Synthesis, structure, and luminescence of di- and trinuclear palladium/gold and platinum/gold complexes with (2,7-di-tert-butylfluoren-9-ylidene) methanedithiolate

Article abstract of DOI:10.1021/ic070164h

Acetone solutions of [Au(OClO₃)(PCy₃)] react with complexes [M{S₂C=(r-Bu-fy)}2f- [t-Bu-fy)}₂]² = 2,7-di-tert-butylfluoren9-ylidene; M = Pd (2a), Pt (2b)] or [M{S ₂C=(t-Bu-fy)}(dbbpy)] [dbbpy = 4,4′-di-tert-butyl-2,2′- bipyridyl; M = Pd (3a), Pt (3b)] to give the heteronuclear complexes [M{S ₂C=(t-Bu-fy)}₂{Au(PCy3)}2] [2:1 molar ratio; M = Pd (4a), Pt (4b)], [M{S₂C=(t-Bu-fy)}(dbbpy){Au(PCy₃)}]ClO ₄ [1:1 molar ratio; M = Pd (5a), Pt (5b)], or [M{S ₂C=(t-Bufy)}(dbbpy){Au(PCy₃)}₂](ClO ₄)₂ [2:1 molar ratio; M = Pd (6a), Pt (6b)]. The crystal structures of 3a, 4a, 4b, 5b, and 6a have been solved by single-crystal X-ray studies and, in the cases of the heteronuclear derivatives, reveal the formation of short Pd...Au or Pt...Au metallophilic contacts in the range of 3.048-3.311 A. Compounds 4a and b and 5a and b undergo a dynamic process in solution that involves the migration of the [Au(PCy₃)]⁺ units between the sulfur atoms of the dithiolato ligands. The coordination of 2a and b and 3a and b to [Au(PCy₃)]⁺ units results in important modifications of their photophysical properties. The dominant effect in the absorption spectra is an increase in the energy of the MLCT (4a and b) or charge transfer to diimine (5a, b, 6a, b) transitions because of a decrease in the energies of the mixed metal/dithiolate HOMOs. The Pd complexes 2a and 4a are luminescent at 77 K, and the features of their emissions are consistent with an essentially metal-centered ³d-d state. The Pt/Au complexes are also luminescent at 77 K, and their emissions can be assigned as originating from a MLCT triplet state (4b) or a mixture of charge transfer to diimine and diimine intraligand π-π* triplet states (5b and 6b).

Full text of DOI:10.1021/ic070164h

Inorg. Chem. 2007, 46, 4718−4732
Synthesis, Structure, and Luminescence of Di- and Trinuclear
Palladium/Gold and Platinum/Gold Complexes with
(2,7-Di-tert-butylfluoren-9-ylidene)methanedithiolate†,1
Jose´ Vicente, Pablo Gonza´lez-Herrero,* and Mar´ıa Pe´rez-Cadenas
Grupo de Qu´ımica Organometa´lica, Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica,
UniVersidad de Murcia, Apdo. 4021, 30071 Murcia, Spain
Peter G. Jones
Institut fu¨r Anorganische und Analytische Chemie, Technische UniVersita¨t Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
Delia Bautista
SACE, UniVersidad de Murcia, Apdo. 4021, 30071 Murcia, Spain
Received January 30, 2007
2
Acetone solutions of [Au(OClO3)(PCy3)] react with complexes [M
9-ylidene; M Pd (2a), Pt (2b)] or [M S2C (t-Bu-fy) (dbbpy)] [dbbpy
(3a), Pt (3b)] to give the heteronuclear complexes [M S2C (t-Bu-fy)}2{Au(PCy3)
Pt (4b)], [M S2C (t-Bu-fy) (dbbpy) Au(PCy3) ]ClO4 [1:1 molar ratio; M Pd (5a), Pt (5b)], or [M
fy) (dbbpy) Au(PCy3) 2](ClO4)2 [2:1 molar ratio; M Pd (6a), Pt (6b)]. The crystal structures of 3a, 4a, 4b, 5b,
and 6a have been solved by single-crystal X-ray studies and, in the cases of the heteronuclear derivatives, reveal
3.311 Å. Compounds 4a
{S2C
)
(t-Bu-fy)
}
]
′
- [t-Bu-fy
)
2,7-di-tert-butylfluoren-
-bipyridyl; M Pd
2] [2:1 molar ratio; M Pd (4a),
S2C (t-Bu-
2
)
{
)
}
)
4,4
-di-tert-butyl-2,2
′
)
{
)
}
)
{
{
)
}
{
}
)
{
)
}
}
)
the formation of short Pd‚‚‚Au or Pt‚‚‚Au metallophilic contacts in the range of 3.048
−
and b and 5a and b undergo a dynamic process in solution that involves the migration of the [Au(PCy3)]+ units
between the sulfur atoms of the dithiolato ligands. The coordination of 2a and b and 3a and b to [Au(PCy3)]+ units
results in important modifications of their photophysical properties. The dominant effect in the absorption spectra
is an increase in the energy of the MLCT (4a and b) or charge transfer to diimine (5a, b, 6a, b) transitions because
of a decrease in the energies of the mixed metal/dithiolate HOMOs. The Pd complexes 2a and 4a are luminescent
3
at 77 K, and the features of their emissions are consistent with an essentially metal-centered d
−d state. The Pt/Au
complexes are also luminescent at 77 K, and their emissions can be assigned as originating from a MLCT triplet
state (4b) or a mixture of charge transfer to diimine and diimine intraligand π−π* triplet states (5b and 6b).
Introduction
having implications for certain biochemical systems and
technological applications.8
The interest in heterometallic complexes, aggregates, and
clusters has grown steadily during the last two decades.2-5
Many of the recent studies in this area have been stimulated
by the intriguing photophysical properties of these materials,
which in many cases have their origin in metallophilic
interactions between metal ions with closed or pseudoclosed
shell electronic configurations (d10, d8, s2).6,7 Such interactions
have thus been acknowledged not only as essential factors
in the molecular and surpramolecular structures, but also as
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* To whom correspondence should be addressed. E-mail:
jvs1@um.es (J.V.); pgh@um.es (P.G.-H.). http://www.um.es/gqo/.
† Dedicated to Professor Miguel Yus on the occasion of his 60th birthday.
(1) (Fluoren-9-ylidene)methanedithiolato Complexes, Part 4. For previous
parts, see refs 16-18.
4718 Inorganic Chemistry, Vol. 46, No. 11, 2007
10.1021/ic070164h CCC: $37.00
© 2007 American Chemical Society
Published on Web 04/13/2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
1,1-Ethylenedithiolates (XYCdCS22-) have long been
recognized for their ability to form clusters9 and heteropoly-
nuclear complexes,10 and some of them are also capable of
making use of multiple donor atoms to form coordination
polymers.11,12 We have recently shown that Pd(II) and Pt-
(II) complexes of the type [M{S2Cd(COMe)2}L2], with M
) Pd, Pt and L ) PPh3, t-BuNC or L2 ) 1,5-cyclooctadiene,
can act as metalloligands toward Ag(I) and Au(I) centers to
form a variety of heterodinuclear, trinuclear, and tetranuclear
structures that display d8-d10 short contacts.13-15 Our
research group has also undertaken the study of the reactivity
and photophysical properties of transition metal complexes
with (fluoren-9-ylidene)methanedithiolate and several di-
substituted derivatives.16-18 These new ligands exhibit sig-
nificant differences with respect to the majority of 1,1-
ethylenedithiolates described to date, which are attributable
to the presence of the extensively conjugated fluoren-9-
ylidene fragment and the absence of electron-withdrawing
functional groups, and affect the reactivity and photophysical
properties of their metal complexes. Thus, the strongly
electron-donating character of these ligands is responsible
for the facile oxidation of certain Au(I) and Pt(II) complexes
under atmospheric conditions, and the unusually low energies
of their charge-transfer absorptions and emissions.16,18 We
have also reported the aerial oxidation of Cu(I) and Cu(II)
complexes with (2,7-di-tert-butylfluoren-9-ylidene)methan-
edithiolate [(t-Bu-fy))CS22-] and the oxidatively promoted
condensation of the ligand in the coordination sphere of Cu-
(I).17
In this paper, we describe the structures, dynamic behavior
in solution, and photophysical properties of a series of Pd/
Au and Pt/Au heterodinuclear and trinuclear complexes with
the (t-Bu-fy)dCS22- ligand, obtained through the aggregation
of [Au(PCy)3]+ units to [M{S2Cd(t-Bu-fy)}2]2- or [M{S2Cd
(t-Bu-fy)}(dbbpy)] (M ) Pd, Pt; dbbpy ) 4,4′-di-tert-butyl-
2,2′-bipyridyl). These precursors belong to the basic types
[M(1,1-dithiolate)2]2- and [M(1,1-dithiolate)(diimine)], which,
for M ) Pt, have been the subject of previous intensive
research because of their interesting excited-state proper-
ties.19-23 The present work is mainly aimed at the evaluation
of metal aggregation as a method of obtaining compounds
with enhanced or modified luminescent properties.
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Experimental Section
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Inorganic Chemistry, Vol. 46, No. 11, 2007 4719

Vicente et al.
Table 1. Crystallographic Data for 3a‚CH2Cl2, 4a, 4b, 5b‚Me2CO, and 6a‚THF‚C6H14
3a‚CH2Cl2
4a
4b
5b‚Me2CO
6a‚THF‚C6H14
formula
fw
T (K)
C41H50Cl2N2PdS2
812.25
133(2)
C80H114Au2P2PdS4
1766.22
100.2(2)
0.71073
monoclinic
P21/c
9.5339(4)
15.1567(7)
26.6961(12)
92.012(2)
3855.3(3)
2
C80H114Au2P2PtS4
1854.91
100.2(2)
0.71073
monoclinic
P21/c
9.5454(4)
15.1537(7)
26.6997(11)
91.988(2)
3859.7(3)
2
C61H87AuClN2O5PPtS2
1450.92
100.2(2)
0.71073
orthorhombic
Pbca
20.3656(9)
17.0378(7)
35.8373(16)
90
12435.0(9)
8
1.550
4.787
0.0207
C83H129Au2Cl2N2O9P2PdS2
1996.18
100.2(2)
0.71073
monoclinic
P21/n
22.6833(9)
14.4450(6)
28.7838(12)
112.831(2)
8692.4(6)
4
λ (Å)
0.71073
monoclinic
P21/c
11.3930(11)
17.702(2)
19.709(2)
97.997(5)
3936.1(7)
4
1.371
0.744
0.0389
0.1138
cryst syst
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
F
calcd (Mg m-3
)
1.521
4.218
0.0227
0.0518
1.596
5.790
0.0429
0.0776
1.525
3.772
0.0313
0.0731
µ (mm-1
R1a
)
wR2b
0.0477
a R1 ) ∑|Fo| - |Fc|/∑|Fo| for reflections with I > 2σ(I). b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]0.5 for all reflections; w-1 ) σ2(F2) + (aP)2 + bP, where
2
2
2
2
P ) (2Fc + Fo )/3 and a and b are constants set by the program.
ate (1) was prepared as reported.24 [PdCl2(dbbpy)] was prepared
by refluxing a suspension of cis-[PtCl2(DMSO)2]25 and 1 equiv of
dbbpy in acetone. The complexes (Pr4N)2[Pt{S2Cd(t-Bu-fy)}2]
(2b),18 [Pt{S2Cd(t-Bu-fy)}(dbbpy)] (3b),18 and [AuCl(PCy3)]16
were prepared following the published procedures. All other
reagents were obtained from commercial sources and used without
further purification. NMR spectra were recorded on Bruker Avance
200, 300, 400, or 600 spectrometers, usually at 298 K unless
otherwise indicated. Chemical shifts are referred to internal TMS
(1H and 13C{H}) or external 85% H3PO4 (31P{H}). The 13C{H}
NMR resonances of the Pr4N+ cation are not given. The assignments
method. All of them were refined anisotropically on F2 using the
program SHELXL-97 (G. M. Sheldrick, University of Go¨ttingen).
