Syntheses and photophysical properties of luminescent mono-cyclometalated gold(III) cis -dialkynyl complexes

Article abstract of DOI:10.1021/ic102216v

A series of novel luminescent neutral cyclometalated gold(III) complexes of the type cis-[(NC)Au(C=CR)₂] (R = aryl, silyl groups) having different cyclometalating cores (NC) have been synthesized by CuI promoted halide to alkynyl metathesis wit

Full text of DOI:10.1021/ic102216v

ARTICLE
pubs.acs.org/IC
Syntheses and Photophysical Properties of Luminescent
Mono-cyclometalated Gold(III) cis-Dialkynyl Complexes
Jai Anand Garg, Olivier Blacque, and Koushik Venkatesan*
Institute of Inorganic Chemistry, University of Z€urich, Winterthurerstrasse 190, CH-8057 Z€urich, Switzerland
S Supporting Information
b
ABSTRACT: A series of novel luminescent neutral cyclometa-
lated gold(III) complexes of the type cis-[(N∧C)Au(CtCR)2]
(R = aryl, silyl groups) having different cyclometalating cores
(N∧C) have been synthesized by CuI promoted halide to
alkynyl metathesis with NEt3 as in situ deprotonating agent.
Along with spectroscopic characterizations (nuclear magnetic
resonance and infrared spectroscopies and electrospray ioniza-
tion mass spectrometry) and elemental analysis, the molecular
structures of some of the complexes have been established by
single-crystal X-ray diffraction studies. Photophysical studies
reveal that the complexes exhibit room-temperature phosphor-
escence (RTP). Experimental observations and density functional theory calculations qualitatively suggest limited participation of
the metal and alkynyl ligands in the lowest energy emitting state. The nature of the emission is mainly governed by metal-perturbed
3IL(πꢀπ*) transitions originating from the cyclometalate part of the molecule, and its variation readily leads to the tuning of the
emission wavelengths. Cyclic voltammetry measurements of selected complexes showed irreversible redox behavior with near-
equivalent cathodic peak potential (Ep,c) assigned to the C∧N core.
’ INTRODUCTION
diaryl/dialkynyl gold(III) complexes. Gold(III) alkynyls,
similar to isoelectronic platinum(II) alkynyl systems (d8-
configuration) could possibly offer tunable electronic and
luminescent properties due to their electron-richness, rigid-
rod nature, and polarizability.8,20 In our previous study, we have
shown that diaryl complexes of the type cis-[(N∧C)AuLn] (L =
aryl, n = 1, 2) containing perfluorinated aryl groups can be quite
stable and offer interesting photophysical properties.21 Very
recently, investigations into gold(III) dialkynyl systems have
appeared in literature further exemplifying their importance.22
From a photophysical standpoint, anionic acetylenic carbon
(ꢀCt) is desirable since strong σ-donating ligands are required
for “lifting” the energy levels of the otherwise low-lying metal-
centered (MC) orbitals. These orbitals are quite susceptible for
thermal population at ambient temperatures which then follows
rapid nonradiative relaxation pathways.2 Here in this work we
report the syntheses of stable mononuclear cyclometalated cis-
gold(III)-σ-dialkynyl complexes and their luminescent properties.
Organogold(I) σ-alkynyl complexes are widely investigated
for their interesting luminescence, nonlinear optical (NLO) pro-
perties and their ability to build metallo-macromolecular entities.1ꢀ9
In sharp contrast, gold(III) alkynyl complexes are relatively less
explored. Notables among the few known examples include
mononuclear gold(III) complexes containing one alkynyl ligand,
viz., [Au(CtCCF3)Me2(L)] and [Au(CtCR)Me2(PPh3)],10,11
[Au(C∧N∧C)(CtCR)],2,12,13 and three alkynyl ligands [Au
(CtCR)3(L)] and four alkynyl ligands [ER4]þ[Au(CtCR)4]ꢀ.14,15
Dinuclear gold(I)ꢀgold(III) complexes bearing two alkynyl
ligands, viz., [AuI(μ-{CH2}PPh2)2AuIII(CtCR)2], have also been
reported16 (Figure 1). In general, gold(III) complexes tend to
exhibit relatively large positive reduction potentials,17,18 and the
consequent instability is a probable reason for their scarcity.
Except for the cyclometalated systems (C∧N∧C) in the above-
noted examples that have been studied for luminescence proper-
ties, the other gold alkynyls have been chiefly explored, either for
catalysis or for studying reductive elimination processes.10,11,14,15
In recent years, extensive investigations carried out by Yam and
co-workers has revealed that cyclometalated gold(III) monoalk-
ynyl complexes with terdentate ligands can exhibit room-tem-
perature phosphorescence.2,12,13 Also, external quantum efficiency
(EQE) to the order of 11.5% in an organic light emitting diode
(OLED) device which is well comparable to cyclometalated Ir(III)
systems has been achieved.19
’ RESULTS AND DISCUSSION
Syntheses and Characterization of Complexes. Dichlorogold-
(III) complexes (AꢀE) with different cyclometalating cores 1ꢀ5
(Scheme 1) were first prepared as precursors to obtain the desired
dialkynyls. Complex [(N∧C)AuCl2] [N∧C = 2-phenylpyridine
In the past few years, we have been interested in a relatively
less explored class of mononuclear cyclometalated neutral
Received: November 4, 2010
Published: May 23, 2011
r
2011 American Chemical Society
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Figure 1. Known gold(III) mono-, di-, and tetraalkynyl complexes.
[N∧C = 2-(2,4-difluorophenyl)pyridine (dfppy); D] and [(N∧C)-
AuCl2] [N∧C = benzo[h]quinoline (bzq); E], were prepared via
analogous25,26 literature known transmetalation sequences from
mercury derivatives. The method essentially takes advantage of
the propensity of mercury(II) salts toward electrophilic substitution
for attaining ortho-activation. The ortho-mercurated dfppy was
obtained in rather low yield of 11% after repeated recrystallization
from ethanol (see Supporting Information for step 1 of D). A single
resonance signal in 199Hg NMR at δ = ꢀ1000 ppm coupled to
fluorine 4JHgꢀF (248.0 Hz) was observed; the same coupling con-
stant to mercury nucleus was observed in 19F NMR, which showed
two sets of signals at ꢀ108.3 and ꢀ110.1 ppm. A characteristic IR
absorption at 342 cmꢀ1 assignable to ν(HgꢀCl) was also found.
These preceding observations unambiguously establish the identity
of the expected ortho-activated [(dfppy)HgIICl] and ruled out the
possibility of any multiple mercuration which is sometimes encoun-
tered in this chemistry.25,26 Transmetalation of ortho-mercurated
bzq (see Experimental Section) required long reaction times (4 days)
under optimized conditions of reflux in a 1:1 mixture of dichlor-
Scheme 1
1
omethane and acetonitrile. The H NMR spectra of the aurated
dichlorides D and E showed diagnostic downfield shifts (mean
difference (Δδ), ca. 2.0 ppm) for aromatic proton attached to carbon
R to N of the pyridyl ring when compared to those of their respective
free dfppy and bzq. In addition IR spectra showed two characteristic
stretching vibrations ν(AuꢀCl) in the region of 300ꢀ415 cmꢀ1
.
