From small molecules to polymeric catalysts in the oscillatory carbonylation reaction: Multiple effects of adding HI

Article abstract of DOI:10.1039/c7cp07747e

The oscillatory palladium-catalysed carbonylation reaction opens new horizons for applications in smart materials due to the versatility of its conditions and substrates, as well as the adjustability of amplitude and period of pH oscillations. A variety o

Full text of DOI:10.1039/c7cp07747e

PCCP
View Article Online
View Journal
PAPER
From small molecules to polymeric catalysts in
the oscillatory carbonylation reaction: multiple
effects of adding HI†
Cite this:DOI: 10.1039/c7cp07747e
Anna Isakova, *a Billy J. Murdochb and Katarina Novakovica
The oscillatory palladium-catalysed carbonylation reaction opens new horizons for applications in smart
materials due to the versatility of its conditions and substrates, as well as the adjustability of amplitude and
period of pH oscillations. A variety of viable substrates have been demonstrated, including polymeric alkyne-
terminated substrates. However, so far, there have not been any reports of polymer-based palladium catalysts
in oscillatory mode. In this paper, we demonstrate pH oscillations in various systems, using commercially
available palladium acetate, a triphenylphosphine palladium acetate complex and a polymer-bound palladium
catalyst. While palladium acetate was able to generate oscillations under the conditions already established
in our previous research on PdI2-catalysed oscillators, the other two catalysts needed the addition of HI to
induce oscillations. HI forced an initial pH drop, bringing pH into the range where oscillations generally
occur. Addition of HI had a significant effect on all catalysts, modifying the amplitude and period of
oscillations, oscillation mode, as well as starting material conversion and product distribution.
Received 16th November 2017,
Accepted 5th February 2018
DOI: 10.1039/c7cp07747e
rsc.li/pccp
useful for industrial application due to a reduction of costs for
isolation and purification,14 applicable to a number of substrates, as
Introduction
Oscillatory chemical reactions have been known for decades.1 demonstrated by Gorodsky.15–17 Recently oscillations in pH were
Currently these reaction systems are generating profound inter- reported for PCOC, where an alkyne-functionalised polymeric sub-
est in materials science as a driving force for smart materials, strate (poly(ethylene glycol)methyl ether acetylene, abbreviated as
owing to the ability of smart materials to sense and react to PEGA) was employed in place of PhAc, extending the opportunities
changes in the environment, generated during the oscillatory of application of PCOC in smart materials.13
process.2 A number of self-oscillating materials and architectures
have been reported, based on such reactions as the Landolt clock studied in depth by Novakovic et al., Gorodsky and Temkin et al.,
or Belousov–Zhabotinsky reaction.3–5
the evidence for other palladium catalysts’ activity displaying similar
Although the PCOC reaction in oscillatory mode has been
The palladium-catalysed oxidative carbonylation (PCOC) dynamics in this reaction system is lacking. While studies of similar
reaction has recently attracted attention due to its ability to carbonylation reactions have demonstrated the application of palla-
exhibit oscillations in pH, redox potential, turbidity and heat of dium diacetate18 and palladium chloride,19 no oscillations were
reaction.6–8 The most studied system employs phenylacetylene reported. In this work, we studied a number of commercially-
(PhAc) as substrate due to the facile analysis of products9 and available palladium catalysts for application in PCOC (Fig. 1), in
uses PdI2 as a catalyst. Oscillations in the PhAc/PdI2 system are order to explore their potential for oscillatory dynamics that could
sustained in a batch reactor for days of monitoring with the lead to future applications in smart materials as part of more
possibility of varying the amplitude and period of oscillations complex architectures. By studying the catalyst on three levels –
by adjusting the temperature of reaction,10,11 concentration of from small molecule through a ligand–metal complex to a polymer-
the catalyst, substrate or even water content.12,13 Besides the supported ligand–metal complex – we obtained a better insight
sustained oscillations, the PCOC reaction has demonstrated a into the working boundaries of the reaction.
temperature-dependent product selectivity, which is potentially
Experimental part
Materials
a School of Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
E-mail: anna.isakova@newcastle.ac.uk
b National EPSRC XPS Users’ Service (NEXUS), School of Engineering,
Materials studied were used as received: palladium acetate
Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c7cp07747e (PdAc), bis(acetato)bis(triphenylphosphine)palladium(II) (L-Cat),
This journal is ©the Owner Societies 2018
Phys. Chem. Chem. Phys.

