Perfluoroalkyl Cobalt(III) Fluoride and Bis(perfluoroalkyl) Complexes: Catalytic Fluorination and Selective Difluorocarbene Formation

Article abstract of DOI:10.1021/jacs.5b12003

Four perfluoroalkyl cobalt(III) fluoride complexes have been synthesized and characterized by elemental analysis, multinuclear NMR spectroscopy, X-ray crystallography, and powder X-ray diffraction. The remarkable cobalt fluoride ¹⁹F NMR chemical shifts (-716 to -759 ppm) were studied computationally, and the contributing paramagnetic and diamagnetic factors were extracted. Additionally, the complexes were shown to be active in the catalytic fluorination of p-toluoyl chloride. Furthermore, two examples of cobalt(III) bis(perfluoroalkyl)complexes were synthesized and their reactivity studied. Interestingly, abstraction of a fluoride ion from these complexes led to selective formation of cobalt difluorocarbene complexes derived from the trifluoromethyl ligand. These electrophilic difluorocarbenes were shown to undergo insertion into the remaining perfluoroalkyl fragment, demonstrating the elongation of a perfluoroalkyl chain arising from a difluorocarbene insertion on a cobalt metal center. The reactions of both the fluoride and bis(perfluoroalkyl) complexes provide insight into the potential catalytic applications of these model systems to form small fluorinated molecules as well as fluoropolymers.

Full text of DOI:10.1021/jacs.5b12003

Article
pubs.acs.org/JACS
Perfluoroalkyl Cobalt(III) Fluoride and Bis(perfluoroalkyl) Complexes:
Catalytic Fluorination and Selective Difluorocarbene Formation
†
†
†
†
,†
‡
Matthew C. Leclerc, Julia M. Bayne, Graham M. Lee, Serge I. Gorelsky, Monica Vasiliu,
†
†
‡
Ilia Korobkov, Daniel J. Harrison, David A. Dixon, and R. Tom Baker*
†Department of Chemistry and Biomolecular Sciences and Centre for Catalysis Research and Innovation, University of Ottawa, 30
Marie Curie, Ottawa, Ontario K1N 6N5, Canada
‡
Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States
*
S Supporting Information
ABSTRACT: Four perfluoroalkyl cobalt(III) fluoride com-
plexes have been synthesized and characterized by elemental
analysis, multinuclear NMR spectroscopy, X-ray crystallog-
raphy, and powder X-ray diffraction. The remarkable cobalt
fluoride 19F NMR chemical shifts (−716 to −759 ppm) were
studied computationally, and the contributing paramagnetic
and diamagnetic factors were extracted. Additionally, the
complexes were shown to be active in the catalytic fluorination
of p-toluoyl chloride. Furthermore, two examples of cobalt(III)
bis(perfluoroalkyl)complexes were synthesized and their
reactivity studied. Interestingly, abstraction of a fluoride ion
from these complexes led to selective formation of cobalt
difluorocarbene complexes derived from the trifluoromethyl
ligand. These electrophilic difluorocarbenes were shown to undergo insertion into the remaining perfluoroalkyl fragment,
demonstrating the elongation of a perfluoroalkyl chain arising from a difluorocarbene insertion on a cobalt metal center. The
reactions of both the fluoride and bis(perfluoroalkyl) complexes provide insight into the potential catalytic applications of these
model systems to form small fluorinated molecules as well as fluoropolymers.
INTRODUCTION
Scheme 1. Alternative Synthetic Route to Transition Metal
Fluorides and Perfluoroalkyls
■
Transition metal complexes bearing fluoride or fluorocarbon
ligands have attracted considerable interest because they are
used to mediate/catalyze C−F or C−R bond-forming
reactions, which are highly important in the pharmaceutical,
F
1
,2
agrochemical, and advanced materials industries. Despite this
widespread interest, the fundamental chemistry of these species
is considerably less developed than that of analogous
hydrocarbon compounds. In particular, reports of complexes
bearing two fluorinated ligands (i.e., one perfluoroalkyl and one
fluoride, or two perfluoroalkyls) are very rare, with most
3
examples belonging to second or third row metals. Recently,
examples of Ni complexes bearing two perfluoroalkyl ligands
4
have been reported. There are synthetic challenges associated
with preparing such complexes: The most direct approach
would be via oxidative addition of the C−F or C−C bond of a
F
addition of R −I to metal complexes has been shown to
perfluoroalkane (CF , C F , C F , etc.) to a low-valent metal,
4
2
6
3
8
5
proceed for group 9 metals, and methods for converting [M]−
but the inert nature of perfluoroalkanes makes this route
6
2,7
1
X (X = halide) to [M]−F or to[M]−CF
are known.
inaccessible. Here, we use alternative synthetic routes to access
3
Reactions between the inexpensive and commercially available
the products of the hypothetical oxidative addition reaction
between perfluoroalkanes and first row metals. Our general
strategy is to utilize the oxidative addition of iodoperfluor-
5
cobalt(I) complex CpCo(CO) (Cp = η -cyclopentadienyl)
2
F
F
and R −I (R = CF3 and CF CF ) furnish cobalt(III)
2
3
F
oalkanes (R −I) to install the first perfluoroalkyl group on the
metal, followed by exchange of the iodide ligand for either a
Received: August 31, 2015
fluoride or a trifluoromethyl group (Scheme 1). Oxidative
©
XXXX American Chemical Society
A
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F
8
complexes CpCo(R )(I)(CO). Substitution of the carbonyl
ligand with a phosphine is facile and leads to the series of
formed from the reaction of the one-electron reductant
cobaltocene with an excess of perfluorodecalin in toluene at
F
isolable starting materials CpCo(R )(I)(L) (1−4), as shown in
low temperature. CoF is commercially available, although it is
3
9
often too reactive to promote transformations in a selective
manner. Of these three systems, only cobaltocenium fluoride
and the cyclometalated cobalt fluoride are truly organometallic
complexes, but they do not offer any opportunity for varying
the ligand environment on cobalt because their scaffolds are
limited as a result of the conditions of forming the fluorides,
contrary to complexes 5−8, which offer the ability to modify
both the nature of the phosphine ligands and the perfluoroalkyl
ligands on cobalt.
Scheme 2.
Scheme 2. Synthetic Scheme for Phosphine Substitutions
In recent reports, we described the two-electron reduction of
X-ray structural studies confirm that complexes 5−8 are well-
III
complexes 1−4 with sodium to furnish a series of nucleophilic
defined monomeric Co fluorides featuring cyclopentadienyl,
I
Co perfluorocarbene complexes, and demonstrated [2 + 2]
phosphine, and perfluoroalkyl ligands (Figure 1). The Co−F
10
cycloaddition reactions with tetrafluoroethylene. The result-
ing cobalt(III) perfluorometallacyclobutane complexes reacted
with both Lewis and Brønsted acids to give ring-opening/
isomerization products. However, the chemistry of cobalt(III)
systems with multiple perfluorinated ligands remains largely
unexplored, and herein we expand that area.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Perfluoroalkyl
Cobalt Fluorides. Seeking to isolate the hypothetical products
that would arise from the oxidative addition of perfluoroalkanes
to a cobalt center, we opted for a pathway involving the
substitution of iodide for fluoride, using a method previously
III
reported by Hughes et al. to afford analogous perfluoroalkyl Ir
6
b
fluorides. Reactions of complexes 1−4 with 3 equiv of AgF in
dichloromethane at room temperature over 20 h in the absence
III
of light afforded perfluoroalkyl Co fluoride complexes of the
F
5
general formula CpCo(R )(F)(L) (Cp = η -cyclopentadienyl,
F
R = CF and CF CF , L = PPh and PPh Me) (5−8) in 68−
3
2
3
3
2
Figure 1. Crystallographic representations of 5 (top left), 6 (top
right), 7 (bottom left), and 8 (bottom right) with 30% probability
thermal ellipsoids. Hydrogen atoms are omitted for clarity. One
molecule of acetonitrile has been removed from 5. Sample of 6
crystallized with two molecules in the unit cell. Selected bond lengths
and angles are presented in Table S1.