Utilizing the above precursor complexes, various gold(III) dia-
lkynyls of the type [Au(C∧N)(CtCR)2] [N∧C = ppy, R =
phenyl (1a), 4-fluorophenyl (1b), 3,4,5-trimethoxyphenyl (1c),
2-thienyl (1d), Si(iPr)3 (1e), 4-(phenylethynyl)phenyl (1f);
N∧C = dfppy, R = phenyl (2a); N∧C = bzq, R = phenyl (3a);
N∧C = thpy, R = 4-fluorophenyl (4a); and N∧C = 5-me-thpy,
R = 4-fluorophenyl (5a)] were synthesized (Scheme 1). Et3N
served as a mild enough base for in situ deprotonation of the
relatively acidic acetylenic proton, and the substitution was aided
with the addition of a catalytic amount of CuI. It is pertinent to
mention here that Yam et al. have recently reported the synthesis
of the same class of compounds by a lithiation protocol.22a
The reaction proceeds smoothly to completion in less than
20 min at room temperature (RT). Generally, products were
obtained in modest yields (25ꢀ60%) following simple workup
and flash-column purification using neutral Al2O3. Longer reac-
tion times, especially for complexes with thienyl C∧N units 4a
and 5a, lead to an increased amount of unidentified impurities. In
the case of 1e, the reaction was notably clean and complete
within 5 min. This could well be expected in light of investiga-
tions upon various silyl acetylenes having similar deprotonation
rates as compared to aryl acetylenes despite the electronegativity
considerations of silicon and carbon.27 All of the products were
(ppy)] (A) was prepared according to the procedure reported by
Constable and Leese involving transmetalation reaction of ortho-
activated ppyHgII chloride with sodium tetrachloroaurate,23 [(N∧C)-
AuCl2] [N∧C = 2-(2-thienyl)pyridine (thpy); B] and[N∧C=2-(5-
methyl-2-thienyl)pyridine(5-me-thpy)][AuCl2;C] weresynthesized
on the basis of direct cycloauration methods.21,24 The remaining
precursor dihalides which were unknown, namely, [(N∧C)AuCl2]
1
completely characterized by H, 13C, and 19F NMR and IR
spectroscopies and elemental microanalyses. 1H and 13C NMR
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of all complexes showed two sets of resonances due to the non-
equivalent alkynyl ligands. The shift of the proton R to the
nitrogen of the pyridyl ring appeared in the range δ = 9.34ꢀ
9.81 ppm. The higher end values of this interval were notably
observed for complexes with bzq and dfppy cores. Such shifts
have also been noted with benzoquinoline platinum(II) dialkynyl
cyclometalated complexes described in the literature.28 From the
flat, and the largest deviations from the main plane defined by the
C∧NAuCC metallacycle atoms were 0.072(1) Å observed for 1b
and 0.063(9) Å for 1e. The maximum twist angle between the
planes comprising N∧CAu and AuCC was 5.85(14)° in 1b. The
metalated AuꢀC(sp2) distances, irrespective of different cyclo-
metalating cores were found to lie in a narrow range of 2.027(3)
ꢀ2.067(2) Å without much deviation from those reported for
their precursor dihalides and other analogous complexes. The
NꢀAuꢀCaryl chelate bite angles of the complexes were found to
range between 80.33(9) and 81.93(9)° with the consequent
enlargement of the opposite CalkynylꢀAuꢀCalkynyl angle which
falls in the range of 88.47(6)ꢀ95.28(14)°. The deviation from
the idealized 90° is commonly observed in related systems21,22
and can be attributed to the steric requirements of the cyclome-
talating ligands. For complexes 1aꢀ1c, 4a, and 5a the Auꢀ
Calkynyl distances trans to nitrogen of the pyridyl ring lie in the
range of 1.965(3)ꢀ2.006(2) Å while the distances to other
metalated acetylenic carbon fall in the range of 1.993(2)ꢀ2.052-
(2) Å, and this slight but distinct variation could be understood
due to the greater trans influence exerted by C(sp2); however, for
complexes 1e and 3a the distances were nearly the same within
the limits of experimental uncertainty. Deviations from colli-
nearity in the range of 168.2(2)ꢀ179.6(3)° were observed for
the interatomic angles comprising AuꢀCRtCβ trans to both N
and the metalated carbon. The other angles connecting the aryl
or silyl part (CRtCβ—Caryl/silyl) however did not show large
1Hꢀ H and Hꢀ C COSY experiments done for 2a, the
aurated carbon AuꢀC(sp2) appeared at 159.0 ppm, which falls
in the range previously observed in the literature for five-membered
gold(III) metalacycles containing N as one of the donor atoms.29
Although the chemical shifts for the metalated R-acetylenic
carbons (δCRt) could not be assigned with certainty, the two
Cβ signals were observed at δ = 99.0 and 104.0 ppm. In the cases
of benzoquinoline platinum(II) dialkynyls the CR have been
unambiguously identified by taking advantage of 195Pt satellites.
IR spectra of the prepared complexes showed the expected two
acetylenic bands ν(CtC) characterized by weak absorption in
1
1
13
the region of 2100ꢀ2200 cmꢀ1
.
Stability and Thermogravimetric Studies. During the initial
stages of the study, examination of the emission properties of
complexes 1a and 1b showed no marked variation, and this
prompted us to prepare complexes with varied cyclometalating
ligands. We chose to use fluorinated aryl acetylides in most of the
complexes, with an anticipation they will improve the stability of
the complexes on similar lines of thought as explained for gold(III)
biaryl complexes presented in our previous study.21 All com-
plexes synthesized were found to be stable to air and moisture in
the solid state under ambient conditions. Homocoupled pro-
ducts, namely, the butadiynes formed through reductive elimina-
variations. The intermolecular Au Au distance for 1c
3 3 3
(3.7285(1) Å) was found to be the shortest among the others,
which fall in the range of 4.1468(2)ꢀ7.6181(1) Å (see Support-
ing Information Table S3). Since the Au Au distances are no
3 3 3
1
tion, were observed as byproduct (confirmed by H NMR and
shorter than the sum of the van der Waals radii between the gold
atoms in the crystal lattice, significant aurophilic interactions could
be ruled out.
GC-MS studies) in some cases such as for 1a and 3a but were not
observed in others, especially for the fluorinated analogues. In
comparison with the gold(III) diaryl complexes,21 these com-
plexes exhibit enhanced stability which could be partly under-
stood on the basis of hybridization considerations of AuꢀC(sp)
vs AuꢀC(sp2).
UVꢀVis Absorption Studies. The UVꢀvis profiles of the
complexes (see Figure 3 and in Supporting Information Figure
S5) with ppy cyclometalate (1aꢀ1f) and also 2a exhibit a low-
energy absorption band centered around 317ꢀ323 nm. Thpy-
cyclometalated complex (4a) and 5-me-thpy (5a) featured bands
at lower energies of 368 and 381 nm, respectively, due to their
inherent internal charge-transfer nature.30,31 Understandably,
π-delocalization causes lower energy absorptions of bzq (3a)
at 383 nm. Typically, the complexes showed molar absorptivities
in the order of 103 to 104 dm3 molꢀ1 cmꢀ1, notably greater in the
case of 1f. In general, the shape of the absorption bands resembled
those of the respective free ligands with bathochromic shifts due
to metal coordination.
Emission Studies. Complexes except 1c and 1d showed
intense long-lived phosphorescence at RT. While 1d showed
weak emission at RT (not shown in figures), 1c was non-emissive
(not shown in figures). Nevertheless, all of the complexes showed
emission at 77 K (me-THF) rigidified media (see Supporting
Information Figure S6). The non-emissive nature of 1c could be
because of thermal equilibrium with deactivating excited states or
due to photoinduced electron transfer, presumably from the
electron rich methoxy substituents. The latter phenomenon with
methoxy-phenylacetylene ligands was also observed previously
with Pt(II) cyclometalated complexes.32 Further studies are due
for definitive conclusions. As mentioned earlier, with initial
observation that 1a and 1b emitting at nearly the same wave-
lengths (see Table 2), we also thought that either extending the
conjugation or changing the cyclometalated ligand can offer
tuning of emission wavelengths. Accordingly, 1f and 2aꢀ5a
It was interesting to note that while 1c containing electron-rich
alkynyl was quite stable both in solid state and in organic solvents, a
dichloromethane solution of 1d showed discernible decomposi-
tion in a few days, and attempts to isolate a complex with
4-ethynyl-N,N-dimethylaniline as an ancillary ligand with a ppy
core (1) was unsuccessful because of its instability. Thermo-
gravimetric analysis (TGA) of 1a and 1b showed the final
decomposition temperature (Td) of the latter occurs at a much
higher temperature around 500 °C than the former at around
290 °C (see Supporting Information Figure S1). This can be
probably attributed to the resulting increase in the stability of the
complex due to the electron withdrawing nature of fluorine.
