New oscillating reaction in catalysis by metal complexes: a mechanism of alkyne oxidative carbonylation

Article abstract of DOI:10.1021/jp972666u

The reaction of phenylacetylene carbonylation to phenyl maleate, phenyl fumarate and dimethoxylactone in the homogeneous catalytic system PdI₂-KI-O₂-NaOAc in methanol solution is studied and is found to exhibit oscillations in the redox potential, pH, and rate of gaseous CO-O₂ mixture consumption. Oscillations are observed for 3.5 h up to 95% conversion of alkyne. The oxidation of CO to CO₂ occurs in parallel with carbonylation. The compositions of the gas and liquid phases are controlled by GC and GLC, respectively. The range of NaOAc concentrations within which oscillations are observed is found to be very narrow: from 0 to 0.01 mol/L.

Full text of DOI:10.1021/jp972666u

©
Copyright 1997 by the American Chemical Society
VOLUME 101, NUMBER 51, DECEMBER 18, 1997
LETTERS
New Oscillating Reaction in Catalysis by Metal Complexes: A Mechanism of Alkyne
Oxidative Carbonylation
Alexander V. Malashkevich, Lev G. Bruk, and Oleg N. Temkin*
LomonosoV State Academy of Fine Chemical Technology, Moscow 117571, Russia
ReceiVed: August 14, 1997; In Final Form: October 27, 1997
The reaction of phenylacetylene carbonylation to phenyl maleate, phenyl fumarate, and dimethoxylactone in
the homogeneous catalytic system PdI
in the redox potential, pH, and rate of gaseous CO-O
2
-KI-O
2
-NaOAc in methanol solution was found to exhibit oscillations
2
mixture consumption. This is the first example of an
oscillating chemical reaction in typical metal-complex catalysis where a complex organic molecule is formed
from simple reactants in solutions of metal complexes. Oscillations were observed for 3.5 h up to 95%
conversion of alkyne. The oxidation of CO to CO occurs in parallel with carbonylation. The products were
2
analyzed by NMR spectroscopy and GLC coupled with mass spectrometry. The compositions of the gas and
liquid phases were controlled by GC and GLC, respectively. The range of NaOAc concentrations within
which oscillations were observed was found to be very narrow: from 0 to 0.01 mol/L. It was shown that
oxygen transfer through the phase boundary is not a cause of oscillations. The run where PdI
2
was replaced
by K Pd exhibited oscillations similar in shape and amplitude. A reaction scheme was proposed, which
2
2 4
I
includes the processes of Pd(II) reduction to the active catalysts of carbonylation, Pd(I) complexes, followed
by the oxidation of palladium(I) complexes by iodine.
Nearly all homogeneous oscillating reactions, like the Be-
lousov-Zhabotinsky or Briggs-Rauscher systems, are facile
oxidations of organic or inorganic substrates (malonic, citric,
Here we show that chemical oscillations in such reactions
are possible. We report a new homogeneous oscillating reaction
of alkyne carbonylation in the presence of palladium complexes
and propose the mechanistic scheme that accounts for the
complex dynamic behavior of this system.
-
and oxalic acids, acetone, phenols, benzaldehyde, NADH, Br ,
-
2-
2-
-
I , SO3 , S2O3 , Sn(II), and HS ) by strong oxidants (KBrO3,
KIO3, H2O2, and O2) catalyzed by metal ions (Ce(IV)/Ce(III),
Mn(III)/Mn(II), Fe(III)/Fe(II), Co(III)/Co(II)).1 In these reac-
tions, metal ions play the role of one-electron oxidants. Until
recently, no oscillations were reported for typical reactions
catalyzed by metal complexes (e.g., hydrogenation, cyclization,
hydroformylation, carbonylation, polymerization, metathesis,
etc.) where an organic molecule is built from simpler blocks
Our study of oxidative alkyne carbonylation in the catalytic
system PdI -KI-O -MeOH, which was described earlier by
2
2
3
other researchers, revealed the oscillating behavior of the
system with PhCtCH in the presence of small amounts of
NaOAc. The reaction occurs in a well-stirred batch reactor at
40 °C under atmospheric pressure of the CO-O2 mixture (1:
1).
(
reactants) in solutions of metal complexes.2
In a typical run, PdI (0.1 mmol), KI (4 mmol), and NaOAc
2
(0.024 mmol) were dissolved in 8 mL of MeOH with vigorous
stirring for 15 min. In due course of the reaction, the reactor
*
Corresponding author. Tel: (095) 437 1120. Fax: (095) 430 7983.
Email: temkin@azeigarnik.msk.ru.
was purged with the CO-O2 mixture. Then, phenylacetylene
S1089-5639(97)02666-2 CCC: $14.00 © 1997 American Chemical Society

