Systematic Study of the Stereoelectronic Properties of Trifluoromethylated Triarylphosphines and the Correlation of their Behaviour as Ligands in the Rh-Catalysed Hydroformylation

Article abstract of DOI:10.1002/ejic.202000887

The stereoelectronic properties of a series of trifluoromethylated aromatic phosphines have been studied using different approaches. The σ-donating capability has been evaluated by nuclear magnetic resonance (NMR) spectroscopy of the selenide derivatives and the protonated form of the different trifluoromethylated phosphines. The coupling constants between phosphorous and selenium (¹J_SeP) and phosphorous and hydrogen (¹J_HP) can be predicted by empirical equations and correlate the basicity of the phosphines with the number and relative position of trifluoromethyl groups. In contrast, the π-acceptor character of the ligands has been evaluated by measuring the frequency of the CO vibration in the infrared (IR) spectra of the corresponding Vaska type iridium complexes ([IrCl(CO)(PAr₃)₂], PAr₃=triarylphosphine). Moreover, the correlation between the electronic properties and the performance of these phosphines as ligands in the rhodium-catalysed hydroformylation of 1-octene has been established. Phosphines with the lowest basicity, that are those with the highest number of trifluoromethyl groups, gave rise to more active catalytic systems.

Full text of DOI:10.1002/ejic.202000887

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Systematic Study of the Stereoelectronic Properties of
Trifluoromethylated Triarylphosphines and the Correlation
of their Behaviour as Ligands in the Rh-Catalysed
Hydroformylation
Daniel Herrera+,[a] Daniel Peral+,[a] Mercedes Cordón,[a] and J. Carles Bayón*[a]
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In loving memory of Dr. Julio Real
The stereoelectronic properties of a series of trifluorometh-
ylated aromatic phosphines have been studied using different
approaches. The σ-donating capability has been evaluated by
nuclear magnetic resonance (NMR) spectroscopy of the selenide
derivatives and the protonated form of the different
trifluoromethylated phosphines. The coupling constants be-
tween phosphorous and selenium (1JSeP) and phosphorous and
hydrogen (1JHP) can be predicted by empirical equations and
correlate the basicity of the phosphines with the number and
relative position of trifluoromethyl groups. In contrast, the π-
acceptor character of the ligands has been evaluated by
measuring the frequency of the CO vibration in the infrared (IR)
spectra of the corresponding Vaska type iridium complexes
([IrCl(CO)(PAr3)2], PAr3 =triarylphosphine). Moreover, the correla-
tion between the electronic properties and the performance of
these phosphines as ligands in the rhodium-catalysed hydro-
formylation of 1-octene has been established. Phosphines with
the lowest basicity, that are those with the highest number of
trifluoromethyl groups, gave rise to more active catalytic
systems.
Introduction
groups (i.e. alkylphosphines) behave as strong bases and thus
have a marked σ-donating behaviour. The same reasoning
applies to phosphines substituted with electron-withdrawing
groups, which are weaker σ-donating ligands. Direct spin-spin
coupling constant in organophosphorus selenides has been
reported as a simple and straightforward manner to evaluate
the σ-donation ability of phosphorus ligands.[2-4] Allen and
The stereoelectronic properties of phosphines can be easily
tuned by using different substituents on the phosphorus atom,
which make them highly versatile ligands. Therefore, phos-
phines have become one of the most important ligands in
coordination chemistry and, particularly, in homogenous catal-
ysis. Trifluoromethylated triarylphosphines have been widely
used as ligands in different catalytic transformations showing
improved catalytic activity and selectivity.[1] The electron-with-
drawing effect of the trifluoromethyl groups on the aromatic
rings of the phosphines decreases the basicity of the ligand
and, as a result, also the electron density provided to the metal
centre. Consequently, the rate of the different steps of a given
catalytic cycle might change, affecting the activity and
selectivity of the reaction.
Two contributors are normally considered when referring to
the electronic properties of phosphines as ligands: the σ-donor
(σ-basicity) and the π-acceptor (π-acidity) character. The σ-
donation ability of a phosphine is related to its capability to
donate the lone pair of the P atom to, for instance, coordinate a
metal atom or to bond a heteroatom, such as oxygen or
selenium. Phosphines substituted with electron-donating
1
Taylor observed that the value of the JPSe in phosphine
selenides increased when introducing electro-withdrawing
groups bonded to the phosphorus atom.[2] These observations
were attributed to an increase in the s character of the
phosphorus lone pair in agreement with Bent’s rule.[5] The
opposite effect was reported with electron-donating or bulky
substituents. X-ray diffraction structures of some phosphine
selenides have shown shorter PÀ Se distances in trifluorometh-
ylated triarylphosphines with respect to triphenylphosphine.[6]
1
Moreover, good correlation between the JPSe in phosphine
selenides and the PÀ Se distance or the Brønsted basicity of the
corresponding phosphines has been reported[3,4]. Deviation of
this trend, though, was observed in phosphines containing
bulky substituents. Another strategy to measure the σ-donation
capability of a phosphine is the coupling constant between the
phosphorous and the proton of protonated phosphines by
NMR spectroscopy. For this technique, quantitative protonation
of the phosphines is required. In this sense, Pestovsky et al.[7]
reported full protonation of arylphosphines in 1.5 M solutions
of CF3SO3H in H2O/CH3CN. Complete protonation of phosphines
in sulfuric acid, fluorosulfuric acid or trifluoroacetic acid has also
[a] Dr. D. Herrera,+ Dr. D. Peral,+ M. Cordón, Prof. J. C. Bayón
Department of Chemistry
Universitat Autònoma de Barcelona
Building C, Faculty of Sciences, 08193 Cerdanyola del Vallés, Spain
E-mail: joancarles.bayon@uab.cat
1
been reported in the literature with similar values of JPH for
[+] Both authors contributed equally to this work
triphenylphosphine.[8] Correlation between the magnitude of
the one-bond H-P coupling constant (1JHP) and the basicity of
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202000887
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protonated phosphines and phosphites has been previously
catalytic processes at industrial level. Trivalent phosphorus
compounds are, by far, the most used ligands in the Rh-
catalysed hydroformylation. A variety of phosphorus ligands
have been described in the literature, especially phosphines or
phosphites, either monodentate or chelating.[16,17] The positive
effect of using triarylphosphines containing electron-withdraw-
ing groups, such as trifluoromethyls, has been widely acknowl-
edged for monophosphines as well as for diphosphines.[18,19,20]
Although the rate-determining step in the rhodium-phosphine-
catalysed hydroformylation strongly depends on the reaction
conditions, it has been generally accepted that under standard
conditions the rate of the reaction is determined in the first
stages of the catalytic cycle. This includes the dissociation of
CO, the coordination of the alkene substrate and the migratory
insertion of the olefin into the RhÀ H bond.[21,22] Gleich and
Hutter showed that the olefin coordination becomes thermody-
namically more favourable when decreasing the basicity of the
phosphine ligand,[22] which would explain the enhanced
performance of the hydroformylation with the electron poor
trifluoromethylated phosphines. The π-accepting features of
these ligands would also decrease the back-donation of the
rhodium to CO ligand, thus weakening the Rh-CO bond and
facilitating the CO dissociation.
