Experimental and theoretical studies on the platinum-mediated selective C(sp)-Si bond cleavage of alkynylsilanes

Article abstract of DOI:10.1021/om5002588

A series of cis-alkynyl(silyl)platinum(II) complexes was prepared via the chemoselective C(sp)-Si bond cleavage of alkynylsilanes by a platinum(0) complex ligated with the P-N hemilabile bidentate ligand. The coordination of the triple bond to the platinum center triggers selective C(sp)-Si bond cleavage. Hammett plots of the ³¹P{¹H} NMR spectroscopic properties (δ and J values) reflect an electronic effect on platinum(II) complexes; trans substituents of arylethynyl groups are influenced, but cis-positioned silyl groups are not affected, as evidenced by ²⁹Si{¹H} NMR. In comparison, Hammett plots show that C(sp)-Si bond cleavage rates are accelerated by electron-rich alkynylsilanes, which is opposite to the ordinary oxidative addition of aryl halides to transition metals often observed in catalytic cross-coupling reactions. A DFT calculation reveals that intermediates and transition states are stabilized by electron-rich alkynylsilanes and that the five-membered hemilabile P-N ligand is essential, in which a reactive electron-deficient 14-electron platinum(0) species is produced via the dissociation of nitrogen, giving rise to a monodentate phosphine coordination. Electron-rich alkynylsilanes allow decreased π back-donation from the platinum center to the ligand, accelerating the dissociation of the more labile nitrogen. Steric congestion between diisopropylphosphino and silyl groups thermodynamically disfavors C(sp)-Si bond cleavage.

Full text of DOI:10.1021/om5002588

Article
pubs.acs.org/Organometallics
Experimental and Theoretical Studies on the Platinum-Mediated
Selective C(sp)−Si Bond Cleavage of Alkynylsilanes
Yasuhiro Okuda,† Yuya Ishiguro,† Seiji Mori,‡ Kiyohiko Nakajima,§ and Yasushi Nishihara*,†,⊥
†Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology, Okayama University,
3-1-1 Tsushimanaka, Okayama 700-8530, Japan
‡Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan
§Department of Chemistry, Faculty of Education, Aichi University of Education, 1 Hirosawa, Igaya, Kariya, Aichi 448-8542, Japan
⊥ACT-C, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
S
* Supporting Information
ABSTRACT: A series of cis-alkynyl(silyl)platinum(II) complexes was prepared via the chemoselective C(sp)−Si bond cleavage
of alkynylsilanes by a platinum(0) complex ligated with the P−N hemilabile bidentate ligand. The coordination of the triple bond
to the platinum center triggers selective C(sp)−Si bond cleavage. Hammett plots of the 31P{1H} NMR spectroscopic properties
(δ and J values) reflect an electronic effect on platinum(II) complexes; trans substituents of arylethynyl groups are influenced,
but cis-positioned silyl groups are not affected, as evidenced by 29Si{1H} NMR. In comparison, Hammett plots show that
C(sp)−Si bond cleavage rates are accelerated by electron-rich alkynylsilanes, which is opposite to the ordinary oxidative addition
of aryl halides to transition metals often observed in catalytic cross-coupling reactions. A DFT calculation reveals that
intermediates and transition states are stabilized by electron-rich alkynylsilanes and that the five-membered hemilabile P−N
ligand is essential, in which a reactive electron-deficient 14-electron platinum(0) species is produced via the dissociation of
nitrogen, giving rise to a monodentate phosphine coordination. Electron-rich alkynylsilanes allow decreased π back-donation
from the platinum center to the ligand, accelerating the dissociation of the more labile nitrogen. Steric congestion between
diisopropylphosphino and silyl groups thermodynamically disfavors C(sp)−Si bond cleavage.
(M = transition metals, X = halides or alkoxy groups),6,7 intra-
INTRODUCTION
■
molecular transformation,8 electrophilic metalation/desilylation,9
Organosilicon compounds have attracted considerable attention,
radical reactions,10 silyl migration,11 and other reactions12 have
owing to their low toxicity, high stability, low cost, and the ready
been reported. Although the inert C(sp3)−Si bond can also be
cleaved in a wide variety of ways, to selectively cleave the target
bond requires the use of transition metals. In general, C(sp2)−Si
bonds have been activated through an aromatic electrophilic
substitution/desilylation sequence, and C(sp)−Si bonds can be
cleaved via transmetalation or oxidative addition.
availability of silicon, the second most abundant element.1
In respect to the utilization of organosilicon compounds, for
example, Hiyama coupling has served as a practical tool in the
preparation of a series of complex natural products,
pharmaceuticals, and agrochemicals.2 Since Hiyama coupling
requires the selective and effective activation of a strong C−Si
bond (BDE ≈ 290 kJ/mol),3 achieving this bond activation has
been regarded as an extremely important research topic. Initially,
the activation of C−Si bonds was achieved by using fluoride or
alkoxide ions.4 Another C−Si bond cleavage, the transition-
metal-mediated activation of C−Si bonds, has recently received
a great deal of attention as a superior method.5 Also,
transmetalation between C−Si bonds and M−X bonds
For practical purposes, the most straightforward method
to cleave C−Si bonds is thought to be transition-metal-
mediated oxidative addition. However, conventional transition-
metal-mediated C−Si bond activation often takes place in an
Received: March 11, 2014
Published: March 27, 2014
© 2014 American Chemical Society
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intramolecular manner, where only C−Si bonds in the auxiliary
ligand are activated.13 Despite recent advances in these fields,
a mechanistic understanding of transition-metal-mediated C−Si
bond cleavage remains elusive.
Jones and co-workers have reported the oxidative addition
of the C(sp)−Si bond of alkynylsilane 3a to a platinum(0)
complex derived from Pt(cod)2 (1) and the P−N bidentate
ligand 2 (Scheme 1).14 This bond activation proceeded under
alkynyl ligands. From this observation, they concluded that
C(sp)−Si bond-forming reductive elimination involves a
concerted three-center mechanism rather than a nucleophilic
attack of one ligand on the other (Scheme 2b).
Herein, we report the details of the C(sp)−Si bond cleavage
of a series of alkynylsilanes 3 by P−N ligated Pt(0) complexes.
The reaction proceeded chemo- and regioselectively under
thermal conditions, and the intermediates, η2-alkyne-coordinat-
ing complexes and their regioisomers, were characterized by
NMR spectroscopy. Additionally, we elucidated the effects of
the substituents of the silyl and aryl groups in alkynylsilanes on
chemical shifts and coupling constants in the 31P{1H} NMR
spectra and on reaction rates of the C(sp)−Si bond cleavage.
Theoretical calculations were performed to disclose the details
of the oxidative addition of the C(sp)−Si bond on the Pt(0)
complex assisted by the hemilabile P−N ligand 2.
Scheme 1. C(sp)−Si Bond Activation of an Alkynylsilane
under Thermal and Photochemical Conditions
RESULTS AND DISCUSSION
■
Synthesis of cis-Alkynyl(silyl)platinum(II) Complexes
by Oxidative Addition of Alkynylsilanes. We prepared
platinum(II) complexes via C(sp)−Si bond cleavage with
various alkynylsilanes 3 using the Jones method.14 We found
that the reactions proceeded smoothly at 70 °C and the
C(sp)−Si bond cleavage was completed within 1 h, except for
3c. The yields and representative chemical shifts and coupling
constants are summarized in Table 1. On the basis of the H−Pt
coupling constants (ca. 30 Hz) assigned to the Si−Me bond in
both thermal (room temperature, 5 days) and photochemical
(UV, −30 °C) conditions. However, under photochemical
conditions the two conformational isomers 5a and 5a′ were
generated, while under thermal conditions only the thermody-
namically stable isomer 5a was formed, due to isomerization.
On the other hand, a notable study on Pt-mediated
C(sp)−Si bond-forming reactions has been reported by
Ozawa and co-workers (Scheme 2a).15 They primarily prepared
1
the H NMR spectra, as well as the reported 31P{1H} NMR
1
data (δ 59.3, JP−Pt = 2760 Hz), in most cases cis-alkynyl-
(silyl)platinum(II) complexes 5-α were exclusively formed in
19−72% yields, where silyl and arylethynyl groups were directly
bonded to a platinum center. In particular, the Si−P coupling
constants (2JSi−P) strongly support the mutual cis configuration
of silyl and phosphine groups, as observed in a previous report.14
In the case of alkynylsilane 3c (Table 1, entry 3), the cor-
Scheme 2. (a) Preparation of cis-Alkynyl(silyl)platinum(II)
and Kinetic Study of C(sp)−Si Bond-Forming Reductive
Elimination and (b) Proposed Mechanism for C(sp)−Si
Bond-Forming Reductive Elimination
responding alkynyl(silyl)platinum(II) complex was not formed.
1
Judging from the reported coupling constants of JP−Pt
=
3952 Hz for 4a-α and 4a-β in the 31P{1H} NMR spectrum,14
we concluded that the η2-alkyne-coordinating complex was
1
mainly formed (4c-α and 4c-β: δ 65.6, JP−Pt = 4006 Hz)
without subsequent C(sp)−Si bond cleavage, presumably
owing to the sterically hindered triisopropylsilyl group. As
shown in entries 1−3, the steric hindrance of the silyl groups
caused drastic thermodynamic destabilization against C(sp)−Si
bond cleavage. The destabilization of complex 5c-α is
attributed to the steric repulsion between diisopropylphosphino
and silyl groups, evidenced by X-ray crystal structure analyses of
the related complexes shown below. It is noteworthy that bond
cleavage proceeded exclusively at the C(sp)−Si bond, even
though alkynylsilanes bear aromatic and heteroaromatic groups
that possess three types of C−Si bonds: C(sp)−Si, C(sp2)−Si,
and C(sp3)−Si (entries 4 and 6). The aliphatic alkynylsilane
1-trimethylsilyl-1-propyne (3g) is susceptible to the present
reaction (entry 7). The present reactions showed a wide range
of functional group compatibility; both electron-deficient and
electron-rich alkynylsilanes could be subjected to C(sp)−Si
bond cleavage (entries 8−13).
