Reductive elimination from platinum(IV) aminotroponiminate dimethyl complexes promoted by sterically hindered lewis bases

Article abstract of DOI:10.1021/om400034y

A series of Pt^II and Pt^IV aminotroponimate (ATI = N-tolyl-aminotroponiminate) complexes has been prepared. The Pt^II complex (ATI)Pt(CH₃)(SMe₂) (1a) is synthesized from the reaction of [Li][ATI] with (Me)(Cl)Pt(SMe₂)₂. Addition of either ethylene or carbon monoxide to 1a results in the formation of (ATI)Pt(CH₃)(η²-C₂H₄) (1b) or (ATI)Pt(CH₃)(CO) (1c), respectively. Oxidative addition of MeOTf or MeI to 1a results in formation of the Pt^IV complex [(ATI)Pt(CH ₃)₂(X)(SMe₂)] (X = OTf (3), I (2)). Complex 3 reacts with isocyanides, which replace the triflate ligand to form [(ATI)Pt(CH₃)₂(CNR)(SMe₂)][OTf] (4). Complex 3 also undergoes ligand substitution reactions with azide or cyanide to form (ATI)Pt(CH₃)₂(N₃)(SMe₂) (5a) or (ATI)Pt(CH₃)₂(CN)(SMe₂) (5b). Addition of PR₃ results in the substitution product [(ATI)Pt(CH₃) ₂(PR₃)(SMe₂)][OTf] for phosphines with cone angles ≤136 (P(OMe)₃, PMe₃, PMe₂Ph). The Pt^IV complex [(ATI)Pt(CH₃)₂(PPh ₂Me)(SMe₂)][OTf] (6c) reductively eliminates [PMe ₂Ph₂][OTf] or [SMe₃][OTf] to form the Pt ^II complex (ATI)Pt(CH₃)(PPh₂Me) (7a) in solution at room temperature. Addition of 1 equiv of PPh₃, which has a cone angle of 145, results in the formation of 50% of Pt^II(ATI) Pt(CH₃)(PR₃) and [MePPh₃][OTf]. Reaction of 3 with PCy₃, which has a cone angle of 170, yields complete and immediate conversion to (ATI)Pt(CH₃)(SMe₂) and [MePCy ₃][OTf].

Full text of DOI:10.1021/om400034y

Article
pubs.acs.org/Organometallics
Reductive Elimination from Platinum(IV) Aminotroponiminate
Dimethyl Complexes Promoted by Sterically Hindered Lewis Bases
Elise Traversa,† Joseph L. Templeton,*,† Hiu Yan Cheng,‡ Megan Mohadjer Beromi,‡ Peter S. White,†
and Nathan M. West*,‡
†W.R. Kenan Laboratory, Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United
States
‡Department of Chemistry and Biochemistry, University of the Sciences, 600 South 43rd Street, Philadelphia, Pennsylvania 19063,
United States
S
* Supporting Information
ABSTRACT: A series of PtII and PtIV aminotroponimate
(ATI = N-tolyl-aminotroponiminate) complexes has been
prepared. The PtII complex (ATI)Pt(CH3)(SMe2) (1a) is
synthesized from the reaction of [Li][ATI] with (Me)(Cl)Pt-
(SMe2)2. Addition of either ethylene or carbon monoxide to
1a results in the formation of (ATI)Pt(CH3)(η2-C2H4) (1b)
or (ATI)Pt(CH3)(CO) (1c), respectively. Oxidative addition
of MeOTf or MeI to 1a results in formation of the PtIV
complex [(ATI)Pt(CH3)2(X)(SMe2)] (X = OTf (3), I (2)).
Complex 3 reacts with isocyanides, which replace the triflate
ligand to form [(ATI)Pt(CH3)2(CNR)(SMe2)][OTf] (4).
Complex 3 also undergoes ligand substitution reactions with
azide or cyanide to form (ATI)Pt(CH3)2(N3)(SMe2) (5a) or (ATI)Pt(CH3)2(CN)(SMe2) (5b). Addition of PR3 results in the
substitution product [(ATI)Pt(CH3)2(PR3)(SMe2)][OTf] for phosphines with cone angles ≤136° (P(OMe)3, PMe3, PMe2Ph).
The PtIV complex [(ATI)Pt(CH3)2(PPh2Me)(SMe2)][OTf] (6c) reductively eliminates [PMe2Ph2][OTf] or [SMe3][OTf] to
form the PtII complex (ATI)Pt(CH3)(PPh2Me) (7a) in solution at room temperature. Addition of 1 equiv of PPh3, which has a
cone angle of 145°, results in the formation of 50% of PtII(ATI)Pt(CH3)(PR3) and [MePPh3][OTf]. Reaction of 3 with PCy3,
which has a cone angle of 170°, yields complete and immediate conversion to (ATI)Pt(CH3)(SMe2) and [MePCy3][OTf].
traditional α-diimine ligand.24−29 The smaller ligand bite
angle has been shown in the past to have a significant effect
INTRODUCTION
■
Reductive elimination of C−X bonds is a critical step in the
on the potential for oxidative addition and reductive
catalytic functionalization of small molecules using a d8/d6
elimination.30−33 The aminotroponiminate ligands also elimi-
transition-metal catalytic cycle.1−4 These C−X eliminations
nate one major problem with nacnac compounds, which is the
nucleophilicity of the γ-carbon of the ligand, which has
have been known for PtIV since the discovery of the Shilov
oxidation of methane to methanol2,5 but have remained elusive
prevented the addition of electrophiles to the metal center in
until recently. There have been studies in the literature of C−
(nacnac)PtII complexes. Despite the large number of bidentate
N, C−O, C−I, C−C, and C−H bond forming reductive
eliminations,1,6−11 but there has been less work done on
nitrogen ligands that have been put on Pt, no reports of (ATI)
Pt complexes appear in the literature.
studying the formation of C−P and C−S bonds using late
Neutral four-coordinate PtII ATI complexes readily undergo
metals;12−18 these reactions could be particularly useful for the
oxidative addition of methyl iodide and methyl triflate to form
catalytic synthesis of chiral phosphines. We report herein the
stable PtIV ATI complexes. The PtIV complexes formed by
reductive elimination of CH3−P and CH3−S bonds from PtIV
oxidative addition of methyl triflate contain a labile ligand
aminotroponiminate (ATI) complexes at room temperature.
which can be readily replaced by isocyanides, azides, cyanides,
Goldberg and Templeton have shown that β-diiminate
and phosphines. Cationic PtIV complexes of small phosphines
(nacnac) ligated PtII methyl complexes will activate the C−H
are stable. However, bulky phosphines favor reductive
bonds of alkanes and ethers with elimination of methane,
elimination of R3PMe+; the presence of excess dimethyl sulfide
in solution also leads to the elimination of Me3S+. Experiments
using phosphines with various steric and electronic properties
forming PtII olefin hydride species.19−23 We sought to extend
this chemistry to the aminotroponiminate class of ligands,
which are similarly symmetrical mononanionic bidentate
nitrogen ligands that form a five-membered chelate rather
than the six-membered chelate formed by the nacnac ligands.
The ATI ligand is essentially an anionic analogue of a
Received: January 16, 2013
Published: March 5, 2013
© 2013 American Chemical Society
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Article
have been used to probe the P−C reductive elimination
reaction, and their results are reported below.
RESULTS AND DISCUSSION
■
Synthesis and Structure of (ATI)Pt(CH3)(L) (1). The
reaction between LiATI (ATI = N-tolyl-aminotroponiminate)
and (Me)(Cl)Pt(SMe2)2 for 2 h yielded (ATI)Pt(CH3)(SMe2)
(1a) and LiCl (eq 1). We have used the p-tolyl-substituted ATI
Figure 1. X-ray structure of (ATI)Pt(CH3)(SMe2) (1a). Thermal
ellipsoids are drawn at the 50% probability level. The hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (deg):
Pt(1)−N(19) = 2.029(7); Pt(1)−C(1) = 2.077(7); Pt(1)−N(4) =
2.092(7); Pt(1)−S(1) = 2.249(2); N(19)−Pt(1)−N(4) = 77.2(3).
ligand so that the tolyl methyl groups provide us with an NMR
handle on the complexes outside of the aromatic region.
