Exploration of the mechanism of platinum(II)-catalyzed C-F activation: Characterization and reactivity of platinum(IV) fluoroaryl complexes relevant to catalysis

Article abstract of DOI:10.1021/om2007562

A series of Pt(IV) complexes relevant to catalytic C-F activation have been prepared and structurally characterized. Pt^IV-F complexes, formed by C-F activation, underwent transmetalation with Me₂Zn to generate Me₃Pt^IV

Full text of DOI:10.1021/om2007562

Article
pubs.acs.org/Organometallics
Exploration of the Mechanism of Platinum(II)-Catalyzed C−F
Activation: Characterization and Reactivity of Platinum(IV) Fluoroaryl
Complexes Relevant to Catalysis
Tongen Wang, Lauren Keyes, Brian O. Patrick, and Jennifer A. Love*
Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, British Columbia, V6T 1Z1
S
* Supporting Information
ABSTRACT: A series of Pt(IV) complexes relevant to
catalytic C−F activation have been prepared and structurally
characterized. PtIV−F complexes, formed by C−F activation,
underwent transmetalation with Me2Zn to generate Me3PtIV
fluoroaryl complexes. In all cases, the Me3PtIV complex under-
went reductive elimination to generate methylated organic
products. The reactivity of both PtIV−F and Me3PtIV fluoroaryl
complexes was strongly affected by the electronic nature of the
cyclometalated fluoroaryl ligand.
conditions to the cross-coupling of electron-deficient fluoro-
arenes has been demonstrated.10d−i While important from the
standpoint of much-needed defluorination technology, the
inability to stop at partial defluorination renders this approach
unsuitable for generating functionalized polyfluoroarenes.
Methodologies for the selective cross-coupling of polyfluoroar-
enes are of particular interest, as the products of these reactions
(partially functionalized aryl fluorides) have potential for
further use as synthetic building blocks. Recently, several
reports of catalytic cross-coupling of polyfluoroarenes based on
group 9 and 10 metal complexes have emerged.10j−o
INTRODUCTION
■
Transition-metal-catalyzed carbon−element bond activation
has been an area of much interest in the synthetic community
for decades. In particular, late-transition-metal complexes have
been extensively utilized as catalysts in cross-coupling reactions,
allowing for the construction of C−C and C−X bonds with
broad scope.1 These methodologies permit the assembly of a
vast array of molecular frameworks and, as such, are routinely
utilized in the preparation of natural products, pharmaceuticals,
and materials.
The oxidative addition of a carbon−halogen (C−X) bond
across a low-valent metal center is the initial step in many cross-
coupling reactions.2 As a result, transition-metal-mediated C−X
bond activation, including C−F bonds, has been well studied.3
Despite this, examples of catalytic conversion of C−F bonds
into C−C bonds are rare in comparison to cross-coupling
reactions of other C−X reagents.4 Therefore, catalytic
activation of C−F bonds remains a considerable challenge to
the field of organometallic chemistry. Furthermore, the catalytic
functionalization of polyfluoroarenes as a means to generate
functionalized aryl fluorides is of particular interest, given the
increasing prevalence of these moieties in pharmaceuticals,5
materials,6 and agrochemicals.5
To this end, several groups have developed methods for the
activation of fluoroaromatics, with a particular emphasis on
using group 97 and 108 metal complexes. Early transition metals
have also been utilized in C−F activation, but to a lesser
extent.9 The first example of a catalytic aryl fluoride cross-
coupling was reported by Kumada in 1973.10a The process
involved the coupling of fluorobenzene with alkyl Grignard
reagents, catalyzed by a Ni salt. However, the development of
additional methodologies for the catalytic cross-coupling of aryl
fluorides is relatively new, with only two additional examples
appearing before the turn of the millennium.10b,c Building on
these initial reports, the application of Stille- and Suzuki-type
Our group has developed a methodology for the catalytic
methylation of a variety of polyfluoroaryl imines in high yields
and high selectivity utilizing a platinum dimer[(CH3)2Pt(μ-
SMe2)]2 (eq 1).11,12 This approach relies on C−F bond
activation with subsequent functionalization at carbon and is
selective for monomethylation. In addition, a range of
substitution patterns on the fluoroaryl ring are well-tolerated,
as are potentially reactive functional groups.
Mechanistic analysis of Pt(II)-catalyzed methylation is
consistent with a typical cross-coupling mechanismimine-
directed C−F activation, transmetalation, and reductive
elimination (Scheme 1; geometries not known).13 The imine
Special Issue: Fluorine in Organometallic Chemistry
Received: August 12, 2011
Published: January 5, 2012
© 2012 American Chemical Society
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PtIV−X·SMe2 (X = F, Br) complexes were easily prepared by
treating a given polyfluoroaryl imine with a stoichiometric
amount of [(CH3)2Pt(μ-SMe2)]2. We were interested in
evaluating electronic effects on the overall reactivity of these
PtIV−X complexes. To this end, PtIV−X complexes with fully
fluorinated (1) and partially fluorinated (216a and 3) cyclo-
metalated ligands were prepared (Scheme 2). The PtIV−Br
Scheme 1. Mechanism of Pt(II)-Catalyzed Methylation of
Polyfluoroaryl Imines
Scheme 2. Preparation of PtIV−X (X = Br, F) Complexes
functionality directs C−F activation to the ortho position of the
aromatic ring, which accounts for the selectivity of the reaction.
This results in the formation of a PtIV−F complex from which
transmetalation with a suitable organometallic reagent and
subsequent reductive elimination generates the ortho-function-
alized polyfluoroaryl imine products. Each step of the reaction
(oxidative addition, transmetalation, and reductive elimination)
was impeded by excess SMe2, as was the catalytic reaction itself.
This is consistent with the mechanistic scheme shown, where
five-coordinate intermediates are part of the catalytic cycle
(vide infra).
A variety of Pt(II) complexes have been found capable of
activating strong carbon−element bonds.14 Indeed, Pt(II)−
Pt(IV) systems have been utilized in other catalytic trans-
formations, such as C−H activation.14 However, in comparison
to other group 10 metals, much less is known about the
fundamental reactivity of Pt-based catalytic systems, particularly
high-valent Pt(IV) complexes. This information is essential to
addressing the current limitations of catalytic C−F activation
and to expand the reaction scope. Therefore, we were
interested in evaluating the reactivity of the Pt(IV) complexes
involved in catalytic C−F activation. We disclose herein the
characterization and systematic study of the formation and
reactivity of a series of Pt(IV) complexes relevant to catalytic
C−F activation. These results build upon our proposed
mechanism of catalytic methylation and provide deeper insight
into each of the fundamental steps involved in catalysis.
complex 3 was prepared using N-(2-bromo-6-fluoroben-
zylidene)benzylamine; the corresponding PtIV−F complex
could not be prepared because of the low reactivity of N-(2-
fluoro-6-fluorobenzylidene)benzylamine (vide infra).
The lability of the SMe2 ligand has largely impeded the
isolation and solid-state characterization of the PtIV−X·SMe2
complexes. Nevertheless, the geometry of these complexes
could be determined on the basis of in situ solution state NMR
spectroscopy. The chemical shift and coupling constant data for
complex 2 match the published data15,16a and are given in Table 1
for comparison with complexes 1 and 3. As expected on the
basis of the work of Crespo and Martinez on 2 and other
related complexes,16a diagnostic features in the H and 19F
1
NMR spectra are indicative of the formation of PtIV−F bonds in
the new complexes 1 and 3. For each complex, the 19F NMR
spectrum shows a broad signal corresponding to the Pt−F
bond; the signal (δ −250 to −270) is considerably upfield
1
relative to other aryl F signals. Characteristic H NMR spectral
data for 1−3 are summarized in Table 1.17 Imine coordination
1
to Pt is evident in the H NMR spectra by the presence of a
singlet, with Pt satellites, ranging from δ 8.88 to 8.23 (Table 1,
entry 1). In addition, the presence of two upfield signals (δ
1.50−0.80, with coupling to both Pt and F) are consistent with
the formation of new Pt−Me bonds (Table 1, entries 3 and 4).
