Synthesis and spectroscopic and electronic characterization of New cis-configured Di- to multiplatinum alkynyls

Article abstract of DOI:10.1021/om060007a

Utilization of Sonogashira coupling reactions with cis-[Pt(dppe)Cl ₂] and varying amounts of the alkynyl ligands HC≡CRC≡CH (where R = p-C₆H₄, p-C₆H₄-p-C ₆H₄) afford the monoplati

Full text of DOI:10.1021/om060007a

Organometallics 2006, 25, 2525-2532
2525
Synthesis and Spectroscopic and Electronic Characterization of New
Cis-Configured Di- to Multiplatinum Alkynyls
Nicholas J. Long,* Chun K. Wong, and Andrew J. P. White
Department of Chemistry, Imperial College London, Exhibition Road,
South Kensington, London, U.K. SW7 2AZ
ReceiVed January 4, 2006
Utilization of Sonogashira coupling reactions with cis-[Pt(dppe)Cl2] and varying amounts of the alkynyl
ligands HCtCRCtCH (where R ) p-C6H4, p-C6H4-p-C6H4) afford the monoplatinum complexes cis-
[Pt(dppe)(CtCRCtCH)2] (R ) p-C6H4 (1a), p-C6H4-p-C6H4 (1b)), the diplatinum complexes cis-
[(HCtCRCtC)Pt(dppe)(CtCRCtC)Pt(dppe)(CtCRCtCH)] (R ) p-C6H4 (2a), p-C6H4-p-C6H4 (2b)),
the triplatinum complexes cis-[(HCtCRCtC)Pt(dppe)(CtCRCtC)Pt(dppe)(CtCRCtC)Pt(dppe)-
(CtCRCtCH)] (R ) p-C6H4 (3a), p-C6H4-p-C6H4 (3b)), and the respective oligomeric species 4a,b, all
in reasonable yields. X-ray diffraction studies of 2a reveal the presence of two independent diplatinum
molecules in the asymmetric unit, each with Ci symmetry. All the complexes have been fully characterized
by NMR and mass spectrometry, and GPC analysis of 4a,b indicate their oligomeric nature, with a degree
of polymerization of ca. 4. Electronic spectral studies indicate that the optical band gap decreases with
increasing chain length but that the intensity of the triplet state emission increases with the number of
repeating units. As expected, there is less effective π-conjugation along the chain in the cis configuration
as compared to the analogous trans-oriented species.
rod species possess a range of properties, including nonlinear
optical effects, liquid crystallinity, electrical conductivity, and
photovoltaic behavior, which differ from those of conventional
organic materials.1-10 The relatively low oxidation states of late
transition metals in the σ-alkynyl complexes are usually
stabilized by the presence of auxiliary ligands, and the com-
plexes can exist in either a trans or a cis configuration.1-5 In
group 10 systems, especially with platinum, owing to the
thermodynamic stability of the trans isomer, the majority of
luminescent investigations have focused on the trans complexes
with monodentate auxiliary ligands (L). The σ-acetylide com-
plexes often exist as the diterminal alkynes trans-[PtL2(CtCR)2]
and polyynes trans-[-PtL2-CtCRCtC-]n with a wide variety
of aromatic ring systems (R).1-4,6,9,10c,11
Introduction
The study of transition-metal alkynyl σ-complexes continues
to attract researchers because of the interesting electronic
properties that they exhibit: i.e., their potential use as large-
area flexible displays in the electronics industry.1-5 The first
reported platinum and palladium acetylides were synthesized
by Hagihara et al. in the 1970s,6 and since then, many new
classes of materials have been extensively studied and inves-
tigated with the introduction of different group 8,1,5,7 group 9,1,8
group 101-4,9 and other transition metals.1,3-5,10 These rigid-
* To whom correspondence should be addressed. E-mail: n.long@
imperial.ac.uk. Tel: +44 (0)20 75945781. Fax: +44 (0)20 75945804.
(1) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586
and references therein.
(2) (a) Wong, W. Y. J. Inorg. Organomet. Polym. Mater. 2005, 15, 197
and references therein. (b) Wong, W. Y. Comments Inorg. Chem. 2005,
26, 39.
(3) Silverman, E. E.; Cardolaccia, T.; Zhao, X.; Kim, K. Y.; Haskins-
Glusac, K.; Schanze, K. S. Coord. Chem. ReV. 2005, 249, 1491 and
references therein.
In the study of cis-platinum ethynyl materials, the introduction
of chelating auxiliary ligands, such as bidentate phosphines
(dppe, dppp) or diimine groups (tBu2bipy),12,13 helps to over-
come the thermodynamic instability of cis isomers, and diimine-
(4) Yam, V. W.-W. Acc. Chem. Res. 2002, 35, 555 and references therein.
(5) Schwab, P. F. H.; Levin, M. D.; Michl, J. Chem. ReV. 1999, 99, 1863.
(6) (a) Fujikura, Y.; Sonogashira, K.; Hagihara, N. Chem. Lett. 1975,
1067. (b) Sonogashira, K.; Yatake, T.; Tahoda, Y.; Takashashi, S.; Hagihara,
N. J. Chem. Soc., Chem. Commun. 1977, 291. (c) Sonogashira, K.;
Takahashi, S.; Hagihara, N. Macromolecules 1977, 879. (d) Sonogashira,
K.; Ohga, K.; Hagihara, N. J. Organomet. Chem. 1980, 188, 237.
(7) (a) Hurst, S. K.; Ren, T. J. Organomet. Chem. 2003, 670, 188. (b)
Long, N. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 21.
(8) (a) Bruce, M. I.; Zaitseva, N. N.; Skelton, B. W.; Somers, N.; White,
A. H. Aust. J. Chem. 2003, 56, 509. (b) Ara, I.; Berenguer, J. R.; Eguiza´bal,
E.; Fornie´s, J.; Lalinde, E.; Mart´ın, A.; Mart´ınez, F. Organometallics 1998,
17, 4578.
(9) (a) D’Amato, R.; Fratoddi, I.; Cappoto, A.; Altamura, P.; Delfini,
M.; Bianchetti, C.; Bolasco, A.; Polzonetti, G.; Russo, M. V. Organome-
tallics 2004, 23, 2860. (b) D’Amato, R.; Furlani, A.; Colapietro, M.;
Portalone, G.; Casalboni, M.; Falconieri, M.; Russo, M. V. J. Organomet.
Chem. 2001, 627, 13.
(10) (a) Horn, C. R.; Mart´ın-Alvarez, J. M.; Gladysz, J. A. Organome-
tallics 2002, 21, 5386. (b) Bruce, M. I.; Hall, B. C.; Skelton, B. W.; Smith,
M. E.; White, A. H. Dalton Trans. 2002, 995. (c) Vicente, J.; Chicote, M.
T.; Alvarez-Falco´n, M. M.; Jones, P. G. Organometallics 2005, 24, 2764.
(11) (a) Adams, C. J.; Bowen, L. E. Dalton Trans. 2005, 2239. (b) Khan,
M. S.; Al-Mandhary, M. R. A.; Al-Suti, M. K.; Hisahm, A. K. Raithby, P.
R.; Ahrens, B.; Mahon, M. F.; Male, L.; Marseglia, E. A.; Tedesco, E.;
Friend, R. H.; Ko¨hler, A.; Feeder, N.; Teat, S. J. Dalton Trans. 2002, 1358.