Structural Characterization. Single-crystal X-ray structures
were determined for seven complexes (1aꢀ1c, 1e, 3a, 4a, and
5a). They were obtained from slow evaporation by layering of
pentane over concentrated solution of the complexes in dichlor-
omethane at 0ꢀ5 °C. The perspective views of 1a, 1e, 3a, and 5a
are shown in Figure 2 (for others, see Supporting Information,
Figures S2ꢀS4), and some relevant bond distances and angles
are given in Table 1. Crystallographic details are provided in the
Supporting Information (Table S1 and Table S2). The structural
analysis indicates the coordination environment around the gold
metal center as a distorted square-planar geometry which is gener-
ally observed for square-planar d8 complexes with non-equivalent
coordination environment. The cyclometalated part is essentially
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Figure 2. X-ray crystal structures of 1a, 1e, 3a, and 5a with selective atomic numbering scheme. Thermal ellipsoids are drawn at the 50% probability
level. Hydrogen atoms and solvent molecules are omitted for clarity.
did show variation in their lowest energy emission maxima.
Interestingly, the structural variation of the cyclometalate such
as in 4a and 5a was more efficient in tuning emission toward
longer wavelengths than that achieved by increasing conjugation
by one alkyne unit in the ancillary ligand, such as in 1f. This
suggests the enhanced participation of cyclometalate in the
excited state and emission tuning could be achieved by the
choice of cyclometalated unit with different πꢀπ* energies.
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Vibrational structured emission profiles even at RT strongly
suggest ligand centered (3IL) dominance as in most cases of
luminescent gold(III) complexes.2,12 Emission spectra measured
at 77 K generally featured strong bands with vibrational progres-
sions of 1200ꢀ1250 cmꢀ1 due to the participating ligands (see
Supporting Information Figure S6). These values relate more
closely to CdN and CdC stretching frequencies and to rocking
aromatic CꢀH modes. Vibrational progressions corresponding
to ν(CtC) stretching modes around 2200 cmꢀ1 were compara-
tively less prominent. No significant residual fluorescence from
the ligands was observed in these complexes. It is worth
mentioning here that the emission of the fluorescent chromo-
phore benzo[h]quinoline λem = 363 nm shifted to 488 nm in 3a.
The quantum yields (Φp) were generally found to lie in the order
of 10ꢀ2 and were notably greater for 1e; this is also qualitatively
in agreement with the quantum yield values observed for Au(III)
complexes described recently in literature.22 As anticipated, there
was an increase in the quantum yield of 3a as compared to 1a,
which could be explained in terms of a partial decrease in
nonradiative decay rates (knr) due to structural rigidification. The
decrease in quantum yield of 5a as compared to 4a could be
understood on the basis of the excited-state structural distortions
associated with complexes accompanying a larger Stokes shift.
Utilization of dfppy ligand 2, popular for blue emission in Ir(III)
33 and Pt(II) 34 complexes in 2a, did show a hypsochromic shift
of 8 nm as compared to 1a. Longer emission wavelengths of 5a as
compared to that of 4a are due to the lowering of the πꢀπ* band
gap consequent from the increased electron richness of the
thienyl unit. The Stokes shift for these complexes are large,
and the excited-state lifetime is in the microsecond regime,
indicating the phosphorescent nature of emission. Considering
the above observations, and also from the longer excited-state
lifetimes (τ), in line with the increasing internal charge-transfer
nature of the C∧N unit, 5a > 4a > 2a, the emission is assigned to
originate from the 3IL (πꢀπ*) state of the cyclometalate
perturbed by the metal.
Table 1. Selected Bond Distances (Å) and Angles (deg) Data
of Complexes 1a, 1e, 3a, and 5a
distance
angle
Complex 1a
C(1)ꢀAu(1)ꢀN(1)
Cyclic Voltammetry Studies. Cyclic voltammetry for selected
complexes 1aꢀ1c, 1f, 4a, and 5a (see Supporting Information
Table S4) showed irreversible oxidation peaks in the range from
þ0.29 to þ0.70 V (vs Fc0/þ couple) and irreversible cathodic
peak potentials in the range from ꢀ2.29 to ꢀ2.48 V (vs Fc0/þ
couple) in CH2Cl2 at RT. Both processes are assignable to ligand-
centered electrochemical events. Due to the similarity of the re-
duction peak potentials within the same C∧N cyclometalate, the
reduction process is attributed to origination from the cyclome-
talated part of the complex and the oxidation from the electron
rich alkynyl unit. On the basis of precedences of CV studies of
related complexes,12,22,35 and due to the oxidizing nature of the
gold(III) complexes, the metal is less likely to be involved in the
redox process. The large electrochemical band gap with oxidation
and the reduction peaks widely separated, along with the absence
of redox activity from the metal, further corroborates our photo-
physical observation of the limited participation of the metal in
the frontier orbitals.
C(12)ꢀAu(1)
C(20)ꢀAu(1)
C(1)ꢀAu(1)
N(1)ꢀAu(1)
1.971(2)
2.052(2)
2.038(2)
2.0596(19)
81.33(9)
90.39(9)
94.19(9)
94.09(8)
C(12)ꢀAu(1)ꢀC(20)
C(1)ꢀAu(1)ꢀC(12)
N(1)ꢀAu(1)ꢀC(20)
Complex 1e
C(7)ꢀAu(1)
N(1)ꢀAu(1)
C(23)ꢀAu(1)
C(12)ꢀAu(1)
2.052(2)
2.0515(19)
1.993(2)
2.006(2)
C(7)ꢀAu(1)ꢀN(1)
C(23)ꢀAu(1)ꢀC12
C(23)ꢀAu(1)ꢀN(1)
C(12)ꢀAu(1)ꢀC(7)
80.33(9)
89.93(9)
94.99(9)
94.75(9)
Complex 3a
C(10)ꢀAu(1)
N(1)ꢀAu(1)
C(14)ꢀAu(1)
C(22)ꢀAu(1)
2.067(2)
2.061(2)
2.008(3)
2.003(3)
N(1)ꢀAu(1)ꢀC(10)
C(22)ꢀAu(1)ꢀC(14)
C(14)ꢀAu(1)ꢀN(1)
C(22)ꢀAu(1)ꢀC(10)
81.93(9)
92.64(10)
92.25(9)
93.14(9)
Complex 5a
Density Functional Theory and Time-Dependent Density
Functional Theory Calculations. To better understand the
absorption and emission properties of the synthesized compounds,
density functional theory (DFT) calculations were carried out for
selected molecules with the Gaussian 03 program package.36 The
N(1)ꢀAu(1)
C(8)ꢀAu(1)
C(14)ꢀAu(1)
C(11)ꢀAu(1)
2.082(2)
2.032(3)
2.040(3)
1.965(3)
C(8)ꢀAu(1)ꢀN(1)
C(11)ꢀAu(1)ꢀC(14)
C(14)ꢀAu(1)ꢀN(1)
C(11)ꢀAu(1)ꢀC(8)
81.07(10)
92.61(11)
94.16(10)
92.20(11)
Figure 3. (Left) Electronic absorption spectra in CH2Cl2 at RT and (right) normalized emission (I) spectra in degassed CH2Cl2 at RT.
