Copper(I) ethylene complexes supported by 1,3,5-triazapentadienyl ligands with electron-withdrawing groups

Article abstract of DOI:10.1021/om300567v

The fluorinated 1,3,5-triazapentadienyl ligands [N{(C₃F ₇)C(2-(NO₂)C₆H₄)N}₂] ^-, [N{(C₃F₇)C(4-(NO₂)C ₆H₄)N}₂]

Full text of DOI:10.1021/om300567v

Article
pubs.acs.org/Organometallics
Copper(I) Ethylene Complexes Supported by 1,3,5-Triazapentadienyl
Ligands with Electron-Withdrawing Groups
Venkata A.K. Adiraju, Jaime A. Flores, Muhammed Yousufuddin, and H. V. Rasika Dias*
Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019-0065, United States
S
* Supporting Information
ABSTRACT: The fluorinated 1,3,5-triazapentadienyl ligands [N{(C3F7)C(2-(NO2)-
C6H4)N}2]−, [N{(C3F7)C(4-(NO2)C6H4)N}2]−, [N{(C3F7)C(2-(CF3)C6H4)N}2]−,
and [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]− have been used as supporting ligands in
copper(I) ethylene chemistry. [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4) (7), [N-
{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) (8), [N{(C3F7)C(2-(CF3)C6H4)N}2]Cu-
(C2H4) (9), and [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(C2H4) (10) are easily isolable, thermally stable solids and display
their ethylene proton and carbon resonances in the δ 3.68−3.48 and 85.2−87.6 ppm regions, respectively. X-ray crystal structures
reveal that 7−10 feature trigonal-planar copper sites and κ2-bonded, U-shaped triazapentadienyl ligands. The Cu(I) carbonyl
adducts [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(CO)(NCCH3) (16) and [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(CO)(NCCH3)
(17) have also been synthesized, and they have pseudotetrahedral copper sites. The CO stretching frequencies of the compounds
16 and 17 and ethylene 13C NMR chemical shift data of 7−10 suggest that these molecules have rather acidic copper sites and
weakly donating triazapentadienyl ligands.
INTRODUCTION
■
Copper(I) ethylene complexes are important in many areas,
including catalysis, biochemistry, and separation science.1,2 For
example, copper mediates oxychlorination of ethylene, which is
an important industrial process.3,4 Copper(I) ethylene
complexes also catalyze very effectively the carbene and nitrene
transfer chemistry to a variety of substrates.5−10 In nature,
ethylene is a plant hormone that regulates several aspects of the
plant life cycle.11−13 It is widely believed that the ethylene
binding site in plants is a copper center. The alkene
coordination ability of copper salts has been explored in
chromatography and as an energy-efficient way to separate
olefins such as ethylene from paraffins, which is currently
achieved via energy-intensive cryogenic distillation.14,15
Figure 1. Copper(I) ethylene adducts of the highly fluorinated ligands
It has been known for many years that copper(I) salts such as
cuprous chloride react with ethylene to form adducts, but these
compounds have limited stability and decompose unless low
temperatures and high ethylene pressures are maintained.1,16,17
Thompson and co-workers first reported structural data on the
copper ethylene complex [HB(3,5-(CH3)2Pz)3]Cu(C2H4) in
1983.18 However, this adduct also loses ethylene easily under
reduced pressure. Overall, there has been significant interest in
thermally stable copper(I) ethylene complexes, but the
isolation of such adducts is challenging in the absence of
proper supporting ligands.
An area of research focus in our laboratory concerns the
chemistry of coinage metal (Cu, Ag, Au) adducts involving
highly fluorinated ligands and weakly coordinating
anions.1,2,7,19−21 We have discovered that fluorinated tris-
(pyrazolyl)borate and 1,3,5-triazapentadienyl ligands such as
[HB(3,5-(CF3)2Pz)3]− and [N{(C3F7)C(C6F5)N}2]− are good
choices to stabilize ethylene adducts 1 and 2 (Figure 1).6,22 For
example, [HB(3,5-(CF3)2Pz)3]Cu(C2H4) (1) is an air-stable
[HB(3,5-(CF3)2Pz)3]− and [N{(C3F7)C(C6F5)N}2]−.
solid that does not lose the ethylene moiety even under
reduced pressure. This feature has been exploited in the
development of an ethylene sensor.23 Copper adducts
supported by weakly donating ligands are also excellent carbene
and nitrene transfer catalysts.6−9 In this paper, we report the
use of 1,3,5-triazapentadienyl ligands with electron-withdrawing
substituents such as fluoroalkyl and nitro groups on the ligand
backbone and on an N-aryl group to stabilize copper ethylene
adducts as thermally stable solids.
Special Issue: Copper Organometallic Chemistry
Received: June 20, 2012
Published: July 24, 2012
© 2012 American Chemical Society
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Cu(C2H4) (9) and [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu-
(C2H4) (10) can be prepared via an route analogous to that
described for 7 and 8, using copper(I) oxide as the copper
source. The synthetic route to 10 is outlined in Figure 3.
