Synthesis, structures and reactions of cyclometallated gold complexes containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6)

Article abstract of DOI:10.1039/b516538e

Reaction of (C₆H₃-2-AsPh₂-n-Me)Li (n = 5 or 6) with [AuBr(AsPh₃)] at -78 °C gives the corresponding cyclometallated gold(i) complexes [Au₂{(-C₆H ₃-n-Me)AsPh₂}₂] [n = 5, (1); n = 6, (9)]. 1 undergoes oxidative addition with halogens and with dibenzoyl peroxide to give digold(ii) complexes [Au₂X₂{(-C₆H ₃-5-Me)AsPh₂}₂] [X = Cl (2a), Br (2b), I (2c) and O₂CPh (3)] containing a metal-metal bond between the 5d ⁹ metal centres. Reaction of 2a with AgO₂CMe or of 3 with C₆F₅Li gives the corresponding digold(ii) complexes in which X = O₂CMe (4) and C₆F₅ (6), respectively. The Au-Au distances increase in the order 4 < 2a < 2b < 2c < 6, following the covalent binding tendency of the axial ligand. Like the analogous phosphine complexes, 2a-2c and 6 in solution rearrange to form C-C coupled digold(i) complexes [Au₂X₂{-2,2′-Ph ₂As(5,5′-Me₂C₆H₃C ₆H₃)AsPh₂}] [X = Cl (5a), X = Br (5b), X = I (5c) and C₆F₅ (7)] in which the gold atoms are linearly coordinated by As and X. In contrast, the products of oxidative additions to 9 depend markedly on the halogens. Reaction of 9 with chlorine gives the gold(i)-gold(iii) complex, [ClAu{-2-Ph₂As(C₆H ₃-6-Me)}AuCl{(6-MeC₆H₃)-2-AsPh ₂}-κ²As,C] (10), which contains a four-membered chelate ring, Ph₂As(C₆H₃-6-Me), in the coordination sphere of the gold(iii) atom. When 10 is heated, the ring is cleaved, the product being the digold(i) complex [ClAu{-2-Ph ₂As(C₆H₃-6-Me)}Au{AsPh₂(2-Cl-3-Me- C₆H₃)}] (11). Reaction of 9 with bromine at 50 °C gives a monobromo digold(i) complex (12), which is similar to 11 except that the 2-position of the substituted aromatic ring bears hydrogen instead halogen. Reaction of 9 with iodine gives a mixture of a free tertiary arsine, (2-I-3-MeC₆H₃)AsPh₂ (13), a digold diiodo compound (14) analogous to 11, and a gold(i)-gold(iii) zwitterionic complex [I₂Au^III{(-C₆H₃-2-AsPh ₂-6-Me)}₂Au^I] (15) in which the bridging units are arranged head-to-head between the metal atoms. The structures of 2a-2c and 4-15 have been determined by single-crystal X-ray diffraction analysis. The different behaviour of 1 and 9 toward halogens mirrors that of their phosphine analogues; the 6-methyl substituent blocks C-C coupling of the aryl residues in the initially formed oxidative addition product. In the case of 9, the greater lability of the Au-As bond in the initial oxidative addition product may account for the more complex behaviour of this system compared with that of its phosphine analogue. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b516538e

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www.rsc.org/dalton | Dalton Transactions
Synthesis, structures and reactions of cyclometallated gold complexes
containing (2-diphenylarsino-n-methyl)phenyl (n = 5, 6)
Kunihiko Kitadai,a Masashi Takahashi,a Masuo Takeda,*a Suresh K. Bhargava,b Steven H. Prive´rb and
Martin A. Bennettb,c
Received 22nd November 2005, Accepted 9th February 2006
First published as an Advance Article on the web 2nd March 2006
DOI: 10.1039/b516538e
Reaction of (C6H3-2-AsPh2-n-Me)Li (n = 5 or 6) with [AuBr(AsPh3)] at −78 ◦C gives the corresponding
cyclometallated gold(I) complexes [Au2{(l-C6H3-n-Me)AsPh2}2] [n = 5, (1); n = 6, (9)]. 1 undergoes
oxidative addition with halogens and with dibenzoyl peroxide to give digold(II) complexes
[Au2X2{(l-C6H3-5-Me)AsPh2}2] [X = Cl (2a), Br (2b), I (2c) and O2CPh (3)] containing a metal–metal
bond between the 5d9 metal centres. Reaction of 2a with AgO2CMe or of 3 with C6F5Li gives the
corresponding digold(II) complexes in which X = O2CMe (4) and C6F5 (6), respectively. The Au–Au
distances increase in the order 4 < 2a < 2b < 2c < 6, following the covalent binding tendency of the
axial ligand. Like the analogous phosphine complexes, 2a–2c and 6 in solution rearrange to form C–C
coupled digold(I) complexes [Au2X2{l-2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2}] [X = Cl (5a), X = Br
(5b), X = I (5c) and C6F5 (7)] in which the gold atoms are linearly coordinated by As and X. In
contrast, the products of oxidative additions to 9 depend markedly on the halogens. Reaction of 9 with
chlorine gives the gold(I)–gold(III) complex, [ClAu{l-2-Ph2As(C6H3-6-Me)}AuCl{(6-MeC6H3)-
2-AsPh2}-j2As,C] (10), which contains a four-membered chelate ring, Ph2As(C6H3-6-Me), in the
coordination sphere of the gold(III) atom. When 10 is heated, the ring is cleaved, the product being the
digold(I) complex [ClAu{l-2-Ph2As(C6H3-6-Me)}Au{AsPh2(2-Cl-3-Me-C6H3)}] (11). Reaction of 9
with bromine at 50 ◦C gives a monobromo digold(I) complex (12), which is similar to 11 except that the
2-position of the substituted aromatic ring bears hydrogen instead halogen. Reaction of 9 with iodine
gives a mixture of a free tertiary arsine, (2-I-3-MeC6H3)AsPh2 (13), a digold diiodo compound (14)
analogous to 11, and a gold(I)–gold(III) zwitterionic complex [I2AuIII{(l-C6H3-2-AsPh2-6-Me)}2AuI]
(15) in which the bridging units are arranged head-to-head between the metal atoms. The structures of
2a–2c and 4–15 have been determined by single-crystal X-ray diffraction analysis. The different
behaviour of 1 and 9 toward halogens mirrors that of their phosphine analogues; the 6-methyl
substituent blocks C–C coupling of the aryl residues in the initially formed oxidative addition product.
In the case of 9, the greater lability of the Au–As bond in the initial oxidative addition product may
account for the more complex behaviour of this system compared with that of its phosphine analogue.
