A triangular triplatinum(0) complex with bridging germylene ligands: Insertion of alkynes into the Pt-Ge bond rather than the Pt-Pt bond

Article abstract of DOI:10.1039/c4cc00727a

A new triangular triplatinum(0) complex with bridging diphenylgermylene ligands, [{Pt(PMe₃)}₃(μ-GePh₂)₃], undergoes insertion of ZCCZ (Z = COOMe) into a Pt-Ge bond. The product contains a μ₃-η²(∥)-CZCZ-GePh₂ ligand on the Pt₃ plane. Two molecules of HCCZ react to afford the Pt₃ complex with chelating C, Ge- and Ge, Ge-ligands. the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc00727a

Showcasing research from K. Osakada’s research group in the
Chemical Resources Laboratory, Tokyo Institute of Technology,
Nagatsuta, Midori-ku, Yokohama, Japan.
As featured in:
A triangular triplatinum(0) complex with bridging
germylene ligands: insertion of alkynes into the
Pt–Ge bond rather than the Pt–Pt bond
A triplatinum complex with bridging germylene ligands reacts
with alkynes to yield unexpected complexes having C,Ge- and
Ge,Ge-ligands via insertion of the CC triple bond into the Pt–Ge
bonds. LUMO spread over the Pt Ge core gave preference
3
3
to the reaction over the conventional addition of alkyne
molecules to a Pt–Pt bond.
See Kohtaro Osakada et al.,
Chem. Commun., 2014, 50, 6839.
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A triangular triplatinum(0) complex with bridging
germylene ligands: insertion of alkynes into the
Pt–Ge bond rather than the Pt–Pt bond†
Cite this: Chem. Commun., 2014,
0, 6839
5
Received 27th January 2014,
Accepted 4th March 2014
Makoto Tanabe, Kimiya Tanaka, Shumpei Omine and Kohtaro Osakada*
DOI: 10.1039/c4cc00727a
www.rsc.org/chemcomm
A new triangular triplatinum(0) complex with bridging diphenyl-
germylene ligands, [{Pt(PMe )} (l-GePh ], undergoes insertion of
3
3
2 3
)
ZCRCZ (Z = COOMe) into a Pt–Ge bond. The product contains a
2
l
3
-g (J)-CZQCZ-GePh
2
ligand on the Pt
3
plane. Two molecules of
HCRCZ react to afford the Pt
Ge-ligands.
complex with chelating C, Ge- and Ge,
3
1
Cyclic triplatinum(0) complexes have long been known and
almost all of them contain carbonyl or isonitrile as the bridging
ligands. The electron-withdrawing ligands are considered to
Scheme 1
10
stabilize the Pt(0) core composed of d metals. The addition of
3
n+
acetylene to cationic triplatinum complexes [Pt
3 3 3
(m-dppm) (m -X)]
but may show new chemical properties provided by the less electron-
(
X = CO and n = 2, X = H and n = 1, dppm = Ph
2
PCH PPh ) were withdrawing silylene and germylene ligands. Herein, we present full
2
2
reported to form their alkyne-coordinated complexes accompa- characterization of a trinuclear Pt(0) complex with bridging germylene
2
nied with cleavage of two Pt–Pt bonds (Scheme 1a). In contrast, ligands and its reaction with alkynes to afford new triplatinum
the neutral triplatinum carbonyl complex, [{Pt(PPh
3
)}
3
(m-CO)
3
], complexes with germaplatinacyclic structures.
reacted with dimethyl acetylenedicarboxylate, ZCRCZ (Z = COOMe),
A platinum complex with diphenylgermyl ligands, trans-
to afford a 1 : 1 adduct of the alkyne to the Pt core below ꢀ50 1C,
3
[Pt(GeHPh
by X-ray crystallography. The heating of an equimolar mixture
of 2 and [Pt(PCy ] in toluene at 100 1C produced a triplatinum
2 2 3 2
) (PMe ) ] (2), was newly obtained and characterized
7
which was converted to the alkyne-bridged Pt complex upon raising
2
3
the reaction temperature (Scheme 1b).