RESULTS AND DISCUSSION
■
The synthesis of [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]H has
been reported.24 The related [N{(C3F7)C(2-(CF3)C6H4)N}2]-
H, [N{(C3F7)C(2-(NO2)C6H4)N}2]H, and [N{(C3F7)C(4-
(NO2)C6H4)N}2]H were synthesized via a similar route using
perfluoro-5-aza-4-nonene, the corresponding aniline 2-(CF3)-
C6H4NH2, 2-(NO2)C6H4NH2, or 4-(NO2)C6H4NH2, and
triethylamine. The synthesis of [N{(C3F7)C(4-(NO2)C6H4)-
N}2]H has been mentioned as a footnote in a publication, but
no other details are available.25 [N{(C3F7)C(2-(NO2)C6H4)-
N}2]H (3) and [N{(C3F7)C(4-(NO2)C6H4)N}2]H (4) are
yellow solids, while [N{(C3F7)C(2-(CF3)C6H4)N}2]H (5) and
[N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]H (6) are white solids.
The room-temperature 19F NMR spectra of these compounds
are somewhat complex, as noted earlier for other fluorinated
1,3,5-triazapentadienes, due to the possible existence of
different conformers and tautomers in solution.25−32
These fluorinated triazapentadienes are weak monoprotic
acids.25 Their copper ethylene adducts can be prepared using
copper(I) oxide as the copper source.22 For example, reaction
of 3 with Cu2O and acetonitrile followed by the treatment of
the resulting copper adduct (presumably, the copper(I)
acetonitrile complex [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu-
(NCCH3), as established for other triazapentadienyl ligands)31
with ethylene led to [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu-
(C2H4) (7) in 58% yield (Figure 2). The analogous
Figure 3. Synthesis of copper(I) ethylene and copper(I) carbonyl
adducts of [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]−.22.
Compounds 9 and 10 are also thermally stable solids. The 13C
1
and H NMR signals of copper(I)-coordinated ethylene in 9
and 10 and the corresponding resonances for several other
adducts are summarized in Table 1. Compounds 7−10 show
Table 1. NMR Spectroscopic Data for Selected Copper
a
Ethylene Complexes
compd
δ(1H) (ppm)
δ(13C) (ppm)
ref
this
[N{(C3F7)C(2-(NO2)C6H4)
N}2]Cu(C2H4) (7)
3.51
85.4
work
this
work
this
work
this
work
22
[N{(C3F7)C(4-(NO2)C6H4)
N}2]Cu(C2H4) (8)
3.68
3.48
87.6
85.3
85.2
86.1
86.0
74.7
[N{(C3F7)C(2-(CF3)C6H4)
N}2]Cu(C2H4) (9)
[N{(C3F7)C(2-F,6-(CF3)C6H3) 3.59
N}2]Cu(C2H4) (10)
[N{(C3F7)C(C6F5)N}2]
Cu(C2H4) (2)
3.86
[N{(C3F7)C(Dipp)N}2]
Cu(C2H4) (13)
3.37
8
[HC{(Me)C(2,6-Me2C6H3)
2.91 (C6D6)
3.63 (at 223 K)
38
N}2]Cu(C2H4) (11)
[tBu2P(Me3SiN)2]Cu(C2H4)
73.0 (C6D6) 41
(12)
a
1H NMR data were acquired in CDCl3 unless otherwise noted; 13C
NMR data have been reported in the same solvent. 13C and 1H NMR
peaks of free ethylene appear at δ 123.3 and 5.40 ppm, respectively.
significant upfield shifts (or shifts toward lower frequency)
relative to the free ethylene chemical shift values. For example,
13C and 1H NMR peaks of free ethylene appear at δ 123.3 and
5.40 ppm, respectively.1
Figure 2. Synthesis of copper(I) ethylene complexes 7 and 8 and
copper(I) carbonyl complexes 16 and 17.
The upfield shift of ethylene has been linked to the metal→
ethylene π back-bonding component, which creates a shielding
effect.33−37 In general, a survey of structurally authenticated
Cu(I) monoethylene adducts (which also include cationic
species) shows that their ethylene 13C resonance appears in the
range δ 89.5−73.0 ppm.1 The ethylene carbon resonance in
copper ethylene adducts 7−10 (δ 85.2−87.6 ppm, Table 1)
appear at the higher chemical shift end of the spectrum, thus
pointing to the presence of a relatively acidic and a poorly back-
bonding metal site. This is not surprising, considering the
weakly donating nature of triazapentadienyl ligands on 7−10
bearing fluoroalkyl and nitro groups. For comparison, the
adduct [HC{(Me)C(2,6-Me2C6H3)N}2]Cu(C2H4) (11),38
[N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) (8) was synthe-
sized via a similar route using the triazapentadiene 4.
Compounds 7 and 8 are thermally stable solids, do not lose
ethylene during sample drying for chemical analysis, and can be
1
handled in air briefly without decomposition. The 13C and H
NMR signals of copper(I)-coordinated ethylene in CDCl3
solution for 7 were observed at δ 85.4 and 3.51 ppm,
respectively. The corresponding resonances of 8 appear at δ
87.6 and 3.68 ppm, respectively.
