Mono- and di-gold(I) naphthalenes and pyrenes: Syntheses, crystal structures, and photophysics

Article abstract of DOI:10.1021/om9005214

(Phosphine)- and (N-heterocyclic carbene)gold(I) derivatives of naphthalene and pyrene are reported, containing one or two gold atoms per hydrocarbon. The new complexes are prepared by arylation of gold(I) substrates by arylboronic acids or aryl pinacolbo

Full text of DOI:10.1021/om9005214

Organometallics 2009, 28, 5669–5681 5669
DOI: 10.1021/om9005214
Mono- and Di-Gold(I) Naphthalenes and Pyrenes: Syntheses,
Crystal Structures, and Photophysics
Lei Gao,† Miya A. Peay,† David V. Partyka,† James B. Updegraff III,† Thomas S. Teets,‡
Arthur J. Esswein,‡ Matthias Zeller,§ Allen D. Hunter,§ and Thomas G. Gray*,†
†Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106,
‡Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and
§Department of Chemistry, Youngstown State University, 1 University Plaza, Youngstown, Ohio 44555
Received June 17, 2009
(Phosphine)- and (N-heterocyclic carbene)gold(I) derivatives of naphthalene and pyrene are
reported, containing one or two gold atoms per hydrocarbon. The new complexes are prepared by
arylation of gold(I) substrates by arylboronic acids or aryl pinacolboronate esters in the presence of
cesium carbonate. Isolated yields range from 52% to 98%. The boron precursors themselves derive
from the parent hydrocarbon, where boron is installed in an iridium-catalyzed reaction, or from the
aromatic bromides, which are borylated with palladium catalysis. Most of the new gold(I) complexes
are air- and moisture-stable colorless solids; they are characterized by multinuclear NMR and optical
spectroscopy, combustion analysis, and high-resolution mass spectrometry. X-ray diffraction crystal
structures are reported for seven. Gold binding red-shifts optical absorption profiles, which are
characteristic of the aromatic skeleton. All compounds show triplet-state luminescence, and dual
singlet and triplet emission occurs in some instances. Phosphorescence persists for milliseconds at 77 K
and for hundreds of microseconds at room temperature. The compounds’ photophysical character-
istics, along with time-dependent density-functional theory calculations, suggest emission from
ππ* states of the aromatic core. Triplet-state geometry optimization finds minimal geometric rearrange-
ment upon one-electron promotion from the (singlet) ground state.
Introduction
groups are gaining recognition.8-13 The spin-orbit coupling
constant of 5d-electrons in gold is 5090 cm
-1 14 that of a 5p-
electron in iodine is 5700 cm-1 15
;
The (phosphine)- and (N-heterocyclic carbene)gold(I) frag-
ments are isolobal with the proton;1,2 they bind terminally to
aromatic carbons much like hydrogen and the halogens.3-7
These gold fragments’ identities as relativistic functional
.
The heavy-atom effect16-22 of gold (Z = 79) influences
both ground- and excited-state properties. Gorin and
Toste23 have summarized relativistic effects on homoge-
neous catalysis with gold. The Lewis acidity of LAuþ frag-
ments (L = PR3, N-heterocyclic carbene) is partly ascribable
to the relativistic contraction of the gold 6s orbital, which
dominates bonding in a two-coordinate linear geometry.24
The low-energy LUMO of LAuþ in turn stabilizes the
LUMOs of gold-alkyne complexes and promotes their re-
activity toward incoming nucleophiles.
*To whom correspondence should be addressed. E-mail: tgray@case.
edu.
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2009 American Chemical Society
Published on Web 09/10/2009
pubs.acs.org/Organometallics

5670 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
Relativity alters the optical properties of organogold
compounds. Aurophilicity, the mutual attraction between
gold centers, derives partly from relativity but also from
electron correlation.25,26 Aurophilic contacts between gold-
(I) sites often produce nonstructured luminescence, espe-
cially at low temperatures.
microwave-assisted protocol that transforms aryl chlorides
into arylpinacolboronate esters.37 Recently Buchwald and
collaborators have reported efficient palladium-catalyzed
borylation reactions of aryl chlorides38 and aryl (pyrollyl)
bromides.39 These reactions require a supporting base and
are promoted by dialkylbiarylphosphine ligands.
Reports from this laboratory demonstrate that aryl-group
transfer from boronic acids or boronate esters attaches
aromatic skeletons to gold(I) under mild conditions.8 Earlier
publications by Fackler, Schmidbaur, and their co-workers
documented phenyl group transfer to gold(I) from tetraphe-
nylborate anion.27,28 An example is 1-naphthyl group trans-
fer to a (phosphine)gold(I) bromide, eq 1:
Precursors to boronate esters need not be aryl halides or
triflates. Much progress40,41 has followed from investiga-
tions of transition element-catalyzed borylation of arenes.
Marder and collaborators have described iridium-catalyzed
borylation reactions of naphthalene, pyrene,42 and other
aromatics.43 These reactions bypass prefunctionalized re-
agents such as aryl iodides or triflates. They differ in regio-
selectivity from electrophilic aromatic substitution. For
example, pyrene borylates at the 2- and 7-positions in one
pot.42,44 To obtain 2- or 2,7-disubstituted pyrenes requires
reduction to a tetrahydropyrene species, followed by elec-
trophilic attack and rearomatization.45-47 The regioselec-
tivity of iridium-catalyzed borylation possibly derives from
an encumbered intermediate, the 16-electron species
[Ir(bpy)(Bpin)3] (bpy = 2,20-bipyridine; Bpin = pinacolbo-
ronato), which is proposed to undergo a rate-limiting C-H
bond activation step.48 Carbon-hydrogen bonds adjacent
to ring junctures or substituents resist borylation.
Thus, palladium- and iridium-catalyzed borylation proto-
cols are complementary. Palladium-catalyzed borylation
necessitates halide or sulfonic ester reactants that are ac-
cessed by electrophilic aromatic substitution. Iridium-based
borylation is dominated by sterics and delivers a different set
of functionalized aromatics that classical methods achieve
with difficulty. However, they can produce mixtures of
products that require nontrivial separation.
This protocol avoids pyrophoric reagents entirely. Two gold-
bearing 1-pyrenyls were prepared from pyrene-1-boronic
acid, and a preliminary account of their syntheses and
photophysics is available.29 Subsequent reports of pyrene
bearing one or two (Ph3P)AuI moieties and of (Ph3P)Au-
(2-naphthyl) have appeared,30,31 but these compounds are
prepared by lithiation of aryl bromide precursors. Access to
organogold complexes is limited by the availability of sui-
table haloaromatic reactants.
The base-supported protocol of eq 1 is simple to execute
and accommodates a range of functionalities. Gold(I) aryls
bearing nitro, carbonyl, and heterocyclic substituents have
all been prepared in good yields.8 These functional groups
are unlikely to survive classical auration reactions, which
entail lithiation or magnesiation protocols.
Reported here are the syntheses, structures, and optical
spectroscopy of new mono- and digold naphthalenes and
pyrenes. The use of boron reagents leads to digold aryls that
appear inaccessible by lithiation because of competing reduc-
tion of gold(I) to the element by dilithioarenes. Emplacement of
a single gold atom endows the hydrocarbon skeleton with
triplet-state photophysics. In several compounds, both singlet
fluorescence and triplet phosphorescence are jointly observable
at room temperature. The result is a direct assessment of the
energy gap between the first singlet and triplet excited states.
