Peri-diaurated naphthalene: Synthesis and reactions of a new class of organogold(I) complexes containing bridging, dianionic naphthalenediyl ligands

Article abstract of DOI:10.1021/om9002335

The dinuclear gold(I) compound [Au₂(μ-C₁₀H ₆){μ Ph₂P(CH₂)₂PPh₂}] was prepared in high yield by the reaction of 1,8-bis(trimethylstannyl) naphthalene with [Au₂Cl_2<

Full text of DOI:10.1021/om9002335

Copyright 2009
Volume 28, Number 10, May 25, 2009
American Chemical Society
Communications
Peri-Diaurated Naphthalene: Synthesis and Reactions of a New
Class of Organogold(I) Complexes Containing Bridging, Dianionic
Naphthalenediyl Ligands
Nadine Meyer,† Christian W. Lehmann,‡ Terence K.-M. Lee,§ Jo¨rg Rust,‡
Vivian W.-W. Yam,§ and Fabian Mohr*,†
Fachbereich C-Anorganische Chemie, Bergische UniVersita¨t Wuppertal, 42119 Wuppertal, Germany,
Max-Planck-Institut fu¨r Kohlenforschung, 45470 Mu¨hlheim an der Ruhr, Germany, and Centre for
Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research, Department of Chemistry and
HKU-CAS Joint Laboratory on New Materials, The UniVersity of Hong Kong, Pokfulam Road,
Hong Kong, People’s Republic of China
ReceiVed March 27, 2009
ridyl)dimethylphosphine8),thebis(ylide)derivatives[Au2(µ-{(CH2)2-
Summary: The dinuclear gold(I) compound [Au2(µ-C10H6){µ-
PR2})2],9,10 and the cycloaurated complexes [Au2(µ-C-E)2] (C-E
Ph2P(CH2)2PPh2}] was prepared in high yield by the reaction
of 1,8-bis(trimethylstannyl)naphthalene with [Au2Cl2(µ-Ph2P-
(CH2)2PPh2)]. OxidatiVe addition with halogens results in the
formation of the dihalodigold(II) complexes [Au2(X)2(µ-C10H6)-
{µ-Ph2P(CH2)2PPh2}] (X ) Cl, Br, I) containing a gold-gold
bond.
) cyclometalated phosphine or arsine).11 In addition, there are
examples of heterobridged dinuclear gold(I) complexes in which
there are two different bridging ligands (from the categories
mentioned above) in the same molecule.12-18 One class of
(4) Åkerstro¨m, S. Ark. Kemi 1959, 14, 387–401.
(5) Hesse, R.; Jennische, P. Acta Chem. Scand. 1972, 26, 3855–3864.
(6) Heinrich, D. D.; Wang, J. C.; Fackler, J. P., Jr. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1990, 46, 1444–1447.
(7) Mazany, A. M.; Fackler, J. P., Jr. J. Am. Chem. Soc. 1984, 106,
801–802.
(8) Inoguchi, Y.; Milewski-Mahrla, B.; Schmidbaur, H. Chem. Ber. 1982,
115, 3085–3095.
(9) Schmidbaur, H., Schier, A. In ComprehensiVe Organometallic
Chemistry III; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier: Amsterdam,
2007; Vol. 2, p 251, and references cited therein.
(10) Schmidbaur, H. Gold: Progress in Chemistry, Biochemistry and
Technology; Wiley: Chichester, U.K., 1999.
(11) Mohr, F.; Prive´r, S. H.; Bhargava, S. K.; Bennett, M. A. Coord.
Chem. ReV. 2006, 250, 1851–1888.
(12) Bardaj´ı, M.; Connelly, N. G.; Gimeno, M. C.; Jime´nez, J.; Jones,
P. G.; Laguna, A.; Laguna, M. J. Chem. Soc., Dalton Trans. 1994, 1163–
1167.