View Article Online
Paper
PCCP
Samples were taken at the end of the experimental runs
(unless otherwise stated within the main text) and filtered over
silica prior to being diluted 1 : 2 with methanol. The samples
were analysed for starting material conversion and product
distribution by a Varian Saturn 2200 gas chromatograph fitted
with a VF-5ms column (30 m) and equipped with a mass
spectrometry detector (GC-MS). The method was as follows:
injector temperature 150 1C; helium flow rate 1 ml minÀ1; oven
temperature 100–195 1C over 35 min in 5 steps.
Fig. 1 Structures of the studied catalysts with their notations.
X-ray photoelectron spectroscopy (XPS)
di(acetato)dicyclohexylphenylphosphinepalladium(II), polymer-
bound FibreCats (Pd B5%, extent of labeling: 0.4–0.6 mmol gÀ1
PPH3 ligand content loading, P-Cat), palladium(II) iodide (Z99.99%
trace metals basis), hydroiodic acid (HI, Z57%), phenylacetylene
(PhAc, 98%), triphenylphosphine (Z95.0% GC), methanol (HPLC
Plus, Z99.9) all Sigma Aldrich; naphthalene (extra pure), potassium
iodide (Z99% GPR RECTAPURs), VWR Chemicals; buffer
solutions: pH 2.00 (glycine), pH 7 (phosphate) and pH 10
(borate) (all NIST Standard, ready to use for pH measurement,
Fisher Chemical). Pure air and carbon monoxide were supplied
by BOC. Na2PdAc2Cl2 was synthesised by mixing 2 equiv. of
NaCl with 1 equiv. of PdAc in methanol for 18 h.
X-ray photoelectron spectroscopy (XPS) was performed on solid
catalysts in a Thermo Scientific K-Alpha spectrometer, using a
monochromated Al K-Alpha source (1486 eV). The flood gun
was used for charge compensation.
Absorbance
Absorbance was measured using a FLUOStar Omega microplate
reader using a multiwell plate (200 ml) in a wavelength range
from 275 to 700 nm with a resolution of 1 nm. Samples (1 ml)
were withdrawn at certain time points throughout the experi-
ment as stated within the main text and diluted 1 : 2 with HPLC
grade methanol.
The reaction
The reaction was performed in a flat-bottom Erlenmeyer flask
(100 ml) at constant stirring, using the HEL Micronote system
to record pH and temperature within the bulk of the reaction.
Results and discussion
Single mode oscillations in PdAc
Prior to the reaction, probes were calibrated at room tempera- Three commercially available palladium catalysts were studied:
ture (17–20 1C) against buffer solutions of pH 2, 7 and 10. The small molecule palladium diacetate salt (denoted as PdAc),
stated amounts of KI (4.150 g, 25 mmol), catalyst (30 mg PdAc, triphenylphosphine ligand palladium acetate (L-Cat) and a
98.5 mg L-Cat or 285 mg P-Cat) and naphthalene (256 mg, used polymer-bound P-Cat (Fig. 1). PdAc and L-Cat are soluble in
as an internal standard for subsequent GC-MS analysis) were all saturated KI solution in methanol, whereas polymer-bound
charged into the flask and dissolved (or suspended for P-Cat) in palladium catalyst P-Cat is crosslinked and insoluble, thus
100 ml HPLC grade methanol. The pH monitoring was initiated providing an insight into the possibility of heterogeneous
while the solids were dissolving with the stabilisation of pH catalysis in the PCOC reaction. The changes in pH were
taken as indication of complete dissolution of KI. At that point, monitored for 4000 min during which the reaction demon-
purging through the solution with CO (15 ml minÀ1) and air strated oscillations (using PdAc) or stable values of pH (using
(15 ml minÀ1) commenced. After 10–20 min (or after stabilisa- L-Cat and P-Cat), Fig. 2.