9
1% isolated yield as dark-green solids (Scheme 3). Complexes
Scheme 3. Synthesis Scheme for Cobalt(III) Fluorides
bond distances in complexes 5−8 range from 1.86 to 1.88 Å
19
(
Table S1), similar to the value of 1.89 Å found in CoF . For
3
perfluoroethyl complexes 7 and 8, the C −F bond distances
α
5
−8 were characterized spectroscopically and structurally, and
(avg. 1.378(2) and 1.393(2) Å) are significantly longer than
the results were further analyzed by density functional theory
C −F (avg. 1.326(2) and 1.333(2) Å) as observed previously
β
1
1
12,13
14,15
6b
(
DFT) calculations with the B3LYP
and PW91
for an Ir analog. The Co−P distances are approximately 0.04
Å shorter with PPh Me as compared to PPh because the
exchange-correlation functionals and polarized double- and
triple-ζ basis sets. Structurally, complexes 5 and 6 represent the
expected products arising from the oxidative addition of
perfluoromethane to cobalt, whereas complexes 7 and 8 are
those that would arise from the same type of reaction with
perfluoroethane. As previously mentioned, these oxidative
addition reactions are not feasible; thus, it is necessary to
utilize other synthetic methods to obtain such complexes.
Cobalt fluorides are uncommon in the literature, and the few
that have been presented mostly feature cobalt in either the +1
2
3
former is known to be a slightly more basic donor ligand.
Moreover, the Co−C bond distances are shorter for the
trifluoromethyl ligand versus the perfluoroethyl fragment by 0.2
Å for the PPh derivatives and 0.4 Å for the PPh Me examples.
3
2
Seminal work by Stone et al. has established that [M]−C bonds
are shorter with perfluoroalkyls than with analogous hydro-
2
0
carbons, an effect observed in this system as well. Recently,
another example of a transition metal simultaneously bearing a
fluoride and a perfluoroalkyl was reported that features a
bis(trifluoromethyl) nickel dimer with bridging fluoride
16
or the +2 oxidation state. There are only three examples
featuring cobalt in the +3 oxidation state: cobaltocenium
21
ligands.
fluoride, CoF , and an example from Klein et al. with a
DFT calculations were used to gain insight into the
electronic structure of 5 as a representative example. TD-
DFT calculations at the B3LYP/TZVP level with the SMD
3
cyclometalated complex featuring azine as an anchoring
1
7
group. Cobaltocenium fluoride was synthesized by Richmond
1
8
22
et al. in 1994, and has been applied to several stoichiometric
solvent model reproduced the electronic absorption spectrum
fluorination reactions. This extremely hygroscopic reagent is
in CH Cl well, with two principal experimental bands at 16
2
2
B
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−
1
−1
−1
−1
3
00 cm (263 M cm , calcd = 15 600 cm ) and 21 800
previously for ClF because of mixing of the appropriate π
orbitals with the σ* orbital in the presence of a magnetic field.
−1
−1
−1
−1
26
cm (1190 M cm , calcd = 21 700 cm ). (See Figure S1
and the band assignments in the Supporting Information.)
Relative to typical Co octahedral inorganic complexes, the
high intensities of these two absorption bands indicate
significant charge-transfer character in the corresponding
electron excitations. Calculated Mayer bond orders for 5
provide values for Co−Cp (2.37), Co−PPh (0.98), and Co−
CF bonds (0.91) that are unsurprising. However, the value for
Although F has the same mixing interactions, the presence of
2
III
23
symmetry prevents the paramagnetic component from being
shielding. The high-lying occupied and low-lying unoccupied
molecular orbitals (HOMO and LUMO, respectively) for
CpCo(CF )(F)(PH ) and CpCo(CF )(F)(PPh ) are shown in
24
3
3
3
3
3
the Supporting Information. The orbitals are essentially the
same for both compounds. The HOMO, HOMO-1, and
HOMO-2 are lone pairs on the F bonded to Co interacting
with different d orbitals on the Co. For the Co contribution, the
3
the Co−F bond (0.61) indicates significant ionic character in
this metal−ligand interaction and that the Co−F is the least
covalent among the metal−ligand bonds.
2 2
x y
2
z
HOMO is the d , the HOMO-1 is the d , and the HOMO-2
1
9
The F NMR spectra of 5−8 exhibit extreme upfield
resonances for the fluoride ligands ranging from δ −716 to
is the d . The LUMO is the Co−F σ* orbital with the d on
xy
xz
the Co, and the LUMO+1 is predominantly the Co−C σ*.
Thus, the HOMO, HOMO-1, and HOMO-2 serve as the
equivalent to the π-type orbitals in ClF, and the LUMO is the
equivalent of the ClF σ*. It is the interaction of these orbitals in
the presence of a magnetic field that leads to the paramagnetic
component being shielding, similar to what is found for ClF.
Reactivity of Fluoride Complexes. The importance of
−
759 ppm. These shifts are significantly upfield from the
analogous Ir complexes previously reported by both Hughes et
6b
19
25
al. (δ( F) = −437 to −446 ppm) and Bergman et al.
19
(
δ( F) = −413 to −415 ppm). To the best of our knowledge,
19
these represent the most upfield resonances reported for a
F
NMR signal. The resonances at half-height are very broad
900−1900 Hz) and featureless, presumably because of the
fluorides being bound to Co, a nuclide with a spin of / , a
natural abundance of 100%, and a large quadrupolar coupling
constant of 42.0 × 10
(
27
fluorinated organic substrates has been amply demonstrated.
5
9
7
2
Efficient, reliable techniques for the introduction of fluorine
into such products have been the subject of widespread
−30
2
m , all of which contribute to a
28
research for many years. Consequently, and encouraged by
significant broadening of the fluoride signal. The addition of
molecular sieves to an NMR sample of 5−8 did not affect the
broadness of the fluoride signals, indicating that the signal is
not broadened artificially by the presence of moisture.
From the results of DFT computational studies, we are now
able to understand the unique nature of these chemical shifts.
The results for all of the calculated Co−F chemical shifts and
their diamagnetic and paramagnetic tensor components are
shown in the Supporting Information. There are minor
quantitative differences between the three sets of chemical
calculations but not qualitative differences. There is reasonable
agreement with experiment for the CF and CF chemical shifts
with differences of up to 30 ppm, which is typical of such
fluorine NMR calculations. The differences between the
experimental and the calculated shifts for the F bonded to
the Co are larger by 30−100 ppm depending on the method,
with the BLYP/TZVP2 results being the closest to experiment
for this shift. The magnitudes of the calculated shifts for the
Co−F were found to be very sensitive to the bond distance,
suggesting why the difference between the calculated and
the ionic character of the Co−F bonds in our system, we
sought to determine the ability of these cobalt systems to
fluorinate simple organic compounds. Reactions with p-toluoyl
chloride were explored as a potential route toward fluorination
to form p-toluoyl fluoride. Gray et al. have recently
demonstrated this reaction in stoichiometric fashion, proceed-
ing through halide metathesis with cyclometalated iridium
29
fluoride complexes. Stoichiometric reactions with complex 6
in C D showed clean and essentially complete conversion of
6
6
the starting substrate within 2 h and formation of the p-toluoyl
fluoride product, proceeding through overall halide metathesis
with the cobalt fluoride complex. Prompted by the initial results
of these stoichiometric reactions, we aimed to develop a
catalytic process whereby, starting with the iodide complex 2,
the fluoride complex 6 could be generated in situ by the
presence of an excess of AgF.
Control experiments convincingly demonstrated that stoi-
chiometric reactions between p-toluoyl chloride and the
fluoride sources AgF, CsF, KF, and CoF3 gave minimal
conversion of the starting reagent to the target compound
overnight in dichloromethane (<5% in all cases). Optimized
reaction conditions led to essentially quantitative conversion of
the starting chloride to the fluoride within 4 h, using 5 mol % of
3
2
experimental values for this shift can be large. For L = PPh and
3
19
R = CF , the calculations predict a small value for the F shift
3
of the CF3 group (ca. −20 ppm as compared to the
experimental value of −2 ppm), so the difference in the
diamagnetic and paramagnetic components are comparable to
2
and 3 equiv of AgF. (See Table 1 for selected control
experiments and Table S16 for a full list.) This catalytic
fluorination occurs cleanly, affording an approximately 1:1
mixture of the Co−F and Co−Cl complexes upon completion.
