A new supramolecular bonding motif involving NH bonds of ammonium salts and macrocycles derived from platinum corners and butadiynediyl linkers

Abstract

The title Pt4C16 species can give roughly planar geometries in crystals, but afford folded forms with ammonium cations, which are captured like unsuspecting prey and potentially fossilized as with the ancient creatures who once roamed the galaxy.

Building Blocks for Molecular Polygons Based on Platinum Vertices and Polyynediyl Edges

“…The bond lengths and angles around platinum are very similar to those in related complexes described earlier. − ,, The platinum–phosphorus bonds in the dichloride complex 2a (2.2290(8) and 2.2320(8) Å, Figure ) are significantly shorter than those in the cis PtCC species (2.2923(9) to 2.3096(14) Å, Table ), consistent with the greater trans effect of alkynyl ligands . As can be seen in Figure S1, some of the chelates exhibit chair-like conformations (e.g., 3b ), others half-chair (e.g., 3a ; see also Figure ), and others different motifs ( 2a , 5a ) with little analogy in cyclohexane rings ( 2a , 5a ).…”

“…Of these, the most important can be seen in the 13 C­{ 1 H} NMR spectra in Figures –. All of the complex coupling patterns are manifested in the 10a core as well as in the similar species III - iv reported earlier . Aside from the n J CX and 2 J PP′ values and other insight provided by the simulations, it is comforting to know that the blip often observed within the dd of Pt C C 13 C­{ 1 H} NMR signals is not an impurity but a consequence of the second-order spin system.…”

“…The presence of the salt was also evidenced by mass spectrometry and microanalysis (correct N/Cl/H (but not C) values). The nature of the macrocycle/salt interactions has been established in earlier work as briefly summarized below . Similar reactions were also carried out with 3a , c , d and the palladium dppp complex (CH 2 (CH 2 P­(C 6 H 5 ) 2 ) 2 )­PdCl 2 .…”

“…Looking ahead, the development of additional routes to III and higher homologues is of importance, especially given the difficulties three groups have experienced in removing the H 2 NEt 2 + Cl – or other ammonium salt coproducts in Schemes and . ,, This attraction largely originates from electrostatic surface potentials as mapped in Figure . The highly negative (red) surface that rings the macrocycle core has no counterpart in the monoplatinum corner units and is furthermore replicated in Pt 3 C 12 and Pt 5 C 20 homologues.…”

“…The chelate encodes the cis geometry required of corner units. For benchmarking purposes, we sought to first apply such bis­(butadiynyl) and dichloride complexes ( I and II , Scheme ) in the syntheses of the four-sided Pt 4 C 16 adducts III , which have been studied by several research groups. − Although no serious solubility issues have arisen in this chemistry, it should be noted that the Pt 4 C 16 macrocycles have extraordinary affinities for ammonium salts, which are coproduced in most preparative routes. Recently, crystal structures of these supramolecular assemblies have been obtained, together with NMR evidence for their persistence in solution…”