X-ray crystal structure analyses were examined for the four
platinum(II) complexes 5e-α, 5f-α, 5g-α, and 5l-α. ORTEP
drawings are shown in Figure 1, and selected bond distances
and bond angles are summarized in Table 2.
As shown in Table 2, the Pt−N bonds in complexes 5
(2.25(4)−2.309(4) Å) are longer than those in ordinary P−N
cis-alkynyl(silyl)platinum(II) complexes and examined the
electronic effect of silyl and alkynyl ligands on reductive
elimination rates using NMR. It was shown that the rates of
reductive eliminations that formed C(sp)−Si bonds were
affected by electron-withdrawing substituents in both silyl and
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a
Table 1. Preparation of Alkynyl(silyl)platinum(II) Complexes Produced via C(sp)−Si Bond Cleavage of Alkynylsilanes 3
alkynylsilanes 3
SiR′3
TMS
1H NMR
δ(Si−Me)/ppm
29Si{1H} NMR
δ/ppm
2JSi−P/Hz
31P{1H} NMR
δ/ppm
1JP−Pt/Hz
entry
R
complex
5a-α
yield/%
3JH−Pt/Hz
1
Ph
Ph
Ph
Ph
Ph
Ph
Me
60
61
0.89
31
−20.8
−1.7
8
8
59.3
58.2
65.6
57.8
59.2
58.2
59.3
59.1
59.2
59.3
59.4
59.4
59.5
2757
2765
4006
2734
2748
2728
2740
2772
2770
2766
2754
2751
2745
2
TES
5b-α
3
TIPS
4c-α (or 4c-β)
5d-α
4
SiMe2Ph
SiMe2Bn
SiMe2Th
TMS
72
48
69
42
58
22
22
49
19
56
1.10
0.70
1.13
0.85
0.78
0.83
0.84
0.86
0.89
0.88
32
b
−22.4
−14.7
−29.2
−21.0
−20.0
−19.9
−20.1
−20.4
−20.4
−20.7
8
8
8
8
8
8
8
8
8
8
5
5e-α
6
5f-α
32
31
30
30
31
30
29
30
7
5g-α
8
4-O2NC6H4
4-CF3C6H4
4-ClC6H4
TMS
5h-α
9
TMS
5i-α
10
11
12
13
TMS
5j-α
4-MeC6H4
4-MeOC6H4
4-Me2NC6H4
TMS
5k-α
TMS
5l-α
TMS
5m-α
a
b
Abbreviations: TMS = trimethylsilyl, TES = triethylsilyl, TIPS = triisopropylsilyl, Bn = benzyl, Th = 2-thienyl. A J value was not determined due to
overlap with other signals.
the silyl group. In addition, N−Pt−P angles are found to be
only 83.5(2)−84.0(9)° and the P−Pt−Si angles are larger than
the other bond angles around platinum, indicating steric
repulsion between diisopropylphosphino and silyl groups.
Substituent Effect of Aryl Groups on the 31P{1H} NMR
Properties. We next systematically examined the substituent
effect of the aryl group in alkynylsilanes 3 on the 31P{1H} NMR
properties of the produced platinum(II) complexes 5-α. Ozawa
and co-workers have reported a correlation between electronic
factors and NMR properties for Hammett substituent constants
at the para position (σp) in similar alkynyl(silyl)platinum(II)
complexes (Scheme 2).15 Plotting σp and the 31P{1H} NMR
values (δ or J) of platinum(II) complexes 5a-α and 5h-5m-α
showed a good correlation with the electronic properties of the
aryl substituents. Figure 2 shows that the electronic effect (the
trans influence) is transferred from the para substituents of aryl
groups even beyond the ethynyl moieties.18
We also plotted Hammett substituent constants against the
values of the 29Si{1H} NMR spectra, but no correlation with
the electronic effect of para substituents on aryl groups was
observed (see the Supporting Information). Hence, we con-
cluded that the steric effect of the cis-positioned silyl groups
and an electronic effect of the trans-positioned arylethynyl
groups influence the thermodynamic stability of platinum(II)
complexes 5-α and their 31P{1H} NMR properties, respectively.
Kinetic Studies. Next, we examined the kinetics of
oxidative addition, using 31P{1H} NMR spectroscopy. Although
there are some equilibria, as previously reported by Jones,14 the
formation of η2-alkyne-coordinating intermediates 4a-α−4m-α
(and 4a-β−4m-β) is found to be quantitative and reasonably
fast. We thus calculated kinetic constants (kobsd) for the con-
version of intermediates 4a-α−4m-α (and 4a-β−4m-β) into
alkynyl(silyl)platinum complexes 5a-α−5m-α. On the basis of
Figure 1. ORTEP drawings of cis-alkynyl(silyl)platinum(II) complexes
5e-α, 5f-α, 5g-α, and 5l-α (30% probability ellipsoids). Hydrogen
atoms are omitted for clarity. Since the 2-thienyl group in 5f-α and the
−CH2NMe2 portion of the P−N ligand in 5g-α showed disorder, only
one contributor is shown.
ligated platinum(II) complexes (2.09−2.20 Å)16 but are similar
to those in P−N ligated platinum(II) complexes possessing
a silyl or methyl group trans to the Pt−N bond (∼2.3 Å).17
These results strongly suggest a significant trans influence from
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Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) in cis-Alkynyl(silyl)platinum(II) Complexes 5a-α,14 5e-α, 5f-α,
5g-α, and 5l-α
5a-α
5e-α
Bond Lengths
5f-α
5g-α
5l-α
Pt(1)−P(1)
Pt(1)−N(1)
Pt(1)−Si(1)
Pt(1)−C(1)
C(1)−C(2)
C(2)−C(3)
2.262(2)
2.25(4)
2.2702(15)
2.298(3)
2.3144(14)
2.010(5)
1.194(7)
1.429(7)
2.274(2)
2.283(8)
2.310(2)
1.983(9)
1.201(14)
1.445(14)
2.2534(10)
2.309(4)
2.3026(15)
2.004(4)
1.180(7)
1.493(9)
2.2658(10)
2.303(3)
2.3139(11)
2.005(4)
1.191(6)
1.452(6)
2.313(2)
1.998(8)
1.199(11)
1.440(11)
Bond Angles
P(1)−Pt(1)−Si(1)
Si(1)−Pt(1)−C(1)
C(1)−Pt(1)−N(1)
N(1)−Pt(1)−P(1)
Pt(1)−C(1)−C(2)
C(1)−C(2)−C(3)
101.63(8)
82.9(2)
103.12(5)
84.63(14)
88.51(17)
83.58(10)
172.6(4)
176.9(5)
101.13(8)
84.2(2)
100.46(4)
83.59(13)
92.04(16)
83.93(11)
178.6(4)
178.5(7)
100.71(3)
83.06(13)
92.71(15)
83.65(8)
175.0(4)
174.4(4)
91.8(9)
91.2(3)
84.0(9)
83.5(2)
176.4(7)
176.3(9)
178.7(9)
178.0(11)
Table 3. First-Order Rate Constants in C(sp)−Si Bond
a
Cleavage Monitored by the 31P{1H} NMR Spectra
alkynylsilane 3
19
entry
R
SiR′3
TMS
10−4kobsd/s−1
σp
1
3a
3b
3c
3d
3e
3f
Ph
Ph
Ph
Ph
Ph
Ph
Me
1.057
0.00
b
2
TES
2.397
3
TIPS
∞
4
SiMe2Ph
SiMe2Bn
SiMe2Th
TMS
0.293
0.521
0.252
5
6
b
7
3g
3h
3i
2.102
8
4-O2NC6H4
4-CF3C6H4
4-ClC6H4
TMS
0.222
0.402
0.837
1.855
0.81
0.53
9
TMS
10
11
12
13
3j
TMS
0.22
3k
3l
4-MeC6H4
4-MeOC6H4
4-Me2NC6H4
TMS
−0.14
−0.28
−0.63
b
TMS
2.583
c
3m
TMS
6.462
a
Abbreviations: TMS = trimethylsilyl, TES = triethylsilyl, TIPS =
1
Figure 2. Dependence of the 31P{1H} NMR properties (δ and JP−Pt
)
b
c
triisopropylsilyl, Bn = benzyl, Th = 2-thienyl. 0−3 h. 0−1 h.
on the σp values of para substituents on the aryl groups (SiR′3 =
TMS).
examined the electronic effect of an R group. A methyl group
accelerated rates twice as much a phenyl group (entry 1 vs
entry 7). Accordingly, the reaction rates were calculated with
alkynylsilanes 3 having para substituents on the benzene ring
(entries 1 and 8−13). The Hammett plot shown in Figure 3
indicates that electron-rich alkynylsilanes accelerate the C(sp)−
Si cleavage reaction. This tendency is completely opposite to the
general order found in the oxidative addition of organic halides
to low-valent transition metals.20
C(sp)−Si Bond Activation Mechanism. To explore
C(sp)−Si bond activation in more detail, we investigated the
possibility of a radical reaction. We confirmed the stability of
alkynyl(silyl)platinum(II) complex 5a-α when it was treated
with TEMPO, finding that no decomposition took place. We
then carried out the reactions of 1, 2, and 3a in the presence of
equimolar TEMPO, as shown in eq 1. After 1 h, the desired
complex 5a-α was formed in 58% yield, indicating that C(sp)−
Si bond activation was not retarded by a radical scavenger.
