Trinuclear and hexanuclear platinum clusters as building blocks for organometallic one-dimensional structures

Article abstract of DOI:10.1039/b307003d

The reaction between the new hexa- and trinuclear clusters {Pt ₆}(CC-C₆H₄-CCH)₂, (4) [{Pt ₆} = Pt₆(CO)₄(μ-PBu^t ₂)₄], and {Pt₃}Cl, (6)

Full text of DOI:10.1039/b307003d

Trinuclear and hexanuclear platinum clusters as building blocks for
organometallic one-dimensional structures†
Piero Leoni,* Fabio Marchetti, Lorella Marchetti and Marco Pasquali
Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa, Italy.
E-mail: leoni@dcci.unipi.it; Fax: +39(0)50/20237
Received (in Cambridge, UK) 19th June 2003, Accepted 29th July 2003
First published as an Advance Article on the web 15th August 2003
The reaction between the new hexa- and trinuclear clusters
{Pt6}(CC–C6H4–CCH)2, (4) [{Pt6} = Pt6(CO)4(m-PBut2)4],
and {Pt3}Cl, (6) [{Pt3} = Pt3(m-PBut2)3(CO)2], in CuI/Amine
gives the thermally and air stable {Pt6}(CC–C6H4–CC{Pt3})2
(7), where the cluster units are separated by conjugated
1,4-diethynylphenyl groups.
rigid-rod molecules. When attached to single metal centres, they
exhibit terminal coordination modes (s, h ) not involving their
1
p electrons, which can therefore take part in the conjugation
along the chain.13 In dinuclear, and still more in cluster
complexes, the alkynyl function often adopts other coordination
modes,13,14 which have been suggested to decrease the
electronic communication between the redox centres.1a These
bonding modes are probably obstructed in 3 by the bulky
phosphides. The metal core of 3 with the phosphido and
Several derivatives containing transition metals alternated with
conjugate organic spacers in the main chain have been
prepared1 and are deeply investigated for their promising
magnetic,2 liquid-crystalline,3 non-linear optical,4 lumines-
cence5 or long-range electron transfer1,6 properties. Most of
them contain isolated transition metal centres located at the
extremes7 or regularly intercalated8 in the main chain; some
recent studies have reported oligomers containing bimetallic
units.9 Ordered structures containing metal clusters intercalated
with conjugated organic spacers, although of great potential
interest, are rare,10 and are unknown with terminal s-alkynyl
spacers. This may be due to the tendency of metal clusters to
undergo fragmentation or condensation processes.
¯
carbonyl ligands show an approximately 4 2m (D2d) local
symmetry. Although the phenyl groups lie out of the pseudo-
mirror planes and do not comply with this symmetry (dihedral
angle ca. 56° between the phenyl planes), the CC, ipso- and
para- carbon atoms of the PhCC units are nearly aligned with
the major pseudo-C2 axis.
Complex 4 reasonably retains the main structural features
observed for 3 and bears two terminal ethynyl groups still
aligned with the main axis. Their reactivity and their location
make complex 4 a promising building block for the construction
of ordered structures containing the hexanuclear {Pt6} unit.
Chain elongation of ethynyl derivatives to give linear, polygo-
nal or 3-D ordered structures has been previously achieved
through self-coupling of CCH groups or their condensation with
aryl- or transition metal halides.1a,7,8,13,15
The trinuclear platinum cluster {Pt3}Cl (6) [{Pt3} = Pt3(m-
PBut2)3(CO)2] contains a halide ligand which can easily be
substituted with s-alkynyl groups;16 the steric bulkiness of the
six tert-butyls again prevents p-bonding of the alkynyl
moiety.
For these reasons complex 6 was believed to be suitable to
insert the {Pt3} unit at the extremes of the main chain of
complex 4. It was easily prepared in 70% yield by reacting the
known tricarbonyl [{Pt3}(CO)]CF3SO3 (5)11 with chloride salts
and was characterised by single crystal X-ray diffraction16 and
by IR and multinuclear NMR spectroscopy. The signals in the
1H, 31P{1H} and 195Pt{1H} NMR spectra were satisfactorily
We obtained suitable precursors for such materials by
exploiting the remarkable stabilization of the central tri-11 or
hexametallic12 core accomplished by bulky phosphido ligands
in platinum clusters. Therefore, the dichloride {Pt6}Cl2 (2)
[{Pt6}
=
Pt6(CO)4(m-PBut2)4] was obtained† from
