دوشنبه ۲۶ شهریور ۰۳ | ۱۳:۴۷ ۸ بازديد
precursor, and stabilized in a supersonic jet of Ar [105]. The complex [AuFXe] has
been detected and characterized in the gas phase using microwave rotational
spectroscopy. As expected, it is the noble gas–noble metal halide complex more
strongly bonded to a very short Au–Xe distance of 2.54 Å [106]. All evidence is
consistent with an AuXe covalent bonding in [AuFXe]. The first gold(I) complex with
an XeAu bond is the cationic [AuXe(AsF3)][Sb2F11] (Figure 1.10), it was prepared by
reaction of [Au(AsF3)]þ[SbF6] with xenon in SbF5-rich HF/SbF5 solutions. The cation
interacts only weakly with the anion and has an Au–Xe distance of 2.607 Å [107].
Another type of neutral gold(I) complex is [AuX(PR3 )] where X is an anionic oxygen
or nitrogen donor ligand such as [Au{N(SO 2 CF 3 )2 }(PR3 )] or [Au(OR)(PR 3 )] or even
[Au(OSO 2 CF3 )(PR 3 )], which are relevant as catalytically-active species or catalytic
precursors [26, 108].
Gold thiolates of the form [Au(SR)(PR3)] are important complexes that are known
for a great variety of thiolate ligands and also serve as building blocks to obtain
polynuclear species [109]. Several applications have been found, for example, in
medicine with the commercialization of the antiarthritic drug Auranofin [Au(SR)
(PEt3)] (Figure 1.11). Many other examples with this stoichiometry have been reported,
which also have antiarthritic, antitumoral or antimicrobial activity. The structure of
another antiarthritic drug, gold thiomalate (myocrysine), has been reported and
crystallized as a mixed sodium/cesium salt Na2Cs[Au2L(LH)] (Figure 1.12), which
is a polymer that consists of two interpenetrating spirals, with approximately fourfold
symmetry [110].
Anionic [AuX 2 ] with halide or pseudohalide ligands are well known and have
been widely used as a starting materials. The salts [Au(SCN) 2] have been structurally
characterized showing, for alkaline metals, infinite linear chains with alternating
Figure 1.10 Structure of [AuXe(AsF3)][Sb2 F11].
Figure 1.11 Structure of Auranofin.
1.2 Chemistry j13
chain of trimers joined at a shared gold atom as the kink, and the [NBu4]þ salts contain
isolated dimers with a short aurophilic interaction [111]. All these complexes with
Au–Au interactions are emissive and, as suggested by Fackler and Schmidbaur [102],
the emission correlates inversely with distance. The anionic gold(I) thiolates,
Bu4N[Au(SC6H4R)2] show luminescence in the solid state, the emission maxima
range from 438 nm (blue) to 529 nm (green), depending on the substituent R [112].
The anionic complexes with the hydrosulfide ligand, [(PPh3)2N][Au(SH)2] and
[AuR(SH)] are the only gold(I) complexes described with this ligand [113].
1.2.4.2 Gold(I) Complexes with Polydentate Ligands
Polydentate ligands have been widely used as bridging or quelating ligands in gold(I)
chemistry. One of the most important types are diphosphines, which give very stable
gold(I) complexes with different structural patterns. Dinuclear (chloro)gold(I) com-
plexes with the phosphorus atoms bridged by one to eight carbon atoms, of the type
[Au 2Cl 2 {m-(PPh 2)2 (CH 2 )n}] (n ¼ 1–8), have been prepared from [AuCl(CO)] or [AuCl
(SR 2 )] with the corresponding bidentate phosphine. They can adopt different
structural patterns, as a result of the formation of Au–Au bonds (see Figure 1.13).
The crystal lattice of the 1,4-bis(diphenylphosphino)butane (n ¼ 4) or hexane (n ¼ 6)
derivatives contain independent molecules (type A) [114, 115], which show no intra-
or inter-molecular Au–Au interactions, in contrast with the structures of the related
gold complexes with shorter or longer chain diphosphines, where intra- (n ¼ 1, type
B) [116] and intermolecular metal–metal interactions with the formation of discrete
dimers (type C) [117, 118] or polymeric chains (type D) are found [114, 115, 119].