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reported, showing larger values of the 1JHP when decreasing the
basicity of the phosphorus ligands.
In coordination chemistry, the π-acidity character of
phosphines is related to the ability of these ligands to accept
electron density from the metal atom. Although still a matter of
research,[9] it has been generally accepted that such electron-
backdonation takes place from the d-orbitals of the metal
centre to the empty σ*-orbitals of the phosphorus ligand, which
are of π-symmetry as the d metal orbital involved.[10,11]
Tolman studied the electron donor-acceptor properties of
different phosphorus ligands measuring the carbonyl A1
stretching frequency of Ni(CO)3L complexes in CH2Cl2.[12] In
analogy with the Ni-carbonyl complexes of Tolman, Vaska-type
complexes can also be used to determine the σ/π-bonding
characteristics of phosphines.[13] Vaska’s compound is the name
given to trans-carbonylchlorobis(triphenylphosphine)iridium(I),
(trans-[Ir(CO)Cl(PPh3)2]). Although it was firstly reported by
Angoletta,[14] its composition was correctly elucidated by Vaska
and DiLuzio two years later.[15] Currently, Vaska-type complexes
are considered those with the general formula trans-[M(CO)X
(L)2], where M can be either Rh or Ir, X is an halogen or
pseudohalogen and L refers to a neutral ligand.[13]
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The reaction of hydroformylation, which consists in the
addition of equimolar amounts of H2 and CO (syngas) to olefins
to form aldehydes, is one of the most employed homogeneous
In this work, a broad family of triarylphosphines containing
trifluoromethyl groups has been synthesised, Figure 1. In order
to cover a wide range of substitution pattern, five novel
Figure 1. Trifluoromethylated phosphines synthesised in this work.
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trifluoromethylated phosphines have been designed and
chlorophosphines after reaction with the corresponding
Grignard reagent followed by PÀ N cleavage.[25]
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synthesised (phosphines 5, 14, 15, 16 and 17 in Figure 1). The
effect produced by the number and relative position of the
trifluoromethyls in the stereoelectronic properties of the ligands
have been studied by 31P NMR of the selenides derivatives and
the protonated phosphines. These experiments have been
further compared to the υ(CO) stretching by FTIR of the
corresponding iridium Vaska’s complexes. Finally, the electronic
properties have been correlated with the catalytic performance
of the Rh/phosphine-catalysed hydroformylation reaction.
The characterization of the phosphines was carried out by
multinuclear NMR spectroscopy (1H, 13C, 19F and 31P), high
resolution mass spectrometry (HR-MS) and elemental analysis (C
and H) and is collected in the experimental section and the
supporting information (S1)
Crystals of good quality for single-crystal X-ray diffraction of
pF
phosphine PArmmFAr2 14 were obtained by slow precipitation
in CH2Cl2. ORTEP diagram and some selected distances and
angles are shown in Figure 2. Helix-like arrangement of the
phosphine is observed in 14, as expected for a triarylphosphine.
Values of PÀ C distances and CÀ P-C angles were also found
within the expected values.
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Results and Discussion
Synthesis of the trifluoromethylated phosphines
The phosphines prepared in this work (Figure 1) have been
designed to cover all the possible monosubstitution patterns
(ortho: AroF, meta: ArmF and para: ArpF). Moreover, different
phosphines containing aromatic rings with double substitution
(meta-meta: ArmmF and ortho-para: AropF) and the combination of
two different patterns (meta-meta with meta and meta-meta
with para) have also been prepared. This way, the number and
the relative position of the electronwithdrawing trifluoromethyl
groups will be correlated with the stereoelectronic properties of
the phosphine ligands.
All the trifluoromethylated phosphines have been synthes-
ised by the corresponding reaction of the Grignard reagent or
organolithium derivative with phosphorous trichloride, or
aromatic chlorophosphines.[23,24] The Grignard reagent or the
organolithium derivative, prepared from the corresponding
trifluoromethylated bromo-aryl derivative with Mg or n-BuLi,
respectively, was reacted with a solution of PCl3, or the
corresponding arylchlorophosphine, in ethereal solvent, to yield
the trifluoromethylated triarylphosphine. It is important to
mention that, while the Grignard reagent was used to prepare
most of these phosphines, this type of reagents cannot be
applied to the bulkier ortho-substituted ones. In this case, the
phosphines are efficiently prepared through the organolithium
derivative.
Study of the electronic properties of the trifluoromethylated
phosphines
The σ-basicity and the π-acidity contributions of the
trifluoromethylated phosphines presented above have been
evaluated by the preparation and characterization of different
derivatives: phosphine selenides and protonated phosphines
(phosphonium ions) for the σ-basicity and the Vaska-type Ir(I)
complexes for the evaluation of the σ-basicity and π-acidity.
σ-Donating character: phosphine selenides and phosphonium
ions. The σ-donation ability of the phosphines was evaluated by
1
measuring the JPSe coupling in the 77Se (s=1/2, 7.63% natural
abundance) isotopomer of the corresponding phosphine
selenides. Given that the PÀ Se bond has a single-bond
character and has little double-bond contribution,[26] it can be
considered that the phosphine selenide coupling constant is
directly related to the σ-donor ability of the ligand. Therefore,
the selenide derivatives of the phosphines presented in this
work were synthesised using a straightforward methodology.