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Table 2. Photophysical Properties of Complexes 1aꢀ1f and 2aꢀ5a
room-temperature solution (CH2Cl2)
absorption λmax (nm; εmax/(dm3 molꢀ1cmꢀ1))
emission λmax (nm)
τ (μs)
ΦP
77 K glassb (2-me-THF; nm)
a
complex
1a
1b
1c
1d
1e
1f
318 (15 310)
463, 491, 524 sh
467, 493, 526 sh
non-emissive
weakly emissive
461, 492, 521 sh
510, 542
4.4
4.5
6.0 ꢁ 10ꢀ3
4.0 ꢁ 10ꢀ2
457, 491, 518
456, 490, 522
458, 492, 520
486, 505, 525
459, 486, 528
502, 533, 563
457, 522, 555
487, 520
318 (13 681)
321 (15 340)
261 (21 290), 323 (10 551)
250 (22 394), 319 (8550), 341 sh (5278)
310 (82 244), 327 sh (71 261)
317 (1825)
1.4
13.0
1.4
0.11
5.9 ꢁ 10ꢀ2
1.6 ꢁ 10ꢀ2
1.2 ꢁ 10ꢀ2
4.4 ꢁ 10ꢀ2
1.5 ꢁ 10ꢀ2
2a
3a
4a
5a
462, 483
289 (38 030), 365 (3910), 383 (4374)
281 (20 314), 368 (7320)
295 (21 950), 381 (8120)
488, 515 sh
534, 575
11.2
7.4
452, 574, 590
556, 591
19.1
545, 570, 598
a Photoluminescence quantum yield determined with quinine sulfate in 1 N H2SO4 as standard at 298 K. b Vibronic structured emission bands.
Table 3. Selected SingletꢀSinglet (S0ꢀSn) and SingletꢀTriplet (S0ꢀTm) Excited States with TDDFT/CPCM Vertical Excitation
Energies (nm), Transition Coefficients, Orbitals Involved in the Transitions, and Oscillator Strengths f for Compounds 1a, 1b, 1e,
and 4a (with f > 0.015)
1a
1b
1e
4a
exp abs λmax
S0ꢀSn
318
318
319
368
n = 3
n = 2
n = 1
n = 1
318 (0.175) H-2 f L (0.67)
339 (0.083) H-1 f L (0.66)
323 (0.079) H f L (0.63)
n = 4
353 (0.038) H f L (0.62)
S0ꢀSn
S0ꢀSn
S0ꢀSn
S0ꢀSn
S0ꢀSn
S0ꢀSn
S0ꢀSn
n = 4
n = 3
n = 2
292 (0.192) H-3 f L (0.65)
318 (0.182) H-2 f L (0.67)
302 (0.150) H-3 f L (0.64)
n = 5
351 (0.138) H-2 f L (0.57)
n = 6
n = 4
n = 3
278 (0.123) H f Lþ2 (0.53)
n = 7
292 (0.181) H-3 f L (0.65)
299 (0.215) H-4 f L (0.63)
n = 7
337 (0.267) H-1 f L (0.68)
n = 5
n = 6
276 (0.032) H-6 f L (0.45)
n = 8
280 (0.054) H-4 f L (0.65)
n = 7
274 (0.139) H f Lþ1 (0.58)
293 (0.199) H-3 f L (0.68)
n = 7
276 (0.034) H-1 f Lþ1 (0.46) 280 (0.028) H-1 f Lþ2 (0.61)
n = 9 n = 8
290 (0.248) H f Lþ2 (0.57)
n = 8
274 (0.311) H-1 f Lþ2 (0.50) 275 (0.291) H f Lþ2 (0.64)
n = 10
284 (0.059) H f Lþ1 (0.60)
n = 9
n = 9
265 (0.143) H-7 f L (0.44)
273 (0.051) H-1 f Lþ1 (0.63)
n = 10
284 (0.133) H-2 f Lþ1 (0.54)
265 (0.161) H-7 f L (0.49)
493
exptl emiss λmax 491
492
575
a
calcd λmax
T1ꢀS0
471 (2.63 eV)
468 (2.65 eV)
468 (2.65 eV)
571 (2.17 eV)
441 H-2 r L (0.66)
442 H-2 r L (0.66)
441 H-4 r L (0.51) H r L (0.41) 518 H-2 r L (0.73)
a Solvent-corrected (CH2Cl2) energy difference between the optimized ground state and lowest triplet state.
molecular structures of the electronic ground states and lowest
triplet states of compounds 1a, 1b, 1e, and 4a were exemplarily
studied. On the basis of the optimized geometries, time-depen-
dent DFT (TD-DFT) calculations37 combined with the conductive
polarizable continuum model (CPCM)38,39 were used to pro-
duce the molecular orbital energy levels and compositions, the
absorption spectra, and the lowest singletꢀsinglet and singletꢀ
triplet electronic transitions in CH2Cl2 media.
Selected TD-DFT singletꢀsinglet electronic transitions, ex-
citation energies, and oscillator strengths of 1a, 1b, 1e, and 4a are
given in Table 3. For 1a, the lowest lying absorption transition
S0 f S3 at 318 nm (f < 0.175, the oscillator strengths for the S0 f S1
and S0 f S2 transitions being very small: f < 0.005) is in good agree-
ment with the low-energy absorption band experimentally centered
at 318 nm. This transition is derived from the HOMO-2 f LUMO
excitation. As shown in Figure 4, both frontier orbitals are dis-
tributed predominantly over the organic ligand ppy (about 90%)
with some contributions from the metal center and the alkynyl
ligands (see Supporting Information for molecular orbital com-
positions). The absorption band can then be ascribed to a transition
with a metal-perturbed intraligand charge-transfer 1ILπfπ*(ppy)CT
character. Other significant higher transitions at 292 nm (S0 f S4,
f = 0.192), 278 nm (S0 f S6, f = 0.123), and 274 nm (S0 f S9,
f = 0.311) are better related to the intense high-energy band
centered around 250ꢀ260 nm. They involve frontier molecular
orbitals located either on the alkynyl ligands (HOMO-1, HOMO,
and LUMOþ2) or on the phenylpyridine (HOMO-3 and LUMO)
with a small contribution from the metal center (less than 5%)
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Figure 4. Isodensity plots of selected frontier orbitals of the ground state of 1a (isodensity value, 0.02).
except for LUMOþ2, which displays 25% of the electron density on
the gold atom (Figure 4). The corresponding absorption band can
be characterized as a transition with an admixture of intraligand
1
charge-transfer ILπfπ*(ppy)CT and metal-perturbed ligand-to-li-
gand 1LLπ(alk)fπ*(alk)CT characters.
For 1b, the lowest significant singletꢀsinglet transitions S0 f
S2, S0 f S3, and S0 f S4 (f = 0.083, 0.182, 0.181; S0 f S1 with
f < 0.010) at 339, 318, and 292 nm are derived from the HOMO-
1 f LUMO, HOMO-2 f LUMO, and HOMO-3 f LUMO
excitations, respectively. Except HOMO-1 which is mainly located
on the alkynyl ligands with a small contribution of the metal, the
other four orbitals are a π/π* combination of the phenylpyridine
ligand. The main absorption band experimentally observed at
318 nm can be attributed to these three transitions characterized
1
by metal-perturbed intraligand charge-transfer ILπfπ*(ppy)CT
and ligand-to-ligand 1LLπ(alk)fπ*(ppy)CT characters. The calcu-
lated electronic transitions for compound 1e show the same
general picture as that for 1b. The influence of the terminal F
atom in 1b and the SiMe3 group in 1e on the alkynyl ligands is
established by the lowest and significant singletꢀsinglet π(alk) f
π*(ppy) transitions with f = 0.083 and 0.079 at 339 and 323 nm,
respectively. Nevertheless, the main character of the lowest
absorption band of 1e remains π f π*(ppy) as shown by the
S0 f S4 and S0 f S5 transitions calculated at 302 and 299 nm
with the larger oscillator strengths f = 0.150 and 0.215, respectively.
Compound 4a differs from 1b by the presence of 2-(2-thie-
nyl)pyridine (thpy) instead of phenylpyridine. Experimentally, thpy
is responsible of a lower energy absorption band at 368 nm for 4a in
comparison with 1aꢀ1f. The lowest transitions at 353, 351, and
337 nm calculated for 4a (f = 0.038, 0.138, 0.267) are in good
agreement with the experimental trend. As in 1a, 1b, and 1e, the
LUMO is localized on the N∧C ligand with a small contribution
from the metal center. HOMO and HOMO-1 are π-alkynyl based
orbitals, and HOMO-2 distributes over thpy; consequently the
corresponding HOMO f LUMO, HOMO-2 f LUMO, and
HOMO-1 f LUMO excitations give rise to the main experi-
mental absorption bands with an admixture of the metal-per-
turbed 1ILπfπ*(thpy)CT and 1LLπ(alk)fπ*(thpy)CT characters.