Although the carbanion 2-C6H4PPh2 commonly forms
mononuclear complexes derived by removal of a hydrogen atom
from an ortho-position of coordinated triphenylphosphine, it can
Introduction
Binuclear complexes in which a pair of linearly coordinated
gold(I) atoms (electron configurations 5d10 · · · 5d10) are held
also function as a bridging ligand with later transition metals, such
as Au, Pt, Pd and Rh.7 The digold(I) complexes [Au2{l-(2-C6H3-
closely together by a pair of 1,1-bifunctional ligands, such as
bis(diphenylphosphino)methane,1 dialkyldithiocarbamate,2 phos-
5-R)PPh2}2] (R = H, Me), which are accessible from the reaction
phorus bis(ylides)3,4 and methylenethiophosphinate,5 have at-
of [AuBr(PEt3)] with (2-Li-4-RC6H3)PPh2, react with halogens
tracted interest because the complexes can undergo oxidative
addition with halogens or pseudohalogens to give metal–metal
bonded (5d9–5d9) digold(II) complexes. The homobinuclear com-
to give initially homobinuclear digold(II) complexes [Au2X2{l-(2-
C6H3-5-R)PPh2}2] (X = Cl, Br, I). These isomerise subsequently
in solution by C–C coupling (reductive elimination) of the aryl
plexes often rearrange spontaneously to heterobinuclear, mixed–
groups, forming biarylbis(diphenylphosphine)-bridged digold(I)
valence, gold(I)–gold(III) species (5d8 · · · 5d10).6
complexes, [XAu{l-2,2ꢀ-Ph2P(5,5ꢀ-R2C6H3C6H3)PPh2}AuX].8–13
In contrast, in the 6-methyl-substituted series, the dihalodigold(II)
complexes formed by halogenation of complexes [Au2{l-(2-
C6H3-6-Me)PPh2}2] rearrange rapidly to gold(I)–gold(III) com-
plexes [XAu{l-2-Ph2P(C6H3-6-Me)}AuX{(6-MeC6H3)-2-PPh2}-
j2P,C], in which one of the originally bridging units is chelated
to the gold(III) atom.10 Heterobineclear complexes of this type are
likely intermediates in the C–C coupling reaction but this process
is sterically blocked in the 6-methyl series.
aDepartment of Chemistry, Toho University, 2-2-1 Miyama, Funabashi,
Chiba, 274-8510, Japan. E-mail: takeda@chem.sci.toho-u.ac.jp; Fax: +81-
47-475-1855; Tel: +81-47-472-4186
bSchool of Applied Chemistry, RMIT University, GPO Box 2476V, Mel-
bourne, Victoria, 3001, Australia
cResearch School of Chemistry, Australian National University, Canberra,
ACT 0200, Australia
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In the platinum(II) series, the monomeric bis(chelate) complexes
[Pt{(C6H3-5-R)-2-PPh2}2-j2P,C] (R = H, Me), which are isolated
from the reaction of (2-Li-4-RC6H4)PPh2 with [PtCl2(SEt2)2],
isomerise in refluxing toluene to binuclear complexes [Pt2{l-(2-
C6H3-5-R)PPh2}2{(2-C6H3-5-R)PPh2-j2P,C}2] (R = H, Me).14–16
However, no corresponding bis(chelate) complex is obtained with
the corresponding tertiary arsine (R = Me). The first product
isolated is a mixture of two dimers, one of which is the arsenic
analogue of the complex cited above. The second dimer, which
is the final stable product of the reaction, is [Pt2{l-(2-C6H3-5-
Me)AsPh2}4], in which all four of the ligands bridge a pair of
platinum atoms in a lantern or paddle-wheel structure.17 These
observations, which imply a preference for the bridging over the
chelate mode for ortho-metallated tertiary arsines, prompted us to
compare the gold chemistry of the (2-C6H3-n-Me)AsPh2 ligands
(n = 5, 6) with that of their PPh2 analogues. The results are reported
here.
through Celite. Evaporation and addition of MeOH gave 1 as a
white, air-stable solid. Yield: 0.453 g, 81%. H NMR (CDCl3):
1
d 2.27 (s, 6H, –CH3), 6.89–7.59 (m, 26H, arom). Positive-ion
+
FAB-MS: m/z 1034 {M + H} . Found: C, 43.90; H, 3.21%.
C38H32As2Au2 requires C, 44.21; H, 3.12%.
9: Yield: 0.628 g, 89%. 1H NMR (CDCl3): d 2.60 (s, 6H, –CH3),
6.95–7.50 (m, 26H, arom). Positive-ion FAB-MS: m/z 1034 {M +
+
H} . Found: C, 44.03; H, 3.11%. C38H32As2Au2 requires C, 44.21;
H, 3.12%.
[Au2X2{l-(2-C6H3-5-Me)AsPh2}2] (X = Cl, 2a; X = Br, 2b;
X = I, 2c). A stirred suspension of 1 (0.108 g, 0.105 mmol)
in dichloromethane (10 ml) was treated with a solution of
iodin◦e, bromine or PhICl2 (0.113 mmol) in dichloromethane at
−78 C. The suspension was stirred for 3 h while being shielded
from light; during work-up the temperature was kept below
−40 ◦C. The suspension was filtered through Celite and the solvent
was removed under reduced pressure. The residue was washed with
hexane (3 × 5 ml) and dried in vacuo.
2a: Yield, 73 mg, 63%. 1H NMR (300 MHz, CD2Cl2): d 2.33 (s,
6H, –CH3), 6.58–7.87 (m, 26H, arom). Positive-ion FAB-MS: m/z
Experimental
Materials and reagents
+
1069 {M − Cl + H} . Found: C, 41.03; H, 2.84%. C38H32As2Au2Cl2
requires C, 41.37; H, 2.92%.
2b: Yield: 141.3 mg, 61%. H NMR (300 MHz, CD2Cl2): d
The compounds [AuBr(AsPh3)] and PhICl2 were prepared as de-
scribed in the literature.12 2-Bromo-3-iodotoluene was prepared in
a four-step sequence from o-toluidine and 3-bromo-4-iodotoluene
in a two-step sequence from p-toluidine.12 These compounds
were converted into (2-bromo-3-methylphenyl)diphenylarsine
and (2-bromo-4-methylphenyl)diphenylarsine by PdCl2(NCMe)2-
catalyzed reaction17 with diphenyl(trimethylsilyl)arsine in yields
of 40 and 47%, respectively. All solvents were dried by standard
procedures.
1
2.31 (s, 6H, –CH3), 6.51–7.72 (m, 26H, arom). Positive-ion FAB-
+
MS: m/z 1113 {M − Br + H} . Found: C, 37.99; H, 2.58%.
C38H32As2Au2Br2 requires C, 38.28; H, 2.71%.
2c: Yield: 71.2 mg, 57%. 1H NMR (300 MHz, CD2Cl2): d 2.34 (s,
6H, –CH3), 6.82–7.87 (m, 26H, arom). Positive-ion FAB-MS: m/z
+
1161 {M − I + H} . Found: C, 35.14; H, 2.29%. C38H32As2Au2I2
requires C, 35.48; H, 2.51%.