An excess of selenium black was added to 0.01 M solutions of
the different phosphines in deuterated chloroform and stirred
for 15 h at room temperature under inert atmosphere. The
excess of selenium was filtered off and the products were
While phosphines 1–4 and 6–13 were previously reported
in the literature, as far as we are concern, phosphines 5, 14, 15,
16 and 17 are firstly described in this paper. Phosphine 5 was
prepared from the reaction between the organolithium
trifluoromethylated derivative and chlordiphenylphosphine. The
new heteroleptic phosphines 14–17 were synthesised from the
reaction between the corresponding chloro- or dichloro-
trifluoromethylphenylphosphine
with
the
Grignard
trifluoromethylbenzene reagents. Two trifluoromethylated
chlorophosphines were therefore prepared using PCl3 as a
trivalent phosphorus precursor and the corresponding Grignard
reagents, which were added in a sequential way. The high
reactivity of PCl3 requires the protection of chlorine groups as
N,N-diethylphosphoramidous dichloride, Et2NPCl2, and N,N,N’,N’-
tetraethylphosphoro-diamidous chloride, (Et2N)2PCl. These com-
pounds were used to selectively form the trifluoromethylated
Figure 2. ORTEP plot (ellipsoid at 50% probability) of 14. Only one
orientation of the disordered CF3 groups is drawn. Aromatic H atoms
omitted for clarity. Distances (Å): P(1)-C(11)=1.834(3), P(1)-C(21)=1.834(3), P
°
(1)-C(31)=1.836(3). Angles( ): C(11)-P(1)-C(21)=101.9(1), C(11)-P(1)-C(31)
=102.3(1), C(21)-P(1)-C(31)=100.9(1).
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analysed by 31P{1H}. Alternatively, for the ortho-substituted
12 did not afford the corresponding selenide under the essayed
conditions. The steric hindrance around the P atom produced
by the three trifluoromethyl groups is thought to be respon-
sible for the inertness of this phosphine towards the formation
of the selenide. Figure 3 shows the 31P{1H} NMR spectrum of the
selenide of the homoleptic phosphine 13, as a representative
example, where it is possible to observe the doublet arising
from the coupling between 77Se and 31P.
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2
3
4
5
6
7
8
°
phosphines (3, 5 and 8), stirring at 50 C was preferred to obtain
the selenide quantitatively. The triply o-substituted phosphine
The protonated form of the full set of the trifluorometh-
ylated phosphines was prepared by dissolving 0.1 mmol of the
corresponding phosphine in 2 ml of concentrated sulfuric acid.
This time, the triply ortho-substituted phosphine 12 was also
reactive. Hydrogen, being a considerably smaller atom than
selenium, is able to bond the sterically hindered phosphorus
atom of this phosphine. Figure 4 shows the comparison of the
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31P and the 1H NMR spectra of the protonated form of
1
phosphine 12. Clear protonation of the phosphine with JHP
=
Figure 3. 31P{1H} (161.98 MHz) NMR spectrum of the selenide of phosphine
13 in CDCl3. δ in ppm. 1JSeP =801 Hz
550 Hz was observed. Due to the broadness of the signal in the
31P NMR produced by the coupling to hydrogen and fluorine
atoms, fine measurement of the coupling constant was
obtained from the 1H NMR spectra.
1
Values of JPSe of the selenides together with the1JHP of the
1
1
phosphoniums are collected in Table 1. Both JPSe and JHP are
cumulative in the whole series of the investigated phosphines
and follow the same trend: the higher the number of
trifluoromethyl groups, the greater the value of the coupling
constants.
1
1
Equations correlating the values of both JPSe and JHP with
the number and position of the trifluormethyl groups were
empirically developed, Eq. (1) and Eq. (2) respectively.
Figure 4. Left- 31P and 31P{1H} (161.98 MHz) NMR spectra of phosphine 12
(0.05 M) in H2SO4 conc. Signals relative to a solution of NH4PF6 (0.08 g/ml in
D2O) used as internal standard. Singlet indicated as * correspond to the
partial degradation of the internal standard. Right- 1H and 1H{31P} (400.13 Hz)
NMR spectra of 12 (0.05 M) in H2SO4 conc.
1JSeP ¼ 731 þ 12ðm=pÞ þ 22ðoÞ
(1)
1JHP ¼ 503 þ 9ðm=pÞ þ 16ðoÞ
(2)
1
1
were (m/p) are the number of trifluoromethyl groups in meta- or
para-positions and (o) are those groups in ortho-positions.
Table 1. Values of JPSe and JHP (Hz) for the corresponding selenides and
phosphonium ions, respectively, of the trifluoromethylated triarylphos-
phines
The selenide of the non-trifluoromethylated triphenylphos-
Number of CF3
Ligand
Selenide
Phosphonium
1
[a]
[b]
1JPSe
1JHP
phine showed a JSeP of 731 Hz (Table 1). The addition of one
trifluoromethyl group in either meta or para position produced
an increase of 12 Hz. In contrast, the effect of the groups in
ortho position was larger, increasing the coupling constant in
c
0
1
PPh3
731 (731)
742 (743)
742 (743)
753 (754)
755 (755)
765 (766)
753 (755)
756 (755)
755 (777)
766 (767)
767 (767)
-
779 (779)
778 (779)
781 (779)
791 (791)
791 (791)
801 (803)
503 (503)
510 (512)
512 (512)
521 (519)
520 (521)
529 (528)
519 (521)
520 (521)
538 (535)
527 (530)
528 (530)
550 (551)[c]
537 (539)
536 (539)
538 (539)
546 (548)
545 (548)
555 (557)
1 (PPh2ArpF)
2 (PPh2ArmF
3 (PPh2AroF)
4 (PPh2ArmmF
)
1
about 22 Hz. While the experimental JPSe for the ortho-
)
)
monosubstituted phosphine 3 and the ortho,para-substituted
phosphine 5 fitted Eq. (1), a large difference between the
experimental value and the calculated one was observed for
the ortho-disubstituted phosphine 8 (755 vs 777). This means
that the two trifluoromethyl groups in phosphine 8, because of
steric grounds, force a longer SeÀ P distance than the one
expected for pure electronic effects.
5 (PPh2AropF
)
pF
2
3
6 (PPhAr2
7 (PPhAr2
8 (PPhAr2
)
mF
)
oF
)
pF
10 (PAr3
11 (PAr3
12 (PAr3
9 (PPhAr2
)
)
mF
oF
)
mmF
pF
4
5
6
14 (PArmmFAr2
15 (PArmmFAr2
)
mF
1
The JHP of the protonated form of triphenylphosphine was
)
16 (PAr2mmFArpF)
503 Hz. In this case, one trifluoromethyl in meta or para position
increased 9 Hz the coupling constant, while those groups in
ortho positions added 18 Hz. Good agreement was found
between all the experimental values and those calculated using
the empirical Eq. (2). Even the bulkiest ortho-trisubstituted
17 (PAr2mmFArmF
)
mmF
13 (PAr3
)
[a] Values obtained from the 31P{1H} in CDCl3. See text for more details. [b]
Values obtained from the 31P NMR in conc. H2SO4. See text for more details.
