Stereoselective Double-Helicate Assembly from Chiral 2,2′:6′,2″:6″,2′′′-Quaterpyridines and Tetrahedral Metal Centres

✍ Scribed by Gerhard Baum; Edwin C. Constable; Dieter Fenske; Catherine E. Housecroft; Torsten Kulke

• Book ID: 102660825
• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 703 KB
• Volume: 5
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(19990604)5:6<1862::aid-chem1862>3.0.co;2-g

✦ Synopsis

A pair of chiral 2,2':6',2'': 6'',2'''-quaterpyridine ligands 1 and 2 have been prepared and shown to diastereoselectively assemble double-helical coordination compounds. The complexation of 1 or 2 with copper(i) or silver(i) leads to dinuclear double helicates [M 2 (L) 2 ] 2 with high diastereoselectivity [diastereomeric excess (d.e.) ! 96 %] for the formation of P or M helicates. Circular dichroism (CD) studies of the helicates in solution reveal intense activity in the region of 320 ± 328 nm that is diagnostic of P or M helical chirality. On the basis of the CD spectra it is proposed that the dominant diastereomers with 1 possess P helicity, whilst those with 2 possess M helical chirality. These proposals have been confirmed by solid-state struc-tural determinations of the dominant diastereomers of [Cu 2 (1) 2 ][PF 6 ] 2 2 MeCN, [Cu 2 (2) 2 ][PF 6 ] 2 ´2 MeCN and [Ag 2 (1) 2 ][PF 6 ] 4 ´0.33 H 2 O. Redistribution reactions of dicopper(i) and disilver(i) helicates lead to the stereoselective assembly of heterodinuclear helicates, whereas the reaction of [Cu 2 (1) 2 ] 2 with [Cu 2 (2) 2 ] 2 leads to the formation of the heterochiral, heterostranded species [Cu 2 (1)(2)] 2 .