Complexes 2a–2c could be also prepared by the reaction of
the bis(benzoato) complexes 3 (see below) with a solution of
the appropriate lithium halide in methanol. The suspension was
filtered through Celite and the product was precipitated by the
addition of hexane to the filtrate. Yields were 80–90%. This
procedure usually gave the purest samples.
Physical measurements
1H NMR spectra were recorded on a JEOL JNM-ECP 400
(400 MHz) or Varian Gemini 300 (300 MHz) Fourier transform
NMR spectrometer with chemical shift values (d, ppm) recorded
relative to solvent. FAB and EI mass spectra were measured on a
JEOL JMS-600H spectrometer and VG ZAB-2SEQ spectrometer,
respectively. Elemental analyses were carried out on a Perkin-
Elmer 2400 analyzer or in the Microanalytical Laboratory of the
Research School of Chemistry, ANU. IR spectra were recorded
on a Perkin-Elmer PE 683 spectrometer on samples prepared as
Nujol mulls.
[Au2(O2CPh)2{l-(2-C6H3-5-Me)AsPh2}2] 3. A stirred suspen-
sion of 1 (0.230 g, 0.223 mmol) in dichloromethane (55 ml)
was treated with an excess of solid dibenzoyl peroxide (0.338 g,
1.40 mmol) at room temperature. The mixture was stirred for
3 days, shielded from light, and filtered through Celite. The solvent
was removed under reduced pressure. The yellow residue was
stirredfor 2 hwithether toremove the excess ofdibenzoyl peroxide,
and was dried again. The solid was dissolved in a small amount
of dichloromethane, and hexane was added. The mixture was
evaporated under reduced pressure until the product began to
precipitate, then set aside at 0 ◦C. The solid was separated by
Synthesis of gold complexes
Most syntheses were performed under a dry argon atmosphere
with use of standard Schlenk techniques, although the solid gold
complexes once isolated were air-stable.
1
filtration and washed with hexane. Yield, 0.221 g, 78%. 3: H
NMR (300 MHz, CD2Cl2): d 2.32 (s, 6H, –CH3), 6.70–7.67 (m,
[Au2{l-(2-C6H3-n-Me)AsPh2}2] (n = 5, 1; n = 6, 9). 1 and 9
were synthesized in a similar manner, and a typical preparation
of 1 is described. A solution of (2-Br-4-Me-C6H3)AsPh2 (0.544 g,
1.36 mmol) in ether (20 ml) was treated with a 1.6 M hexane
solution of nBuLi (0.75 ml). To the solution was added solid
[AuBr(AsPh3)] (0.629 g, 1.08 mmol) at −78 ◦C. The mixture was
stirred overnight at room temperature, and the resulting white solid
was collected and washed with MeOH and ether. The solid was
dissolved in hot dichloromethane, and the solution was filtered
−1
=
36H, arom). IR (Nujol, m/cm ): 1629, 1573 (s) m(C O), 1321,
1300 (s) m (C–O). Positive-ion FAB-MS: m/z 1156 {M − (O2CPh)
+
+ H} . Found: C, 48.74; H, 3.41%. C52H42As2Au2O4 requires C,
49.00; H, 3.32%.
[Au2(O2CMe)2{l-(2-C6H3-5-Me)AsPh2}2] 4. A stirred solu-
tion of 2a (25 mg, 0.023 mmol) in dichloromethane (5 ml) was
treated with an excess of silver acetate (19 mg, 0.114 mmol) at
room temperature. The mixture was stirred for 5 h, while being
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shielded from light. The insoluble silver salts were removed by
centrifugation, the supernatant liquid was evaporated to dryness
under reduced pressure, and the solid product was washed with
hexane and dried in vacuo. Yield, 21 mg, 81%. 1H NMR (300 MHz,
CD2Cl2): d 1.46 (s, 6H, –CH3), 2.33 (s, 6H, –CH3), 6.68–7.57 (m,
temperature. The white solid was separated by filtration and
washed with water. Recrystallisation from hot hexane gave 6
1
as colourless needles. Yield, 18 mg, 71%. H NMR (300 MHz,
CD2Cl2): d 2.12 (s, 6H, –CH3), 6.69–7.36 (m, 26H, arom). Positive-
+
ion EI-MS: m/z 560.5 {M − Ph} . Found: C, 71.86; H, 5.16%.
+
26H, arom). Positive-ion FAB-MS: m/z 1093 {M + H} . Found:
C38H32As2 requires C, 71.48; H, 5.05%.
C, 43.40; H, 3.24%. C42H38As2Au2O4 requires C, 43.85; H, 3.33%.
[ClAu{l-2-Ph2As(C6H3 -6-Me)}AuCl{(6-MeC6H3)-2-AsPh2}-
j2As,C] 10. A stirred solution of 9 (0.108 g, 0.105 mmol) in
dichloromethane (10 ml) was treated with an equimolar amount
of PhICl2 in dichloromethane (5 ml) at room temperature. The
solution was stirred for 2 h and filtered through Celite, then
evaporated to dryness. The white residue was washed with hexane
and dried in vacuo. Yield, 90 mg, 78%. 1H NMR (CDCl3): d 1.65 (s,
3H, –CH3), 2.56 (s, 3H, –CH3), 6.91–7.82 (m, 26H, arom). Positive-
[Au2X2{l-2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2}] (X = Cl, 5a;
X = Br, 5b; X = I, 5c). A typical preparation of 5 is described. A
stirred suspension of 1 (0.225 g, 0.218 mmol) in dichloromethane
(20 ml) was treated with a solution of PhICl2 (0.222 mmol) in
dichloromethane (10 ml) at room temperature. After being stirred
for 3 h, the suspension was filtered through Celite and the solvent
was removed under reduced pressure to dryness. The residue was
dissolved in toluene and heated at 50 ◦C until the solution became
almost colourless. The solution was evaporated under reduced
pressure, and the product was precipitated by addition of hexane.
Yield, 0.195 mg, 70%.
+
ion FAB-MS: m/z 1069 {M − Cl + H} . Found: C, 41.39; H, 3.05;
Cl, 6.49%. C38H32As2Au2Cl2 requires C, 41.37; H, 2.92; Cl, 6.43%.
[ClAu{l-2-Ph2As(C6H3 -6-Me)}Au{AsPh2(2-Cl-3-Me-C6H3)}]
11. A stirred solution of 9 (0.252 g, 0.244 mmol) in toluene
(25 ml) was treated with an equimolar amount of PhICl2 in toluene
(10 ml) at room temperature. The mixture was stirred for 1 h at
room temperature, then heated at 70 ◦C overnight. The colourless
solution was filtered through Celite, evaporated under reduced
pressure, and hexane was added. The product was separated by
filtration and washed with hexane. Yield, 208 mg, 77%. 1H NMR
(CDCl3): d 2.38 (s, 3H, –CH3), 2.60 (s, 3H, –CH3), 6.75–7.54 (m,
5a: 1H NMR (CDCl3): d 1.78 (s, 6H, –CH3), 6.16–7.81 (m, 26H,
+
arom). Positive-ion FAB-MS: m/z 1069 {M − Cl + H} . Found:
C, 41.46; H, 2.99%. C38H32As2Au2Cl2 requires C, 41.37; H, 2.92%.