Restraints to local aromatic ring symmetry or light atom displace-
ment factor components were applied in some cases. Hydrogen
atoms were included using rigid methyl groups or a riding model.
Special Features of Refinement. For compound 3a, the dichlo-
romethane molecule is disordered over two positions with a relative
occupancy of ∼4:1. For compound 5b, the Me groups of one of
the t-Bu groups are disordered over two positions (∼73:27).
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Preparations on a larger scale than
that described here should be avoided.
1
of the H and 13C{H} NMR spectra were made with the help of
HMBC and HSQC experiments. Melting points were determined
on a Reichert apparatus and are uncorrected. Elemental analyses
were carried out with a Carlo Erba 1106 microanalyzer. Infrared
spectra were recorded in the range of 4000-200 cm-1 on a Perkin-
Elmer 16F PC FT-IR spectrophotometer using Nujol mulls between
polyethylene sheets. UV-vis absorption spectra were recorded on
an Unicam UV500 spectrophotometer. Excitation and emission
spectra were recorded on a Jobin Yvon Fluorolog 3-22 spectrof-
luorometer with a 450 W xenon lamp, double-grating monochro-
mators, and a TBX-04 photomultiplier. The solid-state measure-
ments were made in a front-face configuration using polycrystalline
samples between quartz coverslips; the solution measurements were
carried out in a right angle configuration using degassed solutions
of the samples in 10 mm quartz fluorescence cells or 5 mm quartz
NMR tubes. The solvents used were CH2Cl2 at 298 K and CH2Cl2,
DMM (DMF/CH2Cl2/MeOH 1:1:1), or toluene at 77 K, as specified.
For the low-temperature measurements, a liquid nitrogen Dewar
with quartz windows or an Oxford Instruments Optistat-DN cryostat
were employed. Lifetimes were measured using the Fluorolog’s
FL-1040 phosphorimeter accessory.
X-ray Structure Determinations. Crystals of 3a‚CH2Cl2, 4a,
4b, 5b‚Me2CO, and 6a‚THF‚C6H14 suitable for X-ray diffraction
studies were obtained by the liquid-liquid diffusion method from
CH2Cl2/Et2O, Me2CO/Et2O or THF/n-hexane. Numerical details are
presented in Table 1. Data for 4a, b, 5b‚Me2CO, and 6a‚THF‚
C6H14 were recorded on a Bruker Smart APEX diffractometer. The
structures of 4a and 6a‚THF‚C6H14 were solved by direct methods,
and those of 4b and 5b‚Me2CO were solved by the heavy atom
(Pr4N)2[Pd{S2Cd(t-Bu-fy)}2] (2a). Piperidine (100 µL, 1.01
mmol) and Pr4NCl (160 mg, 0.72 mmol) were added to a stirred
suspension of PdCl2 (52 mg, 0.29 mmol) in CH2Cl2 (15 mL). A
turbid, pale yellow solution formed, which was filtered through
Celite to remove small amounts of insoluble material. The addition
of dithioate 1 (301 mg, 0.63 mmol) led to immediate reaction with
precipitation of an orange solid, which was filtered off, washed
with CH2Cl2 (4 mL), and vacuum-dried to give 2a. Yield: 164
mg, 47%. Anal. Calcd for C68H104N2PdS4: C, 68.97; H, 8.85; N,
2.37; S, 10.83. Found: C, 68.74; H, 8.91; N, 2.53; S, 10.58. mp:
230-240 °C (dec). IR (Nujol, cm-1): ν(CdCS2), 1500; ν(Pd-S),
342. 1H NMR [400.9 MHz, (CD3)2SO]: δ 8.97 (d, 4JHH ) 1.6 Hz,
4 H, H1, H8), 7.62 (d, 3JHH ) 8.0 Hz, 4 H, H4, H5), 7.08 (dd, 3JHH
4
) 8.0 Hz, JHH ) 1.6 Hz, 4 H, H3, H6), 3.10 (m, NCH2, 16 H),
1.58 (m, CH2, 16 H), 1.35 (s, 36 H, t-Bu), 0.87 (t, 3JHH ) 7.2 Hz,
24 H, Me, Pr4N+). 13C{1H} NMR [100.8 MHz, (CD3)2SO]: δ 185.6
(CS2), 146.9 (C2, C7), 139.2 (C8a, C9a), 131.7 (C4a, C4b), 124.0
(C9), 119.5 (C4, C5), 118.6 (C3, C6), 117.4 (C1, C8), 34.6 (CMe3),
31.8 (CMe3).
[Pd{S2Cd(t-Bu-fy)}(dbbpy)] (3a). Piperidine (17 µL, 0.17
mmol) and dithioate 1 (76 mg, 0.16 mmol) were added to a
suspension of [PdCl2(dbbpy)] (65 mg, 0.15 mmol) in CH2Cl2 (15
mL). The resulting red solution was stirred for 10 min and
concentrated to ∼2 mL. The addition of Et2O (40 mL) led to the
precipitation of a dark red solid, which was filtered off, washed
with methanol (2 × 2 mL) and Et2O (4 mL), and vacuum-dried to
give 3a. Yield: 85 mg, 80%. Anal. Calcd for C40H48N2PdS2: C,
66.05; H, 6.65; N, 3.85; S, 8.82. Found: C, 65.74; H, 6.72; N,
4.02; S, 8.68. mp: 220 °C. IR (Nujol, cm-1): ν(CdCS2), 1536.
(24) Vicente, J.; Gonza´lez-Herrero, P.; Garc´ıa-Sa´nchez, Y.; Pe´rez-Cadenas,
M. Tetrahedron Lett. 2004, 45, 8859-8861.
(25) Kukushkin, V. Y.; Pombeiro, A. J. L.; Ferreira, C. M. P.; Elding, L.
I. Inorg. Synth. 2002, 33, 189-196.
4
1H NMR (400.9 MHz, CDCl3): δ 8.83 (d, JHH ) 1.4 Hz, 2 H,
H1, H8), 8.54 (d, 3JHH ) 5.7 Hz, 2 H, H6, dbbpy), 8.06 (d, 4JHH
1.5 Hz, 2 H, H3, dbbpy), 7.67 (d, JHH ) 7.9 Hz, 2 H, H4, H5),
)
3
4720 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
4
3
7.53 (dd, JHH ) 1.8 Hz, JHH ) 5.7 Hz, 2 H, H5, dbbpy), 7.26
3JHH ) 5.8 Hz, 2 H, H6, dbbpy), 7.62 (dd, 3JHH ) 5.8 Hz, 4JHH
)
4
3
3
(dd, JHH ) 1.7 Hz, JHH ) 7.9 Hz, 2 H, H3, H6), 1.46 (s, 18 H,
t-Bu, dithiolato), 1.43 (s, 18 H, t-Bu, dbbpy). 13C{1H} NMR (100.8
MHz, CDCl3): δ 163.8 (C4, dbbpy), 162.4 (CS2), 154.6 (C2,
dbbpy), 148.5 (C2, C7, dithiolato + C6, dbbpy), 139.4 (C8a, C9a),
134.6 (C4a, C4b), 127.9 (C9), 123.9 (C5, dbbpy), 121.2 (C3, C6),
119.5 (C1, C8), 119.1 (C3, dbbpy), 117.9 (C4, C5), 35.7 (CMe3,
dbbpy), 34.9 (CMe3, dithiolato), 31.9 (CMe3, dithiolato), 30.3
(CMe3, dbbpy).
1.8 Hz, 2 H, H5, dbbpy), 7.48 (d, JHH ) 7.9 Hz, 2 H, H4, H5),
7.25 (dd, 3JHH ) 8.0 Hz, 4JHH ) 1.7 Hz, 2 H, H3, H6), 1.84 (br m,
3 H, Cy), 1.67 (br m, 6 H, Cy), 1.55 (m, 9 H, Cy), 1.52 (s, 18 H,
t-Bu, dbbpy), 1.48 (s, 18 H, t-Bu, dithiolato), 1.12 (br m, 12 H,
Cy), 0.87 (br m, 3 H, Cy). 13C{1H} (100.8 MHz, CD2Cl2): δ 166.4
(C4, dbbpy), 155.1 (C2, dbbpy), 149.7 (C2, C7), 148.6 (C6, dbbpy),
146.4 (CS2), 138.6 (C8a, C9a), 136.2 (C4a, C4b), 133.9 (C9), 124.8
(C5, dbbpy), 124.1 (C3, C6), 121.2 (C1, C8), 120.6 (C3, dbbpy),
118.8 (C4, C5), 36.4 (CMe3, dbbpy), 35.3 (CMe3, dithiolato), 33.3
[Pd{S2Cd(t-Bu-fy)}2{Au(PCy3)}2] (4a). AgClO4 (53 mg, 0.23
mmol) was added to a stirred suspension of [AuCl(PCy3)] (118
mg, 0.23 mmol) in acetone (10 mL). After 10 min, the mixture
was filtered through Celite to remove the precipitate of AgCl.
Compound 2a (133 mg, 0.11 mmol) was then added to the clear
filtrate, and the mixture was stirred for 30 min. A yellow solid
precipitated, which was filtered off, washed with acetone (5 mL),
recrystallized from CH2Cl2/Et2O, and vacuum-dried to give 4a.
Yield: 136 mg, 88%. Anal. Calcd for C80H114Au2P2PdS4: C, 54.40;
H, 6.51; S, 7.26. Found: C, 54.38; H, 6.87; S, 7.12. mp: 200 °C
(dec). IR (Nujol, cm-1): ν(CdCS2), 1538; ν(Pd-S), 354, 334. 1H
1
(d, JPC ) 28.5 Hz, C1, Cy), 31.9 (CMe3, dithiolato), 31.1 (C2,
3
Cy), 30.4 (CMe3, dbbpy), 27.0 (d, JPC ) 12.2 Hz, C3, Cy), 25.9
(C4, Cy). 31P{H} NMR (162.3 MHz, CD2Cl2): δ 59.9.
