The auration of 2-hydroxy-pyridine (2-pyridone): Preparative and structural studies and a comparison with reactions of related aliphatic O,N-donors

Article abstract of DOI:10.1016/j.ica.2003.11.030

In a study of the isolobal analogy between the proton H⁺ and the ligand-backed gold(I) cations [(R₃P)Au]⁺, the reaction of the mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph₃P)Au]BF₄ has been investigated. It affords the 1:1 complex with the gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph₃P)Au[NC₅H₄-(OH-2)]}⁺BF ₄^-, which is related to known salts with the 2-hydroxy-pyridinium cation such as [HNC₅H₄(OH-2)] ⁺Cl^-. The structure was derived from analytical and spectroscopic data and from a comparison with the salt [(Ph₃P)Au(pyr) ]BF₄, prepared and investigated structurally as a reference compound. An analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex [(Ph₃P)Au([Me ₂NCH₂CH₂OH)]⁺BF₄ ^-, the structure of which has been determined. The OH group is not attached to the gold atom but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph₃P)Au(Me₂NCH ₂CH₂NMe₂)]⁺BF₄ ^- synthesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom, but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph ₃P)Au]BF₄ with an alkali 2-pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product {N,O-[(Ph₃P)Au]₂(NC ₅H₄-O-2)}BF₄. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.

Full text of DOI:10.1016/j.ica.2003.11.030

Inorganica Chimica Acta 357 (2004) 1549–1557
www.elsevier.com/locate/ica
The auration of 2-hydroxy-pyridine (2-pyridone): preparative
and structural studies and a comparison with reactions
of related aliphatic O; N-donors
*
Susanna E. Thwaite, Annette Schier, Hubert Schmidbaur
Anorganisch-chemisches Institut, Technische Universita€t M€unchen, Lichtenbergstrasse 4, 85747 Garching, Germany
Received 10 November 2003; accepted 29 November 2003
Abstract
In a study of the isolobal analogy between the proton Hþ and the ligand-backed gold(I) cations [(R3P)Au]þ, the reaction of the
mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph3P)Au]BF4 has been investigated. It affords the 1:1 complex with the
gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph3P)Au[NC5H4-(OH-2)]}þBF4ꢀ, which is related to known salts with
the 2-hydroxy-pyridinium cation such as [HNC5H4(OH-2)]þClꢀ. The structure was derived from analytical and spectroscopic data
and from a comparison with the salt [(Ph3P)Au(pyr)]BF4, prepared and investigated structurally as a reference compound. An
analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex
[(Ph3P)Au([Me2NCH2CH2OH)]þBF4ꢀ, the structure of which has been determined. The OH group is not attached to the gold atom
ꢀ
but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph3P)Au(Me2NCH2CH2NMe2)]þBF4 syn-
thesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom,
but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site
exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph3P)Au]BF4 with an alkali 2-
pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product
{N; O-[(Ph3P)Au]2(NC5H4–O-2)}BF4. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been
shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are
associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the
cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Gold complexes; Pyridine complexes; 2-Pyridone; 2-Hydroxy-pyridine
1. Introduction
self assembly monolayers, etc. [4] although many of the
precursors are not very well characterized.
For a long time the coordination chemistry of gold(I)
has been largely a success story of complexes with S- and
P-donor ligands, only excelled by cyanide coordination
[1]. Gold thiolates AuSR and their complexes LAuSR
(L ¼ donor ligand) are the most important preparations
for medical applications [2] and for traditional usage in
gilding and modern surface technologies [3], including
The coordination chemistry of the gold(I) oxygen
compounds AuOR/LAuOR is much less developed
owing to preparative difficulties and a more limited
stability of the products. However, it has been demon-
strated that the aryloxides (phenolates) are superior in
their stability to the alkoxides and that phenols may
even be aurated twice to give phenoxy-bridged dinuclear
cations [ArO(AuL)2]þ (Ar ¼ aryl) [5–8].
By the same token, gold(I) complexes with nitrogen
donor functions [9] are less stable than their phosphine
analogues, but both anilines and in particular pyridines
were found to be readily aurated [10].
* Corresponding author. Tel.: +49-8928-913130; fax: +49-8928-
913125.
E-mail address: h.schmidbaur@lrz.tum.de (H. Schmidbaur).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.11.030

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S.E. Thwaite et al. / Inorganica Chimica Acta 357 (2004) 1549–1557
In the present study the most simple combination of
reached the same conclusion for the gas (or matrix)
phase, since because the energy differences between the
two forms are extremely small, slight variations in the
parameters and models employed may cause the results
to favour one or the other form [18–20].