We have also investigated the copper ethylene adducts of
[N{(C3F7)C(2-(CF3)C6H4)N}2]H (5) and [N{(C3F7)C(2-
F,6-(CF3)C6H3)N}2]H (6). [N{(C3F7)C(2-(CF3)C6H4)N}2]-
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Figure 4. ORTEP diagrams of (left) [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4) (7) and (right) [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) (8)
(thermal ellipsoids set at 40% probability).
Figure 5. ORTEP diagrams of (left) [N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) (9) and (right) [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(C2H4)
(10) (thermal ellipsoids set at 40% probability).
́
Table 2. X-ray Bond Distances (Å) and Bond Angles (deg) for Selected 1,3,5-Triazapentadienyl and 1,5-Diazapentadienyl
Copper(I) Ethylene Complexes
N−Cu−N
C−Cu−C
compd
Cu−N (Å)
Cu−C (Å)
(deg)
(deg)
CC (Å)
ref
[N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4) (7) 1.953(2), 1.966(2)
[N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) (8) 1.955(5), 1.958(6)
2.021(3), 2.022(3)
2.027(8), 1.998(8)
2.012(2), 2.012(2)
96.78(9)
96.4(2)
39.36(12)
38.7(4)
1.361(4)
1.332(12)
1.355(5)
this work
this work
this work
[N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) (9)
1.9509(16),
1.9509(16)
96.20(9)
39.34(13)
[N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(C2H4)
(10)
1.9381(12),
1.9411(12)
1.9920(18),
2.0047(18)
96.64(5)
40.10(8)
1.370(3)
this work
[N{(C3F7)C(C6F5)N}2]Cu(C2H4) (2)
[N{(C3F7)C(Dipp)N}2]Cu(C2H4) (13)
1.946(2), 1.955(2)
2.010(3), 2.018(3)
96.66(9)
95.55(4)
39.60(12)
39.52(4)
1.364(4)
22
8
1.9403(9), 1.9406(9)
1.9974(11),
2.0006(11)
1.3518(14)
[HC{(Me)C(2,6-Me2C6H3)N}2]Cu(C2H4) (11) 1.908 (1), 1.917(2)
1.986(2), 1.992(2)
98.68(6)
40.13(9)
1.365(3)
38
which has a relatively electron-rich 1,5-diazapentadienyl ligand
(and therefore, a relatively electron rich copper center), has its
ethylene carbon resonance at δ 74.7 ppm. The 13C chemical
shift is a good indicator of a Cu−ethylene π-bonding
interaction,33−37 where weakly bound ethylene molecules
usually show only a small upfield shift whereas metal adducts
with strong σ/π bonds to ethylene (leading to “metal-
lacyclopropane” type adducts) show a notable upfield shift
(e.g., metal-bound ethylene carbon peaks appear at δ 104.9
ppm for [HB(3,5-(CF3)2Pz)3]Ag(C2H4) and δ 24.85 ppm for
the N-heterocyclic carbene Ni(0) adduct [Ni-
(iPr2Im)2(C2H4)]).34,39,40
copper(I)-coordinated ethylene in 7−10 was observed at δ
3.68−3.48 ppm. In these adducts, high upfield shifts relative to
the free ethylene signal are very likely caused by added shielding
contributions from the ring current effects of N-aryl groups
flanking the ethylene moiety rather than just a result of Cu→
ethylene back-bonding.1,7,21 For comparison, [tBu2P-
(Me3SiN)2]Cu(C2H4) (12),41 which has a relatively electron
rich copper center and no flanking aryl groups, exhibits its
ethylene proton signal at δ 3.63 ppm (in CDCl3 at 223 K),
which is similar to that observed in 7−10, although they have
very different ethylene carbon chemical shifts (δ 73.0 vs 85.2−
87.6 ppm).
The 1H NMR signal of ethylene protons of copper(I)
monoethylene adducts (which also include cationic species)
have been observed in the range δ 5.22−2.92 ppm (cf., 5.40
The X-ray structures of [N{(C3F7)C(2-(NO2)C6H4)N}2]-
Cu(C2H4) (7), [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4)
(8), [N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) (9) and [N-
{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(C2H4) (10) are illus-
1
1
ppm in CDCl3 for free ethylene). The H NMR signal of
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trated in Figures 4 and 5. The key structural parameters are
summarized in Table 2.