[Pt{S2Cd(t-Bu-fy)}(dbbpy){Au(PCy3)}]ClO4‚H2O (5b). This
complex was obtained as an orange solid following the procedure
described for 5a, from [AuCl(PCy3)] (146 mg, 0.28 mmol), AgClO4
(60 mg, 0.29 mmol), and [Pt{S2Cd(t-Bu-fy)}(dbbpy)] (3b) (230
mg, 0.28 mmol). Yield: 350 mg, 88%. Anal. Calcd for C58H83-
AuClN2O5PPtS2: C, 49.37; H, 5.93; N, 1.99; S, 4.55. Found: C,
49.51; H, 6.19; N, 1.98; S, 4.30. mp: 90 °C (dec). IR (Nujol, cm-1):
ν(CdCS2), 1572. 1H NMR (400.9 MHz, CD2Cl2): δ 8.68 (d, 4JHH
) 1.4 Hz, 2 H, H1, H8), 8.32 (d, 3JHH ) 5.9 Hz, 2 H, H6, dbbpy),
8.26 (d, 4JHH ) 1.4 Hz, 2 H, H3, dbbpy), 7.58 (dd, 3JHH ) 5.9 Hz,
4JHH ) 1.5 Hz, 2 H, H5, dbbpy), 7.45 (d, 3JHH ) 7.9 Hz, 2 H, H4,
4
NMR (400.9 MHz, CDCl3): δ 8.91 (d, JHH ) 1.8 Hz, 4 H, H1,
3
3
H8), 7.61 (d, JHH ) 8.0 Hz, 4 H, H4, H5), 7.93 (dd, JHH ) 8.0
4
Hz, JHH ) 1.8 Hz, 4 H, H3, H6), 2.04-1.91 (br m, 18 H, Cy),
1.67 (br m, 12 H, Cy), 1.57-1.48 (br m, 18 H Cy), 1.40 (s, 18 H,
t-Bu), 1.19-1.12 (br m, 18 H, Cy). 13C{1H} NMR (100.8 MHz,
CDCl3): δ 158.7 (CS2), 148.6 (C2, C7), 139.1 (C8a, C9a), 135.2
(C4a, C4b), 131.6 (C9), 121.8 (C3, C6), 121.7 (C1, C8), 117.7
3
4
H5), 7.20 (dd, JHH ) 7.9 Hz, JHH ) 1.7 Hz, 2 H, H3, H6), 1.79
(br m, 3 H, Cy), 1.64 (br m, 6 H, Cy), 1.53 (br m, 9 H, Cy), 1.50
(s, 18 H, t-Bu, dbbpy), 1.47 (s, 18 H, t-Bu, dithiolato), 1.09 (br m,
12 H, Cy), 0.85 (br m, 3 H, Cy). 13C{1H} (100.8 MHz, CD2Cl2):
δ 166.0 (C4, dbbpy), 155.4 (C2, dbbpy), 149.7 (C2, C7), 147.8
(C6, dbbpy), 143.8 (CS2), 138.1 (C8a, C9a), 136.3 (C4a, C4b),
135.9 (C9), 125.4 (C5, dbbpy), 124.1 (C3, C6), 121.2 (C1, C8,
dithiolato + C3, dbbpy), 118.6 (C4, C5), 36.5 (CMe3, dbbpy), 35.3
1
(C4, C5), 35.0 (CMe3), 33.4 (d, JCP ) 27.6 Hz, C1, Cy), 31.8
(CMe3), 30.7 (C2, C6, Cy), 27.0 (d, 3JCP ) 12.1 Hz, C3, C5, Cy),
25.7 (C4, Cy). 31P{1H} NMR (162.3 MHz, CDCl3): δ 57.4.
[Pt{S2Cd(t-Bu-fy)}2{Au(PCy3)}2] (4b). This yellow compound
was prepared as described for 6a, from AgClO4 (13 mg, 0.06
mmol), [AuCl(PCy3)] (33 mg, 0.06 mmol), and (Pr4N)2[Pt{S2Cd
(t-Bu-fy)}2] (2b) (34 mg, 0.03 mmol). Yield: 42 mg, 71%. Anal.
Calcd for C80H114Au2P2PtS4: C, 51.80; H, 6.19; S, 6.91. Found:
C, 52.10; H, 6.43; S, 7.27. mp: 180 °C (dec). IR (Nujol, cm-1):
ν(CdCS2), 1538; ν(Pt-S), 346, 336. 1H NMR (400.9 MHz,
(CMe3, dithiolato), 33.3 (d, 1JPC ) 28.5 Hz, C1, Cy), 31.9 (CMe3,
3
dithiolato), 31.0 (C2, Cy), 30.3 (CMe3, dbbpy), 27.0 (d, JPC
)
12.2 Hz, C3, Cy), 25.9 (C4, Cy). 31P{H} NMR (162.3 MHz, CD2-
Cl2): δ 57.6.
[Pd{S2Cd(t-Bu-fy)}(dbbpy){Au(PCy3)}2](ClO4)2 (6a). This
complex was obtained as a yellowish orange microcrystalline solid,
following the procedure described for 5a, from [AuCl(PCy3)] (163
mg, 0.32 mmol), AgClO4 (70 mg, 0.34 mmol), and 3a (113 mg,
0.16 mmol). Yield: 262 mg, 90%. Anal. Calcd for C76H114Au2-
Cl2N2O8P2PdS2: C, 48.53; H, 6.11; N, 1.49; S, 3.41. Found: C,
48.32; H, 6.41; N, 1.74; S, 3.22. mp: 169 °C (dec). IR (Nujol,
CDCl3): δ 8.77 (d, 4JHH ) 1.4 Hz, 4 H, H1, H8), 7.61 (d, 3JHH
)
3
4
8.0 Hz, 4 H, H4, H5), 7.22 (dd, JHH ) 8.0 Hz, JHH ) 1.7 Hz, 4
H, H3, H6), 2.01-1.95 (br m, 18 H, Cy), 1.72-1.48 (br m, 30 H,
Cy), 1.40 (s, 18 H, t-Bu), 1.17-1.12 (br m, 18 H, Cy). 13C{1H}
(100.8 MHz, CDCl3): δ 150.9 (CS2), 148.7 (C2, C7), 138.4 (C8a,
C9a), 135.3 (C4a, C4b), 133.5 (C9), 121.8 (C3, C6), 121.7 (C1,
1
1
C8), 117.7 (C4, C5), 35.0 (CMe3), 33.4 (d, JCP ) 27.9 Hz, C1,
cm-1): ν(CdCS2) not observed. H NMR (400.9 MHz, CD2Cl2):
Cy), 31.8 (CMe3), 30.7 (C2, C6, Cy), 27.0 (d, 3JCP ) 12.1 Hz, C3,
C5, Cy), 25.7 (C4, Cy). 31P{1H} NMR (81.0 MHz, CDCl3): δ 54.8.
[Pd{S2Cd(t-Bu-fy)}(dbbpy){Au(PCy3)}]ClO4‚H2O (5a). Ag-
ClO4 (33 mg, 0.16 mmol) was added to a stirred suspension of
[AuCl(PCy3)] (80 mg, 0.16 mmol) in acetone (15 mL). After 10
min, the mixture was filtered through Celite to remove the
precipitate of AgCl, and the clear filtrate was added to a suspension
of complex 3a (114 mg, 0.16 mmol) in acetone (10 mL). An
immediate reaction was observed to give a turbid orange solution,
which was stirred for 15 min, filtered through a PTFE syringe filter
(0.45 µm pore size) to remove a small amount of insoluble material,
and concentrated to ∼8 mL. The addition of Et2O (25 mL) led to
the precipitation of an orange solid, which was filtered off, washed
with acetone/Et2O (1:2, 2 × 2 mL), and dried at 60 °C for 4 h to
give 5a. Yield: 180 mg, 87%. Anal. Calcd for C58H83AuClN2O5-
PPdS2: C, 52.69; H, 6.33; N, 2.12; S, 4.85. Found: C, 52.87; H,
6.64; N, 2.15; S, 4.73. mp: 189 °C. IR (Nujol, cm-1): ν(CdCS2),
δ 8.65 (d, 4JHH ) 1.3 Hz, 2 H, H1, H8), 8.45 (d, 3JHH ) 5.9 Hz, 2
H, H6, dbbpy), 8.40 (d, 4JHH ) 1.2 Hz, 2 H, H3, dbbpy), 7.93 (dd,
4
3
3JHH ) 5.7 Hz, JHH ) 1.2 Hz, 2 H, H5, dbbpy), 7.65 (d, JHH
)
3
4
8.0 Hz, 2 H, H4, H5), 7.47 (dd, JHH ) 8.0 Hz, JHH ) 1.5 Hz, 2
H, H3, H6), 1.99 (br m, 6 H, Cy), 1.77 (br m, 12 H, Cy), 1.61 (m,
18 H, Cy), 1.54 (s, 18 H, t-Bu, dbbpy), 1.48 (s, 18 H, t-Bu,
dithiolato), 1.20 (br m, 24 H, Cy), 0.94 (m, 6 H, Cy). 13C{1H}
NMR (100.8 MHz, CD2Cl2): δ 168.3 (C4, dbbpy), 155.6 (C2,
dbbpy), 151.1 (C2, C7), 149.5 (C6, dbbpy), 142.5 (CS2), 137.9 (C8a,
C9a), 137.2 (C4a, C4b), 129.3 (C9), 127.0 (C3, C6), 125.9 (C5,
dbbpy), 122.4 (C1, C8), 121.8 (C3, dbbpy), 119.7 (C4, C5), 36.9
1
(CMe3, dbbpy), 35.4 (CMe3, dithiolato), 33.4 (d, JPC ) 29.0 Hz,
C1, Cy), 31.8 (CMe3, dithiolato), 31.3 (C2, Cy), 30.3 (CMe3,
4
dbbpy), 27.0 (d, 3JPC ) 12.3 Hz, C3, Cy), 25.9 (d, JPC ) 1.2 Hz,
C4, Cy). 31P{1H} NMR (162.3 MHz, CD2Cl2): 61.5.
[Pt{S2Cd(t-Bu-fy)}(dbbpy){Au(PCy3)}2](ClO4)2 (6b). This
complex was obtained as a yellow solid, following the procedure
described for 5a, from [AuCl(PCy3)] (171 mg, 0.33 mmol), AgClO4
(72 mg, 0.35 mmol), and 3b (133 mg, 0.16 mmol). Yield: 211
1
4
1564. H NMR (400.9 MHz, CD2Cl2): δ 8.71 (d, JHH ) 1.3 Hz,
4
2 H, H1, H8), 8.25 (d, JHH ) 1.8 Hz, 2 H, H3, dbbpy), 8.15 (d,
Inorganic Chemistry, Vol. 46, No. 11, 2007 4721

Vicente et al.
a
Scheme 1
Figure 1. Thermal ellipsoid plot (50% probability) of complex 3a.
Hydrogen atoms are omitted for clarity.
cis/trans-[PdCl2(pip)2]. The dithioate 1 displaces the chloro
and piperidine ligands and is then deprotonated by the free
piperidine. The poorly soluble salt 2a precipitated as an
orange solid and was separated from the piperidinium
chloride by washing with CH2Cl2. The neutral complex [Pd-
{S2Cd(t-Bu-fy)(dbbpy)] (3a, dbbpy ) 4,4′-di-tert-butyl-2,2′-
bipyridyl) was prepared in high yield by displacement of
the chloro ligands in [PtCl2(dbbpy)] with dithioate 1 in the
presence of piperidine.
a M ) Pd (2-6a), Pt (2-6b); R ) t-Bu. (i) MCl2, (Pr4N)Cl, pip; (ii)
[MCl2(dbbpy)], pip; (iii) 2[Au(OClO3)(PCy3)]; (iv) 1[Au(OClO3)(PCy3)],
where pip ) piperidine and dbbpy ) 4,4′-di-tert-butyl-2,2′-bipyridyl.
