Full text of DOI:10.1016/S0020-1693(00)87574-X

Complexes
143
(ethanol on silica gel). This compound was
(0.3
in
2 ml of a solution of
identified by
(0.3
H NMR spectrum of the
in
was added. The
is given in Table IV.
NMR and IR spectroscopy as
Using the same method, the
methyldithiocarbamato)gold(III)
phosphine,
dimethylphenylphosphine, and
xanthato)gold(III)dimethylphenylphosphine
Sodium dithiobenzoate
Two ml of
made up of 4 g of chlorobenzene and 0.7 g of magne-
sium in ml of anhydrous ethyl ether. After cooling
was added to a Grignard solution
followed by 12 hr of standing at room temperature,
the mixture was decomposed with ice and aqueous
Dithiobenzoic acid was extracted with ethyl
ether and shaken with an aqueous solution containing
a stoichiometric amount of
dithiobenzoate formed was isolated from the aqueous
layer by vacuum evaporation.
were prepared. The
NMR chemical shifts of the
are given in Table V.
ESCA Studies of Organogold Dithiolates
The sodium
ESCA (Electron Spectroscopy for Chemical
Analyses) has been recognized as a powerful
technique for obtaining new insight into struc-
tural and bonding problems in organometallic chem-
To a suspension of sodium dithiobenzoate (0.25
g in 20 ml THF),
10 ml THF) was added with stirring. After filtra-
tion and removal of the excess solvent under vacuum,
the orange residue was purified
istry
A well-established relationship exists
iodide (0.4 g in
between core-level bonding energy (En) with the
formal oxidation of the metal. An increase of the
positive charge on the atom produces an increase of
the binding energies for the core level. Table III gives
on silica gel).
spectral data are given in Tables I
92-94 “C. The
the binding energies of the
and
levels
and
for two different organogold dithiolates and the gold
and sulfur binding energies of some reference com-
plexes for comparison.
and II, respectively. Yield 73%. Orange-red powder,
very soluble in organic solvents. It is an air-stable
complex. the IR absorption frequencies are given
in Table IV. Anal. Calcd. for
H, 2.90. Found: C, 29.03; H, 3.2.
C, 28.43;
X-Ray Structure
Intensities were measured on the Syntex
diffractometer, with graphite-monochromatic
Reactions of
phosphines
with
radiation
= 0.71069 A). The
scan mode
with stationary background count was used to
collect data. 3253 data
of which 1752 data had I/u(I)
55”) were collected
3.0. The atoms
To a 2
t i o n o f
TABLE V.
NMR Spectra of the Phosphine
cis 0.6
1.8
= 10.2
0.93
= 9.2
cis 0.95
= 9
tram 1.25
= 9.5
2.0
1.1
1.6
=
=
=
10.5
10.5
10.3
cis 0.9
1.99
2.02
= 8.8
1.21
= 9
cis 0.85
= 9
trans 1.95
= 9.3
3.48
7.6
spectra were taken at -40
as a solvent.
shifts in 6 units. ‘Coupling constants in Hz.

H.
C. Paparizos and P.
Jr.
144
were located by direct methods (MULTAN) which
was consistent with the Patterson result. The iso-
tropic refinement resulted in R = 0.158 and
=
0.197. The anisotropic refinement of 2 Au and 2
and isotropic refinement of 8 C resulted in R =
0.104 and
0.078,
= 0.090. Final refinement gave R
0.085 (see Table VI). The atomic scat-
tering factors for neutral atoms were taken from
Cromer and Waber The atomic position
and thermal parameters are presented in Table
VII, and the resulting bond distances and angles
in Table VIII. Figure 1 shows the structure of the
molecule.
TABLE VI. Summary of Refinement.
Weighting Scheme
Data Used
1752
0.116 0.146
0.104 0.090
1.
1
1752
1
0.105 0.133
0.078 0.085
1752
1396
1
check on agreement factors (based on refinement 1) as
function of fixed h, k, 1, sin and revealed that the h =
0, 6 and 7 layers had the high R values R = and
0.347 respectively. The weighting scheme was modified to
(the R was normalized before use, they
X
are 3.9, 1.90, 1.70, 1.39, 1.0, 1.2, 3.1 and 5.63 for h = 0, 1 ,
2, 3, 4, 5, 6, and 7 layers). The refinement 2 shows signifi-
structural
cant improvement on refinement 1.
results of refinement 3 are identical with refinement 3.
result of AGREE analysis and the unit cell packing
diagram suggest that the h
0, 6 and 7 layers have the
absorption and secondary extinction problems. Due to the
sites, Au atoms are very closed to bc plane (see Fig. 2).
Excluding these three layers, the refinement results in the
R
0.078 and 0.085. The structural results are identical
with refinement 2 and 3.
Results and Discussion
The
rhombus
Structural studies of species containing the
rhombus have focused
reported here of
on complexes of
and
The structure
is the first
known
tion. In the related
moiety with a
configura-
complexes
some