Figure 5. MO diagrams for the ground state and lowest triplet state
of 1a.
It is worth noting that the lowest TD-DFT excited states are
calculated to be of triplet character at 441, 442, 441, and 518 nm
for 1a, 1b, 1e, and 4a, respectively (Table 3). These calculated
transitions are not observed in the visible region of the experi-
mental absorption spectra, confirming the spin-forbidden char-
acter of these singletꢀtriplet transitions. For all compounds the
calculated wavelengths corresponding to the T1f S0 transitions
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Figure 6. Isodensity plots of the singlet HOMO (left), singlet LUMO (middle), and the triplet spin density surface of the lowest triplet state of 1a
(isodensity value, 0.02).
are in line with the experimental emission wavelengths (in paren-
theses) with 441 (491), 442 (493), 441 (492), and 518 (575) nm
for 1a, 1b, 1e, and 4a, respectively (Table 3). Nevertheless, the
calculated emission maxima are more reliable when based on the
energy difference between the optimized emissive triplet state
and the optimized ground state. Indeed, the calculated values
reported in Table 3 as calculated λmax of 471 (1a), 468 (1b), 468
(1e), and 571 (4a) are in good agreement with the experimental
values even still underestimated by 4ꢀ25 nm. Careful analyses of
the molecular orbital diagrams of the optimized closed-shell
ground state and open-shell triplet state of 1a (Figure 5) confirm
that the calculated transition LUMO f HOMO-2 is responsible
of the experimental emission at 491 nm. They also reveal some
inversion in the order of the orbitals with geometrical conse-
quences. The ground-state HOMO-2 (ꢀ6.90 eV) is greatly affected
by the one-electron HOMO-2 f LUMO excitation since the
derived singly occupied R orbital of the triplet state is found at
ꢀ7.47 eV as HOMO-7(R) while the corresponding unoccupied
β orbital is the singlet LUMO of the system (ꢀ4.83 eV). The
population of the ground-state LUMO (ꢀ2.13 eV) by one
electron stabilized the singlet molecular orbital which becomes
HOMO(R) in the triplet -state MO diagram (at ꢀ4.22 eV),
while the corresponding unoccupied orbital is only slightly
destabilized as LUMOþ1(β) at ꢀ1.91 eV (Figure 5). The electro-
nic density of the HOMO-2 and LUMO being mainly localized
on the phenylpyridine ligand with a π-antibonding character of
the central CꢀC bridge for the former and contrastingly a
π-bonding character of the central CꢀC bridge for the latter
orbital, the main variation observed in the optimized excited state
with respect to the ground-state geometry is a significant short-
ening of the central CꢀC bond by 0.076 Å (1.388 Å vs 1.464 Å).
The singlet HOMO, singlet LUMO, and the triplet spin density
surface of the lowest triplet state of 1a (Figure 6) visually identify
the emission from a transition with a 3ILCT character originated
by the phenylpyridine ligand. Comparable studies were carried
out for the other selected compounds 1b, 1e, and 4a with no major
differences in comparison with 1a since the frontier orbitals involved
in the calculated emissions and the triplet spin density surfaces of
the lowest triplet states are similar in shape. For all studied
compounds, the calculated phosphorescences are the reverse
processes of the lowest lying absorptions because of the same
transition characters.
’ CONCLUSIONS
In conclusion, we have developed a facile synthetic access
toward tunable phosphorescent gold(III) cis-dialkynyl complexes.
As demonstrated, the method can be applied quite generally to
various gold(III) cyclometalated complexes bearing different
alkynyls. This might help further to understand fundamental
photophysics associated with gold(III) alkynyl complexes and
design molecules with increased quantum yields suitable for
OLEDs. The basic square-planar gold(III) dialkynyl motif could
also be advantageously used for the development of macromo-
lecules which are limited until now as compared to the isoelec-
tronic platinum(II) systems.
’ EXPERIMENTAL SECTION
Material and Methods. All manipulations were carried out with-
out special precautions for excluding air and moisture. 1H and 13C{1H}
NMR were recorded on Bruker AV2-400 or AV-500 spectrometers. 19F
NMR spectra were recorded on either a Varian Mercury spectrometer or
Bruker AV2-400 spectrometers. Chemical shifts (δ) are reported in
parts per million (ppm) referenced to tetramethylsilane (δ 0.00 ppm)
using the residual protio solvent peaks as internal standards (1H NMR
experiments) or the characteristic resonances of the solvent nuclei (13C
NMR experiments). 19F NMR was referenced to CFCl3 (δ 0.00 ppm).
Coupling constants (J) are quoted in hertz, and the following abbrevia-
tions are used to describe the signal multiplicities: s (singlet); d (doublet);
t (triplet); q (quartet); m (multiplet); dd (doublet of doublet); td (triplet of
doublet); dt (doublet of triplet). Proton and carbon assignments have
been made using routine one- and two-dimensional NMR spectroscopies
where appropriate. Infrared (IR) spectra were recorded on a Perkin-
Elmer 1600 Fourier transform spectrophotometer using KBr pellet with
frequencies (ν) quoted in wavenumbers (cmꢀ1). Elemental microana-
lysis was carried out with a Leco CHNS-932 analyzer. Mass spectra were
run on a Finnigan-MAT-8400 mass spectrometer. Thin-layer chroma-
trography (TLC) analysis was performed on precoated Merck silica gel
60F254 slides and visualized by luminescence quenching either at (short
wavelength) 254 nm or (long wavelength) 365 nm. Chromatographic
purification of products was performed on a short column (length,
15.0 cm; diameter, 1.5 cm) using forced flow of eluent. UVꢀvis measure-
ments were carried out on a Perkin-Elmer Lambda 19 UV/vis spectro-
photometer. Emission spectra were acquired on Perkin-Elmer spec-
trophotometer using 450 W xenon lamp excitation by exciting at the
longest wavelength absorption maxima. All samples for emission spectra
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were degassed by at least three freezeꢀpumpꢀthaw cycles in an anaerobic
cuvette and were pressurized with N2 following each cycle. Emission
spectra at 77 K were acquired in frozen 2-methyltetrahydrofuran (2-me-
THF) glass. Luminescence quantum yields (Φp) were determined at
298 K (estimated uncertainty, (15%) using standard methods;40
wavelength-integrated intensities (I) of the corrected emission spectra
were compared to isoabsorptive spectra of quinine sulfate standard
(Φref = 0.546 in 1 N H2SO4 air-equilibrated solution) and was corrected
for solvent refractive index. Phosphorescence lifetimes were measured
by time-correlated single-photon counting method (TCSPC) performed
on an Edinburgh FLS920 spectrophotometer, using nF900 lamp source
at 30 000 Hz frequency with 15 nm excitation and 15 nm emission slit
widths. Thermogravimetric analysis (TGA) was done using a NETZSCH
STA 449C instrument. Cyclic voltammograms were obtained with BAS
100W voltammetric analyzer. The cell was equipped with a gold working
electrode, a Pt counter electrode, and a nonaqueous reference electrode.
All sample solutions (CH2Cl2) were approximately 5 ꢁ 10ꢀ3 M in
substrate and 0.1 M in Bu4NPF6 and were prepared under nitrogen.
Ferrocene was subsequently added and the calibration of voltammograms
recorded. The BAS 100W program was employed for data analysis.
Commercially available reagents were purchased from Aldrich and
were used as such without further purification. Sodium tetrachloroaurate-
(III) dihydrate was purchased from Strem Chemicals. All terminal
alkynes described were either commercially purchased or synthesized
by established sonogashira cross-coupling protocol.
column chromatography (neutral Al2O3:eluent:EtOAc and hexane
mixture) yields respective products as off-white to yellow solids. In
some cases the purification procedures are slightly modified and are
described below individually along with characterization data.