The series of complexes [M{S2Cd(t-Bu-fy)}2{Au(PCy3)}2]
[M ) Pd (4a), Pt (4b)], [M{S2Cd(t-Bu-fy)}(dbbpy){Au-
(PCy3)}]ClO4 [M ) Pd (5a), Pt (5b)], and [M{S2Cd(t-Bu-
fy)}(dbbpy){Au(PCy3)}2](ClO4)2 [M ) Pd (6a), Pt (6b)]
were prepared via the reaction of 2a and b or 3a and b with
acetone solutions of [Au(OClO3)(PCy3)], which in turn were
generated from [AuCl(PCy3)] and AgClO4 and used in situ
in the appropriate molar ratios. The neutral complexes 4a
and b precipitated as yellow solids from the reaction mixtures
and are remarkably stable compounds. The cationic com-
plexes were crystallized from acetone/Et2O as moderately
stable orange (5a, b), yellowish orange (6a), or bright yellow
(6a) solids. The monoaurated derivatives 5a and b are stable
in most common organic solvents, but they undergo ap-
preciable dissociation of [Au(PCy3)]+ units in DMSO, PrCN,
and DMF at concentrations below 10-4 M. The dissociation
of [Au(PCy3)]+ units in solution is more favored for the
diaurated compounds 6a and b because of their dicationic
nature and the diminished donating ability of 5a and b
relative to that of 3a and b. Thus, although 6a and b are
stable in essentially non-coordinating solvents such as
CH2Cl2 and CHCl3, a significant dissociation of [Au(PCy3)]+
units to give 5a and b takes place in all coordinating solvents
and may be complete at concentrations below 10-4 M. These
dissociation processes were revealed by the electronic
absorption spectra and are discussed further below.
mg, 67%. Anal. Calcd for C76H114Au2Cl2N2O8P2PtS2: C, 46.34;
H, 5.83; N, 1.42; S, 3.26. Found: C, 46.16; H, 6.00; N, 1.69; S,
3.02. mp: 180 °C. IR (Nujol, cm-1): ν(CdCS2) not observed. 1H
3
NMR (400.9 MHz, CD2Cl2): δ 8.65 (d, JHH ) 6.0 Hz, 2 H, H6,
dbbpy), 8.60 (d, 4JHH ) 1.2 Hz, 2 H, H1, H8), 8.45 (d, 4JHH ) 1.8
Hz, 2 H, H3, dbbpy), 7.93 (dd, 3JHH ) 6.0 Hz, 4JHH ) 1.9 Hz, 2 H,
3
3
H5, dbbpy), 7.64 (d, JHH ) 8.0 Hz, 2 H, H4, H5), 7.45 (dd, JHH
) 8.0 Hz, 4JHH ) 1.6 Hz, 2 H, H3, H6), 1.94 (br m, 6 H, Cy), 1.75
(br m, 12 H, Cy), 1.59 (br m, 18 H, Cy), 1.54 (s, 18 H, t-Bu, dbbpy),
1.47 (s, 18 H, t-Bu, dithiolato), 1.18 (br m, 24 H, Cy), 0.92 (br m,
6 H, Cy). 13C{1H} NMR (100.8 MHz, CD2Cl2): δ 168.2 (C4,
dbbpy), 155.7 (C2, dbbpy), 151.2 (C2, C7), 148.9 (C6, dbbpy),
144.1 (CS2), 138.0 (C8a, C9a), 136.6 (C4a, C4b), 134.8 (C9), 127.1
(C5, dbbpy), 126.5 (C3, C6), 122.3 (C1, C8, dithiolato + C3,
dbbpy), 119.6 (C4, C5), 36.9 (CMe3, dbbpy), 35.4 (CMe3, dithi-
1
olato), 33.4 (d, JPC ) 28.7 Hz, C1, Cy), 31.8 (CMe3, dithiolato),
3
31.2 (C2, C6, Cy), 30.2 (CMe3, dbbpy), 27.0 (d, JPC ) 12.3 Hz,
C3, C5 Cy), 25.9 (C4, Cy). 31P{1H} NMR (162.3 MHz, CD2Cl2):
δ 59.5.
Results and Discussion
Syntheses. The mononuclear Pd(II) complexes with the
(2,7-di-tert-butylfluoren-9-ylidene)methanedithiolato ligand
can be prepared following the procedures described for the
analogous Pt(II) complexes.18 Thus, the anionic complex
(Pr4N)2[Pd{S2Cd(t-Bu-fy)}2] (2a) was obtained in moderate
yield from the reaction of PdCl2 with piperidine, Pr4NCl,
and piperidinium 2,7-di-tert-butyl-9H-fluorene-9-carbodithio-
ate (1) in molar ratio of 1:2:2:2 in CH2Cl2 (Scheme 1). The
addition of piperidine to CH2Cl2 suspensions of PdCl2 results
in the formation of clear solutions presumably containing
Crystal Structures of Complexes. The crystal structure
of complex 3a (Figure 1) was solved as a CH2Cl2 mono-
solvate. Selected bond distances and angles are listed in Table
2. The molecule exhibits the expected square planar coor-
4722 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
Table 3. Selected Bond Distances (Å) and Angles (deg) for 4a and 4b
4a
4b
M ) Pd
M ) Pt
Au(1)-P(1)
Au(1)-S(2)
Au(1)-M
M-S(2)
2.2630(7)
2.3316(7)
3.04793(14)
2.3259(6)
2.3282(7)
1.749(3)
2.2613(15)
2.3386(14)
3.0529(2)
2.3191(14)
2.3276(15)
1.753(6)
M-S(1)
S(1)-C(10)
S(2)-C(10)
C(9)-C(10)
1.790(3)
1.355(4)
1.790(6)
1.353(7)
P(1)-Au(1)-S(2)
P(1)-Au(1)-M
S(2)-M-S(1)#1
S(2)-M-S(1)
S(1)#1-M-Au(1)
C(10)-S(1)-M
C(10)-S(2)-M
C(10)-S(2)-Au(1)
M-S(2)-Au(1)
S(1)-C(10)-S(2)
175.80(2)
131.494(18)
105.06(2)
74.94(2)
86.995(17)
89.68(9)
88.76(9)
103.28(9)
81.75(2)
175.16(5)
131.81(4)
105.36(5)
74.64(5)
87.42(4)
90.1(2)
89.51(19)
103.31(18)
81.91(4)
105.4(3)
106.22(14)
atoms, which is attributable to their almost equivalent
covalent radii.26 The coordination geometries around these
atoms and the M-S bond distances are also very similar to
those found in the crystal structures of (Me4N)2[Pd{S2Cd
(COMe)2}2]13 and several salts of [M(i-mnt)2]2- (M ) Pd,12,27
Pt).28 The fluoren-9-ylidene moieties are practically planar
[main deviation from plane ) 0.017 (4a), 0.019 (4b) Å] and
rotated by 14.3° in both cases with respect to the S(1)-
C(10)-S(2) plane. The gold atoms are bonded to one of the
sulfur atoms of each dithiolato ligand and lie above and
below the MS4 plane. The arrangement of the gold atoms
with respect to the MS4 core is defined by the angles Au-
S(2)-M of 81.75(2) (4a) or 81.91(4)° (4b) and the torsion
angles Au-S(2)-M-S(1) of 107.70 (4a) or 107.31° (4b).
The coordination around gold is almost linear, and the Au-
S(2) distances of 2.3316(7) (4a) or 2.3386(14) Å (4b) are
comparable to those found in the dinuclear complexes [{Au-
(PR3)}2{S2Cd(t-Bu-fy)}] (R ) Me, Ph) and [{Au(PPh3)}
2{S2Cd(fy)}]16 or the mononuclear complexes [Au{SC(d
S)NEt2}(PCy3)] and [Au{SC(dS)OR}(PCy3)] (R ) Ph, Pr,
i-Pr, Et),29 all of which feature [Au(PR3)]+ units bonded to
nonbridging thiolate functions. Despite the apparent strength
of the Au-S bonds, the coordination of [Au(PCy3)]+ units
to the [M{S2Cd(t-Bu-fy)}2]2- anions does not have a
significant influence on the bond distances and angles in the
MS4 core and causes only a slight lengthening of the C(10)-
S(2) bond distance [1.790(3) (4a), 1.790(6) Å (4b)] as
compared to C(10)-S(1) [1.749(3) (4a), 1.753(6) Å (4b)],
which is attributable to a decrease in the bond order. There
are Au‚‚‚M contacts of 3.0479(1) (4a) and 3.0529(2) Å (4b),
which are shorter than the sum of van der Waals radii for
Au and Pd (3.29 Å) or Pt (3.38 Å)30 and lie in the range
Figure 2. Thermal ellipsoid plot (50% probability) of the centrosymmetric
molecular structure of complex 4a. Hydrogen atoms are omitted for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 3a‚CH2Cl2
Pd-N(21)
Pd-N(31)
Pd-S(1)
Pd-S(2)
2.058(2)
2.079(2)
2.2562(8)
2.2738(7)
S(1)-C(10)
S(2)-C(10)
C(9)-C(10)
1.753(3)
1.752(3)
1.357(4)
N(21)-Pd-N(31)
N(21)-Pd-S(1)
N(31)-Pd-S(1)
N(21)-Pd-S(2)
N(31)-Pd-S(2)
78.50(9)
100.79(6)
176.17(6)
175.47(6)
105.59(6)
S(1)-Pd-S(2)
75.27(3)
90.49(9)
89.92(9)
C(10)-S(1)-Pd
C(10)-S(2)-Pd
S(1)-C(10)-S(2)
104.23(14)
dination around the palladium atom (the mean deviation from
plane S2PdN2 is 0.046 Å). The aromatic rings of the dbbpy
ligand and the fluoren-9-ylidene moiety deviate significantly
from the S2PdN2 mean plane [maximum deviations are found
for the following: C(5), -0.94 Å; C(6), -0.81 Å; C(34),
0.58 Å; C(35), 0.48 Å], resulting in an appreciable bending
of the whole molecule. The coordination geometry around
the metal center is similar to that found for the related
platinum complexes [Pt{S2Cd(MeO-fy)}(dbbpy)]18 (MeO-
fy ) 2,7-dimethoxyfluoren-9-ylidene), [Pt{S2Cd(COMe)2}-
(dbbpy)], and [Pt{S2Cd(CN)(C6H4Br-4}(dbbpy)].22 The
Pd-S and Pd-N bond distances are also comparable to the
Pt-S and Pt-N distances found for the mentioned platinum
homologs, as expected in view of the similar covalent radii
of Pt and Pd.26 As far as we are aware, this is the first
reported crystal structure of a palladium 1,1-ethylenedithi-
olate diimine complex.
The X-ray single-crystal structure analyses of 4a and b
revealed that these complexes are isomorphous. The structure
of 4a is shown in Figure 2. Selected bond distances and
angles for both complexes are listed in Table 3. The
molecules exhibit crystallographic inversion symmetry, and
therefore, the MS4 cores are strictly planar. Both structures
reveal very similar bond distances around the Pd and Pt
(27) (a) Cao, R.; Su, W.; Hong, M.; Tatsumi, K. Chem. Lett. 1999, 1219-
1220. (b) Long, D. L.; Hou, H. W.; Xin, X. Q.; Yu, K. B.; Luo, B. S.;
Chen, L. R. J. Coord. Chem. 1996, 38, 15.
(28) (a) Hummel, H. U. Trans. Met. Chem. 1987, 12, 172-174. (b) Gao,
X.-M.; Dou, J.-M.; Li, D.-C.; Dong, F.-Y.; Wang, D.-Q. J. Mol. Struct.
2005, 733, 181-186.
(29) (a) Siasios, G.; Tiekink, E. R. T. Z. Kristallogr. 1993, 205, 261-270.
(b) Siasios, G.; Tiekink, E. R. T. Z. Kristallogr. 1993, 203, 117-119.
(30) Bondi, A. J. Phys. Chem. 1964, 68, 441-451.
(26) Pauling, L. J. Am. Chem. Soc. 1947, 69, 542-553.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4723

Vicente et al.
expected for d8-d10 metallophilic interactions.6,31 We note
that only five crystal structures in the Cambridge Structural
Database32 display weak Pd‚‚‚Au contacts of similar length,
namely, those of [{Pd(SeH)(PPh3)}2{Au(PPh3)}2(µ3-Se)2]
(3.067 Å),33 [PdCl2{AuCl(PPh2CH2SPh)}2] (3.142 Å),34
[{Pd(CN)2}Au(µ-dcpm)2] [2.954 Å; dcpm ) bis(dicyclo-
hexylphosphino)methane],31 [{Pd(dbbpy)}2{Au(PPh3)}2(µ3-
O)2] (2.985 Å), and [{Pd(dbbpy)}4{Au(PPh3)}2(µ3-O)3](BF4)3
(3.071, 3.065, 3.211 Å),35 while five other structures exhibit
Pd‚‚‚Au distances in the range of 3.300-3.500 Å.36 Com-
plexes with weak Pt‚‚‚Au contacts are more numerous3,31,37
and include the tetranuclear complex [{Pt(PPh3)2}2Au2{S2Cd
(COMe)2}2](ClO4)2 (3.224, 3.334 Å),14 the trinuclear ylide
complex [Au2Pt{CH2P(S)Ph2}] (3.034 Å),38 and several
complexes with bridging sulfido ligands (range of 3.016-
3.495 Å).39 The 1,2-dithiolene complex [Pt(mnt)2{Au-
(PPh3)}2]40 (mnt ) maleonitriledithiolate) is the closest
structural relative to complexes 4a and b and also exhibits
inversion symmetry and similarly situated [Au(PPh3)]+ units,
but with a wider Au-S-Pt angle of 95.45° leading to an
appreciably longer Au‚‚‚Pt distance of 3.415 Å.