The crystal structure of the protonated form (as the
chloride hydrate) has also been elucidated previously
[21], and the results have demonstrated a full conversion
of the 2-pyridone into the hydroxy-pyridinium form [2-
(HO)C5H4NH]þClꢀ.
phenolic and pyridine functions, 2-hydroxy-pyridine,
was probed as a ligand for gold(I). The nature of the
auration product was difficult to predict since the pre-
cursor molecule is an ambidentate donor which may
perform either as the phenol (A) or as the prototropic 2-
pyridone (B). The former would accept the metal cation
at the nitrogen atom (C), the latter at the oxygen atom
(D), while the corresponding anion, generated upon de-
protonation (E), would offer two coordination sites for
donor/acceptor bonding (F). At the phenolate function
even diauration (above) could be envisaged (G).
2. Results
O
OH
N
H
N
2.1. Monoauration of 2-hydroxy-pyridine without action
of a base
B
A
Solutions of 2-hydroxy-pyridine/2-pyridone in tetra-
hydrofuran/methanol are known to contain predomi-
nantly the former of the two components owing to
advantages in its solvation. Treatment of these solutions
with an equimolar quantity of (triphenylphos-
phine)gold(I) tetrafluoroborate, prepared in situ from
the chloride complex and AgBF4 at )78 °C, affords a
colourless precipitate (Eq. (1)).
X
+ AuL
X
+ AuL
Base
X
X
O
N
H
OH
N
LAu
AuL
D
C
BF4
O
N
[(Ph3P)Au]BF4
A/B
E
ð1Þ
X
+ 2AuL
OH
N
X
+ 2AuL
AuPPh3
X
1
X
AuL
O
Evaporation of the solvents in a vacuum and ex-
traction of the residue with dichloromethane give a
colourless solution from which the product can be pre-
cipitated upon addition of dry diethylether in 73% yield
(m.p. 97 °C with decomposition). The composition
of the product (1) has been confirmed by elemental
analysis.
N
O
N
AuL
AuL
AuL
F
G
For several decades, there has been a controversy
about the true nature of 2-hydroxy-pyridine/2-pyridone
[11] in the crystal, in solution and in the gas phase. An
early crystal structure determination at room tempera-
ture (1953) has shown that in the only modification
known to date (orthorhombic, space group P212121; Z ¼
4) the monomeric units appear to be in the 2-pyridone
state, but are associated via intermolecular hydrogen
bonds (O–H–N) into strings [12]. This structure has
subsequently been redetermined and confirmed at least
twice, including studies at low temperature [13,14]. In
solution, the title compound is a mixture of both tau-
tomers (A/B) with the relative abundance being a func-
tion of the polarity of the solvent, the concentration and
the temperature. The monomers can also be associated
into dimers via hydrogen bonds [11,15]. Finally, in the
gas phase, the 2-pyridone form appears to be the dom-
inant species according to a wealth of spectroscopic
evidence [16,17]. Not all quantum-chemical studies have
The FAB mass spectrum shows the [(Ph3P)Au
x(C5H5NO)]þ cation at m=z 554.3 (in 50% relative in-
tensity). However, the cation of highest mass is the di-
nuclear species [(Ph3P)2Au2(C5H4NO)]þ at m=z 1012.6
(50%) indicating the stability of the diaurated cation
(below). [(Ph3P)2Au]þ (m=z 721.5, 20%) is the product of
ligand redistribution, and [(Ph3P)Au]þ is the most
abundant ion at m=z 459.3 (100%). The NMR spectra of
1
solutions in CD2Cl2 at 25 °C show sets of H and 13C
resonances which can be assigned to Ph3P and
[C5H4NOH] ligands. The latter is likely to be in the hy-
droxy-pyridine form because the 31P signal of the Ph3P
ligand in trans position (30.3 ppm) appears in the same
region where the resonance of the model compound
ꢀ
[(Ph3P)Au(pyr)]þBF4 is observed (30.0 ppm). The
proton signal of the OH group could not be located

S.E. Thwaite et al. / Inorganica Chimica Acta 357 (2004) 1549–1557
1551
unambiguously, probably owing to rapid site exchange
processes involving hydrogen bonds with the counterion,
pendent dinuclear formula units (2) in the asymmetric
unit which are linked into tetranuclear dimers through
aurophilic contacts [21]: Au1–Au4 3.2154(3), Au2–Au3
which has its resonances at )2.1 and )153.2 ppm for 11
B
and 19F, respectively. In the IR spectrum (KBr disc), a
broad absorption with a maximum at 3051 cmꢀ1 can be
assigned to an OH group entertaining hydrogen bond-
ing, but a more detailed interpretation is not justified.
3.2780(3) A (Fig. 1).