3 2
)
Recently, a few of the complexes were reported by using silylene complex with bridging diphenylgermylene ligands, [{Pt(PMe )} -
3
3
and germylene ligands instead of the electron-withdrawing brid- (m-GePh ) ] (3), in 67% yield (eqn (1)). Addition of [Pt(PCy ) ] to
2
3
3 2
ging ligands. We obtained a triangular triplatinum(0) complex with the solution of 2 increased the yields of 3.
bridging diphenylsilylene ligands, [{Pt(PMe )} (m-SiPh ] (1), by
the thermal reaction of [Pt(SiHPh ) (PMe ) ]. Braddock-Wilking
3
3
4
2 3
)
2
2
3 2
reported that the reactions of [Pt(CH QCH )(PPh ) ] with sila- and
2
2
3 2
germafluorenes yielded [{Pt(PPh )} {m-E(C H )} ] (E = Si, Ge) stabi-
(1)
3
3
12 8 3
lized by the bridging sila- and germafluorenylidene ligands,
although the Ge-containing complex was characterized without
5,6
X-ray crystallographic results. These trinuclear complexes are iso-
electronic with those having bridging carbonyl and isonitrile ligands,
3 3
X-ray crystallography of complex 3 revealed a planar Pt Ge core
with a 42-electron cluster incorporating three Pt centers, and the
Chemical Resources Laboratory, Tokyo Institute of Technology,
coordination of the bridging GePh ligands. The Pt–Pt bonds of 3
2
4
259-R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
E-mail: kosakada@res.titech.ac.jp; Fax: +81-45-924-5224; Tel: +81-45-924-5224
Electronic supplementary information (ESI) available: Detailed experimental
procedures, crystal structures, NMR spectra and DFT data for complexes. CCDC
79331 (2), 979332 (3), 979333 (4) and 979334 (5). For ESI and crystallographic
(
2.7081(6)–2.7194(6) Å) and 1 (2.697(1)–2.716(3) Å) have similar ranges,
but are significantly longer than those of the complexes with electron-
withdrawing ligands, [{Pt(PCy (m-CO) ] (2.653(2)–2.656(2) Å) and
3 3 3
†
8
a
)}
t
t
8b
[{Pt(CN Bu)}
3
(m-CN Bu)
3
] (2.629(2)–2.637(2) Å).
The Pt–Ge
9
data in CIF or other electronic format see DOI: 10.1039/c4cc00727a
bonds of 3 (2.412(1)–2.423(1) Å) are longer than the Pt–Si bonds
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of 1 (2.337(5)–2.364(5) Å), which make a Pt–Ge–Pt angle of 3
(68.10(3)–68.38(3)1) smaller than the Pt–Si–Pt angle of 1
(
70.2(1)–70.5(1)1). The Pt–Pt coupling constants of 3 (2633 Hz)
1
95
1
and 1 (2950 Hz), estimated from the
Pt{ H} NMR signals at
d ꢀ4195 and ꢀ3980, respectively, are larger than those of
triplatinum complexes with electron-withdrawing CO ligands,
8
c
[
{Pt(PR
Treatment of 3 with equimolar ZCRCZ at 50 1C for 1 h yielded
a triplatinum complex with a m -germadiplatinacyclopentene
3
)}
3
(m-CO)
3
] (J(Pt,Pt) = 1571–1770 Hz).
Scheme 2
3
involves the switching motion of the s,p-vinyl ligand, which
bridges the two Pt centers. Triosmium alkenyl complexes
2
structure [{Pt(PMe
7
3
)}
3
(m
3
-Z (J)-CZQCZ-GePh
2
2 2
)(m-GePh ) ] (4) in
8% yield, as shown in (eqn (2)).
