Dimethylaurate(I) and Tetramethylaurate(III)
Organometallics, Vol. 18, No. 11, 1999 2247
at 0 °C.36 To this solution were added [N(PPh3)2]Cl (487 mg,
0.85 mmol) and 30 mL of THF. The reaction mixture was
stirred overnight at room temperature. Workup similar to that
described above gave [N(PPh3)2][Au(CH3)4] as colorless needle-
like crystals (0.375 g, 55% yield). Anal. Calcd for C40H42NP2-
Au: C, 60.38; H, 5.32; N, 1.76. Found: C, 60.08; H, 5.29; N,
ethylgold(IV) intermediate. In contrast to dimethylgold-
(II), the highly unstable tetramethylgold(IV) undergoes
rapid homolytic cleavage to produce methyl radical and
trimethylgold(III). The latter can be intercepted by
triphenylphosphine to afford Me3AuIIIPPh3. We hope
theoretical analysis will shed some light on the reason
for the different cleavage modes of the Au-C bonds in
tetramethylgold(IV) and dimethylgold(II) intermediates.
1
1.98. H NMR (THF-d8: δ (ppm)): -0.312 (s, 12H, Au-CH3),
7.4-7.9 (m, 30H, C6H5).
Syn th esis of [N(CH3)2(CH2C6H5)2][Au (CH3)4]. A proce-
dure similar to that described above was followed, and
[N(CH3)2(CH2C6H5)2][Au(CH3)4] was obtained as colorless pris-
matic crystals (52% yield). Anal. Calcd for C20H32NAu: C,
Exp er im en ta l Section
1
49.68; H, 6.67; N, 2.90. Found: C, 49.54; H, 6.62; N, 3.01. H
All manipulations were carried out under argon or helium
atmosphere using standard Schlenk techniques or gloveboxes.
Solvents such as ether, THF, benzene, and pentane were dried
over sodium benzophenone ketyl and distilled and stored under
argon before use. Acetonitrile was treated with KMnO4 (1 g/L)
and refluxed for 1 h. The distilled acetonitrile was then
refluxed over P2O5 and CaH2, respectively, and distilled and
stored under argon. Methyllithium (1.4 M solution in ether),
iodomethane, and phenanthrenequinone were used as re-
ceived. Triphenylphosphine, tetrabutylammonium bromide,
NMR (THF-d8; δ (ppm)): -0.084 (s, 12H, Au-CH3), 3.06 (s,
6H, CH3), 4.741 (s, 4H, CH2), 7.509 (m, 6H, Ar-H), 7.643 (m,
4H, Ar-H).
Gen er a l P r oced u r e for th e Oxid a tion s of Dim eth y-
la u r a te(I) a n d Tetr a m eth yla u r a te(III). Oxidation of tet-
rabutylammonium dimethylaurate(I) with ferrocenium hexaflu-
orophosphate is used as an example and described as follows.
To a frozen solution of [N(C4H9-n)4][Au(CH3)2] (47 mg, 0.1
mmol) in 10 mL of THF at -196 °C was added Cp2Fe+PF6
-
(33 mg, 0.1 mmol) under a helium atmosphere. The reaction
flask was then sealed with a rubber septum and warmed to
room temperature. During this period, the reaction mixture
turned to an orange solution and a gold mirror formed
concomitantly. At this point, 0.1 mmol of ethylene was added
into the flask as an internal standard via a gastight syringe.
The gas phase was then analyzed by gas chromatography to
determine the yield of methane and ethane. The solvent was
removed, the residue was dissolved in CDCl3, and 0.1 mmol
of toluene was added to serve as internal standard. The yield
of ferrocene was determined by 1H NMR. The yield of gold
metal was determined gravimetrically by digesting the samples
in concentrated sulfuric acid. In the cases of arenediazonium
cations as the oxidant, the reaction mixture was quenched with
water and extracted with ether. The ether extract was dried
over anhydrous Na2SO4 and analyzed by GC and GC-MS to
determine the yields of arenes. The results are summarized
in Tables 2-6.
