Metal-Controlled Stereoselectivity in Complex Formation: Assembly of Tetranuclear Copper(I) complexes with Four Stereogeic Nitrogen Donor Functions in all-(R) and all-(S) Configurations

摘要

The reaction of N,N'-dialkyl-3,7-diazanonane-1,9-dithiolate (N_2~RS_2) ligands (R=Me, Et) with monovalent copper resulted in the formation of the chiral complexes [Cu_4(N_2~MeS_2)_2] (1) and [Cu_4(N_2EtS_2)_2] (2) which were characterised by means of X-ray diffraction and spectroscopic techniques. They contain copper atoms in both linear {S-Cu-S} fragments, which act as linkers between mononuclear [Cu(N_2~RS_2)]~- subsites, and in {CuS_2N_2} units within these building blocks, which can be described as incomplete coordination octahedra of unusual design. Due to favourable interplay between the spatial demands of the ligand system and the electronic requirements of the copper atom, the nitrogen donor atoms within the [Cu(N_2~RS_2)]~- metallo ligands are restricted to identical absolute configurations. The combination of two [Cu(N_2~RS_2)]~- metallo ligands with two further Cu~I ions to give the tetra-nuclear complexes 1 or 2 via S-Cu-S bridges undeerlies stereochemical control, resulting in optically active systems with (R,R,R,R) and (S,S,S,S) configurations. Consequently, metallo ligands in their enantiomeric forms cannot combine via S-Cu-S bridges to form optically inactive meso complexes with the (R,R,S,S) configuration.