Figure 3. Thermal ellipsoid plot (50% probability) of the cation of complex
5b. Hydrogen atoms are omitted for clarity.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 5b‚Me2CO
The structure of complex 5b (Figure 3) was solved as an
acetone monosolvate. Selected bond distances and angles are
listed in Table 4. The essentially planar [Pt{S2Cd(t-Bu-fy)}-
(dbbpy)] unit (mean deviation of 0.075 Å, excluding the t-Bu
groups) is coordinated to a [Au(PCy3)]+ unit through one of
the sulfur atoms of the dithiolato ligand. The Au-S(1)
distance and the arrangement of the [Au(PCy3)]+ unit relative
to the [Pt{S2Cd(t-Bu-fy)}(dbbpy)] complex are similar to
those found in 4a and b, with the torsion angle Au(1)-S(1)-
Pt(1)-S(2) of 107.66° being almost identical to its coun-
terparts in 4a and b. However, the Au(1)-S(1)-Pt(1) angle
of 91.92(2)° is appreciably wider and leads to a longer
Au‚‚‚Pt contact of 3.3108(2) Å. The Pt-S(1) bond distance
[2.2683(6) Å] is slightly shorter than Pt-S(2) [2.2835(6) Å],
but they are not significantly different from the Pt-S
distances found in [Pt{S2Cd(MeO-fy)}(dbbpy)].18 As for
Au(1)-Pt(1)
Au(1)-P(1)
Au(1)-S(1)
Pt(1)-N(1)
Pt(1)-N(2)
3.31076(17)
2.2735(6)
2.3367(6)
2.035(2)
Pt(1)-S(1)
Pt(1)-S(2)
S(1)-C(10)
S(2)-C(10)
C(9)-C(10)
2.2683(6)
2.2835(6)
1.794(2)
1.755(2)
1.347(3)
2.035(2)
P(1)-Au(1)-S(1)
P(1)-Au(1)-Pt(1) 131.340(17) C(10)-S(1)-Pt(1)
N(1)-Pt(1)-N(2)
N(1)-Pt(1)-S(1)
N(2)-Pt(1)-S(1)
N(1)-Pt(1)-S(2)
N(2)-Pt(1)-S(2)
172.32(2)
S(1)-Pt(1)-S(2)
75.86(2)
89.76(8)
79.47(8)
179.32(6)
101.11(6)
103.57(6)
176.96(6)
C(10)-S(1)-Au(1) 106.06(8)
Pt(1)-S(1)-Au(1)
C(10)-S(2)-Pt(1)
S(2)-C(10)-S(1)
91.92(2)
90.25(8)
104.08(12)
4a and b, the coordination of a [Au(PCy3)]+ unit to one of
the sulfur atoms of the dithiolato ligand causes a lengthening
of the corresponding C-S distance [C(10)-S(1) ) 1.794-
(2) Å] relative to the other one [C(10)-S(2) ) 1.755(2) Å].
The cations of 5b stack in pairs, related by an inversion
center (Figure 4). The distance between the mean planes of
two adjacent [Pt{S2Cd(t-Bu-fy)}(dbbpy)] units is 3.44 Å,
which is typical for π-stacked planar molecules,16,41 and the
closest contacts are found between atoms C(10) and S(1)
(3.462 Å) and between C(25) and C(5) (3.340 Å).
(31) Xia, B. H.; Zhang, H. X.; Che, C. M.; Leung, K. H.; Phillips, D. L.;
Zhu, N. Y.; Zhou, Z. Y. J. Am. Chem. Soc. 2003, 125, 10362-10374.
(32) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58, 380-
388.
(33) Harvey, P. D.; Eichho¨fer, A.; Fenske, D. J. Chem. Soc., Dalton Trans.
1998, 3901-3903.
Complex 6a crystallized with one molecule each of THF
and hexane in the asymmetric unit. The molecular structure
of the dication is shown in Figure 5, and selected bond
distances and angles are given in Table 5. The structure is
composed of one [Pd{S2Cd(t-Bu-fy)}(dbbpy)] unit with two
[Au(PCy3)]+ units bonded to the sulfur atoms of the dithiolato
ligand. The Au(1)-S(1) and Au(2)-S(2) bond distances of
2.3452(9) and 2.3345(9) Å, respectively, compare well to
those found for 4a, and the torsion angles Au(1)-S(1)-Pd-
S(2) and Au(2)-S(2)-Pd-S(1) of 97.38 or 99.25°, respec-
tively, are slightly narrower. The Au(1)-S(1)-Pd angle of
82.94(3)° is similar to the corresponding one in 4a and leads
to a comparably short Pd‚‚‚Au(1) contact of 3.0658(3) Å,
(34) Crespo, O.; Laguna, A.; Ferna´ndez, E. J.; Lo´pez-de-Luzuriaga, J. M.;
Jones, P. G.; Teichert, M.; Monge, M.; Pyykko¨, P.; Runeberg, N.;
Schu¨tz, M.; Werner, H. J. Inorg. Chem. 2000, 39, 4786-4792.
(35) Singh, A.; Sharp, P. R. Dalton Trans. 2005, 2080-2081.
(36) (a) Balch, A. L.; Fung, E. Y.; Olmstead, M. M. Inorg. Chem. 1990,
29, 3203-3207. (b) Chiffey, A. F.; Evans, J.; Levason, W.; Webster,
M. Polyhedron 1996, 15, 591-596. (c) Fornie´s, J.; Mart´ın, A.; Sicilia,
V.; Mart´ın, L. F. Chem.sEur. J. 2003, 9, 3427-3435.
(37) (a) Manojlovic´-Muir, L.; Henderson, A. N.; Treurnicht, I.; Puddephatt,
R. J. Organometallics 1989, 8, 2055-2061. (b) Xu, C. F.; Anderson,
G. K.; Brammer, L.; Braddock-Wilking, J.; Rath, N. P. Organome-
tallics 1996, 15, 3972-3979.
(38) Murray, H. H.; Briggs, D. A.; Garzo´n, G.; Raptis, R. G.; Porter, L.
C.; Fackler, J. P., Jr. Organometallics 1987, 6, 1992-1995.
(39) (a) Li, Z. H.; Loh, Z. H.; Mok, K. F.; Hor, T. S. A. Inorg. Chem.
2000, 39, 5299-5305. (b) Hallam, M. F.; Luke, M. A.; Mingos, D.
M. P.; Williams, I. D. J. Organomet. Chem. 1987, 325, 271-283. (c)
Bos, W.; Bour, J. J.; Schlebos, P. P. J.; Hageman, P.; Bosman, W. P.;
Smits, J. M. M.; Vanwietmarschen, J. A. C.; Beurskens, P. T. Inorg.
Chim. Acta 1986, 119, 141-148.
(41) (a) Smucker, B. W.; Hudson, J. M.; Omary, M. A.; Dunbar, K. R.
Inorg. Chem. 2003, 42, 4714-4723. (b) Ionkin, A. S.; Marshall, W.
J.; Wang, Y. Organometallics 2005, 24, 619-627.
(40) Fritsch, E.; Polborn, K.; Robl, C.; Su¨nkel, K.; Beck, W. Z. Anorg.
Allg. Chem. 1993, 619, 2050-2060.
4724 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
Table 5. Selected Bond Distances (Å) and Angles (deg) for
6a‚THF‚C6H14
Au(1)-P(1)
Au(1)-S(1)
Au(1)-Pd(1)
Au(2)-P(2)
Au(2)-S(2)
Au(2)-Pd(1)
Pd(1)-N(2)
2.2543(10)
2.3452(9)
3.0658(3)
2.2714(10)
2.3345(9)
3.2670(3)
2.047(3)
Pd(1)-N(1)
Pd(1)-S(1)
Pd(1)-S(2)
S(1)-C(10)
S(2)-C(10)
C(9)-C(10)
2.050(3)
2.2839(10)
2.2851(9)
1.784(4)
1.785(4)
1.339(5)
P(1)-Au(1)-S(1)
171.51(3)
N(2)-Pd(1)-Au(2)
N(1)-Pd(1)-Au(2)
92.62(9)
137.41(8)
Au(1)-Pd(1)-Au(2) 124.413(10)
P(1)-Au(1)-Pd(1) 132.92(3)
P(2)-Au(2)-S(2)
P(2)-Au(2)-Pd(1) 131.76(3)
174.94(3)
C(10)-S(1)-Pd(1)
89.46(12)
94.41(12)
82.94(3)
89.39(12)
102.11(12)
90.01(3)
N(2)-Pd(1)-N(1)
N(2)-Pd(1)-S(1)
N(1)-Pd(1)-S(1)
N(2)-Pd(1)-S(2)
N(1)-Pd(1)-S(2)
S(1)-Pd(1)-S(2)
79.30(12) C(10)-S(1)-Au(1)
179.11(9)
101.54(9)
102.78(9)
176.56(9)
76.36(3)
Pd(1)-S(1)-Au(1)
C(10)-S(2)-Pd(1)
C(10)-S(2)-Au(2)
Pd(1)-S(2)-Au(2)
S(1)-C(10)-S(2)
104.61(19)
higher than those in the free dithioate 1, which is generally
observed for coordinated (fluoren-9-ylidene)methanedithi-
olato ligands.16-18
Figure 4. Stacked dimer in the structure of 5b. The shortest contacts are
highlighted by dashed lines. t-Bu and Cy groups are omitted for clarity.
Hydrogen atoms in black are significantly shielded upon stacking in solution
because of the magnetic anisotropy effect of the adjacent aromatic rings.
The dithiolato ligands in the Pd/Au and Pt/Au complexes
4a and b and 5a and b give rise to only three resonances for
the aromatic protons H1/H8, H3/H6, and H4/H5 and one
resonance for the t-Bu groups in the 1H NMR spectra, while
the coordination of one of the sulfur atoms to a [Au(PCy3)]+
unit should make all the aromatic protons and the t-Bu groups
inequivalent. This suggests the existence of dynamic pro-
cesses in solution, which were studied by variable-temper-
1
ature H NMR measurements and are discussed below. In
1
addition, the H NMR spectra of the dinuclear complexes
5a and b are concentration dependent and show that the
resonances of all the aromatic protons except H1/H8 (dithi-
olate) and H3 (dbbpy) shift to lower frequencies with
1
increasing concentration. The H NMR spectra of the Pt
complex 5b at different concentrations in the range from 2.2
× 10-2 to 7.4 × 10-4 M are shown in Figure 6; the H6
protons of the dbbpy ligand are the most affected (∆δ )
0.23 ppm in the studied concentration range), followed by
the H4/H5 and H3/H6 protons of the dithiolate and the H5
protons of the diimine. Similar variations in the chemical
shifts of these protons are observed for the Pd complex 5a
(see Supporting Information). These observations are con-
sistent with the formation of π-stacked dimers in solution,
which affects the chemical shifts of some of the aromatic
protons because of the magnetic anisotropy of adjacent
aromatic rings. Thus, if the dimers in solution are assumed
Figure 5. Thermal ellipsoid plot (50% probability) of the cation of complex
6a. Hydrogen atoms are omitted for clarity.
while the wider Au(2)-S(2)-Pd angle of 90.01(3)° com-
pares to the value found for Au-S(1)-Pt in 5b and leads to
a longer Pd‚‚‚Au(2) contact of 3.2670(3) Å. As expected in
view of the previous structures, the C(10)-S(1) and C(10)-
S(2) bond distances of 1.784(4) and 1.785(4) Å are somewhat
longer than the corresponding distances in 3a, while the
lengthening of the Pd-S(1) and Pd-S(2) distances [2.2839-
(10) and 2.2851(9) Å] relative to 3a is less important.
