Synthesis, characterization, electrochemistry and luminescence studies of heterometallic gold(I)-rhenium(I) alkynyl complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.07.024

The present work provides a brief summary review of the chemistry of luminescent gold(I) alkynyls and their ability to form heterometallic complexes. A series of luminescent heterometallic gold(I)-rhenium(I) alkynyl complexes has been synthesized and characterized. Their electrochemical and photophysical properties have been studied and their emission origins elucidated. The present work provides a brief summary review of the chemistry of luminescent gold(I) alkynyls and their ability to form heterometallic complexes. A series of luminescent heterometallic gold(I)-rhenium(I) alkynyl complexes has been synthesized and characterized. Their electrochemical and photophysical properties have been studied and their emission origins elucidated.

Full text of DOI:10.1016/j.jorganchem.2004.07.024

Journal of Organometallic Chemistry 689 (2004) 4451–4462
www.elsevier.com/locate/jorganchem
Synthesis, characterization, electrochemistry and luminescence
studies of heterometallic gold(I)–rhenium(I) alkynyl complexes
*
Kai-Leung Cheung, Sung-Kong Yip, Vivian Wing-Wah Yam
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research, Department of Chemistry, and HKU-CAS Joint
Laboratory on New Materials, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, PR China
Received 29 April 2004; accepted 15 July 2004
Available online 27 August 2004
Abstract
The present work provides a brief summary review of the chemistry of luminescent gold(I) alkynyls and their ability to form het-
erometallic complexes. A series of luminescent heterometallic gold(I)–rhenium(I) alkynyl complexes has been synthesized and char-
acterized. Their electrochemical and photophysical properties have been studied and their emission origins elucidated.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Gold(I); Rhenium(I); Alkynyl ligands; Luminescence
1. Introduction
[Au(C„CR)L] (L = PPh3, R = Me, Et, Ph, CF3;
L = P(C6H4Me-p)3, R = Ph) by reacting the terminal
acetylene with phosphinegold chlorides in the presence
of sodium ethoxide [6]. The dinuclear gold(I) complexes
[LAuC„CAuL] were afforded by a second reaction of
[Au(C„CH)L]. Bruce et al. [7] then extended the syn-
thesis of an extensive series of R3PAuC„CR0 following
previous studies. Vicente et al. [8] reported the synthesis
of a series of neutral and anionic gold(I) alkynyl com-
plexes. The neutral gold(I) alkynyl complexes,
[Au(C„CR)(NHEt2)], ½AuðCBCRÞðPR03Þꢀ, [Au(C„
CR)(CNtBu)], [Au(C„CR){C(NHtBu)(NEt2)}] and
dinuclear [(AuL)2{l-C„C(CH2)5C„C}] have been pre-
pared by a variety of synthetic methods: (i) reaction be-
tween [PPN][Au(C„CH)2] and [Au(PR3)2]ClO4, (ii)
reaction of terminal alkynes with [Au(acac)(L)], (iii)
reaction of [AuClL] complexes with terminal alkynes
in diethylamine, (iv) substitution reactions; (v) reaction
of diethylamine with alkynyl isocyanide derivatives to
give alkynylcarbene complexes. The anionic gold(I)
alkynyl complexes, [PPN][Au(C„CR)2] were afforded
by employing the reaction of [PPN][Au(acac)2] with
the terminal alkynes RC„CH.
During the last decade, there has been a growing
interest in the study of carbon-rich metal alkynyl com-
plexes, owing to their potential applications in molecu-
lar electronics and materials science [1]. One class of
such compounds that has attracted much attention is
the gold(I) alkynyls. The reason partly stems from the
recent interest in the rich luminescence properties re-
ported of this class of compounds and the ability of
gold(I) to build supramolecular architectures based on
its tendency to form two-coordinate linear geometry
and its aurophilic properties [2,3].
The research on gold(I) alkynyl chemistry has been
initiated by Berthelot who discovered the explosive gold
alkynyl Au2C2 in 1866 [4]. Coates and Parkin [5] re-
ported the synthesis of alkynylgold(I) phosphine com-
plexes in 1962. Cross reported the synthesis of
mononuclear alkynylgold(I) phosphine complexes,
*
Corresponding author. Tel.: +852 2859 2153; fax: +852 2857 1586.
E-mail address: wwyam@hku.hk (V.Wing-Wah Yam).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.024

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K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
Recent reports on the utilization of gold(I) alkynyls
nylphosphine, whereas the low-energy absorptions were
assigned as [p ! p*] intraligand transitions of the alky-
nyl ligands. Both complexes show emission bands at
530–560 nm in dichloromethane and in the solid state
at both room temperature and 77 K, which are sug-
gested to arise from [p(Au–P) ! p*(C„C)] or metal-
perturbed intraligand [p ! p*(C„C)] excited states.
Both of them show electronic absorption changes upon
addition of alkali metal ion. The dinuclear gold(I) com-
plex with benzo-15-crown-5 has binding ability towards
sodium ion, whereas the tetranuclear gold(I) complex
with benzo-18-crown-6 ether show a preferential binding
towards potassium ion.
in the construction of supramolecular architectures such
as catenanes and macrocycles [3] have also been made.
Mingos et al. [3a] reported the novel gold(I) alkynyl
complex [{Au(C„CtBu)}6]2 in the form of two cate-
nated hexanuclear rings. From the X-ray crystal struc-
ture, it was found that the gold atom is p-coordinated
in a mutually perpendicular manner to the alkynyl
group in a g2–g2 coordination mode. Puddephatt and
co-workers [9] reported the self-assembly of rings, caten-
anes, and
a doubly braided catenane [{[l-X(4-
C6H4OCH2CCAu)2][l-(Ph2PCH2CH2CH2CH2PPh2)]}n]
by reaction of the flexible dialkynyldigold(I) precursors
X(4-C6H4OCH2CCAu)2 with 1,4-bis(diphenylphosph-
ino)butane. The complexes were formed readily and
selectively as 25-membered ring compounds with n = 1,
X = O or S; as [2]catenanes with n = 2, X = CH2 or
CMe2, and as a unique doubly braided [2]catenane, con-
taining interlocked 50-membered rings with n = 4,
X = cyclohexylidene by self-assembly.
Reaction of the carbonyl derivatized bis(alkyne)
O@C(4-C6H4OCH2C„CH)2, imine derivatives RN„C-
(4-C6H4OCH2C„CH)2 [R = OH, NHC(O)NH2, NH-
C6H3-2,4-(NO2)2] and 4-bromomethyl-1,3-dioxolane
derivative BrCH2C2H3O2C(4-C6H4OCH2C„CH)2 with
[AuCl(SMe2)] in the presence of base afforded the corre-
sponding insoluble digold(I) dialkynyl oligomers or pol-
ymers [3e]. By reacting the diphosphines Ph2PZPPh2
[Z = CC, trans-HC„CH and (CH2)n, n = 3–5] with
gold(I) dialkynyl oligomers or polymers, macrocyclic
gold(I) complexes [Au2(l-LL)(l-PP)], where LL is the
dialkynyl and PP the diphosphine ligand, were pro-
duced. These macrocyclic gold(I) complexes have been
studied for the ability to self-assemble to [2]catenanes.
It was found that the ketone and imine derivatives did
not form [2]catenanes because the orientation of the aryl
groups was unfavorable, while the 1,3-dioxolane deriva-
tives might catenate if the ring size was optimum.
Mohr and Puddephatt [10] recently reported macro-
cyclic digold(I) complexes of the type [Au2(l-CC)(l-
PP)], where CC is the dialkynyl and PP is a diphosphine
ligand by reacting (AuCCCH2O(CH2CH2O)3CH2
A series of gold(I) alkynylcalix[4]crown-5 complexes,
½ðRnR03ꢁnPÞAuꢀ L (n = 0–3) (R = Ph, R0 = o-Tol, p-Tol;
2
H2L = 5,17-diethynyl-25,27-dimethoxycalix[4]crown-5)
have been synthesized [12]. The photophysical proper-
ties of these complexes have been studied. In general,
they show high-energy absorptions at 270–300 nm which
were assigned as intraligand transitions of the phosphine
and ethynylcalixcrown ligand and low-energy absorp-
tions at ca. 342 nm which were characteristic of the
gold(I) alkynyl system. All the complexes show an emis-
sion band at 578–585 nm in dichloromethane which has
been suggested to be derived from a triplet state of met-
al-perturbed intraligand or ½rðAu–PÞ ! pꢂðRnR30 ꢁnPÞꢀ
character. The binding properties of these complexes to-
wards alkali metal ion, Na+ and K+ have been studied.
It was found that the binding properties of the com-
plexes could be fine-tuned with a change in the different
steric effect of the auxiliary phosphine ligands.
