Differentiation between chelate ring inversion and aryl rotation in a CF3-substituted phosphine-sulfonate palladium methyl complex

Article abstract of DOI:10.1021/om500699t

The solution conformations and dynamic properties of the CF₃-sbustituted (ortho-phosphinoarenesulfonate)Pd complexes (PO-CF₃)PdMe(L) ([PO-CF₃]^- = 2-{(o-CF₃-Ph)₂P}-4-Me-benzenesulfonate, L = 2,6-lutidine (3), pyridine (4)) were studied by NMR spectroscopy, taking particular advantage of ³¹P-¹⁹F through-space couplings and ¹H-¹H and ¹H-¹⁹F nuclear Overhauser effects. In CD₂Cl₂ solution in the temperature range of -80 to 20 °C, 3 adopts an exo₂ conformation. One o-CF₃-Ph ring is positioned such that the CF₃ group points toward Pd (exo) and exhibits through-space ⁴J_PF coupling. The other o-CF₃-Ph ring is positioned such that the CF₃ group points away from Pd (endo) and does not exhibit through-space ⁴J_PF coupling, and the o-H lies in the deshielding region near an axial site of the Pd square plane and exhibits a low-field chemical shift (δ > 9). Complex 4 exists as a 2:1 mixture of exo₂ and exo₃ isomers in CD₂Cl₂ solution at -90 °C. In exo₂-4, one CF₃ group is exo and exhibits through-space ⁴J_PF coupling, while the other CF₃ group is endo and does not exhibit through-space ⁴J_PF coupling. In exo₃-4, both CF₃ groups are exo and exhibit through-space ⁴J_PF couplings. Complex 4 undergoes two dynamic processes: rotation of the axial o-CF₃-Ph ring (A_aR), which interconverts exo₂-4 and exo₃-4 (ΔG^&dagger = 9.9(5) kcal/mol), and chelate ring inversion (RI), which permutes the axial and equatorial o-CF₃-Ph rings (ΔG^&dagger = 21(1) kcal/mol).

Full text of DOI:10.1021/om500699t

Article
pubs.acs.org/Organometallics
Differentiation between Chelate Ring Inversion and Aryl Rotation in
a CF3‑Substituted Phosphine-Sulfonate Palladium Methyl Complex
Ge Feng, Matthew P. Conley, and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
S
* Supporting Information
ABSTRACT: The solution conformations and dynamic properties of the
CF3-sbustituted (ortho-phosphinoarenesulfonate)Pd complexes (PO-CF3)-
PdMe(L) ([PO-CF3]− = 2-{(o-CF3-Ph)2P}-4-Me-benzenesulfonate, L = 2,6-
lutidine (3), pyridine (4)) were studied by NMR spectroscopy, taking
1
particular advantage of 31P−19F through-space couplings and H−1H and
1H−19F nuclear Overhauser effects. In CD2Cl2 solution in the temperature
range of −80 to 20 °C, 3 adopts an exo2 conformation. One o-CF3-Ph ring is
positioned such that the CF3 group points toward Pd (exo) and exhibits
4
through-space JPF coupling. The other o-CF3-Ph ring is positioned such that
the CF3 group points away from Pd (endo) and does not exhibit through-
4
space JPF coupling, and the o-H lies in the deshielding region near an axial
site of the Pd square plane and exhibits a low-field chemical shift (δ > 9).
Complex 4 exists as a 2:1 mixture of exo2 and exo3 isomers in CD2Cl2 solution
at −90 °C. In exo2-4, one CF3 group is exo and exhibits through-space 4JPF coupling, while the other CF3 group is endo and does
not exhibit through-space 4JPF coupling. In exo3-4, both CF3 groups are exo and exhibit through-space 4JPF couplings. Complex 4
undergoes two dynamic processes: rotation of the axial o-CF3-Ph ring (AaR), which interconverts exo2-4 and exo3-4 (ΔG⧧ =
9.9(5) kcal/mol), and chelate ring inversion (RI), which permutes the axial and equatorial o-CF3-Ph rings (ΔG⧧ = 21(1) kcal/
mol).
Jordan,4 Mecking,5 Nozaki,6 Rieger,7 and others.8 These
catalysts polymerize ethylene to linear polyethylene and
copolymerize ethylene with a variety of polar vinyl monomers
to form functionalized linear polymers with functional groups
INTRODUCTION
■
Palladium(II) alkyl complexes that contain ortho-phosphino-
arenesulfonate ligands ([PO]−) exhibit unique behavior in
olefin polymerization.1 After the seminal reports by Drent and
Pugh in 2002,2 (PO)PdR(L) species (L = labile ligand, Scheme
incorporated at both in-chain and chain-end positions.
1) have been studied extensively by the groups of Claverie,3
Additionally, (PO)PdR(L) complexes catalyze the nonalternat-
ing copolymerization of ethylene and CO2b,9 and the
alternating copolymerization of CO with vinyl acetate and
Scheme 1. Possible Dynamic Processes of (PO-
OMe)PdMe(L) Complexes
methyl acrylate.10
In the solid-state structure of the prototypical (PO)Pd
complex (2-{(o-OMe-Ph)2P}-benzenesulfonate)PdMe(py)
(Scheme 1, R1 = R2 = OMe),9d the (PO)Pd chelate ring
adopts a boat conformation, and the o-MeO-Ph rings occupy
pseudoaxial and pseudoequatorial positions. Howell and co-
workers have developed a simple convention for describing the
conformations of Ar3PX species (X = lone pair, O, or metal)
that contain ortho substituents on the Ar rings (Scheme 2).11
The Ar ring is designated as exo if the ortho substituent points
toward the X group (|θX−P−C1‑C2| < 90°) and endo if it points
away from the X group (|θX−P−C1‑C2| > 90°). In (PO)PdMe(L)
−
complexes, the ArSO3− group is always exo because the −SO3
group coordinates to Pd, but the other two P-Ar rings can be
either exo or endo. In (2-{(o-OMe-Ph)2P}-benzenesulfonate)-
PdMe(py) (Scheme 1), the methoxy group on the pseudoaxial
Received: July 3, 2014
Published: August 21, 2014
© 2014 American Chemical Society
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The objective of the present work was to design a system for
which RI and AR could be differentiated. 19F NMR studies have
been widely used to probe the solution conformations and
dynamic properties of fluorinated organometallic species.15
Scheme 2. Endo and Exo Conformations in Ar3PX Species
1
Through-space 19F couplings and H−19F nuclear Overhauser
effects (NOEs) can often provide unique information that is
otherwise unavailable. In this work we exploited these
phenomena to characterize the RI and AR processes in (PO-
CF3)PdMe(py) (4, [PO-CF3]− = 2-{(o-CF3-Ph)2P}-4-Me-
benzenesulfonate).
RESULTS AND DISCUSSION
o-MeO-Ph ring is endo (R1 in A), while that on the
pseudoequatorial ring is exo (R2 in A), and therefore the
[PO]− ligand in this complex adopts an exo2 conformation.
