Partially reduced calix[4]arenes: structures and co-ordination chemistry

Abstract

Reduction of the carbonyl group of tetrahydrocalix[4]arene by NaBH₄ occurred readily to provide a mixture of two diastereomeric cyclohexanol derivatives in which the predominant (95%) species H₄L has the alcohol-carbon hydrogen atom directed towards the ‘upper rim’ but the hydrogen atoms of the adjacent carbon atoms directed away, while the minor species H₄L′ has all three of these hydrogen atoms directed towards the upper rim, as shown by crystal structure determinations. Compound H₄L is isomorphous with its fully aromatic parent, like it being disposed about a crystallographic mirror plane with non-included solvent. In both H₄L and H₄L′, concerted intramolecular hydrogen bonding between the hydroxyl groups, phenolic and aliphatic, appears to be an important aspect of their structure. While in both fusion of the aliphatic ring into the macrocycle takes place through equatorial sites, with the hydroxyl substituent on the intervening carbon atom axial with respect to the macrocycle, the dispositions of the ring axes lie normal and parallel, respectively, to the macrocycle axes. Reaction between H₄L and anhydrous europium(III) trifluoromethanesulfonate in dimethylformamide (dmf) in the presence of triethylamine provided yellow crystals of the neutral, binuclear complex [Eu₂(HL)₂(dmf)₄]·4dmf.