this method, we monitored the reactions by following the
31P{1H} NMR over 6 h, and the calculated rate constants are
given in Table 3. With regard to silyl groups, alkynylsilane 3b
with a triethylsilyl group reacted twice as fast as alkynylsilane 3a
with a trimethylsilyl group, but no C(sp)−Si bond activation
occurred with alkynylsilane 3c with a triisopropylsilyl group
(vide supra) (entries 1−3). This peculiar trend indicates that
the electronic and steric effects of the silyl groups may compete
with as well as complement each other; a sterically hindered silyl
group destabilizes the approach to a platinum center, whereas
electron-rich silyl groups can accelerate oxidative addition. When
one methyl group was replaced with a phenyl or 2-thienyl and
benzyl groups in alkynylsilanes, kinetic constants diminished to
a fourth of that for 3a (entry 1 vs entries 4 and 6) and to half of
that for 3a (entry 1 vs entry 5), respectively. These results imply
that substituents more sterically bulky and less electron donating
than a methyl group suppress C(sp)−Si bond activation. We also
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Table 5. Ligand Effect in C(sp)−Si Bond Activation
Figure 3. Hammett plot of rate constants (kobsd) for oxidative addition
of alkynylsilanes 3 versus σp values, corresponding to Table 3, entries 1
and 8−13.
in Table 5. However, no reaction occurred, except for 2. Only
a trace of a doublet (δ −15.9, JSi−P = 7.1 Hz) assigned to the
2
desired Pt complex was detected in the 29Si{1H} NMR spectrum
when L4 was employed. These results undoubtedly indicate that
an inherent property of ligand 2 controls some important
functions in C(sp)−Si bond activation. Specifically, the following
requirements must be considered for activation of the C(sp)−Si
bond by the Pt(0) complex: the ligand must (1) be bidentate
(vs L1), (2) have a P−N chelate system (vs L2), (3) consist of a
five-membered chelation (vs L3), and (4) enable free rotation
around a P−N coordination mode (vs L4). We assumed that
these requirements must be implicated in the hemilabile property
of the ligand employed. Thus, after the generation of η2-alkyne-
coordinating intermediates, a key 14-electron platinum(0)
complex would be generated through the dissociation of nitrogen
from the platinum center. Consequently, we hypothesized that
the active species in C(sp)−Si bond activation is the 14-electron
platinum(0) species possessing a monodentate phosphine ligand.
Additionally, we supposed that electron-rich alkynylsilanes would
be able to stabilize this inherently electron deficient 14-electron
active species. To elucidate the reaction mechanism, we next
explored theoretical calculations.
Thus, we concluded that a radical pathway can be ruled out in
the present platinum-mediated C(sp)−Si bond activation.
Next, we measured the reaction rate for C(sp)−Si bond
cleavage in different solvents. If oxidative addition proceeds
via polarized or ionized intermediates, the reaction might be
accelerated in polar solvents. As shown in Table 4, in all cases
Table 4. Solvent and Silyl Substituent Effects on Kinetic
Constants
entry
SiR′3
TMS
solvent
10−4kobsd/s−1
Theoretical Studies on the Reaction Mechanism of
C(sp)−Si Bond Activation and Configuration of Com-
plexes 5-α. To study the detailed mechanism of oxidative
addition of alkynylsilanes 3 to Pt(0), we performed density
functional theory (DFT) calculations for the proposed
mechanism, as shown in Scheme 3. As the ideal structure, we
1
2
3
4
5
6
C6D6
1.057
0.320
0.248
0.293
0.168
0.120
TMS
CD3CN
DMF-d7
C6D6
TMS
SiMe2Ph
SiMe2Ph
SiMe2Ph
CD3CN
DMF-d7
Scheme 3. Possible Mechanism of C(sp)−Si Bond Cleavage
the generation of the η2-alkyne-coordinating complex is fast and
quantitative. However, C(sp)−Si bond cleavage was somewhat
retarded in polar solvents such as CD3CN and DMF-d7. From
these results, the following two conclusions can be drawn. (1)
Polarization in the C(sp)−Si bond cleavage step does not affect
reaction rates at all. (2) The coordination of polar solvents to the
vacant coordination site on platinum stabilizes the complexes.
In particular, the latter factor indicates that hemilabile P−N
ligand properties play a key role during the reaction. The
transient platinum complex becomes an unsaturated species by
the dissociation of nitrogen in the ligand, which could be more
reactive for C(sp)−Si bond cleavage. We next screened various
ligands in order to gain more insight into the mechanism of
oxidative addition of alkynylsilanes 3.
Ligand Effect. We examined the series of ligands 2 and
L1−L4 for C(sp)−Si bond activation of 3a by measuring the
1H and 29Si{1H} NMR spectra, because a characteristic singlet
with platinum satellites (3JH−Pt) and a doublet with Si−P coupling
(2JSi−P) are observed, respectively. The results are summarized
tried to examine a 16-electron transition state in oxidative
addition without the dissociation of nitrogen in the P−N
ligand. However, we could not optimize the structure of such a
species and observed that the nitrogen atom, a harder base than
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Table 6. Selected Distances (Å) in Each Optimized Structure in the Reaction of Pt(0)/P−N Ligand with Alkynylsilane 3a at the
a
B3LYP (PCM, Solvent = Toluene)/SDD(Pt)-6-311G(d) Level
4a-α
TS1a-α
4a-α′
TS2a-α
5a-α′
TS3a-α
5a-α
4a-β
TS1a-β
4a-β′
TS2a-β
5a-β′
TS3a-β
5a-β
Pt−P
Pt−N
Pt−Si
Pt−C(α)
Pt−C(β)
C(α)−C(β)
2.326
2.392
3.683
2.058
2.070
1.298
2.322
3.421
3.590
2.107
2.099
1.271
2.312
5.007
3.566
2.136
2.114
1.263
2.303
4.535
2.694
2.010
3.135
1.235
2.374
4.889
2.352
1.979
3.201
1.225
2.375
3.788
2.349
1.978
3.199
1.225
2.343
2.451
2.367
1.996
3.219
1.224
2.315
2.410
3.757
2.112
2.016
1.300
2.326
3.800
3.585
2.120
2.102
1.267
2.312
5.022
3.575
2.133
2.110
1.264
2.303
5.116
2.712
2.007
3.134
1.236
2.368
5.111
2.354
1.979
3.202
1.225
2.488
3.388
2.385
1.916
3.136
1.224
2.444
2.279
2.429
1.948
3.169
1.223
a
C(α) and C(β) denote the α and β carbons of the SiR′3 group in 3a, respectively.
phosphorus, tends to dissociate from the platinum center. We
thus determined a 14-electron species to be the key part of the
transition state in C(sp)−Si bond cleavage. Selected bond
distances in each optimized structure are summarized in Table 6.
In comparison with representative atomic distances, the
root-mean-square deviation of 0.102 Å shows that the DFT-
optimized structures of the heavy atoms (not hydrogen) in
5a-α are in good agreement with its X-ray crystal structure.
The bond distance between platinum and the η2-coordinating
alkyne (Pt−C(α) and Pt−C(β)) becomes larger and the bond
between C(α) and C(β) atoms becomes shorter in the nitrogen
dissociation step (4a-α to 4a-α′or 4a-β to 4a-β′). These
changes indicate that π donation from the alkyne and/or π
back-donation from platinum become weaker during the course
of the nitrogen dissociation step. We discuss the latter issue in
more detail below. In addition, the Pt−Si bond distance also
becomes smaller in the same step, which implies that the
approach of the C(sp)−Si bond onto platinum had already
occurred.
We also found that the activation barrier to the dissociation of
nitrogen (4a-α to TS1a-α; 4a-β to TS1a-β) is comparatively
low (ΔΔG⧧: 7.4 kJ/mol for α selectivity; 14.7 kJ/mol for β
selectivity) and that the generation of the 14-electron species
4a-α′ or 4a-β′ is not favored by ΔH, but is favorable in terms
of ΔG. These features indicate that the dissociation of nitrogen
is an endothermic process, and thus spontaneous; therefore, it
readily takes place in situ.
Consequently, the subsequent C(sp)−Si bond activation step
requires a moderate (70−80 kJ/mol) activation energy. After
the C(sp)−Si bond is cleaved, the intermediates 5a-α′ and
5a-β′ show similar thermodynamic stabilities. However, the
consequent recoordination of nitrogen generates a large energy
difference; TS3a-β is presumed to be a destabilized state
because the recoordination and rearrangement of the coordina-
tion site of the monodentate phosphine ligand occur in concert.
In comparison with 5a-α, the generated 5a-β is also destabilized
due to the P−Pt−Si trans geometry caused by the thermo-
dynamic nature of transition metals, widely known as the trans
effect.21 The silyl group possessing the stronger trans effect
tends to locate at the trans position of the weakly coordinating
platinum−nitrogen bond.
As shown in Figure 4, the thermodynamic difference between
coordination modes (α and β manner) in η2-alkyne-
coordinating intermediates 4a-α and 4a-β is extremely small.
