Cyclic Platina(borasiloxane)s and Platina(siloxane)s and Their Chemical Properties

Article abstract of DOI:10.1021/acs.organomet.7b00690

[Pt(SiHPh₂)₂(dmpe)] (dmpe = 1,2-bis(dimethylphosphino)ethane) reacts with arylboronic acids to produce six-membered platinacycles [Pt(SiPh₂-O-BAr-O-SiPh₂)(dmpe)] (Ar = C₆H₄-4-COMe (1a), C₆H₄-4-CF₃ (1b)). X-ray crystallography of 1a revealed the structure having a planar six-membered ring, composed of Pt, O, B, and Si atoms. Reaction of H₂O with [Pt(SiHPh₂)₂(dmpe)] formed a four-membered cyclic complex, [Pt(SiPh₂-O-SiPh₂)(dmpe)] (2), which was observed in the initial reaction mixture of 4-acetylphenylboronic acid with [Pt(SiHPh₂)₂(dmpe)]. Exposure of solutions of [Pt(SiHPh₂)₂(dmpe)] and of [Pt(SiHAr₂)₂(PMe₃)₂] (Ar = Ph, C₆H₄-4-Me) to air resulted in the formation of the cyclic platina(siloxane)s, [Pt(O-SiPh₂-O-SiPh₂-O)(dmpe)] (3) and [Pt(O-SiAr₂-O-SiAr₂-O)(PMe₃)₂] (4: Ar = Ph; 5: Ar = C₆H₄-4-Me), respectively. The six-membered platina(borasiloxane) 1a reacts with H₂GePh₂ and with CF₃CO₂H to release the cyclic borasiloxanes as the products. The former reaction affords [Pt(GeHPh₂)₂(dmpe)], while the latter produces [Pt(OCOCF₃)₂(dmpe)] as the Pt-containing products. A similar reaction of HCl with platina(siloxane) 4 gives a disiloxanediol via cleavage of the Pt-O bonds. Complex 4 reacts with H₂SiPh₂ to form a triplatinum complex, [{Pt(PMe₃)}₃(μ-SiPh₂)₃] (15), which is obtained under milder conditions than the previously reported reaction starting from [Pt(SiHPh₂)₂(PMe₃)₂].

Full text of DOI:10.1021/acs.organomet.7b00690

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Cyclic Platina(borasiloxane)s and Platina(siloxane)s and Their
Chemical Properties
Hiroki Noda, Kimiya Tanaka, Makoto Tanabe, and Kohtaro Osakada*
Laboratory for Chemistry and Life Science, Tokyo Institute of Technology, 4259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
S
* Supporting Information
ABSTRACT: [Pt(SiHPh2)2(dmpe)] (dmpe = 1,2-bis(dimeth-
ylphosphino)ethane) reacts with arylboronic acids to produce
six-membered platinacycles [Pt(SiPh2-O-BAr-O-SiPh2)(dmpe)]
(Ar = C6H4-4-COMe (1a), C6H4-4-CF3 (1b)). X-ray crystallog-
raphy of 1a revealed the structure having a planar six-membered
ring, composed of Pt, O, B, and Si atoms. Reaction of H2O with
[Pt(SiHPh2)2(dmpe)] formed a four-membered cyclic complex,
[Pt(SiPh2-O-SiPh2)(dmpe)] (2), which was observed in the ini-
tial reaction mixture of 4-acetylphenylboronic acid with [Pt(SiH-
Ph2)2(dmpe)]. Exposure of solutions of [Pt(SiHPh2)2(dmpe)] and
of [Pt(SiHAr2)2(PMe3)2] (Ar = Ph, C6H4-4-Me) to air resulted
in the formation of the cyclic platina(siloxane)s, [Pt(O-SiPh2-O-
SiPh2-O)(dmpe)] (3) and [Pt(O-SiAr2-O-SiAr2-O)(PMe3)2] (4: Ar = Ph; 5: Ar = C6H4-4-Me), respectively. The six-membered
platina(borasiloxane) 1a reacts with H2GePh2 and with CF3CO2H to release the cyclic borasiloxanes as the products. The former
reaction affords [Pt(GeHPh2)2(dmpe)], while the latter produces [Pt(OCOCF3)2(dmpe)] as the Pt-containing products.
A similar reaction of HCl with platina(siloxane) 4 gives a disiloxanediol via cleavage of the Pt−O bonds. Complex 4 reacts with
H2SiPh2 to form a triplatinum complex, [{Pt(PMe3)}3(μ-SiPh2)3] (15), which is obtained under milder conditions than the
previously reported reaction starting from [Pt(SiHPh2)2(PMe3)2].
precursor.7 Recently, Matsumi et al. reported dehydrogenative
copolymerization of diphenyldisilanol with mesitylborane
catalyzed by Rh and Pd complexes. The obtained polymer has
INTRODUCTION
■
Linear, branched, cyclic, and cage-shaped polysiloxanes, com-
posed of the Si−O−Si bonds, have been known as extensively
used inorganic polymers.1,2 They have advantages in thermal
stability, water-repellent properties, as well as biocompatibility.
These properties of the polysiloxanes are attributed to high
stability of the Si−O bond with bond energy of 452 kJ mol−1 and
weak cohesive force of the molecules having −Si−O−Si− linkage
and alkyl substituents on the Si atoms. Linear and cyclic oligo-
siloxanes are easily available as the starting materials of the
polysiloxanes.
a regulated structure, composed of −O−B(C6H2-2,4,6-Me3)−
O−SiPh2− repeating units and functions as an efficient sensor of
fluoride anion.8 Dehydrogenative condensation of diorganosi-
lanes with arylboronic acids using transition metal catalysis would
also form the −B−O−Si−O− linkage because Tilley, Esteruelas,
and Zargarian already reported condensation of organosilanes
with OH-containing compounds to form the Si−O bonds.9
In this study, we conducted reactions of arylboronic acids with Pt
complexes having SiHPh2 ligands and obtained new platinacy-
clohexanes that contain two Si−O−B bonds in the molecule.