Relatively few methods of producing p-toluoyl fluoride exist in
the literature, and they feature either exotic or potentially
those of the standard CFCl (BLYP/TZ2P σ(standard) = 118.8
3
ppm) with the diamagnetic component larger than the
1
9
paramagnetic component. The F chemical shift for the F
bonded to the Co is large and negative, resulting from the fact
that the diamagnetic and paramagnetic components have the
same sign, both shielding. The paramagnetic component is
larger than the diamagnetic component. We note that the
diamagnetic shielding component for the F bonded to C and of
the F bonded to Co are very similar, within ∼10 ppm, so the
large changes are due to the differences in the paramagnetic
components between the “normal” value for the F in the CF3
group and the value predicted for the F bonded to Co.
30
harmful reagents such as cyanuric fluoride, cesium fluorox-
3
1
32
33
ysulfate, potassium bifluoride, and hydrogen fluoride.
Furthermore, this substrate is not commercially available, but
34
Pd-based systems are used to produce it catalytically. Two
stoichiometric reactions were run in parallel, one of them
containing excess PPh Me (5 equiv), and analyzed at the same
2
time. Both reactions provided the same amount of conversion
to the target product. It thus appears unlikely that the reaction
proceeds through a dissociative mechanism, wherein the
The fact that the paramagnetic component tensor has the
same sign as the diamagnetic component tensor has been noted
C
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9a
3
Table 1. Catalytic Fluorination Reactions
and Gagne
́
et al. through the use of palladium(IV)
and
39b
39c−e
platinum(IV), respectively, as well as certain silver salts
40
and some copper complexes. Additionally, Grushin et al. have
reported various fluorination examples with palladium(II) and
41
rhodium(I) systems. Of these examples, only copper stands
out as a nonprecious, first row transition metal. Catalytic
systems incorporating these types of abundant and nontoxic
metals are very important and are active areas of research as the
search for renewable and efficient methods of producing target
fluorinated reagents continues. Moreover, the catalytic
entry
MF (equiv)
catalyst loading (mol %)
t (h)
yield (%)
1
2
3
4
AgF (1.0)
CsF (1.0)
KF (1.0)
16
16
16
16
4
2
5
2
formation of C(sp )−F bonds has mostly been limited to
<1
2
40b,42
40a
examples with palladium
and gold.
as well as a few with copper
CoF (1.0)
38a,b
3
1
1
1
1
0
4
5
6
AgF (3.0)
AgF (3.0)
AgF (3.0)
AgF (3.0)
10
5
99
99
47
26
The tendency of third row transition metals to form weaker
4
bonds to fluorine than most first row transition metals has
1
4
1,43
made them useful for catalytic reactions, but it is essential to
0.1
4
develop methods that utilize inexpensive, nontoxic, and
abundant metals such as cobalt. Interestingly, it appears that
the significant ionic character of the Co−F bond in this system,
as demonstrated by the calculated Mayer bond orders, might be
a major contributing factor to its catalytic potential.
Furthermore, this reaction does not require the use of
extravagant reagents and represents a step toward the potential
uses of cobalt in additional catalytic fluorination reactions.
Synthesis and Characterization of Cobalt Bis-
phosphine could dissociate from the metal and vacate a
coordination site for the acyl chloride to bind.
With this information in hand, a proposed catalytic cycle is
shown in Scheme 4. Starting from iodide complex 2, fluoride
Scheme 4. Proposed Catalytic Cycle for the Fluorination of
p-Toluoyl Chloride
(
perfluoroalkyls). The isolation of perfluoroalkyl cobalt(III)
halide complexes 1−8 motivated efforts to generate bis-
perfluoroalkyl) complexes via transmetalation of the halide
group with CF . Converting [M]−X complexes to [M]−CF is
(
3
3
44
an established process, first presented by Fuchikami et al.
using a copper system and Me SiCF and subsequently by
other groups. We initiated our investigation by studying the
3
3
7c,d
III
reactivity of the Co perfluoroalkyl halide complexes with
Me SiCF , using CsF as the initiator and DMF as solvent.
3
3
Reactions with PPh derivatives mostly resulted in decom-
3
position and very low yields of the desired products. However,
reactions with PPh Me derivatives (2, 4, 6, and 8) led to the
2
desired bis(perfluoroalkyl) products (9 and 10) in good yields
(
9 = 71% and 10 = 75% from [Co]−F, 9 = 57% and 10 = 52%
from [Co]−I) after only 2 h as stable yellow-orange powders
Scheme 5). Although the relative yields are lower when
(
starting from [Co]−I complexes, it is an overall more direct
approach to complexes 9 and 10.
analogue 6 is first formed using AgF as the fluoride source. The
ionic nature of the Co−F bond provides a latent source of
fluoride, which can react readily with the electrophilic carbon
center of the acyl chloride. Expulsion of the chloride from the
organic substrate gives the target compound, generating a
cobalt chloride complex, which can react with AgF to
regenerate the catalytically active complex 6 and form the
inactive AgCl. Many examples of electrophilic fluorination of
Scheme 5. Synthesis Scheme for Cobalt(III)
Bis(perfluoroalkyls)
It has been demonstrated previously that Me SiCF under-
3
3
35
organic substrates have been explored over recent years, and
goes activation by fluoride to liberate CF . Important studies by
3
45 46
efficient catalytic nucleophilic fluorination has more recently
̈
Yagupolskii et al. and Roschenthaler et al. independently
36
made major strides as well. Importantly, transition metals
demonstrated that this activation involves the in situ formation
−
have been used to perform the nucleophilic fluorination of a
of pentacoordinate silicate anions, either [Me SiF(CF )] or
3
3
3
7
38
−
−
variety of alkyl fluorides, alkenyl fluorides, and aryl
[Me Si(CF ) ] , which extrude [CF ] to form Me SiF or
3 3 2 3 3
3
9
fluorides. Alkyl fluorides have been synthesized by Toste et
Me SiCF , respectively. We propose that in our system, CsF
3 3
3
7a
al. from gold(III)
palladium(IV)
systems and by Sanford et al. from
systems. Electrophilic gold(I)
reacts with Me SiCF to produce the cesium salts of the
3 3
3
7c,39a
38a,b
com-
aforementioned pentacoordinate silicates, which then effect the
transmetalation with [Co]−X. This is in contrast to a report by
plexes have been used almost exclusively for the synthesis of
alkenyl fluorides, affording good yields and regioselectivity. Aryl
fluorides have been synthesized by the groups of Sanford et al.
47
Wang et al., where the reaction between AgF and Me SiCF
3
3
forms a proposed [AgCF ] species that can effect trans-
3
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metalation. It is important to note that for [Co]−I complexes 2
and 4, CsI is formed during the course of the reaction. In
addition, experiments in our lab show the following: (1) When
CsI is used in the place of CsF, no transmetalation takes place.
(
2) [Co]−I complexes 2 and 4 do not react with CsF in DMF
to produce [Co]−F complexes 6 and 8. These observations are
consistent with the lower yield of products 9/10 when starting
from [Co]−I (2/4) rather than [Co]−F (6/8).
Complexes 9 and 10 were studied through X-ray
crystallography (Figure 2). The Co−C bond distance of
1
19
Figure 3. Selective 1D H− F HOESY experiment in C D to help in
6
6
the assignment of the two [Co]−CF CF fluorine signals is shown.
2
3
The Cp signals were set to equal intensity for the purposes of clarity.
Colored boxes above the 1H spectrum demonstrate the effect of
selective saturation of the appropriate fluorine signal and showing
which signals are correlated by a through-space interaction.