The 1H NMR spectrum of (2-{(o-OMe-Ph)2P}-4-Me-
benzenesulfonate)PdMe(py) at −80 °C contains two OCH3
resonances, indicating that exchange of the two methoxy groups
is slow on the NMR time scale. However, only one OCH3
resonance is observed at ambient temperature, indicative of fast
methoxy exchange. The barrier for permutation of the methoxy
groups is ΔG⧧ = 10.5 kcal/mol at −50 °C.4c Other
(PO)PdMe(py) complexes that contain ortho-substituted P-Ar
rings exhibit similar dynamic behavior.3c,4c
■
Synthesis and Solid-State Structure of Na[2-{(o-CF3-
Ph)2P}-4-Me-benzenesulfonate] (Na[1], Na[PO-CF3]).
Na[1] was synthesized by the reaction of P(o-CF3-Ph)2Cl
with (i) lithiated isobutyl p-toluenesulfonate followed by
deprotection of the sulfonate ester with NaI or (ii) dilithiated
p-toluenesulfonic acid followed by cation exchange with NaCl
(Scheme 3). The isolated yields for both routes are ca. 65%.
Scheme 3. Synthesis of Na[1]
For (PO)Pd(R)(L) species that contain ortho-substituted P-
Ar groups, several dynamic processes are possible (Scheme 1):
chelate ring inversion (RI), which exchanges the pseudoaxial
and pseudoequatorial P-Ar groups, and rotation of the
pseudoaxial and pseudoequatorial P-Ar rings around the P−
Cipso bonds (AaR, AeR), which exchanges the ortho substituents
between exo and endo positions. The observation of
inequivalent methoxy groups in (2-{(o-OMe-Ph)2P}-4-Me-
benzenesulfonate)PdMe(py) at −80 °C implies that either RI is
slow or, if RI is fast, both AaR and AeR are slow. The
observation of fast methoxy exchange at ambient temperature
requires that RI is fast and AaR and/or AeR is fast. Note that
when RI is fast, AaR and AeR cannot be differentiated. Recently
Caporaso, Mecking, and co-workers reported an experimental
and computational study of the dynamic properties of a series
of [PO]− salts, [PO]H zwitterions, and corresponding
“(PO)PdMe” complexes (generated in situ by halide
abstraction from the cation-bridged [(PO)PdMe(Cl)-μ-M]n
(M = Na or Li) species in CD3OD or DMSO-d6 solution).12
The authors concluded that for “[PO-(o-R-Ph)2]PdMe” species
in the range of −90 to 130 °C chelate ring inversion is always
fast, and the inequivalence of o-R-Ph rings observed at low
temperature is due to slow aryl rotation.13
The dynamic properties of (PO)Pd(R)(L) species may
influence their reactivity in several ways. First, it has been
proposed that insertion of (PO)Pd(R)(ethylene) species in
ethylene polymerization occurs by initial isomerization of the
ground-state cis-P,R isomer to the trans-P,R isomer via a five-
coordinate (κ3-P,O,O-PO)Pd(R)(ethylene) intermediate or
transition state, followed by migratory insertion.4f,6c,14 The
rigidity of the (PO)Pd framework may influence the barrier to
this isomerization process. Second, several interesting stereo-
selective or potentially stereoselective reactions catalyzed by
(PO)Pd(R)(L) complexes have been developed recently,
including the asymmetric copolymerization of vinyl acetate
and CO catalyzed by Pd complexes bearing a P-chiral [PO]−
ligand10c and the homooligomerization of methyl acrylate
catalyzed by “(PO)PdMe” species bearing a series of [PO]−
ligands.13 The dynamic properties of the (PO)Pd(R)(L)
catalysts may influence the stereoselectivity in these reactions.13
The major side product for both reactions was (o-CF3-
Ph)2P(O)P(o-CF3-Ph)2 (2). Compound 2 is probably
formed by oxidation of (o-CF3-Ph)2P-P(o-CF3-Ph)2 during
workup under air; the latter species may form by lithium/
halogen exchange of P(o-CF3-Ph)2Cl followed by coupling of
LiP(o-CF3-Ph)2 and P(o-CF3-Ph)2Cl16 or by single-electron
transfer between Li[isobutyl p-toluenesulfonate] or Li2[p-
toluenesulfonic acid] and P(o-CF3-Ph)2Cl followed by radical
coupling (see Supporting Information).
Slow diffusion of pentane into a wet CH2Cl2 solution of
Na[1] in the presence of 18-crown-6 results in crystallization of
[Na(18-crown-6)(H2O)][1], which was characterized by X-ray
diffraction. The [Na(18-crown-6)(H2O)]+ and [1]− ions form
a dimeric structure that is held together by hydrogen bonds
between the H2O molecules and the ArSO3− groups (Figure 1).
The hydrogen atoms that are involved in the hydrogen bond
network, H10A and H10B, were located, and their positions
were refined isotropically. The O10−O1 (2.94 Å) and O10−
O2 (2.87 Å) distances are consistent with the presence of
hydrogen bonds.17
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state structure. Similar 31P−19F couplings were observed in P(o-
CF3-Ph)3 but not in OP(o-CF3-Ph)3,19,23 suggesting that
these couplings are transmitted through space via lone-
pair(F)−lone-pair(P) interactions.15c,24 As the temperature is
raised, the two doublets broaden and coalesce to one doublet
(4JPF = 60 Hz, Figure 2). The free energy of activation for this
Figure 2. Observed and simulated variable-temperature 19F{1H} NMR
spectra of Na[1] in DMSO-d6 solution.
process, ΔG⧧ = 16.0(4) kcal/mol at 55 °C, was determined
from a full line shape analysis of these spectra over the
temperature range 40−100 °C. A similar value (16.1(5) kcal/
mol) was obtained from the coalescence of the H6 resonances
Figure 1. Molecular structure of [Na(18-crown-6)(H2O)][1]. Hydro-
gen atoms that are not involved in hydrogen bonding are omitted.
Selected bond lengths (Å) and angles (deg): P1−C1 1.853(5), P1−C8
1.856(5), P1−C15 1.845(5); C1−P1−C8 100.4(2), C8−P1−C15
98.8(2), C15−P1−C1 102.1(2).
1
of the o-CF3-Ph groups in the variable-temperature H NMR
spectra (see Supporting Information). A similar barrier (ca. 16
kcal/mol) was reported for Na[2-{(o-CF3-Ph)2P}-benzenesul-
fonate] in DMSO-d6 solution.13
Previous studies by NMR spectroscopy and molecular
mechanics computations have shown that tris(ortho-substi-
tuted-aryl)-phosphines normally adopt exo3 conformations in
solution, consistent with their solid-state structures, and that
exchange of the ortho-substituents occurs via a “three-ring-flip”
mechanism, in which all three aryl rings rotate through the
corresponding X−P−Cipso planes (i.e., flip) in a concerted
manner.11,13,19,25 It is likely that the CF3 groups in [1]− also
exchange by this mechanism, as illustrated in Scheme 4.
