Face and edge directed self-assembly of Pd₁₂ tetrahedral nano-cages and their self-sorting

Abstract

Reactions of a <i>cis</i>-blocked Pd(ii) 90° acceptor [<i>cis</i>-(tmeda)Pd(NO₃)₂] (<b>M</b>) with 1,4-di(1<i>H</i>-tetrazol-5-yl)benzene (<b>H₂L¹</b> ) and [1,3,5-tri(1<i>H</i>-tetrazol-5-yl)benzene] (<b>H₃L²</b> ) in 1 : 1 and 3 : 2 molar ratios respectively, yielded soft metallogels <b>G1</b> and <b>G2</b> [tmeda = <i>N</i>,<i>N</i>,<i>N</i>',<i>N</i>'-tetramethylethane-1,2-diamine]. Post-metalation of the gels <b>G1</b> and <b>G2</b> with <b>M</b> yielded highly water-soluble edge and face directed self-assembled Pd₁₂ tetrahedral nano-cages <b>T1</b> and <b>T2</b>, respectively. Such facile conversion of Pd(ii) gels to discrete tetrahedral metallocages is unprecedented. Moreover, distinct self-sorting of these two tetrahedral cages of similar sizes was observed in the self-assembly of <b>M</b> with a mixture of <b>H₂L¹</b> and <b>H₃L²</b> in aqueous medium. The edge directed tetrahedral cage (<b>T1</b>) was successfully used to perform Michael reactions of a series of water insoluble nitro-olefins assisted by encapsulation into the cage in aqueous medium.