Dicopper Alkyl Complexes: Synthesis, Structure, and Unexpected Persistence

Article abstract of DOI:10.1021/acs.organomet.8b00443

Cationic μ-alkyl dicopper complexes [Cu₂(μ-n¹: n ¹-R)DPFN]NTf₂ (R = CH₃, CH₂CH₃, CH₂C(CH₃)₃; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine NTf₂^- = N(SO₂CF₃)₂^-) were synthesized by treatment of the acetonitrile-bridged dicopper complex [Cu₂(μ- n ¹: n ¹-NCCH₃)DPFN](NTf₂)₂ with LiR or MgR₂. Structural characterization by X-ray crystallography and NMR spectroscopy revealed that the alkyl ligands symmetrically bridge the two copper centers, and the complexes persist in room-temperature solution. Notably, the μ-methyl complex showed less than 20% decomposition after 34 days in room-temperature THF solution. Treatment of the μ-methyl complex with acids allows installation of a range of monoanionic bridging ligands. However, surprisingly insertion into the dicopper-carbon bond was not observed upon addition of a variety of reagents, suggesting that these complexes exhibit a fundamentally new reactivity profile for alkylcopper species. Electrochemical characterization revealed oxidation-reduction events that evidence putative mixed-valence dicopper alkyl complexes. Computational studies suggest that the dicopper-carbon bonds are highly covalent, possibly explaining their remarkable stability.

Full text of DOI:10.1021/acs.organomet.8b00443

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Dicopper Alkyl Complexes: Synthesis, Structure, and Unexpected
Persistence
Micah S. Ziegler,†
and T. Don Tilley*
,‡,§
†,‡
Nicole A. Torquato, Daniel S. Levine, Amel
́
ie Nicolay,†,‡ Hasan Celik,†
†
†
,
†
Department of Chemistry, University of California, Berkeley, California 94720-1460, United States
‡
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
*
S Supporting Information
ABSTRACT: Cationic μ-alkyl dicopper complexes [Cu (μ-
2
1
1
η :η -R)DPFN]NTf (R = CH , CH CH , CH C(CH ) ;
2
3
2
3
2
3 3
DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyri-
−
−
dine NTf2 = N(SO CF ) ) were synthesized by treatment
2
3 2
1
1
of the acetonitrile-bridged dicopper complex [Cu (μ-η :η -
2
NCCH )DPFN](NTf ) with LiR or MgR . Structural
3
2
2
2
characterization by X-ray crystallography and NMR spectros-
copy revealed that the alkyl ligands symmetrically bridge the two copper centers, and the complexes persist in room-temperature
solution. Notably, the μ-methyl complex showed less than 20% decomposition after 34 days in room-temperature THF
solution. Treatment of the μ-methyl complex with acids allows installation of a range of monoanionic bridging ligands.
However, surprisingly insertion into the dicopper−carbon bond was not observed upon addition of a variety of reagents, sug-
gesting that these complexes exhibit a fundamentally new reactivity profile for alkylcopper species. Electrochemical charac-
terization revealed oxidation−reduction events that evidence putative mixed-valence dicopper alkyl complexes. Computational
studies suggest that the dicopper−carbon bonds are highly covalent, possibly explaining their remarkable stability.
INTRODUCTION
the solid state exhibit linear, or nearly linear, binding geo-
1
■
2,22−24
metries.
Metal alkyl complexes have long interested chemists, since they
provide useful synthetic reagents and catalysts, display unusual
bonding motifs, and represent mechanistic intermediates in
As described here, the rigid, dinucleating ligand 2,7-
bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine (DPFN)
that has been shown to support a series of cationic dicopper
1
−4
important transformations.
Of the many transition-metal
25
26
aryl and alkynyl complexes has provided access to isolable
bridging methyl and neopentyl complexes, which have been
thoroughly characterized. An ethyl complex was similarly
synthesized and, despite slight impurities, studied structurally
and spectroscopically. Reactivity accessible to a dicopper−alkyl
core was explored by treating the bridging methyl complex
with a range of acids and unsaturated compounds. In addition,
structural characterization and investigation of the electro-
chemical properties of the μ-methyl complex allow compar-
isons of alkyl, aryl, and alkynyl ligands bound to a dicopper
center. Computational studies corroborate the trends observed
in the solid-state structures, and bonded energy decomposition
analysis (EDA) suggests a high level of covalency in the inter-
actions between the two copper centers and the bridging
carbon atoms.
alkyl compounds that have been discovered, few have found as
wide use in organic and inorganic synthesis as those based on
5
copper. Organocuprates have become especially well known
6−11
for their selectivity and role in conjugate addition reactions.
However, in addition to their utility, organocopper compounds
have also long been known for their high reactivity and insta-
14
8
,12
13
bility. Early work by Reich as well as Gilman and Straley
highlighted the need for low-temperature preparations that
exclude air and water and the lower stability of alkylcopper
compounds in comparison to arylcopper analogues.
This elusiveness of isolable alkylcopper compounds is
exemplified by methylcopper, which upon warming above
0
°C generally decomposes to give metallic copper, methane,
7,15 16
and ethane.
and N-heterocyclic carbenes (NHCs),
Use of various ligands, notably phosphines
17,18
has enabled the
isolation and characterization of monomeric alkylcopper com-
plexes that are significantly more persistent under an inert
atmosphere. Historically, nitrogen-based ligands have generally
DICOPPER ALKYL COMPLEXES
■
Previous work demonstrated that an acetonitrile ligand
bridging two copper centers supported by DPFN is displaced
by treatment with 1 equiv of tetraphenylborate, from which an
19−21
not provided similar stabilization.
Moreover, the bulky
or chelating ligands employed to stabilize [CuMe] and the
propensity for Cu(I) to adopt linear or tetrahedral bonding
geometries often result in monocopper structures and there-
25
aryl group is abstracted to yield a μ-Ph ligand. The latter
12
fore neutral complexes. In addition, a range of ionic diorgan-
Received: June 28, 2018
−
ocuprates, including CuMe , have been isolated and in
2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
complex performs certain C−H bond activations; for example,
upon heating for 4 h at 100 °C, the μ-Ph complex reacts with a
26
terminal alkyne to generate a μ-alkynyl complex and benzene.
Significantly harsher conditions were required to activate aryl
C−H bonds. For example, exchange of the μ-Ph for μ-C F
6
5
upon treatment with excess pentafluorobenzene required heating
for 35 days at 110 °C. As alkyl-bridged dicopper complexes
were expected to be temperature-sensitive, a lower-temper-
ature approach was sought for the introduction of bridging
3
ligands with sp -hybridized carbon atoms.
1
1
Treatment of [Cu (μ-η :η -NCCH )DPFN](NTf ) with
2
3
2 2
dimethylmagnesium (0.51 equiv) in THF at −30 °C resulted
1
in a rapid darkening of the reaction mixture. The H NMR spec-
trum of the primary product revealed a resonance at 0.89 ppm
(
vs SiMe , in THF-d ), which integrates to three protons per
4 8
DPFN ligand. Meanwhile the aromatic resonances suggest that
Figure 1. Solid-state structure of 1 as determined by single-crystal
X-ray diffraction. Only one dicopper cation in the asymmetric unit is
shown; the other cation, two NTf2 counterions, and selected
hydrogen atoms are omitted for clarity. Thermal ellipsoids are set at
the 50% probability level.
the complex retains its C symmetry on the NMR time scale.
2
v
−
1
9
The F NMR spectrum revealed a slight shift of the ligand
resonance from −174.50 to −174.32 ppm (vs CFCl , in THF),
3
further implying that the dicopper complex undergoes a rela-
tively clean conversion. Together, these spectra indicate that
1
1
∠
C31−Cu −Cu angles between 54.84(8) and 55.84(8)°.
the product is [Cu (μ-η :η -CH )DPFN]NTf (1), which was
A
B
2
3
2
The average Cu···Cu distance is 2.3549(3) Å. In addition, the
hydrogen atoms on the bridging methyl ligands of both copies
of the cation were located in the difference electron density
map and refined independently. Their positions imply no sig-
nificant interactions with the copper atoms.
isolated in 51% yield (eq 1).
Recently Molteni and co-workers reported the structure of
another methyl-bridged dicopper complex, [Cu(PPh ) (μ-
3
2
CH )CuCH ], which is described as the coordination of a
3
3
+
2
−
29
Cu(PPh ) unit to a nearly linear CuMe . In comparison to
3
2
this donor−acceptor complex, 1 exhibits a shorter Cu···Cu dis-
tance (for the donor−acceptor complex Cu···Cu 2.4121(4) Å)
and a more symmetrical methyl-binding mode (for the donor−
Other methylating agents were explored for the synthesis
of 1, and methyllithium (1.1 equiv, 1.6 M in diethyl ether) was
also found to afford the bridging methyl complex, in slightly
higher yield (63%). However, the resulting product was some-
times contaminated with a small percentage (≤5%) of the bridging
chloride complex [Cu (μ-Cl)DPFN]NTf (2), which was inde-
acceptor complex Cu−μ-CH distances are 2.011(2) and
3
2
.137(2) Å). Ma and co-workers also observed μ-CH ligands
3
30
bridging two metal centers in six-copper clusters. In com-
parison to 1, the methyl-bridged units of the clusters also exhib-
ited longer Cu···Cu distances (2.4000(4) and 2.4047(4) Å)
and more dissymmetric Cu−μ-CH distances (averages 1.986(2)
and 2.052(2) Å).
2
2
pendently synthesized by treatment of the bridging acetonitrile
complex with a solution of LiCl in THF (eq 2).
3
Complex 1 joins a series of nearly symmetrically bridged
μ-methyl complexes of the heavier coinage metals: {[(SIPr)-
3
1
Ag] (μ-Me)}(OTf) (SIPr = 1,3-bis(2,6-diisopropylphenyl)-
2
Dipp2
imidazolin-2-ylidene) and [Au (μ-Me)(PMe Ar
)2]-
2
2
32
Dipp2
i
(
NTf2) (Ar
= C H -2,6-(C H -2,6- Pr ) ). The silver
6
3
6
3
2 2
and gold dinuclear complexes both have M−C and M···M
distances (for both, M−C ca. 2.22 Å, M···M 2.71 Å) signif-
icantly longer than are observed in 1. The structure of 1 is also
similar to that of trimethylaluminum, a classic organometallic
example of three-center, two-electron bonding, which in com-
parison to 1 exhibits longer M−C distances (for [AlMe ] an
In the synthesis of 1, the appearance of 2 very likely results
from small amounts of LiCl present in solutions of methy-
3
2
27,28
1
19
llithium in diethyl ether.
Measurably different H and
F
average of 2.14(1) Å) and a longer M···M distance (for
33
NMR spectra allow identification and quantification of trace
amounts of 2 in solutions of 1.
[AlMe ] 2.600(4) Å).
3 2
In addition, the structure of 1 can be compared to that of
1
1
+
Layering diethyl ether over a THF solution of 1 and storage
at −35 °C afforded crystals suitable for X-ray diffraction. The
solid-state structure of 1 (at 100 K) contains two independent
copies of the dicopper cation (one is shown in Figure 1 and
Figure S39) in the asymmetric unit and confirms the presence
of a bridging methyl group. The methyl ligand bridges nearly
symmetrically between the two copper atoms, with all
Cu−C distances between 2.060(3) and 2.085(2) Å and all
analogous [Cu (μ-η :η -C H )DPFN] cations that establish a
2 X Y
3
2
series in which the bridging carbon is sp , sp , or sp hybridized
(Figure 2). Across the series, the Cu−C distances shorten and
∠Cu1−C31−Cu2 angles widen, bringing the central carbon
closer to the Cu atoms as the carbon adopts more s character
in the orbital presumably directed toward the three-center,
two-electron bonding interaction. Meanwhile, the Cu···Cu
distance does not show a clear trend with hybridization of the
B
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
The one-bond C−H coupling constant ( JC−H) for the
μ-CH ligand is 115.8 Hz, below the value expected for an
3
3
38
sp -hybridized carbon atom (i.e., 125 Hz in methane ). The
coupling constant is similar to those observed in [AlMe ] (bridge
12.2 Hz, terminal 115.5 Hz, between −60 and −70 °C) and
slightly above those reported for a range of methylcopper com-
plexes generated in situ (108.5−113 Hz). It is also lower
than that reported for the [Au (μ-Me)(PMe Ar
129 Hz).
The lack of any methyl resonances in the DPFN ligand
3
2
39
1
4
0
Dipp2
+
) ] cation
2
2
2
32
(
and triflimide anion presents an opportunity to observe the
vibrational IR modes resulting from the bridging methyl
moiety. Upon comparison with the bridging chloride complex,
−
1
two bands, at 2859 and 2781 cm , in the C−H region were
found only in the spectrum of 1 (Figure S2). These bands
are tentatively assigned as ν(CH ) modes. Their relatively low
frequencies are consistent with those observed for other
1
1
3
Figure 2. Solid-state structures of the dicopper cores of [Cu (μ-η :η -
2
+
C H )DPFN] cations as determined by single-crystal X-ray
X
Y
bridging CH groups, especially those of polymeric dimethyl-
3
diffraction, with key metrics describing the cores’ structures. Selected
hydrogen atoms are omitted for clarity. Thermal ellipsoids are set at
the 50% probability level.
−
1
magnesium (2850 and 2780 cm ) and tetrameric methyl-
lithium (2840 and 2780 cm ). These frequencies are also
−
1
41
similar to some of those reported for [Cu(PPh ) (μ-CH )-
3
2
3
−
1
29
CuCH ] (specifically 2852 and 2781 cm ). To bolster the
3
bridging carbon, with the longest distance observed for the
assignment, the IR spectrum of the cation of 1 was calculated
μ-Ph complex.