[c] Determined from 1H NMR spectra. In brackets, calculated values from
Eq. (1) and Eq. (2).
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phosphine 12 matched the calculated value with a small
deviation.
Finally, excellent correlation was found between the
magnitude of the JPSe in the selenide and the JHP of the
corresponding phosphonium ions, with exception of the bis-
ortho-substituted phosphine 8, Figure 5.
σ/π-bonding character: Vaska-type Ir (I) complexes. Stretching
frequencies of coordinated CO ligands in metal complexes is a
common and simple probe to study the σ/π-bonding behaviour
of phosphines. The increased π-acidity of phosphorus ligands
substituted with more electron-withdrawing groups is clearly
observed by displacement of the CO frequency to higher
values. Electron-backdonation from the metal centre to these
acidic phosphorus ligands is increased as a result of their π-
acceptor ability. This effect reduces the electron density on the
metal centre and, as a consequence, decreases the back-
donation to the CO ligand, resulting in a shorter (stronger) CÀ O
distance, and hence in higher carbonyl frequencies.
Vaska’s analogue complexes of the formula trans-[Ir(CO)Cl
(L)2] with the trifluoromethylated phosphines were prepared
following the synthetic procedure previously described in our
group.[27] Also the Vaska’s compound (trans-[Ir(CO)Cl(PPh3)2])
was prepared for comparison purposes. Vaska-type complexes
of all the trifluoromethylated phosphines were successfully
prepared with exception of the ortho-substituted phosphine 12
which did not coordinate the metal and the bis-meta-
substituted phosphines 7 and 15 which could not be purified
by precipitation in diethyl ether, n-hexane, methanol, water or
combinations of them.
1
2
3
4
5
6
7
8
9
1
1
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11
12
13
14
15
16
17
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The IR spectra of the complexes were registered in CH2Cl2
solution and as solid (ATR-FTIR). Table 2 shows the CO
frequencies for each of the complexes.
The values of the CO vibration in solution showed good
correlation with the number of trifluoromethyl groups in the
phosphines. As expected, when the number of trifluoromethyls
is increased, the CO frequencies are shifted to higher wave-
numbers as a result of a lower σ-donor ability and greater π-
acceptor character of the phosphine ligand. Exception to this
trend was observed in the Vaska complex of the ortho-
substituted phosphine 3, which showed lower CO frequency
than PPh3. A plausible reasoning to this abnormal value could
arise from long-range intramolecular interactions between the
ortho-trifluoromethyl groups and the metal centre. These
interactions would provide extra electron density to the metal,
thus increasing the backdonation to the CO ligand. This
hypothesis was further supported by the single-crystal X-ray
structure of the Ir-Vaska complex of phosphine 3. Figure 6
shows the ORTEP representation of the [IrCl(CO)(PPh2AroF)2]
complex, together with the most relevant bond distances and
angles. The X-ray structure shows a slightly distorted square
planar geometry of the Ir(I) atom with two phosphine ligands in
trans-disposition and Cl and CO ligands in the remaining
coordinative positions. Distances and angles were found within
Figure 5. Correlation between the 1JPSe and the 1JHP of the trifluorometh-
ylated phosphines
Table 2. Carbonyl stretching IR frequencies (cmÀ 1
complexes trans-[Ir(CO)Cl(L)2]
)
of the Vaska-type
Solid (ATR-FTIR)[b]
[a]
Number of CF3
0
Ligand
CH2Cl2
PPh3
1964
1967
1968
1962
1972
1965
1971
1949
1957
1950
1950
1961
1955
1963
1 (PPh2ArpF)
1
2 (PPh2ArmF
3 (PPh2AroF)
4 (PPh2ArmmF
)
)
5 (PPh2AropF
)
pF
2
6 (PPhAr2
7 (PPhAr2
8 (PPhAr2
)
mF
[c]
[c]
)
)
-
-
oF
1969
1975
1976
1967
1974
1982
pF
10 (PAr3
11 (PAr3
12 (PAr3
9 (PPhAr2
)
)
mF
oF
3
4
[d]
[d]
)
-
-
mmF
)
1979
1979
1989
1972
14 (PArmmFAr2
15 (PArmmFAr2
)
)
pF
mF
[c]
[c]
-
-
16 (PAr2mmFArpF)
1983
1983
1986
1973
1988
1979
5
6
17 (PAr2mmFArmF
)
Figure 6. ORTEP plot (ellipsoid at 50% probability) of Ir–Vaska complex of
the ortho-substituted phosphine 3 [IrCl(CO)(PPh2AroF)2]. Only one orientation
of the CO/Cl groups are shown for simplicity. Distances(Å): Ir(1)-P(1)
=2.318(1), Ir(1)-Cl(1)=2.390(6), Ir(1)-C(1)=1.778(18), C(1)-O(1)=1.038(21), Ir
mmF
13 (PAr3
)
[a] IR spectra registered in CH2Cl2. [b] IR spectra registered as solid
compounds. [c] The complex could not be isolated. [d] The ligand did not
coordinate.
°
(1)…F(1)=3.408(4). Angles( ): P(1)-Ir(1)-Cl(1)=88.4(1), P(1)-Ir(1)-C(1)=92.3(5),
Ir(1)-C(1)-O(1)=173.7(6).
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the reported values of this sort of complexes.[28] Most interest-
ingly, the structure shows that the geometry of the
trifluoromethyl groups at the complex allows the intramolecular
coordination of one fluorine atom of the trifluoromethyl group
of each phosphine ligands to the iridium, at a distance of
3.408 Å. This observation is in agreement with the low CO
frequency observed in the Vaska complex of phosphine 3.
Because of the electron donation of the fluorine with the metal
centre, the estimation of the basicity of the phosphine 3, and
most probably also of the other ortho-substituted phosphines,
using the Vaska complexes should be carefully considered. In
these cases, the values of CO frequencies obtained by IR would
be a combination of the electron-withdrawing effect of the
trifluoromethyl groups and the long-distance donor effect of a
fluorine atom of these groups.
No significant differences were found in the CO frequencies
of the Ir-Vaska complexes of the para- and the meta-isomers in
solution. However, the CO frequencies in solid (ATR-FTIR) do
not follow the same tendency and greater differences between
the para- and the meta-isomers were found. These observations
might be tentatively attributed to intermolecular long-distance
FÀ Ir contacts in the solid structures.