Nine new gold(I) compounds are reported, of which seven are
crystallographically characterized. Time-dependent density-
functional theory calculations find the luminescence to be
intraligand in nature. Geometry optimizations of the lowest
The choice of boron-containing precursors does not re-
quire lithiation for eventual gold binding. Mild catalytic
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iodides,32 and triflates33 with (dppf)PdCl2 (dppf = 1,10-bis-
[diphenylphosphino]ferrocene) in the presence of potassium
acetate in polar solvents. Shortly thereafter, Masuda and co-
workers34 reported a similar boronation reaction using
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Article
Organometallics, Vol. 28, No. 19, 2009 5671
triplet states are discussed. Comparisons with optimized
ground states and crystal structures are made. We demonstrate
that (phosphine)- and (N-heterocyclic carbene)gold(I) termini
act as relativistic functional groups that transform the photo-
physics of hydrocarbon frameworks. Portions of this work
have been previously communicated.8,29
Compound 5: Cy3PAuBr (88 mg, 0.16 mmol), 1 (78.8 mg,
0.31 mmol), and Cs2CO3 (197 mg, 0.60 mmol) were suspended in
10 mL of isopropyl alcohol. After degassing, the reaction vessel
was immersed in a 50 ꢀC oil bath and stirred under argon for
24 h. Isopropyl alcohol was removed by rotary evaporation, the
remaining solid was extracted into 50 mL of benzene, and the
solution was filtered through Celite. Benzene was then removed
by rotary evaporation. The residue was washed using hexanes
twice and triturated with pentane. After removing pentane by
rotary evaporation, a white solid was collected. The white solid
was then dissolved in a minimum amount of benzene and filtered
through Celite. Crystallization by diffusing pentane into the
concentrated benzene solution afforded the product as colorless
1
crystals. Yield: 62 mg, 64%. H NMR (C6D6): δ (ppm) 8.58
(d, 1H, J = 6.0 Hz, 2-naphthyl), 8.28 (dd, 1H, J = 8.0 Hz, 4.4
Hz, 2-napththyl), 7.92 (d, 1H, J = 8.0 Hz, 2-naphthyl), 7.86
(d, 1H, J = 8.0 Hz, 2-naphthyl), 7.78 (d, 1H, J = 8.0 Hz,
2-naphthyl), 7.24-7.36 (m, 2H, 2-naphthyl), 1.39-1.90 (m,
33H, C6H11). 31P{1H} NMR (C6D6): δ (ppm) 57.6. HR-MS
(ESþ): calcd m/z = 605.2612 (M þ H)þ; found m/z = 605.2571.
Anal. Calcd for C28H40AuP: C, 55.63; H, 6.67. Found: C,
55.65; H, 6.82. UV-vis (THF): λ (ε) 279 (5.9 ꢀ 103 M-1 cm-1),
289 (5.7 ꢀ 103 M-1 cm-1), 300 (3.8 ꢀ 103 M-1 cm-1), 325 nm
(260 M-1 cm-1). Emission (THF, ex. 279 nm): 355, 480, 516,
553, 600 nm. A 56% yield was obtained when using Cy3PAuN3
as the starting material in an otherwise analogous procedure.
Compound 6: Cy3PAuBr (176 mg, 0.316 mmol), 2 (66.9 mg,
0.176 mmol), and Cs2CO3 (230 mg, 0.704 mmol) were suspended
in 5 mL of isopropyl alcohol. Benzene (5 mL) was added to
promote dissolution of the starting materials. After degassing,
the reaction vessel was immersed in a 50 ꢀC oil bath and stirred
under argon for 24 h. After cooling, the solvents were removed
by rotary evaporation, and the remaining solid was extracted
into 100 mL of dichloromethane. The extract was filtered
through Celite. Dichloromethane was removed by rotary eva-
poration. The residue was washed twice with hexanes (100 mL)
and was then triturated with pentane. An off-white solid was
collected upon vacuum filtration removal of pentane. The solid
was washed with water and hexanes and dried under vacuum.
The solid was then dissolved in a minimum amount of dichlor-
omethane and filtered through Celite. Layering ether onto
this dichloromethane solution yielded 6 as colorless crystals.
Experimental Section
Cy3PAuBr and SIPrAuBr were synthesized using methods
documented for related phosphine-ligated gold(I) chlorides;49
Cy3PAuN3 was prepared as previously.50,51 Caution: Metal
azide complexes are potentially explosive and precautions are
necessary. Cy3PAuOAc was prepared analogously to the tri-
phenylphosphine complex.52 All other solvents and reagents
were used as received. Metalation reaction mixtures were stirred
vigorously under argon to ensure thorough mixing. Combustion
analyses (C, H, and N) were performed by Robertson Microlit
Laboratories, Madison, NJ. NMR spectra (1H, 13C{1H}, and
31P{1H}) were recorded on a Varian AS-400 spectrometer. Che-
mical shifts are reported in parts-per-million relative to Si(CH3)4
(1H, 13C) or 85% aqueous H3PO4 (31P). Mass spectrometry was
performed at The Ohio State University and the University of
Cincinnati mass spectrometry facilities. Compounds 1, 13, and 14
were synthesized following the literature procedures.42 Com-
pound 4 was purchased from Frontier Scientific, Inc.
Syntheses of 4,4,5,5-Tetramethyl-2-(2-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)naphthalen-6-yl)-1,3,2-dioxaborolane
(2) and 4,4,5,5-Tetramethyl-2-(2-(4,4,5,5-tetramethyl-1,3,2-di-
oxaborolan-2-yl)naphthalen-7-yl)-1,3,2-dioxaborolane (3). 2,6-
Dibromonaphthalene or 2,7-dibromonaphthalene (122.2 mg,
0.4273 mmol), bis(pinacolato)diboron (227.9 mg, 0.8975 mmol),
and potassium acetate (KOAc) (126.4 mg, 1.30 mmol) were
mixed in 5 mL of 1,4-dioxane and degassed (solution 1). Pd-
(dba)2 (dba = dibenzylideneacetone) (14 mg, 0.024 mmol) and
tricyclohexylphosphine (PCy3) (16 mg, 0.057 mmol) were mixed
in 5 mL of degassed 1,4-dioxane, and the resultant red solution
was stirred for 30 min (solution 2). Solution 1 was added to
solution 2 with stirring. After 10 min, the mixture was heated to
80 ꢀC for 24 h under an argon atmosphere. During the course of
reaction, the reaction mixture took on a pale yellow color and
later evolved into a black suspension. After 24 h, 1,4-dioxane
was removed by rotary evaporation. The product was extracted
into 100 mL of dichloromethane. The yellow dichloromethane
solution was then washed with water twice, and the organic layer
was collected and dried over MgSO4. The solution was then
filtered through a layer of silica gel and Celite under vacuum.
Solvent was removed and a yellow solid was collected. Sublima-
tion under vacuum at 150-160 ꢀC yielded the analytically pure
white product. Yield for 2: 83.0 mg, 51%. 1H NMR (CDCl3): δ
(ppm) 8.41 (s, 2H, naphthyl), 7.83 (dd, 4H, J = 5.2 Hz, 8.0 Hz,
naphthyl), 1.38 (s, 24 H, C(CH3)4). Yield for 3: 89.3 mg, 55%. 1H
NMR (CDCl3): δ (ppm), 8.35 (s, 2H, naphthyl), 7.83 (dd, 4H,
J = 6.0 Hz, 8.0 Hz, naphthyl), 1.39 (s, 24H, C(CH3)4). These
compounds were used without further purification.
1
Yield: 156 mg, 90%. H NMR (CDCl3): δ (ppm) 7.85 (d, 2H,
J = 5.6 Hz, naphthyl), 7.63-7.64 (m, 2H, naphthyl), 7.55-7.58
(m, 2H, naphthyl) 1.55-2.10 (m, 66H, (C6H11)3). 31P{1H} NMR
(CDCl3): δ (ppm) 58.0. HR-MS (ESþ): calcd m/z = 1081.4519
(M þ H)þ; found m/z = 1081.4612. Anal. Calcd for C46H72-
Au2P2: C, 51.11; H, 6.71. Found: C, 50.84; H, 6.62. UV-vis
(CH2Cl2): λ (ε) 260 (5.74 ꢀ 104 M-1 cm-1), 294 (1.30 ꢀ 104 M-1
cm-1), 304 (1.6 ꢀ 104 M-1 cm-1), 314 (1.3 ꢀ 104 M-1 cm-1),
333 nm (1.18 ꢀ 104 M-1 cm-1). Emission (CH2Cl2, ex. 314 nm):
404, 490, 525, 565, 610 nm.
Compound 7: Cy3PAuBr (176 mg, 0.316 mmol), 3 (73 mg,
0.192 mmol), and Cs2CO3 (250 mg, 0.768 mmol) were suspended
in 5 mL of isopropyl alcohol. Benzene (5 mL) was added to
promote dissolution. After degassing, the reaction vessel was
immersed in a 50 ꢀC oil bath and stirred under argon for 24 h.
