Platinum-Based Organometallic Folders for the Recognition of Electron-Deficient Aromatic Substrates.

A series of platinum complexes with cis-oriented polyaromatic N-heterocyclic carbene ligands were prepared and characterized. The relative disposition of the polyaromatic ligands about the metal cause these compounds to behave as metallofolders, featuring a cavity defined by the void space between the polyaromatic functionalities. The complexes were used as receptors of organic molecules, whereby selective affinity was displayed for electron-deficient aromatic substrates, such as 1,2,4,5-tetracyanobenzene (TCNB), 2,4,7-trinitro-9-fluorenone (TNFLU), and 1,4,5,8-naphtalenetetracarboxylic dianhydride (NTCDA). The binding affinities of two of the metallofolders with these substrates were determined by means of 1 H NMR titrations. Electrospray mass spectrometry (ESI-MS) was also used to assess the affinities. The molecular structure of one of the platinum folders was determined in the presence of TCNB, showing the clear interaction between this guest molecule and the folder formed by the two mutually cis-oriented polyaromatic ligands. This work demonstrates how the presence of the mutually cis-oriented polyaromatic ligands may be a very useful tool for the preparation of metal-based receptors.