Azido, triazolyl, and alkynyl complexes of gold(I): Syntheses, structures, and ligand effects

Article abstract of DOI:10.1021/ic4014569

Gold(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)gold(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (N-heterocyclic carbene)gold(I) azides and two new gold(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be more than a simple matter of ligand donicity.

Full text of DOI:10.1021/ic4014569

Article
pubs.acs.org/IC
Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses,
Structures, and Ligand Effects
Thomas J. Robilotto, Nihal Deligonul, James B. Updegraff, III, and Thomas G. Gray*
Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States
S
* Supporting Information
ABSTRACT: Gold(I) triazolyl complexes are prepared in [3 + 2]
cycloaddition reactions of (tertiary phosphine)gold(I) azides with
terminal alkynes. Seven such triazolyl complexes, not previously
prepared, are described. Reducible functional groups are accommo-
dated. In addition, two new (N-heterocyclic carbene)gold(I) azides
and two new gold(I) alkynyls are described. Eight complexes are
crystallographically authenticated; aurophilic interactions appear in one
structure only. The packing diagrams of gold(I) triazolyls all show
intermolecular hydrogen bonding between N-1 of one molecule and
N-3 of a neighbor. This hydrogen bonding permeates the crystal
lattice. Density-functional theory calculations of (triphenylphosphine)-
gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but
the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be
more than a simple matter of ligand donicity.
of gold(I) alkynyls and nonhydrolyzable azides proceeds in the
presence of added copper. The solvate [Cu(MeCN)4]+ is
effective,71 but CuI or copper turnings are operationally
superior.72 Reactions done with copper turnings proceed in
water/alcohol mixtures. Control experiments tell against a gold-
catalyzed pathway, and no conversion was observed without
added copper. Metzler-Nolte and collaborators have prepared
(triazolato)gold(I) bioconjugates that surmount cisplatin
resistance in a p53 mutant cancer cell line.73 Veige and co-
workers74 report a double-gold click reaction where
(triphenylphosphine)gold(I) azide and a (triphenylphos-
phine)-gold(I) alkynyl join to form a diaurated triazole with
1,5-regioselectivity. Reports from Hashmi and collaborators75,76
describe cycloaddition reactions between gold(I) isonitriles and
azomethine ylides that beget abnormal N-heterocyclic carbene
complexes. (Tricyclohexylphosphine)gold(I) azide reacts in-
stantly and exothermically with NO+ to yield free (phosphine)-
INTRODUCTION
■
The coinage metals in their +I oxidation states are often two-
coordinate, notably gold.1 The two-coordinate gold(I) frag-
ment has re-emerged, mainly in organic synthesis,2−11 but also
for applications in medicine,12−15 luminescence,16−23 sensing,24
and energy storage.25 Gold(I) is metastable: the free ion
disproportionates to gold(III) and two equivalents of the
element in water.26 Stability improves with a strong σ-donor
ligand. (Isonitrile)gold(I) complexes are numerous,27−34 but
(organophosphine) and (N-heterocyclic carbene)gold(I) com-
plexes dominate.35−53 The resulting gold(I) compounds are
frequently stable to air, water, and light, but are not necessarily
monomeric.54−56 Many (phosphine)- and (N-heterocyclic
carbene)gold(I) complexes offer expedient combinations of
crystallinity and solubility. These entities have far-flung catalytic
applications.57,58
Gold-click chemistry seeks reliable gold-element bond-
forming reactions that adhere to the standards of organic
click chemistry.59 Reactions should be operationally simple,
high-yielding, and generate harmless byproducts, if any. Efforts
in gold chemistry exploit the isolobality60−62 of LAu+ and H+,
where L is a σ-donor. The leading click reaction is certainly the
copper-catalyzed azide−alkyne cycloaddition.63−66 Several
reactions of gold species are similar, an example being the
reaction of gold(I) azides with isonitriles to afford C-tetrazolato
complexes.67 In 2007, work in this laboratory demonstrated [3
+ 2] cycloaddition of (organophosphine)gold(I) azides to
terminal alkynes.68 This reaction functionalizes the termini of
poly(benzyl ether) dendrimers with gold(I).69 Also shown68
was the related, formal addition of HN3 to gold(I) alkynyls;70
the azide source is Me3SiN3 in alcoholic media. Cycloaddition
gold(I) cations without need of silver, thallium(I), or Bronsted
̈
acids, Scheme 1. We suggest that this redox-initiated synthesis
of Cy3PAu+ ions is itself a click reaction. The resulting cations
have been arrested with octaethylporphyrin to yield a genuine
Scheme 1. Silver-, Thallium-, and Bronsted-Acid Free
̈
Synthesis of a (Phosphine)gold(I) Cation from the
Corresponding Azide
Received: June 8, 2013
© XXXX American Chemical Society
A
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gold(I) porphyrin, with two gold centers in a sitting-atop
position.77 The combined result is the linking of LAuI
fragments to organic carriers to produce tags, prodrugs, and
precatalysts.