42
1
19
employing the ωB97X-D functional and the def2-TZVP basis
The H and F NMR spectroscopy of 1 in THF-d revealed
8
−1
set. Between 2600 and 3400 cm , three C−H modes were
that symmetrical binding of the methyl group is maintained in
solution on the NMR time scale. The μ-CH3 1H resonance
predicted for the bridging methyl moiety, all at energies lower
than those for the group of C−H modes for DPFN (Figures S49
and S50). The pattern of the calculated IR frequencies and
intensities is consistent with the experimental spectrum of 1
and supports the assignment of the lower energy bands to the
bridging methyl ligand.
at 0.89 ppm (vs SiMe ) is in a region expected for methyl
resonances, while the C{ H} resonance is found significantly
4
1
3
1
upfield at −40.22 ppm (vs SiMe ). The carbon resonance was
4
1
13
first observed indirectly in a H− C HSQC experiment
(
Figure 3b). To confirm that the peak corresponds to a methyl
Surprisingly, 1 is moderately persistent in solution. In room-
temperature THF solution, after 1 day approximately 5% decom-
position is observed, with 20% observed after 34 days, as
1
19
determined by H and F NMR spectroscopy. Upon heating
at 60 °C in THF, 1 decomposes over the course of days,
accompanied by methane and ethane formation, as observed
1
by H NMR spectroscopy. Specifically, after 21 days at 60 °C
in THF, >93% decomposition of complex 1 was observed, as
1
9
determined by F NMR (Figure S3). Similar decomposition
of 1 was observed in THF-d ; heating at 60 °C for 23 days
8
1
19
afforded >97% decomposition as determined by H and
F
NMR spectroscopy (Figures S4 and S5). In the resulting mix-
ture, methane, methane-d , and ethane, in a ratio of 1:1.9:1.5,
1
1
were observed by H NMR spectroscopy (Figure S6). Forma-
tion of methane and ethane is consistent with the products
1
6,37,43
found upon thermal decomposition of phosphine
and
18
NHC-supported methylcopper complexes, except that in the
case of 1 no ethylene production was observed.
1
3
1
1
13
Figure 3. C{ H} (a), H− C HSQC (b), and proton-coupled
1
13
H− C HSQC (c) NMR spectra acquired at 14.1 T (1D experiment)
and 16.4 T (2D experiments) of a solution 1 in THF-d8.
The persistence of 1 starkly contrasts with that of a range of
alkylcopper complexes, notably those supported by nitrogen
donor ligands. Solid methylcopper has been reported to persist
only at low temperatures and decompose upon warming above
moiety, a modified proton-coupled HSQC experiment revealed
a 3:1:1:3 quartet pattern characteristic of a methyl group
7
,15,20,37,44
approximately 0 °C.
Previous attempts to stabilize
3
4
13
(
[
Figure 3c and Figure S1). This C resonance is upfield of both
AlMe ] resonances (bridge −5.34 ppm, terminal −8.03 ppm;
a methylcopper moiety with nitrogen donor ligands, such as
19,20
2,2′-bipyridine, similarly led to thermally unstable species.
3
2
35
at −78 °C in toluene-d ) as well as the methyl resonances in
A putative anionic dicopper μ-methyl complex supported by
8
36
37
a range of cuprates, CH CuPCy , and the aforementioned
a tropocoronand macrocycle was also reported to require low-
3
3
32
21
dinuclear gold complex (−0.1 ppm). The shift observed for 1
is also upfield of the range of solid-state 13C chemical shifts
reported for Molteni and co-workers’ donor−acceptor complex
temperature storage. In contrast, coordination of tertiary phos-
16,43,45
phines to [CuMe] moieties imparts greater thermal stability,1
7,18,46
as does coordination of N-heterocyclic carbene ligands.
29
(
+1 to −16 ppm) and the solution-state shift reported for
Complex 1 is a rare example of an alkylcopper(I) moiety
kinetically stabilized by a nitrogen-based donor ligand. In addition,
30
Ma and co-workers’ hexanuclear cluster (−18.99 ppm).
C
DOI: 10.1021/acs.organomet.8b00443
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Organometallics
is significantly more thermally stable than the aforemen-
Article
1
the μ-CH complex but slightly shorter than those observed for
3
tioned dicopper μ-methyl complex [Cu(PPh ) (μ-CH )-
the μ-phenyl (2.3927(5) Å) and μ-tolylalkynyl (2.3885(4) Å)
complexes. The methylene hydrogen atoms for the cation were
located in the difference electron density map and refined
3
2
3
CuCH ], which is reported to decompose rapidly in solution
3
29
at room temperature.
Considering the relative stability of the bridging-methyl
independently. As with the μ-CH complex, the structure does
3
copper(I) complex in solution, installation of a significantly
not imply significant interactions between the hydrogen and
copper atoms.
1
1
bulkier alkyl group was attempted. Treatment of [Cu (μ-η :η -
2
NCCH )DPFN](NTf ) in THF at −30 °C with neo-
Despite the popularity of neopentyl as a sterically demanding
alkyl ligand for transition-metal complexes, few examples of
species with bridging neopentyl groups have been reported.
Notably, a handful of dimanganese complexes have been shown
to support bridging neopentyl groups, generally with Mn···Mn
3
2 2
1
1
pentyllithium (1.07 equiv) in pentane provided [Cu (μ-η :η -
2
47−52
CH C(CH ) )DPFN]NTf (eq 3), which was isolated in 50%
2
3 3
2
yield.
distances between 2.685 and 2.718 Å, Mn−C
distances
−Mn2 angles
bridge
between 2.185 and 2.645 Å, and ∠Mn1−C
bridge
47−50
between 69.6 and 72.7°.
While the metal−metal and
metal−carbon distances observed in these dimanganese com-
plexes are significantly longer than those observed in 3, the
metal−carbon−metal angles are quite similar.
53
While trimethylsilylmethylcopper is a persistent tetramer,
an analogous neopentylcopper complex has to our knowledge
not been reported. Neopentylcopper species are mentioned as
plausible intermediates in reactions between copper halides
Diffusion of diethyl ether vapor into a THF solution of 3
gave crystals suitable for X-ray diffraction. The solid-state struc-
ture contains four copies of the cation in the asymmetric unit
54−58
and Grignard reagents,
diorganocuprates for Michael additions, and reported in a
employed as supporting ligands in
59
(one of which is shown in Figure 4 and Figures S41 and S42)
22
phosphine-supported complex, Cu(CH CMe )(PMePh ) .
2
3
2 3
However, these examples do not contain structural character-
ization of a [CuCH CMe ] unit by X-ray crystallography.
2
3
In comparison to the bridging trimethylsilylmethyl groups
found in the aforementioned tetramer ([CuCH Si(CH ) ] ),
2
3 3 4
the Cu···Cu distance in 3 is slightly shorter (cf. tetramer 2.418 Å),
while the Cu−C distances in 3 are longer (cf. tetramer 2.042
and 1.982 Å). The ∠Cu1−C31−Cu2 angle in 3 is also more
acute (cf. tetramer 73.84°).
In comparison with the bridging methyl complex, the neo-
pentyl complex is less stable in solution, with approximately
3
1
0% decomposing at room temperature over the course of
1
day in THF and 70% over 2 weeks, as determined by H and
1
9
1
F NMR spectroscopy. By H NMR spectroscopy, the decom-
position of 3 in THF-d produces a variety of tert-butyl-
8
containing products, primarily neopentane, identified by its
1
13
60
H (0.92 ppm vs SiMe ) and C (31.8 and 27.18 ppm) chem-
4
1
13
ical shifts, which were observed with the aid of H− C HSQC
and HMBC experiments. Of this neopentane, approximately 70%
was neopentane-d as determined by H NMR spectroscopy.
2
1
A common feature that favors the persistence of metal
complexes containing methyl and neopentyl ligands is their
lack of β-hydrogen atoms, precluding conversion to a metal
Figure 4. Solid-state structure of 3 as determined by single-crystal
X-ray diffraction. Only one dicopper cation in the asymmetric unit is
shown; the other cations, NTf2 counterions, four THF molecules of
solvation, and selected hydrogen atoms are omitted for clarity.
Thermal ellipsoids are set at the 50% probability level.
61,62
hydride via elimination of an alkene.
To probe the ability
−
of the dicopper−DPFN core to stabilize bridging alkyl groups
containing β-hydrogen atoms, installation of a bridging ethyl
group was pursued. Similar to the synthesis of 1, treatment of
1
1
[
Cu (μ-η :η -NCCH )DPFN](NTf ) with diethylmagnesium
2 3 2 2
1
1
and reveals that the neopentyl group nearly symmetrically
bridges the copper centers, with an average copper−carbon
distance of 2.101(2) Å. However, each cation has one shorter
Cu−C distance (average 2.084(1) Å) and one longer distance
(0.60 equiv) in THF at −30 °C afforded [Cu (μ-η :η -
CH CH )DPFN]NTf (4) in solution (eq 4). While layering
2
2
3
2
diethyl ether over the filtered reaction mixture and storing for
2 days at −35 °C yielded small crystals of 4, the product con-
19
(
average 2.119(1) Å), suggesting a slight dissymmetry in the
tained a few impurities (Figures S7−S9). Notably, F NMR spec-
troscopy suggested the presence of more triflimide than expected
and small amounts (<2%) of complexes 2 and 6 (vide infra).
A range of recrystallization conditions failed to further purify 4.
Attempts to synthesize the bridging ethyl complex with other
solid state. The average Cu−C distance for the neopentyl
complex is longer than that observed for the μ-CH complex,
3
as expected considering the added steric bulk, while the
average ∠Cu1−C31−Cu2 angle (69.1(1)°) is practically the
1
1
same as that of the μ-CH complex (69.27(6)°). The average
reagents also afforded mixtures. Treatment of [Cu (μ-η :η -
3
2
Cu···Cu distance (2.383(1) Å) is longer than that observed for
NCCH )DPFN](NTf ) with a commercial ethyllithium solution
3
2 2
D
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Organometallics
Article
Table 1. Structural and Spectroscopic Data for Dicopper
a
Alkyl DPFN Complexes
metric
μ-methyl
μ-ethyl
μ-neopentyl
Cu···Cu (Å)
Cu−Cavg (Å)
2.3549(3)
2.072(1)
69.27(6)
2.362(1)
2.099(5)
68.5(2)
2.38
2.383(1)
2.101(2)
69.1(1)
1.93
∠Cu−C−Cu (deg)
μ-C−H chem shift (ppm vs SiMe4) 0.89
μ-carbon chem shift (ppm vs
−40.22
−21.22
13.02
SiMe )
4
1
(
1.1 equiv) yielded a mixture of at least three DPFN-containing
μ-C−H JC−H (Hz)
115.8
−174.31
111.7
−173.08
107.4
−166.70
DPFN 19F chem shift (ppm vs
CFCl3)
products, including approximately 84% of 4 and 12% of 2, as
1
9
determined by F NMR spectroscopy. Meanwhile, treatment
of the acetonitrile-bridged complex with sodium tetraethylbo-
rate (1.0 equiv) gave mixtures primarily composed of 4 and,
depending on reaction time, between 20 and 40% of another
unidentified DPFN-containing product, as determined by
a
NMR spectroscopic data collected in THF-d
at 25 °C.
8
resonance of the bridging methylene was observed directly at
1
13
−
21.22 ppm (vs SiMe ) and assigned with the aid of a H− C
4
1
19
HSQC experiment. The one-bond C−H coupling constant
for the bridging ethyl’s methylene unit was determined to be
H and F NMR spectroscopy.
Fortunately, attempts to crystallize 4 from the mixture
1
11.7 Hz, while the constant for the ligand’s methyl moiety
resulting from reaction with diethylmagnesium afforded crys-
tals suitable for X-ray diffraction. As with complexes 1 and 3,
the solid-state structure of 4 reveals a nearly symmetrically
bridging alkyl ligand (Figure 5 and Figures S43 and S44). The
was found to be 123.2 Hz.
1
3
1
Both the C{ H} chemical shift and C−H coupling con-
stants for the ethyl ligand’s bridging carbon are between those
observed for the bridging methyl and neopentyl ligands (Table 1).
One-bond C−H coupling constants are commonly correlated
38,63−66
with their σ-bonds’ s character,
and introduction of
electropositive substituents onto a carbon atom often lowers
67−69
the coupling constants of their α-hydrogens.
The typical
explanation is that electropositive substituents, such as lithium
and magnesium, increase electron density on the carbon atom,
and the localized hybrid orbital involved in bonding to the metal
67−69
consumes more s character to better stabilize this density.
In turn, the carbon atom’s remaining hybrid orbitals adopt
more p character, weakening their bonds and leading to lower
coupling constants. However, in this series of bridging alkyl
complexes, the dicopper−DPFN component remains the same
while the C−H bond coupling is lowered. Thus, this trend is
better explained as the result of increasing steric bulk of the
alkyl ligand expanding the dicopper−carbon core, which in
turn results in increased electron density at the bridging
carbon. The expansion of the Cu −C core is indeed observed,
2
as Cu···Cu and Cu−C bond distances increase across the
avg
Figure 5. Solid-state structure of 4 as determined by single-crystal
X-ray diffraction. Disordered NTf2− counterions, THF molecules of
solvation, and selected hydrogen atoms are omitted for clarity.
Thermal ellipsoids are set at the 50% probability level.
series.
In comparison to complexes 1 and 3, 4 decomposed rather
rapidly in a THF-d solution at room temperature, reaching
8
2
5
2% decomposition after 17 h, 56% after 41 h, and >98% after
1
19
days, as determined by H and F NMR spectroscopy.
1
Cu−C distances are 2.082(6) and 2.116(8) Å, suggesting only
a slight dissymmetry in the solid state, as was observed for
one copy of the bridging methyl complex and all crystallo-
graphically independent copies of the bridging neopentyl
complex. In addition, the Cu···Cu distance of the bridging
ethyl complex (2.362(1) Å) is between those observed for the
bridging methyl and neopentyl complexes, while the ∠Cu1−
C31−Cu2 angle (68.5(2)°) is nearly the same (Table 1). The
methylene hydrogen atoms for the μ-ethyl ligand were located
in the difference electron density map and refined inde-
pendently. As with the μ-methyl and μ-neopentyl ligands, sig-
nificant interactions between the hydrogen and copper atoms
were not observed.
