Carbon-hydrogen bond cleavage reaction in four-coordinate (2,6-dimethylbenzenethiolato)platinum(II) complexes. dramatic acceleration by thiolato hydrogen acceptor

Article abstract of DOI:10.1021/om200345h

The (2,6-dimethylbenzenethiolato)platinum(II) complexes PtR(SC ₆H₃Me₂-2,6-κ¹S)L₂ (R = Me, L = PMe₃ (1a), PPh₃ (1c), L₂ = dppe (1d), dppp (1e); R = Et, L = PPh₃ (2c); R = CH₂CMe ₃, L = PPh₃ (3c)) and Pt(SC₆H ₃Me₂-2,6-κ¹S)₂L₂ (L = PMe₃ (4a), PEt₃ (4b), PPh₃ (4c), L ₂ = dppe (4d), dppp (4e), dppb (4f)) have been prepared. Heating of these compounds results in an internal sp³ C-H bond cleavage reaction, giving the thiaplatinacycle complexes Pt[SC₆H ₃(CH₂-2)(Me-6)-κ²S,C]L₂ (L = PMe₃ (5a), PEt₃ (5b), PPh₃ (5c), L₂ = dppe (5d), dppp (5e), dppb (5f)) in moderate to quantitative yields. The reactions of 1c and 4c proceed via prior dissociation of PPh₃, and a concerted mechanism is proposed. Of particular interest is the sp³ C-H bond activation step, whose observed rate constant for 4c is no less than 10⁴-fold faster than that for 1c. The arenethiolato group is expected to enhance the C-H bond cleavage step as a hydrogen acceptor.

Full text of DOI:10.1021/om200345h

ARTICLE
pubs.acs.org/Organometallics
CarbonꢀHydrogen Bond Cleavage Reaction in Four-Coordinate
(2,6-Dimethylbenzenethiolato)platinum(II) Complexes. Dramatic
Acceleration by Thiolato Hydrogen Acceptor†
Masafumi Hirano,* Shin-ya Tatesawa, Minoru Yabukami, Yoko Ishihara, Yusuke Hara, Nobuyuki Komine,
and Sanshiro Komiya*
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-26 Nakacho,
Koganei, Tokyo 184-8588, Japan
S Supporting Information
b
ABSTRACT: The (2,6-dimethylbenzenethiolato)platinum(II) complexes PtR(SC6-
H3Me2-2,6-k1S)L2 (R = Me, L = PMe3 (1a), PPh3 (1c), L2 = dppe (1d), dppp (1e);
R = Et, L = PPh3 (2c); R = CH2CMe3, L = PPh3 (3c)) and Pt(SC6H3Me2-2,6-
k1S)2L2 (L = PMe3 (4a), PEt3 (4b), PPh3 (4c), L2 = dppe (4d), dppp (4e), dppb
(4f)) have been prepared. Heating of these compounds results in an internal sp3
CꢀH bond cleavage reaction, giving the thiaplatinacycle complexes Pt[SC6H3(CH2-2)-
(Me-6)-k2S,C]L2 (L = PMe3 (5a), PEt3 (5b), PPh3 (5c), L2 = dppe (5d), dppp
(5e), dppb (5f)) in moderate to quantitative yields. The reactions of 1c and 4c
proceed via prior dissociation of PPh3, and a concerted mechanism is proposed.
Of particular interest is the sp3 CꢀH bond activation step, whose observed rate
constant for 4c is no less than 104-fold faster than that for 1c. The arenethiolato
group is expected to enhance the CꢀH bond cleavage step as a hydrogen acceptor.
’ INTRODUCTION
brought in proximity to the Ru(II) center. Consequently, the
following sp3 CꢀH bond cleavage reactions proceeded easily.
More recently, we have revealed the mechanism for a rapid and
reversible sp3 CꢀH bond cleavage reaction in bis(2,6-dimethyl-
benzenethiolato)ruthenium(II) compounds, where a five-coordi-
nate species isanactive compound for the sp3 CꢀH bondcleavage
reaction.10b
The cleavage of sp3 carbonꢀhydrogen bonds at Pt(II) centers
has attracted continuing interest since the pioneering discoveries
of methane activation by Shilov. For example, Shilov found
catalytic activation of methane by K2PtCl4 (and also K2PtCl6)
to give methanol or chloromethane.1,2 In an improvement on the
Shilov approach, Periana developed a remarkable catalysis for the
formation of methyl sulfate.3 On the basis of the principle of
microscopic reversibility, many PtꢀMe σ-bond cleavage reac-
tions have been studied, since they represent the reverse reac-
tions of the methane activation reaction.4 On the other hand,
Whitesides reported an internal γ-CꢀH bond cleavage reaction
of the alkyl group in Pt(CH2CMe3)2L2, giving platinacyclic
compounds.5 In this pioneering example, the neopentyl group
brings the sp3 CꢀH bond in proximity to the Pt(II) center and it
also acts as a hydrogen acceptor. The neopentyl complex Pt-
(CH2CMe3)2L2 is also reported to show high activity toward the
intermolecular sp3 CꢀH bond activations of toluene6 and
methane,7 giving tolyl- and methylplatinum(II) compounds, re-
spectively. Mechanistic investigations reported for bis(alkyl)
platinum(II)8 and (alkyl)(enolato-η1C)platinum(II) phosphine
complexes reveal a pathway involving initial dissociation of an
ancillary phosphine for β-hydride elimination of the alkyl group.
We have documented systematic internal sp3 CꢀH bond
cleavage reactions of (2,6-dimethylphenoxo)-9 and (2,6-dimethyl-
benzenethiolato)ruthenium(II)10 complexes to give oxa- and
thiaruthenacyclic compounds, where the sp3 CꢀH bond in the
o-methyl groups in the aryloxo and thiolato anchoring ligands are
As an extension of this chemistry, we are interested in the
internal sp3 CꢀH bond cleavage reactions of (2,6-dimethyl-
benzenethiolato)platinum(II) compounds, where the PtꢀS an-
choring bond is expected to bring the o-methyl group to the
square-planar Pt(II) center. Such thiolato-promoted sp3 CꢀH
bond cleavage reaction at Pt(II) is unexplored, and only one
pioneering example has been documented for the sp2 CꢀH bond
cleavage reaction by cis-PtH(triptycylthiolato)(PPh3)2 under
severe conditions (10 h in refluxing toluene).11 We have
conducted a study of the internal sp3 CꢀH bond cleavage
reactions infour-coordinate (alkyl)(2,6-dimethylbenzenethiolato)
platinum(II) and bis(2,6-dimethylbenzenethiolato)platinum(II)
complexes, giving thiaplatinacyclic compounds. In this article we
disclose that both cis-PtMe(SC6H3Me2-2,6-k1S)(PPh3)2 (1c) and
cis-Pt(SC6H3Me2-2,6-k1S)2(PPh3)2 (4c) quantitatively give the
corresponding thiaplatinacycle Pt[SC6H3(CH2-2)(Me-6)-k2S,
C](PPh3)2 (5c) with evolution of methane and 2,6-dimethylben-
zenethiol, respectively. Interestingly, 4c produced 5c much more
Received: April 22, 2011
Published: September 12, 2011
r
2011 American Chemical Society
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Scheme 1
Scheme 2
quickly than 1c and this significant enhancement effect on the sp3
CꢀH bond cleavage reaction was ascribed to the arenethiolato
group as a hydrogen acceptor.
complexes Pt(SC6H3Me2-2,6-k1S)2L2 (L = PMe3 (4a), PEt3 (4b),
PPh3 (4c); L2 = dppe (4d), dppp (4e), dppb (4f)) were prepared
by the conventional metathetical reaction of PtI2L2 with 2 equiv of
KSC6H3Me2-2,6 in THF at room temperature (Scheme 2).16
For example, cis-Pt(SC6H3Me2-2,6-k1S)2(PPh3)2 (4c) was
prepared by the treatment of PtI2(PPh3)2 with KSC6H3Me2-
2,6 (2.5 equiv) in 50% yield. This compound was character-
ized by NMR and elemental analysis. The 31P{1H} NMR
spectrum in CD2Cl2 shows a singlet at δ 18.5 (1JPꢀPt = 3043
Hz), and the 1H NMR indicates a singlet at δ 2.17 (12H) and
multiplets at δ 6.58ꢀ6.65 (6H) with aromatic protons at δ
7.13ꢀ7.53 (30H), assignable to the 2,6-dimethyl groups,
aromatic protons in arenethiolato groups, and PPh3, respec-
tively. Although it is difficult to determine the cis/trans
configuration of 4c by the NMR data alone,17 we believe 4c
has the cis configuration in solution because the X-ray analysis
reveals the cis configuration.
The other analogues 4a,b,dꢀf were also prepared by a
similar protocol and the dppe, dppp, and dppb analogues
4dꢀf were isolated as cis forms, which were also characterized
by spectroscopic methods and X-ray structure analyses. The
PMe3 complex 4a was found to exist in a trans configuration.
The X-ray structure of 4a unambiguously showed the trans
configuration, and the PMe3 resonance was observed as a
virtual triplet in the 1H NMR spectrum in CD2Cl2. The PEt3
complex 4b was also characterized to have a trans configura-
tion by the X-ray analysis.
2. Molecular Structures of (2,6-Dimethylbenzenethiolato)
platinum(II) Compounds. The molecular structures of (2,6-di-
methylbenzenethiolato)(neopentyl)platinum(II) (3c) and bis(2,6-
dimethylbenzenethiolato)platinum(II) (4aꢀf)areshowninFigure1,
and selected metric data for the bis(arenethiolato) complexes 4 are
given in Table 1. These complexes adopt a slightly distorted square-
planar geometry containing 2,6-dimethylbenzenethiolato ligand(s).
These structure determinations confirm the stereochemical conclu-
sions drawn from the NMR spectra.
As expected, the PMe3 complex 4a shows a trans config-
uration in a square-planar geometry. Consistently, the angles
S(1)ꢀPt(1)ꢀS(2) (173.01(5)°) and P(1)ꢀPt(1)ꢀP(2)
(175.53(5)°) are slightly smaller than but close to 180°.
Two thiolato groups are on the same side on the square plane.