Scheme 2
Small N-heterocyclic carbenes have proven their value as
tight-binding ligands. Youngs and co-workers have developed a
variety of NHC-bound stabilizers of silver(I).78−83 A number
show appreciable antimicrobial activity.84 Among these are 1,3-
imidazole-2-ylidene and its 4,5-dichloro analogue (Cl2NHC).
Both gold(I) and silver(I) bis(carbene) complexes have been
assayed against malignant human cell lines.85,86 When assayed
against a non-small cell lung cancer cell line, chloro-substituted
complexes showed weaker action (higher inhibitory constants,
IC50) than nonhalogenated analogues. The ligand 1,3-
respectively, Scheme 3. For solubility reasons, the products
4−6 were repeatedly washed with benzene instead of toluene.
All reactions afforded clean triazolyl products after stirring for
72 h at room temperature. Reaction progress can be monitored
by 31P NMR. The 31P{1H} resonance of the starting material of
(triphenylphosphine)gold(I) azide falls at δ 31.1 ppm in
DMSO-d6. During reaction, there is a steady decline of the
starting material resonance with growth of a peak at ∼44−45
ppm for the corresponding triazolyls. Products 3−7 are white
or off-white, air- and moisture-stable solids.
(Tricyclohexylphosphine)gold(I) complex 7, Scheme 4, is
analogous to 5. The trialkylphosphine ligand enhances the
solubility of the organometallic product compared to 5.
Precipitation occurred only on cooling to −78 °C. A white
powder formed, and the supernatant was removed by
decanting. The product was subsequently washed with cold
pentane to afford clean 7 in 52% yield. Compound 7 is both air-
and water-stable.
i
diisopropylimidazol-2-ylidene (Pr2 NHC) is larger and lip-
ophilic. It is similar to the 4,5-dimethyl analogue
i
(Pr2 NHCMe2) used by Holm and co-workers to stabilize
cubane-type Co4 S4 clusters8 7 and all-ferrous
88
i
i
[Fe4S4(Pr2 NHCMe2)4] and [Fe8S8(Pr2 NHCMe2)6]. In
these assemblies, the carbene ligates tetrahedral metal centers
at the vertices of clusters. The bis(carbene) complex
i
[(Pr2 NHC)2Au]Cl has been evaluated in matched tumorigenic
and nontumorigenic liver progenitor cell lines. Programmed
cell death occurs selectively in the tumorigenic line, and
evidence was presented for a mitochondrial mechanism of
cytotoxicity.89 The ligand Pr2 NHC has been bound to gold(I)
i
peracetylthioglucose in place of triethylphosphine,90 to produce
a carbene analogue of auranofin.91,92 The chloro complex
i
(Pr2 NHC)AuCl has been examined as a precursor to gold
nanoparticles.93
Complexes Bearing Coumarin Substituents. Coumar-
ins are naturally occurring compounds first isolated from bean
plants in the early 1800s, with many other varieties being found
in a range of plant sources.95 Complexes bearing coumarin
moieties were pursued, in part to probe the functional group
compatibility of cycloadditions within the coordination sphere
of gold. The heterobicyclic benzo-α-pyrone core, although not
delicate, is subject to attack by nucleophiles and reductants.
Coumarins have biological applications as antibacterials,
anticarcinogenics, and analgesics;96 they are also anti-
inflammatory drugs, antioxidants, and inhibitors of HIV
protease.97 Their photophysical properties make coumarins
attractive as fluorescent tags and laser dyes.98
This work reports the synthesis of gold-click products and
pertinent reagents. Our original disclosure68 focused on
triphenylphosphine complexes; here, complexes of tricyclohex-
i
ylphosphine and the carbene ligands Cl2NHC and Pr2 NHC are
considered. Triazolyl products are bound through carbon,
whereas reactants have gold−nitrogen bonds. Reactions
proceed under mild conditions to yield air- and moisture-
stable products. Some 11 new compounds are described, of
which 8 are crystallographically characterized.