(c) Khan, M. S.; Kakkar, A. K.; Long, N. J.; Lewis, J.; Raithby, P.; Nguyen,
P.; Marder, T. B.; Wittmann, F.; Friend, R. H. J. Mater. Chem. 1994, 4,
1227. (d) Bruce. M. I.; Davy, J. Hall, B. C.; Jansen van Galen, Y.; Skelton,
B. W.; White, A. H. Appl. Organomet. Chem. 2002, 16, 559. (e) Deeming,
A. J.; Hogarth, G.; Lee, M. Y. V.; Saha, M.; Redmond, S. P.; Phetmung,
H. T.; Orpen A. G. Inorg. Chim. Acta 2000, 309, 109. (f) Fratoddi, I.;
Battocchio, C.; Furlani, A.; Mataloni, P.; Polzonetti, G.; Russo, M. V. J.
Organomet. Chem. 2003, 674, 10. (g) Vicente, J.; Chicote, M. T.; Alvarez-
Falco´n, M. M.; Jones, P. G. Chem. Commun. 2004, 2658. (h) Long, N. J.;
White, A. J. P.; Williams, D. J.; Younnus, M. J. Organomet. Chem. 2002,
649, 94.
(12) (a) Bruce, M. I.; Costuas, K.; Halet, J. F.; Hall, P. C.; Low, B. C.;
Nicholson, B. L.; Skelton, B. W.; White, A. H. Dalton Trans. 2002, 383.
(b) Janka, M.; Anderson, G. K.; Rath, N. P. Organometallics 2004, 23,
4382. (c) Wong, W. Y.; Lu, G. L.; Choi, K. H. J. Organomet. Chem. 2002,
659, 107. (d) Bruce, M. I.; Hall, B. C.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1999, 592, 74. (e) Yamazaki, S.; Deeming, A. J. J. Chem.
Soc., Dalton Trans. 1993, 3051.
10.1021/om060007a CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/08/2006

2526 Organometallics, Vol. 25, No. 10, 2006
Long et al.
Scheme 1. General Scheme for the Synthesis of Monomeric Complexes 1a,b and Dimeric Complexes 2a,b and 3a,b
stabilized platinum acetylenic cis complexes exhibit interesting
white14 and red15 optoelectronic properties. However, within this
area, most of the investigations are limited to monoplatinum
dienyl complexes and there are still very few reports on bis-
(ethynyl) and oligomeric species with phosphine-chelating
auxiliary ligands. To address this issue, we report here the
synthesis, characterization, and systematic study of the electronic
properties of a series of cis-configured monomeric (1), dimeric
(2), trimeric (3), and oligomeric (4) platinum complexes with
the ancillary ligand bis(diphenylphosphino)ethane and diacety-
lenic ligands 1,4-diethynylbenzene (a) and 4,4′-diethynylbiphe-
nyl (b). These species represent precursors toward the con-
struction of metal-alkynyl molecular shapes, such as squares,
hexagons, and catenanes.
and the diplatinum complexes cis-[(HCtCRCtC)Pt(dppe)-
(CtCRCtC)Pt(dppe)(CtCRCtCH)] (R ) p-C6H4 (2a),
p-C6H4-p-C6H4 (2b)) with an average 12% yield as the minor
product. However, in the synthesis of the triplatinum derivatives,
where excess monoplatinum species were used instead of excess
HCtCRCtCH, the conventional method mainly resulted in
insoluble products with a small amount of isolated soluble
products characterized as the diplatinum species, owing to the
ligand exchange reaction between triplatinum and monoplatinum
complexes. However, an improved synthesis utilizing a high
dilution method, diisopropylamine and dichloromethane (1/20),
reduced the rate of ligand exchange. The yields of the desired
triplatinum complexes cis-[(HCtCRCtC)Pt(dppe)(CtCRCt
C)Pt(dppe)(CtCRCtC)Pt(dppe)(CtCRCtCH)] (R ) p-C6H4
(3a), p-C6H4-p-C6H4 (3b)) were thus 27% and 23%, respec-
tively, with the formation of byproduct dimeric complexes 2a,b
in yields of 36% and 41%, respectively.
During the course of our research and the preparation of this
paper, compounds 1a,b were independently reported by Raithby
et al.16
Neutral platinum-containing molecular squares using mono-
platinum cis complexes as reactants were first reported by Bruce
and co-workers12a under methanol and anhydrous sodium acetate
reaction conditions. Later, it was discovered that the molecular
squares could be also synthesized under CuI-mediated coupling
conditions in a solvent mixture of diethylamine with CH2Cl2
or THF, as reported by Lin and co-workers17 and Anderson and
co-workers.12b Unfortunately, in our case, the reaction of
monomeric complex 1a and cis-[Pt(dppe)Cl2] in refluxing
diethylamine/THF only yielded an insoluble yellow precipitate
and the same result was obtained in a more polar solvent
system: diisopropylamine/CH2Cl2 (3/40, v/v). Coupling reac-
tions were also attempted between HCtCRCtCH (R )
p-C6H4, p-C6H4-p-C6H4) and cis-[Pt(dppe)Cl2], in a 1/1 ratio
with a polar solvent system: diisopropylamine/CH2Cl2 (3/40,
v/v). The isolated product remained a yellow insoluble precipi-
tate with HCtC-p-C6H4CtCH, whereas with HCtC-p-C6H4-
p-C6H4CtCH, the soluble oligomeric species 4b, along with
an insoluble yellow precipitate, were obtained (Scheme 2). The
result of the HCtC-p-C6H4-p-C6H4CtCH reaction was the
same as that reported in the literature18 synthesized via a less
polar solvent system: refluxing toluene/diethylamine. In addi-
tion, utilizing methanol and anhydrous sodium acetate, the
reactions between monoplatinum complexes (1a,b) and cis-[Pt-
Results and Discussion
Syntheses and Characterization. Scheme 1 illustrates the
reactions used in the syntheses of the complexes 1a,b-3a,b.
The conventional Sonogashira coupling routes using cis-[Pt-
(dppe)Cl2 and excess HCtCRCtCH (R ) p-C6H4, p-C6H4-
p-C6H4) in diisopropylamine and dichloromethane with CuI
catalyst were employed to afford the monoplatinum complexes
cis-[Pt(dppe)(CtCRCtCH)2] (R ) p-C6H4 (1a), p-C6H4-p-
C6H4 (1b)), with an average 70% yield as the major product
(13) (a) Kwok, C. C.; Ngai, H. M. Y.; Chan, S. C.; Sham, I. H. T.; Che,
C. M.; Zhu, N. Inorg. Chem. 2005, 44, 4442. (b) Hissler, M.; Connick, W.
B.; Geiger, D. K.; McGarrah, J. E.; Lipa, D.; Lachicotte, R. J.; Eisenberg,
R. Inorg. Chem. 2000, 39, 447. (c) Adams, C. J.; James, S. J.; Liu, X.;
Raithby, P. R.; Yellowlees, L. J. Dalton Trans. 2000, 63. (d) James, S. L.;
Younus, M.; Raithby, P. R.; Lewis, J. J. Organomet. Chem. 1997, 543,
233. (e) Chan, C. W.; Cheng, L. K.; Che, C. M. Coord. Chem. ReV. 1994,
132, 87.