Monitoring by H NMR spectroscopy revealed a mixture of
many aromatic- and aliphatic-containing decomposition pro-
ducts, including ethane. H{ H} NMR spectroscopy indicates
that approximately 40% of this ethane was ethane-d . However,
1
2
1
despite the potential for β-hydrogen elimination, no ethylene
1
formation was observed by H NMR spectroscopy. Meanwhile,
1
9
F NMR spectroscopy revealed a range of new fluorine-
containing decomposition products, evidenced by the appear-
1
9
ance of at least 13 new F resonances, including formation of
additional 6 (vide infra). The dicopper ethyl complex’s shorter
persistence in solution is consistent with early difficulties in the
15,19
synthesis of ethylcopper
and later reports suggesting that
ethylcopper species generated in situ decompose significantly
1H and 19F NMR spectroscopy of 4 revealed that the
bridging ethyl ligand binds symmetrically between the two
copper centers on the NMR time scale, as was observed for
more quickly than analogous methyl and neopentyl spe-
5
4,56
20
cies.
Similarly, phosphine- and NHC-supported ethyl-
46
copper species were found to be considerably less stable than
their methylcopper analogues.
1
3
1
17,20
the bridging methyl and neopentyl ligands. The C{ H}
E
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
REACTIONS OF A DICOPPER METHYL COMPLEX
■
Considering the ability of the μ-Ph dicopper complex to activate
acidic but strong C−H bonds and exchange the bridging ligand,
the reactivity of 1 toward various protic species was investigated.
Notably, treatment of 1 with excess pentafluorobenzene and
1
1
heating at 60 °C afforded [Cu (μ-η :η -C F )DPFN]NTf in
2
6
5
2
19
6
7% yield (98% conversion) as determined by F NMR spec-
troscopy (Figure S10), with concomitant generation of methane
1
as determined by H NMR spectroscopy (eq 5).
The difference between the 19F NMR determined yield of
Figure 6. Solid-state structure of 5 as determined by single-crystal
−
X-ray diffraction. The NTf2 counterion, two o-C H F molecules, half
6
4 2
the μ-C F complex and conversion of 1 likely results from
6
5
of a pentane molecule of solvation, and hydrogen atoms are omitted for
clarity. Thermal ellipsoids are set at the 50% probability level.
ligand exchange of −CH for −C F competing with decom-
3
6 5
position pathways. In comparison, the same transformation can
be accomplished in higher yield, 85% (99% conversion), by
1
1
heating [Cu (μ-η :η -Ph)DPFN]NTf with excess pentafluor-
bridging ligand that binds with a much less acute central angle.
The Cu−O distances (2.002(2) and 1.989(3) Å) are shorter
than the Cu−C distances observed in the bridging methyl and
phenyl complexes, and the Cu···Cu distance is significantly
longer (2.675(1) Å). As a result, the ∠Cu1−O1−Cu2 angle
(84.18(9)°) is wider than that found in the hydrocarbyl series,
and the average Cu−Nnaphth distance is shorter.
2
2
25
obenzene in o-C H F at 110 °C for 35 days.
6
4 2
Considering its ability to activate strong C−H bonds, 1 was
also treated with water, with the goal of generating a bridging
hydroxide complex. Unfortunately and unexpectedly, addition
of water (ca. 170 equiv) to 1 in THF at room temperature
does not cleanly generate a new complex. Rather, in the pre-
sence of water, 1 very slowly decomposes at room temperature
to a variety of species and after 14 days reaches 96% con-
Within 10 min of treatment with 1 equiv of an even stronger
acid, HNTf
complex incorporating three copper centers and two molecules
of DPFN (eq 7 and Figure S14). This helix, [Cu (DPFN) ]-
(NTf (6), was also generated by treatment of the bridging
phenyl complex with HNTf (1.0 equiv) in o-C , allowing
, complex 1 in THF forms a tricationic helical
2
19
version (as determined by F NMR spectroscopy; Figure S11).
To explore whether a more acidic oxygen-based acid would
cleanly react with 1, a solution of 1 in THF was treated with
pentafluorophenol (10 equiv), which nearly quantitatively
3
2
)
2 3
H F
6 4 2
2
1
1
yielded the bridging phenoxide complex [Cu (μ-η :η -OC F )-
the product to be isolated in 58% yield. Ostensibly, the loss of
the dicopper core structure results from the inability of the
triflimide anion to provide a viable bridge between two copper
centers ligated by DPFN.
2
6 5
DPFN]NTf (5) and methane over the course of 1 h at 22 °C,
2
1
19
as determined by H and F NMR spectroscopy (eq 6 and
Figures S12 and S13). The same product was obtained upon
treatment of the bridging phenyl complex in o-C H F with
6
4 2
pentafluorophenol, allowing the isolation of 5 in 85% yield.
Vapor diffusion of hexanes into an o-C H F solution of 6
6
4 2
and storage for 4 days at −35 °C afforded crystals suitable for
X-ray diffraction, allowing its structure to be elucidated (Figure 7
and Figures S47 and S48). In the solid state, the side-arm
pyridine pairs provide pseudotetrahedral ligand environ-
ments for two copper centers while the third copper is bound
nearly linearly between two naphthyridine nitrogen atoms
Vapor diffusion of pentane into a o-C H F solution of 5
for 15 days at −35 °C afforded crystals suitable for X-ray
diffraction. In comparison to the structures of the bridging
6
4 2
Cu (I,I) alkyl, aryl, and alkynyl complexes, the solid-state
2
structure of 5 (Figure 6 and Figures S45 and S46) reveals a
F
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Organocopper reagents are well-known for their role in
conjugate addition to compounds containing α,β-unsaturated
carbonyl groups, often in reactions that proceed at low temper-
7
−10
atures.
To explore this reactivity, complex 1 was treated
with cyclohexenone (2.1 equiv) in THF. After 6 days at room
temperature, no significant consumption of cyclohexenone
1
was observed by H NMR spectroscopy while 1 appeared to
1
19
decompose, as determined by H and F NMR spectroscopy
Figure S18), which showed loss of 1 and methane formation.
(
Heating the mixture to 80 °C for 21 h lead to additional
decomposition of 1.
Previously reported methylcopper complexes, supported by
20,78−80
17
phosphine
and NHC ligands, have been shown to
react with carbon dioxide to afford copper acetate complexes.
Considering this precedence and the ability of 1 to behave as a
nucleophile upon treatment with acids, reactivity with carbon
dioxide was explored. However, when a solution of 1 in THF-d8
was placed under an atmosphere of carbon dioxide, no signif-
icant reaction was observed over the course of 29 h at room
1
temperature, as determined by H NMR spectroscopy. Heating
the mixture at 60 °C for 2 days appeared to lead to slight decom-
position of 1, as suggested by the formation of both methane and
methane-d1.
Figure 7. Solid-state structure of 6 as determined by single-crystal
X-ray diffraction. The NTf2− counterions, two o-C H F molecules of
solvation, and hydrogen atoms are omitted for clarity. Thermal
ellipsoids are set at the 50% probability level.
6
4 2
To determine whether the dicopper methyl complex would
insert a sterically unencumbered olefin, a solution of 1 in THF
was treated with 1-hexene (ca. 400 equiv). After 1 day at room
temperature no significant reactions of complex 1 or the 1-hexene
(
∠N1−Cu1−N7 174.7(1)°). In addition, the ∠Cu2−Cu1−Cu3
1
angle is 155.66(2)°. In H NMR spectra at room temperature,
1
were observed by H NMR spectroscopy. Subsequent heating
only one doublet is observed for the 4-position hydrogen on
the naphthyridine subunits; in 1 F NMR spectra, a singlet (at
9
of the mixture to 60 °C for 6 days appeared to result in
decomposition of the dicopper complex, indicated by the
formation of methane and a variety of fluorine-containing
−
148.47 ppm vs CFCl in nitrobenzene-d ) is observed for the
3 5
trication. These data suggest that, on the NMR time scale,
the central Cu atom interacts similarly with all four central
naphthyridine nitrogen atoms.
1
19
products, as determined by H and F NMR spectroscopy,
respectively. Similar results were obtained upon treatment of 1
with diphenylacetylene (13 equiv). When the mixture was
heated to 60 °C for 6 days, methane formation and multiple
fluorine-containing products appeared, while no consumption
The reactivity of 1 toward a Lewis acid (BPh ) was also
3
investigated. Transmetalation from boron to copper, albeit a
single copper center in its +2 oxidation state, is predicted to be
a key step in the mechanism of various oxidative cross-coupling
1
of diphenylacetylene was observed, as determined by H and
1
9
7
0−74
F NMR spectroscopy.
reactions (e.g., the Chan−Evans−Lam amination).
Treat-
Taken together, these results suggest that the cationic
ment of a o-C H F solution of 1 with triphenylborane
6
4 2
(
10 equiv) produced the bridging phenyl complex in nearly
dicopper−methyl core in 1 possesses weak nucleophilic char-
acter and in this way seems quite different from organocuprate
reagents. The methyl complex 1 appears to favor reactions with
σ-bonds (including C−H, B−C, and O−H bonds, as described
1
1
quantitative yield (eq 8 and Figures S15 and S16). A new
resonance observed at ∼6 ppm downfield of that for BPh
suggests that the transformation occurs with the formation of
B
3
75,76
BMePh (Figure S17).
above), and delocalization of electron density in the Cu −C
2
2
core appears to mitigate against direct insertion reactions.
Thus, 1 represents a fundamentally new type of molecular alkyl-
copper complex expected to display distinct reactivity trends and
reaction pathways that are yet to be uncovered.
ELECTROCHEMISTRY OF DICOPPER ALKYL
■
COMPLEXES
25
26
Recent discoveries of mixed-valence copper aryl, alkynyl,
81,82
and hydride
complexes inspired electrochemical inves-
tigation of the dicopper alkyl complexes 1 and 3. Specifically,
2
5
26
This carbon−boron bond exchange is consistent with the
dicopper DPFN complexes with bridging aryl and alkynyl
reactivity observed upon treatment of the acetonitrile-bridged
ligands were oxidized chemically to afford mixed-valence
organocopper species. These dicationic mixed-valence com-
plexes were persistent, allowing for their isolation and the struc-
1
1
complex [Cu (μ-η :η -NCCH )DPFN](NTf ) with tetraar-
2
3
2 2
ylborato anions, which results in the formation of bridging aryl
25
complexes and triarylboranes. The reaction is also similar to
tural and spectroscopic characterization of their Cu (I,II)−
2
II
t
the arylation of a Cu O Bu β-diketiminate complex, where
phenyl and Cu (I,II)−p-tolylalkynyl cores. Thus, we sought to
2
treatment with B(C F ) resulted in in aryl transfer to the
determine whether the bridging alkyl complexes would exhibit
similar electrochemistry.
6
5 3
II
77
copper center, forming a Cu C F complex.
6
5
G
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Cyclic voltammetry of 1 revealed a reversible oxidation−
Table 2. Electrochemical Metrics for Reversible and
0/+
reduction process at E°′ = −0.148 V vs [Cp Fe] (i /i
=
Quasireversible Redox Processes for Dicopper DPFN
2
pa pc
a
1
.01, ΔE = 81 mV, both measured at 100 mV/s, Figure 8a and
Complexes
p
formal potential
ratio of peak
(V vs Fc0
/+
)
currents (i /i )
ref
bridging ligand
μ-CH3
pa pc
−0.148
1.01
2.03
1.02
1.12
1.18
1.17
this work
this work
b
μ-CH C(CH )
−0.113
−0.014
0.347
2
3
3
μ-C H5
25
25
25
26
6
μ-(3,5-(CF ) -C H )
3
2
6
3
μ-C6F5
μ-(1,4-bis(4-tolyl)-
,2,3-triazolide))
μ-CC(C H )CH
0.516
0.302
1
0.022
0.120
0.101
0.181
1.04
1.02
1.40
1.15
26
6
4
3
μ-CC(C H )CF
this work
this work
this work
6
4
3
μ-OC F
6
5
μ-Cl
a
Metrics measured for 0.5 mM solutions of a given complex in
n
o-C H F containing 0.1 M [ Bu N][PF ] as a supporting electrolyte
with a scan rate of 100 mV/s. Estimated from voltammograms
obtained at 2000 mV/s.
6
4
2
4
6
b
persistence of the dicopper alkyl complexes, we turned to com-
putations. Gas-phase geometry optimization of the bridging
methyl, phenyl, and p-tolylalkynyl (truncated in the compu-
tations to phenylalkynyl) complexes using the ωB97X-D func-
tional and the def2-SVP basis set provided dicopper core
geometries (Table 3) generally consistent with those observed
Figure 8. Cyclic voltammograms of 0.5 mM solutions of (a) 1 and
n
(
b) 3 in o-C H F with 0.1 M [ Bu N][PF ] supporting electrolyte.
6 4 2 4 6
The arrows indicate the initial potentials and scanning directions.
Scan rate: 100 mV/s.
