the desired product was achieved at ca. 175 °C, and by-
products, such as hexanolactam (0.1%) were detected if the
temperature was further increased to 200 °C (entry 6). From
entries 3, 7 and 8 it can be seen that the best results were
obtained when benzene was employed as solvent, with 95%
selectivity achieved; 92% and 90% selectivities were obtained if
methanol or acetonitrile were used as solvents, respectively.
Au(PPh3)2Cl, Au(PPh3)NO3 and [Au(PPh3)]2S were also
tested for catalytic activity (entries 9–11). The best catalytic
performance was achieved with [Au(PPh3)]2S although the
differences in selectivities for the desired product were not large
with these Au complexes, while the selectivity, when using
HAuCl4 as catalyst, was significantly inferior to that with the
characterize the performance of a catalyst. The differences in
the catalytic performances are clearly shown with TOFP, for
example, at 175 °C the best catalyst is [Au(PPh3)]2S.
In summary, the organic Au( ) complexes mentioned above
I
can effectively catalyse the carbonylation of aliphatic diamines
to produce the corresponding diformamides in the presence of
an appropriate amount of oxygen. To our knowledge, this is the
first reported study of organic Au( ) complexes as homogeneous
I
catalysts for the synthesis of diformamides by carbonylation of
aliphatic diamines. Further optimization towards the gold
catalyst system for the carbonylation reaction is now ongoing.
Au( ) complexes, indicating that the chemical state of Au and
I
Notes and references
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3 L. Prati and M. Rossi, J.Catal., 1998, 176, 552.
4 T. Hayashi, K. Tanaka and M. Haruta, J.Catal., 1998, 178, 566.
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105.
6 J. E. Bailie and G. J. Hutching, Chem. Commun., 1999, 2151.
7 R. J. H. Grisel, P. J. Kooyman and B. E. Nieuwenhuys, J. Catal., 2000,
191, 430.
8 R. D. Waters, J. J. Weimer and J. E. Smith, Catal. Lett., 1995, 30,
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9 Q. Xu, Y. Imamura, M. Fujiwara and Y. Souma, J. Org. Chem., 1997,
62, 1594.
10 H. Ito, T. Yajima, J.-i Tateiwa and A. Hosomi, Tetrahedron Lett., 1999,
40, 7807.
11 V. A. Soloshonok and A. D. Kacharov, Tetrahedron., 1996, 52,
245H.
12 A. S. K. Hashmi, L. Schwarz, J.-H. Choi and T. M. Frost, Angew.
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13 T. Hayashi, M. Sawamura and Y. Ito, Tetrahedron., 1992, 48, 1999.
14 Y. Ito, M. Sawamura and T. Hayashi, J. Am. Chem. Soc., 1986, 108,
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15 J. W. Mitchell and T. A. Johnson, US Patent 5919979.
16 Inorganic Syntheses, ed. R. N. Grimes, Wiley, New York, 1992, 29,
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17 C. A. McAuliffe, R. V. Parish and P. D. Randall, J. Chem. Soc., Dalton.
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the organic ligands played an important role in the selectivity.
The carbonylation of other substrates using Au(PPh3)Cl as
catalyst was further examined under the same reaction condi-
tions (entries 13–15). For decanediamine, almost 100% of
conversion and 98% of selectivity were achieved. But
Au(PPh3)Cl as catalyst was less effective when n-hexylamine
and cyclohexylamine were used as substrates. The selectivities
for the desired products were only 51.8% and 70% respectively,
and the main by-products were the corresponding dialkylureas.
These results suggested that the organic Au( ) complex catalysts
I
used here were especially effective for the carbonylation of
aliphatic diamines to form the corresponding alkyldiforma-
mide.
Pd(PPh3)2Cl2 as catalyst was also employed for this reaction,
and only 79.7% selectivity was obtained at 175 °C (entry 16)
although the conversion could be almost 100%. The main by-
products were hexanolactam (5.7%) and monoformamide
(14.6%). The catalytic performance of Pd(PPh3)2Cl2 was even
poorer at 150 °C. This indicates that Au( ) complexes as
I
catalysts for such specific carbonylation are better than the
corresponding Pd(II) complexes, although it was well known
that Pd complexes are the most effective catalysts for many
other carbonylation processes.
It is worth noting that the TOFs listed in Table 1 do not
distinguish clearly the differences in performance among these
catalysts. For example, the TOFs for entries 1–4 are the same.
So, in this work, TOFP (turnover frequency for product), i.e.
mole product per mole catalyst per hour has been used to
18 F. Canales, C. Gimeno, A. Laguna and M. D. Villacampa, Inorg. Chim.
Acta, 1996, 244, 95.
346
Chem. Commun., 2001, 345–346