(14) (a) Che, C. M.; Chan, S. C.; Xiang, H. F.; Chan, M. C. W.; Liu,
Y.; Wang, Y. Chem. Commun. 2004, 1484. (b) D’Andrade, B. W.; Brooks,
J.; Adamovich, V.; Thompson, M. E.; Forrest, S. R. AdV. Mater. 2002, 14,
1032.
(15) (a) Siemeling, U.; Bausch, K.; Fink, H.; Bruhn, C.; Baldus, M.;
Angerstein, B.; Plessow, R.; Brockhinke, A. Dalton Trans. 2005, 2365. (b)
Lu, W.; Mi, B. X.; Chan, M. C. W.; Hui, Z.; Che, C. M.; Zhu, N.; Lee, S.
T. J. Am. Chem. Soc. 2004, 126, 4958. (c) Lu, W.; Mi, B. X.; Chan, M. C.
W.; Hui, Z.; Zhu, N.; Lee, S. T., Che, C. M. Chem. Commun. 2002, 206.
(16) Saha, R.; Abdul Qaium, M.; Debnath, D.; Younus, M.; Chawdury,
N.; Sultana, N.; Kociok-Ko¨hn, G. K.; Ooi, L. L.; Raithby, P. R.; Kijima,
M. Dalton Trans. 2005, 2760.
(17) (a) Lee, S. J.; Luman, C. R.; Castellano, F. N.; Lin, W. Chem.
Commun. 2003, 2124. (b) Lee, S. J.; Hu, A.; Lin, W. J. Am. Chem. Soc.
2002, 124, 12948.
(18) Iucci, G.; Infante, G.; Polzonetti, G. Polymer 2002, 43, 655.

New Cis-Configured Di- to Multiplatinum Alkynyls
Organometallics, Vol. 25, No. 10, 2006 2527
Scheme 2. Sonogashira Coupling Synthesis of Oligomeric Species 4a,b
Scheme 3. Another Synthetic Pathway for Oligomeric Species 4a,b
(dppe)(OTf)2] gave the oligomeric mixtures 4a,b, respectively,
measured by FAB-MS, whereas the trimeric complexes were
characterized by MALDI-MS and, furthermore, by MALDI
high-resolution mass spectrometry. The molecular weight
distribution of the oligomeric species was measured by gel
permeation chromatography (GPC) methods. The molecular and
crystal structure of the dimeric complex 2a was determined by
single-crystal X-ray crystallography. X-ray analysis of 2a
revealed the presence of two independent diplatinum molecules
(A and B) in the asymmetric unit, each with Ci symmetry
(molecule A is shown in Figure 1 and molecule B in Figure S1
in the Supporting Information). Though the unique platinum
atom in each molecule has a distorted-square-planar coordination
with complex 31P{1H} NMR spectral patterns but no insoluble
precipitate (Scheme 3). No neutral platinum molecular squares
could be isolated from any reaction.
All the complexes and oligomeric species were stable in air
and could be stored without any special precautions. However,
they did not exhibit good solubility and were only soluble in
polar solvents such as dichloromethane and DMF, and this
solubility decreased with an increase in the numbers of the
repeating unit. The new complexes were fully characterized by
IR, 1H and 31P{1H} NMR, and elemental analysis. The molec-
ular weights of the monomeric and dimeric complexes were
Figure 1. Molecular structure of one (A) of the two Ci-symmetric independent molecules present in the crystals of 2a.

2528 Organometallics, Vol. 25, No. 10, 2006
Long et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for the
Two Ci-Symmetric Independent Molecules (A and B) Present
in the Crystals of 2a
A, forming bifurcated C-H‚‚‚π hydrogen bonds with H‚‚‚π
distances and C-H‚‚‚π angles of 2.91 Å and 120° to the C(1)t
C(2) bond and 3.00 Å and 125° to the C(11)tC(12) bond. The
C(9)tC(10) linkage in molecule A is involved in a π‚‚‚π
interaction with the C(3)/C(8) aryl ring in a centrosymmetrically
related counterpart with a centroid‚‚‚centroid separation of ca.
3.48 Å. The closest approach to the C(1′)tC(2′) and C(11′)t
C(12′) bonds in molecule B are from ethyl protons on C(16)
and C(17), respectively, in molecule A (H‚‚‚π ) 3.06 Å and
C-H‚‚‚π ) 106° for the C(1′)tC(2′) bond, H‚‚‚π ) 2.75 Å
and C-H‚‚‚π ) 166° for the C(11′)tC(12′) bond), and the
closest approach to the C(9′)tC(10′) bond is from the C(9)t
C(10)-H proton in molecule A at H‚‚‚π ) 2.95 Å, C-H‚‚‚π
) 160°.
IR spectroscopy is a useful diagnostic tool for the charac-
terization of CtC bond units, as most compounds exhibited a
single IR νCtC stretch at around 2101 cm-1. If more than two
ligand moieties were present in the complexes, multiple νCtC
bands might be observed (i.e. in 2a and 3a, two νCtC stretches
were observed at 2104 and 2116 cm-1). For the IR νCtCH
stretching vibration, only a single absorption peak at around
3296-3301 cm-1 was observed for all the complexes 1a,b-
3a,b and the oligomeric species 4a,b.
In all cases, 1H NMR signals arising from the protons of the
organic fragments were observed and clearly identified in the
alkynyl and aromatic regions. The methylenic protons of the
dppe group, P(CH2)P, gave the expected peaks at δ 2.3-2.5,
and singlet signals were observed at δ 3.05-3.16 due to the
presence of CtCH. Between the two series of complexes, the
CtCH signals in 1a-3a are shifted more upfield than those in
1b-3b, due to the poor shielding effect in CtCH caused by
the presence of an additional phenyl ring in -CtC-p-C6H4-p-
C6H4CtC- moieties. The aromatic protons of dppe and the
ligand moieties gave complicated multiplets around δ 7.1-8.2.
For the complexes 1a-3a, a new singlet at δ 7.04 was observed
in 2a arising from the p-C6H4 moiety in the inner core and the
integral signal intensity was doubled in 3a. This phenomenon
implied that the electron densities on the ligand moieties in the
inner core increased when the number of repeating units
increased. The increased electron density was induced by the
presence of cis-configured platinum atoms in complexes 2a and
3a.
The 31P{1H} NMR signals in the cis complexes were more
complicated than those in the relevant trans complexes. In the
analogous trans complexes, all 31P{1H} signals are singlets with
two Pt-P satellite signals. However, in the cis complexes, this
pattern was only observed in the monomeric complexes 1a,b.
