Bromination of (phosphine)gold(I) bromide complexes: Stoichiometry and structure of products

Article abstract of DOI:10.1039/b502861b

The course of the oxidative addition of elemental bromine to complexes of the type (L)AuBr is strongly influenced by the nature of the tertiary phosphine ligand L. Standard square planar gold(in) complexes (L)AuBr₃ are obtained not only with L = PMe₃ but also with P(ⁱPro) ₃ for which the oxidative addition fails in the corresponding iodine system. Excess bromine is integrated into crystals of the products with the stoichiometry [(Me₃P)AuBr₃] · (Br₂) and {[(ⁱPro)₃P]AuBr₃} · (Br₂). Of the series of iodine analogues, an intercalate [(Me₃P)AuI ₃]₂ · (I₂) has been structurally characterized. [(^tBu)₃P]AuBr undergoes ligand redistribution upon treatment with bromine to give a complex reaction mixture, from which {[(^tBu)₃P]₂Au}⁺(Br ₃)^- · (Br₂) could be crystallized. It contains polymeric anions [(Br₅)^-]_n as zig-zag chains. [(o-Tol)₃P]AuBr is readily brominated to give [(o-Tol) ₃P]AuBr₃. Contrary to the situation in the gold(I) complex with its linear PAuBr unit, the square planar structure of the PAuBr ₃ unit causes steric hindering of the rotation of the tolyl groups about the P-C bonds as demonstrated by solution NMR studies. (The corresponding reaction with iodine is known to give only polyiodides with the oxidation state of the gold atom unchanged.) The even more severe congestion in [(Mes) ₃P]AuBr prevents oxidative addition not only of iodine but also of bromine. With the latter, P-Au cleavage occurs instead affording [(Mes) ₃PBr]⁺[AuBr₄]^-. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b502861b

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F U L L P A P E R
Bromination of (phosphine)gold(I) bromide complexes: stoichiometry
and structure of products
Daniel Schneider, Oliver Schuster and Hubert Schmidbaur*
Department Chemie, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4, 85747 Garching,
Germany
Received 25th February 2005, Accepted 15th April 2005
First published as an Advance Article on the web 29th April 2005
The course of the oxidative addition of elemental bromine to complexes of the type (L)AuBr is strongly influenced by
the nature of the tertiary phosphine ligand L. Standard square planar gold(III) complexes (L)AuBr3 are obtained not
only with L = PMe3 but also with P(iPro)3 for which the oxidative addition fails in the corresponding iodine system.
Excess bromine is integrated into crystals of the products with the stoichiometry [(Me3P)AuBr3]·(Br2) and
{[(iPro)3P]AuBr3}·(Br2). Of the series of iodine analogues, an intercalate [(Me3P)AuI3]2·(I2) has been structurally
characterized. [(tBu)3P]AuBr undergoes ligand redistribution upon treatment with bromine to give a complex
+
reaction mixture, from which {[(tBu)3P]2Au} (Br3)−·(Br2) could be crystallized. It contains polymeric anions [(Br5)−]n
as zig-zag chains. [(o-Tol)3P]AuBr is readily brominated to give [(o-Tol)3P]AuBr3. Contrary to the situation in the
gold(I) complex with its linear PAuBr unit, the square planar structure of the PAuBr3 unit causes steric hindering of
the rotation of the tolyl groups about the P–C bonds as demonstrated by solution NMR studies. (The corresponding
reaction with iodine is known to give only polyiodides with the oxidation state of the gold atom unchanged.) The
even more severe congestion in [(Mes)3P]AuBr prevents oxidative addition not only of iodine but also of bromine.
With the latter, P–Au cleavage occurs instead affording [(Mes)3PBr]+[AuBr4]−.
Introduction
Preparative results
The oxidative addition of elemental halogens X2 to gold(I)
halides AuX and their complexes (L)AuX and [AuX2]− is of
current interest because this process is an important step in
the etching of metallic gold with various halogenating agents.1–6
There are inconsistent reports on the nature and properties of the
final products. A main issue is the stability of gold(III) complexes
(L)AuX3 with the two heavier halogens (X = Br, I) which strongly
depends on the donor capabilities and the steric requirements
of L.1 If L is chosen from the series of tertiary phosphines or
dithiones, the coordination chemistry can also be influenced by
chelation using difunctional ligands.1,3,4
(Trimethylphoshine)gold(I) bromide (Me3P)AuBr (colourless)
was shown to add one equivalent of elemental bromine to
give the orange diamagnetic complex (Me3P)AuBr3 which has
a square planar molecular structure.7 In this study it was noted
that the crystals may trap excess bromine with a deep orange
colour. When following up this observation using stoichiometric
quantities of bromine, a new orange crystalline phase of the net
composition (Me3P)AuBr5 was obtained. Solutions of this phase
in dichloromethane showed NMR signals with chemical shifts
similar to those of (Me3P)AuBr3 and had a significant vapour
pressure of elemental bromine. These properties suggested a
simple adduct, and a single crystal structure determination
confirmed this assumption (below).