Performance of the phosphines as ligands in the Rh-catalysed
hydroformylation
1
2
3
4
5
6
7
8
9
To correlate the stereolectronic properties with the perform-
ance of the trifluoromethylated phosphines in catalysis, the
ligands were tested in the Rh-catalysed hydroformylation of 1-
octene, Scheme 1. Two possible aldehyde products, branched
(2-methyloctanal, b) and linear (nonanal, l), can be formed.
Furthermore, under the reaction conditions, the isomerisation
and/or hydrogenation of the substrate can take place, giving
yield to internal alkenes and octane, respectively.
All the ligands were tested using the same conditions. The
reactions were performed using [Rh(acac)(CO)2] as catalyst
precursor and 5 equivalents of the corresponding phosphine.
The active catalytic species were formed in situ in the autoclave
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
°
using 16 bar of syngas at 80 C, before the addition of the
°
substrate. The reactions were carried out at 80 C and 20 bar of
syngas (H2 :CO, 1:1) for 2 h and the consumption of the gas
was monitored to determine the reaction rate. Finally, the
distribution of the different products was determined by GC.
The catalytic results are shown in Table 3 and Figure 8. As
expected, the performance of the catalytic reactions was
affected by the nature of the trifluoromethylated phosphines.
Conversions above 98% were obtained after 2 h for all the
reactions using the trifluoromethylated phosphines. The cata-
lytic system using the ortho-substituted phosphines gave poor
results in the hydroformylation of 1-octene, with low chemo-
selectivity towards aldehydes. High concentration of internal
alkenes, coming from the isomerization of the substrate, was
observed (Table S2) leading also to low regioselectivities. These
results indicate a low coordination ability of these ligands,
especially when increasing the number of trifluoromethyl
groups, since the values are comparable to those of the
reaction carried out without phosphine ligand.
Figure 7 shows the graphical representation of the CO
vibration frequencies of the Vaska’s complexes in solution
versus the number of trifluoromethyl groups of the phosphines.
Clearly, as in the case of the selenides and the protonated
phosphines, there is a linear relationship between the fre-
quency of the carbonyl in the IR spectra and the number of
trifluoromethyl groups in the phosphines. The frequency
increases with the number of trifluoromethyls due to the
increase in the acidity of the phosphines. Exception to this
trend was found in those phosphines containing only one
trifluoromethyl group in ortho position, phosphines 3 and 5,
and can be explained by the FÀ Ir long-range coordination
observed in the X-ray structure of 3.
Excluding the ortho-substituted phosphines, a smooth drop
in the chemoselectivity was observed when increasing the
number of trifluoromethyl groups, see Figure 8. However,
regioselectivities within 70–73% were observed for all these
phosphines without a significant trend.
Importantly, the rate of the reaction, measured as the TOF
at 50% of conversion in aldehydes, is affected not only by the
number of trifluoromethyl groups in the phosphines but also
by the relative position of these groups. As clearly observed in
Figure 8, meta- and para-substituted phosphines provided
faster reaction rates when increasing the number of
trifluoromethyl groups. Interestingly for the same number of
trifluoromethyls, para-substituted phosphines showed lower
reaction rates than the meta-substituted ones, i.e. 1 vs 2, 6 vs 7,
10 vs 11. Moreover, when using the meta-substituted phos-
Figure 7. CO vibration frequencies of the Vaska’s trans-[Ir(CO)Cl(L)2] com-
plexes of the trifluoromethylated phosphines in CH2Cl2 solution vs the
number of trifluoromethyl groups of the phosphines.
Scheme 1. Formation of linear (l) and branched (b) aldehydes from 1-octene
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Table 3. Rhodium-catalysed hydroformylation of 1-octene with the trifluoromethylated phosphines.[a]
1
2
CF3 groups
Ligand
Conv.[b] [%]
Chemosel.[c] [%]
Regiosel.[d] [%]
TOF 50%[e] [minÀ 1
]
3
4
5
6
7
8
9
no ligand
PPh3
98.4
92.5
98.3
98.8
98.5
98.6
98.2
98.8
98.8
98.0
99.1
98.9
98.2
98.7
99.0
98.8
98.8
98.8
98.9
33.9
98.1
96.0
97.7
62.7
96.3
47.3
97.0
97.1
37.0
96.4
95.0
34.2
91.4
94.3
91.9
89.6
88.6
84.6
53.2
72.9
72.7
73.0
65.1
73.0
60.8
72.3
72.9
54.4
70.7
72.0
55.7
72.9
71.1
71.9
71.2
71.1
67.4
-
0
1
21.0
23.0
36.6
14.3
42.7
4.5
33.9
49.7
-
49.0
58.9
-
56.6
53.7
69.1
54.8
71.5
81.4
1 (PPh2ArpF)
2 (PPh2ArmF
3 (PPh2AroF)
4 (PPh2ArmmF
)
)
)
5 (PPh2AropF
)
pF
2
3
6 (PPhAr2
7 (PPhAr2
8 (PPhAr2
10 (PAr3
11 (PAr3
12 (PAr3
9 (PPhAr2
)
)
mF
oF
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
)
pF
)
mF
oF
)
)
mmF
pF
4
5
6
14 (PArmmFAr2
15 (PArmmFAr2
)
mF
)
16 (PAr2mmFArpF)
17 (PAr2mmFArmF
)
mmF
13 (PAr3
)
°
[a] Conditions: 20 bar CO:H2 (1:1), 80 C, 2 h of reaction, [1-octene]/[Rh]=2500, [L]/[Rh]=5, [Rh]=0.65 mM. solvent: toluene, n-decane 0.17 M as internal
standard. Stirring rate 700 rpm. Catalyst preformation: 16 bar CO:H2 (1:1), 80 C, 30 min. [b] Conversion of 1-octene: (mmol of converted substrate/mmol of
starting substrate)×100. [c] Chemoselectivity towards aldehydes: (mmol of aldehydes/mmol of converted substrate)×100. [d] Regioselectivity towards linear
aldehyde: (mmol of linear aldehyde/mmol of aldehydes)×100. [e] TOF at 50% of conversion in aldehydes
°
contrast to the previous experiments performed for the
evaluation of the stereoelectronic properties in which no clear
difference between meta- and para-isomers was observed.
