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

Abstract

Reaction of 3-pyrazolecarboxylic acid (LH 2) with dibenzyltin dichloride (Bn 2SnCl 2) in the presence of potassium hydroxide afforded a 2D-coordination polymer, [{(Bn 2Sn) 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 η 2-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 LH 2 with the sterically encumbered t-Bu 2SnCl 2 afforded the monomeric dinuclear compound [{( t-Bu 2Sn) 2(μ-L)(LH)(μ-OH)}]·H 2O ( 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.