Complex 1a is air stable and can be purified via column
chromatography; it degrades over time at room temperature,
and so the product was stored in a freezer. Brown crystals
suitable for X-ray diffraction were obtained by layering a
solution of 1a in diethyl ether with pentane and cooling it to
−35 °C (Figure 1). The bite angle of the ATI chelate is 77°,
typical for a five-membered bidentate nitrogen ligand bound to
platinum.34,35 The ATI ligand tolyl rings are twisted nearly
orthogonally to the plane containing the platinum chelate,
while the flat 10-π-electron ATI backbone lies in the PtN2SC
plane. The Pt1−C1 and Pt1−S1 bond lengths of 2.08 and 2.25
Å, respectively, are also consistent with values observed in
related structures, such as the Tp′PtII(Me)(SMe2) complex,
which contains a Pt−C bond length of 2.05 Å and Pt−S bond
length of 2.25 Å.36 The trans influence of the methyl group
causes the Pt1−N4 bond (2.09 Å) to increase by 0.06 Å in
comparison to the Pt1−N19 bond (2.03 Å), which is trans to
the dimethyl sulfide.
the NMR time scale at temperatures well below 300 K. The
coalescence temperature of the ethylene signals in the 1H NMR
spectrum was found to be 228 K, suggesting a rotational barrier
of less than 12 kcal/mol. This stands in contrast to the nacnac
analogue, (nacnac)Pt(CH3)(C2H4), which is static at room
temperature and has a barrier to rotation of 16.7 kcal/mol;21
this illustrates the fact that the ligands are less sterically
encumbered by the ATI aryl rings than in the nacnac
complexes. In (nacnac)Pt(CH3)(C2H4) the methyl carbon to
aryl ipso carbon distance is 2.9 Å, whereas in 1b the C1−C20
distance is 3.2 Å.
If HATI is stirred with Me4Pt2(μ-SMe2)2 overnight in
CH2Cl2/pentane, the major product is 1a. A small amount of
(ATI)Pt(H)(1-pentene) can be observed by 1H NMR;
however, the yield of this product is much lower than in the
analogous reaction with Hnacnac.21 We postulate that the
reason for this is that the reduced steric inhibition of the ATI
ligand allows the SMe2 ligand to coordinate more easily than in
the nacnac case and SMe2 coordination prevents C−H
activation.
A procedure to synthesize the monomethyl (nacnac)PtII
ethylene and CO complexes has been reported.21 We have
synthesized (N-tolyl-ATI)Pt(CH3)(L) (1: L= C2H4 (1b), CO
(1c)) using an analogous procedure (eq 2). Stirring LiATI with
(Me)(Cl)Pt(SMe2)2 for 15 min followed by addition of either
ethylene or CO generates 1b,c in modest yields. The 1H NMR
spectra of 1b,c are similar, but the signals for the platinum-
bound methyl groups are significantly shifted from one another.
In the 1H NMR spectrum of 1b, the Pt−Me resonance appears
at −0.27 ppm with 2JPt−H = 71 Hz. The Pt−Me resonance of 1c
2
appears at 0.25 ppm with JPt−H = 70 Hz. The bound ethylene
in 1b appears as a singlet at 2.89 ppm with platinum satellites
(2JPt−H = 58 Hz) in the 1H NMR spectrum and rotates freely on
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Oxidative Addition of MeI and MeOTf to (ATI)Pt(CH3)-
(SMe2). Addition of 1.2 equiv of MeI to 1a in CH2Cl2 yields
the oxidative addition product (ATI)Pt(CH3)2(I)(SMe2) (2)
(eq 3). Oxidative addition of primary alkyl halides to square-
Scheme 1. Formation and Equilibrium of Complexes 3a,b
Puddephatt et al. noticed similar spectroscopic behavior
following the oxidative addition of MeOTf to PtII dimethyl
complexes containing various bidentate nitrogen ligands.41,42
The PtIV complexes prepared by Puddephatt et al. reductively
eliminate ethane at room temperature;41 however, low-
temperature NMR studies indicate that the complex is an
equilibrium mixture of two complexes. They propose that the
two complexes are a neutral triflato complex and a cationic
aquo complex which are in equilibrium with each other.
Replacement of the triflate ligand by adventitious water is a
facile process due to the lability of the triflate anion. The ratio
of the two complexes is highly variable, since formation of the
aquo complex is dependent upon adventitious water in solution
(Scheme 1). Similar behavior has been observed for
diphosphine-ligated trimethyl PtIV species.41,43
planar complexes usually occurs in a trans fashion via an SN2
reaction, though some isomerization is known to occur.37
Although four NMR distinct isomers are possible, only one is
1
observed by NMR spectroscopy (Figure 2). The H NMR
spectrum shows resonances at 1.51 ppm for the Pt−Me trans to
nitrogen (2JPt−H = 71 Hz) and at 0.71 ppm for the Pt−Me trans
to iodide (2JPt−H = 64 Hz). The assignment is based on data for
PtIV complexes of the form (LL)Pt(Me)3X.38−40 Since the
coordinated sulfur in the dimethyl sulfide ligand is pyramidal,
the Pt−SMe2 methyl groups are diastereotopic and appear at
2.34 ppm (3JPt−H = 32 Hz) and 1.79 ppm (3JPt−H = 35 Hz) in
the PtIV product. Compound 2 is stable at room temperature
and can be purified via column chromatography.
The addition of 1.2 equiv of MeOTf to a −78 °C solution of
The Pt−OH2 resonance in 3a can be observed at 5.5 ppm via
1a in CH2Cl2 yields complex 3, which can be purified by
1
1
low-temperature H NMR spectroscopy. This low-temperature
column chromatography (Scheme 1). The H NMR spectrum
probe is the only viable NMR technique that distinguishes 3a
from 3b. One other Pt−OH2 species has been characterized via
low-temperature NMR spectroscopy, and it is a PtII complex
with a coordinated water resonance at 6.51 ppm.44 Reactions
performed with mixtures of 3a and 3b (referred to as 3 from
here on) are conducted with 3a and 3b generated in situ and
kept air-free; the ratio of 3a to 3b appears to have no effect on
the reactivity we observe.
of this complex is unusual: a broad singlet with platinum
satellites which integrates for 6H appears at 1.05 ppm (2JPt−H
=
71 Hz), and another broad singlet with platinum satellites
integrating for 6H appears at 1.98 ppm (3JPt−H = 32 Hz)
(Figure 3). The 13C NMR spectrum displays a broad signal at
3.1 ppm (1JPt−C = 619 Hz) with platinum satellites. The
platinum coupling of 71 Hz to the proton signal at 1.05 ppm in
1
the H NMR spectrum and its integration for 6H, combined
Slow evaporation of a methylene chloride solution of 3a,b at
room temperature produced X-ray-quality crystals of [(ATI)-
Pt(CH3)2(OH2)(SMe2)][OTf] (3a) (Figure 4). The solid-state
structure of 3a is a distorted octahedron around the PtIV center,
and the geometry of the ATI ligand is similar to that seen for
compound 1a, with a bite angle of 77°. The Pt1−S1 bond
distance of 2.32 Å is slightly longer than in 1a (2.25 Å). The
equatorial Pt1−C4 bond length is longer than the axial Pt1−C5
bond length, 2.08 vs 2.04 Å, respectively, due to the weaker
water ligand being trans to C5. The Pt1−O6 bond length of
2.26 Å is similar to the bond length in the aquo complex
synthesized by Puddephatt et al. (2.28 Å).41 This long Pt−O
with the broad signal with platinum satellites at 3.1 ppm in the
13C NMR spectrum, are suggestive of two methyl groups bound
to platinum which are fluxional on the NMR time scale. Upon
1
1
cooling, the H signal near 1 ppm in the H NMR spectrum
broadens, disappears into the baseline, and then reappears at
low temperature as four distinct methyl signals, indicating the
presence of two NMR distinct complexes. Two methyl signals
1
are seen via low-temperature H NMR spectroscopy for each
compound (one axial and one equatorial with respect to the
ATI plane) (Figure 3). The ratio of the two complexes varies
with each trial.
Figure 2. Four isomers possible from the oxidative addition of MeI to 1a yielding 2.
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1
Figure 3. H NMR of the Pt−Me and Pt−SMe2 groups of 3a,b at 298 K (top) and 193 K (bottom).
bond distance is consistent with the labile nature of the water
ligand.
Substitution of Aquo or Triflate Ligands. The aquo/
triflate ligand on 3 is labile, which opens routes to the synthesis
of other PtIV complexes. Addition of an excess of RNC to a
solution of 3 in CH2Cl2 produces a solution of [(ATI)Pt-
(CH3)2(RNC)(SMe2)][OTf] (4a,b) (eq 4). This is a facile
substitution reaction, with formation of the product within
minutes. The compound is air stable and can be purified via
1
column chromatography. The H NMR spectrum is sharp in
comparison to 3; the Pt methyl groups appear at 1.18 ppm
(2JPt−H = 62 Hz) and 0.46 ppm (2JPt−H = 62 Hz), and the
dimethyl sulfide methyl groups appear at 2.22 ppm (3JPt−H = 34
Hz) and 2.09 ppm (3JPt−H = 37 Hz). The sharpness of the
spectrum shows that, unlike 3, the complex is not fluxional on
the NMR time scale. A CN absorbance can be detected by
IR spectroscopy at 2217 cm−1 for the tert-butyl isocyanide
adduct 4a and at 2196 cm−1 for the aryl isocyanide 4b; these
CN stretches are at much higher frequency than those for
the free isocyanides, which indicates that the Pt is electron
deficient and unable to back-bond to the isocyanides so that
they act as σ-donating-only ligands (Table 1). The stretching
frequency of 4a is 25 cm−1 higher than that for the neutral PtIV
species (nacnac)PtMe3(CNtBu), further illustrating the high
electrophilicity of 4a.45
Slow evaporation of a methylene chloride solution of 4a at
room temperature produced X-ray-quality crystals (Figure 5).