9826 J. Phys. Chem. A, Vol. 101, No. 51, 1997
Letters
Figure 1. Oscillations of the platinum electrode potential (EPt), pH, and volume of the gas mixture CO-O
reaction: (a) initial concentrations are [PdI ) 0.01 mol/L, [KI] ) 0.4 mol/L, [PhCtCH] ) 0.1 mol/L, [NaOAc]
concentrations of reagents are as in (a), but [NaOAc] ) 0.01 mol/L; (c) initial concentrations are the same as in (a), but NaOAc is absent.
2
(V
g
) consumed in the course of
2
]
0
0
0
0
) 0.0024 mol/L; (b) initial
0
dissolved in 2 mL of MeOH was added into the solution. The
overall volume of the solution was 10 mL. Water (2 mmol)
was added together with methanol to maintain the constant
concentration of water at the initial level (∼0.2 mol/L).
fumarate (II), and dimethoxylactone (III). The oxidation of
CO to CO2 (2) occurs in parallel. The potentials of the platinum
(EPt) and glass (pH) electrodes were measured with reference
to the Ag/AgCl,KCl electrode, which contacted with the solution
through the diffusive bridge.
Oscillations were observed for 3.5 h up to 95% conversion
of alkyne. Figure 1 shows the behavior of the redox potential,
pH, and volume of the gaseous mixture consumed. Water is
1
13
The products were analyzed by H and C NMR spectros-
copy and coupled GLC/mass spectrometry. The compositions
of the gas and liquid phases were controlled by GC and GLC,
respectively. Reaction 1 produced phenyl maleate (I), phenyl

