound 6 (0.149 g, 0.5 mmol) for the
ligand. Recrystallized by a slow evaporation of MeOH solution.
Yield: 48%. Mp (TGA; decomp.) 230–232 ◦C.
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[Cu(Mes–dpa)(H2O)(l-OH)]2[BF4]2 (12)
(298 K; CD3OD): d 8.31 (2H, br d, CH, 6,6¢-py), 7.73 (2H, br t,
CH, 4,4¢-py), 7.62 (1H, br d, CH, Ph), 7.61 (1H, br t, CH, Ph),
7.52 (1H, br t, CH, Ph), 7.48 (2H, mult., CH, sty), 7.44 (1H, br
d, CH, Ph), 7.27 (2H, mult., CH, sty), 7.23 (1H, mult., p-CH,
sty), 7.14 (2H, br t, CH, 5,5¢-py), 6.67 (2H, br d, CH, 3,3¢-py),
6.15 [1H, dd, J(H–H) = 15.7 Hz, J(H–H) = 9.6 Hz, CHPh], 4.90
[1H, d, J(H–H) = 15.7 Hz, cis-CH, styrene], 4.49 [1H, d, J(H–
H) = 9.6 Hz, trans-CH, styrene], 2.71 [1H, sept, J(H–H) = 6.8 Hz,
CH(CH3)2], 0.87 [6H, d, J(H–H) = 6.8 Hz, CH(CH3)2].
[Cu(MeCN)4]BF4 (0.314 g, 1.0 mmol) and 2 (0.289 g, 1.0 mmol)
were stirred together in MeOH (5 mL) and H2O (1 mL) in a
vial open to the atmosphere. After the solution had taken on a
dark blue color (ca. 1 h), the solvent was removed under vacuum,
and the resulting powder was dissolved in 5 : 1 MeOH : acetone,
filtered, and cooled to -12 ◦C for several days, yielding dark blue
crystals of the methanol solvate. Yield: 0.569 g (56%). Mp (TGA;
decomp.) 198–202 ◦C.
[Cu(1-naph-dpa)(g2-styrene)]BF4 (16)
[Cu(Ph–dpa)(g2-styrene)]BF4 (13)
This compound was prepared in an analogous manner to that
In a drybox, [Cu(MeCN)4]BF4 (0.314 g, 1.0 mmol) and Ph–dpa
(0.247 g, 1.0 mmol) were charged to separate Schlenk flasks.
After removal from the drybox, EtOH (15 mL) was added via
cannula to the flask containing the ligand, which was stirred
to dissolve the solid. Styrene (ca. 3 mL) in EtOH (12 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 for 6 h. The solution volume was then
reduced under vacuum by approximately half, 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. 5–10 mL. The solution was
gently warmed to dissolve any precipitate, and upon cooling to
i
of compound (13), using PrOH as solvent and compound 6 as
◦
1
ligand. Yield: 58%. Mp (TGA; decomp.) 153–155 C. H-NMR
(298 K; CD3OD): d 8.24 (2H, br s, 6-CH, py), 8.14 (1H, br d, C–H,
naph), 8.07 (1H, br d, C–H, naph), 7.70 (1H, br t, C–H, naph),
7.63 (2H, br t, 4-CH, py), 7.61 (1H, br d, C–H, naph), 7.60 (1H,
br d, C–H, naph), 7.58 (1H, br s, C–H, naph), 7.52 (2H, m, C–H,
sty), 7.48 (1H, br t, C–H, naph), 7.30 (2H, m, C–H, sty), 7.24 (1H,
m, C–H, sty),7.12 (2H, br t, 5-CH, py), 6.58 (2H, br d, 3-CH, py),
6.23 [1H, dd, J(H–H) = 15.9 Hz, J(H–H) = 9.8 Hz, CHPh], 5.03
[1H, d, J(H–H) = 15.9 Hz, cis-CH, styrene], 4.57 [1H, d, J(H–H) =
9.8 Hz, trans-CH, styrene]
[Cu(Mes-dpa)(g2-norbornylene)]PF6 (17)
This compound was prepared in an analogous manner to that
of 13, using 2-butanol as solvent, compound 2 as ligand, and
norbornylene as olefin Yield: 76%. Mp (TGA; decomp.) 176–
178 ◦C. 1H-NMR (298 K; CD3OD): d 8.56 (2H, br d, 6-CH, py),
7.82 (2H, br t, 4-CH, py), 7.25 (2H, br t, 5-CH, py), 7.23 (2H, s,
CH), 6.52 (2H, br d, 3-CH, py), 5.10 (2H, br s, HC CH), 3.13
(2H, br s, CHCH2CH), 2.42 (3H, s, p-CH3), 1.97 (6H, s, o-CH3),
1.66 (2H, m, CH2), 1.29 (1H, m, CHCH2CH), 1.12 (2H, m, CH2),
0.99 (1H, m, CHCH2CH).