The basic features of 7−10 are similar to those observed for
[N{(C3F7)C(C6F5)N}2]Cu(C2H4) (2; Figure 1)22 and [N-
{(C3F7)C(Dipp)N}2]Cu(C2H4) (13; Figure 6).8 The 1,3,5-
triazapentadienyl ligand coordinates to copper in a κ2 fashion,
although it is a versatile ligand that can adopt several different
coordination modes.28,30,42 Copper atoms have a trigonal-
planar geometry. The N-aryl groups and CuN3C2 planes are
fairly orthogonal to each other and flank the Cu ethylene
moiety. Interestingly, trifluoromethyl groups on N-aryls of
[N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) (9) occupy the
same face of the CuN3C2 plane. [N{(C3F7)C(2-F,6-(CF3)-
C6H3)N}2]Cu(C2H4) (10) shows the same feature, while the
nitro groups of [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4)
(7) lie on opposite sides of the CuN3C2 plane. The ethylene
groups adopt essentially a coplanar orientation with the 1,3,5-
triazapentadienyl backbone (as is evident from small C2Cu and
CuN2 dihedral angles, with the largest being 14.5° in 7). These
adducts show several intermolecular contacts such as H···F at
less than 3 Å. Compound 8 also shows intermolecular Cu···O
interactions at 2.84 Å between the copper center and nitro
group of a neighboring molecule. The coplanar orientation of
C2Cu and CuN2 facilitates enhanced interaction of the ethylene
π* orbital with the filled copper d orbitals.38,43 We have
observed a similar orientation in the adduct [N{(C3F7)C-
(Dipp)N}2]Cu(3-hexyne), in which calculations show that the
coplanar N2Cu and CuC2 triangles are about 26 kJ/mol more
stable compared to conformers with a 90° N2Cu and CuC2
dihedral angle.44
These adducts (except 8, for which the crystal quality is not
very satisfactory for detailed data analysis) show a small
lengthening of CC bond as a result of ethylene coordination
to copper. For comparisons, the CC bond length in free
gaseous ethylene is estimated to be 1.3305(10) Å45 while the
corresponding distance from X-ray data is 1.313 Å.1,46
Compounds 7−10 have weakly coordinating ligands and
show slightly longer Cu−N bond distances in comparison to
the corresponding distance of 11, which has a relatively
electron rich diazapentadienyl supporting ligand. The Cu−C
distances are not significantly different (especially at the 3σ
level of esd) for the compounds given in Table 2. Overall,
NMR ethylene 13C carbon resonance data (in solution at room
temperature) and key structural parameters are similar in
compounds 7−10, and they are essentially identical with those
observed even for 13. Thus, these techniques are not
sufficiently sensitive to detect effects of different substituents
on N-aryl groups of the triazapentadienyl adducts given in
Table 1. The ethylene proton chemical shifts, however, appear
to have some correlation with the electron donating/with-
drawing properties of the substituent on the aryl group, but this
value is affected by aryl ring currents, which complicates the
interpretation.
Figure 6. Preparation of [N{(C3F7)C(Dipp)N}2]CuCO and [N-
{(C3F7)C(Dipp)N}2]Cu(C2H4).8,31
{(Me)C(2,6-Me2C6H3)N}2]CuCO (which is the CO analogue
of 11),50 which has a nonfluorinated, relatively electron rich
diazapentadienyl ligand, displays the CO stretch at a much
lower value: νCO 2071 cm−1. Our attempts to prepare Cu−CO
adducts using [N{(C3F7)C(2-(NO2)C6H4)N}2]H (3) or
[N{(C3F7)C(4-(NO2)C6H4)N}2]H (4), Cu2O, and CO (via
a route similar to those followed for 7 and 8) were successful
but resulted in [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(CO)-
(NCCH3) (16) and [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu-
(CO)(NCCH3) (17), which also contain a molecule of
acetonitrile on the copper center (Figure 2). The complete
displacement of acetonitrile leading to the formation of three-
coordinate ethylene adducts 7 and 8, while acetonitrile is
retained during the formation of 16 and 17 with four-
coordinate copper sites may be primarily a result of steric
effects. The η2-bound ethylene occupies more space at
copper(I) in comparison to an end-on-bound CO group. In
fact, the complete displacement of acetonitrile by CO has been
observed when bulkier triazapentadienyl ligands are present on
copper, as in [N{(C3F7)C(Dipp)N}2]CuCO (15; Figure 6).31
We also note that both [Cu(CO)3]+ and [Cu(CO)4]+ are
known among copper carbonyls, while only [Cu(C2H4)3]+ (but
not [Cu(C2H4)4]+) has been reported thus far in the Cu(I)
ethylene family.1,51
Compounds 16 and 17 have been characterized by several
spectroscopic methods and by X-ray crystallography. The
molecular structure of 17 is depicted in Figure 7. Although we
The CO stretching frequency of metal carbonyls is a useful
tool to examine the effect of different ligands on a metal
site.47−49 We have reported [N{(C3F7)C(2-F,6-(CF3)C6H3)-
N}2]CuCO (14; Figure 3) and [N{(C3F7)C(Dipp)N}2]CuCO
(15, Figure 6), and they show clearly different νCO values at
2128 and 2109 cm−1, respectively (Figure 6).22,31 The high νCO
value for [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]CuCO is a sign
of poor Cu→CO back-donation resulting from the presence of
a relatively acidic copper site and a weakly donating
[N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]−. For comparison, [HC-
Figure 7. ORTEP diagram of [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu-
(CO)(NCCH3) (17) (thermal ellipsoids set at 40% probability).
Selected bond lengths (Å) and angles (deg): Cu−N1 = 2.018(2), Cu−
N3 = 2.018(2), Cu−N6 = 2.025(3), Cu−C23 = 1.832(3), N6−C21 =
1.139(4), O5−C23 = 1.123(4); N1−Cu−N3 = 92.37(9), N1−Cu−
C23 = 120.94(12), N3−Cu−C23 = 113.46(12), N1−Cu−N6 =
104.56(10), N3−Cu−N6 = 105.30(9), C23−Cu−N6 = 116.73(12),
Cu−N6−C21 = 176.8(2), Cu−C23−O5 = 174.5(3).