The reaction proceeds via unexpected double condensation of
the boronic acid with the Si ligands rather than formation of the
−OBOAr ligand and its coupling with the silyl ligands. This
paper presents the synthesis, structure, and chemical properties
of the Pt complexes with a new ligand.
Polymers with borasiloxane units, containing both Si−O
bonds and B−O bonds (bond energy 536 kJ mol−1), are expected
to show new properties arising from the presence of a B atom in
the polymer chain. Several research groups have reported on the
synthesis of borasiloxane polymers and oligomers. Condensa-
tion reactions of phenylboronic acid with 1,3-dichlorodisiloxane
and trisiloxane derivatives yield the six- and eight-membered
cyclic compounds containing both Si−O and B−O bonds.3,4
π-Conjugated polymers, containing an eight-membered cyclic
borasiloxane group, change their color rapidly on exposure to
amine moisture.5 Polysiloxane, having a boronic acid terminus,
exhibits self-healing properties because of the network for-
mation via intermolecular coordination of the OH groups to
the B atom.6 A 10-membered cyclic compound having B−O−Si
bonds was prepared by dimerization of the five-membered cyclic
RESULTS AND DISCUSSION
■
Bis(silyl)platinum complex [Pt(SiHPh2)2(dmpe)] reacts with 4-ace-
tylphenylboronic acid and with 4-(trifluoromethyl)phenylboronic
Received: September 9, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00690
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(2, eq 2). Figure 2 shows the molecular structure of complex 2.
The Pt center has a square-planar coordination with Pt−Si bond
acid to form six-membered cyclic platinum complexes [Pt(SiPh2-
O-B(C6H4-4-R)-O-SiPh2)(dmpe)] (1a: R = COMe; 1b: R =
CF3) in 87 and 50% isolated yields, respectively, as shown in
eq 1. Figure 1 shows the molecular structure of 1a. The Pt center
Figure 2. Thermal ellipsoids (50% probability) of 2. Selected bond
distances (Å) and angles (deg): Pt1−P1 2.307(3), Pt1−P2 2.299(3),
Pt1−Si1 2.353(1), Pt1−Si2 2.332(3), Si1−O1 1.70(1), Si2−O1
1.70(1), P1−Pt1−P2 84.7(1), Si1−Pt1−Si2 65.6(1), P1−Pt1−Si1
106.2(1), P2−Pt1−Si2 103.6(1), P1−Pt1−Si2 166.3(1), P2−Pt1−Si1
169.1(1).
distances of 2.353(1) and 2.332(3) Å. The Si1−Pt1−Si2 angle
(65.6(1)°) is smaller than that of 1a (83.3(1)°) because of the
four-membered chelate ring. Complex 2 is the major product of
the reaction, as revealed by the NMR spectra of the reaction
mixture, but its isolation in high yields by fractional crystallization
was not feasible due to its slow conversion to other complexes in
the solution.
Figure 1. Thermal ellipsoids of 1a (50% probability). Selected bond
distances (Å) and angles (deg): Pt1−P1 2.338(3), Pt1−P2 2.322(3),
Pt1−Si1 2.352(3), Pt1−Si2 2.354(3), Si1−O1 1.687(8), B1−O1
1.35(2), B1−O2 1.35(2), Si2−O2 1.678(8). P1−Pt1−P2 84.4(1),
Si1−Pt1−Si2 83.3(1), P1−Pt1−Si1 97.6(1), P2−Pt1−Si2 94.7(1), P1−
Pt1−Si2 178.9(1), P2−Pt1−Si1 174.5(1).
Figure 3 shows a change of the 31P{1H} NMR spectra during
the reaction of 4-acetylphenylboronic acid with [Pt(SiHPh2)2-
(dmpe)], which affords complex 1a as the final product (eq 1).
The spectrum after the reaction for 1 h at room temperature
indicated the formation of four-membered platinacycle 2 (δP
38.0, JPtSi = 1443 Hz) and six-membered platina(borasiloxane)
1a. Further reaction caused decrease of once formed 2 and
formation of an insoluble solid. Dissolution of the insoluble
products in CD2Cl2 and NMR analyses of the solution did not
reveal the structure.
adopts a square-planar coordination with common Pt−Si bond
distances (Pt−Si = 2.352(3), 2.354(3) Å). The six-membered
cyclic platina(borasiloxane) is almost planar, and the two axial
phenyl substituents on the Si atoms are orientated to the same
side relative to the PtP2Si2 plane. Boardman synthesized a six-
membered cyclic platina(siloxane), [PtH(Cp)(SiMe2-O-SiMe2-
O-SiMe2)] (Cp = cyclopentadienyl), from the reaction of
trisiloxane with the Pt precursor, but did not report its crystal
structure.10 The 31P{1H} NMR spectrum of 1a contains a single
signal at δP 36.2 with a 195Pt−31P coupling constant of 1331 Hz,
which is smaller than that of [Pt(SiHPh2)2(dmpe)] (1445 Hz).
The 29Si{1H} NMR signal at δSi 19.4 is observed with coupling
The reaction of 2-methoxyphenylboronic acid with [Pt(SiH-
Ph2)2(dmpe)] formed complex 2 after 2 h at room tempera-
ture, and it became the major species in 24 h, as monitored by
31P{1H} NMR spectroscopy (Figure 4). Heating the solution at
2
constants of JPSi = 12, 157 Hz and JPtSi = 1318 Hz, while the
11B{1H} NMR signal is broadened significantly (δB 1.46).
The above reaction involves double condensation between the
OH groups of the arylboronic acid and the two SiHPh2 ligands.
