Imine-coordinated 2-aminoazole complexes of Au(I): Complicating reactions and verification of products by crystal structure determination

Article abstract of DOI:10.5560/ZNB.2014-4187

When Au(I) is provided with endocyclic soft thioether or endocyclic hard amine, endocyclic borderline imine and exocyclic hard amine coordination sites, the softer borderline endocyclic imine coordination site is favored. This is demonstrated by the synth

Full text of DOI:10.5560/ZNB.2014-4187

Imine-coordinated 2-Aminoazole Complexes of Au(I): Complicat-
ing Reactions and Verification of Products by Crystal Structure
Determination
Leigh-Anne de Jongha, Liliana Dobrzan´skaa,b, Christoph E. Strassera,
Helgard G. Raubenheimera, and Stephanie Cronjea,c
a
Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1,
Matieland, 7602, Stellenbosch, South Africa
Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F - bus 2404,
b
B-3001 Heverlee, Belgium
Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-
c
Laue-Strasse 7, D-60348 Frankfurt am Main, Germany
Reprint requests to Dr. Stephanie Cronje. Fax: +27 (0)21 808-3849. E-mail: scron@sun.ac.za or
stephanie.cronje@gmail.com
Z. Naturforsch. 2014, 69b, 1073 – 1087 / DOI: 10.5560/ZNB.2014-4187
Received August 11, 2014
Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday in recognition of his
numerous important contributions to inorganic and organometallic chemistry
When Au(I) is provided with endocyclic soft thioether or endocyclic hard amine, endo-
cyclic borderline imine and exocyclic hard amine coordination sites, the softer borderline en-
docyclic imine coordination site is favored. This is demonstrated by the synthesis and struc-
tural characterization (IR, MS, 1H, 13C and 31P NMR experiments and single-crystal X-ray
diffraction analysis) of 2-aminoazole (2-amino-4-methylthiazole, 2-aminobenzothiazole and 2-
aminobenzimidazole) complexes of [AuPPh3]+ (1–3). An unusual ring opening is observed for
the reaction of 2-aminothiazoline with [Au(NO3)PPh3] yielding µ2-(2-mercapto-ethyl-cyanamide-
κ,S)bis(triphenylphosphine)gold(I) nitrate (4). Reactions of 2-aminoazoles with Au(C6F5)THT
(THT = tetrahydrothiophene) yield [Au(C6F5)2]− stabilized by various cations. The formation of
Au(2-aminothiazoline)C6F5 is again the exception.
Key words: Au(I), 2-Aminoazole, 5-Membered Heterocycle, Homoleptic Rearrangement,
Aurophilic Interactions, Sulfonium Complex
Introduction
cals, characterization methods in molecular biology
as well as for the immobilization of biomolecules on
Many biomolecules such as proteins, enzymes, nu- metal surfaces [6]. The anti-proliferative, i. e. anti-
cleic acids and some vitamins which are essential to viral, anti-bacterial, anti-fungal, anti-microbial, anti-
life processes contain five-membered azoles (exclud- cancer, anti-inflammatory, and anti-infective activity
ing oxazoles) and their derivatives which are impor- of gold(I) compounds and their clinical use in the
tant units in the basic structure of these molecules [1, treatment of severe rheumatoid arthritis have provided
2]. Numerous metal ions have a crucial function in a powerful incentive for the continued pursuit of the
biochemical processes. Research in bioinorganic and bonding of biologically active molecules to gold(I) and
bioorganometallic chemistry has been driven by the the investigation of their biological effects [7 – 9]. The
elucidation of the role of metal ions in enzyme func- coordination of biologically active molecules to metal
tion, as pharmaceuticals in diagnostics and therapy centers has afforded compounds with amplified activ-
as well as toxicity studies [3 – 5]. The determination ity or therapeutic effect [10].
of the site of metallation of biomolecules is of great
The unexpected N-coordination of the enzyme cy-
interest for the development of metallopharmaceuti- clophilin to gold(I) via the nitrogen atom of an ac-
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
tive His residue, despite the presence of four Cys
In the present study the metal centers [AuPPh3]+
thiol groups, has implications for the understanding of and AuC6F5 were presented with several coordina-
the biochemical mechanisms of gold compounds [11]. tion sites present in various 2-aminoazole ligands, i. e.
The affinity of metal centers for exocylic amine ver- a soft endocyclic thioether, a hard exocyclic amine,
sus endocyclic imines or thioether coordination sites a hard endocyclic amine and a softer borderline endo-
can be studied with simple but useful model com- cyclic imine. The characterization and structural eluci-
pounds such as 2-aminoazoles. We have previously dation of the isolated complexes, confirmed the prefer-
found that the endocyclic imine is the preferred coor- ence of the gold center for the borderline endocyclic
dination site of AuC6F5 units when provided with the imine N unless complicating reactions such as ring
former and exocyclic as well as endocyclic thioether opening of a saturated, substituted azole [22] with
coordination sites [12, 13]. Results have shown that concurrent stabilization of the hypercoordinated phos-
the soft Au(I) acid center in a series of ligand sub- phinogold(I) derivatives around an S center by Au···Au
stitutions, displays the following order in decreasing interactions [23], or homoleptic rearrangements [24] to
preference: C=S > R2NH (hard base) ≫ C=N– yield [Au(C6F5)2]− occur.
(borderline base) > RSR (soft base). This disagrees
with the conventional classification of soft and hard Results and Discussion
acids and bases which indicates a decreasing prefer-
ence C=S > RSR ꢀ C=N– > R2NH. It can be ar- Synthesis
−
gued that the C6F5 ligand hardens the gold center,
and it was necessary to also investigate the coordina-
The treatment of equimolar amounts of the starting
tion site preference of the softer gold in [AuPPh3]+. material Au(NO3)PPh3 [25] suspended in diethyl ether
Exocyclic imine coordination to gold is preferred at room temperature with 2-amino-4-methylthiazole,
by azol-2-ylideneamine ligands (azol-2-ylideneamine 2-aminobenzothiazole, 2-aminobenzimidazole or 2-
= 3,4-dimethyl-3H-thiazol-2-ylideneamine, 3-methyl- aminothiazoline dissolved in diethyl ether readily af-
3H-benzothiazol-2-ylideneamine or 1,3-dimethyl-1,3- forded complexes 1–4 (Scheme 1). After extraction
dihydro-benzimidazol-2-ylideneamine) in reactions of the obtained solids upon stripping of solvent (in
with AuC6F5, [AuPPh3]+ or [Au(1,3-di-tert-butyl- vacuo) with diethyl ether, filtration and concentration,
imidazol-2-ylidene)]+ units [14].
the products were obtained after trituration with pen-
tane. The ‘soft-borderline’ adducts 1–3 and the di-
Coordination of borderline acids such as Co2+
,
Zn2+ and Ni2+ to 2-aminoazole derivatives shows nuclear product, 4, are neither air nor moisture sen-
bonding to the endocyclic imine nitrogen [15]. sitive. These cationic complexes are soluble in more
Cr(CO)5 and W(CO)5 fragments, the former used as polar organic solvents such as methanol, acetone and
a protecting group in peptide synthesis and the latter dichloromethane but insoluble in hexane and pentane.
as a label in biologically active molecules [16, 17], are
Crystals suitable for X-ray diffraction for structure
of interest as soft Lewis acids. In the plethora of pen- determinations were obtained from concentrated solu-
tacarbonyl group 6 metal carbene compounds that have tions of 1 (yellow) or 2 (yellow) in dichloromethane,
been reported, W(CO)5 is a soft Lewis acid but upon 3 in methanol (3b, 3c, colorless) or 4 in acetone (col-
coordination to 2-aminopyrimidine, a hard exocyclic orless) at −22◦C or by vapor diffusion of pentane into
sp3 amine N is preferred [18, 19] even with an addi- a solution of 3 (3a, colorless) under argon at −22◦C.
tional softer aromatic sp2 imine N present, contradict- Single-crystal structure analyses revealed that in 3a the
ing standard HSAB rules [18 – 20]. A sensitive balance unit cell consists of a cation and anion only, while the
has been struck between the coordination of W(CO)5 unit cells of complexes 3b and 3c contain cations, an-
units to exocyclic amino groups or to endocyclic imino ions and solvent molecules.
groups in pyridines, pyrimidines and purines [19, 20].