́
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under reduced pressure. The resulting material was dispersed in
deionized water at 70 °C and filtered hot. The residue was collected
and dried under reduced pressure overnight. It was recrystallized from
hexane to give yellow crystals of [N{(C3F7)C(2-(NO2)C6H4)N}2]H.
Yield: 5.90 g (39%). Mp: 108−109 °C. 19F NMR (CDCl3): δ −80.02
(br, CF3), −113.74 to −116.69 (m, α-CF2), 123.99 (br, β-CF2),
have solved the crystal structure of 16 (see the Supporting
Information; which supports the identity as predicted from
spectroscopic and analytical data), aryl groups and C3F7 suffer
from positional disorder, affecting the overall quality. Both 16
and 17 feature pseudotetrahedral copper sites.
The Cu(I) carbonyl adducts 16 and 17 show a strong
absorption band attributable to a CO stretch at 2106 and 2097
cm−1, respectively. These values suggest relatively weak Cu→
CO back-bonding and indicate the relatively weakly donating
nature of the supporting ligands on copper. The corresponding
signal in [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(CO)-
(NCCH3) (18; Figure 3) is observed at a higher value, 2119
cm−1, indicating the presence of an even more electron poor
copper site. Thus, these findings suggest that [N{(C3F7)C(2-
F,6-(CF3)C6H3)N}2]− is a slightly weaker donor than [N-
{(C3F7)C(2-(NO2)C6H4)N}2]− or [N{(C3F7)C(4-(NO2)-
C6H4)N}2]−. We are presently working on the isolation of
related Cu(I) carbonyls without an acetonitrile ligand to obtain
additional information about the donor properties of [N-
{(C3F7)C(2-(NO2)C6H4)N}2]− or [N{(C3F7)C(4-(NO2)-
C6H4)N}2]− and to see how they compare to those of ligands
such as [N{(C3F7)C(Dipp)N}2]−.
Overall, we have reported the synthesis of easily isolable
copper(I) ethylene adducts supported by 1,3,5-triazapentadien-
yl ligands with fluoroalkyl groups on the ligand backbone and
nitro or fluorine substituents on the N-aryl groups. The
ethylene carbon chemical shift in the 13C NMR and key
structural parameters around copper are very similar for
adducts 7−10. They all feature trigonal-planar copper sites
and κ2-bonded, U-shaped triazapentadienyl ligands. The Cu(I)
carbonyl adducts 16 and 17 have pseudotetrahedral copper
sites with copper bonded to an acetonitrile, CO, and the
chelating triazapentadienyl ligand. A comparison of CO
stretching frequencies suggests that [N{(C3F7)C(2-F,6-(CF3)-
C6H3)N}2]− is a weaker donor than [N{(C3F7)C(2-(NO2)-
C6H4)N}2]− or [N{(C3F7)C(4-(NO2)C6H4)N}2]−. Consider-
ing the catalytic activity displayed by [N{(C3F7)C(Dipp)N}2]-
Cu(C2H4), adducts 7−10 may also effectively mediate carbene
and nitrene transfer chemistry.
1
−125.53 (br, β-CF2). H NMR (CDCl3): δ 10.89 (br, 1H, NH), 8.35
(br, 1H, H-Ar), 8.30 (br, 1H, H-Ar), 7.96 (br, 1H, H-Ar), 7.78 (br, 1H,
H-Ar), 7.53 (br, 1H, H-Ar), 7.37 (br, 1H, H-Ar), 7.22 (br, 1H, H-Ar),
6.99 (br, 1H, H-Ar), Anal. Calcd for C20H9F14N5O4: C, 37.00; H, 1.40;
N, 10.79. Found: C, 36.91; H, 1.25; N, 10.91.
[N{(C3F7)C(4-(NO2)C6H4)N}2]H (4). Perfluoro-5-aza-4-nonene
(2.50 g, 5.8 mmol) was added dropwise to a mixture of triethylamine
(2.42 mL, 17.3 mmol) and p-nitroaniline (1.59 g, 11.5 mmol) in ether
at 0 °C. The solution was then stirred overnight. The mixture was
washed with 6 M HCl (25 mL) solution. The ether layer was then
separated after filtration and washed with deionized water, and the
ether was removed under reduced pressure. The obtained material was
dispersed in deionized water at 70 °C and filtered, and the residue was
collected and dried using reduced pressure. It was then recrystallized
from hexane to give crystals of [N{(C3F7)C(4-(NO2)C6H4)N}2]H.