Complexes
145
TABLE VIII. Significant Intramolecular Bond Distances and Angles of
Bond
Angles
Values
Length (A)
Length (A)
Aul-Sl
Aul-S2
-Cl
Aul-Sl-Au2
Aul-S2-Au2
Sl-Aul-S2
Sl-Aul-Cl
C5
Aul-S2-C7
causes the increased
observation leads us to conclude that three struc-
tural features influence the distance: (1) the
hinge angle which is related to the M-S-M angle,
(2) the M-S distance, and (3) the distance.
In these systems then, all three factors must
distance. This
Fig. 1. ORTEP thermal ellipsoid view (50% probability) and
numbering scheme of
be considered when attempting to deduce
bonding from structural observations.
interaction is suggested. However, the present
structure has a long
A, 0.56 A longer than the
distance of
distance in
Solution Studies
has pointed out that many
(III) complexes undergo inter- or intramolecular
exchanges in solution. For example, by mixing
metallic gold
Structural studies
of
distances of 3.005 and 2.660
respec-
with
an exchange
tively, the latter indicating a strong metal-metal
bond. On going from the to the system, a
metal-metal bond is formed. In isoelectronic
complexes, and only
the complexes have a small dihedral angle
of the halides has been observed.
pentanedionato]
show exchange between bound and free
do not
has been found to
1
acetone.
appear to exchange ligands on the NMR time scale.
NMR resonances of the spectrum are sharp at all
temperatures.
between the
suggesting some
The
planes, the hinge angle
interaction.
Reaction of dimethylgold(III) iodide with sodium
ethyltrithiocarbonate produces.
distance ratio between the different
complexes is about the same as the ratio of angles
(see Table IX). An increase in the M-S-M angle
(eqn. 2).
This compound also was obtained by reacting
sodium ethylmercaptide with dimethylgold iodide.
is proportional to the opening up of the
The ratios of the distances
and the M-S bond distances (Au-S/
1.04) indicate that increasing the M-S
angle.
Although thioxanthate complexes of
with
1
tertiary phosphines as stabilizing ligands have been
Pd-S

Complexes
147
ESCA studies have been carried out for
and to obtain
information about the distribution of electron
density around the Au and S atoms. The data reveal
a pronounced influence of the ligand on the
+ 2
‘ I ’
S
,
+
binding energies. The difference is of the order of
S
0.4
large enough to distinguish the different
electron donor property of the ligands. The
binding energy of
implies a marked increase of elec-
tron density on the metal relative to
The ESCA results thus correlate
2
Au
Au
S
A
B
(2)
with
Furlani
tive d-orbital splittings of the sulfur ligands in the
chemical shifts.
al. have found the following rela-
reported, metal thioxanthate complexes generally
are unstable. In the case of
and
tide-bridged dimers
elimination from dimethyl(thioxanthato)gold(III)
s e r i e s :
This suggests that the S
<
<
the complexes lose
to form
and trimers. The
M n-interaction
with the tilled d orbitals on the M is greater in
the dithiocarbamate complexes than in the
thates or dithiocarboxylates. The net increase of
electron density on the metal atom in the dithio-
carbamates produces the shifts observed in
takes place (reaction 2)
F o r
also.
various
might be expected, particularly in solution.
However, the
NMR spectrum of this complex
does not change over in the temperature range
to -70
NMR chemical and ESCA studies. Also the
NMR
chemical shifts follow the order:
3 (see Table II).
The chemical shielding of
shielding of 1
2
Although metal complexes of
mate are known
ammonium cyanodithioformate with
(III) iodide produces tetraethylammonium
the reaction of
(Table I) is
the highest in the entire series of methylgold dithio-
lates studied. In the ligand
the
shift is essentially com-
shielding of
The and
NMR shielding and coupling cons-
plete in this anionic complex. The
gold-methyl carbon also is the highest of the series.
For complexes of the general formula
the order of
protons follows the order:
>
tants obtained from the spectra of organogold dithio-
lates are summarized in Tables I and II. Because
chemical shifts and coupling constants are solvent
and concentration dependent, all
have been obtained in the same solvent
and concentration. An examination of the
chemical shifts of the methyl-gold protons in the
series of organogold dithiolates suggests the follow-
ing
shielding of methyl-gold
shielding of
and
NMR
>
It is
known that the relative position, in the
chemical series is
<
It is also known
that the relative positions in the nephelauxetic series
For complexes of the general formula
are:
and
<
w h e r e
the
follow the order: shielding of 1
It is well known that derivatives of dithioacids
show contributions of valence bond structures A,
B and C.
X
The
NMR chemical shifts obtained for
chemical shifts of
2
3.
are consistent with the
ligand order in the spectrochemical and nephelauxetic
series.
The interaction of
with the
dithiolates has been demonstrated by the
changes in the NMR spectra of these complexes upon
S
addition of the phosphine. In all cases the
NMR
\
\
S
spectra indicate that the phosphine is bonded to the
gold center.The phosphorus methyl coupling constant
of the methyl group on the. phosphine has been
The contribution of the various valence bond
structures depend on the X group. The special feature
of structure (C) is that additional n-electron density
flows from the X-group to the carbon atoms via
delocalized
changed from 3 Hz in the
to 11 Hz in the complex, typical of a tetrahedral
phosphorus. The assignment of cis and methyl
groups to the coordinated phosphine was based on
the complex
phosphine