The completely different packing of the monomeric molecules of [Au2 Cl 2 {m-
(PPh2 )2 (CH 2 )4 }] and the two polymorphic forms of [Au2 Cl 2{m-(PPh2 )2 (CH 2 )2}],
where the short Au–Au contacts give rise to dimers or to a polymeric chain structure,
are particularly remarkable, since the conformations of the free phosphines show a
close relationship. It has been suggested that packing effects, with or without solvent
Figure 1.12 Structure of gold thiomalate.
14j 1 The Chemistry of Gold
(PPh2 )2 (CH 2 )2 }] the presence of dichloromethane in the crystal leads to a transfor-
mation of the dimeric units present in the solvent-free crystal modification to a
polymeric chain. For the n ¼ 3 and larger chains, the complexes show monomeric
dinuclear molecules connected through intermolecular Au–Au contacts of about
3.30 Å to give polymeric chains.
Analogous structures occur in other diphosphine or diarsine complexes of the type
[AuCl 2 {m-(PPh 2 )2X}] [120–124] where X can be a great variety of bridging moieties;
the structure varies from monomeric molecules without Au–Au interactions
to dimeric complexes with intramolecular metal–metal contacts or polymeric
compounds with intermolecular Au–Au interactions. In the complexes with the
diphosphine PPh2 C(¼PMe 3 )PPh2 , the ligands change their ground state syn/anti
orientation to a symmetrical syn/syn conformation upon coordination to gold(I).
From temperature-dependent NMR studies, the energy of the Au–Au interaction was
estimated to be of the order of 29–33 kJ mol–1 [120, 121]. Figure 1.14 shows some
examples of this type of complex.
Figure 1.13 Different structural patterns of [Au2 Cl2{m-PPh2(CH 2)n}].
Figure 1.14 Some examples of [AuCl2 {m-(PPh2 )2 X}] complexes.
1.2 Chemistry j15
stoichiometry [Au 2 (m-PP) 2 ]2þ and are known for a great variety of diphosphines
R 2 PXPR2 (Figure 1.15) where X can vary from the simple methylene CH2 [125–127],
bis(diphenylphosphino)methane (dppm), for which many studies have been carried
out, to another hydrocarbon chain [128], to NH [129], and so on. Most of these
derivatives are three-coordinate by bonding to the anionic ligand, which may be Cl,
Br, I, S2 CNEt 2, or BH 3 CN and also by formation of Au–Au interactions with
molecules such as [AuCl(GeCl 3 )]. Some of these complexes are luminescent, such
as [Au2 {(PR 2 )2 CH2 }] 2þ (R ¼ Me, Ph, Cy) for which several studies have been carried
out on aurophilic attraction and luminescence [130]. The high luminescent complex
[Au 2{(PPh 2 )2 CH2 }](OTf)2 with a triplet excited state has been postulated to be used in
light-emitting diodes [131]. The dinuclear derivatives [Au 2 {(PR2 )2 X}]2þ (X ¼ CH2 ,
NH) can be easily deprotonated to give the neutral complexes [Au 2 {(PR2 )2 Y}]
(Y ¼ CH, N) [132, 133]. Further coordination of the C or N atoms to other metal
complexes gives tetra or hexanuclear derivatives [133, 134].
Most of the dinuclear gold(I) complexes are homobridged diauracycles with the
same bridging ligand on each side, but some examples of heterobridged derivatives
have been reported. These contain a diphosphine in addition to other bidentate
ligands such as bis(ylide) [135, 136], dithiolate [137], dithiocarbamate [136, 138],
xantate [139], phosphoniodithioformate [140], dithiophosphinate [141], pyridine-2-
thiolate [136], and so on. They can be obtained by reaction of the [Au 2 X2 (m-PP)]
complexes with the bidentate ligand or by ligand exchange reactions between two
different homobridged dinuclear compounds. Examples of these complexes are
shown in Figure 1.16.