Owing to the rich luminescence properties of gold(I)
alkynyl complexes, research on this field has grown
rapidly. The luminescence properties of gold(I) alkynyl
complexes were first reported in 1993 in which the
spectroscopic and photophysical properties of [Au2-
(dppe)(C„CPh)2] were described [13]. From the X-ray
crystal structure, the intramolecular Auꢃ ꢃ ꢃAu separa-
˚
tion was found to be 3.153(2) A. The complex showed
a ligand-centred emission at 420 nm in dichlorometh-
ane solution at 298 K, and a solid-state emission at
550 nm at 298 K. It was suggested that the lower en-
1
1
ꢂ
CCAu)n
and
(AuCCCH2OC6H4O(CH2CH2O)3
ergy emission originated from the ðdd Þ ðprÞ triplet ex-
C6H4O–CH2CCAu)n. The binding properties of these
gold(I) alkynyl macrocyclic complexes towards alkali
metal ions (Li+, Na+, K+, Cs+) have been studied by
electrospray-ioniztion mass spectrometry.
Ethynylcrown ether containing di- and tetranuclear
gold(I) crown ether complexes, [{(Ph3P)AuC„C}2
B15C5-4,5] and [{(Ph3P)AuC„C}4DB18C6-4,40,5,50]
have been reported by Yam and co-workers [11]. Both
complexes exhibit intense absorptions at ca. 268–335
nm with tails extending to ca. 400 nm for the dinuclear
complex and ca. 500 nm for the tetranuclear complex.
The high-energy absorptions have been tentatively as-
signed as intraligand transitions characteristic of triphe-
cited state. Reaction of [Au(C„CPh)] with dppm
1
gave the trinuclear complex [Au3(dppm)2(C„CPh)2]
[Au(C„CPh)2] [14]. The X-ray crystal structure
showed a trinuclear [Au3(dppm)2(C„CPh)2]+ cation
with the three gold atoms adopting an isosceles triangle
with intramolecular Auꢃ ꢃ ꢃAu distances of 3.083(2) and
˚
3.167(2) A. The complex showed a high-energy emis-
sion at 425 nm (so = 0.45 ls) and a low-energy emis-
sion at 600 nm (so = 0.45 ls) in degassed acetonitrile
at 298 K. It was suggested that the high-energy emis-
sion originated from a ligand-centred emission and
1
1
3
ꢂ
the low-energy band originated from a ½ðdd Þ ðprÞ ꢀ
excited state.

K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
4453
The photophysical properties of a series of dinuclear
gold(I) alkynyl complexes, [(Ph)n(Np)3 ꢁ nPAuC„
CAuP(Ph)n(Np)3 ꢁ n] (n = 0–3) and [Fc2PhPAuC„CAu-
PPhFc2] have been studied by Mingos and Yam [2a].
The complexes showed vibronically structured absorp-
thylphosphinomethyl)methylphosphine (dmmp), R = Ph,
C6H4OCH3-4) have been reported by Yam [17]. The
complexes with a bridging 1,4-diethynylbenzene and
9,10-diethynylanthracene showed absorption bands at
ca. 294–328 and 410–464 nm with vibrational progres-
sional spacings of 1980 and 1400 cmꢁ1, respectively.
The absorption was proposed to arise from intraligand
[p–p*(alkynyl)] or 1[r(Au–P) ! p*(alkynyl)] transitions.
For the complexes incorporating dppn as the bridging
phosphine, absorption bands were observed at ca.
290–310 nm with a weaker absorption at ca. 400 nm tail-
ing to ca. 500 nm. It was suggested that these absorption
bands arose from 1[r(Au–P) ! p*(dppn)] transition.
The dinuclear complexes with dmpm ligand and trinu-
clear complexes with dmmp ligand showed strong
absorption bands at ca. 252–290 nm, which were sug-
gested to arise from [p–p*(alkynyl)] or [r(Au–P) !
p*(alkynyl)] transitions, with shoulders at ca. 320–332
nm, which were absent in the mononuclear analogues.
1
tion bands at 296 nm, which were assigned as [r(Au–P)
! p*(Np)] transitions. The solid-state emission energies
of the former complexes at 77 K decreased with increas-
ing substitution of Np on the phosphine ligands. This
was proposed to be in line with the increasing elec-
tron-richness around the Au–P bonds and the presence
3
of a [r(Au–P) ! p*(Np)] excited state. The presence
of the ferrocene moiety in the latter complex resulted
in effective intramolecular reductive electron transfer
quenching, and thus the complex was found to be
weakly emissive.
The
complex
[(C6H4OMe-p)3PAu–C„C–AuP
(C6H4OMe-p)3] was reported to have a well-resolved
vibronic structured emission ranging from 400 to 600
nm with progressional spacings of 2100 cmꢁ1 [15]. The
emission bands have been assigned to arise from the
These low-energy absorption bands have been assigned
1
ꢂ
to originate from a ½dr ! prꢀ transition. However, a
3
2ꢁ
intraligand [p–p*] excited state of C2
.
red shift in the absorption energy was observed from
the mononuclear to the trinuclear species, thus it was
The photophysical properties of a series of dinuclear
gold(I) complexes with bridging dialkynyl ligands [(Cy3-
P)Au–(C„C)n–Au(PCy3)] (n = 1–4) have been reported
by Che et al. [2b,16] recently. The complexes with n = 1
and 2 showed a well-defined absorption band extending
to more than 260 nm which was assigned to
[5d(Au) ! 6p(Au), p*(phosphine)] transition. The com-
plex with n = 4 showed a highly vibronic electronic
absorption at 274–290 nm with vibrational progres-
sional spacings of 2010 cmꢁ1, which was assigned as di-
possible to assign the transition as a metal–metal-to-ligꢂ-
1
ꢂ
and charge-transfer MMLCT ½dr ðAu–AuÞ ! p
ðCBCRÞꢀ transition. The complexes [(Tol)3PAu–(BL)–
AuP(Tol)3] (H2BL = 1,4-diethynylbenzene) showed sol-
id-state emission with a vibronically structured band at
ca. 533 nm, which has been assigned to arise from a lig-
and-centred [p–p*(alkynyl)] or [r(Au–P) ! p*(alkynyl)]
triplet state. Similarly, the complex [(Tol)3PAu–(BL)–
AuP(Tol)3] (H2BL = 9,10-diethynylanthracene) showed
solid-state emission at 580 nm, which was assigned to
be intraligand [p ! p*(anthryl)] or [r(Au–P) ! p*
(anthryl)] in origin. Complexes with dppn ligands dis-
play solid-state emissions at ca. 571–655 nm, which were
pole-allowed [p ! p*] transition of the [(C„C)4]2ꢁ
.
Although the complex with n = 1 was nonemissive in
dichloromethane solution at 298 K, incorporation of
the butadiyne ligand resulted in a long-lived 3[p–p*
(alkynyl)] emission at 417 nm at 298 K. In most media,
the complex with ethynyl ligand showed two broad
emissions centred at kmax 415 and 530 nm, which were
dominant both in the solid and alcoholic glass at 298
K. The lowest-energy 3[p–p*(alkynyl)] excited states
were found to acquire sufficient allowedness via Au
spin-orbit coupling to appear prominently both in the
electronic absorption and emission spectra. The com-
plexes with n = 3 and 4 in alkynyl ligands showed sharp
vibronically structured emission with k0–0 lines at 498
and 575 nm in dichloromethane solutions, with vibronic
progressions of ca. 2120 cm1. This was assigned as the
3
suggested to originate from [r(Au–P) ! p*(naphthyl)]
transition. The complex incorporating dcpn as bridging
ligand showed a much lower energy emission peak at
707 nm, since the presence of the electron-donating
cyclohexyl rings of dcpn increases the electron density
of the phosphorus atoms and therefore render the
r(Au–P) electron-pair to be more donating in nature.
The dinuclear gold(I) dmpm-containing alkynyl com-
plexes with phenyl and methoxyphenyl substituted alky-
nyl ligands showed solid-state emission bands at 490 and
521, respectively, while the corresponding trinuclear
gold(I) dmmp-containing alkynyl complexes with the
same alkynyl ligands display emission bands at 538
and 539 nm, respectively. It was suggested the emission
½p–pꢂðCBCÞn2ꢁꢀ emission.
3
A series of alkynylgold(I) with bridging phosphine or
alkynyl ligands [(Tol)3PAu–(BL)–AuP(Tol)3] (H2BL =
1,4-diethynylbenzene, 9,10-diethynyl-anthracene), [Au2-
(P-P)(C„CR)2] (P-P = 1,8-bis(diphenylphosphino) naph-
thalene (dppn), R = C6H4Ph-4, C6H4OCH3-4, C6H13;
P-P = bis(dimethylphosphino)methane (dmpm), R = Ph,
1
1
3
ꢂ
originated from metal-centred ½ðdd Þ ðprÞ ꢀ state. The
emission energy, which seemed to be insensitive to the
substituent on the alkynyl ligand showed a red shift
from the dimer to the trimer. The photochemical prop-
erties of these alkynylgold(I) have also been studied. For
example, it was found that the phosphorescent state of
n
C6H4OCH3-4) and [Au3(dmmp)(C„CR)3] bis (dime-

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K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
[Au3(dmmp)(C„CPh)3] was quenched by the electron
acceptor, 4-methoxycarbonyl-N-methylpyridinium ion,
have also been studied and the complex was found to re-
act with the solvent leading to the formation of the C–C
coupled product, PhC„CC„CPh in dichloromethane.