The only noteworthy difference in the solid-state structure of
4a versus that of 3a is that the axial Pt methyl carbon bond has
slightly lengthened, 2.07 Å in 4a and 2.04 Å in 3a, due to the
greater trans influence of the isonitrile ligand vs that of the aquo
ligand; the axial Pt−CH3 bond and the Pt−CNR bond are
equal at 2.08 Å.
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Figure 5. X-ray structure of [(ATI)Pt(CH3)2(tBuNC)(SMe2)][OTf]
(4a). Thermal ellipsoids are drawn at the 50% probability level. The
hydrogen atoms and the triflate counterion are removed for clarity.
Selected bond distances (Å) and angles (deg): Pt(1)−N(1) =
2.048(3); Pt(1)−C(1) = 2.071(3); Pt(1)−C(3) = 2.082(3); Pt(1)−
C(2) = 2.083(3); Pt(1)−N(26) = 2.115(2); Pt(1)−S(1) = 2.317(8);
C(3)−N(4) = 1.142(4); N(11)−Pt(1)−N(26) = 76.85(10).
Figure 4. X-ray structure of [(ATI)Pt(CH3)2(OH2)(SMe2)][OTf]
(3a). Thermal ellipsoids are drawn at the 50% probability level. The
hydrogen atoms and the triflate counterion are removed for clarity.
One hydrogen atom on O(6) was found, and one was calculated.
Selected bond distances (Å) and angles (deg): Pt(1)−O(6) =
2.263(5); Pt(1)−C(5) = 2.037(7); Pt(1)−N(7) = 2.039(6); Pt(1)−
C(4) = 2.077(7); Pt(1)−N(22) = 2.119(6); Pt(1)−S(1) =
2.3197(19); N(7)−Pt(1)−N(22) = 77.0(2).
ppm from one another; two distinct signals for the
diastereotopic Pt−SMe2 methyl groups appear around 2 ppm.
The reaction can be monitored via IR spectroscopy, as 5a
Table 1. CN Stretching Data for 4 and Free Isocyanides
shows an IR stretch of νN 2038 cm−1 for the linear azide entity.
compd
R = tBu (4a)
CN stretch (cm−1
)
3
Using the same methods as with NaN3, (ATI)Pt-
(CH3)2(CN)(SMe2) (5b) was synthesized via a reaction with
NaCN. The reaction can also be monitored via IR spectros-
copy, as 5b shows an IR stretch for the cyanide of νCN 2301
cm−1; this stretch is higher in energy in comparison to the value
2217
2196
2136
2116
2192
R = 2,6-dimethylphenyl (4b)
tert-butyl isocyanide
2,6-dimethylphenyl isocyanide
(nacnac)PtMe3(CNtBu)45
of 2125 cm−1 reported for (bpy)PtMe3(CN).46 The H NMR
1
Addition of organic azides, such as phenyl azide, to 3 did not
result in any observed reaction; however, substitution of the
aquo/triflate ligand with NaN3 was successful. Vigorous stirring
of 3 in a solution of CH2Cl2 with a large excess of NaN3
overnight yields the substitution product (ATI)Pt(CH3)2(N3)-
(SMe2) (5a) (eq 5). The 1H spectrum of 5a is similar to that of
spectra of 5a and 5b are similar, but the downfield Pt−-Me
shifts from 1.07 ppm (2JPt−H = 70 Hz) for 5a to 0.69 ppm
(2JPt−H = 56 Hz) in 5b; this upfield shift and reduction in
coupling constant is consistent with known (L)2PtMe3(CN)
complexes.46,47
Addition of Phosphines to 3. Addition of 1 equiv of
PMe3 to a solution of 3 in CH2Cl2 at room temperature
produces the expected aquo/triflate displacement product
1
[(ATI)Pt(CH3)2(PMe3)(SMe2)][OTf] (6a) (eq 6). The H
NMR spectrum of this product clearly shows two Pt−Me
signals which are coupled to phosphorus with 3JP−H = 9 Hz for
the downfield methyl protons and 3JP−H = 8 Hz for the upfield
methyl protons. Only one of the two diastereotopic Pt−SMe2
methyl signals is visible. It appears at 2.23 ppm and is quite
broad. The other Pt−SMe2 methyl signal is obscured by the
bound PMe3 signal. The 31P NMR spectrum also confirms the
addition of PMe3 to the platinum center by exhibiting a singlet
at −30.0 ppm having platinum satellites with 1JPt−P = 1101 Hz.
The compound can be purified by column chromatography and
is also stable in solution for several days at room temperature in
air. The stability indicates that the PMe3 is bound tightly to the
Pt, as it would rapidly oxidize to OPMe3 under these conditions
if the binding was reversible; this oxidation due to reversible
4a,b with the Pt−Me signal trans to the ATI nitrogen (0.38
ppm) and the Pt−Me signal trans to N3 (1.07 ppm) shifted 0.6
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Table 2. Pt−P Coupling Data for Complexes 6a−d
PR3 (6)
1JPt−P (Hz)
cone angle (deg)51
PMe3 (6a)
1101
1004
877
118
122
136
107
PMe2Ph (6b)
PMePh2 (6c)
P(OMe)3 (6d)
1963
(6b). This complex can be purified by column chromatography
and is stable in solution at room temperature for several days.
1
The H NMR spectra of 6a and 6b are quite similar, and the
31P NMR spectrum of 6b exhibits a signal at −24.1 ppm with
platinum satellites: 1JPt−P = 1004 Hz. The addition of 1 equiv of
PPh2Me, which has a cone angle of 136°, to 3 at room
temperature results in the formation of [(ATI)Pt-
(CH3)2(PPh2Me)(SMe2)][OTf] (6c). However, unlike 6a
and 6b, 6c is not stable over time in solution, and over 4
days at room temperature in solution, 6c converts to a second
product, 7a. Complex 6c is stable enough to be dried in vacuo
and triturated with hexane to remove any excess PMePh2 that
may be present. The NMR of 6c is analogous to that of 6a and
6b; the phosphorus signal appears at −23.8 ppm and has a Pt−
P coupling constant of 877 Hz. It is interesting to note that, for
coordination does occur in the related complex (nacnac)Pt-
(H)2(SiPh3)(PMe3).48
A solution of 6a in methylene chloride was layered with
hexanes and stored at −35 °C. This recrystallization produced
brown crystals suitable for X-ray diffraction (Figure 6). The
1
the PtIV PR3 complexes, the JPt−P value decreases with
increasing cone angle (Table 2). This is most likely indicative
of weaker Pt−P bonds due to steric repulsion between PR3 and
the other ligands around Pt.
Complex 7a exhibits a Pt−Me signal coupled to phosphorus
1
with platinum satellites visible in the H NMR spectrum at
−0.34 ppm. The PPh2Me methyl protons resonate as a doublet
at 0.87 ppm. The 31P NMR spectrum shows a peak at 1.5 ppm
1
1
with JPt−P = 3979 Hz. The H and 13C NMR spectra show
resonances corresponding to only one Pt−Me group and
bound PPh2Me. The NMR data are consistent with the PtII
species (ATI)Pt(CH3)(PPh2Me) (7a), and this was confirmed
by X-ray crystallography.
Slow evaporation of a solution of 7a in methylene chloride
produced clear yellow platelike crystals suitable for X-ray
diffraction (Figure 7). The structure is similar to that of 1a,
with a distorted-square-planar geometry about the platinum
center. The Pt(1)−P(1) bond length of 2.22 Å is significantly
Figure 6. X-ray structure of [(ATI)Pt(CH3)2(PMe3)(SMe2)][OTf]
(6a). Thermal ellipsoids are drawn with 50% probability. The
hydrogen atoms, triflate counterion, and a molecule of water are
removed for clarity. Selected bond distances (Å) and angles (deg):
Pt(1)−N(2) = 2.071(3); Pt(1)−C(26) = 2.108(4); Pt(1)−S(1) =
2.3322(10); Pt(1)−C(25) = 2.092(4); Pt(1)−N(1) = 2.159(3);
Pt(1)−P(1) = 2.4176(10); N(2)−Pt(1)−N(1) = 75.64(13).
1
shorter than that in 6a (2.42 Å); this also reflects the JPt−P
values of 3979 Hz for 7a and 1101 Hz for 6a.
In addition to the formation of the product 7c, formation of
1
[PMe2Ph2][OTf] is observed by H and 31P NMR. We also
observe the re-formation of broad methyl signals indicative of 3
in the H NMR spectrum; as conversion increases and the
1
solid-state structure of 6a confirms replacement of the aquo/
triflate ligand on 3 with PMe3. The bond length of 2.11 Å for
the Pt1−C26 trans to PMe3 is longer than that for either the
isocyanide adduct 4a (2.07 Å) or the aquo adduct 3a (2.04 Å),
which is in accordance with the increasing trans influence from
H2O to RNC to PMe3.49,50 The Pt1−S1 bond length of 6a is
also similar to that of 3a and 4a (2.32 Å) at 2.33 Å. Although
the diastereotopic SMe2 signals in the 1H NMR show
significant line broadening, low-temperature H NMR studies
show that the signals for the diastereotopic SMe2 methyl
protons sharpen upon cooling.