The F−H coupling constants are consistent with a cis
orientation of fluorine to both methyl ligands. The Pt−H
coupling constants indicate that the methyl groups are trans to
L-type donor ligands.18 This indicates that the fluorine ligand is
trans to the cyclometalated fluoroaryl ligand (as depicted in
Table 1). The same geometry was also observed with a related
PtIV−Br complex (3). NOE data confirmed the geometrical
assignments for all complexes.18
RESULTS AND DISCUSSION
■
C−F Activation. We began our studies by investigating the
C−F activation of a series of polyfluoroarenes. We had
previously found that coordinatively unsaturated PtIV−F com-
plexes were involved in the catalytic methylation of poly-
fluoroaryl imines (Scheme 1).13 In addition, it was determined
that PtIV−F·SMe2 complexes, which would be formed by SMe2
recoordination, could re-enter the catalytic cycle.13 Importantly,
these Me2PtIV−F complexes did not undergo reductive
elimination to give either methylated imine products or ethane.
Given the important role of PtIV−F complexes in catalysis, we
sought to gain more information about the structure and re-
activity of these complexes.
Previous studies established that the labile SMe2 ligand could
be substituted with PPh3.16 On this basis, we sought to convert
1−3 to the corresponding PtIV−F·PPh3 complexes. Displace-
ment of SMe2 with PPh3 occurred readily at room temperature
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Table 1. Characteristic H NMR Spectroscopic Data for Complexes 1, 2, and 3
Article
a
1
b
ab
,
b
entry
assignt
δ (multiplicity)
δ (multiplicity)
δ (multiplicity)
rel intens
1
2
3
4
CHN
Pt−SMe2
Pt−Meb
Pt−Mea
8.98 (s, JPt−H = 48.0 Hz)
1.96 (s, JPt−H = 12.0 Hz)
8.23 (s, JPt−H = 55.2 Hz)
1.89 (s, JPt−H = 12.0 Hz)
8.40 (s, JPt−H = 48.7 Hz)
1.87 (s, JPt−H = 12.0 Hz)
1.07 (s, JPt−H = 68.4 Hz)
0.71 (s, JPt−H = 69.6 Hz)
1
6
3
3
1.50 (dd, JPt−H = 63.0 Hz, JF−H = 6 Hz)
1.11 (d, JPt−H = 65.7 Hz, JF−H = 8 Hz)
0.80 (d, JPt−H = 66.0 Hz, JPt−F = 6 Hz)
0.72 (d, JPt−H = 68.1 Hz, JPt−F = 8 Hz)
NMR spectral data are consistent with previously reported characterization data for this compound.16a NMR spectral data were obtained under the
a
b
following conditions: acetonitrile-d3, 25 °C, 300 MHz.
1
(Scheme 3). The reactions were monitored by H, 19F, and
Complexes 4 and 6 were characterized by multinuclear NMR
spectroscopy, NOE, HRMS, and X-ray diffraction18 The
formation of the corresponding PtIV−F·PPh3 complexes is
clearly indicated by the 1H and 31P{1H} NMR spectra (Table 2).
The presence of large satellite signals in the 31P{1H} NMR
spectra, corresponding to Pt−P coupling (Table 2; entry 4), are
consistent with PPh3 coordination. The chemical shift of the
PPh3 signal is within the range reported for related Pt−PPh3
complexes.16 In the 1H NMR spectra, coordination of PPh3 can
be seen indirectly through the additional splitting of the Pt−Me
resonances. This new splitting is the result of coupling between
multiple NMR-active nuclei, giving rise to F−H, P−H, and
Pt−H coupling constants as well as complex multiplets (Table 2;
entries 2 and 3).
31P{1H} NMR spectroscopy. Our data for complex 516a match
Scheme 3. Preparation of PtIV−X·PPh3 (X = F, Br)
Complexes
In addition to changes in multiplet structure, coordination of
PPh3 was also found to shift various resonances in the 1H NMR
spectra relative to the SMe2 complexes. The most significant
effect was observed for the CHN resonances of the various
Pt(IV) complexes. For example, the CHN resonance for the
PtIV−F·PPh3 complex 4 shifted upfield by δ 0.42 in comparison
to that for the PtIV−F·SMe2 complex 1 (compare Table 1, entry
1, and Table 2, entry 1). This is consistent with the stronger
σ-donating ability of the PPh3 ligand relative to that of SMe2,
resulting in a more electron rich Pt center. In general, the apical
the published data and are given in Table 2 for comparison with
complexes 4 and 6.
a
Table 2. NMR Spectroscopic Data for Complexes 4, 5, and 6
rel
c
ab
,
c
entry assignt
δ (multiplicity)
δ (multiplicity)
8.23 (s, JPt−H = 55.2 Hz)
δ (multiplicity)
intens
1
2
CHN 8.56 (s, JPt−H = 36.9 Hz)
8.11 (s, JPt−H = 49.8 Hz)
1
3
Pt−Meb 1.62 (m, JPt−H = 59.4 Hz, JF−H = 12 Hz, 1.22 (td, JPt−H = 66.0 Hz, JP−H = 8 Hz) (JF−H = 2 1.49 (d, JPt−H = 69.3 Hz, JP−H = 8 Hz)
JP−H = 5 Hz) Hz)
3
4
Pt−Mea 0.74 (td, JPt−H = 61.0 Hz, JP−H = 12 Hz, 0.62 (td, JPt−H = 61.8 Hz, JP−H = 8 Hz, JF−H = 2 Hz) 0.98 (d, JPt−H = 58.2 Hz, JP−H = 8 Hz)
JF−H = 5 Hz)
3
Pt−PPh3 −0.57 (d, JPt−P = 1614 Hz, JF−P = 52 Hz) −1.72 (d, JPt−P = 1102 Hz, JF−P = 64 Hz)
−7.2 (d, JPt−P = 1005 Hz)
b
N/A
NMR spectral data are consistent with the previously reported characterization data for this compound.16a NMR spectral data were obtained under
the following conditions: acetonitrile-d3, 25 °C, 300 MHz. NMR spectral data were obtained under the following conditions: dichloromethane-d2,
a
c
25 °C, 300 MHz.