In the dimeric complexes 2a,b, due to the two different chemical
environments on the four phosphorus atoms, 2a showed two
doublet signals and 2b displayed an AA′BB′ patternsa pseudo-
quartet with central and satellite 31P{1H} signals. In the trimeric
complexes 3a,b, the 31P{1H} NMR spectra were basically a
combination of the spectra of the respective monomeric and
dimeric complexes (Figure 2). As a result, in the oligomeric
species 4a,b, only complicated multiplet 31P{1H} signals were
observed but all the Pt-P coupling constants were in the range
consistent with reported values.12a,b,e,16
A
B
Pt-P(1)
2.2871(19)
2.019(7)
1.195(10)
1.182(10)
2.2723(18)
2.025(7)
2.2709(18)
2.020(7)
1.202(10)
1.197(9)
2.2701(17)
2.005(6)
1.167(14)
Pt-C(1)
C(1)-C(2)
C(11)-C(12)
Pt-P(2)
Pt-C(11)
C(9)-C(10)
1.170(13)
P(1)-Pt-P(2)
84.82(7)
93.8(2)
85.80(6)
88.4(2)
P(1)-Pt-C(11)
P(2)-Pt-C(11)
Pt-C(1)-C(2)
177.8(2)
168.9(6)
177.7(11)
173.7(10)
172.1(2)
89.0(2)
92.6(3)
173.2(8)
176.8(7)
173.7(2)
171.0(6)
179.0(15)
173.1(8)
176.66(19)
96.88(18)
88.8(3)
C(6)-C(9)-C(10)
C(11)-C(12)-C(13)
P(1)-Pt-C(1)
P(2)-Pt-C(1)
C(1)-Pt-C(11)
C(1)-C(2)-C(3)
Pt-C(11)-C(12)
172.8(8)
170.2(6)
geometry (cis angles in the range 84.82(7)-93.8(2)° for
molecule A and 85.80(6)-96.88(18)° for molecule B; {Pt,P-
(1),P(2),C(1),C(11)} coplanar to within ca. 0.07 Å for molecule
A and to within ca. 0.03 Å for molecule B), the two molecules
have noticeably different relative positions for the alkynyl
substituents (see Figure S4 in the Supporting Information), the
P(2)-Pt-C(1) and P(1)-Pt-C(11) angles varying between the
two molecules by ca. 7.9 and 5.4°, respectively (Table 1).
The complexes have both terminal and bridging alkynyl-
aryl-alkynyl ligands, and it is the orientation of the terminal
ligand that is the main difference between the two independent
molecules (see Figure S4). In molecule A the C(3)/C(8) aryl
ring is oriented near parallel (ca. 10°) to the platinum coordina-
tion plane, while in molecule B this ring is steeply inclined (ca.
82°). In each case the aryl ring of the bridging ligand is almost
parallel with the platinum coordination plane, the inclination
angles being ca. 8 and 6° in molecules A and B, respectively.
It is also noticeable that the two molecules have different bends
away from linearity for the alkynyl units. In molecule A the
bends at C(1) and C(2) move the C(3)/C(8) aryl ring in the
direction of P(2), whereas in molecule B they move the aryl
ring away from P(2). For the C(11)tC(12) unit, the difference
is less marked, but Figure S4 clearly shows a greater bend
toward P(1) in molecule B with regard to molecule A. However,
whereas for the C(1)tC(2) alkynyl moiety the magnitudes of
the departures from linearity were similar for the two molecules
(with a maximum difference of ca. 2°), for the C(11)tC(12)
ligand there is a difference of ca. 7° for the angle at C(11). In
molecule A the Pt-P bond distances are distinctly asymmetric,
with that trans to the terminal alkynyl-aryl-alkynyl ligand
(Pt-P(1) ) 2.2871(19) Å) being longer than that trans to the
bridging ligand (Pt-P(2) ) 2.2723(18) Å). In molecule B, in
contrast, the two bonds are the same, being 2.2709(18) and
2.2701(17) Å to P(1) and P(2), respectively. In each molecule
the Pt-C distances are the same (2.019(7) and 2.025(7) Å in
molecule A, 2.020(7) and 2.005(6) Å in molecule B). The closest
literature examples19 have symmetric terminal alkynyl ligands,
and in each case the Pt-P distances are essentially the same.
The C(9′)tC(10′)-H proton from molecule B approaches
both the C(1)tC(2) and C(11)tC(12) triple bonds in molecule
Mass spectral data for complexes 1a,b-2a,b showed intense
molecular ion peaks at m/z 844 [M + H]+ for 1a, m/z 996 [M]+
for 1b, m/z 1561 [M]+ for 2a, and m/z 1791 [M]+ for 2b. The
loss of ligand fragments also gave sensible fragmentation
patterns. The soft ionization mode MALDI reduces the degree
of fragmentation, enhancing the parent ion signals, as compared
(19) (a) Janka, M.; Anderson, G. K.; Raith, N. P. Organometallics 2004,
23, 4382; (b) Bruce, M. I.; Costuas, K.; Halet, J.-F.; Hall, B. C.; Low, P.
J.; Nicholson, B. K.; Skelton, B. W.; White, A. H. Dalton Trans. 2002,
383. (c) Falvella, L. R.; Fornie´s, J.; Go´mez, J.; Lalinde, E.; Martin, A.;
Moreno, M. T.; Sacrista´n, J. Chem. Eur. J. 1999, 5, 474.

New Cis-Configured Di- to Multiplatinum Alkynyls
Organometallics, Vol. 25, No. 10, 2006 2529
Table 3. Spectral Absorption Data for the Complexes
1a,b-3a,b and Oligomeric Species 4a,b Recorded in CH2Cl2
at Room Temperature
complex
λ
max (nm)a
Eg (eV)
1a
2a
3a
4a
1b
2b
3b
4b
289 (4.05), 298 (3.98), 303 (4.05), 326 (3.71)
290 (6.37), 300 (6.28), 326 (5.58), 359 (4.00)
292 (6.26), 305 sh (6.08), 327 (5.82), 359 (4.86)
218 (15.5), 290 (14.3), 331 (13.5), 359 (11.6)
262 sh (4.27), 325 (10.69)
262 sh (4.68), 334 (11.72)
262 sh (9.69), 344 (24.20)
342 (14.4)
3.28
3.12
3.02
2.42
3.16
3.08
2.86
2.50
a Extinction coefficients are shown in parentheses (×104).
Table 4. Photoluminescence (PL) Data for Complexes
1a,b-3a,b Recorded in CH2Cl2 at Room Temperature
Stokes
shift
intensity
com-
plex
(T1 f S0) ∆Ea ratio (T1 f S0,
λ
em (nm)
(eV)
(eV)
S1 f S0)b
Figure 2. 31P{1H} NMR spectra for complexes 1a-3a.
1a
2a
3a
1b
2b
3b
328, 344, 353, 482, 522
355, 370, 382, 505, 535
339, 353, 505, 535
325, 340, 356, 532, 575
325, 340, 355, 544, 585
337, 353, 369 sh, 546, 584
1.23
1.00
1.00
1.48
1.32
1.35
1.21
1.04
1.20
1.48
1.53
1.41
0.12
0.68
0.82
0.64c
2.03c
8.16c
a Energy difference between singlet emission (S1) and triplet emission
(T1). b Ratio of the intensities of triplet emission to singlet emission at room
temperature. c Scale: 1 × 10-2
.
chromatography, due to their adherence to the packing agents.
The GPC system used for the work was calibrated with a
mixture of narrow-distribution poly(methyl methacrylate) cali-
brants, and the results were expressed as PMMA equivalent
molecular weights. Although there could be considerable
differences between PMMA equivalents and actual molecular
weights of the samples,9 the presence of the end group -Ct
CH signals in NMR and IR data provided evidence that the
degree of polymerization was not high in 4a,b.
