Journal of Catalysis 219 (2003) 372–375
Highly efficient ionic liquid-mediated palladium complex catalyst system
for the oxidative carbonylation of amines
Feng Shi, Jiajian Peng, and Youquan Deng ∗
Center for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China
Received 13 February 2003; revised 3 April 2003; accepted 22 April 2003
Abstract
A highly efficient catalyst system, palladium complex–ionic liquid, was developed for the carbonylation of amines to give carbamate or
urea. The desired products could be precipitated by adding water into the resulting mixture and the catalyst system could be reused with
slight loss of catalytic activity.
2003 Elsevier Inc. All rights reserved.
1. Introduction
Recently, room temperature ionic liquids, a new kind of
reaction media with very low vapor pressure and high dis-
solvability toward many organic and inorganic substances,
have been attracting growing interests, and many catalytic
reactions proceeded in ionic liquids as reaction media were
reported with excellent performance [9–16]. It can be as-
sumed that the diversity of ionic liquids may form an optimal
homogeneous catalyst system with a specific organometallic
complex toward a specific reaction.
In this work, the ionic liquid-mediated palladium (1,10-
phenanthroline)2+ complex catalyst system for the oxidative
carbonylation of amines to give corresponding carbamates
or ureas was investigated without using any additional or-
ganic solvents. The aim is to establish an effective catalytic
system for the carbonylation of amines through the selective
dissolvability and special mediation of ionic liquid.
Isocyanates, e.g., toluene diisocyanate and 4,4ꢀ-diphenyl-
methyldiisocyanate, are currently manufactured by phos-
genation of the corresponding amines with toxic phosgene
in industry, which may cause serious environmental pollu-
tion and equipment corrosion. Therefore, produced either
by oxidative carbonylation of amines or by reductive car-
bonylation of nitro compounds in the presence of an alcohol,
carbamates as intermediates for the synthesis of isocyanates
with nonphosgene routes have been extensively studied for
the past two decades. Pd, Ru, Rh, Au, and other transitional
metal complexes were employed as the catalysts [1–7], in
which complexes of Pd coordinated with N-containing com-
pounds are the most effective catalyst systems [8]. The cor-
responding catalytic turnover frequency (TOF), however, is
still not high enough for industrial application, and large
amounts of volatile organic solvents were inevitably used in
most of these processes. Furthermore, palladium complexes
coordinated with N-containing compounds are usually in-
soluble in most conventional organic solvents, and it is well
known that reaction media play an important role in homo-
geneous catalysis, although, so far, such mediation is still
not very clear. Moreover, organic solvents, for establishing a
suitable homogeneous catalyst system for the carbonylation
of N-containing compounds, are very limited.
2. Experimental
The ionic liquids, BMImBF4 (BMIm = 1-butyl-3-meth-
ylimidazolium), BMImPF6, BMImFeCl4, and BMImCl,
and palladium (1,10-phenanthroline)2+ complexes were re-
spectively synthesized according to previously published
papers [17,18] with slight modifications. Pd(OAc)2 and
Pd(acac)2 were of AR grade. Characterizations of ionic
liquids and palladium complexes were conducted with FT
Raman (Nicolet 910) and FTIR (Bruker H210).
*
Corresponding author.
E-mail address: ydeng@ns.lzb.ac.cn (Y. Deng).
0021-9517/$ – see front matter
2003 Elsevier Inc. All rights reserved.
doi:10.1016/S0021-9517(03)00198-2