1
5b: Yield: 165.5 mg, 68%. H NMR (CDCl3): d 1.79 (s, 6H, –
CH3), 6.18–7.86 (m, 26H, arom). Positive-ion FAB-MS: m/z 1113
+
{M − Br + H} . Found: C, 38.26; H, 2.82%. C38H32As2Au2Br2
requires C, 38.28; H, 2.71%.
5c: Yield: 36.7 mg, 29%. 1H NMR (CDCl3): d 1.80 (s, 6H, –CH3),
6.20–7.88 (m, 26H, arom). Positive-ion FAB-MS: m/z 1161 {M −
+
26H, arom). Positive-ion FAB-MS: m/z 1069 {M − Cl + H} .
+
I + H} . Found: C, 35.77; H, 2.50%. C38H32As2Au2I2 requires C,
Found: C, 41.19; H, 2.67%. C38H32As2Au2Cl2 requires C, 41.37; H,
2.92%.
35.48; H, 2.51%.
[Au2(C6F5)2{l-(2-C6H3-5-Me)AsPh2}2] 6. A stirred solution of
[BrAu{l-2-Ph2As(C6H3-6-Me)}Au{AsPh2(3-Me-C6H4)}] 12.
A toluene solution (20 ml) of 9 (0.202 g, 0.196 mmol) was treated
with an equimolar amount of Br2 as in the same manner to that
for 11 except that the reaction was carried out at 50 ◦C. Yield,
C6F5Br (0.069 mL, 0.55 mmol) in ether (25 ml) was treated with
n
an equimolar amount of 1.6 M solution of BuLi in hexane at
−78 ◦C. The mixture was stirred at low temperature for 1 h, and
the resulting solution of C6F5Li was treated over a 30 min period
with a solution of 3 (0.211 g, 0.166 mmol) in toluene (50 ml).
After being stirred for a further 30 min, the mixture was warmed
to room temperature and was stirred for 1 h. The yellow solution
was filtered through Celite, and the solvent was evaporated to
dryness under reduced pressure. The yellow residue was purified by
passing a toluene solution down a short column of neutral alumina
and eluting with toluene–hexane (1 : 1). The yellow solution was
evaporated under reduced pressure to dryness and washed with
1
178 mg, 82%. H NMR (CDCl3): d 2.35 (s, 3H, –CH3), 2.60 (s,
3H, –CH3), 6.95–7.50 (m, 27H, arom). Positive-ion FAB-MS:
+
m/z 1115 {M + H} . Found: C, 41.24; H, 2.83%. C38H33As2Au2Br
requires C, 41.03; H, 2.90; Br, 7.18%.
Reaction of 9 with iodine. A stirred solution of 9 (0.520 g,
0.504 mmol) in dichloromethane (50 ml) was treated with
an equimolar amount of I2 in dichloromethane (25 ml). The
mixture was stirred for 1 h, filtered through Celite and was
evaporated under reduced pressure to dryness. The residue was
washed with hexane and isolated by filtration. The product was
obtained as a mixture of (2-I-3-Me-C6H3)AsPh2 (13), [ClAu(l-2-
Ph2AsC6H3-6-Me)AuAsPh2(2-Cl-3-Me-C6H3)] (14) and [I2Au{(l-
C6H3-2-AsPh2-6-Me)}2Au] (15), crystals of which were separated
by hand and identified by X-ray crystallography (see text). 380 mg
of the mixture of products was obtained.
1
hexane. Yield, 178 mg, 79%. H NMR (CDCl3): d 2.17 (s, 6H, –
CH3), 6.63–7.59 (m, 26H, arom). Positive-ion FAB-MS: m/z 1201
+
{M − (C6F5) + H} . Found: C, 43.44; H, 1.97%. C50H32As2Au2F10
requires C, 43.95; H, 2.36%.
[Au2(C6F5)2{l-2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2}] 7.
A
stirred solution o◦f 14 (57.6 mg, 0.042 mmol) in toluene (15 ml)
was heated at 70 C for 5 h. The colourless solution was filtered
through Celite and evaporated under reduced pressure to dryness.
The residue was washed with hexane. Yield of 7; 50.5 mg, 88%. 1H
NMR (CDCl3): d 1.84 (s, 6H, –CH3), 6.20–7.58 (m, 26H, arom).
Crystal structure determination
All diffraction data were collected with a Bruker SMART
CCD area detector diffractometer (Mo-Ka radiation, graphite
+
Positive-ion FAB-MS: m/z 1201 {M − (C6F5) + H} . Found: C,
43.70; H, 1.97%. C50H32As2Au2F10 requires C, 43.95; H, 2.36%.
˚
monochromator, k = 0.71073 A) at room temperature. Geometric
2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2 8. A suspension of 5c
(51 mg, 0.040 mmol) in ethanol (2 ml) was stirred overnight
with an aqueous solution of KCN (17 mg, 0.261 mmol) at room
and intensity data were collected using SMART software.18 The
data were processed using SAINT software,19 and corrections for
absorption were applied using SADABS software.20
2562 | Dalton Trans., 2006, 2560–2571
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All structures except 8 were solved by direct methods using
the SHELX-TL package.21 The structure of 8 was solved by the
heavy atom method. All atoms were found by difference Fourier
syntheses and all non-hydrogen atoms were anisotropically re-
fined. Hydrogen atoms were located at the calculated positions
and refined isotropically. Crystallographic data are summarized
in Table 1.
CCDC reference numbers 290381–290397.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b516538e
Results
All the complexes described in this paper have been characterised
1
by H NMR spectroscopy, positive ion FAB-MS, and elemental
analyses. The molecular structures of key complexes have also
been determined by single-crystal X-ray structural analysis.
The digold(I) complexes [Au2{l-(2-C6H3-n-Me)AsPh2}2] (n =
5 (1), 6 (9)) were prepared by the reaction of the appropriate
aryllithium reagents with [AuBr(AsPh3)] and obtained as air-
and moisture-stable white powders. The positive-ion FAB mass
spectra each show a parent-ion molecular peak at m/z 1035 and
Fig. 1 Perspective drawing of 9 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level. The atoms having an additional letter “a” have coordinates at [−x,
y, 1/2 − z].