We conducted the reaction of water with [Pt(SiHPh2)2(dmpe)]
with expectation of a similar dehydrogenative condensation of
the OH and SiH groups. Keeping a hydrated acetone solution of
[Pt(SiHPh2)2(dmpe)] under nitrogen atmosphere at room tem-
perature produces a platinacycle having an oxygen and two Si
60 °C caused the appearance of a minor signal at δP 35.2 (JPtP
=
1310 Hz), which was assigned to platina(borasiloxane) complex
[Pt(SiPh2-O-B(C6H4-2-OMe)-O-SiPh2)(dmpe)] (1c).
Schemes 1 and 2 depict possible pathways for the formation
of the platina(borasiloxane) (eq 1). As shown in Scheme 1,
dehydrocoupling of an OH group of the arylboronic acid with
an SiH group of the bis(silyl)platinum complex results in the
formation of an acyclic intermediate A having a new Si−O−B
bond. The second intramolecular Si−O bond formation occurs
atoms within the four-membered ring, [Pt(SiPh2-O-SiPh2)(dmpe)]
B
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Scheme 2. Pathway for the Formation of 1 via Four-
Membered Platinacycle Intermediate 2
Figure 3. 31P{1H} NMR spectra (202 M Hz, toluene-d8, rt) of the
reaction mixtures of [Pt(SiHPh2)2(dmpe)] and 4-acetylphenylboronic
acid in 1:2 ratio at 60 °C: (a) before addition of the arylboronic acid,
(b) after 1 h. Inset: Expanded spectrum around 1a after 1 h exhibiting
two doublets at δp 34.8 and δp 35.8 (2JPP = 12 Hz), (c) after 3.5 h, and
(d) after 20 h.
complex 2, resulting in the formation of an acyclic intermediate B
with a new Si−O−B bond. The subsequent intramolecular bond
exchange releases an H2O molecule and produces stable six-
membered cyclic platina(borasiloxane) complexes 1. Arylbor-
onic acid is equilibrated with the corresponding boroxine via
reversible cyclotrimerization and hydration of the formed boroxine.
Water, generated by the former reaction, may be responsible for
formation of complex 2 from [Pt(SiHPh2)2(dmpe)]. The reaction
of water with [Pt(SiHPh2)2(dmpe)] (eq 2) occurs at a temperature
lower than that of the arylboronic acids in reaction (eq 1),
although the arylboronic acid is a stronger Brønsted acid (pKa =
8.83) than water.
In order to compare the pathways in Schemes 1 and 2, we
conducted the reaction of 4-acetylphenylboronic acid with com-
plex 2. An excess amount of 4-acetylphenylboronic acid reacts
with complex 2 (5:1 molar ratio) at 70 °C to form 1a as the major
product. An equimolar reaction at the same temperature, how-
ever, results in generation of multiple uncharacterized complexes
in considerable amounts. Thus, equimolar reaction of 4-acetyl-
phenylboronic acid with [Pt(SiHPh2)2(dmpe)] (eq 1) occurs via
the pathway shown in Scheme 1 rather than that involving com-
plex 2 as the intermediate (Scheme 2). The spectra in Figure 3c,d
suggest the disappearance of once formed 2, but it is due to its
conversion into uncharacterized insoluble product rather than
to formation of 1a via the pathway in Scheme 2. 2-Methoxy-
phenylboronic acid shows reactivity much lower than that of
4-acetylphenylboronic acid, and the reaction yielded complex 2 via
contact of H2O with [Pt(SiHPh2)2(dmpe)] as the main product.
West reported the reaction of oxygen with platinum-η2-dis-
ilene complexes [Pt(η2-R2SiSiR2)(dppe)] (R = Me, iPr; dppe =
1,2-bis(diphenylphosphino)ethane) to produce the complex
Figure 4. 31P{1H} NMR spectra (202 M Hz, toluene-d8, rt) of the
reaction mixture of [Pt(SiHPh2)2(dmpe)] and 2-methoxyphenylbor-
onic acid in 1:2 ratio (a) before addition of the boronic acid, (b) for 2 h
at rt after addition of the arylboronic acid, (c) after 24 h at rt, and
(d) after heating for 6.5 h at 60 °C.
Scheme 1. Plausible Pathway for the Formation of
Platina(borasiloxane) Complexes 1
having a Pt−Si−O−Si four-membered ring, [Pt(SiR2-O-SiR2)-
(dppe)], which has a similar structure to complex 2.11 Dioxygen
cleaved the Si−Si bond of the complex to form the four-
membered platinacycle. In order to compare the reaction with
those in this study, we conducted the reaction of oxygen with
[Pt(SiHPh2)2(dmpe)]. Exposure of a solution of [Pt(SiH-
Ph2)2(dmpe)] to air at room temperature produces the com-
plex [Pt(O-SiPh2-O-SiPh2-O)(dmpe)] (3) which shows the
31P{1H} NMR signal at δP 18.0 with a large Pt−P coupling
constant (3566 Hz), as shown in eq 3. Similar complexes having
PMe3 ligands, [Pt(O-SiAr2-O-SiAr2-O)(PMe3)2] (4: Ar = C6H5,
77%, 5: Ar = C6H4-4-Me, 47%), were obtained from O2 exposure
of a toluene solution of [Pt(SiHAr2)2(PMe3)2] (Ar = C6H5,
C6H4-4-Me) at room temperature.
more easily than the intermolecular one and produces stable six-
membered cyclic platina(borasiloxane) complexes 1.