’ RESULTS AND DISCUSSION
1. Preparation of (2,6-Dimethylbenzenethiolato)platinum(II)
Compounds. 1.1. Preparation of (Alkyl)(2,6-dimethylbenzene-
thiolato)platinum(II). The series of (methyl)(2,6-dimethylbenze-
nethiolato)platinum(II) compounds PtMe(SC6H3Me2-2,6-k1S)L2
(L = PMe3 (1a), PPh3 (1c), dppe (1d), dppp (1e)) were prepared
by protonolysis of cis-PtMe2L2 with 1 equiv of 2,6-dimethylbenze-
nethiol in 50ꢀ82% yields (Scheme 1).12
1
These compounds were characterized by H and 31P{1H}
NMR and elemental analysis. Compound 1a has a trans config-
uration, but the other compounds 1cꢀe have cis configurations
1
in a square-planar geometry. For example, the H NMR spec-
trum of 1c shows a characteristic resonance at δ ꢀ0.42 (t, 3H)
possessing a Pt satellite (2JHꢀPt = 30 Hz). This signal is therefore
assigned as the PtꢀMe group in 1c. In addition, resonances at δ
2.44 (s, 6H), 6.81 (t, 1H), 6.97 (d, 2H), and 7.1ꢀ7.6 (m, 30H)
are assignable to the SC6H3Me2-2,6, para and meta aromatic
protons in SC6H3Me2-2,6, and PPh3, respectively. The 31P{1H}
NMR spectrum shows two doublets at δ 24.6 (d, 2JPꢀP = 7.3 Hz,
1JPꢀPt = 3310 Hz, 1P) and 29.5 (d, 2JPꢀP = 7.3 Hz, 1JPꢀPt = 1968
Hz, 1P), suggesting the cis configuration. The former and latter
resonances are assigned as the PPh3 ligand trans to the thiolato
1
and methyl groups because of the characteristic JPꢀPt value
based on the trans influence of the arenethiolato ligand being
weaker than that of the methyl group.13 These NMR data are
consistent with cis-1c. The pyridine-promoted cis to trans one-
way transformation is reported for PtCl(SAr)(PR3)2, suggesting
the trans form is more thermodynamically stable.14 PtH(SAr)-
(PPh3)2 is also reported to be a trans complex.15 However,
compound 1c favors the cis configuration probably because of
the steric repulsion between the 2,6-dimethylbenzenethiolato
group and the PPh3 ligand.
Similarly, cis-PtEt(SC6H3Me2-2,6-k1S)(PPh3)2 (2c) and cis-
Pt(CH2CMe3)(SC6H3Me2-2,6-k1S)(PPh3)2 (3c) were also pre-
pared by the metathetical reaction of corresponding (alkyl)
(chlorido)platinum(II) complex with KSC6H3Me2-2,6 in 58%
and 41% yields, respectively.
1.2. Preparation of Bis(2,6-dimethylbenzenethiolato)platinum-
(II). The series of bis(2,6-dimethylbenzenethiolato)platinum(II)
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Figure 1. Continued
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Figure 1. Molecular structures of cis-Pt(CH2CMe3)(SC6H3Me2-2,6-k1S)(PPh3)2 (3c), trans-Pt(SC6H3Me2-k1S)2(PMe3)2 (4a), trans-Pt(SC6H3Me2-
k1S)2(PEt3)2 (4b), cis-Pt(SC6H3Me2-k1S)2(PPh3)2 (4c), cis-Pt(SC6H3Me2-k1S)2(dppe) (4d), cis-Pt(SC6H3Me2-k1S)2(dppp) (4e), and cis-Pt-
(SC6H3Me2-k1S)(dppb) (4f) with selected numbering schemes. All hydrogen atoms are omitted for clarity. Ellipsoids represent 50% probability.
Table 1. Selected Bond Distances (Å) and Angles (deg) for 4aꢀf
4a
4b
4c
4d
4e
4f
Pt(1)ꢀS(1)
Pt(1)ꢀS(2)
Pt(1)ꢀP(1)
Pt(1)ꢀP(2)
S(1)ꢀC(1)
S(2)ꢀC(9)
2.3331(14)
2.3531(13)
2.3171(16)
2.3082(15)
1.770(7)
2.3593(10)
2.3493(9)
2.3347(10)
2.3360(10)
1.764(4)
2.366(2)
2.341(2)
2.319(2)
2.286(2)
1.771(9)
1.751(8)
2.3627(11)
2.3636(9)
2.2493(11)
2.2626(11)
1.762(4)
2.3601(12)
2.3675(10)
2.2772(8)
2.2688(11)
1.773(4)
2.3756(17)
2.3541(16)
2.2884(16)
2.2854(15)
1.777(7)
1.779(5)
1.771(4)
1.768(3)
1.773(4)
1.777(7)
S(1)ꢀPt(1)ꢀS(2)
P(1)ꢀPt(1)ꢀP(2)
Pt(1)ꢀS(1)ꢀC(1)
Pt(1)ꢀS(2)ꢀC(9)
173.01(5)
175.53(5)
115.06(18)
116.78(17)
176.67(4)
178.29(3)
114.66(13)
117.83(13)
98.55(8)
95.16(9)
118.4(3)
116.6(3)
89.98(3)
87.69(3)
94.57(6)
93.42(6)
112.8(2)
113.0(2)
85.64(3)
92.07(3)
110.09(13)
114.09(12)
112.66(14)
113.33(13)
Though the o-methyl groups, C(8) and C(15), seem to
interact with the platinum center at first sight, the two bond
distances Pt(1)ꢀC(8) and Pt(1)ꢀC(15) are actually 3.523(6)
and 3.534(2) Å, respectively, suggesting no strong interaction
among these atoms. Similarly, the PEt3 complex 4b also has
the trans configuration. In contrast to 4a, the two arenethio-
lato fragments in 4b are arranged one above the other with
respect to the square plane. This may be due to the crystal
packing, where the difference in cavities around the Pt(II)
center formed by the alkylphosphines results in a conforma-
tional change for the arenethiolato ligand during formation of
the crystals. The PPh3 complex 4c shows a cis configuration
with a parallel alignment of two 2,6-dimethylbenzenethiolato
groups. Although they are actually not fully overlapping but twisted
with respect to each other in the front and back directions, the
distances between these aromatic rings (C(1)ꢀC(9) = 3.162(13)
Å, C(2)ꢀC(10) = 3.433(15) Å, C(3)ꢀC(12) = 3.441(15) Å,
C(4)ꢀC(13) = 3.457(16) Å, C(5)ꢀC(14) = 3.497(15) Å,
C(6)ꢀC(14) = 3.393(13) Å) suggest partial stacking by the πꢀπ
interaction.18 A similar parallel alignment is observed for the dppb
complex 4f. The bite angles P(1)ꢀPt(1)ꢀP(2) in 4cꢀf taken from
the molecular structure analysis vary from 85.64(3)° (4d, dppe)
to 92.07(3)° (4e, dppp), 93.42(6)° (4f, dppb), and 95.16(9)°
(4c, PPh3),19 and the S(1)ꢀPt(1)ꢀS(2) angles are in the order of
87.69(3)° (4e, dppp), 89.98(3)° (4d, dppe), 94.57(6)° (4f, dppb),
and 98.55(8)° (4c, PPh3).
The structure of (2,6-dimethylbenzenethiolato)(neopentyl)
platinum(II) (3c) is shown to have the cis configuration. The
P(1)ꢀPt(1)ꢀP(2) and S(1)ꢀPt(1)ꢀC(1) angles are 98.63(4)
and 90.29(10)°, and no significant contact around the arenethiolato
and neopentyl groups and Pt are observed (see the Supporting
Information).
3. Internal sp3 CarbonꢀHydrogen Bond Cleavage Reac-
tion in Four-Coordinate Platinum(II) Compounds. 3.1. Inter-
nal sp3 CꢀH Bond Cleavage Reaction from (Alkyl)(2,6-dimethyl-
benzenethiolato)platinum(II) Compounds. The products ob-
tained by heating the (methyl)(2,6-dimethylbenzenethiolato)
platinum(II) compounds are shown in eq 1, and all examples
produce thiaplatinacycles 5 in high yields. For example, heating
of cis-PtMe(SC6H3Me2-2,6-k1S)(PPh3)2 (1c) at 150 °C in
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spectrum is a 2H triplet resonance at δ 2.85 with Pt satellites.
This signal clearly indicates formation of the PtꢀCH2 bond,
whose methylene protons couple to the cis and trans phosphorus
ligands with coincidentally the same coupling constant. These
NMR data unambiguously support the structure of 5c.20
The formation of 5c from 1c evolves methane as a side
product. This is also attractive for the methane activation from
the viewpoint of microscopic reversibility. To determine whether
the evolution of methane is a reversible process, cis-Pt(CD3)-
(SC6H3Me2-2,6-k1S)(PPh3)2 (1c-d3: up to 99 atom % D) has
been prepared. By heating of 1c-d3 at 110 °C in toluene-d8 for
13 h, 5c was formed in 91% yield and neither the methylene nor
the o-methyl groups in 5c contained deuterium atoms at all.
1
Evolution of methane-d3 was observed by H NMR (δ 0.14
(sept. 2JHꢀD = 1.8 Hz)) and GLC.21 This fact suggests irrever-
sible formation of methane under these conditions.
For the thiaplatinacycle 5d having a dppe ligand, the molecular
structure has been revealed by an X-ray structure analysis, and the
ORTEP diagram is depicted in Figure 2.
The bond distance Pt(1)ꢀC(7) in 5d is in the range of 2.119(6)
Å, consistent with a typical PtꢀC σꢀbond. The bond distance
Pt(1)ꢀS(1) (2.2994(16) Å) and the bond angle Pt(1)ꢀS(1)ꢀ
C(1) (98.1(3)°) in 5d are shorter and narrower than those in 4d
(2.3627(11) Å and 110.09(13)°), which would dispel the distortion
in the formation of five-membered thiaplatinacycles.
Figure 2. Molecular structure of Pt[SC6H3(CH2-2)(Me-6)-k2S,C]-
(dppe) (5d) with selected numbering schemes. All hydrogen atoms
and the incorporated toluene molecule are omitted for clarity. Ellipsoids
represent 50% probability.