Note: During initial optimization experiments, aqueous workup
protocol was followed and compounds were found to be quite stable
to addition of water; later a direct purification procedure as described
above was adopted because it gave improved yields.
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = Phenyl-
acetylene] (1a). The reaction of A (0.10 g, 0.236 mmol) with pheny-
lacetylene (0.06 mL, 0.538 mmol) following the general procedure
yielded 1a as an off-white solid after column chromatography (neutral
Al2O3; eluent, hexane/EtOAc = 5:1). Yield = 0.072 g, 55%. Positive ESI-
MS: m/z 553.0 [Mþ]. IR (KBr): ν(CtC) 2132, 2160 cmꢀ1. 1H NMR
(500 MHz, CDCl3, 298 K): δ 7.33ꢀ7.48 (m, 8H), 7.50ꢀ7.54 (m, 1H),
7.58ꢀ7.63 (m, 4H), 7.81 (d, J = 10.0 Hz, 1H), 8.02 (d, J = 10.0 Hz, 1H),
8.16 (t, J = 10.0 Hz, 1H), 8.32 (d, J = 10.0 Hz, 1H), 9.74 (d, J = 5.0 Hz,
1H). 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 80.8, 99.5, 104.3,
118.3, 121.0, 124.8, 125.4, 126.4, 126.5, 127.6, 128.1, 128.7, 128.8, 132.2
(2C), 132.3, 132.4, 136.2, 142.3, 146.1, 151.4, 156.6, 167.4. Anal. Calc
for C27H18AuN (%): C, 58.60; H, 3.28; N, 2.53. Found: C, 58.39; H,
3.46; N, 2.40.
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = 1-Ethynyl-4-
fluorobenzene] (1b). The reaction of A (0.20 g, 0.473 mmol) with
1-ethynyl-4-fluorobenzene (0.124 mL, 1.08 mmol) following the general
procedure yielded 1b as an off-white solid which was purified by column
chromatography (neutral Al2O3; eluent, hexane/EtOAc = 1:1). Yield =
0.175 g, 63%. Positive ESI-MS: m/z 612.0 [M þ Na]þ. IR (KBr):
Synthesis of [(N∧C)AuCl2] [N∧C = 2-(2,4-Difluorophenyl)pyridine]
(D). (3,5-Difluoro-2-(pyridin-2-yl)phenyl)mercury(II) chloride (0.170 g,
0.398 mmol) was added as a suspension in dichloromethane (DCM)
(15.0 mL) to a solution of sodium tetrachloroaurate(III) dihydrate
(0.158 g, 0.397 mmol) in acetonitrile (15.0 mL), and the mixture was
stirred for 4 h at RT. It was then filtered and washed with cold
acetonitrile (4.0 mL) and dried in vacuo to obtain off-white solid. Yield
= 0.087 g, 48%. Positive ESI-MS: m/z 421.0 [M ꢀ Cl]þ. IR (KBr):
ν(AuꢀCl) 301, 320 cmꢀ1. 1H NMR (500 MHz, DMSO-d6, 298 K): δ
7.35 (td, J = 10.0 Hz, 2.5 Hz, 1H), 7.53 (d, J = 7.0 Hz, 1H), 7.77 (t, J = 7.0
Hz, 1H), 8.26 (d, J = 8.0 Hz, 1H), 8.37 (t, J = 7.5 Hz, 1H), 9.61 (d, J = 7.0
Hz, 1H). 13C{1H} NMR (125 MHz, DMSO-d6, 298 K): δ 105.2 (t,
2JCꢀF = 26.0 Hz), 113.5 (d, 2JCꢀF = 26.0 Hz), 124.3 (d, 2JCꢀF = 19.5
Hz), 125.1, 127.0, 144.4, 148.4, 150.3, 158.8 (dd, 1JCꢀF = 260.0 Hz, 12.3
Hz), 160.5, 161.2 (dd, 1JCꢀF = 260.0 Hz, 12.5 Hz). 19F NMR (282 MHz,
DMSO-d6, 298 K): δ ꢀ107.0, ꢀ102.2. Anal. Calc for C11H6AuCl2F2N
(%): C, 28.84; H, 1.32; N, 3.06. Found: C, 28.62; H, 1.26; N, 3.19.
Synthesis of [(N∧C)AuCl2] [N∧C = Benzo[h]quinoline][AuCl2] (E).
Benzo[h]quinolin-10-ylmercury(II) chloride (0.15 g, 0.362 mmol) in
DCM (20 mL) was added to a solution of sodium tetrachloroaurate(III)
dihydrate (0.143 g, 0.360 mmol) in acetonitrile (20 mL), and the
mixture was refluxed for 4 days. The pale violet solid that separated out
was collected by filtration, washed with cold acetonitrile (15 mL), and
dried under reduced pressure. Yield = 0.093 g, 58%. Positive ESI-MS:
m/z 467.8 [M þ Na]þ. IR (KBr): ν(AuꢀCl) 378, 412 cmꢀ1. 1H NMR
(400 MHz, DMSO-d6, 298 K): δ 7.71 (t, J = 7.5 Hz, 1H), 7.80 (d, J = 7.5
Hz, 1H), 7.9ꢀ8.0 (m, 4H), 8.93 (d, J = 8.5 Hz, 1H), 9.63 (d, J = 5.6 Hz,
1H); 13C{1H} NMR (125 MHz, DMSO-d6, 298 K): δ 125.1, 126.3,
128.5, 128.9, 129.0, 130.0, 130.3, 131.4, 136.3, 143.4, 149.0, 152.2, 155.7.
Anal. Calc for C13H8AuCl2N (%): C, 35.00; H, 1.81; N, 3.14. Found: C,
34.79; H, 1.83; N, 2.97.
1
ν(CtC) 2137, 2165 cmꢀ1. H NMR (500 MHz, CD2Cl2, 298 K):
δ 7.05ꢀ7.11 (m, 4H), 7.40ꢀ7.47 (m, 2H), 7.51 (t, J = 7.5 Hz, 1H),
7.55ꢀ7.61 (m, 4H), 7.78 (d, J = 7.5 Hz, 1H), 8.00 (d, J = 7.5 Hz, 1H),
8.14 (t, J = 7.5 Hz 1H), 8.25 (d, J = 10.0 Hz, 1H), 9.66 (d, J = 5.5 Hz, 1H).
13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 79.6, 97.8, 102.6, 115.1,
115.3, 117.1, 120.5, 121.9, 122.0, 124.3, 124.9, 127.6, 131.8, 133.4, 133.5,
135.6, 141.8, 145.5, 150.9, 155.8, 162.0 (d, 1JCꢀF = 246.0 Hz), 161.7 (d,
1JCꢀF = 246.0 Hz), 166.8. 19F NMR (282 MHz, CD2Cl2, 298 K): δ ꢀ
115.3, ꢀ114.9. Anal. Calc for C27H16AuF2N (%): C, 55.02; H, 2.74; N,
2.38. Found: C, 54.94; H, 2.70; N, 2.25.
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = 5-Ethynyl-
1,2,3-trimethoxybenzene] (1c). The reaction of A (0.10 g, 0.236 mmol)