Due to successful displacement of the triflate/aquo ligand in
3 with PMe3, which has a cone angle of 118°, more sterically
demanding phosphorus containing ligands were investigated
(Table 2).51 The addition of 1 equiv of PPhMe2, which has a
cone angle of 122°, to 3 at room temperature yields the
phosphine adduct [(ATI)Pt(CH3)2(PPhMe2)(SMe2)][OTf]
concentration of free SMe2 increases, the methyl signals shift
slightly and become more broad, consistent with reversible
1
SMe2 binding to 3 (Figure 8). A signal at 3.00 ppm in the H
NMR for [SMe3][OTf] grows in increasingly as the
concentration of SMe2 goes up and that of 6c goes down;
the identity of this compound was confirmed by spiking a
reaction mixture with independently synthesized [SMe3][OTf].
1
1
1
The decomposition of 6c yields about /2 equiv of 7a and /2
equiv of 3. No formation of (ATI)Pt(Me)(SMe2) (1a) is
observed at any time; this is expected, because 1a will react
rapidly with PMePh2 to form 7a. If the reaction is conducted
with 2 equiv or more of phosphine, then no [SMe3][OTf] is
observed; only [PMe2Ph2][OTf] is found and complete
conversion to 7a occurs (Scheme 2).
Addition of PPh3, which has a cone angle of 145°, to a
solution of 3 in CH2Cl2 at room temperature does not generate
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faster than conversion of 3 to 7b. If the reaction was going
through a PtIV phosphine intermediate, which would be
consistent with 6c converting to 7a, its formation would have
to be rate limiting with reductive elimination or phosphine loss
occurring rapidly; we cannot rule out this pathway, but it seems
unlikely on the basis of the stability of 6c.
In order to test whether the divergent reactivity observed
with phosphine ligands was due to steric or electronic factors,
we investigated the reactivity of PCy3, which is electronically
similar to PMe3 but has a large cone angle of 170°. When 1
equiv of PCy3 was added to 3 in CD2Cl2 at room temperature,
we observed rapid and complete conversion to (ATI)Pt(CH3)-
(SMe2) (1a) and [PMeCy3][OTf]; no PtIV phosphine complex
could be observed. This reaction pathway is analogous to the
reaction with PPh3, but reductive elimination occurs at a faster
rate, which prevents displacement of SMe2 by PCy3 in 1a.
These data are consistent with a mechanism that is dominated
by steric factors; the increased rate of reaction is consistent with
the greater nucleophilicity of PCy3 versus PPh3.
We also investigated the opposite end of the spectrum by
using P(OMe)3, which has a small cone angle of 107° but is less
basic and more π acidic than PPh3. The reaction of 3 and 1
equiv of P(OMe)3 at room temperature forms the stable PtIV
compound [(ATI)Pt(CH3)2(P(OMe)3)(SMe2)][OTf] (6d),
from which reductive elimination is not observed. This reaction
is similar to the reaction with PMe3, further indicating that the
reductive elimination is dependent on the cone angle of the
phosphine and not the electronic differences.
Figure 7. X-ray structure of (ATI)Pt(CH3)(PPh2Me) (7a). Thermal
ellipsoids are drawn at the 50% probability level. The hydrogen atoms
are removed for clarity. Selected bond distances (Å) and angles (deg):
Pt(1)−N(23) = 2.090(6); Pt(1)−C(14) = 2.069(7); Pt(1)−N(15) =
2.074(7); Pt(1)−P(1) = 2.216(2); N(15)−Pt(1)−N(23) = 77.3(3).
The strong correlation between ligand cone angle and either
an observable PtIV compound, but over the period of a few
hours conversion of 3 to (ATI)Pt(CH3)(PPh3) (7b) is
observed (eq 7). The 31P NMR spectrum of 7b has a single
binding or nucleophilic attack on the PtIV methyl group
−
explains why we do not observe attack on the methyl with N3
and CN−, both of which are much better nucleophiles than
PPh3 (Scheme 4). On the basis of our observations, the PtIV
metal center is the most electrophilic position on 3, but if the
steric bulk of the incoming nucleophile prevents it from
forming a stable complex, the nucleophile will attack the
electrophilic methyl group trans to the vacant site on Pt. Under
such a mechanism, increasing the nucleophilicity of the
incoming ligand will only increase the rate of C−X bond
formation if the nucleophile has sufficient steric bulk. The
mechanism of C−X bond formation from PtIV in systems such
as the Shilov oxidation of methane to methanol has been shown
to proceed through a similar nucleophilic attack mechanism of
reductive elimination. A similar balance of binding to PtIV or
attacking the PtIV methyl group is present in these reactions,
and a sterically encumbering ligand system on the Pt catalyst
may be able to increase the rate and selectivity of reductive
elimination.
peak at 18.8 ppm with platinum satellites and 1JPt−P = 4134 Hz,
confirming addition of PPh3 to the platinum center. The
CONCLUSION
■
1
reaction can be monitored via H and 31P NMR spectroscopy,
The platinum(II) aminotropimate complexes readily undergo
oxidative addition with electrophilic methyl sources to yield
dimethyl Pt(IV) complexes. The dimethyl Pt(IV) complexes
will readily exchange their X ligand for a number of
monodentate anionic or neutral ligands. In most cases this
allows for the isolation of stable neutral or cationic dimethyl
Pt(IV) complexes, but when bulky phosphine ligands are used,
reductive elimination to form methyl Pt(II) species occurs. No
reductive elimination of ethane is observed under any
conditions, but methyl phosphonium species are reductively
eliminated when bulky phosphine ligands are present. Whether
or not reductive elimination occurs and the pathway by which it
occurs are sensitive to the cone angle of the phosphine that is
but the only Pt compounds observed are 3 and 7b. Along with
formation of 7b, formation of [PMePh3][OTf] is observed
1
both by H and 31P NMR; no formation of [SMe3][OTf] is
observed. Two equivalents of PPh3 is required for complete
conversion of 3 to 7b; addition of 1 equiv results in formation
of 1/2 equiv each of 7b and the phosphonium salt and half of 3
remains. These data are consistent with a mechanism involving
nucleophilic attack of the phosphine on one of the methyl
groups in 3 (likely preceded by dissociation of OTf/H2O) to
re-form 1a; 1a will then readily react with another molecule of
PPh3 and form 7b (Scheme 3). Direct synthesis of 7b by the
reaction of 1a and PPh3 confirms that ligand exchange is much
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1
Figure 8. 31P and H NMR spectra showing the conversion of 6c to 7a.
Scheme 2. Proposed Mechanism for the Conversion of 6c to 7a
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could be a useful method for selective reactions with what
would generally be inferior nucleophiles.
Scheme 3. Proposed Mechanism for the Conversion of 3 to
7b
EXPERIMENTAL SECTION
■
General Procedures. Reactions were performed under an
atmosphere of dry nitrogen or argon using standard drybox and
Schlenk techniques. Argon and nitrogen were purified by passage
through columns of BASF R3-11 catalyst and 4 Å molecular sieves. All
glassware was oven-dried or flame-dried under vacuum and cooled
under a nitrogen atmosphere before use. Methylene chloride, pentane,
and diethyl ether were purified under an argon atmosphere by passage
through a column of activated alumina.52 Tetrahydrofuran was freshly
distilled from sodium/benzophenone ketyl prior to use. Methylene
chloride-d2 was vacuum-transferred from CaH2 and degassed by
53
several freeze−pump−thaw cycles. The complexes Pt2Me4(μ-SMe2)2
and Pt(SMe)2MeCl53 and the ligand N-tolyl-ATI (N-tolyl(2-
tolylamino)troponimine)54,55 were synthesized according to published
procedures. All other reagents were used as received.
For simplicity, the NMR data for the N-tolyl-ATI ligand for all of
the complexes have been compiled in Table 3. Crystal data and data
collection parameters for 1a, 3a, 4a, 6a, and 7a are given in Table 4.
(N-tolyl-ATI)Pt(CH3)(SMe2) (1a). A Schlenk flask containing 211.5
mg (0.71 mmol) of N-tolyl-ATI in THF was cooled to −78 °C, and
0.31 mL (0.78 mmol, 1.1 equiv) of 2.5 M nBuLi was added slowly.
The solution was warmed to room temperature. A solution of 250 mg
(0.68 mmol, 0.95 equiv) of PtMe(SMe2)2Cl in THF was cannula-
transferred to the Schlenk flask containing [Li]+[N-tolyl-ATI]−. After
2 h the solvent was removed under vacuum. The resulting product was
purified via column chromatography using a silica gel column treated
with a 97/3 CH2Cl2/NEt3 solution and a mobile phase of 9/1
hexanes/ethyl acetate to yield 193 mg (0.34 mmol, 48%) of pure 1a.