1
19
The 1D H− F HOESY experiment has been utilized
48
recently by Claridge et al. in the analysis of fluorinated
pyrrolidines. This experiment offers the advantage of being
much faster than the more prevalent 2D 19F− F NOESY
experiments found in the literature. In our case, by taking
19
1
19
advantage of two nuclides in H and F that each have
essentially 100% natural abundance, the 1D method offers the
possibility to obtain similar conformational information in a
matter of minutes, as opposed to several hours for the
traditional 2D method.
Figure 2. Crystallographic representations of 9 (left) and 10 (right)
with 30% probability thermal ellipsoids. Hydrogen atoms are omitted
for clarity. One molecule of toluene has been removed from both 9
and 10. Selected bond lengths and angles are presented in Table S2.
Reactivity of Bis(perfluoroalkyl) Complexes. Transition
metal perfluoroalkyl complexes can be precursors to metal
fluorocarbenes. We previously reported the two-electron
1
.940 Å in 9 is significantly longer than the Ni−C bond
distances in analogous nickel bis(trifluoromethyl) complexes:
The (bipy)Ni(CF ) complex from Vicic et al. has a distance
of 1.88 Å, and an example from Mirica et al. has a distance of
4a
III
3
2
reduction of perfluoroalkyl Co iodide complexes 1−4 to
4b
I
afford Co fluorocarbene complexes, which exhibit nucleophilic
II
10
1
.91 Å with the Ni complex. However, the latter’s bond
type reactivity at the carbene carbon. We are interested in
III
III
lengths increase to 1.97 Å when the metal is oxidized to Ni . A
preparing analogous Co fluorocarbenes in order to probe the
IV
recent report by Sanford et al. features an octahedral Ni
complex, TpNi(Ph)(CF ) (Tp = trispyrazolylborate), with
Ni−C bond distances of 1.99 Å. It is interesting to compare
this complex with 9 because they are both d systems, and the
Ni complex was proven capable of promoting Aryl−CF3
coupling through reductive elimination.
DFT calculations were used to obtain insight into the
electronic structure of 9. TD-DFT calculations at the B3LYP/
TZVP level reproduce the electronic absorption spectrum well
effect that changing the oxidation state of cobalt will have on
III
3
2
carbene reactivity, with the expectation that Co fluorocar-
4c
benes might react as electrophiles. This concept was previously
demonstrated in an elegant study by Roper et al., where they
6
IV
0
II
showed that Ru and Ru fluorocarbenes differed by having
nucleophilic and electrophilic reactivity at the carbene carbon,
49
respectively.
Our strategy to prepare CoIII fluorocarbenes consisted of
abstracting a fluoride from a perfluoroalkyl ligand using a Lewis
acid, similar to the preparation of other fluorocarbene
complexes in the literature. Our initial attempts to abstract a
(
Figure S1). The absorption bands in 9 are blue-shifted relative
to the spectrum of 5. The assignment of two bands at 23 000
−1
−1
−1
−1
III
cm (shoulder) and 25 800 cm (730 M cm ) is shown in
the Supporting Information. Calculated Mayer bond orders for
fluoride from perfluoroalkyl Co iodides 1−4 were un-
successful because reactions with the Lewis acids Me SiOTf
3
9
are 2.31 for the Co−Cp bond, 1.01 for Co−PPh Me, and
and B(C F ) did not result in the formation of fluorocarbenes,
2
6 5 3
0
.93 and 0.95 for the two Co−CF bonds. These bond orders
presumably as a result of a preference by the Lewis acid to
abstract the iodide ligand. However, bis(perfluoroalkyl)
complexes 9−10 were attractive precursors for fluorocarbene
formation because they both eliminate the possibility of an
undesirable metal halide abstraction. Indeed, reactions of 9 and
10 with Lewis acids (Me SiOTf and B(C F ) ) in DCM led to
3
are almost identical to those in 5. Thus, replacement of the
fluoride ligand in 5 with the more strongly covalently bound
CF ligand does not affect the covalency of other Co−ligand
interactions.
Full NMR characterization of these complexes was obtained,
and assignment of the nonequivalent methylene fluorine
3
3
6 5 3
fluoride abstraction and formation of cobalt difluorocarbene
complexes (Int 1−4, Scheme 6). Addition of the Lewis acid to
a solution of the bis(perfluoroalkyl) precursors led to a color
change from yellow-orange to deep red over the course of 1 h
at room temperature, and NMR analysis demonstrated that
1
9
resonances in the various F spectra was achieved. A 1D
1
19
H− F HOESY experiment allowed the selective pulsing of
each of the three different fluorine resonances to determine the
relative spatial proximity to the three closest protons in the
1
9
19
19
structure (Figure 3). Additionally, a F− F NOESY was
collected to observe how the trifluoromethyl ligand correlated
through space to the different methylene fluorines of the
perfluoroethyl ligand (Figure S34). These experiments indicate
that the relative orientation of the ligands is essentially the same
in solution as in the solid state.
quantitative conversion was achieved. The F NMR resonances
for the difluorocarbene ligand in complexes Int 1−4 are highly
characteristic, with downfield chemical shifts ranging between δ
50
178 and 180 ppm. This is in contrast to the difluorocarbene
I
ligand of previously reported Co complexes, with resonances
10
for the two unique fluorine environments at δ 63 and 94 ppm.
E
DOI: 10.1021/jacs.5b12003
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
5
1
52
Scheme 6. Formation of Cobalt(III) Difluorocarbenes
complexes. Previous work by Burton et al. on copper
demonstrated a rare example of this type of perfluoroalkyl chain
growth from CF insertion on a transition metal. This reaction
2
demonstrates a step toward potential perfluoroalkene polymer-
ization using a transition metal catalyst, a sought-after process
that has been stunted at least in part by the difficulties involved
53
in promoting such insertion reactions, in large part due to the
F
strength of various [M]−R bonds. Attaining better control of
this reaction is an area of ongoing study within our group.
The second reaction is the well-known hydrolysis of the
Both Lewis acids provided selective fluoride abstraction from
complex 10 because only abstraction from the trifluoromethyl
ligand was observed, leaving the perfluoroethyl fragment
difluorocarbene ligand by trace H O to furnish a carbonyl
2
54
ligand and 2 equiv of HF (Scheme 8, bottom). This reaction
occurs almost instantaneously and is a common reaction with
49,55
1
9
6
untouched (Scheme 7). This is supported by F NMR,
metal difluorocarbenes that have formal d metal centers.
Although the hydrolysis of difluorocarbene ligands is
undesirable, the observation of electrophilic reactivity by our
Scheme 7. Selectivity of Fluoride Abstraction
III
Co fluorocarbenes further highlights a key difference from our
I
previously reported Co fluorocarbenes, which did not react
with 20 equiv of H O in acetonitrile solutions.
2
CONCLUSIONS
■
III
We have isolated and characterized four perfluoroalkyl Co
fluoride complexes. These complexes exhibit remarkable 9F
NMR shifts, largely due to an unusual paramagnetic component
that is shielding. Additionally, these complexes were shown to
be active in the catalytic fluorination of p-toluoyl chloride.
Furthermore, both the fluoride and iodide complexes could be
1
III
where the only fluorocarbene signal that is observed is the one
associated with the difluorocarbene fragment and not that of
the fluoro(trifluoromethyl) carbene. The selectivity of fluoride
abstraction from CF and not CF CF can be rationalized by
used in the synthesis of Co bis(perfluoroalkyl) complexes,
potential precursors in the development of catalytically relevant
systems. These complexes were shown to react with different
III
Lewis acids to form electrophilic Co difluorocarbenes. The
3
2
3
comparing the π-donating ability of F and CF fragments. Metal
insertion of these difluorocarbenes into the remaining
perfluoroalkyl fragment on the metal demonstrated the
elongation of a perfluoroalkyl chain on a transition metal by
one carbon. Further studies on the catalytic activity of these
complexes are currently underway in our laboratory.