Scheme 2 depicts the other pathway. An OH bond of the
arylboronic acids adds to an Si−O bond of the ring-strained
C
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The isolated complexes, 3−5, were identified by X-ray crystal-
lography and NMR spectroscopy. The molecule of 3 has a six-
membered ring containing two Pt−O bonds (Figure 5). The Pt
Scheme 3. Bond Distances (Å) of Platina(borasiloxane),
Platina(siloxane)s, and Platina(boroxine)s
Pt−O−B−O−B−O linkage.16 Its bond parameters and NMR
data are compared with those of complexes 1a, 3, and 5. The Si−O
(1.687(8), 1.678(8) Å) and B−O bonds (1.35(2) Å) of 1a are
almost within the range of the typical bond distances (Si−O:
1.66, B−O: 1.36 Å).17 The Si−O bonds close to the Pt center
of 3 (1.583(5), 1.576(6) Å) and 5 (1.599(5), 1.606(5) Å) are
shorter than the other Si−O bonds (1.631(4)−1.653(5) Å).
The electron-rich oxygen atom coordinated by the Pt atom18
interacts with the Si atom more significantly than that in the
Si−O−Si linkage. Similar contraction of the proximal B−O
bonds to the Pt center (1.322(4)−1.34(1) Å) is shown com-
pared to the B−O bonds within the B−O−B linkage of the
platina(boroxine)s (1.37(1)−1.40(1) Å).
Figure 5. Thermal ellipsoids (50% probability) of 3. Selected bond
distances (Å) and angles (deg): Pt−P1 2.196(3), Pt−P2 2.192(2), Pt−
O1 2.071(5), Pt−O3 2.064(4), O1−Si1 1.576(5), Si1−O2 1.653(5),
O2−Si2 1.631(5), Si2−O3 1.583(5). P1−Pt−P2 87.13(8), O1−Pt−O3
92.8(2), P1−Pt−O1 91.2(2), P2−Pt−O3 89.0(2), P1−Pt−O3
174.9(2), P2−Pt−O1 176.6(2).
Complex 1a reacts with an excess amount of H2GePh2 and
2 equiv of CF3CO2H to release the cyclic borasiloxanes (six-
membered 8 and eight-membered 9), as shown in Scheme 4.
center adopted a typical square-planar coordination. The Pt−O
bond lengths of 3−5 (2.031(5)−2.071(5) Å) are similar to those
of the reported bis(silanolate)platinum complexes (1.982(7)−
2.036(4) Å).12 The six-membered ring containing a Pt cen-
ter has skewed (3 and 4) or distorted boat (5) conformation.
The 31P{1H} NMR spectra of 3−5 show a singlet with large JPtP
values (3518−3566 Hz). The coupling constants are similar to
the reported coupling constants of other bis(silanolate) plati-
num complexes, [Pt(OSiMe3)2(dppe)] (JPtP = 3595 Hz)13 and
[Pt(OSiMe3)2(PMe3)2] (JPtP = 3400 Hz),14 and much larger
than those of 1 (1304−1336 Hz) due to smaller trans influence of
the O ligand than the Si ligand. The 29Si{1H} NMR spectrum of 4
exhibits a resonance at δSi −37.0, which is close to the position of
hexaphenylcyclotrisiloxane (δSi −33.8).15 The 1H NMR spectra
of 3−5 show a single resonance for the ortho-hydrogens of the
aryl group, indicating that the platinasiloxane ring undergoes
rapid inversion between the conformers on the NMR time scale.
The reaction in eq 3 involves insertion of an oxygen atom into the
Pt−Si bond. Schubert reported oxygenation of the two Pt−Si
bonds of [(κ2-P,N)-(PN)Pt{o-(SiMe2)2C6H4}] (PN = 2-(diphenyl-
phosphino)-N,N-dimethylaniline) to form the bis(silanolate)com-
plex [(κ2-P,N)-(PN)Pt{o-(OSiMe2)2C6H4}].12b The formation of
complexes 3−5 also involves the reaction of oxygen to form
Si−O−Pt bonds, and it is accompanied by elimination of the two
Si−H hydrogens and formation of a new O−Si−O bond.
Scheme 4. Formation of Cyclic Borasiloxanes from the Pt
Precursor 1a
The cyclic borasiloxanes were characterized by mass spectrom-
etry, and the former reaction forms 8 as the product. These reac-
tions form the platinum complex with two germyl ligands
[Pt(GeHPh2)2(dmpe)] and that with two carboxylate ligands,
[Pt(OCOCF3)2(dmpe)]19 (7), respectively. The 31P{1H} NMR
spectrum in the former reaction mixture displays the signals of
[Pt(GeHPh2)2(dmpe)] and unreacted complex 1a, which sug-
gests clean exchange of Ge−H bonds with Pt−Si bonds of the
complex (Figure 6). Continuing the reaction causes formation of
Ge-containing metallacycles, [Pt(GePh2GePh2GePh2)(dmpe)]
Scheme 3 compares the bond parameters of the cyclic platina-
(borasiloxane), platina(siloxane)s, and platina(boroxine)s. We
reported that arylboronic acid reacts with dichloroplatinum (II)
complex to produce the six-membered cyclic complexes having a
(δp = 36.4, JPtP = 1816 Hz) or [Pt(GePh2GePh2GePh2GePh2)-
(dmpe)] (δp = 34.1, JPtP = 1890 Hz),20 which are character-
ized by 31P{1H} NMR spectroscopy. Recently, we reported
D
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The formal trimerization of a Pt-silylene complex26,27 occurs, but
it can be ascribed to initial formation of [Pt(SiHPh2)2(PMe3)2]
or [Pt(SiHPh2)(OSiPh2OSiPh2OH)(PMe3)2] and subsequent
condensation of such monoplatinum complexes. Previously,
we reported that heating of bis(silyl)platinum complex [Pt-
(SiHPh2)2(PMe3)2] at 100 °C also formed 15 in much lower
yield (28%).25a
In summary, we presented the preparation and characteriza-
tion of the six-membered platinacycles composed of borasiloxane
or siloxane rings. The platina(borasiloxane)s were obtained from
the double condensation of the arylboronic acids with two Si−H
groups of [Pt(SiHPh2)2(dmpe)]. It is contrasted with the pre-
vious reports on the catalytic dehydrogenative condensation of
organosilanes with OH compounds, which proceeds via coupling
of the Si and O ligands. Cyclic platina(siloxane)s are produced by
the reactions of O2 with the same starting material via a cyclic
four-membered intermediate complex. The platina(borasiloxane)s
and platina(siloxane)s release the corresponding siloxane units via
the exchange reactions of the Pt−Si and Pt−O bonds.