42
Figures S19−S22). However, voltammetry of 3 revealed a
Table 3. Calculated Geometry Metrics for Dicopper
Hydrocarbyl DPFN Cations
quasireversible wave at a slightly less negative potential
0
/+
(
E°′ = −0.113 V vs [Cp Fe] , measured at 2000 mV/s,
2
metric
μ-methyl
μ-phenyl
μ-phenylalkynyl
Figures S23−S26). At fast scan rates, at and above 1250 mV/s,
Cu···Cu (Å)
Cu−Cavg (Å)
2.35
2.08
68.7
2.39
2.03
72.2
2.40
1.96
75.7
the event’s formal potential remains at −0.113 V and the i /i
pa pc
ratio is approximately 1.5. At slower scan rates, the i /i ratio
pa pc
∠
Cu−C−Cu (deg)
increases, and the reduction wave becomes significantly
distorted (Figure 8b and Figures S24 and S25). These results
suggest that a putative mixed-valence dicopper neopentyl
complex does not significantly persist in room-temperature
solution. Similarly, attempts to synthesize and isolate a mixed-
valence dicopper methyl complex via chemical oxidation have
led to decomposition, suggesting that it too might not persist
over longer time scales. The transience of these dicopper alkyl
complexes upon oxidation is consistent with previous reports
of monomeric NHC-supported copper(I) alkyl complexes decom-
in the solid-state structures (Figure 2). Notably, in the com-
puted structures, the ∠Cu−C −Cu angles were also found
bridging
to widen progressing from the methyl complex to the alkynyl,
while the average copper−carbon distances shortened. In addi-
tion, the Cu···Cu distance is shortest in the methyl complex
and longer in the phenyl and alkynyl complexes. These compu-
tational results suggest that the trends observed in the solid
state are not artifacts of crystal packing.
83
posing after treatment with one-electron chemical oxidants.
Investigation of the canonical orbitals calculated for the
energy-minimized structure of 1 revealed a bonding orbital
that nearly symmetrically bridges the two copper centers and
bridging carbon (Figure 9). Analogous orbitals were also found
for the μ-phenyl and μ-phenylalkynyl complexes (Figures S51
and S52). These orbitals are consistent with the expectation of
a three-center, two-electron bond supporting the bridging
The bridging alkyl groups lead to the most easily oxidized
species in the series of dicopper DPFN complexes (Table 2),
consistent with alkyl substituents generally donating more
electron density than aryl or alkynyl groups. This trend could
also be rationalized by the stabilization ability of the elec-
tronically delocalized bridging phenyl and tolylalkynyl ligands
in comparison to the methyl and neopentyl ligands. Mean-
while, the more electronegative heteroatom-based bridging
groups (e.g., OC F , Cl), even though they could conceivably
62,84,85
hydrocarbyl ligand.
The nature of bonding between various bridging ligands and
the dicopper core was also investigated by bonded energy
6
5
86,87
donate density from electrons localized on the heteroatom
decomposition analysis (EDA).
This method separates the
(
(
i.e., lone pairs), have relatively moderate oxidation potentials
Table 2 and Figures S27−S34) in comparison to the range of
quantum mechanical interaction energy between two molec-
ular fragments into components that correspond to traditional
contributors to bonding interactions (e.g., electrostatics,
polarization, charge transfer). For a given bonding interaction,
this method obtains a chemical “fingerprint” that characterizes
the type of bond present. To develop this fingerprint, bonded
EDA separates the interaction energy into five components.
The first two components are (1) preparation energy, which
those observed for the organic bridging groups with various
electron-withdrawing substituents.
COMPUTATIONAL INSIGHTS
To corroborate our structural observations and investigate the
bonding characteristics that might contribute to the unexpected
■
H
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CONCLUDING REMARKS
■
These results demonstrate that a dicopper core can support
bridging alkyl ligands, and the resulting complexes are unex-
pectedly persistent in solution. Upon treatment with suitably
acidic reagents, the bridging methyl was exchanged for other
bridging ligands. In addition, the dicopper μ-methyl complex
was found to undergo facile alkyl−aryl exchange with BPh ,
3
affording a dicopper μ-phenyl complex. However, no insertion
into the dicopper−carbon bond was observed with a variety of
reagents. Electrochemical characterization revealed a reversible
oxidation−reduction event for the μ-methyl complex and a
quasireversible event for the μ-neopentyl derivative, evidencing
the existence of transient mixed-valence dicopper alkyl complexes.
The dicopper(I,I) alkyl complexes extend a series of hydro-
carbyl fragments bridging two copper centers, allowing for
Figure 9. Primarily three-center, two-electron canonical orbital of 1.
3
2
comparisons of binding through sp -, sp -, and sp-hybridized
carbon atoms. Notably, structural comparisons show that the
Cu−C distances shorten and ∠Cu−C−Cu angles widen with
increasing s character at the bridging carbon. Measurements of
the complexes’ oxidation potentials reveal the μ-alkyl com-
plexes to be significantly more reducing than the μ-aryl and
μ-alkynyl complexes. Computational decomposition of bonding
contributions suggests that the dicopper−carbon bonds are
primarily covalent in nature, possibly contributing to their rela-
tive persistence.
This work further extends the study of discrete cationic
dicopper complexes containing bridging organic ligands. Notably,
the reactivity profile observed suggests that these dicopper
alkyl complexes contain a new type of organocopper moiety
corresponds to geometrically and electronically distorting
the fragments from their separated states to the states they
assume upon interaction, and (2) frozen energy, which is the
sum of the individual components’ electrostatic, Pauli repul-
sion, and dispersion energies. These first two components are
nearly always positive because they represent the geometric/
electronic destabilization of the fragments and the Pauli
repulsion/electrostatics upon their interaction, respectively. The
next three components are generally stabilizing and include (3)
spin-coupling energy, which estimates covalency by determin-
ing how much energy is gained by coupling the bonding
electrons, (4) polarization energy, which relates how electrons
on each fragment respond to the electric field of the other
fragment, and (5) charge-transfer energy, which measures the
energy gained from electrons fluctuating into ionic-like states
between the two fragmentsa process that occurs even in
symmetric bonds.
that could enable yet undiscovered reaction pathways. We
2+
further expect that the [Cu (DPFN)] platform could serve to
2
support a range of other reactive fragments and enable funda-
mental studies of their structure and reactivity. These studies
could aid the discovery of new reagents and catalysts and help
elucidate mechanisms of reactions that occur at a dicopper
core.
The EDA results for complexes 1 and 5, as well as for the
bridging phenyl and alkynyl complexes for comparison, are
3
displayed in Table 4. Progressing from methyl (sp ) to aryl
2
(
sp ) to alkynyl (sp), the more stabilizing (more negative) spin-
coupling component is consistent with the covalent character of
EXPERIMENTAL SECTION
■
the Cu −C bonding interaction increasing with more s character
2
General Considerations. Unless otherwise stated, all reactions
and manipulations were carried out under a dry nitrogen atmosphere
employing either standard Schlenk techniques or VAC Atmospheres
or MBRAUN gloveboxes.
Pentane (HPLC grade), toluene (ACS grade), and acetonitrile
(HPLC grade) were purchased from Fischer Scientific. Diethyl ether
(HPLC grade) and dichloromethane (HPLC grade) were purchased
from Honeywell. Hexanes (HPLC grade) was purchased from JT
Baker. Tetrahydrofuran (THF) (ChromAR) were purchased from
Macron Fine Chemicals, and o-difluorobenzene (o-C H F ) was
purchased from Oakwood. Pentane, toluene, diethyl ether, tetrahy-
drofuran, acetonitrile, dichloromethane, and o-difluorobenzene were
dried and deaerated using a JC Meyers Phoenix SDS solvent purifi-
cation system. Hexanes were dried and deaerated using a VAC Atmo-
spheres solvent purification system. Nitrobenzene-d (C D NO ) was
at the bridging carbon. Similarly, larger, more diffuse π-systems
in the bridging ligands increase their polarizability, affording
additional polarization stabilization. Finally, the ionic character
of the interaction is embodied in the charge-transfer com-
ponent, for which a similar trend is observed. As expected, the
heteroatom bridging ligand exhibits the largest charge-transfer
stabilization. Overall, the Cu −C bonds are primarily covalent,
2
which may explain why treatment with excess water does not
immediately hydrolyze 1 and why exchange of the μ-Me ligand
for pentafluorophenyl is sluggish. In contrast, the computations
suggest that the pentafluorophenoxide complex has no
covalent stabilization, and its interaction is almost exclusively
due to charge transfer, with some polarization, suggesting that
6
4 2
5
6
5
2
the Cu −O bond in 5 is primarily ionic.
purchased from Cambridge Isotope Laboratories. Tetrahydrofuran-d8
2
Table 4. Bonded Energy Decomposition Analysis of the Interaction between [Cu (DPFN)]2+ and Various Bridging Ligands
2
energy component (kcal/mol)
μ-methyl
μ-phenyl
μ-phenylalkynyl
μ-pentafluorophenoxide
preparation and frozen
spin-coupling
polarization
charge-transfer
total energy
128.9
−175.8
−18.7
−33.0
−98.6
141.8
−176.3
−20.3
−59.1
−114.0
202.8
−216.5
−74.7
−61.1
−149.5
17.4
0.0
−26.5
−141.6
−150.6
I
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
in THF-H8 at 23 °C). 11B{ H} spectra were referenced to the
1
(
(
THF-d ) was purchased from Cambridge Isotope Laboratories
8
D, 99.5%) or Aldrich (99.5 atom % D). Nitrobenzene-d was degassed
IUPAC-recommended unified scale (reference compound BF ·Et O
in CDCl ) employing the samples’ tetramethylsilane-referenced
H NMR spectra and the Absolute Reference tool in MestReNova
(v. 10.0.2). H{ H} spectra were similarly referenced to the unified scale
(reference compound: neat Si(CD ) ). Temperatures were calibrated
using methanol (4% in methanol-d ) standards. All coupling constants
are reported as absolute values.
Spectra recorded at 21.1 T were acquired with a 5 mm CPTCI 1H-
13C/15N/D Z-GRD Z44910 probe. Spectra recorded at 16.4 T were
acquired with a 5 mm CPTXI 1H-13C/15N/D Z-GRD Z44906
probe. Spectra recorded at 14.1 T were acquired with a 5 mm PABBO
BB-1H/D Z-GRD Z847801 probe. Spectra recorded at 11.7 T were
acquired with a 5 mm TBI 1H/31P/D-BB Z-GRD Z8641 probe. Spectra
recorded at 9.40 T were acquired with a 5 mm QNP 1H/13C/31P/19F
Z-GRD Z8400 probe.
5
3
2
93
by three freeze−pump−thaw cycles and stored in the dark, under
nitrogen, over 3 Å molecular sieves. Tetrahydrofuran-d was degassed
3
1
8
2
1
by three freeze−pump−thaw cycles and stored in the dark, under
nitrogen over 3 Å molecular sieves. Deaerated water was obtained
from a Millipore Milli-Q water purification system, sparged with
nitrogen for 24 h, and stored in a PTFE-valved flask. All other solvents
were obtained from commercial suppliers, distilled or transferred
under reduced pressure from appropriate drying reagents, and stored
in PTFE-valved flasks.
3
4
4
The ligand 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine
1
1
(
DPFN) and dicopper complexes [Cu (μ-η :η -NCCH )DPFN]-
2
3
1
1
1
1
(NTf ) , [Cu (μ-η :η -Ph)DPFN]NTf , and [Cu (μ-η :η -CC-
C H )CH )DPFN]NTf were synthesized as previously reported.
6 4 3 2
2
2
2
2
2
25,26
(
Additional spectroscopic data for the first three of these compounds
are reported in the Supporting Information. The internal standard
1
pump−thaw cycles and stored under nitrogen over 3 Å molecular
sieves. Tetrabutylammonium hexafluorophosphate ([ Bu N][PF ],
9
as a 1.6 M solution in diethyl ether, was purchased from Aldrich
and stored at −30 °C. Triflimidic acid (95+%) was purchased from
Matrix Scientific. Dimethylmagnesium was synthesized via dioxane
addition to methylmagnesium bromide, and before use a solution
of the product in THF was titrated by H NMR spectroscopy.
Diethylmagnesium was synthesized and titrated similarly. Neo-
For the bridging methyl and neopentyl ligands in complexes 1 and 3,
respectively, one-bond carbon−hydrogen coupling constants ( J
,3,5-tris(trifluoromethyl)benzene was degassed by three freeze−
1
)
C−H
13
1
were determined from the C satellite peaks directly observed in H
NMR spectra. When possible for ligand resonances in complex 1 and
for the bridging ethyl resonances in 4, carbon−hydrogen coupling
n
4
6
9.0+%) was obtained from Fluka and dried in vacuo. Methyllithium,
1
13
constants were measured from satellites observed in H− C HMBC
spectra.
1
13
Proton-coupled H− C HSQC spectra of complex 1 were obtained
at 16.4 T and 298 K by employing a modified hsqcetgpsisp2.2 pulse
sequence in which the H refocusing pulse during the t evolution
period was omitted and replaced with a delay. The J coupling constant
CNST2) was set to 115.8 Hz. Standard H− C HSQC spectra of
complex 1 were also obtained at 16.4 T and 298 K.
88
1
89
1
1
1
90
pentyllithium was synthesized in the usual manner by heating a
mixture of lithium dispersion with high-sodium (∼1.0%) content and
1
13
(
91
deolefinated neopentyl chloride, filtering, and recrystallizing the
product from a concentrated pentane solution cooled to −30 °C.
Ethyllithium, as a 0.5 M solution in benzene/cyclohexane, was purchased
from Sigma-Aldrich. Sodium tetraethylborate (97%) was obtained from
Aldrich. Lithium chloride was dried in vacuo at 210 °C for 12 h.
Pentafluorophenol (≥99%) and triphenylborane were obtained from
Aldrich and used as received. Carbon dioxide (4.8, research grade)
was obtained from Praxair, and 1-hexene was deaerated by three
freeze−pump−thaw cycles and stored over molecular sieves.
Unless otherwise noted, all other liquid reagents were obtained
from commercial suppliers, distilled or transferred under reduced pre-
ssure from appropriate drying reagents, and stored under nitrogen while
all other solid reagents were obtained from commercial suppliers and
used without further purification.
All NMR spectra were analyzed and spin simulations were
performed with MestReNova (v. 10.0.2). Spectra included in the
Supporting Information were annotated using Adobe Illustrator CS6.