2
[Os
3
(CO)10(m-Z -CRQCHR)(m-H)] (R = H, Ph) were reported to
undergo a similar interconversion of the s- and p-bonding
1
0
195
alkenyl ligands on the Os3 core. The
Pt NMR spectrum
contains a doublet of triplets assigned as the Pt1 nucleus at
1
2
195
(
2)
d ꢀ4102 ( J(P,Pt) = 3997 Hz and J(P,Pt) = 307 Hz). Another Pt
NMR signal of the Pt2 and Pt3 atoms is observed as a severely
broadened signal at d ꢀ4466 with J(P,Pt) = ca. 3600 Hz. These
nuclei could not be distinguished by NMR spectroscopy in spite
of the dynamic motion of the molecule, probably owing to the
close signal positions.
I
0
Complex 4 maintains a triangular (Pt ) (Pt ) core, which is
bonded to a m -germavinylene ligand and two bridging germylene
2
1
3
Scheme 3 shows a comparison of the reactions of ZCRCZ with
and [{Pt(PPh )} (m-CO) ]. The complex with bridging GePh2
ligands undergoes insertion of ZCRCZ into a Pt–Ge bond to yield
a germadiplatinacyclopentene (A, upper route). The migration of
the germyl group of the GePh -CZQCZ ligand to the other Pt
affords a more stable 4 as an isolable product. An alternative
2
pathway exists involving the shift of the bridging GePh ligand of A
to the Pt bonded with the vinyl group. The Pt–Pt bonds are
retained during the reaction. In contrast, the carbonyl-bridged Pt3
complex forms adducts of the alkyne on the Pt plane with the
ligands at the opposite side of the Pt
Pt–Pt bond distances of 4 (2.700(2)–2.717(2) Å) are similar to
those of 3 (2.7081(6)–2.7194(6) Å). The m -germavinylene ligand is
s-bonded to Pt1 and Pt3 and p-bonded to Pt2, with a common
3
plane (Fig. 1). The three
3
3
3
3
3
3
2
9
2
m
3
2
-Z (J) bonding mode. The bridging GePh ligands are unsym-
metrically coordinated to two Pt atoms; the Pt1–Ge2 and Pt1–Ge3
bonds (2.799(4) and 2.895(4) Å) are significantly longer than the
Pt2–Ge2 and Pt3–Ge3 bonds (2.393(4) and 2.419(4) Å).
11
1
The H NMR spectrum of 4 at ꢀ20 1C is consistent with the
1
3
crystal structure. Variable-temperature H NMR spectra show
2
m -Z (J) bonding mode and terminal carbonyl ligands (B, lower
3
fluxional behavior of the molecule, which is interpreted by the
route), and undergoes fragmentation of the trinuclear complex to
the dinuclear complex. The two distinct reactions are initiated by
insertion of the alkyne and addition of the alkyl to a Pt–Pt bond,
respectively. The interaction of p-orbitals of the alkynes with
LUMO of the complexes should be important in determining the
reaction pathway. In order to elucidate the details, we compared
interconversion between the m
its enantiomer 4 , as shown in Scheme 2. The dynamic process
3
-germavinylene ligand of 4 and
0
12
molecular orbitals of 3 and [{Pt(PMe )} (m-CO) ].
3
3
3
The HOMOs of these complexes are similar, and exist along the
Pt–EPh and Pt–CO bonds. As shown in Fig. 2, the LUMO of 3 is
2
located along the Pt–Ge bonds, and may take on the character of
the anti-bonding orbital of the Pt-germylene bonds, whereas the
3
Fig. 1 Thermal ellipsoidal plot (50% probability level) of 4. The PMe carbon
atoms and all hydrogen atoms are omitted for clarity. Selected bond lengths [Å]
for 4: Pt1–Pt2 2.706(2), Pt1–Pt3 2.717(2), Pt2–Pt3 2.700(2), Pt1–Ge1 2.356(4),
Pt1–Ge2 2.799(4), Pt1–Ge3 2.895(4), Pt2–Ge2 2.393(4), Pt3–Ge3 2.419(4),
Pt2–C1 2.30(3), Pt2–C2 2.39(3), Pt3–C1 2.06(4), Ge1–C2 2.00(3),
C1–C2 1.43(5).