Synthesis and Solid-State Structure of (PO-CF3)PdMe-
(2,6-lutidine) (3). The reaction of Na[1] with {PdMe(2,6-
lutidine)(μ-Cl)}2 affords (PO-CF3)PdMe(2,6-lutidine) (3) in
69% isolated yield (Scheme 5). The solid-state structure of 3
(Figure 3) is essentially the same as that of the analogous
The [1]− anion adopts an exo3 propeller conformation in
which the aryl rings are rotated ca. 40° off the corresponding
(lone pair)−P−Cipso planes in the same direction.18 The two o-
CF3−Ph rings are thus inequivalent. Tris(ortho-substituted-
aryl)-phosphines normally exhibit exo3 conformations because
the ortho substituents cause less steric congestion when they
point toward the P lone pair (exo) rather than toward the other
aryl rings (endo). For example, P(o-CF3Ph)319 and [HNEt3][2-
{(o-OMe-Ph)2P}-benzenesulfonate]20 also have exo3 structures
in the solid state.
In [Na(18-crown-6)(H2O)][1], the P1−F5 (2.774 Å), P1−
F1 (2.994 Å), and P1−O3 (2.938 Å) distances are all shorter
than the corresponding sums of van der Waals radii (P, F: 3.27
Å; P, O: 3.32 Å),21 and the F1−P1−C15 (169°), F5−P1−C1
(176°), and O3−P1−C8 (170°) angles are all close to 180°.
Scheme 4. Possible Mechanism for the Exchange of CF3
Groups in [1]−
̈
Gabbai and co-workers have noted similar features in the
zwitterionic species 1-Mes2FB(−)-2-MePh2P(+)-benzene and
similar compounds and ascribed them to lone-pair(F) →
σ*(P−C) interactions.22 Similar lone-pair(F) → σ*(P−C) and
lone-pair(O) → σ*(P−C) interactions may be present in
[Na(18-crown-6)(H2O)][1].
Dynamic Properties of [1]−. The 19F{1H} NMR spectrum
of Na[1] in DMSO-d6 at 25 °C consists of two doublets (4JPF
=
62, 55 Hz), which shows that the two o-CF3-Ph rings are
inequivalent on the NMR time scale, consistent with the solid-
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of equal intensity. These spectra are essentially unchanged at 25
°C. These results show that 3 exists as a single conformer with
inequivalent o-CF3-Ph units and that rotation around the Pd−
N bond is slow on the NMR time scale under these conditions.
Only one of the two CF3 groups is coupled with phosphorus. A
detailed analysis, discussed below, shows that it is the exo-CF3
group (CF4F5F6) that engages in this 31P−19F coupling.
Scheme 5. Synthesis of 3 and 4
1
The H NMR spectrum of 3 contains a resonance at δ 9.12
(dd, JPH = 18, JHH = 7) that integrates for 1H. This low-field
chemical shift is characteristic for an ortho hydrogen of a
pseudoaxial P-aryl ring that is positioned in the deshielding
region close to an axial site of the Pd square plane.28 Therefore,
with reference to the solid-state structure, this resonance is
1
assigned to H17 (Figure 3). The H−1H NOESY spectrum
(Figure 4) shows that H17 is close to one of the lutidine-CH3
(PO)PdMe(2,6-lutidine) complex that contains the 2-{(o-CF3-
Ph)2P}-benzenesulfonate ligand.26 In 3, the [PO-CF3]− ligand
binds to the square-planar Pd center in a κ2-P,O mode, and the
chelate ring adopts a boat conformation.27 The phosphine
−
exhibits an exo2 conformation in which the ArSO3 and the
pseudoequatorial o-CF3-Ph (F4, F5, F6) group are exo (point
toward Pd) and the pseudoaxial o-CF3-Ph (F1, F2, F3) group is
endo (points away from Pd). The exo-CF3 group is positioned
below one axial site of the Pd center, and the shortest Pd−F
distance (Pd1−F4 3.079(3) Å) is nearly equal to the sum of the
van der Waals radii (Pd, F: 3.10 Å).21 The other Pd axial site is
occupied by the ortho hydrogen (H17) of the endo o-CF3-Ph
ring, and the Pd1−H17 distance (2.62 Å) is shorter than the
sum of the van der Waals radii (Pd, H: 2.83 Å).21 Close M−H
contacts involving the ortho-hydrogens of arylphosphine ligands
are common in square-planar d8 metal complexes.4c,7c,28
Solution Structure of 3. At −80 °C, the 1H NMR
spectrum of 3 in CD2Cl2 solution contains one Pd-CH3
resonance and two equal-intensity lutidine methyl resonances,
the 31P{1H} spectrum comprises a quartet (4JPF = 24), and the
19F{1H} spectrum consists of a singlet and a doublet (4JPF = 24)
1
Figure 4. H−1H NOESY spectrum of 3 in CD2Cl2 solution.
Figure 3. Two views of the molecular structure of 3. Hydrogen atoms except H17 are omitted. Selected bond lengths (Å) and angles (deg): Pd1−P1
2.2343(16), Pd1−O1 2.134(3), Pd1−N1 2.100(4), Pd1−C8 2.001(5), Pd1−F4 3.079(3), Pd1−H17 2.62; P1−Pd1−O1 94.14(10), O1−Pd1−N1
86.98(15), N1−Pd1−C8 89.09(19), C8−Pd1−P1 90.06(15).
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groups (C7) and the Pd-CH3 group (C8), confirming the exo
conformation of H17. H18−H20 were assigned by the COSY
spectrum. The 19F−1H HOESY spectrum (Figure 5) shows
Chart 1. Pd Complexes That Contain Chelating Phosphines
with o-CF3-Ph Substituents
resonance at δ 9.30 that integrates for 1H, and the 19F{1H}
NMR spectrum consists of a singlet. These results indicate that
the conformers of the o-CF3-Ph rings are similar in the solid
state and solution for B and C. In compound D,31 one CF3
group is exo and one is endo in the solid state. However, the 1H
NMR spectrum of D (CDCl3) contains a resonance at δ 9.05
that integrates for 2H, and the 19F{1H} NMR spectrum consists
of one singlet (6F), consistent with endo conformation for both
o-CF3-Ph rings. In this case, the conformation is different in the
solid state and solution.
1
Dynamic Properties of 3. The H and 19F{1H} NMR
spectra of 3 in CDCl2CDCl2 solution at 100 °C exhibit slight
line broadening, which suggests that a slow dynamic process is
operative. The 19F EXSY spectrum at 100 °C (Figure 6)
Figure 5. 19F−1H HOESY NMR spectrum of 3 in CD2Cl2 solution.