The crystals of 4 showed the formation of µ2-
When provided with endocyclic soft thioether or en- (2-mercapto-ethyl-cyanamide-κ,S)bis(triphenylphos-
docyclic hard amine, endocyclic borderline imine and phine)gold(I) nitrate which reveals an interesting
exocyclic hard amine coordination sites present in 2- ring opening of the ligand, 2-aminothiazoline, via
aminoazoles, the softer endocyclic imine coordination deprotonation of the amine, proton migration to
site is favored by both Cr(CO)5 and W(CO)5 units [21]. the original imine and ring cleavage at the C–S
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1075
Scheme 1.
bond (not necessarily in this order). The concomi-
tant coordination of two [AuPPh3]+ moieties in the
product, µ2-(2-mercapto-ethyl-cyanamide-κ,S)bis(tri-
phenylphosphine)gold(I) nitrate, accentuates the im-
portant mediating influence of the cationic gold frag-
ments. Notably, Laguna and co-workers observed a re-
lated ring opening [22] but by using Au(acac)PPh3 as
reactant effected a second deprotonation, amide coor-
dination of one [AuPPh3]+ ion and the formation of
Scheme 2. i) 1.5 mol equivalents of 2-aminoazole, ii) 0.5 mol
equivalents of 2-aminoazole, iii) 1.0 mol equivalent of 2-
aminoazole, two crystallographically independent moieties
present in the asymmetric unit of the crystals, iv) 1.0 mol
equivalent of 2-aminobenzimidazole.
a neutral product.
The most general route for the preparation of imine-
functionalized heterocyclic (pentafluorophenyl)gold(I)
compounds involves the substitution of the labile THT
ligand in Au(C6F5)THT by an imine ligand, yield-
ing Au(C6F5)L [12]. Such coordination was now a solution of 2-aminothiazoline in diethyl ether with
only observed for 5 (an exception in the series). equimolar amounts of Au(C6F5)THT at room tem-
In all the other experiments a number of prod- perature under inert conditions. From reaction mix-
−
ucts that contain Au(C6F5)2 anions and various tures prepared according to the same protocol with 2-
aquated and/or ligated lithium or 2-aminoazolium amino-4-methylthiazole (using 1.5 or 0.5 mol equiva-
cations were crystallized from the reaction mixtures lents of ligand), 2-aminobenzothiazole and 2-amino-
(Scheme 2). Compound 5 was prepared by treating 1-methylbenzimidazole [21, 26] only crystals of prod-
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
ucts I–IV, resulting from homoleptic rearrangements insoluble in water and alkanes such as pentane and
and interactions of lithium cations with various lig- hexane. Crystals suitable for X-ray diffraction, were
ands, were isolated and characterized by single-crystal obtained from concentrated solutions of 5, I, II, and
structure determinations. Crystallizations were not III in dichloromethane or by vapor diffusion of pen-
performed under inert conditions. Lithium chloride, tane into a solution of IV in acetone.
formed during the preparation of Au(C6F5)THT [27]
probably afforded the solvated or complexed lithium Spectroscopic and spectrometric characterization
cations. The products discussed here are simply those
that crystallized most readily. Product III is particu-
larly interesting owing to the symmetric coordination the new compounds appear slightly downfield to the
of the lithium cations by two aminoazole ligands. chemical shifts of the corresponding starting materi-
Most signals in the NMR spectra (1H, 13C, 31P) of
Such rearrangements with unpredictable inci- als. Although differences in concentration are known
dence are common in gold(I) chemistry and not to influence the NH chemical shifts, it is notable
always reported. Examples are: i) the fragment that coordination to a gold(I) center has a varied,
of [Li(diglyme)2.5(ebtz)]+∞ and the non-interacting but pronounced effect on the NH2 moiety of lig-
Au(C6F5)− which were obtained from the at- ands. In most cases NH2 resonances are shifted sig-
tempted synthesis of [1,2-di(tetrazol-2-yl)ethane] nificantly downfield with respect to free ligand sig-
(pentafluorophenyl)gold(I) by addition of 1,2- nals. This effect is more pronounced for complex 1
di(tetrazol-2-yl)ethane to 2 molar equivalents of (δ = 1.76 ppm) than for 2 (δ = 1.34 ppm), along with
Au(C6F5)THT; ii) the 2-dimethylamino(ethylene)- increasing lone pair electron delocalization over the
trimethylammonium catio−n (TMRDAMe+) and ligand system. In contrast, the NH2 resonance of com-
non-interacting Au(C6F5)2 formed from an at- plex 3 experiences a significant upfield shift (δ =
tempted synthesis of (1-benzyl-4-methyltetrazol- 3.02 ppm). Deshielding of the NH2 protons in 3 by
5-ylidene)(pentafluorophenyl)gold(I) [28]; iii) the close association of the nitrate anion (even in solu-
isolation of [Au(C6F5)2][Au(pdma)2] [pdma
=
tion), could give a plausible explanation for this di-
o-phenylenebis(dimethylarsine)] [29], and iv) the vergence. Additionally, hydrogen bonds between oxy-
conversion of (isothiazol-5-yl)(pentafluorophenyl) gen atoms of the anion and NH2 in the cation ex-
gold(I) – see below [24].
ist in the solid state of 3. NMR studies and single-
While Raubenheimer and co-workers [24] have ob- crystal structure determinations have illustrated a sim-
served a homoleptic rearrangement for (isothiazol- ilar situation for the NH in (3,4-dimethyl-3H-thiazol-
5-yl)(pentafluorophenyl)gold(I), the complex (isothi- 2-ylideneamine)AuPPh3 [14], for the NC(H)N pro-
azol-5-yl)(triphenylphosphine)gold(I) could be read- ton in [{µ2-HCCCH2N=C(H)N(CH=CH2)CH=CH}
ily isolated. In the instance when isothiazole is used Co2(CO)6][B(C6H5)4] [30] and ferrocenyl imida-
as N-heterocyclic ligand in the neutral complex (iso- zolium salts [31, 32]. Resonances for the NH group
thiazol-5-ylidene)(pentafluorophenyl)gold(I), the rear- in 3 and its corresponding free ligand were not ob-
1
rangement occurs slowly and can be followed by H served. The signal for the aliphatic amine in 4 (δ =
NMR measurements. Trace amounts of the rearranged 2.83 ppm) appears upfield from the signal for the pri-
product formed within days, and the reaction reaches mary amine in the starting material, 2-aminothiazoline
an equilibrium after 18 d. The reaction occurs more (δ = 4.71 ppm).
rapidly for the precursor (isothiazol-5-yl)(pentafluoro-
In the 1H NMR spectra, resonances of the
phenyl)gold(I) and can be converted in situ into a car- phenyl protons of benzazole-derived ligands (δ =
bene complex by immediate alkylation. In contrast, 7.1 – 7.5 ppm) clearly show the chemical inequiva-
(triphenylphosphine)(isothiazol-5-yl)gold(I) is stable lence of the phenyl CCH and CCHCH protons upon
in solution and can readily be isolated in pure form. changing from an N atom in 3 (only two doublets of
Subsequent alkylation of this product again affords doublets detected) to an S atom (multiplets observed)
a mixture that includes an ionic homoleptic rearrange- in 2. The signals indicating the presence of the AuPPh3
ment by-product.
moiety, appear as a multiplet in the same region (δ =
Compound 5 is soluble in polar organic solvents 7.6 – 7.7 ppm) integrating for 15 (in the spectrum of 1–
such as acetone, dichloromethane and diethyl ether and 3) or 30 H atoms (in the spectrum of 4).