Figure 1.15 Dinuclear diphosphine complexes.
Figure 1.16 Dinuclear heterobridged diphosphine gold(I) complexes.
16j 1 The Chemistry of Gold
ligands to coordinate gold(I) centers and the structures of the complexes can vary,
depending on the structural requirements of the phosphine ligands. Then com-
plexes with stoichiometry [Au 3 Cl 3 (m-LLL)] [142–144], [Au 3 (m-LLL) 2 ] 3þ [145, 146],
[Au 2 {(PPh 2 ) 2 CHPPh 2 } 2 ] 2þ [143] or [Au 4 Cl 2 (m-LLL) 2 ] 2þ [147] have been prepared but
sometimes with different structural frameworks such as [Au 3 Cl 3 {(PPh 2 ) 3 CH} 2 ],
which forms a triangle of gold atoms, and [Au 3 (PPh 2 CH 2 PPhCH 2 PPh 2 ) 2 ] 3þ, for
which the gold atoms form a linear chain (Figure 1.17).
With tetraphosphines, the usual stoichiometry is [Au4 Cl 4 (m-P4 )], such as those with
tetrakis(diphenylphosphine)methane [148], or tetrakis(diphenylphosphine)tetrathia-
fulvalene, (PPh2 )4 TTF, [149] (Figure 1.18), and gold(I) complexes with dentritic
polymers containing phosphorus atoms as terminal groups have also been de-
scribed [150]. Some of these polyphosphine complexes have been used to synthesize
heteronuclear complexes, such as bis(diphenylphosphino)methane (dppm) [151],
PPh2 CH 2 AsPhCH2 PPh 2 [152], and so on, which lead to several derivatives with the
polydentate ligands bridging two or more metal atoms (Figure 1.19).
Another important class of bidentate ligands in gold chemistry are those composed
of sulfur donor ligands such as dithiocarbamates, dithiolates, dithiocarboxylates,
dithiophosphinates, dithiophosphates, and so on. The complexes prepared with
these ligands are generally of the type [Au2 (m-SS)(PR 3 )2 ]nþ or [Au 2(m-SS)(m-PP)]
[153–155], [Au2 (m-SS) 2 ]n [156, 157] or [Au 3 (m-SS)2 (PPh 3 )2 ] [158]. All these
Figure 1.17 Gold(I) complexes with tritertiary phosphine or phosphine-arsine ligands.
Figure 1.18 Structure of [Au4Cl4 {(PPh2) 4 TTF}].
Figure 1.19 Heteronuclear phosphine gold(I) complexes.
1.2 Chemistry j17
intermolecular contacts. The usual structure for [Au 2(m-SS)(PR 3 )2 ] complexes is
dinuclear but some of them form a supramolecular structure through Au–Au and
Au–S interactions such as in [Au 2 {m-S 2P(OMe 2 )}(PPh3 )2 ]þ. The species [Au 2 (m-
SS) 2]n can be discrete dinuclear units with intramolecular gold–gold contacts or
linear chains through intermolecular aurophilic interactions. As a consequence of
these aurophilic interactions, many of these complexes present luminescence
properties. The compound [Au 4 {m-S2 C 2(CN) 2 } 2 (PTA)2 ] has a dinuclear structure
with the AuPTA fragment bonded to the gold atom with an unsupported Au–Au
interaction and is highly luminescent [159]. A chiral luminescent Au16 ring has been
reported by reaction of [Au 2Cl 2 (m-dppm)] with K 2(pippzdc) (pippzdc ¼ piperazine-
1,4-dicarbodithiolate) which gives the tetramer [Au4 (pippzdc)(dppm) 2 ]4 [160].
Figure 1.20 shows some of these complexes.