The 1H aliphatic region is shown at the top, and the aromatic region is
shown at the bottom.
that the 19F singlet resonance correlates with H20 and therefore
corresponds to the endo-CF3 group, i.e., CF1F2F3. Accordingly,
the 19F doublet is assigned to CF4F5F6. The 19F−1H HOESY
spectrum also shows that the CF4F5F6 group is close to the
other lutidine-CH3 group (C6) and thus establishes that this
CF3 group is exo. Collectively, these NMR results show that the
solution structure of 3 is similar to the solid-state structure and
features an exo2 conformation of the [PO-CF3]− ligand.
Furthermore, the observation that 31P−19F coupling is present
for the exo-CF3 but not the endo-CF3 group, even though the
fluorines on both CF3 groups are four bonds away from the
phosphorus, indicates that this 31P−19F coupling arises by a
through-space mechanism. This through-space coupling may
arise from overlap of lone-pair(F) and σ(P−Pd) orbitals.
Similar 31P−31P through-space coupling was attributed to lone-
pair(P)−σ(P−Pd) interactions.29
Figure 6. 19F EXSY spectrum of 3 in CDCl2CDCl2 solution at 100 °C.
confirms that the exo and endo o-CF3-Ph groups undergo
exchange. Rate constants for this CF3 exchange were obtained
from quantitative 19F EXSY experiments over the temperature
range of 55 to 100 °C.32 The free energy of activation at 100 °C
is ΔG⧧ = 20.2(4) kcal/mol.
Synthesis and Solid-State Structure of (PO-CF3)PdMe-
(pyridine) (4). The reaction of Na[1] with (COD)PdMeCl in
the presence of pyridine affords (PO-CF3)PdMe(pyridine) (4)
in 85% isolated yield (Scheme 5). Slow diffusion of pentane
into a CH2Cl2/benzene solution of 4 results in crystallization of
4·CH2Cl2, which was characterized by X-ray diffraction (Figure
7). The molecular structure of 4 is similar to that of 3. The
(PO-CF3)Pd chelate ring adopts a boat conformation.27 The
phosphine adopts an exo2 conformation, with the exo-CF3
group (CF1F2F3) lying under one Pd axial site (Pd1−F1
3.063(4) Å) and the ortho hydrogen of the endo-o-CF3-Ph ring
lying above the other Pd axial site (Pd1−H22 2.72 Å).
However, the dihedral angle between the pyridine plane and
the Pd square plane is smaller in 4 (θC−Pd−N‑C 52.8(4)°) than
the corresponding dihedral angle in 3 (80.3(4)°).
An important implication of the NMR analysis of 3 is that for
square-planar complexes that contain chelating phosphines with
o-CF3-Ph substituents a low-field H6 resonance (δ > ca. 9) and
4
the absence of JPF coupling are characteristic of an endo-CF3
group, while an H6 resonance in the normal range and the
presence of 4JPF coupling are characteristic of an exo-CF3 group.
Data for related compounds (Chart 1) that contain chelating
phosphines with o-CF3-Ph substituents are consistent with this
trend. For example, in compound B,30 one CF3 group is exo
and one is endo in the solid state. The 1H NMR spectrum of B
(CDCl3) contains a resonance at δ 9.58 that integrates for 1H,
and the 19F{1H} NMR spectrum comprises a singlet and a
doublet. In compound C,31 the CF3 group is endo in the solid
state. The 1H NMR spectrum of C (CD2Cl2) contains a
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Figure 9. 31P{1H} NMR spectrum of 4 in CDCl2F solution at −110
°C. Expanded views of the observed and simulated resonance for the
exo3 isomer (δ −34.8) are shown in the inset. The asterisk indicates an
impurity resonance. Integrations are shown beneath the spectrum.
Figure 7. Molecular structure of 4·CH2Cl2. Hydrogen atoms except
H22 and the CH2Cl2 solvent molecule are omitted. Selected bond
lengths (Å) and angles (deg): Pd1−P1 2.2174(14), Pd1−O1 2.126(3),
Pd1−N1 2.082(4), Pd1−C1 2.059(5), Pd1−F1 3.063(4), Pd1−H22
2.72; P1−Pd1−O1 94.26(9), O1−Pd1−N1 85.61(14), N1−Pd1−C1
90.48(18), C1−Pd1−P1 89.73(14).
phosphorus couples to both CF3 groups indicates that both CF3
groups are exo, and therefore the minor isomer of 4 has an exo3
conformation.33
Dynamic Properties of 4. As the temperature is raised
from −90 °C, the 31P{1H} resonances of exo2-4 and exo3-4
broaden and coalesce, ultimately forming a single broad
resonance at δ 40.7 at 20 °C (CD2Cl2, Figure 10). These
results indicate that the exo2-4 and exo3-4 isomers interconvert
on the NMR time scale. The free energy of activation of this
process, ΔG⧧ = 9.9(5) kcal/mol at −40 °C, was determined
from the coalescence of the two resonances.34 The exo2-4/exo3-
4 ratio decreases from 2:1 at −90 °C to ca. 1:1 at 20 °C.
1
Speciation and Structure of 4 in Solution. The H
NMR spectrum of 4 in CD2Cl2 solution at −90 °C (Figure 8)
1
Figure 8. H NMR spectrum of 4 in CD2Cl2 solution at −90 °C.
Integrations are shown beneath the spectrum.
contains two Pd-CH3 resonances in a 2:1 intensity ratio,
indicating the presence of two isomers. The spectrum contains
a doublet at δ 9.19 (JPH = 16 Hz), which is characteristic for the
ortho-H on an endo o-CF3-Ph ring, based on the results for 3
and other d8 square-planar complexes. The integrated intensity
of this resonance is one-third that of the major Pd-CH3
resonance, indicating that the major isomer has one endo o-
CF3-Ph ring. The 31P{1H} NMR spectrum of 4 in CDCl2F
solution at −110 °C (Figure 9) also contains two resonances in
a 2.4:1 intensity ratio, confirming the presence of two isomers.
The 31P{1H} resonance of the major isomer (δ 45.3) is a
quartet (4JPF = 24 Hz); that is, the phosphorus couples with
only one CF3 group, and so one CF3 group of this isomer must
be exo. These results establish that the major isomer of 4 has an
exo2 conformation.
The 31P{1H} resonance of the minor isomer of 4 comprises a
10-line multiplet at δ −34.8, corresponding to a quartet of
quartets (4JPF = 27, 12 Hz, simulated by gNMR). The fact that
Figure 10. Variable-temperature 31P{1H} NMR spectra of 4 in CD2Cl2
solution.
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1
Similarly, the corresponding H NMR resonances for exo2-4
and exo3-4 broaden and coalesce as the temperature is raised
(Figure 11). The ΔG⧧ values determined from the coalescence
Figure 12. Variable-temperature 19F{1H} NMR spectra of 4 in CD2Cl2
solution. Red: exo2-4, blue: exo3-4, black: rapidly exchanging exo2-4/
●
▲
exo3-4 mixture. : pseudoaxial o-CF3-Ph, : pseudoequatorial o-CF3-
Ph.