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1077
In the 13C NMR spectra, the signal for the served at 3295 cm−1 for 4. A smaller third band
carbon atom situated between two heteroatoms is (3054 – 3123 cm−1) in the spectra of 1–3, considered
shifted downfield upon complexation in the thiazole to be the result of interaction between an overtone of
(1, δ = 189.0 ppm) and thiazoline/2-mercapto-ethyl- the N–H bending absorption band at 1627 – 1641 cm−1
cyanamide (4, δ = 171.4 ppm) compounds but upfield (also in-plane NH2-scissoring) with the symmetric N–
for the benzazole compounds 2 (δ = 142.1 ppm) and 3 H stretching band, is also visible. Notably, N–H and
(δ = 156.9 ppm). In the instance of the phenyl carbon C–N stretching bands (1305 – 1312 cm−1) of the com-
atoms of the benzazole ligands some carbon atoms ap- plexes 1–3 are detected at lower wave lengths and the
pear slightly downfield and others slightly upfield. This C=N stretching bands (1531 – 1465 cm−1) at higher
observation is not unusual as the total chemical shift s wave lengths than in the free ligands suggesting elec-
(s = sparamagnetic + sdiamagnetic) in the 13C NMR spec- tron delocalization over the carbon nitrogen bonds to
trum reflects more than simply shielding and deshield- be more pronounced in the coordinated ligands. In
ing as in the 1H NMR spectrum [33]. In the spectra of the IR spectrum of 4, a C≡N stretching vibration at
1 – 4, four additional sets of doublets are detected in the 2218 cm−1 is clearly visible in addition to the N–H
region δ = 129 – 136 ppm and correspond to the char- bending absorption at 1663 cm−1, the C=N stretching
acteristic C–P coupling of the phenyl carbon atoms of (1618 cm−1) and the C–N aliphatic stretching vibra-
the [AuPPh3]+ moiety. Of these, the doublet at δ = tion at 1310 cm−1. The IR spectra of I–IV show the
129.0 – 130.4 ppm can be assigned to the C–P-coupled presence of 2-aminoazoles and C6F5 species but pro-
ipso-carbon atom, whilst the doublet at δ = 131 ppm vided no unambiguous characterization and are thus
is attributable to the C–P-coupled meta-carbon atom. neither reported nor analyzed here.
Resonances of the ortho- and para-carbon atoms are
Although FAB-MS analysis was attempted for all
observed as doublets in the regions δ = 134.5 – 136.3 complexes, this technique proved unsuccessful for 2,
and 132.8 – 134.3 ppm, respectively.
and the acquired spectra failed to deliver any diag-
In the 31P NMR spectra only one intense singlet nostic peaks other than for AuPPh3+. Nevertheless,
at δ = 30.6 ppm for 1, δ = 33.9 ppm for 3 and δ = m/z values that correspond to the cationic complexes
37.1 ppm for 4 is observed. These values appear some- are observed for 1, 3 and 4. In these spectra, sig-
what downfield compared to the chemical shift in the nals attributable to the homoleptic rearrangement prod-
precursor compound, Au(NO3)PPh3 (δ = 28.9 ppm).
uct [Au(PPh3)2]+ are also present at m/z = 720. The
Compound 5 has been fully characterized previ- molecular ion of 5 was observed but the spectra for I–
ously by Laguna and co-workers [22] thus only its IV did not show any unambiguous diagnostic signals
crystal structure is reported below. Small changes in that were consistent with the formation of Au(C6F5)(2-
chemical shift in the NMR spectra of I–IV made un- aminoazole) compounds or the products of crystalliza-
ambiguous characterization impossible. Although the tion.
C6F5 groups could for instance be observed, it was im-
possible to unequivocally determine whether the sim- Molecular structures
ple coordination compound or products of homoleptic
rearrangement had formed. The spectra are thus nei-
The crystal and molecular structures of compounds
ther reported nor discussed as single-crystal structure 1–5 and I–IV were determined by single-crystal X-
determinations had shown that in the instance of 5 the ray diffraction and are reported for the first time
coordination product had formed but homoleptic rear- (Figs. 1 – 9). The new compounds consist of: i) ei-
rangements had yielded I–IV.
ther a cationic [AuPPh3]+ unit (in 1–3) neutralized by
Solid-state ATR (attenuated total reflectance) FT- a nitrate anion or a AuC6F5 fragment (in 5) coordi-
IR spectra were recorded for the ligands and com- nated to the endocyclic imine nitrogen of a neutral 2-
plexes 1–4. All spectra show very broad bands of weak aminoazole ligand, ii) two [AuPPh3]+ units, both S-
intensity in the range 3054 – 3404 cm−1, assignable coordinated to 2-mercapto-ethyl-cyanamide (4), neu-
to N–H stretching vibrations. The primary amine tralized by a nitrate anion, or iii) [Au(C6F5)2]− neu-
N–H stretches (asymmetric and symmetric) appear tralized by various cations (I–IV), the products of ho-
as 2 bands in the region 3385 – 3054 cm−1 for 1– moleptic rearrangements. For complex 3, three differ-
3 whereas a secondary amine N–H stretch is ob- ent crystal structures were obtained, one without any
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
Fig. 3 (color online). Molecular structure of 3a with displace-
ment ellipsoids drawn at the 50% probability level. Selected
bond lengths (Å) and angles (deg): Au1–N1 2.057(5), Au1–
P11 2.234(2), N1–C2 1.325(7), N1–C5 1.389(7); N1–Au–
P11 167.3(1).
Fig. 1 (color online). Molecular structure of 1 with displace-
ment ellipsoids drawn at the 50% probability level. Selected
bond lengths (Å) and angles (deg): Au1–N1 2.071(3), Au1–
P8 2.245(1), N1–C2 1.322(4), N1–C5 1.404(4); N1–Au–P8
175.5(1).
Fig. 4 (color online). Representation of the dinuclear gold(I)
complex 4 (one of two crystallographically independent
complexes present in the asymmetric unit), with displace-
ment ellipsoids drawn at the 50% probability level; benzene
rings shown as sticks for clarity, intramolecular aurophilic
interactions shown as dotted line. Selected bond lengths (Å)
and angles (deg) with the corresponding values for the other
Fig. 2 (color online). Molecular structure of 2 in its CH2Cl2 complex: Au1···Au2 3.114(1)/Au3···Au4 3.090(1), Au1–
solvate with displacement ellipsoids drawn at the 50% prob- S1 2.320(3), Au2–S1 2.316(3), Au3–S44 2.325(2), Au4–
S44 2.324(3), Au1–P2 2.252(3), Au2–P7 2.258(3), Au3–
P69 2.258(2), Au4–P50 2.270(3); S1–Au1–P2 174.7(1), S1–
Au2–P7 173.5(1), S44–Au3–P69 175.2(1), S44–Au4–P50
178.5(1).
ability level. Selected bond lengths (Å) and angles (deg):
Au1–N1 2.059(3), Au1–P11 2.237(1), N1–C2 1.318(5), N1–
C5 1.401(5); N1–Au1–P11 178.3(1).
solvent molecules (3a) and two others (3b, 3c) that
contain solvent of crystallization. The crystallographic solvates 3b and 3c, with values for the correspond-
data for the solvates do not contribute much to the fur- ing angles of 177.0(2)◦ and 178.53(8)◦, respectively,
ther discussion, and their data are reported in the Sup- and with the nitrate ion located much further from
porting Information available online (see note at the the metal center. The P–Au–S angles [173.5(1)◦ and
end of the paper for availability).