1
NMR Spectra and Dynamic Behavior. The H and 13C
NMR spectra of the Pd complexes 2a and 3a are very similar
to those of their Pt counterparts18 and agree with the proposed
structures (see Experimental Section). The chemical shifts
of the H1 and H8 protons (δ 8.97-8.40) are considerably
Figure 6. Room-temperature 1H NMR spectra of 5b in CD2Cl2 (400.9
MHz) at different concentrations (aromatic region).
Inorganic Chemistry, Vol. 46, No. 11, 2007 4725

Vicente et al.
Table 6. Arrhenius and Eyring Activation Parameters for the Exchange
Processes in 5a,b
EA
∆Hq
∆Sq
Tcoal
∆Gq
coal
compd (kcal mol-1
)
(kcal mol-1
)
(cal mol-1 K-1
)
(K) (kcal mol-1
)
5a
5b
10.6 ( 0.6
7.4 ( 1.1
10.1 ( 0.6
7.1 ( 0.5
-2 ( 2
-12 ( 2
223 10.7 ( 0.2
188
9.3 ( 0.1
Scheme 2
Figure 7. Variable-temperature 1H NMR spectra of complexes 5a and b
in CD2Cl2 (400.9 MHz; H1 and H8 resonances).
to have essentially the structure found for 5b in the solid
state (Figure 4), the H6 and H5 atoms of the dbbpy ligand
(labeled as H30/H21 and H29/H22, respectively, in the
crystal structure of 5b) should be shielded upon stacking in
solution because they are located over the shielding region
of the fluoren-9-ylidene moiety of the adjacent cation, while
the H3 atoms (labeled as H27/H24) lie further apart and
should not be affected. Similarly, the H3/H6 and H4/H5
atoms of the fluoren-9-ylidene groups are located over the
shielding region of the dbbpy ligand of the adjacent cation,
while the H1/H8 atoms lie well outside. Therefore, the
increase of the fraction of π-stacked dimers with concentra-
tion explains the gradual shielding of all the aromatic protons
except H1/H8 (dithiolate) and H3 (dbbpy).
The existence of a dynamic process involving the migra-
tion of the [Au(PCy3)]+ units between the sulfur atoms of
the dithiolato ligands can be clearly confirmed for the
simplest cases 5a and b by means of variable-temperature
1H NMR analyses. The 1H NMR spectrum of the Pd complex
5a at 183 K in CD2Cl2 shows two resonances for the H1
and H8 protons of the dithiolato ligand at δ 8.80 and 8.60,
which coalesce at 223 K and at 293 K and give rise to one
resonance at δ 8.71 (Figure 7). The resonance of the t-Bu
groups of the dithiolato ligand in 5a also splits at 183 K
into two broad singlets at δ 1.45 and 1.41, which coalesce
at 203 K, while the resonance arising from the t-Bu groups
of dbbpy does not split. In the case of the Pt complex 5b,
only the resonances corresponding to the H1 and H8 protons
split at 183 K, appearing as broad signals at δ 8.69 and 8.63
in CD2Cl2 and coalescing at 188 K. The resonances of the
H3/H6 and H4/H5 atoms of the dithiolato ligand and those
of H5 and H6 of the dbbpy ligand broaden and move to
lower frequencies upon cooling to 183 K and only that of
H5 (dbbpy) in 5a splits into two broad signals (see Sup-
porting Information for further details); the shielding of these
protons can be attributed to an increasing fraction of
π-stacked dimers.
cantly higher for the Pd complex 5a than for its Pt counterpart
5b and are also associated with a larger splitting of the H1/
H8 resonances for the Pd complex (0.20 ppm for 5a vs 0.06
ppm for 5b). It is reasonable to propose that the migration
of the [Au(PCy3)]+ unit takes place through a symmetrical
transition state, in which the metallophilic M‚‚‚Au contact
strengthens as the Au-S bond cleaves and a new Au-S bond
begins to form (Scheme 2). The M‚‚‚Au interaction could
thus assist the migration process by lowering the energy of
such a transition state. The higher enthalpy of activation for
5a as compared to 5b would then be the consequence of
Pd‚‚‚Au contacts being weaker, that is, having a lower
interaction energy, than the Pt‚‚‚Au contacts. Additionally,
the stronger Pt‚‚‚Au interaction in 5b could be connected
with a weaker effect of the [Au(PCy3)]+ unit on the H1/H8
atoms and therefore a smaller splitting of their resonances.
The entropy of activation is close to zero for the Pd complex
5a, which is typical for unimolecular processes. However,
the more negative ∆Sq value found for the Pt complex 5b
does not have a clear explanation; the participation of the
perchlorate anion in the formation of the transition state is
one possible cause.
The variable-temperature 1H NMR and 31P NMR spectra
of 4a also confirmed the existence of a dynamic process. In
this case, however, the migration of the [Au(PCy3)]+ units
between the sulfur atoms can lead to three different isomers,
labeled as A, B, and C in Scheme 3. At 183 K, the 1H NMR
spectrum shows that only the resonances of the H1 and H8
protons split, giving three broad signals at δ 8.87, 8.82, and
8.68 with relative intensities of 0.7:1.2:2.0, which coalesce
at 203 K (Figure 8), while the 31P NMR spectrum shows
two broad signals at δ 57.4 and 57.3 with relative intensities
The Arrhenius and Eyring activation parameters corre-
sponding to the exchange processes in 5a and b can be
obtained by means of line-shape analysis of the temperature-
dependent H1/H8 resonances and are listed in Table 6. The
coalescence temperature and activation enthalpy are signifi-
4726 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
that metallophilic interactions between heavier elements are
stronger because of increasing contributions from relativistic
effects.6,42 In connection with this, we note that recent
calculations on the model trans-H2Pd(PH3)2‚‚‚HAuPH3 yielded
an interaction energy of 8.4 kcal mol-1 for the Pd‚‚‚Au
contact (LMP2),34 while in trans-Pt(PH3)2(CN)2‚‚‚Au(PH3)2+,
the Pt‚‚‚Au interaction energy is 10.4 kcal mol-1 (MP2).31
The trinuclear complexes 6a and b are also expected to
undergo a similar dynamic process leading to the interchange
of the [Au(PCy3)]+ units between the sulfur atoms. However,
the dithiolato ligand in these molecules does not have
inequivalent H1 and H8 protons or t-Bu groups, and
therefore, their dynamic behavior cannot be verified by
means of variable temperature NMR measurements.
IR Spectra. The solid-state IR spectra of mononuclear
Pd complexes 2a and 3a show one band at 1500 or 1536
cm-1, respectively, assignable to the ν(CdCS2) mode.43
These energies are identical to those found for the corre-
sponding Pt counterparts 2b and 3b.18 We have previously
shown that the energy of the ν(CdCS2) band in complexes
with (fluoren-9-ylidene)methanedithiolate and its substituted
derivatives is sensitive to variations in the electron-accepting
ability of the metal center.16,18 Usually, a higher oxidation
state or the presence of weaker donor ligands strengthens
the π component of the CdCS2 double bond, thereby
increasing the energy of the corresponding stretching vibra-
tion. This is consistent with the fact that the energy of the
ν(CdCS2) band for the anionic complexes 2a and b is lower
than for the neutral diimine complexes 3a and b. The
replacement of Pt by Pd does not have an effect on the energy
of this band, consistent with the very similar acceptor
character of these metals.
Figure 8. Variable-temperature 1H NMR spectra of complex 4a in CD2-
Cl2 (400.9 MHz; H1 and H8 resonances).
Scheme 3
The energy of the ν(CdCS2) band increases significantly
on going from 2a and b to the trinuclear 4a and b complexes
(1538 cm-1 in both cases) because the coordinated
[Au(PCy3)]+ units withdraw additional electron density from
the dithiolato ligands. Similarly, the cationic complexes 5a
and b display higher energies for this band (1564 or 1572
cm-1, respectively) than their mononuclear precursors 3a and
b. However, the ν(CdCS2) band was not observed in the
IR spectra of the trinuclear complexes 6a and b.
Bands arising from ν(M-S) modes were observed only
for 2a and 4a and b. In the case of 2a, the ν(Pd-S) band
appears at 342 cm-1, which is slightly higher in energy than
the ν(Pt-S) band arising from 2b at 338 cm-1.18 For the
trinuclear complexes, two bands are observed at 354 and
334 cm-1 (4a) or 346 and 336 cm-1 (4b).
Electronic Absorption Spectra. The UV-vis absorption
spectra were measured in CH2Cl2 at 298 K. The absorptions
with λ > 330 nm are listed in Table 7. The intense lowest-
energy absorption band observed for 2a at 459 nm can be
assigned to a metal-to-ligand charge-transfer (MLCT) transi-
tion from the mixed Pd(d)/πdithiolate HOMO and a dithiolate-
based π* orbital.19,44 Its large molar extinction coefficient is
of 1:1.5, which coalesce at 188 K. These data suggest the
presence of two different isomers with inequivalent H1 and
H8 protons in different concentrations, although it is likely
that the three possible isomers are indeed present and that
1
two of them (A and B) give rise to almost co-incident H
and 31P resonances that do not resolve at 183 K. In the case
of the Pt complex 4b, no splitting of the H1/H8 or
phosphorus resonances was observed at 183 K, probably
because of a much lower coalescence temperature. Although
the variable-temperature NMR data of 4a and b did not allow
us to determine any activation parameters, the lower coa-
lescence temperatures compared to those of 5a and b are
indicative of higher rate constants and lower enthalpies of
activation. If we assume a transition state similar to that
proposed for 5a and b, this observation is consistent with
stronger M‚‚‚Au contacts in 4a and b than in 5a and b, which
are expected because of the dianionic nature of the mono-
nuclear precursors 2a and b and the higher Coulombic
contribution to these interactions.5 Analogous reasoning leads
to the conclusion that the Pd‚‚‚Au contacts in 4a must be
weaker than the Pt‚‚‚Au contacts in 4b, which is in agreement
with the differences observed between 5a and b. As far as
we are aware, there are no systematic studies that would
permit a direct comparison of the interaction energies for
Pd‚‚‚Au and Pt‚‚‚Au contacts. However, it is usually accepted
(42) Pyykko¨, P. Angew. Chem., Int. Ed. 2004, 43, 4412-4456.
(43) Jensen, K. A.; Henriksen, L. Acta Chem. Scand. 1968, 22, 1107-
1128.
(44) Werden, B. G.; Billig, E.; Gray, H. B. Inorg. Chem. 1966, 5, 78-81.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4727

Vicente et al.