Figure 11. Variable-temperature 1H NMR spectra of 4 in CD2Cl2
solution. The aromatic and Pd-CH3 regions are shown. Red: exo2-4,
●
blue: exo3-4, black: rapidly exchanging exo2-4/exo3-4 mixture. : o-
6
◆
▲
CF3-Ph-H , : o-py, : Pd-CH3.
CDCl2CDCl2 solution over the temperature range of 25 to 100
°C (Figure S13) contain two resonances of equal intensity.
Minor line broadening of these resonances is observed above
ca. 70 °C, indicative of slow exchange of the CF3 groups. The
CF3 exchange was confirmed by the 19F EXSY spectrum at 100
°C (Figure 13). This CF3 exchange requires chelate ring
inversion (RI). The RI barrier was determined to be ΔG⧧(100
°C) = 21(1) kcal/mol by quantitative 19F EXSY experiments32
over the temperature range 55−100 °C.36
of the H6 resonances of the o-CF3-Ph rings (9.7(5) kcal/mol),
the ortho-H resonances of the pyridine ligand (9.8(5) kcal/
mol), and the Pd-CH3 resonances (9.7(5) kcal/mol) all agree
well with the value determined from the 31P{1H} spectrum.34
The 19F{1H} NMR spectrum of 4 in CD2Cl2 at −90 °C
(Figure 12) contains four resonances, indicating that the two
CF3 groups within each isomer are inequivalent (trivial for exo2,
not for exo3). The resonances at δ −51.6 (d, 4JPF = 23 Hz) and
δ −56.9 (s, br) are assigned to the exo-CF3 and endo-CF3
groups, respectively, of the major exo2-4 isomer, based on the
relative intensities and similarities of these chemical shifts to
those of the corresponding resonances of 3. The resonances at
Proposed Mechanism for the Dynamic Processes of 4.
These dynamic NMR results are most easily explained by the
simple exchange mechanism shown in Scheme 6. The low-
barrier process (ΔG⧧ = 9.9(5) kcal/mol) that interconverts
exo2-4 and exo3-4 without exchanging the pseudoaxial and
pseudoequatorial o-CF3-Ph rings corresponds to rotation
around the P−C bond of the pseudoaxial o-CF3-Ph rings.
The higher barrier process (ΔG⧧ = 21(1) kcal/mol), which
does exchange the pseudoaxial and pseudoequatorial o-CF3-Ph
rings, corresponds to inversion of the (PO-CF3)Pd chelate ring.
Due to the steric congestion around phosphorus, the exo2-4/
exo3-4 exchange probably involves some changes in the (PO-
CF3)Pd chelate ring conformation and the position of the
pseudoequatorial o-CF3-Ph ring, in addition to rotation of the
4
δ −51.9 (d, JPF = 27 Hz) and δ −53.2 (s, br) are assigned to
the exo3-4 isomer.35
As the temperature is raised from −90 °C to 20 °C, the δ
51.6 resonance of exo2-4 and the δ 53.2 resonance of exo3-4
broaden and coalesce, and the δ 56.9 resonance of exo2-4 and
the δ 51.9 resonance of exo3-4 broaden and coalesce (Figure
12). The ΔG⧧ values (9.9(5), 9.8(5) kcal/mol) determined
from these two coalescence phenomena agree well with the
1
values derived from the variable-temperature 31P{1H} and H
NMR spectra noted above.34 These results show that the
dynamic process that permutes exo2-4 and exo3-4 results in
exchange of a given o-CF3-Ph group of one isomer with a
specific o-CF3-Ph group of the other isomer and are consistent
with the sole operation of the AaR process in this temperature
range (Scheme 6).
4
pseudoaxial o-CF3-Ph ring (AaR). The change in the JPF value
for the pseudoequatorial o-CF3-Ph group (23 Hz in exo2-4, 12
Hz in exo3-4) likely reflects these additional conformational
4
changes. In fact, these nonzero JPF values do not distinguish
whether this CF3 group is fixed at an exo position or undergoes
rapid exchange between exo and endo positions (AeR in Scheme
1) in exo2-4 and exo3-4.
The 19F{1H} NMR spectra of the rapidly exchanging exo2-4/
exo3-4 mixture in CD2Cl2 solution at 20 °C (Figure 12) and in
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Scheme 6. Proposed Mechanism for the Dynamic Processes of 4
molecular sieves and Q-5 oxygen scavenger. CD2Cl2 and CDCl3 were
distilled from P2O5. CDCl2F was synthesized by a literature procedure
and distilled from P2O5.37 Hexanes, pentane, and toluene were purified
by passage through activated alumina and BASF R3-11 oxygen
scavenger. Diethyl ether, tetrahydrofuran (THF), and CH2Cl2 were
purified by passage through activated alumina. {PdMe(2,6-lutidine)(μ-
Cl)}2 was synthesized by a literature procedure.38 p-Toluenesulfonic
acid was dehydrated from its monohydrate before use.
NMR spectra were recorded in Teflon-valved tubes at ambient
1
probe temperature unless otherwise indicated. H and 13C chemical
shifts are reported relative to SiMe4 and were determined by reference
to the residual 1H and 13C solvent resonances. 19F and 31P NMR
spectra were referenced externally to neat CFCl3 and 85% H3PO4/
D2O (δ 0) respectively. Coupling constants are reported in hertz (Hz).
The numbering scheme for NMR assignments is given in Scheme 7.
Figure 13. 19F EXSY spectrum of 4 in CDCl2CDCl2 solution at 100
°C.
Scheme 7. Numbering Scheme Used for NMR Assignments
CONCLUSION
■
The exo and endo conformations of the o-CF3-Ph rings in (PO-
CF3)PdMe(L) and related compounds can be identified by
NMR. In the exo conformation, in which the CF3 group points
toward Pd, through-space JPF coupling is observed. In the endo
conformation, in which the CF3 group points away from Pd and
the o-H is positioned in the deshielding region near an axial site
of the Pd square plane, JPF coupling is not observed and the o-H
1H NMR resonance appears at low-field (δ > 9). These trends
were exploited to study the solution conformation and dynamic
properties of (PO-CF3)PdMe(py) (4). Complex 4 exists as a
2:1 mixture of exo2 and exo3 isomers in CD2Cl2 solution at −90
°C. In exo2-4, one CF3 group is exo and exhibits through-space
4JPF coupling, while the other CF3 group is endo and does not
exhibit through-space 4JPF coupling. In exo3-4, both CF3 groups
Electrospray mass spectra (ESI-MS) were recorded on freshly
prepared samples (ca. 1 mg/mL in CH2Cl2 or acetone). In all cases
where assignments are given, the observed isotope patterns closely
matched calculated isotope patterns. The listed m/z value corresponds
to the most intense peak in the isotope pattern.
