A class of luminescent cyclometalated alkynylgold(III) complexes: Synthesis, characterization, and electrochemical, photophysical, and computational studies of [Au(C∧N∧C)(C≡C-R)] (C∧N∧C = κ3C,N,C bis-cyclometalated 2,6-diphenylpyridyl)

Published on Web 03/16/2007

A Class of Luminescent Cyclometalated Alkynylgold(III)

Complexes: Synthesis, Characterization, and

Electrochemical, Photophysical, and Computational Studies

of [Au(C^∧N^∧C)(CtCsR)] (C^∧N^∧C ) K³C,N,C Bis-cyclometalated

2,6-Diphenylpyridyl)

Keith Man-Chung Wong, Ling-Ling Hung, Wai Han Lam, Nianyong Zhu, and

Vivian Wing-Wah Yam*

Contribution from the Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based

Materials Research and Department of Chemistry, The UniVersity of Hong Kong,

Pokfulam Road, Hong Kong

Received November 18, 2006; E-mail: wwyam@hku.hk

Abstract: A new class of luminescent cyclometalated alkynylgold(III) complexes, [Au(RC^∧N(R′)^∧CR)(Ct

CR′′)], i.e., [Au(C^∧N^∧C)(CtCR′′)] (HC^∧N^∧CH ) 2,6-diphenylpyridine) R′′ ) C₆H₅1, C₆H₄sCl-p 2, C₆H₄s

NO₂-p 3, C₆H₄sOCH₃-p 4, C₆H₄sNH₂-p 5, C₆H₄sC₆H₁₃-p 6, C₆H₁₃7, [Au(^tBuC^∧N^∧C^tBu)(CtCC₆H₅)] 8

(H^tBuC^∧N^∧C^tBuH ) 2,6-bis(4-tert-butylphenyl)pyridine), and [Au(C^∧NTol^∧C)(CtCC₆H₄-C₆H₁₃-p)] 9

(HC^∧NTol^∧CH ) 2,6-diphenyl-4-p-tolylpyridine), have been synthesized and characterized. The X-ray crystal

structures of most of the complexes have also been determined. Electrochemical studies show that, in

general, the first oxidation wave is an alkynyl ligand-centered oxidation, while the first reduction couple is

ascribed to a ligand-centered reduction of the cyclometalated ligand with the exception of 3 in which the

first reduction couple is assigned as an alkynyl ligand-centered reduction. Their electronic absorption and

luminescence behaviors have also been investigated. In dichloromethane solution at room temperature,

the low-energy absorption bands are assigned as the π-π* intraligand (IL) transition of the cyclometalated

RC^∧N(R′)^∧CR ligand with some mixing of a [π(CtCR′′) f π*(RC^∧N(R′)^∧CR)] ligand-to-ligand charge transfer

(LLCT) character. The low-energy emission bands of all the complexes, with the exception of 5, are ascribed

to origins mainly derived from the π-π* IL transition of the cyclometalated RC^∧N(R′)^∧CR ligand. In the

case of 5 that contains an electron-rich amino substituent on the alkynyl ligand, the low-energy emission

band was found to show an obvious shift to the red. A change in the origin of emission is evident, and the

emission of 5 is tentatively ascribed to a [π(CtCC₆H₄NH₂) f π*(C^∧N^∧C)] LLCT excited-state origin. DFT

and TDDFT computational studies have been performed to verify and elucidate the results of the

electrochemical and photophysical studies.

Introduction

of organogold compounds, with its growing interest partly

stemming from the recent reports on its rich luminescence

The common oxidation states of gold are found for +1 and

+3, with other oxidation states such as +2, +4, and +5 being

much less common. The chemistry of gold(I) has attracted a

great amount of attention; in particular there has been a recent

revival of interest in light of the observation of weak inter- or

intramolecular gold‚‚‚gold interactions in a number of mono-

and polynuclear gold(I) complexes.¹Studies of gold(I) com-

plexes have further been promoted by the recent reports on the

rich and interesting photophysical and photochemical properties

displayed by a number of gold(I) complexes.^2,3Among the gold-

(I) complexes, gold(I) alkynyls represent an interesting class

properties³and the ability of gold(I) and alkynyl moieties to

build supramolecular architectures based on the tendency of

gold(I) to form two-coordinate linear geometry and aurophilic

interactions,⁴and the tendency of alkynyl units to function as

linear rigid-rod building blocks.

(3) (a) Li, D.; Hong, X.; Che, C. M.; Lo, W. C.; Peng, S. M. J. Chem. Soc.,

Dalton Trans. 1993, 2929. (b) Mu¨ller, T. E.; Choi, S. W. K.; Mingos, D.

M. P.; Murphy, D.; Williams, D. J.; Yam, V. W. W. J. Organomet. Chem.

1994, 484, 209. (c) Lu, W.; Xiang, H. F.; Zhu, N.; Che, C. M.

Organometallics 2002, 21, 2343. (d) Che, C. M.; Chao, H. Y.; Miskowski,

V. M.; Li, Y.; Cheung, K. K. J. Am. Chem. Soc. 2001, 123, 4985. (e) Yam,

V. W. W.; Choi, S. W. K.; Cheung, K. K. Organometallics 1996, 15, 1734.

(f) Yam, V. W. W.; Choi, S. W. K. J. Chem. Soc., Dalton Trans. 1996,

4227. (g) Lu, X. X.; Li, C. K.; Cheng, E. C. C.; Zhu, N.; Yam, V. W. W.

Inorg. Chem. 2004, 43, 2225. (h) Yam, V. W. W.; Yip, S. K.; Yuan, L.

H.; Cheung, K. L.; Zhu, N.; Cheung, K. K. Organometallics 2003, 22,

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Pyykko¨, P. Chem. ReV. 1988, 88, 563.

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C.; Vogler, A. Acc. Chem. Res. 1993, 26, 220. (c) Fung, E. I.; Olmstead,

M. M.; Vickery, J. C.; Balch, A. L. Coord. Chem. ReV. 1998, 171, 151.

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9

4350

J. AM. CHEM. SOC. 2007, 129, 4350-4365

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Chart 1

Gold(III) complexes are mainly dominated by complexation

with nitrogen- or oxygen-donor ligands and halide ligands,⁵

though gold(III) complexes of phosphines and thiolates have

also been reported, mainly in the form of alkyls, aryls, and

ylides.⁵In contrast to the gold(I) system, gold(III) complexes

have been rarely observed to emit, and even if they emit, they

usually would do so at low temperature in the solid state or in

low-temperature glasses, with very few examples that would

emit at room temperature in solution.⁶Probable reason for the

lack of luminescence behavior in gold(III) species is the presence

of low-energy d-d ligand field (LF) states. The presence of a

nonemissive low-lying d-d state would quench the lumines-

cence excited state via thermal equilibration or energy transfer.^6a

Despite a number of organogold(III) complexes reported,⁵most

of them are relatively unstable and readily undergo reductive

elimination reactions to give carbon-carbon coupling products

and gold(I) species, especially in the presence of light. As a

consequence, luminescence studies of organogold(III) complexes

and related studies on luminescent gold(III) systems are scarce⁶

in spite of the fact that the related gold(I) and the isoelectronic

platinum(II) analogues are known to be strongly emissive.

Examples of luminescent organogold(III) compounds include

certain classes of gold(III) aryl compounds^6band cyclometalated

gold(III) compounds^6c-e,7which are rather stable, even upon

visible light irradiation, with interesting luminescence proper-

ties.^6c-e,7The first examples of luminescent organogold(III)

complexes were reported by us in 1993, in which the lumines-

cence behavior of a novel series of stable diaryl- and dialkyl-

gold(III) diimine complexes, [Au(N^∧N)R₂]⁺(N^∧N ) bpy, phen;

R ) CH₂SiMe₃, mesityl), were described.^6bThese complexes

were found to show rich luminescence behavior both in the solid

state and in solution at 298 and 77 K. We envisaged that

introduction of strong σ-donating alkynyls to gold(III) would

render the metal center more electron-rich, with the additional

advantage of raising the energy of the d-d states, resulting in

an improvement or enhancement of the luminescence by

increasing the chances for population of the emissive state.

However, while alkynyl complexes of gold(I)³and the isoelec-

tronic platinum(II)^3j,8,9are known and shown to display rich

photoluminescence properties, the chemistry of alkynylgold-

(III) is essentially rare¹⁰despite the fact that there is increasing

interest in the use of gold(III) compounds for catalysis of organic

synthetic reactions of alkynes,¹¹and their luminescence

behavior is virtually unknown. The alkynyl group, with the

inherent rigidity of its structure, its ability to interact with metal

centers via pπ-dπ overlap which can effectively strengthen the

metal-carbon bonds, and its extended π-electron delocalization,

is an ideal candidate for the construction of luminescent

organometallic materials. Moreover, the introduction of heavy

gold metal centers into the alkynyl backbone in metal-con-

taining oligo- and poly-ynes would also provide a versatile

method to improve the chances of producing triplet emitters,

leading to long-lived triplet emission, as a result of a larger

spin-orbit coupling constant and an enhanced intersystem

crossing efficiency.

We recently communicated the synthesis and rich lumines-

cence properties of a novel class of luminescent alkynylgold-

(III) complexes, [Au(C^∧N^∧C)(CtCsR)] (HC^∧N^∧CH ) 2,6-

diphenylpyridine).⁷These complexes represent isoelectronic and

structural analogues of interesting classes of alkynyl platinum-

(II) terpyridyl,⁹[Pt(N^∧N^∧N)(CtCR)]⁺, and cyclometalated, [Pt-

(C^∧N^∧N)(CtCR)], complexes⁸ⁱthat also exhibit interesting and

affluent photophysical behaviors. As an extension of our

previous studies, together with our great interest in transition

metal alkynyl complexes,^9,12we report herein the synthesis,

characterization, electrochemical, and photophysical studies of

a series of luminescent alkynylgold(III) complexes with various

cyclometalated and alkynyl ligands, [Au(RC^∧N(R′)^∧CR)(Ct

CR′′)], i.e., [Au(C^∧N^∧C)(CtCR′′)] (HC^∧N^∧CH ) 2,6-diphe-

nylpyridine) R′′ ) C₆H₅1, C₆H₄sCl-p 2, C₆H₄sNO₂-p 3,

C₆H₄sOCH₃-p 4, C₆H₄sNH₂-p 5, C₆H₄sC₆H₁₃-p 6, C₆H₁₃7,

[Au(^tBuC^∧N^∧C^tBu)(CtCC₆H₅)] 8 (H^tBuC^∧N^∧C^tBuH ) 2,6-

bis(4-tert-butylphenyl)pyridine), and [Au(C^∧NTol^∧C)(CtCC₆H₄s

(5) Grohmann, A.; Schmidbaur, H. ComprehensiVe Organometallic Chemistry

II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford,

New York, 1995; Vol. 3, Chapter 1.

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Yam, V.W.W.; Choi, S. W. K.; Lai, T. F.; Lee, W. K. J. Chem. Soc., Dalton

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1994, 33, 1266. (d) Wong, K. H.; Cheung, K. K.; Chan, M. C. W.; Che, C.

M. Organometallics 1998, 17, 3505. (e) Mansour, M. A.; Lachicotte, R.

J.; Gysling, H. J.; Eisenberg, R. Inorg. Chem. 1998, 37, 4625.

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Int. Ed. 2005, 44, 3107. (b) Wong, K. M. C.; Zhu, X.; Hung, L. L.; Zhu,

N.; Yam, V. W. W.; Kwok, H. S. Chem. Commun. 2005, 2906.

(8) (a) Sacksteder, L.; Baralt, E.; DeGraff, B. A.; Lukehart, C. M.; Demas, J.

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K.; Johnson, B. F. G.; Marder, T. B.; Fyfe, H. B.; Wittmann, F.; Friend,

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F.; Friend, R. H.; Khan, M. S.; Lewis, J. J. Chem. Phys. 1994, 101, 2694.

(d) Liu, Y.; Jiang, S.; Glusac, K.; Powell, D. H.; Anderson, D. F.; Schanze,

K. S. J. Am. Chem. Soc. 2002, 124, 12412. (e) Chan, C. W.; Cheng, L. K.;

Che, C. M. Coord. Chem. ReV. 1994, 132, 87. (f) Hissler, M.; William, B.

C.; Geiger, D. K.; McGarrah, D. L.; Lachicotte, R. J.; Eisenberg, R. Inorg.

