Regio- and stereoselective addition of trans-Pt(TeAr)(SiMe3)(PEt3)2 to terminal alkynes leading to cis-[(Z)-β-trimethylsilylalkenyl]platinum(II) complexes

Article abstract of DOI:10.1002/hc.21463

Selective insertion of terminal alkynes RC≡CH into the Si—Pt bond of trans-Pt(TeAr)(SiMe₃)(PEt₃)₂ took place readily to produce the corresponding novel alkenyl complexes cis-Pt(TeAr)[(Z)-CR=CHSiMe₃](PEt₃)₂. The structure of the complex was characterized by an X-ray analysis.

Full text of DOI:10.1002/hc.21463

Received: 28 September 2018
DOI: 10.1002/hc.21463
Revised: 14 November 2018
Accepted: 15 November 2018
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S P E C I A L I S S U E A R T I C L E
Regio- and stereoselective addition of trans-Pt(TeAr)(SiMe3)
(PEt3)2 to terminal alkynes leading to
cis-[(Z)-β-trimethylsilylalkenyl]platinum(II) complexes
Li-Biao Han
Farzad Mirzaei
Shigeru Shimada
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National Institute of Advanced Industrial
Science and Technology, Tsukuba, Ibaraki,
Japan
Abstract
Selective insertion of terminal alkynes RC≡CH into the Si—Pt bond of trans-
Pt(TeAr)(SiMe3)(PEt3)2 took place readily to produce the corresponding novel alk-
enyl complexes cis-Pt(TeAr)[(Z)-CR=CHSiMe3](PEt3)2. The structure of the
complex was characterized by an X-ray analysis.
Correspondence
Li-Biao Han, National Institute of Advanced
Industrial Science and Technology,
Tsukuba, Ibaraki, Japan.
Email: libiao-han@aist.go.jp
process are often more complicated and elaborate. Silyl
chalcogenides ArESiX3 (E = S, Se) were able to add to
1
INTRODUCTION
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Metal-catalyzed addition of heteroatom compounds to
unsaturated carbon—carbon bonds is one of the most
straightforward way for the synthesis of new heteroatom
chemicals.[1] These reactions are generally envisaged to
occur via a catalytic cycle consisting of three elemental
steps which are of equal importance: (a) oxidative addition
of a heteroatom-containing bond to the metal, (b) insertion
of a carbon—carbon unsaturated bond to the metal—he-
teroatom bond and (c) reductive elimination forming the
adduct.[1] The first step of the catalytic cycle has been rel-
atively well studied especially when the adduct generated
from the oxidative addition step is isolable. On the other
hand, studies dealing with step (ii) or (iii) of the catalytic
acetylenes in the presence of platinum or palladium cata-
lysts to give the cis adducts with the ArE moiety bound to
the internal carbons of the acetylenes.[2] These reactions
also appear to proceed via similar mechanistic sequences
(Scheme 1), since the generation of R3Si[M]EAr (1) by the
oxidative addition of the Si—chalcogen bond to the metal
has been well established.[3] However, limited information
is available about the events that follow the oxidative addi-
tion. Intermediate 1 can add to an alkyne either at the Si—
Pt bond forming 2 or at the E—Pt bond forming 2′, both
will give the same final product eventually. An attempted
detection of these alkenylplatinum species in order to dis-
tinguish the two possibilities had not succeeded.
R
[M]
+
R
ArESiX3
ArE
SiX3
[M]
R
R
R
ArE[M]SiX3
or
SiX3
ArE
[M]SiX3
1
ArE[M]
M = Pd, Pt; E = S, Se
2
2'
SCHEME 1 Metal-mediated selective addition of ArESiX3 to alkynes
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Heteroatom Chemistry. 2018;e21463.
https://doi.org/10.1002/hc.21463
wileyonlinelibrary.com/journal/hc
© 2018 Wiley Periodicals, Inc.