Isobutyl 2-{(o-CF3-Ph)2P}-4-Me-benzenesulfonate. nBuLi (0.39
mL, 2.5 M in hexanes, 0.98 mmol) was added slowly to a solution
i
of Bu p-toluenesulfonate (0.227 g, 0.995 mmol) in THF (3 mL) at
−78 °C. The mixture was stirred at −78 °C for 3 h. The mixture was
added to a solution of (o-CF3-Ph)2PCl (0.351 g, 0.984 mmol) in
diethyl ether (21 mL) at −78 °C. The mixture was stirred at −78 °C
for 3 h and was allowed to warm to 25 °C. The mixture was stirred at
25 °C for 12 h. The volatiles were removed under vacuum. CH2Cl2
was added to afford a white suspension. The mixture was filtered
through Celite and concentrated under vacuum to afford a yellow
solid, which was purified by flash chromatography (eluant: 15/85 ethyl
acetate/hexanes) to yield isobutyl 2-{(o-CF3-Ph)2P}-4-Me-benzene-
sulfonate (0.329 g, 0.600 mmol, 61% based on (o-CF3-Ph)2PCl) as a
white solid. 1H NMR (500 MHz, CDCl3): δ 8.06 (dd, JHH = 8, JPH = 4,
1H, H3−ArSO3), 7.80−7.76 (m, 2H, H3−ArCF3), 7.52−7.47 (m, 2H,
H4−ArCF3), 7.46−7.40 (m, 2H, H5−ArCF3), 7.33 (d, JHH = 8, 1H,
H4−ArSO3), 6.94 (s, 2H, H6−ArCF3), 6.66 (s, 1H, H6−ArSO3), 4.07−
4.01 (m, 2H, −OCHH2−), 2.26 (s, 3H, ArCH3), 2.08−1.97 (m, 1H,
−CH[CH3]2), 0.96 (d, JHH = 7, 6H, −CH[CH3]2). 13C{1H} NMR
4
are exo and exhibit through-space JPF couplings. Complex 4
undergoes two dynamic processes: rotation of the pseudoaxial
o-CF3-Ph ring (AaR), which interconverts exo2-4 and exo3-4
(ΔG⧧ = 9.9(5) kcal/mol), and chelate ring inversion (RI),
which permutes the pseudoaxial and pseudoequatorial o-CF3-
Ph rings (ΔG⧧ = 21(1) kcal/mol).
EXPERIMENTAL SECTION
General Procedures. All experiments were performed using
glovebox or Schlenk techniques under a N2 atmosphere unless
otherwise noted. N2 was purified by passage through activated
■
(126 MHz, CDCl3): δ 144.1 (d, JPC = 1, C5−ArSO3), 138.1 (d, JPC
=
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27, C2−ArSO3), 137.0 (s, C6−ArSO3), 136.7 (dd, JPC = 31, JFC = 2,
C1−ArCF3), 136.6 (s, C6−ArCF3), 135.8 (s, C6−ArCF3), 135.6 (d, JPC
= 28, C1−ArCF3), 135.5 (d, JPC = 33, C1−ArSO3), 134.4 (qd, JFC = 30,
JPC = 27, C2−ArCF3), 133.8 (qd, JFC = 31, JPC = 27, C2−ArCF3), 131.9
(s, C5−ArCF3), 131.7 (s, C5−ArCF3), 131.3 (d, JPC = 4, C3−ArSO3),
130.2 (s, C4−ArSO3), 129.5 (s, C4−ArCF3), 129.3 (s, C4−ArCF3),
127.0 (m, C3−ArCF3), 124.3 (qd, JFC = 275, JPC = 2, ArCF3), 77.0
(−OCH2−), 28.3 (−CH[CH3]2), 21.7 (ArCH3), 18.7 (−CH[CH3]2).
19F{1H} NMR (471 MHz, CDCl3): δ −57.0 (d, JPF = 56), −57.3 (d,
(PO-CF3)Pd(Me)(2,6-lutidine) (3). A flask was charged with Na[1]
(0.240 g, 0.467 mmol), {PdMe(2,6-lutidine)(μ-Cl)}2 (0.121 g, 0.229
mmol), and CH2Cl2 (7 mL). The mixture was stirred at 25 °C for 6 h.
The mixture was filtered. CH2Cl2 (8 mL) was used to wash the
precipitate and combined with the filtrate. The filtrate was
concentrated under vacuum to afford a pale yellow solid, which was
recrystallized from CH2Cl2/pentane to yield 3 (0.228 g, 0.317 mmol,
69% based on {PdMe(2,6-lutidine)(μ-Cl)}2) as a pale yellow solid.
Crystals of 3 suitable for X-ray diffraction were obtained by slow
diffusion of pentane into a CH2Cl2 solution of 3. 1H NMR (500 MHz,
CD2Cl2): δ 9.12 (dd, JPH = 18, JHH = 7, 1H, H6−ArCF3(A)), 7.95−
7.91 (m, 2H, H3−ArCF3(B), H3−ArSO3), 7.87−7.85 (m, 1H, H3−
ArCF3(A)), 7.81 (t, JHH = 7, 1H, H5−ArCF3(A)), 7.76 (t, JHH = 7, 1H,
H4−ArCF3(A)), 7.70 (t, JHH = 7, 1H, H4−ArCF3(B)), 7.64 (t, JHH = 8,
JPF = 54). 31P{1H} NMR (202 MHz, CDCl3): δ −13.7 (septet, JPF
=
55). ESI-MS (MeOH/CH2Cl2, 1:1 by volume, positive ion scan, m/z):
549.0 (MH+). Anal. Calcd for C25H23F6O3PS: C, 54.75; H, 4.23.
Found: C, 54.72; H, 4.22.