Letters
J. Phys. Chem. A, Vol. 101, No. 51, 1997 9827
1
PhC CH + 2CO + 2MeOH + /2O2
Palladium hydride complex formed by reaction 5 may further
undergo reaction 4 to yield Pd(I) or reactions
Ph
H
Ph
COOMe MeO
O
O
C
C
C
C
HPdI + I f PdI + HI
(6)
(7)
(1)
2
2
MeO
H
MeOOC
COOMe MeOOC
Ph
III (15%)
1
HPdI + / O + HI f PdI + H O
I (70%)
II (4%)
2
2
2
2
1
CO + /2O2
CO2
(2)
We suggest reactions 6 and 7 in our system as the simplest
plausible ones to oxidize HPdI. Iodine is formed by oxidation
of HI by molecular oxygen:
formed in a 1:1 proportion to the products of phenylacetylene
carbonylation by reaction 1 and catalyzes reaction 2. In due
course of experiments, the concentration of water somewhat
increases at the expense of reaction 1.
1
2HI + / O f I + H O
(8)
2
2
2
2
Here, reactions 6-8 are responsible for the complete disap-
pearance of HPdI and Pd2I2, after which phenylacetylene
carbonylation stops. Reaction 3 corresponds to the “upper”
oxidized state of the system, whereas process 5 is associated
with the “lower” reduced state, which is active in oxidative
carbonylation. Reactions 4 and 5 together are the autocatalytic
process of Pd(II) reduction catalyzed by palladium hydride
complex and controlled by the amount of I2 in the system. Upon
I2 consumption, the concentrations of HPdI and HI begin to
grow rapidly. This leads to the inhibition of reaction 3 and
acceleration of reactions 6-8 that return the system to the
Sodium acetate determines the initial pH of the solution,
which affects the oscillations. The range of NaOAc concentra-
tion within which oscillations were observed was found to be
very narrow: from 0 to 0.01 mol/L. Higher concentrations of
NaOAc caused the deep reduction of the system and appearance
of metallic palladium. In the absence of NaOAc, one can see
transition from the rapidly damped oscillations having a small
amplitude to the pseudo-steady state (Figure 1c). The most
prolonged oscillations with the largest amplitudes were attained
at the NaOAc concentration of 0.0024 mol/L (Figure 1a). When
the concentration of NaOAc was 0.01 mol/L, the solution
became inhomogeneous because of palladium precipitation, and
the amplitude of oscillations became smaller (Figure 1b).
Because changing the stirring intensity (stirring rate was
varied from 300 to 600 rpm) had no influence on the magnitude,
shape, or period of oscillations, we believed that oxygen transfer
through the phase boundary is not a cause of oscillations; that
is, the oscillator is of a purely chemical nature.
“
upper”, inactive in carbonylation state.
We may propose a first-approximation mathematical model
based on mechanism 3-8 in more detailed notation to describe
the dynamic behavior of the system. The proposed model agrees
with the experimental data: it correctly describes the period
and shape of oscillations and the transition from oscillations to
the pseudo-steady state, which is observed in the absence of a
base (NaOAc). Discussion of the details of the model will be
reported elsewhere.
Our results prove the possibility of complex dynamic behavior
(such as chemical oscillations) in oxidative reactions of organic
synthesis that are typical organometallic catalytic processes.
Oxygen is the oxidant in the system, while the iodide ion,
carbon monoxide, phenylacetylene, and methanol are reductants.
2-
Palladium(I) complexes of the Pd2X4(CO)2 composition (X
-
-
)
Br , I ) have been shown to be active catalysts of alkyne
4-6
carbonylation in PdX2 solutions.
Therefore, a change in the
value of the platinum electrode potential (EPt), which takes place
when CO and PhCtCH contact the solution PdI2, were
associated with the reduction of Pd(II) to Pd(I). The catalyst
becomes active toward oxidative carbonylation of phenylacety-
lene only if part of Pd(II) is reduced to Pd(I) and EPt decreases
by approximately 200 mV. The run where PdI2 was replaced
Acknowledgment. We acknowledge financial support from
the Russian Fund for Basic Research (Grant 97-03-32324).
References and Notes
(1) Oscillations and TraVeling WaVes in Chemical Systems; Field, R.
J., Burger, M., Eds.; Wiley: New York, 1985.
5
by K2Pd2I4, synthesized by the known technique, exhibited
oscillations similar in shape and amplitude.
(2) One of us observed the first oscillating reaction in the classical
organometallic catalysis. This was the oxidative carbonylation of acetylene
On the basis of the available data on the mechanism of
in the PdBr -HBr-n-BuOH-DMSO system. Only some general features
2
oxidative carbonylation,6-8 one may propose two reactions of
of the reaction were studied (Shulykovskii, G. M.; Temkin, O. N.; Bikanova,
N. V.; Nirkova, A. N. In Chemical Kinetics in Catalysis: Kinetic Models
of Liquid-Phase Reactions; Institute of Chemical Physics: Chernogolovka,
Pd(II) reduction to Pd(I):
1
985; p 112 (in Russian)).
(3) Gabriele, B.; Costa, M.; Salerno, G.; Chiusoli, G. P. J. Chem. Soc.,
CO + H O + PdI f HPdI + HI + CO
2
(3)
(4)
2
2
Perkin Trans. 1 1994, 83.
(
4) Temkin, O. N.; Bruk, L. G. Russ. Chem. ReV. 1983, 52, 117.
HPdI + PdI f Pd I + HI
2
2 2
(5) Bruk, L. G.; Flid, V. R.; Temkin, O. N. React. Kinet. Catal. Lett.
1
978, 9, 303.
6) Bruk, L. G.; Oshanina, I. V.; Kozlova, A. P.; Vorontsov, E. V.;
Temkin, O. N. J. Mol. Catal. A: Chemical 1995, 104, 9.
7) Temkin, O. N.; Kaliya, O. L.; Zhir-Lebed’, L. N.; Mekhryakova,
(
Reaction 3 is a key step of the water-gas shift reaction
9
10
catalyzed by Pd(II) and other metals. Reaction 4 is considered
as the main pathway to Pd(I) compounds.4 Palladium(I)
complex thus formed is active in oxidative carbonylation of
phenylacetylene:
(
N. G.; Bruk, L. G.; Golodov, V. A. Homogeneous Oxidation; Nauka: Alma-
Ata, 1978; p 3 (in Russian).
(
(
8) Bruk, L. G.; Temkin, O. N. Khim. Prom-st. 1993, 57 (in Russian).
9) Zudin, V. N.; Chinakov, V. D.; Nekipelov, V. M.; Rogov, V. A.;
Likholobov, V. A.; Yermakov, Yu. I. J. Mol. Catal. 1989, 52, 27.
(10) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. J. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987.
Pd I + PhCtCH + 2CO + 2MeOH f 2HPdI +
2
2
MeOOCC(Ph)dCHCOOMe (5)