Dinuclear gold(I) complexes in which two gold atoms are
bridged by a pair of suitable ligands have been known and
studied for a number of years. These types of compounds can
be broadly classified into three main categories: neutral or
cationic complexes of the type [Au2(µ-E-E)2] (E-E ) neutral
ormonoanionicbidentatedonorligands.includingPh2P(CH2)PPh2,1-3
dithiocarbamates,4-6 methylenethiophosphinate,7 and (2-py-
* To whom correspondence should be addressed. E-mail: fmohr@
uni-wuppertal.de.
† Bergische Universita¨t Wuppertal.
‡ Max-Planck-Institut fu¨r Kohlenforschung (X-ray crystallography).
§ The University of Hong Kong (photophysical studies).
(1) Schmidbaur, H.; Wohlleben, A.; Schubert, U.; Frank, A.; Huttner,
G. Chem. Ber. 1977, 110, 2751–2757.
(2) Porter, C. C.; Khan, M. N. I.; King, C.; Fackler, J. P., Jr. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1989, 45, 947–949.
(3) Khan, M. N. I.; King, C.; Heinrich, D. D.; Fackler, J. P., Jr.; Porter,
L. C. Inorg. Chem. 1989, 28, 2150–2154.
(13) Bardaj´ı, M.; Laguna, A.; Laguna, M. J. Organomet. Chem. 1995,
496, 245–248.
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A.; Laguna, M. J. Chem. Soc., Dalton Trans. 1995, 2245–2250.
10.1021/om9002335 CCC: $40.75
2009 American Chemical Society
Publication on Web 04/22/2009

2932 Organometallics, Vol. 28, No. 10, 2009
Communications
Scheme 1. Preparation and Reactions of Complex 1
observed in mass spectra of gold(I) compounds. The proposed
structure of complex 1 was confirmed by an X-ray diffraction
study (Figure 1).36
The complex crystallizes in the space group P21/n and
contains three independent molecules of 1 in the unit cell. Each
molecule of 1 consists of a pair of gold atoms bridged by a
2-
C10H6 group and a molecule of Ph2P(CH2)2PPh2. The coor-
dination geometry about gold is almost linear, with C-Au-P
angles ranging from 169.60(16) to 175.22(19)°. The Au · · · Au
distances range from 2.8868(3) to 2.9239(3) Å, which are greater
than those found in the eight-membered gold(I) dimers [Au2(µ-
2-C6H4PPh2)2] (Au · · · Au ) 2.8594(3) Å)27 and [Au2(µ-C6H3-
2-PPh2-6-Me)2] (Au · · · Au ) 2.861(2) Å)27 but less than those
of the ten-membered gold(I) dimer [Au2(µ-2-C6H4CH2PPh2)2]
(Au · · · Au ) 3.0035(9) Å).28 The average Au-P and Au-C
distances in 1 (2.293(5) and 2.060(5) Å) are similar to those
observed in other organometallic gold(I) phosphine complexes.
In general, there is good agreement of all equivalent bond
lengths among the three molecules. Tables S1 and S2 (Sup-
porting Information) show a comparison and statistical analysis
of selected equivalent bonds. The highest degree of conservation
is observed for the naphthyl rings. These exhibit only slight
twisting (atoms deviate between 0.003 and 0.097 Å from the
least-squares planes), and the sum of the bond angles surround-
ing the carbon atom to which the gold atoms are attached falls
into the narrow range between 359.2(9) and 360.0(9)°. The
largest variance is observed for the Au · · · Au distance, which
correlates with the C′-C-Au angle, with C′ being the bridging
carbon atom of the naphthyl ring. The dihedral angles of the
ethyl bridge of the chelating phosphine ligands deviate sub-
stantially from a gauche conformation; however, the resulting
P · · · P distance does not correlate with the corresponding
dihedral angle. Instead, the C-C-P bond angles also deviate
from the ideal 109.5°. This flexibility of some parts of the
molecule (most likely crystal-packing effects will contribute
significantly to the conformation of the dppe ligand) result in a
twisting of the whole molecule expressed through the dihedral
angle between the intramolecular C-Au-P vectors. This angle
varies between 6.3° for the almost planar molecule (Au1 and
Au2) and 28.6° (Au5 and Au6).