Yield: 1.50 g (40%). Mp: 143−145 °C. 19F NMR (CDCl3): δ −79.9
(apparent triplet, J = 12.4 Hz, 7.3 Hz, CF3), −80.2 (apparent triplet, J
= 11.0 Hz, 7.3 Hz, CF3), −115.32 (br, α-CF2), −116.53 (s, α-CF2),
−124.44 (br, β-CF2), −126.07 (br, β-CF2). 1H NMR (CDCl3): δ 8.32
(d, J = 8.4 Hz, 2H, H-Ar), 8.18 (d, J = 8.4 Hz, 2H, H-Ar), 7.43 (d, J =
8.4 Hz, 2H, H-Ar), 7.23 (br, 1H, NH), 6.99 (d, J = 8.4 Hz, 2H, C6H4).
Anal. Calcd for C20H9F14N5O4: C, 37.00; H, 1.40; N, 10.79. Found:
36.92; H, 1.38; N, 10.72.
[N{(C3F7)C(2-(CF3)C6H4)N}2]H (5). Perfluoro-5-aza-4-nonene (4.6
mmol) was added dropwise to a mixture of triethylamine (1.38 mL,
13.8 mmol) and aniline (9.2 mmol) in ether (100 mL), at 0 °C. After
addition the solution was stirred overnight at room temperature. A
nitrogen atmosphere was not necessary after this point during this
ligand synthesis. The mixture was then filtered, and the filtrate was
collected and washed first with 10% HCl and then twice with
deionized water. The ether layer was separated and dried over CaCl2
or Na2SO4. The solvent was removed under reduced pressure to give
[N{(C3F7)C(2-(CF3)C6H4)N}2]H. Pentane was added to the yellow
oily product and the mixture cooled to −20 °C to give transparent
squares upon standing after several days. Yield: 1.76 g (55%). Mp: 53−
56 °C. 19F NMR (CDCl3): δ −61.23 (s, 3F, CF3), −61.43 (s, 3F,
CF3), −80.14 (t, J = 8.7 Hz, 10.9 Hz, 3F, o-CF3), −80.41 (t, J = 8.7 Hz,
3F, o-CF3), −114.34 and −116.04 (br, 4F, α-CF3), −123.76, −124.71,
1
EXPERIMENTAL SECTION
and −126.17 (s, 4F, β-CF2). H NMR (CDCl3): δ 7.68 (apparent
■
doublet, J = 7.8 Hz, 1H, H-Ar), 7.61 to 7.55 (m, 2H, H-Ar), 7.45 to
7.40 (apparent doublet, 2H, H-Ar), 7.37 (t, J = 7.5 Hz, 1H, H-Ar), 7.16
(t, J = 7.5 Hz, 1H, H-Ar), 7.05 (br, 1H, NH), 6.87 (d, 1H, J = 8.3 Hz,
o-Ar). Anal. Calcd for C22H9F20N3: C, 38.00; H, 1.30; N, 6.04. Found:
C, 37.54; H, 1.30; N, 5.86.
All manipulations were carried out under an atmosphere of purified
nitrogen using standard Schlenk techniques or in a drybox. Solvents
were purchased from commercial sources, purified by using an
Innovative Technology SPS-400 PureSolv solvent drying system or by
distilling over conventional drying agents, and degassed by the freeze−
pump−thaw method twice prior to use. Glassware was oven-dried at
150 °C overnight. NMR spectra were recorded at 25 °C on JEOL
Eclipse 500 spectrometer (1H, 500.16 MHz; 13C, 125.77 MHz; 19F,
470.62 MHz). Proton and carbon chemical shifts are reported in ppm
versus Me4Si. 19F NMR chemical shifts were referenced relative to
external CFCl3. Infrared spectra were recorded on a JASCO FT-IR
410 spectrometer. Elemental analyses were performed using a Perkin-
Elmer Series II CHNS/O analyzer. Melting points were obtained on a
Mel-Temp II apparatus and were not corrected. All materials were
obtained from commercial vendors, with the exception of perfluoro-5-
aza-4-nonene52 and [N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]H, which
were synthesized by using published procedures.22,24
[N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4) (7). [N{(C3F7)C(2-
(NO2)C6H4)N}2]H (0.20 g, 0.28 mmol) and Cu2O (0.03 g, 0.20
mmol) were added to acetonitrile (20 mL) and refluxed for 12 h. The
resulting solution was filtered through a bed of Celite. The filtrate was
collected, and the solvent was removed under reduced pressure.
Dichloromethane (3 mL) was added, ethylene (1 atm) was passed
through for 2 min, and the mixture was stirred at room temperature
for 5 h. Later hexane (3 mL) was added to the solution, ethylene was
then passed through again, and the mixture was kept at −20 °C to give
red crystals of [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(C2H4). Yield:
0.12 g (58%). Mp: 74−82 °C dec. 19F NMR (CDCl3): δ −80.21
(apparent triplet, J = 10.9 Hz, 9.5 Hz, CF3), −80.28 (apparent triplet, J
= 9.5 Hz, 9.6 Hz, CF3), −106.56 (apparent quartet, J = 9.1 Hz, α-CF2),
−106.83 (apparent quartet, J = 9.1 Hz, α-CF2), −123.35 (d, J = 13.6
[N{(C3F7)C(2-(NO2)C6H4)N}2]H (3). Perfluoro-5-aza-4-nonene
(10.00 g, 23.0 mmol) was added dropwise to a mixture of
triethylamine (9.70 mL, 69.3 mmol) and o-nitroaniline (6.40 g, 46.2
mmol) in ether (250 mL) at 0 °C. The solution was then stirred
overnight. The resulting mixture was washed with 6 M HCl (64 mL)
solution in an ice bath. The ether layer was then separated after
filtration and washed with deionized water, and ether was removed
1
Hz, β-CF2). H NMR (CDCl3): δ 8.08 (d, J = 7.6 Hz, 2H, H-Ar),
7.64−7.61 (m, 2H, H-Ar), 7.32 (t, J = 7.6 Hz, 2H, H-Ar), 7.19 (d, J =
7.6 Hz, 2H, H-Ar), 3.51 (s, 4H, C2H4), 13C{1H} NMR (CDCl3): δ
selected peaks 85.4 (s, C2H4). Anal. Calcd for C22H12F14N5O4Cu: C,
35.71; H, 1.63; N, 9.47. Found: C, 34.86; H 1.05; N 9.66.