174.7(1)◦] in the two complexes of 4, are slightly less
The geometry around Au(I) in the two-coordinated distorted and correspond well to the values reported for
Au(I) complexes approaches linearity with L1–Au–L2 similar compounds such as [S(Au2dppf)] (dppf = 1,10-
angles ranging from 167.3(1)◦ in 3a to 180.0(4)◦ in bis(diphenylphosphine)ferrocene), 173.8(1)◦ [34] and
II. The distortion of the N–Au–P angle in 3a is most [(AuPPh3)2(µ-SCH2CH2N–CN)], 170.1(1), 176.0(1)
probably caused by weak interactions of the Au(I) ion and 178.8(1)◦ [22].
with a nitrate ion (Au···O separations of 3.270(4) and
Aurophilic interactions are only present in the di-
3.306(5) Å). Such interactions are not present in the nuclear structure 4 (semi-supported intramolecular in-
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1079
Fig. 5 (color online). Molecular structure of 5 with displace-
ment ellipsoids drawn at the 50% probability level. Selected
bond lengths (Å) and angles (deg): Au1–N1 2.052(4), Au1–
C7 1.987(5), N1–C2 1.289(6), N1–C5 1.455(6); N1–Au1–
C7 177.5(2).
Fig. 8 (color online). Representation of III (one of two crys-
tallographically independent moieties present in the asym-
metric unit) with displacement ellipsoids drawn at the 50%
probability level; the missing part of the dimeric unit formed
during Li+ coordination to 2-aminobenzothiazole is shown
in wireframe style. Selected bond lengths (Å) and an-
gles (deg): Au1–C1 2.041(5), Au1–C7 2.039(6), Au2–C13
2.033(5), Au2–C19 2.032(5); C1–Au1–C7 178.6(2), C13–
Au1–C19 178.1(2).
Fig. 6 (color online). Representation of I with displacement
ellipsoids drawn at the 50% probability level. Selected bond
lengths (Å) and angles (deg): Au1–C1 2.044(3), Au1–C7
2.039(3); C1–Au1–C7 175.5(1).
Fig. 9 (color online). Representation of IV with displacement
ellipsoids drawn at the 50% probability level; disorder on
4-hydroxy-4-methylpentan-2-one is omitted for clarity. Se-
lected bond lengths (Å) and angles (deg): Au1–C1 2.048(4),
Au1–C7 2.043(4), Au2–C31 2.052(4), Au2–C19 2.050(4);
C1–Au1–C7 177.6(2), C13–Au2–C19 178.3(1).
Fig. 7 (color online). Representation of II with displace-
ment ellipsoids drawn at the 50% probability level, asym-
metric unit labeled. Selected bond lengths (Å) and angles
(deg): Au1–C1 2.044(6); C1–Au1–C1i 180.0(4), where (i):
1 −x+1, y, −z+1/2.
tion of intramolecular contacts with Au1···Au2 and
Au3···Au4 distances of 3.114(1) and 3.090(1) Å, re-
spectively. These values correspond well to those re-
ported for an analogous compound [S(Au2dppf)], Au–
S–Au 77.76(1)◦, Au...Au 2.882(1) Å [34]. There are
teractions) and the structures of I and IV (inter- no intermolecular aurophilic interactions in 4 but in-
molecular interactions). The sharp Au–S–Au angle, stead, delocalized Au...π(arene) interactions with dis-
with values 83.3(1)/84.4(1)◦ (two crystallographi- tances Au1···(C51–C56) 3.71 Å and Au3···(C8–C13)
cally independent molecules present in the asym- 3.81 Å [35] and weak hydrogen bonds such as N–
metric unit) in compound 4 facilitates the forma- H···O and C–H···O involving the nitrate ions govern
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
its solid-state packing. Intermolecular Au···S contacts, again, hydrogen bonds seem to prevail. In the crystal
Au(2)···S(44) 3.566(3) Å, Au(4)···S(1) 3.358(3) Å, structure, the neutral molecules are connected by weak
akin to those observed in Au(C6F5)(4-methylthiazole- hydrogen bonds, involving the amine hydrogen atoms
2-thione) (3.529(4) Å) [12] are worth mentioning but, (H6A, H6B) and phenyl fluorine atoms from three ad-
because of the rather long separation, it is hard to esti- jacent rings, forming supramolecular layers. These are
mate their contribution.
further supported by weak π-π stacking interactions
The intermolecular aurophilic bonding in I and IV between the phenyl rings (3.512(3) Å with a slippage
is facilitated by the nearly co-planar positioning of of 1.228 Å; (symmetry operation 1 − x, −y, −z) and
the two ring systems connected to the gold atoms C–H···π contacts involving the atoms C5–H5A.
with the angle between the planes of these rings
Substitution of the nitrate ligand in Au(NO3)PPh3
4.1◦ and 2.5◦/3.6◦, respectively. The anionic com- by 2-aminoazole ligands or 2-mercaptoethylcyan-
plexes linked by interactions between gold atoms form amide results in a significant elongation of the
supramolecular centrosymmetric dimers in I, with Au–P bond from 2.208(3) [38] to 2.245(1) Å in 1
Au···Au = 3.450(1) Å and aggregate into columns in to 2.237(1) Å in 2, 2.234(2) Å in 3 and 2.252(3)
IV with Au···Au contacts ranging from 3.489(1) to or 2.258(3) Å in 4. The Au–P bond lengths are
3.659(1) Å. A somewhat different situation transpired similar to those reported for compounds containing
in the crystal structure of III, where despite the co- imine ligands or S-donor ligands coordinated to
planarity of the rings (4.06/3.14◦), aurophilic contacts AuPPh3 moieties e. g. [AuPPh3(ylideneamine)][NO3]
are not present. However the hydrogen bond network is [ylideneamine
=
3,4-dimethyl-3H-thiazol-2-ylid-
abundant, involving many weak C–H···F interactions eneamine (2.229(1) Å), 3-methyl-3H-benzothiazol-
between perfluorinated benzene rings and the phenyl 2-ylideneamine (2.225(1) Å) or 1,3-dimethyl-1,3-di-
moieties from 2-aminobenzothiazole.
hydro-benzimidazol-2-ylideneamine
(2.231(1) Å)]
The preference for the formation of hydrogen bonds [14] as well as [Au{NH=C(NMe2)2(PPh3)}]-
over aurophilic associations may well be an en- [CF3SO3] and [Au(NH=CPh2)(PPh3)][BF4] (2.229(2)
thalpy effect. The energy of an aurophilic interaction and 2.234(2) Å, respectively) [39] or [S(Au2dppf)],
(29 – 33 kJ mol−1) has been estimated by NMR exper- 2.247(2) Å, [34] and [(AuPPh3)2(µ-SCH2CH2N-
iments to be of the same order of magnitude as a typ- CN)], 2.2757(11) Å [22].
ical hydrogen bond (20 – 30 kJ mol−1) [36]. Calcula-
The Au–N bond in the 2-aminoazole ligand in
tions by Laguna and co-workers [37] have shown that 1–3 and 5 seems to be relatively insensitive to
aurophilic interactions and hydrogen bonds are of com- changes in the ligand itself or to influences by lig-
parable strength, and that the competition of these two ands positioned trans thereto. Values vary between
motifs determines the structural arrangement in the 2.071(3) Å (in 1) and 2.040 (5) Å (in 3b). These
crystal structure of the compounds. The formation of distances are comparable to those reported for ex-
several hydrogen bonds per molecule in the crystal amples wherein the gold(I) atom is coordinated to
structures whereas the aurophilic bond per molecule an endocyclic N atom, [Au(C6F5)(4-methylthiazole)]
ratio would be 1 : 2, therefore results in a much greater 2.081(8) Å [12] and [Au(C6F5)(tetrazole)] (tetrazole
gain in energy compared to association via aurophilic = 1-methyltetrazole 2.044(3) Å and 1-benzyltetrazole
bonds.