dinuclear gold(I) complexes that has hitherto been unknown
consists of derivatives of the type [Au2(µ-C-C)(µ-E-E)], where
C-C represents a dianionic carbon-only ligand and E-E a neutral,
bidentate ligand. Given the required geometry and bite angle
to bridge two metal atoms, the 1,8-naphthalenediyl dianion,
C10H62-, seemed a suitable choice for our purpose. Indeed, there
2-
are prior examples of metal compounds in which 1,8-C10H6
adopts a bridging coordination mode. These include derivatives
of Li,19 Mg,20 Ge,21 Sn,22 Ga,23 and Hg.24,25 In the mercury
derivative [Hg2(µ-C10H6)2],24 the two Hg atoms are held 2.797(1)
Å apart, a distance which is close to that typically also observed
in binuclear gold complexes. We therefore attempted to prepare
the binuclear gold(I) complex [Au2(µ-C10H6){µ-Ph2P-
(CH2)2PPh2}] and to study its chemistry. Some preliminary
results of our studies are communicated herein. The desired
dinuclear gold(I) complex [Au2(µ-C10H6){µ-Ph2P(CH2)2PPh2}]
(1), containing both bridging 1,8-C10H62- and Ph2P(CH2)2PPh2
(dppe) ligands, was obtained in 84% yield from the reaction of
1,8-bis(trimethylstannyl)naphthalene
with
[Au2Cl2-
(µ-Ph2P(CH2)2PPh2)] in dichloromethane (Scheme 1).35 Alter-
natively, the complex can also be prepared from the reaction
of 1,8-naphthalenediboronic acid with [Au2Cl2(µ-Ph2P(CH2)2-
PPh2)] in the presence of base.26
Complex 1 was isolated as a pale yellow air- and moisture-
stable solid, which is soluble in halogenated solvents and acetone
but insoluble in diethyl ether and hexane. The 31P NMR
spectrum of 1 shows a singlet resonance, suggesting the presence
of equivalent phosphorus atoms in the molecule. The MALDI-
mass spectrum shows a peak at m/z 918, corresponding to the
molecular ion peak of the compound, in addition to peaks with
higher m/z values due to formation of various adducts, typically
In dichloromethane, complex 1 absorbs strongly in the UV
region, with the absorption bands (Figure 2) being attributed to
1
an admixture of spin-allowed metal-perturbed intraligand IL
(naphthyl and phosphine) and metal-centered transitions.29 The
aerated solution is weakly emissive upon photoexcitation at
room temperature (Figure 2). However, the intense green
emission of the solution is “turned on” under deoxygenated
conditions (Figure 2) with a lifetime in the microsecond range
(21.8 µs). The emission is vibronically structured with vibra-
(15) Bardaj´ı, M.; Jones, P. G.; Laguna, A.; Laguna, M. Organometallics
1995, 14, 1310–1315.
(16) Bardaj´ı, M.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Laguna, M.
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(18) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis,
A. C. Inorg. Chem. 2001, 40, 4271–4275.
(19) Letsinger, R. L.; Gilpin, J. A.; Vullo, W. J. J. Org. Chem. 1962,
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Horn, E.; Kooijman, H.; Smeets, W. J. J.; Spek, A. L. J. Am. Chem. Soc.
1993, 115, 2808–2817.
(21) Cozzi, F.; Sjo¨strand, U.; Mislow, K. J. Organomet. Chem. 1979,
174, C1-C2.
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(27) Bhargava, S. K.; Mohr, F.; Bennett, M. A.; Welling, L. L.; Willis,
A. C. Organometallics 2000, 19, 5628–5636.
(28) Bennett, M. A.; Bhargava, S. K.; Hockless, D. C. R.; Mohr, F.;
Watts, K.; Welling, L. L.; Willis, A. C. Z. Naturforsch. 2004, 59b, 1563–
1569.
(29) (a) Yam, V. W.-W.; Choi, S. W.-K.; Cheung, K.-K. Chem.