Solvents were removed by rotary evaporation, and the remain-
ing solid was extracted into 100 mL of dichloromethane; the
extract was filtered through Celite. Dichloromethane was re-
moved evaporatively. The residue was washed using hexanes
and water several times and was triturated with pentane. After
removing pentane by rotary evaporation, an off-white solid was
collected. The solid was then dissolved in a minimum amount
of dichloromethane and filtered through Celite. Layering
ether onto this dichloromethane solution yielded 7 as colorless
crystals. Yield: 147 mg, 85%. 1H NMR (CDCl3): δ (ppm) 7.87
(d, 2H, J = 5.2 Hz, naphthyl), 7.59-7.62 (m, 2H, naphthyl),
7.50-7.52 (m, 2H, naphthyl), 1.56-2.10 (m, 66H, (C6H11)3).
31P{1H} NMR (CDCl3): δ (ppm) 58.0. Anal. Calcd for
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5672 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
C46H72Au2P2: C, 51.11; H, 6.71. Found: C, 50.98; H, 6.64.
UV-vis (CH2Cl2): λ (ε) 260 nm (6.98 ꢀ 104 M-1cm-1). Emis-
sion (CH2Cl2, ex. 307 nm): 373, 490, 524, 560 nm.
then triturated with pentane. After removing pentane by rotary
evaporation, an off-white solid was collected. This solid was
then dissolved in a minimum amount of dichloromethane, and
hexanes were layered onto the solution. Slow evaporation gave a
precipitate that was the analytically pure product. Yield:
Compound 8: Ph3PAuBr (172 mg, 0.319 mmol), 4 (110 mg,
0.640 mmol), and Cs2CO3 (196 mg, 0.602 mmol) were suspended
in 10 mL of isopropyl alcohol and charged into a round-bottom
flask. After degassing, the reaction vessel was immersed in a
50 ꢀC oil bath and stirred under argon for 24 h. Isopropyl alcohol
was removed by rotary evaporation, and the remaining solid was
extracted into 50 mL of benzene and filtered through Celite.
Benzene was removed by rotary evaporation. The residue was
triturated with pentanes; the resulting powder was transferred to a
vacuum filtration frit and washed with methanol, water, and
pentane, and a white solid was collected. The white solid was then
dissolved in a minimum amount of benzene and filtered through
Celite. Crystallization by diffusing pentane into the concentrated
benzene solution afforded the product as pale yellow crystals.
Yield: 109 mg, 58%. 1H NMR (C6D6): δ (ppm) 8.57 (d, 1H, J =
6.0 Hz, 2-naphthyl), 8.28 (dd, 1H, J = 8.0 Hz, 4.8 Hz, 2-naphthyl),
7.93 (d, 1H, J = 8.0 Hz, 2-naphthyl), 7.87 (d, 1H, J = 8.0 Hz, 2-
naphthyl), 7.79 (d, 1H, J= 7.6 Hz, 2-naphthyl), 7.42-7.48 (m, 5H,
phenyl), 7.26-7.40 (m, 2H, 2-naphthyl), 6.90-7.00 (m, 10H,
phenyl). 31P{1H} NMR (C6D6): δ (ppm) 44.0. HR-MS (ESþ):
calcd m/z = 587.1198 (M þ H)þ; found m/z = 587.1138. Anal.
Calcd for C28H22AuP: C, 57.35; H, 3.78. Found: C, 57.23; H, 3.65.
UV-vis (THF): λ (ε) 276 (8.7 ꢀ 103 M-1 cm-1), 290 (7.6 ꢀ 103
M-1 cm-1), 300 (5.4 ꢀ 104 M-1 cm-1), 325 nm (378 M-1 cm-1).
Emission (THF, ex. 275 nm): 353, 481, 516, 555, 600 nm.
1
189 mg, 91%. H NMR (CDCl3) δ (ppm): 7.34 (t, 4H, J =
8.0 Hz, CH aromatic), 7.18 (d, 8H, J = 8.0 Hz), 7.08-7.11 (m,
4H, naphthyl), 6.89 (d, 2H, J = 8.0 Hz, naphthyl), 3.97 (s, 8H,
CH2 imidazole), 3.13 (septet, 8H, J = 6.8 Hz, CH(CH3)2), 1.44
(d, 24 H, J = 7.2 Hz, CH(CH3)2), 1.32 (d, 24H, J = 7.2 Hz,
CH(CH3)2). 13C NMR (CDCl3) δ (ppm): 217.19 (s, C carbene),
164.02 (s), 146.69 (s), 138.20 (s), 137.36 (s), 134.80 (s), 132.08 (s),
129.29 (s), 124.18 (s), 123.92 (s), 53.66 (s), 28.96 (s), 25.13 (s),
24.05 (s). HR-MS (ESþ): calcd m/z = 1303.6100 (M þ 2H)2þ
;
found m/z = 1301.6012 (Mþ), 1302.6067 (M þ H)þ, 1303.6012
(M þ 2H)2þ. Anal. Calcd for C64H82Au2N4: C, 59.05; H, 6.35;
N, 4.30. Found: C, 58.90; H, 5.96; N, 3.99. UV-vis (CH2Cl2):
λ (ε) 310 nm (1.39 ꢀ 104 M-1 cm-1). Emission (CH2Cl2, ex.
324 nm): 490, 524, 564, 611 nm.
Compound 12: SIPrAuOAc (103.5 mg, 0.1598 mmol), 3
(36.7 mg, 0.0966 mmol), and Cs2CO3 (127 mg, 0.390 mmol)
were suspended in 5 mL of isopropyl alcohol and charged into a
round-bottom flask. Benzene (5 mL) was added to promote
solubility. After degassing, the reaction vessel was immersed in a
45 ꢀC oil bath and stirred under argon for 48 h. Solvents were
then removed by rotary evaporation, and the remaining solid
was extracted into 50 mL of benzene and filtered through Celite.
Benzene was then removed by rotary evaporation. The residue
was washed using hexanes twice and triturated with pentane.
After removing pentane by rotary evaporation, an off-white
solid was collected. Vapor diffusion of ether into a concentrated
benzene solution yielded no crystals. Evaporative concentration
produced an amber solid that was the analytically pure product.
Yield: 66 mg, 63%. 1H NMR (CDCl3): δ (ppm) 7.38 (t, 4H, J =
5.6 Hz, CH aromatic), 7.23 (d, 8H, J = 5.6 Hz, naphthyl), 7.15
(d, 2H, J = 8.0 Hz, naphthyl), 7.09 (s, 2H, naphthyl), 6.83 (d,
2H, J = 8.0 Hz, naphthyl) 3.99 (s, 8H, CH2 imidazole), 3.16
(septet, 8H, J = 6.8 Hz, CH(CH3)2), 1.48 (d, 24 H, J = 7.2 Hz,
CH(CH3)2), 1.35 (d, 24H, J = 7.2 Hz, CH(CH3)2). 13C NMR
(CDCl3): δ (ppm) 217.25 (s, C carbene), 164.93 (s), 146.69 (s),
138.04 (s), 136.70 (s), 134.85 (s), 133.42 (s), 130.44 (s), 129.29 (s),
124.20 (s), 123.88 (s), 53.69 (s), 28.92 (s), 25.10 (s), 24.04 (s).
Anal. Calcd for C64H82Au2N4: C, 59.05; H, 6.35; N, 4.30.
Found: C, 59.33; H, 6.52; N, 4.22. UV-vis (CH2Cl2): λ (ε) 313
nm (6.4 ꢀ 104 M-1 cm-1). Emission (CH2Cl2, ex. 313 nm): 355,
370, 490, 526, 564, 609 nm.
Compound 15: To a 100 mL Schlenk flask, 13 (60.0 mg,
0.183 mmol), Cs2CO3 (65.5 mg, 0.201 mmol), and Cy3PAuN3
(68.7 mg, 0.13 mmol) were suspended in 8 mL of isopropyl
alcohol and degassed. The reaction mixture was then stirred
under argon at 50 ꢀC for 24 h. Formation of a white precipitate
resulted. Solvent was removed by rotary evaporation, and
the resulting white powder was dissolved in dichloromethane
(10 mL) and washed three times with H2O (10 mL portions). The
dichloromethane solution was dried with Na2SO4, and solvent
was removed by rotary evaporation. Trituration was performed
with pentane, and solvent was removed by rotary evaporation.