We also examined the possibility of the dissociation of the
phosphine moiety, and the optimized structure (4a′P‑diss) shows
a linear alkyne−Pt−N coordination geometry with a Pt−P
interaction (Figure 5). The relative energy of 4a′P‑diss is much
Figure 5. Two views of the optimized structure of 4a′P‑diss. Atomic
distances are shown in angstroms. Hydrogen atoms are omitted for
clarity.
higher than that of either 4a-α′ and 4a-β′. We thus concluded
that the dissociation of the nitrogen moiety is the sole driver
that generates the active 14-electron platinum complex.
To determine the origin of the thermodynamically unstable
configuration of complex 5a-β, we compared the relative
energies along each pathway. The results are shown in Figure 6.
The subsequent transition state TS3a-β involves not only a
coordinating nitrogen atom but also a rearrangement of the
coordination site of phosphorus from the trans position of
an alkynyl group to that of a silyl group. This rearrangement
could be observed in IRC analyses from TS3a-β. From these
Figure 4. Thermodynamic plots for C(sp)−Si bond cleavage of
alkynylsilane 3a relative to 1 + 2 + 3a (70 °C, in units of kJ/mol): (a)
enthalpies; (b) Gibbs energies.
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Figure 6. IRC processes from TS3a-β and the presumed transformation into 5a-β′. Hydrogen atoms are omitted for clarity. IRC analyzed values
relative to TS3a-β are shown.
investigations, after the C(sp)−Si bond activation, the re-
gioisomer of oxidative adduct 5a-β is disfavored because the
silyl group is situated in the position trans to the coordinating
phosphine.
We also examined the substituent effect of the aryl groups to
explain how electron-rich alkynylsilanes accelerate the C(sp)−
Si bond cleavage. Starting from 4a-α, 4h-α, and 4m-α, the
DFT results are shown in Figure 8. This thermodynamic plot
Theoretical Studies on the Substituent Effect. In
experiments, we observed that sterically hindered silyl
groups retarded the C(sp)−Si bond cleavage and electron-
rich alkynylsilane accelerated oxidative addition on C(sp)−Si
bonds. To explain this specific trend, we carried out theoretical
investigations of various alkynylsilanes 3. With regard to the sub-
stituent effect of silicon on the reactivity, as shown in Figure 7,
Figure 8. Computed Gibbs free energies (kJ/mol) for C(sp)−Si bond
cleavage of alkynylsilanes bearing various arylethynyl groups (SiR′3 =
TMS).
clearly shows that electron-rich alkynylsilanes stabilize both the
14-electron platinum(0) species 4-α′ and the transition states
in the C(sp)−Si bond cleavage through the transformation
from TS1-α to TS2-α. This can also be demonstrated by
comparing the activation energies for C(sp)−Si bond cleavage
(ΔΔG⧧: 79.7 kJ/mol for 3h (R = 4-O2NC6H4) vs 75.0 kJ/mol
for 3m (R = 4-Me2NC6H4)).
Figure 7. Computed Gibbs free energies (kJ/mol) for the C(sp)−Si
bond cleavage of alkynylsilanes bearing various silyl groups (R = Ph).
a triisopropylsilyl group caused remarkable thermodynamic
destabilization, in comparison to less bulky substituents such as
methyl and ethyl groups. These results unambiguously support
experimental observations showing no occurrence of C(sp)−Si
bond cleavage in the reaction with 3c. From the viewpoint of
the steric factor, the interaction between TIPS and diisopropyl-
phosphino groups would primarily affect the thermodynamic
stability. This trend is also observed in the reaction with 3b
(SiR′3 = TES); the transformation from 5-α′ to 5-α is found to
be destabilized, in comparison to that with 3a (SiR′3 = TMS).
Accordingly, the activation barriers (ΔΔG⧧) are 80.4 kJ/mol for
3a (SiR′3 = TMS) and 87.3 kJ/mol for 3b (SiR′3 = TES),
respectively. However, our kinetic observation indicates that
the reaction with 3b is twice as fast as that with 3a, which is
opposite to this energetic analysis. These results may be ascribed
to the extra isomerization pathway to 5-α. Actually, for 3b
(SiR′3 = TES), the relatively smaller activation barrier (ΔΔG⧧)
from 4-β′ to TS2-β is found to be 76.3 kJ/mol. Otherwise, an
electron-rich platinum(0) complex suppresses solvent coordi-
nation to the vacant site and renders the generation of the
resting state more difficult. Obviously, the latter reason must
be supported by the results of the solvent effect, as shown in
Table 4.
Origin of 14-Electron Platinum(0) Species. We have
found a novel 14-electron platinum(0) species produced by the
dissociation of nitrogen in the P−N ligand 2. Our observation
of this active species prompted additional research to develop
other transformations. Using DFT calculations, we examined
the charge transfers along the entire pathway of the C(sp)−Si
bond cleavage, dividing the complexes into several parts: the
platinum center, P−N ligand, silyl group, alkyne moiety, and
the phenyl group. As shown in Figure 9, the charge mainly
transfers from the alkyne moiety into the platinum center at
the dissociation of nitrogen (4a-α to 4a-α′). As a 14-electron
species, the electronically enriched platinum center is note-
worthy. From this observation, we found that π back-donation
from the platinum center to the alkyne moiety plays a key
role in generating the 14-electron platinum(0) species. As
speculated from the changes in bond lengths, to fulfill the
requirements of this structural arrangement, i.e. stretching the
platinum−alkyne bond and shortening the CC bond, the
electronically enriched platinum center is exclusively derived
from the degeneration of π back-donation. Thus, the weakened
π back-donation from platinum is required for the generation of
this 14-electron species. Meanwhile, an enriched P−N ligand is
derived from the bond dissociation. Followed by the C(sp)−Si
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Figure 9. Computed natural atomic charges around the C(sp)−Si
bond cleavage with the platinum(0)/PN complex and alkynylsilane 3a.
bond-cleavage step (i.e., 4a-α′ to 5a-α′), a charge transfer from
the alkyne moiety to the silyl group occurs. This series of
charge flows might be based on bond formation. Since the
alkynyl group (electronegativity (EN) of carbon: 2.55) has a
stronger electron-withdrawing propensity than the silyl group
(EN of Si: 1.90),22 the polarization of the C(sp)−Si bond is
canceled during bond cleavage. Finally, recoordination of
nitrogen (i.e., 5a-α′ to 5a-α) and charge transfer from the P−N
ligand to the silyl group take place. This is caused by the
formation of the platinum−nitrogen bond, and the charge is
accepted by the silyl group beyond the platinum center. This
trans-electronic effect in the platinum complexes is also supported
by our observations on the 31P{1H} NMR spectra.
MO Interaction between Platinum and Silicon. To
bring about C(sp)−Si bond cleavage, platinum migration from
the triple bond in alkynylsilanes 3 to a C(sp)−Si bond is
essential. We surveyed the origin of this transformation by
examining the MO interactions. From the energy diagram shown
in Figure 10, the HOMO of 4a-α′ is highly stabilized, and the
order of the MOs is inverted. In particular, the orbital coefficient
of HOMO-3 in TS2a-α was mainly distributed between the
inner 3d and 4d orbitals of platinum and the outer 3d orbital
of silicon. Such in-phase orbital interactions should cause
thermodynamic stabilization of the HOMO of 4a-α′. Inherently,
an η2-alkyne-coordinating platinum complex possesses a wide
overlap between platinum and the coordinating η2-alkyne in
HOMO-13. Thus, complex 4a-α′ naturally possesses a wide MO
interaction beyond the alkyne moiety.
Figure 10. (a) MO energy diagram going from 4a-α′ to TS2a-α.
Energies of each MO are shown in parentheses in eV. (b) Selected
MO drawings.
CONCLUSIONS
■
In this study, we have synthesized a series of alkynyl(silyl)-
platinum(II) complexes through the chemoselective C(sp)−Si
bond cleavage of alkynylsilanes. Experimental and theoretical
investigations have revealed the detailed reaction mechanisms.
The chemoselectivity is determined by the fast and quantitative
generation of the η2-alkyne-coordinating complex and the
subsequent thermodynamically favored platinum−silyl MO
interaction. The configuration of the Pt complexes is controlled
by the thermodynamic stability of the oxidative adducts, and this
result can also be understood from the trans effect in platinum(II)
complexes. The ligand for the C(sp)−Si bond cleavage must
form a hemilabile five-membered chelation. However, the P−N
chelation is highly distorted due to steric repulsion between
diisopropylphosphino and silyl groups. The dissociation of
nitrogen in the P−N ligand on a platinum center gives the
inherently electron deficient active 14-electron platinum complex.
Electron-rich alkynylsilanes can stabilize 14-electron species, and
C(sp)−Si bond cleavage is thereby accelerated. Nonpolar solvents
seem to be appropriate for C(sp)−Si bond cleavage, because they
are less able to form a strong coordination to vacant coordination
sites. Weakened π back-donation and an enriched platinum atom
are required for the generation of 14-electron platinum active
species on the pathway to C(sp)−Si bond cleavage.
Jones et al. have reported photochemically induced platinum-
mediated C(sp)−C(aryl) bond cleavage (eq 2).23 In this report,
they concluded that C(sp)−C(aryl) bond cleavage is thermo-
dynamically unfavorable and that the inverse reaction of
reductive elimination occurs under thermal conditions. Photo-
chemical bond cleavage is thought to proceed by utilizing the
LUMO. We also found that the LUMO of 4a-α′ possesses
an MO distribution delocalized among platinum, C(sp)−Si,
and C(sp)−C(aryl) bonds. Hence, we surmise that platinum
migration could occur in both C(sp)−Si and C(sp)−C(aryl)
bonds but that C(sp)−Si bond cleavage offers the most
favorable thermodynamic stabilization.