Commun. 1996, 1173–1174. (b) Partyka, D. V.; Zeller, M.; Hunter, A. D.;
Gray, T. G. Angew. Chem., Int. Ed. 2006, 45, 8188–8191. (c) Naraya-
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D. M.; Elder, R. C.; Bruce, A. E.; Bruce, M. R. M. Inorg. Chem. 1993, 32,
2506. (d) Che, C. M.; Kwong, H. L.; Yam, V. W. W.; Cho, K. C. J. Chem.
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C. M. J. Chem. Soc., Dalton Trans. 1990, 3747–3752.
(23) Tschinkl, M.; Hoefelmeyer, J. D.; Cocker, T. M.; Bachman, R. E.;
Gabba¨ı, F. P. Organometallics 2000, 19, 1826–1828.
(30) (a) Lakowicz, J. Principles of Fluorescence Spectroscopy; Kluwer/
Plenum: New York, 1999. (b) Omary, M. A.; Elbjeirami, O.; Palehepitiya
Gamage, C. S.; Sherman, K. M.; Rasika Dias, H. V. Inorg. Chem. 2009,
48, 1784–1786.
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(25) Gabba¨ı, F. P.; Schier, A.; Riede, J.; Sladek, A.; Go¨rlitzer, H. W.
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Angew. Chem., Int. Ed. Engl. 1987, 26, 260–261.

Communications
Organometallics, Vol. 28, No. 10, 2009 2933
nation (vide supra), we do favor the assignment of a 3IL
(naphthyl) origin with its highly structured emission band.
Treatment of 1 with 1 equiv of PhICl2, Br2, or I2 in dichlo-
romethane at ca. -70 °C gives a red (2a), brown (2b), or rust
red (2c) solution, out of which solid compounds can be isolated
by precipitation with hexane at low temperature.37 These colored
solids are stable to air and moisture and show singlet 31P{1H}
NMR resonances indicative of equivalent phosphorus atoms.
The Raman spectra of the chloro- and bromo derivatives show
Au-Au stretching vibrations at 174 and 135 cm-1, similar to
those observed for the bis(ylide) dihalodigold(II) complexes
[Au2(X)2(µ-{(CH2)2PPh2})2] (ν(Au-Au) 162 and 132 cm-1 for
X ) Cl, Br, respectively).31 On the basis of these data, we
formulate these colored solids as the dihalodigold(II) complexes
[Au2(X)2(µ-C10H6){µ-Ph2P(CH2)2PPh2}] (X ) Cl (2a), Br (2b),
I (2c)). Although the oxidation state +2 is very rare for
mononuclear gold compounds, it is by now well established
for dinuclear gold complexes.11 Among the known cyclometa-
lated aryldihalodigold(II) complexes, there are examples of
various isomerization processes occurring in solution.27,28,32,33
In the present case too, solutions of 2 undergo a change of color
over a period of hours at room temperature; the half-life of 2a
in CH2Cl2 is about 1.5 h, as estimated by UV-vis spectros-
copy.38 Out of these solutions yellow (3a), pale yellow (3b),
and gray (3c) solid products were isolated in good yields. These
compounds show singlet resonances in their 31P{1H} NMR
spectra (δ(P) 32.6 (3a), 35.2 (3b), 38.8 (3c)), indicative of
equivalent phosphorus atoms. The electrospray mass spectra of
these materials all show a strong peak at m/z 721.15 in positive
ion mode, which corresponds to loss of AuX2 from the parent
dihalodigold(II) complex. In negative ion mode signals due to
[AuX2]- anions can be observed. These data suggest that the
isolated complexes are mixed-valence Au(I)/Au(III) salts con-
Figure 1. Molecular structure of one of the independent molecules
of complex 1. Ellipsoids are given at the 50% probability level,
and H atoms as well as CH2Cl2 molecules of solvation have been
omitted for clarity. Selected bond distances (Å) and angles (deg)
of one of the molecules: Au1 · · · Au2 ) 2.9239(3), P1-Au1 )
2.2988(16), P2-Au2 ) 2.2908(16), C17-Au1 ) 2.062(6),
C11-Au2 ) 2.063(6), C1-P1 ) 1.829(6), C2-P2 ) 1.819(6),
C1-C2 ) 1.547(9), C11-C12 ) 1.435(9), C12-C13 ) 1.434(9),
C13-C14 ) 1.418(9), C14-C15 ) 1.371(10), C15-C16 )
1.415(9), C16-C11 ) 1.387(9); C11-Au2-P2 ) 171.94(18),
C17-Au1-P1)174.52(18),C2-P2-Au2)119.1(2),C1-P1-Au1
) 116.1(2), C2-C1-P1 ) 114.3(4), C1-C2-P2 ) 116.1(4),
C12-C11-Au2)123.7(4),C16-C11-Au2)117.8(5),C16-C11-C12
) 118.5(6), C12-C17-Au1 ) 124.9(4), C18-C17-Au1 )
117.4(5), C18-C17-C12 ) 117.7(6).
