A new complex compound of chromium(III) with 5-aminopyridine-2-carboxylate anions – Structure, physicochemical and catalytic properties
Graphical abstract
This report presents the structure of the 5-aminopyridine-2-carboxylate chromium(III) complex. The thermodynamic stability of the title complex has been examined. The conductometric titration confirmed the stoichiometry of the chromium(III) complex. New complex is highly active catalyst in the oligomerization reaction of 2-chloro-2-propen-1-ol.
Introduction
Polymerization of α-olefins can be carried out with the catalysts, which are coordination compounds. Polymerization of α-olefins can occur according to a coordination mechanism, but this is not always the case. The polymerization reaction based on a coordination catalyst can also take place via a radical or ionic mechanism. In the case of coordination polymerization, the complex compound acting as a catalyst takes part in all stages of the process: initiation, propagation and termination [1], [2], [3], [4], [5], [6].
Catalysts based on coordination compounds always have a metal atom or cation as their active center. The active center of the catalyst, i.e. the metal atom, binds to one ligand via an active bond [7]. Coordination polymerization occurs when the used monomer can form a labile complex with a metal atom, which is the active center of the catalyst [8], [9], [10], [11].
The monomer in the coordination mechanism can attach to the central atom in the catalyst system through the π bond occurring in the monomer or through the free electron pair present on the heteroatom. The π-type complexes include hydrocarbon monomers e.g. alkenes (α-olefins), styrene, dialkens and alkynes [12], [13], [14]. The second group of coordination polymerizations, where the process is carried out through coordination compounds having an σ bond, includes heterocyclic and hetero-unsaturated monomers. Examples of such monomers may be cyclic ethers, cyclic sulfides, lactones, cyclic dicarboxylic acid anhydrides, aldehydes or carbon monoxide(IV) [15], [16].
Complex chromium(III) compounds show high catalytic activity in α-olefin polymerization reactions. Very active catalysts for the reaction include [Cr(dipic)2][Cr(bipy)(dipic)H2O]∙2H2O (catalytic activity = 2609.86 g·mmol−1·h−1), [Cr(dipic)2]Hdmbipy·2.5H2O (catalytic activity = 2254.57 g·mmol−1·h−1) and [Cr(2-pic)2(OH2)2]NO3 (catalytic activity = 1434.33 g·mmol−1·h−1) where dipic denotes dipicolinate anion, bipy = 2,2′-bipyridine, Hdmbipy = 4,4′-dimethoxy-2,2′-bipyridine, 2-pic = 2-pyridinecarboxylate [17], [18], [19], [20]. Complex compounds of chromium(III) with 5-aminopyridine-2-carboxylate anions are a group of compounds whose physicochemical properties is unknown.
This publication presents a new complex compound trichloromethane pentahydrate 5-aminopyridine-2-carboxylate chromium(III). Physicochemical properties of this complex were determined. The catalytic activity of the 5-aminopyridine-2-carboxylate chromium(III) complex was examined in the oligomerization reaction of the chloro derivative of the polyallyl alcohol i.e. 2-chloro-2-propene-1-ol. In the first step of the research, a new complex was characterized by crystallographic parameters using single-crystal X-ray diffraction analysis and the summary formula of the examined complex was confirmed by means of the elemental analysis. Then, by means of potentiometric titration, the thermodynamic stability of chemical individuals found in aqueous solution was determined and the stoichiometry of chemical individuals found in aqueous solution was confirmed by conductometric titration.
Infrared spectroscopy was performed to create the full physicochemical characteristics of the new complex. Then the product obtained in the oligomerization reaction of the 2-chloro-2-propene-1-ol alcohol was characterized by infrared spectroscopy identifying characteristic groups in the examined oligomer. Then, mass spectrometry (MALDI - TOF MS) analysis was performed and the number of mer in the resulting oligomerization reaction product was determined, and the catalytic activity of the title complex was determined.
Section snippets
Syntheses
An ethanolic solution of 5-aminopyridine-2-carboxylic acid (4 mmol, 0.55 g) was added to the aqueous solution containing CrCl3·6H2O (2 mmol, 0.54 g) while maintaining constant stirring. In the next step, the whole was heated for about 15 min at 50° C in a heating mantle. After cooling, a mixture of trichloromethane and methanol in the volume ratio 1: 2 was added. The red crystals of the title compound were obtained after 2 months.
X-Ray measurements
Good-quality single-crystal specimens of title compound was
The structure of the new complex
The single crystal of title compound crystallized in the trigonal R3c space group with one molecule of 5-aminopyridine-2-carboxylate chromium(III) complex, 1/3 trichloromethane molecule and 5/3 water molecules in the asymmetric unit (Fig. 1, Table 1). The geometric parameters (bond lengths and angles) appropriate for the crystal structure of the title compound were collected in Table 2.
In the crystal packing of title compounds, arranged around the 3-fold axis of symmetry molecules of
Conclusions
This report presents the structure of the newly obtained chromium(III) coordination compound with 5-aminopyridine-2-carboxylate anions. Potentiometric titration allowed to determine the most thermodynamically stable chemical individuals occurring in aqueous solution is ML3 (logβ = 14.64) and MLH (logβ = 13.02). In addition, the logarithmic constant of 5-aminopyridine-2-carboxylic acid was determined, which is 5.89. The conductometric titration confirmed the stoichiometry of individual forms of
CRediT authorship contribution statement
Jacek Malinowski: Investigation, Formal analysis, Writing - original draft. Artur Sikorski: Investigation, Writing - original draft, Writing - review & editing. Dagmara Jacewicz: Project administration, Formal analysis, Writing - review & editing. Joanna Drzeżdżon: Conceptualization, Formal analysis, Methodology, Writing - review & editing, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by National Science Centre, Poland under Grant number 2015/19/N/ST5/00276.
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