[{Pt6}(CO)2](CF3SO3)2 (1).12 By reacting 2 with phenyl-
acetylene or 1,4-diethynylbenzene, in diethylamine with a
catalytic amount of CuI, we prepared the bis-alkynyl derivatives
{Pt6}(CCR)2 [(3), 90%, R = Ph; (4), 85%, R = C6H4-
4-CCH].
simulated by the following parameters: dP1,2 = 167.8, dP3
=
The NMR spectra of 3 and 4 exhibit a diagnostic complex
signal at ca. 336 ppm (dP, four equivalent P nuclei) and at ca.
23000 and 24675 ppm (dPt), respectively assigned to the
central four and to the apical two equivalent platinum centers.
Significant IR absorptions were found at ca. 2100 (nCC) and
2010 (nCO) cm21; moreover, the ethynyl CH resonances for 4
were found at 3.17 (dH) and 84.7 (dC) ppm. Fig. 1 shows an
ORTEP view of the structure of 3,‡ with the s-alkynyl groups
terminally bonded to the apical platinum centers of the Pt6 core.
Sigma-alkynyl moieties are found in many organometallic
Fig. 1 Molecular structure of 3. H atoms are omitted (thermal ellipsoids of
Pt and P atoms are at 30% probability). Relevant bond distances (Å) and
angles (°): Pt1–Pt3, 2.681(2); Pt1–Pt2, 2.737(2); Pt1–Pt4, 2.854(2); Pt1–
Pt6, 2.856(2); Pt2–C5, 2.00(3); Pt2–Pt3, 2.728(2); Pt3–Pt1–Pt2, 60.45(5);
Pt3–Pt1–Pt4, 62.09(5); Pt2–Pt1–Pt4, 115.60(6); Pt3–Pt1–Pt6, 61.83(5);
Pt2–Pt1–Pt6, 113.79(6); Pt4–Pt1–Pt6, 56.09(4); C5–Pt2–Pt3, 150.6(10);
C5–Pt2–Pt1, 150.6(10); Pt3–Pt2–Pt1, 58.76(5); Pt1–Pt3–Pt2, 60.79(5);
Pt1–Pt3–Pt6, 62.10(5); Pt2–Pt3–Pt6, 114.30(6); Pt1–Pt3–Pt4, 61.92(5);
Pt2–Pt3–Pt4, 115.75(6); Pt6–Pt3–Pt4, 56.12(4); Pt4–Pt6–Pt1, 61.92(5);
Pt3–Pt6–Pt1, 56.07(5); C6–C5–Pt2, 175(3); C14–C13–Pt5, 174(3).
† Electronic supplementary information (ESI) available: experimental
procedures and characterization data. See http://www.rsc.org/suppdata/cc/
b3/b307003d/
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2
46.7, dPt1,2 = 25320.0, dPt3 = 26389.8 ppm, JP1P2 = 252,
2JP1,2P3 = 130, JPt1P1 = JPt2P2 = 1972, JPt1P2 = JPt2P1
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1JPt1,2Pt3 = 2058, 1JPt1Pt2 = 1300 Hz.
The Pt3–Pt6–Pt3 linear complex 7 was prepared by reacting 4
with 2 equiv. of 6 in diethylamine/CuI (1%); it was isolated as
a deep orange air- and thermally stable solid in 92% yield, and
was characterised by microanalytical, IR and multinuclear
NMR and MALDI-TOF MS data. Fig. 2 shows its 31P{1H}
NMR spectrum exhibiting the expected signals for the P nuclei
of the tri- and hexanuclear moieties. The 195Pt{1H} NMR
spectrum of 7 exhibits four signals with the expected shape at
26081.1 (2 Pt), 25717.8 (4 Pt), 24467.5 (2 Pt) and 22993.8 (4
Pt) ppm. The 1H and 13C{1H} NMR spectra are compatible with
structure 7 and significant IR absorptions were found at 2102
(nCC), and 2030, 2013 (nCO) cm21. The utilization of tri- or
hexanuclear clusters derived from complexes 5 and 1 as
building blocks for the construction of other 1-, 2- and 3-D
molecular architectures, and the extent of the charge delocaliza-
tion between the cluster units are currently under investiga-
tion.
We thank the Ministero dell’Istruzione, dell’Università e
della Ricerca (MIUR), Programmi di Interesse Nazionale,
2002–2003 for financial support and Dr Giovanna Tripepi
(Bruker Daltonics SrL) for the MALDI-TOF MS spectrum of
complex 7.
Notes and references
‡
Crystal data for 3: C52H82O4P4Pt6, crystal dimensions 0.28 3 0.24 3
0.10 mm, space group C2/c (No. 15), a = 24.797(4), b = 17.712(2), c =
31.646(6) Å, b = 112.72(2)°, V = 12821(4) Å3, Z = 8, Dc = 2.140 g cm23
m(Mo–Ka) = 13.180 mm23, F(000) = 7632, lMoKa = 0.71073 Å, T =
293(2) K, R(F0) 0.0647. CCDC 199125. See http://www.rsc.org/
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,
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7. Complex 6 (33 mg, 0.029 mmol) and CuI (0.05 mg, 2.6 3 1024 mmol)
were added to a diethylamine (20 mL) solution of complex 4 (30 mg, 0.014
mmol). After stirring 24 h at RT the solvent was evaporated and the orange
residue was washed with H2O to give, after column chromatography on
alumina (Eluent CH2Cl2/n-hexane), 55 mg of 7 (92%). Calcd. for
16 C. Cavazza, P. Leoni, F. Marchetti, L. Marchetti and M. Pasquali,
manuscript in preparation.
C
108H188O8P10Pt12: C, 30.4; H, 4.44. Found: C, 30.1; H, 4.53.
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