2 Au + X2 → 2 AuX
2 AuX + 2 L → 2 (L)AuX
(1)
(2a)
(2b)
(3a)
(3b)
(Me3P)AuBr3 + Br2 → [(Me3P)AuBr3]·(Br2)
(Me3P)AuBr + 2 Br2 → [(Me3P)AuBr3]·(Br2)
2 AuX + 2 X− → 2 [AuX2]−
The same reaction in the iodine system affords an almost black
crystalline 2 : 1 adduct, the decomposition temperature of which
◦
is 10 C higher than that of the (Me3P)AuI3.1 The compound
2 (L)AuX + 2 X2 → 2 (L)AuX3 or 2 [(L)AuX]·(X2)
2 [AuX2]− + 2 X2 → 2 [AuX4]− or 2 [AuX2]−·(X2)
also dissolves in dichloromethane to give the free components.
2 (Me3P)AuI3 + I2 → [(Me3P)AuI3]2·(I2)
Following an account of our recent study of the chemistry of
the iodo complexes with phosphine ligands,1 we now present
results on some bromo analogues. It should be noted that
bromination of gold under standard conditions quite generally
leads to gold(III) complexes which are thermodynamically stable
in a square planar ground state structure (eqns. (3a) and (3b)).7–14
This is in contrast to the iodo compounds which are generally
thermodynamically unstable unless small and powerful donor
ligands shift the redox potential across a threshold to make
oxidative addition of I2 possible. With less potent ligands L
the stoichiometry of the addition compounds may still feign
an (L)AuI3 state (eqn. (3a)), but the extra iodine is actually
only associated to generate a gold(I) polyiodide instead of a
gold(III) triiodide or tetraiodoaurate(III). The literature has been
summarized in a preceding publication.1
2 (Me3P)AuI + 3 I2 → [(Me3P)AuI3]2·(I2)
[Tri(isopropyl)phosphine]gold(I) iodide was found to be
reluctant to undergo oxidative addition of iodine, mainly
for steric reasons. The product with the stoichiometry
{[(iPro)3P]AuI}2·(I2)3 is a polyiodide and not a genuine gold(III)
complex.1 In the analogous reaction of colourless [(iPro)3P]AuBr
with an equimolar amount of bromine the red crystalline gold(III)
complex is readily obtained in 90% yield. The product is stable
to its mp (98 ◦C). With excess bromine a red 1 : 1 adduct
{[(iPro)3P]AuBr3}·(Br2) could be crystallized:
[(iPro)3P]AuBr + Br2 → [(iPro)3P]AuBr3
[(iPro)3P]AuBr + 2 Br2 → {[(iPro)3P]AuBr3}·(Br2)
1 9 4 0
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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[Tri(tbutyl)phosphine]gold(I) iodide has been shown to add
no iodine. Neither a gold(III) complex nor a gold(I) polyiodide
could be isolated.1 The corresponding gold(I) bromide complex,
[(tBu)3P]AuBr, appears to undergo reaction with equimolar
quantities of Br2 in dichloromethane, but no product could be
[Tri(mesityl)phosphine]gold(I) bromide was found to re-
act with excess bromine in dichloromethane to give
a
product of Au–P cleavage, which was identified as bromo-
tri(mesityl)phosphonium tetrabromoaurate(III). Red crystals
were isolated in 87% yield (mp 217 ◦C with decomposition).
1
crystallized. The H NMR spectrum of the reaction mixture
[(Mes)3P]AuBr + 2 Br2 → [(Mes)3PBr]+[AuBr4]−
shows a signal which has a chemical shift similar to that of
the starting material, but its multiplicity has changed from a
simple sharp doublet (A part of an AnX spin systems) to a
“filled in” doublet generally observed for AnXXꢀAꢀn spin systems.
This result suggested a ligand redistribution which leads to
The [(Mes)3PBr]+ cation has been detected as the parent ion
in the mass spectrum of the product. The compound is stable
in air and readily soluble in polar solvents. The 1H, 13C and 31
P
NMR signals appear in the expected shift regions. The rotation
of the mesityl groups about their P–C bonds is hindered (in
dichloromethane at 25 ◦C) rendering the 2,6-methyl groups
and 3,5-hydrogen atoms inequivalent. This pattern suggests a
propeller or paddlewheel structure.15
+
the formation of {[(tBu)3P]2Au} cations. And indeed, with
an excess of bromine a crystalline solid of the composition
+
{[(tBu)3P]2Au} (Br3)−·(Br2) could be isolated and structurally
characterized (below). The by-products could not be identified,
but it is very likely that the anions [AuBr2]− and [AuBr4]−
required by the mass balance are among the counterions
It appears that in the tri(mesityl)phosphine complex—
with three 2,4,6-trimethyl-phenyl groups instead of three 2-
methylphenyl groups in the tri(o-tolyl)phosphine complex—the
gold(I) center is perfectly protected against oxidative addition of
bromine. The situation resembles that of the tri(tbutyl)phosphine
complex, but the reaction takes a different course. The cation
+
which remain in solution. The {[(tBu)3P]2Au} cation was also
observed in the mass spectra of the products.
+
2 [(tBu)3P]AuBr + excess Br2 → {[(tBu)3P]2Au} (Br3)−·(Br2) +
by-products
+
[(Mes)3P]2Au} features a particularly severe steric conflict ow-
ing to the close proximity of two tri(mesityl)phosphine ligands.16
Therefore, any ligand redistribution giving this cation offers no
relief for a crowded system, and in the presence of a strong
oxidizing agent P–Au cleavage is thus the preferred alternative.
This result shows that with the particularly bulky P(tBu)3
ligand even the smaller and more reactive Br2 molecules (as com-
pared to I2 molecules) have no access to the gold(I) center of the
complex and are hence unable to convert it into a gold(III) center.