Figure 6. 31P{1H} NMR spectra (162 M Hz, toluene-d8, rt) of the
reaction mixture of 1a and H2GePh2 in a 1:2.7 ratio at 60 °C (a) before
addition of H2GePh2, (b) 1 h after addition of H2GePh2, (c) after 1 day,
(d) after 2 days, and (e) after 6 days.
EXPERIMENTAL SECTION
■
formation of the metallacycles from the dehydrogenative condensa-
tions of [Pt(GeHPh2)2(dmpe)] with an excess amount of H2GePh2.
Scheme 5 summarizes the reactivity of the cyclic platina(silo-
xane) complex 4. The reactions with excess HCl occur immediately
General Procedures. All manipulations were carried out using
standard Schlenk line techniques under an atmosphere of argon or
nitrogen or in a nitrogen-filled glovebox (Miwa MFG). Hexane, toluene,
and tetrahydrofuran (THF) were purified by using a Grubbs-type
solvent purification system (Glass Contour).28 Dehydrated CH2Cl2 and
acetone were purchased from Kanto Chemical and used as received.
1H, 11B{1H}, 13C{1H}, 19F{1H}, 29Si{1H}, and 31P{1H} NMR spectra
were recorded on Varian Mercury 300 MHz, Bruker Biospin Avance III
400 MHz, and Avance III HD 500 MHz NMR spectrometers. The
chemical shifts in the 1H and 13C{1H} NMR spectra were referenced to
the residual peaks of the solvents used.29 The peak positions of the
11B{1H}, 19F{1H}, 29Si{1H}, and 31P{1H} NMR spectra were referenced
to external BF3·OEt2 (δ 0), CFCl3 (δ 0), SiMe4 (δ 0), and 85% H3PO4
(δ 0) in deuterated solvents. The IR spectrum was recorded on a JASCO
FTIR-4100 spectrometer. Mass spectroscopic data were obtained on a
Bruker Daltonics micrOTOF II (ESI and APCI) spectrometer.
Elemental analyses were performed using a J-science JM10 or Yanaco
HSU-20 autorecorder. The chemical reagents, 4-acetylphenylboronic
acid (Combi-Blocks), 4-(trifluoromethyl)phenylboronic acid (TCI),
2-methoxyphenylboronic acid (Aldrich), CF3CO2H (TCI), 4.0 M HCl
in 1,4-dioxane (Aldrich), 54 wt % HBF4 in Et2O (Aldrich), and 4-meth-
ylbenzoic acid (TCI) were used as received. [Pt(SiHPh2)2(dmpe)] and
[Pt(SiHPh2)2(PMe3)2] were prepared according to the literature.30
H2GePh2 was obtained from reduction of Cl2GePh2 (Aldrich) by LiAlH4.
Scheme 5. Reactivity of Platina(siloxane) Complex 4
Preparation of [Pt(SiPh2-O-B(C6H4-4-COMe)-O-SiPh2)(dmpe)]
(1a). To a toluene (8 mL) solution of [Pt(SiHPh2)2(dmpe)] (712 mg,
1.0 mmol) was added 4-acetylphenylboronic acid (164 mg, 1.0 mmol).
The orange solution was stirred at 80 °C overnight, resulting in pre-
cipitation of a small amount of dark green solid. To remove the impurity
by filtration, the solvent was removed under reduced pressure to give a
yellow solid, which was washed with hexane (3 mL) and Et2O (1 mL)
and dried in vacuo to give 1a as a yellow solid (756 mg, 87%).
Recrystallization of 1a in THF/hexane at −18 °C under inert gas gave a
small amount of crystals suitable for X-ray crystallography. Anal. Calcd
to produce a mixture of cis-[PtCl2(PMe3)2]21 (10) and 1,1,3,3-
tetraphenyldisiloxane-1,3-diol22 (11) in 89 and 64% yields.
A similar reaction of 4 with 4-methylbenzoic acid in 1:2 ratio
yielded a bis(carboxylate)platinum complex cis-[Pt(OCOC6H4-
4-Me)2(PMe3)2] (12) in a quantitative yield. The siloxane
byproduct was not identified in the reaction. The acid interacts
favorably with the M−O bonds of 4, similar to the alkoxide or
aryloxide complexes of group 10 metals, because the oxygen
bonded to the late transition metals exhibits high affinity to the
proton due to repulsion between filled dπ orbitals of the metals
and p orbital of the O atom.18 In contrast, the reaction of HBF4
with 4 yields the cationic Pt complex cis-[Pt(OH2)2(PMe3)2]-
for C38H43BO3P2Si2Pt: C, 52.36; H, 4.97. Found; C, 52.05; H, 5.03. 1H
3
NMR (500 MHz, CD2Cl2, rt): δ 7.93 (d, 2H, BC6H4 ortho, JHH
=
8.0 Hz), 7.81 (d, 2H, BC6H4 meta, 3JHH = 7.5 Hz), 7.61 (d, 8H, SiC6H5
ortho, 3JHH = 6.0 Hz), 7.24−7.27 (m, 12H, SiC6H5 meta and para), 2.53
(s, 3H, COCH3), 1.58−1.54 (m, 4H, PCH2), 0.88 (m, 12H, PCH3, 2JPH
=
10 Hz). 11B{1H} NMR (160 MHz, CD2Cl2, rt): δ 1.46 (br). 13C{1H}
NMR (126 MHz, CD2Cl2, rt): δ 198.9 (COCH3), 147.3 (apparent
23
(BF4)2 (13, 92%) and 1,3-difluoro-1,1,3,3-tetraphenyldisilox-
3
triplet, SiC6H5 ipso, JPC = 7.0 Hz), 138.6 (CH3COC and BC, over-
lapped), 135.6 (apparent triplet, SiC6H5 ortho, JPC = 7.5 Hz), 135.2,
ane24 (14, 87%). The F− ion generated from HBF4 attacks the
electropositive Si atom, forming the stable Si−F bonds.