Colorless crystals were formed from evaporation of an acetone
solution. Yield: 46 mg, 52%. 1H NMR (C6D6): δ (ppm) 8.96 (d,
2H, J = 4.8 Hz, pyrenyl), 8.06 (d, 2H, J = 8.8 Hz, pyrenyl), 7.96
(d, 2H, J = 7.6 Hz, pyrenyl), 7.87 (d, 2H, J = 8.8 Hz, pyrenyl),
7.76 (t, 1H, J = 7.2 Hz, pyrenyl), 1.95-1.05 (m, 33H, C6H11)
ppm. 31P{1H} NMR (C6D6): δ (ppm) 57.5. Anal. Calcd for
C34H42AuP: C, 60.17; H, 6.24. Found: C, 59.95; H, 6.48.
HR-MS (ESþ): calcd m/z = 679.2768; found m/z = 679.3013
(M)þ. UV-vis (CH2Cl2): λ (ε) 264 (5.3 ꢀ 104 M-1 cm-1), 328
(2.7 ꢀ 104 M-1 cm-1), 343 nm (3.7 ꢀ 104 M-1 cm-1). Emission
(CH2Cl2, ex. 328 nm): 373, 383, 389, 393, 601 nm.
Compound 9: Ph3PAuBr (168.7 mg, 0.313 mmol), 2 (65.6 mg,
0.173 mmol), and Cs2CO3 (224 mg, 0.687 mmol) were suspended in
10 mL of isopropyl alcohol and charged into a round-bottom flask.
Benzene (10 mL) was added to promote solubility. After degassing,
the reaction vessel was immersed in a 40 ꢀC oil bath and stirred
under argon for 24 h. Solvents were removed by rotary evapora-
tion, and the remaining solid was extracted into 100 mL of
dichloromethane and filtered through Celite. Dichloromethane
was removed by rotary evaporation. The residue was triturated
with pentane and vacuum filtered. After triturating with hexanes
twice, a pale yellow solid was collected. The solid was then
dissolved in a minimum amount of dichloromethane and filtered
through Celite. Crystallization by layering ether onto this dichlor-
omethane solution afforded the product as colorless crystals.
1
Yield: 169.7 mg, 92%. H NMR (CDCl3): δ (ppm) 7.97 (d, 2H,
J = 5.6 Hz, naphthyl), 7.61-7.69 (m, 16H, aromatic H), 7.44-
7.52 (m,18H, aromatic H). 31P{1H} NMR (CDCl3): δ (ppm) 44.4.
HR-MS (ESþ): calcd m/z = 1045.1697 (M þ H)þ; found m/z =
1045.1682. Anal. Calcd for C46H36Au2P2: C, 52.89; H, 3.47.
Found: C, 52.53; H, 3.40. UV-vis (CH2Cl2): λ (ε) 261 (8.74 ꢀ
104 M-1 cm-1), 296 (2.07 ꢀ 104 M-1 cm-1), 308 (2.88 ꢀ 104 M-1
cm-1), 320 nm (2.47 ꢀ 104 M-1 cm-1). Emission (CH2Cl2, ex. 326
nm): 344, 490, 524, 565, 614 nm.
Compound 10: The same procedure was used as for 9. Spark-
ling grayish plates were obtained as the product. Crystallization
by diffusing ether into the concentrated benzene solution
afforded amber crystals. Yield: 98%. 1H NMR (CDCl3): δ
(ppm) 7.98 (d, 2H, J = 6.0 Hz, naphthyl), 7.58-7.69 (m, 16H,
aromatic H), 7.44-7.53 (m, 18H, aromatic H). 31P {1H} NMR
(CDCl3): δ (ppm) 44.4. Anal. Calcd for C46H36Au2P2: C, 52.89;
H, 3.47. Found: C, 52.87; H, 3.29. UV-vis (CH2Cl2): λ (ε)
290 nm (2.7 ꢀ 103 M-1 cm-1). Emission (CH2Cl2, ex. 310 nm):
345, 361, 380, 490, 525, 563, 680, 724, 760 nm.
Compound 11: SIPrAuBr (214 mg, 0.320 mmol), 2 (67.3 mg,
0.176 mmol), and Cs2CO3 (230 mg, 0.704 mmol) were suspended
in 5 mL of isopropyl alcohol. Benzene (5 mL) was added to
promote solubility. After degassing, the reaction vessel was
heated to 45 ꢀC and stirred under argon for 24 h. Solvents were
removed by rotary evaporation, and the remaining solid was
extracted into 100 mL of dichloromethane and filtered through
Celite. Dichloromethane was removed by rotary evaporation.
The residue was washed using hexanes (2 ꢀ 100 mL) and was
Compound 16: A 100 mL Schlenk flask was charged with
Cs2CO3 (90.4 mg, 0.277 mmol) in 4 mL of isopropyl alcohol. In a

Article
Organometallics, Vol. 28, No. 19, 2009 5673
Table 1. Crystallographic Data for New Compounds Collected at 100 ( 2 K
5
6 CH2Cl2
3
7
9
10
15 C6H5Me
3
16 C6H6 C8H10
3
3
formula
mol wt
cryst syst
space
C28H40AuP
604.54
triclinic
Ph1
C47H74Au2Cl2P2 C46H72Au2P2
C46H36Au2P2
1044.62
monoclinic
P21/n
C52H42Au2P2
1122.73
triclinic
P1h
C34H42AuP
678.61
monoclinic
C2/c
C52H74Au2P2
1155.22
monoclinic
P21/n
1165.84
triclinic
P1h
1080.91
orthorhombic
Cmc21
group
a (A)
b (A)
9.093(3)
9.901(2)
21.8915(17)
21.9518(19)
17.8889(15)
90
90
90
8596.6(12)
8
-24 e h e 29
-29 e k e 20
-19 e l e 23
1.670
7.9096(16)
12.458(3)
18.519(4)
90
101.521(2)
90
1788.1(6)
2
-10 e h e 9
-15 e k e 15
-23 e l e 23
1.940
9.3178(8)
13.9021(13)
17.961(2)
67.6530(10)
89.7330(10)
75.5320(10)
2073.1(4)
2
-11 e h e 11
-17 e k e 17
-22 e l e 23
1.799
25.024(5)
13.5950(19)
17.044(2)
90
101.493(2)
90
5682.1(15)
8
-32 e h e 32
-17 e k e 17
-22 e l e 22
1.587
9.5322(9)
16.7591(15)
17.4417(16)
90
94.5900(10)
90
2777.4(4)
2
-12 e h e 11
-21 e k e 21
-22 e l e 22
1.601
10.851(4)
12.724(4)
83.910(4)
78.774(3)
83.093(4)
1218.0(7)
2
-11 e h e 11
-14 e k e 13
-16 e l e 16
1.648
14.031(3)
18.294(4)
94.149(3)
101.681(3)
107.990(3)
2342.2(9)
2
-13 e h e 13
-18 e k e 18
-24 e l e 24
1.653
c (A)
R (deg)
β (deg)
γ (deg)
V (A)
Z
index ranges
Fcald
(Mg/m3)
abs coeff
6.118
6.469
6.923
8.319
7.182
5.255
5.374
(mm-1
)
θ range (deg) 1.64-27.38
1.15-28.28
1156
23 996
2.18-30.52
4288
23 853
1.98-26.83
1000
18 684
1.23-27.30
1084
23 831
1.71-27.50
2720
33 510
2.34-26.92
1348
30 206
F(000)
604
14 172
total no.
