Size dependent effect of new organometallic triptycene tectons on the dimensions of self-assembled macrocycles

Abstract

The design, synthesis and characterization of two new triptycene-containing ditopic Pt(II) organometallic complexes is being reported. These complexes comprise of two peripheral bis(trans-trialkylphosphine)platinum units either directly σ-bonded to the central triptycene moiety or connected via a bridging ethynyl spacer linkage. The potential utility of these organometallic complexes as ditopic acceptor building blocks for the construction of neutral metallasupramolecular macrocycles containing the triptycene motif is explored. Triptycene motif containing supramolecules were characterized using multinuclear NMR (including ¹H DOSY), mass spectrometry (MALDI-TOF-MS) and elemental analyses. While the self-assembly of a longer acceptor linker with a terephthalate group results in the formation of a [3 + 3] self-assembled macrocycle, the use of a relatively shorter acceptor linker yields the corresponding [2 + 2] supramolecular framework. The shapes and dimensions of these supramolecular structures were also predicted by geometry optimization using PM6 semiempirical molecular orbital methods and the results corroborate well with the experimental observations. These two self-assembled macrocycles are unique examples of triptycene-based neutral “platinamacrocycles” reported in the literature to date. An investigation as to how the shape and size of the resulting discrete supramolecular framework is affected upon changing the length and rigidity of the triptycene-based acceptor linkers is discussed.