(o-CF3-Ph)2P(O)P(o-CF3-Ph)2 (2). In the flash chromatography
described above, after the fractions containing isobutyl 2-{(o-CF3-
Ph)2P}-4-Me-benzenesulfonate were collected, the eluant was
switched to 30/70 ethyl acetate/hexanes. Fractions containing side
products were combined, and volatiles were removed under vacuum to
afford a pale yellow solid (0.138 g) as the crude side product. NMR
spectra showed that 2 is the major species. Crystals of 2 suitable for X-
ray diffraction were obtained by slow diffusion of pentane into a
1H, H4−lutidine), 7.49 (t, JHH = 8, 1H, H5−ArCF3(B)), 7.38 (d, JHH
=
8, 1H, H4−ArSO3), 7.22 (d, JHH = 8, 1H, H3(A)−lutidine), 7.16 (d,
JHH = 8, 1H, H3(B)−lutidine), 7.10 (d, JPH = 12, 1H, H6−ArSO3), 6.99
(dd, JPH = 12, JHH = 8, 1H, H6−ArCF3(B)), 3.20 (s, 3H, CH3(A)−
lutidine), 2.91 (s, 3H, CH3(B)−lutidine), 2.30 (s, 3H, ArCH3), 0.11
(d, JPH = 3, 3H, PdCH3). 13C{1H} NMR (126 MHz, CD2Cl2): δ
159.32 (d, JPC = 1, C2−lutidine), 159.25 (d, JPC = 1, C2−lutidine),
146.3 (d, JPC = 16, C2−ArSO3), 143.3 (d, JPC = 28, C6−ArCF3(A)),
1
diethyl ether solution of the crude side product. H NMR (500 MHz,
139.7 (d, JPC = 7, C5−ArSO3), 139.0 (s, C4−lutidine), 136.5 (d, JPC
=
acetone-d6): δ 8.68−8.67 (m, 2H), 7.88−7.81 (m, 4H), 7.76−7.73 (m,
4H), 7.70−7.65 (m, 4H), 7.54 (t, JHH = 7.8 Hz, 2H). 19F{1H} NMR
(471 MHz, acetone-d6): δ −55.8 (d, JPF = 17, 6F), −56.2 (dd, JPF = 50,
5, 6F). 31P{1H} NMR (202 MHz, acetone-d6): δ 40.3 (doublet of
5, C6−ArCF3(B)), 135.8 (s, C6−ArSO3), 133.7−133.2 (m, C2−
ArCF3), 132.9−132.6 (m, C2−ArCF3), 132.3 (d, JPC = 3, C4−ArSO3),
132.2 (d, JPC = 2, C4−ArCF3(A)), 132.1 (d, JPC = 17, C5−ArCF3(A)),
131.9 (d, JPC = 7, C5−ArCF3(B)), 131.8 (d, JPC = 2, C4−ArCF3(B)),
130.0−129.8 (m, C3−ArCF3(B)), 129.4 (d, JPC = 44, C1−ArCF3(A)),
128.9−128.8 (m, C3−ArCF3(A)), 128.4 (d, JPC = 9, C3−ArSO3), 126.8
(d, JPC = 40, C1−ArCF3(B)), 126.5 (d, JPC = 45, C1−ArSO3), 124.9 (q,
JFC = 276, ArCF3), 123.7 (q, JFC = 274, ArCF3), 123.2 (d, JPC = 3,
C3(A)−lutidine), 123.1 (d, JPC = 3, C3(B)−lutidine), 27.0 (s,
CH3(A)−lutidine), 26.3 (s, CH3(B)−lutidine), 21.2 (s, ArCH3),
−4.4 (s, PdCH3). 19F{1H} NMR (471 MHz, CD2Cl2): δ −52.3 (d,
JPF = 22, ArCF3(B)), −55.7 (s, ArCF3(A)). 31P{1H} NMR (202 MHz,
CD2Cl2): δ 41.6 (q, JPF = 21). ESI-MS (MeOH/H2O, 1:1 by volume,
positive ion scan, m/z): 720.0 (MH+). Anal. Calcd for
C29H26F6NO3PPdS: C, 48.38; H, 3.64; N, 1.95. Found: C, 48.10; H,
3.61; N, 1.62.
1
1
septets, JPP = 243, JPF = 5), −33.0 to −35.7 (m, JPP = 243, JPF = 50,
17). ESI-MS (MeOH/CH2Cl2, 1:1 by volume, positive ion scan, m/z):
659.0 (MH+).
Na[PO-CF3] (Na[1]). Route 1. A flask was charged with isobutyl 2-
{(o-CF3-Ph)2P}-4-Me-benzenesulfonate (0.38 g, 0.69 mmol), NaI
(0.317 g, 2.11 mmol), and CH3CN (10 mL, purged with N2 for 20
min before use). The mixture was refluxed for 15 h. The mixture was
concentrated under vacuum to afford a white solid, which was washed
with H2O and CHCl3 to yield Na[1] (0.24 g, 0.47 mmol, 68%) as a
white fluffy solid. Crystals of [Na(18-crown-6)(H2O)][1] suitable for
X-ray diffraction were obtained by slow diffusion of pentane into a wet
1
CH2Cl2 solution of Na[1] in the presence of 18-crown-6. H NMR
(500 MHz, acetone-d6): δ 7.99 (dd, JHH = 8, JPH = 4, 1H, H3−ArSO3),
7.81 (s, 1H, H3−ArCF3(A)), 7.71 (s, 1H, H3−ArCF3(B)), 7.57−7.55
(m, 1H, H4-ArCF3(A)), 7.51−7.50 (m, 2H, H5−ArCF3(A), H3−
ArCF3(B)), 7.45−7.44 (m, 1H, H5−ArCF3(B)), 7.17 (d, JHH = 8, 1H,
H4−ArSO3), 7.05 (s, 1H, H6−ArCF3(B)), 6.93 (d, JHH = 6, 1H, H6−
ArCF3(A)), 6.52 (s, 1H, H6−ArSO3), 2.11 (s, 3H, ArCH3). 13C{1H}
NMR (126 MHz, acetone-d6): δ 148.8 (d, JPC = 26, C2−ArSO3), 139.8
(d, JPC = 1, C5−ArSO3), 139.5 (s, C1−ArCF3), 139.0 (d, JPC = 30, C1−
ArCF3), 137.7 (s, C6−ArCF3(A)), 136.7 (s, C6−ArCF3(B)), 135.9 (s,
(PO-CF3)Pd(Me)(pyridine) (4). A flask was charged with Na[1]
(0.132 g, 0.257 mmol), (COD)PdMeCl (0.071 g, 0.27 mmol),
pyridine (22 μL, 0.27 mmol), and CH2Cl2 (23 mL). The mixture was
stirred at 25 °C for 2 h. The mixture was filtered and concentrated
under vacuum to afford a pale yellow solid, which was recrystallized
from CH2Cl2/pentane to yield 4 (0.152 g, 0.220 mmol, 85% based on
Na[1]) as a pale yellow solid. Crystals of 4·CH2Cl2 suitable for X-ray
diffraction were obtained by slow diffusion of pentane into a CH2Cl2/
benzene solution of 4. 1H NMR (500 MHz, CD2Cl2): δ 8.73 (d, JHH
=
C6−ArSO3), 134.8 (dq, JPC = 31, JFC = 28, C2−ArCF3), 133.4 (d, JPC
=
5, 2H, H2−pyridine), 8.16 (dd, JPH = 15, JHH = 7, 1H, H6−ArCF3(A)),
8.02−7.97 (m, 2H, H3−ArCF3(B), H3−ArSO3), 7.89−7.86 (m, 2H,
H3−ArCF3(A), H4−pyridine), 7.77−7.67 (m, 3H, H4−ArCF3(A),
H4−ArCF3(B), H5−ArCF3(A)), 7.52−7.45 (m, 3H, H5−ArCF3(A),
H3−pyridine), 7.43 (d, JHH = 8, 1H, H4−ArSO3), 7.03 (dd, JPH = 12,
JHH = 8, 1H, H6−ArCF3(B)), 6.92 (d, JPH = 12, 1H, H6−ArSO3), 2.27
(s, 3H, ArCH3), 0.45 (s, 3H, PdCH3). 13C{1H} NMR (126 MHz,
CD2Cl2): δ 150.8 (s, C2−pyridine), 146.9 (d, JPC = 15, C2−ArSO3),
140.5 (d, JPC = 19, C6−ArCF3(A)), 140.2 (d, JPC = 7, C5−ArSO3),
138.9 (s, C4−pyridine), 136.4 (d, JPC = 4, C6−ArCF3(B)), 135.2 (s,
C6−ArSO3), 134.0 (qd, JFC = 31, JPC = 10, C2−ArCF3), 133.2 (qd, JFC
= 32, JPC = 3, C2−ArCF3), 132.6 (d, JPC = 2, C4−ArSO3), 132.5−132.3
(m, C5−ArCF3), 132.2 (d, JPC = 2, C4−ArCF3), 131.9 (d, JPC = 2, C4−
ArCF3), 129.4 (dq, JPC = 7, JFC = 5, C3−ArCF3), 129.3−129.2 (m, C3−
ArCF3), 129.2 (d, JPC = 9, C3−ArSO3), 128.0 (d, JPC = 43, C1−ArCF3/
C1−ArSO3), 127.7 (d, JPC = 43, C1−ArCF3/C1−ArSO3), 126.4 (d, JPC
27, C1−ArSO3), 133.2−132.7 (m, C2−ArCF3), 132.6 (s, C5−ArCF3),
132.4 (s, C5−ArCF3), 130.1 (s, C4−ArSO3), 129.8 (s, C4−ArCF3(A)),
129.6 (d, JPC = 4, C3−ArSO3), 129.3 (s, C4−ArCF3(B)), 127.2 (dq, JPC
= 6, JFC = 5, C3−ArCF3), 125.6 (q, JFC = 275, ArCF3), 125.4 (q, JFC
=
275, ArCF3), 21.18 (s, ArCH3). 19F{1H} NMR (471 MHz, acetone-
d6): δ −55.9 (d, JPF = 61), −56.4 (d, JPF = 54). 31P{1H} NMR (202
MHz, acetone-d6): δ −14.1 (septet, JPF = 57). ESI-MS (acetonitrile,
positive ion scan, m/z): 493.0 (M − Na+ + 2H+). Multiple elemental
analyses on spectroscopically pure samples of this compound did not
yield satisfactory results.