[Tri(ortho-tolyl)phosphine]gold(I) bromide was found to
readily undergo oxidative addition of a bromine molecule to
give high yields of an orange gold(III) complex of high stability
(mp 150 ◦C with decomposition).
Crystal and molecular structures
(Trimethylphosphine)gold(III) triiodide, (Me3P)AuI3, has re-
cently been structurally characterized. Its gold atom is in a
square planar environment with only minor differences in the
details of bonding for the cis- and trans iodine atoms.1
[(o-Tol)3P]AuBr + Br2 → [(o-Tol)3P]AuBr3
The same structure has now been found for the components
of the new iodine adduct [(Me3P)AuI3]2·(I2). Crystals of this
phase are monoclinic, space group P21/c. The asymmetric unit
contains two inequivalent (Me3P)AuI3 complexes and one I2
molecule. The geometry of the two complexes is very similar, and
in excellent agreement with that of molecules in the phase which
contains no extra iodine. The molecules centered by Au2 have no
contact with the I2 molecule, and their conformation approaches
quite closely the maximum attainable mirror symmetry: The
dihedral angle I21–Au2–P2–C23 is only −1.3◦ (Fig. 2a).
Although the reaction occurs readily and almost
quantitatively, there is severe steric hindrance clearly discernible
in the product: While the three o-tolyl groups have uninhibited
rotational motion in the gold(I) complex, as indicated by their
solution NMR-equivalence (in dichloromethane at 25 ◦C),
these groups are NMR-inequivalent in the gold(III) complex
(Fig. 1). Three separate signals are observed for the three methyl
groups, and a temperature of ca. 80 ◦C is required (in a higher
boiling solvent like chlorobenzene) to induce coalescence. Two
of the three signals have a larger line-width than the third one
already at room temperature, and as the temperature rises, these
two are subject to coalescence first, before the third one also
becomes involved. It is thus obvious that the rotation of the tolyl
groups about the P–C bonds, and possibly even the rotation
of the phosphine ligand about the Au–P bond are restricted
by the cis-bromo substituents of the square planar gold(III)
complex. The ground state conformation was determined by
the crystal structure analysis (below). It shows that only a minor
rotational barrier has to be overcome in order to make two
of the three o-tolyl groups equivalent, the molecule attaining
mirror symmetry. The third substituent is more strongly affected
in its movement and therefore rotates freely only at higher
temperature leading to virtual C3 symmetry.
A pair of molecules, each centered by Au1 is connected by two
I2 molecules as shown in Fig. 2b. Counting all I–I contacts, a 10-
membered ring is formed around a crystallographic center of in-
version. The I–I–I–I bridges are not linear [I1–I2–I13 134.7(1)◦,
I2–I1–I12ꢀ 177.0(1)◦], and the angles at the iodine◦atoms I12
and I13 are strongly different [Au1–I12–I1ꢀ 128.6(1) , Au1–I2–
◦
˚
I13 98.1(1) ]. The I1–I2 distance [2.729(1) A] is significantly
˚
longer than in orthorhombic crystals of iodine [2.667(1) A], and
ꢀ
˚
the distances I1–I12 = 3.360(1) and I2–I13 = 3.570(1) A are
17
˚
shorter than the sum of two van der Waals radii [3.80 A].
The conformation of the molecules centered by Au1 deviates
strongly from mirror symmetry [dihedral angle I13–Au1–P1–
C13 −19.8(5)◦], but it is interesting to note that the Au–I bond
lengths are not affected by the contacts with the I2 molecules
as witnessed by the distances Au1–I11 2.620(1) and Au1–I13
˚
2.623(3) A.
(Trimethylphosphine)gold(III) tribromide, (Me3P)AuBr3, has
already been structurally characterized.7 Crystals have now
been grown for the 1 : 1 bromine adduct [(Me3P)AuBr3]·(Br2)
(orthorhombic, space group Pnma, Z = 4), in which the complex
molecules are linked via bromine molecules into chains (Fig. 3).
Mainly the two cis-bromine atoms (Br2–Br4ꢀ, Br3–Br5) of the
complexes are engaged in this aggregation, but there is also a
sub-van der Waals contact to the trans-bromine atom (Br1–
Br4ꢀ). Surprisingly, all atoms of a chain except for the C1/C1A
atoms (and ignoring the hydrogen atoms) are accommodated on
a crystallographically imposed mirror plane which is bisecting
Fig. 1 1H NMR spectrum of [(o-Tol)3P]AuBr3 (CD2Cl2, 25 ◦C).
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7
1 9 4 1

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Fig. 2 Crystal structure of [(Me3P)AuI]2·(I2). (a) One type of two independent complex molecules, not aggregated with intercalated I2 molecules
(ORTEP, 50% probability ellipsoids, H atoms omitted). (b) Cyclic assembly of [(Me3P)AuI]2·(I2)2 units containing the second type of two independent
◦
˚
complex molecules. The components are related by a centre of inversion (arbitrary radii). Selected bond lengths [A] and angles [ ]: Au1–P1 2.330(3),
Au1–I11 2.6196(9), Au1–I12 2.6617(8), Au1–I13 2.6231(9), Au2–P2 2.340(3), Au2–I21 2.6238(8), Au2–I22 2.6532(8), Au2–I23 2.6257(8); I1–I2
2.729(1), I1–I12ꢀ 3.360(1), I2–I13 3.570(1); I1–I2–I13 134.7(1), I2–I1–I12ꢀ 177.0(1), Au1–I12–I1ꢀ 128.6(1), Au1–I13–I2 98.1(1).
