1,3,5‐Triamino‐1,3,5‐trideoxy‐<i>cis</i>‐inositol, a New Ligand with a Remarkable Versatility for Metal Ions. Part 2. Safe and efficient ligand preparation and structure of the free ligand and the Co^III complex

Abstract

Abstract A new, convenient, and safe route to 1,3,5‐triamino‐1,3,5‐trideoxy‐ cis ‐inositol (taci) was investigated by hydrogenation of azo‐coupled derivatives of phloroglucinol. In the presence of acetic anhydride, the reduction of trisphenylazophloroglucinol (H 2 /Pd(5%) on C) resulted in the formation of tri‐, hexa‐, and nona‐acetylated derivatives of triaminophloroglucinol. All three compounds are air‐stable, colorless solids. However, the succeeding hydrogenation to the cyclohexane derivative failed. Trisodiumtris( p ‐sulfonatophenylazo)phloroglucinol could be hydrogenated in a one‐pot reaction to the desired taci· 1.5H 2 SO 4 using a Pt/Rh oxide as catalyst. taci provides two distinct chair conformations with either three amino or three hydroxy groups for metal binding. The unique metal‐binding properties are discussed in terms of minimal conformational changes required for coordination. Conformational analysis, based on X‐ray structural data of [BiCl 6 ][H 3 (taci)] ·2 H 2 O ( Pnma , a = 24.314 (5) Å, b = 10.215 (2) Å, c = 7.422 (8) Å, R = 5.8%) and [Co(taci) 2 (NO 3 ) 3 ]·2H 2 O ( C 2/ c , a = 22.912 (8) Å, b = 8.942 (2) Å, c = 14.731 (3) Å, β = 128.66 (2)°, R = 4.9%) and the previously investigated [Cr(taci) 2 ] 3+ revealed an almost ideal chair conformation in all three molecules.