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Herein, we report that trans-Pt(TeAr)(SiMe3)(PEt3)2 (3)
reacts with a terminal alkyne at the Si—Pt bond to afford an
alkenylplatinum complex 4.[4] One of such a complex 4b was
full characterized by X-ray analysis (Chart 1).
2
RESULTS AND DISCUSSION
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CHART 1 Structures of the Pt-complexes
Tocomplex3a,quantitativelygeneratedbytreatingPhTeSiMe3
(0.59 mmol) with Pt(PEt3)4 (0.16 mmol) at room temperature
for 10 minutes in dry degassed benzene-d6 (0.50 mL),[3] was
added 1-octyne (0.40 mmol) and the solution was heated at
1
50°C for 5 hours. H NMR spectroscopy of the resulted pale
yellow solution showed that 3a was completely consumed
to generate a new complex 4a in 87% yield (Equation 1).
Pumping off the starting materials and other volatiles under
high vacuum at room temperature left a pale yellow oil. 31P
NMR spectroscopy confirmed the cis configuration at the plat-
inum center; two phosphorus atoms are observed at δ −5.21
(JPP 16.3, JPPt 3290 Hz) and δ 0.57 (JPP 16.3, JPPt 1627 Hz),
both as doublets. The regio- and stereochemistry concerning
the carbon—carbon double bond of 4a was also easily de-
duced from its 13C and 1H NMR spectra; first, the olefinic car-
bon directly bound to platinum (δ 175.1, JCP 9.0 and 97.6 Hz,
JCPt 645.6 Hz) is a quaternary carbon, as indicated by a DEPT
(θ = 135°) experiment. Secondly, the olefinic proton signal
centered at δ 6.59 (JHP 23.6, JHPt 87.2 Hz) is a doublet due
to the coupling with phosphorus and displays satellite bands
with a large coupling constant with platinum, characteristic of
olefinic protons trans to platinum.[5] The two allylic protons
are not equivalent in 1H NMR spectroscopy, displaying signals
at 2.34 and 2.67 ppm, respectively. An NOE experiment by
irradiation at the δ 2.67 signal resulted in a 3.4% enhancement
of the olefinic proton signal at δ 6.59, which further substanti-
ates the Z configuration of the double bond being generated
through the cis-addition of the Pt-Si bond.
H 1
C
C
2
P 1
1
S i
Et3P
Et3P
T e
Pt
SiMe3
P t
TePh
P 2
FIGURE 1 Molecular structure of complex 4b. Selected
distances (Å) and angles (°): Pt—Te 2.645(5), Pt—P(1) 2.278(3),
Pt—P(2) 2.351(3), Pt—C(2) 2.14(1), Si—Tc 3.75(2); Te—Pt—P(1)
164.4(1), P(2)—Pt—C(2) 172.2(3), Tc—Pt—P(2) 94.3(9), Te—Pt—
C(2) 78.5(8), C(2)—Pt—P(1) 87.5(3), P(1)—Pt—P(2) 94.3(9), Te—
Pt—C(2) 78.5(8), C(2)—Pt—P(1) 87.5(3), P(1)—Pt—P(2) 99.7(1)
X-ray analysis of 4b unambiguously confirmed its cis con-
figuration at platinum and the regio- and stereochemistry at
the double bond (Figure 1).a
Platinum complex 4b has a distorted square-planar struc-
ture with bond angles of Te—Pt—P(1) and P(2)—Pt—C(2)
Other terminal alkynes such as phenylacetylene,
3-phenyl-1-propyne reacted similarly with 3 to give the cor-
responding alkenylplatinum complexes. Disappointingly,
however, all of these products were oil. On the other hand,
an internal alkyne, diphenylacetylene did not undergo the
addition reaction with 3a at all. After extensive trials and
errors, very fortunately, we finally succeeded in obtaining a
aCrystal data for 4b: C28H56P2PtSiTe, M = 805.47, monoclinic, space group
P21/n(#14), a = 10.025(2), b = 20.174(2), c = 17.053(2) Å, β = 96.88 (1)°,
V = 3424.1(8) Å3, T = −120.0°C, Z = 4, Dc = 1.562 g/cm3, μ = 50.59 cm−1
,
6722 reflections measured, 4929 observed [I > 3σ(I)], 273 parameters.