The photophysical properties of luminescent phenyle-
thynylgold(I) with isocyanide ligands, [Au{CNC6H3
(CH3)2-2,6}(C„CPh)] and [Au2(L)(C„CPh)2] [L =
tmb, dmb] have been reported [20]. From X-ray crystal-
lographic studies, it was shown that the crystal structure
of [Au{CNC6H3(CH3)2-2,6}(C„CPh)] contained two
weakly interacting molecules, paired up in an anti-config-
uration with an intermolecular Auꢃ ꢃ ꢃAu contact of
with
4.98 · 109 dm3 molꢁ1
nism of this photoinduced reaction, as well as that be-
tween [Au2(dppn)(C„C–C6H4OCH3-4)2] and MV2+
a
bimolecular quenching rate constant of
s
ꢁ1. The electron-transfer mecha-
,
have been studied by nanosecond transient absorption
spectroscopy.
A series of dinuclear and tetranuclear gold(I) alkynyl
complexes have been synthesized by us recently by
reaction of [Au(C„CR)] with 1,4-bis(diphenylphosph-
1
˚
ino)benzene (dppb) and 1,2,4,5-tetrakis(diphenyl-
phosphino)benzene (tppb) in dichloromethane to give
[Au2(dppb)(C„CR)2] (R = nC6H13, Ph, C6H4OCH3-4)
and [Au4(tppb)(C„CR)4] (R = nC6H13, Ph, C6H4O
CH3-4), respectively [18]. The X-ray crystallographic
studies on [Au4(tppb)(C„CPh)4] revealed an intramo-
3.329(4) A. The dinuclear gold(I) complex with tmb
adopted an anti-configuration, with an intermolecular
˚
non-bonding Auꢃ ꢃ ꢃAu separation of 3.565(2) A. The
complex with dmb was found to have an intramolecular
˚
Auꢃ ꢃ ꢃAu interaction of 3.485(3) A. Both complexes
showed an intense high-energy absorption band around
1
˚
lecular Auꢃ ꢃ ꢃAu separation of 3.1541(4) A with two
240 nm, which was assigned as MLCT [dz2 ! p*(isocy-
adjacent Au(C„CPh) units in a crossed geometry.
The electronic absorption bands of these complexes at
anide)] transition, and a lower energy absorption at ca.
273 and 278 nm, which was assigned as typical intralig-
and [p–p*(alkynyl)] transitions. Degassed dichlorometh-
ane solutions of the complexes showed a ligand-centred
[p–p*(alkynyl)] emission at around 420 nm. The com-
plexes in the solid state showed a broad emission band
at ca. 550 nm, which was suggested to be derived from
1
ca. 250–300 nm have been assigned to be [r(Au–P)
! p*(Phbridge)] transitions. Complexes with dppb have
higher absorption energies than those with tppb, due
to the more electron-deficient nature of the bridging
phenyl ring of tppb relative to that of the dppb. In gen-
eral, the complexes with methoxyphenylalkynyl have
lower energy emission than those with phenylalkynyl.
The more electron-rich methoxy moiety on the alkynyl
would reduce the extent of metal-to-ligand back-p-do-
nation to the alkynyl [dp(Au) ! p*(alkynyl)]. This leads
to an increased dp(Au)ꢁ3d(P) overlap and therefore a
higher r(Au–P) orbital energy. The complex,
[Au4(tppb)(C„CC6H4OCH3-4)4] has been studied for
the photoreaction with methyl viologen by nanosecond
transient absorption spectroscopy. The transient
absorption difference spectrum showed a sharp absorp-
tion band at ca. 400 nm and another broad one at ca.
600 nm, typical of the MVÅ+ radical absorptions that
indicates the strongly reducing properties of the phos-
phorescent state of [Au4(tppb)(C„CC6H4OCH3-4)4].
A back electron-transfer rate constant kb of 1.94 · 1010
dm3 molꢁ1 sꢁ1 has also been estimated from a plot of
1/DA versus time for the decay trace.
1
1
3
ꢂ
a metal-centred ½ðdd Þ ðprÞ ꢀ excited state.
A series of polymeric gold(I) conjugated arylalkynyl
complexes [{–Au–C„C–Ar–C„C–Au–L–}n] where
L = diphosphine or bis(isocyanide) were reported by
Puddephatt and co-workers [21]. The complexes
[(CH3)3PAu–C„C–(C6H2–R2-2,5)–C„C–Au–P(CH3)3]
(R = H, CH3) showed emission at ca. 415 nm in dichloro-
methane, which was suggested to arise from an excited
state of [p–p*(alkynyl)]/[r(Au–P) ! p*(alkynyl)] origin.
These complexes showed solid-state emission at ca. 540
nm. With reference to the short intermolecular Auꢃ ꢃ ꢃAu
˚
separation of 3.1361(9) A in [(CH3)3PAu–C„C–(C6H2–
(CH3)2-2,5)–C„C–Au–P(CH3)3] in the crystal structure,
it was suggested that the red shift in emission energy arose
1
1
3
ꢂ
from a metal-centred ½ðdd Þ ðprÞ ꢀ excited state.
The complex [{C6H3–(CH3)2-2,6}–N„C–Au–C„C–
(C6H4–NO2-4)] showed an emission at 633 nm in the so-
lid state and at 503 nm in dichloromethane solution [21].
The low-energy emission has been ascribed to the elec-
tron-withdrawing NO2 group, which stabilizes the p* or-
bital of the alkynyl. It was believed that the stacking
interactions between the phenyl rings of the alkynyl
and the isocyanide of two closest molecules in the crystal
structure gave rise to the exceptionally low solid-state
emission energy.
The photophysical and photochemical properties of
dinuclear gold(I) alkynyl complexes with a bridging
diphosphinoferrocene ligand [Au2(dppf)(C„CR)2]
t
(R = Ph and Bu) have also been studied [19]. The com-
plexes showed an intense vibronically structured elec-
tronic absorption at ca. 270–295 nm with
progressional spacings of ca. 1825 cmꢁ1, typical of
l(C„C) stretching frequencies in the excited state.
The absorptions have been assigned to be intraligand
[p–p*(alkynyl)] transitions. The complexes were none-
missive in the solid state even at 77 K. However, they
showed emission bands at 410 nm in dichloromethane
solution. The photoreactivities of [Au2(dppf)(C„CPh)2]
A series of mono- and binuclear gold(I) complexes
with arylalkynyl moieties coordinated to [Au(PCy3)]+
have been prepared by Che and co-workers [22]. Com-
plexes with short arylalkynyl chains, [Cy3PAu–R1]
(R1 = C„C–C6H5; C„C-1,4-C6H4-X, (X = F, Cl,
Me); (C„C)2–C6H5; C„C–C6H4N) and [Cy3PAu–R2–

K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
4455
AuPCy3] (R2 = C„C-1,4-C6H4-C„C) showed emission
bands at 408–488 nm in dichloromethane solution. In
the solid state, the complexes showed a well-resolved
vibronic structured emission band at 420–493 nm with
three types of progressional spacings of ca. 1100, 1600
dependent on the nature of the alkynyl ligands. The
nuclearity of the metal complexes was also found to
influence the electronic absorption as well as emission
behavior. The trinuclear complexes were found that to
be lowest in emission energy, attributed to the presence
of weak Auꢃ ꢃ ꢃAu interactions that would raise the en-
ergy of the metal-centered dr* orbital. Thus, a red shift
3
and 2100 cmꢁ1 that were assigned to the [p–p*(aryl-
alkynyl)]. Complexes with long arylalkynyl chains, [Cy3-
PAu–R1] (R1 = C„C-1,4-C6H4–C6H5; (C„C-1,4-
C6H4)nC„C–C6H5 (n = 1–3)) and [Cy3PAu–R2–
AuPCy3] (R2 = (C„C-1,4-C6H4)n–C„C (n = 2–4);
C„C–(1,4-C6H4)2–C„C) displayed dual emissions with
high-energy bands at 330–407 nm and low-energy bands
located at 495–558 nm. The high energy emission was
suggested to be delayed fluorescence proposed to occur
via a triplet–triplet annihilation mechanism.
3
in the [r(Au–P) ! p*(C„C)] or the metal-perturbed
3IL [p ! p*(C„C)] mixed with metal-to-alkynyl
3MLCT modified by metal–metal interactions, or the
metal–metal-to-ligand charge transfer (3MMLCT) emis-
sion energy were observed relative to that of the mono-
nuclear complexes.