EXPERIMENTAL SECTION
■
General Considerations. All reactions were carried out under
an argon atmosphere using standard Schlenk techniques. Glassware
was dried in an oven (130 °C) and heated under reduced pressure
before use. Dehydrated toluene and deuterated benzene (C6D6) were
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2
i
1
purchased from Kanto Chemicals Co. Ltd. and CIL Chemicals Ltd.
Nuclear magnetic resonance (1H, 13C{1H}, 19F{1H}, 31P{1H} NMR)
spectra were measured on a spectrometer operating at 400 MHz (1H
NMR), 101 MHz (13C{1H} NMR), 376 MHz (19F{1H} NMR),
20.8 (d, br, JC−P = 5.6 Hz, Pr (−CH3)), 22.4 (d, JC−P = 24 Hz,
1 2
P−CH2−), 25.2 (d, with platinum satellites, JC−P = 27 Hz, JC−Pt
=
i
2
84 Hz, Pr (−CH−)), 48.7 (s, br, N−CH3), 61.4 (d, br, JC−P = 3.2 Hz,
N−CH2−), 103.0 (d, 3JC−P = 29.9 Hz, CC−Pt), 125.1 (s, m-Ph), 128.4
(s, p-Ph), 130.1 (d, 4JC−P = 3.4 Hz, ipso-Ph), 130.8 (d, 2JC−P = 132.5 Hz,
1
161 MHz (31P{1H} NMR), and 119 MHz (29Si{1H} NMR). All H
5
NMR chemical shifts were reported in ppm relative to the proton
resonance in C6D6 at δ 7.16. All 13C{1H} NMR chemical shifts were
reported in ppm relative to the carbon resonance in C6D6 at δ 128.06.
The 19F{1H} NMR chemical shifts were reported in ppm relative to an
external reference of trichlorofluoromethane at δ 0.00. The 31P{1H}
NMR chemical shifts were reported in ppm relative to an external
reference of phosphoric acid at δ 0.00.
Each single crystal of 5e-α, 5f-α, 5g-α, and 5l-α was glued to
the top of a glass fiber with epoxy resin, and X-ray diffraction data
were obtained at ambient temperature using a Rigaku SCXmini
CCD diffractometer with graphite-monochromated Mo Kα radiation
(λ = 0.71073 Å). The data were collected and processed using
the CrystalClear software package24 for all of the complexes, and
numerical absorption corrections were applied.25 The structures were
solved by direct methods (SHELXS9726) and refined by a full -matrix
least-squares method on F2 using the SHELXL97 software package.26
All non-hydrogen atoms were refined anisotropically, and hydrogen
atoms were placed at idealized positions by using riding models. All
calculations were performed with the CrystalStructure crystallographic
software package.27
Experimental Procedures and Spectroscopic Data. [(2-
Phenyl)ethynyl](trimethylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5a-α). In a 20 mL Schlenk tube,
bis(1,5-cyclooctadiene)platinum (1; 41 mg, 0.10 mmol) was dissolved
in toluene (1 mL). (Diisopropylphosphino)(dimethylamino)ethane
(2; 21 μL, 0.10 mmol) and 1-phenyl-2-(trimethylsilyl)ethyne (3a;
19 μL, 0.10 mmol) were added to this solution, and the mixture was
stirred at 70 °C. After 1 h, the solution was warmed to ambient
temperature, filtered with toluene (1 × 3 mL) via a cannula, and
transferred to another Schlenk tube. The combined brown filtrates
were evaporated in vacuo to give a brown solid. The crude product
was washed with hexane (1 × 3 mL) and dried under high vacuum,
affording the title compound 5a-α as an off-white powder (34 mg,
0.060 mmol, 60%). 1H NMR (C6D6, room temperature, 400 MHz): δ
CC−Pt), 131.6 (d, br, JC−P = 1.1 Hz, o-Ph). Anal. Calcd for
C24H44NPSiPt (600.76): C, 47.98; H, 7.38; N, 2.33. Found: C, 47.61; H,
7.02; N, 2.33.
[(2-Phenyl)ethynyl](dimethylphenylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5d-α). This compound was
obtained as a white powder. Yield: 72% (23 mg, 0.036 mmol (0.05
mmol scale)). 1H NMR (C6D6, room temperature, 400 MHz): δ 0.64
(dd, 3JH−P = 12.8 Hz, 3JH−H = 6.8 Hz, 6H, iPr (−CH3)), 0.88−0.93 (m,
2H, iPr (−CH−)), 0.97 (dd, 3JH−P = 17.2 Hz, 3JH−H = 7.2 Hz, 6H, iPr
3
(−CH3)), 1.10 (s, with platinum satellites, JH−Pt = 32.4 Hz, 6H,
3
SiMe2Ph (−CH3)), 1.44−1.53 (m, 2H, P−CH2−), 1.73 (dt, JH−P
=
3
18.4 Hz, JH−H = 6.6 Hz, 2H, N−CH2−), 2.43 (s, br, with platinum
3
satellites, 6H, N−CH3), 7.02 (t, JH−H = 7.4 Hz, 1H, p-Ph or
3
SiMe2Ph), 7.14 (t, JH−H = 8.0 Hz, 2H, m-Ph or SiMe2Ph), 7.18 (t,
3JH−H = 7.2 Hz, 1H, p-Ph or SiMe2Ph), 7.30 (t, JH−H = 7.4 Hz, 2H,
3
3
m-Ph or SiMe2Ph), 7.72 (d, JH−H = 8.4 Hz, 2H, o-Ph or SiMe2Ph),
8.06 (d, 3JH−H = 8.0 Hz, 2H, o-Ph or SiMe2Ph). 13C{1H} NMR (C6D6,
3
room temperature, 101 MHz): δ 6.3 (d, JC−P(cis) = 2.0 Hz, SiMe2Ph
2
i
(−CH3)), 17.8 (d, with platinum satellites, JC−P = 3.1 Hz, Pr
2
i
1
(−CH3)), 21.1 (d, JC−P = 6.0 Hz, Pr (−CH3)), 21.4 (d, JC−P
=
1
i
23 Hz, P−CH2−), 24.4 (d, JC−P = 28 Hz, Pr (−CH−)), 49.0 (s, br,
2
3
N−CH3), 61.7 (d, JC−P = 3.6 Hz, N−CH2−), 104.7 (d, JC−P = 29.8
Hz, CC−Pt), 125.3 (s, m- or p-Ph or SiMe2Ph), 127.2 (s, m- or p-Ph
or SiMe2Ph), 127.3 (s, m- or p-Ph or SiMe2Ph), 128.4 (s, m- or p-Ph or
SiMe2Ph), 131.7 (d, br, 5JC−P = 1.4 Hz, o-Ph), 129.9 (d, 4JC−P = 3.1 Hz,
2
ipso-Ph), 131.6 (d, JC−P = 131.4 Hz, CC−Pt), 135.1 (s, with
3
platinum satellites, SiMe2Ph (o-Ph)), 148.7 (d, JC−P(cis) = 2.8 Hz,
SiMe2Ph (ipso-Ph)). Anal. Calcd for C26H40NPSiPt (620.75): C,
50.31; H, 6.49; N, 2.26. Found: C, 50.50; H, 6.53; N, 2.21.
[(2-Phenyl)ethynyl](benzyldimethylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5e-α). This compound was
obtained as a white powder. Yield: 48% (30.5 mg, 0.048 mmol
(0.10 mmol scale)). 1H NMR (C6D6, room temperature, 400 MHz): δ
3
3
i
0.65 (dd, JH−P = 12.9 Hz, JH−H = 6.9 Hz, 6H, Pr (−CH3)), 0.70
3
3
i
3
0.76 (dd, JH−P = 12.9 Hz, JH−H = 6.9 Hz, 6H, Pr (−CH3)), 0.85 (s,
(s, with platinum satellites, 6H, SiMe2Bn (−CH3)), 0.78 (dd, JH−P
=
3
3
i
i
with platinum satellites, JH−Pt = 31 Hz, 9H, SiMe3(−CH3)), 0.98−
17.2 Hz, JH−H = 7.2 Hz, 6H, Pr (−CH3)), 0.89−0.94 (m, 2H, Pr
1.01 (m, 2H, iPr (−CH−)), 1.05 (dd, 3JH−P = 17.1 Hz, 3JH−H = 7.2 Hz,
3
(−CH−)), 1.61−1.69 (m, 2H, P−CH2−), 1.77 (dt, JH−P = 17.9 Hz,
i
3JH−H = 6.6 Hz, 2H, N−CH2−), 2.45 (s, br, with platinum satellites,
6H, Pr (−CH3)), 1.76−1.84 (m, 4H, PN ligand (−CH2−)), 2.43 (s,
br, with platinum satellites, 6H, N−CH3), 7.01 (t, 3JH−H = 7.3 Hz, 1H,
p-Ph), 7.13 (t, 3JH−H = 7.6 Hz, 2H, m-Ph), 7.73 (d, 3JH−H = 7.3 Hz, 2H,
o-Ph). 13C{1H} NMR (C6D6, room temperature, 101 MHz): δ 7.8 (d,
3
6H, N−CH3), 3.06 (s, br, with platinum satellites, 2H, JH−Pt = 27.3
3
Hz, SiMe2Bn(−CH2−)), 7.02 (t, JH−H = 7.4 Hz, 1H, p-Ph or
3
SiMe2Bn), 7.05 (t, JH−H = 7.4 Hz, 1H, p-Ph or SiMe2Bn), 7.13 (t,
2
3
3JH−H = 7.7 Hz, 2H, m-Ph or SiMe2Bn), 7.23 (t, JH−H = 7.6 Hz, 2H,
3
with platinum satellites, JC−Pt = 89.4 Hz, JC−P(cis) = 2.2 Hz,
2
3
SiMe3(−CH3)), 18.1 (d, br, with platinum satellites, JC−P = 2.6 Hz,
m-Ph or SiMe2Bn), 7.64 (d, JH−H = 7.3 Hz, 2H, o-Ph or SiMe2Bn),
iPr (−CH3)), 20.9 (d, br, 2JC−P = 5.8 Hz, iPr (−CH3)), 22.2 (d, 1JC−P
=
7.74 (d, 3JH−H = 7.2 Hz, 2H, o-Ph or SiMe2Bn). 13C{1H} NMR (C6D6,
1
2
3
23 Hz, P−CH2−), 24.9 (d, with platinum satellites, JC−P = 28 Hz,
room temperature, 101 MHz): δ 5.5 (d, JC−Pt = 91 Hz, JC−2P(cis)
3.0 Hz, SiMe2Bn (−CH3)), 18.0 (d, with platinum satellites, JC−P
i
=
=
2JC−Pt = 83 Hz, iPr (−CH−)), 48.9 (s, br, N−CH3), 61.4 (d, br, 2JC−P
=
3
3
i
2
3.6 Hz, N−CH2−), 103.8 (d, JC−P = 30.0 Hz, CC−Pt), 125.1 (s,
2.4 Hz, JC−Pt = 24 Hz, Pr (−CH3)), 20.4 (d, JC−P = 5.6 Hz, Pr
4
1
1
m-Ph), 128.4 (s, p-Ph), 130.1 (d, JC−P = 3.1 Hz, ipso-Ph), 131.5 (d,
(−CH3)), 22.2 (d, JC−P = 24 Hz, P−CH2−), 24.8 (d, JC−P = 28 Hz,
2JC−P = 131.8 Hz, CC−Pt), 131.7 (d, br, 5JC−P = 1.1 Hz, o-Ph). Anal.