Fig. 3 Crystal structure of [(Me3P)AuBr3]·(Br2) showing the connectivity pattern between the Br2 molecules and the neighbouring (Me3P)AuBr3
complexes. All atoms except for C1 and C1A reside on a crystallographic mirror plane. Two neighbouring chains are related by centres of inversion
◦
˚
(ORTEP, 50% probability ellipsoids, H atoms omitted). Selected bond lengths [A] and angles [ ]: Au1–P1 2.321(2), Au1–Br1 2.4815(8), Au1–Br2
2.4197(9), Au1–Br3 2.4296(8), Br4–Br5 2.3013(12); Br1–Br4ꢀ 3.7047(13), Br2–Br4ꢀ 3.2910(13), Br5–Br3 3.219; Br1–Br4ꢀ–Br5ꢀ 147.57(4), Br2–Br4ꢀ–Br5ꢀ
153.02(5), Br4–Br5–Br3 179.5.
the angles C1–P1–C1A and represents a common coordination
plane for the gold atoms.
Neigbouring chains of the structure run in opposite directions,
referring e.g. to the orientation of the unique bonds P1–C2, and
are related by centers of inversion located between the chains.
[Tri(isopropyl)phosphine]gold(III) tribromide, [(iPro)3P]Au-
Br3, was crystallized as the 1 : 1 adduct with bromine, {[(iPro)3-
P]AuBr3}·(Br2) (monoclinic, space group Cc, Z = 4). As in the
PMe3 complex (above), the coordination compounds are also
aggregated into chains via the bromine molecules, but the con-
nectivity pattern is significantly different. As shown in Fig. 4,
together with the trans-Au–Br bond (Au1–Br2), only one of
the two cis-Au–Br bonds (Au1–Br1) becomes involved, and the
approach of the Br2 molecules is not strictly to the terminal
There is a significant trans influence of the phosphine ligand
˚
which lengthens the Au1–Br1 bond to 2.4815(8) A as compared
˚
to 2.41979(1) for Au1–Br2 and 2.4296(8) A for Au1–Br3, even
though the latter include the bromine atoms functioning as
bridging atoms for the bromine molecules. Nevertheless, the
˚
Br4–Br5 distance in the bromine molecule [2.3013(12) A] is
somewhat lengthened as compared to the value for “free” Br2
ꢀ
˚
˚
[2.284 A], and the contacts Br2–Br4 3.2910(13) and Br3–Br5
3.219 A are shorter than the sum of two van der Waals radii
˚
[3.60 A].
◦
i
˚
Fig. 4 Chain structure of {[( Pro)3P]AuBr3}·(Br2) (arbitrary radii, hydrogen atoms omitted). Selected bond lengths [A] and angles [ ]: Au1–P1
2.351(2), Au1–Br1 2.422(1), Au1–Br2 2.500(1), Au1–Br3 2.412(1), Br4–Br5 2.333(2), Au1–Br5ꢀ 3.534(1), Au1–Br4 3.857(7), Br1–Br4 3.308(2), Br2–
Br5ꢀ 3.098(2); Br1–Br4–Br5 128.7(1), Br2–Br5ꢀ–Br4ꢀ 125.0(1), Br4–Br1–Au1 110.6(1), Au1–Br5ꢀ–Br2 73.4(1) (Au1ꢀ: 1 + x, y, z; Au2ꢀꢀ: −1 + x, y, z).
1 9 4 2
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7

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Fig. 5 Molecular structures of the two independent molecules in crystals of [(o-Tol)3P]AuBr3 (ORTEP, 50% probability ellipsoids, H atoms omitted).
Note, that the tolyl groups C111–C117 and C211–C217 are roughly perpendicular to the coordination plane of the gold atoms, with their methyl
◦
˚
groups oriented away, but with the H-atoms on C112 and C212 orientated towards the metal atoms. Selected bond lengths [A] and angles [ ]: Au1–P1
2.3481(14), Au1–Br11 2.4348(6), Au1–Br12 2.4573(7), Au1–Br13 2.4273(7), Au2–P2 2.3537(14), Au2–Br21 2.4225(6), Au2–Br22 2.4652(6), Au2–Br23
2.4269(6).
bromine atoms but about midway between a gold and a
bromine atom. The angles Br4–Br1ꢀ–Au1ꢀ and Br5–Br2–Au1
are 110.6(1)◦ and 73.4(1)◦. However, with the Br–Br contacts
shorter than the Br–Au contacts in both cases, the bonding is
clearly stronger for the former. The distance Br4–Br5 = 2.333(2)
ature. Unfortunately, temperature-dependent NMR studies are
not straightforward owing to solubility/stability problems. Most
common polar solvents (dimethylsulfoxide, dimethylformamide,
chloroform, tetrahydrofuran, etc.) are readily brominated at ele-
vated temperatures by the increasingly aggressive gold(III) tribro-
mide complex, while others (benzene, chlorobenzene, dioxane,
etc.) feature only limited solubility. Therefore no quantitative
data (based on a line shape analysis) could be collected over a
sufficiently large temperature interval to allow determination of
the energy parameters of the dynamic processes involved.
˚
A in the Br2 molecule shows that this bond is also lengthened
considerably as compared to “free” bromine.
