Steric control in the reactions of 3-pyrazolecarboxylic acid with diorganotin dichlorides

Reaction of 3-pyrazolecarboxylic acid (LH2) with dibenzyltin dichloride (Bn2SnCl2) in the presence of potassium hydroxide afforded a 2D-coordination polymer, [{(Bn2Sn)2(μ-L)(μ-LH)(μ-OH)}2]n (1), which crystallizes as an ethanol solvate. The repeat unit of the coordination polymer 1 is a tetrameric motif which contains two pairs of centrosymmetrically related dimeric stannoxanes; in the latter the two tin atoms are connected to each other by a μ-OH and a η2-μ-pyrazole ligand. The tetrameric units are linked to each other by the bridging coordination action of the pyrazolecarboxylate ligand to generate a 2D-coordination polymer. An analogous reaction of LH2 with the sterically encumbered t-Bu2SnCl2 afforded the monomeric dinuclear compound [{(t-Bu2Sn)2(μ-L)(LH)(μ-OH)}]·H2O (2). In the latter the two tin atoms are linked to each other by a bridging hydroxide as well as a pyrazole ligand affording a 6-membered ring. The steric hindrance of the tert-butyl groups seems to prevent the elaboration of this unit into a coordination polymer. Both 1 and 2 have been characterized by single crystal X-ray, NMR and ESI-MS studies.

Graphical abstractThe reaction of Bn2SnCl2 with 3-pyrazolecarboxylic acid in presence of KOH afforded the 2D-coordination polymer [{(Bn2Sn)2(μ-L)(μ-LH)(μ-OH)}2·2C2H5OH]n (ethanol molecules are shown by space filling model). In contrast, discrete product [{(t-Bu2Sn)2(μ-L)(LH)(μ-OH)}]·H2O was obtained when the reaction was carried out with t-Bu2SnCl2.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Two-dimensional organotin coordination polymers. ► Hydroxide- and pyrazole-bridged dinuclear organotin compound. ► Multi-dentate coordination behavior of pyrazolecarboxylate. ► Organostannoxane macrocycles.