ꢀ
The structures of the two monomers (Fig. 2) are very
similar and differ only in their conformation, i.e. in the
dihedral angles determining the rotation of the Ph3P
propellers about the Au–P axes and the orientation of
the O–Au–P vectors relative to the corresponding pyri-
dinolate planes. Au2–O1–C1–N1: 144.4(4)°; Au4–O2–
C10–N2: )154.5(4)°. The differences are best illustrated
by a superposition as shown in Fig. 3. The coordination
at each of the four gold atoms is very close to linear and
the angles at O1 and O2 are similar at 122.7(2)° and
123.4(4)°, respectively.
The tetrafluoroborate anions and the solvent mole-
cules reside in channels between the large dications,
where no sub-van-der-Waals contacts are discernible.
Each nitrogen and oxygen atom of the pyridinolate
ligands is coordinated strictly to only one gold atom.
2.2. Auration of 2-hydroxypyridine with the action of a
base
2-Hydroxy-pyridine/2-pyridone can be converted into
the phenolate (NaþEꢀ) by treatment with excess ele-
mental sodium in tetrahydrofuran at 25 °C. After re-
moving unreacted sodium metal the sodium salt is
reacted with
a solution of two equivalents of
[(Ph3P)Au]BF4 in tetrahydrofuran at )78 °C. After
evaporation of the solvent in a vacuum the white sus-
pension leaves a colourless residue from which the
product can be extracted with dichloromethane. Addi-
tion of n-pentane leads to the precipitation of a crys-
talline material in 31% yield (2, m.p. 132–134 °C).
The same product (2) can be obtained in a compa-
rable yield using potassium methanolate in methanol as
a base for the 2-hydroxy-pyridine.
ꢀ
The Au–N distances [2.076(5) and 2.098(6) A] are only
slightly longer than the Au–O distances [2.059(4) and
ꢀ
2.055(5) A], as expected from a smaller covalent radius
of oxygen as compared to nitrogen. All four bonds
can be considered strong donor/acceptor bonds which
indicates that the 2-pyridinolate ligand is an efficient
difunctional donor for gold(I). Nitrogen coordination
(F) is clearly preferred over double auration of the
BF4
2[(Ph3P)Au]BF4
Na
E
ð2Þ
O
N
- NaBF4
AuPPh3
AuPPh3
2
The composition of the compound is confirmed by
elemental analysis and the mass spectrum (FAB) which
features the parent cation at m=z 1012.6 in 35% intensity
relative to [(Ph3P)Au]þ (100%). The monoaurated cat-
ion appears at m=z 554.3 (10%) and the cation
[(Ph3P)2Au]þ at 721.5 (50%).
1
The H and 13C NMR spectra of 2 (in CD2Cl2 at 25
°C) show resonances which are very similar in their
chemical shifts and coupling constants to those of
compound 1 (Section 3) suggesting a similar coordina-
tion mode. In particular, one of the two 31P signals of 2
(at 30.6 ppm) is almost in the same position as the single
signal of 1 (30.3 ppm). The presence of a second reso-
nance (at 27.9 ppm) is proof for the inequivalence of the
two [(Ph3P)Au] groups in complex 2. These two signals
broaden and reach coalescence as the temperature is
raised to 40 °C, indicating the onset of a ligand scram-
bling process which is rapid on the NMR time scale.
Single crystals of compound 2 (from dichlorome-
thane/n-pentane at )30 °C) are monoclinic, space group
Pn, with Z ¼ 4 formula units (2) and six molecules of
dichloromethane in the unit cell. There are two inde-
Fig. 1. Dimeric cations in the structure of compound 2 ꢁ 1.5 CH2Cl2
(ORTEP drawing with 50% probability ellipsoids, H-atoms omitted
ꢀ
for clarity). Selected bond lengths [A] and angles [°]: Au1–N1 2.076(5),
Au1–P1 2.238(2), Au2–O1 2.059(4), Au2–P2 2.214(2), Au3–N2
2.098(6), Au3–P3 2.236(2), Au4–O2 2.055(5), Au4–P4 2.218(2),
Au1. . .Au4 3.2154(3), Au2. . .Au3 3.2780(3); N1–Au1–P1 176.7(2),
O1–Au2–P2 177.0(1), N2–Au3–P3 174.7(2), O2–Au4–P4 177.6(2).

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Fig. 2. Crystallographically independent cations of 2 (ORTEP drawing with 50% probability ellipsoids, H-atoms omitted for clarity).
Crystals of 3 obtained from dichloromethane/n-pen-
tane (monoclinic, space group P21=n; Z ¼ 4) are solvate-
free and contain only one cation and one anion in the
asymmetric unit (Fig. 4). The Au–N distance was found
ꢀ
to be 2.073(3) A, very close to at least one of the bond
ꢀ
lengths observed for 2: 2.076(5) A for Au1–N1. The Au–
N coordination of the pyridinolate anion is therefore not
significantly different from standard pyridine coordina-
tion suggesting that the pyridinolate/pyridone resonance
is not grossly affecting the N donor strength. However,
there is a significant difference in length between N1–C2
ꢀ
1.342(5) and N1–C6 1.342(5) A for 3 and N1–C1
ꢀ
1.354(8) and N2–C10 1.366(8) A in 2, which shows the
influence of the oxy/oxo group on the pyridine resonance
reducing the bond order of the N–C(O) part of the ring.