Reaction of 1 with 7-(propargyloxy)coumarin in toluene
affords the derivatized complex, 9, Scheme 4. Complex 9
readily precipitated and was washed with benzene to afford an
off-white solid in 91% yield. The product persists in moist air
over an extended period. Table 1 summarizes triazolyl
1
RESULTS AND DISCUSSION
products, reaction times, and isolated yields. The N-H H
■
(Azido)gold(I) Complexes. Syntheses of (azido)gold(I)
complexes are similar to our earlier preparation of
(tricyclohexylphosphine)gold(I) azide,76,94 Scheme 2. Benzene
solutions of the (carbene)gold(I) acetate are stirred with
trimethylsilyl azide for 16 h, and azido complex 1 or 2 is
isolated upon removal of solvent.
NMR resonance of 9 appears at 14.05 ppm in DMSO-d6.
Gold(I) alkynyls bearing coumarins were also synthesized.
Reactions proceeded as in Scheme 5. Interaction of Cy3PAuCl
or (Cl2NHC)AuCl with a 7-substituted alkynylcoumarin and
sodium tert-butoxide in 2-propanol furnished (alkynyl)gold
species 10 and 11 in 72 and 85% isolated yields, respectively.
Crystal Structures. Eight complexes have been charac-
terized crystallographically. All complexes show the two-
coordinate, nearly linear geometry that is characteristic of
gold(I). Table 2 sets out metric parameters involving gold. The
Supporting Information summarizes crystallographic details.
The structure of azide 1 appears as Figure 1. This compound
crystallizes in the centrosymmetric space group Pnma; the
carbene heterocycle, gold, and azide ligand rest on a mirror
(Triazolyl)gold(I) Complexes. Treatment of a toluene
suspension of (triphenylphosphine)gold(I) azide with 1-
heptyne affords Ph3PAu(n-pentyltriazole) complex 3. The
product formed as a precipitate that was washed repeatedly
with toluene and recovered in 61% yield. In parallel reactions,
the terminal alkynes cyclohexylacetylene, 1-ethynyl-4-methox-
ybenzene, and 3-aminophenylacetylene formed triazolyl com-
plexes 4−6 in isolated yields of 67%, 59%, and 54%,
B
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Scheme 3
Scheme 4
plane normal to the crystallographic b-axis. Neighboring
gold(I) centers are in aurophilic contact at 3.40 Å apart. The
gold-carbene carbon distance is similar to that (1.993(19) Å) of
(Cl2NHC)AuCl,86 and to that in 2. A thermal ellipsoid
representation of 2 appears as Figure S1, Supporting
Information. It is similar to 1, even to the extent that 1 and
2 share the same space group. Compound 2 resides on a
crystallographic mirror plane, except for the isopropyl methyls.
Distances between gold and the bound azido nitrogens are
2.020(6) Å in 1 and 2.033(7) Å in 2, but the difference is not
statistically significant.99 The closest approach of gold centers in
2 exceeds 3.8 Å, and the crystal structure does not show
aurophilic interactions.
positions. Interatomic distances and angles involving gold,
Table 2, are normal.68−72 Complex 3 is representative. Its
asymmetric unit, which contains two crystallographically
independent molecules, appears as Figure 2a. Bond lengths to
gold do not significantly differ between independent copies of
the same molecule. A network of hydrogen bonds threads
through the structure: N-1 and N-3 on an adjacent molecule
are within hydrogen-bonding distance. The five triazolyl
structures reported here all show this pattern of intermolecular
hydrogen bonding. Figure 2b depicts the packing diagram of 3
viewed along a; hydrogen bonds are indicated.
Figure 3 depicts the structure of alkynyl 11. Diffraction-
quality crystals of 11 grew in a saturated tetrahydrofuran
(THF) solution layered with n-pentane, to which a drop (∼20
μL) of benzene was added. Benzene of crystallization occurs in
the asymmetric unit. Four molecules of 11 occupy the unit cell,
The essential structural features of triazolyls 3−7 are similar.