tion of pH following an initial drop), phenylacetylene (1.38 ml,
It can be observed from Fig. 2a that palladium acetate
12.57 mmol) was added. The system was monitored continuously catalysis proceeded as has generally been reported for the PdI2
for changes in pH and temperature of the reaction. It should be catalysed systems in oscillatory mode.10,14 When the system was
noted that the pH electrode was calibrated against aqueous buffer purged with CO/air, an initial drop in pH from 7.9 to 6.4 was
solutions while reaction pH was recorded in methanol solution. As observed, indicating the incorporation of CO and methanol mole-
the standard pH scale is based on measurements in water, pH cules into the structure of the catalyst with a corresponding release
values recorded in non-aqueous solutions need to be adjusted prior of H+ ions (Scheme 1a).14,21,22 Previous studies by other groups
to being converted to hydrogen ion concentrations. It has been have suggested conversion of Pd2+ into Pd+ species at this initial
reported that in 100% methanol, pH values can be adjusted by stage of the reaction, however, the evidence for Pd+ species was not
adding 2.3 to the observed pH measurements to get the equivalent solid.6,23 A further pH drop from 6.4 to 3.8 occurred upon addition
pH value in water.20 As the focus of this paper is comparison of of the substrate and indicated the initial substrate conversion
the oscillatory trend achieved in pH, it was not needed to adjust according to the generally accepted reaction mechanism.14
pH values since the trend remains the same in both recorded and
While general features are similar to those when using PdI2 as
adjusted pH values. A detailed study of the effect a methanol–water catalyst, previously investigated by our group, the oscillations
solvent composition has on recorded pH and actual concentration in the PdAc system started significantly earlier, after 180 min
of acid present in solution has been previously published for the (compared to well over 1000 min for PdI2).10 The reaction system
PdI2/PhAc oscillatory carbonylation system.12
employing PdAc catalyst exhibited a faster pH drop after
Phys. Chem. Chem. Phys.
This journal is ©the Owner Societies 2018

View Article Online
PCCP
Paper
Fig. 2 pH recorded in PCOC of phenylacetylene in methanol using various species of Pd-based catalysts at room temperature, with CO and air
(15 ml minÀ1 each): (a) PdAc; (b) L-Cat; (c) heterogeneous polymeric P-Cat.
addition of phenylacetylene with pH oscillations occurring reported to continue for more than 4000 min in the same mode.
shortly after. The period of oscillations for the PdAc catalyst was The unchanged mode of pH oscillations also indicates that a
also shorter than when PdI2 was used (32 min and 60–70 min, single oscillator is responsible for the recorded pattern.25
respectively). This may be associated with the concentration
On the other hand, the PdAc-based catalysts L-Cat and P-Cat
exhibited no oscillations. A much smaller pH drop occurred
difference (1.336 Â 10À3 M of PdAc against 2.644 Â 10À3
M
PdI2 used in a previous study). When PdAc was used at a higher upon CO/air purging (from 7.1 to 6.9), and after the addition of
concentration of 2.644 Â 10À3 M, similar to that of PdI2 reported substrate, pH decreased gradually to 6.5 and 6.1, respectively,
previously, the oscillations started even earlier (104 min) but where it plateaued (Fig. 2b and c). A ligand exchange model was
severe clogging of gas lines occurred which disrupted the oscilla- proposed for all three catalysts (PdAc, L-Cat and P-Cat) to
tions (see ESI,† Fig. S1). The much shorter induction period with suggest how the ligands affected the initial change of pH during
PdAc compared to PdI2 is most likely associated with the higher CO and air purging (Scheme 1).
solubility of PdAc in KI solution.