2.049(4) Å) [13], as well as an exocyclic N
Intermolecular aurophilic interactions in the com- atom, [Au(C6F5)(ylideneamine)] and [AuPPh3(ylid-
pounds 1–4 are most likely prohibited by the steric de- eneamine)][NO3] [ylideneamine = 3,4-dimethyl-3H-
mands of the bulky ligands while the orientation of the thiazol-2-ylideneamine (2.031(4) and 2.036(4) Å),
two rings coordinated to gold in II and 5, with angles 3-methyl-3H-benzothiazol-2-ylideneamine (2.037(5)
between the planes of 66.1◦ and 82.0◦, respectively, and 2.028(6) Å) or 1,3-dimethyl-1,3-dihydro-benz-
could also prohibit the occurrence of short metal con- imidazol-2-ylideneamine (2.041(5) and 2.040(3) Å)]
tacts.
[14]. Similar Au–N distances have also been re-
It is striking that no intermolecular aurophilic inter- ported for the [Au(imine)(PPh3)]+ complexes [Au-
actions occur in the rather simple, complex 5 that is (NH=CPh2)(PPh3)][BF4] and [Au{NH=C(NMe2)2}-
derived from non-bulky ligands, especially considering (PPh3)][CF3SO3] [2.036(7) Å and 2.044(9) Å, respec-
its remarkable stability in the crystalline form. Once tively] [39].
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1081
The Au–S bonds in compound 4, Au1–S1 the 2-amino-4-methylthiazole molecule (distribu-
2.319(3) Å/Au2–S1 2.315(3) Å and Au3–S44 tion 50/50). The formally single C(sp2)–N(sp2)
2.325(3) Å/Au4–S44 2.324(3) Å, concur with exam- bond, N7–C11, has a length of 1.380(9) Å and the
ples in the literature e. g. [S(Au2dppf)], 2.300(2) Å, C=N double bond, N7–C8, a length of 1.317(8) Å;
[34], [(AuPPh3)2(µ-SCH2CH2N–CN)], 2.3031(10) Å, both of these values correspond to the respective
[22], and other gold compounds with S-donor ligands, values in the uncoordinated cationic 2-amino-4-
[Au(C6F5)(4-methylthiazole-2-thione)], 2.304(4) Å methylthiazolium (1.388(4) and 1.329(3) Å) [42]
[12], [Au(C6F5)(tht)], 2.317(3) and 2.320(3) Å, [40].
and uncoordinated 2-amino-4-methylthiazole in I
Finally, as far as bond lengths are concerned, (1.396(4) and 1.317(4) Å). The single and double
the Au–C bond lengths in I–IV ranging be- bond character is maintained, indicating little or no
tween 2.032(5) – 2.048(4) Å are very similar to those delocalization over these bonds.
in known gold(I) complexes e. g. [Au(C6F5)2][Au-
Hydrogen bonding involving the amine nitrogen
(pdma)2], (2.062(8) and 2.041(9) Å) [29] and in the re- atom and either included solvent molecules or the an-
actant [Au(C6F5)(tht)], (2.014(9) and 2.03(1) Å) [40], ions, together with C–H···π interactions (the latter ones
as well as in the S-coordinated [Au(C6F5)(4-methyl- not present in 3b) determine the solid-state packing
thiazole-2-thione)] (2.057(14) Å) [12], but signif- in the [(2-aminoazole)AuPPh3][NO3] compounds 1–3,
icantly longer than in the product Au(C6F5)(2- further supported by π-π stacking in 2, 3b and 3c.
aminoazole) (5) (1.985(7) Å) or other imine com-
As mentioned earlier the solid-state structures of I
plexes, Au(C6F5)ylideneamine [ylideneamine = 3,4- and IV are defined by a combination of aurophilic in-
dimethyl-3H-thiazol-2-ylideneamine (2.002(5) Å), 3- teractions between [Au(C6F5)2]− anions and hydro-
methyl-3H-benzothiazol-2-ylideneamine (2.009(5) Å) gen bonding involving the ligands of the Li-containing
or 1,3-dimethyl-1,3-dihydro-benzimidazol-2-ylidene- cations, free aminoazole, water and acetone molecules
amine (2.009(7) Å)] [14] or [(C6F5)Au(4-methylthi- (IV), as well as π-π stacking. II and III on the other
azole)] (2.00(1) Å) [12], suggesting that a rather sim- hand, are assembled mostly by a very elaborate net-
ilar electronic influence is exercised by C6F5 and S- work of hydrogen bonds, such as N–H···F and C–H···F
donor ligands and implying a larger trans influence for interactions between the anionic and cationic part of
these two ligands compared to imine ligands.
II, and N–H···F, N–H···O, O–H···S, O–H···N, O–H···F,
Crystallization times of several days under non-inert and C–H···F interactions between the molecules of III.
conditions allowed homoleptic rearrangements and the
formation of [(C6F5)2Au]− and various cations in the Conclusion
instances of I–IV. The Li-containing cations of I, III
The first molecular structures of [AuPPh3]+ and
and IV have a distorted tetrahedral geometry around
AuC6F5 units coordinated to 2-aminoazoles were
determined and confirmed metal coordination to
the softer endocyclic imine rather than the hard
exocyclic amine or endocyclic thioether, save in-
tricacies such as an unanticipated 2-aminoazoline
ring opening to yield a dinuclear gold(I) coordi-
nation compound, µ2-(2-mercapto-ethyl-cyanamide-
κ,S)bis(triphenylphosphine)gold(I) nitrate, with short
Au···Au contacts which stabilize hypercoordination of
the (triphenylphosphine)gold(I) moieties around the
anionic S center, or homoleptic rearrangement to gen-
erate [Au(C6F5)2]− anions that crystallized with vari-
ous cations.
the central Li atom, coordinated to the imine N atom of
2-amino-4-methylthiazole and three water molecules
in I, to the imine and amine N atoms of adjacent 2-
aminobenzothiazole moieties and two water molecules
in III, and bidentately to two O atoms of 4-hydroxy-
4-methylpentan-2-one (resulting from a symmetrical
aldol condensation of acetone [41]) and to two water
molecules in one cation and to four water molecules
in the second cation in IV. Lithium chloride that re-
mained from the synthesis of [(C6F5)Au(tht)] afforded
the formation of the Li+ cations.
For II, an imine atom of the 2-amino-4-
methylthiazole ligand has been protonated forming
the counter ion, with the said H atom shared with
a symmetry-related thiazole unit (symmetry opera-
tion: 1 − x, y, 3/2 − z). This entails that the proton
Experimental Section
Reactions were carried out under argon using stan-
sometimes does and sometimes does not occur on dard Schlenk and vacuum-line techniques. All solvents
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1082
L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1
were predried on ground KOH or molecular sieves and 3J = 12.2 Hz, m-Ph) 129.0 (d, J = 65.0 Hz, i-PPh3), 103.2
freshly distilled prior to use. Tetrahydrofuran (THF), n- (s, SCC) 17.8 (s, CH3). – 31P{1H} NMR ((CD3)2CO):
hexane, n-pentane and diethyl ether were distilled under δ = 30.6 (s, PPh3). – MS (EI): m/z (%) = 1409 (4), 1032
N2 from sodium benzophenone ketyl, acetone from 3 Å (4), 721 (28) [Au(PPh3)2]+, 571 (4) [M–NO3–2H]+, 458
molecular sieves, dichloromethane and methanol from CaH2 (100) [AuPPh3–H]+, 263 (7) [PPh3+H]+, 181 (100), 113
and ethanol from magnesium. 2-Amino-4-methylthiazole, (7) [C4H6N2S–H]+. – C22H21AuN5O3PS (635.44): calcd.