of rflns
no. of indep
rflns
5209 (R(int)
= 0.0231)
9250 (R(int)
= 0.0309)
535
7738 (R(int)
= 0.0458)
628
2808 (R(int)
= 0.0618)
226
9112 (R(int)
= 0.0224)
505
6526 (R(int)
= 0.0456)
325
5929 (R(int)
= 0.0297)
317
no. of params 271
varied
final R
indices
(I > 2σ(I))
R indices
(all data)
GOF
R1=0.0200,
wR2 = 0.0554
R1=0.0545,
wR2 = 0.0833
R1=0.0711,
wR2 = 0.1534
R1=0.0569,
wR2 = 0.1122
R1=0.0223,
wR2 = 0.0734
R1=0.0502
wR2 = 0.1059
R1=0.0183,
wR2 = 0.0422
R1=0.0210,
wR2 = 0.0559
1.050
R1=0.0383,
wR2 = 0.0765
1.086
R1=0.0597,
wR2=0.1465
1.048
R1=0.0315,
wR2 = 0.0868
1.025
R1=0.0196,
wR2 = 0.0641
1.154
R1 = 0.0732
wR2=0.1187
1.058
R1=0.0213,
wR2 = 0.0435
1.104
largest diff
peak and
3.108 and
-1.403
2.084 and
-0.994
6.714 and
-1.747
1.039 and
-1.907
0.879 and
-1.388
2.475 and
-1.837
0.816 and
-0.935
hole (e A-3
)
separate round-bottom flask, 14 (60.0 mg, 0.132 mmol) and
Cy3PAuOAc (212.6 mg, 0.396 mmol) were dissolved in 8 mL of
tetrahydrofuran (THF). After degassing both solutions, the
THF solution was cannulated into the Schlenk flask containing
the isopropyl alcohol suspension, and the mixture was stirred
under argon at 50 ꢀC for 24 h. The white precipitate formed during
the course of the reaction was collected by filtration and washed
with isopropyl alcohol and THF. Colorless crystals were formed
from slow evaporation of a xylene solution. Yield: 118.6 mg, 79%.
1H NMR (C6D6): δ (ppm) 8.91 (d, 4H, J = 4.8 Hz, pyrenyl), 8.08
(s, 4H, pyrenyl), 1.95-1.06 (m, 66H, (C6H11)2). 31P{1H} NMR: δ
(ppm) 57.5. Anal. Calcd for C52H74Au2P2: C, 54.07; H, 6.46.
Found: C, 54.05; H, 6.39. MS (ESþ): calcd m/z = 1155.2, found
m/z = 1155.3 (M þ H)þ. UV-vis (CH2Cl2): λ (ε) 287 (1.1 ꢀ 105
M-1 cm-1), 332 (3.7 ꢀ 104 M-1 cm-1), 348 nm (5.9 ꢀ 104 M-1
cm-1). Emission (CH2Cl2, ex. 332 nm): 374, 389, 393, 593 nm.
Luminescence Measurements. Steady-state emission spectra
were recorded at room temperature on a Cary Eclipse fluores-
cence spectrophotometer or on an automated Photon Techno-
logy International (PTI) QM 4 fluorimeter equipped with a
150 W Xe arc lamp and a Hamamatsu R928 photomultiplier
tube. Excitation light was excluded with appropriate glass
filters. Sample solutions were added to a quartz EPR tube,
freeze pump thaw degassed (four cycles, 1 ꢀ 10-5 Torr), and
flame-sealed. Low-temperature emission spectra were recorded
in rigid solvent glass at 77 K by immersion of the sealed EPR
tubes into a liquid nitrogen-filled dewar. Time-resolved phos-
phorescence lifetime data were collected on a nanosecond laser
system described previously.53
X-ray Structure Determinations. Single-crystal X-ray data
were collected on a Bruker AXS SMART APEX CCD diffract-
ometer using monochromatic Mo KR radiation with the omega
scan technique. The unit cells were determined using SMART54
and SAINTþ.55 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.56 Refinement of extinction coeffi-
cients was found to be insignificant. All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were placed in
(54) Bruker Advanced X-ray Solutions. SMART for WNT/2000
(Version 5.628); Bruker AXS Inc.: Madison, WI, 1997-2002.
(55) Bruker Advanced X-ray Solutions. SAINT (Version 6.45); Bru-
ker AXS Inc.: Madison, WI, 1997-2003.
(56) Bruker Advanced X-ray Solutions; SHELXTL (Version 6.10);
Bruker AXS Inc.: Madison, WI, 2000.
(57) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., , Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; and Pople, J. A. Gaussian 03, Revision D.01; Gaussian, Inc.:
Wallingford, CT, 2004.
(53) Loh, Z.-H.; Miller, S. E.; Chang, C. J.; Carpenter, S. D.; Nocera,
D. G. J. Phys. Chem. A 2002, 106, 11700–11708.

5674 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
Table 2. Syntheses of New Compounds
standard calculated positions, and all hydrogen atoms were
refined with an isotropic displacement parameter 1.2 times that
of the adjacent carbon (1.5 times for methyl hydrogen atoms).
Compound 6 crystallized with one molecule of methylene
chloride disordered over three sites with occupancy rates
of 0.526(3), 0.301(6), and 0.173(6). Its C-Cl distances were
restrained to be the same, and the ADPs of the disor-
dered methylene chloride atoms were restrained to be similar
(SIMU and DELU commands in SHELXTL). Atoms Cl6
and C48, which overlap significantly, were restrained to be
isotropic within a standard deviation of 0.02 A2. Refined
crystallographic parameters and residuals for all structures
appear in Table 1.
Computations. Density-functional theory computations
were performed within the Gaussian03 program suite.57 Com-
putations on singlet structures were spin-restricted; those
on triplets were unrestricted. Calculations employed the
modified Perdew-Wang exchange functional of Adamo

Article
Organometallics, Vol. 28, No. 19, 2009 5675
Scheme 1
here include implicit CH2Cl2 solvation (ε = 8.93, 298.15 K),
which was incorporated in single-point calculations of the gas-
phase geometries with Tomasi’s polarizable continuum model
(PCM).63,64 Stability tests validated the integrity of all con-
verged densities. Percentage compositions of molecular orbitals,
overlap populations, and bond orders between fragments were
calculated using the AOMix program of Gorelsky.65,66
Time-dependent DFT output files were parsed with the program
SpectrumWizard, also by Gorelsky.67
Results and Discussion
Synthesis of Compounds. Table 2 collects new gold(I)
complexes and indicates a numbering scheme. Organogold
derivatives of naphthalene and pyrene were prepared from
boronated precursors. Scheme 1 depicts a representative
synthesis for digold naphthalene derivative 6. Reactions of
boronic acids or pinacolboronate esters of aromatic hydro-
carbons with (phosphine)- or (N-heterocyclic carbene)gold-
(I) complexes in the presence of cesium carbonate in alcohol
solvents yield the corresponding arylgold derivatives. The
reaction cleaves a carbon-boron bond to form carbon-gold
bonds. The use of boron-based reagents avoids stridently
reducing conditions incompatible with gold(I) or with
sensitive organic functionalities. In our hands, attempts
to produce digold complexes from dilithionaphthalene
afforded elemental gold with no evidence of the desired
organometallic products. The gold(I) reactants of choice
for binding to aryl skeletons are the (phosphine)- or (N-
heterocyclic carbene)gold(I) bromides. Arylation reac-
tions proceed for gold(I) acetates or azide complexes, but
lower yields are often recovered. In no case is there evi-
dence for the formation of isomers that would diminish
regioselectivity.
Given a choice of arylboronic acid or pinacolboronate
ester starting material, the ester is preferable. Residual,
unreacted boron reagents typically contaminate crude pro-
ducts. The boronic acid can be washed away with methanol,
but the organogold species are partly soluble in this solvent,
and their isolated yields suffer. Unreacted pinacolboronate
esters are hexanes-soluble, but the gold products are not. The
final gold complexes are purified by washing in air without
loss of yield. If the gold(I) starting material is in excess, then
its surplus contaminates the organometallic product and is
difficult to remove with common solvents. Mohr and co-
workers have applied this boron-based protocol to the
synthesis of a peri-diaurated naphthalene.68
Figure 1. Crystal structures (100 K) of new digold(I) organo-
metallics. (a) 9, (b) 10, and (c) 16; 50% probability ellipsoids are
shown. Hydrogen atoms and solvent molecules are omitted for
clarity. Unlabeled atoms are carbon.
and Barone58 and the original Perdew-Wang correlation func-
tional.59 Test calculations performed using other functionals
yielded closely similar results. Nonmetal atoms were described
with the TZVP basis set of Godbelt, Andzelm, and co-work-
ers.60 Gold orbitals were described with the Stuttgart effective
core potential and the associated basis set,61 which was con-
tracted as follows: Au, (8s,6p,5d) f [7s,3p,4d]. Relativistic
effects with the Stuttgart ECP and its associated basis set are
introduced with a potential term (i.e., a one-electron operator)
that replaces the two-electron exchange and Coulomb operators
resulting from interaction between core electrons and between
core and valence electrons. In this way relativistic effects,
especially scalar effects, are included implicitly rather than as
four-component, one-electron functions in the Dirac equation.