1
the H NMR spectra show only one methyl signal (d 2.3 for 1,
2.6 for 9). Complex 9 has crystallographically imposed twofold
symmetry. The molecular structure, shown in Fig. 1, resembles
that of the phosphorus analogue, [Au2{l-(2-C6H3-6-Me)PPh2}2],11
although the Au–Au distance is significantly greater [2.9543(10)
the bis(benzoato)digold(II) complex [Au2(O2CPh)2{l-(2-C6H3-5-
Me)AsPh2}2] (3) as a yellow powder whose IR spectrum showed
typical carboxylate bands at 1629, 1573 cm−1 [m(C O)] and at
=
vs. 2.861(2) A]. Selected bond lengths and angles in 9 are listed in
1321, 1300 cm−1 [m(C–O)].22 Complex 3 reacted with an excess
of lithium halides to give the dihalodigold(II) complexes 2a–2c
in >80% yield. Treatment of 2a with an excess of silver acetate
at room temperature gave the pale yellow bis(acetato)digold(II)
complex [Au2(O2CMe)2{l-(2-C6H3-5-Me)AsPh2}2] (4). Although
parent ions were absent from the FAB mass spectra of these
complexes, peaks corresponding to the loss of one halide, benzoate
or acetate ion were observed. The 1H NMR spectra of 2a–c, 3 and
˚
Table 2.
The oxidative addition reactions of 1 and 9 are summarized in
Scheme 1 and 2, respectively. Thus, 1 reacted with PhICl2 (acting
as a source of Cl2), Br2 or I2 at −78 ◦C to give the dihalodigold(II)
complexes [Au2X2{l-(2-C6H3-5-Me)AsPh2}2] [X = Cl (2a), Br
(2b), I (2c)] as yellow, orange and deep red solids, respec-
tively. Reaction of 1 with an excess of dibenzoyl peroxide gave
Scheme 1 Reactivity of 1 with halogens.
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◦
˚
Table 2 Selected bond distances (A) and angles ( ) in 9
Au(1) · · · Au(1a) 2.9543(10)
Au(1a)–Au(1)–As(1) 74.03(3)
Au(1)–As(1)
Au(1)–C(1a)
As–C
2.4011(10)
2.040(7)
Au(1a)–Au(1)–C(1a)
As(1)–Au(1)–C(1a)
98.6(2)
169.9(2)
114.7(2)
117.9(6)
1.918(8)–1.944(8) Au(1)–As(1)–C(2)
Au(1)–C(1a)–C(2a)
4 showed just one aromatic methyl singlet at d 2.3. The acetate
methyl resonance of 4 appeared at d 1.5.
The molecular structures of 2a–2c and 4 have been de-
termined by X-ray crystallography, those of 2a and 4 be-
ing shown in Fig. 2 and 3, respectively. These four com-
plexes have crystallographic twofold symmetry and 2a–2c are
isomorphous. The structures are very similar to those of
the phosphorus-containing analogues, [Au2I2{(l-C6H4)PPh2}2]8
and [Au2(O2CPh)2{(l-C6H4)PEt2}2].9 The Au–Au distances are
Fig. 3 Perspective drawing of 4 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level. The atoms having an additional letter “a” have coordinates at [1 −
x, y, 1/2 − z].
˚
˚
˚
2.5526(3) A (2a), 2.5651(3) A (2b), 2.5880(3) A (2c) and 2.5306(2)
˚
A (4). The separation for 2c is identical, within experimental error,
9
˚
with that for [Au2I2{(l-C6H4)PPh2}2] [2.5898(6) A]; that for 4 is
Solutions of the digold(II) complexes 2a–2c in toluene decolour-
ized at 50 ◦C within a few hours and the digold(I) complexes
[Au2X2{l-2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2}] 5a–5c resulting
from C–C coupling of the (5-MeC6H3)AsPh2 units were isolated
only slightly greater than that for [Au2(O2CPh)2{(l-C6H4)PEt2}2]
10
˚
[2.5243(7) A]. Selected bond lengths and angles in 2a, 2b, 2c, 4
and 6 are listed in Table 3.
1
in good yield as colourless solids. Their H NMR spectra show
only one aromatic methyl singlet at d 1.8. The crystals of 5a–5c
belong to the same space group and have similar cell dimensions
to those of [Au2I2{l-2,2ꢀ-Ph2P(5,5ꢀ-Me2C6H3C6H3)PPh2}].11 The
molecular structure of 5c is shown in Fig. 4. The molecules have
crystallographic twofold symmetry. As in the PPh2 iodo-complex,
Fig. 4 Perspective drawing of 5c with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level. The atoms having an additional letter “a” have coordinates at [1 −
x, y, 1/2 − z].
Fig. 2 Perspective drawing of2a with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level. The atoms having an additional letter “a” have coordinates at [1/2 −
x, 3/2 − y, z].
◦
˚
Table 3 Selected bond distances (A) and angles ( ) in 2a–2c, 4 and 6
2a
2b
2c
4
6
Au(1)–Au(1a)
Au(1)–As(2)
Au(1)–C(6a)
Au(1)–X(1)
2.5526(3)
2.4618(4)
2.070(3)
2.5651(3)
2.4623(4)
2.071(4)
2.5880(3)
2.4619(5)
2.072(4)
2.5306(2)
2.4399(3)
2.059(3)
2.116(2)
2.6337(3)
2.4217(6)
2.079(5)
2.124(5)
2.3592(9)
2.4842(4)
2.6520(4)
Au(1a)–Au(1)–As(2)
Au(1a)–Au(1)–C(6a)
As(2)–Au(1)–X(1)
C(6a)–Au(1)–X(1)
Au(1a)–Au(1)–X(1)
As(2)–Au(1)–C(6a)
79.401(10)
89.36(9)
98.16(3)
93.05(9)
177.52(3)
168.20(9)
79.016(11)
89.65(10)
98.089(15)
93.34(10)
176.701(12)
168.10(9)
78.486(13)
89.86(12)
97.961(15)
93.98(12)
174.035(10)
167.68(12)
84.405(10)
91.12(8)
93.36(7)
90.69(11)
175.10(7)
173.13(8)
80.289(16)
93.72(14)
90.47(14)
96.0(2)
168.81(14)
172.44(14)
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◦
˚
Table 4 Selected bond distances (A) and angles ( ) in 5a–5c and 7
5a
5b
5c
7
Au(1) · · · Au(1a)
Au(1)–As(1)
Au(1)–X(1)
2.9963(3)
2.3413(3)
2.2772(9)
2.9913(3)
2.3469(4)
2.3927(5)
2.9932(3)
2.3600(3)
2.5421(3)
3.8139(4)
2.3792(5)
2.038(5)
As(1)–Au(1)–X(1)
As(1)–Au(1)–Au(1a)
X(1)–Au(1)–Au(1a)
C(1)–As(1)–Au(1)
a
173.28(3)
90.286(10)
95.57(3)
119.60(8)
88.79(8)
172.507(17)
91.947(12)
94.486(14)
118.95(11)
85.16(11)
170.931(11)
93.784(9)
94.084(7)
118.31(9)
79.74(9)
173.28(15)
78.07(1)
107.33(13)
117.95(14)
75.43(18)
of [Au2(C6F5)2{l-(2-C6H4)PPh2}2].11 In the molecular structure of
7, determined by X-ray crystallography, the Au · · · Au separation
the biphenyl backbone is twisted about the central C–C bond with
the gold atoms in a mutually syn-orientation. In contrast to the
variations observed in the digold(II) complexes, the Au · · · Au sepa-
˚
[3.8139(4) A] is significantly greater than those in 5a–5c and
ꢀ
11
˚
˚
˚
˚
rations [2.9963(3) A (5a), 2.9913(3) A (5b) and 2.9932(3) A (5c)] are
independent of halide, though they are slightly greater than that in
[Au2I2{l-2,2ꢀ-Ph2P(5,5ꢀ-Me2C6H3C6H3)PPh2}].12 These distances
are in the range expected for weak aurophilic interactions.23 On
the other hand, the As–Au–X angles and the dihedral angles (a)
between the two phenyl rings of the biphenyl unit [173.28, 88.79◦
(5a), 172.51, 85.16◦ (5b), 170.93, 79.74◦ (5c)] decrease in the order
Cl > Br > I, presumably to accommodate the larger halide. Selected
bond lengths and angles in 5a, 5b, 5c and 7 are listed in Table 4.