Similar treatment of the the (ethyl)(2,6-dimethylbenzene-
thiolato)platinum(II) species 2c in anisole at 130 °C for 4 h
produced the thiaplatinacycle 5c in 78% yield, during which time
ethane (43%) and ethylene (45%) were evolved. Heating of the
(2,6-dimethylbenzenethiolato)(neopentyl)platinum(II) complex
3c at 150 °C for 0.2 h quantitatively produced 5c with evolution
of neopentane.
anisole for 1.5 h produced thiaplatinacycle 5c in 98% yield based
on the internal standard by NMR. Qualitative analysis of the gas
phase by GLC indicated the formation of methane.
Thiaplatinacycle 5c was characterized by NMR and elemental
analysis. In the 31P{1H} NMR in CD2Cl2, two doublets are
observed at δ 22.1 (2JPꢀP = 19 Hz, 1JPꢀPt = 1881 Hz) and δ 24.8
(2JPꢀP = 18 Hz, 1JPꢀPt = 3250 Hz). This observation shows that
two phosphorus ligands resonate inequivalently, suggesting a cis
configuration. The small JPꢀPt value for the resonance at δ 22.1
reflects a strong trans influence, suggesting that this phosphorus
3.2. Formation of Dimeric μ-Sulfido Compounds from
(alkyl)(2,6-dimethylbenzenethiolato)platinum(II). During the
course of the reaction of 1c to give 5c, a new dimeric compound
of (methyl)(2,6-dimethylbenzenethiolato)platinum(II) was ob-
served with liberation of PPh3. Upon heating of 1c at 70 °C for
12 h in a nonpolar benzene solvent, anti-6c deposited, which was
recrystallized from cold THF in 72% yield (eq 2).
1
is trans to the carbon atom in the thiaplatinacycle.14 In the H
NMR spectrum, a 3H singlet at δ 2.09, 1H doublets at δ 6.49 and
δ 6.62, and a 1H triplet at δ 6.54 are assignable to the one of the o-
methyl groups, two inequivalent meta aromatic protons, and the
para proton in an aromatic ring adjacent to the thiaplatinacycle,
respectively. The most significant feature in this 1H NMR
anti-6c was characterized by NMR. In the 31P{1H} NMR in
toluene-d8, a singlet was observed at δ 27.8 (1JPꢀPt = 3861 Hz).
1
In H NMR, a 6H doublet was observed at δ 0.13 (3JHꢀP
=
4.5 Hz) with a broad Pt satellite (2JHꢀPt = 76 Hz). This signal
is assignable to the two equivalent PtꢀMe groups. A singlet at
δ 3.13 (s, 12H) and multiplets at δ 6.6ꢀ6.7 (6H) are assigned
as two equivalent thiolato groups. Aromatic protons assign-
able to PPh3 are observed at δ 6.8 (18H) and δ 7.5 (12H).
The most significant feature in this NMR is that all o-methyl
groups are equivalent. According to the molecular sym-
metry deduced from the NMR spectrum, this compound is
consistent with the dimeric species anti-6c having C2h
symmetry.22,23
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Upon heating of anti-6c at 110 °C in toluene, new resonances
assignable to syn-6c were observed by NMR spectroscopy. In the
31P{1H} NMR spectrum in toluene-d8, a singlet peak was
observed at δ 25.3 (1JPꢀPt = 3918 Hz). In the 1H NMR spectrum,
a new 6H doublet at δ 0.16 (3JHꢀP = 4.8 Hz) was observed, which
was assigned to the two magnetically equivalent PtꢀMe
groups.24 On the other hand, two 6H singlets were observed at
δ 2.48 and δ 3.55, assignable to the o-methyl groups in the 2,6-
dimethylbenzenethiolato groups. These spectroscopic features,
two arenethiolato groups being inequivalent while two PtꢀMe
and PPh3 ligands are equivalent, suggest the C2v symmetry that is
consistent with the structure of syn-6c. We therefore assigned this
compound as syn-6c. The final ratio anti-6c/syn-6c was estimated
to be 2/1 under these conditions based on 1H NMR (eq 3).
In toluene-d8 solution, we found that 1c, anti-6c, syn-6c, and PPh3
constituted an equilibrium in the range of 80ꢀ100 °C (eq 4).
Figure 3. Time-course curves of 1c giving 5c at 110 °C in DMF: (])
1c; (O) total amount of syn- and anti-6c based on Pt atom; (b) 5c. Initial
concentration of 1c: 0.011 M.
K1
21c a½anti-6c a syn-6cꢁ þ 2PPh3
ð4Þ
From the van’t Hoff plot based on the variable-temperature
NMR spectra in toluene-d8, thermodynamic parameters between
1c and total amounts of anti- and syn-6c were estimated: K1
(373 K) = 0.542 M, ΔH = 74.0 ( 3.5 kJ molꢀ1, ΔG(298 K) =
15 ( 6 kJ molꢀ1, and ΔS = 197 ( 10 J molꢀ1 Kꢀ1. The positive
ΔG value shows the forward reaction of this equilibrium (K1) to
be slightly endothermic, and the large positive ΔS value is
consistent with the liberation of PPh3. As noted in section 3.3,
a mixture of anti- and syn-6c was observed during the formation
of the thiaplatinacycle 5c from 1c. Moreover, treatment of the
isolated anti-6c with PPh3 at 110 °C in toluene produced the
thiaplatinacycle 5c. These facts support the dimeric compound
6c as being either an intermediate or a resting state in the
formation of 5c.
The (ethyl)(2,6-dimethylbenzenethiolato)platinum(II) com-
plex 2c also gave a 1/4 mixture of anti- and syn-[PtEt(SC6H3Me2-
2,6-μ2S)(PPh3)]2 (7c) in 73% yield by heating of 2c in ben-
zene at 70 °C. Similar treatment of the (2,6-dimethylbenzene-
thiolato)(neopentyl)platinum(II) complex 3c produced a white
precipitate with liberation of 1 equiv of PPh3. Although this
white precipitate was thought to be a similar dimeric compound,
the low solubility of the precipitate toward most of the solvents
prevented a detailed characterization.
Table 2. Effect of Solvent on the Formation Rate Constant of
5c from 1c and 4ca
entry compd
solvent
ε27
temp (°C) 105kobs (sꢀ1
)
1
1c
1c
1c
1c
1c
4c
4c
4c
4c
4c
4c
4c
toluene
2.38
4.33
5.62
110
110
110
110
110
50
2.1 ( 0.2
2
anisole
chlorobenzene
DMF
2.81 ( 0.22
3.47 ( 0.53
7.4 ( 0.1
9.4 ( 0.4
16 ( 1
3
4
5b
36.7
36.7
2.28
DMF
6
benzene
toluene
chloroform
THF
7
2.38
4.70
7.32
50
15 ( 1
8
50
24 ( 1
9
50
36 ( 2
10
11
12c
acetone
DMF
20.7
50
13 ( 1
36.7
36.7
50
17 ( 1
DMF
50
17 ( 1
a Initial concentration of 1c or 4c: 0.0080ꢀ0.010 M. b Galvinoxyl
(0.3 mM) added. c Galvinoxyl (0.08 M) added.
In this reaction, 2,6-dimethylbenzenethiol and the corre-
sponding disulfide were observed as side products. The disulfide
was confirmed by comparison with an authentic sample, and we
believe the disulfide to be formed by spontaneous oxidation of
2,6-dimethylbenzenethiol by DMSO used as the solvent, because
sulfoxide is reported to oxidize arenethiols to the corresponding
disulfide.25 In this reaction the starting compound 4c was comple-
tely consumed and the product 5c was quantitatively yielded. In the
meantime, no intermediate or resting state species was observed by
NMR spectroscopy. The straightforward formation of 5c from 4c
shows a sharp contrast to the system starting from 1c, where 6c is
observed during the course of the reaction.
3.3. Bis(2,6-dimethylbenzenethiolato)platinum(II) Com-
pounds. The cis-bis(2,6-dimethylbenzenethiolato)platinum(II)
compounds 4aꢀf also produced thiaplatinacyclic complexes
5aꢀf by an sp3 CꢀH bond cleavage reaction. As a typical
example, heating of a DMSO solution of 4c at 130 °C yielded
the thiaplatinacycle Pt[SC6H3(CH2-2)(Me-6)-k2S,C](PPh3)2
(5c) in 76% yield in 1 min (eq 5).
In order to confirm the reversibility for the formation of the
thiaplatinacycle from the bis(arenethiolato) complex, the thia-
platinacycle 5c was treated with 11 equiv of 2,6-dimethylbenze-
nethiol in DMF at 50 °C. This treatment gave a complex mixture
but the bis(arenethiolato) compound 4c was undetected.26
Thus, compound 5c must be produced from 4c by an irreversible
CꢀH bond cleavage process.
It is worth noting that while the (methyl)(thiolato)-
platinum(II) complex 1c does not yield 5c at 50 °C in DMF
for 5 h, the bis(thiolato)platinum(II) complex 4c quantitatively
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Figure 4. Effect of added PPh3 on the observed rate constant kobs for 1c
and 4c: (b) 1c; (O) 4c. Conditions: solvent toluene-d8 for 1c and DMF
for 4c, temperature 110 °C for 1c and 50 °C for 4c, initial [1c] =
0.013ꢀ0.0170 M, [4c] = 0.00846ꢀ0.00953 M, [PPh3] = 0.00ꢀ0.416 M.
Figure 5. Time-yield curves of 4c, giving 5c at 50 °C in DMF: (0) 4c;
(b) 5c. Initial concentration of 4c: 0.011 M.
As shown in Table 2, the formation rate constant of 5c does
not show significant dependence on the dielectric constants of
the solvents, excluding a polarized transition state in the rate-
determining step (entries 1ꢀ4). Some alkylplatinum(II) com-
plexes are reported to involve a radical process in CꢀH6,7 and
CꢀX28 bond cleavage reactions. In the present case, the rate
constant is not affected significantly by the addition of galvinoxyl
(entry 5). Although the slight increase of the observed rate
constant by the addition of galvinoxyl is not clear so far, this result
excludes a free radical chain process. Although it is difficult to
completely exclude any radical processes from these experi-
ments, we believe a radical process to be less probable.
The transformation of (methyl)(2,6-dimethylbenzene-
thiolato)platinum(II) complexes with a bidentate ligand to the
thiaplatinacycle 5 proceeded much more slowly and required
high temperature. At 170 °C in DMSO, the dppp complex 1e
produced the thiaruthenacycle 5e in 43% yield after 1.8 h and in
83% yield after 8 h. Under the same conditions, the depe complex
1d produced 5d in 10% yield after 4.5 h and 98% yield after 65 h.