The reaction of 4 with H2SiPh2 in a 1:3 molar ratio at
60 °C produced [{Pt(PMe3)}3(μ-SiPh2)3] (15)25 in 60% yield.
4
128.3, 127.6, and 127.2 (SiC6H5 meta or para, or BC6H4 ortho or meta),
30.6 (m, PCH2), 27.0 (COCH3), 13.3 (m, PCH3). 29Si{1H} NMR
(99 MHz, CD2Cl2, rt): δ 19.4 (dd, 2JPSi = 12, 157 Hz, JPtSi = 1318 Hz).
E
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Article
31P{1H} NMR (202 MHz, CD2Cl2, rt): δ 36.2 (2JSiP = 12, 157 Hz,
JPtP = 1331 Hz). In a NMR tube, to a toluene-d8 solution (0.5 mL)
of [Pt(SiHPh2)2(dmpe)] (5.0 mg, 7 μmol) was added 2 equiv of
4-acetylphenylboronic acid (2.3 mg, 14 μmol). The reaction mixture was
monitored by the 31P{1H} NMR spectroscopy, as shown in Figure 3.
and dried in vacuo to afford 4 as a white solid (412 mg, 77%). The crystals
of 4 suitable for X-ray crystallography were obtained by slow diffusion of
toluene to hexane solution. Anal. Calcd for C30H38O3P2PtSi2: C, 47.42;
H, 5.04. Found: C, 47.18; H, 4.96. 1H NMR (400 MHz, CDCl3, rt): δ
3
7.76 (d, 8H, C6H5 ortho, JHH = 8.0 Hz), 7.24−7.29 (m, 12H, C6H5
2
meta and para), 1.40 (d, 18H, PCH3, JHP = 11 Hz). 13C{1H} NMR
Preparation of [Pt(SiPh2−O-B(C6H4-4-CF3)-O-SiPh2)(dmpe)]
(1b). The reaction of [Pt(SiHPh2)2(dmpe)] (71 mg, 0.1 mmol) and
4-(trifluoromethyl)phenylboronic acid (38 mg, 0.2 mmol) gave 1b
(45 mg, 50%) as a green solid. 1H NMR (500 MHz, CD2Cl2, rt): δ 7.97
(100 MHz, CDCl3, rt): δ 141.0 (C6H5 ipso), 134.6 (C6H5 ortho),
128.2 (C6H5 para), 127.0 (C6H5 meta), 14.7 (m, PCH3). 31P{1H} NMR
(162 MHz, CDCl3): δ −28.9 (JPPt = 3526 Hz). 29Si{1H} NMR (79 MHz,
CDCl3, rt): δ −37.0. IR (KBr): 1115 (νSi−OSi), 996 and 947 (νSi−OPt) cm−1.
(d, 2H, BC6H4 ortho, 3JHH = 10 Hz), 7.61 (d, 8H, SiC6H5 ortho, 3JHH
=
5.0 Hz), 7.51 (d, 2H, BC6H4 meta, 3JHH = 10 Hz), 7.25−7.26 (m, 12H,
C6H5 meta and para), 1.55−1.58 (m, 4H, PCH2), 0.88 (d, 12H, PCH3,
2JPH = 10 Hz). 11B{1H} NMR (160 MHz, CD2Cl2, rt): δ 1.27 (br).
13C{1H} NMR (126 MHz, CD2Cl2, rt): 147.2 (apparent triplet, SiC6H5
ipso, 3JPC = 6.3 Hz), 135.2 (apparent triplet, SiC6H5 ortho, 4JPC = 7.5 Hz),
134.9, 127.9, 127.2 (SiC6H5 meta, para and BC6H4 ortho, meta), 123.6
(quartet, BC6H4 meta, 3JFC = 3.8 Hz), 30.3 (m, PCH2), 12.9 (m, PCH3).
The ipso carbon was not observed due to low intensity. 19F{1H} NMR
(471 MHz, CD2Cl2, rt): δ −62.9 (s). 29Si{1H} NMR (99 MHz, CD2Cl2,
Preparation of [Pt{O−Si(Tol)2−O-Si(Tol)2-O}(PMe3)2] (5). Com-
plex 5 was obtained similarly in 47% yield, and the crystals of 5 suitable
for X-ray crystallography were obtained by slow diffusion of toluene to
hexane solution. Anal. Calcd for C34H46O3P2PtSi2: C, 50.05; H, 5.68.
Found: C, 50.17; H, 5.86. 1H NMR (400 MHz, CDCl3, rt): δ 7.62 (d,
8H, C6H4 ortho, 3JHH = 7.6 Hz), 7.05 (d, 8H, C6H4 meta, 3JHH = 7.6 Hz),
2.30 (s, C6H4CH3, 12H), 1.41 (d, 18H, PCH3, 2JHP = 11 Hz). 13C{1H}
NMR (100 MHz, CDCl3, rt): δ 137.9 (C6H4 ipso), 137.6 (C6H4 para),
134.7 (C6H4 ortho), 127.8 (C6H4 meta), 21.5 (s, C6H4CH3), 14.7 (m,
PCH3). 31P{1H} NMR (162 MHz, CDCl3, rt): δ −29.0 (JPPt = 3518 Hz).