Conclusion
The trifluoromethyl substituents in the aromatic rings of
triarylphosphines were found to dramatically affect the stereo-
electronic properties of this type of ligands. The σ-donating
ability of the phosphines has been evaluated by NMR
spectroscopy of the selenide derivatives and the phosphonium
ions and was found to be inversely proportional to the number
of trifluoromethyl groups. Moreover, the ortho-trifluoromethyl
groups have a higher influence on the donating properties than
the meta and para-trifluoromethyls. Based on the linear trend
observed with the phosphines synthesised in this work, it is
possible to predict the σ-donating ability of
trifluoromethylated phosphine by knowing the position and the
number of the trifluoromethyl groups.
a given
The π-accepting ability of the phosphines is also clearly
affected by the number and the position of the trifluoromethyl
groups, as it was observed through the CO stretching frequency
of the corresponding iridium Vaska-type complexes. The π-
accepting ability increases with the number of trifluoromethyl
groups of the phosphines, except for the ortho-substituted
phosphines due to a long distance interaction of the fluorine
atoms with the metal centre.
The performance of the phosphine in the Rh-catalysed
hydroformylation of 1-octene has been correlated with the
stereolectronic properties of the ligands. Higher reaction rates
were achieved with the phosphines with lower σ-donating
ability and higher π-accepting character, in agreement with the
most accepted hydroformylation mechanism. Poor catalytic
Figure 8. Reaction rate (TOF) and chemoselectivity of the Rh-catalysed
hydroformylation of 1-octene vs the number of trifluoromethyl groups of the
phosphine ligands.
phines, higher values of TOF were observed compared to the
meta-meta-substituted phosphines with the same number of
trifluoromethyls, i.e. 4 vs 7, 9 vs 15. Therefore, for the same
number of trifluoromethyl groups, their location in different
rings has a positive effect in the TOF. These catalytic results
Eur. J. Inorg. Chem. 2021, 354–363
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(2,4-bis(trifluoromethyl)phenyl)diphenylphosphine (5): 20.1 ml of
n-butyllithium (2.5 M in hexanes, 50.3 mmol) was added dropwise
to a solution of 1-bromo-2,4-bis(trifluoromethyl)benzene (50 mmol)
results were obtained with the ortho-substituted phosphines
due to low coordination behaviour of these ligands.
1
2
°
3
4
5
6
7
8
9
in 50 ml of anhydrous diethyl ether at 0 C. Quantitative addition
was ensured with two portions of 10 ml of diethyl ether. After
complete addition, the resulting orange solution was stirred for
Experimental Section
°
30 min at 0 C. At this same temperature, a solution of chlorodiphe-
nylphosphine (45 mmol) in 30 ml of dry Et2O was added dropwise.
The reaction mixture was stirred for 3 hours at room temperature.
Then the orange suspension obtained was cooled down in an ice
bath before the addition of 80 ml of 10% aqueous HCl. The orange
organic phase was separated and the aqueous phase was extracted
three times with 30 ml of Et2O. The organic fractions were
combined and dried over anhydrous MgSO4. After filtration, the
solvent was vacuum evaporated to obtain an orange solid which
was purified through flash column in silica gel (CH2Cl2 :hexanes,
1:1). Pale yellow solid. Yield 12.1 g (67%) 1H NMR (400.13 MHz,
CDCl3) δ 7.99 (bs, 1H, HC3{C6H3(CF3)2}); 7.67 (bd, 1H, HC5{C6H3(CF3)2},
3JHH =8.1 Hz); 7.42–7.33 (m, 6H, HC3-HC4{C6H5}); 7.27 (bd, 1H,
HC6{C6H3(CF3)2}, 3JHH =8.1 Hz) 7.26–7.20 (m, 4H, HC2{C6H5}). 13C{1H}
General Methods
Unless otherwise mentioned, all the synthetic manipulations were
performed under nitrogen atmosphere using standard Schlenk
techniques. Solvents and liquid reagents were deoxygenated by
bubbling nitrogen for 10–15 minutes.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
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28
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
General chemical reagents and solvents were purchased from
commercial suppliers which include Sigma-Aldrich, Scharlab and
Acros Organics. Trifluoromethylated compounds were purchased
from Fluorochem and transition metal compounds were purchased
from Alfa Aesar. All the chemicals were used without further
purification, unless otherwise specified.
1
The nuclear magnetic resonance spectra were recorded at the
NMR (100.61 MHz, CDCl3). δ 142.48 (d, C1{C6H3(CF3)2}, JCP =33.8 Hz);
136.81 (bs, C6{C6H3(CF3)2}; 135.63 (qd, C2{C6H3(CF3)2}, 2JCF =30.8 Hz,
2JCP =25.0 Hz); 135.46 (d, C1{C6H5}, 1JCP =11.9 Hz); 133.93 (d, C2{C6H5},
2JCP =20.7 Hz); 131.32 (q, C4{C6H3(CF3)2}, 2JCF =33.5 Hz); 129.50 (s,
C4{C6H5}); 128.97 (d, C3{C6H5}, 3JCP =7.0 Hz); 128.25 (m,
C5{C6H3(CF3)2}); 123.72 (q, C{o-CF3}, 1JCF =275.20 Hz); 123.57 (sept,
Servei de Ressonància Magnètica Nuclear at the UAB on a Bruker
Avance III 400 spectrometer (400.13 MHz for H, 100.61 MHz for 13C,
1
376.50 MHz for 19F and 161.98 MHz for 31P). Chemical shifts in 1H
and 13C NMR are relative to the signal of the solvent.[29] Chemical
shifts in 31P NMR spectra are relative to 85% H3PO4 (0.0 ppm), used
as external standard. Chemicals shifts in 19F NMR spectra are relative
to flurobenzene (À 113.15 ppm with respect to CFCl3). HR-MS
analyses were performed at the Servei d’Anàlisi Química at UAB in a
Bruker microTOF spectrometer coupled to an Apollo II electrospray
source (ESI). Elemental analyses were performed at the Servei
d’Anàlisi Química at UAB in a Thermo Fisher Scientific Flash EA 2000
CHNS. IR spectra recorded in solution were performed in a Perkin
Elmer 2000 IR-FT spectrometer. Solid ATR-FTIR spectra were
recorded in a Bruker IR Tensor 27 spectrometer equipped with an
ATR Specac Golden Gate single reflexion diamond ATR system.
Single-crystal XRD data were collected on a Bruker SMART-APEX
diffractometer using Mo Kα radiation at the Servei de Difracció de
Raigs X at the UAB.
C3{C6H3(CF3)2}, JCF =3.8 Hz); 123.45 (q, C{p-CF3}, JCF =272.2 Hz); 31P
3
1
{1H} NMR (161.98 MHz, CDCl3) δ À 10.46 (q, 4JFP =52.5 Hz). 19F{1H}
4
NMR (235.39 MHz, CDCl3) δ À 57.41 (d, FoCF3, JFP =52.5 Hz); À 63.09
(s, FpCF3). HR-MS (ESI+ m/z) [M+H]+: calculated for [C20H13F6P]+
399.07; found 399.0735.