The conformation of the P(iPro)3 ligand does not approach
any standard symmetry (point groups C3 or Cs) and it is obvious
that there should be no restricted rotation of the substituents
about the P–C bonds or of the ligand about the Au–P bond
in solution. This is in agreement with the NMR findings in
CD2Cl2 as a solvent, where all◦six methyl groups are equivalent
on the NMR time-scale at 25 C. In the mass spectrum (FAB)
only the products of the reductive elimination of Br2 and ligand
redistribution were observed, including also the dinuclear cation
1
There is another minor detail in the room temperature H
NMR spectrum of [(o-Tol)3P]AuBr3 concerning the resonance
of an aryl proton. Its chemical shift [dd, d 8.70 ppm (3JH,H 7.2,
4JP,H 18.2 Hz), 1H] is well separated from that of the resonances
of the other aryl protons (m, d 7.20–7.70 ppm, 11H) suggesting
exposure of this H atom to the influence of the gold atom (Fig. 1).
The likely candidates are those at C-atoms originally designated
C112 and C212 in the crystal structure (Fig. 5) which have the
right Z (zusammen, “single-cis”) orientation as indicated by the
dihedral angles Au1–P1–C111–C112 = 3.1(5)◦ and Au2–P2–
C211–C212 = −5.2(5)◦.
+
of the type {[(iPro3P)Au]2Br} , for which there are precedents in
the literature.18,19
[Tri(o-tolyl)phosphine]gold(III) tribromide, [(o-Tol)3P]AuBr3,
forms red monoclinic crystals (space group P21/c, Z = 8) with
two independent complex molecules in the asymmetric unit
together with some disordered dichloromethane solvent, which
could not be modeled successfully (see Experimental). The
geometry of the PAuBr3 units is very similar to that of the other
two (R3P)AuBr3 complexes (above) and therefore not discussed
any further (Fig. 5).
{Bis{[tri(tbutyl)phosphine]gold(I)} tribromide crystallizes as
+
the 1 : 1 adduct with bromine, {[(tBu)3P]2Au} (Br3)−·(Br2). The
¯
red crystals are triclinic (space group P1, Z = 1) with half
of the cation, half of the tribromide anion and half of the
bromine molecule in the asymmetric unit, the other halves being
generated by centres of inversion (Fig. 6). The structure of the
cation has been determined previously in salts with Cl− and
The conformation of the P(o-Tol)3 ligands has no symmetry
leaving all o-tolyl groups inequivalent. It should be noted that
only a C3 propeller or a C3v paddlewheel symmetry would lead
to equivalence. In each of the two ligands (with P1 and P2)
the methyl group of one o-tolyl substituent (C117 and C217) is
oriented away from the gold atom, while the other two are closer
to the metal atom. The dihedral angles Au1–P1–C111–C116 =
172.2(4)◦ and Au2–P2–C211–C216 = 171.2(4)◦ are clear indica-
tors for this E (entgegen, “single-trans”) orientation. Rotation
of the aryl groups about the P–C bonds appears to be restricted
as already demonstrated in solution NMR experiments (Fig. 1).
Upon solvation in dichloromethane the two complex
molecules (with Au1 and Au2) become equivalent and only
three methyl signals are observed (instead of six). It is fur-
ther conceivable that upon heating more extended rotational
movements of the aryl groups originally bearing methyl carbon
atoms designated as C127/C137 and C227/C237, respectively,
make these methyl groups equivalent first (leading to a virtual
mirror symmetry of the ligand), as observed in the temperature-
dependent NMR measurements. Full equivalence is achieved as
the third aryl group becomes freely rotating at higher temper-
Fig.
6
Molecular structure of the components of {[(tBu)3P]2-
+
Au} (Br3)−·(Br2) (ORTEP, 50% probability ellipsoids, H atoms omitted).
˚
Selected bond lengths [A]: Au1–P1 2.3213(17), Br1–Br2 2.5494(9),
Br3–Br3ꢀ 2.353(2) (P1ꢀ: 1 − x, −y, −z; Br1ꢀꢀ: −x, 1 − y, 1 − z).
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7
1 9 4 3

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BF4 counterions and requires no discussion.20,21 The Br3 and
Br2 units form zig-zag chains as shown in Fig. 7 for which there
is also precedent in the literature.22,23 Some details are given in
the figure caption.
the gold-containing anion [AuBr4]− required to balance the
stoichiometry could not be crystallized.
−
−
In the triarylphosphine series, tri(o-tolyl)phosphine still per-
mits addition of bromine, but in the product [(o-Tol)3P]AuBr3
there is severe steric hindrance of intramolecular dynamics
rendering the three tolyl groups inequivalent as shown by
solution NMR experiments. In [(Mes)3P]AuBr addition of
bromine to the gold centre is sterically prohibited and P–Au
bond cleavage occurs instead to give a bromo-phosphonium
salt [(Mes)3PBr]+[AuBr4]−.
Experimental
All experiments were carried out in an atmosphere of pure and
dry nitrogen. Glassware was oven-dried and filled with nitrogen,
solvents were dried, distilled and saturated with nitrogen.