Among (methyl)(2,6-dimethylbenzenethiolato)platinum(II) com-
plexes 1, the relative formation rate was estimated to be in the order
1c (PPh3) > 1e (dppp) > 1d (dppe). Thus, the formation rate
seems to reflect the order of bite angle of these tertiary phosphines.
Such relations between the reactivities of the complexes and the bite
angles of the phosphines employed have been widely studied. For
example, bidentate ligands with wide bite angles are known to
accelerate the reductive elimination from the square-planar
compounds29 on the basis of the ThorpeꢀIngold effect.30 On the
other hand, wide bite angles are also reported to induce flexibility
and facile half-dissociation of the ligand.31 In fact, the reaction of the
dppp complex 1e to give 5e was retarded by the addition of dppp
ligand. For example, after 1.8 h at 170 °C, the yields of 5e were as
follows: 43% (0 equiv of dppp), 11% (0.1 equiv of dppp), and 0%
(3 equiv of dppp). Thus, the facile half-dissociation property of the
phosphorus ligand probably accelerates the reaction.
gives 5c under the same conditions. This sharp contrast in
reactivity shows the high activity of the thiolato group toward
the sp3 CꢀH bond cleavage reaction.
4. Kinetic Studies for the Formation of Thiaplatina-
cycles. 4.1. (Methyl)(2,6-dimethylbenzenethiolato)platinum(II)
Complex 1. The isolated (methyl)(2,6-dimethylbenzenethiolato)
platinum(II) compound 1c was heated at 110 °C in DMF, and
the reaction profile was followed by 31P{1H} NMR spectro-
scopy. The time-course curves are shown in Figure 3. Complex
1c immediately decreased with increase of a mixture of syn- and
anti-6c, which finally was converted into the thiaplatinacycle 5c
quantitatively (Figure 3).
The starting compound 1c and syn- and anti-6c decreased with
time at 110 °C in DMF, and the reaction was first-order in the
concentration of the sum total of [1c] and 2[6c]. The observed
rate constant for the total consumption of 1c and 6c was
estimated as (7.4 ( 0.3) ꢂ 10ꢀ5 sꢀ1 in DMF at 110 °C, which
is identical with the formation rate constant of thiaplatinacycle 5c
((7.4 ( 0.1) ꢂ 10ꢀ5 sꢀ1) (Table 2, entry 4). This is consistent
with our assumption where 1c rapidly constitutes rapid pre-
equilibrium between 1c and 6c by releasing a PPh3 ligand under
the conditions from which thiaplatinacycle 5c is slowly produced.
When this reaction was performed at 70 °C in DMF, the
thiaplatinacycle 5c was not formed at all, and the reaction system
reached an equilibrium between 1c (50%) and 6c (50%/Pt) in
5.5 h. Thus, the following sp3 CꢀH bond cleavage process giving
5c must be the rate-determining step.
The formation of thiaplatinacycle 5c from 1c was significantly
ꢀ1
retarded by the addition of PPh3. The dependence of kobs
(the reciprocal observed formation rate constant of 5c) on the
concentration of added PPh3 is shown in Figure 4. These data
indicate that the reaction is inverse first order in phosphine
concentration. This order in added PPh3 ligand demonstrates
that reversible dissociation of PPh3 occurs before the rate-
determining step.
4.2. Bis(2,6-dimethylbenzenethiolato)platinum(II) Complex.
Bis(2,6-dimethylbenzenethiolato)platinum(II) complex 4 also
produced thiaplatinacycle 5, and notably, this reaction proceeded
under conditions much milder than those starting from 1. For
example, the reaction of 4c to give 5c proceeded in DMF even at
50 °C. In contrast to the case for 1c, only 4c and 5c are the
observed platinum species during the course of the reaction
(Figure 5), and the reaction was first order in the concentration
of 4c.
On the basis of these kinetic data, the experimental rate
equation can be expressed as shown in eq 6
d½Ptꢁ
dt
½Ptꢁ
ꢀ
¼ kobs½Ptꢁ ¼
ð6Þ
a½PPh3ꢁ þ b
where [Pt] = [1c] + 2[6c], a = (32 ( 1) ꢂ 104 s Mꢀ1, and
b = (5.5 ( 0.2) ꢂ 103 s at 110 °C.
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The observed rate constant kobs for the consumption of 4c at
Scheme 3
50 °C was estimated as (1.8 ( 0.1) ꢂ 10ꢀ4
s
ꢀ1, which is
comparable to the formation rate constant of 5c ((1.7 ( 0.1) ꢂ
10ꢀ4 sꢀ1) (Table 2, entry 11). This reaction was not retarded by
the addition of a radical scavenger (Table 2, entry 12).
The formation of 5c from 4c is also retarded significantly by
the addition of PPh3. In the presence of an excess amount of
PPh3, the reaction obeyed first-order kinetics in the concentra-
tion of 4c and the reciprocal observed rate constant was propor-
tional to the concentration of added PPh3 with an intercept,
suggesting prior reversible dissociation of PPh3 in the formation
of 5c (Figure 4). According to these kinetic experiments, the
experimental rate for the conversion of 4c into 5c is expressed as
shown in eq 7.
d½4cꢁ
dt
½4cꢁ
ꢀ
¼ kobs½4cꢁ ¼
ð7Þ
c½PPh3ꢁ þ d
where c = (23 ( 1) ꢂ 104 s Mꢀ1 and d = (6.7 ( 0.9) ꢂ 10ꢀ1 s at
50 °C.
The time-course curves for the other bis(2,6-dimethylben-
zenethiolato)platinum(II) complexes 4a,b,dꢀf showed complex
reaction profiles. Heating of the PMe3 complex 4a at 110 °C in
DMF also produced the thiaplatinacycle 5a, but the time-course
curves monitored by NMR showed an induction period of 1.5 h.
Compound 4a finally produced 5a in 39% yield for 30 h.
Meantime, the starting compound 4a also produced an unknown
product, which may be assigned to the cis analogue of 4a, and the
total conversion of 4a was estimated to be 66%. Further heating
of this system at 110 °C for an additional 22 h did not change the
composition. Similar treatment of the PEt3 complex 4b at 110 °C
in DMF also showed an induction period of 20 min, and 4b
finally produced the thiaplatinacycle 5b in 73% yield after 20 h
with 97% conversion of 4b. The time-yield curves for the dppe
complex 5d and the dppp complex 5e starting from 4d and 4e
showed sigmoid curves at 110 °C in DMF, and their final yields
were 73% (260 h) and 90% (14 h), respectively. In contrast to
these dithiolato complexes, the time-yield curve of the dppb
complex 4f to give 5f at 110 °C in DMF showed an almost linear
decrease of 4f with increase of 5f, and the reaction was complete
within 3 h to give a quantitative amount of 5f. Because of the
complex nature of these reaction profiles, we abandoned detailed
kinetic analyses for them.
5. Possible Mechanism for the Formation of Thiaplatina-
cycle. 5.1. Formation Pathway of Thiaplatinacycle from (methyl)
(2,6-dimethylbenzenethiolato)platinum(II) 1c. For the (methyl)
(2,6-dimethylbenzenethiolato)platinum(II) complex 1c, the pre-
sent thermodynamic and kinetic studies described in section 4.1
are consistent with the pathway shown in Scheme 3. This process
can be accounted for by the prerequisite rapid equilibrium among
1c and a mixture of syn- and anti-6c. Although the dimer 6c is
produced by either an associative (through A) or dissociative
(through B) pathway, the associative pathway can be ruled out
because the formation rate of 6c is first order in the concentration
of 1c. In this reaction the methyl group may induce facile
liberation of the PPh3 ligand because of the great trans effect.32
At relatively low temperature (80ꢀ100 °C) in toluene, a
closed equilibrium system between 1c and 6c was constituted, as
described in section 3.2. In this equilibrium the 14-electron
species B must be involved, from which the CꢀH bond cleavage
reaction occurs to give 5c as the rate-determining step. Thus, the
equilibrium constant K1 (K1 = [6c]/([1c]2[PPh3]2)) can be
divided into the two equilibria K2 (K2 = [B][PPh3]/[1c]) and K3
(K3 = [6c]/[B]2). The total concentrations of the monopho-
sphine reactants [PtP1] can be expressed as shown in eq 8.
K2½1cꢁ
½PtP1ꢁ ¼
ð8Þ
½PPh3ꢁ
where [PtP1] = [B] + 2[6c].
By assuming an equilibrium between B and 6c much faster
than the following CꢀH bond activation step k4 and instant
formation of 5c from C, the formation rate of 5c can be defined as
proportional to [PtP1] regardless of the equilibrium constant K3
(eq 9).
d½5cꢁ
¼ k4½PtP1ꢁ
ð9Þ
dt
On the other hand, the total concentration of the reactive Pt
species is expressed as [Pt] ([Pt] = [1c] + [PtP1]). By transfor-
mation of eqs 8 and 9, the rate for the formation of 5c can be
expressed by the term [Pt], as shown in eq 10.
d½Ptꢁ
dt
d½5cꢁ
½Ptꢁ
ꢀ
¼
¼
ð10Þ
ðk4K2Þꢀ1½PPh3ꢁ þ k4
ꢀ1
dt
where [Pt] = [1c] + [PtP1].
Equation 10 is consistent with the present experimental rate
equation (eq 6) because the concentration of [B] is very small.
The rate constant for the sp3 CꢀH bond cleavage reaction k4 is
estimated to be (1.8 (0.1) ꢂ 10ꢀ4 sꢀ1 and the equilibrium constant
K2 to be (1.7 ( 0.2) ꢂ 10ꢀ2 M at 110 °C in toluene for 1c.
In the reaction of the (ethyl)(2,6-dimethylbenzenethiolato)
platinum(II) complex 2c to give the thiaplatinacycle 5c,
we observed evolution of ethane and ethylene (section 3.1).