n
Na[1]. Route 2. BuLi (7.0 mL, 2.9 M in hexanes, 20 mmol) was
added slowly to a solution of p-toluenesulfonic acid (1.64 g, 9.52
mmol) in THF (25 mL) at −78 °C. The mixture was stirred at −78
°C for 4.5 h. The mixture was added to a solution of (o-CF3-Ph)2PCl
(3.39 g, 9.51 mmol) in diethyl ether (25 mL) at −78 °C. The mixture
was stirred at −78 °C for 3 h and was allowed to warm to 25 °C. The
mixture was stirred at 25 °C for 12 h. The volatiles were removed
under vacuum. CH2Cl2 (20 mL) and H2O (20 mL) were added. The
aqueous phase was acidified to pH = 2 by adding aqueous HCl
solution and then separated. Aqueous NaCl solution was added to the
aqueous phase to afford white precipitates. The mixture was filtered to
yield Na[1] (3.18 g, 6.18 mmol, 65%) as a white fluffy solid.
= 47, C1−ArCF3), 125.7 (s, C3−pyridine), 124.7 (qd, JFC = 276, JPC
=
1, ArCF3), 124.2 (qd, JFC = 276, JPC = 1, ArCF3), 21.2 (s, ArCH3), 1.7
(s, PdCH3). 19F{1H} NMR (471 MHz, CD2Cl2): δ −52.7 (d, JPF = 18,
ArCF3(B)), −54.1 (d, JPF = 8, ArCF3(A)). 31P{1H} NMR (202 MHz,
CD2Cl2): δ 40.7 (br). ESI-MS (MeOH/CH2Cl2, 1:1 by volume,
positive ion scan, m/z): 691.9 (MH+). Multiple elemental analyses on
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spectroscopically pure samples of this compound did not yield
satisfactory results.
I.; Cavallo, L.; Mecking, S. J. Am. Chem. Soc. 2010, 132, 4418.
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X-ray Crystallography. Full details are provided in the
Supporting Information. Data were collected on a Bruker Smart
Apex diffractometer using Mo Kα radiation (0.710 73 Å). Direct
methods were used to locate many atoms from the E-map. Repeated
difference Fourier maps enabled location of all expected non-hydrogen
atoms. Following anisotropic refinement of all non-H atoms, ideal H
atom positions were calculated. Final refinement was anisotropic for all
non-H atoms and isotropic-riding for H atoms. ORTEP diagrams are
drawn with 50% probability ellipsoids.
134, 1010. (f) Leicht, H.; Gottker-Schnetmann, I.; Mecking, S. Angew.
Chem., Int. Ed. 2013, 52, 3963.
̈
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ASSOCIATED CONTENT
* Supporting Information
■
S
Crystal structure report for compounds [Na(18-crown-6)-
(H2O)][1], 2, 3, and 4·CH2Cl2; synthesis of compounds;
generation and structure of 2; additional NMR spectra and
analysis of Na[1] and 4; details of 19F EXSY analysis of 3 and 4;
NMR spectra of compounds and crystallographic data in CIF
format. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: rfjordan@uchicago.edu.
■
Anselment, T. M. J.; Frohlich, R.; Rieger, B.; Kehr, G.; Erker, G.
̈
Organometallics 2011, 30, 5248.
Notes
(10) (a) Kochi, T.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem.
Soc. 2007, 129, 7770. (b) Nakamura, A.; Munakata, K.; Ito, S.; Kochi,
T.; Chung, L. W.; Morokuma, K.; Nozaki, K. J. Am. Chem. Soc. 2011,
133, 6761. (c) Nakamura, A.; Kageyama, T.; Goto, H.; Carrow, B. P.;
Ito, S.; Nozaki, K. J. Am. Chem. Soc. 2012, 134, 12366.
(11) Howell, J. A. S.; Palin, M. G.; Yates, P. C.; McArdle, P.;
Cunningham, D.; Goldschmidt, Z.; Gottlieb, H. E.; Hezroni-
Langerman, D. J. Chem. Soc., Perkin Trans. 2 1992, 1769.
(12) These “(PO)PdMe” species are probably solvent adducts or, less
likely, sulfonate-bridged dimers (see ref 4g).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Antoni Jurkiewicz, Ian Steele, and Jin Qin for
assistance with NMR spectroscopy, X-ray crystallography, and
mass spectrometry, respectively. This work was supported by
the National Science Foundation (grants CHE-0911180 and
CHE-1048528).
(13) Neuwald, B.; Caporaso, L.; Cavallo, L.; Mecking, S. J. Am. Chem.
Soc. 2013, 135, 1026.
(14) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger, B.; Ziegler,
T. Organometallics 2006, 25, 4491.
(15) (a) Espinet, P.; Albeniz, A. C.; Casares, J. A.; Martínez-Ilarduya,
́
J. M. Coord. Chem. Rev. 2008, 252, 2180. (b) Hierso, J.-C. In Science
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