Enhanced reductive elimination of dialkylgold(III) complexes in water

Article abstract of DOI:10.1246/cl.2005.1704

Neutral and cationic dimethyl- or diethylgold(III) complexes having a water-soluble phosphine ligand, AuR₂XL and [AuR₂L ₂]X (R = Me or Et; X = Br or I; L = TPPTS, TPPMS, THMP, or DHMPE), are prepared. Reductive elimination involving C-C bond formation at Au(III) in water is faster than those in organic solvents. Copyright

Full text of DOI:10.1246/cl.2005.1704

1704
Chemistry Letters Vol.34, No.12 (2005)
Enhanced Reductive Elimination of Dialkylgold(III) Complexes in Water
Nobuyuki Komine, Kaoru Ichikawa, Anna Mori, Masafumi Hirano, and Sanshiro Komiyaꢀ
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Nakacho, Koganei, Tokyo 184-8588
(Received August 23, 2005; CL-051077)
Neutral and cationic dimethyl- or diethylgold(III) com-
(diphenylphosphino)benzenesulfonic acid sodium salt], THMP
and DHMPE were also prepared similarly. All these complexes
were soluble in water. The 31P{1H} NMR spectrum of 1a in
plexes having a water-soluble phosphine ligand, AuR2XL and
[AuR2L2]X (R ¼ Me or Et; X ¼ Br or I; L ¼ TPPTS, TPPMS,
THMP, or DHMPE), are prepared. Reductive elimination in-
volving C–C bond formation at Au(III) in water is faster than
those in organic solvents.
1
D2O shows a singlet at ꢂ 30.7. The H NMR spectrum of 1a in
D2O shows two doublets at ꢂ 1.33 (3JPH ¼ 8:1 Hz) and 1.57
(3JPH ¼ 8:7 Hz) indicating the square planar cis configuration
of 1a. The 1H NMR of 2a displays a characteristic second
order A3XX0A03 multiplet centered at ꢂ 1.31 also showing its
cis-square planar geometry. Accordingly, the 31P{1H} NMR
spectrum of 2a in D2O shows a singlet at ꢂ 32.8.
Water has recently attracted attention as safe, cheap, and
environmentally benign reaction medium.1 If transition metal-
mediated organic reactions and catalyses are carried out in
water as in organic solvents, it will be highly beneficial in devel-
oping and designing new valuable chemical processes, though
some transition metal-catalyzed reactions in water have been
known.1c,2 However, since putative organometallic intermedi-
ates are simply believed to be unstable in water, very few reports
concerning synthesis and reactions of water-soluble complexes
having metal–carbon ꢀ bonds are known to date in spite of their
intrinsic importance both in fundamental aspects and applica-
tions.3 We previously reported the synthesis and preferential
ꢁ-hydrogen elimination of water-soluble diorganoplatinum(II)
complexes cis-[PtR2L2] (L ¼ TPPTS [3,30,300-phosphinidyne-
tris(benzenesulfonic acid) trisodium salt], THMP [tris(hydroxyl-
methyl)phosphine], or DHMPE {1,2-bis[di(hydroxymethyl)-
phosphino]ethane}) even in aqueous medium.3d,3e We now re-
port the synthesis of water-soluble dialkylgold(III) complexes
which show enhanced reductive elimination including C–C bond
formation in water.
These water-soluble dimethyliodogold(III) complexes
having a TPPTS, TPPMS, or THMP ligand are relatively stable
in organic solvent such as THF or ethanol at room temperature,
but they reductively eliminated ethane in water even at room
temperature, accompanied by formation of Au(I) complex
(eq 1).6
L
Me
30 °C
H2O
Au
Me-Me
+
"Au(I) complex"
(1)
I
Me
L = TPPTS (1a)
TPPMS (1b)
Figure 1 shows the time–yield curves of ethane for the ther-
molysis of 1b having TPPMS ligand in various solvent at 30 ꢁC,
showing unexpected medium effect of water on reductive elim-
ination.
100
80
60
40
20
0
4
After treatment of dimethyliodogold(III) dimer, [AuMe2I]2
with two equivalents of TPPTS in H2O/acetone at 0 ꢁC, excess
acetone was added to give white powder of water-soluble neutral
cis-dimethylgold(III) complex, cis-[AuMe2I(TPPTS)] (1a),
quantitatively (Scheme 1).5 Further addition of an equimolar
amount of TPPTS to 1a or reaction of the dimer with four
equivalents of TPPTS gave a cationic complex cis-[AuMe2-
(TPPTS)2]I (2a). They were purified by reprecipitation from
methanol/acetone.
Analogous dimethylgold(III) complexes having TPPMS [3-
0
50
100
150
200
time (min)
L
I
Me
Me
2 L
Au
2
Figure 1. Solvent effect on time-courses for reductive elimina-
tion of dimethylgold(III) complex (1b) at 30 ꢁC. Ethane evolved
in H2O ( ), THF ( ), EtOH ( ), MeCN ( ), DMSO ( ), and
HCONHMe ( ).