Standard equipment was used throughout. Mass spectra were
recorded on a Finnigan MAT 90 spectrometer using FAB as an
ionization method. NMR spectrawere obtainedat room temper-
ature on JEOL-400 or JEOL-270 spectrometers. Chemical shifts
are reported in d values [ppm] relative to the residual solvent
1
resonances (1H, 13C). 31P{ H} NMR spectra are referenced to
external aqueous H3PO4 (85%). Coupling constants J and N =
ꢀ
ꢀ
JAX + JAX (for AXX spin systems) are given in Hz. Low halogen
contents in the microanalysis data are due to loss of elemental
halogen during manipulation of the crystals. The reagents
were commercially available or prepared following literature
procedures: (Me3P)AuBr3,7 (Me3P)AuI3,1 [(iPro)3P]AuBr,15 [(o-
Tol)3P]AuBr,15 [(tBu)3P]AuBr,25 and [(Mes)3P]AuBr.15
+
Fig. 7 Unit cell of the crystal structure of {[(tBu)3P]2Au} (Br3)−·(Br2)
(arbitrary radii, hydrogen atoms omitted). Zig-zag chain anions
[(Br2)·(Br3)−]n separate layers of cations. All three components reside on
◦
˚
centres of inversion. Selected bond lengths [A] and angles [ ]: Br1–Br3
3.124(2); Br2–Br1–Br3 113.4(1).
[(Me3P)AuBr3]·(Br2)
Bromo-tri(mesityl)phosphonium tetrabromoaurate(III), [(Mes)3-
PBr]+[AuBr4]−, was isolated as triclinic crystals (space group
(Me3P)AuBr3 (153 mg, 0.30 mmol) was dissolved in 5 ml of
dichloromethane and bromine (48 mg, 0.30 mmol) was added
slowly. The mixture◦was used for crystallisation by slow diffusion
of pentane at −30 C. After a few weeks orange crystals were
collected; 161 mg (80% yield), mp 124 ◦C with decomposition.
C3H9AuBr5P (672.6), calcd. C 5.36, H 1.35,◦Br 59.4; found C
¯
P1, Z = 2) with one cation and two halves of anions in the
asymmetric unit, the other two halves being generated by centers
of inversion (Fig. 8). The geometry of the cation approaches
propeller symmetry (point group C3) with the P–Br bond as
the main axis. The dimensions compare well with reference
compounds.24 Both anions are almost ideally square planar. The
packing of the components in the crystal shows no anomalies.
5.42, H 1.38, Br 58.0%. NMR (CD2Cl2, 25 C), 31P{ H}: 21.3
1
1
(s); 13C{ H}: 17.3 (d, J 44.6 Hz); 1H: 2.24 (d, J 13.3 Hz).
[(Me3P)AuI3]2·(I2)
(Me3P)AuI (196 mg, 0.30 mmol) and I2 (38 mg, 0.15 mmol)
were dissolved in dichloromethane (5 ml). Pentane vapour was
allowed to condense into the solution at −30 ◦C. Black crystals
were filtered off and dried in a light vacuum; 172 mg (74%
yield), mp 124 ◦C with decomposition. C3H9AuI4P (780.64),
calcd. C 4.62, H 1.◦16, I 65.0; found C 4.48, H 1.30, I 63.8%.
1
1
NMR (CD2Cl2, 25 C), 31P{ H}: −10.8 (s); 13C{ H}: 19.6 (d, J
32.4 Hz); 1H: 2.27 (d, J 13.4 Hz).
[(iPro)3P]AuBr3
Fig. 8 Structures of the components of the compound [(Mes)3-
PBr]+[AuBr4]− (ORTEP, 50% probability ellipsoids, H atoms omitted).
The gold atoms of the two anions reside on centres of inversion. The
geometry of the cation approaches propeller symmetry (C3). Selected
[(iPro)3P]AuBr (400 mg, 0.92 mmol) was dissolved in
dichloromethane (20 ml) and a solution of Br2 (147 mg,
0.92 mmol) in 10 ml of the same solvent was added slowly
with stirring at 20 ◦C. After 1 h the solvent was evaporated
in a vacuum to leave a red solid, which was crystallized from
dichloromethane/pentane; 496 mg (90% yield), mp 98 ◦C with
decomposition. C9H21AuBr3P (596.92), calcd. C 18.11, H 3.55,
Br 40.2; found C 17.98, H 3.45, Br 39.6%. MS (FAB): m/z
˚
bond lengths [A]: P1–Br1 2.2032(15), Au1–Br11 2.4241(6), Au1–Br12
2.4121(6), Au2–Br21 2.4281(6), Au2–Br22 2.4255(6).
Conclusions
793.4 {[(iPro3P)Au]2Br} , 517.5 [(iPro3P)2Au]+. NMR (CD2Cl2,
+
In the present study it has been demonstrated that oxidative
addition of elemental bromine to gold(I) complexes of the
type (L)AuBr is a facile process for complexes with small
and medium-sized tertiary phosphines L giving quantitative
yields of square planar gold(III) complexes (L)AuBr3. In the
trialkylphosphine series, the limit is reached with L = P (tBu)3,
for which only a ligand redistribution is induced by bromine to
◦
1
1
25 C), 31P{ H}: 77.4 (s); 13C{ H}: 28.0 (d, J 26.0, CH), 19.8 (d,
J 2.6, Me); 1H: 3.40 (dsept, J 12.2 and 7.4, 3H, CH), 1.33 (dd, J
9.7 and 7.2, 18H, Me).