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methyl ligand was more affected by PPh3 coordination, as
observed by greater changes in chemical shift (compare Tables
1 and 2, entry 3). Such a result is expected on the basis of the
trans influence of ligands in octahedral complexes.2 As with our
characterization of the related PtIV−F·SMe2 complexes, the
geometry of these PtIV−F·PPh3 complexes was confirmed by
NOE analysis.18
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Complexes 4 and 6
4
6
entry
1
Pt1−F5
Pt1−C1
Pt1−C2
Pt1−N1
Pt1−P2
Pt1−C27
N1−C36
C1−Pt1−F5
C1−Pt1−C27
F5−Pt1−N1
C27−Pt1−N1
C1−Pt1−C2
C2−Pt1−F5
C27−Pt1−F5
C1−Pt1−P1
F5−Pt−P1
2.0469(17)
2.065(3)
2.075(3)
2.139(3)
2.4259(8)
1.997(3)
1.276(4)
88.49(11)
99.56(14)
91.01(9)
80.28(11)
87.47(15)
86.38(12)
169.06(11)
90.84(10)
89.79(6)
Pt1−Br
Pt1−C1
Pt1−C2
Pt1−N1
Pt1−P1
Pt1−C22
N1−C28
C1−Pt1−Br1
C1−Pt1−C22
Br1−Pt1−N1
C22−Pt1−N1
C1−Pt1−C2
C2−Pt1−Br1
C22−Pt1−Br1
C1−Pt1−Br1
Br1−Pt1−P1
2.5657(8)
2.049(7)
2.093(7)
2.144(6)
2.4146(17)
2.004(7)
1.288(9)
91.4(2)
2
3
Single crystals of complexes 4 and 6 were obtained from
saturated solutions of acetonitrile (Figure 1). Selected bond
4
5
6
7
8
9
93.0(3)
10
11
12
13
14
15
16
94.51(16)
80.5(2)
86.4(3)
88.2(2)
173.47(18)
92.71(2)
93.47(5)
Table 4. Crystallographic Data for Complexes 4 and 6
4
6
empirical formula
formula wt
cryst syst
space group (No.)
a (Å)
C36H35N2FPPtBr
820.63
C34H28NPPtF5Br
851.54
monoclinic
P21/n (14)
9.4945(7)
18.1068(11)
18.3770(10)
90.0
monoclinic
C2/c (15)
28.4705(10)
9.0217(3)
27.1319(14)
90.0
b (Å)
c (Å)
α (deg)
β (deg)
90.972(3)
90.0
118.750(1)
90.0
γ (deg)
V (A3)
3158.8(3)
4
6109.8(4)
8
Z
Dc (g/cm3)
1.726
1.851
T (K)
173
1
173
1
solvent/color
acetonitrile/
colorless
acetonitrile/
colorless
F(000)
1608.00
50.8
3296.00
55.8
2θmax (deg)
total no. of rflns collected
16 842
40 367
7250
no. of unique rflns (F > 4σ(F)) 5795
Rint
0.039
0.037
R1, wR2 (I > 2σ(I))
GoF
peak, hole (e/Å3)
0.038, 0.091
1.1
0.025, 0.054
1.04
Figure 1. ORTEP representation of the solid-state molecular
structures of complexes 4 (top) and 6 (bottom) (ellipsoids plotted
at 50% probability, hydrogen atoms removed for clarity).
2.10, −0.88
1.06, −1.00
Me2PtIV−X complexes.16 For all complexes, the Pt−C2 bond,
which corresponds to the methyl group trans to PPh3, is longer
than the Pt−C1 bond, which corresponds to the methyl group
trans to the nitrogen of the imine (Table 3, entry 2). The increased
bond length is consistent with the smaller Pt−H coupling observed
for this methyl ligand in all complexes (Table 3, entry 2).
Transmetalation. Following C−F activation, the next step
in our proposed mechanism involves transmetalation between
dimethyl zinc and a PtIV−F species to generate a Me3Pt(IV)
complex (Scheme 1). We had previously determined that a
Me3PtIV complex was formed during the course of catalytic
methylation of N-(2,4,6-trifluorobenzylidene)benzylamine (7).13
Several small signals, corresponding to Pt−Me resonances,
lengths and bond angles are summarized in Table 3.
Crystallographic parameters are given in Table 4. The solid-state
molecular structures of complexes 4 and 6 clearly demonstrate the
octahedral geometry of the platinum metal center (Figure 1). The
square plane is defined by C1, C27/C22, N1, and X (X = F, Br),
with C2 and P1 occupying the apical positions. Examination of the
bonding data for complexes 4 and 6 reveals many structural
similarities between the two PtIV−F complexes. Specifically, the
Pt−Caryl and Pt−N bond lengths for both complexes are
equivalent, within experimental error (entries 4 and 6, Table 3).
The Pt−C bond lengths for both complexes, which range from
́
2.04 to 2.09 Å, are within the range reported for other similar
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1
were observed in the 1H and 19F NMR spectra in low
concentration throughout the course of the reaction and were
eventually depleted. Comparison of these spectra with that of
independently synthesized Me3PtIV complex 8 confirmed this
assessment; although we were unable to isolate complex 8, we
were able to obtain NMR spectral data of the crude product.13
The addition of a solution of complex 8 to a catalytic sample
resulted in an increase in those signals which we had attributed
to formation of a Me3PtIV complex during the course of
catalytic methylation. On this basis, we postulated the
mechanism to involve initial formation of a PtIV−F complex
via imine C−F activation followed by transmetalation with
dimethylzinc to generate a Me3PtIV complex that is the catalyst
resting state (Scheme 4).13
be attributed to a specific methyl ligand on the basis of the H
NMR data.18 More specifically, the multiplet at δ 1.38 (dd,
JPt−H = 70.5 Hz, JP−H = 8 Hz, JF−H = 2 Hz) can be assigned as
Meb, the methyl group in the plane of the fluoroaryl ring, on
the basis of the additional F−H coupling (entry 3). The smaller
Pt−H coupling associated with the signal at δ 0.66 (d, JPt−H
=
48.0 Hz, JP−H = 8 Hz) is consistent with a methyl group that is
trans to an X-type ligand (the fluoroaryl ring) (entry 4). Finally,
the signal at δ 0.46 (d, JPt−H = 63.8 Hz, JP−H = 8 Hz) has large
Pt−H coupling, which we previously determined was the result of
a trans orientation relative to an L-type (PPh3) ligand (entry 5).
Crystals of Me3PtIV·PPh3 complex 11 were obtained by
layering pentanes on a saturated solution of dichloromethane.
The solid-state molecular structure is depicted in Figure 2, with
selected bond lengths and bond angles given in Table 6.
Crystallographic parameters are summarized in Table 7.
The solid-state molecular structure of complex 11 clearly
illustrates that there are three methyl ligands attached to the Pt
center. In addition, complex 11 has an octahedral geometry in
which the square plane is defined by the cyclometalated
fluoroaryl ring as well as C2/C3 atoms. The C1 methyl and
PPh3 ligands adopt the apical positions in both structures. This
same geometry was observed for complexes 4 and 6 as well as
in related structures reported by Crespo and Martinez.16
Interestingly, in all complexes, the Pt−C2 bonds are the
longest, in comparison to the other Pt−Me bond lengths
(Table 6, entries 1 −3). This is consistent with the expected
formation of a particularly strong Caryl−Pt bond due to the
highly electron deficient cyclometalated fluoroaryl ring.21
However, the remaining bond lengths and bond angles for
these complexes are essentially identical, within experimental
error, with those calculated for Me2PtIV−F·PPh3 complexes 4
and 6 (Table 6).
Scheme 4. Methylation of N-(2,4,6-
Trifluorobenzylidene)benzylamine (7)
We next sought to examine the role of ligand dissociation in
transmetalation by comparing the relative rates of trans-
metalation of PtIV−F·SMe2 complex 2 in the presence and
absence of excess SMe2 (eqs 3 and 4). Although transmetalation
In order to obtain more complete characterization data for
Me3PtIV complexes resulting from transmetalation, we sought to
prepare and isolate complexes of this type. We anticipated that the
SMe2 complexes were too reactive for isolation but that the
corresponding PPh3 complexes should be isolable. We now report
the synthesis and characterization of Me3PtIV·PPh3 complex 11,
which contains a perfluorinated cyclometalated ligand.21
Complex 11 was readily prepared by treatment of the
Me2PtIV−F·PPh3 complex 10 with dimethylzinc (eq 2).
proceeded too rapidly at room temperature for analysis, we
were able to monitor the reaction at 0 °C using VT NMR
spectroscopy.18 The rate of transmetalation was slowed by the
presence of excess SMe2, which is consistent with a mechanism
that proceeds via a pentacoordinate complex.