Chem. 2000, 39, 447. (g) Whittle, C. E.; Weinstein, J. A.; George, M. W.;

Schanze, K.S. Inorg. Chem. 2001, 40, 4053. (h) James, S. L.; Younus, M.;

Raithby, P. R.; Lewis, J. J. Organomet. Chem. 1997, 543, 233. (i) Lu, W.;

Mi, B. X.; Chan, M. C. W.; Hui, Z.; Che, C. M.; Zhu, N.; Lee, S. T. J.

Am. Chem. Soc. 2004, 126, 4958.

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Organometallics 2001, 20, 4476. (b) Yam, V. W. W.; Wong, K. M. C.;

Zhu, N. J. Am. Chem. Soc. 2002, 124, 6506. (c) Yam, V. W. W.; Wong,

K. M. C.; Zhu, N. Angew. Chem., Int. Ed. 2003, 42, 1400. (d) Yam, V. W.

W.; Chan, K. H. Y.; Wong, K. M. C.; Zhu, N. Chem.sEur. J. 2005, 11,

4535. (e) Wong, K. M. C.; Tang, W. S.; Chu, B. W. K.; Zhu, N.; Yam, V.

W. W. Organometallics 2004, 23, 3459. (f) Wong, K. M. C.; Tang, W. S.;

Lu, X. X.; Zhu, N.; Yam, V. W. W. Inorg. Chem. 2005, 44, 1492. (h)

Tang, W. S.; Lu, X. X.; Wong, K. M. C.; Yam, V. W. W. J. Mater. Chem.

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125, 10921. (b) Hashmi, A. S. K. Gold Bull. 2003, 36, 3.

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Chem. Res. 2002, 35, 555. (c) Lo, W. Y; Lam, C. H.; Yam, V. W. W.;

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9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4351

A R T I C L E S

Scheme 1

Wong et al.

C₆H₁₃-p)] 9 (HC^∧NTol^∧CH ) 2,6-diphenyl-4-p-tolylpyridine)

(Chart 1); DFT and TDDFT computational studies have also

been performed to elucidate the electronic structures of the

complexes and the nature of their excited states.

1. In each case, the gold(III) metal center coordinates to the

bis-cyclometalated tridentate RC^∧N(R′)^∧CR pincer ligand with

the remaining site occupied by an alkynyl ligand to give a

distorted square-planar geometry, characteristic of d⁸metal

complexes. The CsAusC and CsAusN angles of 161.1(4)°s

164.1(9)° and 79.9°-82.6° about the gold(III) metal center

deviate from the idealized values of 180° and 90°, respectively,

due to the restricted bite angle of the tridentate ligand. The [Au-

(RC^∧N(R′)^∧CR)] motif is essentially coplanar, and the AusC

(2.047-2.084 Å) and Au-N (1.999-2.039 Å) bond distances

are similar to those found in other related bis-cyclometalated

gold(III) complexes.^6dThe AusCtC angles range from 171.6°

to 180°, establishing a slightly distorted linear arrangement, with

the AusC (1.945-2.008 Å) bond parameter similar to those

found in the other alkynylgold(III) system,^10c,dwhile the CtC

bond distances (1.124-1.220 Å) are in the range typical of

transition metal alkynyl systems.^{3a,c-i,8e-i,9a-f,10c,d,11c,e,f}The

interplanar angles between the phenyl ring of the alkynyl ligand

and the [Au(RC^∧N(R′)^∧CR)] plane in complexes 1-5, 8, and

9 vary from 16.3° to 88.9°, while that in the two independent

molecules of 5 are 49.4° and 74.0° (Table 3). It is likely that

the energy barrier for the rotation of the phenyl ring relative to

the [Au(RC^∧N(R′)^∧CR)] plane should be very low so that there

is no preference for the coplanar or orthogonal orientation of

the phenyl ring with respect to the [Au(RC^∧N(R′)^∧CR)] plane.

However, crystal packing forces may exert an influence on the

ultimate orientation of the phenyl ring relative to that of the

[Au(RC^∧N(R′)^∧CR)] plane.

Results and Discussion

Synthesis and Characterization. The incorporation of alky-

nyl ligand into the cyclometalated gold(III) moiety, [Au(RC^∧N-

(R′)^∧CR)], was achieved by two methodologies (Scheme 1). In

method a, a reaction mixture of the chlorogold(III) precursor,

alkyne, triethylamine, and a catalytic amount of copper(I) iodide

was allowed to stir for 3 h at room temperature in dichlo-

romethane under a nitrogen atmosphere to give the correspond-

ing alkynylgold(III) complex. In method b, the preparation of

the desired alkynylgold(III) complex was accomplished by

heating a methanolic solution of the chlorogold(III) precursor,

alkyne, and sodium hydroxide at 70 °C for 12 h under a nitrogen

atmosphere. In both cases, pale yellow crude products were

obtained by evaporation of the solvent to dryness, which were

then purified by column chromatography on silica gel using

dichloromethane as eluent. Subsequent recrystallization from

slow diffusion of diethyl ether vapor into the concentrated

solution of the complex resulted in the isolation of the desired

product as pale yellow crystals. In view of the higher product

yield obtained from method a (68-88%) than that from method

b (ca. 40%) as well as the shorter reaction time required, method

a was the method of choice for the synthesis of the target

alkynylgold(III) complexes. All the complexes are found to be

air-stable and thermal-stable. The incorporation of alkynyl ligand

into the gold(III) center renders the products more soluble in

common organic solvents, especially relative to the precursor

complex, [Au(C^∧N^∧C)Cl], which is only soluble in DMSO. The

identities of complexes 1-9 have been confirmed by ¹H NMR

spectroscopy, EI- or FAB-mass spectrometry, IR spectroscopy,

and satisfactory elemental analyses. The IR spectra of the

complexes show a weak band at 2143-2157 cm^-1, typical of

the ν(CtC) stretching frequency. The crystal structures of all

the complexes (with the exception of 6) have also been

determined by X-ray crystallography.

Although the closest Au‚‚‚Au distances (3.846-5.951 Å)

between adjacent molecules are found to be longer than the sum

of van der Waals radii for two gold(III) centers, suggestive of

insignificant Au‚‚‚Au contacts in their crystal lattices, the

shortest interplanar distances between the [Au(RC^∧N(R′)^∧CR)]

planes are found to range from 3.4 to 3.6 Å (Table 3), indicating

the presence of appreciable π-π stacking interactions as

revealed by their crystal packings for many of the structures. It

is interesting to note that their packing arrangements vary from

one structure to another. For crystals of 1, 3, 4, and 8, the

complex molecules are stacked into an extended columnar array

with identical Au‚‚‚Au and π-π separations between them,

while the [Au(RC^∧N(R′)^∧CR)] motifs are partially stacked with

different extents of aromatic overlapping (Figure 2a-d). The

[Au(RC^∧N(R′)^∧CR)] moieties are stacked in a variety of

manners (head-to-tail in 1; head-to-head in 3; partial head-to-

tail in 4) and are shifted laterally with respect to each other,

while the crystal packing of 8 shows that the molecules are

arranged in a head-to-tail fashion without a lateral shift of the

[Au(RC^∧N(R′)^∧CR)] units, probably resulting from the mini-

mization of the mutual repulsion between the sterically bulky

tert-butyl groups (Figure 2e). With 2, 5, 7, and 9, the molecules

X-ray Crystal Structures. Single crystals of 1-5 and 7-9

were obtained by slow diffusion of diethyl ether vapor into a

dichloromethane solution of the respective complexes or by

layering of n-hexane onto a concentrated dichloromethane

solution of the complexes, and their structures were solved by

X-ray crystallography. Crystal structure determination data are

summarized in Table 1. The selected bond distances and bond

angles as well as selected intermolecular parameters are

tabulated in Tables 2 and 3, respectively. The structure of 1

has been previously communicated.^7aThe representative per-

spective views of the crystal structures are depicted in Figure

9

4352 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Table 1. Crystal and Structure Determination Data of 1-5 and 7-9

1

complex

1

2

3

4

‚

/

₂n-hexane

5

7

8

9‚CH₂Cl₂

empirical

C₂₅H₁₆-

AuN

527.35

253(2)

0.710 73

C₂₅H₁₅-

AuClN

561.80

301(2)

0.710 73

C₂₅H₁₅-

AuN₂O₂

C₂₉H₂₅-

AuNO

C₂₅H₁₇-

AuN₂

542.37

243(2)

0.710 73

triclinic

P1h

11.156(2)

12.539(3)

14.737(3)

80.73(3)

70.56(3)

79.77(3)

1901.5(7)

4

C₂₅H₂₄-

AuN

C₃₃H₃₂-

AuN

C₃₉H₃₆-

AuCl₂N

formula

formula weight

temp, K

wavelength, Å

crystal system

space group

a, Å

b, Å

c, Å

R, deg

â, deg

572.36

253(2)

0.710 73

monoclinic

P2₁/c

600.47

253(2)

0.710 73

monoclinic

P2₁/c

12.934(3)

19.404(4)

9.697(2)

90

107.33(3)

90

2323.2(8)

4

535.42

253(2)

0.710 73

triclinic

P1h

8.282(2)

9.029(2)

13.870(3)

84.67(3)

81.18(3)

84.33(3)

1016.7(4)

2

639.56

301(2)

0.710 73

monoclinic

C2/c

19.335(4)

19.732(4)

7.172(1)

90

99.76(3)

90

2696.6(9)

4

786.55

253(2)

0.710 73

monoclinic

P2₁/n

8.637(2)

20.419(4)

18.930(4)

90

101.81(3)

90

3267.8(11)

4

orthorhombic triclinic

P2₁2₁2₁

6.735(1)

14.265(3)

19.583(4)

90

1881.4(6)

4

P1h

7.4590(15)

9.6410(19)

14.086(3)

106.07(3)

97.74(3)

94.98(3)

956.3(3)

2

5.100

15.197(3)

25.241(5)

90

95.58(3)

90

γ, deg

volume, cm³

Z, Å³

1947.0(7)

4

density (calcd),

g cm^-3

1.862

1.951

1.953

1.717

1.895

1.749

1.575

1.599

crystal size,

mm³

0.4 × 0.2 ×

0.2

0.60 × 0.20 × 0.3 × 0.15 ×

0.4 × 0.08 ×

0.4 × 0.25 ×

0.5 × 0.4 ×

0.5 × 0.3 ×

0.4 × 0.25 ×

0.12

0.08

0.04

0.1

0.2

0.25

0.2

index ranges

-7e h e 7

-8 e h e 8

-5 e h e 5

-11 e h e 11 -13 e h e 13 -9 e h e 9

-21 e h e 21 -10 e h e 10

-17 e k e 17 -11 e k e 11 -17 e k e 17 -18 e k e 18 -15 e k e 15 -10 e k e 10 -23 e k e 23 -24 e k e 24

-23 e l e 23 -16 e l e 16 -25 e l e 26 -9 e l e 9

10500/3283

-17 e l e 17 -16 e l e 15 -7 e l e 7

-22 e l e 22

reflections

6885/3260

6962/2432

5419/1894

11979/6372

5744/3299

8818/2286

24194/6106

collected/unique

GOF on F²

0.925

R₁) 0.0262

1.022

R₁) 0.0386

0.915

R₁) 0.0366

0.881

R₁) 0.0514

0.991

R₁) 0.0516

1.054

R₁) 0.0500

0.901

R₁) 0.0262

1.150

R₁) 0.0298

final R indices^a

[I > 2σ(I)]

wR₂) 0.0555 wR₂) 0.0938 wR₂) 0.0855 wR₂) 0.1149 wR₂) 0.1314 wR₂) 0.1276 wR₂) 0.0558 wR₂) 0.0925

0.650 and

-1.556

largest diff peak

and hole, e Å^-3

1.764 and

-2.862

0.550 and

-1.482

1.184 and

-0.575

2.461 and

-3.903

2.311 and

-3.313

0.516 and

-1.714

0.448 and

-1.207

2

^aR_int) ∑|F_o- F_o(mean)|/∑[F_o], R₁) ∑||F_o| - |F_c||/∑||F_o| and wR₂) {∑[w(F_o- F_c)²]/∑[w(F_o)²]}^1/2

.

are stacked together with alternating short and long Au‚‚‚Au

distances to give a “dimeric” configuration. Similar to the

extended columnar structures in 1, 3, 4, and 8, the short Au‚‚

‚Au separations (3.846-5.739 Å) are beyond the range for

substantial intermolecular Au‚‚‚Au interactions. In the “dimeric”

unit, the molecules are stacked into pairs with neighboring

molecules in a head-to-tail or partial head-to-tail arrangement

and are also shifted laterally with respect to each other (Figure

3).

the lower-lying π* orbital owing to the increase in extended

π-conjugation upon introduction of the aryl substituent on the

RC^∧N(R′)^∧CR ligand. Since the reduction potential for the

RC^∧N(R′)^∧CR ligand-centered reduction should not be too

sensitive to the nature of the alkynyl ligand, the occurrence of

the additional reduction wave at -1.08 V in 3 is suggested to

be derived from a ligand-centered reduction of the nitrophenyl

alkynyl ligand, while the second reduction wave at -1.52 V is

assigned as the C^∧N^∧C ligand-centered reduction. This has been

supported by DFT calculation, in which the LUMO is mainly

derived from the π* orbital localized on the CtCC₆H₄sNO₂

ligand.