with 5-ethynyl-1,2,3-trimethoxybenzene (0.104 g, 0.542 mmol) follow-
ing the general procedure yielded 1c as a yellow crystalline solid after
chromatographic purification (neutral Al2O3; eluent, hexane/EtOAc =
1
1:1). Yield = 0.089 g, 50%. IR (KBr): ν(CtC) 2161, 2171 cmꢀ1. H
NMR (500 MHz, CD2Cl2, 298 K): δ 3.82 (s, 6H), 3.83 (s, 6H), 3.89 (s,
3H), 3.90 (s, 3H), 6.84 (s, 2H), 6.86 (s, 2H), 7.41ꢀ7.49 (m, 2H), 7.53
(t, J = 10.0 Hz, 1H), 7.80 (d, J = 10.0 Hz, 1H), 8.00 (d, J = 10.0 Hz, 1H),
8.16 (t, J = 10.0 Hz, 1H), 8.28 (d, J = 5.0 Hz. 1H), 9.70 (d, J = 5.0 Hz,
1H). 13C{1H} NMR (125 MHz, CD2Cl2, 298 K): δ 56.0, 60.5, 79.0,
99.0, 103.9, 108.8, 108.9, 116.4, 120.5, 120.7, 120.9, 124.3, 124.9, 127.6,
128.5, 131.6, 135.6, 138.0, 138.2, 141.8, 142.5, 145.5, 147.8, 150.8, 153.0,
155.9, 166.7. Anal. Calc for C33H30AuNO6 (%): C, 54.03; H, 4.12; N,
1.91. Found: C, 53.95; H, 4.01; N, 1.78.
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = 2-Ethynyl-
thiophene] (1d). The reaction of A (0.10 g, 0.236 mmol) with 2-ethynyl-
thiophene (0.058 g, 0.542 mmol) following the general procedure
yielded 1d as a light brown solid after successive purification by column
chromatography (neutral Al2O3; eluent, hexane/EtOAc = 2:1), and crystal-
lization at ꢀ30 °C in DCM/pentane mixtures (1:1). Yield = 0.033 g,
General Procedure for the Synthesis of Cyclometalated Gold(III)
σ-Dialkynyl Complexes (1aꢀ1f, 2a, 3a, 4a, and 5a). To the suspen-
sion of respective cycloaurated gold(III) dichlorides (1.0 equiv.) in
DCM (ca. 5.0 mL) are sequentially added the corresponding alkynes
(2.3 equiv), triethylamine (0.055 equiv), and CuI (0.15 equiv) at RT.
The suspension quickly turns into clear homogeneous solution, which is
then further stirred for 15 min. Removal of solvents in vacuo, followed by
sufficient pentane wash, yields the crude material. Purification by flash
25%. IR (KBr): ν(CtC) 2145, 2155 cmꢀ1 1H NMR (500 MHz,
.
CDCl3, 298 K): δ 6.95 (dt, J = 9.0 Hz, 3.2 Hz, 2H), 7.13ꢀ7.21 (m, 3H),
7.30ꢀ7.37 (m, 3H), 7.47 (t, J = 5.5 Hz, 1H), 7.78 (d, J = 7.5 Hz, 1H),
7.79 (d, J = 7.5 Hz, 1H), 8.05 (t, J = 5.0 Hz, 1H), 8.09 (d, J = 5.2 Hz, 1H),
9.5 (d, J = 5.5 Hz, 1H). 13C{1H} NMR (125 MHz, CDCl3, 298 K):
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δ 85.2, 91.3, 96.1, 98.4, 120.6, 122.7, 124.3, 125.1, 125.2, 125.8, 126.0,
126.2, 126.8, 127.7, 130.5, 130.9, 131.7, 135.4, 141.8, 145.3, 150.7, 155.4,
166.5. Anal. Calc for C23H14AuNS2 (%): C, 48.85; H, 2.50; N, 2.48.
Found: C, 48.61; H, 2.44; N, 2.42.
Synthesis of [(N∧C)AuL2] [N∧C = 2-(2-Thienyl)pyridine, L = 1-Ethy-
nyl-4-fluorobenzene] (4a). The reaction of B (0.10 g, 0.233 mmol) with
1-ethynyl-4-fluorobenzene (0.061 mL, 0.532 mmol) following the
general procedure yielded 4a as an off-white solid after chromatographic
purfication (neutral Al2O3; eluent, hexane/EtOAc = 1:1). Yield = 0.08 g,
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = Ethynyl-
trisopropylsilane] (1e). The reaction of A (0.072 g, 0.170 mmol) with
ethynyltrisopropylsilane (0.088 mL, 0.390 mmol) following the general
procedure yielded 1e as a white crystalline solid after chromatographic
purification. (neutral Al2O3; eluent, hexane/EtOAc = 2:1). Yield = 0.072 g,
60.0%. Positive EI-MS: m/z 736.3 [M þ Na]þ. IR (KBr): ν(CtC)
57%. IR (KBr): ν(CtC) 2120, 2160 cmꢀ1 1H NMR (500 MHz,
.
CDCl3, 298 K): δ 7.05ꢀ7.10 (m, 4H), 7.36 (t, J = 8.5 Hz, 1H),
7.54ꢀ7.64 (m, 7H), 8.05 (t, J = 8.5 Hz, 1H), 9.43 (d, J = 8.0 Hz, 1H).
13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 99.0, 102.8, 112.5, 115.1,
115.3, 119.6, 121.7, 122.0, 122.4, 130.0, 133.0, 133.4, 133.5, 133.6, 133.7,
1
2095, 2071 cmꢀ1. H NMR (500 MHz, CD2Cl2, 298 K): δ 1.14 (s,
142.3, 145.7, 150.5, 160.3, 161.9 (1JCꢀF = 245.0 Hz), 162.4 (1JCꢀF
=
245.0 Hz). 19F NMR (282 MHz, CD2Cl2, 298 K): δ ꢀ115.1, ꢀ114.8.
Anal. Calc for C25H14AuF2NS (%): C, 50.43; H, 2.37; N, 2.35. Found:
C, 50.35; H, 2.38; N, 2.22.
18H), 1.17 (s, 18H), 1.22 (s, 3H), 1.23 (s, 3H), 7.40ꢀ7.45 (m, 3H), 7.74
(d, J = 7.5 Hz, 2.0 Hz 1H), 7.96 (d, J = 7.5 Hz, 1H), 8.10 (t, J = 7.5 Hz,
1H), 8.31 (dd, J = 7.5 Hz, 2.0 Hz, 1H), 9.78 (d, J = 7.5 Hz, 1H). 13C{1H}
NMR (125 MHz, CD2Cl2, 298 K): δ 11.6, 11.7, 18.6, 18.7, 96.6, 99.0,
102.8, 120.2, 123.7, 124.6, 127.3, 131.3, 136.0, 138.0, 141.7, 145.5 150.7,
156.4, 166.8. Anal. Calc for C33H50AuNSi2 (%): C, 55.52; H, 7.06; N,
1.96. Found: C, 55.60; H, 6.96; N, 1.76.
Synthesis of [(N∧C)AuL2] [N∧C = 2-(5-Methyl-2-thienyl)pyridine,
L = 1-Ethynyl-4-fluorobenzene] (5a). The reaction of C (0.178 g,
0.402 mmol) with 1-ethynyl-4-fluorobenzene (0.105 mL, 0.924 mmol)
following the general procedure, but worked up after 5 min after addition
of CuI, yielded 5a as an off-white solid after chromatographic purifica-
tion (neutral Al2O3; eluent, hexane/EtOAc = 1:1). Yield = 0.10 g, 41%.
Positive EI-MS: m/z 632.1 [M þ Na]þ. IR (KBr): ν(CtC) 2129,
Synthesis of [(N∧C)AuL2] [N∧C = 2-Phenylpyridine, L = 1-Ethynyl-
4-(phenylethynyl)benzene] (1f). The reaction of A (0.10 g, 0.236 mmol)
with 1-ethynyl-4-(phenylethynyl)benzene (0.109 g, 0.542 mmol)
following the general procedure yielded 1f as a yellow solid which
was further purified by column chromatography (acidic Al2O3;
eluent, hexane/EtOAc = 2:1). Yield = 0.1 g, 56.0%. IR (KBr):
ν(CtC) 2129, 2159 cmꢀ1. 1H NMR (500 MHz, CDCl3, 298 K): δ
7.41ꢀ7.44 (m, 7H), 7.45ꢀ7.62 (m, 14H), 7.81 (d, J = 10.0 Hz, 1H),
8.02 (d, J = 10 Hz, 1H), 8.17 (t, J = 10 Hz, 1H), 8.27 (d, J = 5.5 Hz,
1H), 9.70 (d, J = 5.5 Hz, 1H). 13C{1H}NMR (125 MHz, CD2Cl2, 298
K): δ 82.8, 89.2, 90.5, 98.8, 103.6, 120.7, 120.3, 120.5, 121.6, 122.0,
123.0, 124.2, 124.4, 124.5, 124.9, 125.2, 125.8, 125.9, 127.4, 127.6,
128.4, 128.5, 131.1, 131,3, 131.5, 131.6, 131.7, 131.7, 131.9, 135.6,
141.9, 145.5, 150.9, 156.7, 166.9. Anal. Calc for C43H26AuN (%): C,
68.53; H, 3.48; N, 1.86. Found: C, 68.56; H, 3.58; N, 1.62.