All display linear gold(I) without aurophilic or π-stacking
interactions. In no unit cell do molecules occupy special
C
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Table 1. Synthesis of (Triazolyl)gold(I) Complexes
Scheme 5
but they are not crystallographically independent. There are no
obvious intermolecular interactions. The nearest gold−gold
approach exceeds 7 Å, despite the small N-heterocyclic carbene
ligand. Geometric parameters involving gold, Table 2, are
unexceptional,70 as are those of the coumarin.72
alkynyls can all embed gold in organic constructs. The
electronic consequences of alkynyl vs triazolyl binding are
immediate questions. We have performed density-functional
theory computations on 3, which is representative, and its
corresponding alkynyl. Optimized metrics agree well with those
of the two crystallographic modifications. The gold−phospho-
rus bond length trans to the triazolyl is computed to be longer
(0.015 Å) than that opposite the alkynyl. Partial Kohn−Sham
Calculations. Gold(I) alkynyls100−103 and triazolyls are
closely related organometallics. With recent work in gold-click
chemistry, terminal alkynes, organic azides, or premade gold(I)
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Table 2. Selected Interatomic Distances (Å) and Angles (deg)
compound
Au−P
Au−Ccarbene
Au−Ctriazolyl
Au−Calkynyl
∠P/C−Au−N/C
1
2
3
1.967(6)
1.973(8)
175.5(2)
178.6(3)
178.85(7)
171.15(7)
177.4(3)
175.20(12)
177.5(3)
172.9(3)
177.2(3)
177.98(8)
178.24(8)
177.81(8)
177.3(2)
2.2913(6)
2.2761(6)
2.273(3)
2.2798(12)
2.270(3)
2.289(3)
2.278(3)
2.2928(7)
2.2883(8)
2.2775(8)
2.037(2)
2.014(2)
2.018(10)
2.025(4)
2.019(11)
2.032(10)
2.049(10)
2.047(3)
2.030(3)
2.023(3)
4
5
6
7
11
2.013(5)
1.982(5)
Figure 1. Thermal ellipsoid depiction of azido complex 1 (50%
probability). An atom-labeling scheme is indicated. Hydrogen atoms
are omitted for clarity.
orbital energy level diagrams appear in Figure 4, along with
frontier orbital depictions. In both complexes, the highest-
occupied Kohn−Sham orbital (HOMO) resides on the triazolyl
or alkynyl ligand. The lowest unoccupied Kohn−Sham orbital
(LUMO) mainly consists of phenyl p-functions on the capping
PPh3 ligand. The large HOMO−LUMO energy gaps agree
qualitatively with the colorlessness of the pure compounds.
The triazolyl is a modestly stronger trans-influencer than the
alkynyl. Work on trans-influences104 in gold(I) complexes is not
extensive. Jones and Williams,105 on the basis of 35Cl nuclear
quadrupole resonance, find that σ-bonding dominates the trans-
influences of chlorogold(I) complexes. A density-functional
theory study106 reiterates that trans-oriented ligand σ-orbitals
compete for the same sd-hybrid orbital on gold.
A Dapprich−Frenking charge decomposition analysis107
indicates that alkynyls are more electron-releasing than their
respective triazolyls. This result is intuitive if the inductive effect
of three triazolyl nitrogens outweighs the greater electro-
negativity of sp- vs sp2-hybridized carbon. The triazolyl ligand
of 3 donates 0.07 fewer electrons than the corresponding
alkynyl. An attractive possibility is that the triazolyl ring is more
π-acidic than the ethynyl moiety. Similar results prevail for the
other (triphenylphosphine)gold(I) complexes, Table 3. The
table also collects calculated Au−P bond distances. In all cases,
the triazolyl is more trans-influencing by a small margin.
Figure 2. (a) Thermal ellipsoid depiction of triazolyl complex 3 (50%
probability) showing two crystallographically independent molecules
in the asymmetric unit (50% probability). A partial atom-labeling
scheme is indicated. Hydrogen atoms are omitted for clarity; unlabeled
atoms are carbon. (b) View of the unit cell along a. Dashed lines
indicate intermolecular hydrogen bonds.
CONCLUSIONS
■
Gold-click chemistry, in one incarnation, yields triazolyl
complexes from gold(I) azides and terminal alkynes. Earlier
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Figure 3. Thermal ellipsoid depiction of alkynyl complex 11 (50%
probability). Benzene of crystallization (not shown) inhabits the unit
cell. An atom-labeling scheme is indicated. Hydrogen atoms are
omitted for clarity.
work from this laboratory shows that triazolyls can also be
obtained from (phosphine)gold(I) alkynyls and azide ion, or its
equivalents, in protic media.68,69 Here, we enlarge the gold-click
menagerie with (N-heterocyclic carbene)gold(I) azides,
(phosphine)- and (carbene)gold(I) triazolyls, and function-
alized gold(I) alkynyls. Crystal structures are included for eight
new compounds. A recurrent hydrogen-bonding motif is
described for N-protonated gold(I) triazolyls.