Absorbance measurements of the reaction mixtures employing
Furthermore, the pattern of pH oscillations was different different catalysts were performed (see ESI,† Fig. S2).ÀWhen PdAc
from that generally observed in PdI2 systems. pH oscillations in was used, absorbance measurements detected the I3 (generated
the PdAc reaction were highly regular with an amplitude of 0.98 from I2 and IÀ) species upon incorporation of CO into the catalyst,
(Æ0.09) pH units and a period of 31 (Æ4) min. This regularity is which demonstrates that IÀ was released, in agreement with
frequently seen in oscillatory redox systems in a continuous- our tentative scheme. Furthermore, the oscillatory behaviour in
flow stirred tank reactor (CSTR),24–27 but rarely observed in a pH when PdAc was used was accompanied by oscillatory changes
À
batch reactor. The variations in amplitude, associated with in the concentrations of the Pd2+ and I3 species. Within one
substrate consumption and solvent evaporation, are not observed oscillation, during the pH rise the species Pd2+ and I2 were mostly
for the PdAc run, indicating the very slow conversion of substrate observed, while during Àthe pH drop, the Pd2+ peak absorbance
to products and making it one of the most stable batch oscillators decreased and the I3 peak was predominantly observed.
This journal is ©the Owner Societies 2018
Phys. Chem. Chem. Phys.

View Article Online
Paper
PCCP
Scheme 1 Tentative model of ligand exchange proposed for PdAc, L-Cat and P-Cat. Resulting complexes participate further in the reaction to generate
di-esters or are released as mono-ester by-products.
Also, not detectable by UV-Vis but visible to the naked eye, patterns are associated with the existence of two qualitatively
particles of metallic palladium were present during the pH drop. different behaviours replacing one another during the course of
Absorbance measurements of the other two catalysts, however, the reaction, even when all the control parameters remain the
demonstrated that incorporation of CO into the catalyst did not same.29 In such systems, the reaction networks (subnetworks)
result in the formation of I3À, in agreement with Scheme 1.
responsible for occurrence of small and large amplitude oscil-
lations alternate.31 While our system was a batch reaction,
observed oscillations (Fig. 3a) appeared to consist of two over-
Mixed-mode oscillations after addition of HI
For phosphine-bound Pd catalysts (L-Cat and P-Cat), pH did not laid patterns, one with a short period of 20–30 min and another
reach the values where oscillations typically occurred in pre- larger period of 140–290 min.
vious oscillatory carbonylation reactions.7,10,13,17 Therefore,
The heterogeneous polymeric P-Cat demonstrated oscilla-
three catalysts were examined further in a new set of experi- tions after a long induction period of approximately 4000 min
ments where pH was artificially decreased by the addition of HI with the development of a similar, complex oscillatory pattern
after the addition of substrate (Fig. 3). Although when PdAc was with progressively increasing amplitude and period (Fig. 3c).
used, addition of HI was not needed for oscillations to start, The large period took over 330–348 min, whereas the shorter
PdAc was included in this study for comparison.
period was of 20–53 min.
PdAc exhibited delayed oscillations (Fig. 3a), when com-
Catalyst L-Cat did not exhibit oscillations after addition of
pared to the same catalyst without external addition of HI HI (Fig. 3b), although pH gradually decreased over the course
(Fig. 2a). The first series of oscillations with a relatively small of reaction from 6.9 to 3.8, where oscillations were generally
amplitude and a period of 20–30 min were observed after observed. The expected rapid large drop of pH when HI was
1200 min, which then developed into a series of oscillations with added did not occur. This was associated with an immediate
continuously increasing amplitude. The maximum observed consumption of protons by the triphenylphosphine ligands of
amplitude was 1.91 pH. This time the pattern of oscillations was the complex (see test runs in Fig. S3, ESI†), caused by their
irregular and complex, reminiscent of previously observed mixed- reversible dissociation. Increasing the amount of added hydro-
mode oscillations, particularly so-called ‘bursting’ oscillations.28 iodic acid ten-fold saw a more pronounced initial pH drop,
Similar complex oscillations have been reported previously for the similar to the other catalysts and the subsequent development
oscillatory Briggs–Rauscher reaction in a batch set-up.29 In that of pH oscillations. The increase in added HI compensated for
system, intermittent-bursting oscillations were characterised by the HI consumed by the triphenylphosphine ligands during their
the number of oscillations per burst, the duration of periods of dissociation. The oscillations in pH in this instance appeared
bursts as well as the periods of gaps between them. Due to the after an induction period of approximately 4180 min (similar to
constant change in concentration of reactant per s in a batch the induction time using the P-Cat catalyst after the addition of
set-up, a CSTR is considered to be better suited for studying HI (Fig. 3c), Fig. 4), during which the pH slowly rose from 2 to
complex oscillatory behaviour.30 The complex trends in oscillatory 2.8. The oscillations had a short period of 10–15 min and a
Phys. Chem. Chem. Phys.