Homoleptic dithiocarboxilates can be tetrameric as [Au4 (S 2 CMe) 4 ] [161] or hex-
americ as in [Au 6 (S2 C 6H 4 -Me-2) 6 ] [162] (see Figure 1.21). Analogous complexes with
selenium ligands are far less developed although some examples have been reported,
such as [Au2 {m-Se 2 C2 (CN) 2 }]2 [163] (Figure 1.22).
Substituted phenylene-dithiolate ligands have been thoroughly studied and
di-, tri- and tetranuclear complexes of the type [Au 2 (m-S 2 C 6 H 3 R)(PPh 3 ) 2 ], [Au 3 (m-
S 2 C 6 H 3 R)(PPh 3 ) 3 ]þ or [Au 4 (S 2 C 6 H 3 R) 2 L 2 ] have been reported with the ortho
isomer [137, 153, 164–166]. The meta and para isomers present different stoichio-
metries and structures such as [Au 3 (1,3-S 2 C 6 H 4 )(PPh 3 ) 3 ]þ, which shows a
one-dimensional aggregate through head-to-tail aurophilic interactions or the
Figure 1.20 Gold(I) complexes with bidentate sulfur ligands.
Figure 1.21 Dithiocarboxilate gold(I) complexes.
18j 1 The Chemistry of Gold
[AuCl(PPh 3 )] to give the hexanuclear golden wheel [Au 6 (S 6 C 6 )(PPh 3 ) 6 ] [168].
Figure 1.23 shows some of these complexes.
Other complexes with these polydentate ligands include species with diphosphine
ligands such as the complex with the 2-thioxo-1,3-dithiole-4,5-dithiolate (dmit)
ligand, [Au4 (dmit) 2 (dppm)2 ] [169] (Figure 1.24a), the tetracoordinated compound
with the 1,2-dithiolate-o-carborane [Au4 (S 2 C2 B 10H 10 )2 {(PPh2 )2 C2 B 10H 10} 2 ] [170]
(Figure 1.24b), or the gold complex [Au2 Cl 2{Fc(S2 CNEt)2 ] [171] with the bis(dithio-
carbamate)ferrocene ligand in which there are h2 interactions between the gold(I)
atoms and the cyclopentadienyl ligands (Figure 1.24c).
Other types of polydentate ligands are those with different donor atoms that can be
of the type P,C or N,C or S,S,C,C or P,N, and so on, [172–175]. Many gold(I)
complexes with these heterofunctional ligands have been prepared. Figure 1.25
shows some examples.
Figure 1.22 Structure of [Au2{m-Se2C 2 (CN)2}]2.
Figure 1.23 Di- and hexa-thiolate gold(I) complexes.
Figure 1.24 Some gold(I) complexes with bidentate sulfur ligands.
1.2 Chemistry j19
with the ferrocenyl-terpyridine ligand (Figure 1.26a) in which the ligand acts as
tridentate [176], or the tetranuclear derivative with 2,20-bibenzimidazolate
(Figure 1.26b) [177], or the complexes obtained in the reaction of trans-1,2-bis
(4-pyridyl)ethylene with [Au 2 (O 2 CCF 3 ) 2 {m-(PPh 2 ) 2 (CH 2 ) n }] which gives with n ¼ 2
the cyclic compound and with n ¼ 3 or 4 one-dimensional linear or U-shaped
polymers (Figure 1.26c) [178]. In the same reaction with 4,40-bipyridine in solution
the complexes exist as an equilibrium mixture of linear oligomers and cyclic
compounds; when n ¼ 1, 3 or 5 they exist as 26-, 30- and 34 membered macrocyclic
rings, respectively, and only when n ¼ 1 are there significant intramolecular Au –Au
contacts. Some of these compounds are strongly emissive at room temperature and
in the solid state [179].