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Scheme 4
Chart 1
Since the present experiments obeyed first-order kinetics even in the
presence of 0.225 M of PPh3, the k6/(kꢀ5[PPh3]) value was
estimated to be around 10ꢀ5 under these conditions. This is
inconsistent with the large k6/(kꢀ5[PPh3]) assumption. Thus, we
believe the sp3 CꢀH bond cleavage reaction is the rate-determining
step. With agreement, the rate equation is given by eq 12, and K5
((2.9 ( 0.5) ꢂ 10ꢀ6 M) and k6 (1.5 ( 0.2 sꢀ1) are estimated from
the experimental data at 50 °C. Despite the the fact that the kinetic
experiments of 4c were measured under conditions (at 50 °C)
much milder than those for 1c (at 110 °C), the estimated rate for the
sp3 CꢀH bond activation of 4c (k6) was no less than 104-fold faster
than the corresponding rate for 1c (k4). The equilibrium concerning
phosphine dissociation (K5) ismuchsmallerthanK2 ((1.7(0.2) ꢂ
10ꢀ2 M at 110 °C). This is probably because the thiolato ligand has
a much weaker trans effect than the methyl group.34 In addition to
this fact, formation of the dimeric species 6 would stabilize the
monophosphine spices. However, no dimeric intermediate was
observed in the case of 4c, probably due to steric repulsion.
5.3. Mechanistic Insights for the sp3 CꢀH Bond Cleavage
Reaction from 1c and 4c. In the present article, we have
employed the methyl and arenethiolato groups as hydrogen
acceptors in the CꢀH bond cleavage reaction of the o-methyl
group. Of particular interest is the great acceleration of the CꢀH
bond cleavage step by the arenethiolato acceptor. Although the
large difference in the reaction rates makes direct comparison
between these species difficult, the arenethiolato acceptor in-
duces a great leap forward effect (more than 104-fold) on the rate
of the sp3 CꢀH bond activation step. Such a dramatic change
might arise from the mechanistic difference in transition states. In
both cases, the experimental results support sp3 CꢀH bond
activation from the three-coordinate species by a concerted
mechanism.
Since facile β-hydride elimination was reported from the three-
coordinate species, the CꢀH bond cleavage reaction in the o-
methyl groups would compete with β-hydride elimination of the
ethyl group. Thus, the formation of ethylene would support prior
dissociation of PPh3 for the CꢀH bond cleavage reaction.33
5.2. Formation Pathway of Thiaplatinacycle from Bis(2,6-
dimethylbenzenethiolato)platinum(II) 4c. Although no obser-
vable intermediate (or the resting state) has been detected during
the course of the reaction, the mechanistic features for 4c are
basically similar to those for 1c: first-order kinetics in the
concentration of 4c, reciprocal first-order kinetics in the con-
centration of PPh3, no significant solvent effect on the rate
constant, and no retardation by the addition of a radical
scavenger. The present results also support the prior dissociation
of PPh3 for the formation of thiaplatinacycle 5c, and the possible
pathway is depicted in Scheme 4.
In this mechanism, we can assume that the equilibrium K5 lies
far to the 4c side. The sp3 CꢀH bond cleavage reaction in D
occurs to give E, from which 5c is eventually produced by quick
displacement of the arenethiol ligand by PPh3. The rate-
determining step is either the dissociation of PPh3 from 4c to
give D (k5) or the sp3 CꢀH bond cleavage reaction from D to E
(k6). In the case of phosphine dissociation as the rate-determining
step, we can apply a steady-state approximation to the concentra-
tion of D, and the rate equation is derived as shown in eq 11.
One of the possible transition states for 1c concerning release
of methane is the four-center mechanism (TS1 in Chart 1).
Although the successive oxidative addition/reductive elimination
sequence cannot be ruled out, this may be a higher energy
process because a five-coordinate Pt(IV) intermediate is in-
volved. Therefore, we believe TS1 is the most probable transition
state for the present CꢀH bond activation process.
d½4cꢁ
dt
d½5cꢁ
dt
½4cꢁ
ꢀ
¼
¼
ð11Þ
ꢀ1
ꢀ1
ðk5k6=k
Þ ½PPh3ꢁ þ k5
ꢀ5
For the arenethiolato complex 4c, the arenethiol is considered
to remain coordinated after the CꢀH bond cleavage step
(intermediate E in Scheme 3), as shown for the five-coordinate
bis(2,6-dimethylbenzenethiolato)ruthenium(II) compound.10b
Thus, the transition state for the sp3 CꢀH bond cleavage
reaction is most consistent with TS2, as depicted in Chart 1.
Although further investigations are required, TS2 may show an
electrophilic substitution mechanism35,36 because a hydrogen
atom in the o-methyl group finally becomes a proton in the
arenethiolato moiety. Therefore, we believe that a lone pair at the
sulfur atom plays a key role in the significant acceleration of the
sp3 CꢀH bond activation process.
Alternatively, eq 12 would be derived if we assume the CꢀH
bond activation process to be the rate-determining step.
d½Ptꢁ
dt
d½5cꢁ
dt
½Ptꢁ
ꢀ
¼
¼
ð12Þ
ðk6K5Þꢀ1½PPh3ꢁ þ k6
ꢀ1
where [Pt] = [4c] + [D].
If we apply an assumption for the rate-determining step to be
the phosphine dissociation (k5), the intermediate D must
immediately convert into 5c, and k6 would be greater than
k
ꢀ5[PPh3]. However, in this assumption (eq 11), the experimental
result showed a very modest k6/kꢀ5 value: (2.9 ( 0.5) ꢂ 10ꢀ6 M.
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’ EXPERIMENTAL SECTION
δ ꢀ0.42 (t, 3JHꢀP = 6.0 Hz, 2JHꢀPt = 60 Hz, 3H, PtMe), 2.2ꢀ2.5 (m,
3
4H, PC2H4P), 2.36 (s, 6H, SC6H3Me2), 6.75 (t, JHꢀH = 7.2 Hz, 1H,
3
General Procedure. All procedures described in this paper were
carried out under a nitrogen or argon atmosphere by use of Schlenk and
vacuum line techniques. Benzene, hexane, toluene, and Et2O were dried
over dry calcium chloride and were distilled over sodium wire under
nitrogen using benzophenone ketyl as an indicator. THF was distilled
over sodium wire under nitrogen in the presence of benzophenone.
Acetone and dichloromethane were dried over Drierite and distilled
under nitrogen. DMF was dried over molecular sieves 4A and then was
distilled under reduced pressure. 2,6-Dimethylbenzenethiol was pur-
chased from Aldrich and was stored and used under a nitrogen atmo-
sphere. PMe3 and PEt3 were prepared by the reaction of P(OPh)3 with
the corresponding Grignard reagent and were stored under a N2
atmosphere.37 Other tertiary phosphines were purchased from com-
mercial suppliers. The potassium salt of 2,6-dimethylbenzenethiol was
prepared by the treatment of 2,6-dimethylbenzenethiol with KOH in
methanol. The diiodoplatinum(II) complexes PtI2L2 were prepared by
the treatment of PtI2(η4-1,5-COD)38 with the corresponding tertiary
phosphine ligands. PtMe2L2 complexes were prepared by the reaction of
PtMe2(η4-1,5-COD) with the corresponding phosphine ligands.
1H and 31P{1H} NMR spectra were measured on a JEOL LA300 or a
JEOL ECX400P spectrometer. The IR spectra were measured on a
JASCO FT/IR410 or FT/IR4100 spectrometer. Elemental analyses
were performed on a Perkin-Elmer 2400 series II CHN analyzer.
Compounds without elemental analysis were characterized by spectro-
scopic methods. For thermodynamic and kinetic analyses, reliability
intervals indicate 95% probability.
SC6H3Me2), 6.94 (d, JHꢀH = 7.2 Hz, 2H, SC6H3Me2), 7.4ꢀ7.7 (m,
16H, PPh2), 7.8ꢀ8.1 (m, 4H, PPh2). 31P{1H} NMR (122 MHz, DMSO-
d6, room temperature): δ 45.0 (s, 1JPꢀPt = 1813 Hz, 1P, PPh2 trans to C),
1
46.0 (d, JPꢀPt = 3157 Hz, 1P, PPh2 trans to S). Anal. Calcd for
C35H36P2PtS: C, 56.37; H, 4.87. Found: C, 55.66; H, 4.82.
cis-PtMe(SC6H3Me2-2,6-k1S)(dppp) (1e). Colorless crystals,
80% yield. 1H NMR (300 MHz, DMSO-d6, room temperature): δ ꢀ0.69
(t, 3JHꢀP = 6.3 Hz, 2JHꢀPt = 61 Hz, 3H, PtMe), 1.5ꢀ1.9 (m, 2H, PCH2-
CH2CH2P), 2.27 (s, 6H, SC6H3Me2), 2.6ꢀ2.7 (m, 4H, PCH2CH2CH2P),
6.70 (d, 3JHꢀH = 6.9 Hz, 2H, SC6H3Me2), 6.87 (t, 3JHꢀH = 6.9 Hz, 1H,
SC6H3Me2), 7.3ꢀ7.6 (m, 16H, PPh2), 7.7ꢀ8.9 (m, 4H, PPh2). 31P{1H}
NMR (122 MHz, DMSO-d6, room temperature): δ 5.23 (d, 2JPꢀP = 26 Hz,
1JPꢀPt = 1813 Hz, 1P, PPh2 trans to C), 46.0 (d, 2JPꢀP =26Hz,1JPꢀPt = 3157
Hz, 1P, PPh2 trans to S). Anal. Calcd for C36H38P2PtS: C, 56.91; H, 5.04.