Gold(I) alkynyl complexes have also been utilized to
synthesize mixed-metal alkynyl complexes. Abu Salah
reported a number of complexes using the gold(I) alky-
nyl unit to coordinate with copper and silver atoms in
g2-alkynyl mode [26]. The pentanuclear cluster
[Au3Cu2(C2Ph)6]ꢁ was afforded from the reaction be-
tween [{Au(C2Ph)}n] and a mixture of [Au(C2Ph)2]ꢁ
and [{Cu(C2Ph)}n]. The synthesis of the goldꢁsilver
cluster [Au3Ag2(C2Ph)6]ꢁ was achieved by a slightly
modified method [26a]. From the X-ray crystal struc-
ture, each gold(I) atom was r-bonded to two alkynyl
groups and the copper/silver was p-bonded to three
alkynyl groups. Mixed gold-silver and gold-copper phe-
nylalkynyl polymers [{AuM(C2Ph)2}n] (M = Ag, Cu)
were achieved by reaction of [Au(C2Ph)L] (L = AsPh3,
P(OPh)3) with [{Ag(C2Ph)}n] and [{Cu(C2Ph)}n] [26b].
The pentanuclear trimetallic cluster [Au3AgCu(C2Ph)6]ꢁ
has been prepared by the reaction of [Au3Cu2(C2Ph)6]ꢁ
with a mixture of gold phenylalkynyl and silver phenyl-
alkynyl, or reaction of [Au3Ag2(C2Ph)6]ꢁ with [AuCu
(C2Ph)2n], or [Au2Cu(C2Ph)4]ꢁ with [AuAg(C2Ph)2n]
[26c]. The high nuclearity trimetallic cluster
[AuAg6Cu6(C2Ph)14]ꢁ was prepared by conversion of
the [Au3Cu2(C2Ph)6]ꢁ and [Au3Ag2(C2Ph)6]ꢁ [26c].
Bruce et al. [27] reported a gold(I) alkynyl complex
capped by a Cu3(l-dppm)3 triangle [{Cu3(l-dppm)3}
The photophysical properties of [TEE][Au(PCy3)]4
and [TEB][Au(PCy3)]3 ([TEE]H4 = tetraethynylethene;
[TEB]H3 = 1,3,5-triethynylbenzene) was studied [23].
1
[TEE][Au(PCy3)]4 was found to show [p–p*(TEE)] flu-
orescence emission at 428 nm, and [TEB][Au(PCy3)]3
displayed 3[p–p*(TEB)] phosphorescence emission at
479 nm in dichloromethane at 298 K.
Another series of gold(I) arylalkynyl complexes
[(R3P)Au(C„CAr)]
(R = Cy,
Ar = C6H4-4-NO2,
C6H4-4-CF3, C6F5; R = Ph, Ar = C6H4-4-NO2) have
been reported by Che and co-workers [24]. From the
X-ray structure of the complex, [(Cy3P)Au(C„
CC6H4-4-NO2)], two forms namely E- and N-forms exist
and are polymorphs with molecular dipoles in different
orientations and with different dihedral angles between
the neighboring 4-nitro-phenyl moieties. The photo-
physical properties of these complexes have been stud-
ied. It was found that all complexes, except the
N-form of [(Cy3P)Au(C„CC6H4-4-NO2)] showed a
emission bands at 425–521 nm at 298 K. The N-form
[(Cy3P)Au(C„CC6H4-4-NO2)] is nonemissive at 298
K, but it showed an emission band at 486 nm at 77 K.
The photophysical properties of a series of lumines-
cent gold(I) phosphine mono- and diynyl complexes
with nuclearity ranging from one to three [(R3P)Au-
(C„C)2R0] (R = Ph, R0 = C3H7, C6H13, Ph; R = Tol,
R0 = Ph), [Au2(P-P)(C„CR)2] (P-P = dppe, R =
C„CC6H13, C(@CH2)Me; P-P = dppf, R = C4H3S,
C4H2SC4H3S) and [Au3(P-P)2(C„CR)2] [Au(C„CR)2]
(P-P = C6H11, R = C„CC6H13,C(@CH2)Me, C4H3S,
C4H2SC4H3S; P-P = Ph, R = C„CC6H13, C(@CH2)Me,
C4H3S, C4H2SC4H3S; P-P = Tol, R = C(@CH2)Me,
C4H3S; P-P = Me, R = C(@CH2)Me, C4H3S) have been
reported by Yam et al. recently [25]. In general, the high-
energy absorption bands were suggested to arise from
intraligand phosphine-centered and [p ! p*(C„C)]
transitions, whereas the low-energy absorption bands
were assigned as [r(Au–P) ! p*(C„C)] or metal-per-
turbed intraligand [p ! p*(C„C)] mixed with metal-
to-alkynyl MLCT transitions. Both the electronic
absorption and emission energies were found to be
(l3-I)(l3-g1-C„CC„C–Au–C„CC„CH)],
which
was characterized by X-ray crystallography and
the [{Cu3(l-dppm)3(l3-I)}2(l3:l3-C„CC„C–Au–C„
CC„C)]I, which was synthesized by reaction of
[Cu3(l-dppm)3(l3-I)2]I with [PPN][Au(C„CC„CH)2].
Recently, we reported the utilization of gold(I) alkyn-
yls as g2-metallo-ligands in the construction of mixed-
metal gold(I)–copper(I) and silver(I) complexes,
[{g2-(R3P)Au{C„CC(@CH2)Me}}2Cu]PF6 (R = Ph,
p-Tol) and [(dppf)Au2{g2-C„CC(@CH2)Me}2M]X
(M = Cu, X = PF6; M = Ag, X = OTf) [28]. It was found
that these complexes showed ion-induced luminescence
switching behavior. The complexes [(R3P)Au{C„
CC(@CH2)Me}] (R = Ph, p-Tol) showed luminescence
at 454 and 463 nm in the solid state, which were assigned
as derived from metal-perturbed 3[p ! p*(C„C)] IL
and 3[r(Au–P) ! p*(C„C)] MLCT states. Upon

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K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
p-coordination to the copper(I) metal centre, the
p*(C„C) orbital energy was lowered, giving rise a lower
energy emission at ca. 606–664 nm. The complex
[(dppf)Au2{g2-C„CC(@CH2)Me}2], was nonemissive
in the solid state, probably due to efficient quenching
by the ferrocenyl unit. However, [(dppf)Au2{g2-
C„CC-(@CH2)Me}2 gave emission at ca. 565–583
nm, which may be originated from copper(I)/silver(I)
p-alkynyl core.
As an extension of our previous works on gold(I)
alkynyls [2a,17–19,25] and mixed-metal alkynyl com-
plexes of gold(I) [28] as well as rhenium(I) [29], attempts
have been made to synthesize novel heterobimetallic
alkynyl complexes of gold(I) and rhenium(I) by employ-
ing the metalloligand approach. Herein are reported the
synthesis, electronic absorption, electrochemistry, and
luminescence properties of a series of mixed-metal
gold(I)–rhenium(I) alkynyl complexes and their precur-
sor 4-ethynylpyridine gold(I) complexes.
LCQ mass spectrometer. IR spectra were obtained as
KBr pellets on a Bio-Rad FTS-7 fourier-transform
infrared spectrophotometer (4000–400 cmꢁ1). UV-Vis
spectra were obtained on a Hewlett–Packard 8452A
diode array spectrophotometer. Steady-state excitation
and emission spectra were recorded on a Spex Fluorolog
111 spectrofluorometer equipped with a Hamamatsu R-
928 photomultiplier tube. Low-temperature (77 K) spec-
tra were recorded by using an optical Dewar sample
holder. Elemental analyses of the new complexes were
performed on a Carlo Erba 1106 elemental analyzer at
the Institute of Chemistry, Chinese Academy of
Sciences.
Emission lifetime measurements were performed
using a conventional laser system. The excitation source
was the 355-nm output (third harmonic) of a Spectra-
Physics Quanta-Ray Q-switched GCR-150 pulsed Nd-
YAG laser (10 Hz). Luminescence decay signals were
recorded on a Tektronix model TDS-620A (500 MHz,
2 GS/s) digital oscilloscope, and analyzed using a pro-
gram for exponential fits. All solutions for photophysi-
cal studies were prepared under vacuum in a 10-cm3
round-bottom flask equipped with a side-arm 1-cm fluo-
rescence cuvette and sealed from the atmosphere by a
Bibby Rotaflo HP6 Teflon stopper. Solutions were rig-
orously degassed with no fewer than four freeze-pump-
thaw cycles.