Gas-phase equilibrium geometries were optimized in redundant
internal coordinates with imposed maximal symmetry for
ground-state molecules and without symmetry for excited
states. Harmonic frequency calculations verify the resultant
structures to be energy minima, except for the ground-state
digold model complex 160, which exhibits one vibration of
frequency 3.8i cm-1. Animation of this frequency shows it
to be a trimethylphosphine rotor. This imaginary frequency
is rectified upon full optimization without symmetry, but the
discussion herein derives from the calculation in full C2h-sym-
metry. Investigations in other systems have found changes
in optimized geometries upon inclusion of solvent effects to be
small,62 and gas-phase structures are here taken as approximate
solution geometries. All other calculated properties reported
(63) Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 1981, 55, 117–
129.
(64) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999–3093.
(58) Adamo, C.; Barone, V. J. Chem. Phys. 1998, 108, 664–675.
(59) Perdew, J. P.; Wang, Y. Phys. Rev. B 1992, 45, 13244–13249.
(60) Godbout, N.; Salahub, D. R.; Andzelm, J.; Wimmer, E. Can. J.
Chem. 1992, 70, 560–571.
(61) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987,
86, 866–872.
(65) Gorelsky, S. I. AOMix: Program for Molecular Orbital Analysis;
York University: Toronto, 1997, http://www.sg-chem.net.
(66) Gorelsky, S. I.; Lever, A. B. P. J. Organomet. Chem. 2001, 635,
187–196.
(67) Gorelski, S. I.; Swizard program, revision 4.5, http://www.
sg-chem.net/.
(68) Meyer, N.; Lehmann, C. W.; Lee, T. K.-M.; Rust, J.; Yam, V.
(62) Baik, M.-H.; Friesner, R. A. J. Phys. Chem. A 2002, 106, 7407–
7412.
W.-W.; Mohr, F. Organometallics 2009, 28, 2931–2934.

5676 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
˚
Table 3. Selected Interatomic Distances (A) and Angles (deg) for Aurated Naphthalenes (5-7, 9, 10) and Pyrenes (15 and 16)
5
6
7
9
10
15
16
C-Au
2.038(3)
2.035(5)
2.044(5)
2.026(19)
2.00(2)
2.023(5)
2.051(4), 2.036(3)
2.046(7)
2.046(2)
2.050(12)
2.303(4)
2.276(5)
178.7(5)
176.0(6)
177.4(5)
Au-P
2.2922(9)
177.04(7)
2.2984(14)
2.2968(14)
178.75(16)
179.08(15)
2.2643(16)
175.78(17)
2.2874(9), 2.2930(9)
2.300(2)
173.6(2)
2.3044(6)
176.09(7)
—C-Au-P
172.04(10), 174.95(10)
Table 4. 31P NMR Chemical Shifts Relative to 85% H3PO4(aq)
of Phosphine-Ligated Gold Complexes
complex
solvent
C6D6
31P δ (ppm)
starting material
5
57.6
PCy3AuBr (55.5)
PCy3AuOAc (47.9)
PCy3AuN3 (53.9)
PCy3AuBr (55.5)
PCy3AuBr (55.5)
PPh3AuBr (35.2)
PPh3AuBr (35.2)
PPh3AuBr (35.2)
PCy3AuN3 (53.9)
PCy3AuOAc (47.9)
6
7
8
9
10
15
16
CDCl3
CDCl3
C6D6
CDCl3
CDCl3
C6D6
58.0
58.0
44.0
44.4
44.4
57.5
57.5
C6D6
Table 5. 13C Chemical Shifts of Ligand Carbene Carbons Relative
to Tetramethylsilane in NHC-Ligated Gold Complexes
13C δ (ppm)
(carbene C)
complex
13C solvent
CDCl3
starting material
11
217.2
SIPrAuBr (199.0),
SIPrAuN3 (194.7)
SIPrAuOAc (195.5)
12
CDCl3
217.2
Figure 2. Emission spectra of (tricyclohexylphosphine)gold(I)
1-naphthyl 17 at 295 K (black) and 77 K (red) in 2-methylte-
trahydrofuran glass at 5 ꢀ 10-6 M concentration. Inset: a
model29 for the concentration dependence (see text) of triplet-
state emission.
The organogold naphthalenes were isolated by extraction
into benzene (monogold complexes) or dichloromethane
(digold complexes). Solvents were removed in vacuo, and
the residues were triturated with pentane or hexanes. The
products were collected by vacuum filtration and purified by
crystallization. The monogold(I) pyrenyl complex 15 was
isolated by extraction into dichloromethane. Digold pyrene
derivative 16 was collected by filtration.
Figure 3. Absorption (black) and room-temperature emi-
ssion (red) of (a) monogold 5, (b) C2h-symmetric digold 6,
and (c) C2v-symmetric digold 7 in CH2Cl2.
naphthalenes and two of aurated pyrenes. The crystal struc-
ture of 8 has been reported previously.69 Figure 1 depicts
Crystal Structures. Single-crystal X-ray structures of seven
new gold complexes have been obtained: five of aurated
(69) Osawa, M.; Hoshino, M.; Hashizume, D. Dalton Trans. 2008,
2248–2252.

Article
Organometallics, Vol. 28, No. 19, 2009 5677
Table 6. Luminescence Parameters of Gold-Substituted Naphthalenes
compound
solvent
2-MeTHF
2-MeTHF
T (K)
Emax(nm)
λ
em (nm)a
τ (ms)
jem
kr ꢀ 102 (s-1
0.63
)
knr ꢀ 103 (s-1
10.24
)
5
5
5
6
6
6
7
7
8
8
8
9
9
9
10
10
10
11
11
11
12
12
12
295
77
77
295
77
77
295
77
295
77
77
295
77
77
295
77
77
295
77
77
295
77
479
480
480
605
480
485
605
480
480
480
480
605
480
480
605
480
485
605
490
485
605
490
485
605
0.097
1.72
1.72
0.200
0.541
0.48
0.220
1.59
0.108
1.65
1.5
0.210
0.525
0.48
0.20
1.53
1.36
0.26
0.494
0.46
0.32
1.28
1.17
0.0061
2-MeTHF
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
2-MeTHF
2-MeTHF
2-MeTHF
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
2-MeTHF
2-MeTHF
2-MeTHF
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
1:1 2-MeTHF/CH2Cl2
2-MeTHF
489
0.022
1.08
4.89
490
479
0.014
0.012
0.64
1.07
4.48
9.15
490
491
490
490
0.025
0.013
0.032
0.014
1.17
0.64
1.21
0.45
4.64
4.94
3.72
3.08
2-MeTHF
2-MeTHF
77
a Wavelength at which emission lifetime data were collected.
thermal ellipsoid projections of three representative or-
ganometallics: two isomeric digold(I) naphthalenes and a
digold(I) pyrene. Table 3 reports selected interatomic dis-
tances and angles. The asymmetric unit of 6 contains
two half-molecules situated on special positions. In the
asymmetric unit of 7, one complete molecule resides on a
general position, and one half-molecule on a mirror plane. In
the asymmetric unit of 9, one half-molecule resides on a
crystallographic inversion center. Digold pyrene deriva-
tive 16 resides on an inversion center such that half the
molecule constitutes the asymmetric unit. Gold-carbon
bond lengths range from 2.00(2) A for one independent
C-Au bond of 7 to 2.051(4) A for an independent bond in
10. Phosphorus-gold bonds range in length from 2.2643(16)
A for 9 to 2.3044(6) A for 16. These ranges of gold-
(I)-element bond lengths are normal.70-72 Coordination
geometries about gold are essentially linear: C-Au-P bond
angles range from 172.04(10)ꢀ (one such angle in 10) to
179.08(15)ꢀ (one independent molecule of 6).