At this point it is also of interest to compare the
structural results obtained for the diaurated cation in 2
with those of the diprotonated cation of the chloride salt
reported in the literature [21]: The 2-hydroxy-pyridi-
nium cation has similar endocyclic dimensions and its
ꢀ
exocyclic C–O bond [1.28(1) A] can be classified as a
standard single bond involving an sp2-hybridized car-
Fig. 3. Superposition of the two independent cations of 2.
phenolate function (G) which is observed in the absence
of the pyridine donor site [8].
2.3. Comparison to reference compounds
In order to provide benchmark data for the Au–
N(pyr) bond of an unsubstituted pyridine trans to a
Ph3P ligand, the reference salt [(Ph3P)Au(pyr)]BF4 (3)
has also been prepared following the same procedure as
used for 1 and 2 (Eq. (3)), and structurally characterized
by X-ray diffraction.
BF4
[(Ph3P)Au]BF4
PYR
ð3Þ
Fig. 4. Structure of the cation of compound 3 (ORTEP drawing with
50% probability ellipsoids, phenyl H-atoms omitted for clarity). Se-
N
AuPPh3
ꢀ
lected bond lengths [A] and angles [°]: Au1–N1 2.073(3), Au1–P1
2.2364(8); N1–Au1–P1 178.09(8).
3

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1553
bon atom. The exocyclic C–O bonds in 2 are 1.326(8)
ꢀ
and 1.302(8) A for the two independent cations, which is
not much larger considering the range of the standard
deviations, and the angle H–O–C [120.7(11)°] differs by
only 2° from the Au–O–C angles in the cations of
complex 2. These data indicate that protonation and
auration have comparable effects on the pyridinolate
ligand, as suggested by the isolobality principle [22].
2.4. Auration of 2-dimethylamino-ethanol
In order to draw a parallel to auration of the het-
eroaromatic 2-hydroxy-pyridine in the chemistry of
saturated O/N-difunctional compounds, an analogous
reaction was carried out with 2-dimethylamino-ethanol.
Treatment of [(Ph3P)Au]BF4 with Me2NCH2CH2OH or
the corresponding lithium or sodium ethanolate gave
good yields of a colourless crystalline product, which
was identified as the 1:1 addition compound 4 (Eq. (4)).
The mass spectrum (FAB) features the cation
[Me2N(CH2)2OH(AuPPh3)]þ (m=z 547.6) in high inten-
sity (55% rel. abundance), with [(Ph3PAu]þ as the most
abundant ion (100%), and [(Ph3P)2Au]þ as a product of
ligand redistribution (30%).
Fig. 5. Cation and anion of compound 4 (ORTEP drawing with 50%
probability ellipsoids, CH-atoms omitted for clarity). Selected bond
ꢀ
lengths [A] and angles [°]: Au1–N1 2.112(4), Au1–P1 2.227(1); N1–
Au1–P1 177.4(1); O1–H1 0.840, H1. . .F14 2.121, O1. . .F14 2.760; O1–
H1. . .F14 132.7.
Ph3PAu
[(Ph3P)Au]BF4
NMe2
CH2
Me2NCH2CH2OH
ð4Þ
F3BF HO CH2
Fig. 6. View of the packing of anions and cations of compound 4 in the
unit cell.
4
The NMR spectra (in CD2Cl2 at 25 °C) show only
one set of ligand resonances which is proof of free ro-
tation of the aminoethanol chain in a non-cyclic array.
The 31P resonance at 29.3 ppm is in agreement with data
for the Ph3P ligand in a trans position to an amine do-
nor at linearly two-coordinate gold [9]. OH protons are
observed as a broad signal at 4.77 ppm.
cations are held in close proximity in extended, largely
ionic domains, separated by double strings of non-polar
triphenylphosphine ligands. A similar structure can be
proposed for compound 1, with hydrogen bonding be-
tween a phenolic OH group and the anion.
Crystals of compound 4 (from dichloromethane/di-
ꢁ
2.5. Auration of tetramethylethylenediamine
ethylether) are triclinic, space group P1, with Z ¼ 2
formula units in the unit cell. There are no solvent
molecules in the crystal. The asymmetric unit contains
one cation and one anion which are connected via an O–
H–F(BF3) hydrogen bond (Fig. 5).