3
carbene bonds are typically stabilized by contributions of d
III
orbital electrons from the metal. However, because the Co
carbene complexes here have two fewer d electrons compared
I
6
8
to the Co carbenes we reported previously (d vs d ), the M
C bond is likely more reliant on donation from the other
carbene substituents for stabilization. Therefore, because F is a
EXPERIMENTAL SECTION
■
better π-donating substituent than CF , fluoride abstraction
3
General Considerations. All manipulations were carried out using
standard Schlenk techniques or in an MBraun glovebox. All glassware
was oven-dried at >150 °C for a minimum of 2 h prior to use or flame-
dried using a torch. Toluene, hexanes, tetrahydrofuran (THF), diethyl
ether (DEE), and dimethylformamide (DMF) were dried on columns
of activated alumina using a J. C. Meyer (formerly Glass Contour)
solvent purification system. Dichloromethane (DCM), chloroform-d
from CF rather than CF CF is preferred. Efforts to increase
3
2
3
electron density around the metal by utilizing PMe in the
3
hopes of promoting some amount of fluoride abstraction from
the perfluoroethyl ligand were unsuccessful.
The newly formed difluorocarbene complexes underwent
two primary reactions in solution, which prevented their
isolation in pure form. One involves the insertion of
difluorocarbene into the remaining perfluoroalkyl fragment,
effectively increasing the length of the perfluoroalkyl chain on
(
CDCl ), and acetonitrile-d (CD CN) were dried by refluxing over
3 3 3
calcium hydride under a nitrogen flow, followed by distillation and
filtration through a column of activated alumina (ca. 10 wt %).
Benzene-d (C D ) was dried by standing over activated alumina (ca.
6
6
6
the transition metal center by one CF unit (Scheme 8, top).
2
1
0 wt %) overnight followed by filtration. The following chemicals
1
9
These products are clearly identified using F NMR because
the resulting perfluoroethyl and perfluoropropyl ligands have
highly characteristic chemical shifts and splitting patterns,
were used as purchased, without further purification: CpCo(CO) (Cp
2
5
= η -cyclopentadienyl) (Strem, 95%), CF I (SynQuest, 99%),
3
CF CF I (SynQuest, 98%), PPh (Strem, 99%), PPh Me (Strem,
3
2
3
2
III
which are identical to those of previously isolated Co
99%), Me SiOTf (OTf = SO CF ) (Aldrich, 98%), AgF (Strem, 98%),
3 3 3
CsF (Strem, 99+%), KF (Aldrich 99+%), CoF (Aldrich, 98%), and p-
3
F
toluoyl chloride (Aldrich, 98%). Starting complexes CpCo(R )(I)-
CO) (Cp = η -cyclopentadienyl; R = CF3 and CF CF ) were
Scheme 8. Reactivity of Cobalt(III) Difluorocarbenes
5
F
(
2 3
synthesized according to slightly modified literature procedures from
5
CpCo(CO) . From these complexes, facile substitution of the CO
2
ligands provided the phosphine analogues according to a slightly
6
modified literature procedure. (See the Supporting Information for
1
19
19
1
complete details on isolation of these complexes.) H, F, F{ H},
and 31P{ H} NMR spectra were recorded on either a 300 MHz Bruker
Avance or 300 MHz Bruker Avance II spectrometer at room
1
1
temperature. H NMR spectra were referenced to the residual proton
F
DOI: 10.1021/jacs.5b12003
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
peaks associated with the deuterated solvents (C D = 7.16 ppm,
CpCo(CF )(F)(PPh Me) (6). Yield: 198 mg, 83% based on CpCo-
6
6
3
2
19
19
1
CDCl = 7.26 ppm, CD CN = 1.94 ppm). F and F{ H} NMR
(CF )(I)(PPh Me). UV−vis (0.5 mM in CH Cl ) λ (ε) = 450
3
3
3
2
2
2
max
1
2
spectra were referenced to internal 1,3-bis(trifluoromethyl)benzene
BTB) (Aldrich, 99%, deoxygenated by purging with nitrogen and
(1640), 604 (347). H NMR (300 MHz, C D ) δ 1.57 (d, J ≈ 13
Hz, 3H, CH ), 4.60 (s, 5H, Cp), 7.05 (m, 6H, m- and p-CH(PPh)),
6
6
HP
(
3
31
1
3
3
19
stored over 4 Å molecular sieves), set to −63.5 ppm. P{ H} NMR
7.52 (dt, J ≈ 8 Hz, J ≈ 78 Hz, 4H, o-CH(PPh)). F NMR (282
HH
HP
3
spectra were referenced to external H PO (85% aqueous solution),
MHz, C D ) δ −3.3 (d, J ≈ 9 Hz, 3F, CF ), −716 (br, ω ≈ 1300
3
4
6
6
FF
3
1/2
set to 0.0 ppm. The 19F NMR signals corresponding to the different
Hz, 1F, Co−F). P{ H} NMR (121 MHz, C D ) δ 33.7 (br, ω
31 1
≈
6
6
1/2
[
Co]−CF CF complexes are labeled as A and A′. For labeling
130 Hz). Elemental analysis for C H F PCo Calcd: C, 55.36; H,
2
3
19 18 4
information, see Figure S24. Assignments were derived from 2D
4.40. Found: C, 54.98; H, 4.69.
CpCo(CF CF )(F)(PPh ) (7). Yield: 277 mg, 91% based on
experiments with CpCo(CF CF )(CF )(PPh Me) and applied to the
2
3
3
2
2
3
3
other complexes because instrumental constraints did not permit the
CpCo(CF CF )(I)(PPh ). UV−vis (0.5 mM in CH Cl ) λmax(ε) =
2
3
3
2
2
1
same experiments to be undertaken with the various fluoride
473 (1420), 621 (340). H NMR (300 MHz, CDCl ) δ 4.61 (s, 5H,
3
A
complexes. Throughout this manuscript, F refers to the more upfield
Cp), 7.40 (m, 6H, m- and p-CH(PPh)), 7.79 (m, 4H, o-CH(PPh)).
A
19
2
A A
resonance and F ′ refers to the more downfield resonance. UV−vis
F NMR (282 MHz, CDCl ) δ −68.6 (d, J ≈ 240 Hz, 1F, CF F ′;
3
FF
A
4
3
3
spectra were recorded on a Cary 100 instrument, using sealable quartz
cuvettes (1.0 cm path length). Elemental analyses were performed by
F ′), −79.8 (d, J ≈ 10 Hz, 3F, CF ), −81.0 (ddd, J ≈ 8 Hz, J
FF
3
FF
FP
A A A
≈ 46 Hz, 1F, CF F ′; F ), −759 (br, ω ≈ 1000 Hz, 1F, Co−F).
1
/2
́
31
1
the Laboratoire d’Analyse Elem
́
entaire de l’Universite
́
de Montrea
́
l
P{ H} NMR (121 MHz, CDCl ) δ 26.3 (br, ω ≈ 95 Hz).
3
1/2
(
Montreal, Quebec, Canada) and the G. G. Hatch Stable Isotope
́
́
Elemental analysis for C H F PCo Calcd: C, 57.27; H, 3.84. Found:
25
20 6
Laboratory at the University of Ottawa (Ottawa, Ontario, Canada). A
Micromass Q-ToF 1 (positive mode) was used for electrospray
ionization (ESI), with samples diluted to ca. 5 μg/mL in methanol.
Infrared spectroscopy was carried out on a Thermo Nicolet NEXUS
C, 55.93; H, 3.97.
CpCo(CF CF )(F)(PPh Me) (8). Yield: 268 mg, 68% based on
2
3
2
CpCo(CF CF )(I)(PPh Me). UV−vis (0.25 mM in CH Cl ) λ (ε)
2
3
2
2
2
max
1
2
=
461 (3140), 605 (680). H NMR (300 MHz, C D ) δ 1.51 (d, J
6 6 HP
6
70 FTIR instrument. Powder X-ray diffraction (PXRD) experiments
≈
13 Hz, 3H, CH ), 4.60 (s, 5H, Cp), 7.07 (m, 6H, m- and p-
3
were performed using a RIGAKU Ultima IV, equipped with a Cu Kα
radiation source (λ = 1.541836 Å), and a graphite monochromator.