X-ray-quality crystals were formed by recrystallization from layered
used. The reductive elimination appears to proceed through an
SN2 type two-step process rather than a concerted reductive
elimination; because of this, we would expect to see a
dependence on the nucleophilicity of phosphine, but this
seems to make little difference. The most electrophilic site on
the Pt(IV) complex 3 is the Pt itself, so that phosphines
preferentially bind to the metal, but this interaction is sterically
inhibited when large phosphines are used, allowing them to
attack the less electrophilic but more exposed axial methyl
group.
Reductive elimination from Pd(IV) and Pt(IV) has been
shown to be a versatile method of forming new C−X bonds,
but these reactions typically require high temperatures to occur.
In this case we are able to form new P−C bonds at room
temperature via reductive elimination from Pt(IV). The bond-
forming step favors sterically encumbered nucleophiles, which
1
pentane on top of a diethyl ether solution of 1a at −35 °C. H NMR
(δ, CD2Cl2, 400 MHz, 298 K): 2.09 (6H, s, S(CH3)2, 3JPt−H = 48 Hz),
0.05 (3H, s, PtCH3, 2JPt−H = 76 Hz). 13C NMR (δ, CD2Cl2, 100 MHz,
298 K): 22.3 (S(CH3)2), −12.2 (PtCH3, 1JPt−C = 729 Hz). Anal. Calcd
for C24H28N2PtS: C, 50.43; H, 4.94; N, 4.90. Found: C, 50.70; H, 4.89;
N, 4.66.
Scheme 4. Divergent Reaction Pathways Based on Phosphine Cone Angle
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1
Table 3. H and 13C NMR Data for the N-tolyl-ATI Ligand of Complexes 1−7
complex
N-tolyl-ATI aromatic (δ, ppm)
tolyl methyl (δ, ppm)
1a
1H: 7.29 d, 4H, JH−H = 9 Hz; 6.923 d, 2H, JH−H = 7 Hz; 6.87 d, 2H, JH−H = 6 Hz; 6.805 t, 1H; 6.780 t, 1H; 6.324 d, 1H, JH−H 1H: 2.43
= 11 Hz; 6.219 d, 1H, JH−H = 11 Hz; 6.151 t, 1H
13C: 166.75; 163.93, JPt−C = 44 Hz; 148.00; 146.97, JPt−C = 49 Hz; 134.72; 134.57; 131.78; 131.51; 130.41; 130.32; 126.99; 13C: 21.2
125.50; 119.49; 118.74; 117.69, JPt−C = 36 Hz
1b
1c
1H: 7.30 m, 4H; 6.94 m, 2H; 6.87 d, 2H, JH−H = 8 Hz; 6.787 d, 2H, JH−H = 8 Hz; 6.565 t, 2H; 6.446 t, 1H
13C: 168.4; 165.2; 147.0; 144.2; 135.3; 135.1; 133.5; 133.0; 130.7; 130.4; 126.7; 124.9; 121.5; 119.5; 116.8
1H: 7.30 t, 4H; 7.10 d, 2H, JH−H = 8 Hz; 6.99 m, 2H; 6.83 d, 2H, JH−H = 8 Hz; 6.75 d, 1H, JH−H = 12 Hz; 6.48 t, 1H; 6.48 d, 1H: 2.42
1H, JH−H = 11
13C: 169.0; 164.0; 150.4; 144.8; 135.6; 135.5; 133.3; 133.1; 130.5; 130.4; 127.1; 124.4; 122.3; 119.1; 118.8
1H: 2.42
13C: 21.1
13C: 21.0
2
1H: 7.72 d, 1H, JH−H = 7 Hz; 7.50 d, 1H, JH−H = 7 Hz; 7.34 d, 2H, JH−H = 8 Hz; 7.25 d, 2H, JH−H = 7 Hz; 6.87 d, 1H, JH−H
8 Hz; 6.83 d, 1H, JH−H = 7 Hz; 6.71 t, 1H; 6.66 t, 1H; 6.18 d, 1H, JH−H = 12; 6.01 t; 1H; 5.99 d, 1H, JH−H = 12
=
1H: 2.41; 2.40
13C: 165.7, JPt−C = 14 Hz; 164.7, JPt−C = 26 Hz; 146.3, JPt−C = 11 Hz; 144.6; 136.4; 135.7; 133.8; 133.8; 130.8; 130.4; 128.5; 13C: 21.2; 21.1
126.9; 120.1, JPt−C = 10 Hz; 119.9; 118.5; JPt−C = 22 Hz
3
1H (RT): 7.33 t, 4H; 7.13 m, 2H; 7.08 m, 2H; 6.91 t, 1H; 6.85 t, 1H; 6.49 d, 1H, JH−H = 11.2 Hz; 6.29 t, 2H
1H: 2.44; 2.41
13C (RT): 165.9, JPt−C = 23 Hz; 164.8, JPt−C = 32 Hz; 146.1; 144.2, JPt−C = 31 Hz; 136.8; 136.3; 134.23; 134.15; 131.1; 13C: 21.2
131.0; 127.7; 125.3; 122.0; 120.8; 119.5, JPt−C = 30 Hz
1H: 7.38 m, 4H; 6.93 s-broad, 1H; 6.85 m, 4H; 6.78 t, 1H; 6.36 d, 1H, JH−H = 12 Hz; 6.20 t, 1H; 6.12 d, 1H, JH−H = 11 Hz 1H: 2.45; 2.42.
13C: 165.9, JPt−C = 21 Hz; 165.16, JPt−C = 34 Hz; 145.3; 143.9, JPt−C = 28 Hz; 135.2; 135.0; 131.7; 131.6; 123.1; 122.1; 121.1; 13C: 21.2; 21.1.
119.9; 119.6, JPt−C = 25 Hz
1H: 7.42−6.8,16H, (CH3)2C6H3NC and N-tolyl-ATI arom
4a
4b
1H: 2.40 s, 9H,
(CH3)2C6H3NC and ATI
tolyl methyl
13C: 21.2; 21.1
1H: 2.42; 2.41
13C: 20.8, 20.7
1H: 2.41; 2.40
13C: 165.7−119.7, (CH3)2C6H3NC and N-tolyl-ATI arom
1H: 7.33−5.95
13C: 165.2; 164.0; 146.1; 144.2; 136.0; 135.3; 133.7; 133.6; 130.3; 128.1; 126.3; 125.0; 119.8; 119.4; 118.0
1H: 7.29 m, 6H; 6.89 m, 2H; 6.67 t, 1H; 6.61 t, 1H; 6.13 d, 1H, JH−H = 12 Hz; 5.95 t, 1H; 5.92 d, 1H, JH−H = 12 Hz
5a
5b
13C: 165.7, JPt−C = 15 Hz; 164.6; 146.2; 144.6, JPt−C = 21 Hz; 136.3; 135.6; 134.2; 134.1; 131.1; 127.6; 127.0; 125.1; 119.3 13C: 21.2, 21.1
JPt−C = 8 Hz; 117.6 JPt−C = 20 Hz
6a
1H: 7.38 m, 4H; 7.40 d, 1H, JH−H = 8 Hz; 7.00 d, 1H, JH−H = 8 Hz; 6.81 m, 4H; 6.31 d, 1H, JH−H = 12 Hz; 6.20 t, 1H; 6.10 d, 1H: 2.47; 2.45
1H, JH−H = 12 Hz
13C: 165.9, JPt−C = 15 Hz; 165.4, JPt−C = 24 Hz; 146.0, JPt−C = 8 Hz; 143.4, JPt−C = 26 Hz; 137.8; 137.4; 135.2; 134.9; 131.9, 13C: 21.2, 21.1
JP−C = 51 Hz; 131.5, JPt−C = 86 Hz; 127.6; 126.4; 122.4, JP−C = 3 Hz; 122.0, JP−C = 3 Hz; 120.8, JP−C = 3 Hz.