1.2.4.3 Three and Four-Coordinate Gold(I) Complexes
High coordinated gold(I) complexes with monodentate phosphines, arsines or
stibines have been reported. It was first demonstrated by 31 Pf1 Hg NMR studies
that bis-, tris, and even tetrakis(phosphine)gold(I) complexes exist in solution. Owing
to rapid ligand exchange on the NMR time scale the individual complexes can only be
observed at low temperature. The linear complexes [AuX(PR3)] interact with an excess
of phosphine to give a series of species including primarily [AuX(PR3)2], [Au(PR3)3]X
or [Au(PR3)4]X as components of the equilibria, as shown in Equation 1.8. The
Figure 1.25 Gold(I) complexes with mixed donor ligands.
Figure 1.26 Gold(I) derivatives with polydentate nitrogen ligands.
20j 1 The Chemistry of Gold
bulky phosphines, such as PR3 ¼ PCy3, only the two coordinated cation [Au(PCy3)2]þ is
accessible, but with PR3 ¼ PBu3, P(4-Tol)3 or PPh2{CH2CH2(2-py)} both [Au(PR3)2]þ
and [Au(PR3)3]þ are detected; for PR3 ¼ PEt3, PMe2Ph, P(OEt)3 or P(OCH2)3CEt
finally the two- three- and four-coordinated species are observed [180–182].
[AuX(PR3 )] Ð
PR3
[AuX(PR3 )2 ]>[Au(PR 3 )2 ]X Ð
PR3
[Au(PR3 )3 ]X Ð
PR3
[Au(PR 3 ) 4 ]X
ð1:8Þ
Three-coordinate complexes of the type [AuX(PR 3 )2] are known and they show
Au–P distances longer than those in two-coordinate complexes and P–Au–P angles
somewhat wider than 120 [183–185]. Some of these three-coordinate bis(phosphine)
gold(I) complexes luminesce in the solid state, as well as in solution. The emission is
attributed to the metal-centered pz ! (dx2-y2 , dxy) transition [184, 186]. The most
regular three-coordination is observed in compounds where all the three ligands are
identical, as in [Au(PPh 3) 3]þ salts for which several crystal structures with different
anions have been reported [187]. The cation of [Au(PCy2 Ph) 3 ]ClO4 , obtained by
reaction of [AuCl(PCy2 Ph)] with an excess of PCy2Ph in the presence of (NH 4 )ClO 4,
has an almost ideal trigonal planar geometry [P–Au–P angles of 119.3(3)] [188]. The
complexes [Au(TPA)3 ]Cl and [Au(TPPTS) 3 ]8 [TPPTS ¼ tris[(3,30,300-phosphinidyne-
tris(benzenesulfonate)] show luminescence in aqueous solution [189].
Four-coordinate complexes with monodentate ligands [Au(L)4 ]þ have been de-
scribed for PPh3 , PPh 2Me, AsPh 3 and SbPh 3 [190–193]. For triphenylphosphine the
structures of three modifications of the compound have been determined, none of
which shows the expected simple tetrahedral geometry, however, the cation of [Au
(PMePh2 )4 ]PF6 , or those with the arsine or stibine ligands, show a nearly regular
tetrahedral geometry. Other tetra-coordinate complexes are of the form [AuX
(PR 3)3 ] [194] and show the presence of a four-coordinate gold atom in a distorted
tetrahedral geometry, with rather long Au–P and Au–X distances. The water soluble
and luminescent gold(I) complex [AuI(MeTPA) 3 ]I 3 [(MeTPA)I ¼ 1-methyl-1-azonia-
3,5-diaza-7-phosphaadamantane iodide] has been obtained by reaction of [AuCl
(SMe2 )] with three equivalents of (MeTPA)I [195]. The coordination environment
of the gold center is approximately trigonal planar and the iodine is weakly
coordinated to the gold atom perpendicular to the AuP 3 plane [Au–I distance
2.936(1) Å]. The solid shows a yellow emission (598 nm) at 77 K and an orange
emission (686 nm) at 140 K. [AuI(MeTPA) 3 ]I 3 undergoes an unusual phenyl-transfer
reaction in aqueous solution with NaBPh 4 to form [AuPh(MeTPA) 3 ]BPh 4 .
Three-coordinate gold(I) complexes with functionalized l
dfs3434