Scanning of the 2θ range was performed from 5 to 40°. PXRD pattern
was consistent in 2θ values with the generated pattern from XRD, with
slight discrepancies in some intensities of peaks attributed to preferred
crystallite orientation.
3
3
19
CH(PPh)), 7.45 (dt, J ≈ 7 Hz, J ≈ 55 Hz, 4H, o-CH(PPh)).
F
HH
HP
2
A
A
A
NMR (282 MHz, C D ) δ −70.8 (d, J ≈ 248 Hz, 1F, CF F ′; F ′),
6
6
FF
4
3
−
79.7 (d, J ≈ 12 Hz, 3F, CF ), −80.7 (dd, J ≈ 43 Hz, 1F,
FF
3
FP
A A A 31 1
CF F ′; F ), −734 (br, ω ≈ 900 Hz, 1F, Co−F). P{ H} NMR
1/2
(
121 MHz, C D ) δ 31.9 (br, ω ≈ 130 Hz). Elemental analysis for
6
6
1/2
C H F PCo Calcd: C, 51.97; H, 3.93. Found: C, 51.45; H, 4.06.
2
0
18 6
F
F
General Procedure for the Synthesis of CpCo(R )(F)(L) (R =
F
General Procedure for the Synthesis of CpCo(R )(CF )-
3
CF or CF CF ; L = PPh or PPh Me). A 100 mL round-bottomed
Schlenk flask was charged with CpCo(R )(I)(L) (0.58 mmol)
dissolved in CH Cl (ca. 15 mL). AgF (1.74 mmol) was added, and
F
F
3
2
3
3
2
(PPh Me) (R = CF3 or CF CF ). CpCo(R )(I)(PPh Me) (0.877
2 2 3 2
F
mmol) was dissolved in DMF (15 mL), and CsF (2.63 mmol) was
added as a solid. The resulting solution was stirred at room
temperature for 5 min. To this solution was added dropwise Me SiCF
2
2
the resulting solution/suspension was stirred at room temperature for
approximately 20 h in the absence of light. After this time, a color
change to dark green was observed. The resulting mixture was filtered
through a plug of Celite, and the volatiles were removed in vacuo. The
crude product was recrystallized from a concentrated solution of
3
3
(4.22 mmol) in toluene (5 mL) over 3 min, and the reaction was
stirred at room temperature for approximately 3 h. During this time,
the color of the reaction mixture changed from dark green to bright
orange. The mixture was then filtered through a pad of Celite, washed
with ∼10 mL of toluene, and the filtrate was evaporated under vacuum
to dryness. The resulting residue was triturated with DEE (4 × 10
mL). The orange solid was dissolved in minimal toluene and mounted
on a silica-gel column. DEE was used as the eluent and pushed
through the column until the washings were clear. The solvent was
again removed under vacuum to afford pure product as a yellow-
orange powder. Crystals suitable for X-ray crystallography were
obtained from a concentrated solution of the appropriate complex in
toluene cooled to −35 °C.
CH Cl2 and hexanes at −35 °C. Pure product was collected via
2
filtration, washed with cold (−35 °C) hexanes, and dried in vacuo. The
products were obtained as dark-green powders. Crystals suitable for X-
ray crystallography were obtained by diffusion of hexanes into a
concentrated solution of the appropriate complex in toluene.
Complexes 5 and 7 were not viable for elemental analysis
(
approximately 1−2% off) because we suspect a small amount of
unidentified paramagnetic impurity. The latter also potentially
contributes to the broadness of the 1H NMR spectra for these
complexes. The use of various solvents and variable temperature NMR
were unsuccessful in diminishing the broadening. Sublimation,
additional recrystallizations, and column chromatography were
attempted to try and purify these complexes. Column chromatography
with a solvent mixture of THF/MeOH (8:2), followed by
recrystallization from a concentrated solution of toluene proved
most effective, but a small amount of impurity was retained.
Additionally, THF inserts within the crystal lattice and cannot be
CpCo(CF ) (PPh Me) (9). Yield: 231 mg, 57% based on CpCo-
3
2
2
(
(
CF )(I)(PPh Me). UV−vis (0.5 mM in CH Cl ) λmax(ε) = 388
3
2
2
2
1
1335), 430 (shoulder of the principal band). H NMR (300 MHz,
2
C D ) δ 1.70 (d, J ≈ 11 Hz, 3H, CH ), 4.63 (s, 5H, Cp), 7.01 (m,
6
6
HP
3
19
6
H, m- and p-CH(PPh)), 7.34 (m, 4H, o-CH(PPh)). F NMR (282
3
31
1
MHz, C D ) δ 3.6 (d, J ≈ 3 Hz, 6F, CF ). P{ H} NMR (121
6
6
FP
3
MHz, C D ) δ 40.3 (br, ω ≈ 150 Hz). Elemental analysis for
6
6
1/2
C H F PCo Calcd: C, 51.97; H, 3.93. Found: C, 51.83; H, 3.99.
2
0
18 6
−3
removed under high vacuum (ca. 10 mtorr), even with heating. As
such, PXRD patterns were compared with the calculated pattern from
XRD in order to confirm the bulk-phase purity of complex 7 (Figure
S37). The patterns were in excellent agreement with one another, thus
confirming the crystalline-phase purity of the sample. The same
comparison with complex 5 was unsuccessful because of the presence
of solvent within the unit cell of the crystallographic data.
CpCo(CF CF )(CF )(PPh Me) (10). Yield: 235 mg, 52% based on
2
3
3
2
CpCo(CF CF )(I)(PPh Me). UV−vis (0.75 mM in CH Cl ) λmax(ε)
2
3
2
2
2
1
=
375 (730), 450 (shoulder of the principal band). H NMR (300
2
MHz, CD CN) δ 1.69 (d, J ≈ 11 Hz, 3H, CH ), 4.67 (s, 5H, Cp),
3
HP
3
3
3
6
.99 (m, 6H, m- and p-CH(PPh)), 7.31 (dt, J ≈ 9 Hz, J ≈ 40
HH
HP
19
Hz, 4H, o-CH(PPh)). F NMR (282 MHz, CD CN) δ 5.2 (m, 3F,
3
2
3
A
A
A
Co−CF ), −62.3 (dd, J ≈ 258 Hz, J ≈ 16 Hz, 1F, CF F ′; F ′),
3
FF
FP
CpCo(CF )(F)(PPh ) (5). Yield: 245 mg, 89% based on CpCo(CF )-
2
A A
3
3
3
−80.7 (m, 3F, Co−CF CF ), −82.9 (dm, J ≈ 258 Hz, 1F, CF F ′;
2
3
FF
(
(
I)(PPh ). UV−vis (1.0 mM in CH Cl ) λmax(ε) = 459 (1190), 615
A 31 1
3
2
2
F ). P{ H} NMR (121 MHz, CD CN) δ 37.2 (br, ω ≈ 140 Hz).
3
1/2
1
263). H NMR (300 MHz, C D ) δ 4.60 (s, 5H, Cp), 6.98 (m, 6H,
m- and p-CH(PPh)), 7.89 (m, 4H, o-CH(PPh)). F NMR (282 MHz,
6
6
Elemental analysis for C H F PCo Calcd: C, 49.24; H, 3.54. Found:
21 18 8
19
C, 49.16; H, 3.70.
General Procedure for the Determination of NMR Yields in
3
C D ) δ −2.0 (d, J ≈ 8 Hz, 3F, CF ), −734 (br, ω ≈ 1900 Hz,
6
6
FF
3
1/2
31
1
F
F
1
F, Co−F). P{ H} NMR (121 MHz, C D ) δ 29.8 (br, ω ≈ 65
6
6
1/2
the Formation of [CpCo(R )(CF )(PPh Me)](X) (R = CF or
CF CF ; X = OTf or [FB(C F ) ] ) and the Products Derived
2 3 6 5 3
2
2
3
−
−
Hz). Elemental analysis for C H F PCo Calcd: C, 60.77; H, 4.25.