6b
6c
6d
1H: 7.50 −6.04, 18H, PtPPh and N-tolyl-ATI arom
13C: 166.3−121.2, PtPPh and N-tolyl-ATI arom
1H: 7.76−5.93, 23H, PtPPh2 and N-tolyl-ATI arom
13C: 164.7−118.6, PtPPh2 and N-tolyl-ATI arom
1H: 2.39
13C: 21.2, 21.0
1H: 2.38; 2.35
13C: 20.5, 20.4
1H: 7.32 m, 6H; 6.96 m, 7H; 6.8 dd, 1H, JH−H = 12, 2 Hz; 6.74 dd, 1H, JH−H = 12, 2 Hz; 6.34 dd, 1H, JH−H = 12, 2 Hz; 6.10 1H: 2.42; 2.40
dd, 1H, JH−H = 12, 2 Hz
13C: 165.9, JPt−C = 18 Hz; 165.3, JPt−C = 32 Hz; 144.7; 143.3, JPt−C = 30 Hz; 137.1; 136.4; 134.8; 134.5; 131.1; 130.8; 127.2; 13C: 20.7; 20.6
126.4; 125.0; 124.8; 122.6; 121.8; 121.3; 119.4; 119.4
7a
7b
1H: 7.41−6.13, 23H, PtPPh2 and N-tolyl-ATI arom
13C: 166.8−114.7, PtPPh2 and N-tolyl-ATI arom
1H: 7.49−5.98, 28H, PPh3 and N-tolyl-ATI arom
13C: 167.0−117.1, PPh3 and N-tolyl-ATI arom
1H: 2.37; 2.31
13C: 21.0, 20.9
1H: 2.38; 2.31
13C: 21.0, 20.8
(N-tolyl-ATI)Pt(CH3)(η2-C2H4) (1b). A Schlenk flask containing
162 mg (0.54 mmol) of N-tolyl-ATI in THF was cooled to −78 °C,
and 0.24 mL (0.59 mmol, 1.1 equiv) of nBuLi was added slowly. The
solution was warmed to room temperature. A solution of 200 mg (0.54
mmol, 1.0 equiv) of PtMe(SMe2)2Cl in THF was cannula-transferred
to the Schlenk flask containing [Li]+[N-tolyl-ATI]−. The solution was
stirred for 30 min before ethylene gas was bubbled into the solution.
After 30 min of bubbling, the solvent was removed under vacuum, and
the resulting product was purified via column chromatography using a
silica gel column treated with a 97/3 CH2Cl2/NEt3 solution and a
mobile phase of 8/2 hexanes/CH2Cl2. The first band contained the
product 1b, along with free ligand. This product was collected and
reduced to dryness before being chromatographed again using a silica
gel column with a mobile phase of 100% CH2Cl2 to yield 72 mg (0.13
mmol, 24%) of pure 1b. 1H NMR (δ, CD2Cl2, 400 MHz, 298 K): 2.89
Calcd for C25H29N2Pt: C, 53.90; H, 4.65; N, 4.98. Found: C, 53.62; H,
4.88; N, 5.21.
(N-tolyl-ATI)Pt(CH3)(CO) (1c). The same procedure as for 1b was
used to prepare 1c, but CO was bubbled through the solution rather
than ethylene to yield 76 mg of 1c (0.14 mmol, 26%). IR (hexanes):
νCO 2062 cm−1. 1H NMR (δ, CD2Cl2, 400 MHz, 298 K): 0.25 (3H, s,
2
PtCH3, JPt−H = 70 Hz). 13C NMR (δ, CD2Cl2, 100 MHz, 298 K):
1 6 9 . 9 ( P t - C O ) ; − 1 5 . 3 ( P t C H 3 ) . A n a l . C a l c d f o r
C23H22N2OPt·1/2C6H14·1/2CH2Cl2: C, 51.04; H, 4.93; N, 4.49.
Found: C, 51.25; H, 4.53; N, 4.27.
(N-tolyl-ATI)Pt(CH3)2(I)(SMe2) (2). A Schlenk flask containing 30
mg (0.052 mmol) of 1a in CH2Cl2 was cooled to −78 °C, and 4 μL of
MeI (0.063 mmol, 1.2 equiv) was syringed into the flask. The solution
was stirred for 5 min before the flask was warmed to room
temperature, and then it was stirred for an additional 15 min. The
solvent was removed in vacuo, and the resulting product was purified
via flash column chromatography using an alumina column with a
mobile phase of 100% CH2Cl2 to yield 16 mg (0.022 mmol, 42%) of
pure 2. 1H NMR (δ, CD2Cl2, 500 MHz, 298 K): 2.34 (3H, s, S(CH3)2,
2
(4H, s, Pt(η2-CH2CH2), JPt−H = 58 Hz), −0.27 (3H, s, PtCH3,
2JPt−H = 71 Hz). 13C NMR (δ, CD2Cl2, 100 MHz, 298 K): 59.5 (Pt(η2-
1
1
CH2CH2), JPt−C = 204 Hz), −7.2 (PtCH3, JPt−C = 689 Hz). Anal.
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Table 4. Crystal Data and Data Collection Parameters for (N-tolyl-ATI)Pt(CH3)(SMe2) (1a), (N-tolyl-
ATI)Pt(CH3)2(OH2)(SMe2)[OTf] (3a), (N-tolyl-ATI)Pt(CH3)2(tBuNC)(SMe2)[OTf] (4a), and (N-tolyl-
ATI)Pt(CH3)2(PMe3)(SMe2)[OTf] (6a)
1a
3a
4a
6a
7a
empirical formula
fw
C24H28N2PtS
571.63
C26H33F3N2O4PtS2
753.75
C31H40F3N3O3PtS2
818.87
C29H42F3N2O4PPtS2
829.83
C35H35N2PPt
709.71
temp, K
wavelength, Å
cryst syst
space group
a, Å
100(2)
100(2)
100(2)
100(2)
100(2)
1.54178
1.54178
0.71073
1.54178
1.54178
triclinic
monoclinic
P21/n
monoclinic
P21/c
triclinic
monoclinic
P21/c
P1
̅
P1
̅
12.6651(8)
9.9737(6)
18.3405(10)
90
11.6760(5)
19.1569(8)
12.6460(5)
90
9.3286(2)
12.9106(2)
14.9100(3)
83.989(1)
73.274(1)
83.268(1)
1703.13(6)
2
13.5687(7)
19.0331(12)
13.5212(7)
90
10.2555(8)
12.2417(9)
12.6678(10)
95.950(4)
b, Å
c, Å
α, deg
β, deg
106.824(4)
90
94.933(3)
90
110.214(2)
90
100.623(5)
110.784(4)
1436.4(2)
γ, deg
V, Å3
2217.6(2)
4
2818.1(2)
4
3276.8(3)
4
Z
2
ρcalcd, Mg/m3
μ, mm−1
F(000)
1.712
1.777
1.597
1.682
1.641
12.787
11.178
4.293
10.121
9.857
1120
1488
816
1656
704
cryst size, mm3
2θ range, deg
index ranges
0.15 × 0.15 × 0.05
3.78−65.53
−14 ≤ h ≤ 14
0 ≤ k ≤ 11
0 ≤ l ≤ 21
88713
0.10 × 0.10 × 0.10
3.80−70.13
−13 ≤ h ≤ 13
0 ≤ k ≤ 23
0 ≤ l ≤ 15
5178
0.20 × 0.15 × 0.05
2.06−30.59
−13 ≤ h ≤ 13
−17 ≤ k ≤ 18
−21 ≤ l ≤ 21
45821
0.08 × 0.08 × 0.40
3.47−66.24
−16 ≤ h ≤ 16
−22 ≤ k ≤ 17
−16 ≤ l ≤ 15
25356
0.05 × 0.10 × 0.23
3.61−66.58
−9 ≤ h ≤ 11
−14 ≤ k ≤ 14
−14 ≤ l ≤ 15
11579
no. of rflns collected
no. of indep rflns
3815 (R(int) = 0.0493) 5178 (R(int) = 0.0000) 10430 (R(int) = 0.0554) 5742 (R(int) = 0.0340)
4799 (R(int) = 0.0767)
4799/0/356
no. of data/restraints/
params
goodness of fit on F2
3815/0/261
5178/0/360
10430/0/398
5742/3/402
1.094
1.132
1.035
1.160
1.007
final R indices (I > 2σ(I))
R1 = 0.0507, wR2 =
0.1113
R1 = 0.0475, wR2 =
0.1000
R1 = 0.0346, wR2 =
0.0614
R1 = 0.0586, wR2 =
0.1444
R1 = 0.0499, wR2 =
0.1207
R indices (all data)
R1 = 0.0584, wR2 =
0.1145
R1 = 0.0568, wR2 =
0.1036
R1 = 0.0479, wR2 =
0.0654
R1 = 0.0618, wR2 =
0.1467
R1 = 0.0641, wR2 =
0.1280
3
3JPt−H = 32 Hz), 1.79 (3H, s, S(CH3)2, JPt−H = 35 Hz), 1.51 (3H, s,
equiv) of tert-butyl isocyanide. The solution was stirred for 2 h before
the solvent was removed under vacuum. The resulting product was
purified via flash column chromatography using an alumina column
with a mobile phase of 100% CH2Cl2 to wash off organic byproducts
followed by 100% CH3CN. The CH3CN fraction was collected and
reduced to dryness and the residue triturated with pentanes to yield 35
mg (0.043 mmol, 67%) of pure 4a. X-ray-quality crystals were formed
by slow evaporation of a solution of 4a in methylene chloride at room
PtCH3, JPt−H = 71 Hz), 0.71 (3H, s, PtCH3, JPt−H = 64 Hz). 13C
NMR (δ, CD2Cl2, 125 MHz, 298 K): 24.7 (S(CH3)2), 19.0 (S(CH3)2),
13.8 (PtCH3, JPt−C = 474 Hz), 1.7 (PtCH3, JPt−C = 449 Hz). Anal.
Calcd for C25H31IN2PtS: C, 42.43; H, 4.35; N, 4.28. Found: C, 42.08;
H, 4.38; N, 3.93.