This journal is ©the Owner Societies 2018

View Article Online
PCCP
Paper
Fig. 4 Oscillations in pH recorded in PCOC of PhAc in methanol using
catalyst L-Cat, after addition of 0.228 mmol of HI to achieve the pH range
where oscillations normally occurred.
solution two catalytic species, Na2PdAc2Cl2 and K2PdAc2I2,
would become available:
Na2PdAc2Cl2 + 2KI $ K2PdAc2I2 + 2NaCl.
As can be seen in Fig. 5a, complex mixed-mode oscillations
were indeed recorded. Oscillations resembled two oscillatory
patterns overlaying each other: large oscillations with a period of
417–523 min and small oscillations with a period of 10–25 min.
The captured oscillations are similar to the phenomena observed
when PdAc and P-Cat were used with the addition of HI (Fig. 3a
and c, now enlarged in Fig. 5b and c).
The presence of two catalytic species in the PdAc and P-Cat
systems may not be the main/only driver for the existence of
multiple subnetworks causing switching between large and
small amplitude cycles so we also investigated PCOC employing
a mixture of PdAc and PdI2 (4 : 1 molar content). No HI was
externally added to this system. The total content of catalyst
in mol% was identical to that in PdAc only reaction (1.336 Â
Fig. 3 pH recorded in the PCOC of phenylacetylene in methanol using
various species of Pd-based catalysts, using CO/air (each 15 ml minÀ1) at
room temperature. Following the addition of substrate (PhAc), 0.0228 mmol
HI was added.
small amplitude of 0.10–0.15 units until the pH started rising 10À3 M). As can be seen from Fig. 6a, in the mixed catalyst
after 9200 min and the amplitude increased to 0.5 units.
system, oscillations started later (after 1400 min) and initially
had a small amplitude of 0.4–0.5 and period of 35 (Æ6) min
which rapidly increased in amplitude to 2.4 (Æ0.3) and a period
The origin of mixed-mode oscillations
Mixed-mode oscillations in pH have been observed and of 46 (Æ5) min. At approximately 4000 min, the periodic
explained before in other systems,26,30,32 however, due to the oscillations were terminated by a sudden drop in pH. Following
general complexity of the PCOC mechanism (which is not 100% this event, small amplitude ‘‘climbing’’ oscillations developed.
established), it is difficult to confidently assign the mixed-mode The increase in pH and amplitude over time is a characteristic
oscillations in PdAc and P-Cat after addition of HI to certain oscillatory shape in the PCOC reaction employing PdI2,10,12,33
reaction networks, especially since they are also observed in although the majority of catalytic species in this reaction was
certain conditions (at 10 and 20 1C), when PdI2 is used without PdAc. While the oscillatory patterns using PdAc + PdI2 had a
any HI addition. Thus, further studies, including the transition less obvious mixed-mode behaviour than in PdAc + HI, it is
to a CSTR reaction set-up, are needed to clarify the underlying possible to trace the evolution of an overlaid PdI2-induced pattern.
mechanisms of the mixed-mode patterns.
When PdI2 and PdAc were used in a 1 : 1 ratio, only one series of
To expose the effect of two simultaneous processes with oscillations was observed before the system consumed all
differing catalysis rates on the resulting oscillatory patterns, substrate (Fig. 6b) and stopped oscillating. Oscillations started
Na2PdAc2Cl2 catalyst was employed in place of PdAc in an after 1200 min and kept growing in amplitude until they
otherwise identical experimental setup to that used in the reached 4.4 pH units (the last pH fall) while the period also
experiment shown in Fig. 2a (no HI added, same concen- increased from 14 min to 77 min.
trations of KI, PhAc substrate and gas purging rates of
The existence of two catalytic species in PdAc and P-Cat was
15 ml minÀ1). Na2PdAc2Cl2 was selected since in saturated KI not straightforward, but since the mixed-mode oscillations
This journal is ©the Owner Societies 2018
Phys. Chem. Chem. Phys.