Table 7. Electronic Absorption Data for Compounds 2-6a,b in CH2Cl2
Solution (ca. 5 × 10-5 M) at 298 K (λ > 330 nm)
compd
λ/nm (ꢀ/M-1 cm-1
)
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
345 (35 800), 407 (15 000), 435 (sh, 40 800), 459 (100 800)
337 (28 100), 428 (12 200), 490 (57 600)
375 (32 800), 391 (36 000), 467 (5700)
381 (27 800), 397 (31 400), 543 (10 000)
412 (sh, 43 400), 432 (60 800)
437 (sh, 33 300), 470 (49 600)
359 (25 800), 376 (30 400), 431 (5700)
379 (27 900), 494 (8500)
341 (23 400), 353 (24 900)
343 (sh, 19 500), 356 (21 300), 397 (sh, 8200)
typical of charge-transfer transitions in 1,1-ethylenedithiolato
complexes.45 The significantly higher energy of this band
for the Pd complex 2a than for its Pt analog 2b (490 nm)18
is characteristic of MLCT transitions involving these met-
als.44,46 When compared with [Pd(i-mnt)2]2- (377 nm),44 the
energy of the MLCT transition in 2a is much lower because
of the higher electron-donating ability of the (2,7-di-tert-
butylfluoren-9-ylidene)methanedithiolato ligand, which raises
the energy of the HOMO and therefore decreases the
HOMO-LUMO energy gap. In contrast, the analogous
complex with the closely related (cyclopentadienylidene)-
methanedithiolato ligand displays a similar energy for this
band (469 nm).47
The absorption spectra of complexes 4a and b show one
relatively broad band at 432 and 470 nm, respectively, with
a shoulder on the higher-energy slope (412 or 437 nm). The
corresponding molar extinction coefficients are high, but they
are significantly lower than those of the lowest absorption
band of 2a and b. The higher energy of this band for the Pd
relative to the Pt complex is indicative of metal orbital
involvement. Its most probable origin is an MLCT transition
of similar orbital parentage to that observed for the anionic
complexes 2a and b; its higher energy can be reasonably
explained by the effect of the coordination of each dithiolato
ligand to one [Au(PCy3)]+ unit, which necessarily causes a
significant decrease in the energy of the sulfur orbitals and
hence of the mixed metal/dithiolate HOMO, thereby raising
the HOMO-LUMO energy gap.
Figure 9. Electronic absorption spectra of complexes 3, 5, and 6a (top)
and 3, 5, and 6b (bottom) in CH2Cl2 solution at 298 K.
Table 8. Lowest-Energy Absorption Band for Complexes 3a and b and
5a and b as a Function of Solventa
λ
max (nm)
solvent
toluene
THF
CHCl3
CH2Cl2
Me2CO
dimethylsulfoxide
MeCN
3a
3b
5a
5b
545
497
509
467
451
433
446
607
564
572
543
528
511
502
417
419
416
431
417
425
425
466
470
469
494
470
466
463
a 5 × 10-5 M, except for 5b in dimethylsulfoxide, which is 1.5 × 10-4
M.
The absorption spectrum of the diimine complex 3a in
CH2Cl2 (Figure 9) has basically the same profile as that of
its Pt analog 3b.18 The two intense bands at 374 and 391
nm are insensitive to variations in solvent polarity and can
be assigned to dithiolate-based transitions, while the broad
lowest-energy absorption band at 496 nm is strongly solvent-
dependent and corresponds to the charge transfer to diimine
transition typically observed for Pd(II) and Pt(II) diimine
dithiolates.23,46 The UV-vis spectra of 3a in a variety of
organic solvents showed that this band shifts to lower energy
as solvent polarity decreases (Table 8). The plot of this
energy against the Pt(NN)(SS) solvent parameter23 gave a
good linear correlation (R2 ) 0.92; see Supporting Informa-
tion) and yielded a solvatochromic shift of 160 cm-1, which
is slightly lower than that of the Pt counterpart 3b. The higher
energy of the solvatochromic transition in 3a relative to that
of 3b (543 nm) is consistent with significant metal orbital
involvement in this transition.
The coordination of one [Au(PCy3)]+ unit to 3a and b to
give the dinuclear complexes 5a and b causes significant
modifications of the absorption spectra (Figure 9). The
spectrum of 5a in CH2Cl2 shows that the dithiolate-based
bands broaden and blue shift to 359 and 376 nm, while for
5b only one relatively broad band at 379 nm is observed.
This blue shift points to an important involvement of the
sulfur orbitals, most probably in the π-π* transitions. The
broad lowest-energy absorption is centered at 431 nm for
5a and 495 nm for 5b. It is very similar in shape to the
solvatochromic band of 3a and b but significantly blue-
shifted and has a somewhat lower molar extinction coef-
ficient. Again, the energy of this transition is higher for the
(45) Karlin, K. D.; Stiefel, E. I. Progress in Inorganic Chemistry. Dithiolene
Chemistry: Synthesis, Properties, and Applications; Wiley-Inter-
science: New York, 2004; Vol. 52.
(46) Cummings, S. D.; Cheng, L. T.; Eisenberg, R. Chem. Mater. 1997, 9,
440-450.
(47) Bereman, R. D.; Nalewajek, D. Inorg. Chem. 1976, 15, 2981-2984.
4728 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
Table 9. Excitation and Emission Data for 2a, 2b, 3b, 4a, 4b, 5b, and
Pd complex 5a than for its Pt analog 5b, which supports
metal orbital involvement and is consistent with a charge
transfer to diimine, for which the mixed metal/dithiolate
HOMO has a lower energy than that in 3a and b because of
the coordination of one of the sulfur atoms to a [Au(PCy3)]+
unit. The absorption spectra of 5a and b in solvents of
different polarity showed that the energy of this band
undergoes only minor variations that do not follow a regular
trend (Table 7); it is centered at around 420 (5a) or 470 nm
(5b) in most solvents, and in both cases, the largest
divergence is found in CH2Cl2 (431 or 495 nm, respectively).
The drastically diminished solvatochromism of 5a and b as
compared to that of the parent complexes 3a and b is
attributable to a considerable loss of polarity as a conse-
quence of the coordination to a [Au(PCy3)]+ unit. The
changes in polarity between the ground and excited states
are thus expected to be small and not to have a significant
effect on the solvation of the cationic complexes 5a and b.
The dithiolate-based absorptions undergo an additional
shift to higher energies on going from 5a and b to 6a and b
(Figure 9), appearing as two relatively broad and very close
bands at 341 and 353 nm for 6a or 343 and 356 nm for 6b
in CH2Cl2. These data confirm that the sulfur orbitals are
involved in this transition and that their energy decreases as
additional [Au(PCy3)]+ units are bonded to the dithiolato
ligand. The shoulder at 397 nm observed for the Pt complex
6b most probably corresponds to the charge transfer to
diimine transition, which, as expected, is significantly blue-
shifted relative to the monoaurated derivative 5b. The
corresponding absorption is not observed for the Pd complex
6a, probably because it is obscured by the dithiolate-based
bands.
6ba
compd medium (T/K)
λ
exc (nm)
λ
em (nm)
τ (µs)c
2a
2b
solid (77)
395, 456, 485
434, 451, 466
363,456, 554
366, 456, 537
456, 510
690
686
618
632
198
197
10
DMM (77)
solid (298)
solid (77)
DMM (77)
solid (298)
solid (77)
toluene (77)
CH2Cl2 (77)
solid (77)
DMM (77)
solid (298)
solid (77)
DMM (77)
solid (298)
solid (77)
toluene (77)
CH2Cl2 (77)
solid (298)
73
589, 602 155
730 < 10
3b
415, 521, 557, 612
372, 391, 413, 466, 601 689, 730b 9, 18d
380, 403, 529, 580
673
6, 28d
380, 400, 500, 533, 580 673, 732 9, 52d
4a
4b
400, 432, 466, 501
405, 431, 455
370-500
436, 461, 498
471
367-511
366, 518
375, 396, 477, 522
369, 396, 477, 513
375, 503
718
722
665
668
111
88
<10
43
609, 670 127
605, 664 51
603, 658 87
609, 663 38, 121d
604, 663 125
608, 658b
5b
6b
(see text)
solid (77)
toluene (77)
CH2Cl2 (77)
367, 428
351, 398b
354, 399
578, 627 183
566, 618 270
564, 616 346
a The most intense peak is italicized. b Shoulder. c (10%. d Double
exponential.
it is close to 0.40 in toluene, acetone, and THF and reaches
0.77 in MeCN. The observed tendency is consistent with
the formation of solvent complexes of the type [Au(PCy3)-
(solvent)]+, which should be favored by the solvents with a
better coordination ability toward Au(I). It must also be noted
that higher values for R are obtained if the solvents are not
rigorously dry. The effect of the concentration on the
dissociation of 6b was evaluated for THF solutions in the
range from 2.2 × 10-5 to 3.1 × 10-4 M. As commonly
observed for dissociation equilibria, the value of R was found
to increase as the initial concentration of 6b decreased (see
Supporting Information for details). However, a consistent
value for the dissociation constant could not be obtained,
probably because of the instability of the cationic species
[Au(PCy3)(solvent)]+.
Excitation and Emission Spectra. The compounds 2a,
4a and b, 5b, and 6b are photoluminescent at 77 K, and
their excitation and emission spectra have been measured
both in the solid state (polycrystalline samples) and in DMM
(DMF/CH2Cl2/MeOH 1:1:1) glasses or frozen CH2Cl2 solu-
tions. Room-temperature luminescence in the solid state was
observed for the Pt/Au complexes 4b, 5b, and 6b, whereas
only the diimine complex 5b displayed detectable lumines-
cence in fluid CH2Cl2 solution at 298 K. The results of the
measurements are summarized in Table 9. The Pd complexes
3a, 5a, and 6a showed no emission at 77 K either in the
solid state or in solution. The previously reported lumines-
cence data of the Pt complexes 2b and 3b18 are included in
Table 9 for comparison.
The electronic absorption spectra showed that complexes
5a and b and 6a and b undergo dissociation of [Au(PCy3)]+
units in different solvents. For the monoaurated complexes
5a and b, the dissociation of [Au(PCy3)]+ units is detectable
in DMSO solution at concentrations below 2 × 10-4
M
because it causes a red shift of the broad lowest-energy
absorption band because of increasing concentration of the
mononuclear precursors 3a and b. The complete dissociation
was observed at a concentration of 5 × 10-5 M in DMSO,
DMF, and PrCN. In contrast, the absorption spectra of 5a
and b showed no significant shifts of the charge transfer to
diimine absorption maximum in toluene, CH2Cl2, CHCl3,
THF, Me2CO, and MeCN at different concentrations in the
range of 10-4-10-5 M, indicating that in these solvents the
complexes are essentially stable.
The dissociation of [Au(PCy3)]+ units from the diaurated
derivatives 6a and b to give 5a and b was observed in all
the tested solvents. In the case of the Pt complex 6b, the
degree of dissociation R can be determined by using the
absorbance values of the charge transfer to diimine absorption
maximum arising from 5b. However, for the Pd complex
6a the absorbance of the corresponding band of 5a could
not be determined accurately, because this band is partially
overlapped by the dithiolate-based absorptions and appears
as a broad tail. At initial concentrations of around 5 × 10-5
M, the value of R for 6b is very low in CH2Cl2 (0.06), while
The excitation and emission spectra of the Pd complexes
2a and 4a in DMM glass at 77 K are shown in Figure 10. In
both cases, the lowest-energy excitation peaks approximately
coincide in energy with the corresponding MLCT absorp-
tions. The emission spectra show a symmetrical band with
a full width at half-height of 1474 (2a) or 1267 cm-1 (4a)
Inorganic Chemistry, Vol. 46, No. 11, 2007 4729

Vicente et al.
Figure 10. Excitation and emission spectra of complexes 2a (-) and 4a (‚ ‚ ‚)
in DMM glasses at 77 K.