2. Experimental
2.1. Materials
Potassium tetrachloroaurate(III), trans-dichloro-
bis(triphenylphosphine)-palladium(II) and rhenium(I)
pentacarbonyl chloride were obtained from Strem
Chemicals Inc. 2,20-Bipyridine (bpy), copper(I) oxide,
hexafluorophosphoric acid, sodium, 2,20-thiodiethanol,
silver trifluoromethanesulfonate, tri-p-tolylphosphine
and triphenylphosphine were purchased from Aldrich
Chemical Company. Trimethylsilylacetylene, copper(I)
iodide, triethylamine and 4-bromopyridine hydrochlo-
ride were obtained from Lancaster Synthesis Ltd. 4-
Ethynylpyridine [30], chlorogold(I) phosphine precursor
complexes, Au(PPh3)Cl, Au(P(p-Tol)3)Cl [31] and
[Re(L-L)(CO)3(MeCN)]OTf (L-L = bpy or tBu2bpy)
[32] were prepared according to the literature
procedures.
Cyclic voltammetric measurements were performed
by using a CH Instruments, Inc. Model CHI 620 electr-
ochemical analyzer interfaced to a personal computer.
The electrolytic cell used was a conventional two-com-
partment cell. The salt bridge of the reference electrode
was separated from the working electrode compartment
by a Vycor glass. A Ag/AgNO3 (0.1 M in CH3CN) ref-
erence electrode was used. The ferrocenium–ferrocene
couple was used as the internal standard in the electro-
chemical measurements in acetonitrile (0.1
M
nBu4NPF6) [34]. The working electrode was a glassy-car-
bon (Atomergic Chemetals V25) electrode with a plati-
num foil acting as the counter electrode.
Dichloromethane (Lab Scan, AR) were purified and
distilled over CaH2 using standard procedures before
use [33]. Tetra-n-butylammonium hexafluorophosphate
(nBu4NPF6) for electrochemical studies was obtained
from Aldrich Chemical Company. All other solvents
and reagents were of analytical grade and were used as
received.
2.3. Syntheses
All the reactions were carried out under anhydrous
and anaerobic conditions under an inert atmosphere of
nitrogen using standard Schlenk technique.
2.3.1. Syntheses of gold(I) alkynyl phosphine complexes
2.3.1.1. [(PPh3)Au(C„CC5H4N)] (1). An ethanolic
solution (5 ml) of 4-ethynylpyridine (22 mg, 0.21 mmol)
and sodium ethoxide (0.30 mmol, prepared in situ from
Na in EtOH) was added to a solution of [(PPh3)AuCl]
(100 mg, 0.2 mmol) in EtOH/THF (10 ml, 1:1 v/v) and
stirred at room temperature. The colorless solution
changed to pale yellow after 30 min. After stirring for
5 h, the solvent was evaporated to dryness and the
2.2. Physical measurements and instrumentation
1H NMR spectra were recorded on a 300 MHz Bru-
ker DPX300 FT-NMR spectrometer. Chemical shifts
(ppm) were reported relative to tetramethylsilane
(Me4Si). Positive ion FAB mass spectra were collected
on a Finnigan MAT95 mass spectrometer, and positive
ion and negative ion ESI mass spectra on a Finnigan

K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
4457
resulting solid was recrystallized from dichloromethane/
n-hexane to give air-stable pale yellow crystals of 1 (82
mg, 73% yield). 1H NMR (300 MHz, CDCl3, 298 K, rel-
ative to Me4Si): d 7.33 (d, 2H, J = 4.9 Hz, pyridyl pro-
tons meta to N), 7.48-7.55 (m, 15H, PPh3), 8.47 (d,
2H, J = 4.9 Hz, pyridyl protons ortho to N). Positive-
ion FAB-MS: m/z 562 [M]+. IR (KBr disc, m/cmꢁ1):
2117 (w, C„C). Elemental analysis: Found (%): C
53.24, H 3.29, N 2.30. Calc. for C25H19AuPN (%): C
53.49, H 3.41, N 2.50.
Hz, 5- and 50-bipyridyl protons), 7.88 (d, 2H, J = 6.4
Hz, pyridyl protons ortho to N), 8.38 (t, 2H, J = 7.5
Hz, 3- and 30-bipyridyl protons), 9.00 (d, 2H, J = 5.1
Hz, 6- and 60-bipyridyl protons). Positive-ion FAB-
MS: m/z 1030 [M ꢁ OTf]+. IR (KBr disc, m/cmꢁ1):
2120 (w, C„C). Elemental analysis: Found (%): C
42.10,
N3F3O6PSꢃ CH2Cl2 (%): C 41.79, H 2.81, N 3.44.
H 2.94, N 3.14. Calc. for AuReC42H33
1
2
2.3.2.3. [(PPh3)Au(C„CC5H4N)Re(tBu2bpy)(CO)3]
OTf (5). The procedure was similar to that for 3 ex-
cept [Re(tBu2bpy)(CO)3(MeCN)]OTf (73 mg, 0.10
mmol) was used in place of [Re(bpy)(CO)3(MeCN)]OTf
to give air-stable orange crystals of 5 (60 mg, 48% yield).
1H NMR (300 MHz, CDCl3, 298 K, relative to Me4Si):
2.3.1.2. [(P(p-Tol)3)Au(C„CC5H4N)] (2). The
procedure was similar to that for 1 except [(P(p-
Tol)3)AuCl] (107 mg, 0.2 mmol) was used in place
of [(PPh3)AuCl] to give air-stable pale yellow crystals
1
t
of 2 (86 mg, 71% yield). H NMR (300 MHz, CDCl3,
d 1.59 (s, 18H, Bu), 7.50-7.67 (m, 2H, pyridyl protons
298 K, relative to Me4Si): d 2.40 (s, 9H, –CH3), 7.21
(d, 2H, J = 4.9 Hz, pyridyl protons meta to N), 7.21–
7.25 (m, 6H, –C6H4–), 7.40-7.45 (m, 6H, –C6H4–), 7.78
(d, 2H, J = 4.9 Hz, pyridyl protons ortho to N). Posi-
tive-ion FAB-MS: m/z 604 [M]+. IR (KBr disc, m/
cmꢁ1): 2121 (w, C„C). Elemental analysis: Found
(%): C 55.96, H 4.21, N 1.93. Calc. for C28H25AuPN
(%): C 55.73, H 4.18, N 2.32.
meta to N; 15H, PPh3), 8.08 (dd, 2H, J = 2.1 and 5.8
Hz, 5- and 50-bipyridyl protons), 8.58 (d, 2H, J = 6.4
Hz, pyridyl protons ortho to N), 8.89 (d, 2H, J = 2.1 Hz,
3- and 30-bipyridyl protons), 8.96 (d, 2H, J = 6.4 Hz,
6- and 60-bipyridyl protons). Positive-ion FAB-MS: m/
z 1100 [M OTf]+. IR (KBr disc, m/cmꢁ1): 2115 (w,
C„C). Elemental analysis: Found (%): C 41.56, H
3.42,
N
2.68. Calc. for AuReC47H43N3F3O6P-
S Æ 2CH2Cl2 (%): C 41.48, H 3.34, N 2.96.
2.3.2. Syntheses of heterometallic gold(I)–rhenium(I)
alkynyl complexes
2.3.2.4.
[(P(p-Tol)3)Au(C„CC5H4N)Re(tBu2bpy)
2.3.2.1. [(PPh3)Au(C„CC5H4N)Re(bpy)(CO)3]OTf
(3). To a THF solution (20 ml) of [Re(bpy)(CO)3-
(MeCN)]OTf (62 mg, 0.10 mmol) was added 1 (56 mg,
0.10 mmol). The mixture was warmed at ca. 42 ꢁC for
24 h. The resulting solution was evaporated to dryness
under vacuum and orange crystals of 3 (73 mg, 64%
yield) were obtained after slow diffusion of n-hexane
into a concentrated CH2Cl2 solution of the product.
1H NMR (300 MHz, CDCl3, 298 K, relative to Me4Si):
d 7.25 (d, 2H, J = 6.4 Hz, pyridyl protons meta to N),
7.42–7.55 (m, 15H, PPh3), 7.78 (t, 2H, J = 6.2 Hz, 4-
and 40-bipyridyl protons), 7.96 (d, 2H, J = 6.4 Hz, pyr-
idyl protons ortho to N), 8.41 (t, 2H, J = 7.5 Hz,
5- and 50-bipyridyl protons), 8.98 (d, 2H, J = 7.5 Hz,
3- and 30-bipyridyl protons), 9.09 (d, 2H, J = 5.1 Hz,
6- and 60-bipyridyl protons). Positive-ion FAB-MS: m/
z 988 [M ꢁ OTf]+. IR (KBr disc, m/cmꢁ1): 2120 (w,
C„C). Elemental analysis: Found (%): C 40.93, H
2.61, N 3.48. Calc. for AuReC39H27N3F3O6PS (%): C
41.20, H 2.39, N 3.70.