◦
-12 C for several days, yielded colorless crystals of the ◦ethanol
1
solvate. Yield: 0.203 g (37%). Mp (TGA; decomp.) 128 C. H-
NMR (298 K; CD3OD): d 8.06 (2H, br s, CH, 6,6¢-py), 7.83 (2H,
br t, CH, 4,4¢-py), 7.51 (2H, br t, m-CH, Ph), 7.46 (1H, br s, p-
CH, Ph), 7.43 (2H, mult., o-CH, styrene), 7.26 (2H, mult., m-CH,
styrene), 7.22 (2H, br s, CH, Ph), 7.19 (1H, mult., p-CH, styrene),
7.17 (2H, br t, CH, 5,5¢-py), 6.93 (2H, br d, CH, 3,3¢-py), 6.29
[1H, dd, J(H–H) = 16.4 Hz, J(H–H) = 10.0 Hz, CHPh], 5.13 [1H,
d, J(H–H) = 16.4 Hz, cis-CH, Ph], 4.67 [1H, d, J(H–H) = 10.0 Hz,
trans-CH, Ph], 3.60 [2H, q, J(H–H) = 6.9 Hz, OCH2CH3], 1.17
[3H, t, J(H–H) = 6.9 Hz, OCH2CH3].
[Cu(2-iPrC6H4-dpa)(g2-norbornylene)]BF4 (18)
This compound was prepared in an analogous manner to that of
compound 17, using iPrOH as solvent and compound 4 as ligand.
[Cu(Mes-dpa)(g2-styrene)]BF4 (14)
◦
1
Yield: 66%. Mp (TGA; decomp.) 152–155 C. H-NMR (298 K;
CD3OD): d 8.54, 7.80, 7.69 (1H, br d, CH, Ph), 7.66 (1H, br t,
CH, Ph), 7.56 (1H, br t, CH, Ph), 7.45 (1H, br d, CH, Ph), 7.25
(2H, br t, CH, 5-Py), 6.68 (2H, br d, CH, 3-Py), 5.11 (2H, br s,
HC CH), 3.12 (2H, br s, CHCH2CH), 2.87 [1H, sept, J(H–H) =
7.0 Hz, CH(CH3)2], 1.67 (2H, m, CH2), 1.30 (1H, m, CHCH2CH),
1.12 (2H, m, CH2), 1.01 (1H, m, CHCH2CH), 0.97 [6H, d, J(H–
H) = 7.0 Hz, CH(CH3)2].
This compound was prepared in an analogous manner to that
of compound 13, using 2-butanol as solvent and compound 2 as
ligand. Yield: 61%. Mp (TGA; decomp.) 174 ◦C. 1H-NMR (298 K;
CD3OD): d 8.33 (2H, br d, CH, 6,6¢-py), 7.73 [2H, ddd, J(H–H) =
8.9 Hz, J(H–H) = 7.3 Hz, J(H–H) = 2.0 Hz, m-sty], 7.46 (2H, m,
CH, 4,4¢-py), 7.24-7.18 (3H, m, CH, 3,3¢-py and p- CH, styrene),
7.18 (2H, s, m-CH, Mes), 7.13 [2H, ddd, J(H–H) = 6.3 Hz, J(H–
H) = 5.5 Hz, J(H–H) = 0.9 Hz, CH, 5,5¢-py], 6.45 [2H, d, J(H–
H) = 8.9 Hz, CH, o-CH, styrene], 6.11 [1H, dd, J(H–H) = 15.8 Hz,
J(H–H) = 9.6 Hz, CHPh], 4.84 [1H, d, J(H–H) = 15.8 Hz, cis-CH,
styrene], 4.44 [1H, d, J(H–H) = 9.6 Hz, trans-CH, styrene], 2.38
(3H, s, p-CH3), 1.89 (6H, s, o-CH3).