(3,5-bis(trifluoromethyl)phenyl)bis(4-(trifluoromethyl)phenyl)
phosphine
(14)
and
(3,5-bis(trifluoromethyl)phenyl)bis(3-
(trifluoromethyl)phenyl)phosphine (15): The corresponding
trifluoromethylated bromobenzene derivative (13.9 mmol) was
dissolved in 7.5 ml of anhydrous diethyl ether and added dropwise
to a suspension of magnesium chips (16.9 mmol) in 20 ml of
anhydrous diethyl ether. After refluxing the reaction mixture for
2 hours, it was cooled down to room temperature. The excess of
Mg was filtered off and the solution containing the Grignard
Deposition Numbers 2023479 (for [IrCl(CO)(PPh2AroF)2]) and
2023480 (for phosphine PArmmFAr2pF, 14) contain the supplementary
crystallographic data for this paper. These data are provided free of
charge by the joint Cambridge Crystallographic Data Centre and
Fachinformationszentrum Karlsruhe Access Structures service
www.ccdc.cam.ac.uk/structures.
°
derivative was cooled down to 0 C. The solution of the Grignard
derivative was then added dropwise to a solution of (3,5-bis
(trifluoromethyl)phenyl)dichlorophosphine (7.0 mmol) in 7.5 ml of
anhydrous diethyl ether and cooled in an ice bath. The resulting
orange suspension was stirred overnight at room temperature.
°
After that time, the reaction mixture was cooled down to 0 C (ice
Conversions and selectivities of the Rh-catalysed hydroformylation
of 1-octene were obtained by GC with an Agilent 6850 chromato-
graph equipped with a FID detector, an Agilent 7683B injector and
an Agilent HP5 column (25 m long, 0.20 mm ID and 0.33 μm film
thickness). For compound identification an Agilent Technologies
6850 chromatograph equipped with an Agilent Technologies
5975 C VL MSD mass spectrometer detector and an Agilent HP5-MS
column (30 m long, 0.32 mm ID and 0.5 μm film thickness) were
employed.
bath) and 10 ml of 10% aqueous HCl were added. The organic layer
was separated and the aqueous phase was extracted three times
with 10 ml of diethyl ether. The organic fractions were combined
and dried over MgSO4. Filtration and evaporation of the solvent
gave an orange-brown solid which was further purified through
flash silica column (CH2Cl2 :hexanes, 7:3).
1
(14): pale orange solid. 1.9 g (51%) H NMR (400.13 MHz, CDCl3), δ
7.91 (s, 1H, HC4{C6H3(CF3)2}); 7.73 (d, 2H, HC2{C6H3(CF3)2}, 3JHP =6.2 Hz);
7.67 (d, 4H, HC3{C6H3CF3}, 3JHH =7.6 Hz); 7.42 (pseudo-t, 3H,
HC2{C6H4CF3}, 3JHP =3JHH =7.6 Hz). 13C{1H} NMR (100.61 MHz, CDCl3), δ
139.70 (d, C1{C6H3(CF3)2}, 1JCP =19.0 Hz); 139.33 (bd, C1{C6H4CF3},
1JCP =14.0 Hz); 134.13 (d, C2{C6H4CF3}, 2JCP =21.1 Hz); 133.5 (bd,
Synthesis and characterization of trifluoromethylated
phosphines
2
2
C2{C6H3(CF3)2}, JCP =21.0 Hz); 132.5 (qd, C3{C6H3(CF3)2}, JCF =33.5 Hz,
Phosphines from 1 to 4 and from 6 to 13 were prepared according
to previously reported methodologies. Detailed information about
the synthesis and characterization of these compounds together
with the chlorophosphine intermediates can be found in the
supporting information. Warning: the organolithium and the
Grignard reagents used for the preparation of the phosphines
should be carefully handled due to their pyrophoric nature.
2JCP =6.0 Hz); 132.24 (q, C4{C6H4CF3}, 2JCF =32.8 Hz); 126.12 (m,
C3{C6H4CF3}, 3JCP =7.5 Hz, 3JCF =3.8 Hz); 123.89 (q, CF3{C6H4CF3}, 1JCF
=
272.6 Hz); 123.64 (sept, C4{C6H3(CF3)2}, 3JCF =3.6 Hz); 123.17 (q,
CF3{C6H3(CF3)2}, JCF =272.6 Hz). 31P{1H} NMR (161.98 MHz, CDCl3), δ
1
À 4.62 (s). 19F{1H} NMR (376.50 MHz, CDCl3), δ À 62.07 (s, 6F,
CF3{C6H3(CF3)2}); À 62.17 (s, 6F, CF3{C6H4CF3}). HR-MS (ESI+ m/z) [M+
Eur. J. Inorg. Chem. 2021, 354–363
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© 2020 Wiley-VCH GmbH

Full Papers
doi.org/10.1002/ejic.202000887
3
H]+: calculated for [C22H12F12P]+ 535.0480; found 535.0491. Elemen-
tal analysis: calculated for C22H11F12P: C, 49.46; H, 2.08; found: C,
49.94; H, 2.19.
130.29 (d, C5{C6H4CF3}, 3JCP =5.8 Hz); 127.68 (q, C4{C6H4CF3}, JCF
=
1
2
3
4
5
6
7
8
9
3.6 Hz); 124.01 (sept, C4{C6H3(CF3)2}, 3JCF =3.8 Hz); 123.65 (q,
1
CF3{C6H4CF3}, 1JCF =272.5 Hz); 123.00 (q, CF3{C6H3(CF3)2}, JCF
=
273.1 Hz). ). 31P{1H} NMR (161.98 MHz, CDCl3), δ À 3.83 (s). 19F{1H}
NMR (376.50 MHz, CDCl3), δ À 63.04 (bs, 3F, CF3{C6H4CF3}); À 62.33
(bs, 12F, CF3{C6H3(CF3)2}). HR-MS (ESI+ m/z) [M+H]+: calculated for
[C23H11F15P]+ 603.0353; found 603.0371. Elemental analysis: calcu-
lated for C23H10F15P: C, 45.87; H, 1.67; found: C, 45.86; H, 1.66.
1
(15): yellow oil. 2.4 g (63% yield). H NMR (400.13 MHz, CDCl3), δ
7.90 (s, 1H, HC4{C6H3(CF3)2}); 7.71 (d, 4H, HC2{C6H3(CF3)2}-HC4{C6H4CF3});
7.65 (d, 2H, HC2{C6H4CF3}, 3JHP =8.1 Hz); 7.57 (t, 2H, HC5{C6H4CF3},
3JHH =7.8 Hz); 7.45 (pseudo-t, 2H, HC6{C6H4CF3}, 3JHH =3JHP =7.8 Hz).