Additional evidence for rapid dissociation and reassociation
of SMe2 was obtained through an isotopic labeling experiment.
A deuterium-labeled Pt(II) complex, Pt2(CD3)2(SMe2)2, was
used to generate (CD3)2PtIV−F·SMe2 complex 13. Subsequent
transmetalation with Me2Zn resulted in complete scrambling of
Alternatively, complex 11 could be prepared by treatment of
the corresponding Me2PtIV−F·SMe2 complex with dimethyl
zinc followed by ligand exchange with PPh3.18 Both processes
proceeded in high conversion.
This complex was characterized by multinuclear NMR
spectroscopy and X-ray diffraction, and diagnostic signals for
Me3PtIV·PPh3 complex 11 are included in Table 5. The
presence of an imine signal with Pt satellites as well as three
upfield Pt−Me signals of equal intensity are general features of
Me3PtIV complexes. Importantly, each of the Pt−Me signals can
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a
1
Table 5. H NMR Chemical Shifts for Complex 11
entry
δ
multiplicity
rel intens
assignt
1
2
3
4
5
8.48
4.39
1.38
0.66
0.46
s (JPt−H = 41.1 Hz)
1
2
3
3
3
CHN
dd (JH−H = 15.6 Hz) AB pattern
CH2
dd (JPt−H = 70.5 Hz, JPt−H = 8 Hz, JPt−H = 2 Hz)
d (JPt−H = 63.8 Hz, JP−H = 8 Hz)
Meb−Pt
Mec−Pt
Mea−Pt
d (JPt−H = 63.8 Hz, JP−H = 8 Hz)
a
NMR spectral data were obtained under the following conditions: acetonitrile-d3, 25 °C, 300 MHz.
Table 7. Crystallographic Data for Complex 11
empirical formula
C35H31NF4PPtBr
847.58
formula wt
cryst syst
triclinic
space group (No.)
P1 (2)
̅
a (Å)
10.5281(7)
10.5282(7)
15.3290(15)
86.304(3)
76.090(3)
69.947(3)
1548.98(18)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
Dc (g/cm3)
1.817
T (K)
173
solvent/color
F(000)
pentanes/pink
824.00
2θmax (deg)
56.2
total no. of rflns collected
no. of unique rflns (F > 4σ(F))
Rint
33 132
Figure 2. ORTEP representation of the solid-state molecular structure
of complex 11 (ellipsoids plotted at 50% probability, hydrogen atoms
removed for clarity).
7494
0.036
R1, wR2 (I > 2σ(I))
GOF
peak, hole (e/A3)
0.020, 0.041
1.04
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
Complex 11
0.74, −0.88
entry
1
Pt1−C1
Pt1−C2
Pt1−C3
Pt1−N1
Pt1−P1
Pt1−C22
N1−C28
C3−Pt1−C2
C3−Pt1−C22
C2−Pt1−N1
C22−Pt1−N1
C3−Pt1−C1
C1−Pt1−C2
C22−Pt1−C2
C2−Pt1−P1
C3−Pt1−P1
2.076(2)
2.095(2)
2.057(2)
2.1435(17)
2.3743(5)
2.099(2)
1.280(3)
89.43(10)
97.49(9)
93.33(8)
78.81(8)
87.37(9)
86.52(10)
169.52(8)
92.64(7)
90.67(7)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
resulting pentacoordinate species is similar to that in other
(CH3)nPtIV complexes.22
Reductive Elimination. During the course of our initial
investigations of Pt(II)-catalyzed C−F activation, we discovered
that Me3PtIV complexes, upon heating, underwent reductive
elimination to generate the corresponding methylated imines in
high conversion (eq 6).13,23
the deuterium labeling at room temperature, as indicated by the
1:1:1 ratio of the Pt−Me signals in the H NMR spectrum
(eq 5). This result is consistent with transmetalation being
dissociative in SMe2 and also indicates that isomerization of the
1
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reductive elimination is consistent with a dissociative
mechanism.
Comparison between Stoichiometric Studies and
Catalytic C−F Activation. We had previously reported
comparable trends for stoichiometric C−F activation and
catalytic cross-coupling, which was consistent with C−F
activation being part of the catalytic cross-coupling mecha-
nism.13 We anticipated that the rate-determining step may
change, depending on the degree of fluorination. This
prompted us to compare the rates of C−F activation, reductive
elimination, and catalytic methylation for a few fluoroaryl
imines. Table 8 summarizes the half-lives for C−F activation
and the yields of catalytic methylation. The half-lives for
reductive elimination were previously given in Scheme 5.
As was the case with reductive elimination, both stoichio-
metric C−F activation and catalytic methylation were
significantly influenced by the degree of fluorination of the
polyfluoroaryl imine. Crespo and Martinez reported that the
rates of C−F activation were fastest for the most heavily
fluorinated imines, consistent with their proposed oxidative
addition mechanism.16a Our results confirmed these observa-
tions (Table 8, column 1).13 A comparison of some catalytic
reactions provides additional insight. Whereas imines 7 and 17
were readily converted to their corresponding methylated
products in 8 h at 60 °C, the reaction of perfluorinated imine
16 required heating to 80 °C for 12 h (Table 8, column 2). The
reaction was simply slow; the low rate was not due to
decomposition or byproduct formation.13 These results can be
rationalized by considering the differences in the stability of the
intermediate Pt(IV) complexes. The ability of electron-deficient
ligands to stabilize high-valent metal complexes has been
extensively documented.21 This effect has been attributed to
the increased strength of the resulting M−C bonds in
complexes containing electron-deficient ligands. Therefore,
the high reactivity of complex 14 (derived from imine 16)
toward stoichiometric C−F activation can be attributed to the
favorable formation of a more stable Pt(IV) complex. Similarly,
the lower catalytic turnover of imine 16 compared with those of
7 and 17 is a direct result of this increased stability. This is
consistent with the observed slower reductive elimination from
14 (Scheme 5).
Interestingly, we observed a correlation between the rate of
reductive elimination and the number of fluorine substituents
Scheme 5. Reductive Elimination of Me3PtIV Complexes
on the cyclometalated fluoroaryl ring. The reaction half-lives for
reductive elimination of several Me3PtIV complexes are
summarized in Scheme 5. The slowest rate of reductive
elimination was observed for the Me3PtIV complex derived from
14, whereas Me3PtIV complexes 8 and 15 underwent reductive
elimination at a greater rate (Scheme 5). Electron-withdrawing
ligands are known to reduce the rate of reductive elimination.21
The implications of these results on the catalytic methylation of
polyfluoroaryl imines is discussed in greater detail in the
following section (vide infra).
Given the involvement of coordinatively unsaturated Pt(IV)
complexes in both C−F activation and transmetalation, we
sought to examine whether reductive elimination also proceeds
via a dissociative mechanism. The addition of excess SMe2 (10
equiv) to a mixture of Me3PtIV complex 8 resulted in <20%
product formation after 1 h at 60 °C (eq 7). Under standard
These results are indicative of a change in the rate-
determining step depending on the degree of fluorination For
substrates with a lesser degree of fluorination (e.g., 7 and 17),
C−F activation is rate-limiting. For substrates with a greater
degree of fluorination (e.g., 16), reductive elimination is rate-
limiting. As a result, these findings have a significant impact on
the choice of catalytic reaction conditions.
It is also noteworthy to compare imines 7 and 17 (Scheme 6).