In view of the fact that the potentials for the first irreversible

anodic waves, which ranged from +0.76 to +1.68 V, are quite

sensitive to the nature of the alkynyl ligand, together with the

electron-deficient nature and the unlikely redox activity of the

gold(III) metal center, the oxidation wave is assigned as the

alkynyl ligand-centered oxidation. For 1-6 having the same

C^∧N^∧C ligand, these anodic waves were found to show

potentials in the order 5 < 4 < 6 < 1 ≈ 2 < 3, in line with the

electron-donating ability of the alkynyl group: CtCC₆H₄sNH₂

> CtCC₆H₄sOMe > CtCC₆H₄sC₆H₁₃> CtCC₆H₅≈ Ct

CC₆H₄sCl > CtCC₆H₄sNO₂. Thus the better the electron-

donating ability of the alkynyl group is, the less positive the

potential of the alkynyl ligand-centered oxidation is. This is also

consistent with the calculated trend of the HOMO energies (vide

infra). The resemblance of the potentials for this oxidation

process observed for 1 (+1.57 V) and 8 (+1.59 V), which

contain the same alkynyl ligand, and the rather insensitive nature

of this potential to the nature of the RC^∧N(R′)^∧CR ligand further

support this assignment. In general, 7 with the alkyl alkynyl

was found to show a more positive potential for this oxidation

Electrochemistry. In general, the cyclic voltammograms of

1-9 in dichloromethane (0.1 mol dm^{-3 n}Bu₄NPF₆) show one

quasi-reversible reduction couple at -1.52 to -1.69 V (vs SCE)

and two irreversible oxidation waves in the ranges of +0.76 to

+1.68 V and +1.75 to +2.17 V (vs SCE). The electrochemical

data are summarized in Table 4, and the representative cyclic

voltammograms of 2, 4, 7, and 8 are shown in Figure 4. On the

basis of similar potentials observed for the reduction couple in

1, 2, and 4-6 consisting of the same RC^∧N(R′)^∧CR chelate,

the reduction process is assigned as the ligand-centered reduction

of the RC^∧N(R′)^∧CR ligand. The occurrence of this reduction

at a more negative potential in 7 (-1.69 V) is also in line with

this assignment since the alkyl alkynyl, which is a better σ-donor

than the aryl alkynyl, would render the gold(III) metal center

more electron-rich. As a consequence, the dπ orbital of the Au-

(III) center would be higher-lying in energy, causing a desta-

bilization of the π* orbital of the RC^∧N(R′)^∧CR ligand, which

would render it more difficult to be reduced. Similarly, the

electron-rich tert-butyl substituents on the RC^∧N(R′)^∧CR ligand

in 8 would destabilize the π* orbital, reducing its ease of

reduction to give a more negative potential at -1.64 V. On the

other hand, the observation of a less negative potential for the

reduction couple in 9 (-1.52 V) is attributed to the presence of

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4353

A R T I C L E S

Wong et al.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1-5 and 7-9 with Estimated Standard Deviations (esd’s) Given in Parentheses

1

2

3

4

‚

/

₂n-hexane

Bond Lengths (Å)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

1.979(7)

2.073(7)

2.071(7)

1.999(5)

1.185(9)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

1.945(8)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

1.974(10)

2.086(13)

2.057(10)

1.989(9)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

2.008(19)

2.061(16)

2.065(16)

2.039(13)

1.19(2)

2.076(8)

2.084(7)

2.003(6)

1.220(11)

1.195(11)

Bond Angles (deg)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

162.0(3)

178.5(3)

176.6(7)

81.1(2)

80.9(2)

177.6(9)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

162.1(3)

177.9(2)

172.7(7)

80.6(3)

81.5(3)

175.8(8)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

162.7(4)

178.8(4)

172.9(8)

80.9(5)

81.8(4)

177.8(10)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

162.4(7)

178.1(6)

172.9(15)

97.4(7)

81.1(6)

177.2(19)

5

7

8

9‚CH₂Cl₂

Bond Lengths (Å)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

Au(2)-C(26)

Au(2)-C(34)

Au(2)-C(50)

Au(2)-N(3)

C(26)-C(27)

2.008(11)

2.078(10)

2.064(9)

1.998(7)

1.118(3)

1.998(10)

2.053(11)

2.052(11)

2.014(3)

1.126(13)

Au(1)-C(1)

Au(1)-C(9)

Au(1)-C(25)

Au(1)-N(1)

C(1)-C(2)

1.980(10)

2.078(9)

2.045(10)

1.995(7)

1.175(14)

Au(1)-C(1)

Au(1)-C(7)

Au(1)-C(7′)

Au(1)-N(1)

C(1)-C(2)

1.972(6)

2.065(5)

2.028(5)

1.196(8)

Au(1)-C(1)

Au(1)-C(15)

Au(1)-C(27)

Au(1)-N(1)

C(1)-C(2)

1.967(5)

2.073(4)

2.078(5)

2.003(3)

1.191(6)

Bond Angles (deg)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

C(34)-Au(2)-C(50)

N(3)-Au(2)-C(26)

Au(2)-C(26)-C(27)

N(3)-Au(1)-C(34)

N(3)-Au(1)-C(50)

C(26)-C(27)-C(28)

162.0(4)

177.2(3)

172.7(11)

81.6(3)

C(9)-Au(1)-C(25)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(9)

N(1)-Au(1)-C(25)

C(1)-C(2)-C(3)

161.1(4)

178.2(3)

171.6(10)

81.0(3)

80.1(4)

177.9(13)

C(7)-Au(1)-C(7′)

161.9(2)

180.0

81.0(12)

180.0(1)

C(15)-Au(1)-C(27)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(15)

N(1)-Au(1)-C(27)

C(1)-C(2)-C(3)

162.4(16)

177.4(17)

175.0(5)

81.4(17)

81.1(17)

177.6(6)

N(1)-Au(1)-C(1)

Au(1)-C(1)-C(2)

N(1)-Au(1)-C(7)

N(1)-Au(1)-C(7′)

C(1)-C(2)-C(3)

80.4(3)

175.4(12)

162.6(4)

177.2(4)

175.2(10)

81.2(4)

81.4(4)

176.4(12)

Table 3. Shortest Au‚‚‚Au Distances and Interplanar Parameters of 1-5 and 7-9

shortest Au‚‚‚Au

distances/Å

interplanar angles between [Au(RC^∧N(R

and phenyl ring of alkynyl/deg

′

)

^∧CR)]

interplanar separations between

interplanar angles between

[Au(RC^∧N(R ^∧CR)] planes/deg

complex

[Au(RC^∧N(R

′

)

^∧CR)] planes^a/Å

′)

1

2

3

4

5

7

8

9

5.003

4.973

5.100

5.951

3.846

4.937

4.581

5.739

65.0

18.1

88.9

69.8

74.0, 49.4

-

3.38

3.44

3.47

3.40

3.53

3.37

3.57

3.39

2.2

0.0

0.4

5.1

0.0

45.6

16.3

^aCalculated from the average distances of the atoms on the two least-squares planes.

relative to the others with the aryl alkynyl ligand due to the

less π-donating nature of the alkyl alkynyl moiety (see

Computational Studies), with the exception of 3 which contains

the electron-deficient nitro substituent, rendering the nitrophenyl

alkynyl to be the weakest π-donor. For the second oxidation

wave, no correlation has been found between their observed

potentials and the nature of the ligands, although such an

oxidation wave is probably derived from the oxidation of the

cyclometallated RC^∧N(R′)^∧CR ligand. The lack of a rational

trend for this second oxidation potential may be due to the

occurrence of decomposition after the first oxidation process

on the basis of the fact that a strong anodic signal at -0.7 V,

which is typical of electrode adsorption, was observed upon

the reduction scan after the first oxidation.

UV-Visible Absorption Spectroscopy. The UV-vis ab-

sorption spectra of 1-9 in dichloromethane at 298 K feature

an intense absorption band at 290-330 nm and a moderately

intense vibronic-structured absorption in the 362-415 nm range

with extinction coefficients (ꢀ) on the order of 10⁴dm³mol^-1

cm^-1. The photophysical data of 1-9 are summarized in Table

5, and the corresponding electronic absorption spectra of 1, 3,

5, 8, and 9 are depicted in Figure 5. For complexes 1-7, the

absorption energy of the low-energy vibronic band at ca. 400

nm was found to be rather insensitive to the nature of the alkynyl

9

4354 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Figure 1. Perspective drawings of 3 (a), 7 (b), 8 (c), and 9 (d) with atomic numbering scheme. Hydrogen atoms and solvent molecules are omitted for

clarity. Thermal ellipsoids are drawn at the 50% probability level.

Figure 2. Crystal packing diagrams of 1 (a), 3 (b), 4 (c), and 8 (d) showing an extended columnar array with identical Au‚‚‚Au and π-π separations and

(e) the head-to-tail configuration of 8.

ligand. This, together with the observation of vibrational

progressional spacings of 1310-1380 cm^-1typical of the

skeletal vibrational frequency of the RC^∧N(R′)^∧CR ligand and

the observation of similar absorption band for the chloro

counterpart, [Au(C^∧N^∧C)Cl] suggested their assignment as a

metal-perturbed π f π* intraligand (IL) transition of the RC^∧N-

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4355

A R T I C L E S

Wong et al.

Figure 3. Crystal packing diagrams of 2 (a), 5 (b), 7 (c), and 9 (d) showing the dimeric configuration.

Table 4. Electrochemical Data for 1-9^a

complex

oxidation E_pa^b/V vs SCE

reduction E₁^c/V vs SCE

/2

1

2

3

4

5

6

7

8

9

+1.57, +1.75

+1.57, +2.13

+1.96

+1.15, +2.07

+0.76, +1.87

+1.34, +2.02

+1.68, +2.17

+1.59, +2.15

+1.27, +2.13

-1.57

-1.59

-1.08, -1.52, -1.64

-1.58

-1.59

-1.58

-1.69

-1.64

-1.52

^aIn dichloromethane solution with 0.1 M ⁿBu₄NPF₆(TBAH) as

supporting electrolyte at room temperature; scan rate 100 mV s^-1^bE_pa

.

Figure 4. Cyclic voltammograms of 2, 4, 7, and 8 in CH₂Cl₂(0.1 mol

refers to the anodic peak potential for the irreversible oxidation waves.^cE_1/2

) (E_pa+ E_pc)/2; E_paand E_pcare peak anodic and peak cathodic potentials,

respectively.

dm^-3ⁿBu₄NPF₆).

(CtCC₆H₄NH₂) f π*(C^∧N^∧C)] transitions. Complex 8, which

contains the same alkynyl ligand as 1, shows a lower absorption

energy relative to that of 1. This is in accordance with the

assignment of a metal-perturbed π f π*(RC^∧N(R′)^∧CR)

intraligand (IL) transition since the electron-donating tert-butyl

groups on the phenyl rings would narrow the HOMO-LUMO

energy gap in view of the fact that the energy level of the

HOMO π orbital is raised to a larger extent than that of the

LUMO π* orbital. Similarly, the observation of a lower-energy

π f π* IL transition in 9 relative to that of 6 is ascribed to the

stabilization of the π* orbital by the better delocalization over

the C^∧NTol^∧C ligand upon introduction of the tolyl group on

the pyridine ring, which results in a narrowing of the π-π*

energy gap.