Scheme 3
6
840 | Chem. Commun., 2014, 50, 6839--6842
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3 3 3
Fig. 2 LUMO of (a) 3 and (b) [{Pt(PMe )} (m-CO) ], optimized by DFT
calculations.
3 3 3 3 3
LUMO of [{Pt(PMe )} (m-CO) ] spreads over the Pt (CO) plane,
which includes the Pt(0)–Pt(0) bonds. Thus, complex 3 undergoes Fig. 3 Thermal ellipsoidal plot (50% probability level) of 5. The PMe
3
carbon atoms and all hydrogen atoms, except = CH hydrogen, are omitted
facile insertion into the Pt–Ge bond, whereas [{Pt(PMe
prefers addition of the alkyne to a Pt–Pt bond.
3 3 3
)} (m-CO) ]
for clarity. Selected bond lengths [Å] for 5: Pt1–Pt2 2.749(1), Pt1–Pt3
2
2
.816(1), Pt2–Pt3 2.695(1), Pt1–Ge1 2.418(2), Pt2–Ge2 2.370(2), Pt3–Ge3
.389(2), Pt1–C5 2.44(2), Pt1–C6 2.381(2), Pt2–C1 2.20(2), Pt2–C2 2.31(2),
The reaction of 3 with methyl propiolate (ZCRCH) in a 1 : 2 ratio at
room temperature afforded a triplatinum complex with a digermadi- Pt3–C1 2.08(2), Ge1–C2 1.95(2), Ge2–C5 1.98(2), Ge3–C6 2.01(2), C1–C2
platinacyclohexene moiety through the Ge–C bond-forming reactions, 1.45(2), C5–C6 1.34(2).
2
2
[
{Pt(PMe
3
)}
3
(m
3
-Z (J)-CZQCH-GePh
2
)(m
3
-Z (J)-GePh
2 2
-CZQCH-GePh )]
(
5, 65%) (eqn (3)). An equimolar reaction of ZCRCH with 3 forms a
In summary, we prepared and completely characterized
triplatinum complexes with bridging germylene ligands. The
coordination of the electron-releasing germylene ligands with the
mixture of 5 and unreacted 3 instead of intermediates corresponding
to 4. It suggests that the reaction of the second alkyne molecule
occurs rapidly than that of the first. Alkynes without strongly electron-
withdrawing groups, such as PhCRCPh and PhCRCH, did not
react with 3 even upon heating at 70 1C.
10
Pt(0)-phosphine units composed of the d configuration may
enhance the reactivity for the alkyne insertion into the Pt–Ge
bond. Several research groups have employed silylene and
germylene ligands in the synthesis of multinuclear complexes
1
5
16
17
18
19
20
21
22
23
of Fe, Ru, Os, Rh, Ir, Ni, Pd, Pt, and Au. The
reactivities of these complexes, however, were reported in only a
(3)
21
part of them. Further studies in this area will provide new
chemistry of the cluster compounds.
This work was financially supported by Grants-in-Aid for
Scientific Research (B) (No. 24350027) and (C) (No. 25410061)
from the Ministry of Education, Culture, Sports, Science, and
Technology of Japan. We thank our colleagues at the Center for
Advanced Materials Analysis, Technical Department, Tokyo
Institute of Technology, for X-ray crystal analysis and elemental
analysis.
The molecule of 5 also contains a triplatinum core with a
m3-germavinylene ligand, and a digermadiplatinacyclohexene
ligand is bonded at the opposite side of the Pt
3
plane (Fig. 3).
Two of the Pt–Pt bonds of 5 (2.749(1), 2.816(1) Å) are longer
1
3
than those of the complexes 3 and 4. The six-membered
digermadiplatinacycle is stabilized by two Ge–Pt s-bonds and
p-coordination of the vinylene group. A bis(silylene)-bridged
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5
2
2
2 2
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2
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5
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(
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1
action with the Ru
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2
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(
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4
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1
1
3, 1080.
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3 The NMR spectra of the complex before purification contained
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6
842 | Chem. Commun., 2014, 50, 6839--6842
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