These substrates were previously found to have comparable
catalytic reactivity (Table 8, entries 2 and 3).11 However, there
were subtle differences in the reactivity of these two substrates
toward stoichiometric C−F activation as well as reductive
elimination. Imine 17 was somewhat more reactive than imine
7 toward stoichiometric C−F activation, yet the resulting
Me3PtIV complex undergoes reductive elimination more slowly.
Both results are consistent with a presumed effect of the
o-fluorine present in imine 17.21 The selectivity for C−F
activation in 17 is dictated by the formation of a more stable
PtIV−Caryl bond. The Pt(IV) intermediates derived from 17 are
presumably more stable than those derived from 7, due to the
o-fluorine in the former. Complex 15 is, thus, more resistant to
reductive elimination. However, imines 7 and 17 have similar
conditions, reductive elimination from complex 8 proceeds to
give the methylated imine 9 in 69% yield over the same time
interval (eq 8). The net effect of excess SMe2 on the rate of
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Table 8. Comparison of Stoichiometric and Catalytic Reactivity for Polyfluoroaryl Imines
a
b
NMR spectral data were acquired under the following conditions: acetonitrile-d3, 60 °C, 300 MHz. Reaction progress was monitored by 1H and
19F NMR spectroscopy, and results are the average of two independent experiments. Additional details are included in the Supporting Information.
c
d
e
f
Taken from ref 11. Conditions: CH3CN, Me2Zn (0.6 equiv), 80 °C, 12 h. Conditions: CH3CN, Me2Zn (0.6 equiv), 60 °C, 8 h. Data are the
same as those presented in Scheme 5 and are included here for clarity. Details regarding the experimental conditions are included in the Supporting
Information.
Scheme 6. Reactivity of Imines 7 and 17
related Me3PtIV complexes. While both PtIV−F·SMe2 and
Me3PtIV·SMe2 complexes proved to be too unstable to isolate,
the corresponding PPh3 complexes were isolable. Heating of
Me3PtIV·SMe2 complexes resulted, in all cases, in reductive
elimination to generate the same methylated imines that were
formed by catalytic methylation. Heavily fluorinated polyfluor-
oarenes were most effective at directing C−F activation;
however, the resulting Me3PtIV complexes were resistant toward
reductive elimination. These results suggest that while C−F
activation is the rate-determining step of catalysis for the
majority of the substrates, reductive elimination is rate-limiting
for highly activated polyfluoroarenes. Excess SMe2 impeded
each reaction (C−F activation, transmetalation, reductive
elimination), consistent with a mechanism in which the cataly-
tically active Pt(IV) species are pentacoordinate. More detailed
investigations of reductive elimination from Pt(IV) fluoroaryl
complexes is ongoing and will be reported in due course.
EXPERIMENTAL SECTION
■
General Procedures. Manipulation of organometallic compounds
was performed using standard Schlenk techniques under an
atmosphere of dry nitrogen or in a nitrogen-filled Vacuum
Atmospheres drybox (O2 <2 ppm). NMR spectra were recorded on
Bruker Avance 300, Bruker Avance 400, and Bruker Avance 600
1
spectrometers. H and 13C chemical shifts are reported in parts per
million and are referenced to residual solvent. Coupling constant
values were extracted assuming first-order coupling. The multiplicities
are abbreviated as follows: s = singlet, d = doublet, t = triplet, m =
multiplet. All spectra were obtained at 25 °C. Mass spectra were
recorded on a Kratos MS-50 mass spectrometer. Elemental analyses
were performed using a Carlo Erba EA 1108 Elemental Analyzer.
Single-crystal X-ray structure determinations were performed by Dr.
Brian O. Patrick at the Department of Chemistry, University of British
Columbia, using a Bruker X8 Apex CCD area detector with graphite-
monochromated Mo Kα radiation.
Material and Methods. Acetonitrile and dichloromethane were
dried by heating to reflux over calcium hydride, stored over molecular
sieves, and degassed prior to use. Pentanes and hexanes were purified
and dried by passage through a column of activated alumina and
sparged with dinitrogen prior to use. Acetonitrile-d3 was obtained from
Cambridge Isotopes Inc. and degassed prior to use. All organic
rates and yields of catalytic methylation, because C−F
activation is rate-limiting for these substrates.
SUMMARY AND CONCLUSIONS
■
In summary, the synthesis and reactivity of a series of Pt(IV)
fluoroaryl complexes have been described. In general,
polyfluoroaryl substrates that displayed reasonable catalytic
reactivity also underwent stoichiometric C−F activation to
form the corresponding PtIV−F complexes. Subsequent trans-
metalation with dimethylzinc resulted in formation of the
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reagents were obtained from commercial sources and used as received.
1,3,5-Trimethoxybenzene was sublimed prior to use. K2PtCl4 was
purchased from Strem Chemicals and was used without further
purification. PtCl2(SMe2)2, Pt2Me4(SMe2)2, and Pt2(CD3)4(SMe2)2
were prepared using previously reported procedures.24 Dimethylzinc
(1.2 M solution in toluene) was purchased from Aldrich and titrated
with LiCl and I2 prior to use.25
(acetonitrile-d3, 300 MHz): δ 8.56 (s, JPt−H = 36.9 Hz, CHN, 1H),
7.76−7.23 (m, overlapping peaks, aryl H), 4.58 (m, CH2, AB pattern,
2H), 1.62 (dd, JPt−H = 59.4 Hz, JF−H = 12 Hz, JP−H = 5 Hz, Pt−CH3,
3H), 0.74 (dd, JPt−H = 61.0 Hz, JF−H = 12 Hz, JP−H = 5 Hz, Pt−CH3,
3H). 19F NMR (acetonitrile-d3, 282 MHz): δ −126.1 (m, aryl F, 1F),
−139.6 (m, aryl F, 1F), −148.1 (m, aryl F, 1F), −164.1 (m, aryl F, 1F),
−273.5 (s, JPt−H = 31.0 Hz, Pt−F, 1F). 31P{1H} NMR (acetonitrile-d3,
121 MHz): δ −0.57 (d, JPt−H = 1614 Hz, JP−F = 52 Hz, Pt−PPh3).
HRMS (ESI positive ion mode): m/z calcd for C34H27F5NP79Br194Pt:
848.0611, found 848.0608.
Preparation of Polyfluoroarenes. All substrates were prepared
according to literature procedures. Analytical data match previously
reported data.11 See the Supporting Information for details.
General Procedure for Preparation of PtIV−F·SMe2 Com-
plexes. In a 20 mL vial in the glovebox, the polyfluoroarene substrate
(0.034 mmol, 1.0 equiv) and Pt2Me4(SMe2)2 (0.017 mmol, 0.5 equiv)
were dissolved in dried, degassed CD3CN (1.0 mL). The resulting
solution was transferred to a screw-cap NMR tube containing a
septum, which was sealed and removed from the glovebox. The
[PtMe2F(PPh3)(C6F2CHNCH2C6H5)] (5). Based on in situ NMR
spectroscopic characterization, 70% conversion based on integration of
1
the 19F NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.23
(s, JPt−H = 55.2 Hz, CHN, 1H), 7.66−6.28 (m, overlapping signals,
aryl H), 4.95−4.30 (m, overlapping signals, CH2, 2H), 1.22 (td, JPt−H
66.0 Hz, JP−H = 8 Hz, JF−H = 2 Hz, Pt−CH3, 3H), 0.62 (td, JPt−H
=
=
1
reaction was monitored by H and 19F NMR spectroscopy. Analytical
61.8 Hz, JF−H = 8 Hz, JP−H = 2 Hz, Pt−CH3, 3H). 19F NMR
(acetonitrile-d3, 282 MHz): δ −101.8 (m, aryl F, 1F), −110.5 (m, aryl
F, 1F), −281.3 (m, Pt−F, 1F). 31P{1H} NMR (acetonitrile-d3, 121
MHz): δ −1.72 (d, JPt−P = 1102 Hz, JP−F = 64 Hz, Pt-PPh3). HRMS
(ESI positive ion mode): m/z calcd for C34H31F3NP194Pt 736.1794,
found 736.1782.
data for all Pt complexes are included in the Supporting Information.