7930
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Organometallics
Article
[N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) (8). [N{(C3F7)C(4-
(NO2)C6H4)N}2]H (0.30 g, 0.46 mmol) and Cu2O (0.04 g, 0.28
mmol) were added to acetonitrile (25 mL) and refluxed for 12 h. The
resulting solution was filtered through a bed of Celite. The filtrate was
collected, and the solvent was removed under reduced pressure.
Dichloromethane (3 mL) was added to it, ethylene was passed
through for 2 min, and the mixture was stirred at room temperature
for 5 h. Later hexane (3 mL) was added to the solution, ethylene was
then passed through again, and the mixture was kept at −20 °C to give
red crystals of [N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4). Yield:
0.11 g (32%). Mp: 155 °C dec. 19F NMR (CDCl3): δ −80.2
(apparent triplet, J = 11.0 Hz, 11.0 Hz, CF3), −104.04 (apparent
quartet, J = 9.8 Hz, α-CF2), −123.23 (br, β-CF2). 1H NMR (CDCl3):
δ 8.24 (d, J = 8.4 Hz, 4H, H-Ar), 7.13 (d, J = 9.2 Hz, 4H, H-Ar), 3.68
(s, 4H, C2H4). 13C{1H} NMR (CDCl3): δ selected peaks 87.6 (s,
C2H4). Anal. Calcd for C22H12F14N5O4Cu: C, 35.71; H, 1.63; N, 9.47.
Found: C, 35.54; H, 1.44; N, 9.56.
[N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) (9). [N{(C3F7)C(2-(CF3)-
C6H4)N}2]H (0.25 g, 0.36 mmol) and Cu2O (0.03 g, 0.22 mmol)
were mixed in acetonitrile (15 mL) and refluxed at 90 °C overnight.
The solution was filtered and concentrated to give an oily mixture. It
was then dissolved in 5 mL of CH2Cl2/n-hexane (1/1), and the
solution was saturated with ethylene and cooled to −20 °C. Yellow
square rods of [N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) appeared
overnight at 5 °C. Yield: 0.21 g (75%). Mp: darkened at 85 °C, melted
at 94−98 °C. 19F NMR (CDCl3): δ −60.14 (broad, 3F, o-CF3),
−60.41 (broad, 3F, o-CF3), −80.30 (overlapped triplets, J = 10.2 Hz,
6F, CF3), −104.26 to −108.51 (m, 4F, α-CF2), −122.94 (s, 2F, β-
CF2), −123.78 (d, J = 10.9 Hz, 2F, β-CF2). 1H NMR (CDCl3): δ 7.62
(d, J = 7.9 Hz, 2H, H-Ar), 7.50 (t, J = 6.9 Hz, 2H, H-Ar), 7.23 (t, 2H,
H-Ar), 7.03 (d, J = 7.9 Hz, 2H, H-Ar) 3.48 (s, 4H, C2H4). 13C{1H}
NMR (CDCl3): selected δ 85.3 (s, C2H4). Anal. Calcd for
C24H12N3F20Cu: C, 36.68; H, 1.54; N, 5.35. Found: C, 36.68; H,
1.62; N, 5.30.
and the solvent was removed under reduced pressure. CH2Cl2 (3 mL)
was added to it, CO was passed through for 4 min, and the mixture
was stirred at room temperature for 5 h. Later hexane (5 mL) was
added to the solution, CO was then passed through again, and the
mixture was kept at −20 °C to give orange crystals of [N{(C3F7)C(4-
(NO2)C6H4)N}2]Cu(CO)(NCCH3) Yield: 0.25 g (41%). Mp: 126 °C
−130 °C dec. 19F NMR (CDCl3): δ −80.23 (apparent triplet, J = 11
Hz, CF3), −104.00 (br, α-CF2), −123.15 (br, β-CF2), 1H NMR
(CDCl3): δ 8.19 (d, J = 8.6 Hz, 4H, Ar), 7.13 (d, J = 8.6 Hz, 4H, Ar),
2.05 (s, 3H, NCCH3), Anal. Calcd for C23H11F14N6O5Cu: C, 35.38; H,
1.42; N, 10.76. Found: C, 34.43; H, 1.36; N, 10.51. IR (KBr, cm−1):
selected peak 2097 (CO).