Figure 4. Emission spectrum (77 K) of digold pyrene derivative
16 in a 2-methyltetrahydrofuran glass.
NMR Spectroscopy. Multinuclear NMR spectroscopy is
diagnostic of product formation. Table 4 collects 31P chemi-
cal shifts, relative to 85% phosphoric acid, for phosphine-
ligated organometallics. In contrast to an earlier observa-
tion,30 we do not encounter long-range 31P-1H coupling.
Carbene-carbon resonances for N-heterocyclic carbene com-
plexes appear in Table 5. These tables also indicate starting
gold(I) reagents and pertinent chemical shifts in the same
solvents. Most digold complexes here are insoluble in ben-
zene but dissolve readily in dichloromethane and chloro-
form, and hence the choice of NMR solvent. Upon
carbon-gold bond formation, 31P resonances of phosphine
ligands and carbene-carbon 13C resonances shift downfield,
reflecting the lesser electronegativity of carbon compared to
the trans-situated donor atoms in the gold reactants and
possibly also the trans-influence of aryl ligands. In all cases,
the shift suffices to distinguish product from gold(I) reactant.
Optical Spectroscopy. The new organometallics luminesce
in organic solvents. For the gold(I) naphthyl complexes,
oxygen-quenchable, structured emission spans wavelengths
extending from ca. 475 to 650 nm. This emission onset re-
presents a Stokes shift of some 145 nm (9250 cm-1) from the
onset of absorption. For complexes having the same number of
gold atoms, peak emission wavelengths are somewhat insensi-
tive to gold substitution about the naphthalene core.
The gross temperature-sensitivity of emission is that
commonly seen for phosphorescent molecules. An exam-
ple is the previously reported8 (tricyclohexylphosphine)-
gold(I) 1-naphthyl 17. At low concentrations of 17, triplet
emission activates only with cooling. Figure 2 depicts lumines-
cence spectra collected in degassed 2-methyltetrahydrofuran at
77 and 295 K. At room temperature, unstructured ultraviolet
emission appears; this luminescence is unaltered by exposure
to oxygen. At liquid nitrogen temperature, the same lumines-
cence reappears with ingrowing vibronic structure. Near
(70) Partyka, D. V.; Updegraff, J. B.,III; Zeller, M.; Hunter, A. D.;
Gray, T. G. Organometallics 2007, 26, 183–186.
(71) Porter, K. A.; Schier, A.; Schmidbaur, H. Organometallics 2003,
22, 4922–4927.
ꢀ
(72) Fernandez, E. J.; Laguna, A.; Olmos, M. E. Coord. Chem. Rev.
2008, 252, 1630–1667.

5678 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
Figure 5. Optimized interatomic distances of model digold(I) naphthalene and pyrene derivatives. Top: 60. Center: 70. Bottom: 160.
Bond lengths are calculated for the singlet ground state; triplet excited-state distances appear in italics.
475 nm, sharply structured emission appears. This emission is
too long-lived (1-2 s) for lifetime measurement on the nano-
second laser available to us; the laser repetition rate is faster
than emission decay. At higher concentrations (∼10-4 M), this
emission occurs at room temperature and is oxygen-quenched.
This concentration dependence has been encountered pre-
viously, with gold(I)-substituted 1-pyrenyls.73 The inset of
Figure 2 summarizes the proposed mechanism. A nonemissive
excimer lies above the triplet state in energy. This excimer
catalyzes, or pumps, the formation of the triplet, which then
emits long-lifetime, structured luminescence.
according to the substitution pattern of the aromatic skele-
ton. Monogold 5 shows dual luminescence. Structured emis-
sion rises near 310 nm and maximizes at 334 nm. An
approximate mirror-image relationship exists between it
and the absorption feature at 280 nm. The small Stokes shift
(5700 cm-1) suggests fluorescence from a singlet excited
state. A similar emission is less prominent for C2v-symmetric
digold complex 7.
For all three complexes, sharply structured emission sets
in near 470 nm. At least three vibronic peaks are clearly re-
solved with spacings that average 1425 cm-1 for 5, 1365 cm-1
for 6, and 1323 cm-1 for 7. These values concur roughly with
tabulated ring-stretching frequencies of aromatic molecules,
indicating a vibronic origin for the spiked structure of the
475-650 nm emission profile.74
Table 6 summarizes luminescence lifetimes of organogold-
(I) naphthalenes; these are microsecond-scale or longer at
77 and 295 K. The lifetimes, along with the oxygen-quench-
ing of the emission and the large Stokes shifts, indicate triplet
luminescence. The small range of emission maxima com-
plicates standard energy-gap law analyses.75 The orbital
Figure 3 depicts room-temperature absorption and emis-
sion spectra of the new monogold 2-naphthyl complex 5 and
of the isomeric digold naphthalenes 6 and 7 in dichloro-
methane. Arene-centered absorptions set in near 330 nm for
gold(I) naphthalene complexes; absorption features differ
€
(74) Pretsch, E.; Buhlmann, P.; Affolter, C. Structure Determination
of Organic Compounds; Springer: New York, 2000; p 255.
(75) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am.
Chem. Soc. 1982, 104, 630–632.
(73) Partyka, D. V.; Esswein, A. J.; Zeller, M.; Hunter, A. D.; Gray,
T. G. Organometallics 2007, 26, 3279–3282.

Article
Organometallics, Vol. 28, No. 19, 2009 5679
Figure 6. Kohn-Sham orbital energy level diagram of 60 (mpmpw91/Stuttgart ECP and basis on Au); implicit CH2Cl2 solvation is
included through a continuum dielectric model. (Right) Plots of selected orbitals (contour level 0.03 au). Percentage contributions of
(phosphine)gold(I) cation and naphthalene-diyl anion fragments are indicated.
Figure 7. Kohn-Sham orbital energy level diagram of aurated pyrene 160 (mpmpw91/Stuttgart ECP and basis on Au); implicit
CH2Cl2 solvation is included through a continuum dielectric model. (Right) Plots of selected orbitals (contour level 0.03 au). Percentage
contributions of (phosphine)gold(I) cation and pyrene-diyl anion fragments are indicated.
parentage of the emitting states and their structures have
been examined with quantum chemical computations.
Gold(I) pyrene derivatives are also luminescent, as has
been noted previously for complexes isomeric with those
reported here.29,30 Figure 4 reproduces the emission spec-
trum of digold complex 16 at 77 K in 2-methyltetrahydro-
furan glass. Emission is sharply structured with maxima
at 591 and 640 nm. The 77 K lifetime of emission collected
at 600 nm is 13 μs. We assign the red emission near 600 nm
as a triplet-state ππ* transition, and the higher-energy
luminescence as intraligand fluorescence. Such assignments
concur with earlier work8,29,30 and with time-dependent
density-functional theory calculations.
Calculations. Density-functional theory (DFT) and time-
dependent DFT calculations were performed on model
digold(I) complexes. Capping trimethylphosphine ligands
replace tricyclohexylphosphine or N-heterocyclic carbenes
for computational tractability. Geometry optimizations
proceeded with imposed symmetry. Figure 5 collects cal-
culated metrics involving gold for models 60, 70, and 160.
These are in good agreement with the crystallogra-
phic metrics of Table 3. Gold-donor atom bond lengths
are consistently overestimated by ca. 0.02 A for Au-C and
0.08 A for Au-P bonds. This behavior is commonly noted
for DFT, and comparative studies of optimized struc-
tures for a range of common functionals find similar mean

5680 Organometallics, Vol. 28, No. 19, 2009
Gao et al.
absolute errors in bond lengths.76,77 The optimized para-
meters are similar to those stated elsewhere for (phos-
phine)gold(I) and organogold(I) complexes.78-84
Table 7. Calculated Excitation Wavelengths, Oscillator Strengths
f, and Principal Orbital Compositions of the Singlet Excited
States of Model Complexes 60, 70, and 160 Lying beyond 300 nm
(dichloromethane solvent)
Figure 6 depicts a frontier-orbital energy level diagram for
digold model complex 60 in C2h symmetry. Plots of selected
orbitals appear at right. Percentage contributions indicated
in the figure are of the total electron density and are
calculated from Mulliken population analysis.85 The corre-
sponding diagram for the non-centrosymmetric digold com-
plex 70 appears as Figure S5 in the Supporting Information.