Empirical absorption corrections (ψscan) were applied. Final R fac-
tor = 0.063, Rw = 0.103. The PhTe group was disordered into two positions.
Average values of distances and angles containing Te were shown in
Figure 1. CCDC171714 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.ccdc.cam.
ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033;
or deposit@ccdc.cam.ac.uk).
crystalline
product.
Thus,
treating
3a
with
4,4-dimethyl-1-pentyne followed by recrystallization from
pentane (0.5 mL), a pale yellow crystal of alkenylplatinum
complex 4b suitable for X-ray analysis was obtained! The

HAN et Al.
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being 164.4(1) and 172.2(3), respectively. The bond distances
of Pt—P(1) and Pt—P(2) are 2.278(3) and 2.351(3) Å, re-
spectively, reflecting the stronger trans influence of the alke-
nyl group as compared to TePh.[6]
the reaction was run in the presence of an additional PEt3 (1.5
equiv relative to 3b) under otherwise identical conditions, ca.
20% of 3b remained unreacted and 4c was formed in only 58%
NMR yield. This result resembles the behavior of bissilylplati-
num complexes[4] and may suggest that the alkyne insertion to
the Si—Pt bond of 3 proceeds via a three-coordinate platinum
species generated by the dissociation of a PEt3 ligand. In agree-
ment with this assumption, Pt(TePh)(SiMe3)(dmpe) [6, dmpe
= 1,2-bis(dimethylphosphino)ethane] bearing a tightly chelat-
ing phosphine ligand did not undergo such an insertion reaction
with 1-octyne at 50°C.b
Finally, it is noted that when the reaction shown in
Equation 1 was further continued at an elevated temperature
(110°C, 6 hours), 4a completely disappeared to reductively
eliminate vinyl telluride 7b in 67% yield based on 3a used.
This result together with the others herein described inti-
mates the possibility of a catalytic addition of silyl tellurides
to alkynes, which has never been realized so far. Studies
along this line are in progress.c
The stable cis geometry of organotelluroplatinum species
such as 4 is unusual since all other PtR(TeR’)(PEt3)2-type
complexes so far obtained adopt trans geometry.[3,6] Although
cis-PtPh(Tei-Pr)(PEt3)2 could be observed at the beginning of
the reaction of i-PrTePh with Pt(PEt3)[3,6] this complex was
not stable and isomerized quickly to its trans isomer even at
room temperature. A possible driving force for this remark-
able feature of 4 preferring the cis geometry may come from
an interaction between tellurium and silicon.[7] Indeed, the
molecular structure of 4b has revealed the distance between
silicon and tellurium is 3.990(7) Å, which is shorter than the
sum of their van der Waals radii 4.16 Å,[8] indicating such an
interaction.
A careful analysis of the reaction between complex 3b[3]
and 1-octyne revealed a more detailed process of the alkyne
insertion. Thus, 3b (40 mg) was allowed to react with 1-octyne
3
CONCLUSION
(1.5 equiv.) in benzene-d6, at 25°C for 1 hour. NMR spectros-
copy showed no insertion took place at all. However, the for-
mation of ArTeSiMe3 (3b/ArTeSiMe3 = 70/30) and an
equivalent amount alkyne-platinum complex 5 were observed,
indicating an equilibrium as illustrated in Equation 2.b
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A Pt(0) complex easily oxiditively inserts to the Te-Si bond
of ArTeSiMe3 compound to generate a complex bearing a
Subsequent heating of the solution at 50°C for 2.5 hours re-
sulted in a complete consumption of 3b, affording the Si-Pt addi-
tion product 4c in 87% NMR yield. This insertion was retarded,
though not completely, by the addition of free PEt3. Thus, when
backbone of Si-Pt-Te bond. This Si-Pt-Te complex adds to a
terminal alkyne by the selective cis-addition of the Si-Pt bond
(not the Te-Pt bond) to the triple bond to give a new complex
with the Si moiety bonding to the terminal carbon and the Pt
moiety bonding to the internal carbon. Upon heating the new
complex at an elevated temperature, the corresponding cis-
alkenylteruride is obtained.