Reaction of 3 with C6F5Li gave the bis(pentafluorophenyl)-
digold(II) complex [Au2(C6F5)2(l-C6H3-5-Me)AsPh2]2] (6) as a
yellow powder which showed only one aromatic-methyl resonance
in [Au2(C6F5)2(l-2,2 -Ph2PC6H4C6H4PPh2)] [3.0688(8) A]. The
dihedral angle between the phenyl groups of the biphenyl unit
(75.43(18)◦) is also smaller than in these compounds.
The ligand 2,2ꢀ-Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2 (8) was liber-
ated from 5c by reaction with KCN and its molecular structure
determined (see Fig. 6), 8 also has crystallographic twofold
symmetry. The dihedral angle between the phenyl groups of the
biphenyl unit is 82.21(10)◦, i.e., similar to those in the digold(I)
complexes 5a–5c.
1
at d 2.2 in its H NMR spectrum. The molecular structure of
6 determined by X-ray crystallography is shown in Fig. 5; it is
˚
similar to that of 2c and 4, but the Au–Au distance [2.6337(3) A]
is significantly greater that in these compounds. It is also slightly
11
˚
greater than that in [Au2(C6F5)2(l-C6H4)PPh2]2] [2.6139(4) A].
The yellow so◦lution of 6 in toluene turned colourless on heating
for 5 h at 70 C. The C–C coupled product [Au2(C6F5)2{l-2,2ꢀ-
Ph2As(5,5ꢀ-Me2C6H3C6H3)AsPh2}] (7), which was isolated from
the resulting solution, showed just one aromatic-methyl singlet at
1
d 1.8 in its H NMR spectrum. There was no evidence for the
formation of a zwitterionic species analogous to [(C6F5)2AuIII{l-
(2-C6H4)PPh2}2AuI], having a head–to–head arrangement of
the bridging group, which was isolated as a minor product,
together with the C–C coupled product, from the isomerisation
Fig. 6 Perspective drawing of 8 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level. The atoms having an additional letter “a” have coordinates at [1 − x,
˚
y, 1 − z]. Distances (A): As(1)–C(1) 1.969(4), C(2)–C(2a) 1.502(7); angles
(◦): As(1)–C(1)–C(2) 118.6(3), C(1)–C(2)–C(2a) 121.5(3), a = 82.27(10).
From the reaction of 6-methyl substituted digold(I) complex 9
with PhICl2 at room temperature a colourless solid was isolated
which showed two aromatic methyl singlets of equal intensity
1
at d 1.7 and 2.6 in its H NMR spectrum, indicative of the 6-
MeC6H3AsPh2 group in different environments. As shown by X-
ray crystal structure determination, this solid is a gold(I)–gold(III)
complex, [ClAu{l-2-Ph2As(C6H3-6-Me)}AuCl{(6-MeC6H3)-2-
AsPh2}-j2As,C] (10), whose molecular structure is shown in
Fig. 7. The gold(I) centre is coordinated linearly by one chlorine
and one arsenic atom of a bridging group. The carbon atom of
the latter is bound to the gold(III) atom, to which is also attached
a chlorine atom and 6-MeC6H3-2-AsPh2 acting as a bidentate
ligand; the chlorine is trans to the r-bonded carbon atom of the
Fig. 5 Perspective drawing of 6 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level.
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Fig. 8 Perspective drawing of11 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level.
Fig. 7 Perspective drawing of10 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level.
somewhat smaller Au· · ·Au separation in the bromo-phosphine
˚
compound [3.0927(8) A] is attributable to the smaller size of
phosphorus compared with that of arsenic.
A pure product could not be isolated from the reaction
of bromine with 9 at room temperature. At 50 ◦C, however,
the complex isolated showed in its 1H NMR spectrum two
aromatic methyl resonances at d 2.4 and 2.6, suggestive of a
digold(I) structure similar to 11, although elemental analysis was
consistent with the presence of only one bromine atom. These
features were confirmed by the single-crystal X-ray structure
analysis, which showed the compound to be [BrAu{l-(2-C6H3-
6-Me)AsPh2}Au{AsPh2(3-MeC6H4)} (12), the jAs–coordinated
ligand being (3-tolyl)diphenylarsine rather than the expected (2-
bromo-3-methylphenyl)diphenylarsine(Fig. 9). Asin11, bothgold
atoms are coordinated almost linearly, the Au· · ·Au separation,
four-membered ring. The gold(III) atom is in distorted planar
˚
coordination and is located 0.174 A above the least-squares plane
formed by C(1), C(8), Cl(1) and As(1) with mean deviation of
˚
0.106(3) A. The structure of 10 is similar to that of the complex
[IAu{l-2-Ph2P(C6H3-6-Me)}AuI{(6-MeC6H3)-2-PPh2}-j2P,C],
which was isolated from the reaction of iodine with the iodogold(I)
phosphine complex.12 The Au–Au distance in 10, 3.2062(5) A, is
˚
greater than that in the precursor complex 9, but is less than that
˚
in the iodogold-phosphine analogue [3.4692(7) A]. 10 is only the
second example of a structurally characterised orthometallated
chelate complex derived from a triarylarsine. Selected bond
lengths and angles in 10 are listed in Table 5.
˚
3.1304(4) A, being somewhat less than that in 11. Selected bond
Whereas the iodogold phosphine complex decomposed in
heating in toluene to give unidentified materials, complex 10
gave a colourless solution in which the original methyl 1H NMR
singlet at d 1.7 had been replaced by one at d 2.4, the singlet
at d 2.6 remaining unchanged. The crystals obtained from this
solution were identified as the digold(I) complex [ClAu{l-(2-C6H3-
6-Me)AsPh2}Au{AsPh2-2-Cl-3-Me-C6H3}] (11), which is derived
from 10 by migration of Cl into the Au–C r-bond of the four-
membered ring. The gold atoms in 11 (Fig. 8) are 3.2510(6)
lengths and angles in 11 and 14 are listed in Table 6 and of 12 in
Table 7.