2-
sisting of Au(III) cations containing chelating C6H10 and
Ph2P(CH2)2PPh2 ligands as well as [AuX2]- anions. While we
so far have not been able to unambiguously confirm this
structure by X-ray diffraction, there is precedence for both the
chelating mode of the naphthalenediyl dianion in transition-
(34) Tinga, M. A. G. M.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.;
Smeets, W. J. J.; Spek, A. L. Chem. Ber. 1994, 127, 1851–1856.
(35) Synthesis of 1: to a solution of 1,8-bis(trimethylstannyl)naphthalene
(277 mg, 0.610 mmol) in dichloromethane (5 mL) was added [Au2Cl2-
(µ-Ph2P(CH2)2PPh2)] (500 mg, 0.579 mmol). The mixture was stirred
overnight at room temperature. Hexane (5 mL) was subsequently added to
the solution, and the resulting solid was isolated by filtration and washed
with boiling hexane to give 447 mg (84%) of complex 1 as a pale yellow
solid. 1H NMR (400 MHz, CDCl3): δ 2.63 (d, J ) 10.7 Hz, 4 H,
PCH2CH2P), 7.38 (dd, J ) 8.1/6.6 Hz, 2 H, naph-H3), 7.42-7.48 (m, 12
H, m-PPh2, p-PPh2), 7.69 (dd, J ) 8.1/1.0 Hz, 2 H, naph-H2), 7.79-7.85
(m, 8 H, o-PPh2), 7.84 (d, J ) 6.6 Hz, 2 H, naph-H4). 31P{1H}NMR (161.98
MHz, CDCl3): δ 38.3 (s). MALDI-MS (m/z): 595 [Au(dppe)]+, 918 [M]+,
1115 [M + Au]+, 1513 [M + Au(dppe)]+, 2033 [2 M + Au]+. Anal. Calcd
for C36H30Au2P2: C,47.07; H, 3.29. Found: C, 47.11; H, 3.3.
Figure 2. Electronic absorption spectrum (s) and emission spectra
under aerated ( · · · ) and deoxygenated (- - -) conditions of complex
1 in dichloromethane at room temperature.
tional progressional spacings that are typically observed in
naphthalene-based systems.30 The complex in the solid state at
room temperature and at 77 K also shows structured emission
with long emission lifetimes, 7.6 and 50.9 µs, respectively, with
a slight red shift of ca. 10 nm in wavelength. In view of the
long emission lifetimes, large Stokes shifts, severe oxygen
quenching, and vibronic structures, the intense emission is
assigned to originate mainly from spin-forbidden 3IL (naphthyl)
states, stemming from the large spin-orbit coupling associated
with the presence of the heavy gold(I) atoms. The assignment
(36) X-ray crystal structure analysis of 1: C37H30Au2Cl2P2, Mr ) 1001.38,
colorless plate, crystal size 0.15 × 0.12 × 0.04 mm, monoclinic, space
group P21/n, a ) 22.5380(3) Å, b ) 11.1475(2) Å, c ) 39.7366(6) Å, ꢀ )
92.7680(10)°, V ) 9971.9(3) Å3, T ) 100 K, Z ) 12, Dcalcd ) 2.001 g
cm-3, λ ) 0.710 73 Å, µ(Mo KR) ) 9.100 mm-1, empirical absorption
correction (Tmin ) 0.74, Tmax ) 0.99), Nonius KappaCCD diffractometer,
2.92 < θ < 33.17°, 218 901 measured reflections, 37 781 independent
reflections, 24 867 reflections with I > 2σ(I), structure solved by direct
methods and refined by full-matrix least squares against F2 to R1 ) 0.053
(I > 2σ(I)), wR2 ) 0.143, 1162 parameters, H atoms riding, S ) 1.054,
3
is supported by the fact that the IL emission of naphthalene-
residual electron density 2.8/-3.7 e Å-3
.