L = TPPTS (1a) (96%)
TPPMS (1b) (89%)
THMP (1c) (100%)
Me
Me
I
I
Me
Me
Au
Au
2 L
Complexes with TPPTS ligand 1a and 2a also liberated
ethane in water quantitatively at 40 ꢁC in 60 and 80 min, respec-
tively, but they are stable in methanol and DMSO for a few
hours. These results show preferential reductive elimination
involving C–C bond formation over protonolysis at Au(III) in
water, and more interestingly water medium enhanced reductive
elimination in comparison with organic solvents. Simple in-
+
L
L
Me
Me
4 L
-
Au
I
2
L2
=
2 TPPTS (2a) (96%)
2 THMP (2c) (92%)
DHMPE (2d) (95%)
Scheme 1.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.12 (2005)
1705
crease of solvent polarity may not explain the fact.7 Possible co-
ordination of water to Au(III) or solvent effect might be respon-
sible for these results. In contrast, cationic complex 2d having
DHMPE ligand was very stable in water and liberated only 1
and 9% yields of methane and ethane at 80 ꢁC for 30 min, but af-
ter two weeks at 80 ꢁC, the yields of methane and ethane increas-
ed to 51 and 70%, respectively (eq 2). At high temperature hy-
drolysis became significant relative to reductive elimination.
References and Notes
1
a) C.-J. Li and T.-H. Chan, ‘‘Organic Reactions in Aqueous
Media,’’ Wiley, New York (1997). b) ‘‘Organic Synthesis in
Water,’’ ed. by P. A. Grieco, Blackie Academic & Professio-
nal, London (1998). c) ‘‘Aqueous-Phase Organometallic Catal-
ysis, Concepts and Applications,’’ ed. by B. Cornils and W. A.
Herrmann, Wiley-VCH, Weinheim (1998), and references cite
therein.
2
a) ‘‘Appied Homogeneous Catalysis with Organometllic Com-
pounds,’’ ed. by B. Cornils and W. A. Herrmann, VCH, Wein-
heim (1996), Vol. 1 and 2, and references cite therein. b) A.
Fukuoka, W. Kosugi, F. Morishita, M. Hirano, L. McCaffrey,
W. Henderson, and S. Komiya, Chem. Commun., 1999, 489.
c) J. Kovacs, T. D. Todd, J. H. Reibenspies, F. Joo, and D. J.
Darensbourg, Organometallics, 19, 3963 (2000). d) Y. Uozumi
and K. Shibatomi, J. Am. Chem. Soc., 123, 2919 (2001). e) K.
Manabe and S. Kobayashi, Org. Lett., 5, 3241 (2004).
a) J. E. Ellis, K. N. Harrison, P. T. Hoye, A. G. Orpen, P. G.
Pringle, and M. B. Smith, Inorg. Chem., 31, 3026 (1992). b)
D. P. Aterniti and J. D. Atwood, Chem. Commun., 1997,
1665. c) A. A. Bowden, J. L. Kubeika, and J. D. Atwood,
Inorg. React. Mech., 3, 249 (2001). d) S. Komiya, M. Ikuine,
N. Komine, and M. Hirano, Chem. Lett., 2002, 72. e) S.
Komiya, M. Ikuine, N. Komine, and M. Hirano, Bull. Chem.
Soc. Jpn., 76, 183 (2003). f) D. W. Lucey, D. S. Helfer, and
J. D. Atwood, Organometallics, 22, 826 (2003).
+
HO OH
Me
Me
P
P
80 °C
-
(2)
Au
Me-Me
+
Me-H
I
H2O
HO OH
2d
30 min
2 weeks
9%
70%
< 1%
51%
Cationic diethylgold(III) analogues cis-[AuEt2L2]Br (L2 ¼
2TPPTS (3a), 2THMP (3c), and DHPME (3d)) were also
3
8
prepared in situ by the similar reactions of [AuEt2Br]2 with
corresponding water-soluble phosphine ligands (eq 3).
+
Et
Et
Et
Et
Br
Br
Et
Et
L
L
-
Br
Au
(3)
Au
Au
+ 4 L
2
D2O
L
2 = 2 TPPTS (3a) (84%)
2 THMP (3c) (78%)
DHMPE (3d) (87%)
It was difficult to isolate the ethyl analogues in a pure form,
1
4
5
F. H. Brain and C. S. Gibson, J. Chem. Soc., 1939, 761.
Physical and spectroscopic data for 1a, 1b, and 2a are given:
but the formation was unambiguously confirmed by the H and
31P{1H} NMR.
.
[AuMe2I(TPPTS)] (1a) 5H2O: white powder from metha-
Reductive elimination of diethylgold(III) analogues with
TPPTS or THMP was much faster than that of dimethylgold(III)
complexes. They selectively liberated butane quantitatively im-
mediately after dissolving in water at room temperature (eq 4).