148
H. Chen,
Paparizosand
Jr.
free phosphine, it was observed that small amounts
of phosphine M in phosphine per M of
the complex), leads to the loss of the
From the proton NMR relative intensities, the
downfield doublet was assigned as due to the methyl
group
to phosphine and the
doublet cis
coupling but the
tion of free phosphine affects the
the complex and the free ligand are present in the
molar ratio a sharp singlet with zero
is unaffected. Further addi-
to phosphine.
By adding
and when
to a
solution of
the
cleavage of the mercapto bridge was achieved (eqn.
coupling is observed. For the systems
and
CH
the loss of the
coupling
CH,
CH,
S
only, at high temperatures, is evidence for little
phosphine dissociation compared with
where both
+ 2
2
\
3
and
coupling are lost. The more labile inter-
action of phosphine with the alkylgold
(3)
The proton NMR spectrum consists of a quartet
triplet a multiplet for
mate complex, compared with alkylgold xanthates,
and alkylgold dithiophosphates, again relates to the
increased electron density at the gold center in the
case of alkylgold dithiocarbamates and the apparent
and three doublets with relative intensities of 1:
The positions are given in Table V. This pattern
confirms the formation of a cis dialkyl planar arrange-
ment of the ligands at the gold center. The doublets
observed are easily assigned to the tram, cis
stability of the
product.
Similar results have been obtained for the
complexes. With sulfur chelates of
such as xanthates and dithiophosphates,
with
nitrogenous
bases are readily formed. In con-
groups and the
ligand. The difference
trast, the dithiocarbamate complexes of
interact with nitrogenous bases only at liquid nitro-
gen temperatures
in the value (0.4 ppm) between cis and t ra ns-
groups is due to the trans effect of the
phine.
Cleavage of mercapto bridges are known for palla-
dium complexes
studies have been carried out
With dimethylgold(lll),
involving cleavage
Acknowledgements
of thiocyanato, cyanato, selenocyanato bridges with
tertiary phosphines, pyridine and triphenylarsine.
The difference observed here with the mercapto
bridge is that cleavage occurs only with the very basic
tertiary phosphines
Support of the National Science Foundation
8305046 is acknowledged along with that of The
Robert A. Welch Foundation.
Supplementary Material Available
By adding excess dimethylphenylphosphine (five-
Tables of observed and calculated structure fac-
tors (8 pages).Ordering information is given on any
current masthead page.
fold) to the phosphine
spectrum is unaffected. The
the proton NMR
NMR signals are
sharp even at
(the upper limit of thermal stabi-
lity for the compound in solution). The ligand
exchange between
and the excess phosphine thus appears to be
slow on the NMR time scale.
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9, 101 (1970) and references cited therein.
Slow phosphine exchange is in agreement with the
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studies of Schmidbaur
al.
who on the basis
therein.
J. K.
of NMR spectroscopy of a
7 , 3 5 1 ( 1 9 7 4 ) a n d
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no exchange or at least very slow exchange takes
place.
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H. Schmidbaur, ibid., 8, 62 (1975) and references cited
therein.
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149
Complexes
22
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Variable temperature
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18
36 F.
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is light sensitive in
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