Reaction of H2GePh2 with 1a. To a toluene-d8 solution (0.6 mL)
of 1a (8.7 mg, 10 μmol) in a J-Young NMR tube under inert gas was
added H2GePh2 (5.0 μL, 27 μmol). The 31P{1H} NMR spectrum of the
reaction mixture after 1 h at 60 °C appeared at δ 35.5 (JPtP = 1890 Hz),
which was assigned to [Pt(GeHPh2)2(dmpe)].20 Further reaction at the
2
rt): δ 19.6 (dd, JPSi = 12, 158 Hz, JPtSi = 1313 Hz). 31P{1H} NMR
(202 MHz, CD2Cl2, rt): δ 36.2 (2JSiP = 12, 158 Hz, JPtP = 1336 Hz).
HRMS (ESI): calcd for C37H40BF3NaO2P2PtSi2 [M + Na]+ 920.1638;
found m/z 920.1614.
Preparation of [Pt(SiPh2-O-SiPh2)(dmpe)] (2). To an acetone
(2 mL) solution of [Pt(SiHPh2)2(dmpe)] (36 mg, 0.05 mmol) was
added an excess amount of H2O (200 μL). The light yellow solution was
stirred at room temperature overnight, and the solution color changed
to green. The solvent was removed under reduced pressure to give
a light green solid (24 mg) containing 2. The solid product recovered
from the solution containing complex 2 [31P{1H} NMR (202 MHz,
toluene-d8, rt): δ 38.0 (JPtP = 1443 Hz)] as the major species, but its
isolation as the analytically pure crystals was not feasible because
complex 2 was easily oxidized at room temperature under air, resulting
in the formation of 3 and the oxidized products.
same temperature caused the formation of [Pt(GePh2GePh2GePh2)-
(dmpe)] (δp = 36.4, JPtP = 1816 Hz) or [Pt(GePh2GePh2GePh2GePh2)-
(dmpe)] (δp = 34.1, JPtP = 1890 Hz). The HRMS data (APCI) of the
mixture revealed the signals assigned as cyclic borasiloxanes (MeCO-4-
C6H4BO)(SiPh2O)2 (8) and (MeCO-4-C6H4BO)(SiPh2O)3 (9). Data
for 8: calcd for C32H28BO4Si2 [M + H]+ 543.1620; found m/z 543.1604.
Data for 9: calcd for C44H38BO5Si3 [M + H]+ 741.2123; found m/z
741.2120.
Reaction of 1a with CF3CO2H. To a THF solution of 1a (174 mg,
0.2 mmol) was added trifluoroacetic acid (31 μL, 0.4 mmol). The solu-
tion changed from yellow to dark green after being stirred at room
temperature for 30 min, and the reaction was continued overnight. The
solvent was removed under reduced pressure to give a mixture of
[Pt(OCOCF3)2(dmpe)]19 (7) and the borasiloxane compound. The
latter product was extracted by 15 mL of Et2O and evaporated to give a
mixture of cyclic borasiloxanes 8 and 9 in a 7:3 ratio as a brown solid
(106 mg), which was identified as mixtures by HRMS (APCI) and NMR
spectroscopy. 1H NMR assignment for 8 (400 MHz, CD2Cl2, rt): δ 8.13
Reaction of [Pt(SiHPh2)2(dmpe)] with 2-Methoxyphenylbor-
onic Acid. To a toluene (8 mL) solution of [Pt(SiHPh2)2(dmpe)]
(71.2 mg, 0.1 mmol) was added 2-methoxyphenylboronic acid (30.4 mg,
0.2 mmol). The light yellow solution was stirred at 60 °C for 3 h,
resulting in a change to orange and precipitation of a gray solid. After
filtration, the solvent was removed to give a brown solid containing 2,
[Pt(SiPh2−O-B(C6H4-2-OMe)-O-SiPh2)(dmpe)] (1c), and unreacted
[Pt(SiHPh2)2(dmpe)]. Data for 1c: 31P{1H} NMR (202 MHz, toluene-
d8, rt): δ 35.2 (JPtP = 1310 Hz). Recrystallization of this solid in CH2Cl2/
hexane at −18 °C under inert gas gave a small amount of crystals of 2
suitable for X-ray crystallography.
Reaction of (HO)2B(C6H4-4-COMe) with 2. 4-Acetylphenylbor-
onic acid (10.7 mg, 65 μmol) was added to a toluene-d8 solution
(0.5 mL) of 2 (10.0 mg, 13 μmol), which was obtained as a crude prod-
uct. The 31P{1H} NMR spectrum of the mixture at 70 °C for 1 h showed
the major signals of 1a (δ 35.2, JPtP = 1314 Hz), accompanied by
unidentified products. Further reaction for 5.5 h at the same temperature
increased the signal of 2 as the major product and disappearance of the
signal of 2. An equimolar reaction at the same temperature, however,
resulted in the complexes being composed of multiple uncharacterized
products.
(d, 2H, BC6H4 ortho, 3JHH = 8.0 Hz), 7.96 (d, 2H, BC6H4 meta, 3JHH
=
8.0 Hz), 7.72 (d, 8H, SiC6H5 ortho, 3JHH = 6.8 Hz), 7.38−7.43 (m, 12H,
SiC6H5 meta and para), 2.60 (s, 3H, COCH3). 1H NMR assignment for
9: δ 8.17 (d, 2H, BC6H4 ortho, 3JHH = 8.3 Hz), 8.00 (d, 2H, BC6H4 meta,
3JHH = 8.3 Hz), 2.62 (s, 3H, COCH3). The SiC6H5 signals are not
characterized clearly due to overlapping with other signals. 29Si{1H}
NMR (99 MHz, CD2Cl2, rt): δ −21.7 (s for 8), −39.5 (s, 1Si for 9),
−41.5 (s, 2Si for 9). 11B{1H} NMR (160 MHz, CD2Cl2, rt): δ 16.8 (br
for 8 and 9). IR (KBr): 1319, 997 (νBOSi), 1126 cm−1 (νSiOSi).
