Chiral tether-mediated stabilization and helix-sense control of complementary metallo-double helices

• Published in: Chemical science (Cambridge) 2015-01, Vol.6 (1), p.714-723
• Main Authors: Horie, Miki, Ousaka, Naoki, Taura, Daisuke, Yashima, Eiji
• Format: Article
• Language: English
• Subjects: Carboxylic acids; Dimers; Dimethyl sulfoxide; Exchange; Helical; Helices; Ligands; Strands
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c4sc02275k

A series of novel Pt -linked double helices were prepared by inter- or intrastrand ligand-exchange reactions of the complementary duplexes composed of chiral or achiral amidine dimer and achiral carboxylic acid dimer strands joined by -Pt -acetylide complexes with PPh ligands using chiral and achiral chelating diphosphines. The structure and stability of the Pt -linked double helices were highly dependent on the diphosphine structures. An interstrand ligand exchange took place with chiral and achiral 1,3-diphosphine-based ligands, resulting in -Pt -bridged double helices, whose helical structures were quite stable even in dimethyl sulfoxide (DMSO) due to the interstrand cross-link, whereas a 1,2-diphosphine-based ligand produced non-cross-linked -Pt -linked duplexes, resulting from an intrastrand ligand-exchange that readily dissociated into single strands in DMSO. When enantiopure 1,3-diphosphine-based ligands were used, the resulting -Pt -bridged double helices adopted a preferred-handed helical sense biased by the chirality of the bridged diphosphines. Interestingly, the interstrand ligand exchange with racemic 1,3-diphosphine toward an optically-active Pt -linked duplex, composed of chiral amidine and achiral carboxylic acid strands, was found to proceed in a diastereoselective manner, thus forming complete homochiral -Pt -bridged double helices a unique chiral self-sorting.