24
20
4
Found: C, 58.73; H, 4.36.
from These Intermediates. Note that as the difluorocarbene
G
DOI: 10.1021/jacs.5b12003
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Journal of the American Chemical Society
Article
complexes form they react either with any trace quantities of water
present (immediately) or in an insertion reaction (over a period of
several hours). Furthermore, the reactions involving the difluor-
Hz, 1F, Co−CF CF CF ), −116.8 (d, 2JFF = 282 Hz, 1F, Co−
2
2
3
CF CF CF ). MS [ESI (positive mode), solvent: MeOH] Calcd m/z
2
2
3
+
(% intensity) for [CpCo(CF CF CF )(PPh Me) ]: 493.04 (100),
2
2
3
2
ocarbene intermediates occur more quickly when using Me SiOTf as
494.04 (23), 495.05 (3). Found: 493.04 (100), 494.04 (24). Calcd m/
3
+
compared to B(C F ) . Because of the enhanced stability of the
z (% intensity) for [CF CF CF ]: 168.99 (100), 169.99 (3). Found:
6
5
3
3
2
2
difluorocarbenes formed by using B(C F ) , yields for these complexes
168.99 (100), 169.99 (3).
6
5 3
are reported for a certain reaction time. Because of the nature of these
reactions, yields for the products deriving from the reactions with
water and the insertion reactions will be presented for an elapsed
[CpCo(CF )(CO)(PPh Me)][FB(C F ) ] (from Int 3). Yield: 60%
3 2 6 5 3
19
based on CpCo(CF ) (PPh Me) after 4 h. F NMR (282 MHz,
3
2
2
3
CH Cl with C D capillary) δ 12.1 (d, J = 4 Hz, 3F, Co−CF ).
2
2
6
6
FP
3
3
1
1
reaction time with Me SiOTf and when possible with B(C F ) .
3
6
5
3
P{ H} NMR (121 MHz, CH
ω1/2 ≈ 60 Hz).
CpCo(CF CF )(FB(C F ) )(PPh Me) (from Int 3). Yield: 35% based
2
Cl
2
with C
6
D
6
capillary) δ 33.0 (br,
F
Method A. CpCo(R )(CF )(PPh Me) (0.043 mmol) was dissolved
3
2
in DCM (0.8 mL), and BTB (0.043 mmol) was added. The solution
2
3
6
5 3
2
was transferred to an NMR tube, and Me SiOTf (0.043 mmol) was
19
3
on CpCo(CF ) (PPh Me) after 4 h. F NMR (282 MHz, CH Cl
3
2
2
2
2
added with a microliter syringe. The NMR tube was sealed and shaken
vigorously. The 19F NMR yields were determined by integration of
signals with respect to BTB. Complete conversion of starting material
was observed within 60 min.
2
3
with C D capillary) δ −76.7 (dd, J ≈ 251 Hz, J ≈ 14 Hz, 1F,
6
6
FF
FP
A
A
A
2
CF F ′; F ′), −80.5 (br, 3F, Co−CF CF ), −86.6 (dd, J ≈ 251 Hz,
2
3
FF
3
A
A
A
31
1
J
≈ 35 Hz 1F, CF F ′; F ). P{ H} NMR (121 MHz, CH Cl with
FP
2
2
C D capillary) δ 25.2 (br, ω ≈ 96 Hz).
F
6
6
1/2
Method B. CpCo(R )(CF )(PPh Me) (0.043 mmol) was dissolved
3
2
[
CpCo(CF CF )(CO)(PPh Me)][FB(C F ) ] (from Int 4). Yield and
2 3 2 6 5 3
in DCM (0.4 mL), and BTB (0.043 mmol) was added. The solution
was transferred to an NMR tube, and a solution of B(C F ) (0.043
NMR assignments could not be obtained because of peak overlap.
6
5 3
CpCo(CF CF CF )(FB(C F ) )(PPh Me) (from Int 4). Yield: 10%
2
2
3
6
5 3
2
mmol) in DCM (0.4 mL) was added. The NMR tube was sealed and
based on Co−CF CF CF after 24 h. Only the F signals of the
1
9
2
2
3
β
shaken vigorously. The F NMR yields were determined by
integration of signals with respect to BTB. Complete conversion of
starting material was observed within 30 min.
perfluoropropyl fragment could be assigned with certainty because of
19
peak overlap. F NMR (282 MHz, CH Cl with C D capillary) δ
2
2
6
6
2
2
CpCo(CF )(CF )(PPh Me)][OTf] (Int 1). 19F NMR (282 MHz,
−112.6 (d, J
FF = 284 Hz, 1F, Co−CF
Hz, 1F, Co−CF CF CF ).
General Procedure for the Catalytic Formation of p-Toluoyl
Fluoride. The formation of p-toluoyl fluoride could be easily
established by the growth of a sharp singlet at δ( F) = 16.5 ppm.
The only other signals observed via F NMR were a mixture of
2
CF
2
CF ), −114.3 (d, JFF = 284
3
[
3
2
2
2
2
3
CH Cl with C D capillary) δ 180.0 (br, 2F, CoCF ), 9.0 (br, Co−
2
2
6
6
2
−
31
1
CF ), −78.9 (br, 3F, CF SO ). P{ H} NMR (121 MHz, CH Cl
3
3
3
2
2
with C D capillary) δ 40.1 (br, ω ≈ 136 Hz).
19
6
6
1/2
[
CpCo(CF CF )(CF )(PPh Me)][OTf] (Int 2). Yield: 68% based on
Co = CF after 30 min (20% after 4 h). F NMR (282 MHz, CH Cl
2
19
2
3
2
2
19
2
2
2
CpCo(CF )(Cl)(PPh Me) and CpCo(CF )(F)(PPh Me) (6). Yields
3 2 3 2
with C D capillary) δ 179.5 (br, 2F, CoCF ), −58.4 (d, J ≈ 228
6
6
2
FF
A
A
A
2
3
for the formation of the target compound were established by
integration to BTB. See Table 1 for yields and selected control
experiments and Table S16 for a full list.
Control Reactions with Various Fluoride Sources. To 0.8 mL
of DCM in a vial was added AgF (92 mg, 0.72 mmol), CsF (110 mg,
0.72 mmol), KF (42 mg, 0.72 mmol), or CoF (84 mg, 0.72 mmol).
3
To this suspension were added p-toluoyl chloride (32 μL, 0.24 mmol)
and BTB (18.6 μL, 0.12 mmol). The reaction was stirred vigorously
Hz, 1F, CF F ′; F ′), −75.3 (dd, J ≈ 228 Hz, J ≈ 36 Hz 1F,
FF
FP
A
A
A
31
1
CF F ′; F ), −80.9 (br, 3F, Co−CF CF ). P{ H} NMR (121 MHz,
2
3
CH Cl with C D capillary) δ 35.6 (br, ω ≈ 142 Hz).
2
2
6
6
1/2
19
[
CpCo(CF )(CF )(PPh Me)][FB(C F ) ] (Int 3). F NMR (282
3
2
2
6 5 3
MHz, CH Cl with C D capillary) δ 178.8 (br, 2F, CoCF ), 9.4
2 2 6 6 2
3
(
(
br, Co−CF ), −134.4 (d, br, J ≈ 18 Hz, 6F, FB(o-C F ) ), −159.1
3
FF
6 5 3
s, br, 3F, FB(o-C F ) ), −165.8 (m, br, 6F, FB(m-C F ) ), −188.8 (s,
6
5
3
6 5 3
3
1
1
br, 1F, FB(C F ) ). P{ H} NMR (121 MHz, CH Cl with C D
6
5
3
2
2
6
6
(
in the absence of light in the case of AgF) for 16 h and then
capillary) δ 37.6 (br, ω1/2 ≈ 136 Hz).
transferred to an NMR tube with a C D capillary.