{[(iPro)3PAuBr3]·(Br2)}
[(iPro)3P]AuBr3 (150 mg, 0.25 mmol) and Br2 (50 mg, 0.31 mmol)
were dissolved in dichloromethane (10 ml). Red crystals could be
grown by slow diffusion of n-pentane into the reaction mixture at
+
give salts of the cation {[(tBu)3P]2Au} , of which a tribromide
has been crystallized as the adduct with bromine. A salt with
1 9 4 4
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7

View Article Online
−30 ◦C; 125 mg (66% yield), mp 39–41 ◦C with decomposition.
cations. The former has a “filled-in doublet” multiplicity with
N = 14.8 Hz (AꢀnXXꢀAꢀn). Crystals of the tribromide were
obtained as the 1 : 1 adduct with bromine upon reacting
[(tBu)3P]AuBr with bromine in the molar ratio 1 : 4 and allowing
pentane vapour to condense into the solution of the product in
tetrahydrofuran at 4 ◦C; 145 mg (34% yield). The red crystals give
off bromine vapour slowly upon storage at 20 ◦C and rapidly on
heating. C24H54AuBr5P2 (1001.13) calcd. C 28.79, H 5.44; found
C9H21AuBr5P (756.73), calcd. C 14.29, H 2.80, Br 52.8; found C
◦
1
14.65, H 2.69, Br 51.2%. NMR (CD2Cl2, 25 C), 31P{ H}: 77.4
(s); 13C{ H}: 27.9 (d, J 26.1, CH), 19.8 (s, Me); 1H: 3.41 (dsept,
1
J 14.4 and 7.4, 3H, CH), 1.34 (dd, J 17.1 and 7.4, 18H, Me).
[(o-Tol)3P]AuBr3
+
C 28.13, H 5.37%. MS (FAB): m/z 879.5 {[(tBu3P)Au]2Br} ,
[(o-Tol)3P]AuBr (200 mg, 0.34 mmol) was dissolved in
dichloromethane (20 ml), bromine (55 mg, 0.34 mmol) was
added and the mixture was stirred for 1 h at 20 ◦C. The solvent
was evaporated to leave a red solid, which was redissolved
in dichloromethane and precipitated by slow condensation of
606 [(tBu3P)2Au]+. NMR (CD2Cl2, 25 ◦C), 31P{ H}: 96.8 (s);
1
1
13C{ H}: 40.7 (m, AXXꢀ, N = 16.6, CP), 32.8 (s, Me); 1H: 1.57
(m, A27XXꢀAꢀ27, N = 15.6, Me).
◦
pentane; 216 mg (86% yield), mp 150 C with decomposition.
[(Mes)3PBr]+[AuBr4]−
C21H21AuBr3P (741.04), calcd. C 34.04, H 2.86, Br 32.4; found C
33.12, H 2.69, Br 3◦1.2%. MS (FAB): m/z 501.5 [(o-Tol)3PAu]+.
[(Mes)3P]AuBr (200 mg, 0.30 mmol) was reacted with Br2 (96 mg,
0.60 mmol) in a total of 15 ml of dichloromethane at 20 ◦C
with stirring. After 2 h, the volume of the reaction mixture was
reduced to a few ml and the product precipitated by addition of
pentane. Red crystals could be grown upon condensing pentane
1
1
NMR (CD2Cl2, 25 C), 31P{ H}: 32.0 (s); 13C{ H}: 143.1, 133.3,
126.9, 123.1 (three sets of poorly resolved resonances, C6H4),
24.8 (2C) and 23.1 (1C) (broad singlets, Me); 1H: 8.69 (dd, J 18.2
and 7.2, 1H, see text), 7.64–7.32 (m, 11H, aryl); 2.93, 1.96 and
1.65 (3 × s, 3 × 3H, Me).
◦
vapour into a solution in dichloromethane at −30 C; 256 mg
(87% yield), mp 217 ◦C with decomposition. C27H33AuBr5P
(985.02), calcd. C 32.92, H 3.38, Br 40.56; found C 32.75, H
3.24, Br 40.86%. MS (FAB): m/z 468.5 [(Mes)3PBr]+; m/z 515.7
+
{[(tBu)3P]2Au} (Br3)−·(Br2)
[(tBu)3P]AuBr (200 mg, 0.42 mmol) was dissolved in
dichloromethane (10 ml) and treated with a solution of Br2
(67 mg, 0.42 mmol) in 5 ml of the same solvent at −78 ◦C
with stirring. Subsequently the reaction mixture was warmed to
20 ◦C and stirring continued for 3 h. The solvent was removed
in a vacuum to leave a red solid. Solutions in CD2Cl2 showed
[AuBr4]−. NMR (CD2Cl2, 25 ◦C), 31P{ H}: 39.1 (s); 13C{ H}:
148.0 (d, J 3.6, C4), 146.0 (d, J 10.4, C3/5), 144.2 (d, J 15.1,
C5/3), 134.2 (d, J 12.5, C2/6), 133.6 (d, J 13.5, C6/2), C1 not
detected, 25.3 (d, J 6.2, Me2/6), 24.6 (d, J 7.8, Me6/2), 21.5
1
1
1
(s, Me4); H: 7.25 (d, J 4,7, 1H, HC3/5), 7.05 (d, J 7.2, 1H,
HC5/3), 2.45 and 2.43 (2 × s, 2 × 3H, Me2/6), 2.01 (s, 3H,
+
only 1H and 31P NMR signals indicative of {[(tBu)3P]2Au}
Me4).
