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

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 [Pdn(en)n(mu-N,N'-L)m(mu-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(mu-N,N'-L)4]4+ (1) and [Pd3(en)3(mu-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(mu-N,N'-4,6-dimethyl-2-pyrimidinolate)(mu-N,N[prime or minute]-4,7-phen)2]5+ formulation, exhibiting a pinched-cone conformation. 4a contains a tetranuclear parallelogram [Pd4(en)4(mu-N,N'-2-pyrimidinolate)2(mu-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.