Found: C, 57.25; H, 5.88.
cis-PtEt(SC6H3Me2-2,6-k1S)(PPh3)2 (2c). Pale yellow prisms,
58% yield. 1H NMR (400 MHz, CD2Cl2, room temperature): δ
0.24ꢀ0.41 (m, 3H, CH2CH3), 0.43ꢀ0.66 (m, 2H, CH2CH3), 2.52 (s,
3
6H, SC6H3Me2), 6.84 (t, JHꢀH = 7.3 Hz, 1H SC6H3Me2), 6.96 (d,
3JHꢀH = 7.3 Hz, 2H, SC6H3Me2), 709ꢀ7.60 (m, 30H, PPh3). 31P{1H}
2
NMR (162 MHz, CD2Cl2, room temperature): δ 26.87 (d, JPꢀP
=
14 Hz, 1JPꢀPt = 3568 Hz, 1P, PPh3 trans to Et), 27.95 (d, 2JHꢀH = 14 Hz,
1JPꢀPt = 1645 Hz, 1P, PPh3 trans to S). Anal. Calcd for C46H44P2PtS
3
0.5CD2Cl2: C, 57.39; H, 4.74. Found: C, 57.09; H, 4.66.
cis-Pt(CH2CMe3)(SC6H3Me2-2,6-k1S)(PPh3)2 (3c). Pale yellow
prisms, 41% yield. 1H NMR (400 MHz, CD2Cl2, room temperature): δ
0.57 (s, 9H, CH2CMe3), 0.98 (dd, 3JHꢀP = 9.3, 5.3 Hz, 2JHꢀPt = 71 Hz,
2H, CH2CMe3), 2.54 (s, 6H, SC6H3Me2), 6.77 (t, 3JHꢀH = 7.6 Hz, 1H,
SC6H3Me2), 6.90 (d, 3JHꢀH = 7.6 Hz, 2H, SC6H3Me2), 7.10ꢀ7.75 (m,
30H, PPh3). 31P{1H} NMR (162 MHz, CD2Cl2, room temperature): δ
20.61 (d, 2JPꢀP = 16.3 Hz, 1JPꢀPt = 1368 Hz, 1P, PPh3 trans to S), 23.74
(d, 2JPꢀP = 16.3 Hz, 1JPꢀPt = 3706 Hz, 1P, trans to C). Anal. Calcd for
trans-PtMe(SC6H3Me2-2,6-k1S)(PMe3)2 (1a). To a suspension
of PtMe2(PMe3)2 (0.320 g, 0.850 mmol) in benzene (15 mL) was added
2,6-dimethylbenzenethiol (124 μL, 0.935 mmol) by a hypodermic
syringe. After the mixture was stirred for 34 h at room temperature, all
volatile material was removed under reduced pressure. The resulting
pale yellow solid was recrystallized from cold dichloromethane/hexane
at ꢀ30 °C to give pale yellow microcrystals of 1a in 77% yield (0.330 mg,
0.661 mmol). 1H NMR (300 MHz, C6D6, room temperature): δ 0.52
C49H50P2PtS 0.7(toluene): C, 65.93; H, 5.63. Found: C, 64.68; H, 5.69.
3
trans-Pt(SC6H3Me2-2,6-k1S)2(PMe3)2 (4a). Method A. To a
mixture of PtI2(PMe3)2 (0.2161 g, 0.3995 mmol) and potassium 2,6-
dimethylbenzenethiolate (0.1796 g, 1.019 mmol) was added THF
(8 mL). The resulting suspension was stirred for 2 days at room
temperature. After the reaction, all volatile material was removed under
reduced pressure to give a yellow solid, which was extracted with
benzene. The extract was evaporated, and the resulting yellow solid
was recrystallized from cold dichloromethane/hexane at ꢀ30 °C to give
(t, 3JHꢀP = 7.2 Hz, 2JHꢀPt = 29 Hz, 3H, PtMe), 1.03 (vt, 2JHꢀP = 4JHꢀP
=
3.0 Hz, 18H, PMe3), 3.01 (s, 6H, SC6H3Me2), 6.94 (t, 3JHꢀH = 7.8 Hz,
3
1H, SC6H3Me2), 7.13 (d, JHꢀH = 7.8 Hz, 2H, SC6H3Me2). 31P{1H}
NMR (122 MHz, C6D6, room temperature): δ ꢀ16.7 (s, 1JPꢀPt = 2779
Hz). Anal. Calcd for C15H30P2PtS: C, 36.07; H, 6.05. Found: C, 36.17;
H, 6.47.
The following (methyl)(2,6-dimethylbenzenethiolato)platinum(II)
compounds were prepared by a similar method.
1
cis-PtMe(SC6H3Me2-2,6-k1S)(PPh3)2 (1c). Greenish yellow
crystals, 52% yield. 1H NMR (300 MHz, CD2Cl2, room temperature): δ
yellow prisms of 4a in 54% yield (0.1348 g, 0.2400 mmol). H NMR
(300 MHz, CD2Cl2, room temperature): δ 1.24 (vt, 2JHꢀP = 4JHꢀP = 3.6
Hz, 3JHꢀPt = 24.9 Hz, 18H, PMe3), 2.64 (s, 12H, SC6H3Me2), 6.82 (t,
3
2
ꢀ0.42 (t, JHꢀP = 6.3 Hz, JHꢀPt = 30 Hz, 3H, PtMe), 2.44 (s, 6H,
3
3JHꢀH = 7.5 Hz, 2H, SC6H3Me2), 6.95 (d, JHꢀH = 7.2 Hz, 4H,
SC6H3Me2), 6.81 (t, 3JHꢀH = 7.2 Hz, 1H, SC6H3Me2), 6.97 (d, 3JHꢀH
=
SC6H3Me2). 31P{1H} NMR (122 MHz, CD2Cl2, room temperature):
7.2 Hz, SC6H3Me2), 7.1ꢀ7.6 (m, 30H, PPh3). 31P{1H} NMR (122
1
MHz, CD2Cl2, room temperature): δ 24.6 (d, 2JPꢀP = 7.3 Hz, 1JPꢀPt
=
δ ꢀ18.21 (s, JPꢀPt = 2622 Hz). Anal. Calcd. for C22H36P2PtS2: C,
3310 Hz, 1P, PPh3 trans to S), 29.5 (d, 2JPꢀP = 7.3 Hz, 1JPꢀPt = 1968 Hz,
1P, PPh3 trans to C). Anal. Calcd for C45H42P2PtS: C, 61.99; H, 4.86.
Found: C, 61.62; H, 4.87.
42.50; H, 5.84. Found: C, 42.58; H, 5.91.
Method B. Treatment of PtMe2(PMe3)2 (0.397 g, 0.105 mmol) with
2,6-dimethylbenzenethiol (343 μL, 2.58 mmol) at room temperature for
2 days followed by removal of all volatile material produced a yellow
solid. Recrystallization from cold dichloromethane/hexane at ꢀ30 °C
gave yellow prisms of 1a in 79% yield (0.514 g, 0.827 mmol). Anal. Calcd
for C22H36P2PtS2: C, 42.50; H, 5.84. Found: C, 42.63; H, 5.72.
The following bis(2,6-dimethylbenzenethiolato)platinum(II) com-
pounds were prepared by a similar method.
cis-Pt(CD3)(SC6H3Me2-2,6-k1S)(PPh3)2 (1c-d3). CD3Li (0.59 M)
was prepared by the reaction of lithium (246 mg, 35.6 mmol) with CD3I
(975 μL, 15.3 mmol) in Et2O at room temperature for 2 h. 1c-d3 was
prepared by the reaction of Pt(CD3)2(PPh3)2 (385 mg, 0.509 mmol),
which was derived from PtI2(1,5-COD) with CD3Li followed by the
addition of PPh3 with 2,6-dimethylbenzenethiol (74 μL, 0.56 mmol) in
benzene at room temperature for 1 day in 42% yield (186 mg, 0.213 mmol).
No incorporation of H in the CD3 group in 1c-d3 was observed during the
course of the reaction.
trans-Pt(SC6H3Me2-2,6-k1S)2(PEt3)2 (4b). Pale yellow needles,
56% yield. 1H NMR (300 MHz, C6D6, room temperature): δ 0.80 (dt,
3JHꢀH = 7.7 Hz, 3JHꢀP = 15.4 Hz, 18H, PCH2Me), 1.6ꢀ1.8 (m, 12H,
PCH2Me), 2.67 (s, 12H, SC6H3Me2), 6.9ꢀ7.2 (m, 6H, SC6H3Me2). 31P{1H}
NMR (122 MHz, C6D6, room temperature): δ 6.83 (s, 1JPꢀPt = 2809 Hz).
cis-PtMe(SC6H3Me2-2,6-k1S)(dppe) (1d). Colorless crystals,
50% yield. 1H NMR (300 MHz, DMSO-d6, room temperature):
5119
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Organometallics
ARTICLE
Anal. Calcd for C28H48P2PtS2: C, 47.65; H, 6.85. Found: C, 48.53;
H, 6.84.
(2-CH2)(6-Me)), 6.58 (d, 3JHꢀP = 3.6 Hz, 1H, SC6H3(2-CH2)(6-Me)),
7.2ꢀ7.4 (m, 30H, PPh3). 31P{1H} NMR (122 MHz, DMSO-d6, room
2
1
cis-Pt(SC6H3Me2-2,6-k1S)2(PPh3)2 (4c). Light orange prisms,
temperature): δ 22.2 (d, JPꢀP = 19 Hz, JPꢀPt = 1893 Hz, 1P, PMe3
trans to C), 24.7 (d, 2JPꢀP = 19 Hz, 1JPꢀPt = 3234 Hz, 1P, PMe2 trans to S).
Anal. Calcd for C45H40P2PtS: C, 57.45; H, 4.29. Found: C,57.96;
H, 4.75.