View Article Online
Paper
PCCP
Fig. 6 Oscillations in pH recorded in PCOC of PhAc in methanol using a
mixture of PdAc and PdI2 4 : 1 mol catalysts (a) and 1 : 1 mol catalysts (b),
while purging with CO and air (each 15 ml minÀ1) at room temperature.
impurities in these commercially available catalysts is unclear.
Furthermore, it appeared that due to the absence of metallic
palladium in L-Cat (as seen from XPS, Fig. S4, ESI†), the
addition of HI did not lead to the generation of PdI2 which
occurred with PdAc and P-Cat. Therefore, simple periodic
oscillations and lack of mixed-mode patterns in this case could
be characteristic of a system with a single catalytic species.
Further studies involving a longer reaction monitoring time as
well as the transition from batch to a CSTR set-up are needed to
further understand the observed behaviours.
Fig. 5 Enlarged area where mixed-mode oscillations were observed (a)
Na2PdAc2Cl2; (b) PdAc + HI and (c) P-Cat + HI.
Starting material conversion and product distribution
Regarding product generation, both PdAc and P-Cat had a
similar product distribution in both HI and non-HI modes –
with almost 50 : 50 Z-isomer (5) and DMO (3) and only a trace
amount of E-isomer (4, see Table 1). In HI mode, however,
the product conversion increased significantly from 7.3% and
3.5% to 37.4% and 29.5% (for PdAc and P-Cat, respectively).
Moreover, methyl cinnamate (1), generally considered as an
intermediate, was observed in substantial amounts after addi-
tion of HI, suggesting that HI affected the mechanism of the
were observed only after addition of HI, it is possible to suggest
that HI was involved in the generation of PdI2 from a pool of
metallic palladium within the pristine catalyst, as follows:
HI + O2 - I2 + H2O
Pd0 + I2 - PdI2.
Generation of additional PdI2 within the reaction mixture reaction and altered the stoichiometry of the processes.
would facilitate the existence of two catalysts: K2PdAc2I2 L-Cat in both modes had a preferential product – Z-isomer
and K2PdI4, one feasible explanation for multiple reaction (5), which was likely to be associated with steric hindrance from
subnetworks. The presence of metallic palladium in pristine bulky triphenylphosphine ligands. Substrate conversion after
P-Cat and PdAc was confirmed by XPS (Fig. S4, ESI†). The PdAc 4000 min largely depended on the amount of HI added. Thus,
catalyst exhibited a double set of Pd 3d 5/2 and 3/2 peaks, after the addition of 0.228 mmol of HI, substrate conversion
indicating that both metallic palladium and Pd2+ were present was 26.9%, which was higher than the conversion when only
in the catalyst, with the majority being Pd2+ species. P-Cat only 0.0228 mmol of HI was added (14% at 4600 min) and without
exhibited a set of peaks for Pd0 with a shoulder into higher any HI (9.0% at 4000 min) (Table 1). This speaks for the ability
binding energies, indicating the presence of a smaller concen- of HI to improve the catalytic activity of L-Cat. At the time when
tration of Pd2+ species. The source of metallic palladium conversion was measured (4000 min, Fig. 4) the oscillations
Phys. Chem. Chem. Phys.
This journal is ©the Owner Societies 2018

View Article Online
PCCP
Paper
Table 1 Product distribution (in mol%) and substrate (PhAc) conversion for various Pd-based catalysts. Product characterisation is discussed in details in
ref. 9
mmol
E-Isomer (4)
Z-Isomer (5)
DMO (3)
MeCin (1)
MeAt (2)
PhAc conversion (%)
Without HI addition
PdAc 4000 min
L-Cat 4000 min
P-Cat 4000 min
0.16
0.28
0.13
3.50
6.37
1.67
3.34
0.63
1.51
—
—
—
0.13
7.3
9.0
3.5
After addition of 0.0228 mmol HI (1Â)
PdAc 5600 min
L-Cat 4600 min
P-Cat 6800 min
0.45
0.29
0.32
18.34
11.14
12.26
15.15
0.56
10.35
3.43
0.21
5.17
37.4
14.0
29.5
1.19
After addition of 0.228 mmol HI (10Â)
L-Cat 4000 min
L-Cat 10 000 min
1.03
3.74
14.00
16.55
9.79
9.87
0.18
0.19
1.91
1.98
26.9
32.3
had not started, indicating that the conversion process This property of highly acidic HI to initiate oscillations when
happened independently of the observable oscillations. Indeed, using a catalyst that would not otherwise give rise to oscilla-
although the oscillations occurred after 4180 min, the addi- tions is a promising feature for the targeted pH-mediated drug
tional conversion of PhAc was only 5.4% (32.3% at 10 000 min), delivery and release.