2-aminobenzothiazole and 2-aminothiazoline were pur- C 41.58, H 3.33, N 11.02; found C 41.22, H 3.21, N 10.98.
chased from Aldrich and 2-aminobenzimidazole, AgNO3
2-Aminobenzothiazole-κN3-(triphenylphosphine)gold(I)
nitrate (2)
and KH from Fluka. Literature methods were used
to prepare Au(C6F5)THT [27] from Au(Cl)THT [43],
Au(Cl)PPh3 [44] from HAuCl4 [45] and Au(NO3)PPh3 [25]
from Au(Cl)PPh3.
Complex 2 was prepared using the same protocol
as described above with 2-aminobenzothiazole (0.057 g,
0.38 mmol) and Au(NO3)3PPh3 (0.20 g, 0.38 mmol) in di-
ethyl ether (60 mL), yielding a colorless solid (0.19 g,
82%). Colorless crystals of 2 were obtained from a con-
centrated solution of the product in CH2Cl2 at −22◦C. The
unexpected complex, bis(2-aminobenzothiazole)silver(I) ni-
trate, [46] was obtained from a concentrated solution of the
product in acetone at −22◦C. The silver contaminants re-
sult from the treatment of [AuCl(PPh3)] with an excess of
AgNO3 to afford the starting material [AuNO3(PPh3)]. M.
p. 97 – 105◦C. – IR (selected bands): ν = 3304, 3170 and
3054 w (NHstretch), 1639 s (NH2 scissor), 1542 s (C=C),
1465 s (C=N), 1307 bs (C–N) cm−1. – 1H NMR (CD2Cl2):
δ = 8.34 (bs, 2H, NH2), 7.60 (m, 15H, PPh3), 7.38 and
7.25 (m, 4H, CH). – 13C NMR (CD2Cl2): δ = 172.7
(s, NCS), 142.1 (s, NCCHCH), 134.5 (d, 2J = 13.3 Hz, o-
Ph), 132.8 (bs, p-Ph), 130.0 (d, 3J = 11.0 Hz, m-Ph) 129.8
(d, 1J = 67.4 Hz, i-PPh3), 126.9 (s, NCCHCH) 125.2 (s,
NCCHCH), 124.0 (s, SCCHCH), 122.3 (s, SCCHCH), 116.7
(s, SCCHCH). – MS (EI): m/z (%) = 1409 (3), 1032 (4),
721 (28) [Au(PPh3)2]+, 458 (100) [AuPPh3–H]+, 263 (7)
[PPh3+H]+, 181 (44). – C25H21AuN3O3PS (671.47): calcd.
C 44.72, H 3.15, N 6.26; found C 45.02, H 3.10, N 6.20.
Melting points were determined on a Stuart SMP3 appa-
ratus and are uncorrected. Mass spectra were recorded on
an AMD 604 (EI, 70 eV) instrument. NMR spectra were
recorded on a Varian 300/400 FT or INOVA 600 MHz
spectrometer (1H NMR at 300/400/600 MHz, 13C NMR
at 75/100/150 MHz, and 31P NMR at 121/161 MHz) with
the chemical shifts reported (in ppm) relative to TMS with
the solvent resonance as internal reference or 85% H3PO4
(
31P) as external reference. Infrared spectra were recorded on
a Thermo Nicolet Avatar 330FT-IR instrument with a Smart
OMNI ATR (attenuated total reflectance, Zn-Se) sampler. El-
emental analysis was carried out at the School of Chemistry,
University of the Witwatersrand. Prior to elemental analysis,
products were evacuated under high vacuum for 10 h.
2-Amino-4-methylthiazole-κN3-(triphenylphosphine)gold(I)
nitrate (1)
The ligand, 2-amino-4-methylthiazole (0.063 g, 0.55
mmol), was added to an equal molar amount (0.29 g,
0.55 mmol) of Au(NO3)PPh3 in a diethyl ether suspension
(60 mL). The resulting colorless snowflake-like suspension
was stirred for 1.5 h at room temperature. The formation of
the imine coordination complex was accompanied by the for-
mation of a new suspension with a notably different texture
and off-white color. The mixture was then stripped of solvent
in vacuo to yield a colorless solid. The solid was extracted
2-Aminobenzimidazole-κN3-(triphenylphosphine)gold(I)
nitrate (3)
The same protocol as described above was fol-
with diethyl ether (50 mL). The solution containing the de- lowed with Au(NO3)PPh3 (0.090 g, 0.18 mmol) and 2-
sired gold(I) complex was filtered through MgSO4 and the aminobenzimidazole (0.023 g, 0.18 mmol) to obtain a pure
filtrate stripped of solvent in vacuo. The oily yellow residue colorless solid (0.103 g, 98%). Single crystals in the form
was subsequently washed with n-pentane (30 mL) to yield of colorless needles of 3a were obtained from slow dif-
the yellow microcrystalline material (0.30 g, 94%). Single fusion of n-pentane into an acetone solution of the com-
crystals were obtained from a concentrated solution of the pound at −22◦C. Crystals of 3b and 3c were obtained from
product in (CD3)2CO in an NMR tube, producing colorless concentrated solution of the product in methanol in NMR
needles at −22◦C. M. p. 94 – 97◦C. – IR (selected bands): tubes. M. p. 114 – 116◦C. – IR (selected bands): ν = 3385,
ν = 3309, 3172 and 3119 w (NHstretch), 1627 s (NH2 scissor), 3272 and 3123 w (NH)stretch 1641 m (NH)scissor, 1542 m
1583 s (C=C), 1531 s (C=N), 1305 bs (C–N) cm−1. – H (C=C), 1528 m (C=N), 1312 s (C–N) cm−1. – 1H NMR
1
NMR ((CD3)2CO): δ = 8.46 (bs, 2H, NH2), 7.68 (m, 15H, ((CD3)2CO): δ = 7.71 (m, 15H, PPh3), 7.45 (dd, 3J =
PPh3), 6.43 (bs, 1H, SCH), 2.40 (s, 3H, CH3). – 13C NMR 5.9 Hz, 4J = 3.2 Hz, 2H, NCCH), 7.12 (dd, 2H, 3J = 5.9 Hz,
((CD3)2CO): δ = 189.0 (s, NCS), 155.5 (bs, NCC), 136.3 (d, 4J = 2.9 Hz, NCCH(CH)2), 3.19 (bs, 2H, NH2), NH not
2J = 13.2 Hz, o-Ph), 133.4 (d, J = 2.8 Hz, p-Ph), 130.6 (d, observed. – 13C NMR ((CD3)2CO): δ = 156.9 (s, NCN),
4
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
1083
136.2 (d, 2J = 13.9 Hz, o-Ph), 134.3 (d, 4J = 2.2 Hz, p- 1.0 mmol) in diethyl ether (50 mL). The resulting yellow sus-
3
1
Ph), 131.5 (d, J = 11.7 Hz, m-Ph) 130.2 (d, J = 63.8 Hz, pension was stirred for 2 h. Upon evaporation to dryness
i-PPh3), 133.7 (s, NCCHCH), 123.8 (s, NCCHCH), 113.9 in vacuo colorless microcrystalline material was obtained.