Figure 3. MALDI-HRMS and isotopic distribution of the triplati-
num complex 3b.
Spectroscopic Data. The electronic spectral data for all the
complexes 1a,b-3a,b and oligomeric species 4a,b are sum-
marized in Tables 3 and 4, primarily characterized by UV-vis
and photoluminescent spectroscopy at room temperature in CH2-
Cl2. All of the compounds exhibited intense absorptions in the
near-UV region (ca. 262-359 nm). In every case, the first
absorption peak is due to the π - π* transition22 in the organic
system with some LMCT character resulting from the possible
admixture of a metal d orbital and a ligand π* orbital, which
may alter the overall energy of the optical transition.23 We
associate the lowest energy peak with the (0,0) vibronic peak
of a S0 f S1 transition from the highest occupied molecular
orbital (HOMO) to the lowest unoccupied molecular orbital
(LUMO), which are mainly delocalized π and π* orbitals. In
the a series of complexes, as compared to the free ligand, a
new lowest energy absorption peak with increasing extinction
coefficient was observed on going from 1a to 3a (Figure 4),
which indicated that π conjugation is continued through the
metals along the chain with an increase of repeating unit.
Likewise, in the b series (Figure 5), the bathochromic shift in
the first absorption transitions from 1b to 3b arose from an
electron excitation which was also delocalized over more than
Table 2. Structural Properties of the Oligomers
oligomer
Mw
Mn
Mw/Mn
4a
4b
2520
3540
2070
2560
1.2
1.4
with other conventional common ionization methods.20 There-
fore, it was selected as an ionization source in the MALDI-MS
measurements of the trimeric species 3a,b, showing parent peaks
at m/z 2279.4 and 2581.6, respectively. In MALDI-HRMS, the
spectra also exhibited intense parent ion signals for the cations
at m/z 2279.4604 and 2581.5768 (Figure 3), respectively, which
matched the calculated isotopic distribution patterns. The
molecular weight data of the oligomeric species 4a,b determined
by GPC in DMF are tabulated in Table 2. The comparatively
high retention volumes and low Mw values indicated that the
species only contained low-molecular-weight components and
the degree of polymerization calculated from Mn was 4 for both
4a and 4b, very low compared with other known trans-platinum
polyynes.9,11b,c,21 This result could be ascribed to the extremely
low solubility of cis-platinum compounds and higher molecular
weight, more truly polymerized species were too insoluble to
analyze. The oligomers could not be purified via column
(22) (a) Chawdury, N.; Ko¨hler, A.; Friend, R. H.; Younus, M.; Long,
N. J.; Raithby, P. R.; Lewis, J. Macromolecules 1998, 31, 722. (b) Whittle,
C. E.; Weinstein, J. A.; George, M. W.; Schanze, K. S. Inorg. Chem. 2001,
40, 4053.
(23) Wilson, J. S.; Ko¨hler, A.; Friend, R. H.; Al-Suti, M. K.; Al-
Mandhary, M. R. A.; Khan, M. S.; Raithby, P. R. J. Chem. Phys. 2000,
113, 7627.
(20) Karas, M.; Kru¨ger, R. Chem. ReV. 2003, 103, 427.
(21) (a) Wong, W. Y.; Wong, C. K.; Poon, S. Y.; Lee, A. W. M.; Mo,
T.; Wei, S. Macromol. Rapid Commun. 2005, 26, 376. (b) Wong, W. Y.;
Wong, C. L.; Lu, G. L.; Lee, A. W. M.; Cheah, K. W.; Shi, J. X.
Macromolecules 2003, 36, 983.

2530 Organometallics, Vol. 25, No. 10, 2006
Long et al.
Figure 4. Comparison of normalized UV-vis absorption spectra
of complexes 1a-3a and oligomeric 4a.
Figure 6. Comparison of normalized photoluminescent emission
spectra of complexes 1a-3a.
Figure 5. Comparison of normalized UV-vis absorption spectra
of complexes 1b-3b and oligomeric 4b.
Figure 7. Comparison of normalized photoluminescent emission
spectra of complexes 1b-3b.
one repeating unit. It should be noted that the λmax values of
the lowest energy absorptions in 4a,b were not significantly
different from those observed from complexes 3a,b, respec-
tively, which indirectly reflects the fact that 4a,b are mainly a
mixture of low-molecular-weight oligomeric species. The solu-
tion λmax values decreased in the order 4a ≈ 3a ≈ 2a > 4b ≈
3b > 2a > 1a,b. In comparison with the optical results of other
relevant trans-platinum alkynes with (hetero)aromatic spacers,21b
the lowest energy absorptions in these cis-platinum compounds
were generally at higher energies. This confirms that the
electronic delocalization in the cis configuration was less
effective than that in trans configurations for these platinum
systems. The optical band gap Eg(HOMOfLUMO), determined
from the λ0-0 band edge, also gradually decreased with
increasing chain length in the order 1a > 1b > 2a > 2b > 3a
> 3b > 4a > 4b. Generally, the values of Eg in the b series
were smaller than those in the a series, because more electronic
and vibronic structures were present in the b series complexes,
although the first absorption transition maxima were at lower
energies in the a series complexes.
proximate mirror symmetries with the lowest energy excitations
expected as in the Franck-Condon model.24 The intense high-
energy photoluminescence peaks near 330 nm (ca. 3.75 eV)
were the fluorescence from the same singlet excited state (S1
f S0) with small Stokes shifts between the excitation and
emission spectra.11 In comparison with the free ligand emissions,
HCtC-p-C6H4CtCH (328 nm) and HCtC-p-C6H4-p-C6H4-
CtCH (340 nm), there was no significant difference in the high-
energy emissions between the free ligands and complexes 1a,b-
3a,b, indicating that the singlet state emissions were ligand-
based emissions without the influence of the intrusion of
platinum metals in the complexes.
The lower energy bands with substantial Stokes shifts
measured ca. >1.00 eV were the phosphorescence T1 f S0
emissions, which were greatly enhanced by the inclusion of
platinum metals. The triplet state emissions have been previously
assigned in other related polyynes and diynes on the basis of
optical measurements.11,21,25 It was shown that, for the Pt
polyynes with different spacers R, the 0-0 vibrational peak of
phosphorescence always occurs 0.7 eV below the 0-0 vibra-
The room-temperature photoluminescence emission spectra
of complexes 1a,b-3a,b in CH2Cl2 are shown in Figures 6 and
7. All of them exhibited two emission bands in the near-UV
region and from yellow-green to yellow-orange visible regions
at room temperature. The high-energy emissions showed ap-
(24) Parker, C. A. Photoluminescence in Solutions, Elsevier: Amsterdam,
1968.
(25) Wilson, J. S.; Chawdhury, N.; Al-Mandhary, M. R. A.; Younus,
M.; Khan, M. S.; Raithby, P. R.; Ko¨hler, A.; Friend, R. H. J. Am. Chem.
Soc. 2001, 123, 9412.