The aminoethanol ligand is attached to the gold atom
solely via its dimethylamino group. The gold atom is
strictly two-coordinate with an Au–N distance of
The experiments described above have shown that
gold(I) centres engaged in coordinative bonding with
one Ph3P ligand and a pyridine or a tertiary amine do
not accept oxo or hydroxy donor functions available in
the b-position of the primary N-ligand (1, 4). Expressed
in other words, there is a clear preference for the N- over
the O-ligand site. In order to probe the donor/acceptor
capacity of such complexes further, the coordination of
the difunctional N-donor tetramethylethylenediamine
(tmeda) was also investigated.
The reaction of equimolar quantities of the compo-
nents [(Ph3P)Au]BF4 and tmeda in tetrahydrofuran gave
good yields of a colourless crystalline product (5, m.p.
114 °C), which was readily identified by analytical and
spectroscopic data, including FAB-MS with m=z 575.5
for Mþ (100%). In dichloromethane solution at 25 °C,
the 1H and 13C NMR spectra show simple patterns
ꢀ
2.112(4) A and an angle P–Au–N of 177.39(11)°. This
Au–N distance is only slightly longer than in the pyri-
dine complexes (2 and 3, above), reflecting the rehy-
bridization of the nitrogen atom from sp2 in pyridine to
sp3 in the amine. The oxygen atom has no close intra- or
inter-cationic contacts with a metal atom, even though
the aminoethanol chain is in a gauche comformation
rendering this part of the cation rather compact. The
packing of cations and anions is illustrated in Fig. 6. It
appears that the anions and the ammonium parts of the

1554
S.E. Thwaite et al. / Inorganica Chimica Acta 357 (2004) 1549–1557
(only two resonances each for the tmeda part) suggesting
either symmetrical bonding of the metal to both nitrogen
atoms or unsymmetrical bonding with rapid site ex-
change. Lowering the temperature to )80 °C leads to line
broadening but not to line splitting. The 31P resonance
(at 30.1 ppm) indicates strict two-coordination over the
whole temperature range (v. i.).
It therefore appears that two-coordinate gold(I)
centres have a higher affinity for a third ligand with
nitrogen donor atoms as compared to oxygen donor
atoms. N/O difunctional ligands are attached through
the nitrogen atom only, while for N/N ligands there is
strong bonding for the first, but still weak bonding for
the second nitrogen atom. Considering the abundance of
potential N/O donor ligands in biological systems, these
results can help to guide efforts to understand the
physiological function of gold(I) compounds on a mo-
lecular level.
NMe2
[(Ph3P)Au]BF4
Ph3PAu
Me2NCH2CH2NMe2
BF4
CH2
Me2N CH2
5
ð5Þ
3. Experimental
Crystals of compound 5 (from dichloromethane/di-
ethylether at )30 °C) are monoclinic, space group P21,
with Z ¼ 2 formula units and two dichloromethane
molecules in the unit cell. Cations, anions and solvent
molecules have no sub-van-der-Waals contacts. The
cations show disorder of one methylene group over two
positions (Fig. 7). The tmeda ligand is coordinated to
the metal atom by one of its nitrogen atoms in the usual
All experiments were carried out in an atmosphere of
dry nitrogen. Solvents were dried and distilled under
nitrogen, and glassware was oven-dried and filled
with nitrogen. Standard equipment was used through-
out. (Ph3P)AuCl was prepared following a litera-
ture procedure [23]. All other reagents were available
commercially.
ꢀ
way [Au1–N1 2.133(3) A, P1–Au1–N1 172.15(9)°], but
the second nitrogen atom is also oriented towards the
gold atom and approaches to an equilibrium distance
3.1. N-[(Triphenylphosphine)gold]-2-hydroxy-pyridine
tetrafluoroborate (1)
ꢀ
Au1–N2 of 2.782(3) A. The bending of the P1–Au1–N1
axis by ca. 8° and the folding of the tmeda ligand in its
gauche conformation both optimize the geometry for
auxiliary Au1–N2 bonding.
The results of the crystal structure determination of 5
suggest that in solution there may be rapid site exchange
of the [(Ph3P)Au] unit over N1 and N2 as already pro-
posed based on the temperature-dependent NMR in-
vestigations, even though the expected signal splitting
could not yet be observed at the low temperature limit.
Solid (Ph3P)AuCl (100 mg, 0.20 mmol) was added to
a cooled solution of AgBF4 (43 mg, 0.22 mmol) in tet-
rahydrofuran (5 ml) at )78 °C, and the reaction mixture
was stirred for 1 h at this temperature. The supernatant
was separated from the AgCl precipitate by filtration
and added dropwise to a solution of 2-hydroxy-pyridine
(19 mg, 0.20 mmol) in tetrahydrofuran (10 ml) kept at
)78 °C. The resulting white suspension was stirred for 1
h and then evaporated to dryness under reduced pres-
sure. The residue was extracted with dichloromethane
(10 ml), the suspension filtered and its volume reduced
to 5 ml in a vacuum. The product precipitated as a
coarse white solid upon addition of diethyl ether (30 ml);
81 mg (73% yield), m.p. 97 °C with decomposition.