Preparation of Mixtures of [(N-tolyl-ATI)Pt(CH3)2(OH2)-
(SMe2)][OTf] (3a) and (N-tolyl-ATI)Pt(CH3)2(O3SCF3)(SMe2)
(3b). A Schlenk flask containing 145 mg (0.25 mmol) of 1a was
cooled to −78 °C, and 34 μL of MeOTf (0.30 mmol, 1.2 equiv) was
syringed in. The solution was allowed to stirred for 5 min before the
flask was warmed to room temperature and stirred for 15 min more.
The solvent was removed under vacuum. The resulting product was
purified via flash column chromatography using an alumina column
with a mobile phase of 100% CH3CN. The solid was washed with
pentanes and dried to yield 148 mg of 3a,b. X-ray-quality crystals of 3a
were formed by slow evaporation of a solution of 3a in methylene
2
2
1
1
1
temperature. IR (CH2Cl2): νCN 2217 cm−1. H NMR (δ, CD2Cl2,
400 MHz, 298 K): 2.22 (3H, s, S(CH3)2, 3JPt−H = 34 Hz), 2.09 (3H, s,
3
S(CH3)2, JPt−H = 37 Hz), 1.64 (9H, s, CN-But), 1.18 (3H, s, PtCH3,
2
2JPt−H = 62 Hz), 0.46 (3H, s, PtCH3, JPt−H = 62 Hz). 13C NMR (δ,
CD2Cl2, 100 MHz, 298 K): 30.2 (CN-But), 24.8 (S(CH3)2), 19.6
1
1
(S(CH3)2), 8.4 (PtCH3, JPt−C =500 Hz), 2.1 (PtCH3, JPt−C = 536
Hz). Anal. Calcd for C31H40F3N3O3PtS2: C, 45.47; H, 4.92; N, 5.13.
Found: C, 45.71; H, 4.83; N, 5.23.
1
[(N-tolyl-ATI)Pt(CH3)2(CNC6H3Me2)(SMe2)][OTf] (4b). The same
procedure as for 4a was used to prepare 4b, but 2,6-dimethylphenyl
isocyanide was used instead of tert-butyl isocyanide. The yield of 4b
chloride at room temperature. H NMR (δ, CD2Cl2, 400 MHz, 298
3
K): 1.98 (6H, br s, S(CH3)2, JPt−H = 32 Hz), 1.05 (6H, br s, PtCH3,
2JPt−H = 71 Hz). 13C NMR (δ, CD2Cl2, 100 MHz, 298 K): 19.9 (br,
1
1
was 57 mg (0.066 mmol, 94%). IR (CH2Cl2): νCN 2196 cm−1. H
S(CH3)2); 3.1 (br, PtCH3, JPt−C = 619 Hz). Elemental analysis could
not be performed on these compounds, as they are produced as an
equilibrium mixture.
NMR (δ, CD2Cl2, 500 MHz, 298 K): 7.42−6.8 (16H, m,
(CH3)2C6H3NC and N-tolyl-ATI arom), 2.45 (3H, s,
(CH3)2C6H3NC), 2.40 (9H, s, (CH3)2C6H3NC and tolyl methyls),
[(N-tolyl-ATI)Pt(CH3)2(CNBut)(SMe2)][OTf] (4a). A Schlenk flask
containing 40 mg (0.070 mmol) of 1a was purged with nitrogen, and
dry CH2Cl2 was syringed into the flask. The solution was cooled to
−78 °C, and 15.8 μL (0.144 mmol, 2 equiv) of MeOTf was syringed in
to synthesize 3 in situ. The reaction mixture was warmed to room
temperature, and the solvent was removed under vacuum. Dry CH2Cl2
was syringed into the flask followed by 11.9 μL (0.105 mmol, 1.5
2.34 (3H, s, S(CH3)2, 3JPt−H = 34 Hz), 2.14 (3H, s, S(CH3)2, 3JPt−H
=
2
37 Hz), 1.31 (3H, s, PtCH3, JPt−H = 63 Hz), 0.61 (3H, s, PtCH3,
2JPt−H = 62 Hz). 13C NMR (δ, CD2Cl2, 125 MHz, 298 K): 165.7−
119.7 ((CH3)2C6H3NC and N-tolyl-ATI arom), 131.7 (br, CN),
25.3 (S(CH3)2), 19.5 (S(CH3)2), 19.0 ((CH3)2C6H3NC)), 8.5
1
1
(PtCH3, JPt−C = 400 Hz), 1.9 (PtCH3, JPt−C = 430 Hz). Anal.
1948
dx.doi.org/10.1021/om400034y | Organometallics 2013, 32, 1938−1950

Organometallics
Article
Calcd for C35H40F3N3O3PtS2: C, 48.49; H, 4.65; N, 4.85. Found: C,
48.47; H, 4.46; N, 4.77.
instead of PMe3, and the reaction mixture was kept at 0 °C at all times.
6c was not isolated, as it begins to form 7a after being synthesized. 1H
NMR (δ, CD2Cl2, 400 MHz, 298 K): 1.98 (3H, d, P(CH3)), 1.91 (3H,
(N-tolyl-ATI)Pt(CH3)2(N3)(SMe2) (5a). A Schlenk flask containing
20 mg (0.035 mmol) of 1a was purged with nitrogen, and dry CH2Cl2
was added to the flask. The solution was cooled to −78 °C, and 7.9 μL
(0.07 mmol, 2 equiv) of MeOTf was syringed in to synthesize 3 in situ.
The flask was warmed to room temperature, and the solvent was
removed under vacuum. A large excess of NaN3 was added to the
Schlenk flask. Dry CH2Cl2 was syringed into the flask and the solution
stirred for 18 h. The solvent was removed under vacuum. The
resulting product was purified via flash column chromatography using
an alumina column with a mobile phase of 100% CH2Cl2 to remove
excess NaN3 and organic byproducts followed by 100% CH3CN. The
CH3CN fraction was collected and reduced to dryness and the residue
triturated with pentanes to yield 12 mg (0.019 mmol, 54%) of pure 5a.
2
3
br s, S(CH3)2), 1.54 (3H, d, Pt(CH3), JPt−H = 61 Hz, JP−H = 8 Hz),
1.23 (3H, br s, S(CH3)2), 0.50 (3H, d, Pt(CH3), 2JPt−H = 62 Hz, 3JP−H
= 8 Hz). 13C NMR (δ, CD2Cl2, 125 MHz, 193 K): 164.7−118.6
(PPh2Me and N-tolyl-ATI arom), 18.8 (S(CH3)2), 16.5 (S(CH3)2),
2
1
13.8 (PtCH3, JP−C = 97 Hz), 7.4 (PPh2(CH3), JP−C = 20 Hz), 4.4
(PtCH3). 31P NMR (δ, CD2Cl2, 162 MHz, 298 K): −23.8 (PPh2Me,
1JPt−P = 877 Hz).
[(N-tolyl-ATI)Pt(CH3)2(P(OMe)3)(SMe2)][OTf] (6d). The same
procedure as for 6a was used to prepare 6d, but P(OMe)3 was used
instead of PMe3; 6d was obtained in 96% yield (29 mg, 0.034 mmol).
1H NMR (δ, CD2Cl2, 400 MHz, 298 K): 3.88 (9H, d, P(OCH3)3,
3
3JP−H = 10 Hz), 2.18 (3H, br s, S(CH3)2, JPt−H = 32 Hz), 1.82 (3H,
IR (CH2Cl2): νN 2038 cm−1. 1H NMR (δ, CD2Cl2, 400 MHz, 298 K):
S(CH3)2, 3JPt−H = 36 Hz), 1.17 (3H, d, PtCH3, 2JPt−H = 57 Hz, 3JP−H
=
3
12 Hz), 0.45 (3H, d, PtCH3, 2JPt−H = 63 Hz, 3JP−H = 9 Hz). 13C NMR
(δ, CD2Cl2, 100 MHz, 298 K): 54.7 (P(OCH32)3, 1JP−C = 12 Hz), 22.5
(S(CH3)2), 18.9 (S(CH3)2), 13.6 (PtCH3, JP−C = 189 Hz), 2.2
1.97 (3H, s, S(CH3)2, 3JPt−H = 31 Hz), 1.88 (3H, s, S(CH3)2, 3JPt−H
=
2
36 Hz), 1.07 (3H, s, PtCH3, JPt−H = 70 Hz), 0.38 (3H, s, PtCH3,
2JPt−H = 62 Hz). 13C NMR (δ, CD2Cl2, 100 MHz, 298 K): 19.8
(S(CH3)2), 18.0 (S(CH3)2), 3.4 (PtCH3), −4.33 (PtCH3). A
satisfactory elemental analysis was not obtained; therefore, the purity
1
(PtCH3, JPt−C = 536 Hz). 31P NMR (δ, CD2Cl2, 162 MHz, 298 K):
1
83.2 (P(OMe)3, JPt−P = 1963 Hz).