1
50% yield. H NMR (400 MHz, CD2Cl2, room temperature): δ 2.17
(s, 12H, SC6H3Me2), 6.58ꢀ6.65 (m, 6H, SC6H3Me2), 7.13ꢀ7.53 (m,
30H, PPh3). 31P{1H} NMR (162 MHz, CD2Cl2, room temperature): δ
18.52 (s, 1JPꢀPt = 3043 Hz). Anal. Calcd. for C52H48P2PtS2: C, 62.83; H,
4.87. Found: C, 63.73; H, 4.83.
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](dppe) (5d). Similar to the case
for 5a, the formation of 5d was confirmed by NMR studies (100%) and
cis-Pt(SC6H3Me2-2,6-k1S)2(dppe) (4d). Pale yellow needles,
1
X-ray analysis. H NMR (400 MHz, CD2Cl2, room temperature): δ
1
2.24ꢀ2.51 (m, 4H, PC2H4P), 2.82 (dd, 3JHꢀP = 7.6, 4.8 Hz, 2JHꢀPt
=
53% yield. H NMR (400 MHz, CD2Cl2, room temperature): δ 2.14
3
(s, 12H, SC6H3Me2), 2.0ꢀ2.3 (m, 4H, PC2H4P), 6.53ꢀ6.61 (m, 6H,
SC6H3Me2), 7.4ꢀ7.7 (m, 20H, PPh2). 31P{1H} NMR (162 MHz,
CD2Cl2, room temperature): δ 44.78 (s, 1JPꢀPt = 2908 Hz). Anal. Calcd
for C42H42P2PtS2: C, 58.12; H, 4.88. Found: C, 57.56; H, 5.08.
cis-Pt(SC6H3Me2-2,6-k1S)2(dppp) (4e). Pale yellow prisms,
53.8 Hz, 2H, SC6H3(2-CH2)(6-Me)), 6.64 (t, JHꢀH = 7.3 Hz, 1H,
SC6H3(2-CH2)(6-Me)), 6.72 (d, 3JHꢀH = 7.3 Hz, 1H, SC6H3(2-CH2)-
3
(6-Me)), 6.83 (d, JHꢀH = 7.3 Hz, 1H, SC6H3(2-CH2)(6-Me)),
7.12ꢀ7.26 (m, 4H, PPh2), 7.43ꢀ7.90 (m, 16H, PPh2). 31P{1H} NMR
2
(162 MHz, CD2Cl2, room temperature): δ 45.97 (d, JPꢀP = 5 Hz,
1
1JPꢀPt = 3069 Hz, 1P, PMe3 trans to S), 46.17 (d, 2JPꢀP = 5 Hz, 1JPꢀPt
1810 Hz, 1P, PMe2 trans to C).
=
74% yield. H NMR (400 MHz, CD2Cl2, room temperature): δ 2.09
(s, 12H, SC6H3Me2), 1.92ꢀ2.12 (m, 2H, PCH2CH2CH2P), 2.44ꢀ2.61
(m, 4H, PCH2CH2CH2P), 6.57 (s, 6H, SC6H3Me2), 7.3ꢀ7.7 (m, 20H,
PPh2). 31P{1H} NMR (162 MHz, CD2Cl2, room temperature):
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](dppp) (5e). Colorless crystals,
78% yield. 1H NMR (400 MHz, CD2Cl2, room temperature): δ
1.89ꢀ2.06 (m, 2H, PCH2CH2CH2P), 2.17 (s, 3H, SC6H3(2-CH2)(6-
Me)), 2.50ꢀ2.60 (m, 2H, SC6H3(2-CH2)(6-Me)), 2.64ꢀ2.80 (m, 4H,
PCH2CH2CH2P), 6.53ꢀ6.63 (m, 3H, SC6H3(2-CH2)(6-Me)),
7.33ꢀ7.74 (m, 20H, PPh2). 31P{1H} NMR (162 MHz, CD2Cl2,
room temperature): δ ꢀ2.19 (d, 2JPꢀP = 30 Hz, 1JPꢀPt = 1740 Hz, 1P,
PMe3 trans to C), 2.96 (d, 2JPꢀP = 30 Hz, 1JPꢀPt = 3026 Hz, 1P, PMe2
trans to S).
1
δ ꢀ2.64 (s, JPꢀPt = 2908 Hz). Anal. Calcd for C43H44P2PtS2: C,
58.56; H, 5.03. Found: C, 58.05; H, 5.32.
cis-Pt(SC6H3Me2-2,6-k1S)2(dppb) (4f). Pale yellow needles,
35% yield. 1H NMR (400 MHz, DMSO-d6, room temperature):
δ 1.75 (br s, 4H, PC4H8P), 1.85 (s, 12H, SC6H3Me2), 2.70 (br s, 4H,
PC4H8P), 6.48ꢀ6.55 (m, 6H, SC6H3Me2), 7.3ꢀ7.7 (m, 20H, PPh2).
31P{1H} NMR (162 MHz, DMSO-d6, room temperature): δ 12.78
(s, 1JPꢀPt = 2832 Hz).
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](dppb) (5f). Similar to the case
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](PMe3)2 (5a). In an NMR tube
were placed complex 4a (0.0089 g, 0.016 mmol) and triphenylmethane
as an internal standard (0.0127 g, 0.0520 mmol), DMSO-d6 (600 μL)
was added, and then the reaction system was heated at 130 °C for 10 min
to give 5a (30% yield). 1H NMR (300 MHz, DMSO-d6, room
temperature): δ 1.5ꢀ1.6 (m, 18H, PMe3), 2.17 (s, 3H, SC6H3
1
for 5a, the formation of 5f was confirmed by NMR experiments. H
NMR (400 MHz, DMSO-d6, room temperature): δ 1.57ꢀ1.70 (m, 4H,
PC4H8P), 1.98 (s, 3H, SC6H3(2-CH2)(6-Me)), 2.5 (obscured by the
undeuterated DMSO in DMSO-d6, SC6H3(2-CH2)(6-Me)) 2.6 (br s,
2H, PC4H8P), 2.8 (br s, 2H, PC4H8P), 6.38ꢀ6.56 (m, 3H, SC6H3
(2-CH2)(6-Me)), 7.4ꢀ7.7 (m, 20H, PPh2). 31P{1H} NMR (162 MHz,
DMSO-d6, room temperature): δ 12.63 (d, 2JPꢀP = 22 Hz, 1JPꢀPt = 1822
Hz, 1P, PMe3 trans to C), 20.37 (d, 2JPꢀP = 22 Hz, 1JPꢀPt = 3144 Hz, 1P,
PMe2 trans to S).
3
2
(2-CH2)(6-Me)), 3.00 (t, JHꢀP = 6.6 Hz, JHꢀPt = 54.4 Hz, 2H,
SC6H3(2-CH2)(6-Me)), 6.5ꢀ6.7 (m, 3H, SC6H3(2-CH2)(6-Me)).
31P{1H} NMR (122 MHz, DMSO-d6, room temperature): δ ꢀ25.4
2
1
(d, JPꢀP = 22 Hz, JPꢀPt = 1770 Hz, 1P, PMe3 trans to C), ꢀ24.21
(d, 2JPꢀP = 22 Hz, 1JPꢀPt = 3017 Hz, 1P, PMe3 trans to S).
anti-[PtMe(SC6H3Me2-2,6-kS)(PPh3)]2 (anti-6c). Complex 1c
(0.273 g, 0.313 mmol) was heated in benzene (20 mL) at 70 °C. After
removal of all volatile material, the resulting colorless powder was
recrystallized from cold dichloromethane/hexane at ꢀ30 °C to give a
white powder of pure anti-6c in 72%/Pt yield (0.138 mg, 0.113 mmol).
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](PEt3)2 (5b). Similar to the case
for 5a, the formation of 5b was confirmed by NMR experiments (100%
1
yield). H NMR (400 MHz, C6D6, room temperature): δ 0.63ꢀ0.98
(m, 18H, PCH2Me), 1.33ꢀ1.79 (m, 12H, PCH2Me), 2.84 (s, 3H,
SC6H3(2-CH2)(6-Me)), 3.43 (t, 3JHꢀP = 6.6 Hz, 2JHꢀPt = 55.0 Hz, 2H,
SC6H3(2-CH2)(6-Me)), 7.04ꢀ7.27 (m, 3H, SC6H3(2-CH2)(6-Me)).
3
1H NMR (300 MHz, toluene-d8, 20 °C): δ 0.13 (d, JHꢀP = 4.5 Hz,
2JHꢀPt = 76 Hz, 6H, PtMe), 3.13 (s, 12H, SC6H3Me2), 6.6ꢀ6.7 (m, 6H,
SC6H3Me2), 6.8 (m, 18H, PPh3), 7.5 (m, 12H, PPh3). 31P{1H} NMR
(122 MHz, toluene-d8, 20 °C): δ 27.8 (s, 1JPꢀPt = 3861 Hz, 1P, PPh3).
syn-[PtMe(SC6H3Me2-2,6-kS)(PPh3)]2 (syn-6c). Heating of a
toluene-d8 solution of anti-6c at 110 °C for 6 h produced a 2/1 anti-6c/
syn-6c mixture. syn-6c: 1H NMR (300 MHz, toluene-d8, 20 °C) δ 0.16
(d, 3JHꢀP = 4.8 Hz, 2JHꢀPt coupling value was obscured because of the
adjacent anti-6c resonances, 6H, PtMe), 2.48 (s, 6H, SC6H3Me2), 3.55
(s, 6H, SC6H3Me2), 6.6ꢀ6.7 (m, 6H, SC6H3Me2), 6.9ꢀ7.0 (m, 18H,
PPh3), 7.5 (m, 12H, PPh3); 31P{1H} NMR (122 MHz, toluene-d8,
20 °C) δ 25.3 (s, 1JPꢀPt = 3918 Hz, 1P, PPh3).
31P{1H} NMR (162 MHz, C6D6, room temperature): δ 6.80 (d, 2JPꢀP
=
20 Hz, 1JPꢀPt = 1771 Hz, 1P, PMe3 trans to C), 8.48 (d, 2JPꢀP = 20 Hz,
1JPꢀPt = 3054 Hz, 1P, PMe2 trans to S).
Pt[SC6H3(CH2-2)(Me-6)-j2S,C](PPh3)2 (5c). Complex 4c
(0.149 g, 1.72 mmol) was heated in DMSO (5 mL) for 2 h at 180 °C.
After removal of all volatile material under reduced pressure, the
resulting solid was washed with hexane and Et2O. The resulting solid
was recrystallized from cold dichloromethane/hexane at ꢀ30 °C to give
1
colorless crystals of 5c in 77% yield (0.114 g, 0.132 mmol). H NMR
(400 MHz, CD2Cl2, room temperature): δ 2.09 (s, 3H, SC6H3
3
2
anti-[PtEt(SC6H3Me2-2,6-kS)(PPh3)]2 (anti-7c). Heating of a
benzene solution (5 mL) of 2c (108.2 mg, 0.1221 mmol) at 70 °C for
15 min produced a white precipitate. After removal of the solution, the
resulting powder was washed with hexane and dried under reduced
pressure to give a 1/4 anti-7c/syn-7c mixture. Yield: 73% (55.6 mg,
0.0446 mmol). anti-7c: 1H NMR (400 MHz, DMSO-d6, room
temperature) δ 0.05ꢀ0.22 (m, 6H, CH2Me), 0.23ꢀ0.28 (m, 4H,
CH2Me), 2.75 (s, 12H, SC6H3Me2), 6.75 (s, 6H, SC6H3Me2),
7.49ꢀ7.67 (m, 30H, PPh3); 31P{1H} NMR (162 MHz, DMSO-d6,
room temperature): δ 28.06 (s).