(s, NCCHCH). – 31P NMR ((CD3)2CO): δ = 33.9 (s, The solid was dissolved in diethyl ether (60 mL) and fil-
PPh3). – MS (EI): m/z (%) = 721 (5) [Au(PPh3)2]+, 592 tered through MgSO4. With subsequent drying of the filtrate
(49) [M–NO3]+, 459 (44) [AuPPh3]+, 181 (26), 134 (52) in vacuo a colorless product (0.31 g) was obtained. Color-
[C7H8N3]+. C25H22AuN4O3P (654.42): calcd. C 45.87, H less needles suitable for X-ray diffraction were obtained from
3.39, N 8.56; found C 45.63, H 3.31, N 8.44.
a concentrated solution of I in CD2Cl2 in an NMR tube main-
tained at −22◦C for 2 days.
µ2-(2-Mercapto-ethyl-cyanamide-κ,S)bis(triphenyl-
phosphine)gold(I) nitrate (4)
2-Amino-4-methylthiazolium bis(pentafluorophenyl)-
aurate(–I) (II)
Compound 4 was obtained using the experimental pro-
cedure as described for 1 with Au(NO3)PPh3 (0.14 g,
0.26 mmol) and 2-aminothiazoline (0.030 g, 0.26 mmol),
yielding a colorless solid as a product (0.10 g, 70%). Crys-
tals suitable for X-ray diffraction were obtained from a con-
centrated perdeuterated acetone solution of the product in
an NMR tube maintained at −22◦C. M. p. 83 – 87◦C. – IR
(selected bands): ν = 3295 w (NH)stretch, 2218 w (C≡N),
1663 m (NH)bend, 1638 m (C=C), 1618 m (C=N), 1310
s (C–N) cm−1. – 1H NMR ((CD3)2CO): = δ 7.62 (m,
30H, PPh3), 4.03 (dd, 2H, 3J = 7.5 Hz, NCH2), 3.55 (dd,
2H, 3J = 7.5 Hz, SCH2), 2.83 (bs, 1H, NH). – 13C NMR
((CD3)2CO): δ = 136.1 (d, 2J = 13.7 Hz, o-Ph), 134.2 (d,
4J = 2.6 Hz, p-Ph), 131.5 (d, 3J = 12.0 Hz, m-Ph) 130.4 (d,
1J = 59.7 Hz, i-PPh3), 171.4 (s, NC), 52.9 (s, NCH2), 35.0
(s, SCH2). – 31P NMR ((CD3)2CO): δ = 37.1 (s, PPh3). –
MS (EI): m/z(%) = 1409 (6), 1019 (45) [M+–NO3+H]+,
721 (65) [Au(PPh3)2]+, 561 (31) [M–NO3–AuPPh3+H]+,
459 (100) [AuPPh3]+, 280 (15) [C3H5N2S–NH2–H+Au]+.
– C39H35Au2N3O3P2S (1081.68): calcd. C 43.31, H 3.26, N
3.88; found C 44.01, H 3.20, N 3.63.
The same protocol as described for the preparation
of I was used with 2-amino-4-methylthiazole (0.063 g,
0.5 mmol) and Au(C6F5)THT (0.25 g, 0.55 mmol). The re-
sulting mixture was then stirred for 1.5 h and evaporated
to dryness in vacuo. The oily residue was washed with
three 10 mL portions of pentane and dried in vacuo to yield
a colorless solid. The product was dissolved in diethyl ether
(100 mL). After the addition of a second mol equivalent of
Au(C6F5)THT (0.25 g, 0.55 mmol) to the above solution it
was again stirred for 1.5 h and dried in vacuo. The colorless
product was dissolved in diethyl ether (50 mL) and filtered
through MgSO4. The resulting solution was evaporated to
dryness yielding a colorless solid (0.23 g). Crystals suitable
for X-ray diffraction were obtained from a concentrated so-
lution of the product in CD2Cl2 at −22◦C within 4 d.
(2-Aminobenzothiazole-κN3)diaquolithium bis(penta-
fluorophenyl)aurate(–I) (III)
The same experimental procedure as described for com-
pound I was used with 2-aminobenzothiazole (0.11 g,
0.49 mmol) and Au(C6F5)THT (0.22 g, 0.49 mmol), yield-
ing a colorless solid (0.090 g). Colorless needles suitable for
X-ray diffraction were obtained from a concentrated solution
of III in acetone in an NMR tube maintained at −22◦C for
several days.
2-Aminothiazoline-κN3-(pentafluorophenyl)gold(I) (5)
Complex 5 was prepared by adding 2-aminothiazoline
(0.056 g, 0.55 mmol) to a solution of Au(C6F5)THT (0.25 g,
0.55 mmol) in diethyl ether (70 mL) and stirring for 2.5 h.
The colorless suspension was then evaporated to dryness
in vacuo. The colorless residue was extracted with di-
ethyl ether (40 mL) and filtered through MgSO4. The fil-
trate was reduced in vacuo to yield an oily product. The
oily product was washed with pentane (10 mL) and dried in
vacuo. The desired colorless product (0.19 g, 85%) was iso-
lated. Single crystals of 5 were obtained as colorless blocks
from a concentrated solution of the product in deuterated
dichloromethane at −22◦C. M. p. 97 – 105◦C [22].
η2-(4-Hydroxy-4-methylpentan-2-one-κO2:κO4)diaquo-
lithium bis(pentafluorophenyl)aurate(–I) (IV)
The same protocol as described above for compound
I was used with 2-amino-1-methylbenzimidazole (0.14 g,
0.93 mmol) and Au(C6F5)(THT) (0.42 g, 0.93 mmol). Af-
ter evaporation, a beige oily residue was obtained. The
oily residue was rinsed with pentane to yield a beige solid
(0.56 g). Colorless blocks were obtained by the slow diffu-
sion of n-pentane into a concentrated solution of II in acetone
maintained at −22◦C for a week.
(2-Amino-4-methylthiazole-κN3)triaquolithium
bis(pentafluorophenyl)aurate(–I) (I)
X-Ray diffraction experiments
The ligand, 2-amino-4-methylthiazole (0.199 g, 1.6
Crystal data collection and refinement details for com-
mmol), was added to a solution of [Au(C6F5)(tht)] (0.468 g, pounds 1–4 and 5, I–IV are summarized in Tables 1
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1084
L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
Table 1. Crystal structure data for 1–4.
1
2
3a
4
Emperical formula
C22H21AuN2PS
·NO3· x solvent
635.41
C25H21AuN2PS
C25H22AuN3P·NO3
C39H35Au2N2P2S·NO3
·NO3 ·CH2Cl2
Mr
756.37
654.40
block
1081.63
block
Crystal shape
Crystal size, mm3
Temperature, K
Crystal system
Space group
a, Å
needle
needle
0.09 × 0.06 × 0.04
0.15 × 0.08 × 0.04
0.11 × 0.06 × 0.05
0.13 × 0.09 × 0.06
100(2)
100(2)
100(2)
100(2)
triclinic
P1
triclinic
P1
monoclinic
P21/c
14.3047(12)
9.5301(8)
18.8851(19)
90
116.269(1)
90
2308.6(4)
4
1.88
6.5
1272
−13 ≤ h ≤ 17
−11 ≤ k ≤ 11
−23 ≤ l ≤ 22
0.6252
13 222
4706
monoclinic
P21
10.4002(12)
26.355(3)
14.1318(16)
90
106.677(2)
90
3710.6(7)
4
1.94
8.1
2072
−11 ≤ h ≤ 12
−33 ≤ k ≤ 19
−17 ≤ l ≤ 16
0.6271
21 882
13 102
9.510(3)
11.684(4)
12.802(4)
82.913(5)
76.729(5)
73.875(5)
1327.3(8)
2
1.59
5.7
616
−12 ≤ h ≤ 11
−14 ≤ k ≤ 14
−16 ≤ l ≤ 16
0.6315
14 025
5501
11.052(3)
11.107(3)
11.719(3)
105.692(4)
97.679(4)
90.049(4)
1371.5(5)
2
1.83
5.7
736
−13 ≤ h ≤ 13
−13 ≤ k ≤ 13
−14 ≤ l ≤ 14
0.6265
14 750
5576
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
Dcalcd., g cm−3
µ(MoKα), cm−1
F(000), e
hkl range
((sinθ)/λ)max, Å−1
Refl. measured
Refl. unique
Rint
0.0236
0.0335
0.0431
0.0357
Param. refined
R(F)/wR(F2)a,b
[I > 2 σ(I)]
289
342
313
921
0.0255/0.0637
0.0279/0.0628
0.0380/0.0801
0.0409/0.0755
R(F)/wR(F2)a,b
(all refls.)