6
6
[
CpCo(CF CF )(CF )(PPh Me)][FB(C F ) ] (Int 4). Yield: 75%
2
3
2
2
6 5 3
19
Catalytic Reactions with Varying Catalyst Loadings. A stock
solution (0.0152 M) was prepared for the reactions involving 5, 1, and
0.1 mol % CpCo(CF )(I)(PPh Me) (2). The complex (40 mg, 0.076
based on CoCF after 30 min (60% after 4 h). F NMR (282
2
4
MHz, CH Cl with C D capillary) δ 178.2 (t, br, J ≈ 7 Hz, 2F,
2
2
6
6
FF
2
A
A
A
CoCF ), −57.2 (dm, J ≈ 225 Hz, 1F, CF F ′; F ′), −74.6 (dd,
3
2
2
FF
2
3
A
A
A
mmol) was dissolved in DCM (5 mL), affording a dark-yellow-brown
solution.
J
≈ 225 Hz, J ≈ 35 Hz 1F, CF F ′; F ), −80.8 (br, 3F, Co−
FF
FP
31 1
CF CF ), −189.0 (s, br, 1F, FB(C F ) ). P{ H} NMR (121 MHz,
2
3
6 5 3
1
0 mol % Loading. CpCo(CF )(I)(PPh Me) (2) (13 mg, 0.024
3 2
CH Cl with C D capillary) δ 37.5 (br, ω ≈ 148 Hz).
2
2
6
6
1/2
mmol) was added to a vial, along with AgF (92 mg, 0.72 mmol) and
DCM (0.8 mL). To this dark-yellow-brown solution were added p-
toluoyl chloride (32 μL, 0.24 mmol) and BTB (18.6 μL, 0.12 mmol).
The reaction was stirred vigorously (in the absence of light) for 4 h
and then transferred to an NMR with a C D capillary.
Analysis of the Proposed Products Derived from Int 1−4 by
F NMR and Mass Spectrometry. [CpCo(CF )(CO)(PPh Me)][OTf]
1
9
3
2
19
(
(
−
from Int 1). Yield: 14% based on Co−CF after 60 min. F NMR
3
282 MHz, CH Cl with C D capillary) δ 2.79 (br, 3F, Co−CF ),
2
2
6
6
3
−
31
1
78.3 (br, 3F, CF SO ). P{ H} NMR (121 MHz, CH Cl with
6
6
3
3
2
2
−1
5 mol % Loading. CpCo(CF )(I)(PPh Me) (2) (0.79 mL, 0.012
C D capillary) δ 35.8 (br, ω ≈ 75 Hz). IR: 2241 cm (s, br, Co−
CO).
CpCo(CF CF )(OTf)(PPh Me) (from Int 1). Yield: 18% based on
3 2
6
6
1/2
mmol) was added to a vial, along with AgF (92 mg, 0.72 mmol). To
this dark-yellow-brown solution were added p-toluoyl chloride (32 μL,
0.24 mmol) and BTB (18.6 μL, 0.12 mmol). The reaction was stirred
vigorously (in the absence of light) for 4 h and then transferred to an
NMR with a C D capillary.
2
3
2
19
Co−CF CF after 60 min. F NMR (282 MHz, CH Cl with C D
2
3
2
2
6
6
2
A
A
A
capillary) δ −74.7 (dm, J ≈ 247 Hz, 1F, CF F ′; F ′), −78.1 (br,
FF
−
2
3
F, CF SO ), −80.3 (br, 3F, Co−CF CF ), −83.9(dd, J ≈ 247
6
6
3
3
2
3
FF
3
A
A
A
31
1
1
mol % Loading. CpCo(CF )(I)(PPh Me) (2) (0.16 mL, 0.0024
Hz, J ≈ 30 Hz 1F, CF F ′; F ). P{ H} NMR (121 MHz, CH Cl
3 2
FP
2
2
mmol) was added to a vial, along with AgF (92 mg, 0.72 mmol) and
DCM (0.64 mL). To this pale-yellow-brown solution were added p-
toluoyl chloride (32 μL, 0.24 mmol) and BTB (18.6 μL, 0.12 mmol).
The reaction was stirred vigorously (in the absence of light) for 4 h
with C D capillary) δ 30.0 (br, ω ≈ 97 Hz). MS [ESI (positive
6
6
1/2
mode), solvent: MeOH] Calcd m/z (% intensity) for [CpCo-
+
(
CF CF )(PPh Me) ] 443.04 (100), 444.04 (22), 445.05 (2).
2 3 2
Found: 443.04 (100), 444.04 (23).
CpCo(CF CF )(CO)(PPh Me)][OTf] (from Int 2). Yield and NMR
[
and then transferred to an NMR with a C
0.1 mol % Loading. To 0.8 mL of DCM in a vial was added
CpCo(CF )(I)(PPh Me) (2) (79 μL, 0.0012 mmol) and AgF (92 mg,
6 6
D capillary.
2
3
2
assignments could not be obtained because of peak overlap. IR: 2243
−1
cm (s, br, Co−CO).
3
2
CpCo(CF CF CF )(OTf)(PPh Me) (from Int 2). Yield: 13% based on
0.72 mmol). To this pale-yellow-brown solution were added p-toluoyl
chloride (32 μL, 0.24 mmol) and BTB (18.6 μL, 0.12 mmol). The
reaction was stirred vigorously (in the absence of light) for 4 h and
then transferred to an NMR with a C D capillary.
2
2
3
2
Co−CF CF CF after 4 h. Only the F signals of the perfluoropropyl
2
2
3
β
19
fragment could be assigned with certainty because of peak overlap.
NMR (282 MHz, CH Cl with C D capillary) δ −115.1 (d, J = 282
F
2
2
2
6
6
FF
6
6
H
DOI: 10.1021/jacs.5b12003
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
Larichev, R. B.; Smith, J. M.; Ward, A. J.; Willemsen, S.; Zhang, D.;
DiPasquale, A. G.; Zakharov, L. N.; Rheingold, A. L. Organometallics
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.5b12003.
■
*
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optimized Cartesian coordinates in Å, H, F and
31
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P{ H} NMR spectra, IR spectra, and powder X-ray
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(
Crystallographic information file for compound 5. (CIF)
Crystallographic information file for compound 6. (CIF)
Crystallographic information file for compound 7. (CIF)
Crystallographic information file for compound 8. (CIF)
Crystallographic information file for compound 9. (CIF)
Crystallographic information file for compound 10.
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AUTHOR INFORMATION
Corresponding Author
rbaker@uottawa.ca
■
*
(13) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter
Mater. Phys. 1988, 37, 785−789.
(14) Perdew, J. P.; Wang, Y. Phys. Rev. B: Condens. Matter Mater.
Phys. 1992, 45, 13244−13249.
Notes
(15) Burke, K.; Perdew, J. P.; Wang, Y. In Electronic Density
The authors declare no competing financial interest.
Functional Theory: Recent Progress and New Directions; Dobson, J. F.,
Vignale, G., Das. M. P., Eds.; Plenum: New York, 1998.
ACKNOWLEDGMENTS
■
(
16) (a) Dugan, T. R.; Sun, X.; Rybak-Akimova, E. V.; Olatunji-Ojo,
O.; Cundari, T. R.; Holland, P. L. J. Am. Chem. Soc. 2011, 133, 12418−
2421. (b) Dugan, T. R.; Goldberg, J. M.; Brennessel, W. W.; Holland,
P. L. Organometallics 2012, 31, 1349−1360.
(17) Li, X.; Sun, H.; Yu, F.; Florke, U.; Klein, H.-F. Organometallics
2006, 25, 4695−4697.
We thank the NSERC and the Canada Research Chairs
program for generous financial support and the University of
Ottawa, Canada Foundation for Innovation, and Ontario
Ministry of Economic Development and Innovation for
essential infrastructure. Dr. Glenn Facey is thanked for helpful
discussions and assistance with NMR experiments. Rebecca
Holmberg is thanked for PXRD experiments. M.C.L., J.M.B.,
and G.M.L. gratefully acknowledge support from NSERC. A
portion of the computational work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, U.S. Department of Energy
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J. Am. Chem. Soc. XXXX, XXX, XXX−XXX