Table 1. This conversion was associated with an increase in
formation of E and Z-isomers, whereas the concentrations of
other products did not change significantly.
Conflicts of interest
No conflicts of interest to declare.
Conclusions
In this report, we demonstrate oscillatory pH behaviour in
systems catalysed by various palladium-based catalysts – from
Acknowledgements
a small molecule palladium acetate to polymer bound phosphine-
This work was supported by UK Engineering and Physical Sciences
liganded palladium catalyst. While palladium acetate worked
Research Council (EPSRC) grant number EP/N033655/1. X-ray photo-
along the lines of the previously reported PdI2, giving well-
electron spectroscopy (XPS) data were acquired at the National
defined highly regular oscillations in the pH region of 3–4.5 pH,
EPSRC XPS Users’ Service, an EPSRC Mid-Range Facility. Data
the other catalysts only exhibited oscillations after the initial
supporting this publication is openly available under an ‘Open
pH drop was forced by addition of hydroiodic acid. Addition of
Data Commons Open Database License’. Additional metadata
HI not only helped to achieve the oscillations in L-Cat and P-Cat
are available at: http://dx.doi.org/10.17634/153345-1. Please contact
but also dramatically increased phenylacetylene conversion.
Newcastle Research Data Service at rdm@ncl.ac.uk for access
Moreover, after the addition of HI, PdAc and P-Cat demon-
instructions.
strated mixed-mode oscillations. Further studies are required
to identify the reaction subnetworks responsible for the large
and small amplitude cycles. However, based on the evidence
collected here, it was postulated that the observed complex
References
behaviour was a result of HI induced conversion of metallic
palladium into PdI2 meaning that two competing catalysts,
PdAc and PdI2 were present in the system. The overall effect of
externally added HI was complex: (i) it decreased the pH to the
range where oscillations in PCOC system are generally observed;
(ii) it generated additional Pd2+ from metallic palladium, as
observed from XPS; (iii) it led to the observation of complex
mixed-mode oscillatory patterns and (iv) it participated in the
formation of mono-esters which were typically considered
intermediates and not observed among the final products.
1 A. M. Zhabotinsky, Chaos, 1991, 1, 379–386.
2 A. Isakova and K. Novakovic, Eur. Polym. J., 2017, 95,
430–439.
3 P. Topham, J. R. Howse, C. J. Crook, S. P. Armes, R. A. L.
Jones and A. J. Ryan, Macromolecules, 2007, 40, 4393–4395.
4 R. Tamate, A. Mizutani Akimoto and R. Yoshida, Chem. Rec.,
2016, 16, 1852–1867.
5 Y. S. Kim, R. Tamate, A. M. Akimoto, R. Yoshida, J. Groen,
H. W. H. van Roekel, T. F. A. de Greef, W. T. S. Huck and
T. Aida, Mater. Horiz., 2017, 4, 38–54.
This journal is ©the Owner Societies 2018
Phys. Chem. Chem. Phys.