2JC−Pt = 84 Hz, iPr (−CH−)), 33.7 (s, with platinum satellites, 2JC−Pt
=
2
Calcd for C21H38NPSiPt (558.68): C, 45.15; H, 6.86; N, 2.51. Found:
C, 44.88; H, 6.50; N, 2.29.
69 Hz, Bn (−CH2−)), 48.9 (s, br, N−CH3), 61.5 (d, JC−P = 3.2 Hz,
N−CH2−), 104.0 (d, 3JC−P = 30.0 Hz, CC−Pt), 123.0 (s, m- or p-Ph
or SiMe2Bn), 125.3 (s, m- or p-Ph or SiMe2Bn), 127.9 (s, m- or p-Ph
or SiMe2Bn), 128.5 (s, m- or p-Ph or SiMe2Bn), 129.5 (s, SiMe2Bn
(o-Ph)), 130.0 (d, 4JC−P = 3.1 Hz, ipso-Ph), 131.5 (d, 2JC−P = 131.5 Hz,
[(2-Phenyl)ethynyl](triethylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5b-α). This compound was
obtained as a white powder. Yield: 61% (37 mg, 0.061 mmol (0.10
1
5
mmol scale)). H NMR (C6D6, room temperature, 400 MHz): δ 0.76
CC−Pt), 131.6 (d, br, JC−P = 1.1 Hz, o-Ph), 145.3 (s, SiMe2Bn
3
3
i
(dd, JH−P = 12.9 Hz, JH−H = 6.9 Hz, 6H, Pr (−CH3)), 0.97−1.00 (m,
(ipso-Ph)). Anal. Calcd for C27H42NPSiPt (634.78): C, 51.09; H, 6.67;
N, 2.21. Found: C, 50.81; H, 6.56; N, 2.15.
i
3
3
i
2H, Pr (−CH−)), 1.06 (dd, JH−P = 16.9 Hz, JH−H = 7.2 Hz, 6H, Pr
(−CH3)), 1.29 (q, 3JH−H = 7.7 Hz, 6H, Et (−CH2−)), 1.48 (t, 3JH−H = 7.7
Hz, 9H, Et (−CH3)), 1.81 (m, 4H, PN ligand (−CH2−)), 2.44 (s, br,
with platinum satellites, 6H, N−CH3), 7.01 (t, 3JH−H = 7.4 Hz, 1H, p-Ph),
7.13 (t, 3JH−H = 7.4 Hz, 2H, m-Ph), 7.72 (d, 3JH−H = 7.0 Hz, 2H, o-Ph).
13C{1H} NMR (C6D6, room temperature, 101 MHz): δ 10.2 (d, with
[ ( 2 - P h e n y l ) e t h y n y l ] [ d i m e t h y l ( 2 - t h i e n y l ) s i l y l ] -
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5f-α).
This compound was obtained as a white powder. Yield: 69% (43.2 mg,
1
0.069 mmol (0.10 mmol scale)). H NMR (C6D6, room temperature,
3
3
i
400 MHz): δ 0.68 (dd, JH−P = 12.6 Hz, JH−H = 7.0 Hz, 6H, Pr
(−CH3)), 0.95−0.97 (m, 2H, iPr (−CH−)), 1.02 (dd, 3JH−P = 17.6 Hz,
2
3
platinum satellites, JC−Pt = 78 Hz, JC−P(cis) = 2.4 Hz, SiEt3(−CH2−)),
3JH−H = 7.6 Hz, 6H, Pr (−CH3)), 1.13 (s, with platinum satellites,
i
3
10.8 (s, with platinum satellites, JC−Pt = 33 Hz, SiEt3 (−CH3)), 18.1 (d,
2
3
i
with platinum satellites, JC−P = 2.4 Hz, JC−Pt = 26 Hz, Pr (−CH3)),
3JH−Pt = 31.6 Hz, 6H, SiMe2Th (−CH3)), 1.54−1.63 (m, 2H, P−CH2−),
1886
dx.doi.org/10.1021/om5002588 | Organometallics 2014, 33, 1878−1889

Organometallics
Article
3
3
1.77 (dt, JH−P = 18.4 Hz, JH−H = 6.7 Hz, 2H, N−CH2−), 2.44 (s, br,
13C{1H} NMR (C6D6, room temperature, 101 MHz): δ 7.6 (d, with
platinum satellites, 2JC−Pt = 89 Hz, 3JC−P(cis) = 2.4 Hz, SiMe3 (−CH3)),
18.0 (d, br, with platinum satellites, 2JC−P = 2.6 Hz, 3JC−Pt = 24 Hz, iPr
3
with platinum satellites, 6H, N−CH3), 7.01 (t, JH−H = 7.4 Hz, 1H,
p-Ph), 7.10−7.14 (m, 3H, m-Ph and 4-Th), 7.33 (d, 3JH−H = 4.4 Hz, 1H,
3- or 5-Th), 7.66 (d, 3JH−H = 3.2 Hz, 1H, 3- or 5-Th), 7.71 (d, JH−H
=
3
2
i
1
(−CH3)), 20.9 (d, br, JC−P = 5.6 Hz, Pr (−CH3)), 22.1 (d, JC−P
=
6.8 Hz, 2H, o-Ph). 13C{1H} NMR (C6D6, room temperature, 101 MHz):
1
23 Hz, P−CH2−), 25.0 (d, with platinum satellites, JC−P = 28 Hz,
2
3
2JC−Pt = 85 Hz, iPr (−CH−)), 48.9 (s, br, N−CH3), 61.4 (d, br, 2JC−P
=
δ 7.7 (d, with platinum satellites, JC−Pt = 88 Hz, JC−P(cis) = 2.1 Hz,
2
i
3
SiMe2Th (−CH3)), 18.0 (d, with platinum satellites, JC−P = 3.3 Hz, Pr
3.3 Hz, N−CH2−), 103.1 (d, JC−P = 31.1 Hz, CC−Pt), 121.5
(−CH3)), 21.3 (d, br, 1JC−P = 23 Hz, P−CH2−), 21.3 (d, br, 2JC−P = 5.8
4
3
(d, JC−P = 3.0 Hz, 1-trifluorophenyl), 125.3 (q, JC−F = 3.9 Hz,
Hz, iPr (−CH3)), 24.6 (d, with platinum satellites, 1JC−P = 29 Hz, 2JC−Pt
=
3-trifluorophenyl), 125.5 (q, 1JC−F = 271.5 Hz, CF35), 126.5 (q, 2JC−F
=
81 Hz, iPr (−CH−)), 49.1 (s, br, N−CH3), 61.8 (d, br, 2JC−P = 3.2 Hz,
32.1 Hz, 4-trifluorophenyl), 131.6 (d, br, JC−P = 1.3 Hz,
3
2-trifluorophenyl), 136.3 (d, JC−P = 131.2 Hz, CC−Pt). 19F{1H}
2
N−CH2−), 104.6 (d, JC−P = 29.6 Hz, CC−Pt), 125.3 (s, m-Ph),
127.6 (s, 4-Th or 5-Th), 128.4 (s, p-Ph), 128.6 (s, 4-Th or 5-Th), 129.5
NMR (C6D6, room temperature, 376 MHz): δ −61.9 (s). Anal. Calcd
for C22H37F3NPSiPt (626.68): C, 42.17; H, 5.95; N, 2.24. Found: C,
42.33; H, 5.82; N, 2.36.
2
4
(d, JC−P = 130.7 Hz, CC−Pt), 129.9 (d, JC−P = 3.2 Hz, ipso-Ph),
5
131.7 (d, br, JC−P = 1.1 Hz, o-Ph), 133.7 (s, with platinum satellites,
3-Th), 148.5 (s, 3JC−P(cis) = 2.9 Hz, 2-Th). Anal. Calcd for C24H38NPSSiPt
(626.78): C, 45.99; H, 6.11; N, 2.23. Found: C, 46.05; H, 6.21; N, 2.21.