The four (triphenylphosphine)gold(I) triazolyls herein were
chosen for density-functional theory calculations; 3 is a
prototype. Computations have also been performed on the
corresponding alkynyls. The calculations find that the triazolyl
is a slightly better trans-influencer than the corresponding
alkynyl, which is more electron-releasing. The stronger electron
donation from the alkynyl carbon, despite its sp-hybridization,
results from the electronegativity of the triazolyl nitrogens. The
triazolyl ligands are more trans-influencing, but the difference is
slight. These results caution against structural or reactivity
generalizations for LAuI without experimentation or prelimi-
nary calculations.
Figure 4. Frontier Kohn−Sham orbital energy level diagrams of (a) 3
and (b) its alkynyl analogue. Computed gold−phosphorus distances
are indicated, and selected orbitals are inset (contour level 0.03 au). All
calculations are gas-phase. Compositions of the HOMO and LUMO
appear as percentages of fragment electron density.
EXPERIMENTAL SECTION
■
Materials. Reagents were commercial in origin and were used
without further purification unless indicated. Solvents were passed
through activated alumina columns in an MBraun solvent purification
The (phosphine)- or (N-heterocyclic carbene)gold(I) azides used
1
system before use. H and 31P{1H} NMR spectra were collected on a
to synthesize triazolyl complexes were prepared as described
previously.76,93 (Phosphine)gold(I) chlorides and (Pr2 NHC)AuCl
i
Varian AS-400 spectrometer operating at 399.7 and 161.8 MHz,
respectively. For H NMR spectra, chemical shifts were determined
were prepared according to literature procedures.41
1
relative to the solvent residual peaks. For 31P{1H} NMR, chemical
shifts were determined relative to concentrated H3PO4. Microanalyses
(C, H, and N) were undertaken by Robertson Microlit Laboratories.
Mass spectrometry was performed at the University of Cincinnati
Mass Spectrometry facility.
Synthesis. Caution! Metal azide complexes are potentially explosive,
and due precautions should be taken.
(Cl2NHC)AuCl. In 10 mL of tetrahydrofuran was dissolved
(Cl2NHC)AgI (102 mg, 0.255 mmol), followed by 85.0 mg (0.265
mmol) of (THT)AuCl. A white precipitate quickly formed. The
F
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Table 3. Calculated Triazolyl or Alkynyl Net Charge Transfer to (Triphenylphosphine)gold, from Dapprich−Frenking Charge
a
Decomposition Analysis
a
Primes indicate alkynyl complexes.
solution mixture was stirred for 16 h, the solvent was filtered through a
plug of Celite and then removed by rotary evaporation. A white solid
remained that was washed with pentane (3 × 50 mL) and then
vacuum-dried. Yield: 94 mg (93%). 1H NMR (CDCl3): δ 3.83 (s, 6H)
ppm. Anal. Calcd for C5H6AuN2Cl3: C, 15.11; H, 1.52; N, 7.05.
Found: C, 15.49; H, 1.53; N, 7.15%.
CH(CH3)2) ppm. IR (KBr): 2051 (νas NNN, vs), 1285 (νs NNN
,
w) cm−1. Anal. Calcd For C9H16AuN5: C, 27.63; H, 4.12; N, 17.90.
Found: C, 27.54; H, 3.98; N, 17.65%.
Ph3PAu(n-pentatriazole) (3). In 20 mL of toluene was suspended
Ph3PAuN3 (122 mg, 0.24 mmol), and to this suspension was added 1-
heptyne (100 μL, 0.76 mmol). The resultant suspension was stirred
under argon for 72 h. The supernatant was decanted to yield a white
solid. This solid was washed with toluene and n-pentane, and then
(Cl2NHC)AuN3 (1). To 15 mL of benzene was added (Cl2NHC)-
AuCl (155 mg, 0.390 mmol), and to this solution was added silver
acetate (66.8 mg, 0.400 mmol), with formation of a gray precipitate.