(CO)3]OTf (6). The procedure was similar to that
for 5 except 2 (60 mg, 0.10 mmol) was used in place of
1 to give air-stable orange crystals of 6 (62 mg, 48%
yield). H NMR (300 MHz, CDCl3, 298 K, relative to
t
Me4Si): d 1.46 (s, 18H, Bu), 2.46 (s, 9H, –CH3) 7.34–
7.40 (m, 2H, pyridyl protons meta to N; 12H, –C6H4–),
7.55 (d, 2H, J = 6.4 Hz, pyridyl protons ortho to N),
7.68 (dd, 2H, J = 2.1 and 5.9 Hz, 5- and 50-bipyridyl
protons), 8.09 (d, 2H, J = 2.1 Hz, 3- and 30-bipyr-
idyl protons), 8.96 (d, 2H, J = 5.9 Hz, 6- and 60-bipyr-
idyl protons). Positive-ion FAB-MS: m/z 1142
[M ꢁ OTf]+. IR (KBr disc, m/cmꢁ1): 2115 (w, C„C). Ele-
mental analysis: Found (%): C 43.43, H 3.87, N 2.58.
Calc. for AuReC50H49N3F3O6PS ꢃ 112CH2Cl2 (%): C
43.60, H 3.70, N 2.96 (see Scheme 1).
1
3. Results and discussion
3.1. Syntheses and characterization
2.3.2.2. [(P(p-Tol)3)Au(C„CC5H4N)Re(bpy)(CO)3]
OTf (4). The procedure was similar to that for 3 ex-
cept 2 (60 mg, 0.10 mmol) was used in place of 1 to give
The 4-ethynylpyridine gold(I) complexes were pre-
pared by modification of the literature procedure
6b,17–19. The gold(I)–rhenium(I) complexes were pre-
pared by heating the corresponding [Re(L-L)(CO)3
(MeCN)]OTf complexes with the 4-ethynylpyridine
gold(I) complexes in dry THF under an inert atmos-
phere of nitrogen. After allowing the reaction mixture
to heat at ca. 42 ꢁC for 24 h, the solvent was removed
1
air-stable orange crystals of 4 (77 mg, 65% yield). H
NMR (300 MHz, CDCl3, 298 K, relative to Me4Si): d
2.39 (s, 9H, –CH3) 7.13–7.21 (m, 2H, pyridyl pro-
tons meta to N; 2H, 4- and 40-bipyridyl protons; 6H,
–C6H4–), 7.37 (m, 6H, –C6H4–), 7.70 (t, 2H, J = 7.5

4458
K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
PR3
Complex
PPh3
1
2
N
Au PR3
P(p-Tol)3
PR3
Complex
N
N
+
PPh3
3
4
5
6
bpy
bpy
N
C
N
C
P(p-Tol)3
PPh3
OTf-
OC
Re
N
Au PR3
tBu2bpy
tBu2bpy
O
O
P(p-Tol)3
Scheme 1. Schematic drawings of 1–6.
under vacuum, and the solid residue was recrystallized
from dichloromethane-n-hexane to obtain the analyti-
cally pure complexes. In view of the ready decomposi-
tion of gold(I) complexes at high temperature, the
reaction was carried out at moderate temperature, tak-
ing advantage of the easy detachment of the neutral
and weakly bound acetonitrile group of the rhenium(I)
starting materials.
(a)
50 µA
All the newly synthesized gold(I) alkynyl and mixed-
metal gold(I)–rhenium(I) complexes gave satisfactory
elemental analyses and were characterized by 1H
NMR and IR spectroscopy. The identities of all the
complexes were further confirmed by positive-ion FAB
mass spectrometry.
3.2. Electrochemical properties
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4
Potential / V vs .S. C. E.
The cyclic voltammograms of complexes 3–6 showed
a characteristic irreversible oxidation wave at ca. +1.66
to +1.79 V vs. SCE. Cyclic voltammetric data for the
mixed-metal gold(I)–rhenium(I) complexes were col-
lected in Table 1 and a typical cyclic voltammogram
(b)
A
50 µ
Table 1
Electrochemical dataa for 3–5 in acetonitrile solution (0.1 mol dmꢁ3
nBu4NPF6) at 298 K
Complex
Oxidation
Reduction
Epab/V vs. SCE
E1/2 (Epc)d/V vs. SCE
c
3
4
5
6
a
+1.78
+1.79
+1.67
+1.66
ꢁ1.23 (ꢁ1.49)
ꢁ1.23 (ꢁ1.47)
ꢁ1.36 (ꢁ1.58)
ꢁ1.36 (ꢁ1.60)
Working electrode, glassy carbon; scan rate, 100 mV sꢁ1
.
0.0
-0.5
-1.0
-1.5
b
c
Epa is the anodic peak potential of the irreversible oxidation wave.
E1/2 is the average of the cathodic and anodic peaks for the
Potential / V vs .S. C. E.
reversible reduction couples.
d
Epc is the cathodic peak potential of the irreversible reduction
Fig. 1. Cyclic voltammogram showing (a) the oxidation and (b) the
reduction of 3 in acetonitrite (0.1 mol dmꢁ3 nBu4NPF6). Scan
rate = 100 mV sꢁ1
.
wave.

K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
4459
of 4 is shown in Fig. 1. The oxidation wave was found to
be insensitive to the nature of the phosphine ligands pre-
sent but was found to vary with the nature of the dii-
mine ligand. Given the electro-inactive nature of
Au(I), the oxidation was tentatively assigned as a
Re(I)/Re(II) oxidation, as similar observations have also
been reported in other related rhenium(I) diimine sys-
tems [35,36], such as the related [Re(bpy)(CO)3(py)]+
which showed an oxidation wave at +1.74 V vs. SCE
[40]. The assignment of the oxidation as ligand-centered
oxidation was unlikely since both the diimine ligand and
complexes 1 and 2 did not show any appreciable oxida-
tion in the region. The less positive potential observed
rationalized by the presence of electron-donating tert-
butyl groups on the bipyridine ligand, which would
make it more electron-rich and poorer p-accepting,
and hence reduced its ease of reduction.
3.3. Photophysical properties
3.3.1. Electronic absorption spectroscopy
The electronic absorption spectra of the 4-ethynylpy-
ridine gold(I) complexes, 1 and 2 in dichloromethane
show intense absorptions at ca. 250–270 nm, which are
also present in the free phosphines and are tentatively
assigned as phosphine-centered intraligand transitions.
With reference to previous spectroscopic works on
gold(I) alkynyl systems [17–19,25], the intense absorp-
tions at ca. 285 nm, which appear to depend on the alky-
nyl ligands present, are assigned to originate from
intraligand [p ! p*(C„C)] transition. The electronic
absorption spectral data of the 4-ethynylpyridine gold(I)
and gold(I)–rhenium(I) complexes in dichloromethane
at room temperature are tabulated in Table 2.
The electronic absorption spectra of the mixed-metal
gold(I)–rhenium(I) complexes 3–6 show, in addition to
the high-energy absorptions, a low-energy absorption
shoulder at ca. 354–380 nm, which tailed off to ca. 500
nm. With reference to previous spectroscopic work on
related rhenium(I) diimine systems [38,39], this absorp-
tion band, which is absent in complexes 1 and 2, is
most likely assigned as the [dp(Re) ! p*(diimine)]
t
for the complexes with Bu2bpy ligand was in line with
the poorer p-accepting ability and the greater electron
richness of the Bu2bpy, which render the rhenium(I)
metal center more easily to be oxidized.
t
For the reductive scan, a reversible reduction wave at
ca. 1.23–1.36 V vs. SCE and an irreversible wave at ca.
1.47–1.60 V vs. SCE were observed. Based on previous
electrochemical work on the related rhenium(I) system
[36,37] and gold(I) system [17,19], the first reduction
couple was assigned as the diimine ligand-centered
reduction. Similar potentials have also been observed
for a related bipyridyl complex, [Re(bpy)(CO)3(py)]+,
with the reduction couples occurring at ca. 1.09 and
1.39 V vs. SCE [40]. The more negative reduction poten-
tial observed for the tBu2bpy-containing complexes
when compared to the bpy analogues could be readily
Table 2
Photophysical data for 1–6
Complex
Absorptiona
abs/nm (emax/dm3 molꢁ1 cmꢁ1
Emission
k
)
Medium (T/K)
kem/nm (so/ls)
1
254 (23,760), 268 (29,060), 284 (31,450)
Solid (298)
Solid (77)
CH2Cl2 (298)
484 (12.3)
510
487 (4.7)
2
3
4
5
254 (36,140), 270 (32,590), 284 (34,610)
Solid (298)
Solid (77)
CH2Cl2 (298)
514 (14.6)
535
494 (3.0)
270 (21,600), 288 (27,350), 312 (30,860), 322sh (25,450), 380sh (5670)
270 (29,310), 288 (26,440), 312 (32,890), 318sh (26,080), 380sh (3790)
270 (34,700), 288 (34,960), 308 (33,280), 322sh (31,300), 354sh (12,080)
270 (21,930), 288 (27,450), 310 (27,570), 318sh (19,680), 354sh (9660)
Solid (298)
Solid (77)
CH2Cl2 (298)
545 (0.17)
531
550 (0.80)
Solid (298)
Solid (77)
CH2Cl2 (298)
548 (0.23)
528
550 (0.67)
Solid (298)
Solid (77)
CH2Cl2 (298)
521 (0.37)
512
539 (0.73)
6
Solid (298)
Solid (77)
CH2Cl2 (298)
524 (0.56)
525
539 (1.36)
a
In dichloromethane at 298 K.

