in Scheme 1. It may be noted that iodide can stabilise PdIV as in
Cs2PdI6.13
We thank BP Chemicals for support and Dr G. Sunley for
carrying out some extra experiments.
Notes and references
† Bromide and chloride were also effective as promoters but less so than
iodide.
‡ The ligands do seem to have a (second order) effect on the reaction; for
example the tricyclohexylphosphine complexes [M{P(C6H11)3}2Cl2] (M =
Pd, Pt) are significantly less effective than the corresponding triphenylphos-
phine complexes. An effect of the counter-cation is also evident. Both these
points are currently under investigation.
Scheme 1 A possible catalytic cycle for methanol carbonylation based on
PdII/PdIV
.
1 B. L. Shaw, New J. Chem., 1998, 77; B. L. Shaw, S. D. Perera and E. A.
Staley, Chem. Commun., 1998, 1361.
2 I. Toth and C. Elsevier, J. Am. Chem. Soc., 1993, 115, 10 388; G. M.
Kapteijn, A. Dervisi, M. J. Verhoef, M. A. F. H. van den Broek, D. M.
Grove and G. van Koten, J. Organomet. Chem., 1996, 517, 123.
3 P. M. Maitlis, A. Haynes, G. J. Sunley and M. J. Howard, J. Chem. Soc.,
Dalton Trans., 1996, 2187.
4 K. E. Clode, D. J. Watson and C. J. E. Vercauteren (BP Chemicals) EP
616997, priority date, 26/3/93; K. E. Clode, (BP Chemicals) EP 786447,
priority date, 26/3/93; C. S. Garland, M. F. Giles and G. J. Sunley (BP
Chemicals) EP 643034, priority date, 10/9/93; C. S. Garland, M. F.
Giles, A. D. Poole and G. J. Sunley (BP Chemicals) EP 728726, priority
date, 21/2/95; M. J. Baker, M. F. Giles, C. S. Garland and G. Rafaletos
(BP Chemicals) EP 749948, priority date, 21/6/95; see also, Chem. Br.,
1996, 483; M. Howard, Abstracts, XI International Symposium on
Homogeneous Catalysis, St. Andrews, 1998, p. M2.
the presence of only [PPh3Me]I (d 22.2). When K2PtCl4 +
MeOH + MeI + Bu4NI + CO (5 atm/16 h/140 °C) was used as
the catalyst system, a n(CO) 2063 cm21 was observed in the IR
spectrum of the residue once the volatiles had been removed.
This is precisely the wavenumber quoted by Calderazzo and
coworkers for [Pt(CO)I3]2,9 and suggests that this species is
involved in our catalytic cycle. No metal carbonyl was detected
at the end of our palladium catalysed reactions, but Calderazzo
and coworkers noted that [Pd(CO)I3]2 readily lost all its CO
when the pressure was removed, and thus it is not surprising that
we did not observe it.
Palladium catalysed methanol carbonylation, in the presence
of very large amounts of specific promoters, such as sulfolane,
and preferably an amine (e.g. 2,2A-bipyridyl) has been described
in patents by van Leeuwen (Shell).10 Those methanol carbony-
lation reactions required both quite severe conditions (for
example, 182 °C/110 bar CO) and the addition of promoters
such as bipyridyl; methanol carbonylation in the absence of
such promoters was not claimed and platinum salts were
specifically excluded from the Shell patents.
There do not appear to have been any reports of platinum
catalysed carbonylations to methyl acetate, though the carbony-
lation of methanol to methyl formate has been noted,6 and
Kozitsyna and Moiseev reported that an unusual diphenylphos-
phido–platinum species in the presence of BF3 did catalyse the
carbonylation of methyl acetate to acetic anhydride.11
Nickel in the presence of iodide has long been known to
catalyse methanol carbonylation, but only under drastic condi-
tions (200–300 atm/230–350 °C).12 We have tried nickel
catalysts under our conditions and find activity but at quite a low
level in the presence of 50–100 equiv. of iodide.
5 T. Ghaffar, H. Adams, P. M. Maitlis, G. J. Sunley, M. J. Baker and A.
Haynes, Chem. Commun., 1998, 1023.
6 T. W. Dekleva and D. Forster, Adv. Catal., 1986, 34, 81.
7 See, for example, P. M. Maitlis, Organic Chemistry of Palladium, Vol.
II, Catalytic Reactions, Academic Press, New York, 1971, p. 18; R. F.
Heck, Palladium Reagents in Organic Synthesis, Academic Press, New
York, 1985, p. 341; J. Tsuji, Palladium Reagents and Catalysts, Wiley,
Chichester, 1995.
8 D. Forster, J. Am. Chem. Soc., 1975, 97, 951; C. E. Hickey and P. M.
Maitlis, J. Chem. Soc., Chem. Commun., 1984, 1609; A. Fulford, C. E.
Hickey and P. M. Maitlis, J. Organomet. Chem., 1990, 398, 311; J.
Rankin, A. D. Poole, A. C. Benyei and D. J. Cole-Hamilton, Chem.
Commun., 1997, 1835.
9 B. P. Andreini, D. Belli Dell’Amico, F. Calderazzo and G. Pelizzi,
J. Organomet. Chem., 1988, 354, 369; B. P. Andreini, D. Belli
Dell’Amico, F. Calderazzo, M. G. Venturi, G. Pelizzi and A. Segre,
J. Organomet. Chem., 1988, 354, 357.
10 P. W. N. van Leeuwen (Shell Internationale Research Maatschappij BV)
EP 0090443; priority date 30/3/82; P. W. N. van Leeuwen and C. F.
Roobeek (Shell Internationale Research Maatschappij BV) EP
0133331; priority date 25/7/83.
11 N. Yu Kozitsyna and I. I. Moiseev, Kinet. Katal., 1990, 31, 251; 1992,
32, 975.
12 W. Reppe, H. Kroeper, N. von Kutepow and H. J. Pistor, Annalen, 1953,
582, 72; see also A. A. Kelkar, R. S. Ubale, R. M. Deshpande and R. V.
Chaudhari, J. Catal., 1995, 156, 290.
13 D. Sinram, C. Brendel and B. Krebs, Inorg. Chim. Acta, 1982, 64, L131;
see also G. Thiele, K. Brodersen, E. Kruse and B. Holle, Chem. Ber.,
1968, 101, 2771.
In summary, we have shown that, in the presence of excess
iodide, palladium and platinum salts catalyse the carbonylation
of methyl iodide in methanol to methyl acetate at 5 atm CO,
14 °C. The reactions taking place are best described by,
MeI + MeOH + CO ? MeCO2Me + HI
followed by,
HI + MeOH ? MeI + H2O
Catalytic cycles involving either MII/MIV or M0/MII (M =
Pd, Pt) seem possible and an example of the former is illustrated
Communication 8/09197H
180
Chem. Commun., 1999, 179–180