New Cis-Configured Di- to Multiplatinum Alkynyls
Organometallics, Vol. 25, No. 10, 2006 2531
solution (concentration, 1 × 10-6 M), respectively. Elemental
analyses were performed by the Health and Human Science
department of London Metropolitan University. cis-[Pt(dppe)Cl2],27
cis-[Pt(dppe)(OTf)2],28 1,4-diethynylbenzene,29 and 4,4′-diethynyl-
biphenyl30 were prepared according to the literature methods, and
during the course of our research and the preparation of this paper,
compounds 1a,b were independently reported.16
tional peak of fluorescence.11,20,25,26 In our cases, the lower
energy (T1) bands were ca. 1.00-1.40 eV below the fluores-
cence (S1). Generally, the S1-T1 energy gaps were almost the
same for the monomers and dimers as well as the trimers in the
two series of complexes. All values were greater than those
observed from the other analogous monomeric, dimeric, and
trimeric platinum alkynyl trans complexes with different spacers
R.11,21b This result can be attributed to the less effective π
conjugation along the chain in the cis configurations, as
compared to that in the trans orientations. Thus, each chromo-
phore is localized in the backbone, thus reducing the efficiency
of the S1-T1 intersystem crossing. However, from 1a to 3a and
from 1b to 3b, the peak-height ratio of triplet to singlet emission
increased from 0.12 to 0.82 and from 6.4 × 10-3 and 8.16 ×
10-2, respectively. This indicates that although the S1-T1
intersystem-crossing efficiency was reduced in the cis-config-
ured systems, the possibilities of nonradiative decays, e.g.
vibration and electron delocalization, were also decreased in
the excited-localized chromophores, which enhanced in a
stepwise fashion the intensities of triplet-state emissions with
an increase in the number of repeating units.
In addition, all complexes also showed a red shift in the triplet
state emissions from 482 nm (2.57 eV) to 505 nm (2.46 eV) in
1a-3a and from 532 nm (2.33 eV) to 546 (2.27 eV) in 1b-
3b, respectively, due to an increasing number of repeating units.
In 1b-3b, the λmax values of T1 emissions were of lower energy
than those in 1a-3a due to the higher electron density present
in the -p-C6H4-p-C6H4 moieties. This feature not only batho-
chromatically shifted the emission maxima but also reduced the
S1-T1 intensity ratio in 1b-3b, because of the enhanced
nonradiative decay caused by the more vibrational structures
present in the -p-C6H4-p-C6H4 series of complexes.
(A) Preparation of Monoplatinum Complex 1a. To a stirred
mixture of excess 1,4-diethynylbenzene (135.1 mg, 1.07 mmol) and
cis-[Pt(dppe)Cl2] (115 mg, 0.15 mmol) in iPr2NH (20 mL) and CH2-
Cl2 (40 mL) was added CuI (3.8 mg). The solution was stirred at
room temperature over a period of 15 h, after which all volatile
components were removed under vacuum. The crude product was
taken up in CH2Cl2 and purified on alumina column chromatography
with n-hexane/CH2Cl2 (1/3, v/v) as eluent. From the second
colorless band (Rf ) 0.86), 1a was obtained as a white solid (121.3
mg, 83%). Anal. Calcd for C46H34P2Pt: C, 65.48; H, 4.06. Found:
C, 65.29; H, 3.94. FT-IR (CH2Cl2): ν(CtC)/cm-1 2101,
ν(CtCH)/cm-1 3300. 1H NMR (CDCl3): δ 2.39 (t, 2H, P(CH2)2P,
JPH ) 10.8 Hz), 2.46 (t, 2H, P(CH2)2P, JPH ) 10.6 Hz), 3.03 (s,
2H, tCH), 7.03 (d, 4H, C6H4, JHH ) 8.2 Hz), 7.20 (d, 4H, C6H4,
JHH ) 8.4 Hz), 7.28-7.42 (m, 12H, C6H5 in dppe), 7.84-8.02 (m,
8H, C6H5 in dppe). 31P{1H} NMR (CDCl3): δ 42.02 (s, JPt-P
2282 Hz). FAB MS: m/z M+, 844.
)
(B) Preparation of Monoplatinum Complex 1b. A mixture of
cis-[Pt(dppe)Cl2] (98.5 mg, 0.15 mmol) and excess 4,4′-diethynyl-
i
biphenyl (300 mg, 1.5 mmol) in Pr2NH (20 mL) and CH2Cl2 (40
mL) with a catalytic amount of CuI (1.1 mg) was stirred for 17 h
at room temperature. The crude product was dried in vacuo and
was taken up in CH2Cl2 to undergo alumina column chromatog-
raphy purification with n-hexane/CH2Cl2 (1/1, v/v) as eluent. 1b
(85.1 mg, 58%) was collected as a very pale yellow solid from the
second band (Rf ) 0.55). Anal. Calcd for C58H42P2Pt: C, 69.94;
H, 4.25. Found: C, 69.99; H, 4.14. FT-IR (CH2Cl2): ν(CtC)/cm-1
1
2101, ν(CtCH)/cm-1 3301. H NMR (CDCl3): δ 2.39 (t, 2H,
As a result, we conclude that the intensity and the energy of
triplet state emissions of platinum alkynyl complexes can be
fine-tuned by different aromatic spacers R, the number of
repeating units, and the cis and trans configurations of platinum
metal centers.
P(CH2)2P, JPH ) 10.4 Hz), 2.46 (t, 2H, P(CH2)2P, JPH ) 10.4 Hz),
3.09 (s, 2H, tCH), 7.21 (d, 4H, biphenyl, JHH ) 8.4 Hz), 7.34 (d,
4H, biphenyl, JHH ) 8.4 Hz), 7.30-7.45 (m, 12H, C6H5 in dppe),
7.49 (s, 8H, biphenyl), 7.87-8.08 (m, 8H, C6H5 in dppe). 31P{1H}
NMR (CDCl3): δ 41.90 (s, JPt-P ) 2280 Hz). FAB MS: m/z M+,
996.
Experimental Section
(C) Preparation of Diplatinum Complex 2a. (i) From the
Synthesis of Complex 1a. After the purification of the second band,
1a, via alumina column chromatography, n-hexane/CH2Cl2 (1/3,
v/v) was used as eluent to continue the purification. From the third
band (Rf ) 0.44), 2a was isolated as a colorless solid (20.8 mg,
15%).
(ii) From the Synthesis of Complex 3a. To a stirred 4/1 molar
ratio mixture of 1a (103.8 mg, 0.12 mmol) and cis-[Pt(dppe)Cl2]
(20.4 mg, 0.3 mmol) in iPr2NH (3.5 mL) and CH2Cl2 (50 mL) was
added CuI (1.2 mg). The solution was stirred at room temperature
over a period of 18 h, after which all volatile components were
removed under vacuum. The crude product was taken up in CH2-
Cl2 and purified by alumina column chromatography with n-hexane/
CH2Cl2 (1/3, v/v) as eluent. From the second colorless band (Rf )
0.44), the diplatinum complex 2a was obtained as a white solid
(17.2 mg, 36%).