4460
K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
metal-to-ligand charge transfer (MLCT) transition,
characteristic of the rhenium(I) diimine moiety. The
electronic absorption spectra of the gold(I)–rhenium(I)
complexes are shown in Figs. 2 and 3.
are also found in the complexes 1 and 2, are assigned
as phosphine-centered intraligand transition. The
absorption bands centered at ca. 300–322 nm are likely
assigned as mixtures of intraligand [p ! p*(C„C)],
t
Although the bands appear as shoulders and are usu-
ally very broad, a dependence of the energy of the low-
energy absorption on the nature of the diimine ligands is
still readily observed. The slightly higher absorption
energies observed for the tBu2bpy-containing complexes
are consistent with the higher p* orbital energy of
tBu2bpy than bpy, as a result of its poorer p-accepting
abilities derived from the presence of the more elec-
tron-rich tert-butyl groups on the bipyridine ligand.
The high-energy absorptions at ca. 270–288 nm, which
intraligand [p ! p* (bpy or Bu2bpy)] and [dp(Re) !
p*(pyridine)] MLCT transitions, as similar transitions
also occur in their precursor complexes [38–40].
3.3.2. Steady-state emission spectroscopy
The 4-ethynylpyridine gold(I) complexes 1 and 2 gave
intense emission bands at room temperature at 484 and
514 nm, respectively, in the solid state upon photoexci-
tation with k > 350 nm. Their luminescence lifetimes in
the microsecond range suggested that the emissions are
phosphorescence in nature. The photophysical data of
the 4-ethynylpyridine gold(I) and gold(I)–rhenium(I)
complexes are summarized in Table 2. With reference
to previous spectroscopic work on gold(I) alkynyl sys-
tems [17–19,25], the emission is tentatively assigned as
derived from an excited state of 3[r(Au–P) !
p*(C„C)] origin. The slight red shift in emission energy
on going from PPh3 in 1 to PTol3 in 2 is consistent with
an assignment of the emissive state as derived from a
3[r ! p*] transition associated with the [Au(C„CC5-
H4N)] group, since PTol3, being a better electron donor
than PPh3, would render the gold(I) center more elec-
tron rich, and hence leading to the 3[r(Au–
P) ! p*(C„CR)] excited state lower-lying in energy.
In solution, complexes 1 and 2 emit at 487 and 494
nm, respectively. The relatively lower emission energy
of 1 than that of the related [(PPh3)Au(C„CPh)]
[13,21] is in line with the lower p* orbital energies of
C„CC5H4N than C„CPh and the assignment of an ex-
450
500
550
600
650
700
Wavelength / nm
3
cited state of [(Au–P) ! p*(C „CR)] origin.
Fig. 2. Normalized solid state emission spectra of 3 (——) and 5 (-----)
at 298 K.
Excitation of the mixed-metal gold(I)–rhenium(I)
complexes 3–6 at k P 350 nm both in the solid state
and in dichloromethane solution at room temperature
resulted in a yellowish green luminescence centered at
ca. 510–580 nm. The emission spectra of complexes
3–6 are shown in Figs. 2 and 3. The difference in the
emission energy as well as the large discrepancy in the
luminescence lifetime observed for the mixed-metal
complexes and the gold(I) precursor complexes may sug-
gest that their emissions are of different origins. The
dependence of the emission energy on the p* orbital en-
ergy of the bipyridine ligands on the rhenium(I) center,
in which the emission energies of the tBu2bpy complexes
are higher than that of their bpy analogues, is suggestive
of an emission origin of predominantly 3MLCT
[dp(Re) ! p*(bpy)] character. The lack of an alkynyl-
gold(I)-based emission in the mixed-metal complexes
is suggestive of an efficient intramolecular energy
3
400
450
500
550
600
650
700
transfer process from the [r(Au–P) ! p*(C„CR)] to
the lower-lying 3MLCT [dp(Re) ! p*(bpy)] excited
state that give rise to the emission. The slightly higher
emission energy of 3 and 4 relative to their [Re(bpy)-
Wavelength / nm
Fig. 3. Normalized emission spectra of 4 (——) and 6 (-----) in
CH2Cl2 at 298 K.

K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
4461
(CO)3(py)]+ counterparts [40] is suggestive of the pertur-
bation brought about by the presence of the alkynyl-
gold(I) moiety. It is likely that the alkynylgold(I)
moiety upon attachment to the pyridyl unit would re-
duce the r-donor strength of the pyridyl ligand, stabiliz-
ing the dp(Re) orbital, leading to a slightly larger MLCT
[dp(Re) ! p*(bpy)] energy gap. Such an assignment is
also in line with the electrochemical studies, in which
the HOMO has substantial rhenium metal-centered
character while the LUMO is mainly bipyridine lig-
and-based in character. The relatively long radiative life-
times observed are suggestive of an emissive origin of
triplet parentage, possibly derived from the 3MLCT
[dp(Re) ! p*(bpy)] state, modified by the attachment
of the alkynylgold(I) moiety.
(f) V. Cadierno, M.P. Gamasa, J. Gimeno, Organometallics 17
(1998) 697;
(g) G. Roidl, V. Enkelmann, R.D. Adams, U.H.F. Bunz, J.
Organomet. Chem. 578 (1999) 144.
[2] (a) T. Muller, S.W.K. Choi, D.M.P. Mingos, D. Murphy, D.J.
¨
Williams, V.W.W. Yam, J. Organomet. Chem. 484 (1994)
209;
(b) C.M. Che, H.Y. Chao, V.M. Miskowski, Y. Li, K.K. Cheung,
J. Am. Chem. Soc. 123 (2001) 4985;
(c) W. Lu, H.F. Xiang, N. Zhu, C.M. Che, Organometallics 21
(2002) 2343.
[3] (a) D.M.P. Mingos, J. Yau, S. Menzer, D.J. Williams, Angew.
Chem. Int. Ed. 34 (1995) 1894;
(b) F. Mohr, M.C. Jennings, R.J. Puddephatt, Eur. J. Inorg.
Chem. (2003) 217;
(c) R.J. Puddephatt, Coord. Chem. Rev. 216–217 (2001) 313;
(d) C.P. McArdle, S. Van, M.C. Jennings, R.J. Puddephatt, J.
Am. Chem. Soc. 124 (2002) 3959;
(e) F. Mohr, D.J. Eisler, C.P. McArdle, K. Atieh, M.C. Jenningsa,
R.J. Puddephatt, J. Organomet. Chem. 670 (2003) 27.
[4] M.P. Berthelot, Liebigs Ann. Chem. 139 (1866) 150.
[5] G.E. Coates, C. Parkin, J. Chem. Soc. (1962) 3220.
[6] (a) R.J. Cross, M.F. Davidson, A.J. McLennan, J. Organomet.
Chem. 265 (1984) C37;
4. Conclusion
A series of mixed-metal gold(I)–rhenium(I) alkynyl
complexes and their precursor 4-ethynylpyridine gold(I)
complexes have been synthesized and structurally char-
acterized. The electrochemistry of mixed-metal
gold(I)–rhenium(I) complexes has also been studied.
Both the gold(I) precursor complexes and the mixed-me-
tal gold(I)–rhenium(I) alkynyl complexes are found to
be emissive both in the solid state and in dichlorometh-
ane solution. An assignment of the emission of the
mixed-metal gold(I)–rhenium(I) alkynyl complexes as
(b) R.J. Cross, M.F. Davidson, J. Chem. Soc., Dalton Trans.
(1986) 411.
[7] (a) M.I. Bruce, E. Horn, J.G. Matisons, M.R. Snow, Aust. J.
Chem. 37 (1984) 1163;
(b) M.I. Bruce, D.N. Duffy, Aust. J. Chem. 39 (1986) 1697;
(c) M.I. Bruce, K.R. Grundy, M.J. Lidell, M.R. Snow, R.T.
Tiekink, J. Organomet. Chem. 344 (1988) C49.
[8] (a) J. Vicente, M.T. Chicote, M.D. Abrisqueta, J. Chem. Soc.,
Dalton Trans. (1995) 497;
(b) J. Vicente, M.T. Chicote, M.D. Abrisqueta, Organometallics
16 (1997) 5628.
3
derived from a MLCT [dp(Re) ! p*(bpy)] origin that
[9] C.P. McArdle, M.C. Jennings, J.J. Vittal, R.J. Puddephatt, Chem.
