Chiral and Extended pi-Conjugated Bis(2-pyridyl)phospholes as Assembling N,P,N Pincers for Coordination-Driven Synthesis of Supramolecular [2,2]Paracyclophane Analogues

Chiral, pi-conjugated 3,4-butano-1-phenyl-2,5-bis(2-pyridyl)- phosphole derivatives 1a(2-2') and 1a(3) with chiral trans-1,2-diol moieties and fused pinene derivatives, respectively, were prepared from the corresponding chiral diynes by using the Fagan Nugent method. Their UV/Vis absorption and chiroptical properties (optical rotation and circular dichroism) were studied. Their behavior as N,P,N chelates towards coordination of Cu-I and formation of chiral supramolecular assemblies with 2t-conjugated ditopic dicyano ligands was investigated. Chiral C-2-symmetric rectangles that are [2,2]paracyclophane analogues were obtained, as demonstrated by X-ray crystallography. During the course of this study, the first stable water-soluble phosphole derivative (1a(2).2HCl) was prepared. Furthermore, achiral 3,4-butano-1-phenyl-2,5-bis- (aza[4]helicene)phosphole la was synthesized and displays extended 1a(4) conjugation. A supramolecular rectangle was obtained by coordination to Cu-I and assembly with a dicyano stilbene. This coordination-driven supramolecular assembly contains a total of four aza[4]helicene moieties and displays two types of pi-pi stacking interactions in the solid state, that is, between two helicene moieties and between one helicene and a bridging dicyano ligand. All the supramolecular arrangements are discussed by comparing them with previous work on the parent 3,4-butano-1-phenyl-2,5-bis(2-pyridy1)- phosphole.