Select Pt complexes are included below.
[PtMe2F(SMe2)C6F4CHNCH2C6H4Br)] (1). Based on in situ NMR
spectroscopic characterization, 90% conversion based on integration of
1
the 19F NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.98
(s, JPt−H = 48.0 Hz, CHN, 1H), 7.67−7.45 (m, aryl H, 4H), 5.02
[PtMe2Br(PPh3)(C6FCHNCH2C6H5)] (6). Colorless crystals were
obtained from a saturated solution of acetonitrile; 53% yield. 1H NMR
(dichloromethane-d2, 300 MHz): δ 8.11 (s, JPt−H = 49.8 Hz, CHN,
1H), 7.55−7.49 (t, J = 8.7 Hz, 1H), 7.40−7.28 (m, signals overlapping
with PPh3, aryl H), 7.04 (dd, J = 6.6 Hz, J = 4 Hz, 2H), 6.88 (d, AB
pattern, J = 8 Hz), 6.65 (t, J = 9.0 Hz, 1H), 6.45 (d, JPt−H = 43.8 Hz,
1H), 5.03 (d, AB pattern, J = 18.3 Hz). 1.49 (d, Pt−CH3, JH−P = 8 Hz,
JPt−H = 69.3 Hz, 3H), 0.98 (d, Pt−CH3, JH−P = 8 Hz, JPt−H = 58.2 Hz,
(m, 2H), 1.96 (s, JPt−H = 12.0 Hz, S(CH3)2, 6H), 1.50 (dd, JPt−H
=
63.0 Hz, JF−H = 9 Hz, JF−H = 6 Hz, Pt−CH3, 3H), 0.80 (d, JPt−H = 66.0
Hz, JF−H = 6 Hz, Pt−CH3, 3H). 19F NMR (acetonitrile-d3, 282 MHz):
δ −128.2 (m, aryl F, 1F), −139.4 (m, aryl F, 1F), −148.0 (m, aryl F,
1F), −162.8 (m, aryl F, 1F), −253.5 (m, JPt−H = 175 Hz, Pt−F, 1F).
[PtMe2F(SMe2)(C6F2CHNCH2C6H5)] (2). Based on in situ NMR
spectroscopic characterization, 85% conversion based on integration of
1
the 19F NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.78
3H). 19F NMR (dichloromethane-d2, 282 MHz): δ −114.0 (m, JPt−F
=
(s, JPt−H = 47.5 Hz, CHN, 1H), 7.70−6.60 (m, overlapping peaks,
42 Hz, aryl F). 31P{1H} NMR (dichloromethane-d2, 121 MHz): δ
−7.2 (s, JPt−P = 1006 Hz, Pt−PPh3). 13C{1H} NMR (dichloro-
aryl H), 5.05 (m, CH2, 2H), 1.90 (s, JPt−H = 12.1 Hz, S(CH3)2, 6H),
1.11 (d, JPt−H = 65.6 Hz, JF−H = 7 Hz, Pt−CH3, 3H), 0.72 (d, JPt−H
=
methane-d2, 150 MHz): 166.1 (s, JPt−C = 54.8 Hz), 161.1 (d, JF−C =
68.3 Hz, JF−H = 7 Hz, Pt−CH3, 3H). 19F NMR (acetonitrile-d3, 282
MHz): δ −101.8 (m, aryl F, 1F), −110.5 (m, aryl F, 1F), −260.9 (br s,
Pt−F, 1F).
965.0 Hz, JPt−C = 51.3 Hz), 151.5 (d, JF−C = 21.4 Hz, JPt−C = 932.7
Hz), 136.3 (s), 134.4 (s), 131.3 (d, JP−C = 33.8 Hz), 130.9 (d, JF−C
=
146.0 Hz, JPt−C = 11.4 Hz), 130.6 (s), 130.4 (d, JF−C = 9.0 Hz), 130.2
(d, JF−C = 29.9 Hz), 129.2 (s), 128.5 (s), 128.4 (d, JP−C = 18.5 Hz),
124.6 (d, JF−C = 16.9 Hz, JPt−C = 41.0 Hz), 60.5 (s, JPt−C = 12.6 Hz),
10.56 (s, JPt−C = 491.6 Hz), −4.43 (d, JP−C = 7.0 Hz, JPt−C = 618.0 Hz).
HRMS (ESI positive ion mode): m/z calcd for C34H3279BrFNP194Pt
779.1084, found 779.1086. Anal. Calcd for C34H32BrFNPPt: C, 54.69;
H, 4.20; N, 1.82. Found: C, 55.10; H, 4.34; N, 1.60.
[PtMe2Br(SMe2)(C6FCHNCH2C6H5)] (3). Based on in situ NMR
spectroscopic characterization, 95% conversion based on integration of
1
the 19F NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.73
(s, JPt−H = 45.0 Hz, CHN, 1H), 7.80−6.52 (m, overlapping peaks,
aryl H), 4.84 (m, CH2, 2H), 1.87 (s, JPt−H = 12.0 Hz, Pt−S(CH3)2,
6H), 1.07 (s, JPt−H = 68.4 Hz, Pt−CH3, 3H), 0.71 (s, JPt−H = 69.6 Hz,
Pt−CH3, 3H). 19F NMR (acetonitrile-d3, 282 MHz): δ −114.6 (d, J =
10 Hz, aryl F, 1F).
[Pt(CD3)2F(SMe2)(C6F2CHNCH2C6H5)] (13). In a 20 mL vial in the
glovebox, N-(2,4,6-trifluorobenzylidene)benzylamine (0.080 g, 0.032
mmol, 1.0 equiv) and Pt2(CD3)4(SMe2)2 (0.94 g, 0.016 mmol, 0.5
equiv) were dissolved in CD3CN (1.0 mL). The resulting solution was
transferred into an NMR tube, which was then fitted with a screw cap
containing a septum. The reaction was monitored by 1H and 19F NMR
[PtMe2F(PPh3)(C6F4CHNCH2C6H5)] (10). Based on in situ NMR
spectroscopic characterization, 42% conversion based on integration of
1
the 19F NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.71
(s, JPt−H = 39.0 Hz, CHN, 1H), 7.50 −7.31 (m, overlapping peaks,
aryl H), 4.66 (dd, JH−H = 10.8 Hz, CH2, AB pattern, 2H), 1.72 (dd,
JPt−H = 58.5 Hz, JF−H = 12 Hz, JP−H = 5 Hz, Pt−CH3, 3H), 0.72 (dd,
JPt−H = 62.0 Hz, JF−H = 12 Hz, JP−H = 5 Hz, Pt−CH3, 3H). 19F NMR
(acetonitrile-d3, 282 MHz): δ −124.9 (m, aryl F, 1F), −141.1 (m, aryl
F, 1F), −150.3 (m, aryl F, 1F), −165.6 (m, aryl F, 1F), −275.6 (s,
JPt−H = 32.0 Hz, Pt−F, 1F). 31P{1H} NMR (acetonitrile-d3, 121 MHz):
δ −2.0 (d, JPt−H = 999 Hz). HRMS (ESI positive ion mode): m/z calcd
for C34H29F5NP194Pt 772.1606, found 772.1612.
spectroscopy: >95% conversion based on in situ NMR spectroscopic
1
characterization. H NMR (acetonitrile-d3, 300 MHz): δ 8.78 (s, JPt−H
=
47.1 Hz, CHN, 1H), 7.80−6.60 (m, overlapping peaks, aryl H),
5.05 (m, CH2, 2H), 1.89 (s, JPt−H = 12.0 Hz, S(CH3)2, 6H). As
expected, there were no resonances for Pt−CD3 signals. 19F NMR
(acetonitrile-d3, 282 MHz): δ −102.0 (m, aryl F, 1F), −110.7 (m, aryl
F, 1F), −261.8 (br s, Pt−F, 1F).