(R′)^∧CR ligand, probably mixed with the LLCT transitions given

the nonreducing nature of the gold(III) metal center which

eliminates the possibility of a metal-to-ligand charge transfer

(MLCT) transition. Similar assignments have also been reported

for other related gold(III) complexes.^6d

In the case of complex 3, a much more intense absorption

band located at 327 nm was observed which is attributed to the

IL π-π* transition of alkynyl ligand due to the presence of

the nitro substituent. It is noteworthy that an additional shoulder

was observed in the electronic absorption spectrum of 5 at about

415-435 nm. In view of the better electron-donating ability of

the electron-rich amino substituent on the alkynyl ligand, a low-

lying alkynyl-to-RC^∧N(R′)^∧CR ligand-to-ligand charge-transfer

(LLCT) transition becomes feasible and appears as a shoulder

at 415 nm. The low-energy absorptions in 5 are therefore

assigned as an admixture of IL [π f π* (C^∧N^∧C)]/LLCT [π-

Luminescence Spectroscopy. The photoluminescence prop-

erties of this class of alkynylgold(III) complexes have been

previously communicated.^7aUpon excitation at λ > 360 nm,

9

4356 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Table 5. Photophysical Data for 1-9

emission

_max/nm (τ_o

absorption^a

_max/nm (ꢀ_max/dm³mol^-1cm^-

1

b

complex

λ

)

medium (T/K)

λ

/

µ

s)

Φ_em

1

312 (19890), 322 (19980), 364 (5050),

381 (5870), 402 (4870)

CH₂Cl₂(298)^c

solid (298)

476, 506, 541, 582 (<0.05)

588 (<0.05)

1.0 × 10^-3

thin film (298)^d

solid (77)

568 (<0.05)

496 (28.3, 310.4)^f

470, 503, 537, 585 (194)

glass (77)^c,e

2

3

4

5

6

7

8

9

312 (19400), 322 (19640), 365 (4640),

382 (5170), 402 (4305)

CH₂Cl₂(298)^c

solid (298)

solid (77)

476, 506, 539, 584 (<0.05)

550 (<0.05)

2.0 × 10^-4

1.9 × 10^-3

5.0 × 10^-4

2.0 × 10^-3

1.9 × 10^-3

6.0 × 10^-3

2.7 × 10^-3

500 (25.3, 256.6)^f

glass (77)^c,e

470, 504, 534, 590 (151)

312 (26800), 327 (36100), 363 (18545),

382 (10260), 402 (5720)

CH₂Cl₂(298)^c

solid (298)^c

solid (77)

478, 508, 540, 600 (0.3)

565 (<0.05)

515, 550, 600 (0.6)

472, 508, 539, 590 (189, 923)^f

glass (77)^c,e

312 (13820), 322 (13455), 362 (6400),

380 (6245), 400 (4190)

CH₂Cl₂(298)^c

solid (298)

solid (77)

474, 505, 539, 584 (<0.05)

555 (<0.05)

485 (28.4, 268.2)^f

glass (77)^c,e

470, 503, 536, 585 (137)

310 (19195), 322 sh (15680), 365 (8855),

381 (10100), 399 (8300), 415 sh (3410)

CH₂Cl₂(298)

solid (298)

solid (77)

glass (77)^c,e

611 (0.3)

585 (0.2)

548 (0.3, 1.7)^f

470, 503, 535, 587 (107)

313 (18010), 323 (18240), 363 (5130),

381 (5250), 401 (3940)

CH₂Cl₂(298)^c

solid (298)^c

solid (77)

474, 508, 546, 585 (<0.05)

562 (<0.05)

513, 552, 600 (28.7, 227.6)^f

470, 504, 534, 590 (142)

glass (77)^c,e

311 (14860), 320 (14040), 364 (3800),

380 (4840), 400 (4230)

CH₂Cl₂(298)^c

solid (298)^c

solid (77)

471, 508, 535, 553 (<0.05)

561 (<0.05)

513, 533, 585 (32.4, 274.1)^f

469, 503, 535, 585 (221)

glass (77)^c,e

313 (26190), 323 (24460), 374 (6130),

392 (8035), 412 (7465)

CH₂Cl₂(298)^c

solid (298)

solid (77)

484, 514, 548, 593 (0.1)

550 (<0.05)

503 (18.2, 171.9)^f

glass (77)^c,e

478, 512, 548, 600 (200)

290 (42660), 304 (40780), 330 (25220),

364 (6100), 386 (5120), 406 (3540)

CH₂Cl₂(298)^c

solid (298)^c

solid (77)

475, 505, 547, 592 (<0.05)

563 (<0.05)

552 (25.6, 177.9)^f

glass (77)^c,e

470, 505, 540, 585 (83)

^aIn dichloromethane at 298 K. ^bThe luminescence quantum yield, measured at room temperature using [Ru(bpy)₃]²⁺as a standard. ^cVibronic-structured

emission band. ^dPrepared by vacuum deposition. ^eIn CH₂Cl₂/EtOH/MeOH (1:40:10 v/v). ^fDouble exponential decay.

solid samples and dichloromethane solutions of the alkynylgold-

(III) complexes exhibit intense luminescence at 470-611 nm

at both room temperature and 77 K. The photophysical data of

1-9 are tabulated in Table 5. Compared to the chloro analogue,

[Au(C^∧N^∧C)Cl], which are reported to emit only in low-

temperature glasses, the enrichment of the luminescence be-

haviors of 1-9 demonstrates the concept that incorporation of

strong σ-donating alkynyl ligands into gold(III) could enlarge

the d-d ligand field splitting, giving rise to an enhancement of

their luminescence properties. Figure 6 depicts the emission

spectra of 1, 5, 8, and 9 in dichloromethane solution at room

temperature. The long-lived emission with lifetimes in the sub-

microsecond to microsecond range, together with the observed

large Stokes shift, suggests that the emission is of triplet

parentage. In dichloromethane solution at room temperature,

almost identical spectra were observed in 1-4, 6, and 7 which

contain the same C^∧N^∧C ligand, in which a vibronic-structured

emission band with a band maximum at around 480 nm was

observed. These findings suggest that the emission energies of

the compounds are rather insensitive to the nature of the alkynyl

ligands. The vibrational progressional spacings of about 1300

cm^-1are characteristic of the CdC and CdN stretching

frequencies of the tridentate ligand, indicative of the involvement

of the tridentate RC^∧N(R′)^∧CR ligand in the excited-state origin.

The luminescence is assigned as originating from a metal-

3

perturbed [π f π*(RC^∧N(R′)^∧CR)] IL state. Similar assign-

ment has also been made in other related mononuclear [Au-

(C^∧N^∧C)X] complexes.^6dParallel to the electronic absorption

study, the observation of the emission band of 8 at lower energy

than that of 1 is ascribed to the narrower π-π* energy

separation of the RC^∧N(R′)^∧CR ligand due to the attachment

of the electron-donating tert-butyl groups on the phenyl rings

(Figure 6). Although the introduction of the tolyl group on the

pyridyl ring of the C^∧NTol^∧C ligand in 9 is anticipated to lower

the π* orbital energy of the C^∧NTol^∧C ligand as discussed in

the electronic absorption study, only a very small to negligible

shift of this vibronic-structured emission band was observed in

9. Unlike the other members of this series of alkynylgold(III)

complexes, which in general show a vibronic-structured emis-

sion band in dichloromethane, 5 with an amino-phenyl alkynyl

group shows a lower-energy structureless emission band cen-

tered at ca. 610 nm (Figure 6). This structureless emission band

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4357

A R T I C L E S

Wong et al.

Computational Studies. In order to gain further insights into

the structural, electrochemical, and photophysical properties as

well as the electronic structures of the ground and excited states

of this series of luminescent alkynylgold(III) complexes, density

functional theory (DFT) calculations at the B3LYP level of

theory were performed to study complexes 1-5 and 7-9 (for

details, see the Experimental Section). For the sake of reducing

the computational cost, model complexes, [Au(C^∧N^∧C)(CtCs

CH₃)] 7′ and [Au(C^∧NTol^∧C)(CtCC₆H₄sCH₃-p)] 9′, respec-

tively, were used instead of complexes 7 and 9, in which the

hexyl group on the phenyl alkynyl ligand and the alkynyl ligand

were replaced by a methyl group.

Figure 5. Electronic absorption spectra of 1, 3, 5, 8, and 9 in CH₂Cl₂at

Geometry optimizations were performed for the two extreme

forms of complexes 1-5, 8, and 9′, i.e., perpendicular (the aryl

rings lie perpendicular to the RC^∧N(R′)^∧CR plane) and coplanar

forms (the aryl rings lie in the plane of the RC^∧N(R′)^∧CR ring),

which were labeled as 1a-5a, 8a, and 9′a and 1b-5b, 8b, and

9′b, respectively. The energy difference between the two forms

in each complex is quite small, in which the perpendicular forms

of complexes 1-3, 8, and 9′ are relatively more stable than the

corresponding coplanar forms by 0.1-0.6 kcal mol^-1, while the

coplanar forms are more stable than the perpendicular forms

by 0.1 and 0.3 kcal mol^-1in complexes 4 and 5, respectively.

This may account for the observation of both conformations in

their crystal structures. The optimized geometries of 1a-5a,

8a, and 9′a with selected structural parameters as well as the

experimental structural parameters of 1-5, 8, and 9 are shown

in Figure 7 (see Table S1 for the selected structural parameters

of the planar forms). In general, the calculated bond lengths

and angles of 1-5, 7′, 8, and 9′ are in good agreement with

that observed in the X-ray crystal structures (see Figure 7 and

Table S1), implying that the level of theory and basis sets that

we applied are reliable.

room temperature.

Figure 6. Emission spectra of 1, 5, 8, and 9 in degassed CH₂Cl₂at room

temperature.

was found to be concentration-independent in the range 5 ×

10^-6to 1 × 10^-3mol dm^-3, suggesting that excimeric emission

arising from the π-π stacking of the C^∧N^∧C motifs in solution

is unlikely. On the basis of the energetically higher-lying π-

(CtCC₆H₄sNH₂) orbital resulting from the strong electron-

donating amino substituent, the lower-energy emission band in

5 is tentatively assigned as derived from an excited state of

³LLCT [π(CtCC₆H₄NH₂) f π*(C^∧N^∧C)] origin. Such an

assignment is further corroborated by the computational studies

(vide infra) as well as the assignment of the first oxidation wave

in the electrochemical study as an alkynyl ligand-centered

oxidation. On the contrary, 1-9 exhibit a broad low-energy

emission band at 550-585 nm in the solid state at ambient

temperature. The structureless band shape and the red shift of

the solid-state emission band relative to that in dichloromethane

As the effect of the substituents R, R′, and R′′ on the change

of the molecular orbital energies in both structural forms of 1-5,

8, and 9′ is similar, for our convenience, only molecular orbitals

in the perpendicular forms with the symbol “a” will be con-

sidered in the discussion of molecular orbitals. Figure 8 shows

the spatial plots of selected TDDFT/CPCM frontier orbitals in

1a. These orbitals were found to be involved in the electronic

transitions (vide infra). As depicted, the frontier filled orbitals

were mainly contributed by the π systems of the phenyl alkynyl

and the C^∧N^∧C ligands. The HOMO (π_{C≡CC H}) and HOMO-3

6

5

(π_{C≡CC H}_orth) are the two orthogonal sets of π orbitals on the

6

5

3

alkynyl. The remaining filled orbitals are mainly π orbitals of

solution are attributed to the π-π excimeric IL emission due

the C^∧N^∧C ligand, which are HOMO-1 (4π_{C N C}), HOMO-2

∧

to the π-π stacking interaction of the C^∧N^∧C ligand in the

solid state, as revealed by the ordered packing of the molecules

in the X-ray crystal packings of the complexes.

∧

∧ ∧

(3π_{C N C}), HOMO-6 (2π_{C N C}), and HOMO-7 (1π_{C N C}). The

unoccupied molecular orbitals LUMO and LUMO+1 are

essentially π* orbitals localized on the C^∧N^∧C ligand, where

For emission studies in low-temperature glasses, all the

complexes show similar vibronic-structured emission bands with

an emission energy similar to that observed in dichloromethane

solution. It is interesting to note that the emission spectrum of

5 in 77 K glass also exhibits a similar vibronic-structured

emission band, in contrast to that recorded in dichloromethane

solution, in which a structureless emission band was observed.

∧

∧ ∧

they are denoted 1π*_{C N C}and 2π*_{C N C}, with a larger contribu-

tion on the pyridine ring. The LUMO+2 consists of a σ-anti-

bonding interaction between the metal center and the coordinated

ligands (σ*_AuL).