based compounds occurs at similar energies.30 Although the
contribution from metal-centered d-p/d-s excited states modi-
fied by Au(I) · · · Au(I) interactions cannot be completely ex-
cluded, given the short intramolecular Au(I) · · · Au(I) distance
in the current system as revealed by X-ray structure determi-
(37) Oxidative addition reactions: a stirred solution of 1 (60 mg, 0.065
mmol) in dichloromethane (5 mL) at-78 °C was treated with an equimolar
amount of PhICl2, bromine, or iodine. The mixture was stirred for 30 min
at ca.-65 °C. An approximately equal amount of hexane was then added,
and the solution was concentrated under reduced pressure at or below-
20 °C until the product began to precipitate. The solid was isolated by
filtration, washed with hexane, and dried under vacuum. The complexes
were obtained in yields of 60-90%. Characterization data for these
compounds is given in the Supporting Information.
(33) Bennett, M. A.; Bhargava, S. K.; Hockless, D. C. R.; Welling, L. L.;
Willis, A. C. J. Am. Chem. Soc. 1996, 118, 10469–10478.

2934 Organometallics, Vol. 28, No. 10, 2009
Communications
metal complexes of Pt(II) (isoelectronic with Au(III)), Rh(III),
and Ir(III)34 as well as the isomerization of dihalodigold(II)
compounds to Au(I)/Au(III) salts.28 Thus, the chemistry of
complex 1 known so far is that it has similarities to both the
bis(ylide) and the cyclometalated dimers. Oxidative addition
with halogens occurs to give gold-gold-bonded Au(II) com-
plexes. However, oxidative addition reactions with MeI or
dibenzoyl peroxide were unsuccessful with 1. As is the case
for the cyclometalated complexes, the dihalodigold(II) deriva-
tives 2a-c are unstable in solution and isomerize to ionic Au(I)/
Au(III) complexes. In this respect, 2a-c behave more like the
10-membered-ring cyclometalated dihalodigold(II) derivatives
[Au2(µ-2-C6H4CH2PPh2)2] and [Au2(µ-2-CH2C6H4PPh2)2], which
isomerize to the salts [Au(κ2C,P-2-C6H4CH2PPh2)2][AuX2] and
[Au(κ2C,P-2-CH2C6H4PPh2)2][AuX2], respectively.28 Further
studies of the reactivity of complex 1 and its derivatives are
currently ongoing.
Acknowledgment. We thank the DFG (Deutsche Fors-
chungsgemeinschaft) for funding this project (Grant No. MO
1781/4-1). V.W.-W.Y. acknowledges support from The
University of Hong Kong under the Distinguished Research
Achievement Award Scheme and T.K.-M.L. the receipt of
a postgraduate studentship from The University of Hong
Kong. F.M. and N.M. wish to sincerely thank Martin Bennett
for his interest in this project, the many inspirational
discussions, and the suggestion to tackle this problem in the
first place.
Supporting Information Available: Text and tables containing
full experimental and characterization details of all new compounds
as well as a CIF file giving crystallographic details of complex 1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(38) The half-life was estimated by observing the decrease in absorbance
of the peak due to 2a at 320 nm over time.
OM9002335