Eur. J. 7 (2001) 3572.
has been modified by the presence of the alkynylgold(I)
moiety is suggested, and supported by electrochemical
studies.
[10] F. Mohr, R.J. Puddephatt, J. Organomet. Chem. 689 (2004) 374.
[11] X.X. Lu, C.K. Li, E.C.C. Cheng, N. Zhu, V.W.W. Yam, Inorg.
Chem. 43 (2004) 2225.
[12] (a) V.W.W. Yam, K.L. Cheung, L.H. Yuan, K.M.C. Wong,
K.K. Cheung, Chem. Commum. 16 (2000) 1513;
(b) V.W.W. Yam, S.K. Yip, L.H. Yuan, K.L. Cheung, N. Zhu,
K.K. Cheung, Organometallics 22 (2003) 2630.
[13] D. Li, X. Hong, C.M. Che, W.C. Lo, S.M. Peng, J. Chem. Soc.,
Dalton Trans. (1993) 2929.
Acknowledgements
V.W.-W.Y. acknowledges support from The Univer-
sity of Hong Kong Foundation for Educational Devel-
opment and Research. The work described in this
paper has been supported by the Research Grants
Council of the Hong Kong Special Administrative
Region, China (Project HKU7123/00P). K.-L.C. and
S.-K.Y. acknowledge the receipt of a post-graduate stu-
dentship, administered by The University of Hong
Kong.
[14] C.M. Che, H.K. Yip, W.C. Lo, S.M. Peng, Polyhedron 13 (1994)
887.
[15] X. Hong, K.K. Cheung, C.X. Guo, C.M. Che, J. Chem. Soc.,
Dalton Trans. (1994) 1867.
[16] W. Lu, H.F. Xiang, N. Zhu, C.M. Che, Organometallics 21
(2002) 2343.
[17] V.W.W. Yam, S.W.K. Choi, J. Chem. Soc., Dalton Trans. (1996)
4227.
[18] V.W.W. Yam, S.W.K. Choi, K.K. Cheung, Organometallics 15
(1996) 1734.
[19] V.W.W. Yam, S.W.K. Choi, K.K. Cheung, J. Chem. Soc., Dalton
Trans. (1996) 3411.
References
[20] H. Xiao, K.K. Cheung, C.M. Che, J. Chem. Soc., Dalton Trans.
(1996) 3699.
[1] (a) V.W.W. Yam, J. Organomet. Chem. 689 (2004) 1393;
(b) N.J. Long, C.K. Williams, Angew. Chem. Int. Ed. 42 (2003)
2586;
[21] M.J. Irwin, J.J. Vittal, R.J. Puddephatt, Organometallics 16
(1997) 3541.
[22] H.Y. Chao, W. Lu, Y. Li, M.C.W. Chan, C.M. Che, K.K.
Cheung, N. Zhu, J. Am. Chem. Soc. 124 (2002) 14696.
[23] W. Lu, N. Zhu, C.M. Che, J. Organomet. Chem. 607 (2003) 11.
[24] W. Lu, N. Zhu, C.M. Che, J. Am. Chem. Soc. 125 (2003)
16081.
(c) F. Paul, C. Lapinte, Coord. Chem. Rev. 431 (1998) 178;
(d) C. Bruneau, P.H. Dixneuf, Acc. Chem. Res. 32 (1999) 311;
(e) M.I. Bruce, M. Ke, P.J. Low, B.W. Skelton, A.H. White,
Organometallics 17 (1998) 3539;

4462
K.-L. Cheung et al. / Journal of Organometallic Chemistry 689 (2004) 4451–4462
[25] V.W.W. Yam, K.L. Cheung, S.K. Yip, K.K. Cheung, J. Organ-
omet. Chem. 681 (2003) 196.
[35] K. Kalyanasundaram, J. Chem. Soc., Faraday Trans. 2 (82)
(1986) 2401.
[26] (a) O.M. Abu-Salah, A. Al-Ohaly, A. Razzak, J. Chem. Soc.,
Dalton Trans. (1988) 2297;
[36] J.K. Hino, L.D. Ciana, W.J. Dressick, B.P. Sullivan, Inorg.
Chem. 31 (1992) 1072.
(b) O.M. Abu-Salah, J. Organomet. Chem. 387 (1990) 123;
(c) O.M. Abu-Salah, A. Razzak, A. Al-Ohaly, Z.F. Mutter, J.
Organomet. Chem. 391 (1990) 267;
[37] (a) S.A. Moya, J. Guerrero, R. Pastene, R. Schmidt, R. Sariego,
R. Sartori, J. Sanz-Aparocop, I. Fomseca, M. Martinez-Ripoll,
Inorg. Chem. 33 (1994) 2341;
(d) O.M. Abu-Salah, A. Al-Ohaly, A. Razzak, Z.F. Mutter, J.
Organomet. Chem. 389 (1990) 427.
(b) S.A. Moya, R. Pastene, R. Schmidt, J. Cuerrero, R. Sartori,
Polyhedron 11 (1992) 1665;
[27] M.I. Bruce, B.C. Hall, B.W. Skelton, M.E. Smith, A.H. White, J.
Chem. Soc., Dalton Trans. (2002) 995.
(c) R. Lin, Y. Fu, C.P. Brock, T.F. Guarr, Inorg. Chem. 31
(1992) 4336;
[28] V.W.W. Yam, K.L. Cheung, E.C.C. Cheng, N. Zhu, K.K.
Cheung, J. Chem. Soc., Dalton Trans. (2003) 1830.
[29] (a) K.M.C. Wong, S.C.F. Lam, C.C. Ko, N. Zhu, V.W.W. Yam,
S. Roue, C. Lapinte, S. Fathallah, K. Costuas, S. Kahlal, J.F.
Halet, Inorg. Chem. 42 (2003) 7086;
(d) M.K. DeArmond, K.W. Hanck, D.W. Wertz, Coord. Chem.
Rev. 65 (1985) 65;
(e) J.B. Cooper, D.B. MacQueen, J.D. Peterson, D.W. Wertz,
Inorg. Chem. 29 (1990) 3701.
[38] (a) V.W.W. Yam, V.C.Y. Lau, K.K. Cheung, Organometallics 14
(1995) 2749;
(b) V.W.W. Yam, W.Y. Lo, C.H. Lam, W.K.M. Fung, K.M.C.
Wong, V.C.Y. Lau, N. Zhu, Coord. Chem. Rev. 245 (2003) 39;
(c) V.W.W. Yam, W.Y. Lo, N. Zhu, Chem. Commun. (2003)
2446;
(b) V.W.W. Yam, V.C.Y. Lau, K.K. Cheung, Organometallics 15
(1996) 1740;
(c) V.W.W. Yam, S.H.F. Chong, K.K. Cheung, Chem. Commun.
(1998) 2121;
(d) V.W.W. Yam, S.H.F. Chong, K.M.C. Wong, K.K. Cheung,
Chem. Commun. (1999) 1013;
(d) V.W.W. Yam, S.H.F. Chong, K.M.C. Wong, K.K. Cheung,
Chem. Commun. (1999) 1013;
(e) V.W.W. Yam, W.K.M. Fung, K.M.C. Wong, V.C.Y. Lau,
K.K. Cheung, Chem. Commun. (1998) 777.
(e) V.W.W. Yam, K.K.W. Lo, K.M.C. Wong, J. Organomet.
Chem. 578 (1999) 3.
[30] T.B. Hadda, H.L. Bozec, Polyhedron 7 (1988) 575.
[31] M.I. Bruce, B.K. Nicholson, O.B. Shawkataly, Inorg. Synth. 26
(1989) 324.
[39] (a) M.S. Wrighton, D.L. Morse, J. Am. Chem. Soc. 96 (1974)
998;
[32] S.M. Fredericks, J.C. Luong, M.S. Wrighton, J. Am. Chem. Soc.
101 (1979) 7415.
(b) M.S. Wrighton, D.L. Morse, L. Pdungsap, J. Am. Chem.
Soc. 97 (1975) 2073;
[33] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory
Chemical, third ed., Pergamon Press, Oxford, 1988.
[34] (a) R.R. Gagne, C.A. Koval, G.C. Lisensky, Inorg. Chem. 19
(1980) 2854;
(c) G. Tapolsy, R. Duesing, T.J. Meyer, Inorg. Chem. 29 (1990)
2285;
(d) J.K. Hino, L.D. Ciana, W.J. Dressick, B.P. Sullivan, Inorg.
Chem. 31 (1992) 1072.
(b) C.M. Che, K.Y. Wong, F.C. Anson, J. Electroanal. Chem.
Interfacial Electrochem. 226 (1987) 211.
[40] L. Sacksteder, A.P. Zipp, E.A. Brown, J. Sreich, J.N. Demas,
B.A. DeGraff, Inorg. Chem. 29 (1990) 4335.