The energies of the frontier orbitals in 1a as well as the

corresponding orbitals in 2a-5a, 7′, 8a, and 9′a and the

percentage compositions of these frontier orbitals are listed in

Table 6 and Table S3, respectively. The corresponding informa-

tion for the coplanar forms are listed in Tables S2 and S3,

respectively. The energy of the HOMO (π_C≡CR′′) in all the

complexes with the aryl alkynyl ligand was found to show a

3

The change of emission origin in 5 from the LLCT [π(Ct

CC₆H₄NH₂) f π*(C^∧N^∧C)] excited state to the metal-perturbed

³IL [π f π* (C^∧N^∧C)] excited state by a lowering of the

medium temperature indicates that these two excited states are

close-lying in energy.

9

4358 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Figure 7. Selected structural parameters of the B3LYP optimized geometries for 1a-5a, 7′, 8a, and 9′a with the experimental structural parameter shown

in parentheses.

strong dependence on the nature of the substituents at the para

position of the phenyl alkynyl group. Especially for the -OMe

and -NH₂groups in 4a and 5a, the HOMO energy was found

to increase by 0.33 and 0.69 eV in 4a and 5a, respectively,

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4359

A R T I C L E S

Wong et al.

Table 6. TDDFT/CPCM Orbital Energies (eV) in 1a-5a, 7′, 8a,

and 9′a

1a

2a

3a

4a

5a

7′

8a

9′a

σ*_AuL

-0.68 -0.72 -0.80 -0.66 -0.62 -0.61 -0.64 -0.65

-1.56 -1.58 -1.61 -1.55 -1.54 -1.54 -1.52 -1.56

-2.11 -2.13 -2.17 -2.10 -2.08 -2.07 -2.05 -2.19

-5.72 -5.80 -6.14 -5.40 -5.04 -6.09 -5.68 -5.61

-6.12 -6.14 -6.18 -6.12 -6.10 -6.10 -5.99 -6.12

-6.67 -6.69 -6.73 -6.66 -6.65 -6.65 -6.58 -6.65

-6.71 -6.79 -6.92 -6.69 -6.62 -6.50 -6.60 -6.71

-6.84 -6.87 -6.88 -6.83 -6.82 -6.82 -6.68 -6.84

-7.10 -7.14 -7.25 -7.08 -7.05 -7.03 -7.01 -7.10

^∧N(R′)^∧CR

2π*_RC

^∧N(R′)^∧CR

1π*_RC

π_CtCR′′

^∧N(R′)^∧CR

4π_RC

^∧N(R′)^∧CR

3π_RC

π_{CtCR′′ orth}

^∧N(R′)^∧CR

2π_RC

^∧N(R′)^∧CR

1π_RC

0.06 eV, compared to that of 1a, which is ascribed to the

presence of electron-donating tert-butyl substituents on the

t

phenyl rings in the BuC^∧N^∧C^tBu ligand. On the other hand,

on going from 1a to 9′a, the energy of the LUMO is decreased

by 0.08 eV, due to the increase in the extent of π-conjugation

upon attachment of the tolyl group to the pyridine ring in the

C^∧NTol^∧C ligand. The energy of the HOMO in 7′ is decreased

significantly, compared to that in 1a, as a result of the presence

of the antibonding interaction between the π orbitals on the Ct

C triple bond and the attached phenyl group in 1a that would

increase the HOMO energy, which is absent in 7′. On the other

hand, the LUMO energy is increased from 1a to 7′. Presumably,

the more electron-rich aliphatic alkynyl ligand would render

the metal center more electron-rich, raising the metal dπ orbital

energy, leading to a better energy match between the metal dπ

orbital and the π* orbital of the C^∧N^∧C ligand that gave rise to

a higher-lying LUMO. The observed trends are consistent with

the electrochemical data.

A nonequilibrium TDDFT/CPCM calculation using CH₂Cl₂

as the solvent was employed to investigate the nature of the

singlet excited states in the aryl alkynyl Au(III) complexes 1-5,

8, and 9′ with both the perpendicular and coplanar forms, and

the aliphatic alkynyl Au(III) complex 7′ (see Experimental

Section). The selected singlet-singlet excitations of complexes

1a and 1b in the range detected in the absorption spectra are

shown in Table 7. The nature of the orbitals involved in the

excitation¹³is also shown, where the same convention is used

as that in the previous section (see Figure 8). The spectral

assignment is based on the correlation of the experimental band

maxima with the calculated excited-state energies of the

transitions with the oscillator strength greater than 0.005.

From the calculation results, there are two types of transitions

at the low-energy absorption region which resemble those

observed in the experimental UV-visible absorption spectra.

The low-energy allowed transitions located at ca. 380 and 370

nm can be assigned as the metal-perturbed intraligand IL

Figure 8. Spatial plots (isovalue ) 0.04) of the selected TDDFT/CPCM

frontier molecular orbitals of 1a.

when compared to that in 1a. These can be explained by the

strong electron-donating abilities of the methoxy and amino

groups, which significantly raise the HOMO energy. On the

other hand, the HOMO energy was found to decrease signifi-

cantly by 0.41 eV in 3a, when compared to that in 1a, because

of the strong electron-withdrawing ability of the NO₂group.

These results are in agreement with the CV study, in which 3

is the most difficult to be oxidized, while 5 is the easiest to be

oxidized.

∧

∧ ∧

transitions [4π_{C N C}f 1π*_{C N C}] (S₂state in 1a and S₁state

in 1b) and the metal-perturbed ligand-to-ligand charge-transfer

∧

LLCT [π_{C≡CC H}f 1π*_{C N C}] transitions [this transition is

6

5

forbidden in 1a (S₁state),¹⁴but it is allowed in 1b (S₂state)],

respectively. Several transitions are computed in the high-energy

absorption region of 1. They mainly consist of the contributions

from the IL π-π* transitions of the C^∧N^∧C ligand and the

Unlike the LUMO of 1a and the other complexes

∧

(1π*_{RC N(R′) CR}), the LUMO of 3a consists mainly of the π*

orbital localized on the CtCC₆H₄sNO₂ligand (denoted as

π*_{C≡CC H NO}), with an energy of 0.37 eV lower than that of

6

4

2

∧

the 1π*_{C N C}orbital (LUMO+1). The occurrence of the

(13) The character of each excited state is assigned according to the compositions

of the occupied and virtual MOs of the dominant configuration (s) for that

excited state. Different from the one-electron excitation model, the TDDFT

formalism regards excited states as linear combinations of singly excited

determinants. Accordingly, each transition includes a series of excitations,

where some of them outweigh the others and predominate the character of

the transitions.

∧

π*_{C≡CC H NO}orbital at lower energy than the 1π*_{C N C}orbital

6

4

2

is consistent with the additional reduction wave observed at a

less negative potential (-1.08 V) in 3 from the electrochemical

study. The energy of the LUMO of 8a is slightly increased by

9

4360 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

Table 7. Selected Low-Lying Singlet (S_n) Excited States Computed by TDDFT/CPCM, with the Orbitals Involved in the Excitations,

Transition Coefficients, Vertical Excitation Energies (eV and nm), and Oscillator Strengths (f) in 1a and 1b

1a

1b

vertical

excitation energy

transition

oscillator

strength^b

S_n

excitation^a

coefficient

eV

nm

f ^b

state

excitation^a

coefficient

eV

nm

^∧N^∧

C

^∧N^∧

C

S₂

S₅

S₆

S₇

S₈

S₉

S₁₁

4π_{C C}f 1π*_C

0.68

0.67

0.68

0.57

0.67

0.59

3.27

3.95

4.03

4.13

4.14

4.23

4.48

380

314

308

300

299

293

277

0.06

0.17

0.16

0.01

0.10

0.06

0.22

S₁

S₃

S₄

S₅

S₇

S₈

S₁₁

4π_{C C}f 1π*_C

0.68

0.70

0.63

0.66

0.59

0.48

0.55

3.25

3.35

3.93

3.95

4.10

4.12

4.47

381

370

315

314

303

301

283

0.05

0.22

0.13

0.05

0.10

0.07

0.18

^∧N^∧

π_{CtCC H}f 1π*_C

C

3π_{C C}f 1π*_C

6

5

π_{CtCC H orth}f 1π*_C

C

^∧N^{∧ ∧}N^∧

3π_{C C}f 1π*_C

C

6

5

^∧N^∧

C

^∧N^∧

C

2π_{C C}f 1π*_C

π_{CtCC H}f 2π*_C

6

5

^∧N^∧

C

^∧N^∧

C

4π_{C C}f 2π*_C

2π_{C C}f 1π*_C

^∧N^∧

π_{CtCC H}f σ*_AuL

4π_{C C}f 2π*_C

6

5

^∧N^∧

1π_{C C}f 1π*_C

^aThe excitations with the transition coefficients less than 0.4 were not shown. ^bOnly the singlet excited states with f > 0.005 were listed.

LLCT transitions from π orbitals on the CtC triple bond of

the alkynyl unit to the π* orbitals on the C^∧N^∧C ligand. In

general, the calculated singlet-singlet transitions in 2-5, 7′,

8, and 9′ are similar to that in 1 and are shown in Tables S4-

S10.

Basically, the calculated singlet-singlet transitions in 1-5,

7′, 8, and 9 are in reasonable agreement with the experimental

λ_maxin the two major electronic absorption bands observed in

the experimental spectra. For 5b, a significant red shift of the

∧

LLCT [π_{C≡CC H NH}f 1π_{C N C}] transition is found at 459 nm

6

4

2

relative to 1b and it becomes 0.58 eV lower in energy than its

∧

∧ ∧

IL [4π_{C N C}f 1π*_{C N C}] transition, which might account for

the additional shoulder that appeared in the electronic absorption

spectrum of 5 at about 415-435 nm. The low-energy IL

∧

[4π_{RC N(R′) CR}f 1π*_{RC N(R′) CR}] transitions are found to be red-

shifted in 8 (385 nm in 8a and 387 nm in 8b) and 9′ (387 nm

in 9′a and 388 nm in 9′b) relative to 1 (380 nm in 1a and 381

nm in 1b), which is in agreement with the observed trend of

the experimental λ_max(381 nm for 1, 392 nm for 8, and 386

nm for 9) in the lower-energy absorption band. This can be

t

explained by the electron-donating ability of the Bu groups

attached to the two phenyl rings in the BuC^∧N^∧C^tBu ligand

t

and the extended π-conjugation upon introduction of the tolyl

group attached to the pyridine ring in the C^∧NTol^∧C ligand

which destabilizes the 4π^t_{BuC N C Bu}orbital more relative to the

t

∧

t

∧

1π* _{BuC N C Bu}orbital and stabilizes the 1π*_{C N(Tol) C}orbital,

respectively, and thus narrows the gap for the IL [4π_{RC N(R′) CR}f

∧

1π*_{RC N(R′) CR}] transition.

In order to study the nature of the emitting triplet states and

the structural changes from the corresponding ground states of

the Au(III) complexes, an unrestricted Kohn-Sham approach

(UB3LYP) was used to optimize the low-lying triplet states in

1-5, 7′, 8 and 9′. For some of the complexes, optimization of

the triplet states starting from the ground-state perpendicular

structure gave a highly distorted structure, in which the C^∧N^∧C

ligand is unrealistically distorted. As a consequence, only the

triplet states, which were optimized starting from the ground-

state coplanar structures, would be considered here. Figure 9

shows the optimized structure of the triplet excited state of 1

and selected changes in the structural parameters relative to that

of the ground state. The major geometrical changes occur mainly

Figure 9. Optimized structures of the triplet states of in 1 and 5 starting

from the ground-state coplanar structures with the change in bond distances

(in Å), relative to their corresponding ground states. Only differences in

bond distances larger than 0.01 Å were shown.

in the C(1) phenyl ring and the pyridine ring in the C^∧N^∧C

ligand. Inspection of the two singly occupied molecular orbitals

(SOMOs) of the optimized triplet excited state of 1 reveals that

the lower- and higher-energy SOMOs are contributed mainly

from the π and π* orbitals of the C^∧N^∧C ligand, respectively

(see Figure S1). This provides a clear indication that the triplet

excited state of 1 contains the IL [π f π* (C^∧N^∧C)] character.

However, optimization of the triplet state of complex 5 gave a

different type of distortion, in which the major change in the

triplet excited state of 5 occurs mainly in the metal-pyridine

(14) The low intensity of the S₀f S₁transition is presumably associated with

a symmetry restriction. Consider the molecule having a C_2Vsymmetry, the

^∧N^∧

irreducible representations of the HOMO (π_{C≡CC H}) and LUMO (1π*_C

)

are b₂and b₁, respectively. The HOMO-LUMO transition (b₂f b^C₁)

generates the ¹A₂excited state. As no electronic dipole moment component

belongs to A₂symmetry, this transition is forbidden.