◦
˚
Table 6 Selected bond distances (A) and angles ( ) in 11 and 14
11
Au(1) · · · Au(2)
Au(1)–As(1)
Au(1)–X(1)
3.2510(6)
2.3392(10)
2.283(3)
2.089(9)
2.4302(11)
X(1)–Au(1)–As(1)
Au(1)–As(1)–C(13)
As(2)–Au(2)–C(18)
Au(2)–As(2)–C(20)
175.48(8)
110.7(3)
174.8(2)
113.1(3)
Au(2)–C(18)
Au(2)–As(2)
˚
A apart and are, as expected, linearly coordinated. A similar
compound, [BrAu{l-2-Ph2P(C6H3-6-Me)Au(AsPh3)}], has been
isolated as a by-product of the reaction of 2-Ph2P(C6H3-6-Me)Li
with [AuBr(AsPh3)] to give [Au2{l-(2-C6H3-6-Me)PPh2}2].24 The
14
Au(1) · · · Au(2)
Au(1)–As(1)
Au(1)–X(1)
Au(2)–C(18)
Au(2)–As(2)
3.2806(7)
2.3556(11)
2.5367(10)
2.056(11)
2.4115(12)
X(1)–Au(1)–As(1)
Au(1)–As(1)–C(13)
As(2)–Au(2)–C(18)
Au(2)–As(2)–C(20)
174.30(4)
113.5(3)
177.4(3)
115.8(4)
◦
˚
Table 5 Selected bond distances (A) and angles ( ) in 10
Au(1) · · · Au(2)
Au(1)–As(1)
Au(1)–C(1)
3.2063(5)
2.4849(7)
2.071(7)
2.077(7)
Au(1)–Cl(1)
Au(2)–As(2)
Au(2)–Cl(2)
2.3491(18)
2.3305(8)
2.267(2)
◦
˚
Table 7 Selected bond distances (A) and angles ( ) in 12
Au(1)–C(8)
Cl(1)–Au(1)–C(1)
Cl(1)–Au(1)–As(1) 100.20(5)
Cl(1)–Au(1)–C(8)
As(1)–Au(1)–C(8)
As(1)–Au(1)–C(1)
170.17(19) C(8)–Au(1)–C(1)
Au(1)–As(1)–C(2)
88.46(19) As(1)–C(2)–C(1)
163.1(2) Au(1)–C(1)–C(2)
100.2(3)
78.1(2)
105.1(5)
106.4(5)
Au(1) · · · Au(2)
Au(1)–As(1)
Au(1)–C(20)
Au(2)–Br(1)
Au(2)–As(2)
3.1304(4)
2.4082(7)
2.063(6)
2.3839(7)
2.3379(6)
As(1)–Au(1)–C(20)
Au(1)–As(1)–C(1)
Br(1)–Au(2)–As(2)
Au(2)–As(2)–C(25)
172.98(17)
108.4(2)
175.27(3)
111.63(18)
70.27(19) Cl(2)–Au(2)–As(2) 177.42(8)
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Fig. 9 Perspective drawing of12 with atomic numbering. Hydrogen atoms
are omitted for clarity. Thermal ellipsoids are shown at the 30% probability
level.
Fig. 10 Perspective drawing of 15 with atomic numbering. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are shown at the 30%
probability level.
The reaction of iodine with 9 gave an orange solution together
with a precipitate of elemental gold. The 1H NMR spectrum
in the aromatic methyl region showed a pair of equally intense
singlets at d 2.3 and 2.6 accompanied by two singlets at d 2.5
and 2.7, indicating the presence of at least three species. Attempts
to separate the constituents by fractional crystallization or chro-
matography were unsuccessful. Three crystals of different shape
and colour were separated by hand under a microscope and their
molecular structures were determined by X-ray diffraction analy-
sis. The compounds are: (i) a mixed valence, zwitterionic complex
[I2AuIII{l-(2-C6H3-6-Me)AsPh2}2AuI] (15) (orange blocks), (ii) a
digold(I) complex [IAu{l-(2-C6H3-6-Me)AsPh2}Au{AsPh2-2-I-3-
Me-C6H3}] (14) (colourless needles), which is the diiodo analogue
of the dichloro complex 11, and (iii) a free tertiary arsine (2-I-6-
MeC6H3)AsPh2 (13) (colourless blocks). 1H NMR measurements
on the separated compounds established that the signals at d 2.5
and 2.7 belong to 13 and 15, while the two peaks of equal intensity
at d 2.3 and 2.6 are due to 14.
intermediate in that rearrangement.11 A similar zwitterionic com-
plex, which also has a head-to-head arrangement of its bridging
groups, is [AuI(l-mtp)2AuIIII2] [mtp = methylenethiophosphinate,
CH2P(S)Ph2], which was isolated from the reaction of [Au2(l-
mtp)2] with iodine in CH2I2–1,2-C2H4Cl2.5
Discussion
The oxidative addition and subsequent C–C coupling reactions
of [Au2{l-(2-C6H3-5-Me)AsPh2}2] 1 shown in Scheme 1 re-
semble those established for the tertiary phosphine analogues
[Au2{l-(2-C6H3-5-R)PPh2}2] (R = H, Me). As in the phosphine
compounds, no C–C coupling occurs in the bis(acetato)- or
bis(benzoato)-digold(II) compounds, and possible reasons for this
behaviour have been discussed.10,13 The Au–Au distances in the
dihalodigold(II) complexes 2a–2c, the bis(acetato) complex 4, and
the bis(pentafluorophenyl) complex 6 increase in the order 4 <
2a < 2b < 2c < 6. Thus, the Au–Au distance increases, and the
strength of the Au(II)–Au(II) interaction presumably decreases, as
the bond between the axial ligand and the gold atom becomes
more covalent. This trans-influence trend had been foreshadowed
in earlier structural determinations, viz, [Au2X2(l-2-C6H4PR2)2]
[R = Ph, X = I,9 C6F5;11 R = Et, X = O2CPh10], but the more
extensive studies reported here, with a common bridging ligand,
provide strong confirmation. The same trend is also evident from
structural data available for a series of digold(II) bis(ylide) com-
plexes [Au2X2{l-(CH2)2PPh2}2] (X = OAc,25 O2CPh,26 Cl,27 Br,28
NO2,29 CF3,30 and C6F530) and bis(methylenethiophosphinate)
complexes [Au2X2{l-CH2P(S)Ph2}2] (X = Cl,31 I5). We note also
that comparable dihalodigold(II) complexes containing bridging
(aryl)PR2 and (aryl)AsR2 ligands have almost identical Au–Au
bond lengths, despite the greater size of arsenic compared with that
of phosphorus. By contrast, in the precursor digold(I) complexes
[Au2{l-(2-C6H3-6-Me)EPh2}2] (E = P, As), in which metal–metal
interaction is of the weaker aurophilic type, the larger arsenic atom
causes a significantly greater Au· · ·Au separation.