(2-CH2)(6-Me)), 2.85 (t, JHꢀP = 7.2 Hz, JHꢀPt = 56.3 Hz, 2H,
SC6H3(2-CH2)(6-Me)), 6.49 (d, 3JHꢀH = 7.4 Hz, 1H, SC6H3(2-CH2)-
(6-Me)), 6.54 (t, 3JHꢀH = 7.1 Hz, 1H, SC6H3(2-CH2)(6-Me)), 6.62 (d,
3JHꢀH = 7.4 Hz, 1H, SC6H3(2-CH2)(6-Me)), 7.15ꢀ7.47 (m, 30H,
PPh3). 31P{1H} NMR (162 MHz, CD2Cl2, room temperature): δ 22.1
(d, 2JPꢀP = 19 Hz, 1JPꢀPt = 1881 Hz, 1P), 24.8 (d, 2JPꢀP = 19 Hz, 1JPꢀPt
=
3250 Hz, 1P). 1H NMR (300 MHz, DMSO-d6, room temperature): δ
1.93 (s, 3H, SC6H3(2-CH2)(6-Me)), 2.70 (t, 3JHꢀP = 6.9 Hz, 2JHꢀPt
=
3
57.0 Hz, 2H, SC6H3(2-CH2)(6-Me)), 6.35 (d, JHꢀP = 3.6 Hz,
3
1H, SC6H3(2-CH2)(6-Me)), 6.47 (t, JHꢀP = 3.6 Hz, 1H, SC6H3
5120
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syn-[PtEt(SC6H3Me2-2,6-kS)(PPh3)]2 (syn-7c). 1H NMR (400
MHz, DMSO-d6): δ 0.06ꢀ0.22 (m, 6H, CH2Me), 2.00 (s, 6H,
Effect of Added 2,6-Dimethylbenzenethiol on the Forma-
tion Rate of 5c from 4c. Compound 4c (5.2 mg, 0.0052 mmol),
DMF (600 μL), and 9.8 equiv of 2,6-dimethylbenzenethiol (7.2 μL,
0.051 mmol) were added into an NMR tube along, with a flame-sealed
capillary of P(O)(C6H4OMe-4)3/DMSO-d6 as an external standard.
The solution was heated at 50 °C, and the formation rate was estimated
from the 31P{1H} NMR spectrum.
3
SC6H3Me2), 3.24 (s, 6H, SC6H3Me2), 6.41 (d, JHꢀH = 7.8 Hz, 2H,
SC6H3Me2), 6.55 (t, 3JHꢀH = 7.3 Hz, 1H, SC6H3Me2), 6.99 (t, 3JHꢀH
=
3
7.8 Hz, 1H, SC6H3Me2), 7.09 (d, JHꢀH = 7.3 Hz, 2H, SC6H3Me2),
7.49ꢀ7.67 (m, 30H, PPh3). 31P{1H} NMR (162 MHz, DMSO-d6, room
temperature): δ 27.42 (s).
Kinetic Parameters for the Formation of 5c from 1c or 4c.
Similar to the above experiments, the rate was estimated by the 31P{1H}
NMR spectrum on the basis of an external standard of P(O)(C6H4O-
Me-4)3. The rates from 1c were measured in the range 100ꢀ125 °C.
Those from 4c were measured in the range 35ꢀ60 °C.
[Pt(CH2CMe3)(SC6H3Me2-2,6-kS)(PPh3)]2. A DMF solution
(5 mL) of 3c (96.2 mg, 0.104 mmol) at room temperature for 10 min
produced a white precipitate. After removal of the solution, the resulting
powder was washed with benzene and hexane and dried under reduced
pressure to give a white precipitate. This precipitate has low solubility in
most organic solvents, but it slightly dissolved in DMSO and was assigned
as [Pt(CH2CMe3)(SC6H3Me2-2,6-kS)(PPh3)]2. Yield: 70% (48.5 mg,
X-ray Crystallography. Crystallographic data were measured on a
Rigaku RASA-7R Mercury II diffractometer using Mo Kα radiation with
a graphite crystal monochromator. A single crystal was selected by use of
a polarized microscope and mounted on a glass capillary with Paratone
N oil. The crystallographic data and details associated with data
collection for 3c, 4aꢀf, and 5d are given in the Supporting Information.
The R (Rw) values of these crystals are as follows: 3c, 0.0358 (0.0938);
4a, 0.0367 (0.1107); 4b, 0.0303 (0.0884); 4c, 0.0536 (0.1593); 4d,
0.0284 (0.0795); 4e, 0.0300 (0.0725); 4f, 0.0510 (0.1569); 5d, 0.0500
(0.1238). The data were processed using CrystalStructure (version 3.8
or 4.0) package software.39 All non-hydrogen atoms were found by using
the results of direct methods (SIR9240 for 3c and 4a,dꢀf or SHELXL-
9741 for 5d) or PATTY for 4c. All non-hydrogen atoms were found on
difference maps. All hydrogen atoms were located in calculated posi-
tions. The crystal of 5d contained a toluene molecule, which was solved
anisotropically. Crystallographic thermal parameters and bond distances
and angles have been deposited as Supporting Information.
1
0.0364 mmol). H NMR (400 MHz, DMSO-d6, room temperature): δ
0.90 (s, 18H, CH2CMe3), 2.54 (s, 12H, SC6H3Me2), 2.61 (d, 3JHꢀP = 5.5
Hz, 4H, CH2CMe3), 6.33 (d, 3JHꢀH = 7.3 Hz, 2H, SC6H3Me2), 6.53 (t,
3
3JHꢀH = 7.3 Hz, 2H, SC6H3Me2), 6.88 (d, JHꢀH = 7.3 Hz, 2H,
SC6H3Me2), 7.49ꢀ7.67 (m, 30H, PPh3). 31P{1H} NMR (162 MHz,
DMSO-d6, room temperature): δ 28.10 (s, 1JPꢀPt = 3327 Hz).
Preparation of 5c from 1c-d3. Compound 1c-d3 was heated at
110 °C in toluene-d8 for 13 h gave 5c in 91% yield. No incorporation of
D in 5c was observed. Formation of CD3H was observed by 1H NMR at
δ 0.140 (sept, 2JH-D = 1.8 Hz, CD3H).
Preparation of 5c from 2c. Compound 2c (26.8 mg, 0.0303
mmol) was placed in a sample tube, into which anisole (2.00 mL) was
added by a hypodermic syringe. After heating at 130 °C for 4.3 h,
ethylene (0.0135 mmol, 45%) and ethane (0.0131 mmol, 43%) were
evolved (GLC, methane as an internal standard). Formation of 5c was
checked by the 31P{1H} NMR spectrum by use of a flame-sealed
capillary involving C6D6 (5c, 78.4% yield).
’ ASSOCIATED CONTENT
Equilibrium among 1c, syn-6c, and anti-6c. Compound 1c
(9.3 mg, 0.012 mmol) and PPh3 (6.6 mg, 0.025 mmol) were heated in
the range 80ꢀ100 °C in toluene-d8 in the presence of triphenylmethane
(12.8 mg, 0.0524 mmol) as an internal standard.
Effect of Added PPh3 on the Observed Rate Constant from
4c. Compound 4c (5.5 mg, 0.0055 mmol) with 1.1 equiv of PPh3
(1.6 mg, 0.0061 mmol), DMF (600 μL), and a flame-sealed capillary of
P(O)(C6H4OMe-4)3/DMSO-d6 as an external standard were added
into an NMR tube. The rate was estimated from the 31P{1H} NMR
spectrum. Similarly, independent experiments with 3.0, 5.0, 10, 15, and
25 equiv of PPh3 were performed. The rate constant from 1c was also
measured similarly.
S
Supporting Information. Tables and CIF files giving
b
kinetic data for Figures 3ꢀ5 and X-ray crystallographic data for
3c, 4aꢀf, and 5d. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel and fax: +81 423 88 7044. E-mail: hrc@cc.tuat.ac.jp (M.H.);
komiya@cc.tuat.ac.jp (S.K).
Effect of Free Radical Scavenger on the Formation Rate of
5c from 1c. Compound 1c (6.4 mg, 0.0067 mmol), DMF (600 μL),
and a flame-sealed capillary of P(O)(C6H4OMe-4)3/DMSO-d6 as an
external standard were added into an NMR tube. Then, a DMF solution
of garvinoxyl (0.0400 M, 5.00 μL) was added into the NMR tube. The
solution was heated at 110 °C, and the rate was estimated from the
31P{1H} NMR spectrum.
’ ACKNOWLEDGMENT
We are grateful for financial support by a Grant-in-Aid for
Scientific Research on Innovative Areas “Molecular Activation
Directed toward Straightforward Synthesis” from the Ministry of
Education, Culture, Science and Technology of Japan. We thank
Ms. S. Kiyota for elemental analysis.
Effect of Free Radical Scavenger on the Formation Rate of
5c from 4c. Similar to the reaction of 1c with garvinoxyl, compound 4c
(5.7 mg, 0.0057 mmol), DMF (600 μL), and a DMF solution of
garvinoxyl (2.4 mg, 0.0057 mmol) were added into the NMR tube.
The solution was heated at 50 °C, and the rate was estimated from the
31P{1H} NMR spectrum.
’ DEDICATION
†This paper is dedicated to Prof. Christian Bruneau on the
occasion of his 60th birthday.
Effect of Added Potassium 2,6-Dimethylbenzenethiolate
on the Formation Rate of 5c from 4c. Compound 4c (5.8 mg,
0.0058 mmol), DMF (600 μL), and 10 equiv of potassium 2,6-
dimethylbenzenethiolate (10.5 mg, 0.0596 mmol) were added into an
NMR tube, along with a flame-sealed capillary of P(O)(C6H4OMe-4)3/
DMSO-d6 as an external standard. The solution was heated at 50 °C, and
the rate was estimated from the 31P{1H} NMR spectrum.
’ ABBREVIATIONS
dppe = 1,2-bis(diphenylphosphino)ethane (Ph2PC2H4PPh2);
dppp = 1,3-bis(diphenylphosphino)propane (Ph2PC3H6PPh2);
dppb = 1,4-bis(diphenylphosphino)butane (Ph2PC4H8PPh2);
DMF = dimethylformamide (Me2NCHO); COD = cycloo-
ctadiene
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Organometallics
ARTICLE
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5122
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