General Comments. All reactions were carried out under a
nitrogen atmosphere using standard Schlenk and vacuum line
techniques. Dichloromethane and diisopropylamine were purified
by standard methods. Separation and purification of complexes were
achieved by column chromatography, packed by 5% deactivated
Fischer Scientific aluminum oxide neutral particle size 100-250
mesh. All column chromatography separations were carried out in
air using laboratory-grade solvents as eluents. Infrared spectra were
measured on a Perkin-Elmer FTIR1720 spectrometer, using CaF2
cells with a 0.5 mm path length for solution-state spectroscopy. 1H
and 31P{1H} NMR spectra were recorded on a JEOL GS 270 MHz
NMR spectrometer, using deuterated solvents. Chemical shifts were
reported in δ units (parts per million) downfield from tetrameth-
ylsilane and 85% H3PO4 with the solvents as the reference signal
1
in H and 31P{1H} NMR spectra, respectively. FAB mass spectra
were recorded on a VG AutoSpec-Q mass spectrometer, operating
in the positive ion mode, and MALDI mass spectra were obtained
by the EPSRC National Mass Spectrometry Service Centre in the
Chemistry Department of the University of Wales Swansea. The
high-resolution MALDI mass spectra were obtained by the chem-
istry department of the Hong Kong Baptist University. The GPC
molecular weight measurements were carried out by the RAPRA
Technology Co. The UV-absorption spectra and the luminescence
spectra were measured on a Nicolet Evolution 100 spectrometer
and Varian Cary Eclipse fluorescence spectrometer in CH2Cl2
Anal. Calcd for C82H62P4Pt2: C, 63.08; H, 4.00. Found: C, 63.08;
H, 4.05. FT-IR (CH2Cl2): ν(CtC)/cm-1 2104, 2116, ν(CtCH)/
1
cm-1 3296. H NMR (CDCl3): δ 2.38 (t, 4H, P(CH2)2P, JPH
)
10.6 Hz), 2.45 (t, 4H, P(CH2)2P, JPH ) 10.8 Hz), 3.02 (s, 2H, t
(27) (a) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.
Soc. 1976, 98, 6521. (b) Hackett, M.; Whitesides, G. M. J. Am. Chem. Soc.
1988, 110, 1449.
(28) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc.
1995, 117, 6273.
(29) Grouhi, H.; Nast, R. J. Organomet. Chem. 1979, 182, 197.
(30) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara Synthesis
1980, 627.
(26) Manna, J.; John, K. D.; Hopkins, M. D. AdV. Organomet. Chem.
1995, 38, 79.

2532 Organometallics, Vol. 25, No. 10, 2006
Long et al.
CH), 6.87 (s, 4H, C6H4), 7.04 (d, 4H, C6H4, JHH ) 8.4 Hz), 7.20
(d, 4H, C6H4, JHH ) 8.1 Hz), 7.27-7.51 (m, 24H, C6H5 in dppe),
7.82-7.98 (m, 16H, C6H5 in dppe). 31P{1H} NMR (CDCl3): δ
41.33 (d, JP-P ) 6.7 Hz, JPt-P ) 2284 Hz), 41.00 (d, JP-P ) 6.7
Hz, JPt-P ) 2270 Hz). FAB MS: m/z M+, 1561.
(D) Preparation of Diplatinum Complex 2b. (i) From the
Synthesis of Complex 1b. Similarly to the synthesis of 2a,
diplatinum complex 2b was also obtained from the alumina column
chromatography purification of the monoplatinum complex 1b,
using n-hexane/CH2Cl2 (1/3, v/v) as eluent. From the third colorless
band (Rf ) 0.54), the colorless solid diplatinum complex 2b (12.3
mg, 9%) was collected.
(ii) From the Synthesis of Complex 3b. A mixture of cis-[Pt-
(dppe)Cl2] (9.6 mg, 0.01 mmol) and monoplatinum complex 1b
(43.1 mg, 0.04 mmol) in the molar ratio 1/4 was stirred in iPr2NH
(3.5 mL) and CH2Cl2 (50 mL) with a catalytic amount of CuI (1.1
mg) for 17 h at room temperature. The crude yellow product was
dried in vacuo and then taken up in CH2Cl2 to be purified via
alumina column chromatography, using n-hexane/CH2Cl2 (1/3, v/v)
as eluent. The second colorless band (Rf ) 0.54) was collected as
the very pale yellow solid 2b (10.7 mg, 41%).
(ii) AgOTf-Catalyzed Reaction. A solution of anhydrous sodium
acetate (8.7 mg, 0.11 mmol) in MeOH (10 mL) was added to 1a
(22.3 mg, 0.03 mmol) in CH2Cl2 (40 mL). cis-[Pt(dppe)(OTf)2]
(23.6 mg, 0.03 mmol) in CH2Cl2 (20 mL) was added to this mixture
via a pressure-equalizing dropping funnel over a period of 2 h,
during which time the initial pale yellow solution turned to brown.
Removal of solvent after 4 h of reaction, extraction with CH2Cl2,
and filtration into n-hexane gave the brown precipitate 4a (32.4
mg, 42%, 4 repeating units). Anal. Calcd for (C36H28P2Pt)n: C,
60.25; H, 3.93. Found: C, 60.09; H, 3.95. FT-IR (CH2Cl2):
1
ν(CtC)/cm-1 2115, ν(CtCH)/cm-1 3298. H NMR (CDCl3): δ
2.24-2.64 (m, 4H, P(CH2)2P), 3.03 (s, 0.12H, tCH), 6.68-6.86
(m, 2H, p-C6H4), 6.92-7.64 (m, 14H, p-C6H4 and C6H5 in dppe),
7.80-8.18 (m, 8H, C6H5 in dppe). 31P{1H} NMR (CDCl3): δ
40.62-42.55 (m, JPt-P ) 2316 Hz).
(H) Preparation of Polymeric Species 4b. (i) CuI-Catalyzed
Reaction. CuI (1.0 mg) was added to a mixture of 4,4′-diethynyl-
biphenyl (18.9 mg, 0.09 mmol) and cis-[Pt(dppe)Cl2] (62.3 mg,
i
0.09 mmol) in Pr2NH/CH2Cl2 (63 mL, 1/20, v/v). The yellow
solution was stirred at room temperature over a period of 18 h,
after which time the solvents were evaporated off. The residue was
redissolved in CH2Cl2 and filtered through a short layer of
deactivated alumina to remove impurities and any insoluble
precipitate. After removal of the solvent, a yellow solid was
obtained, which was then washed with n-hexane to leave polymer
4b in 44% yield (43.0 mg, 5 repeating units). Anal. Calcd for
(C42H32P2Pt)n: C, 63.55; H, 4.06. Found: C, 63.66; H, 3.95. FT-
Anal. Calcd for C100H74P4Pt2: C, 67.11; H, 4.14. Found: C,
66.98; H, 4.28. FT-IR (CH2Cl2): ν(CtC)/cm-1 2113, ν(CtCH)/
1
cm-1 3299. H NMR (CDCl3): δ 2.38 (t, 8H, P(CH2)2P, JPH
)
10.8 Hz), 2.46 (t, 8H, P(CH2)2P, JPH ) 10.2 Hz), 3.09 (s, 2H, t
CH), 7.09 (d, 4H, biphenyl, JHH ) 8.2 Hz), 7.15 (d, 4H, biphenyl,
JHH ) 8.2 Hz), 7.28 (d, 4H, biphenyl, JHH ) 8.4 Hz), 7.34 (d, 4H,
biphenyl, JHH ) 8.4 Hz), 7.37-7.46 (m, 24H, C6H5 in dppe), 7.47
(s, 8H, biphenyl), 7.88-7.98 (m, 16H, C6H5 in dppe). 31P{1H} NMR
(CDCl3): δ 41.76 (d, JP-P ) 8.1 Hz, JPt-P ) 2268 Hz), 41.84 (d,
JP-P ) 8.0 Hz, JPt-P ) 2267 Hz). FAB MS: m/z M+, 1791.
