α-TEPHOS: a cyclodextrin-derived tetraphosphine for multiple metal binding

Abstract

The tetraphosphine 6^A,6^B,6^D,6^E-tetradeoxy-6^A,6^B,6^D,6^E-tetra(diphenylphosphinyl)-2^A,2^B,2^C,2^D,2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^C,6^F-tetradeca-O-methyl-α-cyclodextrin (α-TEPHOS) has been prepared in high yield by reacting 6^A,6^B,6^D,6^E-tetra-O-methylsulfonyl-2^A,2^B,2^C,2^D, 2^E,2^F,3^A,3^B,3^C,3^D,3^E,3^F,6^C,6^F-tetradeca-O-methyl-α-cyclodextrin with excess PPh₂Li. The product was purified in its BH₃-protected form. α-TEPHOS is the first optically active tetraphosphine in which the four phosphine units are tethered to a cavity-shaped scaffold. When reacted with [AuCl(tetrahydrothiophene)], α-TEPHOS led to the corresponding tetragold complex [(α-TEPHOS)(AuCl)₄] in which the four gold atoms are all located close to the primary face of the cyclodextrin. Reaction with [PdCl(o-C₆H₄CH₂NMe₂)]₂ gave the C₂-symmetrical complex [(α-TEPHOS){PdCl(o-C₆H₄CH₂NMe₂)}₄]. Treatment of the ligand with two equiv. of [Rh(norbornadiene)(tetrahydrofuran)₂]BF₄ afforded selectively the bimetallic complex [(α-TEPHOS){Rh(norbornadiene)}₂](BF₄)₂ in which each metal centre is coordinated to two phosphorus atoms belonging to adjacent glucose units.