X-ray Crystallographic Data. Diffraction data were collected at T
= 100(2) K. The data sets were collected on a Bruker SMART APEX
CCD diffractometer with graphite-monochromated Mo Kα radiation
(λ = 0.710 73 Å). Intensity data were processed using the Saint Plus
program. All the calculations for the structure determination were
carried out using the SHELXTL package (version 6.14).53 Initial
atomic positions were located by direct methods using XS, and the
structures of the compounds were refined by the least-squares method
using XL. Absorption corrections were applied by using SADABS.
Except for hydrogen atoms on the ethylene moiety, other hydrogen
atoms were included at calculated positions and refined in a riding
manner along with the attached carbons. Hydrogen atoms on ethylene
were located in the difference Fourier maps and refined freely.
[N{(C3F7)C(2-(CF3)C6H4)N}2]Cu(C2H4) crystallized in the space
group P21/m, and the molecule sits on a mirror plane containing N2,
Cu, and the ethylene centroid (for a Z value of 2). The crystal of
[N{(C3F7)C(4-(NO2)C6H4)N}2]Cu(C2H4) diffracted poorly. It also
displays disorder of C3F7 moieties, as is evident from the relatively
high thermal parameters. A summary of the refinement details and the
results are given in the Supporting Information.
ASSOCIATED CONTENT
■
[N{(C3F7)C(2-F,6-(CF3)C6H3)N}2]Cu(C2H4) (10). [N{(C3F7)C(2-
F,6-(CF3)C6H3)N}2]H (0.25 g, 0.34 mmol), Cu2O (0.03 g, 0.21
mmol), acetonitrile (5 mL), and THF (10 mL) were stirred overnight
at 80 °C. The solution was cooled, filtered, and concentrated to give
an oily mixture. It was dissolved in 5 mL of CH2Cl2/n-hexane (1/3),
and ethylene was bubbled through for 2 min. The resulting solution
was left to crystallize at −20 °C to afford yellow hexagons overnight.
Yield: 0.25 g (90%). Mp: 102 °C dec. 19F NMR (CDCl3): δ −60.17 (s,
6F, o-CF3), −80.59 (t, J = 9.8 Hz, 6F, CF3), −106.40 and −109.30 (AB
multiplet, JAB = 279.5 Hz, 4F, α-CF2), −121.51 (s, 2F, o-F), −123.20
S
* Supporting Information
Figures, tables, and CIF files giving X-ray crystallographic data
for 7−10 and 17 and the molecular structure and X-ray data for
16. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: dias@uta.edu.
1
(s, 4F, β-CF2). H NMR (CDCl3): δ 7.44 (d, J = 7.8 Hz, 2H, m-Ar),
7.34−7.21 (m, 4H, m- and p-Ar), 3.59 (s, 4H, C2H4). 13C{1H} NMR
(CDCl3): selected δ 85.2 (s, C2H4). Anal. Calcd for C24H10F22N3Cu
(contains 0.1 equiv of NCCH3): C, 35.19; H, 1.26; N, 5.26. Found: C,
34.70; H, 1.40; N, 5.92.
Notes
The authors declare no competing financial interest.
[N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(CO)(NCCH3) (16). [N{(C3F7)C-
(2-(NO2)C6H4)N}2]H (0.56 g, 0.86 mmol) and Cu2O (0.06 g, 0.43
mmol) were added to acetonitrile, and the mixture was refluxed for 14
h. The resulting solution was filtered through a bed of Celite. The
filtrate was collected, and the solvent was removed under reduced
pressure. CH2Cl2 (3 mL) was added to it, CO was passed through for
4 min, and the mixture was stirred at room temperature for 5 h. Later
hexane (5 mL) was added to the solution, CO was then passed
through again, and the mixture was kept at −20 °C to give orange
crystals of [N{(C3F7)C(2-(NO2)C6H4)N}2]Cu(CO)(NCCH3). Yield:
0.32 g (47%). Mp: 65 °C −71 °C dec. 19F NMR (CDCl3): δ −80.29
(br, CF31), −106.32 to −106.49 (m, α-CF2), −123.16 to −123.29 (m,
β-CF2). H NMR (CDCl3): δ 8.05 (d, J = 7.7 Hz, 2H, Ar), 7.59 (br,
2H, Ar), 7.29 (t, J = 7.0 Hz, 2H, Ar), 7.20 (d, J = 7.0 Hz, 2H, Ar), 1.20
(s, 3H, NCCH3). Anal. Calcd for C23H11F14N6O5Cu: C, 35.38; H,
1.42; N, 10.76. Found: C, 34.75, H 1.33; N 10.50. IR (KBr, cm−1),
selected peak: 2106 (CO).
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
(No. CHE-0845321) and the Robert A. Welch Foundation
(Grant Y-1289). The NSF (No. CHE-0840509) is thanked for
providing funds to upgrade the NMR spectrometer used in this
work. X-ray crystallography was performed at the Center for
Nanostructured Materials (CNM) at the University of Texas at
Arlington.
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