1
(N-tolyl-ATI)Pt(CH3)(PPh2Me) (7a). Compound 6c was formed
from 20 mg (0.035 mmol) of 1a by the procedure detailed above and
was stirred at room temperature for 4 days and converted completely
to 7a. The reaction mixture can be heated to increase the rate of
conversion, and 6c will completely convert to 7a in 2 days if heated to
40 °C in CH2Cl2. The resulting product was purified via flash column
chromatography using an alumina column with a mobile phase of
100% CH2Cl2, which was collected, reduced to dryness, and triturated
with pentanes to yield pure 7a as a yellow powder in 88% yield (22
mg, 0.031 mmol). X-ray-quality crystals were formed by slow
evaporation of a solution of 7a in methylene chloride at room
temperature. 1H NMR (δ, CD2Cl2, 500 MHz, 298 K): 7.41−6.13
(23H, PPh2CH3 and N-tolyl-ATI arom), 1.04 (3H, d, PPh2(CH3),
2JP−H = 10 Hz), −0.035 (3H, d, PtCH3, 2JPt−H = 69 Hz, 3JP−H = 5 Hz).
13C NMR (δ, CD2Cl2, 125 MHz, 298 K): 166.8−114.7 (PPh2(CH3)
was determined by H NMR.
(N-tolyl-ATI)Pt(CH3)2(CN)(SMe2) (5b). The same procedure as for
5a was used to prepare 5b, but NaCN was used instead of NaN3 to
give 5.8 mg of the product (0.096 mmol, 27.3%). IR (CH2Cl2): νCN
1
2301 cm−1. H NMR (δ, CD2Cl2, 500 MHz, 298 K): 2.23 (3H, s,
S(CH3)2, 3JPt−H = 35 Hz), 1.97 (3H, s, S(CH3)2, 3JPt−H = 35 Hz), 0.69
2
2
(3H, s, PtCH3, JPt−H = 56 Hz), 0.39 (3H, s, PtCH3, JPt−H = 64 Hz).
13C NMR (δ, CD2Cl2, 125 MHz, 298 K): 24.5 (S(CH3)2), 19.1
(S(CH3)2), 3.3 (PtCH3, JPt−C = 367 Hz), 0.0 (PtCH3, JPt−C = 442
Hz). Anal. Calcd for C26H31N3PtS: C, 50.97; H, 5.10; N, 6.86. Found:
C, 51.19; H, 4.89; N, 6.71.
1
1
[(N-tolyl-ATI)Pt(CH3)2(PMe3)(SMe2)][OTf] (6a). In the glovebox,
in a preweighed vial containing 20 mg (0.035 mmol) of 1a was added
CH2Cl2. MeOTf (4.6 μL, 0.042 mmol, 1.2 equiv) was syringed in to
synthesize 3 in situ. The mixture was allowed to react for 5 min, the
solvent was removed under vacuum, and the residue was triturated
with hexanes and dried to remove any excess MeOTf. The residue was
dissolved in CH2Cl2, and 4.3 μL (0.042 mmol, 1.2 equiv) of PMe3 was
syringed into the vial to form a red solution. The solution was allowed
to react for 5 min, and the solvent and excess PMe3 were removed
under vacuum followed by trituration with hexanes to give 6a in 99%
yield (28 mg, 0.035 mmol). X-ray-quality crystals were formed by
recrystallization from layering hexanes on top of a solution of 6a in
1
and N-tolyl-ATI arom), 12.1 (PPh2(CH3), JP−C = 39 Hz), −10.1
2
(PtCH3, JP−C = 10). 31P NMR (δ, CD2Cl2, 162 MHz, 298 K): 1.6
1
(PPh2(CH3), JPt−P = 3979 Hz).
(N-tolyl-ATI)Pt(CH3)(PPh3) (7b). An NMR tube containing 7.6
mg (0.013 mmol) of 1a was purged with nitrogen, and dry CH2Cl2
was syringed into the NMR tube. The solution was cooled to −78 °C,
and 3 μL (0.026 mmol, 2 equiv) of MeOTf was syringed into the
NMR tube to synthesize 3 in situ. The reaction mixture was warmed to
room temperature, and the solvent was removed under vacuum. A
large excess of PPh3 was added to the NMR tube. Dry CD2Cl2 was
added to form a red solution. The solution was stirred for 2 h. The
resulting product was purified via flash column chromatography using
an alumina column with a mobile phase of 100% CH2Cl2, which was
collected, reduced to dryness, and triturated with pentanes to give pure
1
methylene chloride at −35 °C. H NMR (δ, CD2Cl2, 500 MHz, 298
3
K): 2.23 (3H, br s, S(CH3)2, JPt−H = 35 Hz), 1.58 (9H, d, P(CH3)3,
3H, S(CH3)2), 1.36 (3H, d, PtCH3, 2JPt−H = 57 Hz, 3JP−H = 9 Hz), 0.45
2
3
(3H, d, PtCH3, JPt−H = 62 Hz, JP−H = 8 Hz). 13C NMR (δ, CD2Cl2,
125 MHz, 298 K): 21.6 (S(CH3)2), 18.4 (S(CH3)2), 12.5 (PtCH3,
1JPt−C = 370 Hz, 2JP−C = 103 Hz), 11.2 (P(CH3)3, 1JP−C = 20 Hz), 3.08
1
7b in 95% yield (9.2 mg, 0.033 mmol) as a yellow powder. H NMR
1
(PtCH3, JPt−C = 440 Hz). 31P NMR (δ, CD2Cl2, 162 MHz, 298 K):
(δ, CD2Cl2, 500 MHz, 298 K): 7.49−5.98 (28H, PPh3 and N-tolyl-ATI
−30.0 (PMe3, 1JPt−P = 1101 Hz). Anal. Calcd for C29H40F3N2O3PPtS2:
C, 42.91; H, 4.97; N, 3.45. Found: C, 42.88; H, 4.73; N, 3.42.
[(N-tolyl-ATI)Pt(CH3)2(PPhMe2)(SMe2)][OTf] (6b). The same
procedure as for 6a was used to prepare 6b, but PPhMe2 was used
instead of PMe3; 6b was obtained in 97% yield (30 mg, 0.034 mmol).
1H NMR (δ, CD2Cl2, 500 MHz, 298 K): 7.50−6.04 (18H, Ar, PPhMe2
and N-tolyl-ATI arom), 1.99 (3H, br s, S(CH3)2), 1.90 (3H, d,
2
3
arom), −0.33 (3H, d, Pt(CH3), JPt−H = 69 Hz, JP−H = 5 Hz). 13C
NMR (δ, CD2Cl2, 125 MHz, 298 K): 167.0−117.1 (PPh3 and N-tolyl-
ATI arom), −7.7 (PtCH3, JPt−P = 9 Hz). 31P NMR (δ, CD2Cl2, 162
1
1
MHz, 298 K): 18.8 (PPh3, JPt−P = 4134 Hz).
ASSOCIATED CONTENT
■
2
PtP(CH3)2), 1.77 (3H, d, P(CH3)2), 1.36 (3H, d, PtCH3, JPt−H = 59
S
* Supporting Information
Hz, 3JP−H = 8 Hz), 1.08 (3H, br s, S(CH3)2), 0.46 (3H, d, PtCH3 Eq,
CIF files giving crystallographic data for complexes 1a, 3a, 4a,
6a, and 7a. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
2JPt−H = 62 Hz, JP−H = 8 Hz). 13C NMR (δ, CD2Cl2, 125 MHz, 298
K): 166.3−121.2 (PPhMe2 and N-tolyl-ATI arom), 13.5 (PtCH3, 2JP−C
1
= 100 Hz), 10.4 (S(CH3)2), 10.2 (PPh(CH3)2, JP−C = 4 Hz), 10.1
(S(CH3)2), 3.7 (PtCH3). 31P NMR (δ, CD2Cl2, 162 MHz, 298 K):
1
−24.1 (PPhMe2, JPt−P
= 1004 Hz). Anal. Calcd for
AUTHOR INFORMATION
■
C34H42F3N2O3PPtS2: C, 46.73; H, 4.84; N, 3.21. Found: C, 46.41;
Corresponding Author
H, 4.75; N, 3.10.
*E-mail: joetemp@unc.edu (J.L.T.); n.west@usciences.edu
(N.M.W.).
[(N-tolyl-ATI)Pt(CH3)2(PPh2Me)(SMe2)][OTf] (6c). The same
procedure as for 6a was used to prepare 6c, but PPh2Me was used
1949
dx.doi.org/10.1021/om400034y | Organometallics 2013, 32, 1938−1950

Organometallics
Article
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Acta 2001, 84, 3247.
(36) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L.
Notes
The authors declare no competing financial interest.
Organometallics 2000, 19, 3854.
ACKNOWLEDGMENTS
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Soc. 1999, 121, 252.
■
This work was made possible by funding from the NSF (CHE-
1058675) and by funding from the University of the Sciences in
Philadelphia.
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dx.doi.org/10.1021/om400034y | Organometallics 2013, 32, 1938−1950