6

5

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4361

A R T I C L E S

Wong et al.

Table 8. Calculated and Experimental Emission Maxima for

Selected Complexes

romethane solution, a structureless and red-shifted emission band

was observed in the solid state at room temperature, attributed

to the π-π excimeric ³IL emission due to the π-π interaction

of the C^∧N^∧C ligand, as revealed by the observation of π-π

stacking in the crystal packings of the complexes in the solid

state. The electronic structures of the ground and excited states

for the luminescent alkynylgold(III) complexes 1-5 and 7-9

were studied by DFT calculations. The HOMO for all the

complexes correspond to the π orbital on the alkyl/aryl alkynyl

ligand, while the LUMO consists mainly of the π* orbital on

the RC^∧N(R′)^∧CR ligand with the exception of complex 3, in

which the LUMO is the π* orbital localized on the CtCC₆H₄s

NO₂ligand. These results are in agreement with the electro-

chemical study. The TDDFT/CPCM calculations indicate that

the lowest energy absorption bands are attributed mainly to the

metal-perturbed IL π-π* transition of the cyclometalated

RC^∧N(R′)^∧CR ligand and metal-perturbed LLCT transition from

the π orbital on the alkyl/aryl alkynyl ligands to the π* orbital

on the C^∧N^∧C ligand. The calculated emissive triplet states of

all the complexes with the exception of complex 5 are derived

predominantly from an IL [π f π*(RC^∧N(R′)^∧CR)] origin.

calculated emission maximum

experimental emission maximum (λ_max)

complex

(

λ

_calcd)/nm^a

in CH₂Cl₂at 298 K/nm

1

2

3

4

5

7′

8

466

471

466

520

465

472

466

476

474

611

471

484

478

9′

^aThe energy difference with solvent correction (CH₂Cl₂) between the

optimized ground and triplet excited states (³IL [πfπ* (RC^∧N(R′)^∧CR)]

state for 1-4, 7′, 8, and 9′ and ³IL [πfπ* (CtCC₆H₄NH₂)]/³LLCT [π

(CtCC₆H₄NH₂) f π* (C^∧N^∧C)] state for 5) of the coplanar forms.

and metal-aryl ethynyl units (see Figure 9), suggesting a

difference in the nature of the excited states. In the triplet excited

state of 5, the lower-energy SOMO is mainly a π orbital on the

CtCC₆H₄sNH₂unit, while the higher-energy SOMO is the

π* orbital localized on the C^∧N^∧C and CtCC₆H₄sNH₂ligand

(see Figure S1). This indicates that the excited state contains

3

admixtures of IL [π f π* (CtCC₆H₄NH₂)] character and

³LLCT [π(CtCC₆H₄NH₂) f π*(C^∧N^∧C)] character.

Experimental Section

Table 8 shows the calculated emission maxima of 1-5, 7′,

8, and 9′, estimated from the difference in the solvent-corrected

energy of the ground and triplet-excited states (see Experimental

Materials and Reagents. 1-Octyne, phenylacetylene, (4-aminophe-

nyl)acetylene, (4-methoxyphenyl)acetylene, (4-hexylphenyl)acetylene,

(4-nitrophenyl)acetylene, and (4-chlorophenyl)acetylene were purchased

from Maybridge Chemical Co. Ltd. Potassium tetrachloroaurate(III)

was purchased from Strem. Hg(C^∧N^∧CH)Cl (HC^∧N^∧CH ) 2,6-diphe-

nylpyridine),^6dAu(C^∧N^∧C)Cl,^6d2,6-diphenyl-4-p-tolylpyridine,¹⁵and

2,6-bis(4-tert-butylphenyl)pyridine¹⁵were prepared by modification of

the literature procedures. All solvents were purified and distilled using

standard procedures before use. All other reagents were of analytical

grade and were used as received. Tetra-n-butylammonium hexafluo-

rophosphate (Aldrich) was recrystallized twice from absolute ethanol

before use.

Physical Measurements and Instrumentation. UV-visible spectra

were obtained on a Hewlett-Packard 8452A diode array spectropho-

tometer, and IR spectra, as a KBr disk on a Bio-Rad FTS-7 Fourier

transform infrared spectrophotometer (4000-400 cm^-1). ¹H NMR

spectra were recorded on a Bruker DPX-300 (300 MHz) or Bruker

DPX-400 (400 MHz) Fourier transform NMR spectrometer with

chemical shifts recorded relative to tetramethylsilane (Me₄Si). Positive-

ion FAB or EI mass spectra were recorded on a Finnigan MAT95 mass

spectrometer. Elemental analyses for the metal complexes were

performed on the Carlo Erba 1106 elemental analyzer at the Institute

of Chemistry, Chinese Academy of Sciences, Beijing, China. Steady-

state excitation and emission spectra were recorded on a Spex

Fluorolog-2 model F 111 fluorescence spectrofluorometer equipped with

a Hamamatsu R-928 photomultiplier tube. All solutions for photo-

physical studies were prepared under a high vacuum in a 10-cm³round-

bottomed flask equipped with a sidearm 1-cm fluorescence cuvette and

sealed from the atmosphere by a Rotaflo HP6/6 quick-release Teflon

stopper. Solutions were rigorously degassed on a high-vacuum line in

a two-compartment cell with no less than four successive freeze-

pump-thaw cycles. Solid-state photophysical measurements were

carried out with the solid sample loaded in a quartz tube inside a quartz-

walled Dewar flask. Liquid nitrogen was placed into the Dewar flask

for low temperature (77 K) photophysical measurements. Excited-state

lifetimes of solution samples were measured using a conventional laser

system. The excitation source used was the 355-nm output (third

harmonic, 8 ns) of a Spectra-Physics Quanta-Ray Q-switched GCR-

150 pulsed Nd:YAG laser (10 Hz). Luminescence quantum yields were

3

Section). The calculated emission maxima of IL [π f π*

(RC^∧N(R′)^∧CR)], corresponding to 465-471 nm (2.63-2.67

eV) for 1-4, 7′, and 9′ and 473 nm (2.62 eV) for 8, correlated

well with the experimental emission energies for the Au

complexes with 471-478 nm for 1-4, 7, and 9 and 484 nm

for 8. A slight red shift of the triplet state energy was calculated

in 8, relative to 1, which matches the trend observed in the

experiments. The triplet state in 5 was calculated to be at 520

nm. Although the calculated emission energy was not in good

agreement with that determined experimentally (620 nm), the

switch in the nature of the excited state and the significant red

shift in the calculated emissive state energy successfully mimic

the trend observed in the experiments.

Conclusion

A new class of luminescent cyclometalated alkynylgold(III)

complexes has been synthesized and characterized. The X-ray

crystal structures of most of the complexes have been deter-

mined, and their crystal packings showed the presence of π-π

stacking interactions between adjacent RC^∧N(R′)^∧CR moieties.

Electrochemical studies reveal an RC^∧N(R′)^∧CR ligand-centered

reduction, with the exception of 3, and an alkynyl ligand-

centered oxidation. Their electronic absorption and luminescence

behaviors have also been investigated. In dichloromethane

solution at room temperature, the low-energy absorption bands

are assigned as the π-π* intraligand (IL) transition of the

cyclometalated RC^∧N(R′)^∧CR ligand with some mixing of a

[π(CtCR′′) f π*(RC^∧N(R′)^∧CR)] ligand-to-ligand charge

transfer (LLCT) character. The low-energy emission bands in

dichloromethane solution at room temperature are ascribed to

origins mainly derived from the π-π* IL transition of the

cyclometalated RC^∧N(R′)^∧CR ligand. Complex 5, which con-

tains an electron-rich amino substituent on the alkynyl ligand,

shows a low-energy [π(CtCC₆H₄NH₂) f π*(C^∧N^∧C)] LLCT

absorption. In contrast to the emission spectra in dichlo-

(15) Kro¨hnke, F. Synthesis 1976, 1.

9

4362 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

measured by the optical dilute method reported by Demas and Crosby.^16a

A degassed aqueous solution of [Ru(bpy)₃]Cl₂(Φ ) 0.042, excitation

wavelength at 436 nm) was used as the reference.^16b

Synthesis of [Hg(C^∧NTol^∧CH)Cl] (HC^∧NTol^∧CH ) 2,6-Diphenyl-

4-p-tolylpyridine). The procedure was similar to that for [Hg-

(^tBuC^∧N^∧C^tBuH)Cl], except 2,6-diphenyl-4-p-tolylpyridine was used

in place of 2,6-bis(4-tert-butylphenyl)pyridine (1.41 g, 4.40 mmol).

Cyclic voltammetric measurements were performed by using a CH

Instruments, Inc. model CHI 600A electrochemical analyzer. The

electrolytic cell used was a conventional two-compartment cell.

Electrochemical measurements were performed in acetonitrile solutions

with 0.1 M ⁿBu₄NPF₆(TBAH) as supporting electrolyte at room

temperature. The reference electrode was a Ag/AgNO₃(0.1 M in

acetonitrile) electrode, and the working electrode was a glassy carbon

electrode (CH Instruments, Inc.) with a platinum wire as the counter

electrode. The working electrode surface was first polished with a 1-µm

alumina slurry (Linde), followed by a 0.3-µm alumina slurry, on a

microcloth (Buehler Co.). Treatment of the electrode surfaces was as

reported previously.^17aThe ferrocenium/ferrocene couple (FeCp₂^+/0) was

used as the internal reference.^17bAll solutions for electrochemical studies

were deaerated with prepurified argon gas just before measurements.

1

Yield: 0.78 g (32%). H NMR (400 MHz, CDCl₃, 298 K, relative to

Me₄Si)/ppm: δ 2.46 (s, 3 H, CH₃), 7.35 (d, 8.0 Hz, 2 H, phenyl of

toly), 7.47-7.57 (m, 6 H, phenyl and pyridyl of C^∧NTol^∧CH), 7.66

(d, 8.0 Hz, 2 H, phenyl of toly), 7.91 (s, 1 H, pyridyl of C^∧NTol^∧CH),

7.98-8.00 (m, 3 H, phenyl of C^∧NTol^∧CH), 8.05 (dd, 7.1 and 2.0 Hz,

1 H, phenyl of C^∧NTol^∧CH). Positive FAB-MS: m/z 558 [M]⁺.

Elemental analyses calcd for C₂₄H₁₈NClHg‚¹/₁₀C₆H₁₄(found): C, 52.29

(52.31); H, 3.46 (3.60); N, 2.48 (2.21).

[Au(^tBuC^∧N^∧C^tBu)Cl]. This was synthesized according to the

modification of a reported procedure.^6dA mixture of Hg(^tBuC^∧N^∧C-

^tBuH)Cl (0.60 g, 1.04 mmol) and K[AuCl₄] (0.39 g, 1.04 mmol) in

acetonitrile (60 mL) was refluxed for 24 h to afford a deep yellow

solid. The solid was filtered and air-dried. Yield: 0.28 (47%). ¹H NMR

(400 MHz, CD₃SOCD₃, 298 K, relative to Me₄Si)/ppm: δ 1.31 (s, 18

H, ^tBu), 7.34 (dd, 8.2 and 2.0 Hz, 2 H, phenyl of ^tBuC^∧N^∧C^tBu), 7.77

(d, 2.0 Hz, 2 H, phenyl of ^tBuC^∧N^∧C^tBu), 7.79 (d, 8.2 Hz, 2 H, phenyl

of ^tBuC^∧N^∧C^tBu), 7.88 (d, 8.0 Hz, 2 H, pyridyl of ^tBuC^∧N^∧C^tBu), 8.13

Crystal Structure Determination. Single crystals of 1-5 and 7-9

suitable for X-ray diffraction studies were grown by slow diffusion of

diethyl ether vapor into a dichloromethane solution of the complexes

or by layering of n-hexane onto a concentrated dichloromethane solution

of the complexes. The X-ray diffraction data were collected on a MAR

diffractometer with a 300 mm image plate detector using graphite

monochromatized Mo KR radiation (λ ) 0.710 73 Å). The images were

interpreted and intensities were integrated using DENZO program.¹⁸

The structure was solved by direct methods employing the SIR-97

program¹⁹(for 1 and 5) or SHELXS-97 program²⁰(2-4 and 7-9).

