Table 2 Gold complex-catalyzed hydrosilylation of various carbonyl
compounds
after adding the hydrosilane to reaction mixture and the slow
precipitation of gold(0) was observed in experiment B. These
results indicate that the role of the excess tributylphosphine is
the prevention of catalyst decomposition rather than increasing
the reaction rate.
b
Yield of
4 (%)
Entrya
Carbonyl compounds 1
Conditions
Although the active species of this catalyst is still unclear at
this stage, we propose that colorless monomeric gold complexes
stabilized by the excess tributylphosphines play an important
role in this reaction and that the predominant deactivation
process is the formation of gold clusters and metallic gold(0)
1
2
3
4
5
3-Phenylpropanal 1b
Cinnamaldehyde 1c
Decanal 1d
70 °C, 1.5 h
70 °C, 5.0 h
70 °C, 1.5 h
4b, 93
c
4c, 94
4d, 51
4e, 78
4f, 0d
Cyclohexanecarboxaldehyde 1e 70 °C, 11 h
4-Phenylbutanone 1f 70 °C, 15 h
To a solution of carbonyl compound 1 (1.0 mmol), AuCl(PPh
a
upon reduction of gold( ).
I
3
) ( 3 mol%,
0.03 mmol) and tributylphosphine (20 mol%, 0.20 mmol) in dry DMF (1.0
In conclusion, we have described the unprecedented hydro-
silylation of organic compounds by a gold complex catalyst
with high chemoselectivity. The deactivation of the gold
catalyst was suppressed in the presence of an additional ligand
ml) was added dimethylphenylsilane 2 (2.0 equiv., 2.0 mmol) under
nitrogen. Isolated yield after hydrolysis. c Only a 1,2-reduced product was
detected. The starting material was recovered in good yield (1f, 93%).
b
d
(
tributylphosphine). These results provide an important princi-
ple for the design of gold complex-catalyzed systems.
This work was partly supported by Grants-in-Aid for
Scientific Research and Grants-in-Aid for Scientific Research
on Priority Areas (No. 706: Dynamic Control of Stereo-
chemistry) from the Ministry of Education, Japan, Pfizer Inc.,
and Hitachi Chemical Co., Ltd. We thank Dow Corning Toray
Silicone Co., Ltd., Chisso Co., Ltd., and Shin-Etsu Chemical
Co., Ltd. for a gift of organosilicon compounds.
Although it took four days for the reaction to be complete, the
corresponding reduced product 6 of aldimine 5 was obtained in
good yield (83%).
The effect of the amount of the additional ligand on the
1
reactivity is shown in Fig. 1. Monitoring of the reaction by H
NMR spectroscopy showed that the hydrosilylation product was
formed continuously at 50 °C in the presence of 3 mol% of
chloro(triphenylphosphine)gold(
phosphine with the reaction almost complete after 600 min
experiment A) during which the reaction mixture was colorless
and transparent throughout. In experiment B, which was carried
out with a lower amount of tributylphosphine (10 mol%) than in
experiment A, considerable rate retardation was observed as the
reaction time approached 400 min, though the initial reaction
rate in experiment B was slightly higher than that of A within
I
) and 20 mol% of tributyl-
(
Notes and references
1
Y. Ito, M. Sawamura and T. Hayashi, J. Am. Chem. Soc., 1986, 108,
405; Y. Fukuda and K. Utimoto, J. Org. Chem., 1991, 56, 3729; S.
6
Komiya, T. Sone, Y. Usui, M. Hirano and A. Fukuoka, Gold Bull., 1996,
29, 131; Q. Xu, Y. Imamura, M. Fujiwara and Y. Souma, J. Org. Chem.,
1997, 62, 1594; J. H. Teles, S. Brode and M. Chabanas, Angew. Chem.,
Int. Ed., 1998, 37, 1415.
200 min. A deep-purple coloration was observed immediately
2
3
For heterogeneous gold catalysts, see: J. E. Bailie and G. J. Hutchings,
Chem. Commun., 1999, 2151 and references therein.
Comprehensive Handbook on Hydrosilylation, ed. B. Marciniec,
Pergamon Press, New York, 1992; M. Hudlicky, Reductions in Organic
Chemistry, American Chemical Society, Washington DC, 2nd edn.,
1
996; M. A. Brook, Silicon in Organic, Organometallic, and Polymer
Chemistry, Wiley, New York, 2000.
4
5
6
H. Ito, T. Yajima, J. Tateiwa and A. Hosomi, Tetrahedron Lett., 1999,
4
0, 7807.
C. A. McAuliffe, R. V. Parish and P. D. Randall, J. Chem. Soc., Dalton
Trans., 1979, 1730.
It was reported that the reduction of a gold(I) complex with a hydride
reagent gave metallic gold(0) and deeply colored gold clusters: K. P.
Hall and D. M. P. Mingos, Prog. Inorg. Chem., 1984, 32, 237; G.
Schmid, R. Pfeil, R. Boese, F. Bandermann, S. Meyer, G. H. M. Calis
and J. W. A. van der Velden, Chem. Ber., 1981, 114, 3634.
7
8
When the isolation of the products was carried out by column
2
chromatography (SiO ) without acidic workup both 3a (30%) and 4a
(58%) were obtained.
In the absence of a gold complex and tributylphosphine or in the
presence of tributylphosphine alone as catalyst, no reaction was
observed under the same conditions. See also ref. 3.
Fig. 1 Product formation vs. time for reactions carried out with
benzaldehyde 1a (1.0 mmol), dimethylphenylsilane 2 (2.0 mmol), 3 mol%
of chloro(triphenylphosphine)gold(
I
) (0.03 mmol) and 20 mol% of
9 Although other hydrosilanes were also tested, use of phenyldimethyl-
silane 2 gave good results in most cases.
10 R. C. Larock, Comprehensive Organic Transformations, Wiley, New
York, 2nd edn., 1999, pp. 1089–1096.
tributylphosphine (0.2 mmol) (experiment A, 5) or 10 mol% of tri-
butylphosphine (0.1 mmol) (experiment B, 8) in DMF (1.0 ml) at 50 °C.
1
Yields determined by H NMR spectroscopy.
982
Chem. Commun., 2000, 981–982