DHPME complex 3d was again stable in H2O, but at 80 ꢁC
evolved butane and ethane in 79 and 12% yields, respectively.
+
nol/acetone. Anal. Found: C, 23.19; H, 2.58; S, 9.49%. Calcd
for C20H28AuINa3O14PS3: C, 23.73; H, 2.79; S, 9.50%. IR
(KBr, cmꢂ1): 3449 (ꢃOH), 1191 (ꢃasS=O), 1040 (ꢃsS=O).
1H NMR (D2O, rt): ꢂ 1.33 (d, JPH ¼ 8:1 Hz, 3H, Au-CH3),
3
1.57 (d, 3JPH ¼ 8:7 Hz, 3H, Au-CH3), 7.5–8.0 (m, 12H, aryl).
31P{1H} NMR (D2O, rt) ꢂ 30.7 (s). [AuMe2I(TPPMS)] (1b):
white powder from THF/ether. Anal. Found: C, 34.02; H,
3.14; S, 3.61%. Calcd for C20H20AuINaO3PS: C, 33.44; H,
2.81; S, 4.46%. IR (KBr, cmꢂ1): 1213 (ꢃasS=O), 1040
L
Et
rt, instant
-
Au
(4)
Br
Et-Et + Et-H
D2O
L
Et
(ꢃsS=O). 1H NMR (CD3OD, rt): ꢂ 0.98 (d, JPH ¼ 8:1 Hz,
3
L = TPPTS (3a)
THMP (3c)
99%
94%
0%
0%
3
3H, Au-CH3), 1.34 (d, JPH ¼ 9:0 Hz, 3H, Au-CH3), 7.3–7.9
(m, 14H, aryl). 31P{1H} NMR (CD3OD, rt): ꢂ 29.4 (s).
Addition of five equivalents of free TPPTS to 2a effectively
suppressed the reductive elimination. Such retardation effect of
added tertiary phosphine ligand is well known for the reductive
elimination of organogold(III)9 and organopalladium(II)10 com-
plexes in organic solvent such as benzene, where a dissociation
of tertiary phosphine ligand giving a 3-coordinate intermediate is
the rate determining step for reductive elimination. It is notable
that addition of 5 equiv. of NaI to the water solution of neutral
dimethylgold(III) complex 1a also showed significant suppress-
ing effect on the reaction. Ionization of 1a giving an unstable
cationic 3-coordinate T-shape species such as [AuMe2L]þ in
water may also be another important intermediate for reductive
elimination.
.
[AuMe2(TPPTS)2]I (2a) 5H2O: white powder from methanol/
acetone. Anal. Found: C, 29.05; H, 2.60; S, 11.80%. Calcd for
C38H40AuINa6O23P2S6: C, 28.87; H, 2.55; S, 12.17%. IR
(KBr, cmꢂ1): 3448 (ꢃOH), 1195 (ꢃasS=O), 1040 (ꢃsS=O).
1H NMR (D2O, rt): ꢂ 1.31 (m, 6H, Au-CH3), 7.3–8.1 (m,
12H, aryl). 31P{1H} NMR (D2O, rt): ꢂ 32.8 (s). Other com-
plexes were characterized spectroscopically.
6
Although complete characterization of the gold product was
unsuccessful, Au(I) complex is considered to be formed, since
addition of 3 equivalents of TPPTS after thermolysis of 1a
gave a broad singlet at ꢂ 40.3 (D2O) in 31P NMR, which is ten-
tatively assigned to Na8{Au[P(C6H4SO3)3]3} by comparing
the following reported data: W. A. Herrmann, J. Keller, and
H. Riepl, J. Organomet. Chem., 389, 103 (1990).
The present results would open opportunity and benefits to
apply various nonaqueous organometallic C–C bond forming
reactions and catalyses into various aqueous systems. Further
detailed studies are required to elucidate the role of water in
the facile reductive elimination.
7
8
9
Dielectric constants ("): THF (7.58), EtOH (24.55), MeCN
(35.94), DMSO (46.45), H2O (78.39), HCONHMe (182.4).
A. Buraway, C. S. Gibson, G. C. Hampson, and H. M. Powell,
J. Chem. Soc., 1937, 1690.
a) S. Komiya, T. A. Albright, R. Hoffmann, and J. K. Kochi,
J. Am. Chem. Soc., 98, 7255 (1976). b) S. Komiya and J. K.
Kochi, J. Am. Chem. Soc., 98, 7599 (1976). c) S. Komiya
and A. Shibue, Organometallics, 4, 684 (1985).
This work was partially supported by New Energy and
Industrial Technology Development Organization (NEDO),
Japan Chemical Innovation Institute (JCII), and Ministry of
Education, Culture, Sports, Science and Technology, Japan.
10 F. Ozawa, T. Ito, Y. Nakamura, and A. Yamamoto, Bull.
Chem. Soc. Jpn., 54, 1868 (1981).
Published on the web (Advance View) November 26, 2005; DOI 10.1246/cl.2005.1704