Full-matrix least-squares refinement on F²was used in the structure

refinement. The positions of H atoms were calculated based on the

riding mode with thermal parameters equal to 1.2 times those of the

associated C atoms and participated in the calculation of final R-indices.

In the final stage of least-squares refinement, all non-hydrogen atoms

were refined anisotropically.

t

(t, 8.0 Hz, 1 H, pyridyl of BuC^∧N^∧C^tBu). Positive EI-MS: m/z 575

[M]⁺. Elemental analyses calcd for C₂₅H₂₇NAu (found): C, 52.29

(52.03); H, 4.71 (4.81); N, 2.44 (2.38).

[Au(C^∧NTol^∧C)Cl]. A mixture of Hg(C^∧NTol^∧CH)Cl (0.55 g, 0.99

mmol) and K[AuCl₄] (0.37 g, 0.99 mmol) in acetonitrile (60 mL) was

refluxed for 24 h to afford a deep yellow solid. The solid was filtered

1

and air-dried. Yield: 0.23 (42%). H NMR (400 MHz, CD₃SOCD₃,

298 K, relative to Me₄Si)/ppm: δ 2.44 (s, 3 H, CH₃), 7.34 (dt, 7.4 and

1.3 Hz, 2 H, phenyl of C^∧NTol^∧C), 7.42-7.46 (m, 4 H, phenyl of

C^∧NTol^∧C), 7.71 (d, 7.4 Hz, 2 H, phenyl of C^∧NTol^∧C), 8.12 (d, 8.0

Hz, 4 H, phenyl of toly), 8.30 (s, 2 H, pryidyl of C^∧NTol^∧C). Positive

FAB-MS: m/z 554 [M]⁺. Elemental analyses calcd for C₂₄H₁₇NClAu

(found): C, 52.19 (51.91); H, 3.08 (2.98); N, 2.54 (2.46).

Syntheses of Alkynylgold(III) Complexes. All reactions were

carried out under anaerobic and anhydrous conditions using standard

Schlenk techniques.

Synthesis. Synthesis of [Hg(^tBuC^∧N^∧C^tBuH)Cl] (H^tBuC^∧N^∧C^tBuH

) 2,6-Bis(4-tert-butylphenyl)pyridine). This was synthesized by

modification of a literature procedure.^6dA mixture of 2,6-bis(4-tert-

butylphenyl)pyridine (1.51 g, 4.40 mmol) and mercury(II) acetate (1.40

g, 4.40 mmol) in absolute ethanol (30 mL) was heated under reflux

for 24 h, and a solution of lithium chloride (0.37 g, 8.80 mmol) in

methanol (20 mL) was then added. The mixture was heated for 15

min and was then added to distilled water (60 mL). The white precipitate

was filtered off and washed with water and ice-cold methanol. The

white solid was purified by column chromatography using n-hexane-

ethyl acetate as eluent. Yield: 0.60 g (23%). ¹H NMR (300 MHz, CD₃-

[Au(C^∧N^∧C)(CtCC₆H₅)] (1) by Method a. A mixture of [Au-

(C^∧N^∧C)Cl] (0.20 g, 0.43 mmol) and phenylacetylene (0.07 g, 0.65

mmol) in the presence of a catalytic amount of copper(I) iodide (9

mg) in triethylamine (2 mL) and dichloromethane (35 mL) was stirred

at room tempearture for 3 h. After evaporation to dryness, the solid

residue was purified by column chromatography on silica gel using

dichloromethane as eluent. Subsequent recrystallization from slow

diffusion of diethyl ether vapor into the concentrated solution gave 1

t

SOCD₃, 298 K, relative to Me₄Si)/ppm: δ 1.33 (s, 18 H, Bu), 7.45

1

(dd, 8.2 and 2.0 Hz, 1 H, phenyl of ^tBuC^∧N^∧C^tBu), 7.50 (d, 8.5 Hz, 2

H, phenyl of ^tBuC^∧N^∧C^tBu), 7.77 (d, 2.0 Hz, 1 H, phenyl of ^tBuC^∧N^∧C-

^tBu), 7.85 (d, 7.6 Hz, 1 H, pyridyl of ^tBuC^∧N^∧C^tBu), 7.90 (d, 8.2 Hz,

as pale yellow crystals. Yield: 0.20 g (88%). H NMR (300 MHz,

CD₂Cl₂, 298 K, relative to Me₄Si)/ppm: δ 7.26-7.44 (m, 7 H, C₆H₅Ct

C and C^∧N^∧C), 7.54 (d, 8.0 Hz, 2 H, pyridyl of C^∧N^∧C), 7.62 (m, 4 H,

C₆H₅CtC and C^∧N^∧C), 7.92 (t, 8.0 Hz, 1 H, pyridyl of C^∧N^∧C), 8.04

(dd, 7.4 and 1.0 Hz, 2 H, phenyl of C^∧N^∧C). Positive EI-MS: m/z 527

[M]⁺. IR (KBr): 2147 cm^-1ν(CtC). Elemental analyses calcd for

C₂₅H₁₆NAu (found): C, 56.93 (56.57); H, 3.04 (3.05); N, 2.66 (2.66).

[Au(C^∧N^∧C)(CtCC₆H₅)] (1) by Method b. To a stirred solution

of phenylacetylene (0.07 g, 0.65 mmol) in methanol (60 mL) was added

sodium hydroxide (0.52 g, 1.30 mmol). The resultant solution was

heated at 60 °C for 30 min. [Au(C^∧N^∧C)Cl] (0.20 g, 0.43 mmol) was

added to the reaction mixture which was then further heated under reflux

for 12 h. The mixture was filtered, and the solvent was evaporated to

dryness. The product was isolated by column chromatography on silica

gel using dichloromethane as eluent. Subsequent recrystallization from

slow diffusion of diethyl ether vapor into the concentrated solution

gave 1 as pale yellow crystals. Yield: 0.68 g (30%).

t

1 H, phenyl of BuC^∧N^∧C^tBu), 7.91 (d, 1 H, 7.6 Hz, pyridyl of

t

^tBuC^∧N^∧C^tBu), 7.99 (t, 7.6 Hz, 1 H, pyridyl of BuC^∧N^∧C^tBu), 8.06

t

(d, 8.5 Hz, 2 H, phenyl of BuC^∧N^∧C^tBu). Positive EI-MS: m/z 580

[M]⁺. Elemental analyses calcd for C₂₅H₂₈NClHg‚¹/₅C₆H₁₄(found): C,

52.82 (52.73); H, 5.21 (5.08); N, 2.35 (2.36).

(16) (a) Demas, J. N.; Crosby. G. A. J. Phys. Chem. 1971, 75, 991. (b) van

Houten, J.; Watts, R. J. Am. Chem. Soc. 1976, 98, 4853.

(17) (a) Che, C. M.; Wong. K. Y.; Anson, F. C. J. Electroanal. Chem. Interfacial

Electrochem. 1987, 226, 211. (b) Connelly, N. G.; Geiger, W. E.; Chem.

ReV. 1996, 96, 877.

(18) Written with the cooperation of the program authors Otwinowski, Z., and

Minor, W.: Gewirth, D. DENZO: “The HKL Manuals-A description of

programs DENZO, XDISPLAYF, and SCALEPACK”; Yale University:

New Haven, CT, 1995 .

(19) Sir97: a new tool for crystal structure determination and refinement:

Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo, C.;

Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.

Crystallogr. 1998, 32, 115.

(20) SHELXL97: Sheldrick, G. M. SHELXL97: Programs for Crystal Structure

Analysis (release 97-2); University of Go¨ttingen: Go¨ttingen, Germany,

1997.

[Au(C^∧N^∧C)(CtCC₆H₄sCl-p)] (2). This was synthesized by

method a according to a procedure similar to that of 1 except

(4-chlorophenyl)acetylene (0.09 g, 0.65 mmol) was used in place of

phenylacetylene. Pale yellow crystals of 2 were obtained. Yield: 0.21

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4363

A R T I C L E S

Wong et al.

g (85%). ¹H NMR (300 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 7.25-7.42 (m, 6 H, sC₆H₄CtC and C^∧N^∧C), 7.53 (m, 6 H,

sC₆H₄CtC and pyridyl of C^∧N^∧C), 7.60 (dd, 7.0 and 1.0 Hz, 2 H,

phenyl of C^∧N^∧C), 7.90 (t, 8.0 Hz, 1 H, pyridyl of C^∧N^∧C), 8.00 (dd,

7.2 and 1.0 Hz, 2 H, phenyl of C^∧N^∧C). Positive EI-MS: m/z 562

[M]⁺. IR (KBr): 2157 cm^-1ν(CtC). Elemental analyses calcd for

C₂₅H₁₅NClAu‚¹/₂H₂O (found): C, 52.59 (52.85); H, 2.80 (2.66); N, 2.45

(2.40).

Cl₂, 298 K, relative to Me₄Si)/ppm: δ 0.95 (t, 7.0 Hz, 3 H, sCH₃),

1.37-1.42 (m, 4 H, sCH₂s), 1.63-1.72 (m, 4 H, methylene of C₆H₁₃),

2.49 (t, 6.9 Hz, 2 H, sCH₂s), 7.28 (dt, 7.3 and 1.3 Hz, 2 H, phenyl

of C^∧N^∧C), 7.40 (dt, 7.3 and 1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.53 (d,

8.0 Hz, 2 H, pyridyl of C^∧N^∧C), 7.62 (dd, 7.2 and 1.2 Hz, 2 H, phenyl

of C^∧N^∧C), 7.90 (t, 8.0 Hz, 1 H, pyridyl of C^∧N^∧C), 7.99 (dd, 7.2 and

1.2 Hz, 2 H, phenyl of C^∧N^∧C). Positive FAB-MS: m/z 536 [M]⁺. IR

(KBr): 2140 cm^-1ν(CtC). Elemental analyses calcd for C₂₅H₂₄NAu

(found): C, 56.08 (55.96); H, 4.52 (4.60); N, 2.62 (2.53).

[Au(C^∧N^∧C)(CtCC₆H₄sNO₂-p)] (3). This was synthesized by

method a according to a procedure similar to that of 1 except

(4-nitrophenyl)acetylene (0.10 g, 0.65 mmol) was used in place of

phenylacetylene. Yellow crystals of 3 were obtained. Yield: 0.20 g

[Au(^tBuC^∧N^∧C^tBu)(CtCC₆H₅)] (8). This was synthesized by

method a according to a procedure similar to that of 1 except [Au-

(^tBuC^∧N^∧C^tBu)Cl] (0.20 g, 3.48 mmol) was used in place of [Au-

(C^∧N^∧C)Cl]. Subsequent diffusion of n-pentane vapor into the con-

centrated dichloromethane solution resulted in the formation of deep

1

(81%). H NMR (400 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 7.31 (dt, 7.4 and 1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.42 (dt, 7.4 and

1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.55 (d, 8.0 Hz, 2 H, pyridyl of

C^∧N^∧C), 7.64 (dd, 7.2 and 1.2 Hz, 2 H, phenyl of C^∧N^∧C), 7.73 (d,

9.0 Hz, 2 H, sC₆H₄CtC), 7.93 (t, 8.0 Hz, 1 H, pryidyl of C^∧N^∧C),

8.00 (dd, 7.2 and 1.2 Hz, 2 H, phenyl of C^∧N^∧C), 8.22 (d, 9.0 Hz, 2

H, sC₆H₄CtC). Positive EI-MS: m/z 572 [M]⁺. IR (KBr): 2146 cm^-1

ν(CtC), 1341 and 1588 cm^-1ν(NsO). Elemental analyses calcd for

C₂₅H₁₅N₂O₂Au‚¹/₂H₂O (found): C, 51.65 (51.62); H, 2.77 (2.65); N,

4.82 (4.75).

1

yellow crystals of 8. Yield: 0.19 g (85%). H NMR (400 MHz, CD₂-

t

Cl₂, 298 K, relative to Me₄Si)/ppm: δ 1.39 (s, 18 H, Bu), 7.35 (m, 5

t

H, C₆H₅CtC), 7.46 (d, 8.0 Hz, 2 H, pyridyl of BuC^∧N^∧C^tBu), 7.56

(d, 8.2 Hz, 2 H, phenyl of ^tBuC^∧N^∧C^tBu), 7.60 (dd, 8.2 and 2.0 Hz, 2

H, phenyl of ^tBuC^∧N^∧C^tBu), 7.86 (t, 8.0 Hz, 1 H, pyridyl of ^tBuC^∧N^∧C^t-

t

Bu), 8.18 (d, 2.0 Hz, 2 H, phenyl of BuC^∧N^∧C^tBu). Positive EI-MS:

m/z 640 [M]⁺. IR (KBr): 2149 (w) cm^-1ν(CtC). Elemental analyses

calcd for C₃₃H₃₂NAu‚¹/₂H₂O (found): C, 61.11 (61.02); H, 5.09 (5.08);

N, 2.16 (2.17).