1
13C{1H} NMR (100.61 MHz, CDCl3), δ 140.0 (d, C1{C6H3(CF3)2}, JCP
=
18.1 Hz); 136.85 (bd, C6{C6H4CF3}, 2JCP =16.0 Hz); 136.06 (d,
1
2
C1{C6H4CF3}, JCP =13.7 Hz); 133.25 (bd, C2{C6H3(CF3)2}, JCP =20.4 Hz);
132.42 (qd, C3{C6H3(CF3)2}, 2JCF =34.3 Hz, 2JCP =6.4 Hz); 131.89 (qd,
C3{C6H4CF3}, 2JCF =32.6 Hz, 3JCP =8.7 Hz); 130.70 (dq, C2{C6H4CF3},
2JCP =26.4 Hz, 3JCF =3.7 Hz); 129.93 (d, C5{C6H4CF3}, 3JCP =5.8 Hz);
Acknowledgements
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
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41
42
43
44
45
46
47
48
49
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57
We thank Matgas 2000 A.I.E. for the use of the autoclave for the
hydroformylation reactions under a lease. D.P., D.H. and M.C.
thank Universitat Autònoma de Barcelona for their PIF grant.
3
1
127.10 (q, C4{C6H4CF3}, JCF =3.7 Hz); 123.83 (q, CF3{C6H4CF3}, JCF
=
272.4 Hz); 123.50 (sept, C4{C6H3(CF3)2}, 3JCF =3.8 Hz); 123.17 (q,
CF3{C6H3(CF3)2}, JCF =272.8 Hz). 31P{1H} NMR (161.98 MHz, CDCl3), δ
1
À 3.92 (s). 19F{1H} NMR (376.50 MHz, CDCl3), δ À 62.21 (bs, 6F, CF3);
À 62.33 (bs, 6F, CF3). HR-MS (ESI+ m/z) [M+H]+: calculated for
[C22H12F12P]+ 535.0480; found 535.0489. Elemental analysis: calcu-
lated for C22H11F12P: C, 49.46; H, 2.08; found: C, 50.30; H, 2.11.
Conflict of Interest
Bis(3,5-bis(trifluoromethyl)phenyl)(4-(trifluoromethyl)phenyl)
The authors declare no conflict of interest.
phosphine
(16)
and
bis(3,5-bis(trifluoromethyl)phenyl)(3-
(trifluoromethyl)phenyl)phosphine (17): A solution of the corre-
sponding trifluoromethylated bromobenzene (16.4 mmol) in 10 ml
of anhydrous diethylether was added dropwise to a suspension of
Mg (19.8 mmol) in 20 ml of anhydrous diethyl ether. The mixture
was then refluxed for 1.5 h and, after cooling down to room
temperature, excess magnesium was filtered off. The solution
containing the corresponding Grignard reagent was then added to
a cold solution (ice bath) of bis(3,5-bis(trifluoromethyl)phenyl)
chlorophosphine (16.7 mmol) dissolved in 30 ml of anhydrous
diethyl ether. The resulting orange suspension was stirred over-
night at room temperature. The reaction mixture was then cooled
down in an ice bath and 70 ml of 10% aqueous HCl were added.
The organic layer was separated and the aqueous phase was
extracted three times with 30 ml of Et2O. The organic fractions were
combined and dried over MgSO4. Filtration and evaporation of the
solvent gave a brown oil which was further purified through flash
silica column (CH2Cl2 :hexanes, 7:3).
Keywords: Trifluoromethyl
· Phosphines · Stereoelectronic
properties · Selenide derivatives · Hydroformylation
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13C{1H} NMR (100.61 MHz, CDCl3), δ 138.68 (d, C1{C6H3(CF3)2}, JCP
=
17.1 Hz); 138.22 (bd, C1{C6H4CF3}, 1JCP =15.1 Hz); 134.24 (d,
C2{C6H4CF3}, 2JCP =21.1 Hz); 133.5 (bd, C2{C6H3(CF3)2}, 2JCP =22.1 Hz);
132.82 (qd, C3{C6H3(CF3)2}, 2JCF =33.8 Hz, 2JCP =6.5 Hz); 132.82 (q,
C4{C6H4CF3}, 2JCF =33.8 Hz); 126.46 (m, C3{C6H4CF3}, 3JCP =7.1 Hz,
3JCF =3.5 Hz); 124.09 (sept, C4{C6H3(CF3)2}, 3JCF =3.6 Hz); 123.79 (q,
1
CF3{C6H4CF3}, 1JCF =272.1 Hz); 123.06 (q, CF3{C6H3(CF3)2}, JCF
=
272.7 Hz). 31P{1H} NMR (161.98 MHz, CDCl3), δ À 3.91 (s). 19F{1H} NMR
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CF3{C6H4CF3}). HR-MS (ESI+ m/z) [M+H]+: calculated for
[C23H11F15P]+ 603.0353; found 603.0358. Elemental analysis: calcu-
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3
7.94 (s, 2H, HC4{C6H3(CF3)2}); 7.76 (d, 4H, HC4{C6H4CF3}, JHH =7.8 Hz);
3
7.72 (d, 4H, HC2{C6H3(CF3)2}, JHP =6.5 Hz); 7.68 (d, 1H, HC2{C6H4CF3},
3
3JHP =6.5 Hz); 7.61 (t, 1H, HC5{C6H4CF3}, JHH =7.8 Hz); 7.45 (pseudo-t,
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CDCl3),
δ
138.72 (d, C1{C6H3(CF3)2}, 1JCP =17.9 Hz); 136.79 (bd,
C6{C6H4CF3}, 2JCP =15.4 Hz); 134.84 (d, C1{C6H4CF3}, 1JCP =13.4 Hz);
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133.30 (bd, C2{C6H3(CF3)2}, JCP =21.3 Hz); 132.76 (qd, C3{C6H3(CF3)2},
2JCF =33.7 Hz, 2JCP =6.4 Hz); 132.20 (qd, C3{C6H4CF3}, 2JCF =32.6 Hz,
3JCP =9.1 Hz); 130.92 (dq, C2{C6H4CF3}, 2JCP =28.3 Hz, 3JCF =3.9 Hz);
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Manuscript received: September 21, 2020
Revised manuscript received: November 15, 2020
Accepted manuscript online: November 22, 2020
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