The solution was stirred for 16 h in the absence of light. The solution
was filtered twice through a plug of Celite. To the filtrate 0.05 mL
(3.80 mmol) of trimethylsilyl azide was added by syringe. There was
no visible change. The solution was stirred for 16 h, the solvent
removed by rotary evaporation, and the solid was triturated with
1
vacuum-dried. Yield: 88 mg (61%). H NMR (DMSO-d6): δ 13.92 (s
br, 1H, NH), 7.54−7.67 (m, 15H, CH), 2.68 (t, J = 7.6 Hz, 2H, CH2),
1.70 (m, 2H, CH2), δ 1.21−1.31 (m, 4H, CH2), 0.75 (t, J = 6.8 Hz,
3H, CH3) ppm. 31P{1H} NMR (DMSO-d6): δ 45.0 ppm. Anal. Calcd
for C25H27AuN3P: C, 50.26; H, 4.56; N, 7.03. Found: C, 49.99; H,
4.52; N, 7.02%.
1
pentane and collected. Yield: 144 mg (92%). H NMR (CDCl3): δ
Ph3PAu(cyclohexyltriazole) (4). In 10 mL of toluene was suspended
Ph3PAuN3 (67 mg, 0.13 mmol), and to this suspension was added
cyclohexylacetylene (50 μL, 0.38 mmol). The suspension was stirred
under argon for 72 h. The resultant suspension was dried in vacuo to
yield a white product. This solid was washed with benzene and n-
pentane, and then vacuum-dried. Yield: 54 mg (67%). 1H NMR
(DMSO-d6): δ 13.91 (s br, 1H, NH), 7.52−7.64 (m, 15H, CH), 2.79
(t, J = 11.6 Hz, 1H, CH), 1.05−1.98 (m, 10H, CH2) ppm. 31P{1H}
NMR (DMSO-d6): δ 45.0 ppm. Anal. Calcd for C26H27AuN3P: C,
51.24; H, 4.47; N, 6.89. Found: C, 50.94; H, 4.48; N, 6.74%.
Ph3PAu(4-methoxyphenyltriazole) (5). To 10 mL of toluene was
added Ph3PAuN3 (64 mg, 0.13 mmol), and to this suspension was
added 1-ethynyl-4-methoxybenzene (50 μL, 0.21 mmol). The
suspension was stirred under argon for 72 h, and was dried in vacuo
to yield a white solid. The product was washed with benzene and n-
3.82 (s, 6H) ppm. IR (KBr): 2052 (νas NNN, vs), 1286 (νs NNN
,
w) cm−1. Anal. Calcd for C5H6AuN5Cl2: C, 14.86; H, 1.50; N, 17.33.
Found: C, 14.63; H, 1.53; N, 17.01%.
i
i
(Pr2 NHC)AuN3 (2). To 15 mL of benzene was added (Pr2 NHC)-
AuCl (99 mg, 0.258 mmol), and to this solution was added silver
acetate (45 mg, 0.270 mmol). A gray precipitate quickly formed. The
solution mixture was stirred for 16 h in the absence of light. The
solution was filtered twice through Celite, and the filtrate was
collected. To the filtrate was added 0.05 mL (3.80 mmol) of
trimethylsilyl azide by syringe. There was no visible change. The
solution was stirred for 16 h, the solvent removed by rotary
evaporation, and the solid was triturated with pentane and collected.
1
Yield: 83 mg (82%). H NMR (CDCl3): δ 6.97 (s, 2H, HCCH),
4.97 (sept, J = 6.8 Hz, 2H, CH(CH3)2), 1.46 (d, J = 6.8 Hz, 12H,
G
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pentane, and then vacuum-dried. Yield: 48 mg (59%). 1H NMR
(DMSO-d6): δ 14.27 (s br, 1H, NH), 8.10 (d, J = 8.4 Hz, 2H, CH),
7.56−7.64 (m, 15H, CH), 6.91 (d, J = 8.4 Hz, 2H, CH), 3.78 (s, 3H,
CH3) ppm. 31P{1H} NMR (DMSO-d6): δ 44.7 ppm. Anal. Calcd for
C27H23AuN3OP: C, 51.20; H, 3.66; N, 6.63. Found: C, 51.44; H, 3.92;
N, 6.41%.
Ph3PAu(3-aminophenyltriazole) (6). To 10 mL of toluene was
added Ph3PAuN3 (74 mg, 0.14 mmol), and to this suspension was
added 3-aminophenylacetylene (80 μL, 0.71 mmol). The suspension
was stirred under argon for 72 h. The reaction mixture was dried in
vacuo to yield a light orange product. The product was washed with
benzene and n-pentane, and then vacuum-dried. Yield: 49 mg (54%).
