Supramolecular Ammine‐Copper rac‐BINOLAT Salts through in‐situ R‐ or S‐BINOL Racemization

Abstract

The molecule rac‐1,1'‐binaphthalene‐2,2'‐diol (rac‐1,1'‐bi‐2‐naphthol, rac‐BINOL) shows a propensity for supramolecular, charge‐assisted O–H···O– hydrogen‐bonded strand formation when crystallized with its deprotonated form BINOLAT2– and Cu2+ in conc. ammonia. The naphthyl‐paneled cavities in the {(rac‐BINOLAT2–)(rac‐BINOL)2} strands host the [Cu(NH3)5]2+‐guest cation through second‐sphere N–H···O hydrogen bonding in the structure of [Cu(NH3)5]2+(rac‐BINOLAT2–)(rac‐BINOL)2. Decreasing the copper(II) and ammonia concentrations in the crystallization leads to {(rac‐BINOLAT2–)(rac‐BINOL)} strands, in which rac‐BINOLAT2– coordinates to two copper(II) atoms in the structure of [Cu(NH3)2(μ‐rac‐BINOLAT2–‐κ2O,O':κO)]2(rac‐BINOL)2. In the {Cu2+(NH3)2} moiety two BINOLAT‐oxide atoms act as bridging ligands. Both copper structures could be obtained by using the racemic rac‐BINOL or the enantiomeric R‐ or S‐BINOL, through an in‐situ racemization of the latter.