Figure 11. Excitation (left) and emission (right) spectra of a frozen solution
of 6b in CH2Cl2 at 77 K. The emission spectra were registered with
excitations at 352 (s) or 477 nm (‚ ‚ ‚). The spectra represented as dotted
lines coincide with the excitation and emission spectra of 5b.
and no discernible vibronic structure. The band maximum
is at 686 (2a) or 722 nm (4a), which leads to very large
Stokes shifts of 6882 or 8128 cm-1, respectively. Polycrys-
talline samples of 2a and 4a at 77 K displayed emission
spectra that are very similar to those obtained in DMM
glasses. The large Stokes shifts, lack of vibronic structure
and long decay lifetimes in the microsecond range are
consistent with an essentially metal-centered 3d-d emitting
state.48 As far as we are aware, there are no previous reports
on the luminescence of Pd(II) complexes with 1,1-ethylene-
dithiolato ligands. The dianionic 1,2-dithiolene complex
[Pd(mnt)2]2- displays luminescence at 77 K, which arises
from a triplet excited-state involving a LUMO of essentially
d orbital character and a HOMO of mixed Pd(d)/πdithiolate
orbital character.49 Analogous frontier orbital designation and
luminescence assignment seem appropriate for 2a in view
of the particular electronic properties of (fluoren-9-ylidene)-
methanedithiolato ligands, which have proved to be similar
to those of 1,2-dithiolenes in electron-donating ability.18
Thus, although the lowest-energy absorption observable for
2a arises from a charge-transfer transition between the mixed
metal/dithiolate HOMO and a dithiolate-based π* orbital,
the LUMO is essentially the vacant d orbital of Pd, and a
state that can be approximately designated as 3[Pd(d)/
πdithiolate-Pd(d)] becomes the emitting state. The coordination
of two [Au(PCy3)]+ units and the formation of relatively
strong metallophilic contacts in 4a have the effect of
decreasing the emission energy. We have also considered
the possibility that the emission of 2a arises from an
intraligand transition. However, the characteristics of this
emission and the fact that its energy decreases upon
coordination of two [Au(PCy3)]+ units do not favor such an
assignment. Alkaline salts of the (2,7-di-tert-butylfluoren-
9-ylidene)methanedithiolate ligand could not be isolated, and
therefore their emission spectra are not available. The
compound [2,7-bis(octyloxy)fluoren-9-ylidene]methanedithi-
ol displays an emission maximum at 525 nm at 77 K both
in the solid state and in frozen CH2Cl2, most probably
associated with the CdCS2 moiety.16,24 An emission of
similar shape and energy is observed for (Bu4N)2[Zn{S2Cd
(t-Bu-fy)}2] (522 nm) and probably has the same origin.50
A triplet emission from the fluoren-9-ylidene group should
be expected at a higher energy.51
The emission spectrum of the Pt/Au complex 4b in DMM
glass at 77 K is drastically different from that of its Pd/Au
counterpart 4a, showing one sharp absolute maximum at 609
nm and a less intense peak at 670 nm. The corresponding
excitation spectrum shows the absolute maximum at 471 nm,
which coincides in energy with the lowest absorption band
in CH2Cl2. The vibronic spacing of 1495 cm-1 is comparable
to that observed for the mononuclear precursor 2b18 and
suggests a similar origin for the emission of 4b, that is, a
3MLCT excited state, most probably perturbed by the
metallophilic interactions. The decay lifetimes of 2b and 4b
(Table 9) are also similar to each other and consistent with
excited states of triplet parentage.
The measurement of the excitation and emission data for
the Pt/Au complexes 5b and 6b in solution was problematic
because of their tendency to lose [Au(PCy3)]+ units in glass-
forming solvents such as PrCN and 2-methyltetrahydrofuran
or solvent mixtures such as EtOH/MeOH and DMM. To
minimize dissociation, the solution measurements at 77 K
were made in frozen CH2Cl2 and toluene glasses. Complex
5b displays a bright orange luminescence in the solid state
at 298 and 77 K, which can even be observed under normal
room illumination. Its emission spectrum shows very similar
profiles in the solid state and in frozen CH2Cl2 at 77 K, with
an absolute maximum at 605 nm and a less intense peak at
660 nm (Figure 11). The emission in fluid CH2Cl2 solution
at 298 K is very weak and has a much broader shape, but
the energies of the two maxima coincide with those observed
at 77 K. The excitation spectra of 5b in both frozen and
fluid CH2Cl2 closely reproduce the absorption spectrum in
CH2Cl2 at 298 K but are broad and complicated in the solid
state. Since the formation of π-stacked dimers of 5b at the
low concentrations employed for the solution measurements
(∼5 × 10-5 M) is expected to be negligible at 298 K, the
(48) Crosby, G. A. Acc. Chem. Res. 1975, 8, 231-238.
(49) Gu¨ntner, W.; Gliemann, G.; Kunkely, H.; Reber, C.; Zink, J. I. Inorg.
Chem. 1990, 29, 5238-5241.
(50) Gonza´lez-Herrero, P.; Garc´ıa-Sa´nchez, Y. Unpublished results.
(51) Vo-Dinh, T.; Gammage, R. B. Anal. Chem. 1978, 50, 2054-2058.
4730 Inorganic Chemistry, Vol. 46, No. 11, 2007

Di- and Trinuclear Pd/Au and Pt/Au Complexes
present data indicate that π-stacking does not have a
substantial effect on the emission energy of this complex.
The observed emission of polycrystalline 6b at 298 K is
almost identical (although broader) to that of 5b. However,
at 77 K, two distinct emissions can be observed both in the
solid state and in frozen CH2Cl2. When excited at a 475 nm
or longer wavelength, the emission profile coincides with
that of 5b; but at an excitation wavelength of 400 nm or
shorter, the most intense emission bands occur at 564 and
616 nm (CH2Cl2) or 578 and 627 nm (solid) and overlap
two less intense peaks ar 600 and 660 nm (Figure 11). It is
reasonable that the higher-energy emission corresponds to
the diaurated complex 6b, which is supported by the fact
that the excitation spectrum collected at the 564 nm emission
maximum in frozen CH2Cl2 approximately coincides with
the absortion spectrum of 6b in fluid solution. The lower-
energy emission would then arise from small amounts of
5b, which result from the dissotiation of [Au(PCy3)]+ units
in CH2Cl2 solution. In fact, the emission spectrum of 6b in
toluene glass at 77 K registered at an excitation wavelength
of 352 nm also shows the two emissions, but the relative
intensity of the bands arising from 5b is higher because of
the greater dissociation degree in this solvent compared to
that in CH2Cl2. The presence of 5b in polycrystalline samples
of 6b may be associated with partial decomposition in the
solid state, and it is likely that the observed luminescence at
298 K is dominated by the much more intense emission of
5b. The decay lifetimes measured at 77 K are in the
microsecond range and increase in the sequence 3b < 5b <
6b.
The similarity of the emissions of 5b and 6b, with a single
vibronic spacing, suggests an emitting state of common
origin. This vibronic spacing varies between 1352 and 1497
cm-1, depending on the medium, and thus lies within the
range of 1200-1500 cm-1 typically observed for emissions
that involve a diimine based π* orbital in the excited
state.23,52,53 The increase in the emission energy in the order
3b < 5b < 6b (CH2Cl2, 77 K) is attributable to a stabilization
of the mixed metal/dithiolate HOMO as a consequence of
the coordination of successive [Au(PCy3)]+ units. Therefore,
the present data suggest that the luminescence of 5b and 6b
involves a transition of the same orbital parentage as the
charge transfer to diimine absorption, but from a triplet
excited state. A similar assignment has been made for
heteronuclear complexes of the type [Pt(tdt)(diimine){M2-
(dppm)2}]2+ [M ) Ag, Au; tdt ) 3,4-toluenedithiolate; dppm
) 1,1-bis(diphenylphosphino)methane].4 Nevertheless, the
emissions of 5b and 6b most probably originate from a
mixture of charge transfer to diimine and diimine intraligand
3π-π* contributions. The emissions of mononuclear Pt
diimine complexes containing 1,1-ethylenedithiolates have
been most frequently assigned to charge transfer to diimine
triplet states,23 although in some cases a mixed origin has
been established, which includes both charge transfer to
diimine and diimine-based π-π* triplet states.21,54 An
important contribution of the diimine-based 3π-π* state in
5b and 6b is reasonable because the coordination of 3b to
[Au(PCy3)]+ units increases the energy of the charge transfer
to diimine transition, while the diimine π-π* gap is not
expected to undergo significant variations upon modifications
of the ligands attached to Pt,23,53-55 and thus the two states
should lie closer in energy than in the mononuclear precursor.
The increasing contribution of the diimine 3π-π* state upon
the coordination of successive [Au(PCy3)]+ units could
account for the narrower and more defined vibronic structure
of the emissions of 5b and 6b, compared to those of their
mononuclear precursor 3b, and probably also for their longer
3
lifetimes. In fact, the emissions that originate from π-π*
states are known to have typically very long lifetimes.21,54
Conclusions
The complexes [M{S2Cd(t-Bu-fy)}2]2- [M ) Pd (2a), Pt
(2b)] and [M{S2Cd(t-Bu-fy)}(dbbpy)] [M ) Pd (3a), Pt
(3b)] can act as metalloligands toward [Au(PCy3)]+ units to
form heteronuclear complexes of the types [M{S2Cd(t-Bu-
fy)}2{Au(PCy3)}2] [M ) Pd (4a), Pt (4b)], [M{S2Cd(t-Bu-
fy)}(dbbpy){Au(PCy3)}]ClO4 [M ) Pd (5a), Pt (5b)], and
[M{S2Cd(t-Bu-fy)}(dbbpy){Au(PCy3)}2](ClO4)2 [M ) Pd
(6a), Pt (6b)]. The crystal structures of 4a, 4b, 5b, and 6a
reveal that the [Au(PCy3)]+ units are bonded to one of the
sulfur atoms of the dithiolato ligand and adopt similar
arrangements, which lead to the formation of short Pd‚‚‚Au
or Pt‚‚‚Au metallophilic contacts. The heteronuclear deriva-
tives undergo a dynamic process in solution that involves
the migration of the [Au(PCy3)]+ units between the sulfur
atoms of the dithiolato ligands. The enthalpies of activation
of these processes are higher for the Pd/Au systems than for
their Pt/Au analogs, possibly because Pd‚‚‚Au contacts have
lower interaction energies and are thus less effective in
assisting the migration than Pt‚‚‚Au contacts. The coordina-
tion of 2a and b and 3a and b to [Au(PCy3)]+ units results
in important modifications of their photophysical properties.
The dominant effect that is observable in the absorption
spectra is an increase in the energy of the MLCT (4a and b)
or charge transfer to diimine (5a and b, 6a and b) transitions
because of a decrease in the energies of the mixed metal/
dithiolate HOMOs. The characteristics of the emissions of
the Pd complexes 2a and 4a are compatible with essentially
3
metal-centered d-d states. The emissions of the hetero-
nuclear Pt/Au complexes can be assigned as originating from
a MLCT triplet state (4b) or a mixture of charge transfer to
diimine and diimine intraligand π-π* triplet states (5b and
6b).
Acknowledgment. We thank Ministerio de Educacio´n y
Ciencia (Spain), FEDER (CTQ2004-05396) for financial
(52) (a) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am.
Chem. Soc. 1982, 104, 630-632. (b) Miskowski, V. M.; Houlding,
V. H. Inorg. Chem. 1991, 30, 4446-52. (c) Miskowski, V. M.;
Houlding, V. H.; Che, C. M.; Wang, Y. Inorg. Chem. 1993, 32, 2518-
2524.
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Inorganic Chemistry, Vol. 46, No. 11, 2007 4731

Vicente et al.
temperature 1H NMR spectra of 5a and b, results of the line-shape
analyses, including Eyring and Arrhenius plots, plot of the lowest
absorption energy of 3a versus the Pt(NN)(SS) solvent parameter,
and plot of the degree of dissociation R versus concentration for
6b in THF. This material is available free of charge via the Internet
at http://pubs.acs.org.
support. P.G.-H. thanks Ministerio de Educacio´n y Ciencia
(Spain) and Universidad de Murcia for a contract under the
Ramo´n y Cajal Program. M.P.-C. thanks Ministerio de
Educacio´n y Ciencia (Spain) for a research grant.
Supporting Information Available: Crystallographic data in
CIF format for 3a‚CH2Cl2, 4a, 4b, 5b‚Me2CO, and 6a‚THF‚C6H14,
1H NMR spectra of complex 5a at different concentrations, variable-
IC070164H
4732 Inorganic Chemistry, Vol. 46, No. 11, 2007