IR Spectroscopy. Infrared spectra were recorded with a Bruker
Vertex 80 FTIR spectrometer with a room-temperature DLaTGS
detector using OPUS software (v. 7.2) and employing an A225/Q
Platinum ATR accessory. All measurements were made at 4.0 cm
resolution. Spectra included in the Supporting Information were
plotted in Microsoft Excel 2016.
−1
UV−Visible Spectroscopy. Samples for UV−visible spectropho-
tometry were prepared in a nitrogen-filled glovebox and sealed in
1
cm, air-free quartz cells. UV−visible spectra were obtained on a
Shimadzu UV-2450 UV−visible spectrophotometer using UVProbe
software (v. 2.21).
Analytical Methods. Carbon, hydrogen, and nitrogen elemental
analyses were performed by the College of Chemistry’s Microana-
lytical Facility at the University of California, Berkeley.
X-ray Crystallography. X-ray diffraction data for complexes 2, 3,
, and 6 were collected using a Bruker AXS diffractometer with a
5
Kappa geometry goniostat coupled to an APEX-II CCD detector with
Mo Kα (λ = 0.71073 Å) radiation generated by a microfocus sealed
tube and monochromated by a system of QUAZAR multilayer
mirrors. Data for complexes 1 and 4 were collected at Beamline 11.3.1
of the Advanced Light Source at Lawrence Berkeley National
Laboratory using a Bruker D8 diffractometer coupled to a Photon
100 detector with Si(111)-monochromated synchrotron radiation
NMR Spectroscopy. Unless otherwise stated, NMR spectra were
acquired between 294 and 299 K using Bruker AV-400, DRX-500,
1
AV-500, AV-600, and AV-700 spectrometers. H NMR spectra were
referenced to tetramethylsilane via residual solvent peaks (δ 8.11 for
1
3
1
C D NO , δ 3.58 for THF-d ), while C{ H} NMR spectra were
6
5
2
8
referenced via solvent resonances (δ 148.6 for C D NO , δ 67.21 for
6
5
2
92
19
THF-d8). In deuterated solvents, F NMR spectra were internally
referenced to the 1,3,5-tris(trifluoromethyl)benzene resonance
(16 keV, λ = 0.7749 Å). Unless otherwise noted, crystals were kept at
100(2) K throughout collection. Data collection strategy determi-
(
δ −62.73 ppm vs CFCl in C D NO at 23 °C, δ −62.97 ppm vs
3
6
5
2
nation, integration, scaling, and space group determination were
performed with Bruker APEX2 (v. 2014.11-0) or APEX3 (v. 2016.5-0)
software. Structures were solved with SHELXT-2014 and refined with
CFCl in THF-d at 22 °C), which was in turn referenced to dissolved
CFCl , which was set to 0.00 ppm. Spectra of compounds dissolved in
3
8
3
neat o-difluorobenzene were obtained without lock and by automatic
2
SHELXL-2014 or SHELXL-2018, with refinement of F on all data by
gradient shimming on the solvent resonances in the proton spectrum
94,95
1
full-matrix least squares.
The 3D molecular structure figures were
or by manually shimming on the FID. For H NMR spectroscopy,
these spectra were referenced to tetramethylsilane (via a solvent
resonance), and for F NMR spectroscopy, these spectra were ref-
visualized with ORTEP 3.2 and annotated with Adobe Illustrator
CS6. Disordered cation, anion, and solvent molecules observed in the
crystal structures were modeled atomistically. In addition to dis-
ordered anions and THF molecules, the structure of complex 4 con-
tained a void partially occupied by other highly disordered solvent
molecules, likely diethyl ether. SQUEEZE was employed to treat elec-
tron density in the void as a diffuse solvent contribution to the calcu-
lated structure factors. Average bond distances and angles computed
for complex 3 only incorporate the primary components of the
disordered neopentyl groups. Additional details of each experiment
1
9
erenced to CFCl through either 1,3,5-tris(trifluoromethyl)benzene
3
(
δ −63.58 ppm vs CFCl in o-difluorobenzene at 23 °C) or the solvent
3
fluorine resonance (δ −138.91 ppm vs CFCl in o-difluorobenzene at
2
without lock and by shimming as described above. For H NMR
spectroscopy, they were referenced to tetramethylsilane (via a solvent
resonance), and for F NMR spectroscopy they were referenced to
3
3 °C). Similarly, spectra of compounds in THF-H were obtained
8
1
96
1
9
CFCl via 1,3,5-tris(trifluoromethyl)benzene (δ −62.91 ppm vs CFCl
3
3
J
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
can be found in Table S1 in the Supporting Information and crys-
tallographic information files.
methyllithium in diethyl ether (28 μL, 1.6 M, 1.1 equiv) dropwise.
The red solution became dark and was stirred for 35 min as the
reaction mixture was warmed to room temperature. The resulting
mixture was filtered, and the filtrate was cooled to −30 °C. Diethyl
ether (approximately 18 mL) was layered over the cold filtrate. After
2 days at −35 °C, a dark crystalline solid formed, and the supernatant
was carefully decanted. The solid was briefly rinsed with diethyl ether
(5 × 1 mL), and residual volatile compounds were removed in vacuo
to yield 1 as a dark crystalline solid (0.024 g, 0.026 mmol, 63%).
Crystals obtained from the aforementioned steps were suitable for
diffraction employing synchrotron radiation at Beamline 11.3.1 at the
LBNL Advanced Light Source. Depending on the quality of the
methyllithium solution used, the product sometimes contained a small
percentage (ca. ≤5%) of the bridging chloride complex (2), as deter-
Electrochemistry. All electrochemical experiments were per-
formed inside an MBRAUN glovebox using a pass-through consisting
of gold-plated tellurium copper binding posts connected to tinned
copper conductors shielded with Beldfoil and tinned copper braid.
Experiments employed a glassy-carbon working electrode (polished
with 0.30 and then 0.05 μm alumina slurries, rinsed with water, and
dried in vacuo), a platinum-wire counter electrode, and a Ag/AgNO
3
n
reference electrode (0.1 M [ Bu N][PF ], AgNO (saturated) in THF
4
6
3
1
1
(
or o-C H F for [Cu (μ-η :η -CC(C H )CF )DPFN](NTf ))
immediately before
2
6
4
2
2
6
4
3
2
0
/+
constructed and measured against [Cp Fe]
use). Measurements were made with a BASi EC Epsilon potentiostat/
galvanostat and a PWR-3 Power Module. Sweep direction and scan
rates are included in the relevant figures or their captions. Cyclic
1
19
1
mined by H and F NMR spectroscopy. H NMR (700.13 MHz,
THF-d ): δ 8.83 (ddd, J = 5.0, 1.7, 0.9 Hz, 4H, 6-pyridyl-C−H), 8.77
n
voltammograms were recorded in a 0.1 M [ Bu N][PF ] solution in
8
4
6
o-difluorobenzene at 22 °C with software-determined iR compensation
applied. Data analysis, including peak finding and baseline deter-
mination employing linear regression, was performed with EC-Lab
(d, J = 8.5 Hz, 2H, 4-naphth-C−H), 8.37 (dd, J = 8.5, 3.1 Hz, 2H,
3-naphth-C−H), 8.13 (ddt, J = 8.1, 3.4, 1.1 Hz, 4H, 3-pyridyl-C−H),
8.02 (td, J = 7.9, 1.7 Hz, 4H, 4-pyridyl-C−H), 7.51 (ddd, J = 7.6, 5.0,
(
v. 10.40).
1.1 Hz, 4H, 5-pyridyl-C−H), 0.89 (s, 3H, Cu
2
−CH
H NMR (600.13 MHz, THF-d ): δ 8.83 (ddd, J = 5.1, 1.9, 1.0 Hz,
8
3
, JC−H = 115.8 Hz).
1
General Computational Details. All calculations were per-
9
7
formed with QChem (v. 5.0.1). Starting from the crystallograph-
ically determined atomic coordinates of the relevant complexes, the
anions and cocrystallized solvent molecules were deleted, and the
geometries of the cations were optimized. Visualizations were per-
formed with the IQmol software package.
IR Frequency Calculations. Calculations employed the ωB97X-D
4H), 8.77 (d, J = 8.6 Hz, 2H), 8.37 (dd, J = 8.6, 3.1 Hz, 2H), 8.13
(ddt, J = 8.2, 3.4, 1.1 Hz, 4H), 8.02 (td, J = 7.9, 1.7 Hz, 4H), 7.51
(ddd, J = 7.6, 5.0, 1.2 Hz, 4H), 0.89 (s, 3H, J
= 115.8 Hz).
C−H
1
3
1
C{ H} NMR (150.92 MHz, THF-d ): δ 159.80 (d, J = 30.3 Hz,
8
9
8
2-naphth-C), 154.27 (d, J = 29.2 Hz, 2-pyridyl-C), 150.85 (8a-naphth-C),
149.87 (d, J = 3.0 Hz, 6-pyridyl-C−H, J = 183.3 Hz), 140.79
C−H
4
2
functional and the def2-TZVP basis set for all atoms and used a
99,590) integration grid. As the electronic structure calculation is
approximate and anharmonic effects were not included, the fre-
(d, J = 3.3 Hz, 4-naphth-C−H, J
= 169.7 Hz), 139.32 (d, J =
C−H
(
3.3 Hz, 4-pyridyl-C−H, J
= 167.6 Hz), 125.19 (5-pyridyl-C−H),
C−H
101
123.61 (4a-naphth-C), 121.08 (d,
120.87 (d, J = 14.1 Hz, 3-pyridyl-C−H), 119.85 (d, J = 14.6 Hz,
3-naphth-C−H, J = 172.4 Hz), 94.41 (d, J = 185.4 Hz,
J = 322.6 Hz, −SO −CF ),
2
3
9
9,100
quencies were then scaled by 0.95.
The broadened spectrum was
simulated with Gaussian line shapes overlaid on an impulse repre-
sentation of the frequencies and their intensities.
C−H
1
9
(pyridyl) (naphth)C−F), −40.22 (br, Cu −CH ). F NMR
2
2
3
Energy Decomposition Analysis. Calculations employed the
(564.61 MHz, THF-d ): δ −79.03 (s, 6F, −SO −CF ), −174.31
8
2
3
42
102
1
ωB97X-D functional and the def2-SVP basis set for all atoms and
(q, J = 3.5 Hz, 2F, (pyridyl) (naphth)C−F). H NMR (499.60 MHz,
THF-H ): δ 8.83 (d, J = 5.0 Hz, 4H), 8.77 (d, J = 8.6 Hz, 2H), 8.37 (dd,
2
used a (99,590) integration grid. Energy decomposition analysis
8
86,87
(EDA) was carried out as described previously,
with the final
J = 8.5, 3.1 Hz, 2H), 8.12 (dd, J = 8.2, 3.4 Hz, 4H), 8.01
(td, J = 7.8, 1.7 Hz, 4H), 7.50 (dd, J = 7.6, 4.9 Hz, 4H), 0.89 (s, 3H).
energy scaled as described therein. Though previous reports using this
EDA were concerned primarily with single bonds between pairs of
atoms, the method can be applied to any system in which one pair of
electrons becomes uncoupled when the bond is ruptured. In this
three-center, two-electron (3c−2e) system, the interacting fragments
are a doublet alkyl component and a doublet dicopper−DPFN
1
1
9
F NMR (564.61 MHz, THF-H ): δ −79.01 (6F), −174.32 (2F).
8
H NMR (600.13 MHz, o-C H F ): δ 8.77 (dd, J = 4.9, 1.7 Hz, 4H),
6
4 2
8.22 (d, J = 8.5 Hz, 2H), 8.11 (dd, J = 8.6, 3.0 Hz, 2H), 7.95 (dd, J =
8.2, 3.3 Hz, 4H), 7.74 (td, J = 7.9, 1.7 Hz, 4H), 7.24 (dd, J = 7.6,
1
03
19
5.0 Hz, 4H), 1.05 (s, 3H). F NMR (564.61 MHz, o-C H F ):
6
4
2
−
1
component that interact to form the 3c−2e bond of interest. For
δ −78.54 (s, 6F), −175.13 (q, J = 3.5 Hz, 2F). IR (ATR, ν
̃
(cm )):
•
example, for complex 1 the two components employed were CH
3124 (vw, br), 3066 (vw), 2978 (vw, br), 2859 (vw), 2781 (vw), 1605
(w, sh), 1592 (m), 1575 (w), 1546 (vw), 1500 (w), 1472 (w, sh),
1462 (m), 1439 (w), 1410 (w), 1349 (s), 1331 (m), 1302 (w, sh),
1294 (w), 1240 (w), 1228 (w), 1179 (vs), 1146 (m, sh), 1134 (vs),
1096 (w), 1074 (m), 1061 (s), 1008 (w), 977 (vw, br), 941 (vw),
927 (vw), 903 (vw), 891 (vw), 855 (m), 807 (w), 787 (m), 773 (s),
752 (m), 737 (m), 711 (w), 698 (m), 686 (m), 651 (m), 642 (m),
620 (m), 597 (s), 582 (m), 569 (s), 532 (w), 507 (s), 442 (vw, br),
3
•
+
and Cu DPFN .
2
1
1
Synthesis of [Cu (μ-η :η -CH )DPFN]NTf (1). Method 1. A solu-
tion of [Cu (μ-η :η -NCCH )DPFN](NTf ) (0.050 g, 0.041 mmol)
2
3
2
1
1
2
3
2 2
in THF (2.0 mL) was cooled to −30 °C; to the cold stirred solution
was added a solution of dimethylmagnesium in THF (0.5 mL,
41 mM, 0.021 mmol, 0.51 equiv) dropwise. The reaction mixture
darkened significantly and was stirred rapidly for 1 h while it was
warmed to room temperature (ca. 22 °C). The resulting mixture was
filtered, and the filtrate was cooled to −30 °C. Diethyl ether
−
1
−1
3
430 (vw), 413 (m). UV−vis (THF) λmax, nm (ε, M cm /10 ): 253
(18.3), 295 (12.8), 306 (sh 10.8), 318 (10.8), 347 (sh 4.34), 404
(2.72), 635 (0.404). Anal. Calcd for C H Cu F N O S : C, 42.86;
(approximately 17 mL) was layered over the cold filtrate. After 2 days
3
3
23
2
8
7
4 2
at −35 °C, a dark solid formed, and the dark red supernatant was
carefully decanted. The solid was briefly triturated with diethyl ether
H, 2.51; N, 10.60. Found: C, 42.50; H, 2.70; N, 10.27. IR, UV−vis,
elemental analysis, and cyclic voltammetry (Figures S19−S22) were
performed using samples prepared by Method 1.
