Formation of heterotopic metallacalix[n]arenes (n = 3, 4, 6) containing ethylenediaminepalladium(ii) metal fragments and 4,7-phenanthroline and 2-pyrimidinolate bridges. Synthesis, structure and host–guest chemistry

Abstract

A multicomponent reaction involving ethylenediaminepalladium(II), 2-pyrimidinol derivatives (L) [L = 2-pyrimidinol (a); 4-methyl-2-pyrimidinol (b); 4,6-dimethyl-2-pyrimidinol (c)] and 4,7-phenanthroline (4,7-phen) leads to the formation of heterotopic cyclic metallamacrocycles of the type [Pd_n(en)_n(μ-N,N′-L)_m(μ-N,N′-4,7-phen)_{n − m}]^{(2n − m)+} [n = 3, m = 1 (3); n = 4, m = 2 (4); n = 6, m = 4 (5)]. These species can be obtained by different reaction pathways, including: (i) reaction of ethylenediaminepalladium(II), L and 4,7-phen building blocks and (ii) reaction of the homotopic species [Pd₄(en)₄(μ-N,N′-L)₄]⁴⁺ (1) and [Pd₃(en)₃(μ-N,N′-4,7-phen)₃]⁶⁺ (2). The resulting heterotopic metallamacrocycles have been characterised by 1D and 2D ¹H NMR spectroscopy. Additionally, species 3c and 4a have been studied by X-ray crystallography. The former one contains almost isosceles triangles of [Pd₃(en)₃(μ-N,N′-4,6-dimethyl-2-pyrimidinolate)(μ-N,N′-4,7-phen)₂]⁵⁺ formulation, exhibiting a pinched-cone conformation. 4a contains a tetranuclear parallelogram [Pd₄(en)₄(μ-N,N′-2-pyrimidinolate)₂(μ-N,N′-4,7-phenanthroline)₂]⁶⁺, exhibiting a 1,3-alternate conformation. The host–guest properties of the here reported species have been studied, showing that they are able to interact with cationic as well as with anionic species.