954
Chemistry Letters Vol.35, No.8 (2006)
Metathesis Approach to Linkage of Two Tetraplatinum Cluster Units:
Synthesis, Characterization, and Dimerization
of [Pt4(ꢀ-OCOCH3)7(ꢀ-OCO(CH2)nCH=CH2)] (n ¼ 0{3)
Masato Ohashi, Akihiro Yagyu, Qinghong Xu, and Kazushi Mashimaꢀ
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531
(Received June 7, 2006; CL-060655; E-mail: mashima@chem.es.osaka-u.ac.jp)
Reaction of [Pt4(ꢀ-OCOCH3)8] (1) with 1 equiv of acrylic
Herein, we report the syntheses of several dimers of the Pt4
compounds through successive reactions of (a) the selective
monosubstitution of one of the four in-plane acetates in 1 by
ꢁ,!-alkenyl carboxylic acids, affording [Pt4(ꢀ-OCOCH3)7(ꢀ-
OCO(CH2)nCH=CH2)] (2), and (b) its intermolecular metathe-
sis coupling reaction mediated by Grubbs’ catalysts since alkene
metathesis is one of the promising tools to connect two cluster
moieties with a (CH2)nCH=CH2 fragment.15
Treatment of 1 with an equimolar amount of acrylic acid
yielded a monosubstituted Pt4 complex, [Pt4(ꢀ-OCOCH3)7-
(ꢀ-OCOCH=CH2)] (2a) (eq 2), in which the introduced acry-
late selectively occupied an in-plane coordination site and the
terminal C=C double bond was not involved in the coordination
to any platinum centers. This procedure was applied to other
ꢁ,!-alkenyl carboxylic acids, producing a series of monosubsti-
tuted Pt4 complexes [Pt4(ꢀ-OCOCH3)7{ꢀ-OCO(CH2)nCH=
CH2}] (2b: n ¼ 1; 2c: n ¼ 2; 2d: n ¼ 3). In contrast, the reaction
of 1 with an equimolar amount of 4-vinyl benzoic acid gave a
mixture of the corresponding mono- and disubstituted products.
The addition of excess amounts of acrylic acid to 1 led to the
complete substitution of four in-plane acetates, the same reaction
mode as in the published report using CF3COOH,12 to yield a
[Pt4(ꢀ-OCOCH3)4(ꢀ-OCOCH=CH2)4] (3).16
acid led to the selective monosubstitution of one of the four
in-plane acetates in 1, affording [Pt4(ꢀ-OCOCH3)7(ꢀ-
OCOCH=CH2)] (2a), whereas treatment with excess amounts
of acrylic acid resulted in a full-substitution of four in-plane
acetates, yielding [Pt4(ꢀ-OCOCH3)4(ꢀ-OCOCH=CH2)4] (3).
Similarly, monosubstituted heptaacetate complexes [Pt4(ꢀ-
OCOCH3)7{ꢀ-OCO(CH)nCH=CH2}] (2b–2d: n ¼ 1{3) were
prepared. Catalytic intermolecular coupling reactions of 2c and
2d assisted by Grubbs’ catalysts gave the desired dimers [{Pt4-
(ꢀ-OCOCH3)7 }2 {ꢀ-OCO(CH2)nCH=CH(CH2)n(ꢀ-OCO)}]
(6c: n ¼ 2; 6d: n ¼ 3).
Supramolecular assemblies of metal centers as entities have
recently attracted much attention because the molecular archi-
tecture is tunable through changing the types of metal fragments
and organic linkers as well as the composition ratio between
them.1,2 Although mononuclear units are major building blocks,
multinuclear units, especially metal–metal bonded clusters with
three or more metal centers, are rarely used.3–6 We are interested
in synthetic approaches to metal–metal bonded multinuclear
complexes, such as heteronuclear metal-wires,7 an infinite zig-
zag chain,8 and a Pd6 bicorn tetrahedron,9 because these com-
plexes exhibit unique properties, different from those of mono-
nuclear complexes, due to electron transfer through the metal–
metal bond and, in some cases, synergistic effects of the plural
metal centers.10
(2)
As part of our continuing studies, we embarked on the con-
struction of a new series of supramolecular arrays composed of a
cluster complex, and a tetranuclear platinum octaacetate com-
plex, [Pt4(ꢀ-OCOCH3)8] (1),11 was chosen as a suitable build-
ing block. In 1, four platinum atoms lie at the apexes of a square,
In the 1H NMR spectrum of 2d, the terminal olefinic part of
the 5-hexenyl carboxylate was observed as a typical pattern of
vinyl protons at ꢂH 4.95, 5.08, and 5.86. In addition to the signals
˚
2.50 A per side, and four in-plane acetate ligands are selectively
replaced by free carboxylate ions in solution.12 Thus, we have at-
tempted the syntheses of dicarboxylate-bridged octaplatinum
complexes via the dimerization reaction of 1. However, direct
reaction of 1 with half the amount of dicarboxylic acid resulted
in failure; careful addition of 0.5 equiv of different kinds of
dicarboxylic acids such as sebacic acid and terephthalic acid to
1 induced the precipitation of insoluble black organoplatinum
compounds (eq 1).13,14
1
assignable to the 5-hexenyl carboxylate, the H NMR spectrum
of 2d exhibited three signals attributable to the out-plane ace-
tates at ꢂ 1.98, 2.00, and 2.01, together with two signals of the
in-plane acetates at ꢂ 2.44 and 2.45 with an intensity ratio of
1:1:2 and 2:1, respectively.17 Observation of the solvated ion
peak of m/z 1347, [2d + CH3CN]þ, in the ESI-MS spectrum
of 2d strongly supported the monosubstituted structure.
Complexes 2a–2d were treated with catalytic amounts of
Grubbs’ catalysts, and the results are summarized in Table 1.
Intermolecular metathesis reactions of 2c and 2d afforded the
corresponding octaplatinum clusters [{Pt4(ꢀ-OCOCH3)7}2{ꢀ-
OCO(CH2)nCH=CH(CH2)n(ꢀ-OCO)}] (6c: n ¼ 2; 6d: n ¼ 3)
(eq 3, Table 1, Entries 5–10). In the metathesis reaction of 2d
with the longest methylene the coupling product reached 95%
when 20 mol % of 5 was used as a catalyst over 16 h (Table 1,
(1)
Copyright Ó 2006 The Chemical Society of Japan
Ohashi, Masato