1
NMR (CD2Cl2, 25 °C), H: 7.73, d, J 6.7 Hz, 1H; 6.87,
d, J 8.4 Hz, 1H; 6.69, dd, 1H, all pyr; 7.42–7.68, m, 15H,
Ph. 13C{1H}: 141.62, 133.26, 117.54, all s, pyr; 134.53,
132.82, 129.88, 128.26, all d, J 13.1, 2.9, 12.3, and 64.5
Hz, for o-, p-, m-, and i-Ph. 11B: )2.09, s. 19F: )153.2, s.
31P{1H}: 30.3, s. MS (FAB) m=z: 1012.6 (50%)
[M + AuPPh3]þ; 721.5 (20) [(Ph3P)2Au]þ; 554.3 (50)
[M(cation)]þ; 459.3 (100) [Ph3PAu]þ. Anal. Calc. for
C23H20NOAuPBF4 (641.17): C, 43.09; H, 3.14; N, 2.18;
P, 4.83. Found: C, 44.78; H, 3.32; N, 2.09; P, 5.04%.
3.2. N,O-Bis[(triphenylphosphine)gold]-2-pyridinolate
tetrafluoroborate (2)
Fig. 7. Structure of the cation of compound 5 ꢁ CH2Cl2 (ORTEP
drawing with 50% probability ellipsoids, H-atoms omitted for clarity).
ꢀ
The carbon atom C42 is disordered. Selected bond lengths [A] and
Silver tetrafluoroborate (43 mg, 0.22 mmol) was dis-
solved in tetrahydrofuran (10 ml) and cooled to )78 °C.
angles [°]: Au1–N1 2.133(3), Au1–P1 2.2270(8), Au1. . .N2 2.782(3);
N1–Au1–P1 172.15(9).

S.E. Thwaite et al. / Inorganica Chimica Acta 357 (2004) 1549–1557
1555
(Triphenylphosphine)gold chloride (100 mg, 0.20 mmol)
was added to this solution and the reaction mixture
stirred for 1 h at )78 °C. The AgCl precipitate was re-
moved by filtration and the filtrate added dropwise to
a solution of sodium 2-pyridinolate prepared from 2-
hydroxy-pyridine (10 mg, 0.10 mmol) and elemental
sodium (200 mg, excess) in tetrahydrofuran (15 ml) at
25 °C and removing the excess sodium metal. The re-
sulting white suspension was stirred for 1 h and then
evaporated to dryness under reduced pressure. The
residue was extracted with dichloromethane (10 ml).
After filtration the solution was reduced in volume and
the product precipitated by addition of n-pentane. The
off-white solid was recrystallized from dichloromethane
by careful layering with pentane: 35 mg (31% yield),
m.p. 132–134 °C with decomposition. In an alternative
procedure, potassium 2-pyridinolate was prepared from
2-hydroxy-pyridine (21 mg, 0.22 mmol) and potassium
methanolate (17 mg, 0.24 mmol) in methanol (10 ml)
and reacted with [(Ph3P)Au]BF4 (200 mg, 0.40 mmol) in
tetrahydrofuran (20 ml), with a similar yield. NMR
at )78 °C. The AgCl precipitate was filtered off and the
filtrate added dropwise to a solution of 2-dimethylamino-
ethanol (9 mg, 0.010 ml, 0.10 mmol) in tetrahydrofuran
(10 ml). The resulting off-white suspension was stirred for
2 h before reducing to dryness under vacuum. The residue
was extracted with dichloromethane (5 ml), filtered to
remove insoluble components and crystallized by diethyl
ether vapour diffusion; colourless needles, 0.088 g
(80% yield), m.p. 125 °C with decomposition. The same
product was obtained in the presence of base (NaOMe or
nBuLi) if moisture was not rigorously excluded. NMR
(CD2Cl2, 25 °C), 1H: 7.45–7.70, m, 15H, Ph; 4.77, bs, 1H,
OH; 3.88, t, J 4.7 Hz, 2H, CH2O; 3.05, t, J 4.7 Hz, 2H,
CH2N; 2.83, s, 6H, Me. 13C{1H}: 134.52, 132.67, 129.80,
and 128.20, all d, J 13.5, 0.5, 11.9, and 64.4 Hz, for o-, p-,
m-, and i-Ph, respectively; 65.23, s, CH2O; 58.22, s,
CH2N; 49.42, s, Me. 31P{1H}: 29.3, s. MS (FAB) m=z:
721.5 (30%) [(Ph3P)2Au]þ; 547.6 (55) [M(cation)]þ; 459.3
(100) [(Ph3P)Au]þ. Anal. Calc. for C22H26NOPAuBF4
(635.20) C, 40.57; H, 4.13; N, 2.21; P, 4.88. Found C,
40.57; H, 4.24; N, 2.44; P, 4.59%.