(3 × 2 mL). The resulting solid was suspended in 4 mL of diethyl
ether and transferred to a new vial. After the solid was allowed to
settle, the supernatant was carefully decanted; residual volatile com-
pounds were removed in vacuo to yield 1 as an olive green powder
Synthesis of [Cu (μ-Cl)DPFN]NTf (2). To a stirred solution
2
2
1
1
of [Cu (μ-η :η -NCCH )DPFN](NTf ) (0.050 g, 0.041 mmol) in
2
3
2 2
THF (2 mL) was added a solution of anhydrous lithium chloride in
THF (1.0 mL, 0.041 M, 0.041 mmol, 1.0 equiv) dropwise. The reac-
tion mixture rapidly became dark red and was stirred for 1.25 h. The
mixture was then filtered, and the filtrate was collected and con-
centrated in vacuo. The resulting dark red-purple oil was triturated by
rapid stirring with diethyl ether (4 mL) for 1 h. The solid was allowed
to settle, and the supernatant was carefully decanted. The solid was
similarly triturated twice more with diethyl ether (4 mL for 1 h each
time). The resulting solid was rinsed briefly with diethyl ether (4 mL),
and residual volatile compounds were removed in vacuo to yield 2 as
(
0.019 g, 0.021 mmol, 51%). For long-term storage, the product was
kept under nitrogen at −35 °C and in the dark. Vapor diffusion of
diethyl ether into a o-C H F solution of 1, synthesized employing
6
4 2
dimethylmagnesium, for 14 days at −35 °C afforded X-ray-quality
crystals of 1 suitable for diffraction on a Bruker AXS diffractometer
with Mo Kα radiation.
1
1
Method 2. A solution of [Cu (μ-η :η -NCCH )DPFN](NTf )
2
3
2 2
(
0.050 g, 0.041 mmol) in THF (2.5 mL) was cooled to −30 °C; to
the cold stirred solution was added a similarly cold solution of
K
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a dark gray solid (0.035 g, 0.037 mmol, 90%). Layering of diethyl
ether over a cold (−30 °C), dilute solution of 2 in THF and storage
for 2 days at −35 °C afforded X-ray-quality crystals of 2·C H O.
37.21 (Cu −CH C(CH ) ), 34.45 (Cu −CH C(CH ) ), 13.02
2
2
3
3
2
2
3 3
1
9
(br, Cu −CH C(CH ) ). F NMR (564.61 MHz, THF-d ): δ
2
2
3
3
8
105
−79.01 (s, 6F, −SO −CF ), −166.70 (q,
J = 3.0 Hz, 2F,
4
8
2
3
1
−1
H NMR (700.13 MHz, THF-d ): δ 8.90 (dt, J = 5.0, 0.8 Hz, 4H,
(pyridyl) (naphth)C−F). IR (ATR, ν (cm )): 3111 (vw, br), 3067
̃
8
2
6
-pyridyl-C−H), 8.89 (d, J = 8.6 Hz, 2H, 4-naphth-C−H), 8.47 (dd,
(vw, br), 2950 (w), 2928 (w), 2869 (w), 2846 (w), 2812 (vw, br),
2690 (vw, br), 1607 (w), 1592 (m), 1576 (w), 1550 (vw, br),
1502 (w), 1473 (w, sh), 1464 (m), 1438 (m), 1411 (w, br),
1386 (vw), 1350 (s), 1330 (m), 1298 (w), 1241 (w, sh), 1226 (m),
1186 (vs), 1160 (m, sh), 1133 (s), 1101 (vw), 1072 (m, sh), 1055 (s),
1005 (m), 993 (w, sh), 972 (w, br), 942 (vw), 927 (w), 892 (w, br),
856 (m), 808 (m), 773 (s), 753 (m), 739 (m), 711 (w), 699 (m),
686 (m), 652 (m), 640 (m), 618 (s), 599 (m), 570 (s), 510 (m),
483 (m), 453 (w), 430 (w), 416 (m). UV−vis (THF) λmax, nm
J = 8.6, 3.2 Hz, 2H, 3-naphth-C−H), 8.16 (ddt, J = 8.2, 3.4, 1.1 Hz,
4
7
H, 3-pyridyl-C−H), 8.05 (td, J = 7.9, 1.8 Hz, 4H, 4-pyridyl-C−H),
13 1
.54 (ddd, J = 7.6, 5.0, 1.1 Hz, 4H, 5-pyridyl-C−H). C{ H} NMR
(150.92 MHz, THF-d ): δ 160.18 (d, J = 30.0 Hz, 2-naphth-C),
8
1
53.85 (d, J = 29.7 Hz, 2-pyridyl-C), 150.20 (8a-naphth-C), 149.78
(
d, J = 3.0 Hz, 6-pyridyl-C−H), 141.67 (d, J = 3.5 Hz, 4-naphth-
C−H), 139.67 (d, J = 3.3 Hz, 4-pyridyl-C−H), 125.33 (5-pyridyl-
C−H), 124.14 (4a-naphth-C), 121.08 (d, J = 14.1 Hz, 3-pyridyl-
C−H), 121.04 (q, J = 322.4 Hz, −SO −CF ), 120.46 (d, J = 16.3 Hz,
−
1
−1
3
2
3
(ε, M cm /10 ): 252 (14.7), 295 (9.50), 304 (9.40), 317 (9.10),
343 (sh 4.40), 406 (sh 2.81), 541 (0.633). Anal. Calcd for
C H Cu F N O S : C, 45.31; H, 3.19; N, 10.00. Found: C, 45.15;
3
-naphth-C−H), 93.79 (d, J = 186.6 Hz, (pyridyl) (naphth)C−F).
2
19
F NMR (564.61 MHz, THF-d ): δ −79.05 (s, 6F, −SO −CF ),
8
2
3
37 31
2
8
7
4 2
104
1
−
172.83 (q, J = 3.5 Hz, 2F, (pyridyl) (naphth)C−F). H NMR
H, 3.18; N, 9.85.
Synthesis of [Cu
2
1
1
(
499.60 MHz, THF-H ): δ 8.90 (d, J = 5.1 Hz, 4H), 8.88 (d, J =
2
(μ-η :η -CH )DPFN]NTf
)DPFN](NTf ) (0.020 g, 0.015 mmol) in
2 2
2
CH
3
2
(4). A solution of
8
1
1
8
4
.7 Hz, 2H), 8.46 (dd, J = 8.6, 3.3 Hz, 2H), 8.15 (dd, J = 8.3, 3.4 Hz,
H), 8.05 (t, J = 7.4 Hz, 4H), 7.54 (dd, J = 7.7, 5.0 Hz, 4H). H NMR
[Cu
(μ-η :η -NCCH
2
3
1
THF (0.5 mL) was cooled to −30 °C; to the cold stirred solution was
added a solution of diethylmagnesium in THF (0.25 mL, 36 mM,
0.0090 mmol, 0.6 equiv). The reaction mixture darkened significantly
and was stirred rapidly for 1 h while it was warmed to room tem-
perature (ca. 22 °C). The resulting mixture was filtered, and the
filtrate was cooled to −30 °C. Diethyl ether (approximately 3.25 mL)
was layered over the cold filtrate. After 2 days at −35 °C, a dark solid
formed, and the red supernatant was carefully decanted. The solid was
briefly triturated with diethyl ether (3 × 1 mL). Residual volatile
compounds were removed in vacuo to yield a dark solid (0.0085 g).
(
8
600.13 MHz, o-C H F ): δ 8.90 (d, J = 5.0 Hz, 4H), 8.34 (d, J =
6 4 2
.6 Hz, 2H), 8.22 (dd, J = 8.6, 3.0 Hz, 2H), 7.98 (dd, J = 8.2, 3.3 Hz,
103
4
H), 7.76 (td, J = 7.9, 1.7 Hz, 4H), 7.24 (dd, J = 7.6, 4.9 Hz, 4H).
19
F NMR (564.61 MHz, o-C H F ): δ −78.57 (s, 6F), −173.65
6
4 2
−1
(q, J = 3.5 Hz, 2F). IR (ATR, ν (cm )): 3130 (vw, br), 3074 (vw),
̃
3
1
1
1
1
8
7
5
4
2
057 (vw), 1603 (w, sh), 1593 (m), 1575 (w), 1544 (vw), 1502 (w),
472 (w, sh), 1463 (m), 1439 (w), 1426 (w, sh), 1407 (vw),
350 (s), 1333 (m), 1303 (w), 1293 (w), 1241 (w, sh), 1228 (w),
181 (vs), 1136 (vs), 1096 (w), 1075 (m), 1062 (s), 1012 (w),
001 (w, sh), 979 (vw), 968 (vw), 941 (vw), 928 (vw), 902 (vw),
91 (vw), 858 (m), 807 (w), 787 (m), 773 (s), 765 (m, sh), 751 (m),
38 (m), 711 (w), 699 (w), 686 (m), 652 (m), 646 (m), 619 (m),
96 (s), 581 (m), 569 (s), 532 (w), 507 (s), 456 (vw), 419 (w),
1
1
The dark solid was primarily [Cu (μ-η :η -CH CH )DPFN]NTf
2 2 3 2
1
19
(ca. ≥90%, as determined by H and F NMR spectroscopy). The
product was stored at −35 °C and in the dark. The aforementioned
steps, excluding the removal of volatile compounds in vacuo, provided
13 (w). UV−vis (THF) λ , nm (ε, M− cm /10 ): 252 (20.6),
1
−1
3
1
1
crystals of [Cu
(μ-η :η -CH CH )DPFN](NTf )·1.5C H O·
max
2
2 3 2 4 8
61 (20.6), 280 (sh 16.5), 308 (14.9), 317 (15.3), 378 (3.93), 531
nC 10O suitable for diffraction, employing synchrotron radiation
H
4
(
4
0.932), 719 (sh 0.218). Anal. Calcd for C H ClCu F N O S : C,
at Beamline 11.3.1 at the LBNL Advanced Light Source. Numerous
attempts to further purify the product by recrystallization from a range
of solvent combinations did not provide noticeably purer material, as
3
2
20
2
8
7
4 2
0.66; H, 2.13; N, 10.37. Found: C, 40.29; H, 2.22; N, 10.31.
1
1
Synthesis of [Cu (μ-η :η -CH C(CH ) )DPFN]NTf (3). A solu-
2
2
3 3
2
1
1
1
19
19
tion of [Cu (μ-η :η -NCCH )DPFN](NTf ) (0.0400 g, 0.032 mmol)
determined by H and F NMR spectra. F NMR spectra suggest
2
3
2 2
1
9
in THF (3 mL) was cooled to −30 °C. To the stirred solution was
added a solution of neopentyllithium (0.0027 g, 0.034 mmol) in
pentane (0.75 mL) dropwise, resulting in a darkening of the reaction
mixture. The mixture was stirred for an additional 50 min while it was
warmed to room temperature and then filtered. The filtrate was
collected and cooled to ca. −35 °C, and diethyl ether (approximately
that the remaining impurities include complexes 2 (<2% by F NMR)
1
9
1
13
19
and 6 (<2% by F NMR). Regardless, H, C, and F resonances
assignable to 4 are easily distinguishable (e.g., see Figures S7−S9) and
1
are reported here H NMR (700.13 MHz, THF-d
): δ 8.93 (dd, J =
8
5.0, 1.7 Hz, 4H, 6-pyridyl-C−H), 8.76 (d, J = 8.6 Hz, 2H, 4-naphth-
C−H), 8.36 (dd, J = 8.5, 3.2 Hz, 2H, 3-naphth-C−H), 8.14 (dd, J =
8.2, 3.2 Hz, 4H, 3-pyridyl-C−H), 8.03 (td, J = 7.9, 1.8 Hz, 4H,
4-pyridyl-C−H), 7.52 (ddd, J = 7.6, 5.0, 1.1 Hz, 4H, 5-pyridyl-C−H),
1
7 mL) was layered over the cold filtrate. Dark crystalline solid
formed after storage for 2 days at −35 °C. The supernatant was
carefully decanted, and the solid was washed with diethyl ether (4 ×
2.38 (q, J = 7.9 Hz, 2H, Cu
7.9 Hz, 3H, Cu −CH CH , JC−H = 123.2 Hz). H NMR (600.13 MHz,
THF-d ): δ 8.93 (dd, J = 5.1, 1.6 Hz, 4H), 8.76 (d, J = 8.6 Hz, 2H),
−CH CH , JC−H = 111.7 Hz), 2.14 (t, J =
2
2 3
1
1
mL). Residual volatile compounds were removed in vacuo to yield 3
2
2
3
as a dark crystalline solid (0.016 g, 0.016 mmol, 50%). The product
was stored under nitrogen at −35 °C and in the dark. Vapor diffusion
of diethyl ether into a THF solution of 3 for 7 days at −35 °C
8
8.36 (dd, J = 8.6, 3.1 Hz, 2H), 8.14 (ddt, J = 8.2, 3.4, 1.1 Hz, 4H), 8.03
(td, J = 7.9, 1.7 Hz, 4H), 7.52 (ddd, J = 7.6, 5.0, 1.2 Hz, 4H), 2.38
1
13
1
afforded X-ray-quality crystals of 3·C H O. H NMR (700.13 MHz,
(q, J = 7.9 Hz, 2H), 2.14 (t, J = 7.9 Hz, 3H). C{ H} NMR
(150.92 MHz, THF-d ): δ 159.99 (d, J = 30.3 Hz, 2-naphth-C),
4
8
THF-d ): δ 8.95 (dd, J = 5.1, 1.6 Hz, 4H, 6-pyridyl-C−H), 8.79
8
8
(
d, J = 8.5 Hz, 2H, 4-naphth-C−H), 8.38 (dd, J = 8.6, 3.1 Hz, 2H,
154.54 (d, J = 29.1 Hz, 2-pyridyl-C), 150.98 (8a-naphth-C), 150.13
(d, J = 3.1 Hz, 6-pyridyl-C−H), 140.87 (d, J = 3.4 Hz, 4-naphth-
C−H), 139.35 (d, J = 3.3 Hz, 4-pyridyl-C−H), 125.19 (5-pyridyl-C−H),
3
8
1
1
-naphth-C−H), 8.08 (ddt, J = 8.1, 2.4, 1.1 Hz, 4H, 3-pyridyl-C−H),
.03 (td, J = 7.9, 1.8 Hz, 4H, 4-pyridyl-C−H), 7.55 (ddd, J = 7.5, 5.0,
1
01
.3 Hz, 4H, 5-pyridyl-C−H), 1.93 (s, 2H, Cu −CH C(CH ) , J =
C−H
123.65 (4a-naphth-C), 121.00 (d, J = 321.4 Hz, −SO
2
−CF ), 120.98
3
2
2
3
3
1
07.4 Hz), 1.36 (s, 9H, Cu −CH C(CH ) ). H NMR (600.13 MHz,
(d, J = 14.5 Hz, 3-pyridyl-C−H), 119.80 (d, J = 14.9 Hz, 3-naphth-
2
2
3 3
THF-d ): δ 8.95 (ddt, J = 5.1, 1.8, 0.9 Hz, 4H), 8.79 (d, J = 8.6 Hz,
C−H), 94.41 (d, J = 185.5 Hz, (pyridyl) (naphth)C−F), 19.39 (Cu −
8
2
2
1
9
2
4
4
(
1
H), 8.38 (dd, J = 8.6, 3.1 Hz, 2H), 8.08 (ddt, J = 8.1, 2.4, 1.1 Hz,
CH CH ), −21.22 (br, Cu −CH CH ). F NMR (564.61 MHz,
2
3
2
2
3
106
H), 8.03 (td, J = 7.8, 1.7 Hz, 4H), 7.55 (ddd, J = 7.5, 5.0, 1.3 Hz,
THF-d ): δ −78.99 (s, −SO −CF ), −173.08 (q, J = 3.4 Hz, 2F,
8
2
3
1
3
1
H), 1.92 (s, 2H), 1.36 (s, 9H, JC−H = 123.3 Hz). C{ H} NMR
(pyridyl) (naphth)C−F).