[Au(C^∧N^∧C)(CtCC₆H₄sOCH₃-p)] (4). This was synthesized by

method a according to a procedure similar to that of 1 except

(4-methoxyphenyl)acetylene (0.09 g, 0.65 mmol) was used in place of

phenylacetylene. Pale yellow crystals of 4 were obtained. Yield: 0.21

g (86%). ¹H NMR (400 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 3.88 (s, 3 H, OCH₃), 6.91 (d, 8.9 Hz, 2 H, sC₆H₄CtC), 7.27 (dt,

7.3 and 1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.40 (dt, 7.3 and 1.3 Hz, 2 H,

phenyl of C^∧N^∧C), 7.50-7.56 (m, 4 H, pyridyl of C^∧N^∧C and

sC₆H₄CtC), 7.60 (dd, 7.6 and 1.0 Hz, 2 H, phenyl of C^∧N^∧C), 7.90

(t, 8.0 Hz, 1 H, pyridyl of C^∧N^∧C), 8.02 (dd, 7.6 and 1.0 Hz, 2 H,

phenyl of C^∧N^∧C). Positive EI-MS: m/z 557 [M]⁺. IR (KBr): 2157

cm^-1ν(CtC). Elemental analyses calcd for C₂₆H₁₈NOAu‚¹/₂H₂O

(found): C, 55.12 (55.15); H, 3.36 (3.28); N, 2.47 (2.48).

[Au(C^∧NTol^∧C)(CtCC₆H₄sC₆H₁₃-p)] (9). This was synthesized

by method a according to a procedure similar to that of 6 except

[Au(C^∧NTol^∧C)Cl] (0.24 g, 0.43 mmol) was used in place of

[Au(C^∧N^∧C)Cl]. Yellow crystals of 9 were obtained. Yield: 0.20 g

1

(80%). H NMR (300 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 0.91 (t, 6.8 Hz, 3 H, sCH₃), 1.34 (m, 6 H, sCH₂s), 1.62-1.64 (m,

2 H, sCH₂s), 2.46 (s, 3 H, CH₃of tolyl), 2.64 (t, 7.7 Hz, 2 H, s

CH₂s), 7.17 (d, 8.0 Hz, 2 H, sC₆H₄CtC), 7.27 (dt, 7.5 and 1.0 Hz,

2 H, phenyl of C^∧N(Tol)^∧C), 7.35-7.40 (m, 4 H, phenyl of C^∧N(Tol)^∧C

and pyridyl of C^∧N(Tol)^∧C), 7.47 (d, 8.0 Hz, 2 H, sC₆H₄CtC), 7.66-

7.71 (m, 6 H, phenyl of C^∧N(Tol)^∧C and tolyl), 8.01 (dd, 7.5 and 1.0

Hz, 2 H, phenyl of C^∧N(Tol)^∧C). Positive FAB-MS: m/z 703 [M]⁺.

IR (KBr): 2142 (w) cm^-1ν(CtC). Elemental analyses calcd for C₃₈H₃₄-

NAu (found): C, 64.99 (64.74); H, 4.85 (4.87); N, 2.00 (1.92).

[Au(C^∧N^∧C)(CtCC₆H₄-NH₂-p)] (5). This was synthesized by

method a according to a procedure similar to that of 1 except

(4-aminophenyl)acetylene (0.08 g, 0.65 mmol) was used in place of

phenylacetylene. Deep yellow crystals of 5 were obtained. Yield: 0.19

g (80%). ¹H NMR (300 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 3.84 (s, 2 H, NH₂), 6.67 (d, 8.6 Hz, 2 H, sC₆H₄CtC), 7.30 (dt, 7.5

and 1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.39-7.45 (m, 4 H , phenyl of

C^∧N^∧C and sC₆H₄CtC), 7.56 (d, 8.0 Hz, 2 H, pyridyl of C^∧N^∧C),

7.65 (dd, 7.4 and 1.0 Hz, 2 H, phenyl of C^∧N^∧C), 7.92 (t, 8.0 Hz, 1 H,

pyridyl of C^∧N^∧C), 8.07 (dd, 7.4 and 1.0 Hz, 2 H, phenyl of C^∧N^∧C).

Positive EI-MS: m/z 542 [M]⁺. IR (KBr): 2143 cm^-1ν(CtC), 3338

and 3421 cm^-1ν(NsH). Elemental analyses calcd for C₂₅H₁₇N₂Au‚

¹/₂H₂O (found): C, 54.45 (54.59); H, 3.27 (3.13); N, 5.08 (5.04).

[Au(C^∧N^∧C)(CtCC₆H₄sC₆H₁₃-p)] (6). This was synthesized by

method a according to a procedure similar to that of 1 except

(4-hexylphenyl)acetylene (0.12 g, 0.65 mmol) was used in place of

phenylacetylene. Pale yellow solid of 6 were obtained. Yield: 0.19 g

Computational Details. Calculations were carried out using Gauss-

ian03 software package.²¹Density functional theory (DFT) at the

Becke3LYP (B3LYP) level²²was used to optimize the singlet ground-

state (S₀) geometries of the Au(III) complexes 1-5, 7′, 8, and 9′. Based

on the ground-state optimized geometries in the gas phase, a nonequi-

librium time-dependent (TDDFT) method²³at the same level associated

with a conductor-like polarizable continuum model (CPCM)²⁴was

employed to study the nature of singlet-singlet transitions in the

absorption spectra of 1-5 and 7-9 (CH₂Cl₂as the solvent). The tandem

use of CPCM and TDDFT has been found to be a suitable computa-

tional approach for the treatment of the solvent effects on the excited-

state energies of the transition metal complexes.²⁵The unrestricted

(21) Frisch, M. J., et al. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford,

CT, 2004 (see Supporting Information for the full author list).

(22) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (b) Becke,

A. D. J. Chem. Phys. 1993, 98, 5648. (c) Stephens, P. J.; Devlin, F. J.;

Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623.

(23) (a) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys. 1998,

109, 8218. (b) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996,

256, 454. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. J.

Chem. Phys. 1998, 108, 4439.

(24) (a) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995. (b) Cossi,

M.; Rega, N.; Scalmani, G.; Barone, V. J. Comput. Chem. 2003, 24, 669.

(25) (a) Villegas, J. M.; Stoyanov, S. R.; Huang, W.; Rillema, D. P. Inorg. Chem.

2005, 44, 2297. (b) Villegas, J. M.; Stoyanov, S. R.; Huang, W.; Lockyear,

L. L.; Reibenspies, J. H.; Rillema, D. P. Inorg. Chem. 2004, 43, 6383. (c)

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2004, 7, 838. (d) Vlcˇek, A., Jr.; Za´lisˇ, S. J. Phys. Chem. A 2005, 109,

2991.

1

(72%). H NMR (300 MHz, CD₂Cl₂, 298 K, relative to Me₄Si)/ppm:

δ 0.91 (t, 7.0 Hz, 3 H, sCH₃), 1.31-1.39 (m, 6 H, sCH₂s), 1.62-

1.67 (m, 2 H, sCH₂s), 2.64 (t, 7.7 Hz, 2 H, sCH₂s), 7.18 (d, 8.3

Hz, 2 H, sC₆H₄CtC), 7.25 (dt, 7.4 and 1.3 Hz, 2 H, phenyl of C^∧N^∧C),

7.37 (dt, 7.4 and 1.3 Hz, 2 H, phenyl of C^∧N^∧C), 7.50 (m, 4 H, pyridyl

of C^∧N^∧C and sC₆H₄CtC), 7.57 (dd, 7.3 and 1.1 Hz, 2 H, phenyl of

C^∧N^∧C), 7.87 (t, 8.0 Hz, 1 H, pyridyl of C^∧N^∧C), 8.00 (dd, 7.3 and

1.1 Hz, 2 H, phenyl of C^∧N^∧C). Positive EI-MS: m/z 611 [M]⁺. IR

(KBr): 2149 cm^-1ν(CtC). Elemental analyses calcd for C₃₁H₂₈NAu‚

¹/₂H₂O (found): C, 59.95 (60.00); H, 4.51 (4.60); N, 2.26 (2.26).

[Au(C^∧N^∧C)(CtCC₆H₁₃)] (7). This was synthesized by method a

according to a procedure similar to that of 1 except 1-octyne (0.07 g,

0.65 mmol) was used in place of phenylacetylene. Pale yellow crystals

(26) Andrae, D.; Ha¨ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim.

Acta 1990, 77, 123.

(27) Ehlers, A. W.; Bo¨hme, M.; Dapprich, S.; Gobbi, A.; Ho¨llwarth, A.; Jonas,

V.; Ko¨hler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G. Chem. Phys.

Lett. 1993, 208, 111.

1

of 7 were obtained. Yield: 0.16 g (68%). H NMR (300 MHz, CD₂-

9

4364 J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007

Luminescent Cyclometalated Alkynylgold(III) Complexes

A R T I C L E S

(U)B3LYP was used to optimize the low-lying triplet states of all the

complexes for the investigation of the nature of the emissive states.

The calculated emission maxima were estimated from the differences

between the triplet- and ground-state energies at their corresponding

equilibrium geometries. To account for the solvent effect on the

calculated emission energies, single-point CPCM calculations using

CH₂Cl₂as a solvent were performed on gas-phase optimized ground-

and triplet excited-state geometries. The Stuttgart effective core

potentials (ECPs) and the associated basis set were applied to describe

Au²⁶with an f polarization function (ú_f(Au) ) 1.050),²⁷while, for all

other atoms, the 6-31G(d) basis set²⁸was used. All the geometry

optimizations were carried out with no symmetry constraint. Vibrational

frequencies were calculated for all stationary points to verify that each

was a minimum (NIMAG ) 0) on the potential energy surface.

(Project No. HKU 7049/05P). L.-L.H. acknowledges the receipt

of a postgraduate studentship, and W.H.L. the receipt of a

University Postdoctoral Fellowship, both from The University

of Hong Kong. We also thank Professor Zhenyang Lin from

the Hong Kong University of Science and Technology for his

helpful discussions on the theoretical studies and the Computer

Center at The University of Hong Kong for providing the

computational resources.

Note Added after Print Publication. Due to a production

error, some of the subscript notation did not appear properly in

the Computational Studies section, including Tables 6 and 7,

in the version of this article published on the Web on March

16, 2007 (ASAP), and in the April 11, 2007 issue (Vol. 129,

No. 14, pp 4345-4365). The corrected electronic versions were

published on August 28, 2007, and an Addition and Correction

appears in the September 19, 2007 issue (Vol. 129, No. 37).

Acknowledgment. V.W.-W.Y. acknowledges support from

the University Development Fund, the URC Seed Funding for

Strategic Research Theme on Organic Optoelectronics, and the

Faculty Development Fund of The University of Hong Kong,

The University of Hong Kong Foundation for Educational

Development and Research Limited, and the RGC Central

Allocation Vote (HKU 2/05C). The work described in this paper

has been supported by a CERG Grant from the Research Grants

Council of Hong Kong Special Administrative Region, China

Supporting Information Available: Selected structural pa-

rameters of the coplanar forms, TDDFT/CPCM orbital and

excitation energies, % composition of selected MOs, (U)B3LYP

electronic energies, Cartesian coordinates of optimized struc-

tures, singly occupied orbitals of the optimized triplet state in

1 and 5, crystallographic data for 1-5 and 7-9, and complete

ref 21. This material is available free of charge via the Internet

at http://pubs.acs.org.

(28) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,

2257. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.

(c) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M.

S.; Defrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.

JA068264U

9

J. AM. CHEM. SOC. VOL. 129, NO. 14, 2007 4365

Article Doi

A class of luminescent cyclometalated alkynylgold(III) complexes: Synthesis, characterization, and electrochemical, photophysical, and computational studies of [Au(C∧N∧C)(C≡C-R)] (C∧N∧C = κ3C,N,C bis-cyclometalated 2,6-diphenylpyridyl)

DOI: 10.1021/ja068264u

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