The highest occupied Kohn-Sham orbital (HOMO) of 60
derives (94%) from the naphthalenediyl HOMO-3, which is
a π-combination. The lowest unoccupied Kohn-Sham or-
bital (LUMO) also has preponderant aromatic character
(78%), but with a higher contribution from the two
(phosphine)gold(I) fragments. The calculated HOMO-LU-
MO gap is 3.14 eV; that of C2v isomer 70 is 3.18 eV, and of 2-
naphthyl 50, 3.28 eV. Two occupied orbitals, the HOMO-1
and the HOMO-3, account for the two gold-carbon σ-
bonds. These are an in-phase and antiphase contribution,
respectively. The in-phase combination is the less stable of
the pair because more nodal surfaces transect the aromatic
bridge in it than in the antiphase HOMO-3. The first several
vacant orbitals in the complex have negligible contributions
from the (phosphine)gold(I) fragment LUMOs or from
occupied gold orbitals. Broadly similar observations pertain
to the frontier orbitals of 50 and 70.
Figure 7 depicts an energy-level diagram for the model
digold pyrene 160 with orbital plots at right. This complex is a
potential-energy minimum with C2h symmetry. As with the
metalated naphthalenes, its frontier orbitals are π-functions
of the pyrenediyl bridging ligand. The HOMO-2 and
HOMO-3 compose the two C-Au σ-bonding combina-
tions, with the in-phase orbital again having higher energy.
The calculated HOMO-LUMO of 160 energy levels is 2.59
eV; that of monogold pyrene 150 is 2.60 eV. The Kohn-
Sham orbital energy-level diagrams suggest that low-lying
excited states of aurated naphthalenes and pyrenes possess
predominant π-character.
Compound 60
orbital origin
(percentage contribution)
no.
1
E (nm)
f
347.7
0.2602
HOMO f LUMO (67%)
HOMO f LUMOþ1 (18%)
HOMO-1 f LUMO (97%)
HOMO f LUMOþ1 (44%)
HOMO-2 f LUMO (39%)
HOMO f LUMO (11%)
2
3
327.1
325.8
0
0.0245
4
5
6
7
309.7
309.7
308.1
306.3
0
HOMO f LUMOþ3 (100%)
HOMO f LUMOþ4 (100%)
HOMO f LUMOþ2 (96%)
HOMO-3 f LUMO (96%)
0.0006
0
0.0081
Compound 70
orbital origin
(percentage contribution)
no.
1
E (nm)
f
336.2
0.0094
HOMO f LUMO (78%)
HOMO f LUMOþ4 (7%)
HOMO f LUMOþ1 (73%)
HOMO-2 f LUMO (25%)
HOMO-1 f LUMO (98%)
HOMO f LUMOþ2 (100%)
HOMO f LUMOþ3 (100%)
HOMO-3 f LUMO (92%)
HOMO-1 f LUMOþ1 (7%)
2
334.9
0.0468
3
4
5
6
328.6
311.4
309.0
306.3
0.0039
0
0.0007
0
Compound 160
orbital origin
(percentage contribution)
no.
1
E (nm)
f
390.3
0.0002
HOMO f LUMOþ1 (62%)
HOMO-1 f LUMO (37%)
HOMO f LUMO (72%)
2
381.3
0.3928
HOMO-1 f LUMOþ1 (8%)
HOMO-2 f LUMO (100%)
HOMO-3 f LUMO (100%)
HOMO - 1 f LUMO (47%)
HOMO f LUMOþ1 (27%)
HOMO f LUMOþ8 (11%)
HOMO f LUMOþ2 (86%)
HOMO-4 f LUMO (10%)
HOMO f LUMOþ4 (100%)
HOMO f LUMOþ5 (100%)
HOMO f LUMOþ3 (93%)
HOMO-1 f LUMOþ1 (80%)
HOMO-1 f LUMOþ8 (9%)
HOMO-2 f LUMOþ1 (96%)
3
4
5
356.4
347.6
335.8
0
0
0.1394
Time-dependent DFT calculations find the first several
optically allowed transitions to be localized on the aromatic
ligands, for the metalated napthalenes and pyrenes consid-
ered here. Table 7 assembles computed singlet-singlet tran-
sitions for metalated naphthalenes 60, 70, and 160. Calculated
excitations are typically combinations of one-electron pro-
motions that undergo configuration interaction. Those tran-
sitions having the greatest oscillator strength are typically
6
330.4
0
7
8
9
10
326.8
326.2
324.2
307.3
0.0006
0
0
1.6964
11
302.3
0.0106
delocalized over the aromatic bridge. Where not fully pro-
hibited by symmetry, C-Au σ-to-aryl π*-transitions have
slight oscillator strengths (f < 0.03). The metalated arenes
calculated here have aryl π*-functions as their HOMOs and
LUMOs, and their low-lying excited states can be assigned as
ligand-centered π-states.
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Triplet-state structures have been optimized for mono-
and digold aromatics. All open-shell calculations were spin-
unrestricted. Vibrational analysis finds normal-mode fre-
quencies to be all real numbers, confirming the triplet-state
structures to be minima on the (excited-state) energy hyper-
surface.
Figure 5 assembles calculated metrics of (ground-state)
singlet and lowest triplet 60, 70, and 160. Metric changes upon
excitation are miniscule; the calculated singlet and triplet
geometries are nearer each other than any is to the crystal
structures of the respective digold complexes. Both bond
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€

Article
Organometallics, Vol. 28, No. 19, 2009 5681
lengthening and contraction occur in the excited states of
aurated naphthalenes and pyrenes.
The low-energy optical transitions are intraligand in character.
Excited-state geometry optimizations indicate minimal
ground-state to triplet-state distortions. The prospects for
metalated hydrocarbons in designing red- and near-IR emit-
ters are receiving active study.
Conclusions
Boronic acids and pinacolboronate esters bearing aro-
matic hydrocarbon substituents arylate gold(I) substrates.
Carbon-gold bond formation occurs regiospecifically at
the boron-bearing carbon atom. Aromatics having one or
two gold(I) centers are readily preparable, and the syn-
thesis protocol applies equally to phosphine or N-hetero-
cyclic carbene co-ligands on gold. The choice of boronated
precursors enables gold attachment at ring positions not
amenable to electrophilic aromatic substitution, with iri-
dium-catalyzed borylation reactions of hydrocarbons.42
Mono- and digold derivatives of naphthalene and pyrene
emit primarily through triplet excited states. In some diau-
rated napthalenes (having C2v) microsymmetry, dual singlet-
and triplet-state emission occurs. Luminescence is centered
on the polycyclic aromatic hydrocarbon core, as evidenced
by structured emission profiles with vibronic spacings char-
acteristic of aromatic ring deformation modes.
Acknowledgment. The authors thank the National
Science Foundation (grant CHE-0749086 to T.G.G.)
for support. T.S.T. acknowledges the Fannie and John
Hertz Foundation for a predoctoral fellowship; T.G.G. is
an Alfred P. Sloan Foundation Fellow. The diffract-
ometer at Case Western Reserve was funded by NSF
grant CHE-0541766; that at Youngstown State Univer-
sity, by NSF grant 0087210, by the Ohio Board of
Regents grant CAP-491, and by Youngstown State Uni-
versity. We thank E. J. McLaurin for assistance with
emission lifetime measurements and Professor D. G.
Nocera (Massachusetts Institute of Technology) for ac-
cess to instrumentation.
Supporting Information Available: Thermal ellipsoid projec-
tions of crystallographically characterized compounds; opti-
mized Cartesian coordinates of ground-state and triplet 60, 70,
and 160; Kohn-Sham orbital energy level diagram for C2v
model compound 70. This material is available free of charge
via the Internet at http://pubs.acs.org.
Density-functional theory calculations indicate that the
frontier orbitals of the parent hydrocarbons are also those of
the gold derivatives. Time-dependent DFT calculations reaf-
firm8,29 that the carbon-gold σ-bond is nonchromophoric.