Table 1 Crystal data, data collection and structure refinement
[(Me3P)AuI]2·(I2)
[(Me3P)AuBr3]·(Br2)
{[(iPro)3P]AuBr3}·(Br2)
Crystal data
Formula
Mr
C3H9AuI4P
780.64
Monoclinic
P21/c
7.7199(1)
23.7025(4)
15.9063(2)
90
116.2520(9)
90
C3H9AuBr5P
672.59
Orthorhombic
Pnma
13.9842(3)
7.2404(1)
12.2119(2)
90
90
90
1235.8(2)
3.615
8
C9H21AuBr5P
756.72
Monoclinic
Cc
8.5738(2)
15.1158(3)
14.0133(3)
90
96.6076(8)
90
1804.06(7)
2.775
4
1364
192.95
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
2610.35(6)
3.973
qcalc/g cm−3
Z
F(000)
2664
208.00
1184
281.43
l(Mo-Ka)/cm−1
Data collection
T/◦C
Measured reflections
Unique reflections
Absorption correction
−130
−130
−130
59562
283745
20615
4522 [Rint = 0.045]
DELABS
0.340/0.763
1224 [Rint = 0.053]
DELABS
0.828/1.572
3294 [Rint = 0.064]
DELABS
0.410/0.800
T
min/Tmax
Refinement
Refined parameters
Final R values [I ≥ 2r(I)]
R1
169
67
151
0.0398
0.0254
0.0612
—
a = 0.0252
b = 7.2641
1.381/−1.567
0.0276
0.0686
0.011(11)
a = 0.0306
b = 15.1740
1.781/−1.439
wR2a
0.1076
—
Absolute structure parameter
Weighting scheme
a = 0.0502
b = 49.8084
3.041/−2.313
−3
˚
qfin(max/min)/e A
a wR2 = {R[w(Fo2–Fc2)2]/R[w(Fo2)2]}1/2; w = 1/[r2(Fo2) + (ap)2+bp]; p = (Fo + 2Fc2)/3.
2
D a l t o n T r a n s . , 2 0 0 5 , 1 9 4 0 – 1 9 4 7
1 9 4 5

View Article Online
Table 2 Crystal data, data collection and structure refinement
+
[(o-Tol)3P]AuBr3
{[(tBu)3P]2Au} (Br3)−·(Br2)
[(Mes)3PBr]+[AuBr4]−
Crystal data
Formula
Mr
C21H21AuBr3P
741.04
C24H54AuBr5P2
1001.13
C27H33AuBr5P
985.02
Crystal system
Monoclinic
P21/c
8.5107(1)
35.9228(4)
15.5325(2)
90
Triclinic
P1
Triclinic
P1
¯
¯
Space group
˚
a/A
8.6524(3)
8.9391(3)
11.6377(4)
82.4755(13)
74.3263(17)
88.7371(14)
859.10(5)
1.935
8.2777(2)
8.6329(2)
21.4606(5)
82.4809(10)
88.8961(11)
85.9632(8)
1516.55(6)
2.157
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
95.2154(4)
90
4729.06(10
2.082
8
3
˚
=
V/A
qcalc/g cm−3
Z
1
482
102.00
2
928
115.05
F(000)
2768
113.62
l(Mo-Ka)/cm−1
Data collection
T/◦C
Measured reflections
Unique reflections
Absorption correction
−130
−130
−130
85564
19895
34935
8397 [Rint = 0.061]
DELABS
0.765/1.755
2848 [Rint = 0.074]
DELABS
0.266/0.689
5187 [Rint = 0.047]
DELABS
0.545/0.859
T
min/Tmax
Refinement
Refined parameters
Final R values [I ≥2r(I)]
R1
475
157
319
0.0347
0.0832
a = 0.0402
b = 18.4634
1.951/−0.981
0.0448
0.1281
a = 0.0824
b = 2.8662
1.598/−1.912
0.0317
0.0789
a = 0.0348
b = 4.4526
1.431/−0.827
wR2a
Weighting scheme
−3
˚
qfin(max/min)/e A
2
2
a wR2 = {R[w(Fo − Fc2)2]/R[w(Fo2)2]}1/2; w = 1/[r2(Fo2) + (ap)2 + bp]; p = (Fo + 2Fc2)/3.
Reaction of (Mes3P)AuI with iodine
See http://www.rsc.org/suppdata/dt/b5/b502861b/ for cry-
stallographic data in CIF or other electronic format.
178 mg (0.25 mmol) of [(Mes)3P]AuI and 64 mg (0.25 mmol)
of I2 were dissolved in 15 ml of dichloromethane. After 1 h, the
solvent was removed under reduced pressure to yield a brown
liquid. In solution only the gold(I) species is observed. It was
not possible to crystallize a product for further characterisation.
Acknowledgements
This work was supported by Deutsche Forschungsgemeinschaft,
Fonds der Chemischen Industrie, Volkswagenstiftung, Heraeus
GmbH and Degussa AG.
1
NMR (CD2Cl2), 31P{ H}: 5.6 (s, PAu(I)); 1H: d 7.01 (broad
singlet, 2H, aryl), 2.76 (s, 6H, o-Me), 1.87 (s, 3H, p-Me).
Crystal structure determinations
References
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ends of quartz fibers in F06206R oil and used for intensity
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corrected for absorption effects (DELABS from PLATON).
The structures were solved by a combination of direct methods
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full matrix least-squares calculations on F2 (SHELXL-97).26 The
thermal motion was treated anisotropically for all non-hydrogen
atoms. All hydrogen atoms were calculated and allowed to
ride on their parent atoms with fixed isotropic contributions.
During the structure refinement of [(o-Tol)3P]AuBr3, the atoms
of a dichloromethane molecule were observed but could not
be modelled satisfactorily. The SQUEEZE routine in PLATON
was used to modify the hkl file.
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1 9 4 7