dibenzyldimethylammonium chloride, and Cp2Fe+PF6 were
-
recrystalized from the appropriate solvents. MeAuPPh3,33 Me3-
AuPPh3,9b [NBu4][AuMe4],7 Cp*2Fe+BF4
,
and arenediazo-
-
34
nium salts35 were prepared by the published methods. No
special precaution was exercised (with regard to light sensitiv-
ity) in the handling of these methylaurates. The hydrocarbon
gases were analyzed by gas chromatography using a Gow-Mac
550 gas chromatograph equipped with a thermal conductivity
detector and a 2 ft Porapak Q column. Quantitative analysis
was performed by the internal standard (ethylene) method
after calibration under reaction conditions. The methylgold
products were analyzed by 1H NMR using toluene as the
internal standard. Elemental analyses were conducted by
Atlantic Microlab Inc. UV-visible spectra were measured on
a Hewlett-Packard 8450A diode-array spectrometer. 1H and
13C NMR spectra were recorded on a General Electric QE-300
spectrometer. ESR spectra were recorded on a Varian E-Line
Century Series EPR spectrometer. Cyclic voltmmetry was
performed on a BAS 100A electrochemical analyzer using (n-
Tr appin g of Dim eth ylgold(II) with 9,10-P h en an th r en e-
qu in on e. (I) On e Equ iva len t of 9,10-P h en a n th r en equ in o-
n e. 9,10-Phenanthrenequinone (21.0 mg, 0.10 mmol) was
added to a tetrahydrofuran solution of [N(C4H9-n)4][Au(CH3)2]
(47.0 mg, 0.10 mmol) at -78 °C. To the resulting orange
-
Bu)4N+PF6 (0.1 M) as supporting electrolyte.
Syn th esis of [N(C4H9-n )4][Au (CH3)2]. An ether solution
of LiAu(CH3)2 (1.40 mmol) was prepared by treating CH3-
AuPPh3 (0.65 g, 1.40 mmol) with methyllithium (1.40 mmol)
at 0 °C.9 To this solution was added a solution of [N(C4H9-n)4]-
Br (0.45 g, 1.40 mmol) in 50 mL of benzene. After the reaction
mixture was stirred overnight at room temperature, the
solvent was removed and the residue was extracted with
benzene (2 × 40 mL). Removal of the solvent from the
combined benzene extracts afforded a white solid, which was
washed with pentane and recrystallized by slow diffusion of
diethyl ether into the THF solution to give [N(C4H9-n)4][Au-
(CH3)2] as colorless needlelike crystals (0.52 g, 78% yield). Anal.
Calcd for C18H42NAu: C, 46.05; H, 9.02; N, 2.98. Found: C,
46.30; H, 8.98; N, 3.00. 1H NMR (C6D6; δ (ppm)): 0.329 (s, 6H,
Au-CH3), 0.951 (t, J ) 7.2 Hz, 12H, CH3), 1.398 (m, 8H, CH2),
1.497 (m, 8H, CH2), 3.278 (t, J ) 7.5 Hz, 8H, CH2). 13C NMR
(C6D6; δ (ppm)): 10.837 (Au-CH3), 13.670 (CH3), 19.753 (CH2),
24.096 (CH2), 58.433 (CH2).
solution was added Cp2Fe+PF6 (33.1 mg, 0.10 mmol) at -78
-
°C. The mixture was stirred at this temperature until
Cp2Fe+PF6- dissolved to give an orange solution. Ethane was
produced in 97% yield, as determined by GC analysis of the
gas phase.
(II) Tw o Equ iva len ts of 9,10-P h en a n th r en equ in on e. 9,-
10-Phenanthrenequinone (41.6 mg, 0.20 mmol) was added to
a tetrahydrofuran solution of [N(C4H9-n)4][Au(CH3)2] (46.8 mg,
0.10 mmol) at -78 °C. To the resulting orange solution was
-
added Cp2Fe+PF6 (33.1 mg, 0.10 mmol) at -78 °C. The
-
mixture was stirred at this temperature until Cp2Fe+PF6
dissolved to give a dark green solution. A 1.0 mL portion of
this solution was withdrawn via a gastight syringe and diluted
with 1 mL of THF at -78 °C. The UV-vis spectrum of the
dilute solution was measured at -78 °C, and a broad band at
about 700 nm was observed. The gas phase was analyzed by
gas chromatography, and no methane or ethane was observed.
The reaction mixture was then warmed to room temperature.
The dark green solution turned to orange, and a black
precipitate formed. The orange solution showed neither the
700 nm band nor an ESR signal. GC analysis of the gas phase
indicated that ethane was evolved in 95% yield.
Syn th esis of [N(P P h 3)2][Au (CH3)4]. An ether solution of
LiAu(CH3)4 (0.85 mmol) was prepared by treating (CH3)3-
AuPPh3 (0.427 g, 0.85 mmol) with methyllithium (0.85 mmol)
(33) Coates, G. E.; Parkin, S. J . Chem. Soc. 1962, 3220.
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S. R.; Zhang, J . H.; Reiff, W. M.; Epstein, A. J . J . Am. Chem. Soc. 1987,
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(36) (a) Rice, G. W.; Tobias, R. S. Inorg. Chem. 1975, 14, 2402. (b)
Komiya, S.; Ozaki, S.; Endo, I.; Inoue, K.; Kasuga, N.; Ishizaki, Y. J .
Organomet. Chem. 1992, 433, 337. (c) Komiya, S.; Endo, I.; Ozaki, S.;
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