(Propynyl)(trimethylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5g-α). This compound was
obtained as an off-white powder. Yield: 42% (41.7 mg, 0.084 mmol
[ 2 - ( 4 - C h l o r o p h e n y l ) e t h y n y l ] ( t r i m e t h y l s i l y l ) -
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5j-α).
This compound was obtained as a white powder. Yield: 22%
1
(6.5 mg, 0.011 mmol (0.05 mmol scale)). H NMR (C6D6, room
temperature, 400 MHz): δ 0.73 (dd, 3JH−P = 12.8 Hz, 3JH−H = 6.9 Hz,
1
i
3
(0.2 mmol scale)). H NMR (C6D6, room temperature, 400 MHz): δ
6H, Pr (−CH3)), 0.84 (s, with platinum satellites, JH−Pt = 31.0 Hz,
3
3
i
i
0.75 (dd, JH−P = 13 Hz, JH−H = 6.8 Hz, 6H, Pr (−CH3)), 0.85 (s,
9H, SiMe3 (−CH3)), 0.94−0.99 (m, 2H, Pr (−CH−)), 1.04 (dd,
3
i
3JH−P = 17.2 Hz, 3JH−H = 7.3 Hz, 6H, iPr (−CH3)), 1.71−1.82 (m, 4H,
with platinum satellites, JH−Pt = 31 Hz, 9H, TMS), 0.98 (m, 2H, Pr
(−CH−)), 1.05 (dd, 3JH−P = 17 Hz, 3JH−H = 7.2 Hz, 6H, iPr (−CH3)),
3
PN ligand (−CH2−)), 2.38 (s, br, 6H, N−CH3), 7.07 (d, JH−H = 8.7
5
3
1.75−1.82 (m, 4H, PN ligand (−CH2−)), 2.10 (d, br, JH−P(trans)
=
Hz, 2H, 2- or 3-C6H4), 7.47 (d, JH−H = 8.6 Hz, 2H, 2- or 3-C6H4).
13C{1H} NMR (C6D6, room temperature, 101 MHz): δ 7.7 (d, with
platinum satellites, 2JC−Pt = 89.8 Hz, 3JC−P(cis) = 2.1 Hz, CH3 (−CH3)),
18.1 (d, br, with platinum satellites, 2JC−P = 2.4 Hz, 3JC−Pt = 27 Hz, iPr
2.0 Hz, 3H, alkynyl Me (−CH3)), 2.43 (s, br, with platinum satellites,
3JH−Pt = 12 Hz, 6H, N−CH3). 13C{1H} NMR (C6D6, room temp-
erature, 101 MHz): δ 6.6 (d, 4JC−P(trans) = 3.0 Hz, alkynyl Me(−CH3)),
2
3
2
i
1
7.9 (d, with platinum satellites, JC−Pt = 94 Hz, JC2−P(cis) = 2.4 Hz,
SiMe3 (−CH3)), 18.1 (d, with platinum satellites, JC−P = 2.4 Hz,
3JC−Pt = 25 Hz, iPr (−CH3)), 20.9 (d, br, 2JC−P = 5.9 Hz, iPr (−CH3)),
(−CH3)), 20.9 (d, br, JC−P = 5.8 Hz, Pr (−CH3)), 22.2 (d, JC−P
=
1
23 Hz, P−CH2−), 24.9 (d, with platinum satellites, JC−P = 28 Hz,
2JC−Pt = 86 Hz, iPr (−CH−)), 48.9 (s, br, N−CH3), 61.4 (d, br, 2JC−P
=
1
3
22.2 (d, JC−P = 23 Hz, P−CH2−), 24.8 (d, with platinum satellites,
3.4 Hz, N−CH2−), 102.7 (d, JC−P = 29.9 Hz, CC−Pt), 128.2
1JC−P = 28 Hz, JC−Pt = 83 Hz, Pr (−CH−)), 48.8 (s, with platinum
2
i
4
(d, JC−P = 5.0 Hz, 1-chlorophenyl), 128.6 (s, 3-chlorophenyl), 130.8
2
5
satellites, JC−Pt = 13 Hz, N−CH3), 61.4 (d, with platinum satellites,
(s, 4-chlorophenyl), 132.8 (d, br, JC−P = 1.3 Hz, 2-chlorophenyl),
2JC−P = 3.5 Hz, N−CH2−), 96.6 (d, JC−P(trans) = 31 Hz, CC−Pt),
3
2
133.0 (d, JC−P = 132.0 Hz, CC−Pt). Anal. Calcd for
2
115.8 (d, JC−P(trans) = 133 Hz, CC−Pt). Anal. Calcd for
C21H37ClNPSiPt (593.12): C, 42.53; H, 6.29; N, 2.36. Found: C,
42.42; H, 6.31; N, 2.35.
C16H36NPSiPt (496.61): C, 38.70; H, 7.31; N, 2.82. Found: C,
38.39; H, 7.35; N, 2.75.
[ 2 - ( 4 - M e t h y l p h e n y l ) e t h y n y l ] ( t r i m e t h y l s i l y l ) -
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5k-α).
This compound was obtained as a white powder. Yield: 49% (56.6
mg, 0.099 mmol (0.2 mmol scale)). 1H NMR (C6D6, room temperature,
[2-(4-Nitrophenyl)ethynyl](trimethylsilyl)[(diisopropylphosphino)-
(dimethylamino)ethane]platinum (5h-α). This compound was
obtained as a brown powder. Yield: 58% (70.0 mg, 0.116 mmol
1
3
3
i
(0.2 mmol scale)). H NMR (C6D6, room temperature, 400 MHz): δ
400 MHz): δ 0.76 (dd, JH−P = 12.8 Hz, JH−H = 7.2 Hz, 6H, Pr
(−CH3)), 0.86 (s, with platinum satellites, 3JH−Pt = 30.0 Hz, 9H, SiMe3
(−CH3)), 0.97−1.01 (m, 2H, iPr (−CH−)), 1.06 (dd, 3JH−P = 17.0 Hz,
3
3
i
0.75 (dd, JH−P = 12.6 Hz, JH−H = 6.6 Hz, 6H, Pr (−CH3)), 0.78 (s,
3
with platinum satellites, JH−Pt = 29.6 Hz, 9H, SiMe3 (−CH3)), 0.86−
0.92 (m, 2H, iPr (−CH−)), 1.02 (dd, 3JH−P = 17.4 Hz, 3JH−H = 7.4 Hz,
3JH−H = 7.4 Hz, 6H, Pr (−CH3)), 1.76−1.84 (m, 4H, PN ligand
i
i
6H, Pr (−CH3)), 1.74−1.84 (m, 4H, PN ligand (−CH2−)), 2.36 (s,
(−CH2−)), 2.09 (s, 3H, Me (−CH3)), 2.44 (s, br, 6H, N−CH3), 6.96
(d, 3JH−H = 8.0 Hz, 2H, 2- or 3-C6H4), 7.68 (d, 3JH−H = 7.6 Hz, 2H, 2- or
3-C6H4). 13C{1H} NMR (C6D6, room temperature, 101 MHz): δ 7.8
br, 6H, N−CH3), 7.36 (d, 3JH−H = 8.8 Hz, 2H, 2- or 3-C6H4), 7.87 (d,
3JH−H = 8.8 Hz, 2H, 2- or 3-C6H4). 13C{1H} NMR (C6D6, room
2
2
3
temperature, 101 MHz): δ 7.5 (d, with platinum satellites, JC−Pt
=
(d, with platinum satellites, JC−Pt = 91.1 Hz, JC−P(cis) = 2.5 Hz, SiMe3
3
2
87 Hz, JC−P(cis) = 2.3 Hz, SiMe3 (−CH3)), 18.1 (d, br, with platinum
(−CH3)), 18.1 (d, br, with platinum satellites, JC−P = 2.4 Hz,
2
3
i
iPr(−CH3)), 20.9 (d, br, JC−P = 6.0 Hz, Pr (−CH3)), 21.4 (s, Me
2
i
satellites, JC−P = 2.6 Hz, JC−Pt = 19 Hz, Pr (−CH3)), 20.9 (d, br,
2JC−P = 5.5 Hz, Pr (−CH3)), 22.1 (d, JC−P = 24 Hz, P−CH2−), 25.0
i
1
1
(−CH3)), 22.2 (d, JC−P = 23 Hz, P−CH2−), 24.9 (d, with platinum
1
2
i
1
2
i
(d, with platinum satellites, JC−P = 29 Hz, JC−Pt = 83 Hz, Pr
satellites, JC−P = 28 Hz, JC−Pt = 84 Hz, Pr (−CH−)), 48.9 (s, br,
2
2
3
(−CH−)), 48.9 (s, br, N−CH3), 61.4 (d, br, JC−P = 3.0 Hz,
N−CH3), 61.4 (d, br, JC−P = 3.4 Hz, N−CH2−), 103.7 (d, JC−P
=
3
4
N−CH2−), 103.8 (d, JC−P = 29.6 Hz, CC−Pt), 123.8 (s,
30.0 Hz, CC−Pt), 127.2 (d, JC−P = 3.2 Hz, 1-methylphenyl), 129.1
5
2
3-nitrophenyl), 131.6 (d, JC−P = 1.1 Hz, br, 2-nitrophenyl), 136.7
(s, 3-methylphenyl), 130.2 (d, JC−P = 132.0 Hz, CC−Pt), 131.6 (d,
4
2
5
(d, JC−P = 3.1 Hz, 1-nitrophenyl), 142.6 (d, JC−P = 130.7 Hz,
CC−Pt), 144.9 (s, 4-nitrophenyl). Anal. Calcd for C21H37N2O2-
PSiPt (603.68): C, 41.78; H, 6.18; N, 4.64. Found: C, 41.74; H, 5.78;
N, 4.39.