General Procedure for Preparation of Me3PtIV·SMe2 Com-
plexes. In a 20 mL vial in the glovebox, substrate (0.085 g, 0.034
mmol, 1.0 equiv) and Pt2Me4(SMe2)2 (0.098 g, 0.017 mmol, 0.5
equiv) were dissolved in CD3CN (1.0 mL). Me2Zn (20 μL, 0.040
mmol, 2.0 M solution in toluene) was subsequently added by syringe.
The resulting solution was transferred to an NMR tube, which was
then fitted with a screw cap containing a septum. The NMR tube was
General Procedure for Preparation of Me2PtIV−F·PPh3
Complexes. In a 20 mL vial in the glovebox, the substrate (0.085
g, 0.034 mmol, 1.0 equiv) and Pt2Me4(SMe2)2 (0.098 g, 0.017 mmol,
0.5 equiv) were dissolved in CD3CN (1.0 mL). The vial was left to
stand for 24 h, after which triphenylphosphine (0.090 g, 0.034 mmol,
1.0 equiv) was added into the vial. The vial was stirred until complete
dissolution of the triphenylphosphine; the sample was then transferred
to a screw-cap NMR tube and removed from the glovebox. The
1
removed from the glovebox. The reaction was monitored by H and
19F NMR spectroscopy.
[PtMe3(SMe2)(C6F2CHNCH2C6H5)] (8). Based on in situ NMR
spectroscopic characterization, >95% conversion from PtIV−F·SMe2
1
1
1
reaction was monitored by H, 19F, and 31P{1H} NMR spectroscopy
complex 2 based on integration of the H NMR spectrum. H NMR
(acetonitrile-d3, 300 MHz): δ 8.86 (s, JPt−H = 40.0 Hz, 1H, CHN),
7.37−7.13 (m, overlapping peaks, aryl H), 4.99 (m, CH2, 2H), 1.78 (s,
JPt−H= 13.0 Hz, S(CH3)2, 6H), 0.75 (s, JPt−H = 69.0 Hz, Pt−CH3, 3H),
over 24 h.
[PtMe2F(PPh3)(C6F4CHNCH2C6H4Br)] (4). Colorless crystals were
obtained from a saturated solution of acetonitrile; 40% yield. 1H NMR
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0.36 (s, JPt−H = 73.1 Hz, Pt−CH3, 3H), 0.16 (s, JPt−H = 46.0 Hz, Pt−
CH3, 3H). 19F NMR (acetonitrile-d3, 282 MHz): δ −104.3 (m),
−111.6 (m).
J
Pt−C = 613.9 Hz, JP−C = 11 Hz, JF−C = 4 Hz). HRMS (ESI positive ion
mode): calcd for C35H32F4NP194Pt 768.1856, found 768.1860. Anal.
Calcd for C35H32F4NPPt: C, 54.69; H, 4.20; N, 1.82. Found: C, 54.73;
H, 4.45; N, 1.95.
[PtMe3(SMe2)(C6F4CHNCH2C6H5)] (14). Based on in situ NMR
spectroscopic characterization, >95% conversion from the correspond-
ing PtIV−F·SMe2 complex based on integration of the 1H NMR
spectrum. 1H NMR (acetonitrile-d3, 300 MHz): δ 8.90 (s, JPt−H = 39.0
Hz, 1H, CHN), 7.55−6.87 (m, overlapping signals, aryl H), 4.96
(br m, CH2, 2H), 1.89 (s, JPt−H = 12.6 Hz, 6H, Pt−S(CH3)2), 1.09
(d, JF−H = 3 Hz, JPt−H = 70.8 Hz, 3H, Pt−CH3), 0.53 (s, JPt−H = 72.0
Hz, 3H, Pt−CH3), 0.35 (s, JPt−H = 33.0 Hz, 3H, Pt−CH3). 19F NMR
(acetonitrile-d3, 282 MHz): δ −129.0 (dd, J = 28 Hz, J = 21 Hz, 1F),
−147.9 (m, 1F), −151.8 (dd, J = 28 Hz, J = 18 Hz, 1F), −155.2
(m, 1F).
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, tables, and CIF files giving complete experimental
details and characterization data for all compounds and
crystallographic data for the solid-state molecular structures.
This material is available free of charge via the Internet at
http://pubs.acs.org.
[PtMe3(SMe2)(C6F2CHNCH2C6H5)] (15). Based on in situ NMR
spectroscopic characterization, >95% conversion from the correspond-
ing PtIV−F·SMe2 complex based on integration of the 1H NMR
spectrum. 1H NMR (acetonitrile-d3, 300 MHz): δ 8.97 (s, JPt−H = 38.4
Hz, 1H, CHN), 7.36−7.13 (m, overlapping peaks, aryl H), 6.96−
6.89 (m, 1H), 6.74 (td, J = 9.0 Hz, J = 3.6 Hz, 1H), 4.97 (br m, 2H,
CH2), 1.88 (s, JPt−H = 13.2 Hz, 6H, Pt−S(CH3)2), 1.08 (d, JF−H = 3
Hz, JPt−H = 71.4 Hz, 3H, Pt−CH3), 0.53 (s, JPt−H = 73.2 Hz, 3H, Pt−
CH3), 0.28 (s, JPt−H = 48.6 Hz, 3H, Pt−CH3). 19F NMR (acetonitrile-
d3, 282 MHz): δ −105.4 (d, JF−H = 25 Hz, JPt−F = 302 Hz, 1F), −121.1
(dm, JPt−F = 261 Hz, 1F).
ACKNOWLEDGMENTS
■
We thank the following for support of this research: NSERC
(Discovery, Research Tools and Instrumentation Grants) and
the University of British Columbia.
REFERENCES
■
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[Pt(CD3)2Me(SMe2)(C6F2CHNCH2C6H5)]: Deuterium Labeling
Study. To a solution of complex 13 was added Me2Zn (20 μL,
0.042 mmol, 2.0 M solution in toluene) by syringe. The reaction was
1
monitored by H and 19F NMR spectroscopy. Three resonances for
the three methyl groups appeared with a ratio of 1:1:1; >95%
conversion from PtIV−F·SMe2 complex 13 based on integration of the
1
1H NMR spectrum. H NMR (acetonitrile-d3, 300 MHz): δ 8.86 (s,
J
Pt−H = 39.2 Hz, CHN, 1H), 7.70−6.60 (m, overlapping peaks, aryl
H), 4.98 (m, CH2, 2H), 1.78 (s, JPt−H = 13.2 Hz, S(CH3)2, 6H), 0.74
(s, JPt−H = 69.6 Hz, Pt−CH3, 3H) (overlapped three singlets), 0.36 (s,
JPt−H = 72.8 Hz, Pt−CH3, 3H) (overlapped three singlets), 0.15 (s,
JPt−H = 44.8 Hz, Pt−CH3, 3H) (overlapped three singlets).