2
1
1
150.92 MHz, THF-d ): δ 160.72 (d, J = 30.5 Hz, 2-naphth-C),
Synthesis of [Cu (μ-η :η -OC F )DPFN]NTf (5). To a solution
8
2
6
5
2
1
1
55.40 (d, J = 28.3 Hz, 2-pyridyl-C), 151.22 (8a-naphth-C), 150.11
of [Cu (μ-η :η -Ph)DPFN]NTf (0.020 g, 0.020 mmol) in
2
2
(
d, J = 2.4 Hz, 6-pyridyl-C−H), 141.29 (d, J = 3.3 Hz, 4-naphth-
o-difluorobenzene (1.5 mL) was added a solution of pentafluorophenol
(0.038 g, 0.21 mmol, 10 equiv) in o-difluorobenzene (1.0 mL) drop-
wise. The reaction mixture changed from dark green to dark orange
and was stirred for 1.25 h. The mixture was then concentrated in vacuo,
and the resulting residue was triturated with 3/2 pentane−toluene
C−H), 139.45 (d, J = 2.8 Hz, 4-pyridyl-C−H), 125.39 (5-pyridyl-
101
C−H), 123.69 (4a-naphth-C), 123.21 (d, J = 322.2 Hz, −SO −
2
CF ), 121.71 (d, J = 13.8 Hz, 3-pyridyl-C−H), 120.05 (d, J = 14.9 Hz,
3
3
-naphth-C−H), 95.31 (d, J = 184.4 Hz, (pyridyl) (naphth)C−F),
2
L
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
2.5 mL total) for 1.25 h. The resulting solid was allowed to settle,
solid (0.0118 g, 0.0058 mmol, 58%). Vapor diffusion of hexanes into a
o-C H F solution of 6 for 4 days at −35 °C afforded X-ray-quality
and the supernatant was carefully decanted. The dark solid was rinsed
with pentane (3 × 1 mL) and then dissolved in THF (1.25 mL). This
THF solution was filtered, and the filtrate was collected and cooled to
6
4 2
1
crystals of 6·2o-C H F . H NMR (700.13 MHz, C D NO ): δ 9.33
6
4
2
6
5
2
(d, J = 8.6 Hz, 4H, 4-naphth-C−H), 8.45−8.39 (m, 8H, a-6-pyridyl-
C−H and a-3-pyridyl-C−H), 8.36−8.29 (m, 8H, a-4-pyridyl-C−H
and 3-naphth-C−H), 8.28−8.24 (m, 4H, b-3-pyridyl-C−H), 8.22
(td, J = 7.7, 1.8 Hz, 4H, b-4-pyridyl-C−H), 7.70−7.67 (m, 4H,
a-5-pyridyl-C−H), 6.66 (m, 4H, b-6-pyridyl-C−H), 6.63 (m, 4H,
−
30 °C. Pentane (approximately 19 mL) was carefully layered on top
of the cold filtrate, and storage for 1 day at −35 °C afforded a dark
brown-gray solid. The supernatant was carefully decanted, and the
solid was rinsed with pentane (3 × 1 mL). Residual volatile compounds
were removed in vacuo to yield 5 as a dark solid (0.019 g, 0.017 mmol,
1
08 13
1
b-5-pyridyl-C−H).
C{ H} NMR (150.92 MHz, C D NO ):
6 5 2
8
5%). Vapor diffusion of pentane into an o-difluorobenzene solution
δ 161.37 (d, J = 29.1 Hz, 2-naphth-C), 156.41 (d, J = 30.4 Hz,
a-2-pyridyl-C), 153.31 (d, J = 27.9 Hz, b-2-pyridyl-C), 152.50 (8a-
naphth-C), 150.90 (a-6-pyridyl-C−H), 148.65 (b-6-pyridyl-C−H),
of 5 for 15 d at −35 °C afforded X-ray-quality crystals of 5·2o-
1
109
C H F ·0.5C H . H NMR (600.13 MHz, THF-d ): δ 8.90 (d, J =
6
4
2
5
12
8
8
.6 Hz, 2H, 4-naphth-C−H), 8.83 (dt, J = 5.0, 0.8 Hz, 4H, 6-pyridyl-
143.22 (4-naphth-C−H), 141.09 (a-4-pyridyl-C−H), 139.87 (b-4-
pyridyl-C−H), 126.95 (a-5-pyridyl-C−H), 126.49 (d, J = 4.2 Hz,
3-naphth-C−H), 125.62 (b-5-pyridyl-C−H), 124.74 (d, J = 16.6 Hz,
b-3-pyridyl-C−H), 124.41 (s, 4a-naphth-C), 122.12 (d, J = 14.3 Hz,
a-3-pyridyl-C−H), 121.50 (q, J = 321.9 Hz, −SO −CF ), 96.19
C−H), 8.47 (dd, J = 8.6, 3.3 Hz, 2H, 3-naphth-C−H), 8.19 (dd, J =
8
.2, 3.4 Hz, 4H, 3-pyridyl-C−H), 8.06 (td, J = 7.9, 1.8 Hz, 4H,
4
-pyridyl-C−H), 7.56 (ddd, J = 7.7, 5.0, 1.2 Hz, 4H, 5-pyridyl-C−H).
13
1
C{ H} NMR (150.92 MHz, THF-d ): δ 160.36 (d, J = 30.1 Hz,
8
2
3
1
9
2
-naphth-C), 154.17 (d, J = 30.1 Hz, 2-pyridyl-C), 150.62 (8a-naphth-
(d, J = 180.8 Hz, (pyridyl)
NO ): δ −78.18 (s, 18F, −SO
(pyridyl)
2
(naphth)C−F). F NMR (564.62 MHz,
−CF ), −148.47 (s, 4F,
): δ 9.04
C), 149.78 (d, J = 2.9 Hz, 6-pyridyl-C−H), 141.81 (d, J = 3.4 Hz,
C
6
D
5
2
2
3
1
4
-naphth-C−H), 139.75 (d, J = 3.4 Hz, 4-pyridyl-C−H), 125.56
2
(naphth)C−F). H NMR (400.13 MHz, THF-H
8
(5-pyridyl-C−H), 124.24 (4a-naphth-C), 121.44 (d, J = 14.8 Hz,
(d, J = 8.8 Hz, 4H), 8.19 (t, J = 8.0 Hz, 5H), 8.01 (d, J = 4.5 Hz, 8H),
7.50 (t, J = 6.4 Hz, 4H), 6.44−6.34 (m, 4H), 6.31 (d, J = 5.3 Hz, 4H).
1
01
3
-pyridyl-C−H), 121.03 (d,
J = 322.2 Hz, −SO −CF ), 120.55
2
3
1
9
(
(
d, J = 16.8 Hz, 3-naphth-C−H), 93.31 (d, J = 187.0 Hz,
pyridyl) (naphth)C−F). Carbon resonances assignable to the penta-
F NMR (376.44 MHz, THF-H ): δ −78.81 (s, 18F, −SO −CF ),
8
2
3
1
2
−148.38 (s, 4F, (pyridyl) (naphth)C−F). H NMR (600.13 MHz,
o-C H F ): δ 8.63 (d, J = 8.6 Hz, 4H), 7.86 (d, J = 8.3 Hz, 4H), 7.70
2
1
9
fluorophenolate moiety were not observed. F NMR (564.61 MHz,
THF-d ): δ −79.08 (s, 6F, −SO −CF ), −167.39 (dd, J = 20.0, 9.5 Hz,
6
4 2
8
2
3
(d, J = 5.1 Hz, 4H), 7.65−7.59 (m, 12H), 7.58−7.49 (m, 4H), 6.99
110
110 19
2
F, ortho-OC F ), −168.31 (t, J = 21.5 Hz, 2F, meta-OC F ), −170.88
(dd, J = 7.6, 5.3 Hz, 4H), 6.04 (m, J = 4.7 Hz, 8H).
F NMR
6
5
6 5
107
(q, J = 3.3 Hz, 2F, (pyridyl) (naphth)C−F), −181.02 (tt, J = 22.3,
(564.61 MHz, o-C H F ): δ −78.68 (s, 18F, −SO −CF ), −149.32
2
6
4
2
2
3
1
−1
9
.5 Hz, 1F, para-OC F ). H NMR (600.13 MHz, THF-H ): δ 8.90
(s, 4F, (pyridyl) (naphth)C−F). IR (ATR, ν
̃
(cm )): 3111 (vw),
6
5
8
2
(d, J = 8.6 Hz, 2H), 8.82 (d, J = 5.0 Hz, 4H), 8.46 (dd, J = 8.6, 3.3 Hz,
3080 (vw, br), 3025 (vw), 1596 (w), 1575 (vw), 1507 (w), 1465 (w),
1439 (w), 1382 (w), 1349 (s), 1331 (m), 1303 (w), 1269 (vw),
1226 (m), 1180 (vs), 1132 (s), 1102 (w), 1052 (s), 1020 (m), 1011 (m),
969 (m), 941 (w), 933 (w), 902 (w, br), 858 (m), 807 (w), 772 (m),
754 (m), 739 (m), 710 (w), 695 (w), 686 (w), 651 (w), 613 (s),
598 (s), 569 (s), 532 (w), 509 (s), 470 (w), 454 (w), 424 (w).
2
H), 8.18 (dd, J = 8.3, 3.4 Hz, 4H), 8.06 (t, J = 7.9 Hz, 4H), 7.55
1
9
(dd, J = 7.6, 5.1 Hz, 4H). F NMR (564.61 MHz, THF-H ):
8
δ −79.04 (s, 6F), −167.35 (dd, J = 20.4, 9.5 Hz, 2F), −168.20 (t, J =
2
9
5
1.6 Hz, 2F), −170.89 (q, J = 3.8 Hz, 2F), −180.89 (tt, J = 22.8,
1
.1 Hz, 1F). H NMR (600.13 MHz, o-C H F ): δ 8.91 (d, J =
6
4 2
−
1
−1
3
.1 Hz, 4H), 8.37 (d, J = 8.6 Hz, 2H), 8.22 (dd, J = 8.6, 3.0 Hz, 2H),
UV−vis (o-C H F ) λmax, nm (ε, M cm /10 ): 306.5 (20.4), 361
6
4 2
8
.00 (dd, J = 8.2, 3.4 Hz, 4H), 7.77 (td, J = 7.9, 1.7 Hz, 4H), 7.28 (dd,
(sh 6.01), 422 (sh 2.68). Anal. Calcd for C H Cu F N O S : C,
66 40 3 22 15 12 6
1
03 19
J = 7.6, 5.1 Hz, 4H).
(
2
ν
1
(
F NMR (564.61 MHz, o-C H F ): δ −78.56
38.93; H, 1.98; N, 10.32. Found: C, 39.13; H, 1.90; N, 10.08.