[2-(4-(Trifluoromethyl)phenyl)ethynyl](trimethylsilyl)-
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5i-α).
This compound was obtained as a white powder. Yield: 22%
br, JC−P = 1.1 Hz, 2-methylphenyl), 134.4 (s, 4-methylphenyl). Anal.
Calcd for C22H40NPSiPt (572.71): C, 46.14; H, 7.04; N, 2.45. Found: C,
46.16; H, 6.76; N, 2.67.
[ 2 - ( 4 - M e t h o x y l p h e n y l ) e t h y n y l ] ( t r i m e t h y l s i l y l ) -
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5l-α).
This compound was obtained as a white powder. Yield: 19% (22.7
mg, 0.039 mmol (0.2 mmol scale)). 1H NMR (C6D6, room temperature,
1
3
3
i
(27.4 mg, 0.044 mmol (0.2 mmol scale)). H NMR (C6D6, room
400 MHz): δ 0.76 (dd, JH−P = 12.4 Hz, JH−H = 6.8 Hz, 6H, Pr
(−CH3)), 0.89 (s, with platinum satellites, 3JH−Pt = 28.8 Hz, 9H, SiMe3
(−CH3)), 0.97−1.00 (m, 2H, iPr (−CH−)), 1.06 (dd, 3JH−P = 17.0 Hz,
temperature, 400 MHz): δ 0.73 (dd, 3JH−P = 12.8 Hz, 3JH−H = 6.8 Hz,
i
3
6H, Pr (−CH3)), 0.83 (s, with platinum satellites, JH−Pt = 30.4 Hz,
i
3JH−H = 7.0 Hz, 6H, Pr (−CH3)), 1.75−1.83 (m, 4H, PN ligand
i
9H, SiMe3 (−CH3)), 0.94−0.98 (m, 2H, Pr (−CH−)), 1.03 (dd,
3JH−P = 17.2 Hz, 3JH−H = 7.2 Hz, 6H, iPr (−CH3)), 1.72−1.81 (m, 4H,
(−CH2−)), 2.45 (s, br, 6H, N−CH3), 3.27 (s, 3H, OMe (−OCH3)),
6.75 (d, 3JH−H = 8.4 Hz, 2H, 2- or 3-C6H4), 7.68 (d, 3JH−H = 8.4 Hz, 2H,
2- or 3-C6H4). 13C{1H} NMR (C6D6, room temperature, 101 MHz):
PN ligand (−CH2−)), 2.38 (s, br, 6H, N−CH3), 7.29 (d, 3JH−H = 8.4
3
Hz, 2H, 2- or 3-C6H4), 7.54 (d, JH−H = 8.0 Hz, 2H, 2- or 3-C6H4).
1887
dx.doi.org/10.1021/om5002588 | Organometallics 2014, 33, 1878−1889

Organometallics
Article
δ 6.3 (d, 3JC−P(cis) = 2.0 Hz, SiMe3 (−CH3)), 17.8 (d, br, 2JC−P = 3.1 Hz,
ACKNOWLEDGMENTS
■
iPr (−CH3)), 21.1 (d, br, 2JC−P = 6.0 Hz, iPr (−CH3)), 21.4 (d, 1JC−P
=
This work was partially supported by the program for promoting
the enhancement of research universities (Okayama University)
and a Grant-in-Aid for Scientific Research on Innovative Areas
“Molecular Activation Directed toward Straightforward Synthesis”,
No. 23105507 from MEXT to S.M. The authors gratefully thank
Ms. Megumi Kosaka and Mr. Motonari Kobayashi at the
Department of Instrumental Analysis, Advanced Science Research
Center, Okayama University, for the elemental analyses and the
SC-NMR Laboratory of Okayama University for the NMR
spectral measurements. The generous allotment of computation
time from the Research Center for Computational Science
(RCCS), the National Institutes of Natural Sciences of Japan, is
also gratefully acknowledged.
1
i
23 Hz, P−CH2−), 24.4 (d, with platinum satellites, JC−P = 28 Hz, Pr
(−CH−)), 49.0 (s, br, N−CH3), 61.7 (d, br, 2JC−P = 3.6 Hz, N−CH2−),
3
104.7 (d, JC−P = 29.8 Hz, CC−Pt), 125.3 (s, 3-methoxyphenyl),
2
4
129.9 (d, JC−P = 131.6 Hz, CC−Pt), 129.9 (d, JC−P = 3.1 Hz,
5
1-methoxyphenyl), 131.7 (d, br, JC−P = 1.4 Hz, 2-methoxyphenyl),
135.1 (s, 4-methoxyphenyl). Anal. Calcd for C22H40NOPSiPt (588.71):
C, 44.89; H, 6.85; N, 2.38. Found: C, 44.73; H, 6.49; N, 2.18.
[2-(4-(N,N-Dimethylamino)phenyl)ethynyl](trimethylsilyl)-
[(diisopropylphosphino)(dimethylamino)ethane]platinum (5m-α).
This compound was obtained as an off-white powder. Yield: 56%
1
(67.9 mg, 0.113 mmol (0.2 mmol scale)). H NMR (C6D6, room
temperature, 400 MHz): δ 0.79 (dd, 3JH−P = 13.0 Hz, 3JH−H = 7.0 Hz,
i
3
6H, Pr (−CH3)), 0.88 (s, with platinum satellites, JH−Pt = 30.4 Hz,
i
9H, SiMe3 (−CH3)), 1.02−1.03 (m, 2H, Pr (−CH−)), 1.09 (dd,
3JH−P = 17.0 Hz, 3JH−H = 7.4 Hz, 6H, iPr (−CH3)), 1.78−1.88 (m, 4H,
PN ligand (−CH2−)), 2.49 (s, br, 6H, N−CH3), 2.50 (s, 6H, NMe2
(−CH3)), 6.55 (d, 3JH−H = 8.8 Hz, 2H, 2- or 3-C6H4), 7.70 (d, 3JH−H
=
REFERENCES
■
8.8 Hz, 2H, 2- or 3-C6H4). 13C{1H} NMR (C6D6, room temperature,
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101 MHz): δ 7.9 (d, with platinum satellites, JC−Pt = 90.5 Hz,
3JC−P(cis) = 2.4 Hz, SiMe3 (−CH3)), 18.2 (d, br, with platinum satellites,
2JC−P = 2.4 Hz, iPr (−CH3)), 20.9 (d, br, 2JC−P = 5.8 Hz, iPr (−CH3)),
1
22.4 (d, JC−P = 23 Hz, P−CH2−), 24.9 (d, with platinum satellites,
1JC−P = 28 Hz, 2JC−Pt = 83 Hz, iPr (−CH−)), 40.4 (s, NMe2 (−CH3),
49.0 (s, br, N−CH3), 61.5 (d, br, 2JC−P = 3.5 Hz, N−CH2−), 103.9 (d,
3JC−P = 30.3 Hz, CC−Pt), 113.0 (s, 3-(N,N′-dimethylamino)-
4
phenyl), 118.6 (d, JC−P = 3.4 Hz, 1-(N,N′-dimethylamino)phenyl),
2
5
127.5 (d, JC−P = 132.4 Hz, CC−Pt), 132.5 (d, br, JC−P = 1.2 Hz,
2-(N,N′-dimethylamino)phenyl), 143.6 (s, 4-(N,N′-dimethylamino)-
phenyl). Anal. Calcd for C23H43N2PSiPt (601.75): C, 45.91; H, 7.20;
N, 4.66. Found: C, 45.77; H, 6.83; N, 4.45.
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in C6D6 (600 μL) in an NMR tube were added P−N ligand (11 μL,
0.05 mmol) and alkynylsilanes 3a−m (0.05 mmol). The time-
dependent transformation at 30 °C was determined by integration of
31P{1H} NMR signals after 1, 2, 3, and 6 h (in the case of alkynylsilane
3m, data were recorded after 15, 30, 45, and 60 min).
Computational Methodology. All calculations in the present
study were performed with the Gaussian 09 program28 and by using the
Becke three-parameter plus Lee−Yang−Parr (B3LYP) density func-
tional theory (DFT) method.29 For all geometry optimizations and
normal-coordinate analyses at stationary points, we used the Stuttgart−
Dresden−Cologne (SDD) effective core potential and corresponding
basis set for Pt30 and 6-311G(d) for the others.31 For the correction of
solvation, the polarizable continuum model (PCM)32,33 with a dielectric
constant of 2.3741 (toluene) was also used. Thermal enthalpies and
Gibbs free energies were calculated at a temperature of 343.15 K
(70 °C) and at a pressure of 1 atm. Intrinsic reaction coordinate (IRC)
analyses34−36 from saddle points (transition states) to minima
(reactants, intermediates, and products) were used for confirming the
reaction pathways. Natural population analysis was performed to
examine atomic charges.37
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ASSOCIATED CONTENT
■
S
* Supporting Information
Text, tables, figures, and CIF files giving experimental details,
scanned NMR spectra of all new complexes, crystallographic
data for complexes 5e-α, 5f-α, 5g-α, and 5l-α, and computa-
tional details. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Y.N.: fax, +81-86-251-7855; e-mail, ynishiha@okayama-u.ac.jp.
Notes
The authors declare no competing financial interest.
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