1
(CD2Cl2, 25 °C) H: 7.88, d, J 5.7 Hz, 1H, pyr; 7.35–
7.80, m, 31H, Ph and pyr; 7.09, d, J 8.6 Hz, pyr; 6.87,
dd, 1H, pyr. 13C{1H}: 147.00, 142.16 and 133.21, s, pyr;
134.40, 132.80, 129.84, and 128.15, all d, for o-, p-, m-,
and i-Ph, with J 13.5, 0.3, 11.9, and 64.5 Hz, respec-
tively. 31P{1H}: 30.6, s, 1P, PAuN; 27.9, s, 1P, PAuO.
11B: )2.03, s; )1.16, s (impurity). MS (FAB) m=z: 1012.6
(35%) [M(cation)]þ; 721.5 (50) [(Ph3P)2Au]þ; 554.3 (10)
[M–AuPPh3]þ; 459.4 (100) [Ph3PAu]þ. Anal. Calc. for
C41H34NOAu2P2BF4 (1099.42) C, 43.74; H, 3.62; N,
1.63; P, 5.10. Found C, 44.79; H, 3.12; N, 1.27; P, 5.63%.
3.5. N-[(Triphenylphosphine)gold]-tetramethylethylene-
diamine tetrafluoroborate (5)
A solution of [(Ph3P)Au]BF4 was prepared by stirring
equimolar quantities of (Ph3P)AuCl (100 mg, 0.20
mmol) with AgBF4 (43 mg, 0.22 mmol) in THF (5 ml) at
)78 °C for 1 h and filtering the reaction mixture. This
solution was added dropwise to
a solution of
Me2NCH2CH2NMe2 (excess tmeda, 0.04 ml, 31 mg,
0.30 mmol) in 5 ml of the same solvent kept at )78 °C
with stirring. After 1 h the solvent was removed in a
vacuum and the residue extracted with CH2Cl2 (5 ml).
The extract was filtered and the product precipitated by
addition of diethylether (20 ml). Single crystals were
grown by diethylether vapour diffusion into a solution
of the compound in dichloromethane; 104 mg (69%
yield), m.p. 114 °C with decomposition. NMR (CD2Cl2,
3.3. Triphenylphosphine)(pyridine)gold tetrafluorobo-
rate, (3)
Silver tetrafluoroborate (43 mg, 0.22 mmol) was dis-
solved in tetrahydrofuran (5 ml) and cooled to )78 °C.
(Triphenylphosphine)gold chloride (100 mg, 0.20 mmol)
was added to this solution and the reaction mixture
stirred for 1 h at )78 °C. The AgCl precipitate was re-
moved by filtration and the filtrate added dropwise to a
solution of pyridine (30 mg, 0.03 ml, 0.30 mmol) in THF
(5 ml). The resulting mixture was stirred for 1 h at this
temperature before the solvent was removed to leave a
white residue. This was extracted with 10 ml of CH2Cl2
and the extract filtered, reduced in volume and treated
with 40 ml of diethyl ether to precipitate the product as a
fine white solid; 119 mg (94%).
1
25 °C), H: 7.45–7.60, m, 15H, Ph; 2.79, s, 4H, CH2;
2.51, s, 12H, Me. At )80 °C there is line broadening of
the two tmeda signals. 13C{1H}: 134.31, 132.72, 129.86,
and 128.74, all d (J 14.0, 0.5, 11.9, and 63.3 Hz), for o-,
p-, m-, and i- Ph, respectively; 58.75, s, CH2; 48.56, s,
Me. 31P{1H}: 30.1, s. MS (FAB) m=z: 721.5 (10%)
[(Ph3P)2Au]þ; 575.5 (100) [M(cation)]þ; 516.4 (10)
[M(cation) + Ph3PAu]2þ; 459.3 (40) [(Ph3P)Au]þ. Anal.
Calc for C24H31N2AuPBF4 (662.27): C, 43.53; H, 4.72;
N, 4.23; P, 4.68. Found: C, 42.34; H, 4.81; N, 3.98; P,
4.40%.