Reaction of 4 with HCl. To a CH2Cl2 solution (5 mL) of 4 (248 mg,
0.33 mmol) was added three times molar amounts of 4.0 M HCl in
1,4-dioxane (248 μL, 0.99 mmol). A white solid was rapidly precipitated
from the reaction mixture. The solid was collected through filtra-
tion, washed with hexane twice (3 mL), and dried in vacuo to give
cis-[PtCl2(PMe3)2] (10, 123 mg, 89%), which was consistent with the
literature data (δ −23.9, JPPt = 3468 Hz).21 1,1,3,3-Tetraphenyldisilox-
ane-1,3-diol was isolated from the supernatant solution (11, 87 mg,
64%) and characterized by IR spectroscopy.22 IR (KBr): 3230 (νOH),
1128 (νSiO), 1086, 885, 848 (νSiOH) cm−1.
Preparation of [Pt(O-SiPh2-O-SiPh2-O)(dmpe)] (3). In a NMR
tube, a toluene-d8 solution of [Pt(SiHPh2)2(dmpe)] (5.0 mg, 7 μmol)
was stored at room temperature in air. After 3 days, the 31P{1H} NMR
spectrum of the mixture showed two 31P signals assigned as 3 (δ 18.0,
JPtP = 3566 Hz) and unreacted [Pt(SiHPh2)2(dmpe)]. Slow evaporation
of the solution at room temperature afforded a tiny amount of colorless
crystals of 3, which was suitable for X-ray crystallography.
Reaction of 4 with 4-Methylbenzoic Acid. To a toluene sus-
pension (5 mL) of 4 (145 mg, 0.19 mmol) was added 4-methylbenzoic
acid (52 mg, 0.38 mmol) under air to become a yellow solution imme-
diately with stirring for 1 h. The solution was passed through filter paper
and evaporated under reduced pressure. Addition of 2 mL of ether to
the resulting material separated a platinum complex as a white solid.
Preparation of [Pt(O-SiPh2-O-SiPh2-O)(PMe3)2] (4). A toluene
(10 mL) suspension of [Pt(SiHPh2)2(PMe3)2] (503 mg, 0.70 mmol)
was stirred under O2 atmosphere for 15 h at room temperature. The com-
plex was dissolved in toluene. The solution gradually turned from yellow
to brown, accompanied by precipitation of a white solid. The solid was
collected through filtration and washed with hexane three times (10 mL)
F
DOI: 10.1021/acs.organomet.7b00690
Organometallics XXXX, XXX, XXX−XXX

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Article
The solid was collected through filtration, washed with 2 mL of ether
three times, and dried in vacuo to obtain a di(carboxylate)platinum
complex cis-[Pt(OCOCF3)2(PMe3)2] (12, 109 mg, 93%), which was
crystallized by toluene/hexane solutions. The organosiloxane com-
pounds as byproducts were not characterized in the mixture. Data for
12: Anal. Calcd for C22H32O4P2Pt: C, 42.79; H, 5.22. Found: C, 43.39;
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: kosakada@res.titech.ac.jp.
ORCID
Kohtaro Osakada: 0000-0003-0538-9978
H, 5.40. 1H NMR (300 MHz, CDCl3, rt): δ 7.87 (d, 4H, C6H4, JHH
=
Notes
8.1 Hz), 7.07 (d, 4H, C6H4, JHH = 8.1 Hz), 2.30 (s, 6H, C6H4CH3), 1.68
(d, 18H, PCH3, JHP = 11 Hz, JHPt = 50 Hz). 13C{1H} NMR (75 MHz,
acetone-d6, rt): δ 206.1 (CO), 140.7 (C6H4 para), 135.6 (C6H4 ipso),
130.4 (C6H4 ortho), 128.9 (C6H4 meta), 21.3 (C6H4CH3), 15.0 (d, PCH3,
JCP = 43 Hz, 2JCPt = 31 Hz). 31P{1H} NMR (121 MHz, C6D6, rt): δ −31.2
(JPPt = 3650 Hz). IR (KBr): 1611 (νC=O), 1556 and 1363 (νCO) cm−1.
Reaction of 4 with HBF4. To a CH2Cl2 solution (5 mL) of 4 (109 mg,
0.14 mmol) was added three times molar amounts of 54 wt % HBF4
in diethyl ether (98 μL, 0.43 mmol). Immediately, a white solid was
precipitated from the reaction mixture. The solid was collected through
filtration, washed with hexane twice (3 mL), and dried in vacuo to give a
dicationic aquaplatinum complex cis-[Pt(OH2)2(PMe3)2](BF4)223 (13)
(72 mg, 92%). 1,3-Difluoro-1,1,3,3-tetraphenyldisiloxane24 (14) was
isolated as a white solid from the supernatant solution (51 mg, 87%).
Data for 13: 1H NMR (300 MHz, acetone-d6, rt): δ 1.94 (m, 18H, C6H4
ortho, JHH = 7.5 Hz). 31P{1H} NMR (162 MHz, acetone-d6, rt): δ −24.6
(JPPt = 3752 Hz). Data for 14: 1H NMR (300 MHz, CDCl3, rt): δ 7.66
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by Grants-in-Aid for Scien-
tific Research (B) (JSPS KAKENHI Grant No. 17H03029) and
(C) (No. 16K05789), from Ministry of Education, Culture, Sports,
Science, and Technology, Japan. We thank our colleagues in the
Center for Advanced Materials Analysis, Technical Department,
Tokyo Institute of Technology, for elemental analysis.
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.7b00690.
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CCDC 1570088−1570093 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
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DOI: 10.1021/acs.organomet.7b00690
Organometallics XXXX, XXX, XXX−XXX