bSelected NMR data for 5, 6 and 7. 5: 31P NMR (C6D6) δ 16.5 (JPP = 39.2,
JPPt = 3459 Hz), 13.1 (JPP 39.2, JPPt 3243 Hz). 6 (CDCl3): 1H NMR δ 7.89–
7.91 (m, 2 H), 7.12–7.14 (m, 1 H), 6.98–7.00 (m, 2 H), 1.68 (d, 6 H, JHP 9.7,
JHPt 38.2 Hz), 1.59–1.65 (m, 2 H), 1.40–1.45 (m, 2 H), 0.99 (d, 6 H, JHP 8.2,
JHPt 15.3 Hz), 0.33 (s, 9 H, JHPt 17.7 Hz); 31P NMR δ 34.6 (d, JPP 6.2 Hz, JPPt
1313.5 Hz), 24.7 (d, JPP 6.2 Hz, JPPt 2963.7 Hz). 7 (CDCl3): 1H NMR δ
7.74–7.76 (m, 2 H), 7.20–7.31 (m, 3 H), 6.55 (s, 1 H, JHTe 72.8 Hz), 2.29 (t,
cPartial of this work was first disclosed in the XIXth Internatinal Conferenve
on Organometallic Chemistry, Shanghai, July, 2000. A catalytic addition of
PhTeTMS to acetylenes has not been achieved yet, partly due to the decom-
position of the current Te-Pt complexes that leads to the deactivation of the
catalyst (ref 3). The reason for the regioselectivity of complex 3 with a ter-
minal alkyne generating complex 4 was not clear, though a steric repulsion
of the bulky TMS group may play a crucial role.
2 H, J 7.7 Hz), 1.17–1.48 (m, 8 H), 0.86 (t, 3 H, J 7.4 Hz), 0.22 (s, 9 H); 13
C
NMR δ 141.0, 140.9, 138.8, 129.2, 127.7, 114.0, 46.7, 31.7, 29.6, 28.3, 22.6,
14.1, −0.10; 29Si NMR δ −8.14; 125Te NMR δ −370.4.

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ACKNOWLEDGEMENT
We thank Professor Masato Tanaka for useful discussions.
ORCID
Li-Biao Han
https://orcid.org/0000-0001-5566-9017
[5] H. C. Clark, G. Ferguson, A. B. Goel, E. G. Janzen, H. Ruegger, P.
Y. Siew, C. S. Wong, J. Am. Chem. Soc., 1986, 108, 6961.
[6] L.-B. Han, N. Choi, M. Tanaka, J. Am. Chem. Soc. 1997, 119,
1795.
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How to cite this article: Han L-B, Mirzaei F,
Shimada S. Regio- and stereoselective addition of
trans-Pt(TeAr)(SiMe3)(PEt3)2 to terminal alkynes
leading to cis-[(Z)-β-trimethylsilylalkenyl]platinum(II)
complexes. Heteroatom Chem. 2018;e21463. https://
doi.org/10.1002/hc.21463
[2] A. Ogawa, H. Kuniyasu, M. Takeba, T. Ikeda, N. Sonoda, T. Hirao,
J. Orgnomet. Chem., 1998, 564, 1; L.-B. Han, M. Tanaka, J. Am.
Chem. Soc., 1998, 120, 8249.
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