Crystallographic studies
X-ray data for compounds 1–17 were collected at room temper-
ature (with the exception of 13, for which data was collected at
213 K) on a Bruker SMART 1000 CCD diffractometer equipped
˚
with graphite monochromated Mo-Ka radiation (l = 0.71073 A)
[Cu(2-iPrC6H4-dpa)(g2-styrene)]BF4 (15)
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 atmosphere, followed by
sealing in a thin layer of epoxy resin and securing to the end of a
This compound was prepared in an analogous manner to that
i
of compound (13), using PrOH as solvent and compound 4 as
◦
1
ligand. Yield: 66%. Mp (TGA; decomp.) 156–158 C. H-NMR
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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 methods43
using the program SMART.44 The program SAINT45 was used
for data reduction, and absorption correction was applied using
SADABS.46 Pertinent details are given in Table 8. Heavy atom
sites were located by Patterson methods for complex 11; all other
structures were solved by direct methods, and models were refined
using full-matrix least squares techniques.47 Refinement was per-
formed with anisotropic thermal parameters for all non-hydrogen
atoms: shift/error less than 0.01. All hydrogen atoms, with the
exceptions of those noted below in 1, 7, 8, 12, and 17, were placed in
References
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2010, 40(2), 130.
˚
˚
calculated positions [C–H (alkyl) = 0.97 A, C–H (methyl) = 0.96 A,
˚
˚
˚
C–H (aromatic) = 0.93 A, N–H = 0.86 A, and O–H = 0.82 A] and
refined with fixed isotropic displacement parameters. The amine
hydrogen atom in 1, the pyridyl-bound hydrogen atoms in 7 and 8,
oxygen-bound H atoms in 12, and the norbornyl-H atom showing
slight interaction with the copper center in 17 were located in the
difference map and refined freely. Neutral-atom scattering factors
were taken from the usual source.48 Refinement of positional and
anisotropic displacement parameters led to convergence for all
data. The program used for structure solution and refinement was
SHELXTL Version 6.14.49 The program PLATON was employed
for structure validation, and its squeeze function was utilized for
refinement in compounds 8, 15, and 16, which were found to
contain solvent accessible voids.50,51 Selected bond lengths and
angles are given in Tables 1–7. Refinement of noncentrosym-
metric structures 2 (P212121), 3 (P21), 4 (Pna21), and 10 (Pna21)
was performed according to previously established methods,52,53
using TWIN/BASF instructions, and merging Friedel pairs for
compounds 2–4.
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Compounds 3–5, 14, and 16 were found to crystallize with two
unique molecules in the asymmetric unit. Structure solution and
refinement for compound 3 was performed in the asymmetric
space group monoclinic P21, with TWIN/BASF instructions.
Friedel pairs were merged (MERG 4) for refinement. Molecule
2 of the asymmetric unit is shown in Fig. S1,† and a comparison
of the two comformers are shown in Fig. S2.† Compound 4
crystallized with 2 unique molecules in the asymmetric unit, one of
which exhibited a site occupancy disorder of the isopropyl methyl
groups (see ESI for details†). The disorder in molecule 2 of the
asymmetric unit is shown in Fig. S3,† and a comparison of the two
comformers are shown in Fig. S4.† Molecule 2 of the asymmet-
ric unit of compound 5 is shown in Fig. S5,† and a comparison
of the two comformers are shown in Fig. S6.† The numbering
schemes for the second unique conformers of complexes 14 and 16
are given in Fig. S15 and S19,† and comparisons of the respective
conformers are shown in Figures Fig. S16† and Fig. 21. Refer
to ESI† for details concerning disordered anions in 7, 8, 12–15,
and 17.
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Acknowledgements
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
University.
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The Royal Society of Chemistry 2010
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