1H NMR (DMSO-d6): δ 14.22 (s br, 1H, NH), 7.57−7.66 (m, 15H,
CH), 7.43 (d, J = 7.6 Hz, 2H, CH), 7.39 (s, 1H, CH), 6.97 (t, J = 7.6
Hz, 1H, CH), 6.45 (d, J = 8.0 Hz, 1H, CH), 5.02 (s br, 2H, NH2)
ppm. 31P{1H} NMR (DMSO-d6): δ 44.5 ppm. Anal. Calcd for
C26H22AuN4P·H2O: C, 49.07; H, 3.80; N, 8.80. Found: C, 49.40; H,
3.69; N, 8.70%.
mg, 0.551 mmol). The solution was stirred under argon for 48 h, and a
light yellow precipitate evolved. The yellow precipitate was collected
by filtration and was washed repeatedly with cold 2-propanol and then
with pentane. The light yellow solid was then collected and dried in
1
vacuo. Yield: 48 mg (85%). H NMR (CDCl3): δ .61 (d, J = 9.6 Hz,
1H, CH), 7.33 (d, J = 8.8 Hz, 1H, CH), 7.05 (d, J = 2.4 Hz, 1H, CH),
6.92 (dd, J = 2.4, 8.4 Hz, 1H, CH), 6.22 (d, J = 9.6 Hz, 1H, CH), 4.90
(s, 2H, Ar-OCH2-tri), 3.79 (s, 6H, CH3) ppm. Anal. Calcd for
C17H13AuCl2N2O3·1/2 H2O: C, 35.81; H, 2.47; N, 4.91. Found: C,
35.67; H, 2.33; N, 4.78%.
Crystallography. Single-crystal diffraction studies proceeded on a
Bruker AXS SMART APEX II CCD diffractometer using mono-
chromatic Mo Kα radiation with the omega scan technique.
Measurements were made at 100 K; samples were mounted on a
mitogen tip using Paratone-N, then flash-frozen under a stream of
nitrogen gas. The unit cells were determined using SMART and
SAINT+. Data collection for all crystals was conducted at 100 K
(−173.5 °C). All structures were solved by direct methods and refined
by full matrix least-squares against F2 with all reflections using
SHELXTL. Refinement of extinction coefficients was found to be
insignificant. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed in standard calculated positions and were
refined with an isotropic displacement parameter 1.2 times that of the
adjacent carbon.
Computations. Spin-restricted density-functional theory calcula-
tions were executed in Gaussian 09 rev. A.02.108 Geometries were fully
optimized. Calculations employed the exchange and correlation
functionals of Perdew, Burke, and Ernzerhof,109 and the TZVP basis
set of Godbelt, Andzelm, and co-workers for nonmetals.110 For gold,
the Stuttgart 97 effective core potential and basis set were used;111
scalar relativistic effects are included implicitly. Harmonic frequency
calculations returned real vibrational frequencies, except for the alkynyl
6′, Table 3. A small imaginary frequency, 2.85i cm−1, was calculated for
substituent rotation about the axis of the carbon−carbon triple bond.
The potential energy surface along this coordinate is very flat, and
attempts to locate a true minimum failed. All calculations are gas-
phase. Population analyses were performed with the AOMix-CDA
software of Gorelsky.112,113
Cy3PAu(4-methoxyphenyltriazole) (7). In 5 mL of toluene was
dissolved Cy3PAuN3 (125 mg, 0.241 mmol), and to this solution was
added 1-ethynyl-4-methoxybenzene (120 μL, 0.50 mmol). The
solution was stirred under argon for 72 h. The reaction mixture was
cooled to near freezing in an acetone/dry ice bath. Upon cooling, a
white solid precipitated. The supernatant was decanted while still cold.
The white solid was washed repeatedly with n-pentane, vacuum-dried,
1
and collected. Yield: 82 mg (52%). H NMR (DMSO-d6): δ 14.04 (s
br, 1H, NH), 8.07 (d, J = 8.8 Hz, 2H, CH), 6.88 (d, J = 8.8 Hz, 2H,
CH), 3.75 (s, 3H, CH3), 2.45−1.12 (m, 33H, cyclohexyl) ppm. 31P
NMR (DMSO-d6): δ 60.0 ppm. Anal. Calcd for C27H41AuN3OP: C,
49.77; H, 6.34; N, 6.45. Found: C, 49.73; H, 6.15; N, 6.17%.