3.4. N-[(Triphenylphosphine)gold]-2-dimethylamino-
ethanol tetrafluoroborate (4)
3.6. Crystal structure determinations
Solid (Ph3P)AuCl (100 mg, 0.20 mmol) was added to a
cooled solution of AgBF4 (43 mg, 0.22 mmol) in tetra-
hydrofuran (5 ml) and the reaction mixture stirred for 1 h
Specimens of suitable quality and size of compounds
2, 3, 4 and 5 were mounted on the ends of quartz fibers

1556
S.E. Thwaite et al. / Inorganica Chimica Acta 357 (2004) 1549–1557
Table 1
Crystal data, data collection, and structure refinement
a
2 ꢁ 1.5 CH2Cl2
3
4
5 ꢁ CH2Cl2
Crystal data
a
Formula
Mr
Crystal system
C
42:5H37Au2BCl3F4NOP22
C23H20AuBF4NP
625.15
monoclinic
C22H26AuBF4NOP
635.18
triclinic
C25H33AuBCl2N2P
747.18
monoclinic
1226.76a
monoclinic
Pn
ꢁ
Space group
ꢀ
P21=n
P1
P21
a (A)
14.0873(1)
21.7343(2)
15.0374(2)
90
9.8533(1)
16.6467(3)
13.8064(2)
90
9.1818(1)
9.6179(1)
14.2653(3)
109.450(1)
99.855(1)
91.582(1)
1165.5(1)
1.810
10.8371(2)
9.4656(2)
14.3424(4)
90
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
V (A )
qcalc (g cmꢀ3
Z
93.260(1)
90
98.619(1)
90
102.233(1)
90
3
ꢀ
4596.7(1)
1.773a
2239.1(1)
1.855
1437.8(1)
1.726
)
4
4
1200
2
616
2
732
F (0 0 0)
l (Mo Ka) (cmꢀ1
2348a
)
66.68a
66.85
64.25
54.01
Data collection
T (°C)
Measured reflections
)130
67733
)130
72555
)130
31246
)130
41743
Unique reflections
Absorption correction
17915 [Rint ¼ 0:1480]
DELABS
0.247/0.705
4952 [Rint ¼ 0:043]
DELABS
0.409/0.800
4822 [Rint ¼ 0:034]
DELABS
0.398/0.795
5823 [Rint ¼ 0:0527]
DELABS
0.475/0.830
T
min=Tmax
Refinement
Refined parameters
Final R values [I > 2rðIÞ]
R1
1018
360
280
335
0.0331
0.0876
0.0253
0.0476
0.0331
0.0858
0.0237
0.0591
b
wR2
Absolute structure ꢀp3arameter
0.027(4)
1.421 and )1.447
)0.006(6)
1.729 and )1.689
ꢀ
qfin (max/min) (e A
)
0.532 and )0.645
1.814 and )2.294
a Uncorrected data.
nh
i
o
1=2
P
P
2
2
2
b wR2 ¼
wðFo2 ꢀ Fc2Þ
=
½wðFo2Þ ꢂ
; w ¼ 1=½r2ðFo2Þ þ ðapÞ þ bpꢂ; p ¼ ðFo2 þ 2Fc2Þ=3; a ¼ 0 (2 ꢁ 1.5 CH2Cl2), 0 (3), 0.0481 (4), 0.0059
(5 ꢁ CH2Cl2); b ¼ 0 (2 ꢁ 1.5 CH2Cl2), 4.17 (3), 2.0 (4), 0.5 (5 ꢁ CH2Cl2).
in F06206R oil and used for intensity data collection on
a Nonius DIP2020 diffractometer, employing graphite-
monochromated Mo Ka radiation. Intensity data were
corrected for absorption effects (DELABS from PLA-
TON). The structures were solved by a combination of
direct methods (SHELXS-97) and difference-Fourier
syntheses and refined by full matrix least-squares cal-
4. Supplementary data
Anisotropic thermal parameters and tables of inter-
atomic distances and angles have been deposited with
the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK. The data are available
on request on quoting CCDS-225042–225045.
culations on F 2
(SHELXL-97). The thermal motion was
treated anisotropically for all non-hydrogen atoms. All
hydrogen atoms were either calculated and were allowed
to ride on their parent atoms with fixed isotropic con-
tributions (2, 4, 5), or were located and refined iso-
tropically (3) or were included with a fixed isotropic
contribution (O–H in 4), respectively. Crystals of com-
pound 2 contained some additional disordered solvent
in the lattice, which was not included in the refinement
but was taken care of by the ÔSQUEEZEÕ-procedure
(from PLATON). The volume occupied by the solvent is
Acknowledgements
This work was supported by Deutsche Forschungs-
gemeinschaft, Fonds der Chemischen Industrie, VW-
Stiftung and the Deutsche Akademische Austauschdienst
(S.E.T.). The invaluable assistance of Dr. E. Herdtweck
and Dr. P. Roembke, in the crystallographic and exper-
imental work respectively, is gratefully acknowledged.
3
ꢀ
531 A , the number of electrons per unit cell deduced by
ÔSQUEEZEÕ is 40. Further information on crystal data,
data collection and structure refinement are summarized
in Table 1. Important interatomic distances and angles
are shown in the corresponding figure captions.
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