The molecular structure of 15 is shown in Fig. 10; selected
bond distances and angles are in Table 8. As expected, the
coordination about the cationic gold(I) centre is close to linear,
while that about the anionic gold(III) centre is approximately
˚
planar. The Au· · ·Au separation [2.9365(4) A] is similar to that
in the compound [(C6F5)2AuIII{l-(2-C6H4)PPh2}2AuI] [2.931(1)
˚
A], which was isolated as a by–product of the rearrangement
of the digold(II) complex [Au2(C6F5)2{l-(2-C6H4)PPh2}2] to the
C–C coupled digold(I) compound and shown not to be an
◦
˚
Table 8 Selected bond distances (A) and angles ( ) in 15
Au(1) · · · Au(2)
Au(1)–C(1)
Au(1)–C(8)
Au(1)–I(1)
2.9365(4)
2.120(6)
2.116(6)
2.5965(5)
Au(1)–I(2)
Au(2)–As(1)
Au(2)–As(2)
2.6043(5)
2.3795(7)
2.3820(7)
Au(1)–Au(2)–As(1)
Au(1)–Au(2)–As(2)
As(1)–Au(2)–As(2)
Au(2)–Au(1)–C(1)
Au(2)–Au(1)–C(8)
Au(2)–Au(1)–I(1)
Au(2)–Au(1)–I(2)
87.115(17) C(1)–Au(1)–I(1)
86.621(17) C(1)–Au(1)–C(8) 174.2(2)
88.34(15)
172.71(2)
92.46(16)
93.04(16)
C(1)–Au(1)–I(2)
I(1)–Au(1)–C(8)
I(1)–Au(1)–I(2)
90.78(15)
90.04(15)
176.81(2)
91.13(15)
86.512(19) I(2)–Au(1)–C(8)
90.467(16)
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Scheme 2 Reactivity of 9 with halogens.
3 A. Grohmann and H. Schmidbaur, in Comprehensive Organometallic
Chemistry II, ed. J. Wardell, E. Abel, F. G. A. Stone and G. Wilkinson,
Pergamon, Oxford, 1995, vol. 3, p. 1, and references therein.
4 H. Schmidbaur, A. Grohmann and M. E. Olmos, in Gold, Progress
in Chemistry, Biochemistry and Technology, ed. H. Schmidbaur, Wiley,
Chichester, 1999, p 747, and references therein.
5 A. M. Mazany and J. P. Fackler Jr., J. Am. Chem. Soc., 1984, 106, 801.
6 A. Laguna and M. Laguna, Coord. Chem. Rev., 1999, 193–195, 837.
7 F. Mohr, S. K. Bhargava, S. Prive´r and M. A. Bennett, Coord. Chem.
Rev., in press.
8 M. A. Bennett, S. K. Bhargava, K. D. Griffiths, G. B. Robertson, W. A.
Wickramasinghe and A. C. Willis, Angew. Chem., Int. Ed. Engl., 1987,
26, 258.
9 M. A. Bennett, S. K. Bhargava, K. D. Griffiths and G. B. Robertson,
Angew. Chem., Int. Ed. Engl., 1987, 26, 260.
10 M. A. Bennett, S. K. Bhargava, D. C. R. Hockless, L. L. Welling and
A. C. Willis, J. Am. Chem. Soc., 1996, 118, 10469.
11 M. A. Bennett, D. C. R. Hockless, A. D. Rae, L. L. Welling and A. C.
Willis, Organometallics, 2001, 20, 79.
12 S. K. Bhargava, F. Mohr, M. A. Bennett, L. L. Welling and A. C. Willis,
Organometallics, 2000, 19, 5628.
13 H. L. Hermann, P. Schwerdtfeger, S. K. Bhargava and F. Mohr,
Organometallics, 2003, 22, 2373.
14 M. A. Bennett, D. E. Berry, S. K. Bhargava, E. J. Ditzel, G. B. Robertson
and A. C. Willis, J. Chem. Soc., Chem. Commun., 1987, 1613.
15 M. A. Bennett, S. K. Bhargava, M. Ke and A. C. Willis, J. Chem. Soc.,
Dalton Trans., 2000, 3537.
16 J. Messelha¨user, M. A. Bennett, S. K. Bhargava, E. J. Ditzel, G. B.
Robertson, A. C. Willis and D. E. Berry, Presented at the XIIIth Inter-
national Conference on Organometallic Chemistry, Turin, September
4–9, 1988.
17 M. A. Bennett, S. K. Bhargava, A. M. Bond, A. J. Edwards, S. Guo,
S. H. Prive´r, A. D. Rae and A. C. Willis, Inorg. Chem., 2004, 43, 7752.
18 SMART ver. 5.625 software for the CCD Detector System, Bruker AXS
Inc., Madison, WI, 2001.
The oxidative addition of chlorine to [Au2{l-(2-C6H3-6-
Me)AsPh2}2] 9 is generally similar to the corresponding reaction
with the phosphine analogue. Presumably, as in the latter case, the
first stable product, the gold(I)–gold(III) complex 10, is formed via a
homobinuclear digold(II) intermediate similar to 2a. Also, as in the
(6-methylphenyl)phosphine series, no C–C coupling is observed,
owing to steric hindrance to reductive elimination at the gold(III)
centre by the methyl substitutent.12,13 However, the isomerisation
of 10 to 11 shows that the four-membered ring of 10 is cleaved more
readily than that in its phosphorus counterpart. In the reaction of
9 with bromine and iodine, we have been unable so far to isolate
the bromo and iodo analogues of 10, though complex 14 must
be form from the latter. The greater lability of the arsine relative
to the phosphine system is demonstrated by the formation of the
liberated ligand (2-iodo-3-methylphenyl)diphenylarsine 13. Also,
for the first time, a zwitterionic, mixed-valence complex 15 appears
as a product isolated from direct halogenation. Since 14 and 15
do not interconvert on heating, 15 must arise by an alternative
rearrangement pathway in a precursor, either the iodo-analogue
of 10 or of its diiododigold(II) precursor analogous to 2a.
At present we cannot account for the formation of complex
12 from the reaction of 9 with bromine. Presumably the bromo
analogue of complex 10 is formed but the bromine in the aromatic
ring is then replaced by hydrogen, perhaps derived from the
solvent.
Acknowledgements
19 SAINTPLUS ver. 6.22 software for the CCD Detector System, Bruker
AXS Inc., Madison, WI, 2001.
A part of this work was supported by Joint Research Project
between JSPS and ARC under the Bilaterial Programs FY2003-
FY2004.
20 SADABS program for absorption correction using SMART CCD data
based on the method of Blessing: R. H. Blessing, Acta Crystallogr.,
Sect A, 1995, 33, 51.
21 G. M. Sheldrick, SHELXTL, ver. 6.10, University of Go¨ttingen,
Go¨ttingen, Germany, 1994.
22 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordi-
nation Compounds, Wiley-Interscience, New York, 3rd edn, 1978, p.
232.
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2570 | Dalton Trans., 2006, 2560–2571
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This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2560–2571 | 2571
©