Triazolyl 8. In 20 mL of toluene was dissolved Cy3PAuN3 (156 mg,
0.300 mmol), and to this solution was added 7-(propargyloxy)-
coumarin (30.0 mg, 0.150 mmol). The reaction mixture was stirred
under argon for 48 h. A pale yellow precipitate formed, which was
collected and washed with benzene (3 × 10 mL) and then with
pentane. The remaining light yellow solid was collected and dried.
1
Yield: 71 mg (66%). H NMR (CDCl3): 11.51 (s br, 1H, NH), 7.62
(d, J = 9.2 Hz, 1H, CH), 7.34 (d, J = 8.4 Hz, 1H, CH), 7.04−7.96 (m,
2H, CH), 6.22 (d, J = 9.6 Hz, 1H, CH), 5.31 (s, 2H, Ar-OCH2-tri),
0.85−2.30 (m, 33H, cyclohexyl) ppm. 31P{1H} NMR (CDCl3): δ 58.0
ppm. Anal. Calcd for C30H41AuN3O3P: C, 50.07; H, 5.74; N, 5.84.
Found: C, 49.89; H, 5.54; N, 5.56%.
Triazolyl 9. In 20 mL of toluene was dissolved 1 (80 mg, 0.198
mmol), and to the resulting solution was added 7-(propargyloxy)-
coumarin (20.0 mg, 0.100 mmol). The solution was stirred under
argon for 48 h. A pale white precipitate formed, which was collected
and washed with benzene (3 × 10 mL) and then with pentane. The
off-white solid was collected and dried. Yield: 54 mg (91%). 1H NMR
(DMSO-d6): 14.05 (s br, 1H, NH), 7.93 (d, J = 9.6 Hz, 1H, CH), 7.56
(d, J = 8.8 Hz, 1H, CH), 7.25 (s, 1H, CH), 6.97 (dd, J = 2.4, 8.4 Hz,
1H, CH), 6.22 (d, J = 9.6 Hz, 1H, CH), 5.23 (s, 2H, Ar-OCH2-tri),
3.78 (s, 6H, CH3) ppm. Anal. Calcd for C17H14AuCl2N5O3: C, 33.79;
H, 2.34; N, 11.59. Found: C, 33.55; H, 2.47; N, 11.37%.
ASSOCIATED CONTENT
* Supporting Information
■
S
Thermal ellipsoid depictions of new compounds, table of
crystallographic data, and optimized Cartesian coordinates;
crystallographic files in .cif format. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tgray@case.edu.
■
Notes
The authors declare no competing financial interest.
Alkynyl 10. In 10 mL of 2-propanol was dissolved Cy3PAuN3 (55
mg, 0.105 mmol), and 7-(propargyloxy)coumarin (20.0 mg, 0.100
mmol). To the resulting solution was added sodium tert-butoxide (57
mg, 0.593 mmol). The solution was stirred under argon for 48 h, and a
yellow precipitate formed. The yellow precipitate was collected by
filtration and washed repeatedly with cold 2-propanol and then with
pentane. The yellow-brown solid was then collected and dried in
vacuo. Yield: 49 mg (72%). 1H NMR (CDCl3): δ 7.62 (d, J = 9.6 Hz,
1H, CH), 7.34 (d, J = 8.4 Hz, 1H, CH), 6.82−6.91 (m, 3H, CH), 6.63
(d, J = 2.4 Hz, 2H, CH), 6.59 (t, J = 2.4 Hz, 1H, CH), 6.23 (d, J = 9.2
Hz, 1H, CH), 5.03 (s, 2H, OCH2), 4.74 (s, 2H, OCH2), 1.22−2.08
(m, 33H, cyclohexyl) ppm. 31P{1H} NMR (CDCl3): δ 55.9 ppm. Anal.
Calcd for C30H40AuPO3: C, 53.26; H, 5.95. Found: C, 53.11; H,
6.31%.
ACKNOWLEDGMENTS
■
This work was supported by the U.S. National Science
Foundation, Grant CHE-1057659 to T.G.G., and by an Ohio
Third Frontier fellowship to T.J.R. The diffractometer at Case
Western Reserve was funded by NSF Grant CHE-0541766.
N.D. thanks the Republic of Turkey for a fellowship.
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