View Article Online
Paper
PCCP
6 Alexander V. Malashkevich, A. Lev, G. Bruk and O. N. Temkin, 21 B. Gabriele, L. Veltri, G. Salerno, M. Costa and G. P. Chiusoli,
J. Phys. Chem. A, 1997, 101, 9825–9827. Eur. J. Org. Chem., 2003, 1722–1728.
7 V. R. Khabibulin, A. V. Kulik, I. V. Oshanina, L. G. Bruk, 22 S. N. Gorodskii, A. N. Zakharov, A. V. Kulik, L. G. Bruk and
O. N. Temkin, V. M. Nosova, Y. A. Ustynyuk, V. K. Bel’skii, O. N. Temkin, Kinet. Catal., 2001, 42, 251–263.
A. I. Stash, K. A. Lysenko and M. Y. Antipin, Kinet. Catal., 23 V. N. Zudin, V. D. Chinakov, V. M. Nekipelov, V. A. Rogov,
2007, 48, 228–244.
V. A. Likholobov and Y. I. Yermakov, J. Mol. Catal., 1989, 52,
8 K. Novakovic, C. Grosjean, S. K. Scott, A. Whiting,
27–48.
M. J. Willis and A. R. Wright, Chem. Phys. Lett., 2007, 435, 24 G. Rabai, M. Orban and I. R. Epstein, Acc. Chem. Res., 1990,
142–147. 23, 258–263.
9 C. Grosjean, K. Novakovic, S. K. Scott, A. Whiting, 25 T. G. Szanto and G. Rabai, J. Phys. Chem. A, 2005, 109,
´
´
´
M. J. Willis and A. R. Wright, J. Mol. Catal. A: Chem., 2008,
284, 33–39.
5398–5402.
´
26 G. Rabai and I. Hanazaki, J. Phys. Chem. A, 1999, 103, 7268–7273.
10 K. Novakovic, A. Mukherjee, M. Willis, A. Wright, S. Scott 27 E. C. Edblom, M. Orban and I. R. Epstein, J. Am. Chem. Soc.,
and A. R. Wright, Phys. Chem. Chem. Phys., 2009, 11, 9044. 1986, 108, 2826–2830.
11 J. Parker and K. Novakovic, React. Kinet., Mech. Catal., 2016, 28 M. J. B. Hauser, A. Strich, R. Bakos, Z. Nagy-Ungvarai and
118, 73–85. S. C. Mu¨ller, Faraday Discuss., 2002, 120, 229–236.
12 J. Parker and K. Novakovic, React. Kinet., Mech. Catal., 2018, 29 Z. D. Cupic, L. Z. Kolar-Anic, S. R. Anic, S. R. Macesic,
ˇ
ˇ
´
´
´
´ ˇ ´
´
´
´
123, 113–124.
J. P. Maksimovic, M. S. Pavlovic, M. C. Milenkovic, I. N. M.
Bubanja, E. Greco and S. D. Furrow, Helv. Chim. Acta, 2014,
97, 321–333.
13 L. Donlon and K. Novakovic, Chem. Commun., 2014, 50,
15506–15508.
ˇ
ˇ ˇ
´ ˇ ´ ´
´
ˇ ´
´
14 J. Parker and K. Novakovic, ChemPhysChem, 2017, 18, 1981–1986. 30 I. N. Bubanja, S. Macesic, A. Ivanovic-Sasic, Z. Cupic, S. Anic
´
15 S. N. Gorodsky, Org. Chem. Int., 2012, 1–6.
16 S. N. Gorodsky, Kinet. Catal., 2012, 53, 493–496.
17 S. N. Gorodsky, React. Kinet., Mech. Catal., 2018, 1–20.
18 Y. Sakurai, S. Sakaguchi and Y. Ishii, Tetrahedron Lett., 1999,
40, 1701–1704.
and L. Kolar-Anic, Phys. Chem. Chem. Phys., 2016, 18,
9770–9778.
31 B. D. Aguda, R. Larter and B. L. Clarke, J. Chem. Phys.,
1989, 90, 4168–4175.
32 V. Vukojevic, S. Anic and L. Kolar-Anic, J. Phys. Chem. A,
´
´
´
19 R. F. Heck, J. Am. Chem. Soc., 1972, 94, 2712–2716.
2000, 104, 10731–10739.
20 S. P. Porras and E. Kenndler, J. Chromatogr. A, 2004, 1037, 33 J. Parker and K. Novakovic, Ind. Eng. Chem. Res., 2013, 52,
455–465.
2520–2527.
Phys. Chem. Chem. Phys.
This journal is ©the Owner Societies 2018