General Procedure for Preparation of Me3PtIV·PPh3 Com-
plexes. In the glovebox, a solution of the Me3PtIV·SMe2 complex was
combined with triphenylphosphine (0.090 g, 0.034 mmol, 1.0 equiv).
The vial was stirred until complete dissolution of the triphenylphos-
phine, after which the sample was transferred to a screw-cap NMR
tube and removed from the glovebox. The reaction was monitored by
1H, 19F, and 31P{1H}NMR spectroscopy over 24 h. The complexes
(4) Sun, A. D.; Love, J. A. Dalton Trans. 2010, 39, 10362−10374.
(5) (a) Muller, K.; Faeh, C.; Diedrich, F. Science 2007, 317, 1881−
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Muller, K.; Obst-Sanch, U.; Stahl, M. ChemBioChem 2004, 5, 637−
643.
(6) For recent examples see: (a) Hong, S.; Lee, J.; Kim, M.; Park, Y.;
Park, C.; Kim, M.-H.; Jew, S.-S.; Park, H. J. Am. Chem. Soc. 2011, 133,
4924−4929. (b) Welsh, G. C.; Bazan, G. C. J. Am. Chem. Soc. 2011,
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You, W. J. Am. Chem. Soc. 2011, 133, 4625−4631. (d) Nguyen, J. D.;
Tucker, J. W.; Konieczynska, M. D.; Stephenson, R. J. J. Am. Chem.
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Martin, R. L.; Hay, J. P.; Morris, D. E.; Kiplinger, J. C. Inorg. Chem.
2007, 46, 7477−7488. (g) Hughes, R.; Smith, J. M.; Incarvito, C. D.;
Lam, K.-C.; Rhatigan, B.; Rheingold, A. C. Organometallics 2002, 21,
2136−2144.
(7) For selected examples see: (a) Noveski, D.; Braun, T.; Schulte,
M.; Neumann, B.; Stammler, H. Dalton Trans. 2003, 4075−4083.
(b) Jones, W. D.; Partridge, M. G.; Perutz, R. N. Chem. Commun.
1991, 264−266. (c) Edelbach, B. L.; Jones, W. D. J. Am. Chem. Soc.
1997, 119, 7734−7742. (d) Blum, O.; Frolow, F.; Milstein, D. L.
Chem. Commun. 1991, 258−259. (e) Hughes, R. P.; Lartichev, R. B.;
Zakharov, L. N.; Rheingold, A. L. J. Am. Chem. Soc. 2004, 126, 2308−
2309.
could also be prepared by initial formation of the corresponding PtIV−
F·PPh3 complex followed by transmetalation with Me2Zn. Accord-
ingly, inside the glovebox a solution of Me2PtIV−F·PPh3 was combined
with Me2Zn (20 μL, 0.040 mmol, 2.0 M solution in toluene), which
was added via microsyringe. The resulting solution was transferred to a
screw-cap NMR tube, sealed, and removed from the glovebox.
Reaction progress was monitored by 1H, 19F, and 31P{1H} NMR
spectroscopy.
[PtMe3(PPh3)(C6F5CHNCH2C6H5)] (11). Pink crystals were
obtained by layering pentanes on a saturated solution of dichloro-
1
methane; 46% yield. H NMR (acetonitrile-d3, 300 MHz); δ 8.48 (s,
JPt−H = 41.1 Hz, CHN, 1H), 7.45−7.07 (m, overlapping peaks, aryl
H), 4.39 (dd, JH−H = 15.6 Hz, CH2, 2H, AB pattern), 1.38 (dd, JPt−H
=70.5 Hz, JPt−P = 8 Hz, JF−H = 2 Hz, Pt−CH3, 3H), 0.66 (dd, JPt−H
48.0 Hz, JPt−P = 8 Hz, Pt−CH3, 3H), 0.46 (dd, JPt−H = 63.8 Hz, JP−H
=
=
8 Hz, Pt−CH3, 3H). 19F NMR (acetonitrile-d3, 282 MHz): δ − 126.6
(m, aryl F, 1F), −142.9 (m, aryl F, 1F), −152.2 (m, aryl F, 1F), −167.4
(m, aryl F, 1F). 31P{1H} NMR (acetonitrile-d3, 121 MHz): δ −7.08 (s,
JPt−P = 1038 Hz). 13C{1H} NMR (dichloromethane-d2, 100 MHz): δ
169.2 (br s), 154.7 (s), 151.8 (dm, JF−C = 230 Hz), 148.8 (dm, JF−C
=
(8) For selected examples see: (a) Braun, T.; Perutz, R. N. Chem.
Commun. 2002, 2749−2757. (b) Schaub, T.; Fischer, P.; Steffen, A.;
Braun, T.; Radius, U.; Mix, A. J. Am. Chem. Soc. 2008, 130, 9304−
9317. (c) Fahey, D. R.; Mahan, J. E. J. Am. Chem. Soc. 1977, 99, 1101−
1108. (d) Johnson, S. A.; Huff, C. W.; Mustafa, F.; Saliba, M. J. Am.
Chem. Soc. 2008, 130, 17279−17280.
262 Hz), 143.5 (dm, JF−C = 266 Hz), 137.2 (m, overlaps with
resonances for PPh3), 134.5 (t, JPt−C = 7.6 Hz, overlaps with
resonances for PPh3), 134.3 (d, JP−C = 10 Hz), 132.6 (s), 132.1 (s),
131.8 (d, JPt−C = 10.8 Hz, JP−C = 38 Hz), 130.7 (d, JP−C = 2 Hz), 128.6
(d, JP−C = 8 Hz), 122.9 (s), 59.2 (s, JPt−C = 14.5 Hz), 7.29 (d, JPt−C
=
543.4 Hz, JP−C = 115 Hz), 2.17 (br, s. JPt−C = 478.0 Hz), −12.9 (dd,
1406
dx.doi.org/10.1021/om2007562 | Organometallics 2012, 31, 1397−1407

Organometallics
Article
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(23) No ethane formation was detected when experiments were
performed in sealed J. Young tubes.
(24) Hill, G. S.; Irwin, M. J.; Levy, C. J.; Rendina, L. M.; Puddephatt,
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(12) For relatedexamplesof methoxylation, see: Buckley, H.; Wang,
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(13) For detailed informationregarding the identification and
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(15) Complex 2 has been previously reported.16a
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1
(17) For all Pt(IV) complexes, the signal in the H NMR spectrum
corresponding to the Pt−SMe2 ligand was observed as a singlet from δ
1.96 to 1.87 (JPt−H = 12.0 Hz). The lack of diastereotopic methyl
signals is postulated to be the result of rapid inversion about the Pt−S
bond at room temperature. A variety of metal−thioether complexes
have been reported in which the sulfur ligand was found to undergo
rapid inversion at room temperature, forming diastereotopic signals
only upon cooling below −20 °C. For examples, see: (a) Mendez, N.
Q.; Arif, A. M.; Gladysz, J. A. Organometallics 1991, 10, 2199−2209.
(b) Abel, E. W.; Booth, M.; Orrell, K. G. Dalton Trans. 1980, 9, 1582−
1592. (c) Abel, E. W.; Orrell, K. G.; Rahoo, H.; Sik, V. J. Organomet.
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(18) See the Supporting Information for details.
(19) (a) van Asselt, R.; Rjinberg, E.; Elseiver, C. J. Organometallics
1994, 13, 706−720. (b) Clegg, D. E.; Hall, J. R.; Swile, G. A.
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