Directed Assembly of Transition-Metal-Coordinated Molecular Loops and Squares from Salen-Type Components. Examples of Metalation-Controlled Structural Conversion

Abstract

A series of transition-metal-containing molecular "loops" and "squares" has been prepared via a directed-assembly approach and characterized. The molecular loops were prepared from the reaction of cis-(PEt(3))(2)Pt(OTf)(2) with bis(4-pyridyl)-functionalized free-base salen-type ligands. Zn(II)-metalation of the salen-type ligands in the molecular loops converts the loops to molecular squares. Alternatively, the squares can be obtained by the directed assembly of cis-(PEt(3))(2)Pt(OTf)(2) and bis(4-pyridyl)-functionalized Zn(II)-salen-type ligands. A concentration-dependent dynamic equilibrium between cyclic species was observed when bis(3-pyridyl)-functionalized free-base salen-type ligand was employed in the reaction. Zn(II) or Cr(III) metalation of the free-base ligand shifted the equilibrium to the single dimeric species. The incorporation of multiple reactive metal sites into a single, cavity-containing supramolecular structure points toward catalytic applications for these new assemblies.

Crystal structure of 2,2'-(1,2-ethylenedioxy)bisbenzaldehyde O,O'-dimethyldioxime, C18H20N2O4

“…These compounds can accommodate one, two or more metal centers and form homo-and heteronuclear metal complexes serving as catalysts [ 7], models of reaction centers of metalloenzymes [8], nonlinear optical materials [9] and molecular recognition and biological agents [10].…”

Crystal structure of 3,3′-[2,2′-(1,2-ethylenedioxy)dibenzylmethylimino] bis(acetophenone oxime), C32H30N4O4

“…Oxime-type chelating compounds and their derivatives have drawn much attention in the last few decades because these compounds cana ccommodate one, two or more metal centers and form homo-and heteronuclearmetal complexes with interesting properties [1][2][3][4], such as excellent catalytic activity for epoxidation and aziridination [5].Inaddition, they arealso used as models for reaction centers in metalloenzymes [6],non-linear optical materials [7],a nd molecular recognition and biological activity [8]. …”

Crystal structure of 2,2′-dinitro-2,2′-[(1,4-butylene)dioxybis( nitrilomethylidyne)]dibenzene, C18H18N4O6

“…Many attention has focused on salen and its derivatives [1][2][3][4], because these compounds can easily form metallosalen complexes and some of them may have excellent application [5,6]. To improve such functions, chemical modifications of ab asic salen skeleton is very interesting and important [7][8][9][10][11].…”