6
4 2
1
1
s, 6F), −167.66 (t, J = 21.5 Hz, 2F), −167.89 (dd, J = 19.6, 8.7 Hz,
Reaction of [Cu (μ-η :η -CH )DPFN]NTf with Pentafluoro-
2 3 2
F), −171.72 (d, J = 3.8 Hz, 2F), −179.74 (m, 1F). IR (ATR,
benzene. In a nitrogen-filled glovebox, 1 (0.001 g) was dissolved in
THF (0.5 mL) containing a small drop of 1,3,5-tris(trifluoromethyl)-
benzene. The solution was placed in a J. Young tube that was then
−
1
̃
(cm )): 3116 (vw, br), 3093 (vw, br), 2961 (vw, br), 1647 (vw),
605 (m), 1593 (m), 1575 (w), 1553 (vw), 1503 (s), 1472 (m), 1463
1
19
m, sh), 1439 (m), 1429 (m, sh), 1351 (s), 1341 (s, sh), 1328 (m),
sealed, and baseline H and F NMR spectra were recorded. Then in
1
1
1
8
6
5
302 (w), 1295 (w), 1260 (w), 1240 (w, sh), 1227 (m), 1202 (s, sh),
179 (vs), 1160 (m, sh), 1133 (vs), 1103 (m), 1085 (m), 1058 (s),
010 (s), 983 (s), 941 (w), 928 (w), 900 (vw), 891 (vw), 853 (m),
04 (m), 784 (s, sh), 769 (s), 755 (m), 739 (m), 710 (w), 698 (m),
85 (m), 654 (m), 644 (m, sh), 617 (s), 598 (s), 570 (vs), 532 (m),
08 (s), 482 (m), 463 (m), 454 (m), 428 (m), 416 (m). UV−vis
a nitrogen-filled glovebox, a few drops of pentafluorobenzene (220 equiv,
1
19
determined by H and F NMR spectroscopy) were added to the
1
19
tube. The tube was sealed, and the first H and F NMR spectra were
recorded within 5 min of pentafluorobenzene addition. The tube was
allowed to stand at room temperature, and spectra were recorded at
various intervals. After no change was observed at room temperature,
the tube was heated at 60 °C, and the reaction mixture was monitored
THF) λ , nm (ε, M− cm /10 ): 253 (24.4), 279 (sh 16.9), 305
1
−1
3
(
(
max
1
19
13.5), 317 (12.8), 347 (sh 4.77), 391 (3.44), 521 (0.923). Anal.
by H and F NMR spectra recorded at appropriately spaced
intervals (Figure S10). After 14 days at 60 °C, the reaction mixture
was concentrated in vacuo, and the resulting oil was dissolved in
Calcd for C H Cu F N O S : C, 41.77; H, 1.84; N, 8.97. Found:
38
20
2
13
7
5 2
C, 42.11; H, 1.67; N, 8.80.
Synthesis of [Cu (DPFN) ](NTf ) (6). A solution of triflimidic
acid (0.0057 g, 0.020 mmol, 1.0 equiv) in o-difluorobenzene (1 mL)
was added to a rapidly stirred solution of [Cu (μ-η :η -Ph)DPFN]-
NTf (0.0200 g, 0.020 mmol) in o-difluorobenzene (2 mL). Upon
1
9
3
2
2 3
o-C H F . The F NMR spectra of the product in o-C H F were
6
4
2
6
4 2
1
1
consistent with previously reported spectra of [Cu (μ-η :η -C F )-
2 6 5
25
1
1
2
DPFN]NTf2.
Reaction of [Cu (μ-η :η -CH )DPFN]NTf with Water. In a
1
1
2
2
3
2
addition of the acid, the dark green solution became bright orange.
The mixture was stirred for 1 h and then concentrated in vacuo to an
orange oil that was then triturated by stirring with diethyl ether
nitrogen-filled glovebox, 1 (0.001 g) was dissolved in THF (0.5 mL)
containing 1,3,5-tris(trifluoromethyl)benzene (4.3 mM). The solution
was placed in a J. Young tube that was then sealed, and baseline
1
19
(7 mL) for 5 h. The resulting orange solid was allowed to settle, and
H and F NMR spectra were recorded. Then, the reaction mixture
the supernatant was carefully decanted. The orange solid was washed
with diethyl ether (3 × 2 mL), and then residual volatile com-
pounds were removed in vacuo. The solid was then dissolved in
o-difluorobenzene (3 mL) and filtered, and the filtrate was cooled to
was frozen with liquid nitrogen, and the headspace of the J. Young
tube was briefly evacuated under dynamic vacuum. Deaerated water
was transferred under static vacuum into the reaction mixture, which
remained immersed in liquid nitrogen. The amount of water tran-
sferred was estimated by the change in mass of the sealed tube. The
reaction mixture was carefully thawed, and the reaction was monitored
−30 °C. Diethyl ether (17 mL) was carefully layered on top of the
cold o-difluorobenzene solution, and storage for 2 days at −35 °C
afforded a yellow-orange solid. The supernatant was carefully decanted,
and the solid was rinsed with diethyl ether (3 × 3 mL). Residual volatile
compounds were removed in vacuo to yield 6 as a bright yellow-orange
1
9
by F NMR spectra recorded over the course of 2 weeks (Figure S11).
1
1
Reaction of [Cu (μ-η :η -CH )DPFN]NTf with Pentafluoro-
2
3
2
phenol. In a nitrogen-filled glovebox, a solution of 1 in THF
M
DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
0.5 mL, 2.2 mM, 1.1 μmol) was used to dissolve 1,3,5-
ASSOCIATED CONTENT
■
* Supporting Information
trimethoxybenzene (0.0005 g, 3 μmol). The solution was placed in
S
1
19
a J. Young tube that was then sealed, and baseline H and F NMR
spectra were recorded. Then in a nitrogen-filled glovebox, penta-
fluorophenol (0.0020 g, 11 μmol, 10 equiv) was added to the solution.
The J. Young tube was sealed, and the reaction mixture began to
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.8b00443.
Cartesian coordinates of calculated structures of the
1
change from green to yellow. The reaction was monitored by H and
1
1
cations of 1, 2, and 5, as well as [Cu (μ-η :η -
2
19
F NMR spectra recorded over the course of 1 h (Figures S12 and
Ph)DPFN]+ and [Cu (μ-η :η -CC(C H ))DPFN]
1
1
+
1
19
2
6
5
S13). The H and F product resonances of the product observed
were consistent with those reported for [Cu (μ-η :η -OC F )DPFN]-
NTf (vide supra).
(XYZ)
1
1
2
6 5
Additional experimental details, supplementary figures
and tables as described in the text, crystallographic
figures and data, and computational figures and data
(PDF)
2
1
1
Reaction of [Cu (μ-η :η -CH )DPFN]NTf with Triflimidic
2
3
2
Acid. In a nitrogen-filled glovebox, 1 (0.0023 g, 2.5 μmol) and
,3,5-tris(trifluoromethyl)benzene (0.0042 g, 15 μmol) were dis-
solved in THF (0.5 mL). The solution was placed in a J. Young tube
1
1
19
Accession Codes
that was then sealed, and baseline H and F spectra were recorded.
Then in a nitrogen-filled glovebox, in the tube was placed a solution
of triflimidic acid (0.1 mL, 0.025 M, 2.5 μmol, 1.0 equiv). The J. Young
tube was sealed, and the reaction mixture began to change from green
to orange. H and F NMR spectra were acquired 10 min after
addition (Figure S14). The resonances observed for the mixture
were consistent with those reported for [Cu (DPFN) ](NTf )
2 3
CCDC 1578774−1578778 and 1840857 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
19
3
2
(
vide supra).
Reaction of [Cu (μ-η :η -CH )DPFN]NTf with Triphenylbor-
1
1
2
3
2
AUTHOR INFORMATION
Corresponding Author
*E-mail for T.D.T.: tdtilley@berkeley.edu.
ane. In a nitrogen-filled glovebox, a solution of 1 (0.55 mL, 2.0 mM,
■
1
.1 μmol) in o-C H F containing 1,3,5-tris(trifluoromethyl)benzene
6
4 2
(2.6 mM) was prepared and placed in a J. Young tube that was then
1
19
sealed. Baseline H and F NMR spectra were recorded. Then in a
nitrogen-filled glovebox, to the solution was added triphenylborane
(
reaction mixture remained green. The J. Young tube was sealed, and
the reaction was monitored by H and F NMR spectra recorded
over the course of ca. 4 h (Figures S15 and S16). The H and F pro-
duct resonances of the product observed were consistent with those
reported for [Cu (μ-η :η -Ph)DPFN]NTf (see the Supporting
ORCID
Micah S. Ziegler: 0000-0002-8549-506X
Daniel S. Levine: 0000-0001-8921-3659
T. Don Tilley: 0000-0002-6671-9099
Present Address
0.0026 g, 11 μmol, 10 equiv). The triphenylborane dissolved, and the
1
19
1
19
§
Institute for Data, Systems, and Society, Massachusetts
1
1
2
2
Institute of Technology, Cambridge, Massachusetts 02139,
United States.
Notes
Information). The appearance of a new downfield resonance at approxi-
mately 72.9 ppm (just beyond the resonance for BPh at 67.3 ppm) in
3
the 11B{ H} NMR spectrum suggests the formation of BMePh
1
2
75,76
(Figure S17).
The authors declare no competing financial interest.
General Procedure for Exploring Reactivity between
1
1
[Cu (μ-η :η -CH )DPFN]NTf and Additional Liquid Reagents.
2 3 2
ACKNOWLEDGMENTS
■
In a nitrogen-filled glovebox, a solution of 1 and an appropriate
standard (1,3,5-tris(trifluoromethyl)benzene and/or 1,3,5-trimethox-
ybenzene) in THF was prepared and placed in a J. Young tube that
was then sealed. Baseline H and F NMR spectra were recorded.
Then, back in a nitrogen-filled glovebox, a given reagent was then
This work was primarily funded by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences,
Chemical Sciences, Geosciences, and Biosciences Division,
under Contract No. DE-AC02-05CH11231. We acknowledge
the National Institutes of Health (NIH) for funding the UC
Berkeley CheXray X-ray crystallographic facility under Grant
No. S10-RR027172 and the UC Berkeley College of Chemistry
NMR facility under Grant Nos. SRR023679A and
1S10RR016634-01. We also acknowledge Beamline 11.3.1 of
Lawrence Berkeley National Laboratory’s Advanced Light
Source, which is a DOE Office of Science User Facility under
Contract No. DE-AC02-05CH11231. In addition, M.S.Z. was
supported by a National Science Foundation (NSF) Graduate
Research Fellowship (Grant No. DGE 1106400) and a
Philomathia Graduate Fellowship in the Environmental
Sciences. We thank Prof. Richard A. Andersen and Dr. Eva
M. Nichols for useful conversations. In addition, we thank
Dr. Michael L. Aubrey for electrochemical equipment. Finally,
we thank Dr. Antonio G. DiPasquale for X-ray crystallography
advice and Dr. Jeffrey G. Pelton for NMR spectroscopy advice.
1
19
1
added to the solution in the tube. The tube was resealed, and H and
19
F NMR spectra were acquired. The reaction mixture was allowed to
stand at room temperature (ca. 22 °C), and the reaction was moni-
tored by H and F NMR spectra recorded at appropriate intervals.
After no significant reaction was observed, the mixture was then
heated to 60 or 80 °C, as specified in the main text, with H and
NMR spectra being acquired at appropriate intervals. In these reac-
tions, heating led to decomposition, as suggested by the formation of
methane and/or various fluorine-containing species.
1
19
1
19
F
1
1
Procedure for Exploring Reactivity between [Cu (μ-η :η -
2
CH )DPFN]NTf and Carbon Dioxide. In a nitrogen-filled glove-
box, a solution of 1 (0.35 mL, 4.6 mM, 1.6 μmol) in THF-d was
3
2
8
prepared and placed in a J. Young tube that was then sealed. Baseline
1
H NMR spectra were recorded. The tube was then cycled onto a
Schlenk line, and the reaction mixture was degassed via three freeze−
1
pump−thaw cycles. Carbon dioxide was then placed in the tube. H
NMR spectra were recorded at appropriately spaced intervals while the
reaction mixture was allowed to stand at room temperature (ca. 22 °C).
13
1
C{ H} NMR spectroscopy confirmed the addition of carbon
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(101) This doublet is presumably the central two resonances of a
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2
−CF
3
.
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(
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two equivalent pyridyl protons (3-pyridyl-C−H) and one naphthyr-
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4
(
097−4104.
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(104) Spin simulation (of an AX
AY = 3.22 Hz in THF-d ) suggests that this apparent quartet is a
triplet of doublets, as described earlier
105) Spin simulation (of an AX Y system with J = 2.43 Hz, and
H F ) resonance.
6 4 2
Based Ligand for Assembly of Bridged Dicopper(I) Centers: Three-
Center Two-Electron Bonding Involving an Acetonitrile Donor.
Angew. Chem., Int. Ed. 2011, 50 (51), 12205−12208.
Y system with JAX = 3.37 Hz, and
2
J
8
(
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2
AX
JAY = 3.13 Hz in THF-d ) suggests that this apparent quartet is a
Representation of Three-Centre Two-Electron Bonds in Covalent
8
triplet of doublets, as described earlier.
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(
106) Spin simulation (of an AX Y system with J = 3.24 Hz, and
1
(
1503.
2 AX
JAY = 3.15 Hz in THF-d ) suggests that this apparent quartet it is a
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8
triplet of doublets, as described earlier.
Variational Energy Decomposition Analysis of Chemical Bonding. 1.
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(
107) Spin simulation (of an AX Y system with J = 3.45 Hz, and
2 AX
JAY = 3.30 Hz in THF-d ) suggests that this apparent quartet is a
(
10), 4812−4820.
8
triplet of doublets, as described earlier.
(
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1
3
1
This notation is conserved in the C{ H} NMR assignments.
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2
(
1
1
1
13
via H− H COSY and H− C HSQC and HMBC experiments.
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solvent (o-C H F ) resonance.
(
(
2
(
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DOI: 10.1021/acs.organomet.8b00443
Organometallics XXXX, XXX, XXX−XXX