0.0275/0.0646
0.0319/0.0645
0.0494/0.0847
0.0493/0.0786
GoF (F2)c
∆ρfin (max/min), e Å−3
1.054
2.70/−1.17
1.043
1.12/−0.75
1.048
2.28/−1.39
1.025
1.83/−1.09
a R(F) = Σ||Fo|−|F ||/Σ|Fo|; b wR(F2) = [Σw(Fo2 −F2)2/Σw(Fo2)2]1/2, w = [σ2(Fo2)+(AP)2 +BP]−1, where P = (Max(Fo2,0)+2F2)/3;
c
c
c
c
GoF = [Σw(Fo2 −F2)2/(nobs −nparam)]1/2
.
c
and 2, respectively. The data were collected on a Bruker were placed on some of the corresponding bond lengths
SMART Apex CCD diffractometer equipped with graphite- – especially in the case of water molecules. The program
monochromatized MoKα radiation (λ = 0.71073 Å) [47]. MERCURY [53] was used to prepare molecular graphic
The cell refinement and the data reduction were performed images.
with the software package Bruker SAINT+ [47], and the em-
In the structure of 1, the solvent molecules could not
pirical absorption corrections were performed with SAD- be assigned because of diffuse electron density. Therefore,
ABS [48]. All the structures were solved using Direct the electron density was subtracted, and the SQUEEZE in-
Methods with SHELXS-97 [49, 50] and refined by full- struction of PLATON was applied [54, 55]. As the crystals
matrix least-squares methods based on F2 with SHELXL- were grown from a mixture of solvents, it was difficult to
97 [51, 52]. All non-hydrogen atoms were refined anisotrop- make any assumptions regarding the exact nature of these
ically. Hydrogen atoms, excluding some coming from -NH, molecules. Consequently, the tabulated relative molecular
-OH, were positioned geometrically with C–H 0.95 (aro- mass Mr, F(000), and absorption coefficient (Table 1) are not
matic), 0.98 (methyl) and 0.99 Å (methylene); N–H 0.88 Å correct since solvent molecules were not taken into account
(amine, aromatic) and refined as riding, with Uiso(H) = 1.2 in these calculations.
Ueq (C, N) and 1.5 Ueq (methyl C). The remaining ones
The crystal of 4 was found to be a racemic twin, with
were located in a difference map and refined. Restraints a contribution of the second component of 37%. One of the
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L.-A. de Jongh et al. · Imine-coordinated 2-Aminoazole Complexes of Au(I)
Table 2. Crystal structure data for 5 and I–IV.
1085
5
I
II
III
IV
Emperical formula
C9H6AuF5N2S
C12AuF10·C4H12LiN2 C12AuF10·C8H13 C14H20Li2N4O4S2 2(C12AuF10) C6H16LiO4
O3S·2(C4H6N2S)
N4S2
·2(C12AuF10
)
·H8LiO4·C3H6O·H2O
·2(C7H6N2S)
Mr
466.18
block
934.58
block
760.43
needle
1748.91
1376.40
block
Crystal shape
Crystal size, mm3
Temperature, K
Crystal system
Space group
a, Å
block
0.09 × 0.06 × 0.04 0.22 × 0.20 × 0.02
0.24 × 0.11 × 0.03 0.27 × 0.23 × 0.15 0.27 × 0.20 × 0.09
100(2)
100(2)
100(2)
100(2)
100(2)
monoclinic
P21/c
10.164(3)
9.783(3)
11.455(3)
90
105.455(4)
90
1097.9(5)
4
2.82
13.6
856
−12 ≤ h ≤ 10
−12 ≤ k ≤ 8
−14 ≤ l ≤ 13
0.6263
6207
2253
triclinic
P1
monoclinic
C2/c
triclinic
P1
triclinic
P1
8.2753(8)
13.8941(13)
15.6171(15)
115.099(1)
90.244(2)
96.227(2)
1614.0(3)
2
24.890(6)
7.862(2)
12.595(3)
90
110.796(4)
90
9.3133(12)
11.8829(16)
25.464(3)
103.348(2)
96.384(2)
90.080(2)
2723.9(6)
2
12.9165(15)
13.7196(16)
15.2175(18)
64.202(2)
66.747(2)
62.689(2)
2092.1(4)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
2304(1)
4
Z
Dcalcd., g cm−3
µ(MoKα), cm−1
F(000), e
hkl range
1.92
2.19
2.13
2.19
4.8
6.7
5.7
7.1
908
1448
1680
1308
−10 ≤ h ≤ 10
−17 ≤ k ≤ 17
−19 ≤ l ≤ 19
0.6271
−16 ≤ h ≤ 32
−9 ≤ k ≤ 10
−16 ≤ l ≤ 16
0.6677
7091
−11 ≤ h ≤ 10
−15 ≤ k ≤ 15
−32 ≤ l ≤ 33
0.6638
−16 ≤ h ≤ 16
−17 ≤ k ≤ 17
−19 ≤ l ≤ 19
0.6269
((sinθ)/λ)max, Å−1
Refl. measured
Refl. unique
Rint
17 559
17 360
22 673
6643
2716
12 102
8534
0.0309
163
0.0233/0.0564
0.0280
460
0.0369
169
0.0255
877
0.0269
683
Param. refined
R(F)/wR(F2)a,b
[I > 2 σ(I)]
R(F)/wR(F2)a,b
(all refsl.)
0.0263/0.0587
0.0367/0.0879
0.0414/0.1010
0.0233/0.0548
0.0252/0.0574
0.0299/0.0601
0.0412/0.0899
0.0491/0.1050
0.0280/0.0568
GoF (F2)a
1.051
1.062
1.072
1.080
1.030
∆ρfin (max/min), e Å−3 1.63/−0.59
1.66/−0.89
1.96/−0.85
2.82/−1.19
1.16/−0.93
a
For definition of R values and GoF, as well as information on the weighting scheme applied, see Table 1.
nitrate ions (N92) was found to be disordered over two po- Supporting information
sitions, with refined site occupancies of 0.67(2) : 0.33(2).
Supplementary NMR data for the ligands and crystallo-
graphic reports for the solvates 3b and 3c can be found
as Supporting Information (4 pages) available online (DOI:
10.5560/ZNB.2014-4187).
As a result, bond length restraints were applied to this
anion.
In the structure of IV, 4-hydroxy-4-methylpentan-2-one
was found to be disordered and modeled into two orienta-
tions with refined site occupancies of 0.75(1) : 0.25(1).
CCDC 1018046 – 1018056 contain the supplementary
crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgement
We thank the NRF (National Research Foundation,
South Africa) and the Alexander von Humboldt foundation
(H. G. R.) for financial support.
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