1
2165 cmꢀ1. H NMR (500 MHz, CD2Cl2, 298 K): δ 2.62 (s, 3H),
7.05ꢀ7.10 (m, 4H), 7.16 (s, 1H), 7.27 (t, J = 8.5 Hz, 1H), 7.47 (d, J = 8.5,
1H) 7.54ꢀ7.58 (m, 4H), 8.05 (t, J = 8.5 Hz, 1H), 9.34 (d, J = 5.5 Hz,
1H). 13C{1H} NMR (125 MHz, CDCl3, 298 K): δ 15.4, 71.4, 98.9,
102.2, 113.0, 115.1, 115.3, 118.8, 121.5, 121.7, 121.9, 131.5, 133.4, 133.7,
142.1, 143.1, 146.0, 150.2, 160.4, 161.3, 161.7 (1JCꢀF = 267 Hz), 162.0
(1JCꢀF = 248 Hz). 19F NMR (188 MHz, CD2Cl2, 298 K): δ ꢀ115.1, ꢀ
114.7. Anal. Calc for C26H16AuF2NS (%): C, 51.24; H, 2.65; N, 2.30.
Found: C, 51.15; H, 2.77; N, 2.18.
Computational Details. All calculations were performed with the
Gaussian 03 program package36 using the hybrid functional PBE1PBE41
in conjunction with the Stuttgart/Dresden effective core potentials
(SDD) basis set42 for the Au center augmented with one f-polarization
function (exponent R = 1.050) and the standard 6-31þG(d) basis set43
for the remaining atoms. Full geometry optimizations without symmetry
constraints were carried out in the gas phase for the singlet ground states
(S0) and the lowest triplet excited states (T1). The optimized geometries
were confirmed to be potential energy minima by vibrational frequency
calculations at the same level of theory, because no imaginary frequency
was found. The first 10 singletꢀsinglet and singletꢀtriplet transition
energies were computed at the optimized S0 geometries, by using the
time-dependent DFT methodology.37 Solvent effects were taken into
account using the conductor-like polarizable continuum model (CPCM)39
with dichloromethane as solvent for single-point calculations on all
optimized gas-phase geometries.
X-ray Diffraction Analyses. Relevant details about the structure
refinements are given in Tables S1 and S2 of the Supporting Informa-
tion, and selected geometrical parameters are included in Table 1 and
the captions of the corresponding figures (Figures S2ꢀS4 in the Sup-
porting Information). Intensity data were collected at 183(2) K on an
Oxford Xcalibur diffractometer (four-circle kappa platform, Ruby CCD
detector, and a single-wavelength Enhance X-ray source with Mo KR
radiation; λ = 0.710 73 Å)44 The selected suitable single crystals were
mounted using polybutene oil on the top of a glass fiber fixed on a
goniometer head and immediately transferred to the diffractometer.
Preexperiment, data collection, data reduction, and analytical absorption
corrections were performed with the Oxford program suite CrysAlisPro.45
The crystal structures were solved with SHELXS-9746 using direct
methods. The structure refinements were performed by full-matrix least
squares on F2 with SHELXL-97.46 All programs used during the crystal
structure determination process are included in the WINGX software.47
The program PLATON48 was used to check the result of the X-ray analyses.
CCDC-798717-798723 contains the supplementary crystallographic data
Synthesis of [(N∧C)AuL2] [N∧C = 2-(2,4-Difluorophenyl)pyridine,
L = Phenylacetylene] (2a). The reaction of D (0.060 g, 0.131 mmol)
with phenylacetylene (0.032 mL, 0.298 mmol) following the general
procedure yielded 2a as an off-white solid after chromatographic purifica-
tion (neutral Al2O3; eluent, hexane/EtOAc = 1:1). Yield = 0.032 g, 41%.
IR (KBr): ν(CtC) 2137, 2165, cmꢀ1. 1H NMR (500 MHz, CD2Cl2,
298 K): δ 6.86 (td, J = 8.0 Hz, 2.5 Hz, 1H), 7.30ꢀ7.39 (m, 6H), 7.50 (t,
J = 8.0 Hz, 1H), 7.59ꢀ7.64 (m, 4H), 7.97 (dd, J = 8.0 Hz, 2.5 Hz, 1H),
8.14 (t, J = 7.5 Hz, 1H), 8.35 (d, J = 8.0 Hz, 1H), 9.80 (dd, J = 8.0 Hz, 2.5
Hz, 1H). 13C{1H} NMR (125 MHz, CD2Cl2, 298 K): δ 99.0, 103.8,
2
104.0 (t, JCꢀF = 26.2 Hz), 114.1, 118.8, 119.0, 124.2, 124.4, 124.6,
125.6, 125.8, 127.6, 127.9, 128.5, 128.6, 130.7, 132.0, 132.1, 142.7, 151.6,
1
1
161.2 (d, JCꢀF = 275.0 Hz), 163.9, 164.1(d, JCꢀF = 275.0 Hz). 19F
NMR (188 MHz, CD2Cl2, 298 K): δ ꢀ109.2, ꢀ105.4. Anal. Calc for
C27H16AuF2N.H2O (%): C, 53.39; H, 2.99; N, 2.31. Found: C, 53.20; H,
2.91; N, 2.31. (Note: The elemental analysis was measured on a sample
obtained by aqueous workup which was confirmed to be identical to the
above-described in all respects.)
Synthesis of [(N∧C)AuL2] [N∧C = Benzo[h]quinoline, L = Phenyl-
acetylene] (3a). The reaction of E (0.085 g, 0.190 mmol) with
phenylacetylene (0.048 mL, 0.430 mmol) following the general proce-
dure yielded 3a as an off-white solid after chromatographic purification.
(neutral Al2O3; eluent, hexane/EtOAc = 2:1). Yield = 0.070 g, 64.0%. IR
(KBr): ν(CtC) 2135, 2160 cmꢀ1. 1H NMR (500 MHz, CD2Cl2, 298
K): δ 7.34ꢀ7.44 (m, 6H), 7.64ꢀ7.68 (m, 4H), 7.57ꢀ7.82 (m, 3H), 7.87
(d, J = 8.0 Hz, 1H), 7.94 (d, J = 8.5 Hz, 1H), 8.37 (d, J = 7.0 Hz, 1H), 8.60
(d, J = 8.0 Hz, 1H), 9.81 (d, J = 5.5 Hz, 1H). 13C{1H} NMR (125 MHz,
CDCl3, 298 K): δ 78.3, 99.0, 103.6, 116.2, 122.9, 123.9, 125.8, 125.9,
127.0, 127.4, 128.2, 128.2, 128.4, 130.2, 130.8, 131.6, 131.7, 131.8, 133.5,
134.8, 140.5, 141.2, 149.7, 154.7, 155.7. Anal. Calc for C29H18AuN (%):
C, 60.32; H, 3.14; N, 2.43. Found: C, 60.23; H, 3.27; N, 2.33.
5439
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Inorganic Chemistry
ARTICLE
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Supporting Information. Text describing synthetic de-
b
tails and spectroscopic data of D, XRD details, and computa-
tional details as well as a reference list, figures showing step 1 for
D, thermogravimetric analysis of 1a and 1b, ORTEP plots of 1b,
1c, and 4a, absorption and emission spectra of 1bꢀ1e and 2a,
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Corresponding Author
*E-mail: venkatesan.koushik@aci.uzh.ch.
and references therein.
(30) Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Mukaide, T.;
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’ ACKNOWLEDGMENT
We thank S. V. Rocha and Dr. N. Finney for help with lifetime
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Prof. H. Berke for generous support.
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