(E) Preparation of Triplatinum Complex 3a. The synthetic
procedure was the same as for the synthesis of diplatinum complex
2a. After the separation of 2a by alumina column chromatography,
an n-hexane/CH2Cl2 (1/10, v/v) solvent mixture was used as eluent
to continue the column chromatography purification. The third
isolated band (Rf ) 0.89) was a white solid and was characterized
as the triplatinum complex 3a (18.9 mg, 27%). MALDI MS: m/z
M+, 2279.4. HRMS in MALDI mode: calcd for C118H90P6Pt3,
2279.4509; found, 2279.4604 [M + H+]. FT-IR (CH2Cl2):
ν(CtC)/cm-1 2104, 2115, ν(CtCH)/cm-1 3296. 1H NMR
(CDCl3): δ 2.22-2.54 (m, 12H, P(CH2)2P), 3.02 (s, 2H, tCH),
6.85 (s, 8H, C6H4), 7.05 (d, 4H, C6H4, JHH ) 8.2 Hz), 7.20 (d, 4H,
C6H4, JHH ) 8.4 Hz), 7.32-7.58 (m, 36H, C6H5 in dppe), 7.88-
8.07 (m, 24H, C6H5 in dppe). 31P{1H} NMR (CDCl3): δ 41.27 (s,
JPt-P ) 2272 Hz), 41.31 (d, JP-P ) 8.0 Hz, JPt-P ) 2280 Hz),
41.98 (d, JP-P ) 8.0 Hz, JPt-P ) 2270 Hz).
1
IR (CH2Cl2): ν(CtC)/cm-1 2114. H NMR (CDCl3): δ 2.26-
2.59 (m, 4H, P(CH2)2P), 7.00-7.72 (m, 20H, p-C6H4-p-C6H4 and
C6H5 in dppe), 7.75-8.09 (m, 8H, C6H5 in dppe). 31P{1H} NMR
(CDCl3): δ 41.14-42.30 (m, JPt-P ) 2283 Hz).
(ii) AgOTf-Catalyzed Reaction. To a solution containing
anhydrous sodium acetate (10.1 mg, 0.12 mmol) and complex 1b
(30.7 mg, 0.03 mmol) in MeOH (10 mL) and CH2Cl2 (40 mL)
was added cis-[Pt(dppe)(OTf)2] (27.5 mg, 0.03 mmol) in CH2Cl2
(20 mL) dropwise over a period of 2 h at room temperature with
the exclusion of light. After 4 h of reaction, the solvent was removed
in vacuo and the crude solid extracted with CH2Cl2. The extract
was then evaporated to dryness and washed with n-hexane to give
the brown precipitate 4b (48 mg, 44%, 4 repeating units). Anal.
Calcd for (C42H32P2Pt)n: C, 63.55; H, 4.06. Found: C, 62.66; H,
3.92. FT-IR (CH2Cl2): ν(CtC)/cm-1 2113, ν(CtCH)/cm-1 3299.
1H NMR (CDCl3): δ 2.20-2.67 (m, 4H, P(CH2)2P), 3.08 (s, 0.45H,
tCH), 6.44-7.72 (m, 20H, p-C6H4-p-C6H4 and C6H5 in dppe),
7.78-8.19 (m, 8H, C6H5 in dppe). 31P{1H} NMR (CDCl3): δ
40.80-42.27 (m, JPt-P ) 2279 Hz).
Crystal data for 2a: C82H62P4Pt2‚C6H14, Mr ) 1647.55, triclinic,
P1h (No. 2), a ) 13.0775(4) Å, b ) 13.4008(5) Å, c ) 22.5520(7)
Å, R ) 75.072(3)°, â ) 79.571(3)°, γ ) 88.599(3)°, V )
3754.7(2) Å3, Z ) 2 (two independent Ci-symmetric molecules),
Dc ) 1.457 g cm-3, µ(Mo KR) ) 3.851 mm-1, T ) 173 K, pale
yellow plates, Oxford Diffraction Xcalibur 3 diffractometer; 24 804
independent measured reflections, F2 refinement, R1 ) 0.084, wR2
) 0.182, 20 867 independent observed absorption-corrected reflec-
tions (|Fo| > 4σ(|Fo|), 2θmax ) 65°), 874 parameters. CCDC
290794.
(F) Preparation of Triplatinum Complex 3b. Similar proce-
dures were also applied for the purification of complex 3b. After
the separation of 2b via alumina column chromatography, a CH2-
Cl2/acetone (40/1, v/v) solvent mixture was used as eluent to
continue the column chromatography purification. The third isolated
band (Rf ) 0.60) was a white solid and was characterized as the
triplatinum complex 3b (8.8 mg, 23%). MALDI MS: m/z M+,
2581.6. HRMS in MALDI mode: calcd for C142H106P6Pt3, 2581.5608;
found, 2581.5768. FT-IR (CH2Cl2): ν(CtC)/cm-1 2113, ν(CtCH)/
1
cm-1 3299. H NMR (CD2Cl2): δ 2.42 (t, 6H, P(CH2)2P, JPH
)
Acknowledgment. C.K.W. wishes to thank the Croucher
Foundation, Hong Kong, and the ORS Committee for an
overseas research studentship. We are also grateful to Dr. W.
Y. Wong of Hong Kong Baptist University for the MALDI-
HRMS measurements, RAPRA Technology Limited for the
GPC measurements, and the EPSRC National Mass Spectrom-
etry Service Centre, Swansea, U.K., for MALDI mass spectra.
10.4 Hz), 2.49 (t, 6H, P(CH2)2P, JPH ) 10.1 Hz), 3.16 (s, 2H, t
CH), 7.07-7.22 (m, 12H, biphenyl), 7.07-7.29 (m, 12H, biphenyl),
7.29-7.50 (m, 36H, C6H5 in dppe), 7.51 (s, 8H, biphenyl), 7.85-
8.04 (m, 24H, C6H5 in dppe). 31P{1H} NMR (CD2Cl3): δ 42.06 (s,
JPt-P ) 2272 Hz), 42.08 (d, JP-P ) 5.4 Hz, JPt-P ) 2271 Hz),
42.19 (d, JP-P ) 5.1 Hz, JPt-P ) 2270 Hz).
(G) Preparation of Polymeric Species 4a. (i) CuI-Catalyzed
Reaction. Polymerization was carried out by mixing 1,4-diethyn-
ylbenzene (19.4 mg, 0.15 mmol), cis-[Pt(dppe)Cl2] (102.1 mg, 0.15
Supporting Information Available: Text, tables, and figures
giving additional details of the crystal structure determination for
2a; crystal data are also given as a CIF file. This material is available
free of charge via the Internet at http://pubs.acs.org.
i
mmol), and CuI (1.3 mg) in Pr2NH/CH2Cl2 (63 mL, 1